ELECTROCHEMICAL PROPERTIES OF DEFECTIVE LI-1-XMN2-DELTA O-4 SPINELS PREPARED BY A SOL-GEL METHOD USED AS CATHODES IN LITHIUM CELLS

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 syntheti zed by using a sol-gel method involving dissolution of Mn(acac)(3) (ac ac = acetylacetonate) and Li2CO3 in propionic acid. Gel pyrolysis prod uced pure spinel phases of highly uniform particle shape. Various samp les were prepared over the temperature range 400-800 degrees C and tes ted as cathodic materials in 4 and 3 V lithium cells. Differences in c omposition, lattice microstrain and crystallite and particle size, acc ount for the influence of the firing temperature on the electrochemica l 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 o ver 90% of its lithium content. The cell maintained excellent cyclabil ity at moderate discharge rates. By contrast, the spinels (particularl y the low temperature samples) proved unsuitable as cathodes in 3 V ce lls.