JP4932997B2 - Hydrogen storage alloy electrode and alkaline storage battery using the same - Google Patents
Hydrogen storage alloy electrode and alkaline storage battery using the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、ニッケル−水素蓄電池などの負極に用いられる水素吸蔵合金電極、およびこれを用いたアルカリ蓄電池に関する。
【０００２】
【従来の技術】
水素吸蔵合金を用いて実用化されたニッケル−水素蓄電池は、低環境負荷および高エネルギー密度などの特徴を有する電池として、各種のコードレス機器および電子機器などの電源に広く使用されるようになってきた。また、電気自動車などの動力電源に用いるために大電流放電特性を向上させて高出力を得ること、およびバックアップ用電源に用いるために長期信頼性を向上させることが強く期待されている。
このようなニッケル−水素蓄電池の負極材料としては、一般にＣａＣｕ5型の結晶構造を有するＭｍＮｉ5（Ｍｍは希土類元素の混合物）系合金が、Ｎｉの一部をＣｏ、ＭｎおよびＡｌなどの金属で置換して用いられている。そして、この合金は、鋳型に流し込む鋳造法、回転ディスク上に注湯し薄体状の合金を作製するロール急冷法、および不活性ガスを噴霧して球状合金を作製するアトマイズ法などが知られている。
【０００３】
鋳造法およびロール急冷法においては、合金粉末を得るために機械的に粉砕工程を行なう必要があり、一方、アトマイズ法においては、微細な球状の合金粉末が得られるため、粉砕工程を必要としない。
また、粉砕により得られる合金粉末は、充放電サイクルに伴なって微粉化してしまうが、アトマイズ法により得られる合金粉末は、急冷により作製されるため均一な合金組織を有しており、微粉化が抑制される。
さらに、粉砕により得られる合金粉末に比べて、アトマイズ法により得られる合金粉末は、高密度で充填することが可能である（例えば特開平３−１１６６５５号公報）。
【０００４】
このような理由から、アトマイズ法により得られる合金粉末が主として用いられているが、この合金粉末は球状であるため比表面積が小さく、合金粉末粒子間の接触および合金粉末と集電体との接触が点接触になる。そのため、粉砕により得られる粉末に比べて集電性に劣るという問題がある。
これに対し、例えば、球状粒子からなる合金粉末と非球状粒子からなる合金粉末とを混合して得られる多孔質体集電体を用い、集電性を向上させる方法が提案されている（特開平１１−９７００２号公報）。また、粉砕により得られる合金粒子からなる層とアトマイズ法により得られる合金粒子からなる層を積層して得られる集電体を用い、集電性を向上させる方法も提案されている（特開平１１−２８３６１８号公報）。
すなわち、アトマイズ法により得られる球状合金粉末の集電性を向上させるために、粉砕により得られる非球状合金粉末が併用されているのである。
【０００５】
【発明が解決しようとする課題】
しかし、粉砕により得られる合金粉末は、アトマイズ法により得られる合金粉末に比べて、充放電サイクルに伴なって微粉化し易く、その粒径が１５μｍ程度にまで減少し、作製直後から集電体の集電性が次第に低下してしまう。また、前記微粉化によって新たに電解液と接触する合金粉末の表面積が増加するため、合金を構成する元素が溶出し、電解液をむやみに消費してしまう。そして、これらの結果として、得られる電池の内部抵抗が上昇し、放電容量およびサイクル寿命特性が低下してしまうという問題がある。
そこで、本発明は、アトマイズ法により得られる合金粉末および粉砕により得られる合金粉末からなる水素吸蔵合金電極であって、以上のような問題を有しない水素吸蔵合金電極およびこれを用いたアルカリ蓄電池を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、アトマイズ法もしくは遠心噴霧法により作製した球状またはそれに類似した形状の水素吸蔵合金粉末Ａと機械粉砕法により作製した不定形の水素吸蔵合金粉末Ｂとからなり、前記水素吸蔵合金粉末Ｂのみの表面が、ニッケルおよび／またはコバルトで被覆され、前記水素吸蔵合金粉末Ａと前記水素吸蔵合金粉末Ｂの重量比が、８０：２０〜９５：５であることを特徴とする水素吸蔵合金電極に関する。
【０００７】
また、前記水素吸蔵合金粉末Ａが９０μｍ以下の粒径および２０〜４０μｍの平均粒径を有し、前記水素吸蔵合金粉末Ｂが１０〜１５μｍの平均粒径を有するのが有効である。
さらに、本発明は、上記水素吸蔵合金電極からなる負極、金属酸化物からなる正極、およびアルカリ電解液を具備することを特徴とするアルカリ蓄電池にも関する。
【０００８】
【発明の実施の形態】
本発明は、アトマイズ法もしくは遠心噴霧法により作製した球状またはそれに類似する形状の水素吸蔵合金粉末Ａと機械粉砕法により作製した不定形の水素吸蔵合金粉末Ｂとからなり、少なくとも前記水素吸蔵合金粉末Ｂの表面に、ニッケルおよび／またはコバルトを有することを特徴とする水素吸蔵合金電極に関する。
すなわち、本発明によれば、アトマイズ法もしくは遠心噴霧法により作製された表面が平滑な球状（鶏卵状などの類似の形状を含む。）の水素吸蔵合金粉末Ａと、機械的粉砕法により作製された表面が比較的粗い不定形の水素吸蔵合金粉末Ｂとを併用することにより集電性を向上させ、さらに、前記水素吸蔵合金粉末Ｂの表面を特定の金属で被覆することによって構成元素の溶出を抑制することができる。なお、本発明においていう「被覆」とは、必ずしも均一な層を形成していることをいうのではなく、付着している状態なども含む。
【０００９】
ここで、水素吸蔵合金粉末の表面を被覆する金属としては、有効に合金粉末の表面に付着して被覆層を構成し、水素吸蔵合金を構成する元素がアルカリ電解液中に溶出するのを抑制するという機能を果たすものであれば特に制限はないが、なかでも、合金表面で触媒としても働くニッケルおよび／またはコバルトを用いるのが好ましい。
