Improvement of Rate and Cycle Performence by Rapid Polyaniline

ARTICLE pubs.acs.org/JPCC

Improvement of Rate and Cycle Performence by Rapid Polyaniline Coating of a MWCNT/Sulfur Cathode Feng Wu,†,‡ Junzheng Chen,† Li Li,*,†,‡ Teng Zhao,† and Renjie Chen*,†,‡ †

School of Chemical Engineering and Environment, Beijing Institute of Technology, Beijing Key Laboratory of Environmental Science and Engineering, Beijing, 100081, People's Republic of China ‡ National Development Center of High Technology Green Materials, Beijing 100081, People's Republic of China ABSTRACT: Rapid in situ chemical oxidation polymerization of polyaniline was carried out to coat MWCNT-core/sulfurshell structures. The S-coated-MWCNTs were obtained by ballmilling and thermal treatment. The polymerization was carried out by adding 2.6 g of dispersed S/MWCNT and 0.65 g of aniline hydrochloride to ethanol, and then mixing in a certain amount of ammonium peroxydisulfate dissolved in 0.2 M HCl. The addition of S/MWCNT reduced the polymerization time from 60 to 21 min. The composites were characterized by elemental analysis, FTIR, XRD, SEM, TEM, and electrochemical methods. A 70.0% sulfur, 20.2% emeraldine PANi salt and 9.8% MWCNT composite gave the typical two reduction peaks and two oxidation peaks; these are due to three polysulfide species. The initial discharge capacity was 1334.4 mAh g 1-S for the PANi-S/ MWCNT electrode and the remaining capacity was 932.4 mAh g 1-S after 80 cycles. The columbic efficiency doubled to 92.4% compared to S-MWCNT-2. The rate of the reaction upon using PANi-S/MWCNT electrode was found to be almost twice that of the S/MWCNT composites. Because of the porous polymer, the diffusion distance of the lithium ion from the bulk liquid was reduced. The gel-like cathode composites and the higher conductivities improved the kinetics of the lithium sulfur redox reaction.

’ INTRODUCTION For the widespread application of mobile devices and for potential use in electric vehicles, lithium ion batteries (LIB) and lithium ion polymer batteries have been researched and developed over the past 10 years. Their advantages include high energy densities, high operating voltages, low self-discharge rates, and no memory effects. However, with the development of a new generation of portable electronic devices and pure electric vehicles the enhancement of the capacity of the cathode is urgently needed to meet performance requirements. Since there is only one or no electron reaction during the intercalation process, the theoretical specific energy limitation of the intercalation LIB is only about 568 Wh/kg, which is not sufficient for future vehicles. Lithium/sulfur batteries, which use sulfur as a cathode and Li as an anode, have attracted considerable attention because of their high theoretical capacity (1672 mAh g 1) and specific energy (2600 Whkg 1).1 3 Additionally, sulfur is abundant, low cost, and environmentally friendly. Therefore, lithium sulfur batteries have great potential for the next generation of high energy density lithium batteries. However, the lithium/sulfur battery systems investigated previously have some critical problems.4 6 First, elemental sulfur is electrically and ionically insulating at room temperature, which leads to poor electrochemical performance and the low utilization of sulfur in the cathode. Second, Li2S and other insoluble compounds are generated and cover the active compounds during cycling, which inhibit access to lithium ions. Third, since r 2011 American Chemical Society

the discharge process of the battery is composed of many steps and generates various forms of soluble intermediate lithium polysulfide, the liquid electrolyte can dissolve and cause a rapid irreversible loss of sulfur active materials over repeat cycles. Furthermore, the spread of these polysulfides to the anode can lead to the shuttle mechanism and this may cause more serious capacity loss. Consequently, the battery suffers because of the low utilization of active materials and because of poor cycle life. Some scientists have used different kinds of conducting carbons to activate the electrochemical performance of the elemental sulfur in the cathodes.7 10 Gao et al.11,12 mixed sublimed sulfur with highly porous carbon (HPC) composites and carbon spheres, which have good conductivities and high surface areas, to prevent capacity loss during the charge discharge process. Multiwalled carbon nanotubes (MWCNT), because of its good conductivity and mechanical properties, have been used widely to improve the electrochemical performance of the materials.13 15 It have been introduced into elemental sulfur by thermal treatment or by chemical reactions.8,16,17 Therefore, sulfur coated surfaces of carbon nanotubes and composites have been successfully used in Li/S batteries. However, most of these composite MWCNT sulfur networks have obvious limitations. First, the surface areas and pore volumes of CNTs are much Received: August 17, 2011 Revised: October 17, 2011 Published: October 17, 2011 24411

