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Reducing the stress factor in high-energy silicon/graphite composite electrodes through systematic structuring
Poster Exhibition
Active materials for Lithium-ion batteries

Lithium Ion batteries are the leading technology for energy storage devices such as hybrid, plug-in and all electric vehicles. Intensive efforts have been made to improve the energy density of lithium-ion batteries [1]. The development and application of silicon-containing active material mixtures is a promising for the use in high-capacity anodes. While the use of Si/C composites increases the specific capacity of the anodes the main disadvantage of silicon is its enormous volume expansion during lithiation which can cause cracking and stability loss of the electrode [2]. Consequently, targeted electrode structuring can be a promising approach to create cavities that significantly reduce mechanical stresses by compensating the drastic volume change of silicon during battery operation [3]. Furthermore, the holes shorten lithium-ion pathways and improve lithium-ion diffusion kinetics along the interfacial area. The current state of research to create these cavities is laser-structuring, which has been shown to improve rate capability. However, the process sublimates the active material and the theoretical capacity of the electrode decreases [4, 5].

In the work described here, high-energy lithium-ion battery anodes (8 mAh/cm²) were structured in order to create pores locally in the coating by using an innovative structuring process. In contrast to conventional laser structuring, the novel structuring method injects a fluid into the wet film of the coating. The created pores (<100 µm) extend over the entire thickness (up to 250 µm) of the electrode without loss of active material. Experimental data from structured blend anodes containing Silicon and Graphite are used for the evaluation of this individual method and were compared with unstructured electrodes. Among others, the structured electrodes were characterized by electrochemical impedance spectroscopy (EIS) and further physical tests which enables to show differences between unstructured and structured anodes and allow an initial estimation of the structural properties. Furthermore, electrochemical tests are performed in pouch cells. The different tests reveal that structuring high-energy silicon-graphite anodes can be beneficial for the microstructure in regard to the ionic resistance and electrochemical performance of the electrode. References: [1] Chae, S., Ko, M., Kim, K., Ahn, K., and Cho, J. Confronting Issues of the Practical Implementation of Si Anode in High-Energy Lithium-Ion Batteries. Joule 1, 1, 47–60. (2017). [2] Hatchard, T. D. and Dahn, J. R. In Situ XRD and Electrochemical Study of the Reaction of Lithium with Amorphous Silicon. J. Electrochem. Soc. 151, 6, A838. (2004). [3] Zheng, Y., Seifert, H.J., Shi, H., Zhang, Y., Kübel, C., Pfleging, W.: 3D silicon/graphite composite electrodes for high-energy lithium-ion batteries. Electrochimica Acta 317, 502–508 (2019). [4] Pfleging, W.: A review of laser electrode processing for development and manufacturing of lithium-ion batteries. Nanophotonics 7(3), 549–573 (2018). [5] Habedank, J.B., Endres, J., Schmitz, P., Zaeh, M.F., Huber, H.P.: Femtosecond laser structuring of graphite anodes for improved lithium-ion batteries: Ablation characteristics and process design. Journal of Laser Applications 30(3), 32205 (2018).

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Michael Bredekamp