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

Abstract

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-SnS_2−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-SnS_2−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-SnS_2−x structure and lithium ions, which is advantageous for achieving long-term cycle stability. Importantly, one F-SnS_2−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.