graphite oxide@sulfur composites for high-rate lithium-sulfur batteries

Accepted Manuscript Title: Interface polymerization synthesis of conductive polymer/graphite oxide@sulfur composites for high-rate lithium-sulfur batteries Author: Xiwen Wang Zhian Zhang Xiaolin Yan Yaohui Qu Yanqing Lai Jie Li PII: DOI: Reference:

S0013-4686(14)02601-2 http://dx.doi.org/doi:10.1016/j.electacta.2014.12.142 EA 24018

To appear in:

Electrochimica Acta

Received date: Revised date: Accepted date:

16-9-2014 22-12-2014 23-12-2014

Please cite this article as: Xiwen Wang, Zhian Zhang, Xiaolin Yan, Yaohui Qu, Yanqing Lai, Jie Li, Interface polymerization synthesis of conductive polymer/graphite oxide@sulfur composites for high-rate lithium-sulfur batteries, Electrochimica Acta http://dx.doi.org/10.1016/j.electacta.2014.12.142 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Interface polymerization synthesis of conductive polymer/graphite oxide@sulfur composites for high-rate lithium-sulfur batteries Xiwen Wang, Zhian Zhang*, Xiaolin Yan, Yaohui Qu, Yanqing Lai, Jie Li School of Metallurgy and Environment, Central South University, Changsha, Highlights 410083, China

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*Corresponding author.

A hybrid nanostructure that incorporate the merits of conductive polymer nanorods and

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Highlights

A novel approach based on interface polymerization for synthesizing CP/GO@S ternary

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graphite oxide sheets.

CP/GO@S ternary composite cathode shows enhanced electrochemical properties

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composite.

PEDOT/GO@S composite is the material system that have best electrochemical

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

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compared with CP@S binary composite cathode.

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performance in all CP/GO@S ternary composites.

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Abstract

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The novel ternary composites, conductive polymers (CPs)/graphene oxide

(GO)@sulfur composites were successfully synthesized via a facile one-pot route and used as cathode materials for Li-S batteries The poly(3,4-ethylenedioxythiophene) (PEDOT)/GO and polyaniline (PANI)/GO composites were prepared by interface polymerization of monomers on the surface of GO sheets. Then sulfur was in-situ

deposited on the CPs/GO composites in same solution. The component and structure of the composites were characterized by XPS, TGA, FTIR, SEM, TEM and electrochemical measurements. In this structure, the CPs nanostructures are believed to serve as a conductive matrix and an adsorbing agent, while the highly conductive GO will physically and chemically confine the sulfur and polysulfide within cathode. The PEDOT/GO@S composites with the sulfur content of 66.2 wt% exhibit a

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reversible discharge capacity of 800.2 mAh g-1 after 200 cycles at 0.5 C, which is

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much higher than that of PANI/GO@S composites (599.1 mAh g-1) and PANI@S

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retain a high specific capacity of 632.4 mAh g-1.

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(407.2 mAh g-1). Even at a high rate of 4 C, the PEDOT/GO@S composites still

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1. Introduction

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Recently, with increasing demand of green and renewable energy, great efforts

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have been devoted to develop advanced secondary battery systems with high energy

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density and high power density. Among them, lithium-sulfur (Li-S) batteries is one of

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most attractive candidates due to its high theoretical capacity of 1675 mAh g-1, high

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theoretical energy density of 2600 Wh kg-1, low cost and natural abundance of sulfur

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[1-3]. However, the practical application of Li-S batteries is still limited because of the insulating nature of sulfur, the solubility of polysulfide as well as large volume

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expansion during discharge [4]. Therefore, a novel material design strategy is essential to address the above issues, especially for the dissolution of polysulfide. Tremendous attentions have been focused on the porous carbon materials with different structure and morphology, which could improve electrical conductivity of

electrode, buffer volume expansion during discharge and inhibit the dissolution of polysulfide [5]. Conducting polymers such as polyacrylonitrile (PAN) [6-8], polyaniline (PANI) [9-11], polypyrole (PPY) [12-14], polythiophene (PTH) [15], poly(3, 4-ethylenedioxythiophene) (PEDOT) [16, 17] have also been widely explored as a coating layer or a conductive matrix in sulfur composites, based on their controllable morphologies, good electrochemical stabilities and good compatibility

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with sulfur. Cui also found that the effect of the different conductive polymers on

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improving the long cycling stability and high-rate performance of sulfur cathode

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decreased in the order of PEDOT > PPY > PANI [18]. However, the CP@S

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composites still exhibit relative poor conductivity and limited rate capacities.

