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Nano Research
Nano Res
DOI 10.1007/s12274-015-0757-3
Enhanced Li+ storage properties of few-layered
MoS2–carbon composite microspheres embedded with
Si nanopowders
Seung Ho Choi and Yun Chan Kang ()
Nano Res., Just Accepted Manuscript • DOI 10.1007/s12274-015-0757-3
http://www.thenanoresearch.com on March 4, 2015
© Tsinghua University Press 2015
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1
TABLE OF CONTENTS (TOC)
Enhanced Li+ Storage Properties of Few-Layered
MoS2–Carbon Composite Microspheres Embedded
with Si Nanopowders
Seung Ho Choi, Yun Chan Kang*
Department of Materials Science and Engineering, Korea
University, Republic of Korea.
Few-layered MoS2-carbon composite with high capacities and good
cycling performance is successfully applied as a protective matrix of
silicon nanopowders. The MoS2–C composite material accommodates
the large volume expansion of the Si nanopowders, but it also prevents
the formation and propagation of a SEI layer on the Si surface during
repeated cycling. The MoS2-C composite microspheres embedded with
30 wt% Si nanopowders with enhanced Li+ storage properties are
evaluated as a novel anode material with superior electrochemical
properties for lithium-ion batteries.
Address correspondence to First Yun Chan Kang, email; [email protected]
Nano Research
DOI (automatically inserted by the publisher)
Research Article
Enhanced Li+ Storage Properties of Few-Layered
MoS2–Carbon Composite Microspheres Embedded with
Si Nanopowders
Seung Ho Choi and Yun Chan Kang ()
Received: day month year
ABSTRACT
Revised: day month year
Few-layered MoS2–carbon composite material is studied as a supporting
material of silicon nanopowders. Microspheres of few-layered MoS2–C
composite embedded with 30 wt% Si nanopowders are prepared by one-pot
spray pyrolysis. The Si nanopowders with high capacity are perfectly
surrounded by the few-layered MoS2–C composite matrix. The discharge
capacities of the MoS2–C composite microspheres with and without 30 wt%
Si nanopowders after 100 cycles are 1020 and 718 mA h g-1 at a current
density of 1000 mA g-1, respectively. The spherical morphology of the
MoS2–C composite microspheres embedded with Si nanopowders is
preserved even after 100 cycles because of their high structural stability
during cycling. The MoS2–C composite layer prevents the formation of
unstable solid–electrolyte interface (SEI) layers on the Si nanopowders.
Furthermore, as the MoS2–C composite matrix exhibits high capacities and
excellent cycling performance, these characteristics are also reflected in the
MoS2–C composite microspheres embedded with 30 wt% Si nanopowders.
Accepted: day month year
(automatically inserted by
the publisher)
© Tsinghua University Press
and Springer-Verlag Berlin
Heidelberg 2014
KEYWORDS
Molybdenum sulfide •
Silicon • Anode material •
Lithium batteries • Spray
pyrolysis
1. Introduction
As the technologies for electric vehicles and
However, silicon experiences a large volume
portable electronic devices develop, silicon is
expansion
considered an extremely promising anode material
insertion–extraction process, resulting in poor cycle
for lithium-ion batteries (LIBs) with high capacity
properties because of pulverization of materials and
and fast charging–discharging properties [1-11].
loss of electrical contact between the electronic
Available in abundance, Si is an outstanding LIB
materials and the current collector [1-11].
anode material owing to its low discharge potential
(300%)
Nanostructured
during
materials
and
the
Li+
carbon-based
(< 0.5 V vs. Li/Li ) and the highest theoretical
composite materials have been developed to control
reversible capacity of approximately 4200 mA h g-1,
the volume expansion of the Si electrode [12-36].
which is ten times more than the value for
Various types of Si-based nanostructured materials,
commercial graphite anodes (372 mA h g-1) [1-11].
such as hollow nanospheres, cubic nanocrystals,
+
Address correspondence to First Yun Chan Kang, email; [email protected]
Nano Res.
