Reversibly highly stretchable and self-healable zwitterion-containing polyelectrolyte hydrogel with high ionic conductivity for high-performance flexible and cold-resistant supercapacitor

It remains challenging to develop stretchable and self-healable polymer electrolytes with improved ion-conductive nature for high-performance multifunctional flexible supercapacitors. Herein, a P(AM-SBMA-AMPS)-SiO₂ zwitterion-containing polyelectrolyte hydrogel is fabricated via copolymerization of acrylamide (AM), sulfobetaine methacrylate (SBMA) zwitterionic monomer, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) anionic monomer grafted from the surface of vinyl silica nanoparticles (VSNPs). The hydrogen bonding among polymer chains and the high-density dynamic ionic interactions between SBMA and AMPS work as reversible “sacrificial bonds” to toughen hydrogel, while the VSNPs function as multifunctional crosslinkers and stress transfer centers, which makes these hydrogels tough (fracture energy 2.7 MJ m⁻³), stretchable (fracture strain 4,016%), and self-healable (fracture strain of healable sample 775%). More importantly, this zwitterion-containing polyelectrolyte hydrogel exhibits high ionic conductivities (3.4 S m⁻¹) owing to the highly hydration capacity of the zwitterionic polyelectrolyte copolymer which produced efficient ion migration channels for ion transport. Accordingly, a flexible supercapacitor based on this multifunctional hydrogel as electrolyte demonstrates a high electric double-layer capacitive capacitance of 60.6 F g⁻¹ at 0.5 A g⁻¹ and excellent capacitance retention of ~98% over 1,000 cycles as well as encouraging electrochemical properties at subzero temperature. This work provides new insights into the synthesis of highly conductive and multifunctional polyelectrolyte hydrogels for high-performance flexible supercapacitors. © 2020 Wiley Periodicals, Inc.