Sulfur Composites for

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Polyaniline-Coated Mesoporous Carbon/Sulfur Composites for Advanced Lithium Sulfur Batteries Xiaohui Zhao, Hyojun Ahn, Ki-Won Kim, Kwon-Koo Cho, and Jou-Hyeon Ahn J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp511846z • Publication Date (Web): 25 Mar 2015 Downloaded from http://pubs.acs.org on April 3, 2015

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The Journal of Physical Chemistry

Polyaniline-Coated Mesoporous Carbon/Sulfur Composites for Advanced Lithium Sulfur Batteries Xiaohui Zhao, † Hyo-Jun Ahn, ‡ Ki-Won-Kim, ‡ Kwon-Koo Cho,* , ‡ and Jou-Hyeon Ahn,* , †, ‡ †

Department of Chemical Engineering and Research Institute for Green Energy Convergence

Technology, Gyeongsang National University, 900 Gajwa-dong, Jinju 660-701, Republic of Korea ‡

Department of Materials Engineering and Convergence Technology and RIGET,

Gyeongsang National University, 900, Gajwa-dong, Jinju 660-701, Republic of Korea

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ABSTRACT

Lithium sulfur (Li-S) batteries have been considered as a promising candidate for high energy density applications with a high theoretical capacity of 1675 mAh g-1 and a high energy density of 2600 Wh kg-1. In this work, a polyaniline (PANi)-coated mesoporous carbon composite is synthesized by direct polymerization of aniline monomer in mesoporous Ketjenblack (KB) carbon and is used as cathode material for Li-S batteries. Different mass percentages of PANi can be infiltrated into the pores of KB carbon by simply varying the amount of monomer. Sulfur is encapsulated into the composite by melt diffusion method and the electrochemical performance of lithium sulfur batteries is investigated. The results indicate that the mass percentage of PANi plays a crucial role in the cycle stability of lithium sulfur batteries. The infiltrated PANi is capable of enhancing the intimate contact of sulfur with carbon and trapping polysulfides, which improves the utilization of active material. However, excess PANi diminishes the pore volume of mesoporous KB carbon, which limits sulfur loading and impairs the capability of cells. The cell with the composite containing 30% of PANi shows an improved cyclability of 675 mAh g-1 after 200 cycles at 0.1 C-rate, demonstrating promising applications in Li-S batteries with high energy density.

KEYWORDS: Polyaniline, mesoporous carbon, coating, electrochemical properties, lithium sulfur batteries


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1. INTRODUCTION

The demand for high energy storage in large grid applications and transportation intensifies the interest for the development of new materials with high energy density, long life span, and low cost. Sulfur is regarded as one of the most promising candidates due to its abundance in nature and non-toxicity. Lithium sulfur (Li-S) battery is expected to greatly improve the capability of current batteries, as it possesses a high theoretical capacity of 1675 mAh g-1 and a high energy density of 2600 Wh kg-1.1-3 However, Li-S battery has several intrinsic problems ever since its invention in the 1960s. The electric and ionic insulating nature of sulfur reduces its active material utilization.4 Sulfur undergoes a series of redox reactions during the discharge/charge process to form lithium polysulfide intermediates (Li2Sn, 4≤n≤8), which readily dissolve in the electrolyte to cause active material loss, low Coulombic efficiency, and corrosion of lithium anode.5-6 Many efforts have been made in the fields of cathode, anode, and electrolyte to address these problems. In a major breakthrough, Nazar group accomplished encapsulation of sulfur into the mesopores of CMK carbon matrix.7 As such, the porous carbon serves as a reservoir for confining sulfur and soluble polysulfides. It also supplies an electric pathway for fast transfer of electrons and lithium ions. In this scenario, various carbon networks with different structure or pore size have been synthesized to fabricate sulfur-carbon composites.8-14 However, the synthesis of porous carbon is often energy intensive and time-consuming, which limits carbon production on an industrial scale. In addition, these methods result in low pore volume of the synthesized carbon and thus lead to low sulfur loading. Of special note, lithiation of sulfur undergoes volume expansion due to the lower density of lithium sulfide than that of sulfur. Surprisingly, Zheng et al. observed that lithium sulfide detaches from the inner surface of carbon after the completion of the discharge process.15 3 ACS Paragon Plus Environment