nanowires, and nanotubes, have improved Li+
electrochemical properties of a LIB anode. For
storage properties beyond those of bulk materials
example, Zhu et al. reported that a single-layered
[12-21]. Although these Si-based nanostructures can
MoS2–carbon fiber composite exhibits high capacity
tolerate the large change in volume, the formation
and long cycle stability for LIBs [45]. However, the
of an unstable layer at the solid–electrolyte interface
MoS2-based
(SEI) between the Si surface and the organic
capacities than those of the Si-based materials. The
electrolyte leads to low Coulombic efficiency and a
layered MoS2-carbon composite material with high
decrease in capacity during cycling [8-10,12,21].
structural stability during repeated Li insertion and
Carbon-based silicon composite materials have
desertion processes could be efficient as the
attracted much attention as promising anode
supporting material for the Si materials with high Li
materials with stable and excellent Li
storage
ion storage capacities. To the best of our knowledge,
electrical
metal sulfide–Si composite materials have not been
properties
because
conductivity
carbonaceous
and
of
the
materials
their
high
stress-buffer
layer
of
had
lower
reversible
reported as anode materials for LIBs applications.
Carbon-based
In this study, the few-layered MoS2–C composite
silicon composite materials such as Si–graphite,
microspheres embedded with Si nanopowders were
Si–amorphous
prepared
carbon,
[22-36].
+
materials
Si–C
nanotubes,
and
by
one-pot
spray
pyrolysis,
using
Si–graphene have long cycle life when the silicon
ammonium
content in the composite materials was low [22-35].
polyvinylpyrrolidone (PVP), and Si nanopowders.
As the Si content in a Si–C composite was increased,
Few-layered MoS2 nanosheets embedded in carbon
the Li storage properties deteriorated. However,
spheres served as a protective matrix of silicon
high content of carbon material resulted in
nanopowders. In addition to accommodating the
increases in the initial irreversible capacity and
large volume expansion of the Si nanopowders, the
decreases in the reversible capacity [22-31]. Thus,
MoS2–C
the search for new replacement carbonaceous
formation and propagation of the SEI layer on the Si
supporting material for the Si anode remains a great
surface
challenge.
electrochemical properties of the microspheres were
+
In recent years, transition-metal oxides and metal
sulfides have been widely studied as anode
tetrathiomolybdate,
composite
during
material
repeated
prevented
cycling.
the
The
compared with those of microspheres without the
embedded Si nanopowders.
materials for LIBs because they have higher
theoretical
capacities
than
commercial
2. Experimental section
carbonaceous materials [37-43]. Two-dimensional
2.1 Synthesis of few-layered MoS2–C composite
(2D) layered MoS2 is especially attractive because of
microspheres embedded with Si nanopowders.
its high reversible capacity and good cycling
MoS2–C composite microspheres embedded with Si
performance. Controlled MoS2 materials consisting
nanopowders were directly prepared by ultrasonic
of single layer or few layers facilitate a fast Li
+
spray pyrolysis at 800°C; a schematic of the
charging–discharging process, which allows the
apparatus is shown in Figure S1. A quartz reactor
interlayer distance to relax the strain and lower the
measuring 1200 mm in length and 50 mm in
barrier for Li intercalation [44-47]. Because the
diameter was used; the nitrogen flow rate (carrier
graphene-like layered MoS2 can be very uniformly
gas) was 10 L min-1. A 500-mL volume of distilled
mixed
water
with
carbonaceous
materials,
the
was
added
to
1.8
g
of
ammonium
combination of the two materials has been regarded
tetrathiomolybdate
as
polyvinylpyrrolidone (PVP) to form the spray
a
fundamental
strategy
to
enhance
the
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and
5.0
g
of
Nano Res.
solution. The silicon nanopowders (85 nm) were
ethylene
carbonate
and
dimethyl
carbonate
dispersed in the spray solution with ammonium
(EC–DMC) with 5% fluoroethylene carbonate. The
tetrathiomolybdate and PVP.
charging–discharging characteristics of the samples
were determined through cycling in the potential
2.2 Characterization.
range of 0.001–3.0 V at various fixed current
The crystal structure of the MoS2–C composite
densities.
