JP3653441B2

JP3653441B2 - Method for producing negative electrode for alkaline storage battery

Info

Publication number: JP3653441B2
Application number: JP2000082012A
Authority: JP
Inventors: 彰平川; 太郎赤澤; 哲也菊池
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 2000-03-23
Filing date: 2000-03-23
Publication date: 2005-05-25
Anticipated expiration: 2020-03-23
Also published as: JP2001266858A

Description

【０００１】
【発明の属する技術分野】
本発明はニッケル−カドミウム蓄電池、ニッケル−水素蓄電池等のアルカリ蓄電池に用いられるアルカリ蓄電池用負極およびその製造方法に関する。
【０００２】
【従来の技術】
従来、ニッケル−カドミウム蓄電池に用いるカドミウム負極には、ニッケル粉末を焼結して形成した多孔性焼結基板に酸化カドミウムあるいは水酸化カドミウムよりなる負極活物質を充填した焼結式負極と、酸化カドミウムあるいは水酸化カドミウムよりなる負極活物質と糊料等を混練してペースト状としてパンチングメタル等の導電性芯体に塗着した非焼結式負極とがある。このうち、非焼結式負極は、低コストで高エネルギー密度といった点で主流になりつつある。
【０００３】
近年、アルカリ蓄電池のさらなる高容量化、大電流充放電が可能、長寿命などの要求が高まり、これらの要求に応えるために、この種の非焼結式負極においても種々の改良が行われた。例えば、活物質の充填密度を増加させることにより高容量化がなされるようになった。
しかしながら、活物質の充填密度を増加させると、活物質層内の空孔が減少するため、活物質と酸素ガスの接触がし難くなることから、酸素ガス吸収性能が低下したり、カドミウム負極においては充放電サイクル中に活物質がセパレータに移行するマイグレーションがより加速され、早期にショートに至らしめる等の問題を生じる。
【０００４】
【発明が解決しようとする課題】
そこで、導電性粉末とポリビニルピロリドン（ＰＶＰ）により負極表面に導電層を形成するとともに、導電性粉末とＰＶＰとの混合比率を最適化することが、特開平６−２４３８６３号公報にて提案されるようになった。このように、導電性粉末とＰＶＰを負極表面に備えると、ＰＶＰは耐アルカリ性に優れ、かつ負極表面に塗着、乾燥すると硬質な微多孔膜を形成するため、アルカリ電解液によって膨潤することなく高い強度を維持して、導電層の強度が大きくなり、充放電サイクルが進行しても導電層の破壊が抑制されて、酸素ガス吸収性能を向上させることができる。
【０００５】
しかしながら、特開平６−２４３８６３号公報で提案された負極にあっては、導電層の強度を向上させるためには、ＰＶＰの添加量を多くする必要があるが、ＰＶＰの添加量を多くすると、導電層の導電性が低下してガス吸収性能を悪化させるという問題を生じるようになり、導電層の強度を向上とガス吸収性能とを両立させることが難しく、特に、高率放電、高率充電という過酷なサイクル条件ではこれらを両立させることが困難になるという問題を生じた。
【０００６】
一方、カドミウム負極の表面に金属カドミウム等の導電性粉末とフッ素樹脂粉末との混合層を形成させ、表面層を除く内部活物質層に結着剤としてのポリビニルアルコール（ＰＶＡ）を含有させた負極が、特開平４−１９９６３公報にて提案されている。これによれば、負極表面に形成された混合層に撥水性を有するフッ素樹脂を添加しているので、酸素ガスとの接触が良好になって、ガス吸収性が向上する。
【０００７】
しかしながら、特開平４−１９９６３公報にて提案された負極にあっては、負極表面に形成された導電性粉末を含む混合層に結着剤が含有されいないため、この混合層の強度が弱いとともに、活物質層との接合も充分でない。このため、充放電サイクルの進行に伴って、負極活物質の体積変化に起因して活物質の脱落が生じやすくなるとともに、酸素ガスの吸収性能を維持できないばかりか、マイグレーション（充放電時に負極内に存在する電解液に溶解したカドミウム中間体がセパレータに移動する現象）の抑制効果も維持できないという問題を生じた。
【０００８】
また、水素吸蔵合金を結着剤で一体化して水素吸蔵合金電極とした後、この電極表面に水蒸気を吹き付けて結着剤を溶解除去するとともに、水蒸気中に結着剤の溶解促進剤を含有させることが、特許第２９７５７９０号公報に提案されている。これによれば、電極表面の水素吸蔵合金を被覆した結着剤皮膜が溶解、除去されることにより、酸素ガスとの接触が容易になってガス吸収性能が向上するようになる。
