JP3969718B2

JP3969718B2 - Alkaline battery and manufacturing method thereof

Info

Publication number: JP3969718B2
Application number: JP2002312353A
Authority: JP
Inventors: 範幸伊東; 三七十郎牛島; 真一岩本; 哲夫伊津
Original assignee: Hitachi Maxell Energy Ltd
Current assignee: Maxell Ltd
Priority date: 2002-10-28
Filing date: 2002-10-28
Publication date: 2007-09-05
Anticipated expiration: 2022-10-28
Also published as: JP2004146294A

Description

【０００１】
【発明の属する技術分野】
本発明は、アルカリ電池およびその製造方法に関し、さらに負荷特性に優れたアルカリ電池とその製造方法に関する。
【０００２】
【従来の技術】
亜鉛を負極活物質とするアルカリ電池は、各種電子機器の電源として用いられ、その用途に応じて種々の特性が要求されている。特に、近年普及が著しいデジタルカメラにおいては、撮影可能枚数をできるだけ多くするためには、電池の高容量化と大電流放電特性などの負荷特性のさらなる向上が必要であり、その要求を満たすことのできる電池設計が検討されている。
【０００３】
電池の高容量化のためには、活物質の充填量の増加が必要であるが、活物質が放電に有効に利用されなければ容量増に結びつかないため、単に、活物質の充填量を多くするのみでは目的を達することはできない。放電容量は活物質の利用率との兼ね合いで決定されるものであるから、放電反応がスムーズに進行するように正極、負極および電解液の設計がなされることが必要である。二酸化マンガンを正極活物質とするアルカリ電池の正極の放電反応は、以下の式（１）に従い進行する。
【０００４】
正極：ＭｎＯ_２＋Ｈ_２Ｏ＋ｅ⁻→ＭｎＯＯＨ＋ＯＨ⁻ （１）
【０００５】
上記式より明らかなように、正極では放電時に水が消費されるため、放電反応の面からは、電池内で正極側にできるだけ多くの水分が存在することが望ましく、同様のことがオキシ水酸化ニッケルを正極活物質とした場合にも当てはまる。
【０００６】
ところで、実際のアルカリ電池では、正極活物質と導電剤およびアルカリ電解液とを混合して正極合剤が形成されており、さらに、筒状セパレータの内部に注入されるアルカリ電解液を正極合剤が吸収するため、電池の組み立て後一定時間経つと、正極合剤中にはある程度の水分が含有されることになる（特許文献１参照）。また、この正極合剤形成時に添加する電解液の水酸化カリウム濃度は４０〜５０ｗｔ％が望ましく、セパレータの内部へ注入する電解液の水酸化カリウム濃度は３５〜４５ｗｔ％が望ましいとされている（特許文献１参照）。
【０００７】
また、上記正極合剤中の水分量に関しては、正極合剤中の含有水分率を３．５％〜５．０％とし、電池形成後の正極合剤中に含有させる水酸化カリウム電解液重量を、正極合剤中の固形分重量１００に対して１０．６〜１５．９とすることも提案されている（特許文献２参照）。さらに、安全性および放電特性の観点から、電池全体の水分添加量を、二酸化マンガンの理論放電容量１ＡＨ当たり０．９４７〜１．１４６ｇとする提案もある（特許文献３参照）。これは、活物質１ｇ当たりに換算すると０．２９２〜０．３５３ｇの水分が添加されることとなり、二酸化マンガン１ｇの放電反応に必要とする水分量（０．２０７ｇ）と比べてかなり多い値である。
【０００８】
【特許文献１】
特開２００２−１５７４８号公報（段落番号０００２、段落番号０００７）
【特許文献２】
特開２０００−３０６５７５号公報（段落番号０００６−０００７）
【特許文献３】
特開２００１−６８１２１号公報（段落番号０００６−０００８）
【０００９】
【発明が解決しようとする課題】
ところが、上記正極合剤中の電解液量の範囲では、その水分量としてはまだ不足しており、重負荷において良好な特性を得ることができない。一方、電池の組み立て時に、必要とされる水分を正極合剤にあらかじめ含有させてしまうと、活物質の充填密度が低下し容量低下が避けられなくなる。さらに、合剤成形時に合剤内から水分が出てきたり、成形強度が低下して合剤がうまく成形できなくなるなど製造上の問題も生じるため、正極合剤の形成に際して、合剤中に含有させる水分量はできるだけ少ない方が望ましい。
【００１０】
すなわち、電池の組み立てに使用する正極合剤中の水分量はできるだけ少なくする一方で、電池組み立て後には、正極合剤中に多くの水分を含有させるという相反する要求を満足させることが必要となる。
【００１１】
本発明者らは、正極合剤中の含有水分率の調整や電池全体の水分添加量の調整のみでは、これらの要求を満足させることはできず、電池組み立て後に、必要とされる量の水分が、セパレータあるいは負極の側から正極合剤中に移動するのを可能とする何らかの工夫を行うことが必要であることに気づいた。また、電池内で水分を適正に配分させることにより、電池全体の水分添加量を低減できるとともに、余分な水分が存在しないことにより、高温での貯蔵劣化が少なくなることにも気づいた。
【００１２】
本発明は、上記事情に鑑みてなされたもので、負荷特性や短絡時の安全性および高温貯蔵性に優れたアルカリ電池を提供し、また、そのようなアルカリ電池の製造方法を提供することを課題とするものである。
【００１３】
【課題を解決するための手段】
本発明のアルカリ電池は、二酸化マンガンおよびオキシ水酸化ニッケルの少なくとも一方を活物質として含有する正極合剤の成形体を用いたアルカリ電池であって、電池組み立てから３〜６ヶ月の正極合剤が水酸化カリウムを含むアルカリ電解液を含有し、前記正極合剤が含有する水分量が、電解液を含めた正極合剤の質量に対して８．４〜１０質量％であり、電池系内の水分量の合計が、正極活物質１ｇ当たり０．２３〜０．２７５ｇであることを特徴とする。
【００１４】
また本発明は、上記アルカリ電池の製造方法として、二酸化マンガンおよびオキシ水酸化ニッケルの少なくとも一方と水酸化カリウムを溶解したアルカリ電解液とを含有する正極合剤の成形体を用いてアルカリ電池を組み立てるアルカリ電池の製造方法であって、電池組み立てに使用する正極合剤中に含有させる水酸化カリウムの量を、電解液を含めた正極合剤の質量に対して２．４〜４質量％とし、電池組み立てから３〜６ヶ月の正極合剤が含有する水分量を、電解液を含めた正極合剤の質量に対して８．４〜１０質量％とすることを特徴とするアルカリ電池の製造方法を提供する。
【００１５】
さらに、本発明は、上記アルカリ電池の製造方法として、二酸化マンガンおよびオキシ水酸化ニッケルの少なくとも一方と水酸化カリウムを溶解したアルカリ電解液とを含有する正極合剤の成形体を用いてアルカリ電池を組み立てるアルカリ電池の製造方法であって、電池組み立てに使用する正極合剤中に含有させる水分の量を、電解液を含めた正極合剤の質量に対して３．０〜４．２質量％とし、電池組み立てから３〜６ヶ月の正極合剤が含有する水分量を、電解液を含めた正極合剤の質量に対して８．４〜１０質量％とすることを特徴とするアルカリ電池の製造方法を提供する。
【００１６】
上記製造方法を用いてアルカリ電池の組み立てを行うことにより、電池組み立て後の正極合剤中に放電反応に必要とされる充分な量の水分を含有させることが可能となり、電池内での水分の配分が適正化されるため、電池全体の水分含有量が少なくても負荷特性や短絡時の安全性に優れ、高温での貯蔵劣化の少ないアルカリ電池を得ることができる。
【００１７】
【発明の実施の形態】
以下、本発明のアルカリ電池の作製について述べる。本発明のアルカリ電池は、電池の組み立て後に、正極合剤の含有する水分量が、電解液を含めた正極合剤の質量に対して８．４〜１０質量％となることを特徴とする。そのため、セパレータあるいは負極側から比較的多くの水分が正極内に移動することが求められる。この水分の移動を生じさせるためには、そのための駆動力となるものが必要となるが、この駆動力を生み出す方法として、例えば、あらかじめ正極合剤内に含有させる電解液と、組み立て時に注液する電解液あるいは負極に含有させる電解液のアルカリ濃度の間に大きな差を設け、組み立て後に、前記濃度差によりセパレータあるいは負極側の水分を正極合剤内に移動させる方法が例示される。
【００１８】
正極は、二酸化マンガンおよびニッケル酸化物の少なくとも一方と導電剤と水酸化カリウムを含むアルカリ電解液とを混合することにより合剤化し、これを成形して成形体とすることにより得られる。合剤化の際に添加するアルカリ電解液の水酸化カリウム濃度を５０質量％より高くすることにより、前記駆動力が大きくなり、正極合剤内に多量の水分を取り込むことが可能となる。また、合剤の結着力が向上し均質な混合体が形成されるため、活物質を高密度で充填することも可能となる。このとき、正極合剤の密度は３．２〜３．３５ｇ／ｃｍ^３とするのがよく、必要な活物質充填量を確保しながら、多くの水分を含有させることができる。
【００１９】
なお、活物質である二酸化マンガンやニッケル酸化物は、通常、吸着などにより多少の水分を含有しているため、合剤中に含有されるアルカリ電解液の水酸化カリウム濃度は、最初に添加するアルカリ電解液の水酸化カリウム濃度よりも低くなる。このため、水分量を考える場合は上記活物質に由来する水分も考慮した方がよく、最終的に合剤中に含有される電解液の水酸化カリウム濃度が４０質量％以上となるよう、合剤に添加するアルカリ電解液の濃度を調整することが望ましい。
【００２０】
また、アルカリ電解液の添加量についても、合剤が含有する電解液を含めた合剤全体の質量に対して、水酸化カリウムの質量では２．４〜４質量％の範囲とするのが望ましく、水分量では３．０〜４．２質量％とするのが望ましい。これにより、適切な駆動力が得られ、電池組み立て後の水分量を適正な範囲に調整しやすくなる。
【００２１】
上記正極合剤の作製においては、電解液の水酸化カリウム濃度を５０質量％より高くする場合、室温での水酸化カリウムの飽和溶解度を超えてしまうため、飽和量を超えた水酸化カリウムの析出による合剤の不均質化が予想される。そこで、加温雰囲気下で合剤構成物を混合することにより水酸化カリウムの飽和量を高くし、電解液が飽和濃度に達しないような条件下で正極合剤を作製することが望ましい。温度条件としては、３５℃以上で行うことが望ましく、水分の蒸発により電解液組成が変化するのを防ぐため、７０℃以下の温度で行うことが望ましい。
【００２２】
上記以外に、目的に応じて、導電剤やバインダなどを正極合剤に含有させることもできる。導電剤としては、黒鉛、アセチレンブラック、カーボンブラック、繊維状炭素などの炭素材料を主として用いることができるが、中でも黒鉛が好ましく用いられる。導電剤の添加量は、正極活物質１００に対する質量比で３以上とすることが望ましい。正極合剤中に十分な水分を含有させるとともに、正極の導電性を向上させることにより、活物質の反応性が高まり、負荷特性の一層の向上が期待できる。一方、活物質充填量の低下は好ましくないため、導電剤の割合は８．５以下にすることが望ましい。
【００２３】
また、バインダとしては、カルボキシメチルセルロース、メチルセルロース、ポリアクリル酸塩、ポリテトラフルオロエチレン、ポリエチレンなどを用いることができる。
【００２４】
本発明では、正極の反応性が高められることにより、以下に述べる別の効果を得ることも期待できる。誤って電池を短絡させるなどの異常が生じた場合、過大な短絡電流が流れ続けるため、それに伴う発熱により電池の温度が急激に上昇して、漏液や電池の破裂などの問題が生じやすくなる。一方、本発明の電池では、従来電池よりも正極での放電反応が急速に進行するため、これに対応して負極での放電反応も急速に進行し、短絡発生後、すぐに放電生成物が負極表面に多量に析出して放電反応を抑制することになる。その結果、短時間のうちに短絡電流が大幅に減少し、電池の温度上昇が抑制されるため、上記問題発生を防ぐことができる。
【００２５】
なお、上述した正極への水分の移動を生じさせる駆動力は、上記正極の構成だけで定まるものではなく、負極など他の構成部材との関係、特に、外装体の中に別途注入される電解液や負極合剤に含有される電解液の水酸化カリウム濃度と密接に関係するため、それら構成も最適化されることが望まれる。すなわち、注入電解液または負極合剤に含有される電解液のいずれか一方、より望ましくはそのどちらもが、アルカリ濃度の低い電解液であれば、前記駆動力が大きくなり、より好ましい結果が得られる。
【００２６】
以下では、まず、負極の構成について説明する。負極は、通常、活物質である亜鉛または亜鉛合金粉末とゲル化剤と水酸化カリウムを溶解したアルカリ電解液とを混合したゲル状の合剤として形成される。このとき、負極の電解液の水酸化カリウム濃度は３８質量％以下とすることが望ましい。電解液のアルカリ濃度が低いほど、水分含率が高くなり、電池全体として必要となる水分量を調整しやすくなるからである。さらに、電解液のイオン伝導度を向上させて負極の反応性を高め、負荷特性の向上や、前述した短絡時の発熱抑制効果を得やすくするためには、水酸化カリウム濃度を３５質量％以下、より望ましくは３３．５質量％以下とするのがよい。一方、水酸化カリウム濃度が高いほど、電池を高温で貯蔵したときの特性劣化が少なくなるため、水酸化カリウム濃度を２８質量％以上、より望ましくは３０質量％以上とするのがよい。
【００２７】
また、大電流でのパルス放電のような重負荷に対応するためには、活物質の粒子径を小さくして反応面積を増加させることが望まれる。例えば、２００メッシュのふるい目を通過する活物質粉末の割合を４質量％以上とするのがよく、１５質量％以上とすることにより、負荷特性の向上が顕著となる。一方、均質で流動性の良好な負極合剤を形成するためには、上記微小粒子の割合を４０質量％以下にすることが望ましい。このように、微小粒子を一定の割合で含む場合は、高温での貯蔵時に、活物質と電解液との反応によるガス発生や、放電容量の低下などの問題が生じやすくなる。これを防ぐためには、亜鉛にインジウム、ビスマスおよびアルミニウムなどの元素を含有させるのがよい。これら元素の含有量としては、インジウム、ビスマスおよびアルミニウムが、それぞれ０．０３〜０．０７質量％、０．００７〜０．０２５質量％および０．００１〜０．００４質量％であるのが望ましい。また、粒子径が小さいほど前記短絡時の発熱の問題が深刻となるが、本発明では、上記のような微小粒子を用いた場合でも、発熱抑制効果が十分に発揮される。
【００２８】
上記以外の構成要素として、負極合剤に酸化インジウムなどのインジウム化合物、酸化ビスマスなどのビスマス化合物を少量含有させることもできる。これらの化合物を含有させた場合、亜鉛合金粉末と電解液との反応によるガス発生をより効果的に防ぐことができるが、負荷特性を低下させるおそれがあるので、必要に応じて含有量が決定される。
【００２９】
本発明のアルカリ電池は、上記正極合剤および負極合剤をセパレータと共に外装体内部に封入することにより作製される。ただし、上記正極合剤および負極合剤に含有されるアルカリ電解液のみでは液量が不足するため、通常は、さらに別の電解液を注入してセパレータや正極に吸収させる工程が必要となる。このとき注入されるアルカリ電解液は、水分の含有率を高めて正極への水分の供給を多くするために、水酸化カリウム濃度を３５質量％以下とすることが望ましい。さらに、負荷特性の向上や短絡時の発熱抑制の点からは、３３．５質量％以下とするのが望ましいが、一方で、水酸化カリウム濃度が高いほど、電池を高温で貯蔵したときの特性劣化が少なくなるため、水酸化カリウム濃度を２８質量％以上、より望ましくは３０質量％以上とするのがよい。
【００３０】
また、高温貯蔵時の特性劣化防止の効果を高めるために、正極合剤形成に用いる電解液、負極合剤中形成に用いる電解液および別途注入される電解液のうちの少なくとも１つに、亜鉛化合物を含有させておくことが望ましい。亜鉛化合物としては、酸化亜鉛、ケイ酸亜鉛、チタン酸亜鉛、モリブデン酸亜鉛などの可溶性化合物を用いることができ、特に、酸化亜鉛が好適に用いられる。
【００３１】
電池の組み立て後には、注入された電解液あるいは負極合剤中の電解液から正極側への水分の移動が生じ、正極合剤に吸収されて合剤中の水分量が増加していく。この水分量の変化は、電池の保管温度などの条件に依存するため一概には言えないが、電池の組み立て後およそ１〜３ヶ月程度で終了し、その後は、合剤中の水分量は一定値で維持されていくものと思われる。この状態で、正極合剤に含まれる水分量が、電解液を含めた正極合剤全体の質量に対して、８．４〜１０質量％となるよう、前記正極、負極および注入に用いる各電解液の組成および添加量を調整すればよい。上記水分量が８．４質量％より少ない場合は、負荷特性、短絡時の発熱、高温貯蔵特性のいずれかにおいて問題が生じる。また、１０質量％より多い場合は、正極合剤が含有する電解液量が過剰であることを意味し、合剤の膨潤による導電性低下や、セパレータ側の電解液量不足が生じて、やはり特性上の問題が生じる。
【００３２】
また、電池組み立て後の正極合剤に含まれる電解液の水分量や水酸化カリウム濃度は、電池を分解して正極合剤を分析することにより求められる。例えば、水分量は、真空中や不活性ガス雰囲気中など炭酸ガスの影響を排除した雰囲気中で正極合剤を乾燥させたときの質量変化から求めることができ、水酸化カリウム濃度は、合剤中のカリウム量の測定値から、それがすべて水酸化カリウムに由来するとして水酸化カリウム量を求め、（水酸化カリウム量）／（水酸化カリウム量＋水分量）として求めることができる。なお、水酸化カリウムの濃度としては、３５〜３９．５質量％であるのが望ましいが、このときの正極合剤中の電解液組成と、負極合剤中の電解液組成とは、必ずしも一致するものではなく、正極合剤中のアルカリ濃度の方が高い状態でも前記正極への水分移動が終了し、その状態がそのまま維持される場合もある。
【００３３】
本発明では、上述したように、正極合剤に十分な量の水分を含有させ、電池内での水分の配分が適正化されるため、電池系内の水分量の合計を従来よりも低減することが可能となり、正極活物質１ｇ当たり０．２３〜０．２７５ｇとすることができる。このため、電池系内に余分な水分が存在しなくなって、電池を高温で貯蔵した際の特性劣化が低減されるが、一方で、反応に必要な水分は確保されるので、優れた動作特性を示す電池を得ることができる。
【００３４】
また、本発明では、電池の形状などは特に限定されるものではない。一例として、円筒形の金属製外装缶を用いる場合を示すと、リング状に成形された正極合剤を外装缶内部に配置し、その内側にコップ状のセパレータを配置し、さらにアルカリ電解液をセパレータの内側に注入してから負極合剤を充填し、これら構成要素を外装缶内部に封入することにより電池が組み立てられる。図２に示されるように、円筒形のアルカリ電池においては、外装缶１の開口端部１ａを内方に折り曲げて封口を行った際に、負極端子板２０７の変形を防ぎ、かつ封口体６を内側から支える指示手段として金属ワッシャ９（円板状の金属板）を用いることが一般に行われているが、これでは封口部分１０の占める体積が大きくなってしまうという問題がある。
【００３５】
一方、金属ワッシャをなくし、封口体６を内側から支える指示手段として負極端子板７を利用した図１の電池では、封口部分１０の占める体積を減少させることができるので、正極２および負極４の合剤の充填量をより高めることができる反面、電池の高容量化に伴い、短絡時の発熱は一層大きくなる。しかし、このような高容量設計の電池においても、本発明を用いることにより、電池の異常発熱挙動を防ぐことができるので、電池の実用性を高めることができる。
【００３６】
以下において本発明の実施例を説明するが、もちろん本発明はこれらの実施例に限定されるものではない。
【００３７】
（実施例１）
水分を１．６質量％含有する電解二酸化マンガン、黒鉛、ポリテトラフルオロエチレン粉末および正極合剤形成用のアルカリ電解液（酸化亜鉛を２．９質量％含有した５６質量％水酸化カリウム水溶液）を８７．６：６．７：０．２：５．５の質量比で、５０℃の温度下で混合し、密度が３．２１ｇ／ｃｍ^３の正極合剤を作製した。なお、この合剤中、二酸化マンガンの質量１００に対する黒鉛の質量割合は７．６であった。
【００３８】
上記正極合剤が含有する電解液の水酸化カリウム濃度は、二酸化マンガンの含有水分を考慮すると４４．６質量％となり、水酸化カリウム量および水分量は、電解液を含めた上記正極合剤の質量に対して、それぞれ３．１質量％および３．７質量％となった。
【００３９】
次に、インジウム、ビスマスおよびアルミニウムをそれぞれ０．０５質量％、０．０５質量％および０．００５質量％の割合で含有する亜鉛合金粉末、ポリアクリル酸ソーダ、ポリアクリル酸および負極合剤形成用のアルカリ電解液（酸化亜鉛を２．２質量％含有した３２質量％水酸化カリウム水溶液）を３９：０．２：０．２：１８の質量比で混合し、ゲル状の負極合剤を作製した。なお、上記亜鉛合金粉末は、平均粒径が１２２μｍで、８０メッシュのふるい目を全て通過し、かつ２００メッシュのふるい目を通過しない亜鉛合金粉末であって、その見掛け密度は２．６５ｇ／ｃｍ^３であった。
【００４０】
さらに、外装体として、封口部分１０の厚みが０．２５ｍｍで、胴部分２０の厚みが０．１６ｍｍに加工され、また、電池を落下させたときに正極端子１ｂのへこみを防ぐために、正極端子部分の缶厚を胴部分２０より多少厚くしたキルド鋼板製の単３形アルカリ乾電池用外装缶１を用い、以下のようにしてアルカリ電池を作製した。
【００４１】
上記正極合剤約１１ｇを上記外装缶１に挿入して中空円筒状に加圧成形し、内径９．１ｍｍ、外径１３．７ｍｍ、高さ１３．９ｍｍの３個の正極合剤成形体とした。次に、外装缶１の開口端から高さ方向において３．５ｍｍの位置にグルーブを施し、外装缶１と封口体６との密着性を向上させるために、このグルーブ位置まで外装缶１の内側にピッチを塗布した。
【００４２】
次に、厚みが１００μｍで目付が３０ｇ／ｍ^２のアセタール化ビニロンとテンセルからなる不織布を三重に重ねて筒状に巻き、底部になる部分を折り曲げてこの部分を熱融着し、一端が閉じられたコップ状のセパレータ３とした。このセパレータ３を、外装缶内に挿入された正極１の内側に装填し、注入用のアルカリ電解液（酸化亜鉛を２．２質量％含有した３２質量％水酸化カリウム水溶液）１．３５ｇをセパレータの内側に注入し、さらに、上記負極合剤５．７４ｇをセパレータ３の内側に充填して負極４とした。このとき、電池系内の水分量の合計は、正極活物質１ｇ当たり０．２６１ｇであった。
【００４３】
上記発電要素の充填の後、表面がスズメッキされた真鍮製であり、ナイロン６−６製の封口体６と組み合わされた負極集電棒５を上記負極中央部に差し込み、外装缶１の開口端部１ａの外側からスピニング方式によりかしめることにより、図１に示す単３形アルカリ電池を作製した。ここで、上記負極集電棒５は、打ち抜き・プレス加工により形成された厚さ０．４ｍｍのニッケルメッキ鋼板製の負極端子板７にあらかじめ溶接により取り付けられたものを用いた。また、外装缶１の開口端と負極端子板７との間には、短絡防止のために絶縁板８を装着した。
【００４４】
以上のようにして作製した実施例１の電池について、電池の組み立てから１ヶ月後、３ヶ月後、６ヶ月後の電池をそれぞれ５個ずつ分解し、正極合剤が含有するカリウム量および水分量を以下の方法により求めた。分解後の電池を、正極および外装缶と、負極およびセパレータとに分け、正極および外装缶についてその質量を測定し、これを真空中１１０℃で１２時間乾燥させ、乾燥前の質量と乾燥後の質量との差から、正極合剤が含有している水分量を求めた。次いで、乾燥後の正極合剤を取り出し、二酸化マンガンを酸で溶解し、残渣を取り除いた溶液について、原子吸光分析によりカリウムの質量を求めた。これにより求まるカリウム量から、カリウムの原子量：３９．１、水酸化カリウムの分子量：５６．１として、水酸化カリウム量＝カリウム量×（５６．１／３９．１）の換算により水酸化カリウム量を求め、さらに、水酸化カリウム濃度＝水酸化カリウム量／（水酸化カリウム量＋水分量）の式により、電池組み立て後の正極合剤が含有するアルカリ電解液について、水酸化カリウムの濃度を求めた。
【００４５】
上記水分量および水酸化カリウム濃度について、各電池の平均値を表１に示した。電池の組み立てから１ヶ月後には、必要とされる水分が正極合剤内に取り込まれており、組み立てから３ヶ月後以降は水分量の変化がなくなり、この状態が維持されることがわかる。
【００４６】
【表１】

