JPH0963603A - Multilayer solid electrolyte for solid fuel cell - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To use a material having a composition excellent in mechanical strength and cost as a main constituent material of an electrolyte, and to form a thin layer having high ionic conductivity only on a surface in contact with an electrode. The purpose is to improve the power generation loss in the solid electrolyte with almost no decrease in the mechanical strength and increase in the material cost. In a zirconia-based solid electrolyte to which a rare earth is added, an ionic conductive layer having a high ionic conductivity and a support layer having a low ionic conductivity are provided, and the high ionic conductive layer has a layer thickness of 0.03 to 50 microns. The high ion conductive layer is provided on the surface layer of either or both of the fuel electrode side and the air electrode side of the electrolyte. [Effect] It has an excellent effect that it is possible to obtain a lithium secondary battery having a high energy density, a large charge / discharge capacity, ensuring safety, and a long cycle life.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an ionic conductor and a solid electrolyte for a solid fuel cell.

[0002]

2. Description of the Related Art In recent years, solid electrolyte fuel cells using oxygen ion conductors have been gaining interest. In particular, from the viewpoint of effective use of energy, solid fuel cells have inherently high energy conversion efficiency because they are not restricted by Carnot efficiency, and they also have excellent characteristics such as good environmental protection. There is.

The electrolyte of a solid oxide fuel cell is required to keep DC resistance loss low when ions flow inside,
High ionic conductivity is required. In addition to this, for the thermal stress caused by the temperature change accompanying the operation and shutdown of the fuel cell,
It is necessary to maintain sufficient strength. In addition to this, it is necessary to use inexpensive materials as raw materials in order to suppress manufacturing costs.

The most promising oxygen ion conductors in the past are Y ₂ O ₃ -stabilized ZrO ₂ (YSZ) and Sc ₂ O ₃ −.
There are Al ₂ O ₃ stabilized ZrO ₂ (SAISZ) and the like. These are solid electrolytes based on zirconia, which are added with a rare earth element or the like to exhibit ion conductivity. These materials are considered to be the most promising because they have an oxygen ion transport number of 100% (no electronic conductivity) and can be dense even when fired at a relatively low temperature.

The most studied among these is Y
₂ O ₃ stabilized ZrO ₂ (YSZ). In this system, when the composition is near 0.92ZrO ₂ -0.08Y ₂ O ₃ ,
It is known that the composition has the highest electric conductivity.
On the other hand, the composition with the highest mechanical strength is 0.97ZrO ₂
Is a -0.03Y ₂ O _3, the conductivity is relatively poor. When Sc ₂ O ₃ is used instead of Y ₂ O ₃ , (1-x
_{-Y) ZrO 2 -xSc 2 O 3} -yAl 2 O 3 (0.070
<X + y <0.160 and 0.000 <x <0.02
0), which has the highest ionic conductivity among zirconia-based materials. However, the materials (Sc
_{Since 2} O ₃ ) is very expensive, it is difficult to keep the manufacturing cost low when used in a large amount. As described above, it is difficult to satisfy all the requirements with one material even in the zirconia-based solid electrolyte.

[0006]

An object of the present invention is to use a material having a composition excellent in mechanical strength and cost as a main constituent material of an electrolyte, and to provide a thin layer having a high ionic conductivity only on the surface in contact with an electrode to improve mechanical properties. The purpose is to improve the power generation loss in the solid electrolyte with almost no decrease in strength and increase in material cost.

[0007]

In order to solve the above problems, a multilayer solid electrolyte for a solid fuel cell according to the present invention is a zirconia-based solid electrolyte containing a rare earth element and an ion conductive layer having a high ion conductivity and an ion. The high ionic conductive layer has a layer thickness of 0.03 μm to 50 μm, and the high ionic conductive layer has either a fuel electrode side or an air electrode side of the electrolyte, or both. It is characterized in that it is provided on the surface layer.

According to the present invention, as shown in FIG. 1, in the surface which is in contact with the oxygen electrode 1 and the fuel electrode 2, a high ion conductivity of 0.
92ZrO ₂ -0.08Y ₂ O ₃ or (1-xy) Z
_{rO 2 -xSc 2 O 3 -yAl 2} O 3 (0.070 <x + y
<0.160 and 0.000 <x <0.020) and other high ionic conductive layers 3 are provided. Other parts have relatively low ionic conductivity, but are excellent in mechanical strength and cost. A support layer 4 having another composition is used.

