JP4233234B2 - Method for producing alkaline storage battery - Google Patents
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- JP4233234B2 JP4233234B2 JP2001084752A JP2001084752A JP4233234B2 JP 4233234 B2 JP4233234 B2 JP 4233234B2 JP 2001084752 A JP2001084752 A JP 2001084752A JP 2001084752 A JP2001084752 A JP 2001084752A JP 4233234 B2 JP4233234 B2 JP 4233234B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【０００１】
【発明の属する技術分野】
本発明はニッケル−水素蓄電池などのアルカリ蓄電池に係り、特に、ニッケル−水素蓄電池の負極に備えられた水素吸蔵合金の活性化に関する。
【０００２】
【従来の技術】
近年の市場拡大に伴って、電動工具、アシスト自転車、電気自動車等の用途が拡大し、ニッケル−水素蓄電池の大型化、高容量化、ハイパワー化への需要、要望が高まった。この種のニッケル−水素蓄電池は、電池組立直後においては、充分な電池性能を確保することができず、例えば、室温で充放電するような活性化処理を必要とする。しかしながら、単にこのような活性化処理を施しただけでは、低温や高率での放電において充分な放電容量や作動電圧が得られないという問題があった。
【０００３】
また、水素吸蔵合金は本来極めて活性であるが、外装缶に組み込んで密閉するまでに空気中に放置されたり、製造工程中に加温されるなどによって酸化され、強固な酸化膜が合金表面に形成されて極めて不活性になる。この酸化膜は、活性化処理の充放電の繰り返しにより、部分的に破壊されたり、合金自身にクラックが生じて、新たな合金が表面に露出することにより、活性化が進むとともに、電池の活性度も徐々に高くなる。また、水素吸蔵合金の粒径は、小さいものと比較して大きいものの方が酸化を受けがたい。反面、電池を組み立てた後においては、粒径の大きい水素吸蔵合金は、反応面積の低下によって作動電圧が低下するため、低温や高率での放電に適さないという問題があった。
【０００４】
このような背景にあって、比較的平均粒径の大きい水素吸蔵合金を用いて負極を作製し、活性化工程の充放電で水素吸蔵合金にクラックを生じさせて、平均粒径を５０μｍ以下にしたニッケル−水素蓄電池が特許第２９９４７３１号公報にて提案されるようになった。
この特許第２９９４７３１号公報にて提案されたニッケル−水素蓄電池においては、比較的平均粒径の大きい水素吸蔵合金を用いているため、電極製造時まで水素吸蔵合金が酸化されがたく、また、電池の組立後においても酸化を受けることが少ない。このため、活性化終了後の水素吸蔵合金の酸化は抑制されており、サイクル寿命に有利となる。
【０００５】
また、活性化工程の充放電で水素吸蔵合金にクラックを生じさせ、平均粒径を５０μｍ以下に調整して、水素吸蔵合金の反応面積を増大させるとともに、活性な合金表面を露出させているため、負極の反応性が向上して、放電に有利となる。さらに、上記特許第２９９４７３１号公報においては、活性化処理における充電後の放電を３０〜８０℃の温度雰囲気で行うようにしているため、水素吸蔵合金にクラックが生じ易くなって、さらに平均粒径が小さい水素吸蔵合金が得られるようになる。
【０００６】
【発明が解決しようとする課題】
しかしながら、特許第２９９４７３１号公報にて提案された活性化方法にあっては、充放電サイクル寿命に問題を生じないものの、活性化後の水素吸蔵合金の反応面積が不充分であることに起因して、高率放電（大電流放電）時の作動電圧が低く、場合によっては放電不能になるという問題を生じた。
本発明は上記問題を解決するためになされたものであって、サイクル寿命を低下させることなく、高率放電特性を向上させることができる活性化方法を提案して、放電性およびサイクル寿命に優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。
【０００７】
【課題を解決するための手段】
上記目的を達成するため、本発明は、平均粒径が５０μｍ以上、１２０μｍ以下で組成式がＭｍaＮｉbＣｏcＡｌdＭｎe（但し、ｃ／ａが０．５以上）で表される水素吸蔵合金を含有する負極と、正極と、アルカリ電解液とを備えたアルカリ蓄電池を組み立てた後、充放電を行ってアルカリ蓄電池を活性化する活性化工程を備えたアルカリ蓄電池の製造方法であって、この活性化工程において、初回に行う充放電を、前記負極の容量に対して少なくとも０．６Ｉｔ以上の充電レートで電池容量の６０％以上を充電した後、放電させるともに、活性化工程での充電を３０℃以下の温度雰囲気で行うようにしたことを特徴とする。
【０００８】
このように、初回に行う充放電を、負極の容量に対して少なくとも０．６Ｉｔ以上の充電レートで電池容量の６０％以上を充電した後、放電させるようにして活性化を行うと、活性化工程の初回の充電において、水素吸蔵合金粒子にクラックが生じるとともに、合金粒子が割れて小さな粒径となり、このものを放電させることにより、さらに微細化される。これにより、平均粒径が５０〜１２０μｍの合金粒子が、平均粒径は２０〜４５μｍの合金粒子になるとともに、この合金粒子に多数のクラックが存在することとなる。この結果、水素吸蔵合金粒子に多数の活性面が出現して反応面積が増大するため、高率放電を行っても放電特性が低下することを抑制できるようになる。
【０００９】
この場合、活性化工程の初回の充電での高率充電レートが負極容量に対して０．６Ｉｔ未満であると、水素吸蔵合金粒子の反応面積が不充分になって高率放電特性が低下するため、高率充電レートは負極容量に対して０．６Ｉｔ以上にする必要がある。
また、活性化工程の初回の充電を３０℃より高温の温度雰囲気で行うと、電池温度が上昇して液漏れを生じるため、活性化工程での充電は３０℃以下の温度雰囲気で行うのが望ましい。
【００１０】
また、水素吸蔵合金の耐食性を向上させるためにコバルトを添加した、組成式がＭｍaＮｉbＣｏcＡｌdＭｎeで表される水素吸蔵合金を用いる場合、コバルトの添加量（ｃ／ａ）が減少すると水素吸蔵合金の耐食性が低下するため、活性化終了後に水素吸蔵合金の酸化が進行してサイクル寿命が低下する。このため、水素吸蔵合金にある程度以上のコバルト量を添加する必要がある。そこで、実験を行った結果、コバルトの添加量（ｃ／ａ）が０．５以上であれば耐食性が向上し、サイクル寿命の低下を抑制できることが明らかになった。このため、コバルトの添加量（ｃ／ａ）は０．５以上とするのが望ましい。
【００１１】
また、初回の充電後の放電を３０℃〜８０℃の温度雰囲気とすることにより、負極活性度をさらに向上させることが可能となる。これは、水素吸蔵合金の水素放出反応（放電反応）が吸熱反応であるため、高温下で放電を行うことにより、放電反応が円滑に、かつ効率的に行われ、この円滑な水素の放出が行われるときに、水素吸蔵合金粒子にクラックが生じやすくなり、水素吸蔵合金粒子の反応面積が増大するためである。
【００１２】
さらに、初回の放電後の開路電圧を１．１５Ｖ以上で１．２５Ｖ以下にすることで、正極に含まれるコバルト化合物の還元が抑制されて、高次コバルト化合物を安定化させることが可能となり、高温下でのサイクル容量の劣化を抑制することが可能となる。なお、初回の放電後の開路電圧を１．１５Ｖ以上に調整する方法としては、アルカリ蓄電池に定電流を印加しながら放電を行い、放電時間を調節して放電量を調節する方法、もしくは、アルカリ蓄電池の正負極端子に抵抗を含む回路を接続して放電を行い、放電時間を調節して放電量を調節する方法が適用できる。
【００１３】
【発明の実施の形態】
以下に、本発明をニッケル−水素蓄電池に適用した場合の一実施の形態を説明する。なお、本発明は以下の実施の形態に限定されるものではなく、その要旨を変更しない範囲で適宜変更して実施することができる。
【００１４】
１．水素吸蔵合金負極の作製
ミッシュメタル（Ｍｍ：希土類元素の混合物）、ニッケル、コバルト、アルミニウム、およびマンガンを１．０：３．６：０．６：０．２：０．６の比率で混合し、この混合物をアルゴンガス雰囲気の高周波誘導炉で誘導加熱して合金溶湯となす。この合金溶湯を公知の方法で鋳型に流し込み、冷却して、組成式がＭｍ1.0Ｎｉ3.6Ｃｏ0.6Ａｌ0.2Ｍｎ0.6で表される水素吸蔵合金のインゴットを作製した。
【００１５】
この水素吸蔵合金インゴットを機械的に粗粉砕した後、不活性ガス雰囲気中で平均粒子径が約９０μｍになるまで機械的に粉砕した。このようにして作製した水素吸蔵合金粉末にポリエチレンオキサイド等の結着剤と、適量の水を加えて混合して水素吸蔵合金スラリーを作製した。このスラリーをパンチングメタルからなる活物質保持体の両面に、圧延後の活物質密度が所定量になるように塗着した後、乾燥、圧延を行った後、所定寸法に切断して水素吸蔵合金負極を作製した。
【００１６】
２．ニッケル正極の作製
