JP3617203B2 - Manufacturing method of nickel metal hydride secondary battery - Google Patents
Manufacturing method of nickel metal hydride secondary battery Download PDFInfo
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- JP3617203B2 JP3617203B2 JP21956596A JP21956596A JP3617203B2 JP 3617203 B2 JP3617203 B2 JP 3617203B2 JP 21956596 A JP21956596 A JP 21956596A JP 21956596 A JP21956596 A JP 21956596A JP 3617203 B2 JP3617203 B2 JP 3617203B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Description
【０００１】
【発明の属する技術分野】
本発明は、ニッケル水素二次電池の製造方法に関するものである。
【０００２】
【従来の技術】
近年、アルカリ蓄電池は、携帯機器の普及に伴いその電源として高容量の二次電池が要望されている。特にニッケル−水素電池は、水酸化ニッケルを主体とした活物質からなる正極と、水素吸蔵合金を活物質とした負極からなる二次電池であり、高容量で高信頼性の二次電池として急速に普及してきている。
【０００３】
以下、上記した従来のアルカリ蓄電池用正極について説明する。
アルカリ蓄電池用の正極としては、大別して焼結式と非焼結式とがある。前者はニッケル粉末を焼結して得た多孔度８０％程度の多孔質ニッケル焼結基板に、硝酸ニッケル水溶液等のニッケル塩溶液を含浸し、次いで、アルカリ水溶液に浸漬するなどして多孔質ニッケル焼結基板中に水酸化ニッケル活物質を生成させて製造するものである。この電極は基板の多孔度をこれ以上大きくする事が困難であるため、充填される活物質量を増加させる事ができず、高容量化には限界がある。
【０００４】
また後者の非焼結式正極としては、例えば、特開昭５０−３６９３５号公報に開示された、ニッケル金属よりなる三次元的に連続した多孔度９５％以上のスポンジ状多孔体基板に、活物質である水酸化ニッケルを充填するものが提案され、現在高容量の二次電池の正極として広く用いられている。この非焼結式正極においては高容量化の点から、球状の水酸化ニッケルを充填することが提案されている。スポンジ状多孔体基板の孔部（ポア）サイズは２００〜５００μｍ程度であり、このポアに粒径が数μｍ〜数１０μｍの球状水酸化ニッケルを充填するため、導電ネットワークが保たれるニッケル金属骨格近傍の水酸化ニッケルは充放電反応がスムーズに進行するが、骨格から離れた水酸化ニッケルの反応は十分に進まない。そこでこの非焼結式正極では充填した水酸化ニッケルの利用率を向上させるために、活物質である水酸化ニッケル以外に導電剤を用いて、これで球状の水酸化ニッケル粒子間を電気的に接続させている。この導電剤としては、水酸化コバルト、一酸化コバルトのようなコバルト化合物や、金属コバルト、金属ニッケル等が用いられる。これにより、非焼結式正極では活物質を高密度に充填することが可能となり、焼結式正極に比較し高容量化が図れる。
【０００５】
【発明が解決しようとする課題】
しかしながら上記のような構成の非焼結式正極においても、これら導電剤の添加は、活物質の利用率は向上させるが導電剤自体は活物質として働かないため、基板への活物質の充填密度を実質的に下げてしまい、結果として正極板の容量密度は６００ｍＡｈ／ｃｃ程度になる。
【０００６】
また、ここで水酸化コバルトが導電剤として用いられた場合、水酸化コバルトは強アルカリの電解液にコバルト酸イオンとして溶解する。溶解したコバルト酸イオンは水酸化ニッケル粒子表面や水酸化コバルト粒子表面に再析出して水酸化コバルトとなり、さらに初期の充電によって導電体であるオキシ水酸化コバルトになって、水酸化ニッケル粒子同士を電気的に結合していると考えられている。また溶解しなかった水酸化コバルトも初期充電によりオキシ水酸化コバルトに変化し、これも導電剤として働くこととなる。
【０００７】
しかしながら水酸化コバルト等の溶解度は電解液に対して１００〜２００ｐｐｍ程度であり、この溶解析出により水酸化ニッケル粒子表面に形成されるコバルト層は薄く微弱である。またこのコバルト層は水酸化ニッケル粒子表面のみだけでなく、水酸化ニッケル間の導電網に関与しないスポンジ状多孔体基板骨格表面にも形成される。しかもこのオキシ水酸化コバルトからなる導電網は薄く微弱であるため高放電率条件下ではその集電が放電
反応に追いつけなかったり、高温で保存した場合等ではアルカリ電解液に溶解して導電層がそこなわれ、安定した電池特性を維持する事が困難であった。
【０００８】
