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Multifunctional electrodes for structural supercapacitors are prepared by vacuum infiltration of single‐walled carbon nanotubes (SWCNTs) into woven carbon fibers (CFs); the use of reductive charging chemistry to form nanotubide solutions ensured a high degree of individualization. The route is highly versatile, as shown by comparing four different commercial nanotube feedstocks. In film form, the pure nanotubide networks ("buckypapers") are highly conductive (up to 2000 S cm−1) with high surface area (>1000 m2 g−1) and great electrochemical performance (capacitance of 101 F g−1, energy density of 27.5 Wh kg−1 and power density of 135 kW kg−1). Uniformly integrating these SWCNT networks throughout the CF fabrics significantly increased electrical conductivity (up to 318 S cm−1), surface area (up to 196 m2 g−1), and in‐plane shear properties, all simultaneously. The CNT‐infiltrated CFs electrodes exhibited intrinsically high specific energy (2.6–4.2 Wh kg−1) and power (6.0–8.7 kW kg−1) densities in pure 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) electrolyte. Multifunctional structural supercapacitors based on CNT‐coated CFs offer a substantial increase in capacitive performance while maintaining the tensile mechanical properties of the as‐received CF‐based composite. This non‐damaging approach to modify CFs with highly graphitic, high surface area nanocarbons provides a new route to structural energy storage systems. [ABSTRACT FROM AUTHOR]

Supercapacitors capable of providing high voltage, energy and power density but yet light, low volume occupying, flexible and mechanically robust are highly interesting and demanded for portable applications. Herein, freestanding flexible hybrid electrodes based on MnO 2 nanoparticles grown on macroscopic carbon nanotube fibers (CNTf-MnO 2 ) were fabricated, without the need of any metallic current collector. The CNTf, a support with excellent electrical conductivity, mechanical stability, and appropriate pore structure, was homogeneously decorated with porous akhtenskite ɛ-MnO 2 nanoparticles produced via electrodeposition in an optimized organic-aqueous mixture. Electrochemical properties of these decorated fibers were evaluated in different electrolytes including a neutral aqueous solution and a pure 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid (PYR 14 TFSI). This comparison helps discriminate the various contributions to the total capacitance: (surface) Faradaic and non-Faradaic processes, improved wetting by aqueous electrolytes. Accordingly, symmetric supercapacitors with PYR 14 TFSI led to a high specific energy of 36 Wh· kg MnO 2 − 1 (16 Wh·kg −1 including the weight of CNTf) and real specific power of 17 kW· kg MnO 2 − 1 (7.5 kW kg −1 ) at 3.0 V with excellent cycling stability. Moreover, flexible all solid-state supercapacitors were fabricated using PYR 14 TFSI-based polymer electrolyte, exhibiting maximum energy density of 21 Wh·kg −1 and maximum power density of 8 kW kg −1 normalized by total active material. [ABSTRACT FROM AUTHOR]