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This paradox is most likely due to the leakage of polysulfides from the carbon matrix, as rigid and hydrophobic carbons are not proficient to immobilize the active material. Polyaniline (PANi) has been successfully utilized as either a conductive matrix or a soft framework to modify carbon surface.16-19 PANi is widely used to improve the electrochemical properties of supercapacitors, chemosensors, and fuel cells due to its facile synthesis process, relatively high electrical conductivity, and environmental stability.20-23 More importantly, PANi has been reported to be able to interact with sulfur to form an interconnected network and the sulfur-PANi composite achieved improved cycle performance in Li-S cells.17,18 Ketjenblack (KB) carbon is an inexpensive and highly conductive carbon with high specific surface area and high pore volume, which are qualified to confine high amounts of sulfur. It has been widely used to improve the electric conductivity of sulfur cathodes and enhance the cycle capability of Li-S cells.24,25 In our previous study, a sulfur/PANi-C ternary composite was synthesized with a commercially available PANi-C composite containing 20% of PANi as an interface between sulfur and carbon.26 PANi intensifies the contact between sulfur and carbon and improves the utilization of sulfur. In this study, a PANi-coated mesoporous carbon (PKB) composite was synthesized by in situ polymerization of aniline on the pore surface of KB carbon and used as a reservoir for sulfur. Compared with KB/sulfur (SKB) composite, PANi in PKB composite is expected to serve as a soft padding between KB carbon and sulfur which can reduce their detachment during cycling and even improve the confinement of sulfur and lithium polysulfides (Figure 1). Moreover, the mesoporous PKB composites with varied content of PANi were prepared and the influence of PANi content on the electrochemical performance of Li-S batteries has been investigated.


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Figure 1. Schematic diagram of PANi padding in the interface of KB carbon and sulfur.

2. EXPERIMENTAL

2.1. Materials Aniline (Sigma-Aldrich, 99%) was purified by vacuum distillation. Ketjenblack (KB) carbon (AkzoNobel Corp., EC-600JD), ammonium persulfate (APS, Sigma-Aldrich, 98%), hydrochloric acid (HCl, DUKSAN, 35.0-37.0%), and sulfur (Sigma-Aldrich, 100-mesh particle size powder) were used as received.

2.2. Synthesis of PANi-coated KB (PKB) composites PKB composites were prepared as follows. KB (0.3 g) was dispersed in HCl solution (2 M, 200 ml) with sonication for 2 h. A certain amount of aniline (0.1, 0.25, 0.5, and 1 ml) was added and stirred for 1 h. A solution of APS in HCl (2 M, 50 ml) was added dropwise into the aniline/KB solution at an aniline/APS molar ratio of 1.5 under stirring. After polymerization for 12 h at room temperature, the product was carefully collected and washed repeatedly with 5 ACS Paragon Plus Environment


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distilled water and ethanol. The final product was dried and weighed to estimate PANi mass percentage in PKB composites. The obtained PKB composites were designated as PKB-x (x=10, 20, 30, and 50) according to the weight ratio (%) of PANi in the composites.

2.3. Synthesis of sulfur/PKB (SPKB) composites SPKB composites were prepared by melt diffusion method. Sulfur and PKB were mixed by ball milling at a weight ratio of 7:3 and then subjected to a two-step thermal treatment. The mixture was initially heated to 155 °C for 12 h followed by 300 °C for another 12 h in a sealed glass tube under N2 protection. The composites thus obtained were designated as SPKB-x, in which x represented the mass percentage of PANi. Sulfur/KB (SKB) composite without PANi was also prepared by the same method for comparison.

2.4. Characterizations and electrochemical measurements The morphology of PKB and SPKB composites was examined by field emission scanning electron microscopy (FE-SEM, Philips XL30S FEG). The specific surface area, pore volume, and pore size distribution of PKB composites were measured by Brunauer-Emmett-Teller analysis (BET, ASAP 2010) and calculated with Barrett-Joyner-Halenda (BJH) method. Xray diffraction patterns of samples were recorded by X-ray diffractometer (XRD, D2 Phaser Bruker AXS). The thermal properties of PANi and the mass percentage of PANi and sulfur in the composites were determined with thermogravimetric analyzer (TGA, Q50 TA Instruments) by heating to 600 or 900 °C at 10 °C min-1 under N2 gas. The properties of PANi under thermal treatment were studied by Fourier transformation infrared spectroscopy (FT-IR, SMART-APEX II ULTRA). X-ray photoelectron spectroscopy (XPS, ESCALAB250 VG Scientific) spectra were collected by using a monochromatic Al Kα (1486.6 eV) X-ray source. 6 ACS Paragon Plus Environment

