Battery pack that disconnects the connection of a failed battery cell

Abstract

A battery pack according to an embodiment disclosed in this document includes a battery module including a plurality of battery cell units connected in parallel to each other, and a main power line electrically connected to the plurality of battery cell units within the battery module. Among the plurality of battery cell units, a first battery cell unit includes a first battery cell, a first cell bus bar configured to electrically connect the positive electrode of the first battery cell and the negative electrode of the first battery cell to the main power line, respectively, and a first switch connected in parallel to the first battery cell. A sensor unit configured to detect the states of a plurality of battery cells included in the battery module, and a control unit configured to short-circuit (close) the first switch so that the first cell bus bar is disconnected when a failure of the first battery cell is identified based on the state of the first battery cell detected via the sensor unit.

Description

Technical Field

[0001] The present invention claims the benefit of priority based on Korean Patent Application No. 10-2022-0132744 filed on October 14, 2022, and all the contents disclosed in the document of the Korean Patent Application are incorporated herein by reference in their entirety.

[0002] The embodiments disclosed in this document relate to a battery pack that disconnects the connection of a failed battery cell.

Background Art

[0003] In recent years, research and development on secondary batteries have been actively conducted. Here, a secondary battery is a battery that can be charged and discharged, and includes both conventional Ni / Cd batteries, Ni / MH batteries, etc. and recent lithium-ion batteries. Among secondary batteries, lithium-ion batteries have the advantage of having a much higher energy density compared to conventional Ni / Cd batteries, Ni / MH batteries, etc. In addition, since lithium-ion batteries can be manufactured in a small and lightweight manner, they are used as a power source for mobile devices, and in recent years, their usage range has been extended to the power source of electric vehicles and they have attracted attention as a next-generation energy storage medium.

[0004] A battery pack used as a power source for electronic devices such as electric vehicles is composed of a plurality of battery modules, and each battery module can be composed of one or more battery cells. A battery cell is a component that can be repeatedly charged and discharged and can generate a potential difference by an electrochemical reaction. A battery cell can be composed of a positive electrode, a negative electrode, a separator, and an electrolyte.

[0005] In the aspect that a plurality of battery cells, which are secondary batteries, constitute one battery pack and a plurality of battery packs constitute one large-capacity battery, it is important to maintain the battery safely more than in general portable electrical products.

[0006] Currently, various methods such as using a battery management system (BMS) are being attempted to ensure battery safety. However, due to the electrochemical non-linearity and unstable characteristics of the battery, fundamental safety assurance technologies for battery cell damage and failure have not been developed to date. In particular, a battery pack composed of multiple battery cells has a fatal limitation that the entire battery pack must be replaced if even a single unit cell fails.

Summary of the Invention

Problems to be Solved by the Invention

[0007] Conventionally, when a battery cell failure was diagnosed, a method was used to cut off the power line of the battery module including the failed battery cell by opening a main switching device (e.g., a relay) or a main protection device (e.g., a pyrofuse). However, in the case of an electric vehicle, when the power line of the battery module is cut off by the above method, there is a problem that the power supply to the motor is interrupted and the vehicle stops.

[0008] One object of the embodiments disclosed in this document is to provide a battery pack and its operating method that can disconnect the connection of a failed battery cell without affecting other battery cells included in the battery module when the failure of the battery cell is identified.

[0009] The technical problems of the embodiments disclosed in this document are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the following description.

Means for Solving the Problems

[0010] A battery pack according to an embodiment disclosed in this document includes a battery module including a plurality of battery cell units connected in parallel to each other, and a main power line electrically connected to the plurality of battery cell units within the battery module. Among the plurality of battery cell units, a first battery cell unit includes a first battery cell, a first cell bus bar configured to electrically connect the positive electrode of the first battery cell and the negative electrode of the first battery cell to the main power line, respectively, and a first switch connected in parallel with the first battery cell. The battery pack can include a sensor unit configured to detect states of a plurality of battery cells included in the battery module, and a control unit configured to short-circuit (close) the first switch so that the first cell bus bar is disconnected when a failure of the first battery cell is identified based on the state of the first battery cell detected via the sensor unit.

