WO2018173345A1

WO2018173345A1 - Nickel hydrogen cell and method for manufacturing same

Info

Publication number: WO2018173345A1
Application number: PCT/JP2017/037437
Authority: WO
Inventors: 靖志中村; 亜希子岡部; 後藤　浩之
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2017-03-23
Filing date: 2017-10-17
Publication date: 2018-09-27
Also published as: JPWO2018173345A1; CN110419138B; CN110419138A; JP6719101B2

Abstract

A nickel hydrogen cell is equipped with: an electrode group in which a positive electrode, a negative electrode, and a separator are wound so that the negative electrode constitutes the outermost circumference; and an electrolytic solution, the negative electrode comprising a negative electrode collector having a plurality of through-holes, and a negative electrode active material layer including a hydrogen storage alloy formed on both surfaces thereof. Where an opening of a through-hole in a first part of the negative electrode adjacent at the inside of the outermost circumference of the positive electrode is used as a first opening, and the opening of a through-hole at a second part of the negative electrode adjacent at the outside of the outermost circumference of the positive electrode is used as a second opening, the amount of the hydrogen storage alloy contained per unit area of the second part is less than the amount of the hydrogen storage alloy amount contained per unit area of the first part, and the area S1 of the first opening and the area S2 of the part at which the first opening and the second opening overlap satisfy the relationship 0.4 < S2/S1.

Description

Nickel metal hydride battery and manufacturing method thereof

The present invention relates to a nickel metal hydride battery having a wound electrode group.

The electrode group of the wound nickel-metal hydride battery comprises a strip-shaped positive electrode mainly composed of nickel hydroxide and a strip-shaped negative electrode mainly composed of a hydrogen storage alloy in a spiral shape with a separator interposed therebetween. It is configured to turn. The electrode group is accommodated in a battery case together with an alkaline aqueous solution that is an electrolytic solution. The negative electrode is formed by filling a negative electrode current collector having a plurality of through holes with a composition containing a hydrogen storage alloy. Usually, the outermost periphery of the electrode group is composed of a negative electrode. Since the negative electrode constituting the outermost periphery has little contribution to the battery reaction, it has been proposed to make its thickness thinner than other parts (Patent Document 1).

In order to allow the battery reaction in the electrode group to proceed uniformly, it is desirable that the electrode group is impregnated with a sufficient amount of an alkaline aqueous solution as an electrolyte, and the concentration of the alkaline aqueous solution is also desirably uniform. On the other hand, in the nickel metal hydride battery, a plurality of reactions proceed as follows.

In the positive electrode, the following charging reaction proceeds. The discharge reaction is a reverse reaction.
Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (1)

However, in the positive electrode at the end of charge or overcharge, the following water decomposition reaction proceeds and oxygen is generated.
OH ⁻ → 1/4 O ₂ + 1/2 H ₂ O + e ⁻ (2)

In the negative electrode, the following charging reaction proceeds. The discharge reaction is a reverse reaction.
M + H ₂ O + e ⁻ → MH + OH ⁻ (3)

In the negative electrode, the following water splitting reaction proceeds to generate hydrogen.
H ₂ O + e ⁻ → 1/2 H ₂ + OH ⁻ (4)

The generated hydrogen is absorbed by the hydrogen storage alloy of the negative electrode as described below, and a metal hydride is generated.
M + 1 / 2H ₂ → MH (5)

The metal hydride reacts with oxygen generated at the positive electrode as follows.
MH + 1/4 O ₂ → M + 1/2 H ₂ O (6)

Oxygen and hydrogen generated in the side reactions of formulas (2) and (4) cause an increase in the internal pressure of the battery. Therefore, the reactions of formulas (5) and (6) at the negative electrode are rapidly advanced to convert the gas into water. It is desirable to return.

JP 2005-56774 A

The negative electrode constituting the outermost periphery of the electrode group has little contribution to the battery reaction, so the consumption of water during charging is small, while the contribution to gas absorption generated in the battery is large, and more water is consumed. Generate. Therefore, the concentration of the alkaline aqueous solution tends to decrease in the vicinity of the outermost negative electrode. Moreover, since the thickness of the outermost negative electrode is thinner than other portions, the amount of the alkaline aqueous solution to be impregnated is small, and the influence of the decrease in concentration tends to be large.

Also, when making the outermost negative electrode thinner, it is difficult to uniformly fill the through holes of the negative electrode current collector with the hydrogen storage alloy, and the through holes may not be completely filled with the composition. Thus, when making the outermost negative electrode thinner, it is considered desirable to reduce the diameter of the through hole of the negative electrode current collector or to reduce the density of the through hole. Therefore, the fluidity of the electrolyte tends to be low at the outermost periphery of the electrode group.

In the above environment, the concentration of the alkaline aqueous solution tends to be non-uniform depending on the location of the electrode, the state of charge of the positive electrode varies, and a part that is partially deeply charged occurs. In the deeply charged portion, the self-decomposition reaction of the positive electrode is likely to occur, so that self-discharge (particularly short-term self-discharge) tends to be promoted as compared with the case where the entire electrode is charged uniformly.

In view of the above, the nickel-metal hydride battery according to one aspect of the present disclosure is configured so that the strip-shaped positive electrode, the strip-shaped negative electrode, and the separator interposed between the positive electrode and the negative electrode constitute the outermost periphery. A wound electrode group; an electrolyte; and a battery case that houses the electrode group and the electrolyte. The negative electrode includes a porous negative electrode current collector having a plurality of through holes, and a negative electrode active material layer containing a hydrogen storage alloy formed on both surfaces of the negative electrode current collector. An opening of the through hole in the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is a first opening, and an opening of the through hole in the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode. When the second opening is used, the amount of the hydrogen storage alloy included per unit area of the second portion is smaller than the amount of the hydrogen storage alloy included per unit area of the first portion. Furthermore, the area S1 of the first opening and the area S2 of the portion where the first opening and the second opening overlap satisfy 0.4 <S2 / S1.

