-
Applied Surface Science 258 (2011) 1317 1321
Contents lists available at SciVerse ScienceDirect
Applied Surface Science
j our nal ho me p age: www.elsev ier .com
Facile s semtheir el
Mei Kong hanSchool of Chem l Chem
a r t i c l
Article history:Received 18 MReceived in reAccepted 30
AAvailable onlin
Keywords:CuOHollow nanospSynthesisKirkendall effeLithium ion
ba
rage theraract
miche baollow
and y nanuO n
of ntance
contalithium ion insertion and extraction.
2011 Elsevier B.V. All rights reserved.
1. Introdu
Hollow to their higpotential apdevices anddeveloped fors
includinand ultrasobased methof hollow ndation and from the
didiffusion co
CuO, an gap (Eg = 1.optical switsidering its been prepahollow
micrnanoribbon
CorresponE-mail add
0169-4332/$ doi:10.1016/j.ction
nanostructures have been paid much attention dueh specic surface
area, low density and widespreadplications in drug delivery,
chemical sensors, photonic
lightweight ller [1,2]. A variety of methods have beenor the
synthesis of nanostructures with hollow interi-g template methods
[3,4], hydrothermal treatment [5]nic treatment [6]. In
particularly, the Kirkendall effect-ods have attracted great
interests for the preparationanomaterials in recent years, such as
oxidation, sul-phosphorization of metal nanoparticles, which
resultsfferent diffusion rates between two components in auple
[7,8].important p-type semiconductor with a narrow band2 eV), has
potential applications in sensors, catalysts,ches, lithium ion
batteries and solar cells [9,10]. Con-wide applications, various
CuO hollow structures havered. Liu and Zeng [11] synthesized
dandelion-like CuOospheres with diameters of 48 m, assembled by
CuOs, using Cu(NO3)23H2O, NH3H2O, NaOH and NaNO3
ding author. Tel.: +86 551 2901450; fax: +86 551 2901450.ress:
[email protected] (W. Zhang).
as reactants by solvothermal method at 100 C for 24 h. Liu
andXue [12] reported the synthesis of porous CuO hollow
architectureswith diameters of 11.7 m by thermal oxidation of CuS
and Cu2Ssolid precursors at 700 C for 4 h, respectively. The
precursors weresynthesized by solvothermal method using
Cu(NO3)23H2O andthiourea as reactants with the assistance of PVP at
120 C for 20 h.Bourret and Lennox [13] synthesized porous CuO
hollow micro-spheres assembled by nanoribbons with diameter of 2.55
m bythermolysis of porous Cu(OH)2 hollow microspheres at 600 C
for15 h. The Cu(OH)2 precursor was fabricated by template method
atroom temperature for 35 min, using CuCl22H2O, n-butylamine
asreactants and water-in-oil emulsion as soft template in
H2O/CH2Cl2system.
