【０００１】
【発明の属する技術分野】
本発明は、ニッケル水素電池、ニッケルカドミウム電池等のアルカリ蓄電池に適用する負極とそれを用いたアルカリ蓄電池およびその製造方法に関するものである。
【０００２】
【従来の技術】
アルカリ蓄電池は、耐過充電、耐過放電特性に優れ、一般ユーザーにとって使い易い電池であるところから、携帯電話、小型電動工具および小型パーソナルコンピュータ等の携帯用小型電子機器類用の電源として広く利用されており、これらの小型電子機器類の普及とともに需要が飛躍的に増大している。また、ハイブリッド型電気自動車（ＨＥＶ）の駆動用電源としても実用化されている。そして、アルカリ蓄電池に対してはさらなる容量アップ、充放電サイクル性能の向上が求められている。
【０００３】
前記アルカリ電池の負極は、活物質となる水素吸蔵合金や水酸化カドミウムを主成分とするペーストを、鉄、ニッケルや銅等、耐アルカリ性で良導電性金属の多孔性基板に担持させたものである。
【０００４】
前記負極活物質である水素吸蔵合金粉末やカドミウム粉末は、充放電を行うと容積が変化し、そのために粉末の大きさが変わる。例えば充電を行った場合、水素吸蔵合金粉末は水素を取り込んで容積が増大する。カドミウム電極は水酸化カドミウムから金属カドミウムに変わる時に容積が減少する。放電を行うと充電の逆の減少が起きる。
【０００５】
ところで、前記負極板の基板となる多孔性の基板には、パンチングメタル、金属繊維をフェルト状に成形した繊維式基板、金属をスポンジ状に成形した発泡メタル等を適用する。このうち、低価格で入手が容易であるところからアルカリ蓄電池の負極用基板には薄い板に打ち抜きによって穴を開けたパンチングメタルが重用されている。しかし、該パンチングメタルを基板に、前記のように容積の変化を伴う活物質粉末を担持させた負極板は、活物質粉末と基板との密着が十分でないために、活物質と基板が剥離し易い欠点があった。また、前記密着をよくするために結着剤の比率を高めると電極の電気抵抗が高くなる欠点があった。従って、電極の電気抵抗を高めることなく活物質粉末と基板との密着の改良が求められていた。
【０００６】
活物質粉末と基板との密着を向上させるために、基板の表面に凹凸を付けるのが有効である。凹凸を付けるための一般的な方法には、化学的あるいは電解によるエッチング、サンドペーパーによる研磨等があるが、これらの方法はいずれも基板の機械的強度を損なう。また、芯材としてニッケルメッキを施した鋼板を用いた場合、エッチングや研磨を行うと鉄が露出するため耐食性を損なうことにもなる。
【０００７】
前記のような事情から、機械的強度および耐食性を損なわずに、表面に凹凸を設けた基板の開発が求められていた。
【０００８】
【発明が解決しようとする課題】
本発明は、前記従来技術の欠点に鑑みなされたものであって、アルカリ蓄電池用負極板の活物質粉末と基板の密着性を向上させることによって、充放電サイクル特性および高率放電特性の優れたアルカリ蓄電池を提供せんとするものである。
【０００９】
【課題を解決するための手段】
本発明は、活物質粉末を基板に担持させたアルカリ蓄電池の負極を、耐アルカリ性の金属からなる板状の芯材の表面に斑状にニッケルの凸部を設けた基板を備えた負極とすることによって前記課題を解決する。
【００１０】
前記、本発明に係るアルカリ蓄電池用負極の基板の製造方法は、前記パンチングメタル等の板状芯材の表面にまだら状に撥水処理を施し、その後電解によりメッキ行って芯材の表面に斑状にニッケルの凸部を形成する。
【００１１】
【発明の実施の形態】
本発明に係るアルカリ蓄電池用負極は、水素吸蔵合金電極、カドミウム電極などである。そしてこれらの電極は、ニッケルメッキを施した鉄、ニッケル等の耐アルカリ金属を芯材とする基板に水素吸蔵合金粉末、カドミウム粉末、亜鉛粉末などの負極活物質を担持させたものである。これら活物質粉末の大きさは、１０〜１００μｍである。
【００１２】
本発明に適用する前記負極用の基板は、前記芯材の表面に斑状に、ニッケルの凸部を形成させたものである。芯材には厚さ３０〜２００μｍの鋼板または該鋼板にニッケルメッキを施したものまたはニッケル板が適用できる。さらに前記鋼板またはニッケル板に多数の穴を開けたパンチングメタルが適用できる。基板の機械的強度や活物質層との密着の良さを顧慮して、適用するパンチングメタルの穴径を１〜３ｍｍ、開口率を３０〜５０％とすることが望ましい。
【００１３】
