and Na-Ion Batteries - American Chemical Society

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Flexible Overoxidized Polypyrrole Films with Orderly Structure as High-Performance Anodes for Li-ion and Na-ion Batteries Tao Yuan, Jiafeng Ruan, Weimin Zhang, Zhuopeng Tan, Junhe Yang, Zi-Feng Ma, and Shiyou Zheng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b08901 • Publication Date (Web): 06 Dec 2016 Downloaded from http://pubs.acs.org on December 7, 2016

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ACS Applied Materials & Interfaces

Flexible Overoxidized Polypyrrole Films with Orderly Structure as High-Performance Anodes for Li-ion and Na-ion Batteries Tao Yuana, Jiafeng Ruana, Weimin Zhangb,c, Zhuopeng Tana, Junhe Yanga, Zi-Feng Mab,c,* Shiyou Zhenga,*

a

Material Science & Engineering School, University of Shanghai for Science and

Technology, Shanghai 200093, China.

b

Shanghai Electrochemical Energy Devices Research Center, Department of

Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. c

Sinopoly Battery Research Centre, Shanghai, 200241, China.

KEYWORDS: Orderly structure; Overoxidized; Flexible; Polypyrrole film; Vapor phase polymerization; Free-standing anode; Li-ion battery; Na-ion battery

ABSTRACT: Flexible polypyrrole (PPy) films with highly ordered structures were fabricated by a novel vapor phase polymerization (VPP) process and used as the anode material in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). The PPy films demonstrate excellent rate performance and cycling stability. At a charge/discharge rate of 1 C, the reversible capacities of the PPy film anode reach 284.9 and 177.4 mAh g-1 in LIBs and SIBs, respectively. Even at a charge/discharge rate of 20 C, the reversible capacity of the PPy film anode retains 54.0 % and 52.9 % of the capacity of 1 C in LIBs and SIBs, respectively. After 1000 electrochemical

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cycles at a rate of 10 C, there is no obvious capacity fading. The molecular structure and electrochemical behaviors of Li-ion and Na-ion doping-dedoping in the PPy films are investigated by XPS and ex situ XRD. It is believed that the PPy film electrodes in the overoxidized state can be reversibly charged and discharged through the doping and dedoping of lithium or sodium ions. Because of the self-adaptation of the doped ions, the ordered pyrrolic chain structure can realize a fast charge/discharge process. This result may substantially contribute to the progress of research into flexible polymer electrodes in various types of batteries.

1. Introduction

Recently, there has been increasing market demand for light weight, thin, and flexible electronic devices, such as roll-up displays, bendable smart cards and wearable devices, for a number of special applications.1-4 Therefore, the corresponding

flexible

electrochemical

energy

storage

devices,

such

as

all-polymer-based batteries and supercapacitors, with strength, flexibility, low manufacturing costs, low self-discharge rates, endurance to over-discharge, and long cycle life have gained increasing attention.5-7 Several important conductive polymers such as polypyrrole (PPy),8, 9 polyaniline (PAN),10, 11 polythiophene (PTh)5, 12 and their derivatives have been investigated due to their high stability in air and good electrochemical properties. Compared with LIBs, room temperature sodium-ion batteries (SIBs) have received growing attention in recent years due to the lower cost and higher abundance of


