Method for manufacturing secondary battery

Abstract

Example embodiments provide a secondary battery manufacturing method. The method includes first-order approximation of a measured open circuit voltage (OCV) based on a square root of the OCV with respect to time, and evaluation of the quality of the battery cell based on the first-order approximation.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a secondary battery. This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0137347, filed on October 16, 2023, the entire contents of which are incorporated herein by reference. Background Technology

[0002] Unlike primary batteries, secondary batteries can be charged and discharged multiple times. They have been widely used as a power source for various types of wireless devices, such as cell phones, laptops, and cordless vacuum cleaners. In recent years, as the manufacturing cost per unit capacity of secondary batteries has decreased significantly due to improved energy density and economies of scale, and as the range of battery electric vehicles (BEVs) has increased to the same level as that of gasoline-powered vehicles, the primary use of secondary batteries is shifting from mobile devices to mobility services.

[0003] Secondary batteries are manufactured through an electrode process, an assembly process, and an activation process. In the electrode process, an electrode assembly including a positive electrode, a negative electrode, and a separator is provided. In the assembly process, the electrode assembly and electrolyte are embedded into a casing. In the activation process, the assembled battery cells are charged, discharged, and aged. Through the activation process, the battery cells are activated and stabilized using electrical energy. Summary of the Invention

[0004] Technical issues

[0005] The present invention aims to provide a method for manufacturing secondary batteries with improved productivity.

[0006] Technical solution

[0007] An exemplary embodiment of the present invention provides a method for manufacturing a secondary battery. The method includes: measuring the open-circuit voltage (OCV) of a battery cell at a first time point, wherein the first time point is located within a range of approximately 24 hours to approximately 150 hours after the battery cell has been charged or discharged; measuring the OCV of the battery cell at a second time point, wherein the second time point is after the first time point; and calculating the OCV of the battery cell at a third time point based on the OCV of the battery cell at the first time point, the OCV of the battery cell at the second time point, and the following formula.

[0008] [formula]

[0009] Here, ΔOCV represents the rate of change of OCV between two time points. Let represent the rate of change of the square root of time between two time points, and let a be the rate of change constant of OCV.

[0010] The third time point can be located within the range of 48 hours to 200 hours after the charging or discharging of a single battery cell.

[0011] The method may also include calculating the OCV of a single battery cell at a first time point.

[0012] The first time point can be located within the range of 24 hours to 150 hours after the charging or discharging of a single battery cell.

[0013] The method may also include determining the mass of a battery cell based on the calculated OCV of the battery cell at a first time point and the calculated OCV of the battery cell at a third time point.

[0014] The method may further include: when the difference between the calculated OCV of a battery cell at a first time point and the calculated OCV of a battery cell at a third time point is within the range of 0mV to 50mV, the battery cell is determined to be normal.

[0015] The method may also include measuring the OCV of a single battery cell at a third time point.

[0016] The method may also include determining the quality of a battery cell based on the measured OCV of the battery cell at a third time point and the calculated OCV of the battery cell at the third time point.

[0017] The method may further include: when the measured OCV of a battery cell at a third time point is lower than the calculated OCV of the battery cell at the third time point, the battery cell is identified as defective.

[0018] An example embodiment provides a method for manufacturing a secondary battery. The method includes: measuring the initial velocities (OCV) of a single battery cell at a first time point, wherein the first time point is within a range of 12 hours to 150 hours from the start of charging or discharging the battery cell; measuring the OCV of the battery cell at a second time point, wherein the second time point is after the first time point; and calculating the rate of change constant of the OCV of the battery cell based on the OCV of the battery cell at the first time point, the OCV of the battery cell at the second time point, and the following formula.

[0019] [formula]

[0020] Here, ΔOCV represents the rate of change of OCV between two time points. Let represent the rate of change of the square root of time between two time points, and let a be the rate of change constant of OCV.

[0021] The method may also include determining the mass of a single cell based on a rate of change constant.

[0022] The method may also include: when the rate of change constant is -100 mV / h 1 / 2 Up to 0mV / h 1 / 2 When the range is within the specified range, the individual battery cell is considered normal.

