WO2018169004A1

WO2018169004A1 - Nickel-manganese-based composite oxide and method for producing same

Info

Publication number: WO2018169004A1
Application number: PCT/JP2018/010239
Authority: WO
Inventors: 田渕　光春; 理樹片岡
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2017-03-16
Filing date: 2018-03-15
Publication date: 2018-09-20
Also published as: JP6872816B2; JPWO2018169004A1

Abstract

Provided is a nickel-containing lithium-manganese composite oxide in which the amount of transition metal ions in a Li layer is small, which exhibits excellent cycle characteristics, and which can be advantageously used in a lithium ion secondary battery. The nickel-containing lithium-manganese composite oxide is represented by general formula (1): Li1+x(NiyMn1-y)1-xO2 [in the formula, x and y are such that 0.0 ≤ x < 1/3 and 0.3 ≤ y ≤ 0.6]. The nickel-containing lithium-manganese composite oxide contains a layered halite crystal phase, has a lattice constant a of 2.870 Å or less, and has a lattice volume of 102.0 Å3 or less.

Description

Nickel-manganese complex oxide and method for producing the same

The present invention relates to a nickel-containing lithium manganese composite oxide and a method for producing the same.

Lithium ion secondary batteries used as power sources for Japanese notebook computers, mobile phones, smartphones, etc. (for small consumer products) are widely used as batteries with significantly higher electrical energy (energy density) per battery size and weight. It is utilized. Furthermore, it is a promising battery system that has recently begun to be used in large systems such as electric cars, plug-in hybrid vehicles, houses and power plants.

In the lithium ion secondary battery, it is the material used for the positive electrode that determines the battery capacity and voltage. Many of these are lithium-containing transition metal oxides such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ). Price instability based on the scarcity of resources, low chemical stability during charging, low charge / discharge capacity, etc. are pointed out, and it is an urgent need to secure further material candidates.

As such a material candidate, lithium nickel manganate (LiNi _1/2 Mn _1/2 O ₂ ) has been proposed by Non-Patent Document 1 and has been studied as a promising positive electrode material. However, lithium nickel manganate has a problem that synthesis is not easy. For example, it has been found that lithium nickel manganate can be obtained by a coprecipitation-hydrothermal-firing method (Patent Document 1), but there is a problem that the synthesis method is complicated and cannot be directly used for a practical production process. . Therefore, recently, it has been changed to a nickel cobalt lithium manganate (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) called a ternary system that is easier to synthesize.

However, a battery using nickel cobalt lithium manganate has cobalt, so there is a problem in low chemical stability during charging. This low chemical stability is due to the safety of the battery and the setting of a high upper limit potential. May cause problems with cycle characteristics (for example, 4.5V or more). Therefore, it can still be meaningful to develop an easy synthesis method for a battery using lithium nickel manganate, which is excellent in terms of battery safety and cycle characteristics.

Co-substitution has been performed in the first place in order to facilitate synthesis and reduce the amount of transition metal ions in the Li layer, but cobalt-containing materials have the above-mentioned problems. Therefore, if a material that does not contain cobalt and has a small amount of transition metal ions in the Li layer can be obtained, it is considered to be extremely useful industrially.

Therefore, there has been a demand for a nickel manganese type positive electrode material with a small amount of transition metal ions in the Li layer, which has excellent cycle characteristics and can be used for a lithium secondary ion battery.

JP 2008-127233 A

In view of the circumstances as described above, an object of the present invention is a nickel-containing lithium-manganese composite that can be suitably used for a lithium secondary ion battery having a small amount of transition metal ions in the Li layer and excellent cycle characteristics. It is to provide an oxide.

As a result of intensive studies to achieve the above object, the present inventors have determined that a nickel-containing lithium manganese composite oxide having a predetermined chemical formula including a layered rock salt type crystal phase, and further, the nickel-containing lithium manganese composite oxide. It has been found that a lithium ion secondary battery having excellent cycle characteristics can be obtained by using it. The present inventors have further studied based on such knowledge and have completed the present invention.

That is, the present invention provides the following nickel manganese composite oxide and a method for producing the same.
Item 1.
General formula (1):
Li _{1 + x} (Ni _y Mn _1-y ) _1-x O ₂ (1)
[Wherein, x and y represent 0.0 ≦ x <1/3 and 0.3 ≦ y ≦ 0.6, respectively. ]
Represented by a layered rock salt type crystal phase,
The lattice constant a is 2.870 Å or less and the lattice volume is 102.0 Å ³ or less,
Nickel-containing lithium manganese composite oxide.
Item 2.
Item 2. The nickel-containing lithium manganese composite oxide according to Item 1, wherein in the layered rock salt type crystal phase, the amount of transition metal contained in the lithium layer is 5% or less.
Item 3.
Item 3. The nickel-containing lithium manganese composite oxide according to Item 1 or 2, wherein the amount of transition metal contained in the transition metal layer is 88% or less in the layered rock salt type crystal phase.
Item 4.
Item 4. The nickel-containing lithium manganese composite oxide according to any one of Items 1 to 3, wherein the average valence of nickel ions is 2.5 or more.
Item 5.
Item 5. The nickel-containing lithium manganese composite oxide according to any one of Items 1 to 4, wherein the O / (Ni + Mn) atomic ratio is 2.3 or more.
Item 6.
Item 6. A lithium ion secondary battery comprising the nickel-containing lithium manganese composite oxide according to any one of Items 1 to 5 as a positive electrode active material.
Item 7.
Step 1 of forming a precipitate under an alkaline condition of 20 ° C. or lower from a mixed aqueous solution containing a manganese compound and a nickel compound,
Step 2 of performing wet oxidation treatment on the precipitate,
And a step 3 of heat treatment in an oxidizing atmosphere in the presence of lithium salt,
Item 6. A method for producing a nickel-containing lithium manganese composite oxide according to any one of Items 1 to 5.

The nickel-containing lithium manganese composite oxide according to the present invention can be suitably used for a lithium ion secondary battery having a small amount of transition metal ions in the Li layer and excellent cycle characteristics.

2 is a diagram showing an X-ray diffraction pattern of a sample of Example 1. FIG. 6 is a diagram showing an X-ray diffraction pattern of a sample of Comparative Example 1. FIG. Example 1 is a diagram showing a comparative example 1 and the valence standard material _(Li ₂ MnO 3, NiO and LiNiO ₂₎ of Mn and K near edge X-ray absorption spectrum of Ni (XANES). It is a figure which shows the charging / discharging characteristic evaluation test result of the lithium ion secondary battery of Example 1. It is a figure which shows the charging / discharging characteristic evaluation test result of the lithium ion secondary battery of the comparative example 1. 6 is a diagram showing an X-ray diffraction pattern of a sample of Example 2. FIG. It is a figure which shows the X-ray-diffraction pattern of the sample of the comparative example 2. Example 2 is a diagram showing a comparative example 2 and the valence standard material _(Li ₂ MnO 3, NiO and LiNiO ₂₎ of Mn and K near edge X-ray absorption spectrum of Ni (XANES). It is a figure which shows the charging / discharging characteristic evaluation test result of the lithium ion secondary battery of Example 2. It is a figure which shows the charging / discharging characteristic evaluation test result of the lithium ion secondary battery of the comparative example 2. 6 is a diagram showing an X-ray diffraction pattern of a sample of Example 3. FIG. It is a figure which shows the X-ray-diffraction pattern of the sample of the comparative example 3. Example 3 is a diagram showing a comparative example 3 and the valence standard material _(Li ₂ MnO 3, NiO and LiNiO ₂₎ of Mn and K near edge X-ray absorption spectrum of Ni (XANES). It is a figure which shows the charging / discharging characteristic evaluation test result of the lithium ion secondary battery of Example 3. It is a figure which shows the charging / discharging characteristic evaluation test result of the lithium ion secondary battery of the comparative example 3. 6 is a diagram showing an X-ray diffraction pattern of a sample of Example 4. FIG. Example 4 is a diagram showing a comparative example 4 and the valence standard material _(Li ₂ MnO 3, NiO and LiNiO ₂₎ of Mn and K near edge X-ray absorption spectrum of Ni (XANES). It is a figure which shows the charging / discharging characteristic-evaluation test result of the lithium ion secondary battery of Example 4. 6 is a diagram showing an X-ray diffraction pattern of a sample of Example 5. FIG. It is a figure which shows the charging / discharging characteristic evaluation test result of the lithium ion secondary battery of Example 5.

