Polymorphous Supercapacitors Constructed from Flexible Three


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Energy, Environmental, and Catalysis Applications

Polymorphous supercapacitors constructed from flexible threedimensional carbon network/polyaniline/MnO composite textiles 2

Jinjie Wang, Liubing Dong, Chengjun Xu, Danyang Ren, Xinpei Ma, and Feiyu Kang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b19195 • Publication Date (Web): 12 Mar 2018 Downloaded from http://pubs.acs.org on March 12, 2018

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Polymorphous supercapacitors constructed from flexible three-dimensional carbon network/polyaniline/MnO2 composite textiles Jinjie Wang,† Liubing Dong,*,†,‡ Chengjun Xu,*,† Danyang Ren,†,‡ Xinpei Ma,†,‡ Feiyu Kang †,‡ †

Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China



School of Materials Science and Engineering, Tsinghua University, Beijing 100084,

China *

Corresponding authors:

L. Dong ([email protected]); C. Xu ([email protected])

KEYWORDS: Flexible supercapacitor, activated carbon fiber cloth, polymorphous supercapacitors, textile electrode, fiber-like electrode

ABSTRACT Polymorphous supercapacitors were constructed from flexible three-dimensional (3D) carbon network/polyaniline (PANI)/MnO2 composite textile electrodes. The flexible textile electrodes were fabricated through a layer-by-layer construction strategy: PANI, carbon nanotubes (CNTs) and MnO2 were deposited on activated carbon fiber cloth (ACFC) in turn through electro-polymerization process, “dipping and drying” method

and

in

situ

chemical

reaction,

respectively.

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In

the

fabricated

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ACFC/PANI/CNTs/MnO2 textile electrodes, ACFC-CNT hybrid framework serves as porous and electrically conductive 3D network for rapid transmission of electrons and electrolyte ions, while ACFC, PANI and MnO2 are high-performance supercapacitor electrode materials. In the electrolyte of H2SO4 solution, the textile electrodes based symmetric supercapacitor delivers superior areal capacitance, energy density and power density of 4615 mF cm-2 (for single electrode), 157 µWh cm-2 and 10372 µW cm-2, respectively, while asymmetric supercapacitor assembled with the prepared composite textile as positive electrode and ACFC as negative electrode exhibits improved energy density of 413 µWh cm-2 and power density of 16120 µW cm-2. Based on the ACFC/PANI/CNTs/MnO2 textile electrodes, symmetric and asymmetric solid-state textile supercapacitors with PVA/H2SO4 gel electrolyte were also produced. These solid-state textile supercapacitors exhibit good electrochemical performance and high flexibility. Furthermore, flexible solid-state fiber-like supercapacitor was prepared with fiber bundle electrodes dismantled from above composite textiles. Overall, this work makes a meaningful exploration of the versatile applications of textile electrodes to produce polymorphous supercapacitors.

1.

INTRODUCTION

Flexible supercapacitors are considered as promising candidates for portable and wearable energy storage devices, due to their high power density, long cycle life and good flexibility.1-4 Plenty of flexible electrodes, such as flexible fiber-like, paper-like and textile electrodes, have been prepared to meet the requirements of various wearable electronics and devices.2 Three-dimensional textile electrodes allow a large 2 / 28

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mass loading of electrochemically active materials, thus can achieve high energy output.5-8 Carbon fiber cloth, woven from micrometer-scale carbon fibers, is a typical kind of three-dimensional (3D) substrates for flexible textile electrodes owing to its good conductivity, chemical stability, light weight and high flexibility.9 Nevertheless, the use of carbon fiber cloth substrates notably increases the “dead weight” of these flexible electrodes, because the gravimetric capacitance of carbon fiber cloth itself is almost negligible.10-11 To resolve this issue and improve the areal capacitance of carbon fiber cloth substrate, chemical activation and electrochemical activation approaches have been used.12-15 The obtained activated carbon fiber cloth (ACFC) as an excellent kind of electric double-layer capacitor (EDLC) material gains more and more attentions for flexible and wearable energy storage devices.13,

