Diana Lucia Quintero-Castro

The tunnel-structured metastable polymorph ζ-V2O5 has emerged as a promising insertion host for alkali and multivalent ions, yet the mechanisms governing Na-ion storage remain poorly understood. Here, we combine single-crystal and powder, operando X-ray diffraction, neutron scattering, and ex situ X-ray absorption spectroscopy techniques with electrochemical measurements to elucidate Na-ion insertion and structural evolution in ζ-V2O5. Topochemical sodium insertion is limited to approximately 0.27 Na per formula unit, with Na ions initially occupying split seven-coordinate β sites while preserving the tunnel framework. Electrochemical sodiation accesses higher Na-ion stoichiometries and reveals a sequential filling mechanism involving β, β′, and C sites concomitant with Na-ion redistribution and reversible structural distortions. Despite the larger size of Na ions in comparison to Li ions, the tunnel framework remains intact throughout cycling and is recovered upon desodiation. Operando diffraction and X-ray absorption spectroscopy reveal that approximately 0.3 Na per formula unit remains trapped after the first discharge process, thereby pillaring and stabilizing the framework. The preinserted pillared phase enables subsequent reversible Na-ion storage. The ability to reversibly insert both Li and Na ions in ζ-V2O5 provides the rare opportunity to contrast ion insertion and migration mechanisms. Comparison of lithiation and sodiation mechanisms in ζ-V2O5 demonstrates distinct differences in the thermodynamics and kinetics of ion insertion despite similar insertion sites and ion mobility. These findings provide mechanistic understanding of sodium storage in metastable ζ-V2O5 and establish design principles for robust tunnel-type cathodes for Na-ion and dual-ion batteries.

Low-dimensional materials manifest structural anisotropy, quantum confinement, and tightly bound excitonic states, which make them attractive building blocks that can be assembled within three-dimensional laterally stitched heterostructures, stacked van der Waals solids, and complex moiré superlattices. Ion intercalation in the galleries between layered materials provides a means of modifying interlayer separation and coupling, but it is also known to drive the shearing of the layers. In this article, we explore the distinct ligand coordination environments afforded by vanadyl oxygens of singular [V₄O₁₀] sheets and examine how the size, polarizability, and stoichiometry of Group I cations sandwiched between such layers determine the interlocking of the sheets in stacked structures. Based on the topochemical insertion of alkali-metal ions into the layered λ-V₂O₅, we identify seven types of guest ion coordination sites discretized into four distinct regimes of interlayer shear in units of half octahedral widths. The coordination preferences of intercalated cations govern how they interlock 2D [V₄O₁₀] sheets and engender specific shear conformations. We present evidence that static and dynamic disorder in guest ion arrangement modulate the magnetic structure of the intercalated compounds based on electrostatic polarization, localization of charge and spin density, and lattice distortion. The results illustrate the use of topochemical ion insertion to modulate stacking relationships and magnetic transition characteristics.

Pauflerite β-VOSO₄ has recently been identified as a one-dimensional S = ½ Heisenberg system, of interest both from a fundamental point of view and a potential material for future spintronics applications. The observation of diffuse scattering in a synthetic β-VOSO₄ provides a microscopic interpretation of the underlying correlated disorder, which is linked to the inversion of the short–long V—O distance pairs along VO₆ chains, forming a local defect state. Direct Monte Carlo modeling indicates that such defects form thin layers with a positive inter-layer correlation, forming small domains with inverted vanadyl bonding patterns. Two-dimensional defects in anisotropic magnetic systems may perturb, or even destroy, long-range magnetic ordering leading to unusual interactions. In particular, the lack of inversion symmetry in the defect layers opens up the possibility for the Dzyaloshinskii–Moriya interaction (DMI) and, consequently, chiral magnetism localized in the defect planes. The defect β-VOSO₄ structure, therefore, opens up new possibilities for the study of low-dimensional magnetic systems.