An adhesive cellulose nanocrystal-reinforced nanocomposite hydrogel electrolyte for supercapacitor applications

Hydrogel electrolytes were applied in various energy storage devices, including supercapacitors. However, they still suffer from disadvantages such as low mechanical performance and poor adhesion of the interfaces between electrolytes and electrodes. Herein, an adhesive hydrogel electrolyte with promising mechanical strength and electrochemical performance was designed by introducing hydrophobic carbon chains as long-range physical cross-linkers and cellulose nanocrystal (CNC) as biopolymer nano-reinforcement, and soak-loading liquid electrolytes such as KOH into the hydrogel matrix. The hydrogel electrolyte loaded with 1 M KOH demonstrated the best tensile stress of 362.31 kPa and an elongation of 2479 %, and exhibited self-repairability by applying stimuli on the cut interface. The hydrogel electrolyte showed excellent adhesion on various surfaces, including nonconductive and conductive materials such as cardboard, leather, carbon film, and carbon cloth. Regarding electrochemical properties, the hydrogel electrolyte showed the largest conductivity of 0.207 +/- 0.005 S/cm when soak-loading in 1 M KOH for 24 h. Moreover, the hydrogel electrolyte exhibited promising electrochemical performance when assembled into coin-cell supercapacitors using free-standing activated carbon sheets as electrodes. A capacitance of 67.31 F/g at 0.05 A/g, and almost 100 % capacitance retention at 0.1 A/g after 2200 cycles was achieved.