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Nano SIMS characterization of boron- and aluminum-coated LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium secondary ion batteries

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  • Korea Basic Sci Research Institute, Daejeon, SouthKorea

Abstract and Figures

The LiNi1/3Co1/3Mn1/3O2 powders required for the present study, obtained by coprecipitation method has been surface coated with boron and aluminum. The morphology and crystal structure of powders have been characterized using scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy techniques. The elemental distribution of the coated samples analyzed by transmission electron microscopy images and nano secondary ion mass spectrometry indicates a thin uniform layer of [B, Al]2O3 on the surface of spherical LiNi1/3Co1/3Mn1/3O2. The surface-modified LiNi1/3Co1/3Mn1/3O2 has been explored as a cathode material for lithium secondary ion battery applications. The electrochemical charge–discharge results reveal that the capacity retention rate of coated LiNi1/3Co1/3Mn1/3O2 after 40 cycles at 1 C rate maintains 93% of the initial discharge capacity while the rate of bare LiNi1/3Co1/3Mn1/3O2 maintains only 88%. It is noticed that the small amounts of boron and aluminum coatings on the surface of LiNi1/3Co1/3Mn1/3O2 can significantly improve the electrochemical properties of electrode materials because of the suppression of reaction between the cathode and the electrolytes.
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1 23
Journal of Applied Electrochemistry
ISSN 0021-891X
Volume 42
Number 1
J Appl Electrochem (2012) 42:41-46
DOI 10.1007/s10800-011-0369-x
Nano SIMS characterization of boron- and
aluminum-coated LiNi1/3Co1/3Mn1/3O2
cathode materials for lithium secondary ion
batteries
Tae Eun Hong, E.D.Jeong, S.R.Baek,
M.R.Byeon, Young-Suck Lee, F.Nawaz
Khan & Ho-Soon Yang
1 23
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ORIGINAL PAPER
Nano SIMS characterization of boron- and aluminum-coated
LiNi
1/3
Co
1/3
Mn
1/3
O
2
cathode materials for lithium secondary
ion batteries
Tae Eun Hong E. D. Jeong S. R. Baek
M. R. Byeon Young-Suck Lee F. Nawaz Khan
Ho-Soon Yang
Received: 2 September 2011 / Accepted: 4 November 2011 / Published online: 7 December 2011
ÓSpringer Science+Business Media B.V. 2011
Abstract The LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders required for
the present study, obtained by coprecipitation method has
been surface coated with boron and aluminum. The mor-
phology and crystal structure of powders have been
characterized using scanning electron microscopy, X-ray
diffraction and X-ray photoelectron spectroscopy tech-
niques. The elemental distribution of the coated samples
analyzed by transmission electron microscopy images and
nano secondary ion mass spectrometry indicates a thin
uniform layer of [B, Al]
2
O
3
on the surface of spherical
LiNi
1/3
Co
1/3
Mn
1/3
O
2
. The surface-modified LiNi
1/3
Co
1/3
Mn
1/3
O
2
has been explored as a cathode material for lith-
ium secondary ion battery applications. The electrochem-
ical charge–discharge results reveal that the capacity
retention rate of coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
after 40
cycles at 1 C rate maintains 93% of the initial discharge
capacity while the rate of bare LiNi
1/3
Co
1/3
Mn
1/3
O
2
maintains only 88%. It is noticed that the small amounts
of boron and aluminum coatings on the surface of LiNi
1/3
Co
1/3
Mn
1/3
O
2
can significantly improve the electrochem-
ical properties of electrode materials because of the
suppression of reaction between the cathode and the
electrolytes.
Keywords Lithium secondary ion battery Cathode
material Lithium-nickel-cobalt-manganese oxide
Electrochemical properties Nano secondary ion mass
spectrometry
1 Introduction
Recently, rechargeable lithium-ion batteries have found
their way into portable electronic devices and in other
fields including automotive applications [15]. Recharge-
able lithium-ion batteries have mainly utilized the LiCoO
2
as the cathode material because of the simplicity of pro-
duction and stable cycling performance [6]. However,
LiCoO
2
has its own limitation due to the toxicity and the
high cost of cobalt, and the poor thermal stability when it is
fully charged. In search of highly improved cathode mate-
rials for the lithium-ion battery applications, various systems,
such as carbon-coated LiFePO
4
cathode [7], Al
2
O
3
-and
AlF
3
-coated LiFePO
4
cathode [8], chitosan-added LiFePO
4
cathode [9], and LiCoO
2
cathodes [10,11], are reported.
