In-depth study on the regulation of electrode interface and solvation structure by hydroxyl chemistry

Suppression of dendrite growth and side reactions for Zn-metal aqueous batteries promotes their promising development in the field of energy storage. Here, four advanced and low-cost additives (1-hexanol (1-Hex), 1,2-hexanediol (1,2-Hex), 1,2,5,6-hexanetetraol (1,2,5,6-Hex) and hexanehexol (Hex)) are introduced into slightly acidic electrolyte to regulate the solvation shell and electrode interface for enhancing the Zn reversibility. Combining with density functional theory (DFT) calculations and experimental characterizations, the differences of four additives in regulating hydrated Zn²⁺ structure and the adsorption situation of Zn metal/electrolyte interface are investigated at molecular level. Interestingly, the Hex with 6 hydroxyls is demonstrated to be the most effective additive among four additives, as it can form more hydrogen bonds with active H₂O molecules and achieve stronger adsorption energy with Zn metal. As a proof of mechanism, the Zn//Ti cell in ZnSO₄ with Hex electrolyte delivers a high average Coulombic efficiency (CE) of 99.1% after 650 cycles, which is significantly greater than that of pure ZnSO₄ electrolyte. Encouragingly, the Zn//V₂O₅ cell achieves the excellent stability with the capacity retention of 96.0% after 4000 cycles. The hydroxyl chemistry strategy can be readily generalized to the screening of other electrolyte additives, indicating its practical universality.