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/MnO2 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.

Strategies for the Stabilization of Zn Metal Anodes for Zn‐Ion Batteries

“…Similarly, an array of hexagonal-pyramid-structured ZnO was coated on Zn surface by periodic anodization (Figure 9d). [60] The ZnO layers are thin on top and became thicker toward their bottom, and such a gradient structure can effectively regulate the Zn deposition by impeding the Zn deposition on the top of the array by increasing the charge transfer resistance but facilitating the Zn deposition at the bottom. Due to these advantages, the dendrite formation on this ZnO-modified anode could be alleviated, and the battery life can be extended.…”

“…d) Crosssectional configuration of the ZnO layer coated on Zn hexagonal pyramid core. Reproduced with permission [60]. Copyright 2020, Wiley-VCH.…”

The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

“…Heat treatment is required to crystallize the oxide (300 °C for 1 h) [ 75 ]. Zn/ZnO-hexagonal pyramid array for a Zn-ion battery anode was created by Kim et al [ 76 ] by applying pulsed-galvanostatic anodization in an aqueous solution containing NH 4 Cl and H 2 O 2 . The main parameter used to control the Zn periodic anodizing process was the time ratio between current-on/current-off with a continuous period of 6 s. The anodization was performed for 1 min.…”

“…Regarding other anodized oxides, some studies described the use of nanostructured WO 3 and Sn@Cu x O in LIBs [ 72 , 79 ], SnO x , and Nb 2 O 5 in SIBs [ 148 , 149 , 151 ], and ZnO in ZIBs [ 76 ]. Due to its high theoretical capacity (696 mA·h·g −1 ) [ 72 ], WO 3 is also a potential material for anodes in LIBs.…”

“…Zn-ion batteries are considered a green energy system [ 76 ] using less-flammable electrolytes and low-toxic materials. Kim et al [ 76 ] used the periodic anodizing technique to produce ultra-stable Zn anode in a hexagonal pyramid arrangement with a functionalized ZnO layer for a ZIB device. This structure inhibited the growth of Zn dendrites, which damage the electrode stability.…”