Template-free synthesis of hierarchical vanadium-glycolate hollow microspheres and their conversion to V2O5 with improved lithium storage capability

Article abstract of DOI:10.1002/chem.201203596

Nanosheet-assembled hierarchical V₂O₅ hollow microspheres are successfully obtained from V-glycolate precursor hollow microspheres, which in turn are synthesized by a simple template-free solvothermal method. The structural evolution of the V-glycolate hollow microspheres has been studied and explained by the inside-out Ostwald-ripening mechanism. The surface morphologies of the hollow microspheres can be controlled by varying the mixture solution and the solvothermal reaction time. After calcination in air, hierarchical V₂O₅ hollow microspheres with a high surface area of 70 m² g^-1 can be obtained and the structure is well preserved. When evaluated as cathode materials for lithium-ion batteries, the as-prepared hierarchical V₂O₅ hollow spheres deliver a specific discharge capacity of 144 mA h g^-1 at a current density of 100 mA g^-1, which is very close to the theoretical capacity (147 mA h g^-1) for one Li⁺ insertion per V₂O₅. In addition, excellent rate capability and cycling stability are observed, suggesting their promising use in lithium-ion batteries. Copyright

Full text of DOI:10.1002/chem.201203596

DOI: 10.1002/chem.201203596
Template-Free Synthesis of Hierarchical Vanadium-Glycolate Hollow
Microspheres and Their Conversion to V O with Improved Lithium Storage
2
5
Capability
[
a]
Anqiang Pan, Ting Zhu, Hao Bin Wu, and Xiong Wen (David) Lou*
494
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 494 – 500

FULL PAPER
Abstract: Nanosheet-assembled hier-
the mixture solution and the solvother-
mal reaction time. After calcination in
air, hierarchical V O hollow micro-
ion batteries, the as-prepared hierarchi-
cal V O hollow spheres deliver a spe-
archical V O hollow microspheres are
2
5
2
5
ꢀ
1
successfully obtained from V-glycolate
precursor hollow microspheres, which
in turn are synthesized by a simple
template-free solvothermal method.
The structural evolution of the V-glyco-
late hollow microspheres has been
studied and explained by the inside-out
Ostwald-ripening mechanism. The sur-
face morphologies of the hollow micro-
spheres can be controlled by varying
cific discharge capacity of 144 mAhg
2
5
ꢀ
1
spheres with a high surface area of
at a current density of 100 mAg ,
which is very close to the theoretical
2
ꢀ1
70 m g
can be obtained and the
ꢀ
1
+
structure is well preserved. When eval-
uated as cathode materials for lithium-
capacity (147 mAhg ) for one Li in-
sertion per V O . In addition, excellent
2
5
rate capability and cycling stability are
observed, suggesting their promising
use in lithium-ion batteries.
Keywords: cathodes · hollow mi-
crospheres · lithium-ion batteries ·
nanostructures · vanadium
Introduction
chemical energy storage devices such as LIBs because they
can enhance the electrochemical kinetics, shorten the diffu-
sion distance for lithium ions and accommodate the volume
Vanadium pentoxide (V O ) has been extensively studied in
2
5
[
1,2]
widespread applications, such as chemical sensors,
field-
actua-
change during the lithium intercalation and de-intercalation
[3]
[4]
[5,6]
[17–20]
emitters, catalysis, lithium-ion batteries (LIBs),
processes.
Also, the hierarchical structures can effec-
[
7]
[8]
[21]
tors, and electrochromic devices because a large variety
of atomic and molecular species can be reversibly intercalat-
ed and de-intercalated between the layers of V O . As a typ-
tively prevent the self-aggregation upon cycling. However,
there are far less reports on the fabrication of V O hollow
2
5
nanostructures compared with their low dimensional struc-
tures. As an example, Wan and co-workers reported the
preparation of vanadium pentoxide hollow microspheres in
the presence of poly(vinylpyrrolidone) (PVP), which serves
2
5
ical intercalation compound, V O has been investigated as
2
5
a prospective cathode material for rechargeable lithium bat-
teries since it was firstly reported in 1976 by Whittingham.
However, the development of rechargeable lithium batteries
with vanadium pentoxide as a cathode material has been
hindered by its low lithium ion diffusion efficiency, electron-
[9]
[13]
as a structure-directing reagent.
