Sulfur molding production method and sodium-sulfur battery production method

Abstract

The present invention provides a sulfur molding production method which makes it possible to more reliably supply molten sulfur to an injector. The present invention provides a sulfur molding 1002 production method for producing a sulfur molding 1002 which has a prescribed shape and in which sulfur that is a positive electrode active material for a sodium-sulfur battery 1000 is impregnated in a conductive material 21, said production method comprising a step for, after disposing a conductive material 21 in a mold cavity 20 inside a mold 2, injecting molten sulfur 30 inside the mold cavity 20 from an injector 3 which is connected to the mold 2, wherein: the molten sulfur 30 flows through circulation piping 41 which has one end 41a and another end 41b that are connected to a melting furnace 40 that heats sulfur to generate the molten sulfur 30; and the injector 3 injects the molten sulfur 30 flowing through the circulation piping 41 into the mold cavity 20.

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 for 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 to impregnate the conductive material with sulfur. Patent Document 1 also cites 140°C as an example of the temperature of the molten sulfur injected into the mold cavity.

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

[0005] It is known that sulfur melts when heated to a temperature equal to or higher than its melting point (112.8° C.), and its viscosity increases when heated to a temperature exceeding 160° C. As described in Patent Document 1, by adjusting the temperature of the molten sulfur to about 140° C., the viscosity of the molten sulfur can be made suitable for injection.

[0006] The operation of injecting molten sulfur into the mold cavity is performed at time intervals. That is, after the injection of molten sulfur, the manufactured sulfur mold is removed from the mold, a new conductive material is carried into the mold, the mold is closed, and the conductive material is placed in the mold cavity. Then, the next injection of molten sulfur is performed. For this reason, the molten sulfur produced in the melting furnace is not immediately injected into the mold cavity from the injection machine, and the molten sulfur spends a considerable amount of time stagnating in the piping between the melting furnace and the injection machine. If the temperature of the molten sulfur produced in the melting furnace is set high in consideration of the residence time in the piping, the viscosity of the molten sulfur may increase, which may interfere with the supply of molten sulfur to the injection machine.

[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 more reliably supply molten sulfur to an injector.

[0008] 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 the mold, and then injecting molten sulfur into the mold cavity from an injector connected to the mold. The molten sulfur flows through a circulation pipe having one end and the other end connected to a melting furnace that heats the sulfur and produces molten sulfur, and the injector injects the molten sulfur flowing through the circulation pipe into the mold cavity.

[0009] Item 2. The present invention may relate to the method for producing a sulfur mold according to Item 1, in which a heater and a heat-insulating cover are attached to the outer periphery of the circulation piping.

[0010] Item 3. The present invention may relate to the method for producing a sulfur mold according to Item 1 or 2, wherein the temperature of the molten sulfur in the circulation piping is controlled to be 120°C or higher and 150°C or lower.

[0011] 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 first injector and a second injector, and the first injector and the second injector are connected to a circulation pipe.

[0012] Item 5. 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 4.

[0013] 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 injector injects molten sulfur flowing through the circulation pipe into the mold cavity. Therefore, regardless of the operation of the injector, the molten sulfur maintained at a predetermined temperature can be circulated through the circulation pipe, and the supply of molten sulfur to the injector can be more reliably carried out.

[0014] FIG. 1 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. 2 is an exploded perspective view showing a part of the sodium-sulfur battery of FIG. 1. FIG. 3 is an explanatory view for explaining a method for manufacturing a sulfur mold according to an embodiment of the present invention. FIG. 4 is an explanatory view showing a molten sulfur circulation system connected to the injector of FIG. 3. FIG. 5 is an explanatory view showing the circulation pump of FIG. 4. FIG. 6 is a cross-sectional view of the circulation piping of FIG. 4.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Next, FIG. 3 is an explanatory diagram for explaining a method for manufacturing a sulfur mold 1002 according to an embodiment of the present invention, FIG. 4 is an explanatory diagram showing a circulation system for molten sulfur 30 connected to the injector 3 of FIG. 3, FIG. 5 is an explanatory diagram showing the circulation pump 43 of FIG. 4, and FIG. 6 is a cross-sectional view of the circulation piping 41 of FIG. 4.

[0028] The manufacturing method of the sulfur mold 1002 of this embodiment is for manufacturing the sulfur mold 1002 as described with reference to Fig. 1 and Fig. 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 Fig. 3, and then injecting molten sulfur 30 into the mold cavity 20 from an injector 3 connected to the mold 2. As shown in Fig. 4, the molten sulfur 30 flows through a circulation pipe 41, one end 41a and the other end 41b of which are connected to a melting furnace 40 that heats sulfur to produce molten sulfur 30, and the injector 3 injects the molten sulfur 30 flowing through the circulation pipe 41 into the mold cavity 20.