また、本発明においては、少なくとも粉砕により得られる水素吸蔵合金粉末Ｂの表面を金属で被覆すればよいが、アトマイズ法もしくは遠心噴霧法により得られる水素吸蔵合金粉末Ａの表面と前記水素吸蔵合金粉末Ｂの表面の両方を、ニッケルおよび／またはコバルトで被覆するのが有効である。
これは、アトマイズ法もしくは遠心噴霧法により得られる水素吸蔵合金粉末Ａからも、微量ではあるが構成元素が溶出する場合があるところ、前記水素吸蔵合金粉末Ｂと同様に金属を被覆して、かかる溶出を抑制することができるからである。
【００１０】
つぎに、本発明にかかる水素吸蔵合金電極においては、前記水素吸蔵合金粉末Ａが９０μｍ以下の粒径、および２０〜４０μｍの平均粒径を有するのが有効である。
これは、９０μｍを超える粒径を有する水素吸蔵合金粉末Ａが含まれると、この合金粉末Ａが充放電サイクルに伴って微粉化し易く、電解液を消費してサイクル寿命特性を低下させてしまうからである。また、平均粒径が２０μｍ未満であると、水素吸蔵合金粉末Ａの腐食反応が加速されてしまい、極端に小さな粒径を有する水素吸蔵合金粉末は水素吸蔵能が低く、電極容量が減少してしまうからである。また、平均粒径が４０μｍを超えると、合金粉末Ａの反応面積の減少により、充放電反応性が低下してしまうからである。
【００１１】
一方、前記水素吸蔵合金粉末Ｂが１０〜１５μｍの平均粒径を有するのが有効である。
粉砕により得られる水素吸蔵合金粉末の粒径は、通常、充放電サイクルによって１５μｍ程度にまで微粉化してしまうことが経験的に知られている。そこで、あらかじめそのような粒径にして用いれば、新たに電解液と接触する合金表面の面積が増加することを抑制し、余分な電解液の消費を防ぐことができるからである。
【００１２】
本発明の水素吸蔵合金電極中の前記水素吸蔵合金粉末Ａと前記水素吸蔵合金粉末Ｂの重量比は、８０：２０〜９５：５であることが有効である。すなわち、全水素吸蔵合金粉末の５〜２０重量％が、粉砕により得られる水素吸蔵合金粉末Ｂであるのが好ましい。
これは、水素吸蔵合金粉末Ｂの重量比が２０重量％を超えると、電極の充填性が低下して充分な特性が得られないからであり、５重量％未満の場合には合金間の集電性が不充分となって放電特性の向上が得られないからである。
ここで、本発明における水素吸蔵合金の組成としては、希土類元素、ニッケルおよびニッケル以外の遷移金属元素を含むものであるのが好ましい。
以下に、実施例を用いて本発明をより具体的に説明するが、本発明はこれらのみに限定されるものではない。
【００１３】
【実施例】
《実施例１》
本実施例においては、水素吸蔵合金粉末Ｂにのみ金属被覆を設けた。
（１）アトマイズ法による水素吸蔵合金粉末Ａの作製
まず、市販のＭｍ（ミッシュメタル）、Ｎｉ、Ｍｎ、ＡｌおよびＣｏを、所定の組成比になるように秤量し、不活性ガス雰囲気中で、高周波誘導加熱溶解炉により溶解して得られた溶湯を坩堝の下方から滴下させ、その溶湯に高圧のアルゴンガスを噴霧し、球状の合金粉末を得、９００℃に制御した電気炉内で１時間熱処理を行なった。
【００１４】
ここで、得られた合金粉末の組成を分析したところ、ＭｍＮｉ3.55Ｍｎ0.4Ａｌ0.3Ｃｏ0.75であり、合金組織は極めて均質であった。また、粉末粒子の形状を確認したころ、表面が平滑な球状であった。
さらに、上記合金粉末を粒径が９０μｍ以下となるように篩い分けすることにより、平均粒径が３０μｍである水素吸蔵合金粉末ａ１を得た。なお、平均粒径は、粒度分布の測定により確認した。
【００１５】
（２）粉砕による水素吸蔵合金粉末Ｂの作製
まず、市販のＭｍ（ミッシュメタル）、Ｎｉ、Ｍｎ、ＡｌおよびＣｏを、所定の組成比になるように秤量し、高周波誘導加熱溶解炉により溶解し、鋳型成形によりインゴットを作製した。このインゴットを１１００℃に制御した電気炉内に入れて１時間熱処理を行なった後、不活性ガス中で機械的に粉砕し合金粉末を得た。
ついで、上記合金粉末を平均粒径が１５μｍになるように篩い分け、ＭｍＮｉ3.55Ｍｎ0.4Ａｌ0.3Ｃｏ0.75の組成を有する水素吸蔵合金粉末ｂ１を得た。
【００１６】
（３）水素吸蔵合金粉末Ｂの被覆
さらに、上記水素吸蔵合金粉末ｂ１を酸で洗浄した後、８０℃に加温した３０ｇ／ｌの硫酸ニッケルと１０ｇ／ｌの酢酸ナトリウム混合液中に投入し、その溶液中に１５ｇ／ｌの次亜リン酸ナトリウムを添加し２０分間攪拌した。
その後、水洗および乾燥を行ない、水素吸蔵合金粉末ｂ１の表面にＮｉ被覆を施した水素吸蔵合金粉末ｂ１’を得た。
この水素吸蔵合金粉末ｂ１’のニッケル被覆量を確認したところ、２〜５重量％であった。
【００１７】
（４）電極の作製
以上のようにして得られた水素吸蔵合金粉末ａ１を９０重量部、水素吸蔵合金粉末ｂ１’を１０重量部、増粘材であるカルボキシメチルセルロースを０．１５重量部、導電材であるカーボンブラックを０．３重量部、結着剤であるスチレン−ブタジエン共重合体を０．８重量部、および分散媒である水を混合して合金ペーストを作製した。
このペーストを、厚さ６０μｍ、パンチング孔径１ｍｍ、開孔率４２％のニッケルめっきを施した鉄製パンチングメタルの両面に塗布し、乾燥および加圧を行なった。さらに、その表面にフッ素樹脂粉末をコーティングし、幅３５ｍｍ、長さ１５０ｍｍ、厚さ０．４ｍｍ、容量２２００ｍＡｈの水素吸蔵合金電極１を作製した。
【００１８】
（５）電池の作製
上記水素吸蔵合金電極１、公知の焼結式のニッケル正極およびナイロン不織布セパレータを積層して渦巻き状に巻回して極板群を得、金属ケースに挿入した。その後、金属ケースに比重１．３０のＫＯＨ水溶液に４０ｇ／ｌの水酸化リチウムを溶解した電解液を所定量注入し、ケースを封口して４／５Ａサイズで電池容量１５００ｍＡｈの密閉型電池１を作製した。
【００１９】
《参考例１》
