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Synthesis and electrochemical properties of lithium ion conductive glass, Li3PO4Li2SSiS2
SOLID STATE ELSEVIER
Solid State Ionics 68 (1994) 35-39
IONICS
Synthesis and electrochemical properties of lithium ion conductive glass, Li3PO4-Li2S-SiS2 Noboru Aotani, Kazuya Iwamoto, Kazunori Takada and Shigeo Kondo Technology Laboratory, Matsushita Battery Industrial Co., LTD., 1, Matsushita-cho, Moriguchi, Osaka 5 70, Japan
Abstract
As a continuation of our previous study, further experiments were performed on Li3PO4-Li2S-SiS2 lithium ion conductive glass. In the present study, we employed a twin roller for quenching process instead of liquid nitrogen. We found that the glass forming region expands by twin roller technique and conductivity up to 1.5 × 10-3 S/cm was achieved. Structural analysis on the glass revealed that LiaPO4 doping changes the glass structure of Li2S-SiS2, thereby enhancing the electrical conductivity.
1. Introduction
Lithium batteries are promising candidates to meet the great demands of batteries for their high voltage and high energy densities. However, as a detrimental factor, they use flammable organic electrolytes accompanied by high chemical energy in them, which makes the batteries unsafe in their applications. Hence, there is a necessity to develop nonflammable electrolyte, i.e., solid electrolyte, for lithium batteries. Various attempts have been made to develop such solid electrolytes, all in vain, due to their poor electrical conductivity and chemical stability against lithium metal. In our earlier publication [ 1 ], we have reported that Li3PO4 doping on Li2S-SiS~ enhances the ionic conductivity of the sulfide glass and was stable against electrochemical reduction. In the present study, further experiments are reported on LizS-SiS2 sulfide glass. Ion conductive glasses with high electric conducPresented at the SSI-9 Conference, September 12-19, 1993, The Hague, The Netherlands.
tivity were reported to be obtained in LiI-Li2S-SiS2 system by twin roller quenching, which offers a very high cooling rate [ 2 ]. In this study, we employed a twin roller to synthesize the glass to obtain higher cooling rate for quenching. The glasses were characterized by thermal analysis and infrared spectroscopy.
2. Experimental 2.1. Synthesis o f the glasses
Li3PO4-Li2S-SiS2 glasses were obtained by liquid nitrogen quenching and twin roller quenching. First, the glassy electrolyte was synthesized by quenching in liquid nitrogen. Li3PO4, Li2S and SiS2 were mixed in the appropriate ratios, and the mixtures were put in vitreous carbon crucibles and heated at 950°C in a vertical tube furnace under Ar gas atmosphere. The crucibles were dropped into liquid nitrogen to quench the molten. The glassy electrolyte was also synthesized by twin roller quenching. As described above, the mixtures were heated in vitreous carbon crucibles in a hori-
0167-2738/94/$07.00 © 1994 ElsevierScience B.V. All fights reserved SSDIOI67-2738(93)EO418-D
36
N. Aotani et aL / Solid State lonics 68 (1994) 35-39
zontal tube furnace at 950°C in a current of Ar. The crucibles were removed from the furnace, and the molten were quenched by a twin roller to obtain a glassy electrolyte ribbon.
2.2. Conductivity measurements Ionic conductivities of the obtained glasses were measured by ac impedance technique. The quenched glasses were ground thoroughly and then pressed into a pellet 10 m m (~ inside an axial hole of an insulator tube (a polyimide resin tube). Platinum plates were attached as the electrodes on both sides. Complex impedance was measured with a Solartron 1286 electrochemical interface and a 1260 frequency response analyzer. The signal across the sample was 10 mV, and the frequency range was from 106 to 10 -3 Hz. Electric conductivity measurements were also carried out to get rid of the influences of voids and grain boundary on the conductivities. Carbon pastes were attached on the ribbons as electrodes, and the conductivities were measured by complex impedance analysis.