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SKB and SPKB cathodes were prepared by mixing SKB or SPKB composites, Super-P (SP) carbon black, and poly(vinylidene fluoride) (PVdF) in a weight ratio of 85:5:10 in N-methyl2-pyrrolidone (NMP) and the slurry was cast on an aluminum current collector. All cathodes were prepared in a fixed sulfur loading of ~ 1.2 mg cm-2. The stainless steel (SS) Swagelok® cells were assembled by stacking SPKB or SKB cathode, Celgard® 2400 separator and Li anode in an argon-filled glove box. The electrolyte used was 1 M lithium bis(trifluoromethane)sulfonimide salt (LiTFSI) in a mixed solvent of 1,3-dioxolane (DOL) and dimethyl ether (DME) at a volume ratio of 4:1. Electrochemical impedance spectra (EIS) of cells were measured with an IM6 impedance analyzer over a frequency range of 100 mHz to 2 MHz at an amplitude of 20 mV. Cycle performances were tested with WBCS3000 battery cycler (WonA Tech. Co.) at varied C-rates (1 C = 1675 mA g-1).



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3. RESULTS AND DISCUSSION

The morphologies of KB, PKB, SKB, and SPKB composites were observed by FE-SEM as shown in Figure 2. KB carbon is composed of nanoparticles of around 30-50 nm in size (Figure 2a1).27,28 PKB composites with PANi content of up to 30% exhibit similar morphologies to KB carbon (Figure 2a2-a4). However, particle clumps were clearly observed in PKB-50 composite (Figure 2a5), which probably resulted from an excess of PANi coating on the surface of KB carbon. Distinguishable nanoparticles are visible from FE-SEM images of SKB and SPKB composites (Figure 2b1-b5), demonstrating successful encapsulation of sulfur into the pores. The aggregation of SPKB particles increased with increasing PANi mass percentage to 50% in PKB-50 composite. It is likely due to the reduced pore space for sulfur by the occupation of PANi inside the porous carbon matrix. Excess amount of PANi coated on the surface of KB may also absorb sulfur and further block the tunnel for sulfur being encapsulated into the pores or prevent sulfur vaporization during the second heating step at 300 °C in the melt diffusion process, thus leading to the aggregation in SPKB-50 composites.


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Figure 2. FE-SEM images of (a1-a5) KB, PKB-10, PKB-20, PKB-30 and PKB-50; (b1-b5) SKB, SPKB-10, SPKB-20, SPKB-30, and SPKB-50.



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The change of the porous structure after PANi coating on KB was explored by nitrogen adsorption-desorption isothermal analysis. As shown in Figure 3a, KB carbon showed typical type IV sorption isotherms of mesoporous structure with two hysteresis loops at relative pressure (P/P0) of 0.45-0.9 and 0.9-1.0 which represent a bimodal pore size distribution.29,30 Even after coating with PANi, both the type of sorption isotherms and the two hysteresis loops were well-preserved. It is suggested that PANi must be uniformly coated inside the pores, thus the mesoporous structure of PKB-x (x≤30) is closely akin to that of KB. The same trend occurred with the pore size distribution in Figure 3b. Analysis using BJH method showed two peaks centered at 3.8 nm (Peak 1) and 51.2 nm (Peak 2) for KB as listed in Table 1. The larger pores are probably generated by the aggregation of carbon particles, since the peak is broad with a wide diameter range from 10 to 120 nm. It is also proved that PANi is successfully infiltrated into the mesopores of KB because Peak 1 at 3.8 nm in KB is decreased to 3.7 nm in PKB-10 and 3.6 nm in both PKB-20 and PKB-30. Noticeably, the intensity decreased as the amount of PANi increased. The ratio of larger pores in PKB composites correspondingly increased and the pore diameter peak became much broader with increase in PANi loading. Only one hysteresis loop at relative pressure (P/P0) of 0.9-1.0 was observed in the sorption isotherm of PKB-50 as Peak 1 was found to be sharply depleted. Excess PANi coating may block the smaller pores and further enhance agglomeration of carbon particles. The specific surface area and pore volume of PKB-50 were dramatically reduced to 135 m2 g-1 and 0.8 cm3 g-1 relatively, compared with KB possessing high specific surface area of 1717 m2 g-1 and large pore volume of 3.7 cm3 g-1. The blocked pore structure would further impede sulfur encapsulation and lead to lower sulfur loading. High pore volumes of 3.1, 2.3, and 1.7 cm3 g-1 were observed in PKB-10, PKB-20, and PKB-30, respectively, which are expected to enable high sulfur loading and concurrently maintain enough space for Li+ movement. 10 ACS Paragon Plus Environment

