Micro‐Supercapacitors Based on Interdigital Electrodes of Reduced Graphene Oxide and Carbon Nanotube Composites with Ultrahigh Power Handling Performance

Abstract

A novel method for fabricating micro‐patterned interdigitated electrodes based on reduced graphene oxide (rGO) and carbon nanotube (CNT) composites for ultra‐high power handling micro‐supercapacitor application is reported. The binder‐free microelectrodes were developed by combining electrostatic spray deposition (ESD) and photolithography lift‐off methods. Without typically used thermal or chemical reduction, GO sheets are readily reduced to rGO during the ESD deposition. Electrochemical measurements show that the in‐plane interdigital design of the microelectrodes is effective in increasing accessibility of electrolyte ions in‐between stacked rGO sheets through an electro‐activation process. Addition of CNTs results in reduced restacking of rGO sheets and improved energy and power density. Cyclic voltammetry (CV) measurements show that the specific capacitance of the micro‐supercapacitor based on rGO–CNT composites is 6.1 mF cm−2 at 0.01 V s−1. At a very high scan rate of 50 V s−1, a specific capacitance of 2.8 mF cm−2 (stack capacitance of 3.1 F cm−3) is recorded, which is an unprecedented performance for supercapacitors. The addition of CNT, electrolyte‐accessible and binder‐free microelectrodes, as well as an interdigitated in‐plane design result in a high‐frequency response of the micro‐supercapacitors with resistive‐capacitive time constants as low as 4.8 ms. These characteristics suggest that interdigitated rGO–CNT composite electrodes are promising for on‐chip energy storage application with high power demands.

Scalable fabrication of high-power graphene micro-supercapacitors for flexible and on-chip energy storage

“…The RC time constant of LSG-MSC(16) was calculated to be 19 ms, in comparison with 10,000 ms for the commercial AC-SC and 1.1 ms for the electrolytic capacitor (Supplementary Table S1). This extremely small time constant for the LSG-MSC(16) is very promising compared with previously reported values for planar microsupercapacitors: activated carbon (700 ms) 2 , onion-like carbon (26 ms) 2 and graphene/CNT composite (4.8 ms) 3 . Furthermore, the LSG supercapacitors show excellent cycling stability, retaining 96% of the initial performance after 10,000 charge/discharge cycles.…”

“…3f. This is equivalent to the operation of the device at B1100 A g À 1 LSG/electrode , which is about 3 orders of magnitude higher than the normal discharge current densities used for testing traditional supercapacitors 2,3 . This corresponds to an areal capacitance that varies only slightly from 2.32 mF cm À 2 at 16.8 mA cm À 3 to 1.35 mF cm À 2 at 1.84 Â 10 4 mA cm À 3 .…”

“…Progress in micro-fabrication technology has enabled on-chip micro-supercapacitors in an interdigitated planar form in contrast to the conventional sandwich structure-the latter being incompatible with integrated circuits 1 . Among the most desirable properties of a microsupercapacitor, high-power density, high-rate capability and especially high-frequency response are crucial for future applications 2,3 . From a materials perspective, carbon is earth abundant and inexpensive; hence, many nanostructured carbon-based materials have been studied for use in electric double-layer (EDL) micro-supercapacitors, including activated carbons 4 , carbon nanotubes 5 , carbide-derived carbons 1,6 and onion-like carbon 2 .…”

“…Although this fabrication technique is promising, the poor frequency response and the large internal resistance (6.5 kO) of the as-made devices are not adequate for practical applications. Most recently, Beidaghi et al 3 reported graphene/CNT composite micro-supercapacitors using a combination of micro-fabrication techniques and electrostatic spray deposition. They measured a high volumetric capacitance with an RC time constant as low as 4.8 ms.…”

All-solid-state supercapacitors on silicon using graphene from silicon carbide

“…[13][14][15] Graphene has been intensively investigated for various energy storage devices, [16][17][18] but the use of graphene in the all-solid-state supercapacitors has not been investigated sufficiently, [19][20][21][22][23][24] due to limitations in the availability of a large-scale high-quality graphene on the one hand, and to the difficulties related to the transfer of graphene powders to the substrate/device location, which results in cumbersome fabrication as well as poor reliability on the other hand. These challenges have urged the search for more reliable fabrication methods to obtain graphene on the substrate without further handling, e.g., transfer-free graphene on silicon substrates.…”