JP2004071304A - Positive active material for alkaline storage battery, positive electrode using it, and alkaline storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive active material for an alkaline storage battery with high active material utilization factor, high high-temperature charging efficiency, high life characteristics, and high filling capability to a substrate, and to provide a nickel positive electrode using the positive active material and an alkaline storage battery. <P>SOLUTION: The positive active material for the alkaline storage battery comprises powder, the powder comprises nickel hydroxide particles and a covering layer on the surface of the particles, the covering layer comprises a cobalt oxide, contains at least one element M<SP>1</SP>selected from a group comprising yttrium, ytterbium, lutetium, and calcium, and moreover contains a sulfate group and/or a nitrate group, the total contents of the sulfate group and the nitrate group in the powder is 0.8 wt% or less, and an average valence of cobalt contained in the cobalt oxide is a valence of 3.2 to 3.5. <P>COPYRIGHT: (C)2004,JPO

Description

【００６０】
表１から明らかなように、イットリウム、イッテルビウム、ルテチウムおよびカルシウムからなる群より選ばれた少なくとも１種を含有したコバルト酸化物からなる被覆層を形成させることによって、高温における充電効率が著しく向上することがわかる。なお、電池（Ｆ）のように、酸化イットリウムを極板中に添加しても、充電効率の向上は認められるが、本発明の電池（Ａ）〜（Ｄ）と比較すると劣っていた。なお、電池（Ａ）〜（Ｄ）の充電末期の酸素発生過電圧は、（Ｅ）に対して約３０ｍＶ、（Ｆ）に対して約１５ｍＶ高い値を示した。
【００６１】
《実施例２》
実施例１の＜ステップ２＞に記載のコバルト酸化物被覆層の作製方法において、コバルト酸化物被覆層中の硫酸根含有量の異なるサンプルを得ることを目的として、反応槽内の液のｐＨを１１〜１３の範囲で変化させ、かつ、アンモニア濃度を８〜１１ｇ／Ｌの範囲で変化させた。それ以外は実施例１と同様にして、コバルト酸化物被覆水酸化ニッケル粉末を作製した。
【００６２】
得られた粉末の被覆層中の硫酸根含有量は、活物質粉末全体の重量のうち０．３〜１．３重量％の範囲でばらついた。なお、硝酸根は実施例１と同様に検出されなかった。また、前記硫酸根含有量の違いにより、比表面積およびタップ密度は粉末によって大きく異なる値を示した。なお、これらの粉末の被覆層中のコバルト平均価数は、いずれも３．２価以上３．５価以下であった。
【００６３】
図１は、前記実験の結果を表す図であって、硫酸根含有量と、比表面積と、タップ密度との関係を示す特性図である。この図から、硫酸根含有量が０．８重量％以下で、タップ密度が１．８ｇ／ｃｍ^３以上となり、比表面積が１５ｍ^２／ｇ以下になることがわかる。さらに、硫酸根含有量が０．５重量％以下で、タップ密度が１．９ｇ／ｃｍ^３以上となり、比表面積が１２ｍ^２／ｇ以下になることがわかる。従って、活物質粉末中の硫酸根含有量は、０．８重量％以下、さらには０．５重量％以下であることが好ましい。
【００６４】
タップ密度は正極に充填することが可能な活物質粉末量と相関がある。タップ密度が１．８ｇ／ｃｍ^３以上、好ましくは１．９ｇ／ｃｍ^３以上でなければ、正極への活物質充填量が著しく低下し、正極エネルギー密度が低下する。また、比表面積については、１５ｍ^２／ｇ以下、好ましくは１２ｍ^２／ｇ以下でなければ、寿命特性が著しく低下する。なお、比表面積については実施例４で詳しく説明する。
【００６５】
ここでは、被覆層がイットリウムを含有する例を示したが、上記以外のイットリウム、イッテルビウム、ルテチウムおよびカルシウムからなる群より選ばれた少なくとも１種を含有するコバルト酸化物被覆水酸化ニッケル粉末においても、同様な結果が認められた。
【００６６】
また、ここでは、被覆層の原料に硫酸コバルトおよび硫酸イットリウムを用いたが、硝酸コバルト、硝酸イットリウムなどを用い、硝酸根含有量の異なるコバルト酸化物被覆粉末を作製した場合においても、硝酸根含有量が活物質粉末の全体重量のうち０．８重量％以下、さらには０．５重量％以下の場合において、前記と同様な結果が認められた。また、硫酸コバルトと硝酸イットリウム、または硝酸コバルトと硫酸イットリウムを用いた場合においても、硝酸根と硫酸根の総含有量が活物質粉末の全体重量に対して０．８重量％以下、さらには０．５重量％以下の場合において、前記と同様な結果が認められた。
【００６７】
《実施例３》
実施例１の＜ステップ２＞に記載のコバルト酸化物被覆層の作製方法において、コバルト酸化物被覆層中のコバルト平均価数の異なるサンプルを得ることを目的として、水酸化カリウム水溶液の量を７〜１２ｍｌの範囲で、かつ、酸化時間を１〜３時間の範囲で変化させた。得られた粉末の被覆層中の硫酸根含有量は粉末全体の０．３５重量％であり、コバルト平均価数は、２．８〜３．６価の範囲でばらついた。さらに、被覆層中の硫酸根含有量が粉末全体の０．５重量％、０．８重量％、および０．９２重量％である粉末においても、それぞれ同様にしてコバルト平均価数の異なるサンプルを得た。なお、いずれの粉末においても、硝酸根は検出されなかった。これらのコバルト平均価数の異なる正極活物質、および、それらを用いた円筒密閉電池を作製し、それらの電池特性を評価した。
【００６８】
評価に先立ち、２０℃において、電池を１３０ｍＡの電流で１５時間充電し、２６０ｍＡの電流で１．０Ｖまで放電する充放電サイクルを繰り返した。電池の放電容量が安定した後、２０℃において、電池を１．３Ａの電流で１．２時間充電し、２０℃において、１．３Ａの電流で電池電圧０．８Ｖまで放電し、活物質の利用率を算出した。
【００６９】
図２は、前記実験の結果を表す図であって、コバルト酸化物被覆層中のコバルト平均価数と活物質利用率との関係を示す特性図である。コバルト被覆層中の硫酸根含有量が０．３５重量％、０．５重量％、０．８重量％および０．９２重量％の粉末の結果を、それぞれグラフａ、ｂ、ｃおよびｄに示す。この図から、粉末の被覆層中の硫酸根含有量が粉末全体の０．８重量％以下で、高い活物質利用率を示し、さらに、３．２価以上で特異的に活物質利用率が向上することがわかる。従って、硫酸根含有量が０．８重量％以下で、かつ、コバルト平均価数が３．２価以上であることが好ましい。また、コバルト平均価数が３．５価より大きい場合には、若干ではあるが利用率が低下する傾向が認められる。従って、利用率向上のためには、３．２価以上３．５価以下であることが望ましい。
【００７０】
なお、ここでは被覆層がイットリウムを含有する例を示したが、上記以外のイットリウム、イッテルビウム、ルテチウムおよびカルシウムからなる群より選ばれた少なくとも１種を含有するコバルト酸化物被覆水酸化ニッケル粉末においても、同様な結果が認められた。
【００７１】
《実施例４》
実施例１の＜ステップ２＞に記載のコバルト酸化物被覆層の作製方法において、比表面積の異なるサンプルを得ることを目的として、反応槽内の液のｐＨを１１．５〜１３．０の範囲で変化させた。得られた粉末の窒素ガス吸着により測定されるＢＥＴ比表面積は、４〜１７ｍ^２／ｇの範囲でばらついた。なお、これらの粉末の被覆層中のコバルト平均価数は３．２価以上３．５価以下であり、被覆層中の硫酸根含有量は粉末全体の１．０重量％以下であった。硝酸根は検出されなかった。それ以外は実施例１と同様にして、比表面積の異なる正極活物質、および、それらを用いた円筒密閉電池を作製し、それらの電池特性を評価した。
【００７２】
評価に先立ち、２０℃において、電池を１３０ｍＡの電流で１５時間充電し、２６０ｍＡの電流で１．０Ｖまで放電する充放電サイクルを繰り返した。電池の放電容量が安定した後、２０℃において、電池を１．３Ａの電流で１．２時間充電し、２０℃において、１．３Ａの電流で電池電圧０．８Ｖまで放電するといった充放電を５００サイクル繰り返し、１サイクル目の活物質利用率Ａに対する５００サイクル目の活物質利用率Ｃの比：Ｃ／Ａを百分率で算出した。
【００７３】
図３は、前記実験の結果を表す図であって、比表面積と活物質利用率比：Ｃ／Ａとの関係を示す特性図である。この図から比表面積が１５ｍ^２／ｇ以下、さらには１２ｍ^２／ｇ以下で、利用率比Ｃ／Ａが高い値を示すことがわかる。また、比表面積が５ｍ^２／ｇより小さい場合には、利用率Ａが９０％以下に低下する傾向が観察された。従って、寿命特性、初期の利用率を高めるためには、窒素ガス吸着により測定されるＢＥＴ比表面積は、５ｍ^２／ｇ以上１５ｍ^２／ｇ以下、さらには５ｍ^２／ｇ以上１２ｍ^２／ｇ以下であることが好ましい。
【００７４】
なお、ここでは被覆層がイットリウムを含有する例を示したが、上記以外のイットリウム、イッテルビウム、ルテチウムおよびカルシウムからなる群より選ばれた少なくとも１種を含有するコバルト酸化物被覆水酸化ニッケル粉末においても、同様な結果が認められた。
【００７５】
《実施例５》
実施例１の＜ステップ２＞に記載のコバルト酸化物被覆層の作製方法において、コバルト酸化物被覆層の含有量を、コバルト酸化物被覆水酸化ニッケル粒子全体の重量に対して、２〜１８重量％の範囲で変化させた。なお、これらの粉末の被覆層中のコバルト平均価数は３．２価以上３．５価以下であり、被覆層中の硫酸根含有量は粉末全体の０．８重量％以下であった。硝酸根は検出されなかった。それ以外は実施例１と同様にして、コバルト酸化物被覆量の異なる正極活物質、および、それを用いた円筒密閉電池を作製し、それらの電池特性を評価した。
【００７６】
評価に先立ち、２０℃において、電池を１３０ｍＡの電流で１５時間充電し、２６０ｍＡの電流で１．０Ｖまで放電する充放電サイクルを繰り返した。電池の放電容量が安定した後、２０℃において、電池を１．３Ａの電流で１．２時間充電し、２０℃において、１．３Ａの電流で電池電圧０．８Ｖまで放電し、活物質の利用率を算出した。
【００７７】
図４は、前記実験の結果を表す図であって、コバルト酸化物被覆層の含有量と活物質利用率との関係を示す特性図である。この図から被覆層の含有量が３重量％以上１５重量％以下、さらには５重量％以上１３重量％以下で利用率が高い値を示すことがわかる。従って、利用率をより高めるためには、コバルト酸化物被覆の含有量が、粉末全体の３重量％以上１５重量％以下、さらには５重量％以上１３重量％以下であることが好ましい。
【００７８】
なお、ここでは被覆層がイットリウムを含有する例を示したが、上記以外のイットリウム、イッテルビウム、ルテチウムおよびカルシウムからなる群より選ばれた少なくとも１種を含有するコバルト酸化物被覆水酸化ニッケル粉末においても、同様な結果が認められた。
【００７９】
《実施例６》
実施例１の＜ステップ２＞に記載のコバルト酸化物被覆層の作製方法において、コバルト酸化物被覆層中のイットリウム含有量を、被覆層中の全金属元素に対して、０〜２５モル％の範囲で変化させた。なお、これらの粉末の被覆層中のコバルト平均価数は３．２価以上３．５価以下であり、被覆層中の硫酸根含有量は粉末全体の０．８重量％以下であった。硝酸根は検出されなかった。それ以外は実施例１と同様にして、イットリウム含有量の異なる正極活物質、および、それを用いた円筒密閉電池を作製し、それらの電池特性を評価した。
【００８０】
評価に先立って、２０℃において、電池を１３０ｍＡの電流で１５時間充電し、２６０ｍＡの電流で１．０Ｖまで放電する充放電サイクルを繰り返した。電池の放電容量が安定した後、２０℃において、電池を１．３Ａの電流で１．２時間充電し、２０℃において、１．３Ａの電流で電池電圧０．８Ｖまで放電し、活物質の利用率Ａ（２０℃充電時）を算出した。また、次のサイクルでは、６０℃において、電池を１．３Ａの電流で１．２時間充電し、２０℃において、１．３Ａの電流で電池電圧０．８Ｖまで放電し、その放電容量から活物質の利用率Ｂ（６０℃充電時）を算出した。
【００８１】
図５は、前記実験の結果を表す図であって、コバルト酸化物被覆層中の全金属元素に対するイットリウムの含有量と、２０℃充電時の利用率Ａと、６０℃充電時の利用率Ｂとの関係を示す特性図である。この図から被覆層中のイットリウム含有量が２モル％以上で６０℃充電時の利用率Ｂが高い値を示し、２０モル％以下で２０℃充電時の利用率Ａが高い値を示すことがわかる。従って、高温充電効率および利用率をより高めるためには、被覆層中のイットリウム含有量が２モル％以上２０モル％以下、さらには５モル％以上１５モル％以下であることが好ましい。
