JP3540558B2

JP3540558B2 - Method for producing nickel hydroxide electrode for alkaline storage battery and nickel hydroxide electrode obtained by this method

Info

Publication number: JP3540558B2
Application number: JP23446197A
Authority: JP
Inventors: 茂和安岡; 和昭尾崎; 卓也玉川
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 1997-08-29
Filing date: 1997-08-29
Publication date: 2004-07-07
Anticipated expiration: 2017-08-29
Also published as: JPH1173954A

Description

【０００１】
【産業上の利用分野】
本発明は、正極活物質として水酸化ニッケルを用いたニッケル・水素蓄電池、ニッケル・カドミウム蓄電池、ニッケル・亜鉛蓄電池などのアルカリ蓄電池のニッケル電極の製造方法に係り、特に非焼結式水酸化ニッケル電極の製造方法の改良に関するものである。
【０００２】
【従来の技術】
従来、アルカリ蓄電池用水酸化ニッケル電極としては、ニッケル粉末をパンチングメタル等に塗着したものを焼結させて得た多孔性基板に活物質を含浸させて使用する、所謂焼結式水酸化ニッケル電極が知られている。
【０００３】
この方式の電極は、基板を高多孔度とした場合には強度が弱く、実用上基板の多孔度を８０％とするのが限界であり、また、パンチングメタル等の芯体を必要とすることから活物質の充填密度が小さく、高エネルギー密度を図る上では不利であるという欠点を有している。更に焼結基板の細孔は１０μｍ以下と小さく、活物質の充填方法は繁雑な工程を必要とする溶液含浸法や電着含浸法に限定されるという問題がある。
【０００４】
これらの欠点を改良する試みとして、例えば芯体を持たない多孔度約９５％の発泡ニッケルに水酸化ニッケル活物質粉末を直接充填する、所謂非焼結式水酸化ニッケル電極がある。
【０００５】
非焼結式水酸化ニッケル電極は、充填性が高く焼結式に比べ容量が高いが、γ−ＮｉＯＯＨが生成しやすく、極板が膨化しやすいという問題がある。また、焼結式に比べて孔径が大きく、活物質を保持するために絶縁性の結着剤を添加する必要があるため導電性が低く活物質利用率が低いという問題がある。
【０００６】
前記のような問題を解決する手段として以下の方法が提案されている。
【０００７】
▲１▼ 特開昭５９−１１２５７４号公報
この公報には、水酸化ニッケルにカドミウムや亜鉛等の水酸化物や酸化物を遊離状態で添加する方法が提案されている。
【０００８】
▲２▼ 特開平５−４１２１２号公報
この公報には、水酸化ニッケル中にカドミウムや亜鉛等を固溶状態で添加する方法が提案されている。
【０００９】
▲３▼ 特開平８−２２２２１７号公報
この公報には、水酸化ニッケル粒子表面にコバルト化合物を被覆する際にコバルト被覆層の中にアルミニウム化合物、マグネシウム化合物、インジウム化合物、亜鉛化合物を添加して、酸素とアルカリ共存下で加熱処理する方法が提案されている。
【００１０】
【発明が解決しようとする課題】
しかし、▲１▼の方法のように水酸化ニッケルに導電性の低いカドミウムや亜鉛等の水酸化物や酸化物を遊離状態で添加する場合、極板の導電性が低下して容量や作動電圧が大幅に低下するという問題がある。
【００１１】
また、▲２▼の方法のように水酸化ニッケル粒子内に固溶体としてカドミウムや亜鉛等を存在させる方法では、極板の膨化を抑制するという添加物本来の効果が得られにくいという問題がある。
【００１２】
さらにまた、▲３▼の方法のように水酸化ニッケル粒子表面にコバルト化合物を被覆する際にコバルト被覆層の中に亜鉛化合物等を添加して、酸素とアルカリ共存下で加熱処理する方法では、前記被覆層の導電性が優れているために活物質利用率が向上するが、亜鉛がコバルトと固溶体として存在しているので、極板の膨化を抑制するという添加物本来の効果が得られにくいという問題がある。