Among all those potential applications, CuO as anode materi-als
for lithium ion batteries have attracted much interests becauseof
their high theoretical capacity (670 mAh g1), high safety andlow
cost. It has been reported that the morphology and size ofCuO could
inuence its electrochemical performances [14,15]. Forinstance,
Zheng et al. [16] synthesized CuO nanoparticles with anaverage size
of 10 nm via thermal decomposition of CuC2O4 pre-cursor at 400 C
for 4 h, which could deliver an initial dischargecapacity of 810
mAh g1 at a current density of 0.1 mA cm2. Thesecond and third
discharge capacities were about 350 mAh g1
and 120 mAh g1, respectively. The CuO nanoparticles had a
poorcycle performance. Li et al. reported [17] the synthesis of CuO
nan-otubes by heating Cu nanowires at 600 C for 3 h, which
showed
see front matter 2011 Elsevier B.V. All rights
reserved.apsusc.2011.08.127ynthesis of CuO hollow nanospheres
asectrochemical performance
, Weixin Zhang , Zeheng Yang, Shaoying Weng, Zical Engineering,
Anhui Key Laboratory of Controllable Chemical Reaction and
Materia
e i n f o
ay 2011vised form 29 August 2011ugust 2011e 29 September
2011
heres
cttteries
a b s t r a c t
CuO hollow nanospheres with an avesuccessfully synthesized via a
simpleprecursor. The products have been chand eld emission scanning
electronresults from the Kirkendall effect on telectrochemical
performance of CuO hbeen evaluated by cyclic voltammetryCuO hollow
nanospheres assembled bcycle performance than the reported
Cdemonstrated to take the advantagesshorten the lithium ion
transport disprovide suitable electrode/electrolyte/ loc ate
/apsusc
bled by nanoparticles and
gxian Chenical Engineering, Hefei University of Technology,
Hefei 230009, China
diameter of 400 nm and shell thickness of 40 nm have beenmal
oxidation strategy with Cu2O solid nanospheres as theerized by
X-ray diffraction, transmission electron microscopyroscopy. The
formation of CuO hollow nanospheres mainlysis of
temperature-dependent experiments. Furthermore, the
nanospheres as anode materials for lithium ion batteries
hasgalvanostatic discharge-charge experiments. The
as-preparedoparticles exhibit higher initial discharge capacity and
betteranoparticles. The hierarchical hollow nanospheres have
beenanoparticles and hollow architectures, which could not only
and increase the kinetics of conversion reactions, but alsoct
area and accommodate the volume change associated with
-
1318 M. Kong et al. / Applied Surface Science 258 (2011) 1317
1321
an initial discharge capacity of 910 mAh g1 and the 10th
dis-charge capacity of about 100 mAh g1 at a current density of50
mA g1.
In this paper, we report a facile route to synthesize CuO
hol-low nanospoxidation oCu2O solid scale througout any surCuO
hollowfor lithium show highecompared wets from tnanoparticl
2. Experim
2.1. Synthe
All the rand used wnanosphere[18]. The wperature
unCuSO45H2Otilled waterof NaOH sosolution in quickly pouyellow
precdeionized wat 60 C.
The CuOtion of Cu25 C min1. product wa
2.2. Charac
The as-pdiffraction a Cu K rad80 mA. Fieldsurement
wmicroscopesion electrodiffraction (mission eleof 200 kV. Fon a
Perkindard KBr pe
2.3. Electro
The electype cells (Cwere prepaacetylene bratio of 80slurry was
u70 C for 4 hwith lithiumlene membmixture of e
1
1 1
1|
Rel
ativ
e In
tens
ity
1 1
11 1
1
RD pnt at 4
voluonduina) 13.
on aent
of 0
ults
com by X
of tre. A
No. t obt
in w CuOed inical
2. Af nanhe hsurfay of here
andters s shre. F, it cah an
TEM investigation was used to provide further insight intoO
hollow structure. Fig. 3a shows the TEM image of therecursor,
indicating that the Cu2O nanospheres have a solidre with a diameter
of 400 nm. The TEM image of CuO is
in Fig. 3b. The contrast in brightness between the darknd bright
centers conrms the hollow structure of CuO with
hickness of about 40 nm, which is consistent with FESEM. The
corresponding SAED patterns in Fig. S1a and b (Sup-
g information) display the characteristic diffraction rings
ofu2O and monoclinic CuO, respectively, indicating the poly-line
nature of the products.study the formation mechanism of CuO hollow
structure,s were collected after heating the Cu2O precursor in air
at
and 300 C for 2 h, respectively. After 2 h of thermal treat-n
air at 250 C, a core-shell structure with a little void starts
toheres with uniform diameters in large scale by thermalf Cu2O
solid nanospheres at 400 C for 2 h. The uniformnanospheres as the
precursor were prepared in largeh a solution-phase method at room
temperature with-
factant or organic solvent. The formation mechanism of
nanospheres has been proposed. As anode materialsion batteries, the
as-prepared CuO hollow nanospheresr initial discharge capacity and
better cycle performanceith the reported CuO nanoparticles, which
mainly ben-he hierarchical hollow nanostructures assembled
byes.
