JP3543601B2

JP3543601B2 - Alkaline storage battery

Info

Publication number: JP3543601B2
Application number: JP03995698A
Authority: JP
Inventors: 真澄勝本; 徳勝阿久津; 剛史八尾
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1998-02-23
Filing date: 1998-02-23
Publication date: 2004-07-14
Anticipated expiration: 2018-02-23
Also published as: JPH11238507A

Description

【０００１】
【発明の属する技術分野】
本発明は、ニッケル極を用いたアルカリ蓄電池に関し、深い放電がなされたまま放置した後での充電受入れ性を改良して充電後の容量回復性を高めると共に、その後の放電時にも初期とほぼ同等な正極活物質利用率が得られ、さらに充放電サイクルによる電池抵抗の増大を抑制し、長寿命なアルカリ蓄電池を提供するものである。
【０００２】
【従来の技術】
ニッケル−水素蓄電池、ニッケル−カドミウム蓄電池に代表されるアルカリ蓄電池に用いられる非焼結式ニッケル極は、従来より用いられている焼結式ニッケル極と比較して活物質充填密度が大きいニッケル極が得られ、また製造工程が簡便であるという特長を持つため、現在幅広く用いられている。
【０００３】
非焼結式ニッケル極の代表的なものとしては、９０％以上の多孔度を有するニッケルの発泡状もしくは繊維状の不織布を基体に用い、これにニッケル水酸化物を主成分とする活物質粉末を充填する方法が用いられている。しかし、このような非焼結式ニッケル極では、基体および極板としての導電性が低いために十分な活物質利用率が得られない。したがって活物質の導電性を高め、活物質利用率を向上させる必要があり、そのために導電剤として水酸化コバルト粉末や酸化コバルト粉末といった、２価のコバルト酸化物を導電剤として添加する方法が特開昭６２−２３７６６７号公報で提案されている。
【０００４】
このようにニッケル水酸化物と、水酸化コバルトや酸化コバルトなどの導電剤とを混合して充填したニッケル極は、アルカリ蓄電池に組み込まれると、コバルト化合物が電解液中にコバルト酸イオンとして溶解し、ニッケル水酸化物の表面に一様に分散して、その後、電池の初充電時に導電性の高いオキシ水酸化コバルトに酸化され、活物質相互間及び活物質と多孔性基体との間を繋ぐ導電性ネットワークを形成し、活物質の利用率を向上させる効果を有する。
【０００５】
さらに、電池の充放電サイクル寿命特性を向上させるために、水酸化ニッケルを主活物質とし、これに水酸化コバルトと共に亜鉛化合物を添加することが特開平４−１３７３６８号公報に提案されている。この活物質中に添加された亜鉛化合物は、ニッケル極の充放電の繰り返しにより生成するγ型オキシ水酸化ニッケル（γ−ＮｉＯＯＨ）の生成を抑制する効果を有する。これは、γ−ＮｉＯＯＨが、通常の充放電反応で生成するβ−ＮｉＯＯＨと比較して低密度であるため、充電によって正極板の膨張を引き起こすとともに、セパレータや負極中の電解液を吸収し、電池内の電解液分布の偏在を生じさせる。そして、電池の内部抵抗が増し、放電電圧、放電容量の低下が発生する。活物質中への亜鉛化合物あるいは金属亜鉛の添加によって、上記の電池の内部抵抗の増大を抑制し、電池としての充放電サイクル特性を向上させるものである。
【０００６】
近年の電子携帯機器では、例えばノートパソコンのように電源電池を使用する機会が増すにつれて、電源の切り忘れ等で電源電池が回路につながれた状態のまま、長期間放置されたままになることが増加している。このように電池を回路につないだ状態で長期間放置したままにしておくと、電池は通常の使用電圧範囲（０．８Ｖ以上）以下となるまで放電し、電池の容量がなくなった後もさらにこの放電状態のまま長期間放置された状態、いわゆる深放電状態となる。
【０００７】
深放電状態となった電池は、正極の電位がオキシ水酸化コバルトの還元電位（Ｈｇ／ＨｇＯ電極電位に対して約０Ｖ）以下となるため、導電性ネットワークを形成しているオキシ水酸化コバルトが還元、溶出してしまうという現象が発生する。このため、ひとたび深放電状態となった電池は、活物質相互間及び活物質と多孔性基体間に形成された導電性ネットワークが、部分的あるいは大幅に破壊されるために、充電受入性が低下し、その後に再度充電しても容量回復は十分でなく、ついで放電しても初期と同等の活物質利用率が得られなくなるという課題を有していた。
【０００８】
そこで、本発明者らは特願平９−６７６６９号において、従来より用いられている２価のコバルト酸化物に変わる導電剤として、リチウムとコバルトの複合酸化物粉末を用いることを提案した。リチウムとコバルトの複合酸化物は、還元雰囲気に対して安定であるため深放電により、正極電位が負極相当の電位である−０．９Ｖ（Ｈｇ／ＨｇＯ電極電位に対して）程度にまで低下しても分解、還元などが起こりにくく、深放電状態後の回復充電が効果的に行え、その後の放電で初期と変わらない高い活物質利用率を得ることができる。
【０００９】
【発明が解決しようとする課題】
しかしながら、上記リチウムとコバルトの複合酸化物を導電剤として活物質中に添加した電池は、正極の膨潤に伴う電池の内部抵抗の増大のために、充放電サイクルが進むにつれて放電容量が低下するという課題があった。
【００１０】
【課題を解決するための手段】
上記課題を解決するために本発明は、多孔性基体にニッケル水酸化物を活物質として充填した正極と、負極と、セパレータと、アルカリ電解液とからなるアルカリ蓄電池において、正極は、ニッケル水酸化物粉末を主体とし、これにリチウムとコバルトの複合酸化物粉末（ただし、一般式Ｌｉ _x ＣｏＯ _2-y で表される化合物を除く。）と、亜鉛化合物および／または金属亜鉛とを加えたものとし、前記リチウムとコバルトの複合酸化物粉末はナトリウムおよび／またはカリウムを含有しており、前記ナトリウムおよび／またはカリウムの量はコバルト量に対して２〜３０原子％であり、リチウムの量はコバルトのそれに対して１０〜９０原子％とした。
【００１１】
さらに、正極は、その表面の一部が少なくともリチウムとコバルトの複合酸化物（ただし、一般式Ｌｉ _x ＣｏＯ _2-y で表される化合物を除く。）で覆われたニッケル水酸化物粉末を主体とし、これに亜鉛化合物および／または金属亜鉛を混合する。前記リチウムとコバルトの複合酸化物はナトリウムおよび／またはカリウムを含有しており、前記ナトリウムおよび／またはカリウムの量はコバルト量に対して２〜３０原子％であり、リチウムの量はコバルトのそれに対して１０〜９０原子％とする。このようにしていると、リチウムとコバルトの複合酸化物とニッケル水酸化物粉末との密着性が高くなり、導電剤としての効果を十分に発揮させることができる。