【００１３】
本発明は前記問題点に鑑みてなされたものであり、活物質の利用率及び作動電圧が高く、極板の膨化を抑制した非焼結式水酸化ニッケル電極を得ようとすることを本発明の課題とする。
【００１４】
【課題を解決するための手段】
本発明の製造方法は、水酸化ニッケルまたは水酸化ニッケルを主成分とする粉末と、コバルト化合物又は金属コバルトの一種以上の粉末と、イットリウム、カドミウム、亜鉛、マグネシウム、カルシウム及びマンガンからなる群から選択された少なくとも１種以上の化合物と、アルカリ水溶液とを混合する第１ステップと、前記アルカリ水溶液が混合された混合物を酸素存在下で加熱処理する第２ステップとを備えたことを特徴とする。
【００１５】
また、本発明の製造方法で得られた水酸化ニッケル電極は、水酸化ニッケルまたは水酸化ニッケルを主成分とする粉末にイットリウム、カドミウム、亜鉛、マグネシウム、カルシウム及びマンガンからなる群から選択された少なくとも１種以上の化合物を添加した添加物とを備え、前記水酸化ニッケルまたは水酸化ニッケルを主成分とする粉末の表面と前記添加物の表面に高次コバルト化合物層を形成したことを特徴とする。
【００１６】
【発明の実施の形態】
本発明では、水酸化ニッケル粉末とコバルト化合物または金属コバルトと、イットリウム、カドミウム、亜鉛、マグネシウム、カルシウム及びマンガンからなる群から選択された少なくとも１種以上の化合物と、アルカリ水溶液とを混合する第１ステップと、前記アルカリ水溶液が混合された混合物を酸素存在下で加熱処理する第２ステップとを施して、正極活物質を作製する。
【００１７】
前記の第２ステップで上記混合物にアルカリ溶液を加えて加熱処理を行っているため、コバルト化合物の一部がＨＣｏＯ₂ ^-となってアルカリ溶液中に溶解し、次いで水酸化ニッケルや亜鉛化合物の表面に析出してコバルトの酸化が生じる。
【００１８】
このため、水酸化ニッケルだけでなく亜鉛等の添加物の表面にも導電性の高い高次コバルト化合物（価数が２価よりも大きい）が存在する。この結果、導電性の低い亜鉛化合物等の粉末を添加しても活物質利用率及び作動電圧が低下するという問題を解消することができる。しかも亜鉛化合物は遊離状態で存在するので、極板の膨化を抑制する効果を維持できる。
【００１９】
そして、このように作製した正極活物質をメチルセルロース等の水溶性結着剤と共に、ニッケル金属３次元多孔体等の活物質保持体に保持させてニッケル電極を作製する。尚、極板強度を向上させるために、前記のように作製したニッケル電極をフッ素樹脂が分散した溶液に浸漬処理または、この溶液をニッケル電極の表面に塗布等を行ってもよい。
【００２０】
【実施例】
（水酸化ニッケルの作製）
水酸化ナトリウム水溶液とアンモニア水とを混合した溶液に、硝酸ニッケル水溶液を加え、撹拌混合を行い、ろ過、水洗、乾燥を行い、水酸化ニッケル粉末▲１▼を作製した。この時、混合溶液全体のｐＨを１１になるように硝酸ニッケル水溶液、水酸化ナトリウム水溶液及びアンモニア水の添加量を調整した。
【００２１】
上記硝酸ニッケル水溶液中に硝酸亜鉛を混合し、水酸化ニッケルに亜鉛を固溶体として存在させた水酸化ニッケル粉末▲２▼を作製した。
【００２２】
尚、亜鉛の添加量は水酸化ニッケルに対して、酸化亜鉛に換算して５重量％とした。
【００２３】
（水酸化ニッケル電極の作製）
［実施例１］
上記のように作製した水酸化ニッケル粉末▲１▼１００重量部と水酸化コバルト粉末８重量部と、酸化亜鉛粉末５重量部とを２５重量％の水酸化ナトリウム水溶液中に混合して、空気中で１００℃で１時間加熱処理を行い（以下、この処理方法をアルカリ熱処理と云う）、水酸化ニッケル電極用活物質を作製し、活物質ａと称する。この活物質ａ１００重量部に１重量％のメチルセルロース水溶液２０重量部とを混練して活物質スラリーを作製した。この活物質スラリーを発泡ニッケルに充填して水酸化ニッケル電極を作製し、本発明水酸化ニッケル電極Ａと称する。
【００２４】
［比較例１］
上記のように作製した亜鉛を固溶状態で添加した水酸化ニッケル粉末▲２▼１００重量部に水酸化コバルト粉末８重量部を混合させた活物質を作製した以外は、前記実施例１と同様にして水酸化ニッケル電極を作製し、比較水酸化ニッケル電極Ｂと称する。
【００２５】
尚、亜鉛の添加量の割合は、前記実施例１と同じ割合になるように調整した。
