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Pomegranate-like [email protected] graphitized carbon spheres as high-performance cathode for lithium-sulfur battery
Journal Pre-proofs Pomegranate-like S@N-doped graphitized carbon spheres as high-performance cathode for lithium-sulfur battery Zhanglong Chen, Songpu Cheng, Yuxi Chen, Xiaohong Xia, Hongbo Liu PII: DOI: Reference:
S0167-577X(19)31915-9 https://doi.org/10.1016/j.matlet.2019.127283 MLBLUE 127283
To appear in:
Materials Letters
Received Date: Accepted Date:
23 October 2019 28 December 2019
Please cite this article as: Z. Chen, S. Cheng, Y. Chen, X. Xia, H. Liu, Pomegranate-like S@N-doped graphitized carbon spheres as high-performance cathode for lithium-sulfur battery, Materials Letters (2019), doi: https://doi.org/ 10.1016/j.matlet.2019.127283
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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.
© 2019 Published by Elsevier B.V.
Pomegranate-like
S@N-doped
graphitized
carbon
spheres
as
high-performance cathode for lithium-sulfur battery Zhanglong Chen, Songpu Cheng, Yuxi Chen*, Xiaohong Xia, Hongbo Liu College of Materials Science and Engineering, Hunan University, Changsha 410082, China Abstract To obtain high-performance sulfur cathode for lithium-sulfur (Li-S) battery, porous graphitized carbon spheres with N doping have been fabricated via an in situ Fe catalysis as sulfur host. The in situ generated Fe nanoparticles play double roles as graphitization catalyst and pore template. The electrical conductivity of the graphitized sample (5.6 S cm‒1) is about one order of magnitude higher than that of the amorphous carbon sample (0.63 S cm‒1). Correspondingly, the pomegranate-like S@N-doped graphitized carbon cathode displays very good electrochemical performance. A capacity of 600 mAh g−1 is obtained after 150 charge/discharge cycles at a current density of 1 C with a sulfur content of 73 wt.%. The pomegranate-like S@N-doped graphitized carbon is promising cathode candidate for high-performance Li-S battery.
Keywords: energy storage and conversion; nanocomposites; graphitized carbon; nitrogen doping; lithium-sulfur batteries
*Corresponding author. Email: [email protected] (Yuxi Chen); Tel: +86-731-88664018; Fax: +86-731-88823554
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1. Introduction The theoretical energy density of Li-S battery is over 5 times higher than those of commercial lithium-ion batteries. However, the intrinsic low electrical conductivity and shuttle effect of soluble polysulfides (LiPS) strongly restrict its applications [1,2]. Porous carbon framework can facilitate electron transport and inhibit the shuttle effect by physical containment and chemical adsorption [3]. Therefore, employing porous carbon framework is an effective way to optimize electrochemical performance of Li-S batteries [4]. To date, various carbonaceous materials have been exploited as conductivity sulfur hosts, such as carbon nanotubes [5], carbon nanofibers [6], graphene[7] and porous carbon[8]. Graphite possesses much better electrical conductivity than amorphous carbon, rendering it a promising and favorable sulfur host candidate. Previous investigations indicated that the amorphous carbon can be reconstructed to graphite structure under in situ catalytic effect of transition metal at relatively low temperature (less than 1000 °C) [9,10]. Herein, we report our strategy of designing and fabricating porous graphitized carbon spheres with N-doping to construct pomegranate-like S@N-doped graphitized carbon spheres as high-performance cathode for Li-S battery, as schematically illustrated in Fig. 1a. The pomegranate-like S@N-doped graphitized carbon spheres exhibit superior electrochemical properties to those of the S@N-doped amorphous carbon spheres. 2. Experimental Phenolic resin (0.32 g), ferric nitrate decahydrate (3.18 g), citric acid monohydrate (1.05g) and urea (0.6g) were dissolved into a mixture of alcohol (50mL) and water (70mL) under stirring. The solution was sonicated into mist and carried into a 400 °C tubular furnace by Ar gas flow. The products were then calcined at 550 °C and 750 °C for 2 h under Ar gas flow, respectively. 2 / 10