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Therefore, incorporating carbon with CP@S composites would be an optimized

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strategy to enhance the electrochemical performance. This ternary nanostructure not

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only serves as highly conductive matrix to load abundant active sulfur, but also

sulfur

with

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integrated

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displays co-adsorption with polysulfide [19]. It is also noted that muti-composites both

carbon

and

conductive

polymers,

such

as

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sulfur/graphene/PPy [19] or PAN [20], sulfur/carbon nanotubes/PANI [21] or PPy [22]

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and sulfur/carbon black/Nafion [23] have proved to be effective on improving the

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cycle stability and high-rate capability of the sulfur cathode. Graphene nanosheets as an emerging two-dimensional carbon nanomaterial with

high surface area of 2630 m2 g-1, excellent intrinsic electric conductivity, superior mechanical flexibility and chemical stability, have been considered as an ideal matrix or coating layer for the cathode in advanced lithium-sulfur batteries [24-26].

Graphene oxide (GO) has been explored as a good matrix to anchor sulfur due to the abundant oxygenate functional groups on its surface that absorbs the polysulfides via chemical interaction [27-29]. GO could both physically and chemically suppress the dissolution and diffusion of the polysulfides anions in liquid electrolyte. Moreover, the highly functionalized graphite oxide will form stable dispersions in water, which

size [30] or modified by some functionalized polymers [31].

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make it possible to prepare hybridized materials with controllable morphology and

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Herein, we report a simple one-pot synthesis of CP/GO@S ternary composites

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with a hierarchical nanostructure via interface polymerization of CPs nanostructures

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onto GO, and the subsequent deposition of sulfur nanoparticles to CP/GO binary

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composites in aqueous solution, as illustrated in Fig. 1. It is found that this ternary

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composites can afford a large reversible capacity with high Coulombic efficiency,

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excellent cyclic and rate performance, highlighting the importance of a multiplex

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fixing strategy of sulfur using graphite oxide and conductive polymer for maximum

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utilization of active sulfur in Li-S cells. Moreover, the PEDOT/GO@S composites

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have been proven to be the better option that can achieve a long cycle life and

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high-rate capability for Li-S cells in many CP/GO@S ternary composites.

2. Experimental

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2.1 Preparation of CP/GO@S composites GO was prepared from natural graphite powder by a modified Hummers method [32]. The GO was dispersed into distilled water by ultrasonic agitation for 2 h. The transparent orange-yellow sodium polysulfide (Na2Sx) solution was prepared by

dissolution of stoichiometric quantity sulfur into Na2S solution [27]. Firstly, PEDOT/GO hybrids were synthesized via the interfacial polymerization method. Typically, 5 mL FeCl3 (1 M) aqueous solution as an oxidant was added into 5 mL GO dispersion (1 mg mL-1). Subsequently, the above solution was added slowly into 10 mL of EDOT solution in CHCl3 (0.2 M). The above mixture was kept at 60 °C under static conditions. The dark green products were produced on the interface and

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gradually dispersed into aqueous solution. Finally, the organic solvent at the bottom

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was removed and the Na2Sx solution was added drop-wise. Upon the addition of

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Na2Sx solution, the yellow sulfur precipitates were immediately formed due to the

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acidic and oxidative property of FeCl3 solution. After stirred for 12 h, the precipitate

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was filtered and washed with ethanol and distilled water several times. The obtained

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products were dried at 50 °C in oven for 24 h. For the preparation of PANI/GO@S

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composites, the polymer monomer was changed. 0.2 mL aniline monomer was firstly

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added into CHCl3 solution and followed by the unchanged procedures of

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of GO.