PVP has been demon-
strated to play a key role for the formation of the hollow
microspheres. Recently, Liu et al. reported the synthesis of
new yolk-shelled structures of V O with a smooth surface
[
10–12]
ic conductivity, and fast capacity fading.
In the last
2
5
decade, many efforts have been focused on the synthesis of
nanostructured vanadium oxides to mitigate the slow elec-
trochemical kinetics by acquiring high surface area and
by using a template-free method in N,N-dimethylforma-
[22]
mide.
We have recently developed a template-free
method for synthesis of VO hollow microspheres with dif-
2
[13]
short diffusion distance. To date, various one-dimensional
ferent interior structures, which can be converted to V O
structures upon annealing in air. Therefore, although chal-
lenging, the development of a template-free, low-cost, and
2
5
[
14]
[23]
V O5 nanostructures, such as nanorod arrays,
nano-
2
[15]
[16]
tubes, and nanocables have been successfully fabricated
and exhibit improved intercalation properties when com-
pared with their bulk counterparts. In addition, the mor-
phologies of the nanostructured materials have been found
environmentally benign approach for synthesis of V O5
2
hollow microspheres with unique and hierarchical structures
is still of great importance.
[14]
to have a great effect on their electrochemical properties.
However, the electrochemical performance of V O nano-
Herein, we report the synthesis of hierarchical nanosheet-
constructed hollow V-glycolate microspheres by a template-
free method, by using a cost-effective VOC O solution as
2
5
materials, in particular the cycling stability, is still not very
satisfactory.
Recently, hollow micro/nanostructures with hierarchical
structures have attracted considerable attention in electro-
2
4
the precursor. The formation mechanism of the hollow hier-
archical structure has been studied, and the effects of the ex-
perimental parameters on the surface morphologies of the
microspheres have also been investigated. After calcination
in air, V O hollow hierarchical microspheres with well-pre-
2
5
[
a] Dr. A. Pan, T. Zhu, H. B. Wu, Prof. X. W. Lou
School of Chemical and Biomedical Engineering
Nanyang Technological University
served structures can be obtained, which are found to exhib-
it superior rate capability and cycling stability as cathode
materials for LIBs.
7
0 Nanyang Drive, 637457 (Singapore)
E-mail: xwlou@ntu.edu.sg
Homepage: http://www.ntu.edu.sg/home/xwlou/
Supporting information for this article (including the XRD pattern
and EDX for the V-glycolate hollow microspheres, cycling perform-
Experimental Section
ance of V
and the N
WWW under http://dx.doi.org/10.1002/chem.201203596.
2
O
5
hollow microspheres, more FESEM and TEM images
2
adsorption-desorption isotherm) is available on the
Materials synthesis: In a typical synthesis, V
(molar ratio=1:3) were dissolved in deionized water (40 mL) under vigo-
2 5 2 2 4 2
O (1.2 g) and H C O ·2H O
Chem. Eur. J. 2013, 19, 494 – 500
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
495

X. W. Lou et al.
rous stirring at 808C for several hours until a clear blue VOC
0.33m) was formed due to the reaction: V +3H
O. Different concentrations (0.165, 0.11, 0.0825, 0.065, and
2
O
4
solution
O +
2 4
or part of the microspheres is relatively difficult to crystal-
lize and thus exhibits higher surface energy compared with
the exterior surface. As a result, to reduce the overall sur-
face energy of the materials, the interior material has a
strong tendency to dissolve and relocate to the outer regions
in which re-crystallization takes place (Figure 1, process I)
when the solvothermal reaction is prolonged. A further in-
crease in the reaction time leads to the formation of com-
pletely hollow V-glycolate precursor microspheres (Figure 1,
(
2
0
2
O
5
2
C
2
O
4
!2VOC
CO
2 2
+3H
.055m) of VOC
2
O
4
aqueous solution were obtained by diluting the as-
synthesized VOC
2
O
4
solution (0.33m) with DI water. Ethylene glycol
(
EG, 20 mL) was added into a 50 mL Teflon container, followed by addi-
tion of an aqueous solution of VOC (2 mL, 0.0825m). After stirring
2
O
4
for 20 min, the container was sealed in a steel autoclave and kept in an
electrical oven at 2008C for 12 h. It was cooled down naturally and the
precipitate was collected by centrifugation and washed three times with
pure ethanol. The obtained precipitate is designated as V-glycolate. Re-
actions were also carried out at 1708C for 8, 12, and 16 h to study the
process II). After calcination in air, hierarchical V O5
2
2 4
structural evolution process. Moreover, VOC O solution with different
hollow microspheres can be readily obtained (Figure 1,
process III).
