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Fully-printed Ultra-flexible Supercapacitor Supported by a Single-textile Substrate Huihui Zhang, Yan Qiao, and Zhisong Lu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b11172 • Publication Date (Web): 07 Nov 2016 Downloaded from http://pubs.acs.org on November 7, 2016

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ACS Applied Materials & Interfaces

Fully-printed Ultra-flexible Supercapacitor Supported by a Single-textile Substrate Huihui Zhanga,b, Yan Qiaoa,b and Zhisong Lua,b* a

Chongqing Key Laboratory for Advanced Materials & Technologies of Clean

Energies, Southwest University, 1 Tiansheng Road, Chongqing 400715, P. R. China b

Institute for Clean Energy & Advanced Materials, Faculty of Materials & Energy,

Southwest University, 1 Tiansheng Road, Chongqing 400715, P. R. China.

*: Authors to whom correspondence should be addressed. Tel.: +86-23-68254732; Fax: +86-23-68254969. E-mail: [email protected].

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Abstract

Textile-based supercapacitors have recently attracted much attention owing to their great potentials as energy storage components in wearable electronics. However, fabrication of a high-performance, fully-printed and ultra-flexible supercapacitor based on a single textile still remains a great challenge. Herein, a facile, low-cost and textile-compatible method involving screen printing and transfer printing is developed to construct all-solid-state supercapacitors on a single silk fabric. The system exhibits a high specific capacitance of 19.23 mF cm-2 at a current density of 1 mA cm-2 and excellent cycling stability with capacitance retention of 84% after 2000 charging/discharging cycles. In addition, the device possesses superior mechanical stability with stable performance and structures after 100 times of bending and twisting. A butterfly-patterned supercapacitor was manufactured to demonstrate the compatibility of the printing approaches to textile aesthetics. This work may provide a facile and versatile approach for fabricating a rationally designed ultra-flexible textile-based power-storage elements for potential applications in smart textiles and stretchable/flexible electronics.

Keywords: Wearable electronics; Screen printing technique; Supercapacitor; Flexibility; Silk fabric.


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1. Introduction Development of small-dimensional and flexible wearable devices has been fueled up in the past few years to meet the ever-increasing demands for the real-time health monitoring1-2. In order to realize a long-term detection, sufficient electrical energy should be continuously supplied to power the devices. Thus, energy storage system has been regarded as a very essential component of a wearable device and attracted tremendous attention and research interest3-6. Besides high power density and long cycling life, requirements on small dimension, light-weight and ultra-flexibility should also be considered in designing a power supply unit for wearable devices7.

The electrochemical supercapacitor is a well-studied energy storage device with high power density, long cycling life and high efficiency8-9. By modifying its architectures and construction matrix, the electrochemical supercapacitor could be tailored into a planar all-solid-state structures that may be of great potentials as energy storage units in

wearable electronics10-12.

The

first generation of planar all-solid-state

supercapacitors are fabricated on metals such as copper foil9 and nickel foam13. The metal substrates could be stable supports of the supercapacitors and could effectively transfer electrical charges. However, the metal-based devices are usually too rigid and bulky to be applied in stretchable/flexible electronics. Recently, various types of flexible materials, including polymeric films14-16, papers12, 17-18, fibers/yarns19-20 and fabrics21-22, have been employed to produce the all-solid-state supercapacitors. Among them, fibers/yarns and fabrics are the most eye-catching substrates because of their capability to be integrated into clothes for directly wearable devices23. Nylon fibers 3 ACS Paragon Plus Environment


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and cotton yarns have been modified with carbon nanotubes and graphene nanosheets, respectively, to serve as electronically active fiber electrode components for one-dimensional supercapacitors19-20. They could be readily knitted into textile, but the micro- or even nano-scale surface functionalization process may be too complicated, hindering their practical applications.

