A stretchable and adhesive zwitterionic hydrogel electrolyte and MnO2/polyaniline cathode materials for flexible high-performance zinc-ion batteries†

Flexible zinc-ion batteries (ZIBs) based on hydrogel electrolytes are promising candidates for wearable electronics. However, the inferior intrinsic conductivity of the cathode materials and the poor interfacial adhesion between hydrogel electrolytes and solid electrodes still limit ZIBs’ real application. Herein, a stretchable and adhesive xanthan gum/poly(acrylamide-co-[2-(methacryloyloxy) ethyl] dimethyl-(3-sulfo-propyl) ammonium hydroxide)/(ZnSO₄ + MnSO₄) (XG/P(AM-co-SBMA)) zwitterionic hydrogel electrolyte was prepared by a one-step method. The as-prepared XG/P(AM-co-SBMA) hydrogel electrolyte exhibited favorable mechanical properties (tensile strain of 1560% and strength of 52.06 kPa), high ionic conductivity (46.53 mS cm⁻¹) and strong adhesion with various substrates (maximum adhesive strength of 20.36 kPa). Then, a series of MnO₂/polyaniline (MnO₂/PANI) cathode materials were prepared to explore the coating effect of PANI on the electrochemical performance of the assembled Zn//XG/P(AM-co-SBMA)//MnO₂/PANI flexible ZIBs. Due to the high ionic conductivity of the XG/P(AM-co-SBMA) hydrogel electrolyte and the tight interfacial contact at the electrode/electrolyte interface, the ZIBs could deliver a high specific capacity of 239.5 mA h g⁻¹ at 0.25 A g⁻¹. Furthermore, it can reliably operate for over 500 cycles at 2.0 A g⁻¹ with a capacity retention rate of 84.5% and nearly 100% coulomb efficiency. Moreover, such flexible devices can withstand various deformations such as bending, compressing, and folding without compromising the electrochemical performance.