【００４７】
（実施例２）
負極合剤形成用のアルカリ電解液および注入用のアルカリ電解液として、酸化亜鉛を２．０質量％含有した３０質量％水酸化カリウム水溶液を用いた以外は実施例１と同様にして、単３形アルカリ電池を作製した。このとき、電池系内の水分量の合計は、正極活物質１ｇ当たり０．２６８ｇであった。
【００４８】
（実施例３）
負極の亜鉛合金粉末としてインジウム、ビスマスおよびアルミニウムをそれぞれ０．０５質量％、０．０１５質量％および０．００３質量％の割合で含有し、平均粒径が２００μｍで、３５メッシュのふるい目を全て通過し、かつ２００メッシュのふるい目を通過するものの割合が６質量％であって、見掛け密度が２．９ｇ／ｃｍ^３である亜鉛合金粉末を用いた以外は実施例１と同様にして、単３形アルカリ電池を作製した。
【００４９】
（実施例４）
負極の亜鉛合金粉末として、平均粒径が１３５μｍで、３５メッシュのふるい目を全て通過し、かつ２００メッシュのふるい目を通過するものの割合が２０質量％であって、見掛け密度が２．９ｇ／ｃｍ^３である亜鉛合金粉末を用いた以外は実施例１と同様にして、単３形アルカリ電池を作製した。
【００５０】
（比較例１）
負極合剤形成用のアルカリ電解液および注入用のアルカリ電解液として、酸化亜鉛を２．４質量％含有した３６質量％水酸化カリウム水溶液を用いた以外は実施例１と同様にして、単３形アルカリ電池を作製した。このとき、電池系内の水分量の合計は、正極活物質１ｇ当たり０．２４７ｇであった。
【００５１】
（比較例２）
正極合剤形成用のアルカリ電解液として、酸化亜鉛を２．９質量％含有した４２質量％水酸化カリウム水溶液を用いた以外は実施例１と同様にして、単３形アルカリ電池を作製した。この電池において、電池組み立て前の正極合剤が含有する電解液の水酸化カリウム濃度は、二酸化マンガンの含有水分を考慮すると３３．５質量％となり、水酸化カリウム量および水分量は、電解液を含めた前記合剤の質量に対して、それぞれ２．３質量％および４．４質量％となった。また、電池系内の水分量の合計は、正極活物質１ｇ当たり０．２７０ｇであった。
【００５２】
上記実施例２、比較例１および比較例２の電池各５個について、実施例１と同様にして、組み立てから３ヶ月経過後の正極合剤が含有している水分量と、正極合剤が含有するアルカリ電解液の水酸化カリウム濃度を求めた。これらの結果ならびに前記実施例１の電池の結果を、電池系内の水分量の合計（ただし、正極活物質１ｇ当たりに換算）と合わせて表２に示した。
【００５３】
なお、実施例３および実施例４の電池については、正極合剤が含有している水分量のみ測定したが、実施例１と同様の結果が得られたため表２には示さなかった。
【００５４】
【表２】

