Citation: Hu, B.; Han, K.; Han, C.; Geng, L.; Li, M.; Hu, P.; Wang, X. Solid-Solution-Based Metal Coating Enables Highly Reversible, Dendrite-Free Aluminum Anode. Coatings 2022, 12, 661. https:// doi.org/10.3390/coatings12050661 Academic Editor: Giorgos Skordaris Received: 10 April 2022 Accepted: 9 May 2022 Published: 12 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). coatings Article Solid-Solution-Based Metal Coating Enables Highly Reversible, Dendrite-Free Aluminum Anode Bo Hu 1 , Kang Han 1 , Chunhua Han 1, *, Lishan Geng 1 , Ming Li 1 , Ping Hu 1, * and Xuanpeng Wang 2,3, * 1 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China; 13311621655@163.com (B.H.); hankang@whut.edu.cn (K.H.); gls523@whut.edu.cn (L.G.); m18334708396@163.com (M.L.) 2 Hainan Institute, Wuhan University of Technology, Sanya 572025, China 3 Department of Physical Science & Technology, School of Science, Wuhan University of Technology, Wuhan 430070, China * Correspondence: hch5927@whut.edu.cn (C.H.); huping316@whut.edu.cn (P.H.); wxp122525691@whut.edu.cn (X.W.) Abstract: Aluminum-ion batteries have attracted great interest in the grid-scale energy storage field due to their good safety, low cost and the high abundance of Al. However, Al anodes suffer from severe dendrite growth, especially at high deposition rates. Here, we report a simple strategy for constructing a highly reversible, dendrite-free, Al-based anode through directly introducing a solid- solution-based metal coating to a Zn foil substrate. Compared with Cu foil substrates and bare Al, a Zn foil substrate shows a lower nucleation barrier of Al deposition due to the intrinsic, definite solubility between Al and Zn. During Al deposition, a thin, solid-solution alloy phase is first formed on the surface of the Zn foil substrate and then guides the parallel growth of flake-like Al on Zn substrate. The well-designed, Zn-coated Al (Zn@Al) anode can effectively inhibit dendrite growth and alleviate the corrosion of the Al anode. The fabricated Zn@Al–graphite battery exhibits a high specific capacity of 80 mAh·g −1 and an ultra-long lifespan over 10,000 cycles at a high current density of 20 A·g −1 in low-cost molten salt electrolyte. This work opens a new avenue for the development of stable Al anodes and can provide insights for other metal anode protection. Keywords: aluminum-ion battery; metal coating; solid-solution alloy; dendrite-free anode 1. Introduction With the continuous emission of greenhouse gases and rapid fossil energy consump- tion, the development and utilization of new-type, clean energy, such as wind energy, solar energy, wave energy, etc., is important [1,2]. However, due to the uneven distribution of new-type, clean energy in time and space, an efficient approach is required to convert them into reliable chemical energy through rechargeable batteries [3–5]. At present, lithium-ion batteries have practical applications in energy storage systems [6,7], but their high cost, limited cycling life and safety problems restrict their further development and applica- tion [8]. Therefore, the development of a low-cost, long-life and high-safety energy storage battery is important. Among energy storage batteries, the aluminum-ion battery is one of the promising alternatives [9–11]. However, aluminum-ion batteries also face some problems, especially in seeking a suitable cathode/anode and electrolyte. Aqueous electrolytes are safer and environ- mentally friendly, but the side reactions caused by water decomposition and the severe corrosion/passivation of Al anodes remain huge challenges [12,13]. Most aluminum-ion batteries research focuses on developing cathode materials with high capacity and wide operating voltage windows. The study of anode materials has also gradually become a concern. It has been reported that the metallic properties of Al are likely to induce dendrite formation during reversible plating and stripping of Al, and these dendrites may pierce the Coatings 2022, 12, 661. https://doi.org/10.3390/coatings12050661 https://www.mdpi.com/journal/coatings