Method for manufacturing sodium-sulfur battery

Abstract

Provided is a method for manufacturing a sodium-sulfur battery with which it is possible to suppress local aggregation of sulfur during charging and suppress an increase in internal resistance and / or a decrease in capacity of the sodium-sulfur battery. The method for manufacturing a sodium-sulfur battery is for manufacturing a sodium-sulfur battery that is provided with an electrically conductive material 30 that is impregnated with sulfur as the positive electrode active material, wherein the electrically conductive material 30 is obtained by driving glass fiber felt into graphite fiber felt, the method comprising an inspection step (step S1) for dividing the surface of the electrically conductive material 30 into a plurality of regions A1, and inspecting whether the luminance value of each of the plurality of regions A1 falls within a predetermined range.

Description

Method for manufacturing a sodium-sulfur battery

[0001] The present invention relates to a method for manufacturing a sodium-sulfur battery for manufacturing a sodium-sulfur battery provided with a conductive material impregnated with sulfur as a positive electrode active material.

[0002] As a method for manufacturing this type of sodium-sulfur battery that has been conventionally used, for example, the configurations shown in Patent Document 1 below can be cited. In Cited Document 1, “A felt-like base material made of carbon fiber or graphite fiber is prepared, and a cloth-like body or a cotton-like body made of glass fiber is stacked on one surface of the base material, and the cloth-like body or the cotton-like body is needle-punched into the base material. A method for manufacturing a positive electrode current collector that forms a high-resistance layer, wherein when the relative value of the total reflected light intensity on the surface of the cloth-like body or the cotton-like body stacked on the base material is set to 100, the needle punching is performed so that the relative value of the total reflected light intensity on the surface of the high-resistance layer becomes 25 to 43. is disclosed. Paragraph 0026 of Patent Document 1 explains that the “relative value of the total reflected light intensity” on the surface of the high-resistance layer is measured by irradiating the surface of the high-resistance layer with a light beam (such as a high-frequency fluorescent lamp), receiving the reflected light with a CCD camera, and converting the relative intensity of the reflected light into electrical energy.

[0003] Japanese Patent Application Laid-Open No. 2003-100303

[0004] In the conventional method as described above, the luminance on the surface of the conductive material (high-resistance layer) is measured as an alternative characteristic of the resistance value for each conductive material, and the needle punching is controlled using the luminance. However, variations in luminance within one conductive material are not considered.

[0005] In conductive materials (high-resistance layers), areas containing glass fibers have high resistance and low electron conductivity, resulting in a large amount of sodium polysulfide remaining. This function delays sulfur aggregation during the charging of sodium-sulfur batteries. However, glass fiber felt is not perfectly homogeneous, and even under the same conditions, variations in the amount of glass fibers occur in different regions within a single conductive material. In areas with fewer glass fibers, sulfur aggregates prematurely. Areas where sulfur aggregates are not used for charging and discharging, leading to an increase in the internal resistance and / or a decrease in the capacity of the sodium-sulfur battery.

[0006] The present invention was made to solve the above-mentioned problems, and one of its objectives is to provide a method for manufacturing a sodium-sulfur battery that can suppress localized sulfur aggregation during charging and suppress the increase in internal resistance and / or decrease in capacity of the sodium-sulfur battery.

[0007] <1> In one embodiment, the present invention relates to a method for manufacturing a sodium-sulfur battery, which is equipped with a conductive material impregnated with sulfur as a positive electrode active material, wherein the conductive material is made of graphite fiber felt with glass fiber felt embedded in it, and the method for manufacturing a sodium-sulfur battery includes an inspection step of dividing the surface of the conductive material into a plurality of regions and checking whether the brightness value of each of the plurality of regions falls within a predetermined range.

[0008] <2> The present invention further includes a manufacturing step of creating a conductive material base by embedding glass fiber felt into graphite fiber felt, and a cutting step of obtaining a plurality of conductive materials by cutting the conductive material base in the longitudinal and width directions, wherein the inspection step is performed after the cutting step and relates to the method for manufacturing a sodium-sulfur battery as described in paragraph 1.

[0009] <3> The present invention may further include a method for manufacturing a sodium-sulfur battery as described in paragraph 2, which is performed after the manufacturing step and before the cutting step, and further includes a material verification step in which the surface of the conductive material body is divided into a plurality of material regions, and whether or not the brightness value of each of the plurality of material regions falls within a predetermined range.

