Bus bar and secondary battery

Abstract

To prevent a battery from burning due to heat transfer through a bus bar.SOLUTION: A bus bar electrically connects two batteries and includes a first member connected to one of the two batteries and having a bimetal structure consisting of a first metal and a second metal bonded together, and a second member connected to the other of the two batteries, which is conductive and has a portion in contact with the first metal of the first member, and the thermal expansion coefficient of the first metal is greater than the thermal expansion coefficient of the second metal.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a bus bar and a secondary battery. [Background technology]

[0002] Secondary batteries used as batteries for electric vehicles and the like are known (see, for example, 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 is formed in the heat sink, through which coolant cooled by a radiator flows. Therefore, the secondary battery, which heats up during charging and discharging, is cooled by the heat sink through which coolant flows. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-204151 Summary of the Invention [Problem to be solved by the invention]

[0004] In a secondary battery in which multiple batteries are stacked, the temperature of the battery may rise due to external short circuits caused by external stress such as collisions when the battery is mounted on a vehicle, initial contamination of the electrodes and electrolyte with impurities, internal short circuits between electrodes caused by battery deterioration, or insufficient cooling capacity during high-speed charging and discharging. If the temperature of the battery reaches the ignition temperature of the battery material, the battery may ignite. At this time, the heat generation triggers the decomposition reaction of the negative electrode SEI film (Solid Electrolyte Interface) and the exothermic reaction between the negative electrode and the electrolyte. The heat generation and temperature rise of the battery cause an exothermic reaction between the positive electrode and the electrolyte and a decomposition reaction of the electrolyte, and the temperature of the ignited battery rises rapidly. If one battery ignites, the heat of the ignited battery may be transferred to the adjacent battery through the bus bar that electrically connects the batteries. The bus bar is often made of a metal with high electrical conductivity. The thermal conductivity of a metal bus bar is high, and the heat transferred from the ignited battery to the adjacent battery may cause the adjacent battery to reach the ignition temperature and ignite, causing the adjacent battery to catch fire. However, Patent Document 1 does not take into consideration the risk of battery fire spreading through the busbar.

[0005] In addition, in a conventional structure combining a thermal breaker with a busbar, when the current flowing through the busbar becomes an overcurrent, the busbar's temperature rises due to self-heating caused by the resistor, and the current is cut off by utilizing the displacement caused by the difference in thermal expansion. In other words, the conventional busbar suppresses overcurrent flowing in a specific direction, but does not take into account heat that moves in that specific direction or in other directions.

[0006] The present invention has been made to solve at least some of the above-mentioned problems, and has an object to suppress the spread of battery fire caused by heat transfer through a bus bar. [Means for solving the problem]

[0007] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms.

[0008] (1) According to one aspect of the present invention, there is provided a busbar for electrically connecting two batteries, the busbar comprising: a first member connected to one of the two batteries and having a bimetal structure in which a first metal and a second metal are bonded together; and a second member connected to the other of the two batteries, having electrical conductivity, and having a portion in contact with the first metal of the first member, wherein the thermal expansion coefficient of the first metal is greater than the thermal expansion coefficient of the second metal.

[0009] According to this configuration, the first member has a plate-shaped bimetal structure in which two types of metals or alloys with different thermal expansion coefficients are bonded together. The first member is in contact with the second member on the surface of the first metal with a high thermal expansion coefficient. Therefore, when a battery connected to the first member or the second member ignites, the temperature of the first member rises due to the heat caused by the ignition. When the temperature rises, the first member having a bimetal structure bends toward the second metal with a low thermal expansion coefficient due to the difference in thermal expansion coefficient between the first metal and the second metal. That is, the first member deforms in such a way that it warps away from the second member, and the first member and the second member are separated. Due to the separation, even if one of the two batteries electrically connected by the bus bar ignites, the heat of the ignited battery does not transfer to the battery connected via the bus bar. As a result, in this configuration, the spread of fire of the batteries caused by the heat transfer via the bus bar is suppressed. In particular, in this configuration, the electrical resistance of the bus bar connecting the two batteries is sufficiently small compared to the internal resistance of the batteries. Therefore, the heat generated by the busbar due to the current when the batteries are charged and discharged is sufficiently small. In other words, the busbar of this configuration separates the first and second components not due to its own heat generation, but due to heat transfer between the batteries connected via the busbar. In this configuration, even if either of the two batteries connected via the busbar catches fire, the spread of fire to the batteries is suppressed regardless of the direction of heat transfer.

[0010] (2) In the busbar of the above aspect, the second member may have a bimetal structure in which a third metal and a fourth metal are bonded together, the third metal may be in contact with the first metal, and the thermal expansion coefficient of the third metal may be greater than the thermal expansion coefficient of the fourth metal. According to this configuration, the second member also has a bimetal structure in which the third metal and the fourth metal are bonded together. Furthermore, the second member is in contact with the first metal of the first member on the side of the third metal, which has a higher thermal expansion coefficient. Therefore, when a battery connected to the first member or the second member ignites, both the first member and the second member, whose temperatures have risen due to the heat of the ignition, deform so as to warp in directions away from each other due to the difference in thermal expansion coefficient. As the first member and the second member are separated by the deformation, heat from the ignited battery does not transfer to the adjacent non-ignited batteries via the bus bar, further suppressing the spread of fire among the batteries.

[0011] (3) In the busbar of the above aspect, the first metal and the third metal may have a softening point higher than a temperature of the busbar when one of the two batteries ignites, and the second metal and the fourth metal may be made of Invar material. According to this configuration, the softening points of the second metal and the fourth metal are higher than the temperature of the busbar when one of the two batteries ignites. Furthermore, the second metal and the fourth metal are made of an Invar material with a low expansion coefficient. Therefore, a difference in thermal expansion coefficient is ensured between the first metal and the second metal and between the third metal and the fourth metal. As a result, even if one of the two batteries ignites, the second metal and the fourth metal deform so as to warp in a direction in which the first member and the second member move away from each other. As a result, when one of the two batteries ignites, the first member and the second member are reliably separated, and the transfer of heat from the ignited battery to the adjacent battery via the busbar is suppressed.

[0012] (4) In the busbar of the above embodiment, a joining member may be further provided, the joining member having a melting point and electrical conductivity lower than the temperature of the first metal when at least one of the two batteries ignites, and the first member and the second member may be in contact with each other via the joining member. According to this configuration, the first member and the second member are in contact with each other via a bonding member having a melting point lower than that of the first metal. Since the melting point of the bonding member is low, the bonding member melts even if the temperature of the first metal is low when the battery starts to ignite. Therefore, even if sufficient tensile stress due to a high expansion difference cannot be obtained in the first member at the low temperature when the battery starts to ignite, the bonding strength of the bonding surface decreases, and the first member and the second member are separated from each other due to residual stress acting in a direction that separates them from each other.

[0013] (5) In the busbar of the above aspect, a thickness of the first member may be set to satisfy both a first relational expression for the electrical resistance of the first member and a second relational expression for the amount of displacement of the first member when the one of the batteries ignites, the first relational expression being expressed by the relationship between the electrical resistance of the first member and the internal resistance of the one of the batteries, and the second relational expression being expressed by the relationship between the temperature of the first member when the one of the batteries ignites, the thermal expansion coefficients of the first metal and the second metal, the longitudinal elastic moduli of the first metal and the second metal, and the length from a portion connected to the one of the batteries to a position where it is in contact with the second member. According to this configuration, the relationship between the thickness of the first member and the electrical resistance of the first member is expressed by a first relational expression. In addition, a second relational expression is calculated that expresses the relationship between the temperature of the first member when the battery ignites, the known parameters of the first metal and the second metal that form the first member, and the amount of displacement of the first member. The amount of displacement of the first member when the battery ignites varies depending on the thickness of the first member. Therefore, by setting the thickness of the first member so as to satisfy the first and second relational expressions, the shape of the first member that reliably separates the first and second members when the battery ignites can be easily determined.

