Investigating Lithium-Ion Behavior in Defective Graphite Via Non-Equilibrium Molecular Dynamics and Density Functional Theory

Abstract

The thermodynamic, kinetic and mechanical properties of graphite as negative electrodes for lithium-ion batteries have been systematically studied by combining nonequilibrium molecular dynamics (NEMD) simulation with density functional theory (DFT) calculations in this paper. It was investigated that lithium intercalation properties with Stone-Wales (SW), single vacancy (SV) and double vacancy (DV) defects change when defect density ranges from 0% to 10%. Furthermore, the results indicate that the ranking of defect reconstruction in graphite is as follows: SW (density 0.24%-0.64%) > SV (density 0.64%-0.8%) > DV (density > 0.8%). In addition, it was found that the diffusion of lithium ions (DLi) at different concentrations is affected during the same defect concentration (density≤0.4%). Specifically, at the initial of charging (Li0.02C6), the DLi decreases to 28%~62% of that of perfect graphite, while at the final stage of charging (LiC6), the DLi increases to 200%~300% of perfect graphite. Moreover, it is also found that the mechanical properties of lithium intercalated graphite decrease with increasing defect density when the defect density is ≤ 0.4%. Therefore, it is essential that precise control of defect concentration of graphite negative to optimize the performance of lithium-ion batteries.

Keywords: Graphite Anode Defect Density Lithium-ion Diffusion Mechanical Properties Defect Engineering