The LiNi
1/3
Co
1/3
Mn
1/3
O
2
materials have been recently
utilized as an alternative substitute to conventional LiCoO
2
cathodes in lithium battery applications because of their
advantages, such as high capacity [6,12], relatively good
rate capability [13,14], and enhanced safety [1518].
However, the insufficient rate capability still limits their
further applications. The studies of these mixed transition
T. E. Hong E. D. Jeong S. R. Baek M. R. Byeon
Busan Center, Korea Basic Science Institute,
Busan 618-230, Korea
T. E. Hong (&)H.-S. Yang
Department of Physics, Pusan National University,
Busan 609-735, Korea
e-mail: tehong@kbsi.re.kr
H.-S. Yang
e-mail: hsyang@pusan.ac.kr
Y.-S. Lee
Interdisciplinary School of Green Energy, Ulsan National
Institute of Science and Technology, Ulsan 689-798, Korea
F. N. Khan
School of Advanced Sciences, VIT University,
Tamil Nadu 632-014, India
123
J Appl Electrochem (2012) 42:41–46
DOI 10.1007/s10800-011-0369-x
Author's personal copy
metal oxides reveal that only the trivalent cobalt plays a
more active redox role in the later stages of lithium
removal than the divalent nickel and the tetravalent man-
ganese, by virtue of its being predominantly electrochem-
ically active. However, all these layered oxides have their
inherent thermodynamic instabilities upon lithium
removal; hence, their kinetic instabilities can create prob-
lems if there is any thermal excursion in the electro-
chemical cell. The stability can, however, be improved
with aluminum substitution.
There are several methods of improving the electro-
chemical properties of electroactive materials, such as
covering electrode material surfaces with conductive sur-
face coating [1924], and doping with metals which
improves the stability of electrode by rising electronic
conductivity, and deflating polarization [2532]. Since the
energy density of batteries is very sensitive to the particle
shape and size of cathode materials, it is believed that the
surface coating is a useful and easy way to improve the
electrochemical properties of cathode materials [1924].
Many investigations have reported that surface-coating
approach is an effective way to improve the electrochem-
ical properties of cathode materials [16,17]. Based on the
facts mentioned above, the present study envisions the
coating electroactive materials, LiNi
1/3
Co
1/3
Mn
1/3
O
2
,
with a trivalent oxide of [B, Al]
2
O
3
for the enhancement
of electrochemical properties. In this study, the surface
modification using boron and aluminum elements to sta-
bilize the surface of LiNi
1/3
Co
1/3
Mn
1/3
O
2
has been
explored. LiNi
1/3
Co
1/3
Mn
1/3
O
2
powder has been obtained
by coprecipitation method, and the effect of the surface
modification of LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders is discussed.
2 Experimental
The (Ni
1/3
Co
1/3
Mn
1/3
)(OH)
2
has been prepared from
NiSO
4
, CoSO
4
, and CoSO
4
by coprecipitation [18,3336].
The obtained (Ni
1/3
Co
1/3
Mn
1/3
)(OH)
2
powders were then
dried at 120 °C for 12 h. In order to prepare the LiNi
1/3
Co
1/3
Mn
1/3
O
2
powder, the (Ni
1/3
Co
1/3
Mn
1/3
)(OH)
2
and Li
2
CO
3
at a molar ratio of 1:1.03 were mixed thoroughly and heated
to 900 °C for 10 h in air. The surface of LiNi
1/3
Co
1/3
Mn
1/3
O
2
corresponding to 0.2 mol was coated with boron
(B) and aluminum (Al) by mixing 0.1 mol of the aluminum
isopropoxide and 0.03 mol of boron trifluoridediethyl
etherate dissolved in 100 ml of ethanol at ambient condi-
tion. It was then dried at 100 °C for 6 h and heated up to
700 °C for 10 h. The morphology and crystal structure of
the coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders were character-
ized using a scanning electron microscope (SEM; Nano-
Sem 230, USA), X-ray diffractometry (XRD; Rigaku
D/Max-2200V, Japan) X-ray photoelectron spectrometer
(XPS; Escalab 250, UK) and transmission electron
microscopy (TEM; JEM2011, Japan).
Nano secondary ion mass spectrometry equipped with a
cesium gun (Nano SIMS; Cameca Nano-SIMS 50, France)
having spatial resolution of 50 nm which is superior to
other dynamic SIMS is employed to analyze the compo-
sition and spatial distribution of elements on the surface
and the cross section of materials. The experimental data
were obtained in multi collection detector mode by sput-
tering the sample with a *1pACs
?
primary ion beam
focused into a spot of *100 nm diameter. The primary
ion beam was rastered over 20 920 lm
2
. Samples were
coated with gold for charge compensation, and a
pre-sputtering of the surface was performed before any
measurements to remove the surface contamination of
gold-coated layer. The powders were also mounted using
epoxy resin and then polished with SiC paper to measure
the element distribution on the cross section of the coated
LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders.
