Most current production electric vehicles (EVs) contain cells within a battery pack or module in order to maintain electrical conductivity, prevent fatigue due to vibrations, and provide efficient cooling. Modules may contain cooling fins, thermistors, foam separators, and repeating frame elements to hold the cells. As the cells expand and contract during cycling, the stresses generated can cause the materials in the battery module to deform and crack. This fatigue can result in a loss of electrical or thermal contact and therefore, decreased range, reduced battery life or loss of function, or a loss of heat transfer fluid which could result in electrical shorts. Therefore, it is critical to properly design modules and packs to properly account for the volume change inherent in these pouch cells.

Currently, empirical mechanical data is used to predict the thickness changes of cells with varying electrode porosities, chemistries, and thicknesses. The ability to relate electrode expansion to electrochemical operation and accurately predict cell volume change would save significant time in experimental efforts as well as material costs. Previously, our group developed a coupled electrochemical and mechanical model that accurately predicts the split between electrode porosity and dimensional changes [1-3]. Here, we employ our model along with lithiation-based particle expansion data for graphite [4], lithium nickel-manganese-cobalt oxide (NMC) [5], and lithium manganese oxide (LMO) [5], to predict the thickness change of a large-format pouch cell used in automotive battery packs. Then, we measured the thickness of the cell as the cell was discharged from .99 to .01 state-of-charge. Figure 1 shows the predicted anode and cathode strain compared to the measured cell displacement divided by the sum of the anode and cathode thicknesses. This method allows battery pack designers to appropriately account for new cell types using electrochemical performance and individual particle-level expansion parameters as inputs. Design considerations, as well as cell level volume changes will be discussed.

References

[1] T. R. Garrick, K. Kanneganti, X. Huang, and J. W. Weidner, “ Modeling Volume Change due to Intercalation into Porous Electrodes”, J. Electrochem. Soc. 2014 volume 161, issue 8, E3297-E3301 (2014).

[2] T. R. Garrick, X. Huang, V. Srinivasan, and J. W. Weidner,”Modeling Volume Change in Dual Insertion Electrodes”, J. Electrochem. Soc. 2017 volume 164, issue 11, E3552-E3558 (2017).

[3] T. R. Garrick, K. Higa, S. Wu, Y. Dai, X. Huang, V. Srinivasan, and J. W. Weidner, “Modeling Battery Performance Due to Intercalation Driven Volume Change in Porous Electrodes”, J. Electrochem. Soc. 2017 volume 164, issue 11, E3592-E3597 (2017).

[4] Louli, A. J., et al. "Volume, pressure and thickness evolution of Li-ion pouch cells with silicon-composite negative electrodes." Journal of The Electrochemical Society 164.12 (2017): A2689-A2696.

[5] Nam, Kyung-Wan, et al. "In situ X-ray diffraction studies of mixed LiMn2O4–LiNi1/3Co1/3Mn1/3O2 composite cathode in Li-ion cells during charge–discharge cycling." Journal of Power Sources 192.2 (2009): 652-659.

[6] D. J. Pereira, J. W. Weidner, and T. R. Garrick, "The Effect of Volume Change on the Accessible Capacities of Porous Silicon-Graphite Composite Anodes." J. Electrochem. Soc. 2019 Volume 166, issue 6, A1251-A1256