JP2004331416A - Electroconductive glass having mixed conductivity and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroconductive glass in which ionic conduction and electronic conduction coexist and which exhibits high electroconductivity, and to provide a method for manufacturing the same. <P>SOLUTION: The electroconductive glass is composed, by mol, of 65 to 85% AgI and Ag<SB>2</SB>O and 15 to 35% V<SB>2</SB>O<SB>5</SB>and Fe<SB>2</SB>O<SB>3</SB>, and exhibits mixed electroconductivity. Alternatively, the electro-conductive glass is composed, by mol, of 30 to 50% LiI and Li<SB>2</SB>O and 50 to 70% V<SB>2</SB>O<SB>5</SB>and Fe<SB>2</SB>O<SB>3</SB>, and exhibits mixed electroconductivity. The electroconductive glass is obtained by mixing the composition composed, by mol, of 65 to 85% AgI and Ag<SB>2</SB>O, and 15 to 35% V<SB>2</SB>O<SB>5</SB>and Fe<SB>2</SB>O<SB>3</SB>or a composition composed, by mol, of 30 to 50% LiI and Li<SB>2</SB>O and 50 to 70% V<SB>2</SB>O<SB>5</SB>and Fe<SB>2</SB>O<SB>3</SB>, and then heating, melting, and quenching the composition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a conductive glass having a so-called mixed conductivity in which ionic conduction and electron conduction coexist and a method for producing the same.
[0002]
[Prior art]
For example, in the case of a secondary battery using a solid electrolyte, as disclosed in Japanese Patent Application Laid-Open No. 2001-243984, good ion migration is caused at the interface between the electrode and the electrolyte, and the active material of the positive and negative electrodes is At the interface of the electrolyte, a practical level of battery characteristics is obtained by causing good movement of electrons and ions together with oxidation / reduction reactions. Thus, it is desirable that the material forming the electrode is a conductive material having both ionic conductivity and electronic conductivity.
[0003]
On the other hand, a glass having conductivity is known as a glass having a metal oxide film ITO (Indium Tin Oxide) on the surface thereof, which is mainly composed of an indium oxide film. These transparent and conductive glass plates are widely used as container materials for liquid crystal displays. However, these conductive glasses are based on electron conductivity, and do not have mixed conductivity having both ionic conductivity and electron conductivity required for an electrode of a secondary battery using the solid electrolyte, for example.
[0004]
[Problems to be solved by the invention]
If it is possible to easily obtain a highly conductive material having both ionic conductivity and electron conductivity, it is suitable as an electrode material for a secondary battery or a fuel cell using a solid electrolyte, which is an apparatus involving electrochemical reactions. . The mixed conductive material having both the ionic conductivity and the electronic conductivity is superior to the electric conductivity (10 ⁻⁶ S / cm) of the existing secondary battery electrode material in order to reduce the loss at the electrode and increase the efficiency. It is necessary that the material has good electrical conductivity.
[0005]
An object of the present invention is to provide a conductive glass in which ionic conduction and electronic conduction coexist and the electric conductivity of which is much higher than the electric conductivity of a conventional secondary battery electrode material, and a method for producing the same.
[0006]
[Means for Solving the Problems]
The invention according to claim 1 for solving the above problems, AgI and _Ag 2 O: 65 mol% to 85 _mol%, V 2 _{O 5} and _Fe 2 _O 3: mixture of 15 mol% to 35 mol% It is a conductive glass having conductivity. According to the present invention, it is possible to provide a novel conductive glass in which ionic conduction using Ag ⁺ as a carrier and electron conduction by hopping from V (IV) to V (V) coexist.
[0007]
The second aspect of the present invention is a conductive glass having mixed conductivity of 30 mol% to 50 mol% of LiI and Li ₂ O, and 50 mol% to 70 mol% of V ₂ O ₅ and Fe ₂ O _3. It is. According to the present invention, it is possible to provide a novel conductive glass in which ionic conduction using Li ⁺ as a carrier and electron conduction by hopping from V (IV) to V (V) coexist.
