CN100448066C - A kind of sealing material and sealing method for solid oxide fuel cell - Google Patents

Abstract

The invention discloses a sealing material and sealing method of solid oxide fuel battery in the element sealing material and sealing method, which comprises the following parts: solid particle or solid particle and ceramic fiber, organic binder and plasticizer, wherein the solid particle can be ceramic, metal or glass with size at 0.5-6um; the whole or most of particle is ceramic particle, which is selected from alumina, zirconia, titania or magnesia; the ceramic fiber is ceramic alumina fiber or alumina-silica ceramic fiber with most diameter less than 3um. The making method comprises the following steps: preparing raw material; allocating; pressurizing; heating. The invention possesses chemical stability and electric insulation for industrial manufacturing, which possesses excellent sealing property for sealing plane-typed SOFC and analog ceramic and metal.

Description

A kind of sealing material and sealing method for solid oxide fuel cell

technical field

The invention belongs to a component sealing material and a sealing method, which are used for sealing solid oxide fuel cells.

Background technique

Solid oxide fuel cell (SOFC) is a high-efficiency, non-polluting power generation device. At present, there are three main structures of SOFC: flat plate, tube and corrugated. Flat plate SOFC has the characteristics of simple component manufacturing and assembly, low production cost and high power density. Its cost performance is better than that of tubular and corrugated SOFC, and it is the focus of domestic and foreign development. The main components of planar SOFC are: an electrochemical battery cell composed of a composite cathode and anode on both sides of the electrolyte material, a metal connector with a gas channel, and a sealing material between the battery cell and the metal connector. In order to directly convert the chemical energy in the fuel gas into electrical energy, the anode side of the SOFC cell must be exposed to the fuel gas, the cathode side must be exposed to the air, and all components are in a temperature environment of 600 °C or higher. In order to ensure the normal operation of SOFC, the sealing material must provide sufficient airtightness to ensure that the two working gases do not mix; sufficient electrical insulation must be provided between the battery cell and the metal connector. In addition, the encapsulant should preferably have long-term stability, resistance to thermal cycling, chemical compatibility with adjacent components, low manufacturing cost, and high reliability.

At present, there are mainly two sealing methods for planar SOFC, hard sealing and pressure sealing. Hard sealing refers to a sealing method in which the sealing material and the SOFC component are hard-connected, and the sealing material cannot be plastically deformed after sealing. Its advantage is good air tightness. Such sealing materials are typified by glass and glass-ceramic materials. Glass and glass-ceramic-based sealing materials are easy to prepare on a large scale, simple to seal, and low in cost, but they also have some inevitable defects. The coefficient of thermal expansion of glass or glass-ceramic materials does not exactly match that of adjacent components, which can create stresses during thermal cycling that, due to the inherent brittleness of the glass, can lead to cracking and failure. Glass is a thermodynamically unstable phase. Under long-term high temperature conditions, there is a tendency to change to a more stable crystal phase (crystallization), which may cause changes in volume, thermal expansion coefficient, internal stress, etc., and the service life will be greatly shortened. The chemical compatibility of glass and glass-ceramic materials with battery cells is also insufficient. Studies have shown that alkali metal elements contained in glass materials will poison the cathode, resulting in a decrease in SOFC power.

Compression sealing means that sealing is achieved by compressing the sealing material and the parts to be sealed by external force. Its advantage is that no precise thermal matching is required between the sealing material and adjacent components. In the prior art, the sealing materials adopting the pressure sealing method mainly include mica and ceramic felt. Mica requires high applied pressure to provide an adequate seal, but excessive applied pressure in practice has the potential to damage the electrolyte layer of the battery cell. Some mica-based composites have emerged in the prior art, such as adding glass layers or flexible silver foils at the interface between mica and adjacent components, and impregnating certain phases into mica. Although these techniques improve the airtightness of mica under small applied pressure, they all increase the complexity of sealing. The biggest problem with mica-based sealing materials is that they can leak minerals into the battery, poisoning the catalyst. Ceramic felts or felts impregnated with large amounts of fine solid particles also require greater applied pressure to provide an adequate seal. In addition, due to inconsistencies in the production process of this sealing material, it is difficult to ensure the formation of an effective seal.

