High Voltage Cathode Material LiNi_0.5Mn_1.5O₄ For Li-ion Battery

In accordance with the development of high power lithium ion batteries and as a power supply for electric vehicles and hybrid electric vehicles, there are increasing interestings in the research of high potential cathode materials. LiNio.5Mn1.5O4 spinel synthesized by LiMn2O4 doped with Ni shows excellent electrochemical properties. For example, it has a 4.7V discharge plateau of high potential and high charge-dischanrge specific capacity. It is a hot researching of currently cathode materials.In this thesis, spinel LiNio.5Mn1.5O4 was prepared by rheological method using ethylene glycol as solvent. It has simple preparation process, high crystallinity, pure phase and excellent electrochemical properties. It is found that LiNio.5Mn1.5O4 synthesized by rheological method has obvious advantages on the preparation process and the physical and chemical properties with an integrated view compared with traditional solid phase method and sol-gel method. So it has good prospect of industrial application.In addition, this thesis also studies the effect of solvent and calcination temperature on the component, structure, morphology and electrochemical performance of spinel LiNio.5Mn1.5O4 synthesized by rheological phase. The purpose of it is to explore the optimum preparation conditions for synthesizing spinel LiNio.5Mn1.5O4 by rheological method and realize the performance of spinel LiNio.5Mn1.5O4 improved. The results showed that:First, ethylene glycol and polyethylene glycol have stronger coordination ability, so they can be adsorbed on the surface of the particles and play an active role in the surface and particle dispersion. But this property of ethylene glycol is better than polyethylene glycol. Although polyethylene diol also has a role in inhibiting grain growth occurs, but the product of small reunion make electrochemical performance degradation. Second, structure, morphology and electrochemical properties of the sample are closely linked with the sintering temperature. When the samples calcined at low temperature, it had poor crystallinity, small particles and agglomerates. When the samples calcined at high temperature, it had high crystallinity, good particle dispersion and it showed excellent electrochemical performance. In a word, as the temperature increases, the sample particle size, crystallinity and electrochemical properties improved. However, when the temperature exceeds 900℃, the performance decreased with temperature increases.LiNi0.5Mn1.5O4 synthesized by rheological phase using ethylene glycol as solvent and calcined at 800℃had the best comprehensive properties. The product had high crystallinity, small specific surface area and exhibited excellent electrochemical properties. After 50 cycles, the discharge capacity of the sample was 130.5 mAh/g with a capacity retention rate higher than 99%and coulombic efficiency over 98%at current density of 0.5C. The capacity of the sample almost doesn't decay at current density of 1C after 50 cycles. At current density of 2C and 5C, the capacity retention rate of the sample is 96.8%and 91.8%none the less. Expecially when the current density up to 10C, the capacity retention rate of the sample is still over 85%after 50 cycles. Therefore, the sample has excellent high rate performance.