Microstructure and electrochemical performance of LiNi0.6Co0.4−xMnxO2 cathode materials

LiNi0.6Co0.4−xMnxO2 (0.15 ≦ x ≦ 0.25) cathode materials for lithium-ion batteries are synthesized by calcining a mixture of Ni0.6Co0.4−xMnx(OH)2 and Li2CO3 at 890-950 °C for 15 h in a flowing oxygen atmosphere. The Ni0.6Co0.4−xMnx(OH)2 precursor is obtained by a chemical co-precipitation method at pH = 11. Thermal analysis of the precursor for LiNi0.6Co0.4−xMnxO2 (0.15 ≦ x ≦ 0.25) shows that the weight loss is about 30% until the temperature reaches 750 °C. The X-ray diffraction patterns indicate the pure, layered, hexagonal structure of LiNi0.6Co0.4−xMnxO2. Scanning electron micrographs reveal that the morphology of the samples is characterized by larger agglomerates (5-15 μm) of rather small layered particles (around 100 nm). The particle size tends to decrease with increasing Mn content. The electrochemical behaviour of LiNi0.6Co0.4−xMnxO2 powder is examined by using test cells cycled within the voltage range 3-4.3 V at the 0.1 C rate for the first cycle and then at the 0.2 C rate. LiNi0.6Co0.4−xMnxO2 (0.15 ≦ x ≦ 0.25) cathode materials exhibit good initial discharge capacity (165-180 mAh g−1) and a capacity retention of above 95% after 20 cycles. It is demonstrated that LiNixCoyMn1−x−yO2 electrodes are promising candidates for application as cathodes in lithium-ion batteries.