Novel Additive for Addressing Interfacial Instability in PVDF-HFP/Pyr14FSI Systems for Lithium Metal Batteries at Room Temperature

Self-standing hybrid solid polymer electrolytes (HSPEs) are herein fabricated through a solvent-free process, enabling energy-efficient and industry-compatible production. The HSPEs are based on a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/Pyr14FSI ionic liquid (IL) system incorporating a small amount of divinyl sulfone (DVS) as a functional additive. This design delivers high ionic conductivity together with excellent mechanical integrity and thermal stability. The IL promotes efficient ion conduction and contributes to thermal stability, while incorporating DVS in little amounts (up to 5%) effectively stabilizes the solid–electrolyte interface (SEI) layer and mitigates degradation processes commonly observed in PVDF-HFP/Pyr14FSI-based systems. This study presents the first demonstration of a PVDF-HFP/Pyr14FSI-based electrolyte in which the incorporation of a small amount of DVS enables stable and reversible lithium plating/stripping over 1200 h of continuous cycling at room temperature, with a fixed areal capacity of 0.2 mAh cm−2, in laboratory-scale solid-state lithium metal batteries (SSLMB). Furthermore, laboratory-scale SSLMB cells employing high-energy NMC811 cathodes exhibit excellent electrochemical performance, delivering specific capacities of 120 mAh g−1 at C/20 and 100 mAh g−1 at C/5 under ambient conditions, thereby advancing the development of high-voltage, intrinsically safe, and high-performance next-generation SSLMB technologies.