JP2004115870A - Hydrogen storage alloy and its manufacturing method - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、水素吸蔵合金、特に高容量で水素吸蔵放出時の平衡圧の平坦性が高いニッケル水素二次電池負極活物質等に利用可能な水素吸蔵合金及びその製造方法に関する。
【０００２】
【従来の技術】
水素吸蔵合金は、安全かつ容易にエネルギー源としての水素を貯蔵できる合金であり、様々な分野で研究開発が進められ、実用化に至っている技術も多い。特に、二次電池の分野においてはカドミウムが問題視されているニッカド電池に代わる高容量の電池としてニッケル水素二次電池が開発され実用化されている。この電池は負極活物質としてＡＢ５系水素吸蔵合金とＡＢ２系の水素吸蔵合金が用いられている。
しかし、前者の水素吸蔵合金では理論容量が３７０ｍＡｈ／ｇであり、今後益々強くなる高容量化の要望には応えられなくなってきている。後者の水素吸蔵合金では理論容量は高いが、合金表面に安定な酸化膜を作る等の理由でその容量を十分に使用することができず、加えて、活性化に時間を要し、高率充放電特性が不十分等の今後解決すべき課題が多すぎる。
これらの問題を克服し、ＡＢ５系の使い易さとＡＢ２系の高容量を備えた新しい活物質として、マグネシウム（Ｍｇ）、ニッケル（Ｎｉ）及び希土類元素を主要構成元素とする水素吸蔵合金やその製造方法、該合金を活物質として用いた電池が提案されている（例えば、特許文献１〜３参照）。
しかし、これらＭｇを含む合金は、Ｍｇとその他の元素との物性の違いから、均一な組成の合金を製造することが困難である。例えば、Ｍｇの比重が１．７４に対し、Ｎｉ及びＬａの比重はそれぞれ８．９、６．１５であり、また、Ｍｇの融点が６５０℃であるのに対し、Ｎｉ及びＬａの融点はそれぞれ１４５３℃、９２０℃であるので、一般的な金型鋳造法では均一組成の合金製造が困難である。このような金型鋳造法により得られるＭｇを含む水素吸蔵合金は、ＰＣＴカーブにおけるプラトー部が存在せず、二次電池の活物質として使用する圧力範囲では容量が小さいという問題がある。
そこで、組織を均質化するために得られた合金を、熱処理を行うことも知られている（例えば、特許文献１〜３参照）。しかし、該熱処理は、得られた合金の組織が比較的大きいため、高温で長時間行う必要がある上、熱処理による容量の向上が小さい。
溶湯急冷法による合金の組織は、金型鋳造法で製造した合金に比較して微細となるため、熱処理前の合金では金型鋳造法による合金に比べて容量は大きくなるが、熱処理後の合金では金型鋳造法による合金に比して容量が若干小さくなる。これは、溶湯急冷法で調製した合金の組織が微細で、マクロ的には均質度合いが金型鋳造法の合金と比べて高くなるが、ミクロ的には金型鋳造法で調製した合金組織が微細化したにすぎず、熱処理を行った合金とミクロ的な組織の均質化に差が生じるためであると考えられる。
溶湯急冷法で調製した合金を熱処理した場合、Ｈ／Ｍにおける最終的な容量は増加するが、ＰＣＴカーブが２段以上のプラトー部を示すため、二次電池における実質的な容量はそれほど大きくならない。
【０００３】
【特許文献１】
特開平１１−１６２４５９号公報
【特許文献２】
特開２０００−２６５２２９号公報
【特許文献３】
特許３２４７９３３号明細書
【０００４】
【本発明が解決しようとする課題】
本発明の目的は、Ｍｇを含む系の水素吸蔵合金であって、二次電池における実質的な容量を向上させることが可能な二次電池負極活物質に利用できる水素吸蔵合金を提供することにある。
本発明の別の目的は、Ｍｇを含む系の水素吸蔵合金であって、ＰＣＴカーブにおける多段プラトーがなく、二次電池における実質的な容量を向上させることが可能な二次電池負極活物質に利用できる水素吸蔵合金を提供することにある。
本発明の更に別の目的は、Ｍｇを含む系の水素吸蔵合金であって、二次電池における充放電がし易く、且つ実質的な容量を向上させることが可能な二次電池負極活物質に利用できる水素吸蔵合金を提供することにある。
本発明の他の目的は、Ｍｇを含む系の水素吸蔵合金であって、ＰＣＴカーブにおける多段プラトーがなく、二次電池における充放電がし易い水素吸蔵合金を提供することにある。
本発明の更に他の目的は、二次電池における実質的な容量を向上させることが可能なＭｇを含む系の水素吸蔵合金を効率的に、且つ工業的にも有用に製造することができる方法を提供することにある。
【０００５】
【課題を解決するための手段】
本発明によれば、式（１）で示される組成を有し、液体急冷法を用いて製造された結晶質の合金であって、該合金の４０℃で測定したＰＣＴカーブにおいて、０．５ＭＰａにおけるＨ／Ｍが１．００以上であることを特徴とする水素吸蔵合金が提供される。
Ｌｎ１−ＸＭｇＸＮｉｙＭＺ （１）
（式中、ＬｎはＹ、Ｓｃを含むＬａからＬｕまでの希土類金属元素からなる群より選択される少なくとも１種、ＭはＣｏ、Ｍｎ、Ａｌ、Ｆｅ、Ｖ、Ｃｒ、Ｎｂ、Ｇａ、Ｚｎ、Ｓｎ、Ｃｕ、Ｓｉ、Ｐ、Ｂからなる群より選択される少なくとも１種を示す。０．１≦ｘ≦０．５、２．５≦ｙ≦３．５、０≦ｚ≦０．５、３．０≦ｙ＋ｚ≦３．５である）
また本発明によれば、前記式（１）で示される組成を有し、液体急冷法を用いて製造された結晶質の合金であって、該合金の４０℃で測定したＰＣＴカーブにおいて、Ｈ／Ｍ＝０．４〜０．５におけるＰＣＴカーブの傾きＰｆが０．７以下であることを特徴とする水素吸蔵合金が提供される。
更に本発明によれば、前記式（１）で示される組成を有し、液体急冷法を用いて製造された結晶質の合金であって、該合金の４０℃で測定したＰＣＴカーブにおいて、Ｈ／Ｍ＝０．３〜０．９において実質的に２段以上のプラトー部を示さないことを特徴とする水素吸蔵合金が提供される。
更にまた本発明によれば、前記式（１）で示される組成を構成する金属元素又は母合金を原料とし、該原料を加熱溶解し、液体急冷法により冷却固化して表面温度７００℃以上の合金鋳塊を得た後、該合金鋳塊を１００℃以下に冷却して合金を製造する方法において、冷却固化した表面温度７００℃以上の合金鋳塊を１００℃以下に冷却する前に、５００〜１０００℃から選ばれる１つ以上の温度域で１〜１０分間保持する熱保持工程を行うことを特徴とする前記水素吸蔵合金の製造方法が提供される。
【０００６】
【発明の実施の形態】
以下本発明を更に詳細に説明する。
本発明の水素吸蔵合金は、前記式（１）で示される組成を有する。
式（１）において、ＬｎはＹ、Ｓｃを含むＬａからＬｕまでの希土類金属元素からなる群より選択される少なくとも１種を示す。これら希土類元素は、求められる容量、平衡圧等の特性に応じて適宜選択することができ、ＡＢ５系で用いられる、主にＬａからＮｄまでの混合元素からなるミッシュメタルの組成も含まれる。但し、Ｌｎ中に含まれるＬａ量が少なすぎると平衡圧が上昇したり、水素吸蔵量が減少する恐れがあるので、Ｌｎ中のＬａ量は、通常５０〜１００モル％、好ましくは７０〜１００モル％である。式（１）中のｘは、水素吸蔵合金中のＬａサイトを置換するＭｇの量で０．１≦ｘ≦０．５、好ましくは０．２≦ｘ≦０．４、更に好ましくは０．２５≦ｘ≦０．３５である。ｘが０．１未満ではＭｇの添加効果が低く、０．５を超えると水素の吸放出特性が低下する。
