JP4321997B2 - Positive electrode active material for alkaline storage battery, and positive electrode and alkaline storage battery using the same - Google Patents

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】
《参考例２》
参考例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。それ以外は参考例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、硝酸根は参考例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／ｃｍ³以上となり、比表面積が１５ｍ²／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／ｃｍ³以上となり、比表面積が１２ｍ²／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／ｃｍ³以上、好ましくは１．９ｇ／ｃｍ³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、１５ｍ²／ｇ以下、好ましくは１２ｍ²／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参考例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】
《参考例３》
参考例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】
《参考例４》
参考例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、４〜１７ｍ²／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。それ以外は参考例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１５ｍ²／ｇ以下、さらには１２ｍ²／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５ｍ²／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、５ｍ²／ｇ以上１５ｍ²／ｇ以下、さらには５ｍ²／ｇ以上１２ｍ²／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】
《参考例５》
参考例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。それ以外は参考例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】
《参考例６》
参考例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。それ以外は参考例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】
《参考例７》
参考例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。それ以外は参考例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１》
参考例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。それ以外は参考例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》
参考例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、参考例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、参考例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。それ以外は参考例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》
参考例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１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、参考例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。それ以外は参考例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】
参考例７、実施例１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、参考例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）、参考例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１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】 本発明の参考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】 本発明の参考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】 本発明の参考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】 本発明の参考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】 本発明の参考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]
BACKGROUND 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]
In recent years, the capacity density of a positive electrode for an alkaline storage battery has been dramatically improved by improving the substrate shape, active material particle shape, active material composition, additives, and the like.
The positive electrode for alkaline storage battery is roughly classified into two types, a sintered type and a non-sintered type (paste type). In the former, 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 an aqueous nickel nitrate solution, followed by an alkaline aqueous solution. Thus, nickel hydroxide is deposited in 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 into a foamed nickel substrate having a porosity of about 95% having three-dimensionally continuous voids. Widely used as a positive electrode for alkaline storage batteries.
[0004]
For the nickel hydroxide particles used for the positive electrode, spherical high-density nickel hydroxide particles are employed in order to improve the filling properties of the electrode. Further, in order to improve charge / discharge characteristics and life characteristics, it is common to use a solid solution of nickel hydroxide containing a metal element such as cobalt, zinc, or cadmium. In recent years, a solid solution of nickel hydroxide containing manganese or the like has been proposed with the aim of further increasing the capacity, or a solid solution of nickel hydroxide containing magnesium or the like with the aim of increasing the output.
[0005]
As the conductive material filled in the foamed nickel substrate together with the nickel hydroxide particles, bivalent cobalt oxides such as metallic cobalt, cobalt hydroxide, and cobalt monoxide are employed. These are electrochemically oxidized to cobalt oxyhydroxide having conductivity in the initial charge, and this functions as a conductive network that connects the nickel hydroxide particles and the substrate skeleton. With this conductive network, it is possible to supplement the conductivity and current collection of the non-sintered positive electrode and increase the utilization rate of the active material. Furthermore, as a method for uniformly dispersing the conductive network in the positive electrode, particles obtained by previously coating the surface of nickel hydroxide particles with cobalt oxide have been proposed. Thereby, the current collecting property is improved and the utilization factor of the active material can be further improved.
[0006]
However, since the above-described conductive network uses an electrochemical cobalt oxidation reaction 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 among the batteries tends to vary.
[0007]
In recent years, as a means for improving the imperfection of such a conductive network, a technique has been proposed in which cobalt oxyhydroxide obtained by subjecting cobalt oxide to a chemical oxidation treatment in advance is used as a conductive material. Japanese Patent Application Laid-Open No. 11-97008 discloses a high-order cobalt oxide whose main component is γ-cobalt oxyhydroxide whose average valence is greater than trivalent, and solid solution particles whose main component is nickel hydroxide. A non-sintered positive electrode active material and an alkaline storage battery have been proposed. Furthermore, the same report also proposed a technique in which a coating layer made of a higher cobalt oxide containing γ-cobalt oxyhydroxide as a main component is arranged on the surface of solid solution particles containing nickel hydroxide as a main component. Yes.
[0008]
By the way, as one of the problems of alkaline storage batteries, there is a problem of a decrease in charge acceptability at high temperatures (a decrease in utilization rate). This is because, at the end of charging, the overvoltage of the oxygen gas generation reaction that occurs competitively with the oxidation reaction (charging) of the positive electrode nickel hydroxide significantly decreases at high temperatures, so that the oxygen gas generation reaction proceeds remarkably. This is because the oxidation reaction of nickel is suppressed. In order to solve such a problem of charging at a high temperature, many proposals have been made so far for increasing the oxygen generation overvoltage of the positive electrode and improving the charge acceptability.
[0009]
For example, in Japanese Patent Application Laid-Open No. 5-28992, a compound such as yttrium, indium, antimony, barium, calcium, and beryllium, that is, a material that is effective in increasing the oxygen generation overvoltage is added to the surface of the active material particles or between the particles. It has been proposed.
[0010]
Further, in JP-A-10-21909, the surface of nickel hydroxide particles is coated with a eutectic of yttrium hydroxide and cobalt hydroxide, so that the use of a high active material not only at the initial stage of the charge / discharge cycle but also for a long period of time. It is disclosed to express the rate.
[0011]
Japanese Patent Application Laid-Open No. 11-260360 discloses that utilization efficiency and charging efficiency at high temperatures can be improved by coating at least part of the surface of nickel hydroxide particles with a cobalt compound layer containing ytterbium. Yes.
[0012]
In JP-A-2001-185137, the surface of nickel hydroxide particles is coated with a mixed crystal of cobalt with at least one element selected from aluminum, manganese, iron, yttrium, ytterbium, erbium, and gadolinium. By using an active material that has an average valence of nickel in nickel hydroxide in the range of 2 to 2.3 and a valence of cobalt in the mixed crystal exceeds 3, It is also disclosed that the utilization rate can be improved.