According to another aspect of the present disclosure, a method for manufacturing a nickel-metal hydride battery includes (i) a step of preparing a strip-shaped positive electrode, (ii) a step of preparing a strip-shaped negative electrode, and (iii) the positive electrode and the negative electrode. Interposing a separator between the positive electrode and the negative electrode and winding the negative electrode to form the outermost periphery to form an electrode group; and (iv) forming the electrode group together with an electrolyte into a battery case And a storing step. The negative electrode prepared in the step (ii) includes a negative electrode active material layer including a porous negative electrode current collector having a plurality of through holes and a hydrogen storage alloy formed on both surfaces of the negative electrode current collector. And comprising. An opening of the through hole in the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is a first opening, and an opening of the through hole in the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode. When the second opening is used, the amount of the hydrogen storage alloy included per unit area of the second portion is smaller than the amount of the hydrogen storage alloy included per unit area of the first portion. Further, the electrode group is configured such that an area S1 of the first opening and an area S2 of a portion where the first opening and the second opening overlap satisfy 0.4 <S2 / S1.

According to the present disclosure, since the fluidity of the electrolyte in the outermost periphery of the electrode group is improved, the concentration of the electrolytic solution is made uniform in the electrode group, and the self-discharge of the nickel metal hydride battery is suppressed.

It is a figure which shows an example of the relationship between the 1st opening in the 1st part of the negative electrode adjacent inside the outermost periphery of a positive electrode, and the 2nd opening in the 2nd part of the negative electrode adjacent to the outer side of the outermost periphery of a positive electrode. It is a figure which shows the variation of the arrangement pattern of the through-hole of a negative electrode collector. It is sectional drawing which shows typically the nickel metal hydride battery which concerns on one Embodiment of this invention. FIG. 4 is a cross-sectional view schematically showing the nickel metal hydride battery of FIG. 3. FIG. 5 is an enlarged view of a portion surrounded by a circle indicated by III in FIG. 4.

The nickel metal hydride battery according to the embodiment of the present invention includes a wound electrode group. The wound electrode group is formed by winding a strip-shaped positive electrode, a strip-shaped negative electrode, and a separator interposed between the positive electrode and the negative electrode so that the negative electrode forms the outermost periphery. The electrode group is accommodated in the battery case together with the electrolytic solution.

The negative electrode includes a negative electrode current collector having a plurality of through holes and a negative electrode active material layer formed on both surfaces of the negative electrode current collector. The negative electrode active material layer includes a hydrogen storage alloy. However, the amount of hydrogen storage alloy (Wo) contained per unit area of the second part of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode is per unit area of the first part of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode. The amount of hydrogen storage alloy contained in (Wi) is less. Wo is the amount obtained by dividing the total amount of the hydrogen storage alloy contained in the second part of the negative electrode by the projected area when the second part is flatly developed and the negative electrode is viewed from the thickness direction, and Wi is the negative electrode Is the amount obtained by dividing the total amount of the hydrogen storage alloy contained in the first part by the projected area when the first part is flatly developed and the negative electrode is viewed in the thickness direction.

Typically, the negative electrode includes a thin portion provided in a region having a length L3 from the outer end of the negative electrode, a tapered portion having a length L2 adjacent to the thin portion, and a main body portion having a length L1 other than the thin portion. Prepare. The thickness t1 of the main body and the thickness t3 of the thin portion satisfy t1> t3. The thickness t1 of the main body is preferably 0.1 to 0.6 mm, for example.

The thickness t3 of the thin portion may satisfy t1> t3. The length L3 of the thin portion is, for example, 50 to 115% of the length of the outermost periphery of the negative electrode, and is preferably 70 to 110% or 80 to 105%.

The thickness t2 of the taper portion is gradually reduced from the main body portion toward the thin portion. The length L2 of the tapered portion is preferably longer than 1/6 of the length of the outermost periphery of the negative electrode, and may be 1/5 or more or 1/4 or more. The length L2 of the taper portion is preferably ½ or less of the length of the outermost periphery of the negative electrode.

When the opening of the through hole in the first part of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is the first opening, and the opening of the through hole in the second part of the negative electrode adjacent to the outside of the outer periphery of the positive electrode is the second opening The area S1 of the first opening and the area S2 of the portion where the first opening and the second opening overlap satisfy 0.4 <S2 / S1. By increasing the number of portions where the first opening and the second opening overlap in this way, the fluidity of the electrolyte on the outermost periphery of the electrode group is improved. The positive electrode of the nickel-metal hydride battery is porous, including the core material, and the electrolyte can be distributed in the thickness direction of the positive electrode. Therefore, in the overlapping portion of the first opening and the second opening, a passage communicating between the first portion and the second portion of the negative electrode is formed. As a result, water generated in the vicinity of the outermost periphery can be quickly diffused to the inner peripheral side, and ions on the inner peripheral side can be quickly diffused to the outermost peripheral side. Therefore, the unevenness of the concentration of the alkaline aqueous solution is reduced in the entire electrode group, the variation of the charging reaction is suppressed, and the self-discharge is suppressed.

