Effect of alloying with Ti, V, Mn on the electrochemical properties of Zr-Cr-Ni based Laves phase metal hydride electrodes

The main phase in Zr(CrxNi1-x)(2) Laves phase alloys (0.20 less than or equal to x less than or equal to 0.60) changes from C15 to C14 at x = 0.45-0.50. Electrodes with Cr content in the range 0.30 less than or equal to x less than or equal to 0.50 have favorable electrochemical capacities. The substitution effect of Cr or Ni by V or Mn in the form of Zr(Cr(x)M(y)Ni(2-x-y)) (M = V or Mn, x + y = 0.7-1.2) on the electrochemical discharge capacity was also studied. The alloys with x + y = 0.7-1.0/AB(2) formula have larger hydrogen storage and electrochemical discharge capacities. When Ti is used to partly substitute Zr in Ti(y)Zr(1-y)M(2) (y = 0.0-0.3) alloys, the plateau pressure of the hydride tends to increase with increasing y, however, its electrochemical capacity decreases as well due to lower reversible hydrogen storage density. The electrochemical cycling deterioration increases with increasing Ti content. Electrodes with no Ti or very low Ti content preserve 86% of their discharge capacities after 820 cycles under 65% depth of discharge, exhibiting excellent electrochemical stability.