JP2004319366A - Recovery method of nickel hydrogen battery - Google Patents

Recovery method of nickel hydrogen battery Download PDF

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JP2004319366A
JP2004319366A JP2003114205A JP2003114205A JP2004319366A JP 2004319366 A JP2004319366 A JP 2004319366A JP 2003114205 A JP2003114205 A JP 2003114205A JP 2003114205 A JP2003114205 A JP 2003114205A JP 2004319366 A JP2004319366 A JP 2004319366A
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negative electrode
battery
nickel
hydrogen
capacity
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JP4396127B2 (en
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Tomoyoshi Ueki
智善 上木
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Toyota Motor Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/84—Recycling of batteries or fuel cells

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Abstract

<P>PROBLEM TO BE SOLVED: To provide a recovery method of a nickel hydrogen battery. <P>SOLUTION: On the basis of the finding that reduction in a charge (hydrogen) stored in a negative electrode is probably involved in the mechanism of deterioration of a battery, this nickel hydrogen battery is designed to have a positive electrode capacity regulation, and the negative electrode has a charge reserve with respect to charging side and a discharge reserve for retaining the positive capacity regulation with respect to discharging side (the left in the drawing). When the hydrogen stored in the negative electrode is reduced, and the discharge reserve is eliminated, the battery capacity is regulated in negative electrode capacity (the center in the drawing). Consequently, even if deterioration of a nickel compound and a hydrogen storage alloy is minimized, the battery capacity becomes small relative to a design value. Since the positive electrode is fully charged first even if charging is performed to recover the negative capacity corresponding to the discharge reserve, a sealing reaction precedes to arrest the recovery of the negative electrode capacity (the right in the drawing). Namely, the hydrogen lost from the negative electrode is supplied from the outside and replenished, whereby the negative electrode capacity can be recovered. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、使用によって劣化したニッケル水素電池を再生する方法の改良に関する。
