Extracting the redox orbitals in Sodium-ion battery cathodes using x-ray Compton scattering

Abstract

The reduction oxidation (Redox) process in sodium-ion batteries is the process of sodium conduction electrons transferring from the anode of the battery to the Nax[Fe1/2Mn1/2]O2 cathode. The exact mechanisms of the Redox process are not yet fully understood. There are three possible locations for an electron leaving the valence orbital of Na: Fe, Mn, or O. Compton scattering is a spectroscopy technique that allows extracting of information about the atomic orbitals from the Compton profiles. Both orbital occupation and range (delocalization) are considered. The orbital delocalization parameter is extracted from experimental data using a weighted least squares regression model minimized by the fmincon Matlab command. These models suggest that the electron goes to the oxygen 2p orbital rather than the iron or manganese valence 3d orbitals. While iron and manganese 3d orbitals do not have any changes in occupation, the models suggest that some electrons in the 3d orbitals delocalize for both of these elements.