Highly Stable Zn Metal Anode Enabled by Atomic Layer Deposited Al2O3 Coating for Aqueous Zinc-ion Batteries
Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted increasing attentions as an energy storage technology for large-scale applications, due to their high capacity (820 mAh g-1 and 5854 Ah L-1), inherent high safety, and their low cost. However, the overall performance of ZIBs has been seriously hindered by the poor rechargeability of Zn anode, because of the dendrite growth, passivation, and hydrogen evolution problems associated with Zn anode. Herein, Al2O3 coating by atomic layer deposition (ALD) technique was developed to address the aforementioned problems and improve the rechargeability of Zn anode for ZIBs. By coating the Zn plate with ultrathin Al2O3 layer, the wettability of Zn was improved and corrosion was inhibited. As a result, the formation of Zn dendrite was effectively suppressed, with significantly improved lifetime in the Zn-Zn symmetric cells. With the optimized coating thickness of 100 cycles, 100Al2O3@Zn symmetric cells shown a reduced overpotential (36.5 mV) and a prolonged life span (over 500 h) at 1 mA cm-2. In addition, the 100Al2O3@Zn has been verified in Zn-MnO2 batteries using layered δ-MnO2 as the cathodes and consequently superior electrochemical performance with a high capacity retention of 89.4% after over 1000 cycles at a current density of 1 mA cm-2 (3.33C for MnO2) is demonstrated. Importantly, we have demonstrated the dendrites are mainly Zn(OH)2 nanocrystals imbedded into amorphous matrix by the combination of characterization of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscope (HRTEM). It is expected that the novel design of Al2O3 modified Zn anode may pave the way towards high-performance aqueous ZIBs and shed light on development of other metal anode-based battery systems.