Ion-conductive crystals of poly(vinylidene fluoride) enable the fabrication of fast-charging solid-state lithium metal batteries†

The crystalline phases of solid-state polymer electrolytes (SPEs) are commonly believed to be ionic insulators. Herein, we show that contrary to this prevailing view, lithium ions (Li⁺) can be transported in crystalline phases of poly(vinylidene fluoride) (PVDF) after incorporating dipolar defects into crystals. By increasing the interchain distance, these defects enable an easy flipping and vibrating of –CH₂CF₂ dipoles, which triggers a rapid motion of Li⁺ in crystals through ion–dipole interactions. Such an unexpected transformation from ion-insulated crystals to ion-conductive and defective crystals endowed a PVDF-based SPE with an extremely high ionic conductivity of 7.8 × 10⁻⁴ S cm⁻¹ at 25 °C. The developed SPE showed a high stability with both lithium metal anodes and high-voltage cathodes. In particular, solid-state Li//Li symmetrical cells could cycle for more than 11 000 h (>450 days) at room temperature. Moreover, the solid-state full cell can rapidly charge at 5C (12 min) with a capacity retention of around 100% after 400 cycles at 25 °C. This work paves a new way to improve ionic conductivities of SPEs and realize the fast charging of solid-state lithium metal batteries (LMBs) by including dipolar defects to convert ion-insulated crystals into fast ionic conductors.