Functionalized Zn@ZnO Hexagonal Pyramid Array for Dendrite-Free and Ultrastable Zinc Metal Anodes

Abstract

Here, an electrode comprising a Zn hexagonal pyramid array (HPA) coated with a functionalized ZnO layer (Zn@ZnO HPA) is prepared using a periodic anodizing technique. The HPA structure markedly increases the electroactive surface area of Zn anode, thus decreasing the local current density. Furthermore, the functionalized ZnO coating layer has a gradient thickness that plays an important role in the selective deposition of Zn ions and the mitigation of side reactions at the interface. The electrochemical stability of the Zn@ZnO HPA electrode, which is closely related to the electroactive surface area and charge transfer resistance, is determined by the "split" value, i.e., ratio of current-off to current-on time, a parameter of the periodic anodizing process. Compared with the pristine Zn-based symmetric cell, the Zn@ZnO HPA-based symmetric cell is safely operated in the investigated experimental range with the 10-fold improved running life and 25-fold enhanced current density without Zn dendrite growth. Moreover, the Zn@ZnO HPA/MnO(2)battery exhibits outstanding long-term cyclability (nearly 100%) with greater than 99% Coulombic efficiency after 1000 cycles at a current density of 9 A g(-1). This periodic anodizing technique for ultrastable Zn metal anodes is expected to contribute to the development of inherently safe energy storage systems.