JP3851179B2 - Alkaline storage battery with nickel electrode and method for manufacturing the same - Google Patents
Alkaline storage battery with nickel electrode and method for manufacturing the same Download PDFInfo
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- JP3851179B2 JP3851179B2 JP2002023878A JP2002023878A JP3851179B2 JP 3851179 B2 JP3851179 B2 JP 3851179B2 JP 2002023878 A JP2002023878 A JP 2002023878A JP 2002023878 A JP2002023878 A JP 2002023878A JP 3851179 B2 JP3851179 B2 JP 3851179B2
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Description
【０００１】
【発明の属する技術分野】
本発明はニッケル−水素蓄電池、ニッケル−カドミウム蓄電池などのアルカリ蓄電池に係り、特に、多孔性焼結基板に水酸化ニッケルを主体とする活物質が充填されたニッケル電極を備えたアルカリ蓄電池に関するものである。
【０００２】
【従来の技術】
従来、アルカリ蓄電池の正極に使用されるニッケル電極としては、活物質の利用率が高く、電極の導電性に優れ、かつ放電性能やサイクル特性に優れるなどの特徴を有する焼結式ニッケル電極が広く使用されている。このような焼結式ニッケル電極はニッケル焼結基板（例えばニッケル焼結基板）に、所謂、化学含浸法により水酸化ニッケルを主体とする活物質を充填して製造される。具体的には、まず、ニッケル粉末とカルボキシメチルセルロースなどの増粘剤を水で混練したスラリーを導電性芯体に塗着した後、還元性雰囲気で焼結して多孔性焼結基板を作製する。
【０００３】
この後、得られた多孔性焼結基板を酸性ニッケル塩（例えば、硝酸ニッケル、硫酸ニッケルなど）を主体とする溶液に浸漬して、酸性ニッケル塩を多孔性焼結基板の細孔中に含浸する。ついで、乾燥した後、アルカリ溶液中に浸漬して、多孔性焼結基板の細孔中に含浸した酸性ニッケル塩を水酸化物に活物質化し、水洗、乾燥する。このような化学含浸法にあっては、酸性ニッケル塩の含浸→中間乾燥→活物質化するアルカリ処理→水洗、乾燥の一連の処理が１サイクルとなるが、１サイクルだけでは必要な活物質量を多孔性焼結基板中に充填することができず、通常、必要な充填量が得られるまで充填サイクルを繰り返して行うようにしている。
【０００４】
近年、充放電が可能な二次電池（蓄電池）の需要が高まり、小型の機器のみならず、電動工具、アシスト自転車、電気自動車などの大電流用途にも需要が拡大するようになった。これに伴い、より大きな電流値を取り出すことができるように、正極および負極の両面から改良が進められている。例えば、正極面からの改良としては、水酸化ニッケルを主成分とする活物質に、導電剤として少量のコバルト化合物を添加することが一般に行われている。
【０００５】
ところが、導電剤としてコバルト化合物を添加するだけでは、高容量で高性能なアルカリ蓄電池が得られないため、活物質となる水酸化ニッケル層の表面にコバルト化合物層を形成することが特開２００１−７６７１７号公報にて提案されるようになった。この特開２００１−７６７１７号公報にて提案された焼結式ニッケル電極においては、焼結式ニッケル電極の最表面層をコバルト化合物層で覆うことで、焼結式ニッケル電極の導電性が向上して、正極活物質の利用率が向上し、初期の放電時の作動電圧の低下も抑制できるようになる。
【０００６】
【発明が解決しようとする課題】
しかしながら、上述した焼結式ニッケル電極を使用したアルカリ蓄電池においては、焼結式ニッケル電極の導電性が向上することから、初期の放電時作動電圧が向上するものの、高温の雰囲気下で充放電サイクルを繰り返すと、導電性が向上した効果が低下して、高温でのサイクル寿命特性が劣化する問題が生じた。これは、高温下で充放電を繰り返すことにより、最表面層のコバルト化合物（コバルト水酸化物）がダメージを受け、導電性が低下することで高温サイクル寿命特性が劣化したと考えられる。
【０００７】
即ち、最表面層のコバルト水酸化物は、初回の充電で導電性の高いコバルト酸化物に高次化されて、アルカリ水溶液中（電解液中）で安定になる。これを、高温の雰囲気下で充放電を繰り返すと、放電時に放電深度が深くなるために、コバルト酸化物がコバルト水酸化物に還元されてアルカリ水溶液中（電解液中）に溶出し、析出するようになる。これにより、焼結式ニッケル電極の導電性が次第に低下し、高温雰囲気下でのサイクル寿命が低下したと考えられる。
【０００８】
そこで、本発明はこのような問題点を改善するためになされたものであって、高温の雰囲気下で充放電サイクルを繰り返しても、焼結式ニッケル電極の導電性の低下を防止して、高温でのサイクル特性に優れたアルカリ蓄電池を提供することを目的とする。
【０００９】
【課題を解決するための手段】
上記目的を達成するため、本発明のアルカリ蓄電池は、多孔性焼結基板の細孔内に水酸化ニッケルを主体とする活物質が充填されているとともに、この多孔性焼結基板に充填された水酸化ニッケルを主体とする活物質層の表面にコバルト化合物層を備え、かつこのコバルト化合物層中にニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物を添加するようにしている。
【００１０】
このように、コバルト化合物層中にニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物が添加されていると、水酸化ニッケルを主体とする活物質層の表面を被覆するコバルト化合物が、電解液中に溶解して析出する速度を遅らせることができる。これにより、コバルト化合物層をより緻密な構造に変化させて、焼結式ニッケル電極中に良好な導電ネットワークを維持できるようになる。
【００１１】
この場合、コバルト化合物層に添加するニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物の添加量がコバルト化合物層中のコバルト化合物の質量に対して２質量％（２ｗｔ％）未満であると、被覆したコバルト化合物が電解液中に溶解して析出する速度を遅くする効果が十分に得られないことが分かった。また、その添加量が多すぎると、ニッケル電極中の活物質となる水酸化ニッケル量が相対的に少なくなって、放電容量が減少する。このため、ニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物の添加量は、コバルト化合物の質量に対して２質量％（２ｗｔ％）以上にするのが望ましい。
【００１２】
なお、ニオブ化合物としては、ＮａＮｂＯ3，ＬｉＮｂＯ3，ＫＮｂＯ3，Ｎｂ2Ｏ5・ｘＨ2Ｏ等から選択して用いるのが好ましい。また、チタン化合物としては、Ｎａ2Ｔｉ3Ｏ7，Ｌｉ2ＴｉＯ3，Ｋ2ＴｉＯ3等から選択して用いるのが好ましい。また、タングステン化合物としては、ＷＯ2，ＷＯ3，Ｎａ2ＷＯ4，Ｌｉ2ＷＯ2，Ｋ2ＷＯ4等から選択して用いるのが好ましい。さらに、モリブデン化合物としては、ＭｏＯ3・Ｈ2Ｏ，ＭｏＯ3・２Ｈ2Ｏ，Ｎａ2ＭｏＯ4・２Ｈ2Ｏ，Ｌｉ6Ｍｏ7Ｏ24・１２Ｈ2Ｏ，Ｋ2ＭｏＯ4等から選択して用いるのが好ましい。
【００１３】
そして、多孔性焼結基板の細孔中に水酸化ニッケルを主体とする活物質を充填する活物質充填工程と、活物質が充填された多孔性焼結基板をコバルト塩とを含有する水溶液に浸漬して充填された活物質層の表面にコバルト塩を保持させるコバルト塩保持工程と、コバルト塩が保持された多孔性焼結基板をニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物を含有するアルカリ水溶液に浸漬するアルカリ浸漬工程とを備えるようにすると、水酸化ニッケルを主体とする活物質層の表面を被覆するコバルト化合物層中にニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物が添加されたニッケル電極を簡単、容易に得ることができる。
