Design and fabrication of an all-solid-state polymer supercapacitor

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Design and fabrication of an all-solid-state polymer supercapacitor with highly mechanical flexibility based on polypyrrole hydrogel Limin Zang, Qifan Liu, Jianhui Qiu, Chao Yang, Chun Wei, Chanjuan Liu, and Li Lao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b10321 • Publication Date (Web): 11 Sep 2017 Downloaded from http://pubs.acs.org on September 13, 2017

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ACS Applied Materials & Interfaces

Design and fabrication of an all-solid-state polymer supercapacitor with highly mechanical flexibility based on polypyrrole hydrogel Limin Zang1, Qifan Liu1, Jianhui Qiu2, Chao Yang1,*, Chun Wei1, Chanjuan Liu1, Li Lao1 1

State Key Laboratory Breeding Base of Nonferrous Metals and Specific Materials Processing,

College of Material Science and Engineering, Guilin University of Technology, Guilin 541004, China. 2

Department of Machine Intelligence and Systems Engineering, Faculty of System Science and

Technology, Akita Prefectural University, Yurihonjo 015-0055, Japan

ABSTRACT: A conducting polymer-based hydrogel (PPy/CPH) with a polypyrrole-polyvinyl

alcohol interpenetrating network was prepared by utilization of a chemical crosslinked polyvinyl alcohol–H2SO4 hydrogel (CPH) film as flexible substrate followed by vapor-phase polymerization of pyrrole. Then an all-solid-state polymer supercapacitor (ASSPS) was fabricated by sandwiching the CPH film between two pieces of the PPy/CPH film. The ASSPS is mechanically robust and flexible with a tensile strength of 20.83 MPa and a break elongation of 377% which is superior to other flexible conducting polymer hydrogel-based supercapacitors owing to the strong hydrogen bonding interactions among the layers and the high mechanical properties of the PPy/CPH. It exhibits maximum volumetric specific capacitance of 13.06 F/cm3

ACS Paragon Plus Environment


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and energy density of 1160.9 µWh/cm3. The specific capacitance maintains 97.9% and 86.3% of its initial value after 10000 folding cycles and 10000 charge-discharge cycles, respectively. The remarkable the electrochemical and mechanical performance indicates this novel ASSPS device is promising for flexible electronics.

KEYWORDS: conducting polymers, hydrogel, vapor-phase polymerization, all-solid-state supercapacitors, flexible

INTRODUCTION To satisfy the growing market in portable electronic devices, much effort has been devoted to the developing of power sources that are small, flexible, lightweight and even wearable.1,2,3 Conducting polymer-based supercapacitors feature rapid charge/discharge, high power density, long cycle life and good eco-friendliness, which are ideal power source and have been widely applied in uninterruptible power system, digital products and electrical vehicles.4-8 However, fabrication of flexible conducting polymer-based supercapacitors that maintain excellent electrochemical performance under various strain conditions remains a challenging task.9 In recent years, all-solid-state polymer supercapacitors (ASSPS) consisting of flexible polymer electrode and solid-state electrolyte have been designed to facilitate their overall performance.10,11,12 As the key component for ASSPS, much attention has been devoted to the development of polymer electrodes. Polypyrrole (PPy) is considered to be one of the optimal


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candidates for polymer electrode materials in the light of its high electrical conductivity, outstanding electrochemical properties, ease of preparation and good environmental stability.13-16 However, PPy is limited by its brittleness and low mechanical strength, leading to finite applications in flexible polymer supercapacitors. Incorporation of suitable substrate to achieve polymer electrode offers a valid way of improving mechanical flexibility and meanwhile remaining outstanding supercapacitor performance. To date, most of the previous researches focused on coating electroactive materials onto a flexible substrate (e.g., cotton textile17, cellulose18, polydimethylsiloxane films19, rubber fibers20, carbon fabrics21 and metals22,23), which suffers two major defects. First, the electroactive materials may peel off from the substrate under strong flexibility or long-term repetition condition. Second, this approach is unfavorable for portable electronic devices because of the extra weight and volume in the final ASSPS.24 Herein, we focused attention on freestanding PPy-based hydrogel film as polymer electrode material for ASSPS. To be specific, a chemical crosslinked polyvinyl alcohol–H2SO4 hydrogel (CPH) film with high flexibility was synthesized and served as substrate. The high ionic conductivity of PVA–H2SO4 hydrogel is favorable for enhancing the electrochemical energy storage and stability of pseudocapacitor electrodes.25,26 On the other hand, the PVA–H2SO4 hydrogel after chemical crosslinking can form a freestanding hydrogel film and shows increased flexibility, which is attractive for flexible devices. Subsequently, PPy was embedded in the CPH (PPy/CPH) film as flexible polymer electrode via vapor-phase polymerization (VPP) of pyrrole. Instead of polymerizing on the surface of CPH film, the pyrrole vapor easily permeates into the film and is polymerized in the entire CPH film via VPP process. Finally, a piece of CPH film



