In the presented proposal, we plan post-mortem study of evolution of high-entropy cathodes in the processes of all-solid-state-batteries (SSB) operation. Currently we intensively studying structures and performance of high-entropy chlorides (HECls) that are very promising cathode materials for SSBs. In our studies we are focusing on cubic Li-based spinel-type HECls with Li2[Me2+]Cl4 (Me2+ - Fe, Co, Ni, Mn, Zn and Mg) general composition. Within our previous ESRF experimental section (A20-1-885, September 2024) we studied structural (EXAFS) and chemical (XANES) aspects of these pristine materials. In the proposed study we will go inside of structural and chemical evolution of Li2[Me2+]Cl4 HECls upon their cycling as cathodes in all-solid-state-batteries, especially the oxidation states, and changes in short range structure around d-elements. For that, we plan the series of studies using advanced XANES/EXAFS techniques for a stepwise post-mortem analysis of these materials.