【０００２】
【従来の技術】
一般的なニッケル水素電池は、水酸化ニッケル又はオキシ水酸化ニッケルを主成分とするニッケル化合物からなる正極、水素吸蔵合金からなる負極、水酸化カリウム等を主成分とするアルカリ水溶液からなる電解液とを有する。ニッケル水素電池は高いエネルギー密度及び充分なサイクル特性を有する二次電池として汎用される。
【０００３】
しかしながら、使用条件によっては正常な電池反応から外れ、電池の構成要素に劣化が生じることがあった。ニッケル水素電池の劣化の原因は充放電条件、温度などの使用条件により大きく異なり、正極側の要因としては充放電に伴うγ−ＮｉＯＯＨの生成や電極の膨潤による電極空間への電解液の取り込みや、それに伴う電解液枯れがある。
【０００４】
γ−ＮｉＯＯＨを通常のβ−ＮｉＯＯＨに戻して劣化したニッケル水素電池を再生する従来技術としては、Ｎｉイオン、Ｃｏイオン及びＬａイオンの少なくとも一種を含む濃硫酸を注入して洗浄し、その濃硫酸を注入した状態で６０±１０℃の温度で保持した後、充電する方向に通電し、次いで還元剤を含むアルカリ電解液で洗浄・充填する方法が開示されている（特許文献１）。
【０００５】
また、セパレータ中にＭｎ酸化物及びＣｏ酸化物が析出し、自己放電特性が悪化することがある。セパレータ中に析出したＭｎ酸化物及びＣｏ酸化物に対しては、自然放電等により深放電処理し、電池電圧をＭｎ酸化物及びＣｏ酸化物の安定化電圧より低くして所定期間放置することで溶解・消失することができる（特許文献２）。
【０００６】
【特許文献１】特開平１１−１０２７３３号公報
【特許文献２】特開２００２−３１３４４２号公報
【０００７】
【発明が解決しようとする課題】
ところが、近年の技術向上により電池の構成要素自身の劣化が抑制され、従来技術に示したような方法ではニッケル水素電池の再生を充分に行うことができない場合が増えた。その原因について本発明者が鋭意研究を行った結果、負極に蓄えられている電荷（水素）が電池ケースを透過することで減少し、電池容量が低下する場合があることを見出した。
【０００８】
図１左方に示すように、ニッケル水素電池は正極容量規制になるように設計され、過充電時に負極で水素発生反応が生じないように過剰の未充電部分（充電リザーブ）を設けている。また、放電側に関しては相対的に正極の放電効率や劣化速度が負極のそれに対して優れているので、正極容量規制を保持するために負極には予め充電している部分（放電リザーブ）が設けられている。
【０００９】
負極に蓄えられた水素が減少し放電リザーブがなくなると、電池容量が負極容量（水素量）規制となる（図１中央）。その結果、ニッケル化合物及び水素吸蔵合金の劣化が小さくても、設計値に対し電池容量が小さくなる。放電リザーブに相当する負極容量を回復するために充電を行っても正極が先に満充電となるので、密閉化反応（ガス吸収反応）が先行し、負極容量の回復は阻害される（図１右方）。
【００１０】
本発明は上記実情を鑑みて行われたものであり、劣化の進行したニッケル水素電池の容量を回復できるニッケル水素電池の再生方法を提供することを解決すべき課題とする。
【００１１】
【課題を解決するための手段】
上記課題を解決する本発明のニッケル水素電池の再生方法は、ニッケル酸化物又はニッケル水酸化物を含む正極と、水素吸蔵合金を含む負極と、アルカリ水溶液からなる電解液と、該正極，該負極及び該電解液を収納する電池ケースとを有するニッケル水素電池に対して適用される。
【００１２】
本発明のニッケル水素電池の再生方法は、該電池ケース内に水素を供給して該負極の該水素吸蔵合金に水素を吸蔵させる負極再生工程を有することを特徴とする（請求項１）。
【００１３】
つまり、電池内（負極）から失われた水素を外部から供給して補充することにより、負極容量を回復することができる。負極の水素吸蔵合金に適正量の水素を含有させることで規定された性能を発揮させることができる。
【００１４】
