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Novel microporous carbon prepared from discarded clothes as host materials for high performance lithium-sulfur battery
Materials Letters 232 (2018) 122–125
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Novel microporous carbon prepared from discarded clothes as host materials for high performance lithium-sulfur battery Xu Sun a, Ying Huang a,⇑, Menghua Chen a, Yanli Wang a, Xiaogang Gao a, Lihao Wang b a The MOE Key Laboratory of Material Physics and Chemistry under Extrodinary Conditions, Ministry of Education, School of Science, Northwestern Polytechnical University, Xi’an 710129, China b NO. 203 Research Institute of China Ordnance Industries, Xi’an 710065, China
a r t i c l e
i n f o
Article history: Received 18 June 2018 Received in revised form 10 August 2018 Accepted 20 August 2018
Keywords: Carbon materials Nanoparticles Energy storage and conversion
a b s t r a c t Novel microporous carbon materials (DCMC) with excellent electron conductivity and ultrahigh surface area (1896.9 m2 g 1) are successfully prepared from discarded clothes. The porous carbon-encapsulated sulfur composites were synthesized by a feasible melting process and used as host materials for lithium sulfur batteries. Because of the unique microporous, ultrahigh surface area and irregular wrinkled surface coexisting structure, the resulting microporous carbon/sulfur (DCMC/S) composite cathode possesses a good rate capability and long-term cycling performance. The initial discharge capacity of the DCMC2/S composite electrode with 74.3 wt% sulfur content is 1082.6 mAh g 1 at a current rate of 0.2 C. At a higher current rate of 1 C, it possesses excellent cyclic performance and retained a capacity of 422.8 mAh g 1 after 500 cycles with a low capacity fading rate of 0.11% per cycle. The coulombic efficiency remains over 98% during cycling. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction With an increasing demand for high energy density storage system, more and more attention has been paid to the research of rechargeable Li-ion batteries. Nevertheless, the current Li-ion batteries are limited by the low capacity, high cost, and unsafety [1–3]. Rechargeable lithium-sulfur battery has aroused researchers’ attention because of the high theoretical specific capacity (1675 mAh g 1) and theoretical energy density (2600 Wh kg 1) [4–6]. Sulfur as a suitable cathode material also has other advantages such as natural abundance, nontoxicity and environmental benignity. However, the commercialization of Li-S battery is still hindered by some chronic issues: (1) the sulfur and reduction products (Li2S2 and Li2S) are electronically insulating at room temperature resulting in the low utilization of sulfur and low practical capacity. (2) The highly dissolved polysulfide intermediates spontaneously shuttle between the sulfur cathode and metal lithium anode leading to low coulombic efficiency and capacity decay. (3) The obvious volumetric expansion (80%) of sulfur cathode during charging and discharging process, which causes insufficient cycle life [7–10]. To solve these problems, considerable approaches have been proposed to improve the electrical conductivity of the cathode and retard diffusion of polysulfide in organic electrolytes. ⇑ Corresponding author. E-mail address: [email protected] (Y. Huang). https://doi.org/10.1016/j.matlet.2018.08.112 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
