JP2004063339A

JP2004063339A - Negative electrode for alkaline storage battery and alkaline storage battery using it

Info

Publication number: JP2004063339A
Application number: JP2002221803A
Authority: JP
Inventors: Manabu Kanemoto; 金本　　学; Mitsuhiro Kodama; 児玉　充浩; Minoru Kurokuzuhara; 黒葛原　実
Original assignee: Yuasa Corp; Yuasa Battery Corp
Current assignee: Yuasa Corp
Priority date: 2002-07-30
Filing date: 2002-07-30
Publication date: 2004-02-26

Abstract

【課題】穿孔板を基板に用いたアルカリ蓄電池用負極を備えるアルカリ蓄電池において、高率放電特性および充放電サイクル特性に優れ、且つ電池を充電した時に電池の内圧上昇抑制機能に優れたアルカリ蓄電池を提供する。
【解決手段】耐アルカリ電解液性金属製穿孔板１に水素吸蔵合金粉末や酸化カドミウムまたは水酸化カドミウム粉末からなる活物質粉末２を担持させたアルカリ蓄電池用負極において、電極表面のうち前記穿孔板の開口部４と重なる位置に、形状が前記開口と略相似形であって大きさが開口と等しいかまたはそれ以下であって、開口とほぼ同じ容積の凹部３を形成し、触媒機能を有する粉末を充填した事を特徴とする。
【選択図】　図１Kind Code: A1 An alkaline storage battery provided with a negative electrode for an alkaline storage battery using a perforated plate as a substrate, the alkaline storage battery being excellent in high-rate discharge characteristics and charge-discharge cycle characteristics and excellent in suppressing internal pressure rise of the battery when the battery is charged. provide.
A negative electrode for an alkaline storage battery in which an active material powder 2 composed of a hydrogen storage alloy powder, cadmium oxide or cadmium hydroxide powder is supported on a perforated plate 1 made of an alkali-electrolyte-resistant metal, A recess 3 having a shape substantially similar to that of the opening and having a size equal to or less than the opening and having substantially the same volume as the opening is formed at a position overlapping the opening 4 and having a catalytic function. It is characterized by being filled with powder.
[Selection diagram] Fig. 1

