Dependence of electrochemical properties of spinel LiMn2O4 on Li2CO3 with micro-flaky, micro-flower and nanorod morphologies

Article abstract of DOI:10.1039/c7ra07088h

Herein, the dependence of spinel LiMn₂O₄ on Li₂CO₃ with micro-flaky, micro-flower and nanorod morphologies is investigated. The results show that the as-synthesized LiMn₂O₄ with micron sized Li₂CO₃ as raw materials have a much higher discharge capacity than that of the one prepared with nano sized Li₂CO₃. It delivers an initial charge capacity of 110.1, 105.2 and 104.9 mA h g^-1 followed by a discharge capacity of 109.1, 103.9 and 104.2 mA h g^-1 with the micro-flower, nanorod and micro-flaky Li₂CO₃ morphologies, respectively, at room temperature (about 99% of the charge capacity is discharged). The smaller specific surface area is found in the spinel LiMn₂O₄ with micron sized Li₂CO₃, resulting in a better stable electrochemical performance in LiMn₂O₄ with micro-flower and micro-flaky Li₂CO₃. Their capacities are maintained at 99.2 mA h g^-1 and 94.2 mA h g^-1 after 100 cycles at 1C rate. The capacity retention was more than 90% at the 100^th cycle with the micron-sized Li₂CO₃. Moreover, the as-synthesized spinel LiMn₂O₄ with micro-flower Li₂CO₃ retained more than 95% of its initial discharge capacity (92 mA h g^-1) after 200 cycles at 2C rate. The cubic spinel structure was detected after 200 cycles of LiMn₂O₄ at 2C rate.

Full text of DOI:10.1039/c7ra07088h

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Dependence of electrochemical properties of
spinel LiMn O on Li CO with micro-flaky,
2
4
2
3
Cite this: RSC Adv., 2017, 7, 42289
micro-flower and nanorod morphologies†
Lang Li, Jinsong Sui, Rui Huang, Wei Xiang and Wei Qin
*
Herein, the dependence of spinel LiMn
morphologies is investigated. The results show that the as-synthesized LiMn
Li CO as raw materials have a much higher discharge capacity than that of the one prepared with nano
sized Li
a discharge capacity of 109.1, 103.9 and 104.2 mA h g with the micro-flower, nanorod and micro-flaky
Li CO morphologies, respectively, at room temperature (about 99% of the charge capacity is
discharged). The smaller specific surface area is found in the spinel LiMn with micron sized Li CO
2
O
4
on Li
2
CO
3
with micro-flaky, micro-flower and nanorod
2
O
4
with micron sized
2
3
ꢀ1
2
3
CO . It delivers an initial charge capacity of 110.1, 105.2 and 104.9 mA h g followed by
ꢀ1
2
3
O
2 4
2
3
,
resulting in a better stable electrochemical performance in LiMn
2
O
4
with micro-flower and micro-flaky
ꢀ1
ꢀ1
Li
2
CO
3
. Their capacities are maintained at 99.2 mA h g and 94.2 mA h g after 100 cycles at 1C rate.
Received 26th June 2017
Accepted 9th August 2017
th
The capacity retention was more than 90% at the 100 cycle with the micron-sized Li
2
CO
retained more than 95% of its initial
discharge capacity (92 mA h g ) after 200 cycles at 2C rate. The cubic spinel structure was detected
after 200 cycles of LiMn at 2C rate.
