Accepted Manuscript SiC/C composite mesoporous nanotubes as anode material for high-performance lithium-ion batteries Changzheng Shao, Feng Zhang, Huayan Sun, Baozong Li, Yi Li, Yonggang Yang PII: DOI: Reference:
S0167-577X(17)30902-3 http://dx.doi.org/10.1016/j.matlet.2017.06.021 MLBLUE 22733
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Received Date: Revised Date: Accepted Date:
9 March 2017 23 May 2017 5 June 2017
Please cite this article as: C. Shao, F. Zhang, H. Sun, B. Li, Y. Li, Y. Yang, SiC/C composite mesoporous nanotubes as anode material for high-performance lithium-ion batteries, Materials Letters (2017), doi: http://dx.doi.org/ 10.1016/j.matlet.2017.06.021
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SiC/C composite mesoporous nanotubes as anode material for high-performance lithium-ion batteries Changzheng Shao, Feng Zhang, Huayan Sun, Baozong Li, Yi Li* and Yonggang Yang Jiangsu Key Laboratory of Advanced Functional Polymer Designand Application, Department of Polymer Science and Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P.R. China. Corresponding author Tel: +86 512 65882052; fax: +86 512 65882052 E-mail: Y. Li, [email protected]
Abstract The demand for high energy-storage lithium-ion batteries (LIBs) encourages the development of novel anode materials to substitute graphite. Herein, novel SiC/C composite mesoporus nanotubes derived from resorcinol-formaldehyde resin/silica composites were designed and fabricated towards LIBs anode materials, which contained 31 wt% amorphous C and 69 wt% cubic β-SiC. The electrochemical measurements showed that the SiC/C electrode delivered a high reversible capacity of 527 mAh g-1 after 250 cycles at a current density of 0.1 A g-1, higher than the theoretical capacity of graphite, implying that SiC nanomaterials are potential anode candidate for LIBs. Keywords: Nanoparticles; Composite materials; Energy storage and conversion; Silicon carbide
1. Introduction The fast development of portable electronics and electric vehicles spur the increasing demand of high energy storage lithium-ion batteries (LIBs) . Since graphite, the most commonly used anode material, is limited to its low theoretical capacity (~370 mAh g-1) and poor high-rate capability , while silicon, the most prospective alternative anode material with a capacity up to 4200 mAh g-1, will undergo a large volume change during the electrochemical reactions , it’s of great necessity and importance to explore new anode materials with both high capacity and cycling stability [4, 5]. SiC nanoparticles are usually recognized to be inactive to lithium , and have been used as buffer matrix and/or backbone to enhance the electronic conductivity of composite materials [7-9]. Recently, a few reports investigated the cycling performance of pure SiC nanomaterials. For example, Zhang et al  prepared a nanocrystalline SiC thin film electrode growth on stainless steel, which showed a stable discharge capacity of 309 mAh g-1 over 60 cycles. Hu et al  produced SiC nanowires on graphite paper, which delivered 397 mAh g-1 after 100 cycles. These results reveal that SiC nanomaterials can also serve as anode material for LIBs. Moreover, SiC-based nanocomposites, such as bead curtain shaped [email protected]
core-shell nanowires on graphite paper  and bowl-like 3C-SiC nanoshells encapsulated in hollow graphitic garbon spheres , have been synthesized and exhibited high capacities and good cycling stabilities. Therefore, it is attractive and meaningful to design and fabricate new type SiC-based nanostructure and/or nanocomposite as anode candidate for LIBs. In this work, different from above previous reports, SiC/C composite mesoporous nanotubes were fabricated by pyrolysis of helical resorcinol-formaldehyde (RF) resin-silica composite nanotubes at 1400 oC under argon atmosphere, while the RF resin-silica composite was synthesized via a sol-gel transcription method, using a chiral gelator as the template. We expected that the existence of C in the SiC matrix would enhance its electric conductivity, as SiC is high band gap semiconductor. At the time, the porous structure would buffer the volume change during lithium insertion and extraction. The electrochemical data in deed showed that the SiC/C composite electrode possessed superior lithium-ion storage capability and stability.