Therefore, there is a need in this field for a SOFC sealing material suitable for industrial production control and stable and reliable in quality, so as to alleviate the difficulties of the prior art.

Contents of the invention

The invention provides a sealing material for solid oxide fuel cells, the purpose of which is to have good chemical stability and electrical insulation in the working environment of SOFC, and high sealing reliability, and to overcome the problems existing in the existing pressure sealing materials, and at the same time provide The sealing method using this material is suitable for the sealing of flat SOFC and other similar ceramics and metals.

The solid oxide fuel cell sealing material of the present invention comprises solid particles, an organic binder and a plasticizer, and the mass ratio of the solid particles to the sum of the two substances of the organic binder and the plasticizer is 100:20～ 40. The solid particles are a composition of ceramic particles and glass powder or a composition of ceramic particles, metal powder, and glass powder, and the ceramic particles are aluminum oxide, zirconium oxide, titanium dioxide, or magnesium oxide. One or two; the metal micropowder is one or two of aluminum, titanium, magnesium or silicon, characterized in that:

(1) The quality of the glass powder or the quality of the glass powder and the metal powder are 5 to 35% in the total mass of the solid particles; (2) the glass powder softens at the SOFC working temperature, but does not Coagulation, wherein the total content of sodium oxide and potassium oxide is less than 0.3%; (3) The proportion of solid particles with a size in the range of 0.5-6 μm to the total mass of solid particles is ≥80%.

The sealing material for solid oxide fuel cells is characterized in that: the solid particles are composed of two parts of solid particles with different average sizes, and the mass ratio is: 60% to 80% of the solid particles with a large average size and 60% to 80% of the solid particles with a small average size. 20% to 40% solid particles, the average size of large particles is more than 3 times the average size of small particles.

The sealing material for solid oxide fuel cells is characterized in that: (1) the mass ratio of solid particles to the sum of the two substances of organic binder and plasticizer is 100:20-28; (2) the glass The proportion of the mass of fine powder in the total mass of solid particles is 10-25%; the proportion of the sum of the mass of glass micropowder and metal micropowder in the total mass of solid particles is 15-25%; (3) the size is less than 3 μm The proportion of solid particles to the total mass of solid particles is ≥60%.

The sealing material for the solid oxide fuel cell is characterized in that the average particle size of the metal micropowder and the glass micropowder is smaller than the average particle size of the ceramic particles.

The sealing method using the sealing material for solid oxide fuel cells includes: (1) a material preparation step, cutting the sealing material into a sealing sheet of a required size; (2) an assembly step, directly laying the sealing sheet on The area in the battery stack that needs to be sealed forms a battery stack in the order of connector base, sealing sheet, battery cell, sealing sheet, connector, sealing sheet, battery cell, sealing sheet, connector, and so on; ( 3) Pressurization step, applying a pressure of 150 to 700 kPa to the outermost connector of the battery stack in a direction perpendicular to the sealing surface; (4) Temperature raising step, slowly raising the temperature of the assembled battery stack to the working temperature of the solid oxide fuel cell , heating rate 1 ~ 3 ℃ / min.

The sealing method using the sealing material for solid oxide fuel cells is characterized in that (1) in the material preparation step, after cutting into sealing sheets, they are placed in a press for pre-compression at a pressure of 5-30 MPa, and the pressure is kept 5 to 10 minutes; (2) The assembly process is as follows: lay the first layer of sealing sheet on the base of the connecting body with gas channels, where the battery cells are to be placed, and then put the battery cells, the battery cells The periphery of the body is pressed on the layer of sealing sheet, and then the second layer of sealing sheet is laid on the periphery of the battery cell, and then the second layer of connecting body is placed, and the third layer of sealing sheet is laid on it, and so on, forming Battery stack; (3) In the heating step, the heating rate is 1-1.5°C/min; or the heating rate is 1.5-3°C/min, and the temperature is kept at 200°C for 1-2h.

