WO1999030328A1 - Thin solid electrolyte films and gas sensors made by using the same - Google Patents

Abstract

Thin solid electrolyte films having excellent moisture resistance and high denseness and made of vitreous oxide compositions represented by the general formula: (Li2O)x-(SiO2)y-Mz (wherein M is a member selected from among Al2O3, ZrO2, TiO2, ZnO and CaO; and x, y and z are molar ratios satisfying the relationship: x + y + z = 1). The films can conduct lithium ions, and the integration of the films into gas sensors as the electrolyte makes it possible to produce gas sensors which are excellent in moisture resistance, have high sensitivity, high accuracy and quick responsiveness and are reduced in the sizes.

Description

 One

Akira Ptu Solid electrolyte thin film and gas sensor using it

[Technical field ]

 The present invention relates to a solid electrolyte thin film having excellent moisture resistance and high density, and a gas sensor using the same. More specifically, the present invention relates to a lithium ion having high moisture resistance and high density. The present invention relates to a solid electrolyte thin film composed of a conductive glassy oxide and a gas sensor using the solid electrolyte thin film with high humidity resistance, high sensitivity, high accuracy, and high speed response.

[Background Art]

Solid electrolytes are used in all-solid-state electrochemical devices such as gas sensors, solid-state batteries, and electronic mixers, and their use as decomposed materials is being promoted. Among these areas, especially _{C 0 2, N 0 x,} S 〇 _x, can the measurement of NH ₃ of which the gas concentration with high accuracy and high sensitivity, high moisture resistance Contact and high-speed response was or There is an urgent need to realize a compact gas sensor that has high conductivity.Solid electrolytes that have been used in the past have been used to conduct Alkalion ions, including Alkaryons such as Li + and Na +. This type is called a solid electrolyte.

Actually, a Namu _{1 + X} Zr S 丄 P3-Xu 1 2 (0 ≤ X ≤ 3),? — Α 1 ₂ 0 ₃ L 16-2 y Z n (G e 0 ₄ ) ₄ (0 ≤ y <8), L i ₄ G _{e 0 4 -.. L i} 3 V 0 4, L i A l S i 0 4, L i 3 5 S i 0 5 P 0.5 0 4, L i T i 2 (P 0 4) 3 of which Li Chiu Mion conductors have been used.

 Here, the internal resistance of the all-solid-state electrochemical device increases in proportion to the thickness of the solid electrolyte. Most of the alkali ion conductors used so far are crystalline ceramics sintered compacts, which are usually used as solid electrolytes in bulk form. . Therefore, when the solid electrolyte is used in a bulk form, the internal resistance is more than 100 to 1000 times larger than when the solid electrolyte is used. Therefore, when a bulk solid electrolyte is used, the solid electrolyte that can be used was originally limited to a solid electrolyte having a high ion conductivity.

 On the other hand, when a solid electrolyte having a high ion conductivity is used, the alkali ion, which is a movable ion, generally reacts easily with moisture in the air, and the solid electrolyte tends to change its composition. As a result, all-solid-state electrochemical devices tend to deteriorate.

 Attempts have been made to reduce the thickness of the crystalline ceramics sintered body, but when the crystalline body is reduced in thickness, the oxide composition in the thin film may shift. However, the fact that it is lacking in detail is becoming clear.

On the other hand, in conventional alkali ion conductors, through holes may be formed during sintering of ceramics, which is a crystalline powder, and the denseness of the film is not sufficient. Could not say. For example, if there are vacancies, a gas concentration difference occurs between the electrodes of the gas sensor, and the electromotive force becomes unstable, and gas remains in the vacancies, increasing the hysteresis. From such a point, it is necessary to restart when detecting gas. one

Three

Reality also tended to decline.

Various improvements have been proposed in response to the problems faced by such crystalline ceramics sintered bodies. International Publication W 095/3/345 515 discloses that a lithium ion having high ion conductivity consisting of (Li ₂₀ )-(Si 0 ₂ ) An on-conducting glass is disclosed, and it is described that a dense thin film can be obtained by a method such as sputtering. However, the use of the solid electrolyte thin film in a gas sensor requires even higher moisture resistance.

