JP4475720B2

JP4475720B2 - Method for producing hydrogen storage alloy electrode and nickel metal hydride storage battery

Info

Publication number: JP4475720B2
Application number: JP2000034028A
Authority: JP
Inventors: 美穂嘉山; 行広岡田; 庸一郎辻; ▲吉▼徳豊口
Original assignee: Panasonic Corp; Toyota Motor Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Toyota Motor Corp; Panasonic Holdings Corp
Priority date: 2000-02-10
Filing date: 2000-02-10
Publication date: 2010-06-09
Anticipated expiration: 2020-02-10
Also published as: JP2001229921A

Description

【０００１】
【発明の属する技術分野】
本発明は、アルカリ蓄電池用の負極として用いる水素吸蔵合金電極と、これを用いたニッケル水素蓄電池電池に係り、特に水素吸蔵合金粉末の表面改質による前記電極および電池の高率放電特性と充放電初期サイクルでの放電特性の改良に関するものである。
【０００２】
【従来の技術】
一般に、電池用水素吸蔵合金は、水素吸蔵合金塊を所定の粒子径に粉砕した粉末として用いられ、この粉末が基板に充填されて水素吸蔵合金電極が構成される。この水素吸蔵合金電極は一般的にアルカリ蓄電池の負極として用いられ、その代表的なアルカリ蓄電池として、水酸化ニッケル正極と組み合わせたニッケル水素蓄電池があり、既に広く実用化されている。その他に水素吸蔵合金電極は、マンガン酸化物などの活物質を用いた正極と組み合わせたアルカリ蓄電池の負極としても検討されている。
【０００３】
水素吸蔵合金電極およびこれを用いたアルカリ蓄電池は、充放電の初期サイクル段階から高電圧・大放電容量が得られ、サイクル寿命が長く、さらに高率放電特性が良好なことなどの諸特性が要求されている。
しかしながら、水素吸蔵合金は、酸化されやすい性質を持つため、粉砕工程中や粉砕された水素吸蔵合金粉末の保管中などにおいて、水素吸蔵合金粉末の表面に容易に金属酸化膜が形成される。この酸化膜が形成された水素吸蔵合金粉末を用いた水素吸蔵合金電極を負極として用いた場合、上記酸化膜が充電時の水素吸蔵、放電時の水素放出という電気化学的反応の円滑な進行を妨げる主原因となる。このため、満足すべき高率放電特性が得られず、さらに、特に充放電初期サイクルにおいて、十分な放電電圧と放電容量が得られない問題があった。
【０００４】
従って、この問題を解決して水素吸蔵合金粉末の表面を高活性化させることにより、これを用いた電極あるいは電池の高率放電特性および初期充放電サイクルでの放電特性を向上させることが、従来からの重要な課題とされてきた。
このような課題を解決するために、種々の方法が検討されてきた。例えば、水素吸蔵合金粉末の粒子表面をニッケルや銅でメッキして多孔性の金属層を形成する方法が提案されている。また、水素吸蔵合金を作製後、真空中で熱処理したり、水素吸蔵合金粉末をアルカリ性水溶液中に浸漬する処理（アルカリ処理）や酸性水溶液に浸漬する処理（酸処理）などの表面処理により、上記特性を向上させる方法が提案されている。
【０００５】
前記アルカリ処理では、水素吸蔵合金粉末表面の金属酸化物が部分的に溶解除去されると共に、アルカリ水溶液と反応しやすい希土類元素などの合金成分が酸化されて新たな金属化合物が生成し、これと同時に耐アルカリ性の合金成分（ニッケルなどの金属）と前記新たな金属化合物とを含んだ表面層が形成される。
この際、前記金属化合物は主に水酸化物であり、アルカリ水溶液に部分的に溶解するが、未溶解の水酸化物や溶解度が小さい他の金属化合物は、合金表面に残存して付着し、これが水素吸蔵合金の活性度向上や電極の導電性向上の妨げになっていた。
【０００６】
さらにこの問題を解決するために、アルカリ処理済みの水素吸蔵合金粉末表面に残存して付着している前記金属水酸化物などの化合物を取り除くために、この合金粉末にさらに酸処理を施すことにより、合金粉末表面の活性度や電極の放電特性を向上させる方法が提案されている（特開平１０−１５８７６７号公報）。
また、同様の目的で、水素吸蔵合金をキレートを含む水溶液で処理する方法なども提案されている（特開平５−１９５００８号公報）。
【０００７】
【発明が解決しようとする課題】
しかし、これら化学的な処理方法では、処理溶液の濃度を一定に保って処理することや、処理溶液を各水素吸蔵合金粉末表面の隅々にまで十分に接触させることが困難であり、さらに処理による反応生成物の処理液への溶解が不十分な場合が多い。
そのため、合金表面に存在する金属酸化物、金属水酸化物などの化合物、および取扱中に合金粉末表面に付着した異物を確実に取り除くことができず、有効な解決手段とはなっていない。
【０００８】
本発明は上記従来の問題点を解決し、水素吸蔵合金表面の電気化学的活性度を高め、これにより、高率放電特性と初期充放電サイクルでの放電特性が優れた水素吸蔵合金電極およびこれを用いたニッケル水素蓄電池を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明の第１の水素吸蔵合金電極の製造方法は、水素吸蔵合金粉末をアルカリ性水溶液に接触させるアルカリ処理工程および前記水素吸蔵合金粉末を酸性水溶液に接触させる酸処理工程の少なくとも一方の前処理工程と、前記前処理済みの水素吸蔵合金粉末に不活性雰囲気中でプラズマによるエッチング処理を施す工程を有するものである。
【００１０】
また、本発明の第２の水素吸蔵合金電極の製造方法は、水素吸蔵合金粉末をアルカリ性水溶液に接触させるアルカリ処理工程と、前記アルカリ処理済みの水素吸蔵合金粉末を酸性水溶液に接触させる酸処理工程、および前記酸処理済みの水素吸蔵合金粉末に不活性雰囲気中でプラズマによるエッチング処理を施す工程とを有するものである。
【００１１】
これらの、前処理後にプラズマによるエッチング処理を施す方法により、水素吸蔵合金粉末表面に存在している金属酸化物、金属水酸化物などの化合物や異物がより確実に除去され、電気化学的活性度が一段と高い水素吸蔵合金電極を得ることができる。
また、上記本発明による水素吸蔵合金電極を負極として用いることにより、高率放電特性と初期充放電サイクルでの放電特性が優れた高性能ニッケル水素蓄電池を提供することができる。
【００１２】
【発明の実施の形態】
先述のように通常は、粉砕後の取扱いや保管の過程で、水素吸蔵合金粉末の表面には金属酸化膜が形成され、さらに異物が付着する場合がある。また、アルカリ処理を施された合金粉末表面にはニッケルを主体とする活性な金属および金属水酸化物などが混在する層が形成され、前記金属酸化物や異物も残存している。また、酸処理を施した場合には、前記金属酸化物や金属水酸化物や異物が部分的に除去されるが、各合金表面粉末の隅々まで除去することが困難である。このような、水素吸蔵合金粉末表面に存在する金属酸化物や金属水酸化物などの化合物および異物は、水素吸蔵合金の電気化学的活性度を減少させ、これを用いた電極あるいは電池の充放電反応を阻害し、特に、高率放電特性と充放電初期サイクルでの放電特性低下の主原因となる。
【００１３】
本発明の主眼は、不活性雰囲気中で水素吸蔵合金粉末表面を、プラズマによりエッチング処理することによって、水素吸蔵合金の粉末表面に存在する前記化合物や異物を隅々まで均一に、物理的に取り除くことを可能にしたことにある。そのためには、処理中に新たな化合物が表面に生成しないように、前記処理を酸素を含まない不活性ガスの雰囲気中で行う必要があり、不活性ガスとしてアルゴンガスを用いることが特に好ましい。
【００１４】
また一般的に、反応性ガスと被処理材料との化学反応により、被処理材料をエッチングする方法をプラズマエッチングと言う場合が多いが、本発明で言うプラズマによるエッチング処理は、これと異なり、いわゆるイオンエッチングである。
即ち、材料（水素吸蔵合金）と反応しない不活性ガスをイオン化させ、５００Ｖ〜５ｋＶ程度の電圧で加速し、材料表面を衝撃して材料表面の分子をはじき飛ばすスパッタリング現象を利用した物理的なエッチング処理である。この場合、プラズマからのイオンを直接利用するＲＦスパッタ法とイオン源からのイオンを利用するイオンビーム法があるが、本発明ではＲＦスパッタ法を用いることが好ましい。
【００１５】
本発明では、このようなプラズマによるエッチング処理によって、各水素吸蔵合金粉末表面の隅々にまで、方向性がなく、均一なイオン衝撃が加わり、表面に存在する前記金属化合物などの異物を物理的に隅々まで均一に除去できる。
【００１６】
例えばＲＦスパッタ法の場合には、試料台を兼ねた電極に高周波（Radio Frequency）電力を印加してチャンバー内のガスをプラズマ化し、プラズマ中の電子とイオンの移動度の差により生じる、電極表面とプラズマ間のセルフバイアス電圧によって加速されるイオン、を利用してエッチングを行うものである。なお、通常は、試料を収容したチャンバー内を１．３３×１０^-2〜１．３３Ｐａのアルゴンガス雰囲気にして、高周波電力５００〜１０００Ｗ、処理時間２〜２０分の条件でエッチング処理を行うことができる。
【００１７】
本発明の効果は、所定の粒径に粉砕された水素吸蔵合金粉末に前処理を施さない状態でプラズマによるエッチング処理を施しても得られるが、下記のように、従来法の処理を前処理として施した水素吸蔵合金粉末に、さらにプラズマによるエッチング処理を施すことにより、電気化学的活性度が一層高い水素吸蔵合金粉末が得られる。
即ち、前処理として酸処理を施す場合には、予め部分的に金属酸化物などが化学的に溶解除去された状態の合金粉末表面に、さらにプラズマによるエッチング処理を施すことにより、合金粉末表面に残存して存在する金属酸化物などの化合物や異物を、物理的に隅々まで確実に除去することができる。
【００１８】
また、前処理としてアルカリ処理を施す場合には、予め部分的に金属酸化物などが除去され、新たに生成した金属水酸化物が形成された状態の合金粉末表面に、さらにプラズマによるエッチング処理を施すことにより、表面に存在する金属水酸化物、酸化物などの化合物や異物を、隅々まで確実に除去することができる。この場合、アルカリ処理によって形成されたニッケルを主体とする活性層が表面に残存するため、合金粉末表面を一層高活性化することができる。
【００１９】
さらに、好ましい水素吸蔵合金を得る方法は、まず、粉砕された水素吸蔵合金粉末にアルカリ処理を施した後、酸処理を施す二工程の前処理を施し、次いでプラズマによるエッチング処理を施す方法である。これにより、アルカリ処理で除去しきれなかった金属酸化物およびアルカリ処理で新たに生成した金属水酸化物などの化合物を酸処理により、化学的に概ね除去した状態で、最終活性化処理として、プラズマによる物理的なエッチング処理を施すので、合金粉末表面に残存している化合物や異物を、より一層確実に隅々まで除去できる。さらに、アルカリ処理によって形成された前記活性層の作用とが相俟って、水素吸蔵合金粉末の表面をより一層高活性状態にすることができる。
【００２０】
水素吸蔵合金粉末をアルカリ処理する方法としては、苛性カリ、苛性ソーダなどを溶解した比重１．２〜１．５のアルカリ性水溶液中に、８０〜１５０℃の温度で３０〜１００分間の間浸漬する方法が一般的である。また、酸処理の方法としては、０．０１〜１Ｍの希酢酸、ｐＨ２〜４の希塩酸などの酸性水溶液中に、３０〜１２０℃の温度で１０〜６０分間の間浸漬する方法を採るのが好ましい。また、上記のように処理液に水素吸蔵合金粉末を浸漬する方法以外に、水素吸蔵合金粉末にアルカリ性または酸性の上記処理液を吹き付けたり、処理液を添加し、撹拌して湿潤状態にするなどの方法により、水素吸蔵合金粉末の表面に処理液を接触させる方法を採ることができる。
【００２１】
上記のように、アルカリ処理や酸処理などの従来の処理方法を、プラズマエッチング処理の前処理として付加することにより、両者の相乗作用によって本発明のより一層大きな効果を得ることが可能となる。
なお、前記前処理工程では、水素吸蔵合金粉末と処理液とを所定の条件で接触させた後、水洗乾燥して次工程のプラズマエッチング処理に備える。
【００２２】
また本発明は、水素を電気化学的に吸蔵、放出できるＡＢ₅型、ＡＢ₂型、ＡＢ型などを初めとする、各種の電池用水素吸蔵合金の改質手法として適用できる。これらの合金の中で、ＡＢ₅型水素吸蔵合金は、一般的にアルカリ電解液中で比較的化学的に安定で、比較的優れた充放電サイクル特性が得られるなどの特徴がある。そのため、現在では、水素吸蔵合金電極の主材料として用いられており、これを負極に用いたニッケル水素蓄電池は広く実用化されている。これらのことから、本発明はＡＢ₅型水素吸蔵合金に適用することが、特に効果的である。
【００２３】
ＡＢ₅型水素吸蔵合金は、ＬａＮｉ₅を原型とする合金であり、Ａ元素とＢ元素が化学量論的にほぼ１：５に近い組成の水素吸蔵合金群の総称である。一般的にＡ元素は、Ｌａ単独、ＣｅあるいはＬａなどの希土類元素を主体とする合金（以下、「ミッシュメタル」という）、もしくは希土類元素を主体とし、必要に応じてＴｉ、Ｚｒ、Ｃａなどを少量含ませたものからなる。また、Ｂ元素は、主としてＮｉから構成され、必要に応じて、Ｃｏ、Ｍｎ、Ａｌ、Ｆｅ、Ｃｕ、Ｃｒなどを少量含ませたものからなる。
【００２４】
【実施例】
以下、本発明を実施例および参考例により詳細に説明する。
《参考例１》
水素吸蔵合金粉末としてミッシュメタル（Ｍｍ）を用いたＡＢ₅系合金ＭｍＮｉ_3.55Ｍｎ_0.4Ａｌ_0.3Ｃｏ_0.75を機械的に粉砕した平均粒径２０〜２５μｍのものを用いた。
この水素吸蔵合金粉末１００ｇをチャンバー中に収容し、このチャンバー内を１．３３×１０^-2〜１．３３Ｐａのアルゴンガス雰囲気にして、７００Ｗの高周波電力を１０分間印加し、プラズマによるエッチング処理を施した。
【００２５】
次いで、このプラズマによるエッチング処理を施した水素吸蔵合金粉末をカルボキシメチルセルロース（ＣＭＣ）の１ｗｔ％水溶液と混合撹拌しペースト状にし、これを平均ポアサイズ１５０ミクロン、多孔度９５％、厚さ０．８ｍｍの発泡状ニッケルシート製の電極支持体に充填電気容量が１２００ｍＡｈ／ｃｍ³となるように充填した。これを１２０℃で乾燥してローラープレスで加圧し、さらにその表面にフッ素樹脂粉末をコーティングし、水素吸蔵合金電極を作製した。これを電極Ａとした。
さらに、この電極Ａの特性と比較するために、プラズマエッチング処理を行わない水素吸蔵合金粉末を用いた電極を電極Ａと同条件で作製した。これを電極Ｂとした。
【００２６】
これらの電極ＡおよびＢを負極とし、正極に充填電気容量（６００ｍＡｈ／ｃｍ³）を有する水酸化ニッケル電極を配し、電解液に比重１．３０の水酸化カリウム水溶液を用いて開放系電池を構成し、この電池について、２５℃において充放電試験を行った。充電は水素吸蔵合金１ｇあたり１００ｍＡ（１００ｍＡ／ｇ）で５時間、放電は５０ｍＡ／ｇで端子電圧が０．８Ｖとなるまで行った。放電容量がほぼ一定値に安定した充放電サイクルでの放電容量に対する１サイクル目の放電容量の比率を百分率で表し、これにより初期充放電サイクルでの放電特性（初期活性の度合い）を評価した。また、高率放電特性は、充電１００ｍＡ／ｇ、放電５０ｍＡ／ｇの充放電を１０サイクル行った後、同条件で充電し、これを６００ｍＡ／ｇで放電し、このときの放電容量を５０ｍＡ／ｇで放電した１０サイクル目の放電容量と比較した。
【００２７】
《実施例１》
参考例１と同組成の水素吸蔵合金粉末を用い、水素吸蔵合金１００ｇに対し比重１．３０の水酸化カリウム水溶液２００ｇを加え、８０℃で１時間攪拌しながらアルカリ処理を行った。アルカリ処理した水素吸蔵合金粉末は水洗し、乾燥させた。この水素吸蔵合金粉末に、参考例１と同条件でプラズマによるエッチング処理を施した。この水素吸蔵合金粉末を用いて、参考例１と同条件で作製した電極を作製した。これを電極Ｃとした。
【００２８】
この電極Ｃの特性と比較するために、電極Ｃの場合と同様の水素吸蔵合金粉末を用い、同一条件でアルカリ処理を施した後、プラズマエッチングを施さずに、この水素吸蔵合金粉末を用いて電極を作製した。これを電極Ｄとした。
これらの電極ＣおよびＤを負極として用い、参考例１と同じ方法でそれぞれ開放系のニッケル水素蓄電池を作製した。これらの電池について、参考例１と同様の条件で充放電試験を行った。
【００２９】
《実施例２》
参考例１と同様の水素吸蔵合金粉末を用いて、実施例１と同様のアルカリ処理を施し、水洗した状態の合金粉末を６０℃でｐＨ３．４の酢酸水溶液中に３０分浸漬して攪拌し、水洗した後乾燥した。このようにアルカリ処理に次いで酸処理を前処理として施した水素吸蔵合金粉末に、参考例１と同様のプラズマエッチング処理を施した。この水素吸蔵合金粉末を用いて参考例１と同条件で電極を作製し、これを電極Ｅとした。
この電極Ｅの特性を比較するために、アルカリ処理と酸処理を電極Ｅの場合と同様に施し、プラズマエッチングを行っていない合金粉末から形成した電極を電極Ｆとした。
これらの電極ＥおよびＦを負極として用い、参考例１と同じ方法でそれぞれ開放系のニッケル水素蓄電池を作製した。これらの電池について、参考例１と同様の条件で充放電試験を行った。
表１に、上記各電極Ａ〜Ｆを用いて作製した開放系ニッケル水素蓄電池について、上記のように行った初期特性および高率放電特性の評価試験の結果を示す。
【００３０】
【表１】