【００８２】
なお、ここでは被覆層がイットリウムを含有する例を示したが、上記以外のイットリウム、イッテルビウム、ルテチウムおよびカルシウムからなる群より選ばれた少なくとも１種を含有するコバルト酸化物被覆水酸化ニッケル粉末においても、同様な結果が認められた。
【００８３】
《実施例７》
実施例１の＜ステップ１＞に記載の水酸化ニッケル粒子の作製方法において、コバルトと亜鉛を含む水酸化ニッケルの固溶体の代わりに、アルミニウムを含む水酸化ニッケルの固溶体、およびマグネシウムを含む水酸化ニッケルの固溶体を作製した。従って、ここでは硫酸ニッケルと硝酸アルミニウムの混合水溶液、および、硫酸ニッケルと硫酸マグネシウムの混合水溶液を用いた。なお、それぞれの混合水溶液に含まれる硫酸ニッケルと硝酸アルミニウムのモル比、および硫酸ニッケルと硫酸マグネシウムのモル比は、それぞれ９０モル％：１０モル％とした。
【００８４】
組成分析、Ｘ線回折測定を実施した結果、得られた粉末は、それぞれアルミニウムを１０モル％含む水酸化ニッケルの固溶体、および、マグネシウムを１０モル％含む水酸化ニッケルの固溶体であることが確認された。なお、これらの粉末の被覆層中のコバルト平均価数は３．２価以上３．５価以下であり、被覆層に含まれる硫酸根と硝酸根の総含有量は粉末全体の０．８重量％以下であった。それ以外は実施例１と同様にして、コバルト酸化物被覆水酸化ニッケル粉末を作製し、ニッケル正極、および、それを用いた円筒密閉電池を作製した。
【００８５】
《実施例８》
実施例１の＜ステップ１＞に記載の水酸化ニッケル粒子の作製方法において、コバルトと亜鉛を含む水酸化ニッケルの固溶体の代わりに、マンガンを含む水酸化ニッケルの固溶体を作製した。従って、ここでは硫酸ニッケルと硫酸マンガンの混合水溶液を用いた。なお、混合水溶液に含まれる硫酸ニッケルと硫酸マンガンのモル比は、９０モル％：１０モル％とした。
【００８６】
マンガンを含む水酸化ニッケルの固溶体は、タップ密度の向上、利用率の向上を図るために、マンガンの価数をコントロールする必要がある。そこで、結晶成長過程では、反応槽内に窒素ガスを連続的に供給して、溶存酸素によるマンガンの酸化を抑制することで、結晶成長を促進し、タップ密度の向上を図った。さらに、粉末の乾燥過程では、水酸化ニッケル中のマンガンの酸化を促進するために、大気雰囲気下、９０℃で２日間酸化処理した。
【００８７】
組成分析、Ｘ線回折測定を実施した結果、得られた粉末は、マンガンを１０モル％含む水酸化ニッケルの固溶体であることが確認された。また、マンガンの平均価数は３．４価であった。なお、被覆層中のコバルト平均価数は３．２価以上３．５価以下であり、被覆層に含まれる硫酸根含有量は粉末全体の０．８重量％以下であった。硝酸根は検出されなかった。それ以外は実施例１と同様にして、コバルト酸化物被覆水酸化ニッケル粉末を作製し、ニッケル正極、および、それを用いた円筒密閉電池を作製した。
【００８８】
《比較例３》
実施例１の＜ステップ１＞に記載の水酸化ニッケル粒子の作製方法において、実施例７と同様にして、アルミニウムまたはマグネシウムを１０モル％含む水酸化ニッケルの固溶体を作製した。
次いで、実施例１の＜ステップ２＞に記載のコバルト酸化物被覆層の作製方法において、イットリウムなどの異種金属元素を含有させずに、純粋な水酸化コバルトを固溶体粉末に被覆し、その後、改質処理した。それ以外は実施例１と同様にして、コバルト酸化物被覆水酸化ニッケル粉末を作製し、ニッケル正極、および、それを用いた円筒密閉電池を作製した。
【００８９】
《比較例４》
実施例１の＜ステップ１＞に記載の水酸化ニッケル粒子の作製方法において、実施例８と同様にしてマンガンを１０モル％含む水酸化ニッケルの固溶体を作製した。
次いで、実施例１の＜ステップ２＞に記載のコバルト酸化物被覆層の作製方法において、イットリウムなどの異種金属元素を含有させずに、純粋な水酸化コバルトを被覆し、その後、改質処理した。それ以外は実施例１と同様にして、コバルト酸化物被覆水酸化ニッケル粉末を作製し、ニッケル正極、および、それを用いた円筒密閉電池を作製した。
【００９０】
実施例７、実施例８および比較例３、比較例４の円筒密閉電池を用い、それらの電池特性を評価した。
評価に先立って、２０℃において、電池を１３０ｍＡの電流で１５時間充電し、２６０ｍＡの電流で１．０Ｖまで放電する充放電サイクルを繰り返した。電池の放電容量が安定した後、２０℃において、電池を１．３Ａの電流で１．２時間充電し、２０℃において、１．３Ａの電流で電池電圧０．８Ｖまで放電し、活物質の利用率Ａ（２０℃充電時）および平均放電電圧を算出した。また、次のサイクルでは、６０℃において、電池を１．３Ａの電流で１．２時間充電し、２０℃において、１．３Ａの電流で電池電圧０．８Ｖまで放電し、その放電容量から活物質の利用率Ｂ（６０℃充電時）を算出した。なお、利用率は、活物質中のニッケルが一電子反応したときの理論電気量に対して算出した。表２に、それらの結果を示す。
【００９１】
なお、実施例１において、コバルトと亜鉛を含む水酸化ニッケルの固溶体を用いた電池を（Ａ）、実施例７のアルミニウムを含む水酸化ニッケルの固溶体を用いた電池を（Ｂ）、マグネシウムを含む水酸化ニッケルの固溶体を用いた電池を（Ｃ）、実施例８のマンガンを含む水酸化ニッケルの固溶体を用いた電池を（Ｄ）とした。また、比較例３のアルミニウムを含む水酸化ニッケルの固溶体を用いた電池を（Ｅ）、マグネシウムを含む水酸化ニッケルの固溶体を用いた電池を（Ｆ）、比較例４の電池を（Ｇ）とした。
【００９２】
【表２】

【００９３】
表２の電池（Ｅ）、（Ｆ）の結果から、アルミニウム、マグネシウムを含む水酸化ニッケルの固溶体は、コバルトと亜鉛を含む水酸化ニッケルの固溶体を用いた電池（Ａ）と比較して、放電電圧が著しく向上する。しかし、その一方で、高温充電効率が極めて低いことがわかる。これは、アルミニウムまたはマグネシウムを含む水酸化ニッケルの固溶体は、電極電位が高くなるため、放電電圧だけでなく、充電電圧も上昇するためである。
【００９４】
そこで、電池（Ｂ）、（Ｃ）のように、イットリウムを含有したコバルト酸化物からなる被覆層を形成させることによって、高温における充電効率を著しく向上させることが可能となる。また、マンガンを含む水酸化ニッケルの固溶体を用いた電池（Ｇ）は、放電電圧は低いが、活物質利用率が著しく向上することがわかる。さらに、電池（Ｄ）のように、イットリウムを含有したコバルト酸化物からなる被覆層を形成させることによって、高温における活物質利用率を著しく向上させることが可能となる。
【００９５】
なお、ここでは被覆層がイットリウムを含有する例を示したが、上記以外のイットリウム、イッテルビウム、ルテチウムおよびカルシウムからなる群より選ばれた少なくとも１種を含有するコバルト酸化物被覆水酸化ニッケル粉末においても、同様な結果が認められた。
また、コバルト、亜鉛、マンガン、アルミニウムおよびマグネシウムのうち、２種以上の元素を含む水酸化ニッケルの固溶体においても、同様な結果が認められた。
【００９６】
また、水酸化ニッケルの固溶体中のコバルトおよび亜鉛からなる群より選ばれた少なくとも１種の元素の量、アルミニウムおよびマグネシウムからなる群より選ばれた少なくとも１種の元素の量、またはマンガン量が、それぞれ水酸化ニッケルの固溶体に含まれる全金属元素の０．５モル％以上２０モル％以下の範囲においては、同様な結果が認められた。
【００９７】
【発明の効果】
以上のように、本発明によれば、活物質利用率、高温充電効率、寿命特性に優れ、かつ、基板への充填性にも優れたアルカリ蓄電池用正極活物質、ならびに、これを用いたニッケル正極とアルカリ蓄電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例にかかる正極活物質の硫酸根含有量と、比表面積と、タップ密度との関係を示す図である。
【図２】本発明の実施例にかかる正極活物質のコバルト酸化物被覆層中のコバルト平均価数と活物質利用率との関係を示す図である。
【図３】本発明の実施例にかかる正極活物質の比表面積と活物質利用率比：Ｃ／Ａとの関係を示す図である。
【図４】本発明の実施例にかかる正極活物質のコバルト酸化物被覆層の含有量と活物質利用率との関係を示す図である。
【図５】本発明の実施例にかかる正極活物質のコバルト酸化物被覆層中のイットリウム含有量と、常温充電時の活物質利用率Ａと、高温充電時の活物質利用率Ｂとの関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode active material for an alkaline storage battery, and a positive electrode and an alkaline storage battery using the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, the capacity density of a positive electrode for an alkaline storage battery has been dramatically improved due to improvements in a substrate shape, active material particle shape, active material composition, additives, and the like.
The positive electrodes for alkaline storage batteries are roughly classified into two types: a sintered type and a non-sintered type (paste type). In the former method, a nickel sintered substrate having a porosity of about 80% obtained by sintering a core material such as punching metal and nickel powder is impregnated with a nickel salt solution such as a nickel nitrate aqueous solution, and then impregnated with an alkaline aqueous solution. In this manner, nickel hydroxide is deposited on a porous nickel sintered substrate.
[0003]
Since it is difficult for the positive electrode to further increase the porosity of the substrate, the amount of nickel hydroxide cannot be increased, and there is a limit to increasing the capacity. On the other hand, the latter non-sintered positive electrode is obtained by filling nickel hydroxide particles in a foamed nickel substrate having a porosity of about 95% and having three-dimensionally continuous voids, and a high-capacity type. It is widely used as a positive electrode for alkaline storage batteries.
[0004]
As the nickel hydroxide particles used for the positive electrode, spherical high-density nickel hydroxide particles are employed in order to improve the filling property of the electrode. In addition, in order to improve charge / discharge characteristics and life characteristics, a solid solution of nickel hydroxide containing a metal element such as cobalt, zinc, and cadmium is generally used. In recent years, a solid solution of nickel hydroxide containing manganese or the like has been proposed for further increasing the capacity, and a solid solution of nickel hydroxide containing magnesium or the like has been proposed for achieving a higher output.
[0005]
