水热还原法制备的LiFePO_4/C的性能

Performance of LiFePO_4/C synthesized by thermal reduction method

以水、乙醇和乙二醇为溶剂,絮状聚乙烯醇(PVA)为还原剂和碳包覆剂,用水热还原法制备橄榄石型碳包覆磷酸铁锂(LiFePO4/C)。用XRD、SEM和充放电等测试,对产物的晶体结构、微观形貌及电化学性能进行研究;通过Wu方法计算产物的表面自由能。LiFePO4/C具有单一橄榄石型晶体结构,以乙二醇为溶剂合成的产物粒径细小,为300～400 nm的均匀分布球状体,表面自由能色散分量(γsd)与极性分量(γsp)之比γsd/γsp最大,炭包覆性和导电率最好。在2.2～4.4 V充放电,0.1C首次放电比容量达164.95 mAh/g,第50次循环的容量保持率为96%;10C放电比容量为125 mAh/g,以15C放电,放电比容量为85 mAh/g,循环10次,放电容量保持率都在99%以上。

Olivine-type carbon coated lithium iron phosphate （LiFePO4/C） was synthesized by hydrothermal reduction method using water,ethanol, ethylene glycol as solvent and polyvinylalcohol （PVA） as reductant and carbon-coated agent. The crystalline structure, morphology and electrochemical performance were investigated by XRD, SEM and charge-discharge measurements. The surface free energy was calculated based on the method suggested by Wu. The LiFePO4/C was single olivine type crystal structure and the product prepared with ethylene glycol had the largest ratio of the dispersive part of surface free energy （γs^d） to the polar part （γs^p）, that was γs^d/γs^p,as well as the best coating and conductivity with 300 - 400 nm uniformly spherical structure. The 0.1 C initial specific discharge capacity of the product in 2.2 - 4.4 V was 164.95 mAh/g, the retention was 96% at the 50th cycle. The specific discharge capacity could reach 125 mAh/g at 10 C,85 mAh/g at 15 C,retention was all above 99% after 10 cycles.