Temporally and Spatially Resolved Visualization of Electrochemical Conversion: Monitoring Phase Distribution During Lithiation of Magnetite (Fe3O4) Electrodes

Fundamental understanding of transport properties across multiple size regimes is critical for the rational design of electrodes with conversion materials. While recent studies have effectively interrogated mass transport in the conversion material magnetite (Fe3O4), a remaining challenge is to understand how electron and ion transport progress in a thick electrode. To provide insight, this study performs characterization of Li/Fe3O4 electrochemical cells both in situ and operando using synchrotron energy dispersive energy diffraction (EDXRD). In situ EDXRD measurements performed after 14 days of open circuit voltage recovery exhibit phase homogeneity with no observable reaction front for rocksalt formation. Operando EDXRD results clearly reveal that the insertion and conversion reactions associated with lithiation of Fe3O4 initiate at the Li anode interface and propagate as a reaction front through the electrode. The variation between the in situ and operando measurements necessitated the development of ...