Paste for Electrochemical Cells

Abstract

General formula ABO 3 Provided is an electrochemical cell paste that can sufficiently ensure the bonding property with an interconnector at a temperature lower than conventional temperatures while using a conductive powder having a perovskite-type crystal structure represented by the formula. 【Solution means】The electrochemical cell paste of the present invention is an electrochemical cell paste 1 for joining an air electrode 3 and an interconnector 8. This paste 1 contains a conductive powder having a perovskite-type crystal structure represented by the general formula ABO 3 a resin, a solvent, and an amine.

Description

Technical Field

[0001] The present invention relates to a paste for an electrochemical cell.

Background Art

[0002] Patent Document 1 discloses a conventional paste for an electrochemical cell. This paste for an electrochemical cell contains a conductive powder having a perovskite crystal structure represented by the general formula ABO 3 ethyl cellulose as a resin, and terpineol as a solvent. Specifically, the conductive powder is La 0.6 Sr 0.4 CoO 3 and La 0.9 Sr 0.1 CoO 3 Both the conductive powders, the resin, and the solvent are kneaded by a roll mill to obtain a paste for an electrochemical cell.

[0003] This paste for an electrochemical cell is applied between an air electrode and an interconnector, and is fired together with the air electrode and the interconnector to form an air electrode side joining member that joins the air electrode and the interconnector. Perovskite compounds such as the above lanthanum cobaltite-based materials, lanthanum manganite-based materials, and lanthanum titanate-based materials exhibit very high conductivity as oxides and are stable even in a high-temperature atmosphere, so they are widely used for members used in the high-temperature range.

[0004] The air electrode side interconnector, the air electrode side joining member, and the air electrode, together with an electrolyte, a fuel electrode, a fuel electrode side joining member, and a fuel electrode side interconnector, form a solid oxide fuel cell (SOFC: Solid Oxide Fuel Cell) or a solid oxide electrolysis cell (SOEC: Solid Oxide Electrolysis Cell). In an SOFC or an SOEC, the air electrode, the electrolyte, and the fuel electrode are formed of a plurality of cells, and the interconnector can be a separator provided between the cells. Thus, an SOFC or an SOEC generates electricity or performs electrolysis.

Prior Art Document

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, according to the test results of the inventors, in the case of the conventional paste for an electrochemical cell, unless the firing temperature is high, necking between the particles of the conductive powder does not occur, and sufficient bondability with the interconnector cannot be ensured. When the air electrode or the like is heated to a high temperature, there is a concern that the air electrode or the like may be damaged, and the power generation performance and the electrolysis performance in SOFC or SOEC may deteriorate. In addition, excessive heating at a high temperature consumes a large amount of energy.

[0007] 3 An object of the present invention is to provide a paste for an electrochemical cell that can sufficiently ensure bondability with an interconnector at a temperature lower than that of the prior art while using a conductive powder having a perovskite crystal structure represented by the general formula ABO

Means for Solving the Problems

[0008] The paste for an electrochemical cell of the present invention is a paste for an electrochemical cell for joining an air electrode and an interconnector, and is characterized by containing a conductive powder having a perovskite crystal structure represented by the general formula ABO 3 , a resin, a solvent, and an amine.

[0009] In the test results of the inventors, the paste for an electrochemical cell of the present invention can neck the particles of the conductive powder at a temperature lower than that of the prior art during firing by containing an amine, and can sufficiently ensure bondability with the interconnector at a temperature lower than that of the prior art.

[0010] The inventor considers the reason as follows. (1) The A / B ratio of the conductive powder with a perovskite crystal structure changes depending on the presence or absence of amine addition. When comparing the A / B ratio before firing and the A / B ratio after firing of the conductive powder, the A / B ratio increases after firing, but the increase in the A / B ratio is suppressed by adding an amine. That is, the conductive powder has a perovskite crystal structure represented by the general formula ABO 3 As shown in FIG. 1, this perovskite crystal structure has a cubic unit cell, with a metal RE at each vertex of the cube, a metal M at the body center, and oxygen O located at the center of each face of the cube with the metal M as the center. According to the test results of the inventor, the volatilization of the metal M at the B site is suppressed during firing. The volatilization of the metal M is considered to be mainly due to the volatilization of the ions of the metal M eluted into the paste during firing. When an amine is added to the paste, the elution of the ions of the metal M is suppressed, and as a result, the volatilization of the ions of the metal M during firing is suppressed.

