Ultratough and reversibly stretchable zwitterionic poly(ionic liquid) copolymer hydrogel with high ionic conductivity for high-performance flexible and cold-resistant supercapacitor

Abstract

It remains challenging to develop hydrogel electrolyte with integrated superior mechanical properties and ionic conductivity for high performance flexible supercapacitors. Herein, copolymer hydrogels are prepared via a one-step polymerization of acrylamide (AM), 3-(1-vinyl-3-imidazolio) propanesulfonate (VIPS) zwitterionic monomer and 3-sulfopropyl methacrylate potassium salt anionic monomer (SPMA). On one hand, the ionic interaction as reversible "sacrificial bonds" provided by VIPS and SPMA through SO3--H3N+ makes these hydrogels tough (fracture energy 3.8 MJ m-3), stretchable (fracture strain 5100%), flexible and self-recoverable (~98% recovery efficiency after 1000% strain deformed). On the other hand, high ionic conductivity (3.1 S m-1) is achieved due to the efficient ion migration channels derived from the zwitterionic copolymer with high hydration capacity. Based on this hydrogel, the as-prepared flexible supercapacitor not only exhibits high discharge capacitance of 108.8 F g-1 at 1 A g-1, and retains ~99% of its capacitance after 1000 cycles, but also achieves encouraging performance at subzero temperature due to the prevention of ice formation by zwitterionic polymer. This hydrogel can be easily functionalized with ionic liquid or other functional materials to extend their practical application.