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

Results of microcalorimetric experiments, in relation to self-discharg e in Ni/H-2 batteries are reviewed; the mechanism of self-discharge, a s well as possible methods for its inhibition, are discussed. These st udies indicate that: (i) the self-discharge is due to a direct reactio n of hydrogen with the charged active material (nickel oxide); (ii) th e presence of metallic nickel sinter particles does not affect the rea ction rate; (iii) the reaction rate depends linearly on hydrogen press ure indicating that the reaction is first order with respect to hydrog en; (iv) the reaction rate is higher under starved-electrolyte rather than flooded electrolyte conditions, indicating that the rate is affec ted by a diffusion process of dissolved hydrogen; and (v) the microcal orimetric heat evolution rate correlates with that of a decrease in el ectrode capacity due to the self-discharge reaction. The effects of ad ditives to the active material of the nickel electrode were tested as an approach to reduction of the intrinsic rate of self-discharge. An a lternate method for minimizing this rate is by storing the hydrogen as a hydride and thereby lowering the cell operating pressure. Some allo ys were thus examined for their hydriding/dehydriding characteristics.