JP3744316B2

JP3744316B2 - Positive electrode active material for alkaline storage battery, nickel positive electrode, and alkaline storage battery

Info

Publication number: JP3744316B2
Application number: JP2000181104A
Authority: JP
Inventors: 弘之坂本; 秀勝泉; 徹稲垣; 陽一和泉
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2000-06-16
Filing date: 2000-06-16
Publication date: 2006-02-08
Anticipated expiration: 2020-06-16
Also published as: JP2001357844A

Description

【０００１】
【発明の従属する技術分野】
本発明はアルカリ蓄電池、特にアルカリ蓄電池用正極活物質に関する。
【０００２】
【従来の技術】
近年、アルカリ蓄電池用正極は、基板形状、活物質形状、活物質組成および添加物などの改良により、容量密度が飛躍的に向上し、現在では容量密度６００ｍＡｈ／ｃｃ程度の正極が実用化されている。
【０００３】
しかしながら、機器側からは一層の高出力化が求められ、高率放電時のエネルギー密度の向上が強く求められている。高率放電特性の向上を図るためには、従来から、電極の集電性を高める方法（または、抵抗を下げる方法）や活物質の充放電効率を高める方法が検討されてきた。これに対して、放電電位そのものを高い方向（貴な方向）へシフトさせることができれば、飛躍的な高出力化が期待できる。我々は、これまでに異種金属を固溶させることで水酸化ニッケルの改質を図ってきた。そのなかで、マグネシウムを固溶した水酸化ニッケルは放電電位が高いことに注目し、電極材料としての物性の適正化を検討してきた。
【０００４】
このマグネシウムを固溶した水酸化ニッケルに関しては、従来から広く提案されており、以下のようなものがある。
【０００５】
（１）特開平２−１０９２６１号公報では、マグネシウムを１〜３重量％固溶させた水酸化ニッケルにおいて、内部細孔半径が３０Å以下で、全細孔容積が０．０５ｍｌ／ｇ以下であるものを正極活物質とすることが提案されている。これは、水酸化ニッケル粉末をより高密度化し、更に、マグネシウムの添加によってγ−ＮｉＯＯＨの生成を防止することで長寿命化するとともに、活物質の利用率を向上させたニッケル電極用活物質を提供することを目的とするものである。
【０００６】
（２）特開平５−２１０６４号公報では、正極作成時にマグネシウム等を１〜７重量％水酸化ニッケル粉末中に含有させ、球状または球状に類似した粒子と非球状粒子との混合物からなるものを正極活物質とすることが提案されている。これは、水酸化ニッケルの充填密度を向上させ、かつ、マグネシウムを含む異種金属群を添加することで、過充電時にγ−ＮｉＯＯＨの生成を抑制しサイクル寿命特性を向上させることを目的とするものである。
【０００７】
（３）特開平５−４１２１２号公報では、マグネシウム等を１〜７重量％水酸化ニッケル粉末中に含有させ、０．１μｍ以下の一次粒子が無数に集合した粒子であり、３０Å以上の細孔半径を有する空間体積が全空間体積に対して２０〜７０％である水酸化ニッケルを正極活物質とすることが提案されている。これは、電解液の粒子内部への浸入を容易にすることで、電解液の粒子内部での偏在によるγ−ＮｉＯＯＨの生成を抑制し、更に、充放電初期の活物質利用率を向上させることを目的とするものである。なお、マグネシウムを含む異種金属群の添加は、前記（２）の提案と同様に、γ−ＮｉＯＯＨの生成を抑制しサイクル寿命特性を向上させることを目的とするものである。
【０００８】
（４）特開平５−１８２６６２号公報では、内部細孔容積が０．１４ｍｌ／ｇ以下で、結晶格子が添加元素により一部置換された組織を有する水酸化ニッケル粉末を正極活物質とすることが提案されている。特に、水酸化ニッケルに固溶添加元素としては、活物質としての水酸化ニッケルの特性を損なう物であってはならないという条件から、Ｚｎ、Ｍｇ、Ｃｄ、Ｂａが選ばれる。これは、内部細孔容積が小さい高密度水酸化ニッケル粉末において、マグネシウムを含む異種元素でニッケルの一部を置換することによって、水酸化ニッケル結晶格子に格子欠陥を形成し、プロトン移動の自由度を増加させることで、γ−ＮｉＯＯＨの生成を抑制しサイクル寿命特性を向上させることを目的とするものである。
【０００９】
（５）特開平５−１８２６６３号公報では、内部細孔容積が０．１４ｍｌ／ｇで、結晶格子がＣｏ及びその他の添加元素により複合的に一部置換された組織を有する水酸化ニッケルを正極活物質とすることが提案されている。とくに、水酸化ニッケルに固溶される添加元素としては、Ｚｎ、Ｍｇ、Ｃｄ、Ｂａが選ばれる。これは、Ｃｏ及びその他のマグネシウムを含む異種元素でニッケルの一部を置換することによって、高温における充電効率を向上させ、同時に、γ−ＮｉＯＯＨの生成を抑制しサイクル寿命特性を向上させることを目的としている。
【００１０】
【発明が解決しようとする課題】
しかしながら、上記の提案は、いずれも充放電効率の向上、寿命特性の向上を狙いとしており、本発明者らのようにマグネシウムを固溶状態で含む水酸化ニッケルの高い放電電位を利用して、一層の高出力化を図ることを目的としたものではなかった。事実、上記提案に基づいて電池を試作したところ、目標とする満足な高出力な電池を得ることはできなかった。また、高率充放電特性も満足のいくものではなかった。
【００１１】
従って、本発明は、放電電圧が高く、かつ、高率充放電時に高い利用率を発現する（高率放電特性の優れた）アルカリ蓄電池用活物質およびニッケル正極並びにそれを用いたアルカリ蓄電池を提供することを目的とする。
【００１２】
【発明を解決するための手段】
本発明者らが鋭意検討した結果、マグネシウムを固溶状態で含む水酸化ニッケルは高率放電時に利用率が低下しやすいことを見出した。この原因として、マグネシウムを固溶することで、水酸化ニッケルの結晶内に硫酸根が取り込まれやすくなると共に、マグネシウム固溶水酸化ニッケルの結晶構造が乱れやすくなり、高率放電時の分極が大きくなるとともに、導電性も著しく低下するため、高率放電特性が著しく低下するものと考えている。尚、結晶が乱れる（結晶性が低くなる）ことによって高率放電時の分極が大きくなる現象は、プロトン移動の自由度が低下するためと考えている。上記提案では、このような課題を改善する技術は開示されておらず、従って、高出力化のための活物質およびニッケル正極を得ることができなかったものと考えられる。
【００１３】
この観点より、本発明者らの目的を達成すべく、本発明のマグネシウムを固溶した水酸化ニッケルからなるアルカリ蓄電池用正極活物質は、第１にマグネシウムの含有割合を水酸化ニッケル中の全金属元素に対して２モル％以上７モル％以下とし、第２に粉末のタップ密度を１．９ｇ／ｃｍ³以上とし、第３にＣｕＫα線を使用するＸ線回折の２θ＝３７〜４０゜付近に位置する（１０１）面のピークの半価幅が０．７以上１．２以下の範囲となるようにし、第４に結晶内に含まれる硫酸根が０．５重量％以下となるようにしたものである。
【００１４】
まず、水酸化ニッケルに固溶する異種元素として選択すると、放電電位が高くなるため高出力な電池を得るには好ましい。但し、マグネシウムの含有量が２モル％より少ないと放電電位が高くなる効果が乏しく、逆に７モル％より多い場合は低率放電時においても利用率が低下するとともに、活物質である水酸化ニッケルの量が少なくなるため十分な電池容量が得られなくなる。
【００１５】
水酸化ニッケルに固溶する異種元素としてマグネシウムを選択し、その含有量を２〜７モル％とするのみでは、目的とする高出力な正極は得られず、以下のように水酸化ニッケルの諸物性を適正化することで尚一層の飛躍的な高出力化を達成することができる。
【００１６】
タップ密度としては１．９ｇ／ｃｍ³以上が好ましく、さらに、２．１ｇ／ｃｍ³以上であると特に好ましい。これは、１．９ｇ／ｃｍ³より小さい場合では電極への充填密度が低下し高エネルギー密度化を図ることが困難であるとともに、異種固溶元素がマグネシウムで、硫酸根が結晶内に取り込まれやすいことから、活物質粉末の空隙が硫酸根との間で何らかの原因として関与しているものと考えられる。
【００１７】
ＣｕＫα線を使用するＸ線回折の２θ＝３７〜４０゜付近に位置する（１０１）面のピークの半価幅が０．７以上１．２以下であることが望ましい。この数値範囲にあると、多少の硫酸根では結晶構造が乱れにくくなり、従ってプロトン移動の自由度が低下することがない。
【００１８】
また、結晶内に含まれる硫酸根は０．５重量％以下であることが望ましい。特定のピークの半価幅が特定の値になるように水酸化ニッケルを作製しても、硫酸根が多すぎると、サイクルに伴い結晶構造が乱れてしまうからである。従って、上記結晶構造の適正化によりあまりに低い値を求める必要はないものの、通常、マグネシウム固溶の水酸化ニッケルを合成した場合の硫酸根量よりもわずかに低い値に設定するとよい。
【００１９】
なお、マグネシウムを固溶状態で含む水酸化ニッケルにおいて、結晶が乱れる（結晶性が低くなる）ことによって高率放電時の分極が大きくなる現象は、プロトン移動の自由度が低下するためと考えている。
【００２０】
この本発明の正極活物質を用いて、アルカリ蓄電池を構成すると、放電電圧の向上、高率放電特性の向上を図ることができる。
【００２１】
【発明の実施の形態】
また、本発明の水酸化ニッケルは、さらに、ＣｕＫα線を使用するＸ線回折の２θ＝３７〜４０゜付近に位置する（１０１）面のピークＡに対する、２θ＝１８〜２１゜付近に位置する（００１）面のピーク強度Ｂの比Ｂ／Ａが１．１以上であると望ましい。ピーク強度比Ｂ／Ａが１．１より大きい場合、すなわち、水酸化ニッケルの結晶におけるＣ軸方向の配向性が高い場合、高率放電時の分極を更に抑制することができ、高率放電特性を一層向上させることができる。これは、結晶において結晶面方向の結晶成長が優れており結晶面方向の結晶の均一性を示すものであり、結晶の乱れが少なくプロトン移動の自由度が一層向上したものと考えている。
【００２２】
さらに、本発明の水酸化ニッケルは、マグネシウム以外に、コバルト、マンガンからなる群より選ばれた少なくとも１種の元素を固溶していることが望ましい。前記金属元素を固溶することで、放電末期の放電効率を向上させる（深くまで放電する）ことができ、低率放電時の利用率を向上させる効果がある。これは、コバルト、マンガンといった元素が２価より高い価数になりやすいことで、放電末期においても高い価数のままで存在することから、放電末期のプロトン移動の自由度が高まるためと考えている。
【００２３】
また、コバルト、マンガンからなる群より選ばれた少なくとも１種の固溶元素の含有割合は、水酸化ニッケル中の全金属元素に対して０．５モル％以上３モル％以下が好ましい。０．５モル％より少ないと前記効果が小さくなり、また、３モル％より多いと放電電圧が低下することでマグネシウムの効果が打ち消されてしまう。
【００２４】
また、本発明の水酸化ニッケルは、コバルト酸化物により、その表面が被覆されていると好ましい。これにより、導電材としてのコバルト化合物の分布が均一になり導電性が向上することから、導電材の充填量を減らすことが可能となる。また、導電性の向上により、高率放電特性を一層向上させることができる。
【００２５】
前記コバルト酸化物のコバルトの平均価数は３価より大きいことが好ましい。これにより、コバルト化合物の導電性が著しく向上し、高率放電特性を一層向上させることができる。
【００２６】
【実施例】
次に、本発明の実施例を説明する。
【００２７】
（実施例１）
まず、活物質粒子の合成方法について説明する。
【００２８】
硫酸ニッケルと硫酸マグネシウムを含む混合水溶液、水酸化ナトリウム水溶液、アンモニア水溶液を準備し、４０℃に保持された反応装置内に、それぞれ０．５ｍｌ／ｍｉｎの流量で連続的に供給した。ここで、硫酸ニッケルと硫酸マグネシウムからなる混合水溶液の濃度を２．４ｍｏｌ／ｌとし、そのうち硫酸ニッケルと硫酸マグネシウムの混合比を、ニッケルとマグネシウムの総モル数に対するマグネシウムのモル数が０．５〜１０モル％の範囲になるようにした。また、アンモニア水溶液の濃度は５ｍｏｌ／ｌとし、水酸化ナトリウム水溶液の濃度は５ｍｏｌ／ｌとした。
【００２９】
続いて、反応装置内のｐＨが一定となり、金属塩濃度と金属水酸化物粒子濃度のバランスが一定となり、定常状態になったところで、オーバーフローにて得られた懸濁液を採取し、デカンテーションにより沈殿物を分離した。これをｐＨ１３〜１４の水酸化ナトリウム水溶液でアルカリ処理し、金属水酸化物粒子中の硫酸イオン等のアニオンを除去し、水洗し、乾燥した。このようにして、平均粒径１０μｍの粉末を得た。なお、前記ｐＨ１３〜１４の水酸化ナトリウム水溶液でアルカリ処理を行う時間や回数により、金属水酸化物中の硫酸イオン（硫酸根）含有量をコントロールすることができる。とくに、マグネシウムを固溶した水酸化ニッケルは硫酸根が取り込まれやすいため、温度を高温（６０℃）とし、処理を行う回数を多くする（３回以上）ことで、硫酸根量の含有量が少なくなるようにした。
【００３０】
組成分析を実施した結果、得られた金属水酸化物中のマグネシウム固溶量は、合成に用いた水溶液の混合比と同様に、０．５〜１０モル％であった。また、硫酸根量は０．３±０．０１重量％の範囲であった。また、ＣｕＫα線を用いたＸ線回折パターンを記録したところ、いずれもβ−Ｎｉ（ＯＨ）₂型の単相であることが確かめられ、マグネシウムは水酸化ニッケルに固溶していることが確認された。また、２θ＝３７〜４０゜付近の（１０１）面のピーク半価幅は０．９±０．０２ｄｅｇ．であった。また、タップ密度を測定したところ、いずれも１．９ｇ／ｃｍ³以上を示し、高エネルギー密度化のために適した材料（電極支持体への充填性に優れた材料）であることが確かめられた。
【００３１】
次に、上記方法にて得られた活物質を用いたニッケル正極の作製方法について説明する。
【００３２】
上記のような製造条件で得られた金属水酸化物粉末１００ｇに、１０ｇの水酸化コバルト粉末、３０ｇの水を加え、混練してペースト状にした。このペーストを多孔度９５％の発泡ニッケル基板に充填し、乾燥後、加圧成形することによって、ニッケル正極板を得た。このようにして得られた正極板を切断し、電極リードをスポット溶接し、理論容量１２００ｍＡｈのニッケル正極を得た。ただし、ここで示すニッケル電極の容量密度は、活物質中のニッケルが一電子反応をするものとして計算したものである。
【００３３】
次に、アルカリ蓄電池の作製方法について説明する。
【００３４】
負極には、公知のアルカリ蓄電池用負極を用いた。ここでは、約３０μｍの水素吸蔵合金ＭｍＮｉ_3.55Ｃｏ_0.75Ｍｎ_0.4Ａｌ_0.3粉末からなる負極を用いた。これに水と結着剤のカルボキシメチルセルロースを加えてペースト状に混練した。このペーストを電極支持体に加圧充填して、水素吸蔵合金負極板を得た。この負極板を切断し、容量１９２０ｍＡｈの負極とした。前記の正極と負極を厚さ０．１５ｍｍのスルフォン化ポリプロピレン不織布からなるセパレータを間に介して渦巻状の電極群を構成した。この電極群を電池ケース内に挿入し、７ｍｏｌ／ｌの水酸化カリウム水溶液を２．２ｍｌ注入した後、作動弁圧約２．０ＭＰａの安全弁を持つ封口板により電池ケースの開口部を密閉し、ＡＡサイズの円筒密閉型ニッケル水素蓄電池を作製した。
【００３５】
