JP2004273261A

JP2004273261A - Alkaline storage battery

Info

Publication number: JP2004273261A
Application number: JP2003062002A
Authority: JP
Inventors: Jun Ishida; 潤石田; Tetsuyuki Murata; 徹行村田; Shigekazu Yasuoka; 茂和安岡
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 2003-03-07
Filing date: 2003-03-07
Publication date: 2004-09-30
Anticipated expiration: 2023-03-07
Also published as: JP4342196B2

Abstract

<P>PROBLEM TO BE SOLVED: To enable obtaining of a sufficient cycle lifetime even in the case an amount of alkaline electrolytic solution is reduced in an alkaline storage battery using a hydrogen storage alloy having a crystal structure of Ce<SB>2</SB>Ni<SB>7</SB>type, CeNi<SB>3</SB>type and similar types. <P>SOLUTION: The alkaline storage battery is provided with a positive electrode 1, a negative electrode 2 using the hydrogen storage alloy, and the alkaline electrolytic solution. The hydrogen storage alloy which contains at least a rare earth element, Mg, and Ni, and in which in an x-ray diffraction measurement, an intensity ratio IA/IB between the strongest peak intensity IA to appear within a range of 2θ=30° to 34° and the strongest peak intensity IB to appear within 2θ=40° to 44° is 0.5 or more, is used. An increased amount (Wa-Wo) of a weight ratio Wa of oxygen contained in the hydrogen storage alloy after the alkaline storage battery is activated, and a weight ratio Wo of oxygen contained in this hydrogen storage alloy is made less than 0.9 wt%, or this weight ratio Wa is made less than 1.0 wt%. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
この発明は、正極と、水素吸蔵合金を用いた負極と、アルカリ電解液とを備えたアルカリ蓄電池に係り、特に、少なくとも希土類元素とマグネシウムとニッケルとを含み、Ｃｕ−Ｋα線をＸ線源とするＸ線回折測定において２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢが０．５以上である水素吸蔵合金、具体的にはＣｅ_２Ｎｉ_７型、ＣｅＮｉ_３型及びこれらに類する結晶構造を有する水素吸蔵合金を用いたアルカリ蓄電池において、アルカリ電解液の量を少なくした場合においても、十分なサイクル寿命が得られるようにした点に特徴を有するものである。
【０００２】
【従来の技術】
従来、アルカリ蓄電池として、ニッケル・カドミウム蓄電池が一般に使用されていたが、近年においては、ニッケル・カドミウム蓄電池に比べて高容量で、またカドミウムを使用しないため環境安全性にも優れているという点から、負極に水素吸蔵合金を用いたニッケル・水素蓄電池が注目されるようになった。
【０００３】
そして、このようなニッケル・水素蓄電池が各種のポータブル機器に使用されるようになり、このニッケル・水素蓄電池をさらに高性能化させることが期待されている。
【０００４】
ここで、このニッケル・水素蓄電池においては、その負極に使用する水素吸蔵合金として、ＣａＣｕ_５型の結晶を主相とする希土類−ニッケル系の水素吸蔵合金や、Ｔｉ，Ｚｒ，Ｖ及びＮｉを含むラーベス相系の水素吸蔵合金等が一般に使用されていた。
【０００５】
しかし、これらの水素吸蔵合金は、水素吸蔵能力が必ずしも十分であるとはいえず、ニッケル・水素蓄電池の容量をさらに高容量化させることが困難であるという問題があった。
【０００６】
そして、近年においては、上記の希土類−ニッケル系の水素吸蔵合金にＭｇ等を含有させて、水素吸蔵合金における水素吸蔵能力を向上させたＣｅ_２Ｎｉ_７型、ＣｅＮｉ_３型及びこれらに類する結晶構造を有する水素吸蔵合金を用いるようにしたものが提案されている（例えば、特許文献１参照）。
【０００７】
しかし、上記のＣｅ_２Ｎｉ_７型、ＣｅＮｉ_３型及びこれらに類する結晶構造を有する水素吸蔵合金は、ＣａＣｕ_５型の結晶を主相とする希土類−ニッケル系の水素吸蔵合金に比べて酸化されやすく、アルカリ電解液と反応して、アルカリ電解液が消費されるという問題があった。
【０００８】
特に、近年においては、アルカリ蓄電池におけるエネルギー密度を高めて高容量化させるために、アルカリ蓄電池におけるアルカリ電解液の量を少なくすることが行われており、このようなアルカリ蓄電池において上記のような水素吸蔵合金を用いると、アルカリ電解液が消費されて不足し、サイクル寿命が大きく低下するという問題があった。
【０００９】
【特許文献１】
特開２００２−１６４０４５号公報
【００１０】
【発明が解決しようとする課題】
この発明は、少なくとも希土類元素とマグネシウムとニッケルとを含み、Ｃｕ−Ｋα線をＸ線源とするＸ線回折測定において２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢが０．５以上である水素吸蔵合金、具体的にはＣｅ_２Ｎｉ_７型、ＣｅＮｉ_３型及びこれらに類する結晶構造を有する水素吸蔵合金を用いたアルカリ蓄電池における上記のような問題を解決することを課題とするものである。
【００１１】
すなわち、この発明は、上記のような水素吸蔵合金を用いたアルカリ蓄電池において、アルカリ電解液が上記の水素吸蔵合金と反応して消費されるのを抑制し、アルカリ電解液の量を少なくした場合においても、十分なサイクル寿命が得られるようにすることを課題とするものである。