【００１２】
【発明の実施の形態】
本発明の請求項１記載の発明は、多孔性基体にニッケル水酸化物を活物質として充填した正極と、負極と、セパレータと、アルカリ電解液とからなるアルカリ蓄電池において、前記正極は、ニッケル水酸化物粉末を主体とし、これにリチウムとコバルトの複合酸化物粉末と、亜鉛化合物および／または金属亜鉛とを混合しているアルカリ蓄電池としたものである。
【００１３】
これは、正極活物質の導電剤としてリチウムとコバルトの複合酸化物と、亜鉛化合物および／または金属亜鉛とを混合しているので、これを組み込んだアルカリ蓄電池では、還元雰囲気下で安定なリチウムとコバルトの複合酸化物が導電剤として働き、深放電状態となっても、その後に回復充電を行うことにより初期と同等の高い活物質利用率が得られる。それに加えて、亜鉛化合物および／または金属亜鉛を混合しているので、充放電に伴う正極の膨潤を抑制し、これにつれて電池抵抗の増大も抑制されるため、電池の充放電サイクル寿命特性が向上する。
【００１４】
さらに、従来の正極では、電解液中で溶解する水酸化コバルトや酸化コバルトと同時に亜鉛化合物を添加していたため、溶解したコバルトの錯イオンと亜鉛の錯イオンの混合物が正極上に析出し、導電性を悪化させ、電池の放電特性が低下するという課題を有していたが、本発明では、電解液中で不溶なリチウムとコバルトの複合酸化物と、亜鉛化合物および／または金属亜鉛を添加するため、このような放電特性の低下がないという効果を有している。
【００１５】
また、リチウムとコバルトの複合酸化物粉末は、ナトリウムおよび／またはカリウムをコバルト量に対して２〜３０原子％含有していて、リチウムの量はコバルトのそれに対して１０〜９０原子％であると、リチウムとコバルトの複合酸化物の粉末導電率をさらに向上させることができ、１ＣｍＡ以上の大きな電流で放電する高率放電にも対応した優れたアルカリ蓄電池を提供できる。
【００１６】
さらに、正極のニッケル水酸化物粉末は、その表面の少なくとも一部が上記の導電剤であるリチウムとコバルトの複合酸化物で覆っていると、リチウムとコバルトの複合酸化物とニッケル水酸化物粉末との密着性が高くなり、導電剤としての効果をより良好に発揮させることができる。
【００１７】
【実施例】
以下、本発明における詳細について実施例に基づいて説明する。なお、本発明は下記実施例により何ら限定されるものではなく、その要点を変更しない範囲において、適宜変更して実施することが可能なものである。
【００１８】
（実施例１）
ナトリウム原子を含有したリチウムとコバルトの複合酸化物を以下に示す方法により合成した。
【００１９】
平均粒径０．３μｍ以下であるＣｏ（ＯＨ）₂粒子１００ｇに対して４５重量部の水酸化ナトリウム水溶液２０ｃｃを含浸させ、１２０℃雰囲気下の大気中で１時間加熱酸化し、ナトリウム原子を層間に取り込んだ高次に酸化されたコバルト酸化物を得た。
【００２０】
このコバルト酸化物粉末と２．５ｍｏｌ／ｌの水酸化リチウム水溶液を重量比にて１：１０の割合で混合し、液温を８０℃に保持しながら、２時間攪拌処理し、十分に水洗、乾燥し、リチウムとコバルトの複合酸化物粉末を作製した。このリチウムとコバルトの複合酸化物粉末の平均粒径は０．３μｍ以下であった。
【００２１】
この処理により得られたリチウムとコバルトの複合酸化物の粉末中のリチウム、ナトリウム、コバルト量をＩＣＰ発光分析法で測定すると、リチウムはコバルトに対して４０原子％、ナトリウムはコバルトに対して１５原子％含有していることが確認された。
【００２２】
活物質である平均粒径が２０μｍの水酸化ニッケル粉末１００重量部に対して上記のリチウムとコバルトの複合酸化物粉末を導電剤として１０重量部、酸化亜鉛粉末を５重量部加えて粉末混合し、これらに分散媒として水を全ペーストにしめる量が２５重量部となるように加え、練合してペースト状活物質を作製した。これを多孔度９５％のスポンジ状ニッケル多孔体へ充填し、乾燥、加圧後、所定の寸法に切断して１６００ｍＡｈの理論電気容量を有する本発明の実施例における正極１を作製した。
【００２３】
また、平均粒子径２０μｍの水素吸蔵合金粉末を主体にペーストを調整してこれをパンチングメタルからなる芯体に塗着し、所定の寸法に切断し、理論電気容量２５００ｍＡｈの負極２を作製した。
【００２４】
上記で作製した正極１と、負極２とこの両者の間にポリプロピレン不織布製セパレータ３を介して渦巻き状に巻回して構成した極板群を、金属製電池ケース４の内部に挿入し、アルカリ電解液を所定量注入した後、ケース４の上部を正極端子を兼ねた封口板５で密閉して、図１に示す４／５Ａサイズのニッケル−水素蓄電池Ａを作製した。
【００２５】
（実施例２）
ナトリウム原子を含有したリチウムとコバルトの複合酸化物で被覆された水酸化ニッケル粉末を以下に示す方法により合成した。
【００２６】
平均粒径２０μｍの水酸化ニッケル粉末を水に懸濁させた溶液中に反応中ｐＨを９〜１０に維持するように比重１．３０の硫酸コバルト水溶液と２００ｇ／ｌの水酸化ナトリウム水溶液を添加して、水酸化ニッケルを結晶核として、この核の周囲に水酸化コバルトを析出させた。処理に用いる硫酸コバルト水溶液の添加量を調整することにより水酸化ニッケル粉末の周囲に形成される水酸化コバルトの被覆層の割合は水酸化ニッケル１００重量部に対して７重量部となるようにした。
【００２７】
この処理により得られた水酸化コバルトで被覆された水酸化ニッケル粉末を１２０℃雰囲気下の大気中で１時間加熱し、水酸化コバルト被覆層をナトリウムを層間に取り込んだ高次に酸化されたコバルト酸化物に変化させた。
【００２８】
この処理粉末を、５０ｇ／ｌの水酸化リチウムを溶解したアルカリ水溶液と重量比にて１：５の割合で混合し、液温を８０℃に保持しながら２時間攪拌処理を行うことにより、コバルト酸化物とリチウムを反応させ、リチウムとコバルトの複合酸化物による被覆層を薄く均一に形成させた。
【００２９】
これらに酸化亜鉛粉末を５重量部添加し、分散媒として水を全ペーストに占める量が２５重量部となるように加え、練合してペースト状活物質を作製し、これを多孔度９５％のスポンジ状ニッケル多孔体へ充填し、乾燥、加圧後、所定の寸法に切断して１６００ｍＡｈの理論電気容量を有する本発明における実施例の正極６を作製した。
【００３０】
この正極６を用いた以外は実施例１の電池Ａと同様な構成としたニッケル−水素蓄電池Ｂを作製した。
【００３１】
（比較例）
比較例として、正極中に酸化亜鉛を添加しないで、リチウムとコバルトの複合酸化物のみを導電剤として添加した電池についても評価を行った。
【００３２】
上記実施例１で用いたのと同様の処理により合成したナトリウム原子を含有したリチウムとコバルトの複合酸化物粉末１０重量部を水酸化ニッケル粉末１００重量部に対して添加し、実施例１と同様の処理により比較例による正極７を作製した。
【００３３】
この正極７を用いた以外は、実施例１の電池Ａと同様な構成としたニッケル−水素蓄電池Ｃを作製した。
【００３４】
実施例の電池Ａ，Ｂおよび比較例の電池Ｃについて、以下に示す条件でそれぞれ試験を行い、初期及び深放電状態後の正極活物質の利用率を調べた。
【００３５】
まず、２０℃雰囲気下にて、１６０ｍＡの電流（０．１ＣｍＡ）で１５時間充電し、１時間休止の後、３２０ｍＡの電流（０．２ＣｍＡ）で１．０Ｖの端子電圧に至るまで放電を行った。そのときの正極活物質の理論容量に対する実放電容量を初期の活物質利用率として求めた。
【００３６】
次に実施例の電池Ａ，Ｂ及び比較例電池Ｃに、それぞれ１Ωの抵抗をつないで放電したまま、６５℃雰囲気下に１４日間放置し、深放電状態とした。深放電状態後のそれぞれの電池の活物質利用率を初期の活物質利用率を求めた方法で算出し、すなわち深放電状態後の回復充電を施した後の放電時の正極活物質の利用率を算出し、その結果を（表１）に示す。
【００３７】
【表１】

