Dual Interface Compatibility Enabled via Composite Solid Electrolyte with High Transference Number for Long‐Life All‐Solid‐State Lithium Metal Batteries

Abstract The development of solid‐state electrolytes (SSEs) effectively solves the safety problem derived from dendrite growth and volume change of lithium during cycling. In the meantime, the SSEs possess non‐flammability compared to conventional organic liquid electrolytes. Replacing liquid electrolytes with SSEs to assemble all‐solid‐state lithium metal batteries (ASSLMBs) has garnered significant attention as a promising energy storage/conversion technology for the future. Herein, a composite solid electrolyte containing two inorganic components (Li 6.25 Al 0.25 La 3 Zr 2 O 12 , Al 2 O 3 ) and an organic polyvinylidene difluoride matrix is designed rationally. X‐ray photoelectron spectroscopy and density functional theory calculation results demonstrate the synergistic effect among the components, which results in enhanced ionic conductivity, high lithium‐ion transference number, extended electrochemical window, and outstanding dual interface compatibility. As a result, Li||Li symmetric battery maintains a stable cycle for over 2500 h. Moreover, all‐solid‐state lithium metal battery assembled with LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode delivers a high discharge capacity of 168 mAh g −1 after 360 cycles at 0.1 C at 25 °C, and all‐solid‐state lithium–sulfur battery also exhibits a high initial discharge capacity of 912 mAh g −1 at 0.1 C. This work demonstrates a long‐life flexible composite solid electrolyte with excellent interface compatibility, providing an innovative way for the rational construction of next‐generation high‐energy‐density ASSLMBs.