A Single Robust Hydrogel Film Based Integrated Flexible

Subscriber access provided by University of Winnipeg Library

Article

A Single Robust Hydrogel Film Based Integrated Flexible Supercapacitor Kanjun Sun, Enke Feng, Guohu Zhao, Hui Peng, Ganggang Wei, Yaya Lv, and Guofu Ma ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b02728 • Publication Date (Web): 10 Nov 2018 Downloaded from http://pubs.acs.org on November 12, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

A Single Robust Hydrogel Film Based Integrated Flexible Supercapacitor Kanjun Sun‡*a, Enke Feng‡b,c, Guohu Zhaoa, Hui Pengc, Ganggang Weic, Yaya Lvc, Guofu Ma*c

aCollege

of Chemistry and Environmental Science, Lanzhou City University, 11 Jiefang Road, Lanzhou, 730070,

China. bCollege

of Chemistry and Chemical Engineering, Ningxia Normal University, 161 Beiguan west Road, Guyuan

756000, China. cKey

Laboratory of Eco-Environment-Related Polymer Materials of Ministry of Education, Key Laboratory of

Polymer Materials of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, 967 Anning East Road, Lanzhou 730070, China.

Corresponding Author *E-mail: [email protected] (K. Sun); [email protected] (G. Ma) ‡The

Enke Feng and Kanjun Sun contributed equally to this work.

ABSTRACT: Integrated configuration can greatly improve the stability of an energy-storage device in a large or repeated mechanical deformation process, but there is little attention paid to develop this conceptual energy-storage device. Here, we successfully design two embedded polypyrrole (PPy) layers as electrodes and a boron cross-linked PVA(polyvinyl alcohol)/KCl hydrogel film as electrolyte to construct an integrated electrode-electrolyte-electrode flexible supercapacitor (so-called all-in-one supercapacitor). The boron cross-linked PVA/KCl hydrogel film (B-PVA/KCl) is prepared by simple physical and chemical cross-linking methods. Then, the conducting PPy is embedded in the B-PVA/KCl film by in situ growth to form a PPy/B-PVA/KCl 1

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

composite film, which shows superior toughness and strength when it undergo large deformations, such as stretch, twist and compression. The integrated flexible supercapacitor can obtain a large areal capacitance of 224 mF cm-2 and a remarkable energy density of 20 µWh cm-2. Furthermore, such device exhibits excellent electrochemical stability under various bending angles (0°, 90°, and 180°) or 500 bending-releasing cycles, which due to the integrated electrode-electrolyte-electrode configuration can avoid the fall-off of electrode materials from the substrates and overcome the relative displacement between electrode and electrolyte layers during the consecutive bending cycles. KEYWORDS: Boron cross-links, Robust hydrogel film, Integrated configuration, Large areal capacitance, Flexible supercapacitor INTRODUCTION Strain-tolerant energy-storage devices (e.g., flexible, stretchable and compressible) have attracted significant more attention with the rapid progress of portable, wearable and elastic electronics,1 because they can maintain their inherent electrochemical function under large mechanical strain.2-5 Supercapacitors are very important, among various energy storage devices, for their higher power density, higher rates of charge/dischargeand longer cycle life than that of batteries.6 In order to suitable portable and wearable electronic devices development, flexible supercapacitors are designed which can operate without performance degradation under bending, folding and even twisting conditions.7 The electrodes, electrolytes and configuration are most important factors to supercapacitor performance. The present works on flexible supercapacitor are focused on preparation of high performance flexible electrodes, such as self-supporting carbon films (e.g., carbon nanotube,8 2


Page 2 of 33

Page 3 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


graphene,9 and carbon fiber10) or conducting polymers-based carbon composite films11 and metal oxides-based carbon composite films.12 Moreover, to achieve highly flexible supercapacitor electrodes, various electroactive materials (e.g., carbon material, metallic oxide, conducting polymer, and their composite materials) are coated as thin layer on an elastic substrate which is no electrochemically active (e.g., paper,13 sponge,14cloth,15 rubber fibers,16 and cottonsheets17). However, those substrates will occupy weight and volume significantly in the supercapacitor devices.18 On the other hand, the electroactive materials may fall off the substrates in a large and repeated mechanical deformation process, which can lead to attenuation of the supercapacitor performance. In addition to the flexible electrodes, the electrolyte is also an important factor affecting the performance of flexible supercapacitors. A number of recent studies have indicated that hydrogel polymers are favored as flexible supercapacitors electrolytes because of their exhibit higher thin-film formation ability, flexibility and ionic conductivity than dry polymer electrolytes19, and more remarkable safety than liquid electrolytes.20 The hydrogel polymer electrolytes for flexible supercapacitors can be roughly divided into three categories: (1) polymer matrices based salt/acid/alkali gel polymer electrolytes; (2) polymer matrices based redox active species improved gel polymer electrolytes; (3) polymer matrices based chemically cross-linked or self-healable gel polymer electrolytes. Here, the polymer matrices actually including poly(vinyl alcohol)

(PVA),

poly(ethylene

oxide)

(PEO),

poly(methylmethacrylate)

