JP2015060695A - Positive electrode for alkaline storage battery, and alkaline storage battery using the same - Google Patents

Positive electrode for alkaline storage battery, and alkaline storage battery using the same Download PDF

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JP2015060695A
JP2015060695A JP2013193087A JP2013193087A JP2015060695A JP 2015060695 A JP2015060695 A JP 2015060695A JP 2013193087 A JP2013193087 A JP 2013193087A JP 2013193087 A JP2013193087 A JP 2013193087A JP 2015060695 A JP2015060695 A JP 2015060695A
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positive electrode
electrode mixture
storage battery
battery
zinc compound
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聖司 和田
Seiji Wada
聖司 和田
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FDK Twicell Co Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode for an alkaline storage battery, capable of improving cycle life while maintaining the capacity of an alkaline storage battery at a high level.SOLUTION: The positive electrode for an alkaline storage battery comprises: a positive electrode base material 36 formed of a metal porous body including many pores; and a positive electrode mixture which is held in the pores and on the surface of the positive electrode base material 36 and contains at least a positive electrode active material. The positive electrode base material 36 is formed in a sheet shape and includes: an upper end part 38 and a lower end part 39 extending along the longitudinal direction thereof; and a central part 40 positioned between the upper end part 38 and the lower end part 39. The content of a zinc compound in the positive electrode mixture is higher at the upper end part 38 or the lower end part 39 than at the central part 40.

Description

本発明は、アルカリ蓄電池用の正極及びこの正極を用いたアルカリ蓄電池に関する。   The present invention relates to a positive electrode for an alkaline storage battery and an alkaline storage battery using the positive electrode.

アルカリ蓄電池の一つとして、円筒形のニッケル水素蓄電池が知られている。このニッケル水素蓄電池は、有底円筒形状の外装缶内に円柱状の電極群がアルカリ電解液とともに収容され、封口体により外装缶の上端開口が封口されることにより製造される。前記した電極群は、それぞれ帯状の正極、負極及びセパレータからなり、詳しくは、正極と負極との間にセパレータが挟み込まれた状態で渦巻き状に巻回されて形成される。   A cylindrical nickel-metal hydride storage battery is known as one of alkaline storage batteries. This nickel metal hydride storage battery is manufactured by accommodating a cylindrical electrode group together with an alkaline electrolyte in a bottomed cylindrical outer can and sealing the upper end opening of the outer can with a sealing body. Each of the electrode groups includes a belt-like positive electrode, a negative electrode, and a separator. Specifically, the electrode group is formed by being spirally wound with the separator sandwiched between the positive electrode and the negative electrode.

上記したようなニッケル水素蓄電池は、高容量であることから各種ポータブル機器やハイブリッド電気自動車等、さまざまな用途に使用されるようになっている。このように、さまざまな用途が見出されたことによりニッケル水素蓄電池に対しては、より使い勝手を良くするため、駆動電源として各種の特性の改善が望まれており、特にサイクル寿命特性の向上が望まれている。   Nickel metal hydride storage batteries such as those described above are used in various applications such as various portable devices and hybrid electric vehicles because of their high capacity. As described above, for various purposes, nickel-metal hydride batteries are required to be improved in various characteristics as a drive power source in order to improve usability. It is desired.

ここで、電池のサイクル寿命特性に影響を与える要因の一つとして、充放電の繰り返しにともないセパレータに保持されたアルカリ電解液の分布が不均一化することが挙げられる。このアルカリ電解液の分布の不均一化は以下のようにして起こる。   Here, as one of the factors affecting the cycle life characteristics of the battery, there is a non-uniform distribution of the alkaline electrolyte retained in the separator with repeated charge / discharge. The non-uniform distribution of the alkaline electrolyte occurs as follows.

ニッケル水素蓄電池は、充放電を繰り返し行うと、正極が膨張するいわゆる正極膨化を起こす。この正極膨化が起こると、正極に隣接するセパレータが圧縮されるため、セパレータ内に保持されているアルカリ電解液は押し出されてしまう。このように、セパレータ内のアルカリ電解液が押し出されると、セパレータ内に保持されているアルカリ電解液の分布が不均一となる。   When the nickel metal hydride storage battery is repeatedly charged and discharged, so-called positive electrode expansion occurs in which the positive electrode expands. When this positive electrode swelling occurs, the separator adjacent to the positive electrode is compressed, so that the alkaline electrolyte retained in the separator is pushed out. Thus, when the alkaline electrolyte in the separator is extruded, the distribution of the alkaline electrolyte retained in the separator becomes non-uniform.

このように、セパレータ内のアルカリ電解液の分布が不均一化し、部分的にアルカリ電解液が枯渇すると、充放電反応が阻害されるとともに電池の内部抵抗が上昇して出力が低下し、電池のサイクル寿命は早期に尽きてしまう。   Thus, when the distribution of the alkaline electrolyte in the separator becomes non-uniform and the alkaline electrolyte is partially depleted, the charge / discharge reaction is hindered and the internal resistance of the battery is increased, resulting in a decrease in output. The cycle life runs out early.

電池のサイクル寿命を延ばすには、アルカリ電解液がセパレータ内から押し出されることを抑制することが必要となるため、正極膨化を抑制することが種々試みられている。正極膨化を抑制する方法としては、例えば、特許文献１に示されるような、正極活物質に亜鉛化合物を添加する方法が提案されている。   In order to extend the cycle life of the battery, it is necessary to suppress the alkaline electrolyte from being pushed out of the separator. Therefore, various attempts have been made to suppress the expansion of the positive electrode. As a method for suppressing the positive electrode expansion, for example, a method of adding a zinc compound to the positive electrode active material as shown in Patent Document 1 has been proposed.

この特許文献１の方法によれば、正極へ亜鉛化合物を添加することにより、正極活物質の水酸化ニッケルの充電受入性が抑制される。その結果、充放電を繰り返した際の正極膨化も軽減されるためアルカリ電解液の押し出しも抑制されサイクル寿命特性が改善される。   According to the method of this patent document 1, the charge acceptance property of the nickel hydroxide of a positive electrode active material is suppressed by adding a zinc compound to a positive electrode. As a result, the expansion of the positive electrode when charging / discharging is repeated is also reduced, so that extrusion of the alkaline electrolyte is suppressed and cycle life characteristics are improved.

特開昭５９−８３３４７号公報JP 59-83347 A

ニッケル水素蓄電池のサイクル寿命を延ばすには、上記した亜鉛化合物の正極への添加量を増やすことが考えられる。   In order to extend the cycle life of the nickel metal hydride storage battery, it is conceivable to increase the amount of the zinc compound added to the positive electrode.

しかしながら、亜鉛化合物は、電池の充放電反応に直接は関与しないので、このような亜鉛化合物が増えると、充放電反応に直接関与する正極活物質としての水酸化ニッケルの含有比率が低下するため電池の最大容量の値が低くなる。   However, since the zinc compound does not directly participate in the charge / discharge reaction of the battery, if the amount of such zinc compound increases, the content ratio of nickel hydroxide as the positive electrode active material directly involved in the charge / discharge reaction decreases. The maximum capacity value of becomes low.

つまり、電池のサイクル寿命を延ばそうとすると、電池の容量をある程度犠牲にしなければならず、逆に、電池の最大容量の値をなるべく高くしようとすると電池のサイクル寿命をある程度犠牲にしなければならない。   In other words, if the cycle life of the battery is to be extended, the battery capacity must be sacrificed to some extent, and conversely, if the maximum capacity value of the battery is to be increased as much as possible, the cycle life of the battery must be sacrificed to some extent.

上記したようにニッケル水素蓄電池は、さまざまな用途に使用されるようになっていることから、サイクル寿命特性の改善だけではなく、高い電池容量を維持することも望まれている。しかしながら、サイクル寿命が充分に長く、且つ、電池の最大容量の値も充分に高いニッケル水素蓄電池は未だ得られていないのが現状である。   As described above, since the nickel metal hydride storage battery is used in various applications, it is desired not only to improve the cycle life characteristics but also to maintain a high battery capacity. However, at present, a nickel-metal hydride storage battery having a sufficiently long cycle life and a sufficiently high value of the maximum capacity of the battery has not yet been obtained.

本発明は、上記の事情に基づいてなされたものであり、その目的とするところは、アルカリ蓄電池の容量を高いレベルで維持しつつ、サイクル寿命の向上を図ることができるアルカリ蓄電池用の正極及びこの正極を用いたアルカリ蓄電池を提供することにある。   The present invention has been made based on the above circumstances, and its object is to provide a positive electrode for an alkaline storage battery capable of improving cycle life while maintaining the capacity of the alkaline storage battery at a high level, and It is providing the alkaline storage battery using this positive electrode.

上記目的を達成するために、本発明者は、アルカリ蓄電池に対し充放電サイクルを繰り返した場合の正極の膨化の態様につき検討を行った結果、充放電サイクル数が増えていくと円筒型電池における上下方向の中央部に相当する部分に位置する正極に比べ、上下端部に相当する部分に位置する正極の方がより膨化しやすいことを見出し、本発明に想到した。すなわち、本発明によれば、多数の空孔を含む金属多孔体からなる正極基材と、前記空孔内及び前記正極基材の表面上に保持され、少なくとも正極活物質を含んでいる正極合剤とを備え、前記正極基材は、シート状をなし、その長手方向に沿って延びる上端部及び下端部と、前記上端部及び前記下端部の間に位置付けられる中央部とを含み、前記正極合剤は、前記上端部又は前記下端部における亜鉛化合物の含有率が、前記中央部における亜鉛化合物の含有率よりも高いことを特徴とするアルカリ蓄電池用の正極が提供される。   In order to achieve the above object, the present inventor has examined the mode of expansion of the positive electrode when the charge / discharge cycle is repeated for an alkaline storage battery, and as a result, the number of charge / discharge cycles increases in the cylindrical battery. The present inventors have found that the positive electrode located in the portion corresponding to the upper and lower end portions is more likely to swell than the positive electrode located in the portion corresponding to the central portion in the vertical direction, and has arrived at the present invention. That is, according to the present invention, a positive electrode substrate made of a metal porous body containing a large number of pores, and a positive electrode composite that is held in the pores and on the surface of the positive electrode substrate and contains at least a positive electrode active material. The positive electrode base material is in the form of a sheet, and includes an upper end portion and a lower end portion extending along the longitudinal direction thereof, and a central portion positioned between the upper end portion and the lower end portion, and the positive electrode The mixture is provided with a positive electrode for an alkaline storage battery, wherein the content of the zinc compound at the upper end or the lower end is higher than the content of the zinc compound at the center.

