Using EPR of Mn4+, the microstnlcture of Li1+xMn2-xO4 with 0 less than or equal tox less than or equal to0.33 obtained from lactate precursors and by a solid state reaction has been compared. It has been shown that the microstructure of ex-lactate Li4Mn5O12 is similar to that of the sample obtained by a solid state reaction at 400 degreesC: in addition to the statistically distributed Mn4+ and Li;, there are regions where Li- ions tend to segregate, For 0 less than or equal tox less than or equal to0.1, thermal decomposition of Li-Mn lactate precursors at 450 degreesC in air yields vacancy-rich spinels, in which the excess Mn4+ and the corresponding metal vacancies are randomly distributed. For annealed at 750 degreesC ex-lactate Li1+xMn2-xO4, the spinel microstructure depends on the temperature regime of sample cooling and on the lithium content x. The procedure for the preparation of stoichiometric Li1-xMn2-xO4 with 0 less than or equal tox less than or equal to0.1 and a homogeneous cation distribution from lactate precursors has been specified. (C) 2000 Elsevier Science B.V. All rights reserved.