Towards High‐Performance Aqueous Sodium‐Ion Batteries: Stabilizing the Solid/Liquid Interface for NASICON‐Type Na₂VTi(PO₄)₃ using Concentrated Electrolytes

Aqueous Na‐ion batteries may offer a solution to the cost and safety issues of high‐energy batteries. However, substantial challenges remain in the development of electrode materials and electrolytes enabling high performance and long cycle life. Herein, we report the characterization of a symmetric Na‐ion battery with a NASICON‐type Na 2 VTi(PO 4 ) 3 electrode material in conventional aqueous and “water‐in‐salt” electrolytes. Extremely stable cycling performance for 1000 cycles at a high rate (20 C) is found with the highly concentrated aqueous electrolytes owing to the formation of a resistive but protective interphase between the electrode and electrolyte. These results provide important insight for the development of aqueous Na‐ion batteries with stable long‐term cycling performance for large‐scale energy storage.