Atomically intercalating tin ions into the interlayer. of molybdenum oxide nanobelt toward long-cycling

Transcription

1 Atomically intercalating tin ions into the interlayer of molybdenum oxide nanobelt toward long-cycling lithium battery Chuanqiang Wu, + Hui Xie, + Dongdong Li, Daobin Liu, Shiqing Ding, Shi Tao, Heng Chen, Qin Liu, Shuangming Chen,*, Wangsheng Chu, Bo Zhang, and Li Song*, National Synchrotron Radiation Laboratory, CAS Center for Excellence in Nanoscience, University of Science and Technology of China, Hefei, Anhui , P. R. China Institute of Amorphous Matter Science, School of Materials Science and Engineering, Hefei University of Technology, Hefei, Anhui , P. R. China Department of Physics and Electronic Engineering, Jiangsu Lab of Advanced Functional Materials, Changshu Institute of Technology, Changshu, Jiangsu , China Corresponding Author: * csmp@ustc.edu.cn (S.C.), song2012@ustc.edu.cn (L.S.) 1

2 Experimental section: Material s synthesis The α-moo 3 nanobelts were synthesized via a hydrothermal process according to the earlier reports. Specifically, 2g of molybdenum (Mo) powder was added into 10mL deionized water and stirred to achieve a uniform mixture. Then, 20mL 30 wt% H 2 O 2 was slowly dropped into the obtained mixed solution and the obtained solution gradually turns yellow with stirring. The resultant solution was transferred to a 45mL Teflon-lined stainless steel autoclave and maintained at 180 for 12h, and naturally cooled down to room temperature. The final white product was obtained. The product was washed with deionized water for several times and followed by drying at 60 for 12h at vacuum. The MoO 3 -Sn nanobelts were synthesized by using a simple water bath method in acetone solution. Briefly, 10mg of synthesized α-moo 3 nanobelts powder was added into 10mL acetone solution in bottle flask and ultrasonic to achieve a uniform mixture. Then, put the mixture bottle into water, heating reflux at 52 and added a certain amount of tartaric acid and stannous chloride dihydrate kept just under reflux with continuously stirring. Finally, the blue product was obtained. The product was washed with ethanol and acetone for several times and followed by drying at 60 for 12h at vacuum. Material s characterization Samples were characterized by powder X-ray diffraction (XRD) by a Philips X Pert Pro Super diffractometer equipped with Cu Kα radiation (λ= Å). Raman scattering was taken by a Horiba microscopic Raman spectrometer (XploRA). Field emission scanning electron microscopy (FE-SEM) images were taken via a JEOL JSM-6700F SEM. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) observations and EDS mapping analyses were taken via JEM-2100F field emission electron microscopy with an acceleration voltage of 200 kv. X-ray photoelectron spectroscopy (XPS) measurements were carried out in a VG ESCALAB MK II X-ray photoelectron spectrometer equipped with Mg Kα= ev source. The binding energies obtained in the XPS spectral range were corrected for specimen charging effects using the C 1s level at the energy of 284.5eV as a reference. The Mo K-edge and Sn K-edge XAFS measurements were made at the beamline 14W1 in Shanghai Synchrotron Radiation Facility (SSRF). The X-ray was monochromatized by a double-crystal Si(311) monochromator both for SSRF. The energy was calibrated using a Molybdenum metal foil for the Mo K-edge and a Tin metal foil for the Sn K-edge. The monochromator was detuned to reject higher harmonics. The acquired EXAFS data were processed and analyzed according to the standard procedures by using the WinXAS3.1 program. Theoretical amplitudes and phaseshift functions were further calculated with the FEFF8.2 1,2. Electrochemical analysis The working electrodes were prepared by pasting a mixture of sample (α-moo 3 nanobelts, MoO 3 -Sn nanobelts), acetylene black and poly (vinyl difluoride) at a weight ratio of 70:20:10 in the N-methyl-2-pyrrolidone solvent on a copper (Cu) foil and dried at 110 overnight. The cells 2

3 (CR2032-type coin cells) were assembled in an argon-filled glove box. Celgard 2600 was used as the separator, pure Li metal as the anode, and 1 M LiPF 6 dissolved in ethylene carbonate and dimethyl carbonate with a ratio of 1:1 as the electrolyte. Galvanostatic discharge-charge experiments were evaluated at room temperature using a Land CT2001 battery test system. Cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS) of cells measurements were performed on a CHI660D electrochemical workstation. The CV curves were carried out in the voltage range of V at a scan rate of 0.02 mv s -1 and EIS measurements were with an amplitude of the signal of 10 mv and frequency in the range 10 6 Hz-0.01 Hz. Theoretical modeling and calculations The structural optimization including the lattice parameters and the atomic positions is performed using VASP 3,4, where the energy cutoff of 450 ev and the Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) are adopted 5. The van der Waals (vdw) interactions via the DFT-D2 method is used in order to properly describe the interactions between different layers supercell is used to imitate the nanobelts. 3

