JP3545209B2 - Hydrogen storage alloy for alkaline storage battery and method for producing the same, hydrogen storage alloy electrode for alkaline storage battery and method for producing the same - Google Patents

Hydrogen storage alloy for alkaline storage battery and method for producing the same, hydrogen storage alloy electrode for alkaline storage battery and method for producing the same Download PDF

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JP3545209B2
JP3545209B2 JP18080798A JP18080798A JP3545209B2 JP 3545209 B2 JP3545209 B2 JP 3545209B2 JP 18080798 A JP18080798 A JP 18080798A JP 18080798 A JP18080798 A JP 18080798A JP 3545209 B2 JP3545209 B2 JP 3545209B2
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hydrogen storage
alloy
storage alloy
storage battery
producing
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JP2000012012A (en
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輝彦 井本
洋平 廣田
信幸 東山
菊子 加藤
衛 木本
伸 藤谷
晃治 西尾
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Sanyo Electric Co Ltd
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Sanyo Electric Co Ltd
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    • YGENERAL 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
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    • Y02E60/10Energy storage using batteries

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Description

【0001】
【発明の属する技術分野】
本発明は、アルカリ蓄電池用の負極材料として使用されるアルカリ蓄電池用水素吸蔵合金に係わり、高率放電特性の向上を目的とした電極材料たる水素吸蔵合金粉末の改良に関するものである。
【0002】
【従来の技術】
近年、ニッケル・カドミウム蓄電池に比べて2倍以上の高容量で、且つ、環境適合性にも優れたニッケル・水素蓄電池が、次世代のアルカリ蓄電池として注目されている。そして、各種ポータブル機器の普及を背景として、このニッケル・水素蓄電池は更なる高性能化が期待されている。
【0003】
ニッケル・水素蓄電池の負極に使用する水素吸蔵合金は、一般に自然酸化等によってその表面に酸化物等の被膜が形成されており、このような水素吸蔵合金を用いて水素吸蔵合金を作製し、この水素吸蔵合金電極をニッケル・水素蓄電池の負極に使用した場合には、その初期における水素吸蔵合金の活性度が低く、電池容量が低くなる等の問題があった。
【0004】
このため、近年において、特開平5-225975号公報に示されるように、水素吸蔵合金を塩酸等の酸性溶液中に浸漬して、水素吸蔵合金の表面における酸化被膜を除去する方法が提案されている。
【0005】
ここで、水素吸蔵合金を酸性溶液中に浸漬して、この水素吸蔵合金の表面における酸化被膜等を除去した場合、水素吸蔵合金の表面に活性な金属ニッケル(Ni)、金属コバルト(Co)等の部位が出現する。
【0006】
また、上記の方法で酸化被膜を除去することにより、表面に活性な金属Ni、Co等の部位が出現し、合金粉末同士の電気化学的な接触抵抗が低減するため、高率放電特性は若干向上するが、大幅な改善までには至っていない。
【0007】
【発明が解決しようとする課題】
本発明は、以上の事情に鑑みなされたものであって、その目的とするところは、ニッケル・水素蓄電池に使用される、高率放電特性を向上させた水素吸蔵合金電極に使用されるアルカリ蓄電池用水素吸蔵合金を得ることにある。
【0008】
【課題を解決するための手段】
本発明は、CaCu5型結晶構造を有し、組成式MmNixCoyMnzM1-z[式中Mはアルミニウム(Al)、銅(Cu)から選ばれた少なくとも一種の元素、xはニッケル(Ni)の組成比率であって3.0≦x≦5.2、yはコバルト(Co)の組成比率であって0≦y≦1.2、zはマンガン(Mn)の組成比率であって0.1≦z≦0.9であり、且つ前記x、y、zの合計値が4.4≦x+y+z≦5.4]で表されるアルカリ蓄電池用水素吸蔵合金であって、前記水素吸蔵合金は、その表面に形成された表面領域と、その表面領域で被覆されたバルク領域から構成され、この表面領域は、コバルトのフッ化物を含有しており、前記表面領域におけるNi原子の存在比率が、前記バルク領域におけるNi原子の存在比率よりも大きいことを特徴とする。
【0009】
ここで、前記表面領域は、合金粒子表面から略100nm以下の厚さを有することを特徴とする。
【0010】
また、本発明のアルカリ蓄電池用水素吸蔵合金の製造方法は、CaCu5型結晶構造を有し、 組成式MmNixCoyMnzM1-z[式中Mはアルミニウム(Al)、銅(Cu)から選ばれた少なくとも一種の元素、xはニッケル(Ni)の組成比率であって3.0≦x≦5.2、yはコバルト(Co)の組成比率であって0≦y≦1.2、zはマンガン(Mn)の組成比率であって0.1≦z≦0.9であり、且つ前記x、y、zの合計値が4.4≦x+y+z≦5.4]で表される合金粒子を準備する第1ステップと、前記第1ステップで準備された前記合金粒子を、コバルトのフッ化物を含有させた酸性溶液中で処理を行う第2ステップにより、水素吸蔵合金とすることを特徴とする。
