Potassium-ion storage mechanism of MoS2-WS2-C microspheres and their excellent electrochemical properties

Potassium-ion batteries are receiving increasing interest as a new type of secondary batteries because of their low redox potentials. In particular, two-dimensional transition metal dichalcogenides are being widely studied because they possess a layered structure with a large interlayer distance; these structural characteristics are favorable for hosting potassium-ions. However, capacity decay occurs and the intercalation of potassium-ions is hindered due to the huge volume expansion during the cycling process. Here, MoS2-WS2-C microspheres containing highly porous structure and heterogeneous interfaces are synthesized through facile spray pyrolysis. Benefiting from the unique structure and hetero-interfaces, the composite microspheres exhibit stable cycle performance and an outstanding rate performance. Meanwhile, a reversible capacity of 350 mA h g(-1) is achieved after 100 cycles at the current density of 100 mA g(-1), and even at the high current density of 5.0 A g(-1), it maintains a capacity of 176 mA h g(-1). The potassium-ion storage mechanism of MoS2-WS2-C microspheres is also systematically explored via ex-situ transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). With the advantages of highly reversible intercalation from WS2 and high specific capacity of conversion from MoS2, the MoS2-WS2-C microspheres achieve high rate performance and specific capacity.