Study of a novel supramolecular hydrogel electrolyte for aqueous zinc ion batteries

Abstract

Aqueous zinc ion batteries are promising candidates for large-scale energy storage. Supramolecular gels have been widely used due to their self-assembly, controllability and biocompatibility. Here, a gelator was successfully synthesised using homotetracarboxylic acid and 4-hydroxypyridine to create a novel supramolecular gel electrolyte. The three-dimensional network of the gel resulted in reduced free water content alleviating water-related side reactions, with zinc ions promoting uniform zinc deposition and limiting zinc dendrite growth. We continued to use dimethyl sulfoxide (DMSO) as an additive to the supramolecular gel electrolyte, and the low-temperature conductivity was obviously improved. The conductivity of the gel electrolyte with 20% DMSO (SBU-D20) was 3.7 mS cm⁻¹ at −20 °C and 2.2 mS cm⁻¹ at −30 °C. The solvation structure of Zn²⁺ was modulated by the higher absorption energy of DMSO for Zn²⁺ and (002) facets, inducing Zn²⁺ to form more stable (002) facets. In addition, the stable reconstructed hydrogen bond between DMSO and H₂O significantly reduced the freezing point of the electrolyte. In the SBU-D20 electrolyte, the electrolyte exhibited a long lifetime of over 2300 h in Zn/Zn cells and an average CE of 99.5% after 500 cycles at 1 mA cm⁻² in Zn/Cu cells.