Battery stack

Abstract

To solve a problem in that a battery stack, which has a structure in which bus bar components and electrode terminals are joined by welding, is difficult to dismantle.SOLUTION: A battery stack 1 according to the present invention includes a plurality of battery cells 10 stacked in the stacking direction, and a plurality of busbar components 12 that connect a positive electrode terminal and a negative electrode terminal of adjacent battery cells among the plurality of battery cells 10 and are formed into a U-shape, the plurality of busbar components 12 include a first joint joined to the positive electrode terminal, a second joint joined to the negative electrode terminal, and a connecting portion that connects the first joint and the second joint, and the first joint and the second joint have weak strength portions that are cut in the stacking direction and have cut end portions with an interior angle of 90 degrees or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a battery stack, for example, in which a plurality of battery cells are stacked in a stacking direction.

Background Art

[0002] In a battery stack in which a plurality of battery cells are stacked in a stacking direction, one assembled battery is configured by joining bus bar components to the positive electrode terminal and the negative electrode terminal of adjacent battery cells. Examples of such battery stacks are disclosed in Patent Documents 1 and 2.

[0003] The battery structure described in Patent Document 1 includes an assembled battery formed by electrically connecting a plurality of battery modules each having an electrode terminal, a detachable module cover that covers the assembled battery composed of the plurality of battery modules, and a wiring member that electrically connects the battery modules to each other by connecting the electrode terminals provided in different battery modules to each other. The wiring member releases the connection state between the electrode terminals to be connected in response to the removal of the module cover.

[0004] The storage battery described in Patent Document 2 includes a power storage element, a storage case that houses the power storage element, an electrode terminal provided on the storage case, a bus bar connected to the electrode terminal, and a welding portion that welds the electrode terminal and the bus bar. The electrode terminal includes a first protruding arc portion and a second protruding arc portion that are formed in an arc shape around a center line and protrude upward. The second protruding arc portion is provided at a position farther from the center line than the first protruding arc portion. The bus bar is formed with a first hole portion into which the first protruding arc portion is inserted and extends in an arc shape, and a second hole portion into which the second protruding arc portion is inserted and extends in an arc shape. The length of the first hole portion is longer than the length of the first protruding arc portion, and the length of the second hole portion is longer than the length of the second protruding arc portion. The welding portion is formed to join one of the opening edge portions of the first protruding arc portion and the first hole portion and the opening edge portions of the second protruding arc portion and the second hole portion.

[0005] The battery module described in Patent Document 3 is generally plate-shaped with a thickness that is thin compared to its length and width, and includes a bus bar with linear grooves on its left and right sides along the longitudinal direction, and battery cells that are located on the left and right sides of the bus bar and have their electrode leads fitted into the grooves to make physical contact, thereby electrically connecting them to each other via the bus bar, and the grooves increase in size in the thickness direction at or above a certain temperature, releasing the physical contact between the electrode leads and the bus bar, thereby releasing the electrical connection between the battery cells. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-18933 A [Patent Document 2] JP 2018-142504 A [Patent Document 3] Special Publication No. 2021-524136 Summary of the Invention [Problem to be solved by the invention]

[0007] The techniques described in Patent Documents 1 and 3 do not involve welding of electrode terminals to busbar components, and therefore cannot be applied to battery stacks in which busbar components and electrode terminals are welded together. On the other hand, the technique described in Patent Document 2 involves welding of busbar components and electrode terminals, which may result in damage to the electrode terminals when the battery stack is disassembled.

[0008] The present invention has been made in consideration of the above circumstances, and has an object to improve the dismantling ability of a battery stack having a configuration in which bus bar components and electrode terminals are joined by welding. [Means for solving the problem]

[0009] One aspect of the battery stack according to the present invention includes a plurality of battery cells stacked in a stacking direction, and a plurality of bus bar components that connect the positive electrode terminals and the negative electrode terminals of adjacent battery cells among the plurality of battery cells and are formed in a U shape. The plurality of bus bar components include a first joint portion joined to the positive electrode terminal, a second joint portion joined to the negative electrode terminal, and a connecting portion that connects the first joint portion and the second joint portion. The first joint portion and the second joint portion have a weak strength portion formed by being cut in the stacking direction and having a cut end portion with an inner angle of 90 degrees or less.

