Reducing Ion Transport Friction by Mitigated Diluent-Solvent Interaction for Sodium-Sulfur Battery

Sodium sulfur batteries have emerged as a promising candidate for large-scale energy storage, while their practical implementation is severely hindered by sodium dendrite growth, unstable solid-electrolyte interphase (SEI) films, and the polysulfide shuttle effect. Herein, we design a novel local high-concentration electrolyte (LHCE-DEE/TTEE) to balance the ionic conductivity and interfacial stability. This is achieved by replacing the high solvating DME with the moderate solvating diethyl ether (DEE) to mitigate the diluent-solvent interaction and reduce the local dynamic friction for Na⁺ transport. Additionally, the replacement of DME with DEE weakens the ion-dipole interaction to form stable anion-enriched solvation clusters. Furthermore, the long ethyl chains in DEE provide sufficient steric hindrance to confine sulfur species within the cathode and suppress the polysulfide shuttle effect. Benefiting from these synergistic advantages, the Na||Na symmetric cell in LHCE-DEE/TTEE sustains stable cycling for 2500 h. When coupled with a sulfurized polyacrylonitrile cathode, the designed electrolyte demonstrates robust stability at practical conditions of high sulfur loadings of 8.7 mg cm^-2 and lean electrolyte of 4.6 µL mg^-1 and this is further validated in pouch cell configurations. This work offers new understanding towards LHCE electrolyte design strategy to balance the ionic conductivity and interfacial stability.