WO2015111663A1

WO2015111663A1 - Electrode for lithium ion secondary battery, and lithium ion secondary battery

Info

Publication number: WO2015111663A1
Application number: PCT/JP2015/051709
Authority: WO
Inventors: 智一佐々木
Original assignee: 日本ゼオン株式会社
Priority date: 2014-01-27
Filing date: 2015-01-22
Publication date: 2015-07-30
Also published as: JP6547630B2; KR102304346B1; JPWO2015111663A1; CN105900265A; KR20160113587A; CN105900265B

Abstract

An electrode for a lithium ion secondary battery, the electrode being provided with an electrode active material layer and with a porous layer that contains organic particles and that is provided directly to the electrode active material layer. The organic particles have a core-shell structure that is provided with a core part and with a shell part that partially covers the outer surface of the core part. The core part comprises a polymer that has a degree of swelling of 5-30 times in electrolyte solution. The shell part comprises a polymer that has a degree of swelling of more than 1 and less than or equal to 4 in electrolyte solution.

Description

Electrode for lithium ion secondary battery and lithium ion secondary battery

The present invention relates to an electrode for a lithium ion secondary battery and a lithium ion secondary battery including the same.

In recent years, portable terminals such as notebook computers, mobile phones, and PDAs (Personal Digital Assistants) have been widely used. Lithium ion secondary batteries are frequently used as secondary batteries used as power sources for these portable terminals.
A lithium ion secondary battery generally includes a positive electrode, a negative electrode, and an electrolytic solution. Moreover, in order to prevent the short circuit between a positive electrode and a negative electrode, a separator is normally provided in a lithium ion secondary battery (refer patent documents 1 and 2).

International Publication No. 2005/029614 International Publication No. 2011/040474

Lithium ion secondary batteries generally have a reduced battery capacity due to repeated charge and discharge. In order to realize a long-life lithium ion secondary battery, it is required that the battery capacity does not easily decrease even after repeated charging and discharging. From such a viewpoint, development of a technology capable of realizing a lithium ion secondary battery excellent in high temperature cycle characteristics is required.

The present invention was devised in view of the above problems, and is an electrode for a lithium ion secondary battery capable of producing a lithium ion secondary battery excellent in high temperature cycle characteristics; and a lithium ion secondary excellent in high temperature cycle characteristics. An object is to provide a battery.

As a result of intensive studies to solve the above-mentioned problems, the present inventor is formed of a polymer that can swell with a predetermined degree of swelling with respect to the electrolytic solution, and partially covers the core portion and the outer surface of the core portion. It has been found that by providing a porous layer containing organic particles having a core-shell structure with a shell portion directly on the electrode active material layer of the electrode, a lithium ion secondary battery having excellent high-temperature cycle characteristics can be realized. Completed.
That is, the present invention is as follows.

[1] An electrode for a lithium ion secondary battery comprising an electrode active material layer and a porous layer containing organic particles directly provided on the electrode active material layer,
The organic particles have a core-shell structure including a core portion and a shell portion that partially covers an outer surface of the core portion;
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
An electrode for a lithium ion secondary battery, wherein the shell part is made of a polymer having a swelling degree with respect to an electrolytic solution of greater than 1 and 4 or less.
[2] The glass transition temperature of the polymer of the core part is 0 ° C. or higher and 150 ° C. or lower,
The electrode for a lithium ion secondary battery according to [1], wherein a glass transition temperature of the polymer of the shell portion is 50 ° C. or higher and 200 ° C. or lower.
[3] A lithium ion secondary battery comprising the lithium ion secondary battery electrode according to [1] or [2] and an electrolytic solution.
[4] The lithium ion secondary battery according to [3], wherein a counter electrode is provided on the porous layer side of the lithium ion secondary battery electricity directly or via a member having no shutdown function.
[5] The lithium ion secondary battery according to [3] or [4], wherein the electrode has a flat shape.

According to the electrode for a lithium ion secondary battery according to the present invention, a lithium ion secondary battery excellent in high temperature cycle characteristics can be produced.
The lithium ion secondary battery according to the present invention is excellent in high-temperature cycle characteristics.

FIG. 1 is a cross-sectional view schematically showing an example of organic particles contained in a porous layer.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

In the following description, (meth) acrylic acid includes acrylic acid and methacrylic acid. Further, (meth) acrylate includes acrylate and methacrylate. Furthermore, (meth) acrylonitrile includes acrylonitrile and methacrylonitrile. Moreover, (meth) acrylamide includes acrylamide and methacrylamide.

Furthermore, that a substance is water-soluble means that an insoluble content is less than 1.0% by weight when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C. Further, that a certain substance is water-insoluble means that an insoluble content is 90% by weight or more when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C.
In the case where the solubility in water changes depending on the pH of water, if there is a region that becomes water-soluble, the substance is included in water-solubility.

In addition, in a polymer produced by copolymerizing a plurality of types of monomers, the proportion of the structural unit formed by polymerizing a certain monomer in the polymer is usually that unless otherwise specified. This coincides with the ratio (preparation ratio) of the certain monomer in the total monomers used for polymerization of the polymer.

Furthermore, the “electrode plate” includes not only a rigid plate member but also a flexible sheet and film.

In addition, “monomer composition” is used not only as a composition containing two or more types of monomers but also as a term indicating one type of monomer.

[1. Overview of Lithium Ion Secondary Battery Electrode]
The electrode for a lithium ion secondary battery of the present invention (hereinafter sometimes referred to as “electrode” as appropriate) includes an electrode active material layer and a porous layer provided directly on the electrode active material layer. Usually, the electrode of the present invention includes a current collector. When the current collector is provided, the electrode usually includes a current collector, an electrode active material layer, and a porous layer in this order.

The porous layer includes organic particles having a core-shell structure including a core portion and a shell portion that partially covers the outer surface of the core portion. And the core part and shell part of an organic particle consist of a polymer which has the swelling degree of the predetermined range with respect to electrolyte solution, respectively.
Since the electrode has such a configuration, the following advantages can be obtained.
i. The high temperature cycle characteristics of the lithium ion secondary battery can be improved.
ii. Usually, the swelling of the battery cell accompanying charging / discharging can be suppressed.
iii. Usually, the low-temperature output characteristics of the lithium ion secondary battery can be improved.
iv. Usually, even if an organic separator having a shutdown function is not provided in a lithium ion secondary battery, the lithium ion secondary battery can be provided with a shutdown function.

The reason why such an excellent advantage is obtained is not necessarily clear, but according to the study of the present inventor, it is presumed as follows. However, the present invention is not limited for the reason presumed below.

i. High temperature cycle characteristics:
Generally, in a lithium ion secondary battery, when charging and discharging are repeated, gas may be generated due to decomposition of the electrolytic solution. Such decomposition of the electrolytic solution usually tends to occur in the vicinity of the electrode active material layer of the electrode. When the electrolytic solution is decomposed and gas is generated, the electrode active material cannot be brought into contact with the electrolytic solution at a portion where the electrolytic solution is decomposed, so that the battery capacity may be reduced.
On the other hand, in the electrode of the present invention, the porous layer provided directly on the electrode active material layer contains organic particles having a core-shell structure, and the core portion has a high degree of swelling with respect to the electrolytic solution. Since it has a high degree of swelling, this core part has excellent liquid retention and can store a large amount of electrolyte. Therefore, when the electrolytic solution is insufficient in the vicinity of the electrode active material due to decomposition of the electrolytic solution, the electrolytic solution can be replenished from the core portion to the portion where the electrolytic solution is insufficient. Therefore, in the lithium ion secondary battery including the electrode of the present invention, the contact between the electrode active material and the electrolytic solution is hardly impaired even when charging and discharging are repeated, so that a decrease in battery capacity can be suppressed.

Also, when the electrolyte is greatly swollen, the gaps between the molecules of the polymer are increased, so that ions can easily pass between the molecules. Further, since the shell part partially covers the outer surface of the core part instead of the whole, the movement of ions is difficult to be stopped by the shell part, and the ions can easily enter the core part. Therefore, ions can easily pass through the core of the organic particles in the electrolytic solution. Therefore, since lithium ions are likely to pass through the porous layer, it is usually possible to prevent precipitation of lithium in the electrolytic solution. Therefore, the lithium ion secondary battery including the electrode of the present invention is less likely to increase in resistance due to lithium deposition even after repeated charging and discharging, and thus can suppress an increase in resistance due to repeated charging and discharging.

Furthermore, the lithium ion secondary battery provided with the electrode of the present invention can usually suppress the swelling of the battery cell due to charge / discharge. For this reason, even if charging / discharging is repeated, the distance between the positive electrode and the negative electrode is unlikely to increase, and this can also suppress a decrease in battery capacity.

By combining these factors, it is presumed that the electrode of the present invention can improve the high-temperature cycle characteristics of the lithium ion secondary battery.

ii. Suppression of battery cell swelling:
Generally, in a lithium ion secondary battery, when charging and discharging are repeated, the battery cell may swell due to, for example, generation of gas due to decomposition of the electrolyte and additive and generation of voids due to expansion and contraction of the electrode active material. there were.
However, the polymer constituting the shell part of the organic particles has a high binding property in the electrolytic solution. This high binding property is presumed to be caused by, for example, the activation of the functional group of the polymer in the swollen shell portion to cause a chemical or electrical interaction with the functional group on the surface of the electrode active material layer. Is done. Since the members in the battery are bound by the organic particles having such a high binding property, it is presumed that the swelling of the battery is suppressed.

iii. Low temperature output characteristics:
As described above, since the porous layer easily passes lithium ions in the electrolytic solution, the resistance of the lithium ion secondary battery including the electrode of the present invention can be reduced. Furthermore, according to the electrode of the present invention, lithium deposition can be prevented as described above, and therefore, an increase in resistance due to lithium deposition can be suppressed in the lithium ion secondary battery including the electrode of the present invention. Therefore, it is assumed that the low-temperature output characteristics can be improved. Moreover, if the electrode of this invention is used, the lithium secondary battery which does not have a separator is realizable. Thus, since the lithium ion secondary battery which does not have a separator does not have the resistance by the separator, resistance can be made small. Therefore, it is considered that a lithium ion secondary battery that does not have a separator can further improve the low-temperature output characteristics.

iv. Shutdown function:
The organic particles of the present invention can be melted when heat is generated. Therefore, when the temperature inside the battery becomes high, the organic particles can be melted to close the pores, so that the movement of lithium ions can be prevented and the current can be interrupted. Thus, since the organic particles contained in the porous layer itself can be melted to exhibit the shutdown function, the lithium ion secondary battery can be provided with the shutdown function without separately providing an organic separator having the shutdown function. It is presumed that The shutdown function means that when a member having pores provided between the electrodes of a battery rises in temperature and reaches a predetermined temperature range (usually 130 ° C. ± 5 ° C.), the pores are blocked and current is passed. This is a function that shuts off.

[2. Current collector]
The current collector may be made of a material having electrical conductivity and electrochemical durability. Usually, a metal material is used as the material of the current collector. Examples thereof include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum and the like. Among them, the current collector used for the positive electrode is preferably aluminum, and the current collector used for the negative electrode is preferably copper. Moreover, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The shape of the current collector is not particularly limited, but a sheet having a thickness of about 0.001 mm to 0.5 mm is preferable.

In order to increase the binding strength between the current collector and the electrode active material layer, it is preferable to use the current collector after roughening the surface. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, for example, an abrasive cloth paper to which abrasive particles are fixed, a grindstone, an emery buff, a wire brush provided with a steel wire, or the like is used. In order to increase the binding strength and conductivity of the electrode active material layer, an intermediate layer may be formed on the surface of the current collector.

[3. Electrode active material layer]
The electrode active material layer is a layer containing an electrode active material, and is usually provided on a current collector.
As the electrode active material of the lithium ion secondary battery, a material capable of reversibly inserting or releasing lithium ions by applying a potential in an electrolytic solution can be used.

Examples of the positive electrode active material include lithium-containing mixed metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , and the like. Things.

Furthermore, you may use the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound.
Alternatively, for example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and the composite material may be used as a positive electrode active material. Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.
Furthermore, you may use as a positive electrode active material what carried out the element substitution of the said compound partially.
These positive electrode active materials may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Moreover, you may use the mixture of an inorganic compound and an organic compound as a positive electrode active material.