[0010] One aspect of the battery stack according to the present invention includes a plurality of battery cells stacked in a stacking direction, a plurality of bus bar components that connect the positive electrode terminals and the negative electrode terminals of adjacent battery cells among the plurality of battery cells and are formed in a U shape, and a control unit that determines an abnormality occurring in the plurality of battery cells based on the state of the plurality of bus bar components and performs control during an abnormality corresponding to the abnormality. The plurality of bus bar components include a first joint portion joined to the positive electrode terminal, a second joint portion joined to the negative electrode terminal, and a connecting portion that connects the first joint portion and the second joint portion. The first joint portion and the second joint portion have a weak strength portion formed by being cut in the stacking direction and having a cut end portion with an inner angle of 90 degrees or less. At least one of the plurality of bus bar components is attached with a thermistor that measures the temperature of the bus bar component and a voltmeter that measures the voltage difference between the first joint portion and the second joint portion. The control unit performs the control during an abnormality when it is determined that an excessive load exceeding the assumption is applied to the plurality of battery cells based on the terminal temperature acquired from the thermistor, the voltage difference acquired from the voltmeter, and the terminal resistance calculated from the output current of the plurality of battery cells.

Advantages of the Invention

[0011] According to the battery stack of the present invention, the disassemblability of the battery stack having a configuration in which the bus bar component and the electrode terminal are joined by welding can be improved.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 6

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Figure 8

Figure 9

Figure 10

Modes for Carrying Out the Invention

[0013] For the sake of clarity of explanation, the following descriptions and drawings are appropriately omitted and simplified. In each drawing, the same elements are denoted by the same reference numerals, and redundant explanations are omitted as necessary.

[0014] Embodiment 1 First, FIG. 1 shows a schematic diagram of a battery stack 1 according to Embodiment 1. As shown in FIG. 1, in the battery stack 1 according to Embodiment 1, a plurality of battery cells 10 are stacked in one direction (for example, the stacking direction). Also, the plurality of battery cells 10 are stacked such that the positive electrode terminal and the negative electrode terminal are adjacent to each other. Then, the positive electrode terminal and the negative electrode terminal of adjacent battery cells are connected by a U-shaped bus bar component 12. This bus bar component 12 is joined to each terminal by welding. By connecting between the electrodes with the bus bar component 12 in this way, the plurality of battery cells 10 function as one assembled battery.

[0015] Here, in the battery stack 1 according to Embodiment 1, by providing a weak strength portion in the bus bar component 12, the disassemblability of the battery stack 1 is enhanced, and the load history of the battery stack 1 is acquired. Therefore, FIG. 2 shows a schematic diagram of the bus bar component 12 according to Embodiment 1.

[0016] As shown in FIG. 2, the bus bar component 12 according to Embodiment 1 has a first joint portion 21, a second joint portion 22, and a connecting portion 23. The first joint portion 21 is, for example, a portion joined to the positive electrode terminal of the battery cell 10. The second joint portion 22 is, for example, a portion joined to the negative electrode terminal of the battery cell 10. Note that the polarities of the terminals to which the first joint portion 21 and the second joint portion 22 are joined may be positive or negative, but they are assumed to have different polarities. Also, in FIG. 2, the welding portions WEL are shown as the portions where the first joint portion 21 and the second joint portion 22 are joined to the electrodes. And weak strength portions 24 are formed in the first joint portion 21 and the second joint portion 22.

