Synthesis and electrochemical properties of LiMn2O4 and LiCoO2-coated LiMn2O4 cathode materials

Article abstract of DOI:10.1016/j.jallcom.2011.12.079

The synthesis of spinel LiMn₂O₄ material by a spherical MnO₂ precursor route is reported in this paper. Hydrothermal and solid-state reactions were adopted to investigate the effects of synthetic methods on the morphologies and electrochemical characteristics of the LiMn₂O₄ products, respectively. LiCoO ₂-coated LiMn₂O₄ microspheres were also prepared by a sol-gel route based on the as-prepared LiMn₂O ₄ microspheres. The products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDX), and inductively-coupled plasma emission spectrograph (ICP-ES). The results show that LiMn₂O₄ octahedrons can be obtained under hydrothermal conditions while LiMn₂O₄ microspheres can be prepared by the solid-state reaction. Electrochemical characterization reveals that the resulting LiMn₂O₄ microspheres and LiCoO₂-coated LiMn₂O₄ microspheres display much better cycling properties than those of LiMn₂O₄ octahedrons.

Full text of DOI:10.1016/j.jallcom.2011.12.079

Journal of Alloys and Compounds 517 (2012) 186–191
Contents lists available at SciVerse ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Synthesis and electrochemical properties of LiMn2O4 and LiCoO2-coated LiMn2O4
cathode materials
Hong-En Wanga,b, Dong Qiana,b,∗, Zhou-guang Lua, Yong-kun Lia
a College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, PR China
b State Key Laboratory of Powder Metallurgy, Changsha 410083, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of spinel LiMn2O4 material by a spherical MnO2 precursor route is reported in this paper.
Hydrothermal and solid-state reactions were adopted to investigate the effects of synthetic methods
on the morphologies and electrochemical characteristics of the LiMn2O4 products, respectively. LiCoO2-
coated LiMn2O4 microspheres were also prepared by a sol–gel route based on the as-prepared LiMn2O4
microspheres. The products were characterized by powder X-ray diffraction (XRD), scanning electron
microscopy (SEM), energy-dispersive X-ray spectrum (EDX), and inductively-coupled plasma emission
spectrograph (ICP-ES). The results show that LiMn2O4 octahedrons can be obtained under hydrothermal
conditions while LiMn2O4 microspheres can be prepared by the solid-state reaction. Electrochemical
characterization reveals that the resulting LiMn2O4 microspheres and LiCoO2-coated LiMn2O4 micro-
spheres display much better cycling properties than those of LiMn2O4 octahedrons.
Received 7 August 2009
Received in revised form
18 December 2011
Accepted 19 December 2011
Available online 26 December 2011
Keywords:
Oxide materials
Electrode materials
Chemical synthesis
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
However, pure spinel LiMn2O4 usually suffers a relatively poor
cycle stability and an insufficient rate capability. It is believed that
In recent years, spinel LiMn2O4 has been intensively investi-
gated as a promising candidate for cathode materials of lithium-ion
batteries (LIBs) due to its low cost, non-toxicity, environmental
friendliness, easy preparation, excellent voltage profile, and oper-
ating safety characteristics [1,2]. For the realization of practical
industrial application, it is important to produce LiMn2O4 pow-
ders with excellent capacity and cycle stability. It is known that
the electrochemical properties of the cathode are strongly depen-
dent on its physical characteristics such as the particle size and
morphology [3,4], crystallinity [5] and composition [6]. A lot of
synthetic methods have been successfully developed to prepare
spinel LiMn2O4 materials with different morphologies, grain sizes,
granularity distribution, crystallinity, and composition. The most
common route for the preparation of spinel LiMn2O4 is based on the
solid-state reaction [7,8]. This process is simple and usually requires
mechanical mixing, grinding, and repeating calcinations at high
temperatures. In addition, several other chemical processes such
as co-precipitation [9], emulsion drying [10], sol–gel [11], Pechini
process [12], and hydrothermal [13,14] have also been developed
to produce spinel LiMn2O4 powders.
the capacity fading of LiMn2O4 is mainly attributed to three fac-
tors: (i) the Jahn–Teller distortion caused by the presence of Mn3+
Jahn–Teller ions [15], (ii) the dissolution of Mn ions into electrolyte
[16], and (iii) the decomposition of electrolyte solution during the
charge–discharge process [17]. To solve this problem, on the one
hand, several research groups have tried to improve the cycling
properties of LiMn2O4 by doping various metal elements such as Co,
Cr, Ni, Fe, Ti, Zn, and Nd [18–22]. On the other hand, surface mod-
ification of LiMn2O4 with various oxides such as LiCoO2 [23,24],
Al2O3 [25], TiO2 [26], ZnO [27,28], AlPO4 [29], CeO2 [30], Li4Ti5O12
[31], ZrO2 [32], and Li2O–2B2O3 [33] has been widely undertaken.
