Preparation of graphene/TiO2 anode materials for lithium-ion batteries by a novel precipitation method

Article abstract of DOI:10.1016/j.materresbull.2011.08.046

This paper reports a large-scale production route for graphene/TiO ₂ nanocomposites using water-based in situ precipitation method. In this method, freshly prepared graphene oxides/TiO₂ obtained by precipitating Ti(SO₄)

Full text of DOI:10.1016/j.materresbull.2011.08.046

Materials Research Bulletin 46 (2011) 2403–2407
Contents lists available at SciVerse ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Preparation of graphene/TiO anode materials for lithium-ion batteries
2
by a novel precipitation method
a,b
a,
a
a
a,c
a
Yan-Huai Ding , Ping Zhang *, Hu-Ming Ren , Qin Zhuo , Zhong-Mei Yang , Yong Jiang
a
Institute of Rheology Mechanics, Xiangtan University, Hunan 411105, China
b
Chemical Process Simulation and Optimization Research Center of Ministry of Education, Xiangtan University, Hunan 411105, China
c
College of Chemistry, Xiangtan University, Hunan 411105, China
A R T I C L E I N F O
A B S T R A C T
This paper reports a large-scale production route for graphene/TiO nanocomposites using water-based
Article history:
2
Received 29 April 2011
in situ precipitation method. In this method, freshly prepared graphene oxides/TiO
precipitating Ti(SO with NH O was subjected to heat treatment in the presence of N
resulted in the formation of graphene/TiO nanocomposites. Graphene/TiO composites prepared by our
2
obtained by
Received in revised form 21 July 2011
Accepted 24 August 2011
Available online 1 September 2011
4
)
2
3
H
2
2
, which
2
2
method were found to be suitable as anode materials for lithium ion batteries because of its stable
cycling performance and high capacity.
Keywords:
ß 2011 Elsevier Ltd. All rights reserved.
A. Nanostructure
B. Chemical synthesis
C. Electrochemical measurement
D. Electrochemical properties
1
. Introduction
Graphene, a single atomic layer of graphite with sp bonded
has been investigated extensively [18–20]. It was found the
electrochemical properties of TiO
graphene or GO nanosheets. In this paper, we present a novel
precipitation method for the preparation of graphene/TiO
2
were greatly enhanced by
2
carbon atoms in a honeycomb structure, has attracted great
interest in recent years because of its high surface area, high
chemical stability, and unique mechanical properties. This unique
nanostructure holds great promise for potential applications in
nanoelectronics, nanocomposites, lithium ion batteries (LIBs) and
nanosensors [1–4]. Up to now, several methods have been
developed to prepare graphene, which include chemical vapor
deposition (CVD) [5,6], mechanical exfoliation [7], aerosol pyroly-
sis [8], solvothermal synthesis [9], epitaxial growth and chemical
reduction [10–12]. Among them, chemical method provides the
most effective and economical way to prepare graphene in large
quantity from natural graphite [13]. The attachment of inorganic
nanomaterials onto graphene surface, forming a new functional
material, is one of the most important applications for graphene.
2
nanocomposites. The advantages of the procedure are that it is
less finicky, low-cost, and therefore more effective for large-scale
production.
2. Experimental
2.1. Preparation of GO
GO was prepared by chemical oxidation of natural graphite
using modified Hummers’ method. Natural graphite powder and
NaNO were mixed with H SO in an ice bath with vigorous
agitation. Then KMnO was added to the suspension under stirring
condition and the temperature of the system was maintained at
83 K. Later the ice-bath was removed and the mixture was heated
3
2
4
4
2
TiO is an inexpensive and environmentally benign material
2
that has been extensively used in a wide range of applications
including photocatalysts, LIBs and nanoelectronics [14–18].
Recently, the utilization of various carbonaceous materials, such
as mesoporous carbon, carbon nanotubes, GO and graphene for
at 303 K for 10 h. Next 100 ml deionized water was added
dropwise to the container carefully. The reaction was allowed to
proceed for 2 h at 363 K, and then the resultant bright-yellow
2 2
suspension was diluted and further treated with 30 ml 30% H O .
2
TiO -based nanocomposites for potential anode materials for LIBs
The mixture was followed by centrifugation and carefully washing
by HCl and deionized water until near pH 7. The obtained product
was dried under vacuum to remove the water (323 K). Colloidal
dispersions of individual GO nanosheets were prepared with the
aid of ultrasound.
*
Corresponding author. Tel.: +86 731 58293861, fax: +86 731 58293240.
E-mail address: zhangp@xtu.edu.cn (P. Zhang).
0025-5408/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2011.08.046

