A breathable sheet, an electrolyte membrane for fuel cells, a method for manufacturing a breathable sheet, and a method for manufacturing an electrolyte membrane for fuel cells.

Abstract

This allows for both improved mechanical strength and increased porosity. [Solution] The breathable sheet is formed by laminating multiple nonwoven fabrics 21 and 22. The nonwoven fabrics 21 and 22 are made of synthetic resin nanofibers and have orientation. The orientation directions of the nonwoven fabrics 21 and 22 are different from those of the other.

Description

Technical Field

[0001] The present invention relates to a breathable sheet, a fuel cell electrolyte membrane, a method for manufacturing a breathable sheet, and a method for manufacturing a fuel cell electrolyte membrane.

Background Art

[0002] A solid polymer fuel cell includes a fuel cell stack formed by stacking a plurality of single cells. A single cell includes a membrane electrode assembly composed of a solid polymer electrolyte membrane (hereinafter referred to as an electrolyte membrane) and a pair of catalyst layers sandwiching the electrolyte membrane, a pair of gas diffusion layers sandwiching the membrane electrode assembly, and an anode side separator and a cathode side separator sandwiching the pair of gas diffusion layers.

[0003] The electrolyte membrane includes a reinforcing layer that is a porous membrane and a polymer electrolyte impregnated in the reinforcing layer (see, for example, Patent Document 1). The reinforcing layer is, for example, stretched polytetrafluoroethylene (ePTFE). The polymer electrolyte is, for example, a perfluorosulfonic acid polymer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the reinforcing layer constituting the electrolyte membrane is made of ePTFE, while it has excellent mechanical strength, there is a trade-off in that the proton conductivity is low due to a low porosity. Therefore, in the reinforcing layer of the electrolyte membrane, it is required to achieve both an improvement in mechanical strength and an improvement in proton conductivity, in other words, an increase in porosity.

[0006] Furthermore, these problems are not limited to the reinforcing layer of electrolyte membranes for fuel cells; they also occur in the same way in the breathable sheets that make up the separators of secondary batteries such as lithium-ion batteries. [Means for solving the problem]

[0007] The breathable sheet for solving the above problems is a breathable sheet formed by laminating multiple nonwoven fabrics, wherein the nonwoven fabrics are made of synthetic resin nanofibers and have orientation, and the orientation directions of the nonwoven fabrics are different from those of the other.

[0008] In nonwoven fabrics with orientation, the mechanical strength is high in the orientation direction, while in the plane direction of the nonwoven fabric that is perpendicular to the orientation direction, the mechanical strength is lower compared to the orientation direction.

[0009] According to the above configuration, the breathable sheet is formed by laminating multiple nonwoven fabrics. Furthermore, the orientation directions of the nonwoven fabrics are different from each other. Therefore, the mechanical strength can be increased in multiple different directions of the breathable sheet's surface. In addition, since the nonwoven fabric is formed from nanofibers, it has a large porosity. Thus, it is possible to achieve both improved mechanical strength and increased porosity.

[0010] Furthermore, a method for manufacturing a breathable sheet to solve the above problems comprises: a base material forming step in which a solution containing synthetic resin is drawn from a spinning nozzle to which voltage is applied and stretched toward a collector rotating around a rotation axis by electrospinning to form a nonwoven fabric base material that is made of nanofibers and has orientation; a cutting step in which the nonwoven fabric base material is cut into a nonwoven fabric of a predetermined shape; and a lamination step in which a plurality of the nonwoven fabrics are laminated so that the orientation directions of the nonwoven fabrics are different from each other.

[0011] According to this method, in the raw material formation process, a nonwoven raw material is formed by rotating a collector around a rotation axis, thereby forming a nonwoven raw material made of nanofibers and oriented in the direction of the collector's rotation. Subsequently, in the cutting process, the nonwoven raw material is cut to obtain a nonwoven fabric of a predetermined shape. Subsequently, in the lamination process, multiple nonwoven fabrics are laminated so that the orientation directions of the nonwoven fabrics are different from each other to form a breathable sheet. Therefore, a breathable sheet that achieves both improved mechanical strength and increased porosity can be manufactured. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a perspective view of a breathable sheet constituting an electrolyte membrane for a fuel cell according to one embodiment. [Figure 2] Figure 2(a) is a plan view of the first nonwoven fabric that constitutes the breathable sheet in Figure 1, and Figure 2(b) is a plan view of the second nonwoven fabric that constitutes the breathable sheet in Figure 1. [Figure 3] Figure 3 is a flowchart showing the manufacturing procedure for an electrolyte membrane according to one embodiment. [Figure 4] Figure 4 is a perspective view showing the raw material formation process of one embodiment. [Figure 5] Figure 5 is a SEM image of a nonwoven fabric roll according to one embodiment. [Figure 6] Figure 6 shows an SEM image of the nonwoven fabric raw material of the comparative example. [Figure 7] Figure 7 is a perspective view of a nonwoven fabric roll. [Figure 8] Figure 8 is a plan view showing the lamination process of one embodiment. [Figure 9] Figure 9 is a graph showing the relationship between the elongation rate and strength of a breathable sheet. [Figure 10] Figure 10 is a graph showing the void ratio of each nonwoven fabric roll in this embodiment and comparative example. [Modes for carrying out the invention]