Fabrics have also been investigated as substrates for the construction of flexible supercapacitors21-22. Conventional sandwich-structured supercapacitors supported by two substrates have been produced with nylon lycra22 and cotton fabrics21, 23-24. The two textile substrates in the supercapacitors may not be compatible with the existing one-substrate wearable devices and conventional clothing producing techniques. Furthermore, flexibility of the energy storage system may also be restricted by them. Very recently, an in-plane supercapacitor with the interdigital electrode architecture has been fabricated on a single nylon fabric, showing good capability for stylish designs in textiles. However, in comparison with the above sandwich devices, its capacitive performance is not quite high owing to the less areal energy density for the thin electrodes25-26. Thus, it is highly desirable to design a high-performance and all-solid-state supercapacitor on a single-textile substrate for possible applications in flexible electronics.

Tight and efficient depositions of conductive materials and active materials are of great importance for the mechanical stability and electrochemical performance of the textile-based supercapacitors. Screen printing is a rapid and scalable technique that 4 ACS Paragon Plus Environment

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can transfer inks onto various substrates with fine-controlled position and thickness27-28. It can be adapted to traditional textile industry to print artistic patterns on clothes. In previous works, the technique has been employed to deposit carbonaceous materials on textile to achieve conductive current collectors23. The transfer-printing method has also been applied to fabricate supercapacitor electrodes on smooth substrate materials

29

.

However, as far as we know, the combination of

the screen-printing and the transfer-printing methods for an all-printed textile-based supercapacitor has not been realized.

Herein, commercial silk fabrics were chosen as substrate materials to fabricate all-printed, single

textile-supported

supercapacitors with high

performance,

ultra-flexibility and great mechanical stability. The current collector and the active materials layers were screen-printed on a silk fabric and a PDMS film, respectively. After being pasted with gel electrolyte, the PDMS-based electrode was transferred exactly on the top of the silk fabric-based one to obtain a single textile-supported supercapacitor,

the

design

of

which

is

inspired

from

the

conventional

sandwich-structured ones. Digital photographs and field-emission scanning electron micrographs

were

collected

to

characterize

the

fabrication

process.

The

electrochemical performance was evaluated with cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The mechanical stability and the compatibility of printing techniques to the textile aesthetics were also investigated to demonstrate the feasibility of the as-prepared devices in wearable electronics. 5 ACS Paragon Plus Environment


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2. Experimental section 2.1 Chemicals MnO2-coated hollow carbon microspheres were prepared with fungal conidia as template materials according to our previous work30 and used as the active materials of the supercapacitors in the present study. Phosphoric acid (H3PO4, ACS, ≥85 wt. % in H2O) and polyvinyl alcohol (PVA, Mw 145000) were purchased from Aladdin (Shanghai, China). LA133 aqueous binder and acetylene black were bought from Chengdu Indigo Power Sources Co. Ltd. Other chemicals are of analytical grade and directly used without further purification procedures. Deionized water (resistance over 18 MΩ·cm) was generated by a Millipore water purification system. 2.2 Fabrication of silk fabric-based supercapacitor The MnO2-coated hollow carbon microspheres (active materials), acetylene black (conductive additive) and LA133 (aqueous binder) were mixed with a weight ratio of 7:2:1 for the preparation of printing ink. In briefly, 62.5 mg LA133 was dissolved in 2.85 mL deionized water, stirring at ambient conditions for 30 min. Then, 125 mg acetylene black and 437.5 mg active material power were dispersed in the as-prepared LA133 aqueous solution, stirring at room temperature for another 8 h to produce a homogeneous aqueous printing ink with a solid content of ~18 wt %.

