The relationship between charge transport and structural transformations dictates the properties of electrochemical systems. Despite their importance, the reduction–oxidation (redox) reactions within dynamically coexisting structures have so far eluded direct operando investigation. Here, we use resonant X-ray scattering to select X-ray spectra of a crystal structure coexisting with a different structure during a redox-induced phase transformation in P2-Na2/3Ni1/3Mn2/3O2. The spectra of the P2 structure become static midway through the sodium extraction in an operando coin cell, while the overall desodiation proceeds. The coincident emergence of the O2 structure reveals the rigid link between the local redox and the long-range order in this archetypal sodium-ion battery material. Structure-selective X-ray spectroscopy thus opens a powerful avenue for resolving the dynamic chemistry of different structural phases in multistructure electrochemical systems.