concentrations (0.065m, 0.082m, 0.11m, 0.165m, and 0.33m) was used to
study the concentration effect on the structures and the morphologies of
the V-glycolate microspheres. In addition, the effect of the volume ratio
Hollow microspheres with hierarchical structures can be
easily obtained when the mixture solution is solvothermally
treated at 2008C for 12 h and the obtained precipitate is
designated as V-glycolate. The X-ray diffraction (XRD) pat-
tern of the precursor microspheres (Figure S1, see the Sup-
porting Information) indicates the good crystallinity of the
hierarchical hollow microspheres, and all of the diffraction
peaks can be assigned to vanadyl ethylene glycolate (JCPDS
card no. 49-2797). As revealed by the energy-dispersive X-
ray (EDX) spectroscopy analysis (Figure S2, see the Sup-
porting Information), the microspheres are composed of V,
O, and C elements. Field-emission scanning electron micro-
scope (FESEM) and transmission electron microscope
of VOC
was also investigated. The hierarchical V
obtained by calcining the solvothermally prepared V-glycolate micro-
2
O
4
aqueous solution (0.33m) to EG media on the morphologies
2
O
5
hollow microspheres were
ꢀ1
spheres in air at 3508C for 2 h with a heating rate of 18C min
.
Materials characterization: Crystallographic phases of all the products
were investigated by powder X-ray diffraction (Bruker, D8-Advance
XRD, CuKa, l=1.5406 ꢁ). Morphologies of samples were examined by
field-emission scanning electron microscope (FESEM; JEOL, JSM-
6
700F) and transmission electron microscope (TEM; JEM-2010, 200 kV).
Measurement of specific surface area and analysis of porosity for the va-
nadium oxide products were performed through measuring N adsorp-
2
tion-desorption isotherms at 77 K with a Quantachrome Autosorb AS-6B
system.
Electrochemical measurements: The working electrode slurry was pre-
pared by dispersing V O , carbon black (Super P-Li) and poly(vinylidene
2 5
fluoride) (PVDF) binder in an N-methylpyrrolidone solution at a weight
ratio of 70:20:10. The slurry was spread on aluminum foil disks and dried
in a vacuum oven at 1208C overnight prior to Swagelok-type cells assem-
bly. Lithium foil was used as the counter and reference electrode, and
(
TEM) characterizations provide insights into the morpholo-
gy and detailed structure of the product. A panoramic view
of the product (Figure 2a) reveals the uniformity of these
microspheres with a diameter of around 1 mm. The micro-
spheres with rough surface are interconnected. As shown in
the Figure 2b, each microsphere is composed of nanosheets
with a thickness of about 20 nm. Moreover, the observation
from the window reveals the hollow interior of the micro-
spheres. The shell structure is also studied by TEM observa-
LiPF
6
(1.0m) in ethyl carbonate/dimethyl carbonate (1:1 v/v ratio) was
ꢀ
1
used as the electrolyte. Cyclic voltammetry (CV; 2.5–4.0 V, 0.2 mVs
)
measurements were performed on a CHI660C electrochemical worksta-
tion. Galvanostatic charging/discharging was conducted with a battery
tester (NEWARE).
Results and Discussion
The water-soluble vanadium oxalate (VOC O ), prepared by
2
4
reacting V O with H C O in a molar ratio of 1:3 in distilled
2
5
2
2
4
water, was used as the vanadium source to enable a better
dispersion in ethylene glycol (EG) media. The schematic il-
lustration of the synthesis of hierarchical V O hollow mi-
2
5
crospheres is shown in Figure 1. V-glycolate solid micro-
spheres are first formed through the interaction between
VOC O and ethylene glycol. It is postulated that the interi-
2
4
Figure 1. Schematic illustration of the synthetic procedure of hierarchical
hollow microspheres: I) initial inside-out Ostwald-ripening process;
V
2
O
5
Figure 2. a, b) FESEM and c, d) TEM images of the solvothermal prod-
II) complete evacuation of the interior; and III) the calcination process
in air.
ucts obtained at 2008C for 12 h. The reaction solution contains a solution
of VOC O (2 mL, 0.0825m)+EG (20 mL).
