Studies of the electrochemical properties and thermal stability of LiNi1/3Co1/3Mn1/3O2/LiFePO4 composite cathodes for lithium ion batteries

A series of LiNi1/3Co1/3Mn1/3O2/LiFePO4 composite cathodes with the LiFePO4 mass content ranging from 10 to 30 wt% were prepared by ball milling in order to combine the merits of layered LiNi1/3Co1/3Mn1/3O2 and olivine LiFePO4. The structure and morphology of the samples were characterized by X-ray diffraction and scanning electron microscope. The composite cathodes exhibited improved electrochemical performance compared with pristine LiNi1/3Co1/3Mn1/3O2. Among all the composite cathodes, the one with 20 wt% of LiFePO4 showed the best electrochemical performance in terms of discharge capacity, cycle stability, and rate capability. Electrochemical impedance spectroscopy showed that mixing of LiFePO4 in LiNi1/3Co1/3Mn1/3O2 decreased the internal resistance of the electrode, retarded the formation of SEI film, and facilitated the charge transfer reaction. Differential scanning calorimetry showed that the composite cathode had better thermal stability than pristine LiNi1/3Co1/3Mn1/3O2.