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(playing the role as solid-state electrolyte and separator) was sandwiched between two pieces of the PPy/CPH film (playing a role as electrode) to form an integrated ASSPS. Although the fabrication approach made ASSPS exhibit a conventional multilayer laminated configuration, the strong hydrogen bonding interactions among the layers promote forming a robust device which is not prone to cause relative displacement to each other under flexibility. Moreover, the substrate and solid-state electrolyte are the same composition, which can decrease interface contact resistance among the layers that usually results in poor supercapacitor performance. The results demonstrate that the as-fabricated ASSPS with high mechanical flexibility exhibits large specific capacitance, long cyclic lifetime and high stability during repeating bending, which is suitable for practical application in energy storage devices.

EXPERIMENTAL SECTION Chemicals and Materials. Pyrrole, iron(III) chloride hexahydrate (FeCl3·6H2O), polyvinyl alcohol (PVA, 99% hydrolyzed, degree of polymerization 1700), glutaraldehyde (GDA, 50%, v/v), sulfuric acid (H2SO4, 98%) were analytical grade and purchased from Aladdin Co. Ltd. Synthesis of Flexible Chemical Crosslinked Polyvinyl Alcohol–H2SO4 Hydrogel (CPH) Film. 1.5 g polyvinyl alcohol (PVA) was added to a flask containing 30 mL of 0.5 mol/L H2SO4 aqueous solution. The mixture was heated to 85 °C under mechanical stirring until PVA was completely dissolved, and then cooled to room temperature. Subsequently, 3 mL of 1% GDA solution was added to the PVA–H2SO4 solution and mechanically stirred for 30 s. Following that the blended solution was quickly poured on a Teflon plate substrate while it was fluid. After


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complete crosslinking for 24 h at room temperature, the flexible CPH film was obtained by peeling off the film from the substrate. Preparation of PPy/CPH Film. PPy/CPH film was prepared by vapor-phase polymerization (VPP) of pyrrole. Typically, the dried CPH film was immersed in 50 mL of 115 g/L FeCl3 ethanol solution for 5 min. After being dried in air, the film was placed over a beaker containing 1 mL of fresh distilled pyrrole monomer in a vacuum desiccator. The film was exposed to the pyrrole vapor for 2 h at 4 °C by vacuuming the desiccator. Then the PPy/CPH film was washed with ethanol and deionized water. Assembly of All-Solid-State Polymer Supercapacitor (ASSPS). First, a piece of CPH film and two pieces of PPy/CPH film with a rectangle shape were immersed in 0.5 mol/L H2SO4 aqueous solution for 1h, respectively. Second, the CPH film was sandwiched between two pieces of the PPy/CPH film and pressed together under a pressure of ∼0.5 MPa for 1 h to form an integrated ASSPS. Characterization. The Fourier transform infrared (FTIR) spectroscopy measurements were carried out with a FTIR-Raman spectrometer (NICOLET 6700, USA). The morphology of the samples were investigated with a field emission scanning electron microscope (SEM; S-4800, HITACHI, Japan) at an accelerating voltage of 5.0 kV. The mechanical tensile properties of the CPH, PPy/CPH and ASSPS (10 mm width × 20 mm length) were measured on an electronic universal testing machine (UTM4503SLXY, China) with a crosshead speed of 20 mm/min at 23±2 °C. Electrochemical experiments of the ASSPS were performed on a CHI660E electrochemical workstation (Shanghai, China). The capacitance behaviors were examined by