16

Besides, in

order to fabricate textile substrate based electrodes with large areal capacitance, electrochemically active materials are deposited onto textile substrates.13,

17-23

Polyaniline (PANI) as one of the extensively studied pseudo-capacitive materials has controllable morphologies, facile synthesis procedure, environmental stability and relatively good electrical conductivity.24-26 Among various transition-metal oxides, MnO2 possesses the advantages of ultra-high theoretical specific capacitance, environmental friendliness, natural abundance and low cost.27-29 Besides, optimizing electrode structure such as the distribution state and micro-morphology of deposited active materials on textile substrates is important for the realization of large areal capacitance as well as good flexibility of the composite electrodes.2, 26

In addition, it is necessary to develop flexible supercapacitors with different 3 / 28

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physical forms and functional features to meet the requirements of various wearable electronics products.2,

30-31

However, for most of previously reported flexible

electrodes, they were only utilized to assemble supercapacitor with single form. In other words, it has rarely been reported to construct polymorphous supercapacitors (such as symmetric textile supercapacitor, asymmetric textile supercapacitor and fiber-like supercapacitor) from a fabricated flexible electrode. Obviously, if polymorphous supercapacitors can be fabricated from one given electrode, it will get easier and cheaper for the commercial production and practical application of flexible supercapacitors.

Herein, we proposed a layer-by-layer construction strategy for the preparation of flexible 3D carbon network/PANI/MnO2 composite textile electrodes that can be used to construct polymorphous supercapacitors. PANI nano-rod arrays were firstly electrodeposited onto the ACFC, then continuous carbon nanotube (CNT) networks were constructed inside ACFC/PANI textile, followed by the deposition of MnO2 as shown in Scheme 1. The prepared flexible ACFC/PANI/CNT/MnO2 composite textiles were then utilized to fabricate polymorphous supercapacitors, including symmetric and asymmetric textile supercapacitors with aqueous electrolytes, flexible solid-state textile symmetric and asymmetric textile supercapacitors and flexible solid-state fiber-like supercapacitors. This work is believed to offer a new scope for the diversified applications of fabricated flexible textile electrodes in wearable energy storage devices.

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2.

EXPERIMENTAL SECTION

Materials All the chemical reagents in this work were of analytical reagent grade, and used as received without further purification. ACFC textile with thickness of 400~500 µm was obtained from Nantong Senyou Carbon Fiber Co., Ltd, China. CNT (multi-walled, with the length of 5~15 µm and diameter of 15~25 nm) aqueous paste was purchased from Shenzhen Nanotech Port Co., Ltd, China.

Preparation of ACFC/PANI composite electrode PANI nano-rod arrays were grown on ACFC substrate by a facile electrodeposition process. A piece of ACFC textile (ca. 2.5×4.5 cm) was cut and carefully cleaned in ultrapure water for several times and completely dried at 60 °C before use. The electrodeposition process was conducted in a three-electrode system with the ACFC substrate as the working electrode, a saturated calomel electrode (SCE) as the reference electrode and a graphite electrode as the counter electrode. The electro-polymerization of PANI was carried out under a static potential of 0.9 V in an aqueous solution containing 0.2 M aniline monomer and 0.5 M H2SO4. After electrodeposition, the sample was rinsed with ultrapure water for several times and completely dried at 60 °C. The prepared ACFC/PANI textile electrode with 40 min deposition of PANI is noted as “AP”, in which PANI loading is about 5.62 mg cm-2.

Preparation of ACFC/PANI/CNT composite electrode CNTs were introduced into the AP textile by a “dipping and drying” method.26, 32-33

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The purchased CNT aqueous paste was diluted into 2 wt.% CNT aqueous suspension, and then AP textile was immersed into the CNT suspension for 60 s and dried at 60 °C. The prepared ACFC/PANI/CNT textile electrode is denoted as “APC”, in which CNT loading is about 0.40 mg cm-2.