【００１２】
【課題を解決するための手段】
この発明における第１のアルカリ蓄電池においては、上記のような課題を解決するため、正極と、水素吸蔵合金を用いた負極と、アルカリ電解液とを備えたアルカリ蓄電池において、上記の水素吸蔵合金として、少なくとも希土類元素とマグネシウムとニッケルとを含み、Ｃｕ−Ｋα線をＸ線源とするＸ線回折測定において２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢが０．５以上である水素吸蔵合金を用い、この水素吸蔵合金に含まれる酸素の重量比率Ｗｏに対して、上記のアルカリ蓄電池を活性化させた後における水素吸蔵合金に含まれる酸素の重量比率Ｗａが増加した量（Ｗａ−Ｗｏ）が０．９ｗｔ％未満になるようにしたのである。
【００１３】
また、この発明における第２のアルカリ蓄電池においては、上記のような課題を解決するため、正極と、水素吸蔵合金を用いた負極と、アルカリ電解液とを備えたアルカリ蓄電池において、上記の水素吸蔵合金として、少なくとも希土類元素とマグネシウムとニッケルとを含み、Ｃｕ−Ｋα線をＸ線源とするＸ線回折測定において２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢが０．５以上である水素吸蔵合金を用い、上記のアルカリ蓄電池を活性化させた後における水素吸蔵合金に含まれる酸素の重量比率Ｗａが１．０ｗｔ％未満になるようにしたのである。
【００１４】
そして、上記のような水素吸蔵合金を用いた場合において、第１のアルカリ蓄電池のように、上記の水素吸蔵合金に含まれる酸素の重量比率Ｗｏに対して、アルカリ蓄電池を活性化させた後における水素吸蔵合金に含まれる酸素の重量比率Ｗａが増加した量（Ｗａ−Ｗｏ）が０．９ｗｔ％未満になるようにし、或いは第２のアルカリ蓄電池のように、アルカリ蓄電池を活性化させた後における水素吸蔵合金に含まれる酸素の重量比率Ｗａが１．０ｗｔ％未満になるようすると、このアルカリ蓄電池を繰り返して充放電させた場合においても、水素吸蔵合金との反応によってアルカリ電解液が消費されるのが抑制されるようになる。
【００１５】
このため、この発明の第１及び第２のアルカリ蓄電池においては、アルカリ蓄電池におけるエネルギー密度を高めて高容量化させるために、アルカリ電解液の量を少なくし、アルカリ電解液に対する上記の水素吸蔵合金の割合が４．３ｇ／ｃｃ以上になるようにした場合においても、十分なサイクル寿命が得られるようになる。
【００１６】
そして、水素吸蔵合金に含まれる酸素の重量比率Ｗｏ，Ｗａが上記のような条件を満たすようにするためには、上記の水素吸蔵合金の組成やその粒径等を適切に選択する他、上記の水素吸蔵合金を予め酸化処理しておき、この水素吸蔵合金がアルカリ電解液と反応するのを抑制させるようにすることができる。
【００１７】
ここで、上記の水素吸蔵合金の組成としては、例えば、組成式ＲＥ_１−ｘＭｇ_ｘＮｉ_ｙＭ_ａ（ＲＥは希土類元素から選択される１以上の元素であり、０．１５≦ｘ≦０．３０、２．８≦ｙ≦３．９、３．０≦ｙ＋ａ≦３．６の条件を満たす。）で表わされ、上記のＭとして、酸化を抑制する作用があるＡｌを組成比で０．２程度含むものを用いることが好ましい。また、水素吸蔵合金の粒径が小さいと、比表面積が増大してアルカリ電解液と反応しやすくなるため、体積平均粒径が５３μｍ以上の水素吸蔵合金を用いることが好ましい。
【００１８】
また、上記のように水素吸蔵合金を予め酸化処理するにあたっては、アルカリ溶液や酸溶液を用いて処理することができ、特に、水素吸蔵合金がアルカリ電解液と反応するのを抑制させる上では、同様のアルカリ溶液を用いて処理することが好ましい。
【００１９】
【実施例】
以下、この発明の実施例に係るアルカリ蓄電池について具体的に説明すると共に、比較例を挙げ、この発明の実施例のアルカリ蓄電池においては、サイクル寿命が向上することを明らかにする。なお、この発明におけるアルカリ蓄電池は下記の実施例に示したものに限定されず、その要旨を変更しない範囲において適宜変更して実施できるものである。
【００２０】
（実施例１）
実施例１においては、希土類元素のＬａ，Ｐｒ及びＮｄと、Ｍｇと、Ｎｉと、Ａｌとを、合金組成が（Ｌａ_０．２Ｐｒ_０．４Ｎｄ_０．４）_０．８３Ｍｇ_０．１７Ｎｉ_３．１Ａｌ_０．２になるように混合した後、アルゴン雰囲気中においてアーク溶解し、これを冷却させて水素吸蔵合金のインゴットを作製した。
【００２１】
そして、この水素吸蔵合金のインゴットを熱処理して均質化させた後、不活性雰囲気中において機械的に粉砕し、これを分級して、体積平均粒径（ＭＶ）が６３．２μｍになった上記の（Ｌａ_０．２Ｐｒ_０．４Ｎｄ_０．４）_０．８３Ｍｇ_０．１７Ｎｉ_３．１Ａｌ_０．２からなる組成の水素吸蔵合金粉末を得た。
【００２２】
ここで、このように作製した水素吸蔵合金粉末について、Ｃｕ−Ｋα線をＸ線源とするＸ線回折測定装置（ＲＩＧＡＫＵＲＩＮＴ２０００システム）を用い、スキャンスピード２°／ｍｉｎ，スキャンステップ０．０２°，走査範囲２０°〜８０°の範囲でＸ線回折測定を行い、その結果を図１に示した。また、この測定結果に基づき、２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢを求めたところ、強度比ＩＡ／ＩＢは０．６０２であり、ＣａＣｕ_５型とは異なり、Ｃｅ_２Ｎｉ_７型、ＣｅＮｉ_３型及びこれらに類する結晶構造を有していた。
【００２３】
また、このように作製した水素吸蔵合金粉末について、この水素吸蔵合金中に含まれる酸素の重量比率Ｗｏを求めた結果、この水素吸蔵合金中に含まれる酸素の重量比率Ｗｏは０．０６３ｗｔ％であった。
【００２４】
次に、上記の水素吸蔵合金粉末１００重量部に対して、ポリエチレンオキシドを０．１重量部、ポリビニルピロリドンを０．１重量部、水を２０重量部の割合で混合させてペーストを調製し、このペーストをニッケル鍍金を施したパンチングメタルからなる導電性芯体の両面に均一に塗布し、これを乾燥させてプレスした後、所定の寸法に切断して、負極に用いる水素吸蔵合金電極を作製した。
【００２５】
一方、正極を作製するにあたっては、亜鉛を２．５ｗｔ％，コバルトを１．０ｗｔ％含有する水酸化ニッケルの表面に水酸化コバルトを５ｗｔ％被覆させた後、これに２５ｗｔ％の水酸化ナトリウム水溶液を含浸させ、８５℃で加熱処理した後、これを水洗し乾燥させて、上記の水酸化ニッケルの表面がナトリウム含有コバルト酸化物で被覆された正極材料を得た。
【００２６】
そして、この正極材料を９５重量部、酸化亜鉛を３重量部、水酸化コバルトを２重量部の割合で混合させたものに、０．２ｗｔ％のヒドロキシプロピルセルロース水溶液を５０重量部加え、これらを混合させてスラリーを調製し、このスラリーをニッケル発泡体に充填し、これを乾燥させてプレスした後、所定の寸法に切断して非焼結式ニッケル極からなる正極を作製した。
【００２７】
また、セパレータとしてはポリプロピレン製の不織布を使用し、アルカリ電解液としては、ＫＯＨとＮａＯＨとＬｉＯＨ・Ｈ_２Ｏとが１５：２：１の重量比で含まれる比重１．３０のアルカリ電解液を使用して、設計容量が１８００ｍＡｈになった、図２に示すような円筒型のアルカリ蓄電池を作製した。
