Secondary battery low voltage defect inspection method

Abstract

According to exemplary embodiments, provided is a secondary battery defect inspection method. The method may comprise: a first charging step of charging a secondary battery up to a first state of charge (SOC) at a first C-rate; a second charging step of, after the first charging step, charging the secondary battery up to a second SOC at a second C-rate of 0.003 C or less; and a detection step of, after the second charging step, determining whether the secondary battery has a defect. The second C-rate may be smaller than the first C-rate. The second SOC may be greater than the first SoC.

Description

Low voltage defect inspection method for secondary batteries

[0001] The present invention relates to a method for inspecting low voltage defects in a secondary battery. The present application claims the benefit of Korean application No. 10-2024-0179198, filed on December 5, 2024, which is incorporated herein by reference in its entirety.

[0002]

[0003] Unlike primary batteries, secondary batteries can be charged and discharged multiple times. Secondary batteries are widely used as energy sources for various wireless devices such as handsets, laptops, and cordless vacuum cleaners. Recently, as the manufacturing cost per unit capacity of secondary batteries has decreased dramatically due to improved energy density and economies of scale, and as the driving range of BEVs (battery electric vehicles) has increased to a level equivalent to that of fuel vehicles, the primary use of secondary batteries is shifting from mobile devices to mobility.

[0004] The manufacture of a secondary battery includes an electrode process comprising mixing, coating, roll pressing, slitting, and notching processes; an assembly process for embedding the electrode assembly into a case; and an activation process for electrically activating and stabilizing the secondary battery. After the activation process, the secondary battery can be stacked to form a cell stack. The cell stack can be mounted in a housing together with a module frame, or directly mounted in a housing without a module frame.

[0005] Secondary batteries may experience various types of defects due to various causes during the manufacturing process or use. In particular, some completed secondary batteries exhibit a voltage drop behavior exceeding their self-discharge rate; this phenomenon is referred to as low voltage.

[0006] Such low-voltage failures in secondary batteries are typically caused by internal metallic foreign matter. In particular, if metallic foreign matter such as iron or copper is present on the positive electrode of a secondary battery, it can grow into dendrites on the negative electrode. These dendrites can cause internal short circuits in the secondary battery, leading to battery failure or damage, and in severe cases, even ignition.

[0007] Although some technologies for inspecting low-voltage defects in such secondary batteries have been proposed so far, there are limitations in effectively and rapidly detecting such defects.

[0008]

[0009] The problem that the technical concept of the present invention aims to solve is to provide a defect inspection method for secondary batteries in which the defect detection time is shortened and the inspection accuracy is improved.

[0010]

[0011] According to exemplary embodiments of the present invention for solving the above-described problem, a method for inspecting defects in a secondary battery is provided. The method may include: a first charging step of charging the secondary battery to a first State of Charge (SOC) at a first C-rate; a second charging step of charging the secondary battery to a second SOC at a second C-rate of 0.003 C or less after the first charging step; and a detection step of determining defects in the secondary battery after the second charging step. The second C-rate may be smaller than the first C-rate. The second SOC may be larger than the first SOC.

[0012] The second charging step above can be performed for a period of time from 5 minutes to 30 minutes.

[0013] The detection step above can determine whether the secondary battery is defective based on the amount of voltage change of the secondary battery during the second charging step.

[0014] The detection step above can determine whether the secondary battery is defective based on the slope of the voltage over time of the secondary battery during the second charging step.

[0015] The detection step above can determine whether there is a defect based on the amount of voltage change measured at each of the multiple time intervals during the second charging step.

[0016] Before the first charging step, a first aging step for aging the secondary battery; after the first aging step, a formation step for charging the secondary battery; after the formation step, a second aging step for aging the secondary battery; after the second aging step, a full charging step for fully charging the secondary battery; and after the full charging step, a full discharging step for fully discharging the secondary battery may be included.

[0017] The above second SOC may be 30% or less.

[0018] The above second C-rate is 4 x 10 -10 It can be C or higher.

[0019] The above first C-rate may be 0.1 C or higher and 2.0 C or lower.

[0020] Each of the above first SOC and the above second SOC is the second derivative value (d) of the voltage-SOC in the voltage-SOC profile during the charging process of a normal battery. 2 V / dSOC 2 ) can be selected from the SOC range within this standard range.

[0021] The voltage-SOC profile of the above normal battery is the second derivative value (d) of voltage-SOC between the first SOC and the second SOC. 2 V / dSOC 2It may include intervals where ) is 0.

[0022] Each of the above first SOC and the above second SOC is the second derivative value (d) of the voltage-SOC in the voltage-SOC profile during the discharge process of a normal battery. 2 V / dSOC 2 ) can be selected from the SOC range within this standard range.

