动力电池用磷酸铁锂纳米复合正极材料的的结构设计及电化学性能研究

LiFePO4 has broad application prospects in high power Li-ion battery. But the problems including bad high-rate performance and weak cyclic stability, resulted from its minimal electronic and ionic conductivity and low tap density, which confines it to be widely applied in reality. In this project, by chemical self-assembly, in-situ polymerization and microwave carbothermic reduction methods, graphene/Li3V2(PO4)3/LiFePO4/PANI nanocomposite cathode materials with good dispersion, homogeneous size, core/shell structure and spherical morphology is designed. Firstly, the spherical FePO4/PANI precursor is synthesized via in-situ polymerization technique, and then, fast-ion conductor Li3V2(PO4)3 with high theretical special capacity and graphene with high electronic conductivity are doped simultaneously. Thirdly, by means of the technology including the addition of dual carbon sources, two-step sintering process and spherify, high quality LiFePO4 nanocomposite materials will be abtained. Finally, the nanocomposites graphene/ Li3V2(PO4)3/LiFePO4 coated with PANI will be synthesized via chemical self-assembly process by adding aniline and ammonium peroxydisulfate in different proportions into the as-synthesized LiFePO4 nanocomposite materials.This project aims to find the optical processing conditions,and systematically study the influence of the each species' microstate and cooperative behavior on the electrochemical performances. The result of this project will provide a theoretical basis and technical support for developing high quality new system used in Li-ion power battery in the future.

LiFePO4在大功率锂离子动力电池中具有广阔的应用前景，但材料的（电子、离子）电导率和振实密度非常低，导致高倍率性能和循环性能较差，限制了其在实际中的广泛应用。本项目拟采用化学自组装、原位聚合结合微波碳热还原方法，制备出分散性好、尺寸均匀并具有核壳结构的纳米球形石墨烯/Li3V2(PO4)3/LiFePO4/聚苯胺复合正极材料。首先利用原位聚合方法制备出具有球形形貌的FePO4/聚苯胺,然后掺杂较高理论比容量的快离子导体Li3V2(PO4)3和高电导率的石墨烯,通过双碳源、二步烧结和球形化技术，制备出高质量的LiFePO4纳米复合材料。最后加入不同比例的苯胺和过二硫酸铵，经过化学自组装过程，获得聚苯胺包覆的磷酸铁锂复合体系。本项目旨在通过优化工艺条件，系统研究复合体系中各物种的微观状态、结合行为以及对电化学性能的影响规律，为未来设计出更理想的锂离子动力电池新体系提供理论基础和技术支持。

LiFePO4具有理论比容量高、电压稳定、循环性能好、环境友好等优点，在动力电池中前景广阔。但材料本身极差的电导率限制了其在实际中的广泛应用。本项目采用纳米结构调控，离子掺杂和表面包覆等手段，结合理论计算研究了材料的结构和电化学性能的关系，取得的重要成果有：（1）采用原位聚合、两步烧结、双碳源进行包覆，获得了电化学性能比较理想的LiFePO4/C材料。（2）制备了V元素掺杂的最佳掺杂样品LiFe0.96V0.04PO4/C。然后采用V、F元素复合掺杂，得出最佳掺杂材料为LiFe0.96V0.04(PO4)0.98/3F0.02/C，该材料在0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C倍率下的比容量分别为162.6mAh/g, 143.6 mAh/g, 138.2 mAh/g, 124.3 mAh/g, 94 mAh/g, 76.8 mAh/g，具有较好的倍率性能。（3）计算了LiFePO4和LiFe0.96V0.04(PO4)2.98/3F0.02的能带结构与态密度，结果表明双元素掺杂材料的能隙较小，分态密度峰值增强，表现出更加优异的性能。扩散系数计算结果发现，LiFe0.96V0.04(PO4)2.98/3F0.02具有更强的锂离子扩散能力。（4）采用水热制备，冷冻干燥和碳热还原技术制备了三维石墨烯均匀包覆的LiFePO4/3DG/C复合材料。该材料在0.5 C、1 C、2 C、5 C、10 C不同倍率下的首次放电比容量分别为153.8 mAh/g、144.7 mAh/g、130.4 mAh/g、110.1 mAh/g、91.3 mAh/g，材料在1 C倍率下循环100圈后容量仍能保持99.6%。该课题研究成果将有助于磷酸铁锂材料的性能提升和推广应用，并对其它锂离子电池材料的发展具有重要的理论和指导意义。

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