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. 2013:4:2487.
doi: 10.1038/ncomms3487.

Graphene-based in-plane micro-supercapacitors with high power and energy densities

Affiliations
Free PMC article

Graphene-based in-plane micro-supercapacitors with high power and energy densities

Zhong-Shuai Wu et al. Nat Commun. 2013.
Free PMC article

Abstract

Micro-supercapacitors are important on-chip micro-power sources for miniaturized electronic devices. Although the performance of micro-supercapacitors has been significantly advanced by fabricating nanostructured materials, developing thin-film manufacture technologies and device architectures, their power or energy densities remain far from those of electrolytic capacitors or lithium thin-film batteries. Here we demonstrate graphene-based in-plane interdigital micro-supercapacitors on arbitrary substrates. The resulting micro-supercapacitors deliver an area capacitance of 80.7 μF cm⁻² and a stack capacitance of 17.9 F cm⁻³. Further, they show a power density of 495 W cm⁻³ that is higher than electrolytic capacitors, and an energy density of 2.5 mWh cm⁻³ that is comparable to lithium thin-film batteries, in association with superior cycling stability. Such microdevices allow for operations at ultrahigh rate up to 1,000 V s⁻¹, three orders of magnitude higher than that of conventional supercapacitors. Micro-supercapacitors with an in-plane geometry have great promise for numerous miniaturized or flexible electronic applications.

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Figures

Figure 1
Figure 1. Design of MPG-MSCs on a silicon wafer.
(af) Schematic illustration of the fabrication of MPG-MSCs made up of 30 interdigital fingers integrated onto a silicon wafer. The fabrication process flow includes (a) oxygen plasma surface treatment of silicon, spin-coating of the GO solution on surface-modified silicon, (b) CH4 plasma reduction, (c) masking pattern and deposition of gold current collector, (d) oxidative etching in oxygen plasma, (e) drop casting of the H2SO4/PVA gel electrolyte and (f) solidification of the gel electrolyte. (g) In-plane geometry of MPG-MSCs, revealing that the ions between the electrode gaps can be rapidly transported along the planar graphene sheets with a short diffusion length. (h) Optical and (i) SEM images of the microelectrode patterns. Scale bars, 200 μm. (j) Atomic force microscopy image of the MPG film electrode after etching by oxygen plasma and removal of Au by a KI/I2 aqueous solution. Scale bar, 1 μm. (k) Uniform thickness of ~15 nm, indicated by the height profile of the MPG film.
Figure 2
Figure 2. Electrochemical characterization of MPG-MSCs on silicon wafer.
(ae) CV curves obtained at different scan rates from 1 to 1,000 V s−1 in a H2SO4/PVA gel electrolyte on interdigital micro-supercapacitors with a 15-nm-thick MPG film, showing a typical electric double-layer capacitive behaviour even at different scan rates. (f) A plot of the discharge current as a function of the scan rate (red star line). Linear dependence (magenta dot line) is observed up to at least 200 V s−1 (green dash dot line), suggesting the ultrahigh power ability of MPG-MSCs.
Figure 3
Figure 3. Comparison of MPG-MSCs with TG-MSCs and MPG-SSCs.
(a,b) Evolution of the (a) area capacitance and (b) stack capacitance versus scan rate. The MPG-MSCs can operate at a higher scan rate of 1,000 V s−1 and provide a capacitance 10 times larger than that of the sandwich device, for example, at 200 V s−1, indicating the potential for ultrahigh power delivery. (c) Complex plane plot of the impedance of the microdevices and sandwich device. Inset is a magnified plot of the high-frequency region, showing a vertical intersection with the real axis in MPG-MSCs. (d) Impedance phase angle as a function of frequency for graphene-based microdevices and sandwich device. The −45° phase angle was present at 3,579 Hz for MPG-MSCs, at 2,358 Hz for TG-MSCs and at 16 Hz for MPG-SSCs, demonstrating the fast accessibility of the ions in MPG-MSCs.
Figure 4
Figure 4. Fabrication and characterization of MPG-MSCs-PET.
(a–g) Schematic illustration of the fabrication of flexible MPG-MSCs-PET. The fabrication process includes a sequence of (a) spin-coating of GO solution on Cu foil, (b) CH4 plasma reduction, (c) transfer of MPG film from the Cu foil to PET substrate, (d) masking pattern and deposition of gold current collector, (e) oxidative etching, (f) drop casting of H2SO4/PVA gel electrolyte and (g) solidification of gel electrolyte. (hk) Optical images of (h) a 15-nm-thick MPG film (2 × 3 cm) on a polymethyl methacrylate (PMMA) support floated on the water surface after etching Cu foil by aqueous Fe(NO3)3 solution, (i) the MPG film transferred onto the PET substrate, (j,k) the resulting MPG-MSCs-PET (j) with and (k) without Au collectors, showing the flexible and transparent characteristics of the fabricated microdevices. (l,m) CV curves of the MPG-MSCs-PET obtained at different scan rates from (l) 1, 10 V and (m) 100, 500 and 1,000 V s−1 with a typical electric double-layer capacitive behaviour, even at ultrahigh scan rates, demonstrating its ultrahigh power ability. (n) Area capacitance and stack capacitance of the MPG-MSCs-PET.
Figure 5
Figure 5. Ragone plot of MPG-MSCs.
The comparison of energy and power density of MPG-MSCs with TG-MSCs, MPG-SSCs, commercially applied electrolytic capacitors, lithium thin-film batteries, Panasonic Li-ion battery and conventional supercapacitors (indicated by the pink region), demonstrating that MPG-MSCs exhibit exceptional electrochemical energy storage with simultaneous ultrahigh energy density and power density.

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