Recently, it has been reported that spherical electrode mate-
rials can possess high discharge capacity and good capacity
retention because they can have higher energy density and
reduce the contact interface of electrode with the electrolyte,
resulting in the improvement of cycling properties. He et al.
[34] synthesized spherical MnCO3 by a controlled crystalliza-
tion method, and then obtained spherical LiMn2O4 material by a
solid-state reaction between the MnCO3 precursors and lithium
salts. Sun et al. [35,36] prepared spherical [Ni0.4Co0.2Mn0.4]3O4
and Li[Ni0.8Co0.1Mn0.1]O2/Li[Ni0.8Co0.2]O2 materials for lithium
secondary batteries by an ultrasonic spray pyrolysis and a co-
precipitation process, respectively. Taniguchi et al. [37] synthesized
spherical LiMn2O4 microparticles by a combination of spray
pyrolysis and drying method. In addition, LiMn2O4 nanorods
with fine electrochemical properties have also been prepared by
∗
Corresponding author at: College of Chemistry and Chemical Engineering, Cen-
tral South University, Changsha 410083, PR China. Tel.: +86 731 88879616;
fax: +86 731 88879616.
E-mail address: qiandong6@vip.sina.com (D. Qian).
0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2011.12.079

H.-E. Wang et al. / Journal of Alloys and Compounds 517 (2012) 186–191
187
solid-state reactions with ␣-MnO2 [38] and ␤-MnO2 [39] as pre-
cursors, respectively.
For the electrochemical measurement, two-electrode cells were employed with
lithium foils as the counter and reference electrodes. The working electrode was
fabricated by mixing the prepared LiMn2O4, acetylene black, and PTFE latex with a
mass ratio of 8:1:1. A slurry of the above mixture was dried in a vacuum oven at
120 ◦C, and then uniaxially pressed into a nickel mesh under a pressure of 30 MPa.
1 M lithium hexafluorophosphate (LiPF6) solution in a mixture of ethylene carbonate
(EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 was used as the elec-
trolyte. The lithium-ion cells were assembled in a glove box purged with floating
argon. Electrochemical properties were investigated using the land battery mea-
surement system (Wuhan, PR China). All the galvanostatic charge/discharge tests
were performed at room temperature and cycled in the voltage range of 4.2–3.5 V
at a current rate of 0.2 C.
In our previous paper [40], we synthesized spherical MnO2 par-
ticles, and further made a simple attempt to produce LiMn2O4
microspheres with the prepared MnO2 spheres as precursors. In
this paper, we report the preparation of spinel LiMn2O4 by a spher-
ical MnO2 precursor route. Hydrothermal and solid-state reactions
were adopted to synthesize spinel LiMn2O4 materials, respectively.
The effects of the two different synthetic routes on the morpholo-
gies and electrochemical properties of LiMn2O4 were investigated.
Moreover, LiCoO2-coated LiMn2O4 microspheres were prepared
based on the as-synthesized LiMn2O4 microspheres by a sol–gel
route.
3. Results and discussion
3.1. Characterization of the as-prepared MnO2 spherical
precursors
2. Experimental
All the chemical reagents were of analytically pure grade and used without any
further purification.
Fig. 1 shows the SEM images and EDX pattern of the prepared
MnO2 spherical precursors. Fig. 1a reveals that the prepared MnO2
sample consists of spherical particles with coarse surfaces. The par-
ticle size of the MnO2 sample ranges from 1 to 4 ␮m. Fig. 1b displays
2.1. Synthesis of MnO2 spherical precursors
The synthesis of MnO2 spherical precursors was referred to our previous report
[41] with some modifications. In a typical procedure, 0.05 mol of MnSO4·H2O and
equal amount of K2S2O8 were dissolved in 1000 ml of distilled water to form a clear
and colorless solution, followed by the addition of 5 ml of concentrated sulfuric acid.