Preparation of ACFC/PANI/CNT/MnO2 composite electrode MnO2 was loaded onto the textile electrode by immersing APC textile into 0.1 M neutral solution of KMnO4 for 60 s (the reaction mechanism can be expressed as Equation 1).16, 34-35 The sample was then rinsed with deionized water and completely dried at 60 °C. The prepared ACFC/PANI/CNT/MnO2 composite textile electrode is noted as “APCM”, in which MnO2 loading is about 1.13 mg cm-2. 4 + 3 +  → 4 +   + 2   (1)

Material characterization Morphologies of the prepared composite textiles were characterized using scanning electron microscopy (SEM). Energy-dispersive spectroscopy (EDS) mapping was conducted on the textiles to show the distribution of main elements of the electrodes. The composition of the samples was investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) measurement. Specific surface area and pore structure of the textiles were analyzed by Brunauer-Emmett-Teller (BET) analyzer with N2 adsorption tests. Thermal gravimetric (TG) analyses were also conducted and the weight of the textiles was determined through an electronic balance and TG results.

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Assembly and performance tests of polymorphous supercapacitors Aqueous symmetric textile supercapacitor with APCM textile electrodes and asymmetric textile supercapacitor with ACFC as negative electrode and APCM as positive electrode were assembled in a typical CR2032 coin cell. In this case, 1 M H2SO4 solution served as the aqueous electrolyte. Solid-state supercapacitors were assembled with PVA/H2SO4 gel electrolyte. The gel electrolyte was prepared by stirring a mixture of 2 g PVA, 2 g H2SO4 and 20 mL deionized water at 85 oC for 2 h. The electrodes and separator were immersed into the gel electrolyte for several minutes. Solid-state symmetric textile supercapacitor was assembled by sandwiching the separator into two identical APCM composite electrodes while solid-state asymmetric textile supercapacitor was assembled with APCM composite textile as positive electrode and ACFC as negative electrode. Configuration design was described in detail in the Supporting Information (Figure S1). Solid-state fiber-like supercapacitor with gel electrolyte was prepared by placing two identical fiber-like electrodes together in parallel, and the fiber-like electrodes were obtained by directly dismantling the APCM composite textile electrode into individual fiber bundles.16 Electrochemical properties of the assembled supercapacitors were evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) measurements at a VMP3 electrochemical station.

3.

RESULTS AND DISCUSSION

The morphologies of different textile electrodes were investigated by SEM. Woven

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texture of the ACFC can be observed in Figure 1a. There are many parallel grooves and small bulging spots spreading on the surface of activated carbon fibers (Figure 1b). BET surface area of the ACFC is 1242 m2 g-1 and there are numerous micropores and mesopores in ACFC as shown in Figure S2. The relatively high specific surface area of ACFC means more probable sites for the deposition of electrochemically active materials, which makes it suitable as a promising substrate to prepare composite textile electrode. Electrodeposition is an effective method to grow PANI nano-arrays onto carbon materials with different morphologies.36-37 Figure 1c shows that PANI nano-rod arrays are successfully grown on the surface of the carbon fiber after electro-polymerization process. The PANI nano-rods with diameter of around 30 nm and height of about 100 nm nearly vertically attach to the activated carbon fiber (Figure 1d and Figure S3). The nanostructure of AP is believed to have a good impact on the contact between electrolyte and PANI active material.38 In the APC composite textiles, CNTs networks wrap around the surface of AP in Figure 1e-f. CNTs tangle with each other at both individual fiber surface and inter-space between fibers. The CNTs networks and the activated carbon fibers together form conductive 3D carbon networks in the electrodes. MnO2 particles with the sphere diameter of 10~50 nm coated on CNT network inside APCM textile in Figure 1g-h. The distribution state of PANI and MnO2 was further studied with the assist of EDS measurement (Figure S4 and Figure S5). From EDS mapping, it can be seen that N and Mn elements uniformly distribute on the surface of carbon fiber in AP and APCM, respectively, implying that PANI and MnO2 are well-distributed. The XRD patterns 8 / 28