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Figure 3. (a) Nitrogen sorption isotherms and (b) pore size distribution of KB and PKB composites. Table 1. BET analysis results of KB and PKB composites. Specific surface area (m2 g-1)

Pore volume (cm3 g-1)

Peak 1 (nm)

Peak 2 (nm)

Area ratio of Peak 2 to Peak 1

KB

1717

3.7

3.8

51.2

13.2

PKB-10

1252

3.1

3.7

54.9

18.3

PKB-20

962

2.3

3.6

54.0

20.2

PKB-30

513

1.7

3.6

54.0

32.8

PKB-50

135

0.8

3.8

53.3

350.7

Sample



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TGA plots and derivative thermogram (DTG) of PKB composites and pristine PANi are shown in Figure 4a. PANi undergoes stepwise thermal decomposition as reported.31 The weight loss below 100 °C was derived from the loss of moisture bound in the polymer. The elimination of dopant (HCl) contributed to the second weight loss at around 230 °C. The third step of weight loss from 400 to 800 °C was ascribed to the decomposition of PANi matrix. The thermal properties of PKB composites are similar to that of PANi, and according to the TGA results, the mass percentage of PANi were 7.4, 16.4, 27.0, and 46.4% in PKB-10, PKB20, PKB-30, and PKB-50, respectively. In TGA and DTG plots in Figure 4b, the weight loss of SKB and SPKB composites started from 200 °C and it increased sharply up to 450 °C, which is ascribed to the elimination of sulfur and PANi from PKB composites.26 SKB, SPKB-10, and SPKB-20 composites exhibited a single peak centered at around 320-330 °C, which is higher than the temperature at which pristine sulfur vaporizes (292 °C). It is suggested that sulfur is confined in the pores of KB, PKB-10, and PKB-20 and the slower rate of diffusion out of the pores results in the higher vaporization temperature.32 The vaporization peak shifted to lower temperature for SPKB-30 and SPKB-50, which is probably due to the excess sulfur and PANi located on the surface of the composites.33 The sulfur contents in SKB, SPKB-10, SPKB-20, SPKB-30, and SPKB-50 were thus calculated to be 56, 57, 57, 57 and 55%, respectively.


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Figure 4. TGA (upper) and DTG (lower) plots of (a) PANi, PKB, and (b) sulfur, SKB, and SPKB composites. KB, PKB, SKB, and SPKB composites were further characterized with XRD (Figure 5). Two broad diffraction peaks at 24° and 43°, representing typical amorphous carbon structure, were detected in KB and all PKB composites (Figure 5a).34 A small diffraction peak at 15° was observed, which demonstrates the existence of PANi on the surface of PKB-50.35 It confirms that PANi has been successfully coated inside the pores of KB. Spectrum of pristine sulfur showed sharp peaks at 23° and 28°, belonging to a well crystallized orthorhombic structure with space group Fddd (Figure 5b).36 Such diffraction peaks of pristine sulfur were not detected from SKB, SPKB-10, SPKB-20, and SPKB-30 composites. This result demonstrates that sulfur is well encapsulated inside the pores of KB, PKB-10, PKB-20, and PKB-30. It is worth mentioning that sharp sulfur peaks also appeared in the XRD spectrum of SPKB-50 composite, which validates the FE-SEM observation that excess sulfur still exists on its surface (Figure 2b5). 13 ACS Paragon Plus Environment


