Influences of transition metal on structural and electrochemical properties of Li[NixCoyMnz]O2 (0.6≤x≤0.8) cathode materials for lithium-ion batteries

Li[NixCoyMnz]O2 (0.6≤x≤0.8) cathode materials with a typical hexagonal α-NaFeO2 structure were prepared utilizing a co-precipitation method. It is found that the ratio of peak intensities of (003) to (104) observed from X-ray diffraction (XRD) increases with decreasing the Ni content or increasing the Co content. The scanning electron microscopy (SEM) images reveal that the small primary particles are agglomerated to form the secondary ones. As the Mn content increases, the primary and secondary particles become larger and the resulted particle size for the Li[Ni0.6Co0.2Mn0.2]O2 is uniformly distributed in the range of 100–300 nm. Although the initial discharge capacity of the Li/Li[NixCoyMnz]O2 cells reduces with decreasing the Ni content, the cyclic performance and rate capability are improved with higher Mn or Co content. The Li[Ni0.6Co0.2Mn0.2]O2 can deliver excellent cyclability with a capacity retention of 97.1% after 50 cycles.