Achieving highly reversible zinc metal anode via surface termination chemistry

An oxidation layer on a Zn surface is considered to play a negative role in hindering the practical applications of aqueous zinc ion batteries (AZBs). Herein, we demonstrate the importance of Zn-surface termination on the overall electrochemical behavior of AZBs by revisiting the well-known bottleneck issues. Experimental characterizations in conjugation with theoretical calculations reveal that the formation of a dense Zn₄(OH)₆SO₄·xH₂O (ZSH) layer from the well-designed surface-oxide termination layer improves the interface stability of the Zn anode and reduces the dehydration energy of Zn(H₂O)₆²⁺, thereby accelerating the interface transport kinetics of Zn²⁺. Moreover, instead of directly diffusing over the ZSH layer, a new "edge dehydration-along edge transfer" mechanism of Zn²⁺ is discovered. Owing to the presence of a Zn anode with a ZnO-derived ZSH layer, an ultrahigh stability of over 1200 h with a high cumulative-plated capacity of 6.24mAh cm^-2 is achieved with a symmetrical cell. Furthermore, high cycling stability (over 1000 cycles) and Coulombic efficiency (99.07%) are obtained in the entire AZBs with a MnO₂ cathode. An understanding of the oxygen surface termination mechanism is beneficial to Zn-anode protection and is a timely forward step toward the long-pursued practical application of AZBs.