2
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Y.-H. Ding et al. / Materials Research Bulletin 46 (2011) 2403–2407
2
.2. Preparation of graphene/TiO
2
3. Results and discussions
At first, 10 ml Ti(SO
The mixture and 15 ml NH
alcohols which contained GO and polyethylene glycol (PEG 2000).
The obtained precipitation was followed by centrifugation and
carefully washing by anhydrous ethanol. The prepared precursor
was dried at 353 K for 24 h, and then subjected to heat treatment at
4
)
2
and 10 ml distilled water were mixed.
ÁH O were added dropwire to the 30 ml
Precipitation method is widely used in preparation of anode
and cathode materials for LIBs, but it has not been reported to
3
2
produce graphene/TiO
with NH O as starting materials [16,21]. As shown in Scheme 1,
GO possess reactive carboxylic acid and hydroxyl moieties, which
are easily bind to metal ions. While addition of Ti(SO into
2 4 2
from Precipitation method using Ti(SO )
3 2
H
4 2
)
4+
8
73 K in presence of N
2
to formation graphene/TiO
2
nanocompo-
suspensions of GO, complexation takes place between Ti and
oxygen functionalities. Oxygen functionalities at the GO surface act
sites. As comparison, pure TiO
without adding of GO.
2
was prepared by two-step method
as reactive sites for the nucleation and growth of Ti(OH)
nanoparticles. After heat treatment at high temperature, Ti(OH)
4
4
2.3. Characterization of materials
and GO are converted to TiO
2
and graphene, respectively.
composites on mica
The morphology of GO and graphene/TiO
2
The morphology of GO and graphene/TiO
atomic force microscopy (AFM, DI MultimodeNS-3D, VEECO) and
transmission electron microscopy (TEM, JEM-2100, JEOL). Powder
2
was characterized by
surface was characterized by AFM. As shown in Fig. 1a, AFM
analysis confirms that evaporated dispersions of GO is comprised
of isolated nanosheets. The GO nanosheet has lateral dimensions of
several micrometers and a thickness of 1.5 nm. The average
thickness of graphene obtained in this method is about 1 nm with
lateral dimensions range from several hundred nanometers to
several micrometers. Both surface of the graphene are covered
X-ray diffraction was carried out using a Bruker D8 Advance X-ray
˚
a irradiation, l = 1.5 A). The content of
diffractometer (Cu K
graphene in composites was about 3% confirmed by thermal
gravimetric analysis.
Electrochemical performance of the electrodes was evaluated
by assembling model coin-type cells using lithium foil as a counter
2 2
with TiO nanoparticles. The diameter of TiO on graphene is in the
range of 5–20 nm, which can be ascribed to the large numbers of
nucleation site on the surface of GO. The average diameter of as
and reference electrode, Celgard 2400 as a separator, and 1 M LiPF
6
solution in EC + DMC (1:1, v/v) as an electrolyte. The working
electrode was prepared using the mixture of calcined graphene/
prepared pure TiO
diameter decreased with the adding of GO.
As shown in Fig. 2a, graphene/TiO nanocomposites with 3%
2
was about 30 nm, which illustrated the
TiO
2
, carbon black and poly (vinylidene fluoride) (PVDF) binder
2
dispersed in N-methylpyrrolidone (NMP) solution. Test cells were
assembled in an argon-filled glove box. Charge–discharge experi-
ments were performed in Neware battery testing system (BTS 5 V/
concentration of graphene shows diffraction peaks corresponding
to (1 0 1), (1 0 3), (0 0 4), (1 1 2), (2 0 0), (1 0 5), and (2 1 1) planes
of anatase structure, similar to that of pure TiO
2
nanoparticles. As
= 12.48,
1
0 mA, Neware).
shown in insert, a dominant peak of GO is observed at 2u
2 2
Fig. 1. Morphology of GO and graphene/TiO composites on mica surface. (a) GO and (b) graphene/TiO .

Y.-H. Ding et al. / Materials Research Bulletin 46 (2011) 2403–2407
2405
2
Scheme 1. Growth mechanism of graphene/TiO composites by two-step method.
À1
corresponding to an interlayer distance of 0.72 nm. GO nanosheets
converted to graphene after treated at high temperature. But no
diffraction peaks of graphene were found in the composites due to
the low content. The Raman spectra of GO before and after
the figure, GO exhibited Raman shifts at ꢀ1350 and 1590 cm
corresponding to the D and G bands, respectively. After heat-
treatment at 873 K, the D and G bands of graphene/TiO
2
located at
À1
ꢀ1345 and 1584 cm . The increase of D/G ratio indicated the
deposition of TiO
2
were presented in Fig. 2b. As can be seen from
introduction of defects into reduced GO [22].
2
Fig. 2. XRD patterns and Raman spectra of the GO and graphene/TiO composites. (a) XRD patterns and (b) Raman spectra.