The charge–discharge characteristics of LiNi
1/3
Co
1/3
Mn
1/3
O
2
cathodes have been investigated in CR2016 coin-
type half cells. The coin-type half cell 2016-size contained
a test electrode, a lithium-metal counter-and-reference
electrode, a 15-lm-thick microporous polyethylene sepa-
rator, and an electrolyte solution of 1.15 M LiPF
6
in eth-
ylene carbonate (EC)/dimethyl carbonate (DMC)/diethyl
carbonate (DEC) (3:4:3 vol.%) (LG Chem., Korea). The
amount of active materials in the cathode composite was
20 mg. The cathodes for the battery test cell were made
from the cathode materials, super P carbon black, and
polyvinylidene fluoride (PVdF) binder (Solef) in a weight
ratio of 94:3:3. The electrodes were prepared by coating a
cathode-slurry onto an Al foil followed by drying at 130 °C
for 20 min, and finally subjected to a roll-pressing.
3 Results and discussion
Figure 1a, b represent the SEM images of the bare and the
surface-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
, respectively. The bare
LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders show round shapes with the
10–15 lm size. The SEM images reveal the surface-coated
LiNi
1/3
Co
1/3
Mn
1/3
O
2
remains unaltered even after the surface-
coating process, but the particle size is increased by about 1 lm.
The XRD patterns of the bare and the surface-coated
LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders are presented in Fig. 2a, b,
respectively. All the observed diffraction lines correspond
to those of a a-NaFeO
2
layered structure with a space
group of R-3m [3740]. The lattice parameter aobtained
from Fig. 2is 2.863 A
˚for the both samples, and the cal-
culated lattice parameter cis 14.242 and 14.260 A
˚for the
bare and the coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
, respectively.
These results suggest that the crystal structure of LiNi
1/3
42 J Appl Electrochem (2012) 42:41–46
123
Author's personal copy
Co
1/3
Mn
1/3
O
2
is not affected significantly by the surface
coating.
The Ni and Mn distributions as well as those of boron and
aluminum were examined by means of Nano SIMS 50
having spatial resolution of 100 nm. Figure 3a, b shows the
elemental distributions (B, Al, Ni, and Mn) on the surface
and the cross section of the surface-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders, respectively. The distributions of B and
Al elements are given in the left and the right images,
respectively, at the top in each of (a) and (b), and reveal that
these elements are distributed only on the surface of the
LiNi
1/3
Co
1/3
Mn
1/3
O
2
. The chemical composition of boron
and aluminum elements on the surface was explored by
X-ray photoelectron spectroscopy measurements (Fig. 4).
The core-level spectra analysis reveals that the boron forms
B
2
O
3
and aluminum forms Al
2
O
3
. Nano SIMS images on
the cross section of the surface-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders show that the thickness of coated layer is about
0.7 lm. The distribution of Ni and Mn elements given in the
left and the right images, respectively, at the bottom in each
of (a) and (b) show that Ni and Mn elements are distributed
uniformly throughout the LiNi
1/3
Co
1/3
Mn
1/3
O
2
particles as
desired. It is worth to mention that in enhancing the elec-
trochemical properties, it is important to have dense coating.
In Fig. 3b, the Nano SIMS image shows that the coverage of
the coating is uniformly distributed throughout the entire
surface, even though there is slight variation of the intensity
of the coated material. Furthermore, TEM observation
(Fig. 5) also showed the existence of the the fully covered
dense coating.
The capacity–voltage curves for the first cycle of the
bare and surface-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
, respectively,
as the cell voltages are changed from 3.0 to 4.5 V at a
constant current density, are shown in Fig. 6a, b. The
curves were obtained at the charge–discharge rates of 0.1,
0.2, 0.5, and 1.0 C for each sample. The discharge capac-
ities of the bare LiNi
1/3
Co
1/3
Mn
1/3
O
2
corresponding to 0.1,
0.2, 0.5, and 1.0 C were 181, 177, 166 and 152 mAhg
-1
,
respectively. Similar to the bare sample, the surface-coated
LiNi
1/3
Co
1/3
Mn
1/3
O
2
exhibits the discharge capacities of
182, 177, 163, and 149 mAhg
-1
corresponding to 0.1, 0.2,
0.5 and 1 C, respectively. Previously, Huang et al. [37]
reported that the initial discharge-specific capacities in
LiNi
1/3
Co
1/3
Mn
1/3
O
2
at 0.1, 0.5, 1, and 2 C were 153, 140,
130 and 118 mAhg
-1
, respectively. The discharge capac-
ities of the both samples are significantly improved com-
pared with the previous reported results of LiNi
1/3
Co
1/3
Mn
1/3
O
2
materials [3840].
