Spatial Confinement Effect and Defect‐Dominated Redox Reactions Enhance Energy and Power in Zn‐Ion Capacitors With 150 000 Cycles

Abstract Zinc‐ion capacitors (ZICs) with porous carbon cathodes face low space utilization and restricted ion conduction. A facile hydrothermal coupling dual‐salt activation strategy is innovatively introduced to create oxygen‐doped carbon cathode with abundant 1 nm confined pores. DFT simulations and experimental results for the first time confirm 1 nm pores best match [Zn(H 2 O) 6 ] 2+ , maximizing the spatial confinement effect of restricted pores (0.86–1.72 nm) to enable ordered, efficient ion transport and storage. Beyond this range, pores larger than1.72 nm hinder ion storage via adverse overscreening, and pores smaller than 0.86 nm impede ion desolvation by requiring extra energy. Furthermore, abundant oxygen functional groups and structural defects promote reversible Zn 2+ redox reactions during charge/discharge cycles. The synergistic effect of spatial pore confinement and defect‐dominated redox reactions endows ZICs with 135.5 Wh kg −1 energy density, 24.00 kW kg −1 power density, and unprecedented 108.2% capacity retention over 150 000 cycles. In situ characterizations clarify ion adsorption/desorption and precipitation mechanisms. This work provides a simple, easy‐to‐operate reference for designing high‐performance carbon cathode materials for ZICs.