Controllable synthesis of electric double-layer capacitance and pseudocapacitance coupled porous carbon cathode material for zinc-ion hybrid capacitors

The designability of the porous structure of carbon material makes it a popular material for zinc-ion hybrid capacitors (ZIHCs). However, the micropore confinement effect leads to sluggish kinetics and is not well resolved yet. In this work, a pore-size controllable carbon material was designed to enhance ion accessibility. The experimental and calculated results revealed that suitable pore sizes and defects were beneficial to ion transfer/adsorption. Meanwhile, oxygen-containing functional groups could introduce a pseudocapacitance reaction. Its large specific surface area and interconnecting network structure could shorten the ion/electron transfer length to reach high ion adsorption capacity and fast kinetic behavior. When used as a zinc-ion hybrid capacitor cathode material, it showed 9.9 kW kg^-1 power density and 100 W h kg^-1 energy density. Even at 5 A g^-1, after 50 000 cycles, there was still 93% capacity retention. Systemic ex situ characterization and first-principles calculations indicated that the excellent electrochemical performance is attributed to the electric double layer capacitance (EDLC) - pseudocapacitance coupled mechanism via the introduction of an appropriate amount of oxygen-containing functional groups. This work provides a robust design for pore engineering and mechanistic insights into rapid zinc-ion storage in carbon materials.