Mario Valvo

Fe3O4 is a conversion-type anode material with high storage capacity that suffers from limited cycling performance. Nanosizing Fe3O4 is one promising strategy to enhance its cycling stability and overall electrochemical performance; however, the details of particle size dependent reaction kinetics remain poorly understood. We investigate the conversion reactions of bulk- and 50 nm-sized cubic Fe3O4 particles as active material using a multi-technique approach, by combining operando XRD, SAXS and magnetometry techniques. The results from the operando XRD and SAXS indicate that during initial lithiation reaction, the bulk electrode undergoes phase reduction with amorphization and formation of metallic iron nanograins, whereas the nanoparticle Fe3O4 retains its ccp oxygen anion framework throughout the lithiation process, hindering structural breakdown and amorphization and delaying the the growth of metallic iron nano grains. Operando vibrating sample magnetometry isused to cross-check the transformation and presence of metallic iron nanodomains owing to its unique sensitivity to local structural details hidden in conventional XRD. The reaction products were found to differ when time-resolved investigations are compared to ex-situ prepared specimens. These results highlight the critical importance of integrating complementary operando techniques to ex situ methods, to capture particle size–dependent lithiation pathways and relaxation mechanisms in conversion-type electrodes.

Due to their high potential energy storage, magnetite (Fe₃O₄) nanoparticles have become appealing as anode materials in lithium-ion batteries. However, the details of the lithiation process are still not completely understood. Here, we investigate chemical lithiation in 70 nm cubic-shaped magnetite nanoparticles with varying degrees of lithiation, x = 0, 0.5, 1, and 1.5. The induced changes in the structural and magnetic properties were investigated 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 concentration (x_c), which is determined to be between 0.5< x_c ≤ 1 for Fe_3-δO₄. Diffraction and magnetization measurements clearly show the formation of the antiferromagnetic LiFeO₂ phase. Upon lithiation, magnetization measurements reveal an 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 distributions involved in the lithiation process. Correlating magnetic and structural properties opens the path to increasing the understanding of the processes involved in a variety of nonmagnetic applications of magnetic materials.

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.

The magnetic properties of spinel nanoparticles can be controlled by synthesizing particles of a specific shape and size. The synthesized nanorods, nanodots and cubic nanoparticles have different crystal planes selectively exposed on the surface. The surface effects on the static magnetic properties are well documented, while their influence on spin waves dispersion is still being debated. Our ability to manipulate spin waves using surface and defect engineering in magnetic nanoparticles is the key to designing magnonic devices. We synthesized cubic and spherical nanoparticles of a classical antiferromagnetic material Co₃O₄ to study the shape and size effects on their static and dynamic magnetic proprieties. Using a combination of experimental methods, we probed the magnetic and crystal structures of our samples and directly measured spin wave dispersions using inelastic neutron scattering. We found a weak, but unquestionable, increase in exchange interactions for the cubic nanoparticles as compared to spherical nanoparticle and bulk powder reference samples. Interestingly, the exchange interactions in spherical nanoparticles have bulk-like properties, despite a ferromagnetic contribution from canted surface spins.

The necessity for large scale and sustainable energy storage systems is increasing. Lithium-ion batteries have been extensively utilized over the past decades for a range of applications including electronic devices and electric vehicles due to their distinguishing characteristics. Nevertheless, their massive deployment can be questionable due to use of critical materials as well as limited lithium resources and growing costs of extraction. One of the emerging alternative candidates is potassium-ion battery technology due to potassium’s extensive reserves along with its physical and chemical properties similar to lithium. The challenge to develop anode materials with good rate capability, stability and high safety yet remains. Iron oxides are potentially promising anodes for both battery systems due to their high theoretical capacity, low cost and abundant reserves, which aligns with the targets of large-scale application and limited environmental footprint. However, they present relevant limitations such as low electronic conductivity, significant volume changes and inadequate energy efficiency. In this review, we discuss some recent design strategies of iron oxide-based materials for both electrochemical systems and highlight the relationships of their structure performance in nanostructured anodes. Finally, we outline challenges and opportunities for these materials for possible development of KIBs as a complementary technology to LIBs.