Method for inspecting nonaqueous electrolyte secondary battery

Abstract

Provided is a nonaqueous electrolyte secondary battery inspection method capable of reducing inspection time. The method includes a first period after the end of a cooling process and a second period after the end of the first period. The second period is a period in which the variation in the voltage decrease per unit time in the nonaqueous electrolyte secondary battery is smaller than in the first period. The cooling process is a process in which the nonaqueous electrolyte secondary battery is cooled while being directly or indirectly pressed from the thickness direction at a pressure lower than the pressure in the inspection process or while not being pressed. In the second period, the voltage of the nonaqueous electrolyte secondary battery is measured when a predetermined time has elapsed after the voltage of the nonaqueous electrolyte secondary battery is measured. When the voltage decrease per unit time based on the measured voltage is below a threshold value, the nonaqueous electrolyte secondary battery is determined to be normal.

Description

Technical Field

[0001] This invention relates to a method for inspecting non-aqueous electrolyte secondary batteries, and more specifically, to a method for inspecting non-aqueous electrolyte secondary batteries that can shorten the inspection time for self-discharge testing. Background Technology

[0002] In the past, the presence of internal short circuits in non-aqueous electrolyte secondary batteries led to increased self-discharge, necessitating self-discharge checks. One method for checking non-aqueous electrolyte secondary batteries, as disclosed in Patent Document 1, includes a first aging process, a first measurement process, a second aging process, a second measurement process, and a judgment process. The first aging process involves storing the initially charged secondary battery at a high-temperature environment. The first measurement process involves measuring the voltage of the secondary battery at a high-temperature environment. The second aging process involves storing the secondary battery at room temperature. The second measurement process involves measuring the voltage of the secondary battery at room temperature. The judgment process calculates the voltage difference between the first and second measurement processes in the form of a voltage drop value, and if the voltage drop value exceeds a threshold, the secondary battery is judged as defective.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-29616 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] However, in the invention described in Patent Document 1, the voltage drop value may deviate. In order to suppress the deviation of the voltage drop value, a second measurement process is required after the second aging process has been carried out for a long time, and time is spent on the inspection.

[0008] Methods for solving problems

[0009] An inspection method for a non-aqueous electrolyte secondary battery according to one aspect of the present invention includes the following steps: a high-temperature aging step, wherein the charged non-aqueous electrolyte secondary battery is stored in a high-temperature environment; a cooling step, wherein the non-aqueous electrolyte secondary battery stored in the high-temperature environment during the high-temperature aging step is cooled; and an inspection step, wherein after the cooling step, the non-aqueous electrolyte secondary battery is inspected for normal operation based on the voltage drop value per unit time of the non-aqueous electrolyte secondary battery. The inspection step has a first period after the cooling step and a second period after the first period, wherein the second period is a period in which the deviation of the voltage drop value per unit time of the non-aqueous electrolyte secondary battery is less than that of the first period. The process involves checking whether the non-aqueous electrolyte secondary battery is normal while the electrode body is constrained by pressure applied directly or indirectly in the thickness direction. The cooling process involves cooling the non-aqueous electrolyte secondary battery while the electrode body is constrained by pressure applied directly or indirectly in the thickness direction at a lower pressure than that in the inspection process, or without constraining the electrode body. The inspection process includes the following steps: a first measurement step, measuring the voltage value of the non-aqueous electrolyte secondary battery during the second period; a second measurement step, measuring the voltage value of the non-aqueous electrolyte secondary battery during the second period, after a predetermined time has elapsed since the first measurement step; and a judgment step, determining that the non-aqueous electrolyte secondary battery is normal when the voltage drop per unit time based on the voltage value measured in the first measurement step and the voltage value measured in the second measurement step is below a threshold.

[0010] In addition, the above inspection process may include the following steps: a third measurement step, in which, during the second period, after a time shorter than the specified time has elapsed since the first measurement step was performed, the voltage value of the non-aqueous electrolyte secondary battery is measured; and a first determination step, in which the non-aqueous electrolyte secondary battery is determined to be normal when the voltage drop per unit time based on the voltage value measured in the first measurement step and the voltage value measured in the third measurement step is below a threshold. The determination step is the second determination step, and the second measurement step and the second determination step are performed when the non-aqueous electrolyte secondary battery was not determined to be normal in the first determination step.

[0011] In addition, if the non-aqueous electrolyte secondary battery is determined to be normal in the first determination process, the second measurement process and the second determination process can be omitted.