また、前記正極合剤は、前記上端部又は前記下端部における亜鉛化合物の含有率が、表層の方が内部よりも高い構成とすることが好ましい。   Moreover, it is preferable that the said positive mix is a structure in which the content rate of the zinc compound in the said upper end part or the said lower end part is higher than the inside in the surface layer.

更に、前記正極合剤は、前記中央部における前記亜鉛化合物の金属亜鉛換算での含有率に対して前記上端部又は前記下端部における前記亜鉛化合物の金属亜鉛換算での含有率の方が１〜７質量％高い構成とすることが好ましい。   Furthermore, the positive electrode mixture has a content ratio of the zinc compound in terms of metal zinc of the upper end portion or the lower end portion of the zinc compound in terms of metal zinc in the center portion of 1 to 1. It is preferable that the composition be 7 mass% higher.

また、本発明によれば、上端開口が気密に封口された有底円筒状の外装缶と、前記外装缶内にアルカリ電解液とともに収容された電極群とを備え、前記電極群は、正極及び負極がこれらの間にセパレータを介在させて渦巻き状に巻回されてなり、前記正極は、上記したいずれかの正極であることを特徴とするアルカリ蓄電池が提供される。   Further, according to the present invention, it comprises: a bottomed cylindrical outer can whose upper end opening is hermetically sealed; and an electrode group housed together with an alkaline electrolyte in the outer can, the electrode group comprising a positive electrode and a positive electrode An alkaline storage battery is provided in which a negative electrode is wound in a spiral shape with a separator interposed therebetween, and the positive electrode is any one of the positive electrodes described above.

本発明に係るアルカリ蓄電池用の正極は、正極基材と、この正極基材に保持された正極合剤とを備えている。この正極基材は、シート状をなし、上端部及び下端部と、これら上端部及び下端部の間に位置付けられる中央部とを含み、正極合剤は、前記上端部又は前記下端部における亜鉛化合物の含有率が、前記中央部における亜鉛化合物の含有率よりも高い。前記上端部及び前記下端部は、前記中央部に比べ、充放電サイクルが繰り返されると正極膨化を起こしやすい箇所であるので、かかる箇所に亜鉛化合物を重点的に存在させると、正極膨化が抑制される。これにより、正極膨化にともなうサイクル寿命特性の低下を抑制することができる。このように、正極膨化が起こりやすい箇所に重点的に亜鉛化合物を存在させることにより、その他の部分、すなわち中央部における正極合剤に含有される亜鉛化合物の量を減らすことができる。この亜鉛化合物は電池の充放電反応には直接関与しないので、相対的に正極活物質の量を増やすことができ、電池の容量を高いレベルで維持できる。つまり、本発明に係る正極を備えたアルカリ蓄電池は、電池の容量を高いレベルで維持しつつ、サイクル寿命の向上を図ることができる。   The positive electrode for alkaline storage batteries according to the present invention includes a positive electrode base material and a positive electrode mixture held on the positive electrode base material. The positive electrode base material has a sheet shape, and includes an upper end portion and a lower end portion, and a central portion positioned between the upper end portion and the lower end portion. The positive electrode mixture is a zinc compound in the upper end portion or the lower end portion. Is higher than the zinc compound content in the central portion. Since the upper end portion and the lower end portion are places where the positive electrode expansion is likely to occur when the charge / discharge cycle is repeated as compared with the central portion, the positive electrode expansion is suppressed when a zinc compound is preferentially present in such a portion. The Thereby, the fall of the cycle life characteristic accompanying positive electrode swelling can be suppressed. Thus, the amount of the zinc compound contained in the positive electrode mixture in the other part, that is, the central part can be reduced by making the zinc compound intensively present at the position where the positive electrode is likely to expand. Since this zinc compound does not directly participate in the charge / discharge reaction of the battery, the amount of the positive electrode active material can be relatively increased, and the capacity of the battery can be maintained at a high level. That is, the alkaline storage battery including the positive electrode according to the present invention can improve the cycle life while maintaining the battery capacity at a high level.

本発明に係るニッケル水素蓄電池を部分的に破断して示した斜視図である。It is the perspective view which fractured | ruptured and showed the nickel hydride storage battery which concerns on this invention. 本発明に係るニッケル水素蓄電池につき初期活性化処理後に、電池下部から上部にかけて所定測定ポイントにおける外径を測定した結果を示したグラフである。It is the graph which showed the result of having measured the outer diameter in the predetermined measurement point from the battery lower part to the upper part after the initial activation process about the nickel hydride storage battery which concerns on this invention. 本発明に係るニッケル水素蓄電池に含まれる正極を展開した状態で概略的に示した平面図である。It is the top view shown roughly in the state where the positive electrode contained in the nickel metal hydride storage battery concerning the present invention was developed. 正極基材を展開した状態で概略的に示した平面図である。It is the top view shown schematically in the state where the positive electrode base material was developed. 正極の中間製品を展開した状態で概略的に示した平面図である。It is the top view shown roughly in the state which developed the intermediate product of the positive electrode.

以下、図面を参照して、本発明に係る正極を組み込んだアルカリ蓄電池について説明する。   Hereinafter, an alkaline storage battery incorporating a positive electrode according to the present invention will be described with reference to the drawings.

（第１の実施形態）
本発明が適用されるアルカリ蓄電池としては特に限定されないが、例えば、図１に示すＡＡサイズの円筒形のニッケル水素蓄電池２（以下、単に電池２という）に本発明を適用した場合を例に説明する。 (First embodiment)
The alkaline storage battery to which the present invention is applied is not particularly limited. For example, a case where the present invention is applied to an AA-sized cylindrical nickel-metal hydride storage battery 2 (hereinafter simply referred to as the battery 2) shown in FIG. 1 will be described as an example. To do.

図１に示すように、電池２は、上端が開口した有底円筒形状をなす外装缶１０を備えている。外装缶１０は導電性を有し、その底壁３５は負極端子として機能する。外装缶１０の開口には、封口体１１が固定されている。この封口体１１は、蓋板１４及び正極端子２０を含み、外装缶１０を封口するとともに正極端子２０を提供する。蓋板１４は、導電性を有する円板形状の部材である。外装缶１０の開口内には、蓋板１４及びこの蓋板１４を囲むリング形状の絶縁パッキン１２が配置され、絶縁パッキン１２は外装缶１０の開口縁３７をかしめ加工することにより外装缶１０の開口縁３７に固定されている。即ち、蓋板１４及び絶縁パッキン１２は互いに協働して外装缶１０の開口を気密に閉塞している。   As shown in FIG. 1, the battery 2 includes an outer can 10 having a bottomed cylindrical shape with an open upper end. The outer can 10 has conductivity, and its bottom wall 35 functions as a negative electrode terminal. A sealing body 11 is fixed to the opening of the outer can 10. The sealing body 11 includes a cover plate 14 and a positive electrode terminal 20, and seals the outer can 10 and provides the positive electrode terminal 20. The cover plate 14 is a disk-shaped member having conductivity. A cover plate 14 and a ring-shaped insulating packing 12 surrounding the cover plate 14 are disposed in the opening of the outer can 10, and the insulating packing 12 is formed by caulking the opening edge 37 of the outer can 10. It is fixed to the opening edge 37. That is, the lid plate 14 and the insulating packing 12 cooperate with each other to airtightly close the opening of the outer can 10.

ここで、蓋板１４は中央に中央貫通孔１６を有し、そして、蓋板１４の外面上には中央貫通孔１６を塞ぐゴム製の弁体１８が配置されている。更に、蓋板１４の外面上には、弁体１８を覆うようにしてフランジ付き円筒形状をなす金属製の正極端子２０が電気的に接続されている。この正極端子２０は弁体１８を蓋板１４に向けて押圧している。なお、正極端子２０には、図示しないガス抜き孔が開口されている。   Here, the cover plate 14 has a central through hole 16 in the center, and a rubber valve body 18 that closes the central through hole 16 is disposed on the outer surface of the cover plate 14. Further, a metal positive electrode terminal 20 having a flanged cylindrical shape is electrically connected to the outer surface of the cover plate 14 so as to cover the valve element 18. The positive terminal 20 presses the valve body 18 toward the lid plate 14. The positive electrode terminal 20 has a gas vent hole (not shown).

通常時、中央貫通孔１６は弁体１８によって気密に閉じられている。一方、外装缶１０内にガスが発生し、その内圧が高まれば、弁体１８は内圧によって圧縮され、中央貫通孔１６を開き、この結果、外装缶１０内から中央貫通孔１６及び正極端子２０のガス抜き孔を介して外部にガスが放出される。つまり、中央貫通孔１６、弁体１８及び正極端子２０は電池２のための安全弁を形成している。   Normally, the central through hole 16 is hermetically closed by the valve body 18. On the other hand, if gas is generated in the outer can 10 and its internal pressure increases, the valve body 18 is compressed by the internal pressure and opens the central through hole 16. As a result, the central through hole 16 and the positive electrode terminal 20 are opened from the outer can 10. Gas is released to the outside through the vent holes. That is, the central through hole 16, the valve body 18, and the positive electrode terminal 20 form a safety valve for the battery 2.