【００２８】
ここで、この実施例１のアルカリ蓄電池を作製するにあたっては、図１に示すように、正極１と負極２との間にセパレータ３を介在させ、これらをスパイラル状に巻いて電池缶４内に収容させた後、この電池缶４内に上記のアルカリ電解液を注液し、電池缶４と正極蓋６との間に絶縁パッキン８を介して封口し、正極１を正極リード５を介して正極蓋６に接続させると共に、負極２を負極リード７を介して電池缶４に接続させ、上記の絶縁パッキン８により電池缶４と正極蓋６とを電気的に分離させた。また、上記の正極蓋６と正極外部端子９との間にコイルスプリング１０を設け、電池の内圧が異常に上昇した場合には、このコイルスプリング１０が圧縮されて電池内部のガスが大気中に放出されるようにした。なお、上記のようにアルカリ電解液を注液するにあたっては、アルカリ電解液に対する上記の水素吸蔵合金の割合が４．３ｇ／ｃｃになるようにした。
【００２９】
（実施例２，３）
実施例２，３においては、上記の実施例１における水素吸蔵合金粉末の作製において、水素吸蔵合金のインゴットを粉砕して分級する条件だけを変更し、実施例２では体積平均粒径（ＭＶ）が５３．８μｍになった上記の組成の水素吸蔵合金粉末を、実施例３では体積平均粒径（ＭＶ）が７４．３μｍになった上記の組成の水素吸蔵合金粉末を得た。
【００３０】
ここで、実施例２及び実施例３において作製した各水素吸蔵合金粉末におけるＸ線回折測定の結果は、上記の実施例１において作製した水素吸蔵合金粉末と同じであり、上記の強度比ＩＡ／ＩＢも同じ０．６０２であった。
【００３１】
また、実施例２及び実施例３において作製した水素吸蔵合金粉末について、その水素吸蔵合金中に含まれる酸素の重量比率Ｗｏを求めた結果、実施例２の水素吸蔵合金中に含まれる酸素の重量比率Ｗｏは０．０６１ｗｔ％であり、実施例３の水素吸蔵合金中に含まれる酸素の重量比率Ｗｏは０．０４９ｗｔ％であった。
【００３２】
そして、上記のように作製した水素吸蔵合金粉末を用いる以外は、上記の実施例１の場合と同様にして、実施例２及び実施例３のアルカリ蓄電池を作製した。
【００３３】
（実施例４）
実施例４においては、上記の実施例１の場合と同様にして、体積平均粒径（ＭＶ）が６３．２μｍになった水素吸蔵合金粉末を得た後、この水素吸蔵合金粉末を８０℃になった８規定のＫＯＨ水溶液中において３時間攪拌して、この水素吸蔵合金粉末を酸化処理し、その後、この水素吸蔵合金粉末を水洗して、アルカリを除去し、乾燥させて水素吸蔵合金粉末を得た。
【００３４】
ここで、このように酸化処理した水素吸蔵合金粉末について、上記の実施例１の場合と同様にしてＸ線回折測定を行い、その結果を図３に示した。また、この測定結果に基づき、２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢを求めたところ、強度比ＩＡ／ＩＢは０．５３６であった。
【００３５】
また、上記の水素吸蔵合金粉末について、その水素吸蔵合金中に含まれる酸素の重量比率Ｗｏを求めた結果、この水素吸蔵合金中に含まれる酸素の重量比率Ｗｏは０．４９３ｗｔ％であり、上記の酸化処理により水素吸蔵合金中に含まれる酸素の重量比率Ｗｏが実施例１のものに比べて増大していた。
【００３６】
そして、上記のように作製した水素吸蔵合金粉末を用いる以外は、上記の実施例１の場合と同様にして、実施例４のアルカリ蓄電池を作製した。
【００３７】
（比較例１）
比較例１においては、希土類元素のＬａ，Ｐｒ及びＮｄと、Ｍｇと、Ｎｉとを、合金組成が（Ｌａ_０．２Ｐｒ_０．４Ｎｄ_０．４）_０．８３Ｍｇ_０．１７Ｎｉ_３．３になるように混合した後、アルゴン雰囲気中においてアーク溶解し、これを冷却させて水素吸蔵合金のインゴットを作製した。
【００３８】
そして、この水素吸蔵合金のインゴットを熱処理して均質化させた後、不活性雰囲気中において機械的に粉砕し、これを分級して、体積平均粒径（ＭＶ）が５４．５μｍになった上記の組成の水素吸蔵合金粉末を得た。
【００３９】
ここで、このようにして得た水素吸蔵合金粉末について、上記の実施例１の場合と同様にしてＸ線回折測定を行い、その結果を図４に示した。また、この測定結果に基づき、２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢを求めたところ、強度比ＩＡ／ＩＢは０．５０３であった。
【００４０】
また、上記の水素吸蔵合金粉末について、その水素吸蔵合金中に含まれる酸素の重量比率Ｗｏを求めた結果、この水素吸蔵合金中に含まれる酸素の重量比率Ｗｏは０．０６３ｗｔ％であった。
【００４１】
そして、上記のように作製した水素吸蔵合金粉末を用いる以外は、上記の実施例１の場合と同様にして、比較例１のアルカリ蓄電池を作製した。
【００４２】
（比較例２）
比較例２においては、希土類元素のＬａ，Ｐｒ及びＮｄと、Ｍｇと、Ｎｉと、Ａｌとを、合金組成が（Ｌａ_０．２Ｐｒ_０．４Ｎｄ_０．４）_０．８３Ｍｇ_０．１７Ｎｉ_３．２Ａｌ_０．１になるように混合した後、アルゴン雰囲気中においてアーク溶解し、これを冷却させて水素吸蔵合金のインゴットを作製した。
【００４３】
そして、この水素吸蔵合金のインゴットを熱処理して均質化させた後、不活性雰囲気中において機械的に粉砕し、これを分級して、体積平均粒径（ＭＶ）が４７．０μｍになった上記の組成の水素吸蔵合金粉末を得た。
【００４４】
ここで、このようにして得た水素吸蔵合金粉末について、上記の実施例１の場合と同様にしてＸ線回折測定を行い、その結果を図５に示した。また、この測定結果に基づき、２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢを求めたところ、強度比ＩＡ／ＩＢは０．５５５であった。
【００４５】
また、上記の水素吸蔵合金粉末について、その水素吸蔵合金中に含まれる酸素の重量比率Ｗｏを求めた結果、この水素吸蔵合金中に含まれる酸素の重量比率Ｗｏは０．０６８ｗｔ％であった。
【００４６】
そして、上記のように作製した水素吸蔵合金粉末を用いる以外は、上記の実施例１の場合と同様にして、比較例２のアルカリ蓄電池を作製した。
【００４７】
（比較例３）
比較例３においては、希土類元素のＬａ，Ｐｒ及びＮｄと、Ｍｇと、Ｎｉと、Ａｌとを、合金組成が（Ｌａ_０．２Ｐｒ_０．４Ｎｄ_０．４）_０．８３Ｍｇ_０．１７Ｎｉ_３．０Ａｌ_０．３になるように混合した後、アルゴン雰囲気中においてアーク溶解し、これを冷却させて水素吸蔵合金のインゴットを作製した。
【００４８】
そして、この水素吸蔵合金のインゴットを熱処理して均質化させた後、不活性雰囲気中において機械的に粉砕し、これを分級して、体積平均粒径（ＭＶ）が６４．８μｍになった上記の組成の水素吸蔵合金粉末を得た。
【００４９】
ここで、このようにして得た水素吸蔵合金粉末について、上記の実施例１の場合と同様にしてＸ線回折測定を行い、その結果を図６に示した。また、この測定結果に基づき、２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢを求めたところ、強度比ＩＡ／ＩＢは０．７０５であった。