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sodium resources.13,

14

The battery design architecture and reaction mechanism of

SIBs are similar to those of LIBs. One of the major challenges for SIBs is to develop suitable electrode materials that can stably support a high volume of sodium. The storage of lithium or sodium in conductive polymers is essentially through reversible p-doping (cathode) or n-doping (anode).15, 16 Song et al.17 reported a series of polymer electrodes based on anthraquinone as cathodes for LIBs that exhibited exceptional performance. Zhu et al.16 used polybithiophene as the anodic polymeric material for LIBs and SIBs and revealed the different redox mechanisms of the polymer when used as an anode or a cathode, respectively. An all-polymer SIB was reported by Zhu et al.18 using poly(aniline/o-nitroaniline) as the cathode and poly(anthraquinonyl sulfide) as the anode, which exhibited stable electrochemical properties. However, both polyanthraquinone and polybithiophene are expensive and not ideal for commercial applications. Among the conductive polymers, PPy has attracted the most attention due to its excellent characteristics, including its relatively low cost, notable redox properties, good electrical conductivity, biocompatibility, and chemical stability.8, 9, 19, 20 Most commonly, PPy is used as an effective electrically conductive coating layer to improve the electrochemical performance of metal or metal oxide electrodes, such as SnO2-PPy,21 Fe3O4-PPy,22 ZnFe2O4-PPy,23 MnCo2O4-PPy,24 and Sb/Sb2O3-PPy,25 in LIB and SIB applications. In these composites, the PPy coating layer acts as either a protective layer or the conductive framework to prevent structural collapse during cycling. However, few reports have used PPy as the anode independently. In addition, in numerous reports, PPy is usually



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prepared by electrochemical26-28 or chemical29, 30 oxidation techniques from pyrrole monomers. The electrochemical polymerization method is not suitable for scaling up and cannot be used with non-conducting surfaces. Traditional chemical oxidation, by contrast, is the most well-known synthetic route and is less restricted by the substrate, but it can hardly form a single continuous film.

In this work, we produced a continuous flexible PPy film via a simple, inexpensive and scalable vapor phase polymerization (VPP) method with ferric p-toluenesulfonate (Fe(III) tosylate) as the oxidant. The obtained PPy film possesses a stable continuous structure and a smooth surface. In addition, because of the modified oxidant (Fe(III) tosylate), the PPy film exhibits an ordered structure. As we know, during the discharge process, the cations (Li+ or Na+) stored between the chain layers of the polymers will combine with oxygen atoms to form oxides. Therefore, the distance between the chain layers is important for cation insertion and extraction, especially for sodium ions, which have a larger atomic radius. Therefore, the ordered chain-layer structure makes it suitable for LIB and SIB electrode applications. The structural transformation and the electrochemical mechanism during the charge/discharge processes of the PPy films in LIBs and SIBs are discussed.

2. Experimental Section

2.1. Synthesis of PPy film electrode.

The PPy films were synthesized by a vapor phase polymerization method. Briefly,


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Fe(III) tosylate (Sigma Aldrich) solution (30 % in n-butanol solvent) was spread on the surface of a glass substrate. The coated glass substrate was dried at 75 °C and then exposed to pyrrole vapor at room temperature. After 15 mins, the color of the oxidant coating turned to brown, which indicated the formation of PPy. The film was then peeled off from the glass by soaking in ethanol solvent, follow by drying in air.

2.2. Characterization

The morphologies and microstructure of the samples were studied using a FEI Nova SEM 230 equipped with ultra-high resolution Field Emission Scanning Electron Microscope (FE-SEM) (INCA X-Max 80, Oxford Instruments), and a TEM (JEM-2100F, JEOL Ltd., Japan). X-ray diffraction (XRD) measurement was carried out by Rigaku D/MAX-2200/PC X-ray diffractometer with a Cu Kα radiation source for characterizing the polymer chain layer structure property. The Raman spectroscopy of the PPy film was obtained using a Dispersive Raman Microscope (Senterra R200-L, Germany). X-ray photoelectron spectrometer (XPS, Kratos Axis Ultra DLD) was used to analyze the surface elements and molecular structure of the PPy film.

2.3. Electrochemical measurements

The LIB and SIB electrochemical performances were both measured using 2032 coin cells in a half-cell system at room temperature. The PPy film was cut into round pieces with a diameter of 1.4 cm, which was used as the electrode directly.



