In situ curing enables high performance all-solid-state lithium metal batteries based on ultrathin-layer solid electrolytes

All-solid-state lithium metal batteries (ASSLiMB) are regarded as promising next-generation energy storage systems because of their superior energy density and safety. ASSLiMBs relying on rigid solid-state electrolytes (SSE) are however often challenged by large electrode/SSEs interface resistances that limit energy efficiency and rate capability. We synthesize ultrathin-layer SSEs by in situ UV-curing bisphenol A ethoxylate dimethacrylate composites with the ceramic additive Li_1.5Al_0.5Ge_1.5(PO₄)₃ achieving fast ionic conductivity (1.1 × 10⁻⁴ S·cm⁻¹), wide electrochemical window (up to 5 V) and high thermal decomposition temperature (275 °C). Temperature-dependent lithium-ion diffusion paths are analyzed to design optimal composition and microstructure. When cycling a symmetric Li/SSE/Li cell with a high current density of 2 mA·cm⁻² over 500 h, the overpotential remains stable and no dendrite growth is observed. In situ-curing a thin layer SSE on a lithium iron phosphate (LFP) composite cathode reduces the SSE/cathode interfacial resistance. An LFP/SSE/Li ASSLiMB yields specific discharge capacity of 147.8 mAh·g⁻¹ and retains 131.9 mAh·g⁻¹ after 200 charge/discharge cycles. Direct observation demonstrates that strong binding of the in situ-cured SSE/cathode interface and three-dimensional architecture of the interface diffusion routes cause the high cycling stability. ASSLiMBs with high mass loading of 6.0 mg·cm⁻² were demonstrated to successfully cycle at room temperature.