Method for manufacturing sodium-sulfur battery
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- NGK CORP
- Filing Date
- 2025-01-30
- Publication Date
- 2026-08-06
Smart Images
Figure JP2025003106_06082026_PF_FP_ABST
Abstract
Description
Method for manufacturing a sodium-sulfur battery
[0001] The present invention relates to a method for manufacturing a sodium-sulfur battery, and more particularly to a method for manufacturing a sodium-sulfur battery suitable for evaluating the reliability of a sodium-sulfur battery after assembling the sodium-sulfur battery.
[0002] The sodium-sulfur battery has, for example, a configuration in which a bottomed cylindrical component made of a solid electrolyte such as β-alumina is disposed in a metal container on the anode side, sodium as a cathode active material is accommodated inside the bottomed cylindrical component, and sulfur as an anode active material is accommodated outside. When this sodium-sulfur battery discharges, ionized sodium permeates through the solid electrolyte and reacts with sulfur to generate sodium polysulfide, generating electricity. On the contrary, sodium and sulfur are generated by the reverse reaction to perform charging.
[0003] After such a sodium-sulfur battery is manufactured, the initial conditioning and initial performance characteristic inspection of the battery are performed by heating the manufactured sodium-sulfur battery to a raised temperature and performing charge and discharge. Patent Document 1 describes a method of initializing a battery by raising the temperature of a sodium-sulfur battery in a heating furnace after assembling the battery and discharging it by a resistive discharge method until the initial peak resistance of the battery is obtained.
[0004] Patent Document 2 describes that in the temperature raising step, the sodium-sulfur battery is raised in temperature from room temperature to a temperature equal to or higher than the melting point of sodium polysulfide. In Patent Document 2, it is described that the temperature raising step of the sodium-sulfur battery has three or more temperature gradients until the temperature is raised from room temperature to a temperature equal to or higher than the melting point of sodium polysulfide. Specifically, from 30°C to 90°C, the sodium-sulfur battery is heated at about 8.6°C / h, from 90°C to 150°C, it is heated at about 2.6°C / h, and from 150°C to 300°C, it is heated at about 5.0°C / h.
[0005] Japanese Patent Application Laid-Open No. 2003-163028 International Publication No. 2010 / 082528
[0006] The process of heating sodium-sulfur batteries after manufacturing and testing their initial characteristics through charging and discharging is an important step in ensuring the safety and reliability of sodium-sulfur batteries. However, leaving sodium-sulfur batteries with an excessive thermal history is undesirable, as it may degrade their thermal or mechanical properties.
[0007] Therefore, in conventional heating processes, a method has been used to raise the temperature of the sodium-sulfur battery to around 300°C, which is within the operating temperature range of approximately 285 to 345°C (see, for example, Patent Document 2, paragraphs 0029-0040). However, it has been found that voltage abnormalities can occur in the sodium-sulfur battery during charge-discharge testing, and as a result, the characteristic testing of the sodium-sulfur battery may not be performed efficiently.
[0008] In view of the above issues, the present invention provides a method for manufacturing a sodium-sulfur battery that can suppress the occurrence of voltage abnormalities in the sodium-sulfur battery during charge-discharge testing and can perform characteristic testing of the sodium-sulfur battery more efficiently.
[0009] The inventors have diligently studied to solve the above problems and have created the present invention as illustrated below. [Aspect 1] In one embodiment, the present invention is a method for manufacturing a sodium-sulfur battery, comprising an inspection step for inspecting a sodium-sulfur battery, wherein the inspection step includes a heating step of raising the temperature of the sodium-sulfur battery from room temperature to a maximum temperature of 340 to 400°C before performing a charge-discharge test on the sodium-sulfur battery, and a pretreatment step following the heating step of holding the sodium-sulfur battery at 340°C or higher for 1 minute or more, and then lowering the temperature of the sodium-sulfur battery to the inspection start temperature for the charge-discharge test. [Aspect 2] In one embodiment, the present invention is a method for manufacturing a sodium-sulfur battery according to Aspect 1, comprising: a first heating step of heating the sodium-sulfur battery from room temperature to 100 ± 10°C at a rate of 3.0 to 10.0°C / h; a second heating step following the first heating step of heating the sodium-sulfur battery to 150 ± 10°C at a rate of 1.0 to 5.0°C / h; and a third heating step following the second heating step of heating the sodium-sulfur battery to a maximum temperature at a rate of 1.0 to 6.0°C / h. [Aspect 3] In one embodiment, the present invention is a method for manufacturing a sodium-sulfur battery according to Aspect 1, comprising: a first heating step of heating the sodium-sulfur battery from room temperature to 100 ± 10°C at a rate of 50.0 to 100.0°C / h; a second heating step following the first heating step of heating the sodium-sulfur battery to 300 ± 10°C at a rate of 1.0 to 5.0°C / h; and a third heating step following the second heating step of heating the sodium-sulfur battery to a maximum temperature at a rate of 75.0 to 180.0°C / h or higher. [Aspect 4] In one embodiment, the present invention is a method for manufacturing a sodium-sulfur battery according to any one of Aspects 1 to 3, wherein the heating time from room temperature to the maximum temperature is within 70 hours. [Aspect 5] In one embodiment, the present invention is a method for manufacturing a sodium-sulfur battery according to Aspect 1 or 2, wherein the sodium-sulfur battery includes a module battery in which a plurality of cells are connected in series and parallel within a container. [Aspect 6] In one embodiment of the present invention, the method for manufacturing a sodium-sulfur battery according to aspect 5 includes a post-temperature rise inspection step for inspecting the withstand voltage and / or insulation resistance of the module battery before charge-discharge testing.[Aspect 7] In one embodiment, the present invention is a method for manufacturing a sodium-sulfur battery according to aspect 5 or 6, further comprising a cooling step of circulating air into a container to cool the module battery after a charge-discharge test. [Aspect 8] In one embodiment, the present invention is a method for manufacturing a sodium-sulfur battery according to aspect 7, wherein the cooling step includes starting the supply of air into the container when the module battery has cooled to 90°C to 305°C.
