Sulfur vacancies and morphology dependent sodium storage properties of MoS2-x and its sodiation/desodiation mechanism.

Creating rich vacancies and designing distinct micro-morphology are considered as effective strategies for boosting the electrochemical performances of sodium ion battery (SIB) electrode materials. In this paper, a variety of MoS2 nanostructures with different sulfur vacancies concentration and morphologies are successfully constructed by a hydrothermal method combined with various-temperature calcination treatment in a Ar/H2 mixed atmosphere. Employed as a free-standing anode for SIBs, the flower-like MoS2-x microspheres assembled by the intertwined nanosheet arrays (MoS2-x-800) delivers highest specific capacity of 525.3 mAh g-1 and rate capability, as well as extraordinarily stable cycle life with almost no loss of capacity after 420 cycles. The favorable sodium storage properties are mainly ascribed to the cooperated effects of superior intrinsic conductivity and richer active sites generated by sulfur vacancies, and numerous interspace achieved by the intersection of neighbouring nanosheets. Meanwhile, through ex situ analyses, the reversible charge/discharge mechanism of the obtained MoS2-x-800 is revealed reasonably. This work not only brings new insights into the design of high-performance electrode materials for SIBs, but also makes a great step forward in the practical applications of transition metal sulfides in energy storage systems.