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

Abstract Aqueous Zn | |I 2 batteries, involving I - /I 0 /I + redox, are promising yet usually facing low I 2 utilization dominated by I 0 /I + redox, especially under high loadings. Unlocking alternative pathway to I 0 /I + redox, preferably in noncorrosive dilute electrolytes, is a crucial solution. Here, we report a pathway towards more thermodynamically favorable I 0 /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 | |I 2 batteries with high I 2 loading (8.6 ~ 24.0 mg cm -2 ), featuring improved performances: (1) high I 2 utilizations (55% ~ 80%) at high rates (5.8 ~ 46.4 mA cm -2 ), (2) long lifespan ( $$ > $$ > 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.