Scalable synthesis of ultrasmall SnO2 nanocrystals in carbon conductive matrices: High loading and excellent electrochemical performance

Article abstract of DOI:10.1016/j.jallcom.2016.06.007

Ultrasmall sub-5 nm SnO₂ nanocrystals/carbon composites, with the SnO₂ loading as high as 87.3 wt%, are synthesized via a facile hydrothermal route, followed by calcination. The annealed SnO₂/C composite shows a higher discharge capacity and superior rate performance, compared with the pristine SnO₂/C sample. At the current density of 200 mA g^-1, it can deliver a high reversible capacity of 968 mAh g^-1. When the current density increases to 5000 mA g^-1, a high discharge capacity of 435 mAh g^-1 can still be obtained, much higher than the theoretical capacity of graphite. Our results indicate the potential suitability of synthesizing ultrasmall electrode nanocrystals with high electrochemical performance.

Full text of DOI:10.1016/j.jallcom.2016.06.007

Journal of Alloys and Compounds 686 (2016) 122e129
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Scalable synthesis of ultrasmall SnO2 nanocrystals in carbon
conductive matrices: High loading and excellent electrochemical
performance
,
,
Jie Qu a b, Yongan Yang b, Xiaomin Shi c, Wei Wang d *, Jianning Ding a, Ningyi Yuan a,
Xinsheng Zhao c **, Chao Lai c
,
a School of Materials Science and Engineering, Jiangsu Collaborative Innovation Center for Photovolatic Science and Engineering, Jiangsu Province
Cultivation Base for State Key Laboratory of Photovoltaic Science and Technology, Changzhou University, Changzhou, 213164, China
b Department of Chemistry and Geochemistry, Colorado School of Mines, 1012 14th Street, Golden, CO, 80401, USA
c School of Chemistry and Chemical Engineering, Jiangsu Normal University, Xuzhou, Jiangsu, 221116, China
d Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing, 100871, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Ultrasmall sub-5 nm SnO2 nanocrystals/carbon composites, with the SnO2 loading as high as 87.3 wt%,
are synthesized via a facile hydrothermal route, followed by calcination. The annealed SnO2/C composite
shows a higher discharge capacity and superior rate performance, compared with the pristine SnO2/C
Received 17 February 2016
Received in revised form
14 May 2016
Accepted 2 June 2016
Available online 4 June 2016
sample. At the current density of 200 mA gꢀ1, it can deliver a high reversible capacity of 968 mAh gꢀ1
.
When the current density increases to 5000 mA gꢀ1, a high discharge capacity of 435 mAh gꢀ1 can still be
obtained, much higher than the theoretical capacity of graphite. Our results indicate the potential
suitability of synthesizing ultrasmall electrode nanocrystals with high electrochemical performance.
© 2016 Elsevier B.V. All rights reserved.
Keywords:
Lithium-ion batteries
Ultrasmall SnO2
Carbon
High-rate performance
High loading
1. Introduction
the high reversibility of electrochemical reaction [1e3].
However, the synthesis of ultrasmall nanocrystals is techno-
Lithium-ion (Li-ion) battery has been suggested as the primary
choice for the electric vehicles (EVs), where such potential appli-
cations present a higher requirement on both power and energy
density of the battery [1,2]. For Li-ion batteries, the power density is
directly related to the rate performance of the electrode materials.
One of the effective routes to modify the rate capability is to reduce
the particle size of electrode materials, especially via fabricating
ultrasmall nanocrystals below 10 nm [1e3]. Ultrasmall nano-
particles offer several advantages, such as significantly shortening
the transport distance of electrons and lithium ions, accommoda-
ting the fluctuation of mechanical stress during the discharge-
charge cycles, and offering some other appealing features, such as
logically challenging, since the growth of ultrasmall nanocrystals is
difficult to control. Besides, the propensity of particle aggregation is
an additional issue due to the high surface energy [4,5]. The syn-
thesis of ultrasmall nanocrystals usually involves complicated
procedures, templates, and/or small scale synthesis [4e9]. These
factors could lead to high production costs and inconsistency in
quality of the active material as a result of the scale-up. Therefore,
the design of a scalable and facile synthesis route to prepare ul-
trasmall nanocrystals is becoming a major challenge and of great
importance.