Description

【０００１】
【発明の属する技術分野】
本発明は、水素吸蔵合金電極やカドミウム電極などのアルカリ蓄電池用負極および該負極を適用したアルカリ蓄電池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酸化カドミウムまたは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】
前記負極板の基板となる多孔性の基板には、板に機械的に孔を穿った穿孔板、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がある。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穿孔板が重用されている。図４は、従来のアルカリ蓄電池用負極の断面を模式的に示す図である。図４に示すように、基板となる穿孔板１の両面に水素吸蔵合金や酸化カドミウム等を主成分とする活物質層２を担持させたものである。
【０００５】
従来の穿孔板を基板に用いた水素吸蔵電極やカドミウム電極においては、活物質充填密度にムラがあった。すなわち穿孔板の開口部の活物質充填密度が、非開口部のそれに比べて低かった。基板上に活物質ペーストをコートし、乾燥した後にロールの間を通してプレス加工を施すことによって活物質充填密度を高めるのであるが、前記活物質充填密度にムラが生じるのは、前記プレス加工工程において基板の開口部に充填された活物質層加わる押圧が、非開口部分に加わる押圧に比べて低いためである。水素吸蔵合金電極やカドミウム電極の場合、活物質粉末の充填密度が低いと活物質粉末同士のコンタクトが不十分であることにより電極の導電性が低く、集電機能が不足するために活物質の利用率が低くなる虞が高い。
【０００６】
また、密閉型のニッケル水素蓄電池やニッケルカドミウム蓄電池においては、充電時に正極で発生する酸素を負極で還元して水分子に戻す、いわゆる酸素サイクル機構を採用することによってなり立っている。負極の酸素吸収能力が低いと、充電末期に電池内の空間に酸素ガスが蓄積し、電池の内圧が高まって電解液を構成する水が消失したり、負極活物資が腐食するために充放電サイクル性能に悪影響を及ぼす虞があった。高速（高率）で充電した場合に負極での酸素吸収速度が酸素発生速度に追いつかなくなる虞が高くなる。近年高速での充電の要求が高まるにつれ負極の酸素吸収能の更なる改良が求められていた。また、充放電サイクル性能の更なる向上が求められていた。
【０００７】
【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、穿孔板を基板に用いたアルカリ蓄電池用負極を備えるアルカリ蓄電池であって、高率放電特性に優れたアルカリ蓄電池であって、さらには充放電サイクル特性および充電時の内圧上昇抑制機能に優れたアルカリ蓄電池を提供せんとするものである。
【０００８】
【課題を解決するための手段】
本発明に係るアルカリ蓄電池用負極は、耐アルカリ電解液性金属からなる穿孔板に水素吸蔵合金粉末や酸化カドミウム等からなる活物質粉末を担持させたアルカリ蓄電池用負極であって、電極表面のうち前記穿孔板の開口部と重なる位置に、凹部を形成する。
【０００９】
本発明に係るアルカリ蓄電池用負極は、望ましくは前記凹部をその平面形状が前記開口の平面形状と略相似形であって、前記開口と同じかまたは小さい大きさとする。
【００１０】
本発明に係るアルカリ蓄電池用負極は、望ましくは前記凹部に耐アルカリ性の導電性粉末および／または耐アルカリ性であって、酸素の還元反応に対して触媒機能を有する粉末を充填する。
【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、平均粒径が１０〜８０μｍの水素吸蔵合金粉末や酸化カドミウムまたは水酸化カドミウム粉末を主成分とする活物質の層を、厚さ３０〜１００μｍ、口径０．５〜２ｍｍの開口を有し、開口率３０〜６０％の耐アルカリ性の金属からなる穿孔板製の基板に担持させたものである。
【００１２】
前記穿孔板の材質は、表面にニッケル鍍金を施した鋼板またはニッケルである。本発明に係るアルカリ蓄電池用負極は、前記水素吸蔵合金粉末や酸化カドミウムまたは水酸化カドミウム粉末を主成分とする活物質の層を基板の両面に配置したものであって、電極の総厚さは０．２〜１ｍｍである。
【００１３】
図１（イ）、図１（ロ）は、本発明に係るアルカリ蓄電池用負極の断面を模式的に示したものである。本発明に係るアルカリ蓄電池用負極は、図１に示すように前記活物質の層２の片側、あるいは図２に示すように電極の表裏両側の表面に凹部３を有する。該凹部３は、凸部を設けた押圧面を備えるプレス装置によって電極表面を押圧することによって形成したものであって、前記基板１の開口４と重なる位置にある。該凹部を設けることによって、基板の開口に充填した活物質の充填密度を高めることができる。
【００１４】
前記凹部３の平面形状、大きさ及び深さは特に限定されるものではないが、基板の開口部分と非開口部分に充填した活物質の充填密度をほぼ等しくなるようにするためには、凹部３の平面形状を開口４の平面形状と略相似形であって、その大きさを開口の大きさと等しいかまたは小さくする。ここでいう凹部および開口の平面形状とは、電極および基板の平面を見た時の形状であり、円形を採用することが多い。
【００１５】
前記のように、従来のアルカリ蓄電池用負極の場合、基板の開口部における活物質粉末の充填密度は、非開口部分の活物質粉末の充填密度に比べて低い。本発明では、電極の表面のうち基板の開口部に重なる位置に凹部を設けることによって開口部分の水活物質粉末の充填密度を高める。前記凹部と基板の非開口部は、平面から見て重ならないことが望ましい。両者が重なった部分では活物質粉末に大きな押圧が加わるために粉末の間の空間が極端に小さくなり、電極反応が阻害される虞が生じる。このため、凹部の大きさを開口の大きさと等しいかまたはそれ以下にすることが望ましい。
【００１６】
また、開口の内壁と凹部の周縁部との間の距離が大きいと、両者の間に挟まれた部分の活物質粉末の充填密度が低くなる虞がある。このことを避けるため、凹部と開口の平面形状を略相似形にして、さらに、凹部と開口の大きさをなるべく近くすることが望ましい。以上のことから、開口が円形であってその半径をＲとすると、凹部も円形とし、その半径ｒと前記Ｒの比ｒ／Ｒを望ましくは０．６〜１．０とし、０．７〜０．９とすることがさらに望ましい。