【００２６】
［比較例２］
上記のように作製した水酸化ニッケル粉末▲１▼１００重量部に水酸化コバルト８重量部と酸化亜鉛５重量部とを混合して活物質を作製した以外は、前記実施例１と同様にして水酸化ニッケル電極を作製し、比較水酸化ニッケル電極Ｃと称する。
【００２７】
［比較例３］
上記のように作製した水酸化ニッケル粉末▲１▼１００重量部に水酸化コバルト８重量部を混合して活物質を作製した以外は、前記実施例１と同様にして水酸化ニッケル電極を作製し、比較水酸化ニッケル電極Ｄと称する。
【００２８】
［比較例４］
上記のように作製した水酸化ニッケル粉末▲１▼に４倍の水を加え混合拡散し、この分散液にｐＨが１０になるように２５重量％の水酸化ナトリウム水溶液を加えながら硫酸コバルト及び硫酸亜鉛溶液を混合した溶液に滴下し、水酸化ニッケルの表面に亜鉛とコバルトを混晶させた層を設けて活物質を作製した以外は、前記実施例１と同様にして水酸化ニッケル電極を作製し、比較電極Ｅと称する。
【００２９】
尚、コバルト及び亜鉛の添加量は、前記実施例１と同じ割合になるように調整した。
【００３０】
［比較例５］
上記のように作製した水酸化ニッケル粉末▲１▼に４倍の水を加え混合拡散し、この分散液にｐＨが１０になるように２５重量％の水酸化ナトリウム水溶液を加えながら硫酸コバルト溶液に滴下し、水酸化ニッケルの表面にコバルト化合物層を設けた後、２５重量％の水酸化ナトリウム水溶液中に混合して、空気中で１００℃で１時間加熱処理を行った後、酸化亜鉛を添加して活物質を作製した以外は、前記実施例１と同様にして水酸化ニッケル電極を作製し、比較電極Ｆと称する。
【００３１】
尚、コバルトと亜鉛の添加量は、前記実施例１と同じ割合になるように調整した。
【００３２】
［実験１］
前記のように作製した水酸化ニッケル電極Ａ〜Ｆを試験電極とし、この試験電極に対して充分大きな電気化学容量を持つ公知の焼結式カドミウム電極を対極としてナイロンセパレータを介して完全対向する形で重ね合わせた。これらの電極群をポリエチレン袋に入れて両側より圧力をかけた後、比重１．２３の水酸化カリウム水溶液を入れ試験セルを作製した。このセルを電極の理論容量に対し０．１Ｃの電流で１５時間充電し、その後１／３Ｃの電流でセル電圧が１．０Ｖとなるまで放電するという充放電サイクルを繰り返し、２サイクル目の容量及び作動電圧（放電時の中間電圧）を測定し、活物質の利用率を算出した。セルを解体して同時に極板の厚みを測定し極板膨化率を測定した。
【００３３】
測定結果を下記表１に示す。なお、利用率は比較水酸化ニッケル電極Ｄを１００としたときの指標で示す。
【００３４】
【表１】

【００３５】
前記表１の結果より、亜鉛を添加していない比較電極Ｄの極板膨化率は最も大きく、亜鉛が極板膨化の抑制効果に寄与していることがわかる。
【００３６】
また、亜鉛が水酸化ニッケル中で固溶状態で存在する比較電極Ｂや亜鉛がコバルト被覆層中に存在するＥは、酸化亜鉛が単独で存在する比較電極Ｃに比べて作動電圧の低下や活物質利用率の低下は小さいが、極板の膨化抑制効果が小さいことがわかる。
【００３７】
また、水酸化ニッケル表面にコバルトの被覆層を形成してアルカリ熱処理したものに亜鉛が単独で存在する比較電極Ｆは比較電極Ｃよりも容量及び作動電圧の低下が小さいが充分ではない。
【００３８】
一方、本発明の極板Ａは利用率、作動電圧及び極板膨化の抑制効果のいずれの特性についても優れていることがわかる。
【００３９】
これは、水酸化ニッケル表面だけでなく、単独で存在する亜鉛の表面にも導電性の高い高次コバルト化合物が存在するためであると考えられる。
【００４０】
［実験２］
この実験では、本発明活物質ａの作製時のアルカリ熱処理温度の検討を行った。水酸化ニッケル粉末▲１▼１００重量部と水酸化コバルト粉末８重量部、酸化亜鉛粉末５重量部とを弱アルカリ水溶液中に混合し、この粉末にアルカリ溶液及び酸素存在下（空気中で）で２０℃から３００℃の温度範囲で１時間加熱処理を行った。このように作製した活物質に１重量％のメチルセルロース水溶液２０重量部とを混練して活物質スラリーを作製した。この活物質スラリーを発泡ニッケルに充填して電極を作製した。
【００４１】
このように作製した電極を前記実験１と同様な充放電条件で利用率を測定し、この結果を図１に示す。尚、利用率は２０℃を１００とした指数で示す。
