JP2012089309A - Safety valve and molten salt battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a safety valve capable of sufficiently sealing a battery and a molten salt battery with improved safety.SOLUTION: A safety valve 6 provided in a battery comprises: a bolt 61 penetrating through an upper container 52 of the battery; a plug body 63 closing a flow hole (through-hole) 611 of the bolt 61; a coil spring (compressive elastic member) 64; a cap nut 62 which compresses the coil spring 64 so as to press the plug body 63; and an O-ring 65 fitted onto a shank of the bolt 61. When the internal pressure of the battery rises, a fluid is discharged from the battery through the flow hole 611 against the repulsive force of the coil spring 64. The O-ring 65 is compressed between the cap nut 62 and the upper container 52 so as to seal a gap of the safety valve 6. Further, the repulsive force of the O-ring 65 prevents looseness of the cap nut 62. Furthermore, in a molten salt battery, the through-hole of the upper container 52 is closed by a film-like material which ruptures when the internal pressure rises in order to ensure safety with the safety valve 6 not being working.

Description

  The present invention relates to a safety valve that discharges fluid from the inside when the internal pressure of the battery increases, and a molten salt battery including the safety valve.

  In recent years, utilization of natural energy such as sunlight or wind power has been promoted. When power is generated using natural energy, the amount of power generation is likely to fluctuate. Therefore, in order to supply the generated power, it is necessary to level the supplied power by charging and discharging using a storage battery. . For this reason, in order to promote utilization of natural energy, a storage battery with high energy density and high efficiency is indispensable. As such a storage battery, there is a sodium-sulfur battery disclosed in Patent Document 1. Another high energy density and high efficiency storage battery is a molten salt battery. The molten salt battery is a battery using a molten salt as an electrolyte, and operates in a state where the molten salt is melted. During operation of the molten salt battery, the temperature in the molten salt battery is maintained at or above the melting point of the molten salt.

  A normal battery is provided with a safety valve that discharges the internal gas when the internal pressure rises due to the generation of gas inside. An example of a conventional safety valve is that a bolt with a through hole formed in the central axis passes through a battery container through a bush, and a cap nut with a through hole is screwed to the tip of the bolt, and a spring is formed in the cap nut. Presses the plug into the through hole of the bolt. In a normal state, the through hole of the bolt is closed by a plug in the cap nut. When the internal pressure of the battery rises, the plug body floats in the cap nut, the bolt through hole is opened, and the gas is discharged from the battery through the bolt through hole and the cap nut through hole. After the gas is discharged, the internal pressure of the battery decreases, and the through hole of the bolt is closed again by the elastic member.

JP 2007-273297 A

  In the conventional safety valve, a gap may be formed between the bush and the bolt, and there is a problem that the battery is not sufficiently sealed. Further, since the conventional safety valve has no mechanism for preventing the nut from loosening, there is a problem that the nut is easy to loosen and the battery is not sufficiently sealed by loosening the nut. Further, in the molten salt battery, as the internal gas is discharged, a part of the molten salt is also discharged through the through hole. The temperature of the discharged molten salt falls below the melting point, and the discharged molten salt solidifies and adheres to the through holes of the bolt and the cap nut. For this reason, there is a possibility that the through holes of the bolt and the cap nut are blocked by the solidified molten salt, and the safety valve cannot discharge the gas inside the molten salt battery.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a safety valve capable of sufficiently sealing the battery and a molten salt battery with improved safety.

  The safety valve according to the present invention is a safety valve that discharges fluid from inside a container when the pressure in the container becomes equal to or higher than a predetermined pressure, and has a through hole formed in the axial direction for allowing fluid to flow. A bolt to be installed through the formed hole; a through hole formed in the closed end; a plug for closing the through hole of the bolt; and the plug and the closed end Between the container and the cap nut, and a cap nut screwed into one end of the bolt, with a compression elastic member arranged on the inner side to compress the plug body and press the plug to the tip of the bolt And an o-ring that is externally fitted to the bolt shaft at a position, and a screw thread is not formed on a portion of the bolt shaft to which the o-ring is fitted.

