JP2004303910A - Capacitor and capacitor electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for obtaining a small and large capacitance capacitor with large a electrostatic capacity per unit weight by a simple method. <P>SOLUTION: In the capacitor 10 having a pair of electrodes 2A and 2B, at least one electrode 2A or 2B is constituted by using a hydrogen storage alloy. It is suitable that the equilibrium potential monotonously changes in a noble direction with an increase of oxidation electrical quantity in an electrochemical PCT curve as hydrogen storage alloy. Hydrogen storage alloy can occlude and discharge hydrogen inside, and occlusion/discharge of hydrogen are equivalent to those by electrochemical reaction. Hydrogen storage alloy is applied as the electrode 2A and/or the electrode 2B of the capacitor 10, and it is charged/discharged by electrochemical reaction. Thus, electrostatic capacity of the capacitor 10 is improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

なお、式中、Ｍは水素吸蔵合金、ＭＨは水素化物
【００１９】
充電時には、正極（電極２Ａ）では水素原子が放出されて水が生成される。一方、負極（電極２Ｂ）では、水素吸蔵合金が水の電気分解で生成した水素原子を吸蔵して水素化物となる。具体的には、負極では、電極２Ｂを構成する水素吸蔵合金の水素吸蔵サイトに、水素原子が侵入することにより、電気が蓄えられる。放電時には、逆に負極（電極２Ｂ）より水素原子が放出され水にかえるとともに、電気が生成される。
つまり、従来のキャパシタでは、一対の分極性電極に対するイオンの吸着および脱離を利用して、充放電を行っていた。このため、分極性電極、つまり活性炭の比表面積を大きくすることが、静電容量を向上させる上で重要であり、活性炭をガス賦活させることでその比表面積をできるだけ大きくして静電容量を上げていた。これに対し、電極２Ａ，２Ｂとしての水素吸蔵合金によれば、水素原子を合金内部まで取り込むことができるため、活性炭を用いていた場合のようにわざわざガス賦活せずとも、静電容量を上げることが可能となる。また、水素吸蔵合金は金属であるから、活性炭に較べて導電性が高く、活性炭を用いた場合よりも密度が高い電極を作製することができる。これにより、従来よりもエネルギー密度が大きなキャパシタ１０を得ることができる。そして、高密度な電極を用いることで、キャパシタ１０の小型大容量化を図ることができる。さらに、水素吸蔵合金は接触抵抗が低いため、水素吸蔵合金を電極２Ａ，２Ｂとすることにより、キャパシタ１０の内部抵抗を低減することもできる。
【００２０】
電極２Ａ，２Ｂとして機能する水素吸蔵合金としては、以下の特徴を有するものを採用する。すなわち、電気化学的ＰＣＴ曲線における酸化電気量の増加にともない、平衡電位が単調に貴な方向に変化するものが好適である。水素吸蔵合金は、二次電池用電極として実用化されているが、電池には電圧が一定であることが望まれる。このため、二次電池用電極としての水素吸蔵合金には、電気化学的ＰＣＴ曲線における酸化電気量が変動しても、水素圧の変動が少ない領域があるもの、換言すれば、できるだけ電気化学的ＰＣＴ曲線のプラトーが平坦であるものが望まれる。これに対し、キャパシタには電気量と電圧が比例することが望まれる。電気化学的ＰＣＴ曲線における酸化電気量の増加にともない、平衡電位が単調に貴な方向に変化する水素吸蔵合金は、電気量と電圧が比例するという傾向を示すため、キャパシタとして好適に用いることができる。なお、ｘの定義域に含まれるｘ１＜ｘ２を満たす２点ｘ１、ｘ２に対して、ｆ（ｘ１）＜ｆ（ｘ２）が成り立つとき、単調に貴な方向に変化するという。
【００２１】
ここで、電気化学的ＰＣＴ曲線の傾斜が大きくなればなるほど、電圧が速く変化することになるため、水素吸蔵合金内に蓄電できる容量は小さくなる。一方、電気化学的ＰＣＴ曲線の傾斜が小さくなれば、注入する電気量に対して電圧変化が小さいので、水素吸蔵合金内に蓄電できる容量は大きくなる。よって、電極２Ａ，２Ｂとしての水素吸蔵合金は、電気化学的ＰＣＴ曲線の傾斜が小さい合金の方が望ましい。以下、水素吸蔵合金の望ましい組成について説明する。なお、電気化学的ＰＣＴ曲線の傾斜を制御するには、組成のみならず、製法も重要な要素である。電極２Ａ，２Ｂとして好適に機能する水素吸蔵合金の望ましい製法については、後述する。
【００２２】
電極２Ａ，２Ｂとして機能する水素吸蔵合金として、その組成が以下の式（２）で示されるＴｉ−Ｎｉ系合金または式（３）で示されるＴｉ−Ｃｒ系合金のものが望ましい。Ｔｉ−Ｎｉ系合金またはＴｉ−Ｃｒ系合金の組成を式（２）、（３）で示されるものにすることによって、ｂｃｃ型Ｔｉ−Ｎｉ系合金またはｂｃｃ型Ｔｉ−Ｃｒ系合金を得ることができる。
【００２３】
Ｔｉ_{（１００−ａ−ｂ−ｃ−ｄ）}Ｃｒ_ａＸ_ｂＸ’_ｃＮｉ_ｄ・・・式（２）
但し０≦ａ（ａｔ％）≦８０、０≦ｂ（ａｔ％）≦１０、０≦ｃ（ａｔ％）≦３０、５≦ｄ（ａｔ％）≦５０で表され、前記ＸがＲｕ、Ｒｈ、Ｏｓ、Ｉｒ、Ｐｄ、Ｐｔ、Ｒｅの少なくとも一種の元素、前記Ｘ’がＶ、Ｍｏ、ＷおよびＡｌの少なくとも一種の元素
【００２４】
Ｔｉ_{（１００−ａ’−ｂ’−ｃ’−ｄ’）}Ｃｒ_ａＸ_ｂＸ’_ｃＮｉ_ｄ・・・式（３）