[0012] Furthermore, the electrode body has a positive electrode, a negative electrode, and a separator. The electrode body is constructed by laminating the positive electrode, the negative electrode, and the separator. In the inspection process, the third measurement process and the first determination process can be performed when the opposing capacity ratio (opposite capacity ratio) of the positive electrode and the negative electrode is within a predetermined allowable range.

[0013] In addition, the first and second measurement steps described above can be performed when the SOC of the non-aqueous electrolyte secondary battery is 80% to 90%.

[0014] Another aspect of the present invention is a method for inspecting a non-aqueous electrolyte secondary battery. The method comprises: a high-temperature aging process, in which the charged non-aqueous electrolyte secondary battery is stored in a high-temperature environment; a cooling process, in which the non-aqueous electrolyte secondary battery stored in the high-temperature environment during the high-temperature aging process is cooled; and an inspection process, in which, after the cooling process, the non-aqueous electrolyte secondary battery is inspected for normal operation based on the voltage drop value per unit time. The inspection process includes a first period after the cooling process and a second period after the first period, wherein the second period is a period in which the deviation of the voltage drop value per unit time in the non-aqueous electrolyte secondary battery is less than that in the first period. The inspection process includes: a first measurement process, in which, after the second period... During the second period, the voltage value of the non-aqueous electrolyte secondary battery is measured; in the third measurement step, during the second period, when a time shorter than a predetermined time has elapsed after the first measurement step, the voltage value of the non-aqueous electrolyte secondary battery is measured; in the first determination step, when the voltage drop per unit time based on the voltage value measured in the first measurement step and the voltage value measured in the third measurement step is below a threshold, the non-aqueous electrolyte secondary battery is determined to be normal; in the second measurement step, if the non-aqueous electrolyte secondary battery is not determined to be normal in the first determination step, during the second period, when a predetermined time has elapsed after the first measurement step, the voltage value of the non-aqueous electrolyte secondary battery is measured; and in the second determination step, when the voltage drop per unit time based on the voltage value measured in the first measurement step and the voltage value measured in the second measurement step is below a threshold, the non-aqueous electrolyte secondary battery is determined to be normal.

[0015] The effects of the invention

[0016] According to the present invention, the inspection time of non-aqueous electrolyte secondary batteries can be shortened. Attached Figure Description

[0017] Figure 1 This is a perspective view of the lithium-ion secondary battery according to this embodiment.

[0018] Figure 2 This is a schematic diagram showing the structure of the laminated electrode body of a lithium-ion secondary battery.

[0019] Figure 3 This is a schematic diagram showing the configuration of the end of the electrode body as viewed from the width direction W.

[0020] Figure 4 This is a perspective view showing the inspection configuration of the lithium-ion secondary battery according to this embodiment.

[0021] Figure 5 This is a flowchart illustrating the inspection method of the lithium-ion secondary battery according to the first embodiment.

[0022] Figure 6 This is a diagram showing the open voltage of the lithium-ion secondary battery according to this embodiment.

[0023] Figure 7 This is a graph showing the voltage drop per unit time and the deviation of the open voltage in the lithium-ion secondary battery of this embodiment.

[0024] Figure 8 This is a graph showing the deviation between the constraint strength and the open voltage during the cooling process in the lithium-ion secondary battery of this embodiment.

[0025] Figure 9 This is a flowchart illustrating an embodiment of a method for inspecting a lithium-ion secondary battery.

[0026] Figure 10 This is a graph showing the SOC, open voltage, negative electrode potential, and counter-capacity ratio of the lithium-ion secondary battery of this embodiment.

[0027] Figure 11 This is a graph showing the SOC, negative electrode potential, and counter-capacity ratio of the lithium-ion secondary battery of this embodiment.

[0028] Figure 12 This is a graph showing the SOC, open voltage, and counter-capacity ratio of the lithium-ion secondary battery of this embodiment.

[0029] Figure 13 This is a graph showing the voltage drop relative to the change in SOC and the relative capacity ratio in the lithium-ion secondary battery of this embodiment. Detailed Implementation

[0030] [First Implementation]

[0031] The following describes one implementation method for inspecting non-aqueous electrolyte secondary batteries.

[0032] <Lithium-ion secondary battery 10>

[0033] The structure of the lithium-ion secondary battery, which is the premise of this embodiment, will be briefly described.

