Silver Cadmium Battery Program [1963]

SUMMARY:

The Silver-Cadmium Battery Program (March 1963) documents the second phase of an Air Force–sponsored research effort to develop long-life, sealed silver-cadmium batteries for military aerospace applications.

The primary objective was to fabricate and evaluate sixty 7-ampere-hour sealed cells capable of deep cycling, rapid recharge, and reliable operation across extreme temperatures from −20°F to +120°F. The design target included thousands of charge-discharge cycles, stable voltage performance, and maintenance-free sealed operation.

A major focus of the study was separator development. Numerous separator combinations were tested to balance electrolyte retention, resistance to silver migration, electrical resistance, and mechanical durability. The selected configuration consisted of layered Dynel, Polypor WA (coarse nylon base), fibrous sausage casing, and V (non-woven nylon), arranged to enclose the silver electrode. This combination provided improved cycle life while minimizing short circuits caused by silver deposition. Cells using this system achieved up to 3,000 cycles at 78°F under moderate depth-of-discharge conditions.

The report also introduces an improved highly porous silver oxide electrode. Silver was impregnated into a sintered matrix and thermally decomposed at low temperature, producing fine silver distribution and high active material utilization. Approximately 50% of the cell’s energy was available at the higher Ag₂O voltage plateau, with the remainder delivered at the lower AgO plateau. Utilization efficiencies were significantly higher than commercial comparison electrodes.

Extensive testing was performed on pressure behavior, separator resistance, electrolyte volume calculations, and environmental durability. Pressure-decay modeling allowed prediction of oxygen recombination and internal cell behavior. Environmental tests included vibration, acceleration, and shock resistance, demonstrating suitability for aerospace service.

Charging methodology proved critical. Pure constant-current charging at high rates led to excessive pressure and incomplete silver oxide conversion. Pure constant-potential charging reduced pressure but introduced imbalance risks in multi-cell batteries. The most effective approach combined constant current to restore bulk capacity followed by constant potential finishing charge, optimizing recharge efficiency while limiting internal pressure buildup.

Performance varied at temperature extremes. At −20°F, charging inefficiencies and elevated pressures occurred. At +120°F, thermal management became critical to prevent separator degradation and overheating. Despite these challenges, most cells completed hundreds or thousands of cycles, and the 78°F tests achieved the program’s 3,000-cycle benchmark.

Overall, the program demonstrated that properly engineered separator systems, improved silver electrodes, and optimized charging protocols could produce durable, sealed silver-cadmium batteries suitable for demanding aerospace applications.