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PEDOT/GO@S composites. PANI@S composite were fabricated without the addition

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2.2 Materials characterization The morphology was characterized by scanning electron microscope (SEM,

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Nova NanoSEM 230) and transmission electron microscope (TEM, JEOL JEM-2100F). The Fourier transform infrared spectra (FT -IR) were recorded on a Nicolet560 spectroscopy with KBr pellet technique. Raman spectra were test with Dior LABRAM-1B instrument. X-ray photoelectron spectroscopy (XPS) was

performed on a Thermo Fisher ESCALAB250xi XPS system. The XPS curve-fittings were performed using the XPS Peak 41 program with Gaussiane-Lorentzian functions after subtraction of a Shirley background. The fitting errors of XPS test results using this method are within ±1%. The sulfur content of the composites was determined by thermogravimetric (TGA) analysis (SDTQ600). 2.3 Cell assembly and electrochemical measurements

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The sulfur containing composites powder was mixed with Super-P carbon black

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(Timcal) and Poly(acrylic acid) binder (Aldrich), with mass ratio of 70: 20: 10, in

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suitable amount of distilled water to produce electrode slurry. The slurry was coated

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onto aluminum foil current collector (20 μm thickness) by a doctor blade and dried in

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vacuum oven at 50 °C for 12 h. The typical mass loading of active sulfur was ~1.5 mg

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cm-2. The electrochemical characterization was performed using a CR-2025 type coin

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cell using Celgard 2400 separator and filled with 30 μL liquid electrolyte. These cells

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are assembled in an argon-filled glove box (Universal 2440/750) in which oxygen and

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water contents were less than 1 ppm. 1 M bis (trifluoromethane) sulfonamide lithium

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salt (LiTFSI, Sigma Aldrich) and 0.1 M LiNO3 in a mixture of 1,3-dioxolane (DOL)

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and 1,2-dimethoxyethane (DME) (v/v, 1:1) was used as the electrolyte. Galvanostatic measurements were carried out using a LAND CT2001A

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charge-discharge system. The cells were first discharged to 1.5 V and then the cycle numbers was counted. Electrochemical impedance spectroscopy (EIS) measurement were conducted with PARSTAT 2273 electrochemical measurement system in the frequency range of 100 kHz to 0.01 Hz with an AC amplitude of 5 mV. All the

electrochemical tests were conducted at room temperature.

3. Results and discussion The morphology and microstructure of PANI PANI/GO@S and PEDOT/GO@S composite were investigated by SEM, and shown in Fig. 2. In Fig. 2a, some large sulfur crystallites in size of 1~2 μm coated with extra layer of PANI nanorods can be obviously observed in PANI@S composites. As for the PANI/GO@S composites, the

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SEM image (Fig. 2b) shows plenty of crooked PANI nanorods and crumpled graphite

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oxide sheets. The existence of sulfur is difficult to identify in PANI/GO@S

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composites. It means that the GO film have completely restricted the sulfur within the

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PANI/GO structure and would contributes to a lower degree of polysulfide dissolution

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during cycling process. It can be seen that the PEDOT/GO hybrids consist of a large

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amount of PEDOT nanorods and layered GO nanosheet in Fig. 2c. Different from the

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PANI nanorods in PANI@S and PANI/GO@S composites, the PEDOT nanorods are

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ordered. It also found that the PEODT/GO composites prepared by this interface

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polymerization method are same to the previous reports [33]. After the incorporation

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of sulfur, no large bulk sulfur particles can be easily observed on the surface of the

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PEDOT/GO@S composites (Fig. 2d), implying the sulfur particles are also embedded

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in the PEDOT/GO matrix. A high magnification TEM image (Fig. 3a) reveals that the PANI nanorods in

diameter of about 100 nm are distributed on the sulfur core evenly in PANI@S composites. In contrast, Fig. 3b further indicates that the PANI nanorods and sulfur were tightly covered by GO film in GO/PANI@S composites. As observed in Fig. 3c,

a large amount of the PEDOT nanorods decorate on graphite oxide, and have a width of 30~40 nm and a length of 200~300 nm. After the precipitation of sulfur, the PEDOT/graphite oxide composites still remain the similar 3D-hybrid architecture, while the irregular sulfur microparticles (2 μm) can be detected in a low magnification TEM image (Fig. 3d). As investigated in previous reports [20, 34-36], this unique ternary hybrid which are combination of 1D nanostructure, 2D GO or graphene

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nansheets and sulfur could afford much improved electrochemical performance due to

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(1) the porosity of CP/GO structure, which is beneficial to the sulfur filling and the

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physical absorption of polysulfide anions; (2) the robust connection between the CP

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nanorods and GO, which facilitated the formation of a high conductive pathway; (3)

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the heteroatom in CP and oxygen-containing groups on GO, which can confine

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diffusion of soluble polysulfides through chemical interaction.