本発明に適用する前記負極用の基板は、前記芯材の表面に斑状にニッケルの凸部をそなえる。該凸部の形状と大きさは、特に限定されるものではないが、活物質粉末と基板との間の密着を強固にするためには、凸部の太さが１００μｍ〜１ｍｍ、高さが５０μｍ〜５００μｍであることが望ましい。また、前記ニッケルの凸部同士の間隔も特に限定される物ではないが１００μｍ〜３ｍｍであることが望ましい。
【００１４】
図１は、本発明に係るアルカリ蓄電池用基板の断面の１例を模式的に示す図である。図の１は、鋼板製の芯材で、２は芯材の表面に設けたニッケルの下地メッキ層、３が下地メッキ層の表面に斑状に配置した撥水性樹脂からなる撥水層である。４は、基板の表面に斑状に配置したニッケルの凸部である。該凸部４が、基板の表面に充填した活物質粉末を主成分とする負極の活物質層の中に食い込みアンカー効果を発揮して基板と活物質層が剥離するのを防ぐ。
【００１５】
本発明によれば、図１に示した如く、基板の表面のうち、ニッケルの凸部４を中心にして撥水層３の上にもメッキ層が伸びて撥水層３でコートされた部分にも薄くニッケルが析出する。後述のように、撥水層の大きさや間隔を適宜選択することによって、図で示したように基板の全面がニッケルで被覆させることができるので、このような場合にはニッケルの下地メッキ２を省くことも可能である。
【００１６】
本発明に係る負極の製造方法においては、基板の芯材にエッチングや研磨等の加工をせずに、その表面に斑状にニッケルの凸部を付け加えるのみである。そのために、芯材の機械的な強度や耐食性が損なわれることがない。
【００１７】
本発明においては、前記ニッケルの凸部を形成するために、ニッケルメッキに先だって芯材表面に極く微量撥水性の樹脂をコートすることによって、芯材表面に斑状の撥水層を設ける。本発明に適用する撥水性の樹脂は、特に限定されるものではなく、具体的にはポリテトラフロロエチレン、ポリ３フッ化塩化エチレン、ポリ６フッ化プロピレン、ポリフッ化ビニリデン、ポリ塩化ビニリデン、ポリエチレン、ポリプロピレン、エチレンプロピレンジエンターポリマー（ＥＰＤＭ）等が適用できる。
【００１８】
前記撥水性樹脂の溶液または分散液を芯材の表面に吹き付けることによって芯材の表面に撥水性樹脂を極く微量コートする。芯材表面に樹脂を微量塗布すると、樹脂の凝集作用が働いて樹脂が斑状に分布した撥水層が得られる。該斑状に樹脂が分布した撥水層を形成するためには、撥水性樹脂の塗布量を基板の片面当たり０．００５〜０．１ｇ／ｍ２とすることが望ましい。
【００１９】
前記のように、表面に斑状に樹脂コートした基板にニッケルメッキを施すと、基板の金属が露出した部分にニッケルが析出してニッケルの凸部を形成する。ニッケルの凸部の大きさは、前記撥水性樹脂の塗布量およびメッキ工程の通電量を規定してニッケルの析出量を制御することによって制御する。本発明によれば、撥水層の大きさを選択することによって、前記のようにニッケルの凸部を中心にして撥水層のほぼ全面にわたり薄くニッケルを析出させることができる。そのため、樹脂コートしない場合に比べて負極の集電機能が損なわれることがない。なお、撥水層のほぼ全面にわたり薄くニッケルを析出させるには、撥水層の径をおおよそ３ｍｍ以下、さらには２ｍｍ以下にすることが望ましく、そのためには撥水性樹脂の塗布量を基板の片面当たり０．００５〜０．１ｇ／ｍ２とすることが望ましい。
【００２０】
以下、活物質粉末として水素吸蔵合金粉末を適用した例を中心に実施例に基づき本発明の詳細な説明を行う。
（実施例）
（負極基板芯材表面の斑状撥水層の生成）
表面に厚さ５μｍのニッケルメッキを施した厚さ６０μｍ、開口率４０％の鋼板製パンチングメタルを芯材として用いた。濃度１重量％のＥＰＤＭのトルエン溶液を容易し、スプレーガンを用いて前記芯材の表面（両面）に吹き付けたのち加熱してトルエンを揮発除去した。該吹き付けによって塗布したＥＰＤＭの量は、基板の片面当たり０．０１ｇ／ｍ２であった。
【００２１】
（負極基板芯材表面のニッケル凸部の形成）
１モル／ｄｍ３の塩化ニッケルと１モル／ｄｍ３の塩酸を含む水溶液を電解浴とし、該電解浴中の中心に前記ＥＰＤＭをコートした芯材を中心に、両側にニッケル板を配置し、芯材を負極、ニッケル板を正極として電解を行った。芯材の単位面積に対する電解の電流密度を２０Ａ／ｄｍ２とし、１０分間通電した。メッキによる芯材表面のニッケルの析出量は６．０ｇ／ｄｍ２であった。このようにして基板の表面に太さが平均約３００μｍ、高さが平均約２００μｍのニッケルの凸部を斑状に形成した。この時、前記ＥＰＤＭ製の撥水層のほぼ全表面もニッケルでカバーされていた。
【００２２】
（水素吸蔵合金電極の作製）