但し２０≦ａ’（ａｔ％）≦８０、０≦ｂ’（ａｔ％）≦１０、０≦ｃ’（ａｔ％）≦３０、０≦ｄ’（ａｔ％）≦５０で表され、前記ＸがＲｕ、Ｒｈ、Ｏｓ、Ｉｒ、Ｐｄ、Ｐｔ、Ｒｅの少なくとも一種の元素、前記Ｘ’がＶ、Ｍｏ、ＷおよびＡｌの少なくとも一種の元素
【００２５】
なお、式（３）において、合金組成中にＮｉを含有しない場合、つまり式（３）中でｄ’＝０の場合には、Ｔｉ−Ｃｒ系合金をＮｉドープさせて、合金を電気化学的に活性させればよい。また、式（２）に示したＴｉ−Ｎｉ系合金、式（３）に示したＴｉ−Ｃｒ系合金のいずれの場合においても、さらに、Ｍｎ、Ｆｅ、Ｃｏ、Ｃｕ、Ｎｂ、Ｔａ、ＢおよびＣの少なくとも１種の元素（Ｔ元素）、Ｙおよびランタノイド元素の少なくとも１種の元素（Ｌ元素）、を含有していてもよい。
【００２６】
Ｘ元素は、Ｔｉ−Ｃｒ系合金に微量に含有させるだけで高いｂｃｃ相形成能を有し、有害なＣ_１４型、Ｃ_１５型等のラーベス相をほとんど含まないｂｃｃ単相合金を得ることができる。また、このＸ元素とＸ’元素を同時に含有させることにより、高価なＸ元素の含有量を低く押さえ、コストと単位重量あたりの水素吸蔵量においてバランスのとれた高い実用性を有する水素吸蔵合金を得ることができる。また、Ｔ元素を含有させることによって、熱処理温度の制御、合金の耐食性向上、合金の集電特性等を制御することが可能となる。Ｌ元素は、酸素との親和力が強いため合金中に存在する酸素をＬ元素酸化物として除去する効果を発揮する。その結果、比較的酸素量の多い原料も工業的に有効に利用することも可能となる。
【００２７】
以上、電極２Ａ，２ＢをＴｉ−Ｎｉ系合金またはＴｉ−Ｃｒ系合金で構成する場合について詳述した。以上の組成を採用することで、電極２Ａ，２ＢとしてのＴｉ−Ｎｉ系合金またはＴｉ−Ｃｒ系合金を、ｂｃｃ相を主相とするものとすることができる。合金がｂｃｃ相を主相とするか否かはＸ線回折により判断することができる。本発明においては、回折線の積分強度による以下の式（４）による割合（％）が５０％以上のものをｂｃｃ相が主相の合金と定義する。
ｂｃｃ（１１０）／［ｂｃｃ（１１０）＋｛Ｃ１４Ｌａｖｅｓ（２０１）＋Ｃ１５Ｌａｖｅｓ（３１１）｝×２］…式（４）
【００２８】
また、上記したｂｃｃ相を主相とする水素吸蔵合金の他に、ＣｓＣｌ型の合金を用いて電極２Ａ，２Ｂを構成することもできる。ＣｓＣｌ型の合金としては、Ｔｉ−Ｎｉ系合金、Ｔｉ−Ｎｉ−Ｐｄ系合金、Ｔｉ−Ｎｉ−Ｍｎ系合金、Ｔｉ−Ｎｉ−Ｆｅ系合金等が挙げられる。ＣｓＣｌ型の合金は、上述したｂｃｃ型の合金と同様に、電気化学的ＰＣＴ曲線における酸化電気量の増加にともない、平衡電位が単調に貴な方向に変化する。よって、ＣｓＣｌ型の合金はキャパシタ用電極として好適に用いることができる。ＣｓＣｌ型の合金のなかでは、電解液に対する耐食性という理由から、Ｔｉ−Ｎｉ系合金が好ましい。ＣｓＣｌ型の合金を用いて電極２Ａ，２Ｂを構成する場合には、ＣｓＣｌ型結晶構造単相のもの、もしくはＣｓＣｌ型結晶構造を主相とするものが望ましい。
【００２９】
電極２Ａ，２Ｂとしての水素吸蔵合金粉末の平均粒径は、５〜３００μｍとすることが望ましい。平均粒径が５μｍよりも小さいと、１粒子あたりの水素吸放出量が小さくなってしまう。一方、粉末の平均粒径が大きくなると、水素吸蔵放出反応に伴う体積変化が大きくなり、水素吸蔵合金粉末の微粉化が進行しやすい。微粉化の進行は、水素吸蔵合金粉末の比表面積の増大をもたらし、電極２Ａ，２Ｂでの電解液との接触界面を増大させ、合金の腐食を進行させる。そして、合金の腐食は、単位体積当たりの水素吸蔵量の減少し、導電性の劣化につながるため、好ましくない。この微粉化の進行は、粒径が３００μｍを超えると顕著となる。よって、高い水素吸放出量を確保するためには、水素吸蔵合金粉末の平均粒径を５〜３００μｍとする。望ましい平均粒径は、１０〜１００μｍ、さらに望ましい平均粒径は２０〜７５μｍである。
【００３０】
なお、電極２Ａ，２Ｂの両者を水素吸蔵合金とする場合には、各電極を構成する水素吸蔵合金の組成は同一であってもよいし、相違していてもよい。同様に、電極２Ａ，２Ｂの両者を水素吸蔵合金とする場合には、各電極を構成する水素吸蔵合金の平均粒径は同一であってもよいし、相違していてもよい。
【００３１】
次に、本実施の形態に係るキャパシタ１０の望ましい製造方法について述べる。本実施の形態に係るキャパシタ１０は、水素吸蔵合金作製工程、電極作製工程を含む。なお、ここでは水素吸蔵合金としてＴｉ−Ｎｉ系合金を作製する場合を例にして、水素吸蔵合金作製工程を説明する。
【００３２】
＜水素吸蔵合金作製工程＞
電極２Ａ，２Ｂとして好適に用いられるＴｉ−Ｎｉ系合金母材は、例えばアーク溶解法により作製することができる。ここで、アーク溶解法によりＴｉ−Ｎｉ系合金母材を作製する場合における水素吸蔵合金作製工程は、合金元素の秤量（ステップＳ１０１）、アーク溶解（ステップＳ１０３）、急速急冷（以下、急冷）（ステップＳ１０５）の各工程から構成される。なお、合金組成によっては急冷を行うことなく、電気化学的ＰＣＴ曲線における酸化電気量の増加にともなって平衡電位が単調に貴な方向に変化する水素吸蔵合金を得ることも可能である。
【００３３】
まず、ステップＳ１０１において、得たい水素吸蔵合金を構成する各金属について組成比率に該当する量を秤量する。例えば、Ｔｉ−Ｎｉ系合金をＴｉ−Ｎｉ−Ｃｒ−Ｍｏとしたい場合には、ＴｉとＮｉとＣｒとＭｏとを組成比率に該当する量を秤量する。
【００３４】
ステップＳ１０１において合金元素の秤量を行った後、ステップＳ１０３に進む。ステップＳ１０３では、秤量された各金属がアーク溶解装置（図示せず）に投入され、約７０ｋＰａのアルゴン雰囲気中で溶融・混合する。
【００３５】
ステップＳ１０３においてアーク溶解を行った後、ステップＳ１０５に進む。ステップＳ１０５では、ステップＳ１０３で得られた溶融状態のものをロール急冷し、急冷凝固させる。もしくは、溶融物を水中へ投入することにより、急冷凝固させる。急冷は必須のものではないが、急冷により、電気化学的ＰＣＴ曲線における酸化電気量の増加にともなって平衡電位が単調に貴な方向に変化する、水素吸蔵合金を容易に得ることができる。冷却速度は１０００Ｋ／ｓｅｃ以上とすることが望ましい。
【００３６】
こうして得られたｂｃｃ型Ｔｉ−Ｃｒ系合金のインゴットを粉砕して３００μｍ以下の粉末とする。この粉末を用いて、本実施の形態では電極２Ａ，２Ｂを形成する。なお、粉砕は、スタンプミル等を用いた機械的な粉砕であってもよいし、水素化粉砕でもよい。
