construction ò 3D flowwerlike MoS2

Electrochimica Acta 115 (2014) 165–169

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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta

Construction of 3D flower-like MoS2 spheres with nanosheets as
anode materials for high-performance lithium ion batteries
Ting Yang, Yuejiao Chen, Baihua Qu, Lin Mei, Danni Lei, Haonan Zhang, Qiuhong Li ∗ ,
Taihong Wang
Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education, State Key Laboratory for Chemo/Biosensing and Chemometrics, Hunan
University, Changsha, PR China

a r t i c l e

i n f o

Article history:
Received 18 September 2013
Received in revised form 16 October 2013
Accepted 17 October 2013
Available online 1 November 2013
Keywords:
MoS2
3D flower-like
Nanosheets
Alcohol-assisted
Lithium ion battery

a b s t r a c t

In this work, we constructed 3D flower-like MoS2 spheres with nanosheets (less than 10 nm) by a simple
alcohol-assisted solvothermal route. It was found that the presence of alcohol enhanced the dispersity
of MoS2 samples, and the distilled water facilitated the formation of nanosheets through varying the
volume ratio of alcohol and distilled water. The prepared MoS2 samples delivered high initial discharge
capacity (1346 mA h g−1 at a current density of 100 mA g−1 ), good coulombic efficiency (77.49% retention
for the first cycle and ∼100% for the subsequent cycles), excellent cycling performance (947 mA h g−1 at
100 mA g−1 after 50 cycles) and remarkable rate behavior as anode materials for lithium ion batteries.
The superior behavior of MoS2 samples for lithium ion batteries can be ascribed to the thin nanosheets,
high specific surface area and their unique layered structure.
© 2013 Elsevier Ltd. All rights reserved.

1. Introduction
Lithium-ion batteries (LIBs) [1–3] have been extensively used in
portable electronic devices and even electronic vehicles to tackle
energy and environmental problems owing to their high capacity, no memory effect and environmental friendliness, etc. Up to
now, Graphite materials are most widely applied for anode materials in commercial LIBs with good cycling performance because
of their stable structure. However, their low theoretical capacity (372 mA h g−1 ), in some degrees, could not fulfill the gradually
increased demands for high capacity under the rapid development
of electronic technology [4,5]. Transition metal oxides and sulfides
[6–10] have been paid close attention as anode materials for LIBs
because they own high theoretical capacities. However, some of
them suffer from volume expansion, safety, and resource limited
issues, which restrict their use for next-generation battery applications.
Nowadays, molybdenum disulfide (MoS2 ) has been extensively
studied in different fields, such as, lubricants [11–13], transistors
[14–16] and supercapacitors [17,18], etc, owing to its special layered molecule structures in which Mo and S atoms are firstly
bounded by strong ionic/covalent forces to form two-dimensional
layers, and then these individual layers are further stacked by weak
van der Waals interaction [19,20]. The unique structure can permit

∗ Corresponding author.
E-mail addresses: (T. Yang), (Q. Li).
0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.
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Li ions to insert and extract without remarkable volume damage
because of the weak van der Waals interaction between MoS2 layers. On the other hand, it is quite significant to develop a rational
design to maximize their electrochemically active sites for redox
reactions through obtaining “opened” structures to further increase
their energy storage density [21–23].
In this paper, dispersive 3D flower-like MoS2 spheres with
nanosheets (MoS2 -1) were synthesized through a facile alcoholassisted solvothermal method. The function of alcohol and distilled
water were discussed and a possible growth mechanism was also
proposed according to the time-dependent experiments. We examine the electrochemical properties of MoS2 -1 as anode materials for
LIBs and the results revealed that it delivered a high initial capacities of 1346 mA h g−1 at 100 mA g−1 and the corresponding initial
coulombic efficiencies is 77.49%. The capacity of MoS2 -1 can still
remain 947 mA h g−1 after 50 cycles and it also exhibited excellent rate behaviors. All the remarkable results could be contributed
to large specific area, nano-sized structure and the unique layered structure of MoS2 . It also demonstrated that MoS2 is a very
promising candidate for next generation high performance LIBs.
2. Experimental
2.1. Synthesis of MoS2
Sodium molybdate (Na2 MoO4 ·2H2 O) and thiourea (NH2 CSNH2 )
were used as the reagents to synthesize MoS2 without any further purification. In a typical synthesis of MoS2 -1, 2 mmol of


