Polarity-Mediated β-Phase Reconstruction and Dual-Salt Synergy for Fast Li⁺ Transport in Solid-State Li Metal...

Solid polymer electrolytes (SPEs) based on poly(vinylidene fluoride) (PVDF) hold great promise for safe Li metal batteries but are hindered by low ionic conductivity and insufficient salt dissociation. Here, we propose a molecular polarity-mediated synergistic strategy that integrates tetracyanoethylene (TCNE)-induced β-phase reconstruction with dual-salt chemistry to simultaneously optimize ion transport kinetics and interfacial stability. In this strategy, the strongly electron-withdrawing cyano groups of TCNE engage in dipole interactions with PVDF chains, triggering a nonpolar α-to-polar β-phase transition, which facilitates salt dissociation and shortens the Li⁺ migration pathway; the dual-salt system further ensures fast Li⁺ conduction while constructing a robust, LiF/boron-rich interphase via LiDFOB. The resulting TCNE-modified PVDF electrolyte (PTDL) delivers a high ionic conductivity of 9.32 × 10^{- 4} S cm^{- 1}, a high Li⁺ transference number of 0.76, and a wide electrochemical window of 4.8 V. Thus, the symmetric cells can maintain a low overpotential over 1000 h at 0.2 mA cm^{- 2}, and full cells with LiFePO₄ cathode can run stably for 1000 cycles at 10 C. This work provides a new path for designing high-performance PVDF-based SPEs.