The resulting transparent solution was placed in a 40 ◦C water bath for 48 h. After the
reaction was finished, the black precipitates were filtered off, washed with distilled
water until the absence of SO42−, which was tested by a diluted Ba(NO3)2 aqueous
solution, and then rinsed with ethanol for several times. The resulting samples were
dried in a vacuum oven at 120 ◦C for 6 h and then employed for the synthesis of
LiMn2O4 samples.
2.2. Syntheses of LiMn2O4 samples by hydrothermal and solid-state reaction,
respectively
For the preparation of LiMn2O4 samples, two different methods, namely,
hydrothermal and solid-state reactions were employed, respectively.
For the hydrothermal synthesis of LiMn2O4, 0.87 g of the as-prepared MnO2
spherical precursors and 0.42 g of LiOH·H2O were placed in a 36 ml Teflon-lined
autoclave, followed by the addition of 24 ml of distilled water. After stirring the
mixture for 15 min, the autoclave was sealed, heated in an oven at 180 ◦C for 20 h,
and then allowed to be cooled to room temperature naturally. The black precipitates
were collected by filtration, washed with distilled water and absolute ethanol for
several times, and then dried in a vacuum oven at 120 ◦C for 6 h.
For the solid-state synthesis of LiMn2O4, LiOH·H2O and the as-prepared MnO2
spherical precursors with an appropriate molar ratio of 1.05:2 were mixed and man-
ually ground in an agate mortar for about 10 min. Then the mixture was pre-calcined
in a muffle at 320 ◦C for 12 h, calcined at 750 ◦C for 8 h, and then cooled to room
temperature naturally to give LiMn2O4 product.
2.3. Synthesis of LiCoO2-coated LiMn2O4 by a sol–gel route
LiCoO2-coated LiMn2O4 was synthesized by a sol–gel method. Firstly, citric
acid was dissolved in ethylene glycol with a molar ratio of 1:4 at 80 ◦C to form
a clear and transparent solution. Then, stoichiometric amounts of lithium acetate
(Li(CH3COO)·2H2O) and cobalt acetate (Co(CH3COO)2·4H2O) with a cationic ratio
of Li:Co of 1:1 were dissolved into the above solution and continuously stirred at
80 ◦C until the molar concentration of the solution was condensed to 1 M. Next, an
appropriate amount of LiMn2O4 microspheres synthesized by the solid-state reac-
tion described above with a molar ratio of Co:Mn of 1:20 was added to the solution
along with stirring to form a sol. The sol was further transferred into a vacuum oven
and dried at 120 ◦C to obtain a dry gel. Finally, the dry gel was placed in a muffle
and pre-heated at 320 ◦C for 24 h, followed by calcining at 750 ◦C for 5 h. After cool-
ing to room temperature naturally, LiCoO2-coated LiMn2O4 microspheres would be
obtained as a result.
2.4. Characterization of the as-prepared MnO2, LiMn2O4, and LiCoO2-coated
LiMn2O4 samples
Crystal structures of the prepared samples were identified with powder X-
ray diffraction (XRD) taken on a Rigaku-D-Max rA 12 kW Diffractometer (Cu K␣
˚
radiation, ꢀ = 1.54056 A) at an operation voltage and current of 40 kV and 300 mA,
respectively. Scanning electron micrograph(SEM) and energy-dispersiveX-ray anal-
ysis (EDX) were performed on a JEOL JSM-6360LV scanning electron microscope
equipped with an EDX-GENESIS 60S. Chemical composition of the prepared LiCoO2-
coated LiMn2O4 samples was analyzed by inductively-coupled plasma emission
spectrograph (ICP-ES).
Fig. 1. SEM images and EDX pattern of the as-prepared MnO2 spherical precursors.

188
H.-E. Wang et al. / Journal of Alloys and Compounds 517 (2012) 186–191
No. 35-0782). The sharp diffraction peaks indicate that the pre-
pared LiMn2O4 samples are well crystalline. In addition, the much
sharper reflection peaks in Fig. 2a suggest that the crystallinity of
the LiMn2O4 synthesized by the hydrothermal route is higher than
that prepared by the solid-state reaction. Fig. 2c shows the XRD
pattern of the LiCoO2-coated LiMn2O4 particles. It is found that all
the reflection peaks can be indexed to pure spinel phase similar to
Fig. 2a and b, suggesting that the small amount of surface coating
of LiCoO2 does not change the crystal structure of spinel LiMn2O4.
