(Invited) Modeling the Volume and Porosity Change of Lithium-Ion Cells Due to Lithium Intercalation and External Compression
Authors: Durdel Axel , Brehm Johannes , Elender Valentin , Aufschläger Andreas , Altmann Maximilian , Kotter Philip , Jossen Andreas 
Published: December 2024

Active materials in lithium-ion batteries experience (de-)intercalation-induced volumetric work during cycling [1]. This volumetric work causes a change in coating thickness, porosity, or both [2]. These changes influence the effective transport pathways of lithium ions in the electrolyte, which in turn impact the electrochemical performance of the battery [3], posing a major challenge developing high-performance and long-lasting batteries.

The interplay between volumetric work and external compression depends on the mechanical properties such as Young’s modulus of the anode, the separator, and the cathode. In addition, external compression during battery pack assembly with either free, fixed, or spring-loaded boundary conditions [4] must be considered, as they impact the layer thickness and porosity differently.

Here, we present a novel p2D-mechanical modeling approach to predict the electrochemically induced volume change and subsequent local porosity change of lithium-ion cells under various scenarios of external compression. The model combines physics-based electrochemical processes using the Doyle-Fuller-Newman model [5] with poro-elastic mechanical deformation. The model is parametrized and fitted using experimental data obtained from approx. 5 mAh laboratory cells as well as 5 Ah pouch cells and large format 70 Ah prismatic cells. Preliminary results regarding cell voltage as well as stack thickness change are promising and show satisfying overlap with experimental data. The model predicts a reversible change in porosity during cycling of approx. 5%-points in the anode and 1.7%-points in the cathode, due to different stiffnesses and dilation behaviors of the electrodes. The decrease in anode porosity increases polarization and thus impacts the local anode potential, increasing the risk for lithium plating.

Overall, the bi-directionally coupled system reveals the underlying electrochemical and mechanical interplay that leads to the volume change, which can help design novel cells structures or operating strategies like fast charge profiles, both including realistic mechanical boundary conditions. Our study demonstrates the potential of the p2D modeling approach in predicting the complex electrochemical-mechanical behavior of lithium-ion cells, which can significantly accelerate the development of high-performance and long-lasting batteries for various applications. Especially with increasing silicon content in Si/C blend anodes, the impact of volume expansion and subsequent porosity change will become ever more important to account for in future.

References:

[1]

Franz B. Spingler et al., Electrochemically Stable In-Situ Dilatometry of NMC, NCA and Graphite Electrodes for Lithium-Ion Cells Compared to XRD Measurements (2021), Journal of The Electrochemical Society, Vol. 168 040515

[2]

Parthasarathy M. Gomadam and John W. Weidner, Modeling Volume Changes in Porous Electrodes (2005), Journal of The Electrochemical Society, Vol. 153 A179

[3]

Sara Taslimi Taleghani et al., A Study on The Effect of Porosity and Particles Size Distribution on Li-Ion Battery Performance (2017), Journal of The Electrochemical Society, Vol. 164 E3179

[4]

Verena Müller et al., Effect of Mechanical Compression on the Aging and the Expansion Behavior of Si/C-Composite|NMC811 in Different Lithium-Ion Battery Cell Formats (2019), Journal of The Electrochemical Society, Vol. 166 A3796

[5]

Marc Doyle, Thomas F. Fuller and John Newman, Modeling of Galvanostatic Charge and Discharge of the Lithium/Polymer/Insertion Cell (1993), Journal of The Electrochemical Society, Vol. 140 1526

Figure 1