Thermal Batteries have been used extensively as the primary power source for defense applications, with operating temperatures that typically operate above 400 °C. The battery uses a solid electrolyte that is inactive at ambient temperature and can be stored with little to no power loss for long periods (>25 years)[1]. Recent efforts have been done in the implementation of high porosity ceramic felt separators for electrolyte immobilization in thermal batteries [2], which resulted in a higher specific energy density of the thermal cells with ceramic felt compared to the traditional MgO separators, due to the increased ionic conductivity of the separator layer.

In this research, a low melting point eutectic electrolyte (CsBr-LiBr-KBr) was immobilized in ceramic felt separators and tested for the LiSi/FeS₂ system. Reducing the melting point of the electrolyte has several advantages such as reducing the activation time and the amount of pyrotechnic material needed to activate the battery, and it also opens the opportunity to lower temperature applications (275-400 °C) such as geothermal instrumentation[3]. Findings of this work will be presented at the meeting.

[1] R. A. Guidotti and P. Masset, “Thermally activated (‘thermal’) battery technology. Part I: An overview,” J. Power Sources, vol. 161, no. 2, pp. 1443–1449, 2006, doi: 10.1016/j.jpowsour.2006.06.013.

[2] A. Yazdani, M. Sanghadasa, and G. G. Botte, “Integration of ceramic felt as separator / electrolyte in lithium salt thermal batteries and the prospect of rechargeability,” J. Power Sources, vol. 521, no. January, p. 230967, 2022, doi: 10.1016/j.jpowsour.2021.230967.

[3] R. A. Guidotti and F. W. Reinhardt, “Guidotti, R. A., & Reinhardt, F. W. Characterization of the LiSi/CsBr-LiBr-KBr/FeS (2) System for Potential Use as a Geothermal Borehole Power Source (1999). Characterization of the LiSi/CsBr-LiBr-KBr/FeS (2) System for Potential Use as a Geothermal Borehole Power Source,” . Sandia National Lab No. SAND99-1702C. United States, 1999.