【００１４】
この場合、アルカリ浸漬工程において、コバルト塩が保持された多孔性焼結基板をニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物を含有するアルカリ水溶液に浸漬して、活物質の表面に保持されたコバルト塩を水酸化コバルトに転換させるとともに、該転換された水酸化コバルト層中にニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物を析出させるようにすればよい。また、活物質充填工程において、多孔性焼結基板をニッケル塩とコバルト塩とを含有する水溶液に浸漬した後、アルカリ溶液中に浸漬して水酸化ニッケルを主体とする活物質を多孔性焼結基板の細孔中に充填する操作を所定回数繰り返すようにすればよい。
【００１５】
【発明の実施の形態】
以下に、本発明の実施の形態を詳細に説明するが、本発明はこれに限定されるものでなく、その要旨を変更しない範囲で適宜変更して実施することができる。
１．焼結基板の作製
まず、ニッケル粉末にカルボキシメチルセルロース等の増粘剤および水を混練してスラリーを調製し、このスラリーをパンチングメタルからなる導電性芯体に塗着した。この後、スラリーを塗着した導電性芯体を還元性雰囲気下で焼結して、多孔度が約８５％の多孔性ニッケル焼結基板を作製した。
【００１６】
２．焼結式ニッケル電極の作製
ついで、得られた多孔性ニッケル焼結基板を比重が１．７５の硝酸ニッケルと硝酸コバルトの混合水溶液（ニッケルとコバルトの原子比がＮｉ：Ｃｏ＝１０：１になるように調製している）に浸漬し、多孔性ニッケル焼結基板の細孔内にニッケル塩およびコバルト塩を保持させた。この後、この多孔性ニッケル焼結基板を２５ｗｔ％の水酸化ナトリウム（ＮａＯＨ）水溶液中に浸漬して、ニッケル塩およびコバルト塩をそれぞれ水酸化ニッケルおよび水酸化コバルトに転換させた。ついで、充分に水洗してアルカリ溶液を除去した後、乾燥を行った。
このような一連の活物質充填操作を６回繰り返して、多孔性焼結基板の細孔内に水酸化ニッケルを主体とする活物質が所定量だけ充填された活物質充填極板を得て、これをニッケル電極ｘとした。
【００１７】
ついで、得られたニッケル電極ｘを濃度が４ｍｏｌ／ｌの硝酸コバルト水溶液に浸漬し、多孔性ニッケル焼結基板の細孔内に充填された水酸化ニッケルを主体とする活物質層の表面にコバルト塩を保持させた。この場合、コバルト塩の保持量が少なすぎると導電性を向上させる効果を発揮することができない。また、コバルト塩の保持量が多すぎると相対的に活物質量が減少するようになる。このため、コバルト塩の保持量が活物質となる水酸化ニッケルに対して０．５ｗｔ％〜５．０ｗｔ％になるように、硝酸コバルト水溶液への浸漬時間を調整する必要がある。
【００１８】
ついで、上述のように活物質層の表面にコバルト塩を保持させた多孔性ニッケル焼結基板を水酸化ナトリウム（ＮａＯＨ）水溶液に浸漬した。これにより、活物質層の表面に保持されたコバルト塩は、導電性に優れた水酸化コバルトに転換するこことなる。このようにして得られた極板をニッケル電極ｙとした。
【００１９】
一方、ＮａＮｂＯ3を溶解させた水酸化ナトリウム（ＮａＯＨ）水溶液を用意し、この水酸化ナトリウム（ＮａＯＨ）水溶液中に活物質層の表面にコバルト塩を保持させた多孔性ニッケル焼結基板を浸漬した。これにより、活物質層の表面に保持されたコバルト塩は水酸化コバルトに転換するとともに、この水酸化コバルト層内に均一にニオブ化合物が点在することとなる。この場合、活物質層の表面に形成された水酸化コバルトの質量に対して所定の添加量になるように、ニオブ化合物の濃度および浸漬時間を調整した。
【００２０】
ここで、活物質層の表面に形成された水酸化コバルトの質量に対してニオブ化合物の添加量が１ｗｔ％になるように調製し、所定の寸法になるように切断した極板をニッケル電極ａとした。同様に、２ｗｔ％になるように調製した極板をニッケル電極ｂとし、５ｗｔ％になるように調製した極板をニッケル電極ｃとし、１０ｗｔ％になるように調製した極板をニッケル電極ｄとし、２０ｗｔ％になるように調製した極板をニッケル電極ｅとし、３０ｗｔ％になるように調製した極板をニッケル電極ｆとし、４０ｗｔ％になるように調製した極板をニッケル電極ｇとした。なおこの場合、水酸化ナトリウムに溶解させるニオブ化合物としてはＮａＮｂＯ3，ＬｉＮｂＯ3，ＫＮｂＯ3，Ｎｂ2Ｏ5・ｘＨ2Ｏ等から選択して用いるのが好ましい。
【００２１】
２．水素吸蔵合金電極の作製
ミッシュメタル（Ｍｍ）、ニッケル（Ｎｉ：純度９９．９％）、コバルト（Ｃｏ）、アルミニウム（Ａｌ）、およびマンガン（Ｍｎ）を所定のモル比になるようにそれぞれ混合し、この混合物をアルゴンガス雰囲気の高周波誘導炉で誘導加熱して合金溶湯とした。この合金溶湯を公知の方法で鋳型に流し込み、冷却して、組成式がＭｍＮｉaＣｏbＭｎcＡｌdで表される水素吸蔵合金のインゴットを作製した。この水素吸蔵合金インゴットを機械的粉砕法により、平均粒子径が約６０μｍになるまで粉砕して、水素吸蔵合金粉末とした。ついで、得られた水素吸蔵合金粉末１００質量部に対して、結着剤としての５ｗｔ％のポリエチレンオキサイド（ＰＥＯ）の水溶液を２０質量部を混合して水素吸蔵合金ペーストを作製した。この水素吸蔵合金ペーストをパンチングメタルからなる芯体の両面に塗布し、室温で乾燥させた後、所定の厚みに圧延し、所定の寸法に切断して水素吸蔵合金電極を作製した。
【００２２】
３．ニッケル−水素蓄電池の作製
上述のように作製した焼結式ニッケル電極ａ，ｂ，ｃ，ｄ，ｅ，ｆ，ｇ，ｘ，ｙと水素吸蔵合金負極を用い、これらの間にポリプロピレン製不織布からなるセパレータを介在させ、これらをスパイラル状に巻回して電極群をそれぞれ作製した。ついで、各電極群を外装缶に挿入した後、各電極群の負極から延出する負極リードを外装缶に接続するとともに、正極から延出する正極リードを封口体に設けられた正極蓋に接続した。この後、外装缶内に電解液（例えば、３０ｗｔ％の水酸化カリウム水溶液）を注入し、更に外装缶の開口部を封口体により封止して、公称容量が１０００ｍＡｈのニッケル−水素蓄電池をそれぞれ作製した。
【００２３】
ここで、焼結式ニッケル電極ａを用いたものを電池Ａとし、焼結式ニッケル電極ｂを用いたものを電池Ｂとし、焼結式ニッケル電極ｃを用いたものを電池Ｃとし、焼結式ニッケル電極ｄを用いたものを電池Ｄとし、焼結式ニッケル電極ｅを用いたものを電池Ｅとし、焼結式ニッケル電極ｆを用いたものを電池Ｆとし、焼結式ニッケル電極ｇを用いたものを電池Ｇとした。また、焼結式ニッケル電極ｘを用いたものを電池Ｘとし、焼結式ニッケル電極ｙを用いたものを電池Ｙとした。
【００２４】
４．電池試験
（１）放電容量の測定
ついで、上述のように作製した各電池Ａ〜Ｇ，Ｘ，Ｙを用いて、これらの各電池Ａ〜Ｇ，Ｘ，Ｙを２５℃の温度条件で、１００ｍＡの充電電流で１６時間充電した後、１０００ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させて、放電時間から各電池Ａ〜Ｇ，Ｘ，Ｙの初期放電容量（ｍＡｈ）を求めると、下記の表１に示すような結果になった。
【００２５】
（２）高温サイクル寿命の測定
また、上述のように作製した各電池Ａ〜Ｇ，Ｘ，Ｙを用いて、これらの各電池Ａ〜Ｇ，Ｘ，Ｙを６０℃の高温雰囲気下で、５００ｍＡの充電電流で２時間充電した後、５００ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させるというサイクルを１サイクルとする充放電サイクル試験を繰り返し行った。そして、各サイクル後の放電容量が６０℃での初期放電容量の８０％に達した時点でのサイクル数を高温サイクル寿命として求めると、下記の表１に示すような結果になった。
【００２６】
【表１】
上記表１の結果から明らかなように、水酸化ニッケルを主体とする活物質の表面にコバルト化合物層を形成したニッケル電極ｙを用いた電池Ｙと、水酸化ニッケルを主体とする活物質の表面にコバルト化合物層を形成しなかったニッケル電極ｘを用いた電池Ｘとを比較すると、電池Ｙの方が初期放電容量が大きいことが分かる。これは、水酸化ニッケルを主体とする活物質の表面にコバルト化合物層を形成すると、コバルト化合物層は導電性が優れているので、ニッケル電極の導電性が向上して活物質の利用率が向上したためである。この場合、コバルト化合物量が活物質となる水酸化ニッケルに対して０．５ｗｔ％より少なすぎると導電性を向上させる効果を発揮することができなくなる。逆に、コバルト化合物量が活物質となる水酸化ニッケルに対して５．０ｗｔ％より多すぎると相対的に活物質量が減少するようになる。このため、コバルト化合物量は活物質となる水酸化ニッケルに対して０．５ｗｔ％〜５．０ｗｔ％になるように調整するのが望ましい。