本参考例においては、水素吸蔵合金粉末Ａおよび水素吸蔵合金粉末Ｂの両方に金属被覆を設けた。
（１）水素吸蔵合金粉末Ａの被覆
実施例１の（１）と同様にして得た平均粒径が３０μｍの水素吸蔵合金粉末ａ１を、酸で洗浄した後、８０℃加温した８０℃における比重が１．３０のＫＯＨ水溶液中に浸漬して１時間攪拌した。この合金粉末を水洗した後、さらに８０℃に加温した３０ｇ／ｌの硫酸ニッケルと１０ｇ／ｌの酢酸ナトリウム混合液中に投入し、その溶液中に１５ｇ／ｌの次亜リン酸ナトリウムを添加して２０分間攪拌した。
その後、水洗および乾燥を行ない、水素吸蔵合金粉末ａ１の表面にＮｉ被覆を施した水素吸蔵合金粉末ａ１'を得た。
【００２０】
（２）電極および電池の作製
ついで、水素吸蔵合金粉末ａ１'と、実施例１の（３）と同様にして作製した水素吸蔵合金粉末ｂ１'とを用い、実施例１と同様にして水素吸蔵合金電極２を作製した。さらに、実施例１と同様にして密閉型参考電池１を作製した。
【００２１】
《比較例１および２》
（１）金属被覆を有しない水素吸蔵合金粉末Ａのみを用いた電極および電池
まず、実施例１と同様の方法で球状の水素吸蔵合金粉末ａ１を作製した。
この水素吸蔵合金粉末ａ１を１００重量部、増粘材であるカルボキシメチルセルロースを０．１５重量部、導電材であるカーボンブラックを０．３重量部、結着剤であるスチレン−ブタジエン共重合体を０．８重量部および分散媒である水とを混合して合金ペーストを作製した。
この合金ペーストを用い、実施例１と同様にして比較用の密閉型電池（比較電池）１を作製した。
【００２２】
（２）金属被覆を有しない水素吸蔵合金粉末Ａおよび水素吸蔵合金粉末Ｂを用いた電極および電池
また、実施例１と同様の方法で作製した水素吸蔵合金粉末ａ１を９０重量部と、平均粒径が１５μｍになるように機械的に粉砕した水素吸蔵合金粉末ｂ１を１０重量部混合して合金粉末混合物を得た。
この合金混合物を１００重量部、増粘材であるカルボキシメチルセルロースを０．１５重量部、導電材であるカーボンブラックを０．３重量部、結着剤であるスチレン−ブタジエン共重合体を０．８重量部および分散媒である水を混合して合金ペーストを作製した。この合金ペーストを用い、実施例１と同様にして比較用の密閉型電池（比較電池）２を作製した。
【００２３】
［評価］
以上の方法により作製した電池１および参考電池１、ならびに比較電池１および２について、初期放電特性および寿命特性を評価した。
（１）初期放電特性
初期放電特性を評価するために、電池を２０℃、電流値１．５Ａで理論容量の１２０％まで充電し、０℃、電流値３．０Ａで電池電圧が１．０Ｖに低下するまでの容量（初期放電容量）を測定した。
比較電池１の初期放電容量を１００として、それぞれの電池の測定値を指数で示した。この結果を表１に示した。
【００２４】
（２）寿命特性
寿命特性を評価するために、電池を２０℃、電流値１．５Ａで理論容量の１２０％まで充電し、電流値１．５Ａで電池電圧１．０Ｖまで放電するサイクルを繰り返した。
放電容量が初期放電容量の８０％まで劣化した時のサイクル数を求め、比較電池１のサイクル数を１００とし、それぞれの電池のサイクル数を指数で示した。この結果を表１に示した。なお、電池を実際に使用することを考慮すると、寿命特性は９０以上必要であり、放電特性は１１０以上であればよい。
【００２５】
【表１】
表１から、実施例１および参考例１と比較例１の結果から明らかなように、粉砕により得られる水素吸蔵合金粉末Ｂを混合することにより、放電特性が向上することがわかる。これは、機械粉砕により得られる合金粉末の表面をＮｉ被覆することにより、反応表面積の増加、および芯材と合金粉末との間の集電性が得られたためと考えられる。
また、実施例１と比較例２の結果から明らかなように、機械粉砕した合金表面をＮｉ被覆することにより実用上問題のない寿命特性が確保できることがわかり、さらに参考例１と比較例２の結果から、アトマイズ法により得られる合金粉末の表面をＮｉ被覆することによりさらに寿命特性が向上することがわかる。これは、合金表面をＮｉ被覆することにより合金構成元素と電解液との腐食反応が抑制され電解液の消費を防ぐことができたためと考えられる。
【００２７】
《実施例２〜７》
本実施例においては、アトマイズ法により得られる水素吸蔵合金粉末Ａの粒径が、得られる電池の特性に及ぼす影響を調べた。
水素吸蔵合金粉末Ａと混合する粉砕により得られる水素吸蔵合金粉末Ｂとしては、２０μｍの篩で分級し、その合金表面をＮｉで被覆したものを使用した。また、水素吸蔵合金粉末Ａと水素吸蔵合金粉末Ｂの混合比（重量）は、９０：１０とした。
そして、篩を用いて水素吸蔵合金粉末Ａを分級し、平均粒径が１５、２０、３０、４０、４５または６５μｍの水素吸蔵合金粉末Ａを用いた以外は、参考例１と同様にして本発明の密閉型電池２〜７を作製した。それぞれの電池の電池特性を表２に示した。
【００２８】
【表２】
表２より、水素吸蔵合金粉末Ａの平均粒径を小さくするにつれて、得られる電池の放電特性が向上し、逆に寿命特性が低下する傾向にあることが確認された。しかし、平均粒径が１５μｍの水素吸蔵合金粉末Ａを用いた場合、寿命特性の低下が見られた。これは、粒径を小さくすると合金粉末の比表面積が増加し、放電特性が向上するという効果がある一方、腐食される表面積が増加し、寿命特性が低下してしまったものと考えられる。
【００３０】
また、１５０μｍの篩で分級した平均粒径が６５μｍのものを用いた場合には、反応面積が少ないためにサイクル初期の放電容量は低下した。さらに１００〜１５０μｍ程度の粒径の場合は、充放電サイクルにより合金粉末が微粉化し易いため、サイクル数に伴なって放電容量は向上するが、同時に合金の腐食も進むため寿命特性の低下を招いたものと考えられる。
これらのことから、アトマイズ法により得られる水素吸蔵合金粉末Ａは、９０μｍ以下の粒径および２０〜４０μｍの平均粒径を有するのが好ましいことがわかる。
【００３１】
《実施例８〜１２》
