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Thermal and electrical properties of rapidly quenched glasses in the systems Li2SSiS2LixMOy (LixMOy = Li4SiO4, Li2SO4)
SOLID STATE ELSEVIER
IONICS
Solid State Ionics 78 (199.5)269-273
Thermal and electrical properties of rapidly quenched glasses in the systems Li,S-SiS,-Li,MOY ! Li,MO, = LiJiO,, Li,SO,) Koichi Hirai, Masahiro Tatsumisago Department
*, Tsutomu
Minami
ofApplied Materials Science, Osaka Prefecture University, Sakai, Osaka 593, Japan
Received 5 January 1995; accepted for publication 12 February 1995
Abstract Superionic glasses were prepared in the systems (100 -x) (0.6LizS .0.4SiS,). zLi,MO, (Li,MO, = Li,SiO,, Li,SO,) by twin-roller rapid quenching. Glass transition temperatures (T’) and crystallization temperatures (T,) were determined for the glasses. The difference between Ta and T,, which was one of the measures of glass stability against crystallization, was maxmized at the composition with 5 mol% Li,SiO,. The conductivity at 25°C (gz,) was as high as 10e3 Scm-’ for the glass with 5 mol% Li,SiO,. The doping of Li,SO,, however, did not improve the glass stability against crystallization nor a,,.
Keywords:
Ionic conductivity - lithium; Glass; Lithium silicate; Quenching - glass
1. Introduction The development of excellent solid electrolytes with high Li+ ion conductivities will make it possible to fabricate the all solid state batteries with light weight, high voltage, and high energy density. Oxide-based glasses with high concentration of lithium ions have widely been investigated to be utilized as solid electrolytes for these batteries [l]. However, lithium ion conductivities of oxide-based glasses were limited to lop6 Scm-’ at room temperature. Kennedy et al. [2] have prepared and characterized the L&S-SiS, based sulfide glasses and reported that these glasses exhibited as high ionic conductivities as 10e4 Scm-’ at room temperature. Ribes et al. [3] also investigated glasses in the similar systems
* Corresponding author: Fax: U-722-59-3340. 0167.2738/95/$09.50
prepared by using twin-roller quenching. In order to improve the ionic conductivities of Li,S-SiS, glasses, several kinds of compounds like lithium halides were tried to be doped to these glasses [4-61. The doping of lithium halides, however, decreased the decomposition voltage of the fabricated lithium batteries in spite of the improvement of ionic conductivities. Kondo et al. [7] have reported that the Li,PO,-doped L&S-SiS, glasses have been prepared by liquid nitrogen quenching and that the doping of Li,PO, enhanced the ionic conductivity without decreasing the decomposition voltage. We have also already reported that the Li,PO,-doped Li,S-SiS, glasses prepared by twin-roller quenching have improved the glass stability against crystallization and kept the ionic conductivity very high [8]. Our interest is concentrated on whether or not the similar doping effect is brought about by doping other lithium ortho-oxosalts. Lithium ortho-silicate (Li,SiO,) and lithium ortho-sulfate (L&SO,) are
0 1995 Elsevier Science B.V. All rights reserved
SSDI 0167-2738(95)00094-l
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K. Hirai et al. /Solid
State Ionics 78 (199.5) 269-273
composed of ortho-oxoanions with similar structure and different charges. Moreover, both Li,SiO, and Li,SO, contain one of the common chemical elements to the L&S-SiS, system. In this study, Li,SiO, and Li,SO, were chosen as the dopants and the Li,S-SiS,-Li,SiO, and the Li,S-SiS,-L&SO, glasses were prepared by means of twin-roller rapid quenching. The thermal properties and lithium ion conductivities of these glasses are reported, comparing the properties of the L&S-SiS,-Li3P0, glasses reported previously.