The first opening is a general term for the openings of the plurality of through holes in the first portion of the negative electrode, and the area of the openings of the individual through holes is not referred to as S1. The second opening is a general term for the openings of the plurality of through holes in the second portion of the negative electrode, and the area of the openings of the individual through holes is not referred to as S2. Of the opening divided at the boundary between the first part and the second part, only a part entering the first part becomes the first opening, and the remaining part becomes the second opening. Similarly, only a part of the opening that is divided at the boundary between the first portion and the inner peripheral body portion is the first opening. Similarly, the opening divided at the boundary between the second portion and the thinner portion on the outer peripheral side is only the second opening that enters the second portion.

The through hole of the negative electrode current collector is designed to be quite small from the viewpoint of maintaining the negative electrode strength and suppressing the negative electrode active material layer from falling off. Further, the first portion adjacent to the inner peripheral side of the positive electrode and the second portion adjacent to the outer peripheral side are different in curvature and peripheral length. Therefore, even when the first opening and the second opening that overlap 100% accidentally exist, the overlapping portion becomes small in the first opening and the second opening that are adjacent to each other, and the S2 / S1 ratio is usually 0.4. Less than.

In order to make the S2 / S1 ratio larger than 0.4, the size of the first opening and the second opening, the vertical direction of the through hole (width direction of the negative electrode current collector) and the horizontal direction (length of the negative electrode current collector) It is necessary to strictly design the pitch in the direction), the thickness of the electrode and the separator, and align the first opening and the second opening when configuring the electrode group. According to such work, the S2 / S1 ratio can be increased to 0.5 or more or 0.6 or more.

As the negative electrode current collector having a plurality of through holes, it is preferable to use a metal foil in which through holes generally referred to as punching metal are arranged in a predetermined pattern in a plane. A through-hole is a hole penetrating from one surface of a sheet-like current collector to the other surface. The shape of the cross section of the through hole perpendicular to the thickness direction of the current collector may be, for example, a circle, an ellipse, or a polygon having a rounded corner. These shapes may be distorted.

As an arrangement pattern of the through holes in the negative electrode current collector surface, the through holes are adjacent to six sides of any through hole of the negative electrode current collector (excluding the through holes near the end of the negative electrode current collector). A pattern is preferred. Among these, a pattern in which the centers of the seven through holes are arranged at the center of the regular hexagon and the six apexes thereof is preferable. Such an arrangement is also called a staggered arrangement.

In order to facilitate the production of a negative electrode with a thin outermost periphery and to increase the number of overlapping portions of the through holes, the maximum diameter of the through holes (the diameter or opening diameter when the opening is circular) is set to the first and second portions of the negative electrode. In the portion, 0.5 to 2.0 mm is preferable, and 0.8 to 1.5 mm is more preferable.

The porosity (opening ratio) excluding the uncoated portion of the negative electrode current collector is preferably 25 to 50%, more preferably 30 to 45%. When the through holes with the maximum diameter are arranged in a predetermined pattern so as to have the porosity, the interval between adjacent through holes (that is, the pitch between the centers of gravity of the openings) is optimized, and the overlapping portions of the through holes are It is advantageous to increase.

The pitch in the vertical direction between the center of gravity of the openings (the width direction of the negative electrode current collector) is preferably 1.1 to 1.8 mm, and more preferably 1.2 to 1.75 mm. Further, the pitch in the lateral direction between the center of gravity of the openings (the length direction of the negative electrode current collector) is preferably, for example, 0.55 to 1.0 mm, and more preferably 0.66 to 0.90 mm.

In addition, the overlapping ratio between the first opening and the second opening decreases as the pitch increases and the opening of the through hole decreases. Therefore, it is not easy to satisfy 0.4 <S2 / S1 without using a negative electrode current collector that satisfies the above conditions. Here, FIG. 1 shows a state in which the length of one round is viewed in plan in the positive electrode before winding or the positive electrode when the rolled positive electrode is spread. An example of the relationship between the 1st opening 11b of the 1st part of the negative electrode adjacent to an inner side and the 2nd opening 11a of the 2nd part of the negative electrode adjacent to the outer side of the outermost periphery of a positive electrode is shown. For example, when the opening diameter and pitch of the through holes are both 1.4 mm, the arrangement of the first openings 11b is as shown in FIG. Further, when the peripheral length of the second part of the negative electrode is 41 mm and the peripheral length of the first part is 38 mm, the arrangement of the second openings 11a of the through holes when the peripheral length of the second part is converted (reduced) to 38 mm is As shown in FIG. Therefore, in the wound electrode group, the overlapping relationship between the first opening 11b and the second opening 11a is as shown in FIG. As described above, since the overlapping portion between the first opening 11b and the second opening 11a tends to be small, a design therefor is necessary to satisfy 0.4 <S2 / S1.

For example, even if the porosity (opening ratio) and opening diameter of the negative electrode current collector are the same, S2 / S1 can be increased or decreased by changing the pitch in the vertical or horizontal direction. FIG. 2A shows an arrangement pattern of through holes in which the horizontal pitch is smaller than the vertical pitch. FIG. 2B shows a case where the horizontal pitch and the vertical pitch are the same, and FIG. 2C shows a case where the horizontal pitch is larger than the vertical pitch. Among these, S2 / S1 can be maximized when the pattern of FIG. 2A is used. When the horizontal pitch P1 is made smaller than the vertical pitch P2, the ratio of the vertical pitch P2 to the horizontal pitch P1: P2 / P1 may be larger than 1, for example, 1.05 or more. .