マグネシウムの固溶量の異なるサンプルを正極活物質とし、上記方法にて円筒密閉電池を作製し、それらの電池特性を評価した。２０℃において、１２０ｍＡの電流で１５時間充電し、２４０ｍＡの電流で電池電圧１．０Ｖまで放電する充放電サイクルを繰り返し、放電容量が安定した後、平均放電電圧と活物質の利用率を算出した。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。
【００３６】
図１は、これらの実験の結果を表す図であって、マグネシウム固溶量に対する利用率と平均放電電圧との関係を示す特性図である。この図から、マグネシウム固溶量が２モル％以上で平均放電電圧が顕著に上昇する傾向があることがわかる。また、マグネシウム固溶量が７モル％より多くなると利用率が低下する傾向があることがわかる。従って、マグネシウム固溶量としては、２モル％以上７モル％以下が適切であると考えられる。
【００３７】
（実施例２）
実施例１に記載の活物質粒子合成条件において、硫酸ニッケルと硫酸マグネシウムからなる混合水溶液中の硫酸ニッケルと硫酸マグネシウムの混合比を、ニッケルとマグネシウムの総モル数に対するマグネシウムのモル数が５モル％となるようにした。また、結晶性の異なるサンプルを得ることを目的として、水酸化ナトリウム水溶液の濃度を４．２〜６ｍｏｌ／ｌとした。なお、前記水酸化ナトリウム濃度の違いにより、ｐＨ値は１１〜１２．５の範囲で異なる値を示した。これ以外は実施例１と同様にして金属水酸化物粉末を得た。
【００３８】
得られた金属水酸化物粉末は、いずれも平均粒径１０μｍの球状粉末であり、タップ密度は１．９ｇ／ｃｍ³以上であった。また、いずれもβ−Ｎｉ（ＯＨ）₂型の単相であり、マグネシウム固溶量は５モル％であった。また、硫酸根量は０．３±０．０１重量％の範囲であった。また、ＣｕＫα線を用いたＸ線回折パターンを記録したところ、前記水酸化ナトリウムの濃度の違い（ｐＨ値の違い）により、２θ＝３７〜４０゜付近の（１０１）面のピーク半価幅が異なり、０．６３〜１．３１ｄｅｇであった。
【００３９】
前記の半価幅が異なるサンプルを活物質として、実施例１と同様にして円筒密閉電池を作製し、それらの電池特性を評価した。評価方法は、２０℃において、１２０ｍＡの電流で１５時間充電し、２４０ｍＡの電流で電池電圧１．０Ｖまで放電する充放電サイクルを繰り返し、放電容量が安定した後、利用率Ａ（２４０ｍＡ放電時）を算出した。また、次のサイクルでは、１２０ｍＡの電流で１５時間充電し、３６００ｍＡで放電し、その放電容量から利用率Ｂ（３６００ｍＡ放電時）を算出した。
【００４０】
図２は、前記実験の結果を表す図であって、（１０１）面の半価幅と前記２４０ｍＡ放電時および３６００ｍＡ放電時の利用率との関係を示す特性図である。この図から、（１０１）面の半価幅が０．７ｄｅｇ．以上で低率放電（２４０ｍＡ）時に高い利用率を示し、かつ、１．２ｄｅｇ．以下で高率放電（３６００ｍＡ）時に高い利用率を示すことがわかる。従って、高利用率で、かつ、高率放電特性を高めるためには、ＣｕＫα線を使用するＸ線回折の２θ＝３７〜４０゜付近の（１０１）面のピーク半価幅０．７以上１．２以下であることが好ましい。
【００４１】
（実施例３）
実施例１に記載の活物質粒子合成条件において、硫酸ニッケルと硫酸マグネシウムからなる混合水溶液中の硫酸ニッケルと硫酸マグネシウムの混合比を、ニッケルとマグネシウムの総モル数に対するマグネシウムのモル数が５モル％となるようにした。沈殿物を分離した後、アルカリ処理を行う時間や回数を変えることで、金属水酸化物中の硫酸イオン（硫酸根）含有量の異なる活物質粉末を得た。これ以外は実施例１と同様にして金属水酸化物粉末を得た。
【００４２】
得られた金属水酸化物粉末は、いずれも平均粒径１０μｍの球状粉末であり、タップ密度は１．９ｇ／ｃｍ³以上であった。また、いずれもβ−Ｎｉ（ＯＨ）₂型の単相であり、マグネシウム固溶量は５モル％であった。また、硫酸根量は０．０５〜１．０重量％の範囲であった。また、ＣｕＫα線を用いたＸ線回折パターンを記録したところ、２θ＝３７〜４０゜付近の（１０１）面のピーク半価幅は０．９±０．１ｄｅｇ．であった。
【００４３】
前記の硫酸根含有量が異なるサンプルを活物質として、実施例１と同様にして円筒密閉電池を作製し、それらの電池特性を評価した。評価方法は、２０℃において、１２０ｍＡの電流で１５時間充電し、２４０ｍＡの電流で電池電圧１．０Ｖまで放電する充放電サイクルを繰り返し、放電容量が安定した後、１２０ｍＡの電流で１５時間充電し、３６００ｍＡで放電し、その放電容量から利用率（３６００ｍＡ放電時）を算出した。
【００４４】
図３は、前記実験の結果を表す図であって、硫酸根の含有量と３６００ｍＡ放電時の利用率との関係を示す特性図である。この図から、硫酸根量が０．５重量％以下で高率放電（３６００ｍＡ）時に高い利用率を示すことがわかる。従って、高率放電特性を高めるためには、結晶内に含まれる硫酸根が０．５重量％以下であることが好ましい。
【００４５】
（実施例４）
実施例１に記載の活物質粒子合成条件において、硫酸ニッケルと硫酸マグネシウムからなる混合水溶液中の硫酸ニッケルと硫酸マグネシウムの混合比を、ニッケルとマグネシウムの総モル数に対するマグネシウムのモル数が５モル％となるようにした。また、結晶の配向性の異なるサンプルを得ることを目的として、反応装置内の温度を２０〜７０℃の範囲内で変化させて合成した。これ以外は実施例１と同様にして金属水酸化物粉末を得た。
【００４６】
得られた金属水酸化物粉末は、いずれも平均粒径１０μｍの球状粉末であり、タップ密度は１．９ｇ／ｃｍ³以上であった。また、いずれもβ−Ｎｉ（ＯＨ）₂型の単相であり、マグネシウム固溶量は５モル％であった。また、硫酸根量は０．３±０．０１重量％の範囲であった。また、ＣｕＫα線を用いたＸ線回折パターンを記録したところ、２θ＝３７〜４０゜付近の（１０１）面のピーク半価幅は０．９±０．１ｄｅｇ．であった。また、反応装置内の温度の違いにより、２θ＝３７〜４０゜付近の（１０１）面のピーク強度Ａに対する、２θ＝３７〜４０゜付近の（００１）面のピーク強度Ｂの比Ｂ／Ａが１．０〜１．３の範囲となった。前記のピーク強度比が異なるサンプルを活物質として、実施例１と同様にして円筒密閉電池を作製し、それらの電池特性を評価した。評価方法は、２０℃において、１２０ｍＡの電流で１５時間充電し、２４０ｍＡの電流で電池電圧１．０Ｖまで放電する充放電サイクルを繰り返し、放電容量が安定した後、利用率Ａ（２４０ｍＡ放電時）を算出した。また、次のサイクルでは、１２０ｍＡの電流で１５時間充電し、３６００ｍＡで放電し、その放電容量から利用率Ｂ（３６００ｍＡ放電時）を算出した。
【００４７】
図４は、前記実験の結果を表す図であって、（１０１）面のピーク強度Ａに対する、（００１）面のピーク強度Ｂの比Ｂ／Ａと３６００ｍＡ放電時の利用率との関係を示す特性図である。この図から、Ｂ／Ａの値が１．１以上で高率放電（３６００ｍＡ）時に高い利用率を示すことがわかる。従って、高率放電特性を更に高めるためには、ＣｕＫα線を使用するＸ線回折の２θ＝３７〜４０゜付近に位置する（１０１）面のピークＡに対する、２θ＝１８〜２１゜付近に位置する（００１）面のピーク強度Ｂの比Ｂ／Ａが１．１以上であることが好ましい。
【００４８】
（実施例５）
実施例１に記載の活物質粒子合成条件において、硫酸ニッケルと硫酸マグネシウム以外に、硫酸コバルトまたは硫酸マンガンからなる混合水溶液を用い、これらの混合比を、全金属元素の総モル数に対するマグネシウムのモル数が５モル％と固定し、コバルトまたはマンガンのモル数が０〜４モル％となるようにした。これ以外は実施例１と同様にして金属水酸化物粉末を得た。
【００４９】
得られた金属水酸化物粉末は、いずれも平均粒径１０μｍの球状粉末であり、タップ密度は１．９ｇ／ｃｍ³以上であった。また、いずれもβ−Ｎｉ（ＯＨ）₂型の単相であり、マグネシウム固溶量は５モル％で、コバルトまたはマンガンの固溶量は０〜４モル％の範囲であった。また、硫酸根量は０．３±０．０１重量％の範囲であった。また、ＣｕＫα線を用いたＸ線回折パターンを記録したところ、２θ＝３７〜４０゜付近の（１０１）面のピーク半価幅は０．９±０．０５ｄｅｇ．であった。
【００５０】
前記のコバルトまたはマンガンを固溶したサンプルを活物質として、実施例１と同様にして円筒密閉電池を作製し、それらの電池特性を評価した。評価方法は、２０℃において、１２０ｍＡの電流で１５時間充電し、２４０ｍＡの電流で電池電圧１．０Ｖまで放電する充放電サイクルを繰り返し、放電容量が安定した後、利用率（２４０ｍＡ放電時）を算出した。
【００５１】
図５は、これらの実験の結果を表す図であって、マグネシウムを５モル％固溶した水酸化ニッケルにおけるコバルト固溶量に対する利用率と平均放電電圧との関係を示す特性図である。この図から、コバルト固溶量が０．５モル％以上で利用率が高くなる傾向があることがわかる。また、コバルト固溶量が３モル％より多くなると平均放電電圧が低下する傾向があることがわかる。従って、コバルト固溶量としては、０．５モル％以上３モル％以下が適切であると考えられる。さらに、コバルトに変えてマンガンを固溶した場合において同様にして調べた結果、コバルトと同様な傾向が観察され、マンガン固溶量としては、０．５モル％以上３モル％以下が適切であると考えられる。
【００５２】
（実施例６）
実施例１に記載の活物質粒子合成条件において、硫酸ニッケルと硫酸マグネシウムからなる混合水溶液中の硫酸ニッケルと硫酸マグネシウムの混合比を、ニッケルとマグネシウムの総モル数に対するマグネシウムのモル数が５モル％となるようにした。これ以外は実施例１と同様にして金属水酸化物粉末を得た。
【００５３】
ここで得られた金属水酸化物粉末は、平均粒径１０μｍの球状粉末であり、タップ密度は２．０３ｇ／ｃｍ³であった。また、β−Ｎｉ（ＯＨ）₂型の単相であり、マグネシウム固溶量は５モル％であった。また、硫酸根量は０．３重量％であった。また、ＣｕＫα線を用いたＸ線回折パターンを記録したところ、２θ＝３７〜４０゜付近の（１０１）面のピーク半価幅は０．８９２ｄｅｇ．であった。
【００５４】
続いて、前記金属水酸化物粉末を硫酸コバルト水溶液中に投入し、水酸化ナトリウム水溶液を徐々に加え、３５℃でｐＨが１２を維持するように調整しながら攪拌を続けて、金属酸化物粒子表面に水酸化コバルトを析出させて、水酸化コバルト被覆マグネシウム固溶水酸化ニッケル粉末とした。ここで水酸化コバルトの被覆量については、粒子総重量に対する被覆層重量比率が１０重量％となるように調整した。作製した水酸化コバルト被覆粉末は水洗した後、真空乾燥を行った。ここで得られた水酸化コバルト被覆粉末は、平均粒径１０μｍの球状粉末であり、タップ密度は１．９５ｇ／ｃｍ³であった。
【００５５】
次に、前記水酸化コバルト被覆粉末の改質処理を以下の手順により行った。まず、水酸化コバルト被覆粉末に４５重量％の水酸化カリウム水溶液の適量を含浸させ、これをマイクロ波加熱の機能を備えた乾燥装置内に投入して加熱し、酸素を送りながら粒子を完全乾燥まで導いた。この操作によって、粒子表面の水酸化コバルト被覆層は酸化を受け、粒子は藍色に変化した。得られたコバルト酸化物被覆粉末を水洗した後、真空乾燥を行った。
【００５６】
ヨードメトリー法により全金属のトータル価数を求め、その値よりコバルトの平均価数を算出したところ、被覆層中のコバルトの平均価数は３．２価を示した。
【００５７】
なお、前記水酸化コバルト被覆粉末に含浸させる溶液としては、高濃度の水酸化カリウム水溶液を用いたが、同様にして高濃度の水酸化ナトリウム水溶液を用いても、被覆層中のコバルトの平均価数は３．０価より大きい値を示した。
【００５８】
このコバルト酸化物被覆粉末を活物質として、実施例１と同様にして円筒密閉電池を作製し、それらの電池特性を評価した。評価方法は、２０℃において、１２０ｍＡの電流で１５時間充電し、２４０ｍＡの電流で電池電圧１．０Ｖまで放電する充放電サイクルを繰り返し、放電容量が安定した後、１２０ｍＡの電流で１５時間充電し、３６００ｍＡで放電し、その放電容量から利用率（３６００ｍＡ放電時）を算出した。
【００５９】
その結果、利用率９０％と高い値を示したことから、コバルト酸化物により表面が被覆されている活物質においても、同様に、高率放電特性に優れることがわかる。
【００６０】
（実施例７）
実施例６記載の活物質粒子合成条件において、水酸化カリウムの濃度、酸化時間を変えて酸化処理を実施した。その結果、コバルト酸化物被覆層中のコバルト平均価数は３価前後でばらついた。このコバルト酸化物被覆粉末を活物質として、実施例６と同様にして、３６００ｍＡでの放電容量から利用率（３６００ｍＡ放電時）を算出した。
【００６１】
その結果、コバルト平均価数が３価より小さいと高率放電特性が著しく劣ることがわかった。従って、コバルト酸化物被覆層中のコバルトの平均価数は、３価より大きいことが好ましい。
【００６２】
【発明の効果】
以上のように本発明によれば、放電電圧が高く、かつ、高率放電時に高い利用率を発現する出力特性に優れたアルカリ蓄電池用活物質およびニッケル正極を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例による活物質のマグネシウム固溶量に対する利用率、平均放電電圧の変化を示す図
【図２】本発明の実施例による活物質のＣｕＫα線を使用するＸ線回折の２θ＝３７〜４０゜付近の（１０１）面のピーク半価幅に対する低率放電時の利用率、高率放電時の利用率の変化を示す図
【図３】本発明の実施例による活物質の硫酸根含有量に対する高率放電時の利用率の変化を示す図
【図４】本発明の実施例による活物質のＣｕＫα線を使用するＸ線回折の２θ＝３７〜４０゜付近の（１０１）面のピーク強度Ａに対する、２θ＝３７〜４０゜付近の（００１）面のピーク強度Ｂの比Ｂ／Ａに対する高率放電時の利用率の変化を示す図
【図５】本発明の実施例による活物質のコバルト固溶量に対する利用率、平均放電電圧の変化を示す図[0001]
Dependent technical field of the invention
The present invention relates to an alkaline storage battery, and more particularly to a positive electrode active material for an alkaline storage battery.
[0002]
[Prior art]
In recent years, the positive electrode for alkaline storage batteries has drastically improved capacity density due to improvements in the substrate shape, active material shape, active material composition, and additives, and a positive electrode with a capacity density of about 600 mAh / cc is now in practical use. Yes.
[0003]