[0034] like Figure 1 As shown, the lithium-ion secondary battery 10 is configured as a single-cell battery. The lithium-ion secondary battery 10 includes a cuboid battery casing 11 and a cover 12. The battery casing 11 has an opening (not shown) on its upper side. The cover 12 seals the opening of the battery casing 11. The battery casing 11 and the cover 12 are made of a metal such as aluminum alloy. The cover 12 has a negative external terminal 13 and a positive external terminal 14 used for charging and discharging electricity. The negative external terminal 13 and the positive external terminal 14 can be of any shape.

[0035] The lithium-ion secondary battery 10 includes an electrode body 15. The lithium-ion secondary battery 10 includes a negative current collector 16 and a positive current collector 17. The negative current collector 16 connects the negative electrode of the electrode body 15 to the negative external terminal 13. The positive current collector 17 connects the positive electrode of the electrode body 15 to the positive external terminal 14. The electrode body 15 is housed inside a battery casing 11. A non-aqueous electrolyte 18 is injected into the battery casing 11 through an injection hole (not shown). Thus, the lithium-ion secondary battery 10 includes the non-aqueous electrolyte 18. In the lithium-ion secondary battery 10, a sealed battery cell is formed by mounting a cover 12 to the battery casing 11. Thus, the battery casing 11 houses the electrode body 15 and the non-aqueous electrolyte 18.

[0036] <Non-aqueous electrolyte 18>

[0037] The non-aqueous electrolyte 18 is a composition containing a supporting salt (supporting electrolyte) in a non-aqueous solvent. In this embodiment, ethylene carbonate (EC) can be used as the non-aqueous solvent. The non-aqueous solvent can be one or more materials selected from the group consisting of propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0038] Additionally, as supporting salts, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc., can be used. Alternatively, one or more lithium compounds (lithium salts) selected from these can be used.

[0039] <Electrode 15>

[0040] like Figure 2As shown, the electrode body 15 includes a negative electrode plate 20, a positive electrode plate 30, and a separator 40. The direction of the length of the electrode body 15 is called the "length direction Z". The direction of the thickness of the electrode body 15 is called the "thickness direction D". The direction orthogonal to the length direction Z and the thickness direction D of the electrode body 15 is called the "width direction W".

[0041] <Negative Plate 20>

[0042] The negative electrode plate 20 functions as an example of the negative electrode of the lithium-ion secondary battery 10. The negative electrode plate 20 includes a negative electrode substrate 21 and a negative electrode composite material layer 22. The negative electrode composite material layer 22 is formed on both sides of the negative electrode substrate 21. The negative electrode substrate 21 has a negative electrode connection portion 23 exposed from the electrode body 15. The negative electrode connection portion 23 is provided at one end of the electrode body 15 in the width direction W. That is, the negative electrode connection portion 23 is provided at one end of the negative electrode substrate 21 in the width direction W of the electrode body 15.

[0043] In this embodiment, the negative electrode substrate 21 is made of Cu foil. The negative electrode substrate 21 forms a base that serves as the aggregate of the negative electrode composite material layer 22. The negative electrode substrate 21 functions as a current collector that collects electricity from the negative electrode composite material layer 22.

[0044] The negative electrode composite material layer 22 contains a negative electrode active material. In this embodiment, the negative electrode active material is a material capable of intercalating / deintercalating lithium ions, and a powdered carbon material composed of graphite (black lead) or the like is used. The negative electrode plate 20 is manufactured, for example, by mixing the negative electrode active material, solvent, and binder (adhesive), coating the mixed negative electrode composite material onto the negative electrode substrate 21, and then drying it.

[0045] <Positive Plate 30>

[0046] The positive electrode plate 30 functions as an example of the positive electrode of the lithium-ion secondary battery 10. The positive electrode plate 30 includes a positive electrode substrate 31 and a positive electrode composite material layer 32. The positive electrode composite material layer 32 is formed on both sides of the positive electrode substrate 31. The positive electrode substrate 31 has a positive electrode connection portion 33 exposed from the electrode body 15. The positive electrode connection portion 33 is located at the other end of the electrode body 15 in the width direction W. That is, the positive electrode connection portion 33 is located at the end of the positive electrode substrate 31 on the side opposite to the negative electrode connection portion 23 in the width direction W of the electrode body 15.