【００３１】
表１において、前処理なしの水素吸蔵合金粉末を用いた電極（ＡおよびＢ）を用いた各電池の特性を比較すると、電極Ａを用いた場合に、初期特性、高率放電特性共に優れていることがわかる。また、前処理としてアルカリ処理を行った水素吸蔵合金粉末を用いた電極（ＣおよびＤ）を用いた各電池を比較すると、電極Ｃを用いた場合の特性が優れている。さらに、前処理としてアルカリ処理の後に酸処理を施した水素吸蔵合金粉末を用いた電極（ＥおよびＦ）を用いた各電池を比較すると、電極Ｅを用いた場合の特性が優れている。このような電極Ａ、ＣおよびＥを用いた場合の特性向上効果は、プラズマによるエッチング処理の効果によるものである。
【００３２】
また、プラズマ処理を施した水素吸蔵合金粉末を用いた電極Ａ、ＣおよびＥをうぃ比較すると、ＡよりもＣおよびＥが一段と優れた特性を示し、さらにＣよりもＥが優れた特性を示している。このことから、前処理としてアルカリ処理を施した後、プラズマエッチング処理を施すことにより、両処理の相乗効果によって、大きな効果が得られ、さらに前処理として、アルカリ処理後に酸処理を施すことにより、一段と大きな効果が得られ、水素吸蔵合金電極あるいは電池の初期活性と高率放電特性が一段と向上することがわかる。
【００３３】
《実施例３》
参考例１、実施例１あるいは実施例２と同様に作製した厚さ０．５０ｍｍの水素吸蔵合金電極を、幅３．５ｃｍ、長さ１４．５ｃｍに裁断して作製した負極を用い、参考例１と同様にして作製した厚さ０．８ｍｍの水酸化ニッケル電極を幅３．５ｃｍ、長さ１１ｃｍに裁断して正極とし、ポリプロピレン不織布に親水基を付与したセパレータを介して渦巻き状の電極群を構成した。これを４／５Ａサイズの電槽に収納し、これに比重１．３０の水酸化カリウム水溶液からなる電解液を注入後、封口して密閉形ニッケル水素蓄電池を作製した。正負極には各々リード片を溶接により取り付け、これを正負極端子に各々溶接して接続した。
【００３４】
参考例１、実施例１あるいは実施例２で作製した六種類の水素吸蔵合金電極をそれぞれ上記寸法に裁断した負極を用い、上記の方法により、６種類の密閉形ニッケル水素蓄電池を作製した。これらの内、電極Ａを用いた電池を電池Ｇ、電極Ｂを用いた電池を電池Ｈ、電極Ｃを用いた電池を電池Ｉ、電極Ｄを用いた電池を電池Ｊ、電極Ｅを用いた電池を電池Ｋ、電極Ｆを用いた電池を電池Ｌとした。これらの密閉形ニッケル水素蓄電池は正極容量規制であり、公称容量は１．６Ａｈである。
【００３５】
これらの電池を２５℃において、０．１Ｃで１５時間充電し、０．２Ｃで放電する初充放電処理を施した。その後、負極を活性化させて各サイクルの放電容量が増加してほぼ一定値に安定させるために、０．２Ｃで６時間充電し、０．２Ｃで１．０Ｖを終止電圧として放電する充放電を１０サイクル行った。このように充放電した後、０．１Ｃで１５時間充電し、終止電圧１．０Ｖで２Ｃの高率放電を行い、このときの放電容量と、前記１０サイクル目の０．２Ｃ放電での放電容量とを比較して、高率放電特性を評価した。評価結果を表２に示す。
【００３６】
【表２】