硫酸コバルト粉末を水に溶かした水溶液に水酸化ニッケル粉末を投入し、ついで、水酸化ナトリウム水溶液を撹拌しながら滴下して液のｐＨを調整した後、撹拌した。ついで、生成された沈殿物を濾別し、水洗し、室温（約２５℃）で真空乾燥して、水酸化ニッケル粒子の表面に水酸化コバルトの被覆層が形成された粉末を得た。得られた粉末と水酸化ナトリウム水溶液とを混合し、空気中にて加熱処理した後、水洗、乾燥して、水酸化ニッケル粒子の表面にナトリウム含有コバルト化合物の高導電性被覆層が形成された水酸化ニッケル粉末を得た。
【００１７】
ついで、得られた水酸化ニッケル粉末を主成分とし、これに少量の水酸化コバルトを添加した活物質粉末１００質量部と、０．２質量％のヒドロキシプロピルセルロース水溶液４０質量部と、６０質量％のＰＴＦＥディスパージョン液１質量部とを添加混合して活物質スラリーを作製した。このようにして作製した活物質スラリーを、多孔度が９７％で、厚みが約１．５ｍｍのニッケル発泡体（この発泡体は三次元的に連続した網状骨格を備えている）からなる金属多孔体（活物質保持体）に充填した。ついで、乾燥させた後、厚みが０．７ｍｍになるまで圧延した後、所定寸法に切断し、正極リードを溶接してニッケル正極を作製した。
【００１８】
３．ニッケル−水素電池の作製
ついで、上述のように作製したニッケル正極と、上述のように作製した水素吸蔵合金負極とをポリプロピレン製不織布からなるセパレータ（厚みが約０．１５ｍｍのもの）を介して渦巻状に卷回して渦巻状電極群を作製した。このように作製した渦巻状電極群の負極の端部に負極集電体を接続するとともに、ニッケル正極の端部と正極集電体とを接続して電極体を作製した。ついで、電極体を有底円筒形の金属外装缶内に挿入し、負極集電体を金属製外装缶の底部にスポット溶接した後、正極集電体から延出するリード板を封口体の底部に溶接した。
【００１９】
この後、金属外装缶内に７．０ｍｏｌ／ｌのアルカリ電解液（水酸化リチウム（ＬｉＯＨ）１．０ｍｏｌ／ｌと水酸化ナトリウム（ＮａＯＨ）１．０ｍｏｌ／ｌと水酸化カリウム（ＫＯＨ）５．０ｍｏｌ／ｌを含有した水溶液）を注入し、封口体を封口ガスケットを介して外装缶の開口部にかしめて封口した。これにより、公称容量が２０００ｍＡｈで、容量比が２．０（正極容量が２０００ｍＡｈで、負極容量は４０００ｍＡｈ）の円筒形ニッケル−水素蓄電池を作製した。
【００２０】
４．活性化方法
（１）電池Ａ
上述のようにして作製したニッケル−水素蓄電池を用いて、まず、室温（約２５℃）の温度雰囲気で、２００ｍＡ（正極容量に対して０．１Ｉｔ［なお、Ｉｔ（ｍＡ）は定格容量（ｍＡｈ）／１ｈ（時間）で表される数値である、以下においても同様である］で、負極容量に対して０．０５Ｉｔ）の充電々流で６０分充電（公称容量の１０％）し、２４００ｍＡ（正極容量に対して１．２Ｉｔで、負極容量に対して０．６Ｉｔ）の充電々流で３５分間ハイレート充電（公称容量の７０％）し、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で１２０分充電（公称容量の２０％）して、初回充電を終了させた。この後、６０℃の温度雰囲気で１時間休止した後、定電流を印加して、６０℃の温度雰囲気で４００ｍＡ（０．２Ｉｔ）の放電々流で放電させた。この場合、放電終止後３０分経過した後の開路電圧が１．１５〜１．２５Ｖになるように放電時間を調整して放電量を調整した。このように充放電を行って活性化したニッケル−水素蓄電池を電池Ａとした。
【００２１】
（２）電池Ｂ
上述のようにして作製したニッケル−水素蓄電池を用いて、まず、室温（約２５℃）の温度雰囲気で、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で６０分充電（公称容量の１０％）し、２８００ｍＡ（正極容量に対して１．４Ｉｔで、負極容量に対して０．７Ｉｔ）の充電々流で３０分間ハイレート充電（公称容量の７０％）し、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で１２０分充電（公称容量の２０％）して、初回充電を終了させた。この後、６０℃の温度雰囲気で１時間休止した後、定電流を印加して、６０℃の温度雰囲気で４００ｍＡ（０．２Ｉｔ）の放電々流で放電させた。この場合、放電終止後３０分経過した後の開路電圧が１．１５〜１．２５Ｖになるように放電時間を調整して放電量を調整した。このように充放電を行って活性化したニッケル−水素蓄電池を電池Ｂとした。
【００２２】
（３）電池Ｃ
上述のようにして作製したニッケル−水素蓄電池を用いて、まず、室温（約２５℃）の温度雰囲気で、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で６０分充電（公称容量の１０％）し、３６００ｍＡ（正極容量に対して１．８Ｉｔで、負極容量に対して０．９Ｉｔ）の充電々流で２３分間ハイレート充電（公称容量の７０％）し、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で１２０分充電（公称容量の２０％）して、初回充電を終了させた。この後、６０℃の温度雰囲気で１時間休止した後、定電流を印加して、６０℃の温度雰囲気で４００ｍＡ（０．２Ｉｔ）の放電々流で放電させた。この場合、放電終止後３０分経過した後の開路電圧が１．１５〜１．２５Ｖになるように放電時間を調整して放電量を調整した。このように充放電を行って活性化したニッケル−水素蓄電池を電池Ｃとした。
【００２３】
（４）電池Ｓ
上述のようにして作製したニッケル−水素蓄電池を用いて、まず、室温（約２５℃）の温度雰囲気で、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で１０００分充電（公称容量の１００％）して、初回充電を終了させた。この後、６０℃の温度雰囲気で１時間休止した後、定電流を印加して、６０℃の温度雰囲気で４００ｍＡ（０．２Ｉｔ）の放電々流で放電させた。この場合、放電終止後３０分経過した後の開路電圧が１．１５〜１．２５Ｖになるように放電時間を調整して放電量を調整した。このように充放電を行って活性化したニッケル−水素蓄電池を電池Ｓとした。
【００２４】
（６）電池Ｔ
上述のようにして作製したニッケル−水素蓄電池を用いて、まず、室温（約２５℃）の温度雰囲気で、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で６０分充電（公称容量の１０％）し、１０００ｍＡ（正極容量に対して０．５Ｉｔで、負極容量に対して０．２５Ｉｔ）の充電々流で８４分間ハイレート充電（公称容量の７０％）し、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で１２０分充電（公称容量の２０％）して、初回充電を終了させた。この後、６０℃の温度雰囲気で１時間休止した後、定電流を印加して、６０℃の温度雰囲気で４００ｍＡ（０．２Ｉｔ）の放電々流で放電させた。この場合、放電終止後３０分経過した後の開路電圧が１．１５〜１．２５Ｖになるように放電時間を調整して放電量を調整した。このように充放電を行って活性化したニッケル−水素蓄電池を電池Ｔとした。
【００２５】
（７）電池Ｕ
上述のようにして作製したニッケル−水素蓄電池を用いて、まず、室温（約２５℃）の温度雰囲気で、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で６０分充電（公称容量の１０％）し、２０００ｍＡ（正極容量に対して１．０Ｉｔで、負極容量に対して０．５Ｉｔ）の充電々流で４２分間ハイレート充電（公称容量の７０％）し、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で１２０分充電（公称容量の２０％）して、初回充電を終了させた。この後、６０℃の温度雰囲気で１時間休止した後、定電流を印加して、６０℃の温度雰囲気で４００ｍＡ（０．２Ｉｔ）の放電々流で放電させた。この場合、放電終止後３０分経過した後の開路電圧が１．１５〜１．２５Ｖになるように放電時間を調整して放電量を調整した。このように充放電を行って活性化したニッケル−水素蓄電池を電池Ｕとした。
【００２６】
５．電池試験
（１）高率放電特性の測定
上述のようにして活性化した各電池Ａ〜ＣおよびＳ〜Ｕを用い、室温（約２５℃）の温度雰囲気で、２０００ｍＡ（１Ｉｔ）の充電々流で正極が完全に充電された後に生じる電池電圧の低下（−ΔＶ）が１０ｍＶになるまで充電し、１時間休止した後、３００００ｍＡ（１５Ｉｔ）の放電々流で、終止電圧が０．６Ｖになるまで放電させるという高率放電を行い、このときの作動電圧（３０Ａ放電時の作動電圧）を求めると下記の表１に示すような結果が得られた。
【００２７】
また、上述のようにして活性化した各電池Ａ〜ＣおよびＳ〜Ｕを用い、室温（約２５℃）の温度雰囲気で、２０００ｍＡ（１Ｉｔ）の充電々流で−ΔＶが１０ｍＶになるまで充電し、１時間休止した後、４００００ｍＡ（２０Ｉｔ）の放電々流で、終止電圧が０．６Ｖになるまで放電させるという高率放電を行い、このときの作動電圧（４０Ａ放電時の作動電圧）を求めると下記の表１に示すような結果が得られた。
【００２８】
（２）高温サイクル寿命試験