Energy density, which is related to the charge capacity of elec-
trode material, is another key parameter of Li-ion batteries for their
applications in EVs. In commercial Li-ion batteries, graphite is the
current anode material. However, its capacity is not enough to meet
the energy requirements, and the development of alternative
anode materials has been a hot topic in the past decades. Among all
alternatives, SnO2 is particularly interesting due to its abundance,
high lithiation potential and high reversible theoretical capacity
* Corresponding author.
** Corresponding author.
E-mail addresses: wwang_bj@126.com (W. Wang), xinshengzhao@jsnu.edu.cn
(X. Zhao).
http://dx.doi.org/10.1016/j.jallcom.2016.06.007
0925-8388/© 2016 Elsevier B.V. All rights reserved.

J. Qu et al. / Journal of Alloys and Compounds 686 (2016) 122e129
123
show superior electrochemical performance to graphite. Remark-
ably, the annealed SnO2/C composite contains 87.3% of SnO2 and
shows high rate capability of 435 mAh gꢀ1 at the current density of
5000 mA gꢀ1
.
2. Experimental
2.1. Preparation and characterization
As reported previously, SnO2/C composite is often prepared by
hydrothermal route [32e38]. Different tin salts and hydrothermal
temperatures are used to prepare different morphology of SnO2/C
composite. A scalable synthesis of ultrasmall SnO2/C composite was
achieved via a simple hydrothermal route. Typically, NaOH (9.6 g)
and glucose (12 g) were first dissolved in water (60 mL), and then
added into an ethanol solution (32 mL) of SnCl4 (4.16 g, anhydrous).
After stirring for 1 h, the resultant solution was transferred into an
autoclave (100 mL) and kept at 180 ꢁC for 4 h. The obtained pre-
cipitates were washed with distilled water and ethanol, and
designated as the pristine SnO2/C composite. To further enhance
the electrochemical performance, the pristine composite was
calcined at 600 ꢁC for 2 h under the protection of Argon, with the
obtained composite designated as the annealed SnO2/C composite.
For comparison, a blank carbon was also prepared via a similar
process without adding SnCl4.
The structure and morphology of the final products were
measured by X-ray diffraction (XRD, Rigaku D/max-2500). Thermal
Gravimetric Analysis (TGA, SDT Q600) under Oxygen with a rate of
10 ꢁC/min. Fourier transform infrared (FTIR, BIO-RAD FTS6000)
spectroscopy and scanning electron microscopy (SEM, HITACHI, S-
3500 N) were also used in this work. Transmission electron mi-
croscopy (TEM) was performed on a JEM-2100 instrument. A dilute
ethanol suspension of as-prepared samples was made via an
Scheme 1. Schematic illustration of the synthesis route to annealed SnO2/C
composites.
(790 mAh gꢀ1) [10e14]. Despite its considerable advantages, the
SnO2 electrode is plagued with problems arising from the large
volume fluctuation (up to about 300%) during lithium insertion and
extraction, which leads to structural fractures, material pulveriza-
tion and electrical disconnection from the electrode framework
[15e18].
The cycle life of SnO2 is generally poor due to fast capacity fading
caused by volume change [2]. To solve these problems, one of the
effective strategies is to load nano-sized SnO2 into flexible matrices,
such as polymer and amorphous carbon [19e24]. The highly flex-
ible matrices could effectively buffer the large mechanical strain
during cycling and maintain the integrity of the whole electrodes
[25e31]. Nevertheless, there is still a trade-off between the high
mass loading of SnO2 in the composite and the stable cycle
performance.
In this work, a facile one-step hydrothermal route using SnCl4
and glucose as precursors is developed to synthesize ultrasmall
SnO2 nanocrystals imbedded in amorphous carbon (SnO2/C), which
Fig. 1. XRD patterns of the as prepared nanomaterials, the purple stick patterns are for Sn standard (JCPDS 86-2264) (a); Core-level XPS spectra of Sn 3d of the annealed SnO2/C
composite (b); Core-level XPS spectra of Sn 3d of the SnO2/C composite before and after annealing (c) and TGA curves (d) of carbon, pristine and annealed SnO2/C composites. (For
interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

124
J. Qu et al. / Journal of Alloys and Compounds 686 (2016) 122e129
Fig. 2. SEM images of the carbon (a), pristine (b) and annealed (c,d) SnO2/carbon composite.