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cyclic voltammetry (CV) measurements at scan rates of 5, 10, 20, 50 and 100 mV/s. The EIS test was performed in the frequency range between 0.1 Hz and 1 MHz with a perturbation of 5 mV. And the galvanoststic charge/discharge (GCD) measurements were carried out in the potential range from0 to 0.8 V with applied current densities of 5, 12.5, 25, 37.5 and 50 mA/cm3. For the ASSPS, the volumetric specific capacitance (Csv) and areal specific capacitance (Csa) of single electrode were calculated by using Equation (1) and (2), respectively. The volumetric energy density (Ev), areal energy density (Ea), volumetric power density (Pv) and areal power density (Pa) were calculated according to Equations (3), (4), (5) and (6) respectively. ଶ௜௧

‫ܥ‬௦௩ = ௎௏

ଶ௜௧

‫ܥ‬௦௔ = ௎஺ ‫ܧ‬௩ = ‫ܧ‬௔ =

஼ೞೡ ௎ మ ଶ ஼ೞೌ ௎ మ

ܲ௩ = ܲ௔ =

ଶ ாೡ ௧ ாೌ ௧

(1) (2) (3) (4) (5) (5)

Where i is the applied current; t is the discharged time; U is the discharged potential; V and A is the volume and surface area of one electrode, respectively.

RESULTS AND DISCUSSION A novel flexible all-solid-state polymer supercapacitor (ASSPS) was designed and fabricated in this study and the preparation process is schematically illustrated in Figure 1. The chemical crosslinked polyvinyl alcohol–H2SO4 hydrogel (CPH) film with improved flexibility and tensile


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strength was synthesized and then used as substrate. Then vapor phase polymerization (VPP) technique was applied to prepare flexible polymer electrode via exposure of the oxidant impregnated CPH film to the pyrrole vapor. Finally, a symmetric ASSPS was fabricated by sandwiching the CPH film between two pieces of the PPy/CPH film.

Figure 1. Schematic representation of preparation process of the flexible all-solid-state polymer supercapacitor.

The PVA–H2SO4 hydrogel is usually used as gel electrolyte in all-solid-state supercapacitors owing to its high ionic conductivity and freedom from liquid leakage, which can form a freestanding hydrogel film via crosslinking polyvinyl alcohol (PVA) with glutaraldehyde (GDA) under acidic condition (Scheme S1).27,28 The crosslinking reaction that the −OH groups of PVA



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reacted with −CHO groups of GDA to form acetal bridges was confirmed by FTIR as shown in Figure 2A. Compared with the spectrum of PVA/H2SO4, the peak at 1097 cm-1 in the spectrum of CPH film is much stronger which is attributed to the characteristic stretching vibration of C−O−C at 1097 cm-1 due to the crosslinking reaction. In addition, the characteristic two peaks of C–H from −CHO in 2810~2720 cm-1 cannot be observed in the spectrum of CPH film, indicating the crosslinking reaction is performed completely, which is good for improving the mechanical strength of the hydrogel film. As shown in Figure 2B, the tensile strength of CPH film is ~0.65 MPa and elongation at break is about 260%. The excellent stretchability of the CPH film is attractive for the next preparation of PPy/CPH electrode material. As a typical conducting polymer, PPy has received significant attention in the field of power sources as polymer electrode material for supercapacitors because of its remarkable pseudocapacitance, high electrical conductivity and fine environmental stability. In this study, we adapted VPP technique to prepare a homogeneous interpenetrating network PPy/CPH film that combined the advantages of PPy and CPH film into a single conducting polymer hydrogel film with ultrahigh flexibility and tensile strength. The oxidant impregnated CPH film which was obtained by soaking the film in a FeCl3 ethanol solution, was exposed to pyrrole vapor to initiate the polymerization. From photograph of the CPH film before and after VPP process (Figure S1), the colorless transparent CPH film turned to black due to the generation of PPy. On the FTIR spectrum of the PPy/CPH film (Figure 2A), some characteristic bands of PPy appear, such as stretching vibration of C=C at 1550 cm-1, stretching vibration of C–N at 1320 cm-1, breathing vibration of the pyrrole ring at 1170 cm-1, which prove the formation of PPy.29,30,31 The


