Surface Facet Controlled Zinc Metal Anode for High Performance Aqueous Zinc Ion Energy Storage System

Several issues exist with the current organic electrolyte based electrochemical energy storage system, including the lack of metal resources, thermal expansion problems, and toxicity. In contrast, aqueous Zinc (Zn) ion batteries (AZIBs) have garnered substantial attention due to their abundance in resources and the cost-effectiveness and environmental friendliness of their electrode materials. Additionally, a water-based electrolyte solution can act as a successful block layer, thereby improving thermal stability. However, the use of a water medium can result in the formation of Zn dendrites on the Zn metal anode. The protruding structure of these dendrites can damage the separator and short-circuit the cell. Moreover, the generation of hydrogen and corrosion caused by parasitic surface reactions on the native passivation layers of Zn metal anodes pose significant problems, leading to decreased cycling stability of AZIBs. Therefore, the properties of the Zn metal surface should be well-tailored to address these issues. In this work, we proposed the use of a highly active acidic etching process on the Zn metal anode to increase the effective surface area and control the surface facet for favorable and smooth Zn deposition and stripping. Without any heat treatment, a mere 2-minute etching time can effectively create a closely spaced array within the etched grooves, resulting in a preferential (002) crystal plane orientation on the Zn metal anode. The high surface area can provide more active sites on the Zn metal anode. Moreover, the tailored (002) surface orientation can ensure the continuous deposition of planar zinc metal during the charge-discharge process, which can minimize the growth of protruding Zn dendrites. According to the suggested highly active acidic etching process, the electrochemical performance was greatly improved in terms of stability, specific capacity, and symmetric cell cyclability. Our results demonstrate that using acid-etched planar zinc foils as the anode can effectively increase the electroactive surface area, suppress hydrogen evolution reactions, and inhibit dendrite formation on the Zn metal anodes. As a result, the Zn anode symmetry cell showed long and stable cyclability for 250 hours at both current densities of 3 mA cm^-2 and 1 mAh cm^-2. Moreover, in the full cell configuration with the α-MnO₂ cathode, the full cell displayed a long cycle life with a capacity retention of 73 % for up to 150 cycle at current density 0.5A/g. This acid etching process has a significant advantage of being short and simple in the experimental process compared to previously reported studies, thus providing new opportunities for stable and high-performance AZIBs.