[0011] (2) Amine suppresses the elution of metal M ions. It is considered that amine molecules are adsorbed on the surface of the oxide with a perovskite crystal structure, and the lone pair electrons of the nitrogen atoms of the molecules are given to the metal M at the B site in the oxide. Therefore, a negative charge is given to the oxide, and as a result, it is considered that the ions of the metal M, which are cations, are less likely to elute (separate).

[0012] (3) As a result, the bonding property is improved. As described above, the amine suppresses the elution of the metal M ions and, as a result, suppresses the volatilization during firing. The eluted metal M ions and their volatilization are considered to inhibit the formation of necking during firing. By adding an amine, the inhibitory factor of this necking is reduced, and it is considered that the bonding property is improved because the necking progresses more easily.

Advantages of the Invention

[0013] According to the paste for an electrochemical cell of the present invention, the bonding property with an interconnector can be sufficiently ensured at a temperature lower than before. Therefore, it is sufficient to heat the air electrode or the like at a temperature lower than before, preventing or suppressing damage to the air electrode or the like, and improvement in power generation performance and electrolysis performance in SOFCs and SOECs can be expected. Further, in this case, energy consumption can be reduced.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0015] As the air electrode (cathode, oxygen electrode), (LaSr)MnO 3 , (LaCa)MnO 3 -represented lanthanum manganate (LaMnO 3 ), LaCoO 3 , (LaSr)CoO 3 , (LaSr)(CoFe)O 3 , etc., represented lanthanum cobaltate systems, (LaSr)(TiFe)O 3 , etc., represented lanthanum titanate systems, etc., can be a porous conductive material having a perovskite crystal structure.

[0016] The interconnector can be ferritic stainless steel. Ferritic stainless steel has a relatively low electrical resistance and a small coefficient of thermal expansion compared to austenitic stainless steel. The coefficient of thermal expansion (CTE: coefficient of thermal expansion) of ferritic stainless steel is generally 7 to 12×10 -6 / K. Such a ferrite stainless steel is an iron-chromium alloy (Fe-Cr alloy) containing about 12% or more of Cr, typified by SUS403. Since this alloy material has good thermal conductivity and mechanical strength, it can also be expected to play a role in alleviating the temperature gradient within the cell. It should be noted that it has been pointed out that the interconnect has problems with chemical stability. That is, in SOFC stacks and SOEC stacks using interconnects, chromium vapor can be generated at the operating temperature, so the problem of chromium poisoning of the air electrode cannot be separated. For example, Cr 2 O 3 film and the air electrode is considered to be the cause of performance degradation of SOFCs and SOECs. 4

[0017] The conductive powder has a perovskite crystal structure represented by the general formula ABO 3 . According to the inventor's findings, the conductive powder can be a lanthanum-based perovskite oxide represented by 1-x1 La 1 x1 RE 3 CoO ...(1) Here, in formula (1), RE 1 represents a first chromium-supplementary element which is at least one of Sr and Ba, and x1 represents the ratio of the first chromium-supplementary element among La and the first chromium-supplementary element occupying the A site of the perovskite crystal structure, and 0.4 ≦ x1 ≦ 0.8 can be satisfied.

[0018] Also, according to the inventor's findings, the conductive powder can be a lanthanum-based perovskite oxide represented by 1-x1 La 1 x1 RE y1 Co 1 1-y1 M 3 O ...(2) Here, in formula (2), RE 1 ​represents a first chromium-supplementary element which is at least one of Sr and Ba, M 1 represents a transition metal element which is at least one of Ti, Mn, Fe, Ni and Cu, x1 represents the ratio of the first chromium-supplementary element among La and the first chromium-supplementary element occupying the A site of the perovskite crystal structure, and 0.4 ≦ x1 ≦ 0.8, y1 may represent the ratio of the transition metal element among Co and the transition metal element occupying the B site of the perovskite crystal structure.

[0019] For example, (1) lanthanum cobaltite-based materials such as LaCoO 3 , (LaSr)CoO 3 , (LaSr)(CoFe)O 3 and the like, (2) lanthanum manganate-based materials such as (LaSr)MnO 3 , (LaCa)MnO 3 and the like, (3) lanthanum titanate-based materials such as (LaSr)(TiFe)O 3 and the like can be mentioned. Among them, from the viewpoint of enhancing conductivity, lanthanum cobaltite-based materials are preferred, and La 0.6 Sr 0.4 CoO 3-δ is particularly preferred. The inventor confirmed the effects of the present invention when the conductive powder is La 0.6 Sr 0.4 CoO 3 .

