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Battery Electrode Characterization

Lithium ion batteries (LIBs) have become the most important storage medium for electrical energy in mobile devices. The growing importance of electromobility raises the demand for LIBs with high energy density, which are characterized by small internal resistances at high charge/discharge rates. In batteries, porous electrodes containing active material particles for Li+ storage are used to establish a large real surface area for lithium ion intercalation/deintercalation. The interstitial void space is saturated with a liquid or solid electrolyte. The pore space morphology determines the Li+ ion transport pathways and thus the ion transport resistance of the electrode. The effective ionic resistance, in turn, contributes to the overall internal impedance of the battery and therefore influences its power density. Ion transport pathways in a porous medium can be characterized by the diffusive tortuosity τ, a measure for transport limitations in a porous medium compared to unhindered, bulk transport.

We use a reconstruction-simulation approach to determine this ion transport tortuosity in composite and all-solid-state battery electrodes. In particular, we physically reconstruct the electrode microstructure using focused ion-beam scanning electron microscopy (FIB-SEM) and employ this realistic microstructure as geometrical model to simulate the diffusion process under blocking conditions. Results are compared with measurements from electrochemical impedance spectroscopy. This research is conducted in collaboration with Professor Bernhard Roling at our department. The comprehensive characterization will help us improving battery performance in the future.

Figure: Moritz Kroll

Figure 1: Schematic overview of the experimental and the reconstruction-simulation approach.

Highlighted publications:

  • M. Kroll, D. Hlushkou, S. Schlabach, A. Höltzel, B. Roling, U. Tallarek
    Reconstruction–simulation approach verifies impedance-derived ion transport tortuosity of a graphite battery electrode.
    Journal of The Electrochemical Society 2018, 165, A3156–A3163. DOI: 10.1149/2.0711813jes
  • D. Hlushkou, A.E. Reising, N. Kaiser, S. Spannenberger, S. Schlabach, Y. Kato, B. Roling, U. Tallarek
    The influence of void space on ion transport in a composite cathode for all-solid-state batteries.
    Journal of Power Sources 2018, 396, 363–370. DOI: 10.1016/j.jpowsour.2018.06.041