JP3583837B2

JP3583837B2 - Method for producing hydrogen storage alloy electrode

Info

Publication number: JP3583837B2
Application number: JP24164295A
Authority: JP
Inventors: 考導廣澤; 隆明池町
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 1995-09-20
Filing date: 1995-09-20
Publication date: 2004-11-04
Anticipated expiration: 2015-09-20
Also published as: JPH0992273A

Description

【０００１】
【産業上の利用分野】
本発明は、電気化学的に水素を吸蔵・放出する水素吸蔵合金を負極主材料とした水素吸蔵合金電極の製造方法に関し、特に焼結式の水素吸蔵合金電極の製造方法の改良に関する。
【０００２】
【従来の技術】
最近のエレクトロニクス技術の進歩は目覚ましく、今後もますます加速する傾向にある。これに伴い、電子機器のポータブル化やコードレス化が進むと同時に、これらの機器の電源として、小型で軽量でかつ高エネルギー密度の高性能二次電池の開発が強く望まれている。そこで、負極に水素吸蔵合金を用いた金属水素化物蓄電池は、ニッケルカドミウム蓄電池や鉛蓄電池等よりも高容量で高密度の上、クリーンな電源として最近特に注目されている。
【０００３】
ところで、アルカリ蓄電池用の水素吸蔵合金電極としては、水素吸蔵合金に結着剤としてポリエチレンオキサイドやポリビニルアルコール等を混合してスラリーを作製した後、このスラリーをパンチングメタル等の導電性芯体に塗着して製造する所謂非焼結式の水素吸蔵合金電極が一般的に使用されている。
【０００４】
しかしながら、これらの非焼結式の水素吸蔵合金電極においては、水素吸蔵合金を導電性芯体に保持させるためには、前記のような結着剤を水素吸蔵合金粒子間及び水素吸蔵合金と導電性芯体に介在させなければならない。しかしながら、前記のような結着剤は絶縁性であるため、放電容量の低下は免れ得ない。
【０００５】
そこで、この解決方法として、電極の製造方法を、非焼結式から焼結式に変えることが特公昭５８−４６８２７号公報および特開平２−１２７６５号公報等で提案されている。これらの公報には、水素吸蔵合金に、焼結されやすいＣｏ、Ｎｉ、ＴｉＮｉ_Ｘ等の粉末を混合させ、次にこの混合粉末を、金属製多孔板を中心に配置して加圧成型した後、真空中若しくは不活性雰囲気中で焼結させることによって、焼結体としての強度が強い電極を得る方法を開示している。
【０００６】
【発明が解決しようとする課題】
しかしながら、前記Ｃｏ、Ｎｉ、ＴｉＮｉ_Ｘ等の粉末をＭｎを含有する水素吸蔵合金と混合した後、焼結させると、水素吸蔵合金中のＭｎが合金から流出するため、合金の組成が所望の組成から著しく逸脱して電極の放電容量が低下するという欠点があった。
【０００７】
本発明は、このような問題点に鑑みてなされたものであり、電極の強度を充分維持しつつ、放電容量の低下を抑制した水素吸蔵合金電極を提供しようとすることを本発明の課題とするものである。
【０００８】
【課題を解決するための手段】
本発明に係る水素吸蔵合金電極の製造方法は、所望の組成の水素吸蔵合金に比較して、合金を構成するＭｎ以外の組成物の含有比率を変えずに、Ｍｎの含有比率のみを予め増量させた水素吸蔵合金を作製する工程と、前記水素吸蔵合金に金属ＮｉまたはＮｉ化合物を混合する工程と、前記水素吸蔵合金と金属ＮｉまたはＮｉ化合物の混合物を不活性雰囲気中または還元雰囲気中で焼結させて電極を得ることを特徴とする。
【０００９】
【作用】
Ｍｎを含有する水素吸蔵合金と金属Ｎｉとの混合物を焼結させると、水素吸蔵合金中のＭｎが合金から流出し易く、合金の組成が所望の組成から著しく逸脱する。そこで、焼結する前に予め所望の水素吸蔵合金組成よりもＭｎ含有比率を高くすることによって、焼結後の水素吸蔵合金電極の合金組成を所望の組成範囲にすることが可能となる。また溶出したＭｎが別に添加した金属Ｎｉと導電性の良好なＭｎＮｉ金属を形成する。この金属が水素吸蔵合金間に介在して焼結しているため、良好な焼結強度と集電性が得ることが可能となる。
【００１０】
【実施例】
以下に水素吸蔵合金として、ＭｍＮｉ_３．７Ｃｏ_０．６Ｍｎ_０．６Ａｌ_０．２を所望の組成とした場合の実施例とその比較例を以下に述べる。