【００４２】
この図１より、熱処理温度が５０℃以上２００℃以下にするのが最適なことがわかる。これは、温度が低いとコバルトの酸化が充分に進まないため、酸化亜鉛の表面付近の導電性が充分ではなくなり、また、温度が高すぎるとコバルトの酸化がさらに進み、かえって導電性が低下するためであると考えられる。
【００４３】
［実験３］
この実験３では、酸化亜鉛に代えて酸化イットリウム、水酸化カドミウム、水酸化マグネシウム、酸化マンガン、水酸化カルシウムについても、水酸化コバルトと混合し、前記実施例１と同様にアルカリ熱処理して極板を各々作製した。また、比較として、酸化イットリウム、水酸化カドミウム、水酸化マグネシウム、酸化マンガン、水酸化カルシウムを添加した極板（アルカリ熱処理なし）を各々作製した。
【００４４】
これらの極板について、前記実験１と同じ条件で充放電を繰り返し、２サイクル目の容量を読み取り、活物質利用率の測定を行い、その結果を下記表２に示す。尚、利用率は添加物なしで、かつ、アルカリ熱処理を行わないものを１００とした指標で示す。
【００４５】
【表２】

【００４６】
上記表２より明らかなようにアルカリ熱処理することによって活物質利用率が向上していることがわかる。これは、極板の膨化を抑制するために前記のような添加物を添加すると、添加しないものに比べて導電性が低くなり、活物質利用率が低くなるが、本発明のように前記混合物をアルカリ熱処理を施すことにより、導電性の高い高次コバルト化合物が水酸化ニッケル表面だけでなく、上記の添加物の表面に形成されるため導電性が向上し、活物質利用率も向上したものと考えられる。
【００４７】
また、上記表２より、添加物としてイットリウムを使用することが高容量を図るうえで好ましい。
【００４８】
尚、本実施例では、添加物の酸化物や水酸化物を用いたが、他の化合物についても同様の効果が期待できる。
【００４９】
また、本発明では、アルカリ熱処理時に使用するアルカリ水溶液として、水酸化ナトリウム水溶液を用いたが、これに限らず、水酸化カリウム水溶液または水酸化リチウム水溶液でも同様の効果が期待できる。
【００５０】
【発明の効果】
以上から明らかなように、本発明の製造方法で作製した水酸化ニッケル電極を用いたアルカリ蓄電池は、活物質の利用率及び作動電圧が高く、かつ、電極の膨化の抑制効果が大きく、その工業的価値は極めて高い。
【図面の簡単な説明】
【図１】アルカリ熱処理時の温度と活物質利用率の関係を示す図である。[0001]
[Industrial applications]
The present invention relates to a method for manufacturing a nickel electrode of an alkaline storage battery such as a nickel-hydrogen storage battery, a nickel-cadmium storage battery, and a nickel-zinc storage battery using nickel hydroxide as a positive electrode active material, and particularly to a non-sintered nickel hydroxide electrode. The present invention relates to an improvement in the production method of
[0002]
[Prior art]
Conventionally, as a nickel hydroxide electrode for an alkaline storage battery, a so-called sintered nickel hydroxide electrode is used in which a porous substrate obtained by applying nickel powder to a punching metal or the like is sintered and impregnated with an active material. It has been known.