dx.doi.org/10.1021/jp207893d | J. Phys. Chem. C 2011, 115, 24411–24417

The Journal of Physical Chemistry C smaller than those of active carbons, which limits their capacity to accommodate the sulfur active mass. Moreover, Li ion transport is not favored, since ion mobility can only take place along the long CNT axis and not perpendicular to it.2,16 We have previously studied polythiophene/sulfur as a core/ shell structure composite.18,19 The conducting polymer, as a shell, was found to improve the cycle life of the lithium sulfur battery, and also to increase the high-rate discharge capacities. Polyaniline, as a common conducting polymers, has been investigated as a conductor and cathode for improving battery or supercapacitor performance.20 25 In this work, polyaniline was polymerized using rapid in situ chemical oxidation polymerization to further coat the MWCNT-core/sulfur-shell structures. Polyaniline was used to prevent the dissolution of active sulfur, and also to improve lithium ion transfer to the cathode for improved performance during rate tests.

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Scheme 1. Two-Step Synthesis of the S/MWCNT and PANiS/MWCNT Composites

’ EXPERIMENTAL SECTION Preparation of the Polyaniline Coating Composites. Two synthesis steps are shown in Scheme 1. The first step is the typical procedure to prepare S-coated-MWCNTs (S/MWCNT-1).16 Initially, elemental sulfur (Alfa Aesar) and the MWCNTs (SHEN ZHEN NANOTECH PORT CO, Shenzhen, China; specific surface area 40 300 m2 g 1, diameter 10 20 nm, length 5 15 mm) (80:20,w/w) are mixed by mechanical ball milling for 5 h. The mixture was then sealed in a PTFE container filled with argon gas, and finally the container was placed in an oven at 155 °C for 24 h. The second step is the rapid coating of the S/ MWCNT. PANi was quickly polymerized using aniline hydrochloride and ammonium peroxydisulfate (NH4)2S2O8 as an oxidizer in a water ethanol mixture system.26,27 First, 0.65 g aniline hydrochloride and ammonium peroxydisulfate (both from Alfa Aesar) were dissolved in 50 mL ethanol and 50 mL of 0.2 M HCl, respectively, and 0.2 M HCl was used in the precursor solution as a dopant to obtain good quality composites with PANi. Second, 2.6 g of the MWCNT-core/sulfur-shell composite was dispersed in the ethanol solution by ultrasound. Third, the aqueous solution was slowly added to the abovementioned slurry. After the polymerization, the mixture was filtered and the remaining insoluble solid was collected. After washing with 1 M hydrochloric acid and distilled water the deepgreen mass was dried at 60 °C for 24 h under vacuum to obtain the PANi coated powder. For comparison, the S/MWCNT-2 composite was prepared at a ratio of 7:3 using the same procedure mentioned above without further polymerization. Material Characterization. Elemental analysis was carried out using an Elementar Vario MICRO CUBE (Germany), wherein the error limits for C, H, N is 0.1% and for S is 0.3%. Fourier-transform infrared (FT-IR) spectra were recorded using a Nicolet 7100 (Thermo, USA) from 2000 to 500 cm 1, 4 cm 1 resolution. XRD measurements were performed using a Rigaku X-ray diffractometer (XRD) with a Cu Kα radiation source at a scan rate of 8° min 1. The surface morphology of the composites was obtained by scanning electron microscopy (SEM, S-3500N) and transmission electron microscopy (TEM, JEM-2100). Electrochemical Measurements. The sulfur-MWCNT and PANi-coating composite cathode slurry was produced by mixing the 70% composites, 20% carbon black and 10% PVDF binder in N-methyl-2-pyrrolidinone, and then ball milling for 4 h to form a homogeneous slurry. The pure sulfur cathode slurry containing 50% sulfur, 40% carbon black and 10% PVDF binder was