2.3. Characterization of the glasses The obtained glasses were characterized by differential scanning calorimetry (DSC) and infrared spectroscopy. The test samples were prepared by quenching followed by sealing in aluminum cells. DSC spectra were obtained up to 500°C in Ar gas atmosphere with a scanning rate of 10°C/min by a TAS-200 DSC system (Rigaku). Infrared spectra were obtained by FTIR method. The glasses were ground and diluted with liquid paraffin. The mixtures were sandwiched and then sealed between TII-T1Br crystal plates. IR spectra were obtained by a FTIR-7000 spectrometer (JASCO).
thickness, 5 m m in the width, and 20 m m in the length. They are transparent in Li2S-SiS2 base glasses and slightly red in color in Li3PO4-doped glasses. Glass forming region of the glasses obtained by twin roller quenching was wider than that of liquid nitrogen quenched glass. The electric conductivities of the LizS-SiS 2 base glasses (Li3PO4 non-doped glasses) synthesized by liquid nitrogen quenching and twin roller quenching are indicated in Fig. 1. Glassy samples with higher LizS compositions were obtained by twin roller quenching, and they showed higher ionic conductivities than those quenched by liquid nitrogen. The ionic conductivities were calculated from the resistance values of the cell that consists of a uniaxial pressed pellet of the ground glass. Electric conductivity of sulfide glass was reported to depend on the pelletizing pressure because of its packing density [ 3 ]. The packing density will depend not only on the pressure but also on the particle size of the ground powder. We also investigated the dependence of pressure and particle size on the electric conductivities. Fig. 2 indicates the pressure dependence and the particle size dependence of the conductivity. Larger particle size and higher pressure showed the higher conductivity. The maximum conductivity was 1.5 × 10- 3 S/cm with the composition of 0.01Li3PO4-0.63Li20.365SIS2. This value was comparable to one of the highest conductivities, which has been observed in LiI-Li2S-SiS2 system. l x l O -2 twin roller quenching
lxlO 3
B l x l 0 -4
liq N z quenching
3. Results and discussion lxlO-S
3. I. Electric conductivity
I
0.5
I
O.5S
. . . .
I 0.6
, I , O.6S
i 0.7
Li 2S composition
The dimensions of the glasses obtained by twin roller quenching were typically around 90 ~tm in
Fig. 1. Electric conductivity of Li2S-SiS2 glass quenched by liquid nitrogen and a twin roller.
N. Aotani et al. / S o l i d State lonics 68 (1994) 35-39
2xl
37
der pressed on electric conductivity is not a major factor in the measured conductivity.
0 -3
Particle size
/ "T
3.2. Characterizations of the glass
125~m~
l x 1 0 -3
7 5 ~ 106gin 0 5X10
-4
o ~75gm
o
0xl 00
i 5
0
. . . .
f
t
10
15
Pressure/10 3kgf cm -z
L i 3 P O 4 - L i 2 S - S i S 2 glass was characterized using Li3PO4 doped 0.60Li2S-0.40SiS2 glasses. Electric conductivities obtained for Li3PO4 doped 0.60Li2S-0.40SiS2 glasses were indicated in Fig. 4. Activation energies, preexponential factor (ao), and electric conductivities at ambient temperature (298 K) calculated by least square fitting are indicated in Figs. 5, 6 and 7 respectively. The electric conductivities showed the maximum, and activation energies showed the minimum at around 2% doping of L i 3 P O 4.
Fig. 2. Electric conductivity of powdered 0.01Li3PO4-0.63Li2S0.36SIS2 with the various particle sizes as a function of pelletized pressure.
Ixi0 °
IxI0-~
Ixl0 °
~A~>~ *' C) d~ C~A
g
O O
l x l O -1
b
'5-
x=0.02
0% / °~A t
Ixi0 -z I x i 0 -3
0 % ~ x=O
0
c>~ x=O.O5
E O
lx10-4 O
l x l O -z O
ix10-s
....
L ....
1.5
I ....
2
. . . . 1.5
t 2
,
,
I . . . . 2.5
1 03/T/K
1 . . . . 3
A~
x=0.1
-
I ,,,
2.5
i ....
3
3.5
1 03/T (/K)
O ix10-3
0A ~0
x=0.2
t 3.5
Fig. 4. E l e c t r i c c o n d u c t i v i t y o f L i 3 P O 4 d o p e d 0 . 6 0 L i z S - 0 . 4 0 S i S =
ribbons as a function of absolute temperature.
-I
0.45
Fig. 3. Electric conductivity o f 0.01Li3PO4-0.63Li2S-0.36SiS2 as a quenched ribbon.