However, further higher output is demanded from the equipment side, and improvement in energy density during high rate discharge is strongly demanded. In order to improve the high rate discharge characteristics, conventionally, a method for increasing the current collecting property of the electrode (or a method for decreasing the resistance) and a method for increasing the charge / discharge efficiency of the active material have been studied. On the other hand, if the discharge potential itself can be shifted in a high direction (noble direction), a dramatic increase in output can be expected. We have been working on the modification of nickel hydroxide by solid solution of dissimilar metals. Among them, attention has been paid to the fact that nickel hydroxide having a solid solution with magnesium has a high discharge potential, and the optimization of physical properties as an electrode material has been studied.
[0004]
The nickel hydroxide in which magnesium is dissolved is widely proposed and includes the following.
[0005]
(1) In Japanese Patent Laid-Open No. 2-109261, nickel hydroxide in which 1 to 3% by weight of magnesium is solid-solved has an internal pore radius of 30 mm or less and a total pore volume of 0.05 ml / g or less. It has been proposed to use a positive electrode active material. This is a nickel electrode active material that has a higher density of nickel hydroxide powder and has a longer life by preventing the formation of γ-NiOOH by the addition of magnesium and an improved active material utilization rate. It is intended to provide.
[0006]
(2) In Japanese Patent Application Laid-Open No. 5-21064, magnesium or the like is contained in a nickel hydroxide powder at the time of producing a positive electrode, and a mixture of spherical or spherically similar particles and non-spherical particles is used. It has been proposed to use a positive electrode active material. The purpose of this is to improve the packing density of nickel hydroxide and to suppress the generation of γ-NiOOH during overcharge and improve cycle life characteristics by adding a dissimilar metal group containing magnesium. It is.
[0007]
(3) In Japanese Patent Application Laid-Open No. 5-41212, magnesium or the like is contained in 1 to 7 wt% nickel hydroxide powder, and is a particle in which countless primary particles of 0.1 μm or less are aggregated, and pores of 30 μm or more It has been proposed to use nickel hydroxide whose space volume having a radius is 20 to 70% of the total space volume as the positive electrode active material. This facilitates the penetration of the electrolyte into the particles, thereby suppressing the formation of γ-NiOOH due to the uneven distribution of the electrolyte in the particles, and further improving the active material utilization rate in the early stage of charge and discharge. It is intended. The addition of the heterogeneous metal group containing magnesium is intended to improve the cycle life characteristics by suppressing the formation of γ-NiOOH, as in the proposal (2).
[0008]
(4) In Japanese Patent Laid-Open No. Hei 5-182626, nickel hydroxide powder having an internal pore volume of 0.14 ml / g or less and having a structure in which the crystal lattice is partially substituted by an additive element is used as a positive electrode active material. Has been proposed. In particular, Zn, Mg, Cd, and Ba are selected as a solid solution additive element in nickel hydroxide from the condition that it should not impair the characteristics of nickel hydroxide as an active material. This is because high density nickel hydroxide powder with small internal pore volume forms a lattice defect in the nickel hydroxide crystal lattice by substituting a part of nickel with a different element including magnesium, and the degree of freedom of proton transfer. The purpose is to suppress the generation of γ-NiOOH and improve the cycle life characteristics.
[0009]
(5) In JP-A-5-182663, nickel hydroxide having a structure in which the internal pore volume is 0.14 ml / g and the crystal lattice is partially partially substituted by Co and other additive elements is used as the positive electrode It has been proposed to be an active material. In particular, Zn, Mg, Cd, and Ba are selected as additive elements that are dissolved in nickel hydroxide. The purpose is to improve the charge efficiency at high temperature by replacing part of nickel with different elements including Co and other magnesium, and at the same time, suppress the formation of γ-NiOOH and improve the cycle life characteristics. It is said.
[0010]
[Problems to be solved by the invention]
However, the above proposals are aimed at improving the charge / discharge efficiency and the life characteristics, and using the high discharge potential of nickel hydroxide containing magnesium in a solid solution state as in the present inventors, It was not intended to achieve higher output. In fact, when a battery was prototyped based on the above proposal, it was not possible to obtain the target satisfactory high output battery. Also, the high rate charge / discharge characteristics were not satisfactory.
[0011]
Therefore, the present invention provides an active material for an alkaline storage battery that exhibits a high discharge voltage and a high utilization rate during high rate charge / discharge (excellent high rate discharge characteristics), a nickel positive electrode, and an alkaline storage battery using the same. The purpose is to do.
[0012]
[Means for Solving the Invention]
As a result of intensive studies by the present inventors, it has been found that nickel hydroxide containing magnesium in a solid solution state is likely to have a lower utilization factor during high rate discharge. The cause of this is that solid solution of magnesium makes it easier for sulfate radicals to be taken into the crystal of nickel hydroxide, and the crystal structure of magnesium solid solution nickel hydroxide is likely to be disturbed, resulting in large polarization during high rate discharge. At the same time, the conductivity is also significantly reduced, so that the high rate discharge characteristics are considered to be significantly reduced. Note that the phenomenon that the polarization during high rate discharge increases due to disorder of the crystal (lowering of crystallinity) is considered to be due to a decrease in the degree of freedom of proton movement. In the above proposal, a technique for improving such a problem is not disclosed. Therefore, it is considered that an active material for increasing the output and a nickel positive electrode could not be obtained.
[0013]
From this point of view, in order to achieve the object of the present inventors, the positive electrode active material for alkaline storage batteries comprising nickel hydroxide in which magnesium of the present invention is dissolved is firstly made up of the content of magnesium in the nickel hydroxide. 2 mol% or more and 7 mol% or less with respect to the metal element, and second, the tap density of the powder is 1.9 g / cm 2. ^Three Third, the half width of the peak on the (101) plane located near 2θ = 37 ° to 40 ° in X-ray diffraction using CuKα rays is in the range of 0.7 to 1.2. Fourth, the sulfate radical contained in the crystal is 0.5% by weight or less.
