C composite as a high-performance anode for sodium ion batteries

Electrochimica Acta 242 (2017) 159–164

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Sb/C composite as a high-performance anode for sodium ion batteries Guanhua Wanga,b , Xunhui Xionga,b,* , Zhihua Lina,b , Chenghao Yanga,b,* , Zhang Linb , Meilin Liua,c a Guangzhou Key Laboratory of Surface Chemistry of Energy Materials, New Energy Research Institute, School of Environment and Energy, South China University of Technology, Guangzhou 510006, China b Guangdong Engineering and Technology Research Center for Environmental Nanomaterials, Guangzhou 510006, China c School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA

A R T I C L E I N F O

Article history: Received 30 December 2016 Received in revised form 9 April 2017 Accepted 29 April 2017 Available online 4 May 2017 Keywords: Sb/C composite porous sodium ion battery electrochemical performance anode

A B S T R A C T

Sodium ion batteries (SIBs) have been considered as promising alternative to lithium ion batteries (LIBs) for large-scale energy storage. However, their inferior electrochemical performances, especially cyclability and rate capability become the major challenge for further development of SIBs. Herein, Sb/C composite prepared via an efficient and facile method with alginate as precursor has been evaluated as anode material for sodium ion batteries. This method shows unique role in formation of porous Sb/C composite, controlling the particle size and achieving excellent carbon coating. Such a composite demonstrates high specific capacity (423 mAh g 1 at 0.1 A g 1), good rate capability (226 mAh g 1 at 15 A g 1), and excellent cycle life (81.4% capacity retention for 200 cycles at 2 A g 1). The facile synthesis and superior electrochemical performance of the Sb/C composite render it a promising anode material for high-performance SIBs. Furthermore, our study shows a feasible and effective way to prepare transition metal (oxides) and porous carbon nanocomposite for SIBs. © 2017 Elsevier Ltd. All rights reserved.

1. Introduction The sodium ion batteries (SIBs) have gained significant research interest as a promising alternative to lithium ion batteries (LIBs) for large-scale energy storage systems, due to their low cost, abundant natural resources, and the similar intercalation chemistry of sodium and lithium [1–3]. However, Na ion has a larger radius, which leads to a slower diffusion efficiency in the Na-host materials, a larger volumetric change and more severe pulverization of Na-storage materials. Furthermore, the repeated volume changes will also generate unstable, thick, and electronically insulating solid electrolyte interphase (SEI) layer between active material and electrolyte, which further result in unsatisfactory rate performance and cycle life [4,5]. Particularly, only a few materials suitable for Li-ion batteries can be used to accommodate Na ion and demonstrated sustainable capacity and cyclability [6]. Therefore, one of the main challenges for advanced SIBs lies in

* Corresponding authors at: Guangzhou Key Laboratory of Surface Chemistry of Energy Materials, New Energy Research Institute, School of Environment and Energy, South China University of Technology, Guangzhou 510006, China. E-mail addresses: [email protected] (X. Xiong), [email protected] (C. Yang). http://dx.doi.org/10.1016/j.electacta.2017.04.164 0013-4686/© 2017 Elsevier Ltd. All rights reserved.

the development of appropriate Na storage materials or structures with high specific capacity, high rate capability and outstanding cycle stability [7]. Recently, antimony (Sb) has gained numerous attentions as a potential anode for SIBs due to its appropriate sodium insertion potential and high theoretical specific capacity of 660 mA h g 1 upon full sodiation to Na3Sb [8–11]. Nevertheless, such an alloying reaction is inevitably accompanied by dramatic volume fluctuation of the host materials. It is widely accepted that embedding the nanostructured Sb in a carbon matrix is regarded as one of the effective methods to improve the electrochemical performances [12–19]. The carbon matrix can provide an elastic buffer layer to accommodate the volume expansion while preventing aggregation of active materials during the charge-discharge process, which can increase the stability of active materials during cycling. For example, Sb nanoparticles uniformly-decorated on N-doped porous carbon fabricated by sol-gel route retain the capacity up to 220 mAh g 1 after 180 cycles at a current of 2 A g 1 [13]. Sb-C composite prepared by a synchronous reduction and carbon deposition process exhibits a capacity of 430.9 mAh g 1 at 50 mA g 1 after 100 cycles for SIBs. These composite shows much more promising electrochemical performances than pure Sb, and carbon coating is considered as popular route for improving the electrochemical performance of SIBs [16].

