The stability between perovskite La2/3-xLi3x□1/3-2xTiO3 (3x = 0.3) electrolyte and LiMmOn (M = Mn, Ni and Co) cathodes

Article abstract of DOI:10.1016/j.jallcom.2006.06.024

Perovskite La_2/3-xLi_3x□_1/3-2xTiO₃ (LLT) exhibits high lithium-ion conductivity (～10^-3 S cm^-1) is a potential material for using as solid-state electrolyte in all-solid-state lithium-ion microbatteries. Considering about the LLT and cathode films might undergo high-temperature heat treatment simultaneously, the stability and reaction in the interface of electrolyte and cathode become interesting points to be investigated. In this study, LLT powders were mixed with three kinds of cathodes and then annealed at 500-800 °C. The results indicated that the LLT electrolyte was extremely stable with spinel LiMn₂O₄ even after 800 °C heat treatment for 2 h. The commercial cathode material, HT-LiCoO₂, also shows good stability with LLT electrolyte after 700 °C annealing, but the structures of LLT and LiCoO₂ both showed slight damage after 800 °C heat treatment. Moreover, layered LiNiO₂ showed poor stability with LLT, and, it decomposed into NiO when annealing with LLT above 500 °C.

Full text of DOI:10.1016/j.jallcom.2006.06.024

Journal of Alloys and Compounds 432 (2007) L22–L25
Letter
The stability between perovskite La2 Li ꢀ
TiO (3x = 0.3)
electrolyte and LiM O (M = Mn, Ni and Co) cathodes
/3−x
3x 1/3−2x
3
m n
∗
Cheng-Lung Liao, Chung-Han Wen, Kuan-Zong Fung
Department of Materials Science and Engineering, National Cheng Kung University, No. 1, Ta-Hsueh Road, Tainan 70101, Taiwan
Received 18 May 2006; received in revised form 3 June 2006; accepted 6 June 2006
Available online 11 July 2006
Abstract
Perovskite La2/3−xLi3x
−
3
−1
ꢀ
1/3−2xTiO
3
(LLT) exhibits high lithium-ion conductivity (∼10 S cm ) is a potential material for using as solid-state
electrolyte in all-solid-state lithium-ion microbatteries. Considering about the LLT and cathode films might undergo high-temperature heat treatment
simultaneously, the stability and reaction in the interface of electrolyte and cathode become interesting points to be investigated. In this study, LLT
powders were mixed with three kinds of cathodes and then annealed at 500–800 C. The results indicated that the LLT electrolyte was extremely
◦
◦
stable with spinel LiMn
2
O
4
even after 800 C heat treatment for 2 h. The commercial cathode material, HT-LiCoO
2
, also shows good stability with
◦
◦
LLT electrolyte after 700 C annealing, but the structures of LLT and LiCoO
layered LiNiO
2006 Elsevier B.V. All rights reserved.
2
both showed slight damage after 800 C heat treatment. Moreover,
◦
2
showed poor stability with LLT, and, it decomposed into NiO when annealing with LLT above 500 C.
©
Keywords: Electrode materials; Electrolyte materials; X-ray diffraction; Perovskite LaLiTiO3
1
. Introduction
conductivity highly relatives to and varies with the concentra-
tions of lithium-ions and A-site vacancies. Moreover, to be used
as electrolyte in thin-film microbatteries, the thin-film fabri-
cations and properties of LLT films were widely investigated
recently [3,6–9]. Nevertheless, the stability between this per-
ovskite material and cathodes during the thin-film fabrication
should be an important concern. Because of the as-deposited
LLT films exhibit amorphous structure [3,8,9] and as-deposited
cathodes exhibit poor crystallinity. Therefore, LLT and cathode
films have to undergo a heat treatment to enhance their crys-
tallinities and properties. Therefore, the stability and reaction in
the interface of electrolyte and cathode during the heat treatment
are very important and would affect the properties of the micro-
batteries. Consequently, this study is focused on the stability and
reaction between LLT and three kinds of common-used cathodes
(LiNiO2, LiCoO2 and LiMn2O4) to probe into the feasibility of
LLT as solid electrolyte and find out a suitable cathode for using
with LLT electrolyte.
All-solid-state lithium-ion microbattery, exhibits high energy
density and good cycleability, is a promising alternative power
storage in the recent applications of portable electronics, micro-
electronics, and implantation devices. For fabricating high-
performanced all-solid-state lithium-ion microbatteries, it is an
essential task to investigate and improve the properties of solid
electrolyte. Generally, Li3.3PO3.9N0.17 (LIPON) with lithium-
ion conductivity about 10 S cm is the common electrolyte
material that was first reported by Bates et al. [1,2]. However,
LIPON still has some disadvantages such as sensitive to mois-
ture and/or oxygen and difficult to fabricate reproduceably [3].
Consequently, it is extremely a crucial demand to investigate a
new and stable solid-state electrolyte that exhibits high lithium-
ion conductivity and low electronic conductivity.
−
6
−1
For the last few decades, perovskite La2/3−xLi3xꢀ1/3−2xTiO3
(LLT) was investigated as a new electrolyte for all-solid-state
microbatteries as a result of its high lithium-ion conductivity in
bulk (∼10− S cm ) [4,5]. It was reported that the lithium-ion
3
−1
2
. Experimental
The La0.57Li0.3ꢀ0.13TiO3 (LLT), LiNiO2, LiCoO2, and LiMn2O4 powders
were synthesized by solid-state reaction method from La2O3, TiO2, Li2CO3,
NiO, CoCO3, and MnO2 powders. After mixing the precursor, 6-h calcination
was carried out at 1300 and 800 C for electrolyte and cathodes, respectively.
∗
Corresponding author. Tel.: +886 6 2757575x62903; fax: +886 6 2380208.
E-mail address: kzfung@mail.ncku.edu.tw (K.-Z. Fung).
◦
0
925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2006.06.024