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shows that the deposited MnO2 is a type of birnessite MnO2 (Figure S6). The FTIR spectra of the textile electrodes are shown in Figure S7. Compared with ACFC, the FTIR spectrum of AP, APC and APCM shows a group of typical bands of PANI, where C=C stretching of the quinonoid ring and benzenoid ring appears at 1559 and 1479 cm-1, C-N stretching of aromatic amines appears at 1297 cm-1, and C-H bending of the benzenoid ring and the quinonoid ring appears at 1241 and 1102 cm-1.24, 39-41 The strong peak at 1145 cm-1 is considered to be the “electronic-like band” as a characteristic peak of electrically conductive PANI.24,

41-42

This suggests that the

PANI nano-arrays have good electrochemical activity which is conducive to fabricate high performance textile electrodes. The flexible APCM textile is able to be dismantled into individual fiber bundles with diameter of 450~500 µm (Figure 1i), and the latter ones can be directly used as fiber-like electrodes. 16, 26

The prepared composite textiles were then utilized to construct polymorphous supercapacitors. Figure 2 shows the CV curves of these textile electrodes of ACFC, AP, APC and APCM based symmetric supercapacitors with the electrolyte of 1 M H2SO4 solution. The approximately rectangular CV curves of ACFC in Figure 2a reflect good EDLC performance of ACFC.43 The CV curves of AP in Figure 2b exhibit broad redox peaks and higher response current density after the introduction of PANI. This suggests that the PANI nano-rod arrays endow the AP composite textiles with large pseudocapacitance (Figure 3e).44 The CV curves of APC in Figure 2c show smaller deformation at high scan rates compared to the CV curves of AP. This indicates that rate capability of the electrode is optimized after the introduction of 9 / 28

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CNT networks.45 Introduction of MnO2 into the composite textiles leads to larger area of the CV curves of APCM (Figure 2d), which suggests that better capacitive properties are achieved.8

GCD curves of the aqueous symmetric supercapacitors are shown in Figure 3. The charge-discharge curves of ACFC are nearly symmetric and linear, which demonstrates good EDLC behavior (Figure 3a). ACFC was chosen to serve as both flexible substrate and EDLC active material in our fabricated composite textile electrodes. Its areal capacitance at the current density of 5 mA cm-2 is 2242 mF cm-2. After the deposition of PANI, much longer discharging time is achieved, suggesting larger specific capacitance of AP (Figure 3b). To study the optimal loading of PANI nano-rods grown on the ACFC, AP composite electrodes prepared with different deposition time of PANI were fabricated and their areal capacitance values are summarized in Figure S8. AP composite electrode prepared with 40 min deposition of PANI shows the largest areal capacitance. PANI tends to aggregate on the fiber surface after 60 min deposition (Figure S9), leading to a prominent decrease of areal capacitance. In Figure 3c, GCD curves of symmetric APC supercapacitor exhibit relatively small IR drop because of the improved electrical conductivity of corresponding textile electrodes after introduction of CNT, which can be further confirmed by the EIS results (Figure S10).16, 26, 32 As shown in Figure 3e, compared to pure ACFC textile electrode, AP textile exhibits significantly enhanced areal capacitance with compromised rate capability. The APC textile modified with CNT networks shows much higher capacitance retention at large charge/discharge current 10 / 28

