Method for detecting defective battery cell and battery management system providing the method

Abstract

To provide a method for detecting a defective battery cell with which a defective battery cell reducing the performance of a battery can be detected, and a battery management system providing the method.SOLUTION: A battery management system includes a main control circuit which detects a charged battery cell whose cell voltage is the first to reach a charge upper limit voltage among a plurality of battery cells, for each charge cycle of a battery, detects a discharged battery cell whose cell voltage is the first to reach a discharge lower limit voltage among the plurality of battery cells, for each discharge cycle of the battery, and detects, as a defective battery cell, a battery cell for which a total frequency obtained by adding a first frequency detected as the charged battery cell and a second frequency detected as the discharged battery cell, corresponds to a second reference frequency or more when a sum of a charge cycle frequency and a discharge cycle frequency satisfies a first reference frequency.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] Cross-Citation of Related Applications This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0100431 dated July 30, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for detecting a defective battery cell among a plurality of battery cells that constitute a battery, and a battery management system that provides such a method. [Background technology]

[0003] An electric vehicle is a vehicle that runs on electrical energy output from a battery consisting of a predetermined number of battery packs, for example, two to four. The battery includes multiple battery cells that can be charged / discharged, and its state may change depending on the external environment and its own characteristics. Therefore, a Battery Management System (BMS) monitors and manages the multiple battery cells included in the battery.

[0004] If each of the battery cells has a performance within a predetermined range (hereinafter referred to as a battery cell within a normal range), the cell voltage of each of the battery cells fluctuates similarly within a predetermined range during a charge cycle and a discharge cycle. Therefore, even if the BMS terminates the charge cycle when the first battery cell whose cell voltage reaches the charge final voltage occurs, the battery can still use all of its available battery capacity.

[0005] On the other hand, when a battery is used for a long period of time, the battery cells may deteriorate and produce battery cells (hereinafter referred to as defective battery cells) that deviate from the performance range that has already been set. During a charge or discharge cycle, the cell voltage of a defective battery cell may exhibit characteristics of reaching the upper charge voltage or lower discharge voltage limit more quickly than the cell voltage of other battery cells that are within the normal range.

[0006] If the charging cycle ends when the cell voltage of a defective battery cell reaches the upper charging voltage limit, other battery cells that are within the normal range may end up not fully charged. This can cause the battery to not be able to use all of its available capacity. Furthermore, the defective battery cell may repeatedly use the entire range of its available capacity, accelerating its degradation. Furthermore, if a defect occurs in a battery cell, which is the basic unit that makes up a battery, the overall battery voltage will drop, which can trigger frequent cell balancing and UV (Under Voltage) diagnosis, threatening the stability of the entire battery. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a defective battery cell detection method and a battery management system that provides the method, which can detect defective battery cells that degrade battery performance. [Means for solving the problem]

[0008] According to one aspect of the present invention, a battery management system (BMS) detects a defective battery cell in a battery including a plurality of battery cells, the BMS including: a cell monitoring IC connected to both ends of each of the plurality of battery cells to measure a cell voltage of each of the plurality of battery cells; and a main control circuit configured to detect a charging battery cell among the plurality of battery cells whose cell voltage reaches an upper charging voltage first for each charging cycle of the battery, and to detect a discharging battery cell among the plurality of battery cells whose cell voltage reaches a lower discharging voltage first for each discharging cycle of the battery, and to detect, if a sum of the number of charging cycles and the number of discharging cycles satisfies a first reference number, a battery cell whose total number of times, obtained by adding the first number of times detected as the charging battery cell and the second number of times detected as the discharging battery cell, is equal to or greater than a second reference number, as the defective battery cell.

[0009] The main control circuit may terminate the charging cycle when the charging battery cell is detected.

[0010] The main control circuit may terminate the discharge cycle when the discharging battery cell is detected.