[0008]
The invention according to claim 3 is that, after mixing a composition consisting of AgI and Ag ₂ O: 65 mol% to 85 mol%, V ₂ O ₅ and Fe ₂ O ₃ : 15 mol% to 35 mol%, heating is performed. A method for producing a conductive glass having mixed conductivity, characterized by melting and quenching to obtain glass. According to the present invention, a conductive glass in which ionic conduction and electron conduction coexist and the electric conductivity is much higher than the electric conductivity in the conventional secondary battery electrode material is manufactured by a simple process at low cost. be able to.
[0009]
The invention according to claim 4 is that, after mixing a composition consisting of 30 mol% to 50 mol% of LiI and Li ₂ O, 50 mol% to 70 mol% of V ₂ O ₅ and Fe ₂ O ₃ , and then heating the mixture. A method for producing a conductive glass having mixed conductivity, characterized by melting and quenching to obtain glass. According to the present invention, a conductive glass in which ionic conduction and electron conduction coexist and the electric conductivity is much higher than the electric conductivity in the conventional secondary battery electrode material is manufactured by a simple process at low cost. be able to.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on preferred embodiments.
Looking at glass as a functional material, it has the following features.
{Circle around (1)} It is an isotropic solid and has no grain boundaries as seen in crystals. Therefore, it is a homogeneous substance composed of a single phase. This indicates that glass (amorphous) is a better material than crystal.
{Circle around (2)} Glass has no melting point, and its viscosity changes continuously over 10 orders of magnitude over a wide temperature range. From this, it is possible to obtain a material suitable for the purpose by changing the composition (chemical component ratio) and the temperature of the glass.
{Circle around (3)} Thermodynamically non-equilibrium while retaining the characteristics of the supercooled liquid. Therefore, when heated, the structure changes, and accordingly, the electrical properties, the properties for light, magnetism, and the like change with the heating time. This means that many excellent materials can be developed using glass.
(4) Looking at the structure of glass at the atomic level, the arrangement of atoms has no long-range regularity. For this reason, glass can be considered as an aggregate of ultrafine particles. However, it can be said that the whole glass is an aggregate having continuity of atoms. This can be considered that glass is essentially a solid with a network.
{Circle around (5)} There are many places inside glass that can take in atoms and atomic groups from the outside. This allows atoms added from the outside to become various ions. As a result, it is possible to change (control) the electrical properties of the externally added atoms and the properties of light, magnetism and the like according to the purpose.
[0011]
Utilizing such characteristics of glass, research and development of new glass have been performed, and glass having a new function has been developed. One of them is conductive glass. Usually, glass is an insulator, and its electric conductivity is about 10 ⁻¹³ S / cm. As described above, the conductive glass is mainly an electron conductive type glass in which a metal oxide film such as ITO is formed on the surface of the glass.
[0012]
Glass can be defined as "a supercooled liquid in a solid state." As shown in FIG. 1, the glass is first solidified at a glass transition temperature Tg without being crystallized after being cooled below the freezing point without being crystallized. Things. Thus, although the appearance is a solid, the atomic arrangement is that of a liquid and has an amorphous structure.
[0013]
When the structures of the crystal and the glass are compared, as shown in FIG. 2, the crystal (a) has atoms regularly arranged, whereas the glass (b) has a four-sided structure while retaining the tetrahedral of SiO _4. The body is connected irregularly. The SiO ₄ tetrahedron itself is similar everywhere in the glass, and there is no difference when compared with the SiO ₄ tetrahedron in the crystal. This is called short-range order. However, when the two are observed on a large scale, it can be said that the order is lost in the glass and there is no long-range order. Therefore, while the crystal maintains both short-range order and long-range order, glass maintains short-range order but does not have long-range order.
[0014]
As described above, glass having a structure with more gaps than crystals can capture various ions in the gaps. When Na ₂ O is added to the SiO ₄ glass shown in FIG. 2, the following reaction occurs.