しかしながら、特許第２９７５７９０号公報にて提案された負極にあっては、電極表面の結着剤を活物質表面が露出するまで溶解、除去する必要があるため、電極表面近傍の活物質同士の結着強度が低下するという問題を生じた。
【０００９】
本発明は上記の各問題点を解消するためになされたものであって、密着強度およびガス吸収性能に優れた導電層を電極表面に備えたアルカリ蓄電池用負極を提供して、充放電サイクル特性に優れた設けられたアルカリ蓄電池を提供することを目的とするものである。
【００１０】
【課題を解決するための手段】
上記目的を達成するため、本発明のアルカリ蓄電池用負極は、負極活物質層の表面に導電性粉末と有機高分子糊料とを含有した第１溶液を塗着した後、乾燥させる工程と、第１溶液と同様の導電性粉末と有機高分子糊料とを含有し、かつ第１溶液よりも有機高分子糊料の添加量が少ない第２溶液を第１溶液が塗着乾燥された負極活物質層の表面に塗着した後、乾燥させる工程とを備えるようにしている。これにより、有機高分子糊料の含有割合が導電層の表面から活物質層に向うに伴って高くなるので、活物質層と導電層間の密着強度が向上する。この結果、電池の充放電サイクルに伴う活物質の体積変化、形態変化に対しても導電層が容易に破壊や脱落を生じないため、ガス吸収性能およびマイグレーションの抑制の持続的な効果を維持できるようになる。
【００１１】
また、導電層の表面の有機高分子糊料の添加割合は低くなっているため、導電層の表面の導電性粉末同士の接触抵抗が低減して導電性を向上させることが可能となり、酸素ガスとの接触が容易になって、酸素ガスの吸収性能に優れた負極となる。この場合、第１溶液と第２溶液の少なくとも一方の溶液にフッ素樹脂を含有させたり、あるいは、第１溶液と第２溶液の両方の溶液はフッ素樹脂を含有させるとともに、第２溶液に含有されるフッ素樹脂の添加量を多くすると、フッ素樹脂を導電層の表面近傍に局在させることが可能となる。これにより、導電層の表面での撥水性が向上して、より一層、酸素ガスの吸収性能に優れた負極となる。
【００１２】
なお、導電性粉末としては、ニッケル、カドミウムなどの金属粉末、アセチレンブラック、ケッチェンブラック、黒鉛などの炭素粉末あるいは炭素繊維を使用することができるが、特に、酸素ガス吸収およびカドミウム負極におけるマイグレーション抑制効果、取り扱い易さ、コストの点でアセチレンブラック、ケッチェンブラック、黒鉛などの炭素粉末を用いることが好ましい。また、有機高分子糊料としては、種々の有機高分子糊料を使用することができるが、取り扱い易さの点で水溶性の糊料が望ましく、電池内の雰囲気中での機械的強度および耐分解性に優れたポリビニルピロリドン（ＰＶＰ）を用いることが好ましい。
【００１６】
【発明の実施の形態】
ついで、本発明をニッケル−カドミウム蓄電池に用いられるカドミウム負極に適用した場合の実施の形態を、図に基づいて以下に説明する。なお、図１はカドミウム負極を模式的に示す斜視図であり、図２はカドミウム負極ａ，ｃの要部を拡大して示す断面図であり、図３はカドミウム負極ｂ，ｄの要部を拡大して示す断面図である。また、図４はカドミウム負極ｘの要部を拡大して示す断面図であり、図５はカドミウム負極ｙの要部を拡大して示す断面図である。
【００１７】
１．カドミウム負極の作製
（１）カドミウム負極ａ
酸化カドミウム粉末を主体とし、これに結着剤と水を加えて混練して活物質ペーストを調製した後、この活物質ペーストをパンチングメタルよりなる導電性芯体の両面に塗着し、乾燥させて活物質塗着極板１０を作製した。ついで、この活物質塗着極板１０の表面に、アセチレンブラック１０質量部と、ポリビニルピロリドン（ＰＶＰ）１０質量部と、水８０質量部とからなる第１溶液を塗着した後、乾燥させて、活物質塗着極板１０の表面に導電層１１を形成した。
【００１８】
ついで、表面に導電層１１が形成された活物質塗着極板１０の導電層１１の上に、少量（極板からたれ落ちない程度）の水（第２溶液）を塗布した後、所定時間（例えば、約１分）放置して極板中に浸透させた。ついで、乾燥させてカドミウム負極板を作製した。これをカドミウム負極ａとした。なお、導電層１１の表面に水（なお、水はＰＶＰを溶解させる）を塗布すると、図２に示すように、水はＰＶＰ１２を溶解させながら導電層１１の内部に浸透して行くため、負極活物質層１０の表面に近いほどＰＶＰ１２の含有割合が高くなる。
【００１９】
（２）カドミウム負極ｂ
上述と同様に作製した活物質塗着極板１０を用い、この活物質塗着極板１０の表面に、アセチレンブラック１０質量部と、ＰＶＰ１０質量部と、水８０質量部とからなる第１溶液を塗着した後、乾燥させて、活物質塗着極板１０の表面に導電層１１を形成した。ついで、表面に導電層１１が形成された活物質塗着極板１０の導電層１１の上に、フッ素樹脂（例えば、ＰＴＦＥ）ディスパージョンを加えた水（第２溶液）を塗布した後、所定時間（例えば、約１分）放置して極板中に浸透させた。ついで、乾燥させてカドミウム負極板を作製した。これをカドミウム負極ｂとした。
