Rate capability of LiLi_0．17Mn_0．58Ni_0．25O₂ as high-capacity cathode materials

A carbonate co-precipitation method was used to synthesize LiLi_0.17Mn_0.58Ni_0.25O₂ amples with different morphologies via controlling the crystal process. The LiLi_0.17Mn_0.58Ni_0.25O₂ samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), galvanostatic charge-discharge testing, and electrochemical impedance spectroscopy (EIS). It is found that the LiLi_0.17Mn_0.58Ni_0.25O₂ samples, with high crystallinity, can all be indexed as a α-NaFeO₂ phase (space group R3m). Moreover, the sample with the hexagonal primary particles aggregated along with the long axis shows a much better rate capability than the other. LiLi_0.17Mn_0.58Ni_0.25O₂ delivers the initial discharge capacities of 205.4, 195.5 and 158.5 mA.h·g^-1, in the voltage range of 2.5-4.8 V at the rates of 0.5C, 1.0C and 3.0C, respectively. After 100 cycles, the discharge capacities are 203.5, 187.2and 151.2 mA.h·g^-1, which correspond to 99%, 96% and 95% retention of their initial capacities. The special aggregated morphology of LiLi_0.17Mn_0.58Ni_0.25O₂ particles contributes to the reduced charge transferring impedance and the improved rate capability. Additionally, the electrochemical properties of the materials in different potential windows were also comparatively studied.