Highly Flexible and All-Solid-State Paperlike Polymer Supercapacitors

Sep 10, 2010 - Tsinghua-Foxconn Nanotechnology Research Center and Department of Physics, Tsinghua University,. Beijing 100084, People's Republic of ...
1 downloads 0 Views 3MB Size
Download PDF
pubs.acs.org/NanoLett

Highly Flexible and All-Solid-State Paperlike Polymer Supercapacitors Chuizhou Meng, Changhong Liu,* Luzhuo Chen, Chunhua Hu, and Shoushan Fan Tsinghua-Foxconn Nanotechnology Research Center and Department of Physics, Tsinghua University, Beijing 100084, People’s Republic of China ABSTRACT In recent years, much effort have been dedicated to achieve thin, lightweight and even flexible energy-storage devices for wearable electronics. Here we demonstrate a novel kind of ultrathin all-solid-state supercapacitor configuration with an extremely simple process using two slightly separated polyaniline-based electrodes well solidified in the H2SO4-polyvinyl alcohol gel electrolyte. The thickness of the entire device is much comparable to that of a piece of commercial standard A4 print paper. Under its highly flexible (twisting) state, the integrate device shows a high specific capacitance of 350 F/g for the electrode materials, well cycle stability after 1000 cycles and a leakage current of as small as 17.2 µA. Furthermore, due to its polymer-based component structure, it has a specific capacitance of as high as 31.4 F/g for the entire device, which is more than 6 times that of current high-level commercial supercapacitor products. These highly flexible and all-solid-state paperlike polymer supercapacitors may bring new design opportunities of device configuration for energy-storage devices in the future wearable electronic area. KEYWORDS Supercapacitor, carbon nanotube, polyaniline, nanocomposite, flexible, all-solid-state

N

owadays, portable electronic devices (such as mobile phones, notebook computers, and digital cameras) are becoming much more multifunctional and developing in the trend of being small, thin, lightweight, flexible and even rollup, in order to meet the rapid growing modern market demands. However, the development of technologies for their energy management (such as batteries and supercapacitors) is still inferior. Therefore, fabricating power sources with the superiorities of lightweight (providing much higher energy and power with less device mass) and flexibility (working very well even under the twisting condition) remains a challenging task.1,2 Recently, great efforts have been dedicated to achieve these goals, mainly using carbon nanotube (CNT) networks or graphene nanosheets as flexible electrodes of supercapacitors3-10 and batteries.11,12 It is noted that most of their works were done in the conventional energy-storage device configuration (a separator sandwiched between two electrodes sealed in liquid electrolyte), which suffers two major drawbacks for practical wearable applications. First, liquid electrolyte requires high-standard safety encapsulation materials and technology. Once there is leakage of electrolyte, harmful materials will badly impact our living environment. Second, component parts of the configuration are not an integrate one and will move relative to each other under strong flexibility, which will decrease the electrochemical performances and cycle life of the device. The above two points lead that the dimension of conventional energy-storage devices are difficult to make further smaller. So there are * To whom correspondence should be addressed. mail.tsinghua.edu.cn. Telephone: 86 10 62796011. Received for review: 06/2/2010 Published on Web: 09/10/2010 © 2010 American Chemical Society

E-mail:

only two configuration managements (button and spiral wound cylinder) for current energy-storage devices. Their clumsy bulk shapes have badly limited their further applications in the future advanced thin and wearable electronic area. Incorporating carbon-based materials with pseudocapacitance materials (such as transition metal oxides and conductive polymers) is a promising approach to further achieve better electrochemical performances of devices.13 Carbon nanotube/polyaniline (PANI, which is a typical kind of conductive polymer) nanocomposite thin films as flexible electrodes of supercapacitors with enhanced electrochemical properties were reported in our previous studies.5 In this work, we further researched out a novel kind of device configuration for ultrathin all-solid-state supercapacitors, that is, two slightly separated PANI/CNT nanocomposite electrodes well solidified in the H2SO4-polyvinyl alcohol (PVA) gel electrolyte. Morphology characterizations showed that it was a polymer-based integrative device and the thickness of the entire device was much comparable to that of a piece of standard commercial A4 print paper. Electrochemical measurements showed that these true paperlike devices hold outstanding supercapacitor performance under highly flexible (twisting) conditions. A demo of the practical device was also presented. This approach may provide a facile and easily scalable strategy to fabricating the lightweight and flexible energy-storage devices, which may find numerous potential applications.2 The all-solid-state polymer supercapacitors were fabricated by a simple two-step approach, that is, the formation of the flexible PANI/CNT nanocomposite thin film electrodes5 and the soakage and solidification of two slightly separated electrodes in the H2SO4-PVA gel electrolyte. In a