[0013]
[Problems to be solved by the invention]
However, the technique disclosed in Japanese Patent Application Laid-Open No. 5-28992 and the like has a problem in that the additive effective for increasing the oxygen generation overvoltage is likely to aggregate in the positive electrode, and the effect according to the amount added is not necessarily obtained. There is.
[0014]
In addition, in the cobalt hydroxide-coated nickel hydroxide particles disclosed in the above-mentioned JP-A-10-21909, JP-A-11-260360, etc., when a different element is contained in the cobalt hydroxide coating layer, There is a problem that electrochemical and chemical oxidation is easily inhibited, oxidation of cobalt is suppressed, conductivity between active materials in the positive electrode is lowered, and sufficient utilization cannot be obtained.
[0015]
This is because the inclusion of trivalent elements such as yttrium and ytterbium facilitates the incorporation of anions such as sulfate ions and nitrate ions into the crystal to maintain electrical neutrality, thereby inhibiting proton diffusion. It is considered that the oxidation of cobalt is suppressed. In addition, the inclusion of different elements with different ionic radii from cobalt and the inclusion of sulfate and nitrate radicals suppresses the crystal growth of the cobalt hydroxide coating layer, increasing the specific surface area and decreasing the bulk density (fillability). There is also a problem that it is easy to invite a decrease in As a result, the electrolytic solution moves into the positive electrode, and the cycle life characteristics are likely to deteriorate.
[0016]
On the other hand, Japanese Patent Laid-Open No. 2001-185137 proposes to improve the conductivity by increasing the valence of cobalt to more than 3, but it is sufficient to simply increase the valence of cobalt to more than 3. The utilization rate cannot be obtained.
[0017]
[Means for Solving the Problems]
As a result of investigations by the present inventors, the cobalt valence of the cobalt oxide coating layer containing a different metal is cobalt in the cobalt oxide coating layer described in JP-A-2001-185137 (higher than trivalent). It is clear that the higher-order range is optimal compared to, and the utilization rate is specifically improved in this range. And in order to acquire such a peculiar effect, it became clear that it is necessary to optimize the amount of sulfate radicals and nitrate radicals contained in an 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 made of powder, wherein 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, and the coating layer is further at least one element M selected from the group consisting of yttrium, ytterbium, lutetium, and calcium.¹And the coating layer further includes 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 included in the cobalt oxide. It is related with the positive electrode active material for alkaline storage batteries whose average valence of cobalt is 3.2 or more and 3.5 or less.
[0019]
The tap density of the powder is 1.8 g / cm.^ThreeThe above is preferable.
The powder has a BET specific surface area of 5 m as measured by nitrogen gas adsorption.²/ G or more 15m²/ G or less is preferable.
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 M¹The ratio is preferably 2 mol% or more and 20 mol% or less.
[0020]
  in frontThe particles made of nickel hydroxide consist of a solid solution of nickel hydroxide containing at least manganese.The
  Of the total amount of manganese and nickel contained in the particles made of nickel hydroxide, the manganese ratio is preferably 0.5 mol% or more and 20 mol% or less.
[0021]
  BookThe invention also relates to an alkaline storage battery comprising the above active material, and an alkaline storage battery comprising 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.¹Is uniformly contained in the coating layer, the oxygen generation overvoltage can be increased efficiently, and the charging efficiency at a high temperature can be improved. In addition, by reducing the total amount of sulfate and nitrate radicals in the coating layer to 0.8% by weight or less, it is possible to promote the oxidation of cobalt, improve the conductive performance of the conductive network, Improvements can be made. Furthermore, by limiting (reducing) the sulfate and nitrate content, crystal growth is also promoted, the specific surface area can be reduced, the bulk density can be improved, the electrode fillability 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 3.2 or more and 3.5 or less, the dissimilar metal (element M¹In the cobalt coating layer containing), the conductivity can be remarkably increased, and a high utilization factor required for the alkaline storage battery can be derived.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a positive electrode active material for alkaline storage batteries made of 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, and the coating layer is at least one element M selected from the group consisting of yttrium, ytterbium, lutetium, and calcium.¹Is included.
[0024]
Element M¹In the cobalt oxide coating layer, oxygen generation overvoltage at the end of charging is dramatically increased, and charging efficiency at high temperature can be remarkably improved. With this technique, the oxygen generation overvoltage increases dramatically because the element M¹Is considered to be due to the uniform distribution in the cobalt oxide coating layer, which is the charging reaction field. On the other hand, as described in Japanese Patent Application Laid-Open No. 5-28992, simply adding an yttrium compound, a calcium compound, or the like to the positive electrode may not be sufficient in improving the charging efficiency because the dispersibility of these elements is low. It turns out.
[0025]
Element M¹As a method of uniformly containing the cobalt oxide coating layer, the following method using a reaction crystallization method is preferable.
(1) Cobalt and element M in the presence of nickel hydroxide particles¹An aqueous solution containing a salt of the above and an aqueous alkaline solution are reacted to precipitate (eutectic) hydroxides 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 method and element M¹And the resulting mixture is oxidized in an alkaline aqueous solution, whereby the element M¹Is diffused into the cobalt oxide coating layer.
[0026]
Cobalt salt and element M used in the above method¹These salts are preferably selected from sulfates and nitrates because of their relatively high solubility in aqueous solutions.
However, when these salts are used, when the cobalt oxide is precipitated on the surface of the nickel hydroxide particles, the sulfate group and / or the nitrate group is easily taken into the cobalt oxide crystal and / or into the pores. There is a problem. That is, yttrium, ytterbium, lutetium and calcium salts have lower solubility compared to cobalt salts, and are trivalent salts compared to normal, because cobalt is divalent. A large amount of sulfate and nitrate radicals are incorporated into the active material.