【0011】
また、その製造方法においては、フッ化物の添加量が、前記合金粒子の重量に対して0.01〜5.0重量%であることを特徴とする。
【0012】
更に、その製造方法に関し、第2ステップにおいて、酸性溶液がpH=0.7〜2.0であることを特徴とする。
【0013】
そして、水素吸蔵合金を提供する第1ステップが、ガスアトマイズ法であることを特徴とする。
【0014】
上述の本発明に係るアルカリ蓄電池用水素吸蔵合金を、パンチングメタル、発泡ニッケル等の導電性芯体に充填することによって、アルカリ蓄電池用水素吸蔵合金電極を提供することができる。
【0015】
本発明における第2ステップにおいて、フッ化物を添加した酸性溶液で処理されるので、水素吸蔵合金粒子の表面に形成される酸化物が除去されるとともに、添加したフッ化物が、合金粒子の表面領域に取込まれる。
【0016】
ここで、第2ステップで使用する酸性水溶液としては、塩酸、硝酸、リン酸が例示される。
【0017】
本発明において、合金表面から略100nmの領域を表面領域とし、この表面領域で被覆される領域をバルク領域としているが、略100nm近傍で区別される理由は次のとおりである。即ち、本発明の第2のステップで、組成に関して影響が現れるのが、本発明者らの実験によれば表面から略100nm以下の領域であり、組成変化を生じないのがこの内側のバルク領域である。従って、この変化の度合いを定量化し、電池特性の向上を狙うことに基づく。
【0018】
更に、合金がCaCu5型結晶構造を有し、 組成式MmNixCoyMnzM1-z[式中Mはアルミニウム(Al)、銅(Cu)から選ばれた少なくとも一種の元素、xはニッケル(Ni)の組成比率であって3.0≦x≦5.2、yはコバルト(Co)の組成比率であって0≦y≦1.2、zはマンガン(Mn)の組成比率であって0.1≦z≦0.9であり、且つ前記x、y、zの合計値が4.4≦x+y+z≦5.4]で表わされる水素吸蔵合金としているのは、この組成範囲内の水素吸蔵合金をアルカリ蓄電池に使用すると、電解液中での腐食が抑えられ、水素吸蔵量の増大が狙えるからである。従って、本発明ではこの組成範囲のものとしている。
【0019】
そして、上記フッ化物の添加量を合金粒子に対して0.01〜5.0重量%とするのは、0.01重量%より少ないと析出する表面領域の形成量が少なく、5.0重量%より多いと析出する表面領域へのフッ化物含有量が過剰になり、合金粒子に悪影響を与えるからである。
【0020】
更に、第2ステップにおいて、酸性溶液の好適な初期pHは、0.7〜2.0の範囲である。pHが0.7より低くなると、合金粒子の酸化が急激に生じ、水素吸蔵合金の内部まで溶解されてしまうからであり、pHが2.0より高くなると酸化物の被膜が十分に除去されないからである。
【0021】
上述のようにして、図1に示す構造を有する本発明に係る水素吸蔵合金を得る。図1は、本発明の水素吸蔵合金の状態を模式的に表わした説明図である。この図1に示すとおり、水素吸蔵合金1の合金粒子は、その表面から略100nmまでの表面領域2と、この表面領域2に被覆されたバルク領域3から構成される。表面領域2におけるニッケル原子4の存在比率(atm%)aと、バルク領域3におけるニッケル原子5の存在比率(atm%)bは、a>bとなる関係を有している。そして、この水素吸蔵合金1を電極に用いてニッケル・水素蓄電池を作製すると、高率放電特性を向上させることができる。
【0022】
これらの効果は、アルゴン雰囲気のアーク炉で作製、粉砕した合金粒子は言うまでもなく、ガスアトマイズ法やロール急冷法等により作製した合金粒子であっても同様に期待できる。
【0023】
【発明の実施の形態】
以下、本発明の実施例を公知の比較例とともに詳細に説明するが、本発明は下記実施例に何ら限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施することが可能なものである。
【0024】
《実験1》
この実験1では、アルカリ蓄電池に使用される水素吸蔵合金において、酸処理時のコバルトフッ化物の有無による、電池特性に与える影響を調べた。
【0025】
以下に、合金粒子の作製、各試料の準備、アルカリ蓄電池の組立、詳細な結果という順序で、説明する。
【0026】
[MmNi3.0Co0.9Mn0.6Al0.5合金粒子の作製]
出発材料としてMm(ミッシュメタルMmは希土類元素の混合物であって、La:25重量%、Ce:50重量%、Pr:7重量%、Nd:18重量%)、Ni、Co、Mn、Al(各元素材料は純度99.9%の金属単体を使用)を、モル比1.0:3.0:0.9:0.6:0.5の割合で混合し、アルゴン雰囲気のアーク溶解炉で溶解させた後、自然放冷して、組成式MmNi3.0Co0.9Mn0.6Al0.5で表される合金塊を作製した。この合金塊を空気中で機械的に粉砕し、平均粒径80μmに調整し、合金粒子とした。
【0027】
上記合金粒子を用い、フッ化物であるフッ化コバルト(CoF2)を合金重量に対し1.0重量%含有させた、塩酸水溶液に漬浸、撹拌した。この塩酸処理液のpHは1.0に調整されており、浸漬、撹拌処理は30分行っている。その後、吸引濾過後、水洗乾燥した。そして水素吸蔵合金を得、試料A1とした。
【0031】
一方、比較例として、上記で作製した合金粒子をpH=1.0に調製した塩酸水溶液からなる25℃に保った処理液中で、前記合金粒子を30分間浸漬撹拌し、吸引濾過後水洗乾燥した。このようにして水素吸蔵合金を得、比較試料Xとした。
【0032】
[電池の組立]
上記で作製した各水素吸蔵合金100重量部と、結着剤としてのPEO(ポリエチレンオキサイド)5重量%の水溶液20重量部とを混合して、ペーストを調整し、このペーストをニッケル鍍金を施したパンチングメタルからなる導電性芯体の両面に塗着(充填)し、室温で乾燥した後、所定の寸法に切断して、アルカリ蓄電池用水素吸蔵合金電極を作製した。
【0033】
この水素吸蔵合金電極を負極に使用して、AAサイズの正極支配型のアルカリ蓄電池(電池容量1000mAh)を作製した。正極として、従来公知の焼結式ニッケル極を、セパレータとして耐アルカリ性の不織布を、また、電解液として30重量%水酸化カリウム水溶液をそれぞれ使用した。
【0034】
図2は、組み立てたアルカリ蓄電池の模式断面図であり、正極11及び負極12、セパレータ13、正極リード14、負極リード15、正極外部端子16、負極缶17、封口蓋18などからなる。
【0035】
