Graphene-enhanced electrodes for scalable supercapacitors

A scale-up process of high-rate-capability supercapacitors based on electrochemically exfoliated graphene (EEG) and hybrid activated carbon (AC)/EEG are studied in this work. A comparison of the rate capabilities of large-scale EEG and AC/EEG-based pouch cell and commercial high-power supercapacitors are also presented in this paper. The oxygen content of the EEG used in this work is 9.6 at%, with a C/O ratio of 9.36, and the electrical conductivity is 2.68 x 10(4) Sm-1. The specific capacitance (59 Fg(-1)) of the EEG-based supercapacitors remained above 80% of the maximum value as the scan rate was increased from 5 mVs(-1) to 1 Vs(-1). Furthermore, our study reveals how the rate capability of activated carbon (AC) based supercapacitors can be improved by adding EEG into the electrodes to form a hybrid AC/EEG supercapacitor. Both the EEG-based and AC/EEG supercapacitors were scaled-up to pouch cells with capacitances of tens of farads. The electrochemical response was unchanged when scaling up from a coin cell to a pouch cell, although the specific capacitance fell slightly. The cycle performance of the AC/EEG pouch cell showed good long-term stability, with better than 95% capacitance retention after 10,000 cycles. Both the EEG and AC/EEG (with 1:1 mass ratio) pouch cells had rate capabilities that compared favourably with the commercial high-power supercapacitors. Crown Copyright (C) 2017 Published by Elsevier Ltd. All rights reserved.