1. Nickel-containing lithium manganese composite oxide The nickel-containing lithium manganese composite oxide of the present invention has the general formula (1):
Li _{1 + x} (Ni _y Mn _1-y ) _1-x O ₂ (1)
[Wherein, x and y represent 0.0 ≦ x <1/3 and 0.3 ≦ y ≦ 0.6, respectively. ]
Represented by a layered rock salt type crystal phase,
Lattice constant a 2.870Å or less, the lattice volume is equal to or is 102.0A ³ or less.

In the above general formula (1), x is 0.0 ≦ x <1/3, and more preferably 0.05 ≦ x ≦ 0.25. When x is less than 1/3, generation of excess lithium as an impurity can be suppressed, and as a result, excellent cycle characteristics of the battery can be obtained.

In the general formula (1), the nickel content y is 0.3 ≦ y ≦ 0.6, and more preferably 0.3 ≦ y ≦ 0.5. When y is 0.3 or more, the occurrence of battery voltage drop can be suppressed. Moreover, when y is 0.6 or less, the structural stability of the nickel-containing lithium manganese composite oxide can be maintained well even during charging.

The nickel-containing lithium manganese composite oxide of the present invention includes a layered rock salt type crystal phase. The layered rock-salt crystal structure constituting the layered rock-salt crystal phase is a crystal that frequently appears in inorganic compounds of ABO type ₂ (A is an alkali metal and B is a transition metal) possessed by lithium cobaltate and lithium nickelate. Structure. It has a crystal structure in which transition metal layers and lithium layers are alternately stacked via oxide ions, and it is said that lithium ion desorption and insertion reactions are easy with charge and discharge.

In addition, the layered rock-salt crystal phases are the space group:

Crystal phase of hexagonal layered rock salt structure belonging to, or space group:

It preferably includes a crystal phase of a monoclinic layered rock salt structure belonging to The nickel-containing lithium manganese composite oxide of the present invention preferably contains a crystal phase of the above hexagonal layered rock salt structure or a crystal phase of a monoclinic layered rock salt structure, and a crystal phase of another rock salt structure (for example, , Cubic rock salt structure, etc.). In the case of a mixed phase, the ratio of the crystal phase of the hexagonal layered rock salt structure or the crystal phase of the monoclinic layered rock salt structure is preferably 50 to 90% by mass based on the entire mixed phase. Further, the nickel-containing lithium manganese composite oxide of the present invention may be composed of only the crystal phase of the above hexagonal layered rock salt structure or the crystal phase of the monoclinic layered rock salt structure.

The lattice constant a in the layered rock salt type crystal structure of the nickel-containing lithium manganese composite oxide of the present invention is calculated as the a-axis value in the hexagonal layered rock salt type lattice corresponding to the distance between transition metal ions, and is 2.870Å or less. Yes, it is more preferably 2.865cm or less, further preferably 2.860cm or less. In addition, the lower limit value of the lattice constant a is preferably 2.850% or more from the viewpoint of securing a certain amount of trivalent nickel. Similarly, calculated assuming hexagonal layered rock-salt lattice, the lattice volume is at 102.0A ³ or less, and more preferably 101.0A ³ or less. On the other hand, the lower limit of the lattice volume is preferably 100.0 to ³ or more from the viewpoint of securing a transition metal ordered structure. The lattice constant a and the lattice volume in the present specification mean values calculated assuming a hexagonal layered rock salt lattice.

Regarding the lattice constant a and the lattice volume, by having the above-described configuration, more than half of the nickel ions contained in the nickel-containing lithium manganese composite oxide are oxidized to trivalent. The manganese ion valence remains tetravalent regardless of the production method, but the average valence of nickel ions can vary from divalent to trivalent. High reactivity with lithium ions tends to be trivalent. If the reactivity with lithium ions is low, it tends to remain divalent.

The average valence of nickel ions in the nickel-containing lithium manganese composite oxide of the present invention is preferably 2.5 or more, and more preferably 2.6 or more. By having such a configuration, it is possible to improve the charge / discharge characteristics of a lithium ion secondary battery manufactured using such a nickel-containing lithium manganese composite oxide as a positive electrode material. The average valence of nickel ions is determined from the 1s → 4p transition of each sample using, for example, an X-ray absorption (Ni-K XANES) spectrum in the vicinity of the nickel K end described later, using LiNiO ₂ as trivalent and NiO as divalent standard substances The position of the corresponding peak top can be determined by comparing it with that of the standard. On the other hand, the upper limit of the average valence of nickel ions in the nickel-containing lithium manganese composite oxide is trivalent from the viewpoint of securing as many trivalent nickel ions as possible as a result of incorporating a large amount of Li ions. preferable.

In addition, the nickel-containing lithium manganese composite oxide of the present invention preferably has a large oxygen content (O / (Ni + Mn) molar ratio) with respect to the transition metal, and the composition formula: Li _{1 + x} (Ni _y Mn _1-y ) _1-x In the case of y = 0.5 composition in O ₂ , if Ni is divalent, the composition formula is LiNi _1/2 Mn _1/2 O ₂ and (O / (Ni + Mn) molar ratio) is 2. On the other hand, when Ni is trivalent, the composition formula is Li _1.2 Ni _0.4 Mn _0.4 O ₂ and (O / (Ni + Mn) molar ratio) is 2.5. Since the substance according to the present invention has an Ni average valence of 2.5 or more, the lower limit of the above value is 2.3. However, from the viewpoint of constituting a battery having excellent discharge capacity and cycle characteristics, the lower limit is set. Is preferably 2.4. On the other hand, since the Ni average valence of the substance of the present invention is preferably close to trivalent as described above, the upper limit of the above value is preferably 3. The (O / (Ni + Mn) molar ratio) can be determined by quantifying the amount of transition metal ions and the amount of oxygen in the sample with a fluorescent X-ray analyzer.

Regarding the transition metal ion distribution in the hexagonal layered rock salt type lattice, the tetravalent Mn ion and the trivalent Ni ion are mainly distributed at the 3b position (001/2) in the transition metal layer. Ions or trivalent Mn ions are mainly present at the 3a position (000) in the Li layer. In the nickel-containing lithium manganese composite oxide of the present invention, the amount of transition metal in the Li layer is preferably 7% or less, and preferably 5% or less, out of 100% of the total amount of transition metals in the hexagonal layered rock salt lattice. More preferably. The amount of transition metal contained in the transition metal layer is preferably 88% or less, more preferably 82% or less, out of 100% of the total amount of transition metal in the hexagonal layered rock salt lattice. % Or less is more preferable. By having such a transition metal distribution, not only the amount of tetravalent Mn ions and trivalent Ni ions increases, but also the diffusion of Li ions in the layered rock salt structure is accelerated, so that the charge / discharge characteristics can be improved. I can expect. Further, when the total amount of transition metal per composition formula is reduced, more Li ions can be taken into the transition metal layer, and the Li can move into the Li layer during charging. It suppresses characteristic deterioration caused by repulsion between oxide ions, and contributes to improvement of chemical stability of the positive electrode active material during charging. On the other hand, the amount of transition metal in the Li layer of the nickel-containing lithium manganese composite oxide of the present invention is preferably 0.01% or more. Similarly, the amount of transition metal contained in the transition metal layer is preferably 50% or more.

In the prior art, the amount of transition metal ions in the Li layer was reduced by adding Co. However, the addition of Co reduces the cycle characteristics during high potential charging and the thermal stability of the positive electrode after charging. The substance of the present invention is characterized in that a substance having a low amount of transition metal in the Li layer was obtained without adding Co.