prepared in the same way as the composites. After stirring, the slurry was coated onto an aluminum foil by a roll press. The coated electrodes were dried in a vacuum oven at 60 °C for 24 h. Subsequently, the electrode was cut into disks with a diameter of 11 mm. Coin-type (CR2025) cells were assembled in an argonfilled glovebox to avoid contamination by moisture and oxygen. The electrolyte used was 1 M LiTFSI in a solvent mixture of DOL: DME (1:1, v/v). The cells were discharged and charged on a LAND electrochemical station (Wuhan) from 1.5 3.0 V at different current densities-sulfur to test the cycle life. Cyclic voltammograms (CVs) were recorded on a CHI660c electrochemical workstation (Shanghai Chenhua) between 1.5 V 3.0 V to characterize the redox behavior and the kinetic reversibility of the cell. AC impedance was measured using fresh cells at the open circuit potential (OCP). This was also carried out using a CHI 660C electrochemical workstation. The AC amplitude was (5 mV. The frequency range was applied from 100 kHz to 0.1 Hz.

’ RESULTS AND DISCUSSION The oxidation of aniline is an exothermic reaction and it can easily be followed by monitoring the reaction temperature (Figure 1). A solution of aniline hydrochloride in ethanol containing the MWCNTs was mixed with an aqueous solution of the oxidant. After an induction period the next increase in the temperature was associated with the exothermic polymerization of aniline. The peak temperatures were about 41 46 °C. This indicates that the conversion of aniline to PANi was practically complete, and this was later confirmed by determining the reaction yield26 at >90%. The presence of MWCNTs in the reaction mixture significantly accelerated the rate of aniline oxidation. The addition of S/MWCNT reduced the reaction time from 60 to 21 min by shortening the induction period. The reason for the rapid polymerization is that oligomeric aniline intermediates are adsorbed at the S/MWCNT substrate and the oxidation of aniline is faster at the surface of the MWCNTs resulting in the core shell morphology of the products. In addition, the oxidation of aniline is a typical redox reaction, in which the electrons are abstracted from the aniline molecules and accepted by the oxidant, peroxydisulfate, which is converted to 24412

dx.doi.org/10.1021/jp207893d |J. Phys. Chem. C 2011, 115, 24411–24417

The Journal of Physical Chemistry C

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sulfate. This means that the S/MWCNT adsorbs the aniline and it plays a role as a conductive reactor to catalyze the polymerization. Table 1 gives the elemental weight ratio of carbon, hydrogen, nitrogen, chlorine and sulfur in the composites. The PANi ratio was calculated using the ratio of N to H, and then averaged to give 20.2%. The ratios of elemental sulfur, MWCNT and PANi in the composites were 70.0%, 9.8% and 20.2%, respectively. Figure 2 shows the FT-IR spectra of aniline, the PANi powder and the PANi-coating S-MWCNT composites. The spectral data of the products fully matches those reported previously. The bands at 1567, 1477, 1295, and 1124 cm 1 are attributed to NdQdN stretching and N B N stretching (where Q and B denotes quinoid and benzenoid). The band at 795 cm 1 is attributed to the CH-out of plane bending in 1,4-disubstituted benzene; the broad intense absorption band that extends from ∼1120 to ∼880 cm 1 is a common feature of emeraldine salt, and it often indicates that the conductivity of the polymer has improved compared with the pernigraniline base form of PANi.25 The similarity of the PANi and the PANi-coating S-MWCNT spectra indicates that sulfur and PANi did not chemically react during the polymerization. To investigate the effect of MWCNTs on the electrochemical performance of the sulfur cathode, three types of sulfur composites were used to fabricate cathodes. One was the PANi coated S/MWCNTs composite mentioned above. Another was the S-coated-MWCNTs composite with the same sulfur ratio (S/MWCNT). The third was pure sulfur with carbon black. To confirm the morphology of these composites, Figure 3 shows characteristic XRD spectra of related materials. The polyaniline only showed a broad peak centered at 2θ = 25°, which means it is a typical amorphous structure. In addition, MWCNT had no obvious peaks except for the appearance of slight and broad MWCNTs peaks centered at 2θ = 26°. An XRD analysis of elemental sulfur showed two prominent peaks at 2θ = 23 and 28° that correspond to an Fddd orthorhombic structure.28 This