Here, the thickness of the high ion conductive layer 3 is equal to or smaller than the particle diameter of the electrodes 1 and 2 in contact with it, but at least 0.03 micron or more is required to obtain a good film quality. Need. The particle size of the electrode material varies depending on the manufacturing process, but since the average particle size is usually between 0.2 and 50 μm, the thickness of the high ion conductive layer must be 0.02 μm or more. Depending on the particle size, it will be about 0.02 to 50 microns. However, in order to obtain good film quality, the lower limit of the film thickness of the high ion conductive layer 3 is 0.03 micron. The support layer 4 has a thickness of about 1 to 200 μm. Both the support layer and the high ion conductive layer have a layer thickness of 2
If it is about 0 to 200 μm, it can be manufactured by a tape casting method, a doctor blade method, a dipping method, or an EVD method. If it is 10 microns or less, it can be manufactured by a dipping method, an EVD method, an RF sputtering method, or the like.

[0010]

As shown in FIG. 2, an electrochemical reaction (in the case of an air electrode, O ₂ → 2O, 2O + 4e ⁻
→ 2O ^2- ) is carried out at the three-phase interface in which the reaction gas, the electrode supplying the current, and the electrolyte carrying the ions are in contact at the same time. In FIG. 2, 5 is a fine particle of the electrode.

Here, the electrode material in contact with the electrolyte needs to be porous so as to sufficiently guide the reaction gas to the interface between the electrode and the electrolyte. For this reason, the electrode material must be made of a material having a relatively large grain size. When the oxygen electrode 1 and the fuel electrode 2 are provided directly on both sides of the solid electrolyte 6 as shown in FIG. 7, the ions thus produced are converted into an ionic current inside the electrolyte 4 as shown in FIG. It flows. In this case, since the ionic current flows from the three-phase interface as a source, it tends to concentrate in this vicinity. The larger the particle size of the electrode material, the more remarkable the current concentration becomes, and the current concentration remains deep inside the electrolyte. And
This concentration of current means a substantial reduction in the cross-sectional area of the conductor, which causes a large voltage drop in this portion, which is a major cause of power generation loss in the electrolyte.

For the above reasons, the ionic conductivity near the interface has a great influence on the cell characteristics. In particular, when the thickness of the entire electrolyte is thin, the voltage drop near the interface becomes the main part of the voltage drop in the electrolyte.

If a multilayer solid electrolyte (high ionic conduction layer + support layer) is used in which the vicinity of the interface where the ionic current is concentrated is replaced with the material 3 having high ionic conductivity, the voltage drop in this portion is improved. It At the same time, the concentration of current in the high ion conductive layer 3 is easily alleviated (current distribution is likely to be uniform), and the concentration of current in the support layer 4 is reduced. This is schematically shown in FIG. Therefore, the voltage drop in the electrolyte can be reduced only by providing a very thin high ion conductive layer on the surface. In addition, an ionic conductor having low conductivity but excellent in mechanical strength and material cost is used for the other major portion of the total thickness of the electrolyte. As a result, the power generation loss in the solid electrolyte can be improved with almost no reduction in mechanical strength and increase in material cost.

[0014]

Embodiments of the present invention will be described below. Note that, needless to say, the present invention is not limited to the following embodiments.

[0015]

EXAMPLE 1 FIGS. 5 and 6 are views showing a constitutional example of a single cell solid fuel cell using the material of the present invention. 5 is a plan view and FIG. 6 is a sectional view. In the battery structure of this embodiment, 1 is an oxygen electrode, 2 is a fuel electrode, 3 is a high ion conductive layer, 4 is a support layer, 7 is a platinum mesh for collecting current, 8 is a platinum paste reference electrode, and 9 is alumina. It is a tube (a solid electrolyte is composed of the high ion conductive layer 3 + the support layer 4). La _0.8 Sr _0.2 MnO ₃ was used as the oxygen electrode and N was used as the fuel electrode.
i- the (0.92ZrO ₂ -0.08Y ₂ O ₃₎ was used.
The platinum mesh for current collection was 16 mmφ. The effective area of the cell is equal to the area of the electrode and is about 2 cm ² . The method for producing a single cell is as follows.

