Effect of Al addition on formation of layer-structured LiNiO2

Article abstract of DOI:10.1006/jssc.2002.9624

Kinetics and formation mechanism of undoped and Al-doped LiNiO₂ from Li₂CO₃ and NiO were investigated in this study. Without the addition of Al ions, sluggish kinetics for the formation of undoped LiNiO₂ was observed. The fraction of undoped LiNiO₂ reached 50% after Li₂CO₃ and NiO reacted at 700°C for 150 min. With the addition of 25% of Al ion, the fraction of Al-doped LiNiO₂ reached 50% within 60min at 700°C. The analysis of kinetics study indicates that the formation of undoped and Al-doped LiNiO₂ is a diffusion-controlled process. Furthermore, the rate constant determined from Jander model {[1 - (1 - α)^1/3]² = Kt} was significantly enhanced by the addition of Al. The activation energy for the formation of LiNiO₂ drastically decreased from 190k J/mole (undoped reaction) to 83 kJ/mole when 25% Al was added. The enhancement of LiNiO₂ formation by Al doping is attributed to the structure resemblance between α-LiAlO₂ and LiNiO₂. α-LiAlO₂ acts as the seeding material which provides nucleation sites for the growth of LiNiO₂.

Full text of DOI:10.1006/jssc.2002.9624

Journal of Solid State Chemistry 167, 97–106 (2002)
doi:10.1006/jssc.2002.9624
E¡ect of Al Addition on Formation of Layer-Structured LiNiO2
1
Shih-Pin Lin, Kuan-Zong Fung, Yi-Ming Hon, and Min-Hsiung Hon
Department of Materials Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan
Received January 9, 2002; in revised form April 5, 2002; accepted April 19, 2002
improve its thermal stability (7). Among them, Al doping
3
+
Kinetics and formation mechanism of undoped and Al-doped has received much attention. The Al ions tend to prevent
LiNiO from Li CO and NiO were investigated in this study. the formation of nickel dioxide and promote the structural
2
2
3
Without the addition of Al ions, sluggish kinetics for the
formation of undoped LiNiO was observed. The fraction of
integrity.
It is well known that Li O and Al O can form
2
2
2
3
undoped LiNiO reached 50% after Li CO and NiO reacted at
2
2
3
stable a-LiAlO with the a-NaFeO structure at tempera-
2
2
7
001C for 150 min. With the addition of 25% of Al ion, the
fraction of Al-doped LiNiO2 reached 50% within 60 min at
001C. The analysis of kinetics study indicates that the
tures below 6001C (8–10). The intercalation of a-LiAlO
2
+
gives a voltage of B5 V vs Li/ Li , which is higher
than other lithium transition-metal oxides. Thus, the
solid solution of a-LiAlO2 with lithiated transition-
metal oxide can potentially increase the intercala-
7
formation of undoped and Al-doped LiNiO2 is a diffusion-
controlled process. Furthermore, the rate constant determined
1=3 2
from Jander model f½1 À ð1 À aÞ Š ¼ Ktg was significantly
enhanced by the addition of Al. The activation energy for the tion voltage. Al doping was found to be an acceptable
formation of LiNiO drastically decreased from 190 kJ/mole method to enhance the stability of LiNiO . In addition,
2
2
(
undoped reaction) to 83 kJ/mole when 25% Al was added. The a-LiAlO also provides advantages of light weight, non-
2
enhancement of LiNiO formation by Al dopingis attributed
to the structure resemblance between a-LiAlO2 and LiNiO2.
2
toxicity and low cost.
Most research related to Al-doped LiNiO (11–14) has
2
a-LiAlO2 acts as the seedingmaterial which provides nucleation
focused on electrochemistry, synthesis condition and/or
structure of LiNiO . The formation mechanism and
sites for the growth of LiNiO2. # 2002 Elsevier Science (USA)
Key Words: kinetics; lithium nickel aluminum oxide; cathode
material.
2
reaction kinetics of LiNiO were seldom discussed. For
2
undoped LiNiO , the solid-state reaction method has been
2
studied with various Ni compounds such as Ni metal,
Ni(OH) , NiCO , NiO, LiOH, and Li CO reacted at
2
3
2
3
temperatures ranging from 750 to 900 for 24–48 h (7, 15).
Sluggish reactions were reported. Typically, it requires 48 h
1. INTRODUCTION
to obtain 100% LiNiO at 8001C. With the addition of Al
2
ions, the appearance of a-LiAlO with high stability and
The lithium transition-metal oxides, such as LiCoO2,
LiNiO , and LiMn O , have received a great deal of
2
low synthesis temperature may affect the formation of
LiNiO in a positive way. Therefore, the main objective of
2
2
4
interest as rechargeable cathodes for Li secondary batteries
1–5). Among them, LiNiO provides the advantage over
LiCoO system of being cost effective and environmentally
2
this work was to investigate the effect of Al ions on the
synthesis mechanism and reaction kinetics of LiNiO using
(
2
2
2
Li CO and NiO as the starting materials.
2
safer.
3
LiNiO is, however, known to exhibit thermal instability.
2
For overcharged Li NiO , most of the Ni ions are in the
1
Àx
unstable Ni state which should be avoided (6). NiO is
2
2. EXPERIMENTAL PROCEDURE
4
+
2
quite active toward organic electrolyte oxidation. To solve
the problems of unstable structure and thermal properties
due to the formation of nickel dioxide, several cations, such
as Al, Mn, and Co have been added into LiNiO2 to
2
.1. Sample Preparation
LiNiO samples were prepared from lithium carbonate
2
(99.7%, Fisher) and nickel oxide (99%, Alfa). Aluminum
nitrate (98.5%, Riedel-deHaen) was added as the source of
Al
varied from 0.1/0.9 to 0.25/0.75 accordingly. Starting
3
+
1
for Al-doped LiNiO . The atomicratio of Al/Ni
2
To whom correspondence should be addressed. E-mail: kzfung@mail.
ncku.edu.tw.
9
7
0022-4596/02 $35.00
r 2002 Elsevier Science (USA)
All rights reserved.

