In this paper it is shown that the electrochemical behaviour of vertically aligned multi-walled carbon nanotube (VANT) supercapacitors is influenced by the VANTs' length (electrode thickness), by their axial compression and by their interface with the current collector. It is found that the VANTs, which can be interpreted as a dense array of nanochannels, have an active area available to ions that is strongly affected by the electrode's thickness and compressional state. Consequently, the tested thinner electrodes, compressed electrodes or a combination of the two were found to be characterized by a significant improvement in terms of power density (up to 1246%), knee frequency (58,822% working up to 10 kHz), equivalent series resistance (ESR, up to 67%) and capacitance (up to 21%) when compared with thicker and/or uncompressed electrodes. These values are significantly higher than those reported in the literature where long VANTs with no control on compression are typically used. It is also shown that the ESR can be reduced not only by using shorter and compressed VANTs that have a higher conductance or by improving the electrode/collector electrical contact by changing the contact morphology at the nanoscale through compression, but also by depositing a thin platinum layer on the VANT tips in contact with the current collector (73% ESR decrease).

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Advances toward the development of light-weight fully electric aerospace structures lead to the need of replacing on-board batteries with lighter and more efficient energy storage devices and systems. Here a novel self-rechargeable multifunctional carbon fiber composite is presented. The composite has the capability to monitor internal (such as damage) and external parameters (e.g. flight conditions) with high accuracy, to provide the required energy to the embedded monitoring system as well as to other on-board equipment while keeping its structural integrity and strength, increasing its life-time and power capability and decreasing the global weight of the overall aerospace structure. The self-recharging capability is given by a series of miniaturized supercapacitor cells that are first prefabricated on a strategic support already integrated with the necessary circuitry and then are embedded in a cost-effective manner between the layers of the composite. Here it is also demonstrated that supercapacitor cells made with carbon nanotubes electrodes can become lighter and can provide superior performance by thinning its electrodes. For instance, going from 400μm to 20μm thick CNTs-electrodes a 1246% power increase, a 21% specific capacitance increase and a 60% electrode resistance reduction were recorded. Moreover the ultra-thin supercapacitors were found to provide these high performance responses with a reaction speed about 30% superior than ever reported in the literature and over an extremely wide frequency range (up to 10KHz).