[0011] According to another aspect of the present invention, a battery management system (BMS) for detecting a defective battery cell in a battery including a plurality of battery cells includes: a cell monitoring IC connected to both ends of each of the plurality of battery cells to measure a cell voltage of each of the plurality of battery cells; and a main control circuit for detecting a charging battery cell among the plurality of battery cells whose cell voltage reaches an upper charging voltage first in each charging cycle of the battery, detecting a discharging battery cell among the plurality of battery cells whose cell voltage reaches a lower discharging voltage first in each discharging cycle of the battery, and detecting, as the defective battery cell, a battery cell that was detected as the charging battery cell in an N-th charging cycle and then as the discharging battery cell in an (N+1)-th discharging cycle if a sum of the number of charging cycles and the number of discharging cycles satisfies a first reference number.

[0012] The main control circuit may detect, as the defective battery cell, a battery cell that is detected as the discharging battery cell in an Nth discharging cycle and then detected as the charging battery cell in an (N+1)th charging cycle.

[0013] The main control circuit may terminate the charging cycle when the charging battery cell is detected.

[0014] The main control circuit may terminate the discharge cycle when the discharging battery cell is detected.

[0015] According to another aspect of the present invention, a method for detecting a defective battery cell is a method for a Battery Management System (BMS) to detect a defective battery cell in a battery including a plurality of battery cells, the method including: detecting, for each charge cycle of the battery, a charging battery cell among the plurality of battery cells whose cell voltage reaches an upper charge voltage first; detecting, for each discharge cycle of the battery, a discharging battery cell among the plurality of battery cells whose cell voltage reaches a lower discharge voltage first; determining whether the sum of the number of charge cycles and the number of discharge cycles reaches a first reference number; and, if the sum reaches a first reference number, detecting, as the defective battery cell, a battery cell whose total number of times, obtained by adding the first number of times detected as the charging battery cell and the second number of times detected as the discharging battery cell, is equal to or greater than the second reference number.

[0016] The step of detecting a charged battery cell may terminate the charging cycle when the charged battery cell is detected.

[0017] The detecting the discharged battery cell may terminate the discharge cycle when the discharged battery cell is detected.

[0018] According to another aspect of the present invention, a method for detecting a defective battery cell is a method for a Battery Management System (BMS) to detect a defective battery cell in a battery including a plurality of battery cells, the method including: detecting a charging battery cell among the plurality of battery cells whose cell voltage reaches an upper charging voltage first for each charging cycle of the battery; detecting a discharging battery cell among the plurality of battery cells whose cell voltage reaches a lower discharging voltage first for each discharging cycle of the battery; determining whether the sum of the number of charging cycles and the number of discharging cycles reaches a first reference number; and, if the sum reaches a first reference number as a result of the determination, detecting, as the defective battery cell, a battery cell that was detected as the charging battery cell in an N-th charging cycle and then as the discharging battery cell in an N+1-th discharging cycle.

[0019] The detecting as the defective battery cell may detect, as the defective battery cell, a battery cell that is detected as the discharged battery cell in an Nth discharge cycle and then detected as the charged battery cell in an (N+1)th charge cycle.

[0020] The step of detecting a charged battery cell may terminate the charging cycle when the charged battery cell is detected.

[0021] The detecting the discharged battery cell may terminate the discharge cycle when the discharged battery cell is detected. [Effects of the Invention]

[0022] The present invention can quickly and accurately detect defective battery cells to improve battery stability and prevent battery performance from deteriorating. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating a battery system according to an embodiment. [Figure 2] 1 is a flowchart illustrating a method for detecting defective battery cells according to one embodiment. [Figure 3] 10 is a flowchart illustrating a method for detecting a defective battery cell according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, the embodiments disclosed herein will be described in detail with reference to the accompanying drawings. Identical or similar components will be designated by the same or similar reference numerals, and redundant description thereof will be omitted. The suffixes "module" and / or "section" for components used in the following description are assigned or used interchangeably solely for the convenience of writing the specification, and do not have any distinct meanings or functions. Furthermore, when describing the embodiments disclosed herein, if a detailed description of related known technology is deemed to obscure the gist of the embodiments disclosed herein, such a detailed description will be omitted. Furthermore, the accompanying drawings are merely intended to facilitate understanding of the embodiments disclosed herein, and the accompanying drawings should not be construed as limiting the technical ideas disclosed herein, and should be understood to include all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention.

[0025] Terms including ordinal numbers such as "first," "second," etc. may be used to describe various components, but the components are not limited by the terms. The terms are used only to distinguish one component from another.

