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Accepted Manuscript A Green Route to Synthesize Low-cost and High-performance Hard Carbon as Promising Sodium-ion Battery Anodes from Sorghum Stalk Waste Xiaoming Zhu, Xiaoyu Jiang, Xiaoling Liu, Lifen Xiao, Yuliang Cao PII:

S2468-0257(17)30056-0

DOI:

10.1016/j.gee.2017.05.004

Reference:

GEE 69

To appear in:

Green Energy and Environment

Received Date: 21 March 2017 Revised Date:

21 May 2017

Accepted Date: 22 May 2017

Please cite this article as: X. Zhu, X. Jiang, X. Liu, L. Xiao, Y. Cao, A Green Route to Synthesize Lowcost and High-performance Hard Carbon as Promising Sodium-ion Battery Anodes from Sorghum Stalk Waste, Green Energy & Environment (2017), doi: 10.1016/j.gee.2017.05.004. 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.

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A Green Route to Synthesize Low-cost and High-performance Hard Carbon as Promising Sodium-ion Battery Anodes from Sorghum Stalk Waste

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Xiaoming Zhua,b, Xiaoyu Jiangc, Xiaoling Liua,b, Lifen Xiao d,* and Yuliang Caoc,* a Hubei Collaboration Innovation Center of Non-power Nuclear Technology, Xianning, China. b School of Nuclear Technology & Chemistry and Biology, Hubei University of Science and

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Technology, Xianning, China.

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c Hubei Key Lab. of Electrochemical Power Sources, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, China

d College of Chemistry, Central China Normal University, Wuhan 430079, China. Corresponding

Author

*

Xiao,

[email protected];

Yuliang

Cao,

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[email protected]

Lifen

Abstract: Sodium-ion batteries (SIBs) have been considered to be potential candidates for next-generation low-cost energy storage systems due to the low cost and abundance of Na

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resources. However, it is a big challenge to find suitable anode materials with low cost and good

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performance for the application of SIBs. Hard carbon could be a promising anode material due to high capacity and expectable low cost if originating from biomass. Herein, we report a hard carbon material derived from abundant and abandoned biomass of sorghum stalk through a simple carbonization method. The effects of carbonization temperature on microstructure and electrochemical performance are investigated. The hard carbon carbonized at 1300 °C delivers the best rate capability (172 mAh g-1 at 200 mA g-1) and good cycling performance (245 mAh g-1 after 50 cycles at 20 mA g-1, 96% capacity retention). This contribution provides a green route for

ACCEPTED MANUSCRIPT transforming sorghum stalk waste into "treasure" of promising low-cost anode material for SIBs. Key words: Sorghum stalk; Hard carbon; Anode; Sodium-ion battery; Carbonization;

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1. Introduction Lithium-ion batteries (LIBs) have been developed as power sources for portable electronic devices over the past few decades because of their high energy density and long cycle life.

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However, the scarcity and non-uniform geographic distribution of lithium resource limit its

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application in large-scale electrical energy storage. Therefore, sodium-ion batteries (SIBs) have attracted increasing scientific attention due to their lower cost and wider global abundance [1, 2]. Until now, a large number of potential cathode materials for SIBs have been developed and achieved substantial success.[3-8] However, developing high-performance anode is still an urgent

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issue [9-11]. Alloys[12-15], metal oxides/sulfides[16, 17], organic compounds[18], phosphate[19] and carbon-based materials[20-22] have been widely investigated for potential SIBs anode materials. Among these materials, carbon-based materials are most attractive due to their

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earth-abundant, cost-effective and eco-friendly characteristics [23, 24].

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Hard carbon with large interlayer distance has attracted wide interesting due to its high capacity (200-300 mAh g-1) and low operating potential as potential anode for SIBs [20, 25]. Some hard carbon can be derived from biomass, such as peat moss [2], banana peels[26], corn cob[27], silk[28], wood cellulose[23], leaf[29], peanut shell[30], exhibiting good performance as an anode for SIBs. The advantages to use the renewable biomass are waste recycling and the alleviation of the environmental pollution. Among, sorghum stalk is one of the most abundant biomass resources on earth, which composes of simple reducing sugars, cellulose, hemicelluloses, lignin and

ACCEPTED MANUSCRIPT associated phenolic acids[31]. Although sorghum stalk is considered as a cost-effective feedstock for bioethanol production and raw material for particleboard industry, most of sorghum stalk is burned directly in the fields, causing enormous waste of resources and severe environmental

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disaster[32, 33]. Therefore, it is highly desirable to develop a better way for effective utilizations of the low-cost and renewable natural resources.

