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Cite this: J. Mater. Chem., 2012, 22, 17429
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Self-supporting Co3O4 with lemongrass-like morphology as ahigh-performance anode material for lithium ion batteries†
Yujun Fu, Xiuwan Li, Xiaolei Sun, Xinghui Wang, Dequan Liu and Deyan He*
Received 8th June 2012, Accepted 3rd July 2012
DOI: 10.1039/c2jm33704e
Self-supporting Co3O4 with lemongrass-like morphology exhibits
excellent rate capability and cyclic stability for high-performance Li
ion batteries as electrodes. It retains a high reversible capacity of up
to 981 mA h g�1 after 100 cycles at a rate of 0.5 C and a capacity
higher than 381 mA h g�1 even at a rate as high as 10 C.
Recently, Co3O4 has attractedmuch attention and become one of the
most promising anodematerials for the next generation of lithium ion
batteries (LIBs) due to its superior specific capacity (890 mA h g�1 intheory), low cost, and environmental friendliness.1–5 Until recently,
Co3O4 powders with various morphologies have been synthesized as
anode materials, including hollow spheres,6 nanofibers,7 nanobelts,8
nanotubes,9 nanocapsules,10 nanocages,11 and so on. Despite the high
capacities in the first few cycles, most of the powder materials display
unsatisfactory cycling stability mainly owing to the poor electronic
conduction. Several strategies have been proposed to solve the
problems, in which self-supporting Co3O4 nanostructures grown
directly on current-collecting substrates represent an attractive
approach. Li et al. have prepared mesoporous Co3O4 nanowire
arrays on Ti foil by a template-free method, which deliver a capacity
of 700 mA h g�1 after 20 cycles at a current of 111 mA g�1.12 Fanet al. have synthesized freestanding Co3O4 porous nanosheets on
nickel foil and found that, when the architecture is used as an anode
for LIBs, the capacity maintains 631 mA h g�1 after 50 cycles at a
constant current of 150 mA g�1.13 Wang et al. have prepared the
Co3O4 nanobelt arrays on Ti foil, which retain a specific capacity of
770 mA h g�1 over 25 cycles at a current density of 177 mA g�1.14 Liet al. have fabricated Co3O4 nanowire arrays directly on steel coins
coated by gold nanoparticles, which show a capacity of 743mAh g�1
after 50 cycles at a current density of 100 mA g�1, but the capacitiesgradually fade at higher discharge rates.15 It is clear that, as a qualified
anode material for LIBs for high-power applications, further
School of Physical Science and Technology, Key Laboratory forMagnetism and Magnetic Materials of MOE, Lanzhou University,Lanzhou, 730000, China. E-mail: hedy@lzu.edu.cn; Fax: +86-931-8913554; Tel: +86-931-8912546
† Electronic supplementary information (ESI) available: Experimentaldetails; XRD pattern and SEM images of the as-synthesized precursor;XRD pattern, Raman spectrum, and schematic diagram of Li+
insertion/extraction for self-supporting Co3O4 electrodes; SEM imagesof the self-supporting Co3O4 electrode after 100 discharge–chargecycles at a rate of 0.5 C. See DOI: 10.1039/c2jm33704e
This journal is ª The Royal Society of Chemistry 2012
investigations are essential to improve the rate capacity and cycling
stability of Co3O4 materials.
In this letter, we report a self-supporting Co3O4 with lemongrass-
like morphology grown on a Ni foam substrate by a simple
hydrothermal synthesis with subsequent calcination. The unique
architecture exhibits high capacity, excellent rate capability and cyclic
stability when used as an anode in LIBs. The experimental results
indicate that such a nanostructure of Co3O4 might be a qualified
anode material for LIBs.
Self-supporting Co3O4 with lemongrass-like morphology was
fabricated by a facile hydrothermal growth with subsequent calci-
nation (see ESI† for more experimental details). Fig. 1 shows typical
SEMandTEM images of the obtainedCo3O4. It reveals that the self-
supporting Co3O4 (Fig. 1a and b) still retains the morphology of the
as-synthesized precursor (see ESI, Fig. S1†). The low-magnification
SEM image (Fig. 1a) shows that Co3O4 with lemongrass-like
morphologywas growndirectly on the substrate ofNi foam in a large
area. The architectures are homogeneously aligned and intensively
adhered to Ni foam (inset in Fig. 1a) with an average thickness of
about 2 mm. The detailed morphology of the unique architecture is
Fig. 1 Morphology and structure characterization of the sample. (a)
Low-magnification SEM image, the inset is a side view. (b) High-
magnification SEM image. (c) TEM image of a single blade, the inset
shows its SAED pattern. (d) HRTEM image of the area indicated by the
white rectangle in (c).
