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A Novel 3D Carbon Nanotube–Graphene Architecture with Abundant Chambers and Its Application in Lithium–Silicon Batteries Weili Shi, Jianping Chen, Quanling Yang, Shan Wang, and Chuanxi Xiong J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b03864 • Publication Date (Web): 02 Jun 2016 Downloaded from http://pubs.acs.org on June 8, 2016

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The Journal of Physical Chemistry

A Novel 3D Carbon Nanotube–Graphene Architecture with Abundant Chambers and Its Application in Lithium–Silicon Batteries Weili Shi,† Jianping Chen,† Quanling Yang,*,† Shan Wang,† and Chuanxi Xiong*,† †

State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China.

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ABSTRACT: So far, the fabrication of three-dimensional (3D) architectures of carbon nanotube (CNT) and graphene-based materials remains a significant challenge. In this work, one facile and template-free strategy for fabricating a novel 3D carbon hybrid architecture was reported, which is comprised of CNT and few-layer graphene (FLG) through carbonizing the solvent-free CNT fluids at 700 °C. In this architecture, FLG served as walls and CNT acted as backbones forming abundant chambers. The results of transmission electron microscopy, electron diffraction pattern and Raman spectra all proved that FLG were produced from the long-chain organic ions grafted on CNT surface through carbonization. The analysis of atomic force microscopy showed the thickness of FLG was about 1 nm. The charge-discharge experimental result of Si/CNT‒FLG battery shows that the reversible capacity still remained approximately 1350 mAh g‒1 with 96% capacity retention after 300 cycles at 0.5C, demonstrating an outstanding cycling stability performance, indicating a great potential application of CNT‒FLG in the lithium-ion battery field.


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1. INTRODUCTION Owing to the high aspect ratio, electrical conductivity, and the outstanding thermal conductivity,1‒ 3

one-dimensional (1D) carbon nanotubes (CNTs) have attracted considerable interest for a wide range of

applications during the past decades.4‒7 Although encouraging results have been obtained, achieving an ideal dispersion for the entangled CNT agglomerates remains a challenge. Graphene,8 a single-atom-thick two-dimensional (2D) carbon materials, is recently discovered and has a large specific surface area, high electron mobility and superior mechanical flexibility.9‒11 Although graphene possesses these advantages, the irreversible aggregation or re-stacking of graphene sheets into a graphitic structure dramatically decreases these properties and hinders its widespread applications.12,13 In recent years, extensive efforts have been devoted to the fabrication and applications of three-dimensional (3D) graphene or CNT–graphene architectures, to prevent the aggregation or re-stacking of them to provide a large accessible surface area and multiplexed and highly conductive pathways.14‒17 These advantages combined with their intrinsic extraordinary mechanical properties, make them applicable to various applications. Related investigations have demonstrated that the 3D graphene or CNT–graphene architectures outperformed its 1D or 2D analogues.18‒21 Especially, theoretical studies have predicted that 3D CNT–graphene hybrid had a number of promising applications because of the synergistic integration of 2D graphene and 1D CNT.22‒25 However, experimental fabrication of the 3D CNT–graphene architecture is still in infancy and most of the 3D CNT–graphene hybrid was formed with vertically aligned CNTs grown in between the parallel graphene layers through chemical vapor deposition (CVD) techniques,26‒28 which is expensive and difficult to large-scale produce. Therefore, it is very challenging and promising to develop a facile pathway to fabricate 3D CNT–graphene hybrids. Herein, we report a facile and template-free strategy for fabricating a novel 3D carbon nanotube‒ few-layer graphene architecture (CNT‒FLG) through carbonizing the solvent-free CNT fluids (CNTF) at 700 °C under the nitrogen gas protection. This method of achieving CNT‒FLG makes the process highly ACS Paragon Plus Environment


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cost-effective and easy to scale up. Such structure is distinctly different from the all previous 3D CNT– graphene hybrid in the literature. In CNT‒FLG, FLG served as walls and CNT act as backbone forming abundant chambers, which could not only provide an interconnected conductive network and a large accessible surface area, but also form vast quantities of chambers. These merits is highly desirable for applications in the field of energy storage and conversion. Thus, in this work, it was applied to lithium– silicon (Li‒Si) battery as the mechanical supports and highly conductive networks, and providing adequate empty space to buffer the huge volume change of silicon (>300%) upon lithium insertion and extraction.29,30 The charge‒discharge experimental result revealed that the reversible capacity of Si/CNT‒ FLG battery still remained approximately 1350 mAh g‒1 with 96% capacity retention after 300 charge– discharge cycles at 0.5C, which is about 3.6 times the theoretical capacity of current commercial graphite, illustrating the great potential application of CNT‒FLG in developing high-performance lithium-ion batteries.


