Bi2O3@reduced graphene oxide nanocomposite: An anode material for sodium-ion storage

Article abstract of DOI:10.1002/cplu.201402394

Abstract The high capacity, excellent cyclability, and good rate capability of reduced graphene oxide (rGO) anchored with Bi₂O₃ nanocomposite for sodium-ion batteries is reported. A simple reduction method is adapted to deposit spherical Bi₂O₃ nanoparticles on the surface of rGO sheets. The surfactant cetyltrimethylammonium bromide (CTAB) plays a major role in controlling the morphology of the Bi₂O₃ nanoparticles. This Bi₂O₃@rGO nanocomposite has the advantages of high reversible capacity with a capacity retention (at high rate) of 70.2 % after 200 cycles at a current density of 350 mA g^-1. This superior performance can be attributed to the fact that rGO sheets hamper the volume expansion of Bi₂O₃ nanoparticles and result in faster diffusion of Na⁺ ions (diffusion coefficient: 5.12×10^-8 cm²s^-1) and smaller internal resistance (84.17 Ω) compared with pristine Bi₂O₃ nanoparticles. The results suggest that anchoring rGO sheets with metal oxides is one of the simplest ways to enhance the electrochemical performance of sodium-ion batteries.

Full text of DOI:10.1002/cplu.201402394

DOI: 10.1002/cplu.201402394
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Bi2O3@Reduced Graphene Oxide Nanocomposite: An
Anode Material for Sodium-Ion Storage
Chandrasekaran Nithya*[a]
The high capacity, excellent cyclability, and good rate capabili-
ty of reduced graphene oxide (rGO) anchored with Bi2O3 nano-
composite for sodium-ion batteries is reported. A simple re-
duction method is adapted to deposit spherical Bi2O3 nanopar-
ticles on the surface of rGO sheets. The surfactant cetyltrime-
thylammonium bromide (CTAB) plays a major role in control-
ling the morphology of the Bi2O3 nanoparticles. This
Bi2O3@rGO nanocomposite has the advantages of high reversi-
ble capacity with a capacity retention (at high rate) of 70.2%
after 200 cycles at a current density of 350 mAgÀ1. This superi-
or performance can be attributed to the fact that rGO sheets
hamper the volume expansion of Bi2O3 nanoparticles and
result in faster diffusion of Na+ ions (diffusion coefficient:
5.12”10À8 cm2 sÀ1) and smaller internal resistance (84.17 W)
compared with pristine Bi2O3 nanoparticles. The results suggest
that anchoring rGO sheets with metal oxides is one of the sim-
plest ways to enhance the electrochemical performance of
sodium-ion batteries.
Introduction
Increasing demand for energy and growing environmental
threats, such as CO2 pollution and global warming, are forcing
us to find alternative energy-storage technologies to replace
conventionally used fossil fuel resources. Lithium-ion batteries
are more suitable than other battery technologies as energy-
storage devices to satisfy the current energy crisis. The electric
vehicles market and portable electronics are dominated by lith-
ium-ion batteries owing to their high energy and power densi-
ty.[1,2] However, the demand for lithium-ion batteries has in-
creased and the limited lithium sources are not sufficient to
meet future energy requirements. The next possible alternative
candidate to replace lithium is sodium,[3] which is more abun-
dant and cheaper than lithium, particularly for large-scale ap-
plications. However, the opportunity to explore electrode ma-
terials is less than that of lithium batteries because the large
ionic size of the Na+ ion (1.02 Š)[4] does not facilitate intercala-
tion/deintercalation into structures in the same way as lithium-
ion batteries. Hence, this provides an opportunity to explore
new electrode materials for sodium-ion batteries.
Petroleum coke[5] was the first anode material to be investi-
gated for sodium-ion batteries. This material generates a rever-
sible capacity of 85 mAhgÀ1. In 2000, Stevens and Dahn made
a significant contribution to the development of sodium-ion
batteries, with which they achieved a reversible capacity of
300 mAhgÀ1 when using hard carbon as an anode material.[6]
Various types of anode materials, such as carbonaceous materi-
als, metals, metal oxides and their composites, titanium-based
oxides, and organic anode materials, have subsequently been
investigated for sodium-ion storage.[7–18] However, the chal-
lenges associated with sodium-ion batteries are cyclability and
rate capability, which restricts meeting the need for a high
energy density. The reason for failure in the carbon-based
anode material is that the Na+ ion is large, so it cannot interca-
late/deintercalate easily between graphitic layers.[19,20] Metals,
metal oxides and intermetallic alloys, are successfully devel-
oped as anode materials for lithium- and sodium-ion batteries.