Fig. 1. (a) Schematic of formation of the pomegranate-like S@N-doped graphitized carbon spheres. (b) XRD pattern. TEM images of (c) N-GC and (d) S@N-GC. Inset in (c) is SEM image. TEM images of (e) N-C and (f) S@N-C. The products were etched using 0.5 M HCl under stirring, and then dried at 60 °C in vacuum after filtering and washing using deionized water. The resultant was denoted as N-C and N-GC for the calcination temperature of 550 °C and 750 °C, respectively. S@N-GC (or S@N-C) was obtained by mixing N-GC (N-C) with sulfur with a weight ratio of 1:3 and heated at 155 °C for 10 h. The microstructure was characterized by powder X-ray diffraction (XRD, Bruker D8), Raman spectroscopy (Renishaw invia), scanning electron microscope (SEM) (Hitachi S-4800), transmission electron microscope (TEM) (Titan G2 60-300), X-ray photoelectron spectroscopy (XPS) (AXISHIS 165) and N2 absorption (ASAP Tristar 3020). The sulfur content was determined by thermogravimetric (TG) analyzer (DTG-60) in N2 atmosphere. The electronic conductivity was measured by four-probe resistance tester (SZ-82). Electrodes were prepared by drying a slurry (a mixture of 80 wt.% active materials, 10 wt.% 3 / 10
acetylene black and 10 wt.% polyvinylidene fluoride) at 60 °C for 12 h under vacuum. The sulfur loading
density
is
~1.5
mg
cm−2.
The
electrolyte
was
1
M
lithium
bistrifluoromethanesulfonylimide (LiTFSi) dissolved in a mixed solvent of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (1:1, v/v) containing 1% LiNO3. CR2016 coin-type cells were assembled in an argon-filled glove box with Li metal as counter electrode. Galvanostatic discharge/charge cycles were measured on a battery tester (LAND CT 2001A). Cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS) measurements were recorded on an electrochemical workstation (CHI 660E). 3. Results and discussion XRD patterns indicate that the products calcined at 550 °C and 750 °C can be indexed as Fe3O4 and Fe, respectively (Fig. 1b). After etching off Fe3O4, the remainder N-C shows a characteristic reflection of amorphous carbon. However, N-GC exhibits strong graphite diffractions, demonstrating that the amorphous carbon has been graphitized through Fe catalysis at 750 °C. The sharp peak at 2θ = 22° can be assigned to the (002) diffraction of graphite. According to Mering-Maire formula [11,12], the graphitization degree G can be calculated via the following equation, G = (0.3440-d002)/(3.3440-0.3354)×100%.
(1)
Correspondingly, the graphitization degree of N-GC is 67%. SEM observations indicate spherical morphology of the serial products with sizes in a range of ~100 to ~800 nm (Supporting Information Fig. S1). After sulfur loading, the surfaces of S@N-GC and S@N-C become smooth. TEM observation demonstrates porous structure of N-GC (Fig. 1c). Inset is a SEM image of a broken N-GC sphere, indicating a multi-cavity structure. The loaded sulfur is gathered at the cavities (Fig. 1d), constructing pomegranate-like structure. N-C 4 / 10
displays porous structure (Fig. 1e). TEM contrast becomes dark after sulfur loading (Fig. 1f). High-angle angular dark field (HAADF) imaging and element mapping demonstrate uniform distributions of nitrogen in the two samples (Fig. S2). Sulfur is gathered at the cavities of N-GC. TG analysis indicates that the sulfur contents in S@N-GC and S@N-C are 73 wt.% (Fig. 2a).