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Figure 5. XRD patterns of (a) KB, PKB composites and bulk PANi; (b) SKB, SPKB composites and elemental sulfur. To amplify the change of PANi under thermal treatment and reveal its influence in trapping polysulfides, pristine PANi was thermally treated by the same process with SPKB preparation at 155 °C for 12 h followed by 300 °C for another 12 h. The product thus obtained was designated as PANi-T and was subjected to FT-IR spectroscopy. Typical vibrations of PANi were detected as shown in Figure 6. The stretching vibrations of N-H of secondary amines and C-H bonds are assigned to 3440 and 2922 cm-1, respectively. The stretching vibrations of quinoid (Q) and benzenoid (B) ring are assigned to 1570 and 1489 cm-1, respectively. The bands at 1373, 1292, and 1240 cm-1 are associated to stretching vibrations of -N=Q=N-, C-N, and C-N+• polaron structure, respectively, in which the band at 1240 cm-1 corresponds to the electrically conductive form of PANi. The bands at 1126 and 796 cm-1 are attributed to the vibrations of -NH+ structure and C-H bonds out of plane.37 As PANi is heated, the vibrations at 1373 cm-1 disappeared and a new peak at 1162 cm-1 appeared in PANi-T, demonstrating a de-doping process. Importantly, the stretching C-N+• 14 ACS Paragon Plus Environment

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bond at 1234 cm-1 still remained, indicating that PANi stayed in its protonated state after thermal treatment at 300 °C.18,26 The interaction between sulfur and PANi-C composite has been proved by FT-IR spectroscopy in our previous work.26 PANi bridges sulfur and carbon as a soft buffer agent and is believed to be capable of trapping negative ions of polysulfides, thus an improved electrochemical performance of Li-S cells with SPKB composites can be expected.38

Figure 6. FT-IR spectra of PANi and PANi heated up to 300 °C. The chemical status of nitrogen and sulfur in PKB-30 and SPKB-30 composite has been further analyzed by XPS spectroscopy (Figure 7). The N 1s spectrum of PKB-30 in Figure 7a was deconvoluted into four component peaks at 398.8 eV (=N-), 399.8 eV (-NH-), 401.1 eV (-NH+) and 402.3 eV (-N+•), suggesting the emeraldine salt state of the coated PANi in PKB30.39,40 In consistence with FT-IR spectra (Figure 6), the nitrogen doped state of PANi (N+/N, 35%) was still maintained even under thermal treatment up to 300 °C (PKB-30-T), which mimics the preparing process of SPKB-30 composite. It is generally accepted that the existence of nitrogen facilitates sulfur trapping inside of carbon pores in Li-S batteries. 41,42 The thermal treatment also resulted in the conversion of imine to amine and the redistribution of protonated nitrogen (N+), since PANi undergoes a crosslinking process by opening the quinoid rings and H bonds at 200-300 °C.43 As XPS is a surface-sensitive quantitative 15 ACS Paragon Plus Environment


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spectroscopic technique, the real N 1s spectrum of SPKB-30 composite would be sequestered by sulfur. Nevertheless, SPKB-30 composite exhibits a similar N 1s chemical state to PKB30-T and the doped nitrogen (N+/N) was maintained at 30% as shown in Figure 7b. The S 2p spectrum of SPKB-30 has been deconvoluted into two typical component peaks at 163.9 eV and 165 eV that are associated with S 2p3/2 and S 2p1/2, respectively.33

Figure 7. XPS spectra of (a) N 1s in PKB-30 and PKB-30-T, and (b) N 1s and S 2p deconvolution in SPKB-30. Li-S cells with SKB and SPKB composites were assembled to investigate their electrochemical performances. As shown in Figure 8a, two plateaus at around 2.3 V and 1.92.1 V were observed from all samples representing the two-stage reduction of Li-S cells from sulfur to high ordered polysulfides (Li2Sn, 4≤n≤8) and further to the final products Li2S2/Li2S.44 It is noted that polarization is most severe for SPKB-50, which is likely due to the low electric conductivity of cathodes with excess sulfur covering PKB-50 composite. Long-term cycle performances of the cells at 0.1 C-rate are presented in Figure 8b. Cells with SKB and SPKB-10 composites showed relatively faster capacity fading and approximately 500 and 450 mAh g-1 were remained after 200 cycles, respectively. It is suggested that both 16 ACS Paragon Plus Environment

