碳含量对梭形球状LiFePO_4/C正极材料性能的影响

Effect of carbon coating on performance of spindle spherical LiFePO_4/C cathode material

以葡萄糖为碳源,采用水热法合成了梭状的Li Fe PO4/C的一次颗粒,再经过喷雾干燥法使得梭状颗粒堆积成球形二次颗粒。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)考察了含碳量对样品结构及形貌的影响。结果表明:葡萄糖的加入并没有改变Li Fe PO4的晶体结构,合成的Li Fe PO4/C均未含杂质,其晶体结构均为橄榄石型结构;而且合成的一次颗粒均为梭形结构,并在颗粒表面有一层均匀的碳膜。当葡萄糖的加入量与铁的摩尔比为1∶0.2时,球形粒径在4μm左右,单个梭形颗粒长1μm,宽400 nm。通过EIS和恒流充放电测试,结果表明该样品具有较大的扩散系数(9.42×10-13 cm2/s),在0.1 C倍率下的首次充电比容量为148.9 m Ah/g,放电比容量为144.3 m Ah/g,库仑效率为96.9%,说明具有良好的可逆性能,经过50周循环后容量保持率仍为97.1%,显示了良好的循环性能及容量保持率。

Spindle LiFePO4/C particle was prepared by hydrothermal and spherical LiFePO4/C cathode material was synthesized via spraying dry method using C6H12O6 as carbon source. The structure and morphology of different carbon content on the samples were characterized by X-ray diffraction, scanning electron micrograph and transmission electron microscope. The results show that the synthesis of Li Fe PO4/C do not contain impurities, its crystal structure are olivine structure. The particles were spindle with uniform carbon film on the surface. When the coating amount of C6H12O6 and the molar ratio of iron to 1：0.2, the spindle spherical LiFePO4/C cathode material particle was around 4 μm, the length and width of a single spindle particle were respectively 1 μm and 400 nm. The EIS tests and current charge-discharge tests show that： the sample has great diffusion coefficient（9.42×10^-13 cm^2/s）and the initial charge capacity reached 148.9 m Ah/g at 0.1 C charge/discharge rate and its discharge capacity reached 144.3 m Ah/g. The coulomb efficiency was 96.9%. After 50 cycles, the sample still kept about 97.1% of its initial discharge capacity, which had good cycle performance.