RU2739055C1 - Method of producing paste for thin-film solid electrolyte of electrochemical devices - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to production of paste for production of gas-tight layers of solid electrolytic materials having high ionic conductivity in oxygen, for microtubular solid oxide fuel elements (MT SOFE) of anode-bearing structure. Method of producing the paste involves mixing in an ultrasonic bath and grinding with ceramic balls to viscosity of 0.2 Poise in a bead mill mode of mixing a powder of cerium oxide doped with gadolinium Ce_0.9Gd_0.1O_1.95 (CGO), butylglycol, BYK-111 and polyvinyl butyral in ratio of 40/55/1/2 respectively. Method allows varying viscosity of paste depending on method of coating application and on required thickness of coating by changing ratio of solvent and solid phase of used oxide.

EFFECT: technical result is simpler technology and lower power consumption of making paste with possibility of controlling viscosity of end product.

5 cl, 4 dwg, 14 ex, 2 tbl

Description

The invention relates to the field of production of a paste for producing gas-tight layers of solid electrolytic materials with high ionic oxygen conductivity. First of all, such pastes are interesting for creating microtubular solid oxide fuel cells (MT SOFCs) for anode-supporting structure. Even for planar SOFCs, the manufacture of a gas-tight layer of an anionic conductor is a complex technical problem. The process of creating a gas-tight electrolytic layer in MT SOFCs becomes even more complicated, since difficulties arise with the compaction of electrolyte particles. Accordingly, particles that do not have close contact with each other are poorly sintered and do not form a gas-tight layer.

A known method of obtaining a stabilized aqueous sol of nanocrystalline cerium dioxide doped with gadolinium, (1. Patent RF No. 2503620 publ. 10.01.2014) Such a sol can be used to obtain thin coatings, films with high ionic conductivity. However, it is not possible to control the viscosity of such a sol over a wide range without agglomerating it; therefore, the methods for applying it and creating a layer of the required thickness are very limited. In addition, even with very mild heat treatment and drying conditions, such coatings undergo cracking.

Also known is a method of obtaining a solid thin-film electrolyte for electrochemical devices by the method of ion-plasma spraying (2. Patent RF No. 1840832, publ. 27.07.2012). The essence of this method lies in the fact that a sprayed material of oxides is fed into the plasma jet at high temperatures in an inert gas atmosphere, which melts, and in the form of a two- or three-phase flow is deposited on a substrate in the form of an oxide film, which is further subjected to high-temperature firing. The main disadvantage of this method is its complexity, since it requires the use of complex equipment, high temperatures and an inert gas atmosphere. Moreover, this method is extremely energy consuming and expensive.

Closest to the claimed method is a known method of producing a solid thin-film electrolyte for electrochemical devices (3. RF Pat. No. 2570509, publ. 10.12.2015) In this method, as oxide-forming salts, readily decomposable upon heating and soluble in water, in ethyl alcohol or in aqueous alcohol solutions, oxide-forming salts, for example, nitrates of rare earth and alkaline elements, oxynitrates or oxychlorides of zirconium or hafnium. Polyvinyl alcohol is used as an organic film-former in a mixture containing an aqueous solution of oxide-forming salts, and polyvinyl butyral is used in a mixture containing an alcohol solution of oxy-forming salts. The main disadvantage of this method is the complexity of obtaining gas-tight coatings. To obtain an electrolyte coating with zero gas permeability, the authors had to repeat the coating and heat treatment procedure 5 times. In this case, the number of such cycles can increase with the transition to other electrolytes.

The problem solved by the claimed technical solution is to develop a method that allows you to create a stable, easily applied paste based on cerium oxide, doped with gadolinium, to create uniform, durable, gas-tight coatings of solid electrolytes with high ionic conductivity on any surfaces, including tubes small diameter.