[0010] <4> The present invention relates to a method for manufacturing a sodium-sulfur battery as described in paragraph 3, wherein the manufacturing step includes inserting and removing the needles of a first needle punch into the graphite fiber felt and the glass fiber felt which are stacked on top of each other, and then inserting and removing the needles of a second needle punch, and acquiring the brightness value of the conductive material after inserting and removing the needles of the first needle punch and before inserting and removing the needles of the second needle punch, and in the manufacturing step, the insertion and removal of the needles of the second needle punch is controlled based on the brightness value of the conductive material acquired before inserting and removing the needles of the second needle punch.

[0011] <5> The present invention may relate to a method for manufacturing a sodium-sulfur battery according to any one of the first to fourth paragraphs, wherein the inspection step checks whether (1) the average value of the brightness values ​​for each of the plurality of regions of the conductive material is within a predetermined range, (2) whether the minimum value of the brightness values ​​for each of the plurality of regions of the conductive material is greater than or equal to a predetermined value, and (3) whether the difference between the minimum and maximum values ​​of the brightness values ​​for each of the plurality of regions of the conductive material is less than or equal to a predetermined value.

[0012] According to one embodiment of the method for manufacturing a sodium-sulfur battery of the present invention, the surface of a conductive material is divided into multiple regions, and the brightness value of each region is checked to see if it falls within a predetermined range. This makes it possible to suppress localized sulfur aggregation during charging and to suppress an increase in the internal resistance and / or a decrease in the capacity of the sodium-sulfur battery.

[0013] This is a cross-sectional view of a sodium-sulfur battery manufactured by the sodium-sulfur battery manufacturing method according to an embodiment of the present invention. This is an exploded perspective view showing a part of the sodium-sulfur battery in Figure 1. This is a schematic explanatory diagram showing the inspection process included in the sodium-sulfur battery manufacturing method according to an embodiment of the present invention. This is a plan view showing the conductive material in Figure 3. This is a flowchart showing the sodium-sulfur battery manufacturing method according to an embodiment of the present invention. This is a schematic explanatory diagram showing the fabrication process in Figure 5. This is a schematic explanatory diagram showing the material verification process in Figure 5. This is a schematic explanatory diagram showing the cutting process in Figure 5.

[0014] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and can be materialized by modifying the components without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in each embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components from different embodiments may be appropriately combined.

[0015] <About Sodium-Sulfur Batteries> Figure 1 is a cross-sectional view of a sodium-sulfur battery 1000 manufactured by the manufacturing method of a sodium-sulfur battery 1000 according to an embodiment of the present invention, and Figure 2 is an exploded perspective view showing a part of the sodium-sulfur battery 1000 of Figure 1 disassembled. Note that in Figure 2, some of the components are shown in cross-section.

[0016] The method for manufacturing a sodium-sulfur battery 1000 according to an embodiment of the present invention is for manufacturing a sodium-sulfur battery 1000 as shown in Figures 1 and 2. As shown in Figures 1 and 2, the sodium-sulfur battery 1000 may include a positive electrode container 1001, a plurality of sulfur molds 1002, a β-alumina solid electrolyte tube 1003, a safety tube 1004, a sodium container 1005, sodium 1006, a positive electrode fitting 1007, an insulating ring 1008, and a negative electrode fitting 1009.

[0017] The positive electrode container 1001 is a bottomed cylindrical container. Multiple sulfur molds 1002 are housed inside this positive electrode container 1001. The sulfur molds 1002 are components of a predetermined shape, formed by impregnating a conductive material 30 (see Figure 3, etc.) with sulfur, which is the positive electrode active material. The conductive material 30 is made of graphite fiber felt 301 with glass fiber felt 302 embedded in it (see Figure 6, etc.). As is well known, the melting point of sulfur is 112.8°C, and the sulfur impregnated in the conductive material 30 remains solidified until the sodium-sulfur battery 1000 is started after its manufacture.