【００５５】
表２に示されるように、実施例１および２の電池は、正極合剤が含有している水分量が８．４〜１０質量％の範囲となり、正極活物質の反応に充分な量の水分を正極合剤に含有させることができた。また、正極合剤に含有される電解液の水酸化カリウム濃度も、３５〜３９．５質量％の望ましい範囲とすることができた。
【００５６】
次に、実施例１〜４および比較例１〜２の各電池について、以下のようにして負荷特性、短絡時の電池温度および高温貯蔵特性の測定を行った。
【００５７】
負荷特性は、ベース放電電流を０．５Ａとし、３０秒間隔で２Ａのパルス電流を２秒間流すパルス放電試験を行い、２Ａのパルス電流が流れた時点の電圧が１．０Ｖ以下に低下するまでに要するパルス放電の回数により評価した。
【００５８】
短絡時の電池温度は、電池の外装缶側面の中央部にアルミニウム製のテープで熱伝対を固定し、電池を短絡させた後の外装缶表面温度を測定し、短絡後の最高到達温度で評価した。なお、実施例２および比較例１の電池については、外装缶表面温度だけでなく、短絡電流の時間変化も測定した。
【００５９】
高温貯蔵特性は、高温貯蔵における貯蔵前後の放電容量の変化を調べ、容量の保持率で特性劣化の程度を評価した。すなわち、電池を１Ａの放電電流で放電させ、電池電圧が０．９Ｖになるまでの放電容量を測定してこれを貯蔵前の放電容量とした。また、前記電池とは別の電池を６０℃の恒温槽中に２０日間保存し、取り出してから１日室温で冷却後、同じく１Ａの放電電流で放電させ、電池電圧が０．９Ｖになるまでの放電容量を測定してこれを貯蔵後の放電容量とし、貯蔵前の放電容量に対する貯蔵後の放電容量の割合を求め、これを容量保持率として高温貯蔵特性の評価を行った。
【００６０】
上記パルス放電の回数、外装缶表面の最高温度および容量保持率の測定結果を表３にまとめて示した。また、実施例２および比較例１の電池の外装缶表面温度と短絡電流の時間変化を、実施例２の電池については図３に、比較例１の電池については図４に示した。
【００６１】
【表３】

