Mesoscale Effects of Composition and Calendering in Lithium-Ion Battery Composite Electrodes

Abstract

Macrohomogeneous battery models are widely used to predict battery performance, necessarily relying on effective electrode properties, such as specific surface area, tortuosity, and electrical conductivity. While these properties are typically estimated using ideal effective medium theories, in practice they exhibit highly non-ideal behaviors arising from their complex mesostructures. In this paper, we computationally reconstruct electrodes from X-ray computed tomography of 16 nickel–manganese–cobalt-oxide electrodes, manufactured using various material recipes and calendering pressures. Due to imaging limitations, a synthetic conductive binder domain (CBD) consisting of binder and conductive carbon is added to the reconstructions using a binder bridge algorithm. Reconstructed particle surface areas are significantly smaller than standard approximations predicted, as the majority of the particle surface area is covered by CBD, affecting electrochemical reaction availability. Finite element effective property simulations are performed on 320 large electrode subdomains to analyze trends and heterogeneity across the electrodes. Significant anisotropy of up to 27% in tortuosity and 47% in effective conductivity is observed. Electrical conductivity increases up to 7.5× with particle lithiation. We compare the results to traditional Bruggeman approximations and offer improved alternatives for use in cell-scale modeling, with Bruggeman exponents ranging from 1.62 to 1.72 rather than the theoretical value of 1.5. We also conclude that the CBD phase alone, rather than the entire solid phase, should be used to estimate effective electronic conductivity. This study provides insight into mesoscale transport phenomena and results in improved effective property approximations founded on realistic, image-based morphologies.

3D Quantification of Microstructural Properties of LiNi0.5Mn0.3Co0.2O2 High‐Energy Density Electrodes by X‐Ray Holographic Nano‐Tomography

“…It has been demonstrated by tomography‐based approach as well as experimental measurements (for the case of MCMB AM) to increase with either the non‐spherical AM particles or the calendaring process. [ 59–62 ] A minor tortuosity anisotropy (τ through−plane > τ in−plane ) is reported for NMC electrodes in refs. [ 61,62 ] via simulations using 3D microstructures with numerically‐generated CBD.…”

“…[ 59–62 ] A minor tortuosity anisotropy (τ through−plane > τ in−plane ) is reported for NMC electrodes in refs. [ 61,62 ] via simulations using 3D microstructures with numerically‐generated CBD. The results can be attributed to the roughly spherical geometry of the raw NMC particle.…”

Enhanced Capacity of Lithium Secondary Batteries Using a Li-Powder Anode

“…Flux is proportional to the diffusion coefficient and concentration gradient, according to Fick’s first law. Several studies have been conducted on increasing the diffusion coefficient to improve the Li-ion flux. − However, the diffusion coefficient was the same for both the foil and powder anode cells because the cathode was not modified. Accordingly, the difference in the Li + concentration gradient at the cathode surface between the foil and powder anode cells was investigated by introducing diffusion-limited current density ( i lim ). − The diffusion-limited current density represents the current density when the current is determined by mass transfer rather than charge transfer, considering a region where the overvoltage is significantly high (eq ).…”

“…The capacity of the cell can be increased by improving the Li-ion flux at the cathode interface. To enhance the Li-ion flux, various approaches such as doping, coating, and morphology control have been carried out, in which the Li-ion diffusion coefficient, a parameter of flux according to Fick’s law , − has been improved. The main purpose of the present research is to understand the reason for capacity increase in cells when using a Li-powder anode.…”

Transforming Materials into Practical Automotive Lithium‐Ion Batteries

“…[ 132 ] Bulk effective properties of 3D imaged NMC electrodes across both active material loading fractions and calendering pressures were modeled and predicted by incorporating nanoporous CBD into the particle bed mesostructured. [ 133 ] Specific surface area, tortuosity, electrical conductivity, and elastic modulus were studied with computations performed on 20 large subdomains (representative volume elements) from each of the 16 electrodes. The effect of the calendering process on the wettability of anode electrodes was investigated.…”