[0010] According to one embodiment of the present invention, a method for manufacturing a sodium-sulfur battery can be provided that can suppress the occurrence of voltage abnormalities in the sodium-sulfur battery during charge-discharge testing and that allows for more efficient characteristic testing of the sodium-sulfur battery.
[0011] Figures 1(a) to 1(g) are schematic diagrams showing the positional relationship between the solid electrolyte tube and the safety tube inside the sodium-sulfur battery cell during each heating step and charge / discharge inspection step. Figure 2 is a flowchart showing an example of a cell inspection step according to the first embodiment of the present invention. Figure 3 is a graph showing the charge / discharge characteristics of a sodium-sulfur battery cell when heated using the heating step according to the embodiment of the present invention and when performed using a conventional heating step. Figure 4 is a flowchart showing an example of a module inspection step according to the second embodiment of the present invention. Figure 5 is a schematic diagram showing an example of a method for cooling a module battery according to the second embodiment of the present invention. Figure 6 is a schematic diagram showing a first modified example of the module battery of Figure 5.
[0012] Embodiments of the present invention will be described below with reference to the drawings. The embodiments shown below are illustrative examples of devices and methods for realizing the technical concept of this invention, and the technical concept of this invention is not limited to the structure, arrangement, etc., of the components described below.
[0013] A method for manufacturing a sodium-sulfur battery according to an embodiment of the present invention includes an inspection step for inspecting the sodium-sulfur battery, the inspection step including a heating step of raising the temperature of the sodium-sulfur battery from room temperature to a maximum temperature of 340°C to 400°C before performing a charge-discharge test on the sodium-sulfur battery, and a pre-treatment step following the heating step of holding the sodium-sulfur battery at 340°C or higher for 1 minute or more, and then lowering the temperature of the sodium-sulfur battery to the inspection start temperature for the charge-discharge test.
[0014] The sodium-sulfur batteries to be tested may include single sodium-sulfur cells (hereinafter also referred to as "cells"), or module batteries in which multiple cells are connected in series and parallel within a container to increase the electromotive force.
[0015] The cells of a sodium-sulfur battery have a cylindrical shape. The cell has a cathode chamber formed inside a bottomed cylindrical solid electrolyte tube made of β-alumina, which is arranged inside a container, and an anode chamber formed on the outside. Inside the anode chamber is a mold impregnated with sulfur, which is the anode active material. Inside the solid electrolyte tube that forms the cathode chamber is a cathode container for holding sodium, which is the cathode active material. Outside the cathode container, a bottomed cylindrical safety tube is placed between it and the solid electrolyte tube with a predetermined gap.
[0016] A sodium-sulfur battery module has a configuration in which multiple cells are arranged in a row within a cell housing container, and the multiple cells are electrically connected to each other. Insulating sheets, heaters, wiring, etc. are arranged on the inner surface and bottom of the cell housing container. A sand layer, formed by laying sand, is placed on top of the multiple cells, and a top cover is placed on top of the sand layer via insulating material, heat-resistant material, fire-resistant material, etc.
[0017] The inspection process according to the embodiment of the present invention can be suitably applied to an inspection process for inspecting the electrical characteristics of a sodium-sulfur battery after it has been assembled. For example, this inspection process can be applied to a cell inspection process for inspecting whether predetermined electrical characteristics are met after the cells of a sodium-sulfur battery have been assembled, by raising the temperature of the assembled cells to perform initial conditioning. Furthermore, this inspection process can be applied to a module inspection process for inspecting whether predetermined electrical characteristics are met after a module battery has been assembled by housing a plurality of cells in a container and connecting them in series and parallel. In the following, the first embodiment will be described as a cell inspection process, and the second embodiment will be described as a module inspection process.
[0018] After assembly, sodium-sulfur batteries have traditionally been heated to approximately 300°C before charging and discharging tests to minimize unnecessary thermal history before operation. However, conventional sodium-sulfur batteries can sometimes exhibit voltage abnormalities during charging and discharging tests. Voltage abnormalities refer to phenomena in which the voltage of the sodium-sulfur battery drops during discharging or rises during charging.
