Biopolymer-based carboxylated chitosan hydrogel film crosslinked by HCl as gel polymer electrolyte for all-solid-sate supercapacitors

Gel polymer electrolyte for flexible energy storage devices such as supercapacitors and rechargeable batteries attracts widespread attentions. Herein, we fabricate a flexible, transparent, and eco-friendly gel polymer electrolyte film based on biodegradable polymer of the carboxylated chitosan via phase separation of carboxylated chitosan hydrogel in hydrochloric acid . HCl is the key chemical for crosslinking of film forming, and the process is simple, rapid and non-polluting. The obtained carboxylated chitosan hydrogel film with excellent flexibility exhibits a highest electrolyte uptake rate of 742.0  wt %, and a highest ionic conductivity of 8.69 × 10 −2  S cm −1 . A symmetric all-solid-state supercapacitors using carbon cloth as current collectors, activated carbon film as electrodes, and carboxylated chitosan hydrogel film as a gel polymer electrolyte shows a high specific capacitance of 45.9 F g −1 at 0.5 A g −1 , and the maximum energy density of 5.2 Wh kg −1 at a power density of 226.6 W kg −1 . To our knowledge, this is the first time that carboxylated chitosan hydrogel film being used as gel polymer electrolyte for supercapacitors electrolyte. The good results indicate that the carboxylated chitosan as a new gel polymer electrolyte material has great potential in practical applications of all-solid-state, flexible, and portable energy storage devices.