JP4056207B2

JP4056207B2 - Method for producing alkaline storage battery

Info

Publication number: JP4056207B2
Application number: JP2000288556A
Authority: JP
Inventors: 康彦池田; 幹朗田所; 輝彦井本; 徹行村田; 隆志山口; 泰正近藤; 潔森田; 誠越智; 功祐里口
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 2000-09-22
Filing date: 2000-09-22
Publication date: 2008-03-05
Anticipated expiration: 2020-09-22
Also published as: JP2002100349A

Description

【０００１】
【発明の属する技術分野】
本発明は、水素吸蔵合金粉末が塗着された帯状負極板と正極板とをセパレータを介して渦巻状に巻回した渦巻状電極群を外装缶内に備えたアルカリ蓄電池の製造方法に関する。
【０００２】
【従来の技術】
近年、小型携帯機器の増加に伴い、充放電が可能な二次電池（蓄電池）の需要が高まっており、特に、機器の小型化、薄型化、スペース効率化に伴い、大容量が得られるニッケル−水素蓄電池の需要が急速に高まった。この種のニッケル−水素蓄電池は、活物質に水酸化ニッケルを使用する正極板と、水素吸蔵合金を使用する負極板とをセパレータを介して渦巻状に巻回して渦巻状電極群とし、この渦巻状電極群をアルカリ電解液とともに金属製外装缶（電池ケース）内に収納し、金属製外装缶を密封することにより製造される。
【０００３】
ところで、負極板は水素吸蔵合金層を保持するパンチングメタルからなる導電性芯体の両面に、水素吸蔵合金粉末と水溶性結着剤と純水または水を混練して形成された水素吸蔵合金スラリーを塗着して形成されるが、通常、導電性芯体の両面に水素吸蔵合金スラリーを塗着した後、常温（約２５℃）で自然乾燥する工程を経て作製されるものである。ここで、水素吸蔵合金スラリーが塗着された極板を自然乾燥すると、乾燥速度が遅くて、通常、極板が乾燥するまでに５〜６時間程度の長時間の乾燥時間となるため、極板の生産効率が悪いという問題があった。
【０００４】
そこで、このような問題点を解消するために、導電性芯体の両面に水素吸蔵合金スラリーを塗着した後、高温（約６０℃以上）で乾燥する方法が提案されるようになった。このように水素吸蔵合金スラリーが塗着された極板を高温で乾燥させると、乾燥時間は１５〜３０分程度で乾燥できるようになって、極板の生産効率が向上することとなる。この後、このようにして作製された負極板と正極板とをセパレータを介して渦巻状に巻回して渦巻状電極群とし、この渦巻状電極群をアルカリ電解液とともに金属製外装缶内に収納し、金属製外装缶を密封することによりニッケル−水素蓄電池を得ていた。
【０００５】
【発明が解決しようとする課題】
ところで、極板の生産効率を向上させるために、極板の乾燥速度を上げるようにするには、上述したように高温で乾燥させる必要が生じる。しかしながら、極板を高温で乾燥させるようにすると、水分の蒸発速度が速くなるため、水素吸蔵合金層に含有される水分が極板内部から極板表面（乾燥面側）へ急速に移動するようになる。このため、水素吸蔵合金層に含有される結着剤も水分の移動に伴って移動するため、結着剤は極板表面に偏在して固結することとなる。この結果、極板の中心部に配置された導電性芯体近傍の水素吸蔵合金層中の結着剤量が減少するという現象を生じる。
【０００６】
ここで、導電性芯体近傍の活物質層中の結着剤量が減少すると、導電性芯体と水素吸蔵合金との接着力が低下するため、このような負極板を用いて渦巻状電極群とすると、渦巻状に巻回する際や、渦巻状電極群を金属製外装缶内に挿入する際に、水素吸蔵合金層が導電性芯体より脱落しやすくなるという問題を生じた。特に、金属製外装缶内のスペースを有効利用して高容量の電池とするために、渦巻状電極群の最外周に配置される負極板の外周部にセパレータを被覆せずに負極板を露出させて、この露出した負極板を金属製外装缶に直接接触させるようにした電池にあって、渦巻状電極群を金属製外装缶内に挿入際に、さらに、水素吸蔵合金層が導電性芯体より脱落しやすくなるという問題を生じた。
【０００７】
そこで、本発明は上記問題点を解消するためになされたものであって、水素吸蔵合金が塗着された負極板の乾燥温度を高くして生産効率を向上させても、負極板の強度の低下を抑制できる製造方法を提供して、水素吸蔵合金層が導電性芯体から脱落することが防止できて、高品質なアルカリ蓄電池が得られるようにすることを目的とする。
【０００８】
【課題を解決するための手段およびその作用・効果】
上記目的を達成するため、本発明のアルカリ蓄電池の製造方法は、水素吸蔵合金粉末と結着剤とこの結着剤の溶媒とからなる水素吸蔵合金スラリーを導電性芯体の両面に塗着して塗着極板とする塗着工程と、得られた塗着極板を乾燥させて乾燥極板とする乾燥工程と、得られた乾燥極板の表面に結着剤の溶媒を付着させる付着工程と、結着剤の溶媒を付着された極板を乾燥工程での乾燥温度よりも低温で乾燥させる低温乾燥工程とを備えるようにしている。
【０００９】
水素吸蔵合金スラリーが塗着された極板を乾燥（この場合の乾燥は生産性を上げるために高温となる）させると、乾燥時に、水素吸蔵合金層に含有される水分の移動に伴って結着剤も極板表面（乾燥面側）に移動して固結することとなり、極板中心部に配置された導電性芯体近傍の水素吸蔵合金層中の結着剤量が減少する。このため、導電性芯体と水素吸蔵合金層との接着力が低下して水素吸蔵合金が脱落しやすくなる。