ＣａＣｕ５型結晶構造を有し、ＭｍＮｉ３．６Ａｌ０．２９Ｃｏ０．７５Ｍｎ０．３６（Ｍｍはミッシュメタルであり、Ｌａ、Ｃｅ、ＰｒおよびＮｄからなる希士類元素の混合物である）の組成で示され、平均粒径約５０μｍの水素吸蔵合金粉末１００重量部に対して、増粘剤であるメチルセルロース（ＭＣ）の１ｗｔ％水溶液２０重量部と、結着剤であるスチレンブタジエンゴム１重量部とを加えて混練してペーストを調製した。該ペーストを前記基板の両面に塗布した後乾燥し厚さ１．１ｍｍの極板を得た。乾燥後の極板をロールを通してプレスし、厚さを０．５ｍｍに調整し、水素吸蔵合金電極用原板を得た。
【００２３】
（ニッケル電極活物質粉末の作製）
定法に従いコバルトおよび亜鉛をそれぞれ水酸化物換算で３重量％および５重量％固溶状態で含有させた高密度水酸化ニッケルを核とし、表面に水酸化コバルトの被覆層を形成させた平均粒径が１０μｍの水酸化ニッケルを主成分とするニッケル電極活物質粉末を用意した。なお、該活物質粉末の表面に形成させた前記水酸化コバルトの被覆層の比率を６重量％とした。
【００２４】
（ニッケル電極の作製）
得られたニッケル電極活物質紛末８０重量部に、濃度が１重量％のカルボキシメチルセルロース（ＣＭＣ）水溶液２０重量部を添加混練して、ニッケル電極活物質ペーストを作製した。該ペーストを厚さ１．４ｍｍ、目付量５００ｇ／ｍ２の発泡ニッケル製多孔体基板に充填して乾燥した後、プレスして厚さを０．８ｍｍに調整し、長尺帯状のニッケル電極用原板を得た。
【００２５】
（負極の特性評価用セルの作製）
前記水素吸蔵合金電極用原板から作用面積が２×２ｃｍの大きさの電極を切り取って負極とした。前記ニッケル電極用原板から２．５×２．５ｃｍの電極を切り取って正極とした。負極の両面に厚さ０．２ｍｍの親水化処理を施したポリプロピレン樹脂繊維の不織布からなるセパレータを配置し、負極１枚、正極２枚からなる極板群を構成した。該極板群を所定の容器に挿入し、７モル／ｄｍ３の水酸化カリウム水溶液と１モル／ｄｍ３の水酸化リチウム水溶液とからなる電解液を所定量注入して負極の特性評価用セルとした。また、負極の電位を測定するための参照電極には酸化水銀電極を適用した。
【００２６】
（負極の特性評価試験）
前記セルを温度４０℃において１２時間エージングした後、温度２０℃において化成を行い負極の放電特性が安定したことを確認した後、特性評価試験に供した。初回の充電は、１／５０ＩｔＡの充電電流で２５時間充電し、その後、１／１０ＩｔＡの充電電流にて１０時間充電した。次いで１／５ＩｔＡの放電電流にて放電した。負極の酸化水銀電極に対する電位が−０．６Ｖになった時点で放電を終了させた。２サイクル目以降は、充電を１／１０ＩｔＡ（１７０ｍＡ）の充電電流にて１５時間充電した後、初回の放電と同一の条件で放電した。該充放電サイクルを１サイクルとし、初回の充放電を含めて１０サイクル充放電を繰り返し実施して、負極が安定した放電電圧、放電容量を示すことを確認した。その後、温度２０℃において前記２サイクル目以降と同じ条件で充電した後、０．２ＩｔＡ、１ＩｔＡ、３ＩｔＡおよび５ＩｔＡで放電し、各率放電における放電特性を評価した。
【００２７】
（円筒型ニッケル水素蓄電池の作製）
前記水素吸蔵合金電極用原板および前記ニッケル電極用原板を所定の寸法に裁断して円筒型ニッケル水素蓄電池用の電極とした。活物質充填量から算定されるニッケル電極の容量は、１７００ｍＡｈであった。また、水素吸蔵合金電極とニッケル電極の活物質充填容量の比率を１．６とした。前記ニッケル電極と水素吸蔵合金電極とを、親水化処理を施したポリプロピレン樹脂繊維の不織布からなる厚さ０．１２ｍｍのセパレータを挟んで渦巻状に巻き取り、極板群を製造した。該極板群を円筒状金属ケース内に収納し、７モル／ｄｍ３の水酸化カリウム水溶液と１モル／ｄｍ３の水酸化リチウム水溶液とからなる電解液を所定量注入した。次いで、安全弁を備えた金属製蓋体を用いて金属ケースを封口しＡＡサイズの円筒型ニッケル水素蓄電池を得た。
【００２８】
（化成）
作製したニッケル水素蓄電池を温度４０℃において１２時間エージングした後、温度２０℃において以下に記述する条件にて化成をおこなった。初回の充電は、１／５０ＩｔＡ（３４ｍＡ）の充電電流で１０時間充電し、その後、１／１０ＩｔＡ（１７０ｍＡ）の充電電流にて１０時間充電した。次いで１／５ＩｔＡ（３４０ｍＡ）の放電電流にて放電終止電圧を１．０Ｖとして放電した。２サイクル目以降は、充電を１／１０ＩｔＡ（１７０ｍＡ）の充電電流にて１２時間充電、１／５ＩｔＡ（３４０ｍＡ）の放電電流にて放電終止電圧を１．０Ｖとして放電した。該サイクルを１サイクルとし、初回の充放電を含めて１０サイクル充放電を繰り返し実施した。
【００２９】
