The development and optimization of solid-state batteries with nickel-manganese-cobalt (NMC) electrodes require an understanding of complex processes at different scales. This deliverable presents two modeling approaches at the mesoscopic and atomistic scales: mesoscopic modeling of secondary NMC electrode particles and modeling of lithium (Li) diffusion through solid-state electrolytes. For the mesoscopic modeling of bulk cathode material, which addresses transport, stresses/strains, and volume expansion, a high-fidelity model of the secondary NMC electrode particle was developed. The model provides a consistent virtual representation of the particle's morphology, consisting of numerous single crystalline primary particles. This approach enables the variation of transport properties, such as the diffusion constant of Li within the NMC crystal structure, based on the orientation of the individual primary particles. Additionally, the governing equations incorporate standard stress-strain contributions to the weak residual of the elastomechanic equilibrium equation, the influence of boundary stresses where natural boundary conditions apply, and the chemical contributions to stress. This coupling offers significant insights into the morphology and interactions of particles with the solid-state electrolyte, which importantly impact the efficiency, capacity, and cycle life of the battery. The complex governing equations were formulated in the weak form and solved using the finite element method (FEM) through the Gridap package within the Julia programming language. The results show the model’s capabilities to model transport phenomena, i.e. diffusion of Li inside the inhomogeneous particle during (de)lithiation process. Furthermore, by including the elastomechanics part in the governing equations, the swelling of the particle was also modelled. For the mesoscopic model for interfacial phenomena and Li transport through the solid-state electrolyte, the Nudged Elastic Band (NEB) method within the CP2K framework models Li diffusion was used which allowed calculation of precise diffusion pathways and energy barriers to understand atomic-level ion transport mechanisms. The study of Li diffusion through the solid-state electrolyte revealed the intricate nature of the transport process and the decomposition products of solid-state electrolyte. The high ionic nature and favourable structure of LiCl make it a promising candidate for improving Li diffusion, while Li2S presents challenges due to its susceptibility to phase transformations and structural distortions. This scale-bridging approach allows the knowledge gained at the lower scales to be upscaled to models at higher scales, such as models of elementary electrochemical cells and system-level models of battery packs, thereby improving their accuracy and predictive capabilities.
Jan et al. (Fri,) studied this question.