[0019] It has been found that some sodium-sulfur batteries exhibit voltage abnormalities during the first charge-discharge test cycle, but do not exhibit voltage abnormalities during the second charge-discharge test cycle. One possible cause, though not limited to the following, is suspected to be a faulty assembly when placing the safety tube, which houses the cathode container containing sodium, within the fixed electrolyte tube made of β-alumina, which constitutes part of the sodium-sulfur battery cell. Another possible cause is suspected to be deformation of the safety tube, which is made of aluminum or an aluminum alloy, due to thermal expansion when the temperature rises.
[0020] Figure 1(a) schematically shows the relationship between the shape and position of the safety tube 11 and the solid electrolyte tube 10 before the heating process in a cell 1 where a voltage abnormality occurs when the first charge / discharge test is performed after the cell 1 has been heated to around 300°C and the heating process has been completed. In the cross-section in the diameter direction perpendicular to the main axis of the bottomed cylindrical solid electrolyte tube 10 (cross-sections in Figures 1(a) to 1(g)), it is ideal that a predetermined gap for the passage of sodium, which is the cathode active material, is evenly formed around the entire outer circumference of the safety tube 11 between the safety tube 11 and the solid electrolyte tube 10. However, the assembled cell 1 is not always in such a state. For example, as shown in Figure 1(a), if the safety tube 11 rotates around the main axis of the solid electrolyte tube 10 for some reason during assembly, a part of the outer wall of the safety tube 11 may come into contact with the inner wall of the solid electrolyte tube 10.
[0021] As shown in Figure 1(b), when such a cell 1 is heated to approximately 300°C during the heating process, the aluminum or aluminum alloy safety tube 11 expands thermally within the solid electrolyte tube 10. As a result, the contact area (contact area S) between the inner wall of the solid electrolyte tube 10 and the outer wall of the safety tube 11 increases further compared to before the heating process. When the contact area S increases, the passage for sodium between the inner wall of the solid electrolyte tube 10 and the outer wall of the safety tube 11 is partially blocked, reducing the current-carrying area of the cell 1. Therefore, when the first charge-discharge test is performed on a cell 1 like the one in Figure 1(b), the current-carrying area may not be sufficiently secured, which can lead to a voltage drop failure problem.
[0022] On the other hand, even with cell 1 having the configuration shown in Figure 1(b), the first charge-discharge test can cause cell 1 to be kept at the operating temperature for a certain period of time, resulting in the temperature of cell 1 at the end of the first discharge test being higher than the temperature of cell 1 at the end of the heating process. It is thought that the safety tube 11 of cell 1 can expand to follow the inner diameter of the solid electrolyte tube 10, as shown in Figure 1(c), by being exposed to a predetermined operating temperature for a long period of time. After the first discharge test is completed and cell 1 is cooled, the safety tube 11 contracts within the solid electrolyte tube 10. As a result, as shown in Figure 1(d), after the first discharge test is completed, the outer shape of the safety tube 11 of cell 1 can be reformed to be approximately concentric with the inner diameter of the solid electrolyte tube 10.
[0023] In such a cell 1, an appropriate gap is ensured between the solid electrolyte tube 10 and the safety tube 11 after the first charge / discharge test and before the second charge / discharge test. Therefore, even if a second charge / discharge test is performed on a cell that experienced a voltage abnormality during the first charge / discharge test, it is believed that the voltage abnormality problem will not occur again.
[0024] According to the method for manufacturing a sodium-sulfur battery according to an embodiment of the present invention, before performing a charge-discharge test on the sodium-sulfur battery, the sodium-sulfur battery is heated from room temperature to 340-400°C, which is near or above the upper limit of the operating temperature of the sodium-sulfur battery (285-345°C), so that the safety tube 11 expands sufficiently within the solid electrolyte tube 10. Following the heating step, the sodium-sulfur battery is held at 340°C or higher for at least one minute. As a result, as shown in Figure 1(e), even if, immediately after assembly, the sodium-sulfur battery has a portion where the gap between the solid electrolyte tube 10 and the safety tube 11 is locally narrow due to the rotation of the safety tube 11 within the solid electrolyte tube 10, the safety tube 11 can expand sufficiently within the solid electrolyte tube 10 because the cell 1 is sufficiently heated to the above-mentioned maximum temperature and held therein during the heating step (Figure 1(f)). Subsequently, as cell 1 cools down to approximately 310-320°C, which is the starting temperature for the first charge-discharge test, the safety tube 11 shrinks within the solid electrolyte tube 10, and its outer shape is reformed (Figure 1(g)). As a result, an appropriate gap is formed between the safety tube 11 and the solid electrolyte tube 10 of cell 1 before the start of the first charge-discharge test. Therefore, during the subsequent first charge-discharge test, the problem of reduced current flow due to blocking the sodium passage between the safety tube 11 and the solid electrolyte tube 10 is less likely to occur, and the problem of voltage abnormalities in the sodium-sulfur battery is less likely to occur.
[0025] In the heating process, the maximum temperature is preferably adjusted to a temperature that allows the aluminum or aluminum alloy material of the safety tube 11 to expand appropriately within the solid electrolyte tube 10, while preventing deterioration of the thermal and mechanical properties of the sodium-sulfur cell. The maximum temperature in the heating process is 340°C or higher, preferably 350°C or higher, more preferably 365°C or higher, and even more preferably 370°C or higher. On the other hand, if the maximum temperature is too high, it will leave an excessive thermal history on the sodium-sulfur cell before operation, which is undesirable. The maximum temperature is 400°C or lower, and may even be 380°C or lower. Specifically, the maximum temperature is preferably 340°C to 400°C, more preferably 350°C to 380°C, and even more preferably 365°C to 380°C.