Figure 7shows the capacity as a function of cycle
numbers for the bare and the surface-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
. As the cycle of charge–discharge repeats at a rate
of 1.0 C, the discharge capacity decreases. However, the
variation of capacity as the number of cycle increases is
different between the bare and surface-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
powers. The retention capacity of bare LiNi
1/3
Co
1/3
Mn
1/3
O
2
after 40 cycles is 88% of initial capacity, but
the retention capacity of the surface-coated LiNi
1/3
Co
1/3
Fig. 1 SEM images of (a) bare and (b) [B, Al]
2
O
3
-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
powder
20 30 40 50 60 70
(a)
(b)
2 theta / Deg.
Intensity / a.u.
(003)
(101)
(006)/(102)
(104)
(105)
(107)
(018)
(110)
(113)
Fig. 2 X-ray diffraction patterns of (a) bare and (b) [B, Al]
2
O
3
-
coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
J Appl Electrochem (2012) 42:41–46 43
123
Author's personal copy
Mn
1/3
O
2
improves to 93%. Even though there is no sig-
nificant difference in the irreversible capacity loss between
the bare and the surface-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
.
194 192 190 188
160
180
200
220
B1s raw data
B
2
O
3
curve fit
B2O3
Intensity / a.u.
Binding Energy / eV
(a)
(b)
80 75 70 65
100
200
300
400
Al
2
O
3
Al2p raw data
Al
2
O
3
curve fit
Ni3p curve fit
Ni3p
Intensity / a.u.
Binding Energy (eV)
Fig. 4 X-ray photoelectron spectra of (a) B1s and (b) Al2p on the
surface of [B, Al]
2
O
3
-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
Fig. 5 Transmission electron microscopy image of [B, Al]
2
O
3
-coated
LiNi
1/3
Co
1/3
Mn
1/3
O
2
Fig. 3 Elemental distributions of B, Al, Mn, and Ni on (a) the surface
and (b) the cross section of [B, Al]
2
O
3
-coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
obtained by Nano SIMS. The left and the right images at the top in
both (a) and (b) are the distributions of B and Al, respectively, and the
left and the right images at the bottom are the distributions of Mn and
Ni, respectively
44 J Appl Electrochem (2012) 42:41–46
123
Author's personal copy
4 Conclusions
Spherical LiNi
1/3
Co
1/3
Mn
1/3
O
2
powders forming in a a-
NaFeO
2
crystal structure were synthesized with coprecipi-
tation method. The surface of LiNi
1/3
Co
1/3
Mn
1/3
O
2
powder
was coated successfully with boron and aluminum. The thin
and uniform [B, Al]
2
O
3
layer is observed on the surface of
LiNi
1/3
Co
1/3
Mn
1/3
O
2
by Nano SIMS. There is significant
improvement in the initial discharge specific capacities of
both bare LiNi
1/3
Co
1/3
Mn
1/3
O
2
and [B, Al]
2
O
3
-coated
LiNi
1/3
Co
1/3
Mn
1/3
O
2
compared with the results of others.
Although the coated LiNi
1/3
Co
1/3
Mn
1/3
O
2
has no significant
difference in initial discharge capacity, the capacity reten-
tion is improved compared with bare LiNi
1/3
Co
1/3
Mn
1/3
O
2
.
The enhancement of retention capacity is attributed to the
improvement in the charge transfer kinetics and the stability
in electrolyte due to [B, Al]
2
O
3
coating. We confirm that a
thin coating of boron and aluminum on surface of LiNi
1/3
Co
1/3
Mn
1/3
O
2
can significantly improve the electrochemi-
cal properties as an electrode material.
Acknowledgment This study was supported by KBSI Grant
(T31601) to T. E. Hong.
