Letter
pubs.acs.org/NanoLett
Polymer−Graphene Nanocomposites as Ultrafast-Charge and
-Discharge Cathodes for Rechargeable Lithium Batteries
Zhiping Song,†,⊥ Terrence Xu,† Mikhail L. Gordin,† Ying-Bing Jiang,‡ In-Tae Bae,§ Qiangfeng Xiao,∥
Hui Zhan,⊥ Jun Liu,¶ and Donghai Wang*,†
†
Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802,
United States
‡
Center for Micro-Engineered Materials, University of New Mexico, Albuquerque, New Mexico 87131, United States
§
Small Scale Systems Integration and Packaging Center, State University of New York at Binghamton, Binghamton, New York 13902,
United States
∥
General Motor Technical Center, Warren, Michigan 48092, United States
⊥
Department of Chemistry, Wuhan University, Wuhan 430072, People’s Republic of China
¶
Pacific Northwest National Laboratory, Richland, Washington 99352, United States
S Supporting Information
*
ABSTRACT: Electroactive polymers are a new generation of “green” cathode
materials for rechargeable lithium batteries. We have developed nanocomposites
combining graphene with two promising polymer cathode materials, poly(anthraquinonyl sulfide) and polyimide, to improve their high-rate performance.
The polymer−graphene nanocomposites were synthesized through a simple in
situ polymerization in the presence of graphene sheets. The highly dispersed
graphene sheets in the nanocomposite drastically enhanced the electronic
conductivity and allowed the electrochemical activity of the polymer cathode to
be efficiently utilized. This allows for ultrafast charging and discharging; the
composite can deliver more than 100 mAh/g within just a few seconds.
KEYWORDS: Lithium battery, cathode, polymer, graphene, nanocomposite
also been emphasized recently as a new generation of “green”
lithium battery electrodes due to their sustainability and
environmental benignancy. The electrochemical redox mechanism of an organic cathode is based on the reversible redox
reaction of the organic functional group, such as quinone,4,8,9,11
anhydride,5,7,10 and nitroxide radical,12,13 accompanied by the
association and disassociation of Li+ ions or electrolyte anions.
Scheme 1 shows the electrochemical redox reactions of Li ions
with poly(anthraquinonyl sulfide) (PAQS)9 and polyimide
(PI)10 based on the quinone and anhydride functional groups.
A polymer with a stable skeleton and highly electroactive
functional group can potentially be a high-power cathode
candidate because its redox reaction intrinsically has faster
kinetics than inorganic intercalation cathodes. For example,
anthraquinone can show electrochemical redox activity at a fast
scan rate of 1000 mV/s in cyclic voltammetry tests in
acetonitrile,14 and nitroxide radical polymer can still retain
97% of its theoretical capacity even at a charge rate of 1200 C
R
echargeable lithium batteries have been identified as one
of the most promising energy storage techniques,
especially as power sources for emerging applications such as
plug-in hybrid and electrical vehicles. Besides high energy
density, high power density is another indispensable requirement in these applications. In conventional Li-ion batteries,
cathode materials are typically lithium transition-metal oxides
or phosphates (e.g., LiCoO2 or LiFePO4) that can reversibly
de/reintercalate Li+ ions.1 Although many inorganic intercalation cathode materials have been demonstrated to show high
capacity retention at moderate C-rates such as 1 or 5 C, they
generally fail under more extreme charge−discharge conditions
comparable to those of supercapacitors, for example, releasing
all their energy within several seconds. This can be ascribed to
the relatively slow lithium ion diffusion kinetics in the bulk
particles of inorganic materials. For these materials, the most
efficient way to improve the ultrafast-charge and -discharge
performance is synthesizing nanosized-particle cathodes to
shorten the Li-ion transport pathway,2,3 which may cause other
problems such as low crystallinity and complicated synthesis.