負極再生工程において、電池ケース内に水素を供給する源としては、水素ガスをそのまま電池ケース内に導入する方法が好ましい（請求項２）。また、電解液と反応して水素ガスが発生するアルカリ金属及び／又はアルカリ金属水素化物を電池ケース内に導入する方法も好ましい（請求項３）。これらアルカリ金属及び／又は前記カリ金属水素化物が有するアルカリ金属元素はナトリウムであることが好ましい（請求項４）。更に、電池内で減少した電解質及び／又は水を補充する工程を有することができる（請求項５）。
【００１５】
【発明の実施の形態】
本発明のニッケル水素電池の再生方法について以下に示す実施形態に基づき詳細に説明する。
【００１６】
（ニッケル水素電池）
本実施形態のニッケル水素電池の再生方法が適用されるニッケル水素電池は一般的なものであり、ニッケル酸化物又はニッケル水酸化物を含む正極と、水素吸蔵合金を含む負極と、アルカリ水溶液からなる電解液と、それら正極，負極及び電解液等を収納する電池ケースとを有する。
【００１７】
正極は多孔質の集電体と、これに充填された正極活物質とをもつ。多孔質の集電体は例えばパンチングメタル又は三次元構造を有する多孔質金属（発泡金属と言うこともある）からなる。多孔質金属とは、網目状の骨格部により多数の互いに連通するセルが区画された多孔質の金属（例えばニッケル）をいう。
【００１８】
正極活物質としては、ニッケル酸化物（オキシ水酸化ニッケル：ＮｉＯＯＨ、充電状態）又はニッケル水酸化物（水酸化ニッケル：Ｎｉ（ＯＨ）２、放電状態）を用いる。通常は安定性の高いβ−ＮｉＯＯＨ、β−Ｎｉ（ＯＨ）２を使用する。導電性、利用率及び耐久性向上のため、水酸化ニッケルにコバルト、酸化コバルト等のコバルト化合物、イットリア（Ｙ２Ｏ３）、亜鉛等を単独で又は複数組み合わせて添加することができる。水酸化ニッケルに、コバルト、酸化コバルト及びイットリアを添加する場合、水酸化ニッケル１００質量部に対して、酸化コバルトは１質量部から３０質量部、コバルトは１質量部から３０質量部、そしてイットリアは１質量部から３０質量部、それぞれ添加することが好ましい。
【００１９】
負極は多孔質の集電体と、これに充填された水素吸蔵合金をもつ。多孔質の集電体としては、上記正極の集電体と同じ構造のものを使用することができる。負極に含まれる水素吸蔵合金は種々の合金が知られているが、電解液中で電気化学的に発生させた水素を吸蔵でき、かつ放電時にその吸蔵した水素を容易に放出できるものであればよい。実用性、コスト等を考慮すると、ＭｍＮｉ５−ｘＭｘ（ここで、Ｍｍはミッシュメタルであり、ＭはＡｌ、Ｍｎ、Ｃｏ、Ｃｒ、Ｓｉ及びＦｅのうちの一つ又は二つ以上の元素）を使用することが望ましい。導電材、結着材等とともにこれら水素吸蔵合金をパンチングメタル等に充填した電極が例示できる。
【００２０】
電池の放電時の反応は、正極ではＮｉＯＯＨ＋Ｈ２Ｏ＋ｅ−→Ｎｉ（ＯＨ）２の反応が、負極ではＭＨｘ＋ＯＨ−→ＭＨｘ−１＋Ｈ２Ｏ＋ｅ−の反応が進行する。電池全体としてはＮｉＯＯＨ＋ＭＨｘ→Ｎｉ（ＯＨ）２＋ＭＨｘ−１と表される。一般的には、負極容量を正極容量の１．５倍程度にし正極容量規制としている。
【００２１】
電解液は、公知のものを使用することができる。例えば水酸化カリウム、水酸化ナトリウム、水酸化リチウムをそれぞれ単独で又は複数組み合わせた水溶液が例示できる。
【００２２】
電池ケースは電池の構成要素に対して化学的・物理的に安定なものであれば特に限定しない。例えば、金属、プラスチック等から構成される。なお、本発明者の知見によると、電池ケースからの水素の漏れ（透過）がニッケル水素電池の劣化の大きな要因として挙げられる。従って、電池ケースとしては水素透過性が小さいものを選択することが好ましい。
【００２３】
正負極の間には絶縁性のセパレータを配設する。セパレータとしては、公知のものを使用することができる。例えばポリプロピレン製の不織布、ナイロン製の不織布、ポリプロピレン繊維とナイロン繊維を混繊した不織布のような高分子不織布からなるセパレータである。特に、表面が親水化処理されたポリプロピレン製の不織布がセパレータとして好適である。
【００２４】
（ニッケル水素電池の再生方法）
本実施形態のニッケル水素電池の再生方法は、負極を再生する工程である負極再生工程を有する。負極再生工程は電池ケース内に水素ガスを供給して水素吸蔵合金に水素を吸蔵させる工程である。
【００２５】
水素を供給する方法は、電池ケース内に水素ガスを導入する方法と、電池ケース内に電解液と反応して水素を発生するアルカリ金属及び／又はアルカリ金属水素化物を導入する方法とがある。アルカリ金属及び／又はアルカリ金属水素化物を添加する方法は電解質（アルカリ金属水酸化物）の補充も同時に可能であるので好ましい。
【００２６】
水素ガス、アルカリ金属及び／又はアルカリ金属水素化物を導入する量は減少した電池容量から計算する。負極ＭＨの反応式：２Ｍ＋Ｈ２→２ＭＨより、減少した電池容量１Ａｈ（＝３６００Ｃ）当たり必要な水素（Ｈ２）量は０．０３７ｍｏｌである。
