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Surface Self-Assembly of Functional Electroactive Nanofibers on Textile Yarns as a Facile Approach Towards Super Flexible Energy Storage Mike Tebyetekerwa, Zhen Xu, Weili Li, Xingping Wang, Ifra Marriam, Shengjie Peng, Seeram Ramakrishna, Shengyuan Yang, and Meifang Zhu ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.7b00057 • Publication Date (Web): 13 Dec 2017 Downloaded from http://pubs.acs.org on December 16, 2017
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ACS Applied Energy Materials
Surface Self-Assembly of Functional Electroactive Nanofibers on Textile Yarns as a Facile Approach Towards Super Flexible Energy Storage a†
a§†
Mike Tebyetekerwa , Zhen Xu d,e
Peng
b
a
c
, Weili Li , Xingping Wang , Ifra Marriam , Shengjie e
, Seeram Ramkrishna , Shengyuan Yang
a
*and Meifang Zhua*
a
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China b
School of Materials Science and Engineering, National Demonstration Center for
Experimental Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003 c
Key Laboratory of Textile Science & Technology, Ministry of Education, College of Textiles, Donghua University, Shanghai 201620, PR China
d
College of Materials Science and Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
e
Centre for Nanofibers and Nanotechnology, National University of Singapore, Singapore 117581, Singapore
§ Present Affiliation, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom †
Authors
Contributed
Equally
Towards
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Keywords. energy storage, flexible electrodes, wearable electronics, yarn supercapacitors, electrospinning
Abstract Textile yarns undergo modifications for use in various smart applications such as energy storage, sensing, and others. For energy storage applications in yarn supercapacitors and batteries, one of the most commonly used yarn modification technique is the coating of conductive active materials onto textile yarns. The coating process can be via vapor phase polymerization, dip coating, thin film coating using layer by layer assembly, atomic layer and electrochemical depositions. However, these methods are hectic, uncontrollable and hardly scalable. Beyond these, they also give brittle coatings which tend to crack easily if coated yarns are incorporated into traditional textiles during use or even during post-manufacturing in weaving/knitting and sewing. Herein, a facile concept of the nanofibers coated on yarn via modified electrospinning process is proposed to address the challenges. The method is capable of giving all-textile super flexible nanofibers coated yarns with excellent electrochemical performance, exceptional durability, and excellent flexibility, all courtesy of the electroactive and porous nature of nanofibers coated around textile yarn current collector aiding faster ion diffusion. The method opens up a new scalable strategy to fabricate smart yarns with single nozzle productivity of up to 1.2 m hr-1.
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1. Introduction The wearable energy storage devices such as fiber/yarn supercapacitors and batteries are hugely anticipated for use in the next generation smart textiles.1-6 Remarkable works have been reported mainly with regards to supercapacitor-based flexible functional yarns for energy storage applications,7-13 but still there remains a challenge for sturdy and sufficiently pliable yarns which can be effortlessly woven, knitted or braided into fabrics and garments and also be used by consumers without deterioration of their energy density and power density under unpredictable numerous textile bending positions usually during use. In the various works which reported yarn supercapacitors, the yarns employed suffered from two major challenges. 1) They are yarn-shaped but not real yarns and therefore lack almost all the essential textile properties such as weaveability/ knittability, tenacity, flexibility, and resilience, which features form the credibility of textiles used in clothing.14 2) Their diameters are too low which renders their practical use almost impossible. The functional yarn electrodes are fabricated in a variety of ways of which coating of conducting materials onto insulating yarns is widely employed and considerably reported.15-17 Coatings are preferred because they provide a continuous, uninterrupted and uniform conducting layer. Coating methods can be in-situ solution/vapor phase polymerization, dip coating, thin film coating using layer by layer assembly, atomic layer depositions and electrochemical depositions.18-21 The technique of wrapping of conducting yarns onto the insulating yarns has also been previously reported.22-23 In energy storage applications, for example, Peng’s group23 reported wrapped CNTs on an insulating elastomer fiber which was coated with Polyaniline conducting polymer (CP) to form supercapacitor electrodes. However, despite these previous studies on coated and wrapped yarn supercapacitors, there are some mischiefs such as; 1) the processes involved are long and hectic- therefore not scalable, 2) there is poor control of adhesion, composition, and thickness of yarn electrodes, 3) the processes tend to diminish the surface area of the resultant fibers and active materials and, 4) the coating process partly kills the flexibility of the textile fiber materials involved. ACS Paragon Plus Environment
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The aim of this current work is to simplify the coating process into a controllable and scalable process while increasing the electroactiveness of the resultant functional yarns for energy storage and maintaining their flexibility for use in smart textiles with toughness suitable for various textile processing techniques such as weaving and knitting. To achieve the objectives above, we used a widely known and scalable electrospinning technique to selfassemble, and coat sconducting nanofibers of Polyindole/Carbon Black (Pind/CB) nanocomposites onto stainless steel spun textile yarn (SSY). The resultant best nanofiber coated yarns (NCY) supercapacitor showed a high areal capacitance of 16.44 mF cm-2 at 5 mV s-1 with a high toughness which is attributed to the SSY which acted as the current collector. The yarns could seffortlessly be woven and knitted into textiles, and still maintained their capacitance values with no remarkable changes.
