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Flexible paper electrodes for supercapacitors were prepared with partially-exfoliated graphite and polypyrrole as the active materials. Graphite was coated on paper with pencil drawing and then electrochemically exfoliated using the cyclic voltammetry (CV) technique to obtain the exfoliated graphite (EG)-coated paper (EG-paper). Polypyrrole (PPy) doped with β-naphthalene sulfonate anions was deposited on EG-paper through in-situ polymerization, leading to the formation of PPy-EG-paper. The as-prepared PPy-EG-paper showed a high electrical conductivity of 10.0 S·cm-1 and could be directly used as supercapacitor electrodes. The PPy-EG-paper electrodes gave a remarkably larger specific capacitance of 2148 F·g-1 at a current density of 0.8 mA.cm-2, compared to PPy-graphite-paper (848 F·g-1). The capacitance value of PPy-EG-paper could be preserved by 80.4% after 1000 charge/discharge cycles. In addition, the PPy-EG-paper electrodes demonstrated a good rate capability and a high energy density of 110.3 Wh·kg-1 at a power density of 121.9W·kg-1. This work will pave the way for the discovery of efficient paper-based electrode materials. [ABSTRACT FROM AUTHOR]

Graphene and porous carbon materials are widely used as electrodes in supercapacitors. In order to form mechanically stable electrodes, binders can be added to the conducting electrode material. However, most binders degrade the electrical performance of the electrodes. Here we show that by using nanofibrillated cellulose (NFC) as a binder the electrical properties, such as capacitance, were enhanced. The highest capacitance was measured at an NFC content of approximately 10 % in ratio to the total amount of active material. The NFC improved the ion transport in the electrodes. Thus, electrodes made of a mixture of nanographite and NFC achieved larger capacitances in supercapacitors than electrodes with nanographite only. In addition to electrical properties, NFC enhanced the mechanical stability and wet strength of the electrodes significantly. Furthermore, NFC stabilized the aqueous nanographite dispersions, which improved the processability. Galvanostatic cycling was performed and an initial transient behaviour of the supercapacitors during the first cycles was observed. However, stabilized supercapacitors showed efficiencies of 98-100%. [ABSTRACT FROM AUTHOR]