A New Strategy for Hexagonal Boron Nitride Coating on Zinc Metal Anode for High-Performance Zinc Ion Batteries

The high demand for new electrochemical storage systems with high energy densities and operational stability has driven recent studies on aqueous zinc-ion batteries (AZIBs). AZIBs, which consist of aqueous electrolytes and electrode materials, are promising alternatives to flammable organic batteries. However, further research efforts on Zn metal anodes are still required due to issues such as the formation of protruding Zn deposition morphology (Zn dendrites) and parasitic reactions, including hydrogen evolution reactions between the Zn metal anode and the water electrolyte. These issues can reduce the high-efficiency electrochemical cycling of AZIBs. Therefore, finding a proper protective layer for the Zn metal is crucial to reduce the direct nucleation sites of Zn dendrites, provide high mechanical strength to the Zn anode, and improve selectivity and uniformity at the electrode surface during the charge-discharge process.<br/> Here, we present the first report on utilizing bulk hexagonal boron nitride (h-BN) layers as a promising coating for the Zn metal anode. The thin and uniform bulk h-BN coating reduces the nucleation radius of Zn dendrites, resulting in uniform Zn stripping and deposition. Furthermore, h-BN is a two-dimensional (2D) material with superior insulating properties, making it highly desirable. In particular, the h-BN layers can serve as effective energy barriers, preventing electron tunneling from the Zn metal to the electrolytes. This can minimize the parasitic surface reactions on the surface of the Zn metal anode. <br/> In this study, we propose a practical coating method using commercial h-BN powders, which allows for uniform deposition on the Zn metal anode over a large area. Through the optimization of the coating process and h-BN layer thickness, the Zn/h-BN symmetry cells exhibited a reduced overpotential (29 mV) and extended lifespan (over 250 hours) at a current density of 1 mA cm^-2 during the deposition and stripping processes. Additionally, a full cell configuration of Zn/h-BN//α-MnO2 was fabricated to demonstrate its electrochemical performance. The Zn/h-BN//α-MnO2 full cell displayed a high electrochemical performance of 345 mAh g^-1 at a current density of 0.1 A g^-1, with long-term cyclability of 75.4% after over 500 cycles at a current density of 0.5 A g^-1. This simple and effective coating method utilizing h-BN materials represents a promising approach towards the commercialization of Zn-ion batteries.