[0011] In the battery pack according to an embodiment disclosed in this document, the control unit can open the first switch when a specified time elapses after short-circuiting the first switch.

[0012] In the battery pack according to an embodiment disclosed in this document, the first cell bus bar can be irreversibly disconnected by heat applied by a short-circuit current flowing through the first battery cell, the first cell bus bar, and the first switch during the specified time.

[0013] In the battery pack according to an embodiment disclosed in this document, the first cell bus bar includes a breaking portion that breaks due to the heat applied during the specified time, and the breaking portion can be located between a first point and a second point where the first cell bus bar and the first switch are electrically connected.

[0014] In the battery pack according to one embodiment disclosed in this document, among the plurality of battery cell units, the second battery cell unit includes a second battery cell, a second cell bus bar configured to electrically connect the positive electrode of the second battery cell and the negative electrode of the second battery cell to the main power line respectively, and a second switch connected in parallel with the second battery cell. When a failure of the second battery cell is identified based on the state of the second battery cell detected via the sensor unit, the control unit can short-circuit the second switch so that the second cell bus bar is disconnected.

[0015] The battery pack according to one embodiment disclosed in this document further includes a plurality of other battery cell units connected in series with the plurality of battery cell units and connected in parallel with each other. Among the plurality of other battery cell units, the third battery cell unit includes a third battery cell, a third cell bus bar configured to electrically connect the positive electrode of the third battery cell and the negative electrode of the third battery cell to the main power line respectively, and a third switch connected in parallel with the third battery cell. When a failure of the third battery cell is identified based on the state of the third battery cell detected via the sensor unit, the control unit can short-circuit the third switch so that the third cell bus bar is disconnected.

[0016] In the battery pack according to one embodiment disclosed in this document, the sensor unit detects at least one of the voltage, current, impedance, or temperature of the plurality of battery cells, and the control unit can identify whether there is a failure of the first battery cell based on at least one of the voltage, current, impedance, or temperature of the first battery cell detected via the sensor unit.

Advantages of the Invention

[0017] According to the embodiment disclosed in this document, even when a failure of a battery cell is identified, the battery pack can be safely managed without interrupting the main power line connected to other battery cells by only disconnecting the connection of the bus bar connected to the failed battery cell. In addition to this, various effects that can be grasped directly or indirectly are provided by this document.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3a

Figure 3b

Figure 3c

Figure 4

Modes for Carrying Out the Invention

[0019] Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include various modifications, equivalents, and / or alternatives of the embodiments of the present invention.

[0020] The various embodiments of this document and the terms used therein are not intended to limit the technical features described in this document to specific embodiments, but should be understood to include various modifications, equivalents, or alternatives of such embodiments. In connection with the description of the drawings, similar or related components may be denoted by similar reference numerals. The singular form of a noun corresponding to an item may include one or more of the said item, unless the context clearly indicates otherwise.

[0021] In this document, phrases such as "A or B", "at least one of A and B", "at least one of A or B", "A, B, or C", "at least one of A, B, and C", and "at least one of A, B, or C" may each include any one of the items listed together in the corresponding phrase, or all possible combinations thereof. Terms such as "first", "second", "first", "second", "A", "B", "(a)", or "(b)" may be used merely to distinguish the component from other components, and do not limit the component in other aspects (e.g., importance or order), unless otherwise stated.

[0022] In this document, when a certain (e.g., first) component is referred to as being "coupled", "connected", or "joined" to another (e.g., second) component, with or without the terms "functionally" or "communicatively", or when referred to as "coupled" or "connected", this means that the certain component may be directly (e.g., by wire), wirelessly, or via a third component, to the other component.

