- Open Access
A flexible cable-shaped supercapacitor based on carbon fibers coated with graphene flakes for wearable electronic applications
© The Author(s) 2019
- Received: 3 January 2019
- Accepted: 20 April 2019
- Published: 23 April 2019
This work presents a flexible cable-shaped supercapacitor based on carbon fibers (CFs) coated with graphene flakes (GFs) for wearable electronic applications. The CF bundles were adopted as base materials and the GFs were coated on the surface of CFs using a simple dipping method for the enhancement of the specific surface area and the higher conductivity of flexible electrodes. H2SO4 was mixed with poly(vinyl alcohol) (PVA) to form a gel electrolyte, which can prevent leakage. Polydimethylsiloxane (PDMS) was selected as a packaging material to fabricate the proposed flexible supercapacitor due to its flexibility and good thermal and chemical stability. From the electrochemical analysis, the fabricated device exhibited 15.099–6.492 mF/cm2 of specific capacitance and 2.097–0.902 µWh/cm2 of energy density in the range of 50–300 mV/s of scan rate. These values were about 1.9 times larger than the supercapacitor without being coated with the GFs. In addition, the specific capacitance showed small difference of 3.4% between straight and twisted positions, which assures the mechanical stability of the flexible cable-shaped supercapacitor.
- Flexible supercapacitor
- Carbon fibers
- Graphene flakes
- Gel electrolyte
- Wearable electronics
As wearable electronic devices become popular, there is an increasing demand for flexible energy storage devices which have a large output range and power density [1–2]. Furthermore, energy storage devices should be flexible, lightweight and compatible with wearable electronic devices. Therefore, various types of energy storage devices such as supercapacitors , solar cells , lithium-ion batteries  and thermoelectric generators  have been researched over the last decade. Among those developed devices, supercapacitors, also called electrochemical capacitors or ultracapacitors, have been considered as the most adequate alternative for wearable electronic applications through their attractive features such as long lifecycle and high power density . In addition, they have several advantages like a wide temperature range and chemical stability, which are appropriate for the wearable purpose. For example, Some groups presented supercapacitors based on flexible substrate using photolithography process [8–11]. Meng et al. reported a polymer-based thin supercapacitor with carbon nanotube (CNT)/polyaniline (PANI) nanocomposite electrodes using an electropolymerization method . Some other groups presented printed planar supercapacitor using different printing method [13–16]. However, in these works, the deposited electrode materials were exposed, which can easily be detached from their substrates and nonelastic substrates were applied, which limit their use in wearable electronic applications [17–18].
In this research, to meet the demands of flexibility, we applied a polydimethylsiloxane (PDMS) elastomer due to its simple fabrication process and low Young’s modulus of 1.8 MPa, which also shows an elongation at a failure of 160%, a material with chemical and thermal stability. For example, Chen et al. fabricated a stretchable supercapacitor based on carbon nanotube sheets on the PDMS . However, it showed a limitation for wearable electronic applications since the device was not fully packaged. Therefore, the exposed gel electrolyte can cause performance degradation and its acidic feature is not bio-compatible to human skin. Also, it has the problem of mechanical stability under repeated deformations such as bending and stretching.
In this research, we successfully developed a flexible cable-shaped supercapacitor based on carbon fibers (CFs) coated with graphene flakes (GFs) for wearable electronic applications. For fabricating electrodes, CF bundles were adopted as base materials. For the enhancement of the specific surface area and conductivity of the electrodes, GFs were coated on the CFs using a dipping method. For the electrolyte, H2SO4 was mixed with poly(vinyl alcohol) (PVA) for the formation of the gel phase, which makes it free from leakage problem. Lastly, for packaging all these materials, PDMS was selected owing to its flexibility and good thermal and chemical stability, also maintains the proposed supercapacitor’s electrochemical properties under mechanical deformation.