[0013] Hereinafter, an embodiment will be described with reference to FIGS. 1 to 10. <Electrolyte membrane 10> As shown in FIG. 1, the electrolyte membrane for a fuel cell (hereinafter, electrolyte membrane 10) includes a breathable sheet 20 and a polymer electrolyte (not shown in the figure) impregnated in the breathable sheet 20. The breathable sheet 20 functions as an electrolyte membrane reinforcing layer.

[0014] The polymer electrolyte is, for example, a perfluorosulfonic acid polymer. The breathable sheet 20 is formed by laminating a plurality of non-woven fabrics 21 and 22. The non-woven fabrics 21 and 22 are formed of synthetic resin nanofibers and have orientation. The orientation directions of the non-woven fabrics 21 and 22 are different from each other.

[0015] The non-woven fabrics 21 and 22 of the present embodiment are made of polyvinylidene fluoride (PVDF). The breathable sheet 20 of the present embodiment is composed of a first non-woven fabric 21 and a second non-woven fabric 22 whose orientation directions are different from each other.

[0016] The fiber diameter of the nanofibers constituting the non-woven fabrics 21 and 22 is preferably 200 nm or more and 1000 nm or less. The thickness of each of the non-woven fabrics 21 and 22 is preferably 2 μm or more and 10 μm or less. The thickness of each of the non-woven fabrics 21 and 22 of the present embodiment is 5 μm or more and 8 μm or less.

[0017] The thickness of the breathable sheet 20 is preferably 3 μm or more and 20 μm or less. The thickness of the breathable sheet 20 of the present embodiment is 15 μm. The air permeability of the breathable sheet 20 is preferably 0.1 s / 100 cc or less. In general, the air permeability of a porous membrane made of ePTFE used as a reinforcing layer of an electrolyte membrane is 400 s / 100 cc or more and 800 s / 100 cc.

[0018] Note that the breathable sheet 20 of the present embodiment is not pressed. As shown in Figures 2(a) and 2(b), the orientation direction of the first nonwoven fabric 21 is the left-right direction in Figure 2(a). The orientation direction of the second nonwoven fabric 22 is the up-down direction in Figure 2(b). In the breathable sheet 20 of this embodiment, the orientation direction of the first nonwoven fabric 21 and the orientation direction of the second nonwoven fabric 22 are orthogonal.

[0019] <Method for manufacturing electrolyte membrane 10> As shown in Figure 3, the method for manufacturing the electrolyte membrane 10 comprises a raw material formation step, a cutting step, a lamination step, and an impregnation step.

[0020] The raw material formation process is a process of forming a nonwoven raw material 80 that is formed from nanofibers and has orientation. As shown in Figure 4, the raw material shaping process involves drawing a solution containing synthetic resin from a voltage-applied spinning nozzle 90 toward a collector 91 that rotates around a rotation axis, and stretching it to form a nonwoven raw material 80 by electrospinning. In this embodiment, the stretching speed of the collector 91 is approximately 30 m / s.

[0021] In the raw material formation process, the collector 91 is rotated around its axis of rotation, thereby forming a nonwoven raw material 80 oriented in the direction of rotation of the collector 91. Figure 5 shows an SEM image of the nonwoven fabric base roll 80 of this embodiment.

[0022] As shown in Figure 5, the orientation direction of the nonwoven fabric roll 80 is the vertical direction in Figure 5. Figure 6 shows an SEM image of the nonwoven fabric base of the comparative example. The stretching speed of the collector 91 when forming the nonwoven fabric base of the comparative example is approximately 1 m / s.

