Method for manufacturing sulfur mold and method for manufacturing sodium-sulfur battery

Abstract

The purpose of the present invention is to provide a method for manufacturing a sulfur mold with which it is possible to reduce the necessity of disposing an adjustment object in a mold cavity in order to adjust the size of a space in the mold cavity, and improve manufacturing efficiency. A method for manufacturing a sulfur mold according to the present invention is a method for manufacturing a sulfur mold 1002 having a predetermined shape in which a conductive material is impregnated with sulfur, which is an anode active material of a sodium-sulfur battery, and includes a step for injecting a molten sulfur 30 into a mold cavity 20 from an injector 3 connected to a mold 2 after disposing a conductive material 21 in the mold cavity 20 in the mold 2. The injection of the molten sulfur 30 by the injector 3 is performed at an injection time determined on the basis of the weight of the conductive material 21 measured before the injection of the molten sulfur 30, and at a constant injection pressure.

Description

Method for manufacturing sulfur mold and method for manufacturing sodium-sulfur battery

[0001] The present invention relates to a method for producing a sulfur mold of a predetermined shape in which sulfur, which is a positive electrode active material for sodium-sulfur batteries, is impregnated into a conductive material, and a method for producing a sodium-sulfur battery using the sulfur mold.

[0002] A sodium-sulfur battery is a high-temperature secondary battery that operates at 290 to 360°C. It consists of molten metallic sodium as a cathode active material on one side and molten sulfur as an anode active material on the other side, separated by a β-alumina solid electrolyte that is selectively permeable to sodium ions.

[0003] The following Patent Document 1 describes a method of manufacturing a sulfur mold of a predetermined shape in which a conductive material is placed in a mold cavity within a mold, and then molten sulfur is poured into the mold cavity, thereby impregnating the conductive material with sulfur.

[0004] Japanese Patent Application Laid-Open No. 2004-82461

[0005] In order to place the appropriate amount of sulfur in a sodium-sulfur battery, it is important to impregnate the conductive material with the appropriate amount of sulfur. Although Patent Document 1 describes a mold for manufacturing a sulfur mold, it does not specifically describe a method for injecting molten sulfur into the mold cavity.

[0006] One possible injection method is to inject molten sulfur into the mold cavity for a predetermined fixed time. However, since the size of the space in the mold cavity varies depending on the weight or density of the conductive material, when using this method, it is necessary to place a separate adjustment material in the mold cavity according to the weight or density of the conductive material. However, it takes time to select, place, and remove the adjustment material, which reduces the manufacturing efficiency of sulfur molds.

[0007] The present invention has been made to solve the above-mentioned problems, and one of its objects is to provide a method for manufacturing a sulfur mold and a method for manufacturing a sodium-sulfur battery that can reduce the need to place an adjusting object in the mold cavity to adjust the space within the mold cavity, thereby improving manufacturing efficiency.

[0008] The inventors have carefully investigated the change over time in the amount of molten sulfur injected into the mold cavity. It was previously thought that the amount of molten sulfur injected into the mold cavity would saturate after a certain time, but they have discovered a new finding that, even after the injection amount has reached saturation, by continuing to apply injection pressure to the mold cavity, molten sulfur can be injected into the mold cavity little by little. This is thought to be because the molten sulfur injected into the mold cavity cools and solidifies and shrinks, gradually creating space in the mold cavity for new molten sulfur to be injected. The present invention was completed based on this new finding.

[0009] Item 1. In one embodiment, the present invention relates to a method for manufacturing a sulfur mold having a predetermined shape, in which a conductive material is impregnated with sulfur, which is a positive electrode active material for a sodium-sulfur battery. The method includes a step of placing the conductive material in a mold cavity within a mold, and then injecting molten sulfur into the mold cavity from an injector connected to the mold, in which the injection of the molten sulfur by the injector is carried out at a constant injection pressure and for an injection time determined based on the weight of the conductive material measured before the injection of the molten sulfur.

[0010] Item 2. The present invention may relate to a method for manufacturing a sulfur mold according to Item 1, wherein the injection of molten sulfur by the injector includes a first period in which the mold cavity is filled with molten sulfur, and a second period in which injection pressure is continuously applied to the mold cavity after the first period so as to inject the molten sulfur into a portion of the mold cavity where the molten sulfur has solidified and shrunk.

