Y- and Si-based oxide nanopowders were synthesized by a hydrothermal reaction of Y or Si powders with NaOH or LiOH aqueous solution. Nanoparticles with different morphology such as elongated nanospheres, flower-like nanoparticles and nanowires were produced by a control of processing parameters, in particular, the starting composition of solution. The preliminary result of electrochemical examination showed that the hydrothermally processed nanowires exhibit high initial capacities of Li-ion storage: 653 mAh/g for Y2O3 nanowires as anode materials and 186 mAh/g for Li2Si2O5 nanowires as cathode materials in a Li secondary cell. Compared to the powder with elongated sphere or flower-like shapes, the nanowires showed a higher Li-ion capacity and a better cycle property

A Teeramongkonrasmee

A Xu

B Cheng

CH Ye

CM Su

DF Zhang

Guoxiu Wang

Jung-Ho Ahn

LY Zhang

M Graetzel

M Law

P Myllyperkio

W Wang

Y Wang

Y Zhao

Yong-Jin Kim

English

PubMed

Springer - Publisher Connector

NANO EXPRESS
Hydrothermally Processed Oxide Nanostructures
and Their Lithium–ion Storage Properties
Jung-Ho Ahn • Yong-Jin Kim • Guoxiu Wang
Received: 22 June 2010 / Accepted: 26 July 2010 / Published online: 13 August 2010
 The Author(s) 2010. This article is published with open access at Springerlink.com
Abstract Y- and Si-based oxide nanopowders were
synthesized by a hydrothermal reaction of Y or Si powders
with NaOH or LiOH aqueous solution. Nanoparticles with
different morphology such as elongated nanospheres,
flower-like nanoparticles and nanowires were produced by
a control of processing parameters, in particular, the
starting composition of solution. The preliminary result of
electrochemical examination showed that the hydrother-
mally processed nanowires exhibit high initial capacities of
Li-ion storage: 653 mAh/g for Y2O3 nanowires as anode
materials and 186 mAh/g for Li2Si2O5 nanowires as cath-
ode materials in a Li secondary cell. Compared to the
powder with elongated sphere or flower-like shapes, the
nanowires showed a higher Li-ion capacity and a better
cycle property.
Keywords Hydrothermal reaction  Nanowires 
Li-ion cell  Nanopowders  Crystal growth
Introduction
Nano-sized metal oxides have interesting properties, which
cannot be expected in conventional microcrystalline
materials [1–5]. Due to high specific surface area and
unique structures, they have attracted much attention
among scientists for potential applications in electronic
devices, chemical and physical sensors, photocatalysts,
materials for energy conversion and energy storage, etc. In
particular, one-dimensional (1-D) nanomaterials such as
nanotubes and nanowires are expected to have novel
properties due to higher specific surface area than 2-D or
3-D materials. In the field of energy storage, for instance,
there is a strong demand to replace conventional carbona-
ceous and Li–M–O-based electrode materials to high-per-
formance nanostructured electrodes in Li-ion rechargeable
batteries. Recently, a very high Li-ion storage capacity
combined with good cyclability was reported in nanowires
such as Na–Ti–O [6]. A variety of methods has been
employed to synthesize 1-D nanomaterial [7–10]. The
chemical methods, such as a hydrazine reduction route in
aqueous ethanol solutions assisted by external magnetic
fields, are very effective to synthesize nanowires [11]. As
well, hydrothermal process is considered as one of the most
effective methods for the scaled-up to produce high-quality
nanopowders. By a proper control of processing parameters
such as the composition of starting solution, the morphol-
ogy of nanopowders can be effectively controlled in this
method [12–14].
In the present work, we synthesized Y- and Si-based
oxide nanopowders with different morphology by a
hydrothermal method using metallic Y and Si powders as
starting materials. We also examined Li-ion storage prop-
erty of the synthesized nanopowders to be potentially used
as anode or cathode materials for Li-ion cells.