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(e.g., 50 mA cm-2) than AP. This is attributed to the improvement of electrical conductivity. The APCM textile electrode displays the largest areal capacitance of 4615 mF cm-2 at the current density of 5 mA cm-2. Aqueous symmetric supercapacitor assembled with APCM textile electrodes can possess the maximum energy density of 157 µWh cm-2 and maximum power density of 10372 µWcm-2. 75 % of the original capacitances is retained after cycling for over 10000 times (Figure S11). It is noted that our fabricated composite textile electrodes have much larger areal specific capacitance than many other carbon textile based electrodes as shown in Table S1, which can be ascribed to the optimized utilization of high-performance electrochemical active materials (i.e., ACFC, PANI and MnO2): active materials uniformly distribute on the 3D ACFC-CNT hybrid network, while the 3D carbon network is porous enough and electrically conductive enough for the rapid transport of electrons and electrolyte ions, and as a consequence, ACFC, PANI and MnO2 contribute to superior electrochemical properties.

Solid-state symmetric supercapacitor was directly assembled using the APCM composite textile electrodes. The constructed solid-state symmetric textile supercapacitor is highly flexible and can be bent and folded without destroying structural integrity of the devices, as shown in Figure 4a. It can light the LED for more than 10 min without dimming from visual observation, which means a good energy storage ability. GCD curves in Figure 4b show relatively high IR drops due to compromised contact between the textile electrode and gel electrolyte. 82% of the original capacitance is retained after cycling for 3000 times (Figure S12a). Bending 11 / 28

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tests were conducted to evaluate the flexibility of the solid-state symmetric textile supercapacitors. The supercapacitor maintains good capacitance retention under different

bending

angles,

reflecting

superior

flexibility

of

the

textile

electrode/supercapacitor (Figure 4c). The flexible device was also bent from 0o to 180o repeatedly for several times (Figure 4d). There is no obvious capacitance loss after bending for 50 cycles and 93.4% of the original capacitance is retained after bending for 100 cycles. The superior flexibility of the composite textile supercapacitor is strongly associated with the 3D carbon network inside the textile electrode. (1) The ACFC substrate and CNT network themselves are highly flexible. (2) The activated carbon fiber and nano-scaled CNTs provides large area and more loading sites for the firm adhesion of other active materials. Moreover, electrodeposition method and in situ chemical reaction enhances the contact between pseudocapacitive materials and the carbon network which is beneficial to maintain structural integrity during bending deformation.19

According to the equation E = 1⁄2  , energy density of supercapacitors can be greatly improved by expanding the operation voltage window.46 Designing proper asymmetric supercapacitors is an effective way to expand the voltage window and improve the energy density of supercapacitors.47-49 We constructed a kind of asymmetric textile supercapacitor, adopting pure ACFC as negative electrode and the fabricated APCM as positive electrode according to the potential window shown in (Figure S13). As pointed above, activated carbon fiber is typical EDLC material, and our ACFC electrode possesses areal capacitance of 2242 mF cm-2. Considering that 12 / 28

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APCM textile electrode has a much higher capacitance of 4615 mF cm-2, two pieces of original ACFC textile was actually used as negative electrode (we call it ACFC thick electrode, whose electrochemical properties are displayed in Figure S14) in the asymmetric supercapacitors. In the aqueous electrolyte of 1 M H2SO4 solution, the asymmetric supercapacitor achieves an expanded operation voltage window from 0 to 1.5 V as shown in Figure 5a. The aqueous asymmetric supercapacitor delivers an areal capacitance of 2606 mF cm-2 for device at the current density of 5 mA cm-2 (Figure 5c). It is observed from the ragone plot in Figure 5d that energy density and power density of the asymmetric supercapacitor can be as high as 413 µWh cm-2 and 16120 µW cm-2, respectively, much higher than those of APCM textile electrode based symmetric supercapacitor. Using PVA/H2SO4 as gel electrolyte, flexible solid-state asymmetric supercapacitor was also constructed. The solid-state supercapacitor shows superior flexibility as exhibited in Figure 5e-f and can light a LED (4 V) easily with 3 of them in series as shown in Figure S15.

