Dr. Maximilian Mellin, fresh doctor from the SSL studied how the electronic structure of Li–transition-metal oxide cathodes evolves during lithium removal during charging, a key process governing battery performance. By combining X-ray photoelectron spectroscopy with advanced theoretical modeling (DFT+DMFT and CTM) in close collaboration with theory partners Dr. Ruiwen Xie, Prof. Hongbin Zhang (both TU Darmstadt, Theory of Magnetic Materials) and Prof. Frank M. F. de Groot (Utrecht University), we could show that charge compensation during Li deintercalation deviates from a simple rigid-band picture and is governed by changes in transition-metal–oxygen hybridization. The work further demonstrates that transition-metal XPS satellite intensities provide a sensitive experimental fingerprint of cathode redox chemistry, offering a new route to guide the design of improved battery materials.