Process for making an electrode active material for a lithium ion battery, said process comprising the following steps: (a) Contacting a mixture of (A) a precursor of a mixed oxide according to general formula Li 1+x TM 1-x O 2 , wherein TM is a combination of two or more transition metals selected from Mn, Co and Ni, optionally in combination with at least one more metal selected from Ba, Al, Ti, Zr, W, Fe, Cr, K, Mo, Nb, Mg, Naand V, and x is in the range of from zero to 0.2, and (B) at least one lithium compound, with (C) Br 2 , I 2 , or at least one compound selected from carbon perhalides selected from the bromides and iodides, and interhalogen compounds comprising bromine or iodine, and (b) Subjecting said mixture to heat treatment at a temperature in the range of from 700 to 1000°C.