Topochemically De-Intercalated Phases of V₂O₅ as Cathode Materials for Multivalent Intercalation Batteries: A First-Principles Evaluation

Abstract

The scarce inventory of compounds that allow for diffusion of multivalent cations at reasonable rates poses a major impediment to the development of multivalent intercalation batteries. Here, we contrast the thermodynamics and kinetics of the insertion of Li, Na, Mg, and Al ions in two synthetically accessible metastable phases of V2O5, ζ- and ε-V2O5, with the relevant parameters for the thermodynamically stable α-phase of V2O5 using density functional theory calculations. The metastability of the frameworks results in a higher open circuit voltage for multivalent ions, exceeding 3 V for Mg-ion intercalation. Multivalent ions inserted within these structures encounter suboptimal coordination environments and expanded transition states, which facilitate easier ion diffusion. Specifically, a nudged elastic band examination of ion diffusion pathways suggests that migration barriers are substantially diminished for Na- and Mg-ion diffusion in the metastable polymorphs: the predicted migration barriers for Mg ions in ζ-V2O5 and ε-V2O5 are 0.62–0.86 and 0.21–0.24 eV, respectively. More generally, the results indicate that topochemically derived metastable polymorphs represent an interesting class of compounds for realizing multivalent cation diffusion because many such compounds place cations in “frustrated” coordination environments that are known to be useful for realizing low diffusion barriers.

Comparison of Li, Na, Mg and Al-ion insertion in vanadium pentoxides and vanadium dioxides

“…This is consistent with previous works which reported a barrier for Mg diffusion in a-V 2 O 5 of 0.90-1.15 eV. 28,35 The slow Na diffusion is attributed to the large size of Na ions. The slow Mg and Al diffusion can be attributed to the polarization effect of Mg 2+ and Al 3+ and strong Mg-O/Al-O interactions.…”

Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO2 upon Iridium Doping

“…[7][8][9] However, the binary Hf-O energy landscape appears to be much more sparsely populated as compared to the energy landscapes of binary vanadium oxides VO 2 and V 2 O 5 , which are characterized by a multitude of energetically proximate polymorphs. [10][11][12][13][14][15] Considering the d 0 compound V 2 O 5 , several polymorphs with widely varying lengths of V-O bonds, connectivity of vanadiumcentered polyhedra, and stacking of (V 2 O 5 ) sheets are experimentally accessible. [10,12,15,16] Such compounds allow for a broad range of bandgaps and energy dispersion of V 3d-derived bands as well as define starkly different ion conduction pathways with activation barriers that can differ by an order of magnitude.…”

“…[10][11][12][13][14][15] Considering the d 0 compound V 2 O 5 , several polymorphs with widely varying lengths of V-O bonds, connectivity of vanadiumcentered polyhedra, and stacking of (V 2 O 5 ) sheets are experimentally accessible. [10,12,15,16] Such compounds allow for a broad range of bandgaps and energy dispersion of V 3d-derived bands as well as define starkly different ion conduction pathways with activation barriers that can differ by an order of magnitude. [10,16,17] The close energetic proximity of insulating monoclinic and metallic tetragonal phases of vanadium(IV) oxide or VO 2 make this material a canonical system for investigation of metal-insulator transitions; the monoclinic M 1 phase undergoes a pronounced metal-insulator transition (MIT) to the high temperature (R) phase at 65 C. [18] In addition, several other polymorphs are known such as the M 2 polymorph, which is stabilized by strain or chemical pressure; the M 3 phase; metastable VO 2 (A) and VO 2 (B) phases, often accessible from hydrothermal synthesis; and a mineral phase paramontroseite or VO 2 (P).…”

“…[10,12,15,16] Such compounds allow for a broad range of bandgaps and energy dispersion of V 3d-derived bands as well as define starkly different ion conduction pathways with activation barriers that can differ by an order of magnitude. [10,16,17] The close energetic proximity of insulating monoclinic and metallic tetragonal phases of vanadium(IV) oxide or VO 2 make this material a canonical system for investigation of metal-insulator transitions; the monoclinic M 1 phase undergoes a pronounced metal-insulator transition (MIT) to the high temperature (R) phase at 65 C. [18] In addition, several other polymorphs are known such as the M 2 polymorph, which is stabilized by strain or chemical pressure; the M 3 phase; metastable VO 2 (A) and VO 2 (B) phases, often accessible from hydrothermal synthesis; and a mineral phase paramontroseite or VO 2 (P). [19][20][21][22] The ability to access a rich palette of structural motifs with varying connectivity of V-O bonds, tunable linkages of vanadium-centered polyhedra, and reconfigurable stacking of extended sheets has profound implications for the relative extent of ionicity or covalency and allows for broad tunability of transport properties from insulating to semiconducting and metallic regimes.…”

Systematic Transmission Electron Microscopy Study Investigating Lithium and Magnesium Intercalation in Vanadium Oxide Polymorphs

“…The structural model for the ε-Mg0.5V2O5 phase is shown in Fig 1(c). We will also show that the chemically synthesized sample presents the δ-MgV2O5 phase [2].Recent theoretical calculations have also predicted that the migration barrier for ionic intercalation can be decreased by exploiting different anion coordination environments in metastable vanadium oxide polymorphs, such as ζ-V2O5 [3]. Figure 2a) presents atomic-resolution HAADF image for ζ-V2O5 nanowires clearly showing the heavier V atoms and elucidating the tunnel structure for this novel polymorph; a structural model for the ζ-V2O5 phase is presented in Figure 2b).…”