indicates that no phase transformation of sulfur occurs during the preparation step, and that the sulfur particles coated the surface of the MWCNTs well. After the rapid coating of PANi the pattern was found to be the same as the above-mentioned composites. This means PANi does not affect elemental sulfur and no new phase is formed during the in situ polymerization oxidation process.29 The morphology of the PANi coating composites was observed by TEM, and is shown in Figure 4. The sulfur was coated uniformly onto the surface of the MWCNTs. The diameter of the observed MWCNT was about 10 20 nm, which means that the sulfur layer is about 40 nm compared with the MWCNTs without sulfur. In Figure 4(c), PANi was uniformly coated onto the surface of the S/MWCNT composite and was nearly 20 nm thick, and it was also connected to the MWCNTs to form an amorphous reactor. Therefore, the PANi coating can increase the electrochemical reaction sites at the surface of the nanotubes compared to all the other composites.30 Figure 5 shows typical Nyquist plots of the sulfur containing cathodes at the OCP. From these figures, it is obvious that all the Nyquist plots of the sulfur containing cathodes are composed of a semicircle at high frequencies that correspond to the solution resistance (Rs) and the charge transfer resistance (Rct), which is related to the electrochemical activities of the composites. The short, inclined line in the low frequency region is a result of ion diffusion within the cathode. Because of an effective electronically conductive network the Rct of the composites decreased from 239.6(9) Ωto 116.3(8) Ω. In addition, the PANi coating of the S/MWCNT can further reduce the Rct of the electrode to 76.2(3) Ω, and no new semicircle is present in Figure 5, which means that the polymer improves the conductivities of the composite and also reduces the lithium transfer pathway, because the porous PANi shell and bridge may adsorb some electrolytes onto the cathode from the bulk.

Figure 1. The course of aniline polymerization in the presence of CNTs.

Figure 2. FT-IR spectra of PANi and the PANi-coated composites.

Table 1. Elemental Analysis Results for PANi, S/MWCNT and PANi-S/MWCNT element weight percentage composite

C

N

H

PANi S/MWCNT-1

66.15 20.05

12.91

4.51

PANi-S/MWCNT

21.13

2.47

S/MWCNT-2

29.89

elemental S

Cl 16.43

79.95 0.96

70.00 70.11 24413

5.44

sulfur 0 80.0

MWCNT

PANi 100

20.0

70.0

9.8

70.1

29.9

20.2



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Cyclic voltammograms of the Li/S cells with two composite cathodes were obtained at a scan rate of 0.1 mV s 1, as shown in Figure 6. MWCNTs and polyaniline in the composite was electrochemically inactive in this potential range, and it only served as an electronic conductor and electrochemical reaction interface. Two reduction peaks were clear and they resulted from the multiple reaction mechanisms between sulfur and lithium, as has been reported previously.8,9,31,32 The 2.4 V anodic peaks are related to the open ring reaction that was mentioned before, and the peaks between 1.9 and 2.0 V were caused by the reduction of high order lithium polysulfides (Li2Sn, 4 < n < 8) to low order lithium polysulfides (Li2Sn, n < 4), and even to Li2S. The two oxidation peaks in the vicinity of 2.3 and 2.5 V are associated with