[0023] The voltage-SOC profile of the above normal battery is a second derivative value (d) of voltage-SOC between the first SOC and the second SOC. 2 V / dSOC 2 It may include intervals where ) is 0.

[0024] The above second SOC may be 1% to 5% larger than the above first SOC.

[0025] Between the first charging step and the second charging step, a step of stabilizing the secondary battery may be further included.

[0026]

[0027] According to exemplary embodiments of the present invention, a secondary battery is low-rate charged in an SOC range where the voltage change rate is relatively constant, and a low-voltage defect of the secondary battery can be detected based on the voltage change of the secondary battery during low-rate charging. Accordingly, the speed and accuracy of the low-voltage defect inspection method of the secondary battery can be improved.

[0028] The effects obtainable from the exemplary embodiments of the present invention are not limited to those mentioned above, and other unmentioned effects can be clearly derived and understood by those skilled in the art to which the exemplary embodiments of the present disclosure belong from the following description. That is, unintended effects resulting from the implementation of the exemplary embodiments of the present disclosure can also be derived by those skilled in the art from the exemplary embodiments of the present disclosure.

[0029]

[0030] FIG. 1 is a flowchart illustrating a method for inspecting defects in a secondary battery according to exemplary embodiments.

[0031] FIG. 2 is a flowchart illustrating the activation process of a secondary battery according to exemplary embodiments.

[0032] FIG. 3 is a cross-sectional view showing a secondary battery according to exemplary embodiments.

[0033] Figure 4 is a graph showing the average voltage over time of normal batteries and the average voltage over time of defective batteries.

[0034] Figure 5 is a graph showing the change in voltage over time for each normal battery and each defective battery.

[0035] Figure 6 is a graph showing the average value of the change in voltage over time of normal batteries and the average value of the change in voltage over time of defective batteries.

[0036]

[0037] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms to best describe his invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0038] Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0039] In addition, in describing the present invention, if it is determined that a detailed description of related known components or functions may obscure the essence of the invention, such detailed description is omitted.

[0040] Since embodiments of the present invention are provided to more fully explain the invention to those skilled in the art, the shapes and sizes of the components in the drawings may be exaggerated, omitted, or schematically depicted for clearer explanation. Accordingly, the size or proportion of each component does not entirely reflect the actual size or proportion.

[0041]

[0042] (1st and 2nd embodiments)

[0043] FIG. 1 is a flowchart for explaining a defect inspection method (S100) of a secondary battery according to exemplary embodiments. FIG. 2 is a flowchart for showing an activation method (S120) of a secondary battery according to exemplary embodiments. FIG. 3 is a cross-sectional view showing a secondary battery (BC) according to exemplary embodiments.

[0044]

[0045] Referring to FIG. 1, a defect inspection method (S100) for a secondary battery according to the present invention may include an assembly step (S110), an activation step (S120), a step of charging to a first SOC (S130), a step of charging to a second SOC (S140), and a detection step (S150).

[0046] Referring to FIG. 2, the activation step (S120) may include a first aging step (S121), a formation step (S122), a second aging step (S123), a full charge step (S124), and a full discharge step (S125).

[0047]

[0048] Referring to FIGS. 1 to 3 together, the defect inspection method (S100) of a secondary battery may include the step (S110) of assembling a secondary battery (BC).

[0049] The secondary battery (BC) may include a battery case (CC) and an electrode assembly (EA). The secondary battery (BC) may further include an electrolyte injected into the battery case (CC).

[0050] Hereinafter, the technical concept of the present invention will be explained with reference to an example in which an electrode assembly (EA) is stacked with a plurality of anodes (EP), a plurality of cathodes (EN), and a plurality of separators (SP). A person skilled in the art can easily arrive at an embodiment in which the electrode assembly comprises a coiled structure of an anode, a cathode, and a separator interposed between them, based on what is described herein.

[0051] Each of the plurality of positive electrodes (EP) may include a positive current collector and a positive active material. The thickness of the positive current collector may be in the range from about 3 μm to about 500 μm. The positive current collector may not cause chemical changes in the secondary battery finally manufactured and may have high conductivity. The positive current collector may include, for example, any one of stainless steel, nickel, titanium, calcined carbon, and aluminum. The positive current collector may also include stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The surface of the positive current collector may include a micro-irregular structure to increase the adhesion of the active material. The shape of the positive current collector may include any one of a film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0052] The positive electrode active material is a material capable of causing an electrochemical reaction. The positive electrode active material may be a lithium transition metal oxide. The positive electrode active material is, for example, with the chemical formula Li 1+x M 1-y M' y PO 4-z X zIt may include any one of the olivine-based lithium metal phosphates represented by (where M is a transition metal, more specifically one of Fe, Mn, Co, and Ni; M' is one of Al, Mg, and Ti; X is one of F, S, and N; -0.5≤x≤+0.5; 0≤y≤0.5; and 0≤z≤0.1). The positive electrode active material may include, for example, lithium iron phosphate. The positive electrode active material is Li 1+x M 1-y M' y O 2-z X z It may further include a lithium metal oxide represented by (where M is a main metal one of Fe, Mn, Co, and Ni, M' is a substituent metal element different from M among Fe, Mn, Co, and Ni, and X is a substitutable non-metal element or defect). The positive electrode active material may include, for example, lithium iron oxide.