In this study, we prepared hard carbon material from sorghum stalk through high-temperature

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pyrolysis route, which was used as an anode for SIBs for the first time. The electrochemical

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performance of the hard carbon derived from sorghum stalk depended on the carbonization temperature. The optimized hard carbon (carbonized at 1300 °C) resulted in a stable cycling performance (245.0 mAh g-1 after 50 cycles at 20 mA g-1, 96% capacity retention) and high rate capability (172 mAh g-1 at 200 mA g-1). This study provides not only economic value of sorghum

sorghum stalk. 2. Experimental section

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stalk waste, but also a sustainable approach to solve the pollution problem caused by burning

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2.1 Materials Synthesis

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Sorghum stalk was directly collected from the suburb of Shangdong, China. The raw material was smashed by a blender and then put into a tube furnace and carbonized at 1100, 1300, 1500 °C for 2 h under Ar flow with a heating rate of 2 °C min-1. The obtained hard carbon was wash by 3 M HCl at room temperature to remove the impurities and further rinsed by deionized water and collected by filtration. After dried at 100 °C overnight in vacuum oven, hard carbon was obtained and denoted as SSHC1100, SSHC1300 and SSHC1500, respectively. 2.2 Materials characterization

ACCEPTED MANUSCRIPT X-ray diffraction (XRD) was performed on a Shimazdu, model LabX XRD-6000 instrument using Cu Kα radiation. Raman spectroscopy was carried out by a laser micro-Raman spectrometer (Renishaw in Via, Renishaw, 532 nm excitation wavelength). Scanning electron microscope (SEM)

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was conducted by a field-emission scanning electron microscope (FE-SEM, ZEISS Merlin Compact VP, Germany). Transmission electron microscope (TEM) was performed using a field-emission transmission electron microscope (JEM-2100 HR). Berunauer-Emmett-Teller (BET)

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was used for the surface area determination using Mircromeritics ASAP 2020 at liquid N2

2.3 Electrochemical Measurement

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temperature.

The electrode was prepared by mixing the hard carbon with Super P and polyacrylic acid (PAA) in deionized water (8:1:1, weight ratio). The obtained slurry was pasted on a Cu foil followed by

(PVDF) and

wt% poly(vinylidene fluoride)

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drying in a vacuum oven at 100 °C for 12 h. rGO), 10

10 wt.% super P. The loading of the active material in the electrode is about

1.5 mg cm-2. The 2016-type coin cells with sodium foil as the counter electrode, 1 M NaClO4 in

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ethylene carbonate/diethyl carbonate (1:1, by volume) containing 2 vol% fluoroethylene carbonate

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as the electrolyte were assembled in argon-filled glove box. The coin cells were galvanostatically cycled on a LAND cycler (Wuhan LAND Electronics Co., China) between 0 V and 2 V at a current density of 20 mA g-1. Cyclic voltammetry (CV) measurement was carried out with Autolab PGSTAT128N (Eco Chemie, Netherlands). Cyclic voltammetry measurements were carried out at a scan rate of 0.1 mV s-1 between 0 and 2 V (versus Na/Na+). 3. Results and discussion Figure 1 illustrates the synthesis process of hard carbon pyrolyzed from sorghum stalk, which is

ACCEPTED MANUSCRIPT very simple and controllable route. The yield of carbon from sorghum stalk at 1100, 1300 and 1500 °C (SSHC1100, SSHC1300 and SSHC1500) is 23.3%, 22.6% and 15.5%, respectively. Figure 2 show the SEM and high-resolution TEM (HRTEM) images of the SSHC1100,

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SSHC1300 and SSHC1500. All the hard carbon materials display similar morphology regardless of different carbonization temperatures (Figure 2a, c and e). The carbonized sorghum stalks (SSHC1100, SSHC1300 and SSHC1500) show diverse carbon flake with about 10 µm in the

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width and several hundred nanometer in the thickness, which inherits the macroscopic frameworks

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from sorghum stalk. The elementary compositions of SSHC characterized by energy dispersive X-ray spectroscopy (EDS) indicate that all the three samples are composed of ~96% C element, more than 3% O element and less than 1% other elements, as shown in Figure S1 (supporting information). The HRTEM images of these hard carbons show typical disorder morphology

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(Figure 2b, d and f). It can be found that the carbon layer becomes more ordered with increasing carbonization temperature, indicating higher graphitization degree. All selected area electron diffraction patterns show dispersing diffraction rings, suggesting the amorphous characteristics of

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the hard carbons in long-range scale.

