A Novel Metal-Organic-Framework-Based Composite Solid Electrolyte for Lithium Metal Batteries

Solid-state lithium metal batteries are hindered from practical applications by insufficient room-temperature ionic conductivity and poor electrode/electrolyte interfaces. Herein, we designed and synthesized a high ionic conductivity metal-organic-framework-based composite solid electrolyte (MCSE) with the synergy of high DN value ligands from Uio66-NH₂ and succinonitrile (SN). XPS and FTIR reveal that the amino group (-NH₂) of Uio66-NH₂ and the cyano group (-C≡N) of SN have a stronger solvated coordination with Li⁺, which can promote the dissociation of crystalline LiTFSI, achieving an ionic conductivity of 9.23 × 10^-5 S cm^-1 at RT. Afterward, a flexible polymer electrolyte membrane (FPEM) with admirable ionic conductivity (1.56 × 10^-4 S cm^-1 at RT) and excellent electrode/electrolyte interfaces (86.2 Ω for the Li|20% FPEM|Li cell and 303.1 Ω for the LiFePO₄|20% FPEM|Li cell) was successfully obtained after compounding the MCSE with polyethylene oxide (PEO). Moreover, a stable solid electrolyte layer (SEI) was formed in situ on the surface of the lithium metal, which enables the Li|20% FPEM|Li cell to exhibit remarkable cycling stability (1000 h at a current density of 0.05 mA cm^-2). At the same time, the assembled LiFePO₄|20% FPEM|Li cell offers a discharge-specific capacity of 155 mAh g^-1 at 0.1 C and a columbic efficiency of 99.5% after 200 cycles. This flexible polymer electrolyte provides a possibility for operating long lifespan solid-state electrochemical energy storage systems at RT.