However, these materials suffer from severe volume expansion
during cycling, which leads to mechanical failure in the anode
materials. For example, Gu et al. reported the failure mecha-
nism of SnO2 nanowires for sodium-ion batteries in which al-
loying/dealloying resulted in pores, which led to a structure of
tin particles confined in a hollow matrix of Na2O.[21] These
pores greatly enhance the electrical impedance and result in
poor cyclability of SnO2. To overcome these kinds of issues in
anode materials, highly conductive reduced graphene oxide
(rGO), the in-plane electrical conductivity[22] of which is
5880 ScmÀ1, has been used as a matrix to hold the active
anode materials during cycling. Recently, bismuth-based oxide
(p-Bi2O3/Ni) and sulfide materials have shown superior electro-
chemical performance for lithium-ion batteries[23–25] To the best
of my knowledge, no reports are available to date on Bi2O3
anode material for sodium-ion batteries. Herein, for the first
time, Bi2O3/rGO composite anode material has been investigat-
ed for sodium-ion batteries, in which the rGO matrix greatly
enhances the cycling stability of Bi2O3 anode material.
[a] Dr. C. Nithya
Department of Energy and Environment
National Institute of Technology
Tiruchirappalli 620 015 (India)
E-mail: nithyajcs@gmail.com
Results and Discussion
Figure 1 shows the XRD patterns of graphene oxide (GO),
Bi2O3, and rGO/Bi2O3 (1:5) anode materials. The XRD pattern of
GO depicts the main peak reflection centered at 2q=10.618,
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201402394.
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Figure 1. XRD patterns of GO, Bi2O3, and rGO/Bi2O3.
which is consistent with that reported in the literature.[26,27] All
peaks of Bi2O3 match well with the standard ICDD pattern
(ICDD file no. 00-001-0709). The rGO/Bi2O3 (1:5) composite XRD
pattern reflects both phases of rGO and Bi2O3, in which the
peak centered at 2q=24.878 corresponds to the formation of
rGO[28] (reduction of GO to rGO by using NaBH4) in the synthe-
sized composites. The XRD pattern of the rGO/Bi2O3 composite
does not show any impurity peaks, and also the absence of
the peak at 2q=10.618 indicates that the reducing agent com-
pletely reduces the GO phase to rGO. The rGO content (15% in
the composites) in the synthesized composite is determined
by thermogravimetric analysis (TGA)/differential thermal analy-
sis (DTA; Figure S1 in the Supporting Information).
Figure S2 in the Supporting Information presents SEM
images of GO, Bi2O3 without adding CTAB, Bi2O3 with CTAB,
and rGO/Bi2O3 composite anode materials. The SEM image of
GO (Figure S2a in the Supporting Information) shows the
micron-sized flake-like morphology, which appears as randomly
arranged flakes on top of each other. The size of the flakes
varies from 0.5 to 2 mm. Figure S2b in the Supporting Informa-
tion clearly depicts that Bi2O3 particles synthesized without
CTAB appear as irregularly shaped and sized particles with seri-
ous agglomeration (particle size >2 mm). Figure S2c in the
Supporting Information presents a SEM image of the Bi2O3 ma-
terial (with CTAB), which has a spherical morphology with
a small degree of agglomeration and a particle size of around
200 nm. Thus, it can be clearly understood that the CTAB sur-
factant controls the morphology and size of the synthesized
particles. According to Li et al.,[29] interactions between the sur-
factant molecules and precursors contribute to the formation
of homogeneous nanosized particles. The SEM image of the
rGO/Bi2O3 composite (Figure S2d in the Supporting Informa-
tion) clearly shows Bi2O3 particles and rGO sheets, in which the
Bi2O3 particles exist on the surface of rGO sheets. The particle
size is about 10–100 nm. Figure 2 shows TEM images and se-
lected-area electron diffraction (SAED) patterns of Bi2O3 and
rGO sheets. The size of the Bi2O3 particle is around 10–20 nm.