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More recently, taking advantage of interactions between metal ions and polymers becomes an efficient and facile way to achieve core-shell and/or carbon-coating structure. Huang et al. prepared porous Sb/C composite as anode for SIBs by using chitosan as a selfwrapping precursor [20]. In such a unique method, Sb and carbon source are mixed at a molecular scale, achieving good coating effect. Alginate, belonging to a group of polymers, had been used for the removal of heavy metals from industrial wastes by biosorption. Compared with other polymers, alginates are actually block copolymers, thus specific and strong interactions between alginate and heavy metals happened [21,22]. Furthermore, alginates are excellent gelling agent, so the gels can be formed immediately upon adding the metal ions. With this unique advantage, the gels can be taken out from the solution and simplified the drying process. After carbonization, the gels turn into carbon/metal hybrids with ultrasmall particles. Herein, we emphasize that as the precursor of carbon matrix, the abundant and cheap alginate not only shows a high activity to absorb Sb3+, but also brings a homogeneous distribution of Sb nanoparticles within 3D porous carbon matrix after freeze-drying and thermal treatment. As anode for SIBs, the obtained Sb/C composite exhibits high capacity, long-term cyclability and remarkable high-rate capability.

2.3. Electrochemical Tests

2. Experimental section

CR2032 coin-type cells were fabricated in a glove box filled with Ar to characterize the sodium storage behaviors of Sb/C composite. A homogenous slurry was obtained through mixing the synthesized active materials with conductive agent and carboxymethyl cellulose (70:15:15 in weight) in deionized water, and then it was cast on a copper foil. After dried at 90  C under vacuum, the thickness of the slurry is about 25 mm with a packing density of 1.5 g cm 3. Similar to our previous work [24], the tailored Cu foil coated with Sb/C composite was utilized as work electrode and metallic sodium was used as the counter electrode, and glass fiber was employed as the separator. 1 M NaClO4 dissolved in propylene carbonate (PC) with 5% fluoroethylene carbonate (FEC) additive was prepared and used as the electrolyte. Charge-discharge data were collected using LAND CT2001A battery testing system (Wuhan, China) within the voltage window of 0.01-2.5 V. Cyclic voltammetry (CV) measurements were made using IM6 electrochemical testing station running at a range of potential sweep rates from the open circuit potential to 0.01 V and then back to 2.5 V. For the full cell, the positive electrode was a mixture of Na3V2(PO4)3/C, super P and carboxymethyl cellulose (weight ratio of 85:10:5), and negative electrode, electrolyte and the separator were the same as those used in the half-cell. The weight ratio of positive to negative electrode was 2.9:1.

2.1. Synthesis

3. Results and discussion

All the agents were of analytical grade and used as purchased without further purification. Alginate was dissolved in deionized water to obtain 2.0 wt % sol. In a typical experiment, 20 ml concentrated HCl was mixed with 80 ml water, followed by adding 1.8 g antimony chloride (SbCl3) to obtain a clear solution. Then the alginate sol (30 ml) was added into the SbCl3 solutions. Different from other polymers, the gels can be formed immediately upon adding the metal ions. With this unique advantage, the gels can be taken out of the solution directly and simplified the drying process. The gels were taken out after cross-linking and were frozen by liquid nitrogen and freeze-dried for 24 h. The dried gels were thermally treated at 500  C for 4 h in 5% H2/Ar atmosphere to achieve Sb/C nanocomposite. The obtained powders were washed with deionized water to remove the sodium salts and then dried in vacuum at 80  C for 12 h. Na3V2(PO4)3/C composite was prepared via previous method [23].