【００１０】
ところが、本発明のように、乾燥極板の表面に結着剤の溶媒（例えば、水溶性結着剤の場合は純水または水）を付着させるようにすると、結着剤の溶媒が水素吸蔵合金層中に浸透するため、乾燥時に極板表面で固結した結着剤が再溶解するようになる。これにより、再溶解した結着剤が導電性芯体の近傍まで拡散して、導電性芯体の近傍の結着剤の濃度が増大するようになる。この後、低温乾燥工程で、乾燥工程よりも低温で乾燥させると、蒸発速度が遅いため、拡散した結着剤が再度移動することなく固結する。この結果、導電性芯体の近傍まで拡散した結着剤は導電性芯体の近傍で固結して、導電性芯体と水素吸蔵合金層とが強固に接着されるようになる。これにより、水素吸蔵合金層は剥がれにくくなって、水素吸蔵合金の脱落が防止できるようになる。
【００１１】
そして、水素吸蔵合金層が剥がれ易いのは、渦巻状電極群になった際の帯状負極板の巻き始め部あるいは巻き終わり部であるので、付着工程において乾燥極板の表面に結着剤の溶媒を付着させる際には、乾燥極板の全表面に付着させてもよいが、最低限、渦巻状電極群になった際の帯状負極板の巻き始め部あるいは巻き終わり部とする必要がある。この場合、付着させる結着剤の溶媒の量が少なすぎると、乾燥時に固結した結着剤が導電性芯体の近傍までは拡散しなくなって、導電性芯体と水素吸蔵合金層とが強固に接着されなくなる。また、付着させる結着剤の溶媒の量が多くなりすぎると乾燥させる時間が長時間となって生産効率が低下する。このため、乾燥極板の表面に塗布する結着剤の溶媒の付着量は、極板の単位面積当たり３×１０^-5ｇ／ｍｍ²〜５×１０^-5ｇ／ｍｍ²とするのが好ましい。
【００１２】
【発明の実施の形態】
以下に、本発明の一実施の形態を説明する。
１．水素吸蔵合金粉末の作製
ＭｍＮｉ_3.4Ｃｏ_0.8Ａｌ_0.2Ｍｎ_0.6（なお、Ｍｍはミッシュメタルである）となるように市販の各金属元素（Ｍｍ，Ｎｉ，Ｃｏ，Ａｌ，Ｍｎ）を秤量して混合した。このものを高周波溶解炉に投入して溶解させた後、鋳型に流し込み、冷却してＭｍＮｉ_3.4Ｃｏ_0.8Ａｌ_0.2Ｍｎ_0.6からなる水素吸蔵合金の塊（インゴット）を作製した。この水素吸蔵合金の塊を粗粉砕した後、不活性ガス雰囲気中で平均粒径が５０μｍ程度になるまで機械的に粉砕して、水素吸蔵合金粉末を作製した。なお、得られた水素吸蔵合金粉末の平均粒径はレーザ回折法により測定した値である。
【００１３】
２．水素吸蔵合金極板の作製
（１）実施例１
上述のようにして作製した水素吸蔵合金粉末９９質量％に、水溶性結着剤としてポリエチレンオキサイド（ＰＥＯ）粉末を水素吸蔵合金粉末質量に対して１質量％と、適量の水（あるいは純水）を加えて混練して、水素吸蔵合金スラリーを作製した。ついで、表面にニッケルメッキが施されて開孔が設けられたパンチングメタルからなる導電性芯体の両面に水素吸蔵合金スラリーを塗着して塗着極板を形成した。この後、約６０℃で２０分間乾燥させて、厚みが０．６ｍｍになるように圧延して乾燥圧延極板を作製した。なお、水素吸蔵合金スラリーの塗着量は圧延後の水素吸蔵合金密度が５ｇ／ｃｍ³となるように調整した。
【００１４】
ついで、得られた乾燥圧延極板の全表面に水あるいは純水を塗布して、乾燥圧延極板の全表面に水あるいは純水を付着させた。この後、室温（約２５℃）で約２時間放置して自然乾燥させた後、所定寸法に切断して、実施例１の水素吸蔵合金極板ａを作製した。なお、水あるいは純水の塗布量は０．２０２ｇ（この塗布量は塗布前と塗布後の質量差を求めた値である）であって、極板の単位面積当り３．２９×１０^-5ｇ／ｍｍ²）となる。また、乾燥後の極板に純水または水を塗布するに際しては、刷毛による塗布方法、噴霧による塗布方法、あるいはロールによる塗布方法など、生産性を考慮して適宜の方法を採用して塗布するようにすればよい。
【００１５】
（２）実施例２
上述の実施例１と同様にして乾燥圧延極板を作製した後、得られた乾燥圧延極板の渦巻状電極群とされた際の巻き始め部の表面に水あるいは純水を塗布して、乾燥圧延極板の巻き始め部の表面に水あるいは純水を付着させた。この後、室温（約２５℃）で約２時間放置して自然乾燥させた後、所定寸法に切断して、実施例２の水素吸蔵合金極板を作製した。なお、水あるいは純水の塗布量は０．０７２ｇ（この塗布量は塗布前と塗布後の質量差を求めた値である）であって、塗布部分の極板の単位面積当り３．２９×１０^-5ｇ／ｍｍ²）となる。
【００１６】
（３）実施例３
上述の実施例１と同様にして乾燥圧延極板を作製した後、得られた乾燥圧延極板の渦巻状電極群とされた際の巻き終わり部の表面に水あるいは純水を塗布して、乾燥圧延極板の巻き終わり部の表面に水あるいは純水を付着させた。この後、室温（約２５℃）で約２時間放置して自然乾燥させた後、所定寸法に切断して、実施例３の水素吸蔵合金極板ｃを作製した。なお、水あるいは純水の塗布量は０．０７２ｇ（この塗布量は塗布前と塗布後の質量差を求めた値である）であって、塗布部分の極板の単位面積当り３．２９×１０^-5ｇ／ｍｍ²）となる。
【００１７】
（４）実施例４
上述の実施例１と同様にして、乾燥圧延極板を作製した後、得られた乾燥圧延極板の渦巻状電極群とされた際の巻き始め部と巻終わり部の表面に水あるいは純水を塗布して、乾燥圧延極板の巻き始め部と巻終わり部の表面に水あるいは純水を付着させた。この後、室温（約２５℃）で約２時間放置して自然乾燥させた後、所定寸法に切断して、実施例４の水素吸蔵合金極板ｄを作製した。なお、水あるいは純水の塗布量は０．１４４ｇ（この塗布量は塗布前と塗布後の質量差を求めた値である）であって、塗布部分の極板の単位面積当り３．２９×１０^-5ｇ／ｍｍ²）となる。