chliu@

4025

DOI: 10.1021/nl1019672 | Nano Lett. 2010, 10, 4025–4031

typical synthesis process, first, PANI was polymerized uniformly coating on the freestanding CNT networks made of randomly entangled individual CNTs and CNT bundles through the in situ chemical solution method. Second, two PANI/CNT nanocomposite thin films were immersed in the H2SO4-PVA (either content ∼10 wt %) aqueous solution for 10 min and picked out. After that, the electrode with a thin solution layer coating on was air-dried at room temperature for 4 h to vaporize the excess water. Then the two electrodes were pressed together under a pressure of ∼10 MPa for 10 min. Under this pressure, the thin H2SO4-PVA gel electrolyte layer on either electrode surface could glue into one thin separating layer. (See Supporting Information for details of the process.) The paperlike material could be tailored into any shape, which is benefit for applications in various circumstances. The process of our approach was all solution based, so it would be easily introduced to the formed industrial technology (such as the large-scale print and fast roll-to-roll technics). In the case of conventional polymer gel electrolyte-based supercapacitors, two electrode pellets sandwiched with a solid-state polymer electrolyte membrane were pressed together into one device, where the polymer electrolyte offers bifunctionality of the separator and the electrolyte.7,14-18 The approach that fabricating the electrodes and polymer electrolyte separately and assembling them consequently has two shortcomings. First, the formation of solid-state polymer electrolyte membrane on a Petri dish shows that its thickness could not be too small (the thinnest value reported is 0.150 mm), which limits further minimizing the dimension of the entire device. (If using metallic current collectors, it will be even much thicker.) The middle polymer electrolyte component should be as thin as possible (thick enough to separate two electrodes). Second, solid electrodes contacted with the solid-state electrolyte under pressure show that only part of electrodes near the geometric electrode/electrolyte interface could be well utilized.7 (In our study, comparison measurements showed that less than 25% was well utilized for ∼30 µm thick PANI/CNT nanocomposite electrodes; Figure S1, Supporting Information.) Therefore the amount of electrode materials per area was difficult to increase. By all appearances, a very thick polymer electrolyte membrane united with very thin electrode materials by conventional method is not an effective device management. In comparison, the device configuration (Figure 1A) obtained by the novel approach here overcomes the above two drawbacks. For the electrode materials, individual CNTs and their bundles first randomly intertwined together to form a freestanding CNT networks (Figure S2, Supporting Information), whose electrical conductivity is as high as to 15 000 S/m.19 The volume density of the CNTs was only 30%, leaving 70% of the total networks in the form of porous structure, which made it an ideal template with high specific surface area for which PANI to coat. After the in situ chemical polymerization © 2010 American Chemical Society

of aniline monomer, PANI formed a wholly uniform coating layer (thickness ∼50-90 nm) around the surface of CNTs and their bundles (inset of Figure 1E). Adequate amount of pure PANI in the form of short nanobars (Figure 1C) also attached to the network backbone, which would introduce sufficient large pseudocapacitance. Macroscopically, the typical thickness of the CNT networks before and after PANI coating was 20 and 30 µm, respectively. Here the content of PANI (∼65.1 wt %) was well controlled not to destroy the porous structure of the network. It can be seen that the framework of the ideal CNT networks was well retained after the PANI coating process in the liquid phase, which would lead two advantages for the nanocomposite electrode materials, (1) good porous structure provides extremely large specific surface area of electrode/electrolyte interface, facilitating the fully use of the large pseudocapacitance of PANI; (2) in addition, to ensure the superior mechanical property of flexibility for composite electrodes,5 well interconnections of CNTs and their bundles provide fast electron transport path within the thin film electrode, which leads to low internal resistance. This is especially important for the long direction when the geometry area of the electrode is large. In addition, the nanosized PANI-coating layer means electrons at the surface of PANI would only pass across a much short distance to the highly conducting CNT networks. After the solidification of two slightly separated PANI/CNT nanocomposite thin film electrodes with H2SO4-PVA gel electrolyte, one supercapacitor device was obtained (Figure 1B, top). Macroscopically, the entire device shows the superior mechanical properties of flexibility, which can be bent, twisted, and even rolled up without any cracking. It is noted that all the electrochemical measurements for this allsolid-state device were carried out under highly flexible (twisting) state (Figure 1B, bottom). Figure 1F demonstrates that the advanced configuration of the all-solid-state device (Figure 1A) could be indeed achieved through this novel method. The section of the device was obtained by cracking the sample in liquid nitrogen (N2), so the surface was a little rough. The typical thickness of the entire device was ∼0.110 mm, measured by the screw micrometer, which is very comparable to that of the commercial standard A4 print paper (typically 0.100 mm measured by the screw micrometer). From Figure 1F, the thickness of the device was estimated at ∼113 µm with ∼22-37 µm for either electrode component and ∼30-45 µm for the middle polymer gel electrolyte component. It was also a ∼8 µm polymer gel coating layer on the outside of the device. Concerning both the properties of flexibility and thinness, a truly paperlike device was achieved here. Figure 1G shows that the polymer gel electrolyte incorporates well into the porous structure of the PANI/CNT nanocomposite across the whole thickness direction. No little air holes were observed, which means that all the electrode materials were well contacted with the electrolyte. Besides, no cracking appeared during the intense sample 4026

