Phase‐Engineered Electronic Structure of ZrO ₂ Regulates the Kinetic Thermodynamic Balance of Polyiodide Chemistry in Aqueous Zn–I ₂ Batteries

ABSTRACT

Aqueous Zn–I ₂ batteries are fundamentally limited by the challenge of simultaneously suppressing polyiodide shuttling and maintaining rapid interfacial conversion kinetics. Herein, we demonstrate that crystal‐phase‐dependent electronic reconstruction of ZrO ₂ enables regulation of this adsorption–conversion balance. A tetragonal ZrO ₂ /carbon‐sphere composite (CS/t‐ZrO ₂ ) is constructed through a polydopamine‐assisted confined‐growth strategy, while monoclinic ZrO ₂ (m‐ZrO ₂ ) serves as the phase‐controlled counterpart. Comprehensive structural, spectroscopic, and electrochemical analyses reveal that the tetragonal phase possesses a higher concentration of oxygen‐vacancy‐associated defect states and a lower work function, resulting in enhanced intrinsic interfacial charge‐transfer capability. Operando UV–vis and in situ Raman spectroscopy demonstrate that the carbon framework effectively suppresses polyiodide diffusion, whereas the tetragonal ZrO ₂ interface accelerates reversible iodine conversion, together establishing a favorable adsorption‐conversion balance. Density functional theory calculations further show that the tetragonal phase moderates iodine‐intermediate adsorption and reduces the thermodynamic barriers of the I ₂ /I ⁻ conversion pathway, accounting for the experimentally observed fast reaction kinetics and reduced polarization. Consequently, the CS/t‐ZrO ₂ /I ₂ cathode delivers a reversible capacity of 215 mAh g ⁻¹ with 97% capacity retention after 2000 cycles at an iodine loading of 4.7 mg cm ⁻² . This work establishes crystal‐phase engineering as a viable strategy to modulate interfacial electronic structure for conversion‐type aqueous energy‐storage systems.