【００３７】
表２において、まず、前処理を施さない水素吸蔵合金粉末を用いたＧおよびＨの各電池の高率放電特性を比較すると、電池Ｇが優れていることがわかる。また、前処理としてアルカリ処理を行った水素吸蔵合金粉末を用いたＩおよびＪの各電池を比較すると、電池Ｉの特性が優れている。さらに、前処理としてアルカリ処理の後に酸処理を施した水素吸蔵合金粉末を用いたＫおよびＬの各電池を比較すると電池Ｋの特性が優れている。
【００３８】
このような評価結果は、表１の開放型電池の評価結果と一致している。即ち、電池Ｇ、ＩおよびＫの特性向上効果はプラズマエッチング処理の効果によるものである。また、プラズマ処理を施したもののうち、電池ＧよりもＩおよびＫが一段と優れた特性を示し、さらに電池ＩよりもＫが優れた特性を示している。このことから、前処理としてアルカリ処理を施した後、プラズマエッチング処理を施すことにより、大きな効果が得られ、さらに前処理として、アルカリ処理後に酸処理を付加することにより、相乗効果が一段と高まり、一層大きな効果が得られ、水素吸蔵合金電極あるいは電池の高率放電特性が一段と向上することが再確認された。
【００３９】
《実施例４》
本実施例では、水素吸蔵合金として表３から表６に示す式Ｍｍ_aＮｉ_bＭｎ_cＡｌ_dＣｏ_eＭ_f（ＭはＣｕまたはＦｅを表す）で表される合金を用いた。表３にはａ＝１．０、（ｂ＋ｃ＋ｄ＋ｅ＋ｆ）／ａ＝５．０としてＮｉおよびＣｏ量を変えた合金を示す。（ｂ＋ｃ＋ｄ＋ｅ＋ｆ）／ａは以下Ｂ／Ａで表す。表４はａ＝１．０、Ｂ／Ａ＝５．２としてＮｉおよびＣｏ量を変えた合金、表６はａ＝１．０、Ｂ／Ａ＝５．２としてＮｉおよびＡｌ・Ｍｎ量を変えた合金を表し、表５はｂ＋ｃ＋ｄ＋ｅ＋ｆを固定してＢ／Ａを変えた合金の例を表している。
これら各種組成の水素吸蔵合金粉末について、実施例１と同様のアルカリ処理を施した後、参考例１と同様のプラズマエッチング処理を施した。これらの水素吸蔵合金粉末を用いて参考例１と同条件で電極Ｎｏ．１〜４２を作製した。これらの電極の特性を比較するために、同様にアルカリ処理を施したが、プラズマエッチング処理を施さない合金粉末から形成した電極Ｎｏ．１’〜４２’を作製した。
これらの電極Ｎｏ．１〜４２および１’〜４２’を負極として用い、参考例１と同様の方法でそれぞれ開放系のニッケル水素蓄電池を作製した。これらの電池について、参考例１と同様の条件で充放電試験を行った。
表３〜６に、上記各電極を用いて作製した開放系ニッケル水素蓄電池の試験結果を示す。
なお、サイクル寿命は、放電容量が最大放電容量の６０％以下になったときのサイクル数で表した。
【００４０】
【表３】

【００４１】
【表４】

【００４２】
表３および４には、Ｂ／Ａ値を固定し、ＮｉおよびＣｏ量を変化させた水素吸蔵合金について示されている。初期特性および高率放電特性は、ＮｉおよびＣｏ量にかかわらず、プラズマエッチング処理を施した水素吸蔵合金粉末を用いて作製した電極が、プラズマエッチング処理を施していない合金粉末から作製した電極よりも特性が向上していることがわかる。しかしながら、Ｎｉ量が減ると、Ｎｉ活性層が減少し、初期特性および高率放電特性の絶対値が落ちる。逆に、Ｎｉ量を多くすると、Ｃｏ量が減るため、微粉化し易くなり、初期特性および高率放電特性は向上するが、サイクル寿命が落ちる。このため、Ｎｉ量ｂは、Ｂ／Ａ＝５．０のとき３．５≦ｂ≦３．７、Ｂ／Ａ＝５．２のとき３．９≦ｂ≦４．２の範囲が適当である。また、効果がある範囲において、その他の元素Ｍをｆ＝０．１加えた組成の水素吸蔵合金粉末から作製した電極でも、初期特性および高率放電特性は添加元素Ｍを含まない電極と同等の特性が得られる。
【００４３】
【表５】

【００４４】
表５には、ｂ＋ｃ＋ｄ＋ｅ＋ｆの値を固定して、Ｂ／Ａ値を変化させた水素吸蔵合金について示している。初期特性および高率放電特性は、Ｂ／Ａ値にかかわらず、プラズマエッチング処理を施した水素吸蔵合金粉末を用いて作製した電極がプラズマエッチング処理を施していない合金粉末から作製した電極よりも特性が向上していることがわかる。しかしながら、Ｂ／Ａ値を小さくすることにより、合金の微粉化が進み初期特性および高率放電特性は改善されるが、サイクル寿命が劣る。逆に、Ｂ／Ａ値を大きくすると、微粉化が抑えられるため初期特性および高率放電特性は低下し、合金の平衡圧が上昇するため放電容量が減少する。このため、Ｂ／Ａ値としては、４．９≦Ｂ／Ａ≦５．３の範囲が適当である。また、効果がある範囲において、その他の元素Ｍをｆ＝０．１加えた組成の水素吸蔵合金粉末から作製した電極でも、初期特性および高率放電特性は添加元素を含まない電極と同等の特性が得られる。
【００４５】
【表６】