As the conductive material to be filled into the foamed nickel substrate together with the nickel hydroxide particles, a divalent cobalt oxide such as metal cobalt, cobalt hydroxide, and cobalt monoxide is used. These are electrochemically oxidized to cobalt oxyhydroxide having conductivity at the initial charge, and this functions as a conductive network connecting the nickel hydroxide particles and the substrate skeleton. With this conductive network, the conductivity and current collecting properties of the non-sintered positive electrode can be supplemented, and the utilization rate of the active material can be increased. Further, as a method of uniformly dispersing the conductive network in the positive electrode, particles in which the surface of nickel hydroxide particles is previously coated with cobalt oxide have been proposed. Thereby, the current collecting property is improved, and the utilization rate of the active material can be further improved.
[0006]
However, since the above-mentioned conductive network utilizes the electrochemical oxidation reaction of cobalt in the battery, it is easily affected by the battery capacity, resistance, temperature, charging current, and the like. Therefore, it is difficult to completely change the conductive material to cobalt oxyhydroxide, and the performance tends to vary between batteries.
[0007]
In recent years, as a means for improving such imperfections of the conductive network, a technique has been proposed in which cobalt oxyhydroxide is used as a conductive material by subjecting a cobalt oxide to a chemical oxidation treatment in advance. JP-A-11-97008 discloses that a high-order cobalt oxide containing γ-cobalt oxyhydroxide as a main component having an average valence of cobalt of more than 3 and a solid solution particle containing nickel hydroxide as a main component are disclosed. Non-sintered positive electrode active materials and alkaline storage batteries have been proposed. Furthermore, the same report also proposes a technique of disposing a coating layer composed of a higher cobalt oxide containing γ-cobalt oxyhydroxide on the surface of solid solution particles containing nickel hydroxide as a main component. I have.
[0008]
Incidentally, one of the problems of the alkaline storage battery is a problem of a decrease in charge acceptability at a high temperature (a decrease in utilization factor). This is because, at the end of charging, the overvoltage of the oxygen gas generation reaction, which is competitive with the oxidation reaction (charging) of nickel hydroxide on the positive electrode, drops significantly at high temperatures, so that the oxygen gas generation reaction remarkably progresses, This is because the oxidation reaction of nickel is suppressed. In order to solve the problem of charging at such a high temperature, conventionally, there have been many proposals to increase the oxygen overvoltage of the positive electrode to improve the charge acceptability.
[0009]
For example, in Japanese Patent Application Laid-Open No. 5-28992, a compound such as yttrium, indium, antimony, barium, calcium, beryllium, that is, a material having an effect on increasing the oxygen overvoltage is added to the surface of active material particles or between particles. It has been proposed.
[0010]
In Japanese Patent Application Laid-Open No. 10-21909, the surface of nickel hydroxide particles is coated with a eutectic of yttrium hydroxide and cobalt hydroxide, so that a high active material can be used over a long period of time as well as at the beginning of a charge / discharge cycle. It is disclosed to develop a rate.
[0011]
Japanese Patent Application Laid-Open No. 11-260360 discloses that at least a part of the surface of nickel hydroxide particles can be coated with a cobalt compound layer containing ytterbium to improve the utilization factor and the charging efficiency at high temperatures. I have.
[0012]
In JP-A-2001-185137, the surface of nickel hydroxide particles was coated with a mixed crystal of at least one element selected from aluminum, manganese, iron, yttrium, ytterbium, erbium and gadolinium, and cobalt. By using an active material in which the average valence of nickel in nickel hydroxide is in the range of 2 to 2.3 and the valence of cobalt in the mixed crystal exceeds 3, the conductivity is improved. And that the utilization can be improved.
[0013]
[Problems to be solved by the invention]
However, the method described in Japanese Patent Application Laid-Open No. 5-28992 or the like has a problem in that the additive effective in increasing the oxygen generation overpotential tends to aggregate in the positive electrode, and the effect corresponding to the added amount is not necessarily obtained. There is.
[0014]
Further, in the cobalt hydroxide-coated nickel hydroxide particles disclosed in JP-A-10-21909 and JP-A-11-260360, a different element is contained in the cobalt hydroxide-coated layer. There is a problem that electrochemical and chemical oxidation are easily inhibited, oxidation of cobalt is suppressed, conductivity between active materials in the positive electrode is reduced, and a sufficient utilization rate cannot be obtained.
[0015]
This is because the inclusion of trivalent elements such as yttrium and ytterbium makes it easier for crystals to incorporate anions such as sulfate ions and nitrate ions in order to maintain electrical neutrality, thereby inhibiting proton diffusion. It is believed that the oxidation of cobalt is suppressed. Furthermore, the inclusion of different elements having different ionic radii from that of cobalt, and the inclusion of sulfate and nitrate, suppress the crystal growth of the cobalt hydroxide coating layer, thereby increasing the specific surface area and decreasing the bulk density (filling property). Problem). As a result, the electrolyte solution moves into the positive electrode, and the cycle life characteristics are likely to decrease.
