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Preparation and lithium intercalation properties of rapidly quenched glasses in the system Fe2O3−V2O5
Solid State Ionics 40/41 North-Holland
1990) 589-592
PREPARATION AND LITHIUM INTERCALATION PROPERTIES O F R A P I D L Y Q U E N C H E D G L A S S E S I N T H E S Y S T E M Fe2Oa-V2Os N o b u y a M A C H I D A , Reiko F U C H I D A and T s u t o m u M I N A M I Department of Applied Chemistry, University of Osaka Prefecture, Sakai-Shi, Osaka-Fu 591. Japan
The glasses in the system Fe203-V205 were prepared by rapid quenching and their electrochemical properties as a cathode of lithium cells were investigated. Both the glass-transition temperature and the crystallization temperature increased with an increase in the Fe203 content of the glasses. The lithium cells with those glasses showed the high specific capacity in the range of 230 to 100 Ah kg-l, when the cells discharged under a constant-current density l Am -2 to a cut-off voltage 2.0 V. There was a maximum in the discharge capacities at around 15 tool% Fe~O3of the glasses. A maximum in chemical diffusion coefficients is also observed at around 15 tool% Fe203. These results suggest that the discharge properties of the cells with the FezO3-V2Os glasses are primary governed by the diffusion of lithium ions into the glasses.
1. Introduction M a n y investigations have been carried out on cathode materials for high-energy-density lithium cells [1,2]. In particular, transition-metal oxide glasses exhibiting simultaneously ionic a n d electronic conduction have attracted much attention as candidates for the cathode materials, since those glassy materials have some advantages in c o m p a r i son to the crystalline ones; for example, a wide range o f c o m p o s i t i o n selection, a n d thereby a wide range o f p r o p e r t y control, isotropic properties, easy thinfilm formation, and so on [ 3 - 9 ] . In addition to those advantages it has recently been reported that glassy V205 showed larger chemical diffusion coefficients than the polycrystalline one, and that the rate o f l i t h i u m insertion into the glassy V205 was accordingly larger than that into the polycrystalline one [7,8]. The glassy V205 thus indicated superior kinetic properties as a cathode in lithium cells. In the present work, we report the p r e p a r a t i o n o f rapidly quenched glasses in the system Fe203-V205 and their electrochemical properties as a cathode in lithium cells, in particular the influence o f the addition o f Fe203 on the electrochemical properties.
0167-2738/90/$ 03.50 © Elsevier Science Publishers B.V. ( North-Holland )
2. Experimental
Mixtures o f desired a m o u n t s o f raw materials, reagent grade Fe203 a n d V205, were melted in a plati n u m crucible at a t e m p e r a t u r e higher by 100 K than the liquidus t e m p e r a t u r e o f each c o m p o s i t i o n , and the melt was rapidly quenched by a twin-roller; the r a p i d quenching a p p a r a t u s was previously described in detail [10]. In the following m e a s u r e m e n t s the c o m p o s i t i o n s o f glass were described by the starting batch c o m p o s i t i o n s in mol%. The samples o b t a i n e d by r a p i d quenching were d e t e r m i n e d to be glassy by use o f an X-ray diffraction a p p a r a t u s ( R i g a k u Denki RAD-yA). The glass-transition t e m p e r a t u r e (Ts) and the crystallization t e m p e r a t u r e (To) were d e t e r m i n e d by differential thermal analysis ( D T A ) , using a Rigaku D e n k i thermal analyzer; D T A was measured under a nitrogen gas flow at a heating rate o f 10 K m i n - t. The densities o f the glasses were measured at 298 K by means o f a p y c n o m e t e r m e t h o d using propylene carbonate as a m e d i u m . A three electrode electrochemical cell o f the type o f eq. ( 1 ) was used for studies o f the intercalation reaction o f lithium ions into the glasses:
590 (C) Li
N. Machida et al. / Rapidly quenched g/asses in Fee03-1/205
1M LiCIO4-PC
FeeO3-V20~ glasses ( W )
(R) Li
(1)
The working electrode was made as follows: the Fe203-V205 glass (66.7 wt%), acetylene black (25 wt%), and Teflon powder (8.3 wt%) were mixed, and the mixture was pressed into a pellet of 13 m m in diameter. The total weight of the working electrode was 30 mg. Pure lithium metal was used for the counter and reference electrodes. The electrolyte was a solution of 1 M LiCIO4 dissolved in propylene carbonate (PC). The electrochemical cells were fabricated in a glove box filled with dry argon gas. Chemical diffusion coefficients/9 at 298 K were measured by using the galvanostatic intermittent titration technique ( G I T T ) which was introduced by Weppner and Huggins [ 11,12 ]. These electrochemical measurements were carried out by use o f a potentio-galvanostat (Hokuto HA-501 ) and a function generator ( H o k u t o HB- 104 ).