【００１７】
本発明では、電極の前記基板１の開口４と重なる位置に凹部３を設けることによって開口部に充填した活物質粉末の充填密度を高め、非開口部に充填した活物質粉末の充填密度に近づける。前記凹部の深さは特に限定されるものではないが、前記の目的を達成するためには凹部の容積は、前記基板の開口４の容積と略同一にすることが望ましい。なお、図２に示した電極の表裏両面に凹部を設ける場合、電極の表裏に設けた２つの凹部は、基板の開口を挟んで重なる位置にある。また、２つの凹部の容積の和が基板の開口の容積と略等しくなるようにすることが望ましい。
【００１８】
具体的には、開口の容積をＶ、凹部の容積をｖとした時に両者の比ｖ／Ｖを０．５〜１．２とすることが望ましく、０．９〜１．１にすることがさらに望ましい。
また、凹部３の断面形状もとくに限定されるものではないが、開口内の活物質にもプレス加工時に押圧が加わるようにするには、凹部３の側壁が基板の開口の側壁と略同一の方向を向いていることが望ましい。すなわち図１の（イ）に示すように凹部３の側壁が電極の表面に対して垂直にするかまたは図１の（ロ）に示すように凹部３の側壁に小さめのテーパを設けることが望ましい。
【００１９】
アルカリ蓄電池用負極を前記のような構成にすることによって、基板の開口部分に充填した活物質粉末の充填密度を非開口部上に充填した活物質粉末の充填密度とほぼ同じ程度にまで高めることができる。
【００２０】
前記課題を解決するためには、前記凹部を基板の開口と重なる位置のうちの全てかまたは大部分に設けることが望ましい。該凹部は、前記のように基板表面を活物質層でコートして乾燥した後、電極にプレス加工を施すことによって形成する。
【００２１】
プレス加工は、通常、帯状で長尺の電極を２本のロールの間を通すことによって行う。本発明に適用するプレス加工用のロールの表面には基板と同じ間隔で、基板の開口の形状とほぼ相似の形状の凸部が設けてある。電極の片側のみに凹部を設ける場合は、２本のロールのうち片方のロールの表面に開口と略同容積の凸部を設ける。また、電極の両面に凹部３を形成させる場合には２本のロールの表面に開口の略１／２の容積の凸部を設ける。
【００２２】
前記のように、電極のうち基板の開口部に充填された活物質層には非開口部上に充填された活物質層に比べてプレス圧力の加わり方が小さい。そのため、開口部においては非開口部に比べて水素吸蔵合金粉末の充填密度が低くなって集電機能が劣る欠点がある。前記ロールの表面に凸部を設けて、電極表面の基板の開口部に重なる位置に開口の容積と略同じ容積の凹部を造ることによって、基板の開口部にも非開口部と同じ圧力が加わるようにしたものであって、開口部の活物質粉末の充填密度を非開口部のそれと同程度に高める効果がある。
【００２３】
本発明に係るアルカリ蓄電池用負極においては、図３に示すように前記凹部３に耐アルカリ性の導電性粉末４を充填することが望ましい。また、耐アルカリ性であって、酸素の還元反応に対して触媒機能を有する粉末を充填することが望ましい。
【００２４】
前記耐アルカリ性の導電性粉末としては、黒鉛やケッチェンブラック等の炭素粉末やニッケル粉末が適用できる。また、酸素の還元反応の触媒機能を有する粉末としては、アセチレンブラック等のカーボンブラックや活性炭等の炭素粉末、銀の粉末、ラネーコバルト粉末等を適用出来る。さらに、これらの粉末の表面の一部をポリテトラフロロエチレン等のフッ素樹脂やポリエチレンやポリプロピレンなどのポリオレフィン系樹脂等の撥水性樹脂をコートして粉末の表面に撥水性を付与することが酸素ガスの吸収を促進するのに有効である。
【００２５】
本発明に係る負極は、基板に水素吸蔵合金粉末や酸化カドミウムまたは水酸化カドミウム粉末等の活物質粉末を主成分とする活物質ペーストを塗工充填する。活物質ペーストを充填した極板を乾燥後ロールを通して押圧し、活物質充填密度を高める。また、前記アルカリ蓄電池用負極の表面に設けた凹部は、電解液を収容するスペースを提供し、充放電サイクル性能を向上させるのに有効である。
【００２６】
（実施例１）
（水素吸蔵合金電極の作製）
ＣａＣｕ_５型結晶構造を有し、ＭｍＮｉ_３．６Ａｌ_０．２９Ｃｏ_０．７５Ｍｎ_０．３６（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。
【００２７】
水素吸蔵合金電極の基板には、ニッケル鍍金を施した厚さ７０μｍ、開口径１．５ｍｍ、開口率４０％の鋼板製の穿孔板を適用した。該基板の両面に前記ペーストを塗工した。塗工後の極板を乾燥し、厚さ１．１ｍｍの極板を得た。該極板を表面に径が１．０ｍｍ、高さ０．０８ｍｍの円柱状の複数の凸部を設けた２本のロールの間を通して、極板の仕上がり厚さが０．４ｍｍになるようにプレス加工を施した。また、前記ロールの表面に設けた凸部の間隔を基板の開口の間隔と等しくしておき、極板をロールに通す際にロールの凸部が基板の開口にかさなるように配置した。このようにして、極板の表裏２つの表面の基板の開口と重なる位置に直径１．０ｍｍ、深さ０．０８ｍｍの円柱上の凹部を形成した。該原板を所定の寸法に裁断して水素吸蔵合金電極とした。
【００２８】
（水素吸蔵合金電極の活物質層の見かけの密度の調査）
前記水素吸蔵合金電極の基板の開口部と非開口を直径１．５ｍｍで厚み方向に打ち抜いてサンプルを採取し、その重量を測定した。非開口部ついては、測定した重量を容積で割った値を見掛け密度とした。非開口部については、サンプルの重量および容積から基板の重量および容積を差し引き、その結果得られた重量を容積で割った値を見掛け密度とした。
【００２９】
（ニッケル電極活物質粉末の作製）
所定の方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。
【００３０】
（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／ｍ^２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０．７５ｍｍに調整し、長尺帯状のニッケル電極用原板を得た。該原板を所定の寸法に裁断してニッケル電極とした。活物質充填量から算定されるニッケル電極の容量は、１６００ｍＡｈであった。
【００３１】
（ニッケル水素電池の作製）