(PMMA),

poly(acrylonitrile) (PAN), and poly(vinylidenefluoride) (PVDF). Regrettably, most hydrogel polymer electrolyte systems in flexible supercapacitors, especially polyvinyl alcohol (PVA) systems (PVA-H2SO4, PVA-KOH, and PVA-KCl, etc.), are prepared merely by a simple 3



film-casting and physical cross-linking method. The type of electrolyte system of the exhibits poor integrated structure and mechanical properties.21,22 To address those problem, PVA gel polymers were usually adsorbed onto the commercial flexible separators to obtain high mechanical property and maintaining the good electrochemical performance.23 However, this strategy make the supercapacitor devices have extra passive component (separator). So far, chemical cross-linking by the reaction of the polymer functional groups (e.g., -OH, -COOH, and -NH2) with cross-linkers (e.g., boric acid, adipic acid, and glutaraldehyde) is considered as a good strategy to obtain hydrogel polymer electrolytes with superior mechanical strength. Notably, Wang et al. synthesized a glutaraldehyde cross-linked PVA/H2SO4 hydrogel electrolyte film, which can be stretched up to 300% without obviously performance degradation.19 Huang and co-workers developed a vinyl hybrid silica nanoparticles cross-linked polyacrylamide hydrogel electrolyte, which can be easily stretched to 1500% strain without any breakage or even visible cracking.24 Furthermore, the existing flexible supercapacitors generally exhibit a multilayer laminated configuration composed by a polymeric electrolyte sandwiched between two flexible substrate coated with active materials as electrodes.25 The configuration structure will increase not only the interface contact resistance between electrolyte and electrode, but also the physical deformations (bend, stretch and twist) during application of the solid flexible supercapacitors,26 and inevitably result in relative displacement change, even delamination of the laminate (Figure 1), which severely impedes the electron and ion transportation within the flexible supercapacitors.27 Therefore, a high-performance flexible supercapacitor should be designed to an integrating electrode-electrolyte-electrode configuration (called all-in-one supercapacitor). However, little attention had been paid to develop this conceptual integrated flexible supercapacitor to the best of 4


Page 4 of 33

Page 5 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


our knowledge. In this work, we successfully designed and developed an integrated flexible supercapacitor with electrode-electrolyte-electrode configuration by integrating the electrode (PPy) and electrolyte (boron cross-linked PVA/KCl hydrogel) materials, which differs from the laminated configuration of the traditional supercapacitor. Meanwhile, the obtained integrated supercapacitor is able to possess large areal capacitance, high cyclic stability and structure durability. Therefore, this novel integrated structure supercapacitor can be used as the next generation flexible energy conversion and storage devices for portable and wearable electronics benefited from their superior mechanical and electrochemical performance. EXPERIMENTAL SECTION Materials Polyvinyl alcohol (PVA) with average polymerization degree of 1750 ± 50 and hydrolysis degree of 97%. Pyrrole monomer (Py) was purchased from Aladdin Chemical Reagent Co., Ltd (China), and was distilled under reduced pressure before use. Boric acid (H3BO3) and potassium chloride (KCl) were supplied by Sinopharm Chemical Reagent Co., Ltd (China). Ammonium persulfate (APS) was obtained from Tianjin Damao Chemical Co., Ltd (China). Carbon cloths was purchased from CeTechCo., Ltd, and the model for WOS1009. All other reagents were analytical grades and were used as received without further treatment. Preparation of Free-Standing B-PVA/KCl Hydrogel Film The free-standing boron cross-linked PVA/KCl hydrogel film (B-PVA/KCl) was prepared by simple physical and chemical cross-linking methods. Typically, 3.0 g of PVA was dissolved in 30 mL deionized water under magnetic stirring at 85 oC for 2 h. Then, 10 mL of the 3 mol L-1 KCl 5



solution was added into the above solution with constant stirring until the blended solution became clear. The resultant mixture was evenly poured into three plastic Petridishes (Φ5.5 cm), which were frozen at -25 oC for 24 h and thawed at room temperature for 12 h to obtain the physically cross-linked PVA/KCl hydrogel film. Following that, the round free-standing PVA/KCl hydrogel film was peeled off the dish and immersed in a sufficient volume of boric acid/ammonia solution (1 mgmL-1, pH∼11) for over 24 h to allow for complete the chemical cross-linking between PVA chains and boric acid. The preparation process of B-PVA/KCl hydrogel film and the cross-linking mechanism between PVA and boric acid are detailly described in Figure 2a and 2b, respectively. Preparation of PPy/B-PVA/KCl Hydrogel Film The PPy (0.2 mol L-1)/B-PVA/KCl hydrogel film was prepared through chemical oxidative polymerization process. Firstly, the B-PVA/KCl hydrogel film was immersed in a 120 mL aqueous solution with 1.87 g pyrrole monomer under mechanical agitation for 0.5 h. Secondly, 20 mL aqueous solution dissolved 3.19g APS with pyrrole/APS molar ratio of 2 was dropped into the above solution and kept at 0-5 oC for 8 h to make the pyrrole polymerization completely. Then, the hydrogel film was taken out and washed several times with deionized water. The PPy/B-PVA/KCl hydrogel films with different loading amount of PPy can be controlled preparation by adjusting relative concentrations of the pyrrole, such as 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7 mol L-1. Materials Characterizations The morphologies of freeze-dried hydrogel samples were observed by field emission scanning electronmicroscopy (FE-SEM, Carl Zeiss Ultra Plus, Germany) at anacceleration voltage of 5 kV. The freeze-dried hydrogel samples were obtained using a lyophilization instrument by a 6


Page 6 of 33

Page 7 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


freeze-drying process under -55 oC. The water content of the hydrogel film was examined by both thermogravimetry and comparison of the weight difference of swollen and freeze-driedhydrogel films. A thermal gravimetric analysis (TGA) of sample was evaluated by a thermogravimetric analyzer (TGA-Q50, TA Instrument) with a heating rate of 10 oC min-1. X-ray diffraction (XRD) was tested using a Rigaku D/Max-2400 diffractometer equipped with Cu Kα radiation (k = 1.5418 Å). Infrared absorption spectra were obtained with a Fourier infrared spectrometer (FTIR-FTS3000) from 4000 to 400 cm-1 at room temperature. Fabrication and Electrochemical Measurements of the Integrated Flexible Supercapacitor The round free-standing PPy/B-PVA/KCl hydrogel film was cut off edge-connection to form a sample with a size of 10 mm × 30 mm × 3.5 mm (the thickness of PPy electrode layer and B-PVA/KCl electrolyte layer is about 0.25 mm and 3 mm, respectively) and then immersed in 2 mol L-1 KCl aqueous solution for 20 min. Subsequently, two identical carbon cloth strips as current collector were tightly affixed to both sides of the sample, on the other hand, they were used to connect the integrated supercapacitor and the electrochemical tester. Finally, two PDMS films were used to encapsulate the device under a pressure of ~0.5 MPa, with silicone glue as adhesion agent. Cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) of the integrated supercapacitor were measured by a CHI 760 Eelectrochemical workstation (Shanghai Chenghua instrument Co., Ltd., China). Electrochemical impedance spectroscopy (EIS) was carried out at open circuit potential with the frequency ranges from 0.1 Hz to 100K Hz and the data were fitted using ZView software. The cycle-life stability was performed using computer-controlled cycling testing equipment (CT2001A, Wuhan Land Electronic Co., Ltd., China). 7



