Understanding the Role of Topotactic Anion Exchange in the Robust Cu Ion Storage of CuS_1-xSe_x

Covellite CuS is promising for aqueous Cu ion batteriesowing to its high capacity, low cost, and environmental friendliness.However, multiple phase transitions and poor conduction make CuS lessattractive for electrochemical high-power applications. Herein, we reportthat the topotactic anion exchange in CuS1-xSexcould considerably boostthe electrochemical performance for robust Cu ion storage. Free-standingCuS0.5Se0.5nanosheets afford a high capacity of 491 mAh g-1and retain80% of this capacity at an extremely high current rate of 20 A g-1,dramatically outperforming the CuS counterpart. The role of anionexchange in the kinetic performance of CuS1-xSexhas been systematicallyinvestigated. The anion exchange of S by Se not only suppresses thephase transition but also accelerates the transport of electrons and ionsby reducing the energy barrier. It is suggested that the proposed anion-exchange strategy may open up new possibilities for the design of robust electrode materials for high-power batteries.