[0027]
However, element M, which has a different ion radius from cobalt¹In addition, if the sulfate radical and nitrate radical are contained in a large amount, the crystal growth of the cobalt hydroxide coating layer is suppressed, and it becomes easy to increase the specific surface area and the bulk density of the active material. The filling property to the lowers. In addition, the sulfate group and the nitrate group have problems that the oxidation reaction of the cobalt oxide layer is inhibited or the conductivity is lowered. 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 radicals and nitrate radicals in the powder must be 0.8% by weight or less, It has been found that 0.5 wt% or less is preferred.
[0028]
In order to suppress the total content of sulfate radicals and nitrate radicals in the powder to 0.8% by weight or less, compared to the prior art, (1) the pH of the liquid in the reaction tank during the reaction crystallization is increased ( (Conventional: pH 10.5 to 11.5), (2) Increase the ammonia concentration of the liquid in the reaction tank (Conventional: Ammonia concentration 7 to 9 g / L), (3) Increase 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 reaction crystallization is 11.6 to 13.0, or the ammonia concentration of the liquid in the reaction tank is 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 redox reaction (that is, the valence does not change). There is a problem that the conductivity is lower than that of a 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 studies by the present inventors, it has been found that the conductivity of the active material is dramatically improved by setting the average valence of cobalt to 3.2 or more. Thereby, the utilization factor of the active material can be improved. However, when the average valence of cobalt is greater than 3.5, the utilization factor of the active material tends to decrease. Although the details of the cause are unknown, the electrical balance in the cobalt oxide crystal is not maintained, and the crystallinity is lowered, thereby inhibiting proton diffusion in the cobalt oxide crystal. It is thought to do. Furthermore, due to the decrease in crystallinity as described above, the cobalt oxide coating layer is easily peeled off, current collection performance 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 for oxidizing the cobalt oxide coating layer, a method of performing oxidation with an oxidizing agent or air oxidation in the presence of an aqueous alkaline solution is preferable.
Further, as a method for increasing the average valence of cobalt, compared to the conventional method, (1) the concentration of the aqueous alkali solution added to the powder is increased (conventional: 35 wt% or more and less than 45 wt%), (2) the powder (3) Increase the air oxidation time of cobalt (conventional: less than 1 hour), (4) Increase the air oxidation temperature (conventional: 7-9 ml / 100 g of powder) Conventional methods: 100 ° C. or higher and lower than 110 ° C.) are effective.
For example, in the present invention, the concentration of the alkaline aqueous solution added to the powder is 45 to 48% by weight, the amount of the alkaline aqueous solution is 9.1 to 12 ml / 100 g of 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 of improving utilization by making the cobalt average valence 3.2 or more and 3.5 or less is that the total amount of sulfate radicals and / or nitrate radicals contained in the coating layer is the same as that of the powder. It cannot be obtained unless the content is 0.8% by weight or less. As described above, when many sulfate groups and nitrate groups are present in the powder, the conductivity of the cobalt oxide layer is remarkably decreased, and the effect of improving the utilization rate is extremely decreased.
[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.^ThreeThe above is preferable. Tap density is 1.8g / cm^ThreeWhen smaller, the active material filling amount in the positive electrode is lowered, and the capacity of the positive electrode is lowered. Therefore, the tap density is 1.8 g / cm.^ThreeAbove, further 1.9 g / cm^ThreeThe above is preferable. As mentioned above, the element M¹Nickel hydroxide particles coated with cobalt oxide containing copper tend to be low in bulk density, but the bulk density is prevented by suppressing the total content of sulfate and / or nitrate in the cobalt coating layer. it can.
[0034]
The BET specific surface area measured by adsorption of nitrogen gas of the active material powder is 5 m.²/ G or more 15m²/ G or less is preferable. BET specific surface area is 5m²If it is smaller than / g, the effective area of the solid-liquid interface, which is the charge / discharge reaction field, is too small, so that the polarization increases and the utilization factor of the active material decreases. Also, the BET specific surface area is 15m²When it is larger than / g, the electrolytic solution in the separator and the negative electrode moves into the positive electrode, and the cycle life characteristics are likely to deteriorate. Therefore, the specific surface area is 5m.²/ G or more 15m²/ G or less, and 5m²/ G or more 12m²/ G or less is preferable. As mentioned above, the element M¹The nickel hydroxide particles coated with cobalt oxide containing sulfite tend to have a large BET specific surface area, but the BET specific surface area is increased by suppressing the total content of sulfate and / or nitrate radicals in the cobalt coating layer. 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 cobalt oxide is coated on the surface of the nickel hydroxide particles, 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. When the content is more than 15% by weight, the coating layer is likely to be peeled off. descend. Moreover, when there is too much content of a coating layer, since content of nickel hydroxide in a positive electrode falls, sufficient battery capacity cannot be obtained. Therefore, the content of the coating layer made of cobalt oxide is preferably 3% by weight to 15% by weight, and more preferably 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 layer¹Is preferably 2 mol% or more and 20 mol% or less of the total metal elements in the coating layer. Element M¹If the ratio is less than 2 mol%, the oxygen generation overvoltage hardly rises, so the effect of improving the high-temperature charging efficiency is poor. On the other hand, element M¹If the ratio is more than 20 mol%, the conductivity of the coating layer is lowered and the utilization rate is lowered even if the content of sulfate radicals and nitrate radicals and the average valence of cobalt are controlled as described above. Therefore, the element M in the coating layer¹Is 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 are at least one element M selected from the group consisting of cobalt and zinc.²It is preferably made of a solid solution of nickel hydroxide containing. By including cobalt in nickel hydroxide, the charging voltage can be reduced and the charge acceptability can be improved. Moreover, by making zinc hydroxide contain zinc, the production | generation of (gamma) phase at the time of overcharge can be suppressed, and the swelling of a positive electrode can be suppressed.