【００６２】
本発明の実施例１〜４の電池は、正極合剤の含有水分量を８．４〜１０質量％とすることにより、電池系内の水分量の合計を、正極活物質１ｇ当たり０．２３〜０．２７５ｇに低減したにもかかわらず、負荷特性が優れ、電池の短絡時の発熱が抑制され、高温貯蔵における特性劣化も少なかった。特に、亜鉛合金粉末中に２００メッシュ以下の粉末を６質量％含み、実施例１よりも微小粒子の割合が多い実施例３の電池では、インジウム、ビスマスおよびアルミニウムの含有割合が最適化されることによって、過大な発熱による温度上昇や容量保持率の低下を招くことなく、実施例１の電池よりも負荷特性を向上させることができた。また、実施例３よりもさらに微小粒子の割合を増やした実施例４の電池では、電池の温度は多少上昇したものの、優れた高温貯蔵特性を維持しながら、負荷特性をさらに増加させることができた。
【００６３】
一方、正極合剤の含有水分量が上記範囲に達しなかった比較例１および２の電池では、短絡時の発熱が大きく電池温度が大幅に上昇するか、あるいは高温貯蔵特性が劣化し、いずれも実用的な特性とならなかった。短絡時の温度上昇については、図３および図４に示すように、本発明の電池は短絡電流が短時間で減少するため発熱が少なく、電池の温度上昇が小さいが、比較例の電池では短絡電流の低下が遅く、発熱が大きくなって電池の温度が大幅に上昇したことがわかる。
【００６４】
【発明の効果】
正極合剤の含有水分量を最適化することにより、電池系内の水分量の合計を低減することが可能となり、負荷特性に優れ、短絡時の安全性が高く、高温貯蔵特性に優れるアルカリ電池を提供することができる。
【図面の簡単な説明】
【図１】封口体を内側から支える指示手段として負極端子板を利用したアルカリ電池の全体構造を示す断面図である。
【図２】従来のアルカリ電池の一般的な構造を示す断面図である。
【図３】本発明の実施例２のアルカリ電池を短絡させた際の、短絡電流および外装缶表面温度の変化を示すグラフである。
【図４】本発明の比較例１のアルカリ電池を短絡させた際の、短絡電流および外装缶表面温度の変化を示すグラフである
【符号の説明】
１外装缶
１ａ外装缶の開口端部
２正極
３セパレータ
４負極
５負極集電棒
６封口体
７、２０７負極端子板
８絶縁板
９金属ワッシャ
１０封口部分
２０胴部分[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alkaline battery and a method for manufacturing the same, and further relates to an alkaline battery excellent in load characteristics and a method for manufacturing the same.
[0002]
[Prior art]
An alkaline battery using zinc as a negative electrode active material is used as a power source for various electronic devices, and various characteristics are required depending on its use. In particular, in digital cameras that have become popular in recent years, in order to maximize the number of images that can be taken, it is necessary to increase the capacity of the battery and further improve the load characteristics such as the large current discharge characteristics. Possible battery designs are being studied.
[0003]
In order to increase the capacity of the battery, it is necessary to increase the filling amount of the active material. However, if the active material is not effectively used for discharging, the capacity cannot be increased. Therefore, simply increasing the filling amount of the active material. You can't achieve your goal by just doing it. Since the discharge capacity is determined in consideration of the utilization factor of the active material, it is necessary to design the positive electrode, the negative electrode, and the electrolytic solution so that the discharge reaction proceeds smoothly. The discharge reaction of the positive electrode of the alkaline battery using manganese dioxide as the positive electrode active material proceeds according to the following formula (1).
[0004]
Positive electrode: MnO ₂ + H ₂ O + e ⁻ → MnOOH + OH ⁻ (1)
[0005]
As is clear from the above formula, since water is consumed at the time of discharge at the positive electrode, from the viewpoint of the discharge reaction, it is desirable that as much water as possible exists on the positive electrode side in the battery, and the same is true This also applies when nickel is used as the positive electrode active material.
[0006]
By the way, in an actual alkaline battery, a positive electrode active material, a conductive agent, and an alkaline electrolyte are mixed to form a positive electrode mixture. Further, an alkaline electrolyte injected into a cylindrical separator is used as a positive electrode mixture. Therefore, a certain amount of moisture is contained in the positive electrode mixture after a certain period of time after the battery is assembled (see Patent Document 1). Further, the potassium hydroxide concentration of the electrolytic solution added at the time of forming the positive electrode mixture is desirably 40 to 50 wt%, and the potassium hydroxide concentration of the electrolytic solution injected into the separator is desirably 35 to 45 wt% ( Patent Document 1).
[0007]
In addition, regarding the water content in the positive electrode mixture, the moisture content in the positive electrode mixture is set to 3.5% to 5.0%, and the weight of the potassium hydroxide electrolyte contained in the positive electrode mixture after forming the battery Is also proposed to be 10.6 to 15.9 with respect to the solid content weight 100 in the positive electrode mixture (see Patent Document 2). Furthermore, from the viewpoint of safety and discharge characteristics, there is also a proposal that the water addition amount of the entire battery is 0.947 to 1.146 g per 1 AH of theoretical discharge capacity of manganese dioxide (see Patent Document 3). This means that 0.292 to 0.353 g of water is added per 1 g of the active material, which is considerably larger than the amount of water (0.207 g) required for the discharge reaction of 1 g of manganese dioxide. is there.
[0008]
[Patent Document 1]
JP 2002-15748 A (paragraph number 0002, paragraph number 0007)
[Patent Document 2]
JP 2000-306575 A (paragraph numbers 0006-0007)
[Patent Document 3]
JP 2001-68121 A (paragraph numbers 0006-0008)
[0009]
[Problems to be solved by the invention]
However, in the range of the amount of electrolyte in the positive electrode mixture, the amount of water is still insufficient, and good characteristics cannot be obtained under heavy load. On the other hand, if the required water content is preliminarily contained in the positive electrode mixture at the time of assembling the battery, the packing density of the active material is lowered and a reduction in capacity cannot be avoided. In addition, moisture may come out from the mixture during molding, or production problems may occur such as the molding strength is reduced and the mixture cannot be molded successfully. Therefore, it is contained in the mixture when forming the positive electrode mixture. It is desirable that the amount of water to be generated is as small as possible.
[0010]
That is, while reducing the amount of water in the positive electrode mixture used for battery assembly as much as possible, it is necessary to satisfy the conflicting requirement that a large amount of water be contained in the positive electrode mixture after battery assembly. .
[0011]
The present inventors cannot satisfy these requirements only by adjusting the moisture content in the positive electrode mixture or adjusting the amount of water added to the entire battery, and the required amount of moisture after battery assembly. However, it has been found that it is necessary to make some contrivance to enable movement from the separator or negative electrode side into the positive electrode mixture. It has also been found that by properly distributing the moisture within the battery, the amount of moisture added to the entire battery can be reduced, and the absence of excess moisture reduces storage degradation at high temperatures.
[0012]
The present invention has been made in view of the above circumstances, and provides an alkaline battery excellent in load characteristics, safety during short-circuiting, and high-temperature storage, and also provides a method for producing such an alkaline battery. It is to be an issue.
[0013]
[Means for Solving the Problems]
The alkaline battery of the present invention is an alkaline battery using a molded product of a positive electrode mixture containing at least one of manganese dioxide and nickel oxyhydroxide as an active material, and a positive electrode mixture of 3 to 6 months from the battery assembly. An alkaline electrolyte containing potassium hydroxide is contained, and the amount of water contained in the positive electrode mixture is 8.4 to 10% by mass with respect to the mass of the positive electrode mixture including the electrolytic solution. The total amount of moisture is 0.23 to 0.275 g per 1 g of the positive electrode active material.
[0014]
Further, according to the present invention, as a method for producing the alkaline battery, an alkaline battery is assembled using a molded article of a positive electrode mixture containing at least one of manganese dioxide and nickel oxyhydroxide and an alkaline electrolyte solution in which potassium hydroxide is dissolved. In the method for producing an alkaline battery, the amount of potassium hydroxide contained in the positive electrode mixture used for battery assembly is 2.4 to 4% by mass with respect to the mass of the positive electrode mixture including the electrolyte, A method for producing an alkaline battery, characterized in that the amount of water contained in the positive electrode mixture for 3 to 6 months from the battery assembly is 8.4 to 10% by mass with respect to the mass of the positive electrode mixture including the electrolytic solution. I will provide a.
[0015]
Furthermore, the present invention provides an alkaline battery using a molded article of a positive electrode mixture containing at least one of manganese dioxide and nickel oxyhydroxide and an alkaline electrolyte in which potassium hydroxide is dissolved as a method for producing the alkaline battery. It is a manufacturing method of the alkaline battery to assemble, Comprising: The quantity of the water | moisture content contained in the positive mix used for battery assembly shall be 3.0-4.2 mass% with respect to the mass of the positive mix including electrolyte solution. The production of an alkaline battery is characterized in that the amount of water contained in the positive electrode mixture 3 to 6 months after the battery assembly is 8.4 to 10% by mass with respect to the mass of the positive electrode mixture including the electrolytic solution. Provide a method.
[0016]
By assembling the alkaline battery using the above manufacturing method, it becomes possible to contain a sufficient amount of moisture necessary for the discharge reaction in the positive electrode mixture after the battery is assembled. Since the distribution is optimized, it is possible to obtain an alkaline battery that is excellent in load characteristics and safety at the time of a short circuit and has little storage deterioration at high temperatures even if the moisture content of the whole battery is small.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preparation of the alkaline battery of the present invention will be described. The alkaline battery of the present invention is characterized in that, after the battery is assembled, the amount of water contained in the positive electrode mixture is 8.4 to 10% by mass with respect to the mass of the positive electrode mixture including the electrolytic solution. Therefore, it is required that a relatively large amount of moisture moves from the separator or the negative electrode side into the positive electrode. In order to cause the movement of moisture, a driving force for that purpose is required. As a method for generating this driving force, for example, an electrolyte solution previously contained in the positive electrode mixture and an injection during assembly An example is a method in which a large difference is provided between the alkaline concentration of the electrolytic solution to be contained or the electrolytic solution to be contained in the negative electrode, and after assembly, moisture on the separator or negative electrode side is moved into the positive electrode mixture by the concentration difference.
[0018]
The positive electrode is obtained by mixing at least one of manganese dioxide and nickel oxide, a conductive agent and an alkaline electrolyte containing potassium hydroxide, and molding the mixture to obtain a molded body. By increasing the potassium hydroxide concentration of the alkaline electrolyte to be added at the time of compounding to more than 50% by mass, the driving force is increased, and a large amount of water can be taken into the positive electrode mixture. Moreover, since the binding force of the mixture is improved and a homogeneous mixture is formed, the active material can be filled at a high density. At this time, the density of the positive electrode mixture is 3.2 to 3.35 g / cm. ³ It is preferable that a large amount of water can be contained while ensuring the necessary active material filling amount.
[0019]
In addition, since manganese dioxide and nickel oxide, which are active materials, usually contain some moisture due to adsorption or the like, the potassium hydroxide concentration of the alkaline electrolyte contained in the mixture is added first. It becomes lower than the potassium hydroxide concentration of the alkaline electrolyte. For this reason, when considering the amount of water, it is better to consider the water derived from the above active material, so that the potassium hydroxide concentration of the electrolyte solution contained in the mixture is finally 40% by mass or more. It is desirable to adjust the concentration of the alkaline electrolyte added to the agent.
[0020]
Further, the addition amount of the alkaline electrolyte is preferably in the range of 2.4 to 4% by mass in terms of the mass of potassium hydroxide with respect to the total mass of the mixture including the electrolyte contained in the mixture. The water content is preferably 3.0 to 4.2% by mass. Thereby, an appropriate driving force can be obtained, and it becomes easy to adjust the moisture content after battery assembly to an appropriate range.
[0021]
In the preparation of the positive electrode mixture, when the potassium hydroxide concentration of the electrolytic solution is higher than 50% by mass, the saturation solubility of potassium hydroxide at room temperature is exceeded, so the precipitation of potassium hydroxide exceeding the saturation amount It is expected that the mixture will become heterogeneous. Therefore, it is desirable to increase the saturation amount of potassium hydroxide by mixing the mixture composition in a warm atmosphere, and to produce the positive electrode mixture under conditions such that the electrolyte does not reach the saturation concentration. The temperature condition is preferably 35 ° C. or higher, and preferably 70 ° C. or lower in order to prevent the electrolyte composition from changing due to evaporation of moisture.
[0022]
In addition to the above, according to the purpose, a conductive agent, a binder, and the like can be included in the positive electrode mixture. As the conductive agent, carbon materials such as graphite, acetylene black, carbon black, and fibrous carbon can be mainly used. Among them, graphite is preferably used. The addition amount of the conductive agent is desirably 3 or more by mass ratio with respect to the positive electrode active material 100. By containing sufficient moisture in the positive electrode mixture and improving the conductivity of the positive electrode, the reactivity of the active material is increased, and further improvement in load characteristics can be expected. On the other hand, since the reduction of the active material filling amount is not preferable, the ratio of the conductive agent is desirably 8.5 or less.
[0023]
As the binder, carboxymethylcellulose, methylcellulose, polyacrylate, polytetrafluoroethylene, polyethylene, or the like can be used.
[0024]
In the present invention, it is also possible to expect another effect described below by increasing the reactivity of the positive electrode. If an abnormality such as accidental short-circuiting of the battery occurs, excessive short-circuit current will continue to flow, and the temperature of the battery will rise rapidly due to the heat generated thereby, causing problems such as leakage and battery rupture. . On the other hand, in the battery of the present invention, the discharge reaction at the positive electrode proceeds more rapidly than the conventional battery, and accordingly, the discharge reaction at the negative electrode also proceeds rapidly, and immediately after the occurrence of a short circuit, the discharge product is generated. A large amount is deposited on the negative electrode surface to suppress the discharge reaction. As a result, the short-circuit current is greatly reduced in a short time, and the temperature rise of the battery is suppressed, so that the above problem can be prevented.
[0025]