【００３８】
（表１）に示すように、実施例の電池Ａ，Ｂは比較例の電池Ｃと同様に深放電状態後にも初期と変わらず、高い活物質利用率が得られる。これは正極の導電剤として添加しているリチウムとコバルトの複合酸化物は、酸化還元反応に対する高い安定性を有し、電池が深放電状態となっても分解や溶出反応による導電性ネットワークの破壊が起こりにくいためである。
【００３９】
次に、実施例の電池Ａ，Ｂ及び比較例の電池Ｃについて、以下に示す条件でそれぞれ試験を行い、サイクル充放電特性を調べた。
【００４０】
まず、２０℃雰囲気下にて、１６００ｍＡの電流（１ＣｍＡ）で１．５時間充電し、１時間の放置後、２０℃雰囲気下で１６００ｍＡの電流（１ＣｍＡ）で１．０Ｖの端子電圧に至るまで放電を行った。以上の充放電サイクルを１０００サイクル行い、電池容量の変化を調べた。その結果を図２に示す。
【００４１】
図２に示されるとおり活物質中に酸化亜鉛を添加した実施例電池は、酸化亜鉛を添加していない比較例電池と比べてサイクル充放電の経過に伴う電池容量の劣化が少ない。
【００４２】
また、（表２）に初期並びに１０００サイクル充放電後のそれぞれの電池の内部抵抗（交流抵抗）の比較を示す。
【００４３】
【表２】