【０００７】
式（１）においてＭは、Ｃｏ、Ｍｎ、Ａｌ、Ｆｅ、Ｖ、Ｃｆ、Ｎｂ、Ｇａ、Ｚｎ、Ｓｎ、Ｃｕ、Ｓｉ、Ｐ及びＢからなる群より選択される少なくとも１種の元素で、選択する元素の種類と添加量により、水素吸蔵合金の水素吸放出特性を向上させることができる。例えば、Ｃｏは水素吸放出時のプラトーの平坦性を向上させることができる。添加元素Ｍの添加量ｚは０≦ｚ≦０．５である。添加量が０．５を超えるといずれの元素を選択しても特性の向上を見込めないか、特性の低下が見られる。
【０００８】
式（１）中のｙはＮｉ量を示し、ｙ＋ｚは３．０≦ｘ≦３．５である。ｙ＋ｚが３．０未満では、水素の放出が困難になり実質的な容量が低下する。ｙ＋ｚが３．５を超えると水素の吸蔵量が低下すると共に、プラトーの平坦性が悪くなり多段プラトーの発現が生じる恐れがある。
【０００９】
本発明の水素吸蔵合金の組成は、前記式（１）を充足すれば特に限定されないが、例えば、Ｌａ０．７０Ｍｇ０．３０Ｎｉ３．３０、Ｌａ０．７０Ｍｇ０．３０Ｎｉ３．１５、Ｌａ０．７０Ｍｇ０．３０Ｎｉ３．００、Ｌａ０．７０Ｍｇ０．３０Ｎｉ３．５０、Ｌａ０．７０Ｍｇ０．３０Ｎｉ２．８０Ｃｏ０．５０、Ｌａ０．７０Ｍｇ０．３０Ｎｉ３．００Ｃｏ０．３０、Ｌａ０．７０Ｍｇ０．３０Ｎｉ３．２０Ｃｏ０．１０、Ｌａ０．７０Ｍｇ０．３０Ｎｉ３．００Ｃｏ０．２０Ａｌ０．１０Ｍｎ０．１０、Ｌａ０．７０Ｍｇ０．２５Ｎｉ２．８０Ｃｏ０．５０、Ｌａ０．７０Ｍｇ０．３５Ｎｉ２．８０Ｃｏ０．５０等が挙げられる。
【００１０】
本発明の水素吸蔵合金は、前記組成を有すると共に、液体急冷法を用いて製造された結晶質の合金であって、以下に示す該合金の４０℃で測定したＰＣＴカーブにおける（ａ）〜（ｃ）のいずれかの性質を有するか、若しくはこれらの性質の２以上を有するか、更にはこれらの性質のいずれかと（ｄ）の性質、若しくは（ａ）〜（ｄ）の性質の２以上を有することを特徴とする。ここで、各性質の組合せは、（ａ）＋（ｂ）、（ａ）＋（ｃ）、（ｂ）＋（ｃ）、（ａ）＋（ｄ）、（ｂ）＋（ｄ）、（ｃ）＋（ｄ）、（ａ）＋（ｂ）＋（ｃ）、（ａ）＋（ｂ）＋（ｄ）、（ａ）＋（ｃ）＋（ｄ）、（ｂ）＋（ｃ）＋（ｄ）、（ａ）＋（ｂ）＋（ｃ）＋（ｄ）が挙げられるが、（ａ）〜（ｄ）の全ての性質を充足する合金が本発明においては最も好ましい。
【００１１】
（ａ）４０℃で測定したＰＣＴカーブにおいて、０．５ＭＰａにおけるＨ／Ｍが１．００以上、好ましくは１．０５以上である。
（ｂ）４０℃で測定したＰＣＴカーブにおいて、ＰＣＴカーブの傾きＰｆ（プラトーの傾き）が０．７以下である。
（ｃ）４０℃で測定したＰＣＴカーブにおいて、Ｈ／Ｍ＝０．３〜０．９に実質的な２段以上のプラトー部を示さない。
（ｄ）４０℃で測定したＰＣＴカーブにおいて、Ｈ／Ｍ＝０．５における平衡圧は０．０６ＭＰａ以下、好ましくは０．０５ＭＰａ以下である。
【００１２】
前記（ａ）の圧力におけるＨ／Ｍは、水素吸蔵合金を活物質とした電池の容量を示す指標となる。該（ａ）におけるＨ／Ｍが１．００未満では高容量が得られない。
前記（ｂ）におけるＰｆが０．７を超えると一定圧力における充放電容量が低下する。このＰｆは、水素吸蔵合金を活物質とした電池の充放電のし易さを示すとともに合金組織の均質性をも示す指標となる。この傾きＰｆは、Ｐｆ＝１ｎ（ＰＨ／ＰＬ）で求められる。式中ＰＨはＨ／Ｍ＝０．６における平衡圧であり、ＰＬは、Ｈ／Ｍ＝０．４における平衡圧である。この値が０に近ければプラトーは平坦であることを示し、０より大きければ傾きが存在することを示す。
前記（ｃ）における２段以上の多段プラトーは、合金組織の不均一性に起因する場合が多く、その段差にもよるが、電池にした際の充放電特性に悪影響を及ぼし、プラトー圧によっては電池そのものの容量も低下する。
前記（ｄ）における平衡圧は、水素吸蔵合金を活物質とした電池の充放電のし易さを示す指標となり、この平衡圧が高すぎると充電しづらいものとなり、特に急速充電特性が低下する。この平衡圧が必要以上に低い場合は、放電特性、特に高率放電特性に悪影響が生じる恐れがあるのでその下限値は、好ましくは０．０２ＭＰａ、特に好ましくは０．０２５ＭＰａである。
【００１３】
本発明の水素吸蔵合金は、前述のとおり、液体急冷法を用いて製造された結晶質合金である。ここで、液体急冷法は特に限定されず、公知の液体急冷法等が挙げられるが、好ましくは、タンディッシュを用いたストリップキャスト法が好ましい。また、前記結晶質合金とは、全体がアモルファス状態である合金を除く意であり、結晶を有するものであれば良い。このような結晶の存在は、Ｘ線回折法等により容易に確認することができる。
【００１４】
本発明の水素吸蔵合金は、例えば、前記式（１）で示される組成を構成する金属元素又は母合金を原料とし、該原料を加熱溶解し、液体急冷法により冷却固化して表面温度７００℃以上の合金鋳塊を得た後、該合金鋳塊を１００℃以下に冷却して合金を製造する際に、該合金鋳塊を１００℃以下に冷却する前に特定の熱保持工程を行う本発明の製造方法等により得ることができる。
本発明の製造方法において原料の加熱溶解は、坩堝等の溶融炉を用いてアルゴンガス等の不活性ガス雰囲気中で高周波溶解等によって行うことができる。溶融条件は公知の条件に基づいて合金組成等に応じて適宜選択することができる。
【００１５】
本発明の製造方法において、加熱溶解した合金溶融物から液体急冷法により表面温度７００℃以上、好ましくは８００℃以上の合金鋳塊を得るには、例えば、合金溶融物を薄帯状又は薄片状に冷却固化することによって行うことができる。合金溶融物の薄帯又は薄片化は、例えば、双ロール、単ロール等のロール冷却固化装置、回転円盤等を用いたディスク冷却固化装置、その他公知の冷却固化装置を用いて実施できる。また、各冷却固化装置には、厚さが均一な合金鋳片を得るために、合金溶融物の流れを制御できるタンディッシュ等を設けることができる。特に単ロール法が好ましい。
冷却固化条件は、目的の水素吸蔵合金に応じて公知の条件等を勘案して適宜選択することができる。冷却速度は、通常、１０００〜１００００℃／秒程度、好ましくは１０００〜５０００℃／秒、特に好ましくは１０００〜３０００℃／秒である。
【００１６】
本発明の製造方法では、前記合金鋳塊の表面温度を１００℃以下、好ましくは４００℃以下に冷却する前に、該合金鋳塊を所定温度範囲において所定時間保持する熱保持工程を行って、該合金鋳塊の合金結晶を所望大きさに均一化する。合金鋳塊の表面温度が１００℃以下に降温した後に合金結晶の制御を行う場合、該制御に要するエネルギーのロスが大きくなる。従って、熱保持工程は、得られた合金鋳塊の表面温度が好ましくは４００℃以下、特に好ましくは５００℃以下に降温する前に行う。合金結晶の制御は、通常、合金鋳塊が特定の高温状態で保持される時間が長ければ結晶が大きくなり、その時間が短ければ小さくなる。また、その温度や時間は合金組成によっても異なる。
