Boosting iodine redox kinetics through the inherent electrostatic interaction and electron donor capability of gelatin binder

The notorious shuttle effect of polyiodides in aqueous Zinc-iodine (Zn-I 2 ) batteries impedes their practical application, which renders it imperative to address this issue. Here, we report natural gelatin as an advanced aqueous binder for iodine-loading cathode to enable stable and efficient Zn-I 2 batteries. The positively charged region in gelatin presents electrostatic attraction to the iodine species, while the electron-rich regions could donate electrons to form physical or even covalent bonds with iodine species, thus inhibiting polyiodides shuttle effect and boosting redox reaction. A high reversible capacity of 138 mAh g −1 after 3 000 cycles at 2C and an ultra-long cycling stability of 30 000 cycles at 25C with 107 mAh g −1 capacity was achieved. Gelatin binder also can accommodate high iodine-loading (∼10 ​mg) cathode, punch cells, and severe temperature conditions (−10 °C and 60 ​°C). In-situ UV–vis absorption spectroscopy, in-situ Raman spectra and theoretical calculation revealed the critical role of gelatin binder in suppressing polyiodide shuttling and accelerating reaction kinetics. This work uncovers the potential of natural low-cost binder material in advanced Zn-I 2 batteries and drives future study of designing functional binders.