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Conducting additives or binders were not required for electrode fabrication. After being dried in a vacuum oven at 100 °C for 24 hrs, the PPy film electrodes were transferred into the glove box. For LIBs, lithium metal was used as the counter and reference electrode. A Celgard 2400 film was used as the separator. In addition, 1 M LiPF6 in EC/DMC (1:1) was used as the electrolyte. For SIBs, the coin cells were assembled with sodium metal as the counter and reference electrode, and 1 M NaClO4 in DMC/EMC (1:1) as the electrolyte. The charge/discharge electrochemical performances were examined under a constant current mode using a LANHE CT2001A battery test system (Wuhan Jinnuo Electronics, Ltd.) over a potential range of 0.01 and 3.0 V vs. Li/Li+ or Na/Na+. Cyclic voltammetry (CV) was carried out on a Gamry Reference 3000 Potentiostat (Gamry Co., USA) from 0.01 V to 3.0 V at a scan rate of 0.1 mV s-1.

Samples for ex situ XRD analysis were prepared as follows. The cells were slowly discharged/charged under constant current mode to pre-set potentials, and then the potential was maintained under constant voltage mode (discharge rate is approximately 0.5 mA g-1). Once a stable potential was reached, the coin cell was removed from the battery test system and disassembled in a glove box to remove the PPy film electrode. After being rinsed three times with dimethyl carbonate and dried under Ar, the specified PPy film was characterized by XRD measurement.

3. Results and discussions

3.1. Structural and morphological features


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The PPy films were prepared by the VPP technique. The synthetic mechanism is shown in Figure 1. We used Fe(III) tosylate as the oxidant because organic sulfonates can not only produce smoother PPy films but also effectively restrain the crystallization of dried oxidant layers compared with FeCl3 oxidants.31 Once the slide was coated, the dried Fe(III) tosylate layer was transferred into a pyrrole vapor chamber under ambient conditions, and the polymerization reaction of the pyrrole monomer began. At that moment, the pyrrole monomer was oxidized by Fe3+ to generate a cation radical, and then two cationic free radicals combined to form a bipyrrole. Long PPy chains were thus formed as the reaction continued. After polymerization, the slides were transferred to an ethanol solution to remove the reduced Fe(II) tosylate and residue pyrrole monomers. Meanwhile, the intact PPy films fell off the slide. Figure 2 (a, b) shows the typical digital photos and SEM images of the obtained PPy films. The PPy films show good flexibility and homogeneous morphology with a cross-linked continuous array structure, and all polymer chains are in an oriented arrangement. As observed from the SEM image, the film fiber diameter is 40-60 nm.

Figure 1 Schematic diagram of PPy film preparation.



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Figure 2 (a) digital photograph and (b) SEM image of PPy film.

Figure 3 shows the XRD pattern of the PPy film, which displays two obvious peaks at approximately 2θ=15.5° and 22.4°. It has been reported that the peak at 15.5° (corresponding to a d-spacing of 5.33 Å) arises due to the distance between the pyrrolic planes and the interfaced aromatic rings.32,

33

The peak situated at 22.4°

(corresponding to a d-spacing of 3.97 Å) is attributed to the interplanar distance of two pyrrole rings in the PPy film.34 The d-spacing (~0.53 nm) of the pyrrolic planes is also observed clearly in the HR-TEM lattice image, which is in good agreement with the XRD observation of a peak at 2θ=15.5° for the PPy film. In some reports, PPy exhibited as an amorphous polymer or only a broad peak in the range of 20-25°. 35-37 Therefore, the current result demonstrates that the well-ordered structural arrangement of the PPy film can be achieved by the VPP approach. This may be due to the oxidant Fe(III) tosylate framework possessing an orderly arrangement through electrostatic and van der Waals forces. Thus, the subsequent polymer chains present the same ordered structure. Fortunately, this ordered structure is helpful in improving the electrical conductivity.38, 39


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Figure 3 XRD pattern and HR-TEM image (inset) of PPy film.