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KB carbon and PKB-10 composite are deficient in confining polysulfides, although their high pore volume allows the accommodation of a large amount of sulfur. The cell with SPKB-50 composite also showed low active material utilization, which may be due to the failure of sulfur encapsulation into PKB-50 composite. The best cyclablity and the highest Coulombic efficiency are achieved from cells using SPKB-20 and SPKB-30 cathodes. They generated initial discharge capacities of 1185 and 1338 mAh g-1 and retained 658 and 675 mAh g-1 after 200 cycles at 0.1 C-rate with Coulombic efficiency up to 95%, respectively. It seems that the coating amount of PANi does play an important role in stabilizing cycle performance of Li-S cells. PKB composites with appropriate amount of PANi (20-30%) not only preserve enough space for the infiltration of sulfur, but also enable the movement of Li+. Although the encapsulation of PANi into KB carbon may sacrifice the electric conductivity of composites in some content, it plays a more significant role in confining both sulfur and polysulfides. It is believed that the electrochemical environment in cells can be maintained in a stable state with a suppressed shuttle of lithium polysulfides between cathode and anode, which contributes to improved cycle stability.45 EIS plots of cells with SKB and SPKB composites are depicted in Figure 8c to index the transfer state of Li+ inside the cells. All cells present a semicircular loop and the diameter is defined as the charge-transfer resistance (Rct), which denotes the kinetic resistance of the electrochemical reaction at the interface between the electrode and electrolyte. The cell with SPKB-50 exhibited the highest resistance of 400 Ω among all the cells before cycling. It suggests that excessive coating of both PANi and sulfur on carbon surface reduces the electric conductivity of the composite and further hinders the movement of Li+. The lithiation of sulfur is a process of active material re-distribution in the pores of carbon or composites and this reduces the interfacial resistance of the cells. The resistance of all the cells thus dramatically decreased after 200 cycles and the cells with SPKB-10, SPKB20, and SPKB-30 obtained the lowest Rct value of just around 20 Ω. It is likely that a proper 17 ACS Paragon Plus Environment


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amount of PANi softens the rigidity of carbon by modifying the internal environment of the pores to facilitate contact with sulfur and polysulfides. The cells with SKB and SPKB-50 still exhibited high resistance. It is suggested that a proper amount of PANi coating with adequate pore space for Li+ and electron migration is important to enhance the electrochemical performance of Li-S cells. The cell with SPKB-30 composite was also cycled at higher C-rates to further evaluate the electrode kinetics and stability (Figure 9). The cells delivered high initial discharge capacities of 1289, 1182, and 1071 mAh g-1 at 0.2, 0.5, and 1 C-rates, respectively. Reversible capacities of 759, 706, and 604 mAh g-1 were retained after 120 cycles of discharge/charge, corresponding to a low capacity decay of 0.34%, 0.34%, and 0.36% per cycle, respectively. These results support the fast reaction kinetics and superior reversibility of SPKB-30 composite.


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Figure 8. (a) Discharge-charge capacity vs. voltage plot and (b) cycle performance of cells with SKB and SPKB composites at 0.1 C-rate; (c) EIS plots of cells with SKB and SPKB composites before cycling and after 200 cycles.



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Figure 9. Cycle performance of cells with SPKB-30 composite at higher C-rates.

4. CONCLUSIONS

Conducting polymer-coated mesoporous carbon composites were synthesized with PANi and KB carbon. PANi was polymerized inside the pores of KB carbon and the composite thus prepared exhibits good absorbability to both sulfur and soluble polysulfides. The effect of PANi content in the composite on the electrochemical performance of Li-S cells is investigated. It is found that the amount of PANi plays a crucial role in the electrochemical performance of Li-S cells. Proper amount of PANi does improve the cycle stability of cells, while excess PANi will occupy the interior pore space and cover the surface of carbon, resulting in low sulfur loading and low electric conductivity in the final electrode. The thin PANi layer that is coated inside the pores of carbon acts as a conductive link between carbon and sulfur and enhances their intimate contact. With merits of porous carbon and soft PANi, PKB composites are expected to be a promising material for advanced Li-S batteries. In addition, the low cost of materials and facile synthetic process are also expected to promote the PANi-coated mesoporous carbon composite to large scale production.


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AUTHOR INFORMATION Corresponding Authors *Tel.: +82 55 772 1784; fax: +82 55 772 1789. E-mail: [email protected] (J.H. Ahn). *Tel.: +82 55 772 1668; fax: +82 55 772 1670. E-mail: [email protected] (K.K. Cho). Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and future Planning (No. NRF-2014R1A2A2A04029532).

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Polyaniline-coated mesoporous carbon/sulfur composites for advanced lithium sulfur batteries Xiaohui Zhao, † Hyo-Jun Ahn, ‡ Ki-Won-Kim, ‡ Kwon-Koo Cho,* , ‡ and Jou-Hyeon Ahn,* , †, ‡

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Sulfur Composites for

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