2. Positive electrode material for lithium ion secondary battery and lithium ion secondary battery The nickel-containing lithium manganese composite oxide described above can be used as a positive electrode material for lithium ion secondary battery. A positive electrode can be produced by supporting a positive electrode mixture prepared by mixing such a positive electrode material with a known conductive agent and a binder on a positive electrode current collector such as Al, Ni, stainless steel, or carbon cloth. As the conductive agent, for example, carbon materials such as graphite, cokes, carbon black, and acicular carbon can be used. The negative electrode material is not particularly limited, and examples thereof include metallic lithium, graphite, Si—SiO-based negative electrode, and LTO (Li ₄ Ti ₅ O ₁₂ ) -based negative electrode. These negative electrode materials may be supported on a negative electrode current collector made of Al, Cu, Ni, stainless steel, carbon or the like using a conductive agent, a binder, or the like, if necessary, to produce a negative electrode. The electrolyte is not particularly limited, and an organic electrolytic solution in which LiPF ₆ or the like is used as an electrolyte salt and dissolved in various solvents such as ethyl carbonate (EC) or dimethyl carbonate (DMC), Li ₂ S—P ₂ S ₅ , Li Examples thereof include inorganic sulfide solid electrolytes such as ₂ S—GeS ₂ —P ₂ S ₅ and Li ₂ S—SiS ₂ —Li ₃ PO _4, and polymer polymers having lithium ion conductivity. The separator is not particularly limited, and examples thereof include polyethylene and polypropylene.

3. The method for producing a nickel-containing lithium manganese composite oxide and the present invention further include the above-described method for producing a nickel-containing lithium manganese composite oxide. The method for producing the nickel-containing lithium manganese composite oxide of the present invention comprises:
Step 1 of forming a precipitate under an alkaline condition of 20 ° C. or lower from a mixed aqueous solution containing a manganese compound and a nickel compound,
Step 2 of performing wet oxidation treatment on the precipitate,
And a step 3 of heat-treating in an oxidizing atmosphere in the presence of lithium salt.

3.1. Process 1
The manganese compound to be used is not particularly limited. Manganese chloride (II), manganese sulfate (II), manganese acetate (II), manganese acetate (III), manganese nitrate (II), acetyl manganese acetate (II), acetyl Known products including manganese (III) acetate, potassium permanganate (VII) and the like can be widely used. Manganese oxide and manganese metal can also be used as a water-soluble salt by dissolving them with an appropriate acid.

The nickel compound to be used is not particularly limited, and it is possible to use a wide variety of known compounds including hydrates such as nickel nitrate (II), nickel acetate (II), nickel chloride (II), nickel sulfate (II). it can. Nickel oxide and metallic nickel can also be used as a water-soluble salt by dissolving them with an appropriate acid.

The alkali source used for the alkaline condition is not particularly limited, and a wide variety of known sources such as sodium hydroxide, lithium hydroxide (including hydrates thereof), aqueous ammonia and potassium hydroxide can be used. It is.

The alkali source is added to a mixed aqueous solution obtained by mixing the manganese compound and the nickel compound to obtain an alkaline condition. As a mixing method at this time, a well-known mixing method can be widely adopted, and there is no particular limitation. In addition, water is usually used as the solvent of the mixed aqueous solution, but is not necessarily limited thereto, and alcohols such as ethanol and methanol may be used. These solvents may be used alone or in combination of two or more. Alcohols can also be used as a precipitating material when using potassium permanganate as a manganese source, and can also be used as an antifreeze at the time of dropping at a low temperature of 0 ° C. or lower as described later.

In Step 1, a precipitate is formed in a known container capable of adjusting and maintaining the temperature of the mixed aqueous solution, such as a thermostatic bath. In this case, the temperature of the mixed aqueous solution needs to be set to 20 ° C. or lower. If the temperature is higher than this, the primary particle size of the precipitate is increased, and the reactivity with lithium tends to be lowered. From the same viewpoint, the upper limit of the set temperature of the mixed aqueous solution in step 1 is more preferably 25 ° C. or less, and further preferably 20 ° C. or less. On the other hand, the lower limit value of the set temperature is preferably −10 ° C. or higher, more preferably 0 ° C. or higher, from the viewpoint of ease of production. Here, when setting temperature is 0 degrees C or less, it is preferable to put ethanol as an antifreeze on the alkali side. Further, regarding the alkali concentration, it is sufficient that the alkali concentration (pH 11 or more) is obtained at the end of the preparation of the precipitate in Step 1.

3.2. Process 2
In Step 2, the precipitate obtained in Step 1 is subjected to wet oxidation treatment. In step 2, an oxidizing gas such as air or oxygen gas is blown (bubbled) into an alkaline aqueous solution containing a precipitate to oxidize and precipitate the precipitate to produce a precursor having high reactivity with lithium. The gas to be blown is not particularly limited as long as oxygen gas is contained (for example, air), but oxygen gas is preferable from the viewpoint of shortening the oxidation time. In the case of oxygen gas, an industrial oxygen generator may be used as well as a commonly used cylinder. The temperature of the wet oxidation is not particularly limited, and may be, for example, around room temperature. The wet oxidation time is preferably as long as possible from the viewpoint of allowing the reaction to proceed sufficiently, but is preferably 1 hour or longer, more preferably 24 hours or longer, and even more preferably 48 hours or longer.

3.3. Process 3
In step 3, the aged product obtained in step 2 is subjected to heat treatment in the presence of a lithium salt. Here, from the viewpoint of reducing impurities derived from the water-soluble salts, before performing the heat treatment in the presence of the lithium salt, the aged product obtained in the step 2 is washed with distilled water or the like to remove the salts. After filtration and addition of lithium salt, it is preferable to heat-treat as a heat treatment raw material in an oxidizing atmosphere in the presence of lithium salt. Of course, the reaction product obtained in the above step 2 is used as it is as a heat treatment raw material in step 3. Further, heat treatment may be performed in an oxidizing atmosphere in the presence of a lithium salt.

As a specific method for causing the heat treatment raw material and the lithium salt to coexist during the heat treatment, a known method can be used, and there is no particular limitation. For example, the reaction product obtained in Step 2 above and lithium The method of mixing with a salt can be mentioned. More specifically, if the lithium salt is insoluble in water, dry-mix and then pulverize well with a vibration mill or the like. If water-soluble, the precipitate is sufficiently dispersed in an aqueous solution containing the lithium salt and then uniformly applied to a mixer. It is desirable to make a simple slurry. The slurry or the like is preferably dried by a drier and pulverized again as necessary.

Further, a dried material may be used as the heat treatment raw material. In the case of using a dried product, it is preferable to mix with the lithium salt before drying from the viewpoint of solidifying with residual alkali during drying and avoiding difficulty in uniform mixing with the lithium salt.

As the lithium salt, known lithium salts can be widely used, and there is no particular limitation. Specifically, lithium acetate, lithium nitrate, lithium chloride, or the like can be used in addition to inexpensive lithium carbonate and lithium hydroxide having high reactivity with precipitation. In addition to the above lithium salt, lithium perchlorate and its hydrate can also be used as an oxidizing agent.

The amount of lithium salt added to the heat treatment raw material is adjusted according to the nickel average valence assuming the lithium molar amount (Li / (Ni + Mn) ratio) relative to the number of moles of nickel and manganese in the heat treatment raw material. preferable. That is, as described above, since the nickel-containing lithium manganese composite oxide of the present invention has a valence of Mn of 4 and an average valence of Ni of 2.5 or more, the y value in the composition formula is 0.4 to In the case of 0.6, the Li / (Ni + Mn) ratio is preferably 1.25 or more, more preferably 1.5 or more. There is no particular upper limit for the Li / (Ni + Mn) ratio, but an expensive lithium source is used, so that it is preferably 2.5 or less from the viewpoint of economy. The Li / (Ni + Mn) ratio can be set within the above range depending on the average valence of Mn and Ni constituting the material, but the (Li / (Ni + Mn) ratio) should be 1.25 or more (Li excess composition). Is preferred. By using a Li-excess composition, it is possible to suppress the generation of impurity phases such as LiMn ₂ O ₄ spinel with a small amount of lithium in the sample, stabilization of high-value trivalent nickel ions during high-temperature heat treatment, and flux effects. Contributes to the improvement of the primary and secondary particle size of the heat-treated product.

