A method for manufacturing a solid oxide electrolysis cell composite gasket

Abstract

The application discloses a preparation method of a solid oxide electrolysis cell composite sealing gasket. The sealing gasket is prepared through a double-layer casting process: first, a vermiculite-based sealing gasket is prepared through a casting method; then, a layer of microcrystalline glass sealing slurry is cast on the vermiculite-based sealing gasket, and thus a composite sealing gasket is obtained. The microcrystalline glass has the characteristics of both glass and ceramic, has good thermal stability and a thermal expansion coefficient, and can resist high-humidity gas erosion. The composite sealing gasket prepared by the application has good combination of the glass layer and the cell sheet, high adaptability of the vermiculite layer and the connecting body, and no delamination and falling off between the glass layer and the vermiculite layer, so that the sealing effect is greatly improved, and the reusability of the connecting body plate is increased.

Description

Technical Field

[0001] This invention belongs to the field of sealing material technology, specifically relating to a method for preparing a composite sealing gasket for a solid oxide electrolytic cell. Background Technology

[0002] Solid oxide electrolyzers (SOECs) are a highly efficient and green hydrogen production technology. Under high temperature (600–800℃) and applied voltage, H2O is electrolyzed to produce H2 and O2, converting electrical and thermal energy into chemical energy. This technology features low cost and high energy conversion efficiency. However, due to the high operating temperature, sealing at high temperatures has always been one of the main challenges restricting the widespread adoption of SOEC technology.

[0003] A flat-plate SOEC consists of upper and lower plates, solar cells, connectors, and sealing materials. The connectors have distributed gas channels for the inflow and outflow of fuel gas and air. Appropriately sized current collectors are placed on these gas channels to homogenize the gas flow and collect electricity. However, the placement of the current collectors creates a height difference between the solar cells and the connectors. Therefore, special sealing materials are needed to seal the area, and a certain load pressure is applied to the surface of the upper plate to prevent fuel gas and air leakage and cross-contamination, achieving a good sealing effect.

[0004] Currently, there are two main sealing methods in SOEC (Solar Electrolyte-Enhanced Chemical Cell) stacks: one is sealing with vermiculite-based high-temperature gaskets, and the other is sealing with glass-ceramic sealant or gaskets. Vermiculite is a layered silicate mineral with a 2:1 structure. Under high temperature and chemical action, it can produce a worm-like structure similar to expanded graphite, exhibiting good flexural resilience and excellent oxidation resistance. Vermiculite-based high-temperature gaskets can expand at high temperatures and have a certain degree of compressibility, preventing adhesion to the metal connectors. However, due to the inconsistency in thermal expansion coefficients between the gaskets and the solar cells, gaps may appear and leak when pressure is not concentrated on the stack. On the other hand, in long-term high-humidity environments, the internal adhesive ages due to damp heat, reducing its adhesion and thus decreasing the mechanical strength of the gasket, rendering it unusable after thermal cycling. Glass-ceramic gaskets, on the other hand, become semi-molten at high temperatures, allowing for tight bonding with the solar cells and connectors. Their relatively consistent thermal expansion coefficients ensure the stack's sealing performance. However, the glass gaskets currently used tend to adhere to the battery cells and metal connectors during use. After being heated and cycled back to room temperature, they are difficult to peel off from the battery cells and connectors and cannot be reused, resulting in some waste of the connector material.

[0005] Chinese patent CN 110723923A discloses a method for preparing a vermiculite-based flexible sealing material. This method involves adding solvents, dispersants, binders, and plasticizers, and then using casting and hot-pressing vulcanization to prepare a high-temperature sealing gasket with good sealing properties. However, this sealing gasket contains a large amount of additives, such as binders. After being burned at high temperatures, the binder shrinks in volume, creating gaps between the gasket and the battery cell or electrode, resulting in poor sealing performance. Furthermore, after disassembly, the sealing gasket's strength is significantly reduced due to the hygrothermal aging of the binder, rendering it unusable.

[0006] Chinese patent CN 115959832A discloses a method for preparing and using microcrystalline sealing glass for solid oxide fuel cells (SOFCs). Microcrystalline sealing glass powder with compatibility with SOFC components was successfully prepared by melt quenching. After preparing a glass sealant, molding, and heat treatment, a good sealing effect was achieved between the anode of the battery cell and the connector. However, grain growth at high temperatures caused the sealing glass to adhere to both the battery cell and the connector, making it impossible to disassemble and thus rendering the connector unusable continuously. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing a composite sealing gasket for a solid oxide electrolytic cell. This invention prepares the sealing gasket using a double-layer casting process, specifically by casting a layer of microcrystalline glass sealing slurry onto a vermiculite-based sealing gasket prepared by casting, thereby obtaining a composite sealing gasket.

