Joint Enhancement in the Electrochemical Reversibility and Cycle Lives for Copper Sulfide for Sodium- and Potassium-Ion Storage via Selenium Substitution.

Transition metal sulfides have received considerable interest as the anodes for sodium-ion (SIBs) and potassium-ion batteries (PIBs) owing to their high theoretical capacity and suitable working potential. However, they suffer from poor electrochemical reversibility and limited cycle lives. Herein, we design and synthesize a Se-substituted CuS material, which demonstrates superior electrochemical properties for both potassium and sodium storage because of the enhanced electronic conductivity, lowered diffusion barrier, and shortened diffusion pathway. The anode delivers a specific capacity of 374 mA h g-1 at a current density of 5 A g-1 in SIBs and 341 mA h g-1 at 2 A g-1 in PIBs and nearly 100% capacity retention over 2000 cycles (SIBs) and 600 cycles (PIBs), respectively. Moreover, a combined measurement including X-ray diffraction, Raman, and transmission electron microscopy reveals an interesting discharge product of Na2S0.8Se0.2, which could accelerate the conversion reaction and enhance the electrochemical reversibility.