【００１８】
（５）比較例１
上述の実施例１と同様にして、導電性芯体の両面に水素吸蔵合金スラリーを塗着して塗着極板を形成した後、室温（約２５℃）で約６時間放置して自然乾燥させた後、厚みが０．６ｍｍになるように圧延して乾燥圧延極板を作製した。なお、水素吸蔵合金スラリーの塗着量は圧延後の水素吸蔵合金密度が５ｇ／ｃｍ³となるように調整した。このようにして得られた乾燥圧延極板を所定寸法に切断して、比較例１の水素吸蔵合金極板ｘを作製した。
【００１９】
（６）比較例２
上述の実施例１と同様にして導電性芯体の両面に水素吸蔵合金スラリーを塗着して、活物質層を形成した塗着極板とした後、約６０℃で２０分間乾燥させた後、厚みが０．６ｍｍになるように圧延して乾燥圧延極板を作製した。なお、水素吸蔵合金スラリーの塗着量は圧延後の水素吸蔵合金密度が５ｇ／ｃｍ³となるように調整した。このようにして得られた乾燥圧延極板を所定寸法に切断して、比較例２の水素吸蔵合金極板ｙを作製した。
【００２０】
３．ニッケル−水素蓄電池の作製
ついで、上述のように作製した実施例１〜４の各水素吸蔵合金負極板ａ〜ｄおよび比較例１，２の各水素吸蔵合金負極板ｘ，ｙをそれぞれ用い、これらの各水素吸蔵合金負極板と周知の非焼結式ニッケル正極板とを耐アルカリ性のナイロン製不織布からなるセパレータを介して捲回する。このとき、水素吸蔵合金負極板が外側になるようにして渦巻状に捲回して渦巻状極板群をそれぞれ作製した。
【００２１】
このように作製した各渦巻状極板群をそれぞれ有底円筒状の金属外装缶に挿入した後、各金属外装缶内にそれぞれ水酸化カリウム（ＫＯＨ）、水酸化リチウム（ＬｉＯＨ）および水酸化ナトリウム（ＮａＯＨ）からなる３成分電解液を注液し、密閉することにより公称容量が１７００ｍＡｈの４／５Ａサイズのニッケル−水素蓄電池をそれぞれ作製した。
【００２２】
ここで、水素吸蔵合金負極板ａを用いたものを電池Ａとし、水素吸蔵合金負極板ｂを用いたものを電池Ｂとし、水素吸蔵合金負極板ｃを用いたものを電池Ｃとし、水素吸蔵合金負極板ｄを用いたものを電池Ｄとし、水素吸蔵合金負極板ｘを用いたものを電池Ｘとし、水素吸蔵合金負極板ｙを用いたものを電池Ｙとした。
【００２３】
４．活物質の脱落個数の測定
ここで、上述のように各ニッケル−水素蓄電池Ａ〜ＤおよびＸ，Ｙをそれぞれ１００個ずつ作製する際に、渦巻状電極群の作製時に導電性芯体から水素吸蔵合金が脱落した電極群の個数を測定すると、下記の表１に示すような結果となった。なお、下記の表１において、乾燥温度および乾燥時間はそれぞれ塗着極板の乾燥温度および乾燥時間を示している。
【００２４】
【表１】

【００２５】
上記表１の結果から明らかなように、塗着極板を室温（約２５℃）で自然乾燥して作製した水素吸蔵合金負極板ｘを用いた電池Ｘと、塗着極板を約６０℃で乾燥して作製した水素吸蔵合金負極板ｙを用いた電池Ｙとを比較すると、自然乾燥して作製した水素吸蔵合金負極板ｘを用いた方が脱落数が減少していることが分かる。
これは、塗着極板を約６０℃の高温で乾燥すると、２０分程度の短時間で負極板の乾燥が完了するが、乾燥速度が速いため、水分の蒸発速度が速くなって水素吸蔵合金層に含有される水分の移動に伴って水溶性結着剤も移動し、水溶性結着剤が極板表面（乾燥面側）に偏在して固結することとなる。このため、負極板の中心部に配置された導電性芯体近傍の水素吸蔵合金層中の水溶性結着剤量が減少して、水素吸蔵合金が脱落しやすくなったと考えられる。
【００２６】
一方、塗着極板を室温（約２５℃）で自然乾燥すると、乾燥速度が遅いため、水素吸蔵合金層中の水分の蒸発速度も遅くなる。これにより、水素吸蔵合金層に含有される水溶性結着剤が移動することなく固結するため、負極板の中心部に配置された導電性芯体近傍の水素吸蔵合金層中の水溶性結着剤量が減少することもなく、導電性芯体と水素吸蔵合金との結着強度が良好になったためである。しかしながら、乾燥速度が遅いため、負極板の乾燥が完了するまでに約６時間という長時間を要した。
【００２７】
また、塗着極板を約６０℃の高温で乾燥して乾燥極板とした後、この乾燥極板の全面に水あるいは純水を塗布して乾燥時よりは低温の室温（約２５℃）で自然乾燥して作製した水素吸蔵合金負極板ａを用いた電池Ａ、乾燥極板の渦巻状電極群の巻き始め部となる部分に水あるいは純水を塗布して作製した水素吸蔵合金負極板ｂを用いた電池Ｂ、乾燥極板の渦巻状電極群の巻き終わり部となる部分に水あるいは純水を塗布して作製した水素吸蔵合金負極板ｃを用いた電池Ｃ、および乾燥極板の渦巻状電極群の巻き始め部および巻終わり部となる部分に水あるいは純水を塗布してして作製した水素吸蔵合金負極板ｄを用いた電池Ｄにあっては、電池Ｘと同様に脱落数が減少していることが分かる。
【００２８】
これは、純水または水を乾燥極板の表面に塗布して付着させるようにすると、純水または水が水素吸蔵合金層中に浸透するため、乾燥時に極板表面で固結した水溶性結着剤が再溶解するようになり、この再溶解した水溶性結着剤が導電性芯体の近傍まで拡散して、導電性芯体の近傍の水溶性結着剤の濃度が増大する。この後、乾燥工程よりも低温の室温（約２５℃）で乾燥させると、拡散した水溶性結着剤が固結することとなるが、この固結時に、導電性芯体の近傍まで拡散した水溶性結着剤も再度移動することなく固結して、導電性芯体と水素吸蔵合金とが強固に接着されたためと考えられる。これにより、水素吸蔵合金層は剥がれにくくなって、水素吸蔵合金の脱落が防止できるようになる。
【００２９】
