Characterization of yttrium substituted LiNi0.33Mn0.33Co0.33O2 cathode material for lithium secondary cells

LiNi0.33−xMn0.33Co0.33YxO2 materials are synthesized by Y3+ substitute of Ni2+ to improve the cycling performance and rate capability. The influence of the Y3+ doping on the structure and electrochemical properties are investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and galvanostatic charge/discharge tests. LiNi0.33Mn0.33Co0.33O2 exhibits the capacity retentions of 89.9 and 87.8% at 2.0 and 4.0 C after 40 cycles, respectively. After doping, the capacity retentions of LiNi0.305Mn0.33Co0.33Y0.025O2 are increased to 97.2 and 95.9% at 2.0 and 4.0 C, respectively. The discharge capacity of LiNi0.305Mn0.33Co0.33Y0.025O2 at 5.0 C remains 75.7% of the discharge capacity at 0.2 C, while that of LiNi0.33Mn0.33Co0.33O2 is only 47.5%. EIS measurement indicates that LiNi0.305Mn0.33Co0.33Y0.025O2 electrode has the lower impedance value during cycling. It is considered that the higher capacity retention and superior rate capability of Y-doped samples can be ascribed to the reduced surface film resistance and charge transfer resistance of the electrode during cycling.