The areal capacitance (CA) of the supercapacitor based on single PPy electrode is calculated from its GCD curves according to the equation (1):28 CA = 2 × I ×Δt/ (S ×ΔV)

(1)

The energy density (E) and power density (P) of the supercapacitor are obtained using the equations (2) and (3):19 E =(1/2)×CA×ΔV2 P = E/Δt

(2)

(3)

Where I is the discharge current, Δt is the discharge time, S is geometrical area of hydrogel film and ΔV is the discharge potential window with deduction of IR drop. The ionic conductivity of the B-PVA/KCl gelelectrolyte is examined by the following equation:

σ = L / (R×S)

(4)

Where L and S are the thickness and area of the B-PVA/KCl gel sample, respectively. R is the bulk resistance obtained from EIS, which is the high-frequency intercept on the real impedance axis in the Nyquist plot. RESULTS AND DISCUSSION The free-standing boron cross-linked PVA/KCl hydrogel film (B-PVA/KCl) was produced by combining simple physical and chemical cross-linking methods. As shown in Figure 2a, the PVA/KCl mixed solution was first poured into a plastic Petri dish and treated by freeze-thaw methods to obtain a physically cross-linked PVA/KCl hydrogel film. It is known that the gelatinization of PVA solution and further improve its mechanical properties can be caused by the crystallization and phase separation of PVA during the freeze-thaw process, which are referred as 8


Page 8 of 33

Page 9 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


primary mechanism.29 Subsequently, the obtained PVA/KCl hydrogel film was immersed in a sufficient volume of boric acid/ammonia solution for over 24 h. During this period, the “boron” cross-linked PVA/KCl hydrogel film can be formed by dehydration process between boric acid (B(OH)3) and hydroxyl groups (-OH) that exist in the PVA chains (Figure 2b), which can further improve the mechanical properties of PVA/KCl hydrogel.30 In Figure 2c, the B-PVA/KCl film shows a new peak at 652 cm-1 by comparing to the FT-IR spectra of PVA/KCl film, which is ascribed to the O-B-O bending.31 Moreover, the -OH stretching vibration of PVA at 3429 cm-1 obviously weaken after cross-linking with boric acid. This information confirms the boron cross-linked structure is successfully introduced into PVA molecular chains. Additionally, the water contained in hydrogels has a significant effect on ionic conductivity of electrolytes because it can dissolve ions.32 However, little is evaluated about their water content in recently reports for hydrogel electrolytes based flexible supercapacitors. Here, the water content of the B-PVA/KCl film is examined by both thermogravimetry and comparison of the weight difference of swollen and freeze-driedB-PVA/KCl films. According the thermogravimetric curves (Figure 2d), the water content of the B-PVA/KCl film is about 88%, the result is consistent with the date calculated from the swollen and dried film. Meanwhile, according to the equation (4), the ionic conductivity of B-PVA/KCl gel film is 0.038 S cm-1. Polypyrrole (PPy) has received wide spread attention as the typical electrode material because of its high conductivity, thermal stability, easy synthesis, and nontoxicity.33 In this research, in order to design and develop an integrated flexible supercapacitor with electrode-electrolyte-electrode configuration (so-called all-in-one supercapacitor), the conducting PPy was embedded in the B-PVA/KCl hydrogel film by in situ growth to form a PPy/B-PVA/KCl 9



composite film (Figure 3a-c). In Figure 3c, the entire surface of B-PVA/KCl film is covered by PPy observably, which upper and lower PPy layers are also connected by the side edge of PPy/B-PVA/KCl film. To avoid the short circuit of all-in-one configuration, the side edge PPy should be cut out to separate the top and bottom PPy layers. As shown in Figure 3d, an integrated supercapacitor with electrode-electrolyte-electrode configuration was obtained after cutting edge connected PPy. In this integrated structure prototype, the PPy layers embedded on the top and bottom surface of B-PVA/KCl hydrogel film are used as electrodes, while the middle B-PVA/KCl hydrogel is serviced as electrolyte. Furthermore, the PPy/B-PVA/KCl hydrogel film constructed integrated supercapacitor show superior toughness and strength when they undergo enlarge deformations under stretch (Figure 3e), twist (Figure 3f) and compression (Figure 3g). In previous reports, most hydrogels notably present poor stretchability, typically, an alginate hydrogel exhibits rupture when stretched to 120%.34,35 Surprisingly, the PPy/B-PVA/KCl hydrogel can be easily stretched to approximately 300% strain without any breakage or even visible cracking (Figure 3e). The excellent mechanical properties of PPy/B-PVA/KCl hydrogel film demonstrate that it has great potential for the construction of integrated flexible energy storage devices with electrode-electrolyte-electrode configuration. The surface morphologies of the freeze-dried B-PVA/KCl and PPy/B-PVA/KCl hydrogel films were examined by scanning electron microscopy (SEM). From Figure 4a, the lyophilized B-PVA/KCl film shows a smooth surface when the water was removed by freeze-drying process. In contrast, the surface of lyophilized PPy/B-PVA/KCl hydrogel film appears a relatively rough and orderly wavy-wrinkled structure owing to PPy incorporation (Figure 4b), and the enlarged SEM image (Figure 4c) indicates that a large amount of PPy had grown on the B-PVA/KCl film 10


