A Two-Dimensional Heterogeneous Model of Lithium-Ion Battery and Application on Designing Electrode with Non-Uniform Porosity

Abstract

In this work, a two-dimensional heterogeneous model of lithium-ion battery electrode is developed. The electrode is reconstructed using a non-volume-averaging approach, generating a heterogeneous structure in which solid and liquid phase are characterized separately with respective real spatial occupation and boundaries between them. The heterogeneous model is parameterized using voltage and temperature curves at multiple C-rates. Mass and charge transport in the generated electrodes, coupled with interfacial reactions, are numerically solved. Three cases with different porosity profiles are compared. Without changing the amount of active materials and its particle size distribution, an improvement of rate performance up to 50% is achieved in the case with larger electrode porosity near the electrode-separator interface. Using the heterogeneous model as the benchmark, the precision of the pseudo-two-dimension model of lithium-ion battery electrode, which has been widely adopted in literatures and commercial computational softwares, can be improved by proper parameterization, including using the volume-averaged rather than number-averaged diameter as the negative electrode particle size; using the generated electrode structure, rather than the Bruggeman relationship, to calculate the tortuosity of porous electrodes; and using the size of primary particle, rather than that of the agglomerate, as the particle size at the positive electrode.

Aqueous Manufacturing of Defect-Free Thick Multi-Layer NMC811 Electrodes

“…Considering all electrochemical results, more homogeneous binder distribution and the resulting increase in charge transfer leads to higher discharge capacities in ML cells. In addition, better electrochemical performance roots from a porosity gradient generated inside the cathode -as suggested in literature [30,31].…”

“…Assuming no porosity transition of the base after the second coating, the porosity of the top layer should be 47.5%. According to both Qi et al [30] and Fang et al [31] this lower porosity of the top layer would lead to a decreased cell performance as they suggest an electrode design with an opposite porosity gradient (higher porosity at the top of the electrode with decreasing porosity in the direction of the current collector) to reduce electrode resistance and enhance performance at high C-rates by increasing Li-ion diffusivity. However, the higher observed porosity of the upper layer, as well as the observed bubbles which develop after the second coating is applied, imply that cavities inside the base layer are filled with applied slurry.…”

“…Applying multiple layers of coating on top of each other can help control film properties in a desired manner. Graded porosity was already investigated and presented as an interesting opportunity in the past [29][30][31][32][33]. Reduction in resistance, a more uniform overpotential distribution, and an increase in diffusivity of Li-ions are affected by establishing low porosity regions near the substrate and areas with high porosity in the vicinity of the separator [29][30][31][32].…”

“…Graded porosity was already investigated and presented as an interesting opportunity in the past [29][30][31][32][33]. Reduction in resistance, a more uniform overpotential distribution, and an increase in diffusivity of Li-ions are affected by establishing low porosity regions near the substrate and areas with high porosity in the vicinity of the separator [29][30][31][32]. However, implementing such a gradient is complicated as several subsequent calendaring steps are necessary, which reduces the expected positive effects [33].…”

A Modeling Framework of Electrochemo-Mechanics of Lithium-Ion Battery: Part I. Impedance Response of Single Particle

“…Among these parameters, we can find the stress effect can strongly influence the estimated value of Li + diffusivity, As an important kinetic parameter for modeling and designing of lithiumion batteries, 40 accurately measuring Li + diffusivity can significantly influence the design process. Several suggestions regarding measuring the Li + diffusivity are given here:…”