[0014] (6) The busbar of the above aspect may further include a third member connected to a battery different from the two batteries and having a bimetal structure with a fifth metal and a sixth metal bonded together, and a fourth member connected to a battery different from both the two batteries and the battery to which the third member is connected and having a bimetal structure with a seventh metal and an eighth metal bonded together, wherein the fifth metal is in contact with the first metal on a side of the first metal with which the third metal is in contact, and a thermal expansion coefficient of the fifth metal is greater than a thermal expansion coefficient of the sixth metal, and the seventh metal is in contact with each of the third metal and the fifth metal on a side of the third metal and the fifth metal with which the first metal is in contact, and a thermal expansion coefficient of the seventh metal is greater than a thermal expansion coefficient of the eighth metal. In this configuration, the first metal of the first member is in contact with the third metal of the second member and the fifth metal of the third member. Also, the third metal of the second member and the fifth metal of the third member are in contact with the seventh metal of the fourth member. Therefore, when the members connected to each of the four batteries are electrically connected in parallel, if a battery connected to any of the four members catches fire, the spread of the fire to the other batteries is suppressed.

[0015] (7) The busbar of the above aspect may further include a third member connected to a battery different from the two batteries and having a bimetal structure formed by bonding a fifth metal and a sixth metal, wherein the fifth metal is in surface contact with the first metal at a surface side of the first metal that is in contact with the third metal but is not in surface contact with the third metal, the fifth metal has a thermal expansion coefficient greater than a thermal expansion coefficient of the sixth metal, and the regions of the first metal in surface contact with the third metal and the fifth metal may be regions of the same triangular shape and area. In this configuration, the first member is in contact with the second and third members. According to this configuration, when the members connected to the three batteries are in contact with each other and a battery connected to one of the three members catches fire, the member connected to the battery that caught fire is bent and deformed in a direction away from the other two members. As a result, the member connected to the battery that caught fire is separated from the other members. Since the contact shape of the first member, the second member, and the third member is triangular, they are separated by the thermal expansion difference with a smaller busbar volume than when the contact shape is rectangular, for example. As a result, the spread of fire from the members connected to the battery that caught fire to the other batteries is suppressed by making the busbar even smaller.

[0016] (8) According to another aspect of the invention, there is provided a secondary battery comprising: a plurality of batteries arranged in a predetermined direction; a heat insulating material having thermal insulation properties arranged between each of the plurality of batteries; a heat sink connected to the plurality of batteries and the heat insulating material and extending in the predetermined direction; and a bus bar according to the above aspect electrically connecting at least two of the plurality of batteries. According to this configuration, multiple batteries and insulating materials are stacked, and the batteries are cooled by a heat sink extending along the stacking direction. When the battery generates heat, the temperature rises suddenly due to a decomposition reaction of the negative electrode SEI film that constitutes the battery, and the battery ignites. In contrast, in this configuration, the bus bar that electrically connects the multiple batteries in series or parallel separates them into a first member and a second member at high temperatures. This suppresses the spread of fire between the batteries, which is unique to secondary batteries in which multiple batteries are connected.

[0017] The present invention can be realized in various forms, for example, in the form of a bus bar, a secondary battery, a lithium ion battery, a secondary battery system, a control method for a secondary battery, a system including these devices or implementing these methods, a computer program for executing these devices or methods, a server device for distributing this computer program, a non-transitory storage medium on which a computer program is stored, etc. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic perspective view of a secondary battery according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic diagram of a cross section taken along line AA in FIG. [Diagram 3] FIG. 2 is a schematic perspective view of a bus bar according to the present embodiment. [Figure 4] 4 is a schematic cross-sectional view of a contact portion between a first member and a second member. FIG. [Diagram 5] FIG. 4 is a schematic cross-sectional view of a first member that is bent and deformed when the temperature rises. [Figure 6] 6 is an explanatory diagram of the amount of displacement of a first member that is bent and deformed when the temperature rises. FIG. [Figure 7] FIG. 4 is a schematic cross-sectional view of a second member that is bent and deformed when the temperature increases. [Figure 8] 6 is an explanatory diagram of the amount of displacement of a second member that is bent and deformed when the temperature rises. FIG. [Figure 9] 6 is an explanatory diagram of a stress distribution in a bonded member immediately before separation of a first member and a second member. FIG. [Figure 10] FIG. 4 is an explanatory diagram of the temperature distribution in the joining member immediately before separation of the first member and the second member. [Figure 11] 5 is an explanatory diagram of temperature changes in a plurality of battery cells when one battery cell ignites in the present embodiment. FIG. [Figure 12] FIG. 13 is a schematic perspective view of a bus bar of a comparative example. [Figure 13] FIG. 11 is an explanatory diagram of temperature changes in a plurality of battery cells when one battery cell ignites in a comparative example. [Figure 14] 4 is an explanatory diagram of each parameter during bending deformation of a first member. FIG. [Figure 15] 6A to 6C are diagrams illustrating temperature changes in the first member when a battery ignites in different cooling environments. [Figure 16] 6A to 6C are diagrams illustrating temperature changes in the second member when a battery ignites in different cooling environments. [Figure 17] FIG. 11 is a schematic perspective view of a bus bar according to a third embodiment. [Figure 18]FIG. 11 is a schematic cross-sectional view of a bus bar according to a third embodiment. [Figure 19] 13 is a schematic cross-sectional view of the busbar according to the third embodiment when the first member is bent and deformed. FIG. [Figure 20] FIG. 11 is a schematic cross-sectional view of the bus bar according to the third embodiment when the second member is bent and deformed. [Figure 21] FIG. 13 is a schematic perspective view of a bus bar according to a fourth embodiment. [Figure 22] FIG. 11 is a schematic cross-sectional view of the bus bar according to the fourth embodiment when the second member is bent and deformed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] First Embodiment FIG. 1 is a schematic perspective view of a secondary battery 100 according to an embodiment of the present invention. The secondary battery 100 shown in FIG. 1 has a plurality of battery cells 10 stacked in a predetermined direction (parallel to the X-axis). The plurality of battery cells 10 are electrically connected to each other in series or parallel via a bus bar not shown in FIG. 1. The bus bar is formed so that two members are in contact with each other at room temperature. The two members have a bimetal structure in which two types of metals or alloys with different thermal expansion coefficients are bonded together. When the temperature of the bus bar rises, the two members are bent and deformed so as to warp in directions away from each other due to the difference in thermal expansion coefficient, and are separated from each other. By separating the two batteries, even if the temperature of one battery connected by the bus bar rises, heat is not transferred from one battery to the other battery via the bus bar, and the rise in temperature of the other battery is suppressed.

[0020] As shown in Fig. 1, the secondary battery 100 has a substantially rectangular parallelepiped shape. Fig. 1 also shows an orthogonal coordinate system CS that is composed of an X-axis parallel to the long side of the rectangular parallelepiped secondary battery, a Y-axis parallel to the short side, and a Z-axis perpendicular to the X-axis and Y-axis and parallel to the vertical direction. The orthogonal coordinate system CS in Fig. 1 corresponds to the orthogonal coordinate system CS in Fig. 2 and subsequent figures.

[0021] The secondary battery 100 includes a plurality of battery cells 10 stacked in two rows along the X-axis, a heat insulating material 20 filled between each of the plurality of battery cells 10, a heat sink 30 disposed vertically below the secondary battery 100, and a plurality of bus bars not shown in Fig. 1. In other words, the heat insulating material 20 is disposed between each of the plurality of battery cells 10.

[0022] The battery cell 10 of this embodiment is a lithium-ion battery cell. The insulating material 20 is made of a silica-based insulating material and has a thermal conductivity of 0.1 W / (m·K) or less. In the heat sink 30, cooling water flows as a refrigerant liquid inside a metal partition. Therefore, the heat sink 30 cools the battery cell 10, whose temperature rises during charging and discharging, by the cooling water.

[0023] Fig. 2 is a schematic diagram of the AA cross section in Fig. 1. As shown in Fig. 2, the heat sink 30 includes a partition wall 31, a refrigerant flow path 33 formed inside the partition wall 31, and a refrigerant 32 that flows through the refrigerant flow path 33 along a flow direction DR2. The refrigerant 32 cools the battery cells 10A, 10B via the partition wall 31.

[0024] 2, the secondary battery 100 includes a first tab 50A welded vertically above the battery cell 10A, a second tab 50B welded vertically above the battery cell 10B, and a bus bar 40 that connects the first tab 50A and the second tab 50B. The first tab 50A and the second tab 50B are formed in the shape of a thin plate from a metal such as a copper alloy.

[0025] The bus bar 40 includes a first member 41 joined to a vertically upper surface of the plate-shaped first tab 50A, and a second member 46 joined to a vertically upper surface of the plate-shaped second tab 50B. That is, the first member 41 is connected to one battery cell 10A of the two battery cells 10A, 10B via the first tab 50A. The second member 46 is connected to the other battery cell 10B of the two battery cells 10A, 10B. The first member 41 and the second member 46 have a bimetal structure in which two different types of metals or alloys are bonded together.

