Crosslinked Zwitterionic PVA-g-SBMA/PEDOT:PSS Networks for Mechanically Robust All-Solid-State Electrolytes

Conventional lithium-ion batteries face issues like electrolyte leakage and interface instability. Solid-state lithium batteries with solid electrolytes address these, while solid-state polymer electrolytes (SPEs) offer safety and flexibility. This study primarily aimed to develop and synthesize a graft copolymer, PVA-g-SBMA, which was successfully synthesized by grafting [2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) onto poly(vinyl alcohol) (PVA). PVA provided excellent film-forming ability and mechanical strength, enhancing flexibility and stability in solid-state devices. Meanwhile, SBMA's zwitterionic structure promoted efficient ion transport, improving ionic conductivity and solid electrolyte performance in energy storage applications. From the results, the proton assignment of the PVA-g-PSBMA zwitterionic graft copolymers was investigated via ¹H NMR spectra. The molecular weight of the graft copolymer was determined through aqueous GPC; the number average molecular weight (Mn) was 15,755, and the PDI was 1.17. The grafting efficiency of SBMA was calculated as 25%. However, the material lacked sufficient mechanical properties, leading to brittle membranes. To address this issue, we crosslinked the film to improve its mechanical properties. The grafted copolymer was crosslinked with the PEDOT:PSS as a crosslinkable sulfonated component using (3-glycidyloxypropyl)trimethoxysilane (GOPS) as the crosslinker and dimethyl sulfoxide (DMSO) as solvent to complete the crosslinking reaction. The crosslinking mechanism involved the reaction between hydroxyl groups on PVA and PSS, while the GOPS bonded with PSS, forming a robust crosslinked network. The crosslinking process was completed by heating the mixture to 120 °C. We also compared different crosslinking ratios to discuss the film performance. Lithium salts were incorporated to investigate the effect of varying lithium salt concentrations. According to EIS measurements, the best-performing system was crosslinked PVA-g-SBMA with PEDOT:PSS 0.1 wt% and LiTFSI 0.015 wt%, which reached conductivities of 4.9 × 10^-4 S/cm at room temperature. We also explored the film's thermal properties, morphologies, and chain interactions in this research.