【００１７】
本発明の製造方法において前記熱保持工程は、５００〜１０００℃、好ましくは５００〜８００℃の範囲から選択される１つ以上の温度域で１〜１０分間保持する工程である。このような所定温度範囲で所定時間保持する熱保持工程は従来行われておらず、通常は、常温程度までの冷却が行われた後に熱処理が行われる場合があるに過ぎない。一旦常温まで冷却した合金鋳塊を特定温度まで昇温する従来の熱処理では、温度及び時間によって昇温し易い部分の熱処理が過度に進行してしまう。この傾向は、本発明における熱保持工程を行った後の冷却過程においても同様であるため、熱保持工程後は速やかに常温近傍まで冷却することが好ましい。従って、本発明の製造方法においては、合金鋳塊を１００℃以下、通常常温程度まで冷却した後に、従来法における前記４００℃以上の熱処理工程を行わないことが好ましい。
【００１８】
本発明の製造方法では、前記熱保持工程の後、合金鋳塊を１００℃以下、好ましくは室温程度まで冷却、好ましくは強制冷却することにより所望の水素吸蔵合金を得ることができる。
【００１９】
【発明の効果】
本発明の水素吸蔵合金は、特定の組成を有し、且つ特定のＰＣＴカーブを示す物性を有するので、二次電池における実質的な容量を向上させることが可能な、また、ＰＣＴカーブにおける多段プラトーがない、充放電がし易い等の各性質を有する二次電池負極活物質に利用できるＭｇを含む系の水素吸蔵合金を提供することができる。また、本発明の製造方法では、特定の熱保持工程を行うので、本発明の水素吸蔵合金を、効率的に、且つ工業的にも有用に、従来の熱処理工程を行わないで製造することができる。
【００２０】
【実施例】
以下に実施例及び比較例により本発明を更に詳細に説明するが、本発明はこれらに限定されない。
実施例 １
出発原料として、株式会社三徳製のランタンメタルと、純度９９．９％のＭｇとをを表１に示す組成になるよう配合し、アルゴンガス雰囲気中高周波溶解し、冷却速度２０００〜５０００℃／秒の条件下、単ロール鋳造装置を用いて鋳造し、常温まで冷却させる前に７００℃で５分間保持し、その後速やかに常温近傍まで冷却した。得られた合金をレスカ製のＰＣＴ装置にて４０℃での水素吸蔵放出特性として、Ｈ／Ｍ＝０．５におけるＰＣＴ平衡圧、０．５ＭＰａにおけるＰＣＴ吸蔵量としてのＨ／Ｍ値、Ｈ／Ｍ０．４〜０．５におけるＰｆ値、並びにＨ／Ｍ＝０．３〜０．９における実質的な２段以上のプラトー部の有無を測定した。結果を表２に示す。
続いて、得られた合金粉末１０ｇと、導電剤として銅粉１ｇと、ＦＥＰ粉未（４弗化エチレン６弗化プロピレン共重合体）０．３ｇとを混合し、直径２０ｍｍのペレット電極を調製した。この電極を６規定のＫＯＨ溶液に浸漬し、酸化水銀参照電極を用いて電池を構成した。この電池の１０サイクル後の電池容量をポテンショガルバノスタット（北斗電工社製）により測定した。結果を表２に示す。
【００２１】
実施例 ２ 〜 １０ 、比較例 １ 〜 ３
原料組成を表１に示すとおり代えた以外は、実施例１と全く同様に処理して水素吸蔵合金を製造した。得られた合金について、実施例１と同様にＰＣＴ及び電極特性を測定した。結果を表２に示す。
【００２２】
比較例 ４
原料組成を表１に示すとおり代えた以外は、実施例１と全く同様に鋳造を行った後、常温まで冷却させる前に４００℃で５分間保持し、その後速やかに常湿近傍まで冷却して合金を得た。得られた合金について、実施例１と同様にＰＣＴ及び電極特性を測定した。結果を表２に示す。
【００２３】
比較例 ５
原料組成を表１に示すとおり代えた以外は、実施例１と全く同様に鋳造を行った後、常温まで冷却させる前に７００℃で２０分間保持し、その後速やかに常湿近傍まで冷却して合金を得た。得られた合金について、実施例１と同様にＰＣＴ及び電極特性を測定した。結果を表２に示す。
【００２４】
比較例 ６
原料組成を表１に示すとおり代えた以外は、実施例１と全く同様に鋳造を行った。常温まで冷却させる前に７００℃で５分間保持し、その後速やかに常温近傍まで冷却して合金を得た。得られた合金を更に、アルゴン雰囲気中で９５０℃、６時間熱処理を行った。得られた合金について、実施例１と同様にＰＣＴ及び電極特性を測定した。結果を表２に示す。
【００２５】
比較例 ７
原料組成を表１に示すとおり代えた以外は、実施例１と全く同様に鋳造を行い、常温まで熱保持領域を持たせずに急冷して合金を得た。得られた合金を、アルゴン雰囲気中で９５０℃、６時間熱処理を行った。得られた合金について、実施例１と同様にＰＣＴ及び電極特性を測定した。結果を表２に示す。
【００２６】
比較例 ８
原料組成を表１に示すとおり代えた以外は、実施例１と全く同様に鋳造を行い、常温まで熱保持領域を持たせずに急冷して合金を得た。得られた合金について、実施例１と同様にＰＣＴ及び電極特性を測定した。結果を表２に示す。
【００２７】
【表１】
【表２】
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrogen storage alloy, particularly to a hydrogen storage alloy which can be used for a negative electrode active material of a nickel-hydrogen secondary battery having a high capacity and a high flatness of an equilibrium pressure at the time of hydrogen storage and release, and a method for producing the same.
[0002]
[Prior art]
Hydrogen storage alloys are alloys that can safely and easily store hydrogen as an energy source. Many technologies have been researched and developed in various fields and have been put to practical use. In particular, in the field of secondary batteries, nickel-metal hydride secondary batteries have been developed and put into practical use as high-capacity batteries replacing cadmium batteries, for which cadmium is regarded as a problem. In this battery, an AB5-based hydrogen storage alloy and an AB2-based hydrogen storage alloy are used as negative electrode active materials.
