Preparation of chitosan and citric acid crosslinked membrane and its application in quasi-solid supercapacitors

Quasi-solid electrolytes promote the development of safe and flexible energy storage devices. In this work, a chitosan and citric acid crosslinked membrane is prepared by a freeze–thaw cross-linking method, in which the chemical crosslinking of chitosan and citric acid increase the viscoelastic behavior of the polymer membrane, and the freeze–thaw assist freeze drying process to create abundant interconnected open-pores and three-dimensional (3D) network. Due to the good viscoelasticity, excellent electrolyte loading capacity (596%) and high ion conductivity (7.7 × 10–3 S·cm−1), as quasi-solid electrolyte, our proposed chitosan and citric acid crosslinked membrane helps Zn|CCFT-ZnSO4|AC hybrid supercapacitor to delivers wide operating voltage, high specific capacity of 100.5 F·g−1 and stable cycle life (93% after 1000 cycles), which suggests that our proposed freeze–thaw assisted freeze drying method has great potential in designing quasi-solid state electrolyte for energy storage device.Graphical abstract