Secondary battery system

Abstract

To suppress a spreading fire from a firing battery to the other battery while suppressing performance reduction of a secondary battery.SOLUTION: A secondary battery system comprises: a secondary battery; a housing part in which the secondary battery is stored and which is filled with an oxygen-free medium; and a cooling part which is disposed inside of the housing part and cools the secondary battery via the medium. The secondary battery includes a safety valve which releases a pressure inside of the secondary battery when the pressure inside of the secondary battery reaches a predetermined pressure value, and the safety valve is disposed at a position opposed to the cooling part via the medium.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a secondary battery system.

Background Art

[0002] Secondary batteries used as batteries for electric vehicles and the like are known (for example, see Patent Document 1). In the secondary battery described in Patent Document 1, each of a plurality of battery modules (batteries) is connected to a heat sink via a heat pipe.A cooling water passage through which cooling water cooled by a radiator flows is formed in the heat sink.Therefore, the secondary battery that heats up during charge and discharge is cooled by the heat sink through which cooling water flows inside.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In secondary batteries with multiple cells stacked together, the battery temperature may rise due to external stress such as collisions during vehicle installation, initial contamination of electrodes and electrolytes with impurities, internal short circuits between electrodes due to battery degradation, and insufficient cooling capacity during high-speed charging and discharging. When the battery temperature reaches the ignition temperature of the battery material, the battery may ignite. At this time, the heat generation triggers a decomposition reaction of the negative electrode SEI film (Solid Electrolyte Interface) and an exothermic reaction between the negative electrode and the electrolyte. If the separator melts down due to the exothermic reaction, the entire electrode short-circuits. Due to the heat generation and temperature rise of the battery, an exothermic reaction between the positive electrode and the electrolyte and a decomposition reaction of the electrolyte occur, causing the temperature of the ignited battery to rise rapidly. If one battery ignites in a stacked configuration, heat conduction from the ignited battery through the tube wall, etc., can cause the temperature of adjacent batteries to reach the ignition temperature and ignite, potentially leading to the ignition of multiple batteries in sequence (battery spread). While placing insulating material between multiple batteries can somewhat suppress the spread of fire, there are challenges such as increased costs due to the insulating material and a decrease in volumetric efficiency depending on the volume of the insulating material. Furthermore, even with insulating material placed between batteries, there is a risk of fire spreading due to heat transfer via the heat sink. In this regard, Patent Document 1 does not consider the spread of fire to other batteries caused by the ignition of one battery.

[0005] This invention was made to solve at least some of the above-mentioned problems, and aims to suppress the deterioration of secondary battery performance while also suppressing the spread of fire from one igniting battery to other batteries. [Means for solving the problem]

[0006] The present invention has been made to solve at least some of the above-mentioned problems and can be realized in the following forms. A secondary battery system comprising: a secondary battery; a housing for housing the secondary battery and filled with an oxygen-free medium; a cooling unit disposed inside the housing for cooling the secondary battery via the medium; a temperature acquisition unit for acquiring the battery temperature, which is the temperature of the secondary battery; and a control unit for controlling the temperature and pressure of the medium using the battery temperature, wherein the secondary battery has a safety valve that releases the internal pressure of the secondary battery when the internal pressure of the secondary battery reaches a predetermined pressure value, the safety valve is positioned opposite the cooling unit via the medium, the medium is a fluorocarbon-based medium, the cooling unit is positioned vertically above the secondary battery, and the control unit controls the temperature of the fluorocarbon-based medium to adjust the temperature of the secondary battery using the heat of vaporization of the fluorocarbon-based medium and to change the vapor pressure of the fluorocarbon-based medium. A secondary battery system comprising: a secondary battery; a housing for housing the secondary battery and filled with an oxygen-free medium; a cooling unit disposed inside the housing for cooling the secondary battery via the medium; a first pressure regulating valve for releasing the pressure inside the housing; and a second pressure regulating valve connected in series between the housing and the first pressure regulating valve, wherein the secondary battery has a safety valve that releases the pressure inside the secondary battery when the pressure inside the secondary battery reaches a predetermined pressure value, the safety valve is positioned opposite the cooling unit via the medium, the first pressure regulating valve opens and remains open when the pressure inside the housing reaches a first pressure value, and the second pressure regulating valve opens when the pressure is less than the first pressure value and greater than atmospheric pressure (i.e., a second pressure regulating valve), and closes when the pressure is less than the second pressure value. In addition, the present invention can also be realized in the following forms.

[0007] (1) According to one embodiment of the present invention, a secondary battery system is provided. This secondary battery system comprises a secondary battery, a housing for housing the secondary battery and filled with an oxygen-free medium, and a cooling unit disposed inside the housing for cooling the secondary battery via the medium, wherein the secondary battery has a safety valve that releases the internal pressure of the secondary battery when the internal pressure of the secondary battery reaches a predetermined pressure value, and the safety valve is positioned opposite the cooling unit via the medium.

[0008] In this configuration, when the temperature rises and the internal pressure of the secondary battery ignites increases to a predetermined pressure value, components such as the electrolyte of the secondary battery are released into the containment through the opened safety valve. In this case, some of the main components of the liquid released from the high-pressure secondary battery into the low-pressure containment evaporate. On the other hand, the remaining main components of the liquid are released into the containment as liquid. Since the gas released from the secondary battery contains decomposed oxygen from the secondary battery, when the safety valve is opened, the combustion flame generated by the decomposed oxygen and flammable components in the secondary battery flows into the containment. However, in this configuration, the containment is filled with an oxygen-free medium. Therefore, oxygen in the containment in the atmosphere after the safety valve is opened is blocked, and diffusion combustion by the flammable components in the premixed gas and oxygen components in the atmosphere that would occur if the safety valve were opened in an atmospheric atmosphere is suppressed. Furthermore, because the vapor pressure of the electrolyte components released into the containment is low, the electrolyte components in the gas released from the secondary battery into the containment remain in the containment as liquid without vaporizing. Furthermore, because the safety valve is positioned opposite the cooling section, the cooling section acts as a cooling surface during the impingement jet of gas released from the safety valve. As a result, the combustion flame is extinguished by the heat loss effect due to the strong temperature gradient between the safety valve and the cooling section. Consequently, there is no need to provide, for example, insulation materials to suppress the spread of fire, and the performance degradation of the secondary battery is suppressed, while the spread of fire from one secondary battery to another is also suppressed.

[0009] (2) In the secondary battery system according to the above embodiment, the distance between the safety valve and the cooling unit may be set to be less than or equal to the flame extinguishing distance. In this configuration, the distance between the cooling unit and the safety valve positioned opposite the cooling unit is less than or equal to the flame extinguishing distance. Therefore, the combustion flame that flows from inside the secondary battery into the housing unit is extinguished by a quenching phenomenon caused by the large temperature gradient with the wall surface of the cooling unit.

[0010] (3) In the secondary battery system according to the above embodiment, the system further comprises a temperature acquisition unit that acquires the battery temperature, which is the temperature of the secondary battery, and a control unit that uses the battery temperature to control the temperature and pressure of the medium, wherein the medium is a fluorocarbon-based medium, the cooling unit is located vertically above the secondary battery, and the control unit adjusts the temperature of the secondary battery using the heat of vaporization of the fluorocarbon-based medium by controlling the temperature of the fluorocarbon-based medium, and may also change the vapor pressure of the fluorocarbon-based medium. In this configuration, the medium filled in the containment is a fluorocarbon-based medium with a low boiling point. During charging and discharging when the secondary battery is not ignited, the secondary battery is efficiently cooled by utilizing the latent heat of vaporization of the fluorocarbon-based medium by adjusting the temperature and boiling point during charging and discharging. In addition, ignition of the secondary battery is detected by the battery temperature obtained by the temperature acquisition unit. If the secondary battery ignites, the temperature of the fluorocarbon-based medium is lowered even further than during charging and discharging of the secondary battery, thereby cooling the ignited secondary battery and suppressing the spread of fire between secondary batteries.