The particle size of the positive electrode active material can be selected in consideration of other constituent requirements of the lithium ion secondary battery. From the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, the volume average particle diameter of the positive electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, preferably 50 μm or less, more preferably 20 μm or less. It is. When the volume average particle diameter of the positive electrode active material is within this range, a battery having a large charge / discharge capacity can be obtained, and handling of the slurry for electrodes and the electrodes is easy. Here, the electrode slurry is a fluid composition for producing an electrode, and usually contains an electrode active material and a solvent. Further, the volume average particle diameter of the particles represents a particle diameter at which the cumulative volume calculated from the small diameter side becomes 50% in the particle diameter distribution measured by the laser diffraction method.

The ratio of the positive electrode active material in the electrode active material layer is preferably 90% by weight or more, more preferably 95% by weight or more, and preferably 99.9% by weight or less, more preferably 99% by weight or less. By setting the amount of the positive electrode active material in the above range, the capacity of the lithium ion secondary battery can be increased, and the flexibility of the positive electrode and the binding property between the current collector and the positive electrode active material layer can be improved. .

Examples of the negative electrode active material include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, and pitch-based carbon fibers; and conductive polymers such as polyacene. Further, metals such as silicon, tin, zinc, manganese, iron and nickel, and alloys thereof; oxides of the metals or alloys; sulfates of the metals or alloys; Further, metallic lithium; lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd; lithium transition metal nitride; silicon and the like may be used.

Among them, for example _{SiO, SiO 2, SiOx (0.01} ≦ x <2), SiC, it is preferable to use an active material containing silicon, such as SiOC, SiOx, SiC and SiOC are particularly preferred. By using an active material containing silicon, the battery capacity of the lithium ion secondary battery can be increased. Moreover, the active material containing silicon usually expands or contracts greatly due to charge and discharge. In such an active material that causes large expansion and contraction, the fluctuation of the electrolytic solution becomes large, so that a field where the electrode active material and the electrolytic solution cannot be contacted is likely to occur. However, since the electrode of the present invention can supply an electrolytic solution from the core portion to make it difficult for the electrode active material and the electrolytic solution to come into contact with each other, the capacity of the lithium ion secondary battery can be increased without impairing the high-temperature cycle characteristics. can do.

Among the active materials containing silicon, it is particularly preferable to use SiOx as the active material containing silicon from the viewpoint of suppressing the swelling of the negative electrode active material itself. SiOx can be formed using one or both of SiO and SiO ₂ and metallic silicon as raw materials. This SiOx can be produced, for example, by cooling and precipitating silicon monoxide gas generated by heating a mixture of SiO ₂ and metallic silicon.

As the negative electrode active material, one type may be used alone, or two or more types may be used in combination at any ratio. Therefore, two or more kinds of the negative electrode active materials may be used in combination. Among these, it is preferable to use a negative electrode active material containing a combination of carbon and an active material containing silicon. In a negative electrode active material containing a combination of carbon and an active material containing silicon, Li insertion and desorption from an active material containing silicon occur at a high potential, and Li insertion and desorption from a carbon occur at a low potential. Is presumed to occur. For this reason, since expansion and contraction of the negative electrode active material as a whole are suppressed, the cycle characteristics of the lithium ion secondary battery can be further improved.

The particle size of the negative electrode active material is appropriately selected in consideration of other constituent requirements of the lithium ion secondary battery. From the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics, the volume average particle diameter of the negative electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 5 μm or more. Is 100 μm or less, more preferably 50 μm or less, and still more preferably 20 μm or less.

The specific surface area of negative electrode active material, the output from the viewpoints of improving the density, preferably ^2m 2 / g or more, more preferably ^3m 2 / g or more, more preferably ^{5 m} 2 / g or more, and preferably ^{20 m} 2 / g or less, more preferably 15 m ² / g or less, and further preferably 10 m ² / g or less. The specific surface area of the negative electrode active material can be measured by, for example, the BET method.

The proportion of the negative electrode active material in the electrode active material layer is preferably 85% by weight or more, more preferably 88% by weight or more, and preferably 99% by weight or less, more preferably 97% by weight or less. By setting the amount of the negative electrode active material in the above range, it is possible to realize a negative electrode that exhibits excellent flexibility and binding properties while exhibiting high capacity.

Also, the electrode active material may be one having a conductive material attached to the surface by a mechanical modification method.

The electrode active material layer preferably contains an electrode binder in addition to the electrode active material. By including the electrode binder, the binding property of the electrode active material layer can be improved, and the resistance of the electrode to mechanical force can be increased. In addition, since the electrode active material layer is less likely to be peeled off from the current collector and the porous layer, the possibility of a short circuit due to the detached desorbed material can be reduced.

As the electrode binder, for example, a polymer can be used. Examples of the polymer that can be used as the electrode binder include the following soft polymers.
As a soft polymer, for example,
(I) Polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer, etc. An acrylic soft polymer which is a homopolymer of acrylic acid or a methacrylic acid derivative or a copolymer thereof with a monomer copolymerizable therewith;
(Ii) isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer;
(Iii) Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene・ Diene-based soft polymers such as butadiene, styrene, block copolymers, isoprene, styrene, block copolymers, styrene, isoprene, styrene, block copolymers;
(Iv) silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
(V) Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer Olefinic soft polymers such as polymers;
(Vi) Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
(Vii) epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
(Viii) Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
(Ix) Other soft polymers such as natural rubber, polypeptide, protein, polyester thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyamide thermoplastic elastomer, and the like.
Among these, a diene soft polymer and an acrylic soft polymer are preferable.
In addition, these soft polymers may have a cross-linked structure or may have a functional group introduced by modification.
Furthermore, the electrode binder may be particulate or non-particulate.
Moreover, the binder for electrodes may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The amount of the binder for the electrode in the electrode active material layer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, preferably 10 parts by weight or less, with respect to 100 parts by weight of the electrode active material. More preferably, it is 5 parts by weight or less. By setting the amount of the electrode binder to the lower limit value or more of the above range, the binding property between the current collector and the electrode active material layer can be enhanced. Moreover, the low temperature output characteristic of a battery can be made favorable by setting it as below an upper limit.

Furthermore, the electrode active material layer preferably contains a thickener. As a thickener, for example, a water-soluble polymer can be used. Examples of water-soluble polymers that can be used as thickeners include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium thereof. Salts and alkali metal salts; (modified) polyvinyl alcohol compounds such as polyvinyl alcohol, acrylic acid or copolymers of acrylate and vinyl alcohol, maleic anhydride or maleic acid or copolymers of fumaric acid and vinyl alcohol; polyethylene glycol , Polyethylene oxide, polyvinyl pyrrolidone, modified polyacrylic acid, oxidized starch, phosphate starch, casein, various modified starches, and the like. Among them, it is preferable to use a carboxymethylcellulose salt. Here, “(modified) poly” means “unmodified poly” and “modified poly”. Moreover, a thickener may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
By using a thickener, the viscosity of the electrode slurry used for producing the electrode active material layer can be adjusted. Further, the thickener usually functions as a binder in the electrode active material layer and can bind the binding materials.

The amount of the thickener is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, preferably 5 parts by weight or less, more preferably 3 parts by weight with respect to 100 parts by weight of the electrode active material. Or less. By making the amount of the thickener equal to or higher than the lower limit of the above range, the binding property between the current collector and the electrode active material layer can be enhanced. Moreover, the low temperature output characteristic of a battery can be made favorable by setting it as below an upper limit.

The electrode active material layer may contain any component other than the electrode active material, the electrode binder, and the thickener, as long as the effects of the present invention are not significantly impaired. Examples thereof include a conductive material and a reinforcing material. Moreover, arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Examples of the conductive material include conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube; carbon powder such as graphite; fibers and foils of various metals; . By using the conductive material, the electrical contact between the electrode active materials can be improved, so that battery characteristics such as cycle characteristics can be improved.

The specific surface area of the conductive material is preferably 50 m ² / g or more, more preferably 60 m ² / g or more, particularly preferably 70 m ² / g or more, preferably 1500 m ² / g or less, more preferably 1200 m ² / g. Hereinafter, it is particularly preferably 1000 m ² / g or less. By setting the specific surface area of the conductive material to be equal to or higher than the lower limit of the above range, the low temperature output characteristics of the lithium ion secondary battery can be improved. Moreover, the binding property of an electrode active material layer and an electrical power collector can be improved by setting it as an upper limit or less.

As the reinforcing material, for example, various inorganic and organic spherical, plate, rod or fiber fillers can be used. By using the reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term cycle characteristics can be obtained.

The amount of the conductive material and the reinforcing material used is usually 0 part by weight or more, preferably 1 part by weight or more, preferably 20 parts by weight or less, more preferably 10 parts by weight, with respect to 100 parts by weight of the electrode active material. It is as follows.

The thickness of the electrode active material layer is preferably 5 μm or more, more preferably 10 μm or more, preferably 300 μm or less, more preferably 250 μm or less for both the positive electrode and the negative electrode.

The method for producing the electrode active material layer is not particularly limited. The electrode active material layer is produced, for example, by applying an electrode active material and a solvent, and, if necessary, an electrode slurry containing an electrode binder, a thickener and an optional component on a current collector and drying the electrode slurry. sell. As the solvent, either water or an organic solvent can be used.

[4. Porous layer]
The porous layer is a film containing organic particles. Usually, the gaps between the organic particles constitute the pores of the porous layer.

[4.1. Organic particles)
FIG. 1 is a cross-sectional view schematically showing an example of organic particles contained in a porous layer. As shown in FIG. 1, the organic particle 100 has a core-shell structure including a core part 110 and a shell part 120. Here, the core part 110 is a part which is inside the shell part 120 in the organic particle 100. The shell part 120 is a part that covers the outer surface 110 </ b> S of the core part 110, and is usually the outermost part of the organic particles 100. However, the shell portion 120 does not cover the entire outer surface 110S of the core portion 110 but partially covers the outer surface 110S of the core portion 110.

(4.1.1. Core part)
A core part consists of a polymer which has predetermined | prescribed swelling degree with respect to electrolyte solution. Specifically, the swelling degree of the polymer of the core part with respect to the electrolytic solution is usually 5 times or more, preferably 6 times or more, more preferably 7 times or more, and usually 30 times or less, preferably 25 times or less, more Preferably it is 20 times or less. By keeping the swelling degree of the polymer in the core part within the above range, the liquid retention of the electrolyte solution in the core part can be improved, and thus the high temperature cycle characteristics of the lithium ion secondary battery can be improved. Furthermore, by setting the degree of swelling of the polymer in the core part to the lower limit value of the above range ordinarily, the low-temperature output characteristics of the lithium ion secondary battery can be improved, Usually, the binding property of the porous layer in the electrolytic solution can be effectively increased.

As an electrolytic solution used for measuring the degree of swelling of the polymer in the core portion, a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio ethylene carbonate / diethyl carbonate / vinylene carbonate = 68.5 / 30/1) .5; SP value 12.7 (cal / cm ³ ) ^1/2 ), a solution in which LiPF ₆ is dissolved as a supporting electrolyte at a concentration of 1 mol / liter with respect to the solvent is used.

Specifically, the swelling degree of the polymer in the core part can be measured as follows.
First, the polymer of the core part of organic particle is prepared. For example, a polymer obtained by performing the same process as that for producing the core part in the method for producing organic particles is prepared.
Then, a film is produced with the prepared polymer. For example, if the polymer is solid, the polymer is dried at 25 ° C. for 48 hours, and then the polymer is formed into a film to produce a film having a thickness of 0.5 mm. For example, when the polymer is a solution or dispersion such as latex, the solution or dispersion is placed in a petri dish made of polytetrafluoroethylene and dried under the conditions of 25 ° C. and 48 hours to obtain a thickness of 0. Create a 5 mm film.
The film thus prepared is cut into 1 cm squares to obtain test pieces. The weight of this test piece is measured and set to W0.
Moreover, this test piece is immersed in electrolyte solution at 60 degreeC for 72 hours, and the test piece is taken out from electrolyte solution. The electrolyte solution on the surface of the removed test piece is wiped off, and the weight W1 of the test piece after the immersion test is measured.
Then, using these weights W0 and W1, the degree of swelling S (times) is calculated as S = W1 / W0.