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TGA analyses were performed to determine the precise sulfur content in PANI/S,

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PANI/GO@S and PEDOT/GO@S composite (Fig. 4). The sulfur will evaporate

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completely between 150 °C to 350 °C under N2 atmosphere. In comparison with

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sulfur-containing composites, PANI and two type of CP/GO composites undergoes a

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gradual weight loss before 300 °C due to the decomposition and carbonization of polymer and the removal of some functional groups of GO [27, 37]. The sulfur

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content of PANI@S, PANI/GO@S and PEDOT/GO@S composite could be estimated to be 61.2, 66.4 and 66.2 %, respectively. Moreover, the sulfur in CP/GO@S composite sublimates at a much higher temperature than the PANI@S composites, which implies that the GO sheets could effectively retard the subliming sulfur

escaping from the composites under high temperature, which further indicates the attraction of sulfur and GO sheets [38]. In order to get some insights into the chemical bond structure of conductive polymer/GO@S composite, FTIR spectroscopy was used and present in Fig. 5. Both for PEDOT/GO@S and PANI/GO@S composites, the peak at 1398 cm-1 originate from the characteristic absorption of sulfur [17]. In FTIR spectrum of PANI/GO@S

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composites, two characteristic peaks at 1485 and 1561 cm-1 are assigned to C=C

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stretching of the benzenoid ring and quinoid ring respectively, reflecting the oxidation

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state of emeraldine base PANI. The band at 1301 cm-1 is C-N stretching of secondary

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aromatic amines, while the peak at 1121 cm-1 is related to the -Q=N+H=B- stretch

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vibration [39, 40]. Meanwhile, the presence of PEDOT in PEDOT/GO@S composites

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is evidenced by the peaks at 1539 and 1339 cm-1 (C=C and C-C stretching of the

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quinoid structure of the thiophene in PEDOT), 1201, 1140 and 1087 cm-1 (C-O-C

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anti-symmetric stretching), 978, 838 and 688 cm-1 (C-S bond in the thiophene ring)

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[17, 41]. Additionally, the peak from carboxy, epoxy and alkoxy groups of GO could

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not be detected in these spectra due to the low content of GO in conductive

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polymer/GO@S composites. Additionally, the peak from carboxy, epoxy and alkoxy groups of GO could not be detected in these spectra due to the low content of GO

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(about 5 %) in conductive polymer/GO@S composites. In conjunction with the FTIR spectra, the XPS spectroscopy was carried out to probe electronic structure and surface properties (Fig. 6). Fig. 6a exhibits the survey spectra of PEDOT/GO@S and PANI/GO@S composites, proving the co-existence of

C1s, O1s, S2s and S2p in PEDOT/GO@S and N1s, C1s, O1s, S2s and S2p in PANI/GO@S. The peaks centered at about 285.0 eV and 531.0 eV in two survey spectra corresponds to C1s and O1s. To further determinate the chemical bond state of heteroatom that may interaction with polysulfide, the core-level of N1s of PANI/GO@S and S2p were made. As depict in Fig. 6b, the N1s core level of PANI/GO@S consist of four main peaks centered at about 398.4 eV (=N-), 399.5 eV

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(-NH-), 400.4 eV (=NH+=) and 402.1 eV (-NH2+-). Fig. 6c shows the high resolution

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S2p peaks which can be divided to three components. The S2p3/2 peaks at 163.9 and

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164.5 eV could be attributed to the C-S and O-S species, respectively [29]. However,

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it is hard to separate the contribution of chemical bond between S and GO or S and

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PEDOT. The higher binding energy doublet at 168.3 and 169.5 eV are ascribed to the

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sulfur spin-split coupling from PEDOT+SO42− due to the doping of SO42− formed by

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oxidation of sulfur with residual Fe3+ in solution or in air [29, 42]. Previous studies

