高比容量Li2S@LiFePO4/石墨烯复合材料的构建及其混合储能机理研究

Electrochemical hybrid energy-storage is the new area of the research for chemical power sources in the future. Study of the new hybrid energy-storage materials as well as the synergy mechanism between different components has important application and academic value. This project is proposed to employ a facile rheological phase-carbon thermal reduction method to synthesize a type of core-shell structured Li2S@LiFePO4/graphene (Li2S@LFP/G) cathode composite, in order to simultaneously resolve the problems of LiFePO4 (LFP)-based material with low theoretical specific capacity and Li2S with the dissolution of polysulfide in electrolyte during charge and discharge. Through studying and tuning the synthesize condition, realizing the control of the micro-dimension, structure and composition of the product. As a result, the designed Li2S@LFP/G not only possesses good electrochemical performances including large specific capacity (> 600 mAh/g), long cycling life as well as high-rate performance, but also has good compatibility to match with the no-lithium contained graphite and silicon-carbon anodes. On the other hand, the hybrid energy-storage mechanism of the composite is explored using electrochemical analysis, theoretical calculation, molecular dynamics simulation combined with characterization of the micro-structure and interfacial property of Li2S@LFP/G with different state of charge and discharge. The research of this project is believed to give significant theory basis and study reference for the development of electrochemical hybrid energy-storage.

电化学混合储能是化学电源未来发展的新领域，开发新型混合储能材料，探索混合储能的协同作用机理，具有重要的学术意义和应用价值。本项目拟采用易于规模化的流变相-碳热还原方法，构建一种核壳结构的硫化锂@磷酸铁锂/石墨烯（Li2S@LFP/G）正极混合储能复合材料，以期同时解决LFP基材料比容量低和Li2S中间态多硫化物溶解的问题。通过对合成工艺的考察和研究，实现材料微观尺度、结构和组分比例的调控，有望使其比容量达到600 mAh/g以上，兼具良好的倍率性能和循环稳定性，且能与无锂源石墨、硅碳类负极相匹配。另一方面，通过电化学分析、理论计算、分子动力学模拟和界面性质表征相结合的手段，揭示充放电过程中复合材料的混合储能机理。本项目的研究将为电化学混合储能领域的发展提供重要的理论依据和研究方法。

电化学混合储能可以发挥各组分的优势，是未来化学电源发展的方向之一。本项目构筑了磷酸铁锂/多硫化物混合储能体系，并通过物理表征、电化学测试和密度泛函理论计算揭示了磷酸铁锂和多硫化物组分间的协同储能机制。研究发现磷酸铁锂对多硫化物组分有较强的吸附作用，减轻了多硫化物的“穿梭效应”；磷酸铁锂与多硫化物接触后，其能带结构和态密度分布发生改变，改善了界面区域的电子导电性和电化学活性；磷酸铁锂和多硫化物组分均有电化学活性，并均可贡献容量。进一步优化材料结构，构筑了多孔石墨烯修饰的卵壳结构磷酸铁锂/硫复合储能材料，系统研究了磷酸铁锂组分对复合材料电化学性能的促进作用，以及复合储能材料中石墨烯/磷酸铁锂和磷酸铁锂/硫及多硫化物的复合模型及界面效应。此外，还一进步将构筑混合储能体系的概念拓展至其他材料体系中。本项目的研究为电化学混合储能领域的发展提供了理论依据和研究方法，具有重要的学术意义和应用价值。