Intercalation-Assisted In Situ Exfoliation of Cu2Se Nanosheets as Anode for Ultralong-Life Aqueous "Rocking-Chair" Zinc-Ion Batteries

Aqueous zinc ion batteries (AZIBs) are a potential energy storage device due to their low cost and environmental friendliness. However, the problems of Zn metal anode lead to low coulombic efficiency and safety problems, thus hindering the practical application of AZIBs. Therefore, developing zinc-metal free anode materials can effectively avoid the problems. Herein, an intercalation-assisted in situ exfoliation mechanism is reported to obtain Cu2Se nanosheets (E-Cu2Se) during the electrochemical reaction. The good conductivity of Cu2Se nanosheets ensures the rapid (de)intercalation of zinc ions and excellent charge transport properties in Cu2Se. Furthermore, Cu2Se not only has strong structural stability itself but also can effectively inhibit zinc dendrite through the conversion of copper between the cathode and anode. The results show that the E-Cu2Se electrode has a low intercalation potential (approximate to 0.4 V) and a high specific capacity of 284.8 mAh g(-1) after 100 cycles at 0.1 A g(-1). Meanwhile, a "rocking-chair" aqueous zinc-ion battery assembled with ZnxMnO2 as cathode delivers a specific capacity of 40 mAh g(-1) after 60 000 cycles. The exfoliation mechanism of E-Cu2Se is discussed based on various characterization techniques and theoretical calculations. This study is expected to provide a new avenue for the development high-performance "rocking-chair" AZIBs.