2 4
496
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 494 – 500

V O Hollow Microspheres
2
5
FULL PAPER
tion (Figure 2c and d), which are composed of ultrathin
nanosheets with a size around 200 nm. This is among the
first reports on preparing hollow vanadium precursor micro-
spheres with nanosheet-assembled hierarchical structures. It
is also worth noting that the synthesis is carried out in the
absence of templates or surfactants, which makes the pres-
ent approach more straightforward and environmentally
friendly.
In view of the fast reaction at 2008C, time-dependent ex-
periments were carried out at a lower temperature (1708C)
to better understand the process; the FESEM images of the
products obtained at different reaction stages are shown in
Figure 3. As shown in Figure 3a and b, V-glycolate micro-
Figure 4. FESEM images of V-glycolate microspheres prepared under dif-
ferent solvothermal conditions: a, b) 3 mL of an aqueous solution of
VOC
VOC
VOC
2
O
2
O
2
O
4
4
4
(0.33m) +20 mL of EG; c, d) 3 mL of an aqueous solution of
(0.11m)+20 mL of EG; e, f) 2 mL of an aqueous solution of
(0.33m)+35 mL of EG.
(
0.33m) in EG (20 mL) is used. The hollow microspheres as-
sembled from the nanosheets appear largely interconnected.
It is interesting to find that hierarchical hollow microspheres
can still be obtained if a lower concentration (0.11m) of
VOC O is used, whereas other parameters are unaltered
Figure 3. FESEM images of the products prepared with different reaction
durations: a, b) 8 h, c) 12 h, and d) 16 h.
2
4
spheres with a relatively smooth surface can be obtained
when the mixture solution is solvothermally treated at
(Figure 4c, d). However, it should be noted that the as-syn-
thesized nanosheets on the shell are larger in size. In anoth-
1708C for 8 h. Figure 3c shows that the shell structures com-
er set of experiments, 2 mL of aqueous solutions of VOC O4
2
posed of nanosheets start to appear when the reaction time
is extended to 12 h. In addition, the broken microsphere fur-
ther reveals the nanosheet-assembled shell and smooth core
inside, which shows the typical yolk-shell structure. When
the solvothermal time is further prolonged to 16 h, hierarch-
ical microspheres with a completely hollow interior can be
observed as shown in Figure 3d. The results demonstrate
that the re-crystallization takes place at the exterior surface
of the microspheres and the growth of the nanosheet-struc-
ture on the shell is at the expense of the core. Similar phe-
nomena have been observed for the formation of other
metal oxide hollow structures and can be understood by the
(0.165m, 0.0825m, 0.066m, and 0.055m) were added into EG
(20 mL). The results indicate that hollow hierarchical micro-
spheres can be reliably fabricated and all the products have
good uniformity when a relatively low concentration of
VOC O aqueous solution is used (Figure S3, see the Sup-
2
4
porting Information). Furthermore, the volume ratio of
VOC O solution to EG media also has a distinct effect on
2
4
the morphology of the microspheres. For example, micro-
spheres with smooth surfaces (Figure 4e and f) are produced
when 2 mL of an aqueous solution of VOC O (0.33m) is
2
4
added into 35 mL of EG.
Figure 5 shows the structural characterization results of
V O hierarchical hollow microspheres obtained after an-
[5,18,20,24]
inside-out Ostwald-ripening mechanism.
2
5
The morphologies of the microspheres are not only deter-
mined by the solvothermal time, but are also dependent on
the mixture solution for solvothermal treatment. Figure 4
shows the FESEM images of the microspheres prepared
from different mixture solutions. Hollow microspheres with
assembled nanosheets on the surface (Figure 4a and b) can
be obtained when 3 mL of an aqueous solution of VOC O
nealing the V-glycolate microspheres in air at 3508C for 2 h.
