MICROCALORIMETRY STUDY OF NI/H2 BATTERY SELF-DISCHARGE MECHANISM

Microcalorimetry is one of the most sensitive techniques in determining self-discharge rates of battery cells. Our previous study indicated that the self-discharge reaction in a Ni/H2 cell occurs via a direct reduction of charged active material by hydrogen. The results of the present study which is an effort to further elucidate the self-discharge mechanism show that (i) there is a good correlation between the amount of heat evolved during the self-discharge reaction as measured by microcalorimetry and amount of self-discharge as determined by capacity measurements, indicating that the microcalorimetry is a useful technique for investigation of the self-discharge reaction of a Ni/H2 cell; (ii) the self-discharge rate decreased pronouncedly as the amount of electrolyte around the electrode (degree of wetness) decreased indicating that diffusion of dissolved H2 in the electrolyte significantly affects the rate of the self-discharge reaction; (iii) the self-discharge rate is higher with the beta-phase active material than with the beta-phase active material. Preliminary results also showed that a cadmium additive to the nickel electrode reduces the self-discharge rate.