ついで、上述のようにして活性化した各電池Ａ〜ＣおよびＳ〜Ｕを用い、室温（約２５℃）の温度雰囲気で、２０００ｍＡ（１Ｉｔ）の充電々流で充電を行い、−ΔＶが１０ｍＶになるまで充電した後、１時間休止し、１５０００ｍＡ（７．５Ｉｔ）の放電々流で電池電圧が０．６Ｖに達するまでまで放電させ、１時間休止するという−ΔＶサイクル試験を行い、放電容量が−ΔＶサイクルの初期容量の６０％に達した時点で寿命と判定する高率サイクル寿命試験を行って、各電池Ａ〜ＣおよびＳ〜Ｕのサイクル寿命を求めると下記の表１に示すような結果が得られた。
【００２９】
【表１】
上記表１の結果から明らかなように、充電レートが負極容量に対して０．６Ｉｔ以上の高率で充電して活性化した電池Ａ，Ｂ，Ｃは、３０Ａあるいは４０Ａという高率で放電させても作動電圧がそれほど低下しないことが分かる。一方、充電レートが負極容量に対して０．６Ｉｔ未満で充電して活性化した電池Ｓ，Ｔ，Ｕは、３０Ａあるいは４０Ａという高率で放電させると、作動電圧が低下したり、放電初期に終止電圧（０．６Ｖ）以下に達して放電不能になることが分かる。
これは、初回の充電レートを負極容量に対して０．６Ｉｔ以上の高率で充電すると、水素吸蔵合金粒子により多くのクラックが生じて水素吸蔵合金粒子の反応面積が増大し、高率放電時の作動電圧の低下を抑制できたためと考えられる。ここで、初回の充電レートを高くすることで水素吸蔵合金粒子により多くのクラックが生じ易い理由としては、高率充電することにより、水素吸蔵合金粒子の相変化（体積変化）が急激に生じてクラックが生じやすくなったと考えられる。
【００３１】
一方、サイクル寿命については、初回の充電レートを負極容量に対して、０．０５Ｉｔから０．９Ｉｔの間で変化させても、サイクル寿命は約５００サイクルを維持していることが分かる。このことから、充電レートが負極容量に対して０．６Ｉｔ以上の高率で充電してサイクル寿命に悪影響を与えることなく、高率放電特性を向上させることができるということができる。
なお、初回の充電レートを負極容量に対して１．２Ｉｔ以上にすると、電池温度が急激に上昇してガスを発生し、電池内圧が上昇して電解液の漏洩を生じる可能性が高くなるため、初回の充電レートを負極容量に対して１．０Ｉｔ未満に規制することが望ましい。
【００３２】
６．活性化時の高率充電による充電量の検討
ついで、活性化時の高率充電による充電量について検討した。
（１）電池Ｄ
ここで、上述のようにして作製したニッケル−水素蓄電池を用いて、まず、室温（約２５℃）の温度雰囲気で、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で６０分充電（公称容量の１０％）し、２８００ｍＡ（正極容量に対して１．４Ｉｔで、負極容量に対して０．７Ｉｔ）の充電々流で２５分間ハイレート充電（公称容量の６０％）し、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で１２０分充電（公称容量の２０％）して、初回充電を終了させた。この後、６０℃の温度雰囲気で１時間休止した後、定電流を印加して、６０℃の温度雰囲気で４００ｍＡ（０．２Ｉｔ）の放電々流で放電させて活性化したニッケル−水素蓄電池を電池Ｄとした。
【００３３】
（２）電池Ｖ
一方、上述のようにして作製したニッケル−水素蓄電池を用いて、まず、室温（約２５℃）の温度雰囲気で、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で６０分充電（公称容量の１０％）し、２８００ｍＡ（正極容量に対して１．４Ｉｔで、負極容量に対して０．７Ｉｔ）の充電々流で２１分間ハイレート充電（公称容量の５０％）し、２００ｍＡ（正極容量に対して０．１Ｉｔで、負極容量に対して０．０５Ｉｔ）の充電々流で１２０分充電（公称容量の２０％）して、初回充電を終了させた。この後、６０℃の温度雰囲気で１時間休止した後、定電流を印加して、６０℃の温度雰囲気で４００ｍＡ（０．２Ｉｔ）の放電々流で放電させて活性化したニッケル−水素蓄電池を電池Ｖとした。
【００３４】
ついで、これらの電池Ｄ，Ｖを用いて上述と同様の試験を行って、３０Ａ放電時の作動電圧および４０Ａ放電時の作動電圧を求めるとともに、サイクル寿命を求めると下記の表２に示すような結果が得られた。なお、下記の表２においては、上述した電池Ｂの結果も併せて示している。
【００３５】
【表２】
上記表２の結果から明らかなように、活性化時の高率充電による充電量を公称容量に対して５０％とした電池Ｖにあっては、３０Ａ放電時に作動電圧が大幅に低下し、また４０Ａ放電時には放電初期に終止電圧（０．６Ｖ）以下に達して放電不能になったことが分かる。これは、充電量が少ないと初回充電時に水素吸蔵合金粒子に生じるクラック量が少なく、水素吸蔵合金粒子の反応表面積が不充分であるためと考えられる。一方、充電量を公称容量に対して６０％以上とした電池Ｂ，Ｄにあっては、３０Ａ放電時および４０Ａ放電時に作動電圧がそれほど低下しないことが分かる。このことから、活性化時の高率充電による充電量は６０％以上にするのが好ましいということができる。
【００３７】
７．活性化時の温度雰囲気の検討
ここで、上述のようにして作製したニッケル−水素蓄電池を用いて、上述した電池Ｂと同様の条件で充放電して活性化するに際して、充電温度雰囲気（周囲温度）のみを３０℃にして充電を行って活性化して作製したニッケル−水素蓄電池を電池Ｅとし、また、充電温度雰囲気（周囲温度）のみを４０℃にして充電を行って活性化して作製したニッケル−水素蓄電池を電池Ｗとした。この後、これらの電池Ｅ，Ｗを用いて上述と同様の試験を行って、３０Ａ放電時の作動電圧および４０Ａ放電時の作動電圧を求めるとともに、サイクル寿命を求めると下記の表３に示すような結果が得られた。なお、下記の表３においては、上述した電池Ｂの結果も併せて示している。
【００３８】
【表３】
上記表３の結果から明らかなように、活性化工程で初回の充電を４０℃の温度雰囲気中で高率充電した電池Ｗにあっては、初回充電後に電解液が漏液（リーク）していることが分かった。これは、４０℃程度の高温雰囲気中で高率充電すると、電池温度が上昇して水素ガスが水素吸蔵合金内に吸蔵されにくくなって、電池内に水素ガスが充満したことに起因して、電解液が漏液（リーク）したと考えられる。一方、初回の充電を２５℃あるいは３０℃の温度雰囲気中で高率充電した電池Ｂ，Ｅにあっては、活性化工程で漏液（リーク）の発生は認められず、３０Ａ放電時および４０Ａ放電時の作動電圧、サイクル寿命も充分なレベルにあることが分かる。このことから、活性化工程での初回の充電は３０℃以下の温度雰囲気（周囲温度）で行うのが好ましいということができる。
【００４０】
８．水素吸蔵合金の平均粒径の検討
ついで、水素吸蔵合金の平均粒径について検討した。
（１）電池Ｆ
上述と同様に、組成式がＭｍ1.0Ｎｉ3.6Ｃｏ0.6Ａｌ0.2Ｍｎ0.6で表される水素吸蔵合金のインゴットを作製した後、この水素吸蔵合金インゴットを機械的に粗粉砕した後、不活性ガス雰囲気中で平均粒子径が約５０μｍになるまで機械的に粉砕した。このようにして作製した水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製した後、上述と同様にニッケル−水素蓄電池を作製した。ついで、このニッケル−水素蓄電池を用いて、上述の電池Ｂと同様の条件で活性化して電池Ｆを作製した。なお、活性化後の電池Ｆを解体して水素吸蔵合金の平均粒径を測定したところ、活性化後の水素吸蔵合金の平均粒径は２０μｍであった。
【００４１】
（２）電池Ｇ
上述と同様に、組成式がＭｍ1.0Ｎｉ3.6Ｃｏ0.6Ａｌ0.2Ｍｎ0.6で表される水素吸蔵合金のインゴットを作製した後、この水素吸蔵合金インゴットを機械的に粗粉砕した後、不活性ガス雰囲気中で平均粒子径が約１２０μｍになるまで機械的に粉砕した。このようにして作製した水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製した後、上述と同様にニッケル−水素蓄電池を作製した。ついで、このニッケル−水素蓄電池を用いて、上述の電池Ｂと同様の条件で活性化して電池Ｇを作製した。なお、活性化後の電池Ｇを解体して水素吸蔵合金の平均粒径を測定したところ、活性化後の水素吸蔵合金の平均粒径は４５μｍであった。
【００４２】
（３）電池Ｘ
上述と同様に、組成式がＭｍ1.0Ｎｉ3.6Ｃｏ0.6Ａｌ0.2Ｍｎ0.6で表される水素吸蔵合金のインゴットを作製した後、この水素吸蔵合金インゴットを機械的に粗粉砕した後、不活性ガス雰囲気中で平均粒子径が約３０μｍになるまで機械的に粉砕した。このようにして作製した水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製した後、上述と同様にニッケル−水素蓄電池を作製した。ついで、このニッケル−水素蓄電池を用いて、上述の電池Ｂと同様の条件で活性化して電池Ｘを作製した。なお、活性化後の電池Ｘを解体して水素吸蔵合金の平均粒径を測定したところ、活性化後の水素吸蔵合金の平均粒径は７μｍであった。
【００４３】
（４）電池Ｙ