【００１１】
（実施例１）
［所望の組成よりもＭｎの比率を予め増量させた水素吸蔵合金の作製］
Ｍｍ（希土類元素の混合物）：Ｎｉ：Ｃｏ：Ｍｎ：Ａｌの各金属元素を１：３．７：０．６：１．０：０．２の割合となるように市販の金属元素を秤量し、Ａｒアトマイズ法により、組成式ＭｍＮｉ_３．７Ｃｏ_０．６Ｍｎ_１．０Ａｌ_０．２で表される水素吸蔵合金鋳塊を作製した。ここで、作製された合金は、ＭｍＮｉ_３．７Ｃｏ_０．６Ｍｎ_１．０Ａｌ_０．２であり、ＭｍＮｉ_３．７Ｃｏ_０．６Ｍｎ_０．６Ａｌ_０．２を所望の組成とした合金と比較すると、Ｍｎ以外の組成物（Ｎｉ、Ｃｏ、Ａｌ）の含有比率は変わっておらず、Ｍｎの含有比率のみを０．６から１．０に予め増量させている。
【００１２】
次に、この合金鋳塊を平均粒径約８０μｍとなるように機械的に粉砕し、１５０μｍ以上、２５μｍ以下の粒径のものについては、メッシュパスして取り除いて、水素吸蔵合金粉末を作製した。
［焼結式水素吸蔵合金電極の作製］
この所望の組成よりもＭｎ比率を多くした前記水素吸蔵合金粉末に対して、金属Ｎｉ粉末１０重量％と、ポリエチレンオキサイド約１重量％とを混合し、水を適量を用いてスラリー化し、ニッケルメッキを施した金属製開孔芯体に塗着する。乾燥後、充填密度を上げるため１０％圧縮した後、水素とアルゴン混合ガス（水素４ｖｏｌ％）中、９００℃、１時間還元熱処理させて焼結式の水素吸蔵合金電極を作製し、本発明電極Ａと称する。
【００１３】
本熱処理後の水素吸蔵合金の組成は、ＭｍＮｉ_３．７２Ｃｏ_０．６Ｍｎ_０．５９Ａｌ_０．２となり、所望の組成に近い値が得られている。
【００１４】
また、熱処理時に水素吸蔵合金から溶出したＭｎと金属Ｎｉとが、ＭｎＮｉ金属を形成し、この金属が水素吸蔵合金間に介在して焼結しているので、充分な強度と集電性を保っている。
【００１５】
（実施例２）
実施例１と同様にして作製した水素吸蔵合金粉末に対してＮｉＯ粉末１０重量％と、カーボン粉末約２重量％と、ポリエチレンオキサイド約１重量％とを混合して、実施例１と同様にスラリー化し、ニッケルメッキを施した金属製開孔芯体に塗着する。乾燥後、充填密度を上げるため１０％圧縮した後、水素ガス中、９００℃、１時間還元熱処理させて焼結式の水素吸蔵合金電極を作製し、本発明電極Ｂと称する。
【００１６】
本熱処理後の水素吸蔵合金の組成は、ＭｍＮｉ_３．７Ｃｏ_０．６Ｍｎ_０．５９Ａｌ_０．２となり、所望の組成に近い値が得られている。
【００１７】
本実施例で用いたＮｉＯ粉末は、熱処理時に金属化し、金属Ｎｉとなっており、熱処理時に水素吸蔵合金から溶出したＭｎと前記金属Ｎｉとが、ＭｎＮｉ金属を形成し、この金属が水素吸蔵合金間に介在して焼結しているので、充分な強度と集電性を保っている。
【００１８】
（比較例１）
［所望の組成の水素吸蔵合金の作製］
Ｍｍ（希土類元素の混合物）：Ｎｉ：Ｃｏ：Ｍｎ：Ａｌの各金属元素を１：３．７：０．６：０．６：０．２の割合となるように市販の金属元素を秤量し、Ａｒアトマイズ法により、組成式ＭｍＮｉ_３．７Ｃｏ_０．６Ｍｎ_０．６Ａｌ_０．２で表される水素吸蔵合金鋳塊を作製した。次に、この合金鋳塊を平均粒径約８０μｍとなるように機械的に粉砕し、１５０μｍ以上、２５μｍ以下のものについてはメッシュパスして取り除いて水素吸蔵合金粉末を作製した。
【００１９】
その後、前記実施例１と同様にして前記水素吸蔵合金粉末に対して、金属Ｎｉ粉末１０重量％と、ポリエチレンオキサイド約１重量％とを混合し、水を適量用いてスラリー化し、ニッケルメッキを施した金属製開孔芯体に塗着する。乾燥後、充填密度を上げるため１０％圧縮した後、水素とアルゴン混合ガス（水素４ｖｏｌ％）中、９００℃、１時間還元熱処理させて焼結式の水素吸蔵合金電極を作製し、比較電極Ｘと称する。
［特性試験］
本発明電極Ａ、Ｂ及び比較電極Ｘを用いて、以下の試験セルを作製した。
【００２０】
前記電極Ａ、Ｂ及びＸを負極として用い、負極容量に対して充分な放電容量を有している公知の焼結式Ｎｉ正極を、セパレータを介して、前記負極の両側に配置した後、外装缶に挿入した。その後、この外装缶に３０重量％のＫＯＨ水溶液を注液した後、密閉して公称容量３００ｍＡｈの試験セルをそれぞれ作製した。
【００２１】
そして、これらの各試験セルについて、３０ｍＡの電流で１６時間充電した後、１時間休止し、６０ｍＡの電流で電池電圧が１．０Ｖになる迄放電した時の放電容量を測定した結果を下記表１に示す。
【００２２】
但し、電極Ｘの放電容量を１００としたときの比率で示す。
【００２３】
【表１】