[0011] Item 3. The present invention may relate to the method for producing a sulfur mold according to Item 2, wherein the amount of molten sulfur injected per unit time during the second period is 5 g / second or less.

[0012] Item 4. The present invention may relate to the method for producing a sulfur mold according to any one of Items 1 to 3, wherein the injector includes a cylinder containing molten sulfur and a piston that pushes the molten sulfur out of the cylinder, and the injection of the molten sulfur by the injector is completed before the piston reaches the bottom dead center.

[0013] Item 5. The present invention may relate to the method for producing a sulfur mold according to any one of Items 1 to 4, wherein the conductive material is stored in a drying chamber before being placed in the mold cavity, and the storage of the conductive material in the drying chamber is performed at 200°C for two hours or more.

[0014] Item 6. In one embodiment, the present invention relates to a method for producing a sodium-sulfur battery, the method including a step of producing a sulfur mold by the method for producing a sulfur mold according to any one of Items 1 to 5.

[0015] According to one embodiment of the method for manufacturing a sulfur mold and the method for manufacturing a sodium-sulfur battery of the present invention, the injection of molten sulfur by the injection machine is carried out for an injection time and at a constant injection pressure determined based on the weight of the conductive material measured before the injection of the molten sulfur. This reduces the need to place an adjustment object in the mold cavity to adjust the space size within the mold cavity, thereby improving manufacturing efficiency.

[0016] 6 is a cross-sectional view of a sodium-sulfur battery manufactured by a method for manufacturing a sodium-sulfur battery according to an embodiment of the present invention. FIG. 7 is an exploded perspective view showing a part of the sodium-sulfur battery of FIG. 1 . FIG. 8 is an explanatory view for explaining a method for manufacturing a sulfur mold according to an embodiment of the present invention. FIG. 9 is a graph showing the relationship between the injection time and the injection amount of molten sulfur from the injector of FIG. 3 . FIG. 10 is an enlarged graph showing a second period of FIG. 4 . FIG. 11 is a cross-sectional view of the mold of FIG. 3 when it is in an open state. FIG. 12 is a cross-sectional view of the mold of FIG. 3 when it is in a closed state. FIG. 13 is a cross-sectional view of the mold of FIG. 3 at a position different from that of FIG. 6 .

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and the components can be modified and embodied without departing from the spirit of the present invention. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in each embodiment. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components of different embodiments may be appropriately combined.

[0018] Fig. 1 is a cross-sectional view of a sodium-sulfur battery 1000 manufactured by a method for manufacturing a sodium-sulfur battery 1000 according to an embodiment of the present invention, and Fig. 2 is an exploded perspective view showing a portion of the sodium-sulfur battery 1000 shown in Fig. 1. Note that Fig. 2 shows a portion of the configuration in cross section.

[0019] A 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 an anode container 1001, a plurality of sulfur molds 1002, a β-alumina solid electrolyte tube 1003, a safety tube 1004, a cathode container 1005, metallic sodium 1006, an anode metal fitting 1007, an insulating ring 1008, and a cathode metal fitting 1009.

[0020] The anode vessel 1001 is a cylindrical vessel with a bottom. Multiple sulfur molds 1002 are housed inside the anode vessel 1001. The sulfur mold 1002 is a component of a predetermined shape obtained by impregnating a conductive material 21 (see FIG. 3 ) with sulfur, which is an anode active material. The conductive material 21 may be, for example, a mat. The mat may be a felt in which glass fiber and graphite fiber are intertwined. The mat can be obtained by stacking a glass fiber felt on a graphite fiber felt and inserting multiple needles with barbed tips into the felts multiple times. As is well known, the melting point of sulfur is 112.8°C. Therefore, after the sodium-sulfur battery 1000 is manufactured, the sulfur impregnated in the conductive material 21 remains solidified until the battery is started.

[0021] The sulfur mold 1002 may have multiple side molds 1002a and one bottom mold 1002b. As particularly shown in FIG. 2, the side mold 1002a may be a longitudinal member with arc-shaped end faces. FIG. 2 shows an example of a side mold 1002a in which three side molds 1002a are combined to form a cylindrical shape as a whole. The bottom mold 1002b may be a disk-shaped member. A β-alumina solid electrolyte tube 1003 may be placed inside the cylindrically arranged side mold 1002a, and the bottom mold 1002b may be placed at the bottom of the β-alumina solid electrolyte tube 1003.

