限域空间内构筑石墨烯纳米纤维柔性电极及其电化学动力学研究

Graphene based flexible electrodes have several merits, such as high flexibility, high surface area and high conductivity, which are considered as an idea electrodes for flexible supercapacitors. However, up to now, theres is trade-off among volumetric energy density, gravimetric energy density and power density, caused by the unreasonable structures of electrodes. Herein, we proposed that graphene nanofiber based flexible electrode, combining the large pores and high-density nanoskeletons, has high potential for solving as mentioned problem. The large pores can act as ion channels to reduce the ion transport distance and resistance, where the electrochemical dynamics would be imporved and the gravimetric enrgy density and power density enhanced. Meanwhile, the high density of nanoskeletons guarantees the enhancement of volumetric energy density. Based on the previous works, we proposed that graphene nanofiber electrodes could be abtained by assembling graphene in confined nanospace supplied by co-axial electrospinnning and the fine structure of nanofibers is tunable by controlling the heat treatment process and the addition of pore agent. Furthermore, the effects of fine structure on mechanical properties and electrochemical dynamics will also be investigated. This proposed project could potentially provide a new strategy for preparing graphene based flexible energy storage device with both high energy density and high power density.

石墨烯柔性电极具有高柔韧性、高比表面和高导电性，是一种理想的柔性超级电容器电极。但是，已报道的石墨烯柔性电极的结构不合理，存在体积能量密度、质量能量密度和功率密度相互制约的问题。申请者提出构建石墨烯纳米纤维柔性电极，将大孔结构与致密的纳米骨架相结合，有望解决上述问题。大孔提供的离子通道和纳米尺度的骨架结构，减小离子在电极内部的扩散距离和阻力，能够改善石墨烯柔性电极的电化学动力学过程，提高电极的质量能量密度和功率密度；而致密的骨架结构有利于提高电极的体积能量密度。在前期工作基础之上，申请者拟利用高分子在同轴静电纺丝过程中形成的纳米级限域空间，组装石墨烯纳米纤维，通过调节热处理过程和造孔剂的种类与含量，实现石墨烯纳米纤维柔性电极的可控制备。并建立石墨烯纳米纤维柔性电极的宏观力学性质、电化学动力学过程与微观结构之间的关联，对发展高功率密度和高能量密度的石墨烯基柔性储能器件具有指导和借鉴意义。

本项目采用同轴静电纺丝技术，实现了GO在外层高聚物构筑的管状纳米空腔内连续组装。分别通过固化-清洗和高温热解的方法去除高聚物外壳，得到内层被还原的氧化石墨烯纤维（rGONFs）。电化学性能测试结果表明固化-清洗法得到的纤维，其储钾性能较差，这主要是由于纤维的石墨化程度较低。进一步通过高温热解，得到的石墨烯纳米纤维在容量、倍率性能和循环稳定性三个方面均有不错的表现。通过对比发现这些纤维的储钾性能受石墨化温度影响不大，这是因为石墨烯纳米纤维的间隙可作为离子传输通道缩短了K+的扩散路径以及自身的柔韧性缓冲了体积膨胀的双重效果弥补了石墨嵌钾在反应动力学上的不足。