Designing Anion-Derived Solid Electrolyte Interphase in a Siloxane-Based Electrolyte for Lithium-Metal Batteries

The rational electrolyte design with weak solvation is regarded as an effective way to regulate the electrolyte/electrode interface (SEI) that profoundly affects the performance of Li-metal batteries. Herein, we propose a newly developed siloxane-based weakly solvating electrolyte (SiBE) with contact ion pairs (CIPs) or aggregates (AGGs) dominating the solution structure, which enables the dendrite-free Li deposition and long cycle stability of Li-metal batteries. By altering the combination of Li salts, the SiBE leads to the formation of an inorganic anion-derived solid electrolyte interphase, which is highly stable and Li⁺-conductive. Based on SiBE, the Li||LiFePO₄ (LFP) full cell can stably cycle for 1000 cycles at a 2C rate with a capacity retention of 76.9%. Even with a limited Li-metal anode, it can maintain a capacity retention of 80% after 110 cycles with a high average Coulombic efficiency of 99.8%. This work reveals that siloxane can be a promising solvent to obtain weakly solvating electrolytes, which opens a new avenue for SEI composition regulation of Li-metal batteries.