外装缶１０には、アルカリ電解液（図示せず）とともに電極群２２が収容されている。ここで、アルカリ電解液はセパレータ２８に含浸され、正極２４と負極２６との間での充放電反応を進行させる。このアルカリ電解液の種類としては、特に限定されないが、例えば、水酸化ナトリウム水溶液、水酸化リチウム水溶液、水酸化カリウム水溶液をあげることができる。これら水溶液は、それぞれ単独で用いることができるが、これらのうち２つ以上を混合した混合水溶液として用いることもできる。   The outer can 10 contains an electrode group 22 together with an alkaline electrolyte (not shown). Here, the alkaline electrolyte is impregnated in the separator 28, and the charge / discharge reaction between the positive electrode 24 and the negative electrode 26 proceeds. Although it does not specifically limit as a kind of this alkaline electrolyte, For example, sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution can be mention | raise | lifted. These aqueous solutions can be used alone, but can also be used as a mixed aqueous solution in which two or more of these are mixed.

また、図１から明らかなように、内部短絡防止のため、外装缶１０内には、電極群２２と蓋板１４との間に円形の上部絶縁部材３２が配置されており、電極群２２と外装缶１０の底壁３５との間にも円形の下部絶縁部材３４が配置されている。   As is clear from FIG. 1, a circular upper insulating member 32 is disposed between the electrode group 22 and the cover plate 14 in the outer can 10 to prevent an internal short circuit. A circular lower insulating member 34 is also disposed between the bottom wall 35 of the outer can 10.

電極群２２は、それぞれ帯状の正極２４、負極２６及びセパレータ２８からなり、これらは正極２４と負極２６との間にセパレータ２８が挟み込まれた状態で渦巻状に巻回されている。即ち、セパレータ２８を介して正極２４及び負極２６が互いに重ね合わされている。電極群２２の外周面は負極２６の一部により形成され、外装缶１０の内周壁と接触している。これにより、負極２６と外装缶１０とは互いに電気的に接続されている。   The electrode group 22 includes a strip-like positive electrode 24, a negative electrode 26, and a separator 28, which are wound in a spiral shape with the separator 28 sandwiched between the positive electrode 24 and the negative electrode 26. That is, the positive electrode 24 and the negative electrode 26 are overlapped with each other via the separator 28. The outer peripheral surface of the electrode group 22 is formed by a part of the negative electrode 26 and is in contact with the inner peripheral wall of the outer can 10. Accordingly, the negative electrode 26 and the outer can 10 are electrically connected to each other.

一方、正極２４には、正極リード３０が取り付けられており、この正極リード３０の先端が蓋板１４に接続されている。この蓋板１４には、上記したように正極端子２０が接続されているので、正極端子２０と正極２４とは、正極リード３０及び蓋板１４を介して互いに電気的に接続されている。ここで、図１から明らかなように、正極リード３０は上部絶縁部材３２に設けられたリード通し孔３９を通して延びている。   On the other hand, a positive electrode lead 30 is attached to the positive electrode 24, and the tip of the positive electrode lead 30 is connected to the lid plate 14. Since the positive terminal 20 is connected to the cover plate 14 as described above, the positive terminal 20 and the positive electrode 24 are electrically connected to each other via the positive lead 30 and the cover plate 14. Here, as is apparent from FIG. 1, the positive electrode lead 30 extends through a lead through hole 39 provided in the upper insulating member 32.

ここで、上記した負極２６及びセパレータ２８としては、それぞれ、公知のニッケル水素蓄電池に用いられる負極及びセパレータが好適に用いられる。   Here, as the negative electrode 26 and the separator 28 described above, a negative electrode and a separator used in a known nickel metal hydride storage battery are preferably used, respectively.

正極２４は、非焼結式のニッケル極であり、正極基材３６と、この正極基材３６に保持された正極合剤とを含んでいる。   The positive electrode 24 is a non-sintered nickel electrode, and includes a positive electrode base material 36 and a positive electrode mixture held on the positive electrode base material 36.

正極合剤は、正極活物質粒子、導電材、正極添加剤及び結着剤を含む。この結着剤は、正極活物質粒子、導電材及び正極添加剤を結着させると同時に正極合剤を正極基板に結着させる働きをなす。ここで、結着剤としては、例えば、カルボキシメチルセルロース、メチルセルロース、ＰＴＦＥ（ポリテトラフルオロエチレン）ディスパージョン、ＨＰＣ（ヒドロキシプロピルセルロース）ディスパージョンなどを用いることができる。   The positive electrode mixture includes positive electrode active material particles, a conductive material, a positive electrode additive, and a binder. This binder serves to bind the positive electrode active material particles, the conductive material, and the positive electrode additive, and at the same time, bind the positive electrode mixture to the positive electrode substrate. Here, as the binder, for example, carboxymethylcellulose, methylcellulose, PTFE (polytetrafluoroethylene) dispersion, HPC (hydroxypropylcellulose) dispersion, and the like can be used.

正極活物質粒子は、水酸化ニッケル粒子又は高次水酸化ニッケル粒子である。なお、これら水酸化ニッケル粒子には、亜鉛、マグネシウム及びコバルトのうちの少なくとも一種を固溶させることが好ましい。   The positive electrode active material particles are nickel hydroxide particles or higher order nickel hydroxide particles. In addition, it is preferable to dissolve at least one of zinc, magnesium, and cobalt in these nickel hydroxide particles.

導電材としては、例えば、コバルト酸化物（ＣｏＯ）やコバルト水酸化物（Ｃｏ（ＯＨ）2）などのコバルト化合物及びコバルト（Ｃｏ）から選択された１種又は２種以上を用いることができる。この導電材は、必要に応じて正極合剤に添加されるものであり、添加される形態としては、粉末の形態のほか、正極活物質の表面を覆う被覆の形態で正極合剤に含まれていてもよい。 As the conductive material, for example, one or more selected from cobalt compounds such as cobalt oxide (CoO) and cobalt hydroxide (Co (OH) 2 ) and cobalt (Co) can be used. This conductive material is added to the positive electrode mixture as necessary, and is added to the positive electrode mixture in the form of a powder and a coating covering the surface of the positive electrode active material. It may be.

正極添加剤は、正極活物質の充電受入性を抑制し、充放電サイクルによる正極の膨化を軽減しサイクル寿命を延ばす働きをする。正極添加剤としては、亜鉛化合物が用いられ、この亜鉛化合物としては、水酸化亜鉛又は酸化亜鉛が用いられる。本発明においては、充放電サイクルを多数回繰り返した際に正極膨化が起こりやすい箇所に亜鉛化合物を重点的に配置する。   The positive electrode additive functions to suppress the charge acceptance of the positive electrode active material, reduce the expansion of the positive electrode due to the charge / discharge cycle, and extend the cycle life. A zinc compound is used as the positive electrode additive, and zinc hydroxide or zinc oxide is used as the zinc compound. In the present invention, the zinc compound is preferentially disposed at a location where positive electrode swelling is likely to occur when the charge / discharge cycle is repeated many times.

本発明者は、初期活性化処理直後の電池２に対し、電池２内で電極群が存在する対応箇所において電池２の下部から上部にかけて等間隔に１０箇所の測定ポイントを設け、これら測定ポイントにつき電池２の外径を測定した。その結果を図２のグラフに示す。このグラフより、初期活性化処理直後の電池２においては、電池２の上側の２０％の範囲及び下側の２０％の範囲の外径寸法が電池２の中央部の外径寸法よりも小さいことがわかる。これは、電池２内の電極群２２において、初期活性化処理により正極膨化が起こったことによる。電極群２２においては、初期活性化処理により、その中央部での正極膨化が、電極群の上側の２０％の範囲及び下側の２０％の範囲の正極膨化よりも多めに起こっていると言える。これは以下のような理由によると考えられる。   The present inventor provided 10 measurement points at equal intervals from the lower part to the upper part of the battery 2 in the corresponding part where the electrode group exists in the battery 2 immediately after the initial activation process. The outer diameter of the battery 2 was measured. The result is shown in the graph of FIG. From this graph, in the battery 2 immediately after the initial activation process, the outer diameter dimension of the upper 20% range and the lower 20% range of the battery 2 is smaller than the outer diameter dimension of the central portion of the battery 2. I understand. This is because the positive electrode expansion occurred in the electrode group 22 in the battery 2 due to the initial activation process. In the electrode group 22, it can be said that, due to the initial activation process, the positive electrode expansion at the center portion occurs more than the positive electrode expansion in the upper 20% range and the lower 20% range of the electrode group. . This is considered to be due to the following reasons.

電池２の中央部、すなわち電極群２２の中央部に位置する正極のある一部分（以下、中央反応部という）に対しては、その周囲に存在する負極との間で充放電反応が進行する。   For a certain part of the positive electrode located in the central part of the battery 2, that is, the central part of the electrode group 22 (hereinafter referred to as a central reaction part), a charge / discharge reaction proceeds with the negative electrode present around the part.

一方、電池２の上部又は下部、すなわち電極群２２の上部又は下部に位置する正極のある一部分（以下、末端反応部という）に対しては、正極の上端縁又は下端縁よりも外側の部分に負極は存在していないため、末端反応部と相対する部分及び末端反応部よりも電極群の中央部側に存在する負極との間で充放電反応が進行する。   On the other hand, with respect to a part of the positive electrode located in the upper part or the lower part of the battery 2, that is, the upper part or the lower part of the electrode group 22 (hereinafter referred to as a terminal reaction part), Since the negative electrode does not exist, the charge / discharge reaction proceeds between the portion facing the terminal reaction portion and the negative electrode present on the center portion side of the electrode group from the terminal reaction portion.