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3.0
3.5
4.0
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Cell Potential (V)
Capacity(mAh/g)
(a)
(b)
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2
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O
3
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Co
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Mn
1/3
O
2
at a 1.0 C rate in lithium half
cells
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... In contrast to high toxicity and high cost LiCoO 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 has been regarded as one of the most promising cathode materials due to its large theoretical capacity (~ 270 mA g −1 ) [1], power density, cycling life, and safety, which are basic requirements for the largescale and high-power system applications, such as electric vehicles and hybrid electric vehicles [2][3][4]. Up to now, multiple alternative approaches have been reported to prepare LiNi 1/3 Co 1/3 Mn 1/3 O 2 powders, such as the solid state synthesis [5][6][7], the sol-gel route [8,9], co-precipitation [10][11][12]. The liquid state synthesis can produce the ultrafine powders with better morphologies, but only the solid state method is feasible for large-scale production and has been widely applied in industry at present. ...
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Enhanced thermal decomposition of carbonates is developed to improve the traditional solid state reaction for the synthesis of ultrafine LiNi1/3Co1/3Mn1/3O2 powders. Controllable activation is obtained by optimizing the mechano-chemical treatment time, which is found to affect lattice structure, morphology and electrochemical properties of the as-synthesized ultrafine LiNi1/3Co1/3Mn1/3O2 powders. The optimal mechano-chemical activation time of 10 h results in more stable and integrated structured ultrafine LiNi1/3Co1/3Mn1/3O2 powders with average diameter of 200–500 nm, leading to a high reversible capacity of 114.3 and 140.9 mAh g⁻¹ at 6 C (1620 mA g⁻¹) in the voltage range of 2.5–4.3 and 2.5–4.5 V, respectively. Moreover, the particles exhibit capacity retentions of 80.8% (2.5–4.3 V) and 83.3% (2.5–4.5 V) at 270 mA g⁻¹ after 200 cycles. Importantly, it is revealed that ball-milling has a positive impact on the calcination process, and the decomposition efficiency is about 35.7% higher compared to ball-milling-free process. Graphical abstract The LiNi1/3Co1/3Mn1/3O2 powders prepared by enhancing thermal decomposition show a remarkable high temperature electrochemical property. For optimum performance, the time of mechano-chemical activation should be neither too long nor too short. In addition, the calcination process is further studied in order to understand the transformation regularities of the electrode materials. Open image in new window
... Except for the rare gases, NanoSIMS is able to analyze all the elements or isotopes from hydrogen to uranium. Nowadays, NanoSIMS has been widely used in a variety of fields, such as materialogy (Hong et al., 2012;Lozano-Perez et al., 2008), cosmochemistry (Gyngard et al., 2010;Hoppe et al., 2013), phytoecology (Kilburn et al., 2010;Moore et al., 2010, 2012), geology (McLoughlin et al., 2011Wacey et al., 2008) and edaphology (Heister et al., 2012;Mueller et al., 2012). ...
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Over 3.8 billion years of evolution has enabled many microbial species a versatile metabolism. However, limited by experimental methods, some unique metabolism remains unknown or unclear. A major obstacle is to attribute the incorporation of certain nutrients into a noncultivable species out of a complex microbial community. Such difficulty could be solved if we are able to directly observe substrate uptake at the single-cell level. Nanoscale secondary ion mass spectrometry (NanoSIMS) is a powerful tool for revealing element distribution in nanometer-scale resolution in the fields such as material sciences, geosciences and astronomy. In this review, we focus on another applicability of NanoSIMS in microbiology. In such fields, physiological properties and metabolic activities of microorganisms can be revealed with a single-cell scale resolution by NanoSIMS solely or in combination with other techniques. This review will highlight the features of NanoSIMS in analyzing the metabolic activities of carbon, nitrogen, metal irons by mixed-culture assemblies. Some values of NanoSIMS in environmental microbiology are expected to be discussed via this review.
... However, the substituents are usually electrochemical inactive elements for electrochemical active elements such as Li, Al, Mg, Fe, F and so on in Li, Ni, Co, Mn or O sites. HONG et al [48] reported that the spherical LiNi 1/3 Co 1/3 Mn 1/3 O 2 powders with a thin uniform layer of [B,Al] 2 O 3 on the surface can be obtained via a co-precipitation method. The surfacecoated LiNi 1/3 Co 1/3 Mn 1/3 O 2 particle size was increased by about 1 µm from 10 to 15 µm of the bare LiNi 1/3 Co 1/3 Mn 1/3 O 2 , in which the thickness of coated layer was about 0.7 µm and the calculated lattice parameter c was 14.242 and 14.260 Å for the bare and the coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 , respectively. ...
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The recent advancement in the design, synthesis, and fabrication of micro/nano structured LiNixCoyMnzO2 with one-, two-, and three-dimensional morphologies was reviewed. The major goal is to highlight LiNixCoyMnzO2 materials, which have been utilized in lithium ion batteries with enhanced energy and power density, high energy efficiency, superior rate capability and excellent cycling stability resulting from the doping, surface coating, nanocomposites and nano-architecturing.
