Flexible porous Graphene/Nickel hydroxide composite films with 3D ion transport channels for high volumetric performance asymmetric supercapacitor

Abstract Flexible supercapacitors, as an energy-storage device, have recently attracted great attention from developers of various mobile and wearable electronic products, with low maintenance cost and long cycle life. As a commonly used electrode material for pseudo-supercapacitors, nickel hydroxide-based electrodes, although they provide a high specific capacitance, lack of rate and continuous charge/discharge capabilities, and on account of their inherently poor conductivity and limitations from diffusion process in bulk particle size. Particularly, pure nickel hydroxide is difficult to be directly prepared as a film for flexible electrodes. Here, we report a universal method for the preparation of porous graphene sheets/nickel hydroxide (PGNH) films with fast 3D ions/electrons transport channels through vacuum filtration self-assembly technique. In addition to owning high conductivity, large tap density and good flexibility, the PGNH film electrode also exhibits excellent cycling stability and good rate capability, which is in sharp contrast to conventional nickel hydroxide powders. Furthermore, the PGNH film electrode shows an ultrahigh volumetric specific capacitance of 2321 F cm−3 and a gravimetric specific capacitance of 1209 F g−1. More importantly, the assembled PGNH//porous graphene sheets/carbon nanotube ASC device exhibits considerable volumetric specific energy densities of 89.5 Wh L–1 in 6 M KOH and 44.7 Wh L–1 in PVA/KOH electrolyte.