Note that the driving force that causes the movement of moisture to the positive electrode described above is not only determined by the configuration of the positive electrode, but also the relationship with other components such as the negative electrode, in particular, electrolysis separately injected into the exterior body. Since it is closely related to the potassium hydroxide concentration of the electrolytic solution contained in the liquid or the negative electrode mixture, it is desired that the configuration is also optimized. That is, if either one of the injected electrolyte solution or the electrolyte solution contained in the negative electrode mixture, more desirably, the electrolyte solution has a low alkali concentration, the driving force increases, and a more preferable result is obtained. It is done.
[0026]
Below, the structure of a negative electrode is demonstrated first. The negative electrode is usually formed as a gel-like mixture in which zinc or zinc alloy powder as an active material, a gelling agent, and an alkaline electrolytic solution in which potassium hydroxide is dissolved are mixed. At this time, the potassium hydroxide concentration of the negative electrode electrolyte is desirably 38% by mass or less. This is because the lower the alkali concentration of the electrolytic solution, the higher the water content, making it easier to adjust the amount of water required for the entire battery. Furthermore, in order to improve the ionic conductivity of the electrolytic solution to increase the reactivity of the negative electrode, to improve the load characteristics, and to easily obtain the heat generation suppressing effect at the time of short circuit, the potassium hydroxide concentration is 35% by mass or less. More desirably, the content is 33.5% by mass or less. On the other hand, the higher the potassium hydroxide concentration, the less deterioration of the characteristics when the battery is stored at a high temperature. Therefore, the potassium hydroxide concentration is preferably 28% by mass or more, more preferably 30% by mass or more.
[0027]
In order to cope with a heavy load such as pulse discharge with a large current, it is desired to reduce the particle size of the active material and increase the reaction area. For example, the ratio of the active material powder that passes through the 200 mesh sieve is preferably 4% by mass or more, and when it is 15% by mass or more, the load characteristics are remarkably improved. On the other hand, in order to form a negative electrode mixture that is homogeneous and has good fluidity, the proportion of the fine particles is preferably 40% by mass or less. As described above, when the microparticles are contained at a certain ratio, problems such as gas generation due to a reaction between the active material and the electrolytic solution and a decrease in discharge capacity are likely to occur during storage at a high temperature. In order to prevent this, it is preferable to contain elements such as indium, bismuth and aluminum in zinc. As contents of these elements, indium, bismuth and aluminum are preferably 0.03 to 0.07% by mass, 0.007 to 0.025% by mass and 0.001 to 0.004% by mass, respectively. . Further, the problem of heat generation at the time of short circuit becomes more serious as the particle diameter is smaller. However, in the present invention, even when the above fine particles are used, the effect of suppressing heat generation is sufficiently exhibited.
[0028]
As a component other than the above, the negative electrode mixture can contain a small amount of an indium compound such as indium oxide and a bismuth compound such as bismuth oxide. When these compounds are contained, gas generation due to the reaction between the zinc alloy powder and the electrolyte can be prevented more effectively, but the load characteristics may be reduced, so the content is determined as necessary. Is done.
[0029]
The alkaline battery of the present invention is produced by enclosing the positive electrode mixture and the negative electrode mixture together with a separator in the exterior body. However, since the amount of liquid is insufficient with only the alkaline electrolyte contained in the positive electrode mixture and the negative electrode mixture, a step of injecting another electrolyte into the separator and the positive electrode is usually required. The alkaline electrolyte injected at this time desirably has a potassium hydroxide concentration of 35% by mass or less in order to increase the moisture content and increase the supply of moisture to the positive electrode. Furthermore, from the viewpoint of improvement of load characteristics and suppression of heat generation at the time of short circuit, it is desirable to be 33.5% by mass or less. On the other hand, the higher the potassium hydroxide concentration, the higher the characteristics when the battery is stored. In order to reduce deterioration, the potassium hydroxide concentration is preferably 28% by mass or more, more preferably 30% by mass or more.
[0030]
Further, in order to enhance the effect of preventing characteristic deterioration during high temperature storage, at least one of an electrolytic solution used for forming the positive electrode mixture, an electrolytic solution used for forming the negative electrode mixture, and an electrolytic solution separately injected may be zinc It is desirable to contain a compound. As the zinc compound, soluble compounds such as zinc oxide, zinc silicate, zinc titanate, and zinc molybdate can be used, and zinc oxide is particularly preferably used.
[0031]
After the battery is assembled, moisture moves from the injected electrolyte solution or the electrolyte solution in the negative electrode mixture to the positive electrode side, and is absorbed by the positive electrode mixture to increase the amount of water in the mixture. This change in the amount of moisture depends on conditions such as the storage temperature of the battery, but it cannot be said unconditionally, but it will be completed in about 1 to 3 months after the assembly of the battery, and thereafter the amount of moisture in the mixture is constant. It seems to be maintained at the value. In this state, the amount of water contained in the positive electrode mixture is 8.4 to 10% by mass with respect to the total mass of the positive electrode mixture including the electrolytic solution. What is necessary is just to adjust a composition and addition amount of a liquid. When the water content is less than 8.4% by mass, a problem occurs in any of load characteristics, heat generation during short circuit, and high-temperature storage characteristics. Further, when the amount is more than 10% by mass, it means that the amount of the electrolyte contained in the positive electrode mixture is excessive, resulting in a decrease in conductivity due to swelling of the mixture and insufficient amount of the electrolyte on the separator side. A characteristic problem arises.
[0032]
Moreover, the water content and potassium hydroxide concentration of the electrolyte contained in the positive electrode mixture after battery assembly are obtained by disassembling the battery and analyzing the positive electrode mixture. For example, the amount of water can be determined from the change in mass when the positive electrode mixture is dried in an atmosphere excluding the influence of carbon dioxide such as in a vacuum or an inert gas atmosphere, and the potassium hydroxide concentration is From the measured value of the amount of potassium in the solution, the amount of potassium hydroxide can be obtained as it is derived from potassium hydroxide, and can be obtained as (potassium hydroxide amount) / (potassium hydroxide amount + water content). In addition, as a density | concentration of potassium hydroxide, although it is desirable that it is 35-39.5 mass%, the electrolyte solution composition in the positive mix at this time and the electrolyte composition in a negative mix are not necessarily in agreement. However, even when the alkali concentration in the positive electrode mixture is higher, the moisture transfer to the positive electrode is terminated, and the state may be maintained as it is.
[0033]
In the present invention, as described above, a sufficient amount of moisture is contained in the positive electrode mixture, and the distribution of moisture in the battery is optimized. Therefore, the total amount of moisture in the battery system is reduced as compared with the prior art. Therefore, the amount can be 0.23 to 0.275 g per 1 g of the positive electrode active material. For this reason, excess moisture does not exist in the battery system, and deterioration of characteristics when the battery is stored at high temperature is reduced, but on the other hand, moisture necessary for reaction is ensured, so excellent operating characteristics Can be obtained.
[0034]
In the present invention, the shape of the battery is not particularly limited. As an example, when a cylindrical metal outer can is used, a positive electrode mixture formed in a ring shape is disposed inside the outer can, a cup-shaped separator is disposed inside, and an alkaline electrolyte is further added. A battery is assembled by filling the negative electrode mixture after injecting into the inside of the separator and enclosing these components inside the outer can. As shown in FIG. 2, in the cylindrical alkaline battery, when the opening end 1 a of the outer can 1 is folded inward and sealed, the negative electrode terminal plate 207 is prevented from being deformed, and the sealing body 6 In general, a metal washer 9 (a disk-shaped metal plate) is used as an instruction means for supporting the seal from the inside. However, there is a problem that the volume occupied by the sealing portion 10 becomes large.
[0035]
On the other hand, in the battery of FIG. 1 in which the metal washer is eliminated and the negative electrode terminal plate 7 is used as an instruction means for supporting the sealing body 6 from the inside, the volume occupied by the sealing portion 10 can be reduced. On the other hand, the filling amount of the mixture can be further increased. However, as the capacity of the battery is increased, the heat generation at the time of short circuit is further increased. However, even in a battery with such a high capacity design, by using the present invention, the abnormal heat generation behavior of the battery can be prevented, so that the practicality of the battery can be enhanced.
[0036]
Examples of the present invention will be described below. Of course, the present invention is not limited to these examples.
[0037]
Example 1
Electrolytic manganese dioxide containing 1.6% by mass of water, graphite, polytetrafluoroethylene powder and alkaline electrolyte for forming a positive electrode mixture (56% by mass potassium hydroxide aqueous solution containing 2.9% by mass of zinc oxide) Mixed at a mass ratio of 87.6: 6.7: 0.2: 5.5 at a temperature of 50 ° C. and a density of 3.21 g / cm ³ A positive electrode mixture was prepared. In this mixture, the mass ratio of graphite to 100 masses of manganese dioxide was 7.6.
[0038]
The potassium hydroxide concentration of the electrolyte solution contained in the positive electrode mixture is 44.6% by mass in consideration of the water content of manganese dioxide. The amount of potassium hydroxide and the amount of water are the same as those of the positive electrode mixture including the electrolyte solution. It became 3.1 mass% and 3.7 mass% with respect to the mass, respectively.
[0039]
Next, for forming zinc alloy powder, polyacrylic acid soda, polyacrylic acid, and negative electrode mixture containing 0.05 mass%, 0.05 mass%, and 0.005 mass% of indium, bismuth, and aluminum, respectively. An alkaline electrolyte (32% by mass potassium hydroxide aqueous solution containing 2.2% by mass of zinc oxide) was mixed at a mass ratio of 39: 0.2: 0.2: 18 to prepare a gelled negative electrode mixture. did. The zinc alloy powder is a zinc alloy powder having an average particle size of 122 μm, passing through all 80 mesh screens and not passing through 200 mesh screens, and has an apparent density of 2.65 g / cm. ³ Met.
[0040]
Further, as the exterior body, the sealing portion 10 has a thickness of 0.25 mm, the body portion 20 has a thickness of 0.16 mm, and the positive electrode terminal 1b is prevented from being dented when the battery is dropped. Using the outer can 1 for AA alkaline dry batteries made of a killed steel plate, the thickness of which is slightly thicker than that of the barrel portion 20, an alkaline battery was produced as follows.
[0041]
About 11 g of the positive electrode mixture is inserted into the outer can 1 and pressed into a hollow cylinder, and three positive electrode mixture molded bodies having an inner diameter of 9.1 mm, an outer diameter of 13.7 mm, and a height of 13.9 mm; did. Next, in order to improve the adhesion between the outer can 1 and the sealing body 6 at a position of 3.5 mm in the height direction from the opening end of the outer can 1, the inner side of the outer can 1 up to this groove position. A pitch was applied.
[0042]
Next, the thickness is 100 μm and the basis weight is 30 g / m. ² A non-woven fabric made of acetalized vinylon and tencel was layered three times and wound into a cylindrical shape, and the bottom portion was bent and heat-sealed to form a cup-shaped separator 3 with one end closed. This separator 3 was loaded inside the positive electrode 1 inserted in the outer can, and 1.35 g of an alkaline electrolyte for injection (32% by mass potassium hydroxide aqueous solution containing 2.2% by mass of zinc oxide) was separated into the separator. Further, 5.74 g of the negative electrode mixture was filled into the separator 3 to obtain a negative electrode 4. At this time, the total amount of moisture in the battery system was 0.261 g per 1 g of the positive electrode active material.
[0043]
After filling the power generation element, the negative electrode current collector rod 5, which is made of brass with a tin plating on the surface and combined with the sealing body 6 made of nylon 6-6, is inserted into the central part of the negative electrode, and the open end of the outer can 1 The AA alkaline battery shown in FIG. 1 was produced by caulking from the outside of 1a by a spinning method. Here, the negative electrode current collector rod 5 used was previously attached by welding to a negative electrode terminal plate 7 made of nickel-plated steel plate having a thickness of 0.4 mm formed by punching and pressing. An insulating plate 8 was mounted between the open end of the outer can 1 and the negative electrode terminal plate 7 to prevent a short circuit.
[0044]
With respect to the battery of Example 1 produced as described above, 5 batteries each after 1 month, 3 months, and 6 months from the assembly of the battery were disassembled, and the amount of potassium and moisture contained in the positive electrode mixture Was determined by the following method. The disassembled battery is divided into a positive electrode and an outer can, and a negative electrode and a separator. The mass of the positive electrode and the outer can is measured, and this is dried in a vacuum at 110 ° C. for 12 hours. The amount of water contained in the positive electrode mixture was determined from the difference from the mass. Subsequently, the positive electrode mixture after drying was taken out, manganese dioxide was dissolved with an acid, and the mass of potassium was determined by atomic absorption analysis for the solution from which the residue was removed. From the amount of potassium determined in this way, assuming that the atomic weight of potassium is 39.1 and the molecular weight of potassium hydroxide is 56.1, the amount of potassium hydroxide is calculated as the amount of potassium hydroxide = the amount of potassium × (56.1 / 39.1). Further, the concentration of potassium hydroxide is determined for the alkaline electrolyte contained in the positive electrode mixture after battery assembly by the formula of potassium hydroxide concentration = potassium hydroxide amount / (potassium hydroxide amount + water amount). It was.
[0045]
Table 1 shows the average value of each battery with respect to the water content and the potassium hydroxide concentration. One month after the assembly of the battery, the required moisture is taken into the positive electrode mixture, and after three months from the assembly, the moisture content does not change and this state is maintained.
[0046]
[Table 1]