[0011] (4) In the secondary battery system according to the above embodiment, the cooling unit has a refrigerant flow path through which a refrigerant flows, and the secondary battery system further includes a first thermal expansion valve that expands the refrigerant by the pressure difference between its upstream and downstream sides, and a second thermal expansion valve that expands the refrigerant by a pressure difference between its upstream and downstream sides that is greater than the pressure difference of the first thermal expansion valve, and the control unit may supply the refrigerant to the secondary battery via the first thermal expansion valve when the battery temperature is below the first temperature, and supply the refrigerant to the secondary battery via the second thermal expansion valve when the battery temperature is at or above the first temperature. In this configuration, during charging and discharging of the secondary battery, refrigerant is supplied to the refrigerant flow path via the first thermal expansion valve, and if the secondary battery catches fire, refrigerant is supplied to the refrigerant flow path via the second thermal expansion valve. As a result, when the secondary battery catches fire, refrigerant that has expanded further due to the pressure difference and whose temperature has decreased is supplied to the refrigerant flow path via the second thermal expansion valve. Consequently, the housing containing the ignited secondary battery is supplied with refrigerant at an even lower temperature than when the secondary battery is not ignited, thus cooling the ignited secondary battery.

[0012] (5) The secondary battery system according to the above embodiment may further include a heat transfer layer made of metal, connected to the surface of the secondary battery and connected to the refrigerant flow path, and a porous body made of a porous material, connected to the secondary battery via the heat transfer layer. In this configuration, the liquid fluorocarbon medium, cooled by the refrigerant flowing through the refrigerant channel, rapidly spreads throughout the porous body due to capillary action generated by the porous body connected to the refrigerant channel. The liquid fluorocarbon medium within the porous body exchanges heat with the secondary battery via the heat transfer layer in contact with the porous body. As a result of heat exchange, the fluorocarbon medium changes from liquid to gas, moves upward towards the secondary battery where the refrigerant channel is located, cools, changes back into a liquid, and cools the secondary battery again. In other words, with this configuration, the secondary battery is rapidly cooled by vapor heat transport of the fluorocarbon medium using the capillary action of the porous body. On the other hand, if the secondary battery ignites and reaches a high temperature, the condensation of the fluorocarbon medium may not be fast enough, causing dry-out around the ignited secondary battery. When dry-out occurs, heat is transferred from the ignited secondary battery to adjacent secondary batteries by thermal radiation from the heat transfer layer. In this configuration, the heat transfer layer is rapidly cooled because it is connected to the refrigerant channel, and heat transfer between secondary batteries due to thermal radiation is suppressed.

[0013] (6) In the secondary battery system according to the above embodiment, the system further comprises a tank storing an electrically insulating antifreeze and an on / off valve for opening and closing the connection between the housing and the outside, wherein the control unit may open the on / off valve to release the fluorocarbon medium from inside the housing when the battery temperature changes from below a second temperature to above the second temperature, and after the release of the fluorocarbon medium, supply antifreeze from the tank to inside the housing. In this configuration, when the secondary battery changes from a state below a certain temperature (below 2) where it has not ignited to a state above 2 where it has ignited, the containment is filled with supplied antifreeze. By covering the secondary battery with antifreeze, contact between the ignited secondary battery and oxygen is suppressed, and the temperature of the secondary battery is controlled by the temperature control of the antifreeze. In particular, if there are secondary batteries that have not completely burned, filling the containment with antifreeze suppresses the re-ignition of the incompletely burned secondary batteries several hours or days later.

[0014] (7) In the secondary battery system according to the above embodiment, the system further comprises a first pressure regulating valve for releasing the pressure inside the housing, and a second pressure regulating valve connected in series between the housing and the first pressure regulating valve, wherein the first pressure regulating valve opens when the pressure inside the housing reaches a first pressure value and remains open, and the second pressure regulating valve opens when the pressure is less than the first pressure value and greater than atmospheric pressure (a second pressure value) and closes when the pressure is less than the second pressure value. In this configuration, a second regulating valve, which opens and closes at a low second pressure value, is connected to the housing on the upstream side, and a first regulating valve, which opens at a high first pressure value and remains open, is connected to the downstream side of the second regulating valve. When the secondary battery is charging and discharging without ignition, the fluorocarbon-based medium in the housing cools the secondary battery at a pressure between the second pressure value and the first pressure value. In this case, since the second regulating valve is open and the first regulating valve is closed, the fluorocarbon-based medium in the housing is not released into the atmosphere. On the other hand, if the secondary battery ignites and the pressure in the housing changes to above the first pressure value, both the second and first regulating valves open. In this case, the fluorocarbon-based medium in the housing is released into the atmosphere, and the pressure in the housing decreases. As a result, damage to the housing and other containers due to the increase in pressure inside the housing can be suppressed. Furthermore, if the pressure inside the housing decreases to below the second pressure value after the first regulating valve has opened, the second regulating valve closes. Since the second pressure value is set higher than atmospheric pressure, even if the pressure inside the containment decreases, oxygen-containing air does not flow into the containment from the atmosphere. In other words, with this configuration, the pressure rise when the secondary battery ignites is suppressed, thereby suppressing damage to the containment and other containers, while also suppressing the progression of ignition due to the influx of oxygen from the atmosphere into the containment.

[0015] Furthermore, the present invention can be realized in various forms, for example, as a secondary battery, a lithium-ion battery, a secondary battery system, a method for controlling a secondary battery, and a system comprising these devices or implementing such methods, a computer program for executing these devices or methods, a server device for distributing such computer programs, and a non-temporary storage medium storing the computer program. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic perspective view of a secondary battery system as one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view of a part of a secondary battery system. [Figure 3]It is a schematic block diagram of a secondary battery system according to a second embodiment in a state where a first thermal expansion valve is connected to an external flow path. [Figure 4] It is a schematic block diagram of a secondary battery system according to a second embodiment in a state where a second thermal expansion valve is connected to an external flow path. [Figure 5] It is an example of a P-h diagram of a vapor compression refrigeration cycle in the second embodiment. [Figure 6] It is a schematic cross-sectional view of a part of the secondary battery system according to the second embodiment. [Figure 7] It is an explanatory diagram of the detection positions of the temperatures of eight battery cells arranged in the housing part. [Figure 8] It is an explanatory diagram of the temperature change of each of six battery cells when one battery cell catches fire. [Figure 9] It is an explanatory diagram of the measurement positions of the heat fluxes of eight battery cells arranged in the housing part. [Figure 10] It is an explanatory diagram of the change of the heat flux with time during radiation. [Figure 11] It is an explanatory diagram of the change of the heat flux with time in the heat flow direction of the heat transfer layer. [Figure 12] It is an explanatory diagram of the temperature change of each of eight battery cells in a secondary battery system not provided with a second thermal expansion valve. [Figure 13] It is an explanatory diagram of the change of the heat flux with time during radiation in a secondary battery system not provided with a second thermal expansion valve. [Figure 14] It is a schematic block diagram of a secondary battery system according to a third embodiment during charging and discharging of a battery cell. [Figure 15] It is a schematic block diagram of a secondary battery system according to a third embodiment after a battery cell catches fire. [Figure 16] It is a schematic block diagram of a secondary battery system according to a fourth embodiment. [Figure 17] It is a schematic block diagram of a secondary battery system according to a fifth embodiment. [Figure 18] It is a schematic diagram of a housing part removed from the secondary battery system. [Figure 19]This is a schematic diagram of the housing connected to a cooling circulation system separate from the secondary battery system. [Modes for carrying out the invention]

[0017] <First Embodiment> Figure 1 is a schematic perspective view of a secondary battery system 100 as one embodiment of the present invention. Figure 2 is a schematic cross-sectional view of a part of the secondary battery system 100. The secondary battery system 100 shown in Figure 1 comprises a plurality of battery cells (secondary batteries) 20, a housing 10 that houses the plurality of battery cells 20, and a refrigerant flow path 30 arranged within the housing 10. The housing 10 is filled with an oxygen-free medium 15. As shown in Figure 2, the battery cell 20A is equipped with a safety valve 21A that releases the pressure inside the battery cell 20A. The safety valve 21A is positioned opposite the refrigerant flow path 30 via the medium 15. In this embodiment, when a battery cell 20A ignites and the pressure inside the battery cell 20A reaches a predetermined pressure value, the safety valve 21A opens and the pressure inside the battery cell 20A is released. Because the housing 10 is filled with an oxygen-free medium 15, the ignition of the battery cell 20A is extinguished. Furthermore, since the safety valve 21A is positioned opposite the refrigerant flow path 30, gases released from within the battery cell 20A are quickly cooled.