【００２０】
なお、導電層１１の表面に水を塗布すると、図３に示すように、水はＰＶＰ１２を溶解させながら導電層１１の内部に浸透して行くため、負極活物質層１０の表面に近いほどＰＶＰ１２の含有割合が高くなる。また、水がＰＶＰを溶解させながら導電層１１の内部に浸透して行く際に、フッ素樹脂（例えば、ＰＴＦＥ）は水よりも浸透速度が遅くなるため、図３に示すように、フッ素樹脂１３を導電層１１の表面近傍に局在させることが可能となる。
【００２１】
（３）カドミウム負極ｃ
上述と同様に作製した活物質塗着極板１０を用い、この活物質塗着極板１０の表面に、アセチレンブラック１０質量部と、ＰＶＰ１５質量部と、水８０質量部とからなる第１溶液を塗着した後、乾燥させた。ついで、この表面に、アセチレンブラック１０質量部と、ＰＶＰ５質量部と、水８０質量部とからなる第２溶液を塗着した後、乾燥させ、活物質塗着極板１０の表面に導電層１１を形成して、カドミウム負極板を作製した。これをカドミウム負極ｃとした。なお、導電層中のアセチレンブラック量とＰＶＰ量がカドミウム負極ａと同等になるように調整した。
【００２２】
なお、活物質塗着極板１０の上に第１溶液を塗着するとＰＶＰは活物質塗着極板１０の上に均等に分布した導電層１１が形成される。この上に第１溶液よりＰＶＰの充填量が少ない第２溶液を塗布すると、第２溶液中の水は導電層１１内のＰＶＰ１２を溶解させながら導電層１１の内部に浸透して行くため、図２に示すように、負極活物質層１０の表面に近いほどＰＶＰ１２の含有割合が高くなる。
【００２３】
（４）カドミウム負極ｄ
上述と同様に作製した活物質塗着極板１０を用い、この活物質塗着極板１０の表面に、アセチレンブラック１０質量部と、ＰＶＰ１５質量部と、水８０質量部とからなる第１溶液を塗着した後、乾燥させた。ついで、この表面に、アセチレンブラック１０質量部と、ＰＶＰ５質量部と、固形分として２質量部のフッ素樹脂（例えば、ＰＴＦＥ）ディスパージョンと、水８０質量部とからなる第２溶液を塗着した後、乾燥させ、活物質塗着極板１０の表面に導電層１１を形成して、カドミウム負極板を作製した。これをカドミウム負極ｄとした。なお、導電層中のアセチレンブラック量とＰＶＰ量がカドミウム負極ａと同等になるように調整した。
【００２４】
なお、活物質塗着極板１０の上に第１溶液を塗着するとＰＶＰは活物質塗着極板１０の上に均等に分布した導電層１１が形成される。この上に第１溶液よりＰＶＰの充填量が少ない第２溶液を塗布すると、第２溶液中の水は導電層１１内のＰＶＰ１２を溶解させながら導電層１１の内部に浸透して行くため、図３に示すように、負極活物質層１０の表面に近いほどＰＶＰ１２の含有割合が高くなる。また、第２溶液中にフッ素樹脂（例えば、ＰＴＦＥ）を含有しているので、第２溶液中の水がＰＶＰを溶解させながら導電層１１の内部に浸透して行く際に、フッ素樹脂は水よりも浸透速度が遅くなるため、図３に示すように、フッ素樹脂１３を導電層１１の表面近傍に局在させることが可能となる。
【００２５】
（５）カドミウム負極ｘ
上述と同様に作製した活物質塗着極板１０を用い、この活物質塗着極板１０の表面に、アセチレンブラック１０質量部と、ＰＶＰ１０質量部と、水８０質量部とからなる溶液を塗着した後、乾燥させてカドミウム負極板を作製した。これをカドミウム負極ｘとした。なお、活物質塗着極板１０の上にＰＶＰを含有した溶液を塗着すると、図４に示すように、ＰＶＰ１２が活物質塗着極板１０の上に均等に分布した導電層１１が形成される。
【００２６】
（６）カドミウム負極ｙ
上述と同様に作製した活物質塗着極板１０を用い、この活物質塗着極板１０の表面に、アセチレンブラック１０質量部と、ＰＶＰ１０質量部と、固形分として２質量部のフッ素樹脂（例えば、ＰＴＦＥ）ディスパージョンと、水８０質量部とからなる溶液を塗着した後、乾燥させてカドミウム負極板を作製した。これをカドミウム負極ｙとした。なお、活物質塗着極板１０の上にＰＶＰおよびフッ素樹脂（例えば、ＰＴＦＥ）を含有した溶液を塗着すると、図５に示すように、ＰＶＰ１２およびフッ素樹脂１３が活物質塗着極板１０の上に均等に分布した導電層１１が形成される。
【００２７】
２．ニッケル−カドミウム蓄電池の作製
以上のようにして作製したカドミウム負極ａ，ｂ，ｃ，ｄ，ｘ，ｙと公知の焼結式ニッケル正極とをそれぞれポリオレフィン製のセパレータを介して対向するように卷回してそれぞれの電極体とし、これらの電極体をそれぞれ外装缶内に挿入した後、３０重量％の水酸化カリウム水溶液（ＫＯＨ）をそれぞれ注液し、密閉して、ニッケル−カドミウム蓄電池（公称容量が１０００ｍＡｈのもの）Ａ（負極ａを用いたもの），Ｂ（負極ｂを用いたもの），Ｃ（負極ｃを用いたもの），Ｄ（負極ｄを用いたもの），Ｘ（負極ｘを用いたもの），Ｙ（負極ｙを用いたもの）を作製した。