However, the theoretical capacity of the former hydrogen storage alloy is 370 mAh / g, and it is no longer possible to meet the demand for higher capacity, which will become stronger in the future. Although the latter hydrogen storage alloy has a high theoretical capacity, the capacity cannot be used sufficiently due to the formation of a stable oxide film on the alloy surface, etc. There are too many problems to be solved in the future, such as insufficient charge / discharge characteristics.
As a new active material that overcomes these problems and has an AB5-based ease of use and an AB2-based high capacity, a hydrogen storage alloy containing magnesium (Mg), nickel (Ni), and a rare earth element as main constituent elements, and its production A method and a battery using the alloy as an active material have been proposed (for example, see Patent Documents 1 to 3).
However, it is difficult for alloys containing Mg to produce alloys having a uniform composition due to differences in physical properties between Mg and other elements. For example, while the specific gravity of Mg is 1.74, the specific gravities of Ni and La are 8.9 and 6.15, respectively, and the melting point of Mg is 650 ° C., whereas the melting points of Ni and La are respectively Since the temperature is 1453 ° C. and 920 ° C., it is difficult to produce an alloy having a uniform composition by a general mold casting method. The hydrogen storage alloy containing Mg obtained by such a mold casting method has a problem that the plateau portion does not exist in the PCT curve and the capacity is small in a pressure range used as an active material of a secondary battery.
Therefore, it is also known to perform heat treatment on an alloy obtained for homogenizing the structure (for example, see Patent Documents 1 to 3). However, the heat treatment must be performed at a high temperature for a long time because the structure of the obtained alloy is relatively large, and the improvement in capacity by the heat treatment is small.
The structure of the alloy quenched by the molten metal quenching method is finer than that of the alloy manufactured by the die casting method. In this case, the capacity is slightly smaller than that of the alloy obtained by the die casting method. This is because the structure of the alloy prepared by the melt quenching method is fine, and the degree of homogeneity is higher macroscopically than the alloy of the die casting method, but the alloy structure prepared by the die casting method is microscopic. It is considered that this is because the alloy is only micronized, and there is a difference in homogenization between the heat-treated alloy and the microstructure.
When the alloy prepared by the melt quenching method is heat-treated, the final capacity in H / M increases, but the substantial capacity in the secondary battery does not increase so much because the PCT curve shows a plateau of two or more steps. .
