Method for detecting defective battery cells

Abstract

The present invention relates to a method for determining the quality of a battery cell from the values ​​measured in the second stage, without measuring the time taken between the first and second stages, by including: a first stage of obtaining resistance values ​​based on temperature for a plurality of battery cells belonging to the same type; a second stage of measuring the temperature and resistance of other battery cells belonging to the same type but not corresponding to the plurality of battery cells; and a third stage of determining whether the measured values ​​of the other battery cells meet the good quality standards already set using the data obtained in the first stage.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0127851 filed on September 25, 2023, and all the contents disclosed in the Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for determining defects in battery cells. Specifically, it relates to a method for determining defects in battery cells that can easily, simply, and accurately confirm the quality of completed battery cells regardless of the delay time in the logistics line by creating a database of resistance values according to the temperature of normal battery cells.

Background Art

[0003] Lithium secondary batteries that are charged and discharged by the movement of lithium ions are used not only in the field of small battery cells for mobile devices and small electronic products but also in the field of medium and large battery packs used as energy sources such as electric vehicles and power storage systems that require high output and high voltage, due to their advantages of high energy density and high charging voltage.

[0004] The manufacturing process of lithium secondary batteries includes an electrode plate process of manufacturing electrode plates and laminating or winding them together with a separator to manufacture an electrode assembly, an assembly process of accommodating the electrode assembly in a battery case, injecting an electrolyte, and then sealing it, and a formation process including the charging and discharging process and the aging process of the thus assembled lithium secondary battery. Defective products can be sorted out while going through the formation process to improve performance.

[0005] In particular, the formation process includes an activation process of charging and discharging the lithium secondary battery to impart electrical characteristics to the completed battery cell, and a process of measuring the resistance of the shipped and charged battery cell to confirm the quality of the completed battery cell.

[0006] Depending on the production environment, battery cell charging / discharging and resistance measurement may be performed in separate areas, making it impossible to continuously perform the process of charging / discharging and then measuring the resistance. Furthermore, the time elapsed between charging / discharging and resistance measurement may vary depending on the progress of the logistics line.

[0007] Furthermore, in the case of manual logistics lines, the delay time from charging / discharging to resistance measurement may be longer than in automated logistics lines.

[0008] During the charging and discharging process, the temperature of the battery cells in lithium-ion secondary batteries increases. Even when identical types of battery cells are charged and discharged under the same conditions, the temperature after charging and discharging may not be constant, and temperature variations may occur between individual battery cells.

[0009] Furthermore, the rate at which the battery cell temperature decreases can vary depending on the delay time between the end of charging / discharging and the time of resistance measurement. In other words, the temperature of the battery cell is a factor that affects the resistance value, and if the delay time between the end of charging / discharging and the time of resistance measurement is long, the temperature of the battery cell may decrease. Thus, if the temperature of the battery cell where the resistance is measured is not uniform, the environment in which the resistance is measured changes, which can raise concerns about the reliability of the measured resistance value.

[0010] In this regard, Patent Document 1 relates to a semiconductor device capable of precisely detecting defective battery cells, and includes a temperature measuring unit for measuring the temperature of the battery cell, a voltage measuring unit for measuring the voltage of the battery cell, a current measuring unit for measuring the current supplied from the battery cell, and a control unit. The control unit can count the number of charge-discharge cycles of the battery cell, measure the charge level of the battery cell based on the voltage, and calculate the internal resistance of the battery cell based on the voltage and current. In other words, Patent Document 1 calculates the internal resistance at the time of shipment of battery cells by normalizing the internal resistance based on the number of cycles, temperature, and charge level, and determines whether the battery cell is defective.

[0011] Patent Document 1 presents an apparatus and method for determining whether a battery cell is defective by normalizing its internal resistance based on the number of cycles, temperature, and charge level of the battery cell. However, this is a technology for determining whether commercially available battery cells are defective, and it does not present a method for accurately determining defective battery cells using the same criteria when the charging / discharging stage and resistance measurement stage are performed in separate areas or at regular time intervals before the finished battery cells are shipped.

[0012] Patent Document 2 relates to a method and apparatus for measuring the internal resistance of a battery, and includes the steps of: monitoring the voltage and current of the battery in real time; monitoring the voltage rise and, after the current decreases, starting to collect the voltage and current and saving the collected voltage and current to a data set; and, after monitoring that the current has reached a current threshold, determining the internal resistance of the battery using the voltage and current in the data set.

[0013] Patent Document 2 presents a method for determining the internal resistance of a battery using the results of measuring the battery's voltage and current, without measuring the battery's internal resistance itself. However, it does not offer a solution to the problem that the resistance value changes due to the delay time between charging / discharging and resistance measurement during the lithium secondary battery formation process.