（各率放電試験）
化成終了後の円筒型ニッケル水素蓄電池を、温度２０℃において前記条件にて充電し、０．２ＩｔＡ〜５ＩｔＡの放電レート範囲で各率放電試験に供した。
【００３０】
（充放電サイクル試験）
化成終了後の円筒型ニッケル水素蓄電池を、温度２０℃において充放電サイクル試験に供した。充電はＩｔＡの電流で１．２時間行い、放電はＩｔＡの電流にて放電終止電圧を１．０Ｖとして実施した。該充放電サイクルを１サイクルとして、サイクルを繰り返し実施した。
【００３１】
（比較例）
実施例１において負極の基板に、表面に厚さ５μｍのニッケルメッキを施した厚さ６０μｍ、開口率４０％の鋼板製パンチングメタルををそのまま使用した。それ以外は、実施例と同じ条件で負極の特性評価用セルおよび円筒型ニッケル水素蓄電池を作製し、同一の条件で試験に供した。
【００３２】
図２は、本発明の実施例に係る負極および比較例の負極を各率放電試験に供した試験結果のうち１ＩｔＡおよび３ＩｔＡのレートで放電した時の放電曲線を示すグラフである。実施例に係る負極の方が、比較例の負極に比べて放電電位が卑であって、且つ活物質利用率が高い。これは、実施例に係る負極の方が比較例の負極に比べて集電機能に優れていることによるものと考えられる。
【００３３】
図３は、前記実施例に係る負極と比較例の負極の、放電レートと活物質利用率の関係を示すグラフである。図３に示すように、１ＩｔＡ放電以上の高率放電において、実施例に係る負極の方が、比較例の負極を上回る活物質利用率を示す。また、前記実施例および比較例に係る円筒型のニッケル水素電池の各率放電試験結果に対して、それぞれの電池に適用した負極の特性の差が強く反映され、１ＩｔＡ放電以上の高率放電において、本発明に係る実施例電池の方が比較例電池に比べ高い放電容量を示した。
【００３４】
図４は、円筒型ニッケル水素蓄電池の実施例電池および比較例電池の充放電サイクル性能を示すグラフである。図の縦軸は、実施例電池および比較例電池の放電容量を、各々の電池の初期の放電容量を１００％として示した値である。図に示した通り、実施例電池の方が、比較例電池に比べてサイクルの経過に伴う放電容量の低下が小さい。これは、実施例電池の負極の方が、比較例電池の負極に比べて活物質と基板の密着に優れており、サイクルの経過に伴う特性の低下が抑制されているためと考えられる。
【００３５】
前記の試験結果に示したように、高率放電性能、充放電サイクル性能において実施例電池が優れているのは、いずれも実施例電池に適用した負極の活物質層と基板の密着性が優れているために、実施例電池に適用した負極が集電機能に優れ、かつ、充放電サイクルを繰り返し行っても活物質層と基板の剥離が抑制されるためと考えられる。
【００３６】
なお、前記実施例では水素吸蔵合金およびそれを負極に適用したニッケル水素蓄電池を例に採り上げて説明をしたが、本発明はそれに限定されるものではなくカドミウム電極や亜鉛電極およびこれらの電極を適用したアルカリ蓄電池に対しても有効である。
【発明の効果】
【００３７】
本発明の請求項１に係るアルカリ蓄電池用負極は、活物質粉末と基板の密着性に優れ、集電機能に優れかつ充放電サイクル性能の優れたアルカリ電池用負極である。
【００３８】
本発明の請求項２に係るアルカリ蓄電池用負極の製造方法によれば、該負極に適用する基板の機械的強度と耐食性を損なうことなく基板表面に凸部を形成することができる。
【００３９】
本発明の請求項３に係るアルカリ蓄電池は、高率放電特性と充放電サイクル性能の優れたアルカリ蓄電池である。
【００４０】
【図面の簡単な説明】
【図１】本発明に係る負極の基板の断面形状を示す模式図である。
【図２】本発明の実施例に係る負極と比較例の負極の放電曲線を示すグラフである。
【図３】本発明の実施例に係る負極と比較例の負極の各率放電特性を示すグラフである。
【図４】本発明に係る実施例電池と比較例電池の充放電サイクル性能を示すグラフである。
【符号の説明】
１ 芯材
３ 撥水層
４ ニッケル凸部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a negative electrode applied to an alkaline storage battery such as a nickel metal hydride battery and a nickel cadmium battery, an alkaline storage battery using the same, and a method for manufacturing the same.