なお、乾燥極板表面への純水または水の塗布部位としては、電池Ａのように乾燥極板の全表面であっても、電池Ｂのように乾燥極板の渦巻状電極群の巻き始め部となる部分であっても、電池Ｃのように乾燥極板の渦巻状電極群の巻き終わり部となる部分であっても、あるいは電池Ｄのように乾燥極板の渦巻状電極群の巻き始め部となる部分および巻き終わり部となる部分であっても、脱落数にそれほど差が生じないため、これらのいずれかの部位に塗布するようにすればよいことが分かる。
【００３０】
５．水（純水）の塗布量の検討
上述した各実施例においては、乾燥極板表面への純水または水の塗布量を一定にした場合の塗布部位と脱落数との関係について検討したが、以下では、純水または水の塗布量と極板強度との関係について検討した。この場合においては、上述の実施例１と同様に乾燥極板を作製した後、この乾燥極板の全面に塗布する純水または水の塗布量を極板の単位面積当たり０〜６×１０^-5ｇ／ｍｍ²に変化させて塗布した。ついで、これらの純水または水の塗布量が異なる各極板を、上述した実施例１と同様にして、室温（約２５℃）で約２時間放置して自然乾燥させた後、所定寸法に切断して、図１に示すように、乾燥後の純水または水の塗布量が異なる各極板１０を作製した。
【００３１】
なお、図１に示す極板１０の中心部にはパンチングメタルからなる導電性芯体１１を備えており、この導電性芯体１１の両面に水素吸蔵合金層１２，１３が形成されている。ついで、これらの各極板１０の片面の水素吸蔵合金層１２の表面を切削した後、切削面をウエスで軽く擦って表面の切削くずを除去した。この後、これらの各極板１０の水素吸蔵合金層１２の表面に対して約３０度の角度にカッター（図示せず）を保持した後、カッターの刃先に２５０ｇ程度の荷重が掛かるようにして、水素吸蔵合金層１２を切るように切溝ｘ，ｙを引いた。なお、各切溝ｘ，ｙの間隔は１ｍｍ間隔とし、各切溝ｘ，ｙをそれぞれ１０本ずつ互いに直角に交差するように引いた。
【００３２】
各切溝ｘ，ｙを１０本ずつ互いに直角に交差するように引くことにより、碁盤目状に１００個の升目が形成された。ついで、碁盤目状に１００個の升目が形成された各極板１０をそれぞれ１０枚ずつ用いて、水素吸蔵合金層１２，１３が垂直になるようにして、高さが約１００ｍｍの位置まで持ち上げた後、各極板１０をそれぞれ自由落下させた。この落下試験を３回繰り返して行った後、各極板１０に形成された升目の脱落個数を数えて、その平均値を求めると図２に示すような結果となった。なお、図２の縦軸の脱落個数は升目の脱落個数を示しており、この脱落個数が少なくなると極板の強度、即ち、導電性芯体１１と各水素吸蔵合金層１２，１３との接着力が強いことを意味する。
【００３３】
図２の結果から明らかなように、純水または水の塗布量が多くなるに伴って直線的に脱落個数が減少し、塗布量が極板の単位面積当たり３×１０^-5ｇ／ｍｍ²を越えると減少量が低下し、塗布量が極板の単位面積当たり５×１０^-5ｇ／ｍｍ²を越えるとほぼ一定になることがことが分かる。また、塗布量が極板の単位面積当たり５×１０^-5ｇ／ｍｍ²を越えるほど多くなると、純水または水の塗布後の乾燥時間が長時間になる。このことから、純水または水の塗布量は、３×１０^-5ｇ／ｍｍ²以上で５×１０^-5ｇ／ｍｍ²以下とすることが好ましいということができる。
【００３４】
上述したように、本発明においては、高温で急速乾燥させて生産性を向上させても、乾燥極板の表面に純水または水を付着させるようにして、乾燥時に移動した水溶性結着剤を再溶解させて固結させるようにしているので、導電性芯体と水素吸蔵合金とが強固に接着されるとともに、水素吸蔵合金同士も強固に接着されるようになる。この結果、水素吸蔵合金層が剥がれにくくなって、水素吸蔵合金の脱落が防止できるようになるため、生産性に優れて、高品質なアルカリ蓄電池を得ることが可能となる。
【００３５】
なお、上述した実施の形態においては、水素吸蔵合金としてＭｍ_aＮｉ_bＣｏ_cＭｎ_dＡｌ_eで表されるＮｉの一部をＣｏ，Ｍｎ，Ａｌで置換した水素吸蔵合金を用いる例について説明したが、Ｎｉの一部をＣｏと、Ｃｕ，Ｆｅ，Ｃｒ，Ｓｉ，Ｍｏ等で置換した水素吸蔵合金を用いるようにしてもよい。また、Ｍｍ_aＮｉ_bＣｏ_cＭｎ_dＡｌ_eで表される水素吸蔵合金以外の他のＡＢ₅型希土類系の水素吸蔵合金、例えば、ＬａＮｉ₅系でＮｉの一部をＣｏとＡｌ，Ｗ等で置換した水素吸蔵合金を用いるようにしてもよい。また、上述した実施の形態においては、機械的に粉砕した水素吸蔵合金を用いる例について説明したが、アトマイズ法により作製した水素吸蔵合金あるいはこれに粉砕合金を混合した混合粉末を用いるようにしてもよい。
【図面の簡単な説明】
【図１】活物質の脱落試験を行うために活物質層に碁盤目状の切溝を入れた状態を模式的に示す斜視図である。
【図２】水（純水）の塗布量と極板強度（脱落個数）の関係を示す図である。
【符号の説明】
１０…水素吸蔵合金極板、１１…導電性芯体（パンチングメタル）、１２，１３…水素吸蔵合金層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an alkaline storage battery having a spiral electrode group obtained by winding a strip-like negative electrode plate coated with a hydrogen storage alloy powder and a positive electrode plate in a spiral shape via a separator in an outer can.