Here, if the lithium salt is insoluble in water, dry-mix and then pulverize well with a vibration mill or the like. If water-soluble, the precipitate is sufficiently dispersed in an aqueous solution containing the lithium salt, and then applied to a mixer to form a uniform slurry. It is desirable to produce it. The slurry or the like may be dried with a dryer and pulverized again as necessary. The drying temperature is preferably 100 ° C. or lower, and more preferably 60 ° C. or lower. When dried under a temperature condition exceeding 100 ° C., the slurry viscosity decreases due to the high temperature, and the precipitate is easily separated from the lithium salt. On the other hand, if the drying temperature is too low, it does not dry, so vacuum or freeze drying may be used.

The heat treatment is not particularly limited as long as heat is applied, and widely known methods can be employed. Among them, it is preferable to perform the baking treatment from the viewpoint that the heat treatment can be easily performed. The baking treatment is performed in an oxidizing atmosphere. In this specification, firing in an oxidizing atmosphere means firing in the air or in an oxygen stream. By performing the baking treatment in an oxidizing atmosphere, the lattice constant a and the lattice volume in the composite oxide of the present invention can be set to the above-described numerical ranges, and eventually the nickel-containing lithium manganese composite oxide finally obtained. It becomes possible to increase the average valence of nickel ions in the product. As described above, the lithium ion secondary battery using the nickel-containing lithium manganese composite oxide having a high average valence of nickel ions as the positive electrode material is excellent in charge / discharge characteristics.

The firing temperature is preferably about 750 ° C. to 1000 ° C., although it depends on the composition of the heat treatment raw material. By firing at a temperature of 750 ° C. or higher, the particle diameter of the obtained nickel-containing lithium manganese composite oxide becomes a predetermined size or more. Thereby, the reactivity with the electrolytic solution is not excessive, and a sample excellent in cycle characteristics can be obtained. On the other hand, by setting the firing temperature to 1000 ° C. or lower, it is possible to prevent the resulting nickel-containing lithium manganese composite oxide from having an excessively large particle size. As a result, it is possible to ensure a constant exchange of lithium ions with the electrolytic solution and obtain a sample having excellent discharge rate characteristics. Moreover, by setting the firing temperature to 1000 ° C. or less, it is possible to suppress the volatilization of the Li source and prevent cost loss.

The firing time is preferably 30 minutes or longer, more preferably 3 hours or longer, while maintaining the temperature within the above-mentioned firing temperature range from the viewpoint of sufficient reaction. Although there is no limitation in particular about the upper limit of baking time, it is preferable to set it within 30 hours from a viewpoint of suppressing an increase in manufacturing cost.

After heat treatment, if necessary, excess lithium salt may be removed by washing with water, followed by filtration and drying. Further, if necessary, step 3 may be repeated a plurality of times in order to obtain a nickel-containing lithium manganese composite oxide having more excellent charge / discharge characteristics. The number of repetitions is preferably 2 to 3 times from the viewpoint of simplifying the process and ensuring uniformity.

The embodiments of the present invention have been described above. However, the present invention is not limited to these examples, and it is needless to say that the present invention can be implemented in various forms without departing from the gist of the present invention.

Hereinafter, the embodiments of the present invention will be described more specifically based on examples, but the present invention is not limited to these.

Example 1
36.35 g of nickel (II) nitrate hexahydrate and 24.74 g of manganese (II) chloride tetrahydrate (0.25 mol / batch, Ni: Mn molar ratio 1: 1) were weighed into 500 ml of distilled water. It was completely dissolved. In another titanium beaker, 50 g of sodium hydroxide was added, and 500 ml of distilled water was added and completely dissolved. A sodium hydroxide aqueous solution was fixed in a thermostat kept at 20 ° C., and stirred and held until the solution reached the same temperature. A liquid feed pump was set in the metal salt solution, and the metal salt solution was gradually added to the alkali solution over 3 hours to form a precipitate. It was confirmed that the pH of the alkaline solution was 11 or more even after completion of the precipitation. After completion of the precipitation, the beaker was taken out of the thermostatic bath and stirred at room temperature, and then wet oxidation and aging were performed for 2 days while blowing oxygen into the precipitate using an oxygen gas generator. After aging, the precipitate was washed with distilled water to remove alkali or salts and then filtered. After filtration, 0.25 mol (18.47 g) of lithium carbonate was added to the precipitate and mixed with 200 ml of distilled water to prepare a slurry. The slurry was transferred to a polytetrafluoroethylene petri dish and dried at 50 ° C. for 2 days to produce a firing raw material. The raw material was pulverized by a vibration mill, spread thinly on an alumina crucible lid, subjected to primary firing at 650 ° C. in the atmosphere for 5 hours, and then cooled in a furnace. The fired raw material was pulverized again with a vibration mill and subjected to secondary firing in the air at 850 ° C. for 5 hours. After cooling in the furnace, a sample was taken out, washed with distilled water, filtered and dried to obtain the target composite oxide.

(Comparative Example 1)
A sample was prepared in the same manner as in Example 1 except that the secondary firing was performed in nitrogen instead of in the air.

Evaluation by X-ray diffraction (Example 1)
The actual measurement (+) of the sample of Example 1 obtained above and the calculated (curved) X-ray diffraction (XRD) pattern using a hexagonal layered rock salt unit cell (the following space group) are shown in FIG.

The residual is displayed below the pattern. Around 2θ = 20-25 °, a superlattice peak derived from a monoclinic layered rock-salt unit cell (the following space group) that cannot be fitted with this model (broad peaks around 2θ = 20.5 ° and 21.5 °) ) Was confirmed.

From FIG. 1, the obtained XRD pattern could be attributed to a monoclinic Li ₂ MnO ₃ type structure (the following space group) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time the fit was analyzed by belonging to a hexagonal layered rock salt type crystal phase (the following space group) called α-NaFeO ₂ type structure without a simpler superlattice.

From the X-ray Rietveld analysis (using the analysis program Rietan-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), The lattice constant a = 2.86194 (7) Å, c = 14.2321 (3) Å, lattice volume V = 100.953 (4) was Å ^3.
The occupancy at each lattice position is 4.75 (6)% at the transition metal (3a) position in the Li layer, and 81.14 (16) at the transition metal (3b) position in the transition metal layer. %Met. The sum of both was the amount of transition metal per composition formula, and the value was 85.9 (2)% (0.859 (2)).

Evaluation by X-ray diffraction (Comparative Example 1)
FIG. 2 shows an actual measurement (+) of the sample of Comparative Example 1 obtained above and a calculated (curved) X-ray diffraction (XRD) pattern using a hexagonal layered rock salt unit cell (the following space group).

From FIG. 2, the obtained XRD pattern could be attributed to a monoclinic Li ₂ MnO ₃ type structure (the following space group) phase having a hexagonal network regular arrangement in the transition metal layer.

From the X-ray Rietveld analysis (using the analysis program Rietan-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007)), the lattice constant a = 2.88374 (8) Å, c = 14.2758 (3) Å, and the lattice volume V = 102.812 (4) ^{３ 3} .
As for the occupancy at each lattice position, the occupancy at the transition metal (3a) position in the Li layer is 8.79 (6)%, and the occupancy at the transition metal (3b) position in the transition metal layer is 87.09 (15). %Met. The sum of both was the amount of transition metal per composition formula, and the value was 95.9 (2)% (0.959 (2)).

