Characterization of Li1-xNi1+xO2 prepared using succinic acid as a complexing agent

Article abstract of DOI:10.1134/S0020168506020166

Li_1-xNi_1+xO₂ was prepared by a polymerized complex method using succinic acid as a complexing agent. Ethanolic solutions of lithium acetate dihydrate, nickel acetate tetrahydrate, and succinic acid were mixed to form carboxylate precursors, which were subsequently calcined at 650-800°C for 14-48 h. TGA curves of metal acetates, succinic acid, and the precursors were characterized to determine weight loss and formation temperature of the oxide. By using XRD, SEM, and EDX, pure crystals of Li _1-xNi_1+xO₂ were detected at 750 and 800°C. The maximum and minimum intensity ratios of XRD spectra show that the optimum calcination condition is 750°C for 40 h. At 650-800°C, the particle size distribution is in the range of 0.35-39 μm. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S0020168506020166

ISSN 0020-1685, Inorganic Materials, 2006, Vol. 42, No. 2, pp. 202–209. © Pleiades Publishing, Inc., 2006.
Characterization of Li1 – xNi1 + xO2 Prepared Using Succinic Acid
as a Complexing Agent1
Titipun Thongtem and Somchai Thongtem
Faculty of Science, Chiang Mai University, Chiang Mai, 50200 Thailand
e-mail: ttpthongtem@yahoo.com; ttpthongtem@hotmail.com
Received March 25, 2005; in final form, September 22, 2005
Abstract—Li1 – xNi1 + xO2 was prepared by a polymerized complex method using succinic acid as a complexing
agent. Ethanolic solutions of lithium acetate dihydrate, nickel acetate tetrahydrate, and succinic acid were
mixed to form carboxylate precursors, which were subsequently calcined at 650–800°C for 14–48 h. TGA
curves of metal acetates, succinic acid, and the precursors were characterized to determine weight loss and for-
mation temperature of the oxide. By using XRD, SEM, and EDX, pure crystals of Li1 – xNi1 + xO2 were detected
at 750 and 800°C. The maximum and minimum intensity ratios of XRD spectra show that the optimum calci-
nation condition is 750°C for 40 h. At 650–800°C, the particle size distribution is in the range of 0.35–39 µm.
DOI: 10.1134/S0020168506020166
1
INTRODUCTION
(succinic acid). Stoichiometric amounts of lithium and
nickel salts and succinic acid were dissolved separately
in ethanol, mixed, and subsequently heated at 50–60°C
to remove ethanol. The carboxylate precursors were
precalcined at 450°C to remove organic compounds
and subsequently calcined at 650–800°C in air for
14−48 h. The preparation process is shown schemati-
cally in Fig. 1.
At present, the demand for rechargeable batteries in
electronic devices becomes increasingly important.
LiNiO2 is an oxide of great interest due to its large dis-
charge capacity [1], long cycle life [2], and low cost [2, 3].
It has a layered, α-NaFeO2 type structure with the
rhombohedral space group R3 m [4–6]. The preparation
of the oxide with good electrochemical properties is
rather difficult due to the formation of nonstoichiomet-
ric phase at high temperature [6–8]. Solid-state reac-
tion, a physical process, can be done by heating a mix-
ture at high temperature, but it is time-consuming [9,
10]. The reaction results in a nonstoichiometric phase
[2, 7], inhomogeneity [7, 11], irregular morphology [7],
and larger particle size and size distribution [7]. There-
fore, low-temperature methods, such as the Pechini
process [12], sol–gel method [13], precipitation process
[14], and hydrothermal technique [11, 15], have been
developed.
The carboxylate precursors and powder were char-
acterized by a thermogravimetric analyzer (TGA) with
Succinic acid
(SA)/ethanol
Lithium acetate dihydrate,
nickel acetate
tetrahydrate/ethanol
Li : Ni : SA = 1 : 1 : 2 by mole
Evaporation of
ethanol at 50–60°C
For the present research, Li1 – xNi1 + xO2 powder has
been prepared by a polymerized complex method using
succinic acid as a complexing agent with subsequent
calcination at high temperature for certain time periods.
Optimum conditions, phase, morphology, and size dis-
tribution have been evaluated.
Carboxylate precursors
Drying at 70°C
Precalcination at 450°C for 6 h
Calcination at 650, 700, 750, and
800°C for 14–48 h
EXPERIMENTAL
Following a similar preparation procedure for
LiMn2O4 [16], Li1 – xNi1 + xO2 powder was prepared
from two starting reagents (lithium acetate dihydrate
and nickel acetate tetrahydrate) and a complexing agent
Powder
Fig. 1. Schematic diagram for the preparation of
1 − x 1 + x 2
1
The text was submitted by the authors in English.
Li Ni
O .
202

