Dual mechanism of ion (de)intercalation and iodine redox towards advanced zinc batteries

Abstract

Materials with layered structures have been widely adopted as ion-(de)intercalated-type cathodes for zinc ion batteries but suffer from the limited operating voltage of the restricted redox couple, while the I⁻/I₂ transition at high potential is limited by poor reversibility. Herein, a dual-active ion solution of Zn(CF₃SO₃)₂ and ZnI₂ in ethylene-glycol-substituted solvent is proposed, with a bifunctional cathode of NH₄V₄O₁₀ and porous activated carbon to realize the integration of Zn²⁺ (de)intercalation and I⁻/I₂ redox. The solvation structure of Zn²⁺ with fewer H₂O molecules, formed by monodentate and bidentate coordination with ethylene glycol, ensures stability and reversibility of the interfacial reaction, thus providing enhanced discharge medium voltage (0.96 V) and capacity retention (0.032% per cycle) at 0.2 A g⁻¹. The compatibility of halogen redox and ion-(de)intercalation is deeply explored, offering a direction for mechanistic synergy in constructing advanced zinc-based batteries.