JPH0218803A - Formation of thin film of na+ ion conductive solid electrolyte - Google Patents

Abstract

PURPOSE:To make it possible to provide Na<+> ion electrolytic thin film excellent in its homogeneity by preparing a mixed solution including compounds of groups A, B, C, D, E and F of specified composition, forming a thin film of this mixed solution on a heat resistant base, drying same, and baking it under oxide atmosphere. CONSTITUTION:A mixed solution including A, B, C, D, E and F compounds each having components shown in the below is prepared. The compounds thereof are used as the main ingradients of NASICON. Next, on a heat resistant base, a thin film of the compounds are formed and dried, then baked under oxide atmosphere. It is restrained that each compound is precipitated as hydroxide or oxide in the form of microparticles due to hydrolysis action at every step to the baking process. The F compound acts as a solvent. Further one kind is selected from the groups A-D.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention provides a method for forming a compound of the general formula Na1+ on a heat-resistant substrate, which is suitable for use in sodium-q1 yellow batteries, sodium sensors, etc.
x Z r2 P3-x S i x012 (0≦X
The present invention relates to a method for forming a thin conductive solid electrolyte membrane having Na+ ion conductivity represented by ≦3).

(Prior art) General formula N al, Z r 2 P3-x S ! X
The three-dimensional Na + ion conductive solid electrolyte expressed by 012 (0≦X≦3) was created from the study of the skeletal structure formed by condensed oxygen acid ions, and is generally used for NAS
I CON (Ha-super 1onic co
It is called a conductor. β-alumina, which is well known as a Na ion conductive solid electrolyte, is
It is two-dimensional and has anisotropy not only in its conductivity but also in its thermal expansion coefficient and mechanical properties, and if the orientation of the microcrystals is biased, the conductive path becomes localized and local deterioration due to current flow occurs. NAS I
Although C0N has a conductivity comparable to that of β-alumina, it has three-dimensional conductive paths, so it does not suffer from the above-mentioned local deterioration phenomenon, and has the advantage of being excellent in moisture resistance. Therefore, it is attracting attention as a device that lowers impedance and enables compactness and low-temperature operation, particularly in sodium-sulfur batteries, sodium sensors, and the like.

Now, conventionally known methods for forming such a thin film of NASICON include CVD method (chemical vapor deposition method), sputtering method, PVD method (physical vapor deposition method), and plasma melting method. However, since NASI CON has a large number of constituent elements, and Na2O and P2O5 are volatile during the formation process, all of the above methods have the problem that it is extremely difficult to control the composition and form a single phase. In particular, it is difficult to form a thin film of 10 μm or less.

In an attempt to solve such problems, Japanese Unexamined Patent Application Publication No. 56-99
In the No. 979 invention, N is produced by solid phase reaction of raw material powder.
A mixture of ASI CON powder and Na2CO3 powder is used as a target, and the film is thinned by sputtering while preventing Na2O from volatilizing. However, the thin film produced by this method has problems with compositional homogeneity and has very low ionic conductivity. Also, due to electrical insulation issues,
It is difficult to form a thin film with a thickness of about 5 μm or less.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the above-mentioned problems of the conventional method and form a highly homogeneous Na ion conductive solid electrolyte thin film on a substrate with a simple operation. We are here to provide you with a method.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a step of preparing a mixed solution containing the following compounds of group A, group 8, group 0, group 0, group E, and group E. and Group A: Na, methoxide, ethoxide, propoxide, butoxide, methoxyethoxide or ethoxyethoxide B8: Zr, methoxide, ethoxide, propoxide, butoxide, methoxyethoxide or ethoxyethoxide 0 Group: P, methoxide, ethoxide, propoxide,
Butoxide, methoxyethoxide or ethoxyethoxide Group 0: Sj, methoxide, ethoxide, propoxide, butoxide, methoxyethoxide or ethoxyethoxide Group E: Monoethanolamine, jetanolamine, triethanolamine, mono-2-propanol Amine, di2-propanolamine, acetylacetone, ■ Dilene glycol, diethylene glycol, propylene glycol, dipropylene glycol Group E: methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol A thin film of the above mixed solution is applied on a heat-resistant substrate. Provided is a method for forming a Na ion-conducting solid electrolyte thin film, the method comprising: forming the thin film, drying the thin film, and firing the dried thin film in an oxidizing atmosphere. That is, according to the method of the present invention, the general formula "a1+X Zr2 P3-X S 1x012(0
≦X≦3) A thin film of Na ion conductive solid electrolyte is obtained.

