An Ultra-High-Energy Density Supercapacitor; Fabrication Based on Thiol-functionalized Graphene Oxide Scrolls.

Janardhanan Rani,Jae-Hyung Jang,Ranjith Thangavel,Yun Lee,Se-I Oh

doi:10.3390/nano9020148

Abstract

Present state-of-the-art graphene-based electrodes for supercapacitors remain far from commercial requirements in terms of high energy density. The realization of high energy supercapacitor electrodes remains challenging, because graphene-based electrode materials are synthesized by the chemical modification of graphene. The modified graphene electrodes have lower electrical conductivity than ideal graphene, and limited electrochemically active surface areas due to restacking, which hinders the access of electrolyte ions, resulting in a low energy density. In order to solve the issue of restacking and low electrical conductivity, we introduce thiol-functionalized, nitrogen-doped, reduced graphene oxide scrolls as the electrode materials for an electric double-layer supercapacitor. The fabricated supercapacitor exhibits a very high energy/power density of 206 Wh/kg (59.74 Wh/L)/496 W/kg at a current density of 0.25 A/g, and a high power/energy density of 32 kW/kg (9.8 kW/L)/9.58 Wh/kg at a current density of 50 A/g; it also operates in a voltage range of 0~4 V with excellent cyclic stability of more than 20,000 cycles. By suitably combining the scroll-based electrode and electrolyte material, this study presents a strategy for electrode design for next-generation energy storage devices with high energy density without compromising the power density.

Highlights

The growing demand for energy storage systems in electric vehicles, load-leveling, and portable electronic devices has stimulated research into high-density electrochemical energy storage technologies that can deliver high power for long periods of time [1,2,3]
Even though tremendous progress has been achieved in developing reduced graphene oxide (rGO)-based Electrochemical double-layer supercapacitors (EDLCs) with high energy density using hydrazine reduction (85.6 Wh/kg) [16], microwave exfoliation (70 Wh/kg) [17], and other processes, their energy density values are still significantly lower than the level needed for many practical applications
The test cells were constructed in an argon-filled glove box by compressing the NTGS and rGO electrodes, and the devices were fabricated with an ionic liquid EMIMBF4 electrolyte

Summary

Introduction

The growing demand for energy storage systems in electric vehicles, load-leveling, and portable electronic devices has stimulated research into high-density electrochemical energy storage technologies that can deliver high power for long periods of time [1,2,3]. Two of the major drawbacks of the rGO-based EDLCs that lead to the lower energy density values are the restacking of rGO layers and the low electrical conductivity of rGO. Energy density can be significantly enhanced by (1) preventing the restacking of rGO sheets, (2) increasing the electrical conductivity of the rGO sheets, and (3) creating a narrow pore size distribution in the synthesized rGO electrode. By functionalizing rGOs with a thiol (–SH) group, it is possible to tailor the physical and chemical properties of the rGOs. The synthesized NTGS show high electrical conductivity, which is attributed to (i) the orbital overlap between sulfur 3s and 3p, with π- orbitals in the rGO sheets, and (ii) the presence of lone pair electrons in nitrogen. The fabricated supercapacitor exhibits a very high energy/power density of 206 Wh/kg (59.74 Wh/L)/496 W/kg, at a current density of 0.25 A/g, and a high power/energy density of 32 kW/kg (9.8 kW/L)/9.58 Wh/kg at a current density of 50 A/g, and excellent stability (>20,000 cycles)

Experiment Section

Cell Fabrication

Results and Discussion

Conclusions