2. Experiment Synthetic procedure for resin-silica composite nanotubes and SiC/C composite nanotubes.
N+ ClO4 -
ClO4 + 9 N
Figure 1 Molecular structure of the gelator, LL-1. Gelator LL-1, whose molecular structure is shown in Fig. 1, was synthesized according to the literature . A typical synthesis route of the resin-silica composite nanotubes was following: 200 mg LL-1 (0.19 mmol) and 180 mg resorcinol (1.63 mmol) were dissolved in 48 mL deionized water and 2.0 mL ethanol mixed solution at 40 ºC under vigorous stirring. Then, 0.6 mL concentrated ammonia aqueous solution (25-28 wt%), 0.23 mL formaldehyde (37-40 wt%), and 0.8 mL tetraethylorthosilicate (3.6 mmol) were added into the solution in sequence. The reaction mixture was then stirred at 40 ºC for 10 hr, followed by setting at 80 ºC in static for 24 hr. The as-prepared resin-silica product was then collected by filtration, extracted with ethanol for 48 h to remove the template, and dried in an oven at 50 ºC for 24 hr. The obtained product was brown-reddish powders and denoted as S1. Thereafter, sample S1 was annealed at 350 ºC for 2.0 hr and then at 1400 ºC for 4.0 hr with a heating rate of 2.0 ºC·min-1 in Ar to gain the as-synthesized SiC/C product, denoted as S2. After the sample was cooled down to room temperature naturally, it was immersed in 10 wt% HF aqueous solution for 24 hr at room temperature to remove the resident SiO2, and finally washed with deionized water. 3. Results and Discussion
Figure 2 (a, c) FE-SEM and (b, d) TEM images of S1 (a,b) and S2 (c,d); (e) HR-TEM image and (f) SAED pattern of S2.
The FE-SEM and TEM images of S1 are shown in Figs. 2a and 2b. They are left-handed helical nanotubes with the outer diameters of 60-100 nm, wall thickness of 15-25 nm, and lengths of several microns. When S1 was pyrolyzed at 1400 °C for 4.0 hr under Ar, S2 was obtained, as shown in Figs. 2c and 2d. The helical nanotubular structure is maintained on the whole. The diameter and wall thickness of S2, as calculated from the TEM image, are 60-100 and 15-25 nm, respectively. Disordered pores can be observed in Fig. 2c, which are suggested to be formed during the pyrolysis process. In the HR-TEM image (Fig. 2e), the interplanar distance is 0.25 nm, which is concordant with the lattice fringe of cubic β-SiC. The SAED pattern (Fig. 2f) implies that the obtained SiC is polycrystalline. A few straight or twisted nanorods can also be found in S2, as seen in Fig. S1. They are highly crystalline SiC nanoparticles. TGA analysis (Fig. S2) reveals that ~31 wt% of carbon is found in S2. EDX analysis (Fig. S3) also indicates the uniform distribution of C and Si elements in sample S2. The (111), (200), (220) and (311) planes disclosed in the WAXRD pattern, and D and G bands (IG/ID ratio is approximately 0.67) appeared in the Raman spectrum (Fig. S4) further prove that S2 is composed of crystal SiC and amorphous carbon.
Figure 3 (a) N2 adsorption-desorption isotherm and (b) BJH pore size distribution plot calculated from the adsorption branch for S2.
The N2 adsorption-desorption isotherm and the BJH pore size distribution plot calculated from the adsorption branch for S2 are shown in Fig. 3. H3-type hysteresis loop is observed at P/P0 between 0.65 and 1.0 in the isotherm, indicating the existence of slit-like mesopores. The BET specific surface area for S2 is 190.5 m² g-1. The BJH pore size distribution plot shows a peak at around 3 nm, as shown in Fig. 3b. As reported, porous structures could provide fast transport channels for Li-ions , while hollow structures provided extra space for buffering the volumetric change during the Li 4
insertion/extraction . Consequently, the mesoporous nanotube structure of S2 may benefit its electrochemical performances for LIBs.