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showed that both oxygen and sulfur atoms in PEDOT could strongly bind with

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lithium ions in Li2S and the binding energy is 1.22 eV. In contrast, only the weak

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interaction between nitrogen and the lithium ion in Li2S are in PANI and give a

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binding energy of 0.64 eV. Because of the difference of chemical binding affinity between heteroatoms in CPs and lithium polysulfides, PEDOT/GO@S will provide a

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more stable cycling performance compared to PANI/GO@S [18]. The electrochemical performance of three sulfur containing composites electrodes was tested by EIS and galvanostatic charge/discharge measurements. Fig. 7a displays the charge-discharge voltage profiles of PEDOT/GO@S cathode at 0.5 C,

in which the discharge curves show the typical two-plateau behavior of a Li-S cell. Two discharge plateaus at 2.35 V and 2.05 V are associated with the reversible conversion of sulfur to soluble lithium polysulfide (Li2Sn, 4n8) and finally to insoluble Li2S. The longer plateau around 2.05 V contributes to the majority of the discharge capacity. After 200 cycles, the two plateaus are still evident and flat, suggesting well stability and reversibility of PEDOT/GO@S cathode. The cycling

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performance of PEDOT/GO@S, PANI/GO@S and PANI@S cathode at 0.5 C are

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given in Fig. 7b. The PEDOT/GO@S, PANI/GO@S and PANI@S cathode all could

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deliver a considerable initial discharge capacity of 1195.7, 1037.2, and 986.9 mAh g-1

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respectively. After 200 cycles, the specific capacity of PANI/GO@S cathode

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decreases rapidly to 407.2 mAh g-1, while the PANI/GO@S and PEDOT/GO@S

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cathode still shows a capacity of 599.1 and 800.2 mAh g-1, which corresponds to the

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capacity retention of 41%, 58% and 67% respectively. The higher PEDOT/GO@S

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cathode also exhibits higher capacities and better cycling stability than that of

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CP/GO@S composite reported before [20, 43]. It also noted that the Columbic

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efficiency is almost 100% for three cathodes, except for the first cycle, indicating a

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suppressing shuttle effect of three cathodes during charge-discharge process. Apart from the cycling life, the rate capacity of cell at various current rates was

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tested to estimate the electrode kinetics and stability (Fig. 8b). In contrast with PANI/GO@S and PANI@S, the discharge capacity of PEDOT/GO@S decreases much slowly, as the current rate gradually increases from 0.1 to 4 C. It was shown that the discharge capacities of the PEDOT/GO@S composite at the 1 C, 2 C, and 4 C are

863.8, 768.1, and 632.4 mAh g-1. However, at a high current rate of 4 C, the PANI/GO@S and PANI@S cathode only show much lower capacities of 498.1 and 240.7 mAh g-1, which imply more slow reaction kinetics. When the current rate suddenly turns back to 0.5 C, a stable discharge capacity of 891.5 mAh g-1 can be restored even after 15 cycles for PEDOT/GO@S cathode, compared to 949.7 mAh g-1 in the 15th cycle, indicating the superior stable structure of PEDOT/GO@S cathode.

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As shown in Fig. 8a, the outstanding rate performance of PEDOT/GO@S cathode

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also demonstrated by its voltage profiles at various current rates. As the rate increases

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from 0.1 C to 4 C, two typical discharge plateaus of all curves can be still observed

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with little increase in polarization. Even at 4 C, the lower plateau remains at 1.90 V,

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which is higher than other previous reported CPs/sulfur-based cathode [18, 39]. This

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phenomenon can be owing to unique three-dimensional hybrid nanostructure of

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PEDOT/GO@S composites, which promotes the complete transition from lithium

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polysulfides to insoluble Li2S2 and Li2S under large current.