[0023] An example embodiment provides a method for manufacturing a secondary battery. The method includes: measuring the initial velocities (OCV) of a single battery cell at a first time point, wherein the first time point is within a range of 12 to 150 hours after the battery cell has been charged or discharged; measuring the OCV of a single battery cell at a second time point, wherein the second time point is after the first time point; and calculating the OCV of the battery cell at the first time point and the OCV of the battery cell at the second time point based on the OCV of the battery cell at the first time point and the OCV of the battery cell at the second time point, wherein the OCV of the battery cell at the first time point and the OCV of the battery cell at the third time point are calculated using a first-order approximation of the square root of time.

[0024] Beneficial effects

[0025] According to an exemplary embodiment of the present invention, the time required for open-circuit voltage (OCV) checks after the activation process can be reduced. Therefore, the yield and cost of manufacturing secondary batteries can be reduced.

[0026] The effects achievable according to the exemplary embodiments of the present invention are not limited to those described above, and those skilled in the art to which the exemplary embodiments of the present invention pertain will clearly deduce and understand other effects not described herein based on the following description. In other words, those skilled in the art can deduce unintended effects achieved in implementing the exemplary embodiments of the present invention. Attached Figure Description

[0027] Figure 1 This is a flowchart of a secondary battery manufacturing method according to an example embodiment.

[0028] Figure 2 This is a flowchart of the inspection of individual battery cells based on open-circuit voltage (OCV).

[0029] Figure 3 It is a chart used to describe the OCV-based inspection of individual battery cells.

[0030] Figure 4 It is a chart used to describe the OCV-based inspection of individual battery cells.

[0031] Figure 5 An OCV-based inspection of a battery cell is shown according to other example embodiments.

[0032] Figure 6An OCV-based inspection of a battery cell is shown according to other example embodiments.

[0033] Figure 7 An OCV-based inspection of a battery cell is shown according to other example embodiments. Detailed Implementation

[0034] In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings. Before describing the embodiments of the invention, the terms or expressions used in this specification and claims should not be construed as limited to what is commonly understood or as defined in a common dictionary, but should be understood based on the meanings and concepts corresponding to the invention, as the inventors of this application may appropriately define these terms or expressions to best interpret the principles of the invention.

[0035] Therefore, the embodiments described herein and the configurations shown in the accompanying drawings are merely examples of the present invention and do not reflect all the technical ideas of the present invention. It should be understood that, as of the filing date of this application, various equivalent schemes and modifications to these configurations may already exist.

[0036] When it is determined that well-known configurations or functions related to the description of the present invention would obscure the subject matter of the invention due to unnecessary details, they will not be described in detail.

[0037] Because embodiments of the invention are provided to explain the invention more fully to those skilled in the art, the shapes, dimensions, etc., of the components shown in the accompanying drawings may be exaggerated, omitted, or illustrated schematically for clarity. Therefore, they should not be construed as representing the exact dimensions or proportions of the components.

[0038] (First embodiment)

[0039] Figure 1 A method for manufacturing a secondary battery according to an example embodiment is shown.

[0040] refer to Figure 1 In P110, individual battery cells can be charged or discharged. These individual cells can be rechargeable battery cells. A battery cell is the basic unit of a lithium-ion battery (i.e., a rechargeable battery). A battery cell includes electrode assemblies, an electrolyte, and a casing. Based on the configuration of the electrode assemblies and electrolyte, battery cells can be classified as lithium-ion batteries, lithium-ion polymer batteries, lithium polymer batteries, etc. Due to the low possibility of electrolyte leakage and ease of manufacturing, lithium-ion polymer batteries are gaining a growing market share in the rechargeable battery field.

[0041] Based on the shape of the battery casing, battery cells can be classified as cylindrical, prismatic, or pouch-type battery cells. Cylindrical batteries include electrode assemblies and a cylindrical metal can for housing the electrode assemblies. Prismatic batteries include electrode assemblies and a prismatic metal can for housing the electrode assemblies. Pouch-type battery cells include electrode assemblies and a pouch-shaped casing for housing the electrode assemblies.

[0042] Electrode assemblies may include a positive electrode, a negative electrode, and a separator between the positive and negative electrodes. Depending on their form, electrode assemblies can be classified as jelly roll electrode assemblies or stacked electrode assemblies. Jelly roll electrode assemblies are manufactured by winding a positive electrode, a negative electrode, and a separator inserted between them. Stacked electrode assemblies include multiple positive electrodes, multiple negative electrodes, and multiple separators inserted between them, stacked sequentially.