[0026] FIG. 3 is a schematic perspective view of the busbar 40. As shown in FIG. 2, one end of the first member 41 on the negative X-axis side is joined to the first tab 50A. As shown in FIGS. 2 and 3, the other end of the first member 41 bends vertically upward as it advances toward the positive X-axis side, and extends toward the positive X-axis side after bending. The vertically lower surface of the other end of the first member 41 extending toward the positive X-axis side is in surface contact with the second member 46. The first member 41 and the second member 46 are in indirect contact with each other via a joining member not shown in FIGS. 2 and 3. The joining member will be described later with reference to FIG. 4.

[0027] As shown in Fig. 2, one end of the second member 46 on the positive X-axis direction side is joined to the second tab 50B. As shown in Figs. 2 and 3, the other end of the second member 46 bends vertically upward as it advances toward the negative X-axis direction side, and extends toward the negative X-axis direction after bending. The amount of vertically upward displacement of the second member 46 due to bending is smaller than the amount of vertically upward displacement of the first member 41. The vertically upward surface of the other end of the second member 46 extending toward the negative X-axis direction side is in surface contact with the first member 41.

[0028] Fig. 4 is a schematic cross-sectional view of a contact portion between the first member 41 and the second member 46. The busbar 40 includes a joining member 49 that brings the first member 41 and the second member 46 into indirect contact with each other. As shown in Fig. 4, the first member 41 and the second member 46 are clad materials having a bimetal structure in which two types of metals with different thermal expansion coefficients are bonded together. The first member 41 and the second member 46 are joined (clad) between atoms by controlling the pressure at the metal interface when the two types of metals are rolled (pressed or roll pressed).

[0029] The first member 41 includes a first metal plate (first metal) 42 made of a metal having a large thermal expansion coefficient, and a second metal plate (second metal) 43 made of a metal having a smaller thermal expansion coefficient than the metal forming the first metal plate 42. The second member 46 includes a third metal plate (third metal) 47 made of a metal having a large thermal expansion coefficient, and a fourth metal plate (fourth metal) 48 made of a metal having a smaller thermal expansion coefficient than the metal forming the third metal plate 47. In the first embodiment, examples of metals forming the first metal plate 42 and the third metal plate 47 having a large thermal expansion coefficient include copper (thermal expansion coefficient: 16.8 ppm / K), aluminum (23.8 ppm / K), and brass (33 ppm / K). Examples of metals forming the second metal plate 43 and the fourth metal plate 48 having a small thermal expansion coefficient include iron (11.7 ppm / K) and stainless steel (10.4 ppm / K).

[0030] 4, in the first member 41, the first metal plate 42 is located vertically below the second metal plate 43. The first metal plate 42 is connected to a third metal plate 47 of the second member 46 via a joining member 49. The thermal expansion coefficient of the metal forming the first metal plate 42 is higher than the thermal expansion coefficient of the metal forming the second metal plate 43. Therefore, when the temperature of the first member 41 rises due to, for example, ignition of the battery cell 10A (FIG. 2), the first member 41 is bent and deformed so as to warp vertically upward due to the difference in the thermal expansion coefficient between the first metal plate 42 and the second metal plate 43.

[0031] 5 and 6 are explanatory diagrams of the bending displacement of the first member 41 when the temperature rises. For example, when the battery cell 10A shown in FIG. 2 catches fire, the temperature of the bus bar 40 also rises due to heat transfer from the battery cell 10A. When the battery cell 10A catches fire, heat transfers to another battery cell 10B adjacent to the battery cell 10A via the insulating material 20 along a heat dissipation direction DR3 parallel to the stacking direction (X-axis direction). Similarly, the heat of the battery cell 10A transfers to the heat sink 30 along a heat dissipation direction DR4 from the battery cell 10A toward the heat sink 30. Furthermore, the heat of the battery cell 10A transfers to the battery cell 10B connected by the bus bar 40 along a heat dissipation direction DR1 via the bus bar 40.

[0032] Fig. 5 shows a schematic cross-sectional view of the first member 41 that is bent and deformed when the battery cell 10A ignites and the temperature rises to 500 degrees Celsius (°C). In Fig. 5, in the width direction of the first member 41 along the Y-axis direction, the shape S41M of the central portion after deformation is shown by a solid line, and the shape S41E of the end portion after deformation is shown by a dashed line. As shown in Fig. 5, the amount of displacement of the end portion after deformation is greater than the amount of displacement of the central portion after deformation.

[0033] 6 is a graph showing the amount of displacement at each position along the length L1 in the X-axis direction of the first member 41 in FIG. 5. In FIG. 6, the change in the amount of displacement of the center portion after deformation is shown by a solid curve C41M, and the change in the amount of displacement of the end portion after deformation is shown by a dashed curve C41E. As shown in FIG. 6, when the temperature of the battery cell 10A rises to 500°C, the amount of displacement of the center portion is about 2.3 mm, and the amount of displacement of the end portion is about 2.7 mm. In the example shown in FIGS. 5 and 6, the metal with a high thermal expansion coefficient that forms the first metal plate 42 is steel, and the metal with a low thermal expansion coefficient that forms the second metal plate 43 is an aluminum alloy.

[0034] 4, in the second member 46, the third metal plate 47 is located vertically above the fourth metal plate 48. Because the thermal expansion coefficient of the metal forming the third metal plate 47 is higher than the thermal expansion coefficient of the metal forming the fourth metal plate 48, when the temperature of the second member 46 rises due to, for example, ignition of the battery cell 10B (FIG. 2), the second member 46 is bent and deformed so as to warp vertically downward.

[0035] 7 and 8 are explanatory diagrams of the bending displacement of the second member 46 when the temperature rises. FIG. 5 shows a schematic cross-sectional view of the second member 46 that is bent and deformed when the battery cell 10B ignites and the temperature rises to 500°C. In FIG. 7, in the width direction of the second member 46 in the Y-axis direction, the shape S46M of the center part after bending deformation is shown by a solid line, and the shape S46E of the end part after bending deformation is shown by a dashed line. As shown in FIG. 7, unlike the first member 41, the second member 46 has almost the same displacement at the center and end parts. The second member 46 is bent so as to proceed in the vertical direction, which is the direction away from the battery cell 10B. Therefore, a space is formed vertically downward from the position where the first member 41 and the second member 46 are joined and vertically above the battery cells 10A and 10B. Because this space is formed, the second member 46 can bend vertically downward, which is the direction away from the first member 41.

[0036] 8 is a graph showing the amount of displacement at each position along the length L2 of the second member 46 in FIG. 7 in the X-axis direction. In FIG. 8, the change in the amount of displacement at the center portion is shown by a solid curve C46M, and the change in the amount of displacement at the end portion is shown by a dashed curve C46E. As shown in FIG. 8, when the temperature of the battery cell 10B rises to 500° C., the amount of displacement at both the center portion and the end portion is approximately 2.2 mm. Note that in the example shown in FIGS. 7 and 8, like the first member 41, the metal with a high thermal expansion coefficient that forms the third metal plate 47 is steel, and the metal with a low thermal expansion coefficient that forms the fourth metal plate 48 is an aluminum alloy.

[0037] The joining member 49 that joins the first metal plate 42 of the first member 41 and the third metal plate 47 of the second member 46 shown in Fig. 4 has a lower melting point and electrical conductivity than both the metal forming the first metal plate 42 and the metal forming the third metal plate 47. An example of the joining member 49 is low-temperature solder (melting point: 160°C) made of a solder material mainly composed of tin or lead to which cadmium, bismuth, indium, etc. are added. In this embodiment, the joining member 49 is joined to each of the first member 41 and the second member 46 by soldering. When one of the two battery cells 10A, 10B ignites and the temperature of the bus bar 40 rises, the joining member 49, which has a low melting point, melts.

[0038] FIG. 9 is an explanatory diagram of stress distribution in the joining member 49 immediately before the first member 41 and the second member 46 are separated. FIG. 9 plots stress at each position along the X-axis direction in the joining member 49 and the first member 41 immediately before the battery cell 10A connected to the first member 41 ignites and rises in temperature, causing the first member 41 and the second member 46 to separate. The stress shown in FIG. 9 is a force along the Z-axis direction (vertical direction). The hatched area in FIG. 9 indicates the stress in the joining member 49, and the other area indicates the stress in the first member 41. As shown in FIG. 9, stress is large at the end side of the joining member 49 on the positive X-axis direction side farther from the battery cell 10A.