[0008] According to the first objective of the present invention, the present invention provides a method for preparing a composite sealing gasket for a solid oxide electrolytic cell.

[0009] Specifically, the preparation method of the solid oxide electrolytic cell composite sealing gasket includes the following steps:

[0010] (1) Preparation of vermiculite sealing casting slurry:

[0011] First, the modified mixed powder, solvent, and dispersant are ball-milled once to obtain a primary mixed slurry. Then, a binder and plasticizer are added, and the mixture is ball-milled a second time to obtain a secondary mixed slurry. Subsequently, the mixed slurry is filtered and degassed to obtain a shaped vermiculite sealing slurry. The vermiculite sealing slurry, by weight, consists of 40-60% modified mixed powder, 40-60% solvent, 1-5% dispersant, 4-8% binder, and 4-8% plasticizer.

[0012] (2) Casting and molding vermiculite-based gaskets: Vermiculite sealing slurry is cast and molded, and then dried to obtain vermiculite-based gaskets;

[0013] (3) Preparation of microcrystalline glass fine powder:

[0014] The oxides with a mass composition of 40-60% SrO, 25-50% SiO2, 5%-10% MgO, 1-5% Al2O3, 0.5-1% CaO and 0.5-1% K2O were ball-milled once; then the uniformly mixed powder was heated by a program and kept at a certain temperature; then quenched to obtain glass slag; after drying the glass slag, it was ball-milled a second time to obtain microcrystalline glass raw powder; microcrystalline glass raw powder with a specific particle size was obtained by sieving, and then sand-milled to obtain microcrystalline glass fine powder with a Dv(50) particle size ≤0.5μm;

[0015] (4) Preparation of glass sealing casting slurry:

[0016] First, the microcrystalline glass powder, solvent, and dispersant obtained in step (3) are ball-milled once; then, binder and plasticizer are added and ball-milled a second time to obtain a mixed slurry; subsequently, the mixed slurry is filtered and immediately degassed to obtain a shaped glass sealing slurry; the glass sealing slurry comprises, by mass fraction, 40-60% glass powder, 40-60% solvent, 1-5% dispersant, 4-8% binder, and 4-8% plasticizer;

[0017] (5) Casting glass sealant onto vermiculite-based gaskets:

[0018] Using the dried vermiculite-based gasket from step (2) as a base, a glass sealing slurry is cast onto it and then dried to obtain a composite gasket.

[0019] According to the present invention, the modified mixed powder in step (1) is obtained by modifying the mixed powder, or by modifying the powder and then mixing it. Powder modification is an operation well known to those skilled in the art. The powder comprises one or more of chemically expanded vermiculite powder, physically expanded vermiculite powder, microwave expanded vermiculite powder, talc powder, golden mica powder, alumina powder, and silica powder. The modifier used in the powder modification treatment is selected from one of titanate coupling agents, aluminate coupling agents, silane coupling agents, stearic acid, and sodium polyacrylate. The modified powder is required to have a water contact angle of not less than 90°.

[0020] According to the present invention, the solvent in step (1) is selected from one or more of anhydrous ethanol, toluene, xylene, acetone, butanone, methyl acetate, and ethyl acetate.

[0021] According to the present invention, the dispersant in step (1) is selected from one of polyvinylpyrrolidone, triethanolamine, fish oil, castor oil, tributyl phosphate, and trioleic acid glyceride.

[0022] According to the present invention, the adhesive in step (1) is selected from one of polyvinyl alcohol, polyvinyl butyral, methylcellulose, and ethylcellulose; the plasticizer is selected from one of tributyl citrate, dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyethylene glycol.

[0023] According to the present invention, the ball milling time in step (1) is 0.5-4h and the ball milling speed is 300-400rpm; the ball milling time is 4-8h and the ball milling speed is 300-400rpm.

[0024] According to the present invention, the casting process in step (2) employs conventional techniques in the art. For example, the scraper height can be set to 0.7-1.0 mm, and the scraper advance speed to 1.2-3 m / min. The drying process is a conventional operation in the art, such as a drying temperature of 50℃-65℃ and a drying time of 4-12 h.

