Diffraction studies of relaxation processes in cathode materials for Li-ion batteries

Li-ion batteries are the leading technology for electrochemical energy storage, but there are still processes occurring inside the battery, that are not understood, both during cycling and when the battery is resting. One of these processes is the relaxation of the active materials when the cycling is stopped and the battery is resting, which we recently have shown for graphite (Figure 1). It is very likely that similar processes occur for many different battery materials where metastable phases relax into more stable phases as soon as the electrochemistry is paused. These relaxations could occur differently at different cycling rates, and at different state of charge. Studying these processes is crucial for increasing our understanding of data from so called “post mortem” studies in which material is extracted from batteries after stopping cycling. We plan to study the relaxation processes in well-known battery materials like NMC811, NMC611 and NCA at different cycling rates.