[0020] Also, the particle size of the conductive powder is preferably 10 μm or less. When it is 10 μm or more, the smoothness of the printed film when printing the paste decreases, which becomes a factor for reducing the bonding property. The lower limit of the particle size is not particularly limited, but from the viewpoint of workability, 0.1 μm or more is preferred.

[0021] As the resin, substances generally used as paste components can be used. For example, cellulose resins, butyral resins, acrylic resins, epoxy resins, phenolic resins, ethylene resins, amide resins, etc. can be mentioned. The resin may be any resin that can impart good viscosity and film-forming ability (including, for example, printability, adhesiveness to a substrate, etc.) for preparing the paste, and those conventionally used in this type of paste can be used without particular limitation. Among these, it is particularly preferable that cellulose-based polymers such as ethyl cellulose are included.

[0022] As the solvent, any solvent can be used without particular limitation as long as it can dissolve the above resin and can preferably disperse the conductive powder. For example, from the viewpoints of workability during film formation and storage stability, it is preferable to use a high-boiling organic solvent having a boiling point of generally 200°C or higher, for example, 200 to 300°C as the main component. Specific examples of the high-boiling organic solvent include alcohol solvents such as terpineol, menthanol, texanol, dihydroterpineol, benzyl alcohol, ester solvents such as 2,2,4-trimethyl-1,3-pentanediol-1-monoisobutyrate, isobornyl acetate, glycol ether solvents such as ethyl diglycol acetate, butyl glycol acetate, butyl diglycol acetate, butyl cellosolve acetate, butyl carbitol acetate, butyl carbitol, hydrocarbon solvents such as toluene, xylene, and mineral spirit.

[0023] Amine is a general term for compounds in which a hydrogen atom of ammonia is substituted with a hydrocarbon group or an aromatic group. In the present invention, amino groups (-NH-, -NH 2For compounds having -NHR or -NRR'), various amines can be employed. For example, primary amines and secondary amines with a molecular weight of 500 or less can be used. Examples of primary amines include n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, oleylamine, and the like. Examples of secondary amines include dibutylamine, diisoamylamine, dioctylamine, di(2-ethylhexyl)amine, and the like. The inventor has confirmed that the effects of the present invention can be obtained if the amine is at least one of di(2-ethylhexyl)amine, 2-ethylhexylamine, and oleylamine.

[0024] In the paste for an electrochemical cell of the present invention, a dispersant can be added to disperse the conductive powder. As the dispersant, one type can be used alone or two or more types can be appropriately combined from among those conventionally known. As an example, acid value dispersants such as carboxylic acid-based dispersants having a carboxyl group, phosphoric acid-based dispersants having a phosphonic acid group, and sulfonic acid-based dispersants having a sulfonic acid group can be mentioned. Among them, it is preferable to contain a carboxylic acid-based dispersant.

[0025] In addition, surfactants, leveling agents, wetting agents, defoaming agents, antistatic agents, gelation inhibitors, plasticizers, stabilizers, antioxidants, preservatives, colorants (pigments, dyes), pH adjusters, etc. can be added to the paste for an electrochemical cell of the present invention.

[0026] The electrolyte of SOFC or SOEC is composed of a dense thin layer made of an oxygen ion conducting material. Examples of oxygen ion conducting materials include zirconia stabilized with a stabilizer such as yttria (e.g., YSZ: Yttria stabilized zirconia), ceria doped with a dopant such as gadolinia (e.g., GDC: Gadolinia doped ceria), lanthanum gallate (LaGaO 3 ) and the like.

[0027] As fuel electrodes (anodes, hydrogen electrodes) for SOFCs and SOECs, nickel-based metal materials (e.g., Ni or NiO), and cermets of nickel-based metal materials and solid electrolyte materials (e.g., yttria-stabilized zirconia) are exemplified.

[0028] <Test 1> Hereinafter, the present invention will be described with reference to samples. First, the following materials were prepared. (Conductive powder) La 0.6 Sr 0.4 CoO 3 (Average particle size: 1.5 μm) (Resin) Ethyl cellulose (Dispersant) Carboxylic acid-based dispersant (Solvent) Terpineol (Additive) Di(2-ethylhexyl)amine (secondary amine. The chemical formula is shown in Chemical Formula 1.)