[0023] According to one embodiment, the methods according to the various embodiments disclosed in this document may be provided included in a computer program product. The computer program product may be traded as a commodity between a seller and a purchaser. The computer program product may be distributed in the form of a machine-readable storage medium (e.g., a compact disc read only memory (CD-ROM)), or may be distributed online (e.g., downloaded or uploaded) via an application store or directly between two user devices. In the case of online distribution, at least a part of the computer program product may be stored at least temporarily or generated temporarily in a machine-readable storage medium such as the memory of a manufacturing company's server, an application store's server, or a relay server.

[0024] According to various embodiments, each of the foregoing components (e.g., a module or a program) may include one or more entities, and some of the one or more entities may be separately arranged from other components. According to various embodiments, one or more of the foregoing components or operations may be omitted, or one or more other components or operations may be added. Alternatively or additionally, a plurality of components (e.g., modules or programs) may be integrated into one component. In this case, the integrated component may perform one or more functions of each of the plurality of components in the same or similar manner as those performed by the component among the plurality of components before the integration. According to various embodiments, the operations performed by a module, a program, or other components may be executed sequentially, in parallel, iteratively, or heuristically, or one or more of the operations may be executed in a different order, omitted, or one or more other operations may be added.

[0025] FIG. 1 is a block diagram showing the configuration of a general battery pack. Referring to FIG. 1, a battery control system including a battery pack 1 according to an embodiment of the present invention and a host controller 2 included in a host system is schematically shown.

[0026] As shown in FIG. 1, the battery pack 1 includes a rechargeable battery module 10 composed of one or more battery cells, a switching unit 14 connected in series to the (+) terminal side or (-) terminal side of the battery module 10 to control the flow of the charge and discharge current of the battery module 10, and a battery management system 20 that monitors the voltage, current, temperature, etc. of the battery pack 1 and performs control management to prevent overcharging and overdischarging. At this time, a plurality of battery modules 10, sensors 12, switching units 14, and battery management systems 20 can be provided in the battery pack 1.

[0027] Here, the switching unit 14 is an element for controlling the flow of current for charging or discharging a plurality of battery modules 10. For example, at least one relay, electromagnetic contactor, etc. can be used according to the specifications of the battery pack 1.

[0028] The battery management system 20 is an interface that receives the input of the measured values of the above-described various parameters, and can include a plurality of terminals and a circuit connected to these terminals for processing the received input values. Further, the battery management system 20 can also control the ON / OFF of the switching unit 14, for example, a relay or a contactor, and can monitor the state of each battery module 10 connected to the battery module 10. According to one embodiment, the battery management system 20 can include the cell bus bar control device 290 of FIG. 2. According to other embodiments, the battery management system 20 may be another system different from the cell bus bar control device 290 of FIG. 2. That is, the cell bus bar control device 290 of FIG. 2 may be included in the battery pack 1 or configured as another device external to the battery pack 1.

[0029] The upper controller 2 can transmit a control signal for the battery module 10 to the battery management system 20. Thereby, the operation of the battery management system 20 can be controlled based on the signal applied from the upper controller 2.

[0030] FIG. 2 is a diagram showing the configuration of a battery pack according to an embodiment. Referring to FIG. 2, the battery pack 1 can include a battery module 200 and a cell bus bar control device 290. According to the embodiment, the cell bus bar control device 290 may be included in the battery management system 20 of FIG. 1, or may be another device different from the battery management system 20 of FIG. 1.

[0031] The battery module 200 can include a main power line 201 and a plurality of battery cell units. Here, the battery cell unit can be composed of battery cells 210, 220, 230, or 240, cell bus bars 211, 221, 231, or 241, and switches 215, 225, 235, or 245. For example, the first battery cell unit can be composed of a first battery cell 210, a first cell bus bar 211, and a first switch 215.

