In liquid electrolyte-type lithium-ion batteries, Nickel-rich NCM (Li1+x (Ni1−y−z Co y Mnz)1−x O2) as cathode active material allows for high discharge capacities and good material utilization, while solid-state batteries perform worse despite the past efforts in improving solid electrolyte conductivity and stability. In this work, we identify major reasons for this discrepancy by investigating the lithium transport kinetics in NCM-811 as typical Ni-rich material. During the first charge of battery half-cells, cracks form and are filled by the liquid electrolyte distributing inside the secondary particles of NCM. This drastically improves both the lithium chemical diffusion and charge transfer kinetics by increasing the electrochemically active surface area and reducing the effective particle size. Solid-state batteries are not affected by these cracks because of the mechanical rigidity of solid electrolytes. Hence, secondary particle cracking improves the initial charge and discharge kinetics of NCM in liquid electrolytes, while it degrades the corresponding kinetics in solid electrolytes. Accounting for these kinetic limitations by combining galvanostatic and potentiostatic discharge, we show that Coulombic efficiencies of about 89% at discharge capacities of about 173 mAh gNCM −1 can be reached in solid-state battery half-cells with LiNi0.8Co0.1Mn0.1O2 as cathode active material and Li6PS5Cl as solid electrolyte.

When it comes to energy density, all-solid-state batteries are seen as a promising technology for next-generation electrochemical storage devices. Nevertheless, the performance of all-solid-state cells is still very limited. The reasons are manifold, with insufficient ionic and electronic percolation within the composite cathode being a crucial one. In this work, we investigate percolation characteristics by three-dimensional microstructural modeling with the aim to define and understand boundary conditions for wellpercolating networks. Utilizing spherical active material particles together with convex polyhedra as the solid electrolyte, ionic and electronic conduction clusters are determined and analyzed by means of percolation theory for varying macroscopic parameters, such as composition, porosity, particle size, and electrode thickness. Small active material particles turn out to enhance the effective electronic conductivity, offering high surface areas and thus more possibilities to connect particles, while porosity crucially affects ionic and electronic conduction capabilities. An impact of electrode thickness on the effective electronic conductivity is observed exclusively in thin electrodes, where percolation effects are suppressed implying favorable electrode properties. From microstructural modeling, ideal compositions are derived and guidelines for electrode design are developed at a given porosity and particle size of active material and solid electrolyte.

In the pursuit for future mobility, solid-state batteries open a wide field of promising battery concepts with a variety of advantages, ranging from energy density to power capability. However, trade-offs need to be addressed, especially for large-scale, cost-effective processing, which implies the use of a polymeric binder in the composite electrodes. Here, we investigate three-dimensional microstructure models of the active material, solid electrolyte, and binder to link cathode design and binder content with electrode performance. Focusing on lithium-ion transport, we evaluate the effective ionic conductivity and tortuosity in a flux-based simulation. Therein, we address the influence of electrode composition and active material particle size as well as the process-controlled design parameters of the void space and binder content. Even though added in small amounts, the latter has a strong negative influence on the ion transport paths and the active surface area. The simulation of ion transport within four-phase composites is supplemented by an estimation of the limiting current densities, illustrating that application-driven cell design starts at the microstructure level.