Molecularly Engineered PVDF-HFP Electrolyte with PVDC Analog for High-Performance Solid-State Lithium Metal Batteries

Solid polymer electrolytes (SPEs) are considered promising candidates for next-generation lithium metal batteries due to their superior flexibility, processability, and electrode compatibility. However, the practical application of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based SPEs is hindered by high crystallinity, strong Li⁺ coordination with fluorine atoms, and unstable solid electrolyte interphase (SEI) formation. Herein, we propose a molecular-level modification strategy by incorporating polyvinylidene chloride (PVDC) as a structural analog into the PVDF-HFP matrix. PVDC exhibits excellent compatibility with PVDF-HFP due to their similar - CX₂-CH₂- chain structures, enabling uniform dispersion without phase separation. The modification mechanism operates through three synergistic effects: (1) steric hindrance from PVDC insertion disrupts ordered chain packing, reducing α-phase crystallinity and promoting β-phase formation; (2) the weak Lewis basicity of -Cl groups competitively coordinates with Li⁺, facilitating lithium salt dissociation; (3) -Cl participates in forming a LiCl-LiF composite SEI with enhanced ionic conductivity and mechanical stability. The optimized PH-PVDC-10% SPE delivers a high ionic conductivity of 7.07 × 10^-4 S cm^-1, a lithium-ion transference number of 0.62, and excellent interfacial stability, enabling Li||Li symmetric cells to cycle stably for over 3000 h. Furthermore, Li||LFP cells exhibit a capacity retention of 97.5% after 300 cycles at 0.5 C, while Li||NCM811 cells achieve 90.3% capacity retention after 100 cycles at 0.2 C. This work provides a simple, scalable, and effective strategy for designing high-performance SPEs toward practical solid-state lithium metal batteries.