[0015]
Embedded image
_{-Si-O-Si + Na 2} O → Si-O - ... Na + ... O - -Si-
[0016]
FIG. 3 shows the glass structure at this time. When such a reaction occurs, the glass network is broken. Oxygen that is bonded to only one piece of silicon is called non-bridging oxygen. In contrast, oxygen that is bonded to two silicons is called bridging oxygen. The presence of non-bridging oxygen results in significant changes in the structure and properties of the glass. In the absence of non-crosslinked oxygen, the glass has a very high viscosity even at high temperatures, but the presence of non-crosslinked oxygen causes a sharp drop in viscosity at high temperatures. In addition, since the network modifying ion, Na ^+, can move, an improvement in electric conductivity can be expected.
Thus, a glass whose physical properties can be controlled by a component newly added from the outside is advantageous for the development of a new material. The inventor has conducted research to develop a new conductive glass in which ionic conduction and electronic conduction coexist.
[0017]
Ions, which have a size and mass incomparable to electrons, can move well in liquids but are difficult to move in solids. However, high ionic conductivity can be achieved even in a solid, provided that the structural conditions under which ions can move are satisfied. Glass has a disordered and sparse structure, with more voids than crystals. For ions to move, it is advantageous to have more "voids". As shown in FIG. 4, electric conductivity is improved by vitrification. There is a difference of 10 times or more in electric conductivity between glass and crystal of the same component system. Thus, in order to realize high ionic conductivity, it is important to make the glass (amorphous).
[0018]
In the field of solid electrolyte batteries and electrochromism, ionic conduction and electron transfer are necessary because good transfer of electrons and ions is required along with oxidation and reduction reactions at the interface between the active material of the positive and negative electrodes and the electrolyte. It is desirable that the material has mixed conductivity in which conduction coexists. Ion conduction and electronic conduction can be described by the property of intercalation.
[0019]
Intercalation refers to a phenomenon in which an electron donor or an electron acceptor is inserted between layers of a layered substance by a charge transfer force. In general, the layered substance is mainly composed of a covalent bond that mainly forms a bond, but is bonded by a weak force such as van der Waals force between the layers. Therefore, the electron donor or the electron acceptor exchanges electrons with an atomic group forming a layer, penetrates between the layers, and expands the layer to form a kind of charge transfer complex. This compound is called an interlayer compound. Insertion can be of many types, from the first stage, where all layers are filled by the amount of intercalant added to the layered material, to the n-th stage, which is every nth layer. Since glass has a sparse structure, a reaction similar to intercalation is likely to occur.
[0020]
A solid electrolyte battery generally has a structure of negative electrode / electrolyte / positive electrode. In such a solid electrolyte battery, an ionic conductor is used for the electrolyte. The positive electrode of a solid electrolyte battery utilizes mixed conduction in which ionic conduction and electronic conduction due to an intercalation reaction coexist.
In the case of a secondary battery, not only discharging but also charging is performed. During this charge / discharge, an intercalation reaction and a reverse deintercalation reaction occur. When this reaction occurs, it is accompanied by an increase or decrease in volume. The glass structure has many extra gaps as compared with the crystal, and this volume change is small. That is, glass (amorphous) can increase the number of repetitions of charge and discharge more than crystals. In addition, the charge / discharge capacity of the amorphous state is larger. Thus, glass (amorphous) materials are promising as positive electrode materials for secondary batteries.
[0021]
In the case of glass in which ionic conduction and electronic conduction coexist, the contribution ratio of ionic conduction and electronic conduction to electric conduction is important. In the mixed conductive glass, finding the contribution ratio of the ionic conductivity to the total electric conductivity is important for confirming that the glass has ionic conductivity. The inventor has found a method of determining the contribution ratio as described later.
[0022]
【Example】
Example 1
The xAgI _· (75-x) mixture having a composition of _{Ag 2 O · 24V 2 O 5} · 1Fe 2 O 3, x (mol%) of 40, 45, 50, 55, and 60 is changed to be in an agate pot After mixing well, the mixture was heated and melted at 900 ° C. for 15 minutes, and quenched using a copper plate to obtain glass.
