Supporting Information

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1 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is The Royal Society of Chemistry 2014 Supporting Information Hierarchical Orthorhombic V 2 O 5 Hollow Nanospheres as High Performance Cathode Materials for Sodium-Ion Batteries Dawei Su, a,b Shixue Dou* b and Guoxiu Wang* a a Centre for Clean Energy Technology, School of Chemistry and Forensic Science, Faculty of Science, University of Technology, Sydney, NSW 2007, Australia. b Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia 1

2 Crystallographic Data Table S1. Crystallographic data and Rietveld refinement of vanadyl acetylacetonate (VO(acac) 2 ). Crystal information Crystallographic data Crystal system Triclinic Space group P 2 (No. 2) a / Å b / Å c / Å α / β / γ / Cell volume / Å Z 2 χ R wp 8.76 % R p 8.46 % 2

3 Table S2. Atomic coordinates and occupancies with atomic displacement parameters of VO(acac) 2. Atom x y z g V O O O O O O C C C C C C C C C

4 Table S3. Selected interatomic distances in VO(acac) 2. Atoms Distance / Å V O V O V O V O V O O1 V O1 C O2 V O2 C O3 C O4 C O6 C C1 O C1 C C2 C C3 C C4 C C5 C C6 C C6 C C7 C C7 C C8 O C8 C

5 Table S4. Crystallographic data and Rietveld refinement of vanadyl ethylene glycolate (VEG). Crystal information Crystallographic data Crystal system Monoclinic Space group C2/C (No. 15) a / Å b / Å c / Å α / β / γ / Cell volume / Å Z 8 χ R wp 9.98% R p 7.21 % Table S5. Atomic coordinates and occupancies of VEG. Atom x y z g V C C O O O H H H H

6 Table S6. Selected interatomic distances in VEG. Atoms Distance / Å V O V O V O C1 C C1 O C1 H C1 H C2 O C2 H C2 H O2 V O3 V

7 Table S7. Crystallographic data and Rietveld refinement of V 2 O 5 nanospheres. Crystal information Crystal system Crystallographic data orthorhombic Space group Pmmn (No. 59) a / Å b / Å c / Å α / β / γ / Cell volume / Å Z 2 χ R wp 5.48% R p 7.42 % Table S8. Atomic coordinates and occupancies of V 2 O 5 nanosphere. Atom x y z g V O O O

8 Table S9. Selected interatomic distances in V 2 O 5 nanosphere. Atoms Distance / Å V O V O V O V O V O O1 V O1 V O3 V Table S10. Elastic constants for polycrystalline V 2 O 5. Axis Young s Modulus (GPa) Poisson Ratios X E xy = E xz = Y E yx = E yz = Z E zx = E zy =

9 Table S11. Crystallographic data and Rietveld refinement of discharged NaV 2 O 5 nanospheres. Crystal information Crystal system Crystallographic data orthorhombic Space group Pmmn (No. 59) a / Å b / Å c / Å α / β / γ / Cell volume / Å Z 2 χ R wp 12.53% R p 9.57 % Table S12. Atomic coordinates and occupancies of discharged NaV 2 O 5. Atom x y z g V Na O O O

10 Table S13. Selected interatomic distances in discharged NaV 2 O 5. Atoms Distance / Å Atoms V O V O V O V O V O O2 V O2 V O3 V

11 Figure S1. Low (a, b) and high (c) magnification FESEM images of VEG nanospheres. The inset in (b) shows the magnified view of hollow feature. (c) Features of an individual VEG nanosphere. (d) Corresponding TEM image of a single VEG nanosphere. (e) Lattice resolution HRTEM image taken from the marked region in (d). (f) Atomic resolution HRTEM image. Inset in (f) is the fast Fourier-transform (FFT) pattern along the [ 1 10] zone axis of VEG. 11

12 Figure S2. Low magnification TEM image (a) and corresponding selected area electron diffraction (SAED) ring pattern (b) of the VEG hollow nanospheres. 12

13 Figure S3. Rietveld refinement patterns of X-ray diffraction data for vanadyl acetylacetonate (VO(acac) 2 ) (a) and vanadyl ethylene glycolate (VEG) (b) crystals. The observed and calculated intensities are represented by red crosses and the blue solid line, respectively. The bottom purple line shows the fitting residual difference. Bragg positions are represented as light-green ticks. The insets in (a) and (b) are refined structural models of triclinic VO(acac) 2 and monoclinic VEG, respectively. The diffraction symmetry confirms that VO(acac) 2 crystals are triclinic, with the P 1 space group. The lattice parameters of VO(acac) 2 were calculated as: a = Å, b = Å, c = Å, and α = , β = , γ = , with satisfactory convergence factors (χ 2 = 7.3, R wp = 8.76 %, R p = 8.46 %), which is consistent with previously reported VO(acac) 2. 1 Detailed crystallographic data on VO(acac) 2 are listed in Tables S1-S3. All diffraction peaks of VEG can be indexed to the monoclinic phase with space group C2/C. The lattice parameters were calculated to be a = Å, b = Å, c = Å, and β = (χ 2 = 8.6, R wp = 9.98 %, R p = 7.21 %). No impurity phases were observed. The refined crystal structure is shown as the inset in Figure S3(b), from which the chain structure of VO(OCH 2 -CH 2 O) is visible. More crystallographic data on VEG are listed in Tables S4-S6. 13

