Thick electrodes for Li-Ion batteries: A model based analysis

Kurzfassung

Li-Ion batteries are commonly used in portable electronic devices due to their outstanding energy and power density. A remaining issue which hinders the breakthrough e.g. in the automotive sector is the high production cost. Going ‘giga’ is one solution which is currently pursued by Tesla but requires large investments. Recently, novel battery concepts were presented as an interesting alternative1. Batteries with thicker electrodes (>300 µm) allow to attain high energy densities with only a few electrode layers which reduces production time and cost1,2. However, mass and charge transport limitations can be severe at already small C-rates due to long transport pathways2,3. Novel design and operation strategies of the battery and its components are needed to mitigate these issues. In our contribution we present 3D micro-structure resolved simulations of thick (electrodes > 300µm) Graphite-NMC batteries based on our thermodynamically consistent modeling framework BEST4. The parametrization and validation of our model is presented in a recent publication3 and simulation results agree favourably with experimental data2. Electrode micro-structures are either taken from tomography data provided in the literature5 (NMC) or virtual electrode realizations generated with a stochastic approach6 (graphite). Based on the validated model we evaluate the influence of inhomogeneities in electrode composition and structure. Furthermore, we investigate the effect of different solvents and Li salt concentrations on battery performance. In our simulations we find improved energy densities at elevated concentrations which is counter-intuitive taking into account the nominal decrease in transport parameters. Finally, we will explore different structuring strategies of thick electrodes such as layering and laser perforation. First results indicate that a laser treatment of the electrode layers will improve the rate capability of the battery. Our detailed 3D studies allow important insights on cell operation and are able to predict improved electrode structures and electrolyte formulations. The activities are performed within the BMBF project HighEnergy which investigates the opportunities and processing techniques for Li-ion batteries with high areal loading of active material. References: 1. Hopkins, B. J. et al. Component-cost and performance based comparison of flow and static batteries. J. Power Sources 293, 1032–1038 (2015). 2. Singh, M. et al. Thick Electrodes for High Energy Lithium Ion Batteries. J. Electrochem. Soc. 162, A1196–A1201 (2015). 3. Danner, T. et al. Thick electrodes for Li-ion batteries: A model based analysis. J. Power Sources 334, 191–201 (2016). 4. Latz, A. et al. Multiscale modeling of lithium ion batteries: thermal aspects. Beilstein J. Nanotechnol. 6, 987–1007 (2015). 5. Ebner, M. et al. X-Ray Tomography of Porous, Transition Metal Oxide Based Lithium Ion Battery Electrodes. Adv. Energy Mater. 3, 845–850 (2013). 6. Westhoff, D. et al. Parametric stochastic 3D model for the microstructure of anodes in lithium-ion power cells. Comput. Mater. Sci. 126, 453–467 (2017).