また、水酸化ニッケルと、これに導電剤として添加した水酸化コバルト等を混合してスポンジ状多孔体基板に充填したときの物理的混合状態にも利用率は影響され、安定した特性を常に得ることができないと言う問題点があった。
【０００９】
また、密閉型ニッケル水素二次電池では、正極が満充電状態になると、正極から酸素ガスが発生し内部圧力が増加するのを防ぐため、正極に対する負極の電気容量比率が１．５から１．８倍の極板を用いている。これは満充電時に負極の水素吸蔵合金に過剰の水素が吸蔵できるようにしておき、その水素と正極から発生する酸素とが反応して電池内のガス圧力を低減させるために容量を過剰にしておかなければならないからである。ここで実際に負極容量の正極のそれに対する過剰量を１．５から１．８倍にしなければならないのは、正極の活物質である水酸化ニッケルは、通常のニッケル水素二次電池の動作範囲において放電状態で水酸化ニッケルの平均原子価数で２．２価付近までしか放電することができないからである。
【００１０】
すなわち、この正極に対向する負極も放電時に０．２価相当の水素を吸蔵しておりその分の電気容量は不可逆で電池容量に寄与しない。従って密閉型ニッケル水素二次電池の容量を向上させるためにはこの不可逆容量を削減して実質的な電池容量を向上することが必要となる。
【００１１】
本発明は上記問題点に鑑み、高エネルギー密度のニッケル水素二次電池とその製造方法を提供することを主たる目的としたものである。
【００１２】
【課題を解決するための手段】
上記課題を解決するために、本発明のニッケル水素二次電池は、酸化剤を用いて水酸化ニッケル粉末の表面にオキシ水酸化ニッケルを形成させる第一の過程と、得られた粉末の表面に酸化還元反応を用いてオキシ水酸化コバルトを形成させる第二の過程とを経た正極活物質を備えたものである。
【００１３】
上記した構成によって、あらかじめ活物質である水酸化ニッケル粒子表面に導電剤であるオキシ水酸化コバルトを被覆させているため、強固で均一な導電剤の物理的配置がなされるとともに、導電剤として粒子状の水酸化コバルト等のみを用いる場合よりも活物質の物理的充填性が向上し、さらにこの正極は部分的に酸化された状態であるので不可逆電気容量を削減した電池を構成することができ、高エネルギー密度で安定した電池特性が得られることとなる。
【００１４】
【発明の実施の形態】
本発明は、オキシ水酸化コバルトを表面に有する水酸化ニッケル粉末を活物質としたので、高エネルギー密度で安定した電池特性が得られるニッケル水素二次電池を提供する。
【００１５】
（実施の形態）
本発明のニッケル水素二次電池の製造方法を以下に示す。第一の過程は、水酸化ニッケル粉末を、酸化剤を含む水溶液中で混合、攪拌し水酸化ニッケルの表面を酸化しオキシ水酸化ニッケルを形成させる過程である。第二の過程は、得られた粉末の表面に酸化還元反応を用いてオキシ水酸化コバルトを形成させる過程である。
【００１６】
つぎにニッケル水素二次電池の製造方法について更に詳しく説明する。
【００１７】
【実施例】
（実施例１）
まず第一の工程では、反応容器に純水を所定量入れ、そこに水酸化ニッケル粉末１００ｇを投入し攪拌器で水酸化ニッケル粉末を撹拌分散させた。この分散液を攪拌しながら水酸化ニッケルの表面を酸化してオキシ水酸化ニッケルにするために、酸化剤として次亜塩素酸ナトリウムを加え十分に撹拌した。添加した次亜塩素酸ナトリウムの量は、２価の水酸化ニッケルをその１０ｗｔ％だけ３価に酸化させる量とした。この時オキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末の平均酸化価数は２．１価であることを、化学分析法を用いて確認した。
【００１８】
続いて、得られたオキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末を純水で中性付近まで水洗して不純物を除去した。
【００１９】
第二の工程では、水洗したオキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末を水酸化ナトリウム５ｍｏｌ／ｌの水溶液に投入し、この水溶液を攪拌器で攪拌しながらヒーターにより６５℃に加温した。この水溶液に硫酸コバルト１ｍｏｌ／ｌの水溶液を滴下しながら十分に攪拌した。
【００２０】
この工程において加温した水酸化ナトリウムの溶液中に硫酸コバルトを滴下すると、コバルトはコバルト酸イオンＨＣｏＯ2 -となり、同様に水酸化アルカリの溶液中で標準水素電極電位より貴な電位となるオキシ水酸化ニッケルと次の（化１）で示す酸化還元反応が起き、水酸化ニッケル表面に導電性の高いオキシ水酸化コバルトが成長することとなる。
【００２１】
【化１】
この際滴下する硫酸コバルトの量は被覆させる量に影響するが、ここでは水酸化ニッケルに対して１０ｗｔ％のオキシ水酸化コバルトを被覆させる量をした。
【００２３】