First, the composition is 0.97ZrO ₂ -0.03.
Fine powder of Y ₂ O ₃ was synthesized by a usual solid phase reaction, and a ceramic thin film was formed by the doctor blade method.
Bake at ℃. This plate, which has been baked to about 100 microns, is the portion of the solid electrolyte that corresponds to the support layer 4. Furthermore, the composition is 0.8 on both sides of this plate by the dipping method.
_{8ZrO 2 -0.115Sc 2 O 3 -0.005Al 2} O 3
Layers were laminated and sintered at 1100 ° C., and 5.
A 0 micron high ionic conduction layer was provided. And about 200
Micron-thick fuel electrode Ni-YSZ and air electrode La
_0.8 Sr _0.2 MnO ₃ was baked on each side of the above solid electrolyte plate at 1100 ° C.

The effect of this embodiment is shown in the measurement example of FIG. This is 80 for "cell # 1" created as above
It is a current (current density) -voltage characteristic of a single cell measured at 0 ° C. "Cell # with conventional structure electrolyte for comparison"
0 "was also measured under the same conditions. This is also shown in FIG.
Here, H ₂ , O ₂ and gas are used for the fuel electrode and the oxygen electrode, respectively. As is clear from the figure, this example provided better battery characteristics, that is, current-voltage characteristics, than the conventional example.
Similarly, when the material of the present invention was used for the single-sided multi-layer solid electrolyte, the battery characteristics were all better than those of the conventional example, as in "cell # 2" and "cell # 3". These are shown in Table 1.

Table 1 Output current in a single cell when the composition of the electrolyte and the electrode is a multi-layer of / oxygen electrode / "layer # 1" / "layer # 2" / "layer # 3" / fuel electrode /. The single cell has an oxygen electrode (L
a _0.8 Sr _0.2 MnO ₃ ) / electrolyte / fuel electrode (Ni-Y
SZ). * Current value when the cell output voltage is 0.2V (measured at 800 ° C).

[0019]

Example 2 A cell having the same structure as that of Example 1 except that the thickness of the high ion conductive layer was changed was prepared, and its current-voltage characteristics were measured. As shown in Table 2, only the layer thickness of the high ion conductive layer was changed to 0.5 micron. In all cases, better characteristics were obtained as compared with the conventional "cell # 0" (see Table 1).

Table 2 Dependence of output current on high ionic conduction layer thickness in single cell In the constitution of "cell # 1" as the solid electrolyte, only the high ionic conduction layer thickness was changed. * Current value when cell output voltage is 0.2V (800 ℃
In).

[0021]

Example 3 A cell having the same structure as in Example 1 except that the thickness of the support layer was changed was prepared, and the current-voltage characteristics thereof were measured.
As shown in Table 3, only the layer thickness of the support layer was changed from 50 microns to 150 microns. In all cases, better characteristics were obtained as compared with the conventional "cell # 0" (see Table 1).

Table 3 Dependence of output current in single cell on support layer thickness In the constitution of "cell # 1" as the solid electrolyte, only the support layer thickness was changed. Current value when cell output voltage is 0.2 V (measured at 800 ° C.).

[0023]

Example 4 A cell having the same structure as that of Example 1 except that only the composition of the high ion conductive layer was changed was prepared, and its current-voltage characteristics were measured. Table 4 shows the results. In all cases, better characteristics were obtained as compared with the conventional "cell # 0" (see Table 1).

Table 4 Dependence of the output current in a single cell on the composition of the high ionic conduction layer Only the composition of the high ionic conduction layer was changed in the constitution of "cell # 1" as the solid electrolyte. Current value when cell output voltage is 0.2 V (measured at 800 ° C.).

[0025]

Example 5 A cell having the same structure as that of Example 1 except that only the composition of the supporting layer was changed was prepared, and its current-voltage characteristics were measured. Table 5 shows the results. In all cases, better characteristics were obtained as compared with the conventional "cell # 0" (see Table 1).

Table 5 Dependence of output current in single cell on support layer composition Only the support layer composition was changed in the configuration of "cell # 1" as a solid electrolyte. Current value when cell output voltage is 0.2 V (measured at 800 ° C.).