上記正極11及び負極12は、セパレータ13を介して渦巻き状に巻取られた状態で負極缶17内に収容されており、正極11は正極リード14を介して封口蓋18に、又負極12は負極リード15を介して、負極缶17に接続されている。負極缶17と封口蓋18との接合部には絶縁性のパッキング20が装着されて電池の密閉化がなされている。正極外部端子16と封口蓋18との間には、コイルスプリング19が設けられ、電池内圧が異常に上昇した時に圧縮されて電池内部のガスを大気中に放出し得るようになっている。
【0036】
[詳細な結果]
水素吸蔵合金である試料A1及び比較試料Xの、合金粒子の表面から200nmの深さまでのNi原子の存在比率及び内部のバルク領域のNi原子の存在比率を、走査透過型電子顕微鏡とエネルギー分散型X線分析計を用いて測定した。
【0037】
この方法により、表面領域、バルク領域の各Ni元素存在比率を測定したところ、本発明に係る試料A1では、酸処理により表面領域から希土類元素が溶出することによりNi原子の濃度が高くなっている。この結果、バルク領域におけるNi原子の存在比率よりも、表面領域におけるNi原子の存在比率が高くなっていることが裏付けられた。
【0038】
次に、試料 A1 及び比較試料 Xを使用した電池の高率放電時の放電容量を測定した。
【0039】
この時の条件は、各電池を常温にて、電流値4.0Cで6時間充電した後、電流0.2Cで1.0Vまで放電して、高率放電時の放電容量(mAh)を実測した。
【0040】
この結果を、表1に示す。
【0041】
【表1】

Figure 0003545209
【0042】
この結果より、表面領域及びバルク領域を有する本発明に係る試料 A1の優位性が伺える。尚、試料 A1 において、これに形成されたフッ化物が含有される表面領域は、合金粒子の表面から略50nmの厚さを有していた。
【0043】
尚、この実験1では、水素吸蔵合金の作製工程であるステップ2において、酸性水溶液として塩酸水溶液を使用したが、硝酸、リン酸であっても同様の傾向が観察される。
【0044】
《実験2》
この実験2では、水素吸蔵合金を作製する第2ステップで酸性溶液に添加するフッ化物の添加量を変化させ、電池特性との関係について検討した。尚、添加したフッ化物は、フッ化コバルトである。また、添加量は、水素吸蔵合金の重量に対する重量%である。
【0045】
先ず、上記実験1で準備した合金粒子を、表2に示す各添加量を含有させ、pH=1.0に調製した塩酸水溶液中で30分間浸漬、撹拌し、吸引濾過後、水洗乾燥した。そして水素吸蔵合金とし、試料B1〜試料B7を準備した。そして、上記実験1と同様にして、上記試料B1〜試料B7を用いて7種類の電池を作製した。尚、試料B4と、上記実験1の試料A1とは同一物である。
【0046】
表2に、試料B1〜試料B7で使用した添加フッ化物と、各試料を用いた各電池の高率放電時の放電容量の測定結果を示す。尚、電池の作製条件、容量の測定条件は、上述の実験1と同じである。更に、上述の実験1で使用した比較試料Xを用いた電池の特性についても、合わせて示す。
【0047】
【表2】
Figure 0003545209
【0048】
この結果より、本発明に係る試料B1〜試料B7を用いた電池では、比較試料Xを用いたものに比べて、放電容量が690mAh以上と大きい。更に、本発明に係る試料B1〜試料B7のなかでも、本発明に係る試料B2〜試料B6を用いた電池は放電容量が800mAh以上であり、フッ化コバルトの添加量は、水素吸蔵合金の重量に対して、0.01重量%以上5.0重量%以下とするのが好ましい。
【0049】
上述の実験1では表面層の厚みを略50nm、実験2では略100nmとしているが、150nm以下であれば、好ましい結果が期待できる。特に、フッ化物を含んだ表面層の厚さを略100nm以下とするのが、高率放電時の放電容量を向上させる観点から、最適である。この厚みを変化させるには、フッ化物の種類、添加量、酸処理時間などによって、変化させることが可能である。
【0050】
《実験3》
この実験3では、水素吸蔵合金を作製する第2ステップで酸性溶液に添加する塩酸の添加量を変化させ、電池特性との関係について検討した。尚、添加化合物としては、フッ化コバルト(CoF2)を用いている。
【0051】
先ず、上記実験1で準備した合金粒子を、CoF2を1.0重量%含有させた塩酸水溶液中で30分間浸漬、撹拌し、吸引濾過後、水洗乾燥した。この時、添加する塩酸濃度を変化させて、pHを調整している。この様にして水素吸蔵合金とし、試料C1〜試料C6を準備した。そして、上記実験1と同様にして、試料C1〜試料C6を用いて6種類の電池を作製した。
【0052】
表3に、試料C1〜試料C6を使用した各電池の高率放電時の放電容量の測定結果を示す。尚、電池の作製条件、容量の測定条件は、上述の実験1と同じである。
【0053】
【表3】
Figure 0003545209
【0054】
この結果より、試料C2〜試料C5を用いた各電池では、高率放電時の放電容量が800mAh以上と大きい。更に、電池内圧特性も優れたものであることが理解できる。従って、酸性処理液のpHとして、特に0.7〜2.0が好ましいことがわかる。
【0056】
上記各実験では、アルゴン雰囲気のアーク炉で溶解後、粉砕して準備した合金粒子について示したが、この合金粒子よりも焼結し易いガスアトマイズ法により作製した合金粒子や、ロール急冷法等により作製した合金粒子でも同様の効果が得られた。
【0057】
【発明の効果】
以上詳述したように、本発明に係る水素吸蔵合金及びその製造方法によれば、合金表面の活性を維持することができる。また、この合金を用いて電極を構成し、ニッケル・水素蓄電池の負極に用いることにより、高率放電時の放電容量の増大が図れ、その工業的価値は極めて大きい。
【図面の簡単な説明】
【図1】本発明の水素吸蔵合金の説明図である。
【図2】アルカリ蓄電池の模式的断面図である。
【符号の説明】
1 水素吸蔵合金
2 表面領域
3 バルク領域
4 ニッケル原子
5 ニッケル原子
11 正極
12 負極
13 セパレータ
14 正極リード
15 負極リード
16 正極外部端子
17 負極缶
18 封口蓋
19 コイルスプリング
20 パッキング[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrogen storage alloy for an alkaline storage battery used as a negative electrode material for an alkaline storage battery, and relates to an improvement in a hydrogen storage alloy powder as an electrode material for the purpose of improving high-rate discharge characteristics.