つまり、中央反応部の周囲に存在し充放電反応に関与する負極の面積は、末端反応部の周囲に存在し充放電反応に関与する負極の面積のほぼ倍であるため、初期活性化処理の際、充放電反応は、末端反応部よりも中央反応部の方がより進行しやすいと言える。このため、初期活性化処理直後の電池では、上部及び下部に比べ、中央部でより多く正極膨化が起こるので、中央部の外径寸法が上部及び下部の外径寸法よりも大きくなっている。   In other words, the area of the negative electrode present around the central reaction part and involved in the charge / discharge reaction is approximately twice the area of the negative electrode present around the terminal reaction part and involved in the charge / discharge reaction. In this case, it can be said that the charge / discharge reaction proceeds more easily in the central reaction part than in the terminal reaction part. For this reason, in the battery immediately after the initial activation treatment, the positive electrode swells more in the central portion than in the upper and lower portions, so that the outer diameter dimension of the central portion is larger than the outer diameter dimensions of the upper and lower portions.

ここで、初期活性化処理においては、電極群の中央部で正極膨化が起こりやすい。しかしながら、ある程度正極膨化が進行すると電極群は外装缶により拘束されるので、中央部の正極膨化はそれ以上進行しづらくなる。一方、電極群の上側の２０％の範囲及び下側の２０％の範囲については、外装缶の拘束は未だ受けず、変形に対して自由な状態である。   Here, in the initial activation process, the positive electrode bulges easily at the center of the electrode group. However, since the electrode group is constrained by the outer can when the positive electrode expansion has progressed to some extent, the positive electrode expansion at the central portion does not progress any further. On the other hand, the upper 20% range and the lower 20% range of the electrode group are not yet restricted by the outer can, and are free from deformation.

このため、電池が出荷された後、ユーザーが電池を使用して、充放電サイクルを多数回繰り返していくと、主にこれら上部及び下部において正極膨化が進行していく。つまり、電池においては、初期活性化処理後、充放電サイクルを多数回繰り返した場合、次は電極群の上部及び下部で正極膨化が起こりやすくなると言える。このような知見のもと、本発明では、充放電サイクルを多数回繰り返した場合の正極膨化を抑制すべく、正極２４において電極群２２の上部及び下部に相当する箇所に重点的に亜鉛化合物を配置することとした。   For this reason, when the user uses the battery and repeats the charge / discharge cycle many times after the battery is shipped, the positive electrode expansion mainly proceeds at the upper part and the lower part. That is, in the battery, when the charge / discharge cycle is repeated many times after the initial activation process, it can be said that the positive electrode is likely to swell next at the upper and lower portions of the electrode group. Based on such knowledge, in the present invention, in order to suppress the expansion of the positive electrode when the charge / discharge cycle is repeated many times, the zinc compound is mainly applied to the portions corresponding to the upper and lower portions of the electrode group 22 in the positive electrode 24. Decided to place.

ここで、正極２４の構造について以下に詳しく説明する。
正極２４は、多数の空孔を有する金属多孔体からなる正極基材３６に正極合剤が保持されてなる。ここで、正極合剤は、正極基材３６の空孔内に保持されているとともに正極基材の表面上にも保持されている。このような正極２４は、展開した状態で長方形状をなし、図３中の矢印Ａで示される長手方向すなわち電極群の巻回方向に沿った方向に延びる上端部５０及び下端部５１と、これら上端部５０及び下端部５１の間に位置付けられる中央部５２とを有している。ここで、これら上端部５０及び下端部５１と中央部５２には、上記したように正極合剤が保持されている。本発明においては、外装缶１０の上端開口側に位置する上端部５０に保持されている正極合剤を上端部正極合剤５０ａとし、外装缶１０の底壁側に位置する下端部５１に保持されている正極合剤を下端部正極合剤５１ａとし、中央部５２に保持されている正極合剤を中央正極合剤５２ａとする。なお、上記した巻回方向に直交する方向（矢印Ｂで示す方向）を上下方向とする。 Here, the structure of the positive electrode 24 will be described in detail below.
The positive electrode 24 is formed by holding a positive electrode mixture on a positive electrode base material 36 made of a metal porous body having a large number of pores. Here, the positive electrode mixture is held in the pores of the positive electrode base material 36 and also on the surface of the positive electrode base material. Such a positive electrode 24 has a rectangular shape in an unfolded state, and includes an upper end portion 50 and a lower end portion 51 extending in the longitudinal direction indicated by an arrow A in FIG. 3, that is, the direction along the winding direction of the electrode group, And a central portion 52 positioned between the upper end portion 50 and the lower end portion 51. Here, the positive electrode mixture is held in the upper end portion 50, the lower end portion 51, and the central portion 52 as described above. In the present invention, the positive electrode mixture held at the upper end portion 50 located on the upper end opening side of the outer can 10 is defined as the upper end portion positive electrode mixture 50a and held at the lower end portion 51 located on the bottom wall side of the outer can 10. The positive electrode mixture thus prepared is referred to as a lower end positive electrode mixture 51a, and the positive electrode mixture held in the central portion 52 is referred to as a central positive electrode mixture 52a. In addition, let the direction (direction shown by arrow B) orthogonal to an above-described winding direction be an up-down direction.

本発明において、上端部正極合剤５０ａ及び下端部正極合剤５１ａは、上下方向に所定の幅をもっている。詳しくは、上端部正極合剤５０ａは、正極２４の上端縁５４から正極２４の上下方向における中央部５２側へ所定長さの幅Ｗａをもって電極群２２の巻回方向に沿って延びている。下端部正極合剤５１ａは、正極２４の下端縁５６から正極２４の上下方向における中央部５２側へ所定長さの幅Ｗｂをもって電極群の巻回方向に沿って延びている。   In the present invention, the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a have a predetermined width in the vertical direction. Specifically, the upper end positive electrode mixture 50 a extends along the winding direction of the electrode group 22 from the upper end edge 54 of the positive electrode 24 to the central portion 52 side in the vertical direction of the positive electrode 24 with a predetermined width Wa. The lower end positive electrode mixture 51a extends from the lower end edge 56 of the positive electrode 24 toward the center portion 52 in the vertical direction of the positive electrode 24 along the winding direction of the electrode group with a predetermined width Wb.

本発明に係る正極２４においては、正極添加剤として亜鉛化合物を含んでおり、この亜鉛化合物の含有率を中央正極合剤５２ａとそれ以外の上端部正極合剤５０ａ及び下端部正極合剤５１ａとで差を設けている。詳しくは、中央正極合剤５２ａの亜鉛化合物の含有率の値よりも、上端部正極合剤５０ａ及び下端部正極合剤５１ａのうちの少なくとも一方の亜鉛化合物の含有率の方が高い値に設定されている。   In the positive electrode 24 according to the present invention, a zinc compound is included as a positive electrode additive, and the content ratio of this zinc compound is determined from the central positive electrode mixture 52a and the other upper end positive electrode mixture 50a and lower end positive electrode mixture 51a. There is a difference. Specifically, the content of at least one zinc compound of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a is set to a higher value than the value of the zinc compound content of the central positive electrode mixture 52a. Has been.

ここで、上端部正極合剤５０ａ及び下端部正極合剤５１ａの幅Ｗａ，Ｗｂのそれぞれの長さは、正極２４の上下方向の全体の長さＬに対し、２０％以下に設定することが好ましい。上端部正極合剤５０ａ及び下端部正極合剤５１ａの幅Ｗａ，Ｗｂのそれぞれの長さが正極２４の上下方向の全体の長さＬに対して２０％の範囲を超えると、初期活性化処理により膨化し、その後は膨化が抑制される部分にも亜鉛化合物を含有させることになり、亜鉛化合物が無駄になるとともに正極活物質の量が相対的に減ってしまうからである。また、上端部正極合剤５０ａ及び下端部正極合剤５１ａの幅Ｗａ，Ｗｂのそれぞれの長さが正極２４の上下方向の全体の長さＬに対して０％を超えていれば正極膨化を抑え、サイクル寿命の改善効果は得られる。しかし、正極膨化を抑制し、サイクル寿命の改善効果を充分に得るには、上端部正極合剤５０ａ及び下端部正極合剤５１ａの幅Ｗａ，Ｗｂのそれぞれの長さが正極２４の上下方向の全体の長さＬに対して１０％以上とすることが好ましい。   Here, the lengths of the widths Wa and Wb of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a may be set to 20% or less with respect to the overall length L in the vertical direction of the positive electrode 24. preferable. When the respective lengths Wa and Wb of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a exceed 20% of the overall length L in the vertical direction of the positive electrode 24, an initial activation process is performed. This is because the zinc compound is contained also in the portion where the expansion is suppressed by this, and the zinc compound is wasted, and the amount of the positive electrode active material is relatively reduced. Further, if the respective lengths Wa and Wb of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a exceed 0% with respect to the overall length L in the vertical direction of the positive electrode 24, positive electrode expansion occurs. Suppressing and improving the cycle life can be obtained. However, in order to suppress the positive electrode expansion and sufficiently obtain the effect of improving the cycle life, the respective lengths Wa and Wb of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a are set in the vertical direction of the positive electrode 24. The total length L is preferably 10% or more.

正極２４は、例えば、以下のようにして製造することができる。
まず、図４に示すような正極基材３６が準備される。この正極基材３６は、導電性の金属多孔体からなり、例えば、ニッケルめっきが施された網状、スポンジ状若しくは繊維状の金属体、あるいは、発泡ニッケル（ニッケルフォーム）が用いられる。正極基材３６は、全体としては、図４に示すような長尺のシートであり、その内部は、三次元網目状の構造を有し、相互に連通した多数の空孔を有している。 The positive electrode 24 can be manufactured as follows, for example.
First, a positive electrode base material 36 as shown in FIG. 4 is prepared. The positive electrode base material 36 is made of a conductive metal porous body. For example, a net-like, sponge-like or fibrous metal body plated with nickel, or foamed nickel (nickel foam) is used. The positive electrode base material 36 as a whole is a long sheet as shown in FIG. 4, and the inside thereof has a three-dimensional network structure and has a large number of pores communicating with each other. .

