School of Electrical and Electronic Engineering, The University of Manchester, M13 9PL, Manchester, England, UK

School of Materials, The University of Manchester, M13 9PL, Manchester, England, UK

School of Chemistry, The University of Manchester, M13 9PL, Manchester, England, UK

Graphene was produced by anodic electrochemical exfoliation according to the previous report by Müllen et al. using 0.1 M ammonium sulfate (aqueous solution) as the electrolyte [13]. The poly(tetrafluoroethylene) binder (60 wt% dispersion in water),conductive carbon black(50% compressed, surface area: 75 m2 g_1, average particle size 0.042 mm) and potassium hydroxide (KOH) were purchased from Sigma-Aldrich. Supercapacitor grade AC was purchased from Xiamen TMAX Battery Equipments Limited. The particle size of the AC was around 0.18 mm and the surface area was quoted by the manufacturer to be more than 2100 m2 g_1.

2.2. Electrode preparation A paste of activated materials was synthesized by mixing 80 wt % active materials with 10 wt% PTFE and 10 wt% carbon black. The active materials in this paper are EEG, AC and AC/EEG composite. The paste was then spread evenly with a metallic spatula on a stainless steel current collector and vacuum dried for 24 hours. The dried samples were then pressed to a thickness of 0.2 mm by a electrode calender machine. Calender Machine was purchased from Xiamen TMAX Battery Equipments Limited, The electrodes were vacuum dried for another 24 hours. 2.3. Cell assembly and electrochemistry In this paper, two types of cells, coin cells and pouch cells, are used to investigate the electrochemical properties of the materials and the effect of scaling up, respectively. The coin cell assembly line is based on a symmetrical coin cell architecture (CR2032) reported previously by Bissett et al. [26]. Two identical electrodes (15 mm diameter) were cut using a heavy duty disc cutter, assembled face-to-face against a piece of separator and then enclosed in a coin cell using a electrode disc punching machine . The disc punching machine was purchased from Xiamen TMAX Battery Equipments Limited, The pouch cell manufacturing process is as follows: two identical rectangular electrodes were separated by a piece of separator soaked in the electrolyte and vacuum sealed in an aluminium pouch as a symmetric device. The sizes of electrodes varied from 1 _1 cm2 to 8 _ 8 cm2 depending on the desired cell capacitance. The electrolyte used in this paper was aqueous 6 M KOH. All electrochemical characterisations (including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD)) were carried out using PGSTAT302N (Metrohm Autolab, The Netherlands) and IviumStat measurement devices. CVs were performed at scan rates ranging from 5 to 1000 mVs_1. EIS was performed over a frequency range of 0.01 Hz to 100 kHz with a 10 mV (rms) perturbation and 0 V DC bias.