The procedures for fabrication of a fabric-based supercapacitor are shown in Figure 1. Silk fabrics were cut into desired sizes and used as substrates in the printing process. The silver ink was printed on the fabric surface using a mask with pre-designed


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patterns. After drying at 85 ºC for 1 h to remove solvent, conductive current collectors were formed. The same procedures were repeated to print carbon paste film and the active materials on the top of the silver electrode successively, obtaining one electrode of the supercapacitor. Eight mg active materials were deposited on the electrode to form a 15-µm-thick film. The carbon layer could effectively protect the silver film from corrosion caused by the electrolytes. The typical sheet resistance of the as-prepared silver-carbon current collector is about 3 Ω/square. Another electrode with the same size and structure was fabricated on a piece of PDMS film via screen-printing technique.

Figure 1. Schematic illustration of the fabrication process of a silk-based wearable supercapacitor.

PVA/H3PO4 polymer blend, which was prepared by adding 6 g PVA powder and 6 g H3PO4 into 60 mL deionized water under stirring at 85 °C, was employed as the gel 7 ACS Paragon Plus Environment


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electrolyte in the solid-state flexible supercapacitor due to its high proton conductivity at temperatures below 100 °C 31. The freshly prepared PVA/H3PO4 was poured on the silk fabric- and PDMS-based electrodes, respectively, drying at room temperature for 3 h. Then, those two electrodes were stacked together to form a device with the structure of silk fabric-based current collector/active material/gel electrolyte/active material/PDMS-based current collector. After evaporating excess water, the PDMS film was peeled off to transfer the electrode structure to the silk fabric, obtaining a single textile-supported, all-solid-state symmetric supercapacitor.

2.3

Surface

morphology

and

electrochemical

characterization

of

the

supercapacitor Surface morphologies of the silk fabrics and the supercapacitor devices were characterized using a JSM-6510LV SEM (JEOL, Tokyo, Japan) and a JSM-7600 FESEM (JEOL, Tokyo, Japan). Electrochemical properties of the fabric-based supercapacitor were measured at a two-electrode system by CV, GCD and EIS with a CHI 660D electrochemistry workstation (CHI, USA).

2. Results and discussion


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Figure 2. From a silk fabric to a silk fabric-based fully-printed supercapacitor. (A) A piece of pristine silk fabric; A silk fabric after successively screen printing of silver (B), carbon (C) and active materials layers (D); (E) Removal of the PDMS support from the stacked device; (F) A single textile-supported supercapacitor.

The bio-inspired hollow carbon microspheres modified with MnO2 nanosheets were used as active materials in the symmetric supercapacitors. Physical and chemical properties of the as-prepared carbon microsphere-MnO2 nanosheets composites were characterized with transmission electron microscope, SEM and X-ray diffractometry (Fig. S1 in supporting information), verifying that the quality of the materials could meet the requirements of supercapacitor applications. A silk fabric-based supercapacitor was fabricated step-by-step as shown in Figure 2. Commercially available silk textile was utilized as a flexible substrate for the device construction (Fig. 2A). After screen-printing of the silver ink, a silvery rectangle with a length of 2.5 cm and a width of 1.0 cm is deposited on the white fabric (Fig. 2B). A layer of 9 ACS Paragon Plus Environment


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carbon paste covers most part of the silver rectangle to effectively protect the silver materials from electrolyte-caused corrosion (Fig. 2C)32. The existence of the carbon shielding layer does not significantly affect the capacitive behavior of the final devices (Fig. S2 in Supporting Information). Then a layer of active materials is exactly printed on the top of the current collector film (Fig. 2D). After gel electrolyte coating, a PDMS-based electrode, which is produced with the same electrode structure via the same procedures, is transferred to obtain the single fabric-supported all-solid-state supercapacitor (Fig. 2E and 2F).