【００２８】
３．充放電サイクル試験
ついで、上述したようにして作製したニッケル−カドミウム蓄電池Ａ，Ｂ，Ｃ，Ｄ，Ｘ，Ｙを用いて、室温（２５℃）で２０００ｍＡ（２Ｃ）の充電電流で充電を行い、ピーク電圧を越えた後、電池電圧が１０ｍＶ低下した時点で充電を停止（−ΔＶ方式）する。ついで、１時間充電を休止した後、１０００ｍＡ（１Ｃ）の放電電流で放電し、１時間放電を休止するという充放電サイクルを繰り返して行って、電池容量が所定値以下となった時点で電池寿命とする充放電サイクル試験を行うと、下記の表１に示すような結果となった。
【００２９】
４．電池内部ガス圧試験
ついで、上述したようにして作製したニッケル−カドミウム蓄電池Ａ，Ｂ，Ｃ，Ｄ，Ｘ，Ｙを用いて、室温（２５℃）で２０００ｍＡ（２Ｃ）の充電電流で充電を開始し、充電開始後４５分経過後（充電量は１５０％となる）に、ニッケル−カドミウム蓄電池Ａ，Ｂ，Ｃ，Ｄ，Ｘ，Ｙの各電池の内部圧力を測定すると、下記の表１に示すような結果となった。
【００３０】
【表１】

【００３１】
上記表１において、ニッケル−カドミウム蓄電池Ｘとニッケル−カドミウム蓄電池Ａおよびニッケル−カドミウム蓄電池Ｃとを比較すると、電池Ａ，Ｃの方がサイクル寿命が長く、かつ電池内圧が低いことが分かる。
【００３２】
これは、電池Ａ，ＣはＰＶＰの含有割合が導電層１１の表面から活物質層１０に向うに伴って高くなっているため、活物質層１０と導電層１１間の密着強度が向上し、電池の充放電サイクルに伴う活物質の体積変化、形態変化に対しても導電層１１が容易に破壊や脱落を生じにくくなって、サイクル寿命が長くなり、また、導電層１１の表面のＰＶＰの添加割合が低くくなっているため、導電層１１の表面の導電性粉末同士の接触抵抗が低減して導電性を向上させることが可能となり、酸素ガスとの接触が容易になって酸素ガスの吸収性能が向上し、電池内圧が低下したということができる。
【００３３】
さらに、ニッケル−カドミウム蓄電池Ａおよびニッケル−カドミウム蓄電池Ｃと、ニッケル−カドミウム蓄電池Ｂおよびニッケル−カドミウム蓄電池Ｄとを比較すると、電池Ｂ，Ｄの方が電池内圧が低いことが分かる。これは、電池Ｂ，Ｄは導電層１１にフッ素樹脂（例えば、ＰＴＦＥ）が含有されているとともに、フッ素樹脂は導電層１１の表面近傍に局在しているため、導電層１１の表面付近の撥水性が向上して、電池Ａ，Ｃよりもガス吸収性能が向上して、電池内圧が低下したということができる。なお、電池Ｂ，Ｄの方が電池Ａ，Ｃよりも寿命が僅かに長くなっているのは、添加されたフッ素樹脂（例えば、ＰＴＦＥ）が導電層１１の結着強度を向上させる効果も有していたことによるものである。
【００３４】
上述したように、本発明においては、ＰＶＰ（有機高分子糊料）の含有割合が導電層１１の表面から活物質層１０に向うに伴って導電性粉末よりも高くなるようにした導電層１１を負極活物質層１０の表面に設けているので、活物質層１０と導電層１１間の密着強度が向上して、電池の充放電サイクルに伴う活物質の体積変化、形態変化に対しても導電層１１が容易に破壊や脱落を生じなくなり、ガス吸収性能を持続して維持できるようになるとともに、マイグレーションも持続して抑制できるようになる。
【００３５】
なお、上述した実施形態においては、導電性粉末としてアセチレンブラックを用いる例について説明したが、ケッチェンブラック、黒鉛などの炭素粉末あるいは炭素繊維、あるいはニッケル、カドミウムなどの金属粉末を使用しても同様な結果が得られる。また、有機高分子糊料としては、ポリビニルピロリドン（ＰＶＰ）以外にも種々の有機高分子糊料を使用することができるが、電池内の雰囲気中での機械的強度および耐分解性に優れたものを用いることが望ましい。なお、フッ素樹脂としては、ポリテトラフルオロエチレン（ＰＴＦＥ）などの撥水性を有するものであれば何でも使用することができる。
【図面の簡単な説明】
【図１】カドミウム負極を模式的に示す斜視図である。
【図２】カドミウム負極ａ，ｃの要部を拡大して示す断面図である。
【図３】カドミウム負極ｂ，ｄの要部を拡大して示す断面図である。
【図４】カドミウム負極ｘの要部を拡大して示す断面図である。
【図５】カドミウム負極ｙの要部を拡大して示す断面図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a negative electrode for an alkaline storage battery used in an alkaline storage battery such as a nickel-cadmium storage battery or a nickel-hydrogen storage battery, and a method for producing the same.