  In the safety valve according to the present invention, a taper portion having a diameter that widens outward is formed in the opening portion outside the hole formed in the container, and in the state where the cap nut is screwed to the bolt, The O-ring is compressed between the cap nut and the tapered portion.

  The molten salt battery according to the present invention is a molten salt battery using a molten salt as an electrolyte, and includes a container containing the molten salt therein, and a through hole is formed in the container. Or the safety valve of 2 is attached, It is characterized by the above-mentioned.

  In the molten salt battery according to the present invention, another through hole is formed in the container, and a closed portion is formed by closing the other through hole with a film-like material, and the closed portion is a pressure inside the battery. Is configured to be destroyed when a second predetermined pressure higher than the first predetermined pressure at which the fluid in the battery is discharged from the safety valve is reached.

  In the present invention, the safety valve provided in the battery includes a bolt that penetrates the battery container, a plug that closes a through hole formed in the bolt, a compression elastic member, and a compression elastic member that compresses the compression elastic member. A cap nut to hold down and an O-ring that fits around the shaft of the bolt. When the internal pressure of the battery rises, the plug is pushed out by a force greater than the repulsive force of the compression elastic member, and the fluid is discharged from the battery through the through hole. The O-ring is compressed between the cap nut and the battery container, and seals the gap between the bolt and the container and the gap between the bolt and the cap nut. Moreover, the slack of the cap nut is prevented by the repulsive force of the O-ring.

  In the present invention, the opening portion of the hole formed in the battery container is formed with a tapered portion in which the diameter of the hole widens outward, and the O-ring fits into the tapered portion, and the shaft of the bolt is It is effectively compressed while contacting the side surface, the tip of the cap nut and the tapered portion of the container.

  Moreover, in this invention, the molten salt battery provided with the safety valve is further provided with a closed portion in which the through hole of the container is closed with a membrane material. When the internal pressure of the battery becomes a second predetermined pressure that is larger than the first predetermined pressure when the fluid is discharged from the battery by the safety valve, the closing portion is destroyed and the fluid passes from the battery through the through hole. Is discharged. Even if the safety valve cannot discharge the fluid inside the molten salt battery, the fluid is discharged from the battery due to the destruction of the closed portion.

  In the present invention, it is possible to discharge the fluid from the battery when the internal pressure of the battery is increased by the safety valve. Play.

It is typical sectional drawing which shows the structural example of the molten salt battery of this invention. It is typical sectional drawing which showed the structure of the safety valve. It is typical sectional drawing which showed the structure of the safety valve. It is typical sectional drawing which showed the structure of the closing part.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
FIG. 1 is a schematic cross-sectional view showing a configuration example of the molten salt battery of the present invention. FIG. 1 shows a schematic cross-sectional view of a molten salt battery cut longitudinally. The molten salt battery is configured such that a positive electrode 1, a separator 3, and a negative electrode 2 are arranged side by side in a rectangular parallelepiped box-shaped lower container 51 whose upper surface is open, and an upper container 52 is attached to the lower container 51. The positive electrode 1 and the negative electrode 2 are formed in a rectangular flat plate shape, and the separator 3 is formed in a sheet shape. The separator 3 is interposed between the positive electrode 1 and the negative electrode 2. The positive electrode 1, the separator 3, and the negative electrode 2 are stacked and arranged vertically with respect to the bottom surface of the lower container 51.

  A spring 41 made of corrugated metal is arranged between the negative electrode 2 and the inner wall of the lower container 51. The spring 41 is made of an aluminum alloy and biases a flat plate-like presser plate 42 having inflexibility to press the negative electrode 2 toward the separator 3 and the positive electrode 1 side. The positive electrode 1 is pressed by the reaction of the spring 41 from the inner wall opposite to the spring 41 to the separator 3 and the negative electrode 2 side. The spring 41 is not limited to a metal spring or the like, and may be an elastic body such as rubber, for example. When the positive electrode 1 or the negative electrode 2 expands or contracts due to charge / discharge, the volume change of the positive electrode 1 or the negative electrode 2 is absorbed by the expansion and contraction of the spring 41.