[0018] The sulfur mold 1002 may have a plurality of side molds 1002a and one bottom mold 1002b. As is particularly evident in Figure 2, the side molds 1002a may be longitudinal members with arc-shaped end faces. Figure 2 shows an example of a side mold 1002a that forms a cylindrical shape overall when three side molds 1002a are combined. The bottom mold 1002b may be a disc-shaped member. A β-alumina solid electrolyte tube 1003 may be placed inside the cylindrically arranged side molds 1002a, and the bottom mold 1002b may be placed at the bottom of the β-alumina solid electrolyte tube 1003.

[0019] The β-alumina solid electrolyte tube 1003 is a bottomed cylindrical container that has selective permeability to sodium ions and is positioned inside the positive electrode container 1001. A positive electrode space 1010 is formed between the positive electrode container 1001 and the β-alumina solid electrolyte tube 1003, in which molten sulfur is placed after the sodium-sulfur battery 1000 is started.

[0020] The safety tube 1004 is a bottomed cylindrical container. The sodium container 1005 is a bottomed and lidded cylindrical container. More specifically, the sodium container 1005 has a bottomed cylindrical container body 20 filled with sodium 1006 and a lid 21 attached to the container body 20. The safety tube 1004 is placed inside the β-alumina solid electrolyte tube 1003, and the sodium container 1005 is placed inside the safety tube 1004. The sodium container 1005 is positioned such that the bottom 20a of the container body 20 is facing upwards and the lid 21 is facing downwards. Due to this arrangement, the lid 21 may also be called a bottom lid.

[0021] A predetermined gap is provided between the inner surface of the β-alumina solid electrolyte tube 1003 and the outer surface of the safety tube 1004, and between the inner surface of the safety tube 1004 and the outer surface of the sodium container 1005. The sodium 1006 is contained inside the sodium container 1005. As is well known, the melting point of sodium 1006 is 97.79°C, and the sodium 1006 in the sodium container 1005 remains solidified until the sodium-sulfur battery 1000 is started after its manufacture.

[0022] The positive electrode fitting 1007 is attached to the top of the positive electrode container 1001. The insulating ring 1008 is an annular member made of an insulator and is attached to the top of the β-alumina solid electrolyte tube 1003 together with the negative electrode fitting 1009. Inside the β-alumina solid electrolyte tube 1003, the insulating ring 1008, and the negative electrode fitting 1009, a negative electrode space 1011 is formed where molten sodium 1006 is placed after the sodium-sulfur battery 1000 is started. The sodium container 1005 is placed in the negative electrode space 1011. The insulating ring 1008 may electrically insulate the molten sodium 1006 in the β-alumina solid electrolyte tube 1003, the negative electrode fitting 1009, and the negative electrode space 1011 from the positive electrode fitting 1007.

[0023] The sodium-sulfur battery 1000 is a high-temperature operating secondary battery, and is heated to approximately 300°C when in use. When the sodium-sulfur battery 1000 is heated to approximately 300°C, the sulfur in the sulfur mold 1002 and the sodium 1006 in the sodium container 1005 melt. As shown in Figure 1, the sulfur mold 1002 and the sodium container 1005 are provided with an inert gas generating substance 1012, such as a tablet of sodium azide. When the sodium-sulfur battery 1000 is heated to approximately 300°C, an inert gas (such as nitrogen gas) is generated from the inert gas generating substance 1012.

[0024] Here, the lid 21 of the sodium container 1005 has a flow hole 22 formed therein for the molten sodium 1006 to flow in and out of the sodium container 1005. When the sodium-sulfur battery 1000 is heated to about 300°C, inert gas is generated from the inert gas generating material 1012 in the sodium container 1005. This increases the internal pressure of the sodium container 1005, and the molten sodium 1006 is placed in the negative electrode space 1011 through the flow hole 22.

[0025] The amount of gas generated from the inert gas generating material 1012 in the sulfur mold 1002 and the amount of gas generated from the inert gas generating material 1012 in the sodium container 1005 are set so that the internal pressure of the positive electrode space 1010 is greater than the internal pressure of the negative electrode space 1011. By creating this difference in internal pressure, even if damage occurs to the β-alumina solid electrolyte tube 1003, the molten sodium 1006 in the negative electrode space 1011 will not enter the positive electrode space 1010, and the molten sulfur in the positive electrode space 1010 will enter the sodium container 1005. When the molten sulfur in the positive electrode space 1010 enters the sodium container 1005 and reacts with the molten sodium 1006, reaction heat is generated. The safety tube 1004 has a greater coefficient of thermal expansion than the β-alumina solid electrolyte tube 1003. It expands more than the β-alumina solid electrolyte tube 1003 due to the heat of reaction between the molten sulfur and the molten sodium 1006, and can seal the damaged area of ​​the β-alumina solid electrolyte tube 1003. This limits the amount of reaction between the molten sulfur and the molten sodium 1006 when damage occurs to the β-alumina solid electrolyte tube 1003.