DOI: 10.1021/nl1019672 | Nano Lett. 2010, 10, 4025-–4031

FIGURE 1. Configuration of the highly flexible and all-solid-state paperlike polymer supercapacitors. (A) Schematic illustration of the PANI/ CNT nanocomposite electrodes well solidified in the polymer gel electrolyte. (B) Digital pictures that show the all-solid-state device (size ∼0.5 cm × 2.0 cm) under normal condition (top) and its highly flexible (twisting) state under electrochemical measurements (bottom). (D) Top view of the surface morphology of the PANI/CNT nanocomposite electrode and SEM images that show (E) PANI uniformly coating on the CNT networks and (C) the short pure PANI nanobars attaching to the networks. TEM images in (E) show the PANI coating individual CNT and CNT bundles. (F) SEM side view of the ultrathin all-solid-state device and (G,H) SEM images under different magnifications that show the PANIcoating CNT networks were well bonded with the solid-state H2SO4-PVA gel electrolyte.

preparation condition (cracked in liquid N2), demonstrating that the total device has indeed became an integrative one. Figure 1H displays the electrode/electrolyte interfacial morphology more clearly. The polymer electrolyte enwrapped some extruding PANI/CNT nanocomposite fibers tightly and no obvious air holes were observed in the nanoscale. Here the electrode and electrolyte material combined very well, which may be ascribed to the formation of a synergistic composite structure by the bonding of polymer chains of PANI and PVA.20,21 The mass content of the PANI and PVA elements in the total device was 23.2 and 29.4%, respectively. The proper combination of them assured the polymerbased nature of the device. All of the above superior properties laid the material, structural, and mechanical foundation for its potential applications in wearable electronics. The electrochemical performances of the devices were evaluated at room temperature. Measurements demonstrated that the all-solid-state device showed no capacitance differences while tested in the normal, twisting, and even © 2010 American Chemical Society

folded condition (Figure S3, Supporting Information), thus the electrochemical data in this paper were all obtained in the highly flexible (twisting) condition. The electrical conductivity of the H2SO4-PVA gel electrolyte was 17.3 S/m, which is higher than any reported data.22,23 Together with the proper incorporation of electrolyte into the porous structure of electrodes, such high ionic conductivity shows that the electrochemical performance of the all-solid-state device was nearly equivalent to that of the one assembled in the 0.5 M H2SO4 aqueous solution. Cyclic voltammetry (CV) measurements (Figure 2A) show that the all-solid-state device has almost the same CV curve with the one in 0.5 M H2SO4 solution, where the redox peaks indicate the presence of pseudocapacitance of PANI. The accurate electrochemical values were attained by the galvanostatic chargedischarge measurements. From the inset of Figure 2B, it is found that at ∼1.0 A/g the discharge specific capacitance of the all-solid-state device is 332 F/g, which is only 7.8% smaller than that (360 F/g) of the one in 0.5 M H2SO4 solution, and the internal resistance of the former is 11.1 Ω, which is larger than 4027