Fig. 2. (a) TG curves. High-resolution N 1s peaks of (b) N-GC and (c) N-C. (d) Raman spectra. (e) N2 absorption/desorption isotherms. (f) Pore size distributions. XPS measurements demonstrate presence of carbon, nitrogen and oxygen in the two samples (Fig. S3). High-resolution spectra of N 1s peaks of N-GC (Fig. 2b) and N-C (Fig. 2c) indicate presence of pyridinic N (398.7 eV), pyrrolic N (400.3 eV), graphitic N (401.0 eV) and quaternary N (403.0 eV). The stronger graphitic N peak of N-GC demonstrates its higher graphitization degree than that of N-C. Furthermore, the nitrogen contents in N-GC and N-C are calculated to be 1.1 at.% and 3.4 at.%, respectively. D band (~1360 cm−1) and G band (~1580 cm−1) are presented in Raman spectra of the two samples (Fig. 2d). The intensity ratio of D band to G band ID/IG is calculated to be 0.28 and 0.73 for N-GC and N-C, respectively, demonstrating much higher order and graphitization degree of N-GC [12,13]. Correspondingly, the electrical conductivity of N-GC was measured to be 5.6 S 5 / 10
cm‒1, which is one order of magnitude higher than that of N-C (0.63 S cm‒1). N2 absorption/desorption measurements indicate that the BET surface area of N-GC is 222.4 m2 g−1, which is smaller than that of N-C (765.8 m2 g−1) (Fig. 2e). Micropore and mesopore densities of N-GC are much lower than those of N-C, while the macropore density is higher (Fig. 2f). Electrochemical performances of S@N-GC and S@N-C have been evaluated. Rate capability of S@N-GC is superior to that of S@N-C (Fig. 3a). S@N-GC delivers an initial discharge
Fig. 3. (a) Rate capabilities. Voltage profiles of (b) S@N-GC and (c) S@N-C. (d) Cyclic performances at 1 C. (e) Nyquist plots and (f) proposed equivalent circuit for fitting.
capacity of 1161 mAh g−1 at 0.2 C. Then, a capacity of 514 mAh g−1 is obtained after the current density increases to 2 C. The voltage profiles of S@N-GC and S@N-C are shown in Fig. 3b and c, respectively. It can be seen that the two-stage lithiation characteristics of S@N-GC still exist at high current densities, while those of S@N-C are blurred, indicating higher electrochemical reversibility of S@N-GC than that of S@N-C. The cycling performance of S@N-GC is much better than that of S@N-C (Fig. 3d). 6 / 10
S@N-GC delivers an initial discharge capacity of 857 mAh g−1, and maintains 600 mAh g−1 after 150 cycles at a current density of 1 C. S@N-C deliver a capacity of 419 mAh g−1 after 150 cycles. The Nyquist plots of the two samples (Fig. 3e) have been measured and fitted using an equivalent circuit (Fig. 3f). It can be seen that the fitted data represented by solid curves agree well with the experimental ones. RLi2S values of S@N-GC and S@N-C are fitted to be 47.9 and 61.2 Ω, respectively, while Rct values are fitted to be 5.8 and 400 Ω, respectively. The much better electrochemical performance of S@N-GC is endowed by the unique pomegranate-like structure. The loaded sulfur is gathered at cavities of the graphitized carbon matrix, resulting in fast electron/Li-ion transport. Furthermore, the low micropore and mesopores densities of S@N-GC may give rise to strong impedance of LiPS shuttle. The pomegranate-like S@N-GC is promising cathode material for high-performance Li-S battery. 4. Conclusions Porous graphitized carbon spheres and amorphous carbon spheres with N doping have been fabricated via a facile and controlled aerosol-pyrolysis route. The in situ catalysis effect of Fe nanoparticles induces graphitization of carbon. The pomegranate-like S@N-doped graphitized carbon spheres display superior electrochemical performance to that of the S@N-doped amorphous carbon spheres, which deliver an initial discharge capacity of 857 mAh g−1 and maintains 600 mAh g−1 after 150 cycles at a current density of 1 C. The high electrical conductivity and efficient suppression of LiPS shuttle make the pomegranate-like S@N-doped graphitized carbon spheres promising candidate for Li-S battery. Declaration of competing interest The authors declare that they have no known competing financial interests or personal 7 / 10
relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was supported by National Natural Science Foundation of China (51472083). References [1] C. Li, Z. Xi, D. Guo, X. Chen, L. Yin, Small 14 (2017) 1701986-1702007. [2] Z.W. Seh, Y. Sun, Q. Zhang, Y. Cui, Chem. Soc. Rev. 45 (2016) 5605-5634. [3] F. Li, H. Cheng, Z. Sun, J. Liang, Energy Storage Mater. 2 (2016) 76-106. [4] D. Gueon, J.T. Hwang, S.B. Yang, E. Cho, K. Sohn, D.K. Yang, J.H. Moon, Acs Nano 12 (2018) 226−233. [5] Q.Q. Wang, J.B. Huang, G.R. Li, Z. Lin, B.H. Liu, Z.P. Li, J. Power Sources 339 (2017) 20-26. [6] Y.Z. Zhang, Z. Zhang, S. Liu, G. Li, X.P. Gao, ACS Appl. Mater. Interfaces 10 (2018) 8749-8757. [7] Z. Sun, J. Zhang, L. Yin, G. Hu, R. Fang, H.M. Cheng, L. Feng, Nat. Commun. 8 (2017) 14627. [8] G. Li, J. Sun, W. Hou, S. Jiang, Y. Huang, J Geng, Nat. Commun. 7 (2016) 10601. [9] C.S. Bitencourt, A.P. Luz, C. Pagliosa, V.C. Pandolfelli, Ceram. Int. 41 (2015) 13320-13330. [10] A. Oya, S. Jikihara, S. Otani, Fuel 62 (1983) 50-55. [11] N. Iwashita, R.P. Chong, H. Fujimoto, M. Shiraishi, M. Inagaki, Carbon 42 (2004) 701-714. [12] Y. Niu, Z. Xin, J. Wu, J. Zhao, X. Yan, L. Yao, RSC Adv. 4 (2014) 42569-42576. [13] M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, L.G. Cançado, A. Jorio, R. Saito, Phys. Chem. Chem. Phys 9 (2007) 1276-1290.
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Highlights ►N-doped porous graphitized carbon spheres have been fabricated as sulfur host. ►The in situ formed Fe nanoparticles play double roles as graphitization catalyst and pore template. ►The electrical conductivity of the N-doped porous graphitized carbon spheres reaches 5.6 S cm‒1. ► The pomegranate-like S@N-doped graphitized carbon display good Li-ion storage performance.
Conflict of interest form There are no conflicts of interest.
10 / 10
S0167-577X(19)31915-9 https://doi.org/10.1016/j.matlet.2019.127283 MLBLUE 127283
To appear in:
Materials Letters
Received Date: Accepted Date:
23 October 2019 28 December 2019
Please cite this article as: Z. Chen, S. Cheng, Y. Chen, X. Xia, H. Liu, Pomegranate-like S@N-doped graphitized carbon spheres as high-performance cathode for lithium-sulfur battery, Materials Letters (2019), doi: https://doi.org/ 10.1016/j.matlet.2019.127283
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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.
© 2019 Published by Elsevier B.V.
Pomegranate-like
S@N-doped
graphitized
carbon
spheres
as
high-performance cathode for lithium-sulfur battery Zhanglong Chen, Songpu Cheng, Yuxi Chen*, Xiaohong Xia, Hongbo Liu College of Materials Science and Engineering, Hunan University, Changsha 410082, China Abstract To obtain high-performance sulfur cathode for lithium-sulfur (Li-S) battery, porous graphitized carbon spheres with N doping have been fabricated via an in situ Fe catalysis as sulfur host. The in situ generated Fe nanoparticles play double roles as graphitization catalyst and pore template. The electrical conductivity of the graphitized sample (5.6 S cm‒1) is about one order of magnitude higher than that of the amorphous carbon sample (0.63 S cm‒1). Correspondingly, the pomegranate-like S@N-doped graphitized carbon cathode displays very good electrochemical performance. A capacity of 600 mAh g−1 is obtained after 150 charge/discharge cycles at a current density of 1 C with a sulfur content of 73 wt.%. The pomegranate-like S@N-doped graphitized carbon is promising cathode candidate for high-performance Li-S battery.
