Cationic substitution in γ-type nickel (oxi)hydroxides as a means to prevent self-discharge in Ni/Zn primary batteries

The self-discharge of γ-NiOOH in Ni/Zn primary batteries was studied on real cells and also on chemically simulated ones. The results indicate that it is rooted in a dissolution/re-crystallization process, probably involving an α-type nickel hydroxide intermediate. To minimize this phenomenon, the preparation of a series of diverse metal substituted γ-type nickel hydroxides was attempted by oxidation of α-type precursors containing various amounts of Al, Cd, Co, Cr, Fe or Zn, prepared by direct precipitation at room temperature in an ammonia containing reaction medium. These reactions led to metal substituted γ-type nickel oxihydroxides in all cases except for cadmium and chromium containing samples. For the former phase segregation took place whereas for the latter a complete dissolution of chromium species in the reaction medium was observed. Partial dissolution was found to take place also for aluminium substituted phases. High temperature storage tests conducted on Ni/Zn primary cells using the substituted γ-phases as the positive electrode indicate that iron and cobalt substitution is effective in preventing self-discharge phenomena observed in pure γ-NiOOH, as aged cells presented discharged capacities very similar to fresh cells.