[0026] In a sodium-sulfur battery, the heating process can be stopped immediately after the temperature reaches its maximum, thereby minimizing thermal damage to the sodium-sulfur battery. Furthermore, in order to promote the thermal expansion of the aluminum or aluminum alloy that constitutes the safety tube 11, a pre-treatment process is performed following the heating process, in which the sodium-sulfur battery is held at 340°C or higher for at least one minute, and then cooled down to the test start temperature (290-340°C) for the charge-discharge test.
[0027] The holding temperature of the sodium-sulfur cell during the holding process should be such that it does not leave an excessive thermal history on the sodium-sulfur cell. The holding temperature may be, for example, 350°C or higher, 360°C or higher, or 365°C or higher. The holding time of the sodium-sulfur cell may be as short as, for example, less than 1 minute, but it is preferable to have a sufficiently long time to promote sufficient thermal expansion of the safety tube 11 provided by the sodium-sulfur cell. The holding time is preferably 3 minutes or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. The longer the holding time, the better to promote sufficient thermal expansion of the safety tube 11, but if it is too long, the time required for inspection will be long, which may not be productive. The holding time is preferably within 5 hours, more preferably within 3 hours, even more preferably within 2 hours, and even more preferably within 1.5 hours. For example, the holding time is preferably between 1 minute and 3 hours, and more preferably between 5 minutes and 1.5 hours. This makes it possible to reshape the safety tube 11 into a more reliable and appropriate shape while preventing failure of the sodium-sulfur battery.
[0028] (First Embodiment: Cell Inspection Process) Figure 2 is a flowchart showing an example of a cell inspection process according to the first embodiment of the present invention. After the cells are assembled into a predetermined shape in a cell assembly process (not shown), they are sent to the cell inspection process shown in Figure 2.
[0029] In the cell inspection process, in step S11, the assembled cells are received into a cell inspection area for cell inspection (cell receiving process). Cells received into the cell inspection area undergo sampling inspection to check their electrical characteristics and appearance before heating. After the sampling inspection is completed, the cells are typically arranged in a row in containers provided on a carrier for transporting the cells into the inspection furnace. The number of cells that can be contained in a single container is not particularly limited. For example, a single container may contain about 50 to 100 cells. The cells contained in the containers are connected to a power supply for supplying current to the cells and measuring instruments for measuring the temperature and voltage of the cells during the heating process, and preparations for heating and charge / discharge inspections are made. The temperature and heating rate of the cells during the heating process can be measured by measuring instruments electrically connected to the cells.
[0030] After the inspection preparation is complete, in step S12, the carrier containing the cell is brought into the inspection furnace for heating the cell (inspection furnace loading process). In step S13, the cell heating process is carried out inside the inspection furnace.
[0031] From the perspective of the thermal impact on the cell, it is preferable to have a relatively long heating time, however, if the heating time is too long, production efficiency may decrease. The heating time for the cell is preferably 70 hours or less from the room temperature at the start of heating to the maximum temperature, more preferably 65 hours or less, even more preferably 55 hours or less, and even more preferably 45 hours or less. Details of the heating process will be described later.
[0032] Following the cell heating step, a pretreatment step is performed in step S14. In the pretreatment step S14, the cell is held at 340°C or higher, preferably 350°C or higher, more preferably 360°C or higher, even more preferably 370°C or higher for 1 minute or more, more preferably 3 minutes or more, even more preferably 5 minutes or more, and even more preferably 1 hour or more. After that, the cell is cooled down to 290-340°C, preferably 300-330°C, more preferably 310-320°C, which is the inspection start temperature for the cell charge / discharge test.
[0033] After the cell pretreatment is complete, in step S15, a charge / discharge test of the cell is performed. The specific method of the charge / discharge test is not particularly limited. For example, the cell may be charged and discharged by dividing the discharge current value into multiple stages using a resistance discharge method until the initial peak resistance of the cell is obtained. In the first embodiment, the charge / discharge test of the cell can be performed at approximately 320°C (285°C to 345°C). After the charge / discharge test of the cell is completed, in step S16 the cell is removed from the inspection furnace and cooled to room temperature by natural cooling. In step S17, an appearance inspection of the cell, a voltage test at room temperature, etc. are performed, and the series of cell inspection processes are completed.
[0034] The heating step in step S13 includes heating the cell from room temperature to a maximum temperature of 340°C to 400°C before performing a charge / discharge test on the cell. The cell may be heated from room temperature to the maximum temperature at a constant heating rate, but preferably includes the following heating step (C): A first heating step of heating the sodium-sulfur cell from room temperature to 100±10°C at a rate of 50.0 to 100.0°C / h; a second heating step following the first heating step of heating the sodium-sulfur cell to 300±10°C at a rate of 1.0 to 5.0°C / h; and a third heating step following the second heating step of heating the sodium-sulfur cell to the maximum temperature at a rate of 75.0 to 180.0°C / h.
