Method for determining defect of battery cell

Abstract

The present invention relates to a method comprising: a first step of obtaining resistance values according to the temperature for a plurality of battery cells belonging to the same type; a second step of measuring the temperature and resistance of a different battery cell belonging to the same type but not corresponding to the plurality of battery cells; and a third step of determining whether measurement values of the different battery cell correspond to preset good quality criteria by using data obtained in the first step, such that the method is capable of determining whether the battery cell is defective by means of values measured in the second step without measuring the time required between the first step and the second step.

Description

Method for determining defective battery cells

[0001] This application claims the benefit of priority to Korean Patent Application No. 2023-0127851, filed September 25, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for determining defects in battery cells. Specifically, the method allows for easy, simple, and accurate identification of defects in completed battery cells, regardless of logistics line delays, by creating a database of resistance values ​​based on the temperature of a battery cell in a normal state.

[0003]

[0004] Lithium secondary batteries, which are charged and discharged by the movement of lithium ions, have the advantages of high energy density and high charging voltage, and are used not only in the small battery cell field used in mobile devices and small electronic products, but also in the medium and large battery pack field used as an energy source for electric vehicles and power storage systems that require high output and high voltage.

[0005] The manufacturing process of a lithium secondary battery includes a plate manufacturing process in which electrode plates are manufactured and laminated or wound together with a separator to form an electrode assembly, an assembly process in which the electrode assembly is placed in a battery case, an electrolyte is injected, and then sealed, and a formation process including a charging / discharging process and an aging process of the lithium secondary battery thus assembled. During the formation process, defective products can be sorted out and performance can be improved.

[0006] In particular, the Mars process includes an activation process that charges and discharges lithium secondary batteries to impart electrical characteristics to the completed battery cells, and a process that measures the resistance of the shipped, charged battery cells to check for defects in the completed battery cells.

[0007] Depending on the production environment, battery cell charging / discharging and resistance measurement may be performed in separate areas. Therefore, the process of charging / discharging and measuring resistance may not be continuous. Furthermore, the time between charging / discharging and resistance measurement may vary depending on the progress of the logistics line.

[0008] Moreover, in the case of manual logistics lines, the delay time from charging to resistance measurement may be longer than that of automatic logistics lines.

[0009] During the charging and discharging process of lithium secondary batteries, the temperature of the battery cells increases. Even if the same type of battery cells are charged and discharged under the same conditions, the temperature after charging and discharging is not constant, so temperature deviations may occur between battery cells.

[0010] Additionally, the rate of temperature decrease in a battery cell varies depending on the delay between charging and discharging and the measurement of resistance. Specifically, battery cell temperature is a factor affecting resistance, and if the delay between charging and discharging is long, the cell temperature may decrease. Similarly, if the temperature of the battery cell being measured is not uniform, the measurement environment may vary, posing a risk to the reliability of the measured resistance.

[0011] In this regard, Patent Document 1 relates to a semiconductor device capable of precisely detecting a counterfeit battery cell, 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 counts the number of charge / discharge cycles of the battery cell, measures the charge rate of the battery cell based on the voltage, and can calculate the internal resistance of the battery cell based on the voltage and current. That is, Patent Document 1 determines whether the battery cell is counterfeit by calculating the internal resistance at the time of shipment of the battery cell by normalizing the internal resistance based on the number of cycles, temperature, and charge rate.

[0012] Patent Document 1 presents a device and method for determining whether a battery cell is non-genuine by normalizing the internal resistance based on the number of cycles, temperature, and charge rate of the battery cell. However, as a technology for determining whether a battery cell on the market is non-genuine, it does not present a method for accurately determining a defective battery cell on the same basis when the charging / discharging stage and the resistance measurement stage are performed in separate areas before the shipment of the completed battery cell, or when the charging / discharging stage and the resistance measurement stage have a certain time interval.

[0013] Patent Document 2 relates to a method and device for measuring internal resistance of a battery, comprising: a step of monitoring battery voltage and current in real time; a step of monitoring a voltage increase and starting to collect the voltage and current after the current decreases, and storing the collected voltage and current in a data set; and a step of determining internal resistance of the battery using the voltage and current of the data set after monitoring that the current has reached a current threshold.

[0014] Patent Document 2 proposes a method for determining the internal resistance of a battery by using the results of measuring the voltage and current of the battery without measuring the internal resistance of the battery. However, it does not propose a solution to the problem of the resistance value changing due to the delay in the time between charging and discharging and resistance measurement in the formation process of a lithium secondary battery.

[0015] Therefore, before shipment of the battery cell, a method is needed to determine whether the battery cell is defective, regardless of whether the charging / discharging step for imparting electrical characteristics to the battery cell and the resistance measurement step for checking for defects are performed in separate areas or the time required from charging / discharging to resistance measurement is carried out.

