Electrochemical properties of the non-stoichiometric hydrogen storage alloys for nickel-hydrogen batteries

Behavior of the negative electrodes consisted of alleys with the composition of Mm(Ni3.6Mn0.4Al0.3Co0.7)(x) (Mm = misch metal, 0.88 less than or equal to x less than or equal to 1.12) was investigated to elucidate the effect of stoichiometric ratio on the electrode properties. The maximum discharge capacity at around x = 0.96, which was measured at a current density of 200 mA g(-1), was found to be correlated with the unit-cell volume of the alloys. The discharge efficiency increased with increasing x value and reached about 85.2% even at a high current density of 2000 mA g(-1), for the alloy with x = 1.12. The improvement in high-rate dischargeability was explained on the basis of high diffusibility of hydrogen in bulk of alloys as the result of the relatively low stability of the hydride and the high electrocatalytic activity for the hydrogen electrode reactions of the negative electrode.