Assessment of mixed-cation molten salt electrolytes for Li-based liquid metal batteries

Abstract

The implementation of Li-based liquid metal batteries (LMBs) for grid-scale energy storage has been limited by the high cost of materials, especially for fabrication of Li-halide based molten salt electrolytes (e.g., LiCl, LiBr, LiF, LiI). This study aims to determine the impact of incorporating lower cost alkali/alkaline earth halide salts with foreign cations (e.g., Sr2+, K+) into a Li-based molten salt electrolyte to build a foundation for continued LMB electrolyte design and development. The widely reported LiF–LiCl–LiBr (22-31-47 mol%, Tm = 430–443 °C) electrolyte is used within the Li || Sb–Sn LMB system as a baseline from which to compare the performance of similar systems with eutectic salts of LiCl–SrCl2 (64.3–35.7 mol%, Tm = 489 °C) and LiCl–KCl (59.2–40.8 mol%, Tm = 352 °C) with a specific focus on the positive Sb–Sn electrode in a 3-electrode cell. While good chemical reversibility was maintained for the Li || Sb–Sn systems with mixed-cation molten salts, a shift in the electroactive species from Li + to Sr2+ limited the capacity of the LMB system with a LiCl–SrCl2 electrolyte and reduced rate capability was observed for the LiCl–KCl containing system.