Besides the conventional inorganic materials, organic cathode
materials, including small molecules4−7 and polymers,8−13 have
© 2012 American Chemical Society
Received: November 10, 2011
Revised: March 12, 2012
Published: March 26, 2012
2205
dx.doi.org/10.1021/nl2039666 | Nano Lett. 2012, 12, 2205−2211
Nano Letters
Letter
that graphene-based composites can greatly improve the
specific capacity, cycling stability, and rate capability of several
metal oxide anodes such as TiO2,18 SnO2,19,20 Co3O4,21,22 and
Mn3O4,23 and of LiFePO424 cathodes. For polymer cathode
materials, there are many reports on polymer−CNT
composites synthesized by in situ polymerization.25−29
Researchers have also made many attempts to create polyaniline−graphene composites as high-performance electrodes for
supercapacitors.30−33 Recently, Guo et al.34 attempted to use
graphene to enhance the electrochemical performance of a
nitroxide radical polymer cathode through a dispersion−
deposition process. However, the active material loading in
the electrode composite is only 10%, while the graphene
loading is as high as 60%. It is still necessary to develop
polymer−graphene nanocomposite cathodes that can fully
utilize graphene and obtain significantly enhanced electrochemical performance with low graphene loading. In this paper,
we use PAQS and PI (Scheme 1) as examples to demonstrate a
general one-pot synthesis of polymer−graphene nanocomposites with highly dispersed graphene, which show excellent
ultrafast-charge and -discharge performance as high-power
cathodes for rechargeable lithium batteries. We also illustrate
the effect of graphene content on the electronic conductivity,
surface area, and electrochemical performance of the nanocomposites.
Typical approaches to synthesize polymer−graphene composites are solvent blending, melt blending, and in situ
polymerization.16 Solvent blending is mostly suitable for
soluble polymers and melt blending always leads to poor
dispersion of graphene in the composite. In order to develop
polymer−graphene nanocomposites with well-dispersed graphene to fully utilize its high surface area and high electronic
conductivity, in situ polymerization was adopted, as illustrated
in Scheme 2. Functionalized graphene sheets (FGSs) prepared
by thermal expansion of graphite oxide35−37 were used in this
study because they show higher electronic conductivity than
chemically reduced graphene oxide. A mixture of single-layer
and multilayer graphene sheets was used without purification in
synthesis of the nanocomposites, and the existence of
multilayer graphene sheets does not affect the knowledge
obtained from this study. The polar aprotic solvent 1-methyl-2pyrrolidinone (NMP) was chosen as the solvent because it is
not only one of the best solvents for dispersing pristine
graphene,38,39 but also a good solvent in the synthesis of PAQS
and PI.9,10 This eliminated the need to add surfactants or
Scheme 1. Electrochemical Redox Reactions of Li Ions with
PAQS and PI Based on Quinone and Anhydride Functional
Groups, Respectively
and discharge rate of 60 C in aqueous electrolyte.13 Moreover,
the robust backbone of the polymer can prevent the unwanted
dissolution in nonaqueous electrolyte that is always suffered by
small molecules, and thereby achieve good cycling stablility.9 In
our previous study, some polymers have already shown high
capacity, high Coulombic efficiency, and good cycling
stability,9,10 but the intrinsic electronic insulation and low
mass density of the polymers resulted in unsatisfactory highrate performance and necessitated addition of large amounts of
conductive carbon (e.g., the mass ratio of PAQS/acetylene
black is 1:1 in ref 9) during electrode fabrication for high
utilization of the active materials.
Conductive coating (e.g., carbon, metal oxides, and
conductive polymers) and incorporating conductive additive
to form composites have been demonstrated as efficient
approaches to improving the electron transport in electrodes,
and thus improving the high-rate performance. So far, graphene
and graphene sheets, one or a few layers of atomically thick,
two-dimensional sheets composed of sp2 carbon atoms
arranged in a honeycomb structure,15 have been identified as
excellent conductive additives in nanocomposites due to their
extraordinary electronic conductivity.16 Other advantages of
graphene and graphene sheets in formation of nanocomposites
include its high surface area (theoretical value of 2630 m2/g)17
for improved interfacial contact and potential of low
manufacturing costs compared to mesoporous carbon and
carbon nanotubes (CNTs). Many successful examples show
Scheme 2. In Situ Polymerization Process of PAQS-FGS or PI-FGS Nanocomposite
2206
dx.doi.org/10.1021/nl2039666 | Nano Lett. 2012, 12, 2205−2211
Nano Letters
Letter
polymer matrix, with no obvious aggregation even at the high
FGS loading of PAQS-FGS-b. Figure 1d is a high-magnification
TEM image of PAQS-FGS-b showing a graphene sheet coated
with a polymer layer. Elemental mapping using electron energy
loss spectroscopy (EELS) (Figure 1e,f) was used to establish
the distribution of polymer on the graphene surface by
detecting carbon and sulfur signals from PAQS. The rather
uniform distribution of sulfur along with carbon over the whole
area of PAQS-FGS-b confirms the existence and homogeneous
coating of PAQS on the FGS surface. TEM investigation also
showed the polymer coating of PI samples to be uniform, and
the morphology differences are mainly from the polymer itself.