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The XRD patterns and Raman spectra of hard carbon are given in Figure 3. All XRD patterns show broad peaks at ~23o and ~44o, which can be assigned to (002) and (110) planes of graphite, respectively (Figure 3a). The (002) peak shifts to a higher angle and becomes narrower with increasing carbonization temperature, implying the average graphene interlayer spacing (d002) decreases and thickness of graphitic domains (Lc) increases. Table 1 summarized the results of XRD, Raman and BET analysis. The d002 values of the SSHC1100, SSHC1300 and SSHC1500 are 0.395, 0.381 and 0.372 nm, respectively, which exhibits a dependence on the pyrolyzing

ACCEPTED MANUSCRIPT temperature. It also can be found that these hard carbons have larger carbon layer spacing than that (0.335 nm) of graphite, which allows for facile Na+ insertion/extraction between the carbon planes.[20] Raman spectra (Figure 3b) present that all samples exhibit a broad disorder-induced

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band (D-band) at ~1340 cm-1 and in-plane vibrational band (G-band) at ~1588 cm-1. The half width at half maximum (HWHM) of D- and G-bands in Raman spectra decreases with increasing carbonization temperature, indicating the improvement of local short-range ordering structure. The

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integral intensity ratio of IG/ID increases with increasing carbonization temperature (Table 1),

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suggesting the decrease of (100) direction of graphitic microcrystal. The XRD and Raman spectroscopy results are well consisted with the observations of the TEM and SEAD. The N2 adsorption-desorption isotherms and pore size distributions estimated by Barrett-Joyner-Halenda (BJH) method of the samples are shown in Figure 3c. The BET surface

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area of the SSHC1100, SSHC1300 and SSHC1500 decreases at first from 234.5 m2 g-1 for the SSHC1100 to 35.55 m2 g-1 for the SSHC1300 and then increases to 85.55 m2 g-1 for the SSHC1500. The trend can be explained that the decrease of the surface area for the SSHC1300 is

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mainly due to the micropore closure in the early stages of raising the carbonization temperature,

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and then the increase of the surface area for the SSHC1500 possibly results from the removal of more functional groups and heteroatom from carbon structure to leave more nanovoids.[21] The pore size less than 2 nm are found in the SSHC1100, while very little pores are presented in SSHC1300 and SSHC1500 (Figure 3c). The specific values of the calculated BET surface area and total pore volume are also summarized in Table 1. Figure 4a displays the typical cyclic voltammetry (CV) curve of the SSHC1300 at 0.1 mV s-1 in the voltage range of 0 - 2 V. The CV curve exhibits a pair of sharp cathodic and anodic peaks

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subsequent cycles, the CV curves are almost overlapped, indicating high reversibility of Na insertion/extraction. Figure 4b shows the first charge-discharge curves of different hard carbon samples at a current density of 10 mA g-1 in the voltage range of 0 - 2 V. All the hard carbon

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electrodes exhibit a sloping region and a plateau region. It is easy to observe that the capacity of

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the sloping region decreases while the plateau region increases with increasing carbonization temperature. This could be explained that the sloping region corresponds to sodium storage in active sites of the surface while the plateau region is assigned to the sodium ion insertion between the carbon layers proposed first by Cao et al.[20] The called "adsorption-insertion" mechanism

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was further verified by in-situ XRD, NMR and EPR in recent works.[34] The higher carbonization temperature leads to less defected sites, higher graphitization degree and more ordering structure, suggesting higher capacity in the plateau region. The SSHC1100, SSHC1300 and SSHC1500

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show the discharge/charge capacities of 419.9/241.5, 411.7/256.1 and 440.3/258.9 mAh g-1 with

