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High-valence halogen conversion reactions are promising for realizing high-energy-density aqueous batteries. It has been more challenging to realize a stable and reversible I 0 / I + conversion than the facile I – / I 0 conversion. While interhalogen chemistry has been employed to realize a reversible I – /I 0 / I + (i.e., four-electron) redox couple, the introduction of additional halide species raises corrosion and toxicity issues. Herein, we propose an SN2-type nucleophilic substitution mechanism for the activation of the I 0 / I + redox process. A series of halogen-free intermediates containing imide groups is proven effective in promoting four-electron halogen reactions due to conjugation-stabilized nitrogen anions. A structure–kinetics relationship among various imide-containing molecules is elucidated using two descriptors: the hydrogen dissociation energy ( E d ) of the imide group and the local nucleophilicity (LN) of the corresponding nitrogen anion. A Zn–I 2 battery with a theobromine intermediate exhibits stable cycling (a capacity retention of 93.9% at 5 A g –1 over 1000 cycles). This work provides new insights into the mechanism of the I 0 / I + redox process and a new avenue to the development of high-capacity multielectron iodine cathodes.
Yi et al. (Tue,) studied this question.