A versatile sulfolane-based weakly solvated electrolyte designed for high-safety and high-voltage sodium metal batteries

The design of an oxidation-resistant electrolyte is crucial for achieving a high-voltage sodium metal battery (SMB) system. However, traditional ester-based electrolyte systems demonstrate limitations in oxidative stability and interfacial compatibility with both high-voltage cathode materials and sodium metal anodes. Herein, we propose a novel sulfolane (SL)-based electrolyte that incorporates a film-forming co-solvent fluoroethylene carbonate and low-viscosity dimethyl carbonate as diluent co-solvent. This innovative design not only broadens the electrochemical window of the electrolyte, but also promotes the formation of a unique weakly-solvated structure. Therefore, the electrolyte can induce in-situ formation of high-quality cathode electrolyte interphase and solid electrolyte interphase on electrodes during battery cycling, along with faster Na + transport kinetics. Consequently, the designed electrolyte achieves a high Coulombic efficiency of 97.9% in Na||Cu cells and a substantial lifespan of 1000 h in Na||Na symmetric cells. Furthermore, Na||Na 3 V 2 (PO 4 ) 2 O 2 F cells exhibit a capacity retention of 93.6% after 300 cycles at a high cut-off voltage of 4.5 V. This study provides valuable insights into the future design of SL-based weakly solvated electrolytes for high-voltage SMBs.