The
cyclic
voltammetry
(CV)
microspheres embedded with Si nanopowders was
measurements were carried out at a scan rate of 0.1
investigated by X-ray diffractometry (XRD; X’pert
mV s-1. Dimensions of the negative electrode were 1
PRO MPD, PANalytical, The Netherlands), using
cm × 1 cm and mass loading was approximately 1.2
Cu Kradiation (= 1.5418 Å ). The morphological
mg cm-2.
features were investigated using field-emission
scanning electron microscopy (FE-SEM; S-4800,
Hitachi, Japan) and high-resolution transmission
3. Results and discussion
Scheme 1 shows the formation mechanism of the
electron microscopy (HR-TEM; JEM-2100F, JEOL,
few-layered
Japan) at a working voltage of 200 kV. The specific
embedded with Si nanopowders via the one-step
surface areas of the composite microspheres were
and continuous spray-pyrolysis process. Droplets
calculated from a Brunauer–Emmett–Teller (BET)
were formed from the colloidal spray solution
analysis of nitrogen adsorption isotherms (TriStar
consisting of Si nanopowders dispersed in an
3000
gas
adsorption
MoS2–C
composite
microspheres
analyzer,
Micromeritics, USA). The composite
microspheres were also investigated
using
X-ray
photoelectron
spectroscopy (XPS;ESCALAB 210, VG
Scientific, now Thermo Scientific,
USA) with Al K radiation (1486.6
eV).
2.3 Electrochemical measurements.
The
capacities
properties
of
and
the
cycling
composite
microspheres were determined using
a 2032-type coin cell. The electrode
was
prepared
from
a
mixture
containing 70 wt% of the active
material,
15
wt%
of
Super
P
(conductive carbon black), and 15
wt%
of
sodium
carboxymethyl Scheme 1. Formation mechanism of the few-layered MoS2–C composite microsphere
cellulose (CMC) as the binder. embedded with Si nanopowders via the one-step and continuous spray-pyrolysis
Lithium metal and a microporous process.
polypropylene film were used as the
aqueous solution of ammonium tetrathiomolybdate
counter electrode and separator, respectively. The
and PVP. In this study, PVP acted as a stabilizer for
electrolyte was 1 M LiPF6 in a 1:1 (v/v) mixture of
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Nano Res.
the Si nanopowders and the source material for
amorphous carbon, thus preventing the stacking of
MoS2 layers [45,48]. In the precursor solution, the
surface of the Si nanopowder was functionalized
with water-soluble PVP. The drying of each droplet
produced
a
composite
microsphere
of
Si–ammonium-tetrathiomolybdate–PVP in the front
part of the reactor that was maintained at 800°C.
Thermal
decomposition
of
ammonium
tetrathiomolybdate into MoS2 and carbonization of
PVP under the nitrogen atmosphere resulted in a
Si–MoS2–C composite microsphere at the rear part
of the reactor. In other words, one MoS2–C
composite
microsphere
Si
Figure. 1 Morphologies of the the MoS2-C composite
and
microspheres embedded with 30 wt% Si nanopowders. a,b)
decomposition of one droplet, and few-layered
FE-SEM images, c-f) TEM images, g) elemental mapping
ultra-small nanoplates of MoS2 were embedded
images of Mo, S, Si, and C components.
nanopowders
was
embedded
formed
by
with
drying
within the MoS2–C composite microsphere. The
MoS2–C
elastic
enclosed within the composite microsphere. The
two-dimensional structure completely covered the
TEM images (Figures 1d and e) show the Si
individual Si nanopowders. The content of Si
nanopowders dispersed within the MoS2–C matrix.
nanopowders in the composite microsphere could
Figures 1e and 1f show the amorphous-fluid-like
be controlled by changing the amount of Si
structure
nanopowders dispersed in the spray solution.
