EFFECT OF ALLOY COMPOSITION ON CHARGE AND DISCHARGE CHARACTERISTICS OF THE NEGATIVE ELECTRODE FOR NICKEL-HYDROGEN BATTERIES

Effect of alloy composition on the charge and discharge performance of the negative electrodes was investigated, using MmxNi3.7Mn0.5Al0.4 (Mm = misch metal, x = 0.885-1.00) and MmNi3.6Mn0.5Al0.4M0.1 (M = Cr, Fe, Co and Cu). The -DELTAH values increased monotonously with increasing stoichiometric ratio of the misch metal, but the unit cell volume passed through a maximum at x = 0.96. Under these conditions, the discharge capacity was confirmed to increase in proportion to the unit cell volume. In addition, both the charge retention and the exchange current density of the hydrogen electrode reactions increased with increasing x value, but the high-rate dischargeability decreased. When a part of the nickel was substituted by foreign metals, both the unit cell volume and the -DELTAH value increased with the increasing ingredient radius of the substituted elements. In this case, the charge retention was increased, but both the high-rate dischargeability and the exchange current density were decreased.