The XRD pattern of freeze-dried gels and Sb/C composite is shown in Fig. 1a. It is obvious that the freeze-dried gels are amorphous. This indicates strong interactions between alginate and cations happened, then alginates prevent the hydrolysis of SbCl3 and the formation of crystalline Sb4O5Cl2, which is vital to control the particle size. After carbonization, all the diffraction peaks of composite can be referred to Sb (JCPDS: 35-0732), and no other peaks are observed, demonstrating that Sb3+ was completely converted into Sb during the annealing process. Scherrer’s equation is used to calculate the average crystallite sizes of Sb/C by analyzing the (012) and (104) diffraction peak at intermediate angle of good symmetry and low instrumentation interference:

2.2. Material characterization The X-ray diffraction (XRD) patterns were acquired via a Rigaku D/max 2500 with Cu Ka radiation (l= 1.5418 Å) worked at 40 kV and 40 mA in the 2u range of 10  90 with a scanning step of 0.12 s 1. Morphology of fabricated powders was examined using a fieldemission scanning electron microscope (FESEM, Hitachi S-4700) with an acceleration voltage of 15 kV. Transmission electron microscopy (TEM) was performed on a JEOL microscope (TEM, JEM-2010, 200 kV). Prior to TEM analysis, the Sb/C composite was dispersed in absolute ethanol for several hours with ultrasonic. Thermogravimetric analysis (TGA) involved in determining the carbon content in the Sb/C composite was operated in air (air flow: 150 mL min 1) with heating rate of 2  C min 1 from room temperature to 800  C. Brurauer-Emmerr-Teller (BET) surface area was obtained via a ASAP 2025 instrument by adsorption of N2 at 77 K. Raman spectroscopic measurement was performed using a Renishaw RM1000 microspectroscopic system. A He-Ne laser with a wavelength of 633 nm (Thorlab HRP-170) was used as the excitation laser through a 20x/0.40 objective.

L = Kl/bcosu The calculated crystallite sizes are 18.9 and 19.4 nm, respectively. The XPS spectrum suggests the coexistence of C and Sb elements (Fig. 1b), and no other elements are detected. Raman spectroscopy was also conducted to investigate the composition of Sb/C composite (Fig. 1c). The peaks located between 110 and 150 cm 1 are characteristic Raman shifts of Sb, whereas the bands at 1350 and 1580 cm 1 are attributed to the D-band and G-band of carbon materials, respectively. The results indicate the existence of carbon in the composite and the content of Sb is determined to be 54.5 wt% by dissolving Sb/C in concentrated HCl and weighing the remains. TGA was further conducted to estimate the content of carbon (Fig. 1d). Considering that Sb is converted into Sb2O4 when heated to 800  C in air [25], the Sb content in composite is calculated to be about 54.8 wt. %. The detailed morphology of the composite was characterized via FESEM and TEM. Displayed in Fig. 2a-b are typical SEM images of an interconnected, porous framework with random open pores constructed by carbon. Sb particles with size of 20–40 nm (black) are homogenously embedded in the carbon matrix without obvious aggregation (Fig. 2c). The formation of porous structure can be ascribed to the cross-linking of alginate induced by Sb3+, and the release of gas in the following freeze-drying process. Drying process in air or oven leads to the stack of the cross-linked zones

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Fig. 1. XRD patterns of the freeze-dried gels and Sb/C composite (a), XPS spectra of the Sb/C composite (b), Raman spectra of commercial Sb and Sb/C composite (c), and TG curve of the Sb/C composite in air with heating rate of 2  C min 1 and air flow of 100 mL min 1 (d).