本実施例においては、粉砕により得られる水素吸蔵合金粉末Ｂの粒径が電池特性に及ぼす影響を調べた。
アトマイズ法により作製した水素吸蔵合金粉末Ａとしては、９０μｍの篩で分級した平均粒径が３０μｍのものを使用した。また、９０重量部の水素吸蔵合金粉末Ａと１０重量部の水素吸蔵合金粉末Ｂを混合した合金粉末混合物を用いた。
水素吸蔵合金粉末Ｂを種々の篩を用いて分級し、平均粒径が７、１０、１２、１５または２０μｍのものを用い、その合金表面をＮｉで被覆して用いた以外は、参考例１と同様にして本発明の密閉型電池８〜１２を作製した。
それぞれの電池の電池特性を表３に示した。
【００３２】
【表３】
表３より、粉砕により得られる水素吸蔵合金粉末Ｂの平均粒径が１０〜１５μｍの場合、良好な放電特性が得られ、寿命特性も実用上問題のないことがわかる。しかし、水素吸蔵合金粉末Ｂの平均粒径を７μｍ程度まで小さくした場合（実施例８）や、２０μｍ程度まで大きくした場合（実施例１２）には、良好な放電特性は得られるものの、水素吸蔵合金粉末Ｂの比表面積が増加し、結果としてアルカリ電解液による腐食が進行し寿命特性が低下したものと考えられる。
一方、実施例１２では、水素吸蔵合金粉末Ｂが充放電サイクルにより微粉化し、その結果として新たに生じたＮｉ被覆していない合金表面が腐食され、サイクル寿命特性が低下したものと考えられる。これらのことから、水素吸蔵合金粉末Ｂの平均粒径は、１０〜１５μｍであるのが好ましいことがわかる。
【００３４】
《実施例１３〜１５および参考例２》
本実施例および参考例においては、水素吸蔵合金電極中における、アトマイズ法により得られる水素吸蔵合金粉末Ａと粉砕により得られる水素吸蔵合金粉末Ｂとの重量比が電池特性に及ぼす影響を調べた。水素吸蔵合金粉末Ａと水素吸蔵合金粉末Ｂの重量比は、９５：５、９０：１０、８０：２０または７５：２５とした。
水素吸蔵合金粉末Ａとしては、９０μｍの篩で分級した平均粒径が３０μｍのものを使用し、水素吸蔵合金粉末Ｂとしては、２０μｍの篩で分級した平均粒径が１５μｍで、合金表面をＮｉで被覆したものを使用した。そのほかは、実施例１と同様にして密閉型電池１３〜１５および参考電池２を作製した。それぞれの電池の電池特性を表４に示した。
【００３５】
【表４】
表４より、全合金中において粉砕により得られる水素吸蔵合金粉末Ｂの比率を５〜２０重量％にした場合、良好な放電特性が得られ、寿命特性も実用上問題のないことがわかる。
しかし、２５重量％混合した場合、放電特性は良好であるが、水素吸蔵合金粉末Ｂの混合比率が高いために充放電サイクルに伴って合金の腐食が進行し、電解液を消費してしまうため、実用上必要である特性を確保することができなかったものと考えられる。
これらのことから、全水素吸蔵合金粉末中における水素吸蔵合金粉末Ｂのが入比は、５〜２０重量％であるのが好ましいことがわかる。
【００３７】
以上の実施例では、球状の水素吸蔵合金粉末Ａを作製する方法として、ガスアトマイズ法を用いたが、これに限定されるものではなく、遠心噴霧法などの方法によっても同様な効果が得られる。
また、この水素吸蔵合金粉末の熱処理を９００℃で１時間行なったがこれに限定されるものではく、均質性を維持させることのできる条件であれば同様の効果が得られる。
また、上記実施例では、水素吸蔵合金粉末Ｂは、鋳造法により得られたインゴットを用いて作製したが、これに限定されるものではなく、ロール急冷法、アトマイズ法によって得られたものを粉砕して用いても同様の効果が得られる。
さらに、上記実施例においては、無電解法によりニッケル被覆を行ったが、これに限定されるものではなく、電解法、または酸もしくはアルカリ液を用いたエッチング法などにより、水素吸蔵合金を構成する元素であるニッケルおよびコバルトで粉末表面を被覆しても同様の効果が得られる。
【００３８】
【発明の効果】
以上のように、本発明によれば、アトマイズ法もしくは遠心噴霧法により作製した球状またはそれに類似した形状の水素吸蔵合金粉末Ａと機械粉砕法により作製した不定形の水素吸蔵合金粉末Ｂとからなる水素吸蔵合金電極において、少なくとも前記水素吸蔵合金粉末Ｂの表面をニッケルおよび／またはコバルトで被覆することにより、集電体と水素吸蔵合金粉末との間の集電性を高め、寿命特性と放電特性とを両立させることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen storage alloy electrode used for a negative electrode such as a nickel-hydrogen storage battery, and an alkaline storage battery using the same.
[0002]
[Prior art]
Nickel-hydrogen storage batteries put into practical use using hydrogen storage alloys have come to be widely used as power sources for various cordless devices and electronic devices as batteries having characteristics such as low environmental load and high energy density. It was. In addition, it is strongly expected to improve the large current discharge characteristics to obtain a high output for use in a power source such as an electric vehicle, and to improve long-term reliability for use in a backup power source.