[0016]
On the other hand, Japanese Patent Application Laid-Open No. 2001-185137 proposes to increase the valence of cobalt to be more than 3 to improve conductivity, but it is not enough to make the valence of cobalt larger than 3. Can't get utilization.
[0017]
[Means for Solving the Problems]
As a result of the investigations by the present inventors, the cobalt valence of the cobalt oxide coating layer containing a different metal was determined to be cobalt (higher than trivalent) in the cobalt oxide coating layer described in JP-A-2001-185137. It is clear that the higher range is optimal as compared with, and the utilization is specifically improved in this range. And it became clear that in order to obtain such a unique effect, it is necessary to optimize the amounts of sulfate and nitrate contained in the active material.
[0018]
The present invention has been made in view of the above, and is a positive electrode active material for an alkaline storage battery composed of a powder, wherein the powder comprises particles composed of nickel hydroxide and a coating layer disposed on the surface of the particles. The coating layer is made of cobalt oxide, and the coating layer is further made of at least one element M selected from the group consisting of yttrium, ytterbium, lutetium and calcium. ¹ The coating layer further contains a sulfate group and / or a nitrate group, and the total content of the sulfate group and the nitrate group in the powder is 0.8% by weight or less, and is contained in the cobalt oxide. The present invention relates to a positive electrode active material for an alkaline storage battery having an average valence of cobalt of 3.2 or more and 3.5 or less.
[0019]
The tap density of the powder is 1.8 g / cm. ³ It is preferable that it is above.
The BET specific surface area of the powder as measured by adsorption of nitrogen gas is 5 m ² / G or more 15m ² / G or less.
The content of the coating layer in the powder is preferably 3% by weight or more and 15% by weight or less.
Of all the metal elements contained in the coating layer, the element M ¹ Is preferably 2 mol% or more and 20 mol% or less.
[0020]
The particles made of nickel hydroxide include at least one element M selected from the group consisting of cobalt and zinc. ² It is preferred to be composed of a solid solution of nickel hydroxide containing
Of all the metal elements contained in the nickel hydroxide particles, the element M ² Is preferably 0.5 mol% or more and 20 mol% or less.
The particles made of nickel hydroxide are preferably made of a solid solution of nickel hydroxide containing at least manganese.
It is preferable that the ratio of the manganese is 0.5 mol% or more and 20 mol% or less in the total amount of the manganese and the nickel contained in the particles made of the nickel hydroxide.
[0021]
The particles made of nickel hydroxide include at least one element M selected from the group consisting of at least magnesium and aluminum. ³ It is preferred to be composed of a solid solution of nickel hydroxide containing
Of all the metal elements contained in the nickel hydroxide particles, the element M ³ Is preferably 0.5 mol% or more and 20 mol% or less.
The present invention also relates to a positive electrode for an alkaline storage battery containing the above active material, and an alkaline storage battery including the positive electrode, a negative electrode, a separator, and an alkaline electrolyte.
[0022]
According to the present invention, at least one element M selected from the group consisting of yttrium, ytterbium, lutetium and calcium ¹ Is uniformly contained in the coating layer, the oxygen generation overvoltage can be efficiently increased, and the charging efficiency at high temperatures can be improved. Further, by reducing the total amount of sulfate groups and nitrate groups in the coating layer to 0.8% by weight or less, the oxidation of cobalt can be promoted, and the conductive performance of the conductive network can be increased. Improvement can be achieved. Further, by limiting (reducing) the content of the sulfate group and the nitrate group, crystal growth is promoted, the specific surface area can be reduced, the bulk density can be improved, the filling property to the electrode can be improved, and the life characteristics can be improved. Can be achieved. Further, by setting the average valence of cobalt in the coating layer to be 3.2 or more and 3.5 or less, the above-mentioned different metal (element M ¹ In the case of the cobalt coating layer containing (1), the conductivity can be remarkably increased, and a high utilization factor required for the alkaline storage battery can be obtained.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to a positive electrode active material for an alkaline storage battery comprising a powder.
The powder includes particles made of nickel hydroxide and a coating layer disposed on the surface of the particles. The coating layer is made of a cobalt oxide, and the coating layer is made of at least one element M selected from the group consisting of yttrium, ytterbium, lutetium, and calcium. ¹ Includes
[0024]
Element M ¹ Is contained in the cobalt oxide coating layer, the oxygen generation overvoltage at the end of charging is dramatically increased, and the charging efficiency at high temperatures can be significantly improved. The dramatic increase in oxygen generation overpotential due to this technology is due to the fact that ¹ This is considered to be due to uniform distribution in the cobalt oxide coating layer where the charging reaction takes place.
On the other hand, as described in JP-A-5-28992, simply adding an yttrium compound, a calcium compound, or the like to the positive electrode may not sufficiently improve the charging efficiency because the dispersibility of these elements is low. It is known.
[0025]
Element M ¹ Is preferably contained in the cobalt oxide coating layer by the following method using a reactive crystallization method.
(1) Cobalt and element M in the presence of nickel hydroxide particles ¹ An aqueous solution containing a salt of the above is reacted with an aqueous alkaline solution to precipitate (eutectic) a hydroxide on the surface of the nickel hydroxide particles, and then the particles are oxidized in an aqueous alkaline solution.
(2) Nickel hydroxide coated with cobalt oxide by reactive crystallization and element M ¹ And the resulting mixture is oxidized in an aqueous alkaline solution to give the element M ¹ In the cobalt oxide coating layer.
[0026]
Cobalt salt and element M used in the above method ¹ Is preferably selected from sulfates and nitrates because of their relatively high solubility in aqueous solutions.
However, when these salts are used, when depositing cobalt oxide on the surface of the nickel hydroxide particles, sulfate and / or nitrate are easily taken into the crystals and / or pores of the cobalt oxide. There is a problem. That is, the salt of yttrium, ytterbium, lutetium and calcium has a lower solubility than the cobalt salt, and since cobalt is divalent, it is a trivalent salt. A large amount of sulfate and nitrate is taken into the active material.
[0027]
However, an element M having an ionic radius different from that of cobalt M ¹ In addition to the high content of sulfate and nitrate, the crystal growth of the cobalt hydroxide coating layer is suppressed, the specific surface area of the active material is increased, and the bulk density is easily reduced. The filling property of the resin decreases. In addition, there are problems that the sulfate group and the nitrate group inhibit the oxidation reaction of the cobalt oxide layer and lower the conductivity. As a result of the study by the present inventors, in the positive electrode active material for an alkaline storage battery comprising the powder of the present invention, the total content of sulfate and nitrate in the powder needs to be 0.8% by weight or less, It has been found that 0.5% by weight or less is preferable.
[0028]
In order to suppress the total content of sulfate and nitrate in the powder to 0.8% by weight or less, (1) the pH of the liquid in the reaction tank at the time of reaction crystallization is increased as compared with the conventional method ( (Conventional: pH 10.5-11.5), (2) increasing the ammonia concentration of the liquid in the reaction tank (conventional: ammonia concentration 7-9 g / L), (3) increasing the particle concentration of the liquid in the reaction tank , Etc. are effective.
For example, in the present invention, the pH of the liquid in the reaction tank during the reaction crystallization is set to 11.6 to 13.0, or the ammonia concentration of the liquid in the reaction tank is set to 9.1 to 11.0 g / L. It is effective to do.
[0029]
Here, the cobalt oxide layer according to the present invention contains at least one selected from the group consisting of yttrium, ytterbium, lutetium, and calcium that does not participate in the oxidation-reduction reaction (that is, the valence does not change). There is a problem that the conductivity is lower than that of the conventional active material.
[0030]
Therefore, it is effective to set the average valence of cobalt of the cobalt oxide in the coating layer to 3.2 or more and 3.5 or less. As a result of investigations by the present inventors, it has been found that by setting the average valence of cobalt to 3.2 or more, the conductivity of the active material is dramatically improved. This makes it possible to improve the utilization rate of the active material. However, when the average valence of cobalt is larger than 3.5, the utilization rate of the active material tends to decrease. Although the details of the cause are unknown, it is because the electric balance in the cobalt oxide crystal is not maintained and the crystallinity is reduced, so that the diffusion of protons in the cobalt oxide crystal is inhibited. It is thought to be. Further, due to the above-mentioned decrease in crystallinity, peeling of the cobalt oxide coating layer is apt to occur, so that current collecting property is reduced and discharge performance is reduced. Therefore, it is necessary that the average valence of cobalt is not less than 3.2 and not more than 3.5.
[0031]
As a method of oxidizing the cobalt oxide coating layer, a method of performing oxidation with an oxidizing agent or air oxidation in the presence of an aqueous alkali solution is preferable.
Further, as a method of increasing the average valence of cobalt, (1) increasing the concentration of an aqueous alkali solution to be added to the powder (conventional: 35% by weight or more and less than 45% by weight) as compared with the conventional method; (Conventional: 7 to 9 ml / powder 100 g), (3) prolong the air oxidation time of cobalt (conventionally: less than one hour), and (4) increase the air oxidation temperature ( Conventional: 100 ° C. or higher and lower than 110 ° C.).
For example, in the present invention, the concentration of the aqueous alkali solution to be added to the powder is 45 to 48% by weight, the amount of the aqueous alkali solution is 9.1 to 12 ml / 100 g of the powder, and the air oxidation time of cobalt is 1 to 3 hours. It is effective to set the air oxidation temperature to 110 to 115 ° C.
[0032]
Here, the effect that the utilization factor is improved by setting the average valence of cobalt to 3.2 or more and 3.5 or less is because the total amount of sulfate groups and / or nitrate groups contained in the coating layer is reduced by the amount of the powder. If it is not more than 0.8% by weight, it cannot be obtained. As described above, when many sulfate groups and nitrate groups are present in the powder, the conductivity of the cobalt oxide layer is significantly reduced, and the effect of improving the utilization factor is extremely reduced.
