Investigating the electronic and magnetic properties of Na _x Fe_1/2Mn_1/2O₂ cathode materials with X-ray Compton...

We discuss the electronic and magnetic properties of Na _x Fe_1/2Mn_1/2O₂, a promising Na-ion battery cathode material. Using X-ray Compton scattering, SQUID magnetometry, and density-functional-theory-based modeling, we probe how electrons and spins evolve during sodiation. By comparing the Compton profiles of sodiated and desodiated samples, we show that oxygen 2p orbitals drive the redox process, while transition-metal 3d electrons become more delocalized, explaining the metallic phase at x = 2/3. These profile differences define a quantitative descriptor for the sodiation range associated with improved conductivity. Electron holes on oxygen, reflected in the oxygen magnetization, confirm the important role of oxygen in the electrochemical activity of the cathode.