The TEM image of rGO clearly shows the layer by layer assem-
bly of sheets arranged together and the sizes of the sheets are
Figure 2. SAED patterns of Bi2O3 (a), rGO (c), and rGO/Bi2O3 (e). TEM images
of Bi2O3 (b), rGO (d), and rGO/Bi2O3 composite (f).
about 100 nm. Evidence obtained from the TEM image of the
rGO/Bi2O3 composite (Figure 2e), in which the particle size is
around 10–20 nm, also clearly depicts the rGO sheets and
Bi2O3 particles. This is further confirmed by the SAED pattern
of the rGO/Bi2O3 composite. This pattern contains bright and
dim rings that correspond to the rGO sheets and Bi2O3 parti-
cles. The d spacings calculated from the SAED patterns are
1.391 (400), 1.952 (220), and 2.763 (200) Š for Bi2O3 and 3.621 Š
(002) for rGO,[26] which are in close agreement with JCPDS file
no. 52-1007 (for Bi2O3). The above results are consistent with
XRD observations.
Laser Raman spectroscopy is an essential tool and strongly
sensitive to graphene and graphene-based materials.[30,31] Usu-
ally, two modes of vibration are observed for carbon-based
materials, namely, D (A1g mode) and G (owing to first-order
scattering of the E2g phonon) bands. The D and G bands corre-
spond to sp3- and sp2-hybridized carbon atoms, respectively, in
which the D band is related to a disordered mode and the G
band related to an ordered mode. Figure 3 shows the laser
Raman spectra of GO and rGO/Bi2O3 composites. Two bands
are observed in the laser Raman spectrum of GO, in which the
D band is centered at n˜ =1349 cmÀ1 and the G band is at n˜ =
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Figure 3. Laser Raman spectra of GO and rGO/Bi2O3 nanocomposite.
1583 cmÀ1. These two bands are slightly redshifted in the laser
Raman spectrum of the rGO/Bi2O3 composite material. The D
band is observed at n˜ =1355 cmÀ1 and the G band is at n˜ =
1591 cmÀ1 in the composites in which the intensity of D band
increases after reduction. The intensity ratio of these two
bands (ID/IG) is extensively used to determine the degree of dis-
order in graphene-related materials. This is because GO sheets
may split into smaller domains, which means that more defects
will be created after reduction. From these observations, we
can confirm that most of the oxygenated groups are removed
from the GO domains; therefore, the vacant sites are created
owing to oxygen vacancies in the lattice, which results in de-
fects in the rGO sheets.
Figure 4a shows the initial charge/discharge profiles of
Bi2O3, rGO, and rGO/Bi2O3 anodes cycled between the potential
limits of 0.01 and 2.0 V at a current density of 140 mAgÀ1. For
bare rGO, the specific charge capacity is 501 mAhgÀ1, whereas
pristine Bi2O3 exhibits a charge capacity of 600 mAhgÀ1. The ir-
reversible capacity loss in the first cycle is 528 and
497 mAhgÀ1 for rGO and Bi2O3, respectively. The rGO/Bi2O3
nanocomposite demonstrates the highest charge capacity of
669 mAhgÀ1, which is almost 97% of the theoretical capacity,
whereas the irreversible capacity loss is only 227 mAhgÀ1. The
irreversible capacity losses are attributed to the electrolyte un-
dergoing a reaction with the active sites and decomposition of
the electrolyte taking place on the electrode surface to form
a solid–electrolyte interface (SEI) in the first charge/discharge
process.[32–34] According to Dahn et al.,[35] the irreversible ca-
pacity loss of metal oxides is due to the formation of Li2O on
the surface of the anode, which consumes lithium and forms
a metallic phase. The conversion reaction of Bi2O3 with Na is
expected to proceed as shown in Equation (1).
Figure 4. a) Charge/discharge curves. b) Cycling performance at a current
density of 140 mAgÀ1. c) Cycling performance of rGO/Bi2O3 over 200 cycles.
to Li insertion, Bi2O3 also undergoes an alloying reaction with
Na+ ions and consumes 12 Na ions, so the theoretical capacity
of Bi2O3 for sodium-ion batteries is calculated to be
690 mAhgÀ1. Compared with pristine Bi2O3 and rGO, the com-
posite rGO/Bi2O3 exhibits a high charge capacity, which is at-
tributed to the smaller particles of rGO/Bi2O3 decreasing the
sodium-ion diffusion path length; thereby increasing the
charge capacity. The poor capacity of pristine Bi2O3 is due to
the presence of agglomerated larger particles, which slightly
hinder Na+ diffusion; thereby decreasing the charge
capacity.