[0035] In the first heating step, it is preferable to raise the heating rate from room temperature to 100±10°C, where sodium and sulfur begin to dissolve, at a higher rate than in the second heating step described later. In the first heating step, when sodium and sulfur have not yet dissolved, the stress due to changes in the internal state of the cell is small, allowing for rapid heating. As a result, the total heating time applied to the cell is shortened, and thus the thermal stress applied to the cell can be reduced. In the first heating step, it is preferable to raise the cell temperature at 75.0 to 100.0°C / h, more preferably 80.0 to 100.0°C / h, and even more preferably 90.0 to 100.0°C / h.
[0036] Since the second heating step includes a temperature range in which sodium and sulfur dissolve, if the heating rate is too high, it may accelerate the deterioration of the thermal or mechanical properties of the cell. In the second heating step according to the first embodiment, it is preferable to lower the heating rate in the temperature range from 100±10°C to 300±10°C than the heating rate of the first heating step. It is more preferable to heat the second heating step at 1.5 to 5.0°C / h, more preferably 2.0 to 4.5°C / h, and even more preferably 3.0 to 4.5°C / h.
[0037] In the third heating step, similar to the first heating step, the thermal stress on the cell is reduced by rapidly heating the cell to the maximum temperature. In the third heating step, it is preferable to heat the cell from 300±10°C to the maximum temperature at a rate of 80.0°C / h or higher, more preferably at 120.0°C / h or higher, and even more preferably at 150.0°C / h or higher. If the heating rate in the third heating step is too high, the thermal stress on the solid electrolyte tube 10, which is made of β-alumina or the like, may become too high. It is preferable to heat the cell from 300±10°C to the maximum temperature at a rate of 170.0°C / h or lower, and more preferably at 160.0°C / h or lower.
[0038] In this specification, the rate of temperature rise of the cells or modules constituting the sodium-sulfur battery is expressed as the average rate of temperature rise in "°C / hr". The temperature rise of the sodium-sulfur battery is the temperature obtained by considering a tolerance of ±10°C as a temperature control range from the set value of the temperature rise of the sodium-sulfur battery. This tolerance may be ±7°C, ±5°C, ±3°C, or ±0°C. That is, in this embodiment, for example, 100±10°C substantially means any temperature within the range of 90 to 110°C, but may be within the range of 93 to 107°C considering a tolerance of ±7°C, or within the range of 95 to 105°C considering a tolerance of ±5°C, or within the range of 97 to 103°C considering a tolerance of ±3°C, or it may be 100°C.
[0039] According to the cell inspection process of the first embodiment of the present invention, in the heating process (C), while suppressing excessive thermal history to the cell, the safety tube 11 constituting the cell is sufficiently expanded and contracted to reshape the safety tube 11, thereby ensuring a sufficient predetermined gap for passing sodium between it and the solid electrolyte tube 10. This suppresses the occurrence of voltage abnormalities in the sodium-sulfur battery during charging and discharging due to defective cell assembly, etc., and makes it possible to perform characteristic inspection of the sodium-sulfur battery more efficiently.
[0040] Figure 3 shows an example of the relationship between battery voltage and elapsed time for battery A, which underwent a charge-discharge test after a pretreatment process in which the safety tube inside the solid electrolyte tube in the cell was forcibly rotated to the configuration shown in Figure 1(a), the temperature was raised to the maximum temperature of 340°C in the above-mentioned heating step (C), and then held at 340°C or above for more than 1 minute before cooling, and battery B, which underwent a charge-discharge test immediately after being heated to 310°C using the conventional method. Battery A according to the first embodiment could undergo a charge-discharge test until the end of discharge, whereas battery B using the conventional method experienced a voltage drop after 300 hours and a discharge of 377Ah, and could not undergo a charge-discharge test until the end of discharge.
[0041] As described above, the cell inspection process according to the first embodiment of the present invention includes a pre-treatment step in which, after the heating step (C) in step S13, the cell is held at 340°C or higher for 1 minute or more, and then the cell is adjusted to the inspection temperature for charge-discharge testing. By appropriately adjusting the heating rate in each temperature range of the heating step (C), the thermal impact on the cell during heating is reduced, and in the pre-treatment step S14, the safety tube 11 constituting the cell is sufficiently expanded within the solid electrolyte tube 10 and then contracted. As a result, the outer shape of the safety tube 11 can be reformed to an appropriate shape by the heating step (C) before the charge-discharge testing, and a predetermined gap for passing sodium between it and the solid electrolyte tube 10 can be secured. As a result, the occurrence of voltage abnormalities in the sodium-sulfur battery during charging and discharging due to defective cell assembly, etc., can be suppressed, and the characteristic testing of the sodium-sulfur battery can be performed more efficiently.
[0042] (Modified Example) When performing the pretreatment step S24 on the module battery in the module inspection step according to the second embodiment described below, it is possible to omit the pretreatment step S14 in the cell inspection step according to the first embodiment. This can shorten the working time required for inspection. In that case, the maximum temperature in the temperature increase step (C) of step S13 described above can be set to about 300 to 320°C.