【００４４】
（表２）に示されるとおり、活物質中に酸化亜鉛を添加した実施例電池では、酸化亜鉛を添加していない比較例電池と比べてサイクル充放電後の内部抵抗の増加量が少ないことがわかる。
【００４５】
これらの結果より、リチウムとコバルト複合酸化物を添加した活物質中にさらに酸化亜鉛を添加することにより、サイクル充放電後の内部抵抗の増大が少ない高寿命なアルカリ蓄電池が得られることがわかる。
【００４６】
上記実施例１の正極１では、水酸化ニッケル粉末１００重量部に対してナトリウムを含有させたリチウムとコバルトの複合酸化物粉末を導電剤として１０重量部混合したが、この導電剤の量としては３〜１５重量％の範囲であれば、正極１とほぼ同様な効果が得られる。
【００４７】
また、実施例１では、水酸化ニッケル粉末と平均粒径が０．３μｍ以下のリチウムとコバルトの複合酸化物とを用いて正極１を構成し、その正極１中でのリチウムとコバルトの複合酸化物粉末を均一に分散させた。しかし、水酸化ニッケル粉末と平均粒径が１μｍ以下のリチウムとコバルトの複合酸化物粉末を用いて正極を構成しても、正極１とほぼ同様に正極中のリチウムとコバルトの複合酸化物粉末を均一に分散させることができる。
【００４８】
実施例２の正極６の１００重量部の水酸化ニッケル粉末は、ナトリウムを含有させたリチウムとコバルトの複合酸化物を７重量部で被覆されている。水酸化ニッケル粉末を被覆する導電剤の量としては水酸化ニッケル粉末１００重量部に対して１〜１０重量部の範囲であれば、正極６とほぼ同様な効果が得られる。
【００４９】
また、上記実施例の正極１，６では、導電剤であるリチウムとコバルトの複合酸化物はナトリウムをコバルト量に対して１５原子％、リチウムを４０原子％含有させたが、この導電剤に含有させるナトリウムとリチウムの量は、コバルト量に対して、ナトリウムが２〜３０原子％、リチウムが１０〜９０原子％の範囲であれば、上記の正極１，６とほぼ同様な効果が得られる。
【００５０】
また、正極１，６では、ナトリウムを含有させたリチウムとコバルトの複合酸化物を導電剤として用いたが、これと同じ考えに基づいて、カリウムの単独か、あるいはナトリウムとカリウムの両方を含有させたリチウムとコバルトの複合酸化物を導電剤として用いても、正極１，６とほぼ同様な効果が得られる。
【００５１】
また、正極１，６では水酸化ニッケル１００重量部に対して酸化亜鉛粉末を５重量部添加しているが、水酸化亜鉛粉末または金属亜鉛粉末、あるいはこれらの亜鉛化合物粉末と金属亜鉛粉末との併用でも実施例と同様の効果が得られる。その添加量としては、水酸化ニッケル１００重量部に対して１〜８重量部の範囲の添加であれば実施例と同様の効果が得られる。
【００５２】
さらに、上記実施例では正極活物質粉末として水酸化ニッケルを用いた場合について示したが、水酸化ニッケルを主成分とし、コバルトや亜鉛を少量含有する固溶体粉末においても、実施例とほぼ同様な効果が得られる。また、水酸化ニッケルが一部オキシ水酸化ニッケルに酸化されたニッケル水酸化物粉末を用いた場合でもほぼ同様な効果が得られる。
【００５３】
さらにまた、上記実施例では、電池として正極にニッケル極、負極に水素吸蔵合金極を用いた場合を示したが、本発明はアルカリ蓄電池のニッケル極に関するものであり、負極にカドミウム、鉄、亜鉛極などを用いた電池にも適用できる。
【００５４】
【発明の効果】
以上のように本発明では、多孔性基体にニッケル水酸化物を活物質として充填した正極と、負極と、セパレータと、アルカリ電解液とからなるアルカリ蓄電池の正極に、ニッケル水酸化物を主体とした粉末に、リチウムとコバルトの複合酸化物粉末と亜鉛化合物粉末および／または金属亜鉛粉末を加えたので、電池の深放電後の容量回復特性が優れ、さらに充放電サイクルによる内部抵抗の増大を抑制した、長寿命なアルカリ蓄電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例１におけるニッケル−水素蓄電池の半裁断面図
【図２】本発明の実施例における電池の充放電サイクル数と放電容量との関係を示す図
【符号の説明】
１正極
２負極
３セパレータ
４電池ケース
５封口板[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an alkaline storage battery using a nickel electrode, which improves the charge acceptability after being left in a state where deep discharge has been performed, improves the capacity recovery after charging, and is substantially equivalent to the initial state at the time of subsequent discharge. An object of the present invention is to provide a long-life alkaline storage battery that can obtain a high positive electrode active material utilization rate and further suppresses an increase in battery resistance due to charge / discharge cycles.
[0002]
[Prior art]
Non-sintered nickel electrodes used for alkaline storage batteries typified by nickel-hydrogen storage batteries and nickel-cadmium storage batteries have a nickel electrode having a larger active material filling density than conventionally used sintered nickel electrodes. It is widely used at present because it has the features of being obtained and its simple manufacturing process.
[0003]
As a typical non-sintered nickel electrode, a foamed or fibrous non-woven fabric of nickel having a porosity of 90% or more is used as a substrate, and an active material powder mainly composed of nickel hydroxide is used. Is used. However, in such a non-sintered nickel electrode, a sufficient active material utilization rate cannot be obtained due to low conductivity of the base and the electrode plate. Therefore, it is necessary to increase the conductivity of the active material and improve the utilization rate of the active material. For this purpose, a method of adding a bivalent cobalt oxide such as a cobalt hydroxide powder or a cobalt oxide powder as a conductive agent is a special method. This is proposed in Japanese Unexamined Patent Publication No. 62-237667.
[0004]
When a nickel electrode filled with a mixture of nickel hydroxide and a conductive agent such as cobalt hydroxide or cobalt oxide is incorporated in an alkaline storage battery, the cobalt compound dissolves as cobaltate ions in the electrolytic solution. , Uniformly dispersed on the surface of nickel hydroxide, and then oxidized to highly conductive cobalt oxyhydroxide at the time of initial charging of the battery, connecting between active materials and between the active material and the porous substrate It has the effect of forming a conductive network and improving the utilization rate of the active material.
[0005]
Japanese Patent Application Laid-Open No. Hei 4-137368 proposes that nickel hydroxide is used as a main active material and a zinc compound is added to the main active material together with cobalt hydroxide in order to improve the charge / discharge cycle life characteristics of the battery. The zinc compound added to the active material has an effect of suppressing the generation of γ-type nickel oxyhydroxide (γ-NiOOH) generated by repeated charge and discharge of the nickel electrode. This is because γ-NiOOH has a lower density than β-NiOOH generated by a normal charge / discharge reaction, causes charging to expand the positive electrode plate, and absorbs electrolyte in the separator and the negative electrode, This causes uneven distribution of the electrolyte solution in the battery. Then, the internal resistance of the battery increases, and the discharge voltage and the discharge capacity decrease. By adding a zinc compound or metallic zinc to the active material, an increase in the internal resistance of the battery is suppressed, and the charge / discharge cycle characteristics of the battery are improved.
[0006]
In recent years, with the increasing use of power batteries, such as laptop computers, in electronic portable devices in recent years, the frequency of power batteries being left connected to circuits due to forgetting to turn off the power, etc., has increased for a long time. are doing. If the battery is left for a long time with the battery connected to the circuit, the battery will be discharged until the voltage falls below the normal operating voltage range (0.8 V or more), and even after the battery has run out of capacity. A state in which the discharge state is left for a long time, that is, a so-called deep discharge state.
[0007]
In the battery in the deep discharge state, the potential of the positive electrode becomes equal to or lower than the reduction potential of cobalt oxyhydroxide (about 0 V with respect to the potential of the Hg / HgO electrode). The phenomenon of reduction and elution occurs. For this reason, once the battery is in a deep discharge state, the conductive network formed between the active materials and between the active material and the porous substrate is partially or significantly destroyed, and the charge acceptability decreases. However, there is a problem that even if the battery is recharged thereafter, the capacity is not sufficiently recovered, and even if the battery is subsequently discharged, the same active material utilization as in the initial stage cannot be obtained.
[0008]
Therefore, the present inventors have proposed in Japanese Patent Application No. 9-67669 that a composite oxide powder of lithium and cobalt is used as a conductive agent instead of a conventionally used divalent cobalt oxide. Since the composite oxide of lithium and cobalt is stable in a reducing atmosphere, the potential of the positive electrode drops to about −0.9 V (relative to the potential of the Hg / HgO electrode) corresponding to the negative electrode by deep discharge. However, decomposition, reduction, and the like are unlikely to occur, and recovery charging after a deep discharge state can be performed effectively, and a high active material utilization rate that is the same as the initial state in subsequent discharge can be obtained.
[0009]
[Problems to be solved by the invention]
However, in a battery in which the above-described composite oxide of lithium and cobalt is added as a conductive agent in an active material, the discharge capacity decreases as the charge / discharge cycle progresses due to an increase in internal resistance of the battery due to swelling of the positive electrode. There were challenges.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides an alkaline storage battery including a positive electrode in which a porous substrate is filled with nickel hydroxide as an active material, a negative electrode, a separator, and an alkaline electrolyte. Powder, to which a composite oxide powder of lithium and cobalt ( excluding the compound represented by the general formula Li _x CoO _2-y ) and a zinc compound and / or metallic zinc are added. Wherein the composite oxide powder of lithium and cobalt contains sodium and / or potassium, the amount of sodium and / or potassium is 2 to 30 atomic% based on the amount of cobalt, and the amount of lithium is cobalt Was set to 10 to 90 atomic% .
[0011]
Further, the positive electrode mainly comprises a nickel hydroxide powder whose surface is partially covered with at least a composite oxide of lithium and cobalt ( excluding the compound represented by the general formula Li _x CoO _2-y ). And a zinc compound and / or zinc metal is mixed therein. The composite oxide of lithium and cobalt contains sodium and / or potassium, and the amount of sodium and / or potassium is 2 to 30 atomic% based on the amount of cobalt, and the amount of lithium is based on that of cobalt. 10 to 90 atomic%. By doing so , the adhesion between the composite oxide of lithium and cobalt and the nickel hydroxide powder is increased, and the effect as a conductive agent can be sufficiently exhibited.