[0047]
(Example 2)
In the same manner as in Example 1, except that a 30% by mass aqueous potassium hydroxide solution containing 2.0% by mass of zinc oxide was used as the alkaline electrolyte for forming the negative electrode mixture and the alkaline electrolyte for injection. A shaped alkaline battery was produced. At this time, the total amount of moisture in the battery system was 0.268 g per 1 g of the positive electrode active material.
[0048]
(Example 3)
Indium, bismuth and aluminum are contained in the proportions of 0.05% by mass, 0.015% by mass and 0.003% by mass, respectively, as the zinc alloy powder of the negative electrode, the average particle size is 200 μm, and all 35 mesh sieves The ratio of those passing through and 200 mesh sieve is 6% by mass, and the apparent density is 2.9 g / cm. ³ AA alkaline batteries were produced in the same manner as in Example 1 except that the zinc alloy powder was used.
[0049]
Example 4
The proportion of the negative electrode zinc alloy powder having an average particle diameter of 135 μm, passing through all 35 mesh sieves and passing through 200 mesh sieves is 20% by mass, and the apparent density is 2.9 g / cm ³ AA alkaline batteries were produced in the same manner as in Example 1 except that the zinc alloy powder was used.
[0050]
(Comparative Example 1)
In the same manner as in Example 1, except that a 36% by mass aqueous potassium hydroxide solution containing 2.4% by mass of zinc oxide was used as the alkaline electrolyte for forming the negative electrode mixture and the alkaline electrolyte for injection. A shaped alkaline battery was produced. At this time, the total amount of water in the battery system was 0.247 g per 1 g of the positive electrode active material.
[0051]
(Comparative Example 2)
An AA alkaline battery was produced in the same manner as in Example 1 except that a 42% by mass potassium hydroxide aqueous solution containing 2.9% by mass of zinc oxide was used as the alkaline electrolyte for forming the positive electrode mixture. In this battery, the concentration of potassium hydroxide in the electrolyte solution contained in the positive electrode mixture before battery assembly is 33.5% by mass in consideration of the moisture content of manganese dioxide. It became 2.3 mass% and 4.4 mass%, respectively with respect to the mass of the said mixture to include. The total amount of water in the battery system was 0.270 g per 1 g of the positive electrode active material.
[0052]
For each of the five batteries of Example 2, Comparative Example 1 and Comparative Example 2, the amount of water contained in the positive electrode mixture after 3 months from the assembly and the positive electrode mixture were the same as in Example 1. The potassium hydroxide concentration of the alkaline electrolyte contained was determined. These results and the results of the battery of Example 1 are shown in Table 2 together with the total amount of water in the battery system (however, converted per 1 g of the positive electrode active material).
[0053]
In addition, about the battery of Example 3 and Example 4, although only the moisture content which the positive mix contained was measured, since the result similar to Example 1 was obtained, it was not shown in Table 2.
[0054]
[Table 2]