DOI: 10.1021/nl1019672 | Nano Lett. 2010, 10, 4025-–4031

FIGURE 2. Electrochemical performances of the devices. The data of the all-solid-state device were all obtained under highly flexible conditions. (A,B) Comparison of cyclic voltammetry at 5 mV/s and discharge abilities of the flexible PANI/CNT nanocomposite thin film electrodes in the H2SO4-PVA gel electrolyte and in the 0.5 M H2SO4 aqueous solution. The inset in (B) shows one cycle of galvanostatic charge-discharge curves at 1 A/g. (C) Ragone plots for the electrode materials and for the entire all-solid-state device. The dashed line region for electrochemical capacitors was cited from ref 2. (D) Cycle stability of the all-solid-state device at 1 A/g.

that (8.6 Ω) of the latter. The result was consistent with the CV analysis. For both of them, the specific capacitance decreased gradually while the current density increased (Figure 2B). However, from ∼100 mA/g to 4.0 A/g, the all-solid-state device has a smaller specific capacitance decay (11.4%) compared with the one in 0.5 M H2SO4 solution (17.5%). The specific capacitance of the all-solid-state supercapacitors here is higher than any reported ones for conventional PANI-based supercapacitors.15,24-27 Moreover, due to the adding of PANI with large pseudocapacitance and the complete soakage of the electrode materials in the electrolyte, the specific capacitance per area for the 30 µm thick electrodes here was as high as 0.80 F/cm2, which is at least 16 times the value reported in ref 7. Figure 2C shows the Ragone plots for the electrode materials and the entire device. For the electrode materials (PANI/CNT nanocomposite thin film, including both current collector and electrochemical active materials) among the current density measurement range, it has a high energy density of 7.1 wh/kg and a high power density of 2189 w/kg. These values have been far superior to those of current conventional supercapacitors in Ragone plots.2 What is more, all reported works achieving the advantage of lightweight were merely focused on the high specific capacitance of electrode active materials. However, on the application level, electrode active materials must be integrated with some elements that would poorly reduce the electrochemical performances but have to be used (such as costly and heavy metal current collectors, polymer binding substances, sepa© 2010 American Chemical Society

rator filled with electrolyte and much safety but bulky encapsulation packing) in conventional device configuration management. Therefore, concerning the specific capacitance of the entire device, those values would be even more inferior. For our polymer-based supercapacitors, even concerning the entire device, it is also at the up-right edge of the region of current conventional supercapacitors in the Ragone plots, which indicates the highly flexible all-solidstate supercapacitors also have the merit of lightweight and application potentials. This further demonstrates the advantage of the polymer-based structure. From the density analysis of each of the element materials of the device (see Supporting Information), the mass densities of all element materials are below 1.5 g/cm3, which shows that the density of the total device is only 1.18 g/cm3. Here the mass of the total device was only 2.79 times that of the electrode materials and the specific capacitance of the entire device is as high as 31.4 F/g, which is more than 6 times than the high-level value of current commercial spirally wound supercapacitors (5.2 F/g, weighing 500 g and rated for 2600 F).2 After material and structural optimizing, for example, using less polymer gel electrolyte by further shortening the distance of two electrodes, much higher specific capacitance of the entire device are expected. Figure 2D shows the good cycle stability of the all-solidstate device. After initial 20 charge-discharge cycles, the specific capacitance increased from 322 to 351 F/g. And finally, only 8.1% decay in specific capacitance is observed 4028

DOI: 10.1021/nl1019672 | Nano Lett. 2010, 10, 4025-–4031

FIGURE 3. (A) Leakage current curves of the all-solid-state device charged at 2 mA to a floating potential of 0.8 V and kept at 0.8 V for 2 h. (B) Self-discharge curves of the device after charged at 0.8 V for 15 min. (C,D) Time life stability of the device. CV curves at 5 mV/s and one cycle of galvanostatic charge-discharge curves at 1 A/g.

self-discharge course is very desirable for the applications ofthedevicesinareasofstandbypower,electronicphotoflash, and so on.

after 1000 cycles. The calculated Coulombic efficiency was all along kept ranging from 95.2 to 102.8%. Conductive polymer-supercapacitor-electrode often suffered the cycle degradation issues caused by mechanical problems, that is, the swelling and shrinking during the charge-discharge (doping-dedoping) process.13 Such good electrochemical stability achieved here for conductive polymers can be attributed to the well-formed CNT networks supporting for PANI coating on.