3. Results
and
discussion
The glasses were obtained over the wide composition range of 0 to 50 mol% Fe203. The rapidly quenched Fe203-V205 glasses turned from semitransparent red brown to black in color with an increase in the Fe203 content. Fig. 1 shows the composition dependence of the glass-transition temperature Tg and the crystalliza-
500
,
,
tion temperature T~. In some glasses the crystallization was observed at two different temperatures as shown in the figure. The presence of more than one Tc is probably due to the formation of a metastable crystalline phase. Both Tg and Tc increased with an increase in the Fe203 content of the glasses. Although Tg of the V205 glass without Fe203 could not be perceived by DTA, the V205 glasses containing Fe203 clearly exhibit the glass-transition temperatures. Those results suggest that thermal stability of the Fe203-V205 glasses increases with an increase in the Fe203 content of the glasses. All lithium cells with those rapidly quenched glasses as a cathode showed high initial open circuit voltages ( O C V ) over 3.0 V. The OCV of the cells gradually decreased with an increase in the Fe203 content of the glasses used as a cathode. Fig. 2 shows the relation between the discharge capacities and the Fe203 content of the glasses. The cells were discharged under constant current densities o f 1 Am 2 (open circles) and of 5 Am -2 (closed circles) to a cut-off voltage 2.0 V. A m a x i m u m in discharge capacity is observed at around 15 mol% Fe203 in both discharges. The specific capacities under 5 Am -2 are almost the same as those under 1 Am -2 for the glasses in the composition range of 0 to 25 mol% Fe203. On the other hand, the capacities under 5 A m - 2 are smaller than half of the capacities under 1 Am -2 for the glasses containing Fe203 more than 33.3 mol%. Charge-discharge characteristics of cathode ma-
,
O
I
•
5 Ar~ 2
A m -2
200( 400 ,5 o
300
ill u
8~ 200( /
100
• Tg I
100
0
i 10
i 20 mo[ %
I I 30 40 Fe203
10 50
Fig. 1. Composition dependence of the glass-transition temperature Tg ( • ) and the crystallization temperature Tc ( © ).
J
20 tool %
3~0
40
50
Fez03
Fig. 2. Relation between the discharge capacity and the composition of the glasses in the system Fe203-V2Os under constantcurrent discharge conditions; (O) 1 Am -2 and ( 0 ) 5 Am -2.