The electric conductivity was also measured using quenched glass ribbon to get rid of the influence of voids and grain boundary. Electric conductivity of the glass with the composition of 0.01Li3PO4-0.63Li2S0.365SIS2 is indicated in Fig. 3 as a function of absolute temperature. Activation energy and electric conductivity at room temperature were calculated from the data by the least square fitting. The activation energy was 0.30+0.01 eV and a(298 K) was 1.6 × 10-3 S/cm. The conductivity was close to that obtained by powdered pellet, so that it is considered that influence of voids and grain boundaries in pow-
0.40
v
0.35 Q O
0.30 (
0,2S
,
0
,
~
,
I
. . . .
0.05
[
0.1
,
,
,
I
0.1 5
,
,
,
0.2
Li 3P04 c o m p o s i t i o n
Fig. 5. Activation energy of Li3PO4 doped 0.60Li2S-0.40SiS2 as a function of Li3PO4 composition.
38
N. Aotani et al. /Solid State lonics 68 (1994) 35-39 l x l O -z
"~u
~
lx10-3
/ 0 %
Li3P(
II I--
l x l O -4
"
',,i\
'
,',, i %U. \ /
J
i
," 1"~, , 1 x l o-S
,, 0
i .... 0.05
i ....
i ....
0.1
0.15
0.2
~q I; ~ ' " , ,"Y,,x~ g "~'-
~\t
Li 3P04 composition
1", .
i,M
Fig. 6. Electric conductivityat ambient temperature of Li3PO4 doped 0.60Li2S-0.40SiS2as a function of Li3PO4composition.
i 1'
IF i lIl L .~ 4,, " I "~ i fl" / t.,,f.. [ r.
~'~
~
5%
i '", "~. i
ti
,']
10% ~
r
~ fl, i
t~
lxlO 4
/
J
I
I,%
~7 ~L,~ /" kfl
IxlO 3
0 0
v
0
I
1
, , , , I ....
0
I
I
I
I
I
1000 500 wave number(cm -1) Fig. 8. IR spectra of Li3PO4doped 0.60Li2S-0.40SiS2.
lx10 z
lxlO
I
0.05
I
0.1
,
,
,
I
,
0.15
,
,
,
0.2
Li 3P04 c o m p o s i t i o n
Fig. 7. Preexponential factor of Li3P04doped 0.60Li2S-0.40SiS2 as a function of Li3P04composition. Change in ~(298 K) was larger than that in ao. IR transmittance spectra for Li3PO 4 doped 0.60Li2S-0.40SiS2 glasses are indicated in Fig. 8. Peaks at 911 c m - Land 560 c m - i are identified as the stretching frequency for the Si-S-Si bridging bond and bond-bending vibration frequency [ 4 ]. Absorbance peaks at 1035 cm -~ corresponding to PO43appeared by doping Li3PO4, and no changes in the peak positions corresponding to Li2S-SiS2 glass structure were observed in the IR spectra. (It should be noted that SiO2 impurity in SiS2 glass produces peaks at 1039, 1103, and 1198 cm -~, and the lowest frequency peak cannot be distinguished from that corresponding to PO 3-. ) There were no changes in IR spectra involving
Li2S-SiS 2 glass structure, but Tg increased with doping L%PO4. This phenomenon shows that the PO43ions remain outside the macromolecular chains consisting of glassy SiS2 tetrahedral, but they play a role in forming the glass structure. The PO43- ion observed in IR spectra is known as an isolated glass network forming ion in Ag ÷ ion conductive oxide glasses. It would be concluded that Li3PO4 doping to LIESSiS2 glass produces PO 3- ions, which are isolated glass forming ions. This change in glass structure is considered to enhance the electric conductivity.
4. Conclusions
We have investigated the electrochemical properties of LiaPOg-Li2S-SiS2 glass and found that: High electric conductivity with a value up to 1.5 × 10- 3 S/cm can be achieved in LiaPO4-LiES-SiS2 glass system obtained by twin roller quenching. Li3PO4 doping is considered to change the glass
N. Aotani et al. / Solid State lonics 68 (1994) 35-39
structure of Li2S-SiS2, which enhances the electric conductivity.
5. Acknowledgement The authors want to t h a n k Prof. M i n a m i a n d Dr. Tatsumisago of Osaka Prefecture University for their fruitful discussions.
39
References
[ 1] S. Kondo, K. Takada and Y. Yamamura, Solid State Ionics 53-56 (1992) 1183. [2] A. Pradel and M. Ribes, SolidState lonics 18/19 (1986) 351. [3] J.H. Kennedy and Z. Zhang, J. Electrochem. Soc. 135 (1988) 859. [4] J.H. Kennedy and Y. Yang, J. Solid State Chem. 69 (1987) 252.