[0023]
Example 2
The yLiI _· (38-y) mixture having a composition of _{Li 2 O · 56V 2 O 5} · 6Fe 2 O 3, y a (mol%) 13.5,18.5,23.5, and 28.5 The mixture was changed and mixed well in an agate bowl, heated and melted at 1200 ° C. for 30 minutes, and quenched using ice water to obtain a glass.
[0024]
The reagents used are as follows.
Vanadium pentoxide (V) (99.0%): Iron oxide (III) (99%) manufactured by Wako Pure Chemical Industries, Ltd .: Silver iodide (99.9%) manufactured by Wako Pure Chemical Industries, Ltd .: Rare Metallic Co., Ltd. Silver oxide (99.9%): Lithium iodide (97.0%) manufactured by Fukagawa Riken Co., Ltd .: Aldrich Chemical Company Inc. Lithium carbonate (99.0%) manufactured by Wako Pure Chemical Industries, Ltd. Conductive paste DOTITE (silver paste): manufactured by Fujikura Kasei Co., Ltd.
With respect to the conductive glasses obtained in Example 1 and Example 2, the electric conductivity was measured by various measuring methods.
(1) Measurement by DC Four-Terminal Method In general, the DC four-terminal method is used to measure the electrical conductivity of glass exhibiting semiconductivity, in which electron conductivity is dominant. The glass was cut into a rectangular parallelepiped, silver paste was applied to both ends of the glass, dried for 60 minutes, and electrodes were attached using silver-containing solder. The voltage was measured when the value of the current (I) passed through the glass sample provided with this electrode was changed, and the electrical conductivity was determined from the slope of the IV curve by the following equation.
[0026]
(Equation 1)
ρ (Ωcm) = R · S / l-------------(-)
R: Slope of IV curve S: Cross-sectional area of glass sample (cm ² )
l: distance between electrodes (cm)
1 / ρ: Electric conductivity σ (S / cm)
[0027]
(2) Measurement by AC Two-Terminal Method The AC two-terminal method is generally used for measuring the electrical conductivity of an ionic conductor. FIG. 5 shows a configuration of an AC bridge circuit used for measuring electric conductivity by the AC two-terminal method. In the bridge circuit, the sample was placed in the unknown resistance value _{Z 4,} such that the current _{I D} flowing between cd becomes 0, known resistance _Z 1, _{Z 2,} and changing the _{Z 3.} The relationship among Z ₁ , Z ₂ , Z ₃ , and Z ₄ at this time is as follows.
[0028]
(Equation 2)
Z ₁ Z ₄ = Z ₂ Z ₃ ∴Z ₄ = Z ₂ Z ₃ / Z ₁
[0029]
FIG. 6 shows the change over time in the electrical conductivity of a glass having ion conductivity using Ag ⁺ as a carrier obtained in Example 1 when a direct current is applied for a long time. Immediately after the start of the measurement, both the hopping conduction (electron conduction) of vanadium and the ionic conduction using Ag ⁺ as a carrier are observed, and the electric conductivity shows high electric conductivity, but decreases with time. When a direct current is continuously supplied for 50 minutes, the value of the electric conductivity is stabilized at a low level. This is because in the glass Ag ⁺ has moved polarized near the cathode, Ag ⁺ concentration gradient is caused to move from high to low is Ag ⁺ concentration, and moves Ag ⁺ in the opposite direction to the current It is considered that the ion conduction is hindered as a result. As described above, in a glass in which ionic conduction and electronic conduction coexist, polarization occurs under a direct current.
