两种不同形貌FePO_4的制备及其正电极材料LiFePO_4的电化学性能

Preparation of two kinds of FePO_4 powders with different morphologies and electrochemical properties of LiFePO_4

分别以Fe(NO3)3.9H2O和FeSO4.7H2O为铁源,采用均相沉淀法和氧化-液相沉淀法制备了两种不同形貌的FePO4粉体,再以FePO4为前驱体,与LiOH.H2O、蔗糖混合,采用碳热还原法合成了LiFePO4正电极材料。用XRD和SEM对所制备的FePO4粉体进行结构和表面形貌表征,测试了LiFePO4样品的充放电性能。XRD和SEM测定结果表明,采用均相沉淀法制备的FePO4为六方晶系纯相,颗粒形貌为圆片状,颗粒大小均匀;而液相氧化法制备的FePO4也为六方晶系纯相,但颗粒形貌无规则。由圆片状FePO4和无规则FePO4所合成的LiFePO4的颗粒形貌与其前驱体相同。充放电测试表明在0.5C下圆片状LiFePO4的首次放电比容量为140 mAh/g,无规则LiFePO4的首次放电比容量为89 mAh/g。经过50次循环后,前者的放电比容量仅下降1.43%,后者基本不变。

Two kinds of FePO4 powders with morphologies were prepared with Fe（ NO3 ）3 · 9H2O and FeSO4 · 7H2O as iron source by using homogeneous precipitation method and oxidize-liquid-deposited method respectively. The prepared FePO4 then mixed with LiOH · H2O and sugar to synthesize cathode material LiFePO4 by carbothermal reduction method. The structure and morphology of prepared FePOa and LiFePO4 were characterized by X-ray diffraction （XRD）, scanning electron mi- croscopy （SEM）. The charge-recharge performance of LiFePO4 was also measured. The results show that FePOa particles prepared by homogeneous precipitation method are wafer-like in morphology, while the FePO4 particles prepared by oxidize-liquid-deposited method are shapeless. Both of them are hexagonal structure. Testing of the electrochemical performance shows that the specific discharge capacities of LiFePO4 of wafer-like and shapeless are 140 mAh.g^-1 and 89 mAh.g^-1 respectively at the 0. 5C rate. The discharge capacity decreased 1.43% merely for the former and no change for the later after 50 cycles.