The time stability of the device was also tested. As Figure 3C displays, the capacitance shape and redox peaks were well retained after 1 week and even 2 months. From the galvanostatic charge-discharge curves, about 9.5% specific capacitance decay was found after initial 1 week, and the value was only 11.4% for the one after 2 months. Further water evaporation may cause the specific capacitance decay, however, this reduction lead to a much stable one finally. These experiments demonstrate that our device is very stable for at least 2 months.

On the level of practical applications, leakage current and self-discharge of the device are main concerns, however, very few recent works have been reported on this. As shown in Figure 3A, the leakage current dropped significantly in the beginning (from 1.0 mA to 52.1 µA after 15 min) and then gradually became smaller and more stable (finally to only 17.2 µA after 2 h). Such small value of leakage current, which is ascribed to the self-discharge course in the device, means less shuttle reactions caused by the impurities in the electrode materials.28 The bounding of the electrodes and electrolyte within the PANI-PVA polymer-based matrix may also prevent potential leakage. Figure 3B further shows the time courses of the open-circuit voltage. It undergoes rapid self-discharge course in several minutes, however, the selfdischarge course was quite limited after several hours. Finally the device shows a stable output voltage of ∼0.5 V after 4 h and almost 57.6% of the initial charged potential was well retained even after the time of 1 day. These results are better than all reported ones.29,30 The advantage of low © 2010 American Chemical Society

For a demo usage of the highly flexible and all-solid-state paperlike supercapacitors, we prepared three supercapacitor units (each size ∼0.65 cm × 5.0 cm) in series to light a red light-emitting-diode (LED, the lowest working potential is 1.5 V). Here one supercapacitor unit have a little lower specific capacitance of 296 F/g (89.2% of that of the one with size ∼0.5 cm × 2.0 cm) and larger internal resistance of 11.7 Ω, which may be ascribed to the inhomogeneity of largearea material preparation and device fabrication by rough hand-making. After charged at 2.5 V for 15 min, the rolledup 15 cm long paper-scriplike device could light the LED very well for almost 30 min. At the beginning, the LED glittered very brightly (see Supporting Information, Video 1), demonstrating the high power merit of supercapacitors. Figure 4029

DOI: 10.1021/nl1019672 | Nano Lett. 2010, 10, 4025-–4031

FIGURE 4. Demo application of the highly flexible paperlike device. (A) A digital picture that shows three highly flexible devices in series to light a red light-emitting-diode well. (B) CV curves at 5 mV/s and (C) one cycle of galvanostatic charge-discharge curves at 5 mA of the three in-series supercapacitor group.

Acknowledgment. This work was supported by National Basic Research Program of China (2005CB623606) and the National Natural Science Foundation of China (50673049, 10721404).

4B,C shows that the three in-series supercapacitor group also has proper CV curves and galvanostatic charge-discharge curves. Even though the structure and component material were not yet optimized, the ultrathin highly flexible and all-solidstate supercapacitor device here has already shown the superior flexibility and specific electrochemical performances to the current commercial supercapacitor devices. Prospectively, even higher performance could be achieved by a simple optimization. For instance, by replacing the buckypaper (typical thickness larger than 20 µm) with the superaligned ultrathin continuous CNT sheets (extremely, one single layer of CNTs around 10 nm in diameter could be made)31 and further adjusting the distance of two electrodes carefully, much more effective and lightweight supercapacitor devices will be fabricated. Besides, apart from the devices with flexible CNT/conductive polymer composite electrodes working in acidic PVA gel electrolyte described here, other types of supercapacitors made of flexible CNT/ transition metal oxide composite electrodes32,33 working in alkaline and neutral PVA gel electrolyte22 could also be fabricated through this novel approach. Also, it was ever reported that LiClO4-PVA gel electrolyte showing good reversibility and electrochemical stability up to 4.7 V could be well attained,34 which means that there is much room to enlarge energy and power densities for the device. In summary, we have reported a novel kind of ultrathin all-solid-state supercapacitor configuration with two slightly separated CNT/PANI nanocomposite thin films as electrodes and H2SO4-PVA gel as solid-state electrolyte. The entire device has a thickness comparable to that of a piece of standard commercial A4 print paper and shows outstanding electrochemical performances (such as high specific capacitance, good stable cycle life, and small self-discharge course) under highly flexible (testing) condition. It is a paperlike energy-storage device in the true sense. Furthermore, it is lightweight, owing to the polymer-based component structure, making it greatly surpass current high-level commercial supercapacitors while having great application potential in wearable electronics. © 2010 American Chemical Society

