Ultrahigh-power micrometre-sized supercapacitors based on onion-like carbon

Abstract

Electrochemical capacitors, also called supercapacitors, store energy in two closely spaced layers with opposing charges, and are used to power hybrid electric vehicles, portable electronic equipment and other devices. By offering fast charging and discharging rates, and the ability to sustain millions of cycles, electrochemical capacitors bridge the gap between batteries, which offer high energy densities but are slow, and conventional electrolytic capacitors, which are fast but have low energy densities. Here, we demonstrate microsupercapacitors with powers per volume that are comparable to electrolytic capacitors, capacitances that are four orders of magnitude higher, and energies per volume that are an order of magnitude higher. We also measured discharge rates of up to 200 V s(-1), which is three orders of magnitude higher than conventional supercapacitors. The microsupercapacitors are produced by the electrophoretic deposition of a several-micrometre-thick layer of nanostructured carbon onions with diameters of 6-7 nm. Integration of these nanoparticles in a microdevice with a high surface-to-volume ratio, without the use of organic binders and polymer separators, improves performance because of the ease with which ions can access the active material. Increasing the energy density and discharge rates of supercapacitors will enable them to compete with batteries and conventional electrolytic capacitors in a number of applications.

Ultrahigh‐Power Pseudocapacitors Based on Ordered Porous Heterostructures of Electron‐Correlated Oxides

“…Furthermore, this value is also much higher than the highest values recently reported in EDLCs based on carbon onions,8 graphene/CNT hybrid11 or graphene,13 and pseudocapacitors generated with the hydrogenated TiO 2 /MnO 2 (H‐TiO 2 /MnO 2 /C)6 or ZnO/MnO 2 (H‐ZnO/MnO 2 /C)20 supported by carbon cloths, or MnO 2 /Au multilayers 25. The maximum volumetric power density can reach ≈422 W cm −3 with the energy density of ≈9.3 mWh cm −3 , ≈700‐fold higher than that of a commercial AC supercapacitor (2.75 V/44 mF)9 and more than five orders of magnitude higher than that of lithium thin‐film battery (4 V/500 μAh) with the energy density of ≈8 mWh cm −3 8. To our knowledge, this volumetric power density is the highest value among all TMO‐based pseudocapacitors reported to date.…”

“…Unlike electrochemical double‐layer capacitors (EDLCs),8, 9, 10, 11, 12 in which charge storage is achieved by nonfaradaic electrostatic adsorption in nanostructured carbons with low intrinsic capacitance (≈20 μF cm −2 carbon ),1, 13, 14 pseudocapacitors store high‐density energy on pseudocapacitive materials by fast and reversible surface redox reactions at or near the electrode/electrolyte interface 1, 2, 3, 4, 5, 6, 7, 15, 16, 17. The surface mechanisms are fundamentally distinguished from rate‐limited volumetric reactions in batteries by short charge/discharge time, high power density and long‐term cycling stability 1, 2, 3, 18.…”

“…The surface mechanisms are fundamentally distinguished from rate‐limited volumetric reactions in batteries by short charge/discharge time, high power density and long‐term cycling stability 1, 2, 3, 18. These advantageous features enlist pseudocapacitors to be attractive alternatives or complements to batteries for many high‐power applications in hybrid electric vehicles, portable electronic devices and renewable energy 1, 2, 3, 4, 8, 9, 13. However, conventional pseudocapacitors made from state‐of‐the‐art electrode materials, typically transition‐metal oxides (TMOs) such as MnO 2 ,5, 15, 19, 20 TiO 2 ,6, 16 and Co 3 O 4 ,19, 21 often exhibit much lower power capability than EDLCs due to their intrinsically poor conductivity 15, 21.…”

Ultrafast‐Charging Supercapacitors Based on Corn‐Like Titanium Nitride Nanostructures

“…The data of TiN supercapacitors, as well as a commercial high‐energy lithium thin‐film battery (4 V/500 mAh) and high‐power aluminum electrolytic capacitor (3 V/300 mF) are included 8, 10. Remarkably, our TiN supercapacitors deliver a volumetric energy density of 1.5 mWh cm −3 , which is comparable to the previous carbon‐based microsupercapacitors and lithium thin‐film batteries (10 −3 −10 −2 Wh cm −3 ), and much higher than the previously demonstrated flexible TiN supercapacitor device (0.05 mWh cm −3 ) 14.…”

“…The very high power density of our TiN supercapacitors, 150 W cm −3 at an energy density of 0.30 mWh cm −3 , implies the capability of discharging within an extremely short time (14 ms). Detailed comparisons are listed in Table S1 (Supporting Information) 5, 6, 7, 8, 28, 29, 30, 31, 32. To our best knowledge, this is the first report of noncarbon supercapacitors without microconfiguration having such excellent performance in terms of ultrahigh power and energy densities.…”