2. Experimental Li,SiO, was prepared from reagent-grade chemicals SiO, and Li,CO,. The mixture of SiO, and L&CO, was heated at 1050°C for over 6 h to form Li,SiO,. L&SO, was obtained from Li,SO,. H,O, which was heated at 500°C for 8 h to eliminate water and yield Li, SO,. Li,SiO, or Li,SO, prepared above and reagentgrade Li,S and SiS, were mixed in a vitreous carbon crucible and then the mixture was melted at 1000°C for 2 h in an electric furnace. The molten sample was dropped into a rotating twin-roller to obtain flake-like samples, the thickness of which was about 20 pm. These processes were carried out in a dry N,-filled grove box. X-ray diffraction measurements (Cu K (Y) were performed using a Rigaku Denki Rint-1100 diffractometer for the flake-like samples glued to a glass plate and covered with polyimide thin film to avoid the attack of water and oxygen in air. Differential thermal analyses (DTA) were performed for the glassy samples in Al-pans, using a Mac-Science thermal analyzer. Conductivity measurements were carried out in the temperature range 25-200°C for the flake-like glasses, on which two parallel electrodes of carbon paste were painted, using an impedance analyzer (HP 4192A).
3. Results and discussion The base composition of the L&S-SiS, system was chosen as 0.6Li,S . 0.4SiS,, which had already
Li4SiO4 Li3PO4 Lid304 I
0
I
10 20
I
I
I
30 40 50 60
Mel% LixMOy Fig. 1. Glass-forming regions in the systems (100 - zxO.6Li,S. 0.4SiS,).zLi,MO, (Li,MO, = Li,SiO,, Li,SO,). The Li,PO,doped system is shown for comparison, Ref. [8]. Open circles denote glassy samples. Both of the closed circle and the closed square show partial crystallization. The closed triangle means that the mixture of raw materials did not melt at 1000°C.
been reported to show the highest conductivity in the system [7]. Fig. 1 shows the glass-forming regions of the (100 - z)(O.6Li,S . 0.4SiS,) . zLi,MO, (Li,MO, = Li,SiO,, Li,SO,) systems. The glassforming region of the Li,PO,-doped system was also shown for comparison [8]. The open circles denote glassy samples. The closed circle and the closed square denote partially crystallized samples containing L&S and Li,SiO, crystals, respectively. The closed triangle means that the mixture of raw materials did not melt at 1000°C. In both systems of Li,S-SiS,-Li,SiO, and Li,S-SiS,-Li,SO,, brownish-orange, transparent glasses were obtained, which showed halo patterns in X-ray diffraction and glass-transition phenomena in DTA. The glass-forming regions of the LizS-SiS,-Li,MO, (Li,MO, = Li,SiO,, Li,SO,) systems are limited compared with the region of the Li,S-SiS,-Li,PO, system. Fig. 2 shows the composition dependence of glass transition temperature (T,), crystallization temperature (T,), and the difference between T, and Tg CT,-T,), which is a measure of glass stability against crystallization, for the (100 - z) (0.6Li,S .0.4SiS,) . zLi,SiO, glasses. The values of Tg and T, for the pure sulfide glass (x = 0) agree with the data reported by Kennedy et al. [2] and Pradel et al. [3]. The Tg values are slightly changed with composition. The T, value of the glass doped with 5mol% Li,SiO, is higher than that of the pure sulfide glass. The T, values of the other glasses become lower with the
K. Himi etal./SolidStatelotaics 78 (1995)269-273
271
0.1
j,(
0
l l
*
0 0.4
b
zi 0
193°C
0.15
l
e
‘c
<
0
5
10 15 20 Mel% Li&iO4
0.6
* 0
25
Fig. 2. Com~sition dependence of Ts, T,, and T, -Ts glasses (looz) (0.6Li,S.O,4SiS,). zLi,SiO,.
I
1.6 -
01 6.0 -
l
1
2.4
for the l
0 addition of Li,SiO, more than 5 mol%. Such a composition dependence of T, and T, results in a maximum of T,-T, at a composition with Smol% Li,SiO,. Fig. 3 shows the composition dependence of Tg, T,, and T,-X, for the Li,S-SiS,--L&SO, glasses. The values of TE do not change with composition in the Li,S-SiS,-L&SO, glasses. The T, values of the glass doped with 5 mol% Li,SO, do not change so much with composition and are decreased with fur-
0
Fig. 4. Complex impedance (0.6Li,S .0.4SiS,).SLi,SiO,
l_
9.0
l
l
4'
I
plots for a rapidly quenched at various temperatures.
