三元石墨层间化合物的结构调控及储钠机制研究

Sodium-ion batteries (NIBs) provide a great application prospect for the large-scale electric energy storage. For anode materials, graphite-like carbon-based materials should be intensively focused as competitive candidates for the practical application of NIBs in future. It is an important and meaningful research topic to adjust the interlayer spacing of graphite and to controllably design graphite-like microstructure for fast insertion/extraction and high storage capacity of Na+. This project controllably designs the composition and microstructure at atomic/molecular scale using molten salt synthesis to prepare ternary graphite intercalation compounds (GICs) for sodium ion storage. The influence of insertion guests and synthesis parameters on the microstructures (stage structure, interlayer spacing and distribution homogeneity of guests, etc.) of GICs will be researched. Subsequently, we will study the synergistic effects of different guests and graphene layers. Based on these, the correlations between the compositions, structures and electrochemical properties of GICs will be revealed and the Na+ storage mechanism will be elucidated, moreover, the structure control mechanism of GICs will be established. As a result, a novel design proposal and theoretic foundation will be provided for research and development of sodium ion anode materials in large-scale energy storage field.

钠离子电池在大规模储能方面具有广阔的应用前景，对于负极材料而言，石墨类炭基材料是未来钠离子电池实用化应该重点关注的研发对象。调整石墨的层间距大小，可控制备出既适合Na+嵌入/脱出的微层结构又具有较高储钠容量的石墨类材料，是一项具有重要理论和实际意义的课题。本项目拟采用石墨层间化合物为研究对象，通过熔盐合成法从原子/分子水平控制材料的组成和微观结构，设计适合钠离子储存的三元石墨层间化合物。研究插入客体的种类和合成工艺参数对石墨层间化合物的阶结构、层间距和客体分布均匀性等微观结构的影响规律；探寻插入客体与客体、客体与石墨片层之间的协同作用关系；揭示复合材料的组成、结构特征与其电化学性能之间的构效关系；阐明在复合材料体系下Na+储存的反应机制；建立钠离子电池负极材料用石墨层间化合物的结构调控机制，为大规模储能用钠离子电池负极材料的研究提供一种新的设计思路和理论依据。

石墨层间化合物具有良好的层状结构、高的电子导电性、可调的层间距大小和插入客体种类，探索石墨层间化合物在钠/锂离子电池负极材料中的应用潜力，是一项具有重要理论和实际意义的课题。本项目以金属氯化物插层的石墨层间化合物为研究对象，利用熔盐合成法在石墨层间插入一种或两种氯化物客体，实现二元/三元石墨层间化合物的制备。通过石墨载体/插入客体种类的选择和合成工艺参数的调整，可调控石墨层间化合物的阶结构和层间距等微结构，进而探明了复合材料的组成、结构特征对其电化学性能的影响规律，结合理论计算发现Na+/Li+在石墨层间化合物中的储存机制有别于传统方式。研究表明石墨层间化合物具有高的储锂容量，其容量可高达1371 mAh g-1。为抑制金属氯化物的溶解，在石墨片层上引入环氧官能团改性及在石墨片层间引入金属氧化物的改性方式，能够在很大程度上提升石墨层间化合物作为负极材料的循环稳定性能，保证可逆容量在200次循环内保持稳定。另外，本项目也设计合成了一系列炭材料复合的金属硫化物/磷化物作为储钠储锂负极材料，发现金属硫化物/磷化物在钠离子电池应用方面具有更好的性能，为下一步发展高性能钠离子电池用金属硫化物/磷化物复合的石墨层间化合物提供了创新途径。