few-layered MoS2 nanosheets were uniformly
The
composite
layers
morphologies of the
microspheres
MoS2–C
composite
MoS2–C
matrix,
in
which
distributed within the amorphous carbon matrix;
structure, was fully covered by MoS2–C layers, as
The
composite
shown by the arrows. The enlarged TEM image in
microspheres shown in Figure 1 was 30 wt% based
the inset of Figure 1f reveals clear lattice fringes
on MoS2. The morphology of the commercial Si
separated
nanopowders used in this study is shown in Figure
corresponds to the interplanar distance between the
S2; the nanopowder had a mean size of 85 nm and a
(111) planes of a Si nanoparticle [19]. The elemental
slightly aggregated structure. The FE-SEM and low
mapping
resolution TEM images revealed that the composite
distributions of MoS2, C, and Si nanopowders. The
microspheres had a spherical shape and did not
necking between the Si nanopowders resulted in
show any tendency to aggregate. The surface of the
some segregation of Si component in the low
composite powder, as shown in Figure 1, had an
resolution elemental mapping images as shown in
embossed structure owing to the Si nanopowders
Figure S3. MoS2 and the carbon material were
in
the
amount
the
enclosed Si nanopowders are shown in Figure 1.
content
small
of
the Si nanopowder, which formed an embossed
Si
a
an
of
designed
containing
with
by
distance
images
in
of
Figure
0.31
1g
nm,
which
show
the
uniformly distributed all over the composite
microspheres. The Si nanopowders were also well
dispersed within the MoS2–C composite matrix. The
dozens of the Si nanopowders were dispersed in
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Nano Res.
one composite microsphere as shown in Figure 1g.
microspheres
are
shown
in
Figure
S5.
The
Considering that MoS2 was converted into MoO3
composite microspheres had completely spherical
when heated in air, the carbon content in the
shape and showed no tendency to aggregate. The
composite microspheres was estimated as 23 wt%,
HR-TEM image in Figure S4d shows the uniform
as measured by thermogravimetric analysis (see
distribution of MoS2 nanosheets over the entire
Figure S4).
carbon matrix formed from the carbonization
process that restricted the of MoS2 layers.
Figure
2.
Morphologies
of
the
MoS2-C
composite
microspheres embedded with 60 wt% Si nanopowders: a,b)
Figure
3.
Properties
of
the
MoS2-C
composite
FE-SEM images, c-f) TEM images, and g) elemental mapping
microspheres embedded with 30 wt% and 60 wt% Si
images of Mo, S, Si, and C components.
nanopowders. a) XRD patterns, b) XPS C1s spectrum of
the MoS2-C composite microspheres embedded with 30
The morphologies of the MoS2–C composite
wt%, c) XPS Mo3d spectrum, d) XPS S2p spectrum.
microspheres embedded with a high amount of Si
nanopowders are shown in Figure 2. The designed
The structural characteristics of the MoS2–C
Si content in the composite microspheres was 60
composite
wt% based on MoS2. The composite microsphere
nanopowders are shown in Figure 3. The XRD
shown in Figure 2 had a more embossed structure
patterns of the composite microspheres with low
than that of the microspheres shown in Figure 1
and high amounts of Si nanopowders had broad
because of the high Si nanopowder content. The Si
peaks corresponding to a hexagonal MoS 2 structure
nanopowders were well dispersed within the
and sharp peaks of the Si phase. Broad peaks of
composite microspheres, as shown by arrows in
MoS2 layers were observed at 2θ of approximately
Figures 2d and 2e. The Si nanopowders located near
33° and 59°. However, the (002) reflections of the
the surface of the composite microsphere, as shown
stacked MoS2 layers at 2θ ~ 16° were not observed,
in Figure 2f, had a uniform MoS2–C composite
indicating the presence of only few-layered MoS2
coating. The elemental mapping images in Figure
[45-47]. Therefore, the results of the XRD patterns
2g also show uniform distributions of MoS 2, C, and
confirm
Si nanopowders within the composite microsphere.