[0043] The positive electrode may include a positive current collector and a positive active material. The negative electrode may include a negative current collector and a negative active material.

[0044] The thickness of the positive electrode current collector can range from about 3 μm to about 500 μm. The positive electrode current collector should not cause chemical changes in the final manufactured secondary battery and can have high conductivity. The positive electrode current collector can include, for example, stainless steel, nickel, titanium, sintered carbon, and aluminum. It can also include stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The surface of the positive electrode current collector can include a finely textured, uneven structure to increase the adhesion of the active material. The positive electrode current collector can be in the form of a thin film, sheet, foil, mesh, porous material, foam material, nonwoven fabric, etc.

[0045] The thickness of the negative electrode current collector can range from approximately 3 μm to approximately 500 μm. The negative electrode current collector should not cause chemical changes in the final manufactured secondary battery and can have high conductivity. The negative electrode current collector can include stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum-cadmium alloys. It can also include stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The surface of the negative electrode current collector can include a finely textured, uneven structure to increase the adhesion of the active material. The negative electrode current collector can be in the form of a thin film, sheet, foil, mesh, porous structure, foam material, nonwoven fabric, etc.

[0046] A positive electrode active material is a material that can induce an electrochemical reaction. Positive electrode active materials can be lithium transition metal oxides. For example, positive electrode active materials can include: layered compounds substituted with one or more transition metals, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); lithium manganese oxide substituted with one or more transition metals; or lithium NiO2 oxides. 1-y M yA lithium nickel-based oxide represented by the chemical formula of O2 (where M is Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, and 0.01 ≤ y ≤ 0.7); composed of Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e） A lithium nickel cobalt manganese composite oxide represented by the chemical formula of A, such as Li 1+z Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2 or Li 1+z Ni 0.4 Mn 0.4 Co 0.2 O2 (where, -0.5 ≤ z ≤ 0.5, 0.1 ≤ b ≤ 0.8, 0.1 ≤ c ≤ 0.8, 0 ≤ d ≤ 0.2, 0 ≤ e ≤ 0.2, b + c + d < 1, M is Al, Mg, Cr, Ti, Si or Y, and A is F, P or Cl); composed of Li 1+ x M 1-y M' y PO 4-z X z An olivine-based lithium metal phosphate represented by the chemical formula of (where M is a transition metal, and more specifically Fe, Mn, Co or Ni, M' is Al, Mg or Ti, X is F, S or N, -0.5 ≤ x ≤ +0.5, 0 ≤ y ≤ 0.5 and 0 ≤ z ≤ 0.1).

[0047] The negative electrode active material may include, for example, carbon, such as non-graphitized carbon or graphite-based carbon. The negative electrode active material may include, for example, metal composite oxides, such as Li x Fe2O3 (0 ≤ x ≤ 1), LixWO2 (0 ≤ x ≤ 1) or Sn x Me 1-x Me' y O z (where Me is Mn, Fe, Pb or Ge, Me' is Al, B, P, Si, an element of Group I, Group II or Group III in the periodic table, or a halogen, 0 < x ≤ 1, 1 ≤ y ≤ 3 and 1 ≤ z ≤ 8). The negative electrode active material may include, for example, lithium metal, lithium alloy, silicon-based alloy and tin-based alloy. The negative electrode active material may include, for example, metal oxides, such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 or Bi2O5. The negative electrode active material may include, for example, conductive polymers, such as polyacetylene, Li-Co-Ni-based materials, etc.

[0048] Battery cells can be provided through electrode processes and assembly processes. Electrode processes may include mixing, coating, rolling, optional cutting, and grooving processes. Assembly processes may include embedding electrode assemblies into a housing, and additionally injecting electrolyte into the housing.

[0049] While a battery cell is being charged or discharged, it can be pressurized using a pressurizing fixture. Pressurizing the battery cell prevents gas trapping and lithium plating, and improves the uniformity of the solid electrolyte interphase (SEI) film. Battery cells with a uniform SEI film can have relatively short charge or discharge times.

[0050] An SEI film can be formed on the surface of the negative electrode during the initial charging. The SEI film is a thin film formed on the surface of the negative electrode material during the first charging of the battery cell after its manufacture. When the battery cell is charged, lithium ions in the cell can migrate to the negative electrode, and an SEI film may form on the surface of the negative electrode material due to the chemical reactions that occur during the initial electrolysis of the electrolyte materials during the migration of lithium ions. The SEI film can be a type of separator. As lithium ions migrate from the positive electrode to the negative electrode to charge the battery, the SEI film prevents additional decomposition reactions of the electrolyte.