Chemical analysis (Example 1)
When the amount of Li was estimated by ICP emission analysis and the amount of Mn, Ni and O of the sample of Example 1 were estimated by wavelength dispersive X-ray fluorescence analysis, the resulting Li / (Ni + Mn) molar ratio was 1.30. (1). The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.48 (1) and 2.62 (5), respectively.
From the correspondence with the composition formula, the x value is calculated by the following formula.
x = (Li / (Ni + Mn) molar ratio-1) ÷ (Li / (Ni + Mn) molar ratio + 1)
Therefore, the x value was 0.130 (5).
On the other hand, the y value was 0.48 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Chemical analysis (Comparative Example 1)
When the Li amount was estimated by ICP emission analysis, and the Mn amount, Ni amount, and O amount of the sample of Comparative Example 1 were estimated by wavelength dispersive X-ray fluorescence analysis, the obtained Li / (Ni + Mn) molar ratio was 0.98. (1). The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.50 (1) and 2.11 (6), respectively.
From the correspondence with the composition formula, the x value is calculated by the following formula.
x = (Li / (Ni + Mn) molar ratio-1) ÷ (Li / (Ni + Mn) molar ratio + 1)
Therefore, the x value was -0.01 (1).
On the other hand, the y value was 0.50 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Valence analysis of Mn ions and Ni ions FIGS. 3A and 3B show the X-ray absorption spectra (XANES) near the K-edge of Mn and Ni in the samples of Example 1 and Comparative Example 1, respectively. Incidentally, Li ₂ MnO ₃ , NiO and LiNiO ₂ were used as standard materials for tetravalent Mn, divalent Ni and trivalent Ni, respectively.
At the MnK end, there is no difference between the spectra of Example 1 and Comparative Example 1, and the XANES data of Li ₂ MnO ₃ , which is a tetravalent Mn standard substance, almost overlaps. Similarly to the above, there is no difference in the Mn valence, and it can be judged as tetravalent. On the other hand, the XANES data at the NiK end shows that the peak top position corresponding to the 1s → 4p transition differs greatly between Example 1 and Comparative Example 1. The sample of Example 1 is shifted to a higher energy side than the sample of Comparative Example 1, which reflects the higher Ni ion valence. Therefore, the Ni average valence was estimated using the following calculation formula.
Ni average valence = 2 + {(peak top energy value of example sample) − (peak top energy value of NiO)}
÷ {(peak top energy value of LiNiO ₂ sample) − (peak top energy value of NiO)}
Example 1
Since the energy values of NiO and LiNiO ₂ were 8349.3 and 8351.3 eV, respectively, and the energy value of the example sample was estimated to be 8351 eV, the average valence of the obtained nickel ions was calculated to be 2.85. It was done.
(Comparative Example 1)
The energy values of NiO and LiNiO ₂ were 8349.3 and 8351.3 eV, respectively, and the energy value of the comparative sample was estimated to be 8350 eV, so the average valence of the obtained nickel ions was calculated to be 2.35. It was done.

Evaluation of charge / discharge characteristics After 20 mg of the obtained powder of Example 1 obtained sample was mixed well with 5 mg of acetylene black, a small amount of binder (polytetrafluoroethylene powder) was added to prepare a tablet positive electrode. After vacuum drying at 120 ° C, the negative electrode is metallic lithium and the electrolyte is dissolved in 1M-LiPF ₆ supporting salt in EC (ethylene carbonate) + DMC (dimethyl carbonate) mixed solvent (volume ratio 3: 7) in the glove box A lithium half battery was assembled using the electrolyte solution, and a charge / discharge test for starting charging was performed at 30 ° C. The potential range was 2.0-4.6V. The charge capacity is limited to 80 mAh / g for the first cycle until 1-4 cycles, and the charge capacity is limited to 80 mAh / g for the second cycle after discharge. Charging / discharging was carried out while increasing the charging capacity by 40 mAh / g until the cycle, charging to 4.8 V at the fifth cycle, and then discharging. Thereafter, 29 cycles of charge and discharge were performed in the set potential range. For the sample of Comparative Example 1 as well, a battery was produced under the same conditions, and a similar charge / discharge characteristic evaluation test was performed.
Example 1
FIG. 4 shows a charge / discharge curve at 30 ° C. of a lithium secondary battery using the sample of Example 1 as a positive electrode. The curve that rises to the right corresponds to charge (c), and the curve that falls to the right corresponds to discharge (d). The number indicates the cycle number. From FIG. 4, the charge capacity and discharge capacity at the fifth cycle (corresponding to the initial stage after activation) were 226 mAh / g and 205 mAh / g, respectively, and the charge / discharge efficiency was 93%. Moreover, the average voltage at the time of the fifth cycle discharge is 3.69 V, and the energy density corresponding to the product of the discharge capacity is 757 mWh / g. The discharge capacity of 30 cycles after) was as high as 189 mAh / g, and the discharge capacity maintenance rate at 30 cycles with respect to 5 cycles was as high as 92%. Further, it was also found that there was almost no decrease in potential and capacity from the 24th cycle onwards, and it was confirmed that the lithium ion secondary battery positive electrode material had excellent characteristics.
(Comparative Example 1)
FIG. 5 shows a charge / discharge curve at 30 ° C. of a lithium secondary battery using the sample of Comparative Example 1 as a positive electrode. The curve that rises to the right corresponds to charge (c), and the curve that falls to the right corresponds to discharge (d). From FIG. 5, the charge capacity and discharge capacity at the fifth cycle (corresponding to the initial stage after activation) were 218 mAh / g and 205 mAh / g, respectively, and the charge / discharge efficiency was 93%. In addition, although the average voltage at the fifth cycle discharge is 3.78 V and the energy density corresponding to the product of the discharge capacity is 773 mWh / g, which has sufficient initial characteristics as a high capacity positive electrode, after 34 cycles (after activation 30 Discharge capacity) was as low as 30 mAh / g, and the discharge capacity retention rate at 30 cycles with respect to 5 cycles was 14%. That is, the comparative sample was not sufficient in cycle characteristics as a lithium ion secondary battery positive electrode material.

(Example 2)
Weigh 29.08 g of nickel (II) nitrate hexahydrate and 29.69 g of manganese (II) chloride tetrahydrate (0.25 mol / batch, Ni: Mn molar ratio 4: 6) and completely dissolve in 500 ml of distilled water. Dissolved. An aqueous sodium hydroxide solution was fixed in a thermostatic bath maintained at + 5 ° C., and stirred and held until the solution reached the same temperature. Thereafter, a sample was prepared by the same process as in Example 1 to obtain the target composite oxide.

(Comparative Example 2)
A sample was prepared in the same manner as in Example 2 except that the secondary firing was performed in nitrogen instead of in the air.

Evaluation by X-ray diffraction (Example 2)
The actual measurement (+) of the sample of Example 2 obtained above and the calculated (curved) X-ray diffraction (XRD) pattern using the hexagonal layered rock salt type unit cell (the above space group) are shown in FIG.

From FIG. 6, the obtained XRD pattern could be attributed to a monoclinic Li ₂ MnO ₃ type structure (the following space group) phase having a hexagonal network regular arrangement in the transition metal layer.

From X-ray Rietveld analysis (using the analysis program Rietan-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007)), lattice constant a = 2.85599 (8) Å, c = 14.2254 (3) Å, lattice volume V = 100.487 (5) ^{３ 3} .
The occupancy at each lattice position was 4.03 (8)% for the transition metal (3a) position in the Li layer and 76.6 (2)% for the transition metal (3b) position in the transition metal layer. . The sum of both was the amount of transition metal per composition formula, and the value was 80.6 (3)% (0.806 (3)).

Evaluation by X-ray diffraction (Comparative Example 2)
FIG. 7 shows an actual measurement (+) of the sample of Comparative Example 2 obtained above and a calculated (curved) X-ray diffraction (XRD) pattern using a hexagonal layered rock salt unit cell (the following space group).

From FIG. 7, the obtained XRD pattern could be attributed to a monoclinic Li ₂ MnO ₃ type structure (the following space group) phase having a hexagonal network regular arrangement in the transition metal layer.

From X-ray Rietveld analysis (using the analysis program Rietan-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007)), lattice constant a = 2.71664 (10) Å, c = 14.2729 (4) Å, was lattice volume ^{V = 101.930 (5) Å 3} .
The occupancy at each lattice position was 6.41 (6)% for the transition metal (3a) position in the Li layer and 82.20 (17)% for the transition metal (3b) position in the transition metal layer. . The sum of both was the amount of transition metal per composition formula, and the value was 88.6 (2)% (0.886 (2)).