[0002]
[Prior art]
In recent years, nickel-metal hydride storage batteries that are twice as high as nickel-cadmium storage batteries and have excellent environmental compatibility have attracted attention as next-generation alkaline storage batteries. With the spread of various portable devices, the nickel-hydrogen storage battery is expected to have higher performance.
[0003]
A hydrogen storage alloy used for a negative electrode of a nickel-metal hydride storage battery generally has a coating such as an oxide formed on its surface by natural oxidation or the like, and a hydrogen storage alloy is produced using such a hydrogen storage alloy. When the hydrogen storage alloy electrode is used as a negative electrode of a nickel-metal hydride storage battery, there are problems such as a low activity of the hydrogen storage alloy in the initial stage and a reduction in battery capacity.
[0004]
For this reason, in recent years, as disclosed in JP-A-5-225975, a method has been proposed in which a hydrogen storage alloy is immersed in an acidic solution such as hydrochloric acid to remove an oxide film on the surface of the hydrogen storage alloy. I have.
[0005]
Here, when the hydrogen storage alloy is immersed in an acidic solution to remove an oxide film or the like on the surface of the hydrogen storage alloy, active nickel (Ni), metal cobalt (Co), or the like is formed on the surface of the hydrogen storage alloy. Appears.
[0006]
In addition, by removing the oxide film by the above method, sites of active metal Ni, Co, etc. appear on the surface, and the electrochemical contact resistance between the alloy powders is reduced. It improves, but has not yet reached a significant improvement.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an alkaline storage battery used for a nickel-hydrogen storage battery and a hydrogen storage alloy electrode having improved high-rate discharge characteristics. To obtain a hydrogen storage alloy for industrial use.
[0008]
[Means for Solving the Problems]
The present invention has a CaCu 5- type crystal structure, and has a composition formula of MmNi x Co y Mn z M 1-z wherein M is at least one element selected from aluminum (Al) and copper (Cu), and x is The composition ratio of nickel (Ni) is 3.0 ≦ x ≦ 5.2, y is the composition ratio of cobalt (Co) and 0 ≦ y ≦ 1.2, z is the composition ratio of manganese (Mn) and 0.1 ≦ z ≦ 0.9, and the sum of x, y, z is 4.4 ≦ x + y + z ≦ 5.4], wherein the hydrogen storage alloy has a surface region formed on the surface thereof. A bulk region covered with the surface region, the surface region contains a fluoride of cobalt, and the abundance ratio of Ni atoms in the surface region is larger than the abundance ratio of Ni atoms in the bulk region. Is also large.