Bi2O3 þ 12 Na ! 3 Na2O þ 2 Na3Bi
ð1Þ
According to the groups of Li[23] and Jung,[26] complete con-
version of Bi2O3 with Li should involve 12 Li ions, so the theo-
retical capacity of Bi2O3 is calculated to be 690 mAhgÀ1. Similar
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Figure 4b depicts the cycling performance of Bi2O3, rGO, and
rGO/Bi2O3 composites over 50 cycles at a current density of
140 mAgÀ1. The 50th cycle charging capacities of Bi2O3, Bi2O3
without CTAB (Figure S3 in the Supporting Information), rGO,
and rGO/Bi2O3 are 417, 310, 102, and 607 mAhgÀ1, respective-
ly; the corresponding capacity retentions are 69.5, 59.3, 20.3,
and 89.8%, respectively. The poor performance of Bi2O3 is as-
cribed to the fact that it suffers from crumbling and pulveriza-
tion, and consequent disconnection with the current collector
results in fast capacity fading[36–38] The capacity retention of
rGO is also poor compared with those of Bi2O3 and rGO/Bi2O3
owing to restacking of rGO sheets during the charge/discharge
process. This consumes a large amount of Na+, which reduces
the charge/discharge capacity in subsequent cycles. The ca-
pacity fading of the rGO/Bi2O3 composite is 9.26%. Further-
more, the cell was cycled up to 200 times (Figure 4c) at a cur-
rent density of 350 mAgÀ1. After 200 cycles, the cell retains a re-
versible charge capacity of 413 mAhgÀ1, which is approximate-
ly 70% of the initial charge capacity. This outstanding per-
formance of the rGO/Bi2O3 nanocomposites is ascribed to the
unique spherical morphology of the material. From TEM obser-
vations (Figure 2e), it can be clearly understood that the Bi2O3
nanoparticles are embedded in flexible rGO sheets. Figure 5a
shows the ex situ XRD pattern of the rGO/Bi2O3 electrode after
the first charging cycle (alloying). The pattern matches well
with the P63/mmc space group,[39] and it confirms the forma-
tion of Na3Bi. The cycled (after 200 cycles) rGO/Bi2O3 electrode
was further examined with ex situ TEM, as shown in Figure 5b
and c. It can be clearly observed that the original morphology
of the rGO sheets is preserved; however, the shape of the
Bi2O3 particles is slightly altered owing to the reaction with
Na+ ions. This enhanced performance is due to the nanocrys-
talline nature of Bi2O3 and flexible rGO sheets contributing to
the alleviation of stress and crumbling of the electrode active
materials, which results in high capacity and capacity retention.
Furthermore, the flexible rGO sheets also act as a conductive
matrix for electron transfer during the charge/discharge pro-
cess. As a result, the electrode architecture can be sustained
during cycling, which improves the sodium-ion storage capa-
bility.
Figure 6a and b presents the rate capability curves and cy-
cling performance of the rGO/Bi2O3 composite at different cur-
rent densities. It delivers different capacities at different current
densities, namely, 678 mAhgÀ1 at 140 mAgÀ1, 581 mAhgÀ1 at
350 mAgÀ1, 562 mAhgÀ1 at 700 mAgÀ1, and 529 mAhgÀ1 at
1400 mAgÀ1. Even after 40 cycles, it delivers 213 mAhgÀ1 at
a high current density of 3500 mAgÀ1. The same cell was
cycled again at a current density of 140 mAgÀ1; it recovered
the original capacity of 670 mAhgÀ1, even after 50 cycles.
From this, it can be clearly understood that the rGO/Bi2O3
nanocomposite withstand high rate cycling.