9
8
LIN ET AL.
materials with desired ratio were wet mixed by ball milling at 30 kV and 20 mA, respectively. A scan speed of 11/min
for 24 h. For kinetics study, the powder mixture was dried was selected from 101 to 801 of 2y angles. The volume
and calcined at temperatures ranging from 6501C to 7251C fraction (a) of LiNiO was estimated from the consumption
2
for various periods of time from 15 min to 6 h, followed by of NiO because the reflection intensity of LiNiO was weak
quenching to room temperature. To ensure the complete in the early stage of reaction. The volume fraction
reaction, some samples were also heated at temperatures as consumed was determined from integrated peak intensity
2
high as 8001C.
of (002) reflection of NiO collected from 42.51 to 44.51 of
y angles in a step of 0.011 with a scan rate of 0.51/min. The
same procedure was also conducted on powder mixtures of
NiO and LiNiO with the volume fraction of NiO varying
2
from 0%, 25%, 50%, 75% to 100%. The XRD traces
2
2
.2. Characterization of Calcined LiAl Ni1ÀxO2
x
Powder
X-ray diffraction (XRD) analysis was conducted obtained from these powder mixtures were used as
on calcined powder using Rigaku X-ray Diffraction System standards. SEM observations were conducted using a
model D/MAX III.V) with monochromated CuKa PHILIPS XL 40 to examine the surface morphology of
radiation. The accelerating voltage and current were set LiNiO powder.
(
2
FIG. 1. The XRD patterns for LiAl
at 5001C for 12 h.
x 2 2
Ni1ÀxO synthesized at 8001C for 54 h, when x = (a) 0.00, (b) 0.10, (c) 0.20, (d) 0.25, and (e) LiAlO synthesized

