Technical Report 32-1570 Gravitational Effects on Electrochemical Batteries

The existing work on gravitational effects on electrochemical batteries is summarized, certain conclusions are drawn, and recommendations are made for future activities in this field. Theoretical evaluations of the problem have met with only limited success; theories based upon a treatment of natural convection have fallen short of the mark, pardy because die mass transfer involved in die power-producing electrochemical reactions in a battery is not completely due to convection and partly because a battery is far removed from the idealized models necessarily employed in the development of die dieory. The latter point is best illustrated by die fact that although dieory generally predicts that die limiting current density will vary widi the 1/4 power of die acceleration constant, the experimental data falls in die range of a 1/3 to 1/5 power dependence because of differences in die way die cell is constructed. The effects of sustained high-G environments on cycled silver-zinc and nickel-cadmium cells have been evaluated over four complete cycles in die region of 10 to 75 G. Although no effects on high current discharge performances or on ampere-hour capacity were noted, severe zinc migration and sloughing of active material from the zinc electrode were observed. This latter effect constitutes real damage, and over a long period of time would result in loss of capacity. The work of Arcand, based upon smooth zinc electrodes, predicted a limiting current density of 7 mA/cm. However, the Mariner 7 battery easily provided a current density of 10.5 mA/cm in deep space. Fundamental battery studies performed at zero G are necessary to resolve die conflict. To diis end, experiments have been planned and a breadboard model of an in-flight battery test unit has been designed and fabricated. It is recommended that a zero-G battery experiment be implemented. Both an orbiting satellite and a sounding rocket approach are being considered. JPL TECHNICAL REPORT 32-1 570 Gravitational Effects on Electrochemical Batteries