Ion-Conducting Polymers Based on Photocurable Acrylic Networks: The Role of Sulfur-Based Moieties

In this work, the synthesis and in-depth characterization of three sets of ultraviolet (UV)-curable diacrylate poly(ethylene glycol) (PEG) monomers containing sulfide/thioether, sulfoxide–sulfone, and methyl sulfonium groups are reported. Three series of solid polymer electrolytes are obtained by photopolymerization of each diacrylate monomer incorporating lithium bis(fluorosulfonyl) imide (LiFSI). The effect of the polymeric nature on the ionic conductivity was investigated. All polymer electrolytes exhibit an electrochemical stability of up to 4 V vs Li+/Li. This is extended to 4.3 V vs Li+/Li in polymer-containing methyl sulfonium groups, which possess the highest ionic conductivity (2·10–4 S cm–1 at 70 °C) and lowest plating–stripping overpotentials (≈0.1 V vs Li+/Li). However, polymer electrolytes containing thioether groups show not only high ionic conductivity but also oxidation in sulfoxide/sulfone between 4 and 4.5 V vs Li+/Li. The polymer electrolyte containing sulfoxide–sulfone moieties highlights the lowest ionic conductivity and poorest Li interfacial stability. This work provides useful insights into sulfur-containing solid polymer electrolytes for high-performance lithium batteries and energy storage devices.