Mesoscale transport-geometry interactions in lithium ion cathode active materials: Particle scale galvanostatic simulations based on X-ray nanotomography data

Abstract

Simulation results of lithium diffusion in Li(Ni1/3Mn1/3Co1/3)O2 under galvanostatic discharge (intercalation) conditions are presented for a set of cathode active material particles imaged using X-ray nanotomography. A range of operating conditions from 0.5C to 10C are considered. Behavior of these real particles is compared to idealized spherical particles on the basis of dimensionless parameters that link particle morphology, lithium diffusion and reaction kinetics. These parameters include the particle sphericity, a mass transfer Biot number and a mass transfer Fourier number. At lower C-rates, lower Biot numbers, and higher sphericities the spherical particle model proves sufficient, and the spherical particle model predicts minimum concentrations within one standard deviation of the average behavior of the particle ensemble that is analyzed. However, at higher C-rates, higher Biot numbers, and intermediate Fourier numbers the spherical particle model significantly overestimates the state of charge in the active material particles, an error that may underestimate lithium available for plating at the anode and state of charge dependent degradation in cathode materials. The results presented highlight a need and means for more accurate assessment of the influence of microstructural geometry on battery performance under aggressive current conditions.