【００２４】
表１から、明らかなように、本発明電極Ａ、Ｂは比較電極Ｘよりも高い放電容量が得られている。これは、本発明電極Ａ、Ｂは、焼結する前に予め所望の水素吸蔵合金組成よりもＭｎのみの含有比率を高くした水素吸蔵合金を用いているためであり、焼結時にＭｎが合金から溶出することによって、焼結後の合金が所望の組成が得られること及び前記溶出したＭｎと金属Ｎｉとが、導電性の良好なＭｎＮｉ金属を形成し、この金属が水素吸蔵合金間に介在して焼結していることに起因している。
【００２５】
一方、比較電極Ｘでは、焼結する前に既に所望の組成の水素吸蔵合金組成を用いているため、焼結時にＭｎが合金から溶出することによって、焼結後の合金が所望の組成から著しく逸脱するため、放電容量が本発明電極Ａ、Ｂに比べて低下している。
【００２６】
尚、本実施例では、金属Ｎｉ粉末およびＮｉＯ粉末を用いたが、これらに限らず不活性雰囲気中または還元雰囲気中での熱処理により金属Ｎｉに変化するものであればよく、例えば、ＮｉＯ粉末の代わりにＮｉＮＯ_３粉末、ＮｉＣＯ_３粉末等を用いることができる。また、ＮｉＯ、ＮｉＮＯ_３、ＮｉＣＯ_３の中から選ばれた少なくとも１種以上を用いても良い。
【００２７】
【発明の効果】
以上から明らかなように、本発明の製造方法によれば、極めて簡単な方法により、電極の強度を充分維持しつつ、放電容量の低下を抑制した焼結式の水素吸蔵合金電極が得られ、その工業的価値は極めて高い。[0001]
[Industrial applications]
The present invention relates to a method of manufacturing a hydrogen storage alloy electrode using a hydrogen storage alloy that electrochemically stores and releases hydrogen as a negative electrode main material, and more particularly to an improvement in a method of manufacturing a sintered hydrogen storage alloy electrode.
[0002]
[Prior art]
Recent advances in electronics technology have been remarkable and will continue to accelerate. Along with this, electronic devices have become more portable and cordless, and at the same time, there is a strong demand for the development of small, lightweight, high-energy-density, high-performance secondary batteries as power supplies for these devices. Therefore, a metal hydride storage battery using a hydrogen storage alloy for the negative electrode has recently attracted particular attention as a clean power source with higher capacity, higher density, and higher capacity than nickel cadmium storage batteries, lead storage batteries, and the like.
[0003]
By the way, as a hydrogen storage alloy electrode for an alkaline storage battery, a slurry is prepared by mixing a hydrogen storage alloy with polyethylene oxide, polyvinyl alcohol, or the like as a binder, and then applying the slurry to a conductive core such as punching metal. A so-called non-sintering type hydrogen storage alloy electrode which is manufactured by wearing is generally used.
[0004]
However, in these non-sintering type hydrogen storage alloy electrodes, in order to hold the hydrogen storage alloy on the conductive core, the binder as described above must be applied between the hydrogen storage alloy particles and between the hydrogen storage alloy and the conductive material. Must be interposed in the sexual core. However, since the above-mentioned binder is insulating, a decrease in discharge capacity cannot be avoided.
[0005]
Therefore, as a solution to this problem, it has been proposed in Japanese Patent Publication No. 58-46827 and Japanese Patent Application Laid-Open No. 2-212765 to change the method of manufacturing an electrode from a non-sintering method to a sintering method. These publications, the hydrogen storage alloy, sintered susceptible Co, Ni, by mixing powders such as TiNi _X, then the mixed powder, was pressure-molded to center the metallic porous plate Discloses a method of obtaining an electrode having high strength as a sintered body by sintering in a vacuum or an inert atmosphere.
[0006]
[Problems to be solved by the invention]
However, the Co, Ni, after mixing with hydrogen occlusion alloy containing powder of Mn or the like TiNi _X, when sintering, Mn in the hydrogen absorbing alloy to flow out from the alloy, the composition of the alloy of the desired There is a drawback that the composition deviates significantly from the composition and the discharge capacity of the electrode decreases.
[0007]
The present invention has been made in view of such problems, and it is an object of the present invention to provide a hydrogen storage alloy electrode that suppresses a decrease in discharge capacity while sufficiently maintaining the strength of the electrode. Is what you do.