[0053] Each of the plurality of negative electrodes (EN) may include a negative current collector and a negative active material. The thickness of the negative current collector may be in the range of about 3 μm to about 500 μm. The negative current collector may not cause chemical changes in the secondary battery finally manufactured and may have high conductivity. The negative current collector may include any one of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy. The negative current collector may also include stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The surface of the negative current collector may include a micro-irregular structure to increase the adhesion of the active material. The shape of the negative current collector may include any one of a film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0054] The negative electrode active material may include carbon, for example, non-graphitizable carbon, graphite-based carbon, etc. The negative electrode active material is, for example, Li xFe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z (wherein Me is any one of Mn, Fe, Pb, and Ge, and Me' is any one of Al, B, P, Si, Group 1, Group 2, and Group 3 elements of the periodic table, and halogens; 0 <x≤1 이고; 1≤y≤3 이며; 1≤z≤8) 등의 금속 복합 산화물을 포함할 수 있다. 음극 활물질은, 예컨대, 리튬 금속; 리튬 합금; 규소계 합금; 및 주석계 합금 중 어느 하나를 포함할 수 있다. 음극 활물질은, 예컨대, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 금속 산화물을 포함할 수 있다. 음극 활물질은, 예컨대, 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 포함할 수도 있다.

[0055] A plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) may alternate with separators (SP). Accordingly, one of a plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) may be interposed between two adjacent separators (SP). Each of the separators (SP) may be in contact with at least one of a plurality of positive electrodes (EP) and a plurality of negative electrodes (EN). Each of the separators (SP) may isolate a plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) by preventing direct contact between the plurality of positive electrodes (EP) and a plurality of negative electrodes (EN). Accordingly, a short circuit between a plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) may be prevented. Each of the plurality of positive electrodes (EP) and a plurality of negative electrodes (EN) may have a flat film shape.

[0056] The battery case (CC) may include a cup-shaped receiving portion. The receiving portion may be formed by a pouch forming process. An electrode assembly (EA) may be received in the receiving portion. The battery case (CC) may be any one of a pouch case, a cylindrical can, and a prismatic can. An electrode assembly (EA) may be embedded within the battery case (CC). Hereinafter, the technical concept of the present invention is described based on an example in which the battery case (CC) is an aluminum laminate sheet; however, a person skilled in the art will be able to easily arrive at an example in which the battery case (CC) is one of a cylindrical can and a prismatic can based on what is described herein.

[0057] The battery case (CC) may include an inner resin layer, a metal layer, and an outer resin layer. An adhesive and a corrosion-resistant layer may be further provided between the inner resin layer and the metal layer and between the outer resin layer and the metal layer.

[0058] The inner resin layer may have heat-sealability and may be referred to as a sealant layer. The inner resin layer enables sealing of the battery case (CC). The inner resin layer may include polyolefin-based resins such as polypropylene (PP) and polyethylene (PE), for example. The metal layer may include one of an alloy of iron, carbon, chromium, and manganese, an alloy of iron, chromium, and nickel, and aluminum. The metal layer may be a gas barrier. The metal layer may block the entry and exit of gas from the battery case (CC). The outer resin layer may be a surface protection layer. The outer resin layer may include a material having wear resistance and heat resistance, such as nylon resin.

[0059] The electrolyte may be any one of a non-aqueous electrolyte, an aqueous electrolyte, an ionic electrolyte, and a gel electrolyte. The electrolyte may also be a solid electrolyte. The non-aqueous electrolyte may include organic solvents such as ethylene carbonate and dimethyl carbonate, and lithium salts such as LiPF6 and LiBF4 dissolved in organic solvents. The non-aqueous electrolyte may also include ethylene carbonate dissolved in tetraethylammonium salts. The aqueous electrolyte may include sodium sulfate solution, sulfuric acid solution, hydrochloric acid solution, or sodium hydroxide solution. The ionic electrolyte is an ionic compound that is in a liquid state at room temperature, such as ethylmethylimidazolidium bis(trifluoromethylsulfonyl)amide, and has high thermal stability. The gel electrolyte may be provided by using a liquid electrolyte such as polyacrylonitrile and PVA. The solid electrolyte may include a polymer material doped with a lithium salt (e.g., polyethylene oxide (PEO)) and a ceramic electrolyte composed of ceramic materials such as NASICON and LLZO.

