Catalyst-Electrolyte Synergy Enables Ultrafast and Long-Life Two-Electron Aqueous Zinc-Iodine Batteries

Two-electron aqueous Zn-I₂ batteries deliver doubled cathode capacity yet remain constrained by the thermodynamic instability of I⁺ and sluggish, multistep interfacial kinetics. By systematically correlating electrochemical behavior with ZnCl₂ concentration, we demonstrate that strengthened Cl^- coordination mitigates ICl hydrolysis but concurrently aggravates charge-transfer resistance. Thus, suppressing hydrolysis alone proves insufficient, underscoring the need to address interfacial kinetics. To address this, we design a single-atom catalytic confinement host featuring atomically dispersed Co-N₄ sites on N-doped carbon hollow nanospheres (CoSAs@NC). These isolated Co sites strongly chemisorb polyiodides, expedite electron exchange, and facilitate Zn²⁺ transport within a hierarchically mesoporous framework, coupling high stability with fast kinetics. Operando spectroscopy and kinetic analyses reveal that atomic catalysis significantly decreases the Tafel slope, enhances exchange current density, and reduces charge-transfer resistance. With high-iodine-content cathode, Co-SAs@NC-based cells achieve 190.6 mAh g^-1 at 30 A g^-1, and ultralong cycling stability with only 0.00179% capacity decay per cycle over 20000 cycles. Pouch cells deliver high energy density of 218.6 Wh kg^{- 1} (based on total electrode mass). This integrated catalysis-confinement strategy resolves the intrinsic stability-kinetics trade-off, advancing practical, high-rate Zn-I₂ energy storage.