Ultrasmall Sn nanoparticles embedded in nitrogen-doped porous carbon as high-performance anode for lithium-ion batteries

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1 Supporting Information Ultrasmall Sn nanoparticles embedded in nitrogen-doped porous carbon as high-performance anode for lithium-ion batteries Zhiqiang Zhu, Shiwen Wang, Jing Du, Qi Jin, Tianran Zhang, Fangyi Cheng, and Jun Chen* Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry; Collaborative Innovation Center of Chemical Science and Engineering, Nankai University, Tianjin , China.

2 Contents 1. Synthesis of Sn(Salen) and porous Sn/C composite 2. Material Characterizations 3. Electrochemical investigation 4. Figure S1. IR spectra of SalenH 2 and Sn(Salen). 5. Figure S2. 1 H and 13 C NMR spectrum of Sn(Salen). 6. Figure S3. Raman spectra of 5-Sn/C composite. 7. Figure S4. XPS spectra of 5-Sn/C composite and salen-c. 8. Figure S5. TG curves of 5-Sn/C composite. 9. Figure S6. N 2 sorption isotherms of 5-Sn/C composite. 10. Figure S7. XRD patterns and TEM image of 50-Sn/C composites. 11. Figure S8. Galvanostatic charge-discharge profiles of 50-Sn/C composite. 12. Figure S9. TEM image of 50-Sn/C composite after 100 charge/discharge cycles. 13. Figure S10. Voltage profiles of 5-Sn/C composite under different current densities.

3 1. Synthesis of Sn(Salen) and porous Sn/C composite Sn(Salen) complex was synthesized according the previously reported procedure. 1 In a typical synthesis, 5 mmol SnCl 2 and 5 mmol salenh 2 ligand were added into 50 ml ethanol. Then 1.4 ml triethylamine was slowly dropped into the mixture solution and kept stirring for 24 h at 85 o C. After cooling, the mixture was filtered. The yellow precipitate was washed with ethanol and dried in vacuum. The resulting Sn(Salen) was sintered in a tubular furnace at 650 o C and 700 o C for 2h under Ar atmosphere to afford the final products, 5-Sn/C composite and 50-Sn/C composite, respectively. 2. Material Characterizations Sn(Salen). The FTIR spectra were recorded using KBr pellets on AVATAR 360 spectrometer (Nicolet Instrument Corp., USA) in wavelength range of cm H and 13 C NMR spectra were recorded in D 2 O on Varian Mercury plus-300 ( 1 H 300 MHz, 13 C 100 MHz). Elemental analysis was conducted on Vario EL III elemental analysis instrument (Elementar Inc., Germany). NMR data: 13 C NMR (DMSO-d 6 ) 54.1(CH 2 ) (CH=N); 1 H NMR(DMSO-d 6 ) 3.71(s,2H) 4.0(S,2H) 6.64(M,2H) 6.71(M,2H) 7.3(M,4H) 8.4(d,2H). Elem. Anal.: C,49.91; H,3.67;N,7.28 Found: C,49.84; H,3.69; N,7.31. Sn/C composite. The crystal structures and morphologies of the as-synthesized materials were characterized by powder X-ray diffraction (XRD, Rigaku D/max-2500

4 X-ray generator, Cu Ka radiation), field-emission scanning electron microscopy (SEM, FEI NanoSEM-430, 10 kv), transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM, Philips TecnaiF20, 200 kv). Surface area analysis was performed by measuring the N 2 adsorption-desorption isotherms at 77 K on a BELSORP-mini instrument. XPS data were obtained using a Perkin Elmer PHI 1600 ESCA system. The tin content of Sn/C composite was tested using a TG-DSC analyzer (NETZSCH, STA 449 F3) from room temperature to 650 o C at a heating rate of 5 o C per minute in air. Assuming that only SnO 2 would remain after all the carbon being oxidized into gaseous CO 2 after TGA experiment, the Sn content could be calculated based on the following equation: Sn (wt%) = 100 molecular weight of Sn molecular weight of SnO 2 final weight initial weight 3. Electrochemical investigation Electrochemical measurements were performed with CR2032 coin-type cells assembled in an argon-filled glove box (Mikrouna Universal 2440/750). The electrode was fabricated by pasting a mixture of the active material (80 wt%), super P (10 wt%), and sodium carboxymethyl cellulose (CMC) binder (10 wt%) on copper foil and dried at 100 o C for 10 h in a vacuum oven. Lithium metal was used as the counter electrode. The electrolyte solution was 1.0 M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1. Cyclic voltammetry (CV) was carried out on Parstat 263A potentionstat/galvanostat

