The effect of initial Li:Co ratio, calcination atmosphere, temperature, leaching in H2O or acetic acid solution on reaction completeness, final Li:Co ratio, primary particle size, conductivity and its sensitivity to different atmospheres has been investigated. The calcination gas composition was found to be very important. A powder with a primary particle size of 100-300 nm and with less than 3 wt.% of unreacted Li2CO3 was obtained.