[0002]
[Prior art]
In recent years, the demand for secondary batteries (storage batteries) that can be charged / discharged has increased with the increase in small portable devices. In particular, nickel has a large capacity as devices become smaller, thinner, and more space efficient. -The demand for hydrogen storage batteries increased rapidly. This type of nickel-hydrogen storage battery is a spiral electrode group in which a positive electrode plate using nickel hydroxide as an active material and a negative electrode plate using a hydrogen storage alloy are spirally wound through a separator. The electrode group is housed in a metal outer can (battery case) together with an alkaline electrolyte, and the metal outer can is sealed.
[0003]
By the way, the negative electrode plate is a hydrogen storage alloy slurry formed by kneading a hydrogen storage alloy powder, a water-soluble binder and pure water or water on both sides of a conductive core made of a punching metal that holds a hydrogen storage alloy layer. However, it is usually produced by applying a hydrogen storage alloy slurry on both surfaces of the conductive core and then naturally drying at room temperature (about 25 ° C.). Here, when the electrode plate coated with the hydrogen storage alloy slurry is naturally dried, the drying speed is slow, and usually a long drying time of about 5 to 6 hours is required until the electrode plate dries. There was a problem that the production efficiency of the board was bad.
[0004]
Therefore, in order to solve such problems, a method has been proposed in which a hydrogen storage alloy slurry is applied to both surfaces of a conductive core and then dried at a high temperature (about 60 ° C. or higher). Thus, when the electrode plate coated with the hydrogen storage alloy slurry is dried at a high temperature, the drying time can be dried in about 15 to 30 minutes, and the production efficiency of the electrode plate is improved. Thereafter, the negative electrode plate and the positive electrode plate thus produced are spirally wound through a separator to form a spiral electrode group, and this spiral electrode group is stored in a metal outer can together with an alkaline electrolyte. The nickel-hydrogen storage battery was obtained by sealing the metal outer can.
[0005]
[Problems to be solved by the invention]
Incidentally, in order to increase the electrode plate drying rate in order to improve the production efficiency of the electrode plate, it is necessary to dry it at a high temperature as described above. However, when the electrode plate is dried at a high temperature, the evaporation rate of moisture increases, so that the moisture contained in the hydrogen storage alloy layer moves rapidly from the inside of the electrode plate to the electrode plate surface (dry surface side). become. For this reason, since the binder contained in the hydrogen storage alloy layer also moves with the movement of moisture, the binder is unevenly distributed on the electrode plate surface and solidifies. As a result, a phenomenon occurs in which the amount of the binder in the hydrogen storage alloy layer in the vicinity of the conductive core disposed in the center of the electrode plate decreases.
[0006]
Here, when the amount of the binder in the active material layer in the vicinity of the conductive core decreases, the adhesive force between the conductive core and the hydrogen storage alloy decreases. Therefore, a spiral electrode using such a negative electrode plate is used. As a group, there was a problem that the hydrogen storage alloy layer was easily dropped from the conductive core when it was spirally wound or when the spiral electrode group was inserted into a metal outer can. In particular, in order to effectively use the space in the metal outer can to make a high capacity battery, the negative electrode plate is exposed without covering the outer periphery of the negative electrode plate arranged on the outermost periphery of the spiral electrode group. The exposed negative electrode plate is in direct contact with the metal outer can, and when the spiral electrode group is inserted into the metal outer can, the hydrogen storage alloy layer further has a conductive core. The problem was that it was easier to drop off than the body.
[0007]
Therefore, the present invention has been made to solve the above problems, and even if the drying temperature of the negative electrode plate coated with the hydrogen storage alloy is increased to improve production efficiency, the strength of the negative electrode plate can be improved. It is an object of the present invention to provide a production method capable of suppressing the decrease, to prevent the hydrogen storage alloy layer from falling off the conductive core, and to obtain a high-quality alkaline storage battery.
[0008]
[Means for solving the problems and their functions and effects]
In order to achieve the above object, the method for producing an alkaline storage battery of the present invention comprises applying a hydrogen storage alloy slurry comprising a hydrogen storage alloy powder, a binder, and a solvent for the binder to both surfaces of the conductive core. The coating process to make the coated electrode plate, the drying process to dry the obtained coated electrode plate to make the dried electrode plate, and the adhesion to attach the binder solvent to the surface of the dried electrode plate obtained And a low temperature drying step of drying the electrode plate to which the binder solvent is attached at a temperature lower than the drying temperature in the drying step.
[0009]
When the electrode plate coated with the hydrogen storage alloy slurry is dried (in this case, the drying is performed at a high temperature in order to increase productivity), the moisture content in the hydrogen storage alloy layer is reduced during drying. The adhesive also moves to the electrode plate surface (dry surface side) and solidifies, so that the amount of the binder in the hydrogen storage alloy layer in the vicinity of the conductive core disposed at the center of the electrode plate is reduced. For this reason, the adhesive force between the conductive core and the hydrogen storage alloy layer is reduced, and the hydrogen storage alloy easily falls off.
[0010]
However, as in the present invention, when a binder solvent (for example, pure water or water in the case of a water-soluble binder) is attached to the surface of the dry electrode plate, the binder solvent becomes a hydrogen-occlusion. Since it penetrates into the alloy layer, the binder consolidated on the surface of the electrode plate at the time of drying is redissolved. As a result, the re-dissolved binder diffuses to the vicinity of the conductive core, and the concentration of the binder near the conductive core increases. Thereafter, when drying is performed at a lower temperature than in the drying process in the low temperature drying process, the diffusion rate of the binder is consolidated without moving again because the evaporation rate is low. As a result, the binder diffused to the vicinity of the conductive core is solidified in the vicinity of the conductive core, and the conductive core and the hydrogen storage alloy layer are firmly bonded. This makes it difficult for the hydrogen storage alloy layer to peel off and prevents the hydrogen storage alloy from falling off.