Table 6 Dependence of output current in single cell on supporting layer composition Only the supporting layer composition was changed in the constitution of "cell # 0" as the solid electrolyte. (Conventional cell without high ionic conduction layer) Current value when cell output voltage is 0.2 V (measured at 800 ° C.).

[0028]

As described above, a material having a composition excellent in mechanical strength and cost is used as a main constituent material of the electrolyte, and a thin layer having high ionic conductivity is provided only on the surface in contact with the electrode. As a result, the power generation loss in the solid electrolyte can be improved with almost no decrease in mechanical strength and increase in material cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an electrolyte of the present invention.

FIG. 2 is a schematic diagram of an electrochemical reaction process performed at a three-phase interface.

FIG. 3 is a schematic diagram of an ion current distribution in an electrolyte when a high ion conductive layer is added.

FIG. 4 is a schematic diagram of the configuration of a single cell.

FIG. 5 is a schematic diagram of the configuration of a single cell.

FIG. 6 is a current-voltage characteristic diagram of “cell # 0” and “cell # 1”.

FIG. 7 is a configuration diagram of a conventional electrolyte.

FIG. 8 is a schematic diagram of an ion current distribution in a conventional electrolyte.

[Explanation of symbols]

 1 Oxygen Electrode 2 Fuel Electrode 3 High Ion Conductive Layer 4 Support Layer 5 Electrode Fine Particles 6 Conventional Solid Electrolyte 7 Platinum Mesh for Current Collection 8 Reference Electrode 9 Alumina Tube

Claims (6)

[Claims] 1. A zirconia-based solid electrolyte to which a rare earth is added, which comprises an ion conductive layer having a high ionic conductivity and a supporting layer having a low ionic conductivity, and the layer thickness of the high ionic conductive layer is 0.03 to 50 μm. 2. A multi-layer solid electrolyte for a solid fuel cell, characterized in that the high ionic conductive layer is provided on the surface layer of either or both of the fuel electrode side and the air electrode side of the electrolyte. 2. The high ionic conduction layer according to claim 1, wherein (1-x-
_{y) ZrO 2 -xSc 2 O 3} -yAl 2 O 3 (0.070 <
x + y <0.160 and 0.005 <y <0.020)
An ionic conductor having a composition of
_{x) ZrO 2 -xY 2 O 3} (0.025 <x <0.04
0) is used, The solid fuel cell characterized by the above-mentioned. 3. The high ionic conduction layer according to claim 1, wherein (1-x-
In _{y) ZrO 2 -xSc 2 O 3} -yD 2 O 3 (D = Yb or Lu, and 0.070 <x + y <0.220 and 0.
An ionic conductor having a composition of 015 <y <0.060) is used, and (1-x) ZrO ₂ —xY ₂ O is used for the supporting layer.
₃ (0.025 <x <0.040) is used, The multilayer solid electrolyte for solid fuel cells characterized by the above-mentioned. 4. The high ion conductive layer according to claim 1, wherein (1-x-
_{y) ZrO 2 -xSc 2 O 3} (0.070 <x + y <0.
An ion conductor having a composition of 160 and 0.005 <y <0.020) is used, and (1-x) ZrO ₂ is used for the supporting layer.
_{-XY 2 O 3 (0.070 <x} <0.110) solid fuel cell multilayer solid electrolyte, which comprises using a. 5. The high ion conductive layer according to claim 1, wherein (1-x-
In _{y) ZrO 2 -xSc 2 O 3} -yD 2 O 3 (D = Yb or Lu, and 0.070 <x + y <0.220 and 0.
An ionic conductor having a composition of 015 <y <0.060) is used, and (1-x) ZrO ₂ —xY ₂ O is used for the supporting layer.
₃ (0.070 <x <0.110) is used, The multilayer solid electrolyte for solid fuel cells characterized by the above-mentioned. 6. The high ion conductive layer according to claim 1, wherein (1-x) Z is added.
A conductor having a composition of rO ₂ −xY ₂ O ₃ (0.070 <x <0.110) is used, and (1-x) ZrO is used for the support layer.
_A multi-layer solid electrolyte for a solid fuel cell, characterized by using _2- xY ₂ O ₃ (0.025 <x <0.040).