Carbon Layers and Applications in High Capacity Li-Ion Storage

Transcription

1 Abs (a.u) Supporting Information for: Ultrasmall SnO 2 Nanocrystals: Hot-bubbling Synthesis, Encapsulation in Carbon Layers and Applications in High Capacity Li-Ion Storage Liping Ding, 1 Shulian He, 1 Shiding Miao, 1 * Matthew R. Jorgensen, 2 Susanne Leubner, 4 Chenglin Yan, 2,3 * Stephen G. Hickey, 4 Alexander Eychmüller, 4 Jinzhang Xu, 1 * and Oliver G. Schmidt 2 1 Anhui Key Lab of Controllable Chemical Reaction & Material Chemical Engineering, School of Chemical Engineering, Hefei University of Technology, Tunxi Road. 193, Hefei, Anhui Prov., 239, China; 2 Institute for Integrative Nanosciences (IIN), IFW Dresden, Helmholtzstr. 2, Dresden, D-169, Germany; 3 School of Energy, Soochow University, Suzhou, Jiangsu,2156 P. R. China; 4 Physical Chemistry/Electrochemistry, TU Dresden, Berg Str. 66b, Dresden, D-162, Germany 1. Absorption spectra and analysis min 2 min 3 min 1 hr Wavelength (nm) Figure S1 Absorption spectra of SnO 2 colloidal NCs with different growth time (measured in toluene). 1

2 2. Electronic microscopic analysis of SnO 2 NCs and their annealed sample (a) (b) (c) (d) (e) (f) Figure S2 SEM (a), and HRTEM (b) images of SnO 2 nanoparticles annealed in O 2 at temperature of 6 C (The colloidal SnO 2 NCs were synthesized from the Sn-oleate complex); (c) TEM image of the SnO 2 /C sample annealed in N 2 at 6 C; and (d and inset) TEM and enlarged images of as-synthesized colloidal SnO 2 NCs from di-n-octyltin oxide. (e and f) TEM images of SnO 2 /C nanocrystals obtained after annealing in N 2. 2

3 Raman Intensity (a.u) Weight percentage (%) Heat flow (W/g) 3. Thermoanalysis 1 8 TG DSC 389 o C o C -4 6 DTG Temperature ( o C) Figure S3 Thermoanalysis of SnO 2 colloidal NCs under O 2. The profiles include thermogravimetric (TG, black curve), derivative thermogravimetric (DTG, red curve) and differential scanning calorimeter (DSC, blue curve) profiles. 4. Raman spectrum of SnO 2 NCs 32 A 1g 24 Tetragonal SnO2 16 B 2g E g Wavenumber(cm -1 ) Figure S4 Raman spectrum of the N 2 -calcined SnO 2 nanoparticles. 5. IR spectrum of SnO 2 nanocrystals before and after calcination FT-IR spectroscopic measurements were conducted on as-synthesized colloidal SnO 2 NCs and calcined samples. The FT-IR profile is shown in Figure S5. We found peaks at 659 and 559 cm -1, which are the characteristics of intrinsic vibrations for Sn-O bonds and Sn-O-Sn asymmetric vibrations. 1 This manifests that the prepared sample contains tetragonal SnO 2 3

4 Quantity Adsorbed (cm 3 /g STP) dv/dlog(d) Pore Volume (cm 3 g -1 A) IR Absorption (%) nanocrystals. In the as-synthesized colloidal SnO 2 NCs, peaks at 1539 (asymmetric [ν as (COO - )]) and 1456 cm -1 (symmetric [ν s (COO - )]) were observed suggesting the presence of OA as ligands. Furthermore, the lack of absorption in the 28-3 cm -1 region (C-H vibrations) in the calcined sample suggests the removal of organic ligands after calcination, however, the peak at 1633 cm -1 which is the reminiscence of (RNH 2 ) to form Sn(RNH 2 ) x due to the OLA presented in the NCs system, could be the bending mode of (N-H) - in the annealed sample. 2 This provides an evidence for N-doping in the N 2 -annealling process. The nitrogen doping could come from the ligands. Consequently, the FT-IR spectra show that both OA and oleylamine are capped on the SnO 2 NCs. These ligands yield amorphous carbon after inert gas annealing as well as induce N-doping. before after 1633 (N-H) - COO Wavenumber(cm -1 ) Figure S5 IR spectra of SnO 2 NCs before and after N 2 annealing N 2 adsorption-desorption isotherms and BJH pore size distribution (a) 45 N 2 -Annealed (b) O 2 -annealed 15 O 2 -Annealed Relative Pressure (P/Po) 4 N 2 -annealed 1 1 Pore Diameter (nm)