The flowerlike particles (Figure 1g) with particle size of 0.5−1
μm are observed in pure PI samples. For the PI-FGS-b
nanocomposite, both SEM and TEM images (Figure 1h,i)
consistently show that FGSs are homogeneously coated with
flowerlike PI polymer particles (∼100 nm in size) smaller than
those found in pure PI. The uniform polymer coating on the
FGS surface and the corresponding excellent dispersion of
graphene in the nanocomposite can mainly be attributed to the
NMP solvent, which facilitates both graphene dispersion and
the polymerization process, and to the noncovalent π−π
interaction between the graphene surface and the backbones of
PAQS and PI owing to the conjugated aromatic rings.40
The electrochemical performance of the polymer−graphene
nanocomposites was characterized by galvanostatic charge−
discharge tests of CR2016-type coin cells (see Supporting
Information). The cathodes contained 60 wt % active material
(polymer or polymer−graphene composite), 30 wt %
conductive carbon, and 10 wt % polytetrafluoroethylene
(PTFE) binder. PAQS and its nanocomposites were tested
sequentially at rates of 0.1 C, 0.5 C, 2 C, 10 C, and 0.1 C,
charging and discharging between 1.5 and 3.5 V (vs Li+/Li) for
20 cycles at each rate. As shown in Figure 2a, the discharge
capacity of PAQS, after the initial several activation cycles,
stabilizes at 177 mAh/g and a utilization ratio of 79% can be
achieved relative to the theoretical capacity of 225 mAh/g. The
utilization ratio is defined as a ratio of discharge capacity
contributed by polymer at 0.1 C based on polymer mass
relative to the theoretical capacity of the polymer (see Table 1).
In contrast, the reversible capacity of the PAQS-FGS-a and
PAQS-FGS-b nanocomposites is 187 and 165 mAh/g at 0.1 C
based on the whole mass of the composite, respectively. Under
the same test conditions, FGS itself gives a specific discharge
capacity of only 32 mAh/g at 0.1 C between 1.5 and 3.5 V
(Figure S4 in the Supporting Information), which is consistent
with previous reports.18,41 Thus the discharge capacity
contributed by the graphene sheets is only 2 and 8 mAh/g
for PAQS-FGS-a (6 wt % FGS) and PAQS-FGS-b (26 wt %
FGS), respectively. Deducting this FGS capacity from the total,
the addition of graphene can be seen to significantly improve
the utilization ratio of PAQS to 88 and 95% for PAQS-FGS-a
and PAQS-FGS-b, respectively (Table 1). Moreover, it is found
that the rate performance becomes much better as the FGS
content increases. In particular, PAQS-FGS-b discharged at 10
C still retains 90% of its discharge capacity at 0.1 C. Since this
performance exceeded our expectations, we further tested these
samples at more extreme current rates of up to 200 C. In Figure
2b we compare the discharge specific capacity versus C-rate of
PAQS and all its nanocomposites. Comparing PAQS-FGS-a
and PAQS-CNT-c, we observe that the nanocomposite
containing graphene shows better performance than that
containing a similar amount of carbon nanotubes, which is
perform graphene surface modification to improve its
dispersion, which is a big impediment for many graphenebased nanocomposites synthesized in aqueous solution.18,20,22,23
In our specific synthetic process (Scheme 2), FGSs were first
dispersed well in NMP by sonication. 1,5-Dichloroanthraquinone (DCAQ) or 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) was then added as precursor of PAQS or PI,
respectively, and completely dissolved in NMP. After the
addition of a condensing agent (anhydrous sodium sulfide for
PAQS or ethanediamine for PI), the polymer chains formed
through a polycondensation reaction at high temperature. In
the final product, FGSs are coated with the in situ formed
polymer and homogeneously embedded in the polymer matrix.