(Fig. S1, Supporting Information). In the following carbonization process, the bonded Sb3+ by alginate is in-situ reduced and melted into Sb nanoparticles. The alginates are squeezed to the outside of the Sb particles after broken down to carbon chains, and then prevent the nanoparticles from aggregation. However, higher annealing temperature (600  C) will lead more severe particle aggregation (Fig. S2), which has no benefit to the electrochemical performances. HRTEM image (Fig. 2d) presents the clear lattice fringes with d-spacing of 0.31 nm, corresponding to the (012) plane of Sb. It should be emphasized that, even after a long period of sonication during the samples preparation, Sb crystals are still spatially confined by the carbon framework, suggesting the robust affinity between the Sb nanoparticles and carbon. The tightly coated carbon on Sb will ensure an effective buffer layer to accommodate the volumetric change during sodiation/desodiation process, thus leading to an outstanding cycle stability. Obviously, alginate shows unique role in formation of porous Sb/C composite, controlling the Sb particle and achieving excellent carbon coating. Moreover, the porosity of Sb/C was investigated by measuring the BET surface area of the composite (Fig. 3), which greatly influences the electrochemical properties. The nitrogen absorption-desorption isotherm is a type-IV isotherm, with a distinct hysteresis loop at the relative pressure P/P0 ranging from 0.5 to 1, implying that the composite has no or very small fraction of micropores (pores<2 nm) and contains a large number of mesopores. This is due to the release of gas in the freeze-drying process, along with the gas volatilization during the decomposition of the alginate gels and the pyrolysis of SbCl3. The BET data indicates that the composite has a high surface of 36.8 m2 g 1. In

comparison, the Sb/C composite obtained by drying in air has much lower specific surface area and much less mesopores.

Fig. 2. SEM (a-b), TEM image (c), HRTEM image (d), and elemental mapping images of Sb, and C components for Sb/C composite.

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Fig. 3. N2 adsorption-desorption isotherms Sb/C composite obtained by freeze-drying (a) and drying in air (b).

Electrochemical properties of the Sb/C composite as a SIB anode were evaluated in the voltage range of 0.01  2.5 V (vs. Na+/Na). Fig. 4a shows the typical CVs of the Sb/C composite for the first ten cycles at a scan rate of 0.1 mV s 1. It clearly shows the initial

cathodic scan is remarkablely different from the following ones, indicating an activation process for the first sodiation process [17]. The first sodiation process occurs along a sharp peak at 0.35 V, corresponding to the conversion of crystalline Sb to the crystalline

Fig. 4. Cyclic voltammograms of the initial ten cycles for the Sb/C electrode from 2.5 to 0.01 V vs. Na+/Na at 0.1 mV s 1 (a). Charge/discharge profiles at different cycles of current density of 0.1 A g 1 (b) and cycle performances at different current densities (c). Nyquist plots of Sb/C after different cycles at 0.1 A g 1 in the fully sodiation state (0.01 V) from 1 MHz to 10 mHz with equivalent circuit inset (d). The 2nd charge-discharge curves for various current densities from 0.1 to 15 A g 1 (e). Rate capability of Sb/C (f).

G. Wang et al. / Electrochimica Acta 242 (2017) 159–164

Na3Sb phase and the formation of SEI [17,26–28]. In the second and following cathodic process, three peaks at 0.68, 0.48 and 0.32 V attributed to the multi-step conversion of crystalline Sb into hexagonal Na3Sb by Na+ insertion are continuously shown and well-overlapped [4,29–31], suggesting the occurrence of stable sodiation process [31,32]. For the first anodic process, it presents a broad peak at 0.78 V and a strong oxidative peak at 0.90 V and it splits into two separate peaks at 0.82 and 0.95 V in the following cycles, corresponding to the desodiation of crystalline Na3Sb is a step by step process [4]. Therefore, the CV curves demonstrate that the Sb/C composite can realize a reversible sodiation/desodiation reaction at the given voltage window of 0  2.5 V. Galvanostatic charge/discharge profiles of composite at 0.1 A g 1 are shown in Fig. 4b. In the first discharge profiles, it shows a long plateau at 0.5 V, which is contributed from the formation of SEI film and alloy reaction between Na and Sb. This has been confirmed by the discharge product Na3Sb (Fig. S3). In the second and the following discharge curves, three discharge plateaus are obviously observed. They correspond to the sodiation process from amorphous Sb to amorphous Na3Sb, Na3Sb(hex)/Na3Sb(cub) and Na3Sb(hex) [30,31,33]. In the first charge profile and the following ones, two obvious charge plateaus are always kept, which is assigned to the process of the conversion from Na3Sb(hex) to amorphous Sb and partial crystallization of Sb, respectively [18,31,33]. All of these curves are consistent with the CV curves in Fig. 4a. The initial charge capacity of Sb/C composite at current density of 0.1 A g 1 is 423 mAh g 1 (normalized by weight of Sb/C composite) with Coulombic efficiencies of 78.4%. The high initial capacity loss was caused by the formation of SEI films on the surface of Sb and carbon. Because the carbon can only deliver a low capacity of 128 mAh g 1 (Fig. S4) under the same testing conditions, the initial reversible capacity is very close to the theoretical capacity (419.7 mAh g 1) of the Sb/C composite (660 mAh g 1  54.8% + 128.3 mAh g 1  45.2% = 419.7 mAh g 1). The capacity shows a slight decrease in the cycling performance test, and it exhibited a capacity of 380 mA g 1 after 200 cycles with a capacity retention of 90.3%. The excellent stability can be confirmed by the cycle performances at current density of 0.5 and 2 A g 1 (Fig. 4c). The capacity retentions after 200 cycles at 0.5 and 2 A g 1 are still over 86.2% and 81.4%, respectively. Furthermore, it is worthwhile to note that both charge and discharge curves of different current densities are almost retained after 200 cycles (Figs. 4 b, S5), demonstrating the stable structure of Sb/C composite. Electrochemical impedance spectroscopy (EIS) was used to investigate the mechanism for the stable cycling performance of Sb/C composite. Fig. 4d shows the Nyquist plots for Sb/C composite after different cycles at state of discharge. The semicircle in the high-middle frequency represents charge transfer resistance (Rct) between electrolyte and electrode, and the low frequency straight line corresponds to the Warburg resistance (W)

