Enhancing Sodium Ion Battery Performance by. Strongly Binding Nanostructured Sb 2 S 3 on

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1 Enhancing Sodium Ion Battery Performance by Strongly Binding Nanostructured Sb 2 S 3 on Sulfur-Doped Graphene Sheets Xunhui Xiong, Guanhua Wang, Yuwei Lin, Ying Wang, Xing Ou, Fenghua Zheng, Chenghao Yang,*,a Jeng-Han Wang, and Meilin Liu*, New Energy Research Institute, School of Environment and Energy, South China University of Technology, Guangzhou , P. R. China School of Materials Science and Engineering, South China University of Technology, Guangzhou , P. R. China School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA , USA 1

2 Figure S1. Sb 3d spectrum of pure Sb 2 S 3 and Sb 2 S 3 /SGS. Figure S2. SEM images of the Sb 2 S 3 /SGS composite prepared at 300 o C (a) and 450 o C (b). 2

3 Figure S3. (a) SEM and (b) TEM images of Sb2S3/GS composite. Displayed in Figure S3 are typical SEM and TEM images of an interconnected, porous framework with random open pores constructed from graphene sheets. Numerous Sb2S3 nanoparticles with size of nm are encapsulated within the graphene sheets. The initial morphology of Sb2S3/SGS composite is similar to that of the Sb2S3/GS composite. Figure S4. (a-c) SEM, TEM images and SAED pattern of pure Sb2S3, and SEM image of pure Sb2S3 calcined at 450 oc. Pure Sb2S3 tends to have rod-like agglomerations, with a width of 100 nm and a length of 500 nm. TEM image shown in Fig. S3b confirms the rod-like morphology. High resolution TEM (HRTEM) (Figure S4b) and selected area electron diffraction (SAED) (inset of Figure 3

4 S4c) demonstrate the single-phase crystalline nature of rods. Higher processing temperature (450 o C) results in undesirable growth of Sb 2 S 3 grains (Figure S4d). Figure S5. Nitrogen sorption analysis: N 2 isotherms and calculated BET specific surface area of (a) Sb 2 S 3 /SGS composite, (b) Sb 2 S 3 /GS composite and (c) pure Sb 2 S 3. Figure S6. CV of the first five cycles at a scan rate of 0.1 mv s -1 for pure Sb 2 S 3. CV curves of pure Sb 2 S 3 are shown in Figure S6. As indicated in the figure, four peaks centered at around 0.76 V, 0.46 V and 0.23 V are observed in the sodiation process, which are 4

5 attributed to conversion reaction with sulfur atoms (Sb 2 S 3 +6Na + +6e - 2Sb+3Na 2 S) and the alloying reaction of Sb with Na (2Sb+6Na + +6e - 2Na 3 Sb). The broad peak at 1.20 V is ascribedto the formation reaction of solid electrolyte interface (SEI) layer. The anodic peaks centered at 0.74 V and 1.32 V are related to the dealloying reaction (2Na 3 Sb 2Sb+6Na + +6e - ) and the formation of Sb 2 S 3 (2Sb+3Na 2 S Sb 2 S 3 +6Na + +6e - ). Obviously, the polarization of pure Sb 2 S 3 is larger than that of the Sb 2 S 3 /SGS composite. Figure S7. The second charge/discharge curves of Sb 2 S 3 /SGS composite at various current densities. Figure S8. (a) The initial charge-discharge curves of at Sb 2 S 3 /SGS composite 50 ma g -1. (b) The charge-discharge curves at 50 ma g -1 after rate performance tests for Sb 2 S 3 /SGS composite. 5

6 As shown in Figure S8, the curves before and after rate performance tests are superimposable, suggesting good reversibility of Sb 2 S 3 /SGS composite. Furthermore, the capacity can be fully recovered at mah g -1 when the current density is reset to 0.05 A g -1, which is extremely important for high-power and long cycle life batteries. Figure S9. (a) The initial and second charge-discharge curves of GS and SGS at 50 ma g -1. (b) The corresponding cycle performance at 2 A g -1. Figure S10. The initial charge/discharge curves of Sb 2 S 3 /GS composite at various current densities. 6