Further, according to Japanese Patent Application Laid-Open No. 8-23992 / 18, the oxide composition was further changed (L i ₂₀ )-(S i 0 ₂ ) -M (M is N b ₂ 0 _3, T a ₂ 03 s or the W 0 ₃₎ or al compositions of Na Ru ternary is that is capable thinned. However, since this composition may also generate electron conduction at the same time, if it is used for a gas sensor, a decrease in sensitivity is expected.

 According to Japanese Patent Application Laid-Open No. 6-265550, a carbon dioxide gas sensor using a sintered body crystal having Li, Al, Si, and 0 as main components as a solid electrolyte is described. It has been done. According to the publication, it is stated that the moisture resistance is improved. However, as described above, the improvement of the moisture resistance by using a crystalline ceramics sintered body is naturally considered. There is a limit.

 Accordingly, there is a demand for a solid electrolyte having a higher moisture resistance and a higher density than before.

[Disclosure of the Invention]

Therefore, the object of the present invention is to have excellent moisture resistance and high denseness. An object of the present invention is to provide a lithium ion conductive glassy solid electrolyte thin film.

 A second object of the present invention is to provide a solid electrolyte type gas sensor having high moisture resistance, high sensitivity, high accuracy, and high speed response using the lithium ion conductive glass thin film solid electrolyte. It is to be provided.

That is, the present invention is represented by the general formula (L i ₂ 0) X - I (S i 0 ₂₎ y- glass quality oxide compositions der represented by M z, in here, M is, A 1 ₂ 0 _3, Z r O had T i O have Z n O, C a 0 or et Ri oxide der of one or more kinds also least for a selected Ri by ing group, x, y, z represent mole ratios And a solid electrolyte thin film wherein x + y + z = 1. By employing such an oxide composition and forming a glassy thin film, it is possible to obtain a lithium ion conductive solid electrolyte having excellent moisture resistance and high denseness. Wear .

 The values of x, y, and z above are 0.1 ≤ χ ≤ 0.5, 0.1 ≤ y ≤ 0.8, and 0.01 ≤ z ≤ 0.5, respectively. When the oxide thin film is used, the moisture resistance is further increased and the denseness is also increased. It is more desirable that the thin film be formed by a sputtering method and have a thickness in the range of 0.1 to 10 μm as a solid electrolyte.

 The present invention also relates to a gas sensor using the solid electrolyte membrane, and more particularly to a carbon dioxide gas sensor. [Brief description of drawings]

FIG. 1 is a cross-sectional structural view of a gas sensor showing one embodiment of the present invention. [Best mode for carrying out the invention]

 Next, the present invention will be described specifically. Solid electrolyte thin film

The solid electrolyte membrane according to the present invention is an oxide composition represented by a general formula (L i ₂₀ ) X i (S i 0 _z ) y — M z. In here, M is, Ri Oh in A 1 ₂ 0 have Z r 〇 have T i O have Z n O, C a 0 or we Ri by ing group least for the oxide of one or more kinds are also selected, the molar X, y, and z expressed as ratios have the relationship x + y + z = 1.

Is the _{M A 1 2 0 3, Z} r O have been or are T i 0 ₂ is rather the desired Ri by the point of view these on the moisture propensity, that have been especially Yu A 1 ₂ 0 ₃ Among . A 1 ₂ 0 ₃ is structure of oxygen 4 coordinating glass quality thin film, Chi Sunawa [A 1 0 _4] - the Ru with the idea we are ing. This This, together if by crosslinking the non-crosslinked oxygen in the glass REDUCE diffusion of water molecules, [A 1 0 _4] - is water to strengthen Lee on-coupling force between the L i + It is thought to suppress the reaction of. Why do we are the Yo I Do guess, A 1 ₂ 0 _3, the effect of improving the moisture resistance without compromising Lee on-conductivity rather high, preferably der as the third oxide component You. This point is an effect peculiar to the glass body, and is conspicuous in the present invention.