Chemical analysis (Example 2)
When the Li amount was estimated by ICP emission analysis, and the Mn amount, Ni amount, and O amount of the sample of Example 2 were estimated by wavelength dispersive X-ray fluorescence analysis, the obtained Li / (Ni + Mn) molar ratio was 1.361. (8). The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.398 (1) and 2.43 (3), respectively. From the correspondence with the composition formula, the x value is calculated by the following formula.
x = (Li / (Ni + Mn) molar ratio-1) ÷ (Li / (Ni + Mn) molar ratio + 1)
Therefore, the x value was 0.153 (4).
On the other hand, the y value was 0.398 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Chemical analysis (Comparative Example 2)
When the amount of Li was estimated by ICP emission analysis, and the amount of Mn, Ni and O of the sample of Comparative Example 2 were estimated by wavelength dispersive fluorescent X-ray analysis, the obtained Li / (Ni + Mn) molar ratio was 1.20 (1 )Met. The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.398 (1) and 2.36 (5), respectively. From the correspondence with the composition formula, the x value is calculated by the following formula.
x = (Li / (Ni + Mn) molar ratio-1) ÷ (Li / (Ni + Mn) molar ratio + 1)
Therefore, the x value is 0.090 (6).
On the other hand, the y value was 0.398 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Valence analysis of Mn ions and Ni ions FIGS. 8A and 8B show the X-ray absorption spectra (XANES) near the K-edge of Mn and Ni in the samples of Example 2 and Comparative Example 2, respectively. Incidentally, Li ₂ MnO ₃ , NiO and LiNiO ₂ were used as standard materials for tetravalent Mn, divalent Ni and trivalent Ni, respectively.
At the MnK edge, there is no difference between the spectra of Example 2 and Comparative Example 2 and almost overlaps with the XANES data of Li ₂ MnO ₃ which is a standard material of tetravalent Mn. Similarly to the above, there is no difference in the Mn valence, and it can be judged as tetravalent. On the other hand, the XANES data at the NiK end shows that the peak top position corresponding to the 1s → 4p transition differs greatly between Example 2 and Comparative Example 2. The sample of Example 2 is shifted to a higher energy side than the sample of Comparative Example 2, which reflects the higher Ni ion valence. Therefore, the Ni average valence was estimated using the following calculation formula.
Ni average valence = 2 + {(peak top energy value of example sample) − (peak top energy value of NiO)} ÷ {(peak top energy value of LiNiO ₂ sample) − (peak top energy value of NiO)}
(Example 2)
The energy values of NiO and LiNiO ₂ were 8346.7 and 8348.8 eV, respectively, and the peak top energy value of the example sample was estimated to be 8348.5 eV. Therefore, the average valence of the obtained nickel ions was calculated to be 2.86. .
(Comparative Example 2)
Since the energy values of NiO and LiNiO ₂ were 8346.7 and 8348.8 eV, respectively, and the energy value of the comparative sample was estimated to be 8347.6 eV, the average valence of the obtained nickel ions was calculated to be 2.43.

Evaluation of Charge / Discharge Characteristics A lithium half battery was assembled in the same manner as in Example 1 using the obtained powder of Example 2 as a positive electrode active material, and a charge / discharge test at the start of charging was performed at 30 ° C. The charge / discharge test conditions are the same as in Example 1. For the sample of Comparative Example 2, a battery was prepared under the same conditions, and the same charge / discharge characteristic evaluation test was performed.
(Example 2)
FIG. 9 shows a charge / discharge curve at 30 ° C. of a lithium secondary battery using the sample of Example 2 as a positive electrode. The curve that rises to the right corresponds to charge (c), and the curve that falls to the right corresponds to discharge (d). The number indicates the cycle number. From FIG. 9, the charge capacity and discharge capacity at the fifth cycle (corresponding to the initial stage after activation) were 217 mAh / g and 209 mAh / g, respectively, and the charge / discharge efficiency was 96%. In addition, the average voltage at the fifth cycle discharge is 3.58V, the energy density corresponding to the product of the discharge capacity is 749 mWh / g, and not only has sufficient initial characteristics as a high capacity positive electrode, but also after 34 cycles (after activation) The discharge capacity (corresponding to 30 cycles) was as high as 206 mAh / g, and the discharge capacity retention rate after 30 cycles with respect to 5 cycles was as high as 99%. It was also found that there was almost no decrease in potential and capacity after the 14th cycle, and it was confirmed that it had excellent characteristics as a positive electrode material for lithium ion secondary batteries.
(Comparative Example 2)
FIG. 10 shows a charge / discharge curve at 30 ° C. of a lithium secondary battery using the sample of Comparative Example 2 as a positive electrode. The curve that rises to the right corresponds to charge (c), and the curve that falls to the right corresponds to discharge (d). From FIG. 10, the charge capacity and discharge capacity at the fifth cycle (corresponding to the initial stage after activation) were 218 mAh / g and 206 mAh / g, respectively, and the charge / discharge efficiency was 94%. Moreover, although the average voltage at the time of the fifth cycle discharge is 3.65V and the energy density corresponding to the product of the discharge capacity is 749 mWh / g, it has sufficient initial characteristics as a high capacity positive electrode, but after 34 cycles (30 cycles after activation) The discharge capacity was as low as 126 mAh / g, and the discharge capacity retention rate after 30 cycles with respect to 5 cycles was 61%. That is, the comparative sample was not sufficient in cycle characteristics as a lithium ion secondary battery positive electrode material.

(Example 3)
Weigh 43.62 g of nickel (II) nitrate hexahydrate and 19.79 g of manganese (II) chloride tetrahydrate (0.25 mol / batch, Ni: Mn molar ratio 6: 4) and completely weigh it in 500 ml of distilled water. Dissolved. A sodium hydroxide aqueous solution was fixed in a thermostat kept at 5 ° C., and stirred and held until the solution reached the same temperature. Thereafter, a sample was prepared by the same process as in Example 1 to obtain the target composite oxide.
(Comparative Example 3)
A sample was prepared in the same manner as in Example 3 except that the secondary firing was performed in nitrogen instead of in the air.

Evaluation by X-ray diffraction (Example 3)
FIG. 11 shows an actual measurement (+) of the sample of Example 3 obtained above and a calculated (curved) X-ray diffraction (XRD) pattern using a hexagonal layered rock salt unit cell (the following space group).

The residual is displayed below the pattern. Around 2θ = 20-25 °, a superlattice peak derived from a monoclinic layered rock salt unit cell (the above space group) that cannot be fitted with this model (broad peaks near 2θ = 20.5 ° and 21.5 °) ) Was confirmed.

From FIG. 11, the obtained XRD pattern could be attributed to a monoclinic Li ₂ MnO ₃ type structure (the following space group) phase having a hexagonal network regular arrangement in the transition metal layer.

From X-ray Rietveld analysis (using the analysis program Rietan-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), The lattice constant a = 2.86563 (6) Å, c = 14.2291 (2) Å, lattice volume V = 101.192 (3) was Å ^3.
The occupancy at each lattice position was 4.17 (5)% for the transition metal (3a) position in the Li layer and 84.72 (15)% for the transition metal (3b) position in the transition metal layer. . The sum of both was the amount of transition metal per composition formula, and its value was 88.9 (2)% (0.889 (2)).

Evaluation by X-ray diffraction (Comparative Example 3)
FIG. 12 shows an actual measurement (+) of the sample of Comparative Example 3 obtained above and a calculated (curved) X-ray diffraction (XRD) pattern using a hexagonal layered rock salt unit cell (the following space group).

From FIG. 12, the obtained XRD pattern could be attributed to a monoclinic Li ₂ MnO ₃ type structure (the following space group) phase having a hexagonal network regular arrangement in the transition metal layer.

However, this time the fit was analyzed by belonging to a hexagonal layered rock salt type crystal phase (the above space group) called α-NaFeO ₂ type structure without a simpler superlattice.

From the X-ray Rietveld analysis (using the analysis program Rietan-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007).), The lattice constant a = 2.89131 (5) Å, c = 14.2840 (2) Å, lattice volume V = 103.412 (3) was Å ^3.
The occupancy at each lattice position was 11.11 (5)% for the transition metal (3a) position in the Li layer and 90.32 (14)% for the transition metal (3b) position in the transition metal layer. . The sum of both was the amount of transition metal per composition formula, and the value was 101.43 (19)% (1.0143 (19)).