EFFECT OF Al ADDITION
99
3. RESULTS AND DISCUSSION
3
.1. Structure Analysis of Undoped
and Al-Doped LiNiO2
Figure 1 exhibits the XRD patterns for a-LiAlO2,
undoped LiNiO , and Al-doped LiNiO synthesized.
2
2
All the samples were synthesized at 8001C for 54 h
except a-LiAlO which was synthesized at 5001C for 12 h.
2
Both LiNiO and a-LiAlO exhibit a similar rhombohedral
2
2
ꢀ
structure with a space group of B3m: However, there
exists variation in reflections of (006), (012), (018),
and (110) between undoped LiNiO and a-LiAlO . For
2
2
a-LiAlO2, the intensities for (006) and (012) reflections
are negligible; the reflections of (018) and (110) are,
however, clearly separated. On the other hand,
the intensities for reflections of (006) and (012) of LiNiO2
are noticeable. But, the reflections of (018) and (110) for
LiNiO2 are indistinguishable. The reasons for these
variations can be explained by: (1) The difference in the
atomic scattering factor in Al and Ni. For the reflections of
(
006) and (012) in a rhombohedral LiMO2 (M¼ cationÞ;
the structure factor, S; is calculated as S ¼ 3ðfLi þ fM À
2
1
0
fOÞ: The atomic scattering factors for Li, Al, Ni, and O are
.77, 8.779, 19, and 5.131, respectively. Thus, S is equal to
.861/31.524 for a-LiAlO /LiNiO . Negligible reflections of
2
2
(
006) and (012) in a-LiAlO are expected. (2) The difference
2
in lattice parameters of LiNiO and a-LiAlO . The lattice
2
2
(
(
(
constants a=c are 2.884 A/14.19 A for LiNiO and 2.801 A/
2
(
1
4.23 A for a-LiAlO , respectively. When the hexagonal
2
FIG. 2. Lattice parameters of LiAl
hexagonal setting are plotted as a function of Al concentrations.
x
Ni1Àx
O
2
, a and c; expressed in a
setting is used, the corresponding 2y angles for (018) and
110) reflections are 64.961 and 66.761 for a-LiAlO . For
(
LiNiO , reflections of (018) and (110) are closely located at
2
2
6
4.361 and 64.571. As the content of Al increases, the (006)
reflection of XRD shifts to a lower angle, but (110) line 2:884; (0%x%0:25), where x is the concentration of Al in
shifts to a higher angle. Thus, the splitting of (006) (012) Ni cation sublattice. This result again suggests that the
and (018) (110) reflections of Al-doped LiNiO2 was homogeneous substitution of Al in Ni cation sublattice was
observed. These results indicate that Al-doped LiNiO2 obtained. The trigonal distortion represented by c=a
must form a solid solution with Al homogeneously increases as Al content increases. The result indicates that
3
+
distributed in Ni cation sublattice. The changes in the d- Al addition favors the stabilization of both Ni
and the
spacing of the reflections are also in good agreement with two dimensionality of the crystal lattice. Similar results
the substitution of Al for Ni in LiAl Ni1ÀxO2 solid were reported by Stoyanova et al. (12).
x
solution.
Furthermore, the lattice parameter of LiAl Ni1ÀxO2
x
shows a similar trend as well. Figure 2 shows the hexagonal
unit-cell parameters, a- and c-axis, as a function of x in Al-
3.2. Reaction Kinetics for the Formation of LiNiO2
doped LiNiO . The lattice parameters were refined by a
2
3.2.1. Reaction mechanism of LiNiO2. The isothermal
least-squares method. The a-axis decreases linearly from reaction of undoped or Al-doped LiNiO formation was
2
(
2
1
.884 to 2.87 A and the c-axis increases from 14.19 to examined on the basis of the fraction formed, which was
4.23 A. The ratio of c=a increases from 4.92 to 4.96 due to determined by integrated intensity from XRD traces. The
(
the substitution of Ni ions by Al ions. The unit-cell volume fraction formed of undoped or Al-doped LiNiO , a; was
2
3
(
also decreases from 102.22 to 101.45 A as the content plotted as a function of reaction time under isothermal
of Al increases. The variation of lattice constant, a, can be reaction at 6501C, 7001C, and 7251C, respectively. The
expressed as a function of Al content: a ¼ À0:087x þ results for samples doped with various concentrations of