[0026] When a component is said to be "coupled" or "connected" to another component, it should be understood that it may be directly coupled or connected to the other component, but that there may be other components in between. Conversely, when a component is said to be "directly coupled" or "directly connected" to another component, it should be understood that there are no other components in between.

[0027] In this application, the terms "comprise" or "have" and the like are intended to specify the presence of any feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood as not precluding the possible presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0028] FIG. 1 is a diagram illustrating a battery system according to one embodiment.

[0029] Referring to FIG. 1, a battery system 1 includes a battery 10, a current sensor 20, a relay 30, and a battery management system (hereinafter referred to as 'BMS') 40.

[0030] The battery 10 may include a plurality of battery cells Cell1-Celln electrically connected in series and in parallel. In one embodiment, the battery cells may be rechargeable secondary batteries. A predetermined number of battery cells may be connected in series to form a battery module, a predetermined number of battery modules may be connected in series to form a battery pack, or a predetermined number of battery packs may be connected in parallel to form a battery bank, thereby supplying a desired amount of power. While FIG. 1 illustrates the battery 10 having a plurality of battery cells Cell1-Celln connected in series, the battery 10 is not limited thereto, and may be configured as a battery module, a battery pack, or a battery bank.

[0031] Each of the plurality of battery cells Cell1 to Celln is electrically connected to the BMS 40 through wiring. The BMS 40 collects and analyzes various information related to the battery cells, including information related to the plurality of battery cells Cell1 to Celln, to control charging, discharging, and protection operations of the battery cells, and can control the operation of the relay 30.

[0032] 1, a battery 10 includes a plurality of battery cells Cell1-Celln connected in series and is connected between two output terminals OUT1 and OUT2 of a battery system 1, a relay 30 is connected between the positive terminal of the battery system 1 and the first output terminal OUT1, and a current sensor 20 is connected between the negative terminal of the battery system 1 and the second output terminal OUT2. The configurations and the connections between the configurations shown in FIG. 1 are merely examples, and the invention is not limited thereto.

[0033] The current sensor 20 is connected in series to a current path between the battery 10 and an external device. The current sensor 20 measures the battery current, i.e., the charging current and discharging current, flowing through the battery 10 and transmits the measurement result to the BMS 40.

[0034] The relay 30 controls the electrical connection between the battery system 1 and the external device. When the relay 30 is turned on, the battery system 1 and the external device are electrically connected to perform charging or discharging, and when the relay 30 is turned off, the battery system 1 and the external device are electrically disconnected. In this case, the external device may be a charger in a charging cycle that supplies power to the battery 10 to charge it, or a load in a discharging cycle that the battery 10 discharges power to the external device.

[0035] The BMS 40 includes a cell monitoring IC 41 and a main control circuit 43 .

[0036] The cell monitoring IC 41 is electrically connected to the positive and negative electrodes of each of the plurality of battery cells Cell1-Celln and measures the cell voltage of each of the plurality of battery cells Cell1-Celln. The battery current value measured by the current sensor 20 is transmitted to the cell monitoring IC 41. The cell monitoring IC 41 transmits information regarding the measured cell voltage and battery current to the main control circuit 43. Specifically, the cell monitoring IC 41 measures the cell voltage of each of the plurality of battery cells Cell1-Celln at predetermined intervals during a rest period in which no charging or discharging occurs, and calculates the cell current based on the measured cell voltage. The cell monitoring IC 41 can transmit the cell voltage and cell current of each of the plurality of battery cells Cell1-Celln to the main control circuit 43.

[0037] The main control circuit 43 can detect a defective battery cell based on the charging battery cell and the discharging battery cell if the number of charge / discharge cycles meets a first reference number.

[0038] The charging battery cell may indicate the battery cell whose cell voltage reaches the charge final voltage first in the charging cycle. The discharging battery cell may indicate the discharging battery cell whose cell voltage reaches the discharge final voltage first in the discharging cycle. For example, the main control circuit 43 may use the electrical position of the battery cell in the battery 10 as an identification factor of the battery cell.

[0039] FIG. 2 is a flow chart illustrating a method for detecting defective battery cells according to one embodiment.

