Strategies to Improve Energy and Power Density of Li-Ion Batteries By Virtual Electrode Design

Abstract

Li-ion batteries are commonly used in portable electronic devices due to their outstanding energy and power density. However, in order to reach the requirements of the automotive industry for next-generation electric vehicles regarding safety, life-time, energy density, and fast charging further developments are inevitable. Additionally, a reduction of material and production costs is needed to improve the price competitiveness. In this contribution we will present a study of different electrode design concepts with the goal to optimize energy and power density of Li-Ion battery electrodes and cells by microstructure resolved electrochemical simulations [1]. State-of-the-art NMC positive electrodes with different thickness and density were prepared and characterized electrochemically in collaboration with our partners [2]. In a next step reconstructions of the electrodes were created with the help of synchrotron tomography and a 3D stochastic microstructure generator [3], [4]. The resulting microstructures are then input to electrochemical simulations within our software BEST and good qualitative agreement between the simulations and experimental data can be reported. Especially, the pivotal role of inactive materials for battery performance could be demonstrated through microstructure-resolved impedance simulations. Based on these results different design concepts were evaluated regarding their energy and power density. An attractive strategy to decrease the share of inactive materials is to increase the mass loading of the electrodes [5], [6]. This concept provides a high theoretical capacity and energy density. However, it also shifts the transport limitations of shuttling lithium ions in the electrolyte to lower C-rates and reduces the rate capability and practical capacity of the cell [6], [7]. In order to enable a fast charging of the batteries structuring techniques are investigated. A promising concept is the laser perforation of the electrodes which creates a hierarchical pore network with macroscopic transport pathways between anode and cathode. Our simulations confirm the beneficial effects which are found in the experiments and we perform an extensive simulation study in order to investigate the effect of different hole geometries and configurations on battery performance and life time. Our study shows that this simulation-based approach is a powerful and efficient tool for the analysis and design of porous electrodes for Li-ion batteries. Acknowledgement This work has been funded by the ‘Bundesministerium für Bildung und Forschung’ within the project HighEnergy under the reference numbers 03XP0073D. References: [1] A. Latz and J. Zausch, “Multiscale modeling of lithium ion batteries: thermal aspects,” Beilstein J. Nanotechnol., vol. 6, pp. 987–1007, 2015. [2] H. Y. Tran, C. Täubert, and M. Wohlfahrt-Mehrens, “Influence of the technical process parameters on structural, mechanical and electrochemical properties of LiNi0.8Co0.15Al0.05O2 based electrodes - A review,” Prog. Solid State Chem., vol. 42, no. 4, pp. 118–127, 2014. [3] D. Westhoff et al., “Parametric stochastic 3D model for the microstructure of anodes in lithium-ion power cells,” Comput. Mater. Sci., vol. 126, pp. 453–467, 2017. [4] S. Hein, J. Feinauer, D. Westhoff, I. Manke, V. Schmidt, and A. Latz, “Stochastic microstructure modeling and electrochemical simulation of lithium-ion cell anodes in 3D,” J. Power Sources, vol. 336, pp. 161–171, Dec. 2016. [5] B. Delattre, R. Amin, J. Sander, J. De Coninck, A. P. Tomsia, and Y. Chiang, “Impact of Pore Tortuosity on Electrode Kinetics in Lithium Battery Electrodes: Study in Directionally Freeze-Cast LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA),” J. Electrochem. Soc., vol. 165, no. 2, pp. A388–A395, Feb. 2018. [6] M. Singh, J. Kaiser, and H. Hahn, “Thick Electrodes for High Energy Lithium Ion Batteries,” J. Electrochem. Soc., vol. 162, no. 7, pp. A1196–A1201, 2015. [7] T. Danner, M. Singh, S. Hein, J. Kaiser, H. Hahn, and A. Latz, “Thick electrodes for Li-ion batteries: A model based analysis,” J. Power Sources, vol. 334, pp. 191–201, Dec. 2016.