【００５０】
また、上記の水素吸蔵合金粉末について、その水素吸蔵合金中に含まれる酸素の重量比率Ｗｏを求めた結果、この水素吸蔵合金中に含まれる酸素の重量比率Ｗｏは０．０５５ｗｔ％であった。
【００５１】
そして、上記のように作製した水素吸蔵合金粉末を用いる以外は、上記の実施例１の場合と同様にして、比較例３のアルカリ蓄電池を作製した。
【００５２】
次に、上記のようにして作製した実施例１〜４及び比較例１〜３の各アルカリ蓄電池を、それぞれ１８０ｍＡの電流で１６時間充電させた後、６０℃の温度雰囲気中に２４時間放置し、その後、３６０ｍＡの電流で電池電圧が１．０Ｖになるまで放電させて、各アルカリ蓄電池を活性化させた。
【００５３】
そして、このように活性化された各アルカリ蓄電池を分解して、各アルカリ蓄電池における各水素吸蔵合金を取り出し、活性化後の各水素吸蔵合金中に含まれる酸素の重量比率Ｗａを求めると共に、当初の各水素吸蔵合金中に含まれる酸素の重量比率Ｗｏからの増加量（Ｗａ−Ｗｏ）を算出し、その結果を下記の表１に示した。
【００５４】
また、上記のようにして作製した実施例１〜４及び比較例１〜３の各アルカリ蓄電池を、それぞれ１８００ｍＡの電流で９０分間充電させた後、１８００ｍＡの電流で電池電圧が１．０Ｖになるまで放電させ、これを１サイクルとし、上記の各アルカリ蓄電池の容量が安定するように、５サイクルの充放電を繰り返して行い、この時点における放電容量を初期容量として求めた。
【００５５】
次いで、上記の各アルカリ蓄電池をそれぞれ１８００ｍＡの電流で電池電圧が最大値に達した後、１０ｍＶ低下するまで充電させた後、１８００ｍＡの電流で電池電圧が１．０Ｖになるまで放電させ、これを１サイクルとして充放電を繰り返し、アルカリ蓄電池における放電容量が初期容量の８０％に低下するまでのサイクル数を求め、その結果をサイクル寿命として下記の表１に示した。
【００５６】
【表１】

【００５７】
この結果から明らかなように、Ｘ線回折測定による上記の強度比ＩＡ／ＩＢが０．５以上になったＣｅ_２Ｎｉ_７型、ＣｅＮｉ_３型及びこれらに類する結晶構造を有する水素吸蔵合金を負極に用いたアルカリ蓄電池において、当初の水素吸蔵合金中に含まれる酸素の重量比率Ｗｏに対する活性化後の水素吸蔵合金中に含まれる酸素の重量比率Ｗａの増加量（Ｗａ−Ｗｏ）が０．９ｗｔ％未満であり、また活性化後の水素吸蔵合金中に含まれる酸素の重量比率Ｗａが１．０ｗｔ％未満になった実施例１〜４の各アルカリ蓄電池は、これらの条件を満たしていない比較例１〜３の各アルカリ蓄電池に比べて、サイクル寿命が大幅に向上していた。
【００５８】
また、実施例１〜４のアルカリ蓄電池を比較した場合、予め酸化処理した水素吸蔵合金粉末を用いた実施例４のアルカリ蓄電池は、実施例１〜３の各アルカリ蓄電池に比べて、当初の水素吸蔵合金中に含まれる酸素の重量比率Ｗｏに対する活性化後の水素吸蔵合金中に含まれる酸素の重量比率Ｗａの増加量（Ｗａ−Ｗｏ）がさらに少なくなって、サイクル寿命が大幅に向上していた。
【００５９】
また、実施例１〜３のアルカリ蓄電池の比較した場合、使用する水素吸蔵合金の体積平均粒径（ＭＶ）が大きくなるに従って、当初の水素吸蔵合金中に含まれる酸素の重量比率Ｗｏに対する活性化後の水素吸蔵合金中に含まれる酸素の重量比率Ｗａの増加量（Ｗａ−Ｗｏ）が少なくなり、サイクル寿命も向上していた。
【００６０】
【発明の効果】
以上詳述したように、この発明におけるアルカリ蓄電池においては、水素吸蔵合金として、少なくとも希土類元素とマグネシウムとニッケルとを含み、Ｃｕ−Ｋα線をＸ線源とするＸ線回折測定において２θ＝３０°〜３４°の範囲に現れる最強ピーク強度ＩＡと、２θ＝４０°〜４４°の範囲に現れる最強ピーク強度ＩＢとの強度比ＩＡ／ＩＢが０．５以上である水素吸蔵合金を用いた場合において、上記の水素吸蔵合金に含まれる酸素の重量比率Ｗｏに対して、アルカリ蓄電池を活性化させた後における水素吸蔵合金に含まれる酸素の重量比率Ｗａが増加した量（Ｗａ−Ｗｏ）が０．９ｗｔ％未満になるようにし、或いはアルカリ蓄電池を活性化させた後における水素吸蔵合金に含まれる酸素の重量比率Ｗａが１．０ｗｔ％未満になるようしたため、このアルカリ蓄電池を繰り返して充放電させた場合においても、水素吸蔵合金との反応によってアルカリ電解液が消費されるのが抑制されるようになった。
【００６１】
この結果、この発明におけるアルカリ蓄電池においては、アルカリ蓄電池におけるエネルギー密度を高めて高容量化させるために、アルカリ電解液の量を少なくし、アルカリ電解液に対する上記の水素吸蔵合金の割合が４．３ｇ／ｃｃ以上になるようにした場合においても、十分なサイクル寿命が得られるようになった。
【図面の簡単な説明】
【図１】この発明の実施例１〜３のアルカリ蓄電池に用いた水素吸蔵合金におけるＸ線回折測定結果を示した図である。
【図２】この発明の実施例１〜４及び比較例１〜３において作製したアルカリ蓄電池の概略断面図である。
【図３】この発明の実施例４のアルカリ蓄電池に用いた水素吸蔵合金におけるＸ線回折測定結果を示した図である。
【図４】比較例１のアルカリ蓄電池に用いた水素吸蔵合金におけるＸ線回折測定結果を示した図である。
【図５】比較例２のアルカリ蓄電池に用いた水素吸蔵合金におけるＸ線回折測定結果を示した図である。
【図６】比較例３のアルカリ蓄電池に用いた水素吸蔵合金におけるＸ線回折測定結果を示した図である。
【符号の説明】
１正極
２負極
３セパレータ
４電池缶
５正極リード
６正極蓋
７負極リード
８絶縁パッキン
９正極外部端子
１０コイルスプリング[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline storage battery including an alkaline electrolyte, particularly including at least a rare earth element, magnesium, and nickel, and using a Cu-Kα ray as an X-ray source. In the X-ray diffraction measurement, the intensity ratio IA / IB between the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 ° is 0.5 or more. In an alkaline storage battery using a hydrogen storage alloy, specifically, a Ce ₂ Ni ₇ type, a CeNi ₃ type, and a hydrogen storage alloy having a crystal structure similar to these, even when the amount of the alkaline electrolyte is reduced, It is characterized in that a long cycle life is obtained.