[0022] The β-alumina solid electrolyte tube 1003 is a bottomed cylindrical container that is selectively permeable to sodium ions and is disposed inside the anode container 1001. Between the anode container 1001 and the β-alumina solid electrolyte tube 1003, an anode space 1010 is formed in which molten sulfur is disposed after the sodium-sulfur battery 1000 is started.

[0023] The safety tube 1004 is a cylindrical container with a bottom, and the cathode container 1005 is a cylindrical container with a bottom and a lid. The safety tube 1004 may be disposed inside the β-alumina solid electrolyte tube 1003, and the cathode container 1005 may be disposed inside the safety tube 1004.

[0024] A predetermined gap is provided between the inner peripheral surface of the β-alumina solid electrolyte tube 1003 and the outer peripheral surface of the safety tube 1004, and between the inner peripheral surface of the safety tube 1004 and the outer peripheral surface of the cathode container 1005. Metallic sodium 1006 is accommodated inside the cathode container 1005. As is well known, the melting point of metallic sodium 1006 is 97.79°C, and the metallic sodium 1006 in the cathode container 1005 is solidified after the sodium-sulfur battery 1000 is manufactured and until the sodium-sulfur battery 1000 is started up.

[0025] The anode metal fitting 1007 is attached to the top of the anode 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 cathode metal fitting 1009. A cathode space 1011 in which molten metallic sodium is placed after start-up of the sodium-sulfur battery 1000 is formed inside the β-alumina solid electrolyte tube 1003, the insulating ring 1008, and the cathode metal fitting 1009. The insulating ring 1008 may electrically insulate the β-alumina solid electrolyte tube 1003, the cathode metal fitting 1009, and the molten metallic sodium in the cathode space 1011 from the anode metal fitting 1007.

[0026] The sodium-sulfur battery 1000 is a high-temperature operating secondary battery, and is heated to approximately 300°C during operation. When the sodium-sulfur battery 1000 is heated to approximately 300°C, the sulfur in the sulfur mold 1002 and the metallic sodium 1006 in the cathode container 1005 are melted. As shown in FIG. 1 , the sulfur mold 1002 and the cathode container 1005 are provided with an inert gas generating material 1012, such as a sodium azide tablet. When the sodium-sulfur battery 1000 is heated to approximately 300°C, an inert gas (e.g., nitrogen gas) is generated from the inert gas generating material 1012.

[0027] Here, an opening 1005a is provided at the bottom of the cathode container 1005. When the sodium-sulfur battery 1000 is heated to approximately 300°C, an inert gas is generated from the inert gas generating material 1012 in the cathode container 1005. This increases the internal pressure of the cathode container 1005, and molten metallic sodium is placed in the cathode space 1011 through the opening 1005a of the cathode container 1005.

[0028] 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 cathode vessel 1005 are set so that the internal pressure of the anode space 1010 is greater than the internal pressure of the cathode space 1011. By varying the internal pressure in this manner, even if the β-alumina solid electrolyte tube 1003 is damaged, the molten metallic sodium in the cathode space 1011 will not enter the anode space 1010, and the molten sulfur in the anode space 1010 will enter the cathode vessel 1005. When the molten sulfur in the anode space 1010 enters the cathode vessel 1005 and reacts with the molten metallic sodium, reaction heat is generated. The safety tube 1004 has a larger coefficient of thermal expansion than the β-alumina solid electrolyte tube 1003, and expands more than the β-alumina solid electrolyte tube 1003 due to the heat of reaction between the molten sulfur and the molten metallic sodium, thereby being able to seal the damaged portion of the β-alumina solid electrolyte tube 1003. This makes it possible to limit the amount of reaction between the molten sulfur and the molten metallic sodium when the β-alumina solid electrolyte tube 1003 is damaged.

[0029] Next, Figure 3 is an explanatory diagram for explaining a manufacturing method of a sulfur mold 1002 according to an embodiment of the present invention, Figure 4 is a graph showing the relationship between the injection time and the injection amount of molten sulfur 30 from the injector 3 of Figure 3, and Figure 5 is a graph showing an enlarged view of the second period of Figure 4.

