改进高温固相法制备磷酸锰铁锂正极材料

Preparation of Lithium Manganese Iron Phosphate Cathode Material by Improved High-temperature Solid-state Method

LiMn 1-x Fe x PO 4具有制备成本低廉、环境友好、能量密度高、热稳定和循环稳定等优点,在锂离子电池中具有良好的应用前景。在目前制备LiMn 1-x Fe x PO 4的各种方法中,高温固相法因其工艺简单、成本低廉、产量较高的特点被广泛采用。然而通过高温固相法制得的LiMn 1-x Fe x PO 4普遍存在粒径分布不均匀、颗粒容易团聚等问题。针对以上问题,本实验以蔗糖为碳源,通过一种改进的高温固相法制得了二次包碳的LiMn 0.5 Fe 0.5-PO 4材料。利用X射线衍射法(XRD)、透射电镜(TEM)、扫描电镜(SEM)表征材料的物相结构,结果表明,制备的二次包碳的LiMn 0.5 Fe 0.5 PO 4材料是单相橄榄石结构,平均尺寸为260 nm。采用恒流充放电的测试方法表征材料的电化学性能,其在0.1C、1C和10C的倍率下,放电比容量分别可达到165 mAh/g、132 mAh/g和92 mAh/g,且在1C下循环100周后的容量保持率超过90%,具有良好的倍率性和循环稳定性。同时,本实验还通过循环伏安法(CV)和交流阻抗法(EIS)详细讨论了二次包碳工艺能够改善产物电化学性能的原因。

LiMn1-xFexPO4 with the advantages of low cost,environmental amity,high energy density,good thermal stability as well as superior cycling stability,has a good application prospect for lithium-ion batteries.Among various methods for preparing LiMn 1-x Fe x PO 4,the high-temperature solid-state method has been widely used because of its simple process,low cost and high yield.However,the particle size of LiMn 1-x-Fe x PO 4 is not well-distributed by the high-temperature solid-state method and the particles are easy to aggregate.To solve these problems,the sucrose was used as carbon source to obtain secondary carbon-coated LiMn 0.5 Fe 0.5 PO 4 material by an improved high-temperature solid-state method in this paper.The structure and the morphologies of the as-prepared materials were characterized by X-ray diffraction(XRD),transmission electron microscope(TEM),scanning electron microscope(SEM).The results showed that the secondary carbon-coated LiMn 0.5 Fe 0.5-PO 4 had a single olivine phase and an average particle size of 260 nm.The electrochemical properties of the secondary carbon-coated LiMn 0.5-Fe 0.5 PO 4 were studied by galvanostatic charge-discharge method.The LiMn 0.5 Fe 0.5 PO 4/C could deliver discharge capacities of 165 mAh/g,132 mAh/g and 92 mAh/g at 0.1C,1C,and 10C rate,respectively.The capacity retention was more than 90%after 100 cycles at 1C,showing the excellent rate capability and cyclability.In addition,the reason for the improved electrochemical properties of the secondary carbon-coated LiMn 0.5 Fe 0.5 PO 4 had also been investigated by cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)measurements.