ここでアルカリの温度、硫酸コバルトの濃度、滴下速度が適正な値になされていないと、アルカリ溶液中に水酸化コバルト粒子が析出する。析出した水酸化コバルト粒子は、オキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末とアルカリ溶液中で接触すると酸化されてしまいオキシ水酸化コバルト粒子として溶液中に分散する。オキシ水酸化コバルトは溶解してコバルト酸イオンを生成しないので、酸化還元反応を伴って水酸化ニッケル粉末の表面に被覆される事はない。また、コバルト酸イオンの原料としてアルカリ中に水酸化コバルト粒子を用いた場合も、硫酸コバルト溶液の適正な滴下を行なわなかった場合と同様に、水酸化ニッケル粉末の表面をオキシ水酸化コバルトで被覆する事はできない。
【００２４】
続いて、オキシ水酸化コバルトで被覆された水酸化ニッケル粉末を、不純物を除去するために純水で水洗し乾燥を行なった。
【００２５】
第三の工程では、得られた粉末に２ｗｔ％の酸化亜鉛を加え、純水で含水率を整えペースト状とし、これをスポンジ状多孔体基板に充填しニッケル水素二次電池用正極とした。
【００２６】
第四の工程では、上記オキシ水酸化コバルトで１０ｗｔ％表面を被覆した活物質からなる正極と水素吸蔵合金よりなる負極と組み合わせて、ニッケル水素電池を構成した。この本発明の電池をＡ，比較のためにオキシ水酸化コバルトで被覆しないオキシ水酸化ニッケ
ルを表面に有する水酸化ニッケル粉末に水酸化コバルトを１０ｗｔ％加えた活物質で正極を作成しこれを用いてニッケル水素電池を構成したものを電池Ｂ、水酸化ニッケル活物質に水酸化コバルトを１０ｗｔ％加えて正極を作成し、これを用いてニッケル水素電池を構成したものを電池Ｃとする。
【００２７】
上記電池Ａ，Ｂ，Ｃを充電レート０．１ＣｍＡで１５時間充電し、放電レート０．２ＣｍＡで終止電圧１．０Ｖまで放電するサイクルを５回行ったときの電池容量を測定した。それぞれの電池容量を理論容量（正極に充填した水酸化活物質重量に水酸化ニッケルが１電子反応をするとしたときの電気量２８９ｍＡｈ／ｇを掛けた値）で割った利用率を（表１）に示す。
【００２８】
【表１】
次に電池Ａ，Ｃについて高温での充電効率を測定した。充電は温度４５℃で充電レート０．１ＣｍＡで１５時間充電し、放電は２０℃で０．２ＣｍＡで終止電圧１．０Ｖまで放電した時の利用率を（表２）に示す。
【００３０】
【表２】
以上のように本実施例によれば、酸化還元反応を用いることにより水酸化ニッケルの表面に選択的に化学結合した高導電性のオキシ水酸化コバルトを形成できるため、高エネルギー密度で、安定した電池特性が得られた。
【００３２】
なお、実施例において第一の工程では、酸化剤は次亜塩素酸ナトリウムを用いたが、酸化剤はＫ2Ｓ2Ｏ8，Ｎａ2Ｓ2Ｏ8，（ＮＨ4）2Ｓ2Ｏ8またはＨ2Ｏ2等中性もしくはアルカリ性の酸化剤であればなんでもよい。また酸化量は、２価の水酸化ニッケルをその１０ｗｔ％だけ３価に酸化させる量としたが、被覆させるオキシ水酸化コバルトの被覆量以上であればよく３０ｗｔ％以下が望ましい。
【００３３】
また、第二の工程では、水酸化ナトリウムの水溶液を用いたが水酸化カリウム、水酸化リチウムでもよく、その濃度は１ｍｏｌ／ｌ以上８．５ｍｏｌ／ｌ以下の範囲であればよく、また温度も８０℃以下であればよい。また、コバルトの原料として硫酸コバルトを用いたが、硝酸コバルト、塩化コバルト等のコバルト塩水溶液なら何でも良い。その濃度は常温で析出が起こらない２ｍｏｌ／ｌ以下が望ましい。
【００３４】
また、第三の工程では、添加物として酸化亜鉛を用いたが、酸化カドミウム、水酸化亜鉛等でもよく、特に限定するものではない。
【００３５】
（実施例２）
第一の工程では、実施例１の第一の工程と同様にしてオキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末を作製した。
【００３６】
第二の工程では、第一の工程で作製したオキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末に対して水酸化コバルト粒子を１０ｗｔ％混合して、乾式機械的混合法によりオキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末を水酸化コバルト粒子で被覆した。
【００３７】
第三の工程では、実施例１の第三の工程と同様に、第二の工程で得られた水酸化コバルトで被覆された水酸化ニッケル粉末を活物質として、ニッケル水素二次電池用正極を作製した。
【００３８】
第四の工程では、上記ニッケル水素二次電池用正極と、セパレータと水素吸蔵合金よりなる負極を用いて、スパイラル状に電極群を構成した。
【００３９】
続いて、上記電極群を電池ケース内に挿入し、所定の電解液を注液し、封口板で封口して密閉型ニッケル水素二次電池を作製した。
【００４０】
第五の工程では、電解液を注液し、封口した後、室温以上８０℃以下で２４時間以内で放置した後の電池に初期の充放電を行なった。
【００４１】
この工程の放置時間中に、オキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末を被覆した水酸化コバルトは電解液に溶解してコバルト酸イオンとなり、実施例１と同様の酸化還元反応により水酸化ニッケルの表面に選択的にオキシ水酸化コバルトを形成する。