[0060]

[0061] A method for inspecting defects in a secondary battery (S100) may include a step (S120) of activating the secondary battery (BC). The activation step (S120) may include a first aging step (S121), a formation step (S122), a second aging step (S123), a full charge step (S124), and a full discharge step (S125).

[0062]

[0063] The first aging step (S121) may be a step of aging the secondary battery (BC) assembled in the assembly step (S110) for a predetermined period of time. According to exemplary embodiments, in the first aging step (S121), the secondary battery (BC) may be stored for a predetermined period of time in a chamber where a predetermined temperature condition is maintained constant.

[0064] According to exemplary embodiments, in the first aging step (S121), the secondary battery (BC) may be stored at a temperature of about 10°C or higher. According to exemplary embodiments, in the first aging step (S121), the secondary battery (BC) may be stored at a temperature of about 20°C or higher. According to exemplary embodiments, in the first aging step (S121), the secondary battery (BC) may be stored at a temperature of about 40°C or lower. According to exemplary embodiments, in the first aging step (S121), the secondary battery (BC) may be stored at a temperature of about 30°C or lower.

[0065] According to exemplary embodiments, the first aging step (S121) may be performed for a period of about 24 hours or more. According to exemplary embodiments, the first aging step (S121) may be performed for a period of about 36 hours or more. According to exemplary embodiments, the first aging step (S121) may be performed for a period of about 72 hours or less. According to exemplary embodiments, the first aging step (S121) may be performed for a period of about 48 hours or less. For example, the first aging step (S121) may be configured to be performed for about 30 hours under a temperature condition of about 20°C.

[0066] The first aging step (S121) can be performed immediately after the assembly step (S110) of the secondary battery (BC). That is, the electrode assembly (EA) and the electrolyte are housed inside the battery case (CC), and with the battery case (CC) sealed, the first aging step (S121) can be performed immediately without any other processes.

[0067] The first aging step (S121) can ensure that the electrolyte injected into the interior of the secondary battery (BC) in the assembly step (S110) is uniformly mixed. The first aging step (S121) can ensure that the electrolyte injected into the interior of the secondary battery (BC) in the assembly step (S110) spreads uniformly within the interior of the secondary battery (BC). The first aging step (S121) can facilitate ion exchange between the plurality of positive electrodes (EP) and the plurality of negative electrodes (EN) by ensuring that the electrolyte impregnation is uniformly performed on the plurality of separators (SP).

[0068]

[0069] In the formation step (S122), the secondary battery (BC) that was first aged in the first aging step (S121) can be charged to a predetermined State of Charge (SOC). According to exemplary embodiments, the formation step (S122) may be configured to charge the secondary battery (BC) to an SOC of approximately 30% or higher. According to exemplary embodiments, the formation step (S122) may be configured to charge the secondary battery (BC) to an SOC of approximately 40% or higher. According to exemplary embodiments, the formation step (S122) may be configured to charge the secondary battery (BC) to an SOC of approximately 50% or higher. According to exemplary embodiments, the formation step (S122) may be configured to charge the secondary battery (BC) to an SOC of approximately 70% or lower. According to exemplary embodiments, the formation step (S122) may be configured to charge the secondary battery (BC) to an SOC of about 60% or less. According to exemplary embodiments, the formation step (S122) may be configured to charge the secondary battery (BC) to an SOC of about 50% or less.

[0070] In the formation step (S122), the secondary battery (BC) that was first aged in the first aging step (S121) can be charged for a predetermined period of time. According to exemplary embodiments, the formation step (S122) may be performed for a period of 70 minutes or more. According to exemplary embodiments, the formation step (S122) may be performed for a period of 80 minutes or more. According to exemplary embodiments, the formation step (S122) may be performed for a period of 90 minutes or more. According to exemplary embodiments, the formation step (S122) may be performed for a period of 180 minutes or less. According to exemplary embodiments, the formation step (S122) may be performed for a period of 170 minutes or less. According to exemplary embodiments, the formation step (S122) may be performed for a period of 160 minutes or less.

[0071] The formation step (S122) can be performed at a predetermined C-rate. According to exemplary embodiments, the secondary battery (BC) can be charged at a C-rate of about 0.1 C or higher in the formation step (S122). According to exemplary embodiments, the secondary battery (BC) can be charged at a C-rate of about 0.2 C or higher in the formation step (S122). According to exemplary embodiments, the secondary battery (BC) can be charged at a C-rate of about 0.5 C or higher in the formation step (S122). According to exemplary embodiments, the secondary battery (BC) can be charged at a C-rate of about 2.0 C or lower in the formation step (S122). According to exemplary embodiments, the secondary battery (BC) can be charged at a C-rate of about 1.0 C or lower in the formation step (S122). According to exemplary embodiments, the secondary battery (BC) can be charged with a C-rate of about 0.5 C or less in the formation step (S122).

