In‐situ Polymerized Gel Polymer Electrolytes with High Room‐Temperature Ionic Conductivity and Regulated Na+ Solvation Structure for Sodium Metal Batteries

Abstract Sodium metal batteries (SMBs) are promising candidates for low‐cost but high‐energy energy storage applications. Both long‐term stability and safety of SMBs can be largely enhanced when liquid electrolytes (LEs) are replaced by gel polymer electrolytes (GPEs). However, the low room‐temperature (RT) ionic conductivity and inferior interfacial compatibility of GPEs severely restrain their practical use. Herein, a poly(butyl acrylate)‐based GPE with a high RT ionic conductivity of 1.6 mS cm −1 is developed by in‐situ polymerization. Symmetrical cells assembled with this GPE show ultralong cyclability over 900 h at 0.2 mA cm −2 , and ultralow overpotential of 233 mV at 1 mA cm −2 . Full cells based on Na 3 V 2 (PO 4 ) 3 (NVP) cathodes (NVP||GPE||Na) display significantly improved rate capability than that of LEs, benefiting from the solvation structure of Na + in the GPE with much lower desolvation energy. Furthermore, the NVP||GPE||Na pouch cells exhibit a stable capacity of ≈92 mA h g −1 for 50 cycles at 1 C and excellent flexibility. The work not only provides a reliable GPE to develop RT SMBs but also offers new insight into the role of polymer frameworks in the rate performance of SMBs.