3
. Moreover,
2 4 2 3
the as-synthesized spinel LiMn O with micro-flower Li CO
DOI: 10.1039/c7ra07088h
ꢀ1
rsc.li/rsc-advances
2 4
O
However, the preparation of spinel LiMn O involves the
solid-state reactions starting from the raw materials, such as
2
4
Introduction
Rechargeable batteries are becoming increasingly important manganese oxides, nitrate or carbonate with lithium hydroxide,
recently, particularly in consumer electronic devices such as nitrate or carbonate at elevated temperatures as high as 700–
ꢁ
cellular telephone, notebook computers, compact camcorders, 900 C. The nal products usually contain larger irregular
1
–4
and electronic vehicles. Spinel LiMn O is regarded as one of particles, with a broad size distribution, as well as impurity
2
4
5
the most promising cathode materials for lithium ion batteries
phases. Furthermore, this method could not provide a good
by virtue of its obvious advantages such as abundant and cheap control on the crystalline growth, compositional homogeneity,
resources, environmental friendliness, safe handling and low morphology, and microstructure. To overcome these problems,
6,7
toxicity. However, the disadvantages of structural instability, the purity and particle size distribution of Li
poor cycle efficiency and low energy density have held back its material were optimized. Moreover, the reaction process of
application for large scale production. In general, as for the Li CO and MnO was studied using thermogravimetry (TG),
battery application, LiMn O powder should possess a single- derivative thermogravimetry (DTG) and differential scanning
CO as the cathode
2
3
2
3
2
2
4
phase, homogeneity, uniform particle morphology with calorimetry (DSC). A uniform cubic nanostructured spinel
a submicron size distribution, and a large surface area in order LiMn fused together was obtained. The most suitable
to achieve better electrode properties. The factors such as calcination temperature was programmed using an oven.
crystallinity, crystal structure, the deviation from theoretical
Recently, many studies have been conducted to improve the
stoichiometry of elemental composition as well as the grain size performance of rechargeable lithium ion battery by using
2 4
O
8,9
10,11
and its distribution play important and eventually, decisive cationic doping and the nanostructured electrode
roles in the electrochemical performance of spinel LiMn
have shown to enhance power performance due to the large
that
2 4
O .
The compound was typically obtained by reaction of a mixture surface-to-volume ratio that allows for a large electrode–elec-
12
13
14
of a lithium salt and manganese oxides subjected to high trolyte contact area. Nanocrystal, nanoporous, nanorod,
15–17
18,19
temperature in air for several hours.
nanotube,
nanowire,
and nanotube active materials are
particularly attractive. The disadvantage of nanosized materials
is that they cannot be packed as dense as the micron-sized
materials on the current collector, since the electrodes made
of nanosized materials exhibit a high porosity, thus resulting in
a decrease in the cell capacity. Therefore, the best way to
Department of Chemical Engineering, State Key Laboratory of Chemical Engineering,
Tsinghua University, Beijing 100084, China
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c7ra07088h
1
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improve both the rate capacity and the electrode density would powder. The powder was then calcinated by a two-step calci-
ꢁ
ꢁ
be to use the micron-sized particles that consist of aggregated nation at 650 C and 800 C for 5 hours with the heating rate at
20
ꢁ
ꢀ1
nanoparticles. Most of the nanostructured electrode materials 3 C min in air to produce spinel LiMn O .
2
4
are synthesized by low-temperature treatment processes such as
21
22,23
24
so chemical, sol–gel,
and hydrothermal methods.
Characterization
The prepared Li
Xiangtan, Hunan) (molar ratio, n(Li) : n(Mn) ¼ 1.01 : 2). The
nanostructured spinel LiMn was prepared by the solid-state
combustion synthesis which is a two-step calcination process at
However, little attention has been paid to the effect of the purity
25
2
3 2
CO was mixed and reacted with MnO (EMD,
and the morphology of the cathode material Li
paper, the cubic uniform nanostructured spinel LiMn
together was synthesized by the solid state reaction with Li
2
CO
3
.
In this
fused
CO
2 4
O
2 4
O
2
3
in micro-aky, micro-ower and nanorod forms. Moreover, the
electrochemical characteristics of the as-synthesized spinel
LiMn O were compared with each other to determine the most
ꢁ
ꢁ
ꢁ
ꢀ1
6
5
50 C and 800 C with the heating rate at 3 C min in air for
hours. The spinel LiMn O formation process was studied by
2
4
2
4
thermogravimetry (TG), derivative thermogravimetry (DTG) and
differential scanning calorimetry (DSC). The crystal structure
and morphology were identied by using X-ray diffraction
analysis (XRD; D8-Advance, Bruker, Germany), scanning elec-
tron microscope (SEM; JSM7401, Jeol, Japan), and Tabletop
scanning electron microscope (TM3000, Hitachi, Japan).
Particle size distribution was measured by Malvern particle size
analyzer (Mastersizer2000, Malvern, England). The Li concen-
tration was analysed by using atomic absorption spectropho-
tometer (Z-5000-AAS, Hitachi, Tokyo, Japan). The purity of the
suitable morphology and size of the raw materials.