glass 95
ther doping. Thus the clear maximum in T,--T, is not observed in this system. Fig. 4 shows the frequency-dependent complex impedance plots of the 95(0.6Li,S . 0.4SiS,) . SLi,SiO, glass as an example at several temperatures. The bulk resistance was obtained from the intersection of semicircIe with the real axis.
y 500 2
$400 e $300
0
VT4
15
Fig. 3. Composition dependence of Tp, T,, and T,-Tg glasses (looz) (0.6Li,S.0.4SiSZ).zLi,S04.
for the
2
2.2 2.4 2.6 2.8 3
3.2 3.4
Fig. 5. Temperature dependence of conductivities for the rapidly quenched glasses (looz)(0.6Li,S.0.4SiSZ). zLi,SiO,.
272
K. Hirai et al. /Solid
State Ionics 78 (1995) 269-273
60
lo-* p-3 0 m 2 1o-4
50 r . zz 3 40 ?..
1o-5 1U" 0
10
20 30 40 Mel% LixMOy
30 50
Fig. 6. Composition dependence of flz5 and E, for the rapidly quenched glasses (100 - z)(O.6Li,S 0.4SiS,). zLi,MO, (Li,MOy = Li,SiO,, Li,SO,). Closed and open marks mean crz5 The circles are for the Li,SiO,-doped and E,, respectively. glasses, and the rhombs for the Li,SO,-doped glasses. The squares are for the Li,PO,-doped glasses for comparison [8].
Fig. 5 shows the temperature dependence of conductivities ((T) for the (100 - z) (0.6Li,S .0.4SiS,) . zLi,SiO, glasses. The conductivities showed the same values for both the heating and cooling runs. For all the compositions, the conductivities follow the Arrehenius type equation: u = ma exp( - EJRT)
,
where E, is the activation energy for conduction, a, is a preexponential factor, and R is the gas constant. For the (100 - z) (0.6Li,S . 0.4SiS,) . zLi,SO, glasses, all the plots of log u versus l/T for a given composition also follow the Arrhenius type equation. Fig. 6 shows the composition dependence of conductivities at 25°C (u,) and activation energies for conduction (E,) for the (100 - z) (0.6Li,S . 0.4SiS,). zLi,MO, glasses. The closed and open circles are respectively the values of g25 and E, of the L&S-SiS,-Li,SiO, glasses. The closed and open rhombuses are respectively the values of uZZ and E, of the Li,S-SiS,-L&SO, glasses. The values of a,, and E, of the Li,S-SiS,-LiaPO, glasses, which are characterized by the closed and open squares, are also shown for comparison [8]. The error bars for a,,
are mainly caused by the measurements of sample thickness and distance between electrodes. The a, value of 6OLi,S .4OSiS, (x = 0) was previously reported to be about 1 X lop4 Scm-’ [8]. In this study, conductivity measurements for the 6OLi,S . 4OSiS, glass were carried out many times and decided to be about 7 X lop4 Scm-’ at 25°C for the glass. The lower value of a,, in the previous study may be caused by the fact that the solvents in the carbon paste happened to react with the sample. The glass doped with 5 mol% Li,SiO, shows the crZs value of 2 X 10M3 Scm-‘, which is almost the highest conductivity in all the lithium ion conductive glasses, and E, is 36 kJ mol-’ . Doping of more than 5 mol% Li,SiO, decreases a,, and increases Ea. For the L&SO, doped glasses, a,, is decreased and E, is increased monotonically with an increase in the L&SO, content. We have already reported the composition dependence of uZ and E, for the (100 - z)(O.6Li,S. 0.4SiS,) . zLi,PO, glasses [8]. Since the glass doped with 5 mol% Li,PO, showed the a,, value of 9 X 10e4 Scm-‘, it is suggested that Li,SiO, is more effective to increase the conductivity than Li,PO,. It is noteworthy that the amount of Li,SiO, which gives the best conductivity is 5 mol% like in the case of Li,PO,. Doping of 5 mol% Li,SO,, however, does not increase the conductivity. When 5 mol% Li,PO, were doped to the 0.6Li,S . 0.4SiS, glass, a maximum of T,-T,was observed. In the case of Li,SiO,, the doping of 5 mol% Li,SiO, also maximizes the value of T,--T,. In the case of L&SO,, however, the doping of 5 mol% Li,SO, does not change the value of T,-T,. It is noteworthy that the doping of small amounts of Li,SiO, has improved the glass stability against crystallization and kept high ionic conductivity of about 10M3 Scm-‘. All the lithium ortho-oxosalts used in the present work did not improve the glass stability against crystallization and the lithium ion some kinds of lithium conductivity. However, ortho-oxosalts are very effective to improve the glass stability against crystallization and the lithium ion conductivity. Li,SiO, may react with the base glass and introduce the new structural units which are not present in the base glass. Such structural units would increase the conductivity and glass stability against crystallization. However, L&SO, did not improve
K. Hirai et al. /Solid
State Ionics 78 (1995) 269-273
the conductivity nor the glass stability against crystallization because it would react with the base glass to produce the SO, gas. Now we are in process of structural investigation for the L&S-SiS,-Li,MO, (Li,MO, is lithium ortho-oxosalts) glasses by MAS-NMR, which will be published elsewhere.
