柔性石墨烯电极材料的制备及其性能研究

Flexible electrodes are a kind of current collectors that can keep high mechanical flexibility and stable electrical performances upon repeated bending, folding, twisting and/or stretching operations. The flexible electrodes are one of the important components in flexible energy storage and conversion devices, and have attracted growing attention because of their potential applications in flexible, wearable and portable electronics. Owing to the characteristics of flexible electronics, the corresponding electronic components should be lightweight, small in size, and highly stable under different mechanical deformation conditions. Given the facts that chemically modified graphenes have high mechanical strength, good electrical conductivity, and can be readily prepared by the cost-effective wet chemical approach in large scale, thus, they provide a new chance for developing high-performance graphene-based flexible electrodes. In the present project, we’ll design and synthesize graphene oxides with controllable chemical components, few structure defects, and narrow size distribution, and develop new strategies for preparing reduced graphene oxide films with high mechanical performances and electrical conductivity. The influences of chemical structure, film structure, and reduction method on the mechanical performances and electrical conductivity of graphene films will be explored, and their potential applications in flexible supercapacitors will also be examined. The establishment and implementation of this project will provide solid theoretical and technical supports for fabricating high-performance graphene-based films, flexible electrodes and devices.

柔性电极是指在弯曲、折叠、扭曲或拉伸等机械形变条件下保持结构与导电性能稳定的一类新型电极材料，是柔性能量存储与转化器件的重要组成单元；在柔性电子器件、可穿戴及便携式电子产品中具有广泛应用前景。为契合柔性电子器件的结构特点、优化器件性能，其能源供应组件柔性电极需要具有轻、薄、结构紧凑、尺寸小等结构特点。鉴于石墨烯优异的机械性能、良好的导电性、成本低廉（化学氧化剥离法）且易于加工成膜等特点，有望成为一类理想材料制备柔性导电电极。本项目将设计合成结构缺陷少、尺寸大且分布窄、结构可控的氧化石墨烯，系统地研究氧化石墨烯的化学结构与性能关系。发展新的成膜方法，探讨化学结构、膜结构、还原方法对薄膜机械力学和导电性能的影响，制备机械力学、导电综合性能优异的石墨烯基柔性电极。探索其在高性能柔性超级电容器件中的应用。该项目的确立与完成将对高性能石墨烯薄膜及柔性电极材料研究提供理论基础与技术支撑。

柔性电极材料在柔性电子器件、可穿戴及便携式电子产品中具有广泛应用前景。石墨烯材料具有优异的力、电、热学性质，良好的化学稳定性、环境稳定性与热稳定性，是一类理想的柔性导电电极材料。面向实际应用，发展高效构筑方法和结构控制机制将石墨烯片层组装成力电性能优异的薄膜材料是一个重要课题。本项目发展了一种室温氧化方法，通过调控氧化反应温度（20 oC）、浓硫酸含水量（4 wt%）及反应过程（去除水解氧化步骤），利用改进的Hummers方法实现了官能团化程度较高、低缺陷密度氧化石墨烯的高效制备（120%）；发现氧化石墨烯及还原氧化石墨烯薄膜材料具有面内负泊松比性质。基于实验表征的力学模型刻画了薄膜的多层级特征：石墨烯局部聚集而成密排片层，密排片层进一步弯曲、折叠、起皱形成网络结构。模型分析揭示了载荷作用下微结构的演化规律与负泊松比机制：沿加载方向密排片层受拉发生取向，进而材料厚度方向褶皱幅值被压缩减弱，最终导致横向膨胀；首次实现了氧化石墨烯前驱体片层尺寸与化学结构的独立控制。率先提出并证实了氧化石墨烯前驱体及石墨烯结构单元的化学结构、组装方法、复合组分对宏观组装体薄膜的结构稳定性、力学、电学性能有重要影响。共轭结构大、拓扑结构缺陷少的低缺陷化学修饰石墨烯片层间的相互作用增强，显著提高薄膜力学强度及杨氏模量；同时，低结构缺陷密度有效降低电子在传导过程中的散射，极大地提高了薄膜材料的电导率。以低缺陷氧化石墨烯为前驱体，蒸发诱导组装方法制备了高性能类贝壳结构石墨烯复合薄膜。蒸发诱导组装及复合组分诱使石墨烯片层面内形成更多褶皱结构，有效增强片层间相互作用，使石墨烯复合薄膜具有优异的力学性能和导电性，作为柔性超级电容器件电极材料表现出优异的性能，在柔性电子器件中具有广泛应用前景。上述研究结果揭示了石墨烯薄膜材料结构与性能间的构效关系，为制备高性能石墨烯柔性薄膜电极材料提供了新思路。