Lithium-deficient spinels of formula Li1-xMn2-deltaO4 (x=0.26-0.28) (0 less than or equal to delta less than or equal to 0.04) were synthetized by using a sol-gel method involving dissolution of Mn(acac)(3) (acac = acetylacetonate) and Li2CO3 in propionic acid. Gel pyrolysis produced pure spinel phases of highly uniform particle shape. Various samples were prepared over the temperature range 400-800 degrees C and tested as cathodic materials in 4 and 3 V lithium cells. Differences in composition, lattice microstrain and crystallite and particle size, account for the influence of the firing temperature on the electrochemical behaviour of these materials. The best performance in 4 V cells was exhibited by a sample calcined at 600 degrees C. This spinel delivers a capacity of 105 A h kg(-1), which corresponds to the extraction of over 90% of its lithium content. The cell maintained excellent cyclability at moderate discharge rates. By contrast, the spinels (particularly the low temperature samples) proved unsuitable as cathodes in 3 V cells.