1
00
LIN ET AL.
100
100
o
o
o
o
650 C
700
7
6
50
C
C
C
90
80
70
60
50
40
30
20
10
0
o
o
C
7
00
25
25
C
7
80
60
40
20
0
0
40
80
120
160
200
240
280
320
360
0
40
80
120
160
200
240
280
320
360
(a)
Time(min)
(c)
Time(min)
100
100
o
6
50
C
C
C
650 C
700 C
725 C
o
o
700
725
8
0
0
0
0
80
60
40
20
0
6
4
2
0
0
40
80
120
160
200
240
280
320
360
0
40
80
120
160
200
240
280
320
360
(b)
Time(min)
(d)
Time(min)
FIG. 3. Fraction of LiAl
x
2
Ni1ÀxO plotted as a function of reaction time at 6501C, 7001C, and 7251C for various concentrations of Al doping, when
x ¼ ðaÞ 0.00, (b) 0.10, (c) 0.20, and (d) 0.25.
Al (x ¼ 020:25) are shown in Fig. 3, in which, the kinetics temperature was raised to 7001C and 7251C, the fraction
result for the synthesis of LiNiO from Li CO and NiO of LiNiO reached 50% within 150 and 120 min, respec-
follows a parabolicbehavior. At 650 1C, the fraction tively.
formed of LiNiO (x ¼ 0) was 37% after 180 min reaction. The formation of undoped LiNiO can be expressed by
2
2
3
2
2
2
The fraction formed of LiNiO increased to 50% when the Ohlberg–Strickler equation (14–20):
2
the reaction time was extended to 6 h. The fraction (a)
m
of LiNiO also increased as temperature increased. When
a ¼ 1 À expðÀBt Þ;
½1Š
2

EFFECT OF Al ADDITION
101
MgO–SiO , and some superconductors. For the formation
2
Àln lnð1 À aÞ ¼ ln B þ m ln t;
½2Š
of LiNiO , the Avrami constant, m; was determined to be
2
where a is the fraction transformed, B is a constant around 0.54 based on the slopes shown in Fig. 4. These
depending upon the nucleation frequency and linear rate of results indicate that the reaction mechanism is a diffusion-
grain growth, and m is the Avrami constant depending controlled process, which is also in agreement with the
upon the reaction mechanism and the geometry of the model of 3D growth (14–15).
system (16). By plotting Àln lnð1ÀaÞ as a function of ln t;
the value of m was determined from the value of the slope. for 36 h are shown in Fig. 5(a). The micrograph shows
The SEM micrographs for LiNiO calcined at 7001C
2
This expression has been widely described in the solid-state cubic and spherical grain of LiAl
reaction for many material systems such as BaTiO3, for 3-D geometricgrowth.
Ni1ÀxO , which is typical
x 2
1.5
1.0
0.5
0.0
1.5
1
o
6
50 C
o
650 C
700 C
725 C
700 C
o
7
25 C
0.5
0
-0.5
-1.0
-1.5
-2.0
-2.5
-
0.5
-1
-
1.5
-2
4.6
4.8
5.0
5.2
5.4
5.6
5.8
6.0
2.5
3
3.5
4
4.5
5
5.5
6
(a)
ln t
(c)
ln (t)
1
.5
1.5
1
1
o
650 oC
700 oC
725 oC
6
50
C
o
o
7
7
00
25
C
C
0
.5
0.5
0
0
-
0.5
-0.5
-1
-1
-
1.5
-1.5
-2
-2
4
4.4
4.8
5.2
5.6
2.5
3
3.5
4
4.5
5
5.5
6
(b)
ln (t)
(d)
ln (t)
x 2
FIG. 4. The determination of the Avrami constant m in the crystallization process for LiAl Ni1ÀxO , when x= (a) 0.00, (b) 0.10, (c) 0.20, and
(d) 0.25.

