JPH0221569A - Manufacture of carbon composite member for fuel cell - Google Patents

Abstract

PURPOSE:To increase heat-cycle resistance by forming green precursors of an electrode base, a separator base. and side seal bases, by stacking each green precursor in a specified shape, and by hot-pressing, completely curing, then carbonizing. CONSTITUTION:The green precursor of an electrolyte base 2 is formed by impregnating a solution of thermoset resin whose carbon residual rate is 45% or more in an alpha-cellulose sheet having a porosity of 70% or more and semicuring. Green precursors of a separator base 1 and side seal bases 3 are formed by impregnating a solution of thermoset resin whose carbon residual rate is 45% or more in each of an alpha-cellulose sheet having a porosity of 60% or less, then by semicuring them. Each green precursor of the electrode base 2, separator base 1, and side seal base 3 is stacked in a specified cell shape, hot-pressed, and completely cured, then baked and carbonized in a nonoxidizing atmosphere at 1000 deg.C or higher. Generation of defect such as boundary separation is prevented and heat-cycle resistance is increased.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a carbonaceous composite member for fuel cells, which is formed by integrally forming a porous electrode plate and a dense separator plate made of a carbonaceous material. Regarding the manufacturing method.

[Conventional technology]

Carbonaceous materials that meet required properties such as heat resistance, chemical resistance, good electrical conductivity, and ease of processing are useful for members such as electrode plates and separator plates that constitute fuel cells.

However, carbonaceous materials inherently have low mechanical strength and may break during handling or cell assembly. Recently, in order to reduce the resistance and stack thickness, the electrode plate is approximately 211111%, and the separator plate is 0.2 to 0.
．． The wall thickness is becoming thinner to about 4+a+*, and the degree of damage tends to further increase. In addition, in the conventional method of laminating electrode plates and separator plates, it is difficult to obtain sufficiently uniform close contact between both surfaces, so there is a limit to the reduction in battery internal resistance.

In order to eliminate such inconveniences, improve mechanical strength, reduce electrical and thermal resistance, and simplify cell assembly,
Attempts are rapidly being made to form a composite structure by integrally forming both the electrode plate and the separator plate in advance.

The simplest and most practical means for manufacturing such a composite member is to use an electrode base material and a separator as disclosed in Japanese Unexamined Patent Publication No. 60-2047L, Japanese Utility Model Application No. 60-15759, etc. This is a bonding firing method in which the base material is bonded with an adhesive and then fired.

[Problem to be solved by the invention]

The above bonding and firing methods include a method in which each carbonized carbon electrode plate and a carbonaceous separator plate are joined and fired, and a method in which the electrode plate and separator plate, which are in the green precursor stage before firing, are joined and fired. However, compared to the former method, the latter method is advantageous in that only one sintering and carbonization step is required and the bonding strength is increased.

However, when adopting the latter bonding method at the green precursor stage, if there is a large shrinkage difference between the combined electrode material and separator plate during the firing stage, interfacial peeling, warping, and cracking of the member may occur due to heat cycles during firing or in the practical process. Defect phenomena such as these occur. This tendency becomes more pronounced as the size of the member increases, and is therefore a major bottleneck in practical use.

Moreover, when using this method, it is extremely difficult to reduce the thickness of the separator base material to the current required unit (0.2 to 0.4 inch thickness), and it takes a lot of man-hours to mold the separator base material. There were also problems in terms of productivity and cost.

The present invention was made to solve the above problems,
The present invention provides a method for manufacturing a carbonaceous composite member for a fuel cell, which does not cause defective phenomena such as interfacial peeling during firing or in practical use, and allows the thickness of a separator base material to be extremely thin.

[Means to solve the problem]

That is, the method for manufacturing a carbonaceous composite member for fuel cells according to the present invention is a carbonaceous composite member made of α-cellulose with a porosity of 70.
% or more sheet with a thermosetting resin solution having a residual carbon content of 45% or more, and then semi-curing to form a green precursor for the electrode base material; impregnating the sheet with a thermosetting resin solution having a residual carbon content of 45% or more and semi-curing to form a green precursor of a separator base material and a side seal base material;
The green precursors of the electrode base material, separator base material, and side seal base material were laminated into a predetermined cell shape and bonded under heat and pressure, and then completely cured, and then heated for 100 minutes in a non-oxidizing atmosphere.
The structural feature is that it consists of a step of firing and carbonizing in a temperature range of 0° C. or higher.

(1) Formation step of electrode base material α-cellulose is a cellulose that is insoluble in a 17.5% sodium hydroxide solution, and for the purpose of the present invention, dissolving pulp for paper manufacturing is preferably used. After dispersing this α-cellulose in water, it is formed into a sheet using a papermaking method.

At this time, the dispersion concentration is adjusted to form a dense sheet with a porosity of 70% or more.

When the porosity drops below 70%, it becomes impossible to obtain the porous structure required as an electrode base material.

More preferably, the content of α-cellulose constituting the sheet is 60% or more, and the average pore diameter is 60 to 200 u.
This adjustment of properties makes it possible to form a homogeneous porous structure.

