Density Functional Theory Analysis that Explains the Volume Expansion in Prelithiated Silicon Nanowires

Abstract

This research is a theoretical study that simulates the volume expansion of a prelithiated silicon nanowire during lithium-ion insertion and the application of an electric current. Utilizing density functional theory (DFT) the ground state energy Eg (x) of prelithiated silicon (LixSi) is defined as a function of the lithium-ion (Li+) concentration (x). As the Li+ are increased, Eg (x) become increasingly stable from x = 1.00 through x = 2.415 and decrease in stability as the lithium-ion concentration becomes x > 2.415 until full lithiation of the silicon nanowire is reached at x = 3.75. After the determination of the lithiated silicon ground state energies, an electric current is applied to the lithiated silicon nanowire at various Li+ concentrations x. It was discovered that the volume expansion began at approximately x = 3.25 and increased to over 300% of the original volume of a pristine silicon nanowire at x = 3.75 which at this point was full lithiation. This is in sharp contrast to prior research studies where the ground state energy was not considered. In previous studies, the computation of the volume expansion starts approximately at x = 0.75 and produces a continuous nonlinear volume expansion until the process is terminated at full lithiation.