[0011]
The hydrogen storage alloy layer is easily peeled off at the winding start portion or winding end portion of the strip-shaped negative electrode plate when the spiral electrode group is formed. When it is attached, it may be attached to the entire surface of the dry electrode plate, but at least it is necessary to be the winding start portion or winding end portion of the strip-shaped negative electrode plate when it becomes a spiral electrode group. In this case, if the amount of the binder solvent to be adhered is too small, the binder solidified at the time of drying does not diffuse to the vicinity of the conductive core, and the conductive core and the hydrogen storage alloy layer are formed. It will not be firmly bonded. In addition, if the amount of the binder solvent to be adhered is too large, the drying time becomes long and the production efficiency decreases. For this reason, the adhesion amount of the binder solvent applied to the surface of the dry electrode plate is 3 × 10 ⁻⁵ g / mm ^{2 to} 5 × 10 ⁻⁵ g / mm ² per unit area of the electrode plate. preferable.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below.
1. Production of hydrogen storage alloy powder MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 (Mm is a misch metal) Commercially available metal elements (Mm, Ni, Co, Al, Mn) were weighed and mixed. . This was put into a high frequency melting furnace and melted, then poured into a mold and cooled to prepare a hydrogen storage alloy lump (ingot) composed of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 . This lump of hydrogen storage alloy was coarsely pulverized and then mechanically pulverized in an inert gas atmosphere until the average particle size became about 50 μm to prepare a hydrogen storage alloy powder. In addition, the average particle diameter of the obtained hydrogen storage alloy powder is a value measured by a laser diffraction method.
[0013]
2. Preparation of hydrogen storage alloy electrode plate (1) Example 1
99% by mass of the hydrogen storage alloy powder produced as described above, polyethylene oxide (PEO) powder as a water-soluble binder is 1% by mass with respect to the mass of the hydrogen storage alloy powder, and an appropriate amount of water (or pure water). And kneaded to prepare a hydrogen storage alloy slurry. Next, a hydrogen storage alloy slurry was applied to both surfaces of a conductive core made of a punching metal with nickel plating on the surface and provided with openings to form a coated electrode plate. Then, it dried at about 60 degreeC for 20 minutes, and rolled so that thickness might be set to 0.6 mm, and produced the dry rolling electrode plate. The coating amount of the hydrogen storage alloy slurry was adjusted so that the density of the hydrogen storage alloy after rolling was 5 g / cm ³ .
[0014]
Next, water or pure water was applied to the entire surface of the obtained dry rolled electrode plate, and water or pure water was adhered to the entire surface of the dry rolled electrode plate. Then, after leaving it to stand at room temperature (about 25 ° C.) for about 2 hours and air-drying, it was cut to a predetermined size to produce a hydrogen storage alloy electrode plate a of Example 1. The application amount of water or pure water is 0.202 g (this application amount is a value obtained by calculating a mass difference before and after application), and is 3.29 × 10 ⁻⁵ per unit area of the electrode plate. g / mm ² ). Also, when applying pure water or water to the dried electrode plate, an appropriate method is applied in consideration of productivity, such as a brush application method, a spray application method, or a roll application method. What should I do?
[0015]
(2) Example 2
After producing a dry-rolled electrode plate in the same manner as in Example 1 above, water or pure water was applied to the surface of the winding start portion when it was the spiral electrode group of the obtained dry-rolled electrode plate, Water or pure water was adhered to the surface of the winding start portion of the dry-rolled electrode plate. Then, after leaving it to stand at room temperature (about 25 ° C.) for about 2 hours and air-drying, it was cut to a predetermined size to produce a hydrogen storage alloy electrode plate of Example 2. The application amount of water or pure water is 0.072 g (this application amount is a value obtained by calculating the mass difference before and after application), and is 3.29 × per unit area of the electrode plate of the application part. 10 ⁻⁵ g / mm ² ).
[0016]
(3) Example 3
After producing a dry-rolled electrode plate in the same manner as in Example 1 above, water or pure water was applied to the surface of the winding end portion when it was made the spiral electrode group of the obtained dry-rolled electrode plate, Water or pure water was adhered to the surface of the end of winding of the dry rolled electrode plate. Then, after leaving it to stand at room temperature (about 25 ° C.) for about 2 hours and naturally drying, it was cut to a predetermined size to produce a hydrogen storage alloy electrode plate c of Example 3. The application amount of water or pure water is 0.072 g (this application amount is a value obtained by calculating the mass difference before and after application), and is 3.29 × per unit area of the electrode plate of the application part. 10 ⁻⁵ g / mm ² ).
[0017]
(4) Example 4
After producing a dry rolled electrode plate in the same manner as in Example 1 described above, water or pure water was formed on the surfaces of the winding start portion and the winding end portion when the resulting dried rolled electrode plate was a spiral electrode group. Then, water or pure water was adhered to the surface of the winding start portion and winding end portion of the dry-rolled electrode plate. Then, after leaving it to stand at room temperature (about 25 ° C.) for about 2 hours and naturally drying, it was cut to a predetermined size to produce a hydrogen storage alloy electrode plate d of Example 4. The application amount of water or pure water is 0.144 g (this application amount is a value obtained by calculating a mass difference before and after application), and is 3.29 × per unit area of the electrode plate of the application part. 10 ⁻⁵ g / mm ² ).
[0018]
(5) Comparative Example 1
In the same manner as in Example 1 described above, the hydrogen storage alloy slurry was applied to both surfaces of the conductive core to form a coated electrode plate, and then allowed to stand at room temperature (about 25 ° C.) for about 6 hours to dry naturally. Then, it was rolled to a thickness of 0.6 mm to prepare a dry rolled electrode plate. The coating amount of the hydrogen storage alloy slurry was adjusted so that the density of the hydrogen storage alloy after rolling was 5 g / cm ³ . The dry-rolled electrode plate thus obtained was cut into a predetermined size to produce a hydrogen storage alloy electrode plate x of Comparative Example 1.
[0019]
(6) Comparative Example 2
In the same manner as in Example 1 above, the hydrogen storage alloy slurry was applied to both surfaces of the conductive core to form a coated electrode plate on which an active material layer was formed, and then dried at about 60 ° C. for 20 minutes. And it rolled so that thickness might be set to 0.6 mm, and produced the dry rolling electrode plate. The coating amount of the hydrogen storage alloy slurry was adjusted so that the density of the hydrogen storage alloy after rolling was 5 g / cm ³ . The dry-rolled electrode plate thus obtained was cut to a predetermined size to produce a hydrogen storage alloy electrode plate y of Comparative Example 2.
