氧化沉淀-陈化晶化法制备NH4Fe2(PO4)2(OH)·2H2O及LiFePO4

Preparation of NH4Fe2(PO4)2(OH)·2H2O via oxidizing precipitation followed aging crystallization and LiFePO4

以H3PO4、FeSO4·7H2O、NH3·H2O、H2O2为原料,在pH=5.0时,采用连续的氧化沉淀法制得类球形非晶态的NH4Fe2(PO4)2(OH)·2H2O。将NH4Fe2(PO4)2(OH)·2H2O与一定浓度的H3PO4溶液混合,在90℃陈化2 h,制得结晶完好具有微纳米结构的NH4Fe2(PO4)2(OH)·2H2O前驱体。由该NH4Fe2(PO4)2(OH)·2H2O制得的LiFePO4正极材料具有较好的性能。0.2 C时首次充放电比容量分别为162.9和152.8 mAh/g,首次库仑效率为93.8%;1 C和5 C时可逆放电比容量分别大于120和70 mAh/g;具有较好的倍率性能和循环性能。用X射线衍射(XRD)和扫描电镜(SEM)等对NH4Fe2-(PO4)2(OH)·2H2O和LiFePO4的结构和形貌进行表征。氧化沉淀的pH值对前驱体的成份、结构具有重要影响。

The spherical amorphous NH4Fe2(PO4)2(OH)·2H2O powders were prepared by consecutive oxidizing precipitation method at pH=5.0,using FeSO4·7H2O,H3PO4,H2O2 and NH3·H2O as the raw materials.The amorphous NH4Fe2(PO4)2-(OH)·2H2O powders were mixed with H3PO4 solution and aged at 90℃for 2 h.The crystalline state NH4Fe2(PO4)2(OH)·2H2O with micro-nano-structure were obtained after aging crystallization.Using the NH4Fe2(PO4)2(OH)·2H2O powders as the precursors,the prepared LiFePO4 cathode materials show good electrochemical performance.At 0.2 C,the cathode materials show initial charge and discharge specific capacity of 162.9 and 152.8 mAh/g,respectively.The initial coulomb efficiency is 93.8%.At 1.0 C and 5.0 C,the reversible specific capacity is higher than 120 and 70 mAh/g,respectively.The materials show good rate capability and cycling performance.The structure and morphology of NH4Fe2(PO4)2(OH)·2H2O and LiFePO4 were characterized in detail by XRD and SEM.The pH value of oxidizing precipitation obviously affects the composition and structure of the precursors.