上述と同様に、組成式がＭｍ1.0Ｎｉ3.6Ｃｏ0.6Ａｌ0.2Ｍｎ0.6で表される水素吸蔵合金のインゴットを作製した後、この水素吸蔵合金インゴットを機械的に粗粉砕した後、不活性ガス雰囲気中で平均粒子径が約１５０μｍになるまで機械的に粉砕した。このようにして作製した水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製した後、上述と同様にニッケル−水素蓄電池を作製した。ついで、このニッケル−水素蓄電池を用いて、上述の電池Ｂと同様の条件で活性化して電池Ｙを作製した。なお、活性化後の電池Ｙを解体して水素吸蔵合金の平均粒径を測定したところ、活性化後の水素吸蔵合金の平均粒径は５０μｍであった。
【００４４】
ついで、これらの電池Ｆ，Ｇ，Ｘ，Ｙを用いて、上述と同様の試験を行って、３０Ａ放電時の作動電圧および４０Ａ放電時の作動電圧を求めるとともに、サイクル寿命を求めると下記の表４に示すような結果が得られた。なお、下記の表４においては、上述した電池Ｂの結果（活性化後の電池Ｂを解体して水素吸蔵合金の平均粒径を測定したところ、活性化後の水素吸蔵合金の平均粒径は３５μｍであった）も併せて示している。
【００４５】
【表４】
上記表４の結果から明らかなように、平均粒径が３０μｍの水素吸蔵合金を使用した電池Ｘにあっては、３０Ａ放電時および４０Ａ放電時の作動電圧は問題が生じないものの、サイクル寿命が３５０サイクル（回）で短寿命であることが分かる。これは、平均粒径が３０μｍという比較的平均粒径が小さい水素吸蔵合金を使用したことにより、活性化前から水素吸蔵合金の表面積が大きいことから、極板製造時までに水素吸蔵合金が酸化を受ける可能性が高いとともに、活性化工程においても水素吸蔵合金が酸化を受け易く、結果的に、活性化終了後の水素吸蔵合金は酸化が進行した状態となってサイクル寿命が低下したと考えられる。
【００４７】
また、平均粒径が１５０μｍの水素吸蔵合金を使用した電池Ｙにあっては、サイクル寿命は問題が生じないものの、３０Ａ放電時の作動電圧は極端に低下し、４０Ａ放電時においては放電不能であることが分かる。これは、平均粒径が１５０μｍという平均粒径が大きい水素吸蔵合金を使用したことにより、活性化後であっても水素吸蔵合金の平均粒径は５０μｍと大きいため、反応表面積が不十分であったためと考えられる。
【００４８】
一方、平均粒径が５０〜１２０μｍの水素吸蔵合金を使用した電池Ｂ，Ｆ，Ｇにあっては、サイクル寿命、３０Ａ放電時および４０Ａ放電時の作動電圧が向上していることが分かる。これは、平均粒径が５０〜１２０μｍの範囲であると、活性化により平均粒径が２０〜４５μｍに小さくなるとともに、水素吸蔵合金に多くのクラックが生じて水素吸蔵合金の表面積が大きくなり、反応面積が増大して高率放電特性が向上したと考えられる。これらのことから、本発明の充放電による活性化条件においては、平均粒径が５０〜１２０μｍの水素吸蔵合金を使用するのが望ましいということができる。
【００４９】
９．水素吸蔵合金のコバルト量の検討
ついで、水素吸蔵合金のコバルト量について検討した。
（１）電池Ｈ
上述と同様に、組成式がＭｍ1.0Ｎｉ3.4Ｃｏ0.8Ａｌ0.2Ｍｎ0.6で表される水素吸蔵合金（ＭｍaＮｉbＣｏcＡｌdＭｎeで表した場合のコバルト量（ｃ／ａ）が０．８のもの）のインゴットを作製した後、この水素吸蔵合金インゴットを機械的に粗粉砕した後、不活性ガス雰囲気中で平均粒子径が約９０μｍになるまで機械的に粉砕した。このようにして作製した水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製した後、上述と同様にニッケル−水素蓄電池を作製した。ついで、このニッケル−水素蓄電池を用いて、上述の電池Ｂと同様の条件で活性化して電池Ｈを作製した。
【００５０】
（２）電池Ｉ
上述と同様に、組成式がＭｍ1.0Ｎｉ3.7Ｃｏ0.5Ａｌ0.2Ｍｎ0.6で表される水素吸蔵合金（ＭｍaＮｉbＣｏcＡｌdＭｎeで表した場合のコバルト量（ｃ／ａ）が０．５のもの）のインゴットを作製した後、この水素吸蔵合金インゴットを機械的に粗粉砕した後、不活性ガス雰囲気中で平均粒子径が約９０μｍになるまで機械的に粉砕した。このようにして作製した水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製した後、上述と同様にニッケル−水素蓄電池を作製した。ついで、このニッケル−水素蓄電池を用いて、上述の電池Ｂと同様の条件で活性化して電池Ｉを作製した。
【００５１】
（３）電池Ｚ
上述と同様に、組成式がＭｍ1.0Ｎｉ3.8Ｃｏ0.4Ａｌ0.2Ｍｎ0.6で表される水素吸蔵合金（ＭｍaＮｉbＣｏcＡｌdＭｎeで表した場合のコバルト量（ｃ／ａ）が０．４のもの）のインゴットを作製した後、この水素吸蔵合金インゴットを機械的に粗粉砕した後、不活性ガス雰囲気中で平均粒子径が約９０μｍになるまで機械的に粉砕した。このようにして作製した水素吸蔵合金粉末を用いて、上述と同様に水素吸蔵合金負極を作製した後、上述と同様にニッケル−水素蓄電池を作製した。ついで、このニッケル−水素蓄電池を用いて、上述の電池Ｂと同様の条件で活性化して電池Ｚを作製した。
【００５２】
ついで、これらの電池Ｈ，Ｉ，Ｚを用いて、上述と同様の試験を行って、３０Ａ放電時の作動電圧および４０Ａ放電時の作動電圧を求めるとともに、サイクル寿命を求めると下記の表５に示すような結果が得られた。なお、下記の表５においては、上述した電池Ｂ（ＭｍaＮｉbＣｏcＡｌdＭｎeで表した場合のコバルト量（ｃ／ａ）が０．６の水素吸蔵合金（Ｍｍ1.0Ｎｉ3.6Ｃｏ0.6Ａｌ0.2Ｍｎ0.6）を使用したもの）の結果も併せて示している。
【００５３】
【表５】
上記表５の結果から明らかなように、コバルト量（ｃ／ａ）が０．４の水素吸蔵合金を使用した電池Ｚにあっては、３０Ａ放電時および４０Ａ放電時の作動電圧は問題が生じないものの、サイクル寿命が３８０サイクル（回）で短寿命であることが分かる。これは、コバルト量（ｃ／ａ）を低下させたことで、水素吸蔵合金の耐食性が低下し、活性化終了後の水素吸蔵合金は酸化が進行した状態となってサイクル寿命が低下したと考えられる。
【００５５】
一方、コバルト量（ｃ／ａ）が０．５の水素吸蔵合金を使用した電池Ｉ、コバルト量（ｃ／ａ）が０．６の水素吸蔵合金を使用した電池Ｂおよびコバルト量（ｃ／ａ）が０．８の水素吸蔵合金を使用した電池Ｈにあっては、サイクル寿命の低下が抑制されていることが分かる。これは、コバルト量（ｃ／ａ）を０．５以上添加した水素吸蔵合金は耐食性が向上するためである。また、このときの３０Ａ放電時および４０Ａ放電時の作動電圧にも問題はない。これらのことから、本発明の充放電による活性化条件においては、コバルト量（ｃ／ａ）を０．５以上添加した水素吸蔵合金を使用するのが望ましいということができる。
【００５６】
なお、初回の充電後の放電については雰囲気温度を３０℃〜８０℃とすることにより、負極活性度をさらに向上させることが可能となる。これは、水素吸蔵合金の水素放出反応（放電反応）が吸熱反応であるため、高温下で放電を行うことにより、放電反応が円滑に、かつ効率的に行われ、この円滑な水素の放出が行われるときに、水素吸蔵合金粒子にクラックが生じやすくなり、水素吸蔵合金粒子の反応面積が増大するためである。
【００５７】
一方、高温サイクルによる容量劣化に対しては、初回充放電後の開路電圧が１．１５〜１．２５Ｖになるように放電量を調整することが有効である。このように放電量を調整することで初回の充電により正極中に生成された高次コバルト化合物が還元されることがなく、コバルト錯イオンも生成されないため、導電ネットワークに欠損が生じることがない。これにより、コバルト化合物の還元が抑制されて、高次コバルト化合物を安定化させることが可能となり、高温下でのサイクル容量の劣化を抑制することが可能となる。このため、初回充電後に放電を行うに際しては、高温（３０℃以上８０℃以下）下で放電した後、３０分経過後の開路電圧が１．１５〜１．２５Ｖ以上となるように放電量を調整するのが望ましい。
【００５８】
上述したように、本発明においては、高率充電レートで全充電量の少なくとも６０％以上を充電した後、放電させるようにして活性化を行うようにしているので、活性化工程の初回の充電において、水素吸蔵合金粒子にクラックが生じるとともに、合金粒子が割れて小さな粒径となり、このものを放電させることにより、さらに微細化される。これにより、平均粒径が５０〜１２０μｍの合金粒子が、平均粒径は２０〜４５μｍの合金粒子になるとともに、この合金粒子に多数のクラックが存在することとなる。この結果、水素吸蔵合金粒子に多数の活性面が出現して反応面積が増大するため、高率放電を行っても放電特性が低下することを抑制できるようになる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alkaline storage battery such as a nickel-hydrogen storage battery, and more particularly to activation of a hydrogen storage alloy provided in a negative electrode of a nickel-hydrogen storage battery.