[0002]
[Prior art]
Alkaline storage batteries have excellent resistance to overcharge and overdischarge and are easy to use for general users, so they are widely used as power sources for portable small electronic devices such as mobile phones, small power tools and small personal computers. The demand for these small electronic devices has been dramatically increased with the spread of these small electronic devices. Further, it has been put to practical use as a power supply for driving a hybrid electric vehicle (HEV). Further, there is a demand for further increase in capacity and improvement in charge / discharge cycle performance of alkaline storage batteries.
[0003]
The negative electrode of the alkaline battery is one in which a paste mainly containing a hydrogen storage alloy or cadmium hydroxide as an active material is supported on a porous substrate of an alkali-resistant and highly conductive metal such as iron, nickel and copper. is there.
[0004]
The volume of the hydrogen storage alloy powder or cadmium powder, which is the negative electrode active material, changes when charged and discharged, and thus the size of the powder changes. For example, when charging is performed, the volume of the hydrogen storage alloy powder increases by taking in hydrogen. The cadmium electrode decreases in volume when changing from cadmium hydroxide to metal cadmium. Discharging causes a reverse decrease in charging.
[0005]
By the way, as the porous substrate serving as the substrate of the negative electrode plate, a punching metal, a fibrous substrate in which metal fibers are formed in a felt shape, a foamed metal in which a metal is formed in a sponge shape, or the like is used. Of these, punching metal formed by punching holes in a thin plate is frequently used for a negative electrode substrate of an alkaline storage battery because of its low cost and availability. However, the negative electrode plate in which the punched metal is loaded with the active material powder having a change in volume as described above is not sufficiently adhered to the active material powder and the substrate. There was an easy defect. In addition, when the ratio of the binder is increased to improve the adhesion, there is a disadvantage that the electric resistance of the electrode increases. Therefore, there has been a demand for improvement in adhesion between the active material powder and the substrate without increasing the electric resistance of the electrode.
[0006]
In order to improve the adhesion between the active material powder and the substrate, it is effective to make the surface of the substrate uneven. Common methods for forming the irregularities include chemical or electrolytic etching, sandpaper polishing, and the like, but all of these methods impair the mechanical strength of the substrate. In addition, when a nickel-plated steel sheet is used as the core material, etching or polishing exposes iron, thereby impairing corrosion resistance.
[0007]
Under the circumstances described above, there has been a demand for the development of a substrate having unevenness on its surface without impairing mechanical strength and corrosion resistance.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the disadvantages of the prior art, and has improved charge-discharge cycle characteristics and high-rate discharge characteristics by improving the adhesion between the active material powder and the substrate of the negative electrode plate for an alkaline storage battery. It is intended to provide an alkaline storage battery.
[0009]
[Means for Solving the Problems]
In the present invention, the negative electrode of an alkaline storage battery in which an active material powder is supported on a substrate is a negative electrode including a substrate having a plate-like core material made of an alkali-resistant metal and a surface provided with spot-like nickel projections. Solves the above problem.
[0010]
The method for manufacturing a substrate for a negative electrode for an alkaline storage battery according to the present invention is characterized in that the surface of a plate-shaped core material such as the punched metal is subjected to a water-repellent treatment in a mottled manner, and then subjected to electroplating to form a patchy surface on the core material. Then, a nickel protrusion is formed.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The negative electrode for an alkaline storage battery according to the present invention is a hydrogen storage alloy electrode, a cadmium electrode, or the like. These electrodes are obtained by supporting a negative electrode active material such as a hydrogen storage alloy powder, a cadmium powder, or a zinc powder on a substrate having a core material of an alkali-resistant metal such as iron or nickel plated with nickel. The size of these active material powders is 10 to 100 μm.
[0012]
In the substrate for a negative electrode applied to the present invention, nickel convex portions are formed on the surface of the core material in a patchy manner. As the core material, a steel plate having a thickness of 30 to 200 μm, a plate obtained by plating the steel plate with nickel, or a nickel plate can be used. Further, a punching metal in which a number of holes are formed in the steel plate or the nickel plate can be applied. In consideration of the mechanical strength of the substrate and the good adhesion to the active material layer, it is desirable that the hole diameter of the applied punching metal is 1 to 3 mm and the aperture ratio is 30 to 50%.
[0013]
The substrate for a negative electrode applied to the present invention has a convex portion of nickel in a spot-like manner on the surface of the core material. The shape and size of the projection are not particularly limited, but in order to strengthen the adhesion between the active material powder and the substrate, the thickness of the projection is 100 μm to 1 mm and the height is 100 μm to 1 mm. It is desirable that the thickness be 50 μm to 500 μm. Also, the interval between the nickel protrusions is not particularly limited, but is preferably 100 μm to 3 mm.