One of the most effective means is to encapsulate sulfur with host matrixes to construct composite materials, particularly porous carbon [11]. Porous carbon materials have excellent conductivity, high pore volume and large surface area. They provide excellent conductivity for sulfur and discharging products, improving the utilization rate of active materials. Moreover, the porous structure, large surface area and strong adsorption can alleviate the diffusion of polysufides. Discarded clothes are abundant in our daily life. In this work, we first report a novel and simple way to prepare microporous carbon from discarded clothes (DCMC) by a carbonization and KOH activation process. The optimized microporous carbon DCMC2 with ultrahigh surface area (1896.9 m2 g 1) can encapsulate high sulfur content. The microporous carbon/sulfur composites (DCMC/S) were synthesized by simple melting diffusion treatments. As expected, the electrochemical properties of DCMC/S composite cathode delivered a high specific capacity, excellent cycling stability and good rate capability. 2. Experiment 2.1. Preparation of DCMC/S composites The discarded clothes made of pure cotton were collected, and then cleaned using deionized water. After being dried in the oven at 80 °C for 24 h, they were cut into pieces. The dried discarded
X. Sun et al. / Materials Letters 232 (2018) 122–125
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clothes were carbonized in a tube furnace under Ar atmosphere at 500 °C for 2 h with a heating rate of 2 °C min 1. The obtained carbonized discarded clothes after milling were mixed with KOH (w/ w = 1:2, 1:4) in ethanol. The mixture was stirred thoroughly for 3 h at room temperature, and then dried at 80 °C in an oven. Then the mixture was activated in a tube furnace at 900 °C for 3 h under an argon atmosphere. The obtained carbon materials were washed with 1 M HCl three times, washed several times with deionized water, and then dried at 80 °C in the oven over night to obtain the DCMC1 and DCMC2. The as-prepared DCMC and sublimed sulfur with the weight ratio of 1:4 were ground together, and subsequently heated at 155 °C for 12 h in a sealed glass tube, the resultant denoted as DCMC1/S or DCMC2/S.
2.2. Materials characterization
Fig. 1. SEM images of (a) DCMC, (b) DCMC2, (c–d) DCMC2/S composite.
The surface morphologies of samples were characterized through field-emission scanning electron microscopy (FE-SEM, Carl Zeiss SIGMA). The crystal structure was tested with X-ray diffraction ((XRD, CuKa radiation, PANalytical, Holland). The sulfur content in the DCMC/S composites was determined by the thermo gravimetric/differential thermal analysis (TG/DTA) measurement (Netzsch STA 449C thermal analyzer). The N2 adsorption–desorption isotherm and pore size distribution was obtained using a Brunauer Emmett-Teller (BET, BEL LAPAN, INC. Belsorp2).
Fig. 2. (a) XRD pattern of sulfur, DCMC, DCMC1/S and DCMC2/S; (b) TGA curves of DCMC1/S, DCMC2/S and sulfur; (c) Nitrogen adsorption–desorption isotherms of DCMC1, DCMC2, DCMC1/S and DCMC2/S; (d) Pore size distribution of the DCMC1 and DCMC2.
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Fig. 3. (a) Cycling performances of DCMC1/S and DCMC2/S at 0.2C; (b) galvanostatic charge/discharge profiles; (c) rate performance; (d) cyclic voltammogram profiles; (e) cycle performance for 500 cycles at 1 C of DCMC2/S.
2.3. Electrochemical measurements The electrochemical performances were evaluated via CR2016 coin cell with lithium metal as the anode electrode and Celgard 2400 film as a separator. As for the cathode electrode, it consisted of 80 wt% DCMC1/S composite, 10 wt% super P and 10 wt% poly (vinylidene fluoride) (PVDF) as a binder in N-methylpyrrolidone (NMP) solvent dispersant. The slurry was uniformly coated on an aluminum foil and dried at 60 °C overnight in a vacuum oven
overnight. The electrodes were cut into circular discs with a diameter of 10 mm and the sulfur loading was about 1.1 mg cm 2. The electrolyte solution was 1 M lithium bis-trifluoromethanesulfonyli mide (LiTFSI) and 0.1 M lithium nitrate dissolved in a mixture of 1,3-dioxolane (DOL) and dimethoxymethane (DME) with a volume ration of 1:1. Charge-discharge tests were carried out at different current densities in a voltage window of 1.7–2.8 V under room temperature, using a CT2001A cell test instrument (LAND Electronic Co. Ltd., China). The cyclic voltammetry (CV) was conducted