Page 10 of 33

Page 11 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


surface. To better understand the fused interface between PPy electrode layer and PVA hydrogel electrolyte layer, we characterized the cross-section of PPy/B-PVA/KCl film by optical microscopy and SEM. Optical microscopy image (Figure 4d) illustrates that PPy uniformly grown on the two surfaces of the B-PVA/KCl film. Thus, the PPy/B-PVA/KCl hydrogel film has a PPy(electrode)-B-PVA/KCl(electrolyte)-PPy(electrode) sandwich-like configuration. At the meantime, SEM observation (Figure 4e) found a clear interface between rough PPy layer and smooth PVA hydrogel layer, but at the interface region, there is no gap or interstices, which imply that conducting PPy can be perfectly integrated into the B-PVA/KCl film by an in situ polymerization growth method. Moreover, X-ray diffraction (XRD) was performed to check the crystalline structures of hydrogel films, as shown in Figure 4f. The B-PVA/KCl film reveals strong crystalline reflection with abroad peak at 2 =19.5o, corresponding to the characteristic reflection of crystalline atactic PVA.19 Compared with the B-PVA/KCl film, a more sharp peak was observed at 2 =19.5o in the PPy/B-PVA/KCl film, which is due to a morphous PPy also exist a typical broad and weak reflection in the range of 15~30°.36 Meanwhile, the other peaks in the B-PVA/KCl film obviously weaken after pyrrole polymerization, and the results also confirm that the PPy was successfully attached into B-PVA/KCl film. Electrochemical

performance

of

the

integrated

PPy/B-PVA/KCl

hydrogel

films

supercapacitors prepared with various pyrrole concentrations (0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 mol L-1) was first conducted by galvanostatic charge-discharge (GCD) test at a current density of 0.8 mA cm-2 within the potential window from 0 to 0.8 V to evaluate specific areal capacitance of the PPy electrodes in the devices, and the typical results are shown in Figure 5a and 5b. When the pyrrole concentration is less than 0.6 mol L-1, we found the areal capacitance is enhanced quickly 11



as the pyrrole concentration increasing, and the maximum value is obtained when the pyrrole concentration reached 0.6 mol L-1. However, the areal capacitance slightly decreased when the pyrrole concentration further increases (0.7 mol L-1), which is due to the gelation of the solution. From the tube-inversion experiment (Figure 5c), it can be found that the mixed solution of pyrrole will gelatinize and lose the fluidity when the pyrrole concentration up to 0.7 mol L-1, which impeded the growth of PPy on the B-PVA/KCl hydrogel film in situ polymerization process and thus induced the decreases of the PPy loading amounts in PPy/B-PVA/KCl film. Furthermore, the loading amounts of the PPy in PPy/B-PVA/KCl hydrogel film are evaluated by comparing the weight between the freeze-dried B-PVA/KCl and PPy/B-PVA/KCl film with same area. As shown in Figure 5b, for the various pyrrole concentrations (0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 mol L-1) as-prepared PPy/B-PVA/KCl hydrogel films, the average loading amount of the single PPy layer is 1.6, 2.8, 3.5, 4.7, 6.1 and 5.3 mg cm-2, respectively. This result further proves the above conclusion and reveals the 0.6 mol L-1 pyrrole is the optimal concentration for the integrated supercapacitor based on single PPy/B-PVA/KCl hydrogel film. Figure 5d presents the cyclic voltammetry (CV) curves of the integrated supercapacitor based on single PPy (0.6 mol L-1)/B-PVA/KCl film was nearly rectangular shape between 0 and 0.8 V at the scan rates of 25 ~150 mV s-1, indicating that the integrated supercapacitor device can be operated over a wide range of scan rates and possesses excellent electrochemical behavior and good rate capability. To demonstrate the detailed capacitive behavior, the GCD curves of the single PPy(0.6 mol L-1)/B-PVA/KCl film based integrated supercapacitor at various current densities were display in Figure 5e. The typical triangle-shaped profiles can be observed from all those GCD curves. Meanwhile, the specific areal capacitances calculated from the GCD curves at 12


Page 12 of 33

Page 13 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


various current densities were shown in Figure 5f. At a current density of 0.8 mA cm-2, it can be obtained largest areal capacitance of 224 mF cm-2. It still maintains a high value of 145 mF cm-2 (about 65% capacitance retention) even though the current density increased to 3 mA cm-2. Moreover, the fabricated device can possess the higher areal capacitance than the previous reports for two-electrode, solid-state flexible supercapacitor devices (see Table 1), that's because of effectively improving active material loading amounts per area by in situ growth PPy on the B-PVA/KCl gel film, and the similar conclusions have been confirmed in previous literature reports.19

When different bending angles (0°, 90°, and 180°) are applied to the single PPy(0.6

mol L-1)/B-PVA/KCl film based integrated supercapacitor, it can be found from the CV curves that there is only very slight deviation (Figure 6a), indicating the device possesses remarkably stable capacitive performance under various bending states. Besides, the stable electrochemical performances were also obtained from their GCD curves (Figure 6b). These results demonstrate that the electrode-electrolyte-electrode integrated supercapacitor structure based on single hydrogel film has perfect bent performance and the device capacitive performance cannot be affected by various bending angles. To further explore the resistive and capacitive behavior of the single PPy(0.6 mol L-1)/B-PVA/KCl film based integrated supercapacitor, electrochemical impedance spectroscopy (EIS) measurement was performed under frequency range from 100 kHz to 0.01 Hz. One can see from the Figure 6c, the Nyquist plot of the integrated supercapacitor exhibits a small semicircle in high-frequency region and a greater than 45° vertical line in low-frequency region, indicating the integrated supercapacitor has low charge transfer resistance and good capacitive behavior with small diffusion resistance, respectively.37 The Nyquist plot was also fitted and analyzed by the soft 13