【００４２】
本発明の乾式機械的混合法により、水酸化ニッケル粉末表面に水酸化コバルト粒子を被覆させた活物質で正極を作成し、上述した第五の工程を経てニッケル水素二次電池を構成したものを電池Ｄ、比較のためにオキシ水酸化ニッケルを表面に有する水酸化ニッケル粉末に水酸化コバルト粒子を１０ｗｔ％加え乳鉢で混合した活物質で正極を作成し、ニッケル水素二次電池を構成したものを電池Ｅ、乾式機械的混合法により水酸化ニッケル粒子表面に水酸化コバルトを１０ｗｔ％被覆させた活物質で正極を作成し、ニッケル水素二次電池を構成したものを電池Ｆとする。
【００４３】
上記電池Ｄ，Ｅ，Ｆを充電レート０．１ＣｍＡで１５時間充電し、放電レート０．２ＣｍＡで終止電圧１．０Ｖまで放電したときの電池容量を測定した。それぞれの電池容量を理論容量（正極に充填した水酸化活物質重量に水酸化ニッケルが１電子反応をするとしたときの電気量２８９ｍＡｈ／ｇを掛けた値）で割った利用率を（表３）に示す。
【００４４】
【表３】
上記の結果から、機械的混合法で均一に物理分散した水酸化コバルトを水酸化ニッケル粉末の表面に具備させ、この水酸化コバルトを、水酸化ニッケル表面と化学結合したオキシ水酸化コバルトに変化させることにより、高エネルギー密度で、安定した電池特性が得られる。
【００４６】
ここで第二の工程で水酸化コバルトの添加量を１０ｗｔ％としたが、１０ｗｔ％に限定するものではなくそれ以下であってもよい。
【００４７】
（実施例３）
第一の工程から第二の工程までは、実施例１の第一の工程から第二の工程までと同様の処理により、オキシ水酸化コバルトを表面に有する水酸化ニッケルの活物質を作製した。
【００４８】
第三の工程から第五の工程までは、上記オキシ水酸化コバルトで被覆された水酸化ニッケル粉末を用いて、実施例２の第二の工程から第四の工程までと同様の工程でこのオキシ水酸化コバルトを表面に有する水酸化ニッケル粉末に、さらに水酸化コバルトを被覆した活物質を用いてニッケル水素二次電池を作製した。
【００４９】
このようにしてオキシ水酸化コバルトで５ｗｔ％、さらに水酸化コバルトで５ｗｔ％それぞれ被覆した活物質を用いた正極と水素吸蔵合金よりなる負極と組み合わせて、ニッケル水素二次電池Ｇを構成した。この電池を充電レート０．１ＣｍＡで１５時間充電し、放電レート０．２ＣｍＡで終止電圧１．０Ｖまで放電したときの電池容量を測定した。その電池容量を理論容量（正極に充填した水酸化活物質重量に水酸化ニッケルが１電子反応をするとしたときの電気量２８９ｍＡｈ／ｇを掛けた値）で割った利用率は９７．６％であった。
【００５０】
以上により本実施例では化学結合を持ったオキシ水酸化コバルトと物理的に配置した水酸化コバルトとにより、高エネルギー密度で、安定した電池特性が得られる。
【００５１】
【発明の効果】
以上のように本発明は、あらかじめ活物質である水酸化ニッケル粒子表面に導電剤であるオキシ水酸化コバルトを被覆させることにより、強固で均一な導電剤の物理的配置がなされるとともに、導電剤として粒子状の水酸化コバルト等のみを用いる場合よりも導電剤量を削減することができ、活物質の物理的充填性が向上し、さらに不可逆電気容量を削減した電池を構成することができるため、高エネルギー密度で安定した電池特性を得ることができるニッケル水素二次電池を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a nickel metal hydride secondary battery.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a high-capacity secondary battery is demanded as a power source for alkaline storage batteries with the spread of portable devices. Nickel-hydrogen batteries, in particular, are secondary batteries consisting of a positive electrode made of an active material mainly composed of nickel hydroxide and a negative electrode made of a hydrogen storage alloy as an active material, and has rapidly become a secondary battery with high capacity and high reliability. Has become popular.
[0003]
Hereinafter, the above-described conventional positive electrode for an alkaline storage battery will be described.
