A supercapacitor with graphene-based electrodes was found to exhibit a specific energy density of 85.6 Wh/kg at room temperature and 136 Wh/kg at 80 °C (all based on the total electrode weight), measured at a current density of 1 A/g. These energy density values are comparable to that of the Ni metal hydride battery, but the supercapacitor can be charged or discharged in seconds or minutes. The key to success was the ability to make full utilization of the highest intrinsic surface capacitance and specific surface area of single-layer graphene by preparing curved graphene sheets that will not restack face-to-face. The curved morphology enables the formation of mesopores accessible to and wettable by environmentally benign ionic liquids capable of operating at a voltage >4 V.

b S Supporting Information L ithium ion batteries and electrochemical capacitors (supercapacitors), separately or in combination, are being considered for electric vehicle (EV), renewable energy storage, and smart grid applications. 1À5 A major scientific challenge is to either significantly increase the energy density of conventional supercapacitors or dramatically improve the power density of lithium ion batteries. 2,3 Supercapacitors work on two main charge storage mechanisms: surface ion adsorption (electric double layer capacitance, EDL) and redox reactions (pseudocapacitance). 1,2 Compared with batteries, supercapacitors deliver a higher power density, offer a much higher cycle-life, need a very simple charging circuit, and are generally much safer. However, supercapacitors exhibit very low energy densities (e.g., 5 Wh/kg cell for commercial activated carbon-based supercapacitors versus 100À150 Wh/ kg cell for the commercial Li-ion battery, all based on the total cell weight). 2 Previous attempts to increase the gravimetric energy of supercapacitors have included the use of electrode materials with enhanced gravimetric capacitances 6 or the pseudocapacitance provided by nanostructured transition metal oxides. 7À9 However, the prohibitively high cost of ruthenium-based oxides and the cycling instability of manganese-based oxides 9À11 have impeded the commercial application of these supercapacitors.In 2006, our research group reported graphene-based electrodes for both EDL and redox supercapacitors, 12 which has since become a topic of intensive research. 13À19 Significant progress has been made using pseudocapacitance (e.g., redox pairs between graphene oxideÀMnO 2 16 or grapheneÀpolyaniline 17,18 ) and ionic liquid electrolyte with a high operating voltage 13,19 for improved energy density. However, these supercapacitors have yet to exhibit a sufficiently high energy density or power density for EV and renewable energy applications.Lithium-ion batteries operate on Faradaic reactions in the bulk of the active material. This bulk storage mechanism provides a much higher energy density (120À150 Wh/kg cell ) as compared to supercapacitors. However, storing lithium in the bulk of a material implies that lithium must leave the interior of a cathode active particle and eventually enter the bulk of an anode active particle during recharge, and vice versa during discharge. Because of the extremely low solid-state diffusion rates, these processes are kinetics-limited. As a result, lithium ion batteries deliver a very low power density (100À1000 W/kg cell ), requiring typically hours for recharge.Several efforts have been made to increase the power characteristics of lithium-ion batteries by reducing the dimensions of lithium storage materials down to the nanometer scale, which would reduce the lithium diffusion time. 20À23 However, nanostructured lithium storage electrodes (e.g., nanoparticles of lithium titanate anode or lithium iron phosphate cathode) are still not capable of delivering a power density comparable ...

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Self-assembly of phenolic resins and a Pluronic block copolymer via the soft-template method enables the formation of well-organized polymeric mesostructures, providing an easy way for preparation of ordered mesoporous carbons (OMCs). However, direct synthesis of OMCs with high nitrogen content remains a significant challenge due to the limited availability of nitrogen precursors capable of co-polymerizing with phenolic resins without deterioration of the order of mesostructural arrangement and significant diminishment of nitrogen content during carbonization. In this work, we demonstrate pyrolysis of the soft-templated polymeric composites in ammonia as a direct, facile way towards nitrogen-enriched OMCs (N-OMCs). This approach does not require any nitrogen-containing carbon precursors or post-treatment, but takes advantage of the preferential reaction and/or replacement of oxygen with nitrogen species, generated by decomposition of ammonia at elevated temperatures, in oxygen-rich polymers during pyrolysis. It combines carbonization, nitrogen functionalization, and activation into one simple process, generating N-OMCs with a uniform pore size, large surface area (up to 1400 m 2 g À1 ), and high nitrogen content (up to 9.3 at%). More importantly, the ordering of the meso-structure is well-maintained as long as the heating temperature does not exceed 800 C, above which (e.g., 850 C) a slight structural degradation is observed. When being used as electrode materials for symmetric electric double layer capacitors, N-OMCs demonstrate enhanced capacitance (6.8 mF cm À2 vs. 3.2 mF cm À2 ) and reduced ion diffusion resistance compared to the non-NH 3 -treated sample.