Thermal, electrochemical and structural properties of stabilized LiNi_yCo_1-y-zM_zO₂ lithium-ion cathode material prepared by a chemical route

Layered compounds, such as LiNiO₂ and LiCoO₂ have been extensively studied as active cathodic materials in lithium-ion batteries. Mixed oxides having general formula LiNi_yCo_1-yO₂ represent a good compromise between the limited cyclability of LiNiO₂ and the high cost of LiCoO₂. However, recent studies have demonstrated that LiNi_yCo_1-yO₂ compounds are thermally unstable in their charged state, undergoing exothermic reactions that might cause thermal runaway and safety concern. The stability of the compounds may be greatly controlled by doping with a suitable metal, M = Al, Mg. In this work we further investigate the role of the doping metal on the thermal, electrochemical and structural characteristics of the LiNi_yCo_1-y-zM_zO₂ electrode materials. These materials were prepared using a soft chemistry route, to achieve the proper control of the chemical homogeneity and of the microstructural properties of the final samples. The thermal behavior of the doped LiNi_yCo_1-y-zM_zO₂ where M = Al, was studied using differential scanning calorimetry. The structural properties upon cycling were investigated by a recently, in-house developed, in situ energy dispersive X-ray diffraction (EDXD) technique. The reversibility and rate capabilities of the cathodes in lithium cells were characterized using electrochemical equipment.