[0026] <Regarding the manufacturing method of a sodium-sulfur battery> The manufacturing method of a sodium-sulfur battery 1000 according to an embodiment of the present invention will be described below. Figure 3 is a schematic explanatory diagram showing the inspection process (step S1) included in the manufacturing method of a sodium-sulfur battery 1000 according to an embodiment of the present invention, and Figure 4 is a plan view showing the conductive material 30 in Figure 3.

[0027] The method for manufacturing a sodium-sulfur battery 1000 according to an embodiment of the present invention is for manufacturing a sodium-sulfur battery 1000 that includes a conductive material 30 impregnated with sulfur, which is a positive electrode active material, as described above.

[0028] As shown in Figures 3 and 4, the manufacturing method of this embodiment includes an inspection step (step S1) in which the surface of the conductive material 30 is divided into a plurality of regions A1, and whether the brightness value of each of the plurality of regions A1 falls within a predetermined range. The conductive material 30 that is determined to have the brightness value of each of the plurality of regions A1 falling within a predetermined range is used in the assembly of the sodium-sulfur battery 1000. Specifically, a sulfur mold 1002 (see Figures 1 and 2) is created by impregnating such a conductive material 30 with sulfur, and the sulfur mold 1002 is placed inside the positive electrode container 1001.

[0029] As described later, the conductive material 30 is made by embedding glass fiber felt 302 into graphite fiber felt 301 (see Figure 6, etc.). The higher the proportion of glass fiber on the surface of the conductive material 30, the higher the brightness value. Because the areas where glass fiber is present have high resistance and low electron conductivity, a large amount of sodium polysulfide remains, thus having the function of delaying sulfur aggregation during charging of the sodium-sulfur battery 1000. However, the glass fiber felt 302 is not perfectly homogeneous, and even when embedded under the same conditions, variations in the amount of glass fiber occur in each region A1 within a single conductive material 30, and sulfur aggregates early in areas with fewer glass fibers. Areas where sulfur has aggregated are not used for charging and discharging, causing an increase in the internal resistance and / or a decrease in the capacity of the sodium-sulfur battery 1000.

[0030] As in the manufacturing method of this embodiment, by checking whether the brightness value of each of the multiple regions A1 falls within a predetermined range, localized sulfur aggregation during charging can be suppressed, and the increase in the internal resistance and / or decrease in the capacity of the sodium-sulfur battery 1000 can be suppressed. This is because, by ensuring that glass fibers are uniformly present in a certain range, sodium polysulfide can be uniformly present in a certain range.

[0031] The luminance value for each region A1 can be obtained from image data obtained by imaging means 31 such as a camera, which captures the surface of the conductive material 30. Multiple regions A1 may be set in the image data, and a luminance value may be obtained for each region A1. The luminance value for each region A1 obtained here may be the average value of the luminance values ​​within each region A1. Alternatively, the luminance value for each region A1 may be the minimum or maximum value of the luminance values ​​within each region A1.

[0032] Figures 3 and 4 show how 10 regions A1, which extend across the entire width WD1 of the conductive material 30, are arranged in a single row along the length LD1 of the conductive material 30. However, the number, size, and arrangement of regions A1 can be arbitrarily changed.

[0033] The inspection of whether the brightness values ​​of each of the multiple regions A1 fall within a predetermined range may be performed by a computing device such as a computer operating according to a predetermined program. Notification may be given when the brightness value of any of the multiple regions A1 is outside the predetermined range. Conductive material 30 in which the brightness value of any of the multiple regions A1 is outside the predetermined range may be excluded.

[0034] In the inspection step (step S1), at least one of the following is checked: (1) whether the average value of the brightness values ​​for each of the multiple regions A1 of the conductive material 30 is within a predetermined range; (2) whether the minimum value of the brightness values ​​for each of the multiple regions A1 of the conductive material 30 is greater than or equal to a predetermined value; and (3) whether the difference between the minimum and maximum values ​​of the brightness values ​​for each of the multiple regions A1 of the conductive material 30 is less than or equal to a predetermined value. Preferably, at least two are checked, and more preferably, all are checked.

