Calligraphy-inspired brush written foldable supercapacitors

Chinese brush, made of a bundle of animal hairs in a quasi-parallel arrangement, is an effective tool that can be used to continuously place low-viscosity ink onto different substrates with high ink mass loading. Here, we demonstrate a highly effective approach to coat graphene onto rough and even crumpled substrates by using a Chinese brush. By combining forces including Laplace pressure differential, asymmetric retention and gravity, the low-viscosity graphene oxide ink can be sufficiently transferred onto different substrates through the brush hairs in a controlled manner. The as-prepared graphene films are used as electrodes for all-solid-state foldable supercapacitors. Using series and/or parallel connections, the energy storage performance of the foldable all-solid-state supercapacitors can be tailored to provide different output voltages and currents. The voltage of the three series connected devices with gel electrolyte can be extended to 2.4 V. A parallel connected foldable all-solid-state supercapacitor exhibits promising electrochemical performance, such as high areal capacitance of 258.6 mF cm−2, good energy density of 23.1 μW h cm−2 and power density of 0.2 mW cm−2. This work offers an alternative method of GO ink transfer, graphene film production and the fabrication of flexible electronics.