JP4366729B2

JP4366729B2 - Cathode active material for alkaline storage battery

Info

Publication number: JP4366729B2
Application number: JP24678798A
Authority: JP
Inventors: 秀勝泉; 弘之坂本; 宏和木宮; 陽一和泉; 功松本
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1997-10-06
Filing date: 1998-09-01
Publication date: 2009-11-18
Anticipated expiration: 2018-09-01
Also published as: JPH11176437A

Description

【０００１】
【発明の属する技術分野】
本発明は、アルカリ蓄電池用正極活物質の改良に関するものである。
【０００２】
【従来の技術】
アルカリ蓄電池、特にその小型密閉式電池は、他の電池系と比べて充放電特性、サイクル寿命および安全性・信頼性にバランス良く優れることから、移動体通信機器、パーソナルコンピューターなどに代表される各種ポータブル機器用主電源として普及が著しい。また、大型電源としても充放電特性や信頼性にきわめて優れることから、電気自動車などの移動用主電源としても注目されている。アルカリ蓄電池を代表する電池系は、長い歴史を持つニッケル・カドミウム蓄電池であったが、カドミウム負極の代わりに水素吸蔵合金負極を用いたニッケル・水素蓄電池が工業化され、高エネルギー密度化が図られた。また、電極支持体においても焼結式電極に代わり、高多孔度（９５％以上）の３次元発泡ニッケル多孔体にニッケル酸化物を高密度充填した電極（ＳｐｏｎｇｅＭｅｔａｌＮｉｃｋｅｌＥｌｅｃｔｒｏｄｅ：ＳＭＥ）が工業化され、高エネルギー密度化が図られた。このように、これまでアルカリ蓄電池では、特に電池の小型化・軽量化・高エネルギー密度化に注力されてきた。
【０００３】
一方、アルカリ蓄電池の電気自動車・電動工具等への利用を考えた場合、電池の高出力化、つまり高率放電時における作動電圧の向上が重要な課題となる。また、各種ポータブル機器も定電力放電で作動するものが多く、放電電圧が低下する放電末期には高率放電状態となり、一層の放電電圧の低下が生じる。したがって、小型密閉アルカリ蓄電池においても作動電圧の向上が重要な課題である。
【０００４】
この課題の解決策として、例えば特開平５−１７４８６７号公報では、アルカリ電解液中に水酸化ルビジウムおよび水酸化セシウムのうち少なくとも１種の水酸化物を０．３規定〜３．５規定添加することによって、電解液の導電性が向上し、かつルビジウムイオンおよびセシウムイオンが触媒として作用するため、高率放電時において作動電圧を高めることができることが記載されている。しかし、ルビジウムおよびセシウムといった高価な材料を実際の電池へ使用することは困難であり、実用化されていない。
【０００５】
一方、米国特許５５６７５４９号（１９９６）には、Ｎｉ（ＯＨ）₂へＡｌを固溶させたアルカリ蓄電池用正極活物質について記載されている。その内溶は、Ｎｉ（ＯＨ）₂へＡｌを固溶させることによりα−Ｎｉ（ＯＨ）₂相が安定化され、このα相を含有する多相Ａｌ固溶Ｎｉ（ＯＨ）₂は高次反応を行なうため、電池の高容量化が実現できるというものである。
【０００６】
我々も、Ｎｉ（ＯＨ）₂へのＡｌ添加の効果について研究を行なったところ、Ａｌを共晶状態および／または固溶状態でＮｉ（ＯＨ）₂に添加する（以下、Ａｌ固溶Ｎｉ（ＯＨ）₂と略する）ことにより、前記米国特許５５６７５４９号記載の効果の他にも、放電電圧向上、高率放電特性向上の効果が得られることが分かった。特に、Ｘ線回折パターンにおいてα−Ｎｉ（ＯＨ）₂に帰属する回折線を示すＡｌ固溶Ｎｉ（ＯＨ）₂（以下、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂と略する）において顕著な効果が得られることが分かった。
【０００７】
ところでα類似型Ｎｉ（ＯＨ）₂については、Ｎｉ（ＯＨ）₂のＮｉの一部を酸化数の高い金属原子（例えばＣｏ（III）、Ｍｎ（III）、Ｆｅ（III）など）で置換することで得られることが報告されており（ＳｏｌｉｄＳｔａｔｅＩｏｎｉｃｓ３２／３３，ｐ．１０４（１９８９）、Ｊ．ＰｏｗｅｒＳｏｕｒｃｅｓ，３５，ｐ．２４９（１９９１）など）、酸化数の高い金属原子が固溶したために結晶構造中のニッケルプレート層が正に帯電し、電荷補償として層間にアニオン種（例えばＰＯ₄ ^3-、ＳＯ₄ ^2-、ＣＯ₃ ^2-、ＮＯ₃ ^-など）が入り込み、層間が広がった構造を持つと考えられている（Ｊ．ＰｏｗｅｒＳｏｕｒｃｅｓ，３６，ｐ．１１３（１９９１）、ＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅＦｏｒｕｍ，１５２−１５３，ｐ．２０１（１９９４）など）。したがって、α類似型Ｎｉ（ＯＨ）₂は嵩高く、高密度充填が困難であると考えられるが、我々が検討を行なったα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂に関しても、放電電圧、高率放電特性、利用率は顕著に向上するものの、充填密度がきわめて低く、アルカリ蓄電池用正極活物質として使用できるものではなかった。
【０００８】
また、正極活物質の傾斜機能化による特性改善についても、これまでに多数報告されている。例えば特開平９−１７４２８号公報では、Ｎｉ（ＯＨ）₂またはＮｉ（ＯＨ）₂を主成分とする粒子表面をＣｏおよび／もしくはＮｉ添加物で被覆することによって、利用率を向上させ、放電容量を増大できることが報告されている。また、特開平８−２８７９０７号公報では、Ｎｉ（ＯＨ）₂またはＮｉ（ＯＨ）₂を主成分とする粒子表面をＩＩ族元素の化合物を主成分とする第１化合物で被覆し、さらにその表面をＣｏ化合物を主成分とする第２化合物層で被覆した正極活物質を用いることによって、高容量、かつ長寿命のアルカリ蓄電池を提供できることが報告されている。さらに特開平８−３２９９４３号公報では、ＣａをＮｉ（ＯＨ）₂粒子に固溶させると同時に、含有Ｃａの少なくとも一部を、Ｃａ（ＯＨ）₂としてＮｉ（ＯＨ）₂粒子の表面および細孔内部に被覆、含浸させた正極活物質を用いることによって、利用率、特に高温における利用率を高めたアルカリ蓄電池を提供できることが報告されている。しかしながら、正極活物質の傾斜機能化による放電電圧、高率放電特性の改善に関しては、これまでに何等報告されていない。
【０００９】
【発明が解決しようとする課題】
本発明は、高容量密度かつ放電電圧、高率放電特性に優れたアルカリ蓄電池用正極活物質を提供することを目的とする。
【００１０】
【課題を解決するための手段】
Ｎｉを主たる金属元素とする複数金属元素の酸化物（または水酸化物）を主材料とするアルカリ蓄電池用正極に使用する活物質粉末において、前記複数金属元素の酸化物（または水酸化物）粉末の表面層付近に、Ａｌが共晶状態および／または固溶状態で存在するα類似型Ｎｉ（ＯＨ）₂層を配する。このα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂層は放電電圧、高率放電特性を向上させる作用を有する。本来、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂は嵩高く、高密度充填が困難であるが、表面層付近にのみ配するため充填密度の低下は抑止でき、高容量密度を維持できる。さらに、上記α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層にＣａ，Ｃｒ，Ｙ，Ｔｉ，Ｃｏから選ばれる少なくとも一種の元素を共晶状態および／または固溶状態で添加することにより、放電電圧、高率放電特性、高密度充填に優れ、かつ高温充電効率および／または充放電特性にも優れたアルカリ蓄電池用正極活物質が得られる。また、上記α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆正極活物質粉末の表面をさらにＣｏ酸化物層で被覆することにより、放電電圧、高率放電特性、高密度充填に優れ、かつ充放電特性にも優れたアルカリ蓄電池用正極活物質が得られる。
【００１１】
ここで本発明は、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂が正極活物質粒子内部に存在する（米国特許５５６７５４９号（１９９６））のではなく、正極活物質粒子表面に配されていることに特徴を有する。このような構成とすることにより、正極活物質の高密度充填が可能となる。また、正極活物質粒子への異種金属元素固溶に関しても、正極活物質粒子内部および／または正極活物質粒子表面に配する（特開平９−１７４２８号公報、特開平８−３２９９４３号公報など）のではなく、正極活物質粒子表面に配されたα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層に添加することに特徴を有する。このような構成とすることにより、放電電圧、高率放電特性を向上させ、かつその他の特性が改善された正極活物質が可能となる。さらに、正極活物質粒子とその表面のＣｏ酸化物被覆層との間にα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂層を配することに特徴を有する。このような構成とすることにより、放電電圧、高率放電特性を向上させ、かつ充放電特性が改善された正極活物質が可能となる。
【００１２】
【発明の実施の形態】
本発明はＮｉを主たる金属元素とする複数金属元素の酸化物または水酸化物を主材料とするアルカリ蓄電池用正極活物質粉末において、前記複数金属元素の酸化物または水酸化物粉末の表面層付近に、Ａｌが共晶状態および／または固溶状態で存在するα類似型Ｎｉ（ＯＨ）₂層を配したことを特徴とする。ここで、α類似型Ｎｉ（ＯＨ）₂被覆層中に共晶状態および／または固溶状態で存在するＡｌ量は、α類似型Ｎｉ（ＯＨ）₂被覆層中の金属原子比をＮｉ：Ａｌ＝１−ｘ：ｘと表した場合、０．１０≦ｘ≦０．４０であることを特徴とする。これにより、高容量密度かつ放電電圧、高率放電特性に優れたアルカリ蓄電池用正極活物質が提供できる。
【００１３】
さらに本発明は、前記複数金属元素の酸化物または水酸化物粉末の表面層付近に配された前記α類似型Ｎｉ（ＯＨ）₂層中に、Ｎｉ，Ａｌの他に、Ｃａ，Ｃｒ，Ｙ，Ｔｉ，Ｃｏから選ばれる少なくとも一種の元素が共晶状態および／または固溶状態で存在することを特徴とする。ここで、Ｃａ，Ｃｒ，Ｙ，Ｔｉ，Ｃｏから選ばれる少なくとも一種の元素をＭｅと表した時、α類似型Ｎｉ（ＯＨ）₂層中に共晶状態および／または固溶状態で存在するＭｅ量は、α類似型Ｎｉ（ＯＨ）₂被覆層中の金属原子比をＮｉ＋Ａｌ：Ｍｅ＝１−ｙ：ｙと表した場合、０．０１≦ｙ≦０．２０であることを特徴とする。これにより、容量密度、放電電圧、高率放電特性に優れ、かつ高温充電効率および／または充放電特性に優れたアルカリ蓄電池用正極活物質が提供できる。
【００１４】
さらに本発明は、前記α類似型Ｎｉ（ＯＨ）₂層を表面層付近に配した前記粉末の表面に、さらにＣｏ酸化物層を配したことを特徴とする。これにより、容量密度、放電電圧、高率放電特性に優れ、かつ充放電特性に優れたアルカリ蓄電池用正極活物質が提供できる。
【００１５】
【実施例】
以下、本発明の実施例を説明する。
【００１６】
（実施例１）
まず、正極活物質表面へのα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆の効果について調べた。
（１）ＮｉＳＯ₄水溶液、ＮａＯＨ水溶液、ＮＨ₃水溶液を一定流量で連続的に反応槽中に供給し、槽内温度を３０℃、槽内溶液のｐＨ値を約１１に保った状態で撹拌・混合を行ない、Ｎｉ（ＯＨ）₂粒子を成長させた。採取したＮｉ（ＯＨ）₂粒子を水洗・乾燥し、従来Ｎｉ（ＯＨ）₂粉末Αとした。
（２）Ｎｉ（ＮＯ₃）₂，Ｃｏ（ＮＯ₃）₂およびＣｄ（ＮＯ₃）₂の混合水溶液（Ｎｉ：Ｃｏ：Ｃｄ＝０．９４：０．０３：０．０３（原子比））を用い、上記と同様の合成・処理を行ない、従来Ｃｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｂとした。
（３）従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、ＮｉＳＯ₄およびＡｌ₂（ＳＯ₄）₃の混合水溶液（Ｎｉ：Ａｌ＝０．８０：０．２０（原子比））、ＮａＯＨ水溶液、ＮＨ₃水溶液を一定流量で連続的に反応槽中に供給し、槽内温度を３０℃、槽内溶液のｐＨ値を約１１に保った状態で撹拌混合を行ない、Ｎｉ（ＯＨ）₂粒子表面にＡｌ固溶Ｎｉ（ＯＨ）₂を析出させ被覆を行なった。採取した粒子を水洗・乾燥し、Ａｌ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ｃとした。
（４）従来Ｃｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｂについて上記と同様の被覆処理を行ない、Ａｌ固溶Ｎｉ（ＯＨ）₂被覆Ｃｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｄとした。
【００１７】
以上の粉末の被覆層は粉末断面のＡｌ特性Ｘ線像にてＡｌの存在を確認した。また、粉末Ａ，ＢのＸ線回折パターンにはβ−Ｎｉ（ＯＨ）₂に帰属する回折線のみが現れるのに対し、被覆処理粉末Ｃ，ＤのＸ線回折パターンには新たにα−Ｎｉ（ＯＨ）₂に帰属する回折線が現れることより、被覆層がα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂相を含むことを確認した。被覆粉末のタップ密度は１．９ｇ／ｃｃ〜２．０ｇ／ｃｃと良好であった。
【００１８】
合成粉末１００ｇに１０ｇのＣｏ（ＯＨ）₂粉末、０．５ｇのポリテトラフルオロエチレン（ＰＴＦＥ）粉末、４２ｇの水を加え混練しペースト状にした。これを多孔度９５％の発泡ニッケル基板に充填し、乾燥後加圧成形し、厚さ０．７ｍｍ、容量密度約６３０ｍＡｈ／ｃｃのニッケル正極板を得た。このようにして得られた正極板を３９×７５ｍｍに切断し、基板中にあらかじめ設けたリード接続部に電極リードをスポット溶接し、理論容量１３００ｍＡｈのニッケル正極とした。ここで理論容量はＮｉのみが充放電に寄与すると仮定し、かつＮｉに対し１電子反応をするとして算定したものである。
【００１９】
一方負極には正極に対しその容量が十分大きい水素吸蔵合金負極（ＭｍＮｉ_3.8Ｃｏ_0.5Ｍｎ_0.4Ａｌ_0.3）を用いた。使用した水素吸蔵合金は所望の割合で混合したＭｍ，Ｎｉ，Ｃｏ，Ｍｎ，Ａｌをアーク溶解炉にて溶解することによって得た。この合金塊を不活性雰囲気中でボールミルにて粉砕し、平均粒径３０μｍの粉末とした。これに結着剤としてカルボキシメチルセルロース（ＣＭＣ）を加えた後混練し、電極支持体に加圧充填し、厚さ０．４５ｍｍ、容量密度１３５０ｍＡｈ／ｃｃの水素吸蔵負極板を得た。この負極板を３９×１００ｍｍに切断し理論容量２４００ｍＡｈの負極とした。
【００２０】
この正極と負極を厚さ０．１５ｍｍのスルフォン化ポリプロピレン不織布からなるセパレーターを間に介して渦巻状の電極群に構成し、この電極群を外装缶内に挿入した。電解液として７．２ｍｏｌ／ｌＫＯＨ＋１．０ｍｏｌ／ｌＬｉＯＨ混合アルカリ水溶液を前記電極群を挿入した外装缶内に注入後、作動弁圧が２０kgf／cm²の安全弁を持つ封口体により密閉し、公称容量が１３００ｍＡｈであるＡＡサイズの円筒密閉形ニッケル・水素蓄電池を作製した。
【００２１】
この電池を充放電試験によって評価した。充電を０．１Ｃで１５時間、放電は１．０Ｃで終止電圧１．０Ｖまで、雰囲気温度は２０℃とした。なお、電池の活性化が終了するまで数サイクル要するため、１０サイクルめの平均放電電圧、利用率を比較値とした。ここで利用率は、上記正極の理論容量に対する１．０Ｃの測定容量の比率を％で表したものである。その結果を表１に示す。
【００２２】
【表１】

