Improved Li/BCX (thionyl chloride) cells for space applications

New NASA requirements for the screening of lithium cells for space applications involve thermal soaks at elevated temperatures (149°C). The BCX DD and C size cells were redesigned to pass this test with only marginal losses in capacity as was done previously for the D cells. In addition, the pressure increases in cells subjected to this high-temperature environment were characterized, showing that the earlier designs failed under this exposure due to a lack of void volume. Severe voltage delay problems for BCX cells subjected to partial discharge and storage were eliminated by increasing the BrCl concentration or substituting LiGaCl₄ for LiAlCl₄ as the electrolyte salt. The increase in BrCl concentration decreased the cell capacity. No capacity loss was observed with the gallate substitution. Heat capacity measurements for AA, C, D, and DD cells show that the C_v values lie in the range of 0.20-0.28 cal/g.