Catalytic properties of Co3O4 nanoparticles for rechargeable Li/air batteries
Nanoscale Research Letters
Catalytic properties of Co O nanoparticles for 3 4 rechargeable Li/air batteries
Kwan Su Kim 0
Yong Joon Park 0
0 Department of Advanced Materials Engineering, Kyonggi University , San 94-6, Yiui-dong, Yeongtong-gu, Suwon, Gyeonggi-do, 443-760 , Republic of Korea
Three types of Co3O4 nanoparticles are synthesized and characterized as a catalyst for the air electrode of a Li/air battery. The shape and size of the nanoparticles are observed using scanning electron microscopy and transmission electron microscopy analyses. The formation of the Co3O4 phase is confirmed by X-ray diffraction. The electrochemical property of the air electrodes containing Co3O4 nanoparticles is significantly associated with the shape and size of the nanoparticles. It appears that the capacity of electrodes containing villiform-type Co3O4 nanoparticles is superior to that of electrodes containing cube- and flower-type Co3O4 nanoparticles. This is probably due to the sufficient pore spaces of the villiform-type Co3O4 nanoparticles.
composites; nanostructures; chemical synthesis; electrochemical properties
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Introduction
A significant increase in the energy density of
rechargeable batteries is required to satisfy the demands of
vehicular applications and energy storage systems. One
approach to solving this problem is the introduction of
a new battery system having a higher energy density.
Li/air batteries are potential candidates for advanced
energy storage systems because of their high storage
capability [1-3]. They do not store a ?cathode? in the
system, which allows for a higher energy density than any
other commercial rechargeable batteries. Instead, oxygen
from the environment is reduced by a catalytic surface
inside the air electrode. Thus, catalysts are key materials
that affect the capacity, cycle life, and rate capability of
such batteries.
In this study, the Co3O4 nanoparticles of various
shapes and structures were tested as catalysts of air
electrodes for rechargeable Li/air batteries. Co3O4 with a
spinel structure has attracted a considerable interest as a
potential catalyst in various application fields [4-7]. In
particular, this study was motivated by the notion that
the catalytic efficiency of oxides is highly dependent on
their morphology, size, and crystal structure [8,9].
Herein, three types of Co3O4 of various shapes and
Experimental details
Three types of Co3O4 nanoparticles were prepared by a
hydrothermal reaction using cobalt nitrate (cube type,
flower type) and cobalt chloride (villiform type),
considering previous reports [10,11]. Surfactants such as urea
were also added to obtain nanosized particles. X-ray
diffraction [XRD] patterns of powders were measured using
a Rigaku X-ray diffractometer (Rigaku Corporation,
Tokyo, Japan). The microstructure of the powder was
observed by field-emission scanning electron microscopy
[FE-SEM] (JEOL-JSM 6500F, JEOL Ltd., Akishima,
Tokyo, Japan) and field-emission transmission electron
microscopy [FE-TEM] (JEOL-JEM 2100F JEOL Ltd.,
Akishima, Tokyo, Japan). The electrochemical
performance of the air electrode containing Co3O4
nanoparticles was examined using a modified Swagelok cell,
consisting of a cathode, a metallic lithium anode, a glass
fiber separator, and an electrolyte of 1 M LiTFSI in
EC/PC (1:1 vol.%). The cathode contained carbon (Ketjen
black EC600JD, Akzo Nobel, Amsterdam, The
Netherlands; approximately 1420 m2?g-1), catalysts (Co3O4
nanoparticles), and a binder (PVDF; Sigma-Aldrich, St.
Louis, MO, USA). The molar ratio of carbon to catalysts
was adjusted to 95:5. The binder accounted for 20 wt.%
of the total electrode. The cells were assembled in an
Arfilled glove box and subjected to galvanostatic cycling
using a WonATech (WBCS 3000, Seocho-gu, Seoul,
Korea) charge-discharge system. Experiments were
carried out in 1 atm of O2 using an air chamber.
Results and discussion
Scanning electron microscopy [SEM] and transmission
electron microscopy [TEM] were employed to
investigate the shapes of the samples (Figure 1). Cube-type
Co3O4 nanoparticles have a homogeneous cubic
morphology (Figure 1a). The length of the nanocube was
around 200 nm, and the dominant exposed plane of the
cube-type Co3O4 seemed to be {001}. The villiform-type
Co3O4 particles were formed by a nucleus covered with
numerous micrometer-sized nanorods. In comparison
with the length, the diameter of the nanorod was very
small (less than 100 nm). It is interesting that the
villiform-type Co3O4 has a rough surface. As shown in the
TEM image (Figure 1b), the nanorods seemed to be
stacked with smaller nanoparticles with a diameter of
approximately 80 nm. The flower-type Co3O4 seemed to
have a similar shape and size to those of the
villiformtype Co3O4. However, the nanorods of the flower-type
Co3O4 had a sharper end, smoother surface, and smaller
diameter than those of the villiform-type Co3O4.
Moreover, in contrast with the villiform-type Co3O4, the
nanorods of the flo (...truncated)