2. Results and discussion 2.1 Fabrication, Characterization and Morphology of NCYs
Scheme 1. Preparation of the electrospinning solution recipe (a, b and c) and method for fabrication of NCY via electrospinning (d) The fabrication of NCY electrodes is schematically illustrated in Scheme 1. The process was a quick single step. First, the active materials consisting of Pind and CB were prepared (see experimental section for preparation). Then introduced into the electrospinning ACS Paragon Plus Environment
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syringe and finally electrospun onto the SSY placed at a distance of 8 cm from the alternating spinneret for a duration of ~3-15 minutes (Scheme 1d). For ease, the NCY with nanofibers of Pind, CB, Pind/CB in ratios of 4:1, 1:1, 1:4 will be denoted Pind, CB, Pind/CB 4-1, Pind/CB 1-1 and Pind/CB 1-4, respectively from henceforth.
Figure 1. Materials Characterization. FTIR (a) and Raman (b) spectra of neat CB, neat Pind, and Pind/CB 1-4 composite nanofibers, and (c) TGA curves of pure CB, neat Pind, PVA and Pind/CB 1-4 composite nanofibers FTIR and Raman analysis. To confirm the successful polymerization of Pind polymer and also to understand to compositing of CB, Pind, and PVA, FTIR and Raman analysis were carried out. FTIR spectra (Figure. 1a) confirmed the polymerization of Pind. Characteristic peak in Pind and Pind/CB samples at ~3431 cm-1 for N-H absorption band was observed. The bands observed at 1618 cm-1 and 1456 cm-1 in Pind and Pind/CB are ascribed to the C=C stretching and C-H deformation vibrations, respectively on the benzene ring in the indole. Also, peak 1111 cm-1 is due to the vibration modes of the C-N bond. The remaining characteristic peak at 747 cm-1 that appeared both the Pind and Pind/CB is ascribed to the benzene ring which also together with other peaks at 766 cm-1 and 726 cm-1 existed in monomer indole, but the latter two did not appear in the polymer and polymer composites (See Figure. S1 for monomer indole FTIR spectra).24-28 These bands 726 cm-1 and 766 cm-1 in the monomer (indole) are typical marks for the in-phase vibration of hydrogen species located at the carbon positions 2,3 on the pyrrole ring. Their non-existence in the polymer and polymer composite spectra means they were responsible for polymerization. Indeed, this observation can be used to explain the polymerization mechanism of Pind from indole ACS Paragon Plus Environment
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monomer which is believed to have proceeded as per Scheme 2. Similar results have previously been reported and proposed in the literature.26-27, 29 However, it is worth noting that in the nanofibers composites, the polymer peak at 766 cm-1 was small due to the introduction of PVA and CB to Pind. To further corroborate the FTIR results, Raman spectroscopy was used. In Figure. 1b, two typical D and G bands at ~1330 and ~1590 cm-1 were observed in all samples (Pind, CB and Pind/CB nanofibers) which are characteristic of the sp3 and sp2 carbons.30-31 The D/G intensity ratios of the samples were in the order of: Pind (0.91) < Pind/CB (0.99)