[0029]

Chemical Formula

[0030] <Samples 1 and 2> Each material was mixed by hand at the mixing ratio (mass%) shown in Table 1, and the mixture was kneaded with a three-roll mill. Thus, pastes for Samples 1 and 2 were prepared.

[0031]

Table 1

[0032] <Adhesion evaluation> A 20 mm × 20 mm substrate made of SUS430 was prepared. Screen printing was performed on the substrate so that each paste of Samples 1 and 2 would be in a circular shape with a diameter of 17 mm.

[0033] Each substrate printed with the paste was left standing in a dryer at 120°C for 30 minutes to dry each paste. Thereafter, each substrate printed with the paste was fired in a firing furnace. The heating rate during firing was 100°C / hour. After reaching a firing temperature of 700°C or 800°C, it was held for 2 hours and then allowed to cool. Thus, the joining members of Samples 1 and 2 were obtained.

[0034] The joining property of each joining member was evaluated by the cross-cut method. That is, after making lattice-shaped cuts at 1-mm intervals with a cutter knife on both joining members, an adhesive tape was attached to each joining member. Then, the adhesive tape was peeled off from each joining member, and the area of the joining member adhering to the back surface of the adhesive tape after peeling from the substrate was evaluated as to what percentage (%) it was of the entire joining member.

[0035] If the ratio of the peeled area was 50% or less, the joining property was rated as ○, and if the ratio of the peeled area was more than 50%, the joining property was rated as ×. The smaller the ratio of the peeled area, the higher the joining property. Table 2 shows the relationship between the difference in firing temperature and the joining property in the joining members of Samples 1 and 2.

[0036]

Table 2

[0037] As shown in Table 2, for the joining member of Sample 1 where no amine was added to the paste, the evaluation of the joining property was × when the firing temperature was 700°C. However, for the joining member of Sample 2 where amine was added to the paste, the evaluation of the joining property was ○ even when the firing temperature was 700°C. Therefore, it can be seen that the joining temperature can be lowered by adding amine to the paste.

[0038] The A / B ratios of the joining members of Samples 1 and 2 after firing at 700°C are as shown in Table 3.

[0039]

Table 3

[0040] As shown in Table 3, the joint member of Sample 2 with an amine added to the paste has a smaller A / B ratio. That is, in the joint member of Sample 2, the deficiency of B sites is suppressed. For this reason, in the paste of Sample 2, the amine suppresses the elution of Co, which is a B-site element, into the paste, and it can be considered that the sintering suppression effect by the eluted Co is inhibited.

[0041] As shown in FIG. 2, each paste 1 is used as the air electrode side joint member 2 of an SOFC or an SOEC as follows. First, as shown in FIG. 2(A), a cell 7 composed of an air electrode 3, an electrolyte 4, and a fuel electrode 5, and an interconnector 8 are prepared. Each paste 1 is applied between the air electrode 3 of the cell 7 and the interconnector 7 as shown in FIG. 2(B). Then, as shown in FIG. 2(C), each paste 1 is fired together with the cell 7 and the interconnector 8, and each paste 1 is used as the air electrode side joint member 2 to join the air electrode 3 and the interconnector 8.

[0042] Stacks of SOFCs or SOECs in which a plurality of cells 7 are stacked are assembled as follows. As shown in FIG. 3, the interconnector 8 is used as an end separator 8a or an intermediate separator 8b. Only a first flow path 10a is formed on the back surface of the end separator 8a. A first flow path 10a and a second flow path 10b orthogonal to the first flow path 10a are formed on one surface of the intermediate separator 8b. Then, the end separator 8a, the air electrode side joint member 2, the cell 7, the fuel electrode side joint member 9, the intermediate separator 8b, the air electrode side joint member 2, the cell 7,..., the fuel electrode side joint member 9, and the end separator 8a are sequentially stacked to form a stack of an SOFC or an SOEC.

[0043] In an SOFC, air flows through the first flow path 10a and hydrogen flows through the second flow path 10b, so that oxygen and hydrogen react in each cell 7 to generate an electromotive force. Then, an electric current is obtained from the end separator 8a and the intermediate separator 8b. In an SOEC, water is electrolyzed in each cell when a voltage is applied to the end separator 8a and the intermediate separator 8b. Then, oxygen flows through the first flow path 10a and hydrogen flows through the second flow path 10b.

