A process for preparing a mixed metal oxide, usable as the cathode or intercalation electrode in high energy density primary and secondary batteries, having the formula Li.sub.x M.sub.y O.sub.z where M is at least one metal selected from the group consisting of titanium, chromium, manganese, iron, cobalt and nickel, x is a number from about 0.1 to about 1.1, preferably from about 0.9 to about 1.1, y is a total number from about 1.1 to about 0.1, preferably from about 1.1 to about 0.9, respectively, and z is a number from about 1.9 to about 2.1, such as LiCoO.sub.2 or [Li(Co.sub.0.5 Ni.sub.0.5) O.sub.2 ], is comprised by preparing a mixed solution containing x moles of a soluble oxygen-containing salt of lithium and y total moles of soluble oxygen-containing salt(s) of the at least one metal M in a solvent therefor; concentrating the mixed solution; co-crystallizing a mixed salt of lithium and of the at least one metal M from the concentrated mixed solution; and calcining the co-crystallized mixed salt at a low temperature of from about 400.degree. C. to about 500.degree.C. for a short period of time of from about 1 hour to about 4 hours to form the mixed metal oxide.