[0033]
In the positive electrode active material for an alkaline storage battery comprising the powder of the present invention, the tap density of the powder is 1.8 g / cm. ³ It is preferable that it is above. Tap density 1.8 g / cm ³ If it is smaller, the amount of the active material charged into the positive electrode decreases, and the capacity of the positive electrode decreases. Therefore, the tap density is 1.8 g / cm. ³ Above, furthermore, 1.9 g / cm ³ The above is preferable. Note that, as described above, the element M ¹ The nickel hydroxide particles coated with cobalt oxides containing, tend to have a low bulk density, but by suppressing the total content of sulfate and / or nitrate in the cobalt coating layer, the reduction of the bulk density is prevented. it can.
[0034]
The BET specific surface area of the active material powder measured by adsorption of nitrogen gas is 5 m ² / G or more 15m ² / G or less. BET specific surface area is 5m ² If the ratio is less than / g, the effective area of the solid-liquid interface, which is the site of the charge / discharge reaction, is too small, so that the polarization increases and the utilization rate of the active material decreases. The BET specific surface area is 15m ² If it is larger than / g, the electrolyte solution in the separator and the negative electrode moves into the positive electrode, and the cycle life characteristics are likely to be reduced. Therefore, the specific surface area is 5 m ² / G or more 15m ² / G or less, and 5 m ² / G or more 12m ² / G or less. Note that, as described above, the element M ¹ Nickel hydroxide particles coated with cobalt oxides containing Bt are likely to have a large BET specific surface area. Can be prevented.
[0035]
In the positive electrode active material for an alkaline storage battery comprising the powder of the present invention, the content of the coating layer in the powder is preferably 3% by weight or more and 15% by weight or less. The cobalt oxide in the coating layer functions as a conductive agent in the positive electrode. When the surface of the nickel hydroxide particles is coated with the cobalt oxide, the discharge performance can be further improved by improving the current collecting property. When the content of the coating layer is less than 3% by weight, this effect is small. descend. On the other hand, if the content of the coating layer is too large, the content of nickel hydroxide in the positive electrode decreases, so that a sufficient battery capacity cannot be obtained. Therefore, the content of the coating layer made of cobalt oxide is preferably from 3% by weight to 15% by weight, more preferably from 5% by weight to 13% by weight.
[0036]
At least one element M selected from the group consisting of yttrium, ytterbium, lutetium and calcium contained in the coating layer; ¹ Is preferably 2 mol% or more and 20 mol% or less of all metal elements in the coating layer. Element M ¹ Is less than 2 mol%, the oxygen generation overvoltage hardly increases, and the effect of improving the high-temperature charging efficiency is poor. On the other hand, the element M ¹ Is more than 20 mol%, the conductivity of the coating layer is reduced and the utilization rate is reduced even if the content of sulfate and nitrate and the average valence of cobalt are controlled as described above. Therefore, the element M in the coating layer ¹ Is preferably 2 mol% or more and 20 mol% or less, more preferably 5 mol% or more and 15 mol% or less of all metal elements in the coating layer.
[0037]
The particles made of nickel hydroxide include at least one element M selected from the group consisting of cobalt and zinc. ² It is preferred to be composed of a solid solution of nickel hydroxide containing By including cobalt in nickel hydroxide, the charging voltage is reduced, and the charge acceptability can be improved. In addition, by including zinc in nickel hydroxide, generation of a γ phase during overcharge can be suppressed, and swelling of the positive electrode can be suppressed.
[0038]
Of all the metal elements contained in the nickel hydroxide particles, the element M ² Is preferably 0.5 mol% or more and 20 mol% or less. Element M ² If the ratio is less than 0.5 mol%, a sufficient effect cannot be obtained, and if it is more than 20 mol%, the amount of nickel in nickel hydroxide involved in the reaction decreases, so that a sufficient battery No capacity is obtained.
[0039]
The particles made of nickel hydroxide are preferably made of a solid solution of nickel hydroxide containing at least manganese. By including manganese in nickel hydroxide, a γ phase (γ-NiOOH) is easily generated during charging, and the γ phase can be easily discharged. Thereby, the utilization rate of the active material can be improved, and the capacity can be dramatically increased. In order to further increase the capacity, the valence of manganese is preferably 3.2 or more. Thereby, it is possible to significantly improve the utilization rate of the active material.
By including manganese in nickel hydroxide, the charging voltage is significantly reduced. Therefore, by applying the above-described technology capable of greatly increasing the oxygen generation overvoltage, it is possible to achieve a drastic improvement in charging efficiency that has not been achieved in the past.
[0040]
The proportion of manganese in the total amount of manganese and nickel contained in the nickel hydroxide particles is preferably 0.5 mol% or more and 20 mol% or less. If the proportion of manganese is less than 0.5 mol%, a sufficient effect cannot be obtained, and if it is more than 20 mol%, the amount of nickel in nickel hydroxide involved in the reaction decreases, so Battery capacity cannot be obtained.
[0041]
The particles made of nickel hydroxide include at least one element M selected from the group consisting of magnesium and aluminum. ³ It is preferred to be composed of a solid solution of nickel hydroxide containing Magnesium and aluminum can increase the discharge voltage, and can significantly improve output characteristics. However, not only the discharge voltage but also the charging voltage is significantly increased, which causes a problem that the high-temperature charging efficiency is inferior. Therefore, by applying the above-described technology capable of greatly increasing the oxygen generation overvoltage, it is possible to achieve both improvement in output characteristics and improvement in high-temperature charging efficiency.
[0042]
Of all the metal elements contained in the nickel hydroxide particles, the element M ³ Is preferably 0.5 mol% or more and 20 mol% or less. Element M ³ If the ratio is less than 0.5 mol%, a sufficient effect cannot be obtained, and if it is more than 20 mol%, the amount of nickel in nickel hydroxide involved in the reaction decreases, so that a sufficient battery capacity is obtained. I can't get it.
[0043]
【Example】
Hereinafter, specific examples of the present invention will be described in detail based on experimental results.
<< Example 1 >>
<Step 1: Preparation of nickel hydroxide>
A mixed aqueous solution containing nickel sulfate, cobalt sulfate and zinc sulfate, an aqueous sodium hydroxide solution, and an aqueous ammonia solution are prepared and continuously supplied to the reactor maintained at 40 ° C. at a flow rate of 0.5 ml / min. did. Here, the concentration of sulfate in the mixed aqueous solution containing nickel sulfate, cobalt sulfate, and zinc sulfate was set to 2.4 mol / L. The molar ratio of nickel sulfate, cobalt sulfate and zinc sulfate was 94 mol%: 2 mol%: 4 mol%. The concentration of the aqueous ammonia solution was 5 mol / L, and the concentration of the aqueous sodium hydroxide solution was 5 mol / L.
[0044]
Subsequently, the pH in the reaction vessel became constant at 11.8, and the balance between the metal salt concentration and the metal hydroxide particle concentration in the liquid in the reaction vessel became constant. The obtained suspension was collected, and the precipitate was separated by decantation. This was alkali-treated with an aqueous sodium hydroxide solution having a pH of 13 to 14 and then washed with water and dried.
[0045]
As a result of a composition analysis and an X-ray diffraction measurement of the obtained particles, it was confirmed that the particles were a solid solution of nickel hydroxide containing 2 mol% of cobalt and 4 mol% of zinc.
[0046]
<Step 2: Preparation of Cobalt Oxide Coating Layer>
Subsequently, the nickel hydroxide particles obtained above are put into a mixed aqueous solution containing cobalt sulfate, yttrium sulfate and ammonia, and an aqueous sodium hydroxide solution and an aqueous ammonia solution are continuously added. Stirring was continued while adjusting so as to maintain, and cobalt hydroxide containing yttrium was deposited on the surface of the nickel hydroxide particles.
[0047]
Here, the coating amount of the yttrium-containing cobalt hydroxide was adjusted to be 10% by weight based on the total weight of the cobalt oxide-coated nickel hydroxide particles. The yttrium content was adjusted so that the proportion of yttrium in the total moles of cobalt and yttrium in the coating layer was 15 mol%. The ammonia concentration of the liquid in the reaction tank was adjusted to be 10 g / L in a steady state. Further, by blowing nitrogen gas into the liquid in the reaction tank, oxidation of cobalt by dissolved oxygen was suppressed.
[0048]
The conventional pH value is in the range of 10.5 to 11.5 and the conventional ammonia concentration is in the range of 7 to 9 g / L. Density is set. This makes it possible to suppress the content of sulfate groups in the whole powder obtained to 0.8% by weight or less. Thereafter, the suspension in the reaction tank was collected, and the precipitate was separated by decantation. This was alkali-treated with an aqueous sodium hydroxide solution having a pH of 13 to 14 and then washed with water and dried. Thus, a powder having an average particle size of 10 μm having a coating layer made of cobalt hydroxide was obtained.
[0049]
As a result of a composition analysis and a transmission electron microscope (TEM) observation of the obtained powder, the ratio of yttrium to the total amount of cobalt and yttrium in the coating layer was 15 mol%. The content of the coating layer made of cobalt hydroxide was 10% by weight of the whole powder. As a result of a composition analysis, the content of sulfate in the cobalt hydroxide coating layer was 0.35% by weight of the whole powder. Nitrate was not detected by the composition analysis. Here, the sulfate group content was calculated based on the result of the composition analysis of the nickel hydroxide powder obtained in Step 1 and the result of the composition analysis of the powder coated with cobalt hydroxide. Hereinafter, the same calculation was performed.