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 11-162449 [Patent Document 2]
JP 2000-265229 A [Patent Document 3]
Japanese Patent No. 3247933 specification
[Problems to be solved by the present invention]
An object of the present invention is to provide a hydrogen storage alloy of a system containing Mg, which can be used as a secondary battery negative electrode active material capable of substantially improving the capacity of a secondary battery. is there.
Another object of the present invention is to provide a secondary battery negative electrode active material which is a hydrogen storage alloy containing Mg and has no multi-step plateau in a PCT curve and can substantially improve the capacity in a secondary battery. An object of the present invention is to provide a usable hydrogen storage alloy.
Still another object of the present invention is to provide a secondary battery negative electrode active material which is a Mg-containing hydrogen storage alloy, which can be easily charged and discharged in a secondary battery, and which can substantially improve the capacity. An object of the present invention is to provide a usable hydrogen storage alloy.
It is another object of the present invention to provide a hydrogen storage alloy containing Mg, which does not have a multi-stage plateau in a PCT curve and is easily charged and discharged in a secondary battery.
Still another object of the present invention is to provide a method for efficiently and industrially producing a Mg-containing hydrogen storage alloy capable of substantially improving the capacity of a secondary battery. Is to provide.
[0005]
[Means for Solving the Problems]
According to the present invention, a crystalline alloy having a composition represented by the formula (1) and manufactured by using a liquid quenching method, and having a PCT curve measured at 40 ° C. of 0.5 MPa Wherein the H / M is 1.00 or more.
Ln 1-X Mg X Ni y M Z (1)
(Wherein, Ln is at least one selected from the group consisting of rare earth metal elements from La to Lu containing Y and Sc, and M is Co, Mn, Al, Fe, V, Cr, Nb, Ga, Zn, At least one selected from the group consisting of Sn, Cu, Si, P, and B. 0.1 ≦ x ≦ 0.5, 2.5 ≦ y ≦ 3.5, 0 ≦ z ≦ 0.5, 3.0 ≦ y + z ≦ 3.5)
According to the present invention, there is provided a crystalline alloy having a composition represented by the formula (1) and manufactured by using a liquid quenching method, wherein the PCT curve of the alloy measured at 40 ° C. A hydrogen storage alloy is provided, wherein the slope Pf of the PCT curve at /M=0.4 to 0.5 is 0.7 or less.
According to the present invention, there is further provided a crystalline alloy having a composition represented by the formula (1) and manufactured by using a liquid quenching method, wherein the PCT curve of the alloy measured at 40 ° C. A hydrogen storage alloy characterized by substantially not exhibiting two or more plateau portions at /M=0.3 to 0.9 is provided.
Furthermore, according to the present invention, a metal element or a master alloy constituting the composition represented by the above formula (1) is used as a raw material, and the raw material is heated and melted, solidified by cooling by a liquid quenching method, and has a surface temperature of 700 ° C. or more. After obtaining the alloy ingot, in a method of manufacturing an alloy by cooling the alloy ingot to 100 ° C. or less, before cooling the cooled and solidified alloy ingot having a surface temperature of 700 ° C. or more to 100 ° C. or less, 500 ° C. A method for producing the hydrogen-absorbing alloy is provided, wherein a heat-holding step of holding for 1 to 10 minutes in one or more temperature ranges selected from -1000 ° C is performed.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail.
The hydrogen storage alloy of the present invention has a composition represented by the above formula (1).
In the formula (1), Ln represents at least one selected from the group consisting of rare earth metal elements from La to Lu containing Y and Sc. These rare earth elements can be appropriately selected according to the required characteristics such as capacity and equilibrium pressure, and include the composition of a misch metal mainly used as a mixed element from La to Nd used in AB5 series. However, if the amount of La contained in Ln is too small, the equilibrium pressure may increase or the hydrogen storage amount may decrease. Therefore, the amount of La in Ln is usually 50 to 100 mol%, preferably 70 to 100 mol%. Mol%. X in the formula (1) is the amount of Mg that substitutes for the La site in the hydrogen storage alloy, and is 0.1 ≦ x ≦ 0.5, preferably 0.2 ≦ x ≦ 0.4, and more preferably 0.1 ≦ x ≦ 0.4. 25 ≦ x ≦ 0.35. If x is less than 0.1, the effect of adding Mg is low, and if it exceeds 0.5, the hydrogen absorption / desorption characteristics deteriorate.
[0007]
In the formula (1), M is at least one element selected from the group consisting of Co, Mn, Al, Fe, V, Cf, Nb, Ga, Zn, Sn, Cu, Si, P and B. The hydrogen storage / release characteristics of the hydrogen storage alloy can be improved by the type and amount of the element to be added. For example, Co can improve the flatness of the plateau when hydrogen is absorbed and released. The addition amount z of the additional element M is 0 ≦ z ≦ 0.5. If the addition amount exceeds 0.5, no improvement in characteristics can be expected or deterioration in characteristics can be observed regardless of which element is selected.
[0008]
In the formula (1), y represents the amount of Ni, and y + z satisfies 3.0 ≦ x ≦ 3.5. If y + z is less than 3.0, it becomes difficult to release hydrogen, and the substantial capacity decreases. If y + z exceeds 3.5, the amount of stored hydrogen decreases, and the flatness of the plateau deteriorates, which may cause the occurrence of a multi-stage plateau.
[0009]
The composition of the hydrogen storage alloy of the present invention is not particularly limited as long as the above formula (1) is satisfied. For example, La 0.70 Mg 0.30 Ni 3.30 and La 0.70 Mg 0.30 Ni 3.3 . 15 , La 0.70 Mg 0.30 Ni 3.00 , La 0.70 Mg 0.30 Ni 3.50 , La 0.70 Mg 0.30 Ni 2.80 Co 0.50 , La 0.70 Mg 0.30 Ni 3.00 Co 0.30 , La 0.70 Mg 0.30 Ni 3.20 Co 0.10 , La 0.70 Mg 0.30 Ni 3.00 Co 0.20 Al 0.10 Mn 0.10 , La 0.70 Mg 0.25 Ni 2.80 Co 0.50 , La 0.70 Mg 0.35 Ni 2.80 Co 0.50, and the like.