【００３７】
＜電極作製工程＞
電極作製工程では、水素吸蔵合金作製工程で得られた水素吸蔵合金粉末、結着剤、導電性粉末及び水を混練することによりペーストを調製する。結着剤としては、例えばポリビニルアルコール（ＰＶＡ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等を用いることができる。また、導電性粉末としては、例えば、電解銅、黒鉛、カーボンブラックを用いることができる。導電性粉末の平均粒径は、０．１〜１００μｍ 、特に１０〜８０μｍであることが好ましい。導電性粉末は、水素吸蔵合金粉末に対して０〜２０ｗｔ％、望ましくは０〜５ｗｔ％添加する。電極２Ａ，２Ｂの組成は、重量比で、水素吸蔵合金粉末：結着剤：導電性粉末＝８０〜１００：０〜１０：０〜１０の範囲が好ましい。
次いで、得られたペーストを導電性基板に塗布ないし充填する。導電性基板としては、例えば、パンチドメタルや、網状、スポンジ状、繊維状、もしくはフェルト状の金属多孔体を用いることができる。
続いて、ペーストが塗布ないし充填された導電性基板を乾燥し、プレスを施すことにより電極２Ａ，２Ｂを得ることができる。
【００３８】
こうして得られた電極２Ａ，２Ｂを、本実施の形態ではキャパシタ１０用に用いる。水素吸蔵合金粉末を含む電極２Ａ，２Ｂは、その内部に水素原子を取り込むことができるため、単位重量あたりの静電容量を従来よりも大幅に向上させることができる。しかも、電極２Ａ，２Ｂ自身が金属であり、活性炭と較べて５倍以上も高密度であるため、エネルギー密度の大きなキャパシタ１０を得ることができる。これにより、小型かつ高容量のキャパシタ１０を得ることができる。
【００３９】
【実施例】
以下本発明を具体的な実施例に基づいて説明する。
（実施例１）
前述したアーク溶解装置を用いた溶融・混合・凝固を繰り返すことによって表１に示す７種類の合金（インゴット）を得た。なお、各インゴットは、急冷して得られたものである。
次いで、得られた合金をスタンプミルを用いて７５μｍ以下に粉砕した。なお、Ｎｉを合金組成に含有していない合金については平均粒径１μｍのＮｉ粉末をメカニカルアロイング法で被着させた後、７５μｍ以下に粉砕した。
【００４０】
【表１】

【００４１】
表１に示す７種類の合金について、Ｘ線回折により相同定を行ったところ、いずれもｂｃｃを主相としていることが確認された。
次いで、表１に示した各合金粉末に対し、その重量比が１：３になるように電解銅粉末を混合した。具体的には、電解銅粉３（０．７５ｇ）に対し、合金粉末を１（０．２５ｇ）の割合で混合し、プレス成形して１．０ｇの評価用電極を７種類作製した。この評価用電極をそれぞれ電極２Ａ，２Ｂとして用い、電解液を６ＭＫＯＨとして、充放電させたときの端子電圧と電気量を測定した。その結果、いずれも同様の傾向を示す充放電曲線が得られた。その傾向を図２に概念的に示す。
【００４２】
図２は、本実施例に係る水素吸蔵合金を電極２Ａ，２Ｂとして用いた場合には、充放電曲線における電気量と電圧が比例することを示している。このことから、本実施例に係る水素吸蔵合金は、キャパシタとして好適な充放電曲線を示すことが容易に理解できる。
【００４３】
試料Ｎｏ．１〜７について、図２に示したような充放電曲線を求め、これから各電極の単極容量を求めた。その結果を表１に併せて示す。表１から、各電極は、いずれも２０００Ｆ／ｇ以上という優れた静電容量を得ていることがわかる。特に、合金組成にＮｉを含む試料Ｎｏ．１〜５についてはいずれも３０００Ｆ／ｇ以上という高い静電容量を得ていること、試料Ｎｏ．５については１００００Ｆ／ｇ以上という非常に高い値を得ていることが注目される。
【００４４】
次に、試料Ｎｏ．１を電極２Ａ，２Ｂとして用い、電解液を６ＭＫＯＨとして、キャパシタ１０を作製し、電気化学的ＰＣＴ曲線を測定した。その結果を図３に示す。
図３から、電気化学的ＰＣＴ曲線が、酸化電気量の増加にともない、平衡電位が単調に貴な方向に変化していることがわかる。こうした電気化学的ＰＣＴ曲線を示すということは、キャパシタ１０中の水素吸蔵合金が、電極２Ａ，２Ｂとして有効に機能しているといえる。
【００４５】
（実施例２）
電極２Ａ，２Ｂのうち、一方の電極をＮｉとし、他方の電極を実施例１で得られた試料Ｎｏ．１〜７として、７種類のキャパシタ１０を作製した。なお、セパレータ１としてはポリプロピレン不織布、集電体３Ａ，３Ｂとしてはニッケル板、絶縁性ガスケット４としてはポリプロピレンを用いた。
【００４６】
得られた７種類のキャパシタ１０について、図２に示したような充放電曲線を求め、これから各電極の単極容量を求めた。両極の単極容量を合計した静電容量を表１に併せて示す。
【００４７】
表１に示したように、電極２Ａ，２Ｂのうち、一方の電極のみを水素吸蔵合金とした場合にも、キャパシタ１０として高い静電容量を得ることができることが確認された。
【００４８】
（比較例１）
電極のうち、一方の電極をＮｉとし、他方の電極を活性炭とした以外は、実施例２と同様の手順でキャパシタを作製した。この活性炭は、平均粒径２５μｍ、比表面積１５００ｍ^２／ｇのものである。実施例２と同様の要領で静電容量を測定した結果、静電容量は１８０Ｆ／ｇであった。
【００４９】
（比較例２）
電極のうち、両方の電極を活性炭とした以外は、実施例２と同様の手順でキャパシタを作製した。この活性炭は、平均粒径２５μｍ、比表面積１５００ｍ^２／ｇのものである。実施例２と同様の要領で静電容量を測定した結果、静電容量は９０Ｆ／ｇであった。
【００５０】
【発明の効果】
本発明によれば、単位重量あたりの静電容量が大きく、かつ小型大容量のキャパシタを簡易な方法で得ることができる。
【図面の簡単な説明】
【図１】本実施の形態に係るキャパシタの構成を模式的に示す断面図である。
【図２】実施例１で測定した充放電曲線である。
【図３】実施例１で測定した電気化学ＰＣＴ曲線である。
【符号の説明】
１…セパレータ、２Ａ，２Ｂ…電極（水素吸蔵合金、正極、負極）、３Ａ，３Ｂ…集電体、４…絶縁性ガスケット、１０…キャパシタ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a capacitor having a large capacitance per unit weight, wherein at least one of a pair of electrodes is made of a hydrogen storage alloy.
