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.