► Cr-Mg substituted LiNi0.8Co0.1Mn0.1O2 was synthesized by fast co-precipitation. ► Rietveld refinements show that Cr-Mg substitution suppresses the cation-mixing. ► Cr-Mg substituted samples exhibit superior electrochemical performance. Cr and Mg co-substituted LiNi0.8Co0.1Mn0.1O2 samples are synthesized by fast co-precipitation method and characterized by scanning electron microscope, X-ray diffraction, Rietveld refinement and electrochemical measurements. The Rietveld refinement results show that suitable Cr and Mg co-substitution could lead to synergistic reaction to form a kind of complementary structure, by full Cr occupying in Ni layer, and full Mg occupying in Li layer, respectively, and further attribute to highly ordered layered LiNi0.8Co0.1Mn0.1O2 with low cation mixing degree. Electrochemical studies demonstrate that Cr and Mg co-substitution in LiNi0.8Co0.1Mn0.1O2 also result in improved discharge capacity, initial coulombic efficiency, rate ability and cycling property compared to pristine LiNi0.8Co0.1Mn0.1O2. The improvements of electrochemical property resulted from the stabilized host structure by Cr and Mg incorporation into LiNi0.8Co0.1Mn0.1O2.