In the obtained polymer−graphene nanocomposite, the welldispersed graphene functions as an electron transport pathway
and provides intimate contact with the polymer to enable fast
charge transfer and thus ultrafast charging and discharging. This
one-pot synthesis of polymer−graphene nanocomposite is
similar to that of bare polymer except for the presence of the
graphene and an extra sonication step, so it can easily be
extended to other polymers synthesized in polar aprotic
solvent. In order to study the effect of FGS content on the
electrochemical performance of the nanocomposites, we have
synthesized two composite samples for each polymer with
different FGS weight percentage, named PAQS-FGS-a (6 wt %
FGS), PAQS-FGS-b (26 wt % FGS), PI-FGS-a (6 wt % FGS),
and PI-FGS-b (11 wt % FGS). PAQS-CNT-c (5 wt % CNT)
was also synthesized through the same approach for
comparison between graphene and carbon nanotubes (Table
1).
Table 1. Physical Properties of Polymers and Polymer−
Graphene Nanocomposites
sample
PAQS
PAQSFGS-a
PAQSFGS-b
PAQSCNT-c
PI
PI-FGS-a
PI-FGS-b
additive
content
(wt %)
electronic
conductivity
(S/cm)
surface area
(cm2/g)
utilization
ratioa (%)
0
6
<1 × 10−11
2.9 × 10−5
30
161
79
88
26
6.4 × 10−3
153
95
5
2.8 × 10−6
127
85
0
6
11
<1 × 10−11
1.2 × 10−5
3.5 × 10−4
71
115
156
42
49
62
Utilization Ratio = (Ccomposite − CFGS × PFGS)/[(1 − PFGS) ×
Cpolymer, theoretical], where C is discharge capacity at 0.1 C and P is weight
percentage in the composite.
a
To discover the morphology of the polymer−graphene
nanocomposites, the samples were characterized by both
scanning electron microscopy (SEM) and transmission electron
microscopy (TEM). The SEM image in Figure 1a and TEM
image in Figure 1b are quite consistent in showing that the size
of each FGS is several micrometers and there is a uniform and
thick PAQS coating layer on both sides of the FGS. The porous
structure of the polymer layer should also be noted because it
helps increase the contact area between the cathode and
electrolyte and thus improve the Li-ion conduction. From the
cross-section TEM image of PAQS-FGS-b (Figure 1c), it is
found that FGSs are rather homogeneously distributed in the
2207
dx.doi.org/10.1021/nl2039666 | Nano Lett. 2012, 12, 2205−2211
Nano Letters
Letter
Figure 1. (a) SEM image of PAQS-FGS-a; (b) low-magnification TEM image of PAQS-FGS-a; (c) cross-section TEM image of PAQS-FGS-b; (d)
high-magnification TEM image of PAQS-FGS-b; (e,f) corresponding carbon and sulfur elemental mapping images of PAQS-FGS-b; (g) SEM image
of pure PI; (h) SEM image of PI-FGS-b; (i) low-magnification TEM image of PI-FGS-b.
consistent with our previous study on TiO2−FGS nanocomposite electrodes.18 It is also worth noting that PAQS-FGSb maintains a discharge capacity of 100 mAh/g even at 100 C,
when the whole discharge process takes a mere 16 s. To the
best of our knowledge, there are rarely reports on organic or
inorganic42 cathode materials that can obtain such capacity
under both ultrafast charging and discharging. Figure 2c shows
the charge−discharge curves of PAQS-FGS-b at different Crates and reveals that the polarization becomes serious at above
20 C. Cyclic voltammetry (CV) was also conducted to compare
the electrochemical behavior of PAQS and its nanocomposites
with different FGS loading (Figure 2d). The cyclic voltammogram at a scan rate of 1 mV/s is quite consistent with the
charge−discharge performance at high current rate. Polarization becomes smaller as the FGS loading increases, as
evidenced by smaller separation of the redox peaks and elevated
peak height and peak area.