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2. EXPERIMENTAL SECTION 2.1. Materials. Chloroform, ethanol, concentrated sulfuric acid (H2SO4, purity of 98%) and concentrated nitric acid (HNO3, purity of 65%) were obtained from Sinopharm Chemical Reagent Co., Ltd. The MWCNTs were purchased from Beijing DK nano technology Co. Ltd. (diameter of 8–15 nm, length of 10–30 µm, purity of 95% ). The Ni foam was bought from Desko Electronics Co., Ltd. (diameter of 14 mm). Si nanoparticles were purchased from Beijing DK nano technology Co. Ltd. (diameter of 30–100 nm). 2.2. Preparation of 3D Carbon Nanotube‒Few-Layer Graphene Architecture. First, the CNT fluids were prepared according to our previous work.31‒34 Briefly, the MWCNTs were oxidized in a mixture of concentrated H2SO4/HNO3 (3:1). Then the oxidized CNTs were first modified by [(CH3O)3Si(CH2)3N+(CH3)2 (C18H37)Cl-] (DC5700, Gelest) through condensation with surface oxygen containing groups. The resultant product was subsequently grafted with long chain flexible oligomeric counterions [C9H19C6HO (CH2CH2O)10SO3‾K+] (NPES, Aldrich) by ionic interaction, after that the solvent-free CNT fluids (CNTF) were obtained. The synthesized CNTF was transferred into a ceramic boat and were heated at 700 °C for 4h in a horizontal tube furnace under nitrogen gas protection, to prepare the 3D carbon nanotube‒few-layer graphene architecture (CNT‒FLG). 2.3. Preparation of the Electrodes of Li-Ion Batteries. Appropriate proportion as-fabricated CNT fluids (CNTF) and Si nanoparticles were introduced into the chloroform solvent followed by bath sonication for 2h to make the Si nanoparticles well-dispersed in CNTF. Then the slurry was coated onto the current collectors (Ni foam) with a brush and dried in a vacuum oven at 70 °C for 24h. Subsequently, the products were heated at 700 °C for 4h in a horizontal tube furnace under nitrogen gas protection to obtain the Si/CNT‒FLG anodes. The Si/CNTF anode was fabricated by mixing the above Si/CNTF slurry with acetyl black (10 wt%) and using the same method as that of the Si/CNT‒FLG anode without heating at 700 °C. To estimate the contribution of CNT‒FLG to the capacity of the Si/CNT‒FLG battery, the ACS Paragon Plus Environment


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CNT‒FLG anode without Si nanoparticles was also fabricated using the same method as that of the Si/CNT‒FLG anode. 2.4. Characterization Techniques. The morphological structure of the materials was investigated by using an EDX-equipped field emission scanning transmission electron microscopy (FE-SEM) (FEI Quanta 200FEG) and transmission electron microscopy (TEM) (JEOL JEM2100F). Raman spectra were recorded using INVIA RENISHAW spectrometer with a 633 nm argon laser. The crystal structure was analyzed by X-ray diffraction (XRD) (Bruker D8 advance) with Cu Kα radiation. The shape and thichness of CNT‒FLG was investigated by atomic force microscopy (AFM) with MFP-3D-SA (Glen, USA) in an intermittent tapping mode at a scan rate of 1 Hz using aluminum coated silicon cantilevers. The CNT‒FLG sample was first grinded for 1h in a mortar, then the resultant was transfer into N-2-methyl pyrrolidone (NMP) solvent followed by bath sonication for 10min. After that the obtained solution was droped onto freshly cleaved mica plate (15-20 nm thick produced by Peking XinRui, INC.) to observed the morphology. The specific surface area and the pore size distribution were determined by nitrogen adsorption-desorption isotherms at 77 K on an ASAP 2020M analyzer. The specific surface area was calculated from multipoint adsorption data within the linear segment of the nitrogen adsorption isotherms, using Brunauer-Emmett-Teller theory. The pore size distribution was calculated via a density functional theory (DFT) method by using nitrogen adsorption data and assuming a slit pore model. 2.5. Electrochemical Measurements. The 2016 cells were assembled using lithium metal foil as the counter electrode, polypropylene film (Celgard 2300) as the separator. The electrolytes were 1.0 M LiPF6 solution in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (1:1:1 by volume). The coin cells were assembled in an Ar-filled glove box (MBraun Unilab). Galvanostatic tests were conducted using a cell test instrument (LAND CT21001A) at the voltage range of 0.005–1.4 V (vs Li/Li+). Cyclic voltammetry was performed using an electrochemical station (Wuhan corrtest instruments Co. LTD., CS150) in the voltage range of 0.002–1.4 V at a scan rate of 0.1 mV s–1. ACS Paragon Plus Environment