[0025] According to the present invention, the specific particle size range obtained by the vibrating screen in step (3) is 10-13 μm, and the particle size of the glass powder obtained after sand milling is ≤0.5 μm (Dv(50)). The time for the first ball milling is 0.5-2 h, and the ball milling speed is 100-200 rpm. The programmed heating and holding include: firstly, holding at a temperature between 800-900℃ and 1200-1300℃ for 1-1.5 h respectively (the temperature and time depend on the composition ratio and mass of each oxide), and then heating to 1600℃ and holding for 0.5-1 h. The purpose of holding is, on the one hand, to control the viscosity and expansion behavior of the melt at high temperature and avoid overflow during heating, and on the other hand, to control the nucleation and growth of glass crystals to achieve a good crystallization effect. The time for the second ball milling in step (3) is 12-18 h, and the ball milling speed is 300-400 rpm. The grinding time is 1-3 hours, and the grinding speed is 200-300 rpm.

[0026] According to the present invention, the solvent in step (4) is selected from one or more of anhydrous ethanol, toluene, xylene, acetone, butanone, methyl acetate, and ethyl acetate. The dispersant is selected from one of polyvinylpyrrolidone, triethanolamine, fish oil, castor oil, tributyl phosphate, and trioleic acid glyceride. The binder is selected from one of polyvinyl alcohol, polyvinyl butyral, methylcellulose, and ethylcellulose. The plasticizer is one of one of tributyl citrate, dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyethylene glycol.

[0027] According to the present invention, the time for the first ball milling in step (4) is 0.5-4h, and the ball milling speed is 200-300rpm; the time for the second ball milling is 2-6h, and the ball milling speed is 200-300rpm.

[0028] According to the present invention, the casting process in step (5) employs conventional techniques in the art. For example, the squeegee height can be set to 1-1.6 mm, and the squeegee advance speed to 1.2-3 m / min. The drying process is a conventional operation in the art, such as a drying temperature of 25℃-60℃ and a drying time of 12-20 h.

[0029] According to a second objective of the present invention, the present invention also provides a solid oxide electrolytic cell composite sealing gasket, which is obtained by the preparation method described above.

[0030] According to the present invention, the composite sealing gasket comprises a vermiculite-based sealing gasket and a glass sealing gasket closely bonded thereto.

[0031] According to the present invention, in the composite sealing gasket, the thickness of the vermiculite layer is 0.4-0.6 mm; and the thickness of the glass layer is 0.1-0.3 mm. The composite sealing gasket, after being prepared by a casting process, has moderate softness and exhibits no delamination or peeling.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. The flexible vermiculite / microcrystalline glass composite gasket prepared by casting in this invention has strong process continuity and is suitable for industrial production. The prepared composite gasket has a smooth and flat surface, high flexibility and mechanical strength, and excellent sealing performance at high temperatures (700-800℃).

[0034] 2. A significant advantage of this invention is that the thermal expansion coefficient of the microcrystalline glass layer in the prepared vermiculite / microcrystalline glass composite gasket matches that of the solar cell, resulting in a tight bond at high temperatures and significantly improved sealing. After one thermal cycle, the two layers do not delaminate. Simultaneously, the dense microcrystalline glass layer provides overall support for the composite gasket, improving mechanical strength compared to a single-layer vermiculite gasket, thus meeting the requirements of current flat-plate SOEC single-cell battery test fixtures and stacks. Furthermore, the microcrystalline glass layer is bonded to the solar cell and can be reused; the vermiculite layer is easily separated from the connector, also improving the reusability of the connector plate and reducing unnecessary waste. Microcrystalline glass (glass-ceramic) combines the characteristics of both glass and ceramics, exhibiting good thermal stability and a high coefficient of thermal expansion. At high temperatures, the internal grains continuously grow, and the surface becomes dense, making it resistant to high-humidity gas corrosion. This type of composite sealing gasket has good adhesion between the glass layer and the battery cell, and the vermiculite layer has high compatibility with the connector. There is no delamination or detachment between the glass layer and the vermiculite layer. Compared with current sealing materials, it greatly improves the sealing effect and increases the reusability of the connector plate. Attached Figure Description

[0035] The present invention will be further described in detail below with reference to the accompanying drawings.

[0036] Figure 1 The curve shows the open-circuit voltage change of the battery cell after initial reduction to stabilization at 750°C when the composite sealing gasket prepared in Example 1 is applied to a flat SOEC single-cell fixture.

[0037] Figure 2 The composite sealing gasket prepared in Example 1 is used in a flat SOEC single cell fixture to measure the inlet and outlet flow rates of the cell anode within 12 hours after the open-circuit voltage stabilizes.

[0038] Figure 3 The curves show the open-circuit voltage changes of the cell after initial reduction to stabilization at 750°C when the vermiculite sealing gasket prepared in Comparative Example 1 is applied in a flat SOEC single-cell fixture.

