石墨烯柔性包覆过渡金属氧化物空心纳米球复合材料的制备及锂离子电池负极性能研究

As a new class of promising anode materials for LIBs discovered in 2000, transition-metal oxides (MOs) have shown a number of desirable properties, such as high theoretical capacity (500-1000 mAh/g, compared with 372 mAh/g for conventional graphite), based on a novel conversion mechanism. However, most of the MOs suffer from problems of poor electronic conductivity and rapid capacity fading because of pulverization originating from the huge volume expansion/contraction during cycling, which leads to the breakdown of electrical connection of anode materials from current collectors. To circumvent these obstacles, strategies have been proposed to mitigate the pulverization and further enhance the structural stability of electrode materials. Although significance breakthroughs have been obtained, the problems of MOs used as LIB anodes are still not solved completely and systematically..A novel strategy for the fabrication of graphene-encapsulated metal oxide hollow nanosphere (GE-MOHNS) by coassembly between negatively charged graphene oxide and positively charged oxide nanoparticles was presented in this program. The process is driven by the mutual electrostatic interactions of the two species, and is followed by chemical reduction. The resulting GE-MOHNS would possesse flexible and ultrathin graphene shells that effectively enwrap the oxide nanoparticles. Compared with other carbon/MO composites, the multifunctional features of GE-MOHNS are characterized as follows: (1) hollow structure of MOs and a "flexible confinement" function of GE could compensate for the volume change of MOs more effectively; (2) the enwrapping structure provides a larger contact surface for GE and individual dispersion of well-adhered MO particles and GE acts as an excellent conductive agent to facilitate electron transportation more efficiently, improving the accessible capacity; (3) detachment and agglomeration of pulverized MO particles are prevented effectively because they are separated by GE mutually; (4) porosity formed by the curled morphology of GE and hollow nanosphere structure of MOs provide a high and short way for lithium ions. As a result, this unique laterally confined GE-MOHNS composite can dramatically improve the cycling stability and the rate capability of MOs as anode materials for lithium ion batteries..GE-MOHNS composites will be prepared in this program. The interrelationship of preparation process, morphology and structure, LIB anode performance of GE-MOHNS composite will be revealed. GE-MOHNS composites with good cycling stability and rate capability as anode materials for lithium ion batteries are expected to obtain. Owing to the special well organized and flexibly encapsulated sutructure of prepared compoists, the strategy provided by this program would be helpful for MOs to apply in the next-generation LIB anode materials.

针对过渡金属氧化物作为锂离子电池负极循环性能差的问题，本项目提出了利用基于静电引力的自组装机制，在过渡金属氧化物空心纳米微球外表面柔性包覆石墨烯的新型碳/过渡金属氧化物复合材料制备方法。与其它碳/过渡金属氧化物复合材料相比，制备的复合材料应用于锂离子电池负极具有如下特点：（1）复合材料内部的空心结构和外部的柔性石墨烯包覆层，能更好地缓冲金属氧化物充放电过程中的体积变化；（2）过渡金属氧化物与石墨烯层接触面积更大，电极的电导率得到更好的改善；（3）石墨烯层将过渡金属氧化物颗粒相互隔离，完全避免了充放电过程中过渡金属氧化物颗粒的团聚。基于此，本项目将通过研究复合材料的制备工艺条件与其形貌结构、锂离子电池负极性能的关系，优化制备条件，制备出系列具有良好循环和功率性能的石墨烯柔性包覆过渡金属氧化物空心纳米微球复合材料，为过渡金属氧化物成为下一代锂离子电池负极材料的应用选择提供理论和方法的指导。

针对过渡金属氧化物作为锂离子电池负极循环稳定性差的问题，本项目提出了利用基于静电引力的自组装机制，成功制备了石墨烯-Fe3O4、石墨烯-Zn2SnO4，石墨烯-SnO2、石墨烯-CuO、石墨烯-V2O5等复合材料，其锂离子电池负极性能得到极大改善。其中，石墨烯-Fe3O4复合材料在电流密度为185.2 mA g-1条件下，30次循环后储锂容量可达803.5 mA h g-1, 为第二次放电容量的96%；石墨烯-Zn2SnO4复合材料在100 mA g-1的电流密度下经50次循环后，可逆比容量仍能保持727.2 mA h g-1；石墨烯-SnO2复合材料在158 mA g-1的电流密度下经100次循环后，可逆比容量为422 mA h g-1；石墨烯-CuO复合材料在500 mA g-1的电流密度下循环200次，比容量仍无损失，即使在1.0 A g-1的大电流密度下循环300次，比容量仍保留446 mA h g-1，该复合材料拥有卓越的倍率性能（5 A g-1电流密度下可逆比容量为329.4 mA h g-1）。.本项目还进行了石墨烯-过渡金属硫化物复合材料的制备新方法及其锂离子电池负极性能研究。研究结果表明，石墨烯作为过渡金属硫化物的负载基体，具有与过渡金属氧化物复合后相似的作用，不仅能提高过渡金属硫化物的导电性，而且能缓释过渡金属硫化物在充放电过程中的体积变化，改善其结构稳定性，从而实现过渡金属硫化物锂离子电池负极性能的改善。本项目为过渡金属氧化物成为下一代锂离子电池负极材料的应用选择提供理论和方法的指导，同时为石墨烯/过渡金属硫化物复合材料制备及其储锂性能的改善提供了新方法。.同时，基于本项目提出的复合材料制备思路，制备了Ag修饰氮掺杂石墨烯/TiO2、石墨烯-WO3纳米线簇、氮掺杂石墨烯/WO3纳米线等材料，制备的复合材料表现出了良好的光催化性能。.本项目研究成果合计发表学术论文10篇，投稿论文一篇（ACS Applied Materials & Interfaces Manuscript，第二轮审稿），授权发明专利2项，培养硕士研究生5名。项目完成了预期的研究内容并对研究内容进行了适当拓展，实现了预期的研究目标，各项成果指标超额完成。.谢谢国家自科基金委提供的支持！