The effect of introducing fluorine doping and sulfur vacancies on SnS2 as the anode electrode of LIBs: a density functional theory study

As the anode material of LIBs, the SnS2 electrode boasts a reversible specific capacity as high as 1231 mA h g-1. Additionally, SnS2 possesses a CdI2-type layered structure with a layer spacing of 0.59 nm, which allows it to accommodate numerous lithium ions and facilitate rapid charge transfer. However, as a semiconductor material, SnS2's low electronic conductivity significantly hampers its lithium storage performance. In this paper, we propose enhancing the intrinsic electronic conductance of SnS2 through fluorine doping and the introduction of sulfur vacancies, thereby constructing the F-SnS2-x structure. The stability and superiority of this structure are confirmed by a series of theoretical calculations. The stability and rationality of the structure were characterized using the phonon spectrum. Calculation of the density of states and lithium ion diffusion barriers demonstrates that F-SnS2-x exhibits exceptional electron/lithium ion transport kinetics. Furthermore, the results of lithium ion binding energy and differential charge show that there is a strong interaction between the F-SnS2-x structure and lithium ions, which is advantageous for achieving long-term cycle stability. Importantly, one F-SnS2-x molecule can adsorb up to 4.5 Li atoms, yielding a corresponding theoretical specific capacity of 702 mA h g-1, which surpasses that of SnS2 with 4 atoms (586 mA h g-1). The theoretical calculation results of this work can provide valuable insights for improving the electronic conductivity and lithium storage performance of other metal sulfides.