[0017] The connecting portion 23 connects the end portion of the first joint portion 21 and the end portion of the second joint portion 22 on the opposite side of the welding portion WEL via the weak strength portion 24. The weak strength portion 24 is cut in the stacking direction, and a cut end portion with an inner angle of 90 degrees or less is formed. In the example shown in FIG. 2, the weak strength portions 24 are formed on both of the two opposing sides of the first joint portion 21 in the stacking direction. Also, in the second joint portion 22, the weak strength portions 24 are formed on both of the two opposing sides in the stacking direction.

[0018] The weak strength portion 24 is formed so as to notch the first joint portion 21 and the second joint portion 22. However, when a load is applied such that the relative positions of the battery cells 10 connected by the bus bar component 12 are displaced by forming an inner angle of 90 degrees or less at the cut end of the notch, a crack starting from the cut end is generated. In the battery stack 1 according to the first embodiment, by observing the used battery stack 1 and evaluating the size of the crack, it becomes possible to evaluate how much load has been applied to the battery stack 1 during use.

[0019] Also, the weak strength portion 24 is provided between the welding portion WEL and the connecting portion 23. Therefore, when the bus bar component 12 bends the connecting portion 23 in the vertical direction, it can be easily bent with the weak strength portion 24 as a boundary.

[0020] From the above description, the battery stack 1 according to the first embodiment has disassemblability because the weak strength portion 24 is provided in the bus bar component 12, and the battery cells 10 connected by the bus bar component 12 can be easily disassembled.

[0021] Also, the battery stack 1 according to the first embodiment can function as a crack gauge by forming the inner angle of the cut end of the weak strength portion 24 to be 90 degrees or less. With such a crack gauge function, the battery stack 1 according to the first embodiment can evaluate how much load has been applied to the battery stack 1 during use of the battery stack 1. Such a crack gauge function cannot be realized only by partially reducing the cross-sectional area of the bus bar component 12 for the weak strength portion formed in the bus bar component 12.

[0022] Also, in the example shown in FIG. 1, the weak strength portion 24 is provided in all the bus bar components 12 included in the battery stack 1. However, when only the crack gauge function is to be implemented, the bus bar components provided with the weak strength portion 24 can be limited to only the portions where a large load is expected.

[0023] Second Embodiment In Embodiment 2, a bus bar component 13, which is another form of the bus bar component 12, will be described. In the description of Embodiment 2, for the components that are the same as those described in Embodiment 1, the same reference numerals as those in Embodiment 1 will be given and the description will be omitted.

[0024] FIG. 3 shows a schematic diagram of the battery stack 2 according to Embodiment 2. In the example shown in FIG. 3, among the plurality of battery cells 10 constituting the battery stack 2, the bus bar component that connects between the electrodes of at least two battery cells 10 at the central part of the battery stack in the stacking direction is replaced from the bus bar component 12 to the bus bar component 13. This bus bar component 13 will be described with reference to FIG. 4.

[0025] FIG. 4 shows a schematic diagram of the bus bar component 13 according to Embodiment 2. As shown in FIG. 4, the bus bar component 13 has a first joint portion 31, a second joint portion 32, and a connecting portion 33. The first joint portion 31, the second joint portion 32, and the connecting portion 33 correspond to the first joint portion 21, the second joint portion 22, and the connecting portion 23. The shapes of the weak strength portions are different between the bus bar component 12 and the bus bar component 13. The weak strength portion 34 provided in the bus bar component 13 is formed such that the cut ends face in two or more directions. In the example shown in FIG. 3, the weak strength portion 34 is formed such that the cut ends face in five directions.

[0026] By providing the cut ends in multiple directions in this way, the bus bar component 13 according to Embodiment 2 increases the number of directions of the load applied to the battery stack 2 that can be evaluated by the crack gauge function, and can improve the load evaluation accuracy.

[0027] Embodiment 3 In Embodiment 3, a battery stack 3 and a battery stack 3a, which are another form of the battery stack according to Embodiments 1 and 2, will be described. In the description of Embodiment 3, for the components that are the same as those described in Embodiments 1 and 2, the same reference numerals as those in Embodiment 1 will be given and the description will be omitted.