Now, NAS I CON, that is, N a 1+x Z
r2P3-xSi8012 (O≦X≦3) is Na
Zr2(PO4)3 and Na42r2 (S io+
>3 fractional solid solution, V becomes ['l-(X/3)]
NaZr2(PO4)3 ・(x/3)Na4Zrz
(SiO4)3. Here, Naz
r2 (PO4)3 (rhombohedral crystal system with Although the crystal structure is convenient for conduction of Na ions, the conductivity is not very high.This is because two types of Na ion sites exist in the crystal lattice. Of these, only one is selectively released; the other is presumed to be viable because most of the Na ions are fixed there;
When SiO+>3 is dissolved in solid solution, the other site becomes Na
It becomes partially filled with ions and exhibits high ionic conductivity. The conductivity is X is 2
The solid solution near Na4Zr2PO4・(S
i 04 )2 (monoclinic system) has the largest value, 30
At 0'C, the degree is 3 x 10-1 Ω-1 Clll-1. When X becomes larger than 2, the conductivity decreases.

Hereinafter, this invention will be roughly explained in detail for each step.

Preparation process of mixed solution: In this invention, first, the following A, B, C1D, E,
“Prepare a mixed solution containing each group of compounds.

Group A: Na, methoxide, oxide, propoxide, butoxide, methoxyethoxide or ethoxyethoxide Group S: Zr, methoxide, ethoxide, propoxide, butoxide, methoxyethoxide or ethoxyethoxide C? ! T: P, methoxide, ethoxide, propoxide, butoxide, methoxyethoxide, or ethoxyethoxide Group D: Si, methoxide, ethoxide, propoxide, butoxide, methoxyethoxide, or ethoxyethoxide Details: Monoethanolamine, Tanolamine, triethanolamine, mono-2-propanolamine, di-2-propanolamine, acetylacetone, ethylene glycol, diethyl glycol, propylene glycol, dipropylene glycol (g: methanol, ethanol, propanol, butanol, methoxyethanol, ethoxy Ethanol Propoxide in each of the above groups A, B, C, and D is 1-
It may be either propoxide or 2-propoxide. Moreover, butoxide may be any of 1-butoxide, 2-butoxide, isobutoxide, and t-butoxide. Furthermore, the propanol of Group E may be either 1-propanol or 2-propanol. Furthermore, butanol may be any of 1-butanol, 2-butanol, isobutanol, and t-butanol.

The compounds of the above groups A, B, C, and D are the main components of NΔ5ICON.

In addition, the compounds of Group E suppress the precipitation of compounds of Groups A, B, C, and D as fine particulate hydroxides and oxides due to hydrolysis in each step up to firing. be.

Furthermore, the compounds of Group F act as solvents.

One type is selected and used from each group A, B, C, and D.

Although it is possible to select and use two or more types, there is almost no significant difference in the properties of the resulting thin film, and the disadvantages are far greater, such as increased costs due to complication of the process.

In addition, no matter which compound is selected from each group A, B, C, and D, there is almost no significant difference in the properties of the thin film produced by 1q. That is, there is almost no significant difference in the properties of the resulting thin film due to differences in alkoxy groups or alkoxyalkoxy groups.

Although the mixing ratio of the compounds of each group A, B, C, D, E, and F differs slightly depending on their type, the compound of group A is a mole, the compound of group 8 is b mole, and the compound of group 0 is C When the compound of group D is d mole, the compound of group 1 is e mole, and the compound of group F is f liter, the formula is a:b:c:d=(1+x):2:x:3-xO ≦X≦
3 0.1≦[e/(a+c+d)]≦0.01≦[
It is preferable that the range simultaneously satisfies (a+b+c+d)/f]≦3. That is, in the range of a:b:C:d=(1+X):2:X:3-X3<x, the Na+ ion conductivity of the resulting N film may decrease or it may not become a single phase. Also, if [e/ (a + b + c + d)] < 0.1, then A, B
, C, and D groups may not be sufficiently suppressed. Zarani, [e/ (a + c + d)]
>3, the viscosity of the mixed solution may become too high to form a film. Furthermore, if [(a+b+c+d)/f] <Q, 01, the amount of solvent is too large to be practical. Also, [(a+b+c0d)/
f]>3, compounds of groups A, B, C, and D may remain dissolved.