【００２３】
α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆処理を施したＮｉ（ＯＨ）₂粉末Ｃにおいて、処理前の従来Ｎｉ（ＯＨ）₂粉末Αに比べ、４０ｍＶの放電電圧の向上が確認された。また、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆処理を施したＣｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｄにおいても、処理前の従来Ｃｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｂに比べ、４０ｍＶの放電電圧の向上が確認された。以上の結果から、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆処理により、放電電圧向上が可能であることが明らかである。
【００２４】
また、粉末Ａ，Ｂを比較した場合、Ｃｏ，Ｃｄを固溶させた粉末Ｂの利用率が高く、充放電特性が優れている。Ｎｉ（ＯＨ）₂へのＣｏ，Ｃｄ固溶による充放電特性向上については日本国特許１８２７６３９号（１９８４）および特開平３−５０３８４号公報に記載されている。α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆処理を施した粉末Ｃ，Ｄを比較した場合にも同様の効果が認められることから、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆処理は、内部粒子の特性を損なうことなく、放電電圧向上が可能であることが明らかである。
【００２５】
（実施例２）
次に、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層中のＡｌ固溶量の適切値を求めるために、実施例１で用いた従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、種々のＮｉＳＯ₄およびＡｌ₂（ＳＯ₄）₃の混合水溶液（Ｎｉ：Ａｌ＝１−ｘ：ｘ，ｘ＝０．０５，０．１０，０．３０，０．４０，０．４５（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ε〜Ｉとした。被覆粉末のタップ密度は１．８ｇ／ｃｃ〜２．０ｇ／ｃｃと良好であった。得られた粉末Ε〜Ｉを用い、実施例１と同様の製法で電池を作製し、同様の方法で充放電試験により評価した。得られた結果を表２に示す。
【００２６】
【表２】

【００２７】
放電電圧向上の効果は、被覆層のＡｌ固溶比が０．１０〜０．４５の場合に確認されたが、０．０５の場合には確認されなかった。被覆粉末Ｃ，Ｆ〜ＩのＸ線回折パターンにはα−Ｎｉ（ＯＨ）₂に帰属する回折線が現れるのに対し、被覆粉末ＥのＸ線回折パターンにはα−Ｎｉ（ＯＨ）₂に帰属する回折線が現れなかった。すなわち、被覆粉末Ｃ，Ｆ〜Ｉの被覆層はα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂相を含むため放電電圧が向上するが、被覆粉末Ｅの被覆層はα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂相を含まないため放電電圧向上の効果が現れないと推察される。しかし、Ａｌ固溶比が０．４５の被覆粉末Ｉでは利用率の低下が確認され、容量密度の点で問題である。
【００２８】
以上より、放電電圧向上の効果はα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆処理で得られ、その場合のＡｌ固溶比は被覆層中のＮｉとＡｌの総原子数に対し０．１０〜０．４０である。
【００２９】
（実施例３）
次に、α類似型Ａｌ固溶Ｎｉ₂（ＯＨ）₂被覆層中への異種金属固溶効果について調べた。
（１）従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、Ｎｉ（ＮＯ₃）₂，Ａｌ（ＮＯ₃）₃およびＣａ（ＮＯ₃）₂の混合水溶液（Ｎｉ：Ａｌ：Ｃａ＝０．７５：０．２０：０．０５（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｃａ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ｊとした。
（２）従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、Ｎｉ（ＮＯ₃）₂，Ａｌ（ＮＯ₃）₃およびＣｒ（ＮＯ₃）₃の混合水溶液（Ｎｉ：Ａｌ：Ｃｒ＝０．７５：０．２０：０．０５（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｃｒ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ｋとした。
（３）従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、Ｎｉ（ＮＯ₃）₂，Ａｌ（ＮＯ₃）₃およびＹ（ＮＯ₃）₃の混合水溶液（Ｎｉ：Ａｌ：Ｙ＝０．７５：０．２０：０．０５（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｙ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ｌとした。
（４）従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、ＮｉＣｌ₂，ＡｌＣｌ₃およびＴｉＣｌ₃の混合水溶液（Ｎｉ：Ａｌ：Ｔｉ＝０．７５：０．２０：０．０５（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｔｉ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ｍとした。
（５）従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、ＮｉＳＯ₄，Ａｌ₂（ＳＯ₄）₃およびＣｏＳＯ₄の混合水溶液（Ｎｉ：Ａｌ：Ｃｏ＝０．７５：０．２０：０．０５（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｃｏ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ｎとした。
（６）従来Ｃｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｂを反応槽中に投入し、Ｎｉ（ＮＯ₃）₂，Ａｌ（ＮＯ₃）₃およびＣａ（ＮＯ₃）₃の混合水溶液（Ｎｉ：Ａｌ：Ｃａ＝０．７５：０．２０：０．０５（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｃａ固溶Ｎｉ（ＯＨ）₂被覆Ｃｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｏとした。
（７）従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、Ｎｉ（ＮＯ₃）₂，Ａｌ（ＮＯ₃）₃，Ｃａ（ＮＯ₃）₂およびＣｏ（ＮＯ₃）₂の混合水溶液（Ｎｉ：Ａｌ：Ｃａ：Ｃｏ＝０．７４：０．２０：０．０３：０．０３（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｃａ，Ｃｏ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ｐとした。
（８）従来Ｃｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｂを反応槽中に投入し、Ｎｉ（ＮＯ₃）₂，Ａｌ（ＮＯ₃）₃，Ｃｒ（ＮＯ₃）₃およびＣｏ（ＮＯ₃）₂の混合水溶液（Ｎｉ：Ａｌ：Ｃｒ：Ｃｏ＝０．７４：０．２０：０．０３：０．０３（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｃｒ，Ｃｏ固溶Ｎｉ（ＯＨ）₂被覆Ｃｏ，Ｃｄ固溶Ｎｉ（ＯＨ）₂粉末Ｑとした。
【００３０】
これらすべての被覆粉末のＸ線回折パターンにα−Ｎｉ（ＯＨ）₂に帰属する回折線が現れることより、被覆層がα類似型Ａｌ，異種金属固溶Ｎｉ（ＯＨ）₂相を含むことを確認した。被覆粉末のタップ密度は１．９ｇ／ｃｃ〜２．０ｇ／ｃｃと良好であった。
【００３１】
得られた粉末Ｊ〜Ｑを用い、実施例１と同様の製法で電池を作製し、同様の方法で充放電試験により評価した。さらに、雰囲気温度４５℃にて、充電を０．１Ｃで１５時間行ない、引き続き雰囲気温度２０℃にて、放電を１．０Ｃで終止電圧１．０Ｖまで行なうことにより、高温充電効率の評価を実施した。得られた結果を表３に示す。
【００３２】
【表３】