[0030] The manufacturing method of the sulfur mold 1002 of this embodiment is for manufacturing the sulfur mold 1002 as described with reference to Figures 1 and 2. The manufacturing method of this embodiment includes a step of placing a conductive material 21 in a mold cavity 20 in a mold 2 as shown in Figure 3, and then injecting molten sulfur 30 into the mold cavity 20 from an injection machine 3 connected to the mold 2, and the injection of the molten sulfur 30 by the injection machine 3 is performed at a constant injection pressure and for an injection time determined based on the weight of the conductive material 21 measured before the injection of the molten sulfur 30.

[0031] Here, in order to arrange an appropriate amount of sulfur in the sodium-sulfur battery 1000, more specifically in the anode space 1010, it is important to impregnate the conductive material 21 with an appropriate amount of sulfur.

[0032] As an injection method, it is conceivable to inject molten sulfur 30 into mold cavity 20 for a predetermined fixed time. However, since the size of the space in mold cavity 20 varies depending on the weight or density of conductive material 21, when such a method is adopted, it is necessary to place an adjustment material other than conductive material 21 in mold cavity 20 to adjust the size of the space in mold cavity 20 depending on the weight or density of conductive material 21. However, it takes time to select, place, and remove the adjustment material, which reduces the manufacturing efficiency of sulfur mold 1002.

[0033] The present inventors have carefully examined the change over time in the amount of molten sulfur 30 injected into the mold cavity 20, as shown in Figures 4 and 5. As shown in Figure 4, the amount of molten sulfur 30 injected into the mold cavity 20 saturates after a certain time. However, as shown in Figure 5, the inventors have newly discovered that even after the injection amount saturates, by continuing to apply injection pressure to the mold cavity 20, molten sulfur 30 can be injected little by little into the mold cavity 20. This is thought to be because the molten sulfur 30 injected into the mold cavity 20 cools and solidifies and shrinks, gradually creating space in the mold cavity 20 for new injection of molten sulfur 30.

[0034] Therefore, as described above, by injecting the molten sulfur 30 using the injector 3 for an injection time determined based on the weight of the conductive material 21 measured before injecting the molten sulfur 30 and at a constant injection pressure, the need to place an adjustment material in the mold cavity 20 to adjust the space size within the mold cavity 20 can be reduced, thereby improving manufacturing efficiency.

[0035] The weight of the conductive material 21 may vary depending on the density of the conductive material 21. As the weight or density of the conductive material 21 increases, the space inside the mold cavity 20 becomes smaller, and the amount of molten sulfur 30 injected into the mold cavity 20 becomes saturated sooner. In other words, when the weight or density of the conductive material 21 is large, the amount of molten sulfur 30 injected at the time of saturation becomes smaller than when the weight or density of the conductive material 21 is small. Therefore, as the weight or density of the conductive material 21 increases, the injection time should be set longer, and more molten sulfur 30 should be injected into the mold cavity 20 after the injection amount becomes saturated.

[0036] The mold 2 may have a cooling function for cooling the molten sulfur 30 in the mold cavity 20. For example, the cooling function can be realized by passing a coolant through the inside of the mold 2.

[0037] The injection pressure may be set so that the molten sulfur 30 can be injected into a space newly created by solidification and shrinkage of the molten sulfur 30. Although not limited thereto, the injection pressure may be 2 MPa or more and 4 MPa or less. For example, the injection pressure may be 3 MPa.

[0038] The weight of the conductive material 21 may be measured before placing the conductive material 21 in the mold cavity 20. Before placing the conductive material 21 in the mold cavity 20, the conductive material 21 may be stored in a drying cabinet (not shown), and the storage of the conductive material 21 in the drying cabinet may be performed at 200°C for two hours or more. By storing the conductive material 21 in this manner, the weight of the conductive material 21 can be measured more accurately without being affected by humidity. If the mold 2 can be equipped with a weight scale, the weight of the conductive material 21 may be measured after placing the conductive material 21 in the mold cavity 20 and before injecting the molten sulfur 30 into the mold cavity 20.