C.-L. Liao et al. / Journal of Alloys and Compounds 432 (2007) L22–L25
L23
Then, in order to investigate the stability and reactions between LLT electrolyte
This result indicates that the reaction between LiNiO2 and LLT
◦
◦
and common-used cathodes, LLT and cathode powders were well mixed under
at 600 C was much acuter than that at 500 C. The stability
between LLT electrolyte and LiNiO2 cathode is extremely poor.
In the case of LiCoO2 and LLT mixtures, two well-defined
phases of layered LiCoO2 and perovskite LLT are also observed
in XRD pattern (Fig. 1(a)) of as-mixed sample. After the mix-
◦
1
:1 by weight and underwent heat treatments at 500–800 C for 2 h. After heat
treatment, the mixtures were analyzed by X-ray diffractometer (XRD) using
Cu K␣ radiation (λ = 1.5418 A˚ ). The conductivity variations of mixtures dur-
ing heat treatment were also conducted by pellets (diameter 10 mm, thickness
2
≈
5 mm, CIP pressure = 2000 kg/cm ) of the mixed powders. The conductivity
◦
◦
variations of pellets were measured from ambient temperature to 800 C at a
rate of 5 C/min and then hold at 800 C for 12 h.
tures of LiCoO2 and LLT annealed at 600 C for 2 h, the XRD
◦
◦
pattern (as shown in Fig. 2(b)) shows that the LLT was a lit-
tle affected by LiCoO2 due to the decreasing intensity of LLT
3
. Results and discussion
◦
reflections. Moreover, 700 C-annealed mixtures show the sim-
◦
ilar result with 600 C-annealed one. This result indicates that
these two phases could maintain their structure even after 700 C
The reactions between LLT and cathode materials were inves-
◦
tigated by XRD analysis. Fig. 1 shows the XRD patterns of as-
heat treatment. To compare with LiNiO2, the stability between
LiCoO2 and LLT is better than that between LiNiO2 and LLT.
◦
mixed, 500 and 600 C-annealed mixtures of LLT and LiNiO2.
In Fig. 1(a), two well-defined phases of layered LiNiO2 and
perovskite LLT with superstructure peaks (superlattice) can be
observed. Generally, the superlattices are attributed to the order-
ing of cation vacancies, and, the intensities of superlattices vary
with lithium contents as a consequence of the cation disorder.
◦
However, this stability is broken after 800 C heat treatment.
The decreasing intensity of LiCoO2 and the formation of ␤-LLT
second phase are observed. Finally, the mixtures of LiMn2O4
and LLTO was also underwent the same heat-treatment proce-
dure. The XRD patterns (as shown in Fig. 3) show that there
◦
After annealed the LiNiO2 and LLT mixtures at 500 C for 2 h,
◦
are no reactions between LiMn2O4 and LLT even after 800 C
the intensity of LiNiO2 and superlattice decreases obviously that
can be observed in Fig. 1(b). Because the intensity of superlat-
tice is decreasing with the increasing lithium content in LLT,
therefore, it can be suggested that the decreasing intensity of
superlattice in Fig. 1(b) is due to the lithium in LiNiO2 diffuse
intotheLLTA-sitevacancies. Moreover, itiswellknownthatthe
layered LiNiO2 exhibits poor structural stability when the sto-
ichiometry shows lithium deficiency. Therefore, when lithium-
ions move out from the LiNiO2 layered structure, the layered
structure becomes unstable and might decompose into NiO is
suggested. In addition, La2Ti2O7 and NiO second phases were
heat treatment for 2 h. This result indicates that the stability of
LiMn2O4 between LLT is much better than that of LiNiO2 as
well as than LiCoO2.
Generally, to synthesize stable and stoichiometric LiNiO2
is much more difficult than LiCoO2 and LiMn2O4. In addi-
◦
observed after 600 C annealing for 2 h as shown in Fig. 1(c).
Fig. 1. XRD patterns of (a) as-mixed LiNiO2 and La2/3−xLi3xꢀ1/3−2xTiO3
Fig. 2. XRD patterns of (a) as-mixed LiCoO2 and La2/3−xLi3xꢀ1/3−2xTiO3
◦
◦
◦
◦
(
3x = 0.3) powders, and heat treatment the mixtures at (b) 500 C and (c) 600 C
(3x = 0.3) powders, and heat treatment the mixtures at (b) 600 C, (c) 700 C
◦
for 2 h.
and (d) 800 C for 2 h.