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Coulombic efficiency of 57.5%, 62.2% and 58.8%, respectively. The lower Coulombic efficiencies of the SSHC1100 and SSHC1500 are ascribed to the higher number of functional groups remained at a lower carbonization temperature and larger specific surface area compared with the SSHC1300 (Table 1), which causes more irreversible decomposition of electrolyte. The cycling performances of hard carbon electrodes are shown in Figure 4c. All hard carbon electrodes show good cycling stability at 20 mA g-1 and the specific capacities of the SSHC1300 (245.0 mAh g-1) and SSHC1500 (246.3 mAh g-1) are higher than that (192.9 mAh g−1) of

ACCEPTED MANUSCRIPT SSHC1100 after 50 cycles, corresponding to the capacity retention of 84, 96 and 91%, respectively. A comparison of the performance of SSHC with reduced graphene oxide (rGO) is also presented in Figure 4c. It can be seen that the rGO shows low initial charge capacity (133.5 mAh g−1) and

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poor coulombic efficiency (25.4%). Figure 4d displays the rate performance of the three samples. The SSHC1300 shows the best rate performance with the reversible capacity of 255, 241, 235, 212 and 172 mAh g-1 at 10, 20, 50, 100 and 200 mA g-1, respectively, which is possibly because that

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there is higher graphitization degree to facilitate more Na ion insertion/extraction between the

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carbon layers compared with the SSHC1100, while larger carbon layer spacing to provide fast Na ion diffusion compared with the SSHC1500. This suggests that an appropriate carbonization temperature can optimize the Na ion diffusion approach, which results in excellent rate capability. Besides, the reversible capacity can return to the previous values when the current rate is reduced

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to 20 mA g-1, implying an excellent reversibility and structure stability for all hard carbon samples. We compared the cycling and rate performance of the as-prepared SSHC with several state-of-the-art biomass-derived carbon materials reported in literature and the result is illustrated

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in Table S1[35-40]. As can be seen, the SSHC1300 is comparable to some biomass-derived carbon

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materials in capacity and rate capability. To further understand the excellent electrochemical performance, the EIS and SEM analysis are conducted. Figure S2 shows the Nyquist plots of SSHC electrode after 1 and 20 cycles at a current density of 100 mA g-1. As can be seen, the diameter of semicircle in the high-medium-frequency region for all samples is reduced after 20 cycles, suggesting the charge transfer become easier. The improved impedance characteristics of the SSHC electrode are attributed to the maintenance of its structure and the enhanced kinetics through the activation process with cycling. Figure 5 displays

ACCEPTED MANUSCRIPT the electrodes at the fresh state and after 20 cycles at a current density of 100 mA g-1. All the SSHC electrodes after 20 cycles display similar structure with initial state, but only the surface of the electrode is covered by SEI film. These results demonstrate that the SSHC have excellent

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structure stability during cycling, so as to contribute a good cycling performance.

4. Conclusions

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In summary, the hard carbon materials from sorghum stalk has been successfully synthesized

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via a simple one-step carbonization approach for low-cost sodium-ion batteries. The effects of carbonization temperatures on the carbon structure and electrochemical performances are investigated. The electrochemical tests show that the SSHC1300 electrode exhibits the best rate performance (172 mAh g-1 at 200 mA g-1), high reversible capacity (255 mAh g-1 at 20 mA g-1)

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and good cycling performance (96% capacity retention after 50 cycles). This work provides a promising approach to alleviate environmental pollution as well as realize waste utilization to

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develop low-cost anode materials for large-scale energy storage.

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Acknowledgment

The authors gratefully acknowledge the financial support by the 2011 Program of Hubei Province, National Key R&D Program of China (No. 2015CB251100) and National Science Foundation of China (No. 21673165, 21373155 and 21333007), Natural Science Foundation of Hubei Province, China (Grant No. 2015CFC774), Program for New Century Excellent Talents in University (NCET-12-0419) and Hubei National Funds for Distinguished Young Scholars (2014CFA038).

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References [1] J. Xu, M. Wang, N.P. Wickramaratne, M. Jaroniec, S. Dou, L. Dai, Adv. Mater. 27 (2015) 2042-2048. [2] J. Ding, H. Wang, Z. Li, A. Kohandehghan, K. Cui, Z. Xu, B. Zahiri, X. Tan, E.M. Lotfabad, B.C. Olsen, ACS Nano 7 (2013) 11004-11015.

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[3] N. Yabuuchi, M. Kajiyama, J. Iwatate, H. Nishikawa, S. Hitomi, R. Okuyama, R. Usui, Y. Yamada, S. Komaba, Nat. Mater. 11 (2012) 512-517.

