Deep Eutectic Solvent‐Based Gel Electrolyte with Fast Na Ions Transport in Sodium‐Metal Batteries

Deep eutectic electrolyte (DEE) with intrinsic nonflammability is deemed as a promising electrolyte candidate for high safety sodium‐metal batteries (SMBs). Nevertheless, the leakage risk and inferior electrode compatibility impede their further application toward high‐performance SMBs. Herein, a novel DEE based on sodium bis(fluorosulfonyl)imide (NaFSi) and ethyl‐2‐cyano‐3‐ethoxyacrylate (ECE) is developed through their Lewis acid–base interaction and the further ECE‐based deep eutectic gel electrolyte (GE) is constructed with cross‐linked ploy(vinylene carbonate) (PVC) as matrix network. It is demonstrated that incorporating electron‐withdrawing PVC polymer into the ECE‐based DEE changes the coordination environment of Na + ions, thus facilitating the Na‐ions desolvation and transport and leading to a high transference number of Na‐ions (0.7). Moreover, the strong interaction between PVC chains and Na‐ions can induce the preferential reduction of PVC to form O‐rich inorganic solid electrolyte interphase (SEI), thus promoting the electrode/electrolyte interfacial stability with superior long‐term cycling stability. Benefiting from the stable SEI layer, the Na 3 V 2 (PO 4 ) 3 //Na cell with GE displays outstanding cycling (capacity retention of 94.5% after 300 cycles at 1C) and rate (high capacity of 75.5 mAh g −1 at 2 °C) performance than that of ECE‐based DEE cell, showcasing the promising application of advanced deep eutectic GE in high performance SMBs.