5 workstation with a scan rate of 0.1 mv/s from 2.0 to 0.01 V. The assembled cells were cycled at different current densities between 2.0 and 0.01 V on a LAND-CT2001A battery-testing instrument. Electrochemical impedance spectroscopy (EIS) was measured on an AC voltage of 10 mv amplitude in the frequency range from 100 khz to 100 mhz. Before EIS tests, the assembled cells were first discharged/charged at a current density of 0.2 A/g for 5 cycles to stabilize the cells. 4. Figure S1. IR spectra of SalenH 2 and Sn(Salen). Figure S1. IR spectra of SalenH 2 and as-prepared Sn(Salen)

6 5. Figure S2. 1 H and 13 C NMR spectrum of Sn(Salen). Figure S2. 1 H and 13 C NMR spectrum of Sn(Salen) in DMSO-d 6.

7 6. Figure S3. Raman spectra of 5-Sn/C composite. Figure S3. Raman spectra of as-prepared 5-Sn/C composite.

8 7. Figure S4. XPS spectra of 5-Sn/C composite and salen-c. Figure S4. (a) Sn 3d XPS spectra of as-prepared 5-Sn/C composite. (b) High resolution O1s XPS spectrum of 5-Sn/C. It was fitted into four peaks at 531.3, 532.4, and ev. 2 The peak at ev is attributed to Sn-O bonding, proving the formation of SnO 2. However, the peak at ev originated from C-O bonding indicates that the oxygen also bond with carbon. The other two peaks at and ev are assigned to oxygen in O 2 and H 2 O, respectively, which should be attributed to the adsorbed H 2 O and O 2 on the carbon matrix. (c) Comparison of O 1s spectrums of 5-Sn/C and salen-c synthesized by prolysis of salenh 2 ligand. The O 1s

9 spectrum of 5-Sn/C shows a shift to ev compared to that of salen-c. It should be due to the O species in the SnO 2, further proving the formation of SnO 2. 3 Combined with the existence of O in salen-c, the result reveals that the oxygen in 5-Sn/C composite should be from both the carbon matrix and SnO 2. (d) The full XPS spectrum of 5-Sn/C. Insert shows the N1s spectrum of 5-Sn/C. 8. Figure S5. TG curves of 5-Sn/C composite. Figure S5. TG curves of the prepared 5-Sn/C composite in air with a heating rate of 5 o C per minute.

10 9. Figure S6. N 2 sorption isotherms of 5-Sn/C composite. Figure S6. N 2 sorption isotherms of 5-Sn/C composite. 10. Figure S7. XRD patterns and TEM image of 50-Sn/C composites.

11 Figure S7. (a) XRD patterns and (b) TEM image of as-synthesized 50-Sn/C composites. 11. Figure S8. Galvanostatic charge-discharge profiles of 50-Sn/C. Figure S8. Galvanostatic charge-discharge profiles of 50-Sn/C electrode at a constant current density of 0.2 A/g. 12. Figure S9. TEM image of 50-Sn/C composite after 100 charge/discharge cycles.

12 Figure S9. TEM image of 50-Sn/C composite after 100 charge/discharge cycles. 13. Figure S10. Voltage profiles of as-prepared 5-Sn/C under different current densities. Figure S10. Charge/discharge profiles of as-prepared 5-Sn/C under different current densities. References

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