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T. Yang et al. / Electrochimica Acta 115 (2014) 165–169

Fig. 1. SEM images of (a, b) MoS2 -1and (c, d) MoS2 -0.

Na2 MoO4 ·2H2 O was dissolved in 15 ml distil water, and then 15 ml
ethanol was added. After stirring for several minutes, 4 mmol of
NH2 CSNH2 was mixed. The resulting solution was transferred into
a 50 ml Teflon-lined stainlesss autoclave until it became transparent. The autoclave was heated at 200 ◦ C for 24 h in a furnace and
then cooled to room temperature naturally. Black products were
collected after thoroughly washed by distilled water and dried in
a vacuum oven. To make a contrast, a gathered MoS2 sample with
nanosheets (MoS2 -0) and scattered MoS2 spheres (MoS2 -2) were
obtained by using only distilled water and ethanol as solution and
keeping other reaction conditions unchanged, respectively.
2.2. Characterization
The morphology and microstructure of the as-synthesized
products were characterized by scanning electron microscope
(SEM, Hitachi S4800) and transmission electron microscope (TEM,
JEOL 2010) operated at an accelerating voltage of 200 kV. Their
crystal structures were examined by powder X-ray diffraction
(XRD, Siemens D-5000 diffractometer with Cu-Ka irradiation
˚
Their surface areas were tested by nitrogen
( = 1.5406 A).

adsorption/desorption analysis (Automated Physisorption and
Chemisorption Analyzer, micromeritics ASAP 2020).
2.3. Electrochemical measurements
The electrochemical measurements were done using CR2025type coin cells: the electrode materials were prepared by mixing
active materials (80 wt%), conductivity agent (10 wt%, carbon black,
Super-P-Li) and binder (10 wt%, carboxyl methyl cellulose (CMC),
Aldrich) in distilled water and absolute alcohol mixture and stirred
at a constant speed for 12 h in order to form a homogeneous
slurry. The well-mixed slurry was then spread onto a copper foil

and dried at 80 ◦ C in a vacuum oven for 12 h. A Celgard 2400
microporous polypropylene membrane was used as a separator. The electrolyte contained a solution of 1 M LiPF6 in ethylene
carbonate/dimethyl carbonate/diethyl carbonate (1:1:1, in wt%).
These cells were assembled in the glovebox (Super 1220/750,
Switzerland) filled with highly pure argon gas (O2 and H2 O levels
less than 1 ppm). The cells were aged for 12 h before the measurements to ensure percolation of the electrolyte to the electrodes. The
discharge and charge measurements were carried out on an Arbin

Fig. 2. The schematic of function of alcohol when preparing MoS2 .


T. Yang et al. / Electrochimica Acta 115 (2014) 165–169

167

Fig. 3. The TEM images of MoS2 -1.

Fig. 4. The possible growth mechanism of MoS2 -1 (all scale were 500 nm). The SEM images were obtained with the reaction time (b) 2, (c) 4 and (d) 24 h, respectively.

BT2000 system with the potential window of 0.01–3 V at current
density of 100 mA g−1 .