ental details
sis
eagents used in the experiments were analytical gradeithout
further purication. The synthesis of Cu2O solids as the precursor
was referred to our previous reporthole reaction was conducted in a
beaker at room tem-der constant magnetic stirring. Typically, 0.375
g of
and 2 g of glucose were dissolved in 100 mL of dis-. Then, 25 mL
of NH3H2O solution (0.04 M) and 25 mLlution (0.20 M) were added
dropwise into the aboveturn. 10 min later, 50 mL of ascorbic acid
(0.03 M) wasred into the mixture. After stirring for another 1 h,
theipitates were collected by centrifugation, washed withater and
ethanol for several times and then dried in air
hollow nanospheres were prepared by thermal oxida-O precursor in
air at 400 C for 2 h at a heating rate ofAfter cooling to room
temperature naturally, the blacks obtained.
terization
repared samples were characterized by X-ray powder(XRD) in a
Rigaku D/max-B X-ray diffractometer withiation source ( = 0.154178
nm) operated at 40 kV and-emission scanning electron microscopy
(FESEM) mea-as carried out with a FEI Sirion-200 scanning
electron
operated at an acceleration voltage of 5 kV. Transmis-n
microscopy (TEM) images and selected area electronSAED) patterns
were taken with a Hitachi H-800 trans-ctron microscope performed at
an accelerating voltageourier Transform Infrared (FTIR) spectra
were recordedElmer Spectrum 100 FTIR Spectrometer using the
stan-llet technique in the range of 4004000 cm1.
chemical measurements
trochemical measurements were carried out using coin-R2032) at
room temperature. The working electrodes
red by mixing the as-prepared CuO hollow nanospheres,lack and
polyvinylidene uoride (PVDF) at a weight:10:10 in
N-methylpyrrolidone (NMP). The resultingniformly spread onto a Cu
foil and dried in vacuum at. The cells were assembled in an
argon-lled glove box
disk as counter electrode, microporous polypropy-rane
(Celgard-2400) as separator and 1 M LiPF6 in athylene carbonate
(EC) and dimethyl carbonate (DMC)
Fig. 1. Xtreatme
(1:1 inwere cCo., Chof 0.00formedInstrumrange
3. Res
Theminedpatternperatu(JCPDSproducfor 2 h,oclinicdetect
Typin Fig.sists oscale. Trough pholognanosp400
nmdiamespherestructuFig. 2dis roug
Thethe CuCu2O pstructushownedges ashell timagesportincubic
Ccrystal
To sample250 Cment i0 20 30 40 50 60 70
(b) 1 1 0
2 2
0
2 0
0
1 1
1
1 1
0
2 / degre e
|||
2 2
03
1 1
1 1
32
0 2
0 2
0
2 0
2
(a)
atterns of (a) the precursor and (b) the nal product after
thermal00 C for 2 h in air.
me) as electrolyte. Galvanostatic chargedischarge testscted on a
BTS battery test system (Shenzhen Newareat a current density of 67
mA g1 in a potential range0 V. Cyclic voltammetry (CV) measurements
were per-
CHI604C electrochemical analyzer (Shanghai Chenhua Co., China)
at a scan rate of 0.1 mV s1 in the potential3.0 V.
and discussion
position and phase purity of the products were deter--ray powder
diffraction (XRD). Fig. 1a shows the XRDhe precursor precipitated
in the solution at room tem-ll the diffraction peaks can be indexed
to cubic Cu2O05-0667). Fig. 1b displays the XRD pattern of the
nalained by thermal oxidation of Cu2O precursor at 400 Chich all
the diffraction peaks can be indexed to the mon-
(JCPDS No. 48-1548). No impurities could be obviously the XRD
patterns.FESEM images of the as-prepared products are showns can be
seen in Fig. 2a, the Cu2O precursor con-ospheres with an average
diameter of 400 nm in largeigh-magnication FESEM image in Fig. 2b
displays thece of these nanospheres. Fig. 2c and d shows the
mor-CuO prepared through thermal oxidation of the Cu2Os. The
average diameter and shell thickness are about
40 nm, respectively, without any obvious changes ofcompared with
Cu2O precursor. Many broken hollowown in Fig. 2c reveal the
existence of hollow nano-rom the high-magnication FESEM image
displayed inn be seen that the shell of the CuO hollow nanospheresd
some small nanoparticles can be clearly observed.