[0039] FIG. 10 is an explanatory diagram of the temperature distribution of the bonding member immediately before separation of the first member 41 and the second member 46. FIG. 10 shows temperature changes CT1 at positions along the X-axis direction in the bonding member 49 and the first member 41 immediately before separation of the first member 41 and the second member 46, which are the same as those in FIG. 9. The hatched area in FIG. 10 indicates the temperature of the bonding member 49, and the other area indicates the temperature in the first member 41. As shown in FIG. 10, the temperature of the bonding member 49 immediately before separation decreases the farther it is from the battery cell 10A, and is about 160°C to 184°C. As a result, since the temperature of the bonding member 49 is about 160°C to 184°C, the bonding member 49 melts and the first member 41 and the second member are separated.

[0040] Fig. 11 is an explanatory diagram of the temperature change of adjacent battery cells when a battery cell 10A ignites in this embodiment. Fig. 11 shows temperature changes CTc1, CTc2, and CTc3 of three battery cells 10 arranged in the stacking direction when a battery cell 10A arranged at one end ignites. The temperature change CTc1 shown by a solid line indicates the temperature change of the ignited battery cell 10A. The temperature change CTc2 shown by a dashed line indicates the temperature change of the battery cell 10B adjacent to the battery cell 10A. The temperature change CTc3 shown by a dashed line indicates the temperature change of the battery cell adjacent to the battery cell 10B. The three battery cells 10 arranged in the stacking direction are connected in series by a bus bar 40.

[0041] As shown in FIG. 11, the temperature of the ignited battery cell 10A rises to 700°C or higher. In this embodiment, the bus bar 40 rises in temperature due to heat transfer from the ignited and heated battery cell 10A, and is separated. As a result, the heat of the battery cell 10A is not transferred to the adjacent battery cell 10B via the bus bar 40. Furthermore, since the heat of the battery cell 10A is not transferred to the battery cell 10 connected to the battery cell 10A via the battery cell 10B, the temperature of the battery cell 10 does not rise significantly. In other words, the spread of fire to other battery cells due to the ignition of the battery cell 10A is suppressed.

[0042] Fig. 12 is a schematic perspective view of a busbar 40x of a comparative example. Fig. 13 is a diagram illustrating temperature changes in adjacent battery cells when a battery cell 10A in the comparative example catches fire. As shown in Fig. 12, the busbar 40x of the comparative example is formed integrally from one type of metal, unlike the busbar 40 of the present embodiment shown in Fig. 3. Therefore, unlike the busbar 40 of the present embodiment, separation due to a rise in temperature does not occur in the busbar 40x of the comparative example.

[0043] FIG. 13 shows temperature changes CTc1x to CTc8x of eight battery cells arranged in the stacking direction when one battery cell 10A arranged at one end of the eight battery cells ignites. The temperature changes are numbered CTc2x, CTc3x, ... in ascending order of proximity to the ignited battery cell 10A. Therefore, the temperature change of the battery cell furthest from the ignited battery cell 10A is CTc8x. The horizontal time axis in FIG. 13 has a different scale from the horizontal time axis in FIG. 11. The eight battery cells arranged in the stacking direction are connected in series by each bus bar 40x.

[0044] As shown in FIG. 13, the temperature of the ignited battery cell 10A rises to 700°C or higher. The heat from the ignited and heated battery cell 10A is transferred to the adjacent battery cell 10B via the busbar 40x. As a result, as shown by the broken line temperature change CTc2x, the temperature of the adjacent battery cell 10B also rises to 700°C or higher. As with the heat transfer from the battery cell 10A to the battery cell 10B, in the eight battery cells, heat is transferred to the adjacent battery cells via the busbar 40x over time, and all of the eight battery cells ignite, as shown by the temperature changes CTc1x to CTc8x in FIG. 13. In other words, in the secondary battery of the comparative example having eight battery cells electrically connected by the busbar 40x, the spread of fire to the adjacent battery cells is not suppressed.

[0045] Here, the thickness h of the first member 41 in the busbar 40 of this embodiment is set so as to satisfy both an electrical resistance equation (first relational expression) using the resistance value of the first member 41 and a displacement analysis equation (second relational expression) for the displacement amount δ of the first member 41 when one battery cell 10 ignites. The electrical resistance equation is expressed as follows (1): b (Ω) and the internal resistance R of the battery cell 10 LIB It is expressed in relation to (Ω).

[0046]

number

[0047] Fig. 14 is an explanatory diagram of the displacement analysis formula of the first member 41. Fig. 14 shows a schematic cross-sectional view of the first member 41 in a state where it is deformed by a displacement amount δ. Fig. 14(a) shows a schematic cross-sectional view of the first member 41 as viewed from the negative Y-axis direction. Fig. 14(b) shows a schematic cross-sectional view of the first member 41 as viewed from the negative X-axis direction.

[0048] 14(a) deforms with the end point of the first member 41 in contact with the first tab 50A on the square side of the X-axis as a fulcrum, and the other end of the first member 41 joined to the joining member 49 as a free end. The deflection radius of the first metal plate 42 during bending deformation is R1, and the deflection radius of the second metal plate 43 is R2.

[0049] 14(a) are balanced, and therefore are the same normal stress P. The bending moments M1 and M2 of the first metal plate 42 and the second metal plate 43, respectively, are expressed by the following formula (2).

[0050]

number

[0051] From the relationship of the conservation of expansion and contraction amounts (thermal expansion+elastic contraction) at the bonding surface between the first metal plate 42 and the second metal plate 43, the following formula (3) is derived.

number

[0052] Since the total bending moment in the cross section of the first member 41 is zero, the following formula (4) holds.

number

[0053] From the above equations (2) and (4) regarding the bending moments M1 and M2, the following equation (5) is derived.

number

[0054] By simultaneously solving the above equations (3) and (5) for P / b and 1 / R, the following equation (6) is derived.

number

[0055] Using trigonometric function approximation, the condition under which the displacement amount δ of the first member 41 becomes the preset lower limit threshold value δc is expressed as the following formula (7).

number

[0056] The above formula (7) corresponds to a displacement analysis formula for the displacement amount δ of the first member 41. This displacement analysis formula is expressed as a relationship between the temperature T of the first member 41 when the battery cell 10 ignites, the thermal expansion coefficients α1 and α2 of the first metal plate 42 and the second metal plate 43, the longitudinal elastic moduli E1 and E2 of the first metal plate 42 and the second metal plate 43, and the length l from the portion connected to the battery cell 10 to the position in contact with the second metal plate 43. Therefore, for the length l of the first member 41, a thickness h of the first member 41 is set that satisfies the above formula (7) and the above formula (1) for the electrical resistance.

[0057] As described above, in the bus bar 40 of this embodiment, the first member 41 is connected to one battery cell 10A of the two battery cells 10A, 10B via the first tab 50A. The second member 46 is connected to the other battery cell 10B of the two battery cells 10A, 10B. The first member 41 includes a first metal plate (first metal) 42 made of a metal having a large thermal expansion coefficient, and a second metal plate (second metal) 43 made of a metal having a smaller thermal expansion coefficient than the metal forming the first metal plate 42. The first metal plate 42 is connected to the third metal plate 47 of the second member 46 via a joining member 49. In this embodiment, the first member 41 has a bimetal structure in which two types of metals or alloys having different thermal expansion coefficients are bonded together. The first member 41 is in contact with the third metal plate 47 of the second member 46 on the surface of the first metal plate 42 having a high thermal expansion coefficient. Therefore, when the battery cell 10A, 10B connected to the first member 41 or the second member 46 ignites, the temperature of the first member 41 rises due to the heat caused by the ignition. When the temperature rises, the first member 41 having a bimetal structure bends toward the second member 46, which has a smaller thermal expansion coefficient, due to the difference in thermal expansion coefficient between the first metal plate 42 and the second member 46. That is, the first member 41 deforms so as to bend in a direction away from the second member 46, and the first member 41 and the second member 46 are separated. Due to the separation, even if one of the two battery cells 10A, 10B electrically connected by the bus bar 40 ignites, the heat of the ignited battery cell 10A does not transfer to the adjacent battery cell 10B via the bus bar 40. As a result, in this embodiment, the spread of fire of the battery cells 10A, 10B caused by the heat transfer via the bus bar 40 is suppressed. In particular, in this embodiment, the electrical resistance of the bus bar 40 connecting the two battery cells 10A, 10B is sufficiently small compared with the internal resistance of the battery cells 10A, 10B. Therefore, heat generated by the bus bar 40 due to current during charging and discharging of the battery cells 10A, 10B is sufficiently small. In other words, the bus bar 40 of this embodiment separates the first member 41 and the second member 46 not due to heat generated by itself, but due to heat transfer between the battery cells 10A, 10B connected via the bus bar 40.In this embodiment, even if either of the two battery cells 10A, 10B connected via the bus bar 40 catches fire, the spread of fire to the battery cell 10B is suppressed regardless of the direction in which heat moves.