[0039] Figure 4 The inlet and outlet flow rates of the cell anode in a flat SOEC single-cell fixture prepared in Comparative Example 1 within 12 hours after the open-circuit voltage stabilizes are measured. Detailed Implementation

[0040] The present invention is further illustrated by the following embodiments, but the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The scope of protection of the present invention is not limited to the following embodiments.

[0041] It should be noted that the test method for SOEC cell sealing in this invention is based on the open-circuit voltage of a single cell and the difference in gas flow rates between the anode and cathode. Since the open-circuit voltage depends on the partial pressure of the gas on both sides of the cathode and anode, and this partial pressure is affected by the density and sealing performance of the intermediate electrolyte, the open-circuit voltage can be used to measure the airtightness of the composite sealing gasket and its compatibility with adjacent components when the electrolyte is completely dense. The standard for judging the airtightness of the seal is usually whether the open-circuit voltage is close to the ideal value (1.23V at 750℃). Furthermore, under the condition that the clamping air passages and pipelines are airtight, the difference between the inlet and outlet flow rates of the anode and cathode is also a parameter for measuring the sealing effect.

[0042] Example 1

[0043] The preparation method of the solid oxide electrolytic cell composite sealing gasket in this embodiment includes the following steps:

[0044] (1) Preparation of vermiculite sealing casting slurry

[0045] First, physically expanded vermiculite powder and chemically expanded vermiculite powder were modified with stearic acid, resulting in water contact angles of 95° and 98°, respectively. A mixture of 22% physically expanded vermiculite, 11% chemically expanded vermiculite, 11% talc, 44% ethanol solvent, and 3% castor oil was ball-milled for 2 hours at 300 rpm to obtain a primary slurry. Then, 5% polyvinyl butyral and 4% dibutyl phthalate were added, followed by a secondary ball milling process for 4 hours at 300 rpm to obtain a secondary slurry. The slurry was then filtered and immediately degassed to obtain a shaped vermiculite sealing slurry.

[0046] (2) Casting and molding vermiculite-based sealing gaskets

[0047] The shaped vermiculite sealing slurry was cast using a casting process. The scraper height was set to 0.9 mm, the scraper advance speed was 1.5 m / min, the drying temperature after casting was 50℃, and the drying time was 8 hours.

[0048] (3) Preparation of microcrystalline glass fine powder

[0049] A raw material with a mass fraction of 55% strontium oxide (SrO), 35% silicon dioxide (SiO2), 7% magnesium oxide (MgO), 2% aluminum oxide (Al2O3), 0.5% calcium oxide (CaO), and 0.5% potassium oxide (K2O) was placed in a ball mill and ball-milled for 2 hours at 200 rpm. The uniformly mixed powder was then added to a crucible and heated to 1600℃ in a high-temperature resistance furnace. After holding at this temperature for 0.5 hours, the mixture was quenched in water to obtain glass slag. Temperatures of 800℃ and 1200℃ were held for 1.5 hours each. After drying the glass slag, a second ball milling process was performed for 12 hours at 400 rpm to obtain microcrystalline glass raw powder. Microcrystalline glass raw powder with a particle size of 13 μm was obtained by sieving with a vibrating screen. Then, the 13 μm microcrystalline glass raw powder was further finely sand-milled for 2 hours with a sand mill speed of 200 rpm to obtain microcrystalline glass fine powder with a particle size of 0.4 μm.

[0050] (4) Preparation of glass sealing casting slurry

[0051] 45% (w / w) of microcrystalline glass powder, 45% of ethanol and toluene solvents, and 3% of tributyl phosphate were placed in a ball mill jar and ball-milled for 0.5 hours at 300 rpm to obtain a primary mixed slurry. Then, 4% of polyvinyl butyral and 3% of dibutyl phthalate were added, and the mixture was ball-milled a second time for 5 hours at 300 rpm to obtain a secondary mixed slurry. The mixed slurry was then filtered and degassed to obtain a microcrystalline glass sealing slurry.

[0052] (5) Cast glass sealant onto vermiculite-based gaskets

[0053] Using a dried vermiculite-based gasket as a base, a shaped glass sealing slurry is cast onto it. The scraper height is set to 1.5 mm, the scraper advance speed is 1.5 m / min, the drying temperature is 30℃, and the drying time is 18 h to obtain a vermiculite / microcrystalline glass composite gasket.

[0054] Example 2

[0055] The preparation method of the solid oxide electrolytic cell composite sealing gasket in this embodiment includes the following steps:

[0056] (1) Preparation of vermiculite sealing casting slurry

[0057] First, physically expanded vermiculite powder and chemically expanded vermiculite powder were modified with a silane coupling agent, resulting in water contact angles of 92° and 96°, respectively. A mixture of 15% physically expanded vermiculite, 15% chemically expanded vermiculite, 13% talc, 43% ethanol solvent, and 4% castor oil was ball-milled for 2 hours at 300 rpm to obtain a primary slurry. Then, 5% polyvinyl butyral and 5% dibutyl phthalate were added, followed by a secondary ball milling process for 4 hours at 300 rpm to obtain a secondary slurry. The slurry was then filtered and immediately degassed to obtain a shaped vermiculite sealing slurry.

