Janus interface enables reversible Zn-ion battery by regulating interfacial water structure and crystal-orientation.

To tackle the shortcomings of traditional battery systems, there has been much focus on aqueous Zn-ion batteries due to various advantages. However, they still suffer from poor stability of Zn anodes. Here, a methionine additive with unique Janus properties is proposed to regulate the behavior of the interface between Zn anodes and the electrolyte environment. Systematic characterizations as well as calculations elucidate that the Janus additive is adsorbed on the Zn anode via zincophilic -NH 2 , changing the structure of the electric double layer and breaking the hydrogen bonding network among H 2 O molecules through hydrophobic S-CH 3 . At the same time, it can induce preferential formation of Zn(101) with high reversibility. The above two functions contribute to the dendrite inhibiting ability of Zn anodes. As validated, fabricated Zn//Zn symmetric cells achieve stable cycles of 4500 h, 1165 h, and 318 h at 1, 5 and 10 mA cm -2 /mA h cm -2 , respectively. Furthermore, Zn//Cu asymmetric cells with an average coulombic efficiency of 98.9% for 2200 stable cycles can be realized. Finally, Zn//MnO 2 full cells exhibit 79.9% capacity retention with an ultra-high coulombic efficiency of 99.9% for 1000 cycles, much better than that of the pure Zn(ClO 4 ) 2 system, indicating the great potential of this useful strategy in aqueous batteries.