[0018] As shown in Figure 1, multiple battery cells 20 are arranged in a line along the X-axis, which is parallel to the horizontal direction, so as not to touch each other. The battery cells 20 in this embodiment are lithium-ion batteries having a substantially rectangular parallelepiped shape. Each of the multiple battery cells 20 is the same battery cell. The components of the battery cell 20, such as the electrolyte and electrodes, are sealed by a housing that forms the outer frame. The housing 10 has a substantially rectangular parallelepiped box shape. In Figure 1, the outline of the housing 10 is shown by a dashed line. Also in Figure 1, a Cartesian coordinate system CS is shown. The Cartesian coordinate system CS is composed of mutually orthogonal X, Y, and Z axes parallel to each side of the housing 10, which has a substantially rectangular parallelepiped shape. The Cartesian coordinate system CS shown in Figure 1 corresponds to the Cartesian coordinate system CS shown in Figure 2 and subsequent figures.

[0019] As shown in Figure 1, the battery cell 20 has a roughly rectangular parallelepiped shape extending along the Y-axis. Since the housing 10 is filled with a medium 15, it can be said that each of the multiple battery cells 20 is stacked along the X-axis direction via the medium 15. Within the housing 10, a refrigerant channel 30 through which the refrigerant 32 flows is formed on the vertically upper side of the multiple battery cells 20. As shown in Figure 1, the refrigerant channel 30 has a roughly rectangular parallelepiped shape with a bottom surface parallel to the XY plane and a thickness along the vertical direction (Z-axis direction). Since a space is formed inside the roughly rectangular parallelepiped shape, the refrigerant 32 flows through the refrigerant channel 30. The refrigerant channel 30 is connected to a cylindrical external channel 35 extending from outside the housing 10. The refrigerant 32, which has been heated by a heat sink such as a radiator (not shown in Figure 1), circulates in the direction of the arrow and flows into the refrigerant channel 30 via the external channel 35. The refrigerant flow path 30 and the multiple battery cells 20 are not in direct contact, but are indirectly connected via the medium 15. In this embodiment, water is used as the refrigerant 32.

[0020] Figure 2 shows schematic cross-sectional views of two battery cells 20A and 20B, among a plurality of battery cells 20, parallel to the ZX plane. As shown in Figure 2, battery cells 20A and 20B are equipped with safety valves 21A and 21B positioned opposite the refrigerant flow path 30 located vertically above. In this embodiment, the safety valves 21A and 21B open when the pressure reaches a predetermined pressure value, releasing the pressure inside the battery cells 20A and 20B.

[0021] As shown in Figure 2, the refrigerant flow path 30 has a pipe wall 31 that forms a flow path through which the refrigerant 32 flows. The secondary battery system 100 extends vertically and connects to the pipe wall 31 of the refrigerant flow path 30, and includes heat transfer members 50 formed on the surfaces of the respective battery cells 20A and 20B. The heat transfer members 50 are made of a metal with high thermal conductivity. The battery cells 20A and 20B are cooled by heat exchange with the refrigerant flow path 30 and the medium 15 via the heat transfer members 50.

[0022] Figure 2 shows a state in which one battery cell 20A has ignited and the safety valve 21A has opened. The opened safety valve 21A is shown by a dashed line. Here, the battery cell 20A and the refrigerant flow path 30 are arranged within the housing 10 such that the distance L0 between the safety valve 21A and the refrigerant flow path 30 is less than or equal to the flame extinguishing distance. The flame extinguishing distance is calculated using the dimensionless Peclet number Pe, which is the ratio of the heat generation rate Qp due to flame propagation to the heat loss rate Qd. For example, the flame extinguishing distance for propane flame propagation is set so that the Peclet number Pe is 8 or less.

[0023] Here, the heat generation rate Qp(W) due to flame propagation is expressed by the following equation (1).

number

[0024] The heat loss rate Qd used in the Peclet number Pe is expressed by the following equation (2).

number

[0025] In this embodiment, the distance L0 between the safety valve 21A and the refrigerant flow path 30 shown in Figure 1 is set to be less than or equal to the flame extinguishing distance. As a result, even if a premixed flame generated by premixed combustion in the battery cell 20A is generated in the housing 10, the heat loss rate Qd exceeds the heat generation rate Qp, so the premixed flame is extinguished and combustion in the housing 10 is suppressed.

[0026] When premixed combustion is suppressed within the containment section 10, the electrolyte component 22 (Figure 2) in the gas released from the battery cell 20A changes from high pressure within the battery cell 20A to low pressure within the containment section 10. As a result, the electrolyte component 22 has a low vapor pressure and does not easily volatilize (evaporate), accumulating as droplets vertically downward within the containment section 10. The unburned electrolyte component 22 accumulated in the containment section 10 is recovered after cooling.

[0027] As described above, the secondary battery system 100 of this embodiment, as shown in Figure 1, comprises a battery cell 20, a housing 10 housing the battery cell 20, and a refrigerant flow path 30 arranged within the housing 10. The housing 10 is filled with an oxygen-free medium 15. Furthermore, as shown in Figure 2, the battery cell 20A is equipped with a safety valve 21A that releases the pressure inside the battery cell 20A when the pressure inside the battery cell 20A reaches a predetermined pressure value. The safety valve 21A is positioned opposite the refrigerant flow path 30 via the medium 15. In this embodiment, when the temperature rises and the pressure inside the ignited battery cell 20A rises to a predetermined pressure value, the electrolyte components 22 (e.g., ethylene carbonate, ethyl methyl carbonate, DMC dimethyl carbonate) inside the battery cell 20A are released into the housing 10 through the opened safety valve 21A. In this case, a portion of the electrolyte components 22 released from the high-pressure battery cell 20A into the low-pressure housing 10 evaporates. On the other hand, the remaining electrolyte component 22 is released as liquid into the containment section 10. Since the gas released from the battery cell 20A contains the decomposed oxygen from the battery cell 20A, when the safety valve 21A is opened, the combustion flame generated by the premixed combustion of the decomposed oxygen and combustible components in the battery cell 20A flows into the containment section 10. However, in this embodiment, the containment section 10 is filled with an oxygen-free medium. Therefore, the oxygen in the containment section 10 in the atmosphere after the safety valve 21A is opened is blocked, and diffusion combustion by the combustible components in the premixed gas and the oxygen components in the atmosphere that occurs when the safety valve is opened in an atmospheric atmosphere is suppressed. Furthermore, because the vapor pressure of the electrolyte component 22 is low, the electrolyte component 22 in the gas released from the battery cell 20A into the containment section 10 remains in the containment section 10 as a liquid without vaporizing. In addition, since the safety valve 21A is positioned opposite the refrigerant flow path 30, the refrigerant flow path 30 acts as a cooling surface during the impingement jet of gas released from the safety valve 21A. Therefore, the combustion flame from premixed combustion within the battery cell 20A is extinguished by the heat loss effect due to the strong temperature gradient between the safety valve 21A and the refrigerant flow path 30. As a result, the space between the battery cell 20A and the battery cell 20B, which is filled with the insulating medium 15, does not need to be unnecessarily large.Therefore, in this embodiment, performance degradation of multiple battery cells 20 is suppressed, and the spread of fire from the ignited battery cell 20A to other battery cells 20B is also suppressed.

[0028] Furthermore, in this embodiment, as shown in Figure 2, the battery cell 20A and the refrigerant flow path 30 are arranged within the housing 10 such that the distance L0 between the safety valve 21A of the battery cell 20A and the refrigerant flow path 30 is less than or equal to the flame extinguishing distance. With this configuration, the distance between the refrigerant flow path and the safety valve positioned opposite the refrigerant flow path is less than or equal to the flame extinguishing distance. Therefore, the combustion flame that flows from inside the secondary battery into the housing 10 outside the secondary battery is extinguished by a quenching phenomenon caused by the large temperature gradient with the wall surface of the refrigerant flow path.

