Hydrogen-absorption alloy electrode

Abstract

A hydrogen-absorption alloy electrode includes, as a principal material, particles of a hydrogen-absorption alloy containing a rare earth element, Ni, Co, Al and Mn and leads to reduced deviation in battery characteristics after charging/discharging cycles by having the size distribution of the alloy particles limited such that d90/d10≦8 and d90−d10≦50 μm, where di (where i varies from 0 to 100) means a particle size at which cumulative size frequency with respect to the entire particles is i%. The alloy particles are constructed such that on the surface of the alloy particles, at least one of the following relationships holds: (the amount of Al on the surface/the amount of Al in the alloy)<(the amount of Co on the surface/the amount of Co in the alloy); (the amount of Mn on the surface/the amount of Mn in the alloy)<(the amount of Co on the surface/the amount of Co in the alloy); and (the amount of Al+Mn on the surface/the amount of Al+Mn in the alloy)<(the amount of Co on the surface/the amount of Co in the alloy).

What is claimed is:  
     
         1 . A hydrogen-absorption alloy electrode comprising particles of a hydrogen-absorption alloy, the particles having a size distribution such that d90/d10≦8 and d90−d10≦50 μm, where di (where i varies from 0 to 100) means a particle size at which cumulative size frequency with respect to the entire particles is i%.  
     
     
         2 . The hydrogen-absorption alloy electrode according to  claim 1 , wherein the size of the hydrogen-absorption alloy particles is such that d90≦60 μm.  
     
     
         3 . The hydrogen-absorption alloy electrode according to  claim 1 , wherein the size of the hydrogen-absorption alloy particles is such that d50≦25 μm.  
     
     
         4 . A hydrogen-absorption alloy electrode comprising particles of a hydrogen-absorption alloy including a rare earth element, Ni, Co and Al, wherein on the surface of the alloy, the following relationship holds: (an amount of Al on the surface/an amount of Al in the alloy)<(an amount of Co on the surface/an amount of Co in the alloy).  
     
     
         5 . A hydrogen-absorption alloy electrode comprising particles of a hydrogen-absorption alloy including a rare earth element, Ni, Co and Mn, wherein on the surface of the alloy, the following relationship holds: (an amount of Mn on the surface/an amount of Mn in the alloy)<(an amount of Co on the surface/an amount of Co in the alloy).  
     
     
         6 . A hydrogen-absorption alloy electrode comprising particles of a hydrogen-absorption alloy including a rare earth element, Ni, Co, Al and Mn, wherein on the surface of the alloy, the following relationship holds: (an amount of Al+Mn on the surface/an amount of Al+Mn in the alloy)<(an amount of Co on the surface/an amount of Co in the alloy).  
     
     
         7 . The hydrogen-absorption alloy electrode according to any one of  claims 4  to  6 , wherein the particles have a size distribution such that d90/d10≦8 and d90-d10≦50 μm, where di (where i varies from 0 to 100) means a particle size at which cumulative size frequency with respect to the entire particles is i%.  
     
     
         8 . The hydrogen-absorption alloy electrode according to  claim 7 , wherein the size of the hydrogen-absorption alloy particles is such that d90≦60 μm.  
     
     
         9 . The hydrogen-absorption alloy electrode according to  claim 7 , wherein the size of the hydrogen-absorption alloy particles is such that d50≦25 μm.