As a method for adjusting the degree of swelling of the polymer in the core part, for example, in consideration of the SP value of the electrolytic solution, the kind and amount of the monomer for producing the polymer in the core part are appropriately selected. Can be mentioned. Generally, when the SP value of a polymer is close to the SP value of an electrolytic solution, the polymer tends to swell in the electrolytic solution. On the other hand, when the SP value of the polymer is far from the SP value of the electrolytic solution, the polymer tends to hardly swell in the electrolytic solution.

The SP value means the solubility parameter.
The SP value can be calculated using the method introduced in Hansen Solubility Parameters A User's Handbook, 2ndEd (CRCPless).
The SP value of an organic compound can be estimated from the molecular structure of the organic compound. Specifically, it can be calculated by using simulation software (for example, “HSPiP” (http://www.hansen-solution.com)) that can calculate the SP value from the SMILE equation. The simulation software also includes Hansen SOLUBILITY PARAMETERS A User's Handbook Second Edition, Charles M. Based on the theory described in Hansen.

As the monomer used for producing the core polymer, those having a swelling degree of the polymer in the above range can be used. Examples of such monomers include vinyl chloride monomers such as vinyl chloride and vinylidene chloride; vinyl acetate monomers such as vinyl acetate; styrene, α-methylstyrene, styrenesulfonic acid, butoxystyrene, Aromatic vinyl monomers such as vinylnaphthalene; Vinylamine monomers such as vinylamine; Vinylamide monomers such as N-vinylformamide and N-vinylacetamide; (Meth) acrylic acid such as 2-hydroxyethyl methacrylate Derivatives; (meth) acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and 2-ethylhexyl acrylate; (meth) acrylamide monomers such as acrylamide and methacrylamide; acrylonitrile, (Meth) acryloni such as methacrylonitrile Ril monomers; fluorine-containing acrylate monomers such as 2- (perfluorohexyl) ethyl methacrylate and 2- (perfluorobutyl) ethyl acrylate; maleimide; maleimide derivatives such as phenylmaleimide; 1,3-butadiene, isoprene, etc. And diene monomers. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Among the above monomers, (meth) acrylic acid ester monomers and (meth) acrylonitrile monomers are preferred, and (meth) acrylic acid ester monomers are more preferred. That is, the polymer of the core part preferably contains a (meth) acrylic acid ester monomer unit or a (meth) acrylonitrile monomer unit, and more preferably contains a (meth) acrylic acid ester monomer unit. . Here, the (meth) acrylic acid ester monomer unit refers to a structural unit having a structure formed by polymerizing a (meth) acrylic acid ester monomer. The (meth) acrylonitrile monomer unit means a structural unit having a structure formed by polymerizing (meth) acrylonitrile. Thereby, the degree of swelling of the polymer can be easily controlled. Moreover, the ion diffusibility of the porous layer can be further enhanced.

The total proportion of (meth) acrylic acid ester monomer units and (meth) acrylonitrile monomer units in the polymer of the core part is preferably 50% by weight or more, more preferably 55% by weight or more, and still more preferably. It is 60% by weight or more, particularly preferably 70% by weight or more, preferably 99% by weight or less, more preferably 95% by weight or less, and particularly preferably 90% by weight or less. By keeping the ratio of the (meth) acrylic acid ester monomer unit and the (meth) acrylonitrile monomer unit within the above range, the degree of swelling can be easily controlled within the above range. Moreover, the ion diffusibility of a porous layer can be improved. Furthermore, the low temperature output characteristics of the lithium ion secondary battery can be improved.

The above-mentioned “total of (meth) acrylic acid ester monomer unit and (meth) acrylonitrile monomer unit” may include only a (meth) acrylic acid ester monomer unit, It means that only the acrylonitrile monomer unit may be included, and the (meth) acrylic acid ester monomer unit and the (meth) acrylonitrile monomer unit may be included in combination.

Further, the polymer of the core part may include an acid group-containing monomer unit. As the acid group-containing monomer, the same acid group-containing monomers that can be contained in the shell portion are used. Among these, as the acid group-containing monomer, an unsaturated carboxylic acid monomer is preferable, among which monocarboxylic acid is preferable, and (meth) acrylic acid is more preferable.
Moreover, an acid group containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Further, the ratio of the acid group content body unit in the polymer of the core part is preferably 0.1% by weight or more, more preferably 1% by weight or more, still more preferably 3% by weight or more, preferably 20% by weight. Hereinafter, it is more preferably 10% by weight or less, still more preferably 7% by weight or less. A shell portion that increases the dispersibility of the polymer in the core portion by partially covering the outer surface of the core portion with respect to the outer surface of the polymer in the core portion by keeping the ratio of the acid group content body unit in the above range. It becomes easy to form.

Further, the polymer in the core part preferably contains a crosslinkable monomer unit. A crosslinkable monomer unit is a structural unit having a structure formed by polymerizing a crosslinkable monomer. The crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization by heating or irradiation with energy rays. By including a crosslinkable monomer unit, the degree of swelling of the polymer can be easily within the above range.

Examples of the crosslinkable monomer include polyfunctional monomers having two or more polymerization reactive groups in the monomer. Examples of such polyfunctional monomers include divinyl compounds such as divinylbenzene; di (meta) such as ethylene dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and 1,3-butylene glycol diacrylate. ) Acrylic acid ester compounds; Tri (meth) acrylic acid ester compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; Ethylenically unsaturated monomers containing epoxy groups such as allyl glycidyl ether and glycidyl methacrylate; And polyfunctional monomers having two or more olefinic double bonds such as allyl (meth) acrylate. Among these, from the viewpoint of easily controlling the degree of swelling of the polymer in the core part, a dimethacrylic acid ester compound and an ethylenically unsaturated monomer containing an epoxy group are preferable, and a dimethacrylic acid ester compound is more preferable. preferable. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Generally, when the proportion of the crosslinkable monomer unit in the polymer increases, the degree of swelling of the polymer with respect to the electrolytic solution tends to decrease. Accordingly, the proportion of the crosslinkable monomer unit is preferably determined in consideration of the type and amount of the monomer used. The specific ratio of the crosslinkable monomer unit in the polymer of the core part is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, Preferably it is 5 weight% or less, More preferably, it is 4 weight% or less, Most preferably, it is 3 weight% or less. By setting the ratio of the crosslinkable monomer unit to be equal to or higher than the lower limit of the above range, the binding property of the porous layer in the electrolytic solution can be enhanced. Moreover, the lifetime of a lithium ion secondary battery can be lengthened by making it into an upper limit or less.

The glass transition temperature of the polymer of the core part is preferably 0 ° C. or higher, more preferably 5 ° C. or higher, further preferably 10 ° C. or higher, still more preferably 20 ° C. or higher, particularly preferably 30 ° C. or higher, more particularly preferably. 60 ° C. or higher, preferably 150 ° C. or lower, more preferably 130 ° C. or lower, further preferably 110 ° C. or lower, still more preferably 100 ° C. or lower, particularly preferably 90 ° C. or lower, more particularly preferably 80 ° C. or lower. . By keeping the glass transition temperature of the polymer in the core part within the above range, the expansion of the battery cell due to charging / discharging can be suppressed, so that the shape of the battery cell can be maintained over a long period of time. Moreover, when the glass transition temperature of the polymer of the core part is in the above range, the organic particles can be effectively melted at a temperature at which the organic particles exhibit a shutdown function. The glass transition temperature can be measured according to JIS K7121.

The diameter of the core part is preferably 50% or more, more preferably 60% or more, still more preferably 70% or more, particularly preferably 80% or more, with respect to 100% of the volume average particle diameter of the organic particles. Is 99% or less, more preferably 98.5% or less, and particularly preferably 98% or less. By setting the diameter of the core part to be equal to or greater than the lower limit value of the above range, the ionic conductivity of the porous layer can be increased. Moreover, the binding property of the porous layer in electrolyte solution can be improved by making it into an upper limit or less.
The diameter of the core part can be measured as the volume average particle diameter of the particulate polymer before forming the shell part obtained in the production process of the organic particles. The particulate polymer before forming such a shell portion is a particulate polymer constituting the core portion.

(4.1.2. Shell part)
The shell part is made of a polymer having a predetermined swelling degree smaller than that of the core part with respect to the electrolytic solution. Specifically, the swelling degree of the polymer of the shell part with respect to the electrolytic solution is usually larger than 1 time, preferably 1.1 times or more, more preferably 1.2 times or more, and usually 4 times or less, Preferably it is 3.5 times or less, More preferably, it is 3.0 times or less. By keeping the swelling degree of the polymer of the shell part within the above range, the mechanical strength of the shell part when swollen in the electrolytic solution can be increased, so that external force is not easily transmitted to the core part. Therefore, when the electrolyte solution is not insufficient, unintended delivery of the electrolyte solution from the core portion due to external force can be suppressed, so that the liquid retention of the electrolyte solution in the core portion can be improved. Therefore, the high temperature cycle characteristics of the lithium ion secondary battery can be improved. In addition, by keeping the degree of swelling of the polymer of the shell part in the above range, usually, the binding property of the organic particles in the electrolytic solution can be increased, and consequently the binding property of the porous layer in the electrolytic solution is increased. be able to.

As the electrolytic solution used for measuring the degree of swelling of the polymer in the shell portion, the same electrolytic solution used for measuring the degree of swelling of the polymer in the core portion is used.

Specifically, the swelling degree of the polymer in the shell part can be measured as follows.
First, the polymer of the shell part of organic particles is prepared. For example, in the method for producing organic particles, the monomer composition used for producing the shell portion is used instead of the monomer composition used for producing the core portion, and the polymer is produced in the same manner as the method for producing the core portion. To manufacture.
Thereafter, a film is produced from the polymer in the shell portion by the same method as the method for measuring the degree of swelling of the polymer in the core portion, a test piece is obtained from the film, and the degree of swelling S is measured.

As a method for adjusting the degree of swelling of the polymer of the shell part, for example, considering the SP value of the electrolytic solution, the kind and amount of the monomer for producing the polymer of the shell part are appropriately selected. Can be mentioned.

As the monomer used for producing the polymer of the shell part, those having a swelling degree of the polymer within the above range can be used. As such a monomer, the same example as the monomer illustrated as a monomer which can be used in order to manufacture the polymer of a core part is mentioned, for example. Moreover, such a monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Among these monomers, aromatic vinyl monomers are preferable. That is, the polymer of the shell part preferably contains an aromatic vinyl monomer unit. Here, the aromatic vinyl monomer unit refers to a structural unit having a structure formed by polymerizing an aromatic vinyl monomer. Among aromatic vinyl monomers, styrene derivatives such as styrene and styrene sulfonic acid are more preferable. When an aromatic vinyl monomer is used, it is easy to control the degree of swelling of the polymer. Moreover, the binding property of the porous layer in the electrolytic solution can be enhanced.

The ratio of the aromatic vinyl monomer unit in the polymer of the shell part is preferably 20% by weight or more, more preferably 40% by weight or more, still more preferably 50% by weight or more, still more preferably 60% by weight or more, particularly Preferably it is 80 weight% or more, Preferably it is 100 weight% or less, More preferably, it is 99.5 weight% or less, More preferably, it is 99 weight% or less. By keeping the ratio of the aromatic vinyl monomer unit within the above range, the degree of swelling can be easily controlled within the above range. In addition, the binding force of the porous layer in the electrolyte can be further increased.

Further, the polymer of the shell part may include an acid group-containing monomer unit. The acid group-containing monomer unit is a structural unit having a structure formed by polymerizing a monomer having an acid group. Examples of the acid group-containing monomer include an unsaturated carboxylic acid monomer, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, and a monomer having a hydroxyl group.

Examples of the unsaturated carboxylic acid monomer include monocarboxylic acid and dicarboxylic acid. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and the like.

Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, ethyl (meth) acrylic acid-2-sulfonate, 2-acrylamido-2-methylpropane sulfone. Acid, 3-allyloxy-2-hydroxypropanesulfonic acid and the like.

Examples of the monomer having a phosphoric acid group include phosphoric acid-2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, and ethyl phosphate- (meth) acryloyloxyethyl phosphate. Can be mentioned.