Solid State Ionics 68 (1994) 35-39
IONICS
Synthesis and electrochemical properties of lithium ion conductive glass, Li3PO4-Li2S-SiS2 Noboru Aotani, Kazuya Iwamoto, Kazunori Takada and Shigeo Kondo Technology Laboratory, Matsushita Battery Industrial Co., LTD., 1, Matsushita-cho, Moriguchi, Osaka 5 70, Japan
Abstract
As a continuation of our previous study, further experiments were performed on Li3PO4-Li2S-SiS2 lithium ion conductive glass. In the present study, we employed a twin roller for quenching process instead of liquid nitrogen. We found that the glass forming region expands by twin roller technique and conductivity up to 1.5 × 10-3 S/cm was achieved. Structural analysis on the glass revealed that LiaPO4 doping changes the glass structure of Li2S-SiS2, thereby enhancing the electrical conductivity.
1. Introduction
Lithium batteries are promising candidates to meet the great demands of batteries for their high voltage and high energy densities. However, as a detrimental factor, they use flammable organic electrolytes accompanied by high chemical energy in them, which makes the batteries unsafe in their applications. Hence, there is a necessity to develop nonflammable electrolyte, i.e., solid electrolyte, for lithium batteries. Various attempts have been made to develop such solid electrolytes, all in vain, due to their poor electrical conductivity and chemical stability against lithium metal. In our earlier publication [ 1 ], we have reported that Li3PO4 doping on Li2S-SiS~ enhances the ionic conductivity of the sulfide glass and was stable against electrochemical reduction. In the present study, further experiments are reported on LizS-SiS2 sulfide glass. Ion conductive glasses with high electric conducPresented at the SSI-9 Conference, September 12-19, 1993, The Hague, The Netherlands.
tivity were reported to be obtained in LiI-Li2S-SiS2 system by twin roller quenching, which offers a very high cooling rate [ 2 ]. In this study, we employed a twin roller to synthesize the glass to obtain higher cooling rate for quenching. The glasses were characterized by thermal analysis and infrared spectroscopy.
2. Experimental 2.1. Synthesis o f the glasses
Li3PO4-Li2S-SiS2 glasses were obtained by liquid nitrogen quenching and twin roller quenching. First, the glassy electrolyte was synthesized by quenching in liquid nitrogen. Li3PO4, Li2S and SiS2 were mixed in the appropriate ratios, and the mixtures were put in vitreous carbon crucibles and heated at 950°C in a vertical tube furnace under Ar gas atmosphere. The crucibles were dropped into liquid nitrogen to quench the molten. The glassy electrolyte was also synthesized by twin roller quenching. As described above, the mixtures were heated in vitreous carbon crucibles in a hori-
0167-2738/94/$07.00 © 1994 ElsevierScience B.V. All fights reserved SSDIOI67-2738(93)EO418-D
36
N. Aotani et aL / Solid State lonics 68 (1994) 35-39
zontal tube furnace at 950°C in a current of Ar. The crucibles were removed from the furnace, and the molten were quenched by a twin roller to obtain a glassy electrolyte ribbon.
2.2. Conductivity measurements Ionic conductivities of the obtained glasses were measured by ac impedance technique. The quenched glasses were ground thoroughly and then pressed into a pellet 10 m m (~ inside an axial hole of an insulator tube (a polyimide resin tube). Platinum plates were attached as the electrodes on both sides. Complex impedance was measured with a Solartron 1286 electrochemical interface and a 1260 frequency response analyzer. The signal across the sample was 10 mV, and the frequency range was from 106 to 10 -3 Hz. Electric conductivity measurements were also carried out to get rid of the influences of voids and grain boundary on the conductivities. Carbon pastes were attached on the ribbons as electrodes, and the conductivities were measured by complex impedance analysis.