[0002]
[Prior art]
With the recent market expansion, the use of electric tools, assist bicycles, electric vehicles, etc. has expanded, and the demand and demand for increasing the size, capacity, and power of nickel-hydrogen storage batteries has increased. This type of nickel-hydrogen storage battery cannot ensure sufficient battery performance immediately after battery assembly, and requires, for example, an activation process such as charging and discharging at room temperature. However, there has been a problem that a sufficient discharge capacity and operating voltage cannot be obtained in a discharge at a low temperature or a high rate simply by performing such activation treatment.
[0003]
In addition, hydrogen storage alloys are inherently extremely active, but they are oxidized by being left in the air before being sealed in an outer can and sealed, or heated during the manufacturing process, and a strong oxide film is formed on the alloy surface. It becomes very inert when formed. This oxide film is partially destroyed by repeated charging and discharging of the activation treatment, or cracks are generated in the alloy itself, and a new alloy is exposed on the surface. The degree gradually increases. In addition, the hydrogen storage alloy having a larger particle size is less susceptible to oxidation than a smaller one. On the other hand, after assembling the battery, the hydrogen storage alloy having a large particle size has a problem that the operating voltage is lowered due to the reduction of the reaction area, and therefore it is not suitable for discharge at a low temperature or at a high rate.
[0004]
In such a background, a negative electrode is produced using a hydrogen storage alloy having a relatively large average particle diameter, and cracks are generated in the hydrogen storage alloy by charging and discharging in the activation process, so that the average particle diameter is 50 μm or less. A nickel-hydrogen storage battery has been proposed in Japanese Patent No. 2999431.
In the nickel-hydrogen storage battery proposed in Japanese Patent No. 2999431, a hydrogen storage alloy having a relatively large average particle size is used. Therefore, the hydrogen storage alloy is not easily oxidized until the electrode is manufactured. It is less likely to be oxidized even after assembly. For this reason, the oxidation of the hydrogen storage alloy after completion of activation is suppressed, which is advantageous for the cycle life.
[0005]
In addition, because the hydrogen storage alloy is cracked by charging and discharging in the activation process, the average particle size is adjusted to 50 μm or less, the reaction area of the hydrogen storage alloy is increased, and the active alloy surface is exposed. The reactivity of the negative electrode is improved, which is advantageous for discharge. Furthermore, in the above-mentioned Japanese Patent No. 2999431, since the discharge after the charge in the activation process is performed in a temperature atmosphere of 30 to 80 ° C., the hydrogen storage alloy is easily cracked, and the average particle size is further increased. Can be obtained.
[0006]
[Problems to be solved by the invention]
However, in the activation method proposed in Japanese Patent No. 2999431, although there is no problem in the charge / discharge cycle life, the reaction area of the activated hydrogen storage alloy is insufficient. As a result, the operating voltage during high rate discharge (large current discharge) is low, and in some cases, discharge becomes impossible.
The present invention has been made to solve the above problems, and proposes an activation method capable of improving high rate discharge characteristics without reducing cycle life, and is excellent in discharge performance and cycle life. An object of the present invention is to provide an alkaline storage battery.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has an average particle diameter of 50 μm or more and 120 μm or less and a composition formula of Mm a Ni b Co c Al d Mn e (However, after assembling an alkaline storage battery comprising a negative electrode containing a hydrogen storage alloy represented by (where c / a is 0.5 or more), a positive electrode, and an alkaline electrolyte, charging and discharging are performed to obtain an alkaline storage battery. A method for producing an alkaline storage battery comprising an activation step for activating, wherein in this activation step, the first charge / discharge is performed at a charge rate of at least 0.6 It or more with respect to the capacity of the negative electrode. Discharge after charging more than 60% In both cases, charging in the activation process is performed in an atmosphere of 30 ° C. or lower. It is characterized by doing so.
[0008]
In this way, the first charge / discharge is activated by charging the battery after charging 60% or more of the battery capacity at a charge rate of at least 0.6 It with respect to the capacity of the negative electrode and then discharging it. In the first charge of the process, the hydrogen storage alloy particles are cracked, and the alloy particles are cracked to have a small particle size, which is further refined by discharging the particles. Thereby, alloy particles having an average particle diameter of 50 to 120 μm become alloy particles having an average particle diameter of 20 to 45 μm, and a large number of cracks are present in the alloy particles. As a result, a large number of active surfaces appear in the hydrogen storage alloy particles and the reaction area increases, so that it is possible to suppress a decrease in discharge characteristics even when high rate discharge is performed.
[0009]
In this case, if the high rate charge rate in the first charge of the activation process is less than 0.6 It with respect to the negative electrode capacity, the reaction area of the hydrogen storage alloy particles becomes insufficient, and the high rate discharge characteristics deteriorate. Therefore, the high rate charge rate needs to be 0.6 It or more with respect to the negative electrode capacity.
In addition, if the initial charge in the activation process is performed in a temperature atmosphere higher than 30 ° C., the battery temperature rises and liquid leakage occurs. desirable.
[0010]
In addition, in order to improve the corrosion resistance of the hydrogen storage alloy, cobalt is added and the composition formula is Mm. a Ni b Co c Al d Mn e When the amount of cobalt added (c / a) decreases, the corrosion resistance of the hydrogen storage alloy decreases, so that the oxidation of the hydrogen storage alloy proceeds after activation and the cycle life decreases. To do. For this reason, it is necessary to add a certain amount or more of cobalt to the hydrogen storage alloy. As a result of experiments, it was found that if the amount of cobalt added (c / a) is 0.5 or more, the corrosion resistance is improved and the cycle life can be prevented from decreasing. For this reason, it is desirable that the addition amount of cobalt (c / a) be 0.5 or more.
[0011]
Moreover, it becomes possible to further improve negative electrode activity by making discharge after the first charge into the temperature atmosphere of 30 to 80 degreeC. This is because the hydrogen release reaction (discharge reaction) of the hydrogen storage alloy is an endothermic reaction, so that the discharge reaction is performed smoothly and efficiently by discharging at a high temperature. This is because, when performed, the hydrogen storage alloy particles are likely to crack, and the reaction area of the hydrogen storage alloy particles increases.
[0012]
Furthermore, the reduction of the cobalt compound contained in the positive electrode is suppressed by setting the open circuit voltage after the first discharge to 1.15 V or more and 1.25 V or less, and it becomes possible to stabilize the higher-order cobalt compound. It becomes possible to suppress deterioration of the cycle capacity at high temperatures. In addition, as a method of adjusting the open circuit voltage after the first discharge to 1.15 V or more, the discharge is performed while applying a constant current to the alkaline storage battery, and the discharge amount is adjusted by adjusting the discharge time, or the alkali A method can be applied in which a circuit including a resistor is connected to the positive and negative terminals of the storage battery to perform discharge, and the discharge time is adjusted by adjusting the discharge time.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a nickel-hydrogen storage battery will be described. In addition, this invention is not limited to the following embodiment, In the range which does not change the summary, it can change suitably and can implement.
[0014]
1. Fabrication of hydrogen storage alloy negative electrode
Mish metal (Mm: mixture of rare earth elements), nickel, cobalt, aluminum, and manganese are mixed at a ratio of 1.0: 3.6: 0.6: 0.2: 0.6, and this mixture is mixed with argon gas. Induction heating is performed in a high-frequency induction furnace in an atmosphere to form a molten alloy. The molten alloy is poured into a mold by a known method, cooled, and the composition formula is Mm. 1.0 Ni 3.6 Co 0.6 Al 0.2 Mn 0.6 An ingot of a hydrogen storage alloy represented by
[0015]
The hydrogen storage alloy ingot was mechanically coarsely pulverized and then mechanically pulverized in an inert gas atmosphere until the average particle size reached about 90 μm. A hydrogen storage alloy slurry was prepared by adding a binder such as polyethylene oxide and an appropriate amount of water to the hydrogen storage alloy powder thus prepared and mixing them. After applying this slurry to both sides of the active material holder made of punching metal so that the active material density after rolling becomes a predetermined amount, drying and rolling, the slurry is cut to a predetermined size and hydrogen storage alloy A negative electrode was produced.
[0016]
2. Preparation of nickel positive electrode
Nickel hydroxide powder was added to an aqueous solution in which cobalt sulfate powder was dissolved in water, and then the aqueous solution of sodium hydroxide was added dropwise with stirring to adjust the pH of the solution, followed by stirring. Subsequently, the produced precipitate was separated by filtration, washed with water, and vacuum-dried at room temperature (about 25 ° C.) to obtain a powder in which a coating layer of cobalt hydroxide was formed on the surface of nickel hydroxide particles. The obtained powder was mixed with an aqueous sodium hydroxide solution, heat-treated in air, washed with water and dried to form a highly conductive coating layer of a sodium-containing cobalt compound on the surface of the nickel hydroxide particles. Nickel hydroxide powder was obtained.
