The lithium–manganese-oxide spinels with different δ values (from 0 to 0.20) were obtained by sol–gel method and studied using XRD, TGA/SDTA, DSC and electrical conductivity measurements. Transformation of the initial gels to spinel structure results in a strong exothermic effect in SDTA measurement. It was shown that well-crystallized spinel structures with cationic defects Li1−x Mn2−2x O4, are formed after calcination at 300°C (low-temperature spinel). Evolution of oxygen during thermal treatment of the low-temperature spinel was controlled by TGA/SDTA methods. Three stages of this transformation were distinguished and one of them was irreversible. The electrical conductivity of the spinels correlates with thermal properties and phase changes in the spinels.