[0029] It is known that sulfur melts when heated to a temperature equal to or higher than its melting point (112.8° C.), and its viscosity increases when heated to a temperature exceeding 160° C. By setting the temperature of the molten sulfur to about 140° C., the viscosity of the molten sulfur 30 can be made suitable for injection.

[0030] The operation of injecting molten sulfur 30 into mold cavity 20 is performed at time intervals. That is, after the injection of molten sulfur 30, the manufactured sulfur mold 1002 is removed from mold 2, new conductive material 21 is carried into mold 2, mold 2 is closed, and the conductive material 21 is placed in mold cavity 20, and then the next injection of molten sulfur 30 is performed. For this reason, the molten sulfur 30 produced in melting furnace 40 is not immediately injected into mold cavity 20 from injection machine 3, and the molten sulfur 30 remains in the piping between melting furnace 40 and injection machine 3 for a considerable period of time.

[0031] If the melting furnace 40 were connected to the injector 3 not by the circulation pipe 41 but by a pipe (not shown) starting from the melting furnace 40 and terminating at the injector 3, the temperature of the molten sulfur 30 produced in the melting furnace 40 would have to be set high in consideration of the residence time in the pipe, and an increase in the viscosity of the molten sulfur 30 could hinder the supply of the molten sulfur 30 to the injector 3. In contrast, in the manufacturing method of this embodiment, the injector 3 injects the molten sulfur 30 flowing through the circulation pipe 41 into the mold cavity 20. As a result, the molten sulfur 30 maintained at a predetermined temperature can be circulated through the circulation pipe 41 regardless of the operation of the injector 3, and the supply of the molten sulfur 30 to the injector 3 can be more reliably carried out.

[0032] One end 41 a of the circulation pipe 41 may be an end into which the molten sulfur 30 is introduced from the melting furnace 40 , and the other end 41 b of the circulation pipe 41 may be an end into which the molten sulfur 30 is returned to the melting furnace 40 .

[0033] As shown in Fig. 3, the injector 3 may include a cylinder 31 that accommodates molten sulfur 30 and a piston 32 that pushes the molten sulfur 30 out of the cylinder 31. In the embodiment shown in Fig. 3, the cylinder 31 has an inlet 31a, which is connected to a circulation pipe 41. 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, thereby allowing the molten sulfur 30 in the circulation pipe 41 to be introduced into the cylinder 31.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 4 , the melting furnace 40 may include a first melting furnace 401 and a second melting furnace 402. While molten sulfur 30 produced in one of the first melting furnace 401 and the second melting furnace 402 is flowing through the circulation pipe 41, sulfur may be heated in the other furnace to produce new molten sulfur 30. One end 41a of the circulation pipe 41 may be connected to the first melting furnace 401 and the second melting furnace 402, respectively, and the other end 41b of the circulation pipe 41 may be connected to the first melting furnace 401 and the second melting furnace 402, respectively.

[0038] A strainer 42 for removing foreign matter contained in the molten sulfur 30 may be provided on the circulation pipe 41 between the melting furnace 40 and the injector 3. The strainer 42 may be, for example, a member such as a metal mesh.

[0039] A circulation pump 43 for circulating the molten sulfur 30 may be provided on the circulation pipe 41 between the melting furnace 40 and the injector 3. As shown in FIG. 5 , the circulation pump 43 may be a magnetic pump. The magnetic pump may include an impeller 43a disposed inside the circulation pipe 41, an internal magnet 43b attached to the rotation shaft of the impeller 43a, an external magnet 43c disposed outside the circulation pipe 41, and a motor 43d for rotating the external magnet 43c. The external magnet 43c is rotated by the motor 43d to generate a rotating magnetic field, which rotates the internal magnet 43b and the impeller 43a. Use of such a magnetic pump can prevent foreign matter from being mixed into the molten sulfur 30 and prevent the molten sulfur 30 from leaking to the outside.

[0040] For example, on the circulation pipe 41, on the upstream and downstream sides of each device, such as the melting furnace 40, the injector 3, the strainer 42, and the circulation pump 43, an on-off valve 44 may be provided. By switching the on-off valve 44 between on and off, the flow of the molten sulfur 30 can be controlled. In addition, maintenance of each device, such as removing foreign matter accumulated in the strainer 42, can be performed.

