基于阳离子插层活化MXene的高体积电容特性复合材料的设计、合成和电容机制研究

Low energy density, especially low volumetric energy density, is the most problem that supercapacitors are facing today. To develop new electrode materials with high volumetric capacitance is the key to improve volumetric energy density of supercapacitors. As a new two-dimensional crystal material, MXene is a new type of very promising electrode material with unprecedented high volumetric capacitance. However, the restacking of the two-dimensional MXene sheets and narrow interlayer spacing limit the intercalation/diffusion of electrolyte ions, hindering the full utilization of their surface, and the poor conductivity between the MXene sheets hinders the electronic transfer. In this project, we will design a new type of cation-intercalated MXene/graphene (or carbon nanotube) composite materials, in which the interlayer spacing is expanded by the pre-intercalated cations, facilitating the intercalation/diffusion of electrolyte ions and activating the deep sorption surface of the MXene sheets, graphene (or carbon nanotube) conductive networks increase the conductivity between the MXene sheets. Thus, the composite materials simultaneously afford high-speed nano-passages for both ion intercalation/diffusion and electronic transfer. Based on the systematic material characterization and electrochemical analysis, the activation mechanism and capacitance-forming mechanism of the cation-intercalated MXene will be investigated. The relationship between the composite nanostructure of the prepared composite materials and their volumetric capacitive behavior will be investigated intensively, thus obtaining the MXene-based composite materials with excellent volumetric capacitive performance and drawing its optimized designing rule. Based on the above research, we will explore and optimize the asymmetry supercapacitor. The adaption mechanism of negative and positive electrodes will be studied. The results obtained in this project may provide theoretical basis for designing MXene-based electrode materials.

能量密度低，尤其是体积能量密度低，是超级电容器面临的最大问题。创制具有高体积电容特性的新型电极材料是提升超级电容器体积能量密度的关键。作为一种新型二维晶体，MXene是一类极具前景的高体积比电容电极材料，但存在离子的插入/扩散受限和层间导电性差等缺点。本项目设计合成阳离子插层活化MXene/石墨烯（或碳纳米管）复合材料，利用不同尺寸的阳离子插层调控MXene的层间距和活化深层表面，利用石墨烯（或碳纳米管）提高层间导电性，由此同时构筑离子插入/扩散和电子传输的纳米通道。综合系统的材料表征和电化学分析，研究阳离子插层MXene的插层活化机理和电容形成机制。揭示复合材料的纳米结构与其体积电容特性之间的构效关系，获得高体积电容特性的MXene基电极材料，并形成其优化设计原则。创制和优化基于该类复合材料的不对称电容器，探讨正负极匹配机制。研究成果将为MXene基电极材料的设计提供理论依据。

体积能量密度是储能器件最重要性能指标之一，创制具有高体积电容特性的新型电极材料是提升器件体积能量密度的关键。MXene是一类极具前景的高体积容量电极材料，但仍存在比容量较低、离子的插入/扩散受限差、层间导电性差等缺点，限制了其体积容量特性。本项目重点围绕高体积容量MXene基电极材料的可控制备及储能机制开展研究工作，优化了Ti3C2 MXene的制备条件，合成了多系列阳离子插层Ti3C2 MXene材料及过渡金属氧（硒）化物@MXene复合电极材料，深入研究了其储能机制，揭示了该类材料结构与其储能特性之间的构效关系。主要科学发现包括：（1）阳离子插层可以有效调控MXene材料的层间距与表面化学特性，层间距是水合金属离子柱撑效应、阳离子与MXene之间库伦作用及相互化学反应（对过渡金属离子）等多种因素综合作用的结果；（2）发展了季铵离子插层精确调控MXene层间距的新方法，在保持MXene材料表面化学性质不变的前提下利用季铵离子的尺寸渐变效应实现其层间距的精确控制和连续调节，此方法可推广到其它二维材料；（3）澄清了不同电解液体系与二维材料层间距之间的匹配机制，即当MXene层间距与电解质离子尺寸匹配时其比容量达到最大值，该匹配机制为高体积能量密度的二维电极材料提供设计指导；（4）发展了一种超声促进原位复合法，制备出TMOs(TMSs)@Ti3C2复合材料，实现过渡金属氧（硒）化物和MXene的优势互补，有望作为一种高体积储锂性能的负极材料。本项目的研究成果将丰富MXene材料结构调控科学内容，深化二维材料储能机制认知，为发展新型致密储能电极材料及器件提供一定理论指导和开发思路。