Research On Preparaion And Electrochemical Performance Of Li-rich Layered Solid Solution Cathode Materials For Lithium Ion Battery

As the rapid development of society, lithium ion batteries have been applied in new fields such as electric cars, intelligent power grids and energy storage power stations. For these applications, lithium-ion batteries must have high energy density and power density with good safety and environmental friendliness. The Li-rich layered solid solution xLi2MnO3·(1-x)LiMO2,0<x<1, where M is one or more transition metal elements, has high capacity, low cost, good safety and environmental friendliness. So it has been considered as the ideal next generation cathode material of lithium-ion batteries by many scholars.In this dissertation, the author mainly focused on the synthesis surface modification and electrochemical properties of Li-rich layered solid solution cathode,0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2, which also can be written as Li1.2Mn0.54Ni0.13Co0.13O2, the main contents are as follows:Firstly, Li1.2Mn0.54Ni0.13Co0.13O2was successfully synthesized by a co-precipitation method. And carbon was coated on the surface of Li1.2Mn0.54Ni0.13Co0.13O2using sucrose as the carbon source. The results showed that the amount of adding sucrose has important effect on the electrochemical performance of Li1.2Mn0.54Ni0.13Co0.13O2. Adding sucrose value3%Li1.2Mn0.54Ni0.13Co0.13O2showed the best electrochemical performance, especially the rate capability. Li1.2Mn0.54Ni0.13Co0.13O2releases the discharge capacities of194.5mAh/g at1C,168.7mAh/g at2C,135.7mAh/g at5C. The discharge capacities of adding sucrose value3%Li1.2Mn0.54Ni0.13Co0.13O2are198.1mAh/g at1C,179.6mAh/g at2C,151.3mAh/g at5C.Secondly, CePO4coated Li1.2Mn0.54Ni0.13Co0.13O2was prepared by precipitation method and impregnation method. Comparative study indicated that CePO4coated Li1.2Mn0.54Ni0.13Co0.13O2prepared by precipitation method has the better electrochemical performance and thermal stability than Li1.2Mn0.54Ni0.13Co0.13O2, especially the rate capability. Li1.2Mn0.54Ni0.13Co0.13O2releases the discharge capacities of171mAh/g at1C,103mAh/g at2C,48mAh/g at5C,6mAh/g at IOC. The discharge capacities of CePO4coated Li1.2Mn0.54Ni0.13Co0.13O2prepared by precipitation method are231mAh/g at1C,205mAh/g at2C,172mAh/g at5C,110mAh/g at IOC.Finally, an electrolyte of1M LiPF6in a mixture of1:1(w/w) ethylene carbonate (EC) and diethyl carbonate (DEC) was selected as a baseline electrolyte. A new high-voltage electrolyte was composed of the baseline electrolyte and trimethyl phosphite as an electrolyte additive. The effect of new high-voltage electrolyte on the electrochemical performance and thermal stability of Li1.2Mn0.54Ni0.13Co0.13O2was investigated. The investigation showed that adding trimethyl phosphite value1%electrolyte has the best performance, especially the rate capability. The discharge capacities of the cell using the baseline electrolyte are48mAh/g at5C, lOmAh/g at10C. The cell containing1%trimethyl phosphite releases the discharge capacities of150mAh/g at5C,90mAh/g at10C.