Understanding Deviations between Spatially Resolved and Homogenized Cathode Models of Lithium‐Ion Batteries

Abstract

Porous electrode models are essential for inexpensively predicting the performance and lifetime of lithium‐ion batteries. Physics‐based models range from microscopic 3D models, which spatially resolve the microstructural characteristics of all phases in porous electrodes, to reduced and computationally effective models, which do not resolve the microstructure. The homogenized Newman model, also known as the pseudo‐2D (P2D) model, is well established and widely used. However, the necessary simplification shows its weaknesses, especially for high charge and discharge rates, and these lead to significant differences in comparison with the microscopic 3D model. Herein, the validity of the homogenized Newman model is investigated with respect to variations of the microstructural characteristics of a porous cathode. The effects of 1) a homogenized conductive additive; 2) non‐spherical particle geometries; and 3) overlapping particles on charge/discharge curves are analyzed. The result is a better understanding of the validity limits of P2D models. These new insights about the individual influences of the simplifications will be used to improve the homogenized model. The simulation of complex cathode structures, where several homogenization assumptions are violated, shows that the improved homogenized model reaches a very high accuracy, and, thus, overcomes the existing limitations of the P2D model approach.

Morphology‐Dependent Influences on the Performance of Battery Cells with a Hierarchically Structured Positive Electrode**

“…First, we assumed diffusion paths to be longer than the primary particle radius by a factor of 1.5. Schmidt et al [22] . suggested this assumption if part of the active material particle surface is blocked.…”

“…First, we assumed diffusion paths to be longer than the primary particle radius by a factor of 1.5. Schmidt et al [22] suggested this assumption if part of the active material particle surface is blocked. This is the case for hierarchically structured electrodes, since the primary particles are sintered together.…”

A continuum of physics-based lithium-ion battery models reviewed

“…Additionally, it resolves each variable in the porous geometry so one can model their spatial distributions (e.g. to describe the ion flow around the particles), and any further reduction of this model can cause deviations in the predicted values [116]. However, this does not mean it is the best model to use in practical applications because it poses two main challenges.…”

“…First, this model is extremely computationally expensive which means that it is not viable for most real applications [116]. On top of that, the full microscale geometry of the battery is required (e.g.…”

Multiphysics Electrochemical Impedance Simulations of Complex Multiphase Graphite Electrodes

“…The simulations were parametrized with measured EIS data in the frequency domain and were validated with charging and discharging processes in the time domain. Nonetheless, nonuniformity in complex electrodes cannot be considered in those macroscopically homogeneous models . Another type of modeling was employed to simulate EIS behavior with physics-based information. − For example, Cho et al used reaction and diffusion that can be analytically calculated for spherical, cylindrical, and platelet particles to obtain the stochastic average EIS behavior of a three-dimensional (3D) complex electrode.…”