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cross-section of the PPy/CPH film was checked by SEM (Figure S2). In order to further analyze the distribution of PPy, elemental mapping of N is recorded in Figure 2C. The homogeneous brightness and distribution proves that PPy is not deposited on the surface of the CPH film in this work. Instead, PPy is distributed evenly in the entire CPH film, forming PPy-PVA interpenetrating network. The CPH film with a three-dimensional network structure has many channels/pores in the matrix, so pyrrole vapor can penetrate into the oxidant impregnated CPH film after drying-process and then polymerized in the matrix. Given the unique rigid polymer (PPy)-soft polymer (PVA) interpenetrating network, the obtained PPy/CPH film is mechanically robust and the tensile strength obviously improves to 12.26 MPa with a break elongation of 358% as tested by tensile stress-strain test (Figure 2B), which is superior to other flexible conducting polymer hydrogel-based electrodes for supercapacitors. Li et al. reported PANI-PVA supramolecular hydrogels for flexible supercapacitors, showing a tensile strength of 5.3 MPa and a break elongation of 250%.32 Wang et al. fabricated a flexible supercapacitor by embedding two layers of PANI in a chemically crosslinked PVA hydrogel and the tensile strength of the supercapacitor was 0.35 MPa with a break elongation of 300%.33 Moreover, the PPy/CPH possesses outstanding mechanical flexibility as shown in Figure 2D and can recover its initial shape immediately after being released. The evenly distributed PPy has strong interactions with the substrate, ensuring it wouldn’t peel off from the substrate even under strong flexibility or long-term repetition condition. Due to these advantages the PPy/CPH film is worth looking forward as a polymer electrode material to fabricate ASSPS.



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Figure 2. Characterization of CPH film and PPy/CPH film. (A) FTIR spectra of PVA/H2SO4, CPH film and PPy/CPH film. (B) Tensile stress–strain curves. (C) Back scattered electron image and elemental mapping of N and S of the cross-section of PPy/CPH film. (D) Photographs of PPy/CPH film showing flexibility.

A symmetric ASSPS was fabricated by sandwiching two PPy/CPH electrodes and a CPH film. Compared with the previously reported ASSPS, the main differences of this work are the


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following: (1) Generally, PVA-acid and separator coexist simultaneously as two separate parts in conventional all-solid-state supercapacitors, where the former usually serves as hydrogel polymer electrolyte and the later can prevent short circuiting while still allowing the electrodes to exchange ions. As for our ASSPS, the middle CPH film with good mechanical strength serves a dual function: solid-state gel electrolyte and separator. Avoiding the introduction of extra passive component (e.g., PP or cellulose film that usually is used as a separator in supercapacitors makes no contribution to capacitance) could enhance the specific capacitance of the whole device. Moreover, the high mechanical strength of the middle CPH film is also in favor of improving the mechanical strength of the final ASSPS. (2) For the PPy/CPH electrode, the CPH film also plays a dual role: flexible substrate and solid-state gel electrolyte. The PPy with large pseudocapacitance is uniformly distributed in the CPH film, which guarantees that the electroactive material is sufficiently soaked in the gel electrolyte. (3) The substrate of the polymer electrode and the solid-state electrolyte has the same composition, and there are strong interactions among the layers, which could decrease interface contact resistance among the layers. Figure 3A shows a cross-section of the device by optical microscopy, which illustrates that two PPy/CPH electrodes are pressed close against each side of the CPH film and there is no observable gap between two layers. The thickness of the obtained ASSPS is approximately 425 µm with 25 µm for the middle CPH film and 200 µm for either PPy/CPH electrode. As is expected, the ASSPS succeeds the advantage of PPy/CPH film, showing ultrahigh mechanical stretchability and bendability. The tensile stress-strain curve presented in Figure 3B indicates that the tensile strength of the ASSPS reaches as high as 20.83 MPa with a break elongation of



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377%. The outstanding mechanical flexibility of the device is attributed to the excellent mechanical properties of the PPy/CPH film and strong interactions among the electrode layer (the PPy/CPH film) and solid-state electrolyte layer (the middle CPH film). Reflecting optical microscopy was used to observe the fractured cross-section of the ASSPS after tensile testing (Figure 3S). The ASSPS still keeps integrate three-layer laminated configuration, and no observable gap between two layers, which support our opinion.