Keywords: energy storage and conversion; nanocomposites; graphitized carbon; nitrogen doping; lithium-sulfur batteries
*Corresponding author. Email: [email protected] (Yuxi Chen); Tel: +86-731-88664018; Fax: +86-731-88823554
1 / 10
1. Introduction The theoretical energy density of Li-S battery is over 5 times higher than those of commercial lithium-ion batteries. However, the intrinsic low electrical conductivity and shuttle effect of soluble polysulfides (LiPS) strongly restrict its applications [1,2]. Porous carbon framework can facilitate electron transport and inhibit the shuttle effect by physical containment and chemical adsorption [3]. Therefore, employing porous carbon framework is an effective way to optimize electrochemical performance of Li-S batteries [4]. To date, various carbonaceous materials have been exploited as conductivity sulfur hosts, such as carbon nanotubes [5], carbon nanofibers [6], graphene[7] and porous carbon[8]. Graphite possesses much better electrical conductivity than amorphous carbon, rendering it a promising and favorable sulfur host candidate. Previous investigations indicated that the amorphous carbon can be reconstructed to graphite structure under in situ catalytic effect of transition metal at relatively low temperature (less than 1000 °C) [9,10]. Herein, we report our strategy of designing and fabricating porous graphitized carbon spheres with N-doping to construct pomegranate-like S@N-doped graphitized carbon spheres as high-performance cathode for Li-S battery, as schematically illustrated in Fig. 1a. The pomegranate-like S@N-doped graphitized carbon spheres exhibit superior electrochemical properties to those of the S@N-doped amorphous carbon spheres. 2. Experimental Phenolic resin (0.32 g), ferric nitrate decahydrate (3.18 g), citric acid monohydrate (1.05g) and urea (0.6g) were dissolved into a mixture of alcohol (50mL) and water (70mL) under stirring. The solution was sonicated into mist and carried into a 400 °C tubular furnace by Ar gas flow. The products were then calcined at 550 °C and 750 °C for 2 h under Ar gas flow, respectively. 2 / 10
Fig. 1. (a) Schematic of formation of the pomegranate-like S@N-doped graphitized carbon spheres. (b) XRD pattern. TEM images of (c) N-GC and (d) S@N-GC. Inset in (c) is SEM image. TEM images of (e) N-C and (f) S@N-C. The products were etched using 0.5 M HCl under stirring, and then dried at 60 °C in vacuum after filtering and washing using deionized water. The resultant was denoted as N-C and N-GC for the calcination temperature of 550 °C and 750 °C, respectively. S@N-GC (or S@N-C) was obtained by mixing N-GC (N-C) with sulfur with a weight ratio of 1:3 and heated at 155 °C for 10 h. The microstructure was characterized by powder X-ray diffraction (XRD, Bruker D8), Raman spectroscopy (Renishaw invia), scanning electron microscope (SEM) (Hitachi S-4800), transmission electron microscope (TEM) (Titan G2 60-300), X-ray photoelectron spectroscopy (XPS) (AXISHIS 165) and N2 absorption (ASAP Tristar 3020). The sulfur content was determined by thermogravimetric (TG) analyzer (DTG-60) in N2 atmosphere. The electronic conductivity was measured by four-probe resistance tester (SZ-82). Electrodes were prepared by drying a slurry (a mixture of 80 wt.% active materials, 10 wt.% 3 / 10
acetylene black and 10 wt.% polyvinylidene fluoride) at 60 °C for 12 h under vacuum. The sulfur loading
density
is
~1.5
mg
cm−2.
The
electrolyte
was
1
M
lithium
bistrifluoromethanesulfonylimide (LiTFSi) dissolved in a mixed solvent of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (1:1, v/v) containing 1% LiNO3. CR2016 coin-type cells were assembled in an argon-filled glove box with Li metal as counter electrode. Galvanostatic discharge/charge cycles were measured on a battery tester (LAND CT 2001A). Cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS) measurements were recorded on an electrochemical workstation (CHI 660E). 3. Results and discussion XRD patterns indicate that the products calcined at 550 °C and 750 °C can be indexed as Fe3O4 and Fe, respectively (Fig. 1b). After etching off Fe3O4, the remainder N-C shows a characteristic reflection of amorphous carbon. However, N-GC exhibits strong graphite diffractions, demonstrating that the amorphous carbon has been graphitized through Fe catalysis at 750 °C. The sharp peak at 2θ = 22° can be assigned to the (002) diffraction of graphite. According to Mering-Maire formula [11,12], the graphitization degree G can be calculated via the following equation, G = (0.3440-d002)/(3.3440-0.3354)×100%.