Figure 4 (a) Cycling behavior of SiC/C electrode at current density of 0.1 A g-1; (b) Rate performance of SiC/C electrode at various current densities from 0.1 A g-1 to 5 A g-1; (c) Nyquist plot for SiC/C electrode in the frequency range from 100 KHz to 10 MHz before and after 300 cycles.
Sample S2 was used as electrode material for LIBs and tested in a CR2016 coin-type half-cell, using metallic lithium foil as the opposite electrode. The cycling behavior of the SiC/C electrode at a current density of 0.1 A g-1 is shown in Fig. 4a. The first discharge and charge capacities are 824 and 181 mAh g-1, respectively, with an initial coulombic efficiency of only 22% (Fig. S5). The ca. 78% capacity loss of the SiC/C electrode is mainly owe to the formation of the solid-electrolyte interfacial (SEI) . The discharge capacity decreases to 153 mAh g-1 at the fifth cycle and keeps at that value till about 80 cycles, while the coulombic efficiency increases to and keeps at about 96%. Thereafter, the discharge capacity begins to increase slowly, which could be connected with the continually activation of SiC , and a discharge capacity of 527 mAh g-1 after 250 cycles is achieved, which is
higher than the theoretical capacity of graphite (372 mAh g-1). When the SiC/C electrode was cycled at a higher current density of 0.3 A g-1 for more times, it delivers the first discharge capacity of 725 mAh g-1 and a capacity of 600 mAh g-1 after 500 cycles, as shown in Fig. S6. These results indicate that this SiC/C electrode possesses superior cycling stability. The rating capability of the SiC/C electrode was evaluated at various current densities from 0.1 A g-1 to 5 A g-1, as shown in Fig. 4b. It delivers stable capacities of 140, 100, 70, 55 and 40 mAh g-1 at current demsities of 0.1, 0.3, 1, 2 and 5 A g-1, respectively. When the current densities revert to 0.3 and 0.1 A g-1, the reversible capacities restore to 100 and 140 A g-1, respectively, indicating excellent rating capability. To study the conductivity of the SiC/C electrode, the electrochemical impedance spectra (EIS) were also collected and shown in Fig. 4c, which illustrate an impedance of 176 Ω before cycling and 73 Ω after 300 cycles. The rapidly decreased impedance implies that the SiC/C electrode possesses a good electrical conductivity and a rapid charge-transfer reaction for lithium ion insertion and extraction happened. 4. Conclusion In summary, novel SiC/C composite mesoporous nanotubes were designed and synthesized successfully. When used as anode material for LIBs, they exhibited high initial capacity, good cycling performance and rating capability, and low impedance, which may be in relation to their porous, hollow nanostructure. The results in this work demonstrate that the SiC/C composite is a promising anode candidate for LIBs, which may spur the further investigation of SiC nanomaterials in high-performance LIBs. Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. 21574095, 51473106)，the Priority Academic Program Development of Jiangsu High Education Institutions (PAPD). Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org. References  J. Ou, Y.Z. Zhang, L. Chen, H.Y. Yuan, D. Xiao, RSC Adv. 4 (2014) 63784−63791.  C.Y. Wang, D. Li, C.O. Too, G.G. Wallace, Chem. Mater. 21 (2009) 2604−2606.  R. Zhang, Y. Du, D. Li, D. Shen, J. Yang, Z. Guo, H.K. Liu, A.A. Elzatahry, D.Y. Zhao, Adv. Mater.
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Highlights · Helical RF resin-silica nanotubes were prepared via a sol-gel transcription method. · SiC/C composite mesoporous nanotubes were produced after pyrolysis process. · The SiC/C electrode showed superior electrochemical performance. · SiC nanomaterials are potential anode candidate for lithium ion batteries.