 In the general formula, the values of X, y, and z are preferably 0.1 ≤ χ ≤ 0.5, 0.1 ≤ y ≤ 0.8, and 0.0 1 ≤ z ≤, respectively. 0.5. More preferably, 0.15 ≤ X ≤ 0.40, 0.2 ≤ y ≤ 0.75, and 0.02 ≤ z ≤ 0.45.

If x, y and z are each within the above range, (L The composition consisting of i ₂ 0) x— (S i 0 ₂ ) y—Mz avoids the formation of phase separation, raises the glass transition temperature (T g), and increases the ion conductivity. This facilitates the formation of a glass thin film without lowering the performance. Therefore, it is preferable because the denseness of the thin film is increased and the moisture resistance is also improved. Particularly, stable moisture resistance can be obtained even at high temperatures, so if it is used for a gas sensor that operates at high temperatures, stable sensor characteristics can be obtained.

In involved that glass quality oxide composition of the present invention, in addition to the oxides of, S n 0 ₂ to the _{al, C r 2 03 T a 2} 0 have N b ₂ 0 had M n O have L a ₂ 0 have P b O, M g O, this one least for the well of the B a O or et ing group, which Ru coexist in the ra purpose is not such impaired scope of the present invention I can do it.

 Note that the oxide composition can be measured by an inductively coupled plasma (ICP) emission spectrometry. In addition, the fact that the film is glassy is determined by analyzing the X-ray diffraction method as showing that no beak appears in the diffraction intensity curve and that the film becomes a blade. It can also be judged by observing the cross section of the thin film with a scanning electron microscope (SEM) and by not finding any crystal grain boundaries. When the glass thin film according to the present invention is observed by SEM, it can be understood that, unlike a ceramic sintered body, the thin film is dense because there is no crystal grain boundary. You.

The thickness of the lithium ion conductive glassy thin film is preferably from 0.1 to: L0 / m, more preferably from 0.2 to 5 m. When the thickness of the thin film is within this range, it is preferable because the internal resistance is small when used for a sensor, and thus high sensitivity can be obtained. A method for producing a solid electrolyte thin film from such a glassy oxide composition is to first sufficiently mix the oxide composition, form a sintered body, and then use the sintered body. It is recommended to use a film forming method such as the snorting method, the ion plating method, the ion beam evaporation method, the CVD method, the vacuum evaporation method, and the sol-gel method. I can do it.

Above all, when a thin film is formed by the sputtering method, the oxide composition does not shift and the formed thin film is rapidly cooled. Since a glassy and dense thin film can be obtained, the sputtering ring method is the most preferable thin film forming method. Spa jitter is not particularly limited Li in g conditions, for example, A r / 0 ₂ (volume ratio) of 1:.. 1, scan Roh Tsu evening Li in g pressure 0 133~ 1 33 (P a) The input power can be set in the range of 1.5 to 5.5 (W / cm ² ).

 The thin film obtained by the sputtering method is dense and, unlike the film of a conventional ceramics sintered body, can suppress gas permeation. Therefore, the fluctuation of the sensor output can be minimized. Gas sensor

 The gas sensor according to the present invention uses a solid electrolyte thin film formed from the above-mentioned glassy oxide composition, and includes a carbon dioxide gas sensor, a sulfur oxide gas sensor, and a nitrogen oxide gas sensor. It can be used for gas sensors such as ammonia gas sensor.

The preferred structure of the gas sensor is the laminate structure described below. That is, one side of the oxygen ion conductive substrate A detection electrode layer composed of the solid electrolyte thin film, the detection substance layer, and the first metal electrode layer is stacked in this order on the surface of the substrate, and is opposite to the oxygen-ion conductive substrate. The second metal electrode layer and the first metal layer are similarly laminated on the surface in this order, and the laminated body has a structure integrated as a whole. In this laminated structure, the sensing electrode layer composed of the sensing substance layer and the first metal electrode layer may be stacked in the reverse order, that is, in the order of the first metal electrode layer and the sensing substance layer. . In this gas sensor, the sensing electrode layer side is arranged so as to be in contact with the measurement atmosphere, and the heater side is so arranged as to be in contact with a reference atmosphere such as the atmosphere.