[0058] Moreover, the second member 46 of this embodiment includes a third metal plate (third metal) 47 made of a metal with a large thermal expansion coefficient, and a fourth metal plate (fourth metal) 48 made of a metal with a smaller thermal expansion coefficient than the metal forming the third metal plate 47. In this embodiment, the second member 46 also has a bimetal structure in which the third metal plate 47 and the fourth metal plate 48 are bonded together. Furthermore, in the second member 46, the third metal plate 47 with a high thermal expansion coefficient is in contact with the first metal plate 42 of the first member 41. Therefore, when the battery cell 10A, 10B connected to the first member 41 or the second member 46 ignites, both the first member 41 and the second member 46, whose temperatures have risen due to the heat of the ignition, are deformed so as to warp in directions away from each other due to the difference in thermal expansion coefficient. As a result of the deformation causing the first member 41 and the second member 46 to separate, heat is not transferred from the ignited battery cell 10A to the adjacent non-ignited battery cell 10B via the bus bar 40, thereby further preventing the spread of fire between the battery cells 10A and 10B.

[0059] The bus bar 40 of this embodiment includes a joint member 49 that indirectly brings the first member 41 and the second member 46 into contact with each other. The joint member 49 has a lower melting point than both the metal forming the first metal plate 42 and the metal forming the third metal plate 47, and is electrically conductive. In this embodiment, the first member 41 and the second member 46 are in contact with each other via the joint member 49, which has a melting point lower than that of the first metal plate 42. Since the melting point of the joint member 49 is low, the joint member 49 melts even if the temperature of the first metal plate 42 is low at the start of ignition of the battery cell 10A. Therefore, even if sufficient tensile stress due to a high expansion difference cannot be obtained in the first member 41 at a low temperature at the start of ignition of the battery cell 10A, the joint strength of the joint surface decreases, and the first member 41 and the second member 46 are separated from each other due to residual stress acting in a direction in which the first member 41 and the second member 46 are separated from each other.

[0060] Furthermore, the thickness h of the first member 41 in the busbar 40 of this embodiment is set so as to satisfy both an electrical resistance equation (first relational expression) using the resistance value of the busbar 40 and a displacement analysis equation (second relational expression) for the displacement amount δ of the first member 41 when one battery cell 10 ignites. In this embodiment, the thickness h of the first member 41 and the electrical resistance R b The relationship between the temperature T of the first member 41 and the second member 46 when the battery cell 10 ignites is expressed by an electrical resistance equation such as the above equation (1). In addition, a displacement analysis equation expressed by the above equation (7) is derived that expresses the relationship between the temperature T of the first member 41 when the battery cell 10 ignites, the respective known parameters (e.g., thermal expansion coefficients, etc.) of the first metal plate 42 and the second metal plate 43 that form the first member 41, and the displacement amount δ of the first member 41. The displacement amount δ of the first member 41 when the battery cell 10 ignites varies depending on the thickness h of the first member 41. Therefore, the thickness h of the first member 41 is set so as to satisfy the electrical resistance equation and the displacement analysis equation. This makes it easy to determine the length l and thickness h of the first member 41 that reliably separates the first member 41 and the second member 46 when the battery ignites.

[0061] As shown in FIG. 1, the secondary battery 100 of this embodiment includes a plurality of battery cells 10 stacked along the stacking direction (X-axis direction), a heat insulating material 20 filled between each of the plurality of battery cells 10, a heat sink 30 arranged vertically below the secondary battery 100, and a plurality of bus bars 40 electrically connecting each of the plurality of batteries. In the secondary battery 100 of this embodiment, the plurality of battery cells 10 and the heat insulating material 20 are stacked, and the battery cells 10 are cooled by the heat sink extending along the stacking direction. When the battery cells 10 are triggered by heat generation, the temperature rises suddenly due to a decomposition reaction of the negative electrode SEI film constituting the battery cells 10, and the battery cells 10 ignite. In contrast, in this embodiment, the bus bar 40 electrically connecting the plurality of battery cells 10 in series or parallel separates them into a first member 41 and a second member 46 at high temperatures. Therefore, the spread of fire between the battery cells 10, which is specific to a secondary battery in which a plurality of battery cells 10 are connected, is suppressed.

[0062] <Second embodiment> In the second embodiment, the materials of the first member 41 and the second metal plate 43 forming the first member 41 and the materials of the third metal plate 47 and the fourth metal plate 48 forming the second member 46 are different from those in the first embodiment. In the second embodiment, the first metal plate 42 and the third metal plate 47 are formed of a metal or alloy having a softening point higher than the temperature of the bus bar 40 when one of the two battery cells 10A, 10B ignites. Examples of the first metal plate 42 and the third metal plate 47 in the second embodiment include stainless steel (SUS). In addition, in the second embodiment, the second metal plate 43 and the fourth metal plate 48 are formed of an Invar material with a low expansion coefficient, which is iron containing 36% nickel.

[0063] FIG. 15 is an explanatory diagram of the temperature of the first member 41 at each position along the X-axis direction when a battery ignites. Each position along the X-axis direction in FIG. 15 is the same as each position of the length L1 shown in FIG. 5. In FIG. 15, the cooling environment of the ignited battery cell 10A is a natural convection heat radiation (30 W / (m 2 ·K) and immersed in cooling water for circulating cooling (100W / (m 2 15 shows the temperature change when the first member 41 of the second embodiment is subjected to natural convection heat dissipation and the temperature when the cooling water is circulated is shown by temperature CT22 (thick dashed line). In addition, in FIG. 15, the temperature when the first member 41a, in which the first metal plate 42 is made of an aluminum alloy and the second metal plate 43 is made of steel, is natural convection heat dissipation and the temperature when the cooling water is circulated is shown by temperature CT22a (thin dashed line). The temperatures CT21, CT22, CT21a, and CT22a are the temperatures at the center in the width direction (Y-axis direction). The temperature when the battery cell 10A ignites is approximately 500°C.

[0064] As shown by the temperatures CT21, CT22, CT21a, and CT22a in FIG. 15, the thermal conductivity differs depending on the material, so the temperature change of each metal plate differs when the battery cell 10A ignites. Comparing the temperatures CT21 and CT21a of natural convection heat radiation and the temperatures CT22 and CT22a of circulating cooling in FIG. 15, the temperature of the first members 41 and 41a is lowered by circulating cooling. In particular, in the natural convection heat radiation of the first member 41a in which the first metal plate 42 is made of an aluminum alloy, the temperature CT21a of the first member 41a is the highest at about 430°C to 450°C. The softening point of the aluminum alloy is 415°C, and the melting point is 660°C. If the temperature of the first member 41a reaches the softening point of the aluminum alloy, the first member 41a having a bimetal structure may not be sufficiently deformed due to the difference in thermal expansion coefficient between the first metal plate 42 and the second metal plate 43. As a result, the first member 41a and the second member 46 will not be separated, and there is a risk that the connection of the bus bar 40 will cause the battery cells 10 to catch fire.

[0065] In contrast, the first metal plate 42 in the first member 41 of the second embodiment is made of stainless steel with a softening point of 550°C. Therefore, even if the cooling environment of the battery cell 10 is poor due to natural convection heat dissipation, the temperature of the first metal plate 42 rises only to about 370°C and does not reach the softening point. Furthermore, in the second embodiment, the second metal plate 43, which has a smaller thermal expansion coefficient than the first metal plate 42, is made of Invar material with a low expansion coefficient. Therefore, in the second embodiment, even if the thermal expansion coefficient of the stainless steel forming the first metal plate 42 is smaller than that of the aluminum alloy, the difference in thermal expansion coefficient between the first metal plate 42 made of stainless steel and the second metal plate 43 made of Invar material can be sufficiently ensured. As a result, when the battery cell 10A ignites, the first member 41 is sufficiently bent and deformed, and the first member 41 and the second member 46 are separated.