[0023] As shown in Figure 6, the comparative example's nonwoven fabric base does not have orientation. The nonwoven fabric roll 80 is wound along the rotational direction of the collector 91. As shown in Figure 7, the orientation direction of the nonwoven fabric roll 80 is perpendicular to the winding direction MD of the nonwoven fabric roll 80, that is, the width direction TD.

[0024] The cutting process involves cutting the nonwoven fabric roll 80 into nonwoven fabrics 21 and 22 of a predetermined shape. As shown in Figure 8, the lamination process is a process of forming a breathable sheet 20 by laminating multiple nonwoven fabrics 21 and 22 such that the orientation directions of the nonwoven fabrics 21 and 22 are different from those of the other. In the lamination process of this embodiment, the first nonwoven fabric 21 and the second nonwoven fabric 22 are laminated. After the laminated nonwoven fabrics 21 and 22 are immersed in a solution containing water and ethanol and then dried, the fibers of the nonwoven fabrics 21 and 22 become entangled with each other. This makes it possible to integrate the two nonwoven fabrics 21 and 22, which repel each other due to their negative static charge, thus making the breathable sheet 20 easier to handle.

[0025] The impregnation process involves impregnating the breathable sheet 20 with a polymer electrolyte. In the impregnation process, the breathable sheet 20 is immersed in a liquid containing the polymer electrolyte, thereby impregnating the breathable sheet 20 with the polymer electrolyte.

[0026] Figure 9 shows the measurement results of the tensile test of the breathable sheet 20. The elongation (%) and strength (MPa) were measured while applying a tensile force to the breathable sheet 20 along the orientation direction of the first nonwoven fabric 21.

[0027] As shown by the solid line in Figure 9, in the breathable sheet 20, the tensile strength increased with increasing elongation, and when the elongation reached 150%, the tensile strength was approximately 40 MPa. When the elongation exceeded 150%, the tensile strength rapidly decreased to 2-3 MPa.

[0028] For comparison, the measurement results for nafion® are shown by a dashed line in Figure 9. nafion® is an electrolyte membrane containing a reinforcing layer made of ePTFE and a polymer electrolyte that is a perfluorosulfonic acid polymer.

[0029] In the breathable sheet 20, when the elongation rate exceeded 150%, the strength decreased sharply due to the rupture of the first nonwoven fabric 21, but the elongation rate increased as the unruptured second nonwoven fabric 22 stretched. Furthermore, the breathable sheet 20 has higher strength and a larger elongation rate compared to the comparative example.

[0030] Figure 10 shows the measurement results of the void ratio (%) of the nonwoven fabric raw material 80 of this embodiment and the nonwoven fabric raw material of the comparative example. As shown in Figure 10, the void ratio of the nonwoven fabric base roll 80 of this embodiment, formed by stretching at a stretching speed of approximately 30 m / s by the collector 91, was 87%.

[0031] On the other hand, the void ratio of the comparative example nonwoven fabric roll formed by stretching at a stretching speed of approximately 1 m / s with the collector 91 was 80%. The void ratio of the nonwoven fabric base 80 in this embodiment is higher than that of the nonwoven fabric base in the comparative example. This is thought to be due to a change in void ratio caused by differences in the fiber lamination state.

[0032] <Operation of this embodiment> In the orientation-oriented nonwoven fabrics 21 and 22, high mechanical strength is present in the orientation direction (winding direction MD), while lower mechanical strength is present in the direction perpendicular to the orientation direction (width direction TD) of the surface direction of the nonwoven fabrics 21 and 22 compared to the orientation direction.

[0033] The breathable sheet 20 is formed by laminating multiple nonwoven fabrics 21 and 22. Furthermore, the orientation directions of the nonwoven fabrics 21 and 22 are different from each other. Therefore, the mechanical strength of the breathable sheet 20 can be increased in multiple different directions within its surface. Additionally, since the nonwoven fabrics 21 and 22 are formed from nanofibers, they possess high breathability.

[0034] <Effects of this embodiment> (1) The breathable sheet 20 is formed by laminating multiple nonwoven fabrics 21 and 22. The nonwoven fabrics 21 and 22 are made of synthetic resin nanofibers and have orientation. The orientation directions of the nonwoven fabrics 21 and 22 are different from those of the other.

[0035] With this configuration, the effects of the above embodiment are achieved, making it possible to achieve both improved mechanical strength and increased porosity. (2) The orientation direction of the first nonwoven fabric 21 and the orientation direction of the second nonwoven fabric 22 are orthogonal.