Acknowledgements This work was partly supported by a Grant-in Aid from the Ministry of Education, Science, and Culture of Japan.
References [l] M. Tatsumisago
4. Conclusion glasses doped with lithium The Li, S-SiS, ortho-oxosalts were prepared. When 5 mol% of Li,SiO, was doped to the Li,S-SiS, system, the glass stability against crystallization was improved and the conductivity as high as about 1O-3 Scm-’ was obtained at room temperature. However, doping of Li,SO, to the Li,S-SiS, system did not improve the glass stability against crystallization nor enhance the conductivity.
273
.
and T. Minami, Mat. Chem. Phys. 18 (1987)
[2] i:H. Kennedy, Mat. Chem. Phys. 23 (1989) 29. [3] A. Pradel and M. Ribes, Solid State Ionics 18/19 (1986) 3.51. [4] J.H. Kennedy and Y. Yang, J. Electrochem. Sot. 133 (1986) 2437. [5] J.H. Kennedy, S. Sahami, S.W. Shea, and 2. Zhang, Solid State Ionics 18/19 (1986) 368. [6] J.H. Kennedy and Z. Zhang, J. Electrochem. Sot. 135 (1988) 859. [7] S. Kondo, K. Takada, and Y. Yamamura, Solid State Ionics 53-56 (1992) 1183. [8] M. Tatsumisago, K. Hirai, T. Minami, K. Takada, and S. Kondo, J. Ceram. Sot. Japan 101 (1993) 1315.
IONICS
Solid State Ionics 78 (199.5)269-273
Thermal and electrical properties of rapidly quenched glasses in the systems Li,S-SiS,-Li,MOY ! Li,MO, = LiJiO,, Li,SO,) Koichi Hirai, Masahiro Tatsumisago Department
*, Tsutomu
Minami
ofApplied Materials Science, Osaka Prefecture University, Sakai, Osaka 593, Japan
Received 5 January 1995; accepted for publication 12 February 1995
Abstract Superionic glasses were prepared in the systems (100 -x) (0.6LizS .0.4SiS,). zLi,MO, (Li,MO, = Li,SiO,, Li,SO,) by twin-roller rapid quenching. Glass transition temperatures (T’) and crystallization temperatures (T,) were determined for the glasses. The difference between Ta and T,, which was one of the measures of glass stability against crystallization, was maxmized at the composition with 5 mol% Li,SiO,. The conductivity at 25°C (gz,) was as high as 10e3 Scm-’ for the glass with 5 mol% Li,SiO,. The doping of Li,SO,, however, did not improve the glass stability against crystallization nor a,,.