J. Mater. Chem., 2012, 22, 17429–17431 | 17429
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displayed in Fig. 1b. It can be observed that the architecture is
composed of small blades. The typical TEM image for a single blade
shown in Fig. 1c indicates that it is porous and rough. The blade is
made up of crystalline particles, as confirmed by the selected area
electron diffraction (SAED) pattern (inset of Fig. 1c). All the SAED
rings can be indexed to the spinel phase of Co3O4. The HRTEM
image (Fig. 1d) exhibits clear lattice fringes with spacings of 0.46 nm
and 0.28 nm, which correspond to the (111) and (220) planes of spinel
Co3O4, respectively. The structure and composition of the samples
were further confirmed by XRD and Raman spectrum measure-
ments (see ESI, Fig. S3 and S4†).
Coin-type cells were assembled to investigate the electrochemical
performance of the obtained self-supporting Co3O4 as an anode for
LIBs. Fig. 2a shows the cyclic voltammetric (CV) curves which were
tested at a scan rate of 0.1 mV s�1 over a voltage range from 0.02 to
3.0 V. Three cathodic peaks were observed at 0.50, 0.86, and 1.22V in
the first cycle, which correspond to the electrochemical reduction
reaction of Co3O4 and the formation of the solid electrolyte inter-
phase (SEI).12,16 One anodic peak was recorded at around 2.20 V,
which corresponds to the oxidation reaction of Co3O4. In the
subsequent cycles, only one cathodic peak can be observed around
1.15 V, and the position of the anodic peak shifts to 2.23 V. Theo-
retically, the formation of Co and Li2O and the re-formation of
Co3O4 can be described by the following electrochemical conversion
reaction:12,17
Fig. 2 Electrochemical performances of the self-supporting Co3O4
electrodes. (a) CV curves at a scan rate of 0.1 mV s�1. (b) Cycling
performance and coulombic efficiency at a rate of 0.5 C. The inset shows
the discharge–charge curves for the 1st, 2nd, 10th, and 100th cycles.
17430 | J. Mater. Chem., 2012, 22, 17429–17431
Co3O4 þ 8Liþ þ 8e�discharge�������!charge �������
3Coþ 4Li2O (1)
It is found that both the peak current and the integrated area of the
cathodic/anodic peak are almost constant after the 2nd cycle, indi-
cating that both the formed SEI layer and the electrode material are
highly stable.
Galvanostatic discharge–charge cyclings were measured with a
voltage cut-off window of 0.02–3.0 V. Fig. 2b shows the voltage
profile, cycling behavior and coulombic efficiency of the self-sup-
porting Co3O4 electrode under 100 cycles at a rate of 0.5 C (1 C ¼890 mA g�1). From the first discharge curve in the inset of Fig. 2b, it
can be seen that there are a fine plateau located at 0.95 V and a
distinct long plateau at 0.62 V, which are ascribed to the reduction
processes from Co3O4 to CoO and CoO to Co, respectively.4,12 The
discharge and charge plateaus shift to higher voltages in the subse-
quent cycles, which is consistent with the CV results. The initial
discharge and charge capacities are 1221 and 893 mA h g�1,respectively, corresponding to a coulombic efficiency of 73.2%. The
large irreversible capacity, which is almost inevitable for most anode
materials,18–21 can be mainly attributed to the possible irreversible
processes such as electrolyte decomposition and formation of the SEI
layer.12,22 Nevertheless, the discharge–charge capacity is well retained
during the following cycling, and the coulombic efficiency is increased
to above 97.4%, suggesting excellent capacity retention of the self-
supporting Co3O4 electrode with lemongrass-like morphology.
Despite the large irreversible loss in the first cycling, a very high
charge capacity of 981 mA h g�1 is attained after 100 cycles. The
value is substantially higher than those of the previous Co3O4
nanostructures.10–17,23,24
To obtain further evidence of the high power performance of the
lemongrass-like Co3O4 electrodes, the rate capability was also
investigated. Fig. 3a shows the representative discharge–charge
voltage profiles of the Co3O4 electrode at various rates ranging from
0.5 C to 10 C. The discharge potential decreases and the charge
potential increases with increasing discharge–charge rate, which are
due to kinetic effects of the material.25 The excellent rate capability
and cycling stability of the electrode are explicitly demonstrated in
Fig. 3b. It can be seen that the discharge capacity reaches to about
901mAh g�1 after the first 11 cycles at a low rate of 0.5 C, and then it
slightly reduces to 852, 760, and 610 mA h g�1 at rates of 1 C, 2 C,
and 5 C, respectively. Even at the rate as high as 10 C, the electrode
can deliver a capacity higher than 381 mA h g�1. More importantly,
when the current rate is returned to the initial value of 0.5 C after
51 cycles, the electrode recovers its original capacity or even a little
higher (905 mA h g�1 in the 70th cycle).