[0039] The injection of the molten sulfur 30 by the injector 3 may include a first period in which the mold cavity 20 is filled with the molten sulfur 30, and a second period in which, after the first period, an injection pressure is continuously applied to the mold cavity 20 so as to inject the molten sulfur into a portion of the mold cavity 20 where the molten sulfur 30 has solidified and shrunk. In other words, the manufacturing method of this embodiment includes continuously applying an injection pressure to the mold cavity 20 after the injection amount of the molten sulfur 30 has become saturated.

[0040] As shown in Figure 4, in the first period, the molten sulfur 30 can be smoothly injected into the mold cavity 20, so the amount of molten sulfur 30 injected per unit time increases. When the mold cavity 20 is filled with molten sulfur 30, the resistance to the injection of molten sulfur 30 into the mold cavity 20 increases, and the amount of molten sulfur 30 injected per unit time decreases (the injection amount becomes saturated). However, as described above, the molten sulfur 30 injected into the mold cavity 20 cools and solidifies and shrinks, gradually creating space for new injection of molten sulfur 30 into the mold cavity 20. Even after the injection amount becomes saturated, molten sulfur 30 can be gradually injected into the mold cavity 20.

[0041] The injection amount of molten sulfur 30 per unit time in the second period may be 5 g / sec or less. By making the injection amount of molten sulfur 30 per unit time 5 g / sec or less, the injection amount can be accurately controlled depending on the injection time. The injection amount of molten sulfur 30 per unit time can be controlled by the amount of cooling of the molten sulfur 30 by the mold 2 and the injection pressure of the molten sulfur 30 into the mold cavity 20. The injection amount of molten sulfur 30 per unit time in the second period may be smaller, and may be 3 g / sec or less. In the example shown in FIG. 5, the injection amount of molten sulfur 30 per unit time in the second period is 2 g / sec.

[0042] When the injection rate of the molten sulfur 30 per unit time in the second period is 5 g / sec or less, a state in which the injection rate of the molten sulfur 30 per unit time exceeds 5 g / sec may be understood as the first period or a period before the injection rate of the molten sulfur 30 is saturated. The injection rate of the molten sulfur 30 per unit time in the first period may be 5 times or more, 10 times or more, or 20 times or more, of the injection rate of the molten sulfur 30 per unit time in the second period. The injection rate of the molten sulfur 30 per unit time in the first period may be the injection rate per unit time in a period in which the injection rate changes relatively linearly, and in the example shown in FIG. 4, may be about 120 g / sec for a period of 0 to 4 seconds. The injection rate of the molten sulfur 30 per unit time in the first period may be 200 g / sec or less.

[0043] 3, the injector 3 includes a cylinder 31 containing molten sulfur 30 and a piston 32 that pushes the molten sulfur 30 out of the cylinder 31. The injection of the molten sulfur 30 by the injector 3 may be completed before the piston 32 reaches the bottom dead center. A constant injection pressure can be maintained until a predetermined amount of molten sulfur 30 is injected.

[0044] 3, the cylinder 31 has an inlet 31a, which is connected to a pipe 33 through which the molten sulfur 30 flows. The injector 3 may have an on-off valve 34 that opens and closes the inlet 31a of the cylinder 31. With the inlet 31a open, the piston 32 is moved toward the top dead center, whereby the molten sulfur 30 in the pipe 33 can be introduced into the cylinder 31.

[0045] 3, the cylinder 31 has an outlet 31b, which is connected to an injection needle 36 via a connecting pipe 35. The injection needle 36 may be connected to the mold 2. When the piston 32 is moved toward the bottom dead center with the inlet 31a closed, the molten sulfur 30 in the cylinder 31 is injected into the mold cavity 20 through the outlet 31b, the connecting pipe 35, and the injection needle 36.

[0046] The connecting pipe 35 may be a flexible pipe. The flexibility of the connecting pipe 35 allows the position of the injection machine 3 relative to the position of the mold cavity 20 to be freely selected.

[0047] The volume of the connection pipe 35 is preferably 90% or less of the volume of the molten sulfur 30 injected into the mold cavity 20 at one time. By making the volume 90% or less, the amount of molten sulfur 30 remaining in the connection pipe 35 can be reduced, and accumulation of foreign matter such as dust in the connection pipe 35 can be prevented.