The ordered structure of the obtained PPy film is also proven by the Raman result. As shown in Figure 4 (a), the Raman spectrum of the PPy film has similar characteristics to those of carbon-like materials.40 Two featured Raman peaks at approximately 1570 and 1350 cm-1 were observed in Figure 4 (a). The two bands are always interpreted as the G-band (“graphitic” band, C=C stretching mode of the PPy molecule) and the D-band (“disorder” band, heteroatom defect in PPy).41,

42

The

intensity ratio of the D-band to G-band (ID/IG) is often used to quantify the system disorder. For the PPy film, the calculated intensity ratio ID/IG is 0.83, indicating that the PPy film possesses a suitable degree of order, which coincides with the XRD and TEM results. More detailed information on the surface elements in the PPy film was obtained by XPS analysis. As shown in Figure 4 (b), the PPy film is mainly composed of the elements C, N, and O, along with a small amount of S. The elements and their ratios in the PPy film are displayed in Table 1. The carbon and nitrogen elements originate



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from the pyrrole monomer. Notably, the high proportion of O (8.8 at.%) in the PPy film demonstrates that the obtained PPy sample is in an overoxidized state. In addition, the appearance of sulfur (S 2p at ~167 eV and S 2s at ~230 eV) in the XPS profile means that the PPy molecular chains are doped by a small amount of sulfur. The sulfur atoms should come from the sulfonate of the oxidant. Many previous reports have stated that heteroatom N or S doping can enhance the capacity and rate performance of electrode materials.43, 44

Figure 4 (a) Raman spectrum; (b) XPS survey spectrum and High-resolution XPS spectra of (c) C 1s, (d) O 1s and (e) N 1s of PPy film; (f) Schematic molecular configurations of overoxidized PPy according to the High-resolution XPS spectra analysis.


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The high-resolution C 1s, O 1s and N 1s XPS analysis of the PPy film reveals the structure of the PPy film. As shown in Figure 4 (c), The C 1s peak is decomposed into six components at 284.1, 284.6, 285.4, 286.1, 287.9 and 289.2 eV, and their assignments and percentage compositions are displayed in Table 2. The peaks at 284.1, 284.6 and 285.4 eV are assigned to the -CH- (β-carbons), C-C/C=C and C-N (α-carbons) bonds, respectively, which are the carbon chemical bonds in the PPy molecular chains.45, 46 The peaks at 286.1, 287.9 and 289.2 eV are attributed to the O-C=O, C=O and C-O/O-C-O bonds, respectively, indicating a large proportion of C atoms are combined with O atoms.47 To determine the binding formation of the C and O atoms, the O 1s peak was further analyzed. As shown in Figure 4 (d), the O 1s peak is decomposed into two components, including C=O at 531.3 eV and C-OH at 532.9 eV (Table 2).48 In particular, the C=O bond is remarkable, confirming most of the C=O groups in the obtained PPy film sample. For the N 1s components in Figure 4 (e), the largest peak at 399.6 eV is assigned to the normal N in pyrrole (-NH-) with a percentage of 65.1 %, which indicates that most of the N is contained in pyrrolic rings.49 More significantly, the C-N+ and C=N+ components appear at a higher binding energy of the N 1s peak, indicating polarons and bipolarons of N atoms are formed in the PPy film under the influence of overoxidation.48 Based on the above analysis, the most likely structure of the obtained PPy film is exhibited in Figure 4 (f). Such overoxidized state shows the possibility of producing PPy film as an anodic material for LIB and SIB applications.

3.2. Electrode performance



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The electrochemical performance of the as-obtained PPy films was explored as freestanding anodic electrode materials for LIBs and SIBs.