【００２７】
アルカリ金属及び／又はアルカリ金属水素化物が有するアルカリ金属元素は、ナトリウム、カリウム及びリチウムであることが好ましく、ナトリウムであることがより好ましい。アルカリ金属とアルカリ金属水素化物とでは、アルカリ金属水素化物の方が電解液との反応が穏やかであるので好ましい。参考までにアルカリ金属としてのナトリウム、アルカリ金属水素化物としての水素化ナトリウムが水素を発生する機構を記載する。双方ともに電解液中の水分と反応して水素を発生する。それぞれナトリウム２ｍｏｌ及び水素化ナトリウム１ｍｏｌに対して１ｍｏｌの水素ガスを発生する。
【００２８】
２Ｎａ＋２Ｈ２Ｏ→２ＮａＯＨ＋Ｈ２
ＮａＨ＋Ｈ２Ｏ→ＮａＯＨ＋Ｈ２
更に、電解質及び／又は水を補充する工程を有することもできる。電解質及び／又は水の補充は前述した負極再生工程の前後のいずれに行ってもよい。また、電解質及び水の双方を補充する場合には別々に添加してもよいし溶液にして添加してもよい。補充する電解液等の質量は電池質量の減少量や、アルカリ金属等を添加する量から計算できる。ニッケル水素電池の再生方法を何度も適用した電池においては電解液組成を適正化するために電解液の一部乃至は全部を入れ替えることも好ましい。
【００２９】
電池ケース内に水素ガス、アルカリ金属及び／又はアルカリ金属水素化物を導入する具体的な方法としては特に限定しないが、蓋や、ニッケル水素電池を製造する際に電解液を注入するために電池ケースに設けた電解液注入口等の電池ケースの開口部等を介して行うことができる。
【００３０】
【実施例】
（ニッケル水素電池）
初期定格容量６．５Ａｈのニッケル水素電池であって、使用によって電池容量が６０％（３．９Ａｈ）にまで低下した電池を用いた。Ｎａ添加用、ＮａＨ添加用そして水素ガス添加用の３種類の試験電池を用意した。
【００３１】
正極は多孔質の集電体にニッケルの水酸化物を充填している。集電体は、三次元網目構造をもつ多孔質ニッケルからなり、単位面積当たりの質量は約６００ｇ／ｍ２である。正極活物質は、水酸化ニッケルを１００質量部に対して、酸化コバルト（ＣｏＯ）を５質量部、金属コバルトを６質量部、そしてイットリアを１質量部を混合したものである。この水酸化ニッケルを主成分とする正極活物質ペーストを集電体の気孔に充填している。
【００３２】
負極は多孔質の集電体に水素吸蔵合金を充填している。集電体は上記正極の集電体と同様の構成をもつ。水素吸蔵合金は、ＭｍＮｉ３．５５Ｃｏ０．７５Ａｌ０．３Ｍｎ０．４である。この水素吸蔵合金を結着材等とともに混練してペースト状にし、集電体の気孔内に充填している。
【００３３】
セパレータはポリプロピレン−ポリエチレン製の不織布からなり、厚さ１５０μｍである。アルカリ電解液は、ＫＯＨを３．７５ｍｏｌ／Ｌ、ＮａＯＨを２．２５ｍｏｌ／Ｌ、ＬｉＯＨを０．０８３ｍｏｌ／Ｌの濃度で溶解させたものである。
【００３４】
（試験）
・電解液の補充量
電池質量を測定し、初期質量からの減少量を求め、その質量に相当する電解液を補充した。
【００３５】
・水素及び電解液の導入
電池容量の減少量に応じて水素導入量を算出した。それぞれの試験電池に対して、Ｎａを２．５ｇ（約０．１１ｍｏｌ）、ＮａＨを１．４ｇ（約０．０５８ｍｏｌ）そして水素ガスを２．５Ｌ（約０．１１ｍｏｌ）添加した。電池容量の減少量を３．０Ａｈとして、Ｎａ及びＮａＨは半分の１．５Ａｈ相当の量、水素ガスは３．０Ａｈ相当の量を添加した。更に、電池質量の減少量に応じた電解液を添加した。
【００３６】
（結果）
各試験電池について電池容量を測定し、容量回復率を算出した。Ｎａを添加した試験電池では３８％（１．５Ａｈ換算で７６％）、ＮａＨを添加した試験電池では４６％（１．５Ａｈ換算で９２％）、そして水素ガス添加した試験電池では８３％の容量回復率であった。各方法ともに、蓋の封止時における水素漏れの影響が免れず１００％（＝１．５Ａｈ及び３．０Ａｈ）の効率は得られていない。
【００３７】
更に、ＮａやＮａＨを添加する方法ではこれら化合物が一部酸化等して水素発生効率が低下しているおそれがあることも効率が１００％にならなかった原因と推測できる。
【００３８】
【発明の効果】
本発明のニッケル水素電池の再生方法によると、電池容量の減少量に応じた水素を電池ケース内に導入するだけで簡単に電池容量を回復することができ、効果的にニッケル水素電池を再生することができた。
【図面の簡単な説明】
【図１】ニッケル水素電池の劣化の機構を示した模式図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in a method for regenerating a nickel-metal hydride battery deteriorated by use.
