开放式分级孔结构的含异原子纳米碳纤维自撑膜的可控制备及其超级电容提高机制

Composite pore-forming agents composed of the inorganic molecular such as NH4Cl and the polymer with hydroxyl groups such as polyvinyl alcohol or polyethylene glycol are introduced to melamine resin aqueous solution and heteroatom-incorporated self-standing carbon nanofiber films with open hierarchical pore structure are directly prepared on the foam nickel as the current collector of supercapacitors by electrospinning melamine resin mixture onto the foam nickel, followed by simple carbonization/pore-tuning process. And obtained carbon nanofiber film electrodes can directly be used to assemble supercapacitors. Our purpose is to develop novel nano-carbon electrode materials and supercapacitors with excellent performance. The introduction of composite pore-forming agents can realize the tuning of the hierarchical pore structure in the process of carbonization, especially micropore structure which is suitable for the size of electrolyte, and it is benefit for the remain of heteroatoms. By tests, such as thermogravimetric analysis-infrared spectrometer(TG-IR), thermogravimetric analysis-mass spectrometry(TG-MS) and physisorption analyzer, the influence of the factors, such as the type and amount of composite pore-formed agents, electrospinning and carbonization/pore-tuning process, on the fiber morphology, hierarchical pore structure, existing form and amount of heteroatoms in the nano-carbon are explored. The supercapacitance performance of different carbon nanofibers and supercapacitors are studied in detail. According to the size and type of electrolyte, supercapacitance-enhanced mechanism which is realized by the hierarchical pore structure and heteroatoms is analysed in detail. The study will provide new ideas to improve the electrochemical properties of nano-carbon electrode materials.

本项目利用高压静电纺丝技术，将复合致孔剂（无机分子如NH4Cl、含羟基水溶型高分子聚乙烯醇或聚乙二醇）引入三聚氰胺树脂纺丝水溶液中，通过简单的碳化-调孔同步工艺，实现开放式分级孔结构、高异原子含量的新型纳米碳纤维膜在泡沫镍集流体上的可控制备，并直接用于超级电容器组装，致力于研发新型高性能纳米碳电极材料及其器件。复合致孔剂的引入实现在碳化过程中分级孔结构的调控，尤其是与电解质离子尺寸相匹配的微孔调控,并有利于异原子的保持。利用热重-红外（或质谱）联用技术和氮气吸附-脱附等手段，深入揭示复合致孔剂的种类及用量、纺丝及碳化-调孔工艺条件等对纳米碳材料的纤维形貌、分级孔结构、异原子存在形式及含量等的影响规律。详细研究不同纳米碳纤维及其器件的超级电容性能，并结合电解质离子尺寸和类型重点分析开放式分级孔结构和活性异原子对其超级电容性能提高的机制。本研究为提高纳米碳电极材料的电化学性能提供新思路。

目前超级电容器用纳米碳电极材料存在几方面问题：（1）碳材料受其碳结构的制约，比电容很难大幅度提高。（2）使用纳米粉体材料制备电极时，必须使用胶粘剂如聚四氟乙烯等将其粘结成块，这不仅会影响电极的导电性，也降低电荷储存能力及增加成本。（3）一般采用传统涂敷工艺将纳米粉体浆液在集流体上制备电极片，这种工艺繁琐，电极材料与集流体接触不良而导致体系的内阻较大进而很大程度上影响到材料的电化学性能。项目组针对以上问题，从组成和结构角度将异原子、纳米纤维结构及分级孔结构引入碳材料，从工艺角度采用高压静电纺丝技术在集流体上直接制备不含粘合剂的纳米碳纤维薄膜电极，实现对碳材料超级电容性能的进一步提高。项目组采用环境友好的、高活性异原子氮含量的三聚氰胺树脂（MF）和聚乙烯醇(PVA)混合水溶液通过高压静电纺丝法直接在泡沫镍集流体上可控制备了聚合物纤维膜，经过高温碳化在泡沫镍集流体上成功得到柔韧且独立自撑的含异原子碳纤维膜，进一步将氯化铵、聚乙二醇致孔剂加入到纺丝原液中，通过高压静电纺丝和简单的碳化-调孔同步工艺在泡沫镍集流体上制备分级孔结构高异原子含量的碳纤维膜。揭示致孔剂的种类及用量、纺丝及碳化-调孔工艺条件等对纳米碳材料的影响规律。分析分级孔结构(主要是相互贯通的中孔通道)和活性异原子N-5、N-Q及酚氧对其超级电容性能提高的机制。研制的开放式分级孔结构含异原子碳纤维膜的比电容达到250F/g，高于市售超级电容器用活性碳材料的比电容值。将开放式分级孔结构含异原子碳纤维膜在不加粘结剂的情况下直接制备出电极，进而直接组装成叠片式和卷绕式超级电容器。组装的超级电容器比功率达到1023~2621 W/kg，比能量达到4.3~6.4 Wh/kg，循环寿命≥10000次。这种新颖结构的纤维薄膜电极改善了碳电极材料的导电性和比电容值，并解决超级电容器组装中的工艺问题，从而加快超级电容器这种新型绿色能源的实用化进程，同时为进一步提高碳电极材料的综合电化学性能提供新思路和方法。项目组通过较为系统的研究，获得了一些创新性的研究成果。现已发表SCI、EI收录论文13篇，获得授权专利8项。