【００４６】
表６には、Ｂ／Ａ値を固定し、Ａｌ・ＭｎとＮｉ量を変化させた合金について示されている。初期特性および高率放電特性は、すべての組成の水素吸蔵合金粉末を用いた電極において、プラズマエッチング処理を施した水素吸蔵合金粉末を用いて作製した電極が、プラズマエッチング処理を施していない合金粉末から作製した電極よりも特性が向上していることがわかる。Ｍｎ量とＡｌ量の和が等しい場合、その水素吸蔵合金から作製した電極の初期特性および高率放電特性はほぼ等しいことがわかる。Ｍｎ量とＡｌ量の和が少ない場合、Ｎｉ量が増加するため、合金の平衡圧が上昇し放電容量が減少する。Ｍｎ量とＡｌ量の和が多い場合、ＭｎとＡｌが溶解元素であるため合金の腐食が大きくなりサイクル寿命が落ちたと考えられる。また、Ｎｉ量減少のためＮｉ活性層が減少し、初期特性および高率放電特性の絶対値が落ちる。このため、Ｍｎ量とＡｌ量の和としては、０．６≦ｃ＋ｄ≦０．８が適当である。また、効果がある範囲において、その他の元素Ｍをｆ＝０．１加えた組成の水素吸蔵合金粉末から作製した電極でも、初期特性および高率放電特性は添加元素Ｍを含まない電極と同等である。
以上より、実施例において検討したすべての合金組成に対して、前処理としてアルカリ処理を施した後、プラズマエッチング処理を施すことにより、水素吸蔵合金電極の初期特性および高率放電特性の向上が確認された。
【００４７】
【発明の効果】
本発明によって、水素吸蔵合金粉末にプラズマによるエッチング処理を施すことにより、合金粉末表面に存在する金属酸化物、金属水酸化物などの化合物や異物を物理的に除去し、合金粉末表面の隅々までを電気化学的に活性化できる。
また、前記プラズマによるエッチング処理に先立ち、前処理として、アルカリ処理および酸処理の少なくとも一方の処理を施すことにより、これらの前処理との相乗効果が得られ、より一層大きな本発明の効果を得ることができる。
上記のような、水素吸蔵合金粉末に高活性化処理を施す工程を設けて、水素吸蔵合金電極を製造することにより、高率放電特性と充放電初期サイクルでの放電特性が優れた水素吸蔵合金電極を製造することができ、この電極を用いて高性能のニッケル水素蓄電池を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen storage alloy electrode used as a negative electrode for an alkaline storage battery, and a nickel metal hydride storage battery using the same, and in particular, high rate discharge characteristics and charge / discharge of the electrode and the battery by surface modification of hydrogen storage alloy powder. The present invention relates to improvement of discharge characteristics in the initial cycle.
[0002]
[Prior art]
Generally, a hydrogen storage alloy for a battery is used as a powder obtained by pulverizing a hydrogen storage alloy lump to a predetermined particle diameter, and the powder is filled in a substrate to constitute a hydrogen storage alloy electrode. This hydrogen storage alloy electrode is generally used as a negative electrode of an alkaline storage battery. As a representative alkaline storage battery, there is a nickel hydrogen storage battery combined with a nickel hydroxide positive electrode, which has already been widely put into practical use. In addition, the hydrogen storage alloy electrode has been studied as a negative electrode of an alkaline storage battery combined with a positive electrode using an active material such as manganese oxide.
[0003]
Hydrogen storage alloy electrodes and alkaline storage batteries using them require various characteristics such as high voltage and large discharge capacity from the initial cycle stage of charge and discharge, long cycle life, and good high rate discharge characteristics. Has been.
However, since the hydrogen storage alloy is easily oxidized, a metal oxide film is easily formed on the surface of the hydrogen storage alloy powder during the pulverization process or during storage of the pulverized hydrogen storage alloy powder. When a hydrogen storage alloy electrode using the hydrogen storage alloy powder on which this oxide film is formed is used as the negative electrode, the oxide film smoothly proceeds the electrochemical reaction of hydrogen storage during charge and hydrogen release during discharge. It becomes the main cause to prevent. For this reason, satisfactory high rate discharge characteristics cannot be obtained, and there is a problem that sufficient discharge voltage and discharge capacity cannot be obtained particularly in the initial charge / discharge cycle.
[0004]
Therefore, by solving this problem and activating the surface of the hydrogen storage alloy powder, it is possible to improve the high rate discharge characteristics of the electrode or battery using this and the discharge characteristics in the initial charge / discharge cycle. Has been an important issue.
In order to solve such a problem, various methods have been studied. For example, a method of forming a porous metal layer by plating the particle surface of hydrogen storage alloy powder with nickel or copper has been proposed. Moreover, after producing a hydrogen storage alloy, the surface treatment such as a heat treatment in a vacuum, a treatment of immersing the hydrogen storage alloy powder in an alkaline aqueous solution (alkali treatment), or a treatment of immersing in an acidic aqueous solution (acid treatment) A method for improving the characteristics has been proposed.
[0005]
In the alkali treatment, the metal oxide on the surface of the hydrogen storage alloy powder is partially dissolved and removed, and an alloy component such as a rare earth element that easily reacts with an alkaline aqueous solution is oxidized to produce a new metal compound. At the same time, a surface layer containing an alkali-resistant alloy component (metal such as nickel) and the new metal compound is formed.
At this time, the metal compound is mainly a hydroxide and partially dissolved in the alkaline aqueous solution, but the undissolved hydroxide or other metal compound having a low solubility remains and adheres to the alloy surface, This hinders the improvement of the activity of the hydrogen storage alloy and the improvement of the conductivity of the electrode.
[0006]
In order to solve this problem, the alloy powder is further subjected to an acid treatment in order to remove the metal hydroxide and other compounds remaining on the surface of the alkali-treated hydrogen storage alloy powder. A method for improving the activity of the alloy powder surface and the discharge characteristics of the electrode has been proposed (Japanese Patent Laid-Open No. 10-158767).
For the same purpose, a method of treating a hydrogen storage alloy with an aqueous solution containing a chelate has been proposed (Japanese Patent Laid-Open No. Hei 5-195008).
[0007]
[Problems to be solved by the invention]
However, in these chemical treatment methods, it is difficult to keep the treatment solution concentration constant, or to make the treatment solution fully contact every corner of each hydrogen storage alloy powder surface. In many cases, the reaction product is not sufficiently dissolved in the processing solution.
For this reason, compounds such as metal oxides and metal hydroxides present on the alloy surface, and foreign substances adhering to the alloy powder surface during handling cannot be reliably removed, which is not an effective solution.
[0008]
The present invention solves the above-mentioned conventional problems and enhances the electrochemical activity of the surface of the hydrogen storage alloy, thereby providing a hydrogen storage alloy electrode excellent in high rate discharge characteristics and discharge characteristics in the initial charge / discharge cycle, and An object of the present invention is to provide a nickel-metal hydride storage battery using a battery.
[0009]
[Means for Solving the Problems]
  Of the present inventionFirstThe method for producing a hydrogen storage alloy electrode is a hydrogen storage alloy powder.At least one of an alkali treatment step in which an aqueous solution is brought into contact with an alkaline aqueous solution and an acid treatment step in which the hydrogen storage alloy powder is brought into contact with an acidic aqueous solution, and the pretreated hydrogen storage alloy powderHas a step of performing an etching process with plasma in an inert atmosphere..
[0010]
  Also,BookInventionSecondThe method for producing a hydrogen storage alloy electrode includes an alkali treatment step in which a hydrogen storage alloy powder is brought into contact with an alkaline aqueous solution.An acid treatment step of contacting the alkali-treated hydrogen storage alloy powder with an acidic aqueous solution, and the acidAnd a step of subjecting the treated hydrogen storage alloy powder to plasma etching in an inert atmosphere.Is.
[0011]
By these plasma etching methods after pretreatment, compounds and foreign substances such as metal oxides and metal hydroxides present on the surface of the hydrogen storage alloy powder are more reliably removed, and the electrochemical activity is increased. However, it is possible to obtain a hydrogen storage alloy electrode that is much higher.
Moreover, by using the hydrogen storage alloy electrode according to the present invention as a negative electrode, a high-performance nickel-metal hydride storage battery excellent in high rate discharge characteristics and discharge characteristics in the initial charge / discharge cycle can be provided.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
As described above, normally, in the process of handling and storage after pulverization, a metal oxide film is formed on the surface of the hydrogen storage alloy powder, and foreign matter may adhere. In addition, a layer in which an active metal mainly composed of nickel, a metal hydroxide, and the like are mixed is formed on the surface of the alloy powder that has been subjected to the alkali treatment, and the metal oxide and foreign matter also remain. In addition, when the acid treatment is performed, the metal oxide, metal hydroxide, and foreign matter are partially removed, but it is difficult to remove every corner of each alloy surface powder. Such compounds and foreign substances such as metal oxides and metal hydroxides present on the surface of the hydrogen storage alloy powder reduce the electrochemical activity of the hydrogen storage alloy and charge / discharge the electrode or battery using the same. This hinders the reaction and becomes the main cause of the deterioration of the discharge characteristics particularly in the high rate discharge characteristics and the initial charge / discharge cycle.
[0013]
The main point of the present invention is that the surface of the hydrogen-absorbing alloy powder is etched with plasma in an inert atmosphere, so that the compounds and foreign substances present on the hydrogen-absorbing alloy powder surface are uniformly and physically removed from every corner. It is in making it possible. For that purpose, it is necessary to perform the said process in the atmosphere of the inert gas which does not contain oxygen so that a new compound may not produce | generate on the surface during a process, It is especially preferable to use argon gas as an inert gas.
[0014]
In general, a method of etching a material to be processed by a chemical reaction between the reactive gas and the material to be processed is often referred to as plasma etching. Ion etching.
That is, physical etching using a sputtering phenomenon that ionizes an inert gas that does not react with the material (hydrogen storage alloy), accelerates at a voltage of about 500 V to 5 kV, impacts the surface of the material, and repels molecules on the surface of the material. It is processing. In this case, there are an RF sputtering method that directly uses ions from plasma and an ion beam method that uses ions from an ion source. In the present invention, it is preferable to use an RF sputtering method.
[0015]
In the present invention, the etching process using the plasma as described above causes no directivity and uniform ion bombardment to every corner of the surface of each hydrogen storage alloy powder, thereby physically removing foreign substances such as the metal compound on the surface. Can be removed evenly in every corner.
[0016]