The problem is solved due to the fact that in the inventive method for producing a paste for a thin-film solid electrolyte for electrochemical devices, including mixing an oxide powder and an organic solvent, powdered cerium oxide doped with gadolinium Ce _0.9 Gd _0.1 O _{1 is} used as the oxide powder _{, 95} (CGO10), the powder is dispersed together with a solvent, with a dispersant and a plasticizer at a component ratio (mass fraction) of 40/55/1/2, respectively, in an ultrasonic bath, and then subjected to grinding with ceramic balls in a bead mill mode, adding a polymer binder during grinding to obtain a paste with a viscosity of 0.2 Poise.

Preferably as:

- butyl glycol (BG) is used as a solvent;

Disperbyk-111 (BYK-111) is used as a dispersant;

- dibutyl phthalate (DBF) is used as a plasticizer;

- the polymer binder is used polyvinyl butyral (PVB).

The essential distinguishing features of the proposed technical solution are:

- powdery cerium oxide doped with gadolinium Ce _0.9 Gd _0.1 O _1.95 (CGO10) is used as the oxide powder;

- the powder is dispersed together with a dispersant and a plasticizer at a ratio of components (wt. d.): 40/55/1/2, respectively, in an ultrasonic bath;

- the powder is subjected to grinding with ceramic balls in a bead mill mode, adding a polymer binder during grinding to control the viscosity.

The task is solved due to a set of essential distinctive features.

The conducted patent search confirmed the novelty of the proposed technical solution.

Examples of specific implementation of the proposed method.

Example 1. Obtaining a thin gas-tight layer of electrolyte composition Ce _0.9 Gd _0.1 O _1.95 (CGO10) on the surface of a microtubular anode composite composition NiO / CGO10: 60/40 (wt. E) by the method of joint sintering.

Electrochemical generators based on solid oxide fuel cells (SOFCs) are capable of directly converting the chemical energy of fossil fuels into electricity with high efficiency (up to 70%). Today, the main trend in the field of SOFC technologies is to reduce the operating temperature of the cell from 900 to 500-600 ° C to create portable devices with a thin electrolyte, which will reduce the ohmic resistance and, therefore, achieve higher power. Among the various SOFC designs (tubular and planar), the most suitable for portable technologies is the microtubular (MT) design [1-4], due to its quick start-up capability and high power density.

In the claimed method for producing a thin gas-tight layer of CGO10 electrolyte for microtubular SOFC, the initial electrolyte paste was prepared according to the following procedure:

Stage 1 - powder dispersion. 0.685 g of dispersant (BYK-111) and 1.37 g of plasticizer (DBF) were dissolved in 37.68 g of BG in an ultrasonic bath for 20 minutes. Then, 27.4 g of 10GDC was slowly added with vigorous stirring and placed in an ultrasonic bath for 1 h. Then, dispersion was carried out on a DISPERMAT-55 dissolver in a bead mill mode for 1 h at 300 rpm using ceramic bead balls (YSZ) 1 mm in diameter ... The volume of the balls was equal to the volume of the mixture.

Stage 2 - thickening of the paste. 1.37 g of polymer binder (PVB) was dissolved in 15 ml of BG and the resulting polymer solution was added during milling. Thereafter, the rotational speed of the cutter was increased to 600 rpm and the paste was mixed for another 1 h. The viscosity of the resulting paste, determined by a Brookfield tensometer (USA), was 0.2 (1) cP.

The solvents listed below can be used to prepare the paste either individually or as a mixture of two or more components:

isopropyl alcohol, isobutyl alcohol, methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, butyl glycol acetate, propylene glycol methyl ether propionate, propylene glycol methyl ether acetate, butyl glycol acetate, butyl glycol ether.

Examples of dispersants that can be used to stabilize inorganic nano- and microparticles in a paste:

Solsperse 36000, Solsperse 41000, Solsperse 35000, Solsperse 36000 (manufacturer Avecia, Great Britain), Tego Disperse 650, Tego Disperse 652, Tego Disperse 655 (manufacturer Tego Chemie Service, Germany), Disperbyk 180, Disperbyk 101, Disperbyk 110, Disperbyk 111, BYK 381, BYK-P-104 (manufacturer Chemie-BYK, Germany).