3.2.1. Electrochemical performance of the PPy film for LIBs

Figure 5 (a) shows the cyclic voltammetry (CV) measurement of the PPy film electrode for the first ten cycles in a voltage range of 0.01 to 3.0 V vs. Li/Li+ at a scan rate of 0.1 mV s-1. In the first cathodic branch, an irreversible reduction peak is observed at approximately 1.42 V, which may be attributed to the increase in the surface energy of the PPy film as the lattice spacing expands during lithium insertion.9 This peak disappears in the subsequent cycles. This implies that the loss of surface energy due to lattice spacing expansion only occurs in the first cycle. In addition, there are two additional reversible redox couples. The coupling of the reduction peak at 0.5 V and the oxidation peak at 1.1 V reflects the lithium storage process, i.e., the reversible formation and reduction of Li-O bonds.9 The larger reduction peak area in the first cycle may be caused by electrolyte decomposition and the formation of a solid electrolyte interface (SEI) film on the surface of the PPy anode.50, 51 Moreover, this redox couple appears in subsequent cycles, implying good stability and reversibility of the Li-doped and dedoped PPy molecular chains after the initial cycle. In addition, the other reversible redox peak couple above 2.5 V may be due to the deeper redox reaction of the formation of Li2O, which can occur at high potential or in the presence of a catalyst.9


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Figure 5 (a) First ten cyclic voltammograms curves of PPy film electrode vs. Li at the scanning rate of 0.1 mV s-1; (b) Initial three discharge/charge profiles at 0.2 C (c) Rate performance and (d) Cycling performances of PPy film as anodes of LIBs.

The first three discharge (Li doping) and charge (Li dedoping) profiles of the PPy film are presented in Figure 5 (b). At a current rate of 0.2 C (60 mA g-1), the initial reversible capacity is as high as 309.8 mAh g-1. The initial columbic efficiency reaches 71.1 %. During the first cycle, the discharge potential plateau (at approximately 1.5 V) and other mild charge/discharge slope inflexions are all in good agreement with the CV results. After the first cycle, the remaining reversible capacity stabilizes. Notably, the high rate performance of the PPy film anode is presented in Figure 5 (c). The reversible capacities are 284.9, 248.0, 209.0, 175.8 and 153.8 mAh



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g-1 at 1, 2, 5, 10 and 20 C, respectively. At 20 C (discharge lasts only 3 mins), 54.0 % of the reversible capacity of 1 C is preserved, indicating that the obtained PPy electrode could be adapted for flexible high power energy storage devices. Figure 5 (d) shows the cycling performance of the PPy film electrode at 10 C over 1000 cycles. The reversible capacity gradually increased from 162.0 to 255.5 mAh g-1 in the first 182 cycles, which may be due to the growth of the reversible interfacial Li storage in the polymer film52, 53, which was also shown in the CV results. With an increase in the number of cycles, the current of the redox peaks above 2.5 V in Figure 5 (a) correspondingly increases. This phenomenon of upward capacities with cycling is also observed in other LIBs anodic materials.54,

55

In the subsequent cycles, the

discharge capacities are stable at ~215 mAh g-1, which indicates that the PPy film anode has excellent reversible cycling performance.

3.2.2. The electrochemical performance of the PPy film for SIBs

Because of the much lower cost and abundance of Na resources, SIBs are now being pursued as potential alternatives to current LIBs for possible electric energy storage. However, the lack of suitable anode materials is one of the critical issues for SIBs. Therefore, the development of the Na+-storage mechanism in overoxidized PPy films will open a new path to flexible polymeric electrodes for SIBs.


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Figure 6 (a) First ten cyclic voltammograms curves of PPy film electrode vs. Na at the scanning rate of 0.1 mV s-1; (b) First three discharge/charge profiles (c) Rate performance and (d) Cycling performances of PPy film as anodes of SIBs.

Electrochemical measurements of PPy films for Na-ion storage were carried out in a half-cell conformation with a sodium metal counter electrode and a 1 M NaClO4/DMC/EMC electrolyte. Figure 6 (a) shows the CV curves of the PPy film electrode for the first ten cycles in a voltage range of 0.01 to 3.0 V vs. Na/Na+ at a scan rate of 0.1 mV s-1. Unlike the CV profiles of the LIBs in Figure 5 (a), the CV curves of the SIBs show only one couple and no obvious redox peaks (reduction peak at 1.1 V and oxidation peak at ~1.7 V), which is due to the process of Na+ doping/dedoping in the PPy molecules. In the first cycle, the broad peak of larger area