[0050]
Here, the method for producing the cobalt hydroxide-coated powder containing yttrium was shown, but similarly, the cobalt hydroxide-coated powder containing ytterbium, lutetium and calcium was produced. Note that the content of these elements in the coating layer was 15 mol% of all the metal elements in the coating layer. The total amount of sulfate and nitrate was in the range of 0.3 to 0.5% by weight based on the total weight of the active material powder.
[0051]
Next, the modification treatment of the yttrium-containing cobalt hydroxide-coated nickel hydroxide powder was performed in the following procedure. First, 10 ml of a 45% by weight aqueous solution of potassium hydroxide was added to 100 g of the same powder, and the mixture was kept at 110 ° C. for 2 hours in an air atmosphere and led to complete drying. By this operation, the yttrium-containing cobalt hydroxide coating layer on the particle surface was oxidized, and the particles turned blue. After the obtained powder was washed with water, vacuum drying was performed. The amount of the conventional potassium hydroxide aqueous solution is in the range of 7 to 9 ml per 100 g of the powder, and the conventional oxidation time is about 1 hour. The amount of the aqueous potassium hydroxide solution is large, and the oxidation time is set to be long. This made it possible to increase the average valence of cobalt to 3.2 or more.
[0052]
The total valence of all the metals contained in the powder was determined by the iodometry method, and the average valence of cobalt in the cobalt oxide coating layer was determined from the value.
Here, a high-concentration aqueous solution of potassium hydroxide was used as a solution to be added to the powder, but even when a high-concentration aqueous solution of sodium hydroxide was used, the average valence of cobalt in the coating layer was 3.2 valence. The above values were shown.
As described above, the obtained cobalt oxide-coated nickel hydroxide powder is a spherical powder having an average particle diameter of 10 μm and a tap density of 2.0 g / cm. ³ And the BET specific surface area measured by nitrogen gas adsorption is 8 m ² / G.
In addition, a modification treatment was similarly performed on a cobalt hydroxide-coated powder containing ytterbium, lutetium, or calcium instead of yttrium, and similar results were obtained.
[0053]
<Step 3: Preparation of nickel positive electrode>
26 g of water was added to 100 g of the active material powder obtained under the above manufacturing conditions, and the mixture was kneaded to form a paste. This paste was filled in a foamed nickel substrate having a porosity of 95%, dried, and pressed to obtain a nickel positive electrode plate. The positive electrode plate thus obtained was cut, and the electrode leads were spot-welded to obtain a nickel positive electrode having a theoretical capacity of 1300 mAh. However, the capacity density of the nickel positive electrode shown here was calculated on the assumption that nickel in the active material had a one-electron reaction.
[0054]
<Step 4: Preparation of alkaline storage battery>
As the negative electrode, a known negative electrode of an alkaline storage battery was used. Here, a hydrogen storage alloy MmNi having an average particle size of 30 μm was used. _3.55 Co _0.75 Mn _0.4 Al _0.3 A negative electrode made of a powder was used. Water and carboxymethylcellulose as a binder were added thereto and kneaded into a paste. This paste was filled under pressure into an electrode support to obtain a hydrogen storage alloy negative electrode plate. This negative electrode plate was cut to obtain a negative electrode having a capacity of 2000 mAh. A spiral electrode group was formed between the positive electrode and the negative electrode with a separator made of a sulfonated polypropylene nonwoven fabric having a thickness of 0.15 mm interposed therebetween. After inserting this electrode group into the battery case and injecting 2.2 ml of a 7 mol / l aqueous solution of potassium hydroxide, the opening of the battery case was sealed with a sealing plate having a safety valve with an operating valve pressure of about 2.0 MPa. An AA size cylindrical sealed nickel-metal hydride battery was produced.
[0055]
<< Comparative Example 1 >>
In the method for producing a cobalt oxide coating layer described in Example 1, the procedure was performed except that pure cobalt hydroxide was coated without containing a dissimilar metal element such as yttrium, and then the powder was modified. In the same manner as in Example 1, a positive electrode active material, a nickel positive electrode, and a cylindrical sealed battery using the same were produced.
[0056]
<< Comparative Example 2 >>
In the method for producing a cobalt oxide coating layer described in Example 1, the procedure was performed except that pure cobalt hydroxide was coated without containing a dissimilar metal element such as yttrium, and then the powder was modified. A positive electrode active material was produced in the same manner as in Example 1. Then, when producing the paste of the nickel positive electrode, 1.5 g of yttrium oxide (Y) was prepared in addition to 100 g of the active material powder and 26 g of water. ₂ O ₃ A) A nickel positive electrode and a cylindrical sealed battery using the same were prepared in the same manner as in Example 1 except that powder was added.
[0057]
[Evaluation]
Using the cylindrical sealed batteries of Example 1 and Comparative Examples 1 and 2, their battery characteristics were evaluated.
Prior to the evaluation, a charge / discharge cycle in which the battery was charged at 130 ° C. for 15 hours at 20 ° C. and discharged to 1.0 V at a current of 260 mA was repeated. After the discharge capacity of the battery was stabilized, at 20 ° C., the battery was charged with a current of 1.3 A for 1.2 hours. At 20 ° C., the battery was discharged with a current of 1.3 A to a battery voltage of 0.8 V. The utilization rate A (at the time of charging at 20 ° C.) was calculated. In the next cycle, the battery was charged at 1.3 ° C. for 1.2 hours at 60 ° C., discharged at 1.3 ° C. at 20 ° C. to a battery voltage of 0.8 V, and activated from its discharge capacity. The utilization rate B of the substance (when charged at 60 ° C.) was calculated.
[0058]
The utilization was calculated as a ratio to the theoretical amount of electricity when nickel in the active material was assumed to undergo a one-electron reaction. Table 1 shows the results.
In Example 1, the battery using the cobalt oxide-coated nickel hydroxide containing yttrium was designated as (A), and the battery using the cobalt oxide-coated nickel hydroxide containing ytterbium, lutetium and calcium was similarly used. (B), (C) and (D). The batteries of Comparative Examples 1 and 2 were designated (E) and (F), respectively.
[0059]
[Table 1]

[0060]
As is clear from Table 1, the charging efficiency at high temperatures is significantly improved by forming a coating layer made of a cobalt oxide containing at least one selected from the group consisting of yttrium, ytterbium, lutetium and calcium. I understand. In addition, even when yttrium oxide was added to the electrode plate as in the battery (F), an improvement in charging efficiency was observed, but was inferior to the batteries (A) to (D) of the present invention. The oxygen overvoltage at the end of charging of the batteries (A) to (D) was about 30 mV higher than (E) and about 15 mV higher than (F).
[0061]
<< Example 2 >>
In the method for preparing a cobalt oxide coating layer described in <Step 2> of Example 1, the pH of the liquid in the reaction tank was adjusted to obtain samples having different sulfate groups in the cobalt oxide coating layer. The concentration was changed in the range of 11 to 13, and the ammonia concentration was changed in the range of 8 to 11 g / L. Otherwise in the same manner as in Example 1, a cobalt oxide-coated nickel hydroxide powder was produced.
[0062]
The content of sulfate groups in the coating layer of the obtained powder varied in the range of 0.3 to 1.3% by weight based on the total weight of the active material powder. Incidentally, nitrate was not detected in the same manner as in Example 1. In addition, the specific surface area and the tap density showed values that differed greatly depending on the powder, due to the difference in the sulfate content. In addition, the average valence of cobalt in the coating layer of these powders was 3.2 or more and 3.5 or less.
[0063]
FIG. 1 is a diagram showing the results of the experiment, and is a characteristic diagram showing the relationship among the sulfate content, the specific surface area, and the tap density. From this figure, it is understood that the sulfate group content is 0.8% by weight or less and the tap density is 1.8 g / cm. ³ And the specific surface area is 15m ² / G or less. Further, when the sulfate content is 0.5% by weight or less and the tap density is 1.9 g / cm. ³ And the specific surface area is 12m ² / G or less. Therefore, the content of sulfate in the active material powder is preferably 0.8% by weight or less, more preferably 0.5% by weight or less.
[0064]
The tap density has a correlation with the amount of active material powder that can be filled in the positive electrode. Tap density 1.8 g / cm ³ Above, preferably 1.9 g / cm ³ If not, the amount of the active material charged into the positive electrode decreases significantly, and the energy density of the positive electrode decreases. The specific surface area is 15 m ² / G or less, preferably 12 m ² / G or less, the life characteristics are significantly reduced. The specific surface area will be described in detail in Example 4.
[0065]
Here, the example in which the coating layer contains yttrium is shown, but also in the cobalt oxide-coated nickel hydroxide powder containing at least one selected from the group consisting of yttrium, ytterbium, lutetium and calcium other than the above, Similar results were observed.
[0066]
In addition, here, cobalt sulfate and yttrium sulfate were used as raw materials for the coating layer. When the amount was 0.8% by weight or less, more preferably 0.5% by weight or less based on the total weight of the active material powder, the same result as described above was observed. Also, when cobalt sulfate and yttrium nitrate or cobalt nitrate and yttrium sulfate are used, the total content of nitrate and sulfate is 0.8% by weight or less based on the total weight of the active material powder. When the content was less than 0.5% by weight, the same result as described above was observed.
[0067]
<< Example 3 >>
In the method for preparing a cobalt oxide coating layer described in <Step 2> of Example 1, the amount of the aqueous potassium hydroxide solution was set to 7 in order to obtain samples having different average valences of cobalt in the cobalt oxide coating layer. The oxidation time was varied in the range of 〜12 ml and the oxidation time in the range of 1-3 hours. The content of sulfate groups in the coating layer of the obtained powder was 0.35% by weight of the whole powder, and the average valence of cobalt varied in the range of 2.8 to 3.6. Furthermore, in powders in which the content of sulfate groups in the coating layer is 0.5% by weight, 0.8% by weight, and 0.92% by weight of the whole powder, samples having different average valences of cobalt are similarly obtained. Obtained. No nitrate was detected in any of the powders. These positive electrode active materials having different average valences of cobalt and cylindrical sealed batteries using them were produced, and their battery characteristics were evaluated.
