High-Rate Lithium Cycling and Structure Evolution in Mo4O11

Shear-phase early transition metal oxides, mostly of Nb, andcomprising edge- and corner-shared metal-oxygen octahedra have seen aresurgence in recent years as fast-charging, low-voltage electrodes for Li+-ionbatteries. 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 onlycorner-connected MoO4tetrahedra and MoO6octahedra. We show that anelectrode formed using micrometer-sized particles of Mo4O11as the active materialcan function as a high-rate Li+-ion electrode against Li metal, with a stable capacityof over 200 mAh g-1at the high rate of 5C.OperandoX-ray diffraction (XRD),entropic potential measurements, andex situRaman spectroscopy are employed tounderstand the nature of the charge storage. The crystal structure dramaticallychanges upon thefirst lithiation, and subsequent cycling is completely reversiblewith low capacity fade. It is the newly formed and potentially more layered structure that demonstrates high-rate cycling and smallvoltage polarization. A space group and unit cell for the new structure is proposed. Thisfinding expands the scope of candidate high-rate electrode materials to those beyond the expected Nb-containing shear-phase oxide materials.

Automated summary

Mo4O11 has been studied as a fast-charging electrode in Li-ion batteries. It demonstrates high-rate cycling and low capacity fade due to its newly formed layered structure.