【００２８】
また、コバルト化合物層にニオブ化合物を添加したニッケル電極ａ〜ｇを用いた電池Ａ〜Ｇと、コバルト化合物層にニオブ化合物を添加しなかったニッケル電極ｙを用いた電池Ｙとを比較すると、コバルト化合物層にニオブ化合物を添加した方が高温サイクル寿命が向上することが分かる。これは、コバルト化合物層にニオブ化合物を添加すると、高温雰囲気下での放電時にコバルト化合物が電解液中に溶解して析出する速度を遅らせることができるようになり、良好な導電ネットワークを維持できるようになったためと考えられる。
【００２９】
この場合、電池Ａのように、コバルト化合物層に添加されたニオブ化合物の添加量が１ｗｔ％で少ないと、充分に高温サイクル寿命の向上効果、即ち、コバルト化合物が電解液中に溶解して析出する速度を遅くする効果を発揮できないことが分かる。このことから、コバルト化合物層に添加するニオブ化合物の添加量はコバルト化合物量中のコバルト化合物量に対して２ｗｔ％以上にするのが望ましいということができる。また、電池Ｇのように、コバルト化合物層に添加されたニオブ化合物の添加量が４０ｗｔ％になっても、これ以上は高温サイクル寿命の向上効果を発揮できなく、逆に、相対的に活物質となる水酸化ニッケル量が少なくなって、初期放電容量が減少する。このため、コバルト層に添加するニオブ化合物（Ｎｂ2Ｏ5）の添加量はコバルト量に対して３０ｗｔ％以下にするのが望ましいということができる。
【００３０】
５．添加化合物の検討
上述した例においては、ニオブ化合物をコバルト層に添加する例について説明したが、チタン化合物、タングステン化合物、モリブデン化合物をコバルト層に添加した場合についても検討した。
【００３１】
（１）チタン化合物について
Ｎａ2Ｔｉ3Ｏ7を溶解させた水酸化ナトリウム（ＮａＯＨ）水溶液を用意し、この水酸化ナトリウム（ＮａＯＨ）水溶液中に活物質層の表面にコバルト塩を保持させた多孔性ニッケル焼結基板を浸漬した。これにより、活物質層の表面に保持されたコバルト塩は水酸化コバルトに転換するとともに、この水酸化コバルト層内に均一にチタン化合物が点在することとなる。
【００３２】
この場合、活物質層の表面に形成された水酸化コバルトの質量に対して所定の添加量になるように、チタン化合物の濃度およびアルカリ溶液への浸漬時間を調整した。ここで、活物質層の表面に形成された水酸化コバルトの質量に対してチタン化合物の添加量が１ｗｔ％になるように調製し、所定の寸法になるように切断した極板をニッケル電極ｈとした。同様に、２ｗｔ％になるように調製した極板をニッケル電極ｉとし、５ｗｔ％になるように調製した極板をニッケル電極ｊとした。なお、水酸化ナトリウムに溶解させるチタン化合物としては、Ｎａ2Ｔｉ3Ｏ7，Ｌｉ2ＴｉＯ3，Ｋ2ＴｉＯ3等から選択して用いるのが好ましい。
【００３３】
上述のように作製した焼結式ニッケル電極ｈ，ｉ，ｊと水素吸蔵合金負極を用い、これらの間にポリプロピレン製不織布からなるセパレータを介在させ、これらをスパイラル状に巻回して電極群をそれぞれ作製した。ついで、各電極群を外装缶に挿入した後、各電極群の負極から延出する負極リードを外装缶に接続するとともに、正極から延出する正極リードを封口体に設けられた正極蓋に接続した。この後、外装缶内に電解液（例えば、３０質量％の水酸化カリウム水溶液）を注入し、更に外装缶の開口部を封口体により封止して、公称容量が１０００ｍＡｈのニッケル−水素蓄電池Ｈ，Ｉ，Ｊをそれぞれ作製した。なお、焼結式ニッケル電極ｈを用いたものを電池Ｈとし、焼結式ニッケル電極ｉを用いたものを電池Ｉとし、焼結式ニッケル電極ｊを用いたものを電池Ｊとした。
【００３４】
ついで、上述のように作製した各電池Ｈ，Ｉ，Ｊを用いて、これらの各電池Ｈ，Ｉ，Ｊを２５℃の温度条件で、１００ｍＡの充電電流で１６時間充電した後、１０００ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させて、放電時間から各電池Ｈ，Ｉ，Ｊの初期放電容量（ｍＡｈ）を求めると、下記の表２に示すような結果になった。また、上述のように作製した各電池Ｈ，Ｉ，Ｊを用いて、これらの各電池Ｈ，Ｉ，Ｊを６０℃の高温雰囲気下で、５００ｍＡの充電電流で２時間充電した後、５００ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させるというサイクルを１サイクルとする充放電サイクル試験を繰り返し行った。そして、各サイクル後の放電容量が６０℃での初期放電容量の８０％に達した時点でのサイクル数を高温サイクル寿命として求めると、下記の表２に示すような結果になった。なお、下記の表２には、比較のために上述した電池Ｙの結果も併せて示している。
【００３５】
【表２】
上記表２の結果から明らかなように、コバルト化合物層にチタン化合物を添加したニッケル電極ｈ，ｉ，ｊを用いた電池Ｈ，Ｉ，Ｊと、コバルト化合物層にチタン化合物を添加しなかったニッケル電極ｙを用いた電池Ｙとを比較すると、コバルト化合物層にチタン化合物を添加した方が高温サイクル寿命が向上することが分かる。これは、コバルト化合物層にチタン化合物を添加すると、高温雰囲気下での放電時にコバルト化合物が電解液中に溶解して析出する速度を遅らせることができるようになり、良好な導電ネットワークを維持できるようになったためと考えられる。
【００３７】
この場合、電池Ｈのように、コバルト化合物層に添加されたチタン化合物の添加量が１ｗｔ％で少ないと、充分に高温サイクル寿命の向上効果、即ち、コバルト化合物が電解液中に溶解して析出する速度を遅くする効果を発揮できないことが分かる。このことから、コバルト化合物層に添加するチタン化合物の添加量はコバルト化合物層中のコバルト化合物量に対して２ｗｔ％以上にするのが望ましいということができる。また、上限値については上述したニオブ化合物の場合と同様に、チタン化合物の添加量が３０ｅｔ％以下になるように添加するのが望ましい。
【００３８】
（２）タングステン化合物について
Ｎａ2ＷＯ4を溶解させた水酸化ナトリウム（ＮａＯＨ）水溶液を用意し、この水酸化ナトリウム（ＮａＯＨ）水溶液中に活物質層の表面にコバルト塩を保持させた多孔性ニッケル焼結基板を浸漬した。これにより、活物質層の表面に保持されたコバルト塩は水酸化コバルトに転換するとともに、この水酸化コバルト層内に均一にタングステン化合物が点在することとなる。
【００３９】
この場合、活物質層の表面に形成された水酸化コバルトの質量に対して所定の添加量になるように、タングステン化合物の濃度およびアルカリ溶液への浸漬時間を調整した。ここで、活物質層の表面に形成された水酸化コバルトの質量に対してタングステン化合物の添加量が１ｗｔ％になるように調製し、所定の寸法になるように切断した極板をニッケル電極ｋとした。同様に、２ｗｔ％になるように調製した極板をニッケル電極ｌとし、５ｗｔ％になるように調製した極板をニッケル電極ｍとした。なお、水酸化ナトリウムに溶解させるタングステン化合物としては、ＷＯ2，ＷＯ3，Ｎａ2ＷＯ4，Ｌｉ2ＷＯ2、，Ｋ2ＷＯ4等から選択して用いるのが好ましい。
【００４０】
上述のように作製した焼結式ニッケル電極ｋ，ｌ，ｍと水素吸蔵合金負極を用い、これらの間にポリプロピレン製不織布からなるセパレータを介在させ、これらをスパイラル状に巻回して電極群をそれぞれ作製した。ついで、各電極群を外装缶に挿入した後、各電極群の負極から延出する負極リードを外装缶に接続するとともに、正極から延出する正極リードを封口体に設けられた正極蓋に接続した。この後、外装缶内に電解液（例えば、３０質量％の水酸化カリウム水溶液）を注入し、更に外装缶の開口部を封口体により封止して、公称容量が１０００ｍＡｈのニッケル−水素蓄電池Ｋ，Ｌ，Ｍをそれぞれ作製した。なお、焼結式ニッケル電極ｋを用いたものを電池Ｋとし、焼結式ニッケル電極ｌを用いたものを電池Ｌとし、焼結式ニッケル電極ｍを用いたものを電池Ｍとした。
【００４１】