The positive electrode 1 is formed by applying a positive electrode material 12 including a positive electrode active material such as NaCrO ₂ and a binder on a rectangular plate-shaped positive electrode current collector 11 made of aluminum. The positive electrode active material is not limited to NaCrO ₂ . In the negative electrode 2, a negative electrode material 22 containing a negative electrode active material such as tin is formed on a rectangular plate-shaped negative electrode current collector 21 made of aluminum by plating. When the negative electrode material 22 is plated on the negative electrode current collector 21, tin plating is performed after zinc is plated on the base as a zincate treatment. The negative electrode active material is not limited to tin. For example, tin may be replaced with metallic sodium, carbon, silicon, or indium. The negative electrode material 22 may be formed, for example, by applying a binder to a negative electrode active material powder and applying the powder onto the negative electrode current collector 21. The positive electrode current collector 11 and the negative electrode current collector 21 are not limited to aluminum, and may be stainless steel or nickel, for example. The separator 3 is an insulating material such as silicate glass or resin, and is formed in a shape capable of holding an electrolyte therein and allowing sodium ions to pass therethrough. The separator 3 is a resin formed in, for example, a glass cloth or a porous shape.

  In the lower container 51, the positive electrode material 12 of the positive electrode 1 and the negative electrode material 22 of the negative electrode 2 face each other, and a separator 3 is interposed between the positive electrode 1 and the negative electrode 2. The separator 3 is impregnated with a molten salt that is an electrolyte. The molten salt impregnated in the separator 3 is in contact with the positive electrode material 12 of the positive electrode 1 and the negative electrode material 22 of the negative electrode 2. The inner surface of the lower container 51 has an insulating structure by a method such as coating with an insulating resin in order to prevent a short circuit between the positive electrode 1 and the negative electrode 2. A positive terminal 53 and a negative terminal 54 are provided outside the upper container 52 for connection to the outside. The positive electrode terminal 53 and the negative electrode terminal 54 are insulated from each other, and the portion of the upper container 52 facing the lower container 51 is also insulated by an insulating film or the like. One end of the positive electrode current collector 11 is connected to the positive electrode terminal 53 with a lead wire 55, and one end portion of the negative electrode current collector 21 is connected to the negative electrode terminal 54 with a lead wire 56. The lead wire 55 and the lead wire 56 are insulated from the upper container 52. The upper container 52 is attached to the lower container 51 by welding.

  The molten salt impregnated in the separator 3 is an ionic salt that becomes a conductive liquid in a molten state. The molten salt battery operates as a secondary battery using the molten salt as an electrolyte at a temperature equal to or higher than the melting point of the molten salt. In order to lower the melting point of the molten salt, it is desirable that the molten salt impregnated in the separator 3 is a mixture of a plurality of types of salts. For example, the molten salt is a mixed salt of NaFSA having a sodium ion as a cation and FSA (bisfluorosulfonylamide) as an anion and KFSA having a potassium ion as a cation and FSA as an anion. The configuration of the molten salt battery shown in FIG. 1 is a schematic configuration, and the molten salt battery may include other components (not shown) such as a heater or a temperature sensor for heating the inside. Good. 1 shows a form in which a pair of positive electrodes 1 and negative electrodes 2 are provided, the molten salt of the present invention has a form in which a plurality of positive electrodes 1 and negative electrodes 2 are alternately stacked with separators 3 interposed therebetween. May be.