2.3. Characterization of the glasses The obtained glasses were characterized by differential scanning calorimetry (DSC) and infrared spectroscopy. The test samples were prepared by quenching followed by sealing in aluminum cells. DSC spectra were obtained up to 500°C in Ar gas atmosphere with a scanning rate of 10°C/min by a TAS-200 DSC system (Rigaku). Infrared spectra were obtained by FTIR method. The glasses were ground and diluted with liquid paraffin. The mixtures were sandwiched and then sealed between TII-T1Br crystal plates. IR spectra were obtained by a FTIR-7000 spectrometer (JASCO).
thickness, 5 m m in the width, and 20 m m in the length. They are transparent in Li2S-SiS2 base glasses and slightly red in color in Li3PO4-doped glasses. Glass forming region of the glasses obtained by twin roller quenching was wider than that of liquid nitrogen quenched glass. The electric conductivities of the LizS-SiS 2 base glasses (Li3PO4 non-doped glasses) synthesized by liquid nitrogen quenching and twin roller quenching are indicated in Fig. 1. Glassy samples with higher LizS compositions were obtained by twin roller quenching, and they showed higher ionic conductivities than those quenched by liquid nitrogen. The ionic conductivities were calculated from the resistance values of the cell that consists of a uniaxial pressed pellet of the ground glass. Electric conductivity of sulfide glass was reported to depend on the pelletizing pressure because of its packing density [ 3 ]. The packing density will depend not only on the pressure but also on the particle size of the ground powder. We also investigated the dependence of pressure and particle size on the electric conductivities. Fig. 2 indicates the pressure dependence and the particle size dependence of the conductivity. Larger particle size and higher pressure showed the higher conductivity. The maximum conductivity was 1.5 × 10- 3 S/cm with the composition of 0.01Li3PO4-0.63Li20.365SIS2. This value was comparable to one of the highest conductivities, which has been observed in LiI-Li2S-SiS2 system. l x l O -2 twin roller quenching
lxlO 3
B l x l 0 -4
liq N z quenching
3. Results and discussion lxlO-S
3. I. Electric conductivity
I
0.5
I
O.5S
. . . .
I 0.6
, I , O.6S
i 0.7
Li 2S composition
The dimensions of the glasses obtained by twin roller quenching were typically around 90 ~tm in
Fig. 1. Electric conductivity of Li2S-SiS2 glass quenched by liquid nitrogen and a twin roller.
N. Aotani et al. / S o l i d State lonics 68 (1994) 35-39
2xl
37
der pressed on electric conductivity is not a major factor in the measured conductivity.
0 -3
Particle size
/ "T
3.2. Characterizations of the glass
125~m~
l x 1 0 -3
7 5 ~ 106gin 0 5X10
-4
o ~75gm
o
0xl 00
i 5
0
. . . .
f
t
10
15
Pressure/10 3kgf cm -z
L i 3 P O 4 - L i 2 S - S i S 2 glass was characterized using Li3PO4 doped 0.60Li2S-0.40SiS2 glasses. Electric conductivities obtained for Li3PO4 doped 0.60Li2S-0.40SiS2 glasses were indicated in Fig. 4. Activation energies, preexponential factor (ao), and electric conductivities at ambient temperature (298 K) calculated by least square fitting are indicated in Figs. 5, 6 and 7 respectively. The electric conductivities showed the maximum, and activation energies showed the minimum at around 2% doping of L i 3 P O 4.
Fig. 2. Electric conductivity of powdered 0.01Li3PO4-0.63Li2S0.36SIS2 with the various particle sizes as a function of pelletized pressure.
Ixi0 °
IxI0-~
Ixl0 °
~A~>~ *' C) d~ C~A
g
O O
l x l O -1
b
'5-
x=0.02
0% / °~A t
Ixi0 -z I x i 0 -3
0 % ~ x=O
0
c>~ x=O.O5
E O
lx10-4 O
l x l O -z O
ix10-s
....
L ....
1.5
I ....
2
. . . . 1.5
t 2
,
,
I . . . . 2.5
1 03/T/K
1 . . . . 3
A~
x=0.1
-
I ,,,
2.5
i ....
3
3.5
1 03/T (/K)
O ix10-3
0A ~0
x=0.2
t 3.5
Fig. 4. E l e c t r i c c o n d u c t i v i t y o f L i 3 P O 4 d o p e d 0 . 6 0 L i z S - 0 . 4 0 S i S =
ribbons as a function of absolute temperature.
-I
0.45
Fig. 3. Electric conductivity o f 0.01Li3PO4-0.63Li2S-0.36SiS2 as a quenched ribbon.
The electric conductivity was also measured using quenched glass ribbon to get rid of the influence of voids and grain boundary. Electric conductivity of the glass with the composition of 0.01Li3PO4-0.63Li2S0.365SIS2 is indicated in Fig. 3 as a function of absolute temperature. Activation energy and electric conductivity at room temperature were calculated from the data by the least square fitting. The activation energy was 0.30+0.01 eV and a(298 K) was 1.6 × 10-3 S/cm. The conductivity was close to that obtained by powdered pellet, so that it is considered that influence of voids and grain boundaries in pow-
0.40
v
0.35 Q O
0.30 (
0,2S
,
0
,
~
,
I
. . . .