ついで、上述のように作製した各電池Ｋ，Ｌ，Ｍを用いて、これらの各電池Ｋ，Ｌ，Ｍを２５℃の温度条件で、１００ｍＡの充電電流で１６時間充電した後、１０００ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させて、放電時間から各電池Ｋ，Ｌ，Ｍの初期放電容量（ｍＡｈ）を求めると、下記の表３に示すような結果になった。また、上述のように作製した各電池Ｋ，Ｌ，Ｍを用いて、これらの各電池Ｋ，Ｌ，Ｍを６０℃の高温雰囲気下で、５００ｍＡの充電電流で２時間充電した後、５００ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させるというサイクルを１サイクルとする充放電サイクル試験を繰り返し行った。そして、各サイクル後の放電容量が６０℃での初期放電容量の８０％に達した時点でのサイクル数を高温サイクル寿命として求めると、下記の表３に示すような結果になった。なお、下記の表３には、比較のために上述した電池Ｙの結果も併せて示している。
【００４２】
【表３】
上記表３の結果から明らかなように、コバルト化合物層にタングステン化合物を添加したニッケル電極ｋ，ｌ，ｍを用いた電池Ｋ，Ｌ，Ｍと、コバルト化合物層にタングステン化合物を添加しなかったニッケル電極ｙを用いた電池Ｙとを比較すると、コバルト化合物層にタングステン化合物を添加した方が高温サイクル寿命が向上することが分かる。これは、コバルト化合物層にタングステン化合物を添加すると、高温雰囲気下での放電時にコバルト化合物が電解液中に溶解して析出する速度を遅らせることができるようになり、良好な導電ネットワークを維持できるようになったためと考えられる。
【００４４】
この場合、電池Ｋのように、コバルト化合物層に添加されたタングステン化合物の添加量が１ｗｔ％で少ないと、充分に高温サイクル寿命の向上効果、即ち、コバルト化合物が電解液中に溶解して析出する速度を遅くする効果を発揮できないことが分かる。このことから、コバルト化合物層に添加するタングステン化合物の添加量はコバルト化合物層中のコバルト化合物量に対して２ｗｔ％以上にするのが望ましいということができる。また、上限値については上述したニオブ化合物の場合と同様に、タングステン化合物の添加量が３０ｗｔ％以下になるように添加するのが望ましい。
【００４５】
（３）モリブデン化合物について
Ｎａ2ＭｏＯ4・２Ｈ2Ｏを溶解させた水酸化ナトリウム（ＮａＯＨ）水溶液を用意し、この水酸化ナトリウム（ＮａＯＨ）水溶液中に活物質層の表面にコバルト塩を保持させた多孔性ニッケル焼結基板を浸漬した。これにより、活物質層の表面に保持されたコバルト塩は水酸化コバルトに転換するとともに、この水酸化コバルト層内に均一にモリブデン化合物が点在することとなる。
【００４６】
この場合、活物質層の表面に形成された水酸化コバルトの質量に対して所定の添加量になるように、モリブデン化合物の濃度およびアルカリ溶液への浸漬時間を調整した。ここで、活物質層の表面に形成された水酸化コバルトの質量に対してモリブデン化合物の添加量が１ｗｔ％になるように調製し、所定の寸法になるように切断した極板をニッケル電極ｎとした。同様に、２ｗｔ％になるように調製した極板をニッケル電極ｏとし、５ｗｔ％になるように調製した極板をニッケル電極ｐとした。なお、水酸化ナトリウムに溶解させるモリブデン化合物としては、ＭｏＯ3・Ｈ2Ｏ，ＭｏＯ3・２Ｈ2Ｏ，Ｎａ2ＭｏＯ4・２Ｈ2Ｏ，Ｌｉ6Ｍｏ7Ｏ24・１２Ｈ2Ｏ，Ｋ2ＭｏＯ4等から選択して用いるのが好ましい。
【００４７】
上述のように作製した焼結式ニッケル電極ｎ，ｏ，ｐと水素吸蔵合金負極を用い、これらの間にポリプロピレン製不織布からなるセパレータを介在させ、これらをスパイラル状に巻回して電極群をそれぞれ作製した。ついで、各電極群を外装缶に挿入した後、各電極群の負極から延出する負極リードを外装缶に接続するとともに、正極から延出する正極リードを封口体に設けられた正極蓋に接続した。この後、外装缶内に電解液（例えば、３０質量％の水酸化カリウム水溶液）を注入し、更に外装缶の開口部を封口体により封止して、公称容量が１０００ｍＡｈのニッケル−水素蓄電池Ｎ，Ｏ，Ｐをそれぞれ作製した。なお、焼結式ニッケル電極ｎを用いたものを電池Ｎとし、焼結式ニッケル電極ｏを用いたものを電池Ｏとし、焼結式ニッケル電極ｐを用いたものを電池Ｐとした。
【００４８】
ついで、上述のように作製した各電池Ｎ，Ｏ，Ｐを用いて、これらの各電池Ｎ，Ｏ，Ｐを２５℃の温度条件で、１００ｍＡの充電電流で１６時間充電した後、１０００ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させて、放電時間から各電池Ｎ，Ｏ，Ｐの初期放電容量（ｍＡｈ）を求めると、下記の表４に示すような結果になった。また、上述のように作製した各電池Ｎ，Ｏ，Ｐを用いて、これらの各電池Ｎ，Ｏ，Ｐを６０℃の高温雰囲気下で、５００ｍＡの充電電流で２時間充電した後、５００ｍＡの放電電流で、電池電圧が１．０Ｖになるまで放電させるというサイクルを１サイクルとする充放電サイクル試験を繰り返し行った。そして、各サイクル後の放電容量が６０℃での初期放電容量の８０％に達した時点でのサイクル数を高温サイクル寿命として求めると、下記の表４に示すような結果になった。なお、下記の表４には、比較のために上述した電池Ｙの結果も併せて示している。
【００４９】
【表４】
上記表４の結果から明らかなように、コバルト化合物層にモリブデン化合物を添加したニッケル電極ｎ，ｏ，ｐを用いた電池Ｎ，Ｏ，Ｐと、コバルト化合物層にモリブデン化合物を添加しなかったニッケル電極ｙを用いた電池Ｙとを比較すると、コバルト化合物層にモリブデン化合物を添加した方が高温サイクル寿命が向上することが分かる。これは、コバルト化合物層にモリブデン化合物を添加すると、高温雰囲気下での放電時にコバルト化合物が電解液中に溶解して析出する速度を遅らせることができるようになり、良好な導電ネットワークを維持できるようになったためと考えられる。
【００５１】
この場合、電池Ｎのように、コバルト化合物層に添加されたモリブデン化合物の添加量が１ｗｔ％で少ないと、充分に高温サイクル寿命の向上効果、即ち、コバルト化合物が電解液中に溶解して析出する速度を遅くする効果を発揮できないことが分かる。このことから、コバルト化合物層に添加するモリブデン化合物の添加量はコバルト化合物層中のコバルト化合物量に対して２ｗｔ％以上にするのが望ましいということができる。また、上限値については上述したニオブ化合物の場合と同様に、モリブデン化合物の添加量が３０ｗｔ％以下になるように添加するのが望ましい。
【００５２】
【発明の効果】
上述したように、本発明においては、水酸化ニッケルを主体とする活物質層の表面にコバルト化合物層が形成されており、このコバルト化合物層にニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物が均一に添加されている。このため、活物質層の表面を被覆するコバルト化合物が、電解液中に溶解して析出する速度を遅めることができる。これにより、コバルト化合物層をより緻密な構造に変化させて、導電ネットワークを向上させることが可能になる。
【００５３】
なお、ニッケル電極中にイットリウム、イッテルビウム、カルシウム、アルミニウム、エルビウム、ガドリニウム、ツリウム、ルテチウム、及び亜鉛よりなる群から選ばれた少なくとも１種の元素又はその化合物が添加されているようにすると、高温雰囲気下における充放電特性がより一層向上されるようになる。特に、イットリウム又はその化合物を添加されているようにすると、その作用が大きいため、高温雰囲気下における充放電サイクル特性が著しく向上し、なかでもイットリウム化合物としてＹ2Ｏ3を用いることがより好ましい。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alkaline storage battery such as a nickel-hydrogen storage battery or a nickel-cadmium storage battery, and more particularly to an alkaline storage battery having a nickel electrode filled with an active material mainly composed of nickel hydroxide on a porous sintered substrate. is there.