[0009]
Here, the surface region has a thickness of about 100 nm or less from the surface of the alloy particle.
[0010]
Further, the method for producing a hydrogen storage alloy for an alkaline storage battery according to the present invention has a CaCu 5- type crystal structure, and a composition formula of MmNixCoyMnzM1-z wherein M is at least one selected from aluminum (Al) and copper (Cu). X is a composition ratio of nickel (Ni), 3.0 ≦ x ≦ 5.2, y is a composition ratio of cobalt (Co), 0 ≦ y ≦ 1.2, and z is a composition ratio of manganese (Mn). 0.1 ≦ z ≦ 0.9, and a total value of x, y, and z is 4.4 ≦ x + y + z ≦ 5.4], and the alloy prepared in the first step is prepared. The second step in which the particles are treated in an acidic solution containing cobalt fluoride is made into a hydrogen storage alloy.
[0011]
Further, in the production method, the amount of the fluoride to be added is 0.01 to 5.0% by weight based on the weight of the alloy particles.
[0012]
Further, the method is characterized in that in the second step, the acidic solution has a pH of 0.7 to 2.0.
[0013]
Further, the first step of providing the hydrogen storage alloy is a gas atomization method.
[0014]
By filling the above-mentioned hydrogen storage alloy for an alkaline storage battery according to the present invention into a conductive core such as punched metal or foamed nickel, a hydrogen storage alloy electrode for an alkaline storage battery can be provided.
[0015]
In the second step of the present invention, since the treatment is performed with the acid solution to which the fluoride is added, the oxide formed on the surface of the hydrogen storage alloy particles is removed, and the added fluoride is removed from the surface area of the alloy particles. Is taken in.
[0016]
Here, examples of the acidic aqueous solution used in the second step include hydrochloric acid, nitric acid, and phosphoric acid.
[0017]
In the present invention, a region of approximately 100 nm from the alloy surface is defined as a surface region, and a region covered by this surface region is defined as a bulk region. The reason why the region is discriminated near approximately 100 nm is as follows. That is, in the second step of the present invention, the influence on the composition appears in the region of about 100 nm or less from the surface according to the experiments of the present inventors, and the composition change does not occur in the inner bulk region. It is. Therefore, the degree of this change is quantified to improve battery characteristics.
[0018]
Furthermore, the alloy has a 5 type crystal structure CaCu, composition formula MmNi x Co y Mn z M 1 -z [ wherein M is aluminum (Al), at least one element selected from copper (Cu), x is The composition ratio of nickel (Ni) is 3.0 ≦ x ≦ 5.2, y is the composition ratio of cobalt (Co) and 0 ≦ y ≦ 1.2, z is the composition ratio of manganese (Mn) and 0.1 ≦ z ≦ 0.9 and the total value of x, y, and z is 4.4 ≦ x + y + z ≦ 5.4] because a hydrogen storage alloy within this composition range is used in an alkaline storage battery. This is because corrosion at the surface is suppressed, and an increase in the amount of hydrogen absorbed can be aimed at. Therefore, in the present invention, the composition is within this range.
[0019]
The reason why the addition amount of the above-mentioned fluoride is set to 0.01 to 5.0% by weight based on the alloy particles is that the amount of the surface area to be precipitated is small when the amount is less than 0.01% by weight, and the surface area to be precipitated when the amount is more than 5.0% by weight. This is because the fluoride content in the alloy becomes excessive and adversely affects the alloy particles.
[0020]
Further, in the second step, the preferred initial pH of the acidic solution is in the range of 0.7 to 2.0. If the pH is lower than 0.7, the oxidation of the alloy particles occurs rapidly and the inside of the hydrogen storage alloy is dissolved, and if the pH is higher than 2.0, the oxide film is not sufficiently removed.
[0021]
As described above, the hydrogen storage alloy according to the present invention having the structure shown in FIG. 1 is obtained. FIG. 1 is an explanatory view schematically showing a state of the hydrogen storage alloy of the present invention. As shown in FIG. 1, the alloy particles of the hydrogen storage alloy 1 are composed of a surface region 2 extending from the surface to approximately 100 nm and a bulk region 3 covering the surface region 2. The abundance ratio (atm%) a of the nickel atoms 4 in the surface region 2 and the abundance ratio (atm%) b of the nickel atoms 5 in the bulk region 3 have a relationship of a> b. When a nickel-hydrogen storage battery is manufactured using this hydrogen storage alloy 1 as an electrode, high-rate discharge characteristics can be improved.
[0022]
These effects can be expected not only from alloy particles produced and pulverized in an arc furnace in an argon atmosphere, but also from alloy particles produced by a gas atomizing method or a roll quenching method.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, examples of the present invention will be described in detail together with known comparative examples, but the present invention is not limited to the following examples, and can be implemented by appropriately changing the scope without changing the gist. It is something.