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To further get insight into the electrochemical reaction process, EIS spectra of

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PEDOT/GO@S, PANI/GO@S and PANI @S cathodes before cycling and at fully

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charged after 200 cycles at 0.5 C were carried out. As present in Fig. 9a, the Nyquist impedance plots of three sulfur cathodes before cycling are composed of a depressed

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semicircle in high and a straight line in low frequency regions. According to previous studies, the high frequency semicircle associates with the charge-transfer resistance (Rct) and the constant phase capacitance (CPE1) of the electrode/electrolyte interface [44, 45]. After 200 cycles at 0.5 C, two depressed semicircle appear in the

impendence spectra of all cathodes (Fig. 9b). The semicircle in high frequency also reflects the charge-transfer process at carbon matrix interface, while the semicircle in middle frequency could be attributed to the formation of insulated Li2S (Rs//CPE2) on the cathode surface after cycling. The inclined line in low frequency range represents the Warburg impedance due to the polysulfide diffusion with cathode [46-48]. It is noted that the Rct of three sulfur cathode before and after cycling increase in the order

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of PEDOT/GO@S < PANI/GO@S < PANI @S. The introduction of GO effectively

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improve the conductivity of sulfur-based cathode composites, which in good

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agreement with the observation of rate performance tests. Moreover, the Rs of

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PEDOT/GO@S are smallest among all cathodes, which reveal that less

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non-conductive Li2S on the surface. Therefore, these EIS results further provide the

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evidence of reduced mass loss of sulfur and suppressed shuttle phenomenon in

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PEDOT/GO@S cathode, leading to an admirable cycling stability.

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4. Conclusions

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In general, a facile and scalable strategy to prepare three-dimension CPs/GO

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@sulfur composites via interface polymerization of CPs nanostructure on the surface

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of GO was designed. The incorporation of nanostructured CPs into high conductive GO layers will generate an interlinked network, providing outstanding electron and

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ion pathways. We also found that not only the physical confinement of soluble polysulfides immediates within the CPs/GO hybrid structure, but also chemical absorption of lithium polysulfide by the oxygen-containing functional groups on graphite oxide and the heteroatoms with lone electron pairs played key role in

improved cycling performance of CPs/GO @sulfur composites. As compared with the PANI/GO@S and PANI @S composite, the PEDOT/GO@S composites with 66.2 wt% sulfur exhibits excellent cycling stability of 800.2 mAh g-1 after 200 cycles at 0.5 C and an exceptional high-rate discharge capacity of 632.4 mAh g-1 at an ultrahigh rate of 4 C. Consequently, this study will give a rational direction for design sulfur based cathode materials and a low-cost and easily-achieved synthetic process to make

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our S-based electrode highly promising for practical application in LIBs.

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Acknowledgements

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The authors thank the financial support of the Teacher Research Fund of Central

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South University (2013JSJJ027), the Fundamental Research Funds for the Central

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Universities of Central South University (No. 2013zzts026) and Project supported by

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Hunan Provincial Natural Science Foundation of China (13JJ1003).

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References

D

[1] P. G. Bruce, S. A. Freunberger, L. J. Hardwick and J. M. Tarascon, Nat. Mater., 2012, 11, 19.

TE

[2] Y. X. Yin, S. Xin, Y. G. Guo and L. J. Wan, Angew. Chem. Int. Ed., 2013, 52, 2.

EP

[3] X. L. Ji and L. F. Nazar, J. Mater. Chem., 2010, 20, 9821.

CC

[4] A. Manthiram, Y. Fu and Y. S. Su, Acc. Chem. Res., 2013, 46, 1125. [5] D. W. Wang, Q. C. Zeng, G. M. Zhou, L. C. Yin, F. Li, H. M. Cheng, I.R. Gentle and G. Q. Lu.

A

J. Mater. Chem. A, 2013, 1, 9382. [6] J. Fanous, M. Wegner, J. Grimminger, A. Andresen and M. R. Buchmeiser. Chem. Mater., 2011, 23, 5024. [7] L. Wang, X. M. He, J. J. Li, J. Gao, J. W. Guo, C. Y. Jiang and C. R. Wang. J. Mater. Chem.,

2012, 22, 22077. [8] L. Wang, X. M. He, J. J. Li, M. Chen, J. Gao and C. Y. Jiang. Electrochim. Acta, 2012, 72, 114. [9] L. F. Xiao, Y. L. Cao, J. Xiao, B. Schwenzer, M. H. Engelhard, L. V. Saraf, Z. M. Nie, G. J. Exarhos, and J. Liu. Adv. Mater., 2012, 24, 1176. [10] W. D. Zhou, Y. C. Yu, H. Chen, F. J. Disalvo and H. D. Abruna. J. Am. Chem. Soc., 2013, 135, 16736.

