The importance of passive materials in Li-Ion battery electrodes

Kurzfassung

Li-Ion batteries are commonly used in portable electronic devices and state-of-the-art electric vehicles due to their outstanding energy and power density. A typical Li-Ion battery electrode is a porous composite consisting of active material (particle diameter ~10-20 µm), conductive carbon (particle diameter ~100 nm), and polymeric binder. The carbon black and binder form a microporous phase (CB domain) which is distributed in the macro-pores of the active material network and ensures mechanical stability and electrical contact. However, at high current densities, e.g. during fast charging, the transport of Li-ions in the electrolyte is decisive for the performance of the battery cell and the CB domain increases mass transport limitations. Furthermore, it was shown that the production process, e.g. harsh drying conditions cause binder migration to the electrode surface which enhances performance losses1. In our presentation we will show results of pore-scale simulations of Li-Ion batteries2 which additionally take into account the morphology and distribution of the CB domain. In order to assess the effect of the CB domain we performed intensive simulation studies on reconstructions of NMC electrodes with different thickness and density which were created with the help of synchrotron tomography and a 3D stochastic microstructure generator3. The simulations are in quantitative agreement with galvanostatic cycling data and impedance measurements on symmetrical cells4 which are especially advantageous for the characterization of electrode tortuosity. Based on these results different electrode configurations were evaluated regarding their performance improvements at high C-rates. This virtual screening provides material-structure-function relationships which are a helpful tool for the development of improved functional materials and electrochemical devices. Acknowledgement This work has been funded by the ‘Bundesministerium für Bildung und Forschung’ within the project HighEnergy under the reference numbers 03XP0073D, and 03XP0073E. References: 1. Jaiser, S. et al. Investigation of film solidification and binder migration during drying of Li-Ion battery anodes. J. Power Sources 318, 210–219 (2016). 2. Danner, T. et al. Thick electrodes for Li-ion batteries: A model based analysis. J. Power Sources 334, 191–201 (2016). 3. Westhoff, D., Manke, I. & Schmidt, V. Generation of virtual lithium-ion battery electrode microstructures based on spatial stochastic modeling. Comput. Mater. Sci. 151, 53–64 (2018). 4. Landesfeind, J., Hattendorff, J., Ehrl, A., Wall, W. A. & Gasteiger, H. A. Tortuosity Determination of Battery Electrodes and Separators by Impedance Spectroscopy. J. Electrochem. Soc. 163, A1373–A1387 (2016).