Supporting Information Iron Telluride Decorated Reduced Graphene Oxide Hybrid Microspheres as Anode Materials with Improved Na-Ion Storage Properties Jung Sang Cho 1, Seung Yeon Lee 1, Jung-Kul Lee 2, *, and Yun Chan Kang 1, * Address: 1 Department of Materials Science and Engineering, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 136-713, Republic of Korea. 2 Department of Chemical Engineering, Konkuk University, 1 Hwayang-dong, Gwangjin-gu, Seoul 143-701, Republic of Korea. *Corresponding author. E-mail: yckang@korea.ac.kr, jkrhee@konkuk.ac.kr. S-1
Characterization The crystal structures of the FeTe 2 -rgo hybrid and bare FeTe 2 powders were investigated using X-ray diffractometry (XRD, X pert PRO MPD) with Cu-K α radiation (λ = 1.5418 Å) at the Korea Basic Science Institute (Daegu). The morphologies of the two samples were investigated using scanning electron microscopy (SEM, TESCAN, VEGA3 SBH) and highresolution transmission electron microscopy (HR-TEM, JEOL, JEM-2100F) at a working voltage of 200 kv. The specific surface areas of the powders before and after post-treatment at various temperatures were calculated by a Brunauer-Emmett-Teller analysis of nitrogenadsorption (TriStar 3000). X-ray photoelectron spectroscopy (XPS, Thermo Scientific K- Alpha) of the powders was performed with Al Kα radiation (1486.6 ev). The structure of the carbon in the microspheres was characterized via Raman spectroscopy (Jobin Yvon LabRam HR800, excitation source: 632.8 nm He-Ne laser) at room temperature. To determine the amount of rgo in the FeTe 2 -rgo hybrid powders, thermogravimetric analysis (TGA, TA Instruments, SDT Q600) and elemental analysis (EA, Eurovector, EA3000) was performed in air at a heating rate of 10 C min -1. Electrochemical measurements The electrochemical properties of the FeTe 2 -rgo hybrid and bare FeTe 2 powders were analyzed using a 2032-type coin cell. The anode was prepared by mixing the active material, carbon black, and sodium carboxymethyl cellulose at a weight ratio of 7:2:1. Na metal and microporous polypropylene film were used as the counter electrode and the separator, respectively. The electrolyte was 1 M NaClO 4 and 5% fluoroethylene carbonate dissolved in a mixture of ethylene carbonate/dimethyl carbonate (1:1 v/v). The discharge/charge characteristics of the samples were investigated by cycling over a potential range of 0.001 3.0 V at various current densities. Cyclic voltammograms (CVs) were measured at a scan rate of 0.07 mv s -1. The size of the negative electrode containing the FeTe 2 powders was 1.0 cm 1.0 cm and the mass loading was approximately 2.0 mg cm -2. The electrode density of the FeTe 2 -decorated rgo hybrid powders was approximately 1.62 g cm -3. Electrochemical impedance spectra were obtained by AC electrochemical impedance spectroscopy (EIS, edaq SP1 ZIVE Potentiostat) over a frequency range of 0.01 Hz 1000 khz. S-2
Figure S1. Schematic diagram of the spray pyrolysis applied in the preparation of the Fe 3 O 4 - decorated rgo hybrid powders as a precursor powder. S-3
Figure S2. (a) Schematic diagram and (b) digital photo of the pilot-scale spray drying system applied in the preparation of the precursor powders for the bare Fe 2 O 3 powders. S-4
