Asymmetric Zn-N₄ Single Atom Sites Facilitate Interfacial Desolvation for Ultrafast Zinc-Ion Storage

Aqueous zinc-ion hybrid capacitors (ZIHCs) offer a promising route to safe and low-cost energy storage, yet their rate performance is constrained by sluggish interfacial desolvation of hydrated Zn²⁺ ions and the limited electric double-layer capacitance of carbon cathodes. Here, we introduce a dual interfacial regulation strategy that addresses both limitations through defect-modulated Zn-N₄ single atom sites embedded in carbon cathodes. Spectroscopic studies and theoretical calculations reveal that defect-induced electronic asymmetry downshifts the Zn d-band center and generates nonbonding N/C 2p states near the Fermi level, facilitating Zn²⁺─H₂O bond dissociation and accelerating interfacial desolvation. Simultaneously, enhanced electron delocalization increases surface charge density, favoring electric double-layer formation and rapid charge accumulation. As a result, the optimized ZIHC delivers a high specific capacity of 201.5 mAh g^-1 and an energy density of 146.5 Wh kg^-1, excellent rate capability (56% capacity retention at 100 A g^-1) and long-term durability (92.1% retention after 110,000 cycles). In situ and ex situ characterizations reveal a surface-dominated storage mechanism involving facilitated Zn²⁺ desolvation and reversible interfacial adsorption. This work establishes asymmetric single atom coordination as an effective design strategy for coupling interfacial desolvation with charge regulation in high-rate aqueous energy storage.