Beyond conventional: unveiling the impact of Zn anode pretreatment in aqueous zinc-ion batteries

Despite the simplicity and widespread use of conventional (untreated) Zn foil as a benchmark, conventional Zn foil continues to be the most common anode material in the research of zinc-ion batteries (ZIBs). However, there has been little focus on the inherent structure of the zinc foil itself. The traditional Zn anode has uneven rough surfaces that can lead to nonuniform charge distribution and hinder nucleation, thereby triggering the "tip effect" that can induce the formation of adverse dendrites. In this study, the conventional Zn foil was examined using simple pretreatments such as mechanical polishing and chemical etching that have the potential to substantially improve the electrochemical properties. Compared with bare Zn (b-Zn) and polished Zn (p-Zn), chemically etched Zn (e-Zn) sustained a remarkable life cycle of up to 5000 cycles with similar to 71% cycling retention at a high current density of 5 A g-1 using V2O5<middle dot>nH2O as a cathode material. Besides, the e-Zn & Vert;e-Zn symmetric cell exhibited excellent cycling stability over 300 cycles at a high current density of 10 mA cm-2 with better inhibiting hydrogen production during Zn stripping/plating. Moreover, advanced characterizations such as in situ transmission X-ray microscopy (TXM) and ex situ atomic force microscopy (AFM) have been employed to gain insight into the early stages of Zn dendrite formation on Zn foils in mild acidic aqueous electrolytes during the plating/stripping processes. This superior performance of the e-Zn is attributed to its unique 3D structure that effectively accommodates Zn dendrites, as confirmed by XRD and EBSD analyses, which reveal Zn deposition along the (002) plane with lower surface energy as compared with other planes. This approach provides a straightforward and industrially scalable method for expanding ZIB utilization. Chemically etched Zn shows superior cycling stability in Zn-ion batteries, achieving 5000 cycles with 71% retention. In situ TXM, AFM, and EBSD reveal a unique 3D structure and Zn deposition along the (002) plane, reducing dendrite formation.