As a negative electrode material of such a nickel-hydrogen storage battery, an MmNi 5 (Mm is a mixture of rare earth elements) alloy having a CaCu 5 type crystal structure is generally used, and a part of Ni is made of a metal such as Co, Mn and Al. Used as a replacement. This alloy is known for casting into a mold, roll quenching method in which a molten alloy is poured onto a rotating disk to produce a thin alloy, and atomizing method in which an inert gas is sprayed to produce a spherical alloy. ing.
[0003]
In the casting method and the roll quenching method, it is necessary to perform a pulverization step mechanically in order to obtain an alloy powder. On the other hand, in the atomization method, since a fine spherical alloy powder is obtained, a pulverization step is not required. .
In addition, although the alloy powder obtained by pulverization is pulverized along with the charge / discharge cycle, the alloy powder obtained by the atomization method has a uniform alloy structure because it is produced by rapid cooling, and is pulverized. Is suppressed.
Furthermore, the alloy powder obtained by the atomizing method can be filled at a higher density than the alloy powder obtained by pulverization (for example, JP-A-3-116655).
[0004]
For these reasons, alloy powders obtained by the atomization method are mainly used, but since this alloy powder is spherical, the specific surface area is small, and contact between the alloy powder particles and contact between the alloy powder and the current collector Becomes point contact. Therefore, there exists a problem that it is inferior to current collection compared with the powder obtained by grinding | pulverization.
On the other hand, for example, a method has been proposed in which a current collector is improved by using a porous current collector obtained by mixing an alloy powder composed of spherical particles and an alloy powder composed of non-spherical particles. (Kaihei 11-97002). Also proposed is a method for improving current collection using a current collector obtained by laminating a layer made of alloy particles obtained by pulverization and a layer made of alloy particles obtained by an atomizing method (Japanese Patent Laid-Open No. Hei 11). -283618).
That is, in order to improve the current collecting property of the spherical alloy powder obtained by the atomizing method, the non-spherical alloy powder obtained by pulverization is used in combination.
[0005]
[Problems to be solved by the invention]
However, the alloy powder obtained by pulverization is more easily pulverized with the charge / discharge cycle than the alloy powder obtained by the atomization method, and its particle size is reduced to about 15 μm. Current collecting performance gradually decreases. Moreover, since the surface area of the alloy powder newly brought into contact with the electrolytic solution is increased by the pulverization, elements constituting the alloy are eluted and the electrolytic solution is consumed unnecessarily. As a result, there is a problem that the internal resistance of the obtained battery is increased, and the discharge capacity and the cycle life characteristics are decreased.
Therefore, the present invention provides a hydrogen storage alloy electrode made of an alloy powder obtained by an atomizing method and an alloy powder obtained by pulverization, and does not have the above problems, and an alkaline storage battery using the same. The purpose is to provide.
[0006]
[Means for Solving the Problems]
The present invention is composed of a fabricated spherical or amorphous Prepared by similar hydrogen-absorbing alloy powder A and mechanical grinding method in shape to it hydrogen-absorbing alloy powder B by an atomizing method or centrifugal atomization method, before Symbol hydrogen absorbing alloy powder the surface of B only, coated with nickel and / or cobalt, the weight ratio of the hydrogen-absorbing alloy powder a hydrogen absorbing alloy powder B is 80: 20 to 95: hydrogen and wherein 5 der Rukoto storage about the alloy electrode.
[0007]
Further, the hydrogen absorbing alloy powder A has an average particle size of less than or equal to particle size and 20 to 40 [mu] m 90 [mu] m, the hydrogen absorbing alloy powder B is Ru effective der have an average particle size of 10 to 15 [mu] m.
Furthermore, the present invention also relates to an alkaline storage battery comprising the negative electrode made of the hydrogen storage alloy electrode, the positive electrode made of a metal oxide, and an alkaline electrolyte.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention comprises a spherical or similar shaped hydrogen storage alloy powder A produced by an atomizing method or a centrifugal spray method and an amorphous hydrogen storage alloy powder B produced by a mechanical pulverization method, and at least the hydrogen storage alloy powder The present invention relates to a hydrogen storage alloy electrode characterized by having nickel and / or cobalt on the surface of B.
That is, according to the present invention, the hydrogen storage alloy powder A having a smooth spherical surface (including similar shapes such as hen's egg shape) prepared by the atomization method or the centrifugal spray method, and the mechanical pulverization method are used. In combination with an amorphous hydrogen storage alloy powder B having a relatively rough surface, the current collection is improved, and the surface of the hydrogen storage alloy powder B is coated with a specific metal to elute constituent elements. Can be suppressed. The term “coating” in the present invention does not necessarily mean that a uniform layer is formed, but also includes a state where it is attached.
[0009]
Here, as the metal that coats the surface of the hydrogen storage alloy powder, it effectively adheres to the surface of the alloy powder to form a coating layer and suppresses the dissolution of elements constituting the hydrogen storage alloy into the alkaline electrolyte. There is no particular limitation as long as it fulfills the function of performing, but it is preferable to use nickel and / or cobalt which also serves as a catalyst on the alloy surface.
In the present invention, at least the surface of the hydrogen storage alloy powder B obtained by pulverization may be coated with a metal, but the surface of the hydrogen storage alloy powder A obtained by the atomization method or the centrifugal spray method and the hydrogen storage alloy powder. It is advantageous to coat both surfaces of B with nickel and / or cobalt.
This is because the constituent elements may be eluted from the hydrogen storage alloy powder A obtained by the atomization method or the centrifugal spraying method, although it is a trace amount. This is because elution can be suppressed.
[0010]
Next, in the hydrogen storage alloy electrode according to the present invention, it is effective that the hydrogen storage alloy powder A has a particle size of 90 μm or less and an average particle size of 20 to 40 μm.
This is because if the hydrogen storage alloy powder A having a particle size exceeding 90 μm is included, the alloy powder A is easily pulverized with the charge / discharge cycle, and the electrolytic solution is consumed and the cycle life characteristics are deteriorated. It is. In addition, when the average particle size is less than 20 μm, the corrosion reaction of the hydrogen storage alloy powder A is accelerated, and the hydrogen storage alloy powder having an extremely small particle size has a low hydrogen storage capacity and the electrode capacity is reduced. Because it ends up. In addition, when the average particle size exceeds 40 μm, the charge / discharge reactivity decreases due to the decrease in the reaction area of the alloy powder A.
[0011]
On the other hand, it is effective that the hydrogen storage alloy powder B has an average particle diameter of 10 to 15 μm.