Figure 5. a) Ex situ XRD pattern of the rGO/Bi2O3 composite after the first
charging cycle (Na3Bi formation, P63/mmc space group). b) TEM image of the
cycled rGO/Bi2O3 electrode. c) SAED pattern of the cycled rGO/Bi2O3 elec-
trode.
tween sodium and bismuth oxide in a multistep manner. The
peak at 1.64 V corresponds to the reduction of Bi2O3 to Bi and
the strong peak at 0.63 V is attributed to both SEI formation
and an alloying reaction between Bi and Na, which forms
Na3Bi. Likewise, the peak obtained at 0.89 V in the anodic
region corresponds to the dealloying process of Na3Bi (Fig-
ure 5a), and the broad peak obtained at 1.74 V in the anodic
region is attributed to the formation of Bi2O3 from Bi. The
shape of this peak is similar to the peak obtained in the catho-
dic region, which is ascribed to the Bi2O3 and rGO/Bi2O3 anode
materials possessing high reversibility. Moreover, the shape of
the voltammogram of Bi2O3 and rGO/Bi2O3 appears to be
Figure 6c shows the cyclic voltammograms of Bi2O3 and the
rGO/Bi2O3 nanocomposite recorded between 0.01 and 2 V at
a scan rate of 0.1 mVsÀ1. Multipeak features (1.64 V (hump) can
be observed at approximately 0.63 V (strong peak) in the
cathodic region; one strong peak at approximately 0.89 V in
the anodic region) indicates that the reaction proceeds be-
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Charging:
2 Na3Bi ! 6 Na þ 2 Bi
2 Bi þ 3 Na2O ! Bi2O3 þ 6 Na
ð4Þ
ð5Þ
Figure 7 shows Nyquist plots of Bi2O3 and the rGO/Bi2O3
composite. In each plot there is a semicircle in the high- to
medium-frequency range, which characterizes charge-transfer
resistance, accompanied by a straight line in the low-frequency
region, which corresponds to Warburg impedance owing to
diffusion behavior.[40,41] The obtained Nyquist plot is divided
into three regions, namely, 1) an intersection in the high-fre-
quency region in the real axis, 2) only one depressed semicircle
Figure 7. Nyquist plot of Bi2O3 and the rGO/Bi2O3 nanocomposite.
Figure 6. a) Charge/discharge curves of rGO/Bi2O3 at different current densi-
ties. b) Rate capability of rGO/Bi2O3 at different current densities. c) Cyclic
voltammogram of Bi2O3 and the rGO/Bi2O3 nanocomposite.
in the medium-frequency region, and 3) a sloped line in the
low-frequency region. Both anodes exhibit similar behavior,
except for the size of the semicircle in the medium-frequency
region. Z-view software is used to fit the experimental data to
simulate the obtained experimental data in the present study
(an equivalent circuit is proposed to simulate the obtained ex-
perimental data and is shown in Figure S4 in the Supporting
Information). The circuit elements are Rs (solution resistance in
the bulk electrolyte), RSEI and CSEI (the ionic resistance and ca-
pacitance, respectively, present in the SEI layers), Rct and Cdl
(charge-transfer resistance and double-layer capacitance, re-
spectively, in the electrode–electrolyte interface), and W (the
almost identical, which clearly reveals that the rGO sheets acts
as a matrix that supports the electron-transfer reaction. Thus,
Bi2O3 undergoes the reactions given in Equations (2)–(5) during
charging and discharging:
Discharging:
Bi2O3 þ 6 Na ! Bi þ 3 Na2O
2 Bi þ 6 Na ! 2 Na3Bi
ð2Þ
ð3Þ
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Warburg element, which characterizes diffusion of Na+ ions).
The value of RSEI plays a significant role in determining the
overall internal resistance in the cell, which is 380.43 (for Bi2O3)
and 63.93 W (for rGO/Bi2O3). The Rct values of Bi2O3 and the
rGO/Bi2O3 nanocomposite are 34.16 and 20.24 W, respectively.
Compared with the electrodes composed of rGO/Bi2O3 and
Bi2O3, the rGO/Bi2O3 has a much smaller charge-transfer resist-
ance (84.17 W), which indicates that rGO in the composite as-
sists in the reduction of the interfacial charge-transfer resist-
ance.[42] The Na+-ion diffusion characteristics of Bi2O3 and rGO/
Bi2O3 were calculated by using Equation (6).[43,44]
water (50 mL) by using an ultrasonicator (Model PG Analytics,
230 V, 50 Hz) for 1 h. The dispersed solution was removed from the
sonicator bath and transferred to a magnetic stirrer. Bi(NO3)3·5H2O
(7 g) and CTAB (0.5 g) were added to the above GO dispersion
under continuous stirring. NaBH4 (10 g) was added dropwise to
this mixture and the resulting solid was separated by filtration. For
the preparation of pristine Bi2O3, the same procedure was repeat-
ed, but without the addition of GO. After washing with deionized
water to remove excess ClÀ ions as well as surfactant and other
ions, Bi2O3 and the rGO/Bi2O3 composite were obtained by drying
for 24 h in vacuo.