X. Sun et al. / Materials Letters 232 (2018) 122–125
on a Series G750TM Redefining Electrochemical Measurement (USA GMARY Co.) at a scan rate of 0.1 mV s 1 between 1.7 V and 2.8 V. 3. Results and discussions The morphology and structure of the prepared materials were investigated by SEM, as shown in Fig. 1. Fig. 1(a) exhibits the microstructure of the DCMC with about 5–10 lm in diameter and the outer surface appears to be very rough in the inset image. After an activation treatment by the potassium hydroxide at 900 °C, the inner morphology is exposed and the obtained DCMC2 (Fig. 1(b)) exhibits unique porous structures, which plays a positive role on the infiltration of the electrolyte and lithium-ion. As shown in Fig. 1(c–d), the DCMC2/S composite has a smooth surface and a few of sulfur was observed, indicating the complete diffusion of sulfur into the DCMC The typical XRD of pure sulfur, DCMC, DCMC1/S and DCMC2/S composites are shown in Fig. 2(a). DCMC sample shows two broad diffraction peaks around 25° and 45°, which means that is a high amorphous structure. As for the DCMC1/S and DCMC2/S composites, they show sharp peaks of crystal sulfur, which suggests that the crystal sulfur are evenly incorporated into the amorphous carbon. This is further confirmed by TGA measurements (Fig. 2(b)), in which the sulfur content in the DCMC1/S and DCMC2/S composites are 76.3 and 74.3 wt%, respectively. The desorption temperature of the DCMC1/S and DCMC2/S composites is much higher than that of sublimed sulfur, demonstrating a strong interaction between carbon and sulfur. Fig. 2(c–d) presents the N2 adsorption-desorption isotherms and density functional theory (DFT) pore size distribution curves of the as-prepared materials. The classic type I isotherm (Fig. 2c) shows the microporous nature. The BET surface of DCMC1 and DCMC2 is 1184.9 m2 g 1 and 1896.9 m2 g 1, respectively. The pore size of DCMC1 and DCMC2 both locate between 0.6 nm and 0.9 nm. Fig. 3(a) presents the cycling performance of the DCMC1/S and DCMC2/S composites electrode. The DCMC1/S and DCMC2/S display initial discharge capacity of 1012.1 and 1082.6 mAh g 1 and maintain 655 and 546 mAh g 1 after 100 cycles respectively at 0.2C rate. Fig. 3(b) shows the discharge and charge voltage profiles of DCMC2/S composite cathode for the 1st, 10th, 50th, 100th cycles at 0.2C. There are two typical discharge plateaus at about 2.3 and 2.1 V, which are attributed to the two-step reaction between sulfur with Li during the discharge process. These characteristics are consistent with the CV curves, as shown in Fig. 3(d). The three voltage plateaus almost overlap each other, revealing the cell possesses steady electrochemical reduction and cycle performance. The rate capability of DCMC2/S composite cathode is evaluated at various current rates from 0.1 to 2C in Fig. 3(c). The capacity of 1197.5 mAh g 1, 890.2 mAh g 1, 723.8 mAh g 1, 638.9 mAh g 1
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and 562.6 mAh g 1 was measured at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, respectively. The capacity of every rate decreased gradually with the increased current rate. Nonetheless, when the chargeedischarge current density was reset to 0.1 C, the discharge capacity can recover to 782.1 mAh g 1, demonstrating DCMC2/S composites have an excellent rate capability and reliability. To further investigate the excellent electrochemical performance, the long-cycling performance of DCMC2/S was evaluated at 1 C (Fig. 2(e)). A high discharge capacity of 422.8 mAh g 1 was achieved after 500 cycles with a Coulombic efficiency above 98% during cycling and an ultralow capacity fade rate of 0.11% per cycle. These results prove the cycle performance is improved, which mainly ascribe to the excellent conductivity and the unique microporous structure of the carbon host matrix. 