Here, a novel strategic synthesis process of a battery grade
lithium carbonate was carried out in a homogeneous-like
26
organic phase. Three types of crystal morphology were
prepared: micro-ower, micro-aky, and nanorod. The nano-
structured spinel LiMn O was then synthesized by the solid-
2
4
state reaction with MnO (EMD) with a calcination program at
2
high temperature. The electrochemical performances of the
prepared spinel LiMn
that the nanostructured spinel LiMn
micron sized Li CO as the raw material had the best perfor-
2
O
4
were discussed. The result showed
2 4
O
prepared with the
as-synthesized Li
00-ES, USA).
2 3
CO was determined by ICP-AES (Varian,
2
3
7
mance and maintained more than 90% of its initial capacity
rate aer 100 charge–discharge cycles at 1C rate. The as-
synthesized LiMn O delivered an initial discharge capacity of
Electrochemical measurement
2
4
ꢀ
1
1
09.1 and 104.2 mA h g at 1C rate with the ower and aky
morphologies, respectively. Moreover, the as-synthesized spinel
LiMn with micro-ower Li CO exhibited an excellent
cycling capability, maintaining 95% of its initial capacity aer
00 cycles at a charge–discharge rate of 2C.
Electrochemical measurements were performed by the coin cell
which was prepared in an argon atmosphere inside a Glove Box
2
O
4
2
3
(MIKROUNA, GER). The electrodes for electrochemical studies
were prepared by making a slurry containing 85 wt% active
material of LiMn O , 10 wt% conducting carbon black, and
2
2
4
5
wt% polyvinylidene uoride (PVDF) binder in N-methyl-2-
pyrrolidone (NMP) as a solvent. The slurry was applied onto
an etched aluminum foil current collector using a doctor-blade
and dried at 130 C for 12 h in a vacuum oven. The coated
Experimental section
Li
2
CO
3
synthesis
ꢁ
Battery grade Li
2
CO
3
was synthesized through the reaction cathode foil was then pressed to form a uniform layer and cut
into a square sheet. Lithium metal foil was used as the anode. A
coupled with a solvent extraction process. First, LiCl (>97%
pure, Beijing Yili, Fine, Chemical, Co., Beijing, China) was
dissolved in deionized water. Then, 50 mL LiCl aqueous solu-
1
M solution of LiPF in ethylene carbonate/dimethyl carbonate
6
(EC/DMC, 1 : 1 v/v) was used as the electrolyte with a Cegrad
tion and 200 mL n-butanol (>97%, pure, Beijing, Chemical 2400 membrane as a separator. The charge–discharge cycles
Works, Beijing, China), that served as the extracting agent and were performed at different C rates between 3.0–4.3 V at room
the diluent were added into a 500 mL separating funnel. The temperature using LAND battery testers.
suspension was shaken for 15 min until the water phase and the
alcohol phase reached equilibrium. Further, the upper alcohol
phase was removed and added together with 100 mL tri-n-octyl
amine (Alamine 336 – Sinopec, Beijing, China), which served as
Result and discussion
Synthesis, structure and morphology of Li CO
2
3
the extractant for HCl, to a three-necked ask. The reaction The synthesis of Li CO is described in the Experimental
2
3
mixture was stirred at 150 rpm for approximately 45 min and section. The reaction process was coupled with the solvent
then CO (>95% pure, Tsinghua University, Beijing, China) was extraction process, which is a new approach for producing
2
bubbled into the reactor at a pressure of 0.1 Mpa. The crystals Li CO from LiCl and CO . The equation for the overall reaction
2
3
2
obtained were then collected by ltration, washed with alcohol, as follows:
and dried.
