Three-Phase Multiscale Modeling of a LiCoO2 Cathode: Combining the Advantages of FIB-SEM Imaging and X-Ray Tomography

LiCoO2 electrodes contain three phases, or domains, each having specific-intended functions: ion-conducting pore space, lithium-ion-reacting active material, and electron conducting carbon-binder domain (CBD). Transport processes take place in all domains on different characteristic length scales: from the micrometer scale in the active material grains through to the nanopores in the carbon-binder phase. Consequently, more than one imaging approach must be utilized to obtain a hierarchical geometric representation of the electrode. An approach incorporating information from the micro- and nanoscale to calculate 3D transport-relevant properties in a large-reconstructed active domain is presented. Advantages of focused ion beam/scanning electron microscopy imaging and X-ray tomography combined by a spatial stochastic model, validated with an artificially produced reference structure are used. This novel approach leads to significantly different transport relevant properties compared with previous tomographic approaches: nanoporosity of the CBD leads to up to 42% additional contact area between active material and pore space and increases ionic conduction by a factor of up to 3.6. The results show that nanoporosity within the CBD cannot be neglected.