It has been empirically known that the particle size of the hydrogen storage alloy powder obtained by pulverization usually becomes finer to about 15 μm by the charge / discharge cycle. Therefore, if it is used in such a particle size in advance, it is possible to suppress an increase in the area of the alloy surface newly in contact with the electrolytic solution, and to prevent consumption of excess electrolytic solution.
[0012]
It is effective that the weight ratio of the hydrogen storage alloy powder A and the hydrogen storage alloy powder B in the hydrogen storage alloy electrode of the present invention is 80:20 to 95: 5. That is, 5 to 20% by weight of the total hydrogen storage alloy powder is preferably the hydrogen storage alloy powder B obtained by pulverization.
This is because if the weight ratio of the hydrogen storage alloy powder B exceeds 20% by weight, the filling property of the electrode is lowered and sufficient characteristics cannot be obtained. This is because the electrical properties are insufficient and the improvement of the discharge characteristics cannot be obtained.
Here, the composition of the hydrogen storage alloy in the present invention preferably includes a rare earth element, nickel and a transition metal element other than nickel.
Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
[0013]
【Example】
Example 1
In this example, only the hydrogen storage alloy powder B was provided with a metal coating.
(1) Production of hydrogen storage alloy powder A by atomizing method First, commercially available Mm (Misch metal), Ni, Mn, Al and Co are weighed so as to have a predetermined composition ratio, and in an inert gas atmosphere, A molten metal obtained by melting with a high-frequency induction heating melting furnace is dropped from the bottom of the crucible, and high-pressure argon gas is sprayed on the molten metal to obtain a spherical alloy powder. The electric furnace is controlled at 900 ° C. for 1 hour. Heat treatment was performed.
[0014]
Here, when the composition of the obtained alloy powder was analyzed, it was MmNi 3.55 Mn 0.4 Al 0.3 Co 0.75 , and the alloy structure was extremely homogeneous. Further, when the shape of the powder particles was confirmed, the surface was spherical with a smooth surface.
Furthermore, the alloy powder was sieved so that the particle size was 90 μm or less, thereby obtaining a hydrogen storage alloy powder a1 having an average particle size of 30 μm. The average particle size was confirmed by measuring the particle size distribution.
[0015]
(2) Production of hydrogen storage alloy powder B by pulverization First, commercially available Mm (Misch metal), Ni, Mn, Al, and Co are weighed so as to have a predetermined composition ratio, and dissolved in a high frequency induction heating melting furnace. An ingot was produced by molding. The ingot was placed in an electric furnace controlled at 1100 ° C. and heat-treated for 1 hour, and then mechanically pulverized in an inert gas to obtain an alloy powder.
Next, the above alloy powder was sieved so that the average particle size was 15 μm, and a hydrogen storage alloy powder b1 having a composition of MmNi 3.55 Mn 0.4 Al 0.3 Co 0.75 was obtained.
[0016]
(3) Coating of hydrogen storage alloy powder B Further, the hydrogen storage alloy powder b1 was washed with acid, and then charged into a mixed solution of 30 g / l nickel sulfate and 10 g / l sodium acetate heated to 80 ° C. 15 g / l sodium hypophosphite was added to the solution and stirred for 20 minutes.
Thereafter, washing with water and drying were performed to obtain a hydrogen storage alloy powder b1 ′ in which the surface of the hydrogen storage alloy powder b1 was coated with Ni.
When the nickel coating amount of this hydrogen storage alloy powder b1 'was confirmed, it was 2 to 5 weight%.
[0017]
(4) Production of electrode 90 parts by weight of the hydrogen storage alloy powder a1 obtained as described above, 10 parts by weight of the hydrogen storage alloy powder b1 ′, 0.15 part by weight of carboxymethyl cellulose as a thickener, and conductive An alloy paste was prepared by mixing 0.3 parts by weight of carbon black as a material, 0.8 parts by weight of a styrene-butadiene copolymer as a binder, and water as a dispersion medium.
This paste was applied to both sides of an iron punched metal plated with nickel having a thickness of 60 μm, a punching hole diameter of 1 mm, and a hole area ratio of 42%, followed by drying and pressing. Furthermore, the surface was coated with fluororesin powder, and a hydrogen storage alloy electrode 1 having a width of 35 mm, a length of 150 mm, a thickness of 0.4 mm, and a capacity of 2200 mAh was produced.
[0018]
(5) Production of Battery The hydrogen storage alloy electrode 1, the known sintered nickel positive electrode, and the nylon nonwoven fabric separator were laminated and wound in a spiral shape to obtain an electrode plate group, which was inserted into a metal case. Thereafter, a predetermined amount of an electrolytic solution in which 40 g / l lithium hydroxide is dissolved in a KOH aqueous solution having a specific gravity of 1.30 is injected into a metal case, the case is sealed, and a sealed battery 1 having a 4 / 5A size and a battery capacity of 1500 mAh is obtained. Produced.
[0019]
<< Reference Example 1 >>
In this reference example, both the hydrogen storage alloy powder A and the hydrogen storage alloy powder B were provided with a metal coating.
(1) Coating of hydrogen storage alloy powder A The hydrogen storage alloy powder a1 having an average particle size of 30 μm obtained in the same manner as in (1) of Example 1 was washed with an acid and then heated at 80 ° C. at 80 ° C. It was immersed in a KOH aqueous solution having a specific gravity of 1.30 and stirred for 1 hour. After washing this alloy powder with water, it was further poured into a mixed solution of 30 g / l nickel sulfate and 10 g / l sodium acetate heated to 80 ° C., and 15 g / l sodium hypophosphite was added to the solution. And stirred for 20 minutes.
Thereafter, washing and drying were performed to obtain a hydrogen storage alloy powder a1 ′ in which the surface of the hydrogen storage alloy powder a1 was coated with Ni.
[0020]
(2) electrode and battery fabrication Then, the hydrogen storage alloy powder a1 and 'and, (3) a hydrogen absorbing alloy powder was produced in the same manner as b1 Example 1' using a hydrogen in the same manner as in Example 1 The storage alloy electrode 2 was produced. Further, a sealed reference battery 1 was produced in the same manner as in Example 1.
[0021]
<< Comparative Examples 1 and 2 >>
(1) Electrode and battery using only hydrogen storage alloy powder A having no metal coating First, spherical hydrogen storage alloy powder a1 was produced in the same manner as in Example 1.