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related to Na+ diffusion inside electrode material. Quantitatively, based on the fitted equivalent circuit in the inset of Fig. 4d, the Rct for Sb/C composite is calculated to be about 220.4 V. After the first cycle, Rct is reduced to 122.3 V, which might be the reason for the gradually increased capacity during the initial few cycles (Fig. 4c). Compared with the initial Rct, the decrease of Rct may be attributed to the improved infiltrates of electrolyte [34,35]. After 200 cycles, Rct keeps stable compared with the values at the 50th cycle, demonstrating the stable interface between electrolyte and electrode and explaining the excellent cyclability of the Sb/C composite. Moreover, due to the unique porous structure of Sb/C composite with excellent carbon coating, a significantly high rate capacity is obtained (Fig. 4e-f). When the current density increases from 0.1 to 15 A g 1, it can still deliver a high capacity of 226 mAh g 1, although the gaps between charge and discharge of the composite increase slightly, which means the polarization and mechanical stress increase during the charge and discharge processes [36,37]. More importantly, when the current density is reset to 0.1 A g 1, the capacity almost recovers, indicating the unique structure can preserve the robust structure and accommodate huge volume change in the different current densities. The outstanding cycle performances are confirmed by the comparison between Sb/C composite and previously reported Sb/C materials for SIBs anode (Table S1). The results indicate that the cycle performances of our designed materials are comparable to previously reported Sb/C composites. In contrast, Sb/C composite obtained by drying in air and annealed at higher temperature shows poorer cycle performances (Fig. S6). To better confirm the robust structure prepared by this process, the morphology of cycled Sb/C electrode was studied. Fig. S7 shows SEM image of Sb/C composite cycled at 2 A g 1 after 200 cycles in the fully charge state. The porous structure and geometric confinement of the Sb nanoparticles within the carbon matrix are largely maintained, which prevents pulverization and agglomeration, resulting in excellent electrochemical performances. Furthermore, the structural stability of the Sb/C electrode was investigated using TEM (Fig. S7b). As shown in the HRTEM images, despite the volume change in the sodiation and desodiation process, there is no structural collapse and agglomeration of Sb particles, suggesting the chemical and mechanical robustness of the Sb particles and carbon. Meanwhile, no obvious lattice fringes of Sb particles indicate that they have become amorphous Sb after charge-discharge process. To demonstrate the practical use of Sb/C composite, Sb/C anode was paired up with Na3V2(PO4)3/C cathode to obtain a Na+ full cell. The structure and electrochemical performance of Na3V2(PO4)3/C can be seen in Figs. S8 and S9. The performance of the full cell is evaluated at a current density of 0.2 A g 1 (normalized by the mass of active materials) batween 0.8  3.0 V. From their respective sodiation-desodiation potentials, an average voltage of 2.7 V can be

Fig. 5. Voltage profiles of a full cell consisting of Na3V2(PO4)3/C cathode and Sb/C composite anode between 0.8 and 3 V at 0.2 A g performance (b).

