The reaction mechanisms during calcination of a Li2CO3/Co3O4 mixture in air and CO2 were monitored by thermogravimetry, differential thermal analysis and complementary calcinations at 300 and 500 degrees C. It was determined how weight reduction, specific surface area and the formation of phases develop. Below 400 degrees C the main process is the decomposition of CoCO3. Formation of LiCoO2 starts above 400 degrees C but at high O-2 partial pressures some Li2CO3 seems to react already at 300 degrees C.