Examples of the monomer having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

Among these, unsaturated carboxylic acid monomers are preferable, monocarboxylic acid is preferable, and (meth) acrylic acid is preferable.
Moreover, an acid group containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The ratio of the acid group-containing monomer unit in the polymer of the shell part is preferably 0.1% by weight or more, more preferably 1% by weight or more, still more preferably 3% by weight or more, preferably 20% by weight or less. More preferably, it is 10 weight% or less, More preferably, it is 7 weight% or less. By keeping the ratio of the acid group-containing monomer unit within the above range, the dispersibility of the organic particles in the porous layer can be improved, and good binding properties can be expressed over the entire porous layer.

Further, the polymer of the shell part may contain a crosslinkable monomer unit. As a crosslinkable monomer, the same example as what was illustrated as a crosslinkable monomer which can be used for the polymer of a core part is mentioned, for example. Moreover, a crosslinking | crosslinked monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The ratio of the crosslinkable monomer unit in the polymer of the shell part is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 5%. % By weight or less, more preferably 4% by weight or less, particularly preferably 3% by weight or less.

The glass transition temperature of the polymer of the shell part is preferably 50 ° C. or higher, more preferably 80 ° C. or higher, particularly preferably 100 ° C. or higher, preferably 200 ° C. or lower, more preferably 180 ° C. or lower, still more preferably. Is 150 ° C. or lower, particularly preferably 120 ° C. or lower. By keeping the glass transition temperature of the polymer of the shell part in the above range, the expansion of the battery cell due to charging / discharging can be suppressed, so that the shape of the battery cell can be maintained for a long period of time. Moreover, when the glass transition temperature of the polymer of the shell part is in the above range, the shape of the organic particles can be effectively maintained at a temperature lower than the temperature at which the organic particles exhibit a shutdown function.

The shell part partially covers the outer surface of the core part. That is, the shell part covers the outer surface of the core part, but does not cover the entire outer surface of the core part. Even if it appears that the outer surface of the core part is completely covered by the shell part, the shell part is outside the core part as long as a hole that communicates the inside and outside of the shell part is formed. It is a shell part concerning the present invention which partially covers the surface. Therefore, for example, organic particles including a shell portion having pores communicating from the outer surface of the shell portion to the outer surface of the core portion are included in the organic particles according to the present invention. Here, the outer surface of the shell portion is usually the peripheral surface of the organic particles.

The average ratio at which the outer surface of the core part is covered with the shell part is preferably 10% or more, more preferably 30% or more, still more preferably 40% or more, particularly preferably 60% or more, preferably 99.9%. Below, more preferably 98% or less, still more preferably 95% or less, still more preferably 90% or less, and particularly preferably 85% or less. By keeping the average ratio of the outer surface of the core portion covered by the shell portion within the above range, the balance between the ion diffusibility and the binding property of the porous layer in the electrolytic solution can be improved.

The average ratio at which the outer surface of the core part is covered with the shell part can be measured from the observation result of the cross-sectional structure of the organic particles. Specifically, it can be measured by the method described below.
First, organic particles are sufficiently dispersed in a room temperature curable epoxy resin, and then embedded to produce a block piece containing organic particles. Next, a measurement sample is prepared by cutting out from the block piece into a thin piece having a thickness of 80 nm to 200 nm with a microtome equipped with a diamond blade. Thereafter, if necessary, the measurement sample is dyed using, for example, ruthenium tetroxide or osmium tetroxide.
Next, this measurement sample is set in a transmission electron microscope (TEM), and a cross-sectional structure of the organic particles is photographed. The magnification of the electron microscope is preferably such that the cross section of one organic particle enters the field of view, specifically about 10,000 times.
In the cross-sectional structure of the photographed organic particles, the circumference length D1 corresponding to the outer surface of the core portion and the length D2 of the portion where the outer surface of the core portion abuts on the shell portion are measured. And ratio Rc by which the outer surface of the core part of the organic particle is covered with a shell part is computed by the following (1) formula using measured length D1 and length D2.
Covering ratio Rc (%) = D2 / D1 × 100 (1)
The covering ratio Rc is measured for 20 or more organic particles, and an average value thereof is calculated to obtain an average ratio at which the outer surface of the core part is covered by the shell part.
The covering ratio Rc can be calculated manually from the cross-sectional structure, but can also be calculated using commercially available image analysis software. As commercially available image analysis software, for example, “AnalySIS Pro” (manufactured by Olympus Corporation) can be used.

The shell portion preferably has an average thickness that falls within a predetermined range with respect to the volume average particle diameter of the organic particles. Specifically, the average thickness of the shell part with respect to the volume average particle diameter of the organic particles is preferably 1% or more, more preferably 2% or more, particularly preferably 5% or more, preferably 30% or less, more preferably. Is 25% or less, particularly preferably 20% or less. By setting the average thickness of the shell portion to be equal to or higher than the lower limit of the above range, the low temperature output characteristics of the lithium ion secondary battery can be further enhanced. Moreover, the binding property of the porous layer in electrolyte solution can further be improved by setting it as an upper limit or less.

The average thickness of the shell is determined by observing the cross-sectional structure of the organic particles with a transmission electron microscope (TEM). Specifically, the maximum thickness of the shell portion in the cross-sectional structure of the organic particles is measured, and the average value of the maximum thickness of the shell portions of 20 or more organic particles arbitrarily selected is defined as the average thickness of the shell portion. However, the shell part is composed of polymer particles, and the particles constituting the shell part do not overlap in the radial direction of the organic particles, and the polymer part constitutes the shell part with a single layer. In such a case, the number average particle diameter of the particles constituting the shell portion is defined as the average thickness of the shell portion.

The form of the shell part is not particularly limited, but the shell part is preferably composed of polymer particles. When the shell part is composed of polymer particles, a plurality of particles constituting the shell part may overlap in the radial direction of the organic particles. However, in the radial direction of the organic particles, it is preferable that the particles constituting the shell portion do not overlap each other, and those polymer particles constitute the shell portion as a single layer.

The number average particle diameter of the particles constituting the shell part is preferably 10 nm or more, more preferably 20 nm or more, particularly preferably 30 nm or more, preferably 200 nm or less, more preferably 150 nm or less, particularly preferably 100 nm or less. . By keeping the number average particle diameter within the above range, the balance between the diffusibility of ions in the electrolyte and the binding property of the porous layer can be improved.

The number average particle diameter of the particles constituting the shell portion is determined by observing the cross-sectional structure of the organic particles with a transmission electron microscope (TEM). Specifically, the longest diameter of the particles constituting the shell portion in the cross-sectional structure of the organic particles is measured, and the average value of the longest diameters of the particles constituting the shell portions of 20 or more organic particles arbitrarily selected is determined as the shell. The number average particle diameter of the particles constituting the part.

(4.1.3. Optional components)
The organic particles may include arbitrary components other than the above-described core part and shell part as long as the effects of the present invention are not significantly impaired.
For example, you may have the part formed with the polymer different from a core part inside a core part. As a specific example, the seed particles used when the organic particles are produced by the seed polymerization method may remain inside the core portion.
However, from the viewpoint of remarkably exhibiting the effect of the present invention, the organic particles preferably include only the core part and the shell part.

(4.1.4. Size of organic particles)
The volume average particle diameter of the organic particles is preferably 0.01 μm or more, more preferably 0.1 μm or more, particularly preferably 0.3 μm or more, preferably 10 μm or less, more preferably 5 μm or less, particularly preferably 1 μm or less. It is. By setting the volume average particle diameter of the organic particles to be equal to or greater than the lower limit of the above range, the expansion of the battery cell due to charging / discharging can be suppressed, so that the shape of the battery cell can be maintained for a long period. Moreover, the low temperature output characteristic of a lithium ion secondary battery can be made favorable by setting it as an upper limit or less.

(4.1.5. Amount of organic particles)
The amount of the organic particles is preferably set so that the ratio of the organic particles in the porous layer is within a predetermined range. Specifically, the ratio of the organic particles in the porous layer is preferably 50% by weight or more, more preferably 60% by weight or more, still more preferably 70% by weight or more, particularly preferably 80% by weight or more, preferably 99%. .9% by weight or less, more preferably 99% by weight or less, still more preferably 98% by weight or less, and particularly preferably 96% by weight or less. By setting the amount of the organic particles in the above range, the binding property of the porous layer in the electrolytic solution can be enhanced and the ion diffusibility can be enhanced.

(4.1.6. Method for producing organic particles)
The organic particles, for example, by using a polymer monomer of the core part and a monomer of the polymer of the shell part, and by gradually changing the ratio of these monomers over time, Can be manufactured. Specifically, it can be obtained by a continuous multi-stage emulsion polymerization method and a multi-stage suspension polymerization method in which the polymer in the previous stage is sequentially coated with the polymer in the subsequent stage.

An example of obtaining organic particles having a core-shell structure by a multi-stage emulsion polymerization method is shown.
In the polymerization, according to a conventional method, as an emulsifier, for example, anionic surfactants such as sodium dodecylbenzenesulfonate and sodium dodecylsulfate, nonionic surfactants such as polyoxyethylene nonylphenyl ether and sorbitan monolaurate, or Cationic surfactants such as octadecylamine acetate can be used. Examples of the polymerization initiator include peroxides such as t-butylperoxy-2-ethylhexanoate, potassium persulfate, cumene peroxide, 2,2′-azobis (2-methyl-N- (2 An azo compound such as -hydroxyethyl) -propionamide) or 2,2'-azobis (2-amidinopropane) hydrochloride can be used. One of these emulsifiers and polymerization initiators may be used alone, or two or more thereof may be used in combination at any ratio.

As a polymerization procedure, first, a monomer and an emulsifier that form a core part are mixed in water as a solvent, and then a polymerization initiator is added, and then a particulate polymer that constitutes the core part by emulsion polymerization. Get. Furthermore, the organic particle which has a core shell structure can be obtained by superposing | polymerizing the monomer which forms a shell part in presence of the particulate polymer which comprises this core part.

At this time, from the viewpoint of partially covering the outer surface of the core portion with the shell portion, it is preferable to supply the polymer monomer of the shell portion to the polymerization system in a plurality of times or continuously. By supplying the polymer monomer of the shell part to the polymerization system in a divided or continuous manner instead of supplying it to the polymerization system at one time, the polymer constituting the shell part is usually formed into particles. When the particles are bonded to the core portion, a shell portion that partially covers the core portion can be formed.

When the monomer of the polymer of the shell part is divided and supplied multiple times, the particle diameter of the particles constituting the shell part and the average thickness of the shell part are controlled according to the ratio of dividing the monomer. It is possible. In addition, when continuously supplying the monomer of the polymer of the shell part, by adjusting the supply amount of the monomer per unit time, the particle diameter of the particles constituting the shell part and the average of the shell part It is possible to control the thickness.

In addition, when the monomer forming the polymer of the shell part is a monomer having a low affinity for the polymerization solvent, it tends to easily form a shell part that partially covers the core part. When the polymerization solvent is water, the monomer that forms the polymer of the shell part preferably includes a hydrophobic monomer, and particularly preferably includes an aromatic vinyl monomer.

Moreover, if the amount of the emulsifier used is reduced, there is a tendency to form a shell part that partially covers the core part. By appropriately adjusting the amount of the emulsifier, a shell part that partially covers the core part can be formed. it can.

The volume average particle diameter of the particulate polymer constituting the core part, the volume average particle diameter of the organic particles after forming the shell part, and the number average particle diameter of the particles constituting the shell part are, for example, The desired range can be obtained by adjusting the amount of the emulsifier, the amount of the monomer, and the like.

Furthermore, the average ratio of the outer surface of the core part covered by the shell part corresponds to the volume average particle diameter of the particulate polymer constituting the core part, for example, the amount of emulsifier and the polymer of the shell part By adjusting the amount of the monomer, a desired range can be obtained.

[4.2. (Binder for porous layer)
It is preferable that a porous layer contains the binder for porous layers. By using this porous layer binder, the organic particles can be bound together with the porous layer binder, and the mechanical strength of the porous layer can be increased. Moreover, since the binder for porous layers has the effect | action which binds a porous layer to an electrode active material layer, the binding property of a porous layer and an electrode active material layer can be improved.