After drying, the cellulose sheets are laminated to a predetermined thickness if necessary, and impregnated with a thermosetting resin solution having a residual carbon content of 45% or more. The residual carbon percentage refers to the weight percent of carbon remaining when the resin is fired at a temperature of 1000°C in a non-oxidizing atmosphere, and if this is less than 45%, the strength of the resulting electrode base material will be reduced to a practical level. It is extremely difficult to improve this level. Examples of this type of thermosetting resin having a residual carbon content of 45% or more include phenol formaldehyde,
Examples include furfuryl alcohol and divinylbenzene, all of which can be effectively used for this purpose. The thermosetting resin is converted into a solution by dissolving the resin in a commonly used organic solvent such as alcohol or acetone, and the resin concentration of the solution is preferably set to 5 to 20% by weight. The reason for this is that if the resin concentration falls below 5% by weight, the strength properties will deteriorate, and if it exceeds 20% by weight, the pores will be blocked.

The impregnation treatment is carried out by immersing the cellulose sheet in a thermosetting resin solution, or by applying or spraying the thermosetting resin solution onto the cellulose sheet.

After impregnation, the cellulose sheet is air-dried and then
Semi-cured by heating at low temperature for 5 minutes or more at 0°C,
Use as a green precursor for electrode base material.

(2) Formation process of separator base material and side seal base material In accordance with the formation process of electrode base material, α-
Forms a dense sheet of cellulose. When the porosity exceeds 60%, it becomes impossible to obtain a gas-impermeable tissue structure required for a separator base material and a side seal base material. Furthermore, the content of α-cellulose constituting the sheet is 80% or more, and the average pore diameter is 1 to 50%.
It is desirable to set it within a desired range, and by adjusting the properties in this way, a homogeneous dense structure can be formed.

The cellulose sheet is impregnated with a thermosetting resin solution with a residual carbon content of 45% or more by the same method as the electrode base material forming process, but in this case, the resin concentration of the solution is adjusted to make the tissue structure denser. It is preferable to increase the content to 30 to 60% by weight.

After impregnation, the cellulose sheet is air-dried and then
Low-temperature heating is performed at 0° C. for 5 minutes or more to keep it in a semi-cured state, and it is used as a green precursor for a separator base material and a side seal base material.

(3) Bonding and carbonization firing process The green precursors of the electrode base material, separator base material and side seal base material formed in the above two steps are placed in the center as shown in the figure, with the separator base material 1 at the center and the electrodes at the top and bottom. The base material 2 and side seals 3 are combined on both ends and laminated in a cell form.
Heat-pressure bonding is performed at a temperature of about 50 to 200°C and a pressure of 1 kg/c- or more. The composite green member after joining is 1
After complete hardening at a temperature range of 50 to 250°C, it is calcined and carbonized at 1000 to 2000°C in a non-oxidizing atmosphere by a conventional method, and further graphitized at a temperature of 3000°C if necessary.

The carbonaceous composite member thus obtained is processed into a predetermined size and shape to form a fuel cell.

[For production]

According to the present invention, a green precursor with a porous structure suitable as an electrode base material and a separator base material are obtained by impregnating two types of α-cellulose sheets with different texture properties with a thermosetting resin solution with a high residual carbon content. and a dense green precursor suitable for the side seal base material can be formed at the same time. Since the green precursors of these base materials are the same material, defects such as interfacial peeling, warping, and cracking of parts due to shrinkage differences do not occur during the firing carbonization stage after thermopressure bonding, and the resulting There is no possibility that the carbonaceous composite member will peel off due to the sheet cycle during practical use. Moreover, the thickness of the base material can be easily adjusted by changing the number of stacked α-cellulose sheets, and in particular, the separator base material can be made extremely thin to 0.4 m+s or less.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Example α-Cellulose sheet with cellulose content of 61%, porosity of 70%, and average pore diameter of LO5tH (1000 m in length and width)
m.

0.1 mm thick), and 30 sheets of this were laminated to form a sheet of phenolic resin (manufactured by Sumitomo Durez ■, PR940).
Impregnation treatment was performed by immersing it in a 5-layer ethanol solution. Then, the impregnated sheet was heated at 40°C in a blow dryer.
After air drying for 24 hours, dry at a temperature of 140℃ for 15 minutes.
The green precursor of the electrode base material was formed in a semi-cured state by processing for a minute.

In addition, a cellulose sheet (length and width 1000 squares, thickness O, Im+s) with an α-cellulose content of 85%, a porosity of 58%, and an average pore diameter of 5 μm was made, and five sheets of this were laminated and made of the same phenolic resin as above. It was impregnated by immersing it in a 40% by weight ethanol solution. Subsequently, it was air-dried at 40° C. for 24 hours, and then treated at 120° C. for 15 minutes to form a semi-cured separator base material green precursor.

At the same time, a green precursor for a side seal base material was formed under the same conditions as for the formation of the green precursor for a separator base material, except that 300 sheets each having a length of 1000 mm and a width of 80 mm were stacked.

