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

Abstract 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.