As the binder for the porous layer, a polymer is usually used. Although a non-particulate polymer may be used as the binder for the porous layer, it is preferable to use a particulate polymer from the viewpoint of increasing the pores of the porous layer and improving the ion permeability. As such a particulate polymer, a water-insoluble polymer is usually used. Since a slurry for a porous layer, which is a composition for producing a porous layer, often contains water as a solvent, a water-insoluble polymer is used as the binder for the porous layer, so that the binder for the porous layer in the porous layer is used. Can be easily made into particles.

As the water-insoluble polymer, it is preferable to use a thermoplastic elastomer such as a styrene-butadiene copolymer, a styrene-acrylonitrile copolymer, or a (meth) acrylate polymer. Among these, as the binder for the porous layer, a (meth) acrylic acid ester polymer is preferable. A (meth) acrylic acid ester polymer means a polymer containing a (meth) acrylic acid ester monomer unit. By using the (meth) acrylic acid ester polymer as the binder for the porous layer, the ionic conductivity of the porous layer can be increased, so that the rate characteristics of the lithium ion secondary battery can be improved. In addition, since the (meth) acrylic acid ester monomer unit is electrochemically stable, the high-temperature cycle characteristics of the lithium ion secondary battery can be further improved.

Examples of the (meth) acrylic acid ester monomer corresponding to the (meth) acrylic acid ester monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and t-butyl acrylate. , Alkyl acrylate esters such as pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; and methyl methacrylate, ethyl methacrylate, n -Propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pen Methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Of these, n-butyl acrylate and 2-ethylhexyl acrylate are preferable from the viewpoint of excellent flexibility.

The proportion of the (meth) acrylic acid ester monomer unit in the binder for the porous layer is preferably 50% by weight or more, more preferably 70% by weight or more, particularly preferably 90% by weight or more, preferably 99% by weight or less. More preferably, it is 98 weight% or less, Most preferably, it is 97 weight% or less. By setting the ratio of the (meth) acrylic acid ester monomer unit to the lower limit value or more, the flexibility of the porous layer can be increased and the binding property of the porous layer can be improved. Moreover, the rigidity of a porous layer can be raised by making the ratio of a (meth) acrylic acid ester monomer unit below the said upper limit, and the binding property of a porous layer can also be improved by this.

The porous layer binder preferably contains an amide monomer unit. An amide monomer unit is a structural unit having a structure formed by polymerizing an amide monomer. The amide monomer is a monomer having an amide group and includes not only an amide compound but also an imide compound.

By having an amide monomer unit, the binder for a porous layer can capture halide ions in the electrolytic solution. Therefore, since decomposition | disassembly of the electrolyte solution and SEI (Solid Electrolyte Interphase) caused by halide ion can be suppressed, generation | occurrence | production of the gas accompanying charging / discharging can be suppressed. Moreover, the binder for porous layers can capture transition metal ions in the electrolytic solution. For example, metal ions eluted from the positive electrode can be captured by the porous layer binder. Therefore, precipitation of the transition metal at the negative electrode accompanying charge / discharge can be effectively suppressed. Therefore, if the porous layer binder is used, the degree of decrease in battery capacity due to charge / discharge can be reduced, so that the cycle characteristics of the lithium ion secondary battery can be further improved.

In addition, if the binder for the porous layer is used, the generation of gas accompanying charging / discharging can be suppressed as described above, so that the generation of voids by the gas can be suppressed. Therefore, the low temperature output characteristics of the lithium ion secondary battery can be further improved. The generation amount of such gas can be evaluated by the volume change of the cell of the lithium ion secondary battery when charging / discharging is repeated.

Examples of the amide monomer include a carboxylic acid amide monomer, a sulfonic acid amide monomer, and a phosphoric acid amide monomer.

The carboxylic acid amide monomer is a monomer having an amide group bonded to a carboxylic acid group. Examples of the carboxylic acid amide monomer include (meth) acrylamide, α-chloroacrylamide, N, N′-methylenebis (meth) acrylamide, N, N′-ethylenebis (meth) acrylamide, N-hydroxymethyl (meta) ) Acrylamide, N-2-hydroxyethyl (meth) acrylamide, N-2-hydroxypropyl (meth) acrylamide, N-3-hydroxypropyl (meth) acrylamide, crotonic acid amide, maleic acid diamide, fumaric acid diamide, diacetone Unsaturated carboxylic acid amide compounds such as acrylamide; N-dimethylaminomethyl (meth) acrylamide, N-2-aminoethyl (meth) acrylamide, N-2-methylaminoethyl (meth) acrylamide, N-2-ethylamino Ethyl (meta Acrylamide, N-2-dimethylaminoethyl (meth) acrylamide, N-2-diethylaminoethyl (meth) acrylamide, N-3-aminopropyl (meth) acrylamide, N-3-methylaminopropyl (meth) acrylamide, N- And N-aminoalkyl derivatives of unsaturated carboxylic acid amides such as 3-dimethylaminopropyl (meth) acrylamide.

The sulfonic acid amide monomer is a monomer having an amide group bonded to a sulfonic acid group. Examples of the sulfonic acid amide monomer include 2-acrylamido-2-methylpropanesulfonic acid and Nt-butylacrylamidesulfonic acid.

The phosphoric acid amide monomer is a monomer having an amide group bonded to a phosphoric acid group. Examples of the phosphoric acid amide monomer include acrylamide phosphonic acid and acrylamide phosphonic acid derivatives.

Among these amide monomers, from the viewpoint of enhancing the durability of the porous layer, carboxylic acid amide monomers are preferable, unsaturated carboxylic acid amide compounds are more preferable, (meth) acrylamide and N-hydroxymethyl (meth). Acrylamide is particularly preferred.
Moreover, an amide monomer and an amide monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The ratio of the amide monomer unit in the binder for the porous layer is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 20% by weight. Hereinafter, it is more preferably 15% by weight or less, particularly preferably 10% by weight or less. By making the ratio of the amide monomer unit at least the lower limit of the above range, gas generation in the lithium ion secondary battery can be effectively suppressed, and transition metal ions in the electrolytic solution can be effectively captured. . Moreover, the cycle characteristic of a lithium ion secondary battery can be improved by being below an upper limit.

Moreover, the binder for porous layers may contain an acid group-containing monomer unit. As the acid group-containing monomer unit, for example, those selected from the same range as those described as usable for organic particles can be used. Moreover, an acid group containing monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The ratio of the acid group-containing monomer unit in the binder for the porous layer is preferably 0.2% by weight or more, more preferably 0.4% by weight or more, particularly preferably 0.6% by weight or more, preferably 10%. It is 0.0% by weight or less, more preferably 6.0% by weight or less, and particularly preferably 4.0% by weight or less. By setting the ratio of the acid group-containing monomer unit within the above range, the cohesive failure of the porous layer is suppressed, and the binding property of the porous layer in the electrolytic solution can be improved.

Furthermore, the binder for a porous layer may contain a (meth) acrylonitrile monomer unit. At this time, as the (meth) acrylonitrile monomer corresponding to the (meth) acrylonitrile monomer unit, acrylonitrile may be used, methacrylonitrile may be used, or acrylonitrile and methacrylonitrile are used in combination. May be.

The proportion of the (meth) acrylonitrile monomer unit in the binder for the porous layer is preferably 0.2% by weight or more, more preferably 0.5% by weight or more, particularly preferably 1.0% by weight or more, preferably It is 20.0% by weight or less, more preferably 10.0% by weight or less, and particularly preferably 5.0% by weight or less. By making the ratio of the (meth) acrylonitrile monomer unit equal to or higher than the lower limit, the life of the lithium ion secondary battery can be particularly prolonged. Moreover, the mechanical strength of a porous layer can be improved by making the ratio of a (meth) acrylonitrile monomer unit below the said upper limit.

Moreover, the binder for porous layers may contain a crosslinkable monomer unit. Examples of the crosslinkable monomer corresponding to the crosslinkable monomer unit include the same examples as those exemplified in the description of the organic particles. Furthermore, since N-hydroxymethyl (meth) acrylamide exemplified as a carboxylic acid amide monomer can act as both an amide monomer and a crosslinkable monomer, the N-hydroxymethyl (meth) acrylamide is crosslinked. It may be used as a functional monomer. A crosslinkable monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The proportion of the crosslinkable monomer unit in the binder for the porous layer is preferably 0.2% by weight or more, more preferably 0.6% by weight or more, particularly preferably 1.0% by weight or more, preferably 5. It is 0 wt% or less, more preferably 4.0 wt% or less, and particularly preferably 3.0 wt% or less. By setting the ratio of the crosslinkable monomer unit to the lower limit value or more, the mechanical strength of the porous layer can be increased. Moreover, by making it below the upper limit value, it is possible to prevent the flexibility of the porous layer from being impaired and becoming brittle.

The porous layer binder may further contain any structural unit other than those described above. Examples of the arbitrary structural unit include a structural unit having a structure formed by polymerizing styrene (styrene unit) and a structural unit having a structure formed by polymerizing butadiene (butadiene unit). Moreover, these arbitrary structural units may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The glass transition temperature of the binder for the porous layer is preferably −100 ° C. or higher, more preferably −90 ° C. or higher, particularly preferably −80 ° C. or higher, preferably 0 ° C. or lower, more preferably −5 ° C. or lower, particularly Preferably, it is −10 ° C. or lower. By setting the glass transition temperature of the binder for porous layers to be equal to or higher than the lower limit of the above range, the binding property of the porous layer can be enhanced. Moreover, the softness | flexibility of a porous layer can be improved by making it into an upper limit or less.

When the porous layer binder is a particulate polymer, the volume average particle diameter of the particles of the porous layer binder is preferably 0.01 μm or more, more preferably 0.02 μm or more, and particularly preferably 0.05 μm or more. Yes, preferably 1 μm or less, more preferably 0.9 μm or less, and particularly preferably 0.8 μm or less. The dispersibility of the binder for porous layers can be improved by setting the volume average particle diameter of the binder for porous layers to be equal to or greater than the lower limit of the above range. Moreover, the binding property of a porous layer can be improved by setting it as an upper limit or less.

Examples of the method for producing the porous layer binder include a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among them, the emulsion polymerization method and the suspension polymerization method are preferable because they can be polymerized in water and can be suitably used as the material for the slurry for the porous layer as it is. Moreover, when manufacturing the binder for porous layers, it is preferable that the reaction system contains a dispersing agent. The binder for the porous layer is usually formed of a polymer that substantially constitutes the binder, but it may be accompanied by optional components such as additives used in the polymerization.

The amount of the binder for the porous layer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, preferably 30 parts by weight or less, more preferably 25 parts by weight with respect to 100 parts by weight of the organic particles. Or less. By setting the amount of the binder for the porous layer to be not less than the lower limit of the above range, the expansion of the battery cell due to charging / discharging can be suppressed, so that the shape of the battery cell can be maintained over a long period of time. Moreover, the low temperature output characteristic of a lithium ion secondary battery can be made favorable by setting it as an upper limit or less.

[4.3. (Optional ingredients)
A porous layer can contain arbitrary components other than the organic particle mentioned above and the binder for porous layers. As such optional components, those which do not exert an excessively unfavorable influence on the battery reaction can be used. For example, the porous layer includes non-conductive particles, water-soluble polymers, isothiazoline compounds, chelate compounds, pyrithione compounds, dispersants, leveling agents, wetting agents, antioxidants, thickeners, antifoaming agents, wetting agents, And the electrolyte solution additive etc. which have the function of electrolyte solution decomposition | disassembly suppression may be included. These arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[4.4. (Position of porous layer)
The porous layer is provided directly on the electrode active material layer. That is, the porous layer is in direct contact with the electrode active material layer, and no other layer exists between the porous layer and the electrode active material layer. As a result, since the organic particles contained in the porous layer are in the immediate vicinity of the electrode active material layer, when the electrolyte is decomposed in the vicinity of the electrode active material layer and voids are generated, the electrolyte solution from the core of the organic particles Can be quickly supplied to fill the gap. For this reason, in a lithium ion secondary battery, since the fall of the battery capacity by decomposition | disassembly of electrolyte solution can be suppressed, a high high temperature cycling characteristic is realizable.