[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 of the present invention is directed to an alkaline storage battery including a positive electrode in which a porous substrate is filled with nickel hydroxide as an active material, a negative electrode, a separator, and an alkaline electrolyte. This is an alkaline storage battery mainly composed of an oxide powder and mixed with a composite oxide powder of lithium and cobalt, and a zinc compound and / or zinc metal.
[0013]
This is because a lithium-cobalt composite oxide and a zinc compound and / or metallic zinc are mixed as a conductive agent of the positive electrode active material, and in an alkaline storage battery incorporating the same, lithium stable under a reducing atmosphere is used. Even when the composite oxide of cobalt functions as a conductive agent and is in a deep discharge state, by performing recovery charging thereafter, a high active material utilization rate equivalent to the initial state can be obtained. In addition, since the zinc compound and / or zinc metal is mixed, the swelling of the positive electrode due to charge and discharge is suppressed, and the increase in battery resistance is also suppressed, thereby improving the charge-discharge cycle life characteristics of the battery. I do.
[0014]
Furthermore, in the conventional positive electrode, a zinc compound was added simultaneously with the cobalt hydroxide and cobalt oxide dissolved in the electrolytic solution, so that a mixture of the dissolved cobalt complex ion and zinc complex ion was deposited on the positive electrode, and the conductive material was electrically conductive. However, in the present invention, a composite oxide of lithium and cobalt, which is insoluble in the electrolytic solution, and a zinc compound and / or zinc metal are added. Therefore, there is an effect that the discharge characteristics do not deteriorate.
[0015]
Further, the composite oxide powder of lithium and cobalt contains sodium and / or potassium in an amount of 2 to 30 atomic% based on the amount of cobalt, and the amount of lithium is 10 to 90 atomic% based on that of cobalt. In addition, it is possible to further improve the powder conductivity of the composite oxide of lithium and cobalt, and to provide an excellent alkaline storage battery that can cope with high-rate discharge in which discharge is performed with a large current of 1 CmA or more.
[0016]
Further, when at least a part of the surface of the nickel hydroxide powder of the positive electrode is covered with the above-described composite oxide of lithium and cobalt as the conductive agent, the composite oxide of lithium and cobalt and the nickel hydroxide powder And the adhesiveness to the conductive agent is enhanced, and the effect as a conductive agent can be exhibited more favorably.
[0017]
【Example】
Hereinafter, details of the present invention will be described based on examples. It should be noted that the present invention is not limited in any way by the following examples, and can be implemented with appropriate changes without departing from the scope of the invention.
[0018]
(Example 1)
A composite oxide of lithium and cobalt containing a sodium atom was synthesized by the following method.
[0019]
100 g of Co (OH) ₂ particles having an average particle diameter of 0.3 μm or less are impregnated with 20 cc of a 45 parts by weight aqueous solution of sodium hydroxide, and heated and oxidized for 1 hour in an atmosphere at 120 ° C. To obtain a high-order oxidized cobalt oxide.
[0020]
This cobalt oxide powder and a 2.5 mol / l aqueous solution of lithium hydroxide were mixed at a weight ratio of 1:10, and the mixture was stirred for 2 hours while maintaining the liquid temperature at 80 ° C., and sufficiently washed with water. After drying, a composite oxide powder of lithium and cobalt was prepared. The composite oxide powder of lithium and cobalt had an average particle size of 0.3 μm or less.
[0021]
When the amounts of lithium, sodium and cobalt in the powder of the composite oxide of lithium and cobalt obtained by this treatment were measured by ICP emission spectrometry, lithium was 40 atom% with respect to cobalt, and sodium was 15 atom with respect to cobalt. % Was confirmed.
[0022]
10 parts by weight of the above-mentioned composite oxide powder of lithium and cobalt as a conductive agent and 5 parts by weight of zinc oxide powder were added to 100 parts by weight of nickel hydroxide powder having an average particle size of 20 μm as an active material, and the powders were mixed. Then, water was added as a dispersion medium to the whole paste so that the total amount became 25 parts by weight, and kneaded to prepare a paste-like active material. This was filled into a sponge-like nickel porous body having a porosity of 95%, dried, pressurized, and then cut into a predetermined size to prepare a positive electrode 1 having a theoretical electric capacity of 1600 mAh in an example of the present invention.
[0023]
In addition, a paste was prepared mainly with a hydrogen storage alloy powder having an average particle diameter of 20 μm, and the paste was applied to a core made of punched metal, and cut into a predetermined size to produce a negative electrode 2 having a theoretical electric capacity of 2500 mAh.
[0024]
The positive electrode 1 and the negative electrode 2 prepared as above and the electrode plate group formed by spirally winding the two between the two via a polypropylene nonwoven fabric separator 3 are inserted into the inside of the metal battery case 4, and the alkaline electrolysis is performed. After injecting a predetermined amount of the liquid, the upper part of the case 4 was sealed with a sealing plate 5 also serving as a positive electrode terminal, thereby producing a 4 / 5A size nickel-hydrogen storage battery A shown in FIG.
[0025]
(Example 2)
A nickel hydroxide powder coated with a lithium-cobalt composite oxide containing sodium atoms was synthesized by the following method.
[0026]
An aqueous solution of cobalt sulfate having a specific gravity of 1.30 and an aqueous solution of sodium hydroxide of 200 g / l were added to a solution in which nickel hydroxide powder having an average particle size of 20 μm was suspended in water so that the pH was maintained at 9 to 10 during the reaction. Then, nickel hydroxide was used as a crystal nucleus to precipitate cobalt hydroxide around the nucleus. The proportion of the cobalt hydroxide coating layer formed around the nickel hydroxide powder was adjusted to 7 parts by weight with respect to 100 parts by weight of nickel hydroxide by adjusting the addition amount of the aqueous solution of cobalt sulfate used for the treatment. .
[0027]
The nickel hydroxide powder coated with cobalt hydroxide obtained by this treatment is heated for 1 hour in the air under an atmosphere of 120 ° C. to form a cobalt oxide coating layer containing sodium intercalated between high order oxidized cobalt. Changed to oxide.
[0028]
This treated powder was mixed with an aqueous alkali solution in which 50 g / l of lithium hydroxide was dissolved at a weight ratio of 1: 5, and the mixture was stirred for 2 hours while maintaining the liquid temperature at 80 ° C. to obtain cobalt powder. The oxide and lithium were reacted to form a thin and uniform coating layer of a composite oxide of lithium and cobalt.
[0029]
To these, 5 parts by weight of zinc oxide powder was added, and water was added as a dispersion medium so that the amount occupying 25 parts by weight of the whole paste was kneaded to prepare a paste-like active material. Was dried, pressurized, and then cut to a predetermined size to produce a positive electrode 6 of the present invention having a theoretical electric capacity of 1600 mAh.
[0030]
A nickel-hydrogen storage battery B having the same configuration as the battery A of Example 1 except that the positive electrode 6 was used was produced.
[0031]
(Comparative example)
As a comparative example, a battery in which only a composite oxide of lithium and cobalt was added as a conductive agent without adding zinc oxide to the positive electrode was also evaluated.
[0032]
As in Example 1, 10 parts by weight of a lithium-cobalt composite oxide powder containing sodium atoms synthesized by the same treatment as used in Example 1 was added to 100 parts by weight of nickel hydroxide powder. The positive electrode 7 according to the comparative example was produced by the treatment described above.
[0033]
A nickel-hydrogen storage battery C having the same configuration as that of the battery A of Example 1 except that the positive electrode 7 was used was produced.
[0034]
The batteries A and B of the example and the battery C of the comparative example were respectively tested under the following conditions, and the utilization rates of the positive electrode active material in the initial stage and after the deep discharge state were examined.
[0035]
First, in a 20 ° C. atmosphere, the battery is charged at a current of 160 mA (0.1 CmA) for 15 hours, and after a pause of 1 hour, discharged at a current of 320 mA (0.2 CmA) until a terminal voltage of 1.0 V is reached. Was. The actual discharge capacity with respect to the theoretical capacity of the positive electrode active material at that time was determined as the initial active material utilization rate.
[0036]
Next, each of the batteries A and B of the example and the battery C of the comparative example were left in a 65 ° C. atmosphere for 14 days while being discharged while being connected with a resistance of 1 Ω, to be in a deep discharge state. The active material utilization rate of each battery after the deep discharge state is calculated by the method of obtaining the initial active material utilization rate, that is, the utilization rate of the positive electrode active material at the time of discharge after performing the recovery charge after the deep discharge state Is calculated, and the results are shown in (Table 1).
[0037]
[Table 1]