【００３３】
これらすべての被覆粉末において放電電圧向上の効果が確認された。また、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層にＣａ，Ｃｒ，Ｙ，Ｔｉを固溶させた粉末Ｊ，Ｋ，Ｌ，Ｍ，Ｏにおいて、未固溶のα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂粉末Ｃ，Ｄに比べ、高温充電効率の向上が確認された。
【００３４】
さらに、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層にＣｏを固溶させた粉末Ｎにおいて、未固溶のα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂粉末Ｃに比べ、利用率の向上が確認された。
【００３５】
また、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層にＣａ，ＣｏまたはＣｒ，Ｃｏを固溶させた粉末Ｐ，Ｑにおいて、未固溶のα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆粉末Ｃ，Ｄに比べ、高温充電効率と利用率の向上が確認された。
【００３６】
以上の結果から、上記異種金属元素を固溶させたα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂をＮｉ（ＯＨ）₂粒子に被覆することにより、放電電圧が向上し、かつその他の特性改善も可能であることが明らかである。
【００３７】
（実施例４）
次に、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層中の異種金属固溶量の適切値を求めるために、実施例１で用いた従来Ｎｉ（ＯＨ）₂粉末Αを反応槽中に投入し、種々のＮｉ（ＮＯ₃）₂，Ａｌ（ＮＯ₃）₃およびＣａ（ＮＯ₃）₂の混合水溶液（Ｎｉ：Ａｌ：Ｃａ＝１−ｙ：０．２０：ｙ，ｙ＝０．０１，０．０５，０．１０，０．２０，０．２５（原子比））を用い、実施例１と同様の被覆処理を行ない、Ａｌ，Ｃａ固溶Ｎｉ（ＯＨ）₂被覆Ｎｉ（ＯＨ）₂粉末Ｒ〜Ｕとした。
【００３８】
これらすべての被覆粉末のＸ線回折パターンにα−Ｎｉ（ＯＨ）₂に帰属する回折線が現れることより、被覆層がα類似型Ａｌ，Ｃａ固溶Ｎｉ（ＯＨ）₂相を含むことを確認した。被覆粉末のタップ密度は１．８ｇ／ｃｃ〜１．９ｇ／ｃｃと良好であった。
【００３９】
得られた粉末Ｒ〜Ｕを用い、実施例１と同様の製法で電池を作製し、実施例３と同様の方法で充放電試験により評価した。得られた結果を表４に示す。
【００４０】
【表４】

【００４１】
α類似型Ａｌ，Ｃａ固溶Ｎｉ（ＯＨ）₂被覆層のＣａ固溶比が０．０１〜０．２０の場合に高温充電効率の向上が確認された。しかし、被覆層のＣａ固溶比が０．２５の場合には放電電圧、高温充電効率ともに効果が認められなかった。被覆層にα類似型Ａｌ，Ｃａ固溶Ｎｉ（ＯＨ）₂相を含むにも関わらず、放電電圧が向上しない原因は明らかではないが、実施例３でα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂層に固溶させたすべての異種金属において同様の結果が得られ、０．０１〜０．２０の固溶比の範囲で特性改善の効果が確認された。
【００４２】
以上の結果から、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層に異種金属元素を０．０１〜０．２０の固溶比の範囲で固溶させた場合、放電電圧が向上し、かつその他の特性改善が可能であることが明らかである。
【００４３】
（実施例５）
次に、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆正極活物質表面へのＣｏ酸化物被覆の効果について調べた。
【００４４】
α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆粉末Ｃ，Ｄ，Ｊ，Ｏを反応槽中に投入し、ＣｏＳＯ₄水溶液、ＮａＯＨ水溶液、ＮＨ₃水溶液を一定流量で連続的に反応槽中に供給し、槽内温度を３０℃、槽内溶液のｐＨ値を約１１に保った状態で撹拌混合を行ない、粒子表面にＣｏ（ＯＨ）₂を析出させ被覆を行なった。採取した粒子を水洗・乾燥し、粉末Ｖ〜Ｙとした。
【００４５】
以上の粉末の被覆層は粉末断面のＣｏ特性Ｘ線像にてＣｏの存在を確認した。被覆粉末のタップ密度は１．８ｇ／ｃｃ〜２．０ｇ／ｃｃと良好であった。
【００４６】
このようにして得られた粉末Ｖ〜Ｙを用い、実施例１と同様の製法で電池を作製し、同様の方法で充放電試験により評価した。得られた結果を表５に示す。
【００４７】
【表５】

