Highly reversible, dendrite-free and low-polarization Zn metal anodes enabled by a thin SnO2 layer for aqueous Zn-ion batteries

Aqueous Zn-ion batteries (AZIBs) are attractive for next-generation renewable and secure energy storage systems due to their high safety and low cost. However, dendrite growth and side reactions of Zn metal anodes severely limit their practical applications. Moreover, polarization is an important but easily overlooked factor hampering the development of AZIBs. Herein, a zincophilic, hydrophilic, and thin (similar to 100 nm) SnO2 protective layer is reported to remodel the Zn anode/electrolyte interface via a simple spin-coating approach. The SnO2 layer effectively inhibits the growth of the dendrites, which prolongs the lifetime of Zn anodes to 3900 h. It also alleviates the side reactions and endows Zn||Cu cells with a high Coulombic efficiency of 99.3% over 2000 cycles. Meanwhile, the SnO2 layer presents fast Zn deposition kinetics to ensure reversible Zn anodes at high current/capacity by decreasing electrochemical polarization and concentration polarization. Consequently, SnO2/Zn anodes exhibit a high cumulative capacity of 4.5 A h cm(-2) at an ultrahigh current of 30 mA cm(-2) with a low overpotential of 90 mV and even 3.2 A h cm(-2) at a high capacity of 4 mA h cm(-2) and high current of 8 mA cm(-2). Prototype SnO2/Zn||delta-MnO2 full cells also obtain higher capacities and capacity retention (96.9% after 500 cycles at 2C) than bare Zn. This work offers new insights for ensuring the reversibility and durability of Zn anodes with low polarization at high current/capacity and provides a promising way to promote the practical application of AZIBs.