[0029] <Second Embodiment> Figure 3 is a schematic block diagram of the secondary battery system 100a of the second embodiment. The second embodiment differs significantly from the first embodiment in that it switches a thermal expansion valve that causes the refrigerant 32a to expand when the battery cell 20A ignites, and cools the battery cell 20 by vapor heat transport using a medium 15a, which is a fluorocarbon-based medium with a low boiling point (for example, 20 degrees Celsius (°C) at atmospheric pressure).

[0030] The secondary battery system 100a of the second embodiment is a secondary battery system mounted on a vehicle. As shown in Figure 3, the secondary battery system 100a of the second embodiment includes a housing section 10a that houses a plurality of battery cells 20 and is filled with a medium 15a, a refrigerant flow path 30a located vertically above the housing section 10a, an external flow path 35 connected to the refrigerant flow path 30a, a compressor 60 located on the external flow path 35, a condenser 70, a first thermal expansion valve 81, a second thermal expansion valve 82, a temperature sensor (temperature acquisition unit) S1 that detects the temperature of the battery cells 20A (battery temperature), a low-pressure regulating valve 90, and a control unit 40.

[0031] As shown in Figure 3, along the flow of refrigerant 32a in the refrigerant channel 30a, the compressor 60, condenser 70, first thermal expansion valve 81, and second thermal expansion valve 82 are arranged in order from upstream on the external channel 35. The refrigerant 32a in the second embodiment is a fluorocarbon-based medium used in car air conditioners, etc. (for example, R134a, R1234yf with a boiling point of -29°C at atmospheric pressure), a household refrigerant, or a natural refrigerant (only non-flammable CO2). Alternatively, the refrigerant channel 30a may be used as a heat exchanger, and the refrigerant may be exchanged with an antifreeze such as LLC (Long Life Coolant) that does not freeze even at temperatures below 0°C at atmospheric pressure (for example, -30°C) before flowing into the refrigerant channel 30a (not shown).

[0032] The first thermal expansion valve 81 and the second thermal expansion valve 82 are arranged in parallel with respect to the external flow path 35. Under the control of the control unit 40, only one of the first thermal expansion valve 81 or the second thermal expansion valve 82 is connected to the external flow path 35. In other words, the refrigerant 32a circulates through the refrigerant flow path 30a and the external flow path 35, through the housing 10, the compressor 60, the condenser 70, and either the first thermal expansion valve 81 or the second thermal expansion valve 82.

[0033] The compressor 60 is a compressor that compresses the refrigerant 32a flowing through the external passage 35. The condenser 70 is a radiator mounted on the vehicle that dissipates the heat from the compressed refrigerant 32a to the outside. The first thermal expansion valve 81 and the second thermal expansion valve 82 expand the refrigerant 32a flowing through the external passage 35 due to the pressure difference between their upstream and downstream sides. When the refrigerant 32a expands due to the first thermal expansion valve 81 or the second thermal expansion valve 82, the temperature of the refrigerant decreases. The pressure difference for the second thermal expansion valve 82 is greater than that for the first thermal expansion valve 81. Therefore, the temperature of the refrigerant 32a expanded by the second thermal expansion valve 82 is even lower than the temperature of the refrigerant 32a expanded by the first thermal expansion valve 81. In Figure 3, the state in which the first thermal expansion valve 81 is connected to the external passage 35 is shown. The external passage 35 connecting to the second thermal expansion valve 82, which is not connected to the external passage 35, is shown by a dashed line.

[0034] The low-pressure regulating valve 90 is a valve that releases the medium 15a inside the housing 10a to the outside when any of the battery cells 20 ignite and the pressure inside the housing 10a increases. The gauge pressure of the low-pressure regulating valve 90 is set to atmospheric pressure or a pressure higher than atmospheric pressure. The opening and closing of the low-pressure regulating valve 90 is controlled by a control signal from the control unit 40. The control unit 40 opens the low-pressure regulating valve 90 when any of the multiple battery cells 20 ignite, and keeps the low-pressure regulating valve 90 closed when none of the battery cells 20 have ignited. In Figure 3, none of the battery cells 20 have ignited and the low-pressure regulating valve 90 is closed.

[0035] The control unit 40 controls the temperature of the medium 15a filled in the housing 10a by controlling the temperature of the refrigerant 32a supplied to the refrigerant flow path 30a in the housing 10a using the temperature detected by the temperature sensor S1. By controlling the temperature of the medium 15a, the control unit 40 adjusts the temperature of the multiple battery cells 20 and changes the vapor pressure of the medium 15a using the heat of vaporization of the medium 15a, which is a fluorocarbon medium having a low boiling point.

[0036] The control unit 40 determines that none of the battery cells 20 have ignited if the temperature detected by the temperature sensor S1 is below the threshold of 80°C (first temperature). In this case, the control unit 40 connects the external flow path 35 to the first thermal expansion valve 81, assuming that the battery cells 20 shown in Figure 3 are not igniting during charging and discharging. The control unit 40 supplies refrigerant 32a cooled to 20°C via the first thermal expansion valve 81 to the refrigerant flow path 30a in the housing 10a. As an example, in the second embodiment, if the temperature of the battery cells 20 during charging and discharging is 25°C, the battery cells 20 are cooled by the refrigerant 32a cooled to 0.6 MPa and 20°C by the first thermal expansion valve 81. Meanwhile, the refrigerant 32a discharged from the refrigerant flow path 30a in the housing 10a is compressed to 50°C by the compressor 60. The refrigerant 32a, whose temperature has risen due to the compressor 60, is released to the outside by the condenser 70 and expands again by the first thermal expansion valve 81.

[0037] Figure 4 is a schematic block diagram of the secondary battery system 100a of the second embodiment, in which the second thermal expansion valve 82 is connected to the external flow path 35. Figure 4 shows a schematic block diagram of the secondary battery system 100a when one of the battery cells 20 ignites and the connection destination of the external flow path 35 is changed from the first thermal expansion valve 81 to the second thermal expansion valve 82. When the temperature detected by the temperature sensor S1 reaches 80°C, the control unit 40 determines that one of the battery cells 20 has ignited. In this case, the control unit 40 supplies refrigerant 32a to the refrigerant flow path 30a in the housing 10a via the second thermal expansion valve 82 instead of the first thermal expansion valve 81. The control unit 40 also opens the low-pressure regulating valve 90, which was closed. When the low-pressure regulating valve 90 opens, the medium 15a in the housing 10a is released into the atmosphere, and the pressure in the housing 10a decreases.

[0038] As an example, in the state of the second embodiment shown in Figure 4, if the battery cell 20 ignites and its temperature exceeds 80°C, the battery cell 20 is cooled by the refrigerant 32a, whose temperature has been reduced to -29°C by the second thermal expansion valve 82. On the other hand, the refrigerant 32a discharged from the refrigerant flow path 30a in the housing 10a is compressed to 50°C by the compressor 60, similar to the charging and discharging of the battery cell 20 shown in Figure 3, and then the heat is dissipated by the condenser 70.

[0039] Figure 5 is an example of a Ph diagram of the vapor compression refrigeration cycle in the second embodiment. As shown in Figure 5, during charging and discharging of the battery cell 20 shown in Figure 3, the refrigerant 32a expands to 0.6 MPa and 20°C by the first thermal expansion valve 81. On the other hand, when the battery cell 20 ignites as shown in Figure 4, the refrigerant 32a expands to approximately 0.08 MPa and -29°C by the second thermal expansion valve 82. In the second embodiment, as shown in Figure 5, the amount of work done by the compressor 60 during ignition in Figure 4 is set to three times the amount of work done by the compressor 60 during charging and discharging in Figure 3.

[0040] Figure 6 is a schematic cross-sectional view of a part of the secondary battery system 100a of the second embodiment. As in Figure 2 of the first embodiment, Figure 6 shows schematic cross-sectional views of two battery cells 20A and 20B among a plurality of battery cells 20, parallel to the ZX plane. Unlike the first embodiment, the heat transfer member 50a of the second embodiment comprises a heat transfer layer 51 formed in direct contact with the surfaces of the battery cells 20A and 20B, and a porous body 52 formed of a porous material on the surface of the heat transfer layer 51.