[0010]
The hydrogen storage alloy of the present invention is a crystalline alloy having the above-mentioned composition and manufactured by using a liquid quenching method, and shows (a) to (a) in the following PCT curves of the alloy measured at 40 ° C. c) having any of the properties described above, or having two or more of these properties, and further combining any of these properties with the property of (d), or two or more of the properties of (a) to (d). It is characterized by having. Here, combinations of the properties are (a) + (b), (a) + (c), (b) + (c), (a) + (d), (b) + (d), ( c) + (d), (a) + (b) + (c), (a) + (b) + (d), (a) + (c) + (d), (b) + (c) + (D), (a) + (b) + (c) + (d), and an alloy satisfying all the properties (a) to (d) is most preferable in the present invention.
[0011]
(A) In a PCT curve measured at 40 ° C., H / M at 0.5 MPa is 1.00 or more, preferably 1.05 or more.
(B) In the PCT curve measured at 40 ° C., the PCT curve slope Pf (plateau slope) is 0.7 or less.
(C) In the PCT curve measured at 40 ° C., H / M = 0.3 to 0.9 does not show a substantial two or more plateaus.
(D) In the PCT curve measured at 40 ° C., the equilibrium pressure at H / M = 0.5 is 0.06 MPa or less, preferably 0.05 MPa or less.
[0012]
H / M at the pressure (a) is an index indicating the capacity of a battery using a hydrogen storage alloy as an active material. If the H / M in (a) is less than 1.00, a high capacity cannot be obtained.
When Pf in (b) exceeds 0.7, the charge / discharge capacity at a constant pressure decreases. This Pf is an index indicating the ease of charging and discharging of the battery using the hydrogen storage alloy as an active material and also indicating the homogeneity of the alloy structure. This slope Pf is obtained by Pf = 1n (P H / P L ). The P H wherein a equilibrium pressure in the H / M = 0.6, P L is the equilibrium pressure in the H / M = 0.4. If this value is close to 0, it indicates that the plateau is flat, and if it is larger than 0, it indicates that a slope exists.
The multi-stage plateau of two or more stages in the above (c) is often caused by non-uniformity of the alloy structure, and depending on the level difference, adversely affects the charge / discharge characteristics of a battery, and depends on the plateau pressure. The capacity of the battery itself also decreases.
The equilibrium pressure in the above (d) is an index indicating the ease of charging and discharging of a battery using a hydrogen storage alloy as an active material. . If the equilibrium pressure is lower than necessary, the discharge characteristics, particularly the high-rate discharge characteristics, may be adversely affected. Therefore, the lower limit is preferably 0.02 MPa, particularly preferably 0.025 MPa.
[0013]
As described above, the hydrogen storage alloy of the present invention is a crystalline alloy manufactured using the liquid quenching method. Here, the liquid quenching method is not particularly limited, and a known liquid quenching method and the like can be mentioned. Preferably, a strip casting method using a tundish is preferable. Further, the crystalline alloy is intended to exclude an alloy that is entirely in an amorphous state, and may be any material having a crystal. The presence of such a crystal can be easily confirmed by an X-ray diffraction method or the like.
[0014]
The hydrogen storage alloy of the present invention uses, for example, a metal element or a master alloy constituting the composition represented by the above formula (1) as a raw material, heats and melts the raw material, cools and solidifies it by a liquid quenching method, and has a surface temperature of 700 ° C. After the above alloy ingot is obtained, when the alloy ingot is cooled to 100 ° C. or less to produce an alloy, a specific heat holding step is performed before the alloy ingot is cooled to 100 ° C. or less. It can be obtained by the production method of the invention.
In the production method of the present invention, the heating and melting of the raw material can be performed by high frequency melting or the like in an atmosphere of an inert gas such as an argon gas using a melting furnace such as a crucible. Melting conditions can be appropriately selected according to the alloy composition and the like based on known conditions.
[0015]
In the production method of the present invention, in order to obtain an alloy ingot having a surface temperature of 700 ° C. or higher, preferably 800 ° C. or higher from the melted alloy by heating by a liquid quenching method, for example, the alloy melt is formed into a ribbon or flake. It can be performed by cooling and solidifying. The thinning or thinning of the alloy melt can be carried out, for example, using a roll cooling / solidifying device such as a twin roll or a single roll, a disk cooling / solidifying device using a rotating disk or the like, and other known cooling / solidifying devices. Further, each cooling and solidifying device may be provided with a tundish or the like capable of controlling the flow of the alloy melt in order to obtain an alloy slab having a uniform thickness. Particularly, the single roll method is preferable.
The cooling and solidifying conditions can be appropriately selected in consideration of known conditions and the like according to the target hydrogen storage alloy. The cooling rate is usually about 1000 to 10000C / sec, preferably 1000 to 5000C / sec, particularly preferably 1000 to 3000C / sec.
[0016]
In the production method of the present invention, before cooling the surface temperature of the alloy ingot to 100 ° C. or lower, preferably 400 ° C. or lower, a heat holding step of holding the alloy ingot in a predetermined temperature range for a predetermined time is performed. The alloy crystal of the alloy ingot is homogenized to a desired size. When the alloy crystal is controlled after the surface temperature of the alloy ingot has dropped to 100 ° C. or lower, the energy loss required for the control increases. Therefore, the heat holding step is performed before the surface temperature of the obtained alloy ingot is reduced to preferably 400 ° C. or lower, particularly preferably 500 ° C. or lower. Generally, the control of the alloy crystal is such that the longer the time the alloy ingot is kept at a specific high temperature state, the larger the crystal becomes, and the shorter the time, the smaller the crystal becomes. In addition, the temperature and time vary depending on the alloy composition.
[0017]
In the manufacturing method of the present invention, the heat holding step is a step of holding at one or more temperature ranges selected from the range of 500 to 1000 ° C., preferably 500 to 800 ° C. for 1 to 10 minutes. Such a heat holding step of holding at a predetermined temperature range for a predetermined time has not been conventionally performed, and usually, only a heat treatment may be performed after cooling to about room temperature. In the conventional heat treatment for raising the temperature of an alloy ingot once cooled to room temperature to a specific temperature, the heat treatment of a portion that easily rises in temperature depending on the temperature and time progresses excessively. Since this tendency is the same in the cooling process after the heat holding step in the present invention, it is preferable to quickly cool to near room temperature after the heat holding step. Therefore, in the production method of the present invention, it is preferable that after the alloy ingot is cooled to 100 ° C. or lower, usually at about normal temperature, the heat treatment step at 400 ° C. or higher in the conventional method is not performed.