1

(a) and the corresponding cycling

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delivered for the full cell, as confirmed by the charge/discharge curves of the full cell (Fig. 5). The initial charge capacity is 591 mAh g 1 and the reversible capacity is 419 mAh g 1 (70.7%). After 50 cycles, the full cell still possesses a capacity of 343 mAh g 1, with a relatively high retention of 81.8%. Compared with the half cell, the faster capacity fading in the full cell is most likely caused by the dismatch of weight and current density between the two electrode materials. 4. Conclusion In summary, an efficient and facile method with alginate as precursor has been developed to Sb/C nanocomposite. This method shows unique role in formation of porous Sb/C composite, controlling the particle and achieving excellent carbon coating. Such a composite demonstrates high specific capacity (423 mAh g 1 at 0.1 A g 1), good rate capability (226 mAh g 1 at 15 A g 1), and excellent cycle life (81.4% capacity retention for 200 cycles at 2 A g 1). The facile synthesis and superior electrochemical performance of the Sb/C composite electrode render it a promising anode material for high-performance sodium ion batteries. Acknowledgements We gratefully acknowledge the financial support from China Postdoctoral Science Foundation (2016M590784), Natural Science Foundation of China (51604122), and Natural Science Foundation of Guangdong Province (2016A030310411), Project of Public Interest Research and Capacity Building of Guangdong Province (2014A010106007), Pearl River S&T Nova Program of Guangzhou (201506010030), Guangdong Innovative and Entrepreneurial Research Team Program (No.2014ZT05N200).

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22] [23]

[24]

[25]

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at 10.1016/j.electacta.2017.04.164. References [1] D. Kundu, E. Talaie, V. Duffort, L.F. Nazar, The Emerging Chemistry of Sodium Ion Batteries for Electrochemical Energy Storage, Angew Chem. Int. Ed. 54 (2015) 3431–3448. [2] M.S. Islam, C.A.J. Fisher, Lithium and sodium battery cathode materials: computational insights into voltage, diffusion and nanostructural properties, Chem. Soc. Rev. 43 (2014) 185–204. [3] C. Yang, X. Ou, X. Xiong, F. Zheng, R. Hu, Y. Chen, M. Liu, K. Huang, V5S8-graphite hybrid nanosheets as a high rate-capacity and stable anode material for sodium-ion batteries, Energy Environ. Sci. 10 (2017) 107–113. [4] Y.U. Park, D.H. Seo, H.S. Kwon, B. Kim, J. Kim, H. Kim, I. Kim, H.I. Yoo, K. Kang, A new high-energy cathode for a Na-ion battery with ultrahigh stability, J. Am. Chem. Soc. 135 (2013) 13870–13878. [5] S. Li, Y. Dong, L. Xu, X. Xu, L. He, L. Mai, Effect of carbon matrix dimensions on the electrochemical properties of Na3V2(PO4)3 nanograins for highperformance symmetric sodium-ion batteries, Adv. Mater. 26 (2014) 3545– 3553. [6] Y. Zhao, A. Manthiram, Amorphous Sb2S3 embedded in graphite: a high-rate long-life anode material for sodium-ion batteries, Chem. Commun. 51 (2015) 13205–13208. [7] S.Y. Hong, Y. Kim, Y. Park, A. Choi, N.-S. Choi, K.T. Lee, Charge carriers in rechargeable batteries: Na ions vs. Li ions, Energy Environ. Sci. 6 (2013) 2067– 2081. [8] L. Liang, Y. Xu, C. Wang, L. Wen, Y. Fang, Y. Mi, M. Zhou, H. Zhao, Y. Lei, Largescale highly ordered Sb nanorod array anodes with high capacity and rate capability for sodium-ion batteries, Energy Environ. Sci. 8 (2015) 2954–2962. [9] H. Hou, M. Jing, Z. Huang, Y. Yang, Y. Zhang, J. Chen, Z. Wu, X. Ji, OneDimensional Rod-Like Sb2S3-Based Anode for High-Performance Sodium-Ion Batteries, ACS Appl. Mater. Interfaces 7 (2015) 19362–19369. [10] Z. Liu, X.-Y. Yu, X.W. Lou, U. Paik, Sb@C coaxial nanotubes as a superior long-life and high-rate anode for sodium ion batteries, Energy Environ. Sci. 9 (2016) 2314–2318. [11] X. Xiong, G. Wang, Y. Lin, Y. Wang, X. Ou, F. Zheng, C. Yang, J.-H. Wang, M. Liu, E nhancing Sodium Ion Battery Performance by Strongly Binding

