Ultrathin Polymer Electrolyte With Fast Ion Transport and Stable Interface for Practical Solid‐state Lithium Metal Batteries

Ultrathin solid-polymer-electrolytes (SPEs) are the most promising alternative substituting for the conventional liquid electrolyte to enable high-energy-density, safe lithium-metal-batteries (LMBs). Nevertheless, developing ultrathin SPEs with both high ionic conductivity, and strong Li dendrite retardant is still a significant challenge. Here a scalable fabrication of high-performance ultrathin (≈7.8 µm) polycarbonate-based electrolyte (UPCE) is proposed via electrolyte structural engineering, phase separation-derived poly(vinylidene fluoride-co-hexafluoropropylene) (PVH) porous scaffold, without use of additional liquid additives. The rational electrolyte structural modulation with 1-fluoro-4-(1-methylethenyl)benzene (FMB) enables a weakened Li⁺-polymer interaction due to weak Li⁺ solvation with fluorine, benzene ring, facilitates the formation of LiF-rich solid-electrolyte-interphase on Li metal surface. As a result, the designed UPCE delivers a high ionic conductivity of 4.8 × 10^-4 S cm^-1, an ultrahigh critical current density of 11.5 mA cm^-2 at 25 °C. The solid-state Li symmetric cell attains unprecedented ultralong cycling over 6000 h at 0.5 mA cm^-2. Furthermore, the Li|LiCoO₂ cell cycles stably over 1500 cycles at a high operating voltage of 4.5 V, and the pouch cell can achieve a high energy density of 495 Wh kg^-1 excluding the packaging. This work offers a new pathway inspiring efforts to commercialize ultrathin SPEs for high-energy solid-state LMBs.