CHARACTERIZATION OF Li1 – xNi1 + xO2 PREPARED USING SUCCINIC ACID
203
absorption spectrophotometer (AAS) to determine Li
and Ni contents, and titration to determine Ni3+ ions.
Ni3+ was reduced to Ni2+ by excess ammonium iron(II)
sulfate and titrated back with a standard potassium per-
manganate solution.
100
90
80
70
60
50
40
30
20
10
0
1
RESULTS AND DISCUSSION
2
4
TGA. Lithium acetate dihydrate, nickel acetate tet-
rahydrate, succinic acid, and the carboxylate precursors
were studied by TGA with the results shown in Fig. 2.
The weight loss of lithium acetate dihydrate at 40–228
and 338–470°C is due to the evaporation of adsorbed
water and water of crystallization (lattice water) and
decomposition of acetate ions [17], respectively. Nickel
acetate tetrahydrate shows a weight loss in three steps:
evaporation of adsorbed and lattice water and decom-
position of acetate ions and the residual organic constit-
uents at 40–209 [17], 271–390 [17], and 390–500°C,
respectively. Succinic acid shows a weight loss over the
range of 170–320°C. Carboxylate precursors show a
weight loss in four steps resulting from the evaporation
of ethanol and adsorbed water at 40–170°C and the
decomposition of succinic acid, acetate ions from the
3
100
200
300
400
500
600
Temperature, °C
Fig. 2. TGA of (1) lithium acetate dihydrate, (2) nickel ace-
tate tetrahydrate, (3) succinic acid, and (4) carboxylate pre-
cursors.
a heating rate of 20°C/min in nitrogen atmosphere, an
x-ray diffractometer (XRD) operated at 20 kV and
15 mA, using the Kα line from a Cu target, a scanning
electron microscope (SEM) equipped with an energy
dispersive x-ray (EDX) analyzer operated at 15 kV, a pyrolysis of lithium and nickel acetates, and other
particle size analyzer (laser diffraction), an atomic organic compounds at 170–320, 320–470, and 470–
104
*
Li1 – xNi1 + xO2
*
Li2CO3
003
006
102
Li2Ni8O10
*
*
101
015
*
107
*
800°C
750°C
*
700°C
650°C
10
20
30
40
50
60
2θ, deg
Fig. 3. XRD spectra of the powder produced at 650–800°C calcination for 24 h.
INORGANIC MATERIALS Vol. 42 No. 2 2006

204
003/I104
TITIPUN THONGTEM, SOMCHAI THONGTEM
600°C, respectively. Succinic acid seems to influence
the decomposition of acetate ions. After the weight loss
is terminated, the formation of lithium nickel oxide is
likely to begin at 600°C and higher temperatures.
I
I
006 + 102/I101
2.2
0.70
0.65
0.60
0.55
0.50
0.45
0.40
2.0
1.8
1.6
1.4
1.2
XRD. The powder was analyzed using XRD and a
JCPDS standard [18]. XRD spectra are shown in Fig. 3.
At 650 and 700°C, the powder consists of Li1 – xNi1 + xO2
containing Li2CO3 and Li2Ni8O10 impurities. At 750
and 800°C, the spectra were very sharp, and only the
crystalline phase of Li1 – xNi1 + xO2 was detected. The
diffraction angles of the experimental spectra are in
accord with those of the standard, but the intensity I is
slightly different. The I003/I104 and I006 + 102/I101 intensity
ratios at 650–800°C were calculated and plotted in
Fig. 4. It was found that the intensity ratios were con-
trolled by the evaporation of Li, which influences the
oxide stoichiometry [12]. The I003/I104 ratio increases
with an increase in the calcination temperature to the
maximum value at 750°C and decreases with further
increase in temperature. Li and Ni ions are best ordered
0.35
0.30
1.0
600
650
700
750
800
850
Temperature, °C
Fig. 4. I /I
650−800°C calcination for 24 h.
and I
/I
intensity ratios at
003 104
006 + 102 101
*
Li1–xNi1+xO2
*
*
*
*
*
*
750°C, 48 h
750°C, 46 h
750°C, 44 h
750°C, 40 h
750°C, 34 h
750°C, 24 h
750°C, 14 h
30
10
20
40
50
60
2θ, deg
Fig. 5. XRD spectra of the powder produced at 750°C calcination for 14–48 h.
INORGANIC MATERIALS Vol. 42 No. 2 2006

