Carbon-halogen bond substitution enables high-utilization four-electron iodine redox in noncorrosive dilute electrolytes

Aqueous Zn | |I₂ batteries, involving I^-/I⁰/I⁺ redox, are promising yet usually facing low I₂ utilization dominated by I⁰/I⁺ redox, especially under high loadings. Unlocking alternative pathway to I⁰/I⁺ redox, preferably in noncorrosive dilute electrolytes, is a crucial solution. Here, we report a pathway towards more thermodynamically favorable I⁰/I⁺ redox, via a unique carbon-halogen bond substitution. This pathway is realized with a low-concentrated (0.7 M), noncorrosive organohalide additive (2-bromoacetamide, BrAce), triggering a reversible Br-C···I⁽⁰⁾ and C-I⁽⁺⁾-Br bond substitution. Compared with conventional interhalogen bonding (I-Br) pathway, this pathway synchronously lowers the barrier for I⁰/I⁺ redox and strengthens the anti-hydrolysis of I⁺ species, by elaborately regulating axial δ hole activity of interhalogen bond (I^(δ+)-Br). Notably, this pathway enables sustainable operation of four-electron Zn | |I₂ batteries with high I₂ loading (8.6 ~ 24.0 mg cm^-2), featuring improved performances: (1) high I₂ utilizations (55% ~ 80%) at high rates (5.8 ~ 46.4 mA cm^-2), (2) long lifespan (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>></mml:mo></mml:math>400 cycles) with practical areal capacity ( ~ 3.85 mA h cm^-2) and 99.5% retention even at 47.5 mA cm^-2. This pathway opens an exciting research direction to unlock unusual halogen chemistry for scalable, high-energy, sustainable aqueous batteries.