[0040] Hereinafter, a method for detecting a defective battery cell and a battery management system that provides the method according to an embodiment will be described in detail with reference to FIGS.

[0041] First, the BMS 40 detects the battery cell whose cell voltage reaches the charge final voltage (Vmax) first among the plurality of battery cells Cell1-Celln for each charging cycle in which the battery 10 is charged with power from an external device (S110).

[0042] The upper charging voltage limit (Vmax) may be the maximum voltage (Max Voltage) to which the battery 10 can be charged without causing danger. The higher the upper charging voltage limit (Vmax), the greater the capacity of the battery 10, but overcharging may put the battery 10 at risk. Therefore, the upper charging voltage limit can be appropriately set taking into consideration the capacity and stability of the battery 10.

[0043] The BMS 40 can use the electrical position of a battery cell as an identification factor of the battery cell. For example, in the Nth charging cycle, the BMS 40 can confirm the electrical position of the battery cell whose cell voltage first reaches the upper charging voltage limit (Vmax) among the plurality of battery cells Cell1-Celln, and add one more detection count to the battery cell at that position.

[0044] When the BMS 40 detects a charged battery cell, it can terminate the charging cycle and prevent the charged battery cell from being overcharged until the cell voltages of the remaining battery cells (excluding the charged battery cell) reach the upper charging voltage limit (Vmax), thereby preventing accelerated degradation of the charged battery cell.

[0045] Next, the BMS 40 detects the discharged battery cell whose cell voltage first reaches a discharge final voltage (Vmin) in a discharge cycle in which discharged power of the battery 10 is supplied to an external device (S120).

[0046] The discharge lower limit voltage (Vmin) may be the minimum voltage (Min Voltage) at which the battery 10 can be discharged without causing danger. The lower the discharge lower limit voltage (Vmin), the greater the capacity of the battery 10, but over-discharge may put the battery 10 at risk. Therefore, the discharge lower limit voltage (Vmin) is appropriately set in consideration of the capacity and stability of the battery 10. For example, the discharge lower limit voltage may be referred to as a cut-off voltage.

[0047] The BMS 40 can use the electrical position of a battery cell as an identification factor of the battery cell in the battery 10. For example, in the Nth discharge cycle, the BMS 40 can identify the position of the battery cell whose cell voltage first reaches the lower discharge voltage limit (Vmin) among the plurality of battery cells Cell1-Celln, and add one more detection count to the battery cell at that position.

[0048] When a discharged battery cell is detected, the BMS 40 can terminate the discharge cycle. In this case, an over-discharge state in which the discharged battery cell continues to be discharged until the cell voltages of the remaining battery cells excluding the discharged battery cell reach a lower discharge voltage limit can be interrupted, thereby preventing accelerated degradation (deterioration) of the discharged battery cell.

[0049] Next, the BMS 40 determines whether the total number of charge cycles and the total number of discharge cycles satisfies a first reference number (S130).

[0050] The first reference number may correspond to an optimal number of charge / discharge cycles for detecting a defective battery cell, and may be derived, for example, through routine experiments.

[0051] If the total number of charge / discharge cycles does not satisfy the first reference number (S130, No), the BMS 40 repeats from step S110.

[0052] If the total number of charge / discharge cycles satisfies the first reference number (S130, Yes), the BMS 40 determines whether there is a battery cell whose total number of charge / discharge cycles, which is the sum of the first number detected as a charging battery cell and the second number detected as a discharging battery cell, is equal to or greater than the second reference number (S140).

[0053] For example, assume that battery 10 includes five battery cells Cell1, Cell2, Cell3, Cell4, and Cell115, and the first reference number is 500 and the second reference number is 300. If battery cell 3 is detected a total of 400 times (e.g., 200 times as a charging battery cell and 200 times as a discharging battery cell) and battery cells 1, 2, 4, and 5 are each detected a total of 25 times (e.g., 12 times as a charging battery cell and 13 times as a discharging battery cell), BMS 40 can determine that there are battery cells corresponding to two or more reference numbers.

[0054] Next, if the determination result indicates that there is a battery cell whose total number is equal to or greater than the second reference number (S140, Yes), the BMS 40 diagnoses that there is a defective battery cell among the plurality of battery cells (S150).