[0035] For example, let's assume that the luminance values ​​for each of the 10 regions A1 are 101, 102, 103, 104, 105, 106, 107, 108, 109, and 110. In this case, the average value of the luminance values ​​for each region A1 is 105.5. In inspection (1), it is checked whether this average value is within a predetermined range. By performing inspection (1), it is possible to determine whether the luminance values ​​are within an appropriate range for the entire region of the conductive material 30.

[0036] Furthermore, under the above assumption, the minimum luminance value for each region A1 is 101. In the inspection in (2), it is checked whether this minimum value is equal to or greater than a predetermined value. By performing the inspection in (2), it is possible to determine whether there are areas in the conductive material 30 where the luminance value is low in localized areas.

[0037] Furthermore, under the above assumption, the difference between the minimum (101) and maximum (110) luminance values ​​for each region A1 is 9. In inspection (3), it is checked whether this difference is less than or equal to a predetermined value. By performing inspection (3), it is possible to determine whether the luminance values ​​are uniform throughout the entire region of the conductive material 30.

[0038] Next, Figure 5 is a flowchart showing a method for manufacturing a sodium-sulfur battery 1000 according to an embodiment of the present invention, Figure 6 is a schematic explanatory diagram showing the fabrication process (step S2) of Figure 5, Figure 7 is a schematic explanatory diagram showing the material verification process (step S3) of Figure 5, and Figure 8 is a schematic explanatory diagram showing the cutting process (step S4) of Figure 5.

[0039] As shown in Figure 5, the manufacturing method of this embodiment may further include a fabrication step (step S2), a raw material verification step (step S3), and a cutting step (step S4), in addition to the inspection step (step S1).

[0040] The manufacturing process (step S2) is a process of creating a conductive material base 300 by embedding glass fiber felt 302 into graphite fiber felt 301, as shown in Figure 6. The conductive material base 300 is the material for the conductive material 30. In this embodiment, the conductive material base 300 is longer and wider than the conductive material 30. For example, if the conductive material 30 is 40 cm long and 10 cm wide, the conductive material base 300 may be 45 m long and 1 m wide.

[0041] The glass fiber felt 302 can be punched into the graphite fiber felt 301 by inserting and removing the needles 61a and 62a of needle punches 61 and 62 into the graphite fiber felt 301 and glass fiber felt 302 while the glass fiber felt 302 is stacked on top of the graphite fiber felt 301 and glass fiber felt 302. The graphite fiber felt 301 and glass fiber felt 302 are flowed in the line direction LD0 at a predetermined speed while stacked on top of each other. The needle punches 61 and 62 are positioned above the graphite fiber felt 301 and glass fiber felt 302 flowing in the line direction LD0 and are configured to move up and down at a predetermined speed and stroke. As the needle punches 61 and 62 move up and down, the needles 61a and 62a are inserted and removed into the graphite fiber felt 301 and glass fiber felt 302. Although not shown in detail, the tips of the needles 61a and 62a are provided with barbs, and as the needles 61a and 62a are inserted and removed, the glass fibers of the glass fiber felt 302 are driven in while becoming entangled with the graphite fibers of the graphite fiber felt 301.

[0042] The manufacturing process (step S2) includes inserting and removing the needle 61a of the first needle punch 61 into the graphite fiber felt 301 and glass fiber felt 302 which are stacked on top of each other, and then inserting and removing the needle 62a of the second needle punch 62. These first needle punch 61 and second needle punch 62 may be provided separately, or they may be the same. That is, after the needle 61a of the first needle punch 61 has been inserted and removed into the graphite fiber felt 301 and glass fiber felt 302, the graphite fiber felt 301 and glass fiber felt 302 may be sent under the first needle punch 61 again, and the needle 61a of the first needle punch 61 may be inserted and removed into the graphite fiber felt 301 and glass fiber felt 302 again. For the second pass of insertion and removal, the needle 61a of the first needle punch 61 may be understood as the needle 62a of the second needle punch 62. After inserting and removing the needle 61a of the first needle punch 61 into the graphite fiber felt 301 and the glass fiber felt 302, these graphite fiber felt 301 and glass fiber felt 302 are sometimes referred to as the conductive material base 300.