5 Intensity (a.u) Figure S6 (a) N 2 adsorption-desorption isotherm and (b) BJH pore size distribution profiles of the SnO 2 NCs annealed in N 2 and O EDS analysis of SnO 2 /C annealed under N 2 atmosphere at 6 C (a) (b) Selected area TEM Image 2nm (c) (d) (e) 2k C 1k C N O Sn Cu Sn Cu Binding energy (ev) Figure S7 TEM image (a) of SnO 2 /C and the corresponding EDS mapping figures (b, c and d); (e) The EDS of a selected area in figure (a). 5

6 Table S1 Normalized element percentages of N, O, and Sn in the SnO 2 /C nanoparticles a Element Weight percentage a Atomic percentage N K O K Sn L Total 1. Note: a Due to the carbon from the copper grid, we do not include the carbon content when we calculated the percentage of the elements (Sn, O, N, and C). 8. XPS analysis of the colloidal SnO 2 CNs and their annealed nanocrystals The XPS spectra of SnO 2 colloidal NCs and N 2 -calcined nanocrystals are shown in the following figures where the Sn 3d, O 1s and C1s spectra are presented. It is found that the peaks of Sn(IV) at (Sn 3d 5/2 ) and ev (Sn 3d 3/2 ) in the as-synthesized SnO 2 NCs shifts to and ev after N 2 -annealing, which demonstrates that lower valence Sn species such as Sn(II) (3d 5/2, 487. ev) or Sn() (3d 5/2, 485. ev) are produced. 3 We quantified the percentage of each component (Sn(IV), Sn(II) and Sn()) by decomposing the photoemission XPS peaks of Sn (3d 5/2 and 3d 3/2 ). Figure S8c denotes the deconvolved spectra of XPS peaks at binding energy of about 487 and 495 ev. Three couples of peaks located at 487.3/495.9 ev (Sn(IV)), 487./495.5 ev (Sn(II)) and 485./493.6 ev (Sn()) were obtained after fitting with Gaussian peaks. During the deconvolution the positions were kept at constant binding energy, and the band height and width were only allowed to change. Based on the integral area under each peaks, we estimate the percentage of each species as listed in the following Table S2. The slightly asymmetric spectrum of O 1s can be resolved into two peaks at a relatively lower binding energy value of (53.2 ev) and a higher binding energy peak ( ev) by fitting with Gaussian distributions. They can be assigned to the O1s core peak of O 2- ions in Sn-O band (lattice oxygen) and the band of surface adsorbed hydroxyl groups (OH ), respectively. Table S3 lists the atomic percentage of the main elements (Sn, O, 6

7 XPS Intensity (a.u) XPS Intensity (a.u) XPS Intensity (a.u) XPS Intensity (a.u) XPS Intensity (a.u) XPS Intensity (a.u) and C) that are presented in both samples (SnO 2 and SnO 2 /C) derived from the analysis of XPS. (a) 1.6M SnO2 NCs SnO2 6C (b) 16k SnO 2 NCs SnO 2 6 o C k 8k Binding energy (ev) Binding energy (ev) (c) 21k (d) Sn-O 14k -OH- 7k (e) 2k Binding Energy(eV) SnO2 NCs SnO2 6C (f) Binding Energy (ev) SnO2 NCs Fit SnO2 6C Fit 1k Binding energy (ev) Binding Energy (ev) Figure S8 XPS spectra of the SnO 2 colloidal NCs and N 2 -calcined sample (sample name: SnO 2 6 C): (a) survey spectrum; (b, c) high-resolution XPS of Sn3d and deconvolved profiles; (d) high-resolution XPS of O1s and deconvolved profiles; (e, f) high-resolution XPS of C1s and N1s spectra in both samples. 7

