Ion-Conductive Crystals of Poly (vinylidene fluoride) Enables Fast Charging Solid-State Lithium Metal Batteries

Abstract

The crystalline phases of solid-state polymer electrolytes (SPEs) are commonly believed as ionic insulators. Here we show that contrary to this prevailing view, lithium-ion (Li⁺) can transport in crystalline phases of poly(vinylidene fluoride) (PVDF) after incorporating dipolar defects into crystals. Through 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 transform from ion-insulated crystals to ion-conductive and defective crystals endows PVDF-based SPEs with extremely high ionic conductivity of 7.8 × 10^-4 S cm^-1 at 25 ^oC. The developed SPE shows high stability with both lithium metal anodes and high-voltage cathodes. Especially, the solid-state Li//Li symmetrical cells could cycle for more than 11000 hours (> 450 days) at room temperature. Moreover, the solid-state full cell can charge very fast at 5 C (12 min) with a capacity retention of around 100% after 400 cycles at 25 ^oC. This work paves a new way to improve ionic conductivities of SPEs and realize fast charging of solid-state lithium metal batteries (LMBs) by including dipolar defects to convert ion-insulated crystals into fast ionic conductors.