[0058] (2) Casting and molding vermiculite-based sealing gaskets

[0059] The shaped vermiculite sealant was cast using a casting process. The scraper height was set to 1 mm, the scraper advance speed was 1.8 m / min, and the drying temperature after casting was 65℃ for 4 hours.

[0060] (3) Preparation of microcrystalline glass fine powder

[0061] The raw materials with a mass fraction of 45% SrO, 35% SiO2, 10% MgO, 8% Al2O3, 1% CaO and 1% K2O were placed in a ball mill jar and ball-milled for 2 hours at a speed of 200 rpm. Then, the uniformly mixed powder was added to a crucible and heated to 1600℃ in a high-temperature resistance furnace. After holding at this temperature for 0.5 hours, it was poured into water and quenched to obtain glass slag. The temperature was held for 1.2 hours at 850℃ and 1250℃ respectively. After drying the glass slag, it was ball-milled a second time for 12 hours at a speed of 400 rpm. The microcrystalline glass raw powder with a Dv(50) particle size of 13 μm was obtained by sieving with a vibrating screen. Then, the 13 μm microcrystalline glass raw powder was further finely sand-milled for 1 hour at a speed of 300 rpm to obtain microcrystalline glass fine powder with a Dv(50) particle size of 0.5 μm. (4) Preparation of glass sealing casting slurry

[0062] 40% (w / w) of microcrystalline glass powder, 45% of ethanol and toluene solvents, and 2% of tributyl phosphate were placed in a ball mill and ball-milled for 0.5 hours at 300 rpm to obtain a primary slurry. Then, 7% of polyvinyl butyral and 6% of dibutyl phthalate were added, and the mixture was ball-milled for 5 hours at 300 rpm to obtain a secondary slurry. The slurry was then filtered and degassed to obtain a microcrystalline glass sealing slurry.

[0063] (5) Cast glass sealant onto vermiculite-based gaskets

[0064] Using a dried vermiculite-based gasket as a base, a shaped glass sealing slurry is cast onto it. The scraper height is set to 1.6 mm, the scraper advance speed to 1.5 m / min, the drying temperature to 60℃, and the drying time to 12 h. A vermiculite / microcrystalline glass composite gasket is obtained.

[0065] Example 3

[0066] The preparation method of the solid oxide electrolytic cell composite sealing gasket in this embodiment includes the following steps:

[0067] (1) Preparation of vermiculite sealing casting slurry

[0068] First, physically expanded vermiculite powder and chemically expanded vermiculite powder were modified with a silane coupling agent, resulting in water contact angles of 92° and 96°, respectively. A mixture of 20% physically expanded vermiculite, 20% chemically expanded vermiculite, 5% talc, 45% ethanol solvent, and 2% castor oil was ball-milled for 2 hours at 300 rpm to obtain a primary slurry. Then, 4% polyvinyl butyral and 4% dibutyl phthalate were added, followed by a secondary ball milling process for 4 hours at 300 rpm to obtain a secondary slurry. The slurry was then filtered and immediately degassed to obtain a shaped vermiculite sealing slurry.

[0069] (2) Casting and molding vermiculite-based sealing gaskets

[0070] The shaped vermiculite sealant was cast using a casting process. The scraper height was set to 0.8 mm, the scraper advance speed was 1.3 m / min, the drying temperature after casting was 60℃, and the drying time was 6 h.

[0071] (3) Preparation of microcrystalline glass fine powder

[0072] The raw materials with a mass fraction of 50% SrO, 40% SiO2, 6% MgO, 3% Al2O3, 0.5% CaO and 0.5% K2O were placed in a ball mill jar and ball-milled for 2 hours at a speed of 200 rpm. Then, the uniformly mixed powder was added to a crucible and heated to 1600℃ in a high-temperature resistance furnace. After holding at this temperature for 0.5 hours, it was poured into water and quenched to obtain glass slag. The temperature was held for 1 hour at 900℃ and 1300℃ respectively. After drying the glass slag, it was ball-milled a second time for 18 hours at a speed of 300 rpm. The microcrystalline glass raw powder with a Dv(50) particle size of 11 μm was obtained by sieving with a vibrating screen. Then, the 11 μm microcrystalline glass raw powder was further finely sand-milled for 3 hours at a speed of 200 rpm to obtain microcrystalline glass fine powder with a Dv(50) particle size of 0.3 μm.