From the viewpoint of making it easier for the negative electrode to satisfy 0.4 <S2 / S1, the arrangement patterns may be different from each other in the first part and the second part of the negative electrode, for example, the maximum diameter of the through hole, the porosity, and the opening At least one of the pitches between the centroids may be different from each other.

The thickness of the portion (skeleton) other than the through hole of the negative electrode current collector is preferably 20 to 100 μm, for example, and more preferably 30 to 70 μm.

Examples of the material for the negative electrode current collector include stainless steel, nickel, and nickel alloys.

When at least a part of the separator is made of polypropylene, it is preferable that at least a part of the polypropylene is sulfonated. Since sulfonated polypropylene (SPP) has high affinity with an alkaline aqueous solution, the use of SPP makes it easier to improve the fluidity of the electrolyte in the electrode group.

The amount of hydrogen storage alloy (Wo) contained per unit area of the second part of the negative electrode is preferably 40 to 80% by mass of the amount of hydrogen storage alloy (Wi) contained per unit area of the first part of the negative electrode, More preferable is 70 mass%. Most or all of the second part of the negative electrode is usually a thin part. By limiting the amount of alloy in the thin portion within the above range, the amount of alloy used for gas absorption and promoting the generation of water can be maintained moderately. Moreover, since the volume of the separator in the outermost peripheral region becomes relatively large, it becomes easy to secure a sufficient amount of electrolyte in the outermost peripheral region, and the charge reaction is easily made uniform.

The hydrogen storage alloy generally contains an A element having a high hydrogen affinity and a B element having a low hydrogen affinity. The B element having a low hydrogen affinity plays a role in preventing a remarkable crystal defect from being generated when the alloy expands and contracts due to insertion and extraction of hydrogen. On the other hand, when the ratio of the B element having a low hydrogen affinity to the A element having a high hydrogen affinity (B / A ratio) increases, the hydrogen storage capacity decreases, and it becomes difficult to increase the discharge capacity.

Examples of the hydrogen storage alloy include A ₂ B ₇ type (Ce ₂ Ni ₇ type, Gd ₂ Co ₇ type, etc.), A ₅ B ₁₉ type (Pr ₅ Co ₁₉ type, Ce ₅ Co ₁₉ type, etc.), and AB ₅ type. Those having a crystal structure such as CaCu ₅ type or MmNi ₅ type, AB ₃ type (CeNi ₃ type), AB ₂ type (MgCu ₂ type etc.), or a mixture thereof can be used. Mm represents Misch metal. Among them, A ₂ B ₇ type and A ₅ B ₁₉ type alloys are preferable in terms of being suitable for high capacity.

In the alloy used or a mixture of alloys, the A element is at least one selected from the group consisting of Mg, Zr and rare earth elements, and the B element is an element other than the A element, for example, Ni, Al , Mn, Co and the like. The ratio of the number of moles of element B to the number of moles of element A: B / A is preferably 3.3 to 3.8 from the viewpoint of efficiently increasing the capacity of the negative electrode. If the capacity of the alloy can be increased, it is easy to increase the volume of the separator or the electrolytic solution in the electrode group, which is advantageous for uniform charge reaction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings as necessary.

[Cylindrical NiMH battery]
FIG. 3 schematically shows an exemplary configuration of a cylindrical nickel-metal hydride battery (hereinafter referred to as a cylindrical battery). The cylindrical battery includes a bottomed cylindrical battery case 4 that also serves as a negative electrode terminal, an electrode group housed in the battery case 4, and an electrolyte solution (not shown). In the electrode group, a strip-shaped negative electrode 1, a strip-shaped positive electrode 2, and a strip-shaped separator 3 interposed therebetween are wound in a spiral shape. A sealing plate 7 including a safety valve 6 is disposed in the opening of the battery case 4 via an insulating gasket 8, and the cylindrical battery is sealed by caulking the opening end of the battery case 4 inward. . The sealing plate 7 also serves as a positive electrode terminal, and is electrically connected to the positive electrode 2 via the positive electrode current collector plate 9.

FIG. 4 is a cross-sectional view schematically showing the cylindrical battery of FIG. FIG. 5 shows an enlarged view of the vicinity of the outer ends of the negative electrode 1 and the positive electrode 2 (that is, a portion surrounded by a circle indicated by III in FIG. 4). The negative electrode 1 constitutes the outermost periphery of the electrode group. In nickel-metal hydride batteries, hydrogen gas and oxygen gas are generated during overcharge, but by providing a negative electrode active material layer that does not face the positive electrode on the outer peripheral side of the thin portion, gas generated during overcharge is efficiently absorbed. Along with water. The outermost periphery of the negative electrode 1 is preferably electrically connected by contacting the battery case 4.

The number of negative electrodes can be selected according to the size of the cylindrical battery. For example, when the outer diameter of the cylindrical battery is 6 to 24 mm, it can be 2 to 10, or 3 to 6.

In FIG. 4, the electrode group is arranged so that the outer end of the positive electrode 2 overlaps the taper portion 1 b via the separator 3. It is preferable to arrange the positive electrode and the negative electrode so that the position of the end surface of the outer end of the positive electrode is near the center in the length direction of the tapered portion. For example, the end surface of the positive electrode is positioned in a region of ± 0.2 × L2 (preferably a region of ± 0.1 × L2) across the center in the length direction of the taper portion. It is preferable to overlap the outer end with the tapered portion.