  Furthermore, the upper container 52 is provided with a safety valve 6 that discharges the internal fluid to the outside when the internal pressure of the molten salt battery rises, and a closing portion 7 in which the through hole is closed with aluminum foil. 2 and 3 are schematic cross-sectional views showing the configuration of the safety valve 6. A through hole 521 is formed in the upper container 52, and a bolt 61 penetrates the through hole 521 from the inside. The bolt 61 has a head located inside the upper container 52 and a tip protruding outward. Further, the bolt 61 is in contact with the inner surface of the through hole 521 without passing through the bush, and an O-ring 65 is fitted on the shaft of the bolt 61 projecting out of the upper container 52. The bolt 61 is made of a metal such as aluminum, and the portion located inside the upper container 52 is insulated by an insulating film or the like. A screw thread is formed on the side surface of the shaft of the bolt 61 from the tip to the middle of the shaft, and no thread is formed on the portion that contacts the inner surface of the through hole 521 and the portion that contacts the O-ring 65. . Furthermore, a through hole (through hole) 611 that penetrates the bolt 61 in the central axis direction is formed from the head of the bolt 61 to the tip.

  A cap nut 62 is screwed onto the tip of the bolt 61. FIG. 2 shows a state where the cap nut 62 is not screwed into the bolt 61, and FIG. 3 shows a state where the cap nut 62 is screwed into the bolt 61. The closed end 622 that closes the hole in which the screw nut 62 is formed is formed with a screwless hole 623 that is not formed with a screw thread, and further passes through the closed end 622 in the central axis direction. A through hole (through hole) 621 is formed. A ball-shaped plug body 63 for closing the opening of the flow hole 611 is disposed at the tip of the bolt 61, and a coil is interposed between the plug body 63 and the closed end 622 of the cap nut 62. A spring (compression elastic member) 64 is arranged.

  The plug 63 is formed in a ball shape so that it can close the opening of the flow hole 611 and can enter the screwless hole 623 of the cap nut 62. The plug 63 is made of a material such as a fluororesin that has elasticity and is corrosion resistant to the gas generated in the molten salt battery and the molten salt. The coil spring 64 is a compression spring, and generates a repulsive force by being compressed in the central axis direction. The coil spring 64 is formed of a material having creep resistance at the operating temperature of the molten salt battery that is equal to or higher than the melting point of the molten salt. The coil spring 64 is disposed in the screwless hole 623 of the cap nut 62 so that the center axis direction of the coil spring 64 coincides with the center axis direction of the bolt 61 and the cap nut 62. The O-ring 65 is made of an elastic material such as rubber, and the inner diameter of the O-ring 65 is sized to fit around the shaft of the bolt 61. The O-ring 65 is formed of fluororubber so as to have corrosion resistance against the gas generated in the molten salt battery and the molten salt, and is preferably covered with a fluororesin. The shape of the plug 63 is not limited to the ball shape, and may be any other shape as long as the opening of the flow hole 611 can be closed. The compression elastic member in the present invention is not limited to the coil spring 64, and may be other forms such as a rubber ring as long as it is compressed and generates a repulsive force.

  As shown in FIG. 3, the safety valve 6 provided in the upper container 52 is in a state in which a cap nut 62 is screwed into a bolt 61. When the cap nut 62 is screwed into the bolt 61, the coil spring 64 is compressed between the plug body 63 and the closed end 622 of the cap nut 62. The compressed coil spring 64 generates a repulsive force and presses the stopper 63 against the opening of the flow hole 611 with the repulsive force. By pressing the plug 63 against the opening of the flow hole 611, the flow hole 611 of the bolt 61 is closed. Further, when the cap nut 62 is screwed into the bolt 61, the O-ring 65 is pressed against the upper container 52 by the cap nut 62. A tapered portion 522 whose diameter increases toward the outside is formed in the opening portion outside the through hole 521 formed in the upper container 52. When the O-ring 65 is pressed against the upper container 52, the O-ring 65 fits into the tapered portion 522 and is effective while contacting the side surface of the bolt 61, the tip of the cap nut 62, and the tapered portion 522 of the upper container 52. Compressed. The compressed O-ring 65 seals the gap between the bolt 61 and the inner surface of the through hole 521, and seals the gap between the bolt 61 and the cap nut 62. Since no thread is formed on the portion of the side surface of the bolt 61 that contacts the inner surface of the through-hole 521 and the portion that contacts the O-ring 65, the inner surface of the bolt 61 and the through-hole 521 is formed by the O-ring 65. The gap between the two is effectively sealed.