Fig. 3 shows the SEM micrographs of the LiMn2O4 sample syn-
thesized by the hydrothermal reaction of MnO2 spheres in LiOH
aqueous solution. From Fig. 3a, it is seen that the resultant LiMn2O4
sample mainly consists of large quantities of particles with a size
less than 1 ␮m. Fig. 3b gives a high-magnification image of several
selected LiMn2O4 particles. It is found that the prepared LiMn2O4
sample is composed of particles with well-developed octahedral
shapes (see the arrow) [13,14]. In addition, very few quasi-spherical
particles can also be observed in Fig. 3c as indicated by the arrow.
However, a high-magnification micrograph in Fig. 3d indicates the
outer part of this quasi-spherical LiMn2O4 particle has been evolved
to a lot of small polyhedral particles, suggesting that the spherical
morphology of MnO2 has been destroyed during the hydrothermal
reaction of MnO2 in LiOH solution.
(a)
(b)
(c)
10
20
30
40
50
60
70
2θ / degrees
Fig. 2. XRD patterns of the as-prepared samples: (a) LiMn2O4 prepared by the
hydrothermal reaction, (b) LiMn2O4 synthesized by the solid-state reaction, and
(c) LiCoO2-coated LiMn2O4 obtained by the sol–gel process.
the high-magnification SEM photograph of several MnO2 spheres,
which reveals that one-dimensional nanostructures are vertically
grown on the surfaces of the MnO2 spheres. Fig. 1c presents the
EDX pattern of the prepared sample. From the EDX pattern, it is
clear that only Mn and O elements with a molar ratio of ca. 1:2
exist in the sample, confirming that the prepared sample is MnO2.
Fig. 4 shows the SEM micrographs of the LiMn2O4 sample syn-
thesized by the solid-state reaction of MnO2 spheres and LiOH·H2O.
From Fig. 4a, it is observed that the prepared LiMn2O4 sample is
composed of a large quantity of microspheres with a size rang-
ing from 1 to 8 ␮m in addition to few sintered aggregates. Fig. 4b
presents a high-magnification SEM image of a single LiMn2O4
spherical particle. It indicates that its surface is constructed of large
quantities of small rod-shaped particles. Fig. 4 demonstrates that
the spherical morphology of MnO2 has been well preserved during
the calcination of the mixture of MnO2 and LiOH·H2O.
3.2. Phases and morphologies of the as-synthesized LiMn2O4
samples by different methods
Fig. 2a and b shows the XRD patterns of the LiMn2O4 samples
synthesized by hydrothermal and solid-state reactions, respec-
tively. All the diffraction peaks in Fig. 2a and b can be readily
indexed to pure spinel LiMn2O4 with Fd3m space group (JCPDS card
In current experiments, it is noticed that the morphologies of
LiMn2O4 products are very different when prepared by different
Fig. 3. SEM images of the LiMn2O4 octahedrons synthesized by the hydrothermal reaction.

H.-E. Wang et al. / Journal of Alloys and Compounds 517 (2012) 186–191
189
In contrast, as to the preparation of LiMn2O4 by the solid-state
reaction of MnO2 and LiOH·H2O, the possible chemical reactions
can be expressed in the following:
4MnO2 → 2Mn2O3 + O2↑
(5)
(6)
2LiOH·H2O + 2MnO2 + Mn2O3 → 2LiMn2O4 + 3H2O ↑
The whole reaction equation can be formulated as:
4LiOH·H2O + 8MnO2 → 4LiMn2O4 + 6H2O ↑ + O2↑
(7)
That is, MnO2 will firstly decompose to produce Mn2O3 and O2
at elevated temperature of around 500 ◦C. Next, LiOH, MnO2,
and new-formed Mn2O3 can react under high calcination tem-
perature to form spinel LiMn2O4 crystals, accompanied with
the release of H2O in the form of vapor. Compared with the
hydrothermal process, the whole solid-state reaction takes place
at a high-temperature gas–solid phase atmosphere, in which no
dissolution–recrystallization process will be involved. In addition,
it is also noted that spherical particles have the lowest surface
energies during the calcination process. Hence, the morphology of
MnO2 precursors can be well preserved during the annealing pro-
cess and copied to the resulting LiMn2O4 except for the increase of
particle size due to the growth of crystal grains at high calcination
temperature. Recently, LiMn2O4 nanorods have also been appropri-
ately prepared by the solid-state reaction of MnO2 nanorods and
lithium salts [38,39], which further indicates that the solid-state
reaction may be an appropriate route to synthesize spinel LiMn2O4
with desired morphology by selecting suitable manganese oxide
precursors.