正極基材３６においては、図４中の矢印Ａで示す長手方向すなわち電極群の巻回方向に沿った方向に延びる上端部３８及び下端部３９と、これら上端部３８及び下端部３９の間に位置する中央部４０とを有している。ここで、上端部３８は外装缶１０の上端開口側に位置し、下端部３９は外装缶１０の底壁３５側に位置する。   In the positive electrode base material 36, an upper end 38 and a lower end 39 extending in the longitudinal direction indicated by an arrow A in FIG. 4, that is, a direction along the winding direction of the electrode group, and between the upper end 38 and the lower end 39. And a central portion 40 located therein. Here, the upper end portion 38 is located on the upper end opening side of the outer can 10, and the lower end portion 39 is located on the bottom wall 35 side of the outer can 10.

ここで、正極基材３６の上端部３８は、正極２４の上端部５０と対応し、正極基材３６の下端部３９は、正極２４の下端部５１に対応し、正極基材３６の中央部４０は、正極２４の中央部５２と対応する。
なお、上記した巻回方向に直交する方向（矢印Ｂで示す方向）を上下方向とする。 Here, the upper end portion 38 of the positive electrode base material 36 corresponds to the upper end portion 50 of the positive electrode 24, the lower end portion 39 of the positive electrode base material 36 corresponds to the lower end portion 51 of the positive electrode 24, and the central portion of the positive electrode base material 36. Reference numeral 40 corresponds to the central portion 52 of the positive electrode 24.
In addition, let the direction (direction shown by arrow B) orthogonal to an above-described winding direction be an up-down direction.

次に、正極合剤を準備する。この正極合剤としては、第１正極合剤と、第２正極合剤とを準備する。   Next, a positive electrode mixture is prepared. As this positive electrode mixture, a first positive electrode mixture and a second positive electrode mixture are prepared.

まず、第１正極合剤は、正極活物質粒子、導電材及び結着剤からなる。   First, the first positive electrode mixture includes positive electrode active material particles, a conductive material, and a binder.

第２正極合剤は、第１正極合剤に更に正極添加剤として亜鉛化合物を添加したものである。   The second positive electrode mixture is obtained by adding a zinc compound as a positive electrode additive to the first positive electrode mixture.

まず、第１正極合剤に水を加えて混練し、第１正極合剤スラリーを調製する。得られた第1正極合剤スラリーは、第１充填槽に収容される。   First, water is added to the first positive electrode mixture and kneaded to prepare a first positive electrode mixture slurry. The obtained first positive electrode mixture slurry is accommodated in the first filling tank.

また、第２正極合剤に水を加えて混練し、第２正極合剤スラリーを調製する。得られた第２正極合剤スラリーは、第２充填槽に収容される。   Further, water is added to the second positive electrode mixture and kneaded to prepare a second positive electrode mixture slurry. The obtained second positive electrode mixture slurry is accommodated in the second filling tank.

次に、準備された正極基材３６の上端部３８及び下端部３９にマスキングテープ（図示せず）を貼る。このマスキングテープを貼る領域Ｔａ，Ｔｂは、上端縁４１から上下方向における中央部４０側へ所定長さの範囲及び下端縁４３から上下方向における中央部４０側へ所定長さの範囲に設定される（図４中一点鎖線で示した）。ここで、この所定長さは、正極基材３６の上下方向の全体の長さＬ36に対し、２０％以下に設定することが好ましい。つまり、上端縁から全体の長さＬ36の２０％以下の長さ分の領域Ｔａと、下端縁４３から全体の長さＬ36の２０％以下の長さ分の領域Ｔｂとにマスキングテープが貼られる。これら領域Ｔａ，Ｔｂは、上記した上端部正極合剤５０ａ及び下端部正極合剤５１ａの幅Ｗａ，Ｗｂに対応する。よって、これら領域Ｔａ，Ｔｂの長さは、上記した上端部正極合剤５０ａ及び下端部正極合剤５１ａの幅Ｗａ，Ｗｂと同様な理由により正極基材３６の上下方向の全体の長さＬ36に対し、２０％以下、好ましくは２０％以下１０％以上に設定される。 Next, a masking tape (not shown) is applied to the upper end portion 38 and the lower end portion 39 of the prepared positive electrode base material 36. The areas Ta and Tb to which the masking tape is applied are set to a predetermined length range from the upper end edge 41 to the central portion 40 side in the vertical direction and from the lower end edge 43 to the central portion 40 side in the vertical direction. (Indicated by the alternate long and short dash line in FIG. 4). Here, the predetermined length is preferably set to 20% or less with respect to the overall length L 36 of the positive electrode base material 36 in the vertical direction. That is, the masking tape extends from the upper edge to the region Ta corresponding to a length of 20% or less of the entire length L 36 and from the lower end edge 43 to the region Tb corresponding to a length of 20% or less of the entire length L 36. Pasted. These regions Ta and Tb correspond to the widths Wa and Wb of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a. Therefore, the lengths of these regions Ta and Tb are the total length L of the positive electrode base material 36 in the vertical direction for the same reason as the widths Wa and Wb of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a. For 36 , it is set to 20% or less, preferably 20% or less and 10% or more.

次に、マスキングテープが貼られた正極基材３６は、第１充填槽に投入される。これにより第１正極合剤スラリーが正極基材３６の中央部４０に充填される。第１充填槽から取り出された正極基材３６は、乾燥工程に送られ、ここで第１正極合剤スラリーが乾燥させられる。その後、マスキングテープを剥がし、上端部３８及び下端部３９を露出させる。そして、正極基材３６の上端部３８のみを第２充填槽に浸漬させ、かかる上端部３８に第２正極合剤スラリーを充填した後、正極基材３６を引き上げる。次いで、正極基材３６の下端部３９のみを第２充填槽に浸漬させ、かかる下端部３９に第２正極合剤スラリーを充填した後、正極基材３６を引き上げる。第２正極合剤スラリーが充填された正極基材３６は乾燥工程に送られ、第２正極合剤スラリーが乾燥させられる。その後、第１正極合剤及び第２正極合剤が充填された正極基材３６は、ロール圧延されてから所定寸法に裁断される。これにより、所定厚さの中間製品４４が得られる（図５参照）。得られた中間製品４４は、図５中にて破線で示されるような、リード取付予定領域６０を含んでいる。このリード取付予定領域６０においては、そこに保持されている正極合剤を脱落させることにより、正極基材３６におけるリード取付予定領域６０に相当する部分を露出させた状態とする。かかるリード取付予定領域６０は、更に圧延加工が施され、リード取付部６１に形成される。そして、このリード取付部６１には、正極リード３０が溶接される。なお、正極リード３０は、帯状をなした金属製の薄板からなり、例えば、ニッケル製の薄板が好適に用いられる。このようにして、図３に示すような、リード取付部６１に正極リード３０が溶接されており、第１正極合剤及び第２正極合剤を保持した正極２４が得られる。   Next, the positive electrode base material 36 to which the masking tape is stuck is put into the first filling tank. As a result, the first positive electrode mixture slurry is filled in the central portion 40 of the positive electrode base material 36. The positive electrode base material 36 taken out from the first filling tank is sent to a drying step, where the first positive electrode material mixture slurry is dried. Thereafter, the masking tape is peeled off, and the upper end 38 and the lower end 39 are exposed. And only the upper end part 38 of the positive electrode base material 36 is immersed in a 2nd filling tank, and after filling the 2nd positive electrode mixture slurry in this upper end part 38, the positive electrode base material 36 is pulled up. Next, only the lower end portion 39 of the positive electrode base material 36 is immersed in the second filling tank, and the lower end portion 39 is filled with the second positive electrode mixture slurry, and then the positive electrode base material 36 is pulled up. The positive electrode base material 36 filled with the second positive electrode mixture slurry is sent to the drying step, and the second positive electrode mixture slurry is dried. Thereafter, the positive electrode base material 36 filled with the first positive electrode mixture and the second positive electrode mixture is roll-rolled and then cut into a predetermined dimension. As a result, an intermediate product 44 having a predetermined thickness is obtained (see FIG. 5). The obtained intermediate product 44 includes a lead attachment scheduled region 60 as indicated by a broken line in FIG. In this lead attachment scheduled area 60, the positive electrode mixture held therein is dropped, so that a portion corresponding to the lead attachment scheduled area 60 in the positive electrode base material 36 is exposed. The lead attachment scheduled region 60 is further rolled and formed in the lead attachment portion 61. The positive lead 30 is welded to the lead attachment portion 61. The positive electrode lead 30 is made of a metal thin plate having a band shape, and for example, a nickel thin plate is preferably used. In this way, the positive electrode lead 30 is welded to the lead mounting portion 61 as shown in FIG. 3, and the positive electrode 24 holding the first positive electrode mixture and the second positive electrode mixture is obtained.

ここで、正極基材３６の中央部４０における正極合剤すなわち中央正極合剤５２ａは、第１正極合剤からなり。正極基材３６の上端部３８における正極合剤すなわち上端部正極合剤５０ａ、及び、正極基材３６の下端部３９における正極合剤すなわち下端部正極合剤５１ａは第２正極合剤からなる。   Here, the positive electrode mixture in the central portion 40 of the positive electrode base material 36, that is, the central positive electrode mixture 52a is composed of the first positive electrode mixture. The positive electrode mixture in the upper end portion 38 of the positive electrode base material 36, that is, the upper end portion positive electrode mixture 50a, and the positive electrode mixture in the lower end portion 39 of the positive electrode base material 36, that is, the lower end portion positive electrode mixture 51a are composed of the second positive electrode mixture.