TGA (PerkinElemer/TGA4000) of the rGO/Bi2O3 nanocomposite was
analyzed from 0 to 7008C at a heating rate of 108CminÀ1 in air to
understand the thermal decomposition behavior, as well as the
percentage of carbon present in the composites. The synthesized
GO and rGO/Bi2O3 composites were characterized by means of an
X-ray diffractometer (Rigaku Ultima III XRD) at a scan rate of
1 8 minÀ1 by using CuKa radiation (l=1.5418 Š), while the voltage
and current were held at 40 kV and 20 mA (2q=10–808). The mor-
phology and microstructure of the composites were characterized
by means of SEM (VEGA3 SB, TESCAN Instruments) and TEM (FEI-
Tecnai-20 G2). Raman spectra were recorded for the synthesized
materials in a Renishaw InVia laser Raman microscope with a He–
Ne laser (l=633 nm).
R2T2
2A2n4F4C2o2
ð6Þ
D ¼
Here, R is the gas constant, T is the absolute temperature, n is
the number of electrons per molecule oxidized, A is the active
surface area, F is the Faraday constant, C is the concentration
of Na+ ions, D is the diffusion coefficient, and s is the coeffi-
cient of Warburg impedance obtained from the intersection of
the straight line on the real axis.[44] This equals Rs +RctÀ2s2Cdl.
The diffusion coefficient (DNa) value of rGO/Bi2O3 (5.12”
10À8 cm2 sÀ1) is higher than that of the pristine Bi2O3 anode
(6.18”10À9 cm2 sÀ1). The above results confirmed that Na+ ions
diffused very easily into the interior sites of rGO/Bi2O3 network
compared with the pristine Bi2O3 network. This is supported by
the fact that formation of a very thick surface film over the
active electrodes prevents the diffusion process, as well as ef-
fective charge transfer from or to the electrode/electrolyte in-
terface.[45]
The anodes (pristine Bi2O3 and rGO/Bi2O3 composite) were pre-
pared by mixing 80 wt% prepared composites, 10 wt% Super-P
carbon, and 10 wt% polyvinylidene fluoride (PVDF) binder in N-
methylpyrrolidone (NMP) to form a homogeneous slurry. The slurry
was coated on copper foil and dried under ambient conditions. Cir-
cular discs with a diameter of 18 mm were punched out and dried
in vacuo at 1208C for 12 h. The mass loading of the active materi-
als for Bi2O3 and rGO/Bi2O3 were 1.05 and 1.12 mgcmÀ2, respective-
ly. Finally, coin cells of 2032 type were assembled inside an argon-
filled glove box by using the prepared anode as a working elec-
trode, sodium foil as a reference electrode, celgard 2400 as the
separator, and NaClO4 in 1:1 ethylene carbonate/propylene carbon-
ate (EC/PC) as the electrolyte. Charge–discharge studies of the coin
cells were performed by using a programmable battery tester at
a constant current of 140 mAgÀ1 for 50 cycles in the potential
range of 0.01–2.0 V. Cyclic voltammograms were recorded by using
a Biologic instruments potentiostat/galvanostat at a scan rate of
0.1 mVsÀ1 between 0.01 and 2.0 V. Electrochemical impedance
spectra were measured by using a Biologic instruments potentio-
stat/galvanostat with an alternating current (AC) voltage signal of
5 mV and the frequency range was between 100 kHz and 5 mHz.
Conclusion
A simple chemical reduction method was followed for the syn-
thesis of the rGO/Bi2O3 nanocomposite for sodium-ion batter-
ies. The surfactant CTAB played an important role in determin-
ing the morphology of the synthesized Bi2O3 particles. The
sizes of the Bi2O3 particles were in the range of 10–20 nm and
anchored well on the surface of the rGO sheets. This kind of
embedding of Bi2O3 particles on the surface of rGO sheets buf-
fered the volume change upon Na+-ion insertion and deinser-
tion. The nanocomposite exhibited a superior reversible ca-
pacity, excellent cyclability, and good rate capability during cy-
cling. This superior performance was attributed to the rGO
sheets acting as a conductive matrix during cycling and assist-
ing the fast diffusion of Na+ ions and low impedance. Based
on the above results, the present study provides an idea to de-
velop an efficient metal oxide anode for sodium-ion batteries
with improved performance.