The X-ray phase of the dried electrolytic paste containing CGO10 is shown in (Fig. 1). XRD data confirm the chemical purity of the solid component of the paste after the above procedure (stages 1 and 2), no impurity sats were found.

The electrolyte layer was applied to the anode substrates by the dip-coating method. The speed of dipping and pulling the sample is 40 cm / min. The layer thickness for a single application is 2.0 ± 0.1 µm.

It is shown that the paste obtained by the described method makes it possible to obtain a gas-tight electrolyte layer at a temperature not higher than 1400 ° C.

The microstructure of the fracture of the anode substrates coated with CGO10 electrolyte annealed at 1400 ° C is shown in (Fig. 2). Gas tightness testing was carried out using the NORDTEST 3000 penetrant, the penetration of which is comparable to that of gases.

Example 2. Obtaining a thin gas-tight layer of a lithium-modified electrolyte of the composition Ce _0.9 Gd _0.1 O _1.95 (CGO10) on the surface of a microtubular anode composite of the composition NiO / CGO10: 60/40 mass% by the method of joint sintering in order to lower the maximum processing temperature ...

To lower the operating temperature of SOFCs, the most preferred design option today is a thin gas-tight electrolyte film deposited on a porous substrate based on an anode material. The main problem with cerium oxide is, first of all, the poor sintering properties of commercially available powders, which require high sintering temperatures (~ 1500 ° C) [5-7].

To develop the technology for producing MT SOFCs, it is desirable to reduce the stages of thermal annealing. For this, as a rule, the method of joint sintering of MT SOFC components is used. The sintering temperature of electrode materials (LSCF, LSM, etc.), as a rule, is not higher than 1350 ° C. At higher temperatures, incongruent melting of the electrode material, especially the cathode, occurs, which makes it impossible to co-sinter the cathode and electrolyte. Thus, for joint sintering of MT components of SOFC, it is necessary to reduce the melting temperature of the electrolyte material, as the most refractory component, down to 1350 ° C by adding a sintering additive.

The advantage of the claimed method is the variability in the choice of the solid component. The process for preparing the paste is similar to that given in example 1, except for the composition of the electrolyte powder. So, in this example, we used a modified 3% lithium CGO10, which was obtained by the thermal decomposition of a mixed precursor and was used both in the electrolyte and in the anode composite. The viscosity of the resulting paste, determined by a Brookfield tensometer (USA), was 31.0 (1) cP.

The process of deposition of an electrolyte layer on anode substrates is similar to that given in example 1. The thickness of the layer with a single application is 5.0 ± 0.1 µm, which in one cycle of “2-sided layer application” allows obtaining a 10 µm electrolyte layer, which is a more technologically advanced method. In example 1, this process had to be repeated at least 2 times.

FIG. 3. shows the microstructure of (a) the surface and (b) the fracture of the anode substrates coated with a modified 3% Li electrolyte CGO10, annealed at 1350 ° C. The resulting sample has passed the gas tightness test.

Example 3. Similar to example 1, but the sintering temperature of the electrolyte is 1300 ° C. The shrinkage values of the sample are shown in Table 1. The sample is not gas-tight.

Example 4. Similar to example 1, but the sintering temperature of the electrolyte is 1350 ° C. The shrinkage values of the sample are shown in Table 1. The sample is not gas-tight.

Example 5. Similar to example 1, but the sintering temperature of the electrolyte is 1500 ° C. Shrinkage parameters of the sample are shown in Table 1. The sample is gas-tight.

Example 6. Similar to example 2, but the sintering temperature of the electrolyte is 1300 ° C. The shrinkage values of the sample are shown in Table 1. The sample is not gas-tight.

Example 7. Similar to example 2, but the sintering temperature of the electrolyte is 1400 ° C. Shrinkage parameters of the sample are shown in Table 1. The sample is gas-tight.

Example 8. Similar to example 2, but the sintering temperature of the electrolyte is 1500 ° C. Shrinkage parameters of the sample are shown in Table 1. The sample is gas-tight.