J.-H. Ahn (&)
School of Material Engineering, Andong National University,
388 Songchun-dong, Andong, Gyungbuk 760-010, Korea
e-mail: jhahn@andong.ac.kr
Y.-J. Kim
Functional Materials Division, Korea Institute of Materials
Science, Sangnan-dong, Changwon, Gyungnam 641-010,
Korea
G. Wang
Department of Chemistry and Forensic Science,
University of Technology, Sydney, NSW 2007, Australia
123
Nanoscale Res Lett (2010) 5:1841–1845
DOI 10.1007/s11671-010-9722-y
Experimental Procedure
Pure Y ([99.5%, 10 lm), Si ([99.8%, 20 lm), NaOH and
LiOH were used as starting materials. Y or Si powders
were put into an aqueous solution of NaOH(1–5 M) or
LiOH(1–5 M). The powder containing solution was then
put into a Teflon-sealed mini-autoclave (80/ 9 120 mm).
The sealed mini-autoclave was put in a heated furnace for
hydrothermal reaction. The reaction took place in the
autoclave at 220–250C for several hours. After the
hydrothermal reaction, the solid products remaining in
the solution were isolated by centrifugal separation, fol-
lowed by washing with de-ionized water and ethanol for
three times. The products were then dried at 100C for 3 h.
A portion of the synthesized products was further heat-
treated at 500C in air for an hour. Phase identification and
structural examination were performed by a XRD and a
field-emission SEM.
The Li-ion storage property was evaluated by an elec-
trochemical test using the synthesized nanopowders as
anode or cathode electrodes in Li-ion cell. The electrodes
were made by dispersing 80 wt% nanopowders, 15 wt%
carbon black and 7 wt% polyvinylidene fluoride (PVDF)
binder in n-methyl pyrrolidone (NMP) solvent to form the
slurry. The slurry was then spread onto a Cu foil, followed
by drying in an oven under a vacuum pressure of 30 torr at
120C for 12 h. The dried electrodes were then pressed at a
Table 1 The synthesis condition for the nanopowders in this work
Specimen Starting
composition
Hydrothermal
reaction
Resulting material
1 Y 1 g ? 3 M LiOH 200C, 24 h Y(OH)5
(elongated shere)
2 Y 1 g ? 1 M LiOH 200C, 24 h Y(OH)5
(nanowire)
3 Si 1 g ? 3 M NaOH 180C, 24 h Na2SiO3H2O
(flower-like)
4 Si 1 g ? 1 M LiOH 180C, 24 h Li2Si2O5H2O
(nanowire)
Fig. 1 FF-SEM images of nanopowder with different morphologies after hydrothermal process described in Table 1. a specimen No. 1,
b specimen No. 2, c specimen No. 3 and d specimen No. 4, respectively
1842 Nanoscale Res Lett (2010) 5:1841–1845
123
pressure of 12 kg/mm2. The nanopowder electrodes were
finally assembled to CR2032 coin cells in an argon-filled
glove-box using lithium metal foil as the counter electrode.
The electrolyte was 1 M LiPF6 in a mixture of ethylene
carbonate (EC) and dimethyl carbonate (DMC) (1:1 by
volume, provided by MERCK, Germany). The cells were
galvanostatically charged and discharged over a voltage
range of 0–3.0 and 2.5–4.5 V for anode and cathode
materials, respectively.
Results and Discussions
After a series of hydrothermal experiments determining
optimum working conditions in Y- and Si-oxide based
systems, we could obtain nanopowders with three different
morphologies: elongated nanospheres, flower-like nano-
particles and nanowires. The result of synthesis conditions
is summarized in the Table 1. First, the hydrothermal
reaction of Y with 1–5 M LiOH at 200C for 24 h resulted
20 30 40 50 60 70 80
Y
2
O
3
 (JCPDS: 43-1036)
Y(OH)
3
 (JCPDS: 24-1422)
after heat treatment (480oC)
Y (JCPDS: 65-1870)
(3
20
)
(3
02
)(2
11
)
(2
10
)(2
01
)
(1
01
)
(1
10
)
(6
42
)
(4
40
)
(1
34
)
(4
00
)
In
te
ns
ity
 (
a.
u.
)
Two theta (deg.)
(2
22
)
as-synthesized
20 30 40 50 60 70 80
after heat treatment (310oC/1h)
In
te
ns
ity
 (
a.
u.
)
Two theta (deg.)
Y
2
O
3
 (JCPDS: 43-1036)
after heat treatment (480oC/1h)
YOOH (JCPDS: 20-1413)
Y(OH)
3
 (JCPDS: 24-1422)
as-synthesized
20 30 40 50 60 70 80
Na
2
SiO
3
 xH
2
O (JCPDS: 18-1246)
as-synthesized
In
te
ns
ity
 (
a.
u.
)
Two theta (deg.)
Na
2
SiO
3
 (JCPDS: 01-0836)
after heat treatment (500oC)
20 30 40 50 60 70 80