The crystallinity and the phase of the calcined products are
characterized by XRD and the result is shown in Figure 5a.
All the main diffraction peaks have been indexed and as-
signed to the orthogonal V O phase (JCPDS card no. 41-
2
5
1426, space group: Pmmn (59), a=11.516 ꢁ, b=3.566 ꢁ,
[22,25,26]
c=3.777 ꢁ).
No other peaks were detected, indicating
2
4
Chem. Eur. J. 2013, 19, 494 – 500
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
497

X. W. Lou et al.
Figure 6 shows the electrochemical evaluation of these hi-
erarchical V O hollow microspheres. The cyclic voltamme-
2
5
+
try (CV) technique is first used to evaluate the Li ions in-
sertion and de-insertion behavior in V O at a scan rate of
.2 mVs . As shown in Figure 6a, two potential peaks at
2
5
ꢀ
1
0
3
+
.23 and 3.04 V vs. Li/Li are observed during the cathodic
scan, which indicate the two-step intercalation of the first
+
Li ion in V O host and the phase evolves from V O to
2
5
2
5
[6,26,27]
Li V O and then to LiV O .
The detection of two
0
.5
2
5
2
5
+
anodic peaks at 3.36 and 3.57 V versus Li/Li suggests the
good reversibility of the lithium-insertion process.
[27]
After
two cycles, the CV curves become largely identical, which
indicates the improved cycling stability. Figure 6b shows the
discharge/charge curves of the 1st, 2nd, and 10th cycles in
the voltage range of 2.5–4 V with a current density of
ꢀ
1
3
00 mAg . Two plateaus are observed for both the dis-
charge/charge curves, which are related to the lithium ion
insertion and extraction process. The shape of the curves
does not change significantly upon cycling, demonstrating
+
the good reversibility of the Li ions insertion and extrac-
Figure 5. a) XRD pattern, b) FESEM and c, d) TEM images of the hier-
archical V hollow microspheres obtained by annealing the solvother-
mally prepared V-glycolate hollow microspheres in air at 3508C for 2 h.
The solvothermal conditions: 3 mL of an aqueous solution of VOC
0.33m)+20 mL of EG, at 2008C for 12 h.
2
O
5
tion process. The result agrees well with the CV curves. Fig-
ure 5c shows the cycling performance and the Coulombic ef-
ficiency of the electrode at the current density of
2
O
4
(
ꢀ
1
3
00 mAg . The slight capacity increase in the second cycle
can be attributed to the improved wettability of the elec-
trode, which leads to a specific discharge capacity of
the high purity of the as-obtained V O microspheres. The
2
5
ꢀ
1
[6,26]
morphology and detailed structure of the products were in-
vestigated by FESEM and TEM. As expected, the morphol-
ogy of the V O hollow microspheres is largely determined
137 mAhg for the second cycle.
pacities of 133 and 131 mAhg can still be obtained at the
10th and 20th cycle, respectively. Even after 50 cycles, it can
still deliver a discharge capacity of 128 mAhg , corre-
sponding to a very trivial capacity decay rate of 0.13% per
cycle. Furthermore, the Coulombic efficiency is close to
100% throughout the cycling test. When the V O hollow
Specific discharge ca-
ꢀ
1
2
5
ꢀ
1
by the morphology of the V-glycolate precursor hollow mi-
crospheres. The nanosheet-structured V O hollow micro-
2
5
spheres can be easily obtained from the V-glycolate precur-
sor hollow microspheres as shown in Figure 5b–d (also see
Figure S4 in the Supporting Information). A panoramic
view of the product (Figure 5b) reveals that the intercon-
nected hollow microspheres assembled from nanosheets, in-
dicating that the structures are well-preserved after the cal-
cination. The TEM images (Figure 5c and d) provide the de-
tailed information of the interior structures. The shell of
each hollow microsphere can be well identified with their
thickness similar to the precursor hollow spheres. It should
be mentioned that the hollow hierarchical V O micro-
2
5
microspheres are cycled within a wider voltage window of
ꢀ
1
2–4 V, a higher reversible capacity of about 250 mAhg can
+
be obtained due to the intercalation of the second Li ion
[22,25,27]
(Figure S7, see the Supporting Information).