(S), so the dispersive MoS2 spheres were formed. The relationship
between them could be described as follows:
S=

3. Results and discussion
Fig. 1 shows the typical SEM images of prepared MoS2 samples. Large quantities of MoS2 spheres with the diameter of about
700 nm are clearly observed in Figs. 1a and S1a, while the MoS2 -0 is
agglomerated seriously (Fig. 1c). The formation of dispersed sphere

structures can be attributed to the use of ethanol and the possible mechanism is proposed (Fig. 2). On one hand, according to the
thermodynamic principle, the presence of alcohol can reduce the
solvation power of solvent because the alcohol possesses a lower
permittivity compared to distilled water, which result in a lower
solubility of product (C1 ) and a higher supersaturation of solvent

Fig. 5. The XRD spectrums of both MoS2 samples.

r=

C
C1
2

(1)
s−1 M

vRT s lnS

(2)

On the other hand, large numbers of ethanol molecules exist
because of the low ionization degree of ethanol, so during the formation of MoS2 , ethanol molecules can partially insert the interval
of MoS2 molecules for their similar size [24], and thus dispersive MoS2 spheres formed. We also obtained MoS2 spheres with
nanosheets by changing the volume ratio of the mixed solvent, as
depicted in Fig. S2. In order to further identify the mechanism, other
types of alcohols including ethylene glycol and glycerol, as the similar size of ethanol, were also used as the solvent in place of ethanol
to synthesize MoS2 , and the results showed that similar dispersive
MoS2 spheres with nanosheets were obtained as well (Fig. S3a and
b).

The enlarged SEM images (Fig. 1b and d) demonstrate that
MoS2 -1 and MoS2 -0 are comprised of very thin nanosheets with
the thickness about 7–10 nm (the insets of Fig. 1b and d). Meanwhile, the nanosheets of MoS2 -1 are much looser than MoS2 -0,
which is beneficial for obtaining large surface areas (the surface
area of MoS2 -1 is 23.34 m2 g−1 , while the MoS2 -0 is 12.86 m2 g−1 ).
The formation of nanosheets could be contributed to the utilization of distilled water, as depicted in Fig. S1b. With the absence of
distilled water, there are only dispersed nanoparticles with some
neglectable small nanosheets.
TEM was also carried out to characterize the structure of MoS2 1, as depicted in Fig. 3. The results are coincident with SEM. (The
TEM of MoS2 -0 is shown in Fig. S4.)
In order to study the growth process of 3D flower-like MoS2
spheres with nanosheets in detail, time-dependent experiments


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T. Yang et al. / Electrochimica Acta 115 (2014) 165–169

Fig. 6. CVs of (a) MoS2 -1 and (c) MoS2 -0 electrodes at a scan rate of 0.25 mV s−1 . Charge and discharge curves of (b) MoS2 -1 and (d) MoS2 -0 at a current density of 100 mA g−1 .

were carried out and a possible growth mechanism is proposed,
as depicted in Fig. 4. During the first 2 h (Fig. 4b), MoS2 spherical structure composed of nanoparticles could be obtained. When
the reaction time reached 4 h (Fig. 4c), there were some small
nanosheets scattered on the spherical surfaces. As the reaction time
was prolonged to 24 h (Fig. 4d), 3D flower-like MoS2 spheres with
nanosheets were obtained finally by using mixed solvent of ethanol
and distilled water.
Fig. 5 shows the XRD patterns of both MoS2 samples in different solvents. Though both samples exhibit a broadened feature in
XRD patterns due to low crystallinity, all the diffraction peaks are
in good agreement with the standard data for the pure phase of

MoS2 (JCPDS Card No. 37-1492). According to the previous studies
[25–27], the reaction consists of three steps: (a) the formation of
H2 S through the hydrolysis of thiourea; (b) the production of Mo
(IV) by reduction of Mo (VI); (c) the formation of MoS2 . The process
could be expressed as follows:
CS(NH2 )2 + 2H2 O → 2NH3 + CO2 + H2 S

(3)

4Na2 MoO4 + 15CS(NH2 )2 + 6H2 O → MoS2 + Na2 SO4
+ 6NaSCN + 24NH3 + 9CO2

Fig. 7. (a) Typical cycling behaviors and coulombic efficiency of both MoS2 samples.
(b) Rate capability of both MoS2 samples at different current densities.