前記ニッケル電極と水素吸蔵合金電極を厚さ０．１２ｍｍの親水処理を施したポリプロピレ製不織布を介して積層し、これを捲回して極板群とした。該極板群の負極（水素吸蔵合金電極）と正極（ニッケル電極）の容量の比が１．６対１となるようにした。極板群に正極および負極用集電端子を取り付け金属製電槽に挿入し、水酸化カリウムの水溶液を主成分とする電解液を所定量注入した後封口して円筒型の密閉式ニッケル水素電池とした。
【００３２】
（化成）
得られ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、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（３２ｍＡ）の充電電流で１０時間充電し、その後、１／１０ＩｔＡ（１６０ｍＡ）の充電電流にて１０時間充電した。次いで１／５ＩｔＡ（３２０ｍＡ）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（１６０ｍＡ）の充電電流にて１２時間充電、１／５ＩｔＡ（３２０ｍＡ）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。
【００３３】
（実施例２）
実施例１において水素吸蔵合金電極の表面に設けた凹部に黒鉛粉末を充填した。具体的には、平均粒径５μｍの黒鉛粉末６０重量部に対して濃度５％のＣＭＣの水溶液４０重量部を混ぜて混練した黒鉛のペーストを作製し、水素吸蔵合金電極の表面に塗工したのち、前記凹部を除いて電極の表面に付着した黒鉛ペーストを掻き取った後に乾燥した。それ以外は、実施例１と同じとした。
【００３４】
（実施例３）
実施例１において水素吸蔵合金電極の表面に設けた凹部にラネーコバルト粉末を充填した。具体的には、コバルト５０重量％、アルミニウム５０重量％の合金粉末を苛性アルカリの濃厚溶液に浸漬してアルミニウム溶出させた平均粒径５μｍのラネーコバルト粉末を作製した。該ラネーコバルト８０重量部を平均分子量２００００のポリプロピレンの２％トルエン溶液２０重量部と混練した後に乾燥してトルエンを除去した。該粉末８０重量部に対して濃度２％のＣＭＣの水溶液２０重量部を混ぜて混練したラネーコバルト粉末のペーストを作製し、水素吸蔵合金電極の表面に塗工したのち、前記凹部を除いて電極の表面に付着したラネーコバルト粉末のペーストを掻き取った後に乾燥した。それ以外は、実施例１と同じとした。
【００３５】
（比較例１）
実施例１において、乾燥後の水素吸蔵合金電極をプレス加工する工程で平滑な表面を持つ２つのロールを通した。それ以外は、実施例１と同じとした。
【００３６】
（実施例４）
（カドミウム電極の作製）
平均粒径約１０μｍの酸化カドミウム粉末８０重量部と金属カドミウム粉末２０重量を混合した混合粉末１００重量部に対して、エチレングリコール１６重量部を加えて混練してペーストを調製した。該ペーストニッケル鍍金を施した厚さ７０μｍ、開口径１．５ｍｍ、開口率４０％の鋼板製の穿孔板製基板の両面に前記ペーストを塗工した。塗工後の極板を乾燥し、厚さ１．４ｍｍの極板を得た。該極板を表面に凸部を設けた２本のロールの間を通してプレス加工を施し、極板の厚さを０．７０ｍｍに調整した。該極板の表面に設けた凹部に実施例３同様に、ラネーコバルト粉末を充填した。このようにして得たカドミウム電極用原板を所定の寸法に裁断してカドミウム電極とした。
【００３７】
前記実施例１に記述した水素吸蔵合金電極の場合と同様、前記カドミウム電極の基板の開口部および非開口部の活物質層の密度を測定した。また、前記ニッケル電極とカドミウム電極を組み合わせて、円筒型の密閉式ニッケルカドミウム電池を作製した。
【００３８】
（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／ｍ^２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０．７５ｍｍに調整し、長尺帯状のニッケル電極用原板を得た。該原板を所定の寸法に裁断してニッケル電極とした。活物質充填量から算定されるニッケル電極の容量は、１０００ｍＡｈであった。
【００３９】
（ニッケルカドミウム電池の作製）
前記ニッケル電極とカドミウム電極を厚さ０．１５ｍｍの親水処理を施したポリプロピレ製不織布を介して積層し、これを捲回して極板群とした。該極板群の負極（水素吸蔵合金電極）と正極（ニッケル電極）の容量の比が１．８対１となるようにした。極板群に正極および負極用集電端子を取り付け金属製電槽に挿入し、水酸化カリウムの水溶液を主成分とする電解液を所定量注入した後封口して円筒型の密閉式ニッケル水素電池とした。
【００４０】
（化成）
得られ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、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（２０ｍＡ）の充電電流で１０時間充電し、その後、１／１０ＩｔＡ（１００ｍＡ）の充電電流にて１０時間充電した。次いで１／５ＩｔＡ（２００ｍＡ）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（１００ｍＡ）の充電電流にて１２時間充電、１／５ＩｔＡ（２００ｍＡ）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。
【００４１】
（比較例２）
実施例４において、乾燥後の水素吸蔵合金電極をプレス加工する工程で平滑な表面を持つ２つのロールの間を通した。また、カドミウム電極表面へのラネーコバルト粉末の塗布は実施しなかった。それ以外は、実施例４と同じとした。
【００４２】
（各率放電試験）
化成終了後の実施例電池および比較例電池を、温度２０℃において前記条件にて充電した後、放電レートの範囲を０．２ＩｔＡ〜５ＩｔＡとし、放電終止電圧を１．０Ｖとする各率放電試験に供した。
【００４３】
（過充電時の内圧上昇評価）
化成終了後の実施例電池および比較例電池を１／５ＩｔＡ、終止電圧１．０Ｖで放電した電池に電池の内圧を測定するための圧力計を取り付けた後、該電池を１ＩｔＡで２時間充電を行い、充電中の電池内圧の経時的変化を測定した。
【００４４】
（充放電サイクル試験）
化成終了後の実施例電池および比較例電池を、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。
【００４５】
表１に、実施例１と比較例１に記載した水素吸蔵合金電極の活物質層の見かけの密度および実施例４と比較例２に記載したカドミウム電極の活物質層の見掛け密度を示す。
【表１】