[0014] Therefore, it is necessary to either perform the charge / discharge stage to impart electrical characteristics to the battery cells and the resistance measurement stage to check their quality in a separate area before shipping the battery cells, or to use a method that allows for checking the quality of the battery cells regardless of the time elapsed between the end of charge / discharge and the time of resistance measurement. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] Japanese Patent Publication No. 2019-114437 [Patent Document 2] Chinese Patent Publication No. 115902672 [Overview of the project] [Problems that the invention aims to solve]

[0016] The present invention aims to solve the aforementioned problems and to provide a method for determining whether a battery cell is good or bad, regardless of the time elapsed between charging and discharging the battery cell during the manufacturing process of a lithium secondary battery and measuring its resistance for defect detection. [Means for solving the problem]

[0017] A battery cell defect detection method according to the present invention for achieving this objective includes: a first step of obtaining temperature-dependent resistance values ​​for a plurality of battery cells belonging to the same type; a second step of measuring the temperature and resistance of other battery cells belonging to the same type but not corresponding to the plurality of battery cells; and a third step of determining whether the measured values ​​of the other battery cells meet the good product standards already set using the data obtained in the first step.

[0018] The first step may include a first-first step of charging and discharging the battery cell to activate it, a first-second step of measuring the temperature of the battery cell, and a first-third step of measuring the resistance of the battery cell.

[0019] The area in which the charging and discharging stage 1-1 is performed may be a separate area from the area in which the temperature is measured in stage 1-2 and the resistance is measured in stage 1-3.

[0020] The first and second stages of measuring temperature and the first to third stages of measuring resistance can be performed simultaneously.

[0021] The process further includes a step of measuring the time required from the end of the charging and discharging process until the time of measuring the resistance, dividing the required time into certain intervals and classifying them, and the resistance values ​​based on temperature in the first step can be compiled into a database, taking the required time into further consideration.

[0022] The charging voltage in the first stage of charging and discharging may be the shipped voltage.

[0023] From the first stage to the third stage may be applicable to both manual logistics lines and automated logistics lines.

[0024] The battery cell may be a pouch-type battery cell, a cylindrical battery cell, or a prismatic battery cell.

[0025] The same type may have one or more conditions selected from the group consisting of the type based on the appearance of the battery cell, the cathode material, the anode material, the separator material, the electrolyte material, the additive type, the lot (LOT), the charge-discharge conditions, and the state of charge (SOC) being the same.

[0026] It may further include a fourth stage of classifying the battery cells determined to be defective in the third stage.

[0027] In addition, the present invention can be provided in a form in which various combinations of the solutions to the above problems are made.

Advantages of the Invention

[0028] As described above, when using the method for determining defects in a battery cell according to the present invention, it is possible to easily and accurately determine whether it is good or bad without being affected by the timing of resistance measurement after charge and discharge for activation of the completed battery cell.

[0029] Also, even in a manual logistics line where the time required from charge and discharge to resistance measurement becomes long, it is possible to quickly determine whether the battery cell is good or bad by measuring the temperature and the resistance value without separately measuring the required time.

Brief Description of the Drawings

[0030] [Figure 1] It is a flowchart of the method for determining defects in a battery cell according to the present invention.

Embodiments for Carrying Out the Invention

[0031] Hereinafter, with reference to the attached drawings, embodiments that allow a person with ordinary skill in the art to which the present invention pertains to be easily implemented will be described in detail. In describing the operating principles of embodiments of the present invention in detail, if it is determined that a specific description of a related known function or configuration may unnecessarily obscure the gist of the present invention, such detailed description will be omitted.

[0032] Throughout the drawings, the same reference numerals shall be used for parts that have similar functions and operations. In the specification, when it is said that one part is connected to another part, this includes not only direct connection but also indirect connection through other elements in between. Furthermore, when it is said that a component is included, unless otherwise stated, it does not mean that other components are excluded, but rather that other components may be included.

[0033] Descriptions that limit or specify the constituent elements are applicable to all inventions and are not limited to a particular invention, unless otherwise specified.

[0034] Throughout the description of this invention and the claims, singular nouns include plural nouns unless otherwise specified.

[0035] Throughout the description and claims of this invention, "or" includes "and" unless otherwise specified. Therefore, "including A or B" means three cases: including A, including B, or including both A and B.

[0036] The present invention will be described in detail with reference to the accompanying drawings, along with specific embodiments.

[0037] Figure 1 is a flowchart of the battery cell defect detection method according to the present invention. Referring to Figure 1, the battery cell defect detection method according to the present invention may include: a first step of obtaining temperature-dependent resistance values ​​for a plurality of battery cells belonging to the same type; a second step of measuring the temperature and resistance of other battery cells belonging to the same type but not corresponding to the plurality of battery cells; and a third step of determining whether the measured values ​​of the other battery cells meet the good product standards already set using the data obtained in the first step.