得られた正極２４においては、中央正極合剤５２ａに対し、上端部正極合剤５０ａ及び下端部正極合剤５１ａの方が亜鉛化合物の含有率が高い。ここで、上端部正極合剤５０ａ及び下端部正極合剤５１ａの亜鉛化合物の含有率は、中央正極合剤５２ａの亜鉛化合物の含有率に対し、金属亜鉛換算で１〜７質量％高い値に設定することが好ましい。前記した中央正極合剤５２ａの亜鉛化合物の含有率に対する上端部正極合剤５０ａ及び下端部正極合剤５１ａの亜鉛化合物の含有率の差が、１質量％に満たない場合サイクル寿命特性の改善効果は小さく、７質量％を超えた場合サイクル寿命特性の改善効果は飽和してしまう。   In the obtained positive electrode 24, the content of the zinc compound is higher in the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a than in the central positive electrode mixture 52a. Here, the content of the zinc compound in the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a is 1 to 7% by mass higher in terms of metal zinc than the content of the zinc compound in the central positive electrode mixture 52a. It is preferable to set. When the difference in the zinc compound content of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a with respect to the zinc compound content of the central positive electrode mixture 52a is less than 1% by mass, the cycle life characteristics are improved. When the amount exceeds 7% by mass, the effect of improving the cycle life characteristics is saturated.

なお、本発明では、中央正極合剤５２ａに対し、上端部正極合剤５０ａ及び下端部正極合剤５１ａの方が亜鉛化合物の含有率が高い状態であればよい。つまり、上記したように中央正極合剤５２ａに亜鉛化合物が含まれていなくてもよく、また、中央正極合剤５２ａに亜鉛化合物が含まれていたとしても、その含有率が、上端部正極合剤５０ａ及び下端部正極合剤５１ａの亜鉛化合物の含有率よりも低ければよい。   In the present invention, it is only necessary that the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a have a higher zinc compound content than the central positive electrode mixture 52a. That is, as described above, the central positive electrode mixture 52a may not contain a zinc compound, and even if the central positive electrode mixture 52a contains a zinc compound, the content of the upper positive electrode mixture is not limited. What is necessary is just to be lower than the content rate of the zinc compound of the agent 50a and the lower end positive electrode mixture 51a.

上記した正極２４及び負極２６は、セパレータ２８を介在させた状態で、渦巻き状に巻かれ、電極群２２に形成される。   The positive electrode 24 and the negative electrode 26 described above are spirally wound with the separator 28 interposed therebetween, and are formed in the electrode group 22.

このようにして得られた電極群２２は、外装缶１０内に収容される。このとき、電極群２２は、そこに含まれる正極２４の上端部正極合剤５０ａが外装缶の上端開口側に、下端部正極合剤５１ａが外装缶の底壁側に位置付けられるように収容される。そして、当該外装缶１０内にはアルカリ電解液が所定量注入される。その後、電極群２２及びアルカリ電解液を収容した外装缶１０は、正極端子２０、蓋板１４等を備えた封口体１１により封口され、本発明に係る電池２が得られる。   The electrode group 22 thus obtained is accommodated in the outer can 10. At this time, the electrode group 22 is accommodated such that the upper end positive electrode mixture 50a of the positive electrode 24 included therein is positioned on the upper end opening side of the outer can, and the lower end positive electrode mixture 51a is positioned on the bottom wall side of the outer can. The A predetermined amount of alkaline electrolyte is injected into the outer can 10. Thereafter, the outer can 10 containing the electrode group 22 and the alkaline electrolyte is sealed by the sealing body 11 including the positive electrode terminal 20, the cover plate 14, and the like, and the battery 2 according to the present invention is obtained.

（第２の実施形態）
本発明が適用される第２の実施形態の電池について説明する。
第２の実施形態の電池は、正極２４の上端部正極合剤５０ａ及び下端部正極合剤５１ａにおける亜鉛化合物の分布状態が第１の実施形態の電池２と相違する。よって、既に説明した第１の実施形態と同一の機能を発揮する部材および部位には同一の参照符号を付して、これらの説明は省略し、相違する点のみについて説明する。 (Second Embodiment)
A battery according to a second embodiment to which the present invention is applied will be described.
The battery of the second embodiment is different from the battery 2 of the first embodiment in the distribution state of the zinc compound in the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a of the positive electrode 24. Therefore, members and parts that exhibit the same functions as those of the first embodiment described above are denoted by the same reference numerals, description thereof will be omitted, and only differences will be described.

マスキングテープを貼っていない正極基材３６を第１充填槽に投入し、正極基材３６の全体に第１正極合剤スラリーを充填する。第１充填槽から取り出された正極基材３６は、乾燥工程に送られ、ここで第１正極合剤スラリーが乾燥させられ、第１正極合剤を保持した状態の正極基材３６が得られる。   The positive electrode base material 36 without masking tape is put into the first filling tank, and the entire positive electrode base material 36 is filled with the first positive electrode mixture slurry. The positive electrode base material 36 taken out from the first filling tank is sent to a drying step, where the first positive electrode material mixture slurry is dried to obtain the positive electrode substrate material 36 holding the first positive electrode material mixture. .

一方、亜鉛化合物の粉末を水に投入して攪拌し、亜鉛化合物の水溶液を製造し、得られた亜鉛化合物の水溶液をスプレー装置のタンクに収容する。   On the other hand, the zinc compound powder is put into water and stirred to produce an aqueous solution of the zinc compound, and the obtained aqueous solution of the zinc compound is stored in a tank of a spray device.

次いで、第１正極合剤を保持した状態の正極基材３６に対し、スプレー装置の噴射ノズルから亜鉛化合物の水溶液を噴射する。このとき、亜鉛化合物の水溶液は、正極基材３６の上端縁４１から上下方向の全体の長さＬ36の２０％以下の長さ分の領域Ｔａと、下端縁４３から上下方向の全体の長さＬ36の２０％以下の長さ分の領域Ｔｂとに噴射され、これら領域に塗布される。なお、亜鉛化合物の水溶液は、これら領域の両面に噴射される。その後、亜鉛化合物の水溶液が塗布された正極基材３６は、乾燥工程に送られ亜鉛化合物の水溶液が乾燥させられ、引き続き、ロール圧延されてから所定寸法に裁断される。このように、領域Ｔａ、Ｔｂにのみ亜鉛化合物の水溶液が供給されるので、中央正極合剤５２に対し、上端部正極合剤５０ａ及び下端部正極合剤５１ａの方が亜鉛化合物の含有率が高い正極２４が得られる。ここで、上記した亜鉛化合物の水溶液は、第１正極合剤の領域Ｔａ，Ｔｂにおいて、その表面から内部に向かって徐々に浸透していく。このため、亜鉛化合物の水溶液の乾燥後は、これら領域Ｔａ，Ｔｂにおける亜鉛化合物の含有率は表層の方が内部よりも高くなっている。 Next, an aqueous solution of a zinc compound is sprayed from the spray nozzle of the spray device onto the positive electrode base material 36 in a state where the first positive electrode mixture is held. At this time, the aqueous solution of the zinc compound is a region Ta corresponding to a length of 20% or less of the entire length L 36 in the vertical direction from the upper end edge 41 of the positive electrode base material 36 and the entire length in the vertical direction from the lower end edge 43. is injected into a 20% or less of the length of the region Tb of L 36, it is applied to these areas. In addition, the aqueous solution of the zinc compound is sprayed on both sides of these regions. Thereafter, the positive electrode base material 36 to which the aqueous solution of zinc compound is applied is sent to a drying step, where the aqueous solution of zinc compound is dried, and subsequently rolled and cut into a predetermined dimension. As described above, since the aqueous solution of the zinc compound is supplied only to the regions Ta and Tb, the content of the zinc compound is higher in the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a than in the central positive electrode mixture 52. A high positive electrode 24 is obtained. Here, the aqueous solution of the zinc compound described above gradually permeates from the surface toward the inside in the regions Ta and Tb of the first positive electrode mixture. For this reason, after drying the aqueous solution of the zinc compound, the content of the zinc compound in these regions Ta and Tb is higher in the surface layer than in the interior.

なお、亜鉛化合物の水溶液の塗布方法は、上記したスプレー式に限定されるものではなく、刷毛による塗布等、他の方法による方法を採用しても構わない。   In addition, the application method of the aqueous solution of the zinc compound is not limited to the above-described spray method, and other methods such as application with a brush may be adopted.

このように、亜鉛化合物を塗布により供給する場合、２種類の正極合剤を準備し、別々に正極基材３６へ充填する必要が無くなるので、正極の製造効率が向上する。   Thus, when supplying a zinc compound by application | coating, since it becomes unnecessary to prepare two types of positive electrode mixtures and to fill into the positive electrode base material 36 separately, the manufacturing efficiency of a positive electrode improves.

なお、本発明では、正極において中央正極合剤５２よりも亜鉛化合物を多く含ませるのは、上記したように、正極２４の上端部正極合剤５０ａ及び下端部正極合剤５１ａの両方であることが好ましいが、正極２４の上端部正極合剤５０ａ及び下端部正極合剤５１ａの何れか一方でもよい。
［実施例］ In the present invention, it is both the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a of the positive electrode 24 that contain more zinc compound than the central positive electrode mixture 52 in the positive electrode, as described above. However, any one of the upper end positive electrode mixture 50a and the lower end positive electrode mixture 51a of the positive electrode 24 may be used.
[Example]

１．電池の製造
実施例１
（１）正極の作製
水酸化ニッケル粒子からなる正極活物質粉末１００質量部に対し、水酸化コバルトの粉末１０質量部、ＨＰＣディスバージョン液４０質量部を混合して第１正極合剤スラリーを調製した。この第１正極合剤スラリーは、第１充填槽に収容した。 1. Production of Battery Example 1
(1) Production of positive electrode A first positive electrode mixture slurry is prepared by mixing 10 parts by mass of cobalt hydroxide powder and 40 parts by mass of HPC dispersion liquid with 100 parts by mass of positive electrode active material powder made of nickel hydroxide particles. did. The first positive electrode mixture slurry was accommodated in the first filling tank.