ware of ZSimpWin in the light of the electrical equivalent circuit (the inset of Figure 6c). The integrated supercapacitor has not only low series resistance (Rs, 2.52 Ω cm2) but also small interfacial charge transfer resistance (Rct,2.24 Ω cm2), which calculated from the intercept of x-axis in the high frequency region and the span of the semicircle along the x-axis, respectively.38 The excellent resistive performance of the supercapacitor may be due to the integrated electrode-electrolyte-electrode structure prototype, which can avoid a large inter face contact resistance and facilitate the transportation of electron and ion within the device effectively. Additionally EIS were also employed to understand the resistive performance of the integrated supercapacitor at various bending angles of 0°, 90°, and 180°. Nyquist plots show nearly the same behavior under various bending angles at different frequency portions (Figure 6c), which indicates that the resistive performance is unchanged when various bending strains are applied to the integrated supercapacitor device. The energy density and power density are very important parameters to evaluate the supercapacitors. Figure 6d presents the Ragone plot of the integrated supercapacitor based on single PPy(0.6 mol L-1)/B-PVA/KCl film derived from GCD curves at various current densities. The integrated supercapacitor device shows a large energy density of 20 µWh cm-2 at power density of 600 µW cm-2. When the power density is increased to 2300 µW cm-2, the energy density still maintains a high value of 13 µWh cm-2. The comparison on energy density values of the integrated supercapacitor with other reported solid-state flexible supercapacitor devices are summarized in Table 1. Furthermore, the charge-discharge cycle life of the integrated supercapacitor device was also investigated by consecutive charge-discharge cycles at a current density of 1.5 mA cm-2 for 2000 cycles, as 14


Page 14 of 33

Page 15 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


depicted in Figure 6e. It can be seen that the specific capacitance decays slightly and maintains about 92% of the initial capacitance after 2000 cycles, which is similar to the electrochemical double layer capacitors and the value is higher than most pseudocapacitors obviously. Meanwhile, the resistance of the as-fabricated supercapacitor device after 2000 cycles is slightly larger than the initial cycle (the inset of Figure 6e). Despite all this, it still possesses excellent capacitance behavior since the Nyquist plot similar inclines to the x-axis in the low-frequency region. Moreover, although a large number of flexible solid-state supercapacitors have been recently reported, rarely known about their electrochemical performance under bending-releasing cycles, yet is great significance to develop high-performance flexible supercapacitor devices. Based on this reason, it was further evaluated the capacitance retention of the integrated supercapacitor device under bending-releasing cycles. From Figure 6f, the capacitance of the single PPy(0.6 mol L-1)/B-PVA/KCl film based supercapacitor is very well maintained (3% capacitance loss) after 500 bending-releasing cycles, which is due to the integrated electrode-electrolyte-electrode configuration can avoid the fall-off of electrode materials from the substrates and overcome the relative displacement between electrode and electrolyte layers during the consecutive bending cycles. Furthermore, as shown in Figure S2, the cross-section SEM image and the FTIR spectra of the PPy/B-PVA/KCl film showed no obvious changes after 1000 bending-releasing cycles, indicating that the PPy/B-PVA/KCl film has good mechanical stability. CONCLUSIONS In summary, a novel and integrated flexible supercapacitoris obtained by integrating the electrolyte and electrode materials into a free-standing and robust PPy/B-PVA/KCl film, which can be regarded as a PPy(electrode)-PVA hydrogel(electrolyte)-PPy(electrode) sandwich-like 15



Page 16 of 33

configuration. The single PPy/B-PVA/KCl film based integrated flexible supercapacitor demonstrates outstanding electrochemical performance such as a large areal capacitance of 224 mF cm-2, a high energy density of 20 µWh cm-2 and outstanding cycling stability with 92% capacitance retention after 1000 cycles. Moreover, the presented integrated supercapacitor device also exhibits superior electrochemical stability under various bending angles (0°, 90°, and 180°) or 500

bending-releasing

cycles,

which

is

may

be

due

to

the

integrated

electrode-electrolyte-electrode configuration can avoid the fall-off of electrode materials from the substrates and overcome the relative displacement between electrode and electrolyte layers during the consecutive bending cycles. Based on the overall performance, it is strongly believed that this novel conceptual integrated flexible supercapacitor is more attractive as the next generation flexible power supply for wearable and portable electronic devices. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS We gratefully acknowledge the National Science Foundation of China (21664012), the program for Changjiang Scholars and Innovative Research Team in University (IRT15R56), Basic Scientific Research Innovation Team Project of Gansu Province (1606RJIA324), University Scientific Research Innovation Team of Gansu Provincial (2017C-04), Key Laboratory of Eco-Environment-Related Polymer Materials of Ministry of Education, and Key Laboratory of Polymer Materials of Gansu Province.