[0016]

[0017] (Prior art literature)

[0018] (Patent Document 1) Japanese Patent Publication No. 2019-114437 (July 11, 2019)

[0019] (Patent Document 2) Chinese Patent Publication No. 115902672 (April 4, 2023)

[0020]

[0021] The present invention is intended to solve the above-mentioned problem, and provides a method for determining whether a battery cell is defective, which can accurately determine whether or not it is defective, regardless of the time required from charging and discharging the battery cell to measuring resistance for determining whether or not it is defective during the manufacturing process of a lithium secondary battery.

[0022]

[0023] A method for determining a defect in a battery cell according to the present invention to achieve this purpose may include a first step of obtaining a resistance value according to temperature for a plurality of battery cells belonging to the same type, a second step of measuring the temperature and resistance of another battery cell belonging to the same type but not corresponding to the plurality of battery cells, and a third step of determining whether the measured value of the other battery cell corresponds to a preset good product standard using the data obtained in the first step.

[0024] The above first step may include a step 1-1 for charging and discharging to activate the battery cell, a step 1-2 for measuring the temperature of the battery cell, and a step 1-3 for measuring the resistance of the battery cell.

[0025] The area where the above-mentioned charging and discharging step 1-1 is performed may be a separate area from the area where the above-mentioned temperature measuring step 1-2 and the above-mentioned resistance measuring step 1-3 are performed.

[0026] Steps 1-2 of measuring the temperature and steps 1-3 of measuring the resistance can be performed simultaneously.

[0027] The method further includes a step of measuring the time required until the resistance measurement after the completion of the charging / discharging process, dividing the required time into certain sections and classifying them, and the resistance value according to the temperature of the first step can be stored in a database by further considering the required time.

[0028] The charging voltage of the above-mentioned 1-1 stage charging and discharging may be the shipping voltage.

[0029] The above steps 1 to 3 can be applied to both manual logistics lines and automatic logistics lines.

[0030] The above battery cell may be a pouch-shaped battery cell, a cylindrical battery cell, or a square battery cell.

[0031] The above same type may have at least one condition selected from the group consisting of the type according to the appearance of the battery cell, positive electrode material, negative electrode material, separator material, electrolyte material, additive type, lot (LOT), charge / discharge condition, and SOC.

[0032] A fourth step of classifying battery cells judged as defective in the third step may be further included.

[0033] The present invention can also be provided in a form in which various means for solving the above problem are combined.

[0034]

[0035] As described above, when using the method for determining whether a battery cell is defective according to the present invention, it is possible to easily and accurately determine whether or not a battery cell is defective without being affected by the timing of resistance measurement after charging and discharging for activation of the completed battery cell.

[0036] In addition, even in manual logistics lines where the time required for resistance measurement after charging and discharging is long, it is possible to quickly determine whether a battery cell is defective by measuring the temperature and resistance value without having to separately measure the required time.

[0037]

[0038] Figure 1 is a flowchart of a method for determining defects in a battery cell according to the present invention.

[0039]

[0040] Hereinafter, with reference to the attached drawings, embodiments of the present invention will be described in detail, so that those skilled in the art can easily implement the present invention. When describing the operating principles of the embodiments of the present invention in detail, detailed descriptions of known functions or components will be omitted if they are deemed to unnecessarily obscure the gist of the present invention.

[0041] Parts with similar functions and actions are designated by the same drawing reference numerals throughout the drawings. Throughout the specification, when a part is said to be connected to another part, this includes not only direct connections but also indirect connections with other elements intervening. Furthermore, inclusion of a component does not exclude other components unless otherwise specifically stated, but rather implies the inclusion of additional components.

[0042] The description that concretizes or adds to the components may be applied to all inventions unless there is a special limitation, and is not limited to the description of a specific invention.

[0043] Throughout the description and claims of the invention herein, the singular includes the plural unless otherwise stated.

[0044] Throughout the description and claims of the present invention, the term "or" includes "and" unless otherwise stated. Therefore, "comprising A or B" means all three cases of including A, including B, or including A and B.

[0045] The present invention is described in detail with examples according to the drawings.

[0046] Fig. 1 is a flowchart of a method for determining a defect in a battery cell according to the present invention. Referring to Fig. 1, the method for determining a defect in a battery cell according to the present invention may include a first step of obtaining a resistance value according to temperature for a plurality of battery cells belonging to the same type, a second step of measuring the temperature and resistance of another battery cell belonging to the same type but not corresponding to the plurality of battery cells, and a third step of determining whether the measured value of the other battery cell corresponds to a preset good product standard using the data obtained in the first step.

