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 batteries owing to its high capacity, low cost, and environmental friendliness. However, multiple phase transitions and poor conduction make CuS less attractive for electrochemical high-power applications. Herein, we report that the topotactic anion exchange in CuS1–xSex could considerably boost the electrochemical performance for robust Cu ion storage. Free-standing CuS0.5Se0.5 nanosheets afford a high capacity of 491 mAh g–1 and retain 80% of this capacity at an extremely high current rate of 20 A g–1, dramatically outperforming the CuS counterpart. The role of anion exchange in the kinetic performance of CuS1–xSex has been systematically investigated. The anion exchange of S by Se not only suppresses the phase transition but also accelerates the transport of electrons and ions by 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.