[0043] The creation process (step S2) may further include a process of obtaining the luminance value of the conductive material element 300 (the luminance value of the conductive material element 300 before the second needle punch 62) after the insertion and removal of the needle 61a of the first needle punch 61 and before the insertion and removal of the needle 62a of the second needle punch 62. In the creation process (step S2), the insertion and removal of the needle 62a of the second needle punch 62 may be controlled based on the luminance value of the conductive material element 300 obtained before the insertion and removal of the needle 62a of the second needle punch 62. Thereby, the luminance value of the conductive material element 300 after the second needle punch 62 can be adjusted. If the insertion and removal control of the needle 62a of the second needle punch 62 is fixedly performed without relying on the luminance value of the conductive material element 300, the inspection process (step S1) is performed with the appearance of the material as it is, and there is a possibility that the qualified rate of the conductive material 30 will be maintained in a poor state. As in this embodiment, by adjusting the luminance value of the conductive material element 300 after the second needle punch 62, the qualified rate of the conductive material 30 in the inspection process (step S1) can be improved.

[0044] The luminance value of the conductive material element 300 before the second needle punch 62 can be obtained from, for example, image data obtained by imaging the surface of the conductive material element 300 by imaging means 63, 64 such as a camera. The luminance value of the conductive material element 300 obtained here may be the average value of the luminance values of a predetermined region A2. This region A2 may be one region extending over the entire width direction WD2 of the conductive material element 300.

[0045] The vertical movement speed (punching speed) of the needles 62a of the second needle punch 62 may be controlled based on the brightness value of the conductive material element 300 in front of the second needle punch 62. When the brightness value of the conductive material element 300 in front of the second needle punch 62 is higher than the target brightness, the vertical movement speed of the needles 62a of the second needle punch 62 may be set faster than the reference speed. Conversely, when the brightness value of the conductive material element 300 in front of the second needle punch 62 is lower than the target brightness, the vertical movement speed of the needles 62a of the second needle punch 62 may be set slower than the reference speed. The transport speed of the conductive material element 300 and the stroke of the second needle punch 62 may be constant.

[0046] In the embodiment shown in Figure 6, the brightness value of the conductive material element 300 in front of the second needle punch 62 is acquired by both the first imaging means 63 positioned after the first needle punch 61 and the second imaging means 64 positioned before the second needle punch 62. By acquiring the brightness value of the conductive material element 300 by both the first imaging means 63 and the second imaging means 64, it is possible to monitor changes in the brightness value when there is a time interval between the impact of the needle 61a of the first needle punch 61 and the impact of the needle 62a of the second needle punch 62. However, the brightness value of the conductive material element 300 may be acquired by only one of the first imaging means 63 or the second imaging means 64.

[0047] The base material verification step (step S3) is performed after the creation step (step S2) and before the cutting step (step S4). This step involves dividing the surface of the conductive material base material 300 into multiple base material regions A3 and confirming whether the brightness value of each of the multiple base material regions A3 falls within a predetermined range. By performing the base material verification step (step S3), it is possible to confirm whether the control of inserting and removing the needle 62a of the second needle punch 62 was appropriate.

[0048] In FIG. 7, a state where ten element regions A3 arranged in the width direction WD2 of the conductive material element body 300 are set is shown. The outer shape of each of the element regions A3 may be the same as the outer shape of the conductive material 30 cut out from the conductive material element body 300. In other words, the luminance value for each element region A3 may correspond to the luminance value for each conductive material 30.

[0049] The luminance value of the element region A3 can be obtained from image data obtained by imaging the surface of the conductive material element body 300 with imaging means 65 such as a camera disposed after the second needle punch 62.

[0050] As shown in FIG. 8, the cutting step (step S4) is a step of obtaining a plurality of conductive materials 30 by cutting the conductive material element body 300 in the longitudinal direction LD2 and the width direction WD2. In FIG. 8, after cutting the conductive material element body 300 in the width direction WD2, cutting is performed in the longitudinal direction LD2 at a plurality of positions separated in the width direction WD2, thereby showing a state of obtaining ten conductive materials 30. The order of cutting may be arbitrarily changed. The inspection step (step S1) may be performed after the cutting step (step S4).

