氮化钛/氮掺杂石墨烯三维层次孔结构的可控制备及其有机体系锂-空气电池性能研究

Among various electrochemical energy storage systems explored to date, the lithium-air battery is one of the most promising devices, with a theoretical energy density nearly 10 times higher than that of conventional lithium-ion batteries. The most critical issues that lithium-air battery suffers from are the low practical capacity, low energy efficiency and low cycle life. In order to solve these problems, this project proposes that a hierarchical porous TiN/N-doped graphene hybrid can function as a high-performance cathode material for the organic electrolyte lithium-air battery. The unique hierarchical porous structure, which consists of micro-, meso- and maro-pores, facilitates rapid O2 transfer and diffusion, and provides a high density of reactive and storage sites for Li-O2 reactions, resulting in the improvement of the specific capacity. The N-doped graphene nano-sheets have highly efficient activity for oxygen reduction, and the TiN anchored on graphene nano-sheets can also be used as active catalyst for both the oxygen reduction and evolution reactions during charge/discharge process, resulting in the enhancement of the energy efficiency and cycle life. We will prepare the hierarchical porous TiN/N-doped graphene hybrid using template technique, study the influence of its porous structure, components and N-doping functionalities on its electrochemical performances in lithium-air battery, and discuss the electrochemical mechanism of Li-O2 reactions and the synergistic effect of TiN and N-doped graphene nano-sheets on catalytic activity for Li-O2 reactions. On this basis, we will optimize the preparation procedures of the hierarchical porous TiN/N-doped graphene hybrid and successfully prepare superior hierarchical porous TiN/N-doped graphene hybrid material with high specific capacity, excellent energy efficiency and long cycle life. Through completing this project, we will obtain the key preparation technology of the cathode material for the lithium-air battery, and provide the experimental basis and theoretical guidance for the application of novel three-dimensional graphene-based hierarchical porous materials in the field of the lithium-air batteries.

针对有机体系锂-空气电池中正极材料存在的问题和缺陷，本项目提出以氮化钛（TiN）/氮掺杂石墨烯（N-GNSs）三维层次孔结构材料作为锂-空气电池正极材料。利用层次孔结构为氧气提供快速地传输和扩散通道，为放电产物提供充分地存储空间，提高放电容量；利用具有氧还原催化活性的N-GNSs担载具有氧还原和氧析出双向催化活性的TiN，降低过电位以提高能量效率和循环性能。本项目从材料结构控制入手，通过模板法制备TiN/N-GNSs三维层次孔结构，重点考察材料的孔结构、组分配比及N掺杂状态与锂-空气电池性能之间的关系，从微观层面揭示材料电化学作用机理及TiN与N-GNSs两相之间的协同催化机制，优化制备工艺，最终得到高比容量、高能量效率及优异循环性能的锂-空气电池正极材料，并形成关键制备技术，为促进新型三维GNSs基层次孔结构材料在锂-空气电池中的应用提供可靠的实验依据和理论指导。

本项目以提高锂-空气电池性能作为主要目的，设计一系列材料用作锂-空气电池电极材料，其中主要包括三维Co/CoO-石墨烯-碳化三聚氰胺三维层次孔泡沫、碳纤维/MnO2及三维石墨烯/MnO2复合材料等。系统研究了不同材料对锂-空气电池性能的影响，并详细分析了不同材料的锂-空气电池储能机制，为新型锂-空气电池电极材料的开发提供可靠的实验依据和理论指导。取得的成果主要如下：.1、碳纤维为模板，采用水热法制备了一种新颖的空心管状δ-MnO2，并在锂氧电池中体现出了优异的催化性能。该δ-MnO2具有独特的空心隧道结构，其管壁由高度分散的超细的纳米片构成，这一特征有利于电解液、氧气和放电中间体在催化剂中的传输。作为锂氧电池催化剂，该管状δ-MnO2可显著降低电池的过电势，特别是充电过电势，同时提高了锂氧电池的倍率性能和循环稳定性。.2、在上一个工作的基础上，采用液相合成法，通过控制高锰酸钾的加入量制备了一系列不同δ-MnO2负载量的δ-MnO2/炭同轴纤维，发现当碳纤维与高锰酸钾的质量比为1:4时，可优化得到最佳结构的复合材料。.3、以三维的密胺海绵为最初的支撑骨架，采用一步烧结法制备了核壳结构的Co/CoO 修饰的石墨烯基三维锂氧正极。密胺海绵具有三维连续的框架结构和优异的弹性，碳化后，该框架结构和弹性均得以保持。同时，石墨烯纳米片可被海绵框架完美支撑，呈平整的二维结构并被高度还原。这一特征有助于通过放电产物形貌的观察探索催化剂的催化行为。.4、基于氮摻杂的三维石墨烯气凝胶，通过水热法来制备三维石墨烯/MnO2复合材料，由于所制备的三维石墨烯具有发达的网络结构和高的比表面积，为MnO2的成核生长提供了大量骨架，进而提高MnO2材料的利用率。此外，作为锂氧电池和Li-MnO2电池的阴极材料，三维石墨烯/MnO2表现出良好的催化性能和高的可逆容量。