0.05
[
0.1
,
,
,
I
0.1 5
,
,
,
0.2
Li 3P04 c o m p o s i t i o n
Fig. 5. Activation energy of Li3PO4 doped 0.60Li2S-0.40SiS2 as a function of Li3PO4 composition.
38
N. Aotani et al. /Solid State lonics 68 (1994) 35-39 l x l O -z
"~u
~
lx10-3
/ 0 %
Li3P(
II I--
l x l O -4
"
',,i\
'
,',, i %U. \ /
J
i
," 1"~, , 1 x l o-S
,, 0
i .... 0.05
i ....
i ....
0.1
0.15
0.2
~q I; ~ ' " , ,"Y,,x~ g "~'-
~\t
Li 3P04 composition
1", .
i,M
Fig. 6. Electric conductivityat ambient temperature of Li3PO4 doped 0.60Li2S-0.40SiS2as a function of Li3PO4composition.
i 1'
IF i lIl L .~ 4,, " I "~ i fl" / t.,,f.. [ r.
~'~
~
5%
i '", "~. i
ti
,']
10% ~
r
~ fl, i
t~
lxlO 4
/
J
I
I,%
~7 ~L,~ /" kfl
IxlO 3
0 0
v
0
I
1
, , , , I ....
0
I
I
I
I
I
1000 500 wave number(cm -1) Fig. 8. IR spectra of Li3PO4doped 0.60Li2S-0.40SiS2.
lx10 z
lxlO
I
0.05
I
0.1
,
,
,
I
,
0.15
,
,
,
0.2
Li 3P04 c o m p o s i t i o n
Fig. 7. Preexponential factor of Li3P04doped 0.60Li2S-0.40SiS2 as a function of Li3P04composition. Change in ~(298 K) was larger than that in ao. IR transmittance spectra for Li3PO 4 doped 0.60Li2S-0.40SiS2 glasses are indicated in Fig. 8. Peaks at 911 c m - Land 560 c m - i are identified as the stretching frequency for the Si-S-Si bridging bond and bond-bending vibration frequency [ 4 ]. Absorbance peaks at 1035 cm -~ corresponding to PO43appeared by doping Li3PO4, and no changes in the peak positions corresponding to Li2S-SiS2 glass structure were observed in the IR spectra. (It should be noted that SiO2 impurity in SiS2 glass produces peaks at 1039, 1103, and 1198 cm -~, and the lowest frequency peak cannot be distinguished from that corresponding to PO 3-. ) There were no changes in IR spectra involving
Li2S-SiS 2 glass structure, but Tg increased with doping L%PO4. This phenomenon shows that the PO43ions remain outside the macromolecular chains consisting of glassy SiS2 tetrahedral, but they play a role in forming the glass structure. The PO43- ion observed in IR spectra is known as an isolated glass network forming ion in Ag ÷ ion conductive oxide glasses. It would be concluded that Li3PO4 doping to LIESSiS2 glass produces PO 3- ions, which are isolated glass forming ions. This change in glass structure is considered to enhance the electric conductivity.
4. Conclusions
We have investigated the electrochemical properties of LiaPOg-Li2S-SiS2 glass and found that: High electric conductivity with a value up to 1.5 × 10- 3 S/cm can be achieved in LiaPO4-LiES-SiS2 glass system obtained by twin roller quenching. Li3PO4 doping is considered to change the glass
N. Aotani et al. / Solid State lonics 68 (1994) 35-39
structure of Li2S-SiS2, which enhances the electric conductivity.
5. Acknowledgement The authors want to t h a n k Prof. M i n a m i a n d Dr. Tatsumisago of Osaka Prefecture University for their fruitful discussions.
39
References
[ 1] S. Kondo, K. Takada and Y. Yamamura, Solid State Ionics 53-56 (1992) 1183. [2] A. Pradel and M. Ribes, SolidState lonics 18/19 (1986) 351. [3] J.H. Kennedy and Z. Zhang, J. Electrochem. Soc. 135 (1988) 859. [4] J.H. Kennedy and Y. Yang, J. Solid State Chem. 69 (1987) 252.