Flexible Graphene/Carbon Nanotube Electrochemical Double‐Layer Capacitors with Ultrahigh Areal Performance

The fabrication of electrochemical double‐layer capacitors (EDLCs) with high areal capacitance relies on the use of elevated mass loadings of highly porous active materials. Herein, we demonstrate a high‐throughput manufacturing of graphene/carbon nanotubes hybrid EDLCs. The wet‐jet milling (WJM) method is exploited to exfoliate the graphite into single‐few‐layer graphene flakes (WJM‐G) in industrial volumes (production rate ca. 0.5 kg/day). Commercial single‐/double‐walled carbon nanotubes (SDWCNTs) are mixed with graphene flakes in order to act as spacers between the flakes during their film formation. The WJM‐G/SDWCNTs films are obtained by one‐step vacuum filtration of the material dispersions, resulting in self‐standing, metal‐ and binder‐free flexible EDLC electrodes with high active material mass loadings up to around 30 mg cm−2. The corresponding symmetric WJM‐G/SDWCNTs EDLCs exhibit electrode energy densities of 539 μWh cm−2 at 1.3 mW cm−2 and operating power densities up to 532 mW cm−2 (outperforming most of the reported EDLC technologies). The EDCLs show excellent cycling stability and outstanding flexibility even in highly folded states (up to 180°).