[0043] That is, when the pretreatment step S14 is omitted, the temperature increase step (C) of the cell in step S13 can include the following steps. A first temperature increase step of increasing the temperature of the sodium-sulfur battery from room temperature to 100 ± 10°C at a rate of 50.0 to 100.0°C / h; Subsequently to the first temperature increase step, a second temperature increase step of increasing the temperature of the sodium-sulfur battery to 300 ± 10°C at a rate of 1.0 to 5.0°C / h; Subsequently to the second temperature increase step, a third temperature increase step of increasing the temperature of the sodium-sulfur battery to 310 ± 10°C at a rate of 75.0 to 180.0°C / h.
[0044] When performing the pretreatment step S24 on the module battery, after the end of the third temperature increase step, the temperature increase is promptly stopped, the temperature of the cell is adjusted to the inspection start temperature, and then the charge-discharge inspection S15 of the cell is performed. According to the modified example of the first embodiment, in the second temperature increase step, by setting the temperature increase rate to about 1.0 to 5.0°C / h and slowing down the temperature increase rate in the temperature range where sodium and sulfur melt, the stress due to the heat applied to the cell can be reduced. As a result, deterioration of the thermal properties or mechanical characteristics of the cell can be suppressed.
[0045] (Second Embodiment: Module Inspection Step) FIG. 4 is a flowchart showing an example of the module inspection step according to the second embodiment of the present invention. In step S21, the assembled module battery is received in a module battery inspection area for performing module battery inspection (module battery reception step). In step S22, the module battery received in the module battery inspection area is subjected to room temperature inspections such as inspection of the appearance of the module battery, inspection of the wiring incorporated in the module battery, insulation confirmation of the heater, thermocouple, etc. incorporated in the module battery, and confirmation of the degree of vacuum.
[0046] After the room temperature inspection, in step S23, a temperature increase process of the module battery is performed. The temperature increase of the module battery can be performed by energizing a heater panel laid on the inner wall and the bottom surface of the module battery. Inside the module battery, a temperature measuring device (thermocouple) for measuring the temperature inside the module battery is inserted at a predetermined position of the module battery. The temperature of the module battery can be measured based on the measured value of the temperature measuring device. A plurality of temperature measuring devices are arranged at arbitrary locations inside the module battery, and a plurality of temperature measurement values are obtained. For the temperature control of the module battery in the second embodiment, for example, the measured values of the temperature measuring devices respectively arranged at the center bottom surface of the battery of the module battery and at the central part of the battery side surface can be used. Among them, the measurement result of the center bottom surface of the battery can be adopted as a representative point of the temperature of the module battery.
[0047] The temperature increase process in step S23 includes a process of increasing the temperature of the module battery from room temperature to the maximum temperature of 340°C to 400°C before performing a charge-discharge inspection on the module battery. Note that the temperature control of the module battery may increase the temperature at a constant rate of increase from room temperature to the maximum temperature, but preferably includes the following temperature increase process (R). A first temperature increase process of increasing the temperature of the module battery from room temperature to 100 ± 10°C at 3.0 to 10.0°C / h; Following the first temperature increase process, a second temperature increase process of increasing the temperature of the module battery to 150 ± 10°C at 1.0 to 5.0°C / h; Following the second temperature increase process, a third temperature increase process of increasing the temperature of the module battery to the maximum temperature at 1.0 to 6.0°C / h.
[0048] When the module battery reaches around 100°C, sodium, which is the cathode active material of the cell constituting the module battery, and sulfur, which is the anode active material, start to melt. In the first temperature increase process according to the second embodiment, it is preferable to increase the rate of temperature increase from room temperature to 100 ± 10°C at which sodium and sulfur start to melt higher than that in the second temperature increase process described later, so as to shorten the time of the temperature increase process.
[0049] The first heating step preferably involves heating the module battery at 5.0 to 10.0°C / h, more preferably 7.0 to 10.0°C / h, even more preferably 8.0 to 9.0°C / h, and still more preferably 8.0 to 8.5°C / h. Room temperature refers to a temperature that is approximately equal to the temperature of the atmosphere in which the sodium-sulfur battery is placed.
[0050] Since the second heating step is in the temperature range where sodium and sulfur are dissolved, if the heating rate is too high, it may accelerate the deterioration of the thermal or mechanical properties of the module battery. In the second heating step according to the second embodiment, it is preferable to lower the heating rate in the temperature range from 100±10℃ to 150±10℃ than the heating rate in the first heating step.
[0051] The second heating step is preferably performed at a rate of 1.5 to 4.8°C / h, more preferably at 2.0 to 4.7°C / h, even more preferably at 3.0 to 4.5°C / h, and even more preferably at 3.5 to 4.5°C / h.
[0052] When the module battery housed in the inspection furnace reaches around 150°C, it exceeds the melting point of sodium polysulfide (Na2S5), and sodium polysulfide begins to form. In the third heating step, the heating process generates sodium polysulfide (Na2S5), and by raising the module battery to its maximum temperature, the aluminum or aluminum alloy safety tubes 11 that make up each cell of the module battery can be sufficiently thermally expanded within the solid electrolyte tube 10.
[0053] The third heating step is preferably performed by raising the temperature from 150 ± 10°C to the maximum temperature at a rate of 1.0 to 6.0°C / h, more preferably at a rate of 1.2 to 5.8°C / h, and even more preferably at a rate of 1.3 to 5.5°C / h.