[0017]
Next, 100 parts by mass of the active material powder containing the obtained nickel hydroxide powder as a main component and a small amount of cobalt hydroxide added thereto, 40 parts by mass of a 0.2% by mass hydroxypropylcellulose aqueous solution, and 60% by mass An active material slurry was prepared by adding and mixing 1 part by mass of PTFE dispersion liquid. The active material slurry produced in this way is a porous metal having a porosity of 97% and a nickel foam having a thickness of about 1.5 mm (this foam has a three-dimensional continuous network skeleton). The body (active material holding body) was filled. Next, after drying, the film was rolled to a thickness of 0.7 mm, cut to a predetermined size, and a positive electrode lead was welded to produce a nickel positive electrode.
[0018]
3. Production of nickel-hydrogen battery
Next, the nickel positive electrode prepared as described above and the hydrogen storage alloy negative electrode prepared as described above are spirally wound through a separator (thickness of about 0.15 mm) made of a nonwoven fabric made of polypropylene. The electrode group was produced. A negative electrode current collector was connected to the end of the negative electrode of the spiral electrode group produced in this way, and an end of the nickel positive electrode and the positive electrode current collector were connected to produce an electrode body. Next, after inserting the electrode body into a bottomed cylindrical metal outer can and spot welding the negative electrode current collector to the bottom of the metal outer can, the lead plate extending from the positive electrode current collector is attached to the bottom of the sealing body. Welded to.
[0019]
Then, 7.0 mol / l alkaline electrolyte (lithium hydroxide (LiOH) 1.0 mol / l, sodium hydroxide (NaOH) 1.0 mol / l, and potassium hydroxide (KOH) 5) were placed in the metal outer can. An aqueous solution containing 0 mol / l) was injected, and the sealing body was sealed by caulking the opening of the outer can through a sealing gasket. Thereby, a cylindrical nickel-hydrogen storage battery having a nominal capacity of 2000 mAh and a capacity ratio of 2.0 (positive electrode capacity of 2000 mAh and negative electrode capacity of 4000 mAh) was produced.
[0020]
4). Activation method
(1) Battery A
Using the nickel-hydrogen storage battery manufactured as described above, first, in a temperature atmosphere of room temperature (about 25 ° C.), 200 mA (0.1 It [0.1 mA with respect to the positive electrode capacity [It (mA) is the rated capacity (mAh) ) / 1h (hours), and the same applies to the following.] With a negative current of 0.05 It), the battery was charged for 60 minutes (10% of the nominal capacity) and 2400 mA. High rate charging (70% of nominal capacity) for 35 minutes with a charging current of 1.2 It for the positive electrode capacity and 0.6 It for the negative electrode capacity, 200 mA (0.1 It for the positive electrode capacity, The initial charge was completed by charging for 120 minutes (20% of the nominal capacity) with a charging current of 0.05 It) with respect to the negative electrode capacity. Then, after resting in a 60 ° C. temperature atmosphere for 1 hour, a constant current was applied to discharge at a current flow of 400 mA (0.2 It) in a 60 ° C. temperature atmosphere. In this case, the discharge amount was adjusted by adjusting the discharge time so that the open circuit voltage after 30 minutes from the end of discharge was 1.15 to 1.25V. The nickel-hydrogen storage battery activated by charging and discharging in this manner was designated as battery A.
[0021]
(2) Battery B
Using the nickel-hydrogen storage battery manufactured as described above, first, in a temperature atmosphere of room temperature (about 25 ° C.), 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity). Charging for 60 minutes (10% of nominal capacity) with a charging current, and high-rate charging for 30 minutes with a charging current of 2800 mA (1.4 It for the positive electrode capacity and 0.7 It for the negative electrode capacity) for 30 minutes 70%) and then charged for 120 minutes (20% of the nominal capacity) with a charging current of 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity) to complete the initial charge. . Then, after resting in a 60 ° C. temperature atmosphere for 1 hour, a constant current was applied to discharge at a current flow of 400 mA (0.2 It) in a 60 ° C. temperature atmosphere. In this case, the discharge amount was adjusted by adjusting the discharge time so that the open circuit voltage after 30 minutes from the end of discharge was 1.15 to 1.25V. The nickel-hydrogen storage battery activated by charging and discharging in this manner was designated as battery B.
[0022]
(3) Battery C
Using the nickel-hydrogen storage battery manufactured as described above, first, in a temperature atmosphere of room temperature (about 25 ° C.), 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity). Charging for 60 minutes (10% of nominal capacity) with a charging current and high-rate charging for 23 minutes with a charging current of 3600 mA (1.8 It for positive electrode capacity and 0.9 It for negative capacity) for 23 minutes 70%) and then charged for 120 minutes (20% of the nominal capacity) with a charging current of 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity) to complete the initial charge. . Then, after resting in a 60 ° C. temperature atmosphere for 1 hour, a constant current was applied to discharge at a current flow of 400 mA (0.2 It) in a 60 ° C. temperature atmosphere. In this case, the discharge amount was adjusted by adjusting the discharge time so that the open circuit voltage after 30 minutes from the end of discharge was 1.15 to 1.25V. The nickel-hydrogen storage battery activated by charging and discharging in this manner was designated as battery C.
[0023]
(4) Battery S
Using the nickel-hydrogen storage battery manufactured as described above, first, in a temperature atmosphere of room temperature (about 25 ° C.), 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity). The initial charging was completed after charging for 1000 minutes (100% of the nominal capacity). Then, after resting in a 60 ° C. temperature atmosphere for 1 hour, a constant current was applied to discharge at a current flow of 400 mA (0.2 It) in a 60 ° C. temperature atmosphere. In this case, the discharge amount was adjusted by adjusting the discharge time so that the open circuit voltage after 30 minutes from the end of discharge was 1.15 to 1.25V. The nickel-hydrogen storage battery activated by charging and discharging in this manner was designated as battery S.
[0024]
(6) Battery T
Using the nickel-hydrogen storage battery manufactured as described above, first, in a temperature atmosphere of room temperature (about 25 ° C.), 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity). Charge for 60 minutes (10% of nominal capacity) with a charging current, and high-rate charging for 84 minutes with a charging current of 1000 mA (0.5 It for positive electrode capacity and 0.25 It for negative electrode capacity) (nominal capacity) 70%) and then charged for 120 minutes (20% of the nominal capacity) with a charging current of 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity) to complete the initial charge. . Then, after resting in a 60 ° C. temperature atmosphere for 1 hour, a constant current was applied to discharge at a current flow of 400 mA (0.2 It) in a 60 ° C. temperature atmosphere. In this case, the discharge amount was adjusted by adjusting the discharge time so that the open circuit voltage after 30 minutes from the end of discharge was 1.15 to 1.25V. The nickel-hydrogen storage battery activated by charging and discharging in this manner was designated as battery T.
[0025]
(7) Battery U
Using the nickel-hydrogen storage battery manufactured as described above, first, in a temperature atmosphere of room temperature (about 25 ° C.), 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity). Charging for 60 minutes (10% of nominal capacity) with a charging current, high rate charging (nominal capacity of 42 mA) with a charging current of 2000 mA (1.0 It for positive electrode capacity and 0.5 It for negative capacity) 70%) and then charged for 120 minutes (20% of the nominal capacity) with a charging current of 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity) to complete the initial charge. . Then, after resting in a 60 ° C. temperature atmosphere for 1 hour, a constant current was applied to discharge at a current flow of 400 mA (0.2 It) in a 60 ° C. temperature atmosphere. In this case, the discharge amount was adjusted by adjusting the discharge time so that the open circuit voltage after 30 minutes from the end of discharge was 1.15 to 1.25V. The nickel-hydrogen storage battery activated by charging and discharging in this manner was designated as battery U.
[0026]
5. Battery test
(1) Measurement of high rate discharge characteristics
Batteries produced after the positive electrodes are fully charged with a charging current of 2000 mA (1 It) in a temperature atmosphere of room temperature (about 25 ° C.) using the batteries A to C and S to U activated as described above. The battery is charged until the voltage drop (−ΔV) reaches 10 mV, pauses for 1 hour, and then discharges at a discharge current of 30000 mA (15 It) until a final voltage of 0.6 V is discharged. When the operating voltage at that time (operating voltage at 30 A discharge) was determined, the results shown in Table 1 below were obtained.
[0027]
In addition, using each of the batteries A to C and S to U activated as described above, charging is performed at a room temperature (about 25 ° C.) atmosphere at a charging current of 2000 mA (1 It) until −ΔV becomes 10 mV. Then, after resting for 1 hour, high-rate discharge is performed with a discharge current of 40,000 mA (20 It) until the final voltage reaches 0.6 V, and the operation voltage at this time (operation voltage at 40 A discharge) is When obtained, the results shown in Table 1 below were obtained.
[0028]
(2) High temperature cycle life test
Next, using the batteries A to C and S to U activated as described above, charging is performed at a charging current of 2000 mA (1 It) in a temperature atmosphere of room temperature (about 25 ° C.), and −ΔV is 10 mV. The battery was charged for 1 hour, then rested for 1 hour, discharged at 15000 mA (7.5 It) until the battery voltage reached 0.6 V, and rested for 1 hour. When a high rate cycle life test is performed to determine the life when the battery reaches 60% of the initial capacity of -ΔV cycle, and the cycle life of each of the batteries A to C and S to U is determined, the following table 1 is obtained. Results were obtained.