[0038] First, in the first stage, resistance values ​​under different temperatures are obtained for battery cells that are considered good quality, and these values ​​are added to a database, allowing for the establishment of criteria for determining whether a cell is good or not.

[0039] Specifically, the first step may include a first-first step of charging and discharging the battery cell to activate it, a first-second step of measuring the temperature of the battery cell, and a first-third step of measuring the resistance of the battery cell.

[0040] For example, a battery manufacturing plant can be divided into a battery manufacturing building and a chemical building, and the battery manufacturing process can include electrode plate processing, assembly processing, and chemical processing. The electrode plate processing and assembly processing can be carried out in the battery manufacturing building, and the assembled battery cells can be moved to the chemical building to undergo charging, discharging, and quality control processes.

[0041] The first stage described above can be carried out in an automated logistics line that transports battery cells by conveyor belt within the chemical building, or in a manual logistics line that transports them by workers or robots, and the transport may be delayed depending on the condition of the logistics line.

[0042] The aforementioned stages 1-1, 1-2, and 1-3 are carried out within the chemical building, and at least one of these stages can be carried out in a separate area. For example, the area in which the charging and discharging stage 1-1 is carried out can be separated from the areas in which the temperature measurement stage 1-2 and the resistance measurement stage 1-3 are carried out.

[0043] In other words, after charging and discharging is complete, the battery cells are transferred from the charging / discharging area to the resistance measurement area, where resistance measurement can be performed. Depending on the transfer status of the logistics line, there can be a difference of 300 minutes or more in the time taken from charging / discharging to resistance measurement.

[0044] Since temperature is a factor that affects resistance, accurate resistance values ​​due to temperature can only be obtained when the first and second stages of measuring temperature and the first to third stages of measuring resistance are performed simultaneously.

[0045] In one specific example, the charging voltage in the first-first stage of charging and discharging may be the shipping voltage. This charging voltage refers to the initial charging voltage at which the lithium secondary battery is produced and shipped from the factory.

[0046] Furthermore, the first three steps of measuring the resistance of the battery cell can be performed using the Direct Current Internal Resistance (DCIR) measurement method. Specifically, the resistance value can be obtained by applying charge and discharge current values ​​for each C-rate as pulses over a certain period of time, and converting the resistance value based on the change in voltage and current.

[0047] On the other hand, the resistance of a battery cell can be affected by various factors, and a battery cell whose temperature rises during the charging and discharging process will begin to cool down once charging and discharging is complete. In other words, the delay time between the end of charging and discharging and the time of resistance measurement may be directly related to the amount of temperature decrease of the battery cell.

[0048] In this respect, differences in specific heat among the individual materials that make up a battery cell, such as the positive electrode material, negative electrode material, separation membrane material, electrolyte material, or type of additive, can affect the amount of temperature decrease of the battery cell.

[0049] Even when measuring temperature and resistance in the same area for battery cells that have completed charging and discharging, depending on the working environment, it may be possible to measure resistance after a certain amount of time has elapsed since charging and discharging.

[0050] Therefore, the first step further includes a step of measuring the time required from the end of the activation process to the time of resistance measurement, and the required time is divided into certain intervals and classified, and the resistance values ​​due to temperature in the first step can be compiled into a database taking the required time into further consideration.

[0051] Specifically, the unit for classifying the required time can be set to 1 minute or 5 minutes, including the battery cell with the longest required time.

[0052] For example, if the unit time is 1 minute, the required time can be classified in 1-minute intervals, such as battery cells with a required time of 0 to 1 minute, battery cells with a required time of more than 1 minute but up to 2 minutes, and further battery cells with a required time of more than 2 minutes but up to 3 minutes. After classifying the battery cells in this way, the temperature and resistance of all battery cells are measured and recorded and added to a database.

[0053] In this way, criteria for determining good and defective products can be set as needed within the database of documents.

[0054] Furthermore, the electrical characteristics of the battery cells may change depending on the charge and discharge conditions such as current and voltage in the 1-1 stage and the state of charge (SOC) value, and the electrical characteristics of the battery cells may also change depending on the lot (LOT) on which the battery cells are produced.

[0055] Therefore, the same type defined in the first stage preferably has one or more identical conditions selected from the group consisting of the type of battery cell based on its appearance, such as pouch-type battery cell, cylindrical battery cell, or prismatic battery cell; the positive electrode material, negative electrode material, separation membrane material, electrolyte material, type of additive; lot (LOT); charge / discharge conditions; and SOC; more preferably two or more identical conditions; and most preferably all identical conditions.

[0056] Next, the second stage involves measuring the temperature and resistance of new battery cells that need to be judged as good or bad, in other words, battery cells that are about to be shipped. Of course, it is obvious that these must be the same type of battery cell as those used in the first stage.