[0024]
<< Experiment 1 >>
In Experiment 1, the effect of the presence or absence of cobalt fluoride during acid treatment on the battery characteristics of a hydrogen storage alloy used for an alkaline storage battery was examined.
[0025]
Hereinafter, description will be made in the order of preparation of alloy particles, preparation of each sample, assembly of an alkaline storage battery, and detailed results.
[0026]
[Preparation of MmNi 3.0 Co 0.9 Mn 0.6 Al 0.5 alloy particles]
As starting materials, Mm (Misch metal Mm is a mixture of rare earth elements, La: 25% by weight, Ce: 50% by weight, Pr: 7% by weight, Nd: 18% by weight), Ni, Co, Mn, Al ( Each elemental material is 99.9% pure metal) mixed in a molar ratio of 1.0: 3.0: 0.9: 0.6: 0.5, melted in an arc melting furnace in an argon atmosphere, and allowed to cool naturally. An alloy lump represented by the composition formula MmNi 3.0 Co 0.9 Mn 0.6 Al 0.5 was produced. This alloy lump was mechanically pulverized in the air, and adjusted to an average particle size of 80 μm to obtain alloy particles.
[0027]
The above alloy particles were immersed in a hydrochloric acid aqueous solution containing 1.0% by weight of cobalt fluoride (CoF 2 ), which is a fluoride, based on the weight of the alloy, and stirred. The pH of the hydrochloric acid treatment solution was adjusted to 1.0, and the immersion and stirring processes were performed for 30 minutes. Thereafter, after suction filtration, the product was washed with water and dried. Then, a hydrogen storage alloy was obtained, which was designated as Sample A1.
[0031]
On the other hand, as a comparative example, the alloy particles prepared as described above were immersed and stirred for 30 minutes in a treatment solution consisting of an aqueous hydrochloric acid solution adjusted to pH = 1.0 and kept at 25 ° C., suction-filtered, washed with water and dried. Thus, a hydrogen storage alloy was obtained, which was used as Comparative Sample X.
[0032]
[Battery assembly]
A paste was prepared by mixing 100 parts by weight of each of the hydrogen storage alloys prepared above and 20 parts by weight of a 5% by weight aqueous solution of PEO (polyethylene oxide) as a binder to prepare a paste. The paste was subjected to nickel plating. After coating (filling) on both sides of a conductive core made of punching metal, drying at room temperature, and cutting to a predetermined size, a hydrogen storage alloy electrode for an alkaline storage battery was produced.
[0033]
Using this hydrogen storage alloy electrode as a negative electrode, an AA-size positive electrode-dominated alkaline storage battery (battery capacity 1000 mAh) was produced. A conventionally known sintered nickel electrode was used as a positive electrode, an alkali-resistant nonwoven fabric was used as a separator, and a 30% by weight aqueous solution of potassium hydroxide was used as an electrolyte.
[0034]
FIG. 2 is a schematic cross-sectional view of the assembled alkaline storage battery, which includes a positive electrode 11 and a negative electrode 12, a separator 13, a positive electrode lead 14, a negative electrode lead 15, a positive electrode external terminal 16, a negative electrode can 17, a sealing lid 18, and the like.
[0035]
The positive electrode 11 and the negative electrode 12 are accommodated in a negative electrode can 17 in a state of being spirally wound via a separator 13, the positive electrode 11 is provided on a sealing lid 18 via a positive electrode lead 14, and the negative electrode 12 is provided on the negative electrode can. It is connected to a negative electrode can 17 via a negative electrode lead 15. An insulating packing 20 is attached to the junction between the negative electrode can 17 and the sealing lid 18 to hermetically seal the battery. A coil spring 19 is provided between the positive electrode external terminal 16 and the sealing lid 18 so that when the battery internal pressure rises abnormally, the battery is compressed and the gas inside the battery can be released to the atmosphere.
[0036]
[Detailed results]
The abundance ratio of Ni atoms from the surface of the alloy particles to the depth of 200 nm and the abundance ratio of Ni atoms in the inner bulk region of the hydrogen storage alloy sample A1 and the comparative sample X were measured by a scanning transmission electron microscope and an energy dispersive type. The measurement was performed using an X-ray analyzer.
[0037]
According to this method, when the Ni content ratio in the surface region and the bulk region was measured, in the sample A1 according to the present invention, the concentration of Ni atoms was increased due to elution of the rare earth element from the surface region by the acid treatment. . As a result, it was confirmed that the abundance ratio of Ni atoms in the surface region was higher than that in the bulk region.
[0038]
Next, the discharge capacities of the batteries using the sample A1 and the comparative sample X during high-rate discharge were measured.
[0039]
The conditions at this time were as follows: each battery was charged at room temperature at a current value of 4.0 C for 6 hours, then discharged at a current of 0.2 C to 1.0 V, and the discharge capacity (mAh) during high-rate discharge was measured.
[0040]
The results are shown in Table 1.
[0041]
[Table 1]
Figure 0003545209
[0042]
This result indicates the superiority of the sample A1 according to the present invention having the surface region and the bulk region. In the sample A1 , the surface region containing the fluoride formed therein had a thickness of about 50 nm from the surface of the alloy particles.
