Aqueous Electrolyte Regulation Towards Long-Lasting Zinc Metal Anode
Creators: name: Liu, Liyang
Publisher: name: University of Wollongong
Year: 2025
Subjects: classificationCode: 4016
subject: Materials engineering
subject: FOS: Materials engineering

description: To mitigate the negative impacts on human life caused by the greenhouse effect, people around the world are making great efforts to use clean energy instead of traditional fossil fuels. In this process, the large-scale energy storage systems (EESs) play a crucial role because most of clean energy sources are intermittent and volatile. In recent ten years, aqueous zinc-ion batteries (AZIBs) have attracted great attention as a promising candidate for large-scale EESs due to their high safety, low cost, and environmental friendliness. Nevertheless, issues related to the zinc metal anode, such as hydrogen evolution reactions (HER), corrosion reactions, and dendrite growth, significantly hider the industrial application of AZIBs. Electrolyte regulation is one of the most efficient methods to address these problems. In this doctoral thesis, the issues related to the zinc anode and the recent developments in electrolyte regulation methods, including solvation structure regulation, electric double layer (EDL) regulation, and solid electrolyte interphase (SEI) regulation, are thoroughly summarized. Based on these theories and experiences, one cosolvent and two electrolyte additives have been developed, significantly improving the electrochemical properties of the zinc metal anode.In the first work, log<i>P</i>, where <i>P </i>is the octanol-water partition coefficient, a general parameter to describe the hydrophilicity and lipophilicity of chemicals, is proposed as a standard for selecting co-solvents for Zn(CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub> electrolyte, which demonstrated by testing seven different types of solvents. The solvent with a similar log<i>P </i>value to the salt anion CF<sub>3</sub>SO<sub>3</sub>- can interact with CF<sub>3</sub>SO<sub>3</sub>-, Zn<sup>2+</sup> and H<sub>2</sub>O, leading to a reconstruction of the electrolyte solvation structure. To prove the concept, methyl acetate (MA) is demonstrated as an example due to its similar log<i>P </i>value to CF<sub>3</sub>SO<sub>3</sub>-. Both the experimental and theoretical results illustrate that MA molecules not only enter into the solvation shell of CF<sub>3</sub>SO<sub>3</sub>-, but also coordinate with Zn<sup>2+</sup> or H<sub>2</sub>O, forming a MA and CF<sub>3</sub>SO<sub>3</sub>- involved core-shell solvation structure. The special solvation structure reduces H<sub>2</sub>O activity and contributes to forming an anion-induced ZnCO<sub>3</sub>-ZnF<sub>2</sub>-rich SEI. As a result, the Zn||Zn cell and Zn||NaV<sub>3</sub>O<sub>8</sub>·1.5H<sub>2</sub>O (NVO) cell with MA-involved electrolyte exhibit superior performances to that with MA-free electrolyte.In the second work, a functional group assembly strategy is proposed to design electrolyte additives for modulating the EDL, thereby realizing a long-lasting zinc metal anode. Specifically, by screening ten common functional groups, N, N-dimethyl-1H-imidazole-1-sulfonamide (IS) is designed by assembling an imidazole group, characterized by its high adsorption capability on the zinc anode, and a sulfone group, which exhibits strong binding with Zn<sup>2+</sup> ions. Benefiting from the adsorption functionalization of the imidazole group, the IS molecules occupy the position of H<sub>2</sub>O in the inner Helmholtz layer of the EDL, forming a molecular protective layer to inhibit H<sub>2</sub>O-induced side reactions. Meanwhile, the sulfone group in IS, acting as a binding site to Zn<sup>2+</sup>, promotes the de-solvation of Zn<sup>2+</sup> ions, facilitating compact zinc deposition. Consequently, the utilization of IS significantly extending the cycling stability of Zn||Zn and Zn||NVO full cell.In the third work, ethylene glycol bis(propionitrile) ether (DENE) is developed as a dual-function electrolyte additive to prolong the cycling stability of the zinc metal anode. Due to the abundant polar groups in the structure of DENE, it interacts with H<sub>2</sub>O through hydrogen bond (H-bond), thereby breaking the original H-bond network of H<sub>2</sub>O. Furthermore, DENE exhibits a lower lowest unoccupied molecular orbital compared to H<sub>2</sub>O, causing it to decompose before H<sub>2</sub>O during the battery charging process to form a DENE-derived SEI. These synergistic effects inhibit the HER, corrosion reactions, and zinc dendrite growth, leading to a dramatic increase in the lifespan of both the Zn||Zn and Zn||NVO cells.In summary, this doctoral thesis develops an electrolyte cosolvent selection method, an EDL regulating additive design method, and a dual-function electrolyte regulation additive for promoting the cycling stability of the zinc metal anode. Based on findings described above, I believe this thesis can offer valuable insights and references for further researchers, facilitating the expedited commercialization of AZIBs.