[0002]
[Prior art]
Conventionally, a cadmium negative electrode used in a nickel-cadmium storage battery includes a sintered negative electrode in which a porous sintered substrate formed by sintering nickel powder is filled with a negative electrode active material made of cadmium oxide or cadmium hydroxide, and cadmium oxide. Alternatively, there is a non-sintered negative electrode in which a negative electrode active material made of cadmium hydroxide and a paste are kneaded and applied as a paste to a conductive core such as a punching metal. Among these, non-sintered negative electrodes are becoming mainstream in terms of low cost and high energy density.
[0003]
In recent years, demands for higher capacities of alkaline storage batteries, large current charge / discharge, long life, etc. have increased, and various improvements have been made to this type of non-sintered negative electrode to meet these demands. . For example, the capacity has been increased by increasing the packing density of the active material.
However, when the packing density of the active material is increased, voids in the active material layer are reduced, so that it is difficult to contact the active material and oxygen gas. Causes a problem such that the migration of the active material to the separator during the charge / discharge cycle is further accelerated, resulting in a short circuit at an early stage.
[0004]
[Problems to be solved by the invention]
Therefore, Japanese Patent Laid-Open No. 6-243863 proposes to form a conductive layer on the negative electrode surface with conductive powder and polyvinylpyrrolidone (PVP) and to optimize the mixing ratio of the conductive powder and PVP. It became so. Thus, when conductive powder and PVP are provided on the negative electrode surface, PVP is excellent in alkali resistance and forms a hard microporous film when applied to the negative electrode surface and dried, so that it does not swell with alkaline electrolyte. Maintaining high strength, the strength of the conductive layer is increased, and even when the charge / discharge cycle proceeds, destruction of the conductive layer is suppressed, and oxygen gas absorption performance can be improved.
[0005]
However, in the negative electrode proposed in JP-A-6-243863, in order to improve the strength of the conductive layer, it is necessary to increase the amount of PVP added, but if the amount of PVP added is increased, The conductivity of the conductive layer is lowered and the gas absorption performance is deteriorated, and it is difficult to improve the strength of the conductive layer and the gas absorption performance. Especially, high rate discharge, high rate charge In such severe cycle conditions, it is difficult to achieve both.
[0006]
On the other hand, a negative electrode in which a mixed layer of conductive powder such as metal cadmium and fluororesin powder is formed on the surface of the cadmium negative electrode, and polyvinyl alcohol (PVA) as a binder is contained in the internal active material layer excluding the surface layer Is proposed in Japanese Patent Laid-Open No. 4-19963. According to this, since the fluororesin having water repellency is added to the mixed layer formed on the negative electrode surface, the contact with the oxygen gas is improved, and the gas absorbency is improved.
[0007]
However, in the negative electrode proposed in Japanese Patent Laid-Open No. 4-19963, the mixed layer containing the conductive powder formed on the negative electrode surface does not contain a binder, so that the mixed layer has low strength. Also, the bonding with the active material layer is not sufficient. For this reason, as the charge / discharge cycle progresses, the active material easily falls off due to the volume change of the negative electrode active material, and the oxygen gas absorption performance cannot be maintained. In other words, the effect of suppressing the phenomenon that the cadmium intermediate dissolved in the electrolyte present in the electrolyte moves to the separator cannot be maintained.
[0008]
In addition, after integrating the hydrogen storage alloy with a binder to form a hydrogen storage alloy electrode, water vapor is sprayed onto the electrode surface to dissolve and remove the binder, and the binder contains a dissolution promoter for the binder. This is proposed in Japanese Patent No. 2975790. According to this, since the binder film covering the hydrogen storage alloy on the electrode surface is dissolved and removed, the contact with oxygen gas is facilitated and the gas absorption performance is improved.
However, in the negative electrode proposed in Japanese Patent No. 2975790, it is necessary to dissolve and remove the binder on the electrode surface until the surface of the active material is exposed. There was a problem that the wearing strength was lowered.
[0009]
The present invention has been made to solve the above problems, and provides a negative electrode for an alkaline storage battery provided with a conductive layer on the electrode surface having excellent adhesion strength and gas absorption performance, and charge / discharge cycle characteristics. It is an object of the present invention to provide an alkaline storage battery that is excellent in the above.