1
02
LIN ET AL.
FIG. 5. SEM micrographs for the LiAl
Ni1ÀxO
x 2
2
powders calcined for 36 h in O atmosphere, when x ¼ (a) 0.00, (b) 0.10, (c) 0.20, and (d) 0.25.
3
.2.2. Rate constant for the formation of LiNiO2. The
reaction mechanism can be further represented using a LiNiO2 formation. For undoped mixture of Li CO
3.2.3. Effect of Al addition on the kinetics of
2
3
model of geometric growth which was described by Jander and NiO, the activation energy for the formation
15, 21, 22): of undoped LiNiO2 was found to be as high as
90 kJ/mol. It was observed that the fraction (a) of
(
1
1
=3 2
½
1 À ð1 À aÞ Š ¼ Kt:
½3Š
LiNiO2 was significantly enhanced by the addition
of Al. For example, the fraction of LiNiO2 reached
To determine the rate constant, K in the Jander model, the
1
5
0% within 2.5 h and 1 h when 25% of Ni was substituted
by Al.
The Avrami constant, m; determined from Figs. 4(b)–(d)
=3 2
½
1 À ð1 À aÞ Š was plotted as a function of t at various
temperatures as shown in Fig. 6. The K values for the
formation of LiAl Ni1ÀxO2 (x ¼ 020:25) at various
x
also shows a value of 0.54 which suggests that the re-
actions are diffusion controlled. However, the rate
constant determined from Jander model was enhanced
by the addition of Al. When Al ions were added into
the mixture of Li CO and NiO, the activation energy
temperatures were obtained from the slopes shown in
Fig. 6. Figure 7 shows the variation of rate constant K; as a
function of 1=T: The result indicates that such a reaction is
a thermally activated process and can be expressed by the
following equation:
2
3
for LiNiO2 formation was significantly affected. For
the addition of 10% Al, the activation energy de-
creased slightly to 189 kJ/mole. However, when the
K ¼ K expðÀE =RTÞ;
½4Š
0
a
where K0 is a pre-exponential constant; Ea the activation concentration of Al increased to 20% and 25%, the
energy; R the gas constant; and T the absolute tempera- activation energy drastically reduced to 95 and 83 kJ/mole,
ture.
respectively. The decrease in the activation energy suggests
The activation energy for the formation of LiNiO was that the energy barrier for the formation of LiNiO is
2
2
determined from the slope of the straight line fitted through effectively suppressed by the addition of Al ions. There-
data points. fore, the reaction kinetics of LiNiO2 formation was

EFFECT OF Al ADDITION
103
0
0
0
0
0
0
0
.30
.25
.20
.15
.10
.05
.00
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
o
o
50 C
o
6
50 C
6
7
o
00 C
700 C
o
o
7
25 C
725 C
-
0.05
0.10
-
0
40
80
120
160
200
240
280
320
360
0
40
80
120
160
200
240
280
320
360
(a)
Time (min)
(c)
Time (min)
0
.30
.25
.20
.15
.10
.05
.00
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
o
o
0
650 C
7
650 C
o
o
00 C
700 C
o
o
7
25 C
725 C
0
0
0
0
0
-
0.05
0.10
-
0
40
80
120
160
200
240
280
320
360
0
40
80
120
160
200
240
280
320
360
(b)
Time (min)
(d)
Time (min)
1=3 2
FIG. 6. The plots of ½1 À ð1 À aÞ Š vs t for the formation of LiAl Ni1ÀxO at 6501C, 7001C, and 7251C, when x ¼ (a) 0.00, (b) 0.10, (c) 0.20, and
x 2
(d) 0.25.
enhanced by the incorporation of Al ions into the lattice of of LiNiO using solid-state reaction method was controlled
2
LiNiO2.
by the diffusion of Ni cations. Thus, the activation
energy of 190 kJ/mole observed was close to that for the
formation of Ni vacancies, as described by the following
defect reaction:
3
.3. Role of Al in the Formation of LiNiO2
Á
00
Ni
x
O
According to the results shown in previous sections,
the substitution of Al in Ni cation sublattice enhanced the
1=2 O2ðgÞ
!
2h þ V þ O :
½5Š
NiO
formation of LiNiO . It is important to examine the role As shown previously, the reduction of activation energy
2
of Al in the enhancement of LiNiO2 formation. In from 190 to 95 and 83 kJ/mole was apparently caused by
our previous work (15), it was suggested that the formation the addition of 20% and 25% Al, respectively.