4. Conclusions In summary, a novel DCMC has been prepared and is first used to encapsulate sulfur for Li-S batteries. High surface area and large pore volume make it high sulfur content of 74.3 wt%. The DCMC2/S composite cathode delivered a high initial discharge capacity of 1082.6 mAh g 1 at 0.2 C. In addition, it possesses excellent cyclic performance and retained a capacity of 422.8 mAh g 1 after 500 cycles with a low capacity fading rate of 0.11% per cycle, exhibiting excellent electrochemical performance. Therefore, the DCMC is promising materials for Li-S batteries. Acknowledgments We would like to thank the Analytical & Testing Center of Northwestern Polytechnical University for equipment supporting. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.matlet.2018.08.112. References [1] J.K. Lee, M.C. Kung, L. Trahey, M.N. Missaghi, H.H. Kung, Chem. Mater. 21 (2009) 6–8. [2] G.Y. Zheng, Q.F. Zhang, J.J. Cha, Y. Yang, W.Y. Li, Z.W. Seh, Y. Cui, Nano Lett. 13 (2013) 1265–1270. [3] B. Zhang, X. Qin, G.R. Lia, X.P. Gao, Energy Environ. Sci. 3 (2010) 1531–1537. [4] D. Peramunage, S. Licht, Science 261 (1993) 1029–1032. [5] W. Zhai, W. Tu, Y. Liu, Electrochim. Acta 219 (2016) 143–151. [6] S.S. Zhang, J. Power Sources 231 (2013) 153–162. [7] Z. Cao, C. Wang, J. Chen, Mater. Lett. 225 (2018) 157–160. [8] J.X. Song, Z.X. Yu, M.L. Gordin, D.H. Wang, Nano Lett. 16 (2016) 864–870. [9] Z. Sun, S. Wang, L. Yan, M. Xiao, D. Han, Y. Meng, J. Power Sources 324 (2016) 547–555. [10] K. Mi, Y. Jiang, J. Feng, Adv. Funct. Mater. 26 (2016) 1571–1579. [11] H. Wu, Y. Huang, W. Zhang, J. Alloys Compd. 708 (2017) 743–750.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Novel microporous carbon prepared from discarded clothes as host materials for high performance lithium-sulfur battery Xu Sun a, Ying Huang a,⇑, Menghua Chen a, Yanli Wang a, Xiaogang Gao a, Lihao Wang b a The MOE Key Laboratory of Material Physics and Chemistry under Extrodinary Conditions, Ministry of Education, School of Science, Northwestern Polytechnical University, Xi’an 710129, China b NO. 203 Research Institute of China Ordnance Industries, Xi’an 710065, China
a r t i c l e
i n f o
Article history: Received 18 June 2018 Received in revised form 10 August 2018 Accepted 20 August 2018
Keywords: Carbon materials Nanoparticles Energy storage and conversion
a b s t r a c t Novel microporous carbon materials (DCMC) with excellent electron conductivity and ultrahigh surface area (1896.9 m2 g 1) are successfully prepared from discarded clothes. The porous carbon-encapsulated sulfur composites were synthesized by a feasible melting process and used as host materials for lithium sulfur batteries. Because of the unique microporous, ultrahigh surface area and irregular wrinkled surface coexisting structure, the resulting microporous carbon/sulfur (DCMC/S) composite cathode possesses a good rate capability and long-term cycling performance. The initial discharge capacity of the DCMC2/S composite electrode with 74.3 wt% sulfur content is 1082.6 mAh g 1 at a current rate of 0.2 C. At a higher current rate of 1 C, it possesses excellent cyclic performance and retained a capacity of 422.8 mAh g 1 after 500 cycles with a low capacity fading rate of 0.11% per cycle. The coulombic efficiency remains over 98% during cycling. