Simulation of Li-Plating in Si/Graphite Composite-Electrodes

Kurzfassung

It is a common perception that the demand for high-performance batteries is constantly increasing. While the primary characteristics depend on the application, decisive criteria are energy density, safety, cost, and sustainability of the batteries. Here, Li-ion batteries play a key role especially for electric vehicles and portable electronics. How-ever, additional improvements are needed, for example, to achieve sufficient driving ranges. The per-formance characteristics of the batteries such as high energy or power density can be tuned by the electrode microstructure, composition, or choice of materials. At the negative electrode, Si compounds are mixed with graphite to increase the practical specific energies. On the one hand, Si exhibits a high theoretical capacity and is very abundant. On the other hand, Si shows a large volume expansion and low Li mobility. In order to increase the cycle life of Si containing electrodes, it is critical to trace the degradation processes responsible for their performance loss. One major aging mechanism causing fast degradation and fundamental safety risks is lithium plating. The deposition of a metallic lithium phase on the surface of Si/graphite anodes is barely studied in the literature yet crucial to improve the performance and safety of state-of-the-art Li-Ion batteries. In our contribution we present results of a homogenized model of a Si/Graphite composite electrode including models for plating on representative graphite [1] and Si particles. Moreover, we include the volume changes during lithiation and delithiation of representative Si particles and the effect on transport processes [2]. The model serves as a starting point to understand Li plating in Si containing electrodes and, eventually, the design of better Si/graphite composite-electrodes. [1] Hein et.al., ACS Appl. Energy Mater. 2020, 3, 8519−8531, DOI: 10.1021/acsaem.0c01155 [2] Chandrasekaran et. al., J Electrochem Society 2010, 157, A1139-A1151, DOI: 10.1149/1.3474225