[0030]
On the other hand, the AC bridge method is a method of performing measurement using an AC current, and does not cause polarization when measuring the electric conductivity of the ionic conductor. The results of measuring the electrical conductivity of glass in which ionic conduction and electronic conduction coexist by the AC bridge method using AgI (mol%) as a parameter are shown by ○ in FIG. The electrical conductivity of glass using Ag ⁺ as a carrier, in which ionic conduction and electron conduction coexist, changes within the range of 2.6 × 10 ⁻² S / cm to 3.5 × 10 ⁻⁴ S / cm. And the electrical conductivity decreased with the increase in AgI concentration. Ag present in the glass has the following structure.
[0031]
Embedded image
^{-O-Ag-O- ... Ag +} Ag + ... O - -Ag-O-
[0032]
Ag ⁺ in the above structural formula is derived from AgI, and Ag bound to oxygen is derived from Ag ₂ O. As described above, when the ratio of AgI to Ag ₂ O is 1: 1, it is considered that the movable Ag ⁺ and the space enabling the movement are optimal, and exhibit high electric conductivity.
[0033]
On the other hand, the value of the electric conductivity after polarization indicated by ■ in FIG. 6 (the value of the electric conductivity when a direct current is passed for 50 minutes or more in FIG. 5) is (6.3 to 6.8). ) × 10 ⁻⁶ S / cm. Since the concentrations of V ₂ O ₅ and Fe ₂ O ₃ that cause electron conduction in the glass are all the same, the contribution of ion conduction becomes almost zero when a direct current is passed for 50 minutes or more, and the hopping conduction of vanadium It is considered that only the contribution of electron conduction due to is observed and becomes constant.
[0034]
FIG. 8 shows a change with time of the electrical conductivity when a direct current is applied to glass using Li ⁺ as a carrier for a long time. As in the case of the glass using Ag ⁺ as a carrier, when a direct current is passed for 130 minutes or more, the contribution of ionic conduction is almost zero, and only the contribution of electron conduction is observed, and the electric conductivity is considered to be constant. Can be
[0035]
The measurement result of the electric conductivity of the glass using Li ⁺ as a carrier using an AC bridge is shown by a circle in FIG. As is clear from FIG. 9, the electric conductivity of the glass in which ionic conduction using Li ⁺ as a carrier and ionic conduction and electronic conduction coexist is in the range of (5.3 to 5.6) × 10 ⁻⁶ S / cm. Is changing within. On the other hand, the electric conductivity after polarization (■ in FIG. 9) is constant in a narrow range of (5.1 to 5.2) × 10 ⁻⁶ S / cm.
[0036]
Thus, the contribution of ionic conduction and electronic conduction to electrical conductivity was determined using the following equation.
[0037]
[Equation 3]
Contribution of electron conduction (%) = (electric conductivity after polarization / electric conductivity in a state where ionic conduction and electron conduction coexist) × 100
Contribution of ion conduction (%) = 100-contribution of electron conduction (%)
[0038]
FIGS. 10 and 11 show the degrees of contribution of the ion conduction and the electron conduction obtained in this manner. As is clear from FIG. 10, 98% or more of ionic conduction contributes to glass using Ag ⁺ as a carrier, and the lower the AgI concentration, the greater the contribution of ionic conduction. On the other hand, as is clear from FIG. 11, the glass having Li ⁺ as a carrier contributes only about several percent of the ion conduction, and as the LiI concentration increases, the contribution of the ion conduction increases.
[0039]
In a glass using Ag ⁺ as a carrier, the ratio of the total concentration of AgI and Ag ₂ O contributing to ion conduction to the total concentration of V ₂ O ₅ and Fe ₂ O ₃ contributing to electron conduction is (65). -85): (15-35). Therefore, it is considered that the number of components forming the glass skeleton decreases, and the probability of electron hopping from V (IV) to V (V) decreases.
[0040]
In the electrical conductivity of the vanadate glass, the probability of electron hopping from V (IV) to V (V) is important. Probability hopping by the symmetry of the VO ₄ tetrahedra and VO ₅ pyramids is a glass skeleton increases increases, increases the electronic conductivity. Further, it is considered that glass produced with a small number of skeleton components has many gaps in the skeleton, as in glass using Ag ⁺ as a carrier. As described above, it is considered that the contribution of the electron conduction is reduced and the contribution of the ionic conduction is increased due to the decrease in the probability of hopping and the structure having many gaps.
