Author’s Accepted Manuscript Sn Nanoparticles Uniformly Dispersed in N-doped Hollow Carbon Nanospheres as Anode for Lithium-ion Batteries Cong Guo, Qianqian Yang, Jianwen Liang, Lili Wang, Yongchun Zhu, Yitai Qian www.elsevier.com
PII: DOI: Reference:
S0167-577X(16)31330-1 http://dx.doi.org/10.1016/j.matlet.2016.08.053 MLBLUE21337
To appear in: Materials Letters Received date: 14 May 2016 Revised date: 6 August 2016 Accepted date: 12 August 2016 Cite this article as: Cong Guo, Qianqian Yang, Jianwen Liang, Lili Wang, Yongchun Zhu and Yitai Qian, Sn Nanoparticles Uniformly Dispersed in Ndoped Hollow Carbon Nanospheres as Anode for Lithium-ion Batteries, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2016.08.053 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Sn Nanoparticles Uniformly Dispersed in N-doped Hollow Carbon Nanospheres as Anode for Lithium-ion Batteries Cong Guoa, Qianqian Yanga, Jianwen Lianga, Lili Wanga, Yongchun Zhua*, Yitai Qiana* a
Hefei National Laboratory for Physical Science at Microscale and Department of Chemistry,
University of Science and Technology of China, Heifei, Anhui 230026, PR China [email protected]
(Y. T. Qian) [email protected]
(Y. C. Zhu) *
Corresponding author: 86-551-63601589.
Abstract Sn-contained N-doped carbon composite ([email protected]
) with Sn nanoparticles of 5-30 nm uniformly dispersed in N-doped hollow carbon nanosphere matrix was produced by in situ polymerization of pyrrole, and reduction of SnO2 synchronous with decomposition of polypyrrole. SnO2 nanospheres serve as both the template of hollow carbon nanospheres and the Sn source. Due to the cooperation of the uniformly dispersed Sn particles and N-doped hollow carbon structure, the obtained [email protected]
shows a reversible capacity of 1070 mA h g-1 over 200 cycles at 0.2 C and 500 mA h g-1 over 500 cycles at 5 C. Keywords: Sn nanopartilces; N-doped hollow carbon nanospheres; Lithium-ion batteries; Nanocomposites; Energy storage and conversion 1. Introduction Nowadays, Sn has been explored as a promising lithium-ion battery anode material owing to the high theoretical capacity (993 mA h g-1) and electronic conductivity.[1, 2] However, Sn suffers from
poor cycling performance as a huge volume change (~300%) occurs in charge/discharge process, which results in severe pulverization and particle aggregation upon cycling. To overcome these problems, a variety of Sn/carbon nanocomposites have been designed.[4, 5] For example, Sn nanoparticles of 10 nm in spherical carbon exhibited capacity of 710 mA h g-1 after 130 cycles at 0.25 C (1 C=993 mA g-1). Moreover, compared to solid structure, hollow structures [6, 7] can better relieve structural strain and alleviate volume changes. Different composites of Sn nanoparticles in hollow carbon structures have shown nice electrochemical performances.[8-10] Besides, N-doped carbon can lead to high electrochemical performances due to the defects in the carbon structure and the enhanced electrical conductivity.[11-13] For instance, Sn in N-doped porous carbon showed 722 mA h g-1 at about 0.2 C over 200 cycles. Sn in N-doped carbon nanowires exhibited 760 mA h g-1 at 0.5 C over 600 cycles. Herein, to combine the merits of nanosized Sn and N-doped hollow carbon sturcture, we synthesize [email protected]
with 5-30 nm Sn nanoparticles dispersed uniformly in N-doped hollow carbon nanospheres, which is different from the common carbon coating Sn composites. When used as anode material for lithium-ion batteries, [email protected]
exhibits nice electrochemical performances. 2. Experimental section The detailed synthesis and characterization processes are available in ESI. 3. Results and discussion The designed [email protected]
is formed via the reduction of SnO2 synchronous with the decomposition of polypyrrole (PPy), as shown in Scheme 1. During the process, SnO2 nanospheres serve as the template of hollow carbon nanospheres and Sn source and pyrrole as carbon source with N-doping. Firstly, pyrrole on the surface of SnO2 polymerized in-situ to form [email protected]
core-shell structure.(Fig. S1) 2