Supporting Information Available. Experimental details of device preparations, structural characterizations, electrical conductivity and electrochemical measurements, and density analysis of components. This material is available free of charge via the Internet at http://pubs.acs.org. REFERENCES AND NOTES (1) (2) (3) (4)

(5) (6)

(7) (8) (9) (10) (11) (12)

(13)

4030

Nishide, H.; Oyaizu, K. Toward flexible batteries. Science 2008, 319, 737–738. Simon, P.; Gogotsi, Y. Materials for electrochemical capacitors. Nat. Mater. 2008, 7, 845–854. Kaemfgen, M.; Ma, J.; Gruner, G.; Wee, G.; Mhaisalkar, S. G. Bifunctional carbon nanotube networks for supercapacitors. Appl. Phys. Lett. 2007, 90, 264104. Pushparaj, V. L.; Shaijumon, M. M.; Kumar, A.; Murugesan, S.; Ci, L. J.; Vajtai, R.; Linhardt, R. J.; Nalamasu, O.; Ajayan, P. M. Flexible energy storage devices based on nanocomposite paper. Proc. Nat. Acad. Sci. U.S.A. 2007, 104, 13574–13577. Meng, C. Z.; Liu, C. H.; Fan, S. S. Flexible carbon nanotube/ polyaniline paper-like films and their enhanced electrochemical properties. Electrochem. Commun. 2009, 11, 186–189. Wang, D. W.; Li, F.; Zhao, J. P.; Ren, W. C.; Chen, Z. G.; Tan, J.; Wu, Z. S.; Gentle, I.; Lu, G. Q.; Cheng, H. M. Fabrication of graphene/polyaniline composite paper via in situ anodic electropolymerization for high-performance flexible electrode. ACS Nano 2009, 3, 1745–1752. Kaempgen, M.; Chan, C. K.; Ma, J.; Cui, Y.; Gruner, G. Printable thin film supercapacitors using single-walled carbon nanotubes. Nano Lett. 2009, 9, 1872–1876. 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. Nat. Acad. Sci. U.S.A. 2009, 106, 21490–21494. Hu, L. B.; Pasta, M.; La Mantia, F.; Cui, L. F.; Jeong, S.; Deshazer, H. D.; Choi, J. W.; Han, S. M.; Cui, Y. Stretchable, porous, and conductive energy textiles. Nano Lett. 2010, 10, 708–714. Wu, Q.; Xu, Y. X.; Yao, Z. Y.; Liu, A. R.; Shi, G. Q. Supercapacitors based on flexible graphene/polyaniline nanofiber composite films. ACS Nano 2010, 4, 1963–1970. Kiebele, K.; Gruner, G. Carbon nanotube based battery architecture. Appl. Phys. Lett. 2007, 91, 144104. Chew, S. Y.; Ng, S. H.; Wang, J. Z.; Novak, P.; Krumeich, F.; Chou, S. L.; Chen, J.; Liu, H. K. Flexible free-standing carbon nanotube films for model lithium-ion batteries. Carbon 2009, 47, 2976– 2983. Frackowiak, E. Carbon materials for supercapacitor application. Phys. Chem. Chem. Phys. 2007, 9, 1774–1785. DOI: 10.1021/nl1019672 | Nano Lett. 2010, 10, 4025-–4031

