Abstract: Silicene as a cathode material is promising for alkali metal atomic batteries. However, pure silicene could hardly meet the requirements of practical applications owing to the poor structure stability and conductivity which are related with the sp2-sp3 hybridization. It has been reported that the silicene and tin disulfide recombination and boron doping could solve above problems, but the effects of these two modification methods on other properties of silicene are still unclear, which is not conducive to effectively designing the atomic structure of the material. Considering the difficulty of alkali metal atom adsorption and migration is an important factor in evaluating the performance of negative electrode materials, the effects of the composites of silicene and tin disulfide and further introduction of boron on the adsorption and migration of lithium/sodium atoms were studied in this work based on the first principles. The calculated negative adsorption energies implied that lithium/sodium atoms can be stably adsorbed on the surfaces of different materials. It is attributed to the charge transfers between lithium/sodium atoms and substrates promote the formation of chemical bonds. However, these formed chemical bonds were different, which had an effect on the adsorption and migration of lithium/sodium atoms. For the surface of silicene, composite with tin disulfide can enhance the bonding between silicon and lithium/sodium, leading to a decrease in adsorption and migration energy barriers, which is beneficial for promoting the adsorption and migration of lithium/sodium atoms; The introduction of boron was able to further reduce adsorption energy through the formation of new bonds, while the migration energy barrier was undesirably increased. For the surface of tin disulfide, the composite of the two materials or the introduction of boron element had negligible effect on the bonding of lithium/sodium atoms, and there was no significant change in the migration energy barrier. Therefore, the composite material of silicene and tin disulfide was the best: The adsorption and migration of lithium/sodium atoms were easier on the silicene surface, and the tin disulfide surface enhanced the adsorption of lithium/sodium atoms and maintained their migration ability at the same time. It is expected that this work could gain an insight into the effect of different modification methods on the adsorption and migration behavior of alkali metal atoms and provide theoretical basis for designing effective electrode materials.

Key words: Silicene, Tin disulfide, Electrode materials, Alkali metal atomic adsorption, First principles