Keywords:
Ionic conductivity - lithium; Glass; Lithium silicate; Quenching - glass
1. Introduction The development of excellent solid electrolytes with high Li+ ion conductivities will make it possible to fabricate the all solid state batteries with light weight, high voltage, and high energy density. Oxide-based glasses with high concentration of lithium ions have widely been investigated to be utilized as solid electrolytes for these batteries [l]. However, lithium ion conductivities of oxide-based glasses were limited to lop6 Scm-’ at room temperature. Kennedy et al. [2] have prepared and characterized the L&S-SiS, based sulfide glasses and reported that these glasses exhibited as high ionic conductivities as 10e4 Scm-’ at room temperature. Ribes et al. [3] also investigated glasses in the similar systems
* Corresponding author: Fax: U-722-59-3340. 0167.2738/95/$09.50
prepared by using twin-roller quenching. In order to improve the ionic conductivities of Li,S-SiS, glasses, several kinds of compounds like lithium halides were tried to be doped to these glasses [4-61. The doping of lithium halides, however, decreased the decomposition voltage of the fabricated lithium batteries in spite of the improvement of ionic conductivities. Kondo et al. [7] have reported that the Li,PO,-doped L&S-SiS, glasses have been prepared by liquid nitrogen quenching and that the doping of Li,PO, enhanced the ionic conductivity without decreasing the decomposition voltage. We have also already reported that the Li,PO,-doped Li,S-SiS, glasses prepared by twin-roller quenching have improved the glass stability against crystallization and kept the ionic conductivity very high [8]. Our interest is concentrated on whether or not the similar doping effect is brought about by doping other lithium ortho-oxosalts. Lithium ortho-silicate (Li,SiO,) and lithium ortho-sulfate (L&SO,) are
0 1995 Elsevier Science B.V. All rights reserved
SSDI 0167-2738(95)00094-l
270
K. Hirai et al. /Solid
State Ionics 78 (199.5) 269-273
composed of ortho-oxoanions with similar structure and different charges. Moreover, both Li,SiO, and Li,SO, contain one of the common chemical elements to the L&S-SiS, system. In this study, Li,SiO, and Li,SO, were chosen as the dopants and the Li,S-SiS,-Li,SiO, and the Li,S-SiS,-L&SO, glasses were prepared by means of twin-roller rapid quenching. The thermal properties and lithium ion conductivities of these glasses are reported, comparing the properties of the L&S-SiS,-Li3P0, glasses reported previously.
2. Experimental Li,SiO, was prepared from reagent-grade chemicals SiO, and Li,CO,. The mixture of SiO, and L&CO, was heated at 1050°C for over 6 h to form Li,SiO,. L&SO, was obtained from Li,SO,. H,O, which was heated at 500°C for 8 h to eliminate water and yield Li, SO,. Li,SiO, or Li,SO, prepared above and reagentgrade Li,S and SiS, were mixed in a vitreous carbon crucible and then the mixture was melted at 1000°C for 2 h in an electric furnace. The molten sample was dropped into a rotating twin-roller to obtain flake-like samples, the thickness of which was about 20 pm. These processes were carried out in a dry N,-filled grove box. X-ray diffraction measurements (Cu K (Y) were performed using a Rigaku Denki Rint-1100 diffractometer for the flake-like samples glued to a glass plate and covered with polyimide thin film to avoid the attack of water and oxygen in air. Differential thermal analyses (DTA) were performed for the glassy samples in Al-pans, using a Mac-Science thermal analyzer. Conductivity measurements were carried out in the temperature range 25-200°C for the flake-like glasses, on which two parallel electrodes of carbon paste were painted, using an impedance analyzer (HP 4192A).
3. Results and discussion The base composition of the L&S-SiS, system was chosen as 0.6Li,S . 0.4SiS,, which had already
Li4SiO4 Li3PO4 Lid304 I
0
I
10 20
I
I
I
30 40 50 60
Mel% LixMOy Fig. 1. Glass-forming regions in the systems (100 - zxO.6Li,S. 0.4SiS,).zLi,MO, (Li,MO, = Li,SiO,, Li,SO,). The Li,PO,doped system is shown for comparison, Ref. [8]. Open circles denote glassy samples. Both of the closed circle and the closed square show partial crystallization. The closed triangle means that the mixture of raw materials did not melt at 1000°C.