Acknowledgements
The author wishes to thank Department of Science and Technolo-
gy (DST), India for an INSPIRE Faculty Award.
Keywords: bismuth · electrochemistry · graphene · reduction ·
sodium
[1] X. Huang, B. Sun, S. Chen, G. Wang, Chem. Asian J. 2014, 9, 206–211.
[2] C. Nithya, S. Gopukumar, ChemSusChem 2013, 6, 898–904.
[3] C. Nithya, S. Gopukumar, J. Mater. Chem. A 2014, 2, 10516–10525.
[4] M. D. Slater, D. Kim, E. Lee, C. S. Johnson, Adv. Funct. Mater. 2013, 23,
947–958.
Experimental Section
Graphene oxide was synthesized by using a modified Hummers
method.[46,47] The rGO/Bi2O3 composite was synthesized through
a simple reduction method by using NaBH4 as a reducing agent. In
a typical synthesis, graphite oxide (1 g) was dispersed in distilled
[5] M. M. Doeff, Y. P. Ma, S. J. Visco, L. C. Dejonghe, J. Electrochem. Soc.
1993, 140, L169–170.
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[6] D. A. Stevens, J. R. Dahn, J. Electrochem. Soc. 2001, 148, A803–A811.
[7] Y. Shao, J. Xiao, W. Wang, M. Engelhard, X. Chen, Z. Nie, M. Gu, L. V.
Saraf, G. Exarhos, J. G. Zhang, J. Liu, Nano Lett. 2013, 13, 3909–3914.
[8] T. Matsushita, Y. Ishii, S. Kawasaki, ECS Trans. 2013, 50, 1–6.
[9] J. Qian, Y. Chen, L. Wu, Y. Cao, X. Ai, H. Yang, Chem. Commun. 2012, 48,
7070–7072.
[10] M. K. Datta, R. Epur, P. Saha, K. Kadakia, S. K. Park, P. N. Kumta, J. Power
Sources 2013, 225, 316–322.
[11] P. R. Abel, Y. M. Lin, T. Souza, C. Y. Chou, A. Gupta, J. B. Goodenough,
G. S. Hwang, A. Heller, C. B. Mullins, J. Phys. Chem. C 2013, 117, 18885–
18890.
[28] I. K. Moon, J. Lee, R. S. Ruoff, H. Lee, Nat. Commun. 2010, 1, 73.
[29] Q. Li, F. Zheng, Y. Huang, X. Zhang, Q. Wu, D. Fu, J. Zhang, J. Yin, H.
Wang, J. Mater. Chem. A 2015, 3, 2025–2035.
[30] C. Gómez-Navarro, R. T. Weitz, A. M. Bittner, M. Scolari, A. Mews, M. Bur-
ghard, K. Kern, Nano Lett. 2007, 7, 3499–3503.
[31] M. A. Pimenta, G. Dresselhaus, M. S. Dresselhaus, L. G. Cancado, A. Jorio,
R. Saito, Phys. Chem. Chem. Phys. 2007, 9, 1276.
[32] E. Strauss, G. Ardel, V. Livshits, L. Burstein, D. Golodnitsky, E. Peled, J.
Power Sources 2000, 88, 206–218.
[33] Y. P. Wu, S. B. Fang, Y. Y. Jiang, J. Power Sources 1998, 75, 201.
[34] L. W. Ji, X. W. Zhang, Electrochem. Commun. 2009, 11, 1146–1149.
[35] I. A. Courtney, A. W. Wilson, J. R. Dahn, Abstract#66, 190th Meeting of
the Electrochemical Society, San-Antonio, Texas, 1996.
[12] H. Xiong, M. D. Slater, M. Balasubramanian, C. S. Johnson, T. Rajh, J.
Phys. Chem. Lett. 2011, 2, 2560–2565.
[13] D. A. Tompsett, M. S. Islam, Chem. Mater. 2013, 25, 2515–2526.
[14] Q. Sun, Q. Q. Ren, H. Li, Z. W. Fu, Electrochem. Commun. 2011, 13, 1462–
1464.