[0038]
As shown in (Table 1), the batteries A and B of the example are similar to the battery C of the comparative example even after the deep discharge state, and the high active material utilization is obtained. This is because the composite oxide of lithium and cobalt added as a conductive agent for the positive electrode has high stability against oxidation-reduction reactions, and even when the battery is in a deep discharge state, the conductive network is destroyed due to decomposition and elution reactions. Is difficult to occur.
[0039]
Next, tests were performed on the batteries A and B of the example and the battery C of the comparative example under the following conditions to examine the cycle charge / discharge characteristics.
[0040]
First, charge at 1600 mA current (1 CmA) for 1.5 hours in a 20 ° C. atmosphere, leave for 1 hour, and then reach a terminal voltage of 1.0 V at a current of 1600 mA (1 CmA) in a 20 ° C. atmosphere. Discharge was performed. The above charge / discharge cycle was performed 1000 times, and the change in battery capacity was examined. The result is shown in FIG.
[0041]
As shown in FIG. 2, in the example battery in which zinc oxide was added to the active material, the battery capacity was less deteriorated with the progress of cycle charge and discharge than in the comparative example battery in which zinc oxide was not added.
[0042]
Table 2 shows a comparison of the internal resistance (AC resistance) of each battery at the initial stage and after 1000 cycles of charging and discharging.
[0043]
[Table 2]