A porous sheet 3a is disposed between the outer end of the positive electrode 2 and the tapered portion 1b. The porous sheet 3a is preferably arranged so as to overlap the outer end of the positive electrode 2 so as to protect the outer end of the positive electrode 2. With such a configuration, the electrode group can be easily inserted into the battery case, and the occurrence of an internal short circuit can be suppressed. The length of the porous sheet 3a is, for example, 50 to 200% of L2, and may be 80 to 100%. The porous sheet 3a may be disposed between the taper portion of the negative electrode and the separator as illustrated, or may be disposed between the outer end of the positive electrode and the separator.

Hereinafter, the components of the cylindrical battery will be described more specifically.

(Negative electrode)
The negative electrode has a main body part, a taper part, and a thin part constituting the outermost periphery of the electrode group. Providing a thin-walled portion on the outermost periphery is advantageous because the amount of the negative electrode active material that is not used for the electrode reaction can be reduced and the volume required for it can be reduced. Further, hydrogen gas and oxygen gas generated during overcharge can be absorbed. The main body portion is a region that is located on the center side (or inner peripheral side) of the electrode group, and that both surfaces face the positive electrode, and are mainly responsible for electrode reactions. However, the thickness of the negative electrode active material layer may be partially reduced as necessary in a region of the main body portion that does not face the innermost positive electrode of the negative electrode.

As shown in FIG. 4, most of the first portion of the negative electrode 1 adjacent to the inside of the outermost periphery of the positive electrode 2 is composed of the main body 1 a, and the second portion of the negative electrode 1 adjacent to the outside of the outermost periphery of the positive electrode 2. Most of it consists of the thin part 1c. Since the position of the end face of the outer end of the positive electrode 2 is located near the center in the length direction of the tapered portion 1b, the tapered portion 1b is distributed to the first portion and the second portion.

The negative electrode active material layer only needs to contain at least a negative electrode active material, and may be a negative electrode mixture layer containing a binder, a conductive agent, a thickener, and the like.

Examples of the binder include resin materials such as rubber-like materials such as styrene-butadiene copolymer rubber (SBR), polyolefin resins, fluororesins such as polyvinylidene fluoride, acrylic resins (including their Na ion cross-linked products), and the like. It can be illustrated. Examples of the thickener include carboxymethyl cellulose (CMC) and its salt, polyvinyl alcohol, polyethylene oxide and the like. Examples of the conductive agent include carbon black, conductive fibers, and organic conductive materials.

The negative electrode is formed, for example, by applying a slurry containing the constituent components of the negative electrode active material layer to the negative electrode current collector, compressing in the thickness direction, and drying at an appropriate stage if necessary.

(Positive electrode)
As the positive electrode, either a sintered positive electrode or a paste positive electrode may be used. A sintered positive electrode is manufactured by impregnating a nickel sintered substrate (positive electrode current collector) with a nickel compound. The paste type positive electrode is manufactured by filling a foamed nickel substrate (positive electrode current collector) with a positive electrode mixture paste containing a nickel compound. The positive electrode mixture may contain a conductive agent, a binder, a thickener, and the like in addition to the positive electrode active material. The positive electrode can be obtained by a known method.

Nickel hydroxide, nickel oxyhydroxide, etc. are used as the nickel compound. As the conductive agent, a conductive cobalt oxide such as cobalt hydroxide or cobalt oxyhydroxide may be used.

(Separator)
As a separator, a microporous film, a nonwoven fabric, etc. can be used. The material of the microporous membrane or the nonwoven fabric may be selected as appropriate, and examples thereof include polyolefin resins such as polyethylene and polypropylene, fluororesins, and polyamide resins. The separator may be subjected to a hydrophilic treatment such as a corona discharge treatment, a plasma treatment, or a sulfonation treatment. A sulfonic acid group is introduced into the separator by the sulfonation treatment. Among these, when at least a part of the separator is made of polypropylene, it is preferable to sulfonate at least a part of the polypropylene. By using sulfonated polypropylene (SPP), the fluidity of the electrolyte in the electrode group can be further improved. The thickness of the separator is, for example, 10 to 300 μm, and may be 15 to 200 μm. In addition, although a porous sheet is not specifically limited, It is preferable to form with the material similar to a separator.

The degree of sulfonation of the separator may be, for example, 1 × 10 ⁻³ or more, preferably 1.5 × 10 ⁻³ or more, and more preferably 1.9 × 10 ⁻³ or more. The degree of sulfonation of the separator is, for example, 4.3 × 10 ⁻³ or less, preferably 4.1 × 10 ⁻³ or less, and more preferably 4 × 10 ⁻³ or less. In addition, the sulfonation degree of a separator is represented by the ratio of the sulfur atom with respect to the carbon atom contained in a separator.

(Electrolyte)
An alkaline aqueous solution is used as the electrolytic solution. The specific gravity of the electrolytic solution is, for example, 1.03 to 1.55. Examples of the alkali include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide and sodium hydroxide. From the viewpoint of increasing the charging efficiency, it is preferable that 75 mol% or more of the alkali metal hydroxide is sodium hydroxide. As a result, self-discharge is further easily suppressed.

The hydroxide ion concentration of the electrolytic solution is preferably 5.0 to 8.5 mol / L. The electrolytic solution containing sodium hydroxide has high conductivity in the above concentration range, and in the above concentration range, the conductivity gradually decreases as the hydroxide concentration increases. However, such a decrease in conductivity is very gradual and can maintain a sufficiently high value. On the other hand, when water is generated in the outermost peripheral region and the hydroxide concentration is lowered, the conductivity of the outermost peripheral region is gradually increased, so that the influence of the decrease in the hydroxide concentration is easily mitigated.

Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
An AA cylindrical nickel-metal hydride storage battery having a capacity of 2400 mAh was produced by the following procedure.

