Towards high energy density zinc-based nonaqueous hybrid supercapacitors via regulating oxygen substituents in carbon cathode

Zinc ion hybrid supercapacitors (ZIHCs) combing the merits of supercapacitors and batteries are promising next-generation energy storage devices. Nevertheless, ZIHCs now still encounter a serious challenge in overcoming the low energy density associated with the cathode materials, activated carbon (AC), due to insufficient active sites for storing the zinc ions. Herein, the AC with rich oxygen-containing functional groups is synthesized through the use of the in-situ electrochemical oxidation method. The developed ZIHCs exhibit excellent electrochemical performance and pseudocapacitance-dominated behavior, with an ultrahigh specific capacitance of 436.41 F g−1 at 0.2 A g−1 and outstanding high-rate performance of 298.44 F g−1 at 5 A g−1, in addition to robust capacitance retention rate of 92.7 % after 20,000 cycles with a high Zn-utilization of 2.5 %. The superior energy storage characteristics of ZIHCs are firmly ascribed to Zn2+ redox reacting with carbonyl and carboxyl groups during the charge and discharge process, demonstrating the promising potential of structure-engineered AC as a cathode material of ZIHCs.