[0002]
[Prior art]
The electric double layer capacitor utilizes electric energy stored in the electric double layer formed at the interface between the polarizable electrode and the electrolyte, and is a large-capacity capacitor capable of instantaneously charging and discharging farad-order electric capacity. . Activated carbon has been conventionally used as a polarizable electrode material of an electric double layer capacitor. This activated carbon is obtained by carbonizing synthetic resin such as phenol, coke, and pitch by heat treatment.
[0003]
By the way, the electric double layer capacitance C of the polarizable electrode (single electrode) can be represented by the following equation (1).
C = (ε / d) · Sa (1)
In equation (1),
ε = dielectric constant of electrolyte solution, d = thickness of electric double layer,
Sa = specific surface area effective for forming an electric double layer (Sa = αS, 0 ≦ α ≦ 1 with respect to total specific surface area S)
[0004]
As is apparent from the equation (1), the larger the surface area of the polarizable electrode is, the larger the capacity is obtained from the viewpoint of the capacitance. For this reason, it has been conventionally performed to increase the specific surface area per unit volume of activated carbon as a polarizable electrode material, thereby improving the capacitance of the electric double layer capacitor (for example, Patent Document 1).
[0005]
[Patent Document 1]
JP-A-5-82395 (Claims)
[0006]
[Problems to be solved by the invention]
In order to increase the specific surface area of activated carbon, gas activation is generally performed using steam or the like. Activated carbon as a polarizable electrode that has been activated and has a large specific surface area is sponge-like and very light. For this reason, although the capacitance per unit weight is large, there is a problem that the apparent density of carbon is reduced and the capacity per unit volume is reduced. In order to solve this problem, it is common practice to apply a pressure treatment to activated carbon having a large specific surface area to improve the capacity per unit volume when forming an element. That is, conventionally, in order to obtain a polarizable electrode, at least three steps are required: a process of carbonizing a material such as coke into activated carbon, a process of activating activated carbon gas, and a process of pressurizing activated carbon. are doing.
Therefore, the present invention provides a technique for obtaining a small-capacity, large-capacity capacitor having a large capacitance per unit weight by a simple method using a completely different approach.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present inventor has made various studies. As a result, they have found that it is extremely effective to use a hydrogen storage alloy as an electrode of a capacitor. That is, the present invention is a capacitor including a first electrode and a second electrode, wherein the first electrode and / or the second electrode is configured using a hydrogen storage alloy. To provide a capacitor. The hydrogen storage alloy is an alloy capable of storing and releasing hydrogen therein, and the storage and release of hydrogen respectively correspond to charging and discharging by an electrochemical reaction. As described above, in the present invention, the capacitance of a capacitor is improved by a new approach in which a hydrogen storage alloy is applied as an electrode of the capacitor and charging and discharging are performed by an electrochemical reaction. For this reason, when the hydrogen storage alloy is used, the capacitance of the capacitor can be increased without performing the activation treatment for increasing the specific surface area as in the related art. In a conventional capacitor, a so-called electric double layer is formed at an interface between an electrode and an electrolytic solution by being polarized positively (+) and negatively (-). Due to the increase and decrease of the amount of + and-, the potential of the electrode used in the conventional capacitor changes, and is called a "polarizable electrode". On the other hand, in the present invention, the hydrogen atoms enter the inside of the hydrogen storage alloy as the electrode, and the potential of the hydrogen storage alloy itself as the electrode changes. Therefore, hereinafter, the conventional capacitor electrode is appropriately referred to as “polarizable electrode”, but the capacitor electrode of the present invention is simply referred to as “electrode”.
As the above-mentioned hydrogen storage alloy used as the first electrode and / or the second electrode, an alloy whose equilibrium potential monotonously changes in a noble direction with an increase in the amount of oxidized electricity in an electrochemical PCT curve is preferable. It is. That is, the one in which the equilibrium potential monotonously increases with an increase in the amount of oxidized electricity in the electrochemical PCT curve is suitable as the hydrogen storage alloy used as the first electrode and / or the second electrode. Here, it is desired that the voltage is constant for the battery, while the quantity of electricity is proportional to the voltage of the capacitor. A hydrogen storage alloy whose electrochemical PCT curve has the above-described tendency has a tendency that the quantity of electricity and the voltage are proportional to each other, and thus can be suitably used as a capacitor.
In the capacitor according to the present invention, the first electrode and / or the second electrode can be formed using a Ti—Ni-based hydrogen storage alloy or a Ti—Cr-based hydrogen storage alloy.
In addition, the above-described first electrode and / or second electrode has excellent characteristics such that the capacitance per unit weight of a single electrode is 500 F / g or more.