-
M. Kong et al. / Applied Surface Science 258 (2011) 1317 1321
1319
(c, d)
form, indicainformationbecome larg
Similar pcollected that 400 C forlution aftershown in Fiheating
at 4layer and thing time atand the core15 min of hlow sphere
Fig. 3. TEM im
pleg at 4the b
struginnihin Chereh thFig. 2. FESEM images of (a, b) Cu2O
nanospheres and
ting condensation of abundant vacancies (Supporting, Fig. S2a).
When heated at 300 C for 2 h, the voidser (Supporting information,
Fig. S2b).henomena were also observed when the samples wererough
thermal oxidation of the Cu2O solid nanospheres
different time. The TEM images of the morphology evo- heating
the samples at 400 C for different time wereg. S3 (Supporting
information). It can be seen that after
are comheatin
On hollowthe beand a tnanospthroug00 C for 5 min, a sphere with
voids between the surfacee inside core can be observed (Fig. S3a).
When the heat-
400 C is prolonged to 8 min, the voids become larger-shell
structure becomes more obvious (Fig. S3b). Aftereating at 400 C,
the core almost disappears and a hol-gradually forms (Fig. S3c).
Finally the solid nanospheres
ages of (a) Cu2O nanospheres and (b) CuO hollow nanospheres.
Because of outward thsequently, eappears.
Interestiby Lis grodimethylfotransformein air at 500The
possiblin our workglucose, is To further spectra of
investigatemation). Fignanosphereresponds todue to adsoand 1610
cmbending, reregion corr1460 cm1
ated with tconrms thFTIR spectrthere still eCuO hollow
nanospheres.
tely transformed into hollow nanospheres after 2 h of00 C (Fig.
3d).asis of above observations, the formation process of CuOcture
is much related with the Kirkendall effect [7,8]. Atng of the
thermal oxidation, Cu2O reacts with O2 in airuO layer would be
formed on the surface of Cu2O solids. Subsequently, the Cu+ in the
core diffuse outwarde CuO shell, meanwhile the O2 in air diffuse
inward.
the different diffusion rates, Cu+ diffuse much fasteran O2
inward and the hollow interior forms [19]. Con-xcess vacancies
occur in the core and hollow structure
ngly, the result here is quite different from that reportedup
[20], who used a solution-phase method in N,N-rmamide at 8595 C to
get Cu2O solid nanospheres andd them into CuO solid nanospheres by
thermal oxidation
C for 2 h, without any obvious change of morphology.e reason may
be that the Cu2O nanosphere precursor, synthesized at room
temperature in the presence ofdifferent from the one reported in
the literature [20].characterize the as-prepared Cu2O nanospheres,
FTIRthe as-prepared Cu2O nanospheres and glucose wered,
respectively, as shown in Fig. S4 (Supporting infor-. S4a shows the
FTIR spectra of the as-prepared Cu2Os. The characteristic
absorption band at 629 cm1 cor-
the CuO vibration of the Cu2O nanocrystals. The bandsrptions of
water molecules are observed at 3300 cm11, which are attributed to
the OH stretching and OH
spectively. Besides, the bands in the 28003000 cm1
espond to the CH stretching. The bands located atand 1270 cm1
are assigned to the vibrations associ-he CH2 group, and typically
the band near 1050 cm1
e existence of carbohydrate [21]. Compared with thea of glucose
in Fig. S4b, the result clearly suggests thatxist some glucose
molecules in the Cu2O spheres even
-
1320 M. Kong et al. / Applied Surface Science 258 (2011) 1317
1321
0.0 0.5 1.0 1.5 2.0 2.5 3.0-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
0.83 V
1.01 V
2.36 V
0.73 V 3rd 2nd
1st
Cur
rent
/ m
A
Potential / V vs. Li+/Li
1.15 V
Fig. 4. Cyclic voltammograms of the CuO/Li cell in the rst,
second and third cyclesat a scan rate of 0.1 mV s1.
after washing the samples with water and ethanol several
times[22,23]. Thus, the aggregates of Cu2O nanoparticles with the
mod-ication of the glucose molecules may play an important role
inthe facile formation of CuO hollow nanostructures [24,25].
