Study of nickel electrode oxidation as a function of 80% depth of discharge cycling

Oxidation of nickel sinter used in nickel oxide electrodes in aerospace Ni-Cd secondary cells leads to hydrogen gassing and the potential for cell rupture. The oxidation is directly related to loss of overcharge protection built into the cell during manufacturing. In Ni-H ₂ cells, excessive oxidation of the nickel sinter can eventually lead to a burst before leak situation and is a potential source of failure. It is well known that Ni-Cd cells having nylon separators contribute to loss of overcharge via a hydrolysis reaction of the nylon in the potassium hydroxide electrolyte environment in the cell. The hydrolysis reaction produces lower chain organics which are oxidized by the positive electrode and oxygen. Oxidation of the organics diminishes the overcharge protection. With introduction of the Super NiCd^TM and the Magnum^TM Ni-Cd cells, the nylon hydrolysis reaction is eliminated, but any reducing agent in the cell such as nickel or an organic additive can contribute to loss of overcharge protection. The present effort describes chemical analyses made to evaluate the extent of overcharge protection loss in Ni-Cd cells which do not have nylon hydrolysis, and quantifies the amount of hydrogen buildup in Ni-H₂ cells which are subjected to 80% depth of discharge cycling with and without the presence of cadmium in the positive electrode