ultrasonic dispersion and then dropped onto a copper grid covered
with a carbon film, to make a specimen for the TEM. N2 adsorption
data was measured using a NOVA 2000e (Quantachrome) instru-
ment, while the specific surface area was evaluated by the BET
method.
composite and annealed SnO2/C composite. For the blank carbon,
only a broad peak at around 20ꢁ can be observed, suggesting the
amorphous state of carbon. For the pristine SnO2/C composite and
annealed SnO2/C composite, all peaks can be indexed to the SnO2
tetragonal rutile crystal. Two more peaks around 62ꢁ and 65ꢁ are
observed in the annealed SnO2/C composite, corresponding to the
SnO2 tetragonal rutile crystal planes of (310) and (301) (JCPDS no.
77-0450). And the annealed SnO2/C composite shows a better
crystallinity [4,9]. The average crystalline size of SnO2 after
annealing calculated by Scherrer equation is about 4.3 nm. To
further characterize the chemical compositions of the annealed
composite, XPS measurements were conducted. Initially, 284.8 eV
was used as the charge reference of the adventitious carbon to
adjust the peak shifts. As shown in Fig. 1b, SnO2 was slightly
reduced during annealing, with the surface atom percentages of Sn
and Sn2þ being 4.19% and 5.39%, respectively [4,39]. It still
remained as the main component of the annealed composite. Fig.1c
represents the comparison of XPS spectra of the composite before
and after annealing, and an obvious peak-shift corresponding to
Sn4þ can be observed [39], which suggests the strong interaction
between carbon and Sn. By considering all results above, we can
conclude that the ultrasmall SnO2 nanocrystals are well distributed
in the amorphous carbon matrices for both pristine and annealed
SnO2/C composite. Such structure is favorable to obtain high elec-
trochemical performance. Fig. 1d represents the TGA curves of the
as-prepared samples. There are two obvious weight loss steps for
the pristine SnO2/C composite and the annealed SnO2/C composite.
The initial weight loss below 300 ꢁC can be attributed to the loss of
water and the further carbonization of the amorphous carbon,
whereas the second step is generally designated to the combustion
of carbon [4,23]. According to the TGA curves, the content of SnO2
in the pristine composite is estimated to be 67.5 wt%; in contrast,
the content in the annealed composite is as high as 87.3 wt%. This
loading percent is among the highest, compared with other SnO2/C
composites in the literature [4,19e21,23,40e42].
2.2. Electrochemical measurements
The electrochemical properties were measured using two-
electrode Swagelok cells, for which the working electrode was
prepared by pressing a mixture of active material (75%), Acetylene
Black (18%) and PVDF (Polyvinylidene Fluoride, 7%). Lithium metal
was used as the counter and reference electrode. LiPF6 (1 M) was
used as electrolyte in a mixture of ethylene carbonate (EC) and
diethyl carbonate (DEC) at a weight ratio of 1:1. The galvanostatic
method at the discharge-charge current density of 200 mA gꢀ1
,
500 mA gꢀ1, 1000 mA gꢀ1, 2000 mA gꢀ1 and 5000 mA gꢀ1 was used
to measure the electrochemical capacity of the electrodes at room
temperature using an MTI-BST8-MA (10 mA). The cutoff potentials
for the charge and discharge processes were set vs Liþ/Li at 3.0 V
and 0.01 V respectively. The CV (Cyclic voltammetry) experiments
were conducted using GAMRY REFERENCE 600 at room tempera-
ture. Electrochemical impedance spectra (EIS) were collected using
GAMRY REFERENCE 600. A perturbation of 10 mV was applied and
data collected from 200 kHz to 10 mHz.
3. Results and discussion
Scheme 1 shows the synthesis route of the annealed SnO2/C
composites. Through
a hydrothermal process, SnO2 particles
aggregate together and are loaded on the carbon. After annealing at
600 ꢁC for 2 h under the protection of argon, the SnO2 particles
become smaller and homogeneous, and disperse uniformly in the
carbon substrate.
Fig. 1a shows the XRD patterns of carbon, pristine SnO2/C

J. Qu et al. / Journal of Alloys and Compounds 686 (2016) 122e129
125
Fig. 3. TEM images of the pristine (a,b,c) and annealed (d,e) SnO2/carbon composite.