[0020]
3. Next, each of the hydrogen storage alloy negative electrode plates a to d of Examples 1 to 4 and each of the hydrogen storage alloy negative electrode plates x and y of Comparative Examples 1 and 2 prepared as described above was used. Each of the hydrogen storage alloy negative electrode plate and the well-known non-sintered nickel positive electrode plate are wound through a separator made of an alkali-resistant nylon nonwoven fabric. At this time, a spiral electrode plate group was produced by winding in a spiral shape with the hydrogen storage alloy negative electrode plate on the outside.
[0021]
After inserting each spiral electrode plate group thus produced into a bottomed cylindrical metal outer can, potassium hydroxide (KOH), lithium hydroxide (LiOH) and sodium hydroxide are placed in each metal outer can. A 4 / 5A size nickel-hydrogen storage battery having a nominal capacity of 1700 mAh was prepared by injecting and sealing a three-component electrolyte composed of (NaOH).
[0022]
Here, a battery using the hydrogen storage alloy negative electrode plate a is referred to as a battery A, a battery using the hydrogen storage alloy negative electrode plate b is referred to as a battery B, and a battery using the hydrogen storage alloy negative electrode plate c is referred to as a battery C. A battery using the alloy negative electrode plate d was referred to as a battery D, a battery using the hydrogen storage alloy negative electrode plate x was referred to as a battery X, and a battery using the hydrogen storage alloy negative electrode plate y was referred to as a battery Y.
[0023]
4). Measurement of the number of falling off active materials Here, when producing 100 each of the nickel-hydrogen storage batteries A to D and X, Y, as described above, hydrogen was occluded from the conductive core during the production of the spiral electrode group. When the number of electrode groups from which the alloy had dropped was measured, the results shown in Table 1 below were obtained. In Table 1 below, the drying temperature and drying time indicate the drying temperature and drying time of the coated electrode plate, respectively.
[0024]
[Table 1]

[0025]
As is clear from the results in Table 1 above, the battery X using the hydrogen storage alloy negative electrode plate x produced by naturally drying the coated electrode plate at room temperature (about 25 ° C.) and the coated electrode plate at about 60 ° C. Comparing with the battery Y using the hydrogen storage alloy negative electrode plate y produced by drying at the same time, it can be seen that the number of dropouts is reduced by using the hydrogen storage alloy negative electrode plate x produced by natural drying.
This is because when the coated electrode plate is dried at a high temperature of about 60 ° C., the drying of the negative electrode plate is completed in a short time of about 20 minutes. However, since the drying speed is high, the moisture evaporation rate is increased and the hydrogen storage alloy As the moisture contained in the layer moves, the water-soluble binder also moves, and the water-soluble binder is unevenly distributed on the electrode plate surface (dry surface side) and solidifies. For this reason, it is considered that the amount of the water-soluble binder in the hydrogen storage alloy layer in the vicinity of the conductive core disposed in the central portion of the negative electrode plate is reduced, and the hydrogen storage alloy is easily removed.
[0026]
On the other hand, when the coated electrode plate is naturally dried at room temperature (about 25 ° C.), the drying rate is slow, so the evaporation rate of moisture in the hydrogen storage alloy layer is also slowed. As a result, the water-soluble binder contained in the hydrogen-absorbing alloy layer is consolidated without moving, so that the water-soluble binder in the hydrogen-absorbing alloy layer in the vicinity of the conductive core disposed at the center of the negative electrode plate is used. This is because the binding strength between the conductive core and the hydrogen storage alloy is improved without decreasing the amount of the adhesive. However, since the drying speed is slow, it takes a long time of about 6 hours to complete the drying of the negative electrode plate.
[0027]
Further, after drying the coated electrode plate at a high temperature of about 60 ° C. to obtain a dry electrode plate, water or pure water is applied to the entire surface of the dry electrode plate, and the room temperature (about 25 ° C.) is lower than when drying. The battery A using the hydrogen storage alloy negative electrode plate a produced by natural drying with a hydrogen storage alloy negative electrode plate produced by applying water or pure water to the part of the dry electrode plate that becomes the winding start portion of the spiral electrode group a battery B using b, a battery C using a hydrogen storage alloy negative electrode plate c prepared by applying water or pure water to the end portion of the spiral electrode group of the dry electrode plate, and a dry electrode plate In the battery D using the hydrogen storage alloy negative electrode plate d produced by applying water or pure water to the winding start part and the winding end part of the spiral electrode group, the battery D is dropped in the same manner as the battery X. It can be seen that the number is decreasing.
[0028]
This is because when pure water or water is applied and adhered to the surface of the dry electrode plate, the pure water or water penetrates into the hydrogen storage alloy layer. The adhesive is redissolved, and the redissolved water-soluble binder diffuses to the vicinity of the conductive core, and the concentration of the water-soluble binder in the vicinity of the conductive core increases. Thereafter, when dried at room temperature (about 25 ° C.) lower than the drying step, the diffused water-soluble binder is consolidated, but at the time of consolidation, it diffuses to the vicinity of the conductive core. It is considered that the water-soluble binder was also solidified without moving again, and the conductive core and the hydrogen storage alloy were firmly bonded. This makes it difficult for the hydrogen storage alloy layer to peel off and prevents the hydrogen storage alloy from falling off.
[0029]
In addition, even if it is the whole surface of a dry electrode plate like the battery A as the application | coating part of the pure water or the water to the dry electrode plate surface, the winding start of the spiral electrode group of a dry electrode plate like the battery B is started. Even if it is a part that becomes a winding part, a part that becomes a winding end part of the spiral electrode group of the dry electrode plate like the battery C, or a winding of the spiral electrode group of the dry electrode plate like the battery D It can be seen that even the portion that becomes the start portion and the portion that becomes the winding end portion does not have a significant difference in the number of dropouts, and therefore, it may be applied to any one of these portions.