[0038]
Of all the metal elements contained in the particles made of nickel hydroxide, the element M²The ratio is preferably 0.5 mol% or more and 20 mol% or less. Element M²If the ratio is less than 0.5 mol%, a sufficient effect cannot be obtained, and if it exceeds 20 mol%, the amount of nickel in the nickel hydroxide involved in the reaction decreases, so that a sufficient battery can be obtained. The capacity cannot be obtained.
[0039]
  The particles made of nickel hydroxide are made of a solid solution of nickel hydroxide containing at least manganese.TheBy 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 active material utilization rate can be improved and the capacity can be dramatically increased. In order to further increase the capacity, it is preferable that the valence of manganese is 3.2 or more. Thereby, the active material utilization factor can be significantly improved.
  Inclusion of manganese in nickel hydroxide significantly reduces the charging voltage. Therefore, by applying the above-described technique that can significantly increase the oxygen generation overvoltage, it is possible to achieve a dramatic improvement in charging efficiency that has not been achieved in the past.
[0040]
Of the total amount of manganese and nickel contained in the particles made of nickel hydroxide, the proportion of manganese 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 exceeds 20 mol%, the amount of nickel in the nickel hydroxide involved in the reaction decreases, Battery capacity cannot be obtained.
[0041]
The particles made of nickel hydroxide are at least one element M selected from the group consisting of magnesium and aluminum.^ThreeIt is preferably made of a solid solution of nickel hydroxide containing. Magnesium and aluminum can raise the discharge voltage and can greatly improve the output characteristics. However, since not only the discharge voltage but also the charging voltage rises remarkably, there is a problem that the high-temperature charging efficiency is inferior. Therefore, by applying the above-described technique that can significantly increase 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 particles made of nickel hydroxide, the element M^ThreeThe ratio is preferably 0.5 mol% or more and 20 mol% or less. Element M^ThreeIf the ratio is less than 0.5 mol%, a sufficient effect cannot be obtained, and if it exceeds 20 mol%, the amount of nickel in the nickel hydroxide involved in the reaction is reduced, so that 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.
《referenceExample 1
<Step 1: Preparation of nickel hydroxide>
  Prepare mixed aqueous solution containing nickel sulfate, cobalt sulfate and zinc sulfate, sodium hydroxide aqueous solution and ammonia aqueous solution, and supply them continuously into the reactor maintained at 40 ° C at a flow rate of 0.5 ml / min. did. Here, the concentration of the sulfate in the mixed aqueous solution containing nickel sulfate, cobalt sulfate and zinc sulfate was 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 tank becomes constant at 11.8, and the balance between the metal salt concentration and the metal hydroxide particle concentration in the liquid in the reaction tank becomes constant. The resulting 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, then washed with water and dried.
[0045]
As a result of conducting composition analysis and X-ray diffraction measurement of the obtained particles, it was confirmed that the particles were a solid solution of nickel hydroxide containing 2 mol% cobalt and 4 mol% zinc.
[0046]
<Step 2: Preparation of cobalt oxide coating layer>
Subsequently, the nickel hydroxide particles obtained above were put into a mixed aqueous solution containing cobalt sulfate, yttrium sulfate and ammonia, and an aqueous sodium hydroxide solution and an aqueous ammonia solution were continuously added to adjust the pH to 12 at 40 ° C. 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 of the total weight of the cobalt oxide-coated nickel hydroxide particles. Moreover, about the yttrium content, it adjusted so that the ratio of yttrium might be 15 mol% among the total mole number of cobalt and yttrium in a coating layer. The ammonia concentration of the liquid in the reaction tank was adjusted to 10 g / L in a steady state. Moreover, the oxidation of cobalt by dissolved oxygen was suppressed by blowing nitrogen gas into the liquid in the reaction vessel.
[0048]
Since 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, the above synthesis conditions are higher pH and higher ammonia than conventional. The concentration is set. Thereby, it is possible to suppress the sulfate radical content to the whole powder obtained to 0.8 weight% or less. Thereafter, the suspension in the reaction vessel 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, then washed with water and dried. In this way, a powder having an average particle diameter of 10 μm having a coating layer made of cobalt hydroxide was obtained.
[0049]
As a result of conducting composition analysis and transmission electron microscope (TEM) observation of the obtained powder, the proportion of yttrium in the total amount of cobalt and yttrium in the coating layer was 15 mol%. Moreover, content of the coating layer which consists of cobalt hydroxide was 10 weight% of the whole powder. As a result of the compositional analysis, the sulfate radical content in the cobalt hydroxide coating layer was 0.35% by weight of the total powder. Nitrate radicals were not detected by composition analysis. Here, the sulfate radical 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. The following calculation was performed in the same manner.
[0050]
In addition, although the preparation method of the cobalt hydroxide coating powder containing yttrium was shown here, the cobalt hydroxide coating powder containing ytterbium, lutetium, and calcium was produced similarly, respectively. 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 radicals and nitrate radicals was in the range of 0.3 to 0.5% by weight of the total weight of the active material powder.
[0051]
Next, the modification | reformation process of the said yttrium containing cobalt hydroxide coating nickel hydroxide powder was performed in the following procedures. First, 10 ml of 45% by weight potassium hydroxide aqueous solution was added to 100 g of the same powder, and this was maintained at a temperature of 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 surface of the particles was oxidized, and the particles changed to indigo color. The obtained powder was washed with water and then vacuum-dried. In addition, the addition amount of the conventional potassium hydroxide aqueous solution is in the range of 7 to 9 ml with respect to 100 g of the powder, and the conventional oxidation time is about 1 hour. The amount of the potassium hydroxide aqueous solution is large, and the oxidation time is set long. Thereby, it was possible to make the average valence of cobalt 3.2 or more.