【００４８】
Ｃｏ（ＯＨ）₂被覆粉末Ｖ〜Ｙにおいて、未処理粉末Ｃ，Ｄ，Ｊ，Ｏと比較して利用率の向上が確認された。放電電圧はわずかに低下するが、未被覆処理粉末Ａ，Ｂと比較すると放電電圧は向上しており、α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆処理による放電電圧向上の効果が確認された。
【００４９】
Ｎｉ（ＯＨ）₂またはＮｉ（ＯＨ）₂を主成分とする粒子表面をＣｏ化合物で被覆することにより、利用率を向上できることは特開昭６２−２２２５６６号公報および特開昭６２−２３４８６７号公報に記載されている。
【００５０】
本実施例の結果から、正極活物質粒子とその表面のＣｏ酸化物層との間にα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂層を配することによって、利用率を向上させ、さらに放電電圧を向上できることが明らかである。
【００５１】
なお本発明は、アルカリ蓄電池の正極活物質の改良に関する技術であるため、実施例に記載した以外の組成の水素吸蔵合金を用いるニッケル・水素蓄電池においても同等の効果が得られる。さらにニッケル酸化物をベースにした正極活物質を用いるすべてのアルカリ蓄電池（例えば、ニッケル・カドミウム蓄電池、ニッケル・鉄蓄電池、ニッケル・亜鉛蓄電池等）においても同等の効果が得られる。また、電極支持体、活物質添加物およびセパレータ等が異なる場合についても同等の効果が得られる。また、ＡＡサイズの円筒密閉電池についてのみ記載したが他のサイズの円筒密閉電池、角型密閉電池、据え置き型蓄電池、大型蓄電池、中型蓄電池あるいは開放型電池等についても同等の効果が得られる。さらに、焼結式正極を用いるアルカリ蓄電池においても、正極表面に同様の被覆処理を施した場合に同等の効果が得られる。
【００５２】
【発明の効果】
正極活物質粉末の表面をα類似型Ａｌ固溶Ｎｉ（ＯＨ）₂で被覆することにより、容量密度、放電電圧、高率放電特性に優れたアルカリ蓄電池用正極活物質が提供できる。また、上記α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆層中にＣａ，Ｃｒ，Ｙ，Ｔｉ，Ｃｏから選ばれる少なくとも一種の異種金属元素を固溶させることにより、容量密度、放電電圧、高率放電特性に優れ、かつ高温充電効率および／または充放電特性に優れたアルカリ蓄電池用正極活物質が提供できる。さらに、上記α類似型Ａｌ固溶Ｎｉ（ＯＨ）₂被覆正極活物質粉末の表面をＣｏ酸化物で被覆させることにより、容量密度、放電電圧、高率放電特性に優れ、かつ充放電特性に優れたアルカリ蓄電池用正極活物質が提供できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a positive electrode active material for an alkaline storage battery.
[0002]
[Prior art]
Alkaline storage battery, especially its small sealed battery, has excellent balance of charge / discharge characteristics, cycle life and safety / reliability compared to other battery systems. Therefore, various types represented by mobile communication devices, personal computers, etc. It is very popular as a main power source for portable equipment. In addition, since it is extremely excellent in charge / discharge characteristics and reliability as a large-scale power source, it has been attracting attention as a main power source for mobile use such as electric vehicles. The battery system that represents the alkaline storage battery was a nickel-cadmium storage battery with a long history, but the nickel-hydrogen storage battery using a hydrogen storage alloy negative electrode instead of the cadmium negative electrode was industrialized to achieve higher energy density. . In addition, as an electrode support, instead of a sintered electrode, an electrode (Sponge Metal Nickel Electrode: SME) in which a high-porosity (95% or more) three-dimensional foamed nickel porous body is filled with nickel oxide at a high density has been industrialized. High energy density was achieved. Thus, so far, alkaline storage batteries have been particularly focused on reducing the size, weight and energy density of the batteries.
[0003]
On the other hand, when considering the use of alkaline storage batteries for electric vehicles, power tools, etc., it is an important issue to increase the output of the batteries, that is, to improve the operating voltage during high rate discharge. In addition, many portable devices operate with constant power discharge, and at the end of discharge when the discharge voltage decreases, a high-rate discharge state occurs, causing a further decrease in discharge voltage. Therefore, improvement of the operating voltage is an important issue even in a small sealed alkaline storage battery.
[0004]
As a solution to this problem, for example, in Japanese Patent Application Laid-Open No. 5-174867, at least one hydroxide of rubidium hydroxide and cesium hydroxide is added to the alkaline electrolyte at 0.3 N to 3.5 N Thus, it is described that the electroconductivity of the electrolytic solution is improved, and rubidium ions and cesium ions act as catalysts, so that the operating voltage can be increased during high rate discharge. However, it is difficult to use expensive materials such as rubidium and cesium for an actual battery, and it has not been put into practical use.
[0005]
On the other hand, US Pat. No. 5,567,549 (1996) discloses Ni (OH).₂Describes a positive electrode active material for alkaline storage batteries in which Al is dissolved. Its internal dissolution is Ni (OH)₂Α-Ni (OH) by dissolving Al in₂Multiphase Al solid solution Ni (OH) containing the α phase is stabilized₂Since a higher-order reaction is performed, the capacity of the battery can be increased.
[0006]
We also have Ni (OH)₂As a result of research on the effect of Al addition to Al, Ni (OH) was dissolved in the eutectic state and / or the solid solution state.₂(Hereinafter referred to as Al solid solution Ni (OH)₂In addition to the effect described in US Pat. No. 5,567,549, it has been found that the effect of improving the discharge voltage and improving the high rate discharge characteristic can be obtained. In particular, α-Ni (OH) in the X-ray diffraction pattern₂Al solute Ni (OH) showing diffraction lines attributed to₂(Hereafter, α-similar Al solid solution Ni (OH)₂It was found that a remarkable effect can be obtained.
[0007]
By the way, α-like Ni (OH)₂For Ni (OH)₂Has been reported to be obtained by substituting a part of Ni with a metal atom having a high oxidation number (for example, Co (III), Mn (III), Fe (III), etc.) (Solid State Ionics 32/33). , P. 104 (1989), J. Power Sources, 35, p. 249 (1991), etc.) Since the metal atom having a high oxidation number was dissolved, the nickel plate layer in the crystal structure was positively charged, and charge compensation was made. As anion species (eg PO_Four ^3-, SO_Four ^2-, CO_Three ^2-, NO_Three ^-Etc.) and the layers are spread (J. Power Sources, 36, p. 113 (1991), Materials Science Forum, 152-153, p. 201 (1994), etc.). Therefore, α-like Ni (OH)₂Is bulky and is considered to be difficult to fill with high density, but the α-like Al solid solution Ni (OH) we studied₂Also, although the discharge voltage, high-rate discharge characteristics, and utilization rate are remarkably improved, the packing density is extremely low and it cannot be used as a positive electrode active material for alkaline storage batteries.
[0008]
There have been many reports on improvement in characteristics of the positive electrode active material due to the functional gradient. For example, in Japanese Patent Laid-Open No. 9-17428, Ni (OH)₂Or Ni (OH)₂It has been reported that the utilization rate can be improved and the discharge capacity can be increased by coating the surface of the particle mainly containing Co with a Co and / or Ni additive. Japanese Patent Laid-Open No. 8-287907 discloses Ni (OH).₂Or Ni (OH)₂By using a positive electrode active material in which the surface of a particle having a main component is coated with a first compound having a group II element compound as a main component and the surface is further coated with a second compound layer having a Co compound as a main component. It has been reported that an alkaline storage battery having a high capacity and a long life can be provided. Further, JP-A-8-329943 discloses Ca as Ni (OH).₂At the same time as dissolving in the particles, at least part of the contained Ca is Ca (OH).₂As Ni (OH)₂It has been reported that by using a positive electrode active material coated and impregnated on the surface of particles and the inside of pores, it is possible to provide an alkaline storage battery with increased utilization, particularly utilization at high temperatures. However, nothing has been reported so far regarding the improvement of the discharge voltage and the high rate discharge characteristics by the functionalization of the positive electrode active material.
[0009]
[Problems to be solved by the invention]
An object of this invention is to provide the positive electrode active material for alkaline storage batteries excellent in the high capacity density, discharge voltage, and high rate discharge characteristic.
[0010]
[Means for Solving the Problems]
In an active material powder used for a positive electrode for an alkaline storage battery mainly comprising an oxide (or hydroxide) of a plurality of metal elements containing Ni as a main metal element, the oxide (or hydroxide) powder of the plurality of metal elements Al-like Ni (OH) in which Al is present in the eutectic state and / or solid solution state in the vicinity of the surface layer of₂Arrange the layers. This α-like Al-solution Ni (OH)₂The layer has the effect of improving the discharge voltage and high rate discharge characteristics. Originally, α-like Al solute Ni (OH)₂Is bulky and high density filling is difficult, but since it is arranged only in the vicinity of the surface layer, a decrease in filling density can be suppressed, and a high capacity density can be maintained. In addition, the α-like Al solid solution Ni (OH)₂By adding at least one element selected from Ca, Cr, Y, Ti and Co to the coating layer in a eutectic state and / or a solid solution state, the discharge layer is excellent in discharge voltage, high rate discharge characteristics, high density filling, and A positive electrode active material for an alkaline storage battery excellent in high-temperature charging efficiency and / or charge / discharge characteristics can be obtained. In addition, the α-like Al solid solution Ni (OH)₂By coating the surface of the coated positive electrode active material powder with a Co oxide layer, a positive electrode active material for an alkaline storage battery having excellent discharge voltage, high rate discharge characteristics, high density filling, and excellent charge / discharge characteristics can be obtained. .