[0054] The maximum temperature should be sufficient to adequately expand the safety tubes 11 that make up each cell of the module battery and to adjust the outer shape of the safety tubes 11 so that a predetermined gap is secured between the safety tubes 11 and the solid electrolyte tube 10. The maximum temperature in the module battery heating process (R) is the same as that in the cell heating process (C) described above.
[0055] To minimize the thermal impact on the module battery, it is preferable that the heating time of the module battery be as short as possible. For example, the heating time of the module battery from room temperature (the temperature at the start of heating) to the maximum temperature is preferably 70 hours or less, more preferably 60 hours or less, and even more preferably 55 hours or less.
[0056] Following the heating step of the module battery, a pre-treatment step S24 is performed in which the module battery is held at 340°C or higher for at least one minute, and then the cells are cooled down to the test start temperature for the charge / discharge test. Pre-treatment step S24 is substantially the same as pre-treatment step S14 in the first embodiment.
[0057] After the module battery heating process is completed, in step S25, a post-heating inspection process is performed to inspect the withstand voltage and / or insulation resistance of the module battery before the post-heating charge / discharge test. In this post-heating inspection process, the electrical characteristics of the module battery, such as the main circuit and heater, are inspected before the charge / discharge test. By inspecting the electrical characteristics of the module battery other than the cells, such as the main circuit and heater, in the post-heating inspection process before the charge / discharge test, the charge / discharge characteristics of the cell portion to be inspected in the subsequent charge / discharge test can be properly inspected. After the post-heating inspection process, the charge / discharge test is performed in step S26.
[0058] The charge / discharge test in step S26 is performed in the same way as the charge / discharge test of the individual cells, so that the starting temperature of the module battery is around 320°C (290°C to 340°C). After the charge / discharge test of the module battery is completed, a cooling process is performed in step S27 to lower the temperature of the module battery.
[0059] In the cooling process of step S27, the module battery is cooled by circulating air inside the module battery container. The module battery contains insulating materials and other components, which can make it take time to cool. Therefore, by circulating air inside the container during the cooling process, the cooling period can be shortened compared to allowing the module battery to cool naturally.
[0060] As for specific cooling methods, for example, as shown in Figure 5, it is preferable to send outside air from a fan 103 located on the outer surface of the module battery 100 to a heat dissipation duct 104 located above the battery region 101 where multiple cells are arranged. On the other hand, when the fan is operated to forcibly supply air into the container 102, which includes a cell housing container 102a and an upper lid 102b, and rapidly cool the module battery 100, the temperature difference between the top and bottom of the module battery 100 may become large. As a result, there is a risk that the cells inside the module battery 100 may fail due to the temperature difference caused by cooling. Therefore, as shown in Figure 6, it is also preferable for the module battery 100 to further include a heat dissipation duct 114 located below the battery region 101, so that the cells inside the module battery 100 are cooled indirectly without direct contact with air.
[0061] In the cooling process, if the cooling process is started when the temperature of the module battery 100 is too high, the temperature difference between the top and bottom of the module battery 100 may become too large, potentially causing cell failure. On the other hand, if the cooling process is started when the temperature of the module battery 100 is too low, the cooling effect will be small, and the time required for the cooling process will be prolonged.
[0062] In the cooling process, it is preferable to start supplying air into the container 102 of the module battery 100 when the module battery has cooled to 90 to 305°C, thereby cooling the module battery 100. By starting the cooling of the module battery 100 when the module battery reaches approximately 305°C, the cooling period can be shortened by about two weeks compared to when air is not supplied into the container 102 of the module battery 100. Furthermore, by starting the cooling of the module battery 100 when the module battery 100 reaches approximately 90°C, the rapid cooling by the cooling process occurs after the sodium in the cell has solidified, thus suppressing cell failure due to thermal expansion of the cathode container containing the sodium, etc. As shown in Figure 6, a heat dissipation duct 114 for cooling the lower part of the battery region 101 may be arranged at the bottom of the battery region 101.
[0063] After the cooling process is complete, a pre-shipment inspection is performed in step S28 of Figure 4. During the pre-shipment inspection, the vacuum level, appearance, dimensions, voltage, and operation of the fan 103 for cooling the module battery 100 are measured, and the module inspection process is completed.
[0064] According to the module inspection process of the second embodiment of the present invention, before the charge-discharge inspection of the module battery 100, the safety tubes 11 constituting the cells of the module battery 100 can be sufficiently expanded and contracted within the solid electrolyte tube 10. As a result, the outer shape of the safety tubes 11 can be reformed to an appropriate shape by the heating process before the charge-discharge inspection, and a predetermined gap for passing sodium between the safety tubes 11 and the solid electrolyte tube 10 is secured within the cell. This makes it possible to perform characteristic inspection of sodium-sulfur batteries more efficiently.
[0065] Examples of the present invention are shown below, provided to better understand the present invention and its advantages, and are not intended to limit the present invention.
[0066] Cells 1a, 1b, and 1c, and module batteries 1B and 1C, each containing cells 1b and 1c, were prepared in which the safety tube inside the solid electrolyte tube within the cell was forcibly rotated during assembly so that the solid electrolyte tube and the safety tube were in partial contact.