Comparison of the capacitance, energy density of our supercapacitor with other works
CA (mF cm−2)
EA (μWh cm−2)
Photolithography and in-situ assembled graphene
In summary, this research reports a flexible cable-shaped supercapacitor based on CFs coated with GFs for wearable electronic applications. The graphene-coated flakes on the surface of CFs much improved the electrodes’ specific surface area and electrical conductivity, which leads to higher specific capacitance. From the electrochemical analysis, the obtained rectangular shape of the CV curves showed the ideal EDLC property of the flexible cable-shaped supercapacitor. The high specific capacitance of 15.099–6.492 mF/cm2 and energy density of 2.097–0.902 µWh/cm2 were obtained in the range of 50–300 mV/s of scan rate, respectively. These values were about 1.9 times larger than the supercapacitor without being coated with GFs on the surface of CFs. Also, the specific capacitance just showed 3.4% of difference between straight and twisted position, which assures the mechanical stability of the fabricated flexible cable-shaped supercapacitor.
JK designed fabrication and experiments, and prepared the manuscript of this study. JY and XX participated in the analysis of this study. JYP conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Availability of data and materials
All data generated or analysed during this study are included in this published article.
This work was supported by the Technology Innovation Program (20000773, Development of nanomultisensors based on wearable patch for nonhematological monitoring of metabolic syndrome) funded by the Ministry of Trade, Industry & Energy (MI, Korea).
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Jost K, Stenger D, Perez CR, McDonough JK, Lian K, Gogotsi Y, Dion G (2013) Knitted and screen printed carbon-fiber supercapacitors for applications in wearable electronics. Energy Environ Sci 6:2698–2705View ArticleGoogle Scholar
- Pasta M, La Mantia F, Hu L, Deshazer HD, Cui Y (2010) Aqueous supercapacitors on conductive cotton. Nano Res 3:452–458View ArticleGoogle Scholar
- Xiao X, Li T, Yang P, Gao Y, Jin H, Ni W, Zhan W, Zhang X, Cao Y, Zhong J, Gong L, Yen WC, Mai W, Chen J, Huo K, Chueh YL, Wang JL, Zhou J (2012) Fiber-based all-solid-state flexible supercapacitors for self-powered systems. ACS Nano 6(10):9200–9206View ArticleGoogle Scholar
- Pan S, Yang Z, Chen P, Deng J, Li H, Peng H (2014) Wearable solar cells by stacking textile electrodes. Angew Chem 126:6224–6228View ArticleGoogle Scholar
- Hoshide T, Zheng Y, Hou J, Wang Z, Li Q, Zhao Z, Ma R, Sakaki T, Geng F (2017) Flexible lithium-ion fiber battery by the regular stacking of two-dimensional titanium oxide nanosheets hybridized with reduced graphene oxide. Nano Lett 17(6):3543–3549View ArticleGoogle Scholar
- Francioso L, De Pascali C, Farella I, Martucci C, Creti P, Siciliano P, Perrone A (2011) Flexible thermoelectric generator for ambient assisted living wearable biometric sensors. J Power Sources 196:3239–3243View ArticleGoogle Scholar
- Li X, Wei B (2013) Supercapacitors based on nanostructured carbon. Nano Energy 2:159–173View ArticleGoogle Scholar
- Si W, Yan C, Chen Y, Oswald S, Han L, Schmidt OG (2013) On chip, all solid-state and flexible micro-supercapacitors with high performance based on MnOx/Au multilayers. Energy Environ Sci 6:3218–3223View ArticleGoogle Scholar
- Huang P, Heon M, Pech D, Brunet M, Taberna PL, Gogotsi Y, Lofland S, Hettinger JD, Simon P (2013) Micro-supercapacitors from carbide derived carbon (CDC) films on silicon chips. J Power Sources 225:240–244View ArticleGoogle Scholar