[0002]
[Prior art]
Conventionally, as a nickel electrode used for a positive electrode of an alkaline storage battery, a sintered nickel electrode having characteristics such as high utilization of an active material, excellent electrode conductivity, and excellent discharge performance and cycle characteristics is widely used. in use. Such a sintered nickel electrode is manufactured by filling a nickel sintered substrate (for example, a nickel sintered substrate) with an active material mainly composed of nickel hydroxide by a so-called chemical impregnation method. Specifically, first, a slurry obtained by kneading a nickel powder and a thickener such as carboxymethyl cellulose with water is applied to the conductive core, and then sintered in a reducing atmosphere to produce a porous sintered substrate. .
[0003]
Thereafter, the obtained porous sintered substrate is immersed in a solution mainly composed of acidic nickel salt (for example, nickel nitrate, nickel sulfate, etc.), and the acidic nickel salt is impregnated in the pores of the porous sintered substrate. To do. Next, after drying, the substrate is immersed in an alkaline solution to convert the acidic nickel salt impregnated into the pores of the porous sintered substrate into a hydroxide, which is washed with water and dried. In such a chemical impregnation method, a series of treatments of impregnation of acidic nickel salt → intermediate drying → alkali treatment to make active material → water washing and drying is one cycle, but the amount of active material required in only one cycle Can not be filled into the porous sintered substrate, and the filling cycle is usually repeated until the required filling amount is obtained.
[0004]
In recent years, demand for secondary batteries (storage batteries) that can be charged and discharged has increased, and demand has increased not only for small devices but also for large current applications such as electric tools, assist bicycles, and electric vehicles. Along with this, improvements have been made from both the positive electrode and the negative electrode so that a larger current value can be taken out. For example, as an improvement from the positive electrode surface, a small amount of a cobalt compound is generally added as a conductive agent to an active material mainly composed of nickel hydroxide.
[0005]
However, since a high-capacity and high-performance alkaline storage battery cannot be obtained simply by adding a cobalt compound as a conductive agent, it is possible to form a cobalt compound layer on the surface of a nickel hydroxide layer serving as an active material. No. 76717 has been proposed. In the sintered nickel electrode proposed in Japanese Patent Laid-Open No. 2001-76717, the conductivity of the sintered nickel electrode is improved by covering the outermost surface layer of the sintered nickel electrode with a cobalt compound layer. Thus, the utilization factor of the positive electrode active material is improved, and the decrease in the operating voltage during the initial discharge can be suppressed.
[0006]
[Problems to be solved by the invention]
However, in the alkaline storage battery using the sintered nickel electrode described above, since the conductivity of the sintered nickel electrode is improved, the initial discharge operating voltage is improved, but the charge / discharge cycle is performed in a high-temperature atmosphere. When the process is repeated, the effect of improving the conductivity is lowered, resulting in a problem that the cycle life characteristics at a high temperature deteriorate. It is considered that this is because the cobalt compound (cobalt hydroxide) in the outermost surface layer was damaged by repeated charge and discharge at high temperatures, and the high temperature cycle life characteristics were deteriorated by the decrease in conductivity.
[0007]
That is, the cobalt hydroxide of the outermost surface layer is made higher in order to be highly conductive cobalt oxide by the first charge, and becomes stable in the alkaline aqueous solution (in the electrolytic solution). If this is repeatedly charged and discharged in a high-temperature atmosphere, the depth of discharge increases during discharge, so that the cobalt oxide is reduced to cobalt hydroxide and eluted into the aqueous alkaline solution (in the electrolyte) and deposited. It becomes like this. Thereby, it is considered that the conductivity of the sintered nickel electrode gradually decreased, and the cycle life under a high temperature atmosphere was decreased.
[0008]
Therefore, the present invention was made to improve such problems, and even if the charge / discharge cycle is repeated under a high temperature atmosphere, the decrease in the conductivity of the sintered nickel electrode is prevented, An object of the present invention is to provide an alkaline storage battery having excellent cycle characteristics at high temperatures.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the alkaline storage battery of the present invention is filled with an active material mainly composed of nickel hydroxide in the pores of the porous sintered substrate, and is filled in the porous sintered substrate. A cobalt compound layer is provided on the surface of the active material layer mainly composed of nickel hydroxide, and at least one compound selected from niobium compounds, titanium compounds, tungsten compounds, and molybdenum compounds is added to the cobalt compound layer. I have to.
[0010]
Thus, when at least one compound selected from niobium compounds, titanium compounds, tungsten compounds, and molybdenum compounds is added to the cobalt compound layer, the surface of the active material layer mainly composed of nickel hydroxide is covered. The rate at which the cobalt compound that dissolves and dissolves in the electrolyte can be delayed. As a result, the cobalt compound layer can be changed to a denser structure, and a good conductive network can be maintained in the sintered nickel electrode.
[0011]
In this case, the niobium compound, the titanium compound, the tungsten compound, and the molybdenum compound added to the cobalt compound layer were coated such that the addition amount was less than 2 mass% (2 wt%) with respect to the mass of the cobalt compound in the cobalt compound layer. It has been found that the effect of slowing the rate at which the cobalt compound dissolves and precipitates in the electrolytic solution cannot be obtained sufficiently. Moreover, when there is too much the addition amount, the amount of nickel hydroxide used as the active material in a nickel electrode will become relatively small, and discharge capacity will reduce. For this reason, it is desirable that the addition amount of the niobium compound, titanium compound, tungsten compound, and molybdenum compound is 2 mass% (2 wt%) or more with respect to the mass of the cobalt compound.
[0012]
As the niobium compound, NaNbO Three , LiNbO Three , KNbO Three , Nb 2 O Five XH 2 It is preferable to select from O or the like. Moreover, as a titanium compound, Na 2 Ti Three O 7 , Li 2 TiO Three , K 2 TiO Three It is preferable to select from the above or the like. In addition, as a tungsten compound, WO 2 , WO Three , Na 2 WO Four , Li 2 WO 2 , K 2 WO Four It is preferable to select from the above or the like. Furthermore, as a molybdenum compound, MoO Three ・ H 2 O, MoO Three ・ 2H 2 O, Na 2 MoO Four ・ 2H 2 O, Li 6 Mo 7 O twenty four ・ 12H 2 O, K 2 MoO Four It is preferable to select from the above or the like.
[0013]
Then, an active material filling step of filling the active material mainly composed of nickel hydroxide into the pores of the porous sintered substrate, and the porous sintered substrate filled with the active material into an aqueous solution containing a cobalt salt The cobalt salt holding step for holding the cobalt salt on the surface of the active material layer filled by immersion and the porous sintered substrate holding the cobalt salt are selected from niobium compounds, titanium compounds, tungsten compounds, and molybdenum compounds. And an alkaline immersion step of immersing in an alkaline aqueous solution containing at least one compound, a niobium compound, a titanium compound, and tungsten in the cobalt compound layer covering the surface of the active material layer mainly composed of nickel hydroxide. It is possible to easily and easily obtain a nickel electrode to which at least one compound selected from a compound and a molybdenum compound is added. That.
[0014]
In this case, in the alkali dipping step, the porous sintered substrate holding the cobalt salt is dipped in an aqueous alkaline solution containing at least one compound selected from niobium compounds, titanium compounds, tungsten compounds, and molybdenum compounds, The cobalt salt held on the surface of the active material is converted into cobalt hydroxide, and at least one compound selected from a niobium compound, a titanium compound, a tungsten compound, and a molybdenum compound is converted into the converted cobalt hydroxide layer. What is necessary is just to make it precipitate. In the active material filling step, the porous sintered substrate is immersed in an aqueous solution containing a nickel salt and a cobalt salt, and then immersed in an alkaline solution to porously sinter the active material mainly composed of nickel hydroxide. The operation of filling the pores of the substrate may be repeated a predetermined number of times.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention.
1. Fabrication of sintered substrate
First, a thickening agent such as carboxymethyl cellulose and water were kneaded with nickel powder to prepare a slurry, and this slurry was applied to a conductive core made of a punching metal. Thereafter, the conductive core coated with the slurry was sintered in a reducing atmosphere to prepare a porous nickel sintered substrate having a porosity of about 85%.
