超级电容器用石墨烯薄膜：制备、基元结构及表面调控

石墨烯薄膜是一种以石墨烯纳米片为基元结构的宏观体，通过合理的结构设计和表面修饰使其具有优异的电学、力学和热学性能，将在电化学储能、电子器件、健康和环保等领域具有潜在的应用。本文主要综述了从石墨烯基元调控到二维宏观膜组装以及石墨烯薄膜在超级电容器应用中的研究进展。主要介绍了石墨烯薄膜的简易制备方法，并详细介绍了通过对石墨烯基元的结构调控和表面修饰来优化石墨烯薄膜电化学性能的两大策略，最后对石墨烯薄膜应用所面临的挑战和未来的发展进行了总结与展望。

Graphene Film for Supercapacitors: Preparation,Foundational Unit Structure and Surface Regulation

With the rapid development of the functional applications of portable and wearable electronic products (such as curved smartphones, smartwatches, laptops, and electronic skins), there is an urgent need to fabricate flexible, lightweight, and highly efficient energy storage devices that can provide sufficient power support. Flexible supercapacitors with high power density, high charging/discharging rates, wide operating temperature ranges, low maintenance consumption, and a long cycling lifespan can be integrated with smart wearable electronic products to provide power support. The conventional preparation method for the electrodes of flexible supercapacitors involves directly coating the active materials on flexible substrates. However, inactive materials such as the substrates and binders occupy a large volume and contribute notably to the weight of flexible electrodes, which is unsuitable for highly integrated flexible electronic devices. Owing to its unique characteristics, including large theoretical specific surface area, high electrical conductivity, excellent mechanical flexibility, good chemical stability, and ease of film processing, graphene has been widely used as an electrode material for flexible supercapacitors. The graphene film is a macrostructure with graphene nanosheets as the main structural units. As opposed to conventional flexible electrodes containing non-electrochemical active components such as collectors, conductive agents, and binders, graphene film electrodes are considered highly promising electrode materials for flexible supercapacitors because of their light weight and robust mechanical properties. However, the inevitable aggregation of graphene during electrode preparation creates 'dead volume' in the film electrodes, where the electrolyte cannot reach, further limiting the specific capacitance. In this review, we review the recent research on graphene films used for flexible supercapacitors, with emphasis on the assembling methods for graphene films, regulation of the graphene units, and their electrochemical performance. First, simple preparation methods for graphene films are introduced: vacuum-assisted self-assembly, blade coating, pressing aerogel, wet spinning, and interfacial self-assembly. Second, two major strategies for structural control and surface modification of the graphene units are described in detail: (1) structural control can transform the two-dimensional graphene nanosheets into defect graphene, which not only weakens the van der Waals force and π–π bond interactions between the nanosheets, but also leads to the formation of three-dimensional conductive networks and ion transport channels during the assembly process; (2) surface modification, which can suppress the agglomeration of graphene nanosheets by introducing heteroatoms and reactive functional group molecules, while improving their electrical conductivity and wettability, and introducing pseudocapacitance. Finally, the persisting challenges and future development of the commercial applications of graphene films are discussed.