更に、水酸化ニッケル粒子からなる正極活物質粉末１００質量部に対し、水酸化コバルトの粉末１０質量部、７質量部の酸化亜鉛、４０質量部のＨＰＣディスバージョン液を混合して第２正極合剤スラリーを調製した。この第２正極合剤スラリーは、第２充填槽に収容した。   Furthermore, 10 parts by mass of cobalt hydroxide powder, 7 parts by mass of zinc oxide, and 40 parts by mass of HPC dispersion liquid are mixed with 100 parts by mass of the positive electrode active material powder composed of nickel hydroxide particles. An agent slurry was prepared. The second positive electrode mixture slurry was accommodated in the second filling tank.

一方、正極基材３６として、シート状の発泡ニッケル（ニッケルフォーム）を準備した。このニッケルフォームの長手方向に沿って延びる上端部３８及び下端部３９にマスキングテープを貼った。上端部３８側のマスキングテープ及び下端部３９側のマスキングテープの上下方向の幅の長さは、それぞれ、正極基材３６の上下方向の全体の長さＬ36を１００％とした場合に、２０％の長さに設定した。なお、マスキングテープは、正極基材３６の両面に亘って貼ってある。 On the other hand, sheet-like foamed nickel (nickel foam) was prepared as the positive electrode substrate 36. Masking tape was affixed to the upper end part 38 and the lower end part 39 which extended along the longitudinal direction of this nickel foam. The length of the width in the vertical direction of the masking tape on the upper end 38 side and the masking tape on the lower end 39 side is 20 when the overall length L 36 in the vertical direction of the positive electrode base material 36 is 100%. % Length was set. The masking tape is pasted on both surfaces of the positive electrode base material 36.

次に、マスキングテープが貼られた正極基材３６を第１充填槽に投入し、第１正極合剤スラリーを正極基材３６の露出した中央部４０に充填した。その後、正極基材３６を第１充填槽から取り出し、乾燥装置により第１正極合剤スラリーを乾燥させた。ついで、乾燥処理が終了した正極基材３６よりマスキングテープを剥がし、上端部３８及び下端部３９を露出させた。そして、正極基材３６の上端部３８のみを第２充填槽に浸漬させ、かかる上端部３８に第２正極合剤スラリーを充填した後、正極基材３６を引き上げた。次いで、正極基材３６の下端部３９のみを第２充填槽に浸漬させ、かかる下端部３９に第２正極合剤スラリーを充填した後、正極基材３６を引き上げた。第２正極合剤スラリーが充填された正極基材３６に対しては、乾燥装置により、第２正極合剤スラリーの乾燥処理を施した。その後、第１正極合剤及び第２正極合剤が充填された正極基材３６をロール圧延した後所定寸法に裁断し、所定箇所に正極リード３０を溶接した。これにより、第１正極合剤（中央正極合剤５２ａ）及び第２正極合剤（上端部正極合剤５０ａ及び下端部正極合剤５１ａ）を保持した正極２４を得た。   Next, the positive electrode base material 36 to which the masking tape was applied was put into the first filling tank, and the first positive electrode mixture slurry was filled into the exposed central portion 40 of the positive electrode base material 36. Then, the positive electrode base material 36 was taken out from the 1st filling tank, and the 1st positive electrode mixture slurry was dried with the drying apparatus. Next, the masking tape was peeled off from the positive electrode base material 36 after the drying treatment, and the upper end portion 38 and the lower end portion 39 were exposed. And only the upper end part 38 of the positive electrode base material 36 was immersed in the 2nd filling tank, and after filling the 2nd positive electrode mixture slurry in this upper end part 38, the positive electrode base material 36 was pulled up. Subsequently, only the lower end portion 39 of the positive electrode base material 36 was immersed in the second filling tank, and after filling the lower end portion 39 with the second positive electrode mixture slurry, the positive electrode base material 36 was pulled up. The positive electrode base material 36 filled with the second positive electrode mixture slurry was subjected to a drying process of the second positive electrode mixture slurry by a drying device. Thereafter, the positive electrode base material 36 filled with the first positive electrode mixture and the second positive electrode mixture was roll-rolled and cut into a predetermined dimension, and the positive electrode lead 30 was welded to a predetermined portion. Thereby, the positive electrode 24 holding the first positive electrode mixture (central positive electrode mixture 52a) and the second positive electrode mixture (upper end positive electrode mixture 50a and lower end positive electrode mixture 51a) was obtained.

ここで、分析用の試料として余分に製造した正極２４に対し、発光分光分析装置を用いて正極２４の中央正極合剤５２ａ、上端部正極合剤５０ａ及び下端部正極合剤５１ａの酸化亜鉛の含有率を測定した。その結果、中央正極合剤５２には酸化亜鉛は存在しておらず酸化亜鉛含有率は０質量％であった。一方、上端部合剤５０ａ及び下端部正極合剤５１ａには、酸化亜鉛が７質量％含まれていた。   Here, with respect to the positive electrode 24 manufactured as an extra sample for analysis, an emission spectroscopic analyzer was used to measure the zinc oxide in the central positive electrode mixture 52a, the upper end positive electrode mixture 50a, and the lower end positive electrode mixture 51a of the positive electrode 24. The content rate was measured. As a result, there was no zinc oxide in the central positive electrode mixture 52, and the zinc oxide content was 0% by mass. On the other hand, the upper end portion mixture 50a and the lower end portion positive electrode mixture 51a contained 7% by mass of zinc oxide.

（２）電極群の作製
一般的なニッケル水素蓄電池に用いられる負極２６及びセパレータ２８を準備した。そして、上記のようにして得られた正極２４と、準備した負極２６との間に、準備したセパレータ２８を挟んだ状態で渦巻状に巻回し、電極群２２を作製した。 (2) Production of electrode group A negative electrode 26 and a separator 28 used for a general nickel metal hydride storage battery were prepared. And it wound in the shape of a spiral in the state which pinched the prepared separator 28 between the positive electrode 24 obtained as mentioned above, and the prepared negative electrode 26, and produced the electrode group 22. FIG.

（３）ニッケル水素蓄電池の組み立て
得られた電極群２２を有底円筒形状の外装缶１０内に収納した。このとき、電極群２２は、そこに含まれる正極２４の上端部正極合剤５０ａが外装缶１０の上端開口側に、正極２４の下端部正極合剤５１ａが外装缶１０の底壁３５側に位置するように配置した。そして、この外装缶１０の中に３０質量％の水酸化ナトリウム水溶液からなるアルカリ電解液を２．２ｇ注入した。その後、封口体１１で外装缶１０の開口を塞いでＡＡサイズの密閉型ニッケル水素蓄電池２を組み立てた。この電池を電池ａと称する。 (3) Assembly of Nickel Metal Hydride Battery The obtained electrode group 22 was housed in a bottomed cylindrical outer can 10. At this time, in the electrode group 22, the upper end positive electrode mixture 50 a of the positive electrode 24 included therein is on the upper end opening side of the outer can 10, and the lower end portion positive electrode mixture 51 a of the positive electrode 24 is on the bottom wall 35 side of the outer can 10. Arranged to be located. Then, 2.2 g of an alkaline electrolyte composed of a 30% by mass aqueous sodium hydroxide solution was injected into the outer can 10. Thereafter, the opening of the outer can 10 was closed with the sealing body 11 to assemble the AA size sealed nickel-metal hydride storage battery 2. This battery is referred to as battery a.

（４）初期活性化処理
電池ａに対し、温度２５℃の下にて、２０００ｍＡの充電電流で１６時間の充電を行った後に、２０００ｍＡの放電電流で電池電圧が０．５Ｖになるまで放電させる初期活性化処理を２回繰り返した。このようにして、電池ａを使用可能状態とした。 (4) Initial activation treatment After charging the battery a for 16 hours at a charging current of 2000 mA at a temperature of 25 ° C., the battery a is discharged until the battery voltage reaches 0.5 V with a discharging current of 2000 mA. The initial activation process was repeated twice. In this way, the battery a was made usable.

比較例１
マスキングテープを貼っていない正極基材３６の全体に第２正極合剤スラリーを充填したこと以外は、実施例１と同様なニッケル水素蓄電池を作製した。この電池を電池ｂと称する。 Comparative Example 1
A nickel-metal hydride storage battery similar to that of Example 1 was prepared except that the entire positive electrode base material 36 without a masking tape was filled with the second positive electrode mixture slurry. This battery is referred to as battery b.

比較例２
マスキングテープを貼っていない正極基材３６の全体に第１正極合剤スラリーを充填したこと以外は、実施例１と同様なニッケル水素蓄電池を作製した。この電池を電池ｃと称する。 Comparative Example 2
A nickel-metal hydride storage battery similar to that in Example 1 was prepared except that the entire positive electrode base material 36 without a masking tape was filled with the first positive electrode mixture slurry. This battery is referred to as a battery c.

２．ニッケル水素蓄電池の評価
（１）放電容量
初期活性化処理済みの電池ａ〜電池ｃに対し、２５℃の雰囲気下にて、２０００ｍＡの充電電流で１６時間充電し、その後、同一の雰囲気下にて２０００ｍＡの放電電流で放電終止電圧が１．０Ｖになるまで放電させたときの電池の放電容量を測定した。得られた結果を表１に示した。 2. Evaluation of nickel-metal hydride storage battery (1) Discharge capacity The batteries a to c which have been subjected to initial activation treatment were charged for 16 hours at a charging current of 2000 mA in an atmosphere at 25 ° C., and then in the same atmosphere. The discharge capacity of the battery was measured when it was discharged at a discharge current of 2000 mA until the final discharge voltage reached 1.0V. The obtained results are shown in Table 1.

