1. Synthesis of SnO2 Nanotubes by Electrospinning and Subsequent Heat Treatment17
2. Electrochemical Battery Cell Test
3. Preparation of the Graphene Liquid Cell
4. Performing Real-time TEM
SnO2 nanotubes were fabricated by electrospinning and subsequent calcination, during which the nanotubular and porous structures could be seen clearly, according to the SEM image (Figure 3a). Such a nanotubular structure comes from the decomposition of PVP, while the Sn precursor in the core is moved outward due to the Kirkendall effect17,18. Additionally, Ostwald ripening occurs in addition to the Kirkendall effect, resulting in the growth of SnO2 nanogains19. The TEM image (Figure 3b) shows that such porous sites are more visually clear, indicated by a number of white spots within the SnO2 nanotubes. The crystal structures of SnO2 are polycrystalline cassiterite structures (Figure 3c), in accordance with previously published literature17.
In terms of electrochemical characteristics of the SnO2 nanotubes, various aspects of the SnO2 nanotubes were examined in detail. To start with, the charge and discharge profile of the SnO2 nanotubes in the formation cycle is shown (Figure 4a), which exhibits stable voltage profiles with an initial coulombic efficiency of 67.8%. The voltage plateau, which exists at 0.9 V, can be attributed to the two-phase reaction (the conversion reaction of SnO2 to Sn), similar to descriptions in previous works9,20. The irreversible formation of Li2O during the conversion reaction of SnO2, along with the unstable formation of the solid electrolyte interphase (SEI) layer, resulted in a poorly reversible reaction with Li in the formation cycle. The SnO2 nanotubes exhibit stable cycling at 500 mA g-1, with coulombic efficiencies above 98% (Figure 4b). The rate capabilities of SnO2 nanotubes (Figure 4c) are also presented, where the SnO2 nanotubes retain considerable capacity (> 700 mAh g-1) even at a high current density of 1,000 mA g-1. Nevertheless, initial irreversible capacity loss needs to be examined more in detail using in situ TEM methods.
Overall characterizations of graphene are shown in Figure 5. Figure 5a shows the Raman spectrum of graphene synthesized on Cu foil. The ratio between Ig and I2D was 2.81, which matches well with the ratio of monolayer graphene on polycrystalline Cu substrate, indicating that monolayer graphene was synthesized. The SEM image of transferred graphene on an Au TEM grid is shown in Figure 5b, demonstrating that the coverage of graphene was good after its transfer to the Au TEM grid. The TEM image and the corresponding selected area electron diffraction (SAED) pattern of the transferred graphene are shown in Figure 5c,d. The hexagonal diffraction spots indicate the monolayer graphene well.
Time-series TEM images of GLCs are shown in Figure 6, which are captured from Movie S1. When GLCs are fabricated well, they have multiple liquid pockets whose sizes range from tens of nanometers to hundreds of nanometers, depending on the solution and nanoparticles7,14. In this experiment, using EC/DEC/FEC solution and SnO2 nanotubes, the size of the liquid pocket was 300 – 400 nm. The accelerating voltage was 300 kV and the electron beam dosage 743.9 e–/Å2·s, which is enough for lithiation to proceed but not for severe beam damage. Through constant electron beam irradiation, dissolved electrons and radicals trigger a secondary reaction with the salt and solvent. Here, the decomposition of electrolyte and the formation of an SEI layer were observed at the initial stage, in agreement with some of the previously reported on reuslts6,7,8,9,21.
Figure 1: Digital camera images of the electrospinning setup and prepared SnO2 nanotubes and electrode. (a) Electrospinning, (b) SnO2 nanotubes, and (c) the slurry-cast electrode. Please click here to view a larger version of this figure.
Figure 2: Digital camera images showing the graphene-transferred grid and fabrication of the graphene liquid cells. (a) The synthesized monolayer graphene on Cu foil, (b) an Au TEM grid on Cu foil, (c) the etching process of Cu foils in 0.1 M ammonium persulfate, and (d) stacked Au grids inside a glove box. Please click here to view a larger version of this figure.
Figure 3: Characterization of SnO2 nanotubes before their encapsulation inside the graphene sheet. These panels show (a) an SEM image, (b) a TEM image, and (c) the SAED pattern of the SnO2 nanotubes. Please click here to view a larger version of this figure.
Figure 4: Electrochemical battery cell testing of the SnO2 nanotubes. These panels show (a) the charge and discharge profile, (b) the cycle retention characteristics, and (c) the rate capabilities of the SnO2 nanotubes. Please click here to view a larger version of this figure.