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

Nanostructured Sb2S3 on Sulfur-Doped Graphene Sheets, ACS Nano 10 (2016) 10953–10959. J. Qian, Y. Chen, L. Wu, Y. Cao, X. Ai, H. Yang, High capacity Na-storage and superior cyclability of nanocomposite Sb/C anode for Na-ion batteries, Chem. Commun. 48 (2012) 7070–7072. X. Zhou, Y. Zhong, M. Yang, M. Hu, J. Wei, Z. Zhou, Sb nanoparticles decorated N-rich carbon nanosheets as anode materials for sodium ion batteries with superior rate capability and long cycling stability, Chem. Commun. 50 (2014) 12888–12891. N. Zhang, Y. Liu, Y. Lu, X. Han, F. Cheng, J. Chen, Spherical nano-Sb@C composite as a high-rate and ultra-stable anode material for sodium-ion batteries, Nano Res. 8 (2015) 3384–3393. L. Wu, X. Hu, J. Qian, F. Pei, F. Wu, R. Mao, X. Ai, H. Yang, Y. Cao, Sb-C nanofibers with long cycle life as an anode material for high-performance sodium-ion batteries, Energy Environ. Sci. 7 (2014) 323–328. L. Fan, J. Zhang, J. Cui, Y. Zhu, J. Liang, L. Wang, Y. Qian, Electrochemical performance of rod-like Sb-C composite as anodes for Li-ion and Na-ion batteries, J. Mater. Chem. A 3 (2015) 3276–3280. Y. Zhu, X. Han, Y. Xu, Y. Liu, S. Zheng, K. Xu, L. Hu, C. Wang, Electrospun Sb/C Fibers for a Stable and Fast Sodium-Ion Battery Anode, ACS Nano 7 (2013) 6378–6386. X. Zhou, Z. Dai, J. Bao, Y.-G. Guo, Wet milled synthesis of an Sb/MWCNT nanocomposite for improved sodium storage, J. Mater. Chem. A 1 (2013) 13727–13731. C. Nithya, S. Gopukumar, rGO/nano Sb composite: a high performance anode material for Na+ ion batteries and evidence for the formation of nanoribbons from the nano rGO sheet during galvanostatic cycling, J. Mater. Chem. A 2 (2014) 10516–10525. J. Duan, W. Zhang, C. Wu, Q. Fan, W. Zhang, X. Hu, Y. Huang, Self-wrapped Sb/C nanocomposite as anode material for High-performance sodium-ion batteries, Nano Energy 16 (2015) 479–487. L. Li, Y. Fang, R. Vreeker, I. Appelqvist, E. Mendes, Reexamining the EggBox Model in Calcium-Alginate Gels with X-ray Diffraction, Biomacromolecules 8 (2007) 464–468. K.Y. Lee, D.J. Mooney, Alginate: Properties and biomedical applications, Prog. Polym. Sci. 37 (2012) 106–126. C. Zhu, K. Song, P.A. van Aken, J. Maier, Y. Yu, Carbon-Coated Na3V2(PO4)3 Embedded in Porous Carbon Matrix: An Ultrafast Na-Storage Cathode with the Potential of Outperforming Li Cathodes, Nano Lett. 14 (2014) 2175–2180. X. Ou, X. Xiong, F. Zheng, C. Yang, Z. Lin, R. Hu, C. Jin, Y. Chen, M. Liu, In situ X-ray diffraction characterization of NbS2 nanosheets as the anode material for sodium ion batteries, J. Power Sources 325 (2016) 