N. Machida et al. / Rapidly quenched glasses in Fe20r 1/205
terials depend on both kinetic and static factors. The kinetic factor of the cells is primarily governed by the diffusion coefficient of lithium ions into the cathode glasses. Fig. 3 shows the composition dependence of the chemical diffusion coefficients/5 of the Fe203-V20:5 glasses. In this figure, a stoichiometric parameter x denotes the ratio of the number of inserted lithium ions to that of total transitionmetal atoms included in the glass; i.e. x = L i / ( F e + V ) . In the range of x < 0 . 2 , /5 of the FezO3V205 glasses are almost independent on the Fe203 content of the glasses. On the other hand, a maximum in the chemical diffusion coefficients is observed at around 15 mol% Fe203 in the range of x > 0.4. The position of the maximum in the chemical diffusion coefficients is the same as that of the maximum in the specific capacities of the FezO3V205 glasses. Those results suggest that the discharge characteristics of the cells with Fe203-V205 glasses are primary governed by the kinetic factor and that the poor discharge properties of the glasses containing more than 33.3 mol% Fe203 are caused by the low diffusion coefficients of lithium ions into the glasses. In order to obtain an information about the space in which lithium ions could diffuse, the void fraction of the glasses was estimated by eq. (2) using the mo-
I '°-'6I 0
\xoo~ ,
,
2
10 20 30 tool % Fez03
40
Fig. 3. Composition dependence o f the chemical diffusion coefficients/) of the Fe203-V205 glasses at 298 K. The ratio of the number of intercalated lithium ions to that of total transitionmetal atoms included in the glass is indicated as a stoichiometric parameter x; x = L i / ( V + Fe).
591 I
0.53
I
[
I
FezO3-V205 glasses
0.52
:0 0.51 10
o 0.50
0.49 0
I 10
I 20 mot %
I 30
I 40
I 50
Fez03
Fig. 4. Composition dependence of the void fraction in the Fe203V205 glasses. (See text for detailed explanation).
lar volume of the F e 2 0 3 - V 2 0 5 glasses, which was calculated from their densities. V F = ( M V - T V (O 2- ) - T V (Fe 3+ )
(2)
-TV(VS+))/MV, where VF is the void fraction, MV the molar volume of the glass, T V ( M ) the true volume of the M ions included in the glasses. The TV (M) was calculated from the ionic radius of M ions; the ionic radii of 1.32, 0.64, and 0.59 A were respectively adopted for O 2-, Fe 3+, and V 5+ ions [13]. Fig. 4 shows the relation between the void fraction and the Fe203 content of the glasses. A maximum in the void fraction is observed at around 15 mol% Fe203. The position of the maximum in the void fraction is nearly the same as that of the maximum in the chemical diffusion coefficients and as that of the maximum in the specific capacities of the glasses in the system Fe203-V2Os. This agreement suggests that the increase in the void space in which the lithium ions are able to diffuse brings about the increase in the diffusion coefficients, and consequently leads to the increase in the discharge capacity of the glassy cathode materials.
Acknowledgment This work was supported by a Grant-in-Aid for
592
N. Machida et al. /Rapidly quenched glasses in Fe203-V205
Scientific Research on Priority Areas', New Functionality Materials - Design, Preparation and Control, the Ministry of Education, Science and Culture of Japan (No. 01604592).
References [ 1 ] M.S. Whittingham, Prog. Solid State Chem. 12 (1978) 1. [2]J. Rouxel, Rev. Inorg. Chem. 1 (1979) 245. [3]K. Nassau and D.W. Murphy, J, Non-Cryst. Solids 44 ( 1981 ) 297. [4]Y. Takeda, R. Kanno, Y. Tsuji and O. Yamamoto, J. Electrochem. Soc. 131 (1984) 2006. [ 5 ] Y. Sakurai and J. Yamaki, J. Electrochem. Soc. 135 ( 1988 ) 791.
[6] M. Levy and J.L. Souquet, Mater. Chem. Phys. 23 (1989) 171. [7 ] N. Machida, R. Fuchida, and T. Minami, J. Electrochem. Soc. 136 (1989) 2133. [ 8 ] N. Machida, R. Fuchida and T. Minami, Solid State lonics 35 (1989) 295. [9] N. Machida, R. Fuchida and T. Minami, J, Electrochem. Soc. 137 (1990) 1315. [ 10] M. Tatsumisago, T. Minami and M. Tanaka, J. Am. Ceram. Soc. 64 ( 1981 ) C-97. [ 11 ] W. Weppner and R.A. Huggms, J. Electrochem. Soc. 124 (1977) 1569. [12] W. Weppner and R.A. Huggins, Ann. Rev. Mater. Sci. 8 (1978) 269. [ 13 ] R.C. Weast, ed., in: Handbook of chemistry and physics, 54th Ed. (CRC Press, Cleveland, OH, 1973) F-194.