[0043]
In this experiment 1, a hydrochloric acid aqueous solution was used as the acidic aqueous solution in step 2 which is a manufacturing process of the hydrogen storage alloy, but the same tendency is observed with nitric acid and phosphoric acid.
[0044]
<< Experiment 2 >>
In Experiment 2, the amount of fluoride to be added to the acidic solution in the second step of manufacturing the hydrogen storage alloy was changed to examine the relationship with the battery characteristics. The added fluoride is cobalt fluoride. The amount of addition is% by weight based on the weight of the hydrogen storage alloy.
[0045]
First, the alloy particles prepared in Experiment 1 described above were immersed in a hydrochloric acid aqueous solution containing the respective addition amounts shown in Table 2 and adjusted to pH = 1.0 for 30 minutes, stirred, suction-filtered, washed with water and dried. Samples B1 to B7 were prepared as a hydrogen storage alloy. Then, in the same manner as in Experiment 1, seven types of batteries were manufactured using Samples B1 to B7. Note that the sample B4 is the same as the sample A1 of the experiment 1.
[0046]
Table 2 shows the measured results of the added fluoride used in Samples B1 to B7 and the discharge capacity of each battery using each sample at the time of high-rate discharge. The conditions for producing the battery and the conditions for measuring the capacity were the same as those in Experiment 1 described above. Further, the characteristics of the battery using the comparative sample X used in Experiment 1 described above are also shown.
[0047]
[Table 2]
Figure 0003545209
[0048]
From these results, the batteries using the samples B1 to B7 according to the present invention have a larger discharge capacity of 690 mAh or more than those using the comparative sample X. Further, among the samples B1 to B7 according to the present invention, the batteries using the samples B2 to B6 according to the present invention have a discharge capacity of 800 mAh or more, and the added amount of cobalt fluoride is the weight of the hydrogen storage alloy. Is preferably 0.01% by weight or more and 5.0% by weight or less.
[0049]
In Experiment 1 described above, the thickness of the surface layer is approximately 50 nm, and in Experiment 2, it is approximately 100 nm. If the thickness is 150 nm or less, favorable results can be expected. In particular, it is most preferable that the thickness of the surface layer containing the fluoride be set to approximately 100 nm or less from the viewpoint of improving the discharge capacity at the time of high-rate discharge. In order to change the thickness, it is possible to change the thickness depending on the kind of the fluoride, the added amount, the acid treatment time, and the like.
[0050]
<< Experiment 3 >>
In Experiment 3, the amount of hydrochloric acid added to the acidic solution in the second step of manufacturing the hydrogen storage alloy was changed, and the relationship with the battery characteristics was examined. Note that cobalt fluoride (CoF 2 ) was used as the additive compound.
[0051]
First, the alloy particles prepared in Experiment 1 were immersed in a hydrochloric acid aqueous solution containing 1.0% by weight of CoF 2 for 30 minutes, stirred, suction-filtered, washed and dried. At this time, the pH is adjusted by changing the concentration of hydrochloric acid to be added. Thus, Samples C1 to C6 were prepared as hydrogen storage alloys. Then, in the same manner as in Experiment 1, six types of batteries were manufactured using Samples C1 to C6.
[0052]
Table 3 shows the measurement results of the discharge capacity of each of the batteries using the samples C1 to C6 during high-rate discharge. The conditions for producing the battery and the conditions for measuring the capacity were the same as those in Experiment 1 described above.
[0053]
[Table 3]
Figure 0003545209
[0054]
From these results, in each of the batteries using the samples C2 to C5, the discharge capacity at the time of high-rate discharge was as large as 800 mAh or more. Further, it can be understood that the battery internal pressure characteristics are also excellent. Therefore, it is understood that the pH of the acidic treatment solution is particularly preferably 0.7 to 2.0.
[0056]
In each of the above experiments, alloy particles prepared by melting and then pulverizing in an arc furnace in an argon atmosphere were shown.However, alloy particles produced by a gas atomizing method, which is easier to sinter than these alloy particles, or produced by a roll quenching method, etc. Similar effects were obtained with the alloy particles thus obtained.
[0057]
【The invention's effect】
As described in detail above, according to the hydrogen storage alloy and the method for producing the same according to the present invention, the activity of the alloy surface can be maintained. Further, by forming an electrode using this alloy and using it for a negative electrode of a nickel-metal hydride storage battery, the discharge capacity at the time of high-rate discharge can be increased, and its industrial value is extremely large.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a hydrogen storage alloy of the present invention.