[0014]
First, selection as a different element that dissolves in nickel hydroxide is preferable for obtaining a high-power battery because the discharge potential is increased. However, when the magnesium content is less than 2 mol%, the effect of increasing the discharge potential is poor. Conversely, when the magnesium content is more than 7 mol%, the utilization rate decreases even during low rate discharge, and the active material is hydroxylated. Since the amount of nickel decreases, sufficient battery capacity cannot be obtained.
[0015]
If magnesium is selected as a different element that dissolves in nickel hydroxide and its content is only 2 to 7 mol%, the intended high output positive electrode cannot be obtained. By optimizing the physical properties, it is possible to achieve a much higher output.
[0016]
The tap density is 1.9 g / cm ^Three The above is preferable, and further 2.1 g / cm ^Three The above is particularly preferable. This is 1.9 g / cm ^Three If it is smaller, it is difficult to achieve high energy density because the packing density of the electrode is reduced, and the dissimilar solid solution element is magnesium and the sulfate radical is easily taken into the crystal. Is considered to be involved for some reason with the sulfate radical.
[0017]
It is desirable that the half width of the peak of the (101) plane located in the vicinity of 2θ = 37 to 40 ° of X-ray diffraction using CuKα rays is 0.7 or more and 1.2 or less. If it is in this numerical range, the crystal structure is less likely to be disturbed with some sulfate groups, and therefore the degree of freedom of proton transfer does not decrease.
[0018]
Further, the sulfate group contained in the crystal is desirably 0.5% by weight or less. This is because even if nickel hydroxide is produced so that the half width of a specific peak becomes a specific value, if there are too many sulfate radicals, the crystal structure is disturbed with the cycle. Therefore, although it is not necessary to obtain a very low value by optimizing the crystal structure, it is usually preferable to set it to a value slightly lower than the sulfate radical amount in the case of synthesizing magnesium solid solution nickel hydroxide.
[0019]
In nickel hydroxide containing magnesium in a solid solution state, the phenomenon that the polarization during high-rate discharge increases due to disorder of the crystal (lower crystallinity) is thought to be due to a decrease in the degree of freedom of proton transfer. Yes.
[0020]
When an alkaline storage battery is configured using the positive electrode active material of the present invention, it is possible to improve the discharge voltage and the high rate discharge characteristics.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Further, the nickel hydroxide of the present invention is further located in the vicinity of 2θ = 18 to 21 ° with respect to the peak A of the (101) plane located in the vicinity of 2θ = 37 to 40 ° of X-ray diffraction using CuKα ray. It is desirable that the ratio B / A of the peak intensity B on the (001) plane is 1.1 or more. When the peak intensity ratio B / A is greater than 1.1, that is, when the orientation in the C-axis direction of the nickel hydroxide crystal is high, polarization during high-rate discharge can be further suppressed, and high-rate discharge characteristics Can be further improved. This is because the crystal growth in the crystal plane direction is excellent in the crystal and shows the uniformity of the crystal in the crystal plane direction, and it is considered that the degree of freedom of proton movement is further improved with less crystal disturbance.
[0022]
Furthermore, the nickel hydroxide of the present invention desirably contains at least one element selected from the group consisting of cobalt and manganese in addition to magnesium. By dissolving the metal element in a solid solution, the discharge efficiency at the end of discharge can be improved (discharge deeply), and there is an effect of improving the utilization rate during low-rate discharge. This is because elements such as cobalt and manganese are likely to have a higher valence than divalent, and remain at a high valence even at the end of discharge, which increases the degree of freedom of proton transfer at the end of discharge. Yes.
[0023]
The content ratio of at least one solid solution element selected from the group consisting of cobalt and manganese is preferably 0.5 mol% or more and 3 mol% or less with respect to all metal elements in nickel hydroxide. If the amount is less than 0.5 mol%, the effect is reduced. If the amount is more than 3 mol%, the discharge voltage is lowered, and the effect of magnesium is negated.
[0024]
Moreover, it is preferable that the surface of the nickel hydroxide of the present invention is coated with cobalt oxide. Thereby, since the distribution of the cobalt compound as the conductive material becomes uniform and the conductivity is improved, the filling amount of the conductive material can be reduced. In addition, the high-rate discharge characteristics can be further improved by improving the conductivity.
[0025]
The average valence of cobalt in the cobalt oxide is preferably greater than trivalence. Thereby, the electroconductivity of a cobalt compound improves remarkably and a high rate discharge characteristic can be improved further.
[0026]
【Example】
Next, examples of the present invention will be described.
[0027]
Example 1
First, a method for synthesizing active material particles will be described.
[0028]
A mixed aqueous solution containing nickel sulfate and magnesium sulfate, an aqueous sodium hydroxide solution, and an aqueous ammonia solution were prepared, and each was continuously fed into a reactor maintained at 40 ° C. at a flow rate of 0.5 ml / min. Here, the concentration of the mixed aqueous solution composed of nickel sulfate and magnesium sulfate is 2.4 mol / l, and the mixing ratio of nickel sulfate and magnesium sulfate is such that the number of moles of magnesium is 0.5 to It was made to become the range of 10 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.
[0029]
Subsequently, when the pH in the reaction apparatus becomes constant, the balance between the metal salt concentration and the metal hydroxide particle concentration becomes constant, and when it reaches a steady state, the suspension obtained by overflow is collected and decanted. Separated the precipitate. This was alkali-treated with an aqueous sodium hydroxide solution having a pH of 13 to 14 to remove anions such as sulfate ions in the metal hydroxide particles, washed with water, and dried. In this way, a powder having an average particle size of 10 μm was obtained. The content of sulfate ions (sulfate radicals) in the metal hydroxide can be controlled by the time and number of times of alkali treatment with the aqueous sodium hydroxide solution having a pH of 13 to 14. In particular, since nickel hydroxide in which magnesium is dissolved, the sulfate radical is easily taken in, so the temperature is set to a high temperature (60 ° C.) and the number of treatments is increased (three times or more), so that the content of the sulfate radical is increased. I tried to reduce it.
