Synergistic Effects of Fluorinated Li-Based Metal-Organic Framework Filler on Matrix Polarity and Anion Immobilization in Quasi-Solid State Electrolyte for Lithium-Metal Batteries.

Abstract

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) based electrolyte is a promising alternative to liquid electrolytes in lithium metal batteries. However, its commercial application is limited by high crystallinity and low Li⁺ ion conductivity. In this study, we synthesized a fluorinated Li-based metal-organic framework (Li-MOF-F) and used it as a filler to address these limitations. The strategy for the Li-MOF-F filler stands out in two main aspects: framework structure for rapid Li⁺ ion transport and F-functional group with electronegativity. The LiO₄ with π-π conjugated dicarboxylate enables the reversible Li intercalation in the lattice structure. The fluorine atoms with electronegativity transform the polymer matrix from non-polar to polar phase and immobilize TFSI^- anions by electrostatic interaction. As a result, the PVDF-HFP electrolyte with Li-MOF-F (LMF-PE) achieves the highest polarity and Li transference number. In Li/Li symmetric cell tests, LMF-PE demonstrates stable Li plating/stripping behavior without dendrites. Additionally, we applied lithium nickel manganese cobalt oxide (NCM) with 94 % Ni content as a cathode material in cell test. LMF-PE cell delivers a high initial discharge capacity of 226.9 mAh g^-1 and 80 % capacity retention after 150 cycles, highlighting its superior cycling performance. These enhancements are attributed to the structural and electrostatic benefits of Li-MOF-F.