For example, in the case of RF sputtering, the surface of the electrode is generated due to the difference in mobility between electrons and ions in the plasma by applying high frequency (Radio Frequency) power to the electrode that also serves as the sample stage to turn the gas in the chamber into plasma. Etching is performed using ions accelerated by a self-bias voltage between the plasma and the plasma. Usually, the inside of the chamber containing the sample is 1.33 × 10 6.^-2Etching can be performed under a high-frequency power of 500 to 1000 W and a processing time of 2 to 20 minutes in an argon gas atmosphere of ˜1.33 Pa.
[0017]
The effect of the present invention can be obtained even if the hydrogen storage alloy powder pulverized to a predetermined particle size is subjected to an etching treatment with plasma in a state where no pretreatment is performed. A hydrogen storage alloy powder having a higher electrochemical activity can be obtained by further subjecting the hydrogen storage alloy powder applied as described above to an etching process using plasma.
That is, when acid treatment is performed as a pretreatment, the surface of the alloy powder is subjected to etching treatment with plasma on the surface of the alloy powder in a state where the metal oxide or the like is partially dissolved and removed in advance. The remaining compounds such as metal oxides and foreign substances can be physically removed to every corner.
[0018]
In addition, when an alkali treatment is performed as a pretreatment, an etching treatment using plasma is further performed on the surface of the alloy powder in a state where a metal oxide or the like is partially removed in advance and a newly formed metal hydroxide is formed. By applying, compounds such as metal hydroxides and oxides and foreign substances existing on the surface can be surely removed to every corner. In this case, since the active layer mainly composed of nickel formed by alkali treatment remains on the surface, the surface of the alloy powder can be further activated.
[0019]
Further, a preferable method for obtaining a hydrogen storage alloy is a method in which the ground hydrogen storage alloy powder is first subjected to an alkali treatment, followed by a two-step pretreatment in which an acid treatment is performed, and then an etching treatment using plasma. . As a result, plasma is finally removed as a final activation process in a state in which the metal oxide that has not been completely removed by the alkali treatment and the metal hydroxide newly generated by the alkali treatment are chemically removed by acid treatment. Since the physical etching process is performed, the compounds and foreign matters remaining on the surface of the alloy powder can be more reliably removed to every corner. Furthermore, in combination with the action of the active layer formed by the alkali treatment, the surface of the hydrogen storage alloy powder can be made further highly active.
[0020]
As a method of alkali-treating the hydrogen storage alloy powder, a method of immersing it in an alkaline aqueous solution having a specific gravity of 1.2 to 1.5 in which caustic potash, caustic soda, etc. are dissolved at a temperature of 80 to 150 ° C. for 30 to 100 minutes. It is common. As the acid treatment method, a method of immersing in an acidic aqueous solution such as dilute acetic acid of 0.01 to 1M and dilute hydrochloric acid of pH 2 to 4 at a temperature of 30 to 120 ° C. for 10 to 60 minutes is adopted. preferable. In addition to the method of immersing the hydrogen storage alloy powder in the treatment liquid as described above, the alkaline or acidic treatment liquid is sprayed on the hydrogen storage alloy powder, or the treatment liquid is added and stirred to make it wet. By this method, a method of bringing the treatment liquid into contact with the surface of the hydrogen storage alloy powder can be adopted.
[0021]
As described above, by adding a conventional treatment method such as alkali treatment or acid treatment as a pretreatment for the plasma etching treatment, it is possible to obtain a greater effect of the present invention by their synergistic action.
In the pretreatment step, the hydrogen storage alloy powder and the treatment liquid are brought into contact with each other under predetermined conditions, and then washed with water and dried to prepare for the next plasma etching treatment.
[0022]
The present invention also provides an AB that can electrochemically occlude and release hydrogen._FiveMold, AB₂It can be applied as a modification method for various hydrogen storage alloys for batteries, such as a type and an AB type. Among these alloys, AB_FiveThe type hydrogen storage alloy is generally characterized by being relatively chemically stable in an alkaline electrolyte and having relatively excellent charge / discharge cycle characteristics. Therefore, at present, it is used as a main material of a hydrogen storage alloy electrode, and nickel-metal hydride storage batteries using this as a negative electrode have been widely put into practical use. From these, the present invention is AB._FiveIt is particularly effective to apply it to a type hydrogen storage alloy.
[0023]
AB_FiveType hydrogen storage alloy is LaNi_FiveIs a generic name of a group of hydrogen storage alloys having a composition in which the A element and the B element are stoichiometrically close to approximately 1: 5. In general, the A element is La alone, an alloy mainly composed of rare earth elements such as Ce or La (hereinafter referred to as “Misch metal”), or mainly composed of rare earth elements, and Ti, Zr, Ca, etc. are optionally contained. Consists of small amounts. The B element is mainly composed of Ni and contains a small amount of Co, Mn, Al, Fe, Cu, Cr or the like as required.
[0024]
【Example】
  Examples of the present invention will be described below.And reference examplesWill be described in more detail.
《referenceExample 1
  AB using Misch metal (Mm) as hydrogen storage alloy powder_FiveAlloy MmNi_3.55Mn_0.4Al_0.3Co_0.75Were used which had an average particle size of 20 to 25 μm.
  100 g of this hydrogen storage alloy powder was placed in a chamber, and the inside of this chamber was 1.33 × 10^-2An argon gas atmosphere of ˜1.33 Pa was applied, 700 W high frequency power was applied for 10 minutes, and an etching process using plasma was performed.
[0025]
Next, the hydrogen storage alloy powder subjected to the etching treatment with plasma was mixed and stirred with a 1 wt% aqueous solution of carboxymethyl cellulose (CMC) to form a paste, which had an average pore size of 150 microns, a porosity of 95%, and a thickness of 0.8 mm. Electrode support made of foamed nickel sheet has a filling electric capacity of 1200 mAh / cm^ThreeIt filled so that it might become. This was dried at 120 ° C. and pressurized with a roller press, and the surface thereof was coated with fluororesin powder to prepare a hydrogen storage alloy electrode. This was designated as an electrode A.
Furthermore, in order to compare with the characteristics of the electrode A, an electrode using a hydrogen storage alloy powder not subjected to the plasma etching treatment was manufactured under the same conditions as the electrode A. This was designated as an electrode B.
[0026]
These electrodes A and B are used as negative electrodes, and the positive electrode is filled with electric capacity (600 mAh / cm^ThreeAn open battery was constructed using a potassium hydroxide aqueous solution having a specific gravity of 1.30 as an electrolyte, and a charge / discharge test was conducted at 25 ° C. Charging was performed at 100 mA (100 mA / g) per gram of hydrogen storage alloy for 5 hours, and discharging was performed until the terminal voltage reached 0.8 V at 50 mA / g. The ratio of the discharge capacity in the first cycle to the discharge capacity in the charge / discharge cycle in which the discharge capacity was stabilized at a substantially constant value was expressed as a percentage, and thereby the discharge characteristics (degree of initial activity) in the initial charge / discharge cycle were evaluated. Further, the high rate discharge characteristic is that after charging and discharging at 100 mA / g and discharging at 50 mA / g for 10 cycles, charging is performed under the same conditions, and discharging is performed at 600 mA / g, and the discharging capacity at this time is 50 mA / g. It was compared with the discharge capacity at the 10th cycle discharged with g.
[0027]
"Example1》
  referenceUsing a hydrogen storage alloy powder having the same composition as in Example 1, 200 g of a potassium hydroxide aqueous solution having a specific gravity of 1.30 was added to 100 g of the hydrogen storage alloy, and alkali treatment was performed while stirring at 80 ° C. for 1 hour. The alkali-treated hydrogen storage alloy powder was washed with water and dried. To this hydrogen storage alloy powder,referenceEtching with plasma was performed under the same conditions as in Example 1. Using this hydrogen storage alloy powder,referenceAn electrode produced under the same conditions as in Example 1 was produced. This was designated as an electrode C.
[0028]
  In order to compare with the characteristics of the electrode C, the same hydrogen storage alloy powder as in the case of the electrode C was used, and after the alkali treatment was performed under the same conditions, the hydrogen storage alloy powder was used without performing plasma etching. An electrode was produced. This was designated as an electrode D.
  Using these electrodes C and D as negative electrodes,referenceOpen-type nickel metal hydride storage batteries were produced in the same manner as in Example 1. About these batteriesreferenceA charge / discharge test was performed under the same conditions as in Example 1.
[0029]
"Example2》
  referenceUsing the same hydrogen storage alloy powder as in Example 1,1The alloy powder was subjected to the same alkali treatment and washed in water at 60 ° C. for 30 minutes in an acetic acid aqueous solution having a pH of 3.4, stirred, washed with water and dried. In this way, the hydrogen storage alloy powder that has been subjected to acid treatment as a pretreatment subsequent to alkali treatment,referenceThe same plasma etching treatment as in Example 1 was performed. Using this hydrogen storage alloy powderreferenceAn electrode was produced under the same conditions as in Example 1, and this was designated as an electrode E.
  In order to compare the characteristics of the electrode E, an electrode formed from an alloy powder that was subjected to alkali treatment and acid treatment as in the case of the electrode E and not subjected to plasma etching was designated as an electrode F.
  Using these electrodes E and F as negative electrodes,referenceOpen-type nickel metal hydride storage batteries were produced in the same manner as in Example 1. About these batteriesreferenceA charge / discharge test was performed under the same conditions as in Example 1.
  Table 1 shows the results of the evaluation test of the initial characteristics and the high rate discharge characteristics performed as described above for the open-system nickel metal hydride storage battery produced using the electrodes A to F.
[0030]
[Table 1]