[0032] In FIG. 2, the battery module 200 is shown as including four battery cell units, but it is not limited thereto, and the battery module 200 can include two or more battery cell units. Also, in FIG. 2, the battery cell units connected in parallel in pairs are shown as being connected in series via the main power line 201, but this is not limiting. For example, the number of battery cell units connected in parallel between the main power lines 201 is not limited. However, at least two or more battery cell units must be connected in parallel to the main power line 201.

[0033] The main power line 201 can be electrically connected to the positive and negative electrodes of the battery module 200 within the battery module 200. According to one embodiment, the main power line 201 can be electrically connected to the battery cells 210, 220, 230, or 240 via the cell bus bars 211, 221, 231, or 241. The main power line 201 can transmit the power output from the plurality of battery cells 210, 220, 230, and 240 outside the battery module 200, or transmit the power supplied from outside the battery module 200 to the plurality of battery cells 210, 220, 230, and 240.

[0034] The cell bus bars 211, 221, 231, or 241 can be configured to electrically connect the positive and negative electrodes of the battery cells 210, 220, 230, or 240 to the main power line 201, respectively.

[0035] According to one embodiment, the first cell bus bar 211 can be electrically connected to the positive and negative electrodes of the first battery cell 210 and can be electrically connected to the first point 202 and the second point 203 of the main power line 201. Also, the second cell bus bar 221 can be electrically connected to the positive and negative electrodes of the second battery cell 220 and can be electrically connected to the first point 202 and the second point 203 of the main power line 201. In this case, the first battery cell 210 and the second battery cell 220 can be branched at the first point 202 and the second point 203 of the main power line 201 via the first cell bus bar 211 and the second cell bus bar 221 and connected in parallel to each other.

[0036] According to one embodiment, the third cell bus bar 231 can be electrically connected to the positive and negative electrodes of the third battery cell 230 and can be electrically connected to the third point 204 and the fourth point 205 of the main power line 201. Also, the fourth cell bus bar 241 can be electrically connected to the positive and negative electrodes of the fourth battery cell 240 and can be electrically connected to the third point 204 and the fourth point 205 of the main power line 201. In this case, the third battery cell 230 and the fourth battery cell 240 can be branched at the third point 204 and the fourth point 205 of the main power line 201 via the third cell bus bar 231 and the fourth cell bus bar 241 and connected in parallel to each other.

[0037] The switches 215, 225, 235, or 245 can be electrically connected to two points on the cell bus bars 211, 221, 231, or 241. According to one embodiment, the switches 215, 225, 235, or 245 can be configured to open or close based on a control signal received from the control unit 292.

[0038] According to one embodiment, the first switch 215 can be electrically connected to the first point 212 and the second point 213 on the first cell bus bar 211. Here, the first battery cell 210 can be located between the first point 212 and the second point 213 on the first cell bus bar 211. Thereby, the first switch 215 can be connected in parallel with the first battery cell 210 via the first point 212 and the second point 213 on the first cell bus bar 211.

[0039] According to one embodiment, the second switch 225 can be electrically connected to the third point 222 and the fourth point 223 on the second cell bus bar 221. Here, the second battery cell 220 can be located between the third point 222 and the fourth point 223 on the second cell bus bar 221. Thereby, the second switch 225 can be connected in parallel with the second battery cell 220 via the third point 222 and the fourth point 223 on the second cell bus bar 221.

[0040] According to one embodiment, the third switch 235 can be electrically connected to a fifth point 232 and a sixth point 233 on the third cell bus bar 231. Here, the third battery cell 230 can be located between the fifth point 232 and the sixth point 233 on the third cell bus bar 231. Thereby, the third switch 235 can be connected in parallel with the third battery cell 230 via the fifth point 232 and the sixth point 233 on the third cell bus bar 231.

[0041] According to one embodiment, the fourth switch 245 can be electrically connected to a seventh point 242 and an eighth point 243 on the fourth cell bus bar 241. Here, the fourth battery cell 240 can be located between the seventh point 242 and the eighth point 243 on the fourth cell bus bar 241. Thereby, the fourth switch 245 can be connected in parallel with the fourth battery cell 240 via the seventh point 242 and the eighth point 243 on the fourth cell bus bar 241.