  In a normal state, the flow hole 611 of the bolt 61 is closed by the plug 63 and the molten salt battery is sealed. During operation of the molten salt battery, when gas is generated inside and the internal pressure rises, the force that pushes the plug 63 against the repulsive force of the coil spring 64 increases. When the force that pushes the plug body 63 exceeds the repulsive force of the coil spring 64, the plug body 63 is pushed out from the opening of the flow hole 611 and the flow hole 611 is opened. At this time, the gas is discharged from the molten salt battery through the flow hole 611 of the bolt 61 and the flow hole 621 of the cap nut 62. As the gas is discharged, the internal pressure of the molten salt battery decreases, and when the force pushing out the plug 63 falls below the repulsive force of the coil spring 64, the flow hole 611 of the bolt 61 is closed again by the plug 63, The molten salt battery continues to operate. The coil spring 64 is designed to have a spring constant so that the flow hole 611 of the bolt 61 is opened when the internal pressure of the molten salt battery becomes equal to or higher than a predetermined pressure that does not destroy the molten salt battery. The pressure at which the flow hole 611 of the bolt 61 is opened is, for example, 0.3 MPa.

  By operating the safety valve 6, when the internal pressure of the molten salt battery rises above a predetermined pressure, the internal gas is discharged to reduce the internal pressure, and the molten salt battery is prevented from being destroyed by the increase of the internal pressure. . Since no bush is used for the safety valve 6, the number of parts of the safety valve 6 is reduced as compared with the related art. Further, the compressed O-ring 65 seals the gap between the bolt 61 and the inner surface of the through hole 521 and the gap between the bolt 61 and the cap nut 62, so that the molten salt battery is sufficiently used during normal operation. Is sealed. Note that the bolt 61 may be welded to the upper container 52 in a state of passing through the through hole 521. In this form, the molten salt battery is more sealed. The O-ring 65 compressed by the cap nut 62 generates a repulsive force, and pushes up the cap nut 62 with the repulsive force. When the cap nut 62 is pushed up by the repulsive force of the O-ring 65, the frictional force between the cap nut 62 and the bolt 61 increases, and the cap nut 62 is prevented from loosening. By preventing the cap nut 62 from loosening, the molten salt battery is sufficiently sealed during normal operation.

  FIG. 4 is a schematic cross-sectional view showing the configuration of the closing portion 7. A second through hole 523 is formed in the upper container 52, and the through hole 523 is closed with an aluminum foil (film-like material) 71. The aluminum foil 71 is welded to a position that closes the through hole 523 outside the upper container 52. When the gas in the molten salt battery is discharged from the safety valve 6, a part of the molten salt is discharged together with the gas, the temperature of the discharged molten salt is lower than the melting point, and the discharged molten salt is solidified and passed through. It adheres to the flow hole 611 and the flow hole 621. For this reason, the flow hole 611 and the flow hole 621 are blocked by the solidified molten salt, and the safety valve 6 may not be able to discharge the gas in the molten salt battery. The aluminum foil 71 is strong enough to burst when the internal pressure of the molten salt battery rises above a second predetermined pressure that is greater than the pressure at which the flow hole 611 of the bolt 61 is opened. The internal pressure of the molten salt battery at which the aluminum foil 71 is ruptured is larger than the pressure at which the flow hole 611 of the bolt 61 is opened, and is smaller than the pressure at which the welded portion between the lower container 51 and the upper container 52 is broken.

