Self-rearrangement of silicon nanoparticles. high-energy and long-life lithium-ion batteries

Transcription

1 Supporting Information Self-rearrangement of silicon nanoparticles embedded in micron carbon sphere framework for high-energy and long-life lithium-ion batteries Min-Gi Jeong,, Hoang Long Du, Mobinul Islam,, Jung Kyoo Lee, Yang-Kook Sun,* and Hun-Gi Jung,,* Center for Energy Convergence Research, Green City Technology Institute, Korea Institute of Science and Technology, Hwarangno 14 gil 5, Seongbuk-gu, Seoul 02792, Republic of Korea Department of Energy Engineering, Hanyang University, Seoul 04763, Republic of Korea Department of Energy and Environmental Engineering, Korea University of Science and Technology, Daejeon 34113, Republic of Korea Department of Chemical Engineering, Dong-A University, Pusan 49315, Republic of Korea * s: S-1

2 Materials Synthesis In a typical synthesis, Si nanoparticles (CN-Vision, approximate size 50 nm, 0.4 g) along with cetyltrimethylammonium bromide and polyvinyl pyrrolidone (both 25 wt% that of Si) were ultra-sonicated in distilled water (25 ml). Sucrose and oxalic acid (in a molar ratio of 1:1) were added into the solution, and vigorously stirred for 30 min. Then, the mixed solution was transferred to a Teflon-lined stainless steel autoclave, and held at 200 C for 10 h. After naturally cooling to room temperature, the precipitate was collected by filtration, and washed several times with distilled water and ethanol. After carbonization under argon atmosphere at 750 C for 5 h, the silicon-embedded micron carbon spheres (Si-MCS) were obtained. Experimental Characterization The morphologies of the synthesized samples were observed using field-emission scanning electron microscopy (FE-SEM, Hitachi S-4200) and transmission electron microscopy (TEM, Talos, FEI Corp.). The energy dispersive X-ray spectroscopy (EDS, Super-X, Bruker) instrument attached to the TEM apparatus was employed for the elemental analysis of the Si- MCS samples. The crystalline structures were characterized using X-ray diffraction measurement (XRD, Rigaku X-ray diffractometer) equipped by Cu-Ka (λ = Å) radiation. X-ray photoelectron spectroscopy (XPS, PHI 5000 VersaProbe Ulvac-PHI) was used to detect the surface chemical composition of the Si-MCS. The Brunauer Emmett Teller (BET) method using N 2 sorption isotherms was performed using a Micromeritics apparatus (ASAP 2010) to measure the surface area, average pore diameter, and the change of the total pore volume before and after embedding silicon inside the carbon micron spheres. The amounts of carbon in the synthesized materials were determined by using an elemental analyzer (EA1108/CHNS-0, Carlo Erba/Fisons/CE Instrument) and thermal gravimetric S-2

3 analysis (TGA, Seiko Exstar 6000). The DC electrical conductivity was measured by a direct volt ampere method (CMT-SR2000, AIT Co.) in which disk samples were in contact with a four-point probe. To investigate the electrochemical performance of the Si-MCS anode in LIBs, the slurry composed of Si-MCS, carbon black (acetylene black), and poly acrylic acid (PAA) binder (60:20:20 in weight ratio) and water was cast onto a copper foil current collector. Subsequently, the electrode was dried overnight at 120 C in a vacuum oven to remove the residual solvent. The prepared electrode was about ~30 µm thick, which corresponds to an average loading of ~1.2 mg cm -2 after the roll-pressing process. In the half cell, the prepared Si-MCS electrode was coupled with a Li counter electrode. Meanwhile, in the full Li-ion cell, the Si-MCS anode was combined with a LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cathode, and the capacity ratio of the anode to cathode (N/P ratio) in the full cell was Typically, the NCM622 electrode was prepared by mixing NCM622 (synthesized by a co-precipitation method 1 ) carbon black (Super P and KS6), and polyvinylidene difluoride (PVDF) binder (85:10:5 in weight ratio) on aluminum foil current collector. The separator is made of polypropylene, and the electrolyte is 1.2 M LiPF 6 in ethylene carbonate (EC), ethylmethyl carbonate (EMC) (3:7 in volume) with 5 wt% fluoroethylene carbonate (FEC) as additive. The lithium half and full cells were assembled in CR2032-type coin cells (Wellcos Corporation), after the Si-MCS electrodes were pre-lithiated by direct contact with lithium foils in the electrolyte for 4 h under 1 kg cm -2 pressure in an Ar-filled glove box. All electrochemical tests were conducted in a Maccor (Series 4000) battery testing system at room temperature. S-3

4 Figure S1. Field-emission scanning electron micrographs images of micro carbon spheres (MCS) (a) low and (b) high magnification. Si nanoparticles (c) low and (d) high magnification. S-4

5 Figure S2. (a) Full XPS pattern of the Si-MCS and a mixture of 1 wt% Si nanoparticles with MCS, and (b) the corresponding XPS pattern of Si 2p. We mixed 1 wt.% Si nanoparticles manually with MCS and conducted the surface sensitive XPS analysis, and the results were compared with that of Si-MCS sample. Si-MCS sample couldn t detect the Si clearly as like as mixture sample (Figure S2a), which clarify the embedded Silicon nanoparticles S-5

6 Figure S3. (a) HR-TEM image demonstrates the selected area from edge of one Si-MCS particle, (b) the corresponding fast Fourier transformation (FFT) of indicated area, and (c) inverse FFT image obtained using spots indicated in (b). S-6

7 Figure S4. Thermal gravimetric analysis (TGA) curves for Si-MCS (Air, 10 C/min). S-7

8 Figure S5. (a) First-cycle galvanostatic voltage profile of without prelithiated Si-MCS electrode and (b) Cycling performances of MCS and Si-MCS in lithium half-cell which assembled without prelithiated electrode. S-8

9 Figure S6. Galvanostatic cycling performance of silicon nanoparticles and micro carbon spheres (MCS) in lithium half-cell. S-9

10 Figure S7. After 100 cycles (a) TEM image of one individual Si-MCS, (b) A magnified TEM image for the same Si-MCS along with SAED pattern (inset). S-10

11 Figure S8. (a) Voltage profile at initial cycle and (b) cycling performance of LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cathode in a lithium half-cell. S-11

12 REFERENCES 1. H. J. Noh, S. Youn, C. S Yoon, Y. K. Sun, J. Power Sources 2013, 233, S-12