[0042] According to one embodiment, the cell bus bars 211, 221, 231, or 241 can include break portions 214, 224, 234, or 244. According to one embodiment, the break portions 214, 224, 234, or 244 can be located between two points where the cell bus bars 211, 221, 231, or 241 are electrically connected to the switches 215, 225, 235, or 245. For example, the first break portion 214 can be located between the first point 212 and the second point 213 on the first cell bus bar 211. Here, the first point 212 and the second point 213 can mean the points where a short-circuit current flows through the first battery cell 210, the first cell bus bar 211, and the first switch 215 when the first switch 215 is short-circuited.

[0043] According to one embodiment, the breakage portions 214, 224, 234, or 244 can be configured to irreversibly break due to heat applied by a short-circuit current flowing through the battery cells 210, 220, 230, or 240, the cell bus bars 211, 221, 231, or 241, and the switches 215, 225, 235, or 245 when the switches 215, 225, 235, or 245 short-circuit for a specified time. For example, the cell bus bars 211, 221, 231, or 241 can be realized such that the thickness of the breakage portions 214, 224, 234, or 244 is thinner than the thickness at other locations.

[0044] The cell bus bar control device 290 can include a sensor unit 291 and a control unit 292. According to one embodiment, the sensor unit 291 can detect the states of the plurality of battery cells 210, 220, 230, and 240. According to one embodiment, the sensor unit 291 can detect at least one of the voltage, current, impedance, or temperature of the plurality of battery cells 210, 220, 230, and 240. According to one embodiment, the sensor unit 291 can receive a control signal from the control unit 292 to detect the states of the plurality of battery cells 210, 220, 230, and 240. The sensor unit 291 can detect the states of the plurality of battery cells 210, 220, 230, and 240 each time it receives a control signal from the control unit 292. According to one embodiment, the sensor unit 291 can transmit data regarding the detected states to the control unit 292.

[0045] The control unit 292 can be electrically connected to the sensor unit 291. According to one embodiment, the control unit 292 can execute software to control at least one other component connected to the control unit 292 and can perform various data processing or operations. According to one embodiment, the control unit 292 can control at least one other component connected to the control unit 292 and control the overall operation of the cell bus bar control device 290. The control unit 292 can include at least one of a processing device such as an ASIC (application specific integrated circuit), a DSP (digital signal processor), a PLD (programmable logic devices), an FPGA (field programmable gate arrays), a CPU (central processing unit), a microcontroller, or a microprocessor.

[0046] According to one embodiment, the control unit 292 can detect the states of the plurality of battery cells 210, 220, 230, and / or 240 via the sensor unit 291. According to one embodiment, the control unit 292 can detect at least one of the voltage, current, impedance, or temperature of the plurality of battery cells 210, 220, 230, and / or 240 via the sensor unit 291.

[0047] According to one embodiment, the control unit 292 can identify whether there is a failed battery cell. According to one embodiment, the control unit 292 can identify whether there is a failed battery cell based on the states of the plurality of battery cells 210, 220, 230, and / or 240 detected via the sensor unit 291.

[0048] According to one embodiment, when it is identified that there is a failed battery cell, the control unit 292 can disconnect the cell bus bar electrically connected to the failed battery cell.

[0049] According to one embodiment, when the control unit 292 identifies a failure of the first battery cell 210, it can disconnect the first cell bus bar 211 by controlling the first switch 215. According to one embodiment, the control unit 292 can disconnect the first cell bus bar 211 by short - circuiting the first switch 215. According to one embodiment, after a specified time has elapsed since the control unit 292 short - circuits the first switch 215, the control unit 292 can open the first switch 215. In this case, the first cell bus bar 211 can be irreversibly disconnected by the heat applied by the short - circuit current flowing through the first battery cell 210, the first cell bus bar 211, and the first switch 215 during the specified time.

