In-situ constructing efficient gel polymer electrolyte with fluoride-rich interface enabling high-capacity, long-cycling sodium metal batteries

Sodium metal batteries (SMBs) are considered feasible candidate for large-scale energy systems. However, complicated reactions between the electrode and electrolyte in liquid electrolyte system lead to poor performance and significant safety issues. Therefore, constructing stable electrode-electrolyte interface is necessary to enhance the comprehensive performance of cells. Utilizing gel polymer electrolytes (GPEs) by in-situ polymerization and moderate additive can effectively address these problems. Herein, a series of fluoroethylene carbonate (FEC) modified GPEs have been successfully prepared by one-step in-situ polymerization, in which trimethylolpropane trimethyl acrylate (TMPTMA) and 1,6-hexanediol diacrylate (HDDA) were used as polymer monomers. As a result, the as-optimized electrolyte, THDP-FEC-2%, exhibited high ionic conductivity (3.77 x 10-3 S cm- 1) at 25 degrees C, high Na+ migration number (0.41), and broad electrochemical window (4.6 V). Encouragingly, the NVP|THDP-FEC-2%|Na cell even exhibited ultra-long cycling stability at high rate (95.31% capacity retention at 5C after 1000 cycles). Such excellent electrochemical performances are attributed to the successful establishment of uniform and dense NaF-rich solid electrolyte interface protection layer. This work is expected to offer interface soft protection layer tuned strategy to construct the ideal interface for highperformance SMBs.