[0008]
[Means for Solving the Problems]
The method for producing a hydrogen storage alloy electrode according to the present invention is such that, compared to a hydrogen storage alloy having a desired composition, the content ratio of the composition other than Mn constituting the alloy is not changed, and only the content ratio of Mn is increased in advance. Producing a hydrogen storage alloy having been subjected to the above, a step of mixing metal Ni or a Ni compound with the hydrogen storage alloy, and baking the mixture of the hydrogen storage alloy and the metal Ni or Ni compound in an inert atmosphere or a reducing atmosphere. It is characterized in that an electrode is obtained by tying.
[0009]
[Action]
When sintering a mixture of Mn-containing hydrogen storage alloy and metal Ni, Mn in the hydrogen storage alloy easily flows out of the alloy, and the composition of the alloy significantly deviates from a desired composition. Therefore, by preliminarily increasing the Mn content ratio from the desired hydrogen storage alloy composition before sintering, the alloy composition of the hydrogen storage alloy electrode after sintering can be in a desired composition range. Further, the eluted Mn forms MnNi metal having good conductivity with separately added metal Ni. Since this metal is interposed between the hydrogen storage alloys and sintered, good sintering strength and current collecting properties can be obtained.
[0010]
【Example】
Hereinafter, examples in which MmNi _3.7 Co _0.6 Mn _0.6 Al _0.2 has a desired composition as a hydrogen storage alloy and comparative examples thereof will be described below.
[0011]
(Example 1)
[Production of a hydrogen storage alloy in which the ratio of Mn is increased in advance from the desired composition]
Mm (mixture of rare earth elements): a commercially available metal element is weighed so that each metal element of Ni: Co: Mn: Al is in a ratio of 1: 3.7: 0.6: 1.0: 0.2. Then, a hydrogen storage alloy ingot represented by a composition formula of MmNi _3.7 Co _0.6 Mn _1.0 Al _0.2 was produced by an Ar atomization method. Here, the produced alloy is MmNi _3.7 Co _0.6 Mn _1.0 Al _0.2 , and MmNi _3.7 Co _0.6 Mn _0.6 Al _0.2 has a desired composition. Compared with the alloy, the content ratio of the composition (Ni, Co, Al) other than Mn did not change, and only the Mn content ratio was increased from 0.6 to 1.0 in advance.
[0012]
Next, this alloy ingot was mechanically pulverized so as to have an average particle diameter of about 80 μm, and those having a particle diameter of 150 μm or more and 25 μm or less were removed by a mesh pass to prepare a hydrogen storage alloy powder. .
[Production of sintered hydrogen storage alloy electrode]
To the hydrogen storage alloy powder having an Mn ratio larger than the desired composition, 10% by weight of metal Ni powder and about 1% by weight of polyethylene oxide were mixed, and a suitable amount of water was slurried, and nickel plating was performed. Is applied to the metal core having been subjected to the above. After drying, after compressing by 10% to increase the packing density, the mixture was subjected to a reduction heat treatment in a mixed gas of hydrogen and argon (4 vol% of hydrogen) at 900 ° C. for 1 hour to produce a sintered hydrogen absorbing alloy electrode, and the electrode of the present invention was obtained. Called A.
[0013]
The composition of the hydrogen storage alloy after the main heat treatment was MmNi _3.72 Co _0.6 Mn _0.59 Al _0.2 , and a value close to the desired composition was obtained.
