Anti-perovskite halide Li2(OH)Br1-xClx as a high-performance electrolyte for high-temperature batteries

Anti-perovskites halide salts Li₂(OH)X (X = Halogen) are widely investigated as solid-state electrolytes. Owing to their low melting points and excellent thermal stability, the Li₂(OH)X has been applied in the thermal battery electrolytes. Li₂(OH)Br_1-xCl_x presented low melting points (250–260 °C), outstanding thermal stability (<5 % mass loss at 550 °C), superior ionic conductivity (2.06 S cm⁻¹ at 500 °C for Li₂(OH)Br_0.85Cl_0.15 composite electrolytes), and high decomposition voltages. Cl⁻ doping further optimizes the material's electrochemical properties: the Li-B| Li₂(OH)Br_0.85Cl_0.15|Cu₂O cell provides a high voltage plateau of 1.97 V and a high specific capacity of 356 mAh g⁻¹ at 300 °C; compared to the common low-melting-point electrolyte LiF-LiCl-KBr-CsCl in thermal batteries, it delivers a specific discharge capacity 190 % higher under the same testing conditions (400 °C, 100 mA cm⁻²); compared to Li₂(OH)Br, it delivers a 29.3 % reduction in pulsed internal resistance and a 36.7 % increase in decomposition voltage at 500 °C. This work not only explores the high-temperature electrochemical properties of anti-perovskite halide salts and broadens their application scope but also introduces a novel low-melting-point molten salt into the thermal battery field, holding promise for resolving the long-standing challenge of thermal batteries' inability to achieve high-current discharge at low temperatures.