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The current density set for the tests was referred to the mass of silicon in the anode, except the CNT‒FLG anode, which was based on the mass of CNT‒FLG (1C=4200 mAh g–1).

3. RESULTS AND DISCUSSION 3.1. Fabrication Process of CNT‒FLG. The formation process and the structure of CNT‒FLG are described in Figure 1c. First, the carboxylic multi-walled carbon nanotubes (MWCNTs) were oxidized by a mixture of concentrated H2SO4/HNO3 (3:1). Then the oxidized MWCNTs were successively modified with the DC5700 and NPES (both of them are long-chain organic ions) to synthetize CNTF (Figure 1a, b). Such treatments on MCNTs could make it untangled and well-dispersed even without any solvents. The liquidlike behavior of CNTF was confirmed by the higher loss modulus (G") compared with storage (G') modulus in the temperature-dependent G' and G" measurements (Figure S1, Supporting Information). Finally, the as-synthesized CNTF was carbonized in a tube furnace at 700 °C under nitrogen gas protection to obtain CNT‒FLG. During the carbonizing process, the long-chain organic ions were converted into few-layer graphene tightly attaching on the CNTs surface and continuously covering across the CNT backbones, forming abudant chambers. Such as-constructed architecture has multiple attractive features: (1) It synergistically integrates 1D CNTs and 2D few-layer graphene. CNTs can bridge the defects for electron transfer and increase the layer spacing between graphene sheets to prevent graphene sheets re-stacking. Graphene sheets can provide a large accessible surface area enhancing mass and electron transport. (2) In this architecture, the few-layer graphene serve as walls, the CNT act as backbones, forming abudant chambers and providing 3D interconnected electrical conductive networks, which is particularly favourable for application in lithium ion battery. (3) Especially, the facile and template-free strategy for preparation of CNT–FLG makes the process easy to scale up, and it provides a new perspective on the combination of 1D CNT and 2D graphene-based materials. ACS Paragon Plus Environment


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Figure 1. (a) Photograph of the synthesized CNTF. (b) Schematic of CNTF with the long-chain organic ions grafted on the CNT surface. (c) Schematic of the formation of CNT‒FLG. (d) Schematic representations of the structural evolution of the Si/CNT‒FLG anode material upon charge/discharge cycling. 3.2. Structural Characterization of CNT‒FLG. The morphology structures of CNT‒ FLG are characterized by SEM and TEM. The SEM image of the pristine MCNTs (p–MCNTs) was shown in Figure 2a, in which the nanotubes randomly entangled and agglomerated together constituting sparse macropores. The SEM image of CNT–FLG indicated that it was distinctly different from p–MCNTs (Figure 2b). It could be seen that the CNTs in CNT–FLG formed relatively dense and interconnected conductive networks. From the low-magnification TEM image of CNT–FLG, it could be found that there were ultrathin carbon layers between CNTs, connecting with the CNTs (Figure 2c). From the high-magnification TEM of CNT–FLG, it could be seen typical lattice fringes of thin layer graphene on ACS Paragon Plus Environment

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the interface of ultrathin carbon layers and CNT. It be deduced that the ultrathin carbon layers might be few-layer graphene (Figure 2d). The more complete TEM image of Figure 2d was shown in Figure S2 (Supporting Information). Furthermore, the inset in Figure 2d showed the normal-incidence selected-area diffraction patterns for the ultrathin carbon layers, the hexagonal pattern clearly showed the characteristic of few-layer graphene,35,36 which preliminary illustrated that the long-chain organic ions have turned into few-layer graphene during carbonization process and the expected 3D carbon hybrid architecture comprised of CNT and few-layer graphene was successfully synthesized. The more morphological structures of CNT–FLG are shown in the Figure S2 (Supporting Information).

