Flexible, free-standing and holey graphene paper for high power supercapacitors

Flexible supercapacitors based on bendable electrodes have aroused much interest for integration in clothing materials and portable electronic devices. However, simultaneous achievement of high areal energy and high power densities still presents a great challenge. Herein we report the fabrication of free-standing, flexible graphene papers suitable for high-performance flexible supercapacitors. The binder-free graphene paper is made up of two types of holey graphene units (i.e. wrinkled graphene sheets and graphene nanoscrolls) that produce closely interconnected, porous 3D graphene architectures. The graphene papers reported here can be fabricated with a variety of thicknesses and areal densities, in the 10-70 μm and 1-5 mg cm ranges respectively. They exhibit a remarkable electrochemical performance in aqueous electrolytes: a) a high cell areal capacitance (230-190 mF cm in H2SO4 and 180-170 mF cm in Li2SO4, b) an outstanding capacitance retention of 60 % at ultra-large current densities of 1200 mA cm, c) an excellent long-term cycling stability and d) high areal power (~280 mW cm) and energy densities (~32 and ~60 μWh cm in H2SO4 and Li2SO4 respectively). These highly flexible graphene papers show a great improvement, in terms of areal energy-power densities, in relation to the state-of-the-art graphene-based film electrodes.