The morphology of the obtained composites can be clearly
revealed by SEM and TEM measurements. As shown in SEM images
in Fig. 2, the bulk carbon is transformed into loose aggregates after
the introduction of SnO2 nanoparticles. After annealing, the SnO2
nanoparticles and carbon are connecting tightly together other
than aggregating to blocks. However, the annealed SnO2/C com-
posite shows a microstructure primarily comprising of nano-
particles, different from pristine SnO2/C composite and the bulk
carbon. The detailed microstructures of two composites are further
illustrated by TEM images. For the pristine SnO2/C composite, it is
clear that the SnO2 nanocrystals are well dispersed in the carbon
matrix (Fig. 3aec). The HRTEM images (Fig. 3c and the enlarged
figure) show clear lattice fringes, indicating high crystallinity of the
material. The particle sizes of primary SnO2 nanocrystals are
around 5 nm; the lattice spacings of 0.34 and 0.32 nm can be
assigned to the (110) and (001) planes of rutile SnO2, respectively
[43]. For the annealed SnO2/C composite in Fig. 2d and the inset, it
can be observed that SnO2 nanoparticles are highly dispersed in the
carbon matrix. The well crystallized lattices are clearly illustrated
by HRTEM images in Fig. 3e. The SnO2 particles are around 5e10 nm
in size, as highlighted with red circles, which is almost consistent
with the size (4.3 nm) calculated by Scherrer equation. This small

126
J. Qu et al. / Journal of Alloys and Compounds 686 (2016) 122e129
Fig. 4. CV curves of the obtained carbon, pristine and annealed SnO2/C composite ate
rate of 0.1 mV sꢀ1
.
change in particle size instead of a serious fusion can be attributed
to the spatial restriction of the amorphous carbon during the
annealing process.
To illustrate the electrochemical properties of the obtained
composite, cyclic voltammetry experiments are first conducted. As
presented in Fig. 4, the different CV curves can be observed. For the
blank carbon sample, there are no redox peaks can be observed. For
the pristine SnO2/C composite, there are two broad cathodic peaks
between 0.5 V and 1.1 V, which correspond to the reduction of SnO2
to the metallic Sn and the formation of the solid electrolyte inter-
phase [4]. The anodic peaks appearing at around 0.11 V can be
mainly attributed to the formation of LixSn [4]. For the annealed
SnO2/C composite, two less noticeable cathodic peaks can be
observed, which might result from the partial reduction of SnO2. It
is obvious that the obtained pristine and annealed SnO2/C com-
posite can show higher capacity than that of blank carbon sample.
Fig. 5 shows the initial discharge-charge curves of the obtained
samples. For the pristine SnO2/C composite, two obvious sloping
plateaus can be observed, while for the annealed composite, the
plateau becomes less noticeable, in consistent with the results of
CV. The initial discharge and charge capacities of the pristine
composite are 1474 and 748 mAh gꢀ1 with a coulombic efficiency of
50.7%, while the corresponding values for the annealed composite
increase to 1698 and 916 mAh gꢀ1 with a coulombic efficiency of
53.9%. The large initial irreversible capacity loss could be explained
by the irreversible reduction of SnO2 to Sn, the irreversible for-
mation of Li2O, the formation of a solid electrolyte interface (SEI)
layer, and electrolyte decomposition. The coulombic efficiency is
relatively constant (97%) from the 8th cycle and can keep almost
100% from the 20th cycle, indicating the high stability of the two
SnO2/C composites. To test the rate capability and cycling stability
of the composite, the discharge capacity at different current den-
sities is measured (Fig. 5b). The annealed composite shows the
highest discharge capacity, and both composites display superior
performance to the carbon sample. For the annealed SnO2/C com-
posite, the discharge capacity of 968 mAh gꢀ1 obtained after the
20th cycle at the current density of 200 mA gꢀ1 is about 2.6 times
higher than the theoretical capacity of graphite. When the current
density is increased to 5000 mA gꢀ1, the discharge capacity can be
retained at 435 mAh gꢀ1, still higher than the theoretical capacity of
graphite. More interestingly, after 60 cycles with varying current
densities, the discharge capacity of the annealed composite boun-
ces back to 1015 mAh gꢀ1, even higher than that at the 20th cycle.