CHARACTERIZATION OF Li1 – xNi1 + xO2 PREPARED USING SUCCINIC ACID
205
at 750°C [5, 7]. The I006 + 102/I101 ratio or R-factor is at a
minimum at 750°C. The minimum intensity ratio is the
parameter used to identify the best hexagonal ordering
[5, 7, 19]. Due to the experimental results, the best hex-
agonal ordering or the best ordering of Li and Ni ions
in Li1 − xNi1 + xO2 is at 750°C.
I
003/I104
I
006 + 102 /I101
0.9
0.8
0.7
0.6
1.5
1.4
1.3
1.2
1.1
1.0
In order to find the optimum time for the preparation
of Li1 – xNi1 + xO2, the calcination temperature was fixed
at 750°C, and the experimental time was varied
between 14 and 48 h. The XRD spectra are shown in
Fig. 5. A single phase of Li1 – xNi1 + xO2 produced at
750°C for 14–48 h was detected. The spectra are very
sharp, showing that the powder is crystalline. The
0.5
0.4
I003/I104 and I006 + 102/I101 intensity ratios for 14–48 h
were calculated and are shown in Fig. 6. As the calcina-
tion time increases from 14 to 48 h, the I003/I104 ratio
increases to the maximum value at 40 h. The
10
15
20
25
30
Time, h
35
40
45
50
I
006 + 102/I101 ratio is at a minimum at 40 h. The maxi-
mum and minimum intensity ratios are in accord. This
reflects the best hexagonal ordering or cation ordering
[5, 7, 19], which leads to the best electrochemical prop-
erties [7, 19].
Fig. 6. I /I and I
calcination for 14–48 h.
/I intensity ratios at 750°C
003 104
006 + 102 101
Mean oxidation state of Ni. Li and Ni contents of
the powder produced at 650–800°C calcination for 24 h
were determined and are shown in Fig. 7. During calci-
nation, the percent of Li decreases with increasing tem-
perature due to the evaporation process. This leads to an
increase of the percent of Ni. The mole ratios of Li and
Ni at different temperatures were calculated, and the
chemical formulas of lithium nickel oxide are shown in
Table 1. The evaporation process reflects the stoichiom-
etry of Li1 – xNi1 + xO2 and the oxidation state of Ni. The
mean oxidation state of Ni was calculated using the
equation
7.0
6.8
6.6
74
72
70
68
66
6.4
Nickel
Lithium
6.2
6.0
5.8
5.6
Mean oxidation state of Ni = 2 + N,
640 660 680 700 720 740 760 780 800 820
Temperature, °C
where N is the mole fraction of Ni3+ in the total mole of
Ni. The Ni3+/(Ni3+ + Ni2+) ratio and mean oxidation
state of Ni at different temperatures are also shown in
Table 1. As the calcination temperature increases, the
Ni3+/(Ni3+ + Ni2+) ratio and the mean oxidation state of
Ni increase to the maximum value at the same temper-
Fig. 7. Li and Ni contents of the powder produced at 650–
800°C calcination for 24 h.
dation state of Ni at the best calcination condition
ature of 750°C and then decrease. In addition, the (750°C, 40 h) were determined and are shown in
chemical formula, Ni3+/(Ni3+ + Ni2+), and the mean oxi- Table 1.
Table 1. Chemical formulas, Ni3+/(Ni3+ + Ni2+) ratios, and mean oxidation states of Ni
Calcination conditions
Chemical formulas
Ni3+/(Ni3+ + Ni2+), wt %
Mean oxidation states of Ni
650°C, 24 h
700°C, 24 h
750°C, 24 h
800°C, 24 h
750°C, 40 h
Li1.00Ni1.14O2
Li0.90Ni1.19O2
Li0.83Ni1.21O2
Li0.82Ni1.26O2
Li0.83Ni1.22O2
12.96
48.59
51.63
44.09
60.59
2.13
2.49
2.52
2.44
2.61
INORGANIC MATERIALS Vol. 42 No. 2 2006

206
TITIPUN THONGTEM, SOMCHAI THONGTEM
100
80
60
40
20
(a)
(b)
3
1
3
1
4
2
4
2
0
100
3
1
(c)
(d)
3
1
80
60
40
4
2
4
2
20
0
10–2
10–1
100
101
102
103 10–2
10–1
100
101
102
103
Particle diameter, µm
Fig. 8. Frequency and cumulative frequency distributions of the powder produced at (a) 650, (b) 700, (c) 750, and (d) 800°C calci-
nation for 24 h: (1, 2) nonultrasonic vibration, (3, 4) ultrasonic vibration for 2 min.
Particle size distribution. Size distributions of the volume diameter of 10% powder (D10) produced at
powder were determined using a particle size analyzer 650°C calcination is 3.17 µm, showing that 10% of the
and are shown in Fig. 8. At 650–800°C calcination for particles are equal to or less than 3.17 µm and that 90%
24 h, size distributions of the powder for nonultrasonic are greater than 3.17 µm. Other values of D at a variety
and ultrasonic vibrations are not normal and are over of conditions are interpreted similarly. D50 and mean
the range of 0.5–272 and 0.35–39 µm, respectively. are totally different. D50 divides the powder into two
This shows that ultrasonic vibration may influence the groups containing 50% each, but the mean is the aver-
range of size distribution. The cumulative frequency age of all the values. The volume diameters of D10,
distribution shows that the particles started to count and D50, D90, and mean for nonultrasonic vibration
arrange from the smallest value. The volume diameter decrease with increasing calcination temperatures. This
of 10, 50, and 90% powder (D10, D50, and D90) and shows that a group of particles produced at low temper-
volume mean diameter (mean) were determined and are ature forms more agglomeration than that at high tem-
shown in Table 2. In case of nonultrasonic vibration, the perature. For 2 min ultrasonic vibration, D50, D90, and
INORGANIC MATERIALS Vol. 42 No. 2 2006