On the other hand, in a glass using Li ⁺ as a carrier, the ratio of the total concentration of LiI and Li ₂ O contributing to ion conduction to the total concentration of V ₂ O ₅ and Fe ₂ O ₃ contributing to electron conduction. Is (30 to 50): (50 to 70). In this system, since there are many skeletal components, it is considered that mainly electron conductivity type conductivity is exhibited.
[0041]
As described above, the electric conductivity σ of the glass using Ag ⁺ as a carrier shows the highest value when x = 40, and is 2.6 × 10 ⁻² S / cm. This is an electrical conductivity equivalent to that of a saline solution, and is 10,000 times higher than the electrical conductivity of existing secondary battery electrode materials of 10 ⁻⁶ S / cm.
[0042]
The electrical conductivity of the glass having Li ⁺ as a carrier is (5.3 to 5.6) × 10 ⁻⁶ S / cm. This is 5 to 6 times the electrical conductivity of the existing secondary battery electrode material of 10 ⁻⁶ S / cm.
[0043]
【The invention's effect】
The electrode using the glass having high electric conductivity according to the first and second aspects of the invention is efficient with little loss of the electrode. Thus, the conductive glass of the present invention in which ionic conduction and electron conduction coexist can be suitably used as an electrode material for a secondary battery or an electrode material in a fuel cell.
[0044]
According to the third and fourth aspects of the invention, it is possible to provide a conductive glass in which ionic conduction and electronic conduction coexist at low cost.
[Brief description of the drawings]
[1] crystal and glass (amorphous) graph Figure 2 which shows the relationship between the temperature and the molar volume of the crystalline and glass schematic diagram Figure 3 Na 2 _{O-SiO 2} system glass showing a structural comparison of (amorphous) schematic structure Figure 4 is a circuit diagram showing a graph Figure 5 of the AC bridge configuration AgI-Ag ₂ MO ₄ glass and (amorphous) shown by comparing the electrical conductivity of the crystallized product [6] the Ag ⁺ FIG. 7 is a graph showing a change over time in electric conductivity when a direct current is applied to glass as a carrier. FIG. 7 shows a graph of electric conductivity of Ag ⁺ as a carrier, using AgI (mol%) as a parameter by an AC bridge method. electrical when measurement results and graph showing the electric conductivity mainly by electron conduction after polarization [8] the Li ⁺ was a direct current flows in the glass to the carrier The glasses according to the graph 9 of Li ⁺ carrier showing the time course of Shirubedo, electrical conductivity by LiI (mol%) the electric conductivity mainly electron conductivity after measurement results and polarization as a parameter by the AC bridge method FIG. 10 is a graph showing the ionic conduction contribution of glass using Ag ⁺ as a carrier. FIG. 11 is a graph showing the ionic conduction contribution of glass using Li ⁺ as a carrier.

Claims (4)

AgI and _Ag 2 O: 65 mol% to 85 _mol%, V 2 _{O 5} and _Fe 2 _O 3: 15 mol% to 35 mol% mixed conducting glass having a conductive consisting. A conductive glass having a mixed conductivity of 30 mol% to 50 mol% of LiI and Li ₂ O, and 50 mol% to 70 mol% of V ₂ O ₅ and Fe ₂ O ₃ . AgI and Ag ₂ O: 65 mol% to 85 mol%, V ₂ O ₅ and Fe ₂ O ₃ : 15 mol% to 35 mol% are mixed and then heated, melted, quenched, and mixed with glass. A method for producing a conductive glass having mixed conductivity. After mixing a composition consisting of 30 mol% to 50 mol% of LiI and Li ₂ O, and 50 mol% to 70 mol% of V ₂ O ₅ and Fe ₂ O ₃ , the mixture is heated and melted, quenched, and cooled. A method for producing a conductive glass having mixed conductivity.

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