[0041] The heat transfer layer 51 and the porous body 52 extend along a vertical direction perpendicular to the stacking direction of the multiple battery cells 20A and 20B and are connected to the pipe wall 31 of the refrigerant flow path 30a. The heat transfer layer 51 is made of the same metal with high thermal conductivity as the heat transfer member 50 of the first embodiment. The porous body 52 is formed on the surface of the heat transfer layer 51 which is formed on the surface of the battery cells 20A and 20B, without being in direct contact with the battery cells 20A and 20B. The porous body 52 is made of aluminum with a porosity of 80%, a mesh opening of 100 μm, and a thickness of 0.5 mm.

[0042] Figure 6 shows the state in which battery cells 20A and 20B are being charged and discharged without ignition. During charging and discharging of battery cells 20A and 20B, as shown in Figure 6, the medium 15a that vaporizes by absorbing heat from battery cells 20A and 20B moves vertically upward and is cooled and condensed by the refrigerant 32a in the refrigerant channel 30a. The condensed refrigerant 32a spreads widely throughout the porous body 52 by capillary action. Heat exchange takes place between the refrigerant 32a contained in the porous body 52 and the battery cells 20A and 20B via the heat transfer layer 51, and the refrigerant 32a vaporizes again.

[0043] If either battery cell 20A or battery cell 20B ignites from the state of battery cells 20A and 20B shown in Figure 6, the temperature inside the housing 10a will rise rapidly. When the temperature rises rapidly, the liquid in the medium 15a cooled by the refrigerant 32a does not spread across the entire surface of battery cells 20A and 20B. In other words, a dry-out occurs in which battery cells 20A and 20B cannot be cooled by vapor heat transport using the latent heat of vaporization of the medium 15a. When a dry-out occurs, heat is transferred from the ignited battery cell to the adjacent battery cell by radiant heat between the heat transfer layers 51 formed on the respective surfaces of adjacent battery cells 20A and 20B. However, in the second embodiment, the heat transfer layer 51 is connected to the refrigerant flow path 30a and is therefore cooled quickly, suppressing heat transfer by radiant heat.

[0044] Figures 7 to 11 are explanatory diagrams regarding the spread of fire to the battery cells 20 in the second embodiment. Figure 7 shows eight battery cells 20A to 20H arranged in the housing 10a of the second embodiment. As shown in Figure 7, the temperatures of the eight battery cells 20A to 20H are Ta to Th. In the example shown in Figures 7 to 11, the evaluation of the spread of fire to the other seven battery cells 20B to 20H is shown when battery cell 20A, which is located on the negative side along the X axis, ignites. In the example shown in Figures 7 to 11, the distance L3 between two adjacent battery cells 20 shown in Figure 6 is 4 mm. The distance L2 between the heat transfer layers 51 formed on the surfaces of the two battery cells 20 is 3 mm. The distance L1 between the porous bodies 52 formed on the surfaces of the heat transfer layers 51 of the two battery cells 20 is 2 mm. In other words, the thickness of the heat transfer layer 51 and the porous body 52 along the X-axis direction is 0.5 mm, and the thickness of the space through which the medium 15a flows, formed between adjacent porous bodies 52, is 2 mm.

[0045] Figure 8 shows the temperature changes Cta to Ctf (Figure 7) for the six battery cells 20A to 20F when battery cell 20A ignites. Note that the temperatures Tg and Th of the two battery cells 20G and 20H hardly changed, so their temperature changes are omitted in Figure 8. As shown in Figure 8, the temperatures Ta to Td of the four battery cells 20A to 20D rise to nearly 500°C as time passes. In other words, the fire spread from the ignited battery cell 20A to the three battery cells 20B to 20D. On the other hand, the temperature changes Cte and Ctf of the two battery cells 20E and 20F hardly changed. In other words, the fire did not spread from the ignited battery cell 20A to the four battery cells 20E to 20H, including the two battery cells 20E and 20F.

[0046] Figure 9 shows the measurement locations for the heat flux shown in Figures 10 and 11. As shown in Figure 9, the heat flux on the negative X-axis side of each of the eight battery cells 20A to 20H is QLa to QLh. The heat flux on the positive X-axis side of each of the eight battery cells 20A to 20H is QRa to QRH. In addition, the heat flux on the wall surface on the negative X-axis side within the housing 10a is QL0, and the heat flux on the wall surface on the positive X-axis side is QR0. The measurement location for the heat flux in the Z-axis direction (vertical direction) is midway between the housing 10a and the battery cells 20A to 20H.

[0047] As shown in Figure 9, when the heat flux at each location is defined, Figure 10 shows the change in heat flux over time during radiation, and Figure 11 shows the change in heat flux over time to the cross-section of the heat transfer layer 51. In Figure 10, positive values ​​on the vertical axis represent radiation due to radiation, and negative values ​​represent absorption due to radiation. In Figure 10, the changes in heat flux corresponding to heat fluxes QLa~QLe, QRa~QRd, and QL0 are represented by CLa~CLe, CRa~CRd, and CL0, respectively. For example, the change in heat flux CRa (thin solid line) starts at -10000 W / m 2 Therefore, 10000W / m 2It functions as a heat flux absorption surface and then as a heat flux radiation surface. In the second embodiment, the four battery cells 20E to 20H located on the positive X-axis side do not ignite. Therefore, when the heat fluxes QLf to QLh, QRe to QRh of these battery cells 20E to 20H and the heat flux QR0 of the housing 10a function as radiation radiation surfaces, the heat flux is small.

[0048] Figure 11 shows the changes in heat flux to the heat transfer layer 51 corresponding to heat fluxes QLa~QLe, QRa~QRd, and QL0, expressed as CLa~CLe, CRa~CRd, and CL0, respectively. The changes in heat flux CLa~CLe, CRa~CRd, and CL0 shown in Figure 11 are 8.0 × 10⁻⁶. 6 (W / m 2 The values ​​are larger than ). In other words, each of the heat fluxes QLa~QLe, QRa~QRd, and QL0 radiates more radiation to the heat transfer layer 51 than radiation to the battery cell 20. As a result, the spread of fire to four of the eight battery cells 20A~20H, 20E~20H, is suppressed.

[0049] Figure 12 is an explanatory diagram of the temperature changes Cta to Cth of the eight battery cells 20A to 20H in a secondary battery system 100x without a second thermal expansion valve 82, with temperatures Ta to Th. In contrast to the secondary battery system 100a of the second embodiment, in the secondary battery system 100x without a second thermal expansion valve 82, the refrigerant 32a expands using the first thermal expansion valve 81 even when battery cell 20A ignites. Figure 12 shows the temperature changes Cta to Cth of the eight battery cells 20A to 20H corresponding to Figure 8 in the case of secondary battery system 100x. As shown by the temperature changes Cta to Cth in Figure 12, the temperatures of all eight battery cells 20A to 20H rise to over 500°C within 30 minutes. That is, all eight battery cells 20A to 20H ignite within 30 minutes.

[0050] Figure 13 is an explanatory diagram illustrating the changes in the heat fluxes QLa~QLh, QRa~QRh, QL0, QR0, CLa~CLh, CRa~CRh, CL0, and CR0 of the eight batteries 20A~20H in a secondary battery system 100x without a second thermal expansion valve 82. As shown in the changes in heat flux CLa~CLh, CRa~CRh, CL0, and CR0 in Figure 13, all eight battery cells 20A~20H have ignited, so the changes in heat flux are large in all cases. Thus, compared to the secondary battery system 100x without a second thermal expansion valve 82, the secondary battery system 100a of the second embodiment, which is equipped with a second thermal expansion valve 82, suppresses the spread of fire to the four battery cells 20E~20H.

