Structural and electronic properties of lithiated Si nanowires: An ab initio study

Abstract

Ab initio density-functional theory is used to study the structural changes of a crystalline silicon nanowire during lithiation and delithiation processes. Based on the obtained results quantum transport calculations are performed to shed light on the electrical current flowing at varying lithium concentrations. It is found that inserting lithium atoms into the crystalline silicon system leads to a steplike process, where each Si shell is successively lithiated from the outside. While increasing the Li concentration, the volume of the nanowire quadruples and the silicon network becomes fully amorphous. During delithiation the Li ions are initially homogeneously distributed throughout the nanowire cross section, eliminating the steplike behavior observed in the lithiation cycle. Hereby, the volume of the system decreases to 113% of its initial value, with a small amount of Li ions remaining in the Si network and a loss of storage capacity as a consequence. A simultaneous analysis of the current trajectories within the lithiated nanowires reveals that the main contribution shifts from the center to the surface of the nanostructure as the Li concentration increases.