World Journal Of Engineering STUDY OF THE Sn/C NANOFIBERS

World Journal Of Engineering
Keyu Li, Yunhua Yu, Yu Teng, Xin Li and Xiaoping Yang
Key Laboratory of carbon fiber and functional polymers, Ministry of Education,
Beijing University of Chemical Technology, Beijing 100029, China E-mail:
Electrochemical performance measurements were
performed using 2025 coin cells, which is assembled
according to our previous work [4]. The electrolyte was 1
M LiPF6 in a 1:1 mixture of ethylene carbonate (EC) and
dimethyl carbonate (DMC). Charge and discharge were
executed with a cells testing instrument (LAND
CT2001A) at a current density of 50 mA g-1, with the
cutoff potentials of 0.001 and 3V vs. Li/Li +.
There is an increasing demand for new anode materials of
rechargeable lithium ion batteries (LIBs) possessing high
capacity and long cycle life.
Sn-based materials have been focused on in recent years
because their capacities (Sn 994 mAh g-1) exceed that of
commercial graphite (372 mAh g-1) [1, 2]. However, there
are large changes of volume associated with the
formation of different Li-Sn phases. With this change, the
anode materials were pulverized and the cycle
performance decreased. Jung Won Park [3] fabricated the
Sn-C composite electrodes with well ‘buffering effects’.
Following our previous study [4], it was found that a kind
of nano-sized Sn/C composite nanofibers could supply
good electrochemical performance during their continued
charge/discharge process. When preparing the Sn/C
anode material, the content of Sn have been considered as
key factor influencing their electrochemical performance.
In this work, the Sn/C composite with different Sn
loading were prepared by electrospinning and
carbonization. The purpose of the work was to investigate
the effect of Sn loading on the morphology and
electrochemical performance of the as-prepared Sn/C
composite anode materials.
Results and Discussion
Fig.1 shows SEM images of pure CNFs and the Sn/C
nanofibers with different contents of Sn precursor (0.4,
0.5 and 0.6ml) in the electrospinning solutions. All
nanofibers are continuous and formed a reticular
morphology. The Sn/C nanofibers (Fig.1 A, B, C) were
thicker than pure CNFs (Fig.1D). As increasing content of
Sn, nanofibers diameter increased gradually, from
100-200nm (D) to 400-500nm (C), because of the
compound intermingle.
PAN copolymer fibril(Mw=100, 000 g/mol, 93.0 wt.%
acrylonitrile, 5.3 wt.% methylacrylate, and 1.7 wt.%
itaconic acid, UK Courtaulds Co.) Tin tetrachloride
(SnCl4, 98%, Alfa Aesar) ethylene glycol ((HOCH 2)2,
99%, Alfa Aesar) The amount of adding solution are 0.4,
0.5 and 0.6ml, respectively.
Sn/C nanofibers were prepared through the electrospun
process under an advisable temperature and humidity
follow by carbonization as previous work [4]. Pure CNFs
were also prepared by the same process.
Fig.1 SEM images and diameter distribution insets of
Sn/C nanofibers with different Sn precursor
contents (A) 0.4ml, (B) 0.5 ml, (C) 0.6 ml and (D)
pure CNFs carbonized at 850℃.
Apparatus and Procedures
The surface morphology of Sn/C nanofibers and CNFs
was observed using a scanning electron microscope (SEM,
zeiss supera 55, Germany).
Fig.2 shows the first galvanostatic discharge/charge
profiles of the Sn/C nanofibers and pure CNFs at a
current density of 50 mA g-1, with the cutoff potentials of
World Journal Of Engineering
0.001 and 3V. With formation of solid electrolyte
interface (SEI) film and the decomposition of the
electrolyte, the discharge curve of the first cycle had a
rapid voltage drop to 1V. The second part below 1V is
related with the complicated insertion of Li + into CNFs
and Sn.
From the curves, the capacity of discharge process was
increased with the increase of Sn. The Sn/C nanofibers
content 0.6ml Sn precursor delivered higher discharge
capacity (1102.6 mAh g-1) than others because of more
Li+ insert. But the charge capacity of this sample
decreased to 632.9 mAh g-1, corresponding to coulombic
efficiency of 57.4%. The Sn/C nanofibers content 0.5ml
Sn precursor exhibited higher charge capacity (671.4
mAh g-1) than others with coulombic efficiencies of
71.7%. The thicker fibers (Fig.1C) were probably too
large, and might hinder the diffusion of Li+. Inserted Li+
could not be taken off completely from nanofibers due to
the decrease of charge capacity. So we thought the
diameter of nanofibers and the content of Sn had a
trade-off effect.
Fig.3 Reversible capacities versus cycles of Sn/C
nanofibers with different Sn precursor content and
pure CNFs carbonized at 850℃.
The Sn/C nanofibers with different Sn loading were
carbonization treatment. By increasing the Sn content, the
diameter of the as-prepared Sn/C nanofibers rised, while
the reversible capacity exhibited a point of inflection. The
Sn/C nanofibers with 0.5mL Sn precursor solution
showed the highest reversible capacity and excellent
cycling performance, with a capacity rentation of 520
mAh g-1 after 30 cycles at 50 mA g-1.
1.Besenhard, J.O., Yang, J. and Winter, M. Will advanced
lithium-alloy anodes have a chance in lithium-ion
batteries. J. Power Sources, 68 (1997) 87-90.
Fig.2 Galvanostatic discharge/charge curves for the first
cycle of Sn/C nanofibers with different Sn content
an pure CNFs carbonized at 850℃.
2.Zou, L., Gan, L., Kang, F. Y., Wang, M. X., Shen, W. C.
and Huang, Z. H. Sn/C non-woven film prepared by
electrospinning as anode materials for lithium ion
Fig.3 shows reversible capacities of Sn/C nanofibers with
different Sn content and pure CNFs carbonized at 850℃.
Although the discharge capacities decreased in the first
cycles, all the Sn/C nanofibers anodes had much higher
reversible capacities than that of pure CNFs due to the
loading of Sn. At the 30th cycle, their reversible
capacities decreased to about 480, 520, 450mAh g-1,
showing that the Sn/C nanofibers with 0.5ml Sn precursor
content presented the highest capacity.
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3.Park, J. W., Eom, J. Y. and Kwon, H. S. Fabrication of
Sn–C composite electrodes by electrodeposition and
Electrochemistry Commun., 11 (2009) 596–598.
4.Yu, Y. H., Yang, Q., Teng, D. H., Yang, X. P. and Ryu,
S. K. Reticular Sn nanoparticle-dispersed PAN-based
carbon nanofibers for anode material in rechargeable
lithium-ion batteries, Electrochemistry Commun., 12
(2010) 1187–1190.