Percolation-Enabled Long-Range Ion Transport to Achieve Conductivity Leap in PVDF-Based Electrolytes

Abstract

Poly(vinylidene fluoride) (PVDF)-based polymer electrolytes are a focal point in solid-state batteries due to their exceptional ionic conductivity. However, the critical role of residual solvent in ion transport mechanism remains a long-standing debate. Addressing this critical issue, this work, for the first time, elucidates a percolation mechanism for ion transport in PVDF-based electrolytes dependent on residual solvent content. Key to this mechanism, a critical ~7 wt% N, N-dimethylformamide (DMF) content triggers a two-orders-of-magnitude ionic conductivity leap in PVDF-LiTFSI electrolytes from ~10-6 S cm-1 to ~10-4 S cm-1 at 30 °C. Multi-scale molecular dynamics simulations reveal this transition is not due to local Li-ion solvation changes, but rather the establishment of a long-range, continuous transport pathway as the "free-state" Li-ion conductive network reaches its percolation threshold. This work provides crucial insights into the conduction mechanism of PVDF-based electrolytes and contributes a novel conceptual framework with valuable design principles for optimizing macroscopic ion transport in polymer-small molecule composite systems via precise microstructural control. These findings pave the way for the development of high-performance, safer next-generation solid-state batteries.