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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 %. [ABSTRACT FROM AUTHOR]

Rechargeable room‐temperature sodium–sulfur (RT Na–S) batteries are a promising energy storage technology, owing to the merits of high energy density and low cost. However, their electrochemical performance has been severely hindered by the poor compatibility between the existing electrolytes and the electrodes. Here, we demonstrate that an all‐fluorinated electrolyte, containing 2,2,2‐trifluoro‐N,N‐dimethylacetamide (FDMA) solvent, 1,1,2,2‐tetrafluoroethyl methyl ether (MTFE) anti‐solvent and fluoroethylene carbonate (FEC) additive, can greatly enhance the reversibility and cyclability of RT Na–S batteries. A NaF‐ and Na3N‐rich cathode electrolyte interphase derived from FDMA and FEC enables a "quasi‐solid‐phase" Na–S conversion, eliminating the shuttle of polysulfides. The MTFE not only reduces polysulfide dissolution, but also further stabilizes the Na anode via a tailored solvation structure. The as‐developed RT Na–S batteries deliver a high capacity, long lifespan, and enhanced safety. [ABSTRACT FROM AUTHOR]