[0016]
2. Fabrication of sintered nickel electrodes
The resulting porous nickel sintered substrate was then mixed with an aqueous solution of nickel nitrate and cobalt nitrate having a specific gravity of 1.75 (prepared so that the atomic ratio of nickel and cobalt is Ni: Co = 10: 1). The nickel salt and cobalt salt were held in the pores of the porous nickel sintered substrate. Thereafter, this porous nickel sintered substrate was immersed in a 25 wt% aqueous sodium hydroxide (NaOH) solution to convert the nickel salt and cobalt salt into nickel hydroxide and cobalt hydroxide, respectively. Then, after sufficiently washing with water to remove the alkaline solution, drying was performed.
Such a series of active material filling operations is repeated 6 times to obtain an active material filled electrode plate in which a predetermined amount of an active material mainly composed of nickel hydroxide is filled in the pores of the porous sintered substrate, This was a nickel electrode x.
[0017]
Next, the obtained nickel electrode x is immersed in a cobalt nitrate aqueous solution having a concentration of 4 mol / l, and cobalt is formed on the surface of the active material layer mainly composed of nickel hydroxide filled in the pores of the porous nickel sintered substrate. Salt was retained. In this case, if the amount of cobalt salt held is too small, the effect of improving the conductivity cannot be exhibited. In addition, when the amount of cobalt salt held is too large, the amount of active material is relatively reduced. For this reason, it is necessary to adjust the immersion time in the cobalt nitrate aqueous solution so that the amount of cobalt salt retained is 0.5 wt% to 5.0 wt% with respect to nickel hydroxide as an active material.
[0018]
Next, the porous nickel sintered substrate having the cobalt salt held on the surface of the active material layer as described above was immersed in an aqueous solution of sodium hydroxide (NaOH). Thereby, the cobalt salt held on the surface of the active material layer is converted into cobalt hydroxide having excellent conductivity. The electrode plate thus obtained was designated as a nickel electrode y.
[0019]
On the other hand, NaNbO Three A sodium hydroxide (NaOH) aqueous solution in which was dissolved was prepared, and a porous nickel sintered substrate holding a cobalt salt on the surface of the active material layer was immersed in this sodium hydroxide (NaOH) aqueous solution. As a result, the cobalt salt held on the surface of the active material layer is converted to cobalt hydroxide, and niobium compounds are uniformly scattered in the cobalt hydroxide layer. In this case, the niobium compound concentration and the immersion time were adjusted so that the amount added was predetermined with respect to the mass of cobalt hydroxide formed on the surface of the active material layer.
[0020]
Here, the electrode plate prepared so that the addition amount of the niobium compound is 1 wt% with respect to the mass of the cobalt hydroxide formed on the surface of the active material layer, and cut to a predetermined size is the nickel electrode a It was. Similarly, an electrode plate prepared to be 2 wt% is a nickel electrode b, an electrode plate prepared to be 5 wt% is a nickel electrode c, and an electrode plate prepared to be 10 wt% is a nickel electrode d. The electrode plate prepared so as to be 20 wt% was a nickel electrode e, the electrode plate prepared so as to be 30 wt% was a nickel electrode f, and the electrode plate prepared so as to be 40 wt% was a nickel electrode g. In this case, the niobium compound dissolved in sodium hydroxide is NaNbO. Three , LiNbO Three , KNbO Three , Nb 2 O Five XH 2 It is preferable to select from O or the like.
[0021]
2. Production of hydrogen storage alloy electrodes
Misch metal (Mm), nickel (Ni: purity 99.9%), cobalt (Co), aluminum (Al), and manganese (Mn) are mixed at a predetermined molar ratio, and this mixture is mixed with argon gas. The alloy was melted by induction heating in a high-frequency induction furnace in an atmosphere. The molten alloy is poured into a mold by a known method, cooled, and the composition formula is MmNi. a Co b Mn c Al d An ingot of a hydrogen storage alloy represented by This hydrogen storage alloy ingot was pulverized by a mechanical pulverization method until the average particle size became about 60 μm to obtain a hydrogen storage alloy powder. Next, 20 parts by mass of an aqueous solution of 5 wt% polyethylene oxide (PEO) as a binder was mixed with 100 parts by mass of the obtained hydrogen storage alloy powder to prepare a hydrogen storage alloy paste. This hydrogen storage alloy paste was applied to both sides of a core made of punching metal, dried at room temperature, rolled to a predetermined thickness, and cut to a predetermined size to produce a hydrogen storage alloy electrode.
[0022]
3. Preparation of nickel-hydrogen storage battery
Using the sintered nickel electrodes a, b, c, d, e, f, g, x, y and the hydrogen storage alloy negative electrode prepared as described above, a separator made of a polypropylene nonwoven fabric is interposed therebetween, These were wound in a spiral shape to produce each electrode group. Next, after each electrode group is inserted into the outer can, the negative electrode lead extending from the negative electrode of each electrode group is connected to the outer can and the positive electrode lead extending from the positive electrode is connected to the positive electrode lid provided on the sealing body did. Thereafter, an electrolytic solution (for example, 30 wt% potassium hydroxide aqueous solution) is injected into the outer can, and the opening of the outer can is sealed with a sealing body, so that each nickel-hydrogen storage battery having a nominal capacity of 1000 mAh is obtained. Produced.
[0023]
Here, a battery using the sintered nickel electrode a is referred to as a battery A, a battery using the sintered nickel electrode b is referred to as a battery B, a battery using the sintered nickel electrode c is referred to as a battery C, and sintered. A battery using a nickel electrode d is a battery D, a battery E is a battery using a sintered nickel electrode e, a battery F is a battery using a sintered nickel electrode f, and a sintered nickel electrode g is The battery G was used. Further, a battery X using a sintered nickel electrode x was designated as a battery X, and a battery Y using a sintered nickel electrode y was designated as a battery Y.
[0024]
4). Battery test
(1) Measurement of discharge capacity
Then, using the batteries A to G, X, and Y manufactured as described above, the batteries A to G, X, and Y are charged for 16 hours with a charging current of 100 mA at a temperature condition of 25 ° C. When the discharge current of 1000 mA is discharged until the battery voltage reaches 1.0 V, and the initial discharge capacity (mAh) of each of the batteries A to G, X, and Y is obtained from the discharge time, the following Table 1 It became a result.
[0025]
(2) Measurement of high-temperature cycle life
Further, using the batteries A to G, X, and Y manufactured as described above, the batteries A to G, X, and Y were charged for 2 hours at a charging current of 500 mA in a high temperature atmosphere at 60 ° C. Thereafter, a charge / discharge cycle test was repeated with a cycle of discharging at a discharge current of 500 mA until the battery voltage reached 1.0 V. When the number of cycles when the discharge capacity after each cycle reached 80% of the initial discharge capacity at 60 ° C. was determined as the high temperature cycle life, the results shown in Table 1 below were obtained.
[0026]
[Table 1]
As is clear from the results in Table 1 above, the battery Y using the nickel electrode y in which the cobalt compound layer is formed on the surface of the active material mainly composed of nickel hydroxide, and the surface of the active material mainly composed of nickel hydroxide. In comparison with the battery X using the nickel electrode x in which no cobalt compound layer was formed, it can be seen that the battery Y has a larger initial discharge capacity. This is because when a cobalt compound layer is formed on the surface of an active material mainly composed of nickel hydroxide, the cobalt compound layer has excellent conductivity, so the conductivity of the nickel electrode is improved and the utilization rate of the active material is improved. This is because. In this case, if the amount of cobalt compound is less than 0.5 wt% with respect to nickel hydroxide as an active material, the effect of improving conductivity cannot be exhibited. On the contrary, when the amount of cobalt compound is more than 5.0 wt% with respect to nickel hydroxide as an active material, the amount of active material is relatively decreased. For this reason, it is desirable to adjust the amount of cobalt compound so that it may become 0.5 wt%-5.0 wt% with respect to the nickel hydroxide used as an active material.
[0028]
Further, when batteries A to G using nickel electrodes a to g with a niobium compound added to a cobalt compound layer and a battery Y using a nickel electrode y with no niobium compound added to a cobalt compound layer are compared, cobalt It can be seen that the addition of a niobium compound to the compound layer improves the high-temperature cycle life. This is because when a niobium compound is added to the cobalt compound layer, the rate at which the cobalt compound dissolves and deposits in the electrolyte during discharge in a high-temperature atmosphere can be delayed, and a good conductive network can be maintained. It is thought that it became.