[0051] As described above, the medium 15a in the second embodiment is a low-boiling-point fluorocarbon-based medium. The control unit 40 controls the temperature of the medium 15a by controlling the temperature of the refrigerant 32a supplied to the refrigerant flow path 30a in the housing 10a using the temperature detected by the temperature sensor S1. By controlling the temperature of the medium 15a, the control unit 40 adjusts the temperature of the multiple battery cells 20 using the heat of vaporization of the medium 15a and also changes the vapor pressure of the medium 15a. In this embodiment, during charging and discharging when the battery cells 20 are not ignited, the battery cells 20 are efficiently cooled by utilizing the latent heat of vaporization of the fluorocarbon-based medium 15a by adjusting the temperature and boiling point during charging and discharging. In addition, ignition of the battery cells 20 is detected by the temperature of the battery cells 20 obtained by the temperature sensor S1. If a battery cell 20 ignites, the temperature of the medium 15a is lowered even further than during charging and discharging of the battery cells 20, thereby cooling the ignited battery cell 20 and suppressing the spread of fire between the battery cells 20.

[0052] Furthermore, in the second embodiment, the first thermal expansion valve 81 and the second thermal expansion valve 82 expand the refrigerant 32a flowing through the external passage 35 due to the pressure difference between their upstream and downstream sides. The pressure difference of the second thermal expansion valve 82 is greater than that of the first thermal expansion valve 81. When the temperature detected by the temperature sensor S1 is below the threshold of 80°C, the control unit 40 connects the external passage 35 to the first thermal expansion valve 81. In this case, the control unit 40 supplies the refrigerant 32a cooled to 20°C to the refrigerant passage 30a in the housing 10a via the first thermal expansion valve 81. Also, when the temperature detected by the temperature sensor S1 reaches 80°C, the control unit 40 supplies the refrigerant 32a to the refrigerant passage 30a in the housing 10a via the second thermal expansion valve 82 instead of the first thermal expansion valve 81. In this embodiment, when the battery cell 20 is charged and discharged, the refrigerant 32a is supplied to the refrigerant passage 30a in the housing 10a via the first thermal expansion valve 81. When a battery cell 20 ignites, refrigerant 32a is supplied to the refrigerant flow path 30a within the housing 10a via the second thermal expansion valve 82. As a result, when a battery cell 20 ignites, refrigerant 32a that has expanded further due to the pressure difference and whose temperature has decreased compared to that of the first thermal expansion valve 81 is supplied to the refrigerant flow path 30a via the second thermal expansion valve 82. Consequently, refrigerant 32a at an even lower temperature than when the battery cell 20 is not ignited is supplied to the housing 10a containing the ignited battery cell 20, and the ignited battery cell 20 is cooled.

[0053] Furthermore, the heat transfer member 50a of the second embodiment comprises a heat transfer layer 51 formed in direct contact with the surfaces of the battery cells 20A and 20B, and a porous body 52 formed of a porous material on the surface of the heat transfer layer 51. The heat transfer layer 51 is made of a metal with high thermal conductivity. The porous body 52 is formed on the surface of the heat transfer layer 51 formed on the surfaces of the battery cells 20A and 20B, without being in direct contact with the battery cells 20A and 20B. In this embodiment, the liquid medium 15a cooled by the refrigerant 32a flowing through the refrigerant channel 30a spreads rapidly throughout the porous body 52 by capillary action generated by the porous body 52 connected to the refrigerant channel 30a. The liquid medium 15a in the porous body 52 exchanges heat with the battery cell 20 via the heat transfer layer 51 in contact with the porous body 52. Through heat exchange, the medium 15a, which has changed from a liquid to a gas, moves upward towards the battery cell 20 where the refrigerant channel 30a is located, cools, changes back into a liquid, and cools the battery cell 20 again. In other words, in this embodiment, the battery cell 20 is rapidly cooled by vapor heat transport of the medium 15a using the capillary action of the porous body 52. ​​On the other hand, if the battery cell 20 ignites and becomes hot, the condensation of the medium 15a cannot keep up, and dry-out occurs around the ignited battery cell 20. When dry-out occurs, heat is transferred from the ignited battery cell 20 to the adjacent battery cell 20 by thermal radiation from the heat transfer layer 51. In this embodiment, since the heat transfer layer 51 is connected to the refrigerant channel 30a, it is rapidly cooled, and heat transfer between battery cells 20 by thermal radiation is suppressed.

[0054] <Third Embodiment> Figures 14 and 15 are schematic block diagrams of the secondary battery system 100b of the third embodiment. The secondary battery system 100b of the third embodiment differs from the secondary battery system 100a of the second embodiment in that it has a pressure regulating valve 90a instead of a low-pressure pressure regulating valve 90, and does not have a second thermal expansion valve 82, a control unit 40, or a temperature sensor S1.

[0055] As shown in Figures 14 and 15, the pressure regulating valve 90a of the third embodiment includes a first pressure regulating valve 91 that releases the pressure inside the housing 10, and a second pressure regulating valve 92 connected in series between the housing 10a and the first pressure regulating valve 91. The first pressure regulating valve 91 opens when the pressure inside the housing 10a reaches a first pressure value. Once the first thermal expansion valve 81 opens, it remains open thereafter. The second pressure regulating valve 92 is a valve that opens when the pressure is less than the first pressure value and greater than atmospheric pressure (i.e., a second pressure value), and closes when the pressure is less than the second pressure value.

[0056] In the third embodiment, the pressure resistance of the container within the housing 10a is set to 1.5 MPa. Against this, the first pressure value at which the first pressure regulating valve 91 opens is set to 1.2 MPa. Also, the second pressure value at which the second pressure regulating valve 92 opens is set to 0.1 MPa. Note that the first and second pressure values ​​are gauge pressures. In the third embodiment, during charging and discharging when none of the battery cells 20 within the housing 10a have ignited (Figure 14), the pressure of the medium 15a within the housing 10a is set to 0.8 MPa. In this case, as shown in Figure 14, the first pressure regulating valve 91 is closed and the second pressure regulating valve 92 is open.

[0057] During charging and discharging of the battery cells, if any of the battery cells 20 ignite, and the high pressure of the battery cells 20A is released into the housing 10a by the opening of the safety valve 21A (Figure 1), as shown in Figure 15, the pressure inside the housing 10a increases. When the increased pressure reaches the first pressure value of 1.2 MPa, the first pressure regulating valve 91 opens in addition to the second pressure regulating valve 92. As a result, the pressure inside the housing 10a is maintained at 1.2 MPa or less.

[0058] After the first pressure regulating valve 91 opens, and the ignition of battery cell 20A and the spread of fire to other battery cells 20 subside, and the pressure inside the housing 10a drops to 0.1 MPa, the second pressure regulating valve 92 closes, as shown in Figure 15. This suppresses the inflow of oxygen from the atmosphere into the housing 10a.

[0059] As described above, the pressure regulating valve 90a of the secondary battery system 100b of the third embodiment includes a first pressure regulating valve 91 that releases the pressure inside the housing 10, and a second pressure regulating valve 92 connected in series between the housing 10a and the first pressure regulating valve 91. The first pressure regulating valve 91 opens when the pressure inside the housing 10a reaches a first pressure value. Once the first thermal expansion valve 81 opens, it remains open thereafter. The second pressure regulating valve 92 is a valve that opens when the pressure is less than the first pressure value and greater than atmospheric pressure (i.e., a second pressure value), and closes when the pressure is less than the second pressure value. In this embodiment, when the battery cell 20 is charging and discharging without ignition, the medium 15a inside the housing 10a cools the battery cell 20 at a pressure between the second pressure value and the first pressure value. In this case, since the second pressure regulating valve 92 is open and the first pressure regulating valve 91 is closed, the medium 15a inside the housing 10a is not released into the atmosphere. On the other hand, if the battery cell 20 ignites and the pressure inside the housing 10a changes to above the first pressure value, the first pressure regulating valve 91 opens in addition to the second pressure regulating valve 92. In this case, the medium 15a inside the housing 10a is released into the atmosphere, and the pressure inside the housing 10a decreases. As a result, damage to the housing 10a and other containers due to the increase in pressure inside the housing 10a can be suppressed. Furthermore, if the pressure inside the housing 10a decreases after the first pressure regulating valve 91 has opened and falls below the second pressure value, the second pressure regulating valve 92 closes. Since the second pressure value is set higher than atmospheric pressure, even if the pressure inside the housing 10a decreases, oxygen-containing air does not flow into the housing 10a from the atmosphere. In other words, in this embodiment, by suppressing the pressure rise when the battery cell 20 ignites, damage to the housing 10a and other containers is suppressed, while the progression of ignition due to the influx of oxygen into the housing 10a from the atmosphere is suppressed.

