Lewis acid-base effect and protonation in electrolyte engineering enable shuttle-free, dendrite-free, and HER-free aqueous Zn-I2 batteries

Abstract

Electrolyte engineering has emerged as a facile and efficient strategy to solve side reactions in aqueous Zn-I₂ batteries. However, most of these solutions usually ignore the simultaneous modulation of the cathode and anode. Here, a multifunctional electrolyte additive, pyridoxine (VB6), enables simultaneous regulation of the anode and cathode in Zn-I₂ batteries. For the cathode, VB6 preferentially coordinates with $I^{-}$ ions through Lewis acid-base effect, thereby suppressing the generation of polyiodides and the shuttle effect. For the anode, VB6 can not only significantly restrain the hydrogen evolution reaction (HER) and the pH fluctuation of the electrolyte through protonation, but also promote the fast de-solvation of Zn²⁺ and regulate the Zn deposition benefiting from its structure with multi‑hydroxyl groups. Due to the synergistic effect of VB6, the modified symmetric Zn||Zn cell achieves a remarkable Coulombic efficiency (99.7 %) over 1600 h and excellent cycling stability (2100 h). Most intriguingly, the Zn-I₂ cell exhibits an ultra-long lifespan of 50,000 cycles (> 6 months) at 2 A g^-1 with an exceptional capacity retention of 84.3 %. Even without pressurized equipment, the Zn-I₂ pouch cell with VB6 still maintains prominent performance (76.5 % capacity after 450 cycles) without swelling.