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During solid‐state calcination, with increasing temperature, materials undergo complex phase transitions with heterogeneous solid‐state reactions and mass transport. Precise control of the calcination chemistry is therefore crucial for synthesizing state‐of‐the‐art Ni‐rich layered oxides (LiNi1−x−yCoxMnyO2, NRNCM) as cathode materials for lithium‐ion batteries. Although the battery performance depends on the chemical heterogeneity during NRNCM calcination, it has not yet been elucidated. Herein, through synchrotron‐based X‐ray, mass spectrometry microscopy, and structural analyses, we reveal that the temperature‐dependent reaction kinetics, the diffusivity of solid‐state lithium sources, and the ambient oxygen control the local chemical compositions of the reaction intermediates within a calcined particle. Additionally, we found that the variations in the reducing power of the transition metals (i.e., Ni, Co, and Mn) determine the local structures at the nanoscale. The investigation of the reaction mechanism via imaging analysis provides valuable information for tuning the calcination chemistry and developing high‐energy/power density lithium‐ion batteries. This article is protected by copyright. All rights reserved
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Ni-rich layered oxides (NRLO) are widely considered among the most promising cathode materials for high energy-density lithium ion batteries. However, the high proportion of Ni content accelerates the cycling degradation that restricts their largescale applications. The origins of degradation are indeed heterogeneous and thus there are tremendous efforts devoted to understanding the underlying mechanisms at multi-length scales spanning atom/lattice, particle, porous electrode, solid-electrolyte interface, and cell levels and mitigating the degradation of the NRLO. This review combines various advanced in-situ/ex-situ analysis techniques developed for resolving NRLO degradation at multi-length scales and aims to convey a comprehensive picture of its heterogeneous degradation mechanism. This contribution starts with discussing various factors influencing NRLO stability and proceeds to elaborate the multi-scale characterization, including synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, X-ray imaging, Raman spectroscopy, electron microscopy, online electrochemical mass spectrometry, and secondary ion mass spectrometry. Further, the detailed degradation mechanisms at each length scale are analyzed, and corresponding strategies to alleviate the degradation are evaluated. By conveying the progress (mainly between the years 2015 and 2020), methods, insights, and perspectives, this review contributes significantly to the understanding and tackling the cycling degradation of NRLO.
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Li0.96Na0.04Ni1/3Co1/3Mn1/3O2 with CTAB as additive was synthesized. X-ray diffraction pattern reveals the product of the material with CTAB is pure phase. Scanning electron microscopy shows that the powders are average of 200 nm. Electrochemical test shows it in terms of high initial discharge capacity (175.6 mAhg⁻¹) and exhibits good cycle performance with the capacity retention of 93.39 % after 90 cycles compared to the material has no additive (167.6 mAhg⁻¹ and 71.18 %) at 0.1 C rate. Therefore, CTAB as additive should improve the performance of Li0.96Na0.04Ni1/3Co1/3Mn1/3O2 cathode material.
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Li-rich layered transitional metal oxide Li1.2(Mn0.54Ni0.16Co0.08)O2 was prepared by sol—gel method and further modified by AlF3 coating via a wet process. The bare and AlF3-coated Li1.2(Mn0.54Ni0.16Co0.08)O2 samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscope (HRTEM). XRD results show that the bare and AlF3-coated samples have typical hexagonal α-NaFeO2 structure, and AlF3-coated layer does not affect the crystal structure of the bare Li1.2(Mn0.54Ni0.16Co0.08)O2. Morphology measurements present that the AlF3 layer with a thickness of 5—7 nm is coated on the surface of the Li1.2(Mn0.54Ni0.16Co0.08)O2 particles. Galvanostatic charge—discharge tests at various rates show that the AlF3-coated Li1.2(Mn0.54Ni0.16Co0.08)O2 has an enhanced electrochemical performance compared with the bare sample. At 1C rate, it delivers an initial discharge capacity of 208.2 mA·h/g and a capacity retention of 72.4% after 50 cycles, while those of the bare Li1.2(Mn0.54Ni0.16Co0.08)O2 are 191.7 mA·h/g and 51.6 %, respectively.
