Interfacial Growth of 420 nm Ultrathin and Dense MOFs for Composite Electrolyte to Reduce Li ⁺ Conduction Resistance and Inhibit Lithium Dendrite

Metal organic frameworks (MOFs) have attracted increasing attention in composite solid electrolytes (CSEs), attributed to the tunable pore structures and good thermal and electrochemical stability. However, MOFs‐based CSEs still exist, with a trade‐off between ionic conductivity and lithium dendrite inhibition ability. Herein, 420 nm ultrathin ZIF‐67 layer on polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐HFP) membrane is precisely regulated through the interfacial growth method. The organic ligand 2‐methylimidazole permeates through the straight‐through pore of PVDF‐HFP to react with Co 2+ , which controls the reaction rate to form ultrathin and dense ZIF‐67. The CSE with ultrathin and dense ZIF‐67 layer not only reduces Li + transport resistance but also promotes lithium salts disassociation, contributing to an ionic conductivity of 2.70 mS cm– 1 at 30°C and Li + transference number of 0.71. Meanwhile, the ultrathin ZIF‐67 induces fast Li + transport kinetics, uniform Li + flux, and homogeneous Li deposition, synergizing with high mechanical strength to inhibit lithium dendrite growth. As a result, the NCM811||Li coin battery shows improved cycling performance with a capacity retention of 70% after 446 cycles at 0.5 C and is capable of working at −20°C. This work proposes an innovative design of ultrathin MOFs‐based CSEs with high ion conductivity and low interfacial conduction resistance.