【００４６】
表１に示す如く、本発明に係る実施例電池の場合は、水素吸蔵合金電極、カドミウム電極共に活物質層の見掛け密度が基板の開口部と非開口部との間に差がないのに対して、比較例の場合は、水素吸蔵合金電極、カドミウム電極共に基板開口部の活物質層の見掛け密度が低い。
【００４７】
図５は、実施例および比較例に係るニッケル水素電池の各率放電試験結果を示すグラフである。１ＩｔＡ以上の高率放電試験において、本発明に係る実施例電池がいずれも比較例電池に比べて高い放電性能を示している。これは、実施例電池の水素吸蔵合金電極の集電機能の向上に伴う高率放電性能が向上したことが大きく寄与していると考えられる。特に、実施例２の性能が優れ、水素吸蔵合金電極の表面に設けた凹部に充填した黒鉛粉末が性能向上に寄与していると考えられる。
【００４８】
図６は、実施例および比較例に係るニッケルカドミウム電池の各率放電試験結果を示すグラフである。ニッケル水素電池の場合と同様に１ＩｔＡ以上の高率放電試験において、本発明に係る実施例電池が比較例電池に比べて高い放電性能を示している。これは、実施例電池のカドミウム電極の集電機能の向上に伴い高率放電性能が向上したことが大きく寄与していると考えられる。
【００４９】
図７は、ニッケル水素電池およびニッケルカドミウム電池の実施例電池および比較例電池を過充電したときの内圧上昇の程度を調べた結果を示すグラフである。中では、実施例電池３および実施例電池４の内圧上昇が抑制されている。これは、該電池の負極の表面に設けた凹部に充填したラネーコバルト粉末が、負極表面での酸素の還元反応を促進しているためと考えられる。
【００５０】
図８は、ニッケル水素電池およびニッケルカドミウム電池の実施例電池および比較例電池の充放電サイクル寿命を示すグラフである。ここでは、放電容量が初期の放電容量の８０％にまで低下した時点をもってサイクル寿命とした。ニッケル水素蓄電池同士、ニッケルカドミウム蓄電池同士を比較すると、実施例電池が比較例電池に比べて優れた性能を有してしている。実施例電池の場合、負極の表面に設けた凹部が、電解液の収納スペースを提供しており、比較例電池に比べ電極近傍に余分の電解液を保持できる効果によるものと考えられる。また、ニッケル水素電池においてはとりわけ実施例３が、またニッケルカドミウム電池においては実施例４が優れた性能を示している。これは、負極表面の酸素の還元反応が速やかに進み、酸素による水素吸蔵合金やカドミウムの腐食が抑制された効果によるものと考えられる。
【００５１】
なお、前記実施例では基板の開口および電極表面に設ける凹部の表面形状を円形としたが、本発明においては開口及び凹部の現状は円形に限定されるものではなく、楕円形や多角形も適用できる。また、凹部の大きさや深さも前記実施例に示した値に限定されるものではなく、適当な値を設定することが可能である。また、前記凹部に導電剤粉末と酸素還元触媒粉末を混合して充填することもできる。さらに、表面にコバルト等の遷移金属の酸化物や水酸化物の層を形成した基板を適用することも可能である。
【発明の効果】
【００５２】
本発明の請求項１に係るアルカリ蓄電池用負極は、活物質充填密度にムラがなく、高率放電特性、充放電サイクル特性に優れたアルカリ蓄電池用負極である。
【００５３】
本発明の請求項２に係るアルカリ蓄電池用負極は、請求項１に係る効果をさらにお高めたものである。
【００５４】
本発明の請求項３に係るアルカリ蓄電池用負極は、請求項１の発明に係る特性を有し、且つ集電機能を高めることによりさらに高率放電特性を向上させたアルカリ蓄電池用負極である。
【００５５】
本発明の請求項４に係るアルカリ蓄電池用負極は、請求項１の発明に係る特性を有し、且つさらに酸素還元反応機能に優れたアルカリ蓄電池用負極である。
【００５６】
本発明の請求項５に係るアルカリ蓄電池は、充電時の電池内圧上昇抑制機能に優れ、且つ高率放電特性、充放電サイクル特性に優れたアルカリ蓄電池である。
【００５７】
【図面の簡単な説明】
【図１】本発明に係るアルカリ蓄電池用負極の断面を模式的に示した図である。
【図２】本発明に係るアルカリ蓄電池用負極の断面を模式的に示した図である。
【図３】本発明に係るアルカリ蓄電池用負極の断面を模式的に示した図である。
【図４】従来のアルカリ蓄電池用負極の断面を模式的に示した図である。
【図５】実施例および比較例に係るニッケル水素蓄電池の各率放電試験の結果を示すグラフである。
【図６】実施例および比較例に係るのニッケルカドミウム蓄電池の各率放電試験の結果を示すグラフである。
【図７】実施例電池および比較例電池の過充電時の電池の内圧を示すグラフである。
【図８】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。
【符号の説明】
１　基板
２　活物質層
３　凹部
４　開口
５　導電性粉末[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a negative electrode for an alkaline storage battery such as a hydrogen storage alloy electrode or a cadmium electrode, and an alkaline storage battery using the negative electrode.
[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, a paste containing hydrogen storage alloy or cadmium oxide or cadmium hydroxide as an active material as a main component, iron, nickel, copper, or the like, is supported on a porous substrate of an alkali-resistant, highly conductive metal such as alkali. It is a thing.
[0004]
Examples of the porous substrate serving as the substrate of the negative electrode plate include a perforated plate in which holes are mechanically formed in the plate, a fibrous substrate in which metal fibers are formed in a felt shape, and a foamed metal in which metal is formed in a sponge shape. . Of these, a perforated plate is heavily used for a negative electrode substrate of an alkaline storage battery because of its low price and easy availability. FIG. 4 is a diagram schematically showing a cross section of a conventional negative electrode for an alkaline storage battery. As shown in FIG. 4, a perforated plate 1 serving as a substrate has an active material layer 2 mainly composed of a hydrogen storage alloy, cadmium oxide, or the like supported on both surfaces.
[0005]
In a conventional hydrogen storage electrode or cadmium electrode using a perforated plate as a substrate, the active material packing density was uneven. That is, the active material filling density of the opening of the perforated plate was lower than that of the non-opening. The active material paste is coated on the substrate, and after pressing, the active material filling density is increased by performing a press working through a roll.However, the unevenness in the active material filling density occurs in the press working step. This is because the pressure applied to the active material layer filled in the opening of the substrate is lower than the pressure applied to the non-opening portion. In the case of a hydrogen storage alloy electrode or a cadmium electrode, if the packing density of the active material powder is low, the conductivity of the electrode is low due to insufficient contact between the active material powders, and the current collecting function is insufficient. There is a high possibility that the utilization rate will decrease.
[0006]
Further, sealed nickel-metal hydride storage batteries and nickel cadmium storage batteries are established by employing a so-called oxygen cycle mechanism in which oxygen generated at a positive electrode during charging is reduced by a negative electrode and returned to water molecules. If the oxygen absorption capacity of the negative electrode is low, oxygen gas accumulates in the space inside the battery at the end of charging, the internal pressure of the battery increases, and the water that constitutes the electrolyte disappears, and the negative electrode active material corrodes and charges and discharges. There was a possibility that the cycle performance would be adversely affected. When charged at a high speed (high rate), there is a high possibility that the oxygen absorption rate at the negative electrode cannot keep up with the oxygen generation rate. In recent years, as the demand for high-speed charging has increased, further improvement in the oxygen absorption capacity of the negative electrode has been required. Further, further improvement in charge / discharge cycle performance has been demanded.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the disadvantages of the prior art, and is an alkaline storage battery including a negative electrode for an alkaline storage battery using a perforated plate as a substrate, an alkaline storage battery excellent in high-rate discharge characteristics, It is another object of the present invention to provide an alkaline storage battery having excellent charge / discharge cycle characteristics and a function of suppressing an increase in internal pressure during charging.
[0008]
[Means for Solving the Problems]
The negative electrode for an alkaline storage battery according to the present invention is a negative electrode for an alkaline storage battery in which an active material powder such as a hydrogen storage alloy powder or cadmium oxide is supported on a perforated plate formed of a metal having resistance to an alkaline electrolyte. A recess is formed at a position overlapping the opening of the perforated plate.
[0009]
In the negative electrode for an alkaline storage battery according to the present invention, preferably, the concave portion has a planar shape substantially similar to the planar shape of the opening, and has the same or smaller size as the opening.
[0010]
In the negative electrode for an alkaline storage battery according to the present invention, preferably, the concave portion is filled with an alkali-resistant conductive powder and / or a powder having alkali resistance and having a catalytic function for an oxygen reduction reaction.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The negative electrode for an alkaline storage battery according to the present invention has a layer of an active material mainly composed of a hydrogen storage alloy powder or a cadmium oxide or cadmium hydroxide powder having an average particle diameter of 10 to 80 μm, a thickness of 30 to 100 μm, and a diameter of 0.1 μm. It has an opening of 5 to 2 mm and is supported on a substrate made of a perforated plate made of an alkali-resistant metal having an opening ratio of 30 to 60%.
[0012]
The material of the perforated plate is a steel plate having a surface plated with nickel or nickel. The negative electrode for an alkaline storage battery according to the present invention has a structure in which active material layers mainly containing the hydrogen storage alloy powder or cadmium oxide or cadmium hydroxide powder are arranged on both surfaces of a substrate, and the total thickness of the electrodes is 0.2 to 1 mm.
[0013]
FIGS. 1A and 1B schematically show a cross section of the negative electrode for an alkaline storage battery according to the present invention. The negative electrode for an alkaline storage battery according to the present invention has concave portions 3 on one side of the active material layer 2 as shown in FIG. 1 or on both the front and back surfaces of the electrode as shown in FIG. The concave portion 3 is formed by pressing the electrode surface by a press device having a pressing surface provided with a convex portion, and is located at a position overlapping the opening 4 of the substrate 1. By providing the concave portion, the packing density of the active material filled in the opening of the substrate can be increased.
[0014]