[0029]
In this case, when the amount of niobium compound added to the cobalt compound layer is as low as 1 wt% as in battery A, the effect of improving the high-temperature cycle life, that is, the cobalt compound is dissolved and precipitated in the electrolytic solution. It can be seen that the effect of slowing down the speed cannot be demonstrated. From this, it can be said that the addition amount of the niobium compound added to the cobalt compound layer is desirably 2 wt% or more with respect to the cobalt compound amount in the cobalt compound amount. Further, as in battery G, even when the amount of niobium compound added to the cobalt compound layer becomes 40 wt%, the effect of improving the high-temperature cycle life cannot be exhibited any more, and conversely, the relatively active material When the amount of nickel hydroxide is reduced, the initial discharge capacity is reduced. For this reason, the niobium compound (Nb) added to the cobalt layer 2 O Five It can be said that it is desirable that the addition amount of) be 30 wt% or less with respect to the cobalt amount.
[0030]
5). Study of additive compounds
In the above-described example, the example in which the niobium compound is added to the cobalt layer has been described, but the case where a titanium compound, a tungsten compound, and a molybdenum compound are added to the cobalt layer was also examined.
[0031]
(1) About titanium compounds
Na 2 Ti Three O 7 A sodium hydroxide (NaOH) aqueous solution in which was dissolved was prepared, and a porous nickel sintered substrate holding a cobalt salt on the surface of the active material layer was immersed in this sodium hydroxide (NaOH) aqueous solution. As a result, the cobalt salt held on the surface of the active material layer is converted to cobalt hydroxide, and the titanium compound is uniformly scattered in the cobalt hydroxide layer.
[0032]
In this case, the concentration of the titanium compound and the immersion time in the alkaline solution were adjusted so that the amount added was predetermined with respect to the mass of cobalt hydroxide formed on the surface of the active material layer. Here, the electrode plate prepared so that the addition amount of the titanium compound is 1 wt% with respect to the mass of cobalt hydroxide formed on the surface of the active material layer, and the electrode plate cut to a predetermined size is the nickel electrode h It was. Similarly, the electrode plate prepared to be 2 wt% was a nickel electrode i, and the electrode plate prepared to be 5 wt% was a nickel electrode j. In addition, as a titanium compound dissolved in sodium hydroxide, Na 2 Ti Three O 7 , Li 2 TiO Three , K 2 TiO Three It is preferable to select from the above or the like.
[0033]
Using the sintered nickel electrodes h, i, j produced as described above and the hydrogen storage alloy negative electrode, a separator made of a nonwoven fabric made of polypropylene is interposed between them, and these are wound in a spiral shape to each of the electrode groups. Produced. Next, after each electrode group is inserted into the outer can, the negative electrode lead extending from the negative electrode of each electrode group is connected to the outer can and the positive electrode lead extending from the positive electrode is connected to the positive electrode lid provided on the sealing body did. Thereafter, an electrolytic solution (for example, 30% by mass potassium hydroxide aqueous solution) is injected into the outer can, and the opening of the outer can is sealed with a sealing body, and the nickel-hydrogen storage battery H having a nominal capacity of 1000 mAh. , I, J were prepared. The battery using the sintered nickel electrode h was designated as battery H, the battery using the sintered nickel electrode i was designated as battery I, and the battery using the sintered nickel electrode j was designated as battery J.
[0034]
Next, using each of the batteries H, I, and J manufactured as described above, the batteries H, I, and J were charged at a temperature of 25 ° C. with a charging current of 100 mA for 16 hours, and then discharged with 1000 mA. When the battery was discharged with current until the battery voltage reached 1.0 V and the initial discharge capacities (mAh) of the batteries H, I, and J were determined from the discharge time, the results shown in Table 2 below were obtained. In addition, using each of the batteries H, I, and J manufactured as described above, the batteries H, I, and J were charged for 2 hours at a charging current of 500 mA in a high-temperature atmosphere at 60 ° C. The charge / discharge cycle test was repeated, in which the cycle of discharging until the battery voltage reached 1.0 V with the discharge current was one cycle. When the number of cycles when the discharge capacity after each cycle reached 80% of the initial discharge capacity at 60 ° C. was determined as the high temperature cycle life, the results shown in Table 2 below were obtained. Table 2 below also shows the results of the battery Y described above for comparison.
[0035]
[Table 2]
As is clear from the results in Table 2 above, batteries H, I, J using nickel electrodes h, i, j with a titanium compound added to the cobalt compound layer, and nickel without adding a titanium compound to the cobalt compound layer Comparing with the battery Y using the electrode y, it can be seen that the high temperature cycle life is improved when the titanium compound is added to the cobalt compound layer. This is because when a titanium compound is added to the cobalt compound layer, the rate at which the cobalt compound dissolves and deposits in the electrolyte during discharge in a high-temperature atmosphere can be delayed, and a good conductive network can be maintained. It is thought that it became.
[0037]
In this case, when the amount of titanium compound added to the cobalt compound layer is as low as 1 wt% as in battery H, the effect of improving the high-temperature cycle life, that is, the cobalt compound is dissolved and precipitated in the electrolytic solution. It can be seen that the effect of slowing down the speed cannot be demonstrated. From this, it can be said that the addition amount of the titanium compound added to the cobalt compound layer is desirably 2 wt% or more with respect to the cobalt compound amount in the cobalt compound layer. As for the upper limit value, it is desirable to add so that the amount of titanium compound added is 30 et% or less, as in the case of the niobium compound described above.
[0038]
(2) About tungsten compounds
Na 2 WO Four A sodium hydroxide (NaOH) aqueous solution in which was dissolved was prepared, and a porous nickel sintered substrate holding a cobalt salt on the surface of the active material layer was immersed in this sodium hydroxide (NaOH) aqueous solution. As a result, the cobalt salt held on the surface of the active material layer is converted to cobalt hydroxide, and tungsten compounds are evenly scattered in the cobalt hydroxide layer.
[0039]
In this case, the concentration of the tungsten compound and the immersion time in the alkaline solution were adjusted so that the amount added was predetermined with respect to the mass of cobalt hydroxide formed on the surface of the active material layer. Here, the electrode plate prepared so that the addition amount of the tungsten compound is 1 wt% with respect to the mass of the cobalt hydroxide formed on the surface of the active material layer, and cut to a predetermined size is the nickel electrode k. It was. Similarly, the electrode plate prepared to be 2 wt% was a nickel electrode l, and the electrode plate prepared to be 5 wt% was a nickel electrode m. As a tungsten compound dissolved in sodium hydroxide, WO 2 , WO Three , Na 2 WO Four , Li 2 WO 2 ,, K 2 WO Four It is preferable to select from the above or the like.
[0040]
Using the sintered nickel electrodes k, l, and m prepared as described above and the hydrogen storage alloy negative electrode, a separator made of a nonwoven fabric made of polypropylene is interposed between them, and these are wound in a spiral shape to each of the electrode groups. Produced. Next, after each electrode group is inserted into the outer can, the negative electrode lead extending from the negative electrode of each electrode group is connected to the outer can and the positive electrode lead extending from the positive electrode is connected to the positive electrode lid provided on the sealing body did. Thereafter, an electrolytic solution (for example, 30% by mass potassium hydroxide aqueous solution) is injected into the outer can, and the opening of the outer can is sealed with a sealing body, and the nickel-hydrogen storage battery K having a nominal capacity of 1000 mAh. , L, and M were prepared. A battery using the sintered nickel electrode k was referred to as a battery K, a battery using the sintered nickel electrode l was referred to as a battery L, and a battery using the sintered nickel electrode m was referred to as a battery M.
[0041]
Next, using each of the batteries K, L, and M manufactured as described above, the batteries K, L, and M were charged for 16 hours with a charging current of 100 mA under a temperature condition of 25 ° C., and then discharged with 1000 mA. When the battery was discharged with current until the battery voltage reached 1.0 V, and the initial discharge capacities (mAh) of the batteries K, L, and M were determined from the discharge time, the results shown in Table 3 below were obtained. In addition, using each of the batteries K, L, and M manufactured as described above, the batteries K, L, and M were charged for 2 hours at a charging current of 500 mA in a high-temperature atmosphere at 60 ° C. A charge / discharge cycle test was repeated, in which the cycle of discharging until the battery voltage reached 1.0 V with the discharge current was one cycle. When the number of cycles when the discharge capacity after each cycle reached 80% of the initial discharge capacity at 60 ° C. was determined as the high temperature cycle life, the results shown in Table 3 below were obtained. Table 3 below also shows the results of the battery Y described above for comparison.
[0042]
[Table 3]
As is clear from the results in Table 3 above, batteries K, L, and M using nickel electrodes k, l, and m having a tungsten compound added to the cobalt compound layer, and nickel having no tungsten compound added to the cobalt compound layer Comparing with the battery Y using the electrode y, it can be seen that the high temperature cycle life is improved by adding a tungsten compound to the cobalt compound layer. This is because when a tungsten compound is added to the cobalt compound layer, the rate at which the cobalt compound dissolves and deposits in the electrolyte during discharge in a high-temperature atmosphere can be delayed, and a good conductive network can be maintained. It is thought that it became.
