摘要
The layered-layered-spinel composite cathode materials Li x Mn 4/6 Ni 1/6 Co 1/6 O (1.75+0.5 x ) with different content of Li 2 O have been synthesized by the two-step co-precipitation method and evaluated in lithium cells. Powder X-ray diffraction provides the evidence that the structures of Li x Mn 4/6 Ni 1/6 Co 1/6 O (1.75+0.5 x ) composite transform from ‘layered-layered’ to ‘layered-layered-spinel’ as the content of Li 2 O decreasing. Electrochemical charge/discharge profiles suggest that Li 1.3 Mn 4/6 Ni 1/6 Co 1/6 O 2.4 electrode with low content of Li 2 O delivers a large initial discharge capacity which is about 305.3 mAh·g −1 , and that the discharge capacities of Li 1.3 Mn 4/6 Ni 1/6 Co 1/6 O 2.4 electrode change little at the first three cycles, because of that a considerable amount of spinel phase in electrode facilitating Li ions diffusion. Nevertheless, the discharge capacities of Li 1.4 Mn 4/6 Ni 1/6 Co 1/6 O 2.45 and Li 1.5 Mn 4/6 Ni 1/6 Co 1/6 O 2.5 electrode in the first three cycles gradually rise as cycles continuing, which is expected to be that Li ions diffusion paths are not fully opened. The irreversible electrochemical reaction that Li 2 O component separates from Li 2 MnO 3 to form MnO 2 happens at the first charge at 4.7 V, and the structure of layered Li 2 MnO 3 component converts into the spinel component during continuously cycles. The Li x Mn 4/6 Ni 1/6 Co 1/6 O (1.75+0.5 x ) composites also display good cycling performance and rate performance. The capacity retention of Li x Mn 4/6 Ni 1/6 Co 1/6 O (1.75+0.5 x ) composites exceeds 100%, and its coulombic efficiency is greater than 98% after 50 cycles. We conclude that electrochemical performances of Li x Mn 4/6 Ni 1/6 Co 1/6 O (1.75+0.5 x ) composites are improved by using the two-step co-precipitation preparation method, especially in terms of large discharge capacity of Li 1.3 Mn 4/6 Ni 1/6 Co 1/6 O 2.4 composite due to the appearance of spinel components.
危险品化学品经营许可证（带存储）