Why Charge Rate Capability Tests Fail to Characterize Structured Electrodes in Lithium-Ion Batteries and How to Modify Them

Fast charging is one of the most essential criteria for the user acceptance of battery electric vehicles. Especially for high-loaded electrodes used in automotive applications, the rate capability is limited due to the transport limitations of lithium ions in the pores. 1 Electrode structuring is a powerful tool to overcome those limitations by creating additional directed diffusion channels for lithium ions. 2 Despite the frequently described reduction of the transport limitation of lithium-ion batteries, 3 there are hardly any charge rate capability tests in the literature that demonstrate the improvement through structuring. Instead, most studies present discharge rate capability tests showing the desired performance increase due to structuring. 4-8 This study will explain why charge rate capability tests fail to characterize electrodes in the transport-limiting C-rate range. For this purpose, graphite anodes underwent “structure calendering”, where electrodes are simultaneously mechanically structured and calendered using an embossing roller. Thus, identical electrode properties, except for the lower tortuosity, can be achieved compared to the non-structured graphite anodes that were only calendered. Despite their different tortuosities, we will show that structured and non-structured graphite anodes exhibit minimal capacity differences in the charge rate capability test. This is attributed to lithium plating, which shifts the anode potential to similar values, regardless of the transport properties of the investigated electrode. We will modify the test to characterize the charge rate capability of electrodes in the transport-limiting regime where lithium plating occurs. For this purpose, in the charge rate capability test, the current is superimposed with a sinusoidal signal and the voltage response is measured. This allows the continuous estimation of the cell impedance during charging. Previous studies have shown that this method allows to track the onset of the lithium plating reaction. 9-10 Applying the modified charge rate capability test will demonstrate that this detrimental side reaction occurs significantly later in structured electrodes. Günter, F. J., & Wassiliadis, N. (2022). State of the Art of Lithium-Ion Pouch Cells in Automotive Applications: Cell Teardown and Characterization. Journal of The Electrochemical Society , 169 (3), 030515. https://doi.org/10.1149/1945-7111/ac4e11 Pfleging, W. (2017). A review of laser electrode processing for development and manufacturing of lithium-ion batteries. Nanophotonics , 7 (3), 549–573. https://doi.org/10.1515/nanoph-2017-0044 Mai, W., Usseglio-Viretta, F. L. E., Colclasure, A. M., & Smith, K. (2020). Enabling fast charging of lithium-ion batteries through secondary-/dual- pore network: Part II - numerical model. Electrochimica Acta , 341 , 136013. https://doi.org/10.1016/j.electacta.2020.136013 Keilhofer, J., Schaffranka, L., Wuttke, A., Günter, F., Hille, L., Dorau, F., & Daub, R. (2023). Mechanical Structuring of Lithium‐Ion Battery Electrodes Using an Embossing Roller. Energy Technology . https://doi.org/10.1002/ente.202200869 Dubey, R., Zwahlen, M. D., Shynkarenko, Y., Yakunin, S., Fuerst, A., Kovalenko, M. V., & Kravchyk, K. V. (2021). Laser Patterning of High-Mass-Loading Graphite Anodes for High-Performance Li-Ion Batteries. Batteries and Supercaps , 4 (3), 464–468. https://doi.org/10.1002/batt.202000253 Habedank, J. B., Kriegler, J., & Zaeh, M. F. (2019). Enhanced Fast Charging and Reduced Lithium-Plating by Laser-Structured Anodes for Lithium-Ion Batteries. Journal of The Electrochemical Society , 166 (16), A3940–A3949. https://doi.org/10.1149/2.1241915jes Habedank, J. B., Kraft, L., Rheinfeld, A., Krezdorn, C., Jossen, A., & Zaeh, M. F. (2018). Increasing the Discharge Rate Capability of Lithium-Ion Cells with Laser-Structured Graphite Anodes: Modeling and Simulation. Journal of The Electrochemical Society , 165 (7), A1563–A1573. https://doi.org/10.1149/2.1181807jes Hille, L., Xu, L., Keilhofer, J., Stock, S., Kriegler, J., & Zaeh, M. F. (2021). Laser structuring of graphite anodes and NMC cathodes – Proportionate influence on electrode characteristics and cell performance. Electrochimica Acta , 392 , 139002. https://doi.org/10.1016/j.electacta.2021.139002 Koseoglou, M., Tsioumas, E., Ferentinou, D., Jabbour, N., Papagiannis, D., & Mademlis, C. (2021). Lithium plating detection using dynamic electrochemical impedance spectroscopy in lithium-ion batteries. Journal of Power Sources , 512 (September), 230508. https://doi.org/10.1016/j.jpowsour.2021.230508 Straßer, A., Adam, A., & Li, J. (2023). In operando detection of Lithium plating via electrochemical impedance spectroscopy for automotive batteries. Journal of Power Sources , 580 (July), 233366. https://doi.org/10.1016/j.jpowsour.2023.233366