CHARACTERIZATION OF Li1 – xNi1 + xO2 PREPARED USING SUCCINIC ACID
207
100 nm
100 nm
(a)
(c)
(e)
(b)
1 µm
1 µm
(d)
1 µm
Fig. 9. SEM micrographs of the powder produced at (a) 650°C for 24 h, (b) 700°C for 24 h, (c) 750°C for 24 h, (d) 800°C for 24 h,
and (e) 750°C for 40 h.
O
Ni
Ni
C
Au
2
Ni
0
1
3
4
5
6
7
8
9
10
keV
Fig. 10. EDX spectrum of the powder produced at 750°C calcination for 40 h.
INORGANIC MATERIALS Vol. 42 No. 2 2006

208
TITIPUN THONGTEM, SOMCHAI THONGTEM
Table 2. D10, D50, D90, and mean diameters of the powder for nonultrasonic and ultrasonic vibration
D10, µm
D50, µm
D90, µm Mean, µm D10, µm
D50, µm
D90, µm Mean, µm
Calcination
temperatures, °C
nonultrasonic vibration
ultrasonic vibration (2 min)
650
700
750
800
3.17
2.07
1.74
1.57
32.59
14.57
12.67
10.80
105.99
73.36
44.93
33.21
45.36
27.94
19.38
15.62
0.94
0.85
1.06
1.31
2.88
3.84
4.52
5.55
10.10
12.03
14.69
17.32
4.39
5.30
6.43
7.68
mean increase with an increase in the calcination tem- nation at 650–800°C for 14–48 h. TGA shows that the
perature, but D10 shows some irregularity. The temper- formation of the oxide seems to begin at 600°C and
ature dependence of the diameter reflects on the distri- above. At 650 and 700°C, Li1 – xNi1 + xO2 with some
bution shape. Comparing the mean particle diameters
for nonultrasonic and ultrasonic vibrations, the former
is 2–10 times as large as the latter. When the period of
time for ultrasonic vibration was prolonged to 3 min,
agglomeration of some tiny particles were detected due
to van der Waals attraction. The powder with 750°C
calcination for 40 h was analyzed. It was found that the
mean for nonultrasonic and 2 min ultrasonic vibrations
is 20.81 and 6.55 µm, respectively.
SEM. The powder produced at 650–800°C calcina-
tion was analyzed using SEM. The micrographs are
shown in Fig. 9. The powder shows different sizes of
particles over the range of 0.05–1 µm. The mean diam-
eter increases with increasing calcination temperature,
showing that SEM and particle size (with ultrasonic
vibration) analyses are in accord. Facets on the particles
show that the powder has high crystallinity. Comparing
the ranges of particle diameters determined from SEM
micrographs and from the particle size analyzer, the
former is smaller than the latter due to the agglomera-
tion of tiny particles. SEM micrographs under a high
magnification can identify both tiny particles and their
agglomerates. The particle size analyzer identifies indi-
vidual particles as an agglomerate. In addition, the
powder produced at 750°C calcination for 40 h is in the
range of 0.2–1 µm, which is smaller than that analyzed
by the particle size analyzer.
impurities was detected. A single phase of Li1 – xNi1 + xO2
was detected at 750 and 800°C. The optimum calcina-
tion is at 750°C for 40 h. The content of Ni3+ and mean
oxidation state of Ni at the optimum condition are
60.59 wt % and 2.61, respectively. Ni and O were
detected by EDX, which is in accord with the detection
of Li1 – xNi1 + xO2 by XRD. The particle diameters deter-
mined by the particle size analyzer are larger than those
shown on the SEM micrographs due to the agglomera-
tion of tiny particles.
ACKNOWLEDGMENTS
This research was supported by the National
Research Council of Thailand, Bangkok, and the Fac-
ulty of Science, Chiang Mai University, Chiang Mai,
Thailand.
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