The higher capacity is achieved by the better distribution of the
Fig. 5. (a) Initial discharge-charge curves (c) of the obtained composites; and (b) cycle
performance of the obtained composites at different current densities: 200 mA gꢀ1 for
20 cycles, 500 mA gꢀ1, 1000 mA gꢀ1, 2000 mA gꢀ1, 5000 mA gꢀ1 for 10 cycles each; and
the 200 mA gꢀ1 for 20 cycles.
SnO2 nanoparticles on the carbon matrix, which can react with the
SEI layer to release Liþ [44,45]. The good capacity retention may be
due to the unique structure with high surface area as well as the
small sizes of the SnO2 nanoparticles which can facilitate the
electrolyte penetration and shorten the transport distance of Liþ
ions, ensuring a high flux of Liþ through the interface [46]. And the
carbon matrix can enhance the structural stability, buffer the vol-
ume variation and prevent the agglomeration of SnO2 nano-
particles, leading to enhanced capacity retention [25e31]. For the
pristine composite, the discharge capacity is 769 mAh gꢀ1 at the
current density of 200 mA gꢀ1, and 315 mAh gꢀ1 at the current
density of 5000 mA gꢀ1 over 60 cycles.
As discussed above, SnO2/C structures show high capacity and
good cycle retention, however, the pristine composite does not
offer higher discharge capacity compared with the annealed one,
despite its smaller nanocrystal sizes. The reasons can be summa-
rized as follows: 1) annealing could strengthen the interaction
between SnO2 and carbon and result in good conductivity of the
carbon matrix, which are desirable for fast transport of electrons
and Li-ions. 2) SnO2 nanocrystals in the pristine composite would
aggregate to larger particles, while the size in the annealed com-
posite would be well retained [2,3]. To further understand the
improved discharge-charge capacity and cycle performance of
annealed nanocomposite, EIS tests in Fig. 6 were performed after
discharging to 1 V for two cycles. The semicircle in the high fre-
quency region represent the resistance of SEI film (Rsf) and charge

Fig. 6. Impedance plots for carbon after discharging to 1 V (a), for pristine SnO2/C composite (b) and for annealed SnO2/C composite (c).
Fig. 7. TEM images of the pristine (a and b) and annealed (cee) SnO2/C composites before (a and c) and after (b, d and e) 10 discharge-charge cycles at the current density of 200 mA gꢀ1
.

128
J. Qu et al. / Journal of Alloys and Compounds 686 (2016) 122e129
[7] K. Xi, S. Cao, X. Peng, C. Ducati, R.V. Kumar, A.K. Cheetham, Carbon with hi-
erarchical pores from carbonized metaleorganic frameworks for lithium
sulphur batteries, Chem. Commun. 49 (2013) 2192.
[8] L. Mei, C. Xu, T. Yang, J.M. Ma, L.B. Chen, Q.H. Li, T.H. Wang, Superior elec-
trochemical performance of ultrasmall SnS2 nanocrystalsdecorated on flexible
RGO in lithium-ion batteries, J. Mater. Chem. A 1 (2013) 8658.
[9] W. Wang, C.J. Yu, Z.S. Lin, J.G. Hou, H.M. Zhu, S.Q. Jiao, Microspheric Na2Ti3O7
consisting of tiny nanotubes: an anode material for sodium-ion batteries with
ultrafast chargeedischarge rates, Nanoscale 5 (2013) 594.
[10] Y. Idota, T. Kubota, A. Matsufuji, Y. Maekawa, T. Miyasaka, Tin-based amor-
phous oxide: a high-capacity lithium-ion-storage material, Science 276 (1997)
1395.
[11] X. Xu, J. Liang, H. Zhou, D. Lv, F. Liang, Z. Yang, S. Ding, D. Yu, The preparation
of uniform SnO2 nanotubes with a mesoporous shell for lithium storage,
J. Mater. Chem. A 1 (2013) 2995.
[12] S.-Y. Lee, K.-Y. Park, W.-S. Kim, S. Yoon, S.-H. Hong, K. Kang, M. Kim, Unveiling
origin of additional capacity of SnO2 anode in lithium-ion batteries by realistic
ex situ TEM analysis, Nano. Energy 19 (2016) 234.
[13] S. Ding, X.W. Lou, SnO2 nanosheet hollow spheres with improved lithium
storage capabilities, Nanoscale 3 (2011) 3586.
