Oxygen Evolution Barrier and Lithium-Ion Transport Promotion Effects of MOF-LATP Composite Solid Electrolyte for High-Energy-Density Lithium Batteries

High-energy-density lithium-ion batteries are prone to cathode oxygen evolution, which triggers detrimental crosstalk reactions and potential thermal runaway. In this study, a trilayer functional composite separator is rationally designed by screening metal–organic framework (MOF) and depositing optimized UiO-66-F combined with the inorganic solid electrolyte (LATP) on the cathode-facing side of a polypropylene (PP) substrate, with a PVDF-HFP layer coated on the opposite side. The as-prepared separator exhibits a low oxygen transmission rate of 106.2 s/(in2·100 mL·0.1 kPa) and an oxygen adsorption capacity of 0.99 cc·g–1 (293 K, 1 Torr). Electrochemical characterization reveals a high room-temperature ionic conductivity of 1.30 × 10–3 S·cm–1, a lithium-ion transference number of 0.72, and a wide electrochemical window of 5.4 V. When applied in NCM811||C pouch cells, the composite separator significantly suppresses gas evolution during overcharge (1C, 3 h) and maintains 90.8% capacity retention after 100 cycles at 1C. Furthermore, NCM811||Li cells achieve 79.4% retention after 500 cycles at 1C. Interfacial analysis confirms that the MOF layer effectively captures cathode-released oxygen, while synergistically cooperating with the PVDF-HFP layer to construct a stable, LiF-rich solid electrolyte interphase (SEI), thereby significantly boosting the electrochemical performance and safety of high-voltage lithium-ion batteries.