[0028] Fig. 5 shows a schematic diagram of the battery stack 3 according to Embodiment 3. As shown in Fig. 5, in the battery stack 3 according to Embodiment 3, a thermistor 41 is provided on a bus bar component 12 that connects the battery cells 10 included in the central portion of the battery stack in the stacking direction of the battery stack 2 according to Embodiment 2. Further, in the battery stack 3 according to Embodiment 3, a voltmeter 42 for measuring the voltage difference between the first joint portion 21 and the second joint portion 22 of the bus bar component 12 provided with the thermistor 41 is provided. Note that the voltage measurement point is provided in a region on the welding part WEL side rather than the weak strength part 24 provided on the bus bar component 12. Thereby, in the battery stack 3, it becomes possible to measure with the voltmeter 42 that the resistance value of the bus bar component 12 has increased due to a crack generated in the first joint portion 21 or the second joint portion 22 by the crack gauge function of the weak strength part 24.

[0029] Also, Fig. 6 shows a schematic diagram of the battery stack 3a according to Embodiment 3. As shown in Fig. 6, in the battery stack 3a according to Embodiment 3, a thermistor 41 is provided on a bus bar component 13 that connects the battery cells 10 included in the central portion of the battery stack in the stacking direction of the battery stack 2 according to Embodiment 2. Further, also in the battery stack 3a according to Embodiment 3, a voltmeter 42 for measuring the voltage difference between the first joint portion 31 and the second joint portion 32 of the bus bar component 13 provided with the thermistor 41 is provided. Note that the voltage measurement point is provided in a region on the welding part WEL side rather than the weak strength part 24 provided on the bus bar component 13. Thereby, in the battery stack 3a, it becomes possible to measure with the voltmeter 42 that the resistance value of the bus bar component 13 has increased due to a crack generated in the first joint portion 31 or the second joint portion 32 by the crack gauge function of the weak strength part 24. Here, the bus bar component 13 has more directions in which a load causing a crack is applied than the bus bar component 12, and tends to have a higher load detection ability.

[0030] Note that in FIGS. 5 and 6, illustration of the control unit that performs abnormal control in response to an abnormality occurring in the battery stack 3 based on the information obtained via the thermistor and the voltmeter is omitted. In the battery stack 3 according to Embodiment 3, this control unit is used to detect an abnormality occurring in the battery stack 3 based on the information obtained via the thermistor and the voltmeter, and perform abnormal control. Therefore, in the following description, the battery stack abnormality detection process performed by the control unit according to Embodiment 3 will be described. More specifically, the control unit according to Embodiment 3 performs preset abnormal control when it is determined that an excessive load beyond expectation has been applied to the battery stack based on the terminal temperature acquired from the thermistor, the voltage difference acquired from the voltmeter, and the terminal resistance calculated from the output current of the battery stack. Further, the control unit also performs abnormal control when the resistance increase of the battery cells included in the battery stack is outside the assumed range based on the terminal temperature and the terminal resistance.

[0031] FIG. 7 shows a flowchart for explaining the battery stack abnormality detection process in the control unit according to Embodiment 3. As shown in FIG. 7, when starting the battery stack abnormality detection process, the control unit according to Embodiment 3 first performs terminal temperature measurement to acquire the terminal temperature from the thermistor 41 (step S10). Subsequently, the control unit determines whether the terminal temperature acquired in step S10 is equal to or higher than a preset temperature threshold (step S11). In step S11, if the terminal temperature is lower than the temperature threshold, the control unit determines that there is no abnormality in the battery stack and ends the battery stack abnormality detection process.

[0032] On the other hand, if the terminal temperature is equal to or higher than the temperature threshold in step S11, the control unit acquires the terminal voltage difference from the voltmeter, acquires the input / output current value of the battery stack, and performs terminal resistance measurement to calculate the terminal resistance from the terminal voltage difference and the input / output current value (step S12). Note that the measurement of the input / output current of the battery stack is an operation that the control unit normally performs for the purpose of judging the state of charge and deterioration of the battery stack, and the illustration of an ammeter and the like is omitted in the schematic diagrams shown in FIGS. 5 and 6.

