3, Istituto Italiano di Tecnologia, Genova, , Italy
4, Istituto Italiano di Tecnologia, Genova, , Italy
2, National Technical University of Athens, Athens, , Greece
Supercapacitors are electrochemical energy storage devices that combine the high energy-storage-capability of conventional batteries with the high power-delivery-capability of conventional capacitors. In this contribution we will show the results of our group recently obtained on supercapacitors with electrodes obtained using mixtures of carbonaceous nanomaterials (carbon nanotubes (CNTs), graphite, graphene, oxidised graphene). The electrode fabrication has been performed using a new dynamic spray-gun based deposition process set-up at Thales Research and Technology (patented). First, we systematically studied the effect of the relative concentrations of Multi-Walled Carbon Nanotubes (MWCNTs) and graphite on the energy and power density (using commercial aqueous electrolytes). We obtained a power increase of a factor 2.5 compared to barely MWCNTs based electrodes for a mixture composed by 75% of graphite/graphene. This effect is related to the improvement of the mesoporous distribution of the composites and to the increase of the conductance as pointed out by Coleman et al. After these preliminary results, we decided to test water as a solvent to reduce the heating temperature and to obtain a green type process without toxic solvents. To achieve stable suspensions we oxidised the graphene and the CNTs before putting them in water. After the deposition by spray the electrodes were left in an oven (to deoxidise) and recover a good conductivity. We observed that changing the Graphene Oxide concentrations we obtained different values of capacitance and energy. The best results were obtained with 90% of GO and 10% of CNTs. We obtained 120F/g and a power of 30kW/Kg (using aqueous electrolytes). Finally we performed the same measurements using high quality exfoliated graphene supplied by IIT. We fabricated graphene/single wall carbon nanotubes (SWCNTs)-based hybrid supercapacitors and we achieved a remarkable performance in terms of maximum specific energy (20.8Wh/kg) and power (92.3kW/kg), outperforming devices made both using commercial activated carbon (PICACTIF), and graphene-SWCNT bucky papers. The importance of these results is that it is the first time that these performances have been obtained for graphene related materials using an industrial fabrication suitable technique that can be implemented in roll-to-roll production. Finally, new results using mixtures of Carbon nanofibers and graphene will be also shown. These new composite allow to use ionic liquids, having larger dimensions, as electrolytes and so to increase dramatically the energy stored in the device without reducing the power.