been reported to show the highest conductivity in the system [7]. Fig. 1 shows the glass-forming regions of the (100 - z)(O.6Li,S . 0.4SiS,) . zLi,MO, (Li,MO, = Li,SiO,, Li,SO,) systems. The glassforming region of the Li,PO,-doped system was also shown for comparison [8]. The open circles denote glassy samples. The closed circle and the closed square denote partially crystallized samples containing L&S and Li,SiO, crystals, respectively. The closed triangle means that the mixture of raw materials did not melt at 1000°C. In both systems of Li,S-SiS,-Li,SiO, and Li,S-SiS,-Li,SO,, brownish-orange, transparent glasses were obtained, which showed halo patterns in X-ray diffraction and glass-transition phenomena in DTA. The glass-forming regions of the LizS-SiS,-Li,MO, (Li,MO, = Li,SiO,, Li,SO,) systems are limited compared with the region of the Li,S-SiS,-Li,PO, system. Fig. 2 shows the composition dependence of glass transition temperature (T,), crystallization temperature (T,), and the difference between T, and Tg CT,-T,), which is a measure of glass stability against crystallization, for the (100 - z) (0.6Li,S .0.4SiS,) . zLi,SiO, glasses. The values of Tg and T, for the pure sulfide glass (x = 0) agree with the data reported by Kennedy et al. [2] and Pradel et al. [3]. The Tg values are slightly changed with composition. The T, value of the glass doped with 5mol% Li,SiO, is higher than that of the pure sulfide glass. The T, values of the other glasses become lower with the
K. Himi etal./SolidStatelotaics 78 (1995)269-273
271
0.1
j,(
0
l l
*
0 0.4
b
zi 0
193°C
0.15
l
e
‘c
<
0
5
10 15 20 Mel% Li&iO4
0.6
* 0
25
Fig. 2. Com~sition dependence of Ts, T,, and T, -Ts glasses (looz) (0.6Li,S.O,4SiS,). zLi,SiO,.
I
1.6 -
01 6.0 -
l
1
2.4
for the l
0 addition of Li,SiO, more than 5 mol%. Such a composition dependence of T, and T, results in a maximum of T,-T, at a composition with Smol% Li,SiO,. Fig. 3 shows the composition dependence of Tg, T,, and T,-X, for the Li,S-SiS,--L&SO, glasses. The values of TE do not change with composition in the Li,S-SiS,-L&SO, glasses. The T, values of the glass doped with 5 mol% Li,SO, do not change so much with composition and are decreased with fur-
0
Fig. 4. Complex impedance (0.6Li,S .0.4SiS,).SLi,SiO,
l_
9.0
l
l
4'
I
plots for a rapidly quenched at various temperatures.
glass 95
ther doping. Thus the clear maximum in T,--T, is not observed in this system. Fig. 4 shows the frequency-dependent complex impedance plots of the 95(0.6Li,S . 0.4SiS,) . SLi,SiO, glass as an example at several temperatures. The bulk resistance was obtained from the intersection of semicircIe with the real axis.
y 500 2
$400 e $300
0
VT4
15
Fig. 3. Composition dependence of Tp, T,, and T,-Tg glasses (looz) (0.6Li,S.0.4SiSZ).zLi,S04.
for the
2
2.2 2.4 2.6 2.8 3
3.2 3.4
Fig. 5. Temperature dependence of conductivities for the rapidly quenched glasses (looz)(0.6Li,S.0.4SiSZ). zLi,SiO,.
272
K. Hirai et al. /Solid
State Ionics 78 (1995) 269-273
60
lo-* p-3 0 m 2 1o-4
50 r . zz 3 40 ?..
1o-5 1U" 0
10
20 30 40 Mel% LixMOy
30 50
Fig. 6. Composition dependence of flz5 and E, for the rapidly quenched glasses (100 - z)(O.6Li,S 0.4SiS,). zLi,MO, (Li,MOy = Li,SiO,, Li,SO,). Closed and open marks mean crz5 The circles are for the Li,SiO,-doped and E,, respectively. glasses, and the rhombs for the Li,SO,-doped glasses. The squares are for the Li,PO,-doped glasses for comparison [8].