[15] Y. Liu, Y. Xu, Y. Zhu, J. N. Culver, C. A. Lundgren, K. Xu, C. Wang, ACS
Nano 2013, 7, 3627–3634.
[16] A. Rudola, K. Saravanan, S. Devaraj, H. Gong, P. Balaya, Chem. Commun.
2013, 49, 7451–7453.
[17] Y. Park, D. S. Shin, S. H. Woo, N. S. Choi, K. H. Shin, S. M. Oh, K. T. Lee,
S. Y. Hong, Adv. Mater. 2012, 24, 3562–3567.
[18] R. R. Zhao, Y. L. Cao, X. P. Ai, H. X. Yang, J. Electroanal. Chem. 2013, 688,
93–97.
[19] R. S. Asher, J. Inorg. Nucl. Chem. 1959, 10, 238–249.
[20] P. Ge, M. Fouletier, Solid State Ionics 1988, 28–30, 1172–1175.
[21] M. Gu, A. Kushima, Y. Zhao, J. G. Zhang, J. Liu, N. D. Browning, J. Li, C.
Wang, Nano Lett. 2013, 13, 5203–5211.
[22] L. L. Zhang, X. Zhao, M. D. Stoller, Y. Zhu, H. Ji, S. Murali, Y. Wu, S. Per-
ales, B. Clevenger, R. S. Ruoff, Nano Lett. 2012, 12, 1806–1812.
[23] Y. Li, M. A. Trujillo, E. Fu, B. Patterson, L. Fei, Y. Xu, S. Deng, S. Smirnov,
H. Luo, J. Mater. Chem. A 2013, 1, 12123–12127.
[24] J. C. Perez-Flores, A. Kuhn, F. García-Alvarado, J. Power Sources 2008,
182, 35–369.
[36] C. M. Ban, Z. C. Wu, D. T. Gillaspie, L. Chen, Y. F. Yan, J. L. Blackburn, A. C.
Dillon, Adv. Mater. 2010, 22, E145–149.
[37] G. M. Zhou, D. W. Wang, F. Li, L. L. Zhang, N. Li, Z. S. Wu, L. Wen, G. Q.
Lu, H. M. Cheng, Chem. Mater. 2010, 22, 5306–5313.
[38] J. Z. Wang, C. Zhong, D. Wexler, N. H. Idlris, Z. X. Wang, L. Q. Chen, H. K.
Liu, Chem. Eur. J. 2011, 17, 661–667.
[39] Y. Su, S. Li, D. Wu, F. Zhang, H. Liang, P. Gao, C. Cheng, X. Feng, ACS
Nano 2012, 6, 8349–8356.
[40] X. Cheng, R. Li, Y. Sun, X. Q. Chen, D. Li, Y. Li, Phys. Rev. B 2014, 89,
245201–245205.
[41] L. Yue, H. Zhong, L. Zhang, Electrochim. Acta 2012, 76, 326–332.
[42] A. Yu, H. W. Park, A. Davies, D. C. Higgins, Z. Chen, X. Xiao, J. Phys.
Chem. Lett. 2011, 2, 1855–1860.
[43] K. Yang, Z. Deng, J. Suo, J. Power Sources 2012, 201, 274–279.
[44] M. Shi, Z. Chen, J. Sun, Cem. Concr. Res. 1999, 29, 1111–1115.
[45] J. Zhu, T. K. Sharma, Z. Zeng, X. Zhang, M. Srinivasan, S. Mhaisalkar, H.
Zhang, H. H. Hug, Q. Yan, J. Phys. Chem. C 2011, 115, 8400–8406.
[46] W. S. Hummers, R. E. Offeman, J. Am. Chem. Soc. 1958, 80, 1339–1339.
[47] X. Zhu, Y. Zhu, S. Murali, M. D. Stoller, R. S. Rouff, ACS Nano 2011, 5,
3333–3338.
[25] J. Shen, Y. Hu, M. Shi, X. Lu, C. Qin, C. Li, M. Ye, Chem. Mater. 2009, 21,
3514.
Received: November 13, 2014
Revised: February 17, 2015
[26] H. Jung, C. M. Park, H. J. Sohn, Electrochim. Acta 2011, 56, 2135–2139.
[27] C. N. R. Rao, K. Biswas, K. S. Subramnayam, A. Govindaraj, J. Mater.
Chem. 2009, 19, 2457.
Published online on March 11, 2015
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