[0011]
Here, the present invention relates to α-like Al solid solution Ni (OH).₂Is not present in the positive electrode active material particles (US Pat. No. 5,567,549 (1996)), but is disposed on the surface of the positive electrode active material particles. With such a configuration, high-density filling of the positive electrode active material becomes possible. Further, the solid solution of different metal elements in the positive electrode active material particles is also arranged in the positive electrode active material particles and / or on the surface of the positive electrode active material particles (JP-A-9-17428, JP-A-8-329943, etc.). Instead of α-like Al solid solution Ni (OH) placed on the surface of the positive electrode active material particles₂It is characterized by being added to the coating layer. By adopting such a configuration, a positive electrode active material with improved discharge voltage and high rate discharge characteristics and other characteristics can be obtained. Further, between the positive electrode active material particles and the Co oxide coating layer on the surface thereof, an α-similar Al solid solution Ni (OH)₂It is characterized by arranging layers. By adopting such a configuration, a positive electrode active material having improved discharge voltage and high rate discharge characteristics and improved charge / discharge characteristics can be obtained.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a positive electrode active material powder for an alkaline storage battery mainly comprising an oxide or hydroxide of a plurality of metal elements containing Ni as a main metal element, in the vicinity of the surface layer of the oxide or hydroxide powder of the plurality of metal elements Α-like Ni (OH) in which Al is present in a eutectic state and / or a solid solution state₂It is characterized by arranging layers. Where α-like Ni (OH)₂The amount of Al present in the coating layer in the eutectic state and / or the solid solution state is α-like Ni (OH)₂When the metal atomic ratio in the coating layer is expressed as Ni: Al = 1-x: x, 0.10 ≦ x ≦ 0.40. Thereby, the positive electrode active material for alkaline storage batteries excellent in high capacity density, discharge voltage, and high rate discharge characteristics can be provided.
[0013]
Furthermore, the present invention provides the α-like Ni (OH) that is disposed near the surface layer of the oxide or hydroxide powder of the plurality of metal elements.₂In the layer, in addition to Ni and Al, at least one element selected from Ca, Cr, Y, Ti and Co is present in a eutectic state and / or a solid solution state. Here, when at least one element selected from Ca, Cr, Y, Ti, and Co is expressed as Me, α-like Ni (OH)₂The amount of Me present in the layer in the eutectic state and / or in the solid solution state is α-like Ni (OH)₂When the metal atomic ratio in the coating layer is expressed as Ni + Al: Me = 1−y: y, 0.01 ≦ y ≦ 0.20. Thereby, it is possible to provide a positive electrode active material for an alkaline storage battery that is excellent in capacity density, discharge voltage, and high rate discharge characteristics, and that is excellent in high-temperature charge efficiency and / or charge / discharge characteristics.
[0014]
Furthermore, the present invention provides the α-like Ni (OH).₂A Co oxide layer is further disposed on the surface of the powder in which the layer is disposed near the surface layer. Thereby, the positive electrode active material for alkaline storage batteries excellent in capacity density, discharge voltage, and high rate discharge characteristics and excellent in charge / discharge characteristics can be provided.
[0015]
【Example】
Examples of the present invention will be described below.
[0016]
Example 1
First, α-like Al solid solution Ni (OH) on the surface of the positive electrode active material₂The effect of the coating was investigated.
(1) NiSO_FourAqueous solution, NaOH aqueous solution, NH_ThreeThe aqueous solution was continuously supplied into the reaction tank at a constant flow rate, and stirred and mixed while maintaining the temperature in the tank at 30 ° C. and the pH value of the solution in the tank at about 11, Ni (OH)₂Growing the particles. Collected Ni (OH)₂The particles are washed with water and dried. Conventional Ni (OH)₂Powdered rice cake was used.
(2) Ni (NO_Three)₂, Co (NO_Three)₂And Cd (NO_Three)₂Using a mixed aqueous solution (Ni: Co: Cd = 0.94: 0.03: 0.03 (atomic ratio)), the same synthesis and treatment as described above was performed, and conventional Co and Cd solid solution Ni (OH)₂It was set as powder B.
(3) Conventional Ni (OH)₂Pour the powder soot into the reaction vessel and add NiSO_FourAnd Al₂(SO_Four)_ThreeAqueous solution (Ni: Al = 0.80: 0.20 (atomic ratio)), NaOH aqueous solution, NH_ThreeThe aqueous solution was continuously supplied into the reaction tank at a constant flow rate, and stirring and mixing were performed while maintaining the temperature in the tank at 30 ° C. and the pH value of the solution in the tank at about 11, and Ni (OH)₂Al solid solution Ni (OH) on particle surface₂Was deposited and coated. The collected particles are washed with water and dried, and then Al dissolved Ni (OH)₂Coated Ni (OH)₂It was set as powder C.
(4) Conventional Co, Cd solid solution Ni (OH)₂For powder B, the same coating treatment as above was performed, and Al solid solution Ni (OH)₂Coated Co, Cd solid solution Ni (OH)₂It was set as powder D.
[0017]
The presence of Al in the powder coating layer was confirmed by an Al characteristic X-ray image of the powder cross section. In addition, X-ray diffraction patterns of powders A and B have β-Ni (OH)₂In contrast, only X-ray diffraction patterns attributed to the X-ray diffraction patterns of the coated powders C and D appear in the α-Ni (OH).₂As a result of the appearance of diffraction lines belonging to, the coating layer is an α-like Al solid solution Ni (OH)₂It was confirmed to contain a phase. The tap density of the coating powder was as good as 1.9 g / cc to 2.0 g / cc.
[0018]
10g Co (OH) to 100g synthetic powder₂Powder, 0.5 g of polytetrafluoroethylene (PTFE) powder, and 42 g of water were added and kneaded to obtain a paste. This was filled in a foamed nickel substrate having a porosity of 95%, dried and then pressure-molded to obtain a nickel positive electrode plate having a thickness of 0.7 mm and a capacity density of about 630 mAh / cc. The positive electrode plate thus obtained was cut to 39 × 75 mm, and electrode leads were spot welded to lead connection portions provided in advance in the substrate to obtain a nickel positive electrode having a theoretical capacity of 1300 mAh. Here, the theoretical capacity is calculated on the assumption that only Ni contributes to charging and discharging, and one electron reaction with Ni.
[0019]
On the other hand, the negative electrode is a hydrogen storage alloy negative electrode (MmNi_3.8Co_0.5Mn_0.4Al_0.3) Was used. The hydrogen storage alloy used was obtained by melting Mm, Ni, Co, Mn, and Al mixed at a desired ratio in an arc melting furnace. This alloy lump was pulverized by a ball mill in an inert atmosphere to obtain a powder having an average particle size of 30 μm. Carboxymethylcellulose (CMC) was added thereto as a binder, and then kneaded and pressure filled into an electrode support to obtain a hydrogen storage negative electrode plate having a thickness of 0.45 mm and a capacity density of 1350 mAh / cc. This negative electrode plate was cut into 39 × 100 mm to obtain a negative electrode having a theoretical capacity of 2400 mAh.
[0020]
The positive electrode and the negative electrode were formed into a spiral electrode group with a separator made of a sulfonated polypropylene nonwoven fabric having a thickness of 0.15 mm interposed therebetween, and this electrode group was inserted into an outer can. After pouring a 7.2 mol / l KOH + 1.0 mol / l LiOH mixed alkaline aqueous solution as an electrolyte into the outer can into which the electrode group was inserted, the operating valve pressure was 20 kgf / cm.²AA size cylindrical sealed nickel-hydrogen storage battery with a nominal capacity of 1300 mAh was fabricated.
[0021]
This battery was evaluated by a charge / discharge test. Charging was performed at 0.1 C for 15 hours, discharging was performed at 1.0 C up to a final voltage of 1.0 V, and the ambient temperature was 20 ° C. In addition, since several cycles are required until the activation of the battery is completed, the average discharge voltage and the utilization rate in the 10th cycle were used as comparative values. Here, the utilization factor represents the ratio of the measured capacity of 1.0 C to the theoretical capacity of the positive electrode in%. The results are shown in Table 1.
[0022]
[Table 1]