1
04
LIN ET AL.
-
6
addition of Al0.02Ni0.98O solution, the reaction B, however,
exhibits much slower kinetics than reactions A and C.
x=0.00
x=0.10
x=0.20
x=0.25
-
-
-
-
6.5
These results suggest that a-LiAlO enhanced but Al
2
0.02-
Ni0.98O suppressed the formation of LiNiO in comparison
with reaction C.
2
-7
7.5
3
.3.1. Kinetics suppression by Al0.02Ni0.98O. The
-8
suppression of reaction B by Al0.02Ni0.98O can be
rationalized by the substitution of Ni for Al in NiO. For
the formation of LiNiO from Li O and NiO, the following
8.5
2
2
defect reaction may occur:
-9
1
2
0
Á
x
x
O2þLi2O þ 2NiO
!
2Li þ 2h þ 2Ni þ 4O : ½7Š
Ni Ni o
NiO
9.5
For Eq. [7] to proceed, the availability of Ni cation with
+2 valence is required.
-10
With the formation of Al0.02Ni0.98O solid solution, Al
ions occupy Ni positions and create cation vacancies as
shown in Eq. [6]. In addition, when Li O reacts with
2
-
10.5
0
.98
1
1.02
1.04
1.06
1.08
1.1
1
000/T (1/ k)
Al0.02Ni0.98O, Li ions may fill up the available cation
+
3
FIG. 7. The plot of ln K vs 1000=T for the formation of LiAl
when x varied from 0.00 to 0.25.
x 2
Ni1ÀxO
vacancies instead of forming Ni . Such a reaction may be
described by
0
Ni
0
0
Ni
x
o
Li O þ V
2
!
2Li þ O :
½8Š
The possible reactions for Al with the mixture of Li CO3
2
and NiO may take place by the following routes:
NiO
3
+
With less Ni created in NiO structure, the formation of
(1) Formation of solid solution Al Ni1ÀxO: such a
x
reaction may be expressed by
layered LiNiO tends to be sluggish.
2
Á
00
Ni
x
O
80
Al2O3
!
2AlNi þ V þ 3O :
½6Š
NiO
Reaction A
Reaction B
Thus, the cation diffusion may be enhanced by the
formation of solid solution Al Ni1ÀxO.
70
Reaction C
x
(
oxides can easily form stable lithium aluminate at a
2) Formation of a-LiAlO : Aluminum and lithium
2
60
temperature as low as 5001C.
Thus, to determine the role of Al in the formation of
LiNiO , further examination was needed. In order to
2
5
0
0
distinguish the influence of Al Ni O and a-LiAlO on
x
1Àx
2
the formation of Al-doped LiNiO , three reactions with
different starting materials were studied.
2
4
(
i) Reaction A: The starting materials used were Li CO ,
2 3
a-LiAlO , and NiO in a molar ratio of 49:2:98.
(ii) Reaction B: The starting materials used were Li CO3
2
and Al0.02Ni0.98O in the molar ratio of 1:2.
2
30
20
(iii) Reaction C: The starting materials were Li CO and
2 3
NiO in a molar ratio of 1:2.
After reaction at 7001C for various periods of time,
the fraction formed of layered LiNiO2 for the above-
mentioned reactions is shown in Fig. 8. After heating
at 7001C for 60 min, the reaction A with the addition of a-
LiAlO2 obtained more LiNiO2 than the other ones
3
0
60
90
120
150
180
210
240
270
Time (min)
FIG. 8. Fractions formed of undoped and Al-doped LiNiO
2
are
plotted as a function of reaction time at 7001C when various starting
materials were used, where the reaction C was used as a standard:
especially in the early stage of the reaction. For the (A) 0.49Li CO +0.02 a-LiAlO +0.98NiO; (B) 0.5Li CO +Al0.02Ni0.98O;
2
3
2
2
3
undoped reaction C, the initial reaction was sluggish. The and (C) LiNiO
2
: 0.5Li
2
CO
3
+NiO.