[0008]
Further, the present invention provides a capacitor including a pair of electrodes composed of a positive electrode and a negative electrode, a separator disposed between the pair of electrodes, and an aqueous electrolytic solution impregnating the pair of electrodes and the separator. A capacitor is provided in which at least one of the pair of electrodes is made of a metal having a hydrogen storage site therein, and hydrogen atoms moving in the capacitor enter the hydrogen storage site. . When a conventional activated carbon is used as an electrode, although hydrogen atoms adhere to the surface, the hydrogen atoms did not penetrate into the inside. On the other hand, in the capacitor according to the present invention, a metal having a hydrogen storage site therein is used as an electrode, and hydrogen atoms can be taken into the electrode, so that a high-density and high-capacity capacitor can be obtained.
In the capacitor according to the present invention, the hydrogen atoms penetrate into the hydrogen storage site of the metal serving as the negative electrode, the capacitor is charged, and the hydrogen atoms that have entered the hydrogen storage site of the metal serving as the negative electrode are released, The capacitor is discharged. On the other hand, the metal serving as the positive electrode is charged by discharging hydrogen atoms from the hydrogen storage site, and the capacitor is discharged by entering hydrogen atoms into the hydrogen storage site of the metal serving as the positive electrode. .
Here, it is possible to use, as at least one of the pair of electrodes, a hydrogen storage alloy in which a phase (bcc phase) having a body-centered cubic crystal structure is a main phase and a charge and a voltage in a charge and discharge curve are proportional to a voltage. This is effective in improving the capacitance of the capacitor and reducing the size of the capacitor. As the hydrogen storage alloy whose electric quantity and voltage in the charge / discharge curve are proportional to each other, a Ti—Ni alloy or a Ti—Cr alloy obtained by rapid solidification after melting can be used.
Furthermore, according to the present invention, the bcc-type hydrogen storage alloy or the CsCl-type hydrogen storage alloy whose equilibrium potential changes monotonically in a noble direction with an increase in the amount of oxidized electricity in the electrochemical PCT curve, that is, monotonically increases. An electrode for a capacitor formed using the same is provided.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Capacitors are broadly classified into a stacked type, a wound type, and a coin type in terms of structure. Further, depending on the type of the electrolytic solution, it is roughly classified into an aqueous solution type and an organic type. The most significant feature of the present invention is that a hydrogen storage alloy is used as an electrode of a capacitor. In the present invention, the miniaturization and high capacity of the capacitor are achieved by utilizing a reaction in which water as a solvent is electrolyzed into hydrogen atoms and taken into hydrogen storage sites in a hydrogen storage alloy. Therefore, an aqueous solution that can generate hydrogen atoms by electrolysis is used as the electrolytic solution. Hereinafter, in the present embodiment, a description will be given by taking a laminated type aqueous capacitor as an example.
[0010]
FIG. 1 is a cross-sectional view schematically showing a configuration of the capacitor according to the present embodiment. As shown in FIG. 1, a capacitor 10 according to the present embodiment includes a pair of electrodes 2A and 2B arranged with a separator 1 interposed therebetween, and a current collector 3A provided on a different side of the electrode 2A from the separator 1 side. And a current collector 3B provided on a side of the electrode 2B different from the separator 1 side, electrodes 2A and 2B, and an insulating gasket 4 provided on the periphery of the separator 1.
[0011]
Separator 1 is arranged between electrode 2A and electrode 2B. As the separator 1, a material having low electron conductivity and high ion conductivity, for example, a porous material that transmits ions is used. As such a porous body, for example, a polypropylene microporous membrane, a polyethylene microporous membrane, glass fiber, a nonwoven fabric, or the like can be suitably used.
[0012]
The separator 1 and the electrodes 2A and 2B described later are impregnated with an electrolytic solution having high electric conductivity. In the present invention, an aqueous solution is used as such an electrolytic solution. The reason for using the aqueous electrolyte solution is as described above, and thus the description thereof is omitted here. Examples of aqueous electrolytes include acids such as sulfuric acid and tetrafluoroboric acid, bases such as potassium hydroxide, sodium hydroxide and ammonium hydroxide, chlorides such as potassium chloride, sodium chloride, calcium chloride and ammonium chloride, Carbonates such as potassium carbonate, sodium carbonate, and ammonium carbonate are preferably used. Among these electrolytes, sulfuric acid, tetrafluoroboric acid, potassium hydroxide and sodium hydroxide are particularly preferred in that high electrical conductivity is obtained.
[0013]
The concentration of the aqueous electrolyte solution used in the present invention can be appropriately selected within a range of 10 to 90 wt%. In general, if the concentration exceeds 90 wt%, problems such as the precipitation of solutes occur during cooling, and if the concentration is less than 10 wt%, the electric conductivity decreases and the internal resistance of the capacitor 10 increases, which is not preferable. The dielectric constant ε at 25 ° C. of water used as a solvent for the aqueous electrolytic solution is 78.
[0014]
The current collectors 3A and 3B are electrically connected to electrodes 2A and 2B described later. As the current collectors 3A and 3B, a conductive rubber such as a conductive butyl rubber can be used. In addition, the current collectors 3A and 3B can be configured using a metal net or metal foil such as nickel or aluminum.
[0015]
The insulating gasket 4 is arranged around the electrodes 2A, 2B so as to surround the electrodes 2A, 2B. As the insulating gasket 4, an insulator such as polypropylene, silicone rubber, or butyl rubber may be used.
[0016]
The greatest feature of the present invention is that at least one of the electrodes 2A and 2B is made of a hydrogen storage alloy.
Here, the operating principle of a conventional capacitor using activated carbon as a polarizable electrode will be described. In a conventional capacitor, when a voltage that does not cause electrolysis by immersing a pair of polarizable electrodes in an ionic solution is applied, ions are adsorbed on the surface of the polarizable electrode, and plus and minus electricity are stored ( charging). When electricity is released to the outside, the positive and negative ions leave the polarizable electrode and return to a neutralized state (discharge).
[0017]
On the other hand, the capacitor 10 according to the present invention using the hydrogen storage alloy as the electrode of the capacitor exhibits the following operation principle.
It is assumed that of the electrodes 2A and 2B, the electrode 2A functions as a positive electrode and the electrode 2B functions as a negative electrode. In this case, the following reaction occurs between the positive electrode (electrode 2A) and the negative electrode (electrode 2B).
[0018]

In the formula, M is a hydrogen storage alloy, and MH is a hydride.
[0019]
During charging, hydrogen atoms are released from the positive electrode (electrode 2A) to generate water. On the other hand, in the negative electrode (electrode 2B), the hydrogen storage alloy stores hydrogen atoms generated by the electrolysis of water to become hydrides. Specifically, in the negative electrode, electricity is stored by the entry of hydrogen atoms into the hydrogen storage site of the hydrogen storage alloy constituting the electrode 2B. At the time of discharge, on the contrary, hydrogen atoms are released from the negative electrode (electrode 2B) and are converted to water, and electricity is generated.