[0052]
When 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 that value, it showed 3.4.
Here, a high-concentration potassium hydroxide aqueous solution was used as the solution added to the powder, but even if a high-concentration sodium hydroxide aqueous solution was used, the average valence of cobalt in the coating layer was 3.2 valences. The above values were shown.
The cobalt oxide-coated nickel hydroxide powder obtained as described above is a spherical powder having an average particle size of 10 μm and a tap density of 2.0 g / cm.^ThreeThe BET specific surface area measured by nitrogen gas adsorption is 8 m.²/ G.
The cobalt hydroxide-coated powder containing ytterbium, lutetium, or calcium instead of yttrium was modified in the same manner, 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 production conditions, and kneaded to obtain a paste. This paste was filled in a foamed nickel substrate having a porosity of 95%, dried and then pressure-molded to obtain a nickel positive electrode plate. The positive electrode plate thus obtained was cut, and the electrode lead was 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 has a one-electron reaction.
[0054]
<Step 4: Preparation of alkaline storage battery>
A known alkaline storage battery negative electrode was used as the negative electrode. Here, hydrogen storage alloy MmNi with an average particle size of 30 μm_3.55Co_0.75Mn_0.4Al_0.3A negative electrode made of powder was used. Water and a binder carboxymethylcellulose were added thereto and kneaded into a paste. This paste was pressure filled into the electrode support to obtain a hydrogen storage alloy negative electrode plate. This negative electrode plate was cut into a negative electrode having a capacity of 2000 mAh. A spiral electrode group was formed with the positive electrode and the negative electrode interposed between separators made of a sulfonated polypropylene nonwoven fabric having a thickness of 0.15 mm. After inserting this electrode group into the battery case and injecting 2.2 ml of a 7 mol / l potassium hydroxide aqueous solution, 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, AA-sized cylindrical sealed nickel-metal hydride storage batteries were produced.
[0055]
<< Comparative Example 1 >>
  referenceIn the method for producing a cobalt oxide coating layer described in Example 1, except that pure cobalt hydroxide was coated without containing a different metal element such as yttrium, and then the powder was modified,referenceIn 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 >>
  referenceIn the method for producing a cobalt oxide coating layer described in Example 1, except that pure cobalt hydroxide was coated without containing a different metal element such as yttrium, and then the powder was modified,referenceA positive electrode active material was produced in the same manner as in Example 1. When preparing the nickel positive electrode paste, in addition to 100 g of the active material powder and 26 g of water, 1.5 g of yttrium oxide (Y₂O_Three) Other than adding powder,referenceIn the same manner as in Example 1, a nickel positive electrode and a cylindrical sealed battery using the same were manufactured.
[0057]
[Evaluation]
  referenceUsing the cylindrical sealed batteries of Example 1 and Comparative Examples 1 and 2, their battery characteristics were evaluated.
  Prior to the evaluation, at 20 ° C., the battery was charged with a current of 130 mA for 15 hours, and a charge / discharge cycle in which the battery was discharged to 1.0 V with a current of 260 mA was repeated. After the discharge capacity of the battery is stabilized, the battery is charged with a current of 1.3 A for 1.2 hours at 20 ° C., and discharged at 20 ° C. with a current of 1.3 A to a battery voltage of 0.8 V. Utilization rate A (at 20 ° C. charging) was calculated. In the next cycle, at 60 ° C., the battery is charged with a current of 1.3 A for 1.2 hours, and at 20 ° C., the battery is discharged to a battery voltage of 0.8 V with a current of 1.3 A. Substance utilization rate B (at 60 ° C. charge) was calculated.
[0058]
  The utilization factor was calculated as a ratio with respect to the theoretical electric quantity when nickel in the active material was supposed to react with one electron. Table 1 shows the results.
  In addition,referenceIn Example 1, a battery using cobalt oxide-coated nickel hydroxide containing yttrium was designated as (A), and similarly, a battery using cobalt oxide-coated nickel hydroxide containing ytterbium, lutetium and calcium (B ), (C) and (D). The batteries of Comparative Examples 1 and 2 were designated as (E) and (F), respectively.
[0059]
[Table 1]

[0060]
As is apparent from Table 1, charging efficiency at high temperatures is significantly improved by forming a coating layer made of cobalt oxide containing at least one selected from the group consisting of yttrium, ytterbium, lutetium and calcium. I understand. In addition, even if yttrium oxide was added to the electrode plate as in the battery (F), the charging efficiency was improved, but it was inferior to the batteries (A) to (D) of the present invention. The oxygen generation 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]
《referenceExample 2
  referenceIn the method for producing a cobalt oxide coating layer described in <Step 2> of Example 1, the pH of the liquid in the reaction vessel was adjusted to 11 for the purpose of obtaining samples having different sulfate radical contents in the cobalt oxide coating layer. The ammonia concentration was changed within a range of 8 to 11 g / L. Other than thatreferenceIn the same manner as in Example 1, a cobalt oxide-coated nickel hydroxide powder was produced.
[0062]
  The sulfate radical content in the coating layer of the obtained powder varied in the range of 0.3 to 1.3% by weight of the total weight of the active material powder. The nitrate radical isreferenceIt was not detected as in Example 1. Moreover, the specific surface area and the tap density differed greatly depending on the powder due to the difference in sulfate group content. The average cobalt valence in the coating layer of these powders was 3.2 or more and 3.5 or less.
