The effects of copper and titanium co-substitution on LiNi0.6Co0.15Mn0.25O2 for lithium ion batteries

The Li(Ni0.6Co0.15Mn0.25)(1-x)(CuTi)(x)O-2 (x = 0.00, 0.01, 0.02, 0.03) cathode materials were synthesized via a hydroxide co-precipitation method followed by a solid-state reaction. The elementary composition, crystal structure features, morphology, and electrochemical performances of the powders were investigated in detail by inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), galvanostatic charge/discharge test, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results of XRD and Rietveld refinements demonstrate that Cu and Ti co-substitution does not destroy the crystal structure, but can decrease cation ordering level and improve structural integrity. Electrochemical results show that Cu and Ti addition also results in an improved rate and cycling performances compared to pristine LiNi0.6Co0.15Mn0.25O2. An increase in rate performance and cycle stability upon copper and titanium co-substitution is related to the better hexagonal structure and enhanced kinetics of the intercalation process. Especially, Li(Ni0.6Co0.15Mn0.25)(0.99)(CuTi)(0.01)O-2 exhibits the best rate performance and cycle stability among all samples with discharge specific capacity of 178.8 mAh/g and capacity retention of 90.6% after 30 cycles at 0.2C, which are higher than those of other materials.