[0068]
Prior to the evaluation, a charge / discharge cycle in which the battery was charged at 130 ° C. for 15 hours at 20 ° C. and discharged to 1.0 V at a current of 260 mA was repeated. After the discharge capacity of the battery was stabilized, at 20 ° C., the battery was charged with a current of 1.3 A for 1.2 hours. At 20 ° C., the battery was discharged with a current of 1.3 A to a battery voltage of 0.8 V. The utilization rate was calculated.
[0069]
FIG. 2 is a diagram showing the results of the experiment, and is a characteristic diagram showing the relationship between the average valence of cobalt in the cobalt oxide coating layer and the active material utilization. The results for powders with a sulfate content of 0.35%, 0.5%, 0.8% and 0.92% by weight in the cobalt coating layer are shown in graphs a, b, c and d, respectively. . From this figure, it can be seen that when the content of sulfate in the powder coating layer is 0.8% by weight or less of the whole powder, a high active material utilization rate is exhibited. It turns out that it improves. Therefore, it is preferable that the sulfate group content is 0.8% by weight or less and the average cobalt valence is 3.2 or more. When the average valence of cobalt is more than 3.5, the utilization tends to decrease, albeit slightly. Therefore, in order to improve the utilization rate, it is desirable that the valence is 3.2 or more and 3.5 or less.
[0070]
Here, the example in which the coating layer contains yttrium is shown, but also in the case of the cobalt oxide-coated nickel hydroxide powder containing at least one selected from the group consisting of yttrium, ytterbium, lutetium and calcium other than the above. And similar results were observed.
[0071]
<< Example 4 >>
In the method for producing a cobalt oxide coating layer described in <Step 2> of Example 1, the pH of the liquid in the reaction tank is in the range of 11.5 to 13.0 in order to obtain samples having different specific surface areas. Was changed. The BET specific surface area of the obtained powder measured by nitrogen gas adsorption is 4 to 17 m. ² / G range. The average valence of cobalt in the coating layer of these powders was 3.2 or more and 3.5 or less, and the content of sulfate in the coating layer was 1.0% by weight or less of the whole powder. Nitrate was not detected. Otherwise in the same manner as in Example 1, positive electrode active materials having different specific surface areas and cylindrical sealed batteries using them were produced, and their battery characteristics were evaluated.
[0072]
Prior to the evaluation, a charge / discharge cycle in which the battery was charged at 130 ° C. for 15 hours at 20 ° C. and discharged to 1.0 V at a current of 260 mA was repeated. After the discharge capacity of the battery was stabilized, the battery was charged at 1.3 ° C. for 1.2 hours at 20 ° C., and discharged at 1.3 ° C. to a battery voltage of 0.8 V at 20 ° C. 500 cycles were repeated, and the ratio of the active material utilization C at the 500th cycle to the active material utilization A at the first cycle: C / A was calculated as a percentage.
[0073]
FIG. 3 is a diagram showing the results of the experiment, and is a characteristic diagram showing the relationship between the specific surface area and the active material utilization ratio: C / A. From this figure, the specific surface area is 15m ² / G or less, further 12 m ² It can be seen that the utilization ratio C / A shows a high value below / g. The specific surface area is 5m ² When the ratio is less than / g, a tendency was observed that the utilization rate A was reduced to 90% or less. Therefore, in order to increase the life characteristics and the initial utilization rate, the BET specific surface area measured by nitrogen gas adsorption is 5 m ² / G or more 15m ² / G or less, and 5 m ² / G or more 12m ² / G or less.
[0074]
Here, the example in which the coating layer contains yttrium is shown, but also in the case of the cobalt oxide-coated nickel hydroxide powder containing at least one selected from the group consisting of yttrium, ytterbium, lutetium and calcium other than the above. And similar results were observed.
[0075]
<< Example 5 >>
In the method for producing a cobalt oxide coating layer described in <Step 2> of Example 1, the content of the cobalt oxide coating layer is set to 2 to 18 weight based on the weight of the entire cobalt oxide coated nickel hydroxide particles. %. The average valence of cobalt in the coating layer of these powders was 3.2 or more and 3.5 or less, and the content of sulfate in the coating layer was 0.8% by weight or less of the whole powder. Nitrate was not detected. Otherwise, in the same manner as in Example 1, positive electrode active materials having different cobalt oxide coating amounts and cylindrical sealed batteries using the same were produced, and their battery characteristics were evaluated.
[0076]
Prior to the evaluation, a charge / discharge cycle in which the battery was charged at 130 ° C. for 15 hours at 20 ° C. and discharged to 1.0 V at a current of 260 mA was repeated. After the discharge capacity of the battery was stabilized, at 20 ° C., the battery was charged with a current of 1.3 A for 1.2 hours. At 20 ° C., the battery was discharged with a current of 1.3 A to a battery voltage of 0.8 V. The utilization rate was calculated.
[0077]
FIG. 4 is a diagram showing the results of the experiment, and is a characteristic diagram showing a relationship between the content of the cobalt oxide coating layer and the utilization rate of the active material. From this figure, it can be seen that when the content of the coating layer is 3% by weight or more and 15% by weight or less, and further 5% by weight or more and 13% by weight or less, a high utilization factor is exhibited. Therefore, in order to further increase the utilization rate, the content of the cobalt oxide coating is preferably from 3% by weight to 15% by weight, more preferably from 5% by weight to 13% by weight of the whole powder.
[0078]
Here, the example in which the coating layer contains yttrium is shown, but also in the case of the cobalt oxide-coated nickel hydroxide powder containing at least one selected from the group consisting of yttrium, ytterbium, lutetium and calcium other than the above. And similar results were observed.
[0079]
<< Example 6 >>
In the method for producing a cobalt oxide coating layer according to <Step 2> of Example 1, the content of yttrium in the cobalt oxide coating layer is set to 0 to 25 mol% with respect to all metal elements in the coating layer. Range. The average valence of cobalt in the coating layer of these powders was 3.2 or more and 3.5 or less, and the content of sulfate in the coating layer was 0.8% by weight or less of the whole powder. Nitrate was not detected. Otherwise in the same manner as in Example 1, positive electrode active materials having different yttrium contents, and cylindrical sealed batteries using the same were produced, and their battery characteristics were evaluated.
[0080]
Prior to the evaluation, a charge / discharge cycle in which the battery was charged at a current of 130 mA for 15 hours at 20 ° C. and discharged to a voltage of 1.0 V at a current of 260 mA was repeated. After the discharge capacity of the battery was stabilized, at 20 ° C., the battery was charged with a current of 1.3 A for 1.2 hours. At 20 ° C., the battery was discharged with a current of 1.3 A to a battery voltage of 0.8 V. The utilization rate A (at the time of charging at 20 ° C.) was calculated. In the next cycle, the battery was charged at 1.3 ° C. for 1.2 hours at 60 ° C., discharged at 1.3 ° C. at 20 ° C. to a battery voltage of 0.8 V, and activated from its discharge capacity. The utilization rate B of the substance (when charged at 60 ° C.) was calculated.
[0081]
FIG. 5 is a diagram showing the results of the above-mentioned experiment, in which the content of yttrium with respect to all metal elements in the cobalt oxide coating layer, the utilization factor A at the time of charging at 20 ° C., and the utilization factor B at the time of charging at 60 ° C. FIG. 9 is a characteristic diagram showing a relationship with the graph. From this figure, it can be seen that when the yttrium content in the coating layer is 2 mol% or more, the utilization factor B at 60 ° C. charging shows a high value, and when the yttrium content in the coating layer is 20 mol% or less, the utilization factor A at 20 ° C. charging shows a high value. Understand. Therefore, in order to further increase the high-temperature charging efficiency and the utilization, it is preferable that the yttrium content in the coating layer is 2 mol% or more and 20 mol% or less, and more preferably 5 mol% or more and 15 mol% or less.
[0082]
Here, the example in which the coating layer contains yttrium is shown, but also in the case of the cobalt oxide-coated nickel hydroxide powder containing at least one selected from the group consisting of yttrium, ytterbium, lutetium and calcium other than the above. And similar results were observed.
[0083]
<< Example 7 >>
In the method for producing nickel hydroxide particles according to <Step 1> of Example 1, instead of a solid solution of nickel hydroxide containing cobalt and zinc, a solid solution of nickel hydroxide containing aluminum and nickel hydroxide containing magnesium Was prepared. Therefore, a mixed aqueous solution of nickel sulfate and aluminum nitrate and a mixed aqueous solution of nickel sulfate and magnesium sulfate were used here. The molar ratio of nickel sulfate to aluminum nitrate and the molar ratio of nickel sulfate to magnesium sulfate contained in the respective mixed aqueous solutions were 90 mol%: 10 mol%, respectively.
[0084]
As a result of composition analysis and X-ray diffraction measurement, it was confirmed that the obtained powders were a solid solution of nickel hydroxide containing 10 mol% of aluminum and a solid solution of nickel hydroxide containing 10 mol% of magnesium, respectively. Was. The average valence of cobalt in the coating layer of these powders is not less than 3.2 and not more than 3.5, and the total content of sulfate and nitrate in the coating layer is 0.8% by weight of the whole powder. % Or less. Otherwise in the same manner as in Example 1, a cobalt oxide-coated nickel hydroxide powder was produced, and a nickel positive electrode and a cylindrical sealed battery using the same were produced.