[0003]
This type of electrode has a low strength when the substrate is made to have a high porosity, and has a limit of practically making the porosity of the substrate 80%, and requires a core material such as punched metal. Therefore, it has a drawback that the packing density of the active material is low, which is disadvantageous in achieving a high energy density. Furthermore, the pores of the sintered substrate are as small as 10 μm or less, and the method of filling the active material is limited to a solution impregnation method or an electrodeposition impregnation method that requires complicated steps.
[0004]
As an attempt to remedy these drawbacks, there is a so-called non-sintered nickel hydroxide electrode in which, for example, nickel hydroxide active material powder is directly filled into a foamed nickel having no core and having a porosity of about 95%.
[0005]
The non-sintered nickel hydroxide electrode has a high filling property and a higher capacity than the sintered type, but has a problem that γ-NiOOH is easily generated and the electrode plate is easily expanded. In addition, there is a problem that the pore size is larger than that of the sintering method, and an insulating binder must be added in order to hold the active material.
[0006]
The following methods have been proposed as means for solving the above problems.
[0007]
{Circle around (1)} JP-A-59-112574 In this publication, a method is proposed in which a hydroxide or oxide such as cadmium or zinc is added to nickel hydroxide in a free state.
[0008]
{Circle around (2)} Japanese Patent Application Laid-Open No. 5-41212 This publication proposes a method of adding cadmium, zinc or the like to nickel hydroxide in a solid solution state.
[0009]
{Circle around (3)} JP-A-8-222217 In this publication, an aluminum compound, a magnesium compound, an indium compound, and a zinc compound are added to a cobalt coating layer when a cobalt compound is coated on the surface of nickel hydroxide particles. A method of performing a heat treatment in the presence of oxygen and an alkali has been proposed.
[0010]
[Problems to be solved by the invention]
However, when a hydroxide or oxide such as cadmium or zinc with low conductivity is added in a free state to nickel hydroxide as in the method (1), the conductivity of the electrode plate is reduced and the capacity or operating voltage is reduced. Is greatly reduced.
[0011]
Further, in the method in which cadmium, zinc, or the like is present as a solid solution in the nickel hydroxide particles as in the method (2), there is a problem that it is difficult to obtain the additive's original effect of suppressing the expansion of the electrode plate.
[0012]
Further, in the method of adding a zinc compound or the like to the cobalt coating layer when coating the surface of the nickel hydroxide particles with the cobalt compound as in the method of (3), and performing a heat treatment in the presence of oxygen and an alkali, The active material utilization rate is improved due to the excellent conductivity of the coating layer, but since zinc is present as a solid solution with cobalt, it is difficult to obtain the additive's original effect of suppressing expansion of the electrode plate. There is a problem.
[0013]
The present invention has been made in view of the above problems, and an object of the present invention is to obtain a non-sintered nickel hydroxide electrode having a high utilization rate of an active material and a high operating voltage and suppressing expansion of an electrode plate. Subject.
[0014]
[Means for Solving the Problems]
The production method of the present invention is selected from the group consisting of nickel hydroxide or a powder containing nickel hydroxide as a main component, one or more powders of a cobalt compound or metallic cobalt, and yttrium, cadmium, zinc, magnesium, calcium and manganese. A first step of mixing the obtained at least one compound with an aqueous alkali solution; and a second step of heat-treating the mixture obtained by mixing the aqueous alkali solution in the presence of oxygen.
[0015]
Further, the nickel hydroxide electrode obtained by the production method of the present invention is at least one selected from the group consisting of yttrium, cadmium, zinc, magnesium, calcium, and manganese in a powder containing nickel hydroxide or nickel hydroxide as a main component. An additive to which at least one compound is added, wherein a high-order cobalt compound layer is formed on the surface of the nickel hydroxide or the powder containing nickel hydroxide as a main component and the surface of the additive. .