[0072] The formation step (S122) may be performed at a predetermined temperature. According to exemplary embodiments, the formation step (S122) may be performed at a temperature of about 10°C or higher. According to exemplary embodiments, the formation step (S122) may be performed at a temperature of about 20°C or higher. According to exemplary embodiments, the formation step (S122) may be performed at a temperature of about 40°C or lower. According to exemplary embodiments, the formation step (S122) may be performed at a temperature of about 30°C or lower. For example, the formation step (S122) may be configured to charge the secondary battery to about 50% SOC with a C-rate of about 0.2 C at a temperature of about 25°C.

[0073] By performing the formation step (S122) at the SOC, time, C-rate, and temperature of the conditions described above, the SEI (Solid Electrolyte Interphase) layer of the secondary battery (BC) can be uniformly formed with an appropriate thickness. The formation step (S122) can charge the secondary battery (BC) with a charging voltage of about 3.4 V to about 3.7 V. However, this charging voltage may vary depending on the type or characteristics of the secondary battery (BC).

[0074]

[0075] In the second aging step (S123), the secondary battery (BC) charged in the formation step (S122) can be aged at a predetermined temperature and for a predetermined time.

[0076] According to exemplary embodiments, in the second aging step (S123), the secondary battery (BC) may be stored at a temperature of about 60°C to about 70°C. According to exemplary embodiments, in the second aging step (S123), the secondary battery (BC) may be stored for about 12 hours to about 72 hours. In the second aging step (S123), additional wetting may be performed on the part of the electrode assembly (EA) where the electrolyte has not sufficiently penetrated. Stabilization of the SEI layer may also be performed in the second aging step (S123). Additionally, if there are metal foreign substances inside the secondary battery (BC) that may cause low voltage failure of the secondary battery (BC), additional growth of the metal foreign substances may occur in the second aging step (S123).

[0077]

[0078] In the full charge step (S124), the secondary battery (BC) can be charged until the SOC reaches about 100%. According to exemplary embodiments, in the full charge step (S124), the secondary battery (BC) can be charged with a C-rate of about 0.1 C to about 2.0 C. According to exemplary embodiments, in the full charge step (S124), the secondary battery (BC) can be charged under temperature conditions of about 20 ℃ to about 45 ℃.

[0079] In the full discharge step (S125), the fully charged secondary battery (BC) can be discharged until its SOC becomes about 0%. According to exemplary embodiments, the full discharge step (S125) can discharge the secondary battery (BC) at a C rate of about 0.1 C to about 2.0 C. According to exemplary embodiments, the full discharge step (S125) can discharge the secondary battery (BC) under temperature conditions of about 20 ℃ to about 45 ℃.

[0080] The full charge step (S124) and the full discharge step (S125) can stabilize the SEI layer. Additionally, the full charge step (S124) and the full discharge step (S125) can further grow metal foreign matter inside the secondary battery (BC), thereby improving the accuracy of low-voltage defect detection in the detection step (S150) described later. According to exemplary embodiments, the full charge step (S124) and the full discharge step (S125) may each be performed multiple times.

[0081]

[0082] A method for manufacturing a secondary battery (S100) may include a step (S130) of charging the secondary battery (BC) to a first SOC and a step (S140) of charging the secondary battery (BC) to a second SOC.

[0083] The first SOC in the charging step (S130) and the second SOC in the charging step (S140), respectively, can be determined based on a voltage profile according to the SOC during the charging process of a normal secondary battery (hereinafter, voltage-SOC charging profile). The first SOC and the second SOC can be selected in a section where the rate of change of voltage is relatively constant in the voltage-SOC charging profile of the normal secondary battery. According to exemplary embodiments, the first SOC and the second SOC are the second derivative value (d) of the voltage-SOC in the voltage-SOC charging profile of the normal secondary battery. 2 V / dSOC 2 ) can be selected in an SOC interval within a reference range. According to exemplary embodiments, the first SOC and the second SOC are, in the voltage-SOC charging profile of a normal secondary battery, the second derivative value (d) of the voltage-SOC. 2 V / dSOC 2 It can be selected in an SOC range where ) is substantially 0. According to exemplary embodiments, the voltage-SOC charging profile of a normal battery is such that the second derivative of voltage-SOC (d) between the first SOC and the second SOC 2 V / dSOC 2It may include at least some intervals where ) is substantially 0.

