Experimental and computational analysis of the structure-activity relationship of ionic gel electrolytes based on bistrifluoromethanesulfonimide salts for supercapacitors

Ionic gel electrolytes (IGEs) are emerging as promising components for the development of next-generation supercapacitors, offering benefits in terms of safety, cost-effectiveness, and flexibility. The ionic conductivity, stability and mechanical properties of the gel electrolyte are important factors to be considered and are key to improving the performance of the supercapacitor. However, the structure-activity relationship between the internal structure of ionic gels and supercapacitor properties is not fully understood. Herein, the intuitive and regular structure-activity relationship between the structure and properties of ionic gels was revealed by combining computational simulation and experiment. In terms of conductivity, the ionic liquid ([EMIM][TFSI]) in the ionic gel has a high self-diffusion coefficient calculated by molecular dynamics simulation (MDS), which is conducive to transfer and then improves the conductivity. The radial distribution function (RDF) of the MDS shows that the larger the g(r) between the particles in the polymer network, the stronger the interaction. For stability, ionic gels based on [EMIM][TFSI] and [EOMIM][TFSI] ionic liquids have higher density functional theory (DFT) calculated binding energy, which is reflected in the excellent thermal stability and excellent capacitor cycle stability. Based on the internal pore size distribution and stress-strain characterization of the gel network ([ME3MePy][TFSI] and [BMIM][TFSI] as additive), the highly crosslinked aggregates network significantly reduces the internal mesoporous distribution and plays a leading role in improving the mechanical properties of the network. By using this strategy, it will be possible to design the ideal structure of the ionic gel and to achieve an excellent performance.