As discussed in Figure 1i, APCM textile can be dismantled into fiber bundles. When the fiber bundles are used as flexible fiber-like electrodes, they deliver superior capacitive properties with length, areal, volumetric and gravimetric specific capacitance of 116 mF cm-1, 756 mF cm-2, 62 F cm-3 and 201 F g-1, respectively, at the scan rate of 2 mV s-1, which are much higher than the figures for other fiber-like electrodes as listed in Table S2. The fiber-like electrodes based symmetric supercapacitor with 1 M H2SO4 solution as electrolyte possess an energy density of 2.60 µWh cm-1 and power density of 680 µW cm-1 at current density of 3 mA cm-1. Its 13 / 28

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capacitance retention is about 87% after 10000 charge/discharge cycles (Figure S16). Solid-state fiber-like supercapacitor was also assembled using the fiber-like electrodes (Figure 6d). It can be bent from 0o to 180o, accompanying with a capacitance retention of 96% (Figure 6e), while after 100 repeated bending cycles, 90% of its original capacitance is retained (Figure 6f). Obviously, the construction of flexible fiber-like supercapacitors extensively widens the application field of our APCM composite textile electrode.

4.

CONCLUSIONS

Flexible ACFC/PANI/CNT/MnO2 composite textiles were fabricated by depositing PANI, CNTs and MnO2 in turn on ACFC textile substrate. In the composite textile electrodes, the 3D carbon network composed of ACFC and CNTs guarantees the relatively uniform distribution of electrochemical active materials and the rapid transmission of electrons and electrolyte ions. The flexible textile electrodes were used to construct polymorphous supercapacitors, including symmetric textile supercapacitors and asymmetric textile supercapacitors with aqueous or gel electrolytes. These supercapacitors displayed outstanding electrochemical properties and good flexibility for solid-state devices. In addition, the composite textiles were dismantled into flexible fiber-like electrodes to construct fiber-like supercapacitor. All in all, we believe this work makes a meaningful exploration of the versatile applications of textile electrodes to produce polymorphous supercapacitors.

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Supporting Information. The supporting information is available free of charge on the ACS Publications website.

Additional experimental details, structural characterizations and electrochemical data of different textiles and supercapacitors.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (L. Dong); [email protected] (C. Xu)

ACKNOWLEDGMENTS

This work was financially supported by NSFC (No. 51102139), the National Key Basic Research (973) Program (No. 2014CB932400), Shenzhen Technical Plan Projects (No. JC201105201100A and JCYJ20160301154114273). We also appreciate the financial support from CERC-CVC (2016YFE0102200).