[0036] This configuration makes it possible to increase the strength of the breathable sheet 20 in two mutually orthogonal directions within its planar orientation. (3) The electrolyte membrane 10 includes a breathable sheet 20 and a polymer electrolyte impregnated into the breathable sheet 20.

[0037] With this configuration, the electrolyte membrane 10 has high breathability because it includes a breathable sheet 20. Therefore, the proton conductivity of the electrolyte membrane 10 is improved and its electrical resistance is reduced. Furthermore, the strength of the electrolyte membrane 10 can be increased in multiple directions within its surface. Thus, both improved mechanical strength and improved proton conductivity can be achieved simultaneously.

[0038] (4) The method for manufacturing the breathable sheet 20 comprises a raw material formation step, a cutting step, and a lamination step. According to this method, in the raw material formation process, a nonwoven raw material 80 is formed by rotating the collector 91 around a rotation axis, which is made of nanofibers and oriented in the direction of rotation of the collector 91. Subsequently, in the cutting process, the nonwoven raw material 80 is cut to obtain nonwoven fabrics 21 and 22 of predetermined shapes. Subsequently, in the lamination process, multiple nonwoven fabrics 21 and 22 are laminated so that their orientation directions are different from each other to form a breathable sheet 20. Therefore, a breathable sheet 20 that achieves both improved mechanical strength and increased porosity can be manufactured.

[0039] (5) The method for manufacturing the electrolyte membrane 10 includes an impregnation step of impregnating the breathable sheet 20 with a polymer electrolyte. This method makes it possible to manufacture an electrolyte membrane 10 that achieves both improved mechanical strength and improved proton conductivity.

[0040] <Variation> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0041] The breathable sheet and its manufacturing method according to the present invention are not limited to an electrolyte membrane 10 for fuel cells and its manufacturing method. For example, the present invention can also be embodied as a separator for secondary batteries such as lithium-ion batteries and its manufacturing method.

[0042] The breathable sheet 20 only needs to have orientation directions of the first nonwoven fabric 21 and the second nonwoven fabric 22 that are different from each other, and they do not need to be orthogonal. The breathable sheet 20 may be formed by laminating three or more nonwoven fabrics. For example, when three nonwoven fabrics are layered, the orientation direction of the first nonwoven fabric 21 and the orientation direction of the second nonwoven fabric 22 may be orthogonal, and the orientation direction of the third nonwoven fabric may be different from both the orientation direction of the first nonwoven fabric 21 and the orientation direction of the second nonwoven fabric 22. In this case, the orientation direction of the third nonwoven fabric may be such that the angle it makes with respect to both the orientation direction of the first nonwoven fabric 21 and the orientation direction of the second nonwoven fabric 22 is 45 degrees.

[0043] The breathable sheet 20 may be pressed with a predetermined load to the extent that breathability is not impaired. [Explanation of Symbols]

[0044] 10...Electrolyte membrane 20…Breathable sheet 21...First nonwoven fabric 22…Second nonwoven fabric 80... Nonwoven fabric raw material 90... Spinning nozzle 91... Collector 92...Voltage application device

Claims

1. A breathable sheet formed by laminating multiple nonwoven fabrics, The aforementioned nonwoven fabric is formed from synthetic resin nanofibers and has orientation properties. The orientation directions of the aforementioned nonwoven fabrics are different from each other. Breathable sheet.

2. The plurality of nonwoven fabrics include a first nonwoven fabric and a second nonwoven fabric, The orientation direction of the first nonwoven fabric and the orientation direction of the second nonwoven fabric are perpendicular to each other. The breathable sheet according to claim 1.

3. The breathable sheet according to claim 1 or claim 2, The breathable sheet impregnated with a polymer electrolyte, Electrolyte membrane for fuel cells.

4. A raw material formation step in which a nonwoven raw material formed of nanofibers and having orientation is formed by drawing a solution containing synthetic resin from a spinning nozzle to which voltage is applied toward a collector that rotates around a rotation axis and stretching it by electrospinning, A cutting process for cutting the aforementioned nonwoven fabric roll into a nonwoven fabric of a predetermined shape, The process includes a lamination step of stacking a plurality of nonwoven fabrics such that the orientation directions of the nonwoven fabrics are different from each other. A method for manufacturing a breathable sheet.

5. The method for manufacturing a breathable sheet according to claim 4 comprises an impregnation step of impregnating the breathable sheet with a polymer electrolyte. A method for manufacturing electrolyte membranes for fuel cells.

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