Investigation of Self-Discharge Characteristics of Spacecraft Nickel-Cadmium Cells at Elevated Temperatures

Little is known concerning the self-discharge and heat generation in nickel-cadmium (NiCd) cells when they are subjected to temperatures far in excess of ambient. The work reported here provides such data for initially fully charged cells heated externally to temperatures from 44 to 118C. The cells (35 Ah nominal capacity) were placed into precalibrated insulating liners wired for cell heating; then, the insulated cells were heated in a chamber to the preset initial test temperature. The heat subsequently generated by the open-circuited, charged cells was determined from the cell temperatures and heat loss rates to the test apparatus. The temperature rises recorded for the cells were in the range of 0 C over a 16 hr period at an initial test temperature of 64 C, 1 C over 10 hr at the 82 C setpoint, and 81 C over 13 hr at the 85 C setpoint. At 118 C setpoint, the recorded cell temperature exceeded 220 C, and the cell ruptured at 0.7 hr after attaining the setpoint temperature. Keywords: Elevated temperatures, Self discharge, Nickel cadmium batteries.