REFERENCES

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Adv. Mater. 2015, 27, 3572-3578. (14) Wang, H.; Deng, J.; Xu, C.; Chen, Y.; Xu, F.; Wang, J.; Wang, Y., Ultramicroporous Carbon Cloth for Flexible Energy Storage with High Areal Capacitance. Energy Storage Materials 2017, 7, 216-221. (15) Zhou, X.; Chen, Q.; Wang, A.; Xu, J.; Wu, S.; Shen, J., Bamboo-Like Composites of V2O5/Polyindole and Activated Carbon Cloth as Electrodes for All-Solid-State Flexible Asymmetric Supercapacitors. ACS Appl. Mater. Interfaces 2016, 8, 3776-3783. (16) Dong, L.; Xu, C.; Li, Y.; Wu, C.; Jiang, B.; Yang, Q.; Zhou, E.; Kang, F.; Yang, Q. H., Simultaneous Production of High-Performance Flexible Textile Electrodes and Fiber Electrodes for Wearable Energy Storage. Adv. Mater. 2016, 28, 1675-1681. (17) Jost, K.; Stenger, D.; Perez, C. R.; McDonough, J. K.; Lian, K.; Gogotsi, Y.; Dion, G., Knitted and Screen Printed Carbon-Fiber Supercapacitors For Applications in Wearable Electronics. Energ. Environ. Sci. 2013, 6, 2698-2705. (18) Fan, X.; Wang, X.; Li, G.; Yu, A.; Chen, Z., High-Performance Flexible Electrode Based on Electrodeposition of Polypyrrole/MnO2 on Carbon Cloth for Supercapacitors. J. Power Sources 2016, 326, 357-364. (19) Cheng, Q.; Tang, J.; Ma, J.; Zhang, H.; Shinya, N.; Qin, L.-C., Polyaniline-Coated Electro-Etched Carbon Fiber Cloth Electrodes for Supercapacitors. J. Phys. Chem. C 2011, 115, 23584-23590. (20) Wang, L.; Yang, H.; Liu, X.; Zeng, R.; Li, M.; Huang, Y.; Hu, X., Constructing hierarchical Tectorum-Like α-Fe2O3/PPy Nanoarrays on Carbon Cloth for Solid-State Asymmetric Supercapacitors. Angew. Chem. Int. Ed. 2017, 56, 1105-1110. (21) Bai, M.-H.; Liu, T.-Y.; Luan, F.; Li, Y.; Liu, X.-X., Electrodeposition of Vanadium Oxide– Polyaniline Composite Nanowire Electrodes for High Energy Density Supercapacitors. J. Mater. Chem. A 2014, 2, 10882-10888. (22) Guo, D.; Yu, X.; Shi, W.; Luo, Y.; Li, Q.; Wang, T., Facile Synthesis of Well-Ordered Manganese

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Mater. Interfaces 2015, 7, 25506-25513. (24) Cong, H.-P.; Ren, X.-C.; Wang, P.; Yu, S.-H., Flexible Graphene–Polyaniline Composite Paper for High-Performance Supercapacitor. Energ. Environ. Sci. 2013, 6, 1185-1191. (25) Wen, L.; Li, K.; Liu, J.; Huang, Y.; Bu, F.; Zhao, B.; Xu, Y., Graphene/[email protected] Cloth Composite as A High-Performance Flexible Supercapacitor Electrode Prepared by A One-Step Electrochemical Co-Deposition Method. RSC Adv. 2017, 7, 7688-7693. (26) Dong, L.; Liang, G.; Xu, C.; Liu, W.; Pan, Z.-Z.; Zhou, E.; Kang, F.; Yang, Q.-H., Multi Hierarchical Construction-Induced Superior Capacitive Performances of Flexible Electrodes for Wearable Energy Storage. Nano Energy 2017, 34, 242-248. (27) Su, Z.; Yang, C.; Xu, C.; Wu, H.; Zhang, Z.; Liu, T.; Zhang, C.; Yang, Q.; Li, B.; Kang, F., Co-Electro-Deposition of The MnO2–PEDOT: PSS Nanostructured Composite for High Areal Mass, Flexible Asymmetric Supercapacitor Devices. J. Mater. Chem. A 2013, 1, 12432-12440. (28) Huang, M.; Li, F.; Dong, F.; Zhang, Y. X.; Zhang, L. L., MnO2-Based Nanostructures for High-Performance Supercapacitors. J. Mater. Chem. A 2015, 3, 21380-21423. (29) Yang, Q.; Dong, L.; Xu, C.; Kang, F., High-Performance Supercapacitors Based on Graphene/MnO2/Activated Carbon Fiber Felt Composite Electrodes in Different Neutral Electrolytes. RSC Adv. 2016, 6, 12525-12529. (30) Ren, J.; Li, L.; Chen, C.; Chen, X.; Cai, Z.; Qiu, L.; Wang, Y.; Zhu, X.; Peng, H., Twisting Carbon Nanotube Fibers for Both Wire-Shaped Micro-Supercapacitor and Micro-Battery. Adv. Mater. 2013, 25, 1155-1159. (31) Wang, J.; Li, X.; Zi, Y.; Wang, S.; Li, Z.; Zheng, L.; Yi, F.; Li, S.; Wang, Z. L., A Flexible Fiber-Based Supercapacitor-Triboelectric-Nanogenerator Power System for Wearable Electronics. Adv. Mater. 2015, 27, 4830-4836. (32) Dong, L.; Xu, C.; Yang, Q.; Fang, J.; Li, Y.; Kang, F., High-Performance Compressible Supercapacitors Based on Functionally Synergic Multiscale Carbon Composite Textiles. J. Mater. Chem. A 2015, 3, 4729-4737. (33) Li, W. C.; Mak, C. L.; Kan, C. W.; Hui, C. Y., Enhancing The Capacitive Performance of A Textile-Based CNT Supercapacitor. RSC Adv. 2014, 4, 64890-64900. (34) Ma, S.-B.; Ahn, K.-Y.; Lee, E.-S.; Oh, K.-H.; Kim, K.-B., Synthesis and Characterization of 18 / 28