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, a first mixture of nickel hydroxide powder, a cobalt compound or metallic cobalt, at least one compound selected from the group consisting of yttrium, cadmium, zinc, magnesium, calcium and manganese, and an alkaline aqueous solution is mixed. Step and a second step of heat-treating the mixture in which the alkali aqueous solution is mixed in the presence of oxygen to produce a positive electrode active material.
[0017]
In the second step, an alkali solution is added to the above mixture to perform a heat treatment, so that a part of the cobalt compound becomes HCoO ₂ ^- and dissolves in the alkali solution, and then the surface of the nickel hydroxide or zinc compound is dissolved. And oxidation of cobalt occurs.
[0018]
For this reason, a highly conductive high-order cobalt compound (having a valence of more than 2) is present not only on nickel hydroxide but also on the surface of an additive such as zinc. As a result, even when a powder of a zinc compound or the like having low conductivity is added, the problem that the active material utilization rate and the operating voltage decrease can be solved. Moreover, since the zinc compound exists in a free state, the effect of suppressing the expansion of the electrode plate can be maintained.
[0019]
Then, the positive electrode active material thus prepared is held together with a water-soluble binder such as methylcellulose on an active material holder such as a three-dimensional porous nickel metal material to prepare a nickel electrode. In order to improve the strength of the electrode plate, the nickel electrode prepared as described above may be immersed in a solution in which a fluororesin is dispersed, or this solution may be applied to the surface of the nickel electrode.
[0020]
【Example】
(Preparation of nickel hydroxide)
A nickel nitrate aqueous solution was added to a solution obtained by mixing a sodium hydroxide aqueous solution and ammonia water, and the mixture was stirred and mixed, followed by filtration, washing with water, and drying to produce nickel hydroxide powder (1). At this time, the addition amounts of the aqueous nickel nitrate solution, the aqueous sodium hydroxide solution and the aqueous ammonia were adjusted so that the pH of the whole mixed solution became 11.
[0021]
Zinc nitrate was mixed in the aqueous nickel nitrate solution to prepare nickel hydroxide powder (2) in which zinc was present as a solid solution in nickel hydroxide.
[0022]
The amount of zinc added was 5% by weight in terms of zinc oxide with respect to nickel hydroxide.
[0023]
(Preparation of nickel hydroxide electrode)
[Example 1]
100 parts by weight of the nickel hydroxide powder (1) prepared above, 8 parts by weight of cobalt hydroxide powder, and 5 parts by weight of zinc oxide powder were mixed in a 25% by weight aqueous solution of sodium hydroxide, and For 1 hour at 100 ° C. (hereinafter, this treatment method is referred to as alkali heat treatment) to produce an active material for a nickel hydroxide electrode, which is referred to as an active material a. 100 parts by weight of this active material a was kneaded with 20 parts by weight of a 1% by weight aqueous solution of methylcellulose to prepare an active material slurry. This active material slurry was filled in foamed nickel to produce a nickel hydroxide electrode, which is referred to as the nickel hydroxide electrode A of the present invention.
[0024]
[Comparative Example 1]
Nickel hydroxide powder obtained by adding zinc in a solid solution state as described above (2) Same as Example 1 except that an active material was prepared by mixing 100 parts by weight of cobalt hydroxide powder with 8 parts by weight. To prepare a nickel hydroxide electrode, which is referred to as a comparative nickel hydroxide electrode B.
[0025]
The ratio of the amount of zinc added was adjusted to be the same as that in Example 1.
[0026]
[Comparative Example 2]
Except that the active material was prepared by mixing 8 parts by weight of cobalt hydroxide and 5 parts by weight of zinc oxide with 100 parts by weight of the nickel hydroxide powder (1) prepared as described above, A nickel hydroxide electrode was prepared and is referred to as Comparative Nickel Hydroxide Electrode C.
[0027]
[Comparative Example 3]
A nickel hydroxide electrode was prepared in the same manner as in Example 1 except that an active material was prepared by mixing 8 parts by weight of cobalt hydroxide with 100 parts by weight of the nickel hydroxide powder (1) prepared as described above. , Comparative nickel hydroxide electrode D.