Similar performance improvement was observed for the PI
samples. Although PI’s theoretical capacity is 367 mAh/g based
on a four-electron redox process, usually only two electrons can
be reversibly transferred (Scheme 1) in a practical charge/
discharge process and thus about half of the theoretical capacity
can be achieved.10 As shown in Figure 3a, bare PI delivers a
discharge capacity of 156 mAh/g at 0.1 C, corresponding to a
utilization ratio of 42% compared to the theoretical capacity of
367 mAh/g (Table 1). After adding 6 and 11 wt % graphene,
the capacity of PI-FGS-a and PI-FGS-b increases to 172 and
205 mAh/g, corresponding to a polymer utilization ratio of 49
and 62%, respectively. That is to say, graphene can significantly
elevate the number of electrons transferred in each structure
unit from 1.7 per unit of PI to 2.0 per unit of PI-FGS-a and 2.5
per unit of PI-FGS-b. A similar phenomenon was also observed
for the nitroxide radical polymer cathode.34 Besides the specific
capacity, the high-rate performance is also greatly improved as
the graphene loading increases; the discharge capacity of PIFGS-b at 10 C remains 68% of that at 0.1 C, delivering 135
mAh/g within about 2 min, while pure PI shows no
electrochemical activity at this current rate.
On the basis of the above electrochemical performance, we
conclude that formation of graphene-based nanocomposites
can significantly improve not only the specific capacity, but also
the rate capability of polymer cathode materials, especially at
ultrahigh current rates. To explain the outstanding ultrafastcharge and -discharge performance of polymer−graphene
2208
dx.doi.org/10.1021/nl2039666 | Nano Lett. 2012, 12, 2205−2211
Nano Letters
Letter
Figure 2. (a) Cycling performance of PAQS and its composites at different C-rates; (1.5−3.5 V, 1 C = 225 mA/g). (b) Discharge specific capacity
versus C-rate of PAQS and its composites. (c) Voltage profiles of PAQS-FGS-b at different C-rates. (d) CV curves of PAQS and its composites at a
scan rate of 1 mV/s. The specific capacity is calculated based on the whole mass of the composite.
Figure 3. (a) Cycling performance of PI and its composites at different C-rates; (1.5−3.5 V, 1 C = 367 mA/g). (b) Voltage profiles of PI-FGS-b at
different C-rates. The specific capacity is calculated based on the whole mass of the composite.
nanocomposites, we compared several physical properties
including additive content, electronic conductivity, and surface
area of each sample, as listed in Table 1. The FGS or CNT
content was estimated based on its amount added in the
synthesis and the final yield of the composite, since there was
no obvious loss of FGSs or CNTs during the entire synthesis
process. The electronic conductivity was obtained by measuring
the resistance of a disk of film (diameter = 1.6 cm, thickness =
∼100 μm) made from the corresponding material and PTFE
binder with 6:1 mass ratio, which is the same as the cathode
film but without the conductive carbon. The Brunauer−
Emmett−Teller (BET) surface area of each sample was
determined by N2 sorption isotherm. The utilization ratio of
the active material is also listed in the table to show the
tendency of performance improvement. It is found that the
polymer−graphene nanocomposites possess higher surface area
and several magnitudes higher electronic conductivity compared to the pure polymers. Higher graphene content leads to
higher electronic conductivity and thus higher active material
utilization ratio.
As previously mentioned, in polymer cathode materials for
rechargeable lithium batteries, electroactive organic functional
groups intrinsically have faster redox reaction kinetics43 than
conventional inorganic intercalation cathode materials and the
flexible polymer chain structure is probably more stable than
rigid crystalline particles during the fast charge−discharge
process. Li-ion conduction in polymer cathodes can also be
facilitated by the good penetration of electrolyte into the
polymer due to the porous structure of polymer particles. Thus,
we believe the major impediment to polymer cathodes
2209
dx.doi.org/10.1021/nl2039666 | Nano Lett. 2012, 12, 2205−2211
Nano Letters
achieving ultrafast charging and discharging is the inherent
electronic insulation. As shown in Table 1, the electronic
conductivity of both PAQS and PI is significantly enhanced by
incorporating well-dispersed graphene in the nanocomposite.