[0002]
[Prior art]
In the past, nickel-cadmium storage batteries were generally used as alkaline storage batteries.However, in recent years, they have a higher capacity than nickel-cadmium storage batteries, and they are superior in environmental safety because they do not use cadmium. Attention has been paid to nickel-hydrogen storage batteries using a hydrogen storage alloy for the negative electrode.
[0003]
Then, such nickel-metal hydride storage batteries have come to be used in various portable devices, and it is expected that the nickel-metal hydride storage batteries will have higher performance.
[0004]
Here, in the nickel-hydrogen storage battery, the hydrogen storage alloy used for the negative electrode includes a rare earth-nickel based hydrogen storage alloy having a CaCu type ₅ crystal as a main phase, and Ti, Zr, V and Ni. Laves phase-based hydrogen storage alloys and the like have been commonly used.
[0005]
However, these hydrogen storage alloys do not always have sufficient hydrogen storage capacity, and have a problem that it is difficult to further increase the capacity of the nickel-metal hydride storage battery.
[0006]
In recent years, the rare earth-nickel-based hydrogen storage alloy contains Mg or the like to improve the hydrogen storage capacity of the hydrogen storage alloy. The Ce ₂ Ni ₇ type, the CeNi ₃ type, and the crystal structure similar to these are used. There has been proposed a device using a hydrogen storage alloy having the following (for example, see Patent Document 1).
[0007]
However, the above-mentioned Ce ₂ Ni ₇ type, CeNi ₃ type and the hydrogen storage alloy having a crystal structure similar thereto are more easily oxidized than the rare earth-nickel based hydrogen storage alloy having a CaCu ₅ type crystal as a main phase. There is a problem that the alkaline electrolyte is consumed by reacting with the alkaline electrolyte.
[0008]
In particular, in recent years, in order to increase the energy density and increase the capacity of the alkaline storage battery, the amount of the alkaline electrolyte in the alkaline storage battery has been reduced. When an occlusion alloy is used, there is a problem that the alkaline electrolyte is consumed and becomes insufficient, and the cycle life is greatly reduced.
[0009]
[Patent Document 1]
JP, 2002-164045, A
[Problems to be solved by the invention]
According to the present invention, the strongest peak intensity IA containing at least a rare earth element, magnesium and nickel and appearing in the range of 2θ = 30 ° to 34 ° in X-ray diffraction measurement using Cu-Kα ray as an X-ray source, and 2θ = 40 A hydrogen storage alloy having an intensity ratio IA / IB to the strongest peak intensity IB appearing in the range of ° to 44 ° of 0.5 or more, specifically Ce ₂ Ni ₇ type, CeNi ₃ type and a crystal structure similar thereto. It is an object of the present invention to solve the above-described problems in an alkaline storage battery using a hydrogen storage alloy having the same.
[0011]
That is, the present invention relates to an alkaline storage battery using the above-mentioned hydrogen storage alloy, in which the amount of the alkaline electrolyte is reduced by suppressing the consumption of the alkaline electrolyte by reacting with the hydrogen storage alloy. It is another object of the present invention to obtain a sufficient cycle life.
[0012]
[Means for Solving the Problems]
In the first alkaline storage battery according to the present invention, in order to solve the above-described problems, in the alkaline storage battery including the positive electrode, the negative electrode using the hydrogen storage alloy, and the alkaline electrolyte, as the hydrogen storage alloy, The strongest peak intensity IA containing at least a rare earth element, magnesium and nickel and appearing in the range of 2θ = 30 ° to 34 ° in X-ray diffraction measurement using Cu-Kα ray as an X-ray source, and 2θ = 40 ° to 44 ° The hydrogen storage alloy having an intensity ratio IA / IB to the strongest peak intensity IB appearing in a range of 0.5 ° or more is 0.5 or more, and the above alkaline storage battery is used with respect to the weight ratio Wo of oxygen contained in the hydrogen storage alloy. The amount by which the weight ratio Wa of oxygen contained in the hydrogen storage alloy after activation was increased (Wa-Wo) was set to be less than 0.9 wt%.
[0013]
Further, in the second alkaline storage battery according to the present invention, in order to solve the above-described problems, in the alkaline storage battery including a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, The alloy contains at least a rare earth element, magnesium and nickel, and has the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° in X-ray diffraction measurement using Cu-Kα ray as an X-ray source, and 2θ = 40 ° Using a hydrogen storage alloy having an intensity ratio IA / IB with the strongest peak intensity IB appearing in the range of ~ 44 ° of 0.5 or more, the oxygen contained in the hydrogen storage alloy after activating the above alkaline storage battery. The weight ratio Wa was set to be less than 1.0 wt%.
[0014]
Then, in the case where the above-mentioned hydrogen storage alloy is used, as in the case of the first alkaline storage battery, after the alkali storage battery is activated with respect to the weight ratio Wo of oxygen contained in the hydrogen storage alloy. The amount (Wa-Wo) in which the weight ratio Wa of oxygen contained in the hydrogen storage alloy has increased (Wa-Wo) is set to be less than 0.9 wt%, or after activating the alkaline storage battery like the second alkaline storage battery. When the weight ratio Wa of oxygen contained in the hydrogen storage alloy is less than 1.0 wt%, even when the alkaline storage battery is repeatedly charged and discharged, the alkaline electrolyte is consumed by the reaction with the hydrogen storage alloy. Is suppressed.