The preparation process of the sealing material for solid oxide fuel cells is as follows: according to the raw material ratio of the solid particles or solid particles and ceramic fibers, weigh the required raw materials; Then add the raw materials and ball mill to fully disperse the raw materials, then add organic binder and plasticizer in turn, and ball mill again to form a stable and moderately viscous slurry; vacuum degassing treatment for the slurry, and then The sealing material can be obtained by casting and drying naturally at about 25° C. for a period of time.

The sealing material of the present invention requires uniform thickness, is convenient for cutting or punching according to the desired shape, and has good flexibility. Only when the sealing material has good flexibility, it is easy to achieve a tight fit with adjacent components under a small external pressure. Even if there is a certain roughness on the surface of the battery cell or the connecting body, the sealing material can deform and adapt to it. , so as to ensure a good sealing effect.

The organic components in the sealing material of the present invention will be burned during the heating process, and all or most of the remaining ceramic particles will be gradually oxidized to form a stable ceramic phase, and the glass can also exist stably in the SOFC working environment. These characteristics determine their good chemical stability and electrical insulation in the working environment of SOFC.

The sealing material of the present invention cannot provide a completely airtight seal, and in order to achieve effective sealing, the size of the gas leakage channel in the material must be reduced as much as possible and the tortuosity of the gas leakage path must be increased. Therefore, the selected solid particles satisfy the closest packing as much as possible, and the size of the solid particles is reduced as much as possible. In addition, considering that the particles are reduced to a certain extent, such as below 0.5 μm, agglomeration is easy to occur, which affects the close packing of particles and brings difficulties to the dispersion process in the material preparation process. In the present invention, all or most of the solid particles have a size of micron or submicron level, wherein the solid particles with a size in the range of 0.5 to 6 μm account for more than 80% of the total mass of the solid particles; the solid particles can include larger average particle sizes and The average particle size is divided into two parts, so that the smaller particle size part can fill the gaps between the larger particle size part particles.

In order to further improve the reliability of material sealing, the present invention provides two basic approaches: (1) add metal micropowder, on the one hand utilize the reactive bonding of metal to connect several ceramic particles into interlocking particle chains or irregularly shaped particles On the other hand, there is a certain volume expansion when the metal is oxidized, which can block some air leakage channels, which is beneficial to improve the sealing effect of the material. However, considering that the addition of metal may affect the electrical insulation of the material, the ratio of the mass of metal micropowder to the total mass of solid particles should be less than 30%. (2) Add glass powder, because the selected glass will soften at the working temperature of SOFC, under the action of external pressure, ceramic particles can be embedded in the glass phase, which not only improves the fracture energy of the material, but also improves the compactness of the material, thus The reliability of material sealing can be improved. Considering that when the amount of glass powder added is too much, some problems that occur in glass-ceramic materials will also appear, so the quality of glass powder should be less than 35% in the total mass of solid particles.

The sealing sheet can be further pre-compressed prior to use in the SOFC stack. Since the pressure applied in the pre-compression step can reach more than tens of MPa, the density of the sealing sheet can be greatly improved. However, excessive pre-compression pressure may cause difficulties when the sealing sheet is removed from the press. The compression pressure is generally controlled at 5-30Mpa, and the pressure is maintained for 5-10 minutes.

The sealing effect of the sealing material of the present invention is closely related to the applied pressure, and generally the greater the applied pressure, the better the sealing effect. Under the condition of an external pressure of 150-700Kpa, the air leakage rate of the sealing material of the present invention is usually less than 0.1mL/min/cm, and the air leakage rate of the sealing material added with metal micropowder or glass micropowder will be lower. Since the ceramic particles are not sintered at the working temperature of the SOFC, the material can be slightly bent and will not break when it expands or contracts. Even when there is a thermal difference with adjacent components, the particles can slide against each other without compromising the effectiveness of the material seal.

