用廉价三价铁离子化合物为铁源, 聚丙烯作还原剂和碳源, 两步固相法合成F掺杂原位碳包覆LiFePO4正极材料. 结果表明, 合成产物具有完整的橄榄石型LiFePO4晶体结构, 粉末形状近似球形, 尺寸分布在50~200nm范围内, 两步固相法更好地抑制了LiFePO4晶粒的长大. 电化学测试结果表明, F掺杂提高了材料倍率放电性能, 有效降低了材料电极的极化. 在1C, 2C, 3C(C为150mA/g)充放电倍率下, LiFePO3.98F0.02/C的比容量分别为146mAh/g, 137mAh/g, 122mAh/g, 1C循环55次后放电容量达到初始容量的99.3%.
F-doped lithium iron phosphates were synthesized and in~situ carbon coated by two-step solid-state reaction using Fe(Ⅲ) compound as the iron source and polypropylene as the reductive agent and carbon source. The results show that the synthesized powders are near-spherical particles of 50--200nm with the olivine type LiFePO4 structure. Two-step solid-state reaction inhibits the growth of LiFePO4 particles more efficient compared with one-step solid-state reaction. The results of electrochemical measurement show that fluorin doping improves the rate capability of LiFePO4 and decreases the polarization of LiFePO4 electrode effectively. The discharge capacities of LiFePO3.98F0.02/C cathode material are 146mAh/g, 137mAh/g, 122mAh/g at charge and discharge rates of 1C, 2C, 3C, respectively. Cycling efficiency of 99.3% can be obtained after 55 cycles at 1C rate.
参考文献
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