A new experiment is proposed for operando acquisition of O K-edge XAS spectra through XRS for sodium-ion battery (SIB) cathode. This would be the first experiment suitable for operando investigation of oxygen-redox behaviour, where we can distinguish the formation of the different oxidized O-species in the corresponding potential windows. We expect that it will specifically support or disprove the current theory on oxygen-redox-active sodium¬¬¬-manganese¬ layered oxides. However, in principle, this experiment also will provide evidence for reaching a unified understanding of oxygen-redox processes in any oxygen-redox-active materials and therefore is of high interest for the whole rechargeable battery community.