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Nanoflakes Deposited on Carbon Nanotube Networks for Symmetrical Supercapacitors with Enhanced Performance. J. Power Sources 2017, 341, 27-35. (46) Fan, Z.; Yan, J.; Wei, T.; Zhi, L.; Ning, G.; Li, T.; Wei, F., Asymmetric Supercapacitors Based on Graphene/MnO2 and Activated Carbon Nanofiber Electrodes with High Power and Energy Density. Adv. Funct. Mater. 2011, 21, 2366-2375. (47) Lei, S.; Liu, Y.; Fei, L.; Song, R.; Lu, W.; Shu, L.; Mak, C. L.; Wang, Y.; Huang, H., Commercial

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Scheme 1. Schematic illustration of the fabrication of different textiles: (a) single activated carbon fiber (ACF), depositing (b) PANI, (c) CNTs and (d) MnO2.

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Figure 1. SEM images of (a)(b) ACFC, (c)(d) AP, (e)(f) APC and (g)(h) APCM textiles and (i) fiber bundles (the schematic illustrates the fabrication process of fiber bundles from APCM textile).

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Figure 2. CV curves of (a) ACFC, (b) AP, (c) APC and (d) APCM textile electrodes based symmetric supercapacitors with aqueous electrolyte.

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Figure 3. GCD curves of (a) ACFC, (b) AP, (c) APC and (d) APCM textile electrodes based symmetric supercapacitors with aqueous electrolyte. (e) Areal capacitance of different textile electrodes. (f) Ragone plots of above aqueous symmetric supercapacitors.

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Figure 4. (a) Digital photographs of the assembled flexible solid-state symmetric textile supercapacitors (4 ones in series) lighting light-emitting-diodes (LEDs). (b) GCD curves of the solid-state symmetric supercapacitor. Capacitance retention, digital photos and CV curves of the solid-state symmetric supercapacitor (c) under different bending angles and (d) after bending for various cycles.

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Figure 5. (a) CV curves in different voltage windows, (b) GCD curves, (c) areal capacitance at different current densities of the asymmetric supercapacitor. (d) Ragone plots of the assembled symmetric supercapacitor (SSC) and asymmetric supercapacitor (ASC). Capacitance retention, digital photos and CV curves of the solid-state asymmetric supercapacitor (e) under different bending angles and (f) after bending for various cycles.

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Figure 6. (a) CV curves, (b) GCD curves and (c) length, areal, volumetric and gravimetric specific capacitances of the fiber-like electrode based symmetric supercapacitor with aqueous electrolyte. (d) Digital photographs of the flexible fiber-like electrode (top left) and solid-state fiber-like symmetric supercapacitor with gel electrolyte. Capacitance retention of the assembled solid-state fiber-like symmetric supercapacitor (e) under different bending angles and (f) after bending for various cycles.

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