Unique solvation structure induced by anionic Cl in aqueous zinc ion batteries

Abstract

Aqueous zinc ion batteries (AZIBs) have garnered significant attention in large-scale static energy storage battery systems due to their low cost, high safety and environmental friendliness. However, it has some inherent problems during operation, such as the occurrence of side reactions (hydrogen evolution reaction, HER) and anode corrosion, formation of by-products and growth of metal dendrites. To analyze the mechanism of generation from aspect of the electrolyte solvation structure and make cell efficiency further improvements based on it, so we use DFT calculations to find the most stable solvation structure in AZIBs with ZnCl2 as the electrolyte and analyze it. We define the relative concentration Cr, and calculate different groups metal cation cluster structures such as [Zn(H2O)n]2+, [ZnCl(H2O)n]+, [ZnCl2(H2O)n] and [ZnCl3(H2O)n]‐ that exist at different Cr. We discuss the effect of different clusters formed due to the Cr variations on the battery performance in terms of three aspects: the structural conformation, the cluster characteristics (including the hydrogen bonding network, bond lengths, bond angles, as well as the electrostatic potential ESP) and the cluster performance (including the adsorption energy Ea, binding energy Eb, and desolvation energy Edes). The results shows that the electrolyte metal cation Zn2+ can be coordinated with up to six H2O molecules in first shell, and this metal cation solvation structure contributes to the occurrence and formation of side reactions and by-products, which reduces the battery efficiency. Increasing the electrolyte anion Cl− concentration by appropriately increasing the Cr helps to desolvate the metal cation cluster structure, which greatly improves the battery efficiency and suppresses the side reactions and by-products. Yet the improvement effect was not obviously further improved by further increasing the Cl− concentration.