nanosheets in the MoS2–C composite microspheres
The
embedded with Si nanopowders. Figures 3b-d
morphologies of the
MoS2–C
composite
microspheres
the
formation
embedded
of
with
few-layered
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MoS2
Research
Nano Res.
shows the XPS peaks of the MoS2–C composite
octahedral LixMoS2 [44-47,52-56]. The peak at
microspheres
Si
around 0.6 V corresponds to the conversion
nanopowders. The C1s XPS peak centered at 284.6
reaction, in which LixMoS2 was decomposed into
eV in Figure 3b, which corresponds to the binding
metallic Mo nanocrystals embedded in a Li2S
energy of the sp C–C bond, confirms the formation
matrix, and formation of a SEI layer on the MoS 2–C
of amorphous carbon by the carbonization process
surface, which resulted from electrochemically
of PVP [49]. Two strong Mo3d XPS peaks at around
driven electrolyte degradation [44-47,52-54]. The
229.4 and 232.5 eV in Figure 3c, which can be
third reduction peak located at 0.05 V is attributed
attributed to Mo3d5/2 and Mo3d3/2 binding energies
to the reaction to form Li–Si alloys [12-21]. In the
of MoS2, respectively, confirm the formation of
first anodic scan, three oxidation peaks attributed to
MoS2
ammonium
metallic Mo nanocrystals and Li–Si alloys were
tetrathiomolybdate [50,51]. The peaks at 162.0 and
observed. The first two anodic peaks observed at
163.1 eV, also shown in Figure 2d, can be indexed as
voltages of 0.3 and 0.55 V are attributed to the
S2p [50,51]. The negligible peak intensities of Si2p in
de-alloying reactions of Li–Si alloys [12-21]. The
Figure S6 confirm that the Si nanopowder particles
third anodic peak was observed at a voltage of 2.3
were completed covered by MoS2–C composite
V, which corresponds to the conversion reaction of
layers. The BET surface areas of the MoS2–C
metallic Mo and Li2S to MoS2 [52-56]. From the
composite microspheres with 0 and 30 wt% Si
second cycle onward, the reduction and oxidation
nanopowders
g-1,
peaks overlapped considerably, indicating the
respectively. The addition of Si nanopowders
superior reversible cycling performance of the
increased the porosity of the MoS2–C composite
MoS2–C composite microspheres with 30 wt% Si.
microspheres as shown in Figure S7.
Figure 4b shows the initial discharge and charge
embedded
with
30
wt%
2
by
decomposition
were
17.0
of
and
64.3
m2
The electrochemical properties of
the
MoS2–C
composite
microspheres with and without
embedded Si nanopowders are
presented in Figure 4. Figure 4a
shows the cyclic voltammogram
(CV)
curves
microspheres
of
the
composite
with 30 wt%
Si
during the first four cycles at a scan
rate of 0.1 mV s-1 in the voltage
range of 0.001–3 V. Three reduction
peaks
resulting
from
lithium
insertion into MoS2 and Si were
observed in the first cathodic scan.
The first reduction peak located at
1.4
V
is
attributed
to
the
intercalation of Li ions into the
hexagonal MoS2 lattice, followed
by
phase
transformation
to
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curves of the MoS2–C composite microspheres with
nanopowders decreased steadily to 1129 mA h g-1
and without embedded Si nanopowders at a
for the 100th cycle. However, the composite
current density of 1000 mA g-1. The initial discharge
microspheres with 30 wt% Si nanopowders showed
curves
with
stable discharge capacities during further cycling
embedded Si nanopowders had clear plateaus at
after achieving the maximum capacity at the 20 th
around 0.1 V owing to the reaction of Li with Si to
cycle, and had a value of 1020 mA h g-1 at the 100th
form Li–Si alloys. However, the obvious plateaus
cycle. The embedded Si nanopowders increased the
corresponding to the formation of LixMoS2 and Mo
capacities of the MoS2–C composite microspheres.