[0066] FIG. 16 is an explanatory diagram of the temperature of the second member 46 at each position along the X-axis direction when the battery ignites. Each position along the X-axis direction in FIG. 16 is the same as each position of the length L2 shown in FIG. 7. Like FIG. 15, FIG. 16 shows temperature changes when the cooling environment of the ignited battery cell 10B is performed by natural convection heat dissipation and when the battery cell 10B is immersed in cooling water and cooled by circulation. The third metal plate 47 of the second embodiment is made of the same stainless steel as the first metal plate 42. The fourth metal plate 48 is made of the same Invar material as the second member 46.

[0067] In Fig. 16, the temperature of the second member 46 of the second embodiment during natural convection heat dissipation is indicated by CT31 (thick solid line), and the temperature of the circulating cooling of the cooling water is indicated by temperature CT32 (thick dashed line). Also, in Fig. 16, the temperature of the second member 46a, in which the third metal plate 47 is made of an aluminum alloy and the fourth metal plate 48 is made of steel, during natural convection heat dissipation is indicated by CT31a (thin solid line), and the temperature of the circulating cooling of the cooling water is indicated by temperature CT32a (thin dashed line). Note that the temperatures CT31, CT32, CT31a, and CT32a are the temperatures of the center portion in the width direction (Y-axis direction) like the first members 41 and 41a shown in Fig. 15.

[0068] As shown by the temperatures CT31, CT32, CT31a, and CT32a in FIG. 16, the temperature CT31a of the second member 46a in which the third metal plate 47 is made of an aluminum alloy during natural convection heat dissipation rises to about 450°C, reaching the softening point of the aluminum alloy. Therefore, like the first member 41a shown in FIG. 15, there is a risk that the first member 41 and the second member 46a will not separate when the battery cell 10B ignites. In contrast, in the case of the second member 46 of the second embodiment, the temperature CT31 of the third metal plate 47 during natural convection heat dissipation rises only to about 480°C and does not reach the softening point. In addition, the fourth metal plate 48 of the second member 46 of the second embodiment is made of an Invar material with a low expansion coefficient. Therefore, a sufficient difference in thermal expansion coefficient can be ensured between the third metal plate 47 and the fourth metal plate 48 of the second member 46 for the first member 41 and the second member 46 to separate when the battery cell 10B ignites.

[0069] As described above, the first metal plate 42 and the second metal plate 43 of the second embodiment are formed of a metal or alloy having a softening point higher than the temperature of the busbar 40 when one of the two battery cells 10A, 10B ignites. Moreover, the second metal plate 43 and the fourth metal plate 48 of the second embodiment are formed of an Invar material having a low expansion coefficient, which is iron containing 36% nickel. The softening points of the second metal plate 43 and the fourth metal plate 48 of the second embodiment are higher than the temperature of the busbar 40 when one of the two battery cells 10A, 10B ignites. Furthermore, the second metal plate 43 and the fourth metal plate 48 are formed of an Invar material having a low expansion coefficient. Therefore, a difference in thermal expansion coefficient is ensured between the first metal plate 42 and the second metal plate 43 and between the third metal plate 47 and the fourth metal plate 48. As a result, even if either of the two battery cells 10A, 10B catches fire, the second metal plate 43 and the fourth metal plate 48 deform so as to warp in a direction in which the first member 41 and the second member 46 move away from each other. As a result, if either of the two battery cells 10A, 10B catches fire, the first member 41 and the second member 46 are reliably separated, and heat transfer from the ignited battery cell 10A to the adjacent battery cell 10B via the bus bar 40 is suppressed.

[0070] <Third embodiment> Fig. 17 is a schematic perspective view of a busbar 40b according to the third embodiment. As shown in Fig. 17, the busbar 40b according to the third embodiment includes a first member 41A, a second member 46B, a third member 41C, and a fourth member 46D that are connected in parallel to one another. Each of the four members 41A, 46B, 41C, and 46D is electrically connected to a different battery cell 10 at an end other than the ends connected to one another.

[0071] The first member 41A and the fourth member 46D of the third embodiment have the same shape as the first member 41 of the first embodiment, and are made of the same metal as the first member 41. The second member 46B and the third member 41C of the third embodiment have the same shape as the second member 46 of the first embodiment, and are made of the same metal as the second member 46B.

[0072] Fig. 18 is a schematic cross-sectional view of region B in Fig. 17. As shown in Fig. 18, the first member 41A includes a first metal plate 42A and a second metal plate 43A formed of a metal having a lower thermal conductivity than the first metal plate 42A. Similarly, the second member 46B includes a third metal plate 47B and a fourth metal plate 48B formed of a metal having a lower thermal conductivity than the third metal plate 47B. The fourth member 46D includes a seventh metal plate (seventh metal) 47D and an eighth metal plate (eighth metal) 48D formed of a metal having a lower thermal conductivity than the seventh metal plate 47D.

[0073] As shown in FIG. 18, the first metal plate 42A of the first member 41A and the third metal plate 47B of the second member 46B are connected via a joint member 49A. Similarly, the third metal plate 47B of the second member 46B and the seventh metal plate 47D of the fourth member 46D are connected via a joint member 49B. On the vertically upper surface of the third metal plate 47B of the second member 46B, the regions where the joint members 49A and 49B are joined do not overlap. In other words, on the vertically upper surface of the third metal plate 47B, the region connected to the first metal plate 42A via the joint member 49A is different from the region connected to the seventh metal plate 47D via the joint member 49B. Note that, as shown in FIG. 17, the third member 41C is disposed in a position symmetrical to the second member 46B along the center line parallel to the X-axis of the first member 41A and the fourth member 46D. Therefore, the third member 41C has a bimetal structure in which a fifth metal plate (fifth metal) 42C arranged on the side facing the first member 41A and the fourth member 46D is bonded to a sixth metal plate (sixth metal) 43C having a lower thermal conductivity than the fifth metal plate 42C arranged on the opposite side. The fifth metal plate in the third member 41C is connected to the first metal plate 42A and the seventh metal plate 47D via different bonding members.

[0074] Fig. 19 is a schematic cross-sectional view of the first member 41A of the third embodiment in a bent state. Fig. 19 shows a state in which a battery cell 10 connected to the first member 41A catches fire, the temperature of the first member 41A rises, and the portion of the first member 41A on the positive side of the X-axis is deformed so as to warp vertically upward. The rise in temperature of the first member 41A separates the first member 41A from the other members 46B, 41C, and 46D.

[0075] Fig. 20 is a schematic cross-sectional view of the second member 46B of the third embodiment in a bent state. Fig. 20 shows a state in which a battery cell 10 connected to the second member 46B catches fire, the temperature of the second member 46B rises, and the portion of the second member 46B on the negative Y-axis direction side is deformed so as to warp vertically downward. As the temperature of the second member 46B rises, the second member 46B separates from the other members 41A, 41C, and 46D.

[0076] As described above, in the bus bar 40b of the third embodiment, as shown in FIG. 18, the first metal plate 42A of the first member 41A and the third metal plate 47B of the second member 46B are connected via a joint member 49A. Similarly, the third metal plate 47B of the second member 46B and the seventh metal plate 47D of the fourth member 46D are connected via a joint member 49B. The fifth metal plate 42C of the third member 41C is connected to the first metal plate 42A and the seventh metal plate 47D via different joint members. In the third embodiment, the first metal plate 42A of the first member 46A is in contact with the third metal plate 47B of the second member 46B and the fifth metal plate 42C of the third member 41C. Also, the third metal plate 47B of the second member 46B and the fifth metal plate 42C of the third member 41C are in contact with the seventh metal plate 47D of the fourth member 46D. Therefore, by electrically connecting each of the components 41A, 46B, 41C, and 46D connected to each of the four battery cells 10 in parallel, if a battery cell 10 connected to any of the four components 41A, 46B, 41C, and 46D catches fire, the spread of fire to the other battery cells 10 is suppressed.

[0077] <Fourth embodiment> Fig. 21 is a schematic perspective view of a busbar 40c according to the fourth embodiment. As shown in Fig. 21, a busbar 40b according to the fourth embodiment includes a first member 41E, a second member 46F, and a third member 41G that are connected in parallel to each other. Each of the four members 41E, 46F, and 41G is electrically connected to a different battery cell 10 at an end other than the ends connected to each other.