[0050] Also, when the control unit 292 identifies a failure of the battery cells 220, 230, and / or 240 other than the first battery cell 210 in the above - described manner, it can disconnect the cell bus bars 221, 231, and / or 241 electrically connected thereto.

[0051] Hereinafter, with reference to FIGS. 3a, 3b, and 3c, the operation of disconnecting the first cell bus bar 211 when a failure of the first battery cell 210 is identified will be described. The configurations shown in FIGS. 3a, 3b, and 3c may be the same as the main power line 201, battery cells 210, 220, cell bus bars 211, 221, breaking parts 214, 224, and switches 215, 225 in FIG. 2.

[0052] FIG. 3a is a diagram showing the states of the battery cell, cell bus bar, and switch before a failure of the first battery cell according to one embodiment is identified. Referring to FIG. 3a, the first switch 215 and the second switch 225 can be in an open state. According to one embodiment, the first breaking part 214 (and / or the second breaking part 224) can be realized to have a thickness thinner than the thickness at other points of the first cell bus bar 211 (and / or the second cell bus bar 221).

[0053] Figure 3b is a diagram showing the states of a battery cell, a cell bus bar, and a switch when a failure of a first battery cell according to an embodiment is identified and the first switch is short-circuited for a specified time.

[0054] Referring to Figure 3b, the first switch 215 can be short-circuited for a specified time in response to a control signal received from the control unit 292. According to an embodiment, a short-circuit current 300 can flow through the first battery cell 210, the first cell bus bar 211, and the first switch 215 during the specified time. In this case, heat generated by the short-circuit current 300 can be applied to the first cell bus bar 211. In this process, a first breaking portion 214 that is relatively thinner than other points of the first cell bus bar 211 can be broken by the heat. For this purpose, the first breaking portion 214 can be realized to have a thickness that can be broken by the heat applied during the specified time.

[0055] Figure 3c is a diagram showing the states of a battery cell, a cell bus bar, and a switch after a failure of a first battery cell according to an embodiment is identified and the first switch is short-circuited for a specified time.

[0056] Referring to Figure 3c, the first switch 215 can be opened again in response to a control signal received from the control unit 292. Also, the first breaking portion 214 can be irreversibly broken by the heat applied by the short-circuit current. As a result, the first cell bus bar 211 can be in an irreversibly disconnected state.

[0057] Thus, when a failed battery cell (e.g., the first battery cell 210) is detected, the battery pack 1 according to an embodiment disclosed in this document can prevent the power transmitted through the main power line 201 from being interrupted by disconnecting the cell bus bar (e.g., the first cell bus bar 211) connected to the failed battery cell.

[0058] FIG. 4 is an operation flowchart of a battery pack according to an embodiment. FIG. 4 can be described using the configuration of FIG. 2. The embodiment shown in FIG. 4 is only one embodiment, and the order of steps according to various embodiments of the present invention may be different from that shown in FIG. 4, some steps shown in FIG. 4 may be omitted, the order between steps may be changed, or steps may be merged.

[0059] Referring to FIG. 4, in operation 405, the battery pack 1 can detect the states of the plurality of battery cells 210, 220, 230, and / or 240. According to one embodiment, the battery pack 1 can detect at least one of the voltage, current, impedance, or temperature of the plurality of battery cells 210, 220, 230, and / or 240.

[0060] In operation 410, the battery pack 1 can identify whether there is a failed battery cell. According to one embodiment, the battery pack 1 can identify whether there is a failed battery cell based on the states of the plurality of battery cells 210, 220, 230, and / or 240 detected in operation 405.

[0061] If it is identified in operation 410 that there is no failed battery cell ("NO"), the battery pack 1 can end the operation according to FIG. 4. If it is identified in operation 410 that there is a failed battery cell ("YES"), in operation 415, the battery pack 1 can disconnect the cell bus bar electrically connected to the failed battery cell.