[0014]
FIG. 1 is a diagram schematically showing one example of a cross section of the substrate for an alkaline storage battery according to the present invention. 1 is a core material made of a steel plate, 2 is a nickel base plating layer provided on the surface of the core material, and 3 is a water-repellent layer made of a water-repellent resin arranged in a patch-like manner on the surface of the base plating layer. Numeral 4 is a nickel convex portion arranged in a patch on the surface of the substrate. The protrusions 4 penetrate into the active material layer of the negative electrode mainly composed of the active material powder filled on the surface of the substrate, exhibit an anchor effect, and prevent the substrate and the active material layer from peeling off.
[0015]
According to the present invention, as shown in FIG. 1, a portion of the surface of the substrate where the plating layer extends on the water repellent layer 3 around the nickel protrusion 4 and is coated with the water repellent layer 3. Nickel is also deposited thinly. As described later, by appropriately selecting the size and interval of the water-repellent layer, the entire surface of the substrate can be covered with nickel as shown in the figure. It is also possible to omit it.
[0016]
In the method for manufacturing a negative electrode according to the present invention, the core material of the substrate is not subjected to processing such as etching or polishing, but is simply added with a convex portion of nickel in a spot-like manner on the surface thereof. Therefore, the mechanical strength and corrosion resistance of the core material are not impaired.
[0017]
In the present invention, in order to form the nickel protrusions, a very small amount of water-repellent resin is coated on the surface of the core material prior to nickel plating, thereby providing a patchy water-repellent layer on the surface of the core material. The water-repellent resin applied to the present invention is not particularly limited. Specifically, polytetrafluoroethylene, poly (trifluorochloroethylene), poly (propylene hexafluoride), polyvinylidene fluoride, polyvinylidene chloride, polyethylene , Polypropylene, ethylene propylene diene terpolymer (EPDM) and the like.
[0018]
A very small amount of the water-repellent resin is coated on the surface of the core material by spraying the solution or dispersion of the water-repellent resin onto the surface of the core material. When a small amount of resin is applied to the surface of the core material, a water-repellent layer in which the resin is distributed in a patch-like manner is obtained by the cohesive action of the resin. In order to form a water-repellent layer in which the resin is distributed in a patchy manner, it is desirable that the amount of the water-repellent resin applied is 0.005 to 0.1 g / m 2 per one surface of the substrate.
[0019]
As described above, when nickel plating is applied to a substrate whose surface is resin-coated in a patch-like manner, nickel precipitates on a portion of the substrate where the metal is exposed to form a nickel convex portion. The size of the nickel convex portion is controlled by regulating the amount of nickel deposited by regulating the amount of the water-repellent resin applied and the amount of current applied in the plating step. According to the present invention, by selecting the size of the water-repellent layer, it is possible to deposit nickel thinly over almost the entire surface of the water-repellent layer centering on the nickel protrusions as described above. Therefore, the current collecting function of the negative electrode is not impaired as compared with the case where no resin coating is performed. In order to deposit nickel thinly over almost the entire surface of the water-repellent layer, it is desirable that the diameter of the water-repellent layer be approximately 3 mm or less, and more preferably 2 mm or less. It is desirable to set it to 0.005 to 0.1 g / m 2 per unit.
[0020]
Hereinafter, the present invention will be described in detail based on examples, mainly on examples in which a hydrogen storage alloy powder is applied as an active material powder.
(Example)
(Formation of mottled water-repellent layer on the surface of negative electrode substrate core material)
A punching metal made of a steel plate having a thickness of 60 μm and an aperture ratio of 40% and a nickel plating having a thickness of 5 μm on the surface was used as a core material. A toluene solution of EPDM having a concentration of 1% by weight was facilitated, sprayed onto the surface (both surfaces) of the core material using a spray gun, and then heated to volatilize and remove the toluene. The amount of EPDM applied by the spraying was 0.01 g / m 2 per one surface of the substrate.
[0021]
(Formation of nickel protrusions on the surface of the negative electrode substrate core material)
An aqueous solution containing 1 mol / dm 3 of nickel chloride and 1 mol / dm 3 of hydrochloric acid is used as an electrolytic bath, and nickel plates are arranged on both sides around the EPDM-coated core material at the center of the electrolytic bath, Electrolysis was performed using the core material as a negative electrode and the nickel plate as a positive electrode. The current density of electrolysis per unit area of the core material was set to 20 A / dm 2, and current was supplied for 10 minutes. The amount of nickel deposited on the surface of the core material by plating was 6.0 g / dm 2 . In this way, nickel protrusions having an average thickness of about 300 μm and an average height of about 200 μm were formed on the surface of the substrate in a patchy manner. At this time, almost the entire surface of the EPDM water-repellent layer was also covered with nickel.
[0022]
(Preparation of hydrogen storage alloy electrode)
MnNi 3.6 Al 0.29 Co 0.75 Mn 0.36 (having a CaCu 5- type crystal structure, Mm is a misch metal and is a mixture of rare earth elements composed of La, Ce, Pr and Nd) ), 100 parts by weight of a hydrogen storage alloy powder having an average particle size of about 50 μm, 20 parts by weight of a 1 wt% aqueous solution of methylcellulose (MC) as a thickener, and styrene butadiene rubber as a binder 1 part by weight was added and kneaded to prepare a paste. The paste was applied to both sides of the substrate and dried to obtain an electrode plate having a thickness of 1.1 mm. The dried electrode plate was pressed through a roll, the thickness was adjusted to 0.5 mm, and a hydrogen storage alloy electrode base plate was obtained.