1990) 589-592
PREPARATION AND LITHIUM INTERCALATION PROPERTIES O F R A P I D L Y Q U E N C H E D G L A S S E S I N T H E S Y S T E M Fe2Oa-V2Os N o b u y a M A C H I D A , Reiko F U C H I D A and T s u t o m u M I N A M I Department of Applied Chemistry, University of Osaka Prefecture, Sakai-Shi, Osaka-Fu 591. Japan
The glasses in the system Fe203-V205 were prepared by rapid quenching and their electrochemical properties as a cathode of lithium cells were investigated. Both the glass-transition temperature and the crystallization temperature increased with an increase in the Fe203 content of the glasses. The lithium cells with those glasses showed the high specific capacity in the range of 230 to 100 Ah kg-l, when the cells discharged under a constant-current density l Am -2 to a cut-off voltage 2.0 V. There was a maximum in the discharge capacities at around 15 tool% Fe~O3of the glasses. A maximum in chemical diffusion coefficients is also observed at around 15 tool% Fe203. These results suggest that the discharge properties of the cells with the FezO3-V2Os glasses are primary governed by the diffusion of lithium ions into the glasses.
1. Introduction M a n y investigations have been carried out on cathode materials for high-energy-density lithium cells [1,2]. In particular, transition-metal oxide glasses exhibiting simultaneously ionic a n d electronic conduction have attracted much attention as candidates for the cathode materials, since those glassy materials have some advantages in c o m p a r i son to the crystalline ones; for example, a wide range o f c o m p o s i t i o n selection, a n d thereby a wide range o f p r o p e r t y control, isotropic properties, easy thinfilm formation, and so on [ 3 - 9 ] . In addition to those advantages it has recently been reported that glassy V205 showed larger chemical diffusion coefficients than the polycrystalline one, and that the rate o f l i t h i u m insertion into the glassy V205 was accordingly larger than that into the polycrystalline one [7,8]. The glassy V205 thus indicated superior kinetic properties as a cathode in lithium cells. In the present work, we report the p r e p a r a t i o n o f rapidly quenched glasses in the system Fe203-V205 and their electrochemical properties as a cathode in lithium cells, in particular the influence o f the addition o f Fe203 on the electrochemical properties.
0167-2738/90/$ 03.50 © Elsevier Science Publishers B.V. ( North-Holland )
2. Experimental
Mixtures o f desired a m o u n t s o f raw materials, reagent grade Fe203 a n d V205, were melted in a plati n u m crucible at a t e m p e r a t u r e higher by 100 K than the liquidus t e m p e r a t u r e o f each c o m p o s i t i o n , and the melt was rapidly quenched by a twin-roller; the r a p i d quenching a p p a r a t u s was previously described in detail [10]. In the following m e a s u r e m e n t s the c o m p o s i t i o n s o f glass were described by the starting batch c o m p o s i t i o n s in mol%. The samples o b t a i n e d by r a p i d quenching were d e t e r m i n e d to be glassy by use o f an X-ray diffraction a p p a r a t u s ( R i g a k u Denki RAD-yA). The glass-transition t e m p e r a t u r e (Ts) and the crystallization t e m p e r a t u r e (To) were d e t e r m i n e d by differential thermal analysis ( D T A ) , using a Rigaku D e n k i thermal analyzer; D T A was measured under a nitrogen gas flow at a heating rate o f 10 K m i n - t. The densities o f the glasses were measured at 298 K by means o f a p y c n o m e t e r m e t h o d using propylene carbonate as a m e d i u m . A three electrode electrochemical cell o f the type o f eq. ( 1 ) was used for studies o f the intercalation reaction o f lithium ions into the glasses:
590 (C) Li
N. Machida et al. / Rapidly quenched g/asses in Fee03-1/205
1M LiCIO4-PC
FeeO3-V20~ glasses ( W )
(R) Li
(1)
The working electrode was made as follows: the Fe203-V205 glass (66.7 wt%), acetylene black (25 wt%), and Teflon powder (8.3 wt%) were mixed, and the mixture was pressed into a pellet of 13 m m in diameter. The total weight of the working electrode was 30 mg. Pure lithium metal was used for the counter and reference electrodes. The electrolyte was a solution of 1 M LiCIO4 dissolved in propylene carbonate (PC). The electrochemical cells were fabricated in a glove box filled with dry argon gas. Chemical diffusion coefficients/9 at 298 K were measured by using the galvanostatic intermittent titration technique ( G I T T ) which was introduced by Weppner and Huggins [ 11,12 ]. These electrochemical measurements were carried out by use o f a potentio-galvanostat (Hokuto HA-501 ) and a function generator ( H o k u t o HB- 104 ).