[0018]
In the production method of the present invention, after the heat holding step, the desired hydrogen storage alloy can be obtained by cooling the alloy ingot to 100 ° C. or lower, preferably to about room temperature, preferably by forced cooling.
[0019]
【The invention's effect】
Since the hydrogen storage alloy of the present invention has a specific composition and physical properties showing a specific PCT curve, it is possible to substantially improve the capacity of a secondary battery. It is possible to provide a Mg-containing hydrogen storage alloy that can be used as a secondary battery negative electrode active material having various properties such as no charge and easy charge and discharge. Further, in the production method of the present invention, since the specific heat holding step is performed, it is possible to efficiently and industrially usefully produce the hydrogen storage alloy of the present invention without performing the conventional heat treatment step. it can.
[0020]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
Example 1
As a starting material, lanthanum metal manufactured by Santoku Co., Ltd. and Mg having a purity of 99.9% were blended so as to have a composition shown in Table 1, and were subjected to high frequency melting in an argon gas atmosphere, and a cooling rate of 2000 to 5000 ° C./sec. Under the conditions described above, casting was performed using a single-roll casting apparatus, and the temperature was maintained at 700 ° C. for 5 minutes before cooling to room temperature, and then immediately cooled to around room temperature. The obtained alloy was subjected to hydrogen absorption / desorption characteristics at 40 ° C. using a PCT device manufactured by Resca, as a PCT equilibrium pressure at H / M = 0.5, an H / M value as a PCT storage amount at 0.5 MPa, and H / M. The Pf value at M 0.4 to 0.5 and the presence or absence of substantially two or more plateau portions at H / M = 0.3 to 0.9 were measured. Table 2 shows the results.
Subsequently, 10 g of the obtained alloy powder, 1 g of copper powder as a conductive agent, and 0.3 g of FEP powder (0.3 g of propylene tetrafluoroethylene hexafluoride) were mixed to prepare a pellet electrode having a diameter of 20 mm. did. This electrode was immersed in a 6N KOH solution, and a battery was constructed using a mercury oxide reference electrode. The battery capacity of this battery after 10 cycles was measured with a potentiogalvanostat (Hokuto Denko). Table 2 shows the results.
[0021]
Examples 2 to 10 , Comparative Examples 1 to 3
Except that the raw material composition was changed as shown in Table 1, the same treatment as in Example 1 was performed to produce a hydrogen storage alloy. PCT and electrode characteristics of the obtained alloy were measured in the same manner as in Example 1. Table 2 shows the results.
[0022]
Comparative Example 4
Except that the raw material composition was changed as shown in Table 1, the casting was performed in exactly the same manner as in Example 1, and then kept at 400 ° C. for 5 minutes before cooling to room temperature, and then immediately cooled to near normal humidity. An alloy was obtained. PCT and electrode characteristics of the obtained alloy were measured in the same manner as in Example 1. Table 2 shows the results.
[0023]
Comparative Example 5
Except that the raw material composition was changed as shown in Table 1, the casting was performed in exactly the same manner as in Example 1, and then kept at 700 ° C. for 20 minutes before cooling to room temperature, and then immediately cooled to near normal humidity. An alloy was obtained. PCT and electrode characteristics of the obtained alloy were measured in the same manner as in Example 1. Table 2 shows the results.
[0024]
Comparative Example 6
Casting was carried out in exactly the same manner as in Example 1 except that the raw material composition was changed as shown in Table 1. The alloy was kept at 700 ° C. for 5 minutes before cooling to room temperature, and then quickly cooled to around room temperature to obtain an alloy. The obtained alloy was further heat-treated at 950 ° C. for 6 hours in an argon atmosphere. PCT and electrode characteristics of the obtained alloy were measured in the same manner as in Example 1. Table 2 shows the results.
[0025]
Comparative Example 7
Casting was carried out in exactly the same manner as in Example 1 except that the raw material composition was changed as shown in Table 1, and quenched to room temperature without a heat holding region to obtain an alloy. The obtained alloy was heat-treated at 950 ° C. for 6 hours in an argon atmosphere. PCT and electrode characteristics of the obtained alloy were measured in the same manner as in Example 1. Table 2 shows the results.
[0026]
Comparative Example 8
Casting was carried out in exactly the same manner as in Example 1 except that the raw material composition was changed as shown in Table 1, and quenched to room temperature without a heat holding region to obtain an alloy. PCT and electrode characteristics of the obtained alloy were measured in the same manner as in Example 1. Table 2 shows the results.
[0027]
[Table 1]
[Table 2]
Claims (10)
Ｌｎ１−ＸＭｇＸＮｉｙＭＺ （１）
（式中、ＬｎはＹ、Ｓｃを含むＬａからＬｕまでの希土類金属元素からなる群より選択される少なくとも１種、ＭはＣｏ、Ｍｎ、Ａｌ、Ｆｅ、Ｖ、Ｃｒ、Ｎｂ、Ｇａ、Ｚｎ、Ｓｎ、Ｃｕ、Ｓｉ、Ｐ、Ｂからなる群より選択される少なくとも１種を示す。０．１≦ｘ≦０．５、２．５≦ｙ≦３．５、０≦ｚ≦０．５、３．０≦ｙ＋ｚ≦３．５である）A crystalline alloy having a composition represented by the formula (1) and manufactured by a liquid quenching method, wherein a H / M at 0.5 MPa is 1 in a PCT curve of the alloy measured at 40 ° C. A hydrogen storage alloy, which is not less than 0.000.
Ln 1-X Mg X Ni y M Z (1)
(Wherein, Ln is at least one selected from the group consisting of rare earth metal elements from La to Lu containing Y and Sc, and M is Co, Mn, Al, Fe, V, Cr, Nb, Ga, Zn, At least one selected from the group consisting of Sn, Cu, Si, P, and B. 0.1 ≦ x ≦ 0.5, 2.5 ≦ y ≦ 3.5, 0 ≦ z ≦ 0.5, 3.0 ≦ y + z ≦ 3.5)
冷却固化した表面温度７００℃以上の合金鋳塊を１００℃以下に冷却する前に、５００〜１０００℃から選ばれる１つ以上の温度域で１〜１０分間保持する熱保持工程を行うことを特徴とする請求項１記載の水素吸蔵合金の製造方法。After using a metal element or a mother alloy constituting the composition represented by the formula (1) as a raw material, the raw material is heated and melted, and cooled and solidified by a liquid quenching method to obtain an alloy ingot having a surface temperature of 700 ° C. or higher. In a method of manufacturing an alloy by cooling an alloy ingot to 100 ° C. or less,
Before cooling the cooled and solidified alloy ingot having a surface temperature of 700 ° C. or more to 100 ° C. or less, a heat holding step of holding the alloy ingot in one or more temperature ranges selected from 500 to 1000 ° C. for 1 to 10 minutes is performed. The method for producing a hydrogen storage alloy according to claim 1.