Supporting Information SEM images, FTIR spectra, Figures S1-S2 16


Page 17 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


REFERENCES (1) Son, D.; Lee, J.; Qiao, S.; Ghaffari, R.; Kim, J.; Lee, J. E.; Song, C.; Kim, S. J.; Lee, D. J.; Jun, S. W.; Yang, S.; Park, M.; Shin, J.; Do, K.; Lee, M.; Kang, K.; Hwang, C. S.; Lu, N.; Hyeon, T.; Kim, D. H. Multifunctional Wearable Devices for Diagnosis and Therapy of Movement Disorders. Nat. Nanotechnol. 2014, 9(5), 397-404, DOI 10.1038/nnano.2014.38. (2) Yang, X. W.; Cheng, C.; Wang, Y. F.; Qiu, L.; Li, D. Liquid-Mediated Dense Integration of Graphene Materials for Compact Capacitive Energy Storage. Science 2013, 341(6145), 534-537, DOI 10.1126/science.1239089. (3) Xie, K.; Wei, B. Materials and Structures for Stretchable Energy Storage and Conversion Devices. Adv. Mater. 2014, 26(22), 3592-3617, DOI 10.1002/adma.201305919. (4) Song, Z.; Ma, T.; Tang, R.; Cheng, Q.; Wang, X.; Krishnaraju, D.; Panat, R.; Chan, C. K.; Yu, H.; Jiang, H. Origami Lithium-Ion Batteries. Nat. Commun. 2014, 5, 3140-3146, DOI 10.1038/ncomms4140. (5) Wang, Y. G.; Xia, Y. Y. Recent Progress in Supercapacitors: from Materials Design to System Construction. Adv. Mater. 2013, 25(37), 5336-5342, DOI 10.1002/adma.201301932. (6) Sun, Y.; Wu, Q.; Shi, G. Graphene Based New Energy Materials. Energy Environ. Sci. 2011, 4, 1113-1132, DOI 10.1039/C0EE00683A. (7) Wang, K.; Wu, H. P.; Meng, Y. N.; Wei, Z. X. Conducting Polymer Nanowire Arrays for High Performance Supercapacitors. Small 2014, 10(1), 14-31, DOI 10.1002/smll.201301991 (8) Pushparaj, V. L.; Shaijumon, M. M.; Kumar, A.; Murugesan, S.; Ci, L.; Vajtai, R.; Linhardt, R. J.; Nalamasu, O.; Ajayan, P. M. Flexible Energy Storage Devices Based on Nanocomposite Paper. 17



Page 18 of 33

Proc. Natl. Acad. Sci. USA 2007, 104(34), 13574-13577, DOI 10.1073/pnas.0706508104. (9) Zang, J. F.; Cao, C.Y.; Feng, Y. Y.; Liu, J.; Zhao, X. H. Stretchable and High-Performance Supercapacitors

with

Crumpled

Graphene

Papers.

Sci.

Rep.

2014,

4,

6492,

DOI

10.1038/srep06492. (10) Wang, G.; Wang, H.; Lu, X.; Ling, Y.; Yu, M.; Zhai, T.; Tong, Y.; Li, Y. Solid-State Supercapacitor Based on Activated Carbon Cloths Exhibits Excellent Rate Capability. Adv. Mater. 2014, 26(17), 2676-2682, DOI 10.1002/adma.201304756. (11) Meng, C. Z.; Liu, C. H.; Chen, L. Z.; Hu, C. H.; Fan, S. S. Highly Flexible and All-Solid-State Paper-Like Polymer Supercapacitors. Nano Lett. 2010, 10(10), 4025-4031, DOI 10.1021/nl1019672. (12) Huang, L.; Chen, D.; Ding, Y.; Feng, S.; Wang, Z. L.; Liu, M. Nickel-Cobalt Hydroxide Nanosheets Coated on NiCo2O4 Nnanowires Grown on Carbon Fiber Paper for High-Performance Pseudocapacitors. Nano Lett. 2013, 13(7), 3135-3139, DOI 10.1021/nl401086t. (13) Hu, L. B.; Choi, J. W.; Yang, Y.; Jeong, S.; La Mantia, F.; Cui, L. F.; Cui, Y. Highly Conductive Paper for Energy-Storage Devices. Proc. Natl. Acad. Sci. USA 2009, 106(51), 21490-21494, DOI 10.1073/pnas.0908858106. (14) Chen, W.; Rakhi, R. B.; Hu, L.; Xie, X.; Cui, Y.; Alshareef, H. N. High-Performance Nanostructured Supercapacitors on a Sponge. Nano Lett. 2011, 11(12), 5165-5172, DOI 10.1021/nl2023433. (15) Wang, K.; Zhao, P.; Zhou, X. M.; Wu, H. P.; Wei, Z. X. Flexible Supercapacitors Based on Cloth-Supported Electrodes of Conducting Polymer Nanowire Array/SWCNT Composites. J. Mater. Chem. 2011, 21(41), 16373-16378, DOI 10.1039/C1JM13722K. 18


Page 19 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(16) Yang, Z.; Deng, J.; Chen, X.; Ren, J.; Peng, H. A Highly Stretchable, Fiber-Shaped Supercapacitor.

Angew.

Chem.

Int.

Ed.

2013,

125(50),

13695-13699,

DOI

10.1002/ange.201307619. (17) Hu, L.; Pasta, M.; La Mantia, F.; Cui, L.; Jeong, S.; Deshazer, H. D.; Choi, J. W.; Han, S. M.; Cui, Y. Stretchable, Porous, and Conductive Energy Textiles. Nano Lett. 2010, 10(2), 708-714, DOI 10.1021/nl903949m. (18) Li, L.; Wu, Z.; Yuan, S.; Zhang, X. B. Advances and Challenges for Flexible Energy Storage and Conversion Devices and Systems. Energy Environ. Sci. 2014, 7, 2101-2122, DOI 10.1039/C4EE00318G. (19) Wang, K.; Zhang, X.; Li, C.; Sun, X.; Meng, Q.; Ma, Y.; Wei, Z. Chemically Crosslinked Hydrogel Film Leads to Integrated Flexible Supercapacitors with Superior Performance. Adv. Mater. 2015, 27(45), 7451-7457, DOI 10.1002/adma.201503543. (20) Niu, Z.; Zhou, W.; Chen, X.; Chen, J.; Xie, S. Highly Compressible and All-Solid-State Supercapacitors Based on Nanostructured Composite Sponge. Adv. Mater. 2015, 27(39), 6002-6008, DOI 10.1002/adma.201502263. (21) Kaempgen, M.; Chan, C. K.; Ma, J.; Cui, Y.; Gruner, G. Printable Thin Film Supercapacitors Using

Single-Walled

Carbon

Nanotubes.

Nano

Lett.