[0062] According to one embodiment, when the battery pack 1 identifies a failure of the first battery cell 210, it can disconnect the first cell bus bar 211 by controlling the first switch 215. According to one embodiment, the battery pack 1 can disconnect the first cell bus bar 211 by short-circuiting the first switch 215. According to one embodiment, after a specified time has elapsed after the battery pack 1 short-circuits the first switch 215, the first switch 215 can be opened. In this case, the first cell bus bar 211 can be irreversibly disconnected by the heat applied by the short-circuit current flowing through the first battery cell 210, the first cell bus bar 211, and the first switch 215 during the specified time.

[0063] Also, when the battery pack 1 identifies a failure of battery cells 220, 230, and / or 240 other than the first battery cell 210 in the above-described manner, it can disconnect the cell bus bars 221, 231, and / or 241 that are electrically connected thereto.

[0064] Terms such as "including," "comprising," or "having" described above are to be construed to mean that the component can be inherent therein, unless otherwise stated to the contrary, and do not exclude other components, but may further include other components. All terms, including technical or scientific terms, shall have the same meaning as commonly understood by those of ordinary skill in the technical field to which the embodiments disclosed in this document belong, unless otherwise defined. Commonly used terms such as those defined in a dictionary shall be construed to be consistent with the meaning in the context of the related art and shall not be construed in an ideal or overly formal sense unless clearly defined in this document.

Claims

1. A battery pack, comprising: a battery module including a plurality of battery cell units connected in parallel to each other; a main power line electrically connected to the plurality of battery cell units within the battery module; and among the plurality of battery cell units, a first battery cell unit includes: a first battery cell; a first cell bus bar electrically connecting the positive electrode of the first battery cell and the negative electrode of the first battery cell to the main power line respectively; a first switch connected in parallel with the first battery cell; and the battery pack further includes: a sensor unit for detecting the states of a plurality of battery cells included in the battery module; a control unit for short-circuiting the first switch so that the first cell bus bar is disconnected when a failure of the first battery cell is identified based on the state of the first battery cell detected via the sensor unit. A battery pack.

2. The control unit: releases the first switch when a specified time elapses after short-circuiting the first switch. The battery pack according to Claim 1.

3. The first cell bus bar is irreversibly disconnected by heat applied by a short-circuit current flowing through the first battery cell, the first cell bus bar, and the first switch during the specified time. The battery pack according to Claim 2.

4. The first cell bus bar includes a breaking portion that is broken by the heat applied during the specified time, and the breaking portion is located between a first point and a second point where the first cell bus bar is electrically connected to the first switch. The battery pack according to Claim 3.

5. Among the plurality of battery cell units, a second battery cell unit includes: a second battery cell; a second cell bus bar configured to electrically connect the positive electrode of the second battery cell and the negative electrode of the second battery cell to the main power line respectively; a second switch connected in parallel with the second battery cell; and the control unit: short-circuits the second switch so that the second cell bus bar is disconnected when a failure of the second battery cell is identified based on the state of the second battery cell detected via the sensor unit. The battery pack according to any one of Claims 1 to 4.

6. further includes a plurality of other battery cell units connected in series with the plurality of battery cell units and connected in parallel to each other. Among the plurality of other battery cell units, the third battery cell unit is a third battery cell, a third cell bus bar configured to electrically connect the positive electrode of the third battery cell and the negative electrode of the third battery cell to the main power line, respectively, and a third switch connected in parallel with the third battery cell, The control unit When a failure of the third battery cell is identified based on the state of the third battery cell detected via the sensor unit, the third switch is short-circuited so that the third cell bus bar is disconnected. The battery pack according to any one of claims 1 to 4. **Claim 7** The sensor unit detects at least one of voltage, current, impedance, or temperature of the plurality of battery cells, The control unit identifies a failure of the first battery cell based on at least one of voltage, current, impedance, or temperature of the first battery cell detected via the sensor unit. The battery pack according to any one of claims 1 to 4.

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