100 parts by weight of this hydrogen storage alloy powder a1, 0.15 parts by weight of carboxymethyl cellulose as a thickener, 0.3 parts by weight of carbon black as a conductive material, and a styrene-butadiene copolymer as a binder. An alloy paste was prepared by mixing 0.8 part by weight and water as a dispersion medium.
Using this alloy paste, a comparative sealed battery (comparative battery) 1 was produced in the same manner as in Example 1.
[0022]
(2) Electrode and battery using hydrogen storage alloy powder A and hydrogen storage alloy powder B without metal coating, and 90 parts by weight of hydrogen storage alloy powder a1 produced by the same method as in Example 1, 10 parts by weight of hydrogen storage alloy powder b1 mechanically pulverized so as to have a diameter of 15 μm was mixed to obtain an alloy powder mixture.
100 parts by weight of this alloy mixture, 0.15 parts by weight of carboxymethyl cellulose as a thickener, 0.3 parts by weight of carbon black as a conductive material, and 0.8% of styrene-butadiene copolymer as a binder. An alloy paste was prepared by mixing parts by weight and water as a dispersion medium. Using this alloy paste, a comparative sealed battery (comparative battery) 2 was produced in the same manner as in Example 1.
[0023]
[Evaluation]
The initial discharge characteristics and life characteristics of the battery 1 and the reference battery 1 manufactured by the above method and the comparative batteries 1 and 2 were evaluated.
(1) Initial discharge characteristics In order to evaluate the initial discharge characteristics, the battery was charged to 120% of the theoretical capacity at 20 ° C. and a current value of 1.5 A, and the battery voltage was 1.0 V at 0 ° C. and a current value of 3.0 A. The capacity until initial reduction (initial discharge capacity) was measured.
The initial discharge capacity of the comparative battery 1 was taken as 100, and the measured value of each battery was shown as an index. The results are shown in Table 1.
[0024]
(2) Life characteristics In order to evaluate the life characteristics, the battery is charged to 120% of the theoretical capacity at 20 ° C. and a current value of 1.5 A, and discharged to a battery voltage of 1.0 V at a current value of 1.5 A. It was.
The number of cycles when the discharge capacity deteriorated to 80% of the initial discharge capacity was determined. The number of cycles of the comparative battery 1 was taken as 100, and the number of cycles of each battery was shown as an index. The results are shown in Table 1. In consideration of actual use of the battery, the life characteristic needs to be 90 or more, and the discharge characteristic only needs to be 110 or more.
[0025]
[Table 1]
From Table 1, it is clear from the results of Example 1, Reference Example 1 and Comparative Example 1 that the discharge characteristics are improved by mixing the hydrogen storage alloy powder B obtained by pulverization. This is presumably because the surface of the alloy powder obtained by mechanical pulverization was coated with Ni, thereby increasing the reaction surface area and collecting current between the core material and the alloy powder.
Further, as is clear from the results of Example 1 and Comparative Example 2, it was found that the life characteristics without practical problems could be secured by coating the mechanically pulverized alloy surface with Ni. Further, in Reference Example 1 and Comparative Example 2, From the results, it can be seen that the life characteristics are further improved by coating the surface of the alloy powder obtained by the atomizing method with Ni. This is considered to be because the corrosion reaction between the alloy constituent elements and the electrolytic solution was suppressed by covering the alloy surface with Ni, and consumption of the electrolytic solution could be prevented.
[0027]
<< Examples 2 to 7 >>
In this example, the influence of the particle size of the hydrogen storage alloy powder A obtained by the atomizing method on the characteristics of the obtained battery was examined.
The hydrogen storage alloy powder B obtained by pulverization mixed with the hydrogen storage alloy powder A was classified with a 20 μm sieve and the alloy surface coated with Ni was used. The mixing ratio (weight) of the hydrogen storage alloy powder A and the hydrogen storage alloy powder B was 90:10.
Then, the hydrogen storage alloy powder A was classified using a sieve, and the same procedure as in Reference Example 1 was performed except that the hydrogen storage alloy powder A having an average particle size of 15, 20, 30, 40, 45, or 65 μm was used. Inventive sealed batteries 2-7 were prepared. The battery characteristics of each battery are shown in Table 2.
[0028]
[Table 2]
From Table 2, it was confirmed that as the average particle size of the hydrogen storage alloy powder A was decreased, the discharge characteristics of the obtained battery were improved, and conversely, the life characteristics were liable to be lowered. However, when the hydrogen storage alloy powder A having an average particle size of 15 μm was used, a decrease in life characteristics was observed. This is considered to be because when the particle size is reduced, the specific surface area of the alloy powder is increased and the discharge characteristics are improved, while the corroded surface area is increased and the life characteristics are lowered.
[0030]
In addition, when the average particle diameter classified by a 150 μm sieve was 65 μm, the discharge capacity at the beginning of the cycle was lowered because the reaction area was small. Furthermore, when the particle size is about 100 to 150 μm, the alloy powder is easily pulverized by the charge / discharge cycle, so that the discharge capacity increases with the number of cycles. It is thought that it was.
From these facts, it is understood that the hydrogen storage alloy powder A obtained by the atomizing method preferably has a particle size of 90 μm or less and an average particle size of 20 to 40 μm.
[0031]
<< Examples 8 to 12 >>
In this example, the influence of the particle size of the hydrogen storage alloy powder B obtained by pulverization on the battery characteristics was examined.
As the hydrogen storage alloy powder A produced by the atomizing method, one having an average particle size of 30 μm classified by a 90 μm sieve was used. Further, an alloy powder mixture in which 90 parts by weight of hydrogen storage alloy powder A and 10 parts by weight of hydrogen storage alloy powder B were mixed was used.
Reference Example 1 except that the hydrogen storage alloy powder B was classified using various sieves, the average particle diameter was 7, 10, 12, 15 or 20 μm, and the alloy surface was coated with Ni. In the same manner as above, sealed batteries 8 to 12 of the present invention were produced.
The battery characteristics of each battery are shown in Table 3.