PT

[11] G. Q. Ma, Z. Y. Wen, J. Jin, Y. Lu, X. W. Wu, M. F. Wu and C. H. Chen. J. Mater. Chem. A,

RI

2014, 2, 10350.

SC

[12] J. Shao, X. Y. Li, L. Zhang, Q. T. Qu and H. H. Zheng. Nanoscale, 2013, 5, 1460.

U

[13] Y. G. Zhang, Y. Zhao, A. Konarov, D. Gosselink, Z. Li, M. Ghaznavi and P. Chen. J. Nanopart.

N

Res., 2013, 15, 2007.

A

[14] Y. Z. Fu and A. Manthiram. RSC Adv., 2012, 2, 5927.

M

[15] F. Wu, J. Z. Chen, R. J. Chen, S. X. Wu, L. Li, S. Chen and T. Zhao. J. Phys. Chem. C, 2011,

D

115, 6057.

TE

[16] Y. Yang, G. H. Yu, J. J. Cha, H. Wu, M. Vosgueritchian, Y. Yao, Z. N. Bao and Y. Cui. ACS

EP

Nano, 2011, 5, 9187.

CC

[17] H. W. Chen, W. L. Dong, J. Ge, C. H. Wang, X. D. Wu, W, Lu and L. W. Chen. Sci. Rep., 2013, 3, 1910.

A

[18] W. Y. Li, Q. F. Zhang, G. Y. Zheng, Z. W. She, H. B. Yao and Y. Cui. Nano Lett., 2013, 13, 5534. [19] W. Wang, G. C. Li, Q. Wang, G. R. Li, S. H. Ye and X. P. Gao. J. Electrochem. Soc., 2013, 160, A805.

[20] L. C. Yin, J. L. Wang, F. J. Lin, J. Yang and Y. Nuli. Energy Environ. Sci., 2012, 5, 6966. [21] C. H. Wang, H. W. Chen, W. L. Dong, J. Ge, W. Lu, X. D. Wu, L. Guo and L. W. Chen. Chem. Commun., 2014, 50, 1202. [22] J. Z. Wang, L. Lu, D. Q. Shi, R. Tandiono, Z. X. Wang, K. Konstamtinov and H. K. Liu. ChemPlusChem. 2013, 78, 318. [23] Q. W. Tang, Z. Q. Shan, L. Wang, X. Qin, K. L. Zhu, J. H. Tian and X. S. Liu. J. Power

PT

Sources, 2014, 246, 253.

RI

[24] H. Y. Kim, H. D. Lim, J. S. Kim and K. S. Kang. J. Mater. Chem. A, 2014, 2, 33.

SC

[25] J. Z. Wang, L. Lu, M. Choucair, J. A. Stride, X. Xu and H. K. Liu, J. Power Sources, 2011,

U

196, 7030.

N

[26] X. W. Wang, Z. A. Zhang, Y. H. Qu, Y. Q. Lai and J. Li. J. Power Sources, 2014, 256, 361.

A

[27] L. W. Ji, M. M. Rao, H. M. Zheng, L. Zhang, Y. C. Li, W. H. Duan, J. H. Guo, E. J. Cairns

M

and Y. G. Zhang. J. Am. Chem. Soc., 2011, 133, 18522.

D

[28] S. Y. Zheng, Y. Wen, Y. J. Zhu, Z. Han, J. Wang, J. H. Yang, and C. S. Wang. Adv. Energy

TE

Mater., 2014, DOI: 10.1002/aenm.201400482.

EP

[29] L. Zhang, L. W. Ji, P. A. Glans, Y. G. Zhang, J. F. Zhu and J. H. Guo. Phys. Chem. Chem.

CC

Phys., 2012, 14, 13670. [30] Y. C. Si and E. T. Samuski. Nano Lett., 2008, 8, 1679.

A

[31] M. K. Song, Y. G. Zhang and E. J. Cairns, Nano Lett., 13, 5891. [32] S. Liu, J. Tian, L. Wang and X. Sun, Carbon, 2011, 49, 3158. [33] S. Liu, J. Q. Tian, L. Wang, Y. L. Luo and X. P. Sun. Analyst, 2011, 136, 4898. [34]H. J. Peng, J. Q. Huang, M. Q. Zhao, Q. Zhang, X. B. Chen, X. Y. Liu, W. Z. Qian and F. Wei.

