Mechanically Robust, Highly Ionic Conductive Gels Based on Random Copolymers for Bending Durable Electrochemical Devices

Mechanically robust, highly ionic conductive gels based on a random copolymer of poly[styrene-ran-1-(4-vinylbenzyl)-3-methylimidazolium hexafluorophosphate] (P[S-r-VBMI][PF₆]) and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) are successfully prepared. The gels with either homo P[VBMI][PF₆] or conventional PS-block-poly(methyl methacrylate)-block-PS (SMS) show significant trade-off between ionic conductivity and mechanical resilience. In contrast, the P[S-r-VBMI][PF₆]-based gels exhibit both large elastic modulus (≈0.105 MPa) and ionic conductivity (≈1.15 mS cm⁻¹) at room temperature. To demonstrate that these materials can be used as solid-state electrolytes, the ion gels are functionalized by incorporating electrochromic (EC) chromophores (ethyl viologen, EV²⁺) and are applied to EC devices (ECDs). The devices show low-voltage operation, large optical transmittance variation, and good cyclic coloration/bleaching stability. In addition, flexible ECDs are fabricated to take advantage of the mechanical properties of the gels. The ECDs have excellent bending durability under both compressive and tensile strains. The versatile P[S-r-VBMI][PF₆]-based gel is anticipated to be of advantage in flexible electrochemical applications, such as batteries and electrochemical displays.