Polyoxometalate oxate solution: An electrolyte additive to sustainably improve the anodes electrode of aqueous Zn ion batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) are favored by researchers because of their high safety performance and abundant zinc resources. In this work, low-cost was selected as the electrolyte additive to continuously improve the problems faced by the anode. Molybdenum-based solution can be reduced on the surface of zinc anode to form a uniform protective layer, and polyoxometalate can disperse metal elements more evenly, so that Zn²⁺ deposition is more uniform and AZIBs has more stable cycling performance. The symmetric battery assembled after adding Polyoxometalate oxate solution can maintain a stable potential of more than 1900 h at 5mA cm⁻² and 1mAh cm⁻², which is three times the cycle time of the battery assembled with ZnSO₄ as the electrolyte (600 h). In addition, Mo has a certain anti-corrosion effect, which can prevent the corrosion reaction on the surface of zinc anode. The Tafel diagram shows that the corrosion current decreased from 1.995 mA cm⁻² to 1.584 mA cm⁻² after the addition of polyoxometalate oxate solution. The contrast effect is more obvious in SEM images. Different from the traditional zinc anode surface optimization, the addition of polyoxometalate oxate solution can continuously form auxiliary nucleation sites on the negative electrode surface to make Zn²⁺ deposition more uniform. When Na doped vanadium dioxide was used as the cathode to form full battery, the specific capacity could still reach 143.73mAh g⁻¹ after 1000 cycles at the current density of 2 A/g. In this study, adding low concentration of polyoxometalate oxate solution to the electrolyte can continuously generate a stable protective layer during the battery operation, providing a feasible scheme for continuous improvement of AZIBs zinc anode.