[0002]
[Prior art]
A typical nickel-metal hydride battery has a positive electrode made of a nickel compound containing nickel hydroxide or nickel oxyhydroxide as a main component, a negative electrode made of a hydrogen storage alloy, and an electrolytic solution containing an alkaline aqueous solution containing potassium hydroxide or the like as a main component. Having. Nickel-metal hydride batteries are widely used as secondary batteries having high energy density and sufficient cycle characteristics.
[0003]
However, depending on the use conditions, the battery reaction may deviate from the normal battery reaction, and the components of the battery may deteriorate. The causes of the deterioration of nickel-metal hydride batteries vary greatly depending on the use conditions such as charge and discharge conditions and temperature. , And accompanying electrolyte wither.
[0004]
As a conventional technique for regenerating a deteriorated nickel-metal hydride battery by returning γ-NiOOH to normal β-NiOOH, a concentrated sulfuric acid containing at least one of Ni ions, Co ions, and La ions is injected, washed, and washed. Is maintained at a temperature of 60 ± 10 ° C. in a state of being injected, followed by energizing in a charging direction, and then washing and filling with an alkaline electrolyte containing a reducing agent (Patent Document 1).
[0005]
Further, Mn oxides and Co oxides may precipitate in the separator, and the self-discharge characteristics may deteriorate. The Mn oxide and Co oxide precipitated in the separator are subjected to deep discharge treatment by spontaneous discharge or the like, and the battery voltage is set lower than the stabilized voltage of the Mn oxide and Co oxide, and left for a predetermined period. It can dissolve and disappear (Patent Document 2).
[0006]
[Patent Document 1] JP-A-11-102733 [Patent Document 2] JP-A-2002-313442
[Problems to be solved by the invention]
However, deterioration of the battery components themselves has been suppressed by recent technological improvements, and in many cases, the method described in the prior art cannot sufficiently reproduce a nickel-metal hydride battery. As a result of the inventor's intensive research on the cause, the present inventor has found that the charge (hydrogen) stored in the negative electrode is reduced by permeating the battery case, and the battery capacity may be reduced.
[0008]
As shown in the left side of FIG. 1, the nickel-metal hydride battery is designed so that the positive electrode capacity is regulated, and an excessive uncharged portion (charge reserve) is provided so that a hydrogen generation reaction does not occur at the negative electrode during overcharge. On the discharge side, the discharge efficiency and deterioration rate of the positive electrode are relatively superior to those of the negative electrode, so that the negative electrode has a pre-charged portion (discharge reserve) to maintain the positive electrode capacity regulation. Have been.
[0009]
When the amount of hydrogen stored in the negative electrode decreases and the discharge reserve disappears, the battery capacity is regulated by the negative electrode capacity (hydrogen amount) (center in FIG. 1). As a result, even if deterioration of the nickel compound and the hydrogen storage alloy is small, the battery capacity is smaller than the design value. Even when charging is performed to recover the negative electrode capacity corresponding to the discharge reserve, the positive electrode is first fully charged, so that the sealing reaction (gas absorption reaction) precedes and the recovery of the negative electrode capacity is hindered (FIG. 1). Right).
[0010]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for regenerating a nickel-metal hydride battery capable of recovering the capacity of a deteriorated nickel-metal hydride battery.
[0011]
[Means for Solving the Problems]
A method for regenerating a nickel-metal hydride battery according to the present invention, which solves the above-mentioned problems, comprises a positive electrode containing nickel oxide or nickel hydroxide, a negative electrode containing a hydrogen storage alloy, an electrolytic solution comprising an aqueous alkaline solution, the positive electrode, and the negative electrode. And a battery case containing the electrolytic solution.
[0012]
The method for regenerating a nickel-metal hydride battery according to the present invention includes a negative electrode regenerating step of supplying hydrogen into the battery case to store hydrogen in the hydrogen storage alloy of the negative electrode (claim 1).