Figure S3. Morphologies and phase analysis of the Fe3O4-decorated rgo hybrid powders prepared at 600 oc in Ar atmosphere by spray pyrolysis: (a) SEM image, (b-d) TEM images, (e) HR-TEM image, and (f) XRD pattern. S-5
Figure S4. TG analysis of the FeTe 2 -decorated rgo hybrid powders. Table S1. Elemental analysis of the FeTe 2 -decorated rgo hybrid powders. S-6
Figure S5. SEM images and XRD patterns of the bare FeTe 2 powders prepared (a) after spray drying process, (b) subsequent combustion process for the sake of carbon decomposition in the structure, and (c) subsequent tellurization process. S-7
R e : the electrolyte resistance, corresponding to the intercept of high frequency semicircle at Z re axis R f : the SEI layer resistance corresponding to the high-frequency semicircle Q 1 : the dielectric relaxation capacitance corresponding to the high-frequency semicircle R ct : the denote the charger transfer resistance related to the middle-frequency semicircle Q 2 : the associated double-layer capacitance related to the middle-frequency semicircle Z w : the Na-ion diffusion resistance Figure S6. Randle-type equivalent circuit model used for AC impedance fitting. S-8
Figure S7. CV curves of the bare FeTe 2 powders. S-9
Table S2. Sodium-ion storage properties of various metal compounds materials. Materials FeTe 2 -rgo composite SnS 2 -rgo composite CuO nanorod arrays Voltage range (V) Current rate Initial Coulombic efficiency [%] 0.001-3.0 0.2 A g -1 76 % 0.01-2.5 0-3.0 0.2 A g - 1 75 % 0.2 A g - 1 ~88 % TiO 2 nanotube 0.9-2.5 0.05 A g -1 68 % MoS 2 /graphene composite SnSe/carbon nanocomposite MoSe 2 yolk-shell 0.01-2.0 0.025 A g -1 83 % 0.01-2.0 0.5 A g -1 55.1 % 0.001-3.0 0.2 A g -1 85 % Initial discharge/charge Capacity Final discharge capacity Cycle number 493/373 mah g -1 293 mah g -1 80 Ref This work 839/630 mah g -1 628 mah g -1 100 S1 ~700/~620 mah g -1 290 ma h g -1 450 S2 110/75 mah g -1 150 mah g -1 15 S3 407/338 mah g -1-20 S4 748/412 mah g -1 325 mah g -1 200 S5 527/448 mah g -1 433 mah g -1 50 S6 Sn 4 P 3 0-1.5 0.1 A g -1 - - 718 mah g -1 100 S7 FeSe 2 microspheres Flower-like Sb 2 S 3 MnS hollow microspheres VS 4 /rgo composite powder NiS 2 -graphene nanosheets 0.5-2.9 1 A g -1-0.01-2.0 0.05 A g -1 72.9 0.01-2.6 0.1 A g -1 ~65 % 0.01-2.2 0.1 A g -1 75 % - 0.1 C 65 % Cu 3 P nanowire 0.01-2.5 1 A g -1 - CoSe x -rgo composite NiSe 2 /C porous nanofiber 0.001-3.0 0.3 A g -1 70 % 0.001-3.0 0.2 A g -1 72 % 442/- mah g -1 372 mah g -1 2000 S8 970/707 mah g -1 835 mah g -1 50 S9 ~750/~490 mah g -1 308 mah g -1 125 S10 450/338 mahg -1 241 mah g -1 50 S11 529/- mah g -1 407 mah g -1 50 S12 -/196 mah g -1 134 mah g -1 260 S13 656/460 mah g -1 420 mah g -1 50 S14 717/516 mah g -1 468 mah g -1 100 S15 SnSe alloy 0-2.0 0.143 A g -1 - - 707 mah g -1 50 S16 Reference (S1) Qu, B.; Ma, C.; Ji, G.; Xu, C., Xu, J.; Meng, Y. S.; Wang, T.; Lee, J. Y. Layered SnS 2 Reduced Graphene Oxide Composite A High Capacity, High Rate, and Long Cycle Life Sodium Ion Battery Anode Material. Adv. Mater. 2014, 26, 3854-3859. (S2) Yuan, S.; Huang, X. L.; Ma, D. L.; Wang, H. G.; Meng, F. Z.; Zhang, X. B. Engraving Copper Foil to Give Large Scale Binder Free Porous CuO Arrays for a High Performance Sodium Ion Battery Anode. Adv. Mater. 2014, 26, 2273-2279. S-10
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