Breaking hydrogen-bonds in aqueous electrolytes towards highly reversible zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have attracted significant attention for their potential in large-scale energy storage. However, their practical application is limited by the poor zinc reversibility because of structural deterioration and side reactions induced by water molecules. Herein, we identified pentaerythritol (PTT) as an electrolyte additive to break the H-bond network of water in the conventional aqueous ZnSO4 electrolyte, after considering the cost, toxicity, conductivity, high H-bond donor number, and structure features among several options. The unique symmetry structure of PTT with four hydroxyl groups (-OH) significantly enhances its interaction with water molecules and changes the proportion of different hydrogen-bond (H-bond) types between water molecules. The introduction of PTT therefore could break the water H-bond network and change the Zn2+ solvation structure, as evidenced by both experimental findings and theoretical simulations. Consequently, water-induced side reactions and dendrite growth during cycling are significantly suppressed, leading to improved Zn reversibility and overall battery performance. Notable outcomes include the average coulombic efficiency reaching 99.7% and long-term stability exceeding 1000 h. This research contributes to the development of a cost-effective and efficient electrolyte strategy aimed at addressing water-induced issues in AZIBs. An electrolyte additive with uniquely symmetric structure breaks water's hydrogen bonds and modifies the primary solvation structure of Zn2+ in aqueous zinc batteries, enhancing battery performance and stability.