First-principles simulations of lithiation–deformation behavior in silicon nanotube electrodes

The lithiation mechanisms that occur in silicon nanotube lithium-ion battery electrodes are not well understood at the atomic level. In this study, first-principles calculations were carried out to investigate the mechanism responsible for the insertion of lithium in armchair and zigzag nanotubes. The size dependence of the formation energy and the Young's modulus was investigated for the placement of a single Li atom. Our simulations showed that the elastic softening of a zigzag nanotube will occur when a single Li atom was placed, and that the lithiated configuration will transform from a crystalline structure to an amorphous structure with increasing Li concentration for both armchair and zigzag nanotubes. Formation energy and voltage analyses also demonstrated that zigzag nanotubes exhibit a much steeper descending trend compared with armchair nanotubes. It was found that, under uniaxial tension, the corresponding fracture strength of a silicon nanotube will decrease with increasing Li concentration, and that the ductility of such a nanotube will be improved greatly with increasing Li concentration, meaning that plastic deformation will occur relatively easily. This understanding of the lithiation mechanisms will provide useful guidelines for the designing of silicon nanotube electrodes in lithium-ion batteries.