Mean-while, durinmolecules igases, whicthe formati
The eleclow nanosplithium iongrams of thcycle, two are
attributtrolyte inteat 2.36 V is tice of CuO 0.73 V and indicating
tcycle, the pdecreases s
Fig. 5 diat a currencess, there and 0.80.0CV measur
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Pote
ntia
l / V
vs.
Li+
/Li
Fig. 5. The di67 mA g1 in aperformance o
which is higher than the theoretical capacity of CuO (670 mAh
g1).The extra discharge capacity is mainly attributed to the
formationof a solid electrolyte interface (SEI) lm during the rst
dis-charge/charge process [27,30]. The capacity fades to 425 mAh
g1
in the secocapacity grCuO hollowinitial dischprevious reonly
deliverent density120 mAh g
chical holloand hollowresult fromion transporeactions.
Thierarchicaelectrode/echange asso
4. Conclus
s where
of C. Thrisonhereollow
fromachies. Thignis, ther lith4 mAanopructuain e
suitnopa
the d in
wled
authl Scg the thermal oxidation process, the remnant glucosen
the Cu2O spheres were decomposed into CO2 and H2Oh would emit out
of the spheres and were benecial toon of the CuO hollow
nanostructures [26].trochemical performances of the as-prepared CuO
hol-heres have been evaluated as anode materials for
batteries. Fig. 4 shows the rst three cyclic voltammo-e CuO/Li
cell at a scan rate of 0.1 mV s1. In the rstcathodic peaks located
at 1.01 and 0.83 V (vs. Li+/Li)ed to the electrode reaction and
growth of solid elec-rface, respectively [27,28]. Meanwhile, the
anodic peakcorresponding to the Li extraction from the crystal
lat-[29]. In the following cycle, two cathodic peaks shift to1.15 V
along with the decrease of each peak intensity,hat the reversible
capacity greatly loses. In the thirdeak potentials remain similar
and the peak intensitylightly.splays the dischargecharge curves of
the CuO/Li cellt density of 67 mA g1. During the rst discharge
pro-are two obvious plateaus at the potential of 1.221.0 V1 V (vs.
Li+/Li), which is consistent with the results ofement. The rst
discharge capacity is 1134 mAh g1,
1000
1200
mA
h g
1
2nd3rd
Thinanospdationfor 2 hcompananospCuO hresultseasily procesgreat
sBesiderials foof 113CuO nnanostthe stroffer athe nareduceions
an
Ackno
TheNatura0 1 2 3 4 5 6 7 8 9 100
200
400
600
800
Spec
ific
capa
city
/
Cycle nu mber
0 20 0 40 0 60 0 800 10 00 120 0
3rd
2nd
1st
Specific capacity / mAh g1
1st
schargecharge curves of the CuO/Li cell at a current density of
potential range of 0.0013.0 V. The inset is the corresponding
cyclicf the cell.
20976033 aCentral Uniment of An
Appendix A
Supplemthe online v
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dischargeadually decreased to 190 mAh g1 (inset in Fig. 5). The
nanospheres assembled by nanoparticles show higherarge capacity
and better cycle performance than theport of CuO nanoparticles with
size of 10 nm, which canr an initial discharge capacity of 810 mAh
g1 at a cur-
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Facile synthesis of CuO hollow nanospheres assembled by
nanoparticles and their electrochemical performance1 Introduction2
Experimental details2.1 Synthesis2.2 Characterization2.3
Electrochemical measurements
3 Results and discussion4 ConclusionsAcknowledgementsAppendix A
Supplementary dataAppendix A Supplementary data