Anomeric-Effect-Guided Saturated Weakly Solvating Electrolytes for Ultrastable High-Voltage Sodium Metal Batteries

Sodium metal batteries are promising for next-generation energy storage, leveraging low-cost sodium and highly reversible sodium metal anodes enabled by ether-based electrolytes. However, the low oxidative stability of ether solvents severely limits the energy density of sodium metal batteries. Current strategies are focused on strengthening solvent interactions to improve stability or film-forming electrolyte additives. Here, we propose an approach of designing saturated weakly solvating electrolytes (SWSEs) based on non‑fluorinated ethers and reveal that the overall oxidative stability is commonly governed by the weak solvents and anions. The SWSE saturates at 1 M, far below the concentrations required in locally high‑concentration electrolytes. Moreover, we identify ether solvents exhibiting the anomeric effect possess the notably enhanced oxidative stability through systematic molecular screening. Consequently, the SWSE based on the weak solvent of 1,3-dioxane enables 1000 stable cycles of the sodium metal cell with the high cutoff voltage of 4.5 V. A practical sodium metal pouch cell consisting of a Na_0.67Ni_0.33Mn_0.67O₂ cathode with the mass loading of 13.4 mg cm^-2 and a thin-foil sodium metal anode achieves stable cycling at 4.3 V. This work introduces a new strategy for developing high-voltage sodium metal batteries and is expected to inspire advances in other high-voltage metal batteries.