[0029]
[Table 1]
As is apparent from the results in Table 1 above, the batteries A, B, and C that are activated by charging at a high rate of 0.6 It or more with respect to the negative electrode capacity are discharged at a high rate of 30 A or 40 A. However, it can be seen that the operating voltage does not decrease so much. On the other hand, when the batteries S, T, and U that are activated by charging at a charge rate of less than 0.6 It with respect to the negative electrode capacity are discharged at a high rate of 30 A or 40 A, the operating voltage decreases or the initial discharge It can be seen that the discharge voltage becomes impossible when reaching the end voltage (0.6 V) or less.
This is because when the initial charge rate is charged at a high rate of 0.6 It or more with respect to the negative electrode capacity, many cracks are generated in the hydrogen storage alloy particles, the reaction area of the hydrogen storage alloy particles is increased, and at the time of high rate discharge This is thought to be because the decrease in the operating voltage was suppressed. Here, the reason why many cracks are likely to occur in the hydrogen storage alloy particles by increasing the initial charge rate is that the phase change (volume change) of the hydrogen storage alloy particles is abruptly generated by high-rate charging. It is thought that cracks are likely to occur.
[0031]
On the other hand, with respect to the cycle life, it can be seen that the cycle life is maintained at about 500 cycles even when the initial charge rate is changed between 0.05 It and 0.9 It with respect to the negative electrode capacity. From this, it can be said that the high rate discharge characteristics can be improved without charging the negative electrode capacity at a high rate of 0.6 It or higher and adversely affecting the cycle life.
Note that if the initial charge rate is 1.2 It or more with respect to the negative electrode capacity, the battery temperature rapidly rises to generate gas, and the battery internal pressure rises to increase the possibility of electrolyte leakage. It is desirable to regulate the initial charge rate to less than 1.0 It with respect to the negative electrode capacity.
[0032]
6). Examination of charge amount by high rate charge at the time of activation
Next, the amount of charge by high rate charging at the time of activation was examined.
(1) Battery D
Here, using the nickel-hydrogen storage battery manufactured as described above, first, in a temperature atmosphere at room temperature (about 25 ° C.), 200 mA (0.1 It with respect to the positive electrode capacity, and 0.1 with respect to the negative electrode capacity). 05 It) for 60 minutes (10% of nominal capacity) with a charging current of 2800 mA (1.4 It for the positive electrode capacity and 0.7 It for the negative electrode capacity) for 25 minutes with a high current charging rate (1.4 It for the negative electrode capacity) 60% of the nominal capacity), charge for 120 minutes (20% of the nominal capacity) with a charging current of 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity), and the first charge Ended. Then, after resting for 1 hour in a temperature atmosphere of 60 ° C., a nickel-hydrogen storage battery activated by applying a constant current and discharging at a discharge current of 400 mA (0.2 It) in a temperature atmosphere of 60 ° C. Battery D was designated.
[0033]
(2) Battery V
On the other hand, using the nickel-hydrogen storage battery manufactured as described above, first, in a temperature atmosphere of room temperature (about 25 ° C.), 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity). ) For 60 minutes (10% of the nominal capacity) with a charging current of 2800 mA (1.4 It for the positive electrode capacity and 0.7 It for the negative capacity) for 21 minutes at a high rate (nominal) 50% of the capacity) and charge for 120 minutes (20% of the nominal capacity) at a charging current of 200 mA (0.1 It for the positive electrode capacity and 0.05 It for the negative electrode capacity) to complete the initial charge. I let you. Then, after resting for 1 hour in a temperature atmosphere of 60 ° C., a nickel-hydrogen storage battery activated by applying a constant current and discharging at a discharge current of 400 mA (0.2 It) in a temperature atmosphere of 60 ° C. Battery V was designated.
[0034]
Next, tests similar to those described above were performed using these batteries D and V to determine the operating voltage at the time of 30 A discharge and the operating voltage at the time of 40 A discharge, and the cycle life was as shown in Table 2 below. Results were obtained. In Table 2 below, the results of the battery B described above are also shown.
[0035]
[Table 2]
As is clear from the results in Table 2 above, in the battery V in which the charge amount due to the high rate charge at the time of activation is 50% of the nominal capacity, the operating voltage is greatly reduced at the time of 30 A discharge, It can be seen that at the time of 40 A discharge, the discharge voltage reached the end voltage (0.6 V) or less at the beginning of discharge and became impossible to discharge. This is presumably because if the charge amount is small, the amount of cracks generated in the hydrogen storage alloy particles during the initial charge is small, and the reaction surface area of the hydrogen storage alloy particles is insufficient. On the other hand, in the batteries B and D in which the charge amount is 60% or more with respect to the nominal capacity, it can be seen that the operating voltage does not decrease so much during 30A discharge and 40A discharge. From this, it can be said that it is preferable that the charge amount by the high rate charge at the time of activation is 60% or more.
[0037]
7). Examination of temperature atmosphere during activation
Here, when the nickel-hydrogen storage battery manufactured as described above is used for charging / discharging and activation under the same conditions as the battery B described above, only the charging temperature atmosphere (ambient temperature) is set to 30 ° C. for charging. The nickel-hydrogen storage battery produced by activating the battery was designated as battery E, and the nickel-hydrogen storage battery produced by activating by charging only at the charging temperature atmosphere (ambient temperature) at 40 ° C. was designated as battery W. . Thereafter, the same test as described above was performed using these batteries E and W to obtain the operating voltage at the time of 30 A discharge and the operating voltage at the time of 40 A discharge, and the cycle life was as shown in Table 3 below. Results were obtained. In Table 3 below, the results of the battery B described above are also shown.
[0038]
[Table 3]
As is clear from the results of Table 3 above, in the battery W that was charged at a high rate in the temperature atmosphere of 40 ° C. in the activation process, the electrolyte solution leaked after the first charge. I found out. This is because when the battery is heated at a high rate in a high temperature atmosphere of about 40 ° C., the battery temperature rises and the hydrogen gas is not easily stored in the hydrogen storage alloy, and the battery is filled with the hydrogen gas. It is thought that the electrolyte solution leaked. On the other hand, in the batteries B and E that were charged at a high rate in the temperature atmosphere of 25 ° C. or 30 ° C. for the first time, no leakage (leak) was observed in the activation process. It can be seen that the operating voltage during discharge and the cycle life are at sufficient levels. From this, it can be said that the first charge in the activation step is preferably performed in a temperature atmosphere (ambient temperature) of 30 ° C. or less.
[0040]
8). Examination of average particle size of hydrogen storage alloy
Next, the average particle size of the hydrogen storage alloy was examined.
(1) Battery F
As above, the composition formula is Mm 1.0 Ni 3.6 Co 0.6 Al 0.2 Mn 0.6 Then, the hydrogen storage alloy ingot represented by the formula (1) was mechanically coarsely pulverized, and then mechanically pulverized in an inert gas atmosphere until the average particle size became about 50 μm. Using the hydrogen storage alloy powder thus prepared, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and then a nickel-hydrogen storage battery was prepared in the same manner as described above. Subsequently, using this nickel-hydrogen storage battery, activation was performed under the same conditions as the battery B described above to produce a battery F. In addition, when the activated battery F was disassembled and the average particle size of the hydrogen storage alloy was measured, the average particle size of the activated hydrogen storage alloy was 20 μm.
[0041]
(2) Battery G
As above, the composition formula is Mm 1.0 Ni 3.6 Co 0.6 Al 0.2 Mn 0.6 Then, the hydrogen storage alloy ingot represented by the formula (1) was mechanically coarsely pulverized and then mechanically pulverized in an inert gas atmosphere until the average particle size became about 120 μm. Using the hydrogen storage alloy powder thus prepared, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and then a nickel-hydrogen storage battery was prepared in the same manner as described above. Next, using this nickel-hydrogen storage battery, activation was performed under the same conditions as the battery B described above to produce a battery G. When the activated battery G was disassembled and the average particle size of the hydrogen storage alloy was measured, the average particle size of the hydrogen storage alloy after activation was 45 μm.
[0042]
(3) Battery X
As above, the composition formula is Mm 1.0 Ni 3.6 Co 0.6 Al 0.2 Mn 0.6 Then, the hydrogen storage alloy ingot represented by the formula (1) was mechanically coarsely pulverized and then mechanically pulverized in an inert gas atmosphere until the average particle size became about 30 μm. Using the hydrogen storage alloy powder thus prepared, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and then a nickel-hydrogen storage battery was prepared in the same manner as described above. Subsequently, using this nickel-hydrogen storage battery, activation was performed under the same conditions as the battery B described above to produce a battery X. When the activated battery X was disassembled and the average particle size of the hydrogen storage alloy was measured, the average particle size of the activated hydrogen storage alloy was 7 μm.
[0043]
(4) Battery Y
As above, the composition formula is Mm 1.0 Ni 3.6 Co 0.6 Al 0.2 Mn 0.6 Then, the hydrogen storage alloy ingot represented by the formula (1) was mechanically coarsely pulverized and then mechanically pulverized in an inert gas atmosphere until the average particle size became about 150 μm. Using the hydrogen storage alloy powder thus prepared, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and then a nickel-hydrogen storage battery was prepared in the same manner as described above. Next, using this nickel-hydrogen storage battery, activation was performed under the same conditions as the battery B described above to produce a battery Y. In addition, when the battery Y after activation was disassembled and the average particle size of the hydrogen storage alloy was measured, the average particle size of the hydrogen storage alloy after activation was 50 μm.
