Characterization of yttrium substituted LiNi 0.33Mn 0.33Co 0.33O 2 cathode material for lithium secondary cells

Abstract

LiNi 0.33− x Mn 0.33Co 0.33Y x O 2 materials are synthesized by Y 3+ substitute of Ni 2+ to improve the cycling performance and rate capability. The influence of the Y 3+ 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. LiNi 0.33Mn 0.33Co 0.33O 2 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 LiNi 0.305Mn 0.33Co 0.33Y 0.025O 2 are increased to 97.2 and 95.9% at 2.0 and 4.0 C, respectively. The discharge capacity of LiNi 0.305Mn 0.33Co 0.33Y 0.025O 2 at 5.0 C remains 75.7% of the discharge capacity at 0.2 C, while that of LiNi 0.33Mn 0.33Co 0.33O 2 is only 47.5%. EIS measurement indicates that LiNi 0.305Mn 0.33Co 0.33Y 0.025O 2 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.