the conversion to lithium low order polysulfides and high order polysulfides, respectively. Compared with the S/MWCNT composite the PANi coating extended the reduction and oxidation peak areas, which proves the increase in material capacity. After five cycles the reaction peaks hardly moved, indicating that the electrochemical kinetics of the PANi coated S/MWCNT cathode were well reversible. Both the cathodic and anodic peaks of PANi coated electrode can be divided into three parts, which was shown in the inset figure of Figure 6(a). According to Levillain’s study33 35 three redox couples S32 /S3• , S4 2 /S4• , and S82 /S8 are present between the lower voltage region and the higher voltage region, which contributes to the multipeaks in the cyclic voltammograms. However, the real reactions on the electrodes are more complicated than the typical electrochemical reactions, because disproportionation reactions of the intermediate polysulfides occur during the charge/discharge process. Therefore, the reduction and oxidation peak areas are not one-to-one

Figure 3. XRD patterns of PANi, MWCNTs, the sulfur/MWCNT, and the PANI-coated composites.

Figure 5. Nyquist plots at the OCP and the equivalent circuit for the sulfur containing cathodes.

Figure 4. TEM image of (a),(b) S/MWCNT and (c),(d) PANi-S/MWCNTs. 24414



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Figure 8. Rate performance of (a) the S/MWCNT-2 composites (b) the PANi-S/MWCNT composites.

Figure 6. (a) Typical cyclic voltammograms of sulfur-containing electrodes at a sweep rate 0.1 mV s 1 (inset). The cyclic voltammograms peaks in PANi coated are fitted and shown in detail. (b) Initial charge/ discharge curves of sulfur-containing electrodes.

Figure 7. Discharge capacities vs cycle number for the sulfur-containing composites under a density of 100 mA/g. (inset) Percentage of sulfur in the electrolyte during the cycling test.

and do not correspond to that expected for a conventional battery system. Additionally, the CV results only show multistep electrochemical reactions of elemental sulfur with lithium ions.36 Figure 6(b) shows charge/discharge curves of different batteries. The discharge curves showed two typical plateaus for all the sulfur-containing electrodes, which could be assigned to a twostep reaction of sulfur with lithium during the discharge process, as shown by the CV measurements. the columbic efficiency

between the charge/discharge cycle was 38.3%, 71.9%, and 92.4%, respectively. For the sulfur cathode, without any modification and only MWCNT modified composite, soluble polysulfide dissolved into the electrolytes, so a serious shuttle mechanism happened due to the direct soak of the active sulfur mass into the electrolytes. However, the polymerization created another shell to prevent the direct contact of sulfur with the electrolytes, which led to an increase in the columbic efficiency to 92.4%. Figure 7 shows the cycle performance of the PANi coating composite cathodes. For the sulfur cathode, without any modification, the discharge capacity decreased drastically with an increase in the cycle number. After 80 cycles, the specific capacity of the sulfur electrode reduced to 237.4 mAh g 1-S, which is about 23.7% of the initial capacity. A similar observation has been reported,12 wherein the reversible capacity showed a gradual increase for the S/MWCNT-2 cathode during the first few cycles. This can be explained by its core shell structure, where the high conducting carbon materials are coated by insulating sulfur, while the redox reaction of the sulfur cathode can only occur at the surface of carbon. However, for direct contact with the electrolytes soluble polysulfide caused a serious shuttle effect in the battery system, resulting in a loss of active cathode material mass, and the life performance decreased from 958.4 mAh g 1-S for the first cycle to 540.5 mAh g 1-S after 80 cycles retaining 56.3% of the initial capacity. On the contrary, after the rapid coating of PANi the initial discharge capacity increased to 1334.4 mAh g 1S, because PANi connected the one-dimensional conductors and the S-core/MWCNTS-shell materials with each other to form a conducting network. Therefore, the use of elemental sulfur with the lithium ion was improved by incorporating the additional reactor on the surrounding PANi conductor. Furthermore, the shell polymer disconnect the direct dissolution of the active mass 24415