2009,

9(5),

1872-1876,

DOI

10.1021/nl8038579. (22) Yuan, L.; Lu, X. H.; Xiao, X.; Zhai, T.; Dai, J.; Zhang, F.; Hu, B.; Wang, X.; Gong, L.; Chen, J.; Hu, C.; Tong, Y.; Zhou, J.; Wang, Z. L. Flexible Solid-State Supercapacitors Based on Carbon Nanoparticles/MnO2 Nanorods Hybrid Structure. ACS Nano 2012, 6(1), 656-661, DOI 10.1021/nn2041279. 19



Page 20 of 33

(23) Lu, X. H.; Zeng, Y. X.; Yu, M. H.; Zhai, T.; Liang, C. L.; Xie, S. L.; Balogun, M. S.; Tong, Y. X. Oxygen-Deficient Hematite Nanorods as High-Performance and Novel Negative Electrodes for Flexible Asymmetric Supercapacitors. Adv. Mater. 2014, 26(19), 3148-3155, DOI 10.1002/adma.201305851. (24) Huang, Y.; Zhong, M.; Shi, F.; Liu, X.; Tang, Z.; Wang, Y.; Zhi, C. An Intrinsically Stretchable and Compressible Supercapacitor Containing a Polyacrylamide Hydrogel Electrolyte. Angew. Chem. Int. Ed. 2017, 56(31), 9141-9145, DOI 10.1002/anie.201705212. (25) Lu, X.; Yu, M.; Wang, G.; Tong, Y.; Li, Y. Flexible Solid-State Supercapacitors: Design, Fabrication

and

Applications.

Energy

Environ.

Sci.

2014,

7,

2160-2181,

DOI

10.1039/C4EE00960F. (26) Huang, Y.; Tao, J. Y.; Meng, W. J.; Zhu, M. S.; Huang, Y.; Fu, Y. Q.; Gao, Y. H.; Zhi, C. Y. Super-High Rate Stretchable Polypyrrole-Based Supercapacitors with Excellent Cycling Stability. Nano Energy 2015, 11, 518-525, DOI 10.1016/j.nanoen.2014.10.031. (27) Wang, Z.; Pan, Q. An Omni-Healable Supercapacitor Integrated in Dynamically Cross-Linked Polymer Networks. Adv. Funct. Mater. 2017, 27(24), 1700690-1700698, DOI 10.1002/adfm.201700690. (28) Yang, Y.; Fei, H.; Ruan, G.; Xiang, C.; Tour, J. M. Edge-Oriented MoS2Nanoporous Films as Flexible Electrodes for Hydrogen Evolution Reactions and Supercapacitor Devices. Adv. Mater. 2014, 26(48), 8163-8168, DOI 10.1002/adma.201402847. (29) Holloway, J. L.; Lowman, A. M.; Palmese, G. R. The Role of Crystallization and Phase Separation in the Formation of Physically Cross-Linked PVA Hydrogels. Soft Matter 2013, 9, 826-833, DOI 10.1039/C2SM26763B. 20


Page 21 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(30) Zhu, Y. S.; Wang, X. J.; Hou, Y. Y.; Gao, X. W.; Liu, L. L.; Wu, Y. P.; Shimizu, M. A New Single-Ion Polymer Electrolyte Based on Polyvinyl Alcohol for Lithium Ion Batteries. Electrochim. Acta 2013, 87, 113-118, DOI 10.1016/j.electacta.2012.08.114. (31) Huang, Y. F.; Wu, P. F.; Zhang, M. Q.; Ruan, W. H.; Giannelis, E. P. Boron Cross-Linked Graphene Oxide/Polyvinyl Alcohol Nanocomposite Gel Electrolyte for Flexible Solid-State Electric Double Layer Capacitor with High Performance. Electrochim. Acta 2014, 132, 103-111, DOI 10.1016/j.electacta.2014.03.151. (32) Sun, J. Y.; Keplinger, C.; Whitesides, G. M.; Suo, Z. G. Ionic Skin. Adv. Mater. 2014, 26(45), 7608-7614, DOI 10.1002/adma.201403441. (33) Li, C.; Bai, H.; Shi, G. Conducting Polymer Nanomaterials: Electrosynthesis and Applications. Chem. Soc. Rev. 2009, 38, 2397-2409, DOI 10.1039/B816681C. (34) Sun, J. Y.; Zhao, X.; Illeperuma, W. R. K.; Chaudhuri, O.; Oh, K. H.; Mooney, D. J.; Vlassak, J. J.; Suo, Z. Highly Stretchable and Tough Hydrogels. Nature 2012, 489(7414), 133-136, DOI 10.1038/nature11409. (35) Calvert, P. Hydrogels for Soft Machines. Adv. Mater. 2009, 21(7), 743-756, DOI 10.1002/adma.200800534. (36) Ma, G.; Peng, H.; Mu, J.; Huang, H.; Zhou, X.; Lei, Z. In Situ Intercalative Polymerization of Pyrrole in Graphene Analogue of MoS2 as Advanced Electrode Material in Supercapacitor. J. Power Sources 2013, 229, 72-78, DOI 10.1016/j.jpowsour.2012.11.088. (37) Wang, J.; Yang, Y.; Huang, Z.; Kang, F. A High-Performance Asymmetric Supercapacitor Based on Carbon and Carbon-MnO2 Nanofiber Electrodes. Carbon 2013, 61, 190-199, DOI 10.1016/j.carbon.2013.04.084. 21



