Elsevier

Nano Energy

Volume 11, January 2015, Pages 568-578
Nano Energy

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Foldable supercapacitors from triple networks of macroporous cellulose fibers, single-walled carbon nanotubes and polyaniline nanoribbons

https://doi.org/10.1016/j.nanoen.2014.11.023Get rights and content

Abstract

We report foldable supercapacitor electrodes using a macroporous cellulose fiber network, Kimwipes®, as the scaffold through a simple “dip-absorption-polymerization” method. Single-walled carbon nanotubes (SWCNTs) wrapped around the cellulose fibers as the conductive skin, while ultrathin (~50 nm) and ultralong (tens of microns) polyaniline (PANI) nanoribbons were synthesized in situ between macroporous cellulose fibers and interpenetrated within the SWCNT network. The hybrid material showed good volumetric (40.5 F/cm3) and areal capacitance (0.33 F/cm2), which was attributed to the synergistic effect between electron transport within the SWCNTs network and fast charge transfer of the PANI nanoribbons. The paper-based hybrid electrode was highly flexible and compliant; it could be folded back and forth as an origami crane up to 1000 times without mechanical failure or loss of capacitance. We believe that the combination of triple networks and the unique morphology of PANI nanoribbons played critical roles to the repeated foldability. Finally, we assembled six all-solid-state supercapacitors based on the SWCNT/PANI nanoribbon paper electrodes connected in series, which lighted LED before, during and after folding for 500 times.

Graphical abstract

A lightweight, foldable supercapacitor electrode was fabricated from macroporous Kimwipes® impregnated with semi-interpenetrating networks of single-walled carbon nanotubes and in situ synthesized ultrathin and ultralong polyaniline nanoribbons.

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Introduction

The growing interests in portable and wearable electronic devices have driven the search for low-cost, flexible, lightweight, and environmentally friendly energy storage devices such as supercapacitors (SCs), which bridge the gap between rechargeable batteries and conventional high power density electrostatic capacitors [1], [2], [3], [4], [5]. Typically, the capacitance and cyclability of SCs for such applications should be comparable to conventional SCs. Furthermore, because the devices will be wrapped around an object (e.g. body) or folded into a small piece, which can be reopened later when needed, the SC electrodes should be lightweight and flexible, and more importantly, bendable to a large extent (e.g. with sharp folds) without losing their electrical performance. This has been proved to be a major challenge. Although free-standing graphene and carbon nanotube (CNT)-based composite films have been studied extensively in literature [2], [6], [7], [8], [9], [10], [11], [12], [13], [14], many suffer from poor mechanical reliability [13], [15] in addition to complicated preparation procedures and high material cost. Recently, much attention has been paid to the use of low-cost, flexible substrates, such as paper [16], [17], [18], [19], [20], [21], [22], fabrics [3], [23], [24], [25], [26], [27], and cellulose nanofibers [28] as templates or scaffolds for depositing active conducting materials.

Paper, consisting of cellulose fibers (diameter ranging from tens to hundreds of microns) interconnected with each other, is by far the cheapest and most exploited substrate for flexible SCs. There are two types of paper investigated in literature for SCs, including printing paper, which is rather nonporous, and filter paper and wipes, which are highly porous with macron-sized interconnected pores. Printing paper has been used as a supporting substrate to draw or deposit conducting materials [18], [19], [20], [21], followed by in situ polymerization of nanostructures, for example, polyaniline (PANI) nanowires [18] and polypyrrole nanoparticles [19]. Filter paper, on the other hand, has been used to absorb active materials, for example, graphene nanosheets, which fill the voids between the cellulose fibers [16]. Ethylene-vinyl acetate (EVA) copolymer/CNT has been coated on the surface of lens cleaning paper, followed by electrodeposition of MnO2 [29]. However, very few have reported the capacity of the flexible electrodes after bending. Weng et al. bent graphene-cellulose paper one time [16] and Yuan et al. bent polypyrrole-coated paper 100 times [19], showing almost no change of the electrical performance. It has also been shown that 85% of initial capacitance is retained after bending 800 times from MnO2/EVA/CNT paper with moderate curvature [29]. It remains unclear, however, whether these devices can survive repeated folding/unfolding, and sometime twisting at much larger curvatures, where the active materials could be detached or even destroyed at the interface if they are only deposited on the surface of paper [30].

