氮掺杂碳包覆硅酸亚铁锂的制备及其电化学性能

Preparation of nitrogen-doped carbon coated Li2FeSiO4 and its electrochemical performance

为提高锂离子电池正极材料硅酸亚铁锂(Li2FeSiO4)的容量和倍率性能,以酒石酸为碳源、尿素为氮源,用溶胶凝胶法制备氮掺杂碳包覆硅酸亚铁锂复合材料(NCLFS),通过元素分析、XRD、SEM、拉曼光谱、XPS、恒电流充放电测试和交流阻抗谱等方法对样品的结构及电化学性能进行表征。结果表明:NCLFS复合材料由平均粒径为23nm的Li2FeSiO4纳米晶组成,较小的粒径能够缩短锂离子扩散路径,提高锂离子的迁移速率;N的引入,提高了NCLFS材料的电导率;与无尿素掺杂的CLFS材料相比,NCLFS复合材料表现出了更高的比容量、优异的倍率性能和循环稳定性,0.2C放电倍率下,放电比容量高达223.2mA·h/g(相当于1.34Li^+),循环100周后仍能保持192.9mA·h/g。

In order to improve the capacity and rate of discharging performance of Li2FeSiO4 as cathode material for lithium ion batteries,nitrogen-doped carbon coated Li2FeSiO4(NCLFS) was successfully prepared via sol-gel method by using tartaric acid as carbon source and cheap urea as nitrogen source. Elemental analysis,X-ray diffraction(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectrometer(XPS),Raman spectroscopy,galvano-static charge-discharge and electrochemical impedance spectra were used to characterize the structure and electrochemical properties of the samples. The results show that the NCLFS composite consists of Li2FeSiO4 nanocrystals with an average particle size of 23 nm. The smaller particle size can shorten the lithium ion diffusion path and increase the migration rate of lithium ions. Meanwhile,the nitrogen-doped carbon coating can improve the electrical conductivity of the NCLFS material. Compared with CLFS materials without urea doping,NCLFS composites exhibit higher specific capacity,high rate of discharging performance and cycle stability. The specific discharge capacity of the NCLFS composite at 0.2 C is as high as 223.2 mA·h/g (equivalent to 1.34 Li^+) and can be maintained at 192.9 mA·h/g after 100 cycles.