[0013]
In other words, the capacity of the negative electrode can be recovered by externally supplying and replenishing the hydrogen lost from inside the battery (negative electrode). The specified performance can be exhibited by including an appropriate amount of hydrogen in the hydrogen storage alloy of the negative electrode.
[0014]
In the negative electrode regeneration step, as a source for supplying hydrogen into the battery case, a method in which hydrogen gas is directly introduced into the battery case is preferable (claim 2). Further, a method of introducing an alkali metal and / or an alkali metal hydride which generates hydrogen gas by reacting with the electrolytic solution into the battery case is also preferable (claim 3). It is preferable that the alkali metal element contained in the alkali metal and / or the potassium metal hydride is sodium (claim 4). Furthermore, the method may include a step of replenishing the electrolyte and / or water that have been reduced in the battery (claim 5).
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for regenerating a nickel-metal hydride battery according to the present invention will be described in detail based on the following embodiments.
[0016]
(Ni-MH battery)
A nickel-metal hydride battery to which the method for regenerating a nickel-metal hydride battery of the present embodiment is applied is a general one, and includes a positive electrode containing nickel oxide or nickel hydroxide, a negative electrode containing a hydrogen storage alloy, and an alkaline aqueous solution. It has an electrolyte and a battery case for accommodating the positive electrode, the negative electrode, the electrolyte and the like.
[0017]
The positive electrode has a porous current collector and a positive electrode active material filled therein. The porous current collector is made of, for example, a punching metal or a porous metal having a three-dimensional structure (also referred to as a foamed metal). The porous metal refers to a porous metal (for example, nickel) in which a large number of interconnected cells are defined by a mesh-like skeleton.
[0018]
As the positive electrode active material, nickel oxide (nickel oxyhydroxide: NiOOH, charged state) or nickel hydroxide (nickel hydroxide: Ni (OH) 2 , discharged state) is used. Usually, β-NiOOH and β-Ni (OH) 2 having high stability are used. In order to improve conductivity, utilization and durability, a cobalt compound such as cobalt and cobalt oxide, yttria (Y 2 O 3 ), zinc and the like can be added to nickel hydroxide alone or in combination. When adding cobalt, cobalt oxide and yttria to nickel hydroxide, cobalt oxide is 1 to 30 parts by mass, cobalt is 1 to 30 parts by mass, and yttria is 100 parts by mass of nickel hydroxide. It is preferable to add 1 to 30 parts by mass of each.
[0019]
The negative electrode has a porous current collector and a hydrogen storage alloy filled therein. As the porous current collector, one having the same structure as the above-described positive electrode current collector can be used. Various alloys are known as the hydrogen storage alloy contained in the negative electrode. However, any alloy that can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge can be used. Good. Considering practicality, cost, etc., MmNi 5-x M x (where Mm is a misch metal, and M is one or more elements of Al, Mn, Co, Cr, Si and Fe) ) Is preferred. An electrode in which the hydrogen storage alloy is filled in a punching metal or the like together with a conductive material, a binder and the like can be exemplified.
[0020]
As for the reaction at the time of discharging the battery, the reaction of NiOOH + H 2 O + e − → Ni (OH) 2 proceeds in the positive electrode, and the reaction of MH x + OH − → MH x−1 + H 2 O + e − proceeds in the negative electrode. The entire battery is represented as NiOOH + MH x → Ni (OH ) 2 + MH x-1. Generally, the capacity of the negative electrode is set to about 1.5 times the capacity of the positive electrode to regulate the capacity of the positive electrode.
[0021]
As the electrolyte, a known electrolyte can be used. For example, an aqueous solution in which potassium hydroxide, sodium hydroxide and lithium hydroxide are used alone or in combination of two or more can be exemplified.
[0022]
The battery case is not particularly limited as long as it is chemically and physically stable with respect to battery components. For example, it is made of metal, plastic, or the like. According to the findings of the present inventors, leakage (permeation) of hydrogen from the battery case is cited as a major factor in deterioration of the nickel-metal hydride battery. Therefore, it is preferable to select a battery case having low hydrogen permeability.