[0055]
As shown in Table 2, in the batteries of Examples 1 and 2, the amount of water contained in the positive electrode mixture was in the range of 8.4 to 10% by mass, and a sufficient amount of water for the reaction of the positive electrode active material. In the positive electrode mixture. Moreover, the potassium hydroxide concentration of the electrolyte solution contained in the positive electrode mixture could be within a desirable range of 35 to 39.5% by mass.
[0056]
Next, for the batteries of Examples 1 to 4 and Comparative Examples 1 to 2, the load characteristics, the battery temperature at the time of short circuit, and the high temperature storage characteristics were measured as follows.
[0057]
As for the load characteristics, a base discharge current is set to 0.5 A, and a pulse discharge test is performed in which a 2 A pulse current is passed for 2 seconds at 30 second intervals. The number of pulse discharges required for the evaluation was evaluated.
[0058]
The battery temperature at the time of short-circuit is measured by measuring the temperature of the outer can after fixing the thermocouple with aluminum tape at the center of the side of the outer can of the battery and shorting the battery. evaluated. In addition, about the battery of Example 2 and Comparative Example 1, not only the outer can surface temperature but also the time change of the short circuit current was measured.
[0059]
For high temperature storage characteristics, the change in discharge capacity before and after storage in high temperature storage was examined, and the degree of characteristic deterioration was evaluated by the capacity retention rate. That is, the battery was discharged at a discharge current of 1 A, the discharge capacity until the battery voltage reached 0.9 V was measured, and this was defined as the discharge capacity before storage. Also, a battery other than the above battery is stored in a constant temperature bath at 60 ° C. for 20 days, taken out, cooled at room temperature for 1 day, and then discharged at a discharge current of 1 A until the battery voltage reaches 0.9V. The discharge capacity was measured as the discharge capacity after storage, the ratio of the discharge capacity after storage to the discharge capacity before storage was determined, and this was used as the capacity retention to evaluate the high-temperature storage characteristics.
[0060]
Table 3 summarizes the measurement results of the number of pulse discharges, the maximum temperature of the outer can surface, and the capacity retention. Further, the time variation of the outer can surface temperature and the short-circuit current of the batteries of Example 2 and Comparative Example 1 are shown in FIG. 3 for the battery of Example 2 and FIG. 4 for the battery of Comparative Example 1.
[0061]
[Table 3]

