Exploring lithium ion interactions in graphite electrodes through non-equilibrium molecular dynamics and density functional theory

In molecular dynamics (MD) simulations, selecting an appropriate potential function is a crucial element for accurately simulating the kinetic properties of lithium ion intercalation, storage, and diffusion in graphite systems. This work employed a combination of non-equilibrium molecular dynamics (NEMD) and density-functional theory (DFT) for simulation and analysis. The findings indicate that the AIREBO potential function precisely describes the motion of ordered lithium ions between graphite layers, consistent with the models proposed by Rüdorff and Hofmann (R-H) and Daumas and Hérold (D-H). Conversely, for the folded structure within the graphite layer, the Tersoff potential function provides a more suitable description, consistent with the localized-domains model. Further analysis reveals that with increasing Li-ion concentration, the voltage, Young's modulus, and ultimate tensile strength of the Li_xC₆ system exhibit a decreasing trend. Notably, the diffusion coefficient of lithium ions within the graphite layer varies widely, ranging from 10^-6 cm² s^-1 to 10^-16 cm² s^-1. In summary, this work is anticipated to provide further insights into the mechanism of lithium ion intercalation and diffusion kinetics in graphite electrodes. It also serves as a valuable theoretical framework for guiding the design and optimization of high-performance lithium-ion batteries.