In order to meet consumer demands for lithium-ion battery (LIB) performance, innovative materials are being studied to increase the energy densitiy of the cell. One material in particular is silicon, which exhibits a roughly five times larger theoretical energy density than the state-of-the-art graphite currently used as anode active material. Several studies have been performed by adding small quantities of silicon to the anode, but few investigations are known where the anode exhibits a majority share of silicon.
Multi-layerd pouch-cells with a 70 % silicon content and a capacity of approx. 5 Ah have been manufactured on the pilot line for LIBs at the Institute for Machine Tools and Industrial Management (iwb) of the Technical University of Munich. Besides the high specific capacity, silicon is characterized by a large volume expansion which creates problems such as particle cracking and an increase in electrolyte consumption. These challenges posed by the material were counteracted through the cell design and material characterization, which was the first step of the production. For example, high porosities and a partial lithiation were specifically chosen for the produced cells. Besides a study of the required electrolyte quantity, the effect of a brittle silicon-based anode with a high porosity and low coating thickness became evident along each production step. The timing of the formation with the degassing steps during cell finalization had to be adjusted due to the high gas development. Finally, lifetime cell tests and post-mortem-analyses were performed to provide a complete and holistic insight into the material system. The impact of silicon on key performance indicators like energy density and absolute capacities is evident and will continue to find relevance in the everchanging landscape of battery production.