[0023]
An insulating separator is provided between the positive and negative electrodes. As the separator, a known separator can be used. For example, a separator made of a polymer nonwoven fabric such as a nonwoven fabric made of polypropylene, a nonwoven fabric made of nylon, and a nonwoven fabric in which polypropylene fibers and nylon fibers are mixed. In particular, a polypropylene nonwoven fabric whose surface is hydrophilized is suitable as the separator.
[0024]
(Regeneration method of nickel metal hydride battery)
The method for regenerating a nickel-metal hydride battery according to the present embodiment includes a negative electrode regeneration step for regenerating a negative electrode. The negative electrode regeneration step is a step of supplying hydrogen gas into the battery case to cause the hydrogen storage alloy to store hydrogen.
[0025]
As a method for supplying hydrogen, there are a method of introducing hydrogen gas into a battery case, and a method of introducing an alkali metal and / or an alkali metal hydride that generates hydrogen by reacting with an electrolytic solution into the battery case. The method of adding an alkali metal and / or an alkali metal hydride is preferable because replenishment of an electrolyte (alkali metal hydroxide) is possible at the same time.
[0026]
The amount of hydrogen gas, alkali metal and / or alkali metal hydride introduced is calculated from the reduced battery capacity. From the reaction formula of the negative electrode MH: 2M + H 2 → 2MH, the required amount of hydrogen (H 2 ) per reduced battery capacity 1Ah (= 3600C) is 0.037 mol.
[0027]
The alkali metal element contained in the alkali metal and / or alkali metal hydride is preferably sodium, potassium and lithium, and more preferably sodium. Of the alkali metal and the alkali metal hydride, the alkali metal hydride is preferable because the reaction with the electrolytic solution is gentle. The mechanism by which sodium as an alkali metal and sodium hydride as an alkali metal hydride generate hydrogen will be described for reference. Both react with moisture in the electrolyte to generate hydrogen. 1 mol of hydrogen gas is generated for 2 mol of sodium and 1 mol of sodium hydride, respectively.
[0028]
2Na + 2H 2 O → 2NaOH + H 2
NaH + H 2 O → NaOH + H 2
Further, it may have a step of replenishing the electrolyte and / or water. The replenishment of the electrolyte and / or the water may be performed before or after the above-described negative electrode regeneration step. When both the electrolyte and the water are replenished, they may be added separately or in the form of a solution. The mass of the electrolyte and the like to be replenished can be calculated from the amount of decrease in the mass of the battery and the amount of the alkali metal or the like added. In a battery in which the regenerating method of the nickel-metal hydride battery is applied many times, it is also preferable to replace part or all of the electrolyte solution in order to optimize the electrolyte composition.
[0029]
A specific method for introducing hydrogen gas, alkali metal and / or alkali metal hydride into the battery case is not particularly limited, but a lid or a battery case for injecting an electrolytic solution at the time of manufacturing a nickel metal hydride battery. Through an opening of a battery case such as an electrolyte injection port provided in the battery case.
[0030]
【Example】
(Ni-MH battery)
A nickel-metal hydride battery having an initial rated capacity of 6.5 Ah, whose battery capacity was reduced to 60% (3.9 Ah) by use, was used. Three kinds of test batteries for Na addition, NaH addition and hydrogen gas addition were prepared.
[0031]
The positive electrode has a porous current collector filled with nickel hydroxide. The current collector is made of porous nickel having a three-dimensional network structure, and has a mass per unit area of about 600 g / m 2 . The positive electrode active material is a mixture of 100 parts by mass of nickel hydroxide, 5 parts by mass of cobalt oxide (CoO), 6 parts by mass of metallic cobalt, and 1 part by mass of yttria. The positive electrode active material paste mainly composed of nickel hydroxide is filled in the pores of the current collector.
[0032]
The negative electrode has a porous current collector filled with a hydrogen storage alloy. The current collector has a configuration similar to that of the positive electrode current collector. The hydrogen storage alloy is MmNi 3.55 Co 0.75 Al 0.3 Mn 0.4 . This hydrogen storage alloy is kneaded with a binder and the like to form a paste, which is filled in the pores of the current collector.