[0055] For example, the BMS 40 may detect the third battery cell Cell3, whose total number of times is equal to or greater than the second reference number, as a defective battery cell. According to an embodiment, the defective battery cell may be a battery cell that has degraded (deteriorated) and deviated from a predetermined performance range.

[0056] Next, if the result of the determination is that there is no battery cell whose total number is equal to or greater than the second reference number (S140, No), the BMS 40 diagnoses that there is no defective battery cell among the plurality of battery cells (S160).

[0057] FIG. 3 is a flowchart illustrating a method for detecting defective battery cells according to another embodiment.

[0058] Hereinafter, a method for detecting a defective battery cell and a battery management system that provides the method according to another embodiment will be described in detail with reference to FIGS.

[0059] First, the BMS 40 detects the battery cell whose cell voltage first reaches the charge final voltage (Vmax) during a charge cycle in which the battery 10 is charged with power from an external device (S210).

[0060] The upper charging voltage limit (Vmax) may be the maximum voltage (Max Voltage) to which the battery 10 can be charged without causing danger. The higher the upper charging voltage limit (Vmax), the greater the capacity of the battery 10, but overcharging may put the battery 10 at risk. Therefore, the upper charging voltage limit can be appropriately set taking into consideration the capacity and stability of the battery 10.

[0061] The BMS 40 can use the electrical position of a battery cell as an identification factor of the battery cell. For example, in the Nth charging cycle, the BMS 40 can identify the electrical position of the battery cell whose cell voltage reaches the upper charging voltage limit (Vmax) first among the plurality of battery cells Cell1-Celln, and add one more detection count to the battery cell at that position.

[0062] When the BMS 40 detects a charged battery cell, it can terminate the charging cycle and prevent the charged battery cell from being overcharged until the cell voltages of the remaining battery cells (excluding the charged battery cell) reach the upper charging voltage limit (Vmax), thereby preventing accelerated degradation of the charged battery cell.

[0063] Next, the BMS 40 detects the discharged battery cell whose cell voltage first reaches a discharge final voltage (Vmin) in a discharge cycle in which discharged power of the battery 10 is supplied to an external device (S220).

[0064] The lower limit discharge voltage (Vmin) may be the minimum voltage (Min Voltage) at which the battery 10 can be discharged without causing danger. The lower the lower limit discharge voltage (Vmin), the greater the capacity of the battery 10, but over-discharge may put the battery 10 at risk. Therefore, the lower limit discharge voltage (Vmin) may be appropriately set in consideration of the capacity and stability of the battery 10. For example, the lower limit discharge voltage may be referred to as a cut-off voltage.

[0065] The BMS 40 can use the electrical position of a battery cell as an identification factor of the battery cell in the battery 10. For example, in the Nth discharge cycle, the BMS 40 can confirm the electrical position of the battery cell whose cell voltage first reaches the discharge lower limit voltage (Vmin) among the plurality of battery cells Cell1-Celln, and add one more detection count to the battery cell at that position.

[0066] When a discharged battery cell is detected, the BMS 40 can terminate the discharge cycle. In this case, an over-discharge state in which the discharged battery cell continues to be discharged until the cell voltages of the remaining battery cells excluding the discharged battery cell reach a lower discharge voltage limit can be interrupted, thereby preventing accelerated degradation (deterioration) of the discharged battery cell.

[0067] Next, the BMS 40 determines whether the total number of charge cycles and the total number of discharge cycles satisfies a first reference number (S230).

[0068] The first reference number may correspond to an optimal number of charge / discharge cycles for detecting a defective battery cell, and may be derived, for example, through routine experiments.

[0069] If the total number of charge / discharge cycles does not satisfy the first reference number (S230, No), the BMS 40 repeats from step S210.

[0070] If the total number of charge / discharge cycles satisfies the first reference number (S230, Yes), the BMS 40 determines whether the charging battery cell and the discharging battery cell correspond to the same battery cell consecutively (S240).

[0071] According to one embodiment, if there is a battery cell that is detected as a charging battery cell in the Nth charging cycle and then detected as a discharging battery cell in the (N+1)th discharging cycle, the BMS 40 can determine that the charging battery cell and the discharging battery cell correspond to the same battery cell consecutively.