The superior rate capability and reversibility capacity of the
obtained Co3O4 electrode could be ascribed to the following reasons:
(1) the lemongrass-like morphology of Co3O4 nanoparticles can limit
the mobility and agglomeration of the particles during cycling, which
may endure the volume expansion/contraction during lithiation/
delithiation. The SEM images of the self-supporting Co3O4 electrode
after 100 discharge–charge cycles at a rate of 0.5 C are shown in
Fig. S5 (see ESI†). It is obvious that the lemongrass-like morphology
of the self-supporting Co3O4 is perfectly retained after 100 cycles; (2)
the small nanoparticles of nanoblades shorten the diffusion length for
lithium ions insertion/extraction, hence benefiting the structural
stability and rate capability. A schematic diagram for Li+ insertion/
This journal is ª The Royal Society of Chemistry 2012
Fig. 3 Rate capability of the self-supporting Co3O4 electrodes. (a)
Representative discharge–charge curves at various current rates. (b)
Cycling at various current rates from 0.5 to 10 C.
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extraction of the self-supporting Co3O4 electrode is shown in Fig. S6
(see ESI†); (3) the self-supporting Co3O4 morphology grown directly
on Ni foam can improve electrical contact between Co3O4 and
current-collecting substrate; (4) the three-dimensional architecture
with high surface-to-volume ratio and open space between nano-
blades can enhance the electrolyte/Co3O4 contact area and provide
fast transport channels.
Conclusions
In summary, self-supporting Co3O4 with lemongrass-like
morphology has been fabricated on Ni foam by a facile hydro-
thermal growth with subsequent calcination. As an anode for
LIBs, the unique architecture of Co3O4 exhibits high capacity,
excellent rate capability and cyclic stability. A high reversible
This journal is ª The Royal Society of Chemistry 2012
capacity of 981 mA h g�1 after 100 cycles at a rate of 0.5 C and a
high capacity of 381 mA h g�1 at a rate as high as 10 C made the
material a promising candidate for anode materials of high-power
LIBs. Also, it is envisaged that such a self-supporting Co3O4 with
lemongrass-like morphology could find its interesting applications in
other fields.
The project was financially supported by the National Natural
Science Foundation of China (grant nos. 10974073 and 11179038).
Notes and references
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6 Y. Sun, X. Y. Feng and C. H. Chen, J. Power Sources, 2011, 196, 784.7 Y. H. Ding, P. Zhang, Z. L. Long, Y. Jiang, J. N. Huang, W. J. Yanand G. Liu, Mater. Lett., 2008, 62, 3410.
8 L. Tian, H. L Zou, J. X. Fu, X. F. Yang, Y. Wang, H. L. Guo,X. H. Fu, C. L. Liang, M. M. Wu, P. K. Shen and Q. M. Gao,Adv. Funct. Mater., 2010, 20, 617.
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Q. W. Chen, J. Phys. Chem. C, 2012, 116, 7227.12 Y. G. Li, B. Tan and Y. Y. Wu, Nano Lett., 2008, 8, 265.13 Y. Q. Fan, H. B. Shao, J. M. Wang, L. Liu, J. Q. Zhang and
C. N. Cao, Chem. Commun., 2011, 47, 3469.14 Y. Wang, H. Xia, L. Lu and J. Y. Lin, ACS Nano, 2010, 4, 1425.15 C. C. Li, Q. H. Li, L. B. Chen and T. H.Wang, J. Mater. Chem., 2011,
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S. X. Dou, Electrochim. Acta, 2010, 55, 4805.18 X. W. Li, D. Li, L. Qiao, X. H. Wang, X. L. Sun, P. Wang and
D. Y. He, J. Mater. Chem., 2012, 22, 9189.19 X. H. Wang, X. W. Li, X. L. Sun, F. Li, Q. M. Liu, Q. Wang and
D. Y. He, J. Mater. Chem., 2011, 21, 3571.20 L. M. Li, X. M. Yin, S. Liu, Y. G. Wang, L. B. Chen and T. H. Wang,
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J. Mater. Chem., 2012, 22, 17429–17431 | 17431
Supporting Information
Self-supporting Co3O4 with lemongrass-like morphology as a
high-performance anode material for lithium ion batteries
Yujun Fu, Xiuwan Li, Xiaolei Sun, Xinghui Wang, Dequan Liu, Deyan He*
School of Physical Science and Technology, and Key Laboratory for Magnetism and Magnetic
Materials of MOE, Lanzhou University, Lanzhou, 730000, P. R. China
Experimental details
Sample preparation: For in-situ growth of Co3O4 on Ni foam, 1 mmol of
Co(NO3)2•6H2O and 10 mmol of CO(NH2)2 were dissolved into 50 mL deionized
water under vigorous stirring. After stirring for 20 min, the homogeneous solution was
transferred into a Teflon-lined stainless steel autoclave with a volume of 80 mL, and
then a piece of cleaned Ni foam (with an area of 2×3 cm2) was immersed into it. The
autoclave was tightly sealed and heated at 90 °C for 6 h in an oven, then cooled down
to room temperature naturally. The Ni foam with purple precursors grown was fetched
out and rinsed with deionized water several times. Finally, the as-synthesized
precursors were annealed at 350 °C for 1 h in air.