[0010]
[ Means for Solving the Problems ]
In order to achieve the above object, the negative electrode for an alkaline storage battery of the present invention comprises a step of applying a first solution containing a conductive powder and an organic polymer paste on the surface of the negative electrode active material layer, and then drying the first solution. A negative electrode in which the first solution is coated and dried with the second solution containing the same conductive powder as the first solution and the organic polymer paste and having a smaller amount of organic polymer paste than the first solution. And a step of drying after coating on the surface of the active material layer. Thereby, since the content rate of the organic polymer paste increases from the surface of the conductive layer toward the active material layer, the adhesion strength between the active material layer and the conductive layer is improved. As a result, the conductive layer does not easily break or fall off even when the volume or shape of the active material changes due to the charge / discharge cycle of the battery, so the sustained effect of suppressing gas absorption and migration can be maintained. It becomes like this.
[0011]
In addition, since the addition ratio of the organic polymer paste on the surface of the conductive layer is low, the contact resistance between the conductive powders on the surface of the conductive layer can be reduced and the conductivity can be improved. And a negative electrode excellent in oxygen gas absorption performance. In this case, at least one of the first solution and the second solution contains a fluororesin, or both the first solution and the second solution contain a fluororesin and are contained in the second solution. When the amount of fluororesin added is increased, the fluororesin can be localized near the surface of the conductive layer. Thereby , the water repellency on the surface of the conductive layer is improved, and the negative electrode is further improved in oxygen gas absorption performance.
[0012]
As the conductive powder, metal powder such as nickel and cadmium, carbon powder such as acetylene black, ketjen black, and graphite or carbon fiber can be used. In particular, oxygen gas absorption and migration suppression in a cadmium negative electrode can be used. Carbon powders such as acetylene black, ketjen black, and graphite are preferably used in terms of effects, ease of handling, and cost. In addition, as the organic polymer paste, various organic polymer pastes can be used, but a water-soluble paste is desirable in terms of ease of handling, and the mechanical strength in the atmosphere in the battery and It is preferable to use polyvinyl pyrrolidone (PVP) having excellent decomposition resistance.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment in which the present invention is applied to a cadmium negative electrode used in a nickel-cadmium storage battery will be described below with reference to the drawings. 1 is a perspective view schematically showing a cadmium negative electrode, FIG. 2 is an enlarged cross-sectional view showing a main part of cadmium negative electrodes a and c , and FIG. 3 shows a main part of cadmium negative electrodes b and d. It is sectional drawing expanded and shown. Further, FIG. 4 is an enlarged sectional view showing a main part of the cadmium negative electrode x, FIG. 5 is a sectional view showing an enlarged main part of cadmium negative electrode y.
[0017]
1. Production of cadmium negative electrode (1) Cadmium negative electrode a
After preparing an active material paste mainly composed of cadmium oxide powder, adding a binder and water to this powder, kneading this active material paste onto both sides of the conductive core made of punching metal, and letting it dry Thus, an active material-coated electrode plate 10 was produced. Next, a first solution consisting of 10 parts by mass of acetylene black, 10 parts by mass of polyvinylpyrrolidone (PVP), and 80 parts by mass of water was applied to the surface of the active material-coated electrode plate 10 and then dried. The conductive layer 11 was formed on the surface of the active material-coated electrode plate 10.
[0018]
Then, a small amount of water (second solution) is applied on the conductive layer 11 of the active material-coated electrode plate 10 having the conductive layer 11 formed on the surface, and then for a predetermined time. It was allowed to stand (for example, about 1 minute) and allowed to penetrate into the electrode plate. Subsequently, it was dried to produce a cadmium negative electrode plate. This was designated as a cadmium negative electrode a. When water (where water dissolves PVP) is applied to the surface of the conductive layer 11, water penetrates into the conductive layer 11 while dissolving the PVP 12, as shown in FIG. The closer to the surface of the active material layer 10, the higher the content ratio of PVP12.
[0019]
(2) Cadmium negative electrode b
A first solution composed of 10 parts by mass of acetylene black, 10 parts by mass of PVP, and 80 parts by mass of water is used on the surface of the active material-coated electrode plate 10 produced in the same manner as described above. Then, the conductive layer 11 was formed on the surface of the active material-coated electrode plate 10 by drying. Next, water (second solution) to which a fluororesin (for example, PTFE) dispersion has been applied is applied on the conductive layer 11 of the active material-coated electrode plate 10 having the conductive layer 11 formed on the surface, It was allowed to stand for a time (for example, about 1 minute) and allowed to penetrate into the electrode plate. Subsequently, it was dried to produce a cadmium negative electrode plate. This was designated as a cadmium negative electrode b.
[0020]
When water is applied to the surface of the conductive layer 11, as shown in FIG. 3, water penetrates into the conductive layer 11 while dissolving the PVP 12, so that the PVP 12 is closer to the surface of the negative electrode active material layer 10. The content ratio of becomes higher. In addition, when water penetrates into the conductive layer 11 while dissolving PVP, the fluororesin (for example, PTFE) has a slower permeation rate than water. Therefore, as shown in FIG. Can be localized near the surface of the conductive layer 11.