(1) Production of Negative Electrode As a negative electrode current collector, an iron punching metal whose surface was nickel-plated was prepared. The shape of the cross section of the through hole perpendicular to the thickness direction of the current collector was circular. The arrangement pattern of the through holes was a staggered arrangement in which the centers of the seven through holes were arranged at the center of the regular hexagon and the six apexes thereof. The maximum diameter of the through hole (opening diameter) was 1 mm. The porosity (opening ratio) of the negative electrode current collector was 35%. The pitch between the center of gravity (center) of the openings was 1.42 mm in the vertical direction and 0.79 mm in the horizontal direction. The thickness of the skeleton of the negative electrode current collector was 35 μm.

100 parts by mass of hydrogen storage alloy powder (La _0.40 Ce _0.60 Ni _3.63 Co _0.76 Mn _0.42 Al _0.29 , average particle size = about 45 μm), 0.7 parts by mass of SBR as a binder, CMC 0. 15 parts by mass, 0.3 parts by mass of ketjen black as a conductive agent, 0.7 parts by mass of yttrium oxide as an oxidation inhibitor, and further adding and mixing an appropriate amount of water, the negative electrode mixture slurry Prepared. SBR was used in the form of an aqueous dispersion.

The obtained negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector. At this time, the coating amount of the negative electrode mixture slurry was changed in the length direction of the negative electrode current collector so that the thicknesses of the negative electrode active material layers on both sides were different between the main body part, the tapered part, and the thin part. The coating film of the negative electrode mixture slurry was dried at 95 ° C. for 10 minutes, and then the negative electrode was formed by pressing the coating film together with the negative electrode current collector with a roller.

The ratio (Wo / Wi) of the hydrogen storage alloy amount Wo contained per unit area of the second portion of the negative electrode to the hydrogen storage alloy amount Wi contained per unit area of the first portion is 60% by mass. did.

(2) Production of positive electrode A paste type positive electrode was produced by the following procedure.

First, nickel hydroxide powder containing 2.5% by mass of zinc and 1.0% by mass of cobalt as a coprecipitation component was added to an aqueous cobalt sulfate solution. While stirring the resulting mixture, an aqueous sodium hydroxide solution (sodium hydroxide concentration: 1 mol / L) was gradually added dropwise to adjust the pH to 11, followed by further stirring for a predetermined time. The precipitate was filtered off from the resulting mixture. The precipitate separated by filtration was washed with water and vacuum-dried to obtain a powder in which the surface of nickel hydroxide particles was coated with 5% by mass of cobalt hydroxide.

10 parts by mass of an aqueous sodium hydroxide solution (sodium hydroxide concentration: 48% by mass) was added to 1 part by mass of the powder obtained above. The resulting mixture was heat-treated at 85 ° C. for 8 hours with stirring, then washed with water and dried at 65 ° C. By this heat treatment, in the layer containing cobalt hydroxide on the surface of the nickel hydroxide particles, a part of cobalt hydroxide is made higher-order and converted into cobalt oxyhydroxide, and sodium is introduced. Composite particles in which a coating layer containing cobalt oxyhydroxide and 1% by mass of sodium was formed on the surface of the nickel hydroxide particles were obtained.

By adding and mixing 25 parts by mass of an aqueous solution (CMC concentration: 1% by mass) containing CMC as a binder to 100 parts by mass of the obtained composite particles and zinc oxide mixed powder, An agent slurry was prepared. The mass ratio of the composite particles and zinc oxide in the mixed powder was 100: 2.

The obtained positive electrode mixture slurry was filled in pores of a nickel foam (surface density (unit weight) of about 325 g / m ² , thickness of about 1.2 mm) as a positive electrode current collector and dried. The dried product was rolled to a thickness of 0.66 mm to obtain a positive electrode (length 118 mm, width 44.7 mm, thickness 0.66 μm). In addition, the exposed part of the core material which does not hold | maintain an active material was provided in the one end part of the length direction of a positive electrode electrical power collector, and the positive electrode lead was connected to this exposed part.

(3) Production of nickel-metal hydride storage battery A separator (length: 325 mm, width: 46.7 mm, thickness: 82 μm) is disposed between the negative electrode obtained in (1) above and the positive electrode obtained in (2) above. These were wound in a spiral shape to produce an electrode group. At this time, it wound so that the main-body part of a negative electrode might become an inner peripheral side, a thin part might become an outer peripheral side, and the outer end of a positive electrode might overlap with the taper part of a negative electrode. Further, a porous sheet (length 10 mm, width 46.7 mm, thickness 82 μm) cut out from the same material as the separator was disposed between the outer end of the positive electrode and the tapered portion, and between the tapered portion and the separator. . The porous sheet was arranged so that the end face on the outer peripheral side of the positive electrode was near the center in the length direction. The number of wrinkles of the negative electrode in the electrode group was 6.

As the separator and the porous sheet, a sulfonated polypropylene nonwoven fabric (hereinafter referred to as SPP, degree of sulfonation 1.90 × 10 ⁻³ , thickness 82 μm, mass per unit area 50 g / m ² ) was used.

When the opening of the through hole in the first portion of the negative electrode is the first opening and the opening of the through hole in the second portion of the negative electrode is the second opening, the area S1 of the first opening, the first opening, and the second opening are The area S2 of the overlapping part was designed to satisfy S2 / S1 = 0.50.

