Sol–gel derived Li–V–Mn–O spinels as cathodes for rechargeable lithium batteries

Nearly stoichiometric ternary Li–V–Mn–O spinels were prepared by a sol–gel method using propionic acid to form the resin framework, and subsequent calcination of the gel at 600°C. The resulting material was tested as cathode over the voltage range 5.2–2.0 V in lithium cells. The profiles of the discharge–charge processes were found to be surprisingly similar to that recently reported for thin-film LiMn2O4. The results of X-ray photoelectron spectroscopy (XPS) and elemental analysis are consistent with an oxidation state +5 for V and with +3 and +4 for Mn. Although the spinel preserves its basic framework across the whole potential window, significant capacity fading is observed along the 5.0 and 2.0 V plateaus, the latter effect being associated with a reversible cubic–tetragonal phase transition. The best electrochemical performance of the cell was observed in the potential window 4.6–2.5 V. Over this voltage range, the cell maintains an acceptable capacity (105 Ah/K) upon extensive cycling.