That is, in the conventional capacitor, charging and discharging are performed using the adsorption and desorption of ions to and from the pair of polarizable electrodes. Therefore, it is important to increase the specific surface area of the polarizable electrode, that is, the activated carbon, in order to improve the capacitance. By activating the activated carbon, the specific surface area is increased as much as possible to increase the capacitance. I was On the other hand, according to the hydrogen storage alloys as the electrodes 2A and 2B, the hydrogen atoms can be taken into the inside of the alloy, so that the electrostatic capacity can be increased without the need for gas activation as in the case of using activated carbon. It becomes possible. In addition, since the hydrogen storage alloy is a metal, an electrode having higher conductivity than activated carbon and having a higher density than when activated carbon is used can be manufactured. As a result, the capacitor 10 having a higher energy density than before can be obtained. The use of high-density electrodes enables the capacitor 10 to be reduced in size and capacity. Further, since the hydrogen storage alloy has low contact resistance, the internal resistance of the capacitor 10 can be reduced by using the hydrogen storage alloy as the electrodes 2A and 2B.
[0020]
As the hydrogen storage alloy functioning as the electrodes 2A and 2B, an alloy having the following characteristics is employed. That is, it is preferable that the equilibrium potential monotonously changes in a noble direction with an increase in the amount of oxidized electricity in the electrochemical PCT curve. Although the hydrogen storage alloy has been put to practical use as an electrode for a secondary battery, it is desired that the battery has a constant voltage. For this reason, a hydrogen storage alloy as an electrode for a secondary battery has a region in which the hydrogen pressure does not fluctuate even if the amount of oxidized electricity in the electrochemical PCT curve fluctuates. It is desired that the PCT curve has a flat plateau. On the other hand, it is desired that the quantity of electricity is proportional to the voltage of the capacitor. A hydrogen storage alloy in which the equilibrium potential monotonically changes in a noble direction with an increase in the amount of oxidized electricity in the electrochemical PCT curve shows a tendency that the amount of electricity is proportional to the voltage. it can. Note that when f (x1) <f (x2) is satisfied with respect to two points x1 and x2 that satisfy x1 <x2 included in the domain of x, the direction monotonically changes in a noble direction.
[0021]
Here, the larger the slope of the electrochemical PCT curve, the faster the voltage changes, so that the capacity that can be stored in the hydrogen storage alloy decreases. On the other hand, when the slope of the electrochemical PCT curve is small, the voltage change is small with respect to the amount of electricity to be injected, so that the capacity that can be stored in the hydrogen storage alloy increases. Therefore, as the hydrogen storage alloy as the electrodes 2A and 2B, an alloy having a small slope of the electrochemical PCT curve is preferable. Hereinafter, a desirable composition of the hydrogen storage alloy will be described. To control the slope of the electrochemical PCT curve, not only the composition but also the manufacturing method are important factors. A desirable method for producing a hydrogen storage alloy that suitably functions as the electrodes 2A and 2B will be described later.
[0022]
As the hydrogen storage alloy that functions as the electrodes 2A and 2B, a Ti—Ni-based alloy represented by the following formula (2) or a Ti—Cr-based alloy represented by the following formula (3) is desirable. By setting the composition of the Ti—Ni-based alloy or the Ti—Cr-based alloy to be represented by the formulas (2) and (3), a bcc-type Ti—Ni-based alloy or a bcc-type Ti—Cr-based alloy can be obtained. it can.
[0023]
Ti _(100-abcd) Cr _a X _b X ' _c Ni _d ... Equation (2)
However, 0 ≦ a (at%) ≦ 80, 0 ≦ b (at%) ≦ 10, 0 ≦ c (at%) ≦ 30, 5 ≦ d (at%) ≦ 50, and X is Ru, Rh. , Os, Ir, Pd, Pt, Re, at least one element, and X ′ is at least one element of V, Mo, W, and Al
[0024]
Ti _{(100-a'-b'-c'-d ')} Cr _a X _b X ' _c Ni _d ... Equation (3)
Where 20 ≦ a ′ (at%) ≦ 80, 0 ≦ b ′ (at%) ≦ 10, 0 ≦ c ′ (at%) ≦ 30, 0 ≦ d ′ (at%) ≦ 50, Is at least one element of Ru, Rh, Os, Ir, Pd, Pt and Re; and X ′ is at least one element of V, Mo, W and Al.
[0025]
In the formula (3), when Ni is not contained in the alloy composition, that is, when d ′ = 0 in the formula (3), the Ti—Cr-based alloy is doped with Ni, and the alloy is electrochemically converted. It may be activated. Further, in each case of the Ti—Ni-based alloy represented by the formula (2) and the Ti—Cr-based alloy represented by the formula (3), Mn, Fe, Co, Cu, Nb, Ta, B, and It may contain at least one element of C (T element), at least one element of Y and a lanthanoid element (L element).
[0026]
The X element has a high bcc phase forming ability only by being contained in a small amount in the Ti-Cr alloy, ₁₄ Type, C _Fifteen A bcc single phase alloy containing almost no Laves phase such as a mold can be obtained. Further, by simultaneously containing the X element and the X ′ element, the content of the expensive X element can be kept low, and a hydrogen storage alloy having high practicality balanced in cost and hydrogen storage amount per unit weight can be obtained. Obtainable. Further, by containing the T element, it becomes possible to control the heat treatment temperature, improve the corrosion resistance of the alloy, and control the current collection characteristics of the alloy. Since the L element has a strong affinity for oxygen, it has an effect of removing oxygen present in the alloy as an L element oxide. As a result, a raw material having a relatively high oxygen content can be industrially effectively used.