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To develop lithium-ion batteries with a high rate-capability and low cost, the prevention of capacity loss is one of major challenges, which needs to be tackled in the lithium-ion battery industry. During electrochemical processes, lithium ions diffuse from and insert into battery electrodes accompanied with the phase transformation, whereas ionic diffusivity and concentration are keys to the resultant battery capacity. In the current study, we compare voltage versus capacity of lithium-ion batteries at different current-rates (C-rates) discharging. Larger hysteresis and voltage fluctuations are observed in higher C-rate samples. We investigate origins of voltage fluctuations by quantifying lithium-ion intensity and distribution via a time-of-flight secondary ion mass spectrometry (ToF-SIMS). The result shows that for fully discharged samples, lithium-ion intensity and distribution are not C-rate dependent, suggesting different lithium-ion insertion mechanisms at a higher C-rate discharging might be solely responsible for the observed low frequency voltage fluctuation.
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Conference Paper
For high rate-capability and low cost lithium-ion batteries, the prevention of capacity loss is one of major challenges facing by lithium-ion batteries today. During electrochemical processes, lithium ions diffuse from and insert into battery electrodes accompanied with the phase transformation, where ionic diffusivity and concentration are keys to the resultant battery capacity. In the current study, we first compare voltage vs. capacity curves at different C-rates (1C, 2C, 6C, 10C). Second, lithium-ion distributions and intensity are quantified via the Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). The result shows that voltage vs. capacity relations are C-rate dependent and larger hystereses are observed in the higher C-rate samples. Detailed quantification of lithium-ion intensity for the 1C sample is conducted. It is observed that lithium-ions are distributed uniformly inside the electrode. Therefore, the current study provides a qualitative and quantitative data to better understand C-rate dependent phenomenon of LiFePO4 battery cells.
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The LiFeP powder was synthesized by using the solid state reaction method with Fe(, and chitosan as a carbon precursor material for a cathode of a lithium-ion battery. The chitosan added LiFePO4 powder was calcined at 350 for 5 hours and then 800 for 12 hours for the calcination. Then we calcined again at 800 for 12 hours. We characterized the synthesized compounds via the crystallinity, the valence states of iron ions, and their shapes using TGA, XRD, SEM, TEM, and XPS. We found that the synthesized powders were carbon-coated using TEM images and the iron ion is substituted from 3+ to 2+ through XPS measurements. We observed voltage characteristics and initial charge-discharge characteristics according to the C rate in LiFeP batteries. The obtained initial specific capacity of the chitosan added LiFeP powder is 110 mAh/g, which is much larger than that of LiFeP only powder.
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LiCoO2 powder was synthesized in an aqueous solution by a sol-gel method and used as a cathode active material for a lithium ion rechargeable battery. The layered LiCoO2 powders were prepared by igniting in air for 12 hrs at 600°C (600-LiCoO2) and 850°C (850-LiCoO2). The structure of the LiCoO2 powder was assigned to the space group R bar 3 m (lattice parameters a= 2.814 Å and c= 14.04 Å). The SEM pictures of 600-LiCoO2 revealed homogeneous and fine particles of about 1 μm in diameter. Cyclic voltammograms (CVs) of 600-LiCoO2 electrode displayed a set of redox peaks at 3.80/4.05 V due to the intercalation/deintercalation of the lithium ions into/out of the LiCoO2 structure. CVs for the 850-LiCoO2 electrode had a major set of redox peaks at 3.88/4.13 V, and two small set of redox peaks at 4.18/4.42 V and 4.05/4.25 V due to phase transitions. The initial charge-discharge capacity was 156-132 mAh/g for the 600-LiCoO2 electrode and 158-131 mAh/g for the 850-LiCoO2 electrode at the current density of 0.2 mA/cm2. The cycleability of the cell consisting of the 600-LiCoO2 electrode was better than that of the 850-LiCoO2. The diffusion coefficient of the Li+ ion in the 600-LiCoO2 electrode was calculated as 4.6 × 10-8 cm2/sec.
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LiNi1/3Co1/3Mn1/3O2 (NCM) with a one-dimensional (1-D) porous structure has been developed as a cathode material for Li-ion batteries. The tube-like 1-D structure consists of interlinked, multi-facet nanoparticles approximately 100–500 nm in diameter. The microscopically porous structure originates from the honeycomb-shaped precursor foaming gel, which serves as a self-template during the stepwise calcination process. The as-prepared NCM presents excellent discharge specific capacities as well as high electrochemical activity and cyclic stability, as proven by the cyclic voltammogram and electrochemical impedance spectroscopy.