[0051] Next, in P120, an aging process can be performed on the individual battery cells. During the aging process, the battery cells can be stored at room temperature for a certain period (30 minutes to 3 hours, as a non-limiting example) to stabilize the cells before charging or discharging. The key to the aging process is to uniformly distribute the electrolyte within the pouch cells, allowing it to permeate both the positive and negative electrodes evenly. The aging process can enhance lithium-ion mobility.

[0052] Next, in P130, a degassing process can be performed on the individual battery cells. During the charging / discharging and aging processes, gases may be generated inside the battery cells. The degassing process removes these gases from the inside of the battery cells.

[0053] Next, in P140, performance checks can be performed on individual battery cells. Performance checks may include capacity checks and checks for screening for defects.

[0054] Subsequently, in P150, an open-circuit voltage (OCV) based inspection can be performed on the individual battery cells. This OCV-based inspection allows for the selection of battery cells with low-voltage defects. Low-voltage defects in battery cells can be caused by metallic foreign objects inside the cell. For example, when the positive electrode of a battery cell contains metallic foreign objects such as iron or copper, these foreign objects can grow into dendrites on the negative electrode. Dendrites cause unwanted short circuits inside the battery cell, leading to cell failure and fire.

[0055] Figure 2 This is a flowchart of an OCV-based inspection of a battery cell according to an example embodiment.

[0056] Figure 3 This is a graph used to describe the OCV-based inspection of a battery cell according to an example embodiment. Figure 3 In the diagram, the vertical axis represents the OCV of a single battery cell, while the horizontal axis represents the square root of time.

[0057] Figure 4 This is a graph used to describe the OCV-based inspection of a battery cell according to an example embodiment. Figure 4 In the diagram, the vertical axis represents the OCV of a single battery cell, while the horizontal axis represents time.

[0058] refer to Figure 2 and Figure 3 Performing an OCV-based check on a battery cell (P150) may include measuring the OCV of the battery cell at a first time point t1 (P151), measuring the OCV of the battery cell at a second time point t2 (P153), calculating the OCV of the battery cell at the first time point t1 and the OCV of the battery cell at a third time point t3 (P155), and comparing the calculated OCV of the battery cell at the first time point t1 with the calculated OCV of the battery cell at the third time point t3 (P157).

[0059] The second time point t2 can occur after the first time point t1. In other words, the second time point t2 can appear some time after the first time point t1. For example... Figure 4As shown, the activation process FR of a battery cell may include one or more charging segments CR and one or more discharging segments DR. A first time point t1 may be located within approximately 24 hours to 150 hours from the start of charging or discharging the battery cell. A second time point t2 may be located after the first time point t1. The time difference between the first time point t1 and the second time point t2 may be within the range of approximately 0 hours to approximately 96 hours. As a non-limiting example, the end point of the last charging segment in the one or more charging segments CR may be a reference point between the first time point t1 and the second time point t2. Alternatively, the start and end points of each of the one or more charging segments CR and the one or more discharging segments DR may be reference points between the first time point t1 and the second time point t2.

[0060] like Figure 3 As shown, the change in the OCV of a single battery cell in a specific segment can roughly follow the following formula 1. Figure 3 In the chart, data points based on measurements are indicated by points, and approximate expressions are represented by dashed lines.

[0061] [Formula 1]

[0062] In Formula 1, t represents time, a is a constant representing the rate of change of OCV with respect to the square root of time, and b is a constant representing the offset. That is, within a specific segment, OCV can be approximated by the square root of time in a first-order manner. More specifically, as... Figure 3 As shown in the experimental examples, the OCV can be approximated by the square root of time over a period of approximately 12 hours to approximately 16 days after a single cell is charged or discharged.

[0063] In P115, the OCV of a single cell at the first time point t1 and the third time point t3 can be calculated based on Formula 1 above or Formula 2 derived from Formula 1.

[0064] [Formula 2]

[0065] In Formula 2, ΔOCV represents the rate of change of OCV between two time points. Let represent the rate of change of the square root of time between two time points, and let a be a constant representing the rate of change of OCV.