[0044]
As shown in Table 2, the increase in the internal resistance after cycle charge / discharge was smaller in the example battery in which zinc oxide was added to the active material than in the comparative example battery in which zinc oxide was not added. Understand.
[0045]
From these results, it can be seen that by further adding zinc oxide to the active material to which lithium and cobalt composite oxide has been added, a long-life alkaline storage battery with a small increase in internal resistance after cycle charge / discharge can be obtained.
[0046]
In the positive electrode 1 of Example 1, 100 parts by weight of nickel hydroxide powder and 10 parts by weight of a composite oxide powder of lithium and cobalt containing sodium as a conductive agent were mixed. In the range of 3 to 15% by weight, substantially the same effects as those of the positive electrode 1 can be obtained.
[0047]
In Example 1, the positive electrode 1 was formed using nickel hydroxide powder and a composite oxide of lithium and cobalt having an average particle diameter of 0.3 μm or less, and the composite oxide of lithium and cobalt in the positive electrode 1 was formed. The product powder was uniformly dispersed. However, even when the positive electrode is formed using the nickel hydroxide powder and the composite oxide powder of lithium and cobalt having an average particle diameter of 1 μm or less, the composite oxide powder of lithium and cobalt in the positive electrode is substantially similar to the positive electrode 1. It can be uniformly dispersed.
[0048]
100 parts by weight of nickel hydroxide powder of the positive electrode 6 of Example 2 is coated with 7 parts by weight of a composite oxide of lithium and cobalt containing sodium. As long as the amount of the conductive agent for coating the nickel hydroxide powder is in the range of 1 to 10 parts by weight with respect to 100 parts by weight of the nickel hydroxide powder, substantially the same effect as that of the positive electrode 6 can be obtained.
[0049]
In the positive electrodes 1 and 6 of the above examples, the composite oxide of lithium and cobalt as the conductive agent contained 15 atomic% of sodium and 40 atomic% of lithium with respect to the amount of cobalt. As for the amounts of sodium and lithium to be provided, if sodium is in the range of 2 to 30 at% and lithium is in the range of 10 to 90 at% with respect to the cobalt amount, substantially the same effects as those of the positive electrodes 1 and 6 can be obtained.
[0050]
In the positive electrodes 1 and 6, a composite oxide of lithium and cobalt containing sodium was used as the conductive agent. Based on the same idea, potassium alone or both sodium and potassium were used. Even when the composite oxide of lithium and cobalt is used as the conductive agent, substantially the same effects as those of the positive electrodes 1 and 6 can be obtained.
[0051]
Further, in the positive electrodes 1 and 6, 5 parts by weight of zinc oxide powder was added to 100 parts by weight of nickel hydroxide, but zinc hydroxide powder or metal zinc powder, or a mixture of these zinc compound powder and metal zinc powder was used. The same effect as that of the embodiment can be obtained by the combined use. The same effect as that of the embodiment can be obtained as long as the amount is in the range of 1 to 8 parts by weight with respect to 100 parts by weight of nickel hydroxide.
[0052]
Further, in the above embodiment, the case where nickel hydroxide was used as the positive electrode active material powder was shown. However, even with a solid solution powder containing nickel hydroxide as a main component and a small amount of cobalt or zinc, almost the same effects as those of the embodiment were obtained. Is obtained. In addition, substantially the same effect can be obtained when nickel hydroxide powder in which nickel hydroxide is partially oxidized to nickel oxyhydroxide is used.
[0053]
Furthermore, in the above embodiment, the case where a nickel electrode was used as a positive electrode and a hydrogen storage alloy electrode was used as a negative electrode as a battery, but the present invention relates to a nickel electrode of an alkaline storage battery, and cadmium, iron, and zinc were used as a negative electrode. It can also be applied to batteries using electrodes and the like.
[0054]
【The invention's effect】
As described above, in the present invention, a positive electrode filled with a nickel hydroxide as an active material in a porous substrate, a negative electrode, a separator, and a positive electrode of an alkaline storage battery including an alkaline electrolyte mainly include nickel hydroxide. The lithium-cobalt composite oxide powder, zinc compound powder, and / or zinc metal powder are added to the powder thus obtained, so that the capacity recovery characteristics after deep discharge of the battery are excellent, and the increase in internal resistance due to charge / discharge cycles is suppressed. Thus, a long-life alkaline storage battery can be provided.
[Brief description of the drawings]
FIG. 1 is a half cross-sectional view of a nickel-hydrogen storage battery according to a first embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity of the battery according to the first embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery case 5 Sealing plate

