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

Abstract

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 (VS) in WS2 can enhance its K+ storage capability. However, it is a big challenge to keep the stability of VS while reserving the excellent activity. Herein, we design Se-filled WS2 nanosheets with VS (VS-WS2-Se NS) for PIBs. The Se heteroatom filling into the VS can not only stabilize and activate them, rendering more active sites to adsorb K+, but also further enhance the electrical conductivity. Consequently, the VS-WS2-Se NS anode presents significantly promoted storage capacity and reaction kinetics, superior to the pristine WS2 and WS2 with only VS. Remarkably, the VS-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 VS 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.