Electrode Mesoscale as a Collection of Particles: Coupled Electrochemical and Mechanical Analysis of NMC

Abstract

Battery electrodes are composed of polydisperse particles and a porous, composite binder domain. These materials are arranged into a complex mesostructure whose morphology impacts both electrochemical performance and mechanical response. We present image-based, particle-resolved, mesoscale finite element model simulations of coupled electrochemical-mechanical performance on a representative NMC electrode domain. Beyond predicting macroscale quantities such as half-cell voltage and evolving electrical conductivity, studying behaviors on a per-particle and per-surface basis enables performance and material design insights previously unachievable. Voltage losses are primarily attributable to a complex interplay between interfacial charge transfer kinetics, lithium diffusion, and, locally, electrical conductivity. Mesoscale heterogeneities arise from particle polydispersity and lead to material underutilization at high current densities. Particle-particle contacts, however, reduce heterogeneities by enabling lithium diffusion between connected particle groups. While the porous composite binder domain (CBD) may have slower ionic transport and less available area for electrochemical reactions, its high electrical conductivity makes it the preferred reaction site late in electrode discharge. Mesoscale results are favorably compared to both experimental data and macrohomogeneous models. This work enables improvements in materials design by providing a tool for optimization of particle sizes, CBD morphology, and manufacturing conditions.

The Concept of Effective Porosity in the Discharge Rate Performance of High-Density Positive Electrodes for Automotive Application

“…Moreover, NA3b, NA7b and NA4b tend to have the same εfit, respectively 12, 11 and 10%. As they have same composition and density, their microporosity is expected to be similar, about 13.6% according to equation (8). This trend of slightly decreasing εfit values with increased thickness (active mass loading) is somehow expected.…”

“…The second approach uses numerical simulation and seeks to take into account all the phenomena and properties [7]. It has the great advantage of being able to study a multiplicity of electrode designs, because it has now become possible to create virtual electrodes of realistic microstructure [8] and even integrating the influence of the elaboration process [9]. The first approach is more tedious, time consuming, and risky.…”