[14] L. Zhang, H.B. Wu, B. Liu, X.W. Lou, Formation of porous SnO2 microboxes via
selective leaching for highly reversible lithium storage, Energy Environ. Sci. 7
(2014) 1013.
[15] D. Deng, J.Y. Lee, Hollow core-shell mesospheres of crystalline SnO2 nano-
particle aggregates for high capacity Liþ ion storage, Chem. Mater 20 (2008)
1841.
transfer (Rct) and the slope in the low frequency region correspond
to the diffusion of lithium ions (Warburg impedance). Obviously,
annealed SnO2/C composite shows a lower Rsfþct (70
U) than that of
pristine SnO2/C composite (204 ). And the Warburg impedance of
U
annealed SnO2/C composite is also lower than the other two sam-
ples. The above results suggest much more fast charge transfer and
ion diffusion for annealed SnO2/C composite, which may be caused
by the strengthened interaction between SnO2 and carbon and the
good conductivity of the carbon after annealing. For annealed SnO2/
C composite, the Rsfþct was a little bigger in the 2nd than in the 1st,
indicating a SEI layer formation, which can endure great changes
upon cycling and be beneficial for long cycle life. The structural
change in these two composites responding to the discharge-
charge cycles can be clearly illustrated in Fig. 7. As for the pristine
SnO2/C composite, at the current density of 200 mA gꢀ1, the
nanocrystal sizes are significantly increased after 10 cycles, which is
harmful to the cycle performance. In contrast, for the annealed
SnO2/C composite, the SnO2 nanoparticles are still well distributed
in the carbon matrix after 10 cycles. It can be seen in the HRTEM
images that the crystalline sizes are still below 6 nm. The lattice
spacing of 0.205 nm corresponds to the (220) planes of the Sn
metal. It should also be mentioned that the size of nanoparticles in
the annealed composite has decreased, which results from the fact
that the charging product is Sn, but not SnO2.
[16] W. Wang, P.N. Kumta, Nanostructured hybrid silicon/carbon nanotube het-
erostructures: reversible high-capacity lithium-ion anodes, ACS Nano
(2010) 2233.
4
[17] L. Cui, J. Shen, F. Cheng, Z. Tao, J. Chen, SnO2 nanoparticles@polypyrrole
nanowires composite as anode materials for rechargeable lithium-ion batte-
ries, J. Power Sources 196 (2011) 2195.
[18] X. Zhou, L.-J. Wan, Y.-G. Guo, Binding SnO2 nanocrystals in nitrogen-doped
graphene sheets as anode materials for lithium-ion batteries, Adv. Mater. 25
(2013) 2152.
4. Conclusions
[19] X.W. Lou, C.M. Li, L.A. Archer, Designed synthesis of coaxial SnO2@carbon
hollow nanospheres for highly reversible lithium storage, Adv. Mater 21
(2009) 2536.
[20] M.-Y. Li, C.-L. Liu, Y. Wang, W.-S. Dong, Simple synthesis of carbon/tin oxide
composite as anodes for lithium-ion batteries, J. Electrochem. Soc. 158 (2011)
A296.
[21] L. Zhang, G.Q. Zhang, H.B. Wu, L. Yu, X.W. Lou, Hierarchical tubular structures
constructed by carbon-coated SnO2 nanoplates for highly reversible lithium
storage, Adv. Mater. 25 (2013) 2589.
[22] Y. Yu, C.-H. Chen, Y. Shi, Tin-based amorphous oxide composite with a porous,
spherical, multideck-cage morphology as a highly reversible anode material
for lithium-ion batteries, Adv. Mater. 19 (2007) 993.
[23] R. Yang, W. Zhao, J. Zheng, X.Z. Zhang, X.G. Li, One-step synthesis of carbon-
coated tin dioxide nanoparticles for high lithium storage, J. Phys. Chem. C
114 (2010) 20272.
[24] X. Liu, M. Wu, M. Li, X. Pan, J. Chen, X. Bao, Facile encapsulation of nanosized
SnO2 particles in carbon nanotubes as an efficient anode of Li-ion batteries,
J. Mater. Chem. A 33 (2013) 9527.
[25] J. Liang, X.-Y. Yu, H. Zhou, H.B. Wu, S. Ding, X.W.D. Lou, Bowl-like SnO2@
Carbon hollow particles as an advanced anode material for lithium-ion bat-
teries, Angew. Chem. Int. Ed. Engl. 53 (2014) 12803.
