Electrical double layer capacitors (EDLCs), often also called supercapacitors, have steadily grown in importance as highpower electrochemical energy storage devices with ultra-long cycle-life [ 1 ] , sub-second charging, [ 2 ] and a very wide operational temperature range, [ 3 ] properties that are currently unattainable in Li-ion batteries. The applications of these important devices include use in consumer electronics, uninterruptable power supplies, energy effi cient industrial equipment, electric and hybrid electric vehicles and power grid applications. [ 1 ] Energy storage in EDLCs is based on the electrostatic adsorption of electrolyte ions on the large specifi c surface area of electrically conductive porous electrodes. In spite of the higher capacitance often offered by conductive polymers [ 4 ] and metal oxide-based supercapacitors, [ 5 ] the greater cycle stability and higher electrical conductivity of porous carbons has led to their use in nearly 100% of commercial devices. Multiple factors affect the performance of carbon-based supercapacitors, the most important being the carbon electrodes' surface chemistry [ 6 ] and their pore size distribution (PSD). [ 7 ] The ideal pores should be slightly larger than the size of the de-solvated ions. Smaller pores prevent effi cient ion electroadsorption, [ 8 ] whereas signifi cantly larger pores reduce the capacitance. [ 7 ] The negative effect of larger pores may often be noticed during carbon activation studies, when the longer activation time and the resultant larger specifi c surface area (SSA) commonly leads to capacitance increase only to a surface area of ∼ 1500 m 2 g − 1 (see previous work [ 8a , 9 ] ). Further increase in activation time signifi cantly increases the average pore size, which results in the saturation or decrease in the carbon specifi c capacitance. [ 9 ] Prior to 2006, the energy storage in carbon-based EDLCs was modeled via the Helmholtz electrical double layer (EDL), which consists of solvated ions adsorbed on the internal carbon pore surface. In 2006, systematic studies by Chmiola et al. [ 7a ] and by Raymundo-Pinero et al. [ 7b ] clearly showed signifi cant enhancement of the specifi c capacitance in small micropores, where the ion solvation shell becomes highly distorted and partially removed.[ 7a ] The resulting smaller charge separation distance between the ion centers and the pore walls leads to greatly increased capacitance. [ 7a ] In this case ions form a monolayer or a wire inside a carbon pore for slit or cylindrical shaped pores respectively. [ 10 ] It is still commonly believed that co-existance of large mesopores with micropores in carbons is required for rapid ion transport and high power characteristics of supercapacitors. Studies on the use of carbon nanotubes (CNTs), [ 6b , 11 ] carbon onions, [ 2c , 6b ] and graphene [ 2a ] with very poor volumetric capacitance but fast rate capabilities were motivated by this hypothesis. However, in our recent studies we demonstrated that ultra-fast ion transport is possible...

As electrical energy storage and delivery devices, carbon‐based electrical double‐layer capacitors (EDLCs) have attracted much attention for advancing the energy‐efficient economy. Conventional methods for activated carbon (AC) synthesis offer limited control of their surface area and porosity, which results in a typical specific capacitance of 70–120 F g−1 in commercial EDLCs based on organic electrolytes and ionic liquids (ILs). Additionally, typical ACs produced from natural precursors suffer from the significant variation of their properties, which is detrimental for EDLC use in automotive applications. A novel method for AC synthesis for EDLCs is proposed. This method is based on direct activation of synthetic polymers. The proposed procedure allowed us to produce ACs with ultrahigh specific surface area of up to 3432 m2 g−1 and volume of 0.5–4 nm pores up to 2.39 cm3 g−1. The application of the produced carbons in EDLCs based on IL electrolyte showed specific capacitance approaching 300 F g−1, which is unprecedented for carbon materials, and 5–8% performance improvement after 10 000 charge–discharge cycles at the very high current density of 10 A g−1. The remarkable characteristics of the produced materials and the capability of the fabricated EDLCs to operate safely in a wide electrochemical window at elevated temperatures, suggest that the proposed synthesis route offers excellent potential for large‐scale material production for EDLC use in electric vehicles and industrial applications.

No abstract