（２）サイクル寿命特性
初期活性化処理済みの電池ａ〜電池ｃに対し、２５℃の雰囲気下にて、２０００ｍＡの充電電流で１時間充電を行い、その後、２０分間放置した。
同一の雰囲気下にて２０００ｍＡの放電電流で電池の電圧が１．０Ｖになるまで放電した後、１０分間放置した。 (2) Cycle life characteristics The batteries a to c subjected to the initial activation treatment were charged for 1 hour at a charging current of 2000 mA in an atmosphere at 25 ° C., and then left for 20 minutes.
Under the same atmosphere, the battery was discharged at a discharge current of 2000 mA until the voltage of the battery reached 1.0 V, and then left for 10 minutes.

上記充放電のサイクルを１サイクルとし、各電池につき初期容量を１００％としたとき、この初期容量に対する容量維持率が６０％を下回るまでのサイクル数を数え、その回数をサイクル寿命とした。その結果をサイクル寿命として表１に示した。   When the charge / discharge cycle was 1 cycle and the initial capacity of each battery was 100%, the number of cycles until the capacity maintenance rate with respect to the initial capacity was below 60% was counted, and the number of cycles was defined as the cycle life. The results are shown in Table 1 as cycle life.

Figure 2015060695
Figure 2015060695

（２）考察
実施例１の電池ａは、放電容量の値が比較例１よりも高く、サイクル寿命が比較例２よりも長いことがわかる。この電池ａは、正極２４の上端部正極合剤５０ａ及び下端部正極合剤５１ａの酸化亜鉛の含有率が正極２４の中央正極合剤５２ａよりも高く設定されている。このため、充放電のサイクルを多数回繰り返した際に正極膨化が起こりやすい上端部５０及び下端部５１において、酸化亜鉛が重点的に存在するので、充放電サイクルが多数回繰り返された際の正極膨化が抑制され、それにともないサイクル寿命が延びている。実施例１の電池ａのサイクル寿命特性は、正極全体に酸化亜鉛を含む比較例１の電池ｂのサイクル寿命特性と同等である。一方、正極の中央正極合剤５２ａには、電池反応に関与しない酸化亜鉛が存在しないので、その分正極活物質の量を多く含ませることができている。このため、高容量化が図られている。ここで、実施例１の電池ａの放電容量は、酸化亜鉛を全く含んでいない比較例２の電池ｃの放電容量と同等である。つまり、実施例１の電池ａは、放電容量の値が高められている電池と同等の放電容量値を得つつ、サイクル寿命の向上が図られている。 (2) Discussion It can be seen that the battery a of Example 1 has a higher discharge capacity value than Comparative Example 1 and a longer cycle life than Comparative Example 2. In this battery a, the content of zinc oxide in the upper end positive electrode mixture 50 a and the lower end positive electrode mixture 51 a of the positive electrode 24 is set higher than that of the central positive electrode mixture 52 a of the positive electrode 24. For this reason, since zinc oxide is mainly present at the upper end portion 50 and the lower end portion 51 where the positive electrode expansion is likely to occur when the charge / discharge cycle is repeated many times, the positive electrode when the charge / discharge cycle is repeated many times. Swelling is suppressed and the cycle life is extended accordingly. The cycle life characteristic of the battery a of Example 1 is equivalent to the cycle life characteristic of the battery b of Comparative Example 1 in which the entire positive electrode contains zinc oxide. On the other hand, since the central positive electrode mixture 52a of the positive electrode does not contain zinc oxide that does not participate in the battery reaction, the amount of the positive electrode active material can be increased accordingly. For this reason, the capacity is increased. Here, the discharge capacity of the battery a of Example 1 is equivalent to the discharge capacity of the battery c of Comparative Example 2 that does not contain any zinc oxide. In other words, the battery a of Example 1 is improved in cycle life while obtaining a discharge capacity value equivalent to that of a battery having an increased discharge capacity value.

比較例１の電池ｂでは、正極添加剤として酸化亜鉛が正極全体に添加されているので、全体的に正極膨化が抑制されており、それにともないサイクル寿命が延びている。しかしながら、酸化亜鉛の量が増えると相対的に正極活物質の水酸化ニッケルの量が減るため、放電容量の値が比較的小さくなくなっている。   In the battery b of Comparative Example 1, since zinc oxide is added to the whole positive electrode as a positive electrode additive, the positive electrode expansion is suppressed as a whole, and the cycle life is extended accordingly. However, as the amount of zinc oxide increases, the amount of nickel hydroxide as the positive electrode active material relatively decreases, so that the value of the discharge capacity is not relatively small.

比較例２の電池ｃでは、正極において、電池反応に直接関与しない酸化亜鉛を全く含んでいないので、相対的に正極活物質である水酸化ニッケルの量を多く含有させることができていることから放電容量の値が比較的高い。しかしながら、充放電のサイクル数が増えると正極膨化が起こり、それにともないサイクル寿命は短い電池となっている。   In the battery c of Comparative Example 2, since the positive electrode does not contain any zinc oxide that does not directly participate in the battery reaction, a relatively large amount of nickel hydroxide as the positive electrode active material can be contained. The value of discharge capacity is relatively high. However, as the number of charge / discharge cycles increases, the positive electrode swells, resulting in a battery with a short cycle life.

以上より、正極の上端部及び下端部に位置する正極合剤に含有される亜鉛化合物の含有率を正極の中央部に位置する正極合剤に含有される亜鉛化合物の含有率よりも高くすることにより、正極膨化が起こりやすい正極端部にて膨化を抑制することができ、もって電池のサイクル寿命を向上させることができる。しかも、正極の中央部には正極活物質を相対的に多く存在させることができるので電池の高容量化も図れることがわかる。このように、本発明の正極によれば、高い容量を維持しつつサイクル寿命特性を向上させることができるアルカリ蓄電池を得ることができる。   As mentioned above, making the content rate of the zinc compound contained in the positive electrode mixture located in the upper end part and lower end part of a positive electrode higher than the content rate of the zinc compound contained in the positive electrode mixture located in the center part of a positive electrode As a result, the expansion of the positive electrode can be suppressed at the end of the positive electrode where the positive electrode tends to expand, thereby improving the cycle life of the battery. In addition, it can be seen that a relatively large amount of the positive electrode active material can be present in the central portion of the positive electrode, so that the capacity of the battery can be increased. Thus, according to the positive electrode of the present invention, an alkaline storage battery that can improve cycle life characteristics while maintaining a high capacity can be obtained.

２ ニッケル水素蓄電池
１０ 外装缶
１１ 封口体
１２ 絶縁パッキン
１４ 蓋板
２０ 正極端子
２２ 電極群
２４ 正極
２６ 負極
２８ セパレータ
３８ 上端部
３９ 下端部
４０ 中央部
５０ 上端部
５１ 下端部
５２ 中央部 2 Nickel Metal Hydride Battery 10 Exterior Can 11 Sealing Body 12 Insulating Packing 14 Lid Plate 20 Positive Electrode Terminal 22 Electrode Group 24 Positive Electrode 26 Negative Electrode 28 Separator 38 Upper End 39 Lower End 40 Central 50 Upper End 51 Lower End 52 Central

Claims (4)

多数の空孔を含む金属多孔体からなる正極基材と、
前記空孔内及び前記正極基材の表面上に保持され、少なくとも正極活物質を含んでいる正極合剤とを備え、
前記正極基材は、シート状をなし、その長手方向に沿って延びる上端部及び下端部と、前記上端部及び前記下端部の間に位置付けられる中央部とを含み、
前記正極合剤は、前記上端部又は前記下端部における亜鉛化合物の含有率が、前記中央部における亜鉛化合物の含有率よりも高いことを特徴とするアルカリ蓄電池用の正極。 A positive electrode substrate made of a porous metal body including a large number of pores;
A positive electrode mixture that is held in the pores and on the surface of the positive electrode base material and includes at least a positive electrode active material;
The positive electrode base material has a sheet shape, and includes an upper end portion and a lower end portion extending along the longitudinal direction thereof, and a central portion positioned between the upper end portion and the lower end portion,
The positive electrode mixture is a positive electrode for an alkaline storage battery, wherein the content of the zinc compound at the upper end or the lower end is higher than the content of the zinc compound at the central portion. 前記正極合剤は、前記上端部又は前記下端部における亜鉛化合物の含有率が、表層の方が内部よりも高いことを特徴とする請求項１に記載のアルカリ蓄電池用の正極。   2. The positive electrode for an alkaline storage battery according to claim 1, wherein the positive electrode mixture has a zinc compound content in the upper end portion or the lower end portion higher in the surface layer than in the interior. 前記正極合剤は、前記中央部における前記亜鉛化合物の金属亜鉛換算での含有率に対して前記上端部又は前記下端部における前記亜鉛化合物の金属亜鉛換算での含有率の方が１〜７質量％高いことを特徴とする請求項１又は２に記載のアルカリ蓄電池用の正極。   In the positive electrode mixture, the content of the zinc compound in terms of metal zinc in the upper end or the lower end of the zinc compound in the center is 1 to 7 masses. The positive electrode for an alkaline storage battery according to claim 1 or 2, wherein the positive electrode is% higher. 上端開口が気密に封口された有底円筒状の外装缶と、
前記外装缶内にアルカリ電解液とともに収容された電極群とを備え、
前記電極群は、正極及び負極がこれらの間にセパレータを介在させて渦巻き状に巻回されてなり、
前記正極は、請求項１〜３の何れかに記載の正極であることを特徴とするアルカリ蓄電池。 A bottomed cylindrical outer can whose top opening is hermetically sealed;
An electrode group housed together with an alkaline electrolyte in the outer can,
The electrode group is formed by winding a positive electrode and a negative electrode in a spiral with a separator interposed therebetween,
The alkaline storage battery, wherein the positive electrode is the positive electrode according to claim 1.
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