Low-temperature, high cycling stability, and high Coulombic efficiency liquid metal batteries enabled by lithium halide-potassium halide molten salt electrolytes

Abstract

Liquid metal batteries (LMBs) employ liquid metal as electrodes and inorganic molten salt as electrolytes, which circumvent the capacity degradation mechanism inherent in conventional batteries and are regarded as a promising alternative for grid-level energy storage. LMBs need to operate at high temperatures (typically 500∼550 °C), and it is of paramount importance to reduce the operating temperature. This work abandons the conventional lithium halide mixture electrolytes, and innovatively adopts lithium halide-potassium halide electrolytes, which are previously deemed unstable during the operation of LMBs. First, the Li|LiCl-KCl|Bi batteries are constructed, achieving stable operation at 410 °C with a remarkable capacity retention of 93.6% after 1100 cycles. Furthermore, the Li|LiCl-LiBr-KBr|Bi batteries are designed, demonstrating stable operation at 350 °C without capacity degradation after 660 cycles. The low working temperature significantly improves the Coulombic efficiency (up to 99.96%, the highest value among all reported LMBs to date) and facilitates the battery module to achieve "self-heating". Additionally, the mechanism of the displacement reaction between Li and K+ and the migration kinetics of Li atoms in LiBi/Li3Bi intermetallic compounds are analyzed. This work establishes liquid metal batteries with the advantages of low working temperature, high cycle stability, high Coulombic efficiency, low cost, and large capacity, which effectively promotes the development and practical application of LMBs.