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction With an increasing demand for high energy density storage system, more and more attention has been paid to the research of rechargeable Li-ion batteries. Nevertheless, the current Li-ion batteries are limited by the low capacity, high cost, and unsafety [1–3]. Rechargeable lithium-sulfur battery has aroused researchers’ attention because of the high theoretical specific capacity (1675 mAh g 1) and theoretical energy density (2600 Wh kg 1) [4–6]. Sulfur as a suitable cathode material also has other advantages such as natural abundance, nontoxicity and environmental benignity. However, the commercialization of Li-S battery is still hindered by some chronic issues: (1) the sulfur and reduction products (Li2S2 and Li2S) are electronically insulating at room temperature resulting in the low utilization of sulfur and low practical capacity. (2) The highly dissolved polysulfide intermediates spontaneously shuttle between the sulfur cathode and metal lithium anode leading to low coulombic efficiency and capacity decay. (3) The obvious volumetric expansion (80%) of sulfur cathode during charging and discharging process, which causes insufficient cycle life [7–10]. To solve these problems, considerable approaches have been proposed to improve the electrical conductivity of the cathode and retard diffusion of polysulfide in organic electrolytes. ⇑ Corresponding author. E-mail address: [email protected] (Y. Huang). https://doi.org/10.1016/j.matlet.2018.08.112 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
One of the most effective means is to encapsulate sulfur with host matrixes to construct composite materials, particularly porous carbon [11]. Porous carbon materials have excellent conductivity, high pore volume and large surface area. They provide excellent conductivity for sulfur and discharging products, improving the utilization rate of active materials. Moreover, the porous structure, large surface area and strong adsorption can alleviate the diffusion of polysufides. Discarded clothes are abundant in our daily life. In this work, we first report a novel and simple way to prepare microporous carbon from discarded clothes (DCMC) by a carbonization and KOH activation process. The optimized microporous carbon DCMC2 with ultrahigh surface area (1896.9 m2 g 1) can encapsulate high sulfur content. The microporous carbon/sulfur composites (DCMC/S) were synthesized by simple melting diffusion treatments. As expected, the electrochemical properties of DCMC/S composite cathode delivered a high specific capacity, excellent cycling stability and good rate capability. 2. Experiment 2.1. Preparation of DCMC/S composites The discarded clothes made of pure cotton were collected, and then cleaned using deionized water. After being dried in the oven at 80 °C for 24 h, they were cut into pieces. The dried discarded
X. Sun et al. / Materials Letters 232 (2018) 122–125
123
clothes were carbonized in a tube furnace under Ar atmosphere at 500 °C for 2 h with a heating rate of 2 °C min 1. The obtained carbonized discarded clothes after milling were mixed with KOH (w/ w = 1:2, 1:4) in ethanol. The mixture was stirred thoroughly for 3 h at room temperature, and then dried at 80 °C in an oven. Then the mixture was activated in a tube furnace at 900 °C for 3 h under an argon atmosphere. The obtained carbon materials were washed with 1 M HCl three times, washed several times with deionized water, and then dried at 80 °C in the oven over night to obtain the DCMC1 and DCMC2. The as-prepared DCMC and sublimed sulfur with the weight ratio of 1:4 were ground together, and subsequently heated at 155 °C for 12 h in a sealed glass tube, the resultant denoted as DCMC1/S or DCMC2/S.
2.2. Materials characterization
Fig. 1. SEM images of (a) DCMC, (b) DCMC2, (c–d) DCMC2/S composite.
The surface morphologies of samples were characterized through field-emission scanning electron microscopy (FE-SEM, Carl Zeiss SIGMA). The crystal structure was tested with X-ray diffraction ((XRD, CuKa radiation, PANalytical, Holland). The sulfur content in the DCMC/S composites was determined by the thermo gravimetric/differential thermal analysis (TG/DTA) measurement (Netzsch STA 449C thermal analyzer). The N2 adsorption–desorption isotherm and pore size distribution was obtained using a Brunauer Emmett-Teller (BET, BEL LAPAN, INC. Belsorp2).
