Dry Battery Electrode Manufacturing for Graphite Anodes: Implications on Electrochemical Properties and Cell Manufacturing

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Dry Coating of Lithium-Ion Battery electrodes is widely considered as a gamechanger technology to reduce the cost, energy demand and footprint of battery Gigafactories. By now, industrialization has primarily focused on the negative electrode using graphite and as active material, notably by Tesla.[1] Yet, the full scope of the implications and advancements brought by a dry coating process for graphite anodes on cell properties and downstream manufacturing processes remains unexplored.Current dry coating technologies necessitate using a fibrillizable PTFE binder. While PTFE is very stable towards oxidation when used as a binder in Lithium-Ion Battery cathodes, a reduction of the fluoropolymer in battery anodes at low potentials < 1 V vs. Li/Li+ is reported.[2] We discuss the decomposition reaction of PTFE in graphite anodes during the formation process and the resulting irreversible consumption of Li. Our interest focuses on the decomposition mechanism of PTFE, examining the nature of the decomposition products through XPS analysis. We assess whether the reduction is quantitative and if the decomposition persists beyond the initial lithiation of graphite into subsequent cycles. We contemplate strategies to reduce the irreversible capacity loss and show that reducing the PTFE binder content while maintaining the mechanical integrity of the electrode is a promising approach to enhance the coulombic efficiency during formation.Beyond the electrochemical implications, differences in microstructural properties and the processing conditions during electrode manufacturing between a wet and a dry coated graphite anode offer opportunities for adaptions in the downstream process of Lithium-Ion Battery manufacturing. We demonstrate that the electrolyte filling time of cylindrical cells in a 4695-format is strongly influenced by the coating method and the arising differences in pore size distribution and electrode tortuosity. Also, we show that a vacuum drying of the anodes might not be needed if the electrode is dry coated instead of using water as the solvent for a slurry-based coating.[1] https://www.youtube.com/watch?v=8WPPBhqeekw[2] Y. Suh, J. K. Koo, H. Im, Y.-J. Kim, Chemical Engineering Journal 2023, 476, 146299.