Thin film supercapacitors were fabricated using printable materials to make flexible devices on plastic. The active electrodes were made from sprayed networks of single-walled carbon nanotubes (SWCNTs) serving as both electrodes and charge collectors. Using a printable aqueous gel electrolyte as well as an organic liquid electrolyte, the performances of the devices show very high energy and power densities (6 W h/kg for both electrolytes and 23 and 70 kW/kg for aqueous gel electrolyte and organic electrolyte, respectively) which is comparable to performance in other SWCNT-based supercapacitor devices fabricated using different methods. The results underline the potential of printable thin film supercapacitors. The simplified architecture and the sole use of printable materials may lead to a new class of entirely printable charge storage devices allowing for full integration with the emerging field of printed electronics.

Highly conducting and porous carbon nanotube (CNT) networks are used as the sole electron conducting material in supercapacitors. The high conductivity of CNT networks and the high surface area allow the replacement of both the metallic current collector and the active material that forms one side of the electrochemical double layer. The combination of both functions in one single layer leads to lightweight charge storage devices that can be manufactured using simple and cheap room temperature methods. The authors have demonstrated that the specific capacitance of such CNT electrodes is comparable to that of other carbon electrodes.

The charge transfer properties of a novel asymmetric device configuration combining polyaniline ͑PANI͒ as the battery component and single-wall carbon nanotubes ͑SWNTs͒ as the supercapacitor component were investigated. The scan rate in cyclic voltammetry is an important factor modulating the relative weight of the fast double layer/pseudocapacitance and slow electrochemical capacitance and changing the total charge and energy density output. At a scan rate of 1 mV/s, the energy density of the PANI_SWNTs device is six times higher than that of the bare SWNTs device. At different voltage ranges of galvanostatic discharge, the PANI_SWNTs device exhibits three different discharge behaviors. The SWNT-like discharge dominates the initial stage. The PANI electrochemical reaction dominates the middle stage of the discharge, which coincides with the PANI's conductive state. Once the charge from the PANI electrochemical reaction is used up, the remaining charge in SWNTs sustains the discharge in the final stage. A suspension period was therefore introduced to the middle stage of PANI_SWNTs device discharge, which resulted in a 10% increase of the power density. The understanding of the interaction between the fast double layer/ pseudocapacitance and slow electrochemical capacitance benefits for designing the architecture of supercapacitor-battery satisfying energy and power requirements of practical applications.

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