[0023]
α-like Al solute Ni (OH)₂Ni (OH) coated₂In powder C, conventional Ni (OH) before treatment₂It was confirmed that the discharge voltage was improved by 40 mV compared to the powder soot. In addition, α-like Al solute Ni (OH)₂Co, Cd solid solution Ni (OH) with coating treatment₂Also in the powder D, conventional Co, Cd solid solution Ni (OH) before processing₂Compared to powder B, an improvement in discharge voltage of 40 mV was confirmed. From the above results, α-like Al solid solution Ni (OH)₂It is clear that the discharge voltage can be improved by the coating treatment.
[0024]
Moreover, when the powders A and B are compared, the utilization factor of the powder B in which Co and Cd are dissolved is high and the charge / discharge characteristics are excellent. Ni (OH)₂The improvement of the charge / discharge characteristics by solid solution of Co and Cd is described in Japanese Patent No. 1827639 (1984) and JP-A-3-50384. α-like Al solute Ni (OH)₂Since the same effect is observed when the powders C and D subjected to the coating treatment are compared, α-like Al solid solution Ni (OH)₂It is clear that the coating treatment can improve the discharge voltage without impairing the characteristics of the internal particles.
[0025]
(Example 2)
Next, α-like Al solute Ni (OH)₂Conventional Ni (OH) used in Example 1 in order to obtain an appropriate value of the Al solid solution amount in the coating layer₂The powder soot is put into a reaction vessel and various NiSO_FourAnd Al₂(SO_Four)_ThreeA mixed aqueous solution (Ni: Al = 1-x: x, x = 0.05, 0.10, 0.30, 0.40, 0.45 (atomic ratio)) and the same coating as in Example 1 Processed, Al solid solution Ni (OH)₂Coated Ni (OH)₂It was set as powder candy ~ I. The tap density of the coating powder was as good as 1.8 g / cc to 2.0 g / cc. Using the obtained powder cakes ~ I, a battery was produced by the same production method as in Example 1, and evaluated by a charge / discharge test in the same manner. The obtained results are shown in Table 2.
[0026]
[Table 2]