The positive electrode for the alkaline storage battery is roughly classified into a sintered type and a non-sintered type. In the former, a porous nickel sintered substrate obtained by sintering nickel powder is impregnated with a nickel salt solution such as an aqueous nickel nitrate solution and then immersed in an alkaline aqueous solution. It is produced by producing a nickel hydroxide active material in a sintered substrate. Since it is difficult to increase the porosity of the substrate beyond this electrode, the amount of active material to be filled cannot be increased, and there is a limit to increasing the capacity.
[0004]
As the latter non-sintered positive electrode, for example, a three-dimensionally continuous sponge-like porous substrate having a porosity of 95% or more disclosed in Japanese Patent Application Laid-Open No. 50-36935 is used. A material filled with nickel hydroxide, which is a substance, has been proposed and is currently widely used as a positive electrode of a high-capacity secondary battery. In this non-sintered positive electrode, it has been proposed to fill spherical nickel hydroxide from the viewpoint of increasing the capacity. The pore size of the porous porous substrate is about 200 to 500 μm, and the pore is filled with spherical nickel hydroxide having a particle size of several μm to several tens of μm. In the vicinity of nickel hydroxide, the charge / discharge reaction proceeds smoothly, but the reaction of nickel hydroxide away from the skeleton does not proceed sufficiently. Therefore, in this non-sintered positive electrode, in order to improve the utilization rate of the filled nickel hydroxide, a conductive agent is used in addition to the nickel hydroxide as the active material, thereby electrically connecting the spherical nickel hydroxide particles. Connected. As the conductive agent, cobalt compounds such as cobalt hydroxide and cobalt monoxide, metallic cobalt, metallic nickel and the like are used. As a result, the non-sintered positive electrode can be filled with the active material at a high density, and the capacity can be increased as compared with the sintered positive electrode.
[0005]
[Problems to be solved by the invention]
However, even in the non-sintered positive electrode configured as described above, the addition of these conductive agents improves the utilization rate of the active material, but the conductive agent itself does not work as the active material, so the packing density of the active material on the substrate As a result, the capacity density of the positive electrode plate is about 600 mAh / cc.
[0006]
Further, when cobalt hydroxide is used as a conductive agent, cobalt hydroxide is dissolved as cobaltate ions in a strong alkaline electrolyte. The dissolved cobalt oxide ions re-deposit on the nickel hydroxide particle surface or cobalt hydroxide particle surface to become cobalt hydroxide, and further become cobalt oxyhydroxide, which is a conductor by initial charging, It is considered to be electrically coupled. Moreover, the cobalt hydroxide which did not melt | dissolve also changes to cobalt oxyhydroxide by initial charge, and this will also work as a electrically conductive agent.
[0007]
However, the solubility of cobalt hydroxide or the like is about 100 to 200 ppm with respect to the electrolytic solution, and the cobalt layer formed on the surface of the nickel hydroxide particles by this dissolution and precipitation is thin and weak. The cobalt layer is formed not only on the surface of the nickel hydroxide particles but also on the surface of the sponge-like porous substrate skeleton that does not participate in the conductive network between the nickel hydroxides. Moreover, since the conductive network made of cobalt oxyhydroxide is thin and weak, the current collection cannot catch up with the discharge reaction under high discharge rate conditions, or when stored at a high temperature, the conductive layer dissolves in the alkaline electrolyte. Therefore, it was difficult to maintain stable battery characteristics.
[0008]
The utilization rate is also affected by the physical mixing state when nickel hydroxide and cobalt hydroxide or the like added as a conductive agent are mixed and filled into a sponge-like porous substrate, and stable characteristics are always obtained. There was a problem that it was not possible.
[0009]
Further, in the sealed nickel-metal hydride secondary battery, when the positive electrode is fully charged, oxygen gas is generated from the positive electrode and the internal pressure is prevented from increasing, so that the capacitance ratio of the negative electrode to the positive electrode is 1.5 to 1. An 8-fold plate is used. This is to allow excess hydrogen to be stored in the hydrogen storage alloy of the negative electrode when fully charged, and to increase the capacity in order to reduce the gas pressure in the battery by the reaction of the hydrogen and oxygen generated from the positive electrode. Because you have to leave. Here, the amount of excess of the negative electrode capacity relative to that of the positive electrode must be increased 1.5 to 1.8 times because the nickel hydroxide, which is the active material of the positive electrode, is the operating range of a normal nickel metal hydride secondary battery. This is because, in the discharged state, the discharge can only be performed up to about 2.2 in terms of the average valence of nickel hydroxide.
[0010]
That is, the negative electrode facing the positive electrode also occludes hydrogen corresponding to 0.2 valence at the time of discharge, and the electric capacity is irreversible and does not contribute to the battery capacity. Therefore, in order to improve the capacity of the sealed nickel-metal hydride secondary battery, it is necessary to reduce the irreversible capacity and improve the substantial battery capacity.
[0011]
In view of the above problems, the main object of the present invention is to provide a nickel-hydrogen secondary battery having a high energy density and a method for producing the same.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a nickel metal hydride secondary battery of the present invention includes a first step of forming nickel oxyhydroxide on the surface of nickel hydroxide powder using an oxidizing agent, and a surface of the obtained powder. The positive electrode active material which passed through the 2nd process of forming cobalt oxyhydroxide using oxidation-reduction reaction is provided.
