Synthesis And Modification Of Lithium Manganese Silicate Cathode Material

Considered as the most important storage device, Lithium-ion battery plays an important role in the new energy vehicles because of its high specific capacity, high specific power and good cycling ability and so on. Of course, owing to the high safety and high stability, the polyanion cathode materials receive more and more attention. Li₂MnSiO₄ is also considerably focused just because of its high specific capacity of（333 mAh/g） and high voltage platform（4.1V and 4.5V）. However, three disadvantages exist as follows: one is its difficulty to be prepared; one is its extremely low electronic conductivity; another is its rapid fade in capacity. Just in terms of these defects, the corresponding method is taken: One is using the mixed solvent-thermal method to prepare the mid-product to be the foundation of target product; Also the method is used to coat the carbon source on the surface of the particles; Another is doping the phosphate into the structure of Li₂MnSiO₄ to improve the electrochemical performance.First, from the original silicate to the target product of Li₂MnSiO₄, we record the structures and the morphologies of the different stages to prove the truth of the new method. The temperature and the reaction time of mixed thermal method were optimized for the best particles. Using starch as the carbon source, we discussed the effects of different amounts of carbon coated on the particles to determine the theoretical amount of 20 wt.% as the best one. Combing the carbon coating with phosphate doping, we designed and prepared materials of Li2+xMn_1-x[PO₄]x[SiO₄]_1-x/C. Then we demonstrated the effects of phosphates on the structure and morphology of lithium manganese silicate. Also, the electrochemical performance is measured at room temperature of 0.05 C in voltage range of 1.5V and 4.8V. The results indicate that the electrochemical performance is highly improved by phosphate doping and the capacity retention is improved on a small scale. We also concluded the mechanism for the improvements on the electrochemical performance of cathode material connected with the conversion of [MnO₄] tetrahedrons and [MnO6] octahedrons. The phosphate doping inhibits the conversion of [MnO₄] tetrahedrons to [MnO6] octahedrons, which benefits the structural stability and controls the structuraltransition. Li2-xMn[PO₄]x[SiO₄]_1-x/C is prepared for different components and they were characterized in structure and morphology. The results indicated that Li1.95Mn[PO₄]0.05[SiO₄]0.95/Cis the best with the maximum specific capacity of nearly 250mAh/g and itmaintains at 150 mAh/gafter 30 cycles.