[0044]
In this case, if the amount of tungsten compound added to the cobalt compound layer is as small as 1 wt% as in battery K, the effect of improving the high-temperature cycle life, that is, the cobalt compound is dissolved and precipitated in the electrolytic solution. It can be seen that the effect of slowing down the speed cannot be demonstrated. From this, it can be said that the addition amount of the tungsten compound added to the cobalt compound layer is desirably 2 wt% or more with respect to the cobalt compound amount in the cobalt compound layer. As for the upper limit, it is desirable to add the tungsten compound so that the added amount of the tungsten compound is 30 wt% or less, as in the case of the niobium compound described above.
[0045]
(3) About molybdenum compounds
Na 2 MoO Four ・ 2H 2 A sodium hydroxide (NaOH) aqueous solution in which O was dissolved was prepared, and a porous nickel sintered substrate in which a cobalt salt was held on the surface of the active material layer was immersed in the sodium hydroxide (NaOH) aqueous solution. As a result, the cobalt salt held on the surface of the active material layer is converted into cobalt hydroxide, and the molybdenum compound is uniformly scattered in the cobalt hydroxide layer.
[0046]
In this case, the concentration of the molybdenum compound and the immersion time in the alkaline solution were adjusted so that the amount added was predetermined with respect to the mass of cobalt hydroxide formed on the surface of the active material layer. Here, the electrode plate prepared so that the addition amount of the molybdenum compound is 1 wt% with respect to the mass of the cobalt hydroxide formed on the surface of the active material layer, and the electrode plate cut to a predetermined size is the nickel electrode n. It was. Similarly, an electrode plate prepared to be 2 wt% was a nickel electrode o, and an electrode plate prepared to be 5 wt% was a nickel electrode p. As the molybdenum compound dissolved in sodium hydroxide, MoO Three ・ H 2 O, MoO Three ・ 2H 2 O, Na 2 MoO Four ・ 2H 2 O, Li 6 Mo 7 O twenty four ・ 12H 2 O, K 2 MoO Four It is preferable to select from the above or the like.
[0047]
Using the sintered nickel electrodes n, o, p prepared as described above and the hydrogen storage alloy negative electrode, a separator made of a nonwoven fabric made of polypropylene is interposed between them, and these are wound in a spiral shape to each of the electrode groups. Produced. Next, after each electrode group is inserted into the outer can, the negative electrode lead extending from the negative electrode of each electrode group is connected to the outer can and the positive electrode lead extending from the positive electrode is connected to the positive electrode lid provided on the sealing body did. Thereafter, an electrolytic solution (for example, a 30% by mass potassium hydroxide aqueous solution) is injected into the outer can, and the opening of the outer can is sealed with a sealing body, and the nickel-hydrogen storage battery N having a nominal capacity of 1000 mAh. , O, and P were prepared. The battery using the sintered nickel electrode n was designated as battery N, the battery using the sintered nickel electrode o was designated as battery O, and the battery using the sintered nickel electrode p was designated as battery P.
[0048]
Next, using each of the batteries N, O, and P prepared as described above, the batteries N, O, and P were charged for 16 hours with a charging current of 100 mA under a temperature condition of 25 ° C., and then discharged with 1000 mA. When the battery was discharged with current until the battery voltage reached 1.0 V and the initial discharge capacities (mAh) of the batteries N, O, and P were determined from the discharge time, the results shown in Table 4 below were obtained. In addition, using each of the batteries N, O, and P manufactured as described above, the batteries N, O, and P were charged for 2 hours at a charging current of 500 mA in a high-temperature atmosphere at 60 ° C. A charge / discharge cycle test was repeated, in which the cycle of discharging until the battery voltage reached 1.0 V with the discharge current was one cycle. When the number of cycles when the discharge capacity after each cycle reached 80% of the initial discharge capacity at 60 ° C. was determined as the high temperature cycle life, the results shown in Table 4 below were obtained. Table 4 below also shows the results of the battery Y described above for comparison.
[0049]
[Table 4]
As is clear from the results in Table 4 above, batteries N, O, and P using nickel electrodes n, o, and p with a molybdenum compound added to the cobalt compound layer, and nickel with no molybdenum compound added to the cobalt compound layer Comparing with the battery Y using the electrode y, it can be seen that the high temperature cycle life is improved when the molybdenum compound is added to the cobalt compound layer. This is because when a molybdenum compound is added to the cobalt compound layer, the rate at which the cobalt compound dissolves and deposits in the electrolyte during discharge in a high-temperature atmosphere can be delayed, and a good conductive network can be maintained. It is thought that it became.
[0051]
In this case, if the amount of molybdenum compound added to the cobalt compound layer is as low as 1 wt% as in battery N, the effect of improving the high-temperature cycle life, that is, the cobalt compound is dissolved and precipitated in the electrolytic solution. It can be seen that the effect of slowing down the speed cannot be demonstrated. From this, it can be said that the addition amount of the molybdenum compound added to the cobalt compound layer is desirably 2 wt% or more with respect to the cobalt compound amount in the cobalt compound layer. As for the upper limit, it is desirable to add the molybdenum compound so that the addition amount of the molybdenum compound is 30 wt% or less, as in the case of the niobium compound described above.
[0052]
【The invention's effect】
As described above, in the present invention, a cobalt compound layer is formed on the surface of an active material layer mainly composed of nickel hydroxide, and the cobalt compound layer is selected from niobium compounds, titanium compounds, tungsten compounds, and molybdenum compounds. At least one compound added uniformly. For this reason, the speed | rate which the cobalt compound which coat | covers the surface of an active material layer melt | dissolves in electrolyte solution, and can precipitate can be delayed. This makes it possible to improve the conductive network by changing the cobalt compound layer to a denser structure.
[0053]
When at least one element selected from the group consisting of yttrium, ytterbium, calcium, aluminum, erbium, gadolinium, thulium, lutetium, and zinc or a compound thereof is added to the nickel electrode, a high-temperature atmosphere The lower charge / discharge characteristics are further improved. In particular, when yttrium or a compound thereof is added, the effect is large, so that the charge / discharge cycle characteristics in a high-temperature atmosphere are remarkably improved. 2 O Three It is more preferable to use.
Claims (4)
前記水酸化ニッケルを主体とする活物質層の表面にコバルト化合物層を備えるとともに、
前記コバルト化合物層中にニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物が添加されていることを特徴とするアルカリ蓄電池。An alkaline storage battery comprising a nickel electrode filled with an active material mainly composed of nickel hydroxide on a porous sintered substrate,
A cobalt compound layer is provided on the surface of the active material layer mainly composed of nickel hydroxide,
An alkaline storage battery, wherein at least one compound selected from a niobium compound, a titanium compound, a tungsten compound, and a molybdenum compound is added to the cobalt compound layer.
前記多孔性焼結基板の細孔中に水酸化ニッケルを主体とする活物質を充填する活物質充填工程と、
前記活物質が充填された多孔性焼結基板をコバルト塩とを含有する水溶液に浸漬して前記充填された活物質層の表面にコバルト塩を保持させるコバルト塩保持工程と、
前記コバルト塩が保持された多孔性焼結基板をニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物を含有するアルカリ水溶液に浸漬するアルカリ浸漬工程とを備え、
前記多孔性焼結基板の細孔中に充填された水酸化ニッケルを主体とする活物質層の表面にニオブ化合物、チタン化合物、タングステン化合物、モリブデン化合物から選択される少なくとも１種の化合物を含有するコバルト化合物層を形成するようにしたことを特徴とするアルカリ蓄電池の製造方法。A method for producing an alkaline storage battery comprising a nickel electrode formed by filling a porous sintered substrate with an active material mainly composed of nickel hydroxide,
An active material filling step of filling an active material mainly composed of nickel hydroxide into the pores of the porous sintered substrate;
A cobalt salt holding step in which the porous sintered substrate filled with the active material is immersed in an aqueous solution containing a cobalt salt to hold the cobalt salt on the surface of the filled active material layer;
An alkaline immersion step of immersing the porous sintered substrate holding the cobalt salt in an aqueous alkaline solution containing at least one compound selected from a niobium compound, a titanium compound, a tungsten compound, and a molybdenum compound;
The surface of the active material layer mainly composed of nickel hydroxide filled in the pores of the porous sintered substrate contains at least one compound selected from niobium compounds, titanium compounds, tungsten compounds, and molybdenum compounds. A method for producing an alkaline storage battery, wherein a cobalt compound layer is formed.
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