[0031]
In Table 1, when the characteristics of each battery using the electrodes (A and B) using the hydrogen storage alloy powder without pretreatment are compared, when the electrode A is used, both the initial characteristics and the high rate discharge characteristics are excellent. I understand that. Moreover, when each battery using the electrodes (C and D) using the hydrogen storage alloy powder subjected to the alkali treatment as the pretreatment is compared, the characteristics when the electrode C is used are excellent. Furthermore, when each battery using the electrodes (E and F) using the hydrogen storage alloy powder subjected to the acid treatment after the alkali treatment as a pretreatment is compared, the characteristics when the electrode E is used are excellent. The effect of improving the characteristics when such electrodes A, C and E are used is due to the effect of the etching process using plasma.
[0032]
In addition, when comparing electrodes A, C and E using hydrogen-absorbed alloy powder that has been subjected to plasma treatment, C and E are much better than A, and E is better than C. ing. From this, by performing an alkali treatment as a pretreatment, by performing a plasma etching treatment, a large effect is obtained by a synergistic effect of both treatments, and as a pretreatment, by performing an acid treatment after the alkali treatment, It can be seen that a greater effect is obtained, and the initial activity and high rate discharge characteristics of the hydrogen storage alloy electrode or battery are further improved.
[0033]
  "Example3》
  referenceExample 1,Example 1OrExample 2Using a negative electrode prepared by cutting a hydrogen storage alloy electrode having a thickness of 0.50 mm prepared in the same manner as described above into a width of 3.5 cm and a length of 14.5 cm,referenceA nickel hydroxide electrode having a thickness of 0.8 mm produced in the same manner as in Example 1 was cut into a width of 3.5 cm and a length of 11 cm to form a positive electrode, and a spiral electrode was passed through a separator provided with a hydrophilic group on a polypropylene nonwoven fabric. Groups were made up. This was housed in a 4 / 5A size battery case, and an electrolytic solution composed of an aqueous potassium hydroxide solution having a specific gravity of 1.30 was injected into the battery case, which was then sealed to produce a sealed nickel-metal hydride storage battery. Lead pieces were attached to the positive and negative electrodes by welding, and were connected to the positive and negative terminals by welding.
[0034]
  referenceExample 1,Example 1OrExample 2Using the negative electrodes obtained by cutting the six types of hydrogen storage alloy electrodes prepared in the above to the above dimensions, six types of sealed nickel-metal hydride storage batteries were prepared by the above method. Among these, the battery using the electrode A is the battery G, the battery using the electrode B is the battery H, the battery using the electrode C is the battery I, the battery using the electrode D is the battery J, and the battery using the electrode E Is a battery K, and a battery using the electrode F is a battery L. These sealed nickel-metal hydride storage batteries have positive electrode capacity restrictions and a nominal capacity of 1.6 Ah.
[0035]
These batteries were charged at 0.1 C for 15 hours at 25 ° C. and subjected to initial charge / discharge treatment at 0.2 C. Thereafter, in order to activate the negative electrode to increase the discharge capacity of each cycle and stabilize it at a substantially constant value, charging is performed at 0.2 C for 6 hours, and discharging is performed at 0.2 C with 1.0 V as the end voltage. For 10 cycles. After charging and discharging in this manner, charging is performed at 0.1 C for 15 hours, and a high rate discharge of 2 C is performed at a final voltage of 1.0 V. The discharging capacity at this time and the discharging at 0.2 C discharging at the 10th cycle are performed. The high rate discharge characteristics were evaluated by comparing with the capacity. The evaluation results are shown in Table 2.
[0036]
[Table 2]