Figure 2. SEM images of p–MCNTs (a) and CNT–FLG (b). Low-magnification (c) and high-magnification (d) TEM images of CNT–FLG. The inset image in (d) shows the electron diffraction pattern taken from the position of the white spot.



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Figure 3. Raman spectra of CNT–FLG and p–MCNTs: (a) D-band and G bands, (b) 2D-band. (c) X-Ray diffraction patterns of p–MCNTs, CNTF and CNT–FLG. In order to further verify the existence of graphene flakes in CNT–FLG, the Raman spectroscopy investigation was carried out since the Raman spectroscopy is a powerful tool to investigate the structural and electronic properties of carbon-based materials. The Raman spectra of pristine MCNTs and CNT– FLG are shown in Figure 3a,b. The Raman spectrum of p–MCNTs presents three typical peaks at 1322, 1571, and 2643 cm−1, corresponding to the D, G, and 2D band of MCNTs, respectively.37,38 The D and G bands spectrum of CNT–FLG showed that there is a new peak appeared at about 1608 cm−1 (Figure 3a). Relevant investigations have demonstrated that defective graphene or graphene armchair and zigzag edges could activate this peak,39,40 corresponding to the Dʹ peak of graphene. Furthermore, the 2D band of CNT–FLG is notably different from that of p–MCNTs (Figure 3b), which presents two paratactic 2D peaks at 2647 and 2657 cm−1, and the latter peak of 2657 cm−1 is attributed to the characteristic 2D peak of graphene flakes.41,42 In addition, there is no typically broad peak of amorphous carbon appeared at about 1500 cm−1,43,44 implying that the amorphous carbon was not present in CNT–FLG, which was further confirmed by X-ray diffraction analysis (XRD, Figure 3c). The XRD patterns of p–MCNTs present three peaks at 26.0°, 44.5° and 51.9°, respectively. The peak at 26.0° is owing to C (002) crystal plane of MCNTs.45 For CNTF, there was a new broad peak appeared at about 20.5°, corresponding to the typical diffraction peak of amorphous carbon,43 which resulted from the modification of MCNTs with the long-chain organic ions. However, the broad peak at 20.5o disappeared for CNT–FLG, suggesting that the ACS Paragon Plus Environment

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long-chain organic ions became the graphene sheets during the carbonization process, which is consistent with the results of TEM. To further investigate the shape and thickness of graphene flakes in CNT–FLG, the atomic force microscopy (AFM) was performed. As the height of MWCNTs is quite different from that of graphene sheets, it’s difficult to exactly measure the thickness of the graphene in CNT–FLG by AFM (Figure S3g, supporting information). Thus CNT–FLG was treated with the following processes to make the investigation on the thickness of the graphene sheets more accurately. Firstly, the CNT–FLG sample was acutely grind in a mortar for 1 hour, then they were dissolved in NMP assosiated with sonication for 10 min. During the process, the structure of CNT–FLG was destroied, and part of the few-layer graphene fall away from the CNT, which could make the observation of AFM more precisely. 15 µl of the above liquid were deposited onto freshly cleaved mica plate to allow a natural evaporation before AFM analysis at room tempreture. 1.0

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Figure 4. (a, b) AFM image of CNT–FLG samples deposited on freshly cleaved mica, the right figures show the height profile along the white lines in the left figures. As shown in Figure 4 and Figure S3 (supporting information), some CNTs could be observed, with the thickness ranging from 6 to 20 nm. Some graphene flakes were also seen, and the ananlysis result of AFM revealed that the thickness of graphene flakes was approximately 1 nm and they were uniformly distributed (Figure S3a, supporting information). In addition, a 0.4 nm thick graphene flakes could also be obtained (Figure 4a), which further demonstrated the graphene flakes belong to few-layer graphene according to the nomenclature for two-dimensional carbon materials.46 In order to illustrate our finding was not accidental, a number of few-layer graphene were observed. Some examples of the images of such FLG were shown in Figure S3b-f (supporting information). Some CNT–FLG was also observed in Figure S3g, further indicating that the expected 3D carbon hybrid architecture comprised of CNT and few-layer graphene could be acquired from calcined CNTF. To explore the specific surface area and the pore size distributions of the as-constructed CNT–FLG, N2 adsorption-desorption isothermal analysis was carried out, as shown in Figure 5. Calculated by the Brunauer-Emmett-Teller (BET) model, the specific surface area of CNT–FLG is as high as 2250 m2 g‒1. Such high specific surface area further demonstrated the formation of graphene flakes, which could significantly enhance the mass and electron transport as electrode materials in the field of energy storage and conversion. The pore-size distribution result of CNT–FLG showed that most of the pores distributed in the range of 2–50 nm (inset in Figure 5), which illustrated the considerable mesopores existed in CNT– FLG, although a small number of macropoers with the sizes of 50–60 nm were also present.