The precursor was then treated under 700°C, during which the decomposition of PPy and the reduction from SnO2 to Sn were simultaneously completed. Due to its low melting point (232 °C), molten Sn dispersed uniformly into the hollow carbon nanospheres during the heating process. In this way, [email protected]
with 5-30 nm Sn nanoparticles dispersed in N-doped hollow carbon nanospheres was fabricated. As confirmed by X-ray diffraction (XRD) in Fig. 1a, all the diffraction peaks can be assigned to β-Sn (JCPDS card no.04-0673). No obvious carbon peaks observed in XRD pattern indicates the carbon is amorphous, which coincides with the Raman spectrum in Fig. S2, and the average particle size is calculated as about 16 nm by Scherrer formula (ESI). The content of N-doped carbon in [email protected]
is calculated as 41 wt% due to the analysis by elementary analyzer at CHN mode. The surface properties of [email protected]
are investigated by X-ray photoelectron spectroscopy (XPS) in Fig. S3. Two characteristic peaks of N 1s in Fig. S3c at 398.1 and 400.2 eV are assigned to pyridinic N and pyrrolic N. The nitrogen content in the N-doped carbon of [email protected]
is calculated as 18.9%, consistent with the elemental analysis result. The morphologies and structures of the as-obtained [email protected]
are investigated by field-emitting scanning electron microscope (FESEM), transmission electron microscope (TEM) and high resolution transmission electron microscopy (HRTEM). The FESEM and TEM images of the product in Fig. 1b and 1c show the hollow carbon nanospheres of 80-100 nm with inner diameters of 50-60 nm, consistent with the BJH pore distribution result in Fig. S4b. As observed from HRTEM images (Fig. 1d, Fig. S5), the particle size of Sn is about 5-30 nm. The lattice d-spacing value of Sn nanoparticles is 0.298 nm, which corresponds well with those of (200) planes of the β-Sn. The energy dispersive X-ray
spectrometer (EDX) mapping of the [email protected]
(Fig. 1e) demonstrates the uniform dispersion of Sn in hollow carbon nanospheres. Electrochemical performance of the [email protected]
electrode was evaluated in coin cells with a counter electrode of lithium. The cyclic voltammograms and initial three charge-discharge curves of [email protected]
electrode at 0.2 C are presented and illuminated in Fig. S6. Fig. 2a shows cyclic performance of [email protected]
electrode at 0.2 C within a voltage range of 0.01-3.0 V. The [email protected]
exhibits a capacity of about 892 mA h g-1 after the first cycle and slightly decreases to around 740 mA h g-1 in initial 30 cycles (all capacity is calculated by total mass of [email protected]
). The capacity then starts to increase and finally stabilizes at 1070 mA h g-1 over 200 cycles, which surpasses the theoretical capacity of Sn. The ultrahigh capacity and enhancement in capacity of [email protected]
with cycling which can be occurred in carbon composites with Sn  and transition metal oxides , is probably attributed to the high and rising capacity of the N-doped carbon (Fig. S7),[11, 18] the pseudo-capacitive contribution of the electrode (Fig. S8), as well as reversible formation of gel-like polymer at 0.8 V and its decomposition over 2.1 V in the electrolyte.[20, 21] To verify the point, the cycling performance of [email protected]
with different cut-off potentials is studied in Fig. 2b. The [email protected]
is cycled between 0.01 and 3.0 V for the first 100 cycles and changes to 0.01-1.5 V for the following 50 cycles and changes back to 0.01-3.0 V. It can be seen that the capacity drops from 623 to 410 mA h g-1 when the cut-off potential decreases. This is due to that the polymeric gel-like film formed during the previous cycles at 0.01-3.0 V cannot be dissolved at the cut-off potential of 1.5 V, thus no new gel-like film can form during the following discharge, leading to the drop of reversible capacity. After the cut-off potential returns to 3.0 V, the formation and decomposition of gel-like polymer can proceed again so that the capacity recovers to about 600 mA h g-1.