Figure 3. Characterization of the ASSPS. (A) Cross-section of the ASSPS by optical microscopy. (B) Tensile stress–strain curve.

In order to evaluate the overall electrochemical performance, CV, EIS and GCD of the obtained ASSPS were measured. The CV diagrams from 0 to 0.8 V at different scan rates (Figure 4A) show similar and deformed rectangular shape, indicating ideal capacitive behavior of this device. The charge transport process of the ASSPS was analyzed by EIS and the result is presented in terms of Nyquist plot in Figure 4B. The intercept at high frequency on the real impedance axis is ~3.1 Ω, which represents the cell resistance. The low series resistance of the


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device indicates that the PPy/CPH film and the middle CPH film have good conductivity, as well as the PPy/CPH film and the middle CPH film are fit tightly together which could decrease interface contact resistance among the layers. Meanwhile, the GCD curves at various current densities are given in Figure 4C and all of them exhibit a small voltage drop at the start of the discharge curves. The ASSPS has a high volumetric specific capacitance from 13.06 F/cm3 at 5 mA/cm3 to 2.07 F/cm3 at 50 mA/cm3, and an areal specific capacitance from 261.2 mF/cm2 at 5 mA/cm3 to 40.8 mF/cm2 at 50 mA/cm3. Ragone plots of the ASSPS at different current densities are presented in Figure 4D. The ASSPS shows an excellent volumetric energy density of 1160.9 µWh/cm3 at a volumetric power density of 4000 µW/cm3 and 138.3 µWh/cm3 at a volumetric power density of 60 mW/cm3. The maximum areal energy density is 23.2 µWh/cm2 at an areal power density of 80 µW/cm2 (Figure S4). The charge-discharge cycling stability was examined by GCD tests at 25 mA/cm3 for 10000 cycles (Figure 4E). The ASSPS exhibits good charge-discharge cycle life, with 86.3% capacitance retention after 10000 cycles. As discussed above, PPy is distributed evenly in the entire CPH film which could prevent the pulverization and loss of the electroactive materials during charge-discharge process, leading to outstanding cycling stability of the device. Owing to the excellent flexibility, the ASSPS shows good capacitance retention under repeated folding. As shown in Figure 4F, the specific capacitance maintains 97.9% of its initial value after 10000 folding cycles, which demonstrates that the ASSPS is mechanically robust. The comparison on the overall electrochemical performance of our device with other reported flexible supercapacitors is summarized in Table 1, which indicates the overall electrochemical performance of our ASSPS is remarkable.



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Figure 4. Electrochemical performance of the ASSPS. (A) CV curves at different scan rates. (B) Nyquist plot in the frequency range of 0.1 Hz − 1 MHz. (C) GCD curves at different constant current densities (D) Ragone plots. (E) Capacitance retention during GCD cycles at 25 mA/cm3. (F) Capacitance retention after different folding cycles.


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Table 1. Comparison of recently reported flexible all-solid-state supercapacitors based on conducting polymer electrode materials Electrode materials

