KINETIC ASPECTS OF SELF-DISCHARGE OF NICKEL-HYDROGEN BATTERIES AND METHODS FOR ITS PREVENTION

Results of microcalorimetric experiments, in relation to self-discharge in Ni/H-2 batteries are reviewed; the mechanism of self-discharge, as well as possible methods for its inhibition, are discussed. These studies indicate that: (i) the self-discharge is due to a direct reaction of hydrogen with the charged active material (nickel oxide); (ii) the presence of metallic nickel sinter particles does not affect the reaction rate; (iii) the reaction rate depends linearly on hydrogen pressure indicating that the reaction is first order with respect to hydrogen; (iv) the reaction rate is higher under starved-electrolyte rather than flooded electrolyte conditions, indicating that the rate is affected by a diffusion process of dissolved hydrogen; and (v) the microcalorimetric heat evolution rate correlates with that of a decrease in electrode capacity due to the self-discharge reaction. The effects of additives to the active material of the nickel electrode were tested as an approach to reduction of the intrinsic rate of self-discharge. An alternate method for minimizing this rate is by storing the hydrogen as a hydride and thereby lowering the cell operating pressure. Some alloys were thus examined for their hydriding/dehydriding characteristics.