Superlattice formation in the lithiated vanadium oxide phases Li(0.67)V(6)O(13) and LiV(6)O(13)

Two new lithiated phases of V(6)O(13) 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)V(6)O(13) was obtained at 308 K with a unit cell three times the volume of the original V(6)O(13) cell. A single crystal discharged at ambient temperature was shown to be LiV(6)O(13) and twice the unit-cell volume of the original V(6)O(13) cell. On lithiation, the structures retain their basic V(6)O(13) structure of alternating single and double layers of VO(6) octahedra. The lithium ions occupy chemically equivalent sites, where they coordinate fivefold to O atoms, and associate with the single layers of VO(6) 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 A; this is due to the charge reduction of a specific V atom.