3. Results
and
discussion
The glasses were obtained over the wide composition range of 0 to 50 mol% Fe203. The rapidly quenched Fe203-V205 glasses turned from semitransparent red brown to black in color with an increase in the Fe203 content. Fig. 1 shows the composition dependence of the glass-transition temperature Tg and the crystalliza-
500
,
,
tion temperature T~. In some glasses the crystallization was observed at two different temperatures as shown in the figure. The presence of more than one Tc is probably due to the formation of a metastable crystalline phase. Both Tg and Tc increased with an increase in the Fe203 content of the glasses. Although Tg of the V205 glass without Fe203 could not be perceived by DTA, the V205 glasses containing Fe203 clearly exhibit the glass-transition temperatures. Those results suggest that thermal stability of the Fe203-V205 glasses increases with an increase in the Fe203 content of the glasses. All lithium cells with those rapidly quenched glasses as a cathode showed high initial open circuit voltages ( O C V ) over 3.0 V. The OCV of the cells gradually decreased with an increase in the Fe203 content of the glasses used as a cathode. Fig. 2 shows the relation between the discharge capacities and the Fe203 content of the glasses. The cells were discharged under constant current densities o f 1 Am 2 (open circles) and of 5 Am -2 (closed circles) to a cut-off voltage 2.0 V. A m a x i m u m in discharge capacity is observed at around 15 mol% Fe203 in both discharges. The specific capacities under 5 Am -2 are almost the same as those under 1 Am -2 for the glasses in the composition range of 0 to 25 mol% Fe203. On the other hand, the capacities under 5 A m - 2 are smaller than half of the capacities under 1 Am -2 for the glasses containing Fe203 more than 33.3 mol%. Charge-discharge characteristics of cathode ma-
,
O
I
•
5 Ar~ 2
A m -2
200( 400 ,5 o
300
ill u
8~ 200( /
100
• Tg I
100
0
i 10
i 20 mo[ %
I I 30 40 Fe203
10 50
Fig. 1. Composition dependence of the glass-transition temperature Tg ( • ) and the crystallization temperature Tc ( © ).
J
20 tool %
3~0
40
50
Fez03
Fig. 2. Relation between the discharge capacity and the composition of the glasses in the system Fe203-V2Os under constantcurrent discharge conditions; (O) 1 Am -2 and ( 0 ) 5 Am -2.
N. Machida et al. / Rapidly quenched glasses in Fe20r 1/205
terials depend on both kinetic and static factors. The kinetic factor of the cells is primarily governed by the diffusion coefficient of lithium ions into the cathode glasses. Fig. 3 shows the composition dependence of the chemical diffusion coefficients/5 of the Fe203-V20:5 glasses. In this figure, a stoichiometric parameter x denotes the ratio of the number of inserted lithium ions to that of total transitionmetal atoms included in the glass; i.e. x = L i / ( F e + V ) . In the range of x < 0 . 2 , /5 of the FezO3V205 glasses are almost independent on the Fe203 content of the glasses. On the other hand, a maximum in the chemical diffusion coefficients is observed at around 15 mol% Fe203 in the range of x > 0.4. The position of the maximum in the chemical diffusion coefficients is the same as that of the maximum in the specific capacities of the FezO3V205 glasses. Those results suggest that the discharge characteristics of the cells with Fe203-V205 glasses are primary governed by the kinetic factor and that the poor discharge properties of the glasses containing more than 33.3 mol% Fe203 are caused by the low diffusion coefficients of lithium ions into the glasses. In order to obtain an information about the space in which lithium ions could diffuse, the void fraction of the glasses was estimated by eq. (2) using the mo-
I '°-'6I 0
\xoo~ ,
,
2
10 20 30 tool % Fez03
40
Fig. 3. Composition dependence o f the chemical diffusion coefficients/) of the Fe203-V205 glasses at 298 K. The ratio of the number of intercalated lithium ions to that of total transitionmetal atoms included in the glass is indicated as a stoichiometric parameter x; x = L i / ( V + Fe).
