Lithium manganese oxide particles have been produced with an average diameter less than about 250 nm. The particles have a high degree of uniformity. The particles can be formed by the heat treatment of nanoparticles of manganese oxide. Alternatively, crystalline lithium manganese oxide particles can be formed directly by laser pyrolysis. The lithium manganese oxide particles are useful as active materials in the positive electrodes of lithium based batteries. Improved batteries result from the use of uniform nanoscale lithium manganese oxide particles.