[0021]
(3) Cadmium negative electrode c
A first solution composed of 10 parts by mass of acetylene black, 15 parts by mass of PVP, and 80 parts by mass of water is used on the surface of the active material-coated electrode plate 10 produced in the same manner as described above. Was applied and dried. Next, a second solution consisting of 10 parts by mass of acetylene black, 5 parts by mass of PVP, and 80 parts by mass of water was applied to this surface, and then dried, and the conductive layer 11 was applied to the surface of the active material-coated electrode plate 10. To form a cadmium negative electrode plate. This was designated as a cadmium negative electrode c. In addition, it adjusted so that the amount of acetylene black in a conductive layer and the amount of PVP might become equivalent to the cadmium negative electrode a .
[0022]
When the first solution is applied onto the active material-coated electrode plate 10, the PVP is formed with the conductive layer 11 evenly distributed on the active material-coated electrode plate 10. When a second solution having a lower PVP filling amount than the first solution is applied thereon, the water in the second solution penetrates into the conductive layer 11 while dissolving the PVP 12 in the conductive layer 11. As shown in FIG. 2, the closer to the surface of the negative electrode active material layer 10, the higher the content ratio of PVP12.
[0023]
(4) Cadmium negative electrode d
A first solution composed of 10 parts by mass of acetylene black, 15 parts by mass of PVP, and 80 parts by mass of water is used on the surface of the active material-coated electrode plate 10 produced in the same manner as described above. Was applied and dried. Next, a second solution consisting of 10 parts by mass of acetylene black, 5 parts by mass of PVP, a fluorine resin (for example, PTFE) dispersion of 2 parts by mass as solids, and 80 parts by mass of water was applied to this surface. Then, it was made to dry and the conductive layer 11 was formed in the surface of the active material coating electrode plate 10, and the cadmium negative electrode plate was produced. This was designated as a cadmium negative electrode d. In addition, it adjusted so that the amount of acetylene black in a conductive layer and the amount of PVP might become equivalent to the cadmium negative electrode a .
[0024]
When the first solution is applied onto the active material-coated electrode plate 10, the PVP is formed with the conductive layer 11 evenly distributed on the active material-coated electrode plate 10. When a second solution having a lower PVP filling amount than the first solution is applied thereon, the water in the second solution penetrates into the conductive layer 11 while dissolving the PVP 12 in the conductive layer 11. As shown in FIG. 3, the closer to the surface of the negative electrode active material layer 10, the higher the content ratio of PVP12. Further, since the second solution contains a fluororesin (for example, PTFE), when the water in the second solution penetrates into the conductive layer 11 while dissolving the PVP, the fluororesin is water. Since the permeation rate is slower than that, the fluororesin 13 can be localized near the surface of the conductive layer 11 as shown in FIG.
[0025]
(5) Cadmium negative electrode x
Using the active material-coated electrode plate 10 produced in the same manner as described above, a solution composed of 10 parts by mass of acetylene black, 10 parts by mass of PVP, and 80 parts by mass of water was applied to the surface of the active material-coated electrode plate 10. After being attached, it was dried to prepare a cadmium negative electrode plate. This was designated as a cadmium negative electrode x. When a solution containing PVP is applied on the active material-coated electrode plate 10, a conductive layer 11 in which the PVP 12 is evenly distributed on the active material-coated electrode plate 10 is formed as shown in FIG. Is done.
[0026]
(6) Cadmium negative electrode y
Using the active material-coated electrode plate 10 prepared in the same manner as described above, 10 parts by mass of acetylene black, 10 parts by mass of PVP, and 2 parts by mass of a fluororesin (as a solid content) are formed on the surface of the active material-coated electrode plate 10. For example, a solution composed of a PTFE dispersion and 80 parts by mass of water was applied and then dried to prepare a cadmium negative electrode plate. This was designated as a cadmium negative electrode y. In addition, when a solution containing PVP and a fluororesin (for example, PTFE) is applied onto the active material-coated electrode plate 10, the PVP12 and the fluororesin 13 are converted into the active material-coated electrode plate 10 as shown in FIG. A conductive layer 11 is formed that is evenly distributed on the substrate.
[0027]
2. Production of Nickel-Cadmium Storage Battery The cadmium negative electrodes a, b, c, d, x, y produced as described above and a known sintered nickel positive electrode were wound so as to face each other via a polyolefin separator. and each of the conductive polar bodies Te, these electrostatic polar body after insertion into the outer can each, of 30 wt% aqueous solution of potassium hydroxide (KOH), respectively was injected and sealed, nickel - cadmium battery (nominal Capacitance of 1000 mAh) A (using negative electrode a), B (using negative electrode b), C (using negative electrode c), D (using negative electrode d), X (negative electrode x And Y (using negative electrode y) .