591 I
0.53
I
[
I
FezO3-V205 glasses
0.52
:0 0.51 10
o 0.50
0.49 0
I 10
I 20 mot %
I 30
I 40
I 50
Fez03
Fig. 4. Composition dependence of the void fraction in the Fe203V205 glasses. (See text for detailed explanation).
lar volume of the F e 2 0 3 - V 2 0 5 glasses, which was calculated from their densities. V F = ( M V - T V (O 2- ) - T V (Fe 3+ )
(2)
-TV(VS+))/MV, where VF is the void fraction, MV the molar volume of the glass, T V ( M ) the true volume of the M ions included in the glasses. The TV (M) was calculated from the ionic radius of M ions; the ionic radii of 1.32, 0.64, and 0.59 A were respectively adopted for O 2-, Fe 3+, and V 5+ ions [13]. Fig. 4 shows the relation between the void fraction and the Fe203 content of the glasses. A maximum in the void fraction is observed at around 15 mol% Fe203. The position of the maximum in the void fraction is nearly the same as that of the maximum in the chemical diffusion coefficients and as that of the maximum in the specific capacities of the glasses in the system Fe203-V2Os. This agreement suggests that the increase in the void space in which the lithium ions are able to diffuse brings about the increase in the diffusion coefficients, and consequently leads to the increase in the discharge capacity of the glassy cathode materials.
Acknowledgment This work was supported by a Grant-in-Aid for
592
N. Machida et al. /Rapidly quenched glasses in Fe203-V205
Scientific Research on Priority Areas', New Functionality Materials - Design, Preparation and Control, the Ministry of Education, Science and Culture of Japan (No. 01604592).
References [ 1 ] M.S. Whittingham, Prog. Solid State Chem. 12 (1978) 1. [2]J. Rouxel, Rev. Inorg. Chem. 1 (1979) 245. [3]K. Nassau and D.W. Murphy, J, Non-Cryst. Solids 44 ( 1981 ) 297. [4]Y. Takeda, R. Kanno, Y. Tsuji and O. Yamamoto, J. Electrochem. Soc. 131 (1984) 2006. [ 5 ] Y. Sakurai and J. Yamaki, J. Electrochem. Soc. 135 ( 1988 ) 791.
[6] M. Levy and J.L. Souquet, Mater. Chem. Phys. 23 (1989) 171. [7 ] N. Machida, R. Fuchida, and T. Minami, J. Electrochem. Soc. 136 (1989) 2133. [ 8 ] N. Machida, R. Fuchida and T. Minami, Solid State lonics 35 (1989) 295. [9] N. Machida, R. Fuchida and T. Minami, J, Electrochem. Soc. 137 (1990) 1315. [ 10] M. Tatsumisago, T. Minami and M. Tanaka, J. Am. Ceram. Soc. 64 ( 1981 ) C-97. [ 11 ] W. Weppner and R.A. Huggms, J. Electrochem. Soc. 124 (1977) 1569. [12] W. Weppner and R.A. Huggins, Ann. Rev. Mater. Sci. 8 (1978) 269. [ 13 ] R.C. Weast, ed., in: Handbook of chemistry and physics, 54th Ed. (CRC Press, Cleveland, OH, 1973) F-194.