(3
30
)
(2
02
)
(1
31
)
(1
70
)
(2
41
)
(0
02
)
(2
20
)
(2
00
)
(1
11
)
(0
40
)
(1
30
)
Li
2
Si
2
O
5
 (JCPDS: 40-0376)
after heat treatment (550oC/1h)
In
te
ns
ity
 (
a.
u.
)
Two theta (deg.)
as-synthesized
Li
2
Si
2
O
5
 xH
2
O (JCPDS: 33-0816)
after heat treatment (300oC/1h)
(2
10
)
(0
21
)
(2
20
)
(0
40
) (2
30
)
(2
21
)
(1
50
)
(0
02
)
(3
11
)
(0
60
)
(1
70
)
(2
61
)
(4
40
)
(4
12
)
a b
c d
Fig. 3 XRD patterns of nanopowder before and after heat treatment. a specimen No. 1, b specimen No. 2, c specimen No. 3 and d specimen No.
4, respectively
0 100 200 300 400 500 600 0 100 200 300 400 500 600
-1.6
-1.2
-0.8
-0.4
0.0
Peak:    454.2 oC
Onset:   432.6 oC
End:      480.3 oC 
Temperature ( oC)
Peak:    290.9 oC
Onset:   271.0 oC
End:      304.3 oC 
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
Peak:    533.4 oC
Onset:   511.4 oC
End:      553.4 oC
Temperature ( oC)
exo
Peak:    248.1 oC
Onset:   199.0 oC
End:      277.0 oC
a bFig. 2 DSC curves of
as-hydrothermally synthesized
nanowires: a specimen No. 2
and b specimen No. 4
Nanoscale Res Lett (2010) 5:1841–1845 1843
123
in the formation of Y(OH)5 particles. As the concentration
of LiOH in aqueous solution decreased from 5 to 1 M, the
powder morphology changed gradually from spherical
shape to wire form. As shown in Fig. 1a, b, an elongated
spherical particles formed when using 3 M LiOH solution,
whereas the shape of particles transformed completely to
nanowires when the concentration of LiOH further
decreased to 1 M. Decreasing slightly the concentration
resulted in a better formation of nanowires but reduced the
yield of products. A similar tendency was observed in the
case of Si-based system where Y powders were hydro-
thermally reacted with LiOH or NaOH. The formation of
nanowires was generally facilitated when the concentration
of hydroxide was drop to 1 M. In this case, however,
higher hydroxide concentration resulted in the formation of
flower-like particles (Fig. 1c), instead of spherical powders
seen in the Y-based system. The individual flower-like
particles have the size of about 5–10 lm, but each particle
consists of tiny plates of about 10 nm in thickness. The
resulting materials were Na2SiO3H2O and Li2Si2O5H2O
for the use of NaOH and LiOH solution, respectively. The
diameter of nanowires in both systems was 10–40 nm with
the length of several hundred micrometers.
The behavior of as-synthesized nanopowders during
heat-up was examined by a differential thermal analysis
(Fig. 2). In Y-based system, two endothermic peaks
appeared at 290.0 and 454.2C, corresponding to the
reactions Y(OH)3 ? YOOH and YOOH ? Y2O3, respec-
tively. In Si-based system, on the other hand, both endo-
thermic and exothermic peaks appeared at 248.1 and
533.4C, respectively.
The result of XRD indicated that the hydrothermally
synthesized Y(OH)3 nanopowders were successively
transformed to YOOH and Y2O3 after the heat treatment at
310 and 550C for an hour in air (Fig. 3a, b). In specimen
No. 3 where Si powder had hydrothermally reacted with
3 M NaOH, the Na2SiO3H2O phase was transformed to
Na2SiO3 after the heat treatment at 248.1 at 550C for an
hour in air (Fig. 3c). Slightly different XRD peaks were
reported in specimen No. 4 where Si powder hydrother-
mally reacted with 1 M LiOH: the as-synthesized Li2Si2
O5H2O became an amorphous-like phase at temperature
near 300C and then transformed to Li2Si2O5 at tempera-
ture above 550C. This might be related to the melting of
residual lithium or lithium-rich phase from LiOH solution
near 300C, as seen by Fe-SEM image of Fig. 1d where
tiny droplets are present at the surface of nanowires. The
most intense peak was (221) for Li2Si2O5H2O, whereas
(110) for Li2Si2O5H2O.
Fig. 4 The morphology of the specimen No. 2 after a post-heat
treatment at 550C for 1 h in air
-100 0 100 200 300 400 500 600 700
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
10 th
10 th
2nd
1st
2nd
1st
V
ol
ta
ge
 v
s.
 L
i/L
i+
 (
V
)
Capacity (mAh/g)
0150
200
300
400
