Preparation Of Spherical Li-rich Manganese-based Cathode Material For Lithium-ion Battery By Co-precipitation Controlled Crystallization

This research work is focused on the Li-rich manganese based layered oxide cathode materials for Li-ion batteries. For improving the rate capability and cycle stability of the Li-rich layered oxide cathode materials, this work presents a structural design with high-density spherical particles. Surface modification is also performed to improve the electrochemical performances. The main research results are as follows:Theoretical analysis co-precipitation process was conducted according to the empirical formula of the crystal nucleation. The influence of the concentration of raw material solution, stirring speed, ammonia concentration and pH value on the precipitation process was obtained, which provides a practical methodology for and directional guidance.By the thermodynamic analysis of the co-precipitation reaction system without complexing agents, it is concluded that the probability of basic salt precipitates will increase substantially due to large number of metal free ions, thus demonstrates the necessity of introducing a complexing agent. In the co-precipitation reaction system with a complexing agent, the optimum pH value is about 8, while the impurity phase precipitation occurs more than pH 8, and significant loss of metal ions occurs less than pH 8.The effects of temperature, stirring speed, ammonia concentration and pH value as a single factor on the precursor preparation process were investigated. In the Ni2+-Co2+Mn2+CO32--NH3-H2O system with Na2CO3 as a precipitant, the optimum conditions for the co-precipitation of precursor are as follows:temperature at 15℃, stirring speed of 800 r·min-1, pH=8.0, the ammonia concentration of 0.4 mol·L-1. Under the optimum conditions, the precursor presents a uniform spherical particle morphology, regular particle size distribution (D50=8.69μm).The tap density of the precursor depends on the morphology, particle size and size distribution of the particles. To obtain a high tap density, the particle shape should be spherical in ensuring regular premise optimized particle size and distribution state of the particles as much as possible to achieve close packing of freedom. With an excess of 7 wt% of lithium carbonate as a lithium source, the electrode material sintered at 850℃ for 20 h exhibited the best electrochemical performance, with a discharge capacity of 263 mAh·g-1.AlF3-modified Li-rich layered oxide was prepared. The first coulombic efficiency and cycling stability of the modified electrode material were improved. After 100 cycles, the capacity retention of the surface-modified electrode is 86%, while the bare one is only 64.5%.