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surface area, it is highly desirable for applications in the electrochemical field. The silicon has the highest theoretical specific capacity (~4200 mAh g‒1), but it suffers from huge volume change (>300%) upon lithium insertion and extraction.29,30 Therefore, in this work, the as-prepared CNT–FLG were applied to the Li‒Si battery to provide a highly conductive network for Li+ transport and offer adequate free-standing empty space for accommodating the huge volume change of silicon during repeated cycling. The structural evolution of the Si/CNT–FLG anode material upon charge/discharge cycling is described in Figure 1d. The morphology structures of the Si/CNT–FLG anode material are investigated by SEM and TEM, as shown in Figure 6. The SEM image of Si/CNT–FLG showed that the Si nanoparticles were well-dispersed in an interconnected conductive network (Figure 6a). The energy dispersive X-ray (EDX) analyses disclose that the silicon content in the Si/CNT–FLG anode was about 20 wt% for many defined regions (Figure S4, Supporting Information). From the Figure 6b, It can be observed that Si nanoparticles were sealed in the chambers provided by CNT–FLG and there was still enough empty space when the Si nanoparticles were filled into the rooms. The enlarged view of the remaining empty space showed that the silicon and CNT were interconnected with the generated graphene flakes (Figure 6c). Such unique structure could provide excellent conductivity for silicon to facilitate the lithium ion and electron transport. More micromorphology of Si/CNT–FLG is shown in the Figure S5 (Supporting Information). The existence of graphene flakes in Si/CNT–FLG was further confirmed by Raman spectroscopy and XRD (Figure S6 and S7, Supporting Information).


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Figure 6. SEM image (a) and Low-magnification TEM image (b) of Si/CNT–FLG. (c) High-magnification TEM image of the selected area in (b). To illustrate the important role of CNT–FLG in the Si/CNT–FLG battery, a series of electrochemical measurements were carried out using half cells. For comparison, three different electrodes were investigated including Si/CNT–FLG, Si/CNTF and CNT–FLG electrodes. The last one was a controlled trial to estimate the contribution of CNT–FLG to the capacity of the Si/CNT–FLG battery, which was measured using the same current density as the first one. Figure 7a showed that the Si/CNT– FLG battery exhibited the best electrochemical performance in terms of the specific capacity and cycling stability. The first discharge and charge capacities of Si/CNT–FLG battery were 3263 mAh g‒1 and 1945 mAh g‒1, respectively. The initial irreversible capacity loss was due to the formation of solid electrolyte interface (SEI) and the consumption of CNT–FLG, whose first discharge capacity and Coulombic efficiency were 1148 mAh g‒1 and 29.1%, respectively (Figure S8, Supporting Information). The formation of SEI could be demonstrated from the voltage profiles of the Si/CNT–FLG anode for different cycles. Figure 7c revealed that the first discharge cycle curve showed a platform at about 0.8–0.5V, while subsequent cycles didn’t appear again. Comparing with the Si/CNT–FLG battery, the initial reversible capacity of Si/CNTF battery was only 1046 mAh g‒1 (Figure 7a). The capacity of Si/CNTF battery showed an evident decay for the entire cycles, while the Si/CNT–FLG battery remained almost constant over the 100 cycles investigated. After 100 charge–discharge cycles, the capacity retention of Si/CNTF battery was 64% with the reversible capacity of 670 mAh g‒1, while the capacity retention of the Si/CNT– FLG battery was as high as 93% with the reversible capacity of 1808 mAh g‒1, which could be ascribed to the protection of the present CNT–FLG from the breaking-down of electric connection between the active material and the current collector. This was confirmed by SEM images of the surface of the cycled Si/CNT–FLG electrode (Figure S9, Supporting Information). The CNT–FLG battery also showed good cycling stability maintaining at 310 mAh g‒1 overall cycles, which was 17.1% of the charge capacity ACS Paragon Plus Environment