[0048] Next, the mold 2 of Fig. 3 will be described in more detail with reference to Figs. 6 to 8. Fig. 6 is a cross-sectional view of the mold 2 of Fig. 3 when it is in an open state, and Fig. 7 is a cross-sectional view of the mold 2 of Fig. 6 when it is in a closed state. Fig. 8 is a cross-sectional view of the mold 2 of Fig. 3 at a position different from that shown in Fig. 6. The cross sections shown in Figs. 6 and 7 are cross sections of the mold 2 at a central position in the longitudinal direction of the sulfur mold 1002 (see Figs. 1 and 2), and the cross section shown in Fig. 8 may be a cross section of the mold 2 at an end position in the longitudinal direction of the sulfur mold 1002.

[0049] As shown in FIGS. 6 to 8, the mold 2 may have a lower mold 200 and an upper mold 210 .

[0050] The lower mold 200 may have a lower matrix 201 and a lower metal mold 202. The lower matrix 201 has a recess 201a disposed at the center in the width direction W. The lower metal mold 202 may be accommodated in the recess 201a of the lower matrix 201.

[0051] Similarly, the upper mold 210 may have an upper mother mold 211 and an upper metal mold 212. The upper mother mold 211 has a recess 211a disposed at the center in the width direction W. The upper metal mold 212 may be accommodated in the recess 211a of the upper mother mold 211.

[0052] The upper surface of the lower mold 202 and the lower surface of the upper mold 212 may be provided with arc-shaped cavity surfaces 202a, 212a facing each other. As shown in Fig. 7 , the upper mold 210 may be lowered toward the lower mold 200 to form a mold cavity 20 between these cavity surfaces 202a, 212a. After placing the conductive material 21 on the cavity surface 202a of the lower mold 202 while the upper mold 210 is being raised as shown in Fig. 6 , the upper mold 210 can be lowered toward the lower mold 200 as shown in Fig. 7 to place the conductive material 21 in the mold cavity 20 within the mold 2.

[0053] 6 and 7, the cavity surface 202a of the lower mold 202 may be provided with an injection hole 202b connected to the injection needle 36 of the injection machine 3. The molten sulfur 30 from the injection machine 3 may be injected into the mold cavity 20 through this injection hole 202b.

[0054] 6 , a sealant 212b may be provided on the cavity surface 212a of the upper mold 212. The sealant 212b is provided to prevent the molten sulfur 30 from leaking out of the mold cavity 20 when it is injected into the mold cavity 20. The sealant 212b may be made of rubber and may be provided so as to be sandwiched between the upper mold 210 and the lower mold 200 around the mold cavity 20 when the upper mold 210 is lowered toward the lower mold 200.

[0055] The lower mold 200 may further include slide bars 203 that are arranged on both sides of the recess 201a in the width direction W on the upper surface of the lower matrix 201 and are provided so as to be displaceable in the width direction W. The slide bars 203 may have slide bar pins 203a that extend in the depth direction D (a direction perpendicular to the paper surface of FIGS. 6 and 7). The lower matrix 201 may have cam plate grooves 201c provided below the slide bar pins 203a.

[0056] The upper mold 210 may have a cam plate 213. The cam plate 213 may have a longitudinal plate body 214 fixed to the upper mother mold 211 and extending in the width direction W, and a pair of cam bodies 215 provided at both ends of the plate body 214 in the width direction W. Each of the pair of cam bodies 215 may be provided with a vertical groove 215a extending upward from the lower end of the cam body 215, and an inclined groove 215b extending obliquely upward from the upper end of the vertical groove 215a so as to approach the center of the upper mold 210 in the width direction W as it extends upward.

[0057] As shown in FIG. 7 , when the upper mold 210 is lowered toward the lower mold 200, the cam body 215 enters the cam plate groove 201c. At this time, the slide bar pin 203a enters the vertical groove 215a and the inclined groove 215b. The slide bar pin 203a is pressed by the cam body 215 along the inclined groove 215b, displacing the slide bar 203 toward the center of the lower mold 200 in the width direction W. By displacing the slide bar 203 toward the center of the lower mold 200, the upper mold 210 is lowered toward the lower mold 200, thereby pressing the end of the conductive material 21 toward the center. This allows the conductive material 21 to bend along the cavity surface 202a of the lower mold 202, thereby arranging the conductive material 21 in an arc shape within the mold cavity 20. Note that FIG. 7 does not show some components, such as the plate body 214.

