Imidazolium Cation‐Stabilized Interfacial Chemistry for Durable Aqueous Cadmium‐Iodine Batteries

Aqueous metal batteries are attractive candidates for large-scale energy storage owing to their intrinsic safety and low cost. However, their practical application is constrained by dendrite growth, corrosion, and hydrogen evolution reaction (HER), as well as dissolution-induced parasitic reactions of the cathode materials. Here, we report a durable cadmium-iodine (Cd//I₂) battery enabled by a dual-interfacial chemistry regulation strategy. The Cd²⁺/Cd redox couple offers moderate potential to suppress HER and strong resistance to acidic and polyiodide corrosion, rendering Cd metal a highly stable anode. Moreover, the incorporation of 1-butyl-3-methylimidazolium cation (BMIM⁺) induces preferential adsorption on the Cd anode, forming a functional interphase that lowers local charge density, suppresses dendrite growth, and promotes uniform Cd deposition. At the cathode, strong electrostatic interactions and steric hindrance between BMIM⁺ and polyiodide anions effectively mitigate the shuttle effect. Benefiting from these synergistic effects, the Cd//I₂ battery delivers a high reversible specific capacity of 152.5 mAh g^-1 at 10 A g^-1 and achieves ultralong cycling stability over 50,000 cycles, with an ultralow per-cycle capacity decay of 0.00032%. Even under a high I₂ loading of 17.78 mg cm^-2, the battery maintains 400 cycles with high specific capacity of 173.1 mAh g^-1, underscoring its potential for practical application.