Bicontinuous solid polymer electrolytes using Li+ enriched ionic liquids

Abstract

This study examines the dynamics of bicontinuous solid polymer electrolytes (SPEs) composed of solvate ionic liquids (SIL; lithium solvated in tri- or tetra-glyme with the TFSI/TFSA/NTf2 anion) and epoxy resin, for applications in carbon fiber (CF) structural supercapacitors. The influence of LiTFSI concentration on properties such as ionic conductivity and mechanical strength is investigated. SPEs containing SILs derived from G4 (tetraglyme) exhibited up to 2 times higher ionic conductivity than those containing G3 (triglyme), a trade-off with mechanical strength is observed, posing a challenge in optimising SPEs for structural supercapacitor composites. Flexural testing reveals reduced mechanical properties compared to the resin control (E = 35 MPa vs. control E = 1638 MPa), attributed to faster curing times and reduced resin content of SPEs. Thermo-gravimetric analysis highlights the thermal stability (Td > 210 °C) of these electrolytes. Electrochemical assessments of prototype carbon fiber capacitor devices, 23 % higher capacitance of G4 than G3 (5.5 mF/g vs. 4.5 mF/g), underscore the potential of these SPEs for structural energy storage applications. This comprehensive investigation provides key insights into the relationship between composition and performance in bicontinuous SPEs, contributing to the optimisation of structural supercapacitors.