Non-Flammable Ester Electrolyte with Boosted Stability Against Li for High-Performance Li Metal Batteries

In traditional non-flammable electrolytes a trade-off always exists between non-flammability and battery performance. Previous research focused on reducing free solvents and forming anion-derived solid-electrolyte interphase. However, the contribution of solvated anions in boosting the stability of electrolyte has been overlooked. Here, we resolve this via introducing anions into Li⁺ solvation sheaths using anions with similar Gutmann donor number (DN) to that of solvents. Taking trimethyl phosphate fire-retardant (DN=23.0 kcal mol^-1 ) and NO₃ ^- (DN=22.2 kcal mol^-1 ) as an example, NO₃ ^- is readily involved in the Li⁺ solvation sheath and reduces the polarity of solvent. This results in boosted stability of electrolyte against Li. The developed non-flammable electrolyte has low viscosity, high ionic conductivity and is low cost. The reversibility of Li-Cu cell was improved to 99.49 % and the lifespan of practical LMBs was extended by >100 %.