High capacity microporous molybdenum-vanadium oxide electrodes for rechargeable lithium batteries

Microporous Mo_2.5+yVO_9+δ with channels defined by seven-membered rings of corner-sharing MO₆ (M = Mo^5+/6+ or V^4+/5+) octahedra belongs to the family of isostructural MoVNbTeO compounds, which are very active and selective oxidation catalysts for light alkanes. The large open channels which can accommodate small ions, together with the redox properties of Mo_2.5+yVO_9+δ, make this material of potential interest as a rechargeable intercalation electrode. Microcrystalline Mo_2.5+yVO_9+δ was synthesized by hydrothermal reaction of (NH₄)₆Mo₇O ₂₄·4H₂O and VOSO₄·nH₂O and exists in the composition range -0.13 ≤ y ≤ 0.05. The electrochemical properties of Mo_2.5+yVO_9+δ were investigated in Li/1 M LiPF₆ in ethylene carbonate (EC) and dimethyl carbonate (DMC)/Mo_2.5+yVO_9+δ cells. When the cells are discharged between 3.9 and 1.5 V vs Li/Li⁺, up to 6 Li⁺ ions per formula unit are electrochemically inserted into the framework. Upon recharge, all of the Li⁺ ions can be extracted with minimal structural rearrangement. Unit cell dimensions for Li_xMo _2.5+yVO_9+δ (0 < x ≤ 6) phases prepared by chemical lithiation with n-BuLi have been determined by powder X-ray analysis and are closely related to those of the parent Mo_2.5+yVO _9+δ phase with orthorhombic Pba2 symmetry. Lithium cells of Mo_2.5+yVO_9+δ are rechargeable and exhibit a reversible capacity exceeding 300 mAh/g making Mo_2.5+yVO _9+δ a potential electrode material for secondary lithium batteries.