[0073] (4) Preparation of glass sealing casting slurry

[0074] 43% (w / w) of microcrystalline glass powder, 45% ethanol and toluene solvents, and 2.5% tributyl phosphate were placed in a ball mill and ball-milled for 0.5 hours at 300 rpm to obtain a primary slurry. Then, 5.5% polyvinyl butyral and 4% dibutyl phthalate were added, and the mixture was ball-milled a second time for 5 hours at 300 rpm to obtain a secondary slurry. The slurry was then filtered and degassed to obtain a microcrystalline glass sealing slurry.

[0075] (5) Cast glass sealant onto vermiculite-based gaskets

[0076] Using a dried vermiculite-based gasket as a base, a shaped glass sealing slurry is cast onto it. The scraper height is set to 1.3 mm, the scraper advance speed to 1.4 m / min, the drying temperature to 40℃, and the drying time to 18 h. A vermiculite / microcrystalline glass composite gasket is obtained.

[0077] The NiO-YSZ-LSCF SOEC single cell was sealed with the vermiculite / microcrystalline glass composite gasket prepared in Example 1. The cathode was reduced at 750°C using a nitrogen-hydrogen mixed gas. After stabilization, the open-circuit voltage reached as high as 1.2V, close to the ideal voltage value at that temperature. Figure 1 Simultaneously, after reduction is complete, water vapor is introduced at the cathode; when the inlet flow rate is 100 mL / min, the outlet flow rate can reach 95 mL / min. Figure 2 This indicates excellent airtightness. The thermal expansion coefficient of the double-layer composite sealing gasket matches that of the battery cell and the connector. The glass layer can be tightly bonded to the battery cell, maintaining good airtightness even after repeated thermal cycles. It also has good strength and does not stick to the connector.

[0078] Comparative Example 1

[0079] The vermiculite-based flexible sealing material prepared using the method described in patent CN 110723923 A also employs a casting process. This sealing material features a smooth surface, good flexibility, high tensile strength, uniform performance, and excellent high-temperature resistance. However, unlike the composite sealing gasket prepared in this invention, this gasket cannot tightly adhere to SOEC solar cells at high temperatures. Therefore, it cannot adapt to the bending deformation of SOEC solar cells, and under long-term operating conditions, it is prone to developing micro-gaps with the solar cells, resulting in poor airtightness. Furthermore, after one thermal cycle, the mechanical strength of this sealing material is significantly reduced, rendering it unusable.

[0080] When NiO-YSZ-LSCF SOEC single-cell cells were sealed with this vermiculite-based flexible sealing material, and the cathode was reduced at 750℃ using a nitrogen-hydrogen mixed gas, the stable open-circuit voltage was 1.16V (see attached image). Figure 3 Simultaneously, after reduction is complete, water vapor is introduced at the cathode. When the inlet flow rate at the anode is 100 mL / min, the outlet flow rate is less than 80 mL / min (see appendix). Figure 4 Furthermore, the outlet flow gradually decreases over time, resulting in poor long-term sealing performance.

[0081] Comparative Example 2

[0082] The composite sealing gasket was prepared using the powder and slurry composition described in Example 1, and according to the preparation method mentioned in Chinese Patent CN 117497796 A. Specifically, the following steps were followed:

[0083] Step (1): Preparation of sealing gasket casting slurry

[0084] The slurry consists of 22% physically expanded vermiculite, 11% chemically expanded vermiculite, 11% talc, 44% ethanol solvent, 3% castor oil, 5% polyvinyl butyral, and 4% dibutyl phthalate by mass ratio. The mixed powder, ethanol, and castor oil are added to a ball mill and ball-milled at 300 r / min for 2 hours. Then, polyvinyl butyral and dibutyl phthalate are added, and the mixture is ball-milled at 300 r / min for 4 hours to obtain the slurry.

[0085] Step (2): Cast the above slurry onto the release film.

[0086] The thickness of the film is 500 micrometers. After casting, the cast liquid film is immediately immersed in water for 12 hours. After taking it out, the two sheets are stacked and hot-pressed, and then dried in an oven at 60°C to obtain a dry film strip, which is then cut into a shape suitable for sealing.

[0087] Step (3): Preparation of special glass powder

[0088] After the glass powder is physically mixed evenly, the composition of the glass powder is: 55% strontium oxide (SrO), 35% silicon dioxide (SiO2), 7% magnesium oxide (MgO), 2% aluminum oxide (Al2O3), 0.5% calcium oxide (CaO) and 0.5% potassium oxide (K2O) by mass ratio. The mixture is heated to 1600℃ in a high-temperature furnace at a heating rate of 3℃ / min and held at that temperature for 1 hour. The slurry is then poured into cold water for quenching. After cooling to room temperature, the quenched glass block is ground and stored to obtain glass powder.

