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