PVDF-Based Salt-Concentrated Polymer Electrolyte with High Intrinsic Lithium Salt Dissociation Capability and Ionic Conductivity

Owing to the poor ability of polymers to dissociate lithium salts and transport ions, solid-state polymer electrolytes typically exhibit low room-temperature ionic conductivity. In this work, we first synthesize poly(poly(ethylene glycol) methacrylate) (PPEGMA)-grafted polyvinylidene fluoride (PVDF) (PVDF-g-PPEGMA) via iron-mediated atom transfer radical polymerization (ATRP) using PVDF as the macroinitiator. Then, we prepare solid-state salt-concentrated (bistrifluoromethanesulfonimide lithium salt and lithium difluorodioxaphosphate) polymer electrolytes based on the PPEGMA-grafted PVDF (VPMX%-Li80%) incorporating multiple ion transport pathways to enhance the ionic conductivity at room temperature. The effects of the grafting rate on the electrolyte properties were investigated. The optimized VPM28%-Li80% achieves a high ionic conductivity of 4.79 × 10–4 S cm–1 at 30 °C and surpasses the 10–3 S cm–1 threshold at 70 °C. Moreover, owing to the low LUMO energy level of the multifunctional additive, heptafluorobutyric anhydride (HFA), which preferentially forms a LiF-rich solid electrolyte interphase (SEI) at the Li metal/electrolyte interface, the symmetric Li//Li cell demonstrates an ultralong cycling lifespan (2000 h at 0.1 mA cm–2). This work provides critical insights for high-performance solid-state polymer electrolytes.