[4] M.D. Slater, D. Kim, E. Lee, C.S. Johnson, Adv. Funct. Mater. 23 (2013) 947-958.

[5] Y. Cao, L. Xiao, W. Wang, D. Choi, Z. Nie, J. Yu, L.V. Saraf, Z. Yang, J. Liu, Adv. Mater. 23 (2011) 3155-3160.

[6] Y. Fang, L. Xiao, X. Ai, Y. Cao, H. Yang, Adv. Mater. 27 (2015) 5895-5900.

SC

[7] Y. Fang, J. Zhang, L. Xiao, X. Ai, Y. Cao, H. Yang, Adv. Sci. (2017) 1600392.

[8] Y.-J. Fang, Z.-X. Chen, X.-P. Ai, H.-X. Yang, Y.-L. Cao, Acta Phys.-Chim. Sin. 33 (2017) 211-241. [9] Y. Fang, L. Xiao, J. Qian, X. Ai, H. Yang, Y. Cao, Nano Lett. 14 (2014) 3539-3543.

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[10] Y. Fang, L. Xiao, X. Ai, Y. Cao, H. Yang, Adv. Mater. 27 (2015) 5895-5900.

[11] X. Wu, W. Deng, J. Qian, Y. Cao, X. Ai, H. Yang, J. Mater. Chem. A 1 (2013) 10130-10134. [12] J. Qian, Y. Chen, L. Wu, Y. Cao, X. Ai, H. Yang, Chem. Commun. 48 (2012) 7070-7072. [13] L. Wu, X. Hu, J. Qian, F. Pei, F. Wu, R. Mao, X. Ai, H. Yang, Y. Cao, Energy Environ. Sci. 7 (2014) 323-328.

[14] L. Xiao, Y. Cao, J. Xiao, W. Wang, L. Kovarik, Z. Nie, J. Liu, Chem. Commun. 48 (2012) 3321-3323. [15] W. Luo, P. Zhang, X. Wang, Q. Li, Y. Dong, J. Hua, L. Zhou, L. Mai, J. Power Sources 304 (2016)

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340-345.

[16] L. Wu, H. Lu, L. Xiao, X. Ai, H. Yang, Y. Cao, J. Power Sources 293 (2015) 784-789. [17] R. Sun, Q. Wei, Q. Li, W. Luo, Q. An, J. Sheng, D. Wang, W. Chen, L. Mai, ACS Appl. Mater. Interfaces 7 (2015) 20902-20908.

[18] W. Deng, X. Liang, X. Wu, J. Qian, Y. Cao, X. Ai, J. Feng, H. Yang, Sci. Rep. 3 (2013) 2671-2676.

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[19] Y. Fang, L. Xiao, J. Qian, Y. Cao, X. Ai, Y. Huang, H. Yang, Adv. Energy Mater. 6 (2016) 1502197. [20] Y. Cao, L. Xiao, M.L. Sushko, W. Wang, B. Schwenzer, J. Xiao, Z. Nie, L.V. Saraf, Z. Yang, J. Liu, Nano Lett. 12 (2012) 3783-3787.

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[21] L. Xiao, Y. Cao, W.A. Henderson, M.L. Sushko, Y. Shao, J. Xiao, W. Wang, M.H. Engelhard, Z. Nie, J. Liu, Nano Energy 19 (2016) 279-288. [22] S. Komaba, W. Murata, T. Ishikawa, N. Yabuuchi, T. Ozeki, T. Nakayama, A. Ogata, K. Gotoh, K. Fujiwara, Adv. Funct. Mater. 21 (2011) 3859-3867. [23] F. Shen, H. Zhu, W. Luo, J. Wan, L. Zhou, J. Dai, B. Zhao, X. Han, K. Fu, L. Hu, ACS Appl. Mater. Interfaces 7 (2015) 23291-23296. [24] M.-S. Balogun, Y. Luo, W. Qiu, P. Liu, Y. Tong, Carbon 98 (2016) 162-178. [25] Y. Li, Y.-S. Hu, H. Li, L. Chen, X. Huang, J. Mater. Chem. A 4 (2016) 96-104. [26] E.M. Lotfabad, J. Ding, K. Cui, A. Kohandehghan, W.P. Kalisvaart, M. Hazelton, D. Mitlin, ACS Nano 8 (2014) 7115-7129. [27] P. Liu, Y. Li, Y.-S. Hu, H. Li, L. Chen, X. Huang, J. Mater. Chem. A 4 (2016) 13046-13052. [28] J. Hou, C. Cao, F. Idrees, X. Ma, ACS Nano 9 (2015) 2556-2564. [29] H. Li, F. Shen, W. Luo, J. Dai, X. Han, Y. Chen, Y. Yao, H. Zhu, K. Fu, E. Hitz, ACS Appl. Mater.

