Lignin-based macromolecular composite solid electrolyte enabling high-performance sodium metal batteries via...

Solid polymer electrolytes (SPEs) for sodium metal batteries often suffer from low room-temperature ionic conductivity and unstable electrode/electrolyte interfaces. As a renewable biological macromolecule, alkali lignin possesses a rigid aromatic framework and abundant oxygen-containing functional groups, making it a promising functional component for constructing sustainable solid electrolytes. Herein, we develop a lignin/PVDF hybrid polymer matrix using alkali lignin as a functional polymer component, PVDF as a film-forming co-matrix, and low-cost MgF₂ as an inorganic filler to enhance ion transport and interfacial stability. The optimized electrolyte, denoted as LPM4 and containing 4 wt% MgF₂, exhibits a room-temperature ionic conductivity of 2.23 × 10^-4 S cm^-1 and a wide electrochemical stability window of 4.87 V. Moreover, the corresponding Na₃V₂(PO₄)₃//Na full cell retains 88.14% of its initial capacity after 100 cycles. The results suggest that MgF₂ promotes NaFSI dissociation through Lewis-acidic interactions with anions and contributes to the formation of a more fluorine-rich interphase, thereby enhancing interfacial stability against sodium metal. This work demonstrates an effective route for valorizing industrial lignin waste into biomass-based solid electrolytes and provides a promising materials strategy for high-performance sodium metal batteries.