Higher graphene loading can further increase the electronic
conductivity and improve the rate performance, as illustrated by
PAQS-FGS-a and PAQS-FGS-b. In addition, the high surface
area of well-dispersed FGSs compared to CNTs can promote
intimate contact between polymer and graphene at the
nanoscale level to ensure efficient electron transport in the
nanocomposites, which may explain the performance difference
between PAQS-FGS-a and PAQS-CNT-c. Further morphological studies on fully charged and discharged PAQS-FGS-a
after 20 cycles show no obvious morphological difference
between fresh and cycled polymer−graphene nanocomposites
(Figure S5 in Supporting Information). At both the charged
and discharged states, the graphene sheets are still coated with
the PAQS layer, which indicates the polymer and graphene
sheets can maintain intimate contact during the electrochemical
charge/discharge process and thus enable good high-rate
performance. Moreover, the increased surface area of the
nanocomposites can further facilitate the contact between
cathode and electrolyte and thereby improve the Li-ion
conduction.
In conclusion, we have developed novel polymer−graphene
nanocomposites as high-rate cathode materials for rechargeable
lithium batteries. We have successfully synthesized PAQS-FGS
and PI-FGS nanocomposites through a simple in situ
polymerization process in NMP solvent. In the polymer−
graphene nanocomposite, either PAQS or PI can be coated on
the FGS surface uniformly and FGSs are well-dispersed in the
polymer matrix due to the thorough dispersion of FGSs in
NMP and the nonconvalent interaction between the graphene
surface and the polymers. The surface area and electronic
conductivity of the nanocomposite materials are significantly
enhanced, leading to great improvement of the battery
performance. Compared to the pure polymer, the nanocomposites possess much higher active material utilization
ratios and superior ultrafast-charge and -discharge ability; for
example, PAQS-FGS-b can deliver 100 mAh/g within just 16 s.
The outstanding high-rate performance is explained by the fast
redox kinetics, the fast electron transfer, and the benefits to Li−
ion conduction due to increased surface area in the polymer−
graphene nanocomposites. Since the battery performance of
these kinds of polymer−graphene nanocomposites is so
attractive and the synthesis is very simple, it gives important
insights into improving battery performance of other polymer
cathodes.
■
ACKNOWLEDGMENTS
■
REFERENCES
This work was primarily supported by Penn State startup fund
and the Assistant Secretary for Energy Efficiency and
Renewable Energy, Office of Vehicle Technologies of the
U.S. Department of Energy under Contract No. DE-AC0205CH11231, Subcontract No. 6951378 under the Batteries for
Advanced Transportation Technologies (BATT) Program. J. L.
would like to acknowledge the support by the U.S. Department
of Energy (DOE), Office of Basic Energy Sciences, Division of
Materials Sciences and Engineering, under Award KC020105FWP12152 and the Laboratory Directed Research and
Development Program at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory
operated for DOE by Battelle under Contract DE_AC0576RL01830.
(1) Ellis, B. L.; Lee, K. T.; Nazar, L. F. Chem. Mater. 2010, 22, 691−
714.
(2) Okubo, M.; Hosono, E.; Kim, J.; Enomoto, M.; Kojima, N.;
Kudo, T.; Zhou, H.; Honma, I. J. Am. Chem. Soc. 2007, 129, 7444−
7452.
(3) Hosono, E.; Kudo, T.; Honma, I.; Matsuda, H.; Zhou, H. Nano
Lett. 2009, 9, 1045−1051.
(4) Chen, H.; Armand, M.; Demailly, G.; Dolhem, F.; Poizot, P.;
Tarascon, J.-M. ChemSusChem 2008, 1, 348−355.
