Abstract: The invention relates to the preparation of insertion compounds based on manganese oxide, usable as the positive electrode active material in a lithium battery.These compounds in the hatched area of FIG. 1 can be prepared by reacting in the solid state a manganese oxide powder MnO.sub.2 -.beta., having a specific surface below 7 m.sup.2 /g and an average grain size below 10 .mu.m, with a powder of a lithium compound such as Li.sub.2 CO.sub.3 or LiOH, at a temperature of 150.degree. to 500.degree. C. for an adequate time to convert the .beta.-MnO.sub.2 into manganese and lithium oxide having a lacunary or stoichiometric spinel structure.