The planar shape, size, and depth of the concave portion 3 are not particularly limited. However, in order to make the packing density of the active material filled in the opening portion and the non-opening portion of the substrate substantially equal, the concave portion is used. The planar shape of the opening 3 is substantially similar to the planar shape of the opening 4, and its size is equal to or smaller than the size of the opening. The plane shapes of the concave portion and the opening here are shapes when the planes of the electrode and the substrate are viewed, and a circular shape is often adopted.
[0015]
As described above, in the case of the conventional negative electrode for an alkaline storage battery, the filling density of the active material powder in the opening of the substrate is lower than the filling density of the active material powder in the non-opening portion. In the present invention, the packing density of the water-active material powder in the opening is increased by providing a concave portion at a position on the surface of the electrode that overlaps the opening of the substrate. It is desirable that the concave portion and the non-opening portion of the substrate do not overlap when viewed from a plane. Since a large pressure is applied to the active material powder in a portion where the both overlap, the space between the powders becomes extremely small, and there is a possibility that the electrode reaction is hindered. For this reason, it is desirable that the size of the recess is equal to or smaller than the size of the opening.
[0016]
Further, if the distance between the inner wall of the opening and the peripheral edge of the concave portion is large, the packing density of the active material powder in the portion sandwiched between them may be low. In order to avoid this, it is desirable to make the planar shapes of the concave portion and the opening substantially similar and to make the size of the concave portion and the opening as close as possible. From the above, if the opening is circular and the radius is R, the concave portion is also circular, and the ratio r / R of the radius r to the R is preferably 0.6 to 1.0, and 0.7 to 1.0. More preferably, it is 0.9.
[0017]
In the present invention, the concave portion 3 is provided at a position overlapping the opening 4 of the substrate 1 of the electrode, thereby increasing the packing density of the active material powder filled in the opening and approaching the packing density of the active material powder filled in the non-opening. . Although the depth of the concave portion is not particularly limited, it is desirable that the volume of the concave portion is substantially equal to the volume of the opening 4 of the substrate in order to achieve the above object. In the case where recesses are provided on both the front and back surfaces of the electrode shown in FIG. 2, the two recesses provided on the front and back surfaces of the electrode are located at positions overlapping each other across the opening of the substrate. Further, it is desirable that the sum of the volumes of the two concave portions is substantially equal to the volume of the opening of the substrate.
[0018]
Specifically, when the volume of the opening is V and the volume of the concave portion is v, the ratio v / V between the two is preferably 0.5 to 1.2, and more preferably 0.9 to 1.1. More desirable.
Further, the cross-sectional shape of the concave portion 3 is not particularly limited. However, in order to apply pressure to the active material in the opening at the time of pressing, the side wall of the concave portion 3 is substantially the same as the side wall of the opening of the substrate. It is desirable to face the direction. That is, as shown in FIG. 1A, it is desirable that the side wall of the recess 3 is perpendicular to the surface of the electrode, or that a small taper is provided in the side wall of the recess 3 as shown in FIG. .
[0019]
By making the negative electrode for an alkaline storage battery as described above, the packing density of the active material powder filled in the opening portion of the substrate is increased to approximately the same as the packing density of the active material powder filled in the non-opening portion. Can be.
[0020]
In order to solve the above-mentioned problem, it is desirable to provide the concave portion at all or most of the positions overlapping the opening of the substrate. The recesses are formed by coating the surface of the substrate with the active material layer and drying, and then pressing the electrodes as described above.
[0021]
Pressing is usually performed by passing a strip-shaped and long electrode between two rolls. The surface of the roll for press working applied to the present invention is provided with convex portions having a shape substantially similar to the shape of the opening of the substrate at the same interval as the substrate. When the concave portion is provided only on one side of the electrode, a convex portion having substantially the same volume as the opening is provided on the surface of one of the two rolls. When the concave portion 3 is formed on both surfaces of the electrode, a convex portion having a volume approximately half the opening is provided on the surfaces of the two rolls.
[0022]
As described above, the application of the pressing pressure to the active material layer of the electrode that fills the opening of the substrate is smaller than that of the active material layer that fills the non-opening of the substrate. Therefore, there is a disadvantage that the packing density of the hydrogen storage alloy powder is lower in the opening than in the non-opening, and the current collecting function is inferior. By providing a convex portion on the surface of the roll and forming a concave portion having approximately the same volume as the opening at a position overlapping the opening of the substrate on the electrode surface, the same pressure is applied to the opening of the substrate as that of the non-opening. This has the effect of increasing the packing density of the active material powder in the opening to the same degree as that in the non-opening.
[0023]
In the negative electrode for an alkaline storage battery according to the present invention, it is preferable that the concave portion 3 is filled with an alkali-resistant conductive powder 4 as shown in FIG. Further, it is desirable to fill a powder which is alkali-resistant and has a catalytic function for a reduction reaction of oxygen.
[0024]
As the alkali-resistant conductive powder, a carbon powder such as graphite or Ketjen black or a nickel powder can be used. Further, as the powder having a catalytic function of the oxygen reduction reaction, carbon black such as acetylene black, carbon powder such as activated carbon, silver powder, Raney cobalt powder and the like can be used. Furthermore, it is possible to coat a part of the surface of these powders with a water-repellent resin such as a fluororesin such as polytetrafluoroethylene or a polyolefin-based resin such as polyethylene or polypropylene to impart water repellency to the surface of the powder. It is effective in promoting the absorption of water.
[0025]
In the negative electrode according to the present invention, a substrate is coated with an active material paste mainly composed of an active material powder such as a hydrogen storage alloy powder or a cadmium oxide or cadmium hydroxide powder. The electrode plate filled with the active material paste is dried and pressed through a roll after drying to increase the active material filling density. In addition, the concave portion provided on the surface of the negative electrode for an alkaline storage battery provides a space for accommodating an electrolytic solution, and is effective in improving charge / discharge cycle performance.
[0026]
(Example 1)
(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.
[0027]
As the substrate of the hydrogen storage alloy electrode, a perforated plate made of a steel plate having a thickness of 70 μm, an opening diameter of 1.5 mm, and an opening ratio of 40% plated with nickel was applied. The paste was applied to both sides of the substrate. The coated electrode plate was dried to obtain an electrode plate having a thickness of 1.1 mm. The electrode plate is passed through a pair of rolls having a plurality of cylindrical protrusions having a diameter of 1.0 mm and a height of 0.08 mm on the surface so that the finished thickness of the electrode plate becomes 0.4 mm. Press processing was performed. The interval between the projections provided on the surface of the roll was made equal to the interval between the openings in the substrate, and the electrode was passed through the roll so that the projection of the roll overlapped the opening of the substrate. In this manner, a concave portion on a cylinder having a diameter of 1.0 mm and a depth of 0.08 mm was formed at a position overlapping the opening of the substrate on the front and back surfaces of the electrode plate. The original plate was cut into a predetermined size to obtain a hydrogen storage alloy electrode.
[0028]
(Survey of apparent density of active material layer of hydrogen storage alloy electrode)