(1)
Correspondingly, the graphitization degree of N-GC is 67%. SEM observations indicate spherical morphology of the serial products with sizes in a range of ~100 to ~800 nm (Supporting Information Fig. S1). After sulfur loading, the surfaces of S@N-GC and S@N-C become smooth. TEM observation demonstrates porous structure of N-GC (Fig. 1c). Inset is a SEM image of a broken N-GC sphere, indicating a multi-cavity structure. The loaded sulfur is gathered at the cavities (Fig. 1d), constructing pomegranate-like structure. N-C 4 / 10
displays porous structure (Fig. 1e). TEM contrast becomes dark after sulfur loading (Fig. 1f). High-angle angular dark field (HAADF) imaging and element mapping demonstrate uniform distributions of nitrogen in the two samples (Fig. S2). Sulfur is gathered at the cavities of N-GC. TG analysis indicates that the sulfur contents in S@N-GC and S@N-C are 73 wt.% (Fig. 2a).
Fig. 2. (a) TG curves. High-resolution N 1s peaks of (b) N-GC and (c) N-C. (d) Raman spectra. (e) N2 absorption/desorption isotherms. (f) Pore size distributions. XPS measurements demonstrate presence of carbon, nitrogen and oxygen in the two samples (Fig. S3). High-resolution spectra of N 1s peaks of N-GC (Fig. 2b) and N-C (Fig. 2c) indicate presence of pyridinic N (398.7 eV), pyrrolic N (400.3 eV), graphitic N (401.0 eV) and quaternary N (403.0 eV). The stronger graphitic N peak of N-GC demonstrates its higher graphitization degree than that of N-C. Furthermore, the nitrogen contents in N-GC and N-C are calculated to be 1.1 at.% and 3.4 at.%, respectively. D band (~1360 cm−1) and G band (~1580 cm−1) are presented in Raman spectra of the two samples (Fig. 2d). The intensity ratio of D band to G band ID/IG is calculated to be 0.28 and 0.73 for N-GC and N-C, respectively, demonstrating much higher order and graphitization degree of N-GC [12,13]. Correspondingly, the electrical conductivity of N-GC was measured to be 5.6 S 5 / 10
cm‒1, which is one order of magnitude higher than that of N-C (0.63 S cm‒1). N2 absorption/desorption measurements indicate that the BET surface area of N-GC is 222.4 m2 g−1, which is smaller than that of N-C (765.8 m2 g−1) (Fig. 2e). Micropore and mesopore densities of N-GC are much lower than those of N-C, while the macropore density is higher (Fig. 2f). Electrochemical performances of S@N-GC and S@N-C have been evaluated. Rate capability of S@N-GC is superior to that of S@N-C (Fig. 3a). S@N-GC delivers an initial discharge
Fig. 3. (a) Rate capabilities. Voltage profiles of (b) S@N-GC and (c) S@N-C. (d) Cyclic performances at 1 C. (e) Nyquist plots and (f) proposed equivalent circuit for fitting.
