| Lithium ion battery is widely used in various types of electronic products. Because it has high charge and discharge capacity, cycling performance, low self-discharge rate and environment-friendly, etc. LiFePO4 due to its wide variety of sources, low cost, good thermal stability, recycling performance, outstanding safety performance to become one of the most promising cathode material of lithium ion battery. However, its low conductivity and ion diffusion coefficient and small packing density limited its large-scale use. There are two way to improve its electrochemical performance. One is improve synthesis method to get small and uniform crystal. Another is increase the material conductivity by doping elements.In this paper, LiFePO4 was prepared by liquid coprecipitation method. The sample was characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and electrochemical workstation analysis. Discussion the electrochemical performance effects of LiFePO4. It was prepared by different iron sources, doped with different carbon sources and amount of carbon, different sintering temperature and time, obtains the following results.LiFePO4 was prepared by three different iron sources (FeSO4, Fe(NH4)2(SO4)2, FeC2O4) under appropriate conditions has high purity and good crystallinity. Characterization results indicate that Fe (NH4)2(SO4)2 is good source of iron, the first discharge capacity is 68mAh·g-1.The effects of different carbon doping precursors had been compared. Confirmed that add small carbon could make particle distribution more uniform, increase the surface area of samples, and improve the electrochemical performance. With the increase in carbon-doped, charge and discharge capacity of the sample would experience the process that first and then decreased. The results showed that glucose is a better carbon source, it had higher capacity and more excellent than the charge and discharge performance.Sintering temperature and time on structure and electrochemical properties of samples had great influence. Sintering temperature is too low, the sample particle would be small and some of it contained impurities; sintering temperature is too high, the sample particle agglomeration occurred and the discharge capacity decreased. Sintering time is too short, the sample particle would be irregular shape; sintering time is too long, completed crystal would be re-melted together and the particle size had increased.On conditions of different carbon sources and carbon doping, sintering time and temperature, the study found that LiFePO4 was prepared by use of glucose as carbon source, 5% doping, sintering at 650℃for 10h could obtain better comprehensive performance. Normal temperature and pressure in order to test the 0.1C charge and discharge rate, the first discharge capacity of sample was 160.2mAh·g-1, after 20 cycles, the capacity could meet more than 150mAh·g-1. Experimental results show that LiFePO4 was prepared by different iron sources, carbon sources and processing conditions sintering has a discharge voltage of about 3.4V platform. It confirmed that the high-voltage lithium-ion battery in the application of electronic components area has good prospects. |
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