- Majumdar R, Foroutan V, Paprotny I (2015) Post-release stressengineering of surface-micromachined MEMS structures using evaporated chromium and in-situ fabricated reconfigurable shadow masks. In: Proceedings of the 28th IEEE international conference micro electro mechanical systems (MEMS), pp 296–299Google Scholar
- Majumdar R, Paprotny I (2017) Lithography-free self-reconfigurable post-release stress engineering of surface micro-machined MEMS structures. J Micro Electro Mech Syst 26:671–678View ArticleGoogle Scholar
- Meng C, Liu C, Chen L, Hu C, Fan S (2010) Highly flexible and all-solid-state paperlike polymer supercapacitors. Nano Lett 10:4025–4031View ArticleGoogle Scholar
- Chang Q, Li L, Sai L, Shi W, Huang L (2018) Water-soluble hybrid graphene ink for gravure-printed planar supercapacitors. Adv Electron Mater 4(8):1800059View ArticleGoogle Scholar
- Tanwilaisiri A, Xu Y, Zhang R, Harrison D, Fyson J, Areir M (2018) Design and fabrication of modular supercapacitors using 3D printing. J Energy Storage 16:1–7View ArticleGoogle Scholar
- Hussain SA, Ward S, Mahdavipour O, Majumdar R, Paprotny I (2015) Untethered microscale flight: mechanisms and platforms for future MEMS aerial microrobotics. In: SPIE sensing technology + applications, 94940F-12Google Scholar
- Ward S, Foroutan V, Majumdar R, Mahdavipour O, Hussain SA, Paprotny I (2015) Towards microscale flight: fabrication, stability analysis, and initial flight experiments for 300×300×1.5 sized untethered MEMS microfliers. IEEE Trans Nanobiosci 14:323–331View ArticleGoogle Scholar
- Peng Z, Ye R, Mann JA, Zakhidov D, Li Y, Smalley PR, Lin J, Tour JM (2015) Flexible boron-doped laser-induced graphene microsupercapacitors. ACS Nano 9(6):5868–5875View ArticleGoogle Scholar
- Feng JX, Ye SH, Lu XF, Tong YX, Li GR (2015) Asymmetric paper supercapacitor based on amorphous porous Mn3O4 negative electrode and Ni(OH)2 positive electrode: a novel and high-performance flexible electrochemical energy storage device. ACS Appl Mater Interfaces 7:11444–11451View ArticleGoogle Scholar
- Chen T, Peng H, Durstock M, Dai L (2014) High-performance transparent and stretchable all-solid supercapacitors based on highly aligned carbon nanotube sheets. Sci Rep 4:3612View ArticleGoogle Scholar
- Yao X, Luan C, Zhang D, Lan L, Fu J (2017) Evaluation of CF-embedded 3D printed structures for strengthening and structural-health monitoring. Mater Des 114:424–432View ArticleGoogle Scholar
- Chen Q, Li X, Zang X, Cao Y, He Y, Li P, Wang K, Wei J, Wu D, Zhu H (2014) Effect of different gel electrolytes on graphene-based solid-state supercapacitor. RSC Adv 4:36253–36256View ArticleGoogle Scholar
- McDonald JC, Duffy DC, Anderson JR, Chiu DT, Wu H, Schueller OJA, Whitesides GM (2000) Fabrication of microfluidic systems in poly(dimethylsiloxane). Electrophoresis 21:27–40View ArticleGoogle Scholar
- Song B, Li L, Lin Z, Wu ZK, Moon K, Wong CP (2015) Water-dispersible graphene/polyaniline composites for flexible micro-supercapacitors with high energy densities. Nano Energy 16:470–478View ArticleGoogle Scholar
- El-Kady MF, Kaner RB (2013) Scalable fabrication of high-power graphene micro-supercapacitors for flexible and on-chip energy storage. Nat Commun 4:1475View ArticleGoogle Scholar
- Liu Z, Wu ZS, Yang S, Dong R, Feng X, Mullen K (2016) Ultraflexible In-Plan Micro-Supercapacitors by Direct Printing of Solution-Processable Electrochemically Exfoliated Graphene. Adv Mater 28:2217–2222View ArticleGoogle Scholar