An opening and a non-opening of the substrate of the hydrogen storage alloy electrode were punched out in a thickness direction at a diameter of 1.5 mm to obtain a sample, and its weight was measured. For the non-opening portion, the value obtained by dividing the measured weight by the volume was defined as the apparent density. For the non-opening, the weight and volume of the substrate were subtracted from the weight and volume of the sample, and the resulting weight was divided by the volume to obtain the apparent density.
[0029]
(Preparation of nickel electrode active material powder)
According to a predetermined method, an average having a high density nickel hydroxide containing 3% by weight and 5% by weight of a solid solution in terms of hydroxide in the form of hydroxide as a nucleus and forming a coating layer of cobalt hydroxide 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.
[0030]
(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 foamed nickel porous 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 0.75 mm. An original plate was obtained. The original plate was cut into a predetermined size to obtain a nickel electrode. The capacity of the nickel electrode calculated from the active material filling amount was 1600 mAh.
[0031]
(Production of nickel-metal hydride battery)
The nickel electrode and the hydrogen storage alloy electrode were laminated via a non-woven fabric made of polypropylene having a thickness of 0.12 mm and subjected to a hydrophilic treatment, and this was wound to form an electrode plate group. The capacity ratio of the negative electrode (hydrogen storage alloy electrode) and the positive electrode (nickel electrode) of the electrode plate group was set to 1.6 to 1. Attach the current collecting terminals for the positive electrode and the negative electrode to the electrode plate group, insert them into a metal battery case, inject a predetermined amount of an electrolytic solution containing an aqueous solution of potassium hydroxide as a main component, and then seal the container. And
[0032]
(Chemical)
After aging the obtained nickel-metal hydride storage battery at a temperature of 40 ° C. for 12 hours, formation was performed under the following conditions. The first charging was performed at a charging current of 1/50 ItA (32 mA) for 10 hours, and thereafter, charging was performed at a charging current of 1/10 ItA (160 mA) for 10 hours. Next, the battery was discharged at a discharge current of 1/5 ItA (320 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 (160 mA) for 12 hours, and discharged at a discharge current of 1/5 ItA (320 mA) with a discharge end 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.
[0033]
(Example 2)
In Example 1, the graphite powder was filled in the concave portion provided on the surface of the hydrogen storage alloy electrode. Specifically, a graphite paste was prepared by mixing and kneading 40 parts by weight of a 5% concentration aqueous solution of CMC with 60 parts by weight of graphite powder having an average particle size of 5 μm, and applied to the surface of the hydrogen storage alloy electrode. After that, the graphite paste attached to the surface of the electrode except for the concave portions was scraped off and dried. Other than that, it was the same as Example 1.
[0034]
(Example 3)
In Example 1, the concave portion provided on the surface of the hydrogen storage alloy electrode was filled with Raney cobalt powder. Specifically, an alloy powder of 50% by weight of cobalt and 50% by weight of aluminum was immersed in a concentrated solution of caustic alkali to prepare a Raney cobalt powder having an average particle diameter of 5 μm, which was eluted with aluminum. 80 parts by weight of the Raney cobalt was kneaded with 20 parts by weight of a 2% toluene solution of polypropylene having an average molecular weight of 20,000, and then dried to remove toluene. A paste of Raney cobalt powder was prepared by mixing and kneading 20 parts by weight of a 2% aqueous solution of CMC with 80 parts by weight of the powder, and the paste was coated on the surface of the hydrogen storage alloy electrode. The Raney cobalt powder paste adhered to the surface of the powder was scraped off and dried. Other than that, it was the same as Example 1.
[0035]
(Comparative Example 1)
In Example 1, in the step of pressing the dried hydrogen storage alloy electrode after drying, two rolls having a smooth surface were passed. Other than that, it was the same as Example 1.
[0036]
(Example 4)
(Production of cadmium electrode)
A paste was prepared by adding 16 parts by weight of ethylene glycol to 100 parts by weight of a mixed powder obtained by mixing 80 parts by weight of cadmium oxide powder having an average particle diameter of about 10 μm and 20 parts by weight of metal cadmium powder, and kneading the mixture. The paste was applied to both surfaces of a perforated plate made of steel plate having a thickness of 70 μm, an opening diameter of 1.5 mm, and an opening ratio of 40%, which had been subjected to the nickel plating. The coated electrode plate was dried to obtain a 1.4 mm-thick electrode plate. The electrode plate was subjected to press working by being passed between two rolls provided with convex portions on the surface, and the thickness of the electrode plate was adjusted to 0.70 mm. The concave portions provided on the surface of the electrode plate were filled with Raney cobalt powder in the same manner as in Example 3. The cadmium electrode master plate thus obtained was cut into a predetermined size to obtain a cadmium electrode.
[0037]
As in the case of the hydrogen storage alloy electrode described in Example 1, the density of the active material layer in the opening and the non-opening of the cadmium electrode substrate was measured. Further, a cylindrical sealed nickel cadmium battery was manufactured by combining the nickel electrode and the cadmium electrode.
[0038]
(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 foamed nickel porous 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 0.75 mm. An original plate was obtained. The original plate was cut into a predetermined size to obtain a nickel electrode. The capacity of the nickel electrode calculated from the active material filling amount was 1000 mAh.
[0039]
(Production of nickel cadmium battery)
The nickel electrode and the cadmium electrode were laminated via a polypropylene nonwoven fabric having a thickness of 0.15 mm and subjected to hydrophilic treatment, and this was wound to form an electrode plate group. The capacity ratio of the negative electrode (hydrogen storage alloy electrode) to the positive electrode (nickel electrode) of the electrode plate group was set to 1.8: 1. Attach the current collecting terminals for the positive electrode and the negative electrode to the electrode plate group, insert them into a metal battery case, inject a predetermined amount of an electrolytic solution containing an aqueous solution of potassium hydroxide as a main component, and then seal the container. And
[0040]
(Chemical)
After aging the obtained nickel-metal hydride storage battery at a temperature of 40 ° C. for 12 hours, formation was performed under the following conditions. The first charging was performed at a charging current of 1/50 ItA (20 mA) for 10 hours, and thereafter, charging was performed at a charging current of 1/10 ItA (100 mA) for 10 hours. Next, the battery was discharged with a discharge current of 1/5 ItA (200 mA) and a discharge end voltage of 1.0 V. After the second cycle, the battery was charged at a charge current of 1/10 ItA (100 mA) for 12 hours and discharged at a discharge current of 1/5 ItA (200 mA) with a discharge end 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.
[0041]
(Comparative Example 2)
In Example 4, the dried hydrogen storage alloy electrode was passed between two rolls having a smooth surface in the step of pressing. Further, application of Raney cobalt powder to the surface of the cadmium electrode was not performed. The other conditions were the same as in Example 4.
[0042]
(Each rate discharge test)
After charging the example battery and the comparative example battery at the temperature of 20 ° C. under the above-mentioned conditions, each rate discharge test in which the discharge rate range is 0.2 ItA to 5 ItA and the discharge end voltage is 1.0 V Was served.
[0043]
(Evaluation of internal pressure rise during overcharge)
After the formation of the example battery and the comparative example battery after the formation, the battery was discharged at 1/5 ItA and a final voltage of 1.0 V, and a pressure gauge for measuring the internal pressure of the battery was attached. Then, the battery was charged at 1 ItA for 2 hours. Then, a change with time of the internal pressure of the battery during charging was measured.
[0044]
(Charge / discharge cycle test)
The battery of Example and the battery of Comparative Example after the formation were 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.
[0045]
Table 1 shows the apparent densities of the active material layers of the hydrogen storage alloy electrodes described in Example 1 and Comparative Example 1, and the apparent densities of the active material layers of the cadmium electrodes described in Example 4 and Comparative Example 2.
[Table 1]

