Researchers from Skoltech and Aalto University fabricated and tested novel fully stretchable all-solid supercapacitors based on single-walled carbon nanotubes

Advanced results of joint research project have been recently published in RSC Advances Journal of Royal Chemical Society. In this research study, high quality single-walled carbon nanotubes (SWCNT) films with excellent optoelectrical and mechanical properties were used as the current collectors and active electrodes of the stretchable supercapacitors. The assembling of two PDMS/SWCNT electrodes and a gel electrolyte in between transparent stretchable supercapacitor (TSS) was successfully fabricated (left image, Pict. 1).

SWCNTs possess many unique properties, which are advantageous for a wide variety of applications, including stretchable electronics. They have exceptionally high Young’s modulus of elasticity and tensile strength, and are the strongest known material. The porosity and specific surface area of SWCNT films are very large, and they possess high transparency and flexibility. In addition, SWCNTs can withstand extremely high currents making them an ideal replacement for copper and aluminum in fast-integrated charge/discharge circuits. In this study, SWCNTs were synthesized by an aerosol (floating catalyst) chemical-vapor deposition (CVD) method, based on ferrocene vapor decomposition in a CO atmosphere (central image, Pict.1). Such SWCNTs collected on a filter can be effectively transferred to any substrate, including stretchable substrate materials such as PDMS (polydimethylsiloxane).

One key important feature of the fabricated device is utilization of such type of an electrolyte, as gel polyvinyl alcohol–H2SO4. This was made due to that widely used electrolytes are generally liquid and they are not appropriate for stretchable supercapacitors because of the intrinsic leakage problem. After finally the TSS was fabricated, it was characterized by the potentiostat–galvanostat. The whole device can be bent, folded, and even stretched without any obvious performance change and the transparency of such device is 75% (right image, Pict.1).

Picture 1. Schematic image of fabrication process (left), SEM image of SWCNTs (center), photo of fabricated transparent supercapacitor (right).

Picture 1. Schematic image of fabrication process (left), SEM image of SWCNTs (center), photo of fabricated transparent supercapacitor (right).

 

For further improvement of TSS characteristics under applied strain, researchers developed a pre-stretching approach, which is based on spreading of gel electrolyte on the SWCNT film under applied strain (a, Pict.2). In this study, scientists achieved TSS structure, which can be stretched up to 120% of strain without significant change of the capacitance even after 1000 stretching cycles and after 1000 charge-discharge cycles (b, c, Pict.2). For such pre-stretching approach, the calculated specific capacitance value of Csp is 17.5 F g-1, which is higher than that obtained for the liquid or gel electrolyte without pre-stretching and compared to recent well-known obtained results.

Pict. 2. (a) Scheme of gel electrolyte deposition on pre-stretched SWCNTs on PDMS, (b) Cyclic voltammogramms of TSS made of pre-stretched electrodes at zero applied strain, 40% strain, at first cycle of stretching to 120% and after 1000 cycle of stretching to 120%, (c) cyclic voltammogram of the TSS before and after 1000 cycles between -0.8 and 0.8 V.

Pict. 2. (a) Scheme of gel electrolyte deposition on pre-stretched SWCNTs on PDMS, (b) Cyclic voltammogramms of TSS made of pre-stretched electrodes at zero applied strain, 40% strain, at first cycle of stretching to 120% and after 1000 cycle of stretching to 120%, (c) cyclic voltammogram of the TSS before and after 1000 cycles between -0.8 and 0.8 V.

 

This configuration enabled stretching of the supercapacitor as an integrated unit and overcame the limitation of conventional stretchable supercapacitor configuration wherein two electrodes move relative to the separator under strain. «The performance of the stretchable supercapacitors remained nearly unchanged under 120% strain even under stretched conditions and after 1000 stretching cycles. Superior stretchability of the aerosol CVD synthesized SWCNT films may found broad applications in stretchable electronics, energy storage electrodes. Such high stretchability, combined with transparency and high specific capacitance confirmed that fabricated supercapacitor has a great potential for practical applications in wearable electronics» – said co-author Albert Nasibulin, a professor at the Skolkovo Institute of Science and Technology and an adjunct professor at Aalto University.

Stretchable and transparent supercapacitors based on aerosol synthesized single-walled carbon nanotube films, Evgenia P. Gilshteyn, Tanja Kallio, Petri Kanninen, Ekaterina O. Fedorovskaya, Anton S. Anisimov and Albert G. Nasibulin, RSC Adv., 2016, 6, 93915, DOI: 10.1039/c6ra20319a.

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