[0014]
In addition, Mn and metal Ni eluted from the hydrogen storage alloy during heat treatment form MnNi metal, and this metal is interposed between the hydrogen storage alloys and sintered, so that sufficient strength and current collecting properties are maintained. ing.
[0015]
(Example 2)
10% by weight of NiO powder, about 2% by weight of carbon powder and about 1% by weight of polyethylene oxide were mixed with the hydrogen-absorbing alloy powder produced in the same manner as in Example 1, and the slurry was mixed in the same manner as in Example 1. And applied to a nickel-plated metal core. After drying, after compressing by 10% in order to increase the packing density, reduction heat treatment was performed in hydrogen gas at 900 ° C. for 1 hour to produce a sintered hydrogen storage alloy electrode, which is referred to as electrode B of the present invention.
[0016]
The composition of the hydrogen storage alloy after the main heat treatment was MmNi _3.7 Co _0.6 Mn _0.59 Al _0.2, and a value close to the desired composition was obtained.
[0017]
The NiO powder used in the present example is metallized during heat treatment to become metal Ni, and Mn eluted from the hydrogen storage alloy during the heat treatment and the metal Ni form a MnNi metal, which is a hydrogen storage alloy. Since it is interposed and sintered, sufficient strength and current collecting properties are maintained.
[0018]
(Comparative Example 1)
[Production of hydrogen storage alloy of desired composition]
Mm (mixture of rare earth elements): A commercially available metal element is weighed so that each metal element of Ni: Co: Mn: Al is in a ratio of 1: 3.7: 0.6: 0.6: 0.2. Then, a hydrogen storage alloy ingot represented by a composition formula of MmNi _3.7 Co _0.6 Mn _0.6 Al _0.2 was produced by an Ar atomization method. Next, this alloy ingot was mechanically pulverized so as to have an average particle size of about 80 μm, and those having a diameter of 150 μm or more and 25 μm or less were removed by a mesh pass to prepare a hydrogen storage alloy powder.
[0019]
Thereafter, in the same manner as in Example 1, 10% by weight of metal Ni powder and about 1% by weight of polyethylene oxide were mixed with the hydrogen storage alloy powder, and the mixture was slurried using an appropriate amount of water and nickel-plated. Is applied to the opened metal core. After drying, after compressing by 10% to increase the packing density, the mixture was subjected to a reduction heat treatment at 900 ° C. for 1 hour in a mixed gas of hydrogen and argon (hydrogen 4 vol%) to produce a sintered hydrogen absorbing alloy electrode, and a comparative electrode X Called.
[Characteristic test]
Using the electrodes A and B of the present invention and the comparative electrode X, the following test cells were produced.
[0020]
Using the electrodes A, B and X as a negative electrode, a known sintered Ni positive electrode having a sufficient discharge capacity with respect to the negative electrode capacity is disposed on both sides of the negative electrode with a separator interposed therebetween. Inserted in a can. Thereafter, a 30% by weight KOH aqueous solution was injected into the outer can, and the container was closed to produce test cells having a nominal capacity of 300 mAh.
[0021]
For each of these test cells, the battery was charged for 16 hours at a current of 30 mA, paused for 1 hour, and measured for the discharge capacity when the battery was discharged at a current of 60 mA until the battery voltage reached 1.0 V. 1 is shown.
[0022]
However, the ratio is shown assuming that the discharge capacity of the electrode X is 100.
[0023]
[Table 1]