[0046]
As shown in Table 1, in the case of the example battery according to the present invention, the apparent density of the active material layer of the hydrogen storage alloy electrode and the cadmium electrode did not differ between the opening and the non-opening of the substrate. Thus, in the case of the comparative example, the apparent density of the active material layer in the opening of the substrate is low for both the hydrogen storage alloy electrode and the cadmium electrode.
[0047]
FIG. 5 is a graph showing each rate discharge test result of the nickel hydride batteries according to the example and the comparative example. In the high-rate discharge test of 1 ItA or more, each of the example batteries according to the present invention shows higher discharge performance than the comparative example battery. This is considered to be largely attributable to the improvement in the high-rate discharge performance accompanying the improvement in the current collecting function of the hydrogen storage alloy electrode of the battery of the example. In particular, the performance of Example 2 is excellent, and it is considered that the graphite powder filled in the concave portion provided on the surface of the hydrogen storage alloy electrode contributes to the performance improvement.
[0048]
FIG. 6 is a graph showing each rate discharge test result of the nickel cadmium batteries according to the example and the comparative example. As in the case of the nickel-metal hydride battery, in the high-rate discharge test of 1 ItA or more, the example battery according to the present invention shows higher discharge performance than the comparative example battery. This is considered to be largely attributable to the improvement in the high-rate discharge performance accompanying the improvement in the current collection function of the cadmium electrode of the battery of the example.
[0049]
FIG. 7 is a graph showing the results of examining the degree of increase in internal pressure when the nickel-metal hydride battery and the nickel cadmium battery were overcharged in the example battery and the comparative example battery. Inside, the increase in the internal pressure of Example Battery 3 and Example Battery 4 is suppressed. It is considered that this is because the Raney cobalt powder filled in the concave portion provided on the surface of the negative electrode of the battery promotes the reduction reaction of oxygen on the negative electrode surface.
[0050]
FIG. 8 is a graph showing the charge / discharge cycle life of the nickel-metal hydride battery and the nickel cadmium battery of the example battery and the comparative example battery. Here, the point at which the discharge capacity decreased to 80% of the initial discharge capacity was defined as the cycle life. Comparing the nickel-metal hydride storage batteries and the nickel-cadmium storage batteries, the example battery has better performance than the comparative example battery. In the case of the example battery, the concave portion provided on the surface of the negative electrode provides a storage space for the electrolytic solution, which is considered to be due to the effect that extra electrolytic solution can be retained near the electrode as compared with the comparative example battery. In particular, Example 3 shows excellent performance in nickel hydride batteries, and Example 4 shows excellent performance in nickel cadmium batteries. This is considered to be due to the effect that the reduction reaction of oxygen on the negative electrode surface progressed quickly and the corrosion of the hydrogen storage alloy and cadmium by oxygen was suppressed.
[0051]
In the above embodiment, the surface shape of the opening of the substrate and the concave portion provided on the electrode surface is circular. However, in the present invention, the present state of the opening and the concave portion is not limited to a circle, and an elliptical shape or a polygonal shape may be applied. it can. Further, the size and depth of the concave portion are not limited to the values shown in the above embodiment, but can be set to appropriate values. Further, the recess may be filled with a mixture of the conductive agent powder and the oxygen reduction catalyst powder. Further, a substrate having a layer of a transition metal oxide or hydroxide such as cobalt formed on the surface can be used.
【The invention's effect】
[0052]
The negative electrode for an alkaline storage battery according to claim 1 of the present invention is a negative electrode for an alkaline storage battery that has no unevenness in the active material filling density and has excellent high-rate discharge characteristics and charge-discharge cycle characteristics.
[0053]
The negative electrode for an alkaline storage battery according to a second aspect of the present invention further enhances the effect according to the first aspect.
[0054]
A negative electrode for an alkaline storage battery according to a third aspect of the present invention is the negative electrode for an alkaline storage battery having the characteristics according to the first aspect of the present invention and further improving the high-rate discharge characteristics by enhancing the current collecting function.
[0055]
The negative electrode for an alkaline storage battery according to a fourth aspect of the present invention is a negative electrode for an alkaline storage battery having the characteristics according to the first aspect of the present invention and further having an excellent oxygen reduction reaction function.
[0056]
The alkaline storage battery according to claim 5 of the present invention is an alkaline storage battery that has an excellent function of suppressing an increase in battery internal pressure during charging, and has excellent high-rate discharge characteristics and charge / discharge cycle characteristics.
[0057]
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a cross section of a negative electrode for an alkaline storage battery according to the present invention.
FIG. 2 is a diagram schematically showing a cross section of a negative electrode for an alkaline storage battery according to the present invention.
FIG. 3 is a diagram schematically showing a cross section of a negative electrode for an alkaline storage battery according to the present invention.
FIG. 4 is a diagram schematically showing a cross section of a conventional negative electrode for an alkaline storage battery.
FIG. 5 is a graph showing the results of each rate discharge test of the nickel-metal hydride storage batteries according to Examples and Comparative Examples.
FIG. 6 is a graph showing the results of each rate discharge test of nickel cadmium storage batteries according to Examples and Comparative Examples.
FIG. 7 is a graph showing the internal pressures of the batteries of the example battery and the battery of the comparative example during overcharge.
FIG. 8 is a graph showing the charge / discharge cycle performance of an example battery and a comparative example battery.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 Active material layer 3 Concave part 4 Opening 5 Conductive powder

Claims

A negative electrode for an alkaline storage battery in which an active material powder is supported on a perforated plate made of an alkali-resistant electrolytic metal, wherein a concave portion is formed on the electrode surface at a position overlapping the opening of the perforated plate. For negative electrode.

The negative electrode for an alkaline storage battery according to claim 1, wherein a planar shape is substantially similar to a planar shape of the opening of the perforated plate, and a concave portion having a size equal to or smaller than the opening is formed.

The negative electrode for an alkaline storage battery according to claim 1, wherein the concave portion is filled with an alkali-resistant conductive powder.

4. The negative electrode for an alkaline storage battery according to claim 1, wherein the concave portion is filled with a powder having alkali resistance and having a catalytic function for a reduction reaction of oxygen.

An alkaline storage battery comprising the negative electrode for an alkaline storage battery according to claim 1.