Effect of copper additive on Zr_0.9Ti_0.1V_0.2Mn_0.6Cr_0.05Co_0.05Ni_1.2 alloy anode for nickel-metal hydride batteries

Abstract

Zr_1-x Ti_x V_0.2Mn_0.6Cr_0.05Co_0.05Ni_1.2 (0≤ x≤ 0.3) alloys have been characterized as metal-hydride electrodes for nickel-metal hydride batteries. Although the alloy electrodes with no Ti substitution in place of Zr exhibit a specific capacity value of 375 mA h g^-1, it has been possible to enhance the specific capacity of the electrodes to 395 mA h g^-1 by substituting 10% Ti in place of Zr, that is, with Zr_0.9Ti_0.1V_0.2Mn_0.6Cr_0.05Co_0.05Ni_1.2 alloy. The specific capacity value of Zr_0.9Ti_0.1V_0.2Mn_0.6Cr_0.05Co_0.05Ni_1.2 alloy was further enhanced to 415 mA h g^-1 on copper powder addition. Interestingly, the discharge curves for the latter electrode are quite flat thus providing an advantage of constant specific energy output over the entire regime of electrode discharge. Both a.c. impedance and d.c. linear polarization studies conducted on these electrodes lead to a lower charge-transfer resistance value for the metal-hydride electrode with copper additive suggesting the electrode with copper powder additive to have a higher catalytic activity than those without copper. The electrode with the copper additive also exhibits little change in its capacity over about 100 charge-discharge cycles.