[0084] Alternatively, the first SOC in the charging step (S130) and the second SOC in the charging step (S140), respectively, may be determined based on a voltage profile (hereinafter referred to as the voltage-SOC discharge profile) according to the SOC during the discharge process of a normal secondary battery. The first SOC and the second SOC may be selected in a section where the rate of change of voltage is relatively constant in the voltage-SOC discharge profile of the normal secondary battery. According to exemplary embodiments, the first SOC and the second SOC are the second derivative value (d) of the voltage-SOC in the voltage-SOC discharge profile of the normal secondary battery. 2 V / dSOC 2 ) can be selected in an SOC interval within a reference range. According to exemplary embodiments, the first SOC and the second SOC are, in the voltage-SOC discharge profile of a normal secondary battery, the second derivative value (d) of the voltage-SOC. 2 V / dSOC 2 It can be selected in the SOC range where ) is substantially 0. According to exemplary embodiments, the voltage-SOC discharge profile of the normal battery is such that the second derivative value (d) of the voltage-SOC between the first SOC and the second SOC. 2 V / dSOC 2 It may include at least some intervals where ) is substantially 0.

[0085] That is, the first SOC and the second SOC can be determined within a range where the voltage change rate according to the SOC is relatively constant in the charging profile or discharging profile of a normal secondary battery. Accordingly, the charging step (S140) can be performed in the SOC range where the voltage change rate according to the SOC is relatively constant. Since voltage fluctuations caused by factors other than low voltage defects are relatively small in the range where the voltage change rate according to the SOC is relatively constant, the difference between the voltage of the normal secondary battery and the voltage of the secondary battery with a low voltage defect can be precisely detected during the charging step (S140).

[0086] In contrast, when selecting an SOC section with a large fluctuation range in the voltage change rate according to SOC in the charging profile or discharging profile of a normal secondary battery, voltage fluctuations caused by factors other than low voltage defects are reflected together during the charging step (S140), so the accuracy of detecting defects caused by low voltage may be reduced.

[0087] According to exemplary embodiments, a method for manufacturing a secondary battery (S100) may further include a stabilization step of the secondary battery (BC) between a charging step (S130) and a charging step (S140). During the stabilization step, power supply to the secondary battery (BC) is interrupted, and the secondary battery (BC) may be stabilized. According to exemplary embodiments, the stabilization step may be performed for about 8 hours to about 24 hours. According to exemplary embodiments, the stabilization step may be performed under temperature conditions of about 25°C to about 40°C.

[0088]

[0089] The second SOC of the charging step (S130) may be greater than the first SOC of the charging step (S140). According to exemplary embodiments, the difference between the first SOC and the second SOC may be about 1% or more. According to exemplary embodiments, the difference between the first SOC and the second SOC may be about 2% or more. According to exemplary embodiments, the difference between the first SOC and the second SOC may be about 4% or more. According to exemplary embodiments, the difference between the first SOC and the second SOC may be about 10% or less. According to exemplary embodiments, the difference between the first SOC and the second SOC may be about 6% or less. According to exemplary embodiments, the difference between the first SOC and the second SOC may be about 5% or less.

[0090] According to exemplary embodiments, the first SOC may be about 5% or more. According to exemplary embodiments, the first SOC may be about 10% or more. According to exemplary embodiments, the first SOC may be about 20% or more. According to exemplary embodiments, the first SOC may be about 100% or less. According to exemplary embodiments, the first SOC may be about 50% or less. According to exemplary embodiments, the first SOC may be about 30% or less.

[0091] According to exemplary embodiments, the second SOC may be about 5% or more. According to exemplary embodiments, the second SOC may be about 10% or more. According to exemplary embodiments, the second SOC may be about 20% or more. According to exemplary embodiments, the second SOC may be about 100% or less. According to exemplary embodiments, the second SOC may be about 50% or less. According to exemplary embodiments, the second SOC may be about 30% or less.

[0092]

[0093] In the charging step (S130), the secondary battery (BC) can be charged to a first C-rate. In the charging step (S140), the secondary battery (BC) can be charged to a second C-rate. The second C-rate may be smaller than the first C-rate.

[0094] According to exemplary embodiments, the first C-rate may be about 0.1 C or higher. According to exemplary embodiments, the first C-rate may be about 0.2 C or higher. According to exemplary embodiments, the first C-rate may be about 0.5 C or higher. According to exemplary embodiments, the first C-rate may be about 1.0 C or higher. According to exemplary embodiments, the first C-rate may be about 3.0 C or lower. According to exemplary embodiments, the first C-rate may be about 2.0 C or lower. According to exemplary embodiments, the first C-rate may be about 1.0 C or lower. According to exemplary embodiments, the first C-rate may be about 0.5 C or lower.