[0015]
For this reason, in the first and second alkaline storage batteries of the present invention, in order to increase the energy density and increase the capacity of the alkaline storage batteries, the amount of the alkaline electrolyte is reduced, and the above-mentioned hydrogen storage alloy with respect to the alkaline electrolyte is reduced. Even when the ratio is 4.3 g / cc or more, a sufficient cycle life can be obtained.
[0016]
In order for the weight ratios Wo and Wa of oxygen contained in the hydrogen storage alloy to satisfy the above-described conditions, in addition to appropriately selecting the composition of the above-mentioned hydrogen storage alloy and the particle size thereof, etc. The hydrogen storage alloy can be oxidized in advance to prevent the hydrogen storage alloy from reacting with the alkaline electrolyte.
[0017]
Here, the composition of the hydrogen absorbing alloy, for example, the composition formula _{_{_{_{RE 1-x Mg x Ni y}}}} M a (RE is one or more elements selected from rare earth elements, 0.15 ≦ x ≦ 0 .30, 2.8 ≦ y ≦ 3.9, 3.0 ≦ y + a ≦ 3.6), and the above-mentioned M is Al having a function of suppressing oxidation in a composition ratio. It is preferable to use one containing about 0.2. In addition, when the particle size of the hydrogen storage alloy is small, the specific surface area increases, and the hydrogen storage alloy easily reacts with the alkaline electrolyte.
[0018]
When the hydrogen storage alloy is previously oxidized as described above, the hydrogen storage alloy can be treated using an alkali solution or an acid solution. Particularly, in suppressing the hydrogen storage alloy from reacting with the alkaline electrolyte, It is preferable to perform treatment using the same alkaline solution.
[0019]
【Example】
Hereinafter, the alkaline storage battery according to the embodiment of the present invention will be specifically described, and a comparative example will be given to clarify that the cycle life of the alkaline storage battery according to the embodiment of the present invention is improved. The alkaline storage battery according to the present invention is not limited to those shown in the following embodiments, but can be implemented by appropriately changing the scope of the invention without changing its gist.
[0020]
(Example 1)
In Example 1, the rare earth elements La, Pr, and Nd, Mg, Ni, and Al were alloyed to have an alloy composition of (La _0.2 Pr _0.4 Nd _0.4 ) _0.83 Mg _0.17 After mixing to Ni _3.1 Al _0.2 , the mixture was arc-melted in an argon atmosphere, and cooled to produce a hydrogen storage alloy ingot.
[0021]
Then, after the ingot of the hydrogen storage alloy is heat-treated and homogenized, it is mechanically pulverized in an inert atmosphere, and classified to obtain a volume average particle diameter (MV) of 63.2 μm. A hydrogen storage alloy powder having a composition of (La _0.2 Pr _0.4 Nd _0.4 ) _0.83 Mg _0.17 Ni _3.1 Al _0.2 was obtained.
[0022]
Here, with respect to the hydrogen storage alloy powder thus produced, using an X-ray diffractometer (RIGAKU RINT2000 system) using a Cu-Kα ray as an X-ray source, at a scan speed of 2 ° / min and a scan step of 0.02 °. X-ray diffraction measurement was performed in a scanning range of 20 ° to 80 °, and the results are shown in FIG. Further, based on the measurement results, the intensity ratio IA / IB of the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 ° was determined. However, the intensity ratio IA / IB was 0.602, which was different from the CaCu ₅ type, and had a Ce ₂ Ni ₇ type, a CeNi ₃ type and a crystal structure similar thereto.
[0023]
The weight ratio Wo of oxygen contained in the hydrogen storage alloy was determined for the hydrogen storage alloy powder thus produced. As a result, the weight ratio Wo of oxygen contained in the hydrogen storage alloy was 0.063 wt%. there were.
[0024]
Next, with respect to 100 parts by weight of the above hydrogen storage alloy powder, 0.1 parts by weight of polyethylene oxide, 0.1 parts by weight of polyvinylpyrrolidone, and 20 parts by weight of water were mixed to prepare a paste, This paste is uniformly applied to both sides of a conductive core made of punched metal plated with nickel, dried and pressed, and then cut to a predetermined size to produce a hydrogen storage alloy electrode used for a negative electrode. did.
[0025]
On the other hand, when producing a positive electrode, 5 wt% of cobalt hydroxide was coated on the surface of nickel hydroxide containing 2.5 wt% of zinc and 1.0 wt% of cobalt, and then a 25 wt% aqueous solution of sodium hydroxide was added thereto. And heated at 85 ° C., washed with water and dried to obtain a positive electrode material in which the surface of the nickel hydroxide was coated with a sodium-containing cobalt oxide.
[0026]
To a mixture of 95 parts by weight of this positive electrode material, 3 parts by weight of zinc oxide and 2 parts by weight of cobalt hydroxide, 50 parts by weight of a 0.2 wt% aqueous solution of hydroxypropylcellulose was added. A slurry was prepared by mixing, and the slurry was filled in a nickel foam, dried and pressed, and then cut to a predetermined size to produce a positive electrode made of a non-sintered nickel electrode.
[0027]
A nonwoven fabric made of polypropylene is used as a separator, and an alkaline electrolyte having a specific gravity of 1.30, in which KOH, NaOH, and LiOH.H ₂ O are contained in a weight ratio of 15: 2: 1, is used as an alkaline electrolyte. A cylindrical alkaline storage battery having a designed capacity of 1800 mAh as shown in FIG. 2 was manufactured.
[0028]
Here, in manufacturing the alkaline storage battery of the first embodiment, as shown in FIG. 1, a separator 3 is interposed between a positive electrode 1 and a negative electrode 2, and these are spirally wound into a battery can 4. After being accommodated, the above-mentioned alkaline electrolyte is poured into the battery can 4, and the battery can 4 and the positive electrode lid 6 are sealed with an insulating packing 8 therebetween. While being connected to the positive electrode cover 6, the negative electrode 2 was connected to the battery can 4 via the negative electrode lead 7, and the battery can 4 and the positive electrode cover 6 were electrically separated by the insulating packing 8. Further, a coil spring 10 is provided between the positive electrode lid 6 and the positive electrode external terminal 9. When the internal pressure of the battery rises abnormally, the coil spring 10 is compressed and the gas inside the battery is released to the atmosphere. To be released. When the alkaline electrolyte was injected as described above, the ratio of the hydrogen storage alloy to the alkaline electrolyte was adjusted to 4.3 g / cc.
[0029]
(Examples 2 and 3)
In Examples 2 and 3, the conditions for pulverizing and classifying the hydrogen storage alloy ingot in the preparation of the hydrogen storage alloy powder in Example 1 were changed, and in Example 2, the volume average particle diameter (MV) was changed. Was 53.8 μm, and in Example 3, a hydrogen storage alloy powder having the above composition having a volume average particle size (MV) of 74.3 μm was obtained.