The Journal of Physical Chemistry C so that it gains an increase in the cycle performance of the Li/S battery. After 80 cycles the discharge capacity was 932.4 mAh g 1-S, which is much higher than that of S-MWCNT-2. To confirm how the porous structure of polymer could prevent the dissolution of the active mass, the sulfur content in electrolyte during cycling test was monitored in inset of Figure 7. Without any modification, the sulfur would dissolve into the electrolytes up to 87.5%. After the polymerization, only nearly 20% sulfur loss further proves the inhibition of sulfur dissolution of the PANi shell. Porous structure of PANi may work as an adsorbent to hold the surface electrolyte on the cathode. A same interesting phenomenon has been discovered in our previous works.18 To determine the rate performance after PANi coating, the cell was discharged galvanostatically at different specific rates ranging from 200 to 1600 mA g 1. The cell was always recharged at the same specific current, i.e., 200 mA g 1, to ensure identical initial conditions (shown in Figure 8). Compared with the S/MWCNT composites, after the PANi coating, the discharge capacities decreased with an increase in the discharge rate. However, the initial discharge capacity remained 962.8, 892.9, 699.1, and 600.1 mAh g 1-S, respectively, as the current density increased to 200, 500, 1000, and 1600 mA g 1-S. The cycle life at the different rates improved dramatically after 80 cycles, and the capacity remained at 900.5, 796.8, 639, and 447.1 mAh g 1-S, which was found to be twice that of the S/MWCNT composites. The capacity retention rate was about 93.5%, 89.2%, 91.4% and 74.5% of the initial capacity, respectively. According to Wang28 the fabrication of a cathode with more pores may be an effective way to increase the use of active materials and a decrease in capacity with high current density should result from the low ionic diffusion in the electrode.37 40 With the PANi coating, the composite gains many porous surfaces and it can therefore adsorb the electrolytes in the bulk and keep them on the cathode. Because of the porous polymer the diffusion distance of the lithium ion from the bulk liquid decreased because of the gel-like cathode composites, and the increased conductivities improved the kinetics of the lithium sulfur redox reaction.

’ CONCLUSIONS Rapid in situ chemical oxidation polymerization of polyaniline was carried out to coat MWCNT-core/sulfur-shell structures. The addition of S/MWCNT accelerated the polymerization reactions from 60 to 21 min, because the oligomeric aniline intermediates that were adsorbed at the S/MWCNT substrate started the growth of the PANI chains more readily, and MWCNT offered an electron pathway to catalyze the oxidation polymerization. The composite containing 70.0% sulfur, 20.2% emeraldine PANi salt and 9.8% MWCNT gave the typical two reduction peaks and two oxidation peaks, which could be associated to three polysulfide species. The initial discharge capacity was 1334.4 mAh g 1-S for the PANi-S/MWCNT electrode and the remaining capacity was 932.4 mAh g 1-S after 80 cycles. The columbic efficiency doubled to 92.4% compared to S-MWCNT-2. The rate performance in capacity of the PANiS/MWCNT electrode was found to be twice that of the S/ MWCNT composites. Because of the porous polymer, the diffusion distance for the lithium ion from the bulk liquid was reduced and both the gel-like cathode composites and the higher conductivities improved the kinetics of the lithium sulfur redox reaction and the cyclability of the cell.

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’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; [email protected].

