Thanks to their high voltage and delivered capacity, Li-rich transition metal (TM) oxide positive electrode (cathode) materials are among the most promising for next-generation lithium-ion-batteries, where Co-free Li-rich cathodes join reduced costs with competitive performance. However, their cycle-life remains limited, and the individual role of TMs is still not fully understood. The investigation of the TM chemical species’ evolution along the first charge for Li1.2Mn0.56Ni0.16Co0.08O2 and Li1.2Mn0.6Ni0.2O2 has been accessed by means of operando multi edge XAS. The charge compensation mechanism has been studied and the effect induced by removing Co has been revealed. The absence of Co results in an accelerated and completed Ni oxidation along the first stage of charge and an inhibited formation of the undesired spinel phase and oxygen release at the end of the high voltage plateau. Interestingly, the oxygen release in the Co-containing material involves mainly the oxygen close to the Mn site and occurs while local structural interlayer re-arrangements are taking place.