3.3. Characterization of the as-prepared LiCoO2-coated LiMn2O4
microspheres
Fig. 5 shows the SEM images and EDX pattern of the LiCoO2-
coated LiMn2O4 sample synthesized by a sol–gel method. From
Fig. 5a and b, it is found that the sample consists of a large quantity
of spherical particles with a size range of 1–10 ␮m in addition to
a few irregular agglomerates. Fig. 5c and d gives the microscopic
morphologies of two individual LiCoO2-coated LiMn2O4 spherical
particles. It is observed that the surfaces of LiMn2O4 microspheres
after coating with LiCoO2 have become more smooth than that of
pure LiMn2O4 microspheres synthesized by the solid-state reaction
(Fig. 4b), suggesting that LiCoO2 has been successfully coated on
the LiMn2O4 microspheres. The EDX pattern of the LiCoO2-coated
LiMn2O4 microspheres is presented in Fig. 5e. From Fig. 5e, it is
found that only Mn, O, and Co elements are detected in the EDX
pattern. For the analysis of cobalt content in the final LiCoO2-coated
LiMn2O4 sample, ICP-ES analysis was performed. From the ICP anal-
ysis as shown in Table 1, it is seen that 3.2 mol% of cobalt was coated
on the surface of LiMn2O4 microspheres.
Fig. 4. SEM images of the LiMn2O4 microspheres synthesized by the solid-state
reaction.
synthetic methods. We think this should be mainly caused by the
different reaction environments involved.
In the synthesis of LiMn2O4 by the hydrothermal reaction
of MnO2 in LiOH solution, several processes may be involved.
Recently, it has been reported [42–44] that MnO2 nanowires can
be directly obtained by hydrothermal treatment of commercial
MnO2 particles in neutral or alkaline solutions via a dissolution–
recrystallization process. Likewise, it is worthy believing that the
as-prepared MnO2 spherical precursors in present experiments will
also undergo a similar dissolution–recrystallization process during
the hydrothermal treatment. That is, part of MnO2 spheres would
dissolve into the LiOH solution during the hydrothermal treatment.
In addition, some MnO2 molecules would be reduced by OH− in
the solution simultaneously to form MnOOH molecules along with
the production of O2 [43]. The resulting MnOOH thus can further
react with LiOH and MnO2 to form LiMn2O4 nuclei. Next, spinel
LiMn2O4 microcrystals will be produced via the preferential growth
of LiMn2O4 nuclei along its specific crystal facets. Finally, spinel
LiMn2O4 octahedrons would be obtained as a result. The possible
chemical reactions that occurred during the hydrothermal process
can be formulated as follows:
3.4. Electrochemical properties of the as-prepared LiMn2O4 and
LiCoO2-Coated LiMn2O4 samples
Fig. 6 shows the initial charge–discharge curves and cycling
properties of LiMn2O4 and LiCoO2-coated LiMn2O4 samples. From
Fig. 6, it is noted that all the three samples show two clear plateaus
during the electrochemical charge–discharge processes, corre-
sponding to the well-defined spinel LiMn2O4 materials, revealing
that the surface coating of small amount of LiCoO2 does not alter
[MnO2]n → xMnO2 + [MnO2](n−x)
(1)
(2)
(3)
4MnO2 + 2H2O → 4MnOOH + O2↑
Table 1
LiOH + MnO2 + MnOOH → LiMn2O4 + H2O
The overall reaction equation can thus be expressed as follows:
4LiOH + 8MnO2 → 4LiMn2O4 + 2H2O + O2↑
ICP analysis result of the LiCoO2-coated LiMn2O4 sample.