2
2 2 2 3
LiCl + CO + H O + 2S / Li CO + 2S$HCl
Synthesis of LiMn
The as-synthesized Li
ground with high purity ethanol to produce a well-mixed initial concentration of LiCl. The aky, ower-like, and nanorod
2 4
O
where S is referred to the extractant alamine 336. Three types of
were morphologies of Li CO were synthesized by changing the
2
CO
3
(0.50 g) along with 2.32 g MnO
2
2
3
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particles were prepared with the initial concentration of LiCl at LiMn
2
O
4
, the formation process was studied by thermog-
ꢀ1
2, 3, 4, and 5 mol L (Fig. 1a–d, respectively). The purity of the ravimetry (TG), derivative thermogravimetry (DTG) and differ-
as-synthesized Li CO was tested by ICP-MS with the mass ential scanning calorimetry (DSC) (Fig. 2a). The weight loss of
2
3
ꢁ
fraction higher than 99.95% (see Table S1 in the ESI†). By the mixtures occurred at two discrete regions of 30–650 C and
ꢁ
ꢁ
comparing the purity of commercial Li
2
CO
3
, the as-synthesized 700–800 C and terminated at 800 C. The weight loss at the
ꢁ
Li
Li
2
2
CO
CO
3
has purity higher than that of the required battery temperature range of 30–650 C is attributed to the loss of water
(99.5%). With such high purity of raw material, the as- followed by the decomposition of MnO
also exhibited a higher purity, which can peak concentrated at 450–550 C in the DTG curve. The weight
improve the electrochemical performance of all sides of the loss at the temperature range of 700–800 C and a large
3
2
, whose exothermic
ꢁ
synthesized LiMn
2
O
4
ꢁ
ꢁ
surface of the resultant cathode. SEM images showed that the exothermic peak at 800 C in the DTG curve can be considered
higher was the concentration of LiCl solution, the smaller was as the result of the formation of spinel LiMn O . Two
2
4
the particle size obtained. Thus, at a low concentration of LiCl, exothermic peaks were observed in the DSC curve at the
ꢁ
ꢁ
the synthesized crystals typically consisted of the aky and the temperature of 480 C and 820 C. The possible chemical
ower-like morphologies with micron size, while the nanorod reactions occurring in the synthesis of spinel LiMn was as

2 4
O
particles were obtained with a high concentration of LiCl follows:
solution. Particle size distribution showed that the crystals
were in micron and nanometer range with an approximate size
of 8 ꢂ 1 mm and 80 ꢂ 10 nm (Fig. 1f), which are consistent with
SEM images. The XRD patterns of the reaction-extraction of
as-synthesized Li CO correspond to JCPDS data no. 87-0729,
4
MnO / 2Mn O + O
2
2
3
2
2
Li CO
2
3
+ 4Mn
2
O
3
/ 4LiMn
2
O
4 2
+ CO
2
3
The calcination procedure was programmed following a two-
and no additional impurity peaks were detected (Fig. 1e). Three
different crystal morphologies are involved in two types of
crystallization mechanism (see the explanation in the ESI†).
ꢁ
ꢁ
step calcination at 650 C and 800 C for 5 hours with the
heating rate at 3 C min in air.
Fig. 2b shows the XRD patterns of the products. All the
samples were synthesized under the same reaction conditions.
ꢁ
ꢀ1
Synthesis, structure and morphology of LiMn
Spinel LiMn
calcination reaction by using the prepared Li
2 4
O
The LiMn
was synthesized by a traditional solid-state spinel structure with Fd m space group (JCPDS card no.
CO
of three 35-0782), with no peaks of the Li CO phase detected. The
2 4
O XRD diffraction diagram shows the features of the
3
2 4
O
2
3
2
3
different morphologies as the raw materials. To optimize the characteristic peaks of planes such as [111], [311], [222], [400],
structure, morphology and size of the as-synthesized spinel [331], [511], [440] and [531] can be clearly identied. Thus, the
Fig. 1 SEM images, XRD pattern and particle-size distribution of the as-synthesized Li
Li CO
2 3
2
CO
with the initial concentration of LiCl at 2, 3, 4 and 5 mol L , respectively, (e) XRD pattern, and (f) particle size distribution of the
as-synthesized Li CO
3
. (a) Micro-flaky, (b) micro-flower and (c, d) nanorod
ꢀ1
2
3
.
