Towards the practical application of Zn metal anodes for mild aqueous rechargeable Zn batteries

Rechargeable aqueous Zn batteries have been widely investigated in recent years due to the merits of high safety and low cost. However inevitable dendrite growth, corrosion and hydrogen evolution of Zn anodes severely compromise the practical lifespan of rechargeable Zn batteries. Despite the encouraging improvements for Zn anodes reported in the literature, the comprehensive understanding of Zn anodes under practical conditions is still often neglected. In this article, we focus on the "less-discussed" but critically important points for rechargeable aqueous Zn batteries, including revisit of the relationship between the coulombic efficiency and lifespan of Zn anodes, the rational control of the pH environment in the vicinity of Zn anodes, the design of appropriate aqueous separators and the relevant estimation of practical energy density for aqueous Zn batteries. It concludes that energy density of 60-80 W h kg^-1 for aqueous Zn batteries should be realistic in practice with appropriate cell design. We also propose practical technical recommendations for the rational development of aqueous Zn batteries based on research experience from the community and our group. We hope this article offers readers more practical insights into the future development of aqueous Zn batteries as competitive technology for practical use.