First Principles Method for Predicting Lithiation-Induced Volume Change and Open Circuit Voltage of NCM Cathode Materials

Abstract density functional theory in the Vienna Ab Initio Simulation Package (VASP), and van der Waals dispersion-corrected functionals, was applied to compute open circuit voltage (OCV) vs. x, volume change ∆V% vs x, and ∆V% vs OCV for seven NCM (LiNixCoyMn1-x-yO2) cathode materials; NCM811, NCM721, NCM622, NCM523, NCM111, NCM361, and NCM271. The method is based upon two main assumptions for an isolated electrode particle: (1) free volumetric change during lithiation/de-lithiation, (2) single crystal with partial lithium (Li) occupancy (no other defects). Both fully and partially occupied NCM structures were initially constructed with the structure enumeration algorithm for input to VASP. A down-selection process for the partially occupied structures was then employed via “convex hulls” which map the formation energy vs. x where x is state of lithiation (0.0≤x≤1.0). Structures whose formation energies fall on the convex hull were then selected for the volume change predictions. Results were compared with available experimental data from the literature with generally good agreement although disparities between predicted ∆V% vs. OCV and experimental data were found to increase with decreasing state of lithiation.