[0030]
As a result of conducting the composition analysis, the magnesium solid solution amount in the obtained metal hydroxide was 0.5 to 10 mol%, similarly to the mixing ratio of the aqueous solution used in the synthesis. The sulfate radical amount was in the range of 0.3 ± 0.01% by weight. Further, when X-ray diffraction patterns using CuKα rays were recorded, both were β-Ni (OH). ₂ It was confirmed that it was a single phase of the mold, and it was confirmed that magnesium was dissolved in nickel hydroxide. The peak half-value width of the (101) plane near 2θ = 37 to 40 ° is 0.9 ± 0.02 deg. Met. Moreover, when the tap density was measured, all were 1.9 g / cm. ^Three As described above, it was confirmed that the material is suitable for increasing the energy density (a material excellent in filling property to the electrode support).
[0031]
Next, a method for producing a nickel positive electrode using the active material obtained by the above method will be described.
[0032]
10 g of cobalt hydroxide powder and 30 g of water were added to 100 g of the metal hydroxide 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 1200 mAh. However, the capacity density of the nickel electrode shown here is calculated on the assumption that nickel in the active material undergoes a one-electron reaction.
[0033]
Next, a method for producing an alkaline storage battery will be described.
[0034]
A known negative electrode for an alkaline storage battery was used as the negative electrode. Here, a hydrogen storage alloy MmNi of about 30 μm _3.55 Co _0.75 Mn _0.4 Al _0.3 A 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 1920 mAh. A spiral electrode group was formed by interposing a separator made of a sulfonated polypropylene nonwoven fabric having a thickness of 0.15 mm between the positive electrode and the negative electrode. 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, and AA A cylindrical sealed nickel-metal hydride storage battery of a size was produced.
[0035]
Cylindrical sealed batteries were produced by the above method using samples with different magnesium solid solution amounts as the positive electrode active material, and their battery characteristics were evaluated. At 20 ° C., the battery was charged with a current of 120 mA for 15 hours, and a charge / discharge cycle of discharging to a battery voltage of 1.0 V with a current of 240 mA was repeated. After the discharge capacity was stabilized, the average discharge voltage and the utilization rate of the active material were 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.
[0036]
FIG. 1 is a diagram showing the results of these experiments, and is a characteristic diagram showing the relationship between the utilization rate and the average discharge voltage with respect to the magnesium solid solution amount. From this figure, it can be seen that the average discharge voltage tends to increase remarkably when the magnesium solid solution amount is 2 mol% or more. Moreover, it turns out that there exists a tendency for a utilization factor to fall, when the amount of magnesium solid solution exceeds 7 mol%. Accordingly, it is considered that the magnesium solid solution amount is suitably 2 mol% or more and 7 mol% or less.
[0037]
(Example 2)
In the active material particle synthesis conditions described in Example 1, the mixing ratio of nickel sulfate and magnesium sulfate in the mixed aqueous solution composed of nickel sulfate and magnesium sulfate was set such that the number of moles of magnesium was 5 mol% with respect to the total number of moles of nickel and magnesium. It was made to become. Moreover, the density | concentration of sodium hydroxide aqueous solution was 4.2-6 mol / l for the purpose of obtaining the sample from which crystallinity differs. In addition, the pH value showed the different value in the range of 11-12.5 by the difference in the said sodium hydroxide density | concentration. Except for this, a metal hydroxide powder was obtained in the same manner as in Example 1.
[0038]
The obtained metal hydroxide powders are all spherical powders having an average particle size of 10 μm, and the tap density is 1.9 g / cm. ^Three That was all. In both cases, β-Ni (OH) ₂ It was a single phase of the mold, and the magnesium solid solution amount was 5 mol%. The sulfate radical amount was in the range of 0.3 ± 0.01% by weight. Moreover, when an X-ray diffraction pattern using CuKα rays was recorded, the peak half-value width of the (101) plane near 2θ = 37 to 40 ° was found due to the difference in the concentration of sodium hydroxide (difference in pH value). The difference was 0.63 to 1.31 deg.
[0039]
Cylindrical sealed batteries were produced in the same manner as in Example 1 using the samples having different half widths as active materials, and their battery characteristics were evaluated. The evaluation method is charging at a current of 120 mA at 20 ° C. for 15 hours, repeating a charge / discharge cycle of discharging to a battery voltage of 1.0 V at a current of 240 mA, and after the discharge capacity is stabilized, the utilization rate A (at 240 mA discharge) Was calculated. In the next cycle, the battery was charged at a current of 120 mA for 15 hours, discharged at 3600 mA, and the utilization rate B (at the time of 3600 mA discharge) was calculated from the discharge capacity.
[0040]
FIG. 2 is a characteristic diagram showing the relationship between the half-value width of the (101) plane and the utilization factor during the 240 mA discharge and the 3600 mA discharge. From this figure, the half width of the (101) plane is 0.7 deg. The above shows a high utilization factor at low rate discharge (240 mA), and 1.2 deg. In the following, it can be seen that a high utilization rate is exhibited during high rate discharge (3600 mA). Therefore, in order to enhance the high utilization factor and the high rate discharge characteristic, the peak half-value width of 0.7 or more of the (101) plane in the vicinity of 2θ = 37 to 40 ° of X-ray diffraction using CuKα rays is 1 .2 or less is preferable.
[0041]
Example 3
