Intermolecular insights on low-temperature electrolyte design for practical aqueous zinc batteries

Aqueous zinc batteries (AZBs) have garnered attention as a low-cost and safe alternative to commercial lithium-ion batteries. However, the use of aqueous electrolytes has plagued electrochemical performance of AZBs particularly at sub-zero temperatures, which has hindered the expansion of their applications. Most previous studies have focused on the weakening of hydrogen bonds between water molecules, with little attention to the underlying intermolecular interactions such as dipole−dipole, dipole−ion, and ion−ion. Here, we review the design principles of low-temperature electrolytes for practical AZBs based on the mechanistic insights into the relevant intermolecular interactions, in addition to the previously prevalent approaches of hydrogen bond regulation. The electrokinetic phenomena behind the sluggish ion transport in the bulk electrolytes and the limited charge transfer at the electrode−electrolyte interface below freezing temperatures are described together with the theoretical elucidation. Based on this understanding, key determinants for the low-temperature aqueous electrolytes and their contribution to the electrochemical performance of AZBs are discussed in terms of intermolecular interactions. Lastly, we suggest the development directions and outlook of the low-temperature aqueous electrolytes, with a focus on elucidation of atomic-scale intermolecular interactions, electrode−electrolyte interface engineering, electrolyte restructuring, and cell design and electrolyte requirements for practical energy-dense AZB applications.