The obtained green precursors were stacked in a cell shape as shown in the figure, and bonded together by hot pressing at a temperature of 150° C. and a pressure of 10 kg/c for 5 minutes.

The joined body was completely cured by heating at 180° C. for 1 hour in a blow dryer, then packed in an electric furnace maintained in a nitrogen atmosphere, and fired and carbonized at a temperature of 1300° C.

After the treatment, the carbon material was subjected to the specified processing, and the length and width were 700 mm, and the thickness was 3.5 mm (including the thickness of the separator base material, 0.3 mm).
) carbonaceous composite member for fuel cells was obtained.

The characteristics of this carbonaceous composite member are the apparent ratio TKO of the electrode base material.
, 51g/cc, porosity 60%, average pore diameter 51, and gas permeation rate of the separator base material is 10'cc/cd・m.
in, and all of them satisfied the required characteristics as materials. Furthermore, the strength of the joint (tensile strength measured by an autograph tester, the same applies hereinafter) is 96 kg/cj, and the electrical resistance of the relevant part (voltage drop method according to JIS R7202, the same applies hereinafter) is 170 x 10' Ω mark, and the resistance from room temperature to 25
A heat cycle test (the same applies hereinafter) in which the temperature was repeatedly raised and lowered by 0° C. was conducted, and it was confirmed that no peeling phenomenon occurred even after 1000 cycles.

Comparative Example 1 α-cellulose content 70%, porosity 62%, average pore diameter 40 μm as a base for electrode substrate green precursor
- Cellulose sheet and α-cellulose sheet with an α-cellulose content of 70%, a porosity of 70%, and an average pore diameter of 65 were used as the green precursor base for the separator base material and the side seal base material, and the same as in the example. Depending on the conditions, resin impregnation, bonding, and firing carbonization treatments were performed to obtain a carbonaceous composite member for fuel cells.

The characteristics of the carbonaceous composite member obtained in this way are that the apparent specific gravity of the electrode base material is 0.7 sr/cc, the porosity is 41%, the average pore diameter is 31%, and the gas permeation rate of the separator base material is 10 sr/cc.
-'cc/c4 e win, which did not meet the required characteristics for fuel cells.

Comparative Example 2 30 parts by weight of fine graphite powder with an average particle size of 5 μm and 70 parts by weight of phenol resin (manufactured by Sumitomo Durez ■, PR940) were kneaded in a kneader, and the mixture was kneaded using an extrusion press to form a mixture with a length of 150+.
It was extruded into a plate shape with a width of 20 hm and a thickness of 3 m+s.

After the extrusion molding, the plate-shaped body is further rolled and molded to a length and width of 800 mm.
A separator base material green precursor having a thickness of 0.8 mm was molded. This green plate-like body is extremely brittle and has zero after carbonization.
．． It was difficult to maintain a thickness of 4 mm or less.

Electrode base material green precursor formed as described above under the same conditions as in Example and Example 1
A carbonaceous composite member for a fuel cell was obtained by thermopressure bonding and firing carbonization in the same manner as above.

The obtained carbonaceous composite member has a thickness of 4.5 mm, the strength of the joint part is 52 kg/cd, and the electrical resistance of the convenient part is 2.
50XlO'Ω mouth, heat cycle test result is 50
A peeling phenomenon was observed at 0 cycles, and the properties were inferior to those of Examples.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to manufacture a carbonaceous composite member that satisfies the required characteristics for electrodes and separators in a short process and has excellent bonding strength and heat cycle resistance. It is extremely useful for batteries and secondary batteries such as chlorine-zinc batteries.

BRIEF DESCRIPTION OF THE DRAWINGS The figure is a perspective explanatory view showing a state in which green precursors of an electrode base material, a separator base material, and a side seal base material are joined into a cell shape in the present invention. 1... Separator base material 2... Electrode base material 3...
・Side seal patent applicant Tokai Carbon Co., Ltd.

Claims (1)

[Claims] 1. A sheet made of α-cellulose and having a porosity of 70% or more is impregnated with a thermosetting resin solution having a residual carbon content of 45% or more and then semi-cured to form a green precursor for an electrode base material. and a step of forming a porosity of 60 composed of α-cellulose.
% or less with a thermosetting resin solution having a residual carbon content of 45% or more and then semi-curing to form a green precursor for the separator base material and the side seal base material, and the electrode base material and separator base material. The green precursors of the material and the side seal base material are laminated into a predetermined cell shape, thermo-pressure bonded, completely cured, and then fired and carbonized in a non-oxidizing atmosphere at a temperature range of 1000°C or higher. A method for manufacturing a carbonaceous composite member for fuel cells, characterized by: 2. The carbon material for fuel cells according to claim 1, wherein the sheet made of α-cellulose and having a porosity of 70% or more has an α-cellulose content of 60% or more and an average pore diameter of 60 to 200 μm. Method for manufacturing composite parts. 3. The carbon material for fuel cells according to claim 1, wherein the sheet composed of α-cellulose and having a porosity of 60% or less has an α-cellulose content of 80% or more and an average pore diameter of 1 to 50 μm. Method for manufacturing composite parts.