Fig. 5 shows the temperature dependence of conductivities ((T) for the (100 - z) (0.6Li,S .0.4SiS,) . zLi,SiO, glasses. The conductivities showed the same values for both the heating and cooling runs. For all the compositions, the conductivities follow the Arrehenius type equation: u = ma exp( - EJRT)
,
where E, is the activation energy for conduction, a, is a preexponential factor, and R is the gas constant. For the (100 - z) (0.6Li,S . 0.4SiS,) . zLi,SO, glasses, all the plots of log u versus l/T for a given composition also follow the Arrhenius type equation. Fig. 6 shows the composition dependence of conductivities at 25°C (u,) and activation energies for conduction (E,) for the (100 - z) (0.6Li,S . 0.4SiS,). zLi,MO, glasses. The closed and open circles are respectively the values of g25 and E, of the L&S-SiS,-Li,SiO, glasses. The closed and open rhombuses are respectively the values of uZZ and E, of the Li,S-SiS,-L&SO, glasses. The values of a,, and E, of the Li,S-SiS,-LiaPO, glasses, which are characterized by the closed and open squares, are also shown for comparison [8]. The error bars for a,,
are mainly caused by the measurements of sample thickness and distance between electrodes. The a, value of 6OLi,S .4OSiS, (x = 0) was previously reported to be about 1 X lop4 Scm-’ [8]. In this study, conductivity measurements for the 6OLi,S . 4OSiS, glass were carried out many times and decided to be about 7 X lop4 Scm-’ at 25°C for the glass. The lower value of a,, in the previous study may be caused by the fact that the solvents in the carbon paste happened to react with the sample. The glass doped with 5 mol% Li,SiO, shows the crZs value of 2 X 10M3 Scm-‘, which is almost the highest conductivity in all the lithium ion conductive glasses, and E, is 36 kJ mol-’ . Doping of more than 5 mol% Li,SiO, decreases a,, and increases Ea. For the L&SO, doped glasses, a,, is decreased and E, is increased monotonically with an increase in the L&SO, content. We have already reported the composition dependence of uZ and E, for the (100 - z)(O.6Li,S. 0.4SiS,) . zLi,PO, glasses [8]. Since the glass doped with 5 mol% Li,PO, showed the a,, value of 9 X 10e4 Scm-‘, it is suggested that Li,SiO, is more effective to increase the conductivity than Li,PO,. It is noteworthy that the amount of Li,SiO, which gives the best conductivity is 5 mol% like in the case of Li,PO,. Doping of 5 mol% Li,SO,, however, does not increase the conductivity. When 5 mol% Li,PO, were doped to the 0.6Li,S . 0.4SiS, glass, a maximum of T,-T,was observed. In the case of Li,SiO,, the doping of 5 mol% Li,SiO, also maximizes the value of T,--T,. In the case of L&SO,, however, the doping of 5 mol% Li,SO, does not change the value of T,-T,. It is noteworthy that the doping of small amounts of Li,SiO, has improved the glass stability against crystallization and kept high ionic conductivity of about 10M3 Scm-‘. All the lithium ortho-oxosalts used in the present work did not improve the glass stability against crystallization and the lithium ion some kinds of lithium conductivity. However, ortho-oxosalts are very effective to improve the glass stability against crystallization and the lithium ion conductivity. Li,SiO, may react with the base glass and introduce the new structural units which are not present in the base glass. Such structural units would increase the conductivity and glass stability against crystallization. However, L&SO, did not improve
K. Hirai et al. /Solid
State Ionics 78 (1995) 269-273
the conductivity nor the glass stability against crystallization because it would react with the base glass to produce the SO, gas. Now we are in process of structural investigation for the L&S-SiS,-Li,MO, (Li,MO, is lithium ortho-oxosalts) glasses by MAS-NMR, which will be published elsewhere.
Acknowledgements This work was partly supported by a Grant-in Aid from the Ministry of Education, Science, and Culture of Japan.
References [l] M. Tatsumisago
4. Conclusion glasses doped with lithium The Li, S-SiS, ortho-oxosalts were prepared. When 5 mol% of Li,SiO, was doped to the Li,S-SiS, system, the glass stability against crystallization was improved and the conductivity as high as about 1O-3 Scm-’ was obtained at room temperature. However, doping of Li,SO, to the Li,S-SiS, system did not improve the glass stability against crystallization nor enhance the conductivity.
273
.
and T. Minami, Mat. Chem. Phys. 18 (1987)
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