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may arise from the formation of SEI films. The CV curves were very similar from the 3rd to the 10th cycle, implying the high reversibility and stability of the PPy film as an anodic electrode in SIBs. The discharge and charge profiles for the initial three cycles at a charge/discharge rate of 0.2 C in SIBs are shown in Figure 6 (b). Similar to the LIBs, the PPy film electrode presented an initial irreversible discharge capacity in the first cycle, again caused by electrolyte decomposition and deposition of the SEI film on the PPy anode. The charge/discharge coulombic efficiency rises to almost 100 % in subsequent cycles. To obtain information on its rate performance, the rate capability of the PPy film as an SIB anode was evaluated. Shown in Figure 6 (c) are the corresponding charge-discharge profiles with high rates from 1 to 20 C. At discharge rates of 1, 2, 5, 10 and 20 C, the reversible capacities reached 177.4, 151.9, 135.5, 118.2, and 93.8 mAh g-1, respectively, exhibiting excellent rate performance as an Na-storage electrode. Figure 6 (d) presents the Na-cell cycling performance of the as-synthesized PPy film electrode. At the initial stage, the reversible capacity is ~149.1 mAh g-1 at a rate of 10 C, and 86.5 % is retained after 1000 cycles with ~100 % coulombic efficiency.

3.3. Structural changes in the PPy electrode during the charge-discharge process in LIBs and SIBs

To understand the doping/dedoping processes of the Li ions and Na ions in the PPy anodic electrode, ex situ XRD analyses were conducted during the initial cycling of the LIBs and SIBs at selected cell voltages. Figure 7 (a) shows the ex situ XRD data


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of the PPy electrode in the LIB. The ex situ XRD curves correspond to the potentials from a to i marked in Figure 5 (b). The main XRD peaks of the PPy film electrode in the initial state of discharge were located at 2θ=15.5° and 22.4°, which are similar to the XRD peaks of the original PPy film in Figure 3. When discharge occurs, the diffraction peaks of the PPy electrode at 15.5° and 22.4° are gradually widened and shrunk, indicating that the ordered pyrrolic plane interspaces decrease during lithiation. During the de-lithiation process, the two peaks in the ex situ XRD curves from points f to i appear gradually. The ex situ XRD data of the PPy electrode in the SIB show the same behavior during the initial discharge-charge process (Figure 7 (b)). This phenomenon has also been reported in other anodic electrodes.56 In addition, it is worth noting that the ex situ diffraction peak at 2θ=15.5° shifts to a slightly lower angle after the initial discharge-charge cycle. This phenomenon may indicate that after intercalation of Li+/Na+ into the PPy electrode, the spacing between the PPy chains increases slightly.



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Figure 7 Ex-situ XRD patterns evolution of PPy film electrodes during intercalation and de-intercalation of (a) Li-ions and (b) Na-ions.

As we know, the Li+ storage mechanism of PPy displays reversible n-doped behavior.15 From the XPS and ex situ XRD results, the Li and Na storage mechanism of the PPy films is proposed as follows: upon discharge, Li ions or Na ions are stored along the polymer backbones of the PPy film (Figure 8) and may combine with oxygen atoms according to the reaction in Equation (1).


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OLi/Na

O

Li+/Na+, eN

N

H

H

(1)

Accordingly, the ordered layer structure decreases during the discharge process. The Li-O or Na-O bond is decomposed during the recharging process. Meanwhile, the ordered layered structure of the pyrrolic chains is restored. However, after Li-ion or Na-ion storage, the d-spacing between the pyrrolic chain layers increases slightly due to the flexibility of the polymer. Therefore, it means that the PPy film has a memory effect to self-adapt to the intercalated ionic radius. Such structural change is beneficial to subsequent cell cycling.

Figure 8 Schematic diagram of Li+/Na+ -ions storage in PPy films.