Claims

Positive electrode filled with nickel hydroxide as an active material in a porous substrate, a negative electrode, a separator, in an alkaline storage battery comprising an alkaline electrolyte, the positive electrode,
(A) A mixture mainly composed of nickel hydroxide powder, (b) (i) cobalt hydroxide and (ii) an aqueous solution of sodium hydroxide and / or potassium hydroxide, and heating. A composite oxide powder of lithium and cobalt obtained by heating in
(C) mixed with a zinc compound and / or metallic zinc,
The composite oxide powder of lithium and cobalt contains sodium and / or potassium, the amount of the sodium and / or potassium is 2 to 30 atomic% based on the amount of cobalt, and the amount of lithium is Alkaline storage batteries whose content is 10 to 90 atomic%.

Alkaline storage battery of claim 1 Symbol placement average particle size of the composite oxide powder of lithium and cobalt is 1μm or less.

Mixing of the composite oxide powder of lithium and cobalt, according to claim 1 Symbol placement alkaline storage battery 3 to 15 parts by weight per 100 parts by weight of nickel hydroxide powder.

Zinc compounds, according to claim 1 Symbol placement alkaline storage battery is zinc oxide or zinc hydroxide.

Zinc compounds and / or mixtures of metal zinc claim 1 Symbol placement alkaline storage battery 1 to 8 parts by weight per 100 parts by weight of nickel hydroxide powder.

In an alkaline storage battery comprising a positive electrode filled with a nickel hydroxide powder as an active material in a porous substrate, a negative electrode, a separator, and an alkaline electrolyte, the positive electrode has at least a part of a composite oxide of lithium and cobalt. (Except for the compound represented by the general formula Li _x CoO _2-y ), which is mainly composed of a nickel hydroxide powder covered with a zinc compound and / or metallic zinc. The composite oxide of lithium and cobalt contains sodium and / or potassium, and the amount of sodium and / or potassium is 2 to 30 atomic% based on the amount of cobalt, and the amount of lithium is based on that of cobalt. An alkaline storage battery of 10 to 90 atomic%.

The alkaline storage battery according to claim 6 , wherein the amount of the composite oxide of lithium and cobalt is 1 to 10 parts by weight based on 100 parts by weight of the nickel hydroxide powder.

The alkaline storage battery according to claim 6 , wherein the zinc compound is zinc oxide or zinc hydroxide.

The alkaline storage battery according to claim 6 , wherein the amount of the zinc compound and / or zinc metal is 1 to 8 parts by weight based on 100 parts by weight of the nickel hydroxide powder.