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Fig. 2 (a) TG, DTG and DSC curves of the mixtures of Li
2
CO
3
and MnO
2
with the ratio of n(Li)/n(Mn) ¼ 1.01 : 2, (b) XRD patterns, and (c–e) SEM
2 4 2 3
images of the as-synthesized spinel LiMn O with the cathode material Li CO in micro-flaky, micro-flower, and nanorod morphologies,
respectively.
reaction between MnO and Li CO produced the pure LiMn O
same preparation route, as a function of cycle number has been
compared with each other (Fig. 3b). The charge and discharge
2
2
3
2
4
4
phase. To analyze the morphological differences of LiMn
prepared with different morphologies of Li CO
2
O
ꢀ
1
2
3
, the SEM capacity was measured with the power rate at 1C (148 mA g ). It
method was applied. Fig. 2c–e show that the synthesized was observed that E1 and E2 had a much higher charge capacity
products are highly crystalline and exhibit spinel structure than E3. Moreover, E1 and E2 showed better stability since their
ꢀ
1
ꢀ1
along with the three types of Li
2 3
CO shown in Fig. 1a–c, capacities were maintained at 94.2 mA h g and 99.2 mA h g
respectively. It can be seen that the spinel structure displayed in aer 100 cycles at the 1C rate, respectively. On the other hand,
ꢀ1
Fig. 2c and d is more uniform than that shown in Fig. 2e. The the discharge capacity decreased to 28.2 mA h g in E3. The
th
distinctive, well-dened crystal faces exhibit the single spinel capacity retention was more than 90% at 100 cycle with the
crystals of octahedral shape with well-developed planes. The as- micron-sized Li
synthesized spinel LiMn has an average size of 100 nm. To better understand the correlation between the structure
and the electrochemical performance of the spinel LiMn
prepared with the raw material of micron-sized Li CO , the TEM
images and the ED patterns of LiMn E2 were analyzed. The
2 3
CO .
2 4
O
2 4
O
Electrochemical performance
2
3
2 4
O
The electrochemical measurements of three types of cathode
materials were performed on the coin cell. The as-synthesized
LiMn O with aky, ower-like and nanorod Li CO forms is
results are shown in Fig. 4. TEM images and diffraction patterns
showed that spinel LiMn O is a cubic single crystal. To obtain
excellent battery performance, the surface of the active mate-
rials is a very important factor. Based on the facet plane, one can
conclude that the surface of this spinel LiMn
and clean. The results showed that it is advantageous to obtain
uniform cubic spinel nanostructured LiMn with micron-
sized Li CO as the raw material. The excellent cycle perfor-
mance is possibly because the spinel LiMn prepared with
the micron sized Li CO and MnO has a better particle size
2
4
2
4
2
3
abbreviated as E1, E2, and E3, respectively. The galvanostatic
charge/discharge tests were performed at room temperature
and shown in Fig. 3a. The rst charge and discharge curves were
carried out at a current density of 1C. It delivered an initial
2 4
O is very pure
ꢀ
1
2 4
O
charge capacity of 110.1, 105.2 and 104.9 mA h g followed by
ꢀ
1
2
3
a discharge capacity of 109.1, 103.9 and 104.2 mA h g with
2 4
O
Li CO in micro-ower, nanorod and micro-aky morphologies,
2
3
2
3
2
respectively, at room temperature (about 99% of the charge
capacity is discharged). The discharge specic capacity of the
three types of cathode materials, which were prepared from the
distribution and uniform morphology. Particle size distribution
of the micron-sized Li CO raw material was limited to a narrow
2
3
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Fig. 3 (a) The charge and discharge curves at 1C rate of the as-
synthesized spinel LiMn
flower, micro-flaky and nanorod. (b) The discharge capacity of
curves of the as-synthesized spinel LiMn with the cathode material
Li CO in micro-flower, micro-flaky and nanorod vs. number of cycles
at 1C rate.
2 4 2 3
O with the raw material Li CO in micro-
Fig. 5 (a) The specific surface area of the as-synthesized Li
b) the specific surface area of the as-synthesized LiMn
2 3
CO and
(
2 4
O .
2 4
O
2
3
2 3
(Fig. 5b) with micron-sized Li CO represented a smaller
specic surface area. This exhibited an adverse result to the
specic surface area of Li CO . The as-synthesized LiMn O
2 4
2
3
with micron-sized Li CO showed a similar specic surface area
2
3
2
ꢀ1
2
ꢀ1
(
3.08 m
synthesized LiMn
a higher specic surface area (7.344 m
g
and 3.076 m
g
, respectively) while the as-
CO exhibited
). Moreover, the
2
O
4
with nano-sized Li
2
3
2
ꢀ1
g
results showed that the excellent electrochemical performance
was probably because of the smaller specic surface area of the
as-synthesized LiMn
Fig. 6a shows the discharge capacity of LiMn O E2 with the
power rate at 2C. Its capacity was maintained at 87.5 mA h g
2 4
O .