(38) Wang, J.; Xu, Y.; Yan, F.; Zhu, J.; Wang, J. Template-Free Prepared Micro/Nanostructured Polypyrrole with Ultrafast Charging/Discharging Rate and Long Cycle Life. J. Power Sources 2011, 196, 2373-2379, DOI 10.1016/j.jpowsour.2010.10.066. (39) Wang, K.; Meng, Q.; Zhang, Y.; Wei, Z.; Miao, M. High-Performance Two-Ply Yarn Supercapacitors Based on Carbon Nanotubes and Polyaniline Nanowire Arrays. Adv. Mater. 2013, 25(10), 1494-1498, DOI 10.1002/adma.201204598. (40) Bae, J.; Song, M. K.; Park, Y. J.; Kim, J. M.; Liu, M. Wang, Z. L. Fiber Supercapacitors Made of Nanowire-Fiber Hybrid Structures for Wearable/Flexible Energy Storage. Angew. Chem. Int. Ed. 2011, 50(7), 1683-1687, DOI 10.1002/anie.201006062. (41) Ren, J.; Bai, W.; Guan, G.; Zhang, Y.; Peng, H. Flexible and WeaveableCapacitor Wire Based on a Carbon Nanocomposite Fiber. Adv. Mater. 2013, 25(41), 5965-5970, DOI 10.1002/adma.201302498. (42) Kou, L.; Huang, T.; Zheng, B.; Han, Y.; Zhao, X.; Gopalsamy, K.; Gao, C. Coaxial Wet-Spun Yarn Supercapacitors for High-Energy Density and Safe Wearable Electronics. Nat. commun. 2014, 5, 3754-3764, DOI 0.1038/ncomms4754. (43) Fu, Y.; Wu, H.; Ye, S.; Cai, X.; Yu, X.; Hou, S.; Zou, D. Integrated Power Fiber for Energy Conversion and Storage. Energy Environ. Sci. 2013, 6, 805-812, DOI 10.1039/C3EE23970E. (44) Gao, K.; Shao, Z.; Li, J.; Wang, X.; Peng, X.; Wang, W.; Wang, F. Cellulose Nanofiber-Graphene All Solid-State Flexible Supercapacitors. J. Mater. Chem. A 2013, 1, 63-67, DOI 10.1039/C2TA00386D. (45) Fu, Y.; Cai, X.; Wu, H.; Lv, Z.; Hou, S.; Peng, M.; Zou, D. Fiber Supercapacitors Utilizing Pen Ink for Flexible/Wearable Energy Storage. Adv. Mater. 2012, 24(42), 5713-5718, DOI 22


Page 22 of 33

Page 23 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10.1002/adma.201202930.

23



Figure captions Figure 1 The defects of supercapacitors with multilayer laminated configuration under external force. Figure 2 (a) Schematic of the preparation process of B-PVA/KCl hydrogel film. (b) The cross-linking mechanism between PVA chains and boric acid. (c) FT-IR spectra of the PVA/KCl film and B-PVA/KCl film. (d) TGA curves of the swollen B-PVA/KCl film and freeze-dried B-PVA/KCl film. Figure 3 (a) Schematic of the formation of an integrated supercapacitor based on single PPy/B-PVA/KCl film. (b), (c) and (d) Optical images of the B-PVA/KCl film, PPy/B-PVA/KCl film and integrated supercapacitor with electrode-electrolyte-electrode configuration, respectively. (e), (f) and (g) the stretch, twist and compression properties of the integrated supercapacitor, respectively. Figure 4 (a) SEM image of the surface morphology of the freeze-dried B-PVA/KCl film. (b) and (c) Surface morphology of the freeze-dried PPy/B-PVA/KCl film. (d) Cross-section of the PPy/B-PVA/KCl film by optical microscopy. (e) Cross-section of the freeze-dried PPy/B-PVA/KCl film by SEM. (f) XRD patterns of the B-PVA/KCl film and PPy/B-PVA/KCl film. Figure 5 (a) GCD curves of the supercapacitors based on various PPy/B-PVA/KCl films at 0.8 mA cm-2. (b) The areal capacitance of the supercapacitors based on various PPy/B-PVA/KCl films and the loading amount of single PPy layer in various PPy/B-PVA/KCl films. (c) Optical image of the mixed solution with various pyrrole concentrations after polymerization. (d) CV curves and (e) GCD curves of the single PPy(0.6 mol L-1)/B-PVA/KCl film based supercapacitor. (f) The area capacitance of the single PPy(0.6 mol L-1)/B-PVA/KCl film based supercapacitor at various 24


Page 24 of 33

Page 25 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


current densities. Figure 6 (a) CV curves of the supercapacitor with various bending angles at 75 mV s-1. (b) GCD curves of the supercapacitor with various bending angles at 1.5 mA cm-2, inset: the definition of bending angle. (c) Nyquist impedance plots of the supercapacitor with various bending angles, the inset showed an equivalent circuit used to fit the Nyquist spectra. (d) Ragone plots of the supercapacitor device. (e) Cycling performances of the supercapacitor device, and the inset is GCD curves of the supercapacitor at the 1st and 1000th cycles. (f) Capacitance retention of the supercapacitor during 500 bending-releasing cycles, and the inset showed a bending-releasing cycle demo. Table 1 The comparison on specific capacitance and energy density of our device with other reported solid-state flexible supercapacitors.

25



Figure 1

26


Page 26 of 33

Page 27 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2

27



Figure 3

28


Page 28 of 33

Page 29 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4

29



Figure 5

30


Page 30 of 33

Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6

31



Page 32 of 33

Table 1

Electrodes

Active materials content in single electrode

Maxarea capacitance (mF cm-2)

Max energy density (μWh cm-2)

Ref

PANI/CNT

0.12 mg cm-2

[email protected] mA cm-2

3.4

39

ZnO/MnO2

-----

2.4@1 μA

0.027

40

PANI

5.6 mg cm-2

488 @0.2 mA cm-2

42

19

CNT/OMC

0.041 mg cm-2

39.7@10 μA

1.77

41

RGO-CNT

-----


3.84

42

PANI/stainless steel

0.3 mg cm-2


0.95

43

CNF-RGO

-----

158 @ 0.7 mA cm-2

20

44

Pen ink

-----


2.7

45

This research

6.1 mg cm-2

224 @0.8 mA cm-2

20

32


Page 33 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC: Flexible supercapacitor with electrode-electrolyte-electrode integrated configuration is prepared which shows highly mechanical and electrochemical stability.

33


A Single Robust Hydrogel Film Based Integrated Flexible

Recommend Documents