SEM was carried out to investigate surface morphological changes of the silk fabrics at micro- and nano-scale during the device fabrication (Fig. 3). Bundles of silk fibers, which possess a very smooth surface and the diameter of ~10 µm, are interlocked with each other to form a fabric (Fig. 3A). After printing of silver ink, the interlocked structure of the fabric still can be observed. However, the edge of the fibers in each bundle become fuzzy, suggesting the deposition of a layer of silver on the silk fabric (Fig. 3B). A lot of micro-sized flakes appear on the fabric surface due to the coating of carbon paste, agreeing well with the size and shape of graphite particles in the printing ink33. Features of the textile are totally blanketed by the stacking of silver and carbon layers (Fig. 3C). Effective immobilization of active materials determines the capacitive performance of the prepared device. After their printing, numerous of microspheres are uniformly distributed on the surface of the fabric and the size of the microspheres is consistent with that of carbon microsphere-MnO2 nanosheets composites30. The SEM images show successful deposition of the active material 10 ACS Paragon Plus Environment

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layer on the silk fabric via screen-printing technique (Fig. 3D). A smooth device surface could be observed after transfer of the PDMS-based electrode (Fig. 3E). From the cross-sectional view, it can be found that a multilayered film with a thickness of ~200 µm is tightly attached on the silk fabric (Fig. 3F).

Figure 3. Surface morphologies of a pristine silk fabric before (A) and after successively screen printing of silver (B), carbon (C) and active materials layers (D), respectively; (E) Surface morphology of the device after removal of PDMS; (F) Cross-sectional view of a silk fabric-supported supercapacitor. Inset images are the corresponding SEM images with a higher magnification.



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Figure 4. (A) CV curves of a supercapacitor at various scan rates; (B) Galvanostatic charge-discharge curves over a potential window from 0 to 0.8 V at different current densities; (C) Nyquist plot of a supercapacitor; (D) Cycle life of a supercapacitor at the scan rate of 50 mV s−1.

Electrochemical properties of the silk fabric-based supercapacitors are investigated with a two-electrode system by CV, GCD and EIS at room temperature (Fig. 4). Fig. 4A shows that the CV curves of a supercapacitor device possess quasi-rectangle shapes at the scan rates varying from 10 to 500 mV s−1, which indicate that the fabric-based electrode has good capacitive performance at a wide range of scan rates. It is noted that no apparent redox peak is observed in the CV curves over a potential 12 ACS Paragon Plus Environment

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range of 0 to 0.8 V. The finding may suggest that the electrode materials are quite stable in the presence of the PVA/H3PO4 gel electrolyte. The discharge plots in Fig. 4B are almost linear and symmetrical at different current densities (1-5 mA cm-2), revealing the ideal capacitive behavior and the excellent reversibility of the device. The capacitance of the flexible device was calculated to be 19.23 mF cm-2 at a current density of 1 mA cm-2, which is much better than those of the flexible capacitors supported by cellulose nanofibers/carbon nanotubes34, PET35 and graphite flake12. The value is also more than 2 times higher than that (8.19 mF cm-2) of the in-plane textile supercapacitors26. Due to the addition of binder into the active material inks, the performance still cannot compete with those of the supercapacitors based on hierarchical MnO2/carbon strip microsphere and carbon nanotube/MnO2 nanotube hybrid porous films 36-37. However, the silk fabric-based supercapacitors may be used as flexible energy supply elements to power some wearable devices. Nyquist plot of an as-prepared supercapacitor between 0.1 and 1000 kHz is exhibited in Fig. 4C and its inset. The equivalent series resistance (ESR) is about 4.6 Ω based on the intercept of the Nyquist plot on real axis. A very short 45° Warburg region appeared at the medium frequencies implies the fast ion transport at the interface of active materials and the gel electrolyte. The straight and nearly vertical line in the low frequency portion of the spectrum, indicating the perfect capacitive behavior of the silk fabric-based all-solid-state supercapacitor. Hierarchical NiCo2O4 nanomaterials, CoO@NiO core/shell nanostructures, NiCo2O4@NiCo2O4 core/shell nanostructures, and Zn2SnO4/MnO2 core/shell nanocables have been in-situ grown on conductive 13 ACS Paragon Plus Environment


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textiles for fabricating flexible high-performance supercapacitors

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38-41

. Although the

systems containing active materials with rationally designed nanostructures deliver better energy storage performance than the as-prepared all-printing supercapacitors, their practical applications may be greatly hampered by the strict requirements on the synthesis conditions and well-trained professionals. Cycling stability is another critical characteristic that needs to be considered for a supercapacitor. After 2000 times of charging/discharging cycles, the device could still maintain 84% of its initial capacitance, which demonstrates the remarkable long-term cycling life of our flexible supercapacitors (Figure. 4D). The results reveal that the as-prepared single textile-supported supercapacitor could be utilized as a very promising micro-power supply component in wearable electronics.