[0028]
[Comparative Example 4]
4 times water is added to the nickel hydroxide powder (1) produced as described above, mixed and diffused. Cobalt sulfate and sulfuric acid are added to the dispersion while adding a 25% by weight aqueous solution of sodium hydroxide so that the pH becomes 10. A nickel hydroxide electrode was prepared in the same manner as in Example 1 except that an active material was prepared by dropping a solution containing a zinc solution and providing a layer in which zinc and cobalt were mixedly crystallized on the surface of nickel hydroxide. And is referred to as a comparative electrode E.
[0029]
The amounts of cobalt and zinc added were adjusted so as to be the same ratio as in Example 1.
[0030]
[Comparative Example 5]
4 times water is added to the nickel hydroxide powder (1) prepared as described above, mixed and diffused, and a 25% by weight aqueous solution of sodium hydroxide is added to the dispersion to adjust the pH to 10 while adding the cobalt sulfate solution. After dropping, providing a cobalt compound layer on the surface of nickel hydroxide, mixing in a 25% by weight aqueous solution of sodium hydroxide, performing heat treatment in air at 100 ° C. for 1 hour, and then adding zinc oxide. A nickel hydroxide electrode was prepared in the same manner as in Example 1 except that the active material was prepared as described above, and was referred to as Comparative electrode F.
[0031]
The amounts of cobalt and zinc added were adjusted so as to be the same as in Example 1.
[0032]
[Experiment 1]
The nickel hydroxide electrodes A to F prepared as described above are used as test electrodes, and a well-known sintered cadmium electrode having a sufficiently large electrochemical capacity is used as a counter electrode to face the test electrodes completely via a nylon separator. Superimposed. After placing these electrode groups in a polyethylene bag and applying pressure from both sides, a potassium hydroxide aqueous solution having a specific gravity of 1.23 was added to prepare a test cell. The cell is charged at a current of 0.1 C with respect to the theoretical capacity of the electrode for 15 hours, and then discharged at a current of 1/3 C until the cell voltage reaches 1.0 V. And the operating voltage (intermediate voltage at the time of discharge) was measured, and the utilization rate of the active material was calculated. The cell was disassembled and the thickness of the electrode plate was measured at the same time to measure the electrode plate expansion rate.
[0033]
The measurement results are shown in Table 1 below. The utilization rate is indicated by an index when the comparative nickel hydroxide electrode D is set to 100.
[0034]
[Table 1]

[0035]
From the results in Table 1, it can be seen that the electrode plate expansion ratio of the comparative electrode D to which zinc was not added was the largest, and that zinc contributed to the effect of suppressing the electrode plate expansion.
[0036]
The comparison electrode B in which zinc is present in a solid solution state in nickel hydroxide and E in which zinc is present in the cobalt coating layer have lower operating voltage and lower activity than the comparison electrode C in which zinc oxide is present alone. It can be seen that the reduction in the substance utilization is small, but the effect of suppressing the expansion of the electrode plate is small.
[0037]
Further, the comparison electrode F in which zinc is present alone in the case where a coating layer of cobalt is formed on the surface of nickel hydroxide and subjected to alkali heat treatment has a smaller decrease in capacity and operating voltage than the comparison electrode C, but is not sufficient.
[0038]
On the other hand, it is understood that the electrode plate A of the present invention is excellent in all of the characteristics of the utilization factor, the operating voltage, and the effect of suppressing the expansion of the electrode plate.
[0039]
This is presumably because the high-order cobalt compound having high conductivity exists not only on the surface of nickel hydroxide but also on the surface of zinc alone.
[0040]
[Experiment 2]
In this experiment, the alkali heat treatment temperature at the time of producing the active material a of the present invention was examined. 100 parts by weight of nickel hydroxide powder {circle around (1)}, 8 parts by weight of cobalt hydroxide powder and 5 parts by weight of zinc oxide powder are mixed in a weakly alkaline aqueous solution, and the powder is mixed with an alkaline solution and oxygen (in air). The heat treatment was performed in a temperature range of 20 ° C. to 300 ° C. for 1 hour. The active material thus prepared was kneaded with 20 parts by weight of a 1% by weight aqueous solution of methylcellulose to prepare an active material slurry. This active material slurry was filled in nickel foam to prepare an electrode.
