JPS6228546B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cell separator made of a material that provides excellent performance when applied to phosphoric acid fuel cells. In a phosphoric acid fuel cell, a unit cell is constructed by arranging porous electrode plates carrying a platinum catalyst on both sides of an electrolyte layer holding phosphoric acid, and each unit cell is electrically connected via a separator. It is formed into a predetermined stack structure. The separator is
Depending on whether or not the fuel gas and oxidizing gas supply passages are attached to the porous electrode plate, the shape can be divided into flat plate or ribbed type, but this type has sufficient stability at the battery operating temperature (approximately 190°C). In addition, it is necessary to satisfy the functions of preventing gas permeation, being a medium for current passage, removing generated heat, and maintaining the battery structure, so materials must be heat resistant, chemical resistant, gas impermeable, and electrically conductive. Various properties such as thermal conductivity, mechanical strength, etc. are required. Conventionally, graphite materials have been considered useful as meeting the above-mentioned required characteristics, but they do not fully satisfy the characteristics. In other words, currently, the methods for manufacturing graphite materials for fuel cell cell separators include a method in which a graphite base material is impregnated with a thermosetting resin liquid such as phenol resin and cured (resin impregnation method), and a method in which carbon powder is injected into a phenol resin or vinylidene fluoride. A method of heat molding using a resin or the like as a binder (resin bonding method) is known. However, these methods have a fundamental drawback in that the resin used does not have sufficient heat and chemical resistance for the purpose, and the resin impregnation method has a high level of resistance even after repeated impregnation treatments. It is difficult to impart gas impermeability to carbon powder, and on the other hand, in the case of resin bonding, an amount of resin equivalent to approximately 20 to 30% of the carbon powder is required to impart gas impermeability. This caused a problem that led to a decrease in electrical conductivity. The present invention was developed after conducting a multifaceted study on the optimal material for a cell separator, and after confirming that glassy carbon satisfies all required properties. Glassy carbon refers to a carbonaceous material with an extremely dense and homogeneous macroscopic structure obtained by carbonizing furan resin, phenolic resin, or a mixed resin thereof, and is manufactured as a cell separator as follows. Ru. A liquid furan-based or phenol-based resin or a mixed resin thereof flows into a cylindrical centrifugal molding machine together with a fluid deformation-preventing mold release agent that does not cause a chemical reaction with the resin liquid and has a large specific gravity. The centrifugal molding machine has a smooth inner surface when obtaining a flat cell separator, and an inner surface having uneven stripes in the axial direction that are preset in consideration of carbonization shrinkage when obtaining a ribbed separator. Next, a rotational force is applied while heating to form a semi-hardened tubular resin body with a uniform wall thickness on the inner surface of the centrifugal molding machine. By appropriately changing the design of the diameter and length of the centrifugal molding machine and further adjusting the amount of resin liquid, the size, shape, wall thickness, etc. of the resulting tubular resin body can be changed arbitrarily. After the molded semi-hardened tubular resin body is released from the mold, it is opened by cutting it in the vertical direction, and is heated while being sandwiched between mirror-finished metal plates from above and below to complete curing. The cured resin plate is carbonized by a conventional method and further graphitized if necessary. The fuel cell separator obtained in this way is a plate-like body with a glass-like nonporous structure with extremely uniform dimensional accuracy, and has complete gas impermeability and excellent gas impermeability even at a wall thickness of about 1 mm. With electrical conductivity, thermal conductivity and mechanical strength,
Furthermore, since it has an integral carbonaceous structure with no intervening resinous parts, it has heat resistance and chemical resistance that could not be provided with graphite separators manufactured using conventional methods. As described above, the fuel cell separator made of the new material provided by the present invention satisfies all the material properties required for this purpose, so it is always stable without material deterioration even during long-term battery operation. Power generation performance is guaranteed. Example Using a centrifugal molding machine equipped with a steel cylindrical container with an inner diameter of 200 mm and a length of 680 mm, 2000 g of fluororesin oil [DaiFloil, manufactured by Daikin Industries, Ltd.] was injected into the cylindrical container as a mold release agent to prevent deformation. Next, 1300g of liquid furan resin [Hitafuran, manufactured by Hitachi Chemical Co., Ltd.]
A molding raw material mixed with 13 g of aniline sulfate was poured into the mold. While maintaining the cylindrical container at a temperature of 50℃
The raw resin was centrifugally molded into a semi-hardened state by rotating at a rotational speed of 3200 rpm for 1.5 hours. After the molded tubular semi-cured resin product was released from the cylindrical container, it was cut open in the longitudinal direction, expanded, and held between stainless steel flat plates and heated at 50°C and 70°C under a pressure of approximately 0.1 kg/ ^cm2.
C. and 90.degree. C. for 48 hours each to complete curing. The cured resin body was fired and carbonized at a temperature of 1000°C in an inert air stream to obtain a flat glass-like carbon having a length of 500 mm, a width of 450 mm, and a wall thickness of 2.0 mm. The obtained flat glass-like carbon had a mirror-like surface with a uniform wall thickness exhibiting the characteristics shown in the table below, and the overall thickness variation was 0.02 mm.

[Table] Each property value in the table above fully satisfies the material properties required for fuel cell separators.
In particular, properties such as gas impermeability in thin walls, excellent heat resistance, and chemical resistance cannot be imparted by conventional resin impregnation and resin bonding methods. This cell separator is used to construct a phosphoric acid fuel cell, and the operating temperature is 190℃, per unit area.
When discharged at 200mA for 1000 hours, no deterioration of the separator material was observed, and the device operated stably with almost no voltage drop.

Claims (1)

[Claims] 1. A fuel cell separator characterized by being composed of glassy carbon.