The sealing material of the present invention has good chemical stability and electrical insulation, simple preparation method, and is suitable for industrial production; it is easy to assemble when used, can closely match with adjacent components under a small external pressure, and has good sealing performance, even with adjacent components. There is a certain thermal mismatch between components, and good sealing ability can also be maintained.

Description of drawings

Fig. 1 is a structural schematic diagram of a flat SOFC stack seal, showing the position of the sealing material of the present invention;

Fig. 2 is a scanning electron microscope photo at 2000 times after use of the sealing material composed of alumina particles with an average particle size of 3 μm;

Fig. 3 is the scanning electron microscope photograph under 2000 times after the sealing material that is made of the aluminum oxide particle that 80wt% average particle diameter is 3 μm and the aluminum powder of 20wt% average particle diameter is 1.5 μm is used;

Fig. 4 is a scanning electron micrograph at 2000 times after use of a sealing material composed of 80 wt% alumina particles with an average particle diameter of 3 μm and 20 wt% alumina ceramic fibers with an average diameter of 2 μm.

Detailed ways

See Tables 1-3 for the mass ratio of raw materials in Examples 1-20.

Table 1 The proportioning of ceramic particles, metal micropowder, organic binder and plasticizer

Note: The particle size of solid particles given in the table is the average particle size of solid particles.

Table 2 The proportioning of ceramic particles, metal micropowder, glass micropowder, organic binder and plasticizer

Note: The particle size of solid particles given in the table is the average particle size of solid particles.

*1 means that the glass here is BaO-Al ₂ O ₃ -CaO-SiO ₂ glass, which softens but does not condense at the working temperature of SOFC. The mass proportions of BaO, Al ₂ O ₃ , CaO and SiO ₂ are respectively 40.8%, 2.5%, 8.4% and 35.3%; without sodium oxide and potassium oxide.

Table 3 The proportioning of ceramic particles, ceramic fibers, metal micropowder, glass micropowder, organic binder and plasticizer

Note: The particle size of solid particles given in the table is the average particle size of solid particles. ^* 2 means that the glass here is BaO-B2O3-MgO-ZnO-SiO2 glass, which softens but does not condense at the working temperature of SOFC, and the mass proportions of BaO, B2O3, MgO, ZnO and SiO2 are 25.5%, 17.5% respectively %, 13.4%, 13.5% and 30.1%; without sodium oxide and potassium oxide.

In Examples 1-6, there are only solid particles, which are ceramic particles. The proportion of solid particles with a size ranging from 0.5 to 6 μm in the total mass of solid particles is greater than 80%. Wherein in embodiment 1～3, the solid particle of size less than 3 μ m scope accounts for the proportion of solid particle total mass ≥ 60%; Embodiment 3～6 the mass ratio of solid particle and organic binder+plasticizer is 100: 20～28 The large solid particle 60～80% of average size among the embodiment 4～6, the small solid particle 20～40% of average size, the large particle average size is more than 3 times of small particle average size.

In Examples 7-10, only solid particles are ceramic particles and metal fine powder. The proportion of solid particles with a size ranging from 0.5 to 6 μm in the total mass of solid particles is greater than 80%. Wherein embodiment 7,8 the ratio of the solid particle that size is less than 3 μ m scope accounts for solid particle total mass ≥ 60%; Among embodiment 9 and 10, the ratio of metal micropowder quality in solid particle total mass is 10～20%; Embodiment The average particle size of 8, 9 and 10 metal micropowders is smaller than the average particle size of ceramic particles.

