Investigating the Electronic and Magnetic Properties of Na$_x$Fe$_{1/2}$Mn$_{1/2}$O$_2$ Cathode Materials with X-ray Compton Scattering

TL;DR

This study investigates the electronic and magnetic changes in Na$_x$Fe$_{1/2}$Mn$_{1/2}$O$_2$ cathodes during sodiation using advanced scattering and modeling techniques, revealing oxygen's key role in redox and conductivity.

Contribution

It provides new insights into the redox mechanism and electronic structure evolution of Na$_x$Fe$_{1/2}$Mn$_{1/2}$O$_2$ during battery operation, highlighting oxygen's active participation.

Findings

Oxygen 2$p$ orbitals drive the redox process.

Transition-metal 3$d$ electrons become more delocalized at certain sodiation levels.

Oxygen magnetization confirms oxygen's role in electrochemical activity.

Abstract

We discuss electronic and magnetic properties of Na$_x$Fe$_{1/2}$Mn$_{1/2}$O$_2$, 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 Compton profiles of sodiated and desodiated samples, we show that oxygen 2$p$ orbitals drive the redox process, while transition-metal 3$d$ 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 oxygen magnetization, confirm the important role of oxygen in the electrochemical activity of the cathode.