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of the Si/CNT–FLG battery, indicating that the capacity contribution was dominated by silicon in the Si/CNT–FLG battery (Figure 7a). To confirm it, the cyclic voltammetry performance was conducted. Figure 7d showed that the 20th and 30th cycle curves of the Si/CNT–FLG battery appeared a reduction peak at 0.16 V and two oxidation peaks at 0.3 and 0.5 V, which was corresponded to the phase transformation between amorphous Si and LixSi.48,49 Except those peaks, there were no other redox peaks observed verifying the above inference. To explore the cycling stability of the Si/CNT–FLG battery at higher current rate, the Si/CNT–FLG battery was measured at charging/discharging rate of 0.5C for up to 300 cycles. Figure 7b showed that the reversible capacity was stable at 1410 mAh g‒1 after 20 cycles and still remained approximately 1350 mAh g‒1 after 300 cycles with the capacity retention of 96%, demonstrating the outstanding cycling stability performance. The superior electrochemical performance of Si/CNT–FLG battery was attributed to the unique CNT–FLG structure, which provided not only multiplexed and highly conductive pathways minimizing the lithium-ion diffusion lengths but also sufficient free-standing empty space accommodating the volume change of silicon during repeated cycling. Furthermore, the Si/CNT–FLG battery also showed a good rate performance (Figure S10, Supporting Information). These results also illustrated the great potential application of CNT–FLG in developing high-performance lithium-ion batteries.


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Cycle Number

1.5

0.3

c

0.3V

d

0.5V

Current (mA)

1.2

Voltage (V)

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0.9

0.6

1st 2nd 50th

0.3

0.0

-0.3

20th 30th

0.16V

-0.6

0.0 0

500

1000

1500

2000

2500

3000

0.0

0.3

Capacity (mAh/g)

0.6

0.9

1.2

1.5

Potential (V)

Figure 7. (a) Comparison of cycling performance of the Si/CNT–FLG, Si/CNTF and CNT–FLG electrodes at the charge/discharge rate of 0.1C for 100 cycles (1C=4200 mAh g–1). (b) Charge /discharge capacities of the Si/CNT–FLG electrode at 0.5 C for 300 cycles. (c) Charge‒discharge profiles of the Si/CNT–FLG electrode at different cycles. (d) CV curves of the 20th and 30th cycles of the Si/CNT–FLG electrode.

4. CONCLUSION In summary, we have demonstrated a facile and template-free strategy to achieve a novel 3D carbon hybrid architecture comprised of CNT and few-layer graphene, where the few-layer graphene served as walls and the CNT founctioned as backbones, forming abudant chambers. It is distinctly different from all the previous reported 3D CNT–graphene hybrid, where the vertical aligned CNTs were grown between on the parallel graphene sheets through CVD technique. This finding would provide a new perspective on the combination of CNTs and graphene-based materials. Furthermore, the obtained CNT–FLG was further applied to the Li‒Si battery to alleviate the huge volume change of silicon during repeated cycling. ACS Paragon Plus Environment


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The superior electrochemical performance of the Si/CNT–FLG battery exhibits a great potential for application of CNT–FLG in the lithium-ion battery field. This kind of carbon material is also expected to be applicable to other fields such as supercapacitors, photocatalysis, biological and chemical sensors, etc.


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ASSOCIATED CONTENT Supporting Information. Temperature–dependent modulus of CNTF, EDX spectrum of Si/CNT–FLG, SEM images of cycled Si/CNT–FLG electrode, Voltage profiles of CNT–FLG electrode, rate performance of the Si/CNT–FLG battery, additional TEM images, AFM images, XRD patterns and Raman spectra. This material is available free of charge via the Internet at http://pubs.acs.org.



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AUTHOR INFORMATION Corresponding Author: Prof. Chuanxi Xiong, and Quanling Yang Tel.: +86-27-87652879. E-mail address: [email protected] (C. Xiong); [email protected] (Q. Yang) Notes: The authors declare no competing ﬁnancial interest.


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ACKNOWLEDGEMENTS The authors acknowledge financial support from National Natural Science Foundation of China (51072151 and 51173139) and the Fundamental Research Funds for the Central Universities (WUT:2016IVA002). The authors thank Dr. X. Liu and Ms. Y. Guo from Materials Analysis Center of Wuhan University of Technology for TEM characterization.



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