Fig. 4 (a and b) Low and high resolution TEM of LiMn
cathode material Li CO in micro-flower morphology, and (c) the
electron diffraction pattern of LiMn
2 4
O with the
2
3
2
4
ꢀ1
2
O
4
.
aer 200 cycles at this rate. The capacity retention is about 95%
th
at 200 cycle. The inset illustrates the charge–discharge curves
micron range; thus, it resulted in the uniform cubic spinel of Li/LiMn
morphology of LiMn . They were fused together forming two voltage plateaus at approximately 4.0 and 4.1 V, which is
2 4
a polyhedral structure which made the Li entering the surface a typical feature of the spinel LiMn O . Two voltage plateaus
2 4
O cells. It can clearly be seen that the samples have
2 4
O
+
of the spinel diffuse through the huge inner structure. More- specify that the insertion and extraction of lithium ion occurred
over, the high purity of the as-synthesized Li CO also plays in two stages. The rst voltage plateau, at about 4.0 V, is
2
3
a key positive role on the electrochemical performance of the as- attributed to the removal of lithium ions from half of the
synthesized LiMn O . The TEM images and the electron tetrahedral sites in which Li–Li interactions occur. The second
2
4
diffraction patterns also conrmed the cubic spinel structure of voltage plateau observed at about 4.1 V is due to the removal of
the as-synthesized LiMn lithium ions from the other tetrahedral sites, in which lithium
2 4
O .
The specic surface area has a signicant effect on the ions do not have Li–Li interactions. Fig. 6b illustrates the
electrochemical performance of the as-synthesized spinel discharge specic capacity at various rates; the charge capacity
LiMn
2 4
O . Thus, the specic surface areas of the as-synthesized was measured with the power rate from 0.2C (29.6 mA h) to 5C
Li CO and LiMn O were analyzed. The results showed that the (740 mA h). It is observed that the as-synthesized spinel
2
3
2 4
specic surface area of nanosized Li CO was larger than that of LiMn O has a much higher discharge capacity than the
2
3
2 4
the micron-sized Li CO (Fig. 5a), which indicates that the commercial powders at different power rates. At the lowest
2
3
particle size of micron-sized Li
2 3
CO was larger than that of value of current (from cycle 1 to 10), the sample has a specic
ꢀ
1
nano-sized Li CO . However, the as-synthesized spinel LiMn
2
3
2
O
4
capacity of 107.8 mA h g . By increasing the rate to 1C, the
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Fig. 8 (a and b) SEM images of spinel LiMn
thorn ball besides the spinel LiMn
Low and (d), high resolution TEM of spinel LiMn
the 2C rate. And (e) the electron diffraction pattern image of spinel
LiMn after 200 cycles at the 2C rate.
O
2 4
after 200 cycles, the
2
O
4
was detected to be impurities. (c)
after 200 cycles at
2
O
4
2 4
O
performance results of E1, E2 and E3, it is observed that the
as-synthesized LiMn with micron-level Li CO shows
2
O
4
2
3
a better electrochemical performance. The better cycle and rate
performance are owing to the smaller specic surface area of
the as-synthesized LiMn O .
2
4
The anode lithium metal foil was immersed in the electrolyte
for 6 hours, then washed with alcohol and dried in a vacuum
dryer before the analysis methods were conducted. SEM images
Fig. 6 (a) Discharge specific capacity and efficiency curves vs. number
of cycles at the 2C rate. The inset image in (a) is the charge and
discharge curves of LiMn
capacity of spinel LiMn
2 4
O
2 4
at the 2C rate, and (b) the discharge of spinel LiMn O aer 200 cycles are shown in Fig. 8a and b. It
2
O
4
at various charge–discharge currents.
is seen that the spinel structure was maintained aer 200 cycles.