Structural characterization: The crystalline structures and morphologies of the
samples were characterized by X-ray diffraction (XRD, X’ Pert PRO PHILIPS, Cu Kα
radiation, λ=1.54056 Å), micro-Raman spectrometer (Raman, Jobin-Yvon LabRAM
HR800) with a radiation of 532 nm, field emission scan electron microscopy
* Corresponding author. Tel.: +86 931 8912546; fax: +86 931 8913554. E-mail address: hedy@lzu.edu.cn
Electronic Supplementary Material (ESI) for Journal of Materials ChemistryThis journal is © The Royal Society of Chemistry 2012
(FE-SEM, Hitachi S-4800), and high-resolution transmission electron microscopy
(HRTEM, FEI, Tecnai G2 F30).
Electrochemical characterizations: Electrochemical characterizations were carried
out with CR2032 coin type half cells by using the grown Co3O4 on Ni foam as the
working electrode and lithium foil as the counter and reference electrodes. The cell
preparation process has been described in our previous paper.[1] Celgard 2320 was
used as the separator membrane. The electrolyte was 1 M lithium
hexafluorophosphate (LiPF6) dissolved in ethylene carbonate: dimethyl carbonate:
ethyl methyl carbonate in a 1:1:1 volume ratio. The cyclic voltammetry and
galvanostatic discharge-charge cycling were carried out at room temperature by using
an electrochemical workstation (CHI 660C) and a multichannel battery tester (Neware
BTS-610), respectively.
Supporting figures
Figure S1. Low-magnification and high-magnification images of the precursor on Ni
foam. The lemongrass-like morphologies of the samples before and after annealing in
air are similar, which were grown directly on the substrate of Ni foam in a large area.
Electronic Supplementary Material (ESI) for Journal of Materials ChemistryThis journal is © The Royal Society of Chemistry 2012
Figure S2. XRD pattern of the precursor on Ni foam. Besides the diffraction peaks
marked “#” from the Ni foam substrate, the other obvious diffraction peaks can be
indexed to the orthorhombic Co(CO3)0.5(OH)·0.11H2O (JCPDS card No. 48-0083),
showing that the cobalt carbonate hydroxide hydrate precursor has been grown on Ni
foam.
Figure S3. XRD patterns of the sample after annealing in air. Besides the diffraction
peaks marked “#” from the Ni foam substrate, the other diffraction peaks can be
indexed to (111), (220), (311), (222), (422), (511) and (440) lattice planes of spinel
Co3O4, respectively (JCPDS Card No. 42-1467), indicating that the cobalt carbonate
Electronic Supplementary Material (ESI) for Journal of Materials ChemistryThis journal is © The Royal Society of Chemistry 2012
hydroxide hydrate precursor was turned into crystalline Co3O4 completely.
Figure S4. Raman spectrum of the sample after annealing in air. The peaks centered
at 187, 466, 512, 609, and 674 cm-1, can be attributed to the F2g, Eg, F2g, F2g, and A1g
vibration modes of spinel Co3O4 phase,[2] respectively, which is consistent with the
results of SAED, HRTEM and XRD examinations.
Figure S5 SEM images of the self-supporting Co3O4 electrode after 100
discharge/charge cycles at a rate of 0.5 C. It can be seen that no obvious exfoliation
can be found and the lemongrass-like morphology was remained perfectly.
Electronic Supplementary Material (ESI) for Journal of Materials ChemistryThis journal is © The Royal Society of Chemistry 2012
Figure S6. A schematic diagram for Li+ insertion/extraction of self-supporting Co3O4
with lemongrass-like morphology on Ni foam electrode.
References
[1] X.W. Li, D. Li, L. Qiao, X.H. Wang, X.L. Sun, P. Wang, D.Y. He, J. Mater.
Chem. 22 (2012) 9189.
[2] V.G. Hadjiev, M.N. Iliev, I.V. Vergilov, J. Phys. C: Solid State Phys. 21 (1988)
L199.
Electronic Supplementary Material (ESI) for Journal of Materials ChemistryThis journal is © The Royal Society of Chemistry 2012