[0063]
FIG. 1 is a characteristic diagram showing the relationship between the sulfate radical content, the specific surface area, and the tap density. From this figure, the sulfate radical content is 0.8% by weight or less and the tap density is 1.8 g / cm.^ThreeThe specific surface area is 15m²/ G or less. Furthermore, the sulfate radical content is 0.5% by weight or less and the tap density is 1.9 g / cm.^ThreeThe specific surface area is 12m²/ G or less. Therefore, the sulfate radical content 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 correlates with the amount of active material powder that can be filled in the positive electrode. Tap density is 1.8g / cm^ThreeOr more, preferably 1.9 g / cm^ThreeOtherwise, the amount of active material charged into the positive electrode is significantly reduced, and the positive electrode energy density is reduced. The specific surface area is 15m.²/ G or less, preferably 12 m²If it is not less than / g, the life characteristics are remarkably deteriorated. For specific surface areareferenceExample 4 will be described in detail.
[0065]
Here, although the example in which the coating layer contains yttrium was shown, 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]
Here, cobalt sulfate and yttrium sulfate were used as the raw material for the coating layer. However, even when cobalt oxide-coated powders having different nitrate radical contents were prepared using cobalt nitrate, yttrium nitrate, etc., the nitrate radical contained When the amount was 0.8% by weight or less, further 0.5% by weight or less of the total weight of the active material powder, the same result as above was observed. Even when cobalt sulfate and yttrium nitrate, or cobalt nitrate and yttrium sulfate are used, the total content of nitrate and sulfate radicals is 0.8% by weight or less based on the total weight of the active material powder, and further 0 In the case of less than 5% by weight, the same result as above was observed.
[0067]
《referenceExample 3
  referenceIn the method for producing a cobalt oxide coating layer described in <Step 2> of Example 1, the amount of the potassium hydroxide aqueous solution is set to 7 to 7 for the purpose of obtaining samples having different cobalt average valences in the cobalt oxide coating layer. The oxidation time was changed in the range of 12 ml and the oxidation time in the range of 1 to 3 hours. The sulfate radical content 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, samples having different cobalt average valences were similarly applied to powders having a sulfate content in the coating layer of 0.5%, 0.8% and 0.92% by weight. Obtained. Nitrate radicals were not 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, at 20 ° C., the battery was charged with a current of 130 mA for 15 hours, and a charge / discharge cycle in which the battery was discharged to 1.0 V with a current of 260 mA was repeated. After the discharge capacity of the battery is stabilized, the battery is charged with a current of 1.3 A for 1.2 hours at 20 ° C., and discharged at 20 ° C. with a current of 1.3 A to a battery voltage of 0.8 V. Utilization rate was calculated.
[0069]
FIG. 2 is a characteristic diagram showing the relationship between the average valence of cobalt in the cobalt oxide coating layer and the active material utilization rate, showing the results of the experiment. The results for powders having a sulfate radical content of 0.35 wt%, 0.5 wt%, 0.8 wt% and 0.92 wt% in the cobalt coating layer are shown in graphs a, b, c and d, respectively. . From this figure, when the sulfate radical content in the powder coating layer is 0.8% by weight or less of the whole powder, it shows a high active material utilization rate. It turns out that it improves. Therefore, it is preferable that the sulfate group content is 0.8% by weight or less and the cobalt average valence is 3.2 or more. Further, when the cobalt average valence is larger than 3.5, the utilization rate tends to decrease slightly. Therefore, in order to improve the utilization rate, it is desirable that the valence is 3.2 to 3.5.
[0070]
In addition, although the example in which the coating layer contains yttrium is shown here, 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.
[0071]
《referenceExample 4
  referenceIn the method for producing a cobalt oxide coating layer described in <Step 2> of Example 1, the pH of the liquid in the reaction vessel is set in the range of 11.5 to 13.0 for the purpose of obtaining samples having different specific surface areas. Changed. The BET specific surface area measured by nitrogen gas adsorption of the obtained powder is 4 to 17 m.²/ G in the range. In addition, the cobalt average valence in the coating layer of these powders was 3.2 or more and 3.5 or less, and the sulfate radical content in the coating layer was 1.0% by weight or less of the whole powder. Nitrate radicals were not detected. Other than thatreferenceIn 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, at 20 ° C., the battery was charged with a current of 130 mA for 15 hours, and a charge / discharge cycle in which the battery was discharged to 1.0 V with a current of 260 mA was repeated. After the discharge capacity of the battery is stabilized, the battery is charged at a current of 1.3 A for 1.2 hours at 20 ° C., and discharged to a battery voltage of 0.8 V at a current of 1.3 A at 20 ° C. Repeated 500 cycles, the ratio of the active material utilization rate C of the 500th cycle to the active material utilization rate A of the first cycle: C / A was calculated as a percentage.
[0073]
FIG. 3 is a characteristic diagram showing the relationship between the specific surface area and the active material utilization ratio: C / A, showing the results of the experiment. From this figure, the specific surface area is 15m.²/ G or less, or 12m²/ G or less, it turns out that utilization factor ratio C / A shows a high value. The specific surface area is 5m²When it was smaller than / g, a tendency that the utilization factor A decreased to 90% or less was observed. 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 15m²/ G or less, and 5m²/ G or more 12m²/ G or less is preferable.
[0074]
In addition, although the example in which the coating layer contains yttrium is shown here, 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.
[0075]
《referenceExample 5
  referenceIn 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 2 to 18% by weight with respect to the total weight of the cobalt oxide-coated nickel hydroxide particles. The range was changed. In addition, the cobalt average valence in the coating layer of these powders was 3.2 or more and 3.5 or less, and the sulfate radical content in the coating layer was 0.8% by weight or less of the whole powder. Nitrate radicals were not detected. Other than thatreferenceIn 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, at 20 ° C., the battery was charged with a current of 130 mA for 15 hours, and a charge / discharge cycle in which the battery was discharged to 1.0 V with a current of 260 mA was repeated. After the discharge capacity of the battery is stabilized, the battery is charged with a current of 1.3 A for 1.2 hours at 20 ° C., and discharged at 20 ° C. with a current of 1.3 A to a battery voltage of 0.8 V. Utilization rate was calculated.