[0085]
<< Embodiment 8 >>
In the method for producing nickel hydroxide particles described in <Step 1> of Example 1, a solid solution of nickel hydroxide containing manganese was produced instead of a solid solution of nickel hydroxide containing cobalt and zinc. Therefore, a mixed aqueous solution of nickel sulfate and manganese sulfate was used here. The molar ratio of nickel sulfate to manganese sulfate contained in the mixed aqueous solution was 90 mol%: 10 mol%.
[0086]
In a solid solution of manganese-containing nickel hydroxide, it is necessary to control the valence of manganese in order to improve the tap density and the utilization factor. Therefore, in the crystal growth process, nitrogen gas was continuously supplied into the reaction tank to suppress oxidation of manganese due to dissolved oxygen, thereby promoting crystal growth and improving the tap density. Further, in the process of drying the powder, in order to promote the oxidation of manganese in the nickel hydroxide, the powder was oxidized at 90 ° C. for 2 days in an air atmosphere.
[0087]
As a result of a composition analysis and an X-ray diffraction measurement, it was confirmed that the obtained powder was a solid solution of nickel hydroxide containing 10 mol% of manganese. The average valence of manganese was 3.4. The average valence of cobalt in the coating layer was 3.2 or more and 3.5 or less, and the content of sulfate groups in the coating layer was 0.8% by weight or less of the whole powder. Nitrate was not detected. Otherwise in the same manner as in Example 1, a cobalt oxide-coated nickel hydroxide powder was produced, and a nickel positive electrode and a cylindrical sealed battery using the same were produced.
[0088]
<< Comparative Example 3 >>
In the method for producing nickel hydroxide particles described in <Step 1> of Example 1, a solid solution of nickel hydroxide containing 10 mol% of aluminum or magnesium was produced in the same manner as in Example 7.
Next, in the method for preparing a cobalt oxide coating layer described in <Step 2> of Example 1, pure solid cobalt hydroxide was coated on the solid solution powder without containing a dissimilar metal element such as yttrium. Quality treated. Otherwise in the same manner as in Example 1, a cobalt oxide-coated nickel hydroxide powder was produced, and a nickel positive electrode and a cylindrical sealed battery using the same were produced.
[0089]
<< Comparative Example 4 >>
In the method for producing nickel hydroxide particles described in <Step 1> of Example 1, a solid solution of nickel hydroxide containing 10 mol% of manganese was produced in the same manner as in Example 8.
Next, in the method for manufacturing a cobalt oxide coating layer described in <Step 2> of Example 1, pure cobalt hydroxide was coated without containing a dissimilar metal element such as yttrium, and then modified. . Otherwise in the same manner as in Example 1, a cobalt oxide-coated nickel hydroxide powder was produced, and a nickel positive electrode and a cylindrical sealed battery using the same were produced.
[0090]
Using the cylindrical sealed batteries of Examples 7 and 8, and Comparative Examples 3 and 4, their battery characteristics were evaluated.
Prior to the evaluation, a charge / discharge cycle in which the battery was charged at a current of 130 mA for 15 hours at 20 ° C. and discharged to a voltage of 1.0 V at a current of 260 mA was repeated. After the discharge capacity of the battery was stabilized, at 20 ° C., the battery was charged with a current of 1.3 A for 1.2 hours. At 20 ° C., the battery was discharged with a current of 1.3 A to a battery voltage of 0.8 V. The utilization rate A (at the time of charging at 20 ° C.) and the average discharge voltage were calculated. In the next cycle, the battery was charged at 1.3 ° C. for 1.2 hours at 60 ° C., discharged at 1.3 ° C. at 20 ° C. to a battery voltage of 0.8 V, and activated from its discharge capacity. The utilization rate B of the substance (when charged at 60 ° C.) was calculated. The utilization rate was calculated with respect to the theoretical amount of electricity when nickel in the active material reacted with one electron. Table 2 shows the results.
[0091]
In Example 1, the battery using the solid solution of nickel hydroxide containing cobalt and zinc was (A), the battery using the solid solution of nickel hydroxide containing aluminum in Example 7 was (B), and the battery contained magnesium. The battery using the solid solution of nickel hydroxide was designated as (C), and the battery using the solid solution of nickel hydroxide containing manganese of Example 8 was designated as (D). The battery using the solid solution of nickel hydroxide containing aluminum of Comparative Example 3 was (E), the battery using the solid solution of nickel hydroxide containing magnesium was (F), and the battery of Comparative Example 4 was (G). did.
[0092]
[Table 2]

[0093]
From the results of the batteries (E) and (F) in Table 2, the solid solution of nickel hydroxide containing aluminum and magnesium was more discharged than the battery (A) using a solid solution of nickel hydroxide containing cobalt and zinc. The voltage is significantly improved. However, on the other hand, it can be seen that the high-temperature charging efficiency is extremely low. This is because a solid solution of nickel hydroxide containing aluminum or magnesium has a high electrode potential, so that not only the discharge voltage but also the charging voltage increases.
[0094]
Therefore, by forming a coating layer made of a cobalt oxide containing yttrium as in the batteries (B) and (C), the charging efficiency at a high temperature can be significantly improved. Further, it can be seen that the battery (G) using a solid solution of nickel hydroxide containing manganese has a low discharge voltage, but significantly improves the utilization rate of the active material. Further, by forming a coating layer made of a cobalt oxide containing yttrium as in the battery (D), it is possible to significantly improve the active material utilization at a high temperature.
[0095]
Here, the example in which the coating layer contains yttrium is shown, but also in the case of the cobalt oxide-coated nickel hydroxide powder containing at least one selected from the group consisting of yttrium, ytterbium, lutetium and calcium other than the above. And similar results were observed.
Similar results were also observed in a solid solution of nickel hydroxide containing two or more of cobalt, zinc, manganese, aluminum and magnesium.
[0096]
Further, the amount of at least one element selected from the group consisting of cobalt and zinc, the amount of at least one element selected from the group consisting of aluminum and magnesium, or the amount of manganese in the solid solution of nickel hydroxide is: Similar results were observed in the range of 0.5 mol% to 20 mol% of all metal elements contained in the solid solution of nickel hydroxide.
[0097]
【The invention's effect】
As described above, according to the present invention, a positive electrode active material for an alkaline storage battery having excellent active material utilization, high-temperature charging efficiency, excellent life characteristics, and excellent filling properties to a substrate, and nickel using the same. A positive electrode and an alkaline storage battery can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship among a sulfate group content, a specific surface area, and a tap density of a positive electrode active material according to an example of the present invention.
FIG. 2 is a view showing a relationship between an average valence of cobalt in a cobalt oxide coating layer of a positive electrode active material and an active material utilization rate according to an example of the present invention.
FIG. 3 is a view showing a relationship between a specific surface area of a positive electrode active material and an active material utilization ratio: C / A according to an example of the present invention.
FIG. 4 is a diagram showing the relationship between the content of a cobalt oxide coating layer of a positive electrode active material and the utilization rate of an active material according to an example of the present invention.
FIG. 5 shows the relationship between the yttrium content in the cobalt oxide coating layer of the positive electrode active material according to the example of the present invention, the active material utilization A during normal temperature charging, and the active material utilization B during high temperature charging. FIG.

Claims (13)

A positive electrode active material for an alkaline storage battery comprising a powder,
The powder comprises particles made of nickel hydroxide, and a coating layer disposed on the surface of the particles,
The coating layer is made of cobalt oxide,
It said coating layer comprises further, yttrium, ytterbium, an element M ¹ of at least one selected from the group consisting of lutetium and calcium,
The coating layer further contains a sulfate group and / or a nitrate group,
The total content of the sulfate and nitrate in the powder is 0.8% by weight or less;
A positive electrode active material for an alkaline storage battery, wherein the average valence of cobalt contained in the cobalt oxide is 3.2 or more and 3.5 or less. The tap density of the powder, the positive electrode active material for an alkaline storage battery according to claim 1, wherein at 1.8 g / cm ³ or more. BET specific surface area of the powder as measured by adsorption of nitrogen gas, the positive electrode active material for an alkaline storage battery according to claim 1, wherein at most 5 m 2 / ^g or more 15 m 2 / ^g. The positive electrode active material for an alkaline storage battery according to claim 1, wherein the content of the coating layer in the powder is 3% by weight or more and 15% by weight or less. 2. The positive electrode active material for an alkaline storage battery according to claim ¹ , wherein a ratio of the element M1 is 2 mol% or more and 20 mol% or less of all metal elements contained in the coating layer. The composed of nickel hydroxide particles, cobalt and at least one of claims 1 positive electrode active material for an alkaline storage battery according composed of a solid solution of nickel hydroxide containing an element M ² selected from the group consisting of zinc. All of the metal elements, the proportion of the element M ² is a positive electrode active material for an alkaline storage battery according to claim 6, wherein at most 20 mol% to 0.5 mol% included in particles composed of the nickel hydroxide. The positive electrode active material for an alkaline storage battery according to claim 1, wherein the particles made of nickel hydroxide are made of a solid solution of nickel hydroxide containing at least manganese. The positive electrode active material for an alkaline storage battery according to claim 8, wherein the ratio of the manganese is 0.5 mol% or more and 20 mol% or less in the total amount of the manganese and nickel contained in the particles made of nickel hydroxide. The composed of nickel hydroxide particles, the positive electrode active material for an alkaline storage battery according to claim 1, wherein comprising a solid solution of nickel hydroxide containing at least one element M ³ selected from the group consisting of at least magnesium and aluminum. All of the metal elements, the proportion of the element M ³ is a positive electrode active material for an alkaline storage battery according to claim 10, wherein at most 20 mol% to 0.5 mol% included in particles composed of the nickel hydroxide. A positive electrode for an alkaline storage battery, comprising the active material according to claim 1. An alkaline storage battery comprising the positive electrode, the negative electrode, a separator, and an alkaline electrolyte according to claim 12.

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