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, Mo4O11, that has a structure comprising only corner-connected MoO4 tetrahedra and MoO6 octahedra. We show that an electrode formed using micrometer-sized particles of Mo4O11 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 high-rate electrode materials to those beyond the expected Nb-containing shear-phase oxide materials.