Figure 5. (A) CV curves of an as-prepared single textile-based supercapacitor rolled on pens with different diameters; (B) Stretching-forces to the textile-attached electrodes in the single-substrate and two-substrate devices at the bent state.

To explore the mechanical property of the fabricated supercapacitor, we evaluated capacitive behaviors of an as-prepared single textile-based supercapacitor at different 14 ACS Paragon Plus Environment

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bending states (Fig. 5). As shown in the digital photographs, a single textile-supported device was tightly twined around pens with the diameters of 0.5, 0.8, 1.0 and 1.5 cm. In comparison with the CV curve of the device at the flat state, there are negligible changes on those of the bent ones, suggesting that the device could be bent at different levels without changing the capacitive performance (Fig. 5A). The same experiments were also conducted to examine the flexibility of a supercapacitor with a conventional two-substrate structure, which was produced with identical materials and techniques. Unlike the results of the single textile-supported device, the CV curves gradually change from a nearly rectangle to spindle shapes with the increase of the pen diameter (Fig. S3 in Supplementary Information). The above results clearly verify that the single-substrate structure could provide much better mechanical stability than the conventional two-substrate conformation. At the flat state, the textile simply serves as a support of the supercapacitor. When the device is twined around a pen, the curved textile substrate could exert a stretching force on its surface-attached materials, which may possibly cause the structure distortion. In a single-textile based system, the traction force comes from the only substrate. However, for a two-textile supported sandwich conformation, the top and the bottom textile substrates give opposite forces to the multilayered structure, respectively. The above analysis may explain the better performance of the single-textile supported capacitor at its bent states (Fig. 5B).



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Figure 6. Effects of bending and twisting on the capacitive performance of the single-textile-supported supercapacitors. CV curves (A) and Nyquist plots (B) of a supercapacitor after 20, 40, 60, 80 and 100 times of bending; CV curves (C) and Nyquist plots (D) of a supercapacitor after 20, 40, 60, 80 and 100 times of twisting.

Since the silk fabric-based supercapacitors have great potentials as miniaturized power storage elements in wearable electronics, the tolerance to bending and twisting is another important parameter that needs to be examined. CV and EIS were carried out in the present study to investigate effects of bending and twisting on performance of the supercapacitors (Fig. 6). As the bending number increases from 20 to 100, there is no obvious alteration on the CV curves (Fig. 6A). The Nyquist plots in Fig. 6B show that the line at the low frequency region keeps straight and vertical with a slight enhancement of the ESR from ~4 Ω to ~5 Ω after 100 times of bending (Fig. 6B). Similar to the findings of the bending tests, no significant change on CV and EIS data 16 ACS Paragon Plus Environment

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could be observed after 100 times of twisting (Fig. 6C and 6D). After the bending and twisting tests, the capacitance retention rates could reach 98.5 % and 96.8 %, respectively. SEM was employed to check the morphology of the tested devices at the exact locations of bending and twisting (Fig. S4 in Supplementary Information). A few twinkles appear on the surface, but no clear crack could be seen from both images of the top- and cross-sectional views. The results indicate that the silk fabric-supported supercapacitor possess outstanding tolerance to the repeated bending and twisting, which meets the requirements of stretchable/wearable electric devices on flexibility. Flexible batteries based on textile substrates have already been reported in previous studies42-45. The silk fabrics may also be used as ideal flexible supports for wearable batteries.



