Tailoring Mechanical Properties and Ionic Conductivity of Poly(ionic liquid)-Based Ion Gels by Tuning Anion Compositions

Poly(ionic liquid) (PIL)-based ion gels have emerged as promising materials for advanced electrochemical applications because of their excellent miscibility with ionic liquids (IL), tunable mechanical properties, and high ionic conductivity. Despite extensive studies on PIL-based ion gels, a comprehensive understanding of how different anion combinations in the system affect physicochemical properties is lacking. In this study, we systematically investigate the effect of different anion species, such as bis(trifluoromethanesulfonyl)imide (TFSI) and hexafluorophosphate (PF₆), on the mechanical, viscoelastic, and ion conductive behaviors of PIL-based ion gels. We investigate the interplay between anion size, packing density, and polymer segmental dynamics by varying the anion composition in both the PIL network and IL component. Rheological analysis and uniaxial tensile testing results indicate that PF₆-containing ion gels exhibit enhanced higher Young’s modulus because of their restricted chain mobility resulting in higher glass transition temperature (T_g). In addition, we confirm the anion exchange between PIL and IL during gel preparation and find that the mechanical and ion conductive properties of the gels are governed by the total molar ratio of anions in the gels. Our findings highlight that tuning the anion composition in PIL-based ion gels provides an effective strategy to tailor their performance, with potential applications for flexible electronics and solid-state electrochemical devices.