The obtained electrode group was inserted into an AA bottomed cylindrical metal battery case (outer diameter 14.60 mm) having a ring-shaped groove on the opening side, and the outermost negative electrode (thin wall portion) was inserted. The battery case was brought into contact with the inner surface. Moreover, the positive electrode lead connected to the positive electrode was welded to the inner bottom surface of the cover plate of the sealing body. The sealing body is arranged so as to close the gas vent hole at the center of the top plate of the lid plate having a circular vent hole at the center, the insulating packing attached to the periphery of the lid plate, and the lid plate. And a cap-like positive electrode terminal having a protrusion that covers the valve body.

Next, an alkaline aqueous solution was injected into the battery case as an electrolytic solution, and the opening of the battery case was covered with a sealing body, and sealed by insulating caulking. The diameter was reduced by pressing the peripheral surface of the battery case from the outside. And the groove part formed in the opening part side of the battery case was crimped | bonded so that a battery total height might be set to 50.25 mm by pressing a battery case in a height direction.

As the alkaline aqueous solution, a 5.0 mol / L sodium hydroxide aqueous solution was used.

The donut-shaped insulating member was arranged on the upper part of the sealing body with the protruding portion of the positive electrode terminal protruding from the central hole of the insulating member. Next, by attaching an exterior label so as to cover the peripheral part of the sealing body (peripheral part of the insulating member disposed on the sealing body), the peripheral surface of the battery case, and the peripheral part of the bottom surface of the battery case A nickel metal hydride storage battery (A1) was obtained. A total of 50 batteries A1 were produced in the same procedure.

(4) Evaluation (self-discharge index)
At 20 ° C., it was charged at 240 mA for 16 hours, discharged at 2400 mA for 30 minutes, charged at 240 mA for 11 hours, discharged at 2400 mA for 30 minutes, and then stored at 45 ° C. for 72 hours to activate the negative electrode. After cooling to 20 ° C., discharging was performed at 2400 mA to 1.0 V. Next, after charging for 16 hours at 240 mA, the cycle of discharging to 1.0 V at 2400 mA was repeated three times, and the discharge capacity at the third cycle was defined as the capacity before storage. Next, the battery was charged at 240 mA for 16 hours and then allowed to stand at 45 ° C. for 7 days. Thereafter, the battery was discharged at 2400 mA to 1.0 V, and the capacity after storage was determined.

For 50 batteries, the difference between the capacity before storage and the capacity after storage was determined as the self-discharge amount, and the average value of 50 cells was determined and indexed. Specifically, the average value of the self-discharge rate obtained from (capacity before storage−capacity after storage) / (capacity before storage) × 100 is obtained by comparing the self-discharge rate of the battery of Example A2 with the reference value 100. The self-discharge index was standardized. The results are shown in Table 1.

Example 2
The opening diameter and the opening ratio are the same as in Example 1, and the area of the first opening is changed by changing the pitch between the centers of the openings in the height direction (vertical direction) of the battery and the pitch between the centers of the openings in the lateral direction. Nickel metal hydride storage battery (A2) in the same manner as in Example 1 except that S1 and the area S2 of the portion where the first opening and the second opening overlap satisfy S2 / S1 = 0.40. 50 were prepared and evaluated.

Example 3
The opening diameter and the opening ratio are the same as those of Example 1, and the pitch between the centers of the openings in the height direction of the battery and the pitch between the centers of the openings in the lateral direction are changed, and the area S1 of the first opening, 50 nickel-metal hydride storage batteries (A3) were produced in the same manner as in Example 1, except that the area S2 where the first opening and the second opening overlap each other satisfied S2 / S1 = 0.60. And evaluated.

Example 4
The aperture diameter and the aperture ratio are the same as those in Example 1, the pitch between the center of the opening in the height direction of the battery in the first opening, the pitch between the center of the opening in the lateral direction, and the height of the battery in the second opening. The pitch between the centers of the openings in the direction and the pitch between the centers of the openings in the lateral direction were changed to different values. Thus, the same as in Example 1 except that the area S1 of the first opening and the area S2 of the portion where the first opening and the second opening overlap satisfy S2 / S1 = 0.80. 50 nickel-metal hydride storage batteries (A4) were produced and evaluated.

Comparative Example 1
The opening diameter and the opening ratio are the same as those of Example 1, and the pitch between the centers of the openings in the height direction of the battery and the pitch between the centers of the openings in the lateral direction are changed, and the area S1 of the first opening, 50 nickel-metal hydride storage batteries (B1) were produced in the same manner as in Example 1 except that the area S2 where the first opening and the second opening overlap each other satisfied S2 / S1 = 0.35. And evaluated.

Comparative Example 2
Except for changing the material of the separator to a polypropylene non-woven fabric (hereinafter referred to as PP, thickness 82 μm, mass per unit area 50 g / m ² ) hydrophilized by corona discharge, the same as in Comparative Example 1, 50 nickel-metal hydride storage batteries (B2) were produced and evaluated.

Example 5
The ratio (Wo / Wi) of the hydrogen storage alloy amount Wo contained per unit area of the second portion of the negative electrode to the hydrogen storage alloy amount Wi contained per unit area of the first portion is 80% by mass. Except for this, 50 nickel-metal hydride storage batteries (A5) were produced and evaluated in the same manner as in Example 1.

Example 6
The ratio (Wo / Wi) of the hydrogen storage alloy amount Wo contained per unit area of the second portion of the negative electrode to the hydrogen storage alloy amount Wi contained per unit area of the first portion is 40% by mass. Except for this, 50 nickel-metal hydride storage batteries (A6) were produced and evaluated in the same manner as in Example 1.