’ ACKNOWLEDGMENT This work was supported by the National Key Program for Basic Research of China (2009CB220100), the International S&T Cooperation Program of China (2010DFB63370), the National 863 Program (2011AA11A256), New Century Educational Talents Plan of Chinese Education Ministry (NCET-100038), Beijing Novel Program (2010B018), and National Undergraduate Innovative Test Program (101000734). ’ REFERENCES (1) Ellis, B. L.; Lee, K. T.; Nazar, L. F. Chem. Mater. 2010, 22, 691. (2) Ji, X. L.; Nazar, L. F. J. Mater. Chem. 2010, 20, 9821. (3) Zheng, W.; Hu, X. G.; Zhang, C. F. Electrochem. Solid State Lett. 2006, 9, A364. (4) Cheon, S. E.; Ko, K. S.; Cho, J. H.; Kim, S. W.; Chin, E. Y.; Kim, H. T. J. Electrochem. Soc. 2003, 150, A796. (5) Cheon, S. E.; Ko, K. S.; Cho, J. H.; Kim, S. W.; Chin, E. Y.; Kim, H. T. J. Electrochem. Soc. 2003, 150, A800. (6) Mikhaylik, Y. V.; Akridge, J. R. J. Electrochem. Soc. 2004, 151, A1969. (7) Wu, F.; Wu, S. X.; Chen, R. J.; Chen, S.; Wang, G. Q. Chin. Chem. Lett. 2009, 20, 1255. (8) Wu, F.; Wu, S. X.; Chen, R. J.; Chen, S.; Wang, G. Q. New Carbon Mater. 2010, 25, 421. (9) Choi, Y. J.; Chung, Y. D.; Baek, C. Y.; Kim, K. W.; Ahn, H. J.; Ahn, J. H. J. Power Sources 2008, 184, 548. (10) Lai, C.; Li, G. C.; Ye, S. H.; Gao, X. P. Prog. Chem. 2011, 23, 527. (11) Zhang, B.; Qin, X.; Li, G. R.; Gao, X. P. Energy Environ. Sci. 2010, 3, 1531. (12) Lai, C.; Gao, X. P.; Zhang, B.; Yan, T. Y.; Zhou, Z. J. Phys. Chem. C 2009, 113, 4712. (13) Zhou, D.; Mei, X. G.; Ouyang, J. Y. J. Phys. Chem. C 2011, 115, 16688. (14) Wu, P.; Du, N.; Zhang, H.; Yu, J. X.; Yang, D. R. J. Phys. Chem. C 2010, 114, 22535. (15) Li, J. X.; Wu, C. X.; Guan, L. H. J. Phys. Chem. C 2009, 113, 18431. (16) Yuan, L. X.; Yuan, H. P.; Qiu, X. P.; Chen, L. Q.; Zhu, W. T. J. Power Sources 2009, 189, 1141. (17) Han, S. C.; Song, M. S.; Lee, H.; Kim, H. S.; Ahn, H. J.; Lee, J. Y. J. Electrochem. Soc. 2003, 150, A889. (18) Wu, F.; Chen, J. Z.; Chen, R. J.; Wu, S. X.; Li, L.; Chen, S.; Zhao, T. J. Phys. Chem. C 2011, 115, 6057. (19) Wu, F.; Wu, S. X.; Chen, R. J.; Chen, J. Z.; Chen, S. Electrochem. Solid State Lett. 2010, 13, A29. (20) Lei, Z. B.; Chen, Z. W.; Zhao, X. S. J. Phys. Chem. C 2010, 114, 19867. (21) Wang, K.; Huang, J. Y.; Wei, Z. X. J. Phys. Chem. C 2010, 114, 8062. (22) Liu, J. L.; Sun, J.; Gao, L. A. J. Phys. Chem. C 2010, 114, 19614. (23) Mishra, A. K.; Ramaprabhu, S. J. Phys. Chem. C 2011, 115, 14006. (24) Huang, Y. H.; Goodenough, J. B. Chem. Mater. 2008, 20, 7237. (25) Patil, D. S.; Shaikh, J. S.; Dalavi, D. S.; Karanjkar, M. M.; Devan, R. S.; Ma, Y. R.; Patil, P. S. J. Electrochem. Soc. 2011, 158, A653. (26) Konyushenko, E. N.; Stejskal, J.; Trchova, M.; Hradil, J.; Kovarova, J.; Prokes, J.; Cieslar, M.; Hwang, J. Y.; Chen, K. H.; Sapurina, I. Polymer 2006, 47, 5715. (27) Stejskal, J.; Gilbert, R. G. Pure Appl. Chem. 2002, 74, 857. (28) Wang, Q.; Wang, W.; Huang, Y.; Wang, F.; Zhang, H.; Yu, Z.; Wang, A.; Yuan, K. J. Electrochem. Soc. 2011, 158, A775. 24416



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Improvement of Rate and Cycle Performence by Rapid Polyaniline

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