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Figure 7. (A) Galvanostatic charge/discharge curves of a single supercapacitor (black curve) and three supercapacitors connected in series (red curve); (B) Digital photograph of a red LED powered by three supercapacitors connected in series; CV curve (C) and digital photograph (D) of a specially designed supercapacitor with a butterfly pattern.

To demonstrate the feasibility of the silk fabric-based supercapacitor, three devices are connected in series to generate sufficient voltage and capacitance to power a red light-emitting diodes (LED, the lowest working voltage is 1.5 V) (Fig. 7A and 7B). Three in-series connected textile-supported supercapacitors exhibit a potential up to 2.4 V, which is three times higher than that of a single device. The 18 ACS Paragon Plus Environment

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charging/discharging time of the tandem system is the same as that of a single device (Fig. 7A). The charged tandem supercapacitors could power a commercial red LED lamp (Fig. 7B). Since screen printing technique is compatible with textile industry28, a supercapacitor with pre-designed patterns could be constructed on a fabric via the layer-by-layer screen printing method. As shown in Fig. 7D, the device with a butterfly pattern is printed on a silk fabric using the antennae as conductive clamping pads. A quasi-rectangle CV curve could be obtained with the butterfly-patterned device at a scanning rate of 100 mV s-1, showing its good capacitive property (Fig. 7C). The use of the screen printing technique for the fabrication of a supercapacitor could combine both functionality and aesthetics, which are two very essential issues for the feasible applications of the textile-based wearable electronic devices. A roll-to-roll process has been employed to synthesize flexible electrodes for scalable production of energy storage devices46. The screen printing technique may also be modified to further reduce time, energy and cost needed for the electrode fabrication, achieving high throughput manufacturing of textile-based supercapacitors. Conclusions In summary, an all-solid-state, ultra-flexible supercapacitor with a single-textile substrate is fabricated on a silk fabric using screen-printing and transfer-printing techniques. The as-prepared supercapacitor achieves a high specific capacitance of 19.23 mF cm-2 at a current density of 1 mA cm-2 and the excellent cycling stability with capacitance retention of 84% after 2000 charging/discharging cycles. In comparison with the conventional two-substrate ones, it possesses much better 19 ACS Paragon Plus Environment


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mechanical stability at the bent state. The device can tolerate 100 times of bending and twisting without influencing its performance and structures. The in-series connected supercapacitors can power a commercial red LED lamp. Furthermore, the supercapacitors could be fabricated on textile into specially designed patterns for the combination of both functionality and aesthetics. This work may not only develop rationally designed ultra-flexible textile-based power-storage elements for potential applications in smart textiles or wearable electronics, but also provides a facile and versatile approach to fabricate single-textile supported stretchable/flexible electronic devices.

Supporting Information Details of the material synthesis; Calculation of the device performance; Characterization data of the active materials; CV curves of the silk fabric-supported supercapacitors with or without the active materials; CV curves of an as-prepared two textile-based supercapacitor; Morphologies of the devices after bending and twisting; Ragone plot of the silk fabric-supported supercapacitors.

Acknowledgements This work is financially supported by Chongqing Key Laboratory for Advanced Materials and Technologies of Clean Energies under cstc2011pt-sy90001, Start-up grant under SWU111071 from Southwest University and Fundamental Research Funds for the Central Universities under XDJK2015B016. Z. S. Lu would like to thank the supports by the Specialized Research Fund for the Doctoral Program of 20 ACS Paragon Plus Environment