[0030]
5. Examination of application amount of water (pure water) In each of the examples described above, the relationship between the application site and the number of drops when the application amount of pure water or water on the dry electrode plate surface was made constant was examined. Below, the relationship between the application amount of pure water or water and the electrode plate strength was examined. In this case, after producing a dry electrode plate in the same manner as in Example 1 described above, the amount of pure water or water applied to the entire surface of the dry electrode plate is set to 0 to 6 × 10 ⁻ per unit area of the electrode plate. ^The coating was applied at ⁵ g / mm ² . Next, each electrode plate with different amounts of pure water or water applied is left to stand at room temperature (about 25 ° C.) for about 2 hours and air-dried in the same manner as in Example 1 described above. After cutting, as shown in FIG. 1, each electrode plate 10 having a different amount of pure water or water after drying was produced.
[0031]
1 includes a conductive core 11 made of a punching metal at the center of the electrode plate 10, and hydrogen storage alloy layers 12 and 13 are formed on both surfaces of the conductive core 11. Next, after cutting the surface of the hydrogen storage alloy layer 12 on one side of each of the electrode plates 10, the cutting surface was lightly rubbed with a waste cloth to remove cutting chips on the surface. Thereafter, a cutter (not shown) is held at an angle of about 30 degrees with respect to the surface of the hydrogen storage alloy layer 12 of each electrode plate 10, and then a load of about 250 g is applied to the blade edge of the cutter. The kerfs x and y were drawn so as to cut the hydrogen storage alloy layer 12. The intervals between the kerfs x and y were 1 mm, and 10 kerfs x and y were drawn so as to intersect each other at right angles.
[0032]
By pulling 10 each of the kerfs x and y so as to cross each other at right angles, 100 grids were formed in a grid pattern. Next, 10 electrode plates 10 each having 100 grids formed in a grid pattern are used to lift the hydrogen storage alloy layers 12 and 13 vertically and to a height of about 100 mm. After that, each electrode plate 10 was dropped freely. After this drop test was repeated three times, the number of dropouts of the grids formed on each electrode plate 10 was counted, and the average value was obtained as shown in FIG. The number of drops on the vertical axis in FIG. 2 indicates the number of dropouts of the meshes. When the number of dropouts decreases, the strength of the electrode plate, that is, the adhesion between the conductive core 11 and the hydrogen storage alloy layers 12 and 13 is shown. It means that power is strong.
[0033]
As is clear from the results of FIG. 2, as the amount of pure water or water applied increases, the number of dropouts decreases linearly and the amount applied is 3 × 10 ⁻⁵ g / mm ² per unit area of the electrode plate. It can be seen that the amount of decrease decreases when the amount exceeds 50, and the amount of coating becomes almost constant when the amount exceeds 5 × 10 ⁻⁵ g / mm ² per unit area of the electrode plate. Further, if the coating amount increases so as to exceed 5 × 10 ⁻⁵ g / mm ² per unit area of the electrode plate, the drying time after application of pure water or water becomes long. From this, it can be said that the application amount of pure water or water is preferably 3 × 10 ⁻⁵ g / mm ² or more and 5 × 10 ⁻⁵ g / mm ² or less.
[0034]
As described above, in the present invention, even if the productivity is improved by rapid drying at a high temperature, the water-soluble binder moved during drying so that pure water or water adheres to the surface of the dry electrode plate. Therefore, the conductive core and the hydrogen storage alloy are firmly bonded together, and the hydrogen storage alloys are also firmly bonded to each other. As a result, the hydrogen storage alloy layer becomes difficult to peel off and the hydrogen storage alloy can be prevented from falling off, so that it is possible to obtain a high-quality alkaline storage battery with excellent productivity.
[0035]
In the embodiment described above, and describes some of the Ni represented by _{_{_{_{Mm a Ni b Co c Mn d}}}} Al e as a hydrogen absorbing alloy Co, Mn, for example using a hydrogen storage alloy obtained by substituting Al However, a hydrogen storage alloy in which a part of Ni is substituted with Co and Cu, Fe, Cr, Si, Mo, or the like may be used. _{_{_{Further, Mm a Ni b Co c Mn}}} d Al other AB ₅ type rare earth hydrogen storage alloy other than hydrogen absorbing alloy represented by _e, for example, a portion of the Ni Co and Al with LaNi ₅ type, W, etc. You may make it use the hydrogen storage alloy substituted by. In the above-described embodiments, examples of using a mechanically pulverized hydrogen storage alloy have been described. However, a hydrogen storage alloy prepared by an atomizing method or a mixed powder in which a pulverized alloy is mixed with the hydrogen storage alloy may be used. Good.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing a state in which a grid-like cut groove is formed in an active material layer in order to perform an active material drop-out test.
FIG. 2 is a graph showing the relationship between the amount of water (pure water) applied and the electrode plate strength (the number of drops).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Hydrogen storage alloy electrode plate, 11 ... Conductive core (punching metal), 12, 13 ... Hydrogen storage alloy layer

Claims

A method for producing an alkaline storage battery comprising a spirally wound electrode group in which a belt-like negative electrode plate and a positive electrode plate coated with a hydrogen storage alloy powder are spirally wound through a separator,
A coating process in which a hydrogen storage alloy slurry comprising the hydrogen storage alloy powder, a binder, and a solvent for the binder is applied to both surfaces of the conductive core to form a coating electrode;
A drying step of drying the coated electrode plate to form a dry electrode plate;
A solvent attachment step of attaching a solvent of the binder to the surface of the dry electrode plate;
A method for producing an alkaline storage battery, comprising: a low-temperature drying step for drying at a lower temperature than a drying temperature in the drying step after the solvent attaching step .

In the solvent adhering step, the bonding is performed on at least one surface or the entire surface of a portion that becomes a winding start portion or a winding end portion of the strip-shaped negative electrode plate when the dry electrode plate becomes the spiral electrode group. 2. The method of manufacturing an alkaline storage battery according to claim 1, wherein a solvent for the adhesive is adhered.

The amount of the solvent of the binder to be adhered to the surface of the dry electrode plate is 3 × 10 ⁻⁵ g / mm ^{2 to} 5 × 10 ⁻⁵ g / mm ² per unit area of the strip-shaped negative electrode plate. The manufacturing method of the alkaline storage battery of Claim 1 or Claim 2 to do.