[0067] (Example 1) A carrier containing cell 1a was placed in an inspection furnace and heated from room temperature to 100°C at a rate of 100.0°C / h. After cell 1a reached 100°C, it was heated to 300°C at a rate of 4.4°C / h. After cell 1a reached 300°C, it was heated to the maximum temperature (350°C) at a rate of 150°C / h and then the heating was stopped. After heating, cell 1a was held at 350°C or higher in the inspection furnace for 5 minutes, and then allowed to cool naturally to 320°C, which is the starting temperature for the charge / discharge test in this example.
[0068] (Example 2) Module battery 1B, including cell 1b, was heated from room temperature to 100°C at a rate of 8.1°C / hr. After the measured temperature at the bottom center of module battery 1B reached 100°C, module battery 1B was heated to 150°C at a rate of 3.7°C / h. After module battery 1B reached 150°C, module battery 1B was heated to the maximum temperature (350°C) at a rate of 5.1°C / h, and the heating was stopped. After heating, cell 1b was held at 350°C or higher in the inspection furnace for 5 minutes, and then allowed to cool naturally to 320°C, which is the starting temperature for the charge / discharge test in this example.
[0069] (Comparative Example) Module battery 1C, including cell 1c, was heated from room temperature to 90°C at a rate of 10.0°C / hr. After module battery 1C reached 90°C, module battery 1C was heated to 140°C at a rate of 5.0°C / h. After module battery 1C reached 140°C, module battery 1C was heated to 290°C at a rate of 5.0°C / h or higher, and the heating was stopped. After heating, the temperature was raised to 320°C, which is the starting temperature for the charge / discharge test in this embodiment.
[0070] The internal state of cells 1a, 1b, and 1c, as well as the positional relationship between the solid electrolyte tube and the safety tube, after the heating process in Examples 1, 2, and the Comparative Example was confirmed by placing them in a non-destructive testing device. In cells 1a and 1b of Examples 1 and 2, no contact points between the solid electrolyte tube and the safety tube were detected, whereas in cell 1c of the Comparative Example, multiple contact points were observed between the inner wall of the solid electrolyte tube and the outer wall of the safety tube.
[0071] When charge-discharge tests were performed on cells 1a to 1c after the heating process, Examples 1 and 2 were able to perform discharge tests appropriately until the end of the discharge in the first discharge test. On the other hand, in the comparative example, a voltage drop occurred after discharge, and it was not possible to perform discharge tests until the end of the discharge.
[0072] 1, 1a, 1b, 1c: Cell 10: Solid electrolyte tube 11: Safety tube 100: Module battery 101: Battery area 102: Container 103: Fan 104, 114: Heat dissipation duct
Claims
1. A method for manufacturing a sodium-sulfur battery, comprising an inspection step for inspecting a sodium-sulfur battery, wherein the inspection step includes: a heating step of raising the temperature of the sodium-sulfur battery from room temperature to a maximum temperature of 340 to 400°C before performing a charge-discharge test on the sodium-sulfur battery; and a pre-treatment step following the heating step of holding the sodium-sulfur battery at 340°C or higher for 1 minute or more, and then lowering the temperature of the sodium-sulfur battery to the inspection start temperature for the charge-discharge test.
2. A method for manufacturing a sodium-sulfur battery according to claim 1, wherein the heating step comprises: a first heating step of heating the sodium-sulfur battery from room temperature to 100 ± 10°C at a rate of 3.0 to 10.0°C / h; a second heating step, following the first heating step, of heating the sodium-sulfur battery to 150 ± 10°C at a rate of 1.0 to 5.0°C / h; and a third heating step, following the second heating step, of heating the sodium-sulfur battery to the maximum temperature at a rate of 1.0 to 6.0°C / h.
3. A method for manufacturing a sodium-sulfur battery according to claim 1, wherein the heating step comprises: a first heating step of heating the sodium-sulfur battery from room temperature to 100 ± 10°C at a rate of 50.0 to 100.0°C / h; a second heating step, following the first heating step, of heating the sodium-sulfur battery to 300 ± 10°C at a rate of 1.0 to 5.0°C / h; and a third heating step, following the second heating step, of heating the sodium-sulfur battery to the maximum temperature at a rate of 75.0 to 180.0°C / h.
4. A method for manufacturing a sodium-sulfur battery according to any one of claims 1 to 3, wherein the time required to raise the temperature from room temperature to the maximum temperature is within 70 hours.
5. The method for manufacturing a sodium-sulfur battery according to claim 1 or 2, wherein the sodium-sulfur battery includes a module battery in which a plurality of cells are connected in series and parallel within a container.
6. The method for manufacturing a sodium-sulfur battery according to claim 5, comprising a post-temperature rise inspection step of inspecting the withstand voltage and / or insulation resistance of the module battery before the charge-discharge inspection.
7. The method for manufacturing a sodium-sulfur battery according to claim 5, further comprising a cooling step of circulating air inside the container to cool the module battery after the charge-discharge test.
8. The method for manufacturing a sodium-sulfur battery according to claim 7, wherein the cooling step includes starting the supply of air into the container when the module battery has been cooled to 90°C to 305°C.