ACCEPTED MANUSCRIPT Interfaces 8 (2016) 2204-2210. [30] W. Lv, F. Wen, J. Xiang, J. Zhao, L. Li, L. Wang, Z. Liu, Y. Tian, Electrochim. Acta 176 (2015) 533-541. [31] E. Billa, D.P. Koullas, B. Monties, E.G. Koukios, Ind. Crops Prod. 6 (1997) 297-302. [32] H.-Z. Chen, Z.-H. Liu, S.-H. Dai, Biotechnol. Biofuels 7 (2014) 53-65. [33] A. Khazaeian, A. Ashori, M.Y. Dizaj, Carbohydr. Polym. 120 (2015) 15-21. [34] S. Qiu, L. Xiao, M.L. Sushko, K.S. Han, Y. Shao, M. Yan, X. Liang, L. Mai, J. Feng, Y. Cao, X. Ai, H. Yang, J. Liu, Adv. Energy Mater. (2017) 1700403.

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[35] L. Guo, Y. An, H. Fei, J. Feng, S. Xiong, L. Ci, Materials Technology (2017) 1-6 DOI: 10.1080/10667857.2017.1286555.

[36] F. Zhang, Y. Yao, J. Wan, D. Henderson, X. Zhang, L. Hu, ACS Appl. Mater. Interfaces 9 (2017) 391-397.

[37] K. Wang, Y. Jin, S. Sun, Y. Huang, J. Peng, J. Luo, Q. Zhang, Y. Qiu, C. Fang, J. Han, ACS Omega 2 (2017) 1687-1695. Chem. A (2017) DOI: 10.1039/C7TA01394A.

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[38] M. Dahbi, M. Kiso, K. Kubota, T. Horiba, T. Chafik, K. Hida, T. Matsuyama, S. Komaba, J. Mater. [39] H. Liu, M. Jia, S. Yue, B. Cao, Q. Zhu, N. Sun, B. Xu, J. Mater. Chem. A (2017) DOI:

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10.1039/C7TA01891F.

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[40] P. Wang, X. Zhu, Q. Wang, X. Xu, X. Zhou, J. Bao, J. Mater. Chem. A 5 (2017) 5761-5769.

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Figure 1. Schematic illustration of the material synthesis process.

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Figure Captions

Figure 2. SEM images of SSHC1100 (a), SSHC1300 (c) and SSHC1500 (e). HRTEM images of SSHC1100 (b), SSHC1300 (d) and SSHC1500 (f). The inset shows the corresponding SEAD pattern.

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Figure 3. XRD patterns (a), Raman spectra (b), N2 adsorption–desorption isothermal curves (c) and the corresponding pore size distribution (d) of the SSHC carbonized at different temperatures.

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Figure 4. Cyclic voltammetry (CV) curve of SSHC1300 (a), the first discharge/charge profiles (b), and rate capability (d) of SSHC carbonized at different temperatures. Cyclic performance of SSHC (20 mA g-1) and rGO (50 mA g-1) electrode (c).

Figure 5. SEM images of SSHC1100, SSHC1300 and SSHC1500 electrodes before cycling (a-c) and after cycling for 20 cycles (d-f), respectively.

ACCEPTED MANUSCRIPT Table 1 Physical parameters and electrochemical properties for SSHC1100, SSHC1300 and SSHC1500. d002(Ǻ)

Lc(nm)

IG/ID

SBET(m2 g-1)

Vt(cm3 g-1)

RC(mAh g-1)

ICE(%)

SSHC1100 SSHC1300 SSHC1500

0.395 0.381 0.372

0.80 0.88 0.95

2.81 1.92 1.67

234.5 35.55 85.55

0.118 0.033 0.060

241.5 256.1 258.9

57.5% 62.2% 58.8%

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Sample

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Vt: total pore volume, RC: the reversible capacity, ICE: the initial Coulombic efficiency