[0037]
In Table 2, when the high rate discharge characteristics of the G and H batteries using the hydrogen storage alloy powder not subjected to the pretreatment are compared, it can be seen that the battery G is superior. Moreover, when each battery of I and J using the hydrogen storage alloy powder which performed the alkali treatment as pre-processing is compared, the characteristic of the battery I is excellent. Further, when the K and L batteries using the hydrogen storage alloy powder subjected to the acid treatment after the alkali treatment as a pretreatment are compared, the characteristics of the battery K are excellent.
[0038]
Such an evaluation result coincides with the evaluation result of the open type battery in Table 1. That is, the effect of improving the characteristics of the batteries G, I and K is due to the effect of the plasma etching process. Among the plasma-treated materials, I and K are more excellent than battery G, and K is more excellent than battery I. From this, after performing an alkali treatment as a pretreatment, a large effect can be obtained by performing a plasma etching treatment, and by further adding an acid treatment after the alkali treatment as a pretreatment, the synergistic effect is further enhanced. It was reconfirmed that a greater effect was obtained and the high rate discharge characteristics of the hydrogen storage alloy electrode or battery were further improved.
[0039]
"Example4》
  In this example, the formula Mm shown in Tables 3 to 6 as the hydrogen storage alloy._aNi_bMn_cAl_dCo_eM_fAn alloy represented by (M represents Cu or Fe) was used. Table 3 shows alloys in which the amounts of Ni and Co are changed with a = 1.0 and (b + c + d + e + f) /a=5.0. (B + c + d + e + f) / a is hereinafter represented by B / A. Table 4 shows alloys with different Ni and Co contents when a = 1.0 and B / A = 5.2. Table 6 shows Ni and Al.Mn contents when a = 1.0 and B / A = 5.2. Table 5 shows an example of an alloy in which B / A is changed by fixing b + c + d + e + f.
  Examples of these hydrogen storage alloy powders of various compositions1After performing the same alkali treatment asreferenceThe same plasma etching treatment as in Example 1 was performed. Using these hydrogen storage alloy powdersreferenceUnder the same conditions as in Example 1, electrode no. 1-42 were produced. In order to compare the characteristics of these electrodes, an electrode No. 2 formed from an alloy powder that was similarly subjected to alkali treatment but not subjected to plasma etching treatment. 1'-42 'was produced.
  These electrode Nos. 1-42 and 1'-42 'are used as negative electrodes,referenceOpen nickel-metal hydride storage batteries were produced in the same manner as in Example 1. About these batteriesreferenceA charge / discharge test was performed under the same conditions as in Example 1.
  Tables 3 to 6 show the test results of the open nickel-metal hydride storage batteries prepared using the above-described electrodes.
  The cycle life was represented by the number of cycles when the discharge capacity was 60% or less of the maximum discharge capacity.
[0040]
[Table 3]

