A fluoride-incorporated composite electrolyte enabling high-voltage all-solid-state sulfide-based lithium batteries

Abstract

All-solid-state lithium metal batteries (ASSLMBs) employing sulfide electrolytes exhibit remarkable energy density and inherent safety, and the integration of high-voltage cathode materials further enhances their advantage in performance. Nevertheless, the interfacial degradation between high-voltage cathodes and sulfides during long-term cycling remains a significant challenge. Herein, a biphasic composite electrolyte integrating halide electrolyte Li₃AlF₆ with sulfide electrolyte Li_5.5PS_4.5Cl_1.5 is constructed to combine high ionic conductivity and high-voltage adaptability in ASSLMBs. Specifically, the biphasic electrolyte obtained via ball-milling retains ionic conductivity exceeding 1 mS cm⁻¹. Furthermore, Li₃AlF₆ effectively mitigates surface degradation and irreversible phase transitions in the LiCoO₂ cathode material at high voltages by enhancing interfacial charge transfer kinetics. As a result, ASSLMBs integrating the biphasic electrolyte and uncoated LiCoO₂ cathode deliver an ultra-high specific capacity of 152.5 mA h g⁻¹ at 0.1C (4.2 V vs. Li–In), excellent rate performance of 128.3 mA h g⁻¹ at 1C, and long-term cyclability retaining 86.0 mA h g⁻¹ after 100 cycles. This discovery underscores the significant efficacy of the halide compositing strategy in improving the electrochemical stability of sulfide electrolytes. It also offers valuable insights for the design of ASSLMBs tailored to high-voltage applications.