[0058] 8, the lower mold 200 may be provided with a push-up pin 204, and the sulfur mold 1002 can be released from the cavity surface 202a of the lower mold 202 by displacing the push-up pin 204 upward so as to protrude from the cavity surface 202a of the lower mold 202 as shown by the two-dot chain line in the figure. Similarly, the upper mold 210 may be provided with a drop pin 216, and the sulfur mold 1002 can be released from the cavity surface 212a of the upper mold 212 by displacing the drop pin 216 downward so as to protrude from the cavity surface 212a of the upper mold 212 as shown by the two-dot chain line in the figure.

[0059] 7 , the push-up pin 204 may be displaced upward to release the sulfur mold 1002 from the cavity surface 202a of the lower mold 202, and the sulfur mold 1002 may be raised together with the upper mold 210. After the upper mold 210 and the sulfur mold 1002 have been raised, a receiving stand (not shown) may be inserted between the lower mold 200 and the upper mold 210, and the drop pin 216 may be displaced downward to release the sulfur mold 1002 from the cavity surface 212a of the upper mold 212, and the dropped sulfur mold 1002 may be received by the receiving stand and transported to the next process.

[0060] A coating layer 220 made of polytetrafluoroethylene (PTFE) may be provided on the cavity surface 202a of the lower mold 202 and the cavity surface 212a of the upper mold 212. By providing such a coating layer 220, the sulfur mold 1002 can be more smoothly released from the cavity surface 202a of the lower mold 202 and the cavity surface 212a of the upper mold 212.

[0061] The manufacturing method for the sodium-sulfur battery 1000 of this embodiment includes a step of manufacturing the sulfur mold 1002 by the above-described method for manufacturing the sulfur mold 1002. The manufacturing method for the sodium-sulfur battery 1000 of this embodiment may further include a step of incorporating the manufactured sulfur mold 1002 into an anode container 1001, and a step of arranging a β-alumina solid electrolyte tube 1003, a safety tube 1004, and a cathode container 1005 inside the sulfur mold 1002, attaching an anode metal fitting 1007 to the top of the anode container 1001, and attaching an insulating ring 1008 and a cathode metal fitting 1009 to the top of the β-alumina solid electrolyte tube 1003.

[0062] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0063] 2: Mold 3: Injector 20: Mold cavity 21: Conductive material 30: Molten sulfur 31: Cylinder 32: Piston 1000: Sodium-sulfur battery 1002: Sulfur mold

Claims

1. A method for manufacturing a sulfur mold of a predetermined shape, in which a conductive material is impregnated with sulfur, which is a positive electrode active material for a sodium-sulfur battery, the method comprising the steps of: placing the conductive material in a mold cavity within a mold; and injecting molten sulfur into the mold cavity from an injector connected to the mold; and injecting the molten sulfur by the injector at a constant injection pressure and for an injection time determined based on the weight of the conductive material measured before injecting the molten sulfur.

2. The method for manufacturing a sulfur mold according to claim 1, wherein the injection of the molten sulfur by the injection machine includes a first period during which the mold cavity is filled with the molten sulfur, and a second period during which the injection pressure is continuously applied to the mold cavity after the first period so as to inject the molten sulfur into a portion of the mold cavity where the molten sulfur has solidified and shrunk.

3. The method for manufacturing a sulfur mold according to claim 2, wherein the amount of molten sulfur injected per unit time during the second period is 5 g / sec or less.

4. The method for manufacturing a sulfur mold according to claim 1, wherein the injector includes a cylinder containing the molten sulfur and a piston that pushes the molten sulfur out of the cylinder, and the injection of the molten sulfur by the injector is completed before the piston reaches bottom dead center.

5. The method for manufacturing a sulfur mold according to claim 1, wherein the conductive material is stored in a drying chamber before being placed in the mold cavity, and the storage of the conductive material in the drying chamber is carried out at 200°C for two hours or more.

6. A method for producing a sodium-sulfur battery, comprising the step of producing a sulfur mold by the method for producing a sulfur mold according to any one of claims 1 to 5.

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