EFFECT OF Al ADDITION
105
3
.3.2. Kinetics enhancement by a-LiAlO2. On the sluggish reaction for the formation of undoped LiNiO was
2
contrary, the presence of LiAlO2 in the powder observed. It is believed that a-LiAlO with rhombohedral
2
mixture enhances the formation of LiNiO . In order to structure acts as the seeding material for the formation of
investigate the role of a-LiAlO in the enhancement of LiNiO2.
2
2
LiNiO2 formation, various amounts of a-LiAlO2 were
After adding different amounts of a-LiAlO into the
2
added into the mixture of Li CO and NiO. The results are mixture of Li CO and NiO, the reflections in XRD
shown in Figs. 9 and 10. representing LiNiO2 appeared, and its fraction was
The kinetics were greatly enhanced in the beginning of calculated as shown in Fig. 10, in which more LiNiO2
2
3
2
3
isothermal reaction as shown in Fig. 8. Without the was formed when the concentration of a-LiAlO increased.
2
addition of a-LiAlO2, considerable amounts of Li CO
Fig. 9(e) shows the XRD trace for LiAlO heated at
2
3
2
and lithated-NiO were still observed, Fig. 9(a). Again, a 7251C for 2 h. Both g-LiAlO2 and a-LiAlO2 coexisted.
∆
:
Li Al (CO )(OH) *xH2O
2
4
3
12
α : α−LiAlO2
γ : γ−LiAlO2
LAN: Li Al Ni1-xO2
y
x
o: NiO
γ
LN:Li Ni2-xO
γ
x
2
γ
x: Li CO3
2
(e)
α
α
∆
γ
α
∆
∆
γ
γ γ
α α
γ
∆
γ
α
γ γ
γ
∆
γ
∆
∆
∆
o
o
γ
∆
γ
LAN
α
o
o
(d)
LAN
o
γ ×
×
γ
o
LAN
LAN
×
γ
××
o
o
LAN
(
c)
b)
α
LAN
o
γ
γ
o
o
××× γ
γ
× ×
LAN
LAN
×
×
(
o
o
LAN
o
×
×
LAN
o
o
α
γ
γ ×
γ γ
×
×
LAN
LAN
×
×
×
(a)
o
o
×
o
o
×
×
LN
×
×
LN
×
×
×
10
20
30
40
50
60
70
80
2
θ
2 2 3
FIG. 9. The XRD patterns of compound synthesized at 7251C for 2 h using a-LiAlO , NiO and Li CO as starting materials. Various amounts of
a-LiAlO were used as (a) 0.00, (b) 0.10, (c) 0.20, (d) 0.25, and (e) 1.00.
2

1
06
LIN ET AL.
90
80
70
60
50
40
30
20
was kept at 7001C, 50% of Al-doped LiNiO was obtained
2
in about 60 min.
3. The activation energy for the formation of LiNiO was
also suppressed by the addition of Al. With the addition of
x=0.00
x=0.02
x=0.10
2
2
5% Al, the activation energy estimated was only 83 kJ/
mole, compared with 190 kJ/mole for undoped LiNiO2.
. The faster kinetics for the formation of Al-doped
x=0.25
4
LiNiO2 may be due to the similar structure between
LiNiO2 and a-LiAlO . When the dissolution between
2
3
+
a-LiAlO and lithiated NiO occurs, Al substitution for
Ni may further enhance the cation diffusion and reaction.
2
ACKNOWLEDGMENT
This work was supported by the National Science Council of Taiwan,
the Republicof China, under Contra tc No. NSC 89-2216-E-006-094,
which is gratefully acknowledged.
60
120
180
240
300
Time (min)
REFERENCES
x 2
FIG. 10. Fractions of LiAl Ni1ÀxO formed plotted as a function of
reaction time at 7001C, when x varied from 0.00 to 0.25.
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2
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2
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2
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4. CONCLUSIONS
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1
1
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conclusions may be drawn:
2
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1
. Using solid-state reaction method, the formation of
1
LiNiO from Li CO and NiO reaction is sluggish. For 17. J. Beretka, J. Am. Ceram. Soc. 67, 615 (1984).
2
2
3
1
8. J. H. Sharp, G. W. Brindley, and B. N. Narahari Achar, J. Am.
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5
2
1
2
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2
and NiO, the formation of Al-doped LiNiO2 was
. With the addition of Al into the mixture of Li CO
2 3
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