In the active material particle synthesis conditions described in Example 1, the mixing ratio of nickel sulfate and magnesium sulfate in the mixed aqueous solution composed of nickel sulfate and magnesium sulfate was set such that the number of moles of magnesium was 5 mol% with respect to the total number of moles of nickel and magnesium. It was made to become. After separating the precipitate, active material powders having different sulfate ion (sulfate radical) contents in the metal hydroxide were obtained by changing the time and number of times of alkali treatment. Except for this, a metal hydroxide powder was obtained in the same manner as in Example 1.
[0042]
The obtained metal hydroxide powders are all spherical powders having an average particle size of 10 μm, and the tap density is 1.9 g / cm. ^Three That was all. In both cases, β-Ni (OH) ₂ It was a single phase of the mold, and the magnesium solid solution amount was 5 mol%. The amount of sulfate radical was in the range of 0.05 to 1.0% by weight. When an X-ray diffraction pattern using CuKα rays was recorded, the peak half-value width of the (101) plane near 2θ = 37 to 40 ° was 0.9 ± 0.1 deg. Met.
[0043]
Cylindrical sealed batteries were produced in the same manner as in Example 1 using the samples having different sulfate radical contents as active materials, and their battery characteristics were evaluated. The evaluation method is to charge at 120 ° C. for 15 hours at a current of 20 mA, repeat the charge / discharge cycle of discharging to a battery voltage of 1.0 V at a current of 240 mA, and after the discharge capacity has stabilized, charge for 15 hours at a current of 120 mA. The battery was discharged at 3600 mA, and the utilization factor (at the time of 3600 mA discharge) was calculated from the discharge capacity.
[0044]
FIG. 3 is a graph showing the results of the experiment, and is a characteristic diagram showing the relationship between the sulfate radical content and the utilization factor during 3600 mA discharge. From this figure, it can be seen that when the sulfate radical amount is 0.5% by weight or less, a high utilization rate is exhibited during high rate discharge (3600 mA). Therefore, in order to improve the high rate discharge characteristics, it is preferable that the sulfate radical contained in the crystal is 0.5% by weight or less.
[0045]
(Example 4)
In the active material particle synthesis conditions described in Example 1, the mixing ratio of nickel sulfate and magnesium sulfate in the mixed aqueous solution composed of nickel sulfate and magnesium sulfate was set such that the number of moles of magnesium was 5 mol% with respect to the total number of moles of nickel and magnesium. It was made to become. In addition, for the purpose of obtaining samples having different crystal orientations, synthesis was performed by changing the temperature in the reaction apparatus within a range of 20 to 70 ° C. Except for this, a metal hydroxide powder was obtained in the same manner as in Example 1.
[0046]
The obtained metal hydroxide powders are all spherical powders having an average particle size of 10 μm, and the tap density is 1.9 g / cm. ^Three That was all. In both cases, β-Ni (OH) ₂ It was a single phase of the mold, and the magnesium solid solution amount was 5 mol%. The sulfate radical amount was in the range of 0.3 ± 0.01% by weight. When an X-ray diffraction pattern using CuKα rays was recorded, the peak half-value width of the (101) plane near 2θ = 37 to 40 ° was 0.9 ± 0.1 deg. Met. Further, the ratio B / A of the peak intensity B of the (001) plane near 2θ = 37 to 40 ° to the peak intensity A of the (101) plane near 2θ = 37 to 40 ° due to the temperature difference in the reactor. Was in the range of 1.0 to 1.3. Cylindrical sealed batteries were produced in the same manner as in Example 1 using samples having different peak intensity ratios as active materials, and their battery characteristics were evaluated. The evaluation method is charging at a current of 120 mA at 20 ° C. for 15 hours, repeating a charge / discharge cycle of discharging to a battery voltage of 1.0 V at a current of 240 mA, and after the discharge capacity is stabilized, the utilization rate A (at 240 mA discharge) Was calculated. In the next cycle, the battery was charged at a current of 120 mA for 15 hours, discharged at 3600 mA, and the utilization rate B (at the time of 3600 mA discharge) was calculated from the discharge capacity.
[0047]
FIG. 4 is a diagram showing the results of the experiment, and shows the relationship between the ratio (B / A) of the peak intensity B of the (001) plane to the peak intensity A of the (101) plane and the utilization rate at the time of 3600 mA discharge. FIG. From this figure, it can be seen that when the B / A value is 1.1 or more, a high utilization rate is exhibited during high rate discharge (3600 mA). Therefore, in order to further enhance the high rate discharge characteristics, the X-ray diffraction using CuKα rays is located near 2θ = 18-21 ° with respect to the peak A of the (101) plane located near 2θ = 37-40 °. The ratio (B / A) of the peak intensity B on the (001) plane is preferably 1.1 or more.
[0048]
(Example 5)
In the active material particle synthesis conditions described in Example 1, in addition to nickel sulfate and magnesium sulfate, a mixed aqueous solution composed of cobalt sulfate or manganese sulfate was used, and the mixing ratio thereof was determined based on the moles of magnesium with respect to the total number of moles of all metal elements. The number was fixed at 5 mol%, and the number of moles of cobalt or manganese was 0 to 4 mol%. Except for this, a metal hydroxide powder was obtained in the same manner as in Example 1.
[0049]
The obtained metal hydroxide powders are all spherical powders having an average particle size of 10 μm, and the tap density is 1.9 g / cm. ^Three That was all. In both cases, β-Ni (OH) ₂ It was a single phase of the mold, the magnesium solid solution amount was 5 mol%, and the cobalt or manganese solid solution amount was in the range of 0 to 4 mol%. The sulfate radical amount was in the range of 0.3 ± 0.01% by weight. Further, when an X-ray diffraction pattern using CuKα rays was recorded, the peak half-value width of the (101) plane near 2θ = 37 to 40 ° was 0.9 ± 0.05 deg. Met.
[0050]
Cylindrical sealed batteries were produced in the same manner as in Example 1 using the above-described sample in which cobalt or manganese was dissolved as active materials, and their battery characteristics were evaluated. The evaluation method is to charge at a current of 120 mA for 15 hours at 20 ° C., and repeat a charge / discharge cycle of discharging to a battery voltage of 1.0 V at a current of 240 mA. After the discharge capacity is stabilized, the utilization rate (at 240 mA discharge) is obtained. Calculated.
[0051]