[0033] Subsequently, the control unit determines whether the terminal resistance calculated in step S12 is greater than or equal to a preset resistance threshold (step S13). In step S13, if the terminal resistance is greater than or equal to the resistance threshold, the control unit determines that an excessive load greater than expected may have been applied to the battery stack (step S14), and performs control to stop the battery stack as abnormal-time control, or issues an alert prompting the user for maintenance inspection (step S15). On the other hand, in step S13, if the terminal resistance is less than the resistance threshold, the control unit determines that the resistance of the battery cells included in the battery stack has increased due to deterioration or the like (step S16), and issues an alert prompting the user for maintenance inspection (step S17).

[0034] From the above description, the battery stack according to Embodiment 3 provides a thermistor and a voltmeter for a bus bar component in which cracks progress due to a load being applied to the battery stack, and measures the terminal temperature and the terminal resistance. Thereby, the battery stack according to Embodiment 3 can evaluate the load applied to the battery stack without visually observing the battery stack or the like. Further, the battery stack according to Embodiment 3 can distinguish between the resistance deterioration of the battery cells and the load applied to the battery stack based on the terminal temperature acquired from the thermistor.

[0035] Note that since the battery stack according to Embodiment 3 is used in a state where both ends are supported by a case or the like, the load applied to the vicinity of the central portion in the stacking direction of the battery stack tends to be the largest. Therefore, by providing a thermistor and a voltmeter for the bus bar component installed near the central portion in the stacking direction of the battery stack, the accuracy of load evaluation can be improved.

[0036] Embodiment 4 In Embodiment 4, a battery stack 4 and a battery stack 4a, which are another form of the battery stack according to Embodiment 3, will be described. Regarding the components that are the same as those described in Embodiments 1 - 3 in the description of Embodiment 3, the same reference numerals as those in Embodiment 1 are given and the description is omitted.

[0037] FIG. 8 shows a schematic view of the battery stack 4 according to Embodiment 4. As shown in FIG. 8, in the battery stack 3 according to Embodiment 4, in addition to the bus bar component 12 that connects the battery cells 10 included in the central portion of the battery stack in the stacking direction of the battery stack 3 according to Embodiment 3, thermistors are also provided on the bus bar components 12 arranged at the stack tip and the stack rear end. In the example shown in FIG. 8, a thermistor 51 and a voltmeter 52 are provided on the bus bar component 12 at the stack center, a thermistor 53 and a voltmeter 54 are provided on the bus bar component 12 at the stack tip, and a thermistor 55 and a voltmeter 56 are provided on the bus bar component 12 at the stack rear end. Thereby, in the battery stack 4, it becomes possible to measure that the resistance values of the bus bar components 12 arranged at three locations have increased due to the cracks generated in the first joint portion 21 or the second joint portion 22 by the crack gauge function of the weak strength portion 24.

[0038] Also, FIG. 9 shows a schematic view of the battery stack 4a according to Embodiment 4. As shown in FIG. 9, in the battery stack 4a according to Embodiment 4, the bus bar component 13 is used as the bus bar component arranged at the stack center, the stack tip, and the stack rear end of the battery stack 3a according to Embodiment 3. Also, in the example shown in FIG. 9, a thermistor 51 and a voltmeter 52 are provided on the bus bar component 13 at the stack center, a thermistor 53 and a voltmeter 54 are provided on the bus bar component 13 at the stack tip, and a thermistor 55 and a voltmeter 56 are provided on the bus bar component 13 at the stack rear end. That is, in Embodiment 4, the bus bar component 13 having the same shape is used as the bus bar component provided with the thermistor and the voltmeter. In this way, by using the bus bar component provided with the thermistor and the voltmeter, it becomes possible to improve the accuracy when evaluating cracks and battery deterioration based on the relative difference between the bus bars, as will be described later.