410–416. H. Hou, M. Jing, Y. Yang, Y. Zhang, W. Song, X. Yang, J. Chen, Q. Chen, X. Ji, Antimony nanoparticles anchored on interconnected carbon nanofibers networks as advanced anode material for sodium-ion batteries, J. Power Sources 284 (2015) 227–235. Y. Cao, L. Xiao, M.L. Sushko, W. Wang, B. Schwenzer, J. Xiao, Z. Nie, L.V. Saraf, Z. Yang, J. Liu, Sodium Ion Insertion in Hollow Carbon Nanowires for Battery Applications, Nano Lett. 12 (2012) 3783–3787. K. Tang, L. Fu, R.J. White, L. Yu, M.-M. Titirici, M. Antonietti, J. Maier, Hollow Carbon Nanospheres with Superior Rate Capability for Sodium-Based Batteries, Adv. Energy Mater. 2 (2012) 873–877. H.-g. Wang, Z. Wu, F.-l. Meng, D.-l.. Ma, X.-l. Huang, L.-m. Wang, X.-b. Zhang, Nitrogen-Doped Porous Carbon Nanosheets as Low-Cost, High-Performance Anode Material for Sodium-Ion Batteries, ChemSusChem 6 (2013) 56–60. C. Villevieille, C.M. Ionica-Bousquet, B. Ducourant, J.C. Jumas, L. Monconduit, NiSb2 as negative electrode for Li-ion batteries: An original conversion reaction, J. Power Sources 172 (2007) 388–394. H. Hou, M. Jing, Y. Yang, Y. Zhang, Y. Zhu, W. Song, X. Yang, X. Ji, Sb porous hollow microspheres as advanced anode materials for sodium-ion batteries, J. Mater. Chem. A 3 (2015) 2971–2977. A. Darwiche, C. Marino, M.T. Sougrati, B. Fraisse, L. Stievano, L. Monconduit, Better Cycling Performances of Bulk Sb in Na-Ion Batteries Compared to Li-Ion Systems: An Unexpected Electrochemical Mechanism, J. Am. Chem. Soc. 134 (2012) 20805–20811. L. Baggetto, H.-Y. Hah, J.-C. Jumas, C.E. Johnson, J.A. Johnson, J.K. Keum, C.A. Bridges, G.M. Veith, The reaction mechanism of SnSb and Sb thin film anodes for Na-ion batteries studied by X-ray diffraction, 119Sn and 121Sb Mössbauer spectroscopies, J. Power Sources 267 (2014) 329–336. M. He, K. Kravchyk, M. Walter, M.V. Kovalenko, Monodisperse Antimony Nanocrystals for High-Rate Li-ion and Na-ion Battery Anodes: Nano versus Bulk, Nano Lett. 14 (2014) 1255–1262. Z.-S. Wu, Y. Sun, Y.-Z. Tan, S. Yang, X. Feng, K. Müllen, Three-Dimensional Graphene-Based Macro- and Mesoporous Frameworks for High-Performance Electrochemical Capacitive Energy Storage, J. Am. Chem. Soc. 134 (2012) 19532–19535. X. Zhou, L.-J. Wan, Y.-G. Guo, Binding SnO2 Nanocrystals in Nitrogen-Doped Graphene Sheets as Anode Materials for Lithium-Ion Batteries, Adv. Mater. 25 (2013) 2152–2157. V.A. Sethuraman, V. Srinivasan, A.F. Bower, P.R. Guduru, In Situ Measurements of Stress-Potential Coupling in Lithiated Silicon, J. Electrochem. Soc. 157 (2010) A1253–A1261. V.A. Sethuraman, V. Srinivasan, J. Newman, Analysis of Electrochemical Lithiation and Delithiation Kinetics in Silicon, J. Electrochem. Soc. 160 (2013) A394–A403.