Chemical analysis (Example 3)
When the amount of Li was estimated by ICP emission analysis and the amount of Mn, Ni and O of the sample of Example 3 were estimated by wavelength dispersive X-ray fluorescence analysis, the resulting Li / (Ni + Mn) molar ratio was 1.119 (18 )Met. The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.596 (1) and 2.40 (10), respectively.
From the correspondence with the composition formula, the x value is calculated by the following formula.
x = (Li / (Ni + Mn) molar ratio-1) ÷ (Li / (Ni + Mn) molar ratio + 1)
Therefore, the x value was 0.056 (9).
On the other hand, the y value was 0.596 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Chemical analysis (Comparative Example 3)
When the amount of Li was estimated by ICP emission analysis and the amount of Mn, Ni and O of the sample of Comparative Example 3 were estimated by wavelength dispersive X-ray fluorescence analysis, the obtained Li / (Ni + Mn) molar ratio was 0.906 (2 )Met. The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.595 (1) and 2.20 (2), respectively.
From the correspondence with the composition formula, the x value is calculated by the following formula.
x = (Li / (Ni + Mn) molar ratio-1) ÷ (Li / (Ni + Mn) molar ratio + 1)
Therefore, the x value is -0.0493 (10). This x value was a negative value.
On the other hand, the y value was 0.595 (1) because it was the Ni / (Ni + Mn) molar ratio itself.

Valence analysis of Mn ion and Ni ion FIGS. 13A and 13B show the X-ray absorption spectra (XANES) near the K-edge of Mn and Ni in the samples of Example 3 and Comparative Example 3, respectively. Incidentally, Li ₂ MnO ₃ , NiO and LiNiO ₂ were used as standard materials for tetravalent Mn, divalent Ni and trivalent Ni, respectively.
At the MnK end, there is no difference between the spectra of Example 3 and Comparative Example 3, and almost overlaps with the XANES data of Li ₂ MnO ₃ which is a standard substance of tetravalent Mn. Similarly to the above, there is no difference in the Mn valence, and it can be judged as tetravalent. On the other hand, the XANES data at the NiK end shows that the peak top position corresponding to the 1s → 4p transition is greatly different between Example 3 and Comparative Example 3. The sample of Example 3 is shifted to a higher energy side than the sample of Comparative Example 3, which reflects that the Ni ion valence is high. Therefore, the Ni average valence was estimated using the following calculation formula.
Ni average valence = 2 + {(peak top energy value of example sample) − (peak top energy value of NiO)} ÷ {(peak top energy value of LiNiO ₂ sample) − (peak top energy value of NiO)}
(Example 3)
The energy values of NiO and LiNiO ₂ were 8346.7 and 8348.8 eV, respectively, and the peak top energy value of the example sample was estimated to be 8348.2 V. Therefore, the average valence of the obtained nickel ions was calculated to be 2.71. .
(Comparative Example 3)
Since the energy values of NiO and LiNiO ₂ were 8346.7 and 8348.8 eV, respectively, and the energy value of the comparative sample was estimated to be 8347.2 eV, the average valence of the obtained nickel ions was calculated to be 2.24.

Evaluation of Charge / Discharge Characteristics Using the obtained powder of Example 3 as a positive electrode active material, a lithium half battery was assembled in the same manner as in Example 1, and a charge / discharge test at the start of charging was performed at 30 ° C. The charge / discharge test conditions are the same as in Example 1. For the sample of Comparative Example 3, a battery was prepared under the same conditions, and the same charge / discharge characteristic evaluation test was performed.

(Example 3)
FIG. 14 shows a charge / discharge curve at 30 ° C. of a lithium secondary battery using the sample of Example 3 as a positive electrode. The curve that rises to the right corresponds to charge (c), and the curve that falls to the right corresponds to discharge (d). The number indicates the cycle number. From FIG. 14, the charge capacity and discharge capacity at the fifth cycle (corresponding to the initial stage after activation) were 164 mAh / g and 156 mAh / g, respectively, and the charge / discharge efficiency was 95%. In addition, the average voltage during the fifth cycle discharge is 3.80 V, and the energy density corresponding to the product of the discharge capacity is 592 mWh / g, which is not only a sufficient initial characteristic as a high capacity positive electrode, but also after 34 cycles (after activation) The discharge capacity of 30 cycles) was as high as 142 mAh / g, and the discharge capacity retention rate after 30 cycles with respect to 5 cycles was as high as 91%. It was also found that the potential and capacity decrease from the 14th cycle onward were small, and it was confirmed that the lithium ion secondary battery positive electrode material had excellent characteristics.
(Comparative Example 3)
FIG. 15 shows a charge / discharge curve at 30 ° C. of a lithium secondary battery using the sample of Comparative Example 3 as a positive electrode. The curve that rises to the right corresponds to charge (c), and the curve that falls to the right corresponds to discharge (d). From FIG. 15, the charge capacity and discharge capacity at the fifth cycle (corresponding to the initial stage after activation) were 175 mAh / g and 169 mAh / g, respectively, and the charge / discharge efficiency was 97%. Moreover, although the energy density corresponding to the product of the discharge voltage and the average voltage at the 5th cycle is 3.83 mWh / g, which has sufficient initial characteristics as a high capacity positive electrode, after 34 cycles (equivalent to 30 cycles after activation) The discharge capacity was as low as 105 mAh / g, and the discharge capacity retention rate after 30 cycles with respect to 5 cycles was as low as 62%. That is, the comparative sample was not sufficient in cycle characteristics as a lithium ion secondary battery positive electrode material.

Example 4
Weigh 29.08 g of nickel (II) nitrate hexahydrate and 29.69 g of manganese chloride (II) tetrahydrate (0.25 mol / batch, Ni: Mn molar ratio 4: 6) in 500 ml of distilled water. It was completely dissolved. In another titanium beaker, 50 g of sodium hydroxide was added, and 500 ml of distilled water was added and completely dissolved. Thereafter, 200 ml of ethanol was added as an antifreeze and stirred well. The sodium hydroxide solution was fixed in a thermostat kept at −10 ° C., and stirred and held until the solution reached the same temperature. A liquid feed pump was set in the metal salt solution, and the metal salt solution was gradually added to the alkali solution over 3 hours to form a precipitate. It was confirmed that the pH of the alkaline solution was 11 or more even after completion of the precipitation. After completion of the precipitation, the beaker was taken out of the thermostatic bath and stirred at room temperature, and then wet oxidation and aging were performed for 2 days while blowing oxygen into the precipitate using an oxygen gas generator. After aging, the precipitate was washed with distilled water to remove alkali or salts and then filtered. After filtration, 0.5 mol (20.98 g) of lithium hydroxide monohydrate was added to the precipitate, dissolved in 200 ml of distilled water, and then mixed with the aged precipitate and a mixer to prepare a slurry. The slurry was transferred to a polytetrafluoroethylene petri dish and dried at 50 ° C. for 2 days to produce a firing raw material. The raw material was pulverized by a vibration mill, spread thinly on an alumina crucible lid, subjected to primary firing in an oxygen stream at 500 ° C. for 20 hours, and then cooled in a furnace. The fired raw material was pulverized again with a vibration mill and subjected to secondary firing in nitrogen at 850 ° C. for 5 hours. After cooling in the furnace, a sample was taken out, washed with distilled water, filtered and dried to obtain the target composite oxide.

Evaluation by X-ray diffraction (Example 4)
FIG. 16 shows the actual measurement (+) of the sample of Example 4 obtained above and the calculated (curved) X-ray diffraction (XRD) pattern using a hexagonal layered rock salt unit cell (the following space group).

From FIG. 16, the obtained XRD pattern could be attributed to a monoclinic Li ₂ MnO ₃ type structure (the following space group) phase having a hexagonal network regular arrangement in the transition metal layer.

From X-ray Rietveld analysis (using the analysis program Rietan-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007)), the lattice constant a = 2.86135 (8) ８, c = 14.2379 (3) Å, lattice volume V = 100.953 (4) was Å ^3.
The occupancy at each lattice position is 4.85 (6)% for the transition metal (3a) position in the Li layer and 79.78 (17) for the transition metal (3b) position within the transition metal layer. %Met. The sum of both was the amount of transition metal per composition formula, and the value was 84.6 (2)% (0.846 (2)).

Chemical analysis (Example 4)
When the amount of Li was estimated by ICP emission analysis, and the amount of Mn, Ni and O of the sample of Example 4 were estimated by wavelength dispersive X-ray fluorescence analysis, the obtained Li / (Ni + Mn) molar ratio was 1.32. (5). The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.395 (10) and 2.7 (2), respectively.
From the correspondence with the composition formula, the x value is calculated by the following formula.
x = (Li / (Ni + Mn) molar ratio-1) ÷ (Li / (Ni + Mn) molar ratio + 1)
Therefore, the x value was 0.14 (2).
On the other hand, the y value was 0.395 (10) because it was the Ni / (Ni + Mn) molar ratio itself.