Graphite/PANI paper

Specific capacitance

3.55 F/cm3 @ 4.57 mA/cm3 2

77.8 mF/cm @ 0.1 mA/cm Graphene/PANI fabric

2

23 mF/cm @ 0.1 mA/cm

2

2

Maximum energy

Maximum power

density

density

320 µWh/cm3

54 mW/cm3

7.0 µWh/cm

2

1.5 µWh/cm

2

1.18 mW/cm

2

2

1 mW/cm

Stability

Ref

83% retention after

34

10000 cycles 100% retention after

35

2000 cycles TiO2@PPy nanowires

146 mF/cm3 @ 0.25 mA/cm2

13 µWh/cm3

‒

96.4% retention after

36

1000 cycles PANI/CNT yarn

2

38 mF/cm @ 0.01 mA/cm

2

3.4 µWh/cm

2

800 µW/cm

2

91% retention after

37

800 cycles CQDs-PANI

2

169.2 mF/cm @ 1.0 mA/cm

2

33.8 µWh/cm

2

27.1 µWh/cm

2

600 µW/cm

2

78% retention after

38

1000 cycles Hollow rGO/PEDOT: PSS fiber

2

304.5 mF/cm @ 0.08 mA/cm

2

66.5 µW/cm

2

96% retention after

39

10000 cycles CNT doped GO/PPy

2

72.3 mF/cm @ 0.5 mA/cm

2

6.3 µWh/cm

2

2

3.7 mW/cm


40

10000 cycles CNF/PANI-GO

5.86 mF/cm2 @ 4.3 µA/cm2

‒

‒


41

1000 cycles PANI/stainless steel wire

2

19 mF/cm @ 0.32 mA/cm

2

0.95 µWh/cm

2

12.9 µWh/cm

2

2

4.2 mW/cm

100% retention after

42

10000 cycles PPy/GO

2

97 mF/cm @ 1 mA/cm

2

5.76 mW/cm

2


43

10000 cycles PPy-PVA hydrogel

3

13.06 F/cm @ 5 mA/cm 2

3

261.2 mF/cm @ 0.1 mA/cm

3

1160.9 µWh/cm 2

23.2 µWh/cm

2

60 mW/cm

3 2

1.2 mW/cm


This

10000 cycles

work

2

195.1 mF/cm @ 5 mV/s

CONCLUSION In summary, a novel all-solid-state polymer supercapacitor with highly mechanical flexibility was designed and fabricated. The CPH film plays multiple roles in this work. PPy is uniformly embedded in the CPH film via VPP of pyrrole to form PPy/CPH flexible polymer electrode, where the CPH provides mechanical flexibility and guarantees that the electroactive material



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(PPy) is sufficiently soaked in the gel electrolyte (CPH). Then the pure CPH film was sandwiched between two pieces of the PPy/CPH electrode to form an integrated ASSPS, where the CPH film is used as solid-state gel electrolyte and separator. With this novel design, the assembled ASSPS exhibits high mechanical strength of 20.83 MPa, and has large specific capacitance and energy density, excellent cycle stability, and outstanding capacitance retention under repeated folding. Given the remarkable overall performance, this novel device shows great potential application in the field of flexible power source.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge. Crosslinking reaction of PVA with glutaraldehyde catalyzed by acid; Photographs of the CPH film before and after VPP process; Reflecting optical microscopy of fractured cross-section of the ASSPS after tensile testing; SEM images of cross-section of the dried PPy/CPH film; Ragone plots of the ASSPS. (PDF)

AUTHOR INFORMATION Corresponding Author * Tel: +86-18707738320. Fax: +86-773-5896672. E-mail: [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.


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Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 51763008, 51303035) and the Scientific Research Foundation of Guilin University of Technology (No. GUTQDJJ2017002).

REFERENCES (1) El-Kady, M. F.; Strong, V.; Dubin, S.; Kaner, R. B. Laser Scribing of High-performance and Flexible Graphene-based Electrochemical Capacitors. Science 2012, 335, 1326−1330. (2) Meng, Y.; Zhao, Y.; Hu, C.; Cheng, H.; Hu, Y.; Zhang, Z.; Shi, G.; Qu, L. All-Graphene Core-Sheath Microfibers for All‐Solid‐State, Stretchable Fibriform Supercapacitors and Wearable Electronic Textiles. Adv. Mater. 2013, 25, 2326−2331. (3) Wang, Z. L.; Zhu, G.; Yang, Y.; Wang, S.; Pan, C. Progress in Nanogenerators for Portable Electronics. Mater. Today 2012, 15, 532−543. (4) Kotz, R; Carlen, M. Principles and Applications of Electrochemical Capacitors. Electrochim. Acta 2000, 45, 2483−2498. (5) Snook, G. A.; Kao, P.; Best, A. S. Conducting-polymer-based Supercapacitor Devices and Electrodes. J. Power Sources 2011, 196, 1−12. (6) Ramya, R.; Sivasubramanian, R.; Sangaranarayanan, M. V. Conducting Polymers-based Electrochemical Supercapacitors—Progress and Prospects. Electrochim. Acta 2013, 101,



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109−129. (7) Wang, Z.; Carlsson, D. O.; Tammela, P.; Hua, K.; Zhang, P.; Nyholm, L.; Strømme, M. Surface

Modified

Nanocellulose

Fibers

Yield

Conducting

Polymer-based

Flexible

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Table Of Contents (TOC)


Design and fabrication of an all-solid-state polymer supercapacitor

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