Customized composition of lithium metal solid-electrolyte interphase by electric field modulation of anion motion direction

In high-voltage lithium-metal battery systems, electrolyte characteristics are crucial for achieving the optimal balance between non-flammability and battery performance. Herein, an electrolyte system based on triethyl phosphate solvent with lithium oxide difluoroborate, lithium tetrafluoroborate and lithium nitrate as solutes is proposed. TEP, as the sole solvent, ensures the inherent non-flammability of the electrolyte, while the solutes LiODFB, LiBF4 and LiNO3, benefit from the different binding energies of the three anions and lithium ions, to optimize the structure of the solvation shell and direction of anion movement, thereby forming a favorable interfacial phase. Consequently, solid electrolyte interphase enriched with B-O and Li3N in the inner layer and LiF in the outer layer is formed, which improves the stability and reversibility of the lithium metal negative electrode. The Li | |NCM811 cell with the as-prepared electrolyte can be stably cycled for 600 cycles at a high cut-off voltage of 4.5 V with a capacity retention of 90.19%. Even at 60 °C for 600 cycles, the capacity retention rate remains at 81.18%. This work demonstrates an effective strategy for the design of high-voltage non-flammable LMBs. High-voltage lithium-metal batteries face safety and stability challenges. Here, authors develop a non-flammable triethyl phosphate-based electrolyte using a triple-salt solute strategy to induce a bilayer solid electrolyte interphase, enabling long-term cycling of 4.5 V Li metal batteries.