 As the oxygen-ion conductive substrate, for example, it is possible to use a stabilized zirconium or the like, and a solid electrolyte thin film is formed on one surface thereof.

 When this gas sensor is used as a carbon dioxide gas sensor, the sensing substance layer is formed by a metal carbonate that dissociates with carbon dioxide gas. The metal carbonate may be at least one of lithium carbonate, sodium carbonate, potassium carbonate, barium carbonate, strontium carbonate, and calcium carbonate. The use of lithium carbonate is particularly preferred. This layer is formed into a thin film, and its thickness is generally in the range of 0.01 to 3 mm.

Also, the when using this Gasuse capacitors foremost detection of NO and N 0 ₂ of which nitrogen oxide gas, sensing material layer, nitrate Li Ji © beam (L i N 0 _3), nitrite Li Ji U beam (L i N 0 ₂ ) or the like. Et al is sometimes to use for the detection of sulfur oxide gases such as sulfur dioxide, rather I be formed with sulfuric Li Ji U beam (L i S 0 ₄₎ or the like, when used for detection of ammonia gas is one

9

It may be formed of lithium amide (LiNH ₂ ) or the like.

 The first electrode is a gas detection electrode for measuring an electromotive force depending on the gas concentration, and the second electrode functions as a reference electrode. Each electrode is usually formed by a method such as sputtering using a noble metal such as platinum, gold, or silver. In addition, a conductive adhesive such as gold paste is used for the second electrode, and the aluminum adhesive substrate and the oxygen ion conductive substrate are adhered by the conductive adhesive. You may combine them.

 In the light exposure, a Pt film serving as a heating source may be formed on the alumina substrate. In that case, the material of the heater prevents heat diffusion under high temperature, so the range of choice of the heater material is expanded. The second electrode surface is bonded to the surface of the aluminum substrate opposite to the surface on which the Pt film is formed, so that the second electrode and the heater do not come into direct contact with each other. Example

 Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

 (Example 1)

_{L i 2 0, S i 0} 2, to create and A 1 ₂ 0 ₃ and are mixed predetermined amounts sintered body. Then, using it as a target, an oxygen-reactive high-frequency sputtering method was used to form a 1-m-thick layer on a quartz substrate.

_{(L i 2 0) 0.43 (} S i 〇 _{2) 0.54 - (A 1 2} 0 3) to form a 0.03 Li Chiu Mui on-conducting glass electrolyte film or et ing composition.

Next, on the surface of the lithium ion conductive glassy thin film, —

Ten

A pair of gold electrodes was formed from a certain distance by the sputtering ring method. Thereafter, the temperature is changed in a tube furnace, and the frequency between the pair of gold electrodes is changed between 10 Hz and 5 MHz by an impedance analyzer, whereby the complex impedance is changed. Analysis was performed. Then, the conductivity of the lithium ion conductive glass thin film was determined from the total resistance component.

 After leaving this sample under a constant temperature and constant humidity of 60 ° C. and 92% RH, the conductivity was measured in the same manner as described above. Table 1 shows the electrical conductivity at 450 ° C before and after standing.

 (Example 28)

 A lithium ion conductive glassy thin film was prepared in the same manner as in Example 1 except that the composition of the thin film was changed, and the conductivity was evaluated in the same manner as in Example 1 using the thin film. Table 1 shows the results.

 The composition (molar ratio) of the thin film was as follows.

Example 2;

V i- * 1 2 ^ / 0.48- (S i 0 2) 0.46 one (A 1 ₂ 0 ₃₎ 0.06 Example 3;

(L ί ₂₀ ) 0.3!-(S i 0)) 0.65-1 (A 0 ₃ ) 0.04 Example 4;

1 · 2 0.28-(S i 0)) 0.70-1 (A 1 ₂ 〇 ₃ ) 0.02 Example 5;

, Ij 1 20) 0.40 - ( S i 0 2) 0.30 - (A 1 2 0 3) 0. 30 Example 6;

V 1 _{2 〇) 0.23 (S i 0 2)} 0.72 - (A 1 2 0 3) 0.05 Example 7; (L ί 20) 0.30-(S ί 02) 0.47— (A 1203). ₂₃ Example 8;

^{(L ί 20) o .44 -} (1 02) 0.33- (A 1 2 03) 0.23

(Comparative Example 13)

 A lithium ion conductive glassy thin film was prepared in the same manner as in Example 1 except that the composition of the thin film was changed, and the conductivity was evaluated in the same manner as in Example 1 using the thin film. Table 1 shows the results.