[0041]
[Table 4]

[0042]
Tables 3 and 4 show hydrogen storage alloys in which the B / A value is fixed and the amounts of Ni and Co are changed. The initial characteristics and the high rate discharge characteristics are such that, regardless of the amount of Ni and Co, an electrode made using a hydrogen storage alloy powder that has been subjected to plasma etching is more than an electrode made from an alloy powder that has not been subjected to plasma etching. It can be seen that the characteristics are improved. However, when the amount of Ni decreases, the Ni active layer decreases, and the absolute values of the initial characteristics and the high rate discharge characteristics decrease. On the contrary, if the Ni content is increased, the Co content is reduced, so that it is easy to make fine powder and the initial characteristics and the high rate discharge characteristics are improved, but the cycle life is reduced. For this reason, the amount of Ni b is appropriately in the range of 3.5 ≦ b ≦ 3.7 when B / A = 5.0, and 3.9 ≦ b ≦ 4.2 when B / A = 5.2. is there. In addition, within the effective range, even with an electrode manufactured from a hydrogen storage alloy powder having a composition in which other element M is added to f = 0.1, the initial characteristics and the high rate discharge characteristics are the same as those of the electrode not containing the additive element M. Characteristics are obtained.
[0043]
[Table 5]

[0044]
Table 5 shows hydrogen storage alloys in which the value of b + c + d + e + f is fixed and the B / A value is changed. Regardless of the B / A value, the initial characteristics and high rate discharge characteristics are higher than those of electrodes made from the hydrogen-absorbing alloy powder that has been subjected to plasma etching, compared to electrodes made from alloy powder that has not been subjected to plasma etching. It can be seen that is improved. However, by decreasing the B / A value, the alloy becomes finer and the initial characteristics and high rate discharge characteristics are improved, but the cycle life is inferior. On the contrary, when the B / A value is increased, the pulverization is suppressed, so that the initial characteristics and the high rate discharge characteristics are lowered, and the equilibrium pressure of the alloy is increased, so that the discharge capacity is reduced. For this reason, as a B / A value, the range of 4.9 <= B / A <= 5.3 is suitable. In addition, even in an electrode produced from a hydrogen storage alloy powder having a composition in which other element M is added at f = 0.1 within the effective range, the initial characteristics and the high rate discharge characteristics are the same as those of the electrode containing no additive element. Is obtained.
[0045]
[Table 6]

[0046]
Table 6 shows alloys with fixed B / A values and varying amounts of Al · Mn and Ni. Initial characteristics and high-rate discharge characteristics are as follows. In the electrode using the hydrogen storage alloy powder of all compositions, the electrode powder prepared using the hydrogen storage alloy powder subjected to the plasma etching treatment is not subjected to the plasma etching treatment. Thus, it can be seen that the characteristics are improved as compared with the electrode fabricated from the above. When the sum of the amount of Mn and the amount of Al is equal, it can be seen that the initial characteristics and the high rate discharge characteristics of the electrode prepared from the hydrogen storage alloy are substantially equal. When the sum of the amount of Mn and the amount of Al is small, the amount of Ni increases, so that the equilibrium pressure of the alloy increases and the discharge capacity decreases. When the sum of the amount of Mn and the amount of Al is large, it is considered that since the Mn and Al are dissolved elements, the corrosion of the alloy is increased and the cycle life is reduced. In addition, the Ni active layer decreases due to a decrease in the amount of Ni, and the absolute values of the initial characteristics and the high rate discharge characteristics fall. For this reason, 0.6 ≦ c + d ≦ 0.8 is appropriate as the sum of the Mn amount and the Al amount. In addition, in the effective range, even with an electrode made from a hydrogen storage alloy powder having a composition in which other element M is added at f = 0.1, the initial characteristics and the high rate discharge characteristics are the same as those of the electrode not containing additive element M. is there.
Based on the above, it was confirmed that the initial characteristics and high-rate discharge characteristics of the hydrogen storage alloy electrode were improved by performing plasma etching after performing alkali treatment as a pretreatment for all alloy compositions examined in the examples. It was done.
[0047]
【The invention's effect】
According to the present invention, the hydrogen storage alloy powder is subjected to plasma etching to physically remove compounds such as metal oxides and metal hydroxides existing on the surface of the alloy powder and foreign matters, and the surface of the alloy powder is completely removed. Can be activated electrochemically.
In addition, by performing at least one of an alkali treatment and an acid treatment as a pretreatment prior to the plasma etching treatment, a synergistic effect with these pretreatments can be obtained, and a greater effect of the present invention can be obtained. be able to.
A hydrogen storage alloy having high rate discharge characteristics and excellent discharge characteristics in the initial charge / discharge cycle by producing a hydrogen storage alloy electrode by providing a process for performing a high activation treatment on the hydrogen storage alloy powder as described above. An electrode can be manufactured and a high performance nickel metal hydride storage battery can be obtained using this electrode.

Claims

At least one pretreatment step of contacting the hydrogen storage alloy powder with an alkaline aqueous solution and an acid treatment step of contacting the hydrogen storage alloy powder with an acidic aqueous solution, and an inert atmosphere in the pretreated hydrogen storage alloy powder The manufacturing method of the hydrogen storage alloy electrode which has the process of performing the etching process by plasma in it.

An alkali treatment step in which the hydrogen storage alloy powder is brought into contact with an alkaline aqueous solution, an acid treatment step in which the alkali-treated hydrogen storage alloy powder is brought into contact with an acidic aqueous solution, and the acid-treated hydrogen storage alloy powder in an inert atmosphere. The manufacturing method of the hydrogen storage alloy electrode which has the process of performing the etching process by plasma.

The method for producing a hydrogen storage alloy electrode according to claim 1 or 2 , wherein the hydrogen storage alloy powder is an AB type ₅ hydrogen storage alloy powder.

Nickel-metal hydride storage battery having a hydrogen storage alloy electrode obtained by the production method of the hydrogen storage case electrode according to any one of claims 1 to 3 as a negative electrode.