[0013]
With the above-described configuration, the surface of the nickel hydroxide particle, which is an active material, is coated with cobalt oxyhydroxide, which is a conductive agent, so that a strong and uniform physical arrangement of the conductive agent is made and the particles as the conductive agent are used. As compared with the case using only cobalt hydroxide or the like, the physical filling property of the active material is improved, and furthermore, since this positive electrode is in a partially oxidized state, a battery with reduced irreversible electric capacity can be configured. Thus, stable battery characteristics can be obtained at a high energy density.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a nickel metal hydride secondary battery capable of obtaining stable battery characteristics at a high energy density because nickel hydroxide powder having cobalt oxyhydroxide on its surface is used as an active material.
[0015]
(Embodiment)
The manufacturing method of the nickel metal hydride secondary battery of the present invention is shown below. The first process, the nickel hydroxide powder, mixed in an aqueous solution containing an oxidizing agent, a stirring process of causing formation of an oxide and oxyhydroxide nickel surface of the nickel hydroxide. The second process is a process of forming cobalt oxyhydroxide on the surface of the obtained powder using an oxidation-reduction reaction .
[0016]
Next, the manufacturing method of the nickel metal hydride secondary battery will be described in more detail.
[0017]
【Example】
(Example 1)
First, in a first step, a predetermined amount of pure water was put into a reaction vessel, and 100 g of nickel hydroxide powder was put therein, and the nickel hydroxide powder was stirred and dispersed with a stirrer. In order to oxidize the surface of nickel hydroxide to nickel oxyhydroxide while stirring this dispersion, sodium hypochlorite was added as an oxidizing agent and sufficiently stirred. The amount of sodium hypochlorite added was such that 10% by weight of divalent nickel hydroxide was oxidized to trivalent. At this time, it was confirmed by chemical analysis that the average oxidation valence of nickel hydroxide powder having nickel oxyhydroxide on the surface was 2.1.
[0018]
Subsequently, the obtained nickel hydroxide powder having nickel oxyhydroxide on the surface was washed with pure water to near neutrality to remove impurities.
[0019]
In the second step, nickel hydroxide powder having nickel oxyhydroxide washed with water on the surface was put into an aqueous solution of 5 mol / l sodium hydroxide, and this aqueous solution was heated to 65 ° C. with a heater while stirring with a stirrer. . The aqueous solution was sufficiently stirred while dropping a 1 mol / l aqueous solution of cobalt sulfate.
[0020]
When cobalt sulfate is dropped into the heated sodium hydroxide solution in this step, cobalt becomes cobaltate ion HCoO 2 − , and similarly, oxywater having a potential higher than the standard hydrogen electrode potential in the alkali hydroxide solution. The oxidation-reduction reaction shown by the following (Chemical Formula 1) occurs with nickel oxide, and cobalt oxyhydroxide having high conductivity grows on the nickel hydroxide surface.
[0021]
[Chemical 1]
The amount of cobalt sulfate dripped at this time affects the amount to be coated, but here, the amount to coat 10 wt% cobalt oxyhydroxide with respect to nickel hydroxide was used.
[0023]
Here, if the alkali temperature, the concentration of cobalt sulfate, and the dropping rate are not set to appropriate values, cobalt hydroxide particles are precipitated in the alkaline solution. The precipitated cobalt hydroxide particles are oxidized when they come into contact with a nickel hydroxide powder having nickel oxyhydroxide on the surface in an alkaline solution, and are dispersed in the solution as cobalt oxyhydroxide particles. Since cobalt oxyhydroxide dissolves and does not produce cobaltate ions, it is not coated on the surface of the nickel hydroxide powder with a redox reaction. In addition, when cobalt hydroxide particles are used in the alkali as a raw material for cobalt oxide ions, the surface of the nickel hydroxide powder is coated with cobalt oxyhydroxide in the same manner as when the cobalt sulfate solution is not properly dropped. I can't do it.
[0024]
Subsequently, the nickel hydroxide powder coated with cobalt oxyhydroxide was washed with pure water and dried to remove impurities.
[0025]
In the third step, 2 wt% zinc oxide was added to the obtained powder, the water content was adjusted with pure water to make a paste, and this was filled in a sponge-like porous substrate to obtain a positive electrode for a nickel metal hydride secondary battery.
[0026]
In the fourth step, a nickel-metal hydride battery was constructed by combining a positive electrode made of an active material whose surface was coated with 10% by weight of cobalt oxyhydroxide and a negative electrode made of a hydrogen storage alloy. This battery of the present invention was prepared by using a positive electrode made of an active material obtained by adding 10 wt% of cobalt hydroxide to nickel hydroxide powder having nickel oxyhydroxide not coated with cobalt oxyhydroxide on the surface for comparison. The battery constituting the nickel-metal hydride battery is referred to as battery B, and the positive electrode is prepared by adding 10 wt% of cobalt hydroxide to the nickel hydroxide active material.
