High-Rate Lithium Cycling and Structure Evolution in Mo₄O₁₁

Abstract

Shear-phase early transition metal oxides, mostly of Nb, and comprising edge-and corner-shared metal−oxygen octahedra have seen a resurgence in recent years as fast-charging, low-voltage electrodes for Li + -ion batteries. Mo oxides, broadly, have been less well studied as fast-charging electrodes.Here we examine a reduced Mo oxide, Mo 4 O 11 , that has a structure comprising only corner-connected MoO 4 tetrahedra and MoO 6 octahedra. We show that an electrode formed using micrometer-sized particles of Mo 4 O 11 as the active material can function as a high-rate Li + -ion electrode against Li metal, with a stable capacity of over 200 mAh g −1 at the high rate of 5C. Operando X-ray diffraction (XRD), entropic potential measurements, and ex situ Raman spectroscopy are employed to understand the nature of the charge storage. The crystal structure dramatically changes upon the first lithiation, and subsequent cycling is completely reversible with low capacity fade. It is the newly formed and potentially more layered structure that demonstrates high-rate cycling and small voltage polarization. A space group and unit cell for the new structure is proposed. This finding expands the scope of candidate highrate electrode materials to those beyond the expected Nb-containing shear-phase oxide materials.

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

“…With operating potentials between 1 V and 1.5 V and excellent rate capabilities, they offer a pathway to safe, highpower Li-ion batteries as alternatives to graphite and Li 4 Ti 5 O 12 . [6][7][8] Wadsley-Roth (WR) materials can also have multielectron redox, in which more than one redox reaction occurs per redox active transition metal, contributing to high energy densities, e.g., reduction of Nb 5+ to Nb 3+ , allowing for storage of >1 mol Li per transition metal, M. 5,[9][10][11][12] In addition to being technologically relevant, WR materials provide a foundation for identifying atomic and electronic structure features that support effective transport of ions and electrons. 9,13,14 WR materials have ReO 3 -like blocks, in which [ MO 6 ] octahedra are corner-sharing (Fig.…”

“…6–8 Wadsley–Roth (WR) materials can also have multi-electron redox, in which more than one redox reaction occurs per redox active transition metal, contributing to high energy densities, e.g. , reduction of Nb 5+ to Nb 3+ , allowing for storage of >1 mol Li per transition metal, M. 5,9–12…”

Molybdenum Oxide Constructed by {Mo6O21}6– Pentagonal Unit Assembly and Its Redox Properties

“…Other than the XRD peaks attributed to α-MoO 3 , XRD peaks derived from the Mo 4 O 11 structure appeared. 39,40 At the same time, new Raman bands attributed to Mo 4 O 11 appeared at 905 and 790 cm −1 in addition to the Raman bands of α-MoO 3 (995, 819, and 666 cm −1 ) (Figure 6D). 41 TPO was then conducted on α-MoO 3 -TPR1.…”

“…The XRD pattern of α-MoO 3 after TPR is shown in Figure C. Other than the XRD peaks attributed to α-MoO 3 , XRD peaks derived from the Mo 4 O 11 structure appeared. , At the same time, new Raman bands attributed to Mo 4 O 11 appeared at 905 and 790 cm –1 in addition to the Raman bands of α-MoO 3 (995, 819, and 666 cm –1 ) (Figure D) . Mo 4 O 11 is composed of the corner sharing between {MoO 6 } octahedral and {MoO 4 } tetrahedral as shown in Figure S11.…”

Reversible Electrochemical Lithium Cycling in a Vanadium(IV)- and Niobium(V)-Based Wadsley–Roth Phase

“…Many more early-TM oxides containing Ti, Nb, Mo, and W have been identified as potential Li-ion anodes. The vast majority of them are Nb-based, such as TiNb 2 O 7 (WR), NbO 2 F (ReO 3 -type), , Nb 3 O 7 F (WR), Nb 16 W 5 O 55 (WR), , Nb 18 W 16 O 93 (TTB), Nb 18 W 8 O 69 (TTB), Nb 2 O 5 polymorphs, and PNb 9 O 25 (WR) .…”