[0027]
The case where the electrodes 2A and 2B are made of a Ti-Ni-based alloy or a Ti-Cr-based alloy has been described in detail. By adopting the above composition, the Ti-Ni-based alloy or the Ti-Cr-based alloy as the electrodes 2A and 2B can have the bcc phase as the main phase. Whether or not the alloy has the bcc phase as the main phase can be determined by X-ray diffraction. In the present invention, an alloy having a proportion (%) of 50% or more according to the following equation (4) based on the integrated intensity of diffraction lines is defined as an alloy having a bcc phase as a main phase.
bcc (110) / [bcc (110) + {C14Labes (201) + C15Laves (311)} × 2] ... Equation (4)
[0028]
In addition, the electrodes 2A and 2B may be formed using a CsCl type alloy in addition to the hydrogen storage alloy having the bcc phase as a main phase. Examples of the CsCl type alloy include a Ti-Ni-based alloy, a Ti-Ni-Pd-based alloy, a Ti-Ni-Mn-based alloy, and a Ti-Ni-Fe-based alloy. As with the bcc-type alloy described above, the equilibrium potential of the CsCl-type alloy monotonically changes in a noble direction with an increase in the amount of oxidized electricity in the electrochemical PCT curve. Therefore, a CsCl type alloy can be suitably used as a capacitor electrode. Among the CsCl-type alloys, a Ti-Ni-based alloy is preferable because of its corrosion resistance to an electrolytic solution. When the electrodes 2A and 2B are formed using a CsCl type alloy, it is desirable that the electrodes have a single phase of a CsCl type crystal structure or a main phase having a CsCl type crystal structure.
[0029]
The average particle size of the hydrogen storage alloy powder as the electrodes 2A and 2B is desirably 5 to 300 μm. If the average particle size is smaller than 5 μm, the amount of hydrogen absorbed and released per particle will be small. On the other hand, when the average particle size of the powder increases, the volume change accompanying the hydrogen storage and release reaction increases, and the pulverization of the hydrogen storage alloy powder tends to proceed. The progress of the pulverization causes an increase in the specific surface area of the hydrogen-absorbing alloy powder, increases the contact interface between the electrodes 2A and 2B with the electrolytic solution, and promotes the corrosion of the alloy. Further, corrosion of the alloy is not preferable because the amount of hydrogen absorbed per unit volume decreases, leading to deterioration of conductivity. This progress of pulverization becomes remarkable when the particle size exceeds 300 μm. Therefore, in order to secure a high hydrogen absorption / release amount, the average particle diameter of the hydrogen storage alloy powder is set to 5 to 300 μm. A desirable average particle size is 10 to 100 μm, and a more desirable average particle size is 20 to 75 μm.
[0030]
When both the electrodes 2A and 2B are made of a hydrogen storage alloy, the composition of the hydrogen storage alloy constituting each electrode may be the same or different. Similarly, when both the electrodes 2A and 2B are made of a hydrogen storage alloy, the average particle diameter of the hydrogen storage alloy constituting each electrode may be the same or different.
[0031]
Next, a preferred method of manufacturing capacitor 10 according to the present embodiment will be described. The capacitor 10 according to the present embodiment includes a hydrogen storage alloy manufacturing step and an electrode manufacturing step. Here, the case of manufacturing a Ti—Ni-based alloy as the hydrogen storage alloy will be described as an example, and the hydrogen storage alloy manufacturing process will be described.
[0032]
<Process for preparing hydrogen storage alloy>
The Ti—Ni-based alloy base material suitably used as the electrodes 2A and 2B can be manufactured by, for example, an arc melting method. Here, in the case of preparing a Ti—Ni-based alloy base material by the arc melting method, the hydrogen storage alloy manufacturing step includes weighing of alloy elements (step S101), arc melting (step S103), rapid quenching (hereinafter, quenching) ( It consists of each step of step S105). Note that, depending on the alloy composition, it is also possible to obtain a hydrogen storage alloy in which the equilibrium potential monotonically changes in a noble direction with an increase in the amount of oxidized electricity in the electrochemical PCT curve without quenching.
[0033]
First, in step S101, the amount corresponding to the composition ratio of each metal constituting the hydrogen storage alloy to be obtained is weighed. For example, when it is desired to use Ti-Ni-Cr-Mo as the Ti-Ni-based alloy, an amount corresponding to the composition ratio of Ti, Ni, Cr, and Mo is weighed.
[0034]
After weighing the alloy elements in step S101, the process proceeds to step S103. In step S103, the weighed metals are put into an arc melting device (not shown) and melted and mixed in an argon atmosphere of about 70 kPa.
[0035]
After performing arc melting in step S103, the process proceeds to step S105. In step S105, the molten material obtained in step S103 is rapidly cooled by a roll and rapidly solidified. Alternatively, the molten material is rapidly cooled and solidified by being poured into water. Although the quenching is not essential, the quenching makes it possible to easily obtain a hydrogen storage alloy in which the equilibrium potential monotonously changes in a noble direction with an increase in the amount of oxidized electricity in the electrochemical PCT curve. The cooling rate is desirably 1000 K / sec or more.
[0036]
The ingot of the bcc-type Ti—Cr alloy thus obtained is pulverized to a powder of 300 μm or less. In this embodiment, the electrodes 2A and 2B are formed using this powder. The pulverization may be mechanical pulverization using a stamp mill or the like, or may be hydrogenation pulverization.
[0037]
<Electrode fabrication process>
In the electrode preparation step, a paste is prepared by kneading the hydrogen storage alloy powder, binder, conductive powder and water obtained in the hydrogen storage alloy preparation step. As the binder, for example, polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), or the like can be used. Further, as the conductive powder, for example, electrolytic copper, graphite, and carbon black can be used. The average particle size of the conductive powder is preferably 0.1 to 100 μm, particularly preferably 10 to 80 μm. The conductive powder is added in an amount of 0 to 20 wt%, preferably 0 to 5 wt%, based on the hydrogen storage alloy powder. The composition of the electrodes 2A and 2B is preferably in a weight ratio of hydrogen storage alloy powder: binder: conductive powder = 80 to 100: 0 to 10: 0 to 10.
Next, the obtained paste is applied or filled on a conductive substrate. As the conductive substrate, for example, a punched metal, a mesh-like, sponge-like, fibrous, or felt-like porous metal body can be used.
Subsequently, the electrodes 2A and 2B can be obtained by drying and pressing the conductive substrate coated or filled with the paste.
[0038]
The electrodes 2A and 2B thus obtained are used for the capacitor 10 in the present embodiment. Since the electrodes 2A and 2B containing the hydrogen storage alloy powder can take in hydrogen atoms therein, the capacitance per unit weight can be greatly improved as compared with the conventional case. In addition, since the electrodes 2A and 2B are made of metal and have a density that is at least five times higher than that of activated carbon, the capacitor 10 having a large energy density can be obtained. Thereby, a small and high-capacity capacitor 10 can be obtained.
[0039]
【Example】
Hereinafter, the present invention will be described based on specific examples.
(Example 1)
Seven kinds of alloys (ingots) shown in Table 1 were obtained by repeating melting, mixing and solidification using the above-described arc melting apparatus. Each ingot was obtained by quenching.