Adv. Funt. Mater., 2014, DOI: 10.1002/adfm.201303296. [35] J. Xie, J. Yang, X. Y. Zhou, Y. L. Zou, J. J. Tang, S. C. Wang, F. Chen. J. Power Sources, 2014, DOI: 10.1016/j.jpowsour.2013.12.074. [36] M. Q. Zhao, X. F. Liu, Q. Zhang, G. L. Tian, J. Q. Huang, W. C. Zhu and F. Wei. ACS Nano. 2012, 6, 10759. [37] Z. Q. Tong, Y. N. Yang, J. Y. Wang, J. P. Zhao, B. L. Su and Y. Li. J. Mater. Chem. A, 2014, 2,

PT

4642.

RI

[38] X. He, L. Wang, J. Li, J. Gao, M. Fang, G. Tian, J and Wang, S. Fan. J. Power Sources, 2013,

SC

239, 623.

U

[39] G. C. Li, G. R. Li, S. H. Ye and X. P. Gao. Adv. Energy Mater., 2012, 2, 1238.

N

[40] F. Wu, J. Z. Chen, L. Li, T. Zhao and R. J. Chen. J. Phys. Chem. C, 2011, 115, 24411.

A

[41] X. F. Xu, Y. Wang, J. J. Liang, Y. Huang, Y. F. Ma, X. J. Wan and Y. S. Chen. Nano Res.,

M

2009, 2, 343.

D

[42] J. T. Zhang and X. S. Zhao. J. Phys. Chem. C, 2012, 116, 5420.

EP

2013, 241, 517.

TE

[43] Y. Zhang, Y. Zhao, A. Konarov, D. Gosselink, H. G. Soboleski and P. Chen, J. Power Sources,

CC

[44] V. S. Kolosnitsyn, E. V. Kuz’mina, E. V. Karaseva and S. E. Mochalov, Russ. J. Electrochem., 2011, 47, 793.

A

[45] Q. W Tang, Z. Q Shan, L. Wang, X. Qin, K. L. Zhu, J. H. Tian and X. S. Liu, J. Power Sources, 2014, 246, 253. [46] M. Ghaznavi and P. Chen, Electrochem. Acta, 2014, 137, 575. [47] D. N. Fronczek and W. G. Bessler, J. Power Source, 2013, 244, 183.

A

CC

EP

TE

D

M

A

N

U

SC

RI

PT

[48] Y. C. Lu, Q. He and H. A. Gasteiger, J. Phys. Chem. C., 2014,118, 5733.

Figure captions Fig. 1 Schematic illustration of synthesis process of the CPs/GO@S composites Fig. 2 Typical SEM images of (a) PANI @S, (b) PANI/GO@S, (c) PEDOT/GO and (d) PEDOT/GO@S composites. Fig. 3 TEM images of (a) PANI @S, (b) PANI/GO@S, (c) PEDOT/GO and (d) PEDOT/GO@S composites.

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Fig. 4 TGA thermograms for PANI, CPs/GO and CPs/GO@S composites in nitrogen

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atmosphere.

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Fig. 5 FTIR spectra of PEDOT/GO@S and PANI/GO@S composites.

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Fig. 6 (a) XPS survey spectra of PEDOT/GO@S and PANI/GO@S composites; (b)

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N1s spectrum of PANI/GO@S composites; (c) S2p spectrum of PEDOT/GO@S

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Fig. 7 (a) Discharge/charge voltage profiles of PEDOT/GO@S cathode in various

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PANI @S cathodes at 0.2 C; Inset shows the corresponding coulombic efficiency

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Fig. 8 (a) Discharge/charge voltage profiles of PEDOT/GO@S cathode at various

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rates from 0.1 to 4 C; (b) Comparison of rate capability of PEDOT/GO@S, PANI/GO@S and PANI @S cathodes at different rates from 0.1 C to 4 C.

Fig. 9 Nyquist plots of PEDOT/GO@S, PANI/GO@S and PANI @S cathodes (a) before cycles and (b) after 200 cycles at 0.2 C.

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