L24
C.-L. Liao et al. / Journal of Alloys and Compounds 432 (2007) L22–L25
Fig. 3. XRD patterns of (a) as-mixed LiMn2O4 and La2/3−xLi3xꢀ1/3−2xTiO3
◦ ◦
3x = 0.3) powders, and heat treatment the mixtures at (b) 700 C and (c) 800 C
(
for 2 h.
Fig. 4. The conductivity variations of the electrolyte and cathode mixtures.
When lithium-ions move into the LLT A-site vacancies, the
lithium content in layered LiNiO2 is decreasing. Therefore,
the equation tends to go to left side to form NiO and results
in the decreasing conductivity. But for LiCoO2 + LLT and
LiMn2O4 + LLT, these two systems didn’t show obviously
changes in conductivity due to the LiMn2O4 and LiCoO2 phases
still existed in the mixture. From the results of XRD and conduc-
tivity test, LiMn2O4 is the most stable cathode among LiNiO2,
LiCoO2, and LiMn2O4 to be used with LLT electrolyte. In other
words, LLT can be used as high-performanced electrolyte when
choosing a suitable cathode such as LiMn2O4.
tion, the Gibbs energies for LiNiO2, LiCoO2, and LiMn2O4
formations from elements at 300 K are −514.96, −619.65, and
−
1315.61 kJ/mol can be estimated, respectively. It indicates that
once the LiMn2O4 formed, the LiMn2O4 would be the most sta-
ble material among LiNiO2, LiCoO2, and LiMn2O4. In other
words, it means that the LiNiO2 is the most unstable cathode
among three of them, and, it is the easiest cathode material to
decompose and react with LLT electrolyte. Consequently, con-
sidering about a suitable cathode for LLT electrolyte, LiCoO2
and LiMn2O4 might be the considerable ones.
There is another experiment to investigate the reactions
between LLT and LiMmOn. The mixtures of LLT and LiMmOn
were shaped into pellets and conducted the variation of con-
ductivity. The conductivity versus test time plot is showed in
Fig. 4. In this figure, step 1 is for heating the specimens to
4. Conclusion
Three kinds of cathodes, LiNiO2, LiCoO2, and LiMn2O4,
were reacted with La2/3−xLi3xꢀ1/3−2xTiO3 (3x = 0.3) electrolyte
◦
◦
8
00 C under a constant rate (5 C/min), and, step 2 is for
to investigate the stability between cathode and electrolyte. The
◦
holding the temperature at 800 C. Because of the conductiv-
ity of cathodes and electrolyte are about 10 and 10 S cm
LiMn2O4 showed well stability with LLT electrolyte even after
−
2
−6
−1
,
◦
8
00 C heat treatment. LiCoO2 + LLT system can remain stable
therefore, the conductivity variation of this test could be just
attributed to cathode materials and the conductivity contribution
of LLT could be ignored. It can be observed that the conduc-
tivities of LiNiO2 + LLT, LiCoO2 + LLT, and LiMn2O4 + LLT
specimens increasing with the increasing temperature that are
reasonable variation for ceramics. However, the conductivity of
◦
◦
at 700 C, but a second phase ␤-LLT was observed after 800 C
heat treatment. The LiNiO2 showed poor stability with LLT
electrolyte, it decomposed into NiO obviously with a La2Ti2O7
◦
phase formation from LLT after annealing above 500 C. Conse-
quently, for the application in thin-film microbattery, LiMn2O4
cathode with LLT electrolyte might be the appropriate choice
for the demand of high-temperature annealing.
◦
LiNiO2 + LLT was dropping quickly over 500 C in step 1. This
result can be connected with the XRD result due to the decompo-
sition of LiNiO2 into NiO. The defect equation for the formation
of LiNiO2 can be written as follows:
Acknowledgement
This work was supported under the grant no. NSC94-2120-
M-006-002 by National Science Council (NSC), Taiwan.
NiO
+
1
2
ꢀ
Ni
•
x
Li + O2←→ Li + h + OO

C.-L. Liao et al. / Journal of Alloys and Compounds 432 (2007) L22–L25
L25
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