All-solid-state lithium ion batteries are promising due to high safety and energy density, but suffer from fatigue caused by mechanical stresses. Based on an experimental microstructure of a mixed cathode (LiCoO2/Li7La3Zr2O12: LCO/LLZO), we calculated the thermal stresses after manufacturing and the electrochemical stresses after charging to study the impact of microstructural parameters (LCO contents and relative density) on the stresses yielding a stress-optimised structure. Here, these stresses in complex cathode materials and their homogeneity will be measured including the two different stress components of manufacturing and charging. In addition, the stress development over the electrochemical cycling will be measured which will confirm the role of stresses in the degradation behaviour in traditional and optimised cells. This will be the first direct crystallographic stress measurement and it will help to overcome a remaining main issue of these batteries.