[4.5. (Thickness of porous layer)
The thickness of the porous layer is preferably 0.1 μm or more, more preferably 0.2 μm or more, particularly preferably 0.5 μm or more, preferably 30 μm or less, more preferably 25 μm or less, and particularly preferably 20 μm or less. By setting the thickness of the porous layer to be equal to or greater than the lower limit of the above range, the expansion of the battery cell due to charging / discharging can be suppressed, so that the shape of the battery cell can be maintained over a long period of time. Moreover, the low temperature output characteristic of a lithium ion secondary battery can be made favorable by setting it as an upper limit or less.

[4.6. Action by porous layer)
As described above, when the electrolyte is decomposed along with charge / discharge, the porous layer has an effect of suppressing the decrease in battery capacity by supplying the electrolyte lost from the decomposition from the core. Demonstrate. Moreover, this porous layer can also express the following effects, for example.
Usually, when the shell part of organic particles swells in the electrolyte solution, high binding properties are expressed. For this reason, the porous layer containing the organic particles can have high binding properties in the electrolytic solution. Even when the organic particles are not swollen in the electrolytic solution, the organic particles can exhibit binding properties by being heated to a certain temperature or higher (for example, 60 ° C. or higher).
Since the porous layer contains organic particles, pores are easily formed in the porous layer. Therefore, the porous layer usually has porosity and can exhibit excellent ion diffusibility. Furthermore, the core part of organic particles usually has high ion diffusibility. Therefore, since lithium ions can easily permeate the porous layer, the resistance of the lithium ion secondary battery can be reduced.
Usually, since the shell part of the organic particle does not swell so much as to impair the rigidity excessively, the organic particle has an appropriate rigidity. Therefore, the porous layer is excellent in mechanical strength. Since the porous layer having excellent mechanical strength is directly provided on the electrode active material layer in this way, the desorption of particles such as the electrode active material from the electrode active material layer and the current collector of the electrode active material layer Can be prevented.

[4.7. (Method for forming porous layer)
The porous layer includes, for example, a step of applying a slurry for the porous layer on the electrode active material layer to obtain a film of the slurry for the porous layer, and a step of removing a solvent such as water by drying from the film as necessary. It can form by the manufacturing method containing. Here, the slurry for a porous layer is a fluid composition containing components contained in the porous layer, a solvent, and optional components as necessary.

It is preferable to use water as the solvent. Since the organic particles and the binder for the porous layer are usually water-insoluble, when water is used as the solvent, the organic particles and the binder for the porous layer are dispersed in the form of particles in water.

As a solvent, a solvent other than water may be used in combination with water. Examples of the solvent that can be used in combination with water include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate and acetic acid Esters such as butyl, γ-butyrolactone, ε-caprolactone; nitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, etc. Alcohols; amides such as N-methylpyrrolidone (NMP) and N, N-dimethylformamide; and the like. One of these may be used alone, or two or more of these may be used in combination at any ratio. However, it is preferable to use water alone as the solvent.

The amount of the solvent in the porous layer slurry is preferably set so that the solid content concentration of the porous layer slurry is within a desired range. The solid content concentration of the specific slurry for the porous layer is preferably 10% by weight or more, more preferably 15% by weight or more, particularly preferably 20% by weight or more, preferably 80% by weight or less, more preferably 75% by weight. % Or less, particularly preferably 70% by weight or less. Here, the solid content of a certain composition means a substance remaining after the composition is dried.

Each component contained in the slurry for the porous layer usually has high dispersibility. Therefore, the viscosity of the slurry for the porous layer can usually be easily lowered. The specific viscosity of the slurry for the porous layer is preferably 10 mPa · s to 2000 mPa · s from the viewpoint of improving the coating property when the porous layer is produced. The viscosity is a value when measured at 25 ° C. and a rotation speed of 60 rpm using an E-type viscometer.

The slurry for the porous layer can be produced, for example, by mixing the components described above. There is no restriction | limiting in particular in the mixing order of each component. There is no particular limitation on the mixing method. Usually, in order to disperse particles quickly, mixing is performed using a disperser as a mixing device. The disperser is preferably an apparatus capable of uniformly dispersing and mixing the above components. Examples include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer. Among them, a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix is particularly preferable because a high dispersion share can be added.

Examples of the method for applying the slurry for the porous layer include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Among these, the dipping method and the gravure method are preferable in that a uniform porous layer can be obtained.

Examples of the method for drying the porous layer slurry include: drying with warm air, hot air, low-humidity air, etc .; vacuum drying; drying method by irradiation with infrared rays, far infrared rays, and electron beams.

The temperature during drying is preferably 40 ° C. or higher, more preferably 45 ° C. or higher, particularly preferably 50 ° C. or higher, preferably 90 ° C. or lower, more preferably 80 ° C. or lower, particularly preferably 70 ° C. or lower. . By setting the drying temperature to be equal to or higher than the lower limit of the above range, it is possible to efficiently remove the solvent and the low molecular weight compound from the porous layer slurry. Moreover, the deformation | transformation by the heat | fever of the electrode active material layer as a base material can be suppressed by setting it as below an upper limit.

The drying time is preferably 5 seconds or more, more preferably 10 seconds or more, particularly preferably 15 seconds or more, preferably 3 minutes or less, more preferably 2 minutes or less, and particularly preferably 1 minute or less. By setting the drying time to be at least the lower limit of the above range, the solvent can be sufficiently removed from the slurry for the porous layer, so that the output characteristics of the battery can be improved. Moreover, manufacturing efficiency can be improved by setting it as an upper limit or less.

In the method for producing the porous layer, any operation other than those described above may be performed.
For example, the porous layer may be subjected to pressure treatment by a pressing method such as a mold press and a roll press. By performing the pressure treatment, the binding property between the electrode active material layer and the porous layer can be improved. However, from the viewpoint of keeping the porosity of the porous layer within a preferable range, it is preferable to appropriately control the pressure and pressurization time so as not to become excessively large.
In order to remove residual moisture, it is preferable to dry in, for example, vacuum drying or a dry room.
Further, for example, heat treatment is also preferable. Thereby, the thermal crosslinking group contained in the polymer component can be crosslinked, and the binding property of the porous layer can be enhanced.

[5. Lithium ion secondary battery]
The lithium ion secondary battery of this invention is equipped with the electrode and electrolyte solution of this invention. Specifically, the lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution, and includes the electrode of the present invention as at least one of the positive electrode and the negative electrode. Since the electrode of the present invention is provided, the lithium ion secondary battery of the present invention is excellent in high temperature cycle characteristics.

Moreover, in the lithium ion secondary battery of the present invention, the electrode of the present invention may have a flat shape without being folded or bent. A lithium ion secondary battery including an electrode having a flat shape in this way has a configuration in which electrodes having the flat shape are stacked, and thus is called a stacked battery. Since the laminated battery is manufactured without a process of applying high pressure such as bending and winding, the distance between the electrodes is generally increased by charging and discharging, and the battery characteristics such as cycle characteristics and output characteristics are improved. There is a tendency to be inferior. However, since the electrode of the present invention has a high binding property in the porous layer in the electrolytic solution, the porous layer can strongly bind the positive electrode and the negative electrode. Therefore, even if the lithium ion secondary battery provided with the electrode of the present invention is a laminated type, it is difficult for the distance between the electrodes to increase, and thus the battery characteristics can be improved.

As the electrolytic solution, a polymer that can swell the polymer of the core portion and the polymer of the shell portion of the organic particles with the above-described predetermined degree of swelling can be used. As such an electrolytic solution, an organic electrolytic solution containing an organic solvent and a supporting electrolyte dissolved in the organic solvent can be preferably used.

For example, a lithium salt is used as the supporting electrolyte. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among them, LiPF ₆ , LiClO ₄ and CF ₃ SO ₃ Li are preferable because they are easily soluble in a solvent and exhibit a high degree of dissociation. Moreover, a supporting electrolyte may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Since the lithium ion conductivity tends to increase as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

The concentration of the supporting electrolyte in the electrolytic solution is preferably 1% by weight or more, more preferably 5% by weight or more, preferably 30% by weight or less, more preferably 20% by weight or less. Depending on the type of the supporting electrolyte, the supporting electrolyte is preferably used at a concentration of 0.5 mol / liter to 2.5 mol / liter. By keeping the amount of the supporting electrolyte within this range, the ionic conductivity can be increased, so that the charging characteristics and discharging characteristics of the lithium ion secondary battery can be improved.

As the organic solvent used for the electrolytic solution, a solvent capable of dissolving the supporting electrolyte can be used. Examples of the organic solvent include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate (MEC), vinylene carbonate (VC), and the like. Preferred examples include carbonate compounds of the following: ester compounds such as γ-butyrolactone and methyl formate; ether compounds such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Among them, a carbonate compound is preferable because it has a high dielectric constant and a stable potential region in a wide range. Moreover, since the lithium ion conductivity tends to increase as the viscosity of the solvent used decreases, the lithium ion conductivity can be adjusted depending on the type of the solvent.

Moreover, the electrolytic solution may contain an additive as necessary. An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Among the electrolytes described above, it is preferable to use a solvent having a desired SP value as the solvent of the electrolyte from the viewpoint of easily controlling the degree of swelling of the polymer of the core part and the polymer of the shell part of the organic particles. . The specific SP value of the solvent of the electrolytic solution is preferably 8 (cal / cm ³ ) ^1/2 or more, more preferably 9 (cal / cm ³ ) ^1/2 or more, and preferably 15 (cal / Cm ³ ) ^1/2 or less, more preferably 14 (cal / cm ³ ) ^1/2 or less. Examples of the solvent having an SP value that falls within the above range include cyclic ester compounds such as ethylene carbonate and propylene carbonate; chain ester compounds such as ethyl methyl carbonate and diethyl carbonate; and the like.

In the lithium ion secondary battery of the present invention, it is not necessary to provide a separator between the electrode of the present invention and its counter electrode. Therefore, you may provide a counter electrode directly in the porous layer side of the electrode of this invention. Here, providing the counter electrode directly means that there is no separate member between the electrode of the present invention and the counter electrode on the porous layer side of the electrode of the present invention. Since the porous layer is an insulating layer, a short circuit between the positive electrode and the negative electrode can be prevented without providing a separator as a separate member from the porous layer. Also in this case, since the porous layer usually has a shutdown function, the safety of the lithium ion secondary battery is good. Furthermore, since resistance can be reduced by not providing a separator, the low-temperature output characteristic of a battery can be improved.

In the lithium ion secondary battery of the present invention, even when an arbitrary member is provided between the electrodes, a member having a shutdown function may not be provided between the electrode of the present invention and its counter electrode. Therefore, you may provide a counter electrode through the member which does not have a shutdown function in the porous layer side of the electrode of this invention. Thus, even if a member having a shutdown function is not provided between the electrodes, the porous layer of the electrode of the present invention normally has a shutdown function, and thus the safety of the lithium ion secondary battery is good. Even when a separator is provided as an optional member between the electrodes, the separator does not have to have a shutdown function, so that the range of selection of the separator material can be increased. Therefore, the range of separators that can be selected can be expanded, and as a result, a wide range of actions corresponding to the separators can be imparted to the battery. Moreover, you may provide components other than the separator which does not have a shutdown function, such as a heat resistant layer, for example between electrodes.

The method for producing the lithium ion secondary battery of the present invention is not particularly limited. For example, the above-described negative electrode and positive electrode may be overlapped, placed in a battery container, and an electrolytic solution may be injected into the battery container for sealing. Furthermore, if necessary, an expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the battery may be any of, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.
In the following description, “%” and “part” representing amounts are based on weight unless otherwise specified. In addition, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Evaluation methods]
(1) Measuring method of cell volume change before and after high-temperature cycle test The 1000 mAh laminated lithium ion secondary battery manufactured in Examples and Comparative Examples was allowed to stand in an environment of 25 ° C. for 24 hours. Thereafter, in an environment of 25 ° C., a charge / discharge operation was performed in which the battery was charged at 0.1 C to 4.35 V and discharged at 0.1 C to 2.75 V. The cell of this battery was immersed in liquid paraffin, and the volume X0 of the cell was measured.
Furthermore, the charge / discharge operation was repeated 1000 cycles under the same conditions as described above in a 60 ° C. environment. The cell of the battery after 1000 cycles was immersed in liquid paraffin, and the volume X1 of the cell was measured.
The volume change ΔX of the battery cell before and after repeating charge and discharge for 1000 cycles was calculated by “ΔX (%) = (X1−X0) / X0 × 100”. A smaller value of the volume change ΔX indicates that the battery is more excellent in suppressing cell swelling.