Conducting polymers, such as polyaniline (PANI), are promising electrode materials because of their high specific pseudocapacitance, good environment stability, redox reversibility and low cost [31], [32], [33]. Nanostructured PANIs of different morphologies (e.g., nanofibres [34], nanorods [35], and nanowire arrays [36]) and their composites with carbon based materials (e.g. CNTs [37] and graphene [7]) have been synthesized. It has been suggested that the morphologies of nanostructured PANIs and their aggregations play important roles in energy storage, including material utilization, electron transport/ion diffusion pathways, and mechanical properties [38], [39], [40]. It is known that networks of high-aspect-ratio nanostructured materials (e.g., nanofibers, nanowires, and nanotubes) can be easily percolated, thus, offering improved mechanical strength and electrical conductivity.[6], [41], [42] Recently, we showed that dual-interpenetrating networks of single-walled carbon nanotubes (SWCNTs) and ultrathin PANI nanoribbons can be prepared as free-standing, flexible lithium ion battery (LIB) electrodes with high capacity and good cyclability.[40] The SWCNT aerogel and surfactants assembled on SWCNTs are critical to the formation of PANI nanoribbons. It will be attractive to exploit the macroporous network of cellulose fibers to grow SWCNT/PANI nanoribbons, and study the resulting electrical and mechanical performance, specifically, foldability and cyclability.

Here, we coated the macroporous cellulose fibers (Kimwipes®) with SWCNTs, followed by infiltration and in situ polymerization of aniline monomers. The SWCNTs were found wrapping around the interpenetrating cellulose fibers, and ultrathin and ultralong PANI nanoribbons were formed within the network of SWCNTs. The prepared SC electrodes were lightweight (0.34 g/cm3), and exhibited fairly high capacitance (40.5 F/cm3 or 0.33 F/cm2). The electrodes could be folded/unfolded repeatedly up to 1000 times without mechanical failure or loss of capacitance, which was in sharp contrast to SWCNT/PANI nanoparticle paper SCs with 35% loss of capacitance.

Section snippets

Materials

All reagents were used without further purification. Commercial Kimwipes® (KIMTECH Science⁎ brand delicate task wipers, Kimberly-Clark Corporation) with density of ~0.25 g/cm3 or 2 mg/cm2 was used. Single walled carbon nanotubes (SWCNTs) were purchased from Cheap Tubes Inc. (purity>90% with ashes<1.5 wt%) with diameter of 1~2 nm and length of 5~30 µm. Sodium dodecylbenzene sulfonate (SDBS), aniline (An), camphorsulfonic acid (CSA), ammonium peroxydisulfate (APS), isopropyl alcohol (IPA), and ethanol

Results and discussion

The SWCNT/PANI nanoribbon paper was prepared in three steps, including dipping the commercially available Kimwipes® into the aqueous solution of SWCNT and sodium dodecylbenzene sulfonate (SDBS), adsorption of aniline monomer onto SWCNTs, and in situ polymerization of PANI nanoribbons (see Scheme 1). The Kimwipes® delicate task wipers we used here are lint-free cellulose fibers interweaved together (see Fig. 1a). They have little chemical additives and are commonly used in laboratories for

Conclusions

In summary, we prepared a lightweight and highly foldable supercapacitor electrode using Kimwipes® with macroporous cellulose fibers as scaffold. Through a “dip-absorption-polymerization (DAP)” approach, we created triple semi-interpenetrating networks of SWCNTs and ultrathin and ultralong PANI nanoribbons, wrapping around the interconnected cellulose fibers instead of simply coating the fiber surface or filling in-between. The resulting SWCNT/PANI nanoribbon paper was lightweight (0.34 g/cm3)

Acknowledgments

LY would like to acknowledge the support from the National Natural Science Foundation of China (No. 5112068). Penn Nanoscale Characterization Facility (NCF) is acknowledged for access SEM. Tianqi Li from Prof. Yury Gogotsi׳s group is acknowledged for the help in electrochemical testing of solid-state paper-based supercapacitors.