[0044] Therefore, if the paste 1 of Sample 2 is applied between the air electrode and the interconnector of an SOFC or an SOEC and fired to form the air electrode side joining member 2, the particles of the conductive powder can be necked at a lower temperature than before during firing, and sufficient joinability with the interconnector 8 can be ensured at a lower temperature than before. For this reason, it is sufficient to heat the air electrode 3 or the like at a lower temperature than before, damage to the air electrode 3 or the like can be prevented or suppressed, and an improvement in power generation performance and electrolysis performance in an SOFC or an SOEC can be expected. Also, in this case, energy consumption can be reduced.

[0045] <Test 2> To confirm the effects of other compounds having an amino group, 2-ethylhexylamine which is a primary amine (the chemical formula is shown in Chemical Formula 2) and oleylamine which is a primary amine (the chemical formula is shown in Chemical Formula 3) were prepared. Also, oleic acid (the chemical formula is shown in Chemical Formula 4) was prepared as a compound having a carboxylic acid group and approximating oleylamine. Further, the difference in effects depending on the addition amount of di(2-ethylhexyl)amine was confirmed.

[0046]

Chemical Formula

[0047]

Chemical Formula

[0048]

Chemical Formula

[0049] These were mixed by hand at the compounding ratios (mass %) shown in Tables 4 and 5, and pastes of Samples 1 to 8 were prepared in the same manner as in Test 1. Also, each of the pastes 1 to 8 was fired at 700°C in the same manner as in Test 1. Then, in the same manner as in Test 1, the A / B ratio of the joined member after firing was measured, and the joinability was evaluated by the cross-cut method.

[0050] In the evaluation of joinability, if the ratio of the peeled area was 40% or less, the joinability was rated as ◎; if the ratio of the peeled area exceeded 40% and was 50% or less, the joinability was rated as ○; and if the ratio of the peeled area was 50% or more, the joinability was rated as ×. These measurement results and evaluation results are also shown in Table 4.

[0051]

Table 4

[0052]

Table 5

[0053] From Table 4, it can be seen that when using di(2-ethylhexyl)amine, the effects of the present invention can be obtained by adding 0.1 to 5% by mass, and it is particularly preferable to add 0.5 to 5% by mass.

[0054] Also, if it has an amino group, whether it is 2-ethylhexylamine or oleylamine, the effects of the present invention can be obtained. There is not much difference in the effects between primary amines and secondary amines. On the other hand, it can be seen that oleic acid has a carboxylic acid group instead of an amino group, so the effects of the present invention cannot be obtained.

[0055] In the above, the present invention has been described with reference to the samples, but it goes without saying that the present invention is not limited to the above samples and can be appropriately modified and applied without departing from the gist thereof.

Industrial Applicability

[0056] The present invention can be used in SOFCs and SOECs.

Description of Reference Numerals

[0057] 3... air electrode 8, 8a, 8b... interconnects (8a, 8b... separators) 1... paste

Claims

1. A paste for electrochemical cells for joining an air electrode and an interconnector, comprising: General formula ABO 3 1. A paste for electrochemical cells comprising a conductive powder having a perovskite crystal structure represented by the formula (I) above, a resin, a solvent, and an amine.

2. The conductive powder is La 1-x1 R.E. 1 x1 CoO 3 …(1) is a lanthanide perovskite oxide represented by the formula: Here, in Equation 1 R.E. 1 represents a first chromium supplementary element, which is at least one of Sr and Ba; 2. The electrochemical cell paste according to claim 1, wherein x1 represents a ratio of the first chromium supplementary element to La and the first chromium supplementary element occupying the A site of the perovskite crystal structure, and 0.4≦x1≦0.

8.

3. The conductive powder is La 1-x1 R.E. 1 x1 Co y1 M 1 1-y1 O 3 …(2) is a lanthanide perovskite oxide represented by the formula: Here, in Equation 2 R.E. 1 represents a first chromium supplementary element, which is at least one of Sr and Ba; M 1 represents at least one transition metal element selected from the group consisting of Ti, Mn, Fe, Ni, and Cu; x1 represents a ratio of the first chromium supplementary element to La occupying the A site of the perovskite crystal structure and the first chromium supplementary element, and 0.4≦x1≦0.8; 2. The paste for electrochemical cells according to claim 1, wherein y1 represents a ratio of said transition metal element to Co and said transition metal element occupying the B site of the perovskite crystal structure.

4. The conductive powder is La 0.6 Sr 0.4 CoO 3 3. The paste for electrochemical cells according to claim 2,

5. 5. The paste for electrochemical cells according to claim 1, wherein the amine is at least one of di(2-ethylhexyl)amine, 2-ethylhexylamine, and oleylamine.

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