FIG. 2 is a schematic sectional view of an alkaline storage battery.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hydrogen storage alloy 2 Surface area 3 Bulk area 4 Nickel atom 5 Nickel atom 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive lead 15 Negative lead 16 Positive external terminal 17 Negative can 18 Sealing lid 19 Coil spring 20 Packing

Claims (8)

CaCu5型結晶構造を有し、組成式MmNixCoyMnzM1-z[式中Mはアルミニウム(Al)、銅(Cu)から選ばれた少なくとも一種の元素、xはニッケル(Ni)の組成比率であって3.0≦x≦5.2、yはコバルト(Co)の組成比率であって0≦y≦1.2、zはマンガン(Mn)の組成比率であって0.1≦z≦0.9であり、且つ前記x、y、zの合計値が4.4≦x+y+z≦5.4]で表されるアルカリ蓄電池用水素吸蔵合金であって、前記水素吸蔵合金は、その表面に形成された表面領域と、その表面領域で被覆されたバルク領域から構成され、
前記表面領域は、コバルトのフッ化物を含有しており、
前記表面領域におけるNi原子の存在比率が、前記バルク領域におけるNi原子の存在比率よりも大きいことを特徴とするアルカリ蓄電池用水素吸蔵合金。
It has a CaCu 5 type crystal structure, a composition formula MmNi x Co y Mn z M 1 -z [ wherein M is aluminum (Al), copper least one element selected from (Cu), x is a nickel (Ni) 3.0 ≦ x ≦ 5.2, y is a composition ratio of cobalt (Co) and 0 ≦ y ≦ 1.2, z is a composition ratio of manganese (Mn) and 0.1 ≦ z ≦ 0.9, And a total value of x, y, and z is 4.4 ≦ x + y + z ≦ 5.4], wherein the hydrogen storage alloy has a surface region formed on a surface thereof and a surface region thereof. Consisting of a bulk region coated with
The surface region contains a fluoride of cobalt ;
A hydrogen storage alloy for an alkaline storage battery, wherein the abundance ratio of Ni atoms in the surface region is larger than the abundance ratio of Ni atoms in the bulk region.
前記表面領域が、合金粒子表面から略100nm以下の厚さを有することを特徴とする請求項1記載のアルカリ蓄電池用水素吸蔵合金。The hydrogen storage alloy according to claim 1, wherein the surface region has a thickness of about 100 nm or less from the surface of the alloy particles. 前記請求項1記載のアルカリ蓄電池用水素吸蔵合金を、導電性芯体に充填したことを特徴とするアルカリ蓄電池用水素吸蔵合金電極。A hydrogen storage alloy electrode for an alkaline storage battery, wherein the conductive core is filled with the hydrogen storage alloy for an alkaline storage battery according to claim 1. CaCu5型結晶構造を有し、 組成式MmNixCoyMnzM1-z[式中Mはアルミニウム(Al)、銅(Cu)から選ばれた少なくとも一種の元素、xはニッケル(Ni)の組成比率であって3.0≦x≦5.2、yはコバルト(Co)の組成比率であって0≦y≦1.2、zはマンガン(Mn)の組成比率であって0.1≦z≦0.9であり、且つ前記x、y、zの合計値が4.4≦x+y+z≦5.4]で表される合金粒子を準備する第1ステップと、
前記第1ステップで準備された前記合金粒子を、コバルトのフッ化物を含有させた酸性溶液中で処理を行う第2ステップにより、水素吸蔵合金とすることを特徴とするアルカリ蓄電池用水素吸蔵合金の製造方法。
It has a CaCu 5 type crystal structure, a composition formula MmNi x Co y Mn z M 1 -z [ wherein M is aluminum (Al), copper least one element selected from (Cu), x is a nickel (Ni) 3.0 ≦ x ≦ 5.2, y is a composition ratio of cobalt (Co) and 0 ≦ y ≦ 1.2, z is a composition ratio of manganese (Mn) and 0.1 ≦ z ≦ 0.9, And a first step of preparing alloy particles in which the sum of x, y, and z is represented by 4.4 ≦ x + y + z ≦ 5.4],
A second step of treating the alloy particles prepared in the first step in an acidic solution containing cobalt fluoride , whereby the hydrogen storage alloy for an alkaline storage battery is characterized by being a hydrogen storage alloy. Production method.
前記フッ化物の添加量が、前記合金粒子の重量に対して0.01
〜5.0重量%であることを特徴とする請求項4記載のアルカリ蓄電池用水素吸蔵合金の製造方法。
The amount of the fluoride added is 0.01 to the weight of the alloy particles.
5. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 4, wherein the amount is from 5.0 to 5.0% by weight.
前記第2ステップにおいて、酸性溶液がpH=0.7〜2.0であることを特徴とする請求項4記載のアルカリ蓄電池用水素吸蔵合金の製造方法。The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 4, wherein in the second step, the pH of the acidic solution is 0.7 to 2.0. 前記第1ステップが、ガスアトマイズ法であることを特徴とする請求項4記載のアルカリ蓄電池用水素吸蔵合金の製造方法。The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 4, wherein the first step is a gas atomization method. 前記請求項1記載のアルカリ蓄電池用水素吸蔵合金を、導電性芯体に充填することを特徴とするアルカリ蓄電池用水素吸蔵合金電極の製造方法。A method for producing a hydrogen storage alloy electrode for an alkaline storage battery, comprising filling a conductive core with the hydrogen storage alloy for an alkaline storage battery according to claim 1.
JP18080798A 1998-06-26 1998-06-26 Hydrogen storage alloy for alkaline storage battery and method for producing the same, hydrogen storage alloy electrode for alkaline storage battery and method for producing the same Expired - Fee Related JP3545209B2 (en)

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