[0077]
FIG. 4 is a characteristic diagram showing the relationship between the content of the cobalt oxide coating layer and the active material utilization rate, showing the results of the experiment. From this figure, it can be seen that 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 shows a high utilization factor. Therefore, in order to further increase the utilization rate, the content of the cobalt oxide coating is preferably 3% by weight to 15% by weight, more preferably 5% by weight to 13% by weight of the entire powder.
[0078]
In addition, although the example in which the coating layer contains yttrium is shown here, 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.
[0079]
《referenceExample 6
  referenceIn the method for producing a cobalt oxide coating layer described in <Step 2> of Example 1, the yttrium content in the cobalt oxide coating layer is in the range of 0 to 25 mol% with respect to all the metal elements in the coating layer. It was changed with. In addition, the cobalt average valence in the coating layer of these powders was 3.2 or more and 3.5 or less, and the sulfate radical content in the coating layer was 0.8% by weight or less of the whole powder. Nitrate radicals were not detected. Other than thatreferenceIn 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, at 20 ° C., the battery was charged with a current of 130 mA for 15 hours, and a charge / discharge cycle in which the battery was discharged to 1.0 V with a current of 260 mA was repeated. After the discharge capacity of the battery is stabilized, the battery is charged with a current of 1.3 A for 1.2 hours at 20 ° C., and discharged at 20 ° C. with a current of 1.3 A to a battery voltage of 0.8 V. Utilization rate A (at 20 ° C. charging) was calculated. In the next cycle, at 60 ° C., the battery is charged with a current of 1.3 A for 1.2 hours, and at 20 ° C., the battery is discharged to a battery voltage of 0.8 V with a current of 1.3 A. Substance utilization rate B (at 60 ° C. charge) was calculated.
[0081]
FIG. 5 is a diagram showing the results of the experiment, in which the yttrium content with respect to all the metal elements in the cobalt oxide coating layer, the utilization rate A at 20 ° C. charging, and the utilization rate B at 60 ° C. charging. It is a characteristic view which shows the relationship. From this figure, when the yttrium content in the coating layer is 2 mol% or more, the utilization rate B at 60 ° C. is high, and when it is 20 mol% or less, the utilization rate A at 20 ° C. is high. Recognize. Therefore, in order to further increase the high-temperature charging efficiency and utilization rate, the yttrium content in the coating layer is preferably 2 mol% or more and 20 mol% or less, and more preferably 5 mol% or more and 15 mol% or less.
[0082]
In addition, although the example in which the coating layer contains yttrium is shown here, 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.
[0083]
《referenceExample 7
  referenceIn the method for producing nickel hydroxide particles described in <Step 1> of Example 1, instead of the solid solution of nickel hydroxide containing cobalt and zinc, a solid solution of nickel hydroxide containing aluminum and nickel hydroxide containing magnesium A solid solution was prepared. Therefore, here, a mixed aqueous solution of nickel sulfate and aluminum nitrate and a mixed aqueous solution of nickel sulfate and magnesium sulfate were used. The molar ratio of nickel sulfate and aluminum nitrate and the molar ratio of nickel sulfate and magnesium sulfate contained in each mixed aqueous solution were 90 mol%: 10 mol%, respectively.
[0084]
  As a result of conducting composition analysis and X-ray diffraction measurement, it was confirmed that the obtained powder was a solid solution of nickel hydroxide containing 10 mol% of aluminum and a solid solution of nickel hydroxide containing 10 mol% of magnesium. It was. The average cobalt valence in the coating layer of these powders is 3.2 or more and 3.5 or less, and the total content of sulfate radicals and nitrate radicals contained in the coating layer is 0.8 weight of the whole powder. % Or less. Other than thatreferenceIn 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]
"Example1》
  referenceIn 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 the solid solution of nickel hydroxide containing cobalt and zinc. Therefore, here, a mixed aqueous solution of nickel sulfate and manganese sulfate was used. The molar ratio of nickel sulfate to manganese sulfate contained in the mixed aqueous solution was 90 mol%: 10 mol%.
[0086]
The solid solution of nickel hydroxide containing manganese needs to control the valence of manganese in order to improve the tap density and the utilization rate. Therefore, in the crystal growth process, nitrogen gas was continuously supplied into the reaction vessel to suppress oxidation of manganese by dissolved oxygen, thereby promoting crystal growth and improving the tap density. Furthermore, in the drying process of the powder, oxidation treatment was performed at 90 ° C. for 2 days in an air atmosphere in order to promote oxidation of manganese in nickel hydroxide.
[0087]
  As a result of conducting composition analysis and X-ray diffraction measurement, it was confirmed that the obtained powder was a solid solution of nickel hydroxide containing 10 mol% of manganese. Moreover, the average valence of manganese was 3.4. The cobalt average valence in the coating layer was 3.2 or more and 3.5 or less, and the sulfate radical content contained in the coating layer was 0.8% by weight or less of the entire powder. Nitrate radicals were not detected. Other than thatreferenceIn 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 >>
  referenceIn the method for producing nickel hydroxide particles described in <Step 1> of Example 1,referenceIn the same manner as in Example 7, a solid solution of nickel hydroxide containing 10 mol% of aluminum or magnesium was prepared.
  ThenreferenceIn the method for producing a cobalt oxide coating layer described in <Step 2> of Example 1, pure cobalt hydroxide was coated on a solid solution powder without containing a different metal element such as yttrium, and then modified. . Other than thatreferenceIn 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 >>
  referenceIn the method for producing nickel hydroxide particles described in <Step 1> of Example 1,1Similarly, a solid solution of nickel hydroxide containing 10 mol% of manganese was produced.
