Urea-induced interfacial engineering enabling highly reversible aqueous zinc-ion battery

Aqueous zinc-ion batteries (AZIBs) have been regarded as prospective rechargeable energy storage devices because of the high theoretical capacity and low redox potential of Zn metal. However, the uncontrollable formation of dendrites and the water-induced side reactions at the Zn/electrolyte interface, and the poor reversibility under a high current density (> 2 mA·cm −2 ) and large area capacity (> 2 mAh·cm −2 ) still limit the practical applications of AZIBs. Therefore, a strategy that can overcome these difficulties is urgently needed. Here, we introduce an environmentally friendly and low-cost additive, namely urea, to the electrolyte of AZIBs to induce uniform Zn deposition and suppress the side reactions. Measurements of the adsorption behavior, electrochemical characterization, and observations of the morphology revealed the interfacial modification induced by urea on the Zn/electrolyte interface, demonstrating its huge potential in AZIBs. Consequently, the long-term cycling stability (over 2100 h) of a Zn/Zn symmetric cell under a high current density of 5 mA·cm −2 and a capacity of 5 mAh·cm −2 was achieved with a 1 mol·L −1 ZnSO 4 electrolyte with the urea additive. Additionally, the assembled Zn/NH 4 V 4 O 10 full cell with urea exhibited excellent cycling performance and an outstanding average Coulombic efficiency of 99.98%. These results indicate that this is a low-cost and effective additive strategy for realizing highly reversible AZIBs. Graphical abstract