[0030]
Here, the result of the X-ray diffraction measurement of each of the hydrogen storage alloy powders produced in Example 2 and Example 3 was the same as that of the hydrogen storage alloy powder produced in Example 1 above, and the intensity ratio IA / IB was also 0.602.
[0031]
Further, with respect to the hydrogen storage alloy powder produced in Example 2 and Example 3, the weight ratio Wo of oxygen contained in the hydrogen storage alloy was determined. As a result, the weight of oxygen contained in the hydrogen storage alloy of Example 2 was obtained. The ratio Wo was 0.061 wt%, and the weight ratio Wo of oxygen contained in the hydrogen storage alloy of Example 3 was 0.049 wt%.
[0032]
Then, the alkaline storage batteries of Examples 2 and 3 were produced in the same manner as in Example 1 except that the hydrogen storage alloy powder produced as described above was used.
[0033]
(Example 4)
In Example 4, in the same manner as in Example 1 described above, after obtaining a hydrogen storage alloy powder having a volume average particle diameter (MV) of 63.2 μm, the hydrogen storage alloy powder was heated to 80 ° C. The resulting hydrogen storage alloy powder was oxidized by stirring in an 8N aqueous KOH solution for 3 hours, and then the hydrogen storage alloy powder was washed with water to remove alkali, and dried to remove the hydrogen storage alloy powder. Obtained.
[0034]
Here, the hydrogen storage alloy powder thus oxidized was subjected to X-ray diffraction measurement in the same manner as in Example 1 above, and the results are shown in FIG. Further, based on the measurement results, the intensity ratio IA / IB of the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 ° was determined. However, the intensity ratio IA / IB was 0.536.
[0035]
The weight ratio Wo of oxygen contained in the hydrogen storage alloy was determined for the hydrogen storage alloy powder. As a result, the weight ratio Wo of oxygen contained in the hydrogen storage alloy was 0.493 wt%. By the oxidation treatment, the weight ratio Wo of oxygen contained in the hydrogen storage alloy was increased as compared with that in Example 1.
[0036]
Then, an alkaline storage battery of Example 4 was manufactured in the same manner as in Example 1 except that the hydrogen storage alloy powder manufactured as described above was used.
[0037]
(Comparative Example 1)
In Comparative Example 1, the rare earth elements La, Pr, and Nd, Mg, and Ni were used, and the alloy composition was (La _0.2 Pr _0.4 Nd _0.4 ) _0.83 Mg _0.17 Ni _3. After mixing so as to obtain No. ₃ , arc melting was performed in an argon atmosphere, and this was cooled to produce a hydrogen storage alloy ingot.
[0038]
Then, after heat-treating and homogenizing the ingot of the hydrogen-absorbing alloy, it is mechanically pulverized in an inert atmosphere, and classified to obtain a volume average particle size (MV) of 54.5 μm. A hydrogen storage alloy powder having the following composition was obtained.
[0039]
Here, the hydrogen storage alloy powder thus obtained was subjected to X-ray diffraction measurement in the same manner as in Example 1 above, and the results are shown in FIG. Further, based on the measurement results, the intensity ratio IA / IB of the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 ° was determined. However, the intensity ratio IA / IB was 0.503.
[0040]
The weight ratio Wo of oxygen contained in the hydrogen storage alloy was determined for the above hydrogen storage alloy powder. As a result, the weight ratio Wo of oxygen contained in the hydrogen storage alloy was 0.063 wt%.
[0041]
Then, an alkaline storage battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the hydrogen storage alloy powder produced as described above was used.
[0042]
(Comparative Example 2)
In Comparative Example 2, the rare earth elements La, Pr, and Nd, Mg, Ni, and Al were alloyed with an alloy composition of (La _0.2 Pr _0.4 Nd _0.4 ) _0.83 Mg _0.17 After mixing to Ni _3.2 Al _0.1 , the mixture was arc-melted in an argon atmosphere, and cooled to produce a hydrogen storage alloy ingot.
[0043]
Then, after heat-treating and homogenizing this ingot of the hydrogen storage alloy, it is mechanically pulverized in an inert atmosphere, and classified to obtain a volume average particle size (MV) of 47.0 μm. A hydrogen storage alloy powder having the following composition was obtained.
[0044]
Here, the hydrogen storage alloy powder thus obtained was subjected to X-ray diffraction measurement in the same manner as in Example 1 above, and the results are shown in FIG. Further, based on the measurement results, the intensity ratio IA / IB of the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 ° was determined. However, the intensity ratio IA / IB was 0.555.
[0045]
The weight ratio Wo of oxygen contained in the hydrogen storage alloy was determined for the above hydrogen storage alloy powder. As a result, the weight ratio Wo of oxygen contained in the hydrogen storage alloy was 0.068 wt%.
[0046]
Then, an alkaline storage battery of Comparative Example 2 was manufactured in the same manner as in Example 1 except that the hydrogen storage alloy powder manufactured as described above was used.
[0047]
(Comparative Example 3)
In Comparative Example 3, the rare earth elements La, Pr, and Nd, Mg, Ni, and Al were alloyed to have an alloy composition of (La _0.2 Pr _0.4 Nd _0.4 ) _0.83 Mg _0.17 After mixing so as to be Ni _3.0 Al _0.3 , the mixture was arc-melted in an argon atmosphere, and the mixture was cooled to produce a hydrogen storage alloy ingot.
[0048]
Then, the ingot of the hydrogen storage alloy is heat-treated and homogenized, then mechanically pulverized in an inert atmosphere, and classified to obtain a volume average particle size (MV) of 64.8 μm. A hydrogen storage alloy powder having the following composition was obtained.
[0049]
Here, the obtained hydrogen storage alloy powder was subjected to X-ray diffraction measurement in the same manner as in Example 1 above, and the results are shown in FIG. Further, based on the measurement results, the intensity ratio IA / IB of the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 ° was determined. However, the intensity ratio IA / IB was 0.705.
[0050]
The weight ratio Wo of oxygen contained in the hydrogen storage alloy was determined for the above hydrogen storage alloy powder. As a result, the weight ratio Wo of oxygen contained in the hydrogen storage alloy was 0.055 wt%.
[0051]
Then, an alkaline storage battery of Comparative Example 3 was manufactured in the same manner as in Example 1 except that the hydrogen storage alloy powder manufactured as described above was used.
[0052]
Next, each of the alkaline storage batteries of Examples 1 to 4 and Comparative Examples 1 to 3 produced as described above was charged with a current of 180 mA for 16 hours, and then left in a 60 ° C temperature atmosphere for 24 hours. Thereafter, the battery was discharged at a current of 360 mA until the battery voltage became 1.0 V, and each alkaline storage battery was activated.