[0078] The first member 41E of the fourth embodiment is formed of the same metal as the second member 46 of the first embodiment. That is, as shown in FIG. 21, the first member 41E has a bimetal structure in which a second metal plate 43E on the vertically lower side and a first metal plate 42E formed of a metal having a higher thermal expansion coefficient than the second metal plate 43E are bonded together. The second member 46F and the third member 41G of the third embodiment are formed of the same metal as the first member 41 of the first embodiment. That is, as shown in FIG. 21, the second member 46F has a bimetal structure in which a fourth metal plate 48F on the vertically upper side and a third metal plate 47F formed of a metal having a higher thermal expansion coefficient than the fourth metal plate 48F are bonded together. In addition, the third member 41G has a bimetal structure in which a sixth metal plate 43G on the vertically upper side and a fifth metal plate 42G formed of a metal having a higher thermal expansion coefficient than the sixth metal plate 43G are bonded together. The first metal plate 42E of the first member 41E is in surface contact with each of the third metal plate 47F of the second member 46F and the fifth metal plate 42G of the third member 41G via a joining member (not shown).

[0079] As shown in Fig. 21, the area where the first metal plate 42E of the first member 41E is in surface contact with the third metal plate 47F of the second member 46F and the fifth metal plate 42G of the third member 41G is a triangular area. Also, the area where the third metal plate 47F of the second member 46F is in surface contact with the first metal plate 42E and the area where the fifth metal plate 42G of the third member 41G is in surface contact with the first metal plate 42E are triangular areas of the same area. Furthermore, the two areas having the same area are line-symmetrical with respect to the YZ plane passing through the center of the width direction along the X axis of the first member 41E. That is, the two areas having the same area are the same triangular areas.

[0080] Fig. 22 is a schematic cross-sectional view of the second member 46F of the fourth embodiment in a bent and deformed state. Fig. 22 shows a state in which a battery cell 10 connected to the second member 46F ignites, the temperature of the second member 46F rises, and the portion of the second member 46F in contact with the first member 41E is deformed so as to warp vertically upward. As the temperature of the second member 46F rises, the second member 46F is separated from the first member 41E and the third member 41G.

[0081] As described above, the first metal plate 42E of the first member 41E of the fourth embodiment is in surface contact with the third metal plate 47F of the second member 46F and the fifth metal plate 42G of the third member 41G through the joining member. The area where the first metal plate 42E is in surface contact with the third metal plate 47F and the fifth metal plate 42G is a triangular area. The area where the third metal plate 47F is in surface contact with the first metal plate 42E and the area where the fifth metal plate 42G is in surface contact with the first metal plate 42E are triangular areas of the same area. In the fourth embodiment, the first member 41E is in contact with the second member 46F and the third member 41G. When the battery cell 10 connected to the second member 46F ignites after the members 41E, 46F, and 41G connected to the three battery cells 10 are in contact with each other, the second member 46F is bent and deformed in a direction away from the first member 41E and the third member 41G as shown in FIG. 22. This causes the second member 46F to separate from the first member 41E and the third member 41G. Since the contact shape between the first member 41E, the second member 46F, and the third member 41G is triangular, the separation occurs due to the thermal expansion difference with a smaller volume of the busbar 40c compared to when the contact shape is rectangular, for example. As a result, the spread of fire from the battery cell 10 connected to the second member 46F to the battery cells 10 connected to the first member 41E and the third member 41G is suppressed by further reducing the size of the busbar 40c.

[0082] <Modifications of the embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the present invention, for example, the following modifications are possible: In the above-described embodiment, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware.

[0083] <Variation 1> In the above first to fourth embodiments, an example of the busbars 40, 40b, 40c that electrically connect the multiple battery cells 10 has been described. However, the busbars can be deformed within a range in which the busbars have a bimetal structure in which the second metal plate 43 and the first metal plate 42 having a thermal expansion coefficient larger than that of the second metal plate 43 are bonded together. For example, one of the first member 41 and the second member 46 in the first embodiment may be formed of a conductive material that does not have a bimetal structure. In this case, when the battery cell 10 connected to the first member 41 or the second member 46 catches fire, the temperature of the first member 41 and the second member 46 rises. Due to the temperature rise, one of the first member 41 and the second member 46 that has a bimetal structure is bent and deformed in a direction away from the other member. As a result, the first member 41 and the second member 46 are separated, and the spread of fire between the batteries connected to the first member 41 and the second member 46 is suppressed.

[0084] In the first embodiment, as shown in FIG. 4, the first metal plate 42 of the first member 41 and the third metal plate 47 of the second member 46 are in indirect contact with each other via the joint member 49. However, they may be in direct contact without the joint member 49. Instead of the joint member 49, the first metal plate 42 and the third metal plate 47 may be in contact with each other via a material having a melting point higher than the temperature of the first metal plate 42 when the battery cell 10 ignites. The contact method may be surface contact as in the above embodiment, or line contact or point contact. The bus bar 40 may be directly connected to the battery cells 10A and 10B without being connected to the battery cells 10A and 10B via the first tab 50A and the second tab 50B shown in FIG. 2. Alternatively, the bus bar 40 may be connected to the battery cells 10A and 10B via another member other than the first tab 50A and the like. It is preferable that the first member 41 and the second member 46 are in contact with each other via a bonding member 49 that has electrical conductivity and a melting point lower than the temperature of the first member 41 when the battery cell 10 ignites. Specifically, the melting point of the bonding member 49 is preferably 160°C or higher and 300°C or lower.

[0085] In the first embodiment, the first member 41 and the second member 46 are clad materials having a bimetal structure in which two types of metals or alloys are bonded together, but they may be materials in which three or more types of metals or alloys are bonded together. When the connected battery cell 10 ignites, the first member 41 or the second member 46 is deformable to a degree that causes it to bend in a direction that separates it due to the difference in thermal expansion coefficient. The temperature at the time when the battery cell 10 ignites is set to, for example, 400°C or higher and 550°C or lower.

[0086] In the first embodiment, one bus bar 40 electrically connects two battery cells 10. However, instead of one battery cell 10, one battery in which a plurality of battery cells are stacked may be connected by the bus bar 40. In setting the thickness h of the first member in the first embodiment, the lower limit threshold value δc of the displacement amount δ is preferably 1 mm or more. If the displacement amount δ is 1 mm or more, the electrical connection between the first member 41 and the second member can be released. Note that, when the thickness of the second member 46 is set in addition to the first member 41, it is preferable that the displacement amount of the first member 41 and the displacement amount of the second member 46 are combined to be 1 mm or more.

[0087] In the above embodiment, the secondary battery 100 including the two battery cells 10A, 10B connected by the bus bar 40 has been described as an example. However, the configuration of the secondary battery 100 can be modified. The secondary battery 100 does not have to have a substantially rectangular parallelepiped shape as shown in FIG. 1. The position of the heat sink 30 and the like relative to the battery cell 10 can also be modified. In the above embodiment, the heat sink 30 is located vertically below the battery cell 10, and the bus bar 40 is located vertically above the battery cell 10. However, the positional relationship between them can be reversed, for example. The coolant 32 flowing through the heat sink 30 can also flow in a direction perpendicular to the stacking direction of the battery cells 10. The vertical direction and the like defined in the Cartesian coordinate system CS are a coordinate system defined to explain the secondary battery 100 shown in FIG. 1, and these directions can be rotated as appropriate.

[0088] <Variation 2> In the second embodiment, the first metal plate 42 and the third metal plate 47 have a softening point higher than the temperature of the bus bar 40 when the connected battery cell 10 ignites, and the second metal plate 43 and the fourth metal plate 48 are made of Invar material. However, the first metal plate 42 and the third metal plate 47 do not have to have a softening point higher than the temperature of the bus bar 40 when the battery cell 10 ignites. In addition, the second metal plate 43 and the fourth metal plate 48 do not have to be made of Invar material. In this case, as shown in FIGS. 15 and 16, if a cooling environment is provided in which the temperature rise of the first member 41 and the second member 46 is suppressed, the first member 41 and the second member 46 can be separated when the battery cell 10 ignites, even if the first member 41 and the third metal plate 47 have a low softening point.

[0089] <Modification 3> In the above third embodiment, as shown in Fig. 17, the four battery cells 10 connected to the four members 41A, 46B, 41C, and 46D of the bus bar 40b are connected in parallel. However, the method of connecting the multiple battery cells 10 by the bus bar 40b can be modified. For example, five or more battery cells 10 may be connected in parallel. Furthermore, some of the battery cells 10 may be connected in series and the other battery cells 10 may be connected in parallel by the bus bar 40b.