(5) Walker, W.; Grugeon, S.; Mentre, O.; Laruelle, S.; Tarascon, J.M.; Wudl, F. J. Am. Chem. Soc. 2010, 132, 6517−6523.
(6) Geng, J.; Bonnet, J.-P.; Renault, S.; Dolhem, F.; Poizot, P. Energy
Environ. Sci. 2010, 3, 1929−1933.
(7) Renault, S.; Geng, J.; Dolhem, F.; Poizot, P. Chem. Commun.
2011, 47, 2414−2416.
(8) Le Gall, T.; Reiman, K. H.; Grossel, M. C.; Owen, J. R. J. Power
Sources 2003, 119−121, 316−320.
(9) Song, Z.; Zhan, H.; Zhou, Y. Chem. Commun. 2009, 448−450.
(10) Song, Z.; Zhan, H.; Zhou, Y. Angew. Chem., Int. Ed. 2010, 49,
8444−8448.
(11) Liu, K.; Zheng, J.; Zhong, G.; Yang, Y. J. Mater. Chem. 2011, 21,
4125−4131.
(12) Oyaizu, K.; Nishide, H. Adv. Mater. 2009, 21, 2339−2344.
(13) Koshika, K.; Sano, N.; Oyaizu, K.; Nishide, H. Chem. Commun.
2009, 836−838.
(14) Belding, S. R.; Limon-Petersen, J. G.; Dickinson, E. J. F.;
Compton, R. G. Angew. Chem., Int. Ed. 2010, 49, 9242−9245.
(15) Allen, M. J.; Tung, V. C.; Kaner, R. B. Chem. Rev. 2010, 110,
132−145.
(16) Verdejo, R.; Bernal, M. M.; Romasanta, L. J.; Lopez-Manchado,
M. A. J. Mater. Chem. 2011, 21, 3301−3310.
(17) Peigney, A.; Laurent, Ch.; Flahaut, E.; Bacsa, R. R.; Rousset, A.
Carbon 2001, 39, 507−514.
(18) Wang, D.; Choi, D.; Li, J.; Yang, Z.; Nie, Z.; Kou, R.; Hu, D.;
Wang, C.; Saraf, L. V.; Zhang, J.; Aksay, I. A.; Liu, J. ACS Nano 2009,
3, 907−914.
(19) Paek, S.-M.; Yoo, E.; Honma, I. Nano Lett. 2009, 9, 72−75.
(20) Wang, D.; Kou, R.; Choi, D.; Yang, Z.; Nie, Z.; Li, J.; Saraf, L.
V.; Hu, D.; Zhang, J.; Graff, G. L.; Liu, J.; Pope, M. A.; Aksay, I. A. ACS
Nano 2010, 4, 1587−1595.
(21) Wu, Z.-S.; Ren, W.; Wen, L.; Gao, L.; Zhao, J.; Chen, Z.; Zhou,
G.; Li, F.; Cheng, H.-M. ACS Nano 2010, 4, 3187−3194.
(22) Yang, S.; Feng, X.; Ivanovici, S.; Müllen, K. Angew. Chem., Int.
Ed. 2010, 49, 8408−8411.
(23) Wang, H.; Cui, L.-F.; Yang, Y.; Sanchez Casalongue, H.;
Robinson, J. T.; Liang, Y.; Cui, Y.; Dai, H. J. Am. Chem. Soc. 2010, 132,
13978−13980.
(24) Zhou, X.; Wang, F.; Zhu, Y.; Liu, Z. J. Mater. Chem. 2011, 21,
3353−3358.
ASSOCIATED CONTENT
S Supporting Information
*
Detailed description of the synthesis, characterization and
electrochemical measurements. This material is available free of
charge via the Internet at http://pubs.acs.org.
■
■
Letter
AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected].
Notes
The authors declare no competing financial interest.
2210
dx.doi.org/10.1021/nl2039666 | Nano Lett. 2012, 12, 2205−2211
Nano Letters
Letter
(25) Sivakkumar, S. R.; Kim, D.-W. J. Electrochem. Soc. 2007, 154,
A134−A139.
(26) Sivakkumar, S. R.; MacFarlane, D. R.; Forsyth, M.; Kim, D.-W. J.