[0027]
The batteries A, B, and C were charged at a charge rate of 0.1 CmA for 15 hours, and the battery capacity was measured when a cycle of discharging to a final voltage of 1.0 V at a discharge rate of 0.2 CmA was performed five times. The utilization rate obtained by dividing the capacity of each battery by the theoretical capacity (the value obtained by multiplying the weight of the hydroxide active material charged in the positive electrode by the amount of electricity of 289 mAh / g when nickel hydroxide performs one-electron reaction) (Table 1). Shown in
[0028]
[Table 1]
Next, the charging efficiency at high temperature was measured for batteries A and C. Charging is performed at a temperature of 45 ° C. for 15 hours at a charging rate of 0.1 CmA, and discharging is performed at 20 ° C. at 0.2 CmA at a final voltage of 1.0 V (Table 2).
[0030]
[Table 2]
As described above, according to this example, by using an oxidation-reduction reaction, highly conductive cobalt oxyhydroxide selectively chemically bonded to the surface of nickel hydroxide can be formed, so that it is stable at a high energy density. Battery characteristics were obtained.
[0032]
In the examples, sodium hypochlorite was used as the oxidizing agent in the first step, but the oxidizing agents were K 2 S 2 O 8 , Na 2 S 2 O 8 , (NH 4 ) 2 S 2 O 8. Alternatively, any neutral or alkaline oxidizing agent such as H 2 O 2 may be used. The oxidation amount is such that 10% by weight of the divalent nickel hydroxide is oxidized to the trivalent amount. However, it may be more than the coating amount of the cobalt oxyhydroxide to be coated, and is preferably 30% by weight or less.
[0033]
In the second step , an aqueous solution of sodium hydroxide was used, but potassium hydroxide or lithium hydroxide may be used. The concentration may be in the range of 1 mol / l to 8.5 mol / l, and the temperature is also set. What is necessary is just 80 degrees C or less. Further, although cobalt sulfate is used as a raw material for cobalt, any cobalt salt aqueous solution such as cobalt nitrate or cobalt chloride may be used. The concentration is desirably 2 mol / l or less at which precipitation does not occur at room temperature.
[0034]
In the third step , zinc oxide is used as an additive, but it may be cadmium oxide, zinc hydroxide, or the like, and is not particularly limited.
[0035]
(Example 2)
In the first step, nickel hydroxide powder having nickel oxyhydroxide on the surface was produced in the same manner as in the first step of Example 1.
[0036]
In the second step, the cobalt hydroxide particles against the nickel hydroxide powder having a nickel oxyhydroxide prepared in the first step to the surface by mixing 10 wt%, a nickel oxyhydroxide by dry mechanical mixing method The nickel hydroxide powder on the surface was coated with cobalt hydroxide particles.
[0037]
In the third step , as in the third step of Example 1, using the nickel hydroxide powder coated with cobalt hydroxide obtained in the second step as an active material, a positive electrode for a nickel metal hydride secondary battery is formed. Produced.
[0038]
In the fourth step , an electrode group was formed in a spiral shape using the above-described positive electrode for nickel-hydrogen secondary battery and a negative electrode made of a separator and a hydrogen storage alloy.
[0039]
Then, the said electrode group was inserted in the battery case, predetermined | prescribed electrolyte solution was poured, and it sealed with the sealing board, and produced the sealed nickel-hydrogen secondary battery.
[0040]
In the fifth step , after the electrolyte was poured and sealed, the battery after being left at room temperature or higher and 80 ° C. or lower for 24 hours or less was initially charged and discharged.
[0041]
During the standing time of this step, cobalt hydroxide coated with nickel hydroxide powder having nickel oxyhydroxide on the surface dissolves in the electrolytic solution to become cobaltate ions, and is oxidized by the oxidation-reduction reaction similar to Example 1. Cobalt oxyhydroxide is selectively formed on the nickel surface.
[0042]
A positive electrode is made of an active material in which cobalt hydroxide particles are coated on the surface of nickel hydroxide powder by the dry mechanical mixing method of the present invention, and a nickel metal hydride secondary battery is configured through the fifth step described above. For battery D, for comparison purposes, a nickel hydride secondary battery is constructed by making a positive electrode with an active material in which nickel hydroxide powder having nickel oxyhydroxide on the surface and 10 wt% cobalt hydroxide particles are added and mixed in a mortar. A battery E is formed by forming a positive electrode with an active material in which nickel hydroxide particles are coated with 10 wt% of cobalt hydroxide on the surface of nickel hydroxide particles by a dry mechanical mixing method, and a nickel hydrogen secondary battery is configured as a battery F.