[0072] In another embodiment, if a charging battery cell is detected as a discharging battery cell in the Nth discharge cycle and then a charging battery cell is present in the (N+1)th charge cycle, the BMS 40 may determine that the charging battery cell and the discharging battery cell correspond to the same battery cell consecutively.

[0073] Assume that battery 10 includes five battery cells Cell1, Cell2, Cell3, Cell4, and Cell115, and the first reference number is 500. For example, if fourth battery cell Cell4 is detected as a charged battery cell in the 35th charge cycle and then as a discharged battery cell in the 36th discharge cycle, BMS 40 can determine that the charged battery cell and the discharged battery cell correspond to the same battery cell in succession. As another example, if fifth battery cell Cell5 is detected as a discharged battery cell in the 37th discharge cycle and then as a charged battery cell in the 38th charge cycle, BMS 40 can determine that the charged battery cell and the discharged battery cell correspond to the same battery cell in succession.

[0074] Next, if the determination result indicates that the charging battery cell and the discharging battery cell correspond to the same battery cell consecutively (S240, Yes), the BMS 40 diagnoses that there is a defective battery cell among the plurality of battery cells (S250).

[0075] For example, the BMS 40 may detect the fourth battery cell Cell4, which was detected as a charged battery cell in the 35th charge cycle and then as a discharged battery cell in the 36th discharge cycle, as a defective battery cell. As another example, the BMS 40 may detect the fifth battery cell Cell5, which was detected as a discharged battery cell in the 37th discharge cycle and then as a charged battery cell in the 38th charge cycle, as a defective battery cell. Depending on the embodiment, the defective battery cell may be a battery cell that has degraded (deteriorated) and corresponds to a performance level lower than a previously set performance level.

[0076] Next, if the determination result shows that the charging battery cell and the discharging battery cell do not correspond to the same battery cell consecutively (S240, No), the BMS 40 diagnoses that there is no defective battery cell among the plurality of battery cells (S260).

[0077] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art to which the present invention pertains also fall within the scope of the present invention.

Claims

1. A battery management system (BMS) for detecting a defective battery cell in a battery including a plurality of battery cells, comprising: a cell monitoring IC connected to both ends of each of the plurality of battery cells to measure a cell voltage of each of the plurality of battery cells; a main control circuit that detects a charging battery cell whose cell voltage has reached an upper charging limit voltage among the plurality of battery cells during a charging cycle of the battery, and detects a discharging battery cell whose cell voltage has reached a lower discharging limit voltage among the plurality of battery cells during a discharging cycle of the battery, and detects a defective battery cell based on at least one of a first number of times the battery cell is detected as a charging battery cell and a second number of times the battery cell is detected as a discharging battery cell.

2. The main control circuit The battery management system of claim 1 , wherein the charging cycle is terminated when the charging battery cell is detected.

3. The main control circuit The battery management system of claim 1 or 2, wherein the discharge cycle is terminated when the discharged battery cell is detected.

4. The main control circuit The battery management system according to claim 1 or 2, wherein the defective battery cell is detected based on a total number of times obtained by adding the first number of times and the second number of times.

5. A method for a battery management system (BMS) to detect a defective battery cell in a battery including a plurality of battery cells, comprising: Detecting a charging battery cell whose cell voltage has reached an upper charging voltage limit among the plurality of battery cells during a charging cycle of the battery; Detecting a discharged battery cell whose cell voltage has reached a lower limit discharge voltage among the plurality of battery cells in a discharge cycle of the battery; and detecting a defective battery cell based on at least one of a first number of times the battery cell is detected as a charged battery cell and a second number of times the battery cell is detected as a discharged battery cell.

6. Detecting the charging battery cell comprises:

6. The method of claim 5, further comprising terminating the charging cycle when the charging battery cell is detected.

7. Detecting the discharged battery cell comprises:

7. The method for detecting defective battery cells according to claim 5 or 6, wherein the discharge cycle is terminated when the discharged battery cell is detected.

8. The step of detecting a defective battery cell includes: The method for detecting a defective battery cell according to claim 5 or 6, further comprising detecting the defective battery cell based on a total number of times obtained by adding the first number of times and the second number of times.

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