Cathode-separator synergy unlocks ultralow self-discharge and shuttle-free high loading zinc-iodine batteries

The practical application of aqueous zinc-iodine batteries (AZIBs) remains hindered by sluggish iodine redox kinetics, severe shuttle effects from irreversible polyiodide byproducts, and dendrite formation and corrosion at the Zn anode. Herein, we introduce a cathode-separator synergy strategy, which integrates the porous carbon cathode physical confines iodine, while the NiS₂-modified separator provides strong chemisorption and catalytic conversion of iodine species. Benefiting from this coupling effect, the Zn//NiS₂@GF//PC/I₂ battery delivers a superior rate capability of 334.2 mAh g⁻¹ at 0.2 A g⁻¹, remains above 1.31 V within 464 h with an ultralow self-discharge rate of 0.000625 V h⁻¹, and an outstanding lifespan exceeding 7500 cycles with ∼100% average Coulombic efficiency. Moreover, a pouch cell with high iodine loading of 6.0 mg cm⁻² likewise demonstrates excellent cycling stability of 167.0 mAh g⁻¹ at 0.3 A g⁻¹. Notably, these performances exhibit exceptional competitiveness among AZIBs with modified separator systems. Comprehensive ex-situ Raman/XPS analysis and detailed DFT theoretical calculations reveal that the coupled adsorption-catalysis mechanism reduces the adsorption energy and conversion energy barrier of iodine species, while simultaneously accelerating the conversion of polyiodide and suppressing side reactions at the Zn anode, thereby achieving ultralow self-discharge and shuttling-free behavior. Note that in-situ EIS and DRT electrochemical tests were innovatively used to reveal the charge transfer mechanism at the cathode-separator interface, further supporting the reversibility of iodine redox. This work provides mechanism insights and universal modification strategies for advancing AZIBs, significantly promoting the further development of aqueous zinc iodine energy technology for practical applications.