The mixing operation may be performed by simultaneously adding and mixing the compounds of each group A, B, C, and D to a mixed solution of the compound of group 1 and the compound of group F, or the compound of group 1 and the compound of group F. A, B, C, or D group compound may be added to a mixed solution of the compound, and a mixed solution may be prepared separately, and a predetermined amount may be taken from each solution and mixed. Note that until the mixing operation is completed,
It is preferable to avoid exposing the compounds of groups B, C, and D to moisture as much as possible, and it is preferable to carry out the operation in a glove box filled with dry nitrogen, etc. However, further operations should not be performed in the atmosphere. It can be carried out.

The resulting mixed solution is a clear or almost clear liquid;
Depending on the type and amount of impurities contained in the compounds of each group A, B, C, and D, the colors appear orange or yellow.

Step of forming a thin film of the mixed solution: In the present invention, next, a thin film of the mixed solution is formed on the heat-resistant substrate. In other words, a film is formed.

The substrate may be of any type as long as it can withstand the firing temperature described below.
Metals such as gold, silver, platinum, alloys containing at least one of these metals as a main component, carbon, alumina, magnesia,
Inorganic materials such as zirconia, strontium titanate, titania, boron nitride, silicon nitride, boron carbide, silicon carbide, etc. can be used. The shape may be fibrous, film, plate, bulk, or the like.

It is preferable that the surfaces of these substrates be polished to make them smooth or washed to remove dirt caused by oil or the like.

The thin film can be formed by coating with a brush, roller, etc., by spraying, or by a dip coating method in which the substrate is immersed in a mixed solution and then pulled up. Among these, the dip coating method is preferred because it is relatively simple and allows the film thickness to be changed by changing the pulling speed.

Drying step: In this invention, next, the thin film formed on the substrate is dried, and the compounds of group F, that is, the solvent, are evaporated to form A, B,
A gelled thin film consisting of compounds of groups C, D, and E is prepared. This step may be performed at room temperature or at a constant temperature of about 50 to 100°C.

Firing step: In the present invention, the dried thin film is then fired together with the substrate in an oxidizing atmosphere to decompose and evaporate the organic components and oxidize the compounds of groups A, B, C, and D. Then, a thin film of NASI CON is obtained. This firing is performed, for example, as follows.

That is, the thin film is placed together with the substrate in a heating furnace, heated to a firing temperature in an oxidizing atmosphere, maintained at that temperature for a certain period of time, and then cooled to room temperature. The firing atmosphere is air or 1 to 1.
00% concentration of oxygen.

The heating rate is 1 to b 10'C/min. If it is less than 1°C/min, it takes too long to raise the temperature and is not practical. If the temperature exceeds 500° C./min, cracks may occur in the thin film. The firing temperature is 35
The temperature is 0 to 900°C, preferably 600 to 800°C. 3
At temperatures below 50°C, organic components within the thin film may remain.
If the temperature exceeds 900'C, part of the thin film may evaporate or the thin film may react with the substrate. The firing time may range from several tens of minutes to several hours. The cooling rate was also changed from 1 to 1b (Example) for the same reason as in the case of temperature increase.
0.015 mol of hexide, 0.0 mol of Zr methoxide
Take 09()11l, 1″ of eth4-cyto of 1 mol of Si (1,(0)!i Tle),
Monoethanolamine was added thereto to give a concentration of 0.04 mol, 200 ml of ethanol was added to the colander, and the mixture was stirred for 30 minutes using a Stark shaker to obtain a transparent mixed solution.

On the other hand, a platinum plate having a thickness of Q and 5 mm was ultrasonically cleaned using trichloroethylene, acetone, ethanol, and pure water for 3 minutes each, and then dried by blowing dry nitrogen at a high temperature.

Next, the platinum plate was immersed in the mixed solution, and after 1 minute, was pulled up vertically at a speed of 10 cm/min to form a thin film of the mixed solution on the platinum plate.

Next, the thin film was dried in a constant temperature bath at 50'C for 30 minutes.

Next, the dried thin film was placed in an electric furnace together with the platinum plate at 6°C.
The temperature was raised to 700'C at a rate of 6°C/min, held at that temperature for 1 hour, and then cooled to room temperature at a rate of 6°C/min.

The thin film thus obtained had a film thickness of 2Q nm. In addition, when analyzed using X-ray diffraction method, A↑゛1 crystal σ
) times 11il-Noah recognized Fl /;-,,n;I-
)17,? l? :#; Analysis by X-ray method revealed that the composition was Na5Zr2S I 2 P 1012. Further, when it was roughly observed under a microscope with a magnification of 600 times, no precipitation of fine particles or cracks were observed, and it was found to be extremely homogeneous. In addition, the Na ion conductivity of the thin film at 300°C is
It was 2°0×10”Ω−1, Cm−1.

