Vanadium K-Edge X-ray Absorption Spectroscopy as a Probe of the Heterogeneous Lithiation of V₂O₅: First-Principles Modeling and Principal Component Analysis

Abstract

Understanding the diffusion mechanisms of Li ions through host materials and the resulting phase evolution of intercalated phases is of paramount importance for designing electrode materials of rechargeable batteries. The formation of lithiation gradients and discrete domains during intercalation leads to the development of strain within the host material and is responsible for the observed capacities of most cathode materials being well below theoretically predicted values. Such mesoscale heterogeneity has also been implicated in the loss of capacity upon cycling. Due to their inherent complexity, the analysis of such heterogeneity is rather complex and precise understanding of the evolution of metal sites remains underexplored. In this work, we use phase-pure, single-crystalline V 2 O 5 nanowires with dimensions of 183 ± 50 nm and lengths spanning tens of microns as a model cathode material and demonstrate that V K-edge Xray absorption near-edge structure can be used as an effective probe of the local valence and geometry of vanadium sites upon lithiation. We demonstrate that a highly lithiated phase is nucleated and grows at the expense of a homogeneous low-lithiumcontent α-phase without mediation of a solid-solution with intermediate lithium content. Density functional theory calculations allow for assignment of the pre-edge feature to dipolar transitions that are particularly sensitive to the V 3d−O 2p hybridization of the vanadyl bond and the local geometry of the distorted [VO 5 ] square pyramid. The quantitative analysis of multiple vanadium sites and their evolution as a function of Li-ion content provides insight into the mechanism of phase evolution and the nature of lithiation gradients. The phase coexistence and segregation is further observed in scanning transmission X-ray microscopy images of individual lithiated V 2 O 5 nanowires. The mechanisms and the dynamics of nucleation and growth unraveled here are of great importance for the design and discovery of Li-ion cathode materials.

Understanding the electrochemical reaction mechanism of VS2 nanosheets in lithium-ion cells by multiple in situ and ex situ x-ray spectroscopy

“…More specifically, the intensity of the feature located at ~516 eV continuously decreases during discharge upon discharge, and therefore the spectral shape change mainly occurs at the low energy region of the L3-edge. [40][41] At the end of charge back to 3.0 V, the V L-edge line shape (spectrum H) is not fully recovered to that of pristine VS2. These observations, consistent with the V K-edge XAS results, indicate that the redox reaction of V is only partially reversible during the first cycle, which explains the low Coulombic efficiency observed in the electrochemical results.…”

Transport properties of electron small polarons in a V2O5 cathode of Li-ion batteries: a computational study

“…26,39 In addition, several experimental and computational works have extensively been studied and reported evolution of atomic and electronic structures of various V 2 O 5 phases upon lithiation in the context of cathode materials for Li-ion batteries. 26,27,[38][39][40][41] For the sake of completeness, in this work, we re-examined the atomic and electronic structures of polaron formation in V 2 O 5 to ensure the validity of our computations. We considered the formation of an electron polaron in two different situations, i.e.…”

“…Our calculated results are consistent with those obtained from the recent studies that the character of split-off conduction band has been identied through an interpretation of X-ray absorption near-edge structure (XANES) spectra and time-dependent DFT calculations. 38,74 The electronic structures (PDOS) of the electron-doped and the lithiated systems are very similar. Their key features of the polaronic states are identical as illustrated through the position of the localized gap state of 1 electron at the V 3d xy , Fig.…”

“…[32][33][34][35][36][37] The geometrical and electronic structures among Li x V 2 O 5 phases are different leading to variation of the charge transport mechanisms in the materials. 27,38 As illustrated in a computational study, the calculated polaron migration barriers are varied in different Li x V 2 O 5 phases as a-Li 0.083 V 2 O 5 ($0.34 eV), 3-Li 0.083 V 2 O 5 ($0.37 eV), and z-Li 0.083 V 2 O 5 ($0.24 eV). 39 In addition, the phase transformation upon lithiation can bring about dislocations at the interface between the parent lattice and the Li-rich phase.…”

Ultra‐Thin Manganese Dioxide‐Encrusted Vanadium Pentoxide Nanowire Mats for Electrochromic Energy Storage Applications

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is relatively inexpensive and eco-friendly material that exhibits outstanding theoretical capacitance values with a distinct electro-polychromism. [18] Constructing the thin film-based EESD electrodes needs a critical selection of components. The main hindrance in V 2 O 5 electrode usage for potential commercial applications is their electrochemical instability, write-erase stability, and trapping-related degradations.

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