In Examples 11-20, only solid particles are ceramic particles and glass powder, or ceramic particles, metal powder and glass powder. The proportion of solid particles with a size ranging from 0.5 to 6 μm in the total mass of solid particles is greater than 80%. Wherein the mass ratio of embodiment 15 solid particle and organic binder+plasticizer is 100: 20～28; The ratio of the quality of embodiment 16,17 glass micropowder in the total mass of solid particle is 10～25%; Embodiment The average particle size of 16, 17, 18 metal micropowder and glass micropowder is smaller than the average particle size of ceramic particles; embodiment 18, 19, 20 the ratio of the quality of glass micropowder+metal micropowder in the total mass of solid particles is 15～25%.

In Examples 21 to 28, solid particles and ceramic fibers were combined. Ceramic fibers with a diameter less than 3 μm account for more than 75% of the total mass of ceramic fibers. Example 24 The mass ratio of solid particles + ceramic fibers to organic binder + plasticizer is 100: 20-28; Examples 25-28 The percentage of ceramic fibers accounting for the total mass of solid particles and ceramic fibers is 10-15%; Examples 27 and 28 The ratio of the mass of glass micropowder+metal micropowder to the total mass of solid particles is 15-25%; the average particle size of the metal micropowder and glass micropowder in Examples 25-28 is smaller than the average particle size of ceramic particles.

Embodiment 29 Preparation of sealing material

According to the raw material ratio of Example 4 in Table 1, 70 g of Al ₂ O ₃ ceramic particles with an average particle size of 3 μm and 30 g of Al ₂ O ₃ ceramic particles with an average particle size of 0.6 μm were weighed, totaling 100 g. Add 300g of zirconia balls, 68ml of xylene/ethanol mixed solution and 2g of herring oil successively into the ball mill tank, then add a total of 100g of ceramic particles, and ball mill for 20 hours to fully disperse the raw materials, then add 8g of BBP, 9g of PVB and 8g of PAG, ball milled again for about 24 hours to form a stable, moderately viscous slurry. The slurry is degassed, then cast, and dried naturally for 24 hours to obtain the required sealing material.

The preparation of embodiment 30 sealing material

According to the raw material ratio of Example 23 in Table 3, weigh 65g of _Al2O3 ceramic particles with an average particle size of _2.5μm , 15g of _ZrO2 ceramic particles with an average particle size of 0.7μm, and 20g of _Al2O with a diameter of less than 2μm. ₃ Ceramic fiber, total amount 100g. Add 300g of zirconia balls, 76ml of xylene/ethanol mixed solution and 2g of herring oil in turn to the ball mill jar, then add 80g of ceramic granules and 10g of ceramic fibers, and then add the remaining 10g of ceramic fibers after ball milling for 3 hours, and continue ball milling for 17 hours. Fully disperse the raw materials, then add 11g BBP, 11g PMA and 12g PAG in sequence, and ball mill again for about 24 hours to form a stable and moderately viscous slurry. The slurry is degassed, then cast, and dried naturally for 24 hours to obtain the required sealing material.

Embodiment 31 The implementation of SOFC stack sealing, as shown in Figure 1:

The sealing material prepared in Example 4 in Table 1 was cut into sealing sheets of required size. Place the connector base 1 with gas channels on the first layer, lay the first layer of sealing sheet 2 on the position where the battery cell is to be placed, and put the battery cell 3 on it. The periphery of the battery cell is just pressed against this A second layer of sealing sheet 2 is laid on the periphery of the battery cell, and then a second layer of connector material 4 is placed, and a third layer of sealing material 2 is laid, and so on, to form a battery stack. Apply a pressure of 300Kpa on the outside of the cell stack perpendicular to the sealing surface, and heat up to the working temperature of the solid oxide fuel cell at a rate of 1°C/min to achieve the sealing of the cell stack.