[0027]
The effect of improving the discharge voltage was confirmed when the Al solid solution ratio of the coating layer was 0.10 to 0.45, but not when 0.05. The X-ray diffraction pattern of the coating powders C and F to I is α-Ni (OH)₂Diffraction lines attributed to γ appear, whereas the X-ray diffraction pattern of the coating powder E shows α-Ni (OH)₂Diffraction lines attributed to did not appear. That is, the coating layer of the coating powders C and F to I is an α-like Al solid solution Ni (OH)₂The discharge voltage is improved because it contains a phase, but the coating layer of the coating powder E is an α-similar type Al solid solution Ni (OH)₂It is presumed that the effect of improving the discharge voltage does not appear because the phase is not included. However, in the coating powder I having an Al solid solution ratio of 0.45, a decrease in the utilization rate is confirmed, which is a problem in terms of capacity density.
[0028]
From the above, the effect of improving the discharge voltage is α-like Al solid solution Ni (OH)₂The Al solid solution ratio in this case is 0.10 to 0.40 with respect to the total number of Ni and Al atoms in the coating layer.
[0029]
(Example 3)
Next, α-like Al solid solution Ni₂(OH)₂The effect of different metal solid solution in the coating layer was investigated.
(1) Conventional Ni (OH)₂The powder cake is put into the reaction vessel and Ni (NO_Three)₂, Al (NO_Three)_ThreeAnd Ca (NO_Three)₂Using a mixed aqueous solution (Ni: Al: Ca = 0.75: 0.20: 0.05 (atomic ratio)), the same coating treatment as in Example 1 was performed, and Al, Ca solid solution Ni (OH)₂Coated Ni (OH)₂It was set as powder J.
(2) Conventional Ni (OH)₂The powder cake is put into the reaction vessel and Ni (NO_Three)₂, Al (NO_Three)_ThreeAnd Cr (NO_Three)_ThreeUsing a mixed aqueous solution (Ni: Al: Cr = 0.75: 0.20: 0.05 (atomic ratio)), the same coating treatment as in Example 1 was performed, and Al, Cr solid solution Ni (OH)₂Coated Ni (OH)₂It was set as powder K.
(3) Conventional Ni (OH)₂The powder cake is put into the reaction vessel and Ni (NO_Three)₂, Al (NO_Three)_ThreeAnd Y (NO_Three)_ThreeUsing a mixed aqueous solution (Ni: Al: Y = 0.75: 0.20: 0.05 (atomic ratio)), the same coating treatment as in Example 1 was performed, and Al, Y solid solution Ni (OH)₂Coated Ni (OH)₂It was set as powder L.
(4) Conventional Ni (OH)₂Pour the powder soot into the reaction vessel and add NiCl₂, AlCl_ThreeAnd TiCl_ThreeUsing a mixed aqueous solution (Ni: Al: Ti = 0.75: 0.20: 0.05 (atomic ratio)), the same coating treatment as in Example 1 was performed, and Al, Ti solid solution Ni (OH)₂Coated Ni (OH)₂Powder M was designated.
(5) Conventional Ni (OH)₂Pour the powder soot into the reaction vessel and add NiSO_Four, Al₂(SO_Four)_ThreeAnd CoSO_FourUsing a mixed aqueous solution (Ni: Al: Co = 0.75: 0.20: 0.05 (atomic ratio)), the same coating treatment as in Example 1 was performed, and Al, Co solid solution Ni (OH)₂Coated Ni (OH)₂Powder N was designated.
(6) Conventional Co, Cd solid solution Ni (OH)₂Powder B is put into the reaction vessel and Ni (NO_Three)₂, Al (NO_Three)_ThreeAnd Ca (NO_Three)_ThreeUsing a mixed aqueous solution (Ni: Al: Ca = 0.75: 0.20: 0.05 (atomic ratio)), the same coating treatment as in Example 1 was performed, and Al, Ca solid solution Ni (OH)₂Coated Co, Cd solid solution Ni (OH)₂It was set as powder O.
(7) Conventional Ni (OH)₂The powder cake is put into the reaction vessel and Ni (NO_Three)₂, Al (NO_Three)_Three, Ca (NO_Three)₂And Co (NO_Three)₂Using a mixed aqueous solution (Ni: Al: Ca: Co = 0.74: 0.20: 0.03: 0.03 (atomic ratio)), the same coating treatment as in Example 1 was performed, and Al, Ca, Co solid solution Ni (OH)₂Coated Ni (OH)₂Powder P was designated.
(8) Conventional Co, Cd solid solution Ni (OH)₂Powder B is put into the reaction vessel and Ni (NO_Three)₂, Al (NO_Three)_Three, Cr (NO_Three)_ThreeAnd Co (NO_Three)₂Using a mixed aqueous solution (Ni: Al: Cr: Co = 0.74: 0.20: 0.03: 0.03 (atomic ratio)), the same coating treatment as in Example 1 was performed, and Al, Cr, Co solid solution Ni (OH)₂Coated Co, Cd solid solution Ni (OH)₂It was set as powder Q.
[0030]
All these coating powders have X-ray diffraction patterns with α-Ni (OH)₂As a result of the appearance of diffraction lines belonging to, the coating layer is α-like Al, dissimilar metal solid solution Ni (OH)₂It was confirmed to contain a phase. The tap density of the coating powder was as good as 1.9 g / cc to 2.0 g / cc.
[0031]
Using the obtained powders J to Q, a battery was produced by the same production method as in Example 1, and evaluated by a charge / discharge test in the same manner. Furthermore, charging was performed at 0.1C for 15 hours at an ambient temperature of 45 ° C, and then the discharging was performed at an ambient temperature of 20 ° C to a final voltage of 1.0V at 1.0C to evaluate high-temperature charging efficiency. did. The obtained results are shown in Table 3.
[0032]
[Table 3]