[0066] In addition to Formula 1 or 2, the OCV of a battery cell at the first time point t1' and the OCV of the battery cell at the third time point t3 can also be calculated based on the OCV of the battery cell measured at the first time point t1 and the OCV of the battery cell measured at the second time point t2. More specifically, the rate of change constant and the offset constant can be determined by substituting the OCV of the battery cell measured at the first time point t1 and the OCV of the battery cell measured at the second time point t2 into Formula 1 or 2.

[0067] Here, due to measurement tolerances, the OCV measured at the first time point t1 may differ from the OCV measured at the first time point t1' where the actual measurement is to be performed. In this example, the OCV is measured at the first time point t1' where the actual measurement is to be performed to eliminate errors caused by measurement tolerances. Therefore, when performing OCV checks on multiple battery cells, errors in the quality of battery cells due to randomness at measurement time points can be prevented, and the consistency and predictability of battery cell manufacturing can be improved. Since the first time point t1' and the first time point t1 are within the tolerance range, according to the example embodiment, the accuracy of the battery quality judgment may not deteriorate regardless of whether the calculated OCV at the first time point t1' is used. To distinguish between the first time point t1' and the first time point t1, the first time point t1' can be referred to as the expected time point, while the first time point t1 can be referred to as the actual measurement time point.

[0068] In addition to the first time point t1', the third time point t3 can also be included within the range where the first-order approximations of Equations 1 and 2 hold. The third time point t3 can occur after the first time point t1 and the second time point t2. The third time point t3 can occur some time after the second time point t2. The third time point t3 can be located within the range of approximately 48 hours to approximately 200 hours after the charging or discharging of a single battery cell.

[0069] The OCV of a single battery cell at the first time point t1' and the OCV of a single battery cell at the third time point t3 can be calculated based on Formula 1 or 2, the measured OCV at the first time point t1, and the measured OCV at the second time point t2. For example, the rate of change constant and the offset constant can be determined according to Formula 1 above based on the first time point t1, the OCV of the single battery cell at the first time point t1, the second time point t2, and the OCV of the single battery cell at the second time point t2. Then, the OCV of the single battery cell at the first time point t1' is calculated by substituting the first time point t1' into Formula 1, and the OCV at the third time point t3 can be calculated by substituting the third time point t3 into Formula 1.

[0070] As another example, the rate of change constant can be determined by formula 2 based on the first time point t1, the OCV of the battery cell at the first time point t1, the second time point t2, and the OCV of the battery cell at the second time point t2. Then, the OCV at the first time point t1' can be calculated by substituting the first time point t1, the OCV at the first time point t1, and the first time point t1' into formula 2. The OCV at the third time point t3 can be calculated by substituting the first time point t1, the OCV at the first time point t1, and the third time point t3 into formula 2.

[0071] In P157, the quality of a battery cell can be determined based on the calculated OCV of the battery cell at the first time point t1' and the calculated OCV of the battery cell at the third time point t3. For example, when the difference between the calculated OCV of the battery cell at the first time point t1' and the calculated OCV of the battery cell at the third time point t3 is in the range of about 0mV to about 50mV, the battery cell can be determined to be normal.

[0072] Here, OCV can be compared with each other based on their absolute values. That is, OCV can be compared in terms of magnitude. Therefore, even when the polarity is changed during the measurement of OCV (i.e., even when the (+) and (-) poles of the cell being measured are reversed), the decrease in OCV due to discharge can be accurately accounted for.

[0073] According to an example embodiment, based on the OCV measured at a first time point t1 and a second time point t2, which are relatively short periods after the start of charging or discharging of a battery cell, a first-order approximation of the OCV is made using the square root of time, thereby reducing the time required for OCV-based inspection of battery cells. Therefore, the productivity of secondary batteries can be improved and production costs can be reduced.

[0074] Furthermore, based on the above description, those skilled in the art will be able to easily derive an example in which the OCV of a battery cell is calculated at a second time point t2 instead of a first time point t1, and the mass of the battery cell is determined based on the calculated OCV of the battery cell at the second time point t2 and the calculated OCV of the battery cell at a third time point t3.

[0075] (Second Embodiment)

[0076] Figure 5 An OCV-based inspection of a battery cell is shown according to other example embodiments.

