Electrolyte Solvation Engineering Stabilizing Anode‐Free Sodium Metal Battery With 4.0 V‐Class Layered Oxide Cathode

Abstract Anode‐free sodium metal batteries (AFSMBs) are regarded as the “ceiling” for current sodium‐based batteries. However, their practical application is hindered by the unstable electrolyte and interfacial chemistry at the high‐voltage cathode and anode‐free side, especially under extreme temperature conditions. Here, an advanced electrolyte design strategy based on electrolyte solvation engineering is presented, which shapes a weakly solvating anion‐stabilized (WSAS) electrolyte by balancing the interaction between the Na + ‐solvent and Na + ‐anion. The special interaction constructs rich contact ion pairs (CIPs) /aggregates (AGGs) clusters at the electrode/electrolyte interface during the dynamic solvation process which facilitates the formation of a uniform and stable interfacial layer, enabling highly stable cycling of 4.0 V‐class layered oxide cathode from −40 °C to 60 °C and excellent reversibility of Na plating/stripping with an ultrahigh average CE of 99.89%. Ultimately, industrial multi‐layer anode‐free pouch cells using the WSAS electrolyte achieve 80% capacity remaining after 50 cycles and even deliver 74.3% capacity at −30 °C. This work takes a pivotal step for the further development of high‐energy‐density Na batteries.