[0060] <Fourth Embodiment> Figure 16 is a schematic block diagram of the secondary battery system 100d of the fourth embodiment. As shown in Figure 16, the secondary battery system 100d of the fourth embodiment is a system that replaces the low-pressure pressure regulating valve 90a of the second embodiment with the pressure regulating valve 90a of the third embodiment. Therefore, in the fourth embodiment, if the battery cell 20 ignites, a medium 15a with an even lower temperature than during charging and discharging is supplied into the housing 10a, similar to the second embodiment. This further cools the battery cell 20 and suppresses the spread of fire between the battery cells 20.

[0061] Furthermore, in the fourth embodiment, if the battery cell 20 ignites, the first pressure regulating valve opens in addition to the second pressure regulating valve 92, similar to the third embodiment. As a result, the medium 15a in the housing 10a is released into the atmosphere, and the pressure inside the housing 10a decreases. Due to the decrease in pressure inside the housing 10a, the electrolyte components released from the ignited battery cell 20 into the housing 10a remain in the housing 10a as liquid without vaporizing. As a result, in the secondary battery system 100d of the fourth embodiment, compared to the second embodiment in which the four battery cells 20A to 20D shown in Figure 8 ignited, only one battery cell 20 ignited, and the spread of fire to the other battery cells was suppressed. In other words, in the fourth embodiment, the spread of fire to the battery cells 20 is further suppressed compared to the second embodiment.

[0062] <Fifth Embodiment> Figure 17 is a schematic block diagram of the secondary battery system 100c of the fifth embodiment. The secondary battery system 100c of the fifth embodiment differs from the secondary battery system 100a of the second embodiment in that it further includes a tank TK for storing antifreeze, a pump P1 for circulating the antifreeze, and on-off valves 93 and 94. Figure 17 shows the state after the state shown in Figure 6, where the low-pressure regulating valve 90 is opened after the battery cell 20 in the housing 10a ignites, as in the second embodiment.

[0063] The antifreeze stored in tank TK has electrical insulating properties. For example, an antifreeze with an electrical insulating property has a volume resistivity of 1.0 × 10⁻⁶. 13This refers to antifreeze with a viscosity of (Ω·m) or higher. The on-off valves 93 and 94 open and close the flow path connecting the tank TK and the inside of the housing 10a, as shown in Figure 17, according to the control signal from the control unit 40c. When the on-off valves 93 and 94 are open and the tank TK and the inside of the housing 10a are connected, the pump P1 circulates the antifreeze between the tank TK and the inside of the housing 10a.

[0064] Similar to the second embodiment, when the temperature detected by the temperature sensor S1 changes from below 80°C (second temperature) to 80°C or higher, the control unit 40c opens the low-pressure regulating valve 90 to release the medium 15a in the containment section 10a into the atmosphere. Subsequently, as shown in Figure 17, the control unit 40c closes the low-pressure regulating valve 90, then opens the on-off valves 93 and 94 respectively to operate the pump P1 and supply antifreeze from the tank TK into the containment section 10a. When the containment section 10a is filled with antifreeze to a predetermined level or higher, the control unit 40c stops the operation of the pump P1 and closes the on-off valves 93 and 94 respectively.

[0065] Figure 18 is a schematic diagram of the housing 10a removed from the secondary battery system 100c. Once the housing 10a is filled with antifreeze, the housing 10a becomes removable. The removed housing 10a is transported to a destruction facility, for example, to prevent re-ignition and for safety reasons.

[0066] Figure 19 is a schematic diagram of a housing unit 10a connected to a cooling circulation system SY, which is different from the secondary battery system 100c. During transport, the housing unit 10a is connected to the cooling circulation system SY shown in Figure 19, for example, to perform heat exchange and cool the antifreeze inside the housing unit 10a. As shown in Figure 19, the cooling circulation system SY includes a heat exchanger 75 capable of exchanging heat with the antifreeze and a pump P2 for circulating the antifreeze. After the inside of the housing unit 10a is connected to the flow path of the cooling circulation system SY, the on-off valves 93 and 94 open, and the pump P2 starts operating, and the antifreeze is cooled by the heat exchanger 75.

[0067] As described above, the secondary battery system 100c of the fifth embodiment includes a tank TK that stores electrically insulating antifreeze. When the temperature detected by the temperature sensor S1 changes from below 80°C to 80°C or higher, the control unit 40c opens the low-pressure regulating valve 90 to release the medium 15a in the containment section 10a into the atmosphere. Subsequently, as shown in Figure 17, the control unit 40c closes the low-pressure regulating valve 90, then opens the on-off valves 93 and 94 respectively to operate the pump P1 and supply antifreeze from the tank TK into the containment section 10a. In this embodiment, when the battery cell 20 changes from a non-ignited state to an ignited state, the containment section 10a is filled with the supplied antifreeze. By covering the battery cell 20 with antifreeze, contact between the ignited battery cell 20 and oxygen is suppressed, and the temperature of the battery cell 20 is controlled by controlling the temperature of the antifreeze. In particular, if there are battery cells 20 that have not completely burned, filling the housing 10a with antifreeze suppresses the re-ignition of the unburned battery cells 20 after several hours or several days.

[0068] <Modified examples of embodiments> The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit. For example, the following modifications are possible. Furthermore, in the above embodiments, some of the configurations implemented by hardware may be replaced with software, and conversely, some of the configurations implemented by software may be replaced with hardware.

[0069] <Example 1> In each of the first to fifth embodiments described above, examples of secondary battery systems 100, 100a, 100b, 100c, and 100d were explained. However, the secondary battery system is deformable within the range in which battery cells are housed in a housing, an oxygen-free medium is filled in the housing, and a safety valve for releasing pressure inside the battery cells is positioned opposite the cooling unit. In the first embodiment described above, a refrigerant flow path 30 through which a refrigerant 32 flows was explained as an example of a cooling unit that cools the battery cells 20 via the medium 15. However, the cooling unit located inside the housing 10 may be a heat sink made only of metal material. In this case, the heat sink may dissipate heat using a condenser 70 or the like connected outside the housing 10. As shown in Figure 3, in the second embodiment, the battery cells 20 were cooled by a refrigeration cycle using a refrigerant 32a, but the battery cells 20 may also be cooled by a system in which a liquid circulation system via antifreeze is placed between the refrigeration cycle and the battery cells 20.

[0070] The medium filled in the housing 10 may be a medium other than a fluorocarbon-based medium, such as nitrogen. For example, in the second embodiment shown in Figure 6, a heat insulating member having heat insulating properties may be placed in a part between the opposing porous bodies 52. The housing 10 and the battery cell 20 may have shapes other than a rectangular parallelepiped. Instead of a battery cell 20, a battery in which multiple battery cells are stacked may be used.

[0071] The position in which the refrigerant flow path 30 is formed within the housing 10 may be other than vertically above the battery cell 20, for example, vertically below it. In the case where the battery cell 20 is cooled by vapor heat transport using the latent heat of vaporization utilizing the low boiling point of the fluorocarbon medium, as in the second embodiment, it is preferable that the refrigerant flow path 30a is positioned vertically above the battery cell. Note that the vertical direction and other directions defined in the Cartesian coordinate system CS are coordinate systems defined to explain the secondary battery system 100 shown in Figure 1, and these directions may be rotated as appropriate.

[0072] The predetermined pressure value at which the safety valve 21A opens, the temperature of the battery cell 20 at which the control unit 40 switches the connection between the first thermal expansion valve 81 and the second thermal expansion valve 82 in the second embodiment, the pressure value at which the low-pressure regulating valve 90 opens, and the first pressure value at which the first regulating valve 91 opens and the second pressure value at which the second regulating valve 92 opens and closes in the third embodiment can be modified according to the specifications of the secondary battery system 100 and the battery cell 20. For example, in the second embodiment, when the temperature of the battery cell 20 is 80°C, it is determined that the battery cell 20 is on fire, and the refrigerant 32a expands due to the second thermal expansion valve 82. However, for example, when the temperature of the battery cell 20 reaches 100°C, the connection may be switched from the first thermal expansion valve 81 to the second thermal expansion valve 82. Furthermore, a modified secondary battery system may be equipped with three or more thermal expansion valves that expand the refrigerant 32a due to different pressure differences. In this case, the connection of the three or more thermal expansion valves may be switched according to the temperature detected by two or more temperature sensors S1.