(2) HOT-ER test (Shutdown performance evaluation method)
The 1000 mAh laminated lithium ion secondary batteries produced in the examples and comparative examples were allowed to stand for 24 hours in an environment of 25 ° C. Thereafter, in an environment of 25 ° C., a charge / discharge operation was performed in which the battery was charged at 0.1 C to 4.35 V and discharged at 0.1 C to 2.75 V. Next, while the cell of this battery was pressed at a pressure of 500 kgf, the temperature was increased to 200 ° C., and the cell resistance R was measured with a resistance measuring instrument (“Loresta MCP-TP06P” manufactured by Mitsubishi Chemical Analytech). The value of the measured cell resistance R was evaluated according to the following evaluation criteria. It shows that it is excellent in shutdown property, so that the value of cell resistance R is large.

(Evaluation criteria for shutdown performance)
E: R = 0 (Ω)
D: 0 (Ω) <R ≦ 1 (Ω)
C: 1 (Ω) <R <10 (Ω)
B: 10 (Ω) ≦ R <100 (Ω)
A: 100 (Ω) ≦ R (Ω)

(3) Evaluation method of high-temperature cycle characteristics The 1000 mAh laminated lithium ion secondary batteries produced in Examples and Comparative Examples were allowed to stand for 24 hours in an environment of 25 ° C. Thereafter, under an environment of 25 ° C., a charge / discharge operation of charging up to 4.35 V at 0.1 C and discharging to 2.75 V at 0.1 C was performed, and the initial capacity C0 was measured.
Furthermore, charging and discharging were repeated 1000 cycles under the same conditions as described above in a 60 ° C. environment, and the capacity C1 after 1000 cycles was measured.
The capacity retention ratio ΔC was calculated by “ΔC = C1 / C0 × 100 (%)”. The higher the capacity retention ratio ΔC, the better the high-temperature cycle characteristics of the lithium ion secondary battery, and the longer the battery life.

(4) Evaluation Method of Low-Temperature Output Characteristics The 1000 mAh stacked lithium ion secondary battery manufactured in the examples and comparative examples was left to stand for 24 hours in an environment of 25 ° C. Thereafter, charging was performed for 5 hours at a charging rate of 0.1 C under an environment of 25 ° C., and the voltage V0 at that time was measured. Thereafter, a discharge operation was performed at a discharge rate of 1 C in an environment of −10 ° C., and the voltage V1 15 seconds after the start of discharge was measured.
The voltage change ΔV was calculated by “ΔV = V0−V1”. It shows that it is excellent in low temperature output characteristics, so that the value of this voltage change (DELTA) V is small.

(5) Method for Measuring Amount of Metal Lithium Deposited on Negative Electrode The 1000 mAh laminated lithium ion secondary battery manufactured in Examples and Comparative Examples was allowed to stand in an environment at 25 ° C. for 24 hours. Thereafter, in an environment of −10 ° C., an operation of charging to 4.35 V for 1 hour at a charging rate of 1 C was performed. Then, the negative electrode was taken out from the battery in a room temperature argon environment. The taken-out negative electrode was observed and the area Ws (cm ² ) where lithium metal was deposited was measured. The measured area was evaluated according to the following evaluation criteria. The smaller the area on which the lithium metal is deposited, the less lithium metal is deposited due to charge / discharge, indicating that the negative electrode can smoothly accept lithium ions in the electrolyte. Thus, it is said that it is excellent in a low-temperature receiving characteristic that a negative electrode can receive the lithium ion in electrolyte solution smoothly.
(Evaluation criteria for lithium metal deposition)
A: 0 (cm ² ) ≦ Ws <1 (cm ² )
B: 1 (cm ² ) ≦ Ws <5 (cm ² )
C: 5 (cm ² ) ≦ Ws <10 (cm ² )
D: 10 (cm ² ) ≦ Ws <15 (cm ² )
E: 15 (cm ² ) ≦ Ws <20 (cm ² )
F: 20 (cm ² ) ≦ Ws ≦ 25 (cm ² )

(6) Method for measuring the degree of swelling of the polymer in the core part In the same manner as the method for producing the aqueous dispersion containing the polymer constituting the core part in the examples and comparative examples, the weight constituting the core part of the organic particles An aqueous dispersion containing coalescence was produced. This aqueous dispersion was put into a petri dish made of polytetrafluoroethylene and dried under the conditions of 25 ° C. and 48 hours to produce a film having a thickness of 0.5 mm.

This film was cut into a 1 cm square to obtain a test piece. The weight of this test piece was measured and designated as W0.
The test piece was immersed in an electrolytic solution at 60 ° C. for 72 hours. Then, the test piece was taken out from the electrolytic solution, the electrolytic solution on the surface of the test piece was wiped off, and the weight W1 of the test piece after the immersion test was measured.
Using these weights W0 and W1, the degree of swelling S (times) was calculated as S = W1 / W0.

At this time, as the electrolytic solution, a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio EC / DEC / VC = 68.5 / 30 / 1.5; SP value 12.7 (cal / cm ³ )) ^{In 1/2} ), a support electrolyte in which LiPF ₆ was dissolved in a solvent at a concentration of 1 mol / liter was used.

(7) Method for measuring degree of swelling of polymer in shell part Examples and Comparative Examples except that the monomer composition used for the production of the shell part was used instead of the monomer composition used for the production of the core part In the same manner as in the method for producing an aqueous dispersion containing organic particles, an aqueous dispersion containing a polymer constituting the shell part was produced. Except for using an aqueous dispersion containing the polymer constituting the shell part as an aqueous dispersion for producing the test piece, the shell part was measured in the same manner as in the method for measuring the degree of swelling of the polymer in the core part. The degree of swelling S of the polymer was measured.

(8) Measuring method of average ratio of outer surface of core part covered by shell part After organic particles are sufficiently dispersed in visible light curable resin (“D-800” manufactured by JEOL Ltd.), embedded And the block piece containing an organic particle was produced. Next, the sample for a measurement was produced by cutting out with a microtome provided with a diamond blade into a thin piece having a thickness of 100 nm. Thereafter, the measurement sample was dyed using ruthenium tetroxide.

Next, the stained measurement sample was set in a transmission electron microscope (“JEM-3100F” manufactured by JEOL Ltd.), and a cross-sectional structure of organic particles was photographed at an acceleration voltage of 80 kV. The magnification of the electron microscope was set so that the cross section of one organic particle was in the visual field.

In the cross-sectional structure of the photographed organic particles, the circumference D1 of the core part and the length D2 of the part where the outer surface of the core part abuts on the shell part are measured, and the following equation (1) The ratio Rc of the outer surface of the core part of the organic particles covered by the shell part was calculated.
Covering ratio Rc (%) = D2 / D1 × 100 (1)
The coating ratio Rc was measured for 20 arbitrarily selected organic particles, and the average value thereof was calculated to obtain the average ratio at which the outer surface of the core part was covered with the shell part.

(9) Measuring method of volume average particle size of particles The particle size distribution of the sample particles was measured with a laser diffraction particle size distribution measuring device ("SALD-3100" manufactured by Shimadzu Corporation). In the measured particle size distribution, the particle size at which the cumulative volume calculated from the small diameter side was 50% was determined as the volume average particle size.

(10) Measuring method of core-shell ratio The average thickness of the shell part of the organic particles was measured by the following procedure.
In the case where the shell part is composed of polymer particles, in the same manner as described in the method of measuring the average ratio of the outer surface of the core part covered by the shell part, the The cross-sectional structure was observed. From the observed cross-sectional structure of the organic particles, the longest diameter of the polymer particles constituting the shell portion was measured. For 20 arbitrarily selected organic particles, the longest diameter of the polymer particles constituting the shell portion was measured by the above-described method, and the average value of the longest diameters was defined as the average thickness of the shell portion.

Further, when the shell portion has a shape other than particles, the transmission electron microscope is used to perform organic analysis in the same manner as described in the method of measuring the average ratio in which the outer surface of the core portion is covered by the shell portion. The cross-sectional structure of the particles was observed. From the observed cross-sectional structure of the organic particles, the maximum thickness of the shell portion was measured. About 20 organic particles arbitrarily selected, the maximum thickness of the shell portion was measured by the above-described method, and the average value of the maximum thickness was defined as the average thickness of the shell portion.

Then, the core shell ratio was calculated by dividing the measured average thickness of the shell part by the volume average particle diameter of the organic particles.

[Example 1]
(1-1. Production of binder for porous layer)
To a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (“Emal 2F” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, and 0.5 part of ammonium persulfate were respectively supplied. The gas phase was replaced with nitrogen gas, and the temperature was raised to 60 ° C.
On the other hand, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, 94 parts of butyl acrylate, 2 parts of acrylonitrile, 2 parts of methacrylic acid, allyl as a polymerizable monomer A monomer mixture was obtained by mixing 1 part of methacrylate and 1 part of acrylamide. This monomer mixture was continuously added to the reactor over 4 hours to carry out polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was further terminated by stirring at 70 ° C. for 3 hours to produce an aqueous dispersion containing a (meth) acrylic polymer as a particulate porous layer binder.
The obtained (meth) acrylic polymer particles had a volume average particle diameter D50 of 0.36 μm and a glass transition temperature of −45 ° C.

(1-2. Production of organic particles)
In a 5 MPa pressure vessel with a stirrer, 75 parts of methyl methacrylate, 4 parts of methacrylic acid and 1 part of ethylene dimethacrylate as monomer composition used for the production of the core part; 1 part of sodium dodecylbenzenesulfonate as emulsifier; ion-exchanged water 150 parts; and 0.5 part of potassium persulfate as a polymerization initiator was added and stirred sufficiently. Then, it heated to 60 degreeC and superposition | polymerization was started. By continuing the polymerization until the polymerization conversion rate reached 96%, an aqueous dispersion containing a particulate polymer constituting the core part was obtained.

Subsequently, 19 parts of styrene and 1 part of methacrylic acid were continuously added to the aqueous dispersion as a monomer composition used for the production of the shell part, and the polymerization was continued by heating to 70 ° C. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to produce an aqueous dispersion containing organic particles. The obtained organic particles had a volume average particle diameter D50 of 0.45 μm. About the obtained organic particle, the average ratio by which the core shell ratio and the surface of a core part are covered with a shell part was measured by the method mentioned above.

(1-3. Production of slurry for porous layer)
100 parts of the aqueous dispersion containing the organic particles in the amount of organic particles, 6 parts of the aqueous dispersion containing the (meth) acrylic polymer in the amount of the (meth) acrylic polymer, and the polyethylene glycol type interface A slurry for a porous layer was produced by mixing 0.2 part of an activator (“SN Wet 366” manufactured by San Nopco).

(1-4. Production of binder for negative electrode)
In a 5 MPa pressure vessel with a stirrer, 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 0.4 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water and a polymerization initiator After adding 0.5 part of potassium persulfate and stirring sufficiently, the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing particulate negative electrode binder (SBR). The mixture containing the negative electrode binder was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution. Then, the unreacted monomer was removed by heating under reduced pressure, and the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing a particulate negative electrode binder.

(1-5. Production of slurry for negative electrode)
90 parts of artificial graphite (volume average particle diameter 15.6 μm), 10 parts of SiOx particles (volume average particle diameter 5 μm), and 2% aqueous solution of carboxymethylcellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) as a thickener After mixing 1.0 part in terms of solid content and adding ion exchange water to adjust the solid content concentration to 68%, the mixture was mixed at 25 ° C. for 60 minutes. Further, ion exchange water was added to adjust the solid content concentration to 62%, and the mixture was further mixed at 25 ° C. for 15 minutes. In the mixed solution thus obtained, 1.5 parts of the aqueous dispersion containing the above-mentioned negative electrode binder was added in an amount corresponding to the solid content, and further adjusted with ion-exchanged water to a final solid content concentration of 52%, Mix for another 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode slurry having good fluidity.

