Modification And Electrochemical Li-storage Properties Of Electrodes (Li₂Ru_0.6Mn_0.4O₃,Li₂MnO₃)

Nowadays, with the shortage of energy, lithium ion batteries are receiving enormous attention as energy storage devices in the renewable energy field. Li₂MnO₃ layered oxides have been considered as the potential alternative of the traditional cathode material LiCoO₂ because its high working voltage, high discharge specific capacity, low cost and environmental friendly. Rescentlly, the research on these materials has atracted more attention. But, as its disadvantage such as low coulombic efficiency and poor rate performance and cycle life make the preparation and modification work very important. In this thesis, we use the Ru element to replace the Mn element in the Li₂MnO₃ and Li₂MnO₃ were treated by acidification, the modified cathode material and other materials are combined. Specific contents are as follows:?1? Li₂Ru_0.6Mn_0.4O₃ cathode material has been successfully prepared through the single-step high temperature solid state systhesis method and hydrothermal method and sol-gel method following with high temperature solid state systhesis method. Though the analysis of microstructure, morphology and electrochemical performance, the product by single-step high temperature solid state systhesis method has the best electrochemical performance.?2? Here we report products were obtained by mixing graphene oxide?GO? and Mg-doped in the solid-state prepared Li₂Ru_0.6Mn_0.4O₃. GO mixed samples keep the original good layered structure of Li₂Ru_0.6Mn_0.4O₃. Electrochemical tests show that the mass ratio of 1:10 of sample exhibits the best improvements on cycle performance and rate properties. Mg-doped layered Li₂Ru_0.6Mn_0.4-xMg_xO₂ materials have been prepared via single-step high temperature solid state systhesis method. The research shows that the cation mixing degree decrease after Mg doping, and the cycle performance of the materials are improved. Li₂Ru_0.6Mn_0.38Mg_0.02O₂ shows the best electrochemical properties.?3? The electrochemical properties of Li₂MnO₃ were studied by means of acid treatment, and then the Li₂MnO₃ and olivine type LiFePO₄/C two composite electrode was obtained. After acidification, the material was no longer maintained the spherical morphology of the original Li₂MnO₃ sample, and transformed into nanorods. The charge/discharge capacity and cycling performance of Li₂MnO₃ were significantly improved after acid treatment which could be attributed to the nano-structured morphology with short Li+ diffusion distance.We develop a facile way to prepare binary Li₂MnO₃- LiFePO₄/C by physical mixing method. LiFePO₄/C typically shows a flat charge/discharge curve which usually leads to great difficulty in the voltage-based state of charge?SOC? estimation. The sudden voltage rise/drop near the end of charge/discharge is significantly modified by adopting the binary Li₂MnO₃-LiFePO₄/C nanocomposite, which shows a tunerable sloped voltage profile.