The [email protected]
also exhibits nice rate capability as shown in Fig. 2c. The capacity of [email protected]
decreases from 783 to 698, 649, 574, 475 mA h g-1 and recover to 770 mA h g-1 when the rate changes from 0.2 to 0.5, 1, 2, 5 C and back to 0.2 C, indicating the good kinetic property of [email protected]
The electrode shows a capacity of 929 mA h g-1 after 400 cycles at 1 C (Fig. S9) and 500 mA h g-1 after 500 cycles at 5 C (Fig. 2d). We could attribute the nice rate and cycling performances of [email protected]
to the following merits. First, the combination of Sn nanoparticles and carbon matrix could mitigate the aggregation of Sn nanoparticles as well as buffer the volume variation and pulverization during cycling.[5, 11] The hollow carbon structure can further relieve the structural strain and alleviate the large volume change. Moreover, due to the uniformly dispersion of Sn nanoparticles, Sn can be well utilized to store Li+ thus to provide high capacity, and the stress generated during cycling will be evenly distributed in the whole composite which can better prevent local cracking. Besides, the presence of electronegative N atoms is beneficial for Li+ diffusion, and the defects in carbon provided by N-doping is in favor of Li+ storage. This results in the enhanced electrical conductivity and capacity of N-doped carbon.[23, 24] The formation/decomposition of the gel-like polymer during cycling and the pseudo-capacitive contribution of the electrode may be both accountable for the high capacity as well. To further understand the good cycling performance of the [email protected]
, more electrochemical impedance spectroscopy (EIS) and TEM analyses have been taken. According to the fitting results (Fig. 3a), The Rct of [email protected]
after 100 cycles (14.26 Ω) shows a small increase when compared with that of [email protected]
after 2 cycles (5.28 Ω), indicating good cycle performance of the electrode. And the TEM image of [email protected]
after cycling 100 times at 1 C in Fig. 3b shows that the [email protected]
anode can almost retain its original appearance after cycling.
4. Conclusions In summary, [email protected]
composite with Sn nanoparticles uniformly dispersed in N-doped hollow carbon nanospheres was produced via in situ polymerization of pyrrole and synchronous reduction of SnO2 with the decomposition of PPy. These nice performances can be attributed to the combined effect of uniformly dispersed Sn particles and the N-doped hollow carbon nanospheres. The formation/decomposition of gel-like polymer during cycling and some pseudo-capacitive behavior of the electrode may also be account for the high and rising capacity. Acknowledgements This work was financially supported by the National Natural Science Fund of China (Grant 21521001， 21471142). Appendix A. Supplementary material Supplementary data associated with article can be found in the online version at http://www.sciencedirect.com. References  F. Cheng, J. Liang, Z. Tao, J. Chen, Adv. Mater. 23 (2011) 1695-1715.  M. Noh, Y. Kwon, H. Lee, J. Cho, Y. Kim, M.G. Kim, Chem. Mater. 17 (2005) 1926-1929.  M. Winter, J.O. Besenhard, Electrochim. Acta 45 (1999) 31-50.  Y. Xu, Q. Liu, Y. Zhu, Y. Liu, A. Langrock, M.R. Zachariah, C. Wang, Nano Lett. 13 (2013) 470-474.  N. Zhang, Q. Zhao, X.P. Han, J.G. Yang, J. Chen, Nanoscale 6 (2014) 2827-2832.  X.W. Lou, Y. Wang, C. Yuan, J.Y. Lee, L.A. Archer, Adv. Mater. 18 (2006) 2325-2329.  Y. Wang, H.C. Zeng, J.Y. Lee, Adv. Mater. 18 (2006) 645-649.