14 5 Weight Loss (%) Temperature Difference ( o C) Temperature ( o C) -25 Figure S4. TG/DTA curves of VEG. Two regions with different slopes can be observed in the weight loss curve. The first, ~ 10 % weight loss below 220 C, should correspond to the evaporation of moisture or gaseous contents in the porous material, as well as hydrous groups attached to the VEG crystals, while the main weight loss (~ 20 %) that took place between 220 and 340 C is likely to be related to the phase transition of VEG. 14

15 (001) Simulated bulk Pmmn-V 2 O 5 XRD Bragg Intensity (a.u.) (110) (degree) Figure S5. Simulated bulk Pmmn-V 2 O 5 XRD pattern, in which the (001) and (110) diffraction peaks are indexed for comparison of the relative intensity. 15

16 (001) (110) 500 o C Intensity (a.u.) 400 o C 350 o C (degree) Figure S6. XRD patterns of V 2 O 5 synthesized at different sintering temperatures (350, 400, and 500 C). 16

17 Figure S7. Schematic diagram of Na + ions inserted into V 2 O 5 along the [010] direction. V, O, and Na atoms are coloured in tan, green, and red, respectively. 17

18 Figure S8. FESEM images of the as-prepared V 2 O 5 hollow nanospheres at different magnifications. 18

19 Figure S9. Low magnification TEM image (a) and corresponding selected area electron diffraction (SAED) ring pattern (b) of the as-prepared V 2 O 5 hollow nanospheres. 19

20 Figure S10. Low (a, c), and high (b, d) magnification FESEM images of the as-prepared V 2 O 5 hollow nanospheres obtained by sintering the VEG precursor at 400 C (a, b), and 500 C (c, d). 20

21 Figure S11. FT-IR spectra of PVP, VO(acac) 2, EG, VEG, and V 2 O 5. 21

22 Figure S12. Orthorhombic V 2 O 5 crystal structure, in which the six-fold coordinated V and three types of structurally different oxygen atoms are present. 22

23 Figure S13. The as-prepared VEG without the addition of PVP. 23

24 Current ( A) Voltage (V) vs. Na/Na + Figure S14. 1 st 5 th cyclic voltammograms of V 2 O 5 hollow nanosphere cathodes in sodium ion cells. 24

25 4 Voltage (V) vs. Na/Na st Cycle 40, 80, 160, 320 ma g -1 2 nd Cycle 320, 160, 80, 40 ma g Capacity (ma h g -1 ) Figure S15. 1 st and 2 nd cycle charge and discharge profiles of V 2 O 5 hollow nanospheres at current densities of 40, 80, 160, and 320 ma g

26 a Voltage (V) vs. Na/Na st 2 nd 100 th b Voltage (V) vs. Na/Na Capacity (ma h g -1 ) st nd 100 th Capacity (ma h g -1 ) Figure S16. 1 st, 2 nd, and 100 th cycle discharge and charge profiles of V 2 O 5 hollow nanospheres at current densities of 640 ma g -1 (a), and 1280 ma g -1 (b). 26

27 b Intensity (a.u.) (001) (110) (degree) Figure S17. FESEM image (a) and XRD pattern (b) of solid Pmmn V 2 O 5 nanocrystals. 27

28 a 4.0 Voltage (V) vs. Na/Na st 2 nd 3 rd b Capacity (ma h g -1 ) Capacity (ma h g -1 ) Charge Discharge Cycle number Figure S18. 1 st, 2 nd, and 3 rd cycle discharge and charge profiles (a) and cyclability (b) of solid V 2 O 5 nanocrystals at current density of 80 ma g

29 Figure S19. Refined structural model of Pmmn NaV 2 O 5, viewed along the [001] direction. The brown base-faced square-pyramidal VO 5 unit is composed of one vanadium atom and five oxygen atoms, which are coloured yellow and red, respectively, while the Na + ions are coloured in green. Reference: (1) Dodge, R. P.; Templeton, D. H.; Zalkin, J. Chem. Phys. 1961, 35,