Embodiment 32 The implementation of SOFC stack sealing, as shown in Figure 1:

The sealing material prepared in Example 23 was cut into sealing sheets of required size, pre-compressed on a hydraulic press at a pressure of 20 MPa, and stabilized for 10 minutes. Place the connector base 1 with gas channels on the first layer, lay the first layer of sealing sheet 2 on the position where the battery cell is to be placed, and put the battery cell 3 on it. The periphery of the battery cell is just pressed against this A second layer of sealing sheet 2 is laid on the periphery of the battery cell, and then a second layer of connector material 4 is placed, and a third layer of sealing material 2 is laid, and so on, to form a battery stack. Apply a pressure of 500Kpa on the outside of the cell stack perpendicular to the sealing surface, raise the temperature to 200°C at a rate of 2°C/min, keep it at 200°C for 1.5h, and then continue to heat up to the solid oxide fuel cell at a rate of 2°C/min The working temperature can realize the sealing of the battery stack.

Claims (6)

1. A sealing material for a solid oxide fuel cell, comprising solid particles, an organic binder and a plasticizer, and the mass ratio of the sum of the solid particles to the organic binder and the plasticizer is 100:20 ~40; the solid particles are a composition of ceramic particles and glass powder or a composition of ceramic particles, metal powder, and glass powder, and the ceramic particles are alumina, zirconia, titania or magnesia One or two of them; the metal micropowder is one or two of aluminum, titanium, magnesium or silicon, characterized in that: (1) The quality of the glass powder or the quality of the glass powder and the metal powder are 5 to 35% in the total mass of the solid particles; (2) the glass powder softens at the SOFC working temperature, but does not Coagulation, wherein the total content of sodium oxide and potassium oxide is less than 0.3%; (3) The proportion of solid particles with a size in the range of 0.5-6 μm to the total mass of solid particles is ≥80%. 2. The sealing material for solid oxide fuel cells as claimed in claim 1, wherein the solid particles are composed of two parts of solid particles with different average sizes, and the mass ratio is: 60-80% of the solid particles with a larger average size. %, 20-40% of solid particles with small average size, and the average size of large particles is more than 3 times the average size of small particles. 3. The sealing material for solid oxide fuel cell as claimed in claim 1 or 2, characterized in that: (1) the mass ratio of the sum of solid particles to organic binder and plasticizer is 100: 20 to 28; (2) The ratio of the quality of glass powder to the total mass of solid particles is 10 to 25%; the ratio of the mass of glass powder and metal powder to the total mass of solid particles is 15 to 25% %; (3) The proportion of solid particles with a size less than 3 μm in the total mass of solid particles is ≥60%. 4. The sealing material for solid oxide fuel cells according to claim 3, characterized in that: the average particle size of the metal fine powder and the glass fine powder is smaller than the average particle size of the ceramic particles. 5. The sealing method using the sealing material for solid oxide fuel cells according to claim 1 or 2, comprising: (1) material preparation step, cutting the sealing material into sealing sheets of required size; (2) assembling step, Spread the sealing sheet directly on the area that needs to be sealed in the battery stack, in the order of connector base, sealing sheet, battery cell, sealing sheet, connector, sealing sheet, battery cell, sealing sheet, connector, and so on By analogy, a battery stack is formed; (3) pressurization step, applying a pressure of 150 to 700 kPa to the outermost connector of the battery stack in the direction perpendicular to the sealing surface; (4) heating step, slowly raising the temperature of the assembled battery stack to Solid oxide fuel cell operating temperature, heating rate 1 ~ 3 ℃ / min. 6. The sealing method using the solid oxide fuel cell sealing material as claimed in claim 5, characterized in that (1) in the material preparation step, after being cut into sealing sheets, it is placed in a press for pre-compression, and the pressure is 5 ~ 30MPa, hold the pressure for 5 ~ 10min; (2) The assembly process is as follows: lay the first layer of sealing sheet on the connector base with gas channels, and lay the first layer of sealing sheet on the position where the battery cell is to be placed, and then put The battery cell, the periphery of the battery cell is pressed on this layer of sealing sheet, and then the second layer of sealing sheet is laid on the periphery of the battery cell, and then the second layer of connecting body is placed, and the third layer of sealing sheet is laid on it , and so on, to form a battery stack; (3) in the heating step, the heating rate is 1-1.5°C/min;

Images