N‐Doped Holey Graphene/Porous Carbon/Cellulose Nanofibers Electrode and Hydrogel Electrolyte for Low‐temperature Zinc‐ion Hybrid Supercapacitors

The susceptibility to freezing of the electrolyte and mismatched cathode make the aqueous zinc-ion hybrid supercapacitors (ZHSCs) have inferior electrochemical performance at low temperature. Herein, a novel freeze-tolerant hydrogel electrolyte (CEEZ) and matched graphene/porous carbon/cellulose nanofibers cathode (GPCN) are respectively fabricated via chemical cross-linking and a two-step process to assemble ZHSCs. The prepared electrode has a highly porous structure, abundant edge active sites, and increased interlayer spacing, which collectively reduces ion transport complexity and enhances the contact area with the electrolyte, promoting rapid ionic conduction pathways. For the CEEZ, the use of ethylene glycol reduces the saturated vapor pressure of water, thereby enhancing the frost resistance of the hydrogel electrolyte. Consequently, the ZHSCs assembled from GPCN, CEEZ, and Zn anode exhibit excellent specific capacitances of 1.11 F cm⁻² (21.35 F cm⁻³) at 20 °C and 0.74 F cm⁻² (14.23 F cm⁻³) at -20 °C. These results demonstrate the promising application potential of these ZHSCs in cold environments while maintaining impressive energy storage capabilities. This work provides valuable insights and a robust strategy for the design of high-performance low-temperature ZHSCs, enhancing their practical applicability in renewable energy storage systems.