[0077] refer to Figure 4 and Figure 5 Performing an OCV-based inspection (P150') on individual battery cells can be replaced with... Figure 1P150. Performing an OCV-based check on a battery cell (P150') may include measuring the OCV of the battery cell at a first time point t1 (P151), measuring the OCV of the battery cell at a second time point t2 (P153), calculating the OCV of the battery cell at a third time point t3 (P155), measuring the OCV of the battery cell at the third time point t3 (P156), and comparing the measured OCV at the third time point t3 with the calculated OCV at the third time point t3 (P158).

[0078] Here, the processes on pages 151 and 153 are the same as those in the reference above. Figure 2 and Figure 3 The process described is basically the same, and redundant descriptions are omitted here.

[0079] In P154, the OCV of a single battery cell can be measured at the third time point t3. Therefore, the measured OCV of the single battery cell at the third time point t3 can be obtained.

[0080] Except for omitting the calculation of OCV at the first time point t1', P155' and Figure 2 The same applies to P155. In P155', in order to prevent errors due to the tolerance of the measurement at the third time point t3, the OCV of the battery cell can be calculated based on the time point determined by the measurement of the OCV of the battery cell at the third time point t3 (i.e., the time point including the tolerance).

[0081] Next, on page 158, the quality of a battery cell can be determined based on the measured OCV of the battery cell at the third time point t3 and the calculated OCV of the battery cell at the third time point t3. For example, when the measured OCV of the battery cell at the third time point t3 is lower than the calculated OCV of the battery cell at the third time point t3, the battery cell can be identified as defective. As another example, when the measured OCV of the battery cell at the third time point t3 is equal to or higher than the calculated OCV of the battery cell at the third time point t3, the battery cell can be identified as normal.

[0082] (Third embodiment)

[0083] Figure 6 An OCV-based inspection is shown according to other example embodiments.

[0084] refer to Figure 4 and Figure 6 Performing an OCV-based inspection (P150'') on individual battery cells can be replaced with... Figure 1P150. Performing an OCV-based inspection on a battery cell (P150) may include measuring the OCV of the battery cell at a first time point (P151), measuring the OCV of the battery cell at a second time point t2 (P153), and evaluating the quality of the battery cell based on the rate of change constant (P156).

[0085] Here, the processes on pages 151 and 153 are the same as those in the reference above. Figure 2 and Figure 3 The process described is basically the same, and redundant descriptions are omitted here.

[0086] In P156, the quality of a single battery cell can be evaluated based on the rate of change constant. The rate of change constant of OCV relative to the square root of time can be calculated by substituting the OCV measured at the first and second time points t2 into Equation 1 or 2. For example, when the rate of change constant is approximately -100 mV / h... 1 / 2 Up to 0mV / h 1 / 2 When the range is within a certain range, a single battery cell can be considered normal. As another example, when the rate of change constant is less than approximately -100 mV / h... 1 / 2 In such cases, a single battery cell can be identified as defective.

[0087] (Fourth embodiment)

[0088] Figure 7 An OCV-based inspection of a battery cell is shown according to other example embodiments.

[0089] refer to Figure 4 and Figure 7 Performing an OCV-based inspection (P150''') on individual battery cells can be replaced with Figure 1 P150. Performing an OCV-based check on a battery cell (P150') may include measuring the OCV of the battery cell at a first time point t1 (P151), measuring the OCV of the battery cell at a second time point t2 (P153), measuring the OCV of the battery cell at a reference time point (P154'), calculating the OCV of the battery cell at a third time point t3 (P155), and comparing the OCV measured at the third time point t3 with the calculated OCV at the third time point t3 (P158).

[0090] Here, the processes on pages 151 and 153 are the same as those in the reference above. Figure 2 and Figure 3 The described process is basically the same, and 155' is the same as the reference above. Figure 5 The descriptions are the same, and therefore redundant descriptions are omitted here.

[0091] In P154', the OCV of a single battery cell at a reference time point can be measured. The reference time point can be after the first time point t1 and the second time point t2. The reference time point can occur some time after the second time point t2. The reference time point can be different from the third time point t3. The reference time point can be earlier than the third time point t3. That is, the reference time point can be located between the second time point t2 and the third time point t3. According to the example embodiment, the reference time point can be located within the range of 24 hours to 150 hours after the battery cell has been charged or discharged.

[0092] P154' and P155' can be executed in reverse order. That is, the OCV of a single cell at the third time point t3 can be calculated in P155', and then the OCV of a single cell at the reference time point can be measured in P154'.

