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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]

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]

Rechargeable alkali metal (i.e., lithium, sodium, potassium)‐based batteries are considered as vital energy storage technologies in modern society. However, the traditional liquid electrolytes applied in alkali metal‐based batteries mainly consist of thermally unstable salts and highly flammable organic solvents, which trigger numerous accidents related to fire, explosion, and leakage of toxic chemicals. Therefore, exploring non‐flammable electrolytes is of paramount importance for achieving safe batteries. Although replacing traditional liquid electrolytes with all‐solid‐state electrolytes is the ultimate way to solve the above safety issues, developing non‐flammable liquid electrolytes can more directly fulfill the current needs considering the low ionic conductivities and inferior interfacial properties of existing all‐solid‐state electrolytes. Moreover, the electrolyte leakage concern can be further resolved by gelling non‐flammable liquid electrolytes to obtain quasi‐solid electrolytes. Herein, a comprehensive review of the latest progress in emerging non‐flammable liquid electrolytes, including non‐flammable organic liquid electrolytes, aqueous electrolytes, and deep eutectic solvent‐based electrolytes is provided, and systematically introduce their flame‐retardant mechanisms and electrochemical behaviors in alkali metal‐based batteries. Then, the gelation techniques for preparing quasi‐solid electrolytes are also summarized. Finally, the remaining challenges and future perspectives are presented. It is anticipated that this review will promote a safety improvement of alkali metal‐based batteries. [ABSTRACT FROM AUTHOR]

Abstract: Due to high energy density, low cost, and nontoxicity, lithium–sulfur (Li–S) batteries are considered as the most promising candidate to satisfy the requirement from the accelerated development of electric vehicles. However, Li–S batteries are subjected to lithium polysulfides (LiPSs) shuttling due to their high dissolution in liquid electrolyte, resulting in low columbic efficiency and poor cycling performance. Moreover, the Li metal as an indispensable anode of Li–S batteries shows serious safety issues derived from the lithium dendrite formation. The replacement of liquid electrolytes with solid‐state electrolytes (SSEs) has been recognized as a fundamental approach to effectively address above problems. In this review, the progress on applying various classes of SSEs including gel, solid‐state polymer, ceramic, and composite electrolytes to solve the issues of Li–S batteries is summarized. The specific capacity of Li–S batteries is effectively improved due to the suppression of LiPSs shuttling by SSEs, while the rate and cycling performance remain relatively poor owing to the limited ionic conductivity and high interfacial resistance. Designing smart electrode/electrolyte integrated architectures, enabling the high ionic transportation pathway and compatible electrode/electrolyte interface, may be an effective way to achieve high performance solid‐state Li–S batteries. [ABSTRACT FROM AUTHOR]