[0041]
The utilization rate of the electrode thus manufactured was measured under the same charge / discharge conditions as in Experiment 1, and the results are shown in FIG. Incidentally, the utilization rate is indicated by an index with 20 ° C. being 100.
[0042]
From FIG. 1, it is understood that it is optimal to set the heat treatment temperature at 50 ° C. or more and 200 ° C. or less. This is because, when the temperature is low, the oxidation of cobalt does not proceed sufficiently, so that the conductivity near the surface of zinc oxide is not sufficient, and when the temperature is too high, the oxidation of cobalt further proceeds, and on the contrary, the conductivity decreases. It is thought that it is.
[0043]
[Experiment 3]
In this experiment 3, in place of zinc oxide, yttrium oxide, cadmium hydroxide, magnesium hydroxide, manganese oxide, and calcium hydroxide were also mixed with cobalt hydroxide, and subjected to alkali heat treatment in the same manner as in Example 1 to obtain an electrode plate. Were each produced. For comparison, electrode plates to which yttrium oxide, cadmium hydroxide, magnesium hydroxide, manganese oxide, and calcium hydroxide were added (without alkali heat treatment) were produced.
[0044]
For these electrode plates, charge and discharge were repeated under the same conditions as in Experiment 1 above, the capacity in the second cycle was read, and the active material utilization was measured. The results are shown in Table 2 below. In addition, the utilization rate is shown by an index with 100 without additives and without alkaline heat treatment.
[0045]
[Table 2]

[0046]
As is clear from Table 2 above, it is found that the active material utilization rate is improved by the alkali heat treatment. This is because, when the above additive is added in order to suppress the expansion of the electrode plate, the conductivity is lower than that of the additive that is not added, and the active material utilization rate is lower. By performing an alkali heat treatment on the nickel hydroxide surface, a highly conductive higher order cobalt compound is formed not only on the surface of the nickel hydroxide, but also on the surface of the above-mentioned additive, thereby improving the conductivity and improving the active material utilization rate. it is conceivable that.
[0047]
From Table 2 above, it is preferable to use yttrium as an additive in order to achieve a high capacity.
[0048]
In this example, oxides and hydroxides as additives were used, but similar effects can be expected with other compounds.
[0049]
In the present invention, an aqueous sodium hydroxide solution is used as the aqueous alkali solution used in the alkali heat treatment. However, the present invention is not limited to this, and the same effect can be expected with an aqueous potassium hydroxide solution or an aqueous lithium hydroxide solution.
[0050]
【The invention's effect】
As is clear from the above, the alkaline storage battery using the nickel hydroxide electrode produced by the production method of the present invention has a high utilization rate of the active material, a high operating voltage, and a large effect of suppressing the expansion of the electrode. The target value is extremely high.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a temperature during an alkali heat treatment and an active material utilization rate.

Claims

A powder containing nickel hydroxide or nickel hydroxide as a main component, a powder of one or more of a cobalt compound or metallic cobalt, and at least one or more selected from the group consisting of yttrium, cadmium, zinc, magnesium, calcium and manganese A method for producing a nickel electrode for an alkaline storage battery, comprising: a first step of mixing a compound and an alkaline aqueous solution; and a second step of heat-treating the mixture in which the alkaline aqueous solution is mixed in the presence of oxygen. .

The method for producing a nickel hydroxide electrode for an alkaline storage battery according to claim 1, wherein the temperature of the heat treatment in the second step is 50C or more and 200C or less.

2. The aqueous solution of at least one selected from the group consisting of an aqueous solution of potassium hydroxide, an aqueous solution of sodium hydroxide and an aqueous solution of lithium hydroxide as the alkaline aqueous solution mixed in the first step. A method for producing a nickel hydroxide electrode for an alkaline storage battery.

For an alkaline storage battery, comprising nickel hydroxide or an additive obtained by adding at least one compound selected from the group consisting of yttrium, cadmium, zinc, magnesium, calcium, and manganese to a powder containing nickel hydroxide as a main component. In a nickel electrode, a nickel hydroxide electrode for an alkaline storage battery, wherein a high-order cobalt compound layer is formed on a surface of the nickel hydroxide or a powder containing nickel hydroxide as a main component and a surface of the additive.