4. Conclusions

In summary, a facile VPP method was proposed to synthesize PPy films as



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free-standing anodes for both LIBs and SIBs. The PPy films possess a highly ordered, layered structure of pyrrolic chains and present excellent rate capability and cycling stability. The specific capacity is maintained at 216.7 mAh g-1 for LIBs and 129.0 mAh g-1 for SIBs, even at 10 C after 1000 cycles. The repeated discharge/charge processes do not change the orderly structure of the PPy films, showing a self-adapting effect for the intercalated ions. Our results indicate that the overoxidized PPy films derived from the VPP method are promising free-standing anode materials for flexible LIBs and SIBs. It is believed that the PPy films can be applied not only to LIBs and SIBs but also to many different electrochemical energy devices, such as aluminum-ion and magnesium-ion batteries.

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected]; [email protected]

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the support of the National Science Foundation of China (21403139, 51472161, 51472160, 51671135, 21336003, 21676165), the Key Program for the Fundamental Research of the Science and Technology Commission of Shanghai Municipality (15JC1490800, 12JC1406900), the Shanghai Pujiang Program (No. 14PJ1407100), and the International Cooperation Program of the Science and Technology Commission of Shanghai Municipality (14520721700). We


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acknowledge the support of the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning (TP2014048), the support for young teachers in Shanghai colleges and universities (ZZsl15059) and the Hujiang Foundation of China (B14006).

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Tables

Table 1 Elemental composition of PPy films. Elements

C

N

O

S

Ratios (%at.)

78.6

11.4

8.8

1.2

Table 2 Assignments and percentage composition in the C 1s, O 1s and N 1s region of PPy film. Functional group Binding energy (eV) Ratios (%area) -CH-, β-carbons

284.1

27.4

C-C / C=C

284.6

23.3

C-N, α-carbons

285.4

11.0

C-O, O-C-O

286.1

31.7

C=O

287.9

2.4

O-C=O

289.2

4.2

C=O

531.3

86.5

C-OH

532.9

13.5

C=N

397.9

12.1

-NH-, pyrrole

399.6

65.1

C-N+

401.1

16.2

C=N+

402.7

6.6

C 1s

O 1s

N 1s


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Table Of Contents (TOC) Graphic：：



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Figure 1 Schematic illustration of the synthesis process of PPy film. Figure 1 214x223mm (300 x 300 DPI)


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Figure 2 (a) digital photograph and (b) SEM image of PPy film. Figure 2 214x223mm (300 x 300 DPI)



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Figure 3 XRD pattern and HR-TEM image (inset) of PPy film. Figure 3 214x223mm (300 x 300 DPI)


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Figure 4 (a) Raman spectrum; (b) XPS survey spectrum and High-resolution XPS spectra of (c) C 1s, (d) O 1s and (e) N 1s of PPy film; (f) Schematic molecular configurations of overoxidized PPy according to the High-resolution XPS spectra analysis. Figure 4 214x223mm (300 x 300 DPI)



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Figure 5 (a) First ten cyclic voltammograms curves of PPy film electrode vs. Li at the scanning rate of 0.1 mV s-1; (b) First three discharge/charge profiles (c) Rate performance and (d) Cycling performances of PPy film as anodes of LIBs. Figure 5 214x223mm (300 x 300 DPI)


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Figure 6 (a) First ten cyclic voltammograms curves of PPy film electrode vs. Na at the scanning rate of 0.1 mV s-1; (b) First three discharge/charge profiles (c) Rate performance and (d) Cycling performances of PPy film as anodes of SIBs. Figure 6 214x223mm (300 x 300 DPI)



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Figure 7 Ex-situ XRD patterns evolution of PPy film electrodes during intercalation and de-intercalation of (a) Li-ions and (b) Na-ions. Figure 7 214x223mm (300 x 300 DPI)


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Figure 8 Schematic representation of Li+/Na+ -ions storage in PPy films. Figure 8 214x223mm (300 x 300 DPI)


and Na-Ion Batteries - American Chemical Society

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