Howev-
er, the capacity retention is not as good as that with a nar-
rower voltage window of 2.5–4 V. Figure 6d shows the rate
performance of the electrode at various current densities. A
ꢀ
1
specific discharge capacity of 144 mAhg can be delivered
ꢀ
1
at 2C/3 (100 mAg ), which is very close to the theoretical
2
5
ꢀ
1
+
spheres can retain their structural integrity even after ultra-
sonic dispersion. The nanosheets of the V O hierarchical
capacity of 147 mAhg
for one Li ion insertion into
[6,13,25]
V O .
After 14 cycles, the current density is set to 2C
(300 mAg ), under which a specific discharge capacity of
135 mAhg can be obtained. High specific discharge ca-
pacities of 131 and 125 mAhg can be retained even at
very high rates of 4C and 8C, respectively. When the cur-
rent density is re-set to 2/3C after 58 cycles, a specific dis-
charge capacity of 131 mAhg can be recovered. The re-
sults demonstrate that the hierarchical V O hollow micro-
2
5
2
5
ꢀ1
hollow microspheres are slightly smaller in size compared
with those of V-glycolate hollow microspheres. The shrink-
age can be attributed to the decomposition of the precursor,
at which crystal reorganization occurs during the calcination.
As revealed by the nitrogen adsorption-desorption measure-
ment, the porous structure gives rise to a relatively high
ꢀ
1
ꢀ
1
ꢀ
1
2
ꢀ1
Brunauer–Emmett–Teller (BET) surface area of 70 m g
with relatively high single-point pore volume of
.56 cm g (Figure S5, see the Supporting Information).
2
5
a
spheres exhibit very good rate capability and cycling stabili-
ty as a cathode material for LIBs. The superior electrochem-
ical performance might be related to the new hierarchical
hollow structure. Specifically, the nanosheet-assembled
porous structure with a hollow interior will increase the con-
tact area between the electrode and electrolyte and allow
3
ꢀ1
0
When the V-glycolate hollow microspheres are heated in air
at 5008C for 2 h, the obtained product is composed of thick
nanoplates (Figure S6, see the Supporting Information) due
to crystal growth.
498
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 494 – 500

V O Hollow Microspheres
2
5
FULL PAPER
ꢀ
1
Figure 6. Electrochemical characterizations hierarchical V
2 5
O hollow microspheres: a) cyclic voltammetry (CV) curves at a scan rate of 0.2 mVs ; b) dis-
ꢀ
1
charge/charge curves of the first, second, and tenth cycles; c) cycling performance at the current density of 300 mAg ; d) the rate performance (1C=
ꢀ
1
1
50 mAg ).
easy penetration of the electrolyte. Moreover, the nanosized
thickness of the nanosheets will reduce the transport dis-
tance for electrons and Li ions diffusion.
Acknowledgements
+
The authors acknowledge the financial support from the Institute of
Nanosystems Interface Science and Technology (INSIST) at Nanyang
Technological University.
Conclusion
A template-free solvothermal method has been developed
to synthesize hierarchical V-glycolate hollow microspheres,
which can be easily transformed to hierarchical V O hollow
microspheres with a well-maintained structure. The V-glyco-
late hollow microspheres are composed of nanosheets in the
shell. The structural evolution process has been studied and
discussed by the inside-out Ostwald-ripening mechanism.
The morphologies of the microspheres can be controlled by
tuning the experimental parameters. After calcination in air,
these V-glycolate hollow spheres can be easily converted to
[
1] L. Biette, F. Carn, M. Maugey, M.-F. Achard, O. Maquet, N. Steu-
nou, J. Livage, H. Serier, R. Backov, Adv. Mater. 2005, 17, 2970.
2
5
[2] J. Dexmer, C. M. Leroy, L. Binet, V. Heresanu, P. Launois, N. Steu-
nou, C. Coulon, J. Maquet, N. Brun, J. Livage, R. Backov, Chem.
Mater. 2008, 20, 5541.
[3] T. Zhai, H. Liu, H. Li, X. Fang, M. Liao, L. Li, H. Zhou, Y. Koide,
Y. Bando, D. Golberg, Adv. Mater. 2010, 22, 2547.
[4] X. Gao, S. Liu, Y. Zhang, X. Du, Z. Luo, K. Cen, Catal. Today 2011,
175, 164.