(14) Lewandowski, A.; Zajder, M.; Frachowiak, E.; Beguin, F. Supercapacitor based on activated carbon and polyethylene oxideKOH-H2O polymer electrolyte. Electrochim. Acta 2001, 46, 2777– 2780. (15) Prasad, K. R.; Munichandraiah, N. Electrochemical studies of polyaniline in a gel polymer electrolyte. Electrochem. Solid-State 2002, 5, A271–A274. (16) Staiti, P.; Lufrano, F. A study of the electrochemical behaviour of electrodes in operating solid-state supercapacitors. Electrochim. Acta 2007, 53, 710–719. (17) Aoki, M.; Tadanaga, K.; Tatsumisago, M. All-solid-state electric double-layer capacitor using ion conductive inorganic-organic hybrid membrane based on 3-glycidoxypropyltrimethoxysilane. Electrochem. Solid-State 2010, 13, A52–A54. (18) Sivaraman, P.; Kushwaha, R. K.; Shashidhara, K.; Hande, V. R.; Thakur, A. P.; Samui, A. B.; Khandpekar, M. M. All solid supercapacitor based on polyaniline and crosslinked sulfonated poly[ether ether ketone]. Electrochim. Acta 2010, 55, 2451–2456. (19) Wang, D.; Song, P. C.; Liu, C. H.; Wu, W.; Fan, S. S. Highly oriented carbon nanotube papers made of aligned carbon nanotubes. Nanotechnology 2008, 19, No. 075609. (20) Mirmohseni, A.; Wallace, G. G. Preparation and characterization of processable electroactive polyaniline-polyvinyl alcohol composite. Polymer 2003, 44, 3523–3528. (21) Adhikari, S.; Banerji, P. Polyaniline composite by in situ polymerization on a swollen PVA gel. Synth. Met. 2009, 159, 2519– 2524. (22) Choudhury, N. A.; Shukla, A. K.; Sampath, S.; Pitchumani, S. Cross-linked polymer hydrogel electrolytes for electrochemical capacitors. J. Electrochem. Soc. 2006, 153, A614–A620. (23) Kumar, M. S.; Bhat, D. K. Polyvinyl alcohol-polystyrene sulphonic acid blend electrolyte for supercapacitor application. Physica B 2009, 404, 1143–1147. (24) Wang, Y. G.; Zhang, X. G. All solid-state supercapacitor with phosphotungstic acid as the proton-conducting electrolyte. Solid State Ionics 2004, 166, 61–67.

© 2010 American Chemical Society

(25) Ryu, K. S.; Hong, Y. S.; Park, Y. J.; Wu, X. L.; Kim, K. M.; Lee, Y. G.; Chang, S. H.; Lee, S. J. Polyaniline doped with dimethylsulfate as a polymer electrode for all solid-state power source system. Solid State Ionics 2004, 175, 759–763. (26) Cuentas-Gallegos, A.; Lira-Cantu, M.; Casan-Pastor, N.; GomezRomero, P. Nanocomposite hybrid molecular materials for application in solid-state electrochemical supercapacitors. Adv. Funct. Mater. 2005, 15, 1125–1133. (27) Sivaraman, P.; Rath, S. K.; Hande, V. R.; Thakur, A. P.; Patri, M.; Samui, A. B. All-solid-supercapacitor based on polyaniline and sulfonated polymers. Synth. Met. 2006, 156, 1057–1064. (28) Conway, B. E. Electrochemical Supercapacitors; Kluwer Academic/ Plenum Publishers: New York, 1999; pp 459-460. (29) Ganesh, B.; Kalpana, D.; Renganathan, N. G. Acrylamide based proton conducting polymer gel electrolyte for electric double layer capacitors. Ionics 2008, 14, 339–343. (30) Wang, X. F.; Ruan, D. B.; Wang, D. Z.; Liang, J. Hybrid electrochemical supercapacitors based on polyaniline and activated carbon electrodes. Acta Phys. -Chim. Sin. 2005, 21, 261–266. (31) Xiao, L.; Chen, Z.; Feng, C.; Liu, L.; Bai, Z. Q.; Wang, Y.; Qian, L.; Zhang, Y. Y.; Li, Q. Q.; Jiang, K. L.; Fan, S. S. Flexible, stretchable, transparent carbon nanotube thin film louderspeakers. Nano Lett. 2008, 8, 4539–4545. (32) Chou, S. L.; Wang, J. Z.; Chew, S. Y.; Liu, H. K.; Dou, S. X. Electrodeposition of MnO2 nanowires on carbon nanotube paper as free-standing, flexible electrode for supercapacitors. Electrochem. Commun. 2008, 10, 1724–1727. (33) Zhou, R. F.; Meng, C. Z.; Zhu, F.; Li, Q. Q.; Liu, C. H.; Fan, S. S.; Jiang, K. L. High-performance supercapacitors using a nanoporous current collector made from super-aligned carbon nanotubes. Nanotechnology 2010, 21, 345701. (34) Subramania, A.; Kalyana Sundaram, N. T.; Vijaya Kumar, G.; Vasudevan, T. New polymer electrolyte based on (PVA-PAN) blend for Li-ion battery applications. Ionics 2006, 12, 175–178.

4031

DOI: 10.1021/nl1019672 | Nano Lett. 2010, 10, 4025-–4031