高容量正极材料Li[Li_(0.17)Mn_(0.58)Ni_(0.25)]O_2的倍率性能

Rate capability of Li[Li_(0.17)Mn_(0.58)Ni_(0.25)]O_2 as high-capacity cathode materials

采用碳酸盐共沉淀工艺,通过控制结晶合成了显微形貌呈现较大差异的Li[Li_(0.17)Mn_(0.58)Ni_(0.25)]O_2样品,并对样品进行了X射线衍射、高分辨透射电镜、场发射扫描电镜分析以及恒电流充放电和交流阻抗测试.合成的Li[Li_(0.17)Mn_(0.58)-Ni_(0.25)]O_2材料均具有良好的结晶度,可标定为α-NaFeO_2结构(空间群R3m).其中,具有一次颗粒沿六方棱柱长轴方向形成'簇形'团聚的材料比其他样品具有优异的倍率性能,在电压范围为2.5～4.8 V,倍率分别为0.5C、1.0C和3.0C时,Li[Li_(0.17)Mn_(0.58)Ni_(0.25)]O_2材料首次放电比容量分别达到205.4、195.5和158.5 mA·h·g^(-1),100次循环后放电比容量保持在203.5、187.2和151.2 mA·h·g^(-1),容量保持率分别为99%、96%和95%.Li[Li_(0.17)Mn_(0.58)Ni_(0.25)]O_2材料特殊的颗粒团聚状态降低了界面的电荷转移阻抗,材料的倍率性能显著提高.同时,文中对Li[Li_(0.17)Mn_(0.58)Ni_(0.25)]O_2材料在不同截止电压下的电化学性能进行了对比分析.

A carbonate co-precipitation method was used to synthesize Li[Li0.17Mn0.5sNi0.25]O2 amples with different morphologies via controlling the crystal process. The Li[Li0.17Mn0.5sNi0.25]O2 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 Li[Li0.17Mn0.5sNi0.25]O2 samples, with high crystallinity, can all be indexed as a a-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. Li[Li0.17Mn0.5sNi0.25]O2 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 Li[Li0.17Mn0.5sNi0.25]O2 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.