Ultrafast UV Curing Enabling A Stable Interphase and Interface for Solid-State Sodium–Metal Batteries

Designing advanced solid-state sodium batteries (SSBs) demands simultaneously overcoming the low ionic conductivity of solid-state electrolytes (SSEs) and the poor interfacial compatibility between electrodes and SSEs. Herein, a composite solid-state electrolyte (CSE) with high ionic conductivity was prepared by using an efficient UV polymerization in 45 s. A stable interphase and interface were achieved simultaneously through solvent structure tuning and in situ curing. By introduction of fluoroethylene carbonate (FEC) to form a competitive solvation structure in CSE-F, the low lowest unoccupied molecular orbital (LUMO) allowed preferential reduction of FEC in the solvation shell. A dense and uniform NaF-rich interphase was constructed to inhibit the growth of the dendrites. Simultaneously, the integrated cathode and electrolyte constructed a tight-contact interface, enabling uniform and efficient ion transport. The Na||CSE-F@Na 3 V 2 (PO 4 ) 3 (NVP) cell showed a capacity retention of 91.78% after 2100 cycles. This work provides a solution to simultaneously achieve a rational interphase and an electrode/electrolyte interface design for SSBs.