[0090] <Variation 4> In the above-described fourth embodiment, the portions where the three members 41E, 46F, and 41G of the busbar 40c come into surface contact with each other are triangular, as shown in Figures 21 and 22. However, the shape of the surface contact portions and the shape of the other ends of the members 41E, 46F, and 41G that are not connected to the battery may be shapes other than triangular.

[0091] Although the present aspect has been described above based on the embodiment and modified examples, the above-mentioned embodiment of the aspect is intended to facilitate understanding of the present aspect and does not limit the present aspect. The present aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents are included in the present aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0092] The present invention can also be realized in the following forms. [Application example 1] A bus bar electrically connecting two batteries, a first member connected to one of the two batteries and having a bimetal structure in which a first metal and a second metal are bonded together; a second member connected to the other of the two batteries, having electrical conductivity, and having a portion in contact with the first metal of the first member; The first metal has a coefficient of thermal expansion greater than a coefficient of thermal expansion of the second metal. [Application example 2] The bus bar according to Application Example 1, The second member is It has a bimetal structure in which a third metal and a fourth metal are bonded together. the third metal contacts the first metal; The third metal has a coefficient of thermal expansion greater than a coefficient of thermal expansion of the fourth metal. [Application example 3] The busbar according to Application Example 1 or Application Example 2, the first metal and the third metal have a softening point higher than a temperature of the bus bar when one of the two batteries ignites; The busbar, wherein the second metal and the fourth metal are formed of an Invar material. [Application example 4] The busbar according to any one of Application Examples 1 to 3, further comprising: a bonding member having a melting point and electrical conductivity lower than the temperature of the first metal when at least one of the two batteries ignites; The first member and the second member are in contact with each other via the joining member. [Application example 5] The bus bar according to any one of Application Examples 1 to 4, a thickness of the first member is set so as to satisfy both a first relational expression regarding the electrical resistance of the first member and a second relational expression regarding the amount of displacement of the first member when the one of the batteries ignites; The first relational expression is expressed by a relationship between the electrical resistance of the first member and the internal resistance of the one battery, the second relational expression is expressed by the relationship between the temperature of the first member when the one of the batteries ignites, the thermal expansion coefficients of the first metal and the second metal, the longitudinal elastic moduli of the first metal and the second metal, and the length from the portion connected to the one of the batteries to a position where it is in contact with the second member. [Application Example 6] The busbar according to any one of Application Examples 1 to 5, further comprising: a third member connected to a battery different from the two batteries and having a bimetal structure in which a fifth metal and a sixth metal are bonded together; a fourth member connected to a battery different from any of the two batteries and the battery to which the third member is connected, the fourth member having a bimetal structure in which a seventh metal and an eighth metal are bonded together; the fifth metal is in contact with the first metal on a side of the first metal that is in contact with the third metal, The thermal expansion coefficient of the fifth metal is greater than the thermal expansion coefficient of the sixth metal, the seventh metal is in contact with each of the third metal and the fifth metal on a side of the third metal and the fifth metal on which the first metal is in contact; The seventh metal has a coefficient of thermal expansion greater than a coefficient of thermal expansion of the eighth metal. [Application Example 7] The busbar according to any one of Application Examples 1 to 6, further comprising: a third member connected to a battery different from the two batteries and having a bimetal structure in which a fifth metal and a sixth metal are bonded together; the fifth metal is in surface contact with the first metal at a portion of the first metal that is in surface contact with the third metal and that is not in surface contact with the third metal, The thermal expansion coefficient of the fifth metal is greater than the thermal expansion coefficient of the sixth metal, A busbar, wherein regions where the first metal makes surface contact with the third metal and the fifth metal respectively have the same triangular shape and area. [Application Example 8] A secondary battery, A plurality of batteries arranged in a predetermined direction; a heat insulating material having heat insulating properties and disposed between each of the plurality of batteries; a heat sink connected to the plurality of batteries and the thermal insulation material and extending along the predetermined direction; A secondary battery comprising: the busbar according to any one of Application Examples 1 to 7, which electrically connects at least two batteries among the plurality of batteries. [Explanation of symbols]

[0093] 10, 10A, 10B…Battery cell (battery) 20…Insulation material 30…Heat sink 31...Bulkhead 32…Refrigerant 33... Coolant flow path 40, 40b, 40c, 40x… Busbars 41, 41a, 41A, 41E...First member 41C, 41G…Third member 42,42A,42E…First metal plate (first metal) 42C, 42G...Fifth metal plate (fifth metal) 43,43A,43E…Second metal plate (second metal) 43G…6th metal plate (6th metal) 46, 46a, 46B, 46F...Second member 46D…Fourth member 47,47B,47F…Third metal plate (third metal) 47D…7th metal plate (7th metal) 48,48B,48F…4th metal plate (4th metal) 48D…8th metal plate (8th metal) 49, 49A, 49B...Jointing members 50A…1st tab 50B…2nd tab 100…Secondary battery E1, E2: Modulus of longitudinal elasticity M1, M2...Bending moment P, P1, P2: Normal stress R, R2, R3... Deflection radius R LIB …Internal resistance R b …Electrical resistance value α1, α2…Thermal expansion coefficient δc…Displacement threshold

Claims

1. A bus bar that electrically connects two batteries, a first member connected to one of the two batteries and having a bimetal structure in which a first metal and a second metal are bonded together; a second member connected to the other of the two batteries, having electrical conductivity, and having a portion in contact with the first metal of the first member; The first metal has a coefficient of thermal expansion greater than a coefficient of thermal expansion of the second metal.

2. 2. The bus bar of claim 1, The second member is It has a bimetal structure in which a third metal and a fourth metal are bonded together, the third metal contacts the first metal; The third metal has a coefficient of thermal expansion greater than a coefficient of thermal expansion of the fourth metal.

3. 3. The bus bar according to claim 2, the first metal and the third metal have a softening point higher than a temperature of the bus bar when one of the two batteries ignites; The bus bar, wherein the second metal and the fourth metal are formed of an Invar material.

4. 4. The busbar of claim 3, further comprising: a joining member having a melting point and electrical conductivity lower than the temperature of the first metal when at least one of the two batteries ignites; The first member and the second member are in contact with each other via the joining member.

5. 2. The bus bar of claim 1, a thickness of the first member is set so as to satisfy both a first relational expression regarding the electrical resistance of the first member and a second relational expression regarding the amount of displacement of the first member when the one of the batteries ignites; The first relational expression is expressed by a relationship between the electrical resistance of the first member and the internal resistance of the one battery, the second relational expression is expressed by the relationship between the temperature of the first member when the one of the batteries ignites, the thermal expansion coefficients of the first metal and the second metal, the longitudinal elastic moduli of the first metal and the second metal, and the length from the portion connected to the one of the batteries to a position where it is in contact with the second member.

6. 3. The busbar of claim 2, further comprising: a third member connected to a battery different from the two batteries and having a bimetal structure in which a fifth metal and a sixth metal are bonded together; a fourth member connected to a battery different from either the two batteries or the battery to which the third member is connected, the fourth member having a bimetal structure in which a seventh metal and an eighth metal are bonded together; the fifth metal is in contact with the first metal on a side of the first metal that is in contact with the third metal, The fifth metal has a thermal expansion coefficient greater than the thermal expansion coefficient of the sixth metal, the seventh metal is in contact with each of the third metal and the fifth metal on a side of the third metal and the fifth metal on which the first metal is in contact; A bus bar, wherein the seventh metal has a greater thermal expansion coefficient than the eighth metal.

7. 3. The busbar of claim 2, further comprising: a third member connected to a battery different from the two batteries and having a bimetal structure in which a fifth metal and a sixth metal are bonded together; the fifth metal is in surface contact with the first metal at a portion of the first metal that is in surface contact with the third metal and that is not in surface contact with the third metal, The fifth metal has a thermal expansion coefficient greater than the thermal expansion coefficient of the sixth metal, A busbar, wherein regions where the first metal makes surface contact with each of the third metal and the fifth metal have the same triangular shape and area.

8. A secondary battery, A plurality of batteries arranged in a predetermined direction; a heat insulating material having heat insulating properties and disposed between each of the plurality of batteries; a heat sink connected to the plurality of batteries and the thermal insulation material and extending along the predetermined direction; A secondary battery comprising: the bus bar according to claim 1 , which electrically connects at least two batteries of the plurality of batteries.

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