 The composition of the thin film was as follows.

Comparative Example 1;

_{(L i 2 0) 0.48 -} . (S i 0 2) 0 52

Comparative Example 2

(L i ₂₀ ) 0.39-(S i 0 ₂ ) 0.61

Comparative Example 3

1 ₂ 0 0.53 1 V-> 1 0 ₂ ) 0.40 ~~ 20 3) 0.07 From the results in Table 1, in Examples 1 to 8, the ion conductivity changes little even after standing. I haven't. On the other hand, in Comparative Example 13, it was found that the initial ion conductivity was higher than that of any of the examples, but the ion conductivity sharply decreased to the same level as that of the examples after standing.

Table 1 Solid electrolyte composition (mol _^0/0) b on-conductivity (xl ^O-3 S / cm)

 After anonymous leaving (leaving time)

Li ₂ 0 S i 0 ₂ A1 ₂ 0 ₃ 50 hours 100 hours 400 hours 1000 hours Example 1 43 54 3 17 8.4.4, 2 Example 2 48 46 6 9.3 8.0 6.5 Example 3 31 65 4 5.2 5.0 3.9 Example 4 28 70 2 2.6 2.5 2.4 Wei Example 5 40 30 30 3.9 3.3.3 3.1 Example 6 23 72 5 1. 5 1. 5 1.5 Example 7 30 47 23 3. 6 3. 63, 6 Example 8 44 33 23 6.4 6.0 5.0 Comparative example 1 48 52 190 3.4 Comparative example 2 39 61 69 6.5 Comparative Example 3 53 40 7 69 4.1

(Example 9)

 The gas sensor element 10 shown in FIG. 1 was manufactured by the method described below with reference to the drawings.

 First, as the oxygen ion conductive substrate 5, an yttria (3 mol%) stabilized zirconium substrate (YSZ substrate: 3 mm × 3 mm × 0.3 mm) was used.

A solid electrolyte thin film 4 was formed on the surface. This _{film, L i 2 0, S i} 0 2, and A 1 ₂ 0 ₃ and the using a predetermined amount mixed sintered body te r g e t preparative oxygen reactive RF Spa jitter Li in g method With a thickness of about 1.5 〃m

, J_i l ₂ Li Roh 0.43- (u 1 02) 0.54- (eight丄2 O 3) 0.03 was Tsu der Li Ji U Mui on- conductive glass thin film composition or et ing.

Et al on the solid electrolyte thin film layer 4 is, by applying a Li Ji U Muaruko key shea de solution, Ri by the heat decomposing this carbonate Li Ji um (L i C 0 ₃₎ or al of that thickness of about A metal carbonate layer 3 of 2 zm was formed. A first electrode 2 made of gold was formed thereon by a snow ring method.

 On the other hand, an aluminum substrate 8 made of platinum was formed on the surface of the aluminum substrate 7 (3 mm × 3 mm × 0.3 mt) by a sputtering ring method. The back surface of the alumina substrate 7 on which the heater 8 is formed and the back surface of the oxygen-ion conductive substrate 5 on which the first electrode 2, the metal carbonate layer 3, and the solid electrolyte thin film 4 are formed are connected to the second electrode 6. A gas sensor element 10 was fabricated by bonding together with a gold paste.

Next, a DC voltage was applied to the gas sensor element 10 from the heater power supply 9 to reach 450 ° C., and the gas sensor element 10 was connected from the ends of the first electrode 2 and the second electrode 6 respectively. The lead wire was extracted, and the sensor sensitivity was examined by the following method. In other words, the sensor sensitivity measurement uses a voltmeter in which air with the carbon dioxide concentration changed from 200 ppm to 1% flows over sensor 10 and is connected to a lead wire. This was done by measuring the change in electromotive force in step 1.