[0089] Step (4): Preparation of special glass paste

[0090] Mix 60% special glass powder, 35% 2wt% ethyl cellulose terpineol solution, and 5% herring oil in a mixer until homogeneous, and then roll the mixture through a three-roll mill for later use.

[0091] Step (5): Screen print special glass paste onto the sealing film tape.

[0092] The screen printing thickness is 100 micrometers. After printing on one side, it is dried in an oven at 70°C for 6 hours. Then, the other side is printed and dried in an oven at 60°C overnight to obtain the solid oxide fuel cell sealing material.

[0093] The sealing material prepared in step (5) was used to seal NiO-YSZ-LSCF SOEC single cell to test its sealing performance under SOEC conditions. After one thermal cycle, the test fixture was disassembled. It was visible to the naked eye that the glass layers screen-printed on both sides of the sealing material were adhered to the connector. The strong adhesion on both sides caused the liquid film prepared by stacking in the middle to delaminate and break during disassembly.

[0094] Comparative Example 3

[0095] The composite sealing gasket is prepared using the powder and slurry composition described in invention patent CN 117497796 A and according to the preparation method in embodiment 1.

[0096] The prepared composite sealing gasket was used to seal a NiO-YSZ-LSCF-based SOEC single cell to test its sealing performance under SOEC conditions. The cathode was reduced with a nitrogen-hydrogen mixed gas at 750℃. After the open-circuit voltage stabilized, it reached 1.18V. Constant current electrolysis was then performed by introducing 100mL of water vapor through the cathode. After 100 hours, the cell degradation rate exceeded 10%, the cathode exhaust gas flow rate decreased to 50mL, and the open-circuit voltage dropped to 1.15V after electrolysis was stopped, indicating poor sealing performance.

[0097] Comparative Example 4

[0098] The composite sealing gasket was prepared using the powder and slurry composition and preparation method of Example 1. The difference is that after obtaining powder with a particle size of 13μm by sieving with a vibrating screen in step (4), it is no longer sand milled.

[0099] After drying, the prepared composite sealing gasket exhibited visible microcracks on the glass surface. When the NiO-YSZ-LSCF SOEC single-cell battery was sealed, stress concentration and cracking caused by surface defects in the glass layer led to gas leakage channels. No gas was detected leaking out at the exhaust gas outlet after gas was introduced into the cathode, indicating poor sealing performance.

[0100] Comparative Example 5

[0101] The composite sealing gasket was prepared using the powder and slurry composition and preparation method in the invention patent CN 117497796 A. The difference is that after grinding in step (3), it was finely ground again with sand mill to a particle size of 0.5μm as in Example 1.

[0102] After drying, no obvious defects appeared on the surface of the glass layer of the prepared composite sealing gasket. When this composite sealing gasket was used to seal a NiO-YSZ-LSCF SOEC single-cell battery, the cathode was reduced at 750℃ using a nitrogen-hydrogen mixed gas. After stabilization, the open-circuit voltage was 1.19V. Constant-current electrolysis was then performed by introducing 100mL of water vapor at the cathode. After 100 hours, the battery cell degradation rate exceeded 10%, the cathode exhaust gas flow rate dropped to 60mL, and the open-circuit voltage dropped to 1.15V after electrolysis was stopped, indicating a poor sealing effect.

Claims

1. A method of making a solid oxide electrolysis cell composite gasket, characterized by, Includes the following steps: (1) Preparation of vermiculite sealing casting slurry: First, the modified mixed powder, solvent, and dispersant are ball-milled once to obtain a primary mixed slurry; then, a binder and plasticizer are added and the mixture is ball-milled a second time to obtain a secondary mixed slurry; finally, the mixed slurry is filtered and degassed to obtain a molded vermiculite sealing slurry. (2) Casting and molding vermiculite-based gaskets: The molten vermiculite sealing slurry is cast and molded, and then dried to obtain vermiculite-based gaskets; (3) Preparation of fine powder of microcrystalline glass: The oxides with a mass composition of 40-60% SrO, 25-50% SiO2, 5%-10% MgO, 1-5% Al2O3, 0.5-1% CaO and 0.5-1% K2O were ball-milled once; then the uniformly mixed powder was heated by a program and kept at a certain temperature; then quenched to obtain glass slag; after drying the glass slag, it was ball-milled a second time to obtain microcrystalline glass raw powder; microcrystalline glass raw powder with a specific particle size was obtained by sieving and then sand-milled to obtain microcrystalline glass fine powder with a Dv(50) particle size ≤ 0.5μm; (4) Preparation of glass sealing casting slurry: First, the microcrystalline glass powder, solvent, and dispersant obtained in step (3) are ball-milled once; then, binder and plasticizer are added and ball-milled a second time to obtain a mixed slurry; subsequently, the mixed slurry is filtered and degassed to obtain a shaped glass sealing slurry; the glass sealing slurry includes, by mass fraction, 40-60% glass powder, 40-60% solvent, 1-5% dispersant, 4-8% binder, and 4-8% plasticizer; (5) Casting glass sealant onto vermiculite-based gaskets: Using the vermiculite-based gasket obtained in step (2) as a base, a microcrystalline glass sealing slurry is cast on top of it and then dried to obtain a composite gasket.