[0095] According to exemplary embodiments, the second celate is about 4 x 10 -10 It may be C or higher. According to exemplary embodiments, the second C-rate is about 1 x 10 -9 It may be C or higher. According to exemplary embodiments, the second C-rate is about 1 x 10 -8 It may be C or higher. According to exemplary embodiments, the second C-rate may be about 0.003 C or lower. According to exemplary embodiments, the second C-rate may be about 0.001 C or lower. According to exemplary embodiments, the second C-rate may be about 0.0001 C or lower.

[0096] In the charging step (S140), the secondary battery (BC) is charged at the second C-rate of the low rate described above, so that voltage fluctuations caused by overpotential or resistance loss, etc., can be minimized. That is, the voltage of the secondary battery (BC) measured in the charging step (S140) can be close to the Open Circuit Voltage (OCV) that reflects the equilibrium state of the chemical reaction inside the secondary battery (BC). Accordingly, in the subsequent detection step (S150), based on the amount of voltage change of the secondary battery (BC) in the charging step (S140), a low voltage defect caused by internal defects of the secondary battery (BC) can be detected.

[0097] The charging step (S140) may be performed for a predetermined amount of time. According to exemplary embodiments, the charging step (S140) may be performed for a time of about 3 minutes or more. According to exemplary embodiments, the charging step (S140) may be performed for a time of about 5 minutes or more. According to exemplary embodiments, the charging step (S140) may be performed for a time of about 10 minutes or more. According to exemplary embodiments, the charging step (S140) may be performed for a time of about 15 minutes or more. According to exemplary embodiments, the charging step (S140) may be performed for a time of about 60 minutes or less. According to exemplary embodiments, the charging step (S140) may be performed for a time of about 50 minutes or less. According to exemplary embodiments, the charging step (S140) may be performed for a time of about 40 minutes or less. According to exemplary embodiments, the charging step (S140) may be performed for a time of about 30 minutes or less.

[0098] A defect inspection method (S100) for a secondary battery according to exemplary embodiments of the present invention can detect a low voltage defect in a secondary battery (BC) by charging the secondary battery (BC) at a low C-rate in a range where the voltage change rate is relatively constant and based on the voltage change of the secondary battery (BC) caused by charging. Unlike conventional inspection methods that age the secondary battery (BC) for several days (e.g., 2 to 7 days) to observe the voltage change of the secondary battery (BC), the defect inspection method (S100) for a secondary battery according to the present invention significantly reduces the inspection time, thereby improving the efficiency of the inspection process and enhancing the precision and reliability of the inspection.

[0099]

[0100] A method for manufacturing a secondary battery (S100) may include a detection step (S150) for detecting a low voltage defect of the secondary battery (BC).

[0101] The detection step (S150) can determine whether the secondary battery (BC) has a low voltage defect based on the voltage data over time of the secondary battery (BC) recorded in the charging step (S140).

[0102] According to exemplary embodiments, the detection step (S150) can determine whether the secondary battery (BC) is defective based on the amount of voltage change of the secondary battery (BC) during the charging step (S140). If the amount of voltage change of the secondary battery (BC) under inspection matches the amount of voltage change of a normal secondary battery within an allowable error range, the secondary battery (BC) under inspection can be determined to be normal. On the other hand, if the amount of voltage change of the secondary battery (BC) under inspection deviates from the allowable error range of the amount of voltage change of a normal secondary battery, the secondary battery (BC) under inspection can be determined to be defective. According to other exemplary embodiments, the detection step (S150) may divide the charging step (S140) into a plurality of time intervals and determine whether the secondary battery (BC) is defective based on the amount of voltage change of the secondary battery (BC) measured for each time interval.

[0103] According to other exemplary embodiments, the detection step (S150) can determine whether the secondary battery (BC) is defective based on the voltage slope over time of the secondary battery (BC) during the charging step (S140). If the voltage slope over time of the secondary battery (BC) under inspection matches the voltage slope over time of a normal secondary battery within an allowable error range, the secondary battery (BC) under inspection can be determined to be normal. On the other hand, if the voltage slope over time of the secondary battery (BC) under inspection deviates from the voltage slope over time of a normal secondary battery within an allowable error range, the secondary battery (BC) under inspection can be determined to be defective.

[0104]

[0105] FIGS. 4 through 6 are embodiments to aid in understanding the present invention. Embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited thereto. Embodiments of the present invention are provided to explain the present invention to a person skilled in the art.

[0106] FIGS. 4 to 6 are graphs illustrating voltage changes during the charging step (S140) of eight normal batteries (NV) and eight defective batteries (LV). For each normal battery (NV) and each defective battery (LV), prior to the charging step (S140), the activation step (S120) and the charging step (S130) of FIG. 1 were performed under the same conditions.