FIG. 5 is a graph showing the results of these experiments, and is a characteristic diagram showing the relationship between the utilization rate and the average discharge voltage with respect to the amount of cobalt solid solution in nickel hydroxide containing 5 mol% of magnesium as a solid solution. From this figure, it can be seen that the utilization rate tends to increase when the cobalt solid solution amount is 0.5 mol% or more. Moreover, it turns out that there exists a tendency for an average discharge voltage to fall, when cobalt solid solution amount exceeds 3 mol%. Accordingly, it is considered that 0.5 mol% or more and 3 mol% or less is appropriate as the cobalt solid solution amount. Furthermore, as a result of investigating in the same manner when manganese was dissolved in place of cobalt, the same tendency as cobalt was observed, and the amount of manganese solid solution is suitably 0.5 mol% or more and 3 mol% or less. it is conceivable that.
[0052]
(Example 6)
In the active material particle synthesis conditions described in Example 1, the mixing ratio of nickel sulfate and magnesium sulfate in the mixed aqueous solution composed of nickel sulfate and magnesium sulfate was set such that the number of moles of magnesium was 5 mol% with respect to the total number of moles of nickel and magnesium. It was made to become. Except for this, a metal hydroxide powder was obtained in the same manner as in Example 1.
[0053]
The metal hydroxide powder obtained here is a spherical powder having an average particle size of 10 μm, and the tap density is 2.03 g / cm. ^Three Met. Β-Ni (OH) ₂ It was a single phase of the mold, and the magnesium solid solution amount was 5 mol%. The sulfate radical amount was 0.3% by weight. Further, when an X-ray diffraction pattern using CuKα rays was recorded, the peak half width of the (101) plane near 2θ = 37 to 40 ° was 0.892 deg. Met.
[0054]
Subsequently, the metal hydroxide powder was put into a cobalt sulfate aqueous solution, a sodium hydroxide aqueous solution was gradually added, and stirring was continued while adjusting the pH to be maintained at 35 ° C. to obtain metal oxide particles. Cobalt hydroxide was precipitated on the surface to obtain a cobalt hydroxide-coated magnesium solid solution nickel hydroxide powder. Here, the coating amount of cobalt hydroxide was adjusted so that the coating layer weight ratio to the total particle weight was 10% by weight. The prepared cobalt hydroxide-coated powder was washed with water and then vacuum-dried. The cobalt hydroxide-coated powder obtained here is a spherical powder having an average particle size of 10 μm, and the tap density is 1.95 g / cm. ^Three Met.
[0055]
Next, the modification treatment of the cobalt hydroxide-coated powder was performed according to the following procedure. First, impregnating the cobalt hydroxide-coated powder with an appropriate amount of 45% by weight potassium hydroxide aqueous solution, putting it in a drying device equipped with a microwave heating function, heating it, and completely drying the particles while sending oxygen Led to. By this operation, the cobalt hydroxide coating layer on the particle surface was oxidized, and the particles changed to indigo. The obtained cobalt oxide-coated powder was washed with water and then vacuum-dried.
[0056]
When the total valence of all metals was calculated | required by the iodometry method and the average valence of cobalt was computed from the value, the average valence of cobalt in the coating layer showed 3.2 valence.
[0057]
As the solution to be impregnated into the cobalt hydroxide-coated powder, a high-concentration potassium hydroxide aqueous solution was used. However, even if a high-concentration sodium hydroxide aqueous solution was used in the same manner, the average value of cobalt in the coating layer was The number showed a value greater than 3.0.
[0058]
Using this cobalt oxide-coated powder as an active material, cylindrical sealed batteries were produced in the same manner as in Example 1, and their battery characteristics were evaluated. The evaluation method is to charge at 120 ° C. for 15 hours at a current of 20 mA, repeat the charge / discharge cycle of discharging to a battery voltage of 1.0 V at a current of 240 mA, and after the discharge capacity has stabilized, charge for 15 hours at a current of 120 mA. The battery was discharged at 3600 mA, and the utilization factor (at the time of 3600 mA discharge) was calculated from the discharge capacity.
[0059]
As a result, since the utilization factor was as high as 90%, it can be understood that the active material whose surface is coated with cobalt oxide is similarly excellent in high-rate discharge characteristics.
[0060]
(Example 7)
Under the active material particle synthesis conditions described in Example 6, the oxidation treatment was performed by changing the concentration of potassium hydroxide and the oxidation time. As a result, the average valence number of cobalt in the cobalt oxide coating layer varied around around 3. Using this cobalt oxide-coated powder as an active material, the utilization factor (at the time of 3600 mA discharge) was calculated from the discharge capacity at 3600 mA in the same manner as in Example 6.
[0061]
As a result, it was found that when the average cobalt valence is less than trivalent, the high rate discharge characteristics are remarkably inferior. Therefore, it is preferable that the average valence of cobalt in the cobalt oxide coating layer is greater than 3.
[0062]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an alkaline storage battery active material and a nickel positive electrode that have a high discharge voltage and an excellent output characteristic that expresses a high utilization rate at the time of high rate discharge.
[Brief description of the drawings]
FIG. 1 is a graph showing changes in utilization rate and average discharge voltage with respect to magnesium solid solution of an active material according to an embodiment of the present invention.
FIG. 2 shows the utilization factor and the high rate during low rate discharge with respect to the peak half-value width of (101) plane in the vicinity of 2θ = 37 to 40 ° of X-ray diffraction using CuKα ray of the active material according to the embodiment of the present invention Diagram showing changes in utilization during discharge
FIG. 3 is a graph showing a change in utilization rate during high rate discharge with respect to the sulfate content of an active material according to an embodiment of the present invention.
FIG. 4 shows the X-ray diffraction using the CuKα ray of the active material according to the embodiment of the present invention. The peak intensity A of the (101) plane near 2θ = 37 to 40 ° is about (001 = 37 ° to 40 °). ) A graph showing the change in the utilization rate during high rate discharge with respect to the ratio B / A of the peak peak intensity B of the surface.
FIG. 5 is a graph showing changes in utilization rate and average discharge voltage with respect to the amount of cobalt solid solution of an active material according to an embodiment of the present invention.