nanocrystals embedded in a Li 2S matrix were not
The Coulombic efficiencies of the composite
observed in the initial discharge curves of the three
microspheres
samples
amorphous-fluid-like
nanopowders (Figure 4c) had high values above
structure of the MoS2–C composite. The initial
99.5% from the 2nd cycle. The Li ion storage
discharge capacities of the MoS2–C composite
properties of the MoS2–C composite microspheres
microspheres
Si
were compared with those of the MoS2 powders
nanopowders were 1100, 1448, and 1746 mA h g ,
prepared by the spray pyrolysis process reported in
respectively, and their initial Coulombic efficiencies
the previous literature [52]. The bare MoS2 powders
were 69.5, 65.3, and 67.8%, respectively.
with filled and yolk-shell structures had discharge
of
the
composite
because
of
with
microspheres
the
0,
30,
and
60
wt%
-1
embedded
with
30
wt%
Si
The cycling performances of the three samples at
capacities of 362 and 687 mA h g-1 for 100th cycle at a
a current density of 1000 mA g-1 are shown in
current density of 1 A g-1, respectively. Embedding
Figure 4c. The MoS2–C composite microspheres
of Si nanopowders with high capacities improved
without Si nanopowders had discharge capacities of
the Li ion storage properties of the MoS2 material.
740 and 718 mA h g for the 2
-1
nd
and 100 cycles,
th
Electrochemical impedance spectroscopy (EIS)
respectively. The capacity retention of the MoS2–C
was
composite microspheres without Si nanopowders
electrochemical properties of the MoS2–C composite
measured from the 2
microspheres
that
the
nd
cycle was 97%, indicating
few-layered
to
confirm
embedded
with
the
30
superior
wt%
Si
composite
nanopowders. The impedance measurements were
microspheres had excellent cycling performance
carried out at room temperature before and after 10,
even at a high current density of 1000 mA g-1. The
30, 50, and 100 cycles at a current density of 1000
discharge capacities of the MoS2–C composite
mA g-1. The resulting Nyquist plots, shown in
microspheres with embedded Si nanopowders
Figure
increased during cycling for the first 20 cycles. The
medium-frequency range, which is assigned to the
gradual
Si
charge-transfer resistance of the electrodes, and a
nanopowders with a mean size of 85 nm during the
line inclined at ~45° to the real axis at low
first 20 cycles increased the capacities of the
frequencies, which corresponds to lithium diffusion
composite microspheres with increasing cycle
within the electrode [58,59]. The charge-transfer
number [28,57]. The increase in the oxidation peak
resistance of the electrode decreased after the first
intensity in the CV curves in Figure 3a, related to
cycle owing to the transformation of the crystalline
the de-alloying reaction of Li–Si alloys during
structure into an amorphous-fluid-like structure
cycling, also indicates gradual activation of the Si
during
nanopowders. After achieving the maximum value
charge-transfer resistance then remained constant
of 1390 mA h g , the discharge capacity of the
through the 100th cycle. The line inclined at ~45° to
composite
the real axis at low frequencies was also well
activation
of
MoS2–C
conducted
highly
crystalline
-1
microspheres
with
60
wt%
Si
S8,
the
indicate
first
a
semicircle
discharge
in
process.
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maintained during the first 100 cycles, indicating
the
good
lithium-diffusion
properties
of
the
electrode. The morphology of the composite
microsphere
embedded
with
30
wt%
Si
nanopowders after 100 cycles are shown in Figure
S9.