  ThenreferenceIn the method for producing a cobalt oxide coating layer described in <Step 2> of Example 1, pure cobalt hydroxide was coated without containing a foreign metal element such as yttrium, and then a modification treatment was performed. Other than thatreferenceIn 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]
  referenceExample 7, Example1The cylindrical sealed batteries of Comparative Examples 3 and 4 were used, and their battery characteristics were evaluated.
  Prior to the evaluation, at 20 ° C., the battery was charged with a current of 130 mA for 15 hours, and a charge / discharge cycle in which the battery was discharged to 1.0 V with a current of 260 mA was repeated. After the discharge capacity of the battery is stabilized, the battery is charged with a current of 1.3 A for 1.2 hours at 20 ° C., and discharged at 20 ° C. with a current of 1.3 A to a battery voltage of 0.8 V. Utilization rate A (at 20 ° C. charge) and average discharge voltage were calculated. In the next cycle, at 60 ° C., the battery is charged with a current of 1.3 A for 1.2 hours, and at 20 ° C., the battery is discharged to a battery voltage of 0.8 V with a current of 1.3 A. Substance utilization rate B (at 60 ° C. charge) was calculated. In addition, the utilization factor 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 addition,referenceIn Example 1, a battery using a solid solution of nickel hydroxide containing cobalt and zinc (A),referenceA battery using a solid solution of nickel hydroxide containing aluminum in Example 7 (B), a battery using a solid solution of nickel hydroxide containing magnesium (C), Example1A battery using a solid solution of nickel hydroxide containing manganese was designated as (D). In addition, the battery using the solid solution of nickel hydroxide containing aluminum of Comparative Example 3 is (E), the battery using the solid solution of nickel hydroxide containing Magnesium is (F), and the battery of Comparative Example 4 is (G). did.
[0092]
[Table 2]

[0093]
From the results of batteries (E) and (F) in Table 2, the solid solution of nickel hydroxide containing aluminum and magnesium was discharged in comparison with the battery (A) using the 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, which increases not only the discharge voltage but also the charge voltage.
[0094]
Therefore, by forming a coating layer made of cobalt oxide containing yttrium as in the batteries (B) and (C), it is possible to remarkably improve charging efficiency at high temperatures. In addition, the battery (G) using a solid solution of nickel hydroxide containing manganese has a low discharge voltage, but the active material utilization rate is significantly improved. Further, by forming a coating layer made of cobalt oxide containing yttrium as in the battery (D), the active material utilization at high temperatures can be remarkably improved.
[0095]
In addition, although the example in which the coating layer contains yttrium is shown here, 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.
Moreover, the same result was recognized also in the solid solution of nickel hydroxide containing 2 or more types of elements among cobalt, zinc, manganese, aluminum, and magnesium.
[0096]
Further, the amount of at least one element selected from the group consisting of cobalt and zinc in the solid solution of nickel hydroxide, the amount of at least one element selected from the group consisting of aluminum and magnesium, or the amount of manganese, Similar results were observed in the range of 0.5 mol% or more and 20 mol% or less 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, the positive electrode active material for an alkaline storage battery having excellent active material utilization, high-temperature charging efficiency, 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 of the present inventionreferenceIt is a figure which shows the relationship between the sulfate radical content of the positive electrode active material concerning an example, a specific surface area, and a tap density.
FIG. 2 of the present inventionreferenceIt is a figure which shows the relationship between the cobalt average valence in the cobalt oxide coating layer of the positive electrode active material concerning an example, and an active material utilization factor.
FIG. 3 of the present inventionreferenceIt is a figure which shows the relationship between the specific surface area of the positive electrode active material concerning an example, and active material utilization ratio: C / A.
FIG. 4 of the present inventionreferenceIt is a figure which shows the relationship between content of the cobalt oxide coating layer of the positive electrode active material concerning an example, and an active material utilization factor.
FIG. 5 of the present inventionreferenceIt is a figure which shows the relationship between the yttrium content in the cobalt oxide coating layer of the positive electrode active material concerning an example, the active material utilization factor A at the time of normal temperature charge, and the active material utilization factor B at the time of high temperature charge.

Claims (8)

A positive electrode active material for alkaline storage batteries made of 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;
The coating layer further includes at least one element M ¹ selected from the group consisting of yttrium, ytterbium, lutetium, and calcium;
The coating layer further includes a sulfate group and / or a nitrate group,
The total content of the sulfate and nitrate radicals in the powder is 0.8% by weight or less,
Average valence of cobalt contained in said cobalt oxide state, and are 3.2 or more valences 3.5 valence less,
The composed of nickel hydroxide particles, the positive electrode active material for Na Ru alkaline storage battery of a solid solution of nickel hydroxide containing at least manganese. The positive electrode active material for an alkaline storage battery according to claim 1, wherein the powder has a tap density of 1.8 g / cm ³ or more. ^{2. The} positive electrode active material for an alkaline storage battery according to claim 1, wherein the powder has a BET specific surface area of 5 m ² / g or more and 15 m ² / g or less as measured by adsorption of nitrogen gas.   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 wt% or more and 15 wt% or less. 2. The positive electrode active material for an alkaline storage battery according to claim ¹ , wherein a ratio of the element M ¹ is 2 mol% or more and 20 mol% or less among all metal elements contained in the coating layer. Wherein of the total amount of manganese and nickel, the ratio of the manganese, the positive electrode active material for an alkaline storage battery according to claim 1, wherein at most 20 mol% to 0.5 mol% included in particles composed of the nickel hydroxide. The positive electrode for alkaline storage batteries containing the active material in any one of Claims 1-6 . An alkaline storage battery comprising the positive electrode according to claim 7 , a negative electrode, a separator, and an alkaline electrolyte.

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