capacity of 1161 mAh g−1 at 0.2 C. Then, a capacity of 514 mAh g−1 is obtained after the current density increases to 2 C. The voltage profiles of S@N-GC and S@N-C are shown in Fig. 3b and c, respectively. It can be seen that the two-stage lithiation characteristics of S@N-GC still exist at high current densities, while those of S@N-C are blurred, indicating higher electrochemical reversibility of S@N-GC than that of S@N-C. The cycling performance of S@N-GC is much better than that of S@N-C (Fig. 3d). 6 / 10
S@N-GC delivers an initial discharge capacity of 857 mAh g−1, and maintains 600 mAh g−1 after 150 cycles at a current density of 1 C. S@N-C deliver a capacity of 419 mAh g−1 after 150 cycles. The Nyquist plots of the two samples (Fig. 3e) have been measured and fitted using an equivalent circuit (Fig. 3f). It can be seen that the fitted data represented by solid curves agree well with the experimental ones. RLi2S values of S@N-GC and S@N-C are fitted to be 47.9 and 61.2 Ω, respectively, while Rct values are fitted to be 5.8 and 400 Ω, respectively. The much better electrochemical performance of S@N-GC is endowed by the unique pomegranate-like structure. The loaded sulfur is gathered at cavities of the graphitized carbon matrix, resulting in fast electron/Li-ion transport. Furthermore, the low micropore and mesopores densities of S@N-GC may give rise to strong impedance of LiPS shuttle. The pomegranate-like S@N-GC is promising cathode material for high-performance Li-S battery. 4. Conclusions Porous graphitized carbon spheres and amorphous carbon spheres with N doping have been fabricated via a facile and controlled aerosol-pyrolysis route. The in situ catalysis effect of Fe nanoparticles induces graphitization of carbon. The pomegranate-like S@N-doped graphitized carbon spheres display superior electrochemical performance to that of the S@N-doped amorphous carbon spheres, which deliver an initial discharge capacity of 857 mAh g−1 and maintains 600 mAh g−1 after 150 cycles at a current density of 1 C. The high electrical conductivity and efficient suppression of LiPS shuttle make the pomegranate-like S@N-doped graphitized carbon spheres promising candidate for Li-S battery. Declaration of competing interest The authors declare that they have no known competing financial interests or personal 7 / 10
relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was supported by National Natural Science Foundation of China (51472083). References [1] C. Li, Z. Xi, D. Guo, X. Chen, L. Yin, Small 14 (2017) 1701986-1702007. [2] Z.W. Seh, Y. Sun, Q. Zhang, Y. Cui, Chem. Soc. Rev. 45 (2016) 5605-5634. [3] F. Li, H. Cheng, Z. Sun, J. Liang, Energy Storage Mater. 2 (2016) 76-106. [4] D. Gueon, J.T. Hwang, S.B. Yang, E. Cho, K. Sohn, D.K. Yang, J.H. Moon, Acs Nano 12 (2018) 226−233. [5] Q.Q. Wang, J.B. Huang, G.R. Li, Z. Lin, B.H. Liu, Z.P. Li, J. Power Sources 339 (2017) 20-26. [6] Y.Z. Zhang, Z. Zhang, S. Liu, G. Li, X.P. Gao, ACS Appl. Mater. Interfaces 10 (2018) 8749-8757. [7] Z. Sun, J. Zhang, L. Yin, G. Hu, R. Fang, H.M. Cheng, L. Feng, Nat. Commun. 8 (2017) 14627. [8] G. Li, J. Sun, W. Hou, S. Jiang, Y. Huang, J Geng, Nat. Commun. 7 (2016) 10601. [9] C.S. Bitencourt, A.P. Luz, C. Pagliosa, V.C. Pandolfelli, Ceram. Int. 41 (2015) 13320-13330. [10] A. Oya, S. Jikihara, S. Otani, Fuel 62 (1983) 50-55. [11] N. Iwashita, R.P. Chong, H. Fujimoto, M. Shiraishi, M. Inagaki, Carbon 42 (2004) 701-714. [12] Y. Niu, Z. Xin, J. Wu, J. Zhao, X. Yan, L. Yao, RSC Adv. 4 (2014) 42569-42576. [13] M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, L.G. Cançado, A. Jorio, R. Saito, Phys. Chem. Chem. Phys 9 (2007) 1276-1290.
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9 / 10
Highlights ►N-doped porous graphitized carbon spheres have been fabricated as sulfur host. ►The in situ formed Fe nanoparticles play double roles as graphitization catalyst and pore template. ►The electrical conductivity of the N-doped porous graphitized carbon spheres reaches 5.6 S cm‒1. ► The pomegranate-like S@N-doped graphitized carbon display good Li-ion storage performance.
Conflict of interest form There are no conflicts of interest.
10 / 10