[0023]
(Preparation of nickel electrode active material powder)
Average particle size of a high-density nickel hydroxide containing 3% by weight and 5% by weight of hydroxide in solid solution in terms of hydroxide according to a standard method, and a coating layer of cobalt hydroxide formed on the surface. A nickel electrode active material powder mainly composed of nickel hydroxide having a particle size of 10 μm was prepared. The ratio of the cobalt hydroxide coating layer formed on the surface of the active material powder was 6% by weight.
[0024]
(Preparation of nickel electrode)
To 80 parts by weight of the obtained nickel electrode active material powder, 20 parts by weight of a 1% by weight aqueous solution of carboxymethyl cellulose (CMC) was added and kneaded to prepare a nickel electrode active material paste. The paste was filled into a porous nickel foam substrate having a thickness of 1.4 mm and a basis weight of 500 g / m 2 , dried, and then pressed to adjust the thickness to 0.8 mm. An original plate was obtained.
[0025]
(Preparation of cell for evaluating negative electrode characteristics)
An electrode having an action area of 2 × 2 cm was cut out from the hydrogen storage alloy electrode master plate to form a negative electrode. A 2.5 × 2.5 cm electrode was cut from the nickel electrode master plate to form a positive electrode. A separator made of a nonwoven fabric of a polypropylene resin fiber having been subjected to a hydrophilic treatment and having a thickness of 0.2 mm was arranged on both surfaces of the negative electrode, to form an electrode plate group including one negative electrode and two positive electrodes. The electrode group was inserted into a predetermined container, and a predetermined amount of an electrolytic solution comprising a 7 mol / dm 3 aqueous solution of potassium hydroxide and a 1 mol / dm 3 aqueous solution of lithium hydroxide was injected thereinto, and a cell for evaluating the characteristics of the negative electrode was obtained. And A mercury oxide electrode was used as a reference electrode for measuring the potential of the negative electrode.
[0026]
(Characteristic evaluation test of negative electrode)
The cell was aged at a temperature of 40 ° C. for 12 hours, and then formed at a temperature of 20 ° C. to confirm that the discharge characteristics of the negative electrode were stabilized, and then subjected to a characteristic evaluation test. In the first charging, the battery was charged at a charging current of 1/50 ItA for 25 hours, and then charged at a charging current of 1/10 ItA for 10 hours. Subsequently, discharge was performed at a discharge current of 1/5 ItA. The discharge was terminated when the potential of the negative electrode with respect to the mercury oxide electrode became -0.6 V. After the second cycle, the charge was performed at a charge current of 1/10 ItA (170 mA) for 15 hours, and then discharged under the same conditions as the first discharge. The charge / discharge cycle was defined as one cycle, and charge / discharge was repeated for 10 cycles including the first charge / discharge, and it was confirmed that the negative electrode exhibited stable discharge voltage and discharge capacity. Thereafter, the battery was charged at a temperature of 20 ° C. under the same conditions as the second and subsequent cycles, and then discharged at 0.2 ItA, 1 ItA, 3 ItA, and 5 ItA, and the discharge characteristics at each rate discharge were evaluated.
[0027]
(Production of cylindrical nickel-metal hydride battery)
The original plate for a hydrogen storage alloy electrode and the original plate for a nickel electrode were cut into predetermined dimensions to form electrodes for a cylindrical nickel-metal hydride storage battery. The capacity of the nickel electrode calculated from the active material filling amount was 1700 mAh. In addition, the ratio of the active material filling capacity of the hydrogen storage alloy electrode and the nickel electrode was set to 1.6. The nickel electrode and the hydrogen storage alloy electrode were spirally wound with a separator made of a nonwoven fabric of a hydrophilically treated polypropylene resin fiber having a thickness of 0.12 mm therebetween to produce an electrode plate group. The electrode group was housed in a cylindrical metal case, and a predetermined amount of an electrolytic solution comprising a 7 mol / dm 3 aqueous solution of potassium hydroxide and a 1 mol / dm 3 aqueous solution of lithium hydroxide was injected. Next, the metal case was sealed using a metal lid provided with a safety valve to obtain an AA-size cylindrical nickel-metal hydride storage battery.
[0028]
(Chemical)
The resulting nickel-metal hydride storage battery was aged at a temperature of 40 ° C. for 12 hours, and then formed at a temperature of 20 ° C. under the following conditions. In the first charging, the battery was charged at a charging current of 1/50 ItA (34 mA) for 10 hours, and then charged at a charging current of 1/10 ItA (170 mA) for 10 hours. Next, discharge was performed at a discharge current of 1/5 ItA (340 mA) with a discharge end voltage of 1.0 V. After the second cycle, the battery was charged at a charge current of 1/10 ItA (170 mA) for 12 hours, and discharged at a discharge current of 1/5 ItA (340 mA) with a discharge termination voltage of 1.0 V. The cycle was defined as one cycle, and the charge and discharge were repeated for 10 cycles including the first charge and discharge.