Figure 5: Characterization of synthesized graphene. These panels show (a) the Raman spectrum, (b) the SEM image, (c) the TEM image, and (d) the SAED pattern of the monolayer graphene. Please click here to view a larger version of this figure.
Figure 6: Real-time TEM images of the lithiation process of GLCs. Decomposed electrolyte and the formation of an SEI layer on the surface of an SnO2 nanotube are observed for 0 – 45 s. Please click here to view a larger version of this figure.
Movie S1. Lithiation of GLCs. The surface of an SnO2 nanotube is visualized inside liquid electrolyte. Please click here to view this video. (Right-click to download.)
Tin chloride dihyrate | Sigma Aldrich | CAS 10025-69-1 | In a glass bottle |
Ethanol | Merck | CAS 64-17-5 | In a glass bottle |
Dimethylformamide | Sigma Aldrich | CAS 68-12-2 | In a glass bottle |
Polyvinylpyrrolidone | Sigma Aldrich | CAS 9003-39-8 | In a plastic bottle |
Cell tester | KOREA THERMO-TECH | Maccor Series 4000 | |
Cell tester 2 | WonaTech | WBCS4000 | |
Sodium perchlorate | Sigma Aldrich | CAS 7601-89-0 | In a glass bottle |
25 gauge needle | Hwa-In Science Ltd. | ||
1.3 M of lithium hexafluorophosphate (LiPF6) dissolved in EC/DEC with 10 wt% of FEC | PANAX ETEC | In a stainless steel bottle | |
Propylene carbonate | Sigma Aldrich | CAS 108-32-7 | In a glass bottle |
Super P Carbon Black | Alfa-Aesar | CAS 1333-86-4 | In a glass bottle |
Cell components (bottom cell, top cell, separator, gasket, spring, spacer) | Wellcos Corporation | ||
Cell punch | Wellcos Corporation | ||
Glove Box | Moisture Oxygen Technology (MOTEK) | ||
Box Furnace | Naytech | Vulcan 3-550 | |
Electrospinning device | NanoNC | ||
Hydrofluoric acid | Junsei | 84045-0350 | 85% |
Cu foil | Alfaaesar | 38381 | Copper Thinfoil, 0.0125mm thick, 99.9% |
Holy carbon Au grid | SPI | Quantifoil R2/2 Micromachined Holey Carbon Grids, 300 Mesh Gold | Quantifoil R2/2 Micromachined Holey Carbon Grids, 300 Mesh Gold |
Isoprophyl alchol | Sigmaaldrich | W292907 | 99.70% |
Ammonium persulfate | Sigmaaldrich | 248614 | 98% |
Transmission electron microscope (TEM) | JEOL | JEOL JEM 3010 | 300 kV |
Chemical vapor depistion (CVD) | Scientech | ||
Charge coupled device (CCD) | Gatan | Orius SC200 | |
Plasma Cleaner | Femtoscience | VITA | |
Electrospinning program | NanoNC | NanoNC eS- robot |
In this work, we introduce the preparation of graphene liquid cells (GLCs), encapsulating both electrode materials and organic liquid electrolytes between two graphene sheets, and the facile synthesis of one-dimensional nanostructures using electrospinning. The GLC enables in situ transmission electron microscopy (TEM) for the lithiation dynamics of electrode materials. The in situ GLC-TEM using an electron beam for both imaging and lithiation can utilize not only realistic battery electrolytes, but also the high-resolution imaging of various morphological, phase, and interfacial transitions.
In this work, we introduce the preparation of graphene liquid cells (GLCs), encapsulating both electrode materials and organic liquid electrolytes between two graphene sheets, and the facile synthesis of one-dimensional nanostructures using electrospinning. The GLC enables in situ transmission electron microscopy (TEM) for the lithiation dynamics of electrode materials. The in situ GLC-TEM using an electron beam for both imaging and lithiation can utilize not only realistic battery electrolytes, but also the high-resolution imaging of various morphological, phase, and interfacial transitions.
In this work, we introduce the preparation of graphene liquid cells (GLCs), encapsulating both electrode materials and organic liquid electrolytes between two graphene sheets, and the facile synthesis of one-dimensional nanostructures using electrospinning. The GLC enables in situ transmission electron microscopy (TEM) for the lithiation dynamics of electrode materials. The in situ GLC-TEM using an electron beam for both imaging and lithiation can utilize not only realistic battery electrolytes, but also the high-resolution imaging of various morphological, phase, and interfacial transitions.