2. The production method according to claim 1, characterized by, The vermiculite sealing slurry, by weight, consists of 40-60% modified mixed powder, 40-60% solvent, 1-5% dispersant, 4-8% binder and 4-8% plasticizer.

3. The production method according to claim 1 or 2, characterized by, The mixed powder comprises one or more of the following: chemically expanded vermiculite powder, physically expanded vermiculite powder, microwave expanded vermiculite powder, talc powder, golden mica powder, alumina powder, and silica powder; the water contact angle of the powder is not less than 90°.

4. The preparation method according to claim 1, characterized in that, The solvent used in step (1) is selected from one or more of the following: anhydrous ethanol, toluene, xylene, acetone, butanone, methyl acetate, and ethyl acetate; and / or, The dispersant mentioned in step (1) is selected from one of polyvinylpyrrolidone, triethanolamine, fish oil, castor oil, tributyl phosphate, and trioleic acid glyceride.

5. The preparation method according to claim 1, characterized in that, The adhesive used in step (1) is selected from one of polyvinyl alcohol, polyvinyl butyral, methylcellulose, and ethylcellulose; and / or The plasticizer is selected from one of the following: tributyl citrate, dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyethylene glycol.

6. The preparation method according to claim 1, characterized in that, The ball milling time in step (1) is 0.5-4 hours, and the ball milling speed is 300-400 rpm; and / or The secondary ball milling time in step (1) is 4-8 hours, and the ball milling speed is 300-400 rpm.

7. The preparation method according to claim 1, characterized in that, The ball milling time in step (3) is 0.5-2 hours, and the ball milling speed is 100-200 rpm; and / or; The secondary ball milling time in step (3) is 12-18 hours, and the ball milling speed is 300-400 rpm; and / or The grinding time in step (3) is 1-3 hours, and the grinding speed is 200-300 rpm.

8. The preparation method according to claim 1, characterized in that, The programmed heating and holding process described in step (3) includes: first holding the temperature at one of the following temperatures for 1-1.5 hours, then heating it to 1500-1600℃ and holding it for 0.5-1 hours.

9. The preparation method according to claim 1, characterized in that, The solvent mentioned in step (4) is selected from one or more of anhydrous ethanol, toluene, xylene, acetone, butanone, methyl acetate, and ethyl acetate; and / or The dispersant mentioned in step (4) is selected from one of polyvinylpyrrolidone, triethanolamine, fish oil, castor oil, tributyl phosphate, and trioleic acid glyceride; and / or The adhesive used in step (4) is selected from one of polyvinyl alcohol, polyvinyl butyral, methylcellulose, and ethylcellulose; and / or The plasticizer mentioned in step (4) is one of the following: tributyl citrate, dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, and polyethylene glycol.

10. The preparation method according to claim 1, characterized in that, The ball milling time in step (4) is 0.5-4 hours and the ball milling speed is 200-300 rpm; the ball milling time in step (4) is 2-6 hours and the ball milling speed is 200-300 rpm.

11. The preparation method according to claim 1, characterized in that: The conditions for casting in step (2) are: scraper height of 0.7-1.0 mm, scraper advance speed of 1.2-3 m / min; and / or, The conditions for casting in step (5) are: the height of the scraper is 1-1.6 mm and the scraper advance speed is 1.2-3 m / min.

12. The solid oxide electrolytic cell composite sealing gasket obtained by any of the preparation methods described in claims 1-11.

13. The composite sealing gasket for a solid oxide electrolytic cell according to claim 12, characterized in that, The composite sealing gasket includes a vermiculite-based sealing gasket and a glass sealing gasket closely bonded thereto; wherein the thickness of the vermiculite layer is 0.4-0.6 mm; and the thickness of the glass layer is 0.1-0.3 mm.

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