[0041] 5, a heater 410 and a heat-insulating cover 411 may be attached to the outer periphery of the circulation pipe 41. By attaching the heater 410, heating can be performed by the heater 410 in addition to heating by the melting furnace 40, and temperature control of the molten sulfur 30 can be more reliably performed. By attaching the heat-insulating cover 411, a decrease in the temperature of the molten sulfur 30 can be suppressed, and temperature control of the molten sulfur 30 can be more reliably performed.

[0042] Any device may be used as the heater 410, but in the illustrated embodiment, a linear cable heater is used that extends in the extension direction of the circulation pipe 41. Any insulating material may be used as the heat-retaining cover 411, and as in the illustrated embodiment, it is preferable that it is provided so as to surround the periphery of the circulation pipe 41 and the heater 410. Note that any material may be used as the circulation pipe 41, but in view of corrosion resistance and the like, stainless steel pipes may be used.

[0043] In the circulation pipe 41, the temperature of the molten sulfur 30 is preferably controlled to be 120°C or higher and 150°C or lower. By controlling the temperature of the molten sulfur 30 within this range, the viscosity of the molten sulfur 30 can be made suitable for injection. The temperature control may include heating by the melting furnace 40. When a heater 410 is attached to the outer periphery of the circulation pipe 41 as in the present embodiment, the temperature control may include heating by the heater 410.

[0044] As shown in FIG. 4 , the injectors 3 may include a first injector 301 and a second injector 302, and the first injector 301 and the second injector 302 may be connected to the circulation pipe 41. In the illustrated embodiment, the injectors 3 further include a third injector 303 and a fourth injector 304, and the third injector 303 and the fourth injector 304 are further connected to the circulation pipe 41. That is, a plurality of injectors 3 may be connected to the circulation pipe 41. The number of injectors 3 may be changed as desired. In this embodiment, the plurality of injectors 3 (the first injector 301, the second injector 302, the third injector 303, and the fourth injector 304) is not provided with a dedicated melting furnace 40 for each of them, but rather the melting furnace 40 is shared by the plurality of injectors 3.

[0045] Although not shown, each of the multiple injection machines 3 may be connected to a separate mold 2. In the illustrated embodiment, the multiple injection machines 3 are connected in parallel on the circulation pipe 41, but the multiple injection machines 3 may also be connected in series on the circulation pipe 41. In the illustrated embodiment, on-off valves 44 are provided before and after the parallel connection of the first injection machine 301 and the second injection machine 302, and on-off valves 44 are provided before and after the parallel connection of the third injection machine 303 and the fourth injection machine 304. However, the arrangement of the on-off valves 44 may be changed as desired, for example, on-off valves 44 may be provided before and after each of the first injection machine 301, the second injection machine 302, the third injection machine 303, and the fourth injection machine 304.

[0046] The diameter of the circulation pipe 41 may gradually decrease from one end 41a to the other end 41b. In particular, when multiple injectors 3 are provided as in the illustrated embodiment, the diameter of the circulation pipe 41 from the circulation pump 43 to each of the multiple injectors 3 may be smaller than the diameter of the circulation pipe 41 from the melting furnace 40 to the circulation pump 43. Also, the diameter of the circulation pipe 41 from each of the multiple injectors 3 to the melting furnace 40 may be smaller than the diameter of the circulation pipe 41 from the melting furnace 40 to the circulation pump 43.

[0047] 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.

[0048] 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.

[0049] 2: Mold 3: Injector 20: Mold cavity 21: Conductive material 30: Molten sulfur 40: Melting furnace 41: Circulation piping 301: First injector 302: Second injector 410: Heater 411: Thermal insulation cover 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; the molten sulfur flows through a circulation pipe having one end and the other end connected to a melting furnace that heats the sulfur and produces the molten sulfur; and the injector injects the molten sulfur flowing through the circulation pipe into the mold cavity.

2. The method for manufacturing sulfur molds according to claim 1, wherein a heater and a heat-insulating cover are attached to the outer periphery of the circulation pipe.

3. The method for producing a sulfur mold according to claim 1, wherein the temperature of the molten sulfur in the circulation pipe is controlled to be 120°C or higher and 150°C or lower.

4. The method for manufacturing a sulfur mold according to claim 1, wherein the injectors include a first injector and a second injector, the first injector and the second injector are connected to the circulation pipe, and the first injector and the second injector are connected to the circulation pipe.

5. 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 4.

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