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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 × 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. [ABSTRACT FROM AUTHOR]

• Energy-based optimisation of graphene additives for supercapacitor electrodes. • Operating voltage window increased to 3.2 V. • Energy density of optimised cells is double that of symmetric, non-graphene cells. We present a new strategy to optimise the energy density of supercapacitor cells, by systematically varying the amount of graphene-related additive, while mass balancing the positive and negative electrodes. The capacitance and the electrochemically stable potential window of the electrodes have been determined for several electrodes with different additive loadings by using a recently reported electrode optimisation technique. These key factors for calculating the mass balance were obtained based on the constant current charge/discharge cycling with a coin-cell-incorporated quasi-reference electrode. Then, multi-pairing of electrodes is proposed based on the maximum theoretical energy density, and optimised supercapacitor cells have been assembled. Using this strategy, these cells are shown to reach a voltage of 3.2 V within stability conditions, providing an energy density of 37.9 W h kg−1 (double the value for a symmetric non-graphene cell) and a power density of 149 kW kg−1 at 2 A g−1, using 1 M tetraethylammonium tetrafluoroborate (TEABF 4) in acetonitrile as the electrolyte, placing these cells in between traditional and hybrid supercapacitors. [ABSTRACT FROM AUTHOR]