Flexible supercapacitors with large power and energy densities, long life cycles and good operational safety are necessary devices for various applications. In this work, we demonstrate the integration of a composite based on graphene nanosheets/multiwalled carbon nanotubes in an in-plane supercapacitor configuration by using a straightforward preparation involving the filtration of nanomaterials to produce an electrode film. Reduced graphene oxide (RGO) received 15 wt % carbon nanotubes to act as a conducting additive, which led to a flexible and transferable thin film (RGO/MW) with an average conductivity of 20.0 S cm (1). Three ionic liquids were tested as electrolytes for the supercapacitor, among which 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMITFSI) was observed to exhibit the best performance. The specific capacitance of the supercapacitor based on RGO/MWEMITFSI reached 153.7 F g (1) at a current density of 0.2 A g (1) and exhibited a capacitance retention of 88% after 2000 cycles. The maximum energy and power densities were calculated to be 41.3 Wh kg (1) and 3.5 kW kg (1), respectively, for the RGO/MW-EMITFSI supercapacitor. (C) 2015 Elsevier Ltd. All rights reserved.