In this work, ultrasmall SnO2 nanocrystals in carbon matrices
are synthesized through a facile one-step hydrothermal route.
Compared with the conventional anode material graphite, the
annealed SnO2/C composite, in which the active material loading of
SnO2 is as high as 87.3 wt% and its crystal sizes are around 5e10 nm,
shows superior electrochemical performance. At the current den-
sity of 200 mA gꢀ1, the initial discharge and charge capacities are up
to 1698 and 916 mAh gꢀ1 respectively. Due to the strong interaction
between the carbon matrix and the active material, the annealed
SnO2/C composite can endure a wide change of low and high cur-
rent densities. After cycles, the SnO2 nanoparticles are still well
distributed in the carbon matrix, resulting in long cycle life and
excellent stability. Furthermore, the annealed carbon can enhance
the conductivity of the electrode, which is beneficial to the high
rate performance of Li-ion batteries.
[26] M. Dirican, M. Yanilmaz, K. Fu, Y. Lu, H. Kizil, X.W. Zhang, Carbon-enhanced
electrodeposited SnO2/carbon nanofiber composites as anode for lithium-ion
batteries, J. Power. Sources 264 (2014) 240.
Acknowledgments
[27] Y.N. Ko, S.B. Park, Y.C. Kang, Energy storage: design and fabrication of new
nanostructured SnO2-carbon composite microspheres for fast and stable
lithium storage performance, Small 10 (2014) 3198.
[28] S. Oro, K. Urita, I. Moriguchi, Enhanced chargeedischarge properties of SnO2
nanocrystallites in confined carbon nanospace, Chem. Commun. 50 (2014)
7143.
[29] W. Fu, F.-H. Du, K.-X. Wang, T.-N. Ye, X. Wei, J.-S. Chen, In situ growth of
ultrafine tin oxide nanocrystals embedded in graphitized carbon nanosheets
for use in high-performance lithium-ion batteries, J. Mater. Chem. A 2 (2014)
6960.
This work has been supported by the National Natural Science
Foundation of China (21301022 and 21376113) and the startup fund
for YY from Colorado School of Mines.
References
[1] R.V. Noorden, The rechargeable revolution:
(2014) 26.
a better battery, Nature 507
[30] H. Guo, R. Mao, D. Tian, W. Wang, D. Zhao, X. Yang, S. Wang, Morphology-
controlled synthesis of SnO2/C hollow coreeshell nanoparticle aggregates
with improved lithium storage, J. Mater. Chem. A 1 (2013) 3652.
[31] K. Xi, P.R. Kidambi, R. Chen, C. Gao, X. Peng, C. Ducati, S. Hofmann, R.V. Kumar,
Binder free three-dimensional sulphur/few-layer graphene foam cathode
with enhanced high-rate capability for rechargeable lithium sulphur batteries,
Nanoscale 6 (2014) 5746.
[32] M.-S. Wang, M. Lei, Z.-Q. Wang, X. Zhao, J. Xu, W. Yang, Y. Huang, X. Li,
Scalable preparation of porous micron-SnO2/C composites as high perfor-
mance anode material for lithium ion battery, J. Power Sources 309 (2016)
238.
[33] Z.-G. Wu, J.-T. Li, Y.-J. Zhong, J. Liu, X.-D. Guo, L. Huang, B.-H. Zhong, S.-G. Sun,
Synthesis of hierarchical worm-like SnO2@C aggregates and their enhanced
lithium storage properties, J. Alloy. Compd. 620 (2015) 407.
[34] S. Ding, D. Luan, F.Y.C. Boey, J.S. Chen, X.W. Lou, SnO2 nanosheets grown on
graphene sheets with enhanced lithium storage properties, Chem. Commun.
[2] J.S. Chen, X.W. Lou, SnO2-Based nanomaterials: synthesis and application in
lithium-ion batteries, Small 9 (2013) 1877.
[3] A.S. Arico, P.G. Bruce, B. Scrosati, J.M. Tarascon, W.V. Schalkwijk, Nano-
structured materials for advanced energy conversion and storage devices, Nat.
Mater. 4 (2005) 366.
