Solid polymer electrolytes containing poly(ethylene glycol) and renewable cardanol moieties for all-solid-state rechargeable lithium batteries

A series of self-crosslinkable polymers composed of different amounts of ionic conducting units (poly(ethylene glycol) methyl ether methacrylate) and crosslinkable units (2-hydroxy-3-cardanylpropyl methacrylate) obtained from a renewable resource, cardanol, were prepared for application to solid polymer electrolytes. Free-standing solid polymer electrolytes were prepared by mixing the polymers with lithium bis(trifluoromethanesulfonyl)imide followed by UV irradiation to induce reaction of the double bonds in the cardanol moiety, forming the cross-linked structures. The ionic conductivity of the solid crosslinked polymer electrolyte prepared from the polymers containing 8 mol% of the cross-linkable cardanol monomeric units was 1.9 × 10⁻⁴ S cm⁻¹ at 60 °C, which is close to those of poly(poly(ethylene glycol) methyl ether methacrylate) in the waxy state. The all-solid-state lithium battery prepared using this solid polymer electrolyte without a separator exhibited stable cell operation, showing 81.4% of capacity retention after 100 charge-discharge cycles, and demonstrating that the self-crosslinkable polymer from the renewable resource is suitable for high-temperature and high-voltage lithium secondary battery applications.