[0039] In Embodiment 4 as well, abnormal control is performed using a control unit not shown in FIGS. 8 and 9. Specifically, the control unit according to Embodiment 4 performs preset abnormal control when it is determined that an excessive load exceeding the assumption is applied to the battery stack based on the terminal temperature acquired from the thermistor, the voltage difference acquired from the voltmeter, and the terminal resistance calculated from the output current of the battery stack. Further, the control unit also performs abnormal control when the resistance increase of the battery cells included in the battery stack is outside the assumed range based on the terminal temperature and the terminal resistance.

[0040] FIG. 10 shows a flowchart for explaining the battery stack abnormality detection process in the control unit according to Embodiment 4. As shown in FIG. 10, when starting the battery stack abnormality detection process, the control unit according to Embodiment 4 first performs terminal temperature measurement to acquire the terminal temperature from the thermistors 51, 53, and 55 (step S20). Subsequently, the control unit calculates the inter-terminal temperature difference, which is the temperature difference between the three bus bar components, using the terminal temperature acquired in step S20, and determines whether the maximum value of the plurality of inter-terminal temperature differences is equal to or greater than a preset first temperature threshold (step S21).

[0041] In step S21, if the maximum value of the inter-terminal temperature differences is less than the first temperature threshold, it is determined whether the maximum value of the plurality of terminal temperatures is equal to or greater than a second temperature threshold (step S22). In step S22, if the maximum value of the terminal temperatures is less than the second temperature threshold, the control unit determines that there is no abnormality in the battery stack and ends the battery stack abnormality detection process. On the other hand, in step S22, if the maximum value of the terminal temperatures is abnormal with respect to the second temperature threshold, the control unit determines that the resistance value of the battery cells included in the battery stack has increased overall (step S23), and issues an alert prompting maintenance inspection to the user (step S24).

[0042] Also, when the temperature difference between terminals in step S21 is equal to or higher than the first temperature threshold, the control unit acquires the voltage difference between terminals from the voltmeters 52, 54, and 56, acquires the input / output current value of the battery stack, and performs terminal resistance measurement to calculate a plurality of terminal resistances corresponding to the three bus bar components from the voltage difference between terminals and the input / output current value (step S25). Note that the measurement of the input / output current of the battery stack is an operation that the control unit normally performs for determining the state of charge or degradation of the battery stack, and the illustration of an ammeter or the like is omitted in the schematic diagrams shown in FIGS. 8 and 9.

[0043] Subsequently, the control unit determines whether or not the inter-terminal resistance difference, which is the difference between the three terminal resistances calculated in step S25, is equal to or higher than a preset resistance threshold (step S26). In step S26, when the inter-terminal resistance difference is equal to or higher than the resistance threshold, the control unit determines that an excessive load greater than expected may have been applied to the battery stack (step S27), and performs control to stop the battery stack as abnormal-time control, or issues an alert prompting maintenance inspection to the user (step S28). On the other hand, in step S26, when the inter-terminal resistance difference is less than the resistance threshold, the control unit determines that the resistance of some of the battery cells included in the battery stack has increased due to degradation or the like (step S29), and issues an alert prompting maintenance inspection to the user (step S30).

[0044] From the above description, in the battery stack according to Embodiment 4, regarding the terminal temperature and the terminal resistance, since the propriety is determined based on the relative values of the temperatures or voltage differences acquired from different positions of the same battery stack, it becomes possible to more accurately evaluate the increase in the terminal resistance and the resistance degradation of the battery cells.

[0045] Note that the present invention is not limited to the above-described embodiments, and can be appropriately modified without departing from the spirit thereof.