[0107] Figure 4 shows the average voltage of normal batteries (NV) and the average voltage of defective batteries (LV) over time, respectively.

[0108] FIG. 5 illustrates lines connecting the voltage at 0 seconds and the voltage at 1750 seconds of each normal battery (NV), and lines connecting the voltage at 0 seconds and the voltage at 1750 seconds of each defective battery (LV).

[0109] Figure 6 shows a line connecting the average voltage at 0 seconds and the average voltage at 1750 seconds of normal batteries (NV), and a line connecting the average voltage at 0 seconds and the average voltage at 1750 seconds of defective batteries (LV).

[0110] As illustrated in FIGS. 4 to 6, when a charging step (S140) is performed under the same conditions, the voltage increase of the defective batteries (LV) during the charging step (S140) may be smaller than the voltage increase of the normal batteries (NV). This may be due to a voltage drop or internal short circuit caused by metal foreign matter inside the defective batteries (LV). In the detection step (S150), the voltage change amount of the defective batteries (LV) or the voltage slope over time may be compared with the voltage change amount or the voltage slope over time of the normal batteries (NV) to determine whether the batteries are defective.

[0111]

[0112] The present invention has been described in more detail above through drawings and embodiments. However, the configurations described in the drawings or embodiments described in this specification are merely one embodiment of the present invention and do not represent all technical concepts of the present invention; therefore, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

Claims

1. A first charging step of charging a secondary battery to a first State of Charge (SOC) at a first C-rate; After the first charging step, a second charging step of charging the secondary battery to a second SOC at a second C rate of 0.003 C or less; and After the second charging step, the detection step for determining a defect in the secondary battery is included. The second celate is smaller than the first celate, and A method for inspecting defects in a secondary battery, wherein the above-mentioned second SOC is greater than the above-mentioned first SOC.

2. In Paragraph 1, A method for inspecting defects in a secondary battery, characterized in that the second charging step is performed for a period of 5 to 30 minutes.

3. In Paragraph 1, A method for inspecting defects in a secondary battery, wherein the detection step determines whether the secondary battery is defective based on the amount of voltage change of the secondary battery during the second charging step.

4. In Paragraph 1, A method for inspecting defects in a secondary battery, wherein the detection step determines whether the secondary battery is defective based on the voltage slope over time of the secondary battery during the second charging step.

5. In Paragraph 1, A method for inspecting defects in a secondary battery, wherein the detection step determines whether there is a defect based on a voltage change amount measured at each of a plurality of time intervals during the second charging step.

6. In Paragraph 1, Prior to the first charging step mentioned above, A first aging step for aging the above secondary battery; After the above first aging step, a formation step for charging the secondary battery; After the above formation step, a second aging step for aging the secondary battery; After the above second aging step, a full charging step for fully charging the secondary battery; and A method for inspecting defects in a secondary battery, comprising a full discharge step of fully discharging the secondary battery after the full charge step.

7. In Paragraph 1, A method for inspecting defects in a secondary battery, characterized in that the above-mentioned second SOC is 30% or less.

8. In Paragraph 1, The above second C-rate is 4 x 10 -10 A method for inspecting defects in a secondary battery, characterized by being C or higher.

9. In Paragraph 1, A method for inspecting defects in a secondary battery, characterized in that the first C-rate is 0.1 C or higher and 2.0 C or lower.

10. In Paragraph 1, Each of the above first SOC and the above second SOC is the second derivative value (d) of the voltage-SOC in the voltage-SOC profile during the charging process of a normal battery. 2 V / dSOC 2 A method for inspecting defects in a secondary battery, characterized by selecting from an SOC range within a standard range.

11. In Paragraph 10, The voltage-SOC profile of the above normal battery is the second derivative value (d) of voltage-SOC between the first SOC and the second SOC. 2 V / dSOC 2 A method for inspecting defects in a secondary battery, characterized by including a section where ) is 0.

12. In Paragraph 1, Each of the above first SOC and the above second SOC is the second derivative value (d) of the voltage-SOC in the voltage-SOC profile during the discharge process of a normal battery. 2 V / dSOC 2 A method for inspecting defects in a secondary battery, characterized by selecting from an SOC range within a standard range.

13. In Paragraph 12, The voltage-SOC profile of the above normal battery is a second derivative value (d) of voltage-SOC between the first SOC and the second SOC. 2 V / dSOC 2 A method for inspecting defects in a secondary battery, characterized by including a section where ) is 0.

14. In Paragraph 1, A method for inspecting defects in a secondary battery, characterized in that the second SOC is 1% to 5% larger than the first SOC.

15. In Paragraph 1 A method for inspecting defects in a secondary battery, characterized by further including a step of stabilizing the secondary battery between the first charging step and the second charging step.

Images