(1-6. Production of electrode plate for negative electrode)
The negative electrode slurry obtained above was applied to one side of a 20 μm thick copper foil as a current collector with a comma coater so that the film thickness after drying was about 150 μm, and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain an electrode plate raw sheet before pressing provided with a negative electrode active material layer on one side. The electrode plate original was rolled with a roll press to obtain a negative electrode plate having a negative electrode active material layer having a thickness of 80 μm on one side of the current collector.

In addition, after applying the negative electrode slurry to one side of the current collector and drying in the same manner as in the above-described process for producing the original electrode plate before pressing, the negative electrode is similarly applied to the other side of the current collector. The coating slurry was applied and dried, and further heat-treated at 120 ° C. for 2 minutes to obtain an electrode plate raw sheet before pressing provided with a negative electrode active material layer on both sides. The electrode plate original was rolled with a roll press to obtain an electrode plate for a negative electrode having a negative electrode active material layer having a thickness of 80 μm on each side of the current collector.

(1-7. Production of negative electrode)
On each negative electrode active material layer of the negative electrode plate obtained above, the slurry for porous layer was applied with a comma coater so as to have a dry thickness of 12 μm and dried. Drying was performed by conveying the electrode plate in an oven at 60 ° C. at a speed of 0.5 m / min for 1 minute. Thus, a negative electrode having a negative electrode active material layer and a porous layer on one side of the current collector (hereinafter sometimes referred to as “single-sided negative electrode” as appropriate), and a negative electrode active material layer and a porous layer on both sides of the current collector. Negative electrode (hereinafter sometimes referred to as “double-sided negative electrode” as appropriate).

(1-8. Production of slurry for positive electrode)
100 parts of LiCoO ₂ having a volume average particle diameter of 12 μm as the positive electrode active material, ₂ parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive material, and polyvinylidene fluoride (manufactured by Kureha Co., # as the binder for the positive electrode) 7208) was mixed in an amount corresponding to the solid content, and N-methylpyrrolidone was added thereto to adjust the total solid content concentration to 70%. This was mixed by a planetary mixer to obtain a positive electrode slurry.

(1-9. Production of positive electrode)
The positive electrode slurry was applied onto a 20 μm thick aluminum foil as a current collector by a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by conveying the aluminum foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, it heat-processed for 2 minutes at 120 degreeC, and obtained the positive electrode original fabric before the press which equips one side with a positive electrode active material layer. This positive electrode raw material was rolled by a roll press to obtain a positive electrode having a positive electrode active material layer having a thickness of 80 μm on one side of the current collector (hereinafter sometimes referred to as “single-sided positive electrode” as appropriate).

In addition, after applying the positive electrode slurry on one side of the current collector and drying in the same manner as in the above-described process for producing the positive electrode raw material before pressing, the other side of the current collector is also used for the positive electrode. The slurry was applied and dried, and further heat-treated at 120 ° C. for 2 minutes to obtain a positive electrode raw material before pressing having a positive electrode active material layer on both surfaces. The positive electrode fabric was rolled with a roll press to obtain a positive electrode (hereinafter sometimes referred to as “double-sided positive electrode” as appropriate) having a positive electrode active material layer having a thickness of 80 μm on both sides of the current collector.

(1-10. Production of lithium ion secondary battery)
A single-sided positive electrode and a double-sided positive electrode were cut into 5 cm × 15 cm. Moreover, the single-sided negative electrode and the double-sided negative electrode were cut out to 5.5 cm x 15.5 cm. A single-sided positive electrode, a double-sided negative electrode, a double-sided positive electrode and a single-sided negative electrode were arranged in this order to obtain an electrode laminate. At this time, the orientation of the single-sided positive electrode was such that the positive electrode active material layer and the current collector were arranged in this order from the side closer to the double-sided negative electrode. Furthermore, the orientation of the single-sided negative electrode was such that the porous layer, the negative electrode active material layer, and the current collector were arranged in this order from the side closer to the double-sided positive electrode.
This electrode laminate was wrapped with an aluminum wrapping exterior. An electrolyte solution (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 volume ratio, electrolyte: LiPF _{6 with a} concentration of 1 M) was injected into the exterior so that no air remained. Furthermore, in order to seal the opening of an aluminum packaging material exterior, the aluminum packaging material exterior was closed by giving a 150 degreeC heat seal, and the battery exterior body was obtained. Thereafter, the battery outer package was subjected to flat plate press treatment at 100 ° C. for 2 minutes at 100 kgf to produce a 1000 mAh laminated lithium ion secondary battery.
The lithium ion secondary battery thus obtained was evaluated by the method described above.

[Example 2]
In the monomer composition used for producing the core part according to the step (1-2), the amount of methyl methacrylate was changed to 75.85 parts, and the amount of ethylene dimethacrylate was changed to 0.15 parts.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 3]
In the monomer composition used for producing the core part according to the step (1-2), the amount of methyl methacrylate was changed to 71.5 parts, and the amount of ethylene dimethacrylate was changed to 4.5 parts.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 4]
In the monomer composition used for producing the core part according to the step (1-2), the amount of methyl methacrylate was changed to 76.85 parts, and the amount of ethylene dimethacrylate was changed to 0.05 parts.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 5]
In the monomer composition used for producing the core part according to the step (1-2), instead of 75 parts of methyl methacrylate, 55 parts of methyl methacrylate and 20 parts of 2-ethylhexyl acrylate were used in combination.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 6]
In the monomer composition used for producing the core part according to the step (1-2), acrylonitrile was used instead of methyl methacrylate.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 7]
In the monomer composition used for producing the core part according to the step (1-2), 65 parts of acrylonitrile and 10 parts of 2-ethylhexyl acrylate were used in combination instead of 75 parts of methyl methacrylate.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 8]
In the monomer composition used for producing the shell part according to the step (1-2), 9 parts of styrene and 10 parts of acrylonitrile were used in combination instead of 19 parts of styrene.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 9]
In the monomer composition used for producing the shell part according to the step (1-2), 4 parts of styrene and 15 parts of acrylonitrile were used in combination instead of 19 parts of styrene.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 10]
In the monomer composition used for producing the shell part according to the step (1-2), instead of using 19 parts of styrene and 1 part of methacrylic acid in combination, 20 parts of sodium salt of styrenesulfonic acid was used.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 11]
In the monomer composition used for producing the shell part according to the step (1-2), instead of using 19 parts of styrene and 1 part of methacrylic acid in combination, 15 parts of sodium salt of styrene sulfonic acid and 5 parts of acrylonitrile are used. Used in combination.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 12]
Using the single-sided positive electrode and double-sided positive electrode having no porous layer produced in Example 1 as electrode plates, the slurry for the porous layer is 12 μm in dry thickness on each positive electrode active material layer of these electrode plates. It was applied with a comma coater and dried. Drying was performed by conveying the electrode plate in an oven at 60 ° C. at a speed of 0.5 m / min for 1 minute. As a result, a positive electrode having a positive electrode active material layer and a porous layer on one side of the current collector, and a positive electrode having a positive electrode active material layer and a porous layer on both sides of the current collector were obtained.

In the step (1-10), instead of the single-sided positive electrode and double-sided positive electrode having no porous layer, the single-sided positive electrode and double-sided positive electrode having the porous layer produced as described above were used.
In the step (1-10), instead of the single-sided negative electrode having a porous layer, a negative electrode plate having a negative electrode active material layer on one side of the current collector but not having a porous layer is used. Instead of the double-sided negative electrode, a negative electrode plate having a negative electrode active material layer on both sides of the current collector but no porous layer was used.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 13]
In the step (1-10), instead of the single-sided positive electrode and double-sided positive electrode having no porous layer, the single-sided positive electrode and double-sided positive electrode having the porous layer produced in Example 12 were used.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 14]
In the step (1-10), a cell guard 2500 (thickness: 25 μm, as a separator) is provided between the single-sided positive electrode and the double-sided negative electrode, between the double-sided negative electrode and the double-sided positive electrode, and between the double-sided positive electrode and the single-sided negative electrode. Material: polypropylene, manufactured by Celgard).
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 1]
In the step (1-3), 100 parts of alumina particles (volume average particle diameter of 0.5 μm) were used instead of the organic particles.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 2]
In the monomer composition used for producing the core part according to the step (1-2), 80 parts of styrene was used instead of 75 parts of methyl methacrylate, 4 parts of methacrylic acid and 1 part of ethylene dimethacrylate. .
Further, in the monomer composition used for producing the shell part according to the step (1-2), 20 parts of styrene was used instead of using 19 parts of styrene and 1 part of methacrylic acid in combination.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.
The comparative example 2 is an example using organic particles having a core-shell structure in which both the core part and the shell part are made of polystyrene.

[Comparative Example 3]
In the monomer composition used for producing the core part according to the step (1-2), the amount of methyl methacrylate was changed to 50 parts, the amount of methacrylic acid was changed to 5 parts, and ethylene dimethacrylate 1 part Instead of 25 parts acrylonitrile was used.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 4]
In the monomer composition used for producing the shell part according to the step (1-2), instead of 19 parts of styrene, 10 parts of methyl methacrylate and 9 parts of acrylonitrile were used in combination.
Except for the above, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

"result"
The results of Examples and Comparative Examples are shown in the following table. In the following table, the meanings of the abbreviations are as follows. In the table below, the numerical value described next to the abbreviation of the monomer in the monomer section represents the weight part of the monomer. Furthermore, in the table below, the numerical value described next to the name of the active material in the section of active material represents the weight part of the active material.
LCO: LiCoO ₂
MAC350HC: Carboxymethylcellulose sodium salt ST: Styrene BD: 1,3-butadiene IA: Itaconic acid PVDF: Polyvinylidene fluoride MMA: Methyl methacrylate MAA: Methacrylic acid EDMA: Ethylene dimethacrylate 2-EHA: 2-ethylhexyl acrylate AN: Acrylonitrile NaSS: Sodium salt of styrene sulfonic acid Tg: Glass transition temperature Core-shell ratio: Core-shell ratio Coverage: Average ratio of outer surface of core part covered by shell part D50: Volume average particle diameter BA: Butyl acrylate AMA: Allyl methacrylate AAm: Acrylamide SN366: Polyethylene glycol type surfactant

[Consideration]
From the results of Examples and Comparative Examples, it was confirmed that a lithium ion secondary battery excellent in high-temperature cycle characteristics can be realized by the present invention. From the comparison between Comparative Examples 2 and 3 and the Examples, it can be seen that keeping the degree of swelling of the polymer in the core part within a predetermined range has technical significance in improving the high-temperature cycle characteristics. Further, it can be seen from the comparison between Comparative Example 4 and Examples that keeping the degree of swelling of the polymer in the shell portion within a predetermined range has technical significance in improving the high-temperature cycle characteristics.
Further, since Examples 1 to 13 are superior to Example 14 in low-temperature output characteristics, lithium is excellent not only in high-temperature cycle characteristics but also in low-temperature output characteristics by omitting the separator by utilizing the shutdown function of the porous layer. It was confirmed that an ion secondary battery could be realized.

100 Organic particle 110 Core part 110S Outer surface of core part 120 Shell part

Claims

An electrode for a lithium ion secondary battery comprising an electrode active material layer and a porous layer containing organic particles directly provided on the electrode active material layer,
The organic particles have a core-shell structure including a core portion and a shell portion that partially covers an outer surface of the core portion;
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
An electrode for a lithium ion secondary battery, wherein the shell part is made of a polymer having a swelling degree with respect to an electrolytic solution of greater than 1 and 4 or less.
The glass transition temperature of the polymer of the core part is 0 ° C. or higher and 150 ° C. or lower,
2. The electrode for a lithium ion secondary battery according to claim 1, wherein a glass transition temperature of the polymer of the shell part is 50 ° C. or higher and 200 ° C. or lower.
A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to claim 1 or 2 and an electrolytic solution.
The lithium ion secondary battery according to claim 3, comprising a counter electrode on the porous layer side of the electrode for the lithium ion secondary battery directly or through a member having no shutdown function.
The lithium ion secondary battery according to claim 3 or 4, wherein the electrode has a flat shape.