[0057] The third stage involves comparing the temperature and resistance of the new battery cell with the criteria set by the database acquired in the first stage to determine whether it is a good or defective product.

[0058] The temperature and resistance of the battery cell measured in the second stage can be compared with the good and bad product judgment criteria in the database to determine whether the battery cell is good or bad.

[0059] Thus, the present invention pre-measures the temperature-dependent resistance of multiple battery cells, and additionally, reflects the time elapsed from charging / discharging to resistance measurement in the temperature-dependent resistance value, creating a database to establish a defect judgment criterion. Therefore, it is possible to determine whether a new battery cell is defective simply by matching its temperature and resistance value with the database data.

[0060] Therefore, in order to determine whether a new battery cell is good or bad, it is possible to determine its quality using a simple method that matches the temperature and resistance value of the new battery cell with the already established failure criteria, without having to consider the time elapsed from charge / discharge to resistance measurement or the measurement space.

[0061] On the other hand, generally, due to the characteristics of manual logistics lines, the time required from charging / discharging to resistance measurement is longer or less consistent than that of automatic logistics lines. As mentioned above, the longer the time required, the greater the temperature change during which the battery cells are cooled. Therefore, in order to improve the reliability of the measured resistance value, it is necessary to take this time into consideration.

[0062] Therefore, since the present invention databases the resistance values ​​based on temperature, taking into account the time required, the battery cell defect determination method, including the first to third stages, can be applied to both manual and automatic logistics lines. Thus, even when using a manual logistics line with low reliability regarding resistance values, the present invention makes it possible to quickly and accurately determine the quality of battery cells.

[0063] On the other hand, a fourth stage may be included for classifying the battery cells that were determined to be defective in the third stage. If the cause of the defect can be removed, the defective battery cells are sent to the shipping process after the cause of the defect is removed; if the cause of the defect cannot be removed, they are discarded. Of course, battery cells that were determined to be good in the third stage are sent to the shipping process.

[0064] The battery cells in the present invention include pouch-type battery cells in which the electrode assembly is housed in a pouch-type battery case made of a laminate sheet, cylindrical battery cells or rectangular battery cells in which the electrode assembly is inserted into a cylindrical or rectangular can made of a metal material and sealed, and a description of the pouch-type battery cell, cylindrical battery cell or rectangular battery cell can be applied using already known technology, so a specific description is omitted in this specification.

[0065] A person with ordinary skill in the field to which this invention belongs will be able to make various applications and modifications within the scope of this invention based on the above description.

Claims

1. The first step involves obtaining temperature-dependent resistance values ​​for multiple battery cells belonging to the same type, A second step involves measuring the temperature and resistance of other battery cells that belong to the same type as described above but do not correspond to the aforementioned multiple battery cells, A method for determining whether a battery cell is defective, comprising: a third step of determining whether the measured values ​​of the other battery cells meet the good product standards already set using the data obtained in the first step.

2. The first stage is, The first stage involves charging and discharging the battery cells to activate them, The first and second stages involve measuring the temperature of the battery cells, A method for determining a defective battery cell according to claim 1, comprising the steps of measuring the resistance of the battery cell.

3. The battery cell defect determination method according to claim 2, wherein the area in which the first-first stage of charging and discharging is performed is a separate area separated from the area in which the first-second stage of measuring temperature and the first-third stage of measuring resistance are performed.

4. The battery cell defect detection method according to claim 2, wherein the first and second steps of measuring temperature and the first to third steps of measuring resistance are performed simultaneously.

5. The process further includes a step of measuring the time required from the completion of the first-first charging / discharging stage to the first-third stage of measuring the resistance, The aforementioned required time is divided into certain intervals and classified, The method for determining a battery cell defect according to any one of claims 2 to 4, wherein the resistance value due to the temperature in the first stage is stored in a database, taking into further consideration the time required.

6. The battery cell defect detection method according to claim 2, wherein the charging voltage in the first-first stage of charging and discharging is the shipping voltage.

7. The battery cell defect detection method according to claim 1, wherein the first to third steps are applicable to both manual and automated logistics lines.

8. The method for determining a defect in a battery cell according to claim 1, wherein the battery cell is a pouch-type battery cell, a cylindrical battery cell, or a prismatic battery cell.

9. The method for determining a defective battery cell according to claim 1, wherein the same type is defined as having the same one or more conditions selected from the group consisting of the type based on the appearance of the battery cell, the positive electrode material, the negative electrode material, the separation membrane material, the electrolyte material, the type of additive, the lot (LOT), the charge / discharge conditions, and the SOC.

10. The method for determining defects in battery cells according to claim 1, further comprising a fourth step of classifying the battery cells determined to be defective in the third step.

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