With the ongoing transformation to e-mobility, lithium all-solid-state batteries are promising candidates for advanced mobile energy storage. Other than in conventional lithium-ion cells, the rigid solid electrolyte entails its own morphology and does not wet residual voids in composite electrodes, which can limit the cell performance. We therefore take a closer look at the influence of microstructural characteristics on different scales in composite cathodes by means of electrochemical simulation using the finite element method. Cathode active material particle arrangements are constructed to validate the model against experimental data. We highlight the significance of the active material particle size distribution and state-of-charge dependent input parameters, such as the lithium diffusion coefficient in NCM811 and the exchange current density at the interface of NCM811 and Li6PS5Cl. We zoom in on that interface under the presence of void space which can result from manufacturing or arise from inter-particle contact loss upon volume changes. In a 1-particle-void model, the impact of the active surface area covered by voids is studied as well as the influence of the void distribution and the void size on the electrochemical performance. Beyond that, we simulate a tortuosity-optimized structured electrode and provide first guidelines for laser-patterned all-solid-state cathodes.
We present a spectral approach to perform nanoindentation simulations using three-dimensional nodal discrete dislocation dynamics. The method relies on a two step approach. First, the contact problem between an indenter of arbitrary shape and an isotropic elastic half-space is solved using a spectral iterative algorithm, and the contact pressure is fully determined on the half-space surface. The contact pressure is then used as a boundary condition of the spectral solver to determine the resulting stress field produced in the simulation volume. In both stages, the mechanical fields are decomposed into Fourier modes and are efficiently computed using fast Fourier transforms. To further improve the computational efficiency, the method is coupled with a subcycling integrator and a special approach is devised to approximate the displacement field associated with surface steps. As a benchmark, the method is used to compute the response of an elastic half-space using different types of indenter. An example of a dislocation dynamics nanoindentation simulation with complex initial microstructure is presented.
Aluminum sheets used for beverage cans show a significant anisotropic plastic material behavior in sheet metal forming operations. In a deep drawing process of cups this anisotropy leads to a non-uniform height, i.e., an earing profile. The prediction of this earing profiles is important for the optimization of the forming process. In most cases the earing behavior cannot be predicted precisely based on phenomenological material models. In the presented work a micromechanical, texture-based model is used to simulate the first two steps (cupping and redrawing) of a can forming process. The predictions of the earing profile after each step are compared to experimental data. The mechanical modeling is done with a large strain elastic visco-plastic crystal plasticity material model with Norton type flow rule for each crystal. The response of the polycrystal is approximated by a Taylor type homogenization scheme. The simulations are carried out in the framework of the finite element method. The shape of the earing profile from the finite element simulation is compared to experimental profiles.
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