Poly(Ethylene Oxide) Solid Electrolytes Supported by Electrospun Poly(Vinylidene Fluoride) Graft Copolymer Fibers

Poly(ethylene oxide) (PEO) is a promising candidate to fabricate solid polymer electrolytes (SPEs). To improve the comprehensive performances of PEO-based SPEs, vinylidene fluoride (VDF) copolymers grafted with poly(ethylene glycol) were electrospun and applied as a support for the PEO matrix. The grafting of PEG onto the VDF copolymer was achieved by the nucleophilic substitution of a chlorine atom in the VDF copolymer by methoxy-polyethylene-glycol thiol. The ionic conductivity of the VDF copolymer was increased with the grafting site density of PEG at the same bis(trifluoromethane sulfonimide) (LiTFSi) concentration. SPEs were fabricated by solution casting of PEO/LiTFSi onto electrospun VDF graft copolymer fibers. Electric field poling induces a beneficial α -to- β phase transition in the VDF copolymer, and the compatibility between the VDF copolymer and PEO was improved due to the incorporated PEG side chains, which facilitate lithium ion (Li + ) transport through additional conduction pathways and enhance lithium-ion solvation. The supported PEO SPEs exhibited good mechanical strength and toughness, and the optimized SPE with an EO/Li ratio of 6:1 exhibits excellent electrochemical performance at 60°C, including an ionic conductivity of 1.79 × 10 −4 S cm −1 , a Li + transference number of 0.49, and a wide ESW of 5.46 V (vs. Li + /Li).