8 Voltage (V) Table S2 Atomic percentage of different valence states Sn(IV), Sn(II) and Sn() derived from the deconvoled bands in Sn3d XPS peak. Spieces Sn(IV) Sn(II) Sn() Atomic percentage 9.5% 7.27% 2.68% Table S3 Chemical compositions of the surface of SnO 2 colloidal NCs and N 2 -calcined sample derived from XPS analysis. Element SnO 2 colloidal NCs (Atomic percentage, %) SnO 2 annealed at 6 C (Atomic percentage, %) Sn O C Voltage profiles of LIBs measurements k 4k 6k 8k Time (s) Figure S9 Typical discharge-charge voltage profile for the first five cycles at a current density of.5 C. 1. Voltage profiles of LIBs measurements 8

9 Specific capacity (ma h g -1 ) 16 SnO2/C SnO Discharge Runs Figure S1 (a) Voltage profiles of the N 2 -annealed SnO 2 /C in half cells cycled between.1 and 2. V at a rate of.5 mv/s; (b) Galvanostatic discharge/charge profiles the SnO 2 /C and SnO 2 nanoparticles at a density of.5 C. ~61 ma h g TEM analysis of the SnO 2 synthesized under control conditions Figure S11 (a) TEM image of SnO 2 synthesized after prolonged time (1.5 hrs) in ODE solution via the hot-bubbling route; (b) TEM image of SnO 2 synthesized in ODE solution 9

10 without air bubbling at a growth time of 3 hrs; (c) SEM image of flower-shaped SnO 2 synthesized in OLA solution using Sn(acac) 2 as precursor and corresponding EDS (d) circled 12. Electron microscope analysis of the samples prepared in control experiments Figure S12 SEM images of the SnO 2 /C modified anodes (a) before and (b) after charge/discharge for 2 cycles. 13. TEM and linked EDS mapping analysis of SnO 2 /C after charge/discharge for 2 cycles in LIBs 1

11 Intensity (a.u) (a) (b) 5nm Selected area (c) (d) (e) 3k C C Cu 2k 1k O N F P Si S Sn Sn Cu Cu 2 4 Binding energy (ev) Figure S13 TEM image (a) of SnO 2 /C after charge/discharge for 2 cycles and the corresponding EDS mapping figures (b, c and d); (e) The EDS profile of a selected area in figure (a). Table S4 Normalized element percentages of N, O, F, P, S, and Sn presented in the SnO 2 /C after charge/discharge for 2 cycles. a Element Weight percentage Atomic percentage 11

12 Z'' (Ohms) Z'' (Ohms) N K O K F K P K S K Sn L Total 1. Note: a The carbon was not included when we calculated the percentage of the elements (Sn, O, N, F, P and S). 14. Nyquist plots derived from the EIS measurements (a) 12 6 SnO2/C after 2 cycles SnO2/C SnO2 SnO2 after 2 cycles (b) Z' (Ohms) 5 1 Z' (Ohms) Figure S14 Nyquist plots (a) and an enlarged area at the high frequency (b) of the dummy cells consisting of two identical electrodes made with SnO 2 /C and bare SnO 2 nanoparticle annealed in O 2. Inset in Figure S14b is the equivalent electrical circuit. Table S5 The parameter of dummy cells made with SnO 2 /C and bare SnO 2 nanoparticle annealed in O 2 derived from Nyquist plots in Figure S14. Sample Rs /(Ω) Rct /(Ω) CPE Zw /(Ω -1 ) 12

13 SnO SnO 2 /C SnO 2 after 2 cycles SnO 2 /C after 2 cycles Phase transitions in the synthesis Figure S15 Photographic images of the phase transitions of the SnO x (OH) 2(2-x) +OA+ODE+ OLA system during the heating process: (a) 1 C; (b) 18 C; (c) 22 C; (d) 28 C after bubbling with air for 3 min (The solution in (d) has been sampled, so the volume is less than that of the other three-necked bottles). 16. Reference 1 Ghosh, S., Das, K., Chakrabarti, K.& De, S. K. Effect of oleic acid ligand on photophysical, photoconductive and magnetic properties of monodisperse SnO 2 quantum dots. Dalton Trans. 42, (213). 13

14 2 Su, L. T., Tok, A. I. Y., Zhao, Y., Ng, N.& Boey, F. Y. C. Synthesis and Electron-Phonon Interactions of Ce 3+ -Doped YAG Nanoparticles. J. Phys. Chem. C 113, (29). 3 Herrera, M., Maestre, D., Cremades, A.& Piqueras, J. Growth and Characterization of Mn Doped SnO 2 Nanowires, Nanobelts, and Microplates. J. Phys. Chem. C 117, (213). 14