Example 7
Example 1 except that the hydrogen storage alloy was changed to an alloy Zr _0.01 La _0.44 Nd _0.45 Mg _0.10 Ni _3.15 Al _0.15 Co _0.20 whose main phase was A ₂ B ₇ type, and the thickness of the separator was changed to 92 μm. Similarly, 50 nickel-metal hydride storage batteries (A7) were produced and evaluated.

Example 8
Fifty nickel-metal hydride storage batteries (A8) were produced and evaluated in the same manner as in Example 1 except that an aqueous solution containing a hydroxide ion concentration of 7.0 mol / L in an alkaline aqueous solution was used. .

Example 9
Fifty nickel-metal hydride storage batteries (A9) were produced and evaluated in the same manner as in Example 1 except that an aqueous solution containing a hydroxide ion concentration of 8.5 mol / L in an alkaline aqueous solution was used. .

Table 1 shows the results of Examples and Comparative Examples. As shown in Table 1, it can be understood that the battery of Comparative Example 1 has a high self-discharge index, whereas the larger the S2 / S1 ratio, the lower the self-discharge index. Further, the self-discharge index can be reduced to 93 by further improving other configurations. In addition, it shows that self-discharge does not advance easily, so that a self-discharge index | exponent is low.

Next, each of the batteries after the evaluation is opened, and misalignment marking is applied to the first part of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode and the second part of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode. did. Thereafter, the electrode group was disassembled, and the arrangement of the first opening in the first portion, the arrangement of the second opening in the second portion, and the area S1 of the first opening were measured. Next, the circumference of the second part is converted into the circumference of the first part, and the arrangement of the first openings is calculated when the circumference is reduced in the lateral direction. The first opening and the second opening at that time overlap. The area S2 of the part was calculated | required and S2 / S1 was confirmed. As a result, in any of the examples, the S2 / S1 value of 45 or more batteries out of 50 has an error of ± 3% from the designed S2 / S1 value, and is considered substantially the same as the design value. I was able to. From the above, when the S2 / S1 value of 90% or more of the batteries of 50 or more satisfies 0.4 <S2 / S1, these batteries are regarded as manufactured by the manufacturing method according to the present invention. Can do.

The S2 / S1 value can also be calculated directly from the correspondence pattern between the first opening and the second opening measured from the array pattern of the through holes of the negative electrode current collector and the cross-sectional image of the battery (for example, a CT image). Good.

The nickel metal hydride battery according to the present invention is useful as, for example, a memory backup power source or a vehicle power source because self-discharge is suppressed.

DESCRIPTION OF SYMBOLS 1: Negative electrode 1a: Main-body part 1b: Tapered part 1c: Thin part 2: Positive electrode 3: Separator 3a: Porous sheet 4: Battery case 6: Safety valve 7: Sealing plate 8: Insulating gasket 9: Positive electrode current collecting plate 11: Negative electrode Current collector 11b: first opening 11a: second opening

Claims

An electrode group in which a strip-shaped positive electrode, a strip-shaped negative electrode, and a separator interposed between the positive electrode and the negative electrode are wound so that the negative electrode forms the outermost periphery, an electrolyte solution, and the electrode group And a battery case containing the electrolytic solution,
The negative electrode includes a negative electrode current collector having a plurality of through holes, and a negative electrode active material layer containing a hydrogen storage alloy formed on both surfaces of the negative electrode current collector,
An opening of the through hole in the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is a first opening, and an opening of the through hole in the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode. When the second opening
The amount of the hydrogen storage alloy included per unit area of the second portion is less than the amount of the hydrogen storage alloy included per unit area of the first portion, and the area S1 of the first opening and the first opening And the area S2 of the portion where the second opening overlaps satisfies a relation of 0.4 <S2 / S1.
The nickel according to claim 1, wherein the amount of the hydrogen storage alloy contained per unit area of the second portion is 40 to 80% by mass of the amount of the hydrogen storage alloy contained per unit area of the first portion. Hydrogen battery.
The hydrogen storage alloy includes an A element and a B element,
The element A is at least one selected from the group consisting of Mg, Zr and rare earth elements,
B element is an element other than A element,
The nickel metal hydride battery according to claim 1 or 2, wherein the ratio of the number of moles of element B to the number of moles of element A: B / A is 3.3 to 3.8.
At least a portion of the separator is formed of polypropylene;
The nickel metal hydride battery according to any one of claims 1 to 3, wherein at least a part of the polypropylene is sulfonated.
The electrolyte includes an alkali metal hydroxide;
75 mol% or more of the alkali metal hydroxide is sodium hydroxide,
The nickel metal hydride battery according to any one of claims 1 to 4, wherein a hydroxide ion concentration of the electrolytic solution is 5.0 to 8.5 mol / L.
(I) preparing a belt-like positive electrode;
(Ii) preparing a strip-shaped negative electrode;
(Iii) interposing a separator between the positive electrode and the negative electrode so that the negative electrode forms the outermost periphery, and forming an electrode group;
(Iv) storing the electrode group together with an electrolytic solution in a battery case,
The negative electrode prepared in the step (ii) includes a negative electrode current collector having a plurality of through holes, and a negative electrode active material layer including a hydrogen storage alloy formed on both surfaces of the negative electrode current collector. Prepared,
An opening of the through hole in the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is a first opening, and an opening of the through hole in the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode. When the second opening
The amount of the hydrogen storage alloy included per unit area of the second portion is less than the amount of the hydrogen storage alloy included per unit area of the first portion, and the area S1 of the first opening and the first opening And the area S2 where the second opening overlaps, the electrode group is configured such that 0.4 <S2 / S1 is satisfied.