Example 9. Similar to example 1, but instead of the CGO10 electrolyte, a high-temperature 8YSZ electrolyte was used. The sintering temperature was 1450 ° C. The number of dips is 2. The thickness of the electrolyte layer is given in Table 2.

Example 10. Similar to example 6, but the number of immersions is 4. Indicators of the thickness of the electrolyte layer are shown in table 2.

Example 11. Similar to example 10, but instead of the 8YSZ electrolyte, a Ba cathode material was used_0.5Sr_0.5Co_0.75Fe_0.2Mo_0.05O_3-z (BSCFM5). Indicators of the thickness of the electrolyte layer are shown in table 2.

Example 12. Similar to example 10, but instead of the 8YSZ electrolyte, a cathode material of the composition SrCo was used_0.9Ta_0.1O_3-z (SCT10). Indicators of the thickness of the electrolyte layer are shown in table 2.

Example 13. Similar to example 10, but instead of the 8YSZ electrolyte, a Ba cathode material was used_0.5Sr_0.5Co_0.78Fe_0.2W_0.02O_3-z (BSCFW2). Indicators of the thickness of the electrolyte layer are shown in table 2.

Example 14. Similar to example 10, but instead of the 8YSZ electrolyte, a cathode material of the composition SrCoO was used_3-z (SC). Indicators of the thickness of the electrolyte layer are shown in table 2.

From the data in Table 1 it can be seen that shrinkage> 20 provides a gas-tight electrolyte layer. From the data in Table 2, it can be seen that the proposed method makes it possible to use as a solid filler not only nanosized CGO10, obtained by the thermal decomposition of a mixed precursor, but also other compositions, including promising cathode materials.

The achieved technical result obtained by using this solution consists in simplifying the technology and reducing the energy consumption of making a paste with the possibility of finely adjusting the viscosity of the final product, simplifying the technology for applying the paste, which makes it possible to obtain layers of various thicknesses and relative densities, up to the formation of gas-dense layers.

Advantages of the paste obtained using this technology in comparison with the prototype:

- the ability, depending on the coating method and the required coating thickness, to control the viscosity of the paste by changing the ratio of the solvent and the solid phase of the oxide used;

- the ability to apply the paste by various methods: for example, dip coating (dipping the sample into the paste), spin coating (uniform coating with intensive rotation of the sample) and paint-brushing (manual application of thin layers with various tools);

- the possibility of varying the composition of the solid component of the paste depending on the required functionality of the layer.

Table 1

Electrolyte Shrinkage at 1300 ° C,% Shrinkage at 1350 ° C,% Shrinkage at 1400 ° C,% Shrinkage at 1500 ° C,% CGO10 17 21 23 27 CGO10 + 3% Li 17 21 23 27

table 2

The composition of the paste Viscosity of the paste, cPoise Number of dips Thickness, micron CGO10 0.2 4 8-10 CGO10 + 3% Li 31 2 ten 8YSZ 31 2 ten 8YSZ 31 4 25 BSCFM5 31 4 25 SCT10 31 4 25 BSCFW2 31 4 25 SC 31 4 25

Claims (5)

1. A method of producing a paste for a thin-film solid electrolyte of electrochemical devices, including mixing an oxide powder and an organic solvent, as the oxide powder, powdered cerium oxide doped with gadolinium Ce _0.9 Gd _0.1 O _1.95 (CGO10) is used, the powder is dispersed together with a solvent, with a dispersant and a plasticizer at a ratio of components (wt. d.): 40/55/1/2, respectively, in an ultrasonic bath, and then subjected to grinding with ceramic balls in a bead mill mode, adding a polymer binder during grinding to obtain a paste with viscosity 0.2 Poise. 2. The method according to claim 1, characterized in that butyl glycol (BG) is used as the solvent. 3. The method according to claim 1, characterized in that Disperbyk-111 (BYK-111) is used as a dispersant. 4. The method according to claim 1, characterized in that dibutyl phthalate (DBF) is used as the plasticizer. 5. The method according to claim 1, characterized in that polyvinyl butyral (PVB) is used as the polymer binder.

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