Towards high-performance supercapacitors with cellulose-based carbon for zinc-ion storage

Aqueous zinc-ion hybrid supercapacitors (ZHSs) are desirable as promising energy storage devices due to their high energy/power density, stability, and safety. Designing a carbon cathode is the key to improving the performance of ZHSs. A cotton pulp paper is used as the starting material to prepare the porous cellulose-derived carbon (CDC) by a ZnCl2 molten salt activation method. Different zinc salts are then employed as aqueous electrolytes to match the CDC for improving the capacitance performance. The CDC-assembled ZHS using a ZnCl2 electrolyte reaches a high capacitance of 357 F g−1 at the current density of 0.5 A g−1. The excellent capacitance of CDC in ZHSs can be attributed to the abundant mesoporous and macroporous structures. Using the cotton pulp paper and ZnCl2, a ZnCl2-included cellulose hydrogel can also be assembled as a solid-state electrolyte. The solid-state ZHS with CDC shows an extremely high capacity of 247 mAh g−1 and energy density of 243 W h kg−1 at the power density of 492 W kg−1, as well as excellent stability with a capacity retention of 85% after 20,000 cycles.