Electrochem. Soc. 2007, 154, A834−A838.
(27) Kim, D.-W.; Sivakkumar, S. R.; MacFarlane, D. R.; Forsyth, M.;
Sun, Y.-K. J. Power Sources 2008, 180, 591−596.
(28) Sivakkumar, S. R.; Howlett, P. C.; Winther-Jensen, B.; Forsyth,
M.; MacFarlane, D. R. Electrochim. Acta 2009, 54, 6844−6849.
(29) Canobre, S. C.; Almeida, D. A. L.; Fonseca, C. P.; Neves, S.
Electrochim. Acta 2009, 54, 6383−6388.
(30) Wang, D.-W.; Li, F.; Zhao, J.; Ren, W.; Chen, Z.-G.; Tan, J.; Wu,
Z.-S.; Gentle, I.; Lu, G. Q.; Cheng, H.-M. ACS Nano 2009, 3, 1745−
1752.
(31) Wu, Q.; Xu, Y.; Yao, Z.; Liu, A.; Shi, G. ACS Nano 2010, 4,
1963−1970.
(32) Yan, J.; Wei, T.; Shao, B.; Fan, Z.; Qian, W.; Zhang, M; Wei, F.
Carbon 2010, 48, 487−493.
(33) Yan, J.; Wei, T.; Fan, Z.; Qian, W.; Zhang, M.; Shen, X.; Wei, F.
J. Power Sources 2010, 195, 3041−3045.
(34) Guo, W.; Yin, Y.-X.; Xin, S.; Guo, Y.-G.; Wan, L.-J. Energy
Environ. Sci. 2012, 5, 5221−5225.
(35) Schniepp, H. C.; Li, J.-L.; McAllister, M. J.; Sai, H.; HerreraAlonso, M.; Adamson, D. H.; Prud’homme, R. K.; Car, R.; Saville, D.
A.; Aksay, I. A. J. Phys. Chem. B 2006, 110, 8535−8539.
(36) McAllister, M. J.; Li, J.-L.; Adamson, D. H.; Schniepp, H. C.;
Abdala, A. A.; Liu, J.; Herrera-Alonso, M.; Milius, D. L.; Car, R.;
Prud’homme, R. K.; Aksay, I. A. Chem. Mater. 2007, 19, 4396−4404.
(37) Ramanathan, T.; Abdala, A. A.; Stankovich, S.; Dikin, D. A.;
Herrera-Alonso, M.; Piner, R. D.; Adamson, D. H.; Schniepp, H. C.;
Chen, X.; Ruoff, R. S.; Nguyen, S. T.; Aksay, I. A.; Prud’homme, R. K.;
Brinson, L. C. Nat. Nanotechnol. 2008, 3, 327−331.
(38) Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.;
De, S.; McGovern, I. T.; Holland, B.; Byrne, M.; Gun’ko, Y. K.;
Boland, J. J.; Niraj, P.; Duesberg, G.; Krishnamurthy, S.; Goodhue, R.;
Hutchison, J.; Scardaci, V.; Ferrari, A. C.; Coleman, J. N. Nat.
Nanotechnol. 2008, 3, 563−568.
(39) Coleman, J. N. Adv. Funct. Mater. 2009, 19, 3680−3695.
(40) Kozhemyakina, N. V.; Englert, J. M.; Yang, G.; Spiecker, E.;
Schmidt, C. D.; Hauke, F.; Hirsch, A. Adv. Mater. 2010, 22, 5483−
5487.
(41) Yoo, E.; Kim, J.; Hosono, E.; Zhou, H.-S.; Kudo, T.; Honma, I.
Nano Lett. 2008, 8, 2277−2282.
(42) Kang, B.; Ceder, G. Nature 2009, 458, 190−193.
(43) Lee, S. W.; Yabuuchi, N.; Gallant, B. M.; Chen, S.; Kim, B.-S.;
Hammond, P. T.; Shao-Horn, Y. Nat. Nanotechnol. 2010, 5, 531−537.
2211
dx.doi.org/10.1021/nl2039666 | Nano Lett. 2012, 12, 2205−2211