高体积容量石墨烯插层过渡金属氮化物的设计合成和电容储能机理

Supercapacitors (SCs) are promising power sources because of their fast charge and discharge rates, good safety, and long cycle life. However, the limited volumetric capacitance and energy densities of SCs hinder their wide application in energy storage. The volumetric energy density of a SC depends on the volumetric capacitance and working voltage. Thus, it is an effective way to increase volumetric energy density by enhancing volumetric capacitance. According to the charge storage mechanisms, SCs are divided into electric double layer capacitors and pseudocapacitors. Pseudocapacitive materials like transition metal oxides/hydroxides and conducting polymers can deliver higher capacitance than electric double layer capacitive materials such as carbon nanotubes or graphene. However, the low electrical conductivity of metal oxides and kinetics irreversibility of conducting polymers usually result in low rate capability, small power density, and/or poor cycling stability. Consequently, the design and development of new electrode materials that combine high electrical conductivity, high density and large specific capacitance is crucial to the development of high-performance SCs with high volumetric energy densities. In this project, we aim at designing and fabricating mesoporous transition metal nitrides/N-doped graphene nanohybrids (TMNs/NG) and assembling high-performance SCs with large volumetric energy/power densities. The TMNs/NG will be synthesized by nitriding organic amine molecules intercalated transition metal oxide layers such as MoO3, V2O5, or Nb2O5. The as-produced 2D TMN/NG hybrids have large specific surface area and abundant active sites for charge storage and the interlayered graphene nanosheet not only provides mechanical stability and support for 2D mesoporous TMN but also suppresses electrochemical oxidation and dissolution of the TMNs in the electrolytes to achieve long-term cycling stability. On the other hand, the enhanced electroconductivity of 2D TMN/C hybrids leads to higher utilization ratio of active materials, faster ion and electrons transport and thus enabling more efficient storage and producing larger specific capacitance and higher rate capability. The evolution of chemical composition and states, microstructure, surface topography, wettability as well as charge transfer events of 2D TMN/C hybrids during charging-discharging will be investigated by in situ experiments including in-situ Raman, in-situ microscopy, in-situ energy spectroscopy. The physical mechanisms underlying charge storage in TMN/NG hybrids will be understood and proposed. High-performance flexible TMN/NG hybrids electrode materials and supercapacitors with high volumetric capacitance, high volumetric energy/power density will be fabricated. This project offers perspectives to the development of next-generation SCs with high volumetric capacitance and energy density, which could find promising applications in electrochemical energy storage.

超级电容器是一种重要的储能器件，具有充放电速率快、寿命长、安全性高等优点，然而低的体积能量密度限制了其应用范围。研发高体积容量电极材料是实现超级电容器致密储能的关键。本项目提出利用空间限域反应策略，以有机胺插层二维过渡金属氧化物为前驱物和模板，可控制备出超高体积容量的石墨烯插层过渡金属氮化物电极材料。过渡金属氮化物和石墨烯在纳米尺度下逐层复合，提供了连续的离子运输通道，增加了离子接触表面积和储能活性位点，提高了电极材料的电化学利用率和空间利用率，提升了金属氮化物的电化学循环稳定性。研究电极材料的形貌、微观结构、组成、表面积、化学状态和孔结构等对双电层电容和赝电容的影响。利用原位Raman和X射线吸收谱分析充放电过程的中间产物、电极表面化学状态以及金属价态的变化，提出电容储能机理和赝电容反应电化学模型。本项目的研究为设计高体积容量超级电容电极材料提供了理论指导，具有重要的科学意义和应用价值。

过渡金属氮化物具有高导电性、高振实密度、良好的化学稳定性以及大的赝电容等优点，是一类极具应用前景的高体积容量电极材料，然而目前的金属氮化物材料存在比容量较低、离子扩散慢、赝电容储能机理不明晰等问题，限制了其在高能量密度储能器件中的应用。针对上述关键问题，本项目围绕高体积容量过渡金属氮化物/碳复合电极材料的设计、可控制备、电容性能、储能机理等方面开展了研究工作。主要创新性研究成果如下：（1）创制了高体积容量的石墨烯插层过渡金属氮化物复合电极材料，发展了普适性的空间限域合成方法，以有机胺插层过渡金属氧（或硫）化物为前驱物，通过限域热氮化反应，可控制备了高体积容量的过渡金属氮化物/类石墨烯碳复合电极材料。金属氮化物和石墨烯碳在纳米尺度层层复合，实现了不同材料的结构协同优化和兼容储能，大幅提升材料电子和离子传输性能，从而获得大的体积容量、高的倍率性能和长循序寿命。（2）揭示了过渡金属氧化物到过渡金属氮化物过程中，材料的电容性能变化及规律，发现了材料中N/O比的变化与电容性能之间的映射关系。结合原位Raman光谱和理论计算，提出了过渡金属氮化物赝电容储能机制。制备了体积容量高达1203 F/cm3的VN/C复合材料并研制了超高体积能量密度和功率密度的全固态超级电容器。（3）设计合成了几种金属氮化物基异质界面复合材料，研究了复合材料的电解水析氢性能，以及在锂硫电池中的电催化性能，开发了高性能的电解水析氢催化剂和金属氮化物基高载硫量锂硫电池正极材料，拓展了金属氮化物电极材料在电化学储能中的应用。本项目研究成果推进了金属氮化物基电极材料在高性能固态超级电容器以及电化学储能器件的研发进程，具有重要的理论意义和潜在的应用前景。项目执行期间，发表SCI论文24篇，申请中国发明专利7项，培养博士生6名，已毕业博士2人，毕业硕士研究生8名，完成了预期的研究目标。