[0044]
Then, using these batteries F, G, X, and Y, the same test as described above was performed to determine the operating voltage at 30 A discharge and the operating voltage at 40 A discharge, and the cycle life was determined as shown in the following table. Results as shown in 4 were obtained. In Table 4 below, as a result of the above-described battery B (when the average particle size of the hydrogen storage alloy was measured by disassembling the activated battery B, the average particle size of the hydrogen storage alloy after activation was (It was 35 μm).
[0045]
[Table 4]
As is clear from the results in Table 4 above, in the battery X using the hydrogen storage alloy having an average particle size of 30 μm, the operating voltage at the time of 30 A discharge and 40 A discharge does not cause a problem, but the cycle life is long. It can be seen that the life is short in 350 cycles (times). This is because a hydrogen storage alloy having a relatively small average particle diameter of 30 μm was used, and the surface area of the hydrogen storage alloy was large before activation, so that the hydrogen storage alloy was oxidized before the electrode plate was manufactured. In the activation process, the hydrogen storage alloy is susceptible to oxidation, and as a result, the hydrogen storage alloy after the activation is in a state where the oxidation has progressed and the cycle life is considered to have decreased. It is done.
[0047]
In addition, in the battery Y using the hydrogen storage alloy having an average particle size of 150 μm, although the cycle life does not cause a problem, the operating voltage at the time of 30 A discharge is extremely reduced, and the battery cannot be discharged at the time of 40 A discharge. I understand that there is. This is because a hydrogen storage alloy having a large average particle diameter of 150 μm was used, and even after activation, the average particle diameter of the hydrogen storage alloy was as large as 50 μm, so that the reaction surface area was insufficient. This is probably because
[0048]
On the other hand, in the batteries B, F and G using the hydrogen storage alloy having an average particle size of 50 to 120 μm, it can be seen that the cycle life, the operating voltage at the time of 30 A discharge and the operating voltage at the time of 40 A discharge are improved. When the average particle size is in the range of 50 to 120 μm, the average particle size is reduced to 20 to 45 μm by activation, many cracks are generated in the hydrogen storage alloy, and the surface area of the hydrogen storage alloy is increased. It is considered that the reaction area was increased and the high rate discharge characteristics were improved. From these facts, it can be said that it is desirable to use a hydrogen storage alloy having an average particle size of 50 to 120 μm in the activation conditions by charge and discharge of the present invention.
[0049]
9. Examination of cobalt content of hydrogen storage alloy
Next, the amount of cobalt in the hydrogen storage alloy was examined.
(1) Battery H
As above, the composition formula is Mm 1.0 Ni 3.4 Co 0.8 Al 0.2 Mn 0.6 Hydrogen storage alloy (Mm a Ni b Co c Al d Mn e In this case, the hydrogen storage alloy ingot was mechanically coarsely pulverized, and then the average particle size was adjusted in an inert gas atmosphere. The material was mechanically pulverized to about 90 μm. Using the hydrogen storage alloy powder thus prepared, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and then a nickel-hydrogen storage battery was prepared in the same manner as described above. Next, using this nickel-hydrogen storage battery, the battery H was produced by activation under the same conditions as the battery B described above.
[0050]
(2) Battery I
As above, the composition formula is Mm 1.0 Ni 3.7 Co 0.5 Al 0.2 Mn 0.6 Hydrogen storage alloy (Mm a Ni b Co c Al d Mn e In this case, the hydrogen storage alloy ingot is mechanically coarsely pulverized, and then the average particle size is reduced in an inert gas atmosphere. The material was mechanically pulverized to about 90 μm. Using the hydrogen storage alloy powder thus prepared, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and then a nickel-hydrogen storage battery was prepared in the same manner as described above. Next, using this nickel-hydrogen storage battery, activation was performed under the same conditions as the battery B described above to produce a battery I.
[0051]
(3) Battery Z
As above, the composition formula is Mm 1.0 Ni 3.8 Co 0.4 Al 0.2 Mn 0.6 Hydrogen storage alloy (Mm a Ni b Co c Al d Mn e In this case, the hydrogen storage alloy ingot is mechanically coarsely pulverized, and then the average particle size is reduced in an inert gas atmosphere. The material was mechanically pulverized to about 90 μm. Using the hydrogen storage alloy powder thus prepared, a hydrogen storage alloy negative electrode was prepared in the same manner as described above, and then a nickel-hydrogen storage battery was prepared in the same manner as described above. Next, using this nickel-hydrogen storage battery, activation was performed under the same conditions as the battery B described above to produce a battery Z.
[0052]
Next, using these batteries H, I, and Z, the same test as described above was performed to determine the operating voltage at the time of 30 A discharge and the operating voltage at the time of 40 A discharge, and the cycle life was determined as shown in Table 5 below. The results shown were obtained. In Table 5 below, the battery B (Mm a Ni b Co c Al d Mn e The hydrogen storage alloy (Mm) having a cobalt amount (c / a) of 0.6 1.0 Ni 3.6 Co 0.6 Al 0.2 Mn 0.6 ))) Results are also shown.
[0053]
[Table 5]
As is clear from the results in Table 5 above, in the battery Z using the hydrogen storage alloy having a cobalt amount (c / a) of 0.4, the operation voltage at the time of 30 A discharge and 40 A discharge is problematic. Although it is not, it can be seen that the cycle life is 380 cycles (times) and the life is short. This is because the corrosion resistance of the hydrogen storage alloy decreased due to the decrease in the amount of cobalt (c / a), and the hydrogen storage alloy after the activation was in a state where the oxidation progressed and the cycle life decreased. It is done.
[0055]
On the other hand, Battery I using a hydrogen storage alloy having a cobalt amount (c / a) of 0.5, Battery B using a hydrogen storage alloy having a cobalt amount (c / a) of 0.6, and a cobalt amount (c / a) It can be seen that in the battery H using a hydrogen storage alloy of 0.8), the decrease in cycle life is suppressed. This is because the hydrogen storage alloy to which 0.5 or more of the cobalt amount (c / a) is added has improved corrosion resistance. Also, there is no problem with the operating voltage at the time of 30A discharge and 40A discharge. From these facts, it can be said that it is desirable to use a hydrogen storage alloy to which a cobalt amount (c / a) of 0.5 or more is added in the activation conditions by charge and discharge of the present invention.
[0056]
In addition, about discharge after the first charge, it becomes possible to further improve a negative electrode activity by setting atmospheric temperature to 30 to 80 degreeC. This is because the hydrogen release reaction (discharge reaction) of the hydrogen storage alloy is an endothermic reaction, so that the discharge reaction is performed smoothly and efficiently by discharging at a high temperature. This is because, when performed, the hydrogen storage alloy particles are likely to crack, and the reaction area of the hydrogen storage alloy particles increases.
[0057]
On the other hand, for capacity deterioration due to a high temperature cycle, it is effective to adjust the discharge amount so that the open circuit voltage after the first charge / discharge is 1.15 to 1.25V. By adjusting the discharge amount in this manner, the higher-order cobalt compound generated in the positive electrode by the first charge is not reduced, and no cobalt complex ions are generated, so that no defects occur in the conductive network. Thereby, the reduction | restoration of a cobalt compound is suppressed, it becomes possible to stabilize a higher-order cobalt compound, and it becomes possible to suppress degradation of the cycle capacity under high temperature. For this reason, when discharging after the initial charge, after discharging at a high temperature (30 ° C. or more and 80 ° C. or less), the discharge amount is set so that the open circuit voltage after 30 minutes has passed is 1.15 to 1.25 V or more. It is desirable to adjust.
[0058]
As described above, in the present invention, at least 60% or more of the total charge amount is charged at a high rate of charge and then activated so as to be discharged. In the above, cracks are generated in the hydrogen storage alloy particles, and the alloy particles are cracked to have a small particle size, which is further refined by discharging the particles. Thereby, alloy particles having an average particle diameter of 50 to 120 μm become alloy particles having an average particle diameter of 20 to 45 μm, and a large number of cracks are present in the alloy particles. As a result, a large number of active surfaces appear in the hydrogen storage alloy particles and the reaction area increases, so that it is possible to suppress a decrease in discharge characteristics even when high rate discharge is performed.
Claims (5)
前記活性化工程において、初回に行う充放電を、前記負極の容量に対して少なくとも０．６Ｉｔ以上の充電レートで電池容量の６０％以上を充電した後、放電させるとともに、
前記活性化工程での充電を３０℃以下の温度雰囲気で行うようにしたことを特徴とするアルカリ蓄電池の製造方法。Average particle diameter of 50μm or more, a negative electrode composition formula in 120μm below contains Mm a Ni b Co c Al d Mn e ( where, c / a is 0.5 or more) hydrogen absorbing alloy represented by a positive electrode And, after assembling an alkaline storage battery comprising an alkaline electrolyte, a method for producing an alkaline storage battery comprising an activation step of activating the alkaline storage battery by charging and discharging,
In the activation step, the first charge / discharge is performed after charging 60% or more of the battery capacity at a charge rate of at least 0.6 It with respect to the capacity of the negative electrode ,
A method for producing an alkaline storage battery, characterized in that charging in the activation step is performed in a temperature atmosphere of 30 ° C. or lower .
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