[0033]
The effect of improving the discharge voltage was confirmed in all these coating powders. In addition, α-like Al solute Ni (OH)₂In powders J, K, L, M, and O in which Ca, Cr, Y, and Ti are solid-dissolved in the coating layer, α-like Al solid solution Ni (OH) that is not dissolved yet₂Compared to powders C and D, improvement in high-temperature charging efficiency was confirmed.
[0034]
Furthermore, α-like Al solid solution Ni (OH)₂In powder N in which Co is solid-dissolved in the coating layer, α-like Al solid solution Ni (OH) that is not dissolved yet₂Compared to powder C, an improvement in utilization rate was confirmed.
[0035]
In addition, α-like Al solute Ni (OH)₂In powders P and Q in which Ca, Co or Cr, Co is dissolved in the coating layer, α-like Al solid solution Ni (OH) which is not dissolved yet₂Compared with the coating powders C and D, improvement in high-temperature charging efficiency and utilization rate was confirmed.
[0036]
From the above results, α-like Al solid solution Ni (OH) in which the different metal element is dissolved.₂Ni (OH)₂It is clear that the discharge voltage is improved and other characteristics can be improved by coating the particles.
[0037]
(Example 4)
Next, α-like Al solute Ni (OH)₂Conventional Ni (OH) used in Example 1 in order to obtain an appropriate value of the solid solution amount of dissimilar metals in the coating layer₂Powder soot is put into a reaction vessel and various Ni (NO)_Three)₂, Al (NO_Three)_ThreeAnd Ca (NO_Three)₂And a mixed aqueous solution (Ni: Al: Ca = 1-y: 0.20: y, y = 0.01, 0.05, 0.10, 0.20, 0.25 (atomic ratio)) The same coating treatment as in Example 1 was performed, and Al and Ca solid solution Ni (OH)₂Coated Ni (OH)₂Powders R to U were used.
[0038]
All these coating powders have X-ray diffraction patterns with α-Ni (OH)₂As a result of the appearance of diffraction lines belonging to, the coating layer is α-like Al, Ca solid solution Ni (OH)₂It was confirmed to contain a phase. The tap density of the coating powder was as good as 1.8 g / cc to 1.9 g / cc.
[0039]
Using the obtained powders R to U, a battery was produced by the same production method as in Example 1, and evaluated by a charge / discharge test in the same manner as in Example 3. Table 4 shows the obtained results.
[0040]
[Table 4]

[0041]
α-like Al, Ca solid solution Ni (OH)₂Improvement of high-temperature charging efficiency was confirmed when the Ca solid solution ratio of the coating layer was 0.01 to 0.20. However, when the Ca solid solution ratio of the coating layer was 0.25, neither discharge voltage nor high temperature charging efficiency was recognized. Α-like Al, Ca solid solution Ni (OH) for coating layer₂The reason why the discharge voltage is not improved despite the inclusion of the phase is not clear, but in Example 3, the α-similar Al solid solution Ni (OH)₂Similar results were obtained for all the different types of metals dissolved in the layer, and the effect of improving the characteristics was confirmed within the range of the solid solution ratio of 0.01 to 0.20.
[0042]
From the above results, α-like Al solid solution Ni (OH)₂It is apparent that the discharge voltage is improved and other characteristics can be improved when different metal elements are dissolved in the coating layer in the range of 0.01 to 0.20.
[0043]
(Example 5)
Next, α-like Al solute Ni (OH)₂The effect of Co oxide coating on the surface of the coated positive electrode active material was investigated.
[0044]
α-like Al solute Ni (OH)₂Coating powders C, D, J, and O are charged into the reaction vessel, and CoSO_FourAqueous solution, NaOH aqueous solution, NH_ThreeThe aqueous solution was continuously supplied into the reaction tank at a constant flow rate, and stirring and mixing were performed with the temperature in the tank maintained at 30 ° C. and the pH value of the solution in the tank maintained at about 11, and Co (OH) was applied to the particle surface.₂Was deposited and coated. The collected particles were washed with water and dried to obtain powders V to Y.
[0045]
The presence of Co in the powder coating layer was confirmed by a Co characteristic X-ray image of the powder cross section. The tap density of the coating powder was as good as 1.8 g / cc to 2.0 g / cc.
[0046]
Using the powders V to Y thus obtained, a battery was produced by the same production method as in Example 1, and evaluated by a charge / discharge test in the same manner. The results obtained are shown in Table 5.
[0047]
[Table 5]

[0048]
Co (OH)₂In the coating powders V to Y, improvement in utilization rate was confirmed as compared with the untreated powders C, D, J, and O. Although the discharge voltage is slightly reduced, the discharge voltage is improved as compared with the uncoated powders A and B, and α-like Al solid solution Ni (OH)₂The effect of improving the discharge voltage by the coating treatment was confirmed.
[0049]
Ni (OH)₂Or Ni (OH)₂It has been described in JP-A-62-222566 and JP-A-62-234867 that the utilization factor can be improved by coating the surface of the particle mainly containing Co with a Co compound.
[0050]
From the results of this example, the α-like Al solid solution Ni (OH) is formed between the positive electrode active material particles and the Co oxide layer on the surface thereof.₂It is clear that the utilization can be improved and the discharge voltage can be further improved by arranging the layers.
[0051]
In addition, since this invention is a technique regarding the improvement of the positive electrode active material of an alkaline storage battery, the same effect is acquired also in the nickel hydrogen storage battery using the hydrogen storage alloy of compositions other than having described in the Example. Further, the same effect can be obtained in all alkaline storage batteries (for example, nickel / cadmium storage battery, nickel / iron storage battery, nickel / zinc storage battery) using a positive electrode active material based on nickel oxide. The same effect can be obtained when the electrode support, the active material additive, the separator, and the like are different. Moreover, although only the AA size cylindrical sealed battery has been described, the same effect can be obtained for other sizes of cylindrical sealed batteries, square sealed batteries, stationary storage batteries, large storage batteries, medium storage batteries, or open batteries. Furthermore, in an alkaline storage battery using a sintered positive electrode, the same effect can be obtained when the same coating treatment is applied to the positive electrode surface.
[0052]
【The invention's effect】
The surface of the positive electrode active material powder is α-similar Al solid solution Ni (OH)₂By coating with, a positive electrode active material for an alkaline storage battery excellent in capacity density, discharge voltage, and high rate discharge characteristics can be provided. In addition, the α-like Al solid solution Ni (OH)₂By dissolving at least one dissimilar metal element selected from Ca, Cr, Y, Ti, and Co in the coating layer, it is excellent in capacity density, discharge voltage, and high rate discharge characteristics, and has high temperature charge efficiency and / or charge. A positive electrode active material for an alkaline storage battery having excellent discharge characteristics can be provided. In addition, the α-like Al solid solution Ni (OH)₂By coating the surface of the coated positive electrode active material powder with Co oxide, it is possible to provide a positive electrode active material for an alkaline storage battery that is excellent in capacity density, discharge voltage, high rate discharge characteristics, and excellent charge / discharge characteristics.

Claims

An active material powder used for a positive electrode for an alkaline storage battery mainly comprising an oxide or hydroxide of a plurality of metal elements containing Ni as a main metal element, the surface of the oxide or hydroxide powder of the plurality of metal elements A positive electrode active material for an alkaline storage battery, wherein an α-like Ni (OH) ₂ layer in which Al is present in a eutectic state and / or a solid solution state is disposed in the vicinity of the layer.

The amount of Al present in the α-like Ni (OH) ₂ layer in the eutectic state and / or the solid solution state is determined by the metal atomic ratio in the α-like Ni (OH) ₂ layer as Ni: Al = 1−x. : The positive electrode active material for an alkaline storage battery according to claim 1, wherein x represents 0.10 ≦ x ≦ 0.40.

The α-like Ni (OH) ₂ layer arranged near the surface layer of the oxide or hydroxide powder of multiple metal elements is selected from Ca, Cr, Y, Ti and Co in addition to Ni and Al. The positive electrode active material for an alkaline storage battery according to claim 1, wherein at least one element is present in a eutectic state and / or a solid solution state.

When at least one element selected from Ca, Cr, Y, Ti, Co existing in the eutectic state and / or the solid solution state in the α-like Ni (OH) ₂ layer is expressed as Me, the Me amount is The metal atom ratio in the α-like Ni (OH) ₂ layer is expressed as Ni + Al: Me = 1-y: y, and 0.01 ≦ y ≦ 0.20. Positive electrode active material for alkaline storage batteries.

5. The alkaline storage battery according to claim 1, wherein a Co oxide layer is further disposed on the surface of the active material powder in which an α-similar Ni (OH) ₂ layer is disposed in the vicinity of the surface layer. Positive electrode active material.