Hydrogen absorbing alloy powder and electrodes formed of the hydrogen absorbing alloy powder

Abstract

Provided is a hydrogen absorbing alloy powder for use in nickel-metal hydride storage batteries having a high capacity, excellent initial characteristics and a long life. Specifically provided is a process for the production of a hydrogen absorbing alloy powder which includes the steps of treating a hydrogen absorbing alloy powder with an acid solution, and subsequently treating the hydrogen absorbing alloy powder with a solution containing a condensed phosphoric acid having 2 to 20 phosphorus atoms per molecule and/or phytic acid, as well as an electrode formed of the hydrogen absorbing alloy powder produced by the above process. Also provided is a hydrogen absorbing alloy powder of the AB 5 type in which A is exothermic metal and B is endothermic metal, the hydrogen absorbing alloy powder being obtained by providing a hydrogen absorbing alloy in which A comprises a mixture composed of 20 to 50% by weight of Ce, 20 to 50% by weight of La, and the balance comprising rare earth elements other than Ce and La and inclusive of Y (yttrium), treating the hydrogen absorbing alloy powder with an acid solution, and further treating the hydrogen absorbing alloy powder with a solution containing a phosphorus compound, as well as an electrode formed of this hydrogen absorbing alloy powder.

1 . A process for the production of a hydrogen absorbing alloy powder which comprises steps of treating a hydrogen absorbing alloy powder with an acid solution, and subsequently treating the hydrogen absorbing alloy powder with a solution containing a condensed phosphoric acid having 2 to 20 phosphorus atoms per molecule and/or phytic acid.  
     
     
         2 . A process for the production of a hydrogen absorbing alloy powder as claimed in    claim 1    wherein the acid solution is a solution containing at least one compound selected from the group consisting of sulfonic acids, sulfinic acids, sulfenic acids and salts thereof.  
     
     
         3 . A process for the production of a hydrogen absorbing alloy powder as claimed in    claim 1    wherein the total amount of condensed phosphoric acid and/or phytic acid used is in the range of 0.01 to 10 parts by weight per 100 parts by weight of the hydrogen absorbing alloy.  
     
     
         4 . A process for the production of a hydrogen absorbing alloy powder as claimed in    claim 2    wherein the total amount of condensed phosphoric acid and/or phytic acid used is in the range of 0.01 to 10 parts by weight per 100 parts by weight of the hydrogen absorbing alloy.  
     
     
         5 . An electrode formed of the hydrogen absorbing alloy powder produced by a process as claimed in    claim 1   .  
     
     
         6 . An electrode formed of the hydrogen absorbing alloy powder produced by a process as claimed in    claim 2   .  
     
     
         7 . An electrode formed of the hydrogen absorbing alloy powder produced by a process as claimed in    claim 3   .  
     
     
         8 . An electrode formed of the hydrogen absorbing alloy powder produced by a process as claimed in    claim 4   .  
     
     
         9 . A hydrogen absorbing alloy powder of the AB 5  type in which A is exothermic metal and B is endothermic metal, the hydrogen absorbing alloy powder being obtained by providing a hydrogen absorbing alloy in which A comprises a mixture composed of 20 to 50% by weight of Ce, 20 to 50% by weight of La, and the balance comprising rare earth elements other than Ce and La and inclusive of Y (yttrium), treating the hydrogen absorbing alloy with an acid solution, and subsequently treating the hydrogen absorbing alloy with a solution containing a phosphorus compound.  
     
     
         10 . A hydrogen absorbing alloy powder as claimed in    claim 9    wherein the acid solution is a solution of an organic acid and the phosphorus compound is a condensed phosphoric acid having 2 to 20 phosphorus atoms.  
     
     
         11 . An negative electrode for use in nickel-metal hydride batteries which is formed of a hydrogen absorbing alloy powder as claimed in    claim 9   .  
     
     
         12 . An negative electrode for use in nickel-metal hydride batteries which is formed of a hydrogen absorbing alloy powder as claimed in    claim 10   .