Description of Reference Numerals

[0046] 1, 2, 3, 3a, 4, 4a Battery stack 10 Battery cell 12, 13 Bus bar component 21, 31 First joint 22, 32 Second joint 23, 33 Connecting part 24, 34 Weak strength part 41, 51, 53, 55 Thermistor 42, 52, 54, 56 Voltmeter WEL Welding part

Claims

1. A plurality of battery cells stacked in a stacking direction, and a plurality of bus bar components that connect the positive electrode terminal and the negative electrode terminal of adjacent battery cells among the plurality of battery cells and are formed in a U-shape. The plurality of bus bar components include a first joint portion joined to the positive electrode terminal, a second joint portion joined to the negative electrode terminal, and a connecting portion that connects the first joint portion and the second joint portion. The first joint portion and the second joint portion are cut in the stacking direction, and the battery stack has a weak strength portion in which a cut end portion with an inner angle of 90 degrees or less is formed.

2. The battery stack according to claim 1, wherein the weak strength portion is provided in all of the bus bar components.

3. The battery stack according to claim 1, wherein the cut end portion is formed in two or more directions.

4. The bus bar component in which the weak strength portion is formed in the two or more directions connects between the electrodes of at least two of the battery cells at the center of the battery stack in the stacking direction among the plurality of battery cells. The battery stack according to claim 3.

5. At least one of the plurality of bus bar components is equipped with a thermistor for measuring the temperature of the bus bar component, and a voltmeter for measuring the voltage difference between the first joint portion and the second joint portion, and further has a control unit that performs preset abnormal control when it is determined that an excessive load greater than expected is applied to the battery stack based on the terminal temperature obtained from the thermistor, the voltage difference obtained from the voltmeter, and the terminal resistance calculated from the output current of the battery stack. The battery stack according to claim 1.

6. When the terminal temperature acquired from the thermistor is equal to or higher than a preset temperature threshold and the terminal resistance is equal to or higher than a preset resistance threshold, the control unit determines that an excessive load beyond expectation is applied to the plurality of battery cells, and performs the abnormal-time control. The battery stack according to claim 5.

7. The thermistor and the voltmeter are attached to at least two of the bus bar components. The control unit When the temperature difference between terminals, which is the difference in terminal temperatures acquired by two thermistors arranged at different positions, is equal to or higher than a preset first temperature threshold, and the difference in terminal resistances between the bus bar components arranged at different positions, which is calculated using the voltage values acquired by two voltmeters arranged at different positions, is equal to or higher than the preset first temperature threshold, the control unit determines that an excessive load beyond expectation is applied to the battery stack and performs the abnormal-time control. When the temperature difference between terminals is less than the first temperature threshold and the maximum value of the terminal temperatures acquired by the different thermistors is equal to or higher than a preset second temperature threshold, the control unit determines that the overall resistance of the plurality of battery cells has increased and performs the abnormal-time control. When the temperature difference between terminals is equal to or higher than the preset first temperature threshold and the difference in terminal resistances is less than the preset first temperature threshold, the control unit determines that the resistance of a part of the plurality of battery cells has increased and performs the abnormal-time control. The battery stack according to claim 5.

8. A plurality of battery cells stacked in a stacking direction, A plurality of bus bar components that connect the positive electrode terminals and negative electrode terminals of adjacent battery cells among the plurality of battery cells and are formed in a U-shape, A control unit that determines an abnormality occurring in the plurality of battery cells based on the states of the plurality of bus bar components and performs abnormal-time control corresponding to the abnormality. The plurality of bus bar components A first joint portion joined to the positive electrode terminal, A second joint portion joined to the negative electrode terminal, It has a connecting portion that connects the first joint portion and the second joint portion. The first joint portion and the second joint portion have a weak strength portion in which a cut end portion is formed by being cut in the stacking direction and the inner angle becomes 90 degrees or less. At least one of the plurality of bus bar components has a thermistor that measures the temperature of the bus bar component, a voltmeter that measures the voltage difference between the first joint portion and the second joint portion, attached thereto. The control unit performs the abnormal-time control when it is determined that an excessive load exceeding the assumption is applied to the plurality of battery cells based on the terminal temperature acquired from the thermistor, the voltage difference acquired from the voltmeter, and the terminal resistance calculated from the output current of the plurality of battery cells. A battery stack.

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