 K.T. Lee, Y.S. Jung, S.M. Oh, J. Am. Chem. Soc. 125 (2003) 5652-5653.  W.M. Zhang, J.S. Hu, Y.G. Guo, S.F. Zheng, L.S. Zhong, W.G. Song, L.J. Wan, Adv. Mater. 20 (2008) 1160-1165.  Y. Yu, L. Gu, C. Wang, A. Dhanabalan, P.A. van Aken, J. Maier, Angew. Chem. Int. Edit. 48 (2009) 6485-6489.  L. Qie, W.M. Chen, Z.H. Wang, Q.G. Shao, X. Li, L.X. Yuan, X.L. Hu, W.X. Zhang, Y.H.Huang, Adv. Mater. 24 (2012) 2047-2050.  Y. Jiang, M. Wei, J.K. Feng, Y.C. Ma, S.L. Xiong, Energy Environ. Sci., 9 (2016) 1430-1438.  G.Y. Ma, K.S. Huang, Q.C. Zhuang, Z.C. Ju, Mater. Lett., 174 (2016) 221-225.  Z. Zhu, S. Wang, J. Du, Q. Jin, T. Zhang, F. Cheng, J. Chen, Nano Lett. 14 (2013) 153-157.  J. Chen, L. Yang, S. Fang, Z. Zhang, A. Deb, S. Hirano, Electrochim. Acta 127 (2014) 390-396.  Y. Jiang, X.J. Ma, J.K. Feng, S.L. Xiong, J. Mater. Chem. A, 3 (2015) 4539-4546.  C. Guo, L.L. Wang, Y.C. Zhu, D.F. Wang, Q.Q. Yang, Y.T. Qian, Nanoscale 7 (2015) 10123-10129.  J. Hou, C. Cao, F. Idrees, X. Ma, Acs Nano 9 (2015) 2556-2564.  Y. Zhou, D. Yan, H. Xu, J. Feng, X. Jiang, J. Yue, J. Yang, Y.T. Qian, Nano Energy 12 (2015) 528-537.  Y.H. Xu, J.C. Guo, C.S. Wang, J. Mater. Chem. 22 (2012) 9562-9567.  S. Laruelle, S. Grugeon, P. Poizot, M. Dollé, L. Dupont, J.M. Tarasconz, J. Electrochem. Soc. 149 (2002) A627-A634.  Z. Wang, L. Zhou, X.W. Lou, Adv. Mater, 24 (2012) 1903-1911.  L. Zhao, Y.S. Hu, H. Li, Z. Wang, L. Chen, Adv. Mater, 23 (2011) 1385-1388.
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Figure Captions Scheme 1 Schematic sketch for the growth procedure of [email protected]
Fig. 1 (a) XRD pattern of the [email protected]
; (b), (c) and (d) are the FESEM, TEM and HRTEM images of [email protected]
; (e) EDX mapping images of [email protected]
Fig. 2 (a) Cycling performance of [email protected]
at 0.2 C within the range of 0.01-3.0 V; (b) Cycling performance of [email protected]
at 1 C with the cut-off potentials of 3.0 V and 1.5 V; (c) Rate performance of [email protected]
and (d) Cycling performance of [email protected]
at 5 C within the range of 0.01-3.0 V. Fig. 3 (a) Nyquist plots of [email protected]
after 2 cycles and 100 cycles at 1 C. The fitted spectra are given as a continuous line. The equivalent circuit is exhibited in the inset; (b) TEM image of [email protected]
after cycling at 1 C over 100 cycles.
Highlights: Sn nanoparticles are uniformly dispersed in N-doped hollow carbon nanospheres. SnO2 serves as both self-template and Sn source. The [email protected]
structure makes for good lithium storage performances.