Hydrogen-absorbing alloy and hydrogen-absorbing alloy electrode

Abstract

To provide a hydrogen absorbing alloy having a BCC (body-centered cubic structure) as a crystal structure, and particularly a hydrogen-absorbing alloy for a nickel-hydride cell having excellent discharge capacity and durability (cycle characteristics), said hydrogen-absorbing alloy having a composition expressed by the general formula Ti(100-a-b-c-d)CraVbNicXd, where X is at least one member selected from the group consisting of Y (yttrium), lanthanoids, Pd and Pt, and each of a, b, c and d is represented, in terms of at %, by the relations 8≦a≦50, 30 <b≦60, 5≦c≦15, 2≦d≦10 and 40≦a+b+c+d≦90, wherein the crystal structure of a principal phase is a body-centered cubic structure, and further, the alloy contains at least one of Mo and W in place of V and at least one member selected from the group consisting of Y (yttrium), lanthanoids, Pd and Pt, and its crystal structure is converted to the body-centered cubic structure by heat-treatment.

1 . A hydrogen-absorbing alloy comprises a composition expressed by the general formula: 
       Ti (100- a - b - c - d ) Cr a V b Ni c X d , 
       where x is at least one member selected from the group consisting of y (yttrium), lanthanoids, pd and pt, each of a, b, c and d is represented, in terms of atomic %, by the relations 8≦a≦50, 30<b≦60, 5≦c≦15, 2≦d≦10 and 40≦a+b+c+d≦90; and a crystal structure of a principal phase which is a body-centered cubic structure.  
     
     
         2 . A hydrogen-absorbing alloy comprises a composition expressed by the general formula: 
       Ti(100- a - b - c - d )Cr a V b Ni c X d , 
       where X is at least one member selected from the group consisting of Y (yttrium), lanthanoids, Pd and Pt and each of a, b, c and d is represented, in terms of atomic %, by the relations 8≦a≦50, 0<b≦30, 5≦c≦15, 2≦d≦10 and 40≦a+b+c+d≦90; and a crystal structure of a principal phase which is converted to a body-centered cubic structure by heat-treatment.  
     
     
         3 . A hydrogen-absorbing alloy comprises a composition expressed by the general formula: 
       Ti (100- a - b - c - d ) Cr a M b Ni c X d , 
       where M is at least one of Mo and W, X is at least one member selected from the group consisting of Y (yttrium), lanthanoids, Pd and Pt, and each of a, b, c and d is expressed, in terms of atomic %, by the relations 8≦a≦50, 30<b≦60, 5≦c≦15, 2≦d≦10 and 40≦a+b+c+d≦90; and a crystal structure of a principal phase which is converted to a body-centered cubic structure by heat-treatment.  
     
     
         4 . A hydrogen-absorbing alloy having the composition according to any of claims  1  through  3 , wherein the principle phase exists within the range where a body-centered cubic structure appears and a spinodal decomposition occurs, exclusive of a C14 single-phase region, where C14 is a typical structure of a Laves phase and MgZn 2  type crystal structure; and said principal phase has a regular periodical structure and its apparent lattice constant is from 0.2950 nm to 0.3150 nm.  
     
     
         5 . A hydrogen-absorbing alloy according to  claim 2  or  3 , wherein heat-treatment comprises solution treatment conducted for 1 min to 100 hr at a temperature range of from 700 to 1500° C., and one or both treatments selected from quenching and aging of from 350 to 1200° C. after solution treatment.  
     
     
         6 . A cell electrode comprising said hydrogen-absorbing alloy according to any one of claims  1  through  4 .  
     
     
         7 . A cell electrode according to  claim 6 , wherein said cell electrode has excellent cell characteristics in the maximum discharge capacity and the capacity retaining ratio after 100 charge/discharge cycles.  
     
     
         8 . A cell electrode according to  claim 7 , wherein the maximum discharge capacity is 375 to 465 mAh/g and the capacity retaining ratio after 100 charge/discharge cycles is 80 to 95%.