  When the capacity of the molten salt battery is 250 Wh, a maximum of 3 L of gas per minute is generated inside the molten salt battery. The internal pressure of the molten salt battery rises to 7.0 MPa at the maximum, the welded portion between the lower container 51 and the upper container 52 breaks, and the molten salt battery is destroyed. The internal pressure of the molten salt battery at which the aluminum foil 71 bursts is, for example, 1.5 MPa. From the viewpoint of airtightness, the thickness of the aluminum foil 71 is essential to be 5 μm or more, and the thickness of the aluminum foil 71 is desirably 100 μm so that the aluminum foil 71 is ruptured at an internal pressure of 1.5 MPa. In addition, as long as the material which bursts when the internal pressure of a molten salt battery raises more than 2nd predetermined pressure, the film-like material in this invention may be materials other than aluminum foil. Further, the closing portion 7 may be configured such that when the internal pressure of the molten salt battery rises to a second predetermined pressure or more, the membrane material does not rupture but the adhesive portion between the membrane material and the upper container 52 is removed. Good.

  When the internal pressure of the molten salt battery increases in a state where the safety valve 6 cannot discharge the gas in the molten salt battery due to the solidified molten salt, the aluminum foil 71 bursts before the molten salt battery is destroyed, The gas in the molten salt battery is discharged through the through hole 523. By discharging the gas in the molten salt battery, the internal pressure of the molten salt battery is reduced, and the molten salt battery is prevented from being destroyed by the increase of the internal pressure. After the aluminum foil 71 is ruptured, the hermeticity inside the molten salt battery is lost, and the operation of the molten salt battery becomes impossible. As described above, the provision of the closing portion 7 prevents the molten salt battery from being destroyed due to an increase in internal pressure even when the safety valve 6 cannot discharge the gas in the molten salt battery. Therefore, the safety of the molten salt battery is improved.

  In this embodiment, the safety valve 6 and the closing part 7 are provided in the upper container 52. However, the molten salt battery of the present invention is provided with the safety valve 6 and the closing part 7 in the lower container 51. The form may be sufficient. The safety valve 6 and the closing portion 7 are not limited to the molten salt battery, and may be provided in other batteries such as a lithium ion battery.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 51 Lower container 52 Upper container 521,523 Through-hole 522 Tapered part 6 Safety valve 61 Bolt 611 Through-hole (through-hole)
62 Cap nut 621 Flow hole (through hole)
622 Closed end 623 Screwless hole 63 Plug body 7 Closed portion 71 Aluminum foil (film-like material)

Claims (4)

In the safety valve that discharges fluid from the container when the pressure in the container exceeds the specified pressure,
A through hole for allowing fluid to flow is formed in the axial direction, and a bolt to be installed through the hole formed in the container;
A through hole is formed in the closed end, and a plug for closing the through hole of the bolt, and the plug is compressed between the plug and the closed end to move the plug to the tip of the bolt. In a state where the compression elastic member for pressing is arranged inside, a cap nut screwed to one end of the bolt;
An O-ring that fits around the shaft of the bolt at a position between the container and the cap nut;
The safety valve according to claim 1, wherein a thread is not formed on a portion of the bolt shaft on which the O-ring is fitted. In the opening part outside the hole formed in the container, a tapered part whose diameter extends outward is formed,
The safety valve according to claim 1, wherein the O-ring is compressed between the cap nut and the tapered portion in a state where the cap nut is screwed onto the bolt. In a molten salt battery using molten salt as an electrolyte,
Provided with a container containing molten salt inside,
A through hole is formed in the container;
The molten salt battery, wherein the safety valve according to claim 1 or 2 is attached to the through hole. Other through holes are formed in the container,
A closing portion for closing the other through-hole with a membrane material is provided;
The closing portion is configured to be broken when a pressure in the battery becomes a second predetermined pressure larger than a first predetermined pressure at which the fluid in the battery is discharged from the safety valve. The molten salt battery according to claim 3.

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