[0062]
In the batteries of Examples 1 to 4 of the present invention, the total water content in the battery system was 0.23 per gram of the positive electrode active material by setting the water content of the positive electrode mixture to 8.4 to 10% by mass. Despite being reduced to ˜0.275 g, the load characteristics were excellent, the heat generation at the time of short-circuiting of the battery was suppressed, and the characteristic deterioration during high-temperature storage was small. In particular, the content of indium, bismuth, and aluminum is optimized in the battery of Example 3 that contains 6% by mass of powder of 200 mesh or less in the zinc alloy powder and has a higher proportion of fine particles than that of Example 1. As a result, the load characteristics could be improved as compared with the battery of Example 1 without causing an increase in temperature or a decrease in capacity retention due to excessive heat generation. Further, in the battery of Example 4 in which the proportion of fine particles was further increased from that of Example 3, the load characteristic could be further increased while maintaining excellent high-temperature storage characteristics, although the battery temperature slightly increased. It was.
[0063]
On the other hand, in the batteries of Comparative Examples 1 and 2 in which the water content of the positive electrode mixture did not reach the above range, the heat generation at the time of short circuit was large and the battery temperature was significantly increased, or the high temperature storage characteristics were deteriorated. It did not become a practical characteristic. Regarding the temperature rise at the time of short circuit, as shown in FIG. 3 and FIG. 4, the battery of the present invention generates less heat because the short circuit current decreases in a short time, and the temperature rise of the battery is small. It can be seen that the current decrease was slow, the heat generation increased, and the battery temperature increased significantly.
[0064]
【The invention's effect】
By optimizing the water content of the positive electrode mixture, the total amount of water in the battery system can be reduced, and the alkaline battery has excellent load characteristics, high safety during short-circuiting, and excellent high-temperature storage characteristics. Can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the overall structure of an alkaline battery using a negative terminal plate as an instruction means for supporting a sealing body from the inside.
FIG. 2 is a cross-sectional view showing a general structure of a conventional alkaline battery.
FIG. 3 is a graph showing changes in short-circuit current and outer can surface temperature when the alkaline battery of Example 2 of the present invention is short-circuited.
FIG. 4 is a graph showing changes in short circuit current and outer can surface temperature when the alkaline battery of Comparative Example 1 of the present invention is short-circuited.
[Explanation of symbols]
1 Exterior can
1a Open end of outer can
2 Positive electrode
3 Separator
4 Negative electrode
5 Negative current collector
6 Sealing body
7,207 Negative terminal plate
8 Insulation plate
9 Metal washers
10 Sealing part
20 trunk

Claims

An alkaline battery using a molded article of a positive electrode mixture containing at least one of manganese dioxide and nickel oxyhydroxide as an active material, wherein the positive electrode mixture for 3 to 6 months from the battery assembly contains potassium hydroxide containing liquid, the amount of water the positive electrode mixture contains is a 8.4 to 10 wt% with respect to the positive electrode mixture weight, including the electrolyte solution, the total amount of water in the battery system, the positive electrode An alkaline battery, characterized in that the amount is 0.23 to 0.275 g per gram of active material.

2. The alkaline battery according to claim 1, wherein the density of the positive electrode mixture before battery assembly is 3.2 to 3.35 g / cm ³ .

3. The alkaline battery according to claim 1, wherein the potassium hydroxide concentration of the alkaline electrolyte contained in the positive electrode mixture before assembling the battery is 40% by mass or more.

2. The alkaline electrolyte contained in the positive electrode mixture for 3 to 6 months after battery assembly has a potassium hydroxide concentration of 35 to 39.5% by mass determined from the amount of potassium and the amount of water. The alkaline battery in any one of -3.

The alkaline battery according to any one of claims 1 to 4, wherein the alkaline electrolyte contains a zinc compound.

The alkaline battery according to any one of claims 1 to 5, wherein the proportion of the zinc alloy powder that uses the zinc alloy powder as a negative electrode active material and passes through a 200-mesh sieve is 4 to 40% by mass. .

The alkaline battery according to claim 6, wherein the zinc alloy powder contains indium, bismuth and aluminum.

Indium, claim 7 in which the content of bismuth and aluminum, respectively 0.03 to 0.07 wt%, characterized in that it is a 0.007 to 0.025 wt% and 0.001 to 0.004 wt% The alkaline battery described in 1.

An alkaline battery manufacturing method for assembling an alkaline battery using a molded body of a positive electrode mixture containing at least one of manganese dioxide and nickel oxyhydroxide and an alkaline electrolyte in which potassium hydroxide is dissolved , and used for battery assembly the amount of potassium hydroxide to be contained in the positive electrode mixture, and 2.4 to 4 wt% with respect to the positive electrode mixture weight, including the electrolyte, the positive electrode mixture 3 to 6 months from the battery assembly containing the The manufacturing method of the alkaline battery characterized by making the moisture content to be 8.4-10 mass % with respect to the mass of the positive mix including electrolyte solution.

An alkaline battery manufacturing method for assembling an alkaline battery using a positive electrode mixture containing at least one of manganese dioxide and nickel oxyhydroxide and an alkaline electrolyte in which potassium hydroxide is dissolved. the amount of water to be contained in the agent, and 3.0 to 4.2 wt% with respect to the positive electrode mixture weight, including the electrolyte, the amount of water positive electrode mixture contains 3-6 months from the battery assembly Is made into 8.4-10 mass % with respect to the mass of the positive mix containing electrolyte solution, The manufacturing method of the alkaline battery characterized by the above-mentioned.

11. The method for producing an alkaline battery according to claim 9, wherein the alkaline electrolyte contained in the positive electrode mixture before battery assembly has a potassium hydroxide concentration of 40% by mass or more.

10. The potassium hydroxide concentration determined from the amount of potassium and the amount of water in an alkaline electrolyte contained in a positive electrode mixture for 3 to 6 months after battery assembly is 35 to 39.5% by mass. The manufacturing method of the alkaline battery in any one of -11.

The method for producing an alkaline battery according to any one of claims 9 to 12, wherein the total amount of water in the battery system is 0.23 to 0.275 g per g of the positive electrode active material.

The method for producing an alkaline battery according to any one of claims 9 to 13, wherein the positive electrode mixture is formed at a temperature of 35 to 70 ° C.