Fig. 2. (a) XRD pattern of sulfur, DCMC, DCMC1/S and DCMC2/S; (b) TGA curves of DCMC1/S, DCMC2/S and sulfur; (c) Nitrogen adsorption–desorption isotherms of DCMC1, DCMC2, DCMC1/S and DCMC2/S; (d) Pore size distribution of the DCMC1 and DCMC2.
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Fig. 3. (a) Cycling performances of DCMC1/S and DCMC2/S at 0.2C; (b) galvanostatic charge/discharge profiles; (c) rate performance; (d) cyclic voltammogram profiles; (e) cycle performance for 500 cycles at 1 C of DCMC2/S.
2.3. Electrochemical measurements The electrochemical performances were evaluated via CR2016 coin cell with lithium metal as the anode electrode and Celgard 2400 film as a separator. As for the cathode electrode, it consisted of 80 wt% DCMC1/S composite, 10 wt% super P and 10 wt% poly (vinylidene fluoride) (PVDF) as a binder in N-methylpyrrolidone (NMP) solvent dispersant. The slurry was uniformly coated on an aluminum foil and dried at 60 °C overnight in a vacuum oven
overnight. The electrodes were cut into circular discs with a diameter of 10 mm and the sulfur loading was about 1.1 mg cm 2. The electrolyte solution was 1 M lithium bis-trifluoromethanesulfonyli mide (LiTFSI) and 0.1 M lithium nitrate dissolved in a mixture of 1,3-dioxolane (DOL) and dimethoxymethane (DME) with a volume ration of 1:1. Charge-discharge tests were carried out at different current densities in a voltage window of 1.7–2.8 V under room temperature, using a CT2001A cell test instrument (LAND Electronic Co. Ltd., China). The cyclic voltammetry (CV) was conducted
X. Sun et al. / Materials Letters 232 (2018) 122–125
on a Series G750TM Redefining Electrochemical Measurement (USA GMARY Co.) at a scan rate of 0.1 mV s 1 between 1.7 V and 2.8 V. 3. Results and discussions The morphology and structure of the prepared materials were investigated by SEM, as shown in Fig. 1. Fig. 1(a) exhibits the microstructure of the DCMC with about 5–10 lm in diameter and the outer surface appears to be very rough in the inset image. After an activation treatment by the potassium hydroxide at 900 °C, the inner morphology is exposed and the obtained DCMC2 (Fig. 1(b)) exhibits unique porous structures, which plays a positive role on the infiltration of the electrolyte and lithium-ion. As shown in Fig. 1(c–d), the DCMC2/S composite has a smooth surface and a few of sulfur was observed, indicating the complete diffusion of sulfur into the DCMC The typical XRD of pure sulfur, DCMC, DCMC1/S and DCMC2/S composites are shown in Fig. 2(a). DCMC sample shows two broad diffraction peaks around 25° and 45°, which means that is a high amorphous structure. As for the DCMC1/S and DCMC2/S composites, they show sharp peaks of crystal sulfur, which suggests that the crystal sulfur are evenly incorporated into the amorphous carbon. This is further confirmed by TGA measurements (Fig. 2(b)), in which the sulfur content in the DCMC1/S and DCMC2/S composites are 76.3 and 74.3 wt%, respectively. The desorption temperature of the DCMC1/S and DCMC2/S composites is much higher than that of sublimed sulfur, demonstrating a strong interaction between carbon and sulfur. Fig. 2(c–d) presents the N2 adsorption-desorption isotherms and density functional theory (DFT) pore size distribution curves of the as-prepared materials. The classic type I isotherm (Fig. 2c) shows the microporous nature. The BET surface of DCMC1 and DCMC2 is 1184.9 m2 g 1 and 1896.9 m2 g 1, respectively. The pore size of DCMC1 and DCMC2 both locate