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Figure Captions Figure 1. Schematic illustration of the fabrication process of a silk-based wearable supercapacitor. Figure 2. From a silk fabric to a silk fabric-based fully-printed supercapacitor. (A) A piece of pristine silk fabric; A silk fabric after successively screen printing of silver (B), carbon (C) and active materials layers (D); (E) Removal of the PDMS support from the stacked device; (F) A single textile-supported supercapacitor. Figure 3. Surface morphologies of a pristine silk fabric before (A) and after successively screen printing of silver (B), carbon (C) and active materials layers (D), respectively; (E) Surface morphology of the device after removal of PDMS; (F) Cross-sectional view of a silk fabric-supported supercapacitor. Inset images are the corresponding SEM images with a higher magnification. Figure 4. (A) CV curves of a supercapacitor at various scan rates; (B) Galvanostatic charge-discharge curves over a potential window from 0 to 0.8 V at different current densities; (C) Nyquist plot of a supercapacitor; (D) Cycle life of a supercapacitor at the scan rate of 50 mV s−1. Figure 5. (A) CV curves of an as-prepared single textile-based supercapacitor rolled on pens with different diameters; (B) Stretching-forces to the textile-attached electrodes for the single-substrate and two-substrate devices. Figure 6. Effects of bending and twisting on the capacitive performance of the single-textile-supported supercapacitors. CV curves (A) and Nyquist plots (B) of a supercapacitor after 20, 40, 60, 80 and 100 times of bending; CV curves (C) and 28 ACS Paragon Plus Environment

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Nyquist plots (D) of a supercapacitor after 20, 40, 60, 80 and 100 times of twisting. Figure 7. (A) Galvanostatic charge/discharge curves of a single supercapacitor (black curve) and three supercapacitors connected in series (red curve); (B) Digital photograph of a red LED powered by three supercapacitors connected in series; CV curve (C) and digital photograph (D) of a specially designed supercapacitor with a butterfly pattern.



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Figure 1. Schematic illustration of the fabrication process of a silk-based wearable supercapacitor. 180x99mm (300 x 300 DPI)

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Figure 2. From a silk fabric to a silk fabric-based fully-printed supercapacitor. (A) A piece of pristine silk fabric; A silk fabric after successively screen printing of silver (B), carbon (C) and active materials layers (D); (E) Removal of the PDMS support from the stacked device; (F) A single textile-supported supercapacitor. 122x100mm (300 x 300 DPI)



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Figure 3. Surface morphologies of a pristine silk fabric before (A) and after successively screen printing of silver (B), carbon (C) and active materials layers (D), respectively; (E) Surface morphology of the device after removal of PDMS; (F) Cross-sectional view of a silk fabric-supported supercapacitor. Inset images are the corresponding SEM images with a higher magnification. 311x142mm (300 x 300 DPI)


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Figure 4. (A) CV curves of a supercapacitor at various scan rates; (B) Galvanostatic charge-discharge curves over a potential window from 0 to 0.8 V at different current densities; (C) Nyquist plot of a supercapacitor; (D) Cycle life of a supercapacitor at the scan rate of 50 mV s−1. 474x374mm (300 x 300 DPI)



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Figure 5. (A) CV curves of an as-prepared single textile-based supercapacitor rolled on pens with different diameters; (B) Stretching-forces to the textile-attached electrodes for the single-substrate and twosubstrate devices. 489x177mm (300 x 300 DPI)


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Figure 6. Effects of bending and twisting on the capacitive performance of the single-textile-supported supercapacitors. CV curves (A) and Nyquist plots (B) of a supercapacitor after 20, 40, 60, 80 and 100 times of bending; CV curves (C) and Nyquist plots (D) of a supercapacitor after 20, 40, 60, 80 and 100 times of twisting. 199x150mm (300 x 300 DPI)



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Figure 7. (A) Galvanostatic charge/discharge curves of a single supercapacitor (black curve) and three supercapacitors connected in series (red curve); (B) Digital photograph of a red LED powered by three supercapacitors connected in series; CV curve (C) and digital photograph (D) of a specially designed supercapacitor with a butterfly pattern. 151x145mm (300 x 300 DPI)


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Table of Contents Graphic 39x24mm (300 x 300 DPI)


Fully Printed Ultraflexible Supercapacitor ... - ACS Publications

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