4 Figure. S1 (a, b,c) SEM, TEM and HRTEM (selected area electron diffraction pattern inserted) images of MoO 3 -Sn nanobelts, (d) the EDS analysis graphics of MoO 3 -Sn nanobelts. According to the HRTEM observations, it can be found that the α-moo 3 nanobelts did not change in the inner planes after intercalation of Sn atoms. This means that the lattice constant value of a and c are not change. The diffraction peaks of MoO 3 -Sn nanobelts at (020), (040), (060) planes show obvious blue shift which indicates the enlarged interlayer spacing along the [010] direction due to Sn atoms intercalation. Thus, we can calculate the change of the lattice constant of b based on the peak shift of XRD pattern, in terms of the following equation: 2dsinθ λ ----(1) ----(2) d: interplanar spacing λ: wavelength h, k, l: crystal indices a, b, c: lattice constant It can be concluded that the lattice constant of b increases from to after intercalation. 4

5 Table. S1 The content of Sn element in MoO 3 nanobelts test by EDS and XPS. element Sn L (EDS) Sn d (XPS) At% Table. S2 Local structural parameters for absorbed Sn in MoO 3 -Sn nanobelts and bulk SnO 2 fitted from EXAFS data. Central atoms Path N σ 2 (10-3 Å 2 ) Bond length (Å) Calculation (Å) MoO 3 -Sn nanobelts Sn-O SnO 2 Sn-O N, coordination number; R, bond distance; σ 2, Debye-Waller factor; Error bounds (accuracies) were estimated as N, ±5%; R, ±1%; σ 2, ±5%. 5

6 Figure. S2 (a) XANES spectra of Mo edge and (b) the corresponding FT analyses reveal the Mo-O bond length and coordination state for MoO 3 foil, α-moo 3 nanobelts and MoO 3 -Sn nanobelts. 6

7 Figure. S3 Comparison between experimental data and the fitting curves for SnO 2 (a) and MoO 3 -Sn nanobelts (b). 7

8 Figure. S4 Different DFT model of the Sn atoms bonding environment in MoO 3 crystal structure. 8

9 Table. S3 The total energy of different Sn atoms position. Site Sn 1 Sn 2 Sn 3 Sn 4 Sn 5 Sn 6 Sn 7 Energy (ev) Table. S4 The Mo-O bond length of [MoO 6 ] octahedral in α-moo 3 nanobelts and MoO 3 -Sn nanobelts. Bond length (Å) Mo-O 1 Mo-O 2 Mo-O 3 Mo-O 4 Mo-O 5 Mo-O MoO 3 -Sn α-moo 3 9

10 Figure. S5 Electronic band structure along the high-symmetry points for α-moo 3 nanobelts (left) and MoO 3 -Sn nanobelts (right), the red line mean conduction band minimum and the blue line mean the impurity states. 10

11 Figure. S6 The cycling performance of the MoO 3 -Sn nanobelts at a current density of 100 (a), 500 and 1000 ma g -1 (b). 11

12 Figure S7. Plots comparison of Z Re vs ω -0.5 for α-moo 3 nanobelts and MoO 3 -Sn nanobelts. The diffusion coefficient of Li + ion can be calculated from EIS plots method. The D EIS was calculated from the inclined line in the Warburg region using the following equation 7 : /2 σ ---(1) where R is the gas constant (8.314 J mol -1 K -1 ), T is the absolute temperature (K), A is the surface area of the anode (cm 2 ), n is the number of electrons per molecule during oxidization, F is the Faraday s constant, C is the Li + concentration, and σ is the Warburg factor associated with Z Re. σ ω. ---(2) Z Re is the real part of impedance, thus the Warburg factor σ can be obtained from the linear fitting of Z Re vsω -0.5 as plotted in Figure 2. Using Eq. (2) the DEIS at different temperatures can be calculated. As a result, the diffusion coefficient of MoO 3 -Sn nanobelts ( cm 2 s -1 ) is higher than α-moo 3 nanobelts ( cm 2 s -1 ) 12

13 Figure. S8 XRD patterns of MoO 3 -Sn nanobelts after Li insertion. 13

14 Figure. S9 The CV curves (left) α-moo 3 nanobelts and (right) MoO 3 -Sn nanobelts. 14

15 REFERENCES (1) Ressler, T. WinXAS: a program for X-Ray absorption spectroscopy data analysis under MS-Windows. J. Synchrotron Radiat. 1998, 5, (2) Ankudinov, A. L.; Ravel, B.; Rehr, J. J.; Conradson, S. D. Real-space multiple-scattering calculation and interpretation of X-ray-absorption near-edge structure. Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 58, (3) Kresse, G.; Hafner, J. Ab initio molecular dynamics for liquid metals. Phys. Rev. B. 1993, 47, (4) Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B. 1996, 54, (5) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, (6) Grimme, S. Semiempirical GGA-type density functional constructed with a long-range dispersion correction. J. Comput. Chem. 2006, 27, (7) Chou, S. L.; Wang, J. Z.; Liu, H. K.; Dou, S. X. Rapid synthesis of Li 4 Ti 5 O 12 microspheres as anode materials and its binder effect for lithium-ion battery. J. Phys. Chem. C, 2011, 115,