between 0.6 nm and 0.9 nm. Fig. 3(a) presents the cycling performance of the DCMC1/S and DCMC2/S composites electrode. The DCMC1/S and DCMC2/S display initial discharge capacity of 1012.1 and 1082.6 mAh g 1 and maintain 655 and 546 mAh g 1 after 100 cycles respectively at 0.2C rate. Fig. 3(b) shows the discharge and charge voltage profiles of DCMC2/S composite cathode for the 1st, 10th, 50th, 100th cycles at 0.2C. There are two typical discharge plateaus at about 2.3 and 2.1 V, which are attributed to the two-step reaction between sulfur with Li during the discharge process. These characteristics are consistent with the CV curves, as shown in Fig. 3(d). The three voltage plateaus almost overlap each other, revealing the cell possesses steady electrochemical reduction and cycle performance. The rate capability of DCMC2/S composite cathode is evaluated at various current rates from 0.1 to 2C in Fig. 3(c). The capacity of 1197.5 mAh g 1, 890.2 mAh g 1, 723.8 mAh g 1, 638.9 mAh g 1
125
and 562.6 mAh g 1 was measured at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, respectively. The capacity of every rate decreased gradually with the increased current rate. Nonetheless, when the chargeedischarge current density was reset to 0.1 C, the discharge capacity can recover to 782.1 mAh g 1, demonstrating DCMC2/S composites have an excellent rate capability and reliability. To further investigate the excellent electrochemical performance, the long-cycling performance of DCMC2/S was evaluated at 1 C (Fig. 2(e)). A high discharge capacity of 422.8 mAh g 1 was achieved after 500 cycles with a Coulombic efficiency above 98% during cycling and an ultralow capacity fade rate of 0.11% per cycle. These results prove the cycle performance is improved, which mainly ascribe to the excellent conductivity and the unique microporous structure of the carbon host matrix. 4. Conclusions In summary, a novel DCMC has been prepared and is first used to encapsulate sulfur for Li-S batteries. High surface area and large pore volume make it high sulfur content of 74.3 wt%. The DCMC2/S composite cathode delivered a high initial discharge capacity of 1082.6 mAh g 1 at 0.2 C. In addition, it possesses excellent cyclic performance and retained a capacity of 422.8 mAh g 1 after 500 cycles with a low capacity fading rate of 0.11% per cycle, exhibiting excellent electrochemical performance. Therefore, the DCMC is promising materials for Li-S batteries. Acknowledgments We would like to thank the Analytical & Testing Center of Northwestern Polytechnical University for equipment supporting. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.matlet.2018.08.112. References [1] J.K. Lee, M.C. Kung, L. Trahey, M.N. Missaghi, H.H. Kung, Chem. Mater. 21 (2009) 6–8. [2] G.Y. Zheng, Q.F. Zhang, J.J. Cha, Y. Yang, W.Y. Li, Z.W. Seh, Y. Cui, Nano Lett. 13 (2013) 1265–1270. [3] B. Zhang, X. Qin, G.R. Lia, X.P. Gao, Energy Environ. Sci. 3 (2010) 1531–1537. [4] D. Peramunage, S. Licht, Science 261 (1993) 1029–1032. [5] W. Zhai, W. Tu, Y. Liu, Electrochim. Acta 219 (2016) 143–151. [6] S.S. Zhang, J. Power Sources 231 (2013) 153–162. [7] Z. Cao, C. Wang, J. Chen, Mater. Lett. 225 (2018) 157–160. [8] J.X. Song, Z.X. Yu, M.L. Gordin, D.H. Wang, Nano Lett. 16 (2016) 864–870. [9] Z. Sun, S. Wang, L. Yan, M. Xiao, D. Han, Y. Meng, J. Power Sources 324 (2016) 547–555. [10] K. Mi, Y. Jiang, J. Feng, Adv. Funct. Mater. 26 (2016) 1571–1579. [11] H. Wu, Y. Huang, W. Zhang, J. Alloys Compd. 708 (2017) 743–750.