Example 2 In a glove box flowing with dry nitrogen, 0.015 mol of Na propoxide and 0.0 mol of Zr butoxide were added.
1 mole, 0.01 mole of methoxyethoxide, P
Measure out 0.005 mol of ethoxyethoxide, add dienolamine to it to make it 0.04 mol, add 200 ml of methanol, stir for 30 minutes using a Stark shaker, and make a clear mixed solution). It's q. Thereafter, in the same manner as in Example 1, a thin film was obtained on a platinum plate.

The obtained thin film had a thickness of 20 nm. Moreover, the diffraction peak obtained by X-ray diffraction was indicative of monoclinic crystal.

The composition is N a3 Z I” 2 S! 2 Pl 0
There were 12 te. Furthermore, similar to that obtained in Example 1, no precipitation of fine particles or cracks was observed, and the product was extremely homogeneous and solid. Further, the Na + ion conductivity of the thin film at 300°C was 2.0×10 −1 Ω−’ −cm−’r.

Example 3 In a glove box flowing with dry nitrogen, 0.0125 mol of Na ethoxyethoxide, 0.01 mol of 7-r ethoxide, and 0.0 mol of 3i methoxyethoxide
Weigh out 0.0075 mol of P propoxide, add trienolamine to 0.0375 mol, and further add 200 ml of methanol.
Stir for 30 minutes using a Stark shaker to make a clear mixed solution)
Ta.

Thereafter, in the same manner as in Example 1, a thin film was obtained on a platinum plate.

The 1q thin film had a film thickness of 20 nm. Also, X
The diffraction peak obtained by line diffraction was indicative of rhombohedral crystals. The composition is Na2.5 Z r 2 S I tsP
It was 1,5012. Furthermore, like the one obtained in Example 1, no precipitation of fine particles or cracks was observed, and the material was extremely homogeneous. Further, the Na + ion conductivity of the thin film at 300° C. was 3.8×10 −20 −1 cm′.

Example 4 In a glove box flowing with dry nitrogen, 0.0175 mol of Na propoxide and 0.0 mol of Zr butoxide were added.
Weigh out 0.0125 mole of methoxy ethoxide of 01 mole, 0.0125 mole of 3i ethoxide, and 0.0025 mole of ethoxide of P, add mono-2-propanolamine to this so that it becomes 0.0425 mole, and further add 200 ml of butanol.
Stir for 30 minutes using a Stark shaker to obtain a clear mixed solution.

Thereafter, in the same manner as in Example 1, a thin film was obtained on a platinum plate.

The obtained thin film had a film thickness of 2Q nm. Moreover, the diffraction peak obtained by X-ray diffraction was indicative of rhombohedral crystals. The composition is Na3.52'2S'2.5P0.
It was 5012. Furthermore, like the one obtained in Example 1, no precipitation of fine particles or cracks was observed, and the material was extremely homogeneous. In addition, the Na
The ionic conductivity was 5.5×10 −20 −1 cm′.

(Effects of the Invention) The method of the present invention provides A, B, C,
D A thin film is formed on the heat-resistant substrate from the mixed solution all at once while suppressing the hydrolysis of each group of compounds, dried, and fired in an oxidizing atmosphere.As shown in the examples, the operation is simple. And, NASICON with excellent homogeneity, that is,
General formula Na1+XZ r2 P3-x Si x01
2 (0≦X≦3), it becomes possible to easily obtain a thin film of a three-dimensional Na 2 ion conductive solid electrolyte.

Claims (1)

[Scope of Claims] (a) A step of preparing a mixed solution containing the following compounds of group A, group B, group C, group D, group E, and group F, and group A: Na
Methoxide, ethoxide, propoxide, butoxide, methoxyethoxide or ethoxyethoxide Group B: Zr methoxide, ethoxide, propoxide, butoxide, methoxyethoxide or ethoxyethoxide Group C: P methoxide, ethoxide, propoxide,
Butoxide, methoxyethoxide or ethoxyethoxide Group D: Si, methoxide, ethoxide, propoxide, butoxide, methoxyethoxide or ethoxyethoxide Group E: Monoethanolamine, diethanolamine, triethanolamine, mono-2-propanolamine, Di2-propanolamine, acetylacetone, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol Group F: methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol (b) Form a thin film of the above mixed solution on a heat-resistant substrate (c) drying the thin film; and (d) firing the dried thin film in an oxidizing atmosphere. Formation method.