Superlattice formation in the lithiated vanadium oxide phases Li0.67V6O13 and LiV6O13

Two new lithiated phases of V6O13 were formed by carefully tuning the temperature of electrochemical lithiation in a 'coffee-bag' type Li-ion battery at 2.78 V versus Li/Li+. These were studied by single-crystal X-ray diffraction. A phase with the composition Li-2/3 V6O13 was obtained at 308 K with a unit cell three times the volume of the original V6O13 cell. A single crystal discharged at ambient temperature was shown to be LiV6O13 and twice the unit-cell volume of the original V6O13 cell. On lithiation, the structures retain their basic V6O13 structure of alternating single and double layers of VO6 octahedra. The lithium ions occupy chemically equivalent sites, where they coordinate fivefold to O atoms, and associate with the single layers of VO6 octahedra. The insertion of lithium causes a significant elongation of one of the V-O bonds in each structure, which expands from 1.65 to 1.89 Angstrom; this is due to the charge reduction of a specific V atom.