[
[
5] D. Yu, C. Chen, S. Xie, Y. Liu, K. Park, X. Zhou, Q. Zhang, J. Li, G.
Cao, Energy Environ. Sci. 2011, 4, 858.
6] A. Q. Pan, J. G. Zhang, Z. M. Nie, G. Z. Cao, B. W. Arey, G. S. Li,
S. Q. Liang, J. Liu, J. Mater. Chem. 2010, 20, 9193.
hierarchical V O hollow microspheres with little structural
2
5
alteration. When used as cathode materials for lithium-ion
batteries, these hierarchical V O hollow spheres show re-
markable electrochemical performance with excellent rate
capability and cycling stability.
[7] G. Gu, M. Schmid, P.-W. Chiu, A. Minett, J. Fraysse, G.-T. Kim, S.
Roth, M. Kozlov, E. MuÇoz, R. H. Baughman, Nat. Mater. 2003, 2,
2
5
3
16.
[
[
8] Y. Yang, D. Kim, P. Schmuki, Electrochem. Commun. 2011, 13, 1021.
9] M. S. Whittingham, J. Electrochem. Soc. 1976, 123, 315.
[
10] Z. Chen, V. Augustyn, J. Wen, Y. Zhang, M. Shen, B. Dunn, Y. Lu,
Adv. Mater. 2011, 23, 791.
Chem. Eur. J. 2013, 19, 494 – 500
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
499

X. W. Lou et al.
[
[
[
11] J. Wang, C. J. Curtis, D. L. Schulz, J.-G. Zhang, J. Electrochem. Soc.
004, 151, A1.
12] R. Baddour-Hadjean, J. P. Pereira-Ramos, C. Navone, M. Smirnov,
Chem. Mater. 2008, 20, 1916.
[21] L. Mai, L. Xu, C. Han, X. Xu, Y. Luo, S. Zhao, Y. Zhao, Nano Lett.
2010, 10, 4750.
[22] J. Liu, Y. Zhou, J. Wang, Y. Pan, D. Xue, Chem. Commun. 2011, 47,
10380.
[23] A. Q. Pan, H. B. Wu, L. Yu, T. Zhu, X. W. Lou, unpublished results.
[24] J. S. Chen, C. M. Li, W. W. Zhou, Q. Y. Yan, L. A. Archer, X. W.
Lou, Nanoscale 2009, 1, 280.
[25] Y. S. Hu, X. Liu, J.-O. Mꢂller, R. Schlçgl, J. Maier, D. S. Su, Angew.
Chem. 2009, 121, 216; Angew. Chem. Int. Ed. 2009, 48, 210.
[26] A. Q. Pan, H. B. Wu, L. Yu, T. Zhu, X. W. Lou, ACS Appl. Mater.
Interfaces 2012, 4, 3874.
2
13] A. M. Cao, J. S. Hu, H. P. Liang, L. J. Wan, Angew. Chem. 2005, 117,
4
465; Angew. Chem. Int. Ed. 2005, 44, 4391.
[
[
14] Y. Wang, G. Z. Cao, Adv. Mater. 2008, 20, 2251.
15] S. D. Perera, B. Petel, J. Bonso, M. Grunewald, J. P. Ferraris, K. J.
Balkus, ACS Appl. Mater. Interfaces 2011, 3, 4512.
[16] K. Takahashi, Y. Wang, G. Cao, J. Phys. Chem. B 2005, 109, 48.
[17] X. W. Lou, L. A. Archer, Z. C. Yang, Adv. Mater. 2008, 20, 3987.
[18] X. W. Lou, Y. Wang, C. L. Yuan, J. Y. Lee, L. A. Archer, Adv.
Mater. 2006, 18, 2325.
[27] X. F. Zhang, K. X. Wang, X. Wei, J. S. Chen, Chem. Mater. 2011, 23,
5290.
[
[
19] Z. Wang, L. Zhou, X. W. Lou, Adv. Mater. 2012, 24, 1903.
20] H. B. Wu, J. S. Chen, H. H. Hng, X. W. Lou, Nanoscale 2012, 4,
Received: October 9, 2012
2
526.
Published online: November 28, 2012
500
www.chemeurj.org
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 494 – 500