 In addition, in order to examine the effect of humidity on sensor sensitivity, sensor element 10 was left in an environment of 60 ° C and 92% RH for a certain period of time. The change in sensitivity was examined. Table 2 shows the measurement results.

 (Examples 10 to 13)

 A carbon dioxide sensor was prepared in the same manner as in Example 9 except that the composition of the solid electrolyte thin film 4 was changed, and then sensor sensitivity was measured. The results are shown in Table 2.

 The composition of the thin film used was as follows.

Example 10;

(L i ₂ 0) 0.48 one VS ΐ 02) 0.46 - (A 1 2 0 3) 0.06 Example 11;

_{(L i 2 0) 0. 1} - (S i 0 2) 0.65 - (A 1 2 0 3) 0.04 Example 12;

_{(L i 2 0) 0.28 (} S i 0 2) 0.70 - (A 1, 0 3) 0.02 Example 13;

_{(L i 2 0) 0.40 -} (S i 0 2) 0.30 (A 1 2 0 3) 0.30 to cormorants by kana result or Akira Luo et shown in Table 2, carbonate were shown in Examples 9 to 1 3 Gasuse The sensor showed little decrease in sensitivity even when left under high temperature and high humidity, indicating that it had high moisture resistance. 2 Table

-

16

 [Industrial applicability]

Oxide composition that involved in the present invention, the _{L i 2 0, S i 0} 2 in a composition of the third oxide was added a predetermined amount to such a glass substance, to the this was or thinned Therefore, the obtained solid electrolyte thin film has excellent moisture resistance and high denseness, and is suitable for all gas sensors, solid-state batteries, electoric aperture chromic elements, etc. It can be used for solid-state electrochemical devices.

 In addition, the gas sensor using this solid electrolyte thin film as a lithium ion conductive electrolyte is more glassy than a crystalline ceramics sintered body, so it is denser. High sensitivity and excellent sensitivity and accuracy.

 In addition, the vitreous thin film has excellent moisture resistance, and the gas sensor provided with the thin film can be used under high temperature and high humidity conditions without taking any particular measures to block moisture. It has a stable output with little change over time, and has a high-speed response. In addition, miniaturization is possible, thereby reducing power consumption and excellent mass productivity.

 Furthermore, since this gas sensor uses a solid electrolyte compared to conventional semiconductor gas sensors, the selectivity of the detection gas is high, and carbon dioxide, nitrogen oxide, sulfur dioxide, ammonia gas, etc. It can be suitably used as a gas sensor for such applications.

Claims

The scope of the claims  1. General formula (L i ₂ 0) X — (S i 0 ₂ ) y-M z A vitreous oxide composition represented in, in here, M _{is, A 1 2 0 3, Z} r 0 2, T i 0 2, Z n O, chosen Ri by C a O or Ranaru group A solid electrolyte thin film characterized in that X, y, and z are each represented by a molar ratio, and x + y + z = 1.  2. The values of x, y, and z satisfy 0.l ≤ x ≤ 0.5, 0.1 ≤ y ≤ 0.8, and 0.01 ≤ z ≤ 0.5, respectively. The solid electrolyte thin film according to claim 1, wherein: 3. Said M is a solid electrolyte thin film according to claim 1 preceding claims, characterized in that it is a A 1 ₂ 0 _3. 4. The solid electrolyte thin film according to any one of claims 1 to 3, wherein the thickness of the solid electrolyte thin film is 0.1 to: L0 m.  5. The solid electrolyte thin film according to any one of claims 1 to 4, wherein the solid electrolyte thin film is formed by a sputtering method.  6. A gas sensor comprising the solid electrolyte thin film according to any one of claims 1 to 5. 7. On one surface of the oxygen ion conductive substrate, a detection electrode layer comprising the solid electrolyte thin film layer according to any one of claims 1 to 5, a detection substance layer, and a first metal electrode layer is provided. And a second metal electrode layer and a heat conductive layer are stacked in this order on the surface on the opposite side of the oxygen ion conductive substrate. A gas sensor characterized in that it is an integrated laminate. 8. The gas sensor according to claim 7, wherein the detection substance layer is a metal carbonate layer.