JPH0221104B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen gas concentration battery using a zirconia solid electrolyte.

Oxygen gas concentration cells using zirconia as a solid electrolyte are widely used as fuel cells or oxygen concentration meters for industrial measurement control and automobile exhaust gas control.

Conventionally, various attempts have been made to increase the circuit voltage by connecting these oxygen gas concentration batteries in series. For example, a negative electrode (fuel electrode) is attached to the inner surface of a tapered cylindrical zirconia electrolyte and a positive electrode (air electrode) is attached to the outer surface to form a unit cell, and these are connected in series in a comb shape, or porous A plurality of single cells are partially deposited on a supporting ceramic substrate by chemical vapor deposition (CVD), plasma spraying, etc.
There are methods such as forming a negative electrode, a zirconia electrolyte, and a positive electrode in that order, and connecting these cells with an interconnector, but all of these methods have the drawbacks of complicated processes, difficulty in ensuring reliability, and high costs. Ta. In order to improve this point, we created a raw zirconia sheet containing thermoplastic resin as a binder, and screen-printed it on both sides.
Form leads for series connection with the negative and positive electrodes, heat and press them to create a hollow part,
After that, it may be sintered at high temperature to obtain an oxygen gas concentration battery, but cells with different potentials are lined up on the same zirconia thin plate, and the distance between each cell is close to prevent leakage between each cell. In addition, there was a drawback that the connection lead could not be crossed between both sides of the zirconia thin plate.

In particular, when used in an automobile exhaust gas sensor, it is desirable to install the sensor by placing one end of the sensor into the exhaust gas through the insertion hole, and the opening on the air electrode side should face the outside, and the output signal lead should be taken out from this part. Due to their nature, it is impossible to avoid the proximity or crossover of the lead-out lead and the series-connected lead of each unit cell, resulting in a problem in that the output voltage decreases due to leakage.

In order to improve the above-mentioned conventional drawbacks, this invention forms a layer that has the same crystal structure and component elements as the base zirconia electrolyte, but has a different composition ratio, at the location where leakage prevention is required. The aim is to make it possible to manufacture oxygen gas concentration batteries with low output power loss without compromising chemical or mechanical stability.

Further, FIG. 1 is a flowchart explaining the process of manufacturing a cylindrical oxygen gas concentration battery using a raw sheet of zirconia solid electrolyte. Generally, zirconia (ZrO ₂ ) solid electrolyte is used as a cubic crystal stabilizer to prevent embrittlement due to crystal transformation from tetragonal to monoclinic, and at the same time as a semiconducting agent to generate oxygen ion vacancies. , CaO,
It is manufactured by mixing 4 to 16 mol % of a rare earth element oxide such as Y _{2 O 3 or} Gd ₂ O 3 or Yb ₂ O ₃ with ZrO ₂ and calcining the mixture to form a solid solution. Y ₂ O ₃
To explain the case of stabilization, the amount of Y ₂ O ₃ dissolved in solid solution differs depending on whether emphasis is placed on mechanical performance or electrical performance. When emphasis is placed on mechanical performance, use a partially stabilized product containing 6 to 8 mol% solid solution with some monoclinic crystals remaining, and when emphasis is placed on electrical performance, a partially stabilized product with a maximum electrical conductivity of 10 is used. A solid solution in the vicinity of mol% is used. The conductivity at 800℃ is 1×10 ^-2 Ω ^-1 /cm, 10 mol% in a 6 mol% solid solution.
In solid solution, it is 1.5×10 ^-2 Ω ^-1 /cm.

Using the zirconia electrolyte stabilized in this way, it can be pulverized and slurried according to the process shown in Figure 1, and a green sheet can be created using a doctor blade method using a thermoplastic resin as an organic binder. The electrode portion and current collection lead portion are easily formed by screen printing. A raw sheet made of the same material is inserted as a spacer for forming a hollow cylinder between two raw sheets printed in this way, and after being heat-pressed and integrally formed, the inner and outer surfaces of the hollow cylinder are sintered. An oxygen gas concentration battery consisting of a group of single cells having electrodes is obtained. However, when connecting a desired number of individual cells in series or parallel, each lead may be close to each other on the same plane, or the leads with a large potential difference after connection may cross across the base electrolyte. Many cases arise where this is necessary. In such a case, it is necessary to lift the lead part from the base electrolyte surface or to insert an insulating layer between it and the base electrolyte. Alumina and the like are usually used as high-temperature insulating ceramics, but it is desirable to complete as much of the wiring as possible before firing, as in the green sheet method.
When oxides of different elements are used, they react with the substrate during firing, and the difference in their diffusion rates tends to cause minute cracks, resulting in a lack of reliability.

