Diluent-driven solvation sheath compression in nonflammable carbonate-carboxylic hybrid electrolytes achieving stable F, B-rich solid electrolyte interface for high-performance lithium metal batteries

Despite the high energy density, lithium metal batteries (LMBs) face significant cycling instability and safety challenges, especially at subzero temperatures. Herein, we report a rationally designed low-concentrated electrolyte system that employs a low-freezing-point diluent to compress solvation sheaths, enabling the formation of a compact anion-dominated solvation structure that enhances interfacial stability and safety. Molecular dynamics reveal the unique solvation structure with close packing of anions in this low-concentration electrolyte from the micro-mesoscopic scale. The optimized electrolyte combines cost-effectiveness, superior wettability, intrinsic nonflammability, and high stability, concurrently promoting a hybrid organic–inorganic solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) for uniform lithium deposition. As a result, the Li||LiFePO4 (LFP) full cells demonstrate stable cycling for 700 cycles at the current density of 4 C. Remarkably, the electrolyte demonstrates exceptional low-temperature performance, indicating broad operational viability. This work provides a promising electrolyte design strategy that addresses both safety and excellent electrochemical performance in high-energy–density metal-based batteries, including but not restricted to Li, Na, K and Zn multivalent ion systems.