Claims

Nickel hydroxide containing at least magnesium in a solid solution state, wherein the magnesium content is 2 mol% or more and 7 mol% or less with respect to all metal elements in the nickel hydroxide, and the tap density is 1.9 g / a cm ³ or more powder, located in the vicinity of 2 [Theta] = 37 to 40 ° in X-ray diffraction using a CuKα ray (101) half width of the peak of the surface is less than 1.2 ° to 0.7 ° The peak intensity B of the (001) plane located in the vicinity of 2θ = 18-21 ° relative to the peak intensity A of the (101) plane located in the vicinity of 2θ = 37-40 ° of X-ray diffraction using the CuKα ray. The B / A ratio is 1.1 or more and the sulfate radical contained in the crystal is 0.5% by weight or less.

2. The positive electrode active material for an alkaline storage battery according to claim 1, wherein the nickel hydroxide is a solid solution of at least one element selected from the group consisting of cobalt and manganese in addition to magnesium.

3. The alkali according to claim 2 , wherein a content ratio of at least one element selected from the group consisting of cobalt and manganese is 0.5 mol% or more and 3 mol% or less with respect to all metal elements in nickel hydroxide. Positive electrode active material for storage battery.

The positive electrode active material for an alkaline storage battery according to claim 1, wherein the nickel hydroxide powder has a surface coated with cobalt oxide.

The positive electrode active material for an alkaline storage battery according to claim 4, wherein an average valence of cobalt of the cobalt oxide is larger than trivalent.

X-ray using nickel hydroxide containing at least magnesium in a solid solution, wherein the magnesium content is 2 mol% or more and 7 mol% or less with respect to all metal elements in nickel hydroxide. The half-value width of the peak of the (101) plane located in the vicinity of 2θ = 37-40 ° of diffraction is in the range of 0.7 ° to 1.2 °, and 2θ = 37 of X-ray diffraction using CuKα rays. The ratio B / A of the peak intensity B of the (001) plane located near 2θ = 18 to 21 ° to the peak intensity A of the (101) plane located near ˜40 ° is 1.1 or more. A positive electrode active material for alkaline storage batteries.

The positive electrode active material for an alkaline storage battery according to claim 6, wherein the positive electrode active material is a powder having a tap density of 1.9 g / cm 3 or more.

The positive electrode active material for an alkaline storage battery according to claim 6, wherein the sulfate radical contained in the crystal is 0.5% by weight or less.

The nickel hydroxide is not only magnesium but also cobalt and manganese.
The positive electrode active material for an alkaline storage battery according to claim 6, wherein at least one element selected from the group consisting of the above is dissolved.

10. The alkali according to claim 9, wherein a content ratio of at least one element selected from the group consisting of cobalt and manganese is 0.5 mol% or more and 3 mol% or less with respect to all metal elements in nickel hydroxide. Positive electrode active material for storage battery.

The positive electrode active material for an alkaline storage battery according to claim 6, wherein a surface of the nickel hydroxide powder is coated with cobalt oxide.

The positive electrode active material for an alkaline storage battery according to claim 11, wherein an average valence of cobalt of the cobalt oxide is larger than trivalence.

A positive electrode for an alkaline storage battery comprising a positive electrode active material according to any one of claims 1 to 12.

An alkaline storage battery using the positive electrode for an alkaline storage battery according to claim 13 .