Layer-Structured Composite Solid-State Electrolyte with a Li_1.3Al_0.3Ti_1.7(PO₄)₃-Coated Separator for High-Voltage Lithium Metal Batteries by In Situ Polymerization

The poor interfacial contact between solid-state electrolytes (SSEs) and electrodes, which hinders the applications of solid-state batteries (SSBs), could be improved by in situ polymerization. However, the limited electrochemical window and insufficient mechanical strength of in situ-polymerized electrolytes make them unable to match high-voltage cathodes and inhibit lithium dendrites. Here, a layered organic–inorganic composite solid-state electrolyte structure is designed by introducing a Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP)-coated polyethylene separator and fluoroethylene carbonate (FEC) into in situ-polymerized 1,3-dioxolane (DOL). The high-voltage stable fluoride-rich cathode–electrolyte interface formed in situ by FEC widens the electrochemical window of the composite solid-state electrolyte. In addition, the LATP coating layer inhibits the growth of lithium dendrites and increases the Li-ion conductivity by reacting with FEC to generate FEC derivatives. The Li/LiCoO 2 battery exhibits good cycling and rate performance with a cutoff voltage of 4.3 V at room temperature. It provides a simple and practical solution to improve the performance of high-voltage lithium metal batteries based on in situ polymerization.