熔盐-卤化法可控制备微孔纳米炭纤维及微孔储能机制研究

Pore is one of the most important factors deciding the electrochemical performance of carbon-based supercapacitors. The preparation of microporous carbon with optimum pore size and nanometer pore length is very important for high-performanced supercapacitors and deepenning of storage mechanism of porous carbons. Herein,we propose to introduce the highly-controllable micropores into carbon nanofibers by molten salt-halogenation method,in which non-carbon atoms are introduced into carbon nanofibers and then extracted in the flow of chlorine at high temperature to creat pores at the atomic level.Carbon nanofibers with high surface area and nanometer pore length are obtained. Pore size can be regulated and optimized by selecting various kinds of non-carbon elements, e. g. Titanium, Silicon, Zirconium, Vanadium.By adjusting process conditions of molten salt-halogenation,the micropore quantity can be tuned and connectivity of pores can be improved. The research tries to find out the key process and influential factors of porous structure during molten salt and halogenation process. The formation and development of pores is studied. The electrochemical performance of microporous carbon nanofibers is measured as electrode material of supercapacitors.The relationship between specific surface area, porous structure and electrochemical performance (area-normalized capacitance, gravimetric capacitance and rate performance) as well as electroadsorption and transportation behavior of electrolyte ions in micropores are investigated. The purpose of the research is to explore a new strategy and method to high-performanced carbon-based supercapacitors, and to break the development bottleneck of porous carbon for supercapacitors.

孔是决定炭基电容器电化学性能的重要因素。制备具有最优孔径和纳米孔深的微孔炭对获得高性能炭电极和多孔炭储能机理的深化均有着重要的意义。本课题提出从纳米炭纤维出发，采用熔盐-卤化的方法，将特定非碳原子引入到纳米炭纤维再进行卤化刻蚀，实现对纳米炭纤维的原子级造孔，引入新微孔，获得高比表面积的微孔纳米炭纤维。通过选择不同的非碳元素（硅、钛、锆、钒）实现微孔孔径的调控与优化。通过改变熔盐-卤化过程参数实现微孔含量的调控和孔道贯通性的优化。掌握熔盐-卤化制备中的关键过程，研究影响微孔结构的过程参数，探讨熔盐-卤化过程中微孔的形成与演变。将微孔纳米炭纤维用作电容器电极材料，考察其电化学性能。探讨微孔炭比表面积、孔结构与电化学性能（表面电容、质量电容、倍率性能）的关联以及离子在微孔孔道中的吸附迁移行为。本研究的目的在于探索开发高性能电容器炭基材料的新思路和新方法，突破目前多孔炭电容器的性能瓶颈。

可控制备高比表面积的微孔/介孔纳米炭材料不仅对突破多孔炭电极性能瓶颈有着重要的意义，而且有助于多孔炭储能机理的探讨与深化。本项目通过熔盐处理、原液掺杂等一系列手段实现了电纺纳米炭纤维的孔结构可控制备和比表面积的提升，重点考察微孔/介孔的储能机制，具体如下：1）以甲阶酚醛树脂/PVP/乙醇为纺丝体系，添加正硅酸乙酯，经静电纺丝、后期热处理以及酸洗等过程制备纳米炭纤维。所得纳米炭纤维为典型的微孔炭，随着TEOS量的增加，比表面积从823 m2/g增加到2164 m2/g，最大比电容达到317 F/g。2）通过在甲阶酚醛树脂/PVP/正硅酸乙酯乙醇纺丝体系中加入嵌段共聚物F127，在原本的微孔体系中很有效的引入了中孔。中孔率从19%提升到64%。电化学测试和对比研究显示，微孔具有更高的储能密度，而介孔对倍率性能的提高十分有利。3）通过KOH熔融盐处理固化的酚醛纤维制备高比表面积的纳米炭纤维。该方法实现了对固化纤维的液相活化，活化更加均匀，更加可控。4）在酚醛树脂/PVP乙醇纺丝体系中同时添加硝酸镁/F127作为硬/软模板制备了具有取向介孔的纳米碳纤维。所得纳米碳纤维比表面积达674 m2/g，中孔率高达95％。在20A/g时保持186F/g的比电容，体现取向介孔在倍率性能上的优势。5）以木质素为碳前驱体，通过调节木质素/PVP比例实现孔结构调节与比表面积提升。随着PVP含量的提高，比表面积和微孔率均先提高后减小，比表面积达到600 m2/g，微孔率达到94.3%，比电容能达到264F/g。6）在木质素/PVP体系中添加硝酸镁制备了分级多孔碳纳米纤维，通过调节硝酸镁的添加量实现微孔/中孔比例调节。随着硝酸镁的增加，比表面积和中孔率均不断提高，最大比表面积达到1140 m2/g，比电容达到248 F/g。7）以纤维素/聚丙烯腈为前驱体制备多孔纳米炭纤维，通过氯化锌原位活化制备比表面积达1355m2/g的微孔纳米碳纤维。8）从甲阶酚醛树脂/PVP/乙醇纺丝体系出发，添加硝酸钴和纳米氧化镁为模板剂制备多孔纳米炭纤维。加入硝酸钴所制得的纤维呈现明显的带状形态，而添加纳米氧化镁则得到分级多孔纤维。