Valence analysis of Mn ion and Ni ion FIGS. 17A and 17B show the X-ray absorption spectra (XANES) near the K-edge of Mn and Ni in the sample of Example 4. Incidentally, Li ₂ MnO ₃ , NiO and LiNiO ₂ were used as standard materials for tetravalent Mn, divalent Ni and trivalent Ni, respectively.
At the MnK end, the spectrum of the sample of Example 4 almost overlaps with the XANES data of Li ₂ MnO ₃ which is a standard substance of tetravalent Mn, so that the Mn valence can be determined to be tetravalent. On the other hand, the peak top value accompanying the 1s → 4p transition of the XANES data at the NiK edge of the sample of Example 4 was present at a position approximately in the middle between the two kinds of reference materials with known valences. Therefore, the Ni average valence was estimated using the following calculation formula.
Ni average valence = 2 + {(peak top energy value of example sample) − (peak top energy value of NiO)}
÷ {(peak top energy value of LiNiO ₂ sample) − (peak top energy value of NiO)}
Since the energy values of NiO and LiNiO ₂ were 8346.3 and 8348.4 eV, respectively, and the energy value of the sample of Example 4 was estimated to be 8347.5 eV, the average valence of the obtained nickel ions was calculated to be 2.57. From the above, it is shown that if an oxidizing atmosphere is selected as the primary firing, the target substance can be obtained even if an inert gas atmosphere such as in a nitrogen stream is selected during the secondary firing.

Evaluation of Charge / Discharge Characteristics After 20 mg of the obtained powder of Example 4 sample was mixed well with 5 mg of acetylene black, a small amount of binder (polytetrafluoroethylene powder) was added to prepare a tablet positive electrode. Thereafter, a battery was produced under the same conditions as in Example 1, and a charge / discharge characteristic evaluation test was performed under the same test conditions.
FIG. 18 shows a charge / discharge curve at 30 ° C. of a lithium secondary battery using the sample of Example 4 as a positive electrode. The curve that rises to the right corresponds to charge (c), and the curve that falls to the right corresponds to discharge (d). The number indicates the cycle number. As shown in FIG. 18, the charge capacity and discharge capacity at the fifth cycle (corresponding to the initial stage after activation) were 240 mAh / g and 228 mAh / g, respectively, and the charge / discharge efficiency was 95%. In addition, the average voltage at the fifth cycle discharge is 3.67V, the energy density corresponding to the product of the discharge capacity is 838 mWh / g, and not only has sufficient initial characteristics as a high capacity positive electrode, but also after 34 cycles (after activation) The discharge capacity (corresponding to 30 cycles) was also as high as 218 mAh / g, and the 34-cycle discharge capacity maintenance rate with respect to 5 cycles was as high as 96%. In addition, there is almost no decrease in capacity from the 14th cycle onwards, and the potential drops slightly in the vicinity of 3.5-3.0V during discharge as the cycles from the 14th cycle onwards, but it has excellent characteristics as a positive electrode material for lithium ion secondary batteries. It was confirmed that it had.

(Example 5)
A sample was prepared in the same manner as in Example 4 except that the secondary firing atmosphere was changed from nitrogen to air.

Evaluation by X-ray diffraction (Example 5)
An actual measurement (+) of the sample of Example 5 obtained above and a calculated (curved) X-ray diffraction (XRD) pattern using a hexagonal layered rock salt unit cell (the following space group) are shown in FIG.

From FIG. 19, the obtained XRD pattern could be attributed to a monoclinic Li ₂ MnO ₃ type structure (the following space group) phase having a hexagonal network regular arrangement in the transition metal layer.

From X-ray Rietveld analysis (using the analysis program Rietan-FP, F. Izumi and K. Momma, Solid State Phenom, 130 15-20 (2007)), lattice constant a = 2.85259 (9) Å, c = 14.2235 (4) Å, lattice volume V = 100.234 (5) ^{３ 3} .
The occupancy at each lattice position was 3.65 (8)% for the transition metal (3a) position in the Li layer, and 77.7 (2)% for the transition metal (3b) position in the transition metal layer. . The sum of both was the amount of transition metal per composition formula, and its value was 81.4 (3)% (0.814 (3)).

Chemical analysis (Example 5)
When the Li amount was estimated by ICP emission analysis, and the Mn amount, Ni amount, and O amount of the sample of Example 5 were estimated by wavelength dispersive X-ray fluorescence analysis, the obtained Li / (Ni + Mn) molar ratio was 1.37 (5 )Met. The Ni / (Ni + Mn) molar ratio and the O / (Ni + Mn) molar ratio were 0.400 (5) and 2.64 (9), respectively.
From the correspondence with the composition formula, the x value is calculated by the following formula.
x = (Li / (Ni + Mn) molar ratio-1) ÷ (Li / (Ni + Mn) molar ratio + 1)
Therefore, the x value was 0.16 (2).
On the other hand, the y value was 0.400 (5) because it was the Ni / (Ni + Mn) molar ratio itself.

Evaluation of Charge / Discharge Characteristics After mixing 20 mg of the obtained powder of Example 5 sample well with 5 mg of acetylene black, a small amount of binder (polytetrafluoroethylene powder) was added to prepare a tablet positive electrode. Thereafter, a battery was produced under the same conditions as in Example 1, and a charge / discharge characteristic evaluation test was performed under the same test conditions.
FIG. 20 shows a charge / discharge curve at 30 ° C. of a lithium secondary battery using the sample of Example 5 as a positive electrode. The curve that rises to the right corresponds to charge (c), and the curve that falls to the right corresponds to discharge (d). The number indicates the cycle number. From FIG. 20, the charge capacity and discharge capacity at the fifth cycle (corresponding to the initial stage after activation) were 231 mAh / g and 222 mAh / g, respectively, and the charge / discharge efficiency was 96%. In addition, the average voltage at the fifth cycle discharge is 3.50V, and the energy density corresponding to the product of the discharge capacity is 778 mWh / g and not only has sufficient initial characteristics as a high capacity positive electrode, but also after 34 cycles (after activation) The discharge capacity (corresponding to 30 cycles) was as high as 218 mAh / g, and the 34-cycle discharge capacity retention rate with respect to 5 cycles was as high as 98%, confirming that it had excellent characteristics as a positive electrode material for lithium ion secondary batteries.

Claims

General formula (1):
Li 1 + x (Ni y Mn 1-y ) 1-x O 2 (1)
[Wherein, x and y represent 0.0 ≦ x <1/3 and 0.3 ≦ y ≦ 0.6, respectively. ]
Represented by a layered rock salt type crystal phase,
The lattice constant a is 2.870 Å or less and the lattice volume is 102.0 Å 3 or less,
Nickel-containing lithium manganese composite oxide.
The nickel-containing lithium manganese composite oxide according to claim 1, wherein the amount of transition metal contained in the lithium layer is 5% or less in the layered rock salt type crystal structure.
The nickel-containing lithium manganese composite oxide according to claim 1 or 2, wherein in the layered rock salt type crystal structure, the amount of transition metal contained in the transition metal layer is 88% or less.
The nickel-containing lithium manganese composite oxide according to any one of claims 1 to 3, wherein the valence of nickel ions is 2.5 or more.
The nickel-containing lithium manganese composite oxide according to any one of claims 1 to 4, wherein the O / (Ni + Mn) atomic ratio is 2.3 or more.
A lithium ion secondary battery comprising the nickel-containing lithium manganese composite oxide according to any one of claims 1 to 5 as a positive electrode active material.
Step 1 of forming a precipitate under an alkaline condition of 20 ° C. or lower from a mixed aqueous solution containing a manganese compound and a nickel compound,
Step 2 of performing wet oxidation treatment on the precipitate,
And a step 3 of heat treatment in an oxidizing atmosphere in the presence of lithium salt,
The method for producing a nickel-containing lithium manganese composite oxide according to any one of claims 1 to 5.