[0053]
Then, each activated alkaline storage battery thus activated is disassembled, each hydrogen storage alloy in each alkaline storage battery is taken out, and the weight ratio Wa of oxygen contained in each activated hydrogen storage alloy is determined. Was calculated from the weight ratio Wo of oxygen contained in each hydrogen storage alloy (Wa-Wo), and the results are shown in Table 1 below.
[0054]
After the alkaline storage batteries of Examples 1 to 4 and Comparative Examples 1 to 3 produced as described above were charged at a current of 1800 mA for 90 minutes, the battery voltage became 1.0 V at a current of 1800 mA. The alkaline storage battery was repeatedly discharged and charged for 5 cycles so that the capacity of each alkaline storage battery was stabilized, and the discharge capacity at this time was determined as an initial capacity.
[0055]
Next, each of the alkaline storage batteries described above was charged with a current of 1800 mA until the battery voltage reached the maximum value, and then charged until the battery voltage decreased by 10 mV, and then discharged with a current of 1800 mA until the battery voltage became 1.0 V. The charge / discharge was repeated as one cycle, and the number of cycles until the discharge capacity of the alkaline storage battery was reduced to 80% of the initial capacity was obtained. The result is shown in Table 1 below as the cycle life.
[0056]
[Table 1]

[0057]
As is apparent from these results, the Ce ₂ Ni ₇ type, CeNi ₃ type and the hydrogen storage alloy having a crystal structure similar to these having the above-mentioned intensity ratio IA / IB of 0.5 or more by X-ray diffraction measurement were used as a negative electrode. In the alkaline storage battery used in (1), the increase (Wa-Wo) of the weight ratio Wa of oxygen contained in the hydrogen storage alloy after activation with respect to the weight ratio Wo of oxygen originally contained in the hydrogen storage alloy is 0.9 wt. % And the weight ratio Wa of oxygen contained in the hydrogen storage alloy after activation is less than 1.0 wt%, the alkaline storage batteries of Examples 1 to 4 do not satisfy these conditions. The cycle life was significantly improved as compared with the alkaline storage batteries of Examples 1 to 3.
[0058]
When the alkaline storage batteries of Examples 1 to 4 were compared, the alkaline storage battery of Example 4 using the hydrogen storage alloy powder that had been oxidized in advance had a higher initial hydrogen storage capacity than the alkaline storage batteries of Examples 1 to 3. The increase (Wa-Wo) of the weight ratio Wa of oxygen contained in the hydrogen storage alloy after activation with respect to the weight ratio Wo of oxygen contained in the storage alloy is further reduced, and the cycle life is greatly improved. Was.
[0059]
Further, when comparing the alkaline storage batteries of Examples 1 to 3, as the volume average particle size (MV) of the hydrogen storage alloy used increases, the activation of the oxygen contained in the hydrogen storage alloy to the weight ratio Wo of the initial hydrogen storage alloy increases. The increase amount (Wa-Wo) of the weight ratio Wa of oxygen contained in the later hydrogen storage alloy was reduced, and the cycle life was also improved.
[0060]
【The invention's effect】
As described in detail above, in the alkaline storage battery of the present invention, the hydrogen storage alloy contains at least a rare earth element, magnesium, and nickel, and 2θ = 30 ° in X-ray diffraction measurement using Cu-Kα radiation as an X-ray source. In the case of using a hydrogen storage alloy having an intensity ratio IA / IB of 0.5 or more between the strongest peak intensity IA appearing in the range of ~ 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 °, The amount (Wa-Wo) obtained by increasing the weight ratio Wa of oxygen contained in the hydrogen storage alloy after activating the alkaline storage battery with respect to the weight ratio Wo of oxygen contained in the hydrogen storage alloy is 0.0. The weight ratio Wa of oxygen contained in the hydrogen storage alloy after activating the alkaline storage battery is set to less than 9 wt% or less than 1.0 wt%. Therefore, even when allowed to discharge by repeating this alkaline storage battery, that the alkaline electrolyte is consumed it came to be inhibited by the reaction between hydrogen storage alloy.
[0061]
As a result, in the alkaline storage battery according to the present invention, in order to increase the energy density of the alkaline storage battery and increase the capacity, the amount of the alkaline electrolyte is reduced, and the ratio of the hydrogen storage alloy to the alkaline electrolyte is 4.3 g. / Cc or more, a sufficient cycle life can be obtained.
[Brief description of the drawings]
FIG. 1 is a view showing an X-ray diffraction measurement result of a hydrogen storage alloy used in alkaline storage batteries of Examples 1 to 3 of the present invention.
FIG. 2 is a schematic sectional view of an alkaline storage battery manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 of the present invention.
FIG. 3 is a view showing an X-ray diffraction measurement result of a hydrogen storage alloy used for an alkaline storage battery according to Example 4 of the present invention.
FIG. 4 is a view showing an X-ray diffraction measurement result of a hydrogen storage alloy used for an alkaline storage battery of Comparative Example 1.
FIG. 5 is a diagram showing an X-ray diffraction measurement result of a hydrogen storage alloy used for an alkaline storage battery of Comparative Example 2.
FIG. 6 is a diagram showing an X-ray diffraction measurement result of a hydrogen storage alloy used for an alkaline storage battery of Comparative Example 3.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery can 5 Positive electrode lead 6 Positive electrode cover 7 Negative lead 8 Insulating packing 9 Positive external terminal 10 Coil spring

Claims

A positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline storage battery including an alkaline electrolyte, wherein the hydrogen storage alloy contains at least a rare earth element, magnesium, and nickel, and a Cu-Kα ray is used as an X-ray source. In the X-ray diffraction measurement, the intensity ratio IA / IB between the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 ° is 0.5 or more. The amount by which the weight ratio Wa of oxygen contained in the hydrogen storage alloy after activating the alkaline storage battery is increased with respect to the weight ratio Wo of oxygen contained in the hydrogen storage alloy using the hydrogen storage alloy (Wa-Wo) is less than 0.9% by weight.

A positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline storage battery including an alkaline electrolyte, wherein the hydrogen storage alloy contains at least a rare earth element, magnesium, and nickel, and a Cu-Kα ray is used as an X-ray source. In the X-ray diffraction measurement, the intensity ratio IA / IB between the strongest peak intensity IA appearing in the range of 2θ = 30 ° to 34 ° and the strongest peak intensity IB appearing in the range of 2θ = 40 ° to 44 ° is 0.5 or more. The weight ratio Wa of oxygen contained in the hydrogen storage alloy after activating the alkaline storage battery using the hydrogen storage alloy is less than 1.0 wt%.

The alkaline storage battery according to claim 1 or 2, wherein a ratio of the hydrogen storage alloy to the alkaline electrolyte is 4.3 g / cc or more.

The alkaline storage battery according to any one of claims 1 to 3, wherein the hydrogen storage alloy is oxidized.