The
spherical
shape
of
the
composite
microsphere remained even after 100 cycles because
of their high structural stability during cycling as
Figure 5. Long-term cycling properties of the MoS2-C
the Si nanopowders with high capacities were
composite microspheres embedded with 30 wt% Si at a current
completely surrounded by the few-layered MoS2–C
density of 5.0 A g-1.
composite matrix. The elemental mapping images
revealed the uniform distributions of MoS2, C, and
microspheres
Si nanopowders within the composite microsphere
nanopowders at an extremely high current density
even after cycling. The elastic MoS2–C composite
of 5 A g-1. The gradual activation during cycling for
matrix accommodated the large volume change of
the
the Si nanopowders during the repeated process of
capacities of the composite microspheres. The
Li+ ion insertion–extraction. As a result, the
composite microspheres attained the maximum
formation of a stable SEI layer outside the surface
discharge capacity of 728 mA g h-1 after the first 100
during
electrochemical
cycles and then steadily maintained this capacity
properties of the composite microspheres, while the
for another 400 cycles. The discharge capacity of the
MoS2–C composite layer prevented the formation of
composite microspheres for the 500th cycle was 695
unstable SEI layers on the Si nanopowders.
mA h g-1, and their capacity retention measured
Furthermore,
from the 100th cycle was 95.4%.
cycling
improved
the
MoS2–C
the
composite
matrix
embedded
with
30
first 100 cycles increased
the
wt%
Si
discharge
exhibited high capacities and excellent cycling
performances, which were then shown by the
MoS2–C composite microspheres embedded with 30
4. Conclusions
In
summary,
a
few-layered
MoS2-carbon
wt% Si nanopowders. The rate performance of the
composite with high capacities and good cycling
MoS2–C composite microspheres embedded with 30
performance
wt% Si nanopowders is shown in Figure 4d. The
protective matrix of silicon nanopowders. Each
current densities increased stepwise from 0.5 to 7 A
MoS2–C composite microsphere embedded with Si
g-1; for each step, 10 cycles were measured to
nanopowders
evaluate the rate performance. The stable reversible
decomposing one droplet containing ammonium
discharge capacities of the composite microspheres
tetrathiomolybdate, PVP, and Si nanopowders. The
decreased from 1175 to 677 mA h g-1 as the current
MoS2–C composite material accommodated the
density increased from 0.5 to 7 A g-1. The discharge
large volume expansion of the Si nanopowders, but
capacity of the composite microspheres recovered
it also prevented the formation and propagation of
to 1190 mA h g-1 as the current density was restored
a SEI layer on the Si surface during repeated
to 0.5 A g-1.
cycling. The embedded Si nanopowders increased
Figure
5
shows
the
long-term
performance of the MoS2–C composite
cycling
was
was
successfully
formed
by
applied
drying
as
a
and
the capacity of the MoS2–C composite microspheres,
and
its
volume
fraction
in
the
composite
microspheres could be controlled by changing the
amount of Si nanopowders dispersed in the spray
| www.editorialmanager.com/nare/default.asp
Nano Res.
solution. The amount of MoS2 and carbon in the
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composite microspheres could also be controlled by
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concentrations
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ammonium
tetrathiomolybdate and PVP that were dissolved in
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[7] Choi, N. S.; Chen, Z.; Freunberger, S. A.; Ji, X.; Sun, Y. K.;
This work was supported by the National Research
Amine, K.; Yushin, G.; Nazar, L. F.; Cho, J.; Bruce, P. G.
Foundation of Korea (NRF) grant funded by the
Challenges
Korea
Double-Layer Capacitors. Angew. Chem. Int. Ed. 2012, 51,
government
(MEST)
(No.
Facing
Lithium
Batteries
and
Electrical
2012R1A2A2A02046367). This work was supported
9994–10024.
by the Creative Industrial Technology Development
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Program (10045141) funded By the Ministry of
High Energy Lithium Ion Batteries. Nano Today 2012, 7,
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Electronic Supplementary Material: Supplementary
material
(Schematic
diagram
of
one-pot
and
continuous spray pyrolysis process, FE-SEM image
of the Si nanopowders, TG curve of the MoS2-C
composite
MoS2-C
microspheres,
composite
Morphologies
microspheres
of
the
without
Si
nanopowders, XPS Si2p spectra of, Nyquist plots,
and TEM images after 100 cycles of the MoS2-C
composite microspheres embedded with 30 wt% Si
nanopowders) is available in the online version of
this
article
at
http://dx.doi.org/10.1007/s12274-***-****-*
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