Hydrogen absorbing alloy and nickel-metal hydride rechargeable battery

Abstract

An object of the present invention is to provide a hydrogen absorbing alloy which can improve a high rate discharge property while suppressing particle size reduction, exhibits cycle life characteristics equal to or higher than those of conventional alloys even when its cobalt content is decreased, and has a high capacity. Specifically, the present invention provides a hydrogen absorbing alloy having a CaCu 5 type crystal structure in its principal phase, wherein the La content in the alloy is in the range of 24 to 33% by weight and the Mg or Ca content in the alloy is in the range of 0.1 to 1.0% by weight, as well as the aforesaid alloy wherein the Co content in the alloy is not greater than 9% by weight.

1 . A hydrogen absorbing alloy having a CaCu 5  type crystal structure in its principal phase, comprising La in the range of 24 to 33% by weight in the alloy, and Mg or Ca in the range of 0.1 to 1.0% by weight in the alloy.  
     
     
         2 . A hydrogen absorbing alloy according to  claim 1 , further comprising 9% by weight or less of Co in the alloy.  
     
     
         3 . A hydrogen absorbing alloy according to  claim 1 , further comprising 6% by weight or less of Co in the alloy.  
     
     
         4 . A hydrogen absorbing alloy according to  claim 1 , wherein the Co content is 6 to 9% by weight, and the atomic ratio B/A is 5.0 to 5.25, where A represents a rare earth element including La, and B represents a rare earth element, transition metal or Al.  
     
     
         5 . A hydrogen absorbing alloy according to  claim 1 , further comprising one or more selected from the group consisting of Ti, Zr and V.  
     
     
         6 . A hydrogen absorbing alloy having a CaCu 5  type crystal structure in its principal phase, comprising Mg and having a-axis length of 4.990 to 5.050 Å and c-axis length of 4.030 to 4.070 Å for the lattice constants in the CaCu 5  type crystal structure.  
     
     
         7 . A hydrogen absorbing alloy according to any one of  claims 1  to  4  having a-axis length of 4.990 to 5.050 Å and c-axis lenth of 4.030 to 4.070 Å for the lattice constants in the CaCu 5  type crystal structure.  
     
     
         8 . A method for manufacturing a hydrogen absorbing alloy having a CaCu 5  type crystal structure in its principal phase, characterized in that a Mg-supply material is added to dissolution of component elements for hydrogen absorbing alloy in an amount of 0.1 to 1.0% by weight in an entire hydrogen absorbing alloy.  
     
     
         9 . A method for manufacturing a hydrogen absorbing alloy according to  claim 8 , characterized in that at least Ni and Co are melted in a melting vessel, and then the Mg-supply material is added to the melting vessel.  
     
     
         10 . A method for manufacturing a hydrogen absorbing alloy according to  claim 8  or  9 , characterized in the Mg-supply material is selected from metallic Mg and Mg alloy with melting point of 650° C. or higher.  
     
     
         11 . A nickel-metal hydride rechargeable battery using the hydrogen absorbing alloy of any one of  claims 1  to  7  for an electrode thereof.