[0029]
(Each rate discharge test)
After the formation, the cylindrical nickel-metal hydride storage battery was charged at a temperature of 20 ° C. under the above-mentioned conditions, and subjected to a discharge test at each rate in a discharge rate range of 0.2 ItA to 5 ItA.
[0030]
(Charge / discharge cycle test)
The nickel-metal hydride storage battery after the formation was subjected to a charge / discharge cycle test at a temperature of 20 ° C. Charging was performed with an ItA current for 1.2 hours, and discharging was performed with an ItA current with a discharge end voltage of 1.0 V. The cycle was repeated with the charge / discharge cycle as one cycle.
[0031]
(Comparative example)
In Example 1, a steel plate punched metal having a thickness of 60 μm and an aperture ratio of 40%, the surface of which was plated with nickel having a thickness of 5 μm, was used as it was on the negative electrode substrate. Other than that, a cell for evaluating the characteristics of the negative electrode and a cylindrical nickel-metal hydride storage battery were prepared under the same conditions as in the example, and were subjected to the test under the same conditions.
[0032]
FIG. 2 is a graph showing a discharge curve when the negative electrode according to the example of the present invention and the negative electrode of the comparative example were discharged at a rate of 1 ItA and 3 ItA among the test results subjected to each rate discharge test. The negative electrode according to the example has a lower discharge potential and a higher active material utilization rate than the negative electrode according to the comparative example. This is considered to be because the negative electrode according to the example has a better current collecting function than the negative electrode according to the comparative example.
[0033]
FIG. 3 is a graph showing the relationship between the discharge rate and the active material utilization of the negative electrode according to the example and the negative electrode of the comparative example. As shown in FIG. 3, in a high-rate discharge of 1 ItA discharge or more, the negative electrode according to the example has a higher active material utilization than the negative electrode of the comparative example. In addition, the difference in the characteristics of the negative electrodes applied to the respective batteries was strongly reflected on the results of the respective rate discharge tests of the cylindrical nickel-metal hydride batteries according to the above Examples and Comparative Examples, and in high rate discharges of 1 ItA discharge or more, The battery of the example according to the present invention showed a higher discharge capacity than the battery of the comparative example.
[0034]
FIG. 4 is a graph showing the charge / discharge cycle performance of an example battery and a comparative example battery of a cylindrical nickel-metal hydride storage battery. The vertical axis of the figure is a value indicating the discharge capacity of the battery of the example and the battery of the comparative example, with the initial discharge capacity of each battery being 100%. As shown in the drawing, the battery of the example has a smaller decrease in the discharge capacity with the passage of the cycle than the battery of the comparative example. This is considered to be because the negative electrode of the battery of the example had better adhesion between the active material and the substrate than the negative electrode of the battery of the comparative example, and the deterioration of the characteristics with the passage of cycles was suppressed.
[0035]
As shown in the above test results, the high performance of the example battery in the high rate discharge performance and the charge / discharge cycle performance is due to the excellent adhesion between the active material layer of the negative electrode applied to the example battery and the substrate. Therefore, it is considered that the negative electrode applied to the battery of Example has an excellent current collecting function, and the separation of the active material layer and the substrate is suppressed even when the charge and discharge cycle is repeated.
[0036]
In the above-described embodiment, the hydrogen storage alloy and the nickel-metal hydride storage battery in which the hydrogen storage alloy is applied to the negative electrode have been described as examples. It is also effective for alkaline storage batteries.
【The invention's effect】
[0037]
The negative electrode for an alkaline storage battery according to claim 1 of the present invention is a negative electrode for an alkaline battery having excellent adhesion between the active material powder and the substrate, excellent current collecting function, and excellent charge / discharge cycle performance.
[0038]
According to the method for manufacturing a negative electrode for an alkaline storage battery according to the second aspect of the present invention, a convex portion can be formed on the substrate surface without impairing the mechanical strength and corrosion resistance of the substrate applied to the negative electrode.
[0039]
The alkaline storage battery according to claim 3 of the present invention is an alkaline storage battery having excellent high rate discharge characteristics and excellent charge / discharge cycle performance.
[0040]
[Brief description of the drawings]
FIG. 1 is a schematic view showing a cross-sectional shape of a substrate of a negative electrode according to the present invention.
FIG. 2 is a graph showing discharge curves of a negative electrode according to an example of the present invention and a negative electrode of a comparative example.
FIG. 3 is a graph showing each rate discharge characteristic of a negative electrode according to an example of the present invention and a negative electrode of a comparative example.
FIG. 4 is a graph showing the charge / discharge cycle performance of an example battery according to the present invention and a comparative example battery.
[Explanation of symbols]
1 core material 3 water repellent layer 4 nickel protrusion