[0033]
The separator is made of a polypropylene-polyethylene nonwoven fabric and has a thickness of 150 μm. The alkaline electrolyte is obtained by dissolving 3.75 mol / L of KOH, 2.25 mol / L of NaOH, and 0.083 mol / L of LiOH.
[0034]
(test)
Amount of replenishment of electrolytic solution The mass of the battery was measured, the amount of decrease from the initial mass was determined, and an electrolytic solution corresponding to the mass was replenished.
[0035]
Introducing hydrogen and electrolyte The amount of hydrogen introduced was calculated according to the amount of decrease in battery capacity. To each test battery, 2.5 g (about 0.11 mol) of Na, 1.4 g (about 0.058 mol) of NaH, and 2.5 L (about 0.11 mol) of hydrogen gas were added. Assuming that the amount of decrease in battery capacity is 3.0 Ah, Na and NaH were added in half amounts corresponding to 1.5 Ah, and hydrogen gas was added in amounts equivalent to 3.0 Ah. Further, an electrolytic solution corresponding to the amount of decrease in the mass of the battery was added.
[0036]
(result)
The battery capacity of each test battery was measured, and the capacity recovery rate was calculated. 38% (76% in terms of 1.5 Ah) for the test cell to which Na was added, 46% (92% in terms of 1.5 Ah) for the test cell to which NaH was added, and 83% for the test cell to which hydrogen gas was added. Recovery rate. In each of the methods, the effect of hydrogen leakage at the time of sealing the lid was inevitable, and an efficiency of 100% (= 1.5 Ah and 3.0 Ah) was not obtained.
[0037]
Furthermore, in the method of adding Na or NaH, the fact that these compounds may be partially oxidized or the like and the hydrogen generation efficiency may be reduced may be a reason why the efficiency did not become 100%.
[0038]
【The invention's effect】
According to the method for regenerating a nickel-metal hydride battery of the present invention, the battery capacity can be easily recovered simply by introducing hydrogen according to the amount of reduction in the battery capacity into the battery case, and the nickel-metal hydride battery is effectively regenerated. I was able to.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a mechanism of deterioration of a nickel-metal hydride battery.

Claims (5)

ニッケル酸化物又はニッケル水酸化物を含む正極と、水素吸蔵合金を含む負極と、アルカリ水溶液からなる電解液と、該正極，該負極及び該電解液を収納する電池ケースとを有するニッケル水素電池に対して、
該電池ケース内に水素を供給して該負極の該水素吸蔵合金に水素を吸蔵させる負極再生工程を有することを特徴とするニッケル水素電池の再生方法。A nickel-metal hydride battery having a positive electrode containing nickel oxide or nickel hydroxide, a negative electrode containing a hydrogen storage alloy, an electrolytic solution composed of an aqueous alkaline solution, and a battery case containing the positive electrode, the negative electrode, and the electrolytic solution for,
A method for regenerating a nickel-metal hydride battery, comprising a negative electrode regenerating step of supplying hydrogen into the battery case to occlude hydrogen in the hydrogen storage alloy of the negative electrode. 前記負極再生工程は前記電池ケース内に水素ガスを導入する工程である請求項１に記載のニッケル水素電池の再生方法。The method for regenerating a nickel-metal hydride battery according to claim 1, wherein the negative electrode regenerating step is a step of introducing hydrogen gas into the battery case. 前記負極再生工程は前記電池ケース内にアルカリ金属及び／又はアルカリ金属水素化物を導入して前記電解液と反応させる工程である請求項１に記載のニッケル水素電池の再生方法。The method for regenerating a nickel-metal hydride battery according to claim 1, wherein the negative electrode regeneration step is a step of introducing an alkali metal and / or an alkali metal hydride into the battery case to react with the electrolyte. 前記アルカリ金属及び／又は前記アルカリ金属水素化物が有するアルカリ金属元素はナトリウムである請求項３に記載のニッケル水素電池の再生方法。The method of claim 3, wherein the alkali metal element contained in the alkali metal and / or the alkali metal hydride is sodium. 更に、電解質及び／又は水を補充する工程を有する請求項１〜４のいずれかに記載のニッケル水素電池の再生方法。The method for regenerating a nickel-metal hydride battery according to any one of claims 1 to 4, further comprising a step of replenishing the electrolyte and / or water.
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