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| EP1602857A2 (en) | 2004-05-31 | 2005-12-07 | Tsubakimoto Chain Co. | Hydraulic tensioner |
| WO2006085542A1 (en) * | 2005-02-08 | 2006-08-17 | Mitsui Mining & Smelting Co., Ltd. | Hydrogen-occluding alloy with low cobalt content |
| WO2007018292A1 (en) * | 2005-08-11 | 2007-02-15 | Gs Yuasa Corporation | Hydrogen-storage alloy, hydrogen-storage alloy electrode, secondary cell, and process for producing hydrogen-storage alloy |
| WO2007034760A1 (en) * | 2005-09-21 | 2007-03-29 | Sanyo Electric Co., Ltd. | Alkaline storage battery |
| EP1826283A1 (en) * | 2006-02-28 | 2007-08-29 | Saft | Hydridable alloy for alkaline storage battery |
| JP2008084818A (en) * | 2006-02-09 | 2008-04-10 | Sanyo Electric Co Ltd | Storage battery and hydrogen-absorbing alloy for same |
| US7820325B2 (en) | 2005-05-26 | 2010-10-26 | Saft | Alkaline electrolyte storage battery having an anode formed of an active material composition |
| US8105715B2 (en) * | 2007-08-30 | 2012-01-31 | Sanyo Electric Co., Ltd. | Hydrogen-absorbing alloy and nickel-metal hydride storage battery |
| EP2487270A1 (en) | 2010-11-29 | 2012-08-15 | Saft | Active material for a negative electrode of a nickel-metal hydride alkaline accumulator |
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| JPH0925529A (en) * | 1995-07-10 | 1997-01-28 | Santoku Kinzoku Kogyo Kk | Rare earth metal-nickel based hydrogen storage alloy and its production, and cathode for nickel-hydrogen secondary battery |
| JP2002069554A (en) * | 2000-09-06 | 2002-03-08 | Toshiba Corp | Hydrogen storage alloy, alkali secondary battery, hybrid car and electric vehicle |
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| JPH0925529A (en) * | 1995-07-10 | 1997-01-28 | Santoku Kinzoku Kogyo Kk | Rare earth metal-nickel based hydrogen storage alloy and its production, and cathode for nickel-hydrogen secondary battery |
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| EP1602857A2 (en) | 2004-05-31 | 2005-12-07 | Tsubakimoto Chain Co. | Hydraulic tensioner |
| WO2006085542A1 (en) * | 2005-02-08 | 2006-08-17 | Mitsui Mining & Smelting Co., Ltd. | Hydrogen-occluding alloy with low cobalt content |
| US7820325B2 (en) | 2005-05-26 | 2010-10-26 | Saft | Alkaline electrolyte storage battery having an anode formed of an active material composition |
| US8277582B2 (en) | 2005-08-11 | 2012-10-02 | Gs Yuasa International Ltd. | Hydrogen absorbing alloy, hydrogen absorbing alloy electrode, secondary battery, and production method of hydrogen absorbing alloy |
| JP5146934B2 (en) * | 2005-08-11 | 2013-02-20 | 株式会社Ｇｓユアサ | Hydrogen storage alloy, hydrogen storage alloy electrode, secondary battery, and method for producing hydrogen storage alloy |
| US7951326B2 (en) | 2005-08-11 | 2011-05-31 | Gs Yuasa International Ltd. | Hydrogen absorbing alloy, hydrogen absorbing alloy electrode, secondary battery and production method of hydrogen absorbing alloy |
| WO2007018292A1 (en) * | 2005-08-11 | 2007-02-15 | Gs Yuasa Corporation | Hydrogen-storage alloy, hydrogen-storage alloy electrode, secondary cell, and process for producing hydrogen-storage alloy |
| US8257862B2 (en) | 2005-09-21 | 2012-09-04 | Sanyo Electric Co., Ltd. | Alkaline storage battery |
| JP5252920B2 (en) * | 2005-09-21 | 2013-07-31 | 三洋電機株式会社 | Alkaline storage battery |
| WO2007034760A1 (en) * | 2005-09-21 | 2007-03-29 | Sanyo Electric Co., Ltd. | Alkaline storage battery |
| US8317950B2 (en) | 2006-02-09 | 2012-11-27 | Sanyo Electric Co., Ltd. | Method of making hydrogen-absorbing alloy for alkaline storage battery, and alkaline storage battery |
| JP2008084818A (en) * | 2006-02-09 | 2008-04-10 | Sanyo Electric Co Ltd | Storage battery and hydrogen-absorbing alloy for same |
| EP1826283A1 (en) * | 2006-02-28 | 2007-08-29 | Saft | Hydridable alloy for alkaline storage battery |
| FR2897875A1 (en) * | 2006-02-28 | 2007-08-31 | Accumulateurs Fixes | HYDRURABLE ALLOY FOR ALKALINE ACCUMULATOR |
| US20150118557A1 (en) * | 2006-08-09 | 2015-04-30 | Gs Yuasa International Ltd. | Hydrogen Storage Alloy, Hydrogen Storage Alloy Electrode, Secondary Battery, And Method For Producing Hydrogen Storage Alloy |
| US9496550B2 (en) * | 2006-08-09 | 2016-11-15 | Gs Yuasa International Ltd. | Hydrogen storage alloy, hydrogen storage alloy electrode, secondary battery, and method for producing hydrogen storage alloy |
| US8105715B2 (en) * | 2007-08-30 | 2012-01-31 | Sanyo Electric Co., Ltd. | Hydrogen-absorbing alloy and nickel-metal hydride storage battery |
| EP2487270A1 (en) | 2010-11-29 | 2012-08-15 | Saft | Active material for a negative electrode of a nickel-metal hydride alkaline accumulator |
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