Investigation Of High Performance Cathode Materials For Lithium Ion Batteries And Design For Industrial Application

The coming of energy crisis and rapid development of renewable energy urge on the worldwide researches in batteries for energy storage and industrial application, especially on the lithium ion batteries. As the cathod material for lithium ion batteries, LiFePO4 is favored for its excellent electrichemical performance and abundunt sources of raw materials and considered as the useful prospects for industrial application. However, LiFePO4 materials prepared in industrializaton at present may be a little expensive and the synthetic particle size does not have a uniform distributtion, with a consequence of different performances of different batches. To conquer these defects of LiFePO4 materials, we report a simple route to synthesize LiFePO4/PAS nanocomposite from a pretreatment of iron phosphate and investigate its electrochemical performance in a wide-range temperature. Furthermore, in order to investigate the industrial application of cathode materials, we took part in the design of lithium ion batteries in a company, including the mixture formula of cathodes for different materials and some other parameters of assembling. The main research contents can be devided into the following two parts.1. Nanosized LiFePO4 particles coated by uniform thin polyacene layer are synthesized from a pretreatment of FePO4·2H2O. The polyacene layer arises from carbonization of the phenolic-formaldehyde resin which is in situ polymerization to coat the amorphous FePO4·2H2O. The average particle size of the LiFePO4/ polyacene nanocomposite is in the range of 20-60 nm. This LiFePO4/polyacene nanocomposite delivers discharge capacities of 142,135,124,110 and 80 mAh/g at 1 C,2 C,5 C,10 C and 20 C, respectively. The cyclic voltammetry curve and electrochemical impedance spectroscopy reveal low polarization of LiFePO4/polyacene due to the complete coating of polyacene layer on the nanosized LiFePO4 particles. Also the LiFePO4/polyacene nanocomposite shows good electrochemical performances in the temperatures ranging from -20℃to 60℃. It has high discharge voltage platform at 1 C at low temperatures and delivers a discharge capacity of 80 mAh/g at -20℃, without capacity fade after 50 cycles, while the capacity dimishes after 50 cycles at high temperature of 60℃.2. With the help of participating into the design of technics and production of lithium ion batteries, we have designed the parameters in the requirements of cylinder batteries with high-energy and high-power. We also designed different formula of cathode materials, area density cand ompacted density of coating, corresponding strip length, numbers of the polar and so on. And the batteries with excellent low-temperature electrochemical performances were produced. Moreover, the effect of electrolyte content on the electrochemical performance of batteries was analyzed, which had a guiding significance to the battery production.