Dengteng Ge received his B.S. (2005), M.S. (2007) and Ph.D. degree (2011) in Materials Science and Engineering from Harbin Institute of Technology (HIT), China. He joined in Prof. Shu Yang׳s group at University of Pennsylvania (USA) as a post-doctoral researcher from May 2012 to now. His current research interests include flexible electrical devices, structure color, and surface wettability.

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  • Cited by (0)

    Dengteng Ge received his B.S. (2005), M.S. (2007) and Ph.D. degree (2011) in Materials Science and Engineering from Harbin Institute of Technology (HIT), China. He joined in Prof. Shu Yang׳s group at University of Pennsylvania (USA) as a post-doctoral researcher from May 2012 to now. His current research interests include flexible electrical devices, structure color, and surface wettability.

    Lili Yang received her B.S. degree (2003) in Polymer Science and Engineering, M.S. degree (2005) and Ph.D. degree (2009) in Materials Science and Engineering from Harbin Institute of Technology (HIT), China. She is now an associate professor in School of Transportation Science and Engineering at HIT. Her research focuses on novel functional materials and their applications in transportation. She visited Prof. Shu Yang׳s group at University of Pennsylvania in 2012 and worked on the design and fabrication of flexible energy storage systems.

    Lei Fan received his Ph.D. degree from Yangzhou University in June 2009, China. He now works at Yangzhou University on surface and colloid interface science. During 2013 to 2014, he was a visiting scholar at Drexel University (USA), working with Prof. Yury Gogotsi. His research interests include fabrication of metal oxide nanomaterials in colloid systems and their applications in supercapacitors and batteries.

    Chuanfang Zhang received his B.S and M.S. from East China University of Science and Technology (ECUST), Shanghai, China in 2011 and now a Co-Ph.D. candidate of ECUST and Drexel University, Philadelphia, USA under the supervision of Prof. Yury Gogotsi. His research interests mainly lie in the transition metal oxide/carbon composites for supercapacitor and Li-ion battery. He developed various advanced electrode fabrication techniques and optimized fundamental testing methods for supercapacitor. Currently he works on two-dimensional carbides for energy storage applications.

    Xu Xiao received his B.S. degree in School of Physics from Huazhong University of Science and Technology (HUST), PR China in Jun, 2011. Now he is a Ph.D. candidate in Wuhan National Laboratory for Optoelectronics (WNLO) and School of Optical and Electronic Information at HUST. His research interests include flexible electronics and flexible solid-state supercapacitors for self-powered systems.

    Yury Gogotsi is Distinguished University Professor and Trustee Chair of Materials Science and Engineering at Drexel University. He is also the founding Director of the A.J. Drexel Nanomaterials Institute and Associate Editor of ACS Nano. His Ph.D. is in Physical Chemistry from Kiev Polytechnic and D.Sc. in Materials Engineering from Ukrainian Academy of Sciences. He works on nanostructured carbons and other nanomaterials for energy related and biomedical applications. He has coauthored 2 books, more than 400 journal papers and obtained more than 50 patents. He has received numerous national and international awards for his research, was recognized as Highly Cited Researcher by Thomson-Reuters in 2013 and elected a Fellow of AAAS, MRS, ECS and ACerS and a member of the World Academy of Ceramics.

    Shu Yang is Professor in the Department of Materials Science and Engineering at University of Pennsylvania (Penn). She received her B. S. degree in Materials Chemistry from Fudan University, China in 1992, and Ph. D. degree in Chemistry and Chemical Biology from Cornell University in 1999. She worked at Bell Laboratories, Lucent Technologies as a Member of Technical Staff before joining Penn in 2004. Her research interests include synthesis and engineering of well-­‐defined polymers and inorganic materials with controlled size, shape, and morphology over multiple lengthscales, study of their directed assembly and unique surface, optical, and mechanical properties, as well as dynamic tuning.

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