[0047] First, in the first step, resistance values ​​according to temperature are obtained for battery cells corresponding to good products and stored in a database, so that a standard for determining whether a product is good or bad can be established.

[0048] Specifically, the first step may include a step 1-1 of charging and discharging to activate the battery cell, a step 1-2 of measuring the temperature of the battery cell, and a step 1-3 of measuring the resistance of the battery cell.

[0049] For example, a battery manufacturing plant might be divided into a battery manufacturing building and a formation building, and the battery manufacturing process might include a plate manufacturing process, an assembly process, and a formation process. The plate manufacturing and assembly processes might be conducted in the battery manufacturing building, and assembled battery cells might be moved to the formation building for charging / discharging and defect inspection.

[0050] The above first step may be carried out through an automatic logistics line in which battery cells are transported via a conveyor within the Mars building, or through a manual logistics line in which cells are transported by workers or robots, and transport may be delayed depending on the situation of the logistics line.

[0051] Steps 1-1, 1-2, and 1-3 are performed within the Mars building, but at least one of these steps may be performed in a separate area. For example, the area where Step 1-1, which involves charging and discharging, is performed may be separated from the area where Step 1-2, which involves measuring temperature, and Step 1-3, which involves measuring resistance.

[0052] That is, a battery cell that has completed charging and discharging may be transferred from the charging and discharging area to the resistance measurement area, and then resistance measurement may be performed in the resistance measurement area. Depending on the transport situation of the logistics line, the time required from charging and discharging to resistance measurement may differ by more than 300 minutes.

[0053] Since temperature is a factor that affects the resistance value, steps 1-2 for measuring temperature and steps 1-3 for measuring resistance must be performed simultaneously to obtain an accurate resistance value according to temperature.

[0054] In one specific example, the charging voltage of the first-stage charging / discharging step may be the shipping voltage. The charging voltage refers to the initial charging voltage when the lithium secondary battery is produced and shipped from the factory.

[0055] In addition, steps 1-3 of measuring the resistance of the battery cell can be performed according to the DCIR (Direct Current Internal Resistance) measurement method, and specifically, the resistance value can be obtained by providing the charge / discharge current value in pulse form for a certain period of time for each C-rate and converting the resistance value into the amount of change in voltage and current.

[0056] Meanwhile, the resistance of a battery cell can be influenced by various factors. A battery cell whose temperature increases during the charging and discharging process begins to cool once the charging and discharging process is complete. Therefore, the delay between the end of the charging and discharging process and the measurement of resistance can be directly related to the amount of temperature decrease in the battery cell.

[0057] In this respect, the difference in specific heat of individual materials that make up the battery cell, such as the cathode material, anode material, separator material, electrolyte material, or type of additive, can affect the amount of temperature reduction in the battery cell.

[0058]

[0059] Even if the temperature and resistance of a battery cell that has been charged and discharged are measured within the same area, the resistance measurement may be performed after a certain period of time has passed after charging and discharging, depending on the working environment.

[0060] Accordingly, the first step further includes a step of measuring the time required from the end of the activation process to the measurement of the resistance, and classifies the required time by dividing it into certain sections, and the resistance value according to the temperature of the first step can be databased by further considering the required time.

[0061] Specifically, the battery cell with the longest required time can be included, but the unit for classifying the required time can be set to 1 minute, 5 minutes, etc.

[0062] For example, if the unit time is 1 minute, the required time can be classified into battery cells with a required time of 0 to 1 minute, battery cells with a required time exceeding 1 minute to 2 minutes, and battery cells with a required time exceeding 2 minutes to 3 minutes, at 1-minute intervals. After classifying the battery cells in this way, the temperature and resistance of all battery cells are measured and recorded to be stored in a database.

[0063] Within the data databased in this way, criteria for judging good and bad products can be set as needed.

[0064] In addition, the electrical characteristics of the battery cell may vary depending on the charge / discharge conditions such as current and voltage of the above-mentioned step 1-1, and the SOC value, and the electrical characteristics of the battery cell may also vary depending on the lot (LOT) that produces the battery cell.

[0065] Therefore, the same type defined in the first step is preferably the same in at least one condition among the group consisting of the type of battery cell, such as a pouch-shaped battery cell, a cylindrical battery cell, or a square battery cell, the type of positive electrode material, the negative electrode material, the separator material, the electrolyte material, the type of additive, the lot (LOT), the charge / discharge condition, and the SOC, more preferably the same in two or more conditions, and most preferably the same in all conditions.

[0066]

[0067] Next, the second step involves measuring the temperature and resistance of new battery cells, i.e., the cells to be shipped, to determine whether they are defective. Of course, it goes without saying that these cells must be of the same type as those used in the first step.