[0093] Then, on page 158', the quality of a battery cell can be determined based on the measured OCV of the battery cell at a reference time point and the calculated OCV of the battery cell at a third time point t3. For example, when the difference between the calculated OCV of the battery cell at the reference time point and the calculated OCV of the battery cell at the third time point t3 is in the range of about 0 mV to about 50 mV, the battery cell can be determined to be normal.

[0094] The present invention has been described in more detail above with reference to the accompanying drawings and embodiments. However, the configurations shown in the drawings or the embodiments described in this specification are merely embodiments of the present invention and do not reflect all the technical ideas of the present invention. Therefore, it should be understood that various equivalent solutions and modifications to these configurations may already exist as of the filing date of this application.

Claims

1. A method for manufacturing a secondary battery, comprising: The OCV of a single battery cell is measured at a first time point, wherein the first time point is within the range of 24 hours to 150 hours after the charging or discharging of the battery cell. Measure the OCV of the battery cell at a second time point, wherein the second time point is after the first time point; and The OCV of the battery cell at the third time point is calculated based on the OCV of the battery cell at the first time point, the OCV of the battery cell at the second time point, and the following formula: [formula] ， Wherein, ΔOCV represents the rate of change of OCV between two time points. Let represent the rate of change of the square root of time between the two time points, and let a be the rate of change constant of the OCV.

2. The method for manufacturing a secondary battery according to claim 1, wherein, The third time point is located within the range of 48 hours to 200 hours after the charging or discharging of the battery cell.

3. The secondary battery manufacturing method according to claim 1 further includes calculating the OCV of the battery cell at the first time point.

4. The method for manufacturing a secondary battery according to claim 1, wherein, The first time point is located within the range of 24 hours to 150 hours after the charging or discharging of the battery cell.

5. The secondary battery manufacturing method according to claim 3 further includes: The mass of the battery cell is determined based on the calculated OCV of the battery cell at the first time point and the calculated OCV of the battery cell at the third time point.

6. The method for manufacturing a secondary battery according to claim 5 further includes: When the difference between the calculated OCV of the battery cell at the first time point and the calculated OCV of the battery cell at the third time point is within the range of 0mV to 50mV, the battery cell is determined to be normal.

7. The secondary battery manufacturing method according to claim 1 further includes measuring the OCV of the battery cell at the third time point.

8. The secondary battery manufacturing method according to claim 7 further includes determining the mass of the battery cell based on the measured OCV of the battery cell at the third time point and the calculated OCV of the battery cell at the third time point.

9. The method for manufacturing a secondary battery according to claim 7, further comprising: When the measured OCV of the battery cell at the third time point is lower than the calculated OCV of the battery cell at the third time point, the battery cell is determined to be defective.

10. A method for manufacturing a secondary battery, comprising: The OCV of a single battery cell is measured at a first time point, wherein the first time point is within the range of 12 hours to 150 hours from the start of charging or discharging of the battery cell. Measure the OCV of the battery cell at a second time point, wherein the second time point is after the first time point; and The rate of change constant of the OCV of the battery cell is calculated based on the OCV of the battery cell at the first time point, the OCV of the battery cell at the second time point, and the following formula: [formula] Wherein, ΔOCV represents the rate of change of OCV between two time points. Let represent the rate of change of the square root of time between the two time points, and let a be the rate of change constant of the OCV.

11. The secondary battery manufacturing method according to claim 10 further includes determining the mass of the battery cell based on the rate of change constant.

12. The method for manufacturing a secondary battery according to claim 10, further comprising: when the rate of change constant is located at -100 mV / h 1 / 2 up to 0mV / h 1 / 2 When the range is within the specified range, the battery cell is determined to be normal.

13. A method for manufacturing a secondary battery, comprising: The OCV of a single battery cell is measured at a first time point, wherein the first time point is within the range of 12 hours to 150 hours after the charging or discharging of the battery cell. Measure the OCV of the battery cell at a second time point, wherein the second time point is after the first time point; and The OCV of the battery cell at the first time point and the OCV of the battery cell at the second time point are calculated based on the OCV of the battery cell at the first time point and the OCV of the battery cell at the second time point. The OCV of the battery cell at the first time point and the OCV of the battery cell at the third time point are calculated using a first-order approximation of the square root of time.

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