LiFePO_4/石墨烯复合材料的电化学性能比较

Comparative Study of Electrochemical Performance of LiFePO_4/Graphene Composites

分别以水热合成的石墨烯(H-Gr)和商业化石墨烯(C-Gr)为载体,以溶胶-凝胶法合成的LiFePO4(S-LFP)和商业化的LiFePO4(C-LFP)为活性组分,通过固相法制备了4个LiFePO4/石墨烯复合物。采用X射线粉末衍射(XRD)、扫描电镜(SEM)和电化学性能测试,对上述LiFePO4/石墨烯复合物进行了对比研究。实验结果表明,C-LFP/H-Gr显示了最高的可逆放电容量,0.1C倍率下,达到155.0mA.h.g-1,其次是C-LFP/C-Gr(144.6mA.h.g-1)和S-LFP/H-Gr(131.5mA.h.g-1),S-LFP/C-Gr的性能最差,仅为119.6mA.h.g-1。C-LFP/H-Gr较高的电化学容量,一方面可归结于商业化的LiFePO4较小的粒径和良好的晶型结构;另一方面水热合成的石墨烯小的片层结构对LiFePO4的良好包覆,不仅增强了材料导电性,而且提高了活性物质LiFePO4的利用率。

Using hydrothermal--synthesized graphene （H--Gr） and commercial graphene （C--Gr） as the carries, respectively, four LiFePO4/Graphene composites were prepared by a solid--state method with sol --gel--synthesized LiFePO4 （S--LFP） and commercial LiFePO4 （C--LFP） as the active ingredient, respectively. The structures and electrochemical performances of those composites were investigated and compared by X--ray powder diffraction （XRD）, scanning electron microscopy （SEM）, and electrochemical measurements. The experimental results indicated that the C--LFP/H--Gr composite exhibited a highest reversible discharge-- capacity of 155.0mA h g-1 at 0. 1C rate, followed by C-- LFP/C-- Gr （144. 6mA h g-l） and S--LFP/H--Gr （131.5mA h g-l）, and S--LFP/C--Gr showed the lowest capacity of 119.6mA h g-1 among four samples. The improved electrochemical capacity of the C-- LFP/H--Gr composite might due to the smaller particle size and well--crystallized structure of commercial LiFePO4. On the other hand, LiFePO4 is well--coated by small nanosheets of hydrothermal--synthe sized graphene, which not only enhanced the conductivity of composites, but also improved the utilization of the active ingredient.