Filling Selenium into Sulfur Vacancies in Ultrathin Tungsten Sulfide Nanosheets for Superior Potassium Storage

The development of WS₂ as an anode for potassium-ion batteries (PIBs) is severely confined by the low K⁺ storage capacity and poor intrinsic electrical conductivity. Our previous study demonstrated that the creation of sulfur vacancies (V_S) in WS₂ can enhance its K⁺ storage capability. However, it is a big challenge to keep the stability of V_S while reserving the excellent activity. Herein, we design Se-filled WS₂ nanosheets with V_S (V_S-WS₂-Se NS) for PIBs. The Se heteroatom filling into the V_S can not only stabilize and activate them, rendering more active sites to adsorb K⁺, but also further enhance the electrical conductivity. Consequently, the V_S-WS₂-Se NS anode presents significantly promoted storage capacity and reaction kinetics, superior to the pristine WS₂ and WS₂ with only V_S. Remarkably, the V_S-WS₂-Se NS anode exhibits the highest specific capacity of 363.9 mA h g^-1 at 0.05 A g^-1. Simultaneously, a high reversible capacity of 144.2 mA h g^-1 after 100 cycles at 2.0 A g^-1 is shown. Ex situ analyses demonstrated that the potassium storage mechanism involves the intercalation and conversion reaction between WS₂ and K⁺. Moreover, DFT calculations revealed that the Se filling into V_S can further enhance the electrical conductivity and reduce the K-insertion energy barriers of WS₂ and thus account for the outstanding electrochemical performance. This study demonstrates that engineering the vacancies by the heteroatom filling strategy offers a novel and feasible route for designing high-performance electrode materials in various energy-storage systems.