This invention focuses on the phenomenon that conductivity decreases when a stabilizer such as Y ₂ O ₃ is dissolved in zirconia as a material for forming a high resistance layer in an amount greater than the amount that exhibits the maximum conductivity. It was made by
It is completely identical in composition to the base zirconia electrolyte,
By using materials that differ only in composition ratio, the high-resistance layer (hereinafter referred to as the insulating layer) and the base zirconia electrolyte can be completely integrated during sintering without forming crystallographically different layers, creating an airtight structure. It is an object of the present invention to provide an oxygen gas concentration battery that can provide an insulating layer with high electrical insulation properties that can sufficiently withstand use even when formed on a heat-compression bonded part that requires high properties.

The invention is illustrated by a simplified model experimental example. FIG. 2 shows the configuration of the test piece used to verify the electrical insulation effect and the integrity of the bond. First, green sheets 1 and 1a containing zirconia powder stabilized with 10 mol % of Y ₂ O ₃ , polyvinyl butyral as an organic binder, and polyethylene glycol and octyl phthalate as plasticizers were prepared. Next, as a paint for forming an insulating layer, zirconia (ZrO ₂ ) powder to which Y ₂ O ₃ of 18 mol % or more and 60 mol % or less was added was mixed with diacetone alcohol in which the same organic substance components as those of the raw sheet were dissolved, and Cellsolve, It was dispersed in a mixture of ethylene chloride, Cellsolve acetate, and xylene. Applying the above paint to both sides of the raw sheet 1 by screen printing,
This is dried at 80°C to form electrically insulating layers 2 and 2a.
was formed. Next, current collecting platinum leads 3, 3a are formed on this by screen printing with platinum paint, and then the raw sheet 1a is overlapped so that a part of the thin platinum wire 4 is embedded between the platinum lead 3a and the raw sheet 1a. Then, using a press machine with a heating plate,
Heat and pressure bonding was carried out at 150℃. This sample was heated to 300℃~500℃
After sufficient debinding treatment at a temperature of
Sintering was performed at 160°C for 5 hours to obtain a substrate as shown in Figure 3. After baking a platinum wire with platinum paint as a lead wire on the platinum lead 3, it is inserted into an electric furnace at 800°C and a DC voltage of 1V is applied between both leads, causing a current to flow between the platinum leads 3 and 3a. The current was measured. Each dimension of the sample is sheet thickness 0.4mm,
The insulating layer print width is 5 mm, length is 30 mm, and thickness is 10 μm, and the platinum lead width is 4 mm, length is 30 mm, and thickness is 15 μm. Figure 4 shows the results of current measurement. As is clear from FIG. 4, by forming a zirconia layer containing a large amount of Y ₂ O ₃ between the platinum lead and the base zirconia electrolyte, the leakage current can be significantly reduced. These samples were then cooled from 800°C to 300°C at a rate of 200°C per minute, then heated to 800°C at the same rate for 20 cycles of rapid heating and cooling, and then subjected to scanning electron microscopy. The cross sections of four locations on each sample were observed using
In the case of 60 mol%, no abnormality was observed except for the observation of microcracks.

In the above examples, the case where Y ₂ O ₃ was used as a stabilizer was described, but CaO or Yb ₂ O ₃ ,
Rare earth element oxide stabilizers such as Gd ₂ O ₃ may also be used. The reason for limiting the lower limit to 18 mol% or more is
The reason why the upper limit was set to 50 mol% or less as a value that can be clearly expected to be effective when applied industrially is that it is within the range where reliability by thermal shock can be ensured.

As explained above, according to the present invention, it is possible to form a stable leak prevention layer between the current collecting leads without impairing airtightness or thermal shock characteristics, and the oxygen gas concentration battery is made of a zirconia solid electrolyte with low output power loss. This has the effect of making it possible to provide the following.

[Brief explanation of drawings]

Figure 1 is a manufacturing flowchart of an oxygen gas concentration battery using a zirconia solid electrolyte green sheet.
The figure is a perspective view of a test piece before crimping showing one embodiment of the present invention, FIG. 3 is a perspective view of the test piece after sintering, and FIG. It is a Y ₂ O ₃ content relationship diagram. 1, 1a... Zirconia raw sheet, 2, 2a...
...Screen printed zirconia high resistance layer, 3,3a
...Platinum current collector lead, 4...Externally extracted platinum thin wire. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In an oxygen gas concentration battery made of a zirconia solid electrolyte, a high-resistance layer between the base electrolyte and the lead contains 18 mol% or more of a rare earth element oxide such as CaO _{or Y2O3} . An oxygen gas concentration battery characterized by forming a stabilized zirconia layer containing mol% or less. 2. The oxygen gas concentration battery according to claim 1, wherein the high resistance layer is formed by screen printing.