2
406
Y.-H. Ding et al. / Materials Research Bulletin 46 (2011) 2403–2407
(
a) 200
0.2C
180
160
140
120
100
80
60
0
5
10
15
20
25
30
35
40
45
50
Cycle number
b) 200
Fig. 3. Voltage–capacity relationship of graphene/TiO
2 2
and raw anatase TiO at
(
0.2 C.
1
80
60
40
1C
The effect of graphene on Li-ion insertion/extraction properties
in the TiO was investigated. As can be seen from Fig. 3, the
graphene/TiO shows a slope profile of voltage–capacity relation-
ship at both the charge and discharge state, similar to that of pure
anatase-phase TiO . There are distinct potential plateaus at 1.75
and 1.85 V for discharging (Li insertion) and charging (Li
extraction), respectively. For graphene/TiO , the discharge capaci-
ty at voltage plateau is larger than that of pure anatase-phase TiO
indicating the better reversibility of Li insertion/extraction in
graphene/TiO . Compared to raw TiO , the first discharge capacity
of nanocomposites increased from 160 mAh/g to 172 mAh/g. A
typical TEM image of the TiO on graphene surface is shown in
1
2
3
C
2
1
5
C
1
0C
2
120
100
80
2
2
,
2
2
60
2
0
5
10
15
20
25
30
35
40
insert. It is apparent that the composites consisted of uniform
nanoparticles with diameters of about 10 nm. The higher capacity
Cycle number
might be ascribed to a shorter diffusion length for both the electron
+
2
Fig. 5. Cyclic performance of graphene/TiO at different current density.
and Li , and a larger electrode/electrolyte contact area of TiO
2
+
nanoparticles compared with pure TiO
insertion and extraction [23–25].
2
, which facilitate the Li
is in accordance with the plateaus of the discharging/charging
+
The electrochemical behaviors of the TiO
2
and graphene/TiO
2
curves. The insertion/extraction of Li in graphene/TiO
2
was highly
. The low Li and electronic
conductivity is the main obstacle for the practical applications of
TiO . The insulative GO nanosheets in precursor converted to high
conductive graphene under heat treatment, resulting in the
improvement of conductivity in graphene/TiO anode materials.
Shown in Fig. 5a is the cyclic performance of graphene/TiO at a
+
composites prepared in this work were characterized by cyclic
voltammograms. Only one pair of cathodic/anodic peaks (located
reversible compared to pure TiO
2
at 1.60, 2.08 V for TiO
2
and 1.68, 2.01 V for graphene/TiO
2
2
composites) can be observed in Fig. 4. The location of redox peaks
2
2
current density of 0.2 C. The discharge and charge capacities match
each other well during cycling due to the good reversibility of
TiO2
graphene/TiO2
graphene/TiO
approximately 100% with an excellent cycling stability even in the
0th cycles. The high-rate cycling behavior of graphene/TiO
2
. It is also observed the coulombic efficiency is
5
2
nanocomposites is illustrated in Fig. 5b. As can be seen, when
applying a current density of 1 C, the capacity is about 160 mAh/g
in the 1st cycle and 150 mAh/g in the 10th cycle. At a current
density of 3 C, the discharging capacity reduces a little to 140 mAh/
g. Even running at 10 C, the discharge capacity of graphene/TiO
2
maintained at 110 mAh/g without obvious fading in the 10th cycle.
Brunauer–Emmett–Teller (BET) surface analysis shows the specific
2
surface area of graphene without deposition of TiO
2
was 326.3 m /
2
g, which was significant lower than theoretical value (ꢀ2600 m /
g). The decrease of surface area was caused by aggregation of
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
graphene. Graphene/TiO
specific surface area of 125.5 m /g. The excellent high-rate
performance of nanocomposites could be ascribed to the large
2
nanocomposites exhibited a high
2
+
Potential Li/Li (V)
Fig. 4. Cyclic voltammograms of as-prepared TiO
2
and nanocomposites at a scan
surface area of graphene/TiO
composites.
2
and the fast Li insertion/extraction in
rate of 0.05 mV/s.

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2407
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