[0024]
As is apparent from Table 1, the electrodes A and B of the present invention have a higher discharge capacity than the comparative electrode X. This is because the electrodes A and B of the present invention use a hydrogen storage alloy in which the content ratio of only Mn is higher than the desired hydrogen storage alloy composition before sintering. , The desired composition of the alloy after sintering is obtained, and the eluted Mn and the metal Ni form an MnNi metal having good conductivity, and this metal is interposed between the hydrogen storage alloys. And sintering.
[0025]
On the other hand, in the comparative electrode X, since the hydrogen storage alloy composition having a desired composition is already used before sintering, Mn is eluted from the alloy at the time of sintering. Due to the deviation, the discharge capacity is lower than the electrodes A and B of the present invention.
[0026]
In the present embodiment, the metal Ni powder and the NiO powder are used. However, the present invention is not limited thereto, and any material may be used as long as it changes into metal Ni by heat treatment in an inert atmosphere or a reducing atmosphere. Instead, NiNO ₃ powder, NiCO ₃ powder or the like can be used. In addition, at least one selected from NiO, NiNO ₃ , and NiCO ₃ may be used.
[0027]
【The invention's effect】
As is clear from the above, according to the production method of the present invention, a sintered hydrogen absorbing alloy electrode in which the strength of the electrode is sufficiently maintained and the decrease in the discharge capacity is suppressed is obtained by an extremely simple method, Its industrial value is extremely high.

Claims

In the method for producing a hydrogen storage alloy electrode provided with a hydrogen storage alloy having a desired composition containing Mn, the content ratio of a composition other than Mn constituting the alloy is changed as compared with the hydrogen storage alloy having the desired composition. Producing a hydrogen storage alloy in which only the content ratio of Mn is increased in advance, mixing metal Ni or a Ni compound with the hydrogen storage alloy, and mixing the hydrogen storage alloy with a metal Ni or a Ni compound. Sintering in an inert atmosphere or a reducing atmosphere to obtain an electrode.

2. The method for manufacturing a hydrogen storage alloy electrode according to claim 1, wherein the Ni compound is changed into metallic Ni by heat treatment in an inert atmosphere or a reducing atmosphere.

The Ni as a compound, _NiO, NiNO 3, the manufacturing method of the hydrogen storage alloy electrode according to claim 1, characterized by using at least one kind selected from among NiCO _3.