[0028]
3. Charging / discharging cycle test Next, using the nickel-cadmium storage batteries A, B, C, D, X, and Y produced as described above, charging was performed at room temperature (25 ° C.) with a charging current of 2000 mA (2C), After the peak voltage is exceeded, charging is stopped (−ΔV method) when the battery voltage drops by 10 mV. Next, after charging is stopped for 1 hour, a charge / discharge cycle of discharging at 1000 mA (1C) discharge current and stopping discharge for 1 hour is repeated, and when the battery capacity becomes a predetermined value or less, the battery life is reached. When the charge / discharge cycle test was performed, the results shown in Table 1 below were obtained.
[0029]
4). Battery internal gas pressure test Next, using nickel-cadmium storage batteries A, B, C, D, X, and Y produced as described above, charging started at room temperature (25 ° C.) with a charging current of 2000 mA (2C). When the internal pressures of the nickel-cadmium storage batteries A, B, C, D, X, and Y are measured after 45 minutes have elapsed since the start of charging (the charge amount is 150%), the following Table 1 is obtained. The result was as shown.
[0030]
[Table 1]

[0031]
In Table 1 above, when the nickel-cadmium storage battery X, the nickel-cadmium storage battery A, and the nickel-cadmium storage battery C are compared, it can be seen that the batteries A and C have a longer cycle life and a lower battery internal pressure.
[0032]
This is because the batteries A and C have a higher PVP content from the surface of the conductive layer 11 toward the active material layer 10, so that the adhesion strength between the active material layer 10 and the conductive layer 11 is improved. Even when the volume and shape of the active material change due to the charge / discharge cycle of the battery, the conductive layer 11 does not easily break or fall off, and the cycle life is prolonged. Since the addition ratio is low, the contact resistance between the conductive powders on the surface of the conductive layer 11 can be reduced and the conductivity can be improved, and the contact with the oxygen gas is facilitated. It can be said that the absorption performance is improved and the internal pressure of the battery is reduced.
[0033]
Further, comparing the nickel-cadmium storage battery A and the nickel-cadmium storage battery C with the nickel-cadmium storage battery B and the nickel-cadmium storage battery D, it can be seen that the batteries B and D have lower battery internal pressure. This is because the batteries B and D contain a fluororesin (for example, PTFE) in the conductive layer 11 and the fluororesin is localized near the surface of the conductive layer 11. It can be said that the water repellency is improved, the gas absorption performance is improved as compared with the batteries A and C, and the battery internal pressure is lowered. The batteries B and D have a slightly longer life than the batteries A and C because the added fluororesin (for example, PTFE) has an effect of improving the binding strength of the conductive layer 11. It is because of what was done.
[0034]
As described above, in the present invention, the conductive layer 11 in which the content ratio of PVP (organic polymer paste) becomes higher than the conductive powder as it goes from the surface of the conductive layer 11 to the active material layer 10. Is provided on the surface of the negative electrode active material layer 10, the adhesion strength between the active material layer 10 and the conductive layer 11 is improved, and the volume change and shape change of the active material accompanying the charge / discharge cycle of the battery are also improved. The conductive layer 11 does not easily break or fall off, and the gas absorption performance can be maintained continuously, and the migration can also be suppressed continuously.
[0035]
In the above-described embodiment, an example in which acetylene black is used as the conductive powder has been described. However, the same applies even when carbon powder such as ketjen black or graphite, carbon fiber, or metal powder such as nickel or cadmium is used. Results. In addition to polyvinyl pyrrolidone (PVP), various organic polymer pastes can be used as the organic polymer paste, but they have excellent mechanical strength and decomposition resistance in the atmosphere in the battery. It is desirable to use one. Any fluororesin can be used as long as it has water repellency such as polytetrafluoroethylene (PTFE).
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing a cadmium negative electrode.
FIG. 2 is an enlarged cross-sectional view showing a main part of cadmium negative electrodes a and c .
FIG. 3 is an enlarged cross-sectional view showing a main part of cadmium negative electrodes b and d .
FIG. 4 is an enlarged cross-sectional view showing a main part of a cadmium negative electrode x .
FIG. 5 is an enlarged cross-sectional view showing a main part of a cadmium negative electrode y .

Claims

A method for producing a negative electrode for an alkaline storage battery in which a conductive layer containing a conductive powder and an organic polymer paste is formed on the surface of a negative electrode active material layer,
Applying a first solution containing a conductive powder and an organic polymer paste on the surface of the negative electrode active material layer, followed by drying;
The first solution is coated with a second solution containing the same conductive powder as the first solution and an organic polymer paste, and the amount of the organic polymer paste added is smaller than that of the first solution. A method for producing a negative electrode for an alkaline storage battery, comprising: a step of applying the dried negative electrode active material layer to the surface of the negative electrode active material layer and then drying the applied layer.

The method for producing a negative electrode for an alkaline storage battery according to claim 1 , wherein the second solution contains a fluororesin, and the first solution does not contain a fluororesin.

2. The alkaline storage battery according to claim 1 , wherein both the first solution and the second solution contain a fluororesin, and the amount of the fluororesin contained in the second solution is increased. Manufacturing method for negative electrode.