Zwitterionic triple-network hydrogel electrolyte for advanced flexible zinc ion batteries

Aqueous zinc ion battery (ZIB) is auspicious for wearable energy storage devices due to its low cost and high safety. For ZIBs to meet the flexibility and mechanical properties desirable for wearable electronics, it is imperative to develop a lithely high-performance electrolyte material with good tensile and compressible strength to withstand the electrochemical reactions. In this work, we rationally fabricated a novel zwitterionic triple-network structure hydrogel electrolyte of polyacrylamide (PAM)/gelatin/[2-methylacryloxy) ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide (DMAPS) for flexible textile-based ZIBs. Apart from the excellent flexibility and mechanical stability, the zwitterionic triple-network hydrogel electrolyte also ensured high ionic conductivity and enhanced Zn2+ transference number. As expected, the symmetric cell with such electrolyte acquired a cycle stability of over 400 h. Additionally, the corresponding flexible ZIBs delivered a stable capacity of 175 mAh·g−1 for 100 cycles at 500 mA g−1 with excellent Coulombic efficiency of over 99%. The fabricated battery can even light a 2 V bulb under heavy weight pressure of 500 g or in any bending state. Therefore, this work provides a simple yet industrially scalable approach to the commercial fabrication of flexible ZIBs.