[0073] The embodiments of this specification have been described above based on the embodiments and modifications described above. The embodiments described above are for the purpose of facilitating understanding of this specification and do not limit it. This specification may be modified and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in this specification. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.

[0074] The present invention can also be realized in the following forms. [Application Example 1] A secondary battery system, Rechargeable batteries and A housing section containing the aforementioned secondary battery and filled with an oxygen-free medium, A cooling unit is disposed inside the housing and cools the secondary battery via the medium, Equipped with, The secondary battery has a safety valve that releases the internal pressure of the secondary battery when the internal pressure reaches a predetermined pressure value. A secondary battery system in which the safety valve is positioned opposite the cooling section via the medium. [Application Example 2] The secondary battery system described in Application Example 1, A secondary battery system in which the distance between the safety valve and the cooling unit is set to be less than or equal to the flame extinguishing distance. [Application Example 3] A secondary battery system as described in Application Example 1 or Application Example 2, further, A temperature acquisition unit that acquires the battery temperature, which is the temperature of the secondary battery, A control unit that uses the battery temperature to control the temperature and pressure of the medium, Equipped with, The aforementioned medium is a fluorocarbon-based medium. The cooling unit is positioned vertically above the secondary battery. The control unit controls the temperature of the fluorocarbon medium, thereby adjusting the temperature of the secondary battery using the heat of vaporization of the fluorocarbon medium and changing the vapor pressure of the fluorocarbon medium, in a secondary battery system. [Application Example 4] A secondary battery system described in any one of Application Examples 1 to 3, The cooling unit has a refrigerant flow path through which a refrigerant flows, The secondary battery system is further, A first thermal expansion valve that expands the refrigerant due to the pressure difference between its upstream and downstream sides, A second thermal expansion valve expands the refrigerant by a pressure difference between its upstream and downstream sides that is greater than the pressure difference of the first thermal expansion valve, Equipped with, The control unit, When the battery temperature is below the first temperature, the refrigerant is supplied to the secondary battery via the first thermal expansion valve. A secondary battery system that supplies the refrigerant to the secondary battery via the second thermal expansion valve when the battery temperature is equal to or greater than the first temperature. [Application Example 5] A secondary battery system described in any one of Application Examples 1 to 4, further comprising: A heat transfer layer made of metal, connected to the surface of the secondary battery and connected to the refrigerant flow path, A porous body formed of a porous material is connected to the secondary battery via the heat transfer layer, A secondary battery system equipped with this feature. [Application Example 6] A secondary battery system described in any one of Application Examples 1 to 5, further comprising: A tank storing an antifreeze with electrical insulating properties, A shut-off valve for opening and closing the connection between the housing and the outside, Equipped with, The control unit, When the battery temperature changes from below the second temperature to above the second temperature, the on / off valve is opened to release the fluorocarbon-based medium from inside the housing. A secondary battery system that supplies antifreeze from the tank into the interior of the storage unit after the release of the fluorocarbon-based medium. [Application Example 7] A secondary battery system described in any one of Application Examples 1 to 6, further comprising: A first pressure regulating valve that releases the pressure inside the housing, A second pressure regulating valve is connected in series between the housing section and the first pressure regulating valve, Equipped with, The first pressure regulating valve opens when the pressure inside the housing reaches a first pressure value, and maintains the open state. A secondary battery system wherein the second pressure regulating valve opens when the pressure is greater than or equal to a second pressure value that is less than the first pressure value and greater than atmospheric pressure, and closes when the pressure is less than the second pressure value. [Explanation of Symbols]

[0075] 10,10a... Containment area 15,15a…medium 20, 20A~20H... Battery cell (rechargeable battery) 21A, 21B… Safety valves 22...Electrolyte component 30,30a… Refrigerant flow path 31…tube wall 32,32a… Refrigerant 35…External channel 40,40c…Control Unit 50,50a… Heat transfer element 51…Heat transfer layer 52…Porous material 60... Compressor 70...Condenser 75...Heat exchanger 81...First thermal expansion valve 82...Second thermal expansion valve 90... Low-pressure pressure regulating valve 90a... Pressure regulating valve 91...First pressure regulating valve 92... Second pressure regulating valve 93... Shut-off valve 100, 100a, 100b, 100c, 100x… Secondary battery system CS… Cartesian coordinate system P1, P2... pumps S1…Temperature sensor (temperature acquisition unit) SY…Cooling circulation system TK... Tank

Claims

1. A secondary battery system, Rechargeable batteries and A housing section containing the aforementioned secondary battery and filled with an oxygen-free medium, A cooling unit is disposed inside the housing and cools the secondary battery via the medium, A temperature acquisition unit that acquires the battery temperature, which is the temperature of the secondary battery, A control unit that uses the battery temperature to control the temperature and pressure of the medium, Equipped with, The secondary battery has a safety valve that releases the internal pressure of the secondary battery when the internal pressure reaches a predetermined pressure value. The safety valve is positioned opposite the cooling section via the medium, The aforementioned medium is a fluorocarbon-based medium. The cooling unit is positioned vertically above the secondary battery. The control unit controls the temperature of the fluorocarbon medium, thereby adjusting the temperature of the secondary battery using the heat of vaporization of the fluorocarbon medium and changing the vapor pressure of the fluorocarbon medium, in a secondary battery system.

2. A secondary battery system, Rechargeable batteries and A housing section containing the aforementioned secondary battery and filled with an oxygen-free medium, A cooling unit is disposed inside the housing and cools the secondary battery via the medium, A first pressure regulating valve that releases the pressure inside the housing, A second pressure regulating valve is connected in series between the housing section and the first pressure regulating valve, Equipped with, The secondary battery has a safety valve that releases the internal pressure of the secondary battery when the internal pressure reaches a predetermined pressure value. The safety valve is positioned opposite the cooling section via the medium, The first pressure regulating valve opens when the pressure inside the housing reaches a first pressure value, and maintains the open state. A secondary battery system wherein the second pressure regulating valve opens when the pressure is greater than or equal to a second pressure value that is less than the first pressure value and greater than atmospheric pressure, and closes when the pressure is less than the second pressure value.

3. A secondary battery system according to claim 1 or claim 2, A secondary battery system in which the distance between the safety valve and the cooling unit is set to be less than or equal to the flame extinguishing distance.

4. A secondary battery system according to claim 1, The cooling unit has a refrigerant flow path through which a refrigerant flows, The secondary battery system is further, A first thermal expansion valve that expands the refrigerant due to the pressure difference between its upstream and downstream sides, A second thermal expansion valve expands the refrigerant by a pressure difference between its own upstream and downstream sides that is greater than the pressure difference of the first thermal expansion valve, Equipped with, The control unit, When the battery temperature is below the first temperature, the refrigerant is supplied to the secondary battery via the first thermal expansion valve. A secondary battery system that supplies the refrigerant to the secondary battery via the second thermal expansion valve when the battery temperature is equal to or greater than the first temperature.

5. The secondary battery system according to claim 4, further, A heat transfer layer made of metal, connected to the surface of the secondary battery and connected to the refrigerant flow path, A porous body formed of a porous material is connected to the secondary battery via the heat transfer layer, A secondary battery system equipped with this feature.

6. A secondary battery system according to claim 1, further, A tank storing an antifreeze with electrical insulating properties, A shut-off valve for opening and closing the connection between the housing and the outside, Equipped with, The control unit, When the battery temperature changes from below the second temperature to above the second temperature, the on / off valve is opened to release the fluorocarbon-based medium from inside the housing. A secondary battery system that supplies antifreeze from the tank into the interior of the storage unit after the release of the fluorocarbon-based medium.

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