Elements
Li
Mn
Co
Amount (mol%)
32.3
64.5
3.2
(4)

190
H.-E. Wang et al. / Journal of Alloys and Compounds 517 (2012) 186–191
Fig. 5. SEM images and EDX pattern of the LiCoO2-coated LiMn2O4 microspheres.
the intrinsic electrochemical properties of LiMn2O4 as well as its
spinel structure. The initial discharge capacity for the LiMn2O4
octahedrons (Fig. 6a) obtained by the hydrothermal reaction is
128 mAh g−1 while that of the LiMn2O4 microspheres (Fig. 6b) syn-
thesized by the solid-state reaction is 120.6 mAh g−1. The higher
first discharge capacity of LiMn2O4 octahedrons may be due to
the relatively high crystallinity and a small particle size compared
to that of LiMn2O4 microspheres. After surface coating, the dis-
charge capacity of the LiCoO2-coated LiMn2O4 (Fig. 6c) increases
to 124.5 mAh g−1, which may be ascribed to the higher discharge
capacity of LiCoO2 compared to that of LiMn2O4. The cycling sta-
bility of the three electrodes is presented in Fig. 7. Obviously,
the LiMn2O4 octahedrons exhibit a distinct discharge capacity
loss during every charge–discharge cycle (Fig. 7a) compared to
that of the LiMn2O4 microspheres (Fig. 7b). After being cycled
for 50 times, the discharge capacity of the LiMn2O4 octahedrons
retains 114.4 mAh g−1, which is slightly higher than that of the
LiMn2O4 microspheres (112.5 mAh g−1). The capacity retentions of
the LiMn2O4 octahedrons and LiMn2O4 microspheres are 89.4%
and 93.3%, respectively. The better cycling properties of the
LiMn2O4 microspheres may be attributed to the fact that the
larger spherical particles can reduce the contact interface of elec-
trode with electrolytes, resulting in the reduction of dissolution
4.4
4.2
4.0
3.8
3.6
3.4
(c)
(b)
(a)
(a)
(b)
(c)
0
20
40
60
80
100 120 140
Capacity / mAh g-1
Fig. 6. First charge–discharge curves of the as-prepared samples: (a) LiMn2O4 octa-
hedrons, (b) LiMn2O4 microspheres, and (c) LiCoO2-coated LiMn2O4 microspheres.

H.-E. Wang et al. / Journal of Alloys and Compounds 517 (2012) 186–191
191
140
120
100
80
Acknowledgments
This work was financially supported by Provincial Natural Sci-
ence Foundation of Hunan (No. 09JJ3024) and the opening subject
of State Key Laboratory of Powder Metallurgy (No. 2008112032).
(c)
(a)
(b)
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of Mn ions into the electrolyte during the electrochemical reactions.
After surface modification, as shown in Fig. 7c, the LiCoO2-coated
LiMn2O4 electrode shows even superior cycle characteristics.
The discharge capacity of the LiCoO2-coated LiMn2O4 retains
117.2 mAh g−1, with a capacity retention of 94.1%. This result indi-
cates that the surface coating of appropriate amount of LiCoO2 can
both increase the discharge capacity and improve the cycle prop-
erties of the spinel LiMn2O4.
4. Conclusions
Spinel LiMn2O4 materials with different morphologies have
been synthesized by two different methods with pre-prepared
spherical MnO2 particles as precursors. The LiMn2O4 sample
obtained by the hydrothermal reaction mainly consists of large
quantities of octahedral particles with a size less than 1 ␮m
while the LiMn2O4 product prepared by the solid-state reaction
is composed of microspheres with a size ranging from 1 to 8 ␮m.
The morphology difference should be ascribed to the different
reaction processes involved under different reaction conditions.
Moreover, LiCoO2 was coated on the surface of LiMn2O4 micro-
spheres by a sol–gel route. Electrochemical measurements indicate
that the as-synthesized LiMn2O4 octahedrons have a higher ini-
tial discharge capacity (128 mAh g−1) compared to that of the
as-prepared LiMn2O4 microspheres (120.6 mAh g−1) and LiCoO2-
coated LiMn2O4 (124.5 mAh g−1). However, LiMn2O4 microspheres
and LiCoO2-coated LiMn2O4 microspheres display much superior
capacity retentions than that of LiMn2O4 octahedrons. After cycling
for 50 times, the capacity retentions of the LiMn2O4 octahedrons,
LiMn2O4 microspheres, and LiCoO2-coated LiMn2O4 microspheres
are 89.4%, 93.3%, 94.1%, respectively. The synthetic method for the
preparation of LiMn2O4 microspheres by the solid-state reaction
presented here can be potentially developed to synthesize other
Li–Mn–O oxides and metal-doped spinel LiMn2O4 with fine electro-
chemical properties by controlling appropriate stoichiometry ratio
of the initial precursors and optimizing experimental parameters.
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