Cation reordering instead of phase transitions: Origins and implications of contrasting lithiation mechanisms in 1D ζ- and 2D α-V ₂ O ₅

Abstract

Substantial improvements in cycle life, rate performance, accessible voltage, and reversible capacity are required to realize the promise of Li-ion batteries in full measure. Here, we have examined insertion electrodes of the same composition (V2O5) prepared according to the same electrode specifications and comprising particles with similar dimensions and geometries that differ only in terms of their atomic connectivity and crystal structure, specifically two-dimensional (2D) layered α-V2O5 that crystallizes in an orthorhombic space group and one-dimensional (1D) tunnel-structured ζ-V2O5 crystallized in a monoclinic space group. By using particles of similar dimensions, we have disentangled the role of specific structural motifs and atomistic diffusion pathways in affecting electrochemical performance by mapping the dynamical evolution of lithiation-induced structural modifications using ex situ scanning transmission X-ray microscopy, operando synchrotron X-ray diffraction measurements, and phase-field modeling. We find the operation of sharply divergent mechanisms to accommodate increasing concentrations of Li-ions: a series of distortive phase transformations that result in puckering and expansion of interlayer spacing in layered α-V2O5, as compared with cation reordering along interstitial sites in tunnel-structured ζ-V2O5. By alleviating distortive phase transformations, the ζ-V2O5 cathode shows reduced voltage hysteresis, increased Li-ion diffusivity, alleviation of stress gradients, and improved capacity retention. The findings demonstrate that alternative lithiation mechanisms can be accessed in metastable compounds by dint of their reconfigured atomic connectivity and can unlock substantially improved electrochemical performance not accessible in the thermodynamically stable phase.

Tunnel-Structured ζ-V2O5 as a Redox-Active Insertion Host for Hybrid Capacitive Deionization

“…ζ-V 2 O 5 has attracted substantial recent attention as a battery positive electrode material owing to its high theoretical capacity (441 mA h/g), outstanding thermal and chemical stability, ability to accommodate Li and Mg ions through reordering of cation occupancies but without distortive phase transitions, low stress accumulation upon cation insertion, and excellent cyclability. 20,30 The ζ-V 2 O 5 polymorph comprises three crystallographically distinct vanadium centers, specifically two distorted VO 6 octahedra interwoven by VO 5 square pyramids, which define a 1D tunnel oriented along the b-axis. 30 19,30,34,35 The prepared nanowires are crystallized in a monoclinic C2/m space group with a β-angle of 110.0°.…”

“…18 In this article, we describe an electrochemical approach for desalination and selective ion capture based on sequestration of ions on surfaces and within the one-dimensional (1D) tunnels of ζ-V 2 O 5 , a versatile intercalation host for monovalent and multivalent ions. 19,20 In conventional capacitive deionization (CDI) techniques, dissolved ions are removed from saline water by the application of a potential across a deionization cell comprising two high-surface-area carbon electrodes. 21−23 In this process, the dissolved ions migrate to electrified interfaces and constitute an electric double layer of solvated ions; the concentration of stored ions is directly proportional to the accessible surface area of the electrodes.…”

“…As such, hybrid capacitive deionization methods hold promise not just for enabling reuse of FPW in hydraulic fracturing operations but also for enabling the extraction of high-value ions . In this article, we describe an electrochemical approach for desalination and selective ion capture based on sequestration of ions on surfaces and within the one-dimensional (1D) tunnels of ζ-V 2 O 5 , a versatile intercalation host for monovalent and multivalent ions. , …”

Crystallographic design of intercalation materials

“…By doing so, they not only tailor its lattice parameters with a precision of ∼ 0.01Å, but also can accurately design a facile structural transformation mitigating its mechanical degradation with repeated use [54,55,53].…”

Multivariate hyperspectral data analytics across length scales to probe compositional, phase, and strain heterogeneities in electrode materials

“…By combining statistical approaches with curated reference spectra, we demonstrate a generalizable approach to composition, phase, and stress mapping, which provides critical insights into modulating battery chemistry and electrode architecture to alleviate common degradation mechanisms. 18 , 34 , 35 …”