Next, the obtained alloy was ground to 75 μm or less using a stamp mill. In addition, about the alloy which does not contain Ni in the alloy composition, Ni powder having an average particle diameter of 1 μm was applied by a mechanical alloying method, and then pulverized to 75 μm or less.
[0040]
[Table 1]

[0041]
The seven alloys shown in Table 1 were subjected to phase identification by X-ray diffraction. As a result, it was confirmed that all of the alloys had bcc as the main phase.
Next, electrolytic copper powder was mixed with each alloy powder shown in Table 1 so that the weight ratio was 1: 3. Specifically, the alloy powder was mixed with the electrolytic copper powder 3 (0.75 g) at a ratio of 1 (0.25 g) and press-molded to produce seven types of 1.0 g evaluation electrodes. The electrodes for evaluation were used as electrodes 2A and 2B, respectively, and the terminal voltage and the quantity of electricity were measured when the electrolyte was charged and discharged with 6M KOH. As a result, charge / discharge curves showing the same tendency were obtained in each case. FIG. 2 conceptually shows this tendency.
[0042]
FIG. 2 shows that when the hydrogen storage alloy according to the present embodiment is used as the electrodes 2A and 2B, the quantity of electricity and the voltage in the charge / discharge curve are proportional. From this, it can be easily understood that the hydrogen storage alloy according to the present example shows a charge / discharge curve suitable for a capacitor.
[0043]
Sample No. With respect to Nos. 1 to 7, charge / discharge curves as shown in FIG. 2 were obtained, and the single electrode capacity of each electrode was obtained therefrom. The results are shown in Table 1. Table 1 shows that each of the electrodes has obtained an excellent capacitance of 2000 F / g or more. In particular, in Sample No. No. Samples Nos. 1 to 5 have high capacitances of 3000 F / g or more. It is noted that for No. 5, a very high value of 10,000 F / g or more was obtained.
[0044]
Next, the sample no. 1 was used as the electrodes 2A and 2B, and the electrolytic solution was 6M KOH to prepare the capacitor 10, and the electrochemical PCT curve was measured. The result is shown in FIG.
From FIG. 3, it can be seen that the electrochemical PCT curve monotonically changes the equilibrium potential in a noble direction with an increase in the amount of oxidized electricity. Showing such an electrochemical PCT curve indicates that the hydrogen storage alloy in the capacitor 10 effectively functions as the electrodes 2A and 2B.
[0045]
(Example 2)
Of the electrodes 2A and 2B, one electrode was Ni and the other electrode was the sample No. 1 obtained in Example 1. As 1 to 7, seven types of capacitors 10 were produced. In addition, a polypropylene nonwoven fabric was used as the separator 1, a nickel plate was used as the current collectors 3A and 3B, and a polypropylene was used as the insulating gasket 4.
[0046]
With respect to the obtained seven types of capacitors 10, charge / discharge curves as shown in FIG. 2 were obtained, and from this, the single-electrode capacity of each electrode was obtained. Table 1 also shows the total capacitance of the unipolar capacitances of both electrodes.
[0047]
As shown in Table 1, it was confirmed that even when only one of the electrodes 2A and 2B was made of a hydrogen storage alloy, a high capacitance could be obtained as the capacitor 10.
[0048]
(Comparative Example 1)
A capacitor was manufactured in the same procedure as in Example 2, except that one of the electrodes was made of Ni and the other electrode was made of activated carbon. This activated carbon has an average particle size of 25 μm and a specific surface area of 1500 m ² / G. As a result of measuring the capacitance in the same manner as in Example 2, the capacitance was 180 F / g.
[0049]
(Comparative Example 2)
A capacitor was manufactured in the same procedure as in Example 2 except that both electrodes were activated carbon. This activated carbon has an average particle size of 25 μm and a specific surface area of 1500 m ² / G. As a result of measuring the capacitance in the same manner as in Example 2, the capacitance was 90 F / g.
[0050]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the capacitance per unit weight is large, and a small and large-capacity capacitor can be obtained by a simple method.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a configuration of a capacitor according to an embodiment.
FIG. 2 is a charge / discharge curve measured in Example 1.
FIG. 3 is an electrochemical PCT curve measured in Example 1.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Separator, 2A, 2B ... Electrode (hydrogen storage alloy, positive electrode, negative electrode), 3A, 3B ... Current collector, 4 ... Insulating gasket, 10 ... Capacitor

Claims (9)

A capacitor comprising a first electrode and a second electrode,
The capacitor, wherein the first electrode and / or the second electrode is formed using a hydrogen storage alloy. In the hydrogen storage alloy used as the first electrode and / or the second electrode, an equilibrium potential monotonously changes in a noble direction with an increase in the amount of oxidized electricity in an electrochemical PCT curve. The capacitor according to claim 1, wherein The capacitor according to claim 2, wherein the first electrode and / or the second electrode are formed using a Ti-Ni-based hydrogen storage alloy or a Ti-Cr-based hydrogen storage alloy. 4. The capacitor according to claim 1, wherein the first electrode and / or the second electrode have a capacitance per unit weight of a single electrode of 500 F / g or more. 5. A pair of electrodes composed of a positive electrode and a negative electrode,
A separator disposed between the pair of electrodes,
An aqueous electrolytic solution impregnating the pair of electrodes and the separator, and a capacitor comprising:
At least one of the pair of electrodes is made of a metal having a hydrogen storage site therein, and a hydrogen atom moving in the capacitor enters the hydrogen storage site. The capacitor is charged by the hydrogen atoms penetrating into the hydrogen storage site of the metal serving as the negative electrode,
6. The capacitor according to claim 5, wherein the capacitor is discharged by releasing the hydrogen atoms that have entered the hydrogen storage site of the metal serving as the negative electrode. 7. Either of the pair of electrodes,
7. The hydrogen storage alloy according to claim 5, wherein a phase (bcc phase) having a body-centered cubic crystal structure is used as a main phase, and a hydrogen storage alloy whose electric quantity and voltage in a charge / discharge curve are proportional to each other is used. A capacitor as described. Either of the pair of electrodes,
The capacitor according to any one of claims 5 to 7, wherein the capacitor is a Ti-Ni-based alloy or a Ti-Cr-based alloy obtained by rapid solidification after melting. An electrode for a capacitor formed using a bcc-type hydrogen storage alloy or a CsCl-type hydrogen storage alloy whose equilibrium potential monotonically changes in a noble direction as the amount of oxidized electricity in an electrochemical PCT curve increases.

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