500
600
700
C
ap
ac
it
y 
(m
A
h
/g
)
Cycle number
 No.1 (elongated nanospheres)
 No.2 (nanowires)
a
b
Fig. 5 Li-ion storage property of the Y-based specimens as anode
materials in Li rechargeable cell: a the discharge–charge profiles of
the specimen No. 2 and b comparison of the discharge capacity versus
cycle number between the specimen No. 1 and 2
1844 Nanoscale Res Lett (2010) 5:1841–1845
123
An interesting feature was observed after subsequent
heat treatments of the as-hydrothermally synthesized
nanostructures. Although the phases identified by XDR
were altered by the subsequent heat treatment, the initial
morphology remained unchanged in all examined systems.
An example is shown in Fig. 4, which was produced after
the heat treatment of the specimen No. 2 shown in Fig. 1b.
The synthesized nanopowders were electrochemically
tested as anode materials for Y-based system (specimen
No. 1 and 2) and as cathode materials for Si-based system
(specimen 4) in Li-ion cells. The testing for anode mate-
rials was conducted over the voltage range of 0.01–3.0 V
versus a Li/Li? counter electrode. The discharge capacity
of Y-based nanowire (specimen No. 2) was 653 mAh/g at
first cycle but reduced to 533 mAh/g during charge
(Fig. 5a). The difference might stem from the formation of
a SEI film (solid electrolyte interface) on the surface of the
nanowires, consuming irreversibly a certain amount of
Li-ions. The Li-ion intercalation capacity was relatively well
stabilized upon cyclying: 513 and 472 mAh/g after second
and tenth cycle, respectively. The values are higher than
that of conventional carbon-based anode materials (372
mAh/g) in Li-ion batteries. Compared to the nanowires, the
anode made from the slightly spherical nanopowders
exhibited a lower discharge capacity with a poor retention
upon repeated cycles (Fig. 5b). The higher discharge
capacity of nanowires might be related to their higher
surface area compared with spherical particles. For cathode
materials, hydrothermally Si-based nanowires were exam-
ined by charge–discharge test over the voltage range of
2.5–3.5 V versus a Li/Li? counter electrode (Fig. 6). The
charge capacity of the Si-based nanowire after the first
cycle was 186 mAh/g, showing higher value than that of
conventional Li–Mn–O or Li–Co–O cathode materials with
relatively good cycle property.
Conclusions
Y- and Si-oxide based nanoparticles with variable mor-
phology were easily produced by a hydrothermal method
using metallic Y or Si powders. The difference in resulting
morphology might be related to the supercritical condition
of metal hydroxide solution at high pressure, influencing
the crystal growth, but the knowledge of detailed mecha-
nism is required to clarify the formation of nanowires.
The preliminary result of the Li-ion storage property of the
hydrothermally nanopowders showed clearly that the
nanowires exhibit much higher capacity of Li-insertion
than 2-D (flower-shaped) or 3-D(spherical) nanostructures.
Further study is needed to optimize further electrochemical
characteristics to be practically applicable to Li-ion cell.
Acknowledgments This research was supported by a grant from the
Center for Advanced Materials Processing (CAMP) of the 21st
Century Frontier R&D Program funded by the Ministry of Knowledge
Economy (MKE), Korea.
Open Access This article is distributed under the terms of the
Creative Commons Attribution Noncommercial License which per-
mits any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and source are credited.
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0       20    40      60    80    100   120   140   160   180    200
2.5
3.0
3.5
4.0
4.5
L
i/L
i+
  (
V
)
Capacity (mAh/g)
02010
100
120
140
160
180
200
C
ap
ac
it
y 
(m
A
h
/g
)
Cycle number
a
b
Fig. 6 Li-ion storage property
of the Si-based specimen (No.
4) as cathode materials in Li
rechargeable cell: charge
capacity versus cycle number
and its first charge profile
Nanoscale Res Lett (2010) 5:1841–1845 1845
123