[4] L.P. Ding, S.L. He, S.D. Miao, M.R. Jorgensen, S. Leubner, C.L. Yan, S.G. Hickey,
A. Eychmüller, J.Z. Xu, O.G. Schmidt, Ultrasmall SnO2 nanocrystals: hot-
bubbling synthesis, encapsulation in carbon layers and applications in high
capacity Li-Ion storage, Sci. Rep. 4 (2014) 4647.
[5] A. Jahel, C.M. Ghimbeu, L. Monconduit, C. Vix-Guterl, Confined ultrasmall SnO2
particles in micro/mesoporous carbon as an extremely long cycle-life anode
material for Li-Ion batteries, Adv. Energy Mater 4 (2014) 1400025.
[6] R. Chen, T. Zhao, T. Tian, S. Cao, P.R. Coxon, K. Xi, D. Fairen-Jimenez,
R.V. Kumar, A.K. Cheetham, Graphene-wrapped sulfur/metal organic
framework-derived microporous carbon composite for lithium sulfur batte-
ries, Apl. Mater 2 (2014) 124109.

J. Qu et al. / Journal of Alloys and Compounds 686 (2016) 122e129
enhanced lithium ion storage properties, Adv. Mater 24 (201) (1405).
129
47 (2011) 7155.
[35] M. He, L. Yuan, X. Hu, W. Zhang, J. Shu, Y. Huang, A SnO2@carbon nanocluster
anode material with superior cyclability and rate capability for lithium-ion
batteries, Nanoscale 5 (2013) 3298.
[41] H. Liu, S. Chen, G.X. Wang, S.Z. Qiao, Ordered mesoporous core/shell SnO2/C
nanocomposite as high-capacity anode material for lithium-ion batteries,
Chem. Eur. J. 19 (2013) 16897.
[36] W. Wang, P. Li, Y. Fu, X. Ma, The preparation of double-void-space SnO2/
carbon composite as high-capacity anode materials for lithium-ion batteries,
J. Power Sources 238 (2013) 464.
[42] S. Yang, W.B. Yue, J. Zhu, Y. Ren, X.J. Yang, Graphene-based mesoporous SnO2
with enhanced electrochemical performance for lithium-ion batteries, Adv.
Funct. Mater 23 (2013) 3570.
[37] J. Wang, H. Zhao, X. Liu, J. Wang, C. Wang, Electrochemical properties of SnO2/
carbon composite materials as anode material for lithium-ion batteries,
Electrochim. Acta 56 (2011) 6441.
[43] C. Wang, Y. Zhou, M.Y. Ge, X.B. Xu, Z.L. Zhang, J.Z. Jiang, Large-scale synthesis
of SnO2 nanosheets with high lithium storage capacity, J. Am. Chem. Soc. 132
(2010) 46.
[38] S. Ding, D. Zhang, H.B. Wu, Z. Zhang, X.W. Lou, Synthesis of micro-sized SnO2@
carbon hollow spheres with enhanced lithium storage properties, Nanoscale 4
(2012) 3651.
[44] B. Guo, J. Shu, K. Tang, Y. Bai, Z. Wang, L. Chen, Nano-Sn/hard carbon com-
posite anode material with high-initial coulombic efficiency, J. Power Sources
177 (2008) 205.
[39] Q.H. Tian, Z.X. Zhang, L. Yang, S.I. Hirano, Synthesis of SnO2/Sn@carbon
nanospheres dispersed in the interspaces of a three-dimensional SnO2/Sn@
carbon nanowires network, and their application as an anode material for
lithium-ion batteries, J. Mater. Chem. A 2 (2014) 12881.
[45] H.-X. Zhang, C. Feng, Y.-C. Zhai, K.-L. Jiang, Q.-Q. Li, S.-S. Fan, Cross-stacked
carbon nanotube sheets uniformly loaded with SnO2Nanoparticles: a novel
binder-free and high-capacity anode material for lithium-ion batteries, Adv.
Mater. 21 (2009) 2299.
[40] B. Luo, B. Wang, M.H. Liang, J. Ning, X.L. Li, L.J. Zhi, Reduced graphene oxide-
mediated growth of uniform tin-core/carbon-sheath coaxial nanocables with
[46] P.G. Bruce, B. Scrosati, J.-M. Tarascon, Nanomaterials for rechargeable lithium
batteries, Angew. Chem. Int. Ed. 47 (2008) 2930.