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 the 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 that is dependent on residual solvent content. Central to this mechanism, a critical ∼7 wt% N,N-dimethylformamide (DMF) content triggers a two-order-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 that this transition is not due to local Li-ion solvation changes but rather due to 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, offering 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.