[0051] Using the image data obtained to obtain the luminance value of the conductive material 30 or the conductive material element body 300, an appearance inspection for inspecting the appearance defects of the conductive material 30 or the conductive material element body 300 may be further performed. Examples of the appearance defects detected in the appearance inspection include attachments such as vinyl used for the packaging material of the raw material, oil-based attachments dropped or transferred from peripheral devices, misalignment of the glass fiber felt 302 with respect to the graphite fiber felt 301, and damage such as breakage of the conductive material 30 or the conductive material element body 300. Notification may be made when an appearance defect is detected. The conductive material 30 or the conductive material element body 300 in which a defect is detected may be excluded.

[0052] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and it is naturally understood that these also belong to the technical scope of the present invention.

[0053] The present invention will be described more specifically below with reference to examples. The present invention is not limited to these examples.

[0054] The inventor created a conductive material base by embedding glass fiber felt into graphite fiber felt, and then produced a conductive material measuring 40 cm in length and 10 cm in width. A camera was placed above this conductive material, and its surface was imaged. A Sony XC-HR57 CCD camera was used, and the distance between the surface of the conductive material and the camera was 820 mm. For illumination, a CCS LB-600X100SW LED light with an adjustable illumination power supply was used. The distance between the surface of the conductive material and the LED light was 450 mm.

[0055] Image analysis of image data captured by a camera was performed using a PC with original image analysis software installed. In the image analysis, the surface of the conductive material was divided into eight regions, and it was checked whether the brightness value of each of the eight regions fell within a predetermined range. At this time, it was checked whether the average brightness value of each of the eight regions was between 90 and 150, whether the minimum brightness value of each region was 60 or higher, and whether the average brightness value of each region was 80 or lower. Conductive materials that met all of these conditions were deemed acceptable. When the acceptable conductive materials were incorporated into a sodium-sulfur battery, it was possible to suppress localized sulfur aggregation during charging, and the increase in the internal resistance and / or decrease in capacity of the sodium-sulfur battery was suppressed.

[0056] 30: Conductive material 301: Graphite fiber felt 302: Glass fiber felt 1000: Sodium-sulfur battery

Claims

1. A method for manufacturing a sodium-sulfur battery, comprising a conductive material impregnated with sulfur as a positive electrode active material, wherein the conductive material is made of graphite fiber felt with glass fiber felt embedded in it, and the method includes an inspection step of dividing the surface of the conductive material into a plurality of regions and inspecting whether the brightness value of each of the plurality of regions falls within a predetermined range.

2. A method for manufacturing a sodium-sulfur battery according to claim 1, further comprising: a manufacturing step of creating a conductive material base by embedding the glass fiber felt into the graphite fiber felt; and a cutting step of obtaining a plurality of the conductive materials by cutting the conductive material base in the longitudinal and width directions, wherein the inspection step is performed after the cutting step.

3. A method for manufacturing a sodium-sulfur battery according to claim 2, further comprising a material verification step performed after the manufacturing step and before the cutting step, in which the surface of the conductive material material is divided into a plurality of material regions, and it is confirmed whether or not the brightness value of each of the plurality of material regions falls within a predetermined range.

4. The manufacturing step includes the steps of inserting and removing the needles of a first needle punch into the graphite fiber felt and the glass fiber felt which are stacked on top of each other, and then inserting and removing the needles of a second needle punch; and the step of obtaining the brightness value of the conductive material after inserting and removing the needles of the first needle punch and before inserting and removing the needles of the second needle punch, wherein the manufacturing step controls the insertion and removal of the needles of the second needle punch based on the brightness value of the conductive material obtained before inserting and removing the needles of the second needle punch, the method for manufacturing a sodium-sulfur battery according to claim 3.

5. The method for manufacturing a sodium-sulfur battery according to any one of claims 1 to 4, wherein the inspection step checks whether at least one of the following is true: (1) whether the average value of the luminance values ​​for each of the plurality of regions of the conductive material is within a predetermined range; (2) whether the minimum value of the luminance values ​​for each of the plurality of regions of the conductive material is greater than or equal to a predetermined value; and (3) whether the difference between the minimum and maximum values ​​of the luminance values ​​for each of the plurality of regions of the conductive material is less than or equal to a predetermined value.

Images