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

分别以Fe(NO_3)_3·9H_2O和FeSO_4·7H_2O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FePO_4粉体,再以FePO_4为前驱体,与LiOH·H_2O、蔗糖混合,采用碳热还原法合成了LiFePO_4正电极材料.用XRD和SEM对所制备的FePO_4粉体进行结构和表面形貌表征,测试了LiFePO_4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FePO_4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FePO_4也为六方晶系纯相,但颗粒形貌无规则.由圆片状FePO_4和无规则FePO_4所合成的LiFePO_4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LiFePO_4的首次放电比容量为140 mAh/g,无规则LiFePO_4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.

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

Two kinds of FePO_4 powders with morphologies were prepared with Fe (NO_3)_3· 9H_3O and FeSO_4· 7H_2O as iron source by using homogeneous precipitation method and oxidize-liquid-de-posited method respectively. The prepared FePO_4 then mixed with LiOH· H_2O and sugar to synthe-size cathode material LiFePO_4 by carbothermal reduction method. The structure and morphology of prepared FePO_4 and LiFePO_4 were characterized by X-ray diffraction (XRD), scanning electron mi-croscopy(SEM). The charge-recharge performance of LiFePO_4 was also measured. The results show that FePO_4 particles prepared by homogeneous precipitation method are wafer-like in morphology, while the FePO_4 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 LiFePO_4 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.