Activation of laves phase-related bcc metal hydride alloys for electrochemical applications

Abstract

Laves phase-related BCC metal hydride alloys historically have limited electrochemical capabilities. Laves phase-related BCC metal hydride alloys are provided herein with greater than 200 mAh/g capacities and commonly at or greater than 400 mAh/g capacities. By decreasing the temperature or increasing the hydrogen pressure the phase structure of the material a synergistic effect between multiple phases in the resulting alloy is achieved thereby greatly improving the electrochemical capacities.

We claim: 
     
         1 . An activated mixed BCC and Laves phase metal hydride alloy comprising the composition of Formula I:
   Ti w V x Cr y M z    (I)
   
       where w+x+y+z=1, 0.1≦w≦0.6, 0.1≦x≦0.6, 0.01≦y≦0.6, and M is selected from the group consisting of B, Al, Si, Sn and transition metals,
 said alloy having a capacity in excess of 400 milliampere hours per gram at cycle 10. 
 
     
     
         2 . The alloy of  claim 1 , wherein the alloy is predominantly a combination of BCC phase and Laves phase, said BCC phase in a phase abundance of greater than 5 weight % and less than 95 weight %, said Laves phase in abundance of greater than 5 weight % and less than 95 weight %. 
     
     
         3 . The alloy of  claim 1  comprising a BCC phase crystallite size of less than 400 angstroms. 
     
     
         4 . The alloy of  claim 1  having a capacity in excess of 420 milliampere hours per gram. 
     
     
         5 . The alloy of  claim 1  comprising Formula II:
   Ti 0.4+x/6 Zr 0.6−x/6 Mn 0.44 Ni 1.0 Al 0.02 Co 0.09 (VCr 0.3 Fe 0.063 ) x    (II)
 
 
       where x is 0.7 to 2.8.