Effect of introducing fluorine doping and sulfur vacancy on SnS2 as anode electrode of LIBs: a density functional theory

Abstract

As the anode material of LIBs, the SnS2 electrode boasts a reversible specific capacity as high as 1231 mAh 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 the lithium storage performance. In this paper, we propose enhancing intrinsic electronic conductance of SnS2 through fluorine doping and the introducing 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 by phonon spectrum. Calculation of the density of state and lithium ion diffusion barrier demonstrate that F-SnS2-x has 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 F-SnS2-x structure and lithium ion, which is advantageous for achieving long-term cycle stability. Importantly, one F-SnS2-x molecule can adsorb up to 4.5 Li atom, yielding a corresponding theoretical specific capacity of 702 mAh g-1, which surpasses that of SnS2 with 4 atoms (586 mAh 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.