(4)

The electrochemical property of prepared MoS2 -1 and MoS2 -0
were tested as anode materials of LIBs with the potential window of 0.01–3 V at the current density of 100 mA g−1 and the scan
rate of CVs is 0.25 mV s−1 . Fig. 6b and d shows the charge and
discharge curves of initial three cycles of MoS2 -1 and MoS2 -0,
respectively. In the first discharge process, two redox plateaus were
observed at ∼1.3 V and ∼0.6 V, which were coincident with the
first cathodic peaks in the CV sweeps, respectively. The plateau
at 1.3 V resulted from the formation of Lix MoS2 , and the plateau
at 0.6 V can be attributed to a conversion reaction process, which
first entails the in situ decomposition of MoS2 into Mo particles
embedded into a Li2 S matrix and then the formation of a gel-like
polymeric layer resulting from electrochemically driven electrolyte
degradation [28]. In the subsequent cycles, both products reveal

T. Yang et al. / Electrochimica Acta 115 (2014) 165–169

two potential plateaus at 1.9 V and 1.2 V, and the potential plateau
at 0.6 V disappears. In the charge process, remarkable potential
plateaus are observed at 2.2 V of both samples. These data of charge
and discharge curves agreed with the CV analysis. MoS2 -1 delivers
a high initial capacity of 1346 mA h g−1 , and it remains a reversible
capacity of 1043 mA h g−1 , while MoS2 -0 reveals a discharge and
charge capacities of 1325 mA h g−1 and 863 mA h g−1 , respectively.
The cycling performances and rate behaviors of both MoS2 samples are presented in Fig. 7a and b. MoS2 -1 and MoS2 -0 still exhibit
high capacities of 947 and 710 mA h g−1 after 50 cycles at the current density of 100 mA h g−1 (Fig. 7a). As shown in Fig. 7b, when the
current density increase to 200, 500, 1000 and 2000 mA g−1 , MoS2 1 and MoS2 -0 remain 906, 818, 707, 544 mA h g−1 and 698, 647,
554, 475 mA h g−1 , respectively. Even when the current density up
to 5000 mA g−1 , the prepared MoS2 -1 and MoS2 -0 still deliver 211
and 165 mA h g−1 . After the current density return to 100 mA g−1 ,
the two electrodes perform 931 and 715 mA h g−1 . Both MoS2 samples deliver excellent cycling and rate performance owing to its
unique layered structure, which can provide a relative stable environment for Li+ insertion and extraction when testing. Moreover,
MoS2 -1 shows a relative higher capacity than MoS2 -0, which can
be attributed to the formed dispersive 3D flower-like spheres with
larger specific surface area.
The excellent electrochemical performance of 3D flower-like
MoS2 spheres with nanosheets can be attributed to the following
factors:
(1) Dispersive 3D flower-like spheres with nanosheets structure owns lots of open spaces and large specific surface area, which
can afford a large number of reaction sites, so 3D flower-like MoS2
spheres with nanosheets can deliver a high specific capacitance. (2)
The nanometer size (7–10 nm) of MoS2 sheet and its distinct layered structure can reduce the diffusion length of ions within MoS2
and afford a stable environment during the charge and discharge

process, so we can obtain excellent cycling and rate performance.

Acknowledgements
We acknowledge the financial support of the National Natural
Science Foundation of China (Grant No. 21003041), the Specialized Research Fund for the Doctoral Program of Higher Education
of China (20120161110016), the Hunan Provincial Natural Science
Foundation of China (Grant No. 11JJ7004), and the Hunan Provincial Major Project of Science and Technology Department (Grant
No. 2012TT1004).
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at />2013.10.098.
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4. Conclusions

We have successfully synthesized 3D flower-like MoS2 spheres
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The tests show the unique MoS2 structure own high capacity and
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