[0043]
The batteries D, E, and F were charged at a charge rate of 0.1 CmA for 15 hours, and the battery capacity when discharged to a final voltage of 1.0 V at a discharge rate of 0.2 CmA was measured. The utilization rate obtained by dividing the capacity of each battery by the theoretical capacity (value obtained by multiplying the weight of the hydroxide active material charged in the positive electrode by the amount of electricity 289 mAh / g when nickel hydroxide performs a one-electron reaction) (Table 3). Shown in
[0044]
[Table 3]
From the above results, the surface of the nickel hydroxide powder is provided with cobalt hydroxide that is uniformly physically dispersed by a mechanical mixing method, and this cobalt hydroxide is converted into cobalt oxyhydroxide that is chemically bonded to the nickel hydroxide surface. As a result, stable battery characteristics can be obtained at a high energy density.
[0046]
Here, although the addition amount of cobalt hydroxide is 10 wt% in the second step, it is not limited to 10 wt%, and may be less.
[0047]
(Example 3)
From the first step to the second step , an active material of nickel hydroxide having cobalt oxyhydroxide on the surface was produced by the same treatment as in the first step to the second step of Example 1.
[0048]
From the third step to the fifth step , using the nickel hydroxide powder coated with the cobalt oxyhydroxide, this oxy-oxygen is produced in the same steps as the second step to the fourth step in Example 2 . A nickel metal hydride secondary battery was fabricated using an active material in which cobalt hydroxide was coated on nickel hydroxide powder having cobalt hydroxide on the surface .
[0049]
In this way, a nickel-hydrogen secondary battery G was constructed by combining a positive electrode using an active material coated with 5 wt% of cobalt oxyhydroxide and further 5 wt% of cobalt hydroxide and a negative electrode made of a hydrogen storage alloy. This battery was charged at a charge rate of 0.1 CmA for 15 hours, and the battery capacity when discharged to a final voltage of 1.0 V at a discharge rate of 0.2 CmA was measured. The utilization rate obtained by dividing the battery capacity by the theoretical capacity (the weight of the hydroxide active material charged in the positive electrode multiplied by the amount of electricity 289 mAh / g when nickel hydroxide performs one electron reaction) was 97.6%. there were.
[0050]
As described above, in this embodiment, stable battery characteristics can be obtained at high energy density by using cobalt oxyhydroxide having a chemical bond and cobalt hydroxide physically disposed.
[0051]
【The invention's effect】
As described above, according to the present invention, the surface of nickel hydroxide particles, which is an active material, is coated with cobalt oxyhydroxide, which is a conductive agent, so that a strong and uniform physical arrangement of the conductive agent is achieved. As compared with the case where only particulate cobalt hydroxide or the like is used, the amount of the conductive agent can be reduced, the physical filling property of the active material is improved, and a battery with further reduced irreversible electric capacity can be configured. It is possible to provide a nickel metal hydride secondary battery capable of obtaining stable battery characteristics at a high energy density.
Claims (4)
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| JP21956596A JP3617203B2 (en) | 1996-07-04 | 1996-08-21 | Manufacturing method of nickel metal hydride secondary battery |
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| JP8-174710 | 1996-07-04 | ||
| JP17471096 | 1996-07-04 | ||
| JP21956596A JP3617203B2 (en) | 1996-07-04 | 1996-08-21 | Manufacturing method of nickel metal hydride secondary battery |
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| JP3617203B2 true JP3617203B2 (en) | 2005-02-02 |
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Cited By (1)
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| JP2007095544A (en) * | 2005-09-29 | 2007-04-12 | Sanyo Electric Co Ltd | Positive plate for alkaline secondary battery and alkaline secondary battery |
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| JP3448510B2 (en) * | 1998-04-28 | 2003-09-22 | 三洋ジ−エスソフトエナジー株式会社 | Nickel hydroxide powder for alkaline batteries and nickel hydroxide electrode using the same |
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| JP2005327564A (en) * | 2004-05-13 | 2005-11-24 | Matsushita Electric Ind Co Ltd | Process for producing alkaline battery and positive electrode active material for alkaline battery |
| CN100336249C (en) * | 2005-11-11 | 2007-09-05 | 河南新飞科隆电源有限公司 | Method of cladding hydroxy cobalt oxide on spherical nickel hydroxide surface |
| CN115966414B (en) * | 2023-01-11 | 2025-06-20 | 浙江工业大学 | Preparation and application of supercapacitors and their electrodes, NiOOH-Co(OH)2 composite electrode active materials |
| CN119650605B (en) * | 2024-11-14 | 2025-07-18 | 广东新力能源有限公司 | A nickel-hydrogen battery, positive electrode material and preparation method and application thereof |
| CN119284978A (en) * | 2024-12-11 | 2025-01-10 | 河南科隆新能源股份有限公司 | Preparation method and application of cobalt-coated spherical nickel hydroxide with cobalt oxidation on the surface and nickel oxidation in the core |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2007095544A (en) * | 2005-09-29 | 2007-04-12 | Sanyo Electric Co Ltd | Positive plate for alkaline secondary battery and alkaline secondary battery |
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