7 Figure S11. Cycling performances of Sb 2 S 3 /SGS, Sb 2 S 3 /GS, Sb 2 S 3 /GS, pure Sb 2 S 3 and commercial Sb 2 S 3 in terms of area capacity of the electrode. Figure S12. Cycling performaces of pure Sb 2 S 3 and Sb 2 S 3 /SGS composites with different amount of SGS at 0.5 A g -1 (Insert is the initial charge-discharge curves of Sb 2 S 3 /SGS composites with 7.82 wt.% SGS and wt.%. Sb 2 S 3 /SGS composites with different amounts of SGS were also studied (shown in Figure S12). SGS/Sb 2 S 3 with 7.82 wt.% SGS shows the highest specific capacity, the best cyclability at 0.5 A g -1, as well as the highest initial coulombic efficiency. 7

8 Figure S13. The charge capacities of the Sb 2 S 3 /SGS electrode with different active materials mass at 2 A g -1. Table S1 Cycling performance comparison of the as-prepared Sb nanorod arrays with previously reported Sb-based anodes. Materials Current density/a g -1 Cycles Retention Last cycle capacity/mah g -1 rgo/sb 2 S % Sb/C fibers % 350 Sb-C nanofibers % 450 Sn-Ge-Sb thin film % 662 alloys 4 Monodisperse Sb % 580 Nanocrystals 5 SnSb-porous carbon % 345 nanofibers 6 Bulk Sb % 576 3D interconnected NiSb hollow nanospheres Sb 2 S 3 /SGS % (this work) %

9 Figure S14. (a, b) SEM images of pure Sb 2 S 3 after 200 cycles at 2 A g -1. The pure Sb 2 S 3 experienced severe pulverization and rod-like morphology was totally destroyed, resulting in breakdown and reformation of SEI, and eventually a rapid deterioration of the cyclability. Figure S15. The optimized structure in DFT calculation, showing the interactions of Na 3 Sb with (a) pure graphene and (b) sulfur-doped graphene. The upper are top views, and the bottom are side views. The carbon (C), sulfur (S), antimony (Sb), and hydrogen (H) atoms are denoted by gray, yellow, celadon, and white spheres, respectively. 9

10 The adsorption energy between Na 3 Sb and SGS is ev, higher than that of graphene/sb 2 S 3 (-1.48 ev), which is benificial to preventing the discharge products from aggregation. REFERENCES 1. Yu, D. Y.; Prikhodchenko, P. V.; Mason, C. W.; Batabyal, S. K.; Gun, J.; Sladkevich, S.; Medvedev, A. G.; Lev, O., High-Capacity Antimony Sulphide Nanoparticle-Decorated Graphene Composite as Anode for Sodium-Ion Batteries. Nat. Commun. 2013, 4, Zhu, Y.; Han, X.; Xu, Y.; Liu, Y.; Zheng, S.; Xu, K.; Hu, L.; Wang, C., Electrospun Sb/C Fibers for a Stable and Fast Sodium-Ion Battery Anode. ACS Nano 2013, 7, Wu, L.; Hu, X.; Qian, J.; Pei, F.; Wu, F.; Mao, R.; Ai, X.; Yang, H.; Cao, Y., Sb-C Nanofibers with Long Cycle Life as An Anode Material for High-Performance Sodium-Ion Batteries. Energy Environ. Sci. 2014, 7, Farbod, B.; Cui, K.; Kalisvaart, W. P.; Kupsta, M.; Zahiri, B.; Kohandehghan, A.; Lotfabad, E. M.; Li, Z.; Luber, E. J.; Mitlin, D., Anodes for Sodium Ion Batteries Based on Tin-Germanium-Antimony Alloys. ACS Nano 2014, 8, He, M.; Kravchyk, K.; Walter, M.; Kovalenko, M. V., Monodisperse Antimony Nanocrystals for High-Rate Li-Ion and Na-Ion Battery Anodes: Nano versus Bulk. Nano Lett. 2014, 14, Ji, L.; Gu, M.; Shao, Y.; Li, X.; Engelhard, M. H.; Arey, B. W.; Wang, W.; Nie, Z.; Xiao, J.; Wang, C.; Zhang, J.-G.; Liu, J., Controlling SEI Formation on SnSb-Porous Carbon Nanofibers for Improved Na Ion Storage. Adv. Mater. 2014, 26, Darwiche, A.; Marino, C.; Sougrati, M. T.; Fraisse, B.; Stievano, L.; Monconduit, L., Better Cycling Performances of Bulk Sb in Na-Ion Batteries Compared to Li-Ion Systems: An Unexpected Electrochemical Mechanism. J. Am. Chem. Soc. 2012, 134,

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