Material Parameters affecting Li Plating in Si/Graphite Composite Electrodes

Abstract

The global demand for high-performance batteries continues to grow. While the primary characteristics depend on the application, the key criteria are energy density, safety, cost, and sustainability of the batteries. Lithium-ion batteries play a key role, especially for electric vehicles and portable electronics. Silicon, a favored active material in negative electrodes, promises significant improvements in energy density. However, it suffers from large volume changes during cycling, necessitating its combination with graphite. Understanding the electrochemical and mechanical interactions of composite materials is key to optimizing battery performance and predicting aging phenomena. Even though lithium plating is a critical degradation process affecting both lifetime and safety, a systematic analysis of material parameters affecting plating in composite electrodes is missing. We present a comprehensive parameter study of Si/Graphite composite materials employing 3D microstructure-resolved simulations. The underlying model implemented in BEST [1] describes transport processes within lithium-ion batteries as well as the formation of the metallic lithium phase on the surface of active material particles [2,3]. We investigate the influence of critical material parameters such as open circuit voltage, electronic conductivity, chemical diffusion coefficient, and exchange current density on the onset and quantity of deposited metallic lithium in simple and interpretable model geometries consisting of Si and graphite particles. The simulations reveal the importance of chemical diffusion and exchange current density, as well as their ratio, in predicting plating. Finally, the set of material parameters is applied to a complex electrode geometry reconstructed from FIB/SEM tomography data of commercial LG INR21700-M50T anode material. In our study we analyse the spatial distribution of plated lithium for different operating conditions. In conclusion, this study highlights the importance of understanding material parameters in composite electrodes for mitigating plating and enhancing battery performance. Moreover, it underscores the role of simulations in unravelling complex electrochemical processes, paving the way for future advancements in battery technology. The authors would like to acknowledge the funding by the German Federal Ministry of Education and Research (BMBF) of the projects CharLiSiKo (03XP0333C) and MiCha (03XP0317B) within the AQua-Cluster managed by Projektträger Jülich (PTJ). [1] Fraunhofer Institute for Industrial Mathematics (ITWM), BEST - Battery and Electrochemistry Simulation Tool, https://www.itwm.fraunhofer.de/best [2] A. Latz and J. Zausch, J. Power Sources. 2011, 196, 3296–3302, DOI: 10.1016/j.jpowsour.2010.11.088 [3] Hein et. al., ACS Appl. Energy Mater. 2020, 3, 8519−8531, DOI: 10.1021/acsaem.0c01155