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Layered (1 − z) Li[Li1/3Mn2/3]O2 − (z) Li[Mn0.5 − yNi0.5 − yCo2y]O2 (y = 1/12, 1/6, 1/3 and 0.25 ≤ z ≤ 0.75) solid solutions have been surface modified with 3 wt.% Al2O3, CeO2, ZrO2, SiO2, ZnO, and AlPO4 and 0.05 atom F− per formula unit and characterized by X-ray diffraction and charge–discharge measurements in lithium cells. The surface modified cathodes show lower irreversible capacity (IRC) loss in the first cycle and higher discharge capacity than the unmodified samples. An analysis of the first charge and discharge capacity values suggests that part of the oxide ion vacancies resulting from the irreversible loss of oxygen during the first charge is retained in the lattice. Surface modification leads to the retention of even more number of oxide ion vacancies in the lattice after the first charge. Surface modification with Al2O3 and AlPO4 are particularly found to be effective in retaining more number of oxide ion vacancies and suppressing the IRC values.
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Li4AlxTi5−xFyO12−y compounds were prepared by a solid-state reaction method. Phase analyses demonstrated that both Al3+ and F− ions entered the structure of spinel-type Li4Ti5O12. Charge–discharge cycling results at a constant current density of 0.15 mA cm−2 between the cut-off voltages of 2.5 and 0.5 V showed that the Al3+ and F− substitutions improved the first total discharge capacity of Li4Ti5O12. However, Al3+ substitution greatly increased the reversible capacity and cycling stability of Li4Ti5O12 while F− substitution decreased its reversible capacity and cycling stability slightly. The electrochemical performance of the Al3+–F−-co-substituted specimen was better than the F−-substituted one but worse than the Al3+-substituted one.
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Non-spherical Li(Ni1/3Co1/3Mn1/3)O2 powders have been synthesized using a two-step drying method with 5% excess LiOH at 800 °C for 20 h. The tap-density of the powder obtained is 2.95 g cm−3. This value is remarkably higher than that of the Li(Ni1/3Co1/3Mn1/3)O2 powders obtained by other methods, which range from 1.50 g cm−3 to 2.40 g cm−3. The precursor and Li(Ni1/3Co1/3Mn1/3)O2 are characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XPS studies show that the predominant oxidation states of Ni, Co and Mn in the precursor are 2+, 3+ and 4+, respectively. XRD results show that the Li(Ni1/3Co1/3Mn1/3)O2 material obtained by the two-step drying method has a well-layered structure with a small amount of cation mixing. SEM confirms that the Li(Ni1/3Co1/3Mn1/3)O2 particles obtained by this method are uniform. The initial discharge capacity of 167 mAh g−1 is obtained between 3 V and 4.3 V at a current of 0.2 C rate. The capacity of 159 mAh g−1 is retained at the end of 30 charge–discharge cycle with a capacity retention of 95%.
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The 5 V spinel cathode LiMn1.42Ni0.42Co0.16O4 with cation disorder in the 16d octahedral sites has been surface modified with 2 wt % nanosize Al2O3, ZnO, Bi2O3, and AlPO4 by an electrostatic self-assembly method. The bare and surface-modified samples have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (TEM), charge−discharge measurements in lithium cells, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The surface-modified samples exhibit better cycling performance, better rate capability, and better rate capability retention during cycling compared to the bare sample. EIS and XPS studies show that the inferior electrochemical performances of the bare LiMn1.42Ni0.42Co0.16O4 are closely related to the formation of thick solid-electrolyte interfacial (SEI) layer at the high operating voltages of 5 V. Surface modifications with nanosize Al2O3, ZnO, Bi2O3, and AlPO4 suppress the formation of thick SEI layers on LiMn1.42Ni0.42Co0.16O4 and thereby improve the electrochemical performances significantly. Moreover, the differences in the surface compositions formed during the annealing or electrochemical cycling processes also influence the electrochemical properties.
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Li4Ti5O12/C composite was synthesized via a simple solid-state reaction using Super-P-Li conductive carbon black as reaction precursor. The prepared samples were characterized by XRD, SEM, TG and granularity analysis and their electrochemical performance was also investigated in this work. The results showed that the Li4Ti5O12/C composite had a spinel crystal structure and the particle size of the powder was uniformly distributed with an average particle size of 480nm. The conductive carbon was embedded in the Li4Ti5O12 particles without incorporation in the Li4Ti5O12 crystal lattice during the sintering process. The added Super-P-Li carbon played an important role in improving the electronic conductivity and electrochemical performance of the Li4Ti5O12/C electrode. Compared with raw Li4Ti5O12, the Li4Ti5O12/C composite exhibited higher rate capability and excellent reversibility. The initial discharge capacity of Li4Ti5O12/C composite was 174.5mAhg−1 at 0.5C and 169.3mAhg−1 at 1C.