Aqueous zinc-ion batteries (AZIBs) as one of the highly anticipated areas in the new generation of battery technologies have broad application prospects and potential. Compared to conventional lithium-ion batteries, AZIBs have higher safety, cost-effectiveness, environmental friendliness, and higher energy density, making them highly sought after in energy storage and renewable energy. Nevertheless, a high concentration of water molecules in the AZIBs can result in the decomposition of water into H⁺ and OH^- during the charging/discharging process, which triggers significant hydrogen evolution reactions and corrosion problems, ultimately compromising the stability of the metal zinc electrode. Meanwhile, zinc dendrites are easily formed due to the uneven zinc deposition. To address these issues, this paper innovatively proposed an electrolyte additive of ethylene glycol methyl ether (MECS) to enhance the stability of the zinc electrode. The impact of MECS electrolyte additives on the AZIBs performance was systematically investigated via the experiments and theoretical calculations.

An electrolyte was prepared via adding different concentrations of MECS into 2 mol/L ZnSO₄ solution. The concentrations of MECS additives used were 2%, 4%, and 9% (in volume fraction, referred to as '2% MECS', '4% MECS', and '9% MECS').

V₆O₁₃·H₂O was prepared. Firstly, 2.73 g of V₂O₅ and 4.52 g of H₂C₂O₄ were added to 40 mL of deionized water (referred to as "solution A") and stirred at 90 ℃ for 1 h. Subsequently, 10 mL of H₂O₂ and 30 mL of ethanol were added to solution A, which was then transferred to a high-pressure vessel lined with PTFE. The vessel was heated at 180 ℃ for 3 h. Finally, the product was filtered, washed with ethanol and deionized water for at least 3 times, and then the washed material was dried in vacuum at 60 ℃ for 24 h. The preparation steps for the cathode plate were as follows: V₆O₁₃·H₂O, conductive agent (acetylene black), and PVDF were mixed at a weight ratio of 7∶2∶1, with NMP used as a solvent, and stirred evenly. The obtained slurry was coated on Ti foil, and dried in vacuum at 80 ℃ for 24 h. The samples were characterized by nuclear magnetic resonance (NMR), Fouier transform infrared spectroscopy (FTIR) and Raman spectroscopy (RS). Also, the binding energy was calculated based on the density functional theory (DFT).

Based on the results by BMR, FTIR and RS, the shift of ¹H peaks and the stretching vibrations of O—H both indicate a change in the solvation structure of Zn²⁺ in the solution with the MECS additives. The analysis of the DFT calculation results reveals that the binding energy between MECS and Zn²⁺ is significantly higher than that between Zn²⁺ and H₂O, indicating the preference of MECS to coordinate with Zn²⁺ and replace the positions of water molecules in the solvation structure of Zn²⁺. The restructured solvation structure of Zn²⁺ reduces the number of active water molecules in the electrolyte, thereby lowering the activity of parasitic reactions and enhancing the stability of the metal zinc anode.

The effect of MECS additives on the electrochemical performance of batteries was thoroughly investigated via assembling Zn//Zn symmetrical cells, Zn//Ti cells, and full cells. Under relatively mild testing conditions (i.e., 0.5 mA/cm² and 0.5 mA·h/cm²), Zn//Zn symmetrical cells with MECS additives can cycle stably for 1 250 h, while those without MECS additives only cycle for about 250 h before short-circuiting occurs. The batteries with MECS additives demonstrate an excellent performance even under different testing conditions due to the regulation effect of MECS at the zinc anode/electrolyte interface.

A novel electrolyte additive (MECS) was developed to stabilize zinc metal anode. Based on experimental and theoretical calculations, MECS molecules could participate in altering the solvation structure of Zn²⁺, reduce the quantity of active water molecules at the zinc anode interface through strong coordination with Zn²⁺, resulting in a smooth zinc deposition and a decreased by-product formation. Consequently, Zn//Zn symmetrical cells assembled with the improved electrolyte demonstrated stable cycling for over 1 250 h. In addition, the assembled Zn//V₆O₁₃·H₂O full cell also showed an excellent performance, maintaining a high capacity even after 800 cycles at a current density of 1 A/g. This study could present a simple, effective, and economic electrolyte modification approach to achieve effective utilization of zinc in aqueous zinc-ion batteries, providing innovative pathways for the development of next-generation secondary batteries.