[0032]
[Table 3]
From Table 3, it can be seen that when the average particle size of the hydrogen storage alloy powder B obtained by pulverization is 10 to 15 μm, good discharge characteristics are obtained and the life characteristics are practically not problematic. However, when the average particle size of the hydrogen storage alloy powder B is reduced to about 7 μm (Example 8 ) or increased to about 20 μm (Example 1 2 ), good discharge characteristics can be obtained. It is considered that the specific surface area of the occlusion alloy powder B is increased, and as a result, the corrosion by the alkaline electrolyte proceeds and the life characteristics are lowered.
On the other hand, in Example 1 2, micronised by hydrogen-absorbing alloy powder B is charge-discharge cycle, as a result the newly resulting Ni uncoated alloy surface corrosion is believed that the cycle life characteristics declined. From these, it can be seen that the average particle size of the hydrogen storage alloy powder B is preferably 10 to 15 μm.
[0034]
<< Examples 13 to 15 and Reference Example 2 >>
In this example and the reference example , the influence of the weight ratio of the hydrogen storage alloy powder A obtained by the atomizing method and the hydrogen storage alloy powder B obtained by pulverization on the battery characteristics in the hydrogen storage alloy electrode was examined. The weight ratio of the hydrogen storage alloy powder A and the hydrogen storage alloy powder B was 95: 5, 90:10, 80:20, or 75:25.
As the hydrogen storage alloy powder A, one having an average particle size of 30 μm classified by a 90 μm sieve is used, and as the hydrogen storage alloy powder B, the average particle size classified by a 20 μm sieve is 15 μm, and the alloy surface is Ni. The one coated with is used. In addition it was made dense closed cell 13-15 and the reference battery 2 in the same manner as in Example 1. The battery characteristics of each battery are shown in Table 4.
[0035]
[Table 4]
From Table 4, it can be seen that when the ratio of the hydrogen storage alloy powder B obtained by pulverization in all alloys is 5 to 20% by weight, good discharge characteristics can be obtained and the life characteristics are not problematic in practice.
However, when mixed by 25% by weight, the discharge characteristics are good, but since the mixing ratio of the hydrogen storage alloy powder B is high, the corrosion of the alloy proceeds with the charge / discharge cycle, and the electrolyte is consumed. It is considered that the characteristics necessary for practical use could not be secured.
From these facts, it is understood that the insertion ratio of the hydrogen storage alloy powder B in the total hydrogen storage alloy powder is preferably 5 to 20% by weight.
[0037]
In the above embodiment, the gas atomization method is used as a method for producing the spherical hydrogen storage alloy powder A, but the present invention is not limited to this, and the same effect can be obtained by a method such as a centrifugal spray method.
Further, the heat treatment of the hydrogen storage alloy powder was performed at 900 ° C. for 1 hour. However, the present invention is not limited to this, and the same effect can be obtained as long as the homogeneity can be maintained.
Moreover, in the said Example, although the hydrogen storage alloy powder B was produced using the ingot obtained by the casting method, it is not limited to this, The thing obtained by the roll quenching method and the atomizing method is grind | pulverized. Even if used, the same effect can be obtained.
Further, in the above embodiment, nickel coating was performed by an electroless method, but the present invention is not limited to this, and the hydrogen storage alloy is formed by an electrolytic method or an etching method using an acid or an alkali solution. The same effect can be obtained by coating the powder surface with the elements nickel and cobalt.
[0038]
【Effect of the invention】
As described above, according to the present invention, the hydrogen storage alloy powder A having a spherical shape similar to or similar to that produced by the atomizing method or the centrifugal spraying method and the amorphous hydrogen storage alloy powder B produced by the mechanical pulverization method are used. In the hydrogen storage alloy electrode, by covering at least the surface of the hydrogen storage alloy powder B with nickel and / or cobalt, the current collection between the current collector and the hydrogen storage alloy powder is improved, and the life characteristics and discharge characteristics are increased. Can be made compatible.
Claims (3)
前記水素吸蔵合金粉末Ｂのみの表面が、ニッケルおよび／またはコバルトで被覆され、前記水素吸蔵合金粉末Ａと前記水素吸蔵合金粉末Ｂの重量比が、８０：２０〜９５：５であることを特徴とする水素吸蔵合金電極。A hydrogen storage alloy powder A having a spherical shape or a similar shape produced by an atomizing method or a centrifugal spraying method and an amorphous hydrogen storage alloy powder B produced by a mechanical grinding method,
Surface prior Symbol hydrogen-absorbing alloy powder B only, coated with nickel and / or cobalt, the weight ratio of the said hydrogen-absorbing alloy powder A hydrogen-absorbing alloy powder B is 80: 20 to 95: 5 der Rukoto A hydrogen storage alloy electrode.
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| JP2001037624A JP4932997B2 (en) | 2001-02-14 | 2001-02-14 | Hydrogen storage alloy electrode and alkaline storage battery using the same |
| PCT/JP2001/006954 WO2002017415A1 (en) | 2000-08-22 | 2001-08-10 | Alkali storage battery and hydrogen absorbing alloy electrode for use therein |
| CNB018145272A CN1260837C (en) | 2000-08-22 | 2001-08-10 | Alkali storage battery and hydrogen absorbing alloy electrode for use therein |
| US10/370,265 US7247409B2 (en) | 2000-08-22 | 2003-02-21 | Alkaline storage battery and hydrogen storage alloy electrode used therefor |
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| JPH10172546A (en) * | 1996-12-12 | 1998-06-26 | Sumitomo Metal Ind Ltd | Hydrogen storage alloy powder and electrode for battery |
| JPH10326613A (en) * | 1997-03-28 | 1998-12-08 | Matsushita Electric Ind Co Ltd | Electrode of hydrogen storage alloy |
| JP4441936B2 (en) * | 1998-07-03 | 2010-03-31 | 株式会社ジーエス・ユアサコーポレーション | Hydrogen storage electrode |
| JP2000285913A (en) * | 1999-03-31 | 2000-10-13 | Yuasa Corp | Hydrogen storage alloy, and hydrogen storage alloy electrode using the same |
| JP3685643B2 (en) * | 1999-03-31 | 2005-08-24 | 三洋電機株式会社 | Hydrogen storage alloy electrode and nickel metal hydride storage battery using the electrode |
| JP3370071B2 (en) * | 2000-09-22 | 2003-01-27 | 三洋電機株式会社 | Hydrogen storage alloy electrode and nickel-metal hydride storage battery using this electrode |
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