R-Nb₂O₅ has an ‘idealized’ V₂O₅ structure and Wadsley–Roth-like structural stability during Li-ion battery cycling

Abstract

R-Nb2O5 has minimal structure changes with cycling and symmetric cycling profiles. With Wadsley–Roth ‘slabs’ and an ‘idealized’ V2O5 structure, metastable R-Nb2O5 bridges understanding of two well-studied families of Li-ion battery electrodes.

Chemical and Structural Factors Affecting the Stability of Wadsley–Roth Block Phases

“…The Wadsley–Roth family of crystal structures is adopted by a wide variety of early transition metal oxides containing Ti, V, Nb, Ta, Cr, Mo, and W. Many Wadsley–Roth phases are promising anode materials for Li-ion batteries due to their ability to intercalate Li ions at high rates and at low voltages. ,,,− ,,,,,,− They are also important for structural applications as they are formed by many of the early transition metals of multiprinciple element refractory alloys. Their open crystal structures, however, make them unsuited as protective oxide scales for corrosive or high-temperature structural applications, and strategies are desired to suppress their formation in favor of more dense and protective oxide scales.…”

Redox Mechanisms upon the Lithiation of Wadsley–Roth Phases

“…The corresponding zero Kelvin voltage curves, relative to a lithium metal reference electrode, are shown in (c) and (d). The experimental voltage curves for the E­[2 × ∞ ] (R-Nb 2 O 5 ) and E 1 [4 × 4] (N-Nb 2 O 5 ) forms of Nb 2 O 5 were measured by Parui et al . and Lian et al, respectively.…”

“…Figure c illustrates the T[3 × 3] structure of PNb 9 O 25 , which has phosphorus cations (P 5+ ) residing in tetrahedral sites. , Also shown in Figures d and e are two very different Wadsley–Roth structures that can be adopted by Nb 2 O 5 . The E­[2 × ∞ ] structure shown in Figure d, known as R-Nb 2 O 5 , consists of 2 × ∞ corner-sharing octahedral blocks − and is the stable polymorph of γ-Ta 2 O 5 , , while the E 1 [4 × 4] structure shown in Figure e consists of 4 × 4 blocks shifted relative to each other by one octahedral spacing and is an important polymorph of Nb 2 O 5 . This polymorph is also known as N-Nb 2 O 5 . ,− …”

Rapid and Reversible Lithium Insertion in the Wadsley–Roth-Derived Phase NaNb13O33

“…Wadsley–Roth compounds are characterized by m × n blocks of corner-sharing MO 6 octahedra joined by edge-sharing octahedra in “shear” planes, as first described by Roth in 1965. , Unlike one-dimensional shear structures and layered vacancy-ordered Wadsley–Roth derivatives that exhibit relatively poor capacity retention upon electrochemical cycling, − Wadsley–Roth phases exhibit good stability upon repeated lithium (de)­intercalation because of the structural rigidity and minimal volume expansion imparted by the shear planes. ,− Moreover, a combination of experimental and computational studies on Wadsley–Roth phases have provided evidence for rapid, quasi-one-dimensional lithium diffusion down parallel octahedral block channels paired with facile interchannel hopping, which helps to redistribute lithium and prevent blockages. ,, This combination of long-range diffusion and short-range redistribution accounts for the extremely high lithium diffusion coefficients reported for Wadsley–Roth electrodes, which are on par with those of lithium-conducting solid electrolytes. ,, Additional studies have shown good electronic conductivity in Wadsley–Roth phases once they are partially reduced by either oxygen loss or lithium insertion. ,,− This rapid intercalation behavior has been observed in micrometer-scale particles, indicating that Wadsley–Roth phases do not require nanostructuring for high-rate performance.…”

“… 9 , 10 Unlike one-dimensional shear structures and layered vacancy-ordered Wadsley–Roth derivatives that exhibit relatively poor capacity retention upon electrochemical cycling, 22 − 24 Wadsley–Roth phases exhibit good stability upon repeated lithium (de)intercalation because of the structural rigidity and minimal volume expansion imparted by the shear planes. 18 , 25 − 28 Moreover, a combination of experimental and computational studies on Wadsley–Roth phases have provided evidence for rapid, quasi-one-dimensional lithium diffusion down parallel octahedral block channels paired with facile interchannel hopping, which helps to redistribute lithium and prevent blockages. 26 , 29 , 30 This combination of long-range diffusion and short-range redistribution accounts for the extremely high lithium diffusion coefficients reported for Wadsley–Roth electrodes, which are on par with those of lithium-conducting solid electrolytes.…”