Elucidating the lithiation process in Fe3–δO4 nanoparticles by correlating magnetic and structural properties

Due to their high potential energy storage magnetite (Fe3O4) nanoparticles have become appealing for anode materials in lithium-ion batteries. However, the details of the lithiation process are still not completely understood. Here, we investigate chem- ical lithiation in 70 nm cubic shaped magnetite nanoparticles with varying degree of lithiation x = 0, 0.5, 1, 1.5. The induced changes on the structural and magnetic properties were investigated by using X-ray techniques along with electron microscopy and magnetic measurements. The results indicate that a structural transformation from spinel to rock salt phase occurs above a critical limit for the lithium concentra- tion (xc), which is determined to be between 0.5< xc≤1 for Fe3–δO4. Magnetization measurements clearly shows the formation of the LiFeO2 phase with its distinct anti- ferromagnetic behaviour below its Need temperature. Upon lithiation, magnetization measurements reveal exchange bias in the hysteresis loops with an asymmetry, which can be attributed to the formation of mosaic-like LiFeO2 subdomains. The combined characterization techniques enabled us to unambiguously identify the phases and their distribution involved in the lithiation process. Correlating magnetic and structural properties opens the path to increase the understanding of the processes involved in a variety of non-magnetic applications of magnetic materials.