Hydrothermally Processed Oxide Nanostructures and Their Lithium–ion Storage Properties

Y- and Si-based oxide nanopowders were synthesized by a hydrothermal reaction of Y or Si powders with NaOH or LiOH aqueous solution. Nanoparticles with different morphology such as elongated nanospheres, flower-like nanoparticles and nanowires were produced by a control of processing parameters, in particular, the starting composition of solution. The preliminary result of electrochemical examination showed that the hydrothermally processed nanowires exhibit high initial capacities of Li-ion storage: 653 mAh/g for Y 2O 3 nanowires as anode materials and 186 mAh/g for Li 2Si 2O 5 nanowires as cathode materials in a Li secondary cell. Compared to the powder with elongated sphere or flower-like shapes, the nanowires showed a higher Li-ion capacity and a better cycle property. © 2010 The Author(s)

Ahn, JH

Kim, YJ

Wang, G

OPUS - University of Technology Sydney

Nanoscale Research Letters

Hydrothermally processed oxide nanostructures and their lithium-ion storage properties

Crossref

Abstract Y- and Si-based oxide nanopowders were synthesized by a hydrothermal reaction of Y or Si powders with NaOH or LiOH aqueous solution. Nanoparticles with different morphology such as elongated nanospheres, flower-like nanoparticles and nanowires were produced by a control of processing parameters, in particular, the starting composition of solution. The preliminary result of electrochemical examination showed that the hydrothermally processed nanowires exhibit high initial capacities of Li-ion storage: 653 mAh/g for Y2O3 nanowires as anode materials and 186 mAh/g for Li2Si2O5 nanowires as cathode materials in a Li secondary cell. Compared to the powder with elongated sphere or flower-like shapes, the nanowires showed a higher Li-ion capacity and a better cycle property.</p

Kim Yong-Jin

Wang Guoxiu

Ahn Jung-Ho

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Hydrothermally Processed Oxide Nanostructures and Their Lithium&#8211;ion Storage Properties

C a p a c i t y ( m A h / g ) Cycle number a b

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Hydrothermally Processed Oxide Nanostructures and Their Lithium–ion Storage Properties

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