Elucidation of synergistic effect of Mg-co-doping on electrochemical performance of Mn-doped LiNiO2

•The Li+/Ni2+ cation mixing can be reduced by Mg co-doping.•The Mg co-doping may suppress the alteration of the lattice volume.•The Mg co-doping has a negligible effect on the interfacial property.•The superior performance of material is further gained via Mg co-doping.•The Mg-Mn co-doping has synergistic effects on stabilizing the LiNiO2 material.