[0068]

[0069] In the third step, when the temperature and resistance of the new battery cell are matched to the criteria set according to the database obtained in the first step, it can be confirmed whether it is a good product or a defective product.

[0070] The temperature and resistance of the battery cell measured in the second step can be input into the criteria for determining whether the battery cell is defective or not based on the database data.

[0071] In this way, the present invention measures the resistance of a plurality of battery cells according to temperature in advance, and additionally, reflects the time required from charging and discharging to the resistance measurement in the resistance value according to temperature and stores it in a database to establish a criterion for determining a defect, so that it is possible to determine whether a new battery cell is defective simply by matching the temperature and resistance value of the new battery cell to the database data.

[0072] Therefore, in order to determine whether a new battery cell is defective, it is possible to determine whether it is defective by a simple method of matching the temperature and resistance value of the new battery cell to a preset defect determination standard, without having to consider the time or measurement space required from the time of charging and discharging to the time of resistance measurement.

[0073] Meanwhile, due to the nature of manual logistics lines, the time required for resistance measurement after charging and discharging is typically longer or more erratic than that required for automated logistics lines. As explained above, the longer this time, the greater the temperature change during battery cell cooling. Therefore, to increase the reliability of measured resistance values, the time required must be taken into account.

[0074] Accordingly, since the present invention considers the above-mentioned time and stores the resistance value according to temperature in a database, the method for determining the defect of a battery cell, including steps 1 through 3, can be applied to both manual and automated logistics lines. Therefore, even when using a manual logistics line with low reliability in resistance value, the present invention can quickly and accurately determine whether a battery cell is defective.

[0075] Meanwhile, a fourth step may be further included to classify battery cells determined to be defective in the third step. If the cause of the defect can be eliminated, the defective battery cells are transferred to the shipping process. If the cause of the defect cannot be eliminated, the cells are discarded. Of course, battery cells determined to be good in the third step are transferred to the shipping process.

[0076] The battery cell of the present invention includes a pouch-type battery cell in which an electrode assembly is accommodated in a pouch-type battery case made of a laminated sheet, a cylindrical battery cell or a square battery cell in which an electrode assembly is inserted and sealed in a cylindrical or square can made of a metal material, and a description of the pouch-type battery cell, cylindrical battery cell or square battery cell is omitted in this specification because already known technologies can be applied.

[0077]

[0078] Anyone with ordinary knowledge in the field to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims

1. A first step of obtaining resistance values ​​according to temperature for multiple battery cells belonging to the same type; A second step of measuring the temperature and resistance of another battery cell belonging to the same type but not corresponding to the plurality of battery cells; and A method for determining a defect in a battery cell, characterized by including a third step of determining whether the measured value of the other battery cell corresponds to a preset good product standard using the data obtained in the first step.

2. In paragraph 1, The above first step is, Step 1-1: Charging and discharging to activate the battery cell; Step 1-2 of measuring the temperature of the battery cell; and A method for determining a defect in a battery cell, characterized by including steps 1-3 of measuring the resistance of the battery cell.

3. In paragraph 2, A method for determining a defect in a battery cell, characterized in that the zone in which the above-mentioned 1-1 step of charging and discharging is performed is a separate zone from the zone in which the 1-2 step of measuring the temperature and the 1-3 step of measuring the resistance are performed.

4. In paragraph 2, A method for determining a defect in a battery cell, characterized in that steps 1-2 of measuring the temperature and steps 1-3 of measuring the resistance are performed simultaneously.

5. In paragraph 2, Further comprising a step of measuring the time required until the resistance measurement after the above charging and discharging process is completed, The above time is divided into certain sections and classified. A method for determining a defect in a battery cell, characterized in that the resistance value according to the temperature of the first step is stored in a database while further considering the required time.

6. In paragraph 2, A method for determining a defect in a battery cell, characterized in that the charging voltage of the first-first stage of charging and discharging is the shipping voltage.

7. In paragraph 1, A method for determining defects in a battery cell, characterized in that the first to third steps above can be applied to both manual logistics lines and automatic logistics lines.

8. In paragraph 1, A method for determining defects in a battery cell, characterized in that the battery cell is a pouch-shaped battery cell, a cylindrical battery cell, or a square battery cell.

9. In paragraph 1, The above-mentioned same type is a method for determining a defect in a battery cell, characterized in that at least one condition selected from the group consisting of a type according to the appearance of the battery cell, a cathode material, a cathode material, a separator material, an electrolyte material, an additive type, a lot (LOT), a charge / discharge condition, and a SOC is the same.

10. In paragraph 1, A method for determining a defect in a battery cell, characterized by further including a fourth step of classifying battery cells determined to be defective in the third step.

Images