具有三维导电网络的磷酸铁锂复合材料的构建及性能研究

As one of the most promising cathode materials for power lithium ion batteries, lithium iron phosphate LFP(LiFePO4) with the olivine structure has attracted much attention due to certain safety, good cycling stability, environmental benignity, and low cost of the raw materials since its discovery in 1997. Considerable efforts have been made to overcome the electronic and ionic transport limitations of LiFePO4. However, the electrochemical performance of LFP deteriorates with increasing charge/discharge rates due to its low electronic conductivity and Li ion diffusion rate. Carbon coating and particle size reduction have been developed to enhance the electrochemical performance. However, the rate-performance enhancement of LFP is still limited, for thin carbon layer arising from low carbon content can hardly form an effective continuous carbon network that bridges the particles to enhance the electrical contact, and if the volume of carbon is increased to form a continuous network, the energy density of the cell will be decreased. Carbon nanotubes (CNs)and graphene exhibit extraordinary electrical properties， high surface area and chemical tolerance, and have a huge potential in lithium ion battery materials. Therefore, a better combination manner for LFP/graphene/CNs composite is needed to realize an optimum charge/discharge performance. In this project, we assume to establish a three-dimensional highly conductive network in LFP/graphene/CNs composite to solve the problem mentioned above. We designed several routes and try to find the best conditions to prepare C-LiFePO4 composite which is embedded in graphene matrix and CNs as nanoparticles to establish three-dimensional conductive network. The electrochemical performances of LFP composites will be studied, and the effecs of synthesis conditions, surface topography and particles size of LFP composite on its performances will be disccussed. The capacity of above composites should maintain 115mAh/g under 10C charge/discharge.

自1997年磷酸铁锂被首次报道以来，它因优越的安全性能、良好的循环性能及低价环保等优点，被认为是最有发展潜力的动力锂离子电池的正极材料。近来，碳包覆和材料纳米化被认为是有效解决磷酸铁锂较低的导电性和锂离子扩散系数的方法，以改善其倍率性能.但由于碳材料的包覆量较低，包覆后仍很难建立搭建在磷酸铁锂颗粒之间的连续有效的高导电网络，而碳包覆量的增加会导致电池能量密度的降低。 为解决以上问题，项目计划使用具有高导电性能的石墨烯及碳纳米管材料，将其与磷酸铁锂纳米材料复合，最终构建点面、点线结合的三维高导电性网络。我们将通过不同的实验过程和方法来探索制备三维导电网络复合材料的最优方法和条件，通过研究其电化学性能，分析制备方法条件、材料形貌、尺寸与其电化学性能的关联，最终达到合成具有优异高倍率性能的磷酸铁锂复合材料的目的，预期10C倍率时，材料容量保持在115mAh/g以上。

自1997年磷酸铁锂被首次报道以来，它因优越的安全性能、良好的循环性能及低价环保等优点，被认为是最有发展潜力的动力锂离子电池的正极材料。近来，碳包覆和材料纳米化被认为是有效解决磷酸铁锂较低的导电性和锂离子扩散系数的方法，以改善其倍率性能，但由于碳材料的包覆量较低，包覆后仍很难建立搭建在磷酸铁锂颗粒之间的连续有效的高导电网络，而碳包覆量的增加会导致电池能量密度的降低。................ 为解决以上问题，项目使用具有高导电性能的石墨烯及碳纳米管材料，将其与磷酸铁锂纳米材料复合，最终构建点面、点线结合的三维高导电性网络。我们通过不同的实验过程和方法来探索制备三维导电网络复合材料的最优方法和条件，通过研究其电化学性能，分析制备方法条件、材料形貌、尺寸与其电化学性能的关联，最终合成具有优异高倍率性能的磷酸铁锂复合材料。.