The impurity was detected at the same time as shown in Fig. 8a
as a thorn ball was located besides the spinel LiMn
sample still has a discharge capacity of 100 mA h g . The probably because LiMn had not been washed throughout,
discharge capacity can return to 104 mA h g at the 0.5C rate while as shown in Fig. 8b the pure spinel LiMn was detected
aer the high rate discharge cycles, resulting in excellent cycle without any impurity phases existing. Moreover, TEM was
performance. The rate performance of E1 and E3 are shown in tested to determine the cubic spinel structure of LiMn . From
2 4
O . It is
ꢀ
1
O
2 4
ꢀ1
O
2 4
2 4
O
Fig. 7. The results show that E1 delivered a better rate perfor- the images shown in Fig. 8c–e, clear lattice images were
mance. By analyzing the cycle performance and rate observed. The electron diffraction patterns indicate that the
single crystalline cubic spinel structure is maintained aer 200
cycles. The plane [111] is observed in the TEM images with
a lattice parameter of 0.478 nm which corresponds to one of the
peaks of LiMn O .
2
4
Conclusion
2 4
The cubic spinel LiMn O was synthesized with three different
morphologies of the raw material Li
2
CO
3
by the solid-state
calcination synthesis. The effects of Li
2
CO
3
with micro-aky,
micro-ower and nanorod morphologies on the electro-
chemical properties of spinel LiMn were analyzed. The
2 4
O
electrochemical measurements showed that the as-synthesized
spinel LiMn O (E1, E2 and E3) delivered a discharge capacity of
2
4
ꢀ1
1
04.2, 109.1 and 103.9 mA h g at the 1C charge–discharge
rate. The results showed that the as-synthesized spinel LiMn
with micron sized Li CO exhibited excellent electrochemical
2 4
O
Fig. 7 Comparison of E1 and E3 at different charge–discharge
currents.
2
3
42294 | RSC Adv., 2017, 7, 42289–42295
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cyclability because of its well-crystalline nanostructure, and it
maintained more than 90% of its initial capacity aer 100
charge–discharge cycles at the 1C rate. Moreover, the as-
synthesized spinel LiMn O E2 retained more than 95% of its
initial discharge capacity aer 200 cycles at the 2C rate. The
cubic spinel structure was detected aer 200 cycles of LiMn O
2 4
7 H. L. Zhu, Z. Y. Chen, S. Ji and V. Linkov, Solid State Ionics,
2008, 179, 1788–1793.
8 R. Singhal, S. R. Das, O. Oviedo, M. S. Tomar and
R. S. Katiyar, J. Power Sources, 2006, 160, 651–656.
9 C. H. Lu, Y. Lin and H. C. Wang, J. Mater. Sci. Lett., 2003, 22,
615–618.
2
4
at this rate. By comparing three types of morphologies of raw 10 S. Nieto, S. B. Majumder and R. S. Katiyar, J. Power Sources,
material Li CO , the Li CO particles with micron size were 2004, 136, 88–98.
found to be more suitable than those of nano size for calcina- 11 H. Uchiyama, E. Hosono, H. Zhou and H. Imai, J. Mater.
2
3
2
3
tion with MnO to produce the cubic spinel LiMn O .
Chem., 2009, 19, 4012–4016.
2
2 4
1
1
1
2 K. M. Shaju and P. G. Bruce, Chem. Mater., 2008, 20, 5557–
5562.
Conflicts of interest
3 Q. Qu, L. Fu, X. Zhan, D. Samuelis, J. Maier, L. Li, S. Tian,
Z. Li and Y. Wu, Energy Environ. Sci., 2011, 4, 3985–3990.
4 D. K. Kim, P. Muralidharan, H. Lee, R. Ruffo, Y. Yang,
C. K. Chan, H. Peng, R. A. Huggins and Y. Cui, Nano Lett.,
There are no conicts to declare.
Abbreviation
2
008, 8, 3948–3952.
5 W. Tang, Y. Hou, F. Wang, L. Liu and Y. Wu, Nano Lett., 2013,
3, 2036–2040.
6 H. Xia, K. R. Ragavendran, J. Xie and L. Lu, J. Power Sources,
012, 212, 28–34.
1
1
1
E1
E2
E3
LiMn O with micro-aky as raw material
2 4
1
LiMn O with ower as raw material
2
4
LiMn O with nanorod Li CO as raw material
2
4
2
3
2
7 Y. Ding, J. Xie, G. Cao, T. Zhu, H. Yu and X. Zhao, Adv. Funct.
Mater., 2011, 21, 348–355.
Acknowledgements
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Nano Lett., 2009, 9, 1045–1051.
This work was supported by the National Natural Science
Foundation of China under Grant (U1607118).
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