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The capacity and coefficient of utilization of the positive active material of nickel-hydrogen cells show a significant increase when the cells are charged at −20°C or subjected to extended overcharge at 50°C. An interesting aspect of cells in which the positive plates show very high utilization is the appearance of a second wave in the overcharge region. The second wave seems to indicate the formation of a higher-valent nickel. The additional capacity obtained at very low temperature is less stable than that of 10°C when cycled. Destructive physical analysis of these cells reveals increased positive plate swelling. Rapid reaction of oxygen with hydrogen, otherwise known as popping, is more likely to occur in cells that contain positive plates which have endured significant swelling, since swelling occludes the gas channels.

High cell impedance, which is associated with an electrolyte water loss mechanism, has developed in INTELSAT V Ni-H2 battery cells, resulting in voltage degradation. This phenomenon was first observed in the discharge behavior of specific cells of the INTELSAT V life test battery, which is INTELSAT supported and under test at COMSAT Laboratories. The mechanism responsible for the voltage degradation was identified by removing both anomalous and normal cells from the battery and fitting valve assemblies to their fill tubes. The cells were then returned to life testing. The valves were opened at intervals to release any accumulated fluid. Only the anomalous cells produced an accumulation of fluid, and, on analysis, the fluid proved to be essentially water. Subsequently, in-orbit performance mimicked that of the life-test, and a technique based on enhanced vapor diffusion of the displaced water returning into the stack electrolyte was developed.