[0047] In this embodiment, the positive electrode substrate 31 is made of Al foil or Al alloy foil. The positive electrode substrate 31 forms a base that serves as the aggregate for the positive electrode composite material layer 32. The positive electrode substrate 31 functions as a current collector that collects electricity from the positive electrode composite material layer 32.

[0048] The positive electrode composite layer 32 contains a positive electrode active material. This active material is a material capable of lithium intercalation / deintercalation, such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), or lithium nickel oxide (LiNiO2). Alternatively, a material formed by mixing LiCoO2, LiMn2O4, and LiNiO2 in any proportion can be used. The positive electrode composite layer 32 contains a conductive material. Examples of conductive materials include acetylene black (AB), carbon black such as Ketjen black, and graphite (lead black). The positive electrode plate 30 can be manufactured, for example, by mixing the positive electrode active material, conductive material, solvent, and binder (adhesive), coating the mixed positive electrode composite material onto the positive electrode substrate 31, and then drying it.

[0049] <Separator 40>

[0050] The separator 40 holds the non-aqueous electrolyte 18 between the negative electrode plate 20 and the positive electrode plate 30. The separator 40 is a non-woven fabric made of porous resin such as polypropylene. The separator 40 can also be a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, or a lithium-ion or ion-conductive polymer electrolyte membrane, used alone or in combination. When the electrode body 15 is immersed in the non-aqueous electrolyte 18, the non-aqueous electrolyte 18 permeates from the ends of the separator 40 towards the center.

[0051] <Manufacturing process of lithium-ion secondary battery 10>

[0052] Here, a summary of the manufacturing process of the lithium-ion secondary battery 10 according to this embodiment will be described.

[0053] In this embodiment, an initial process (source engineering) is performed. The initial process is the manufacturing process of the battery elements of the lithium-ion secondary battery 10. Specifically, the initial process is the process of manufacturing the negative electrode plate 20 and the positive electrode plate 30 that constitute the battery elements of the lithium-ion secondary battery 10.

[0054] At the end of the initial process, a lamination process is performed. In the lamination process, the negative electrode plate 20, positive electrode plate 30, and separator 40 are laminated in the order of negative electrode plate 20, positive electrode plate 30, and separator 40. That is, the electrode body 15 is constructed by laminating the negative electrode plate 20 and positive electrode plate 30 with the separator 40 in between. The negative electrode composite material layer 22 and the positive electrode composite material layer 32 are arranged opposite each other with the separator 40 in between. The negative electrode plate 20 and the separator 40 are arranged such that the negative electrode connection portion 23 protrudes from the separator 40 at one end in the width direction W of the electrode body 15. The positive electrode plate 30 and the separator 40 are arranged such that the positive electrode connection portion 33 protrudes from the separator 40 at the other end in the width direction W of the electrode body 15. That is, in the electrode body 15, a negative electrode connection portion 23 exposing the negative electrode substrate 21 is formed at one end, and a positive electrode connection portion 33 exposing the positive electrode substrate 31 is formed at the other end.

[0055] At the end of the lamination process, a winding process is performed. In the winding process, the electrode body 15 is supported and wound around a winding axis in the width direction W. A flat portion in the shape of a racing track and curved portions at both ends of the flat portion are formed in the electrode body 15.

[0056] When the winding process is completed, a winding body pressing process is performed. The electrode body 15 is compressed by pressing it from the thickness direction D with a force not exceeding a specified pressure. In this embodiment, 100kN is used as the specified pressure, but it is not limited to this.

[0057] In detail, such as Figure 3 As shown, in the electrode body 15, the negative electrode plate 20 and the positive electrode plate 30 are stacked in an overlapping state with spacers 40 in between, supported around a winding axis and wound along the length direction Z. By applying pressure to the electrode body 15 from the thickness direction D, which is orthogonal to the width direction W, the end of the electrode body 15, viewed from the width direction W, is shaped into a flat shape resembling a racetrack.

[0058] When the winding pressing process is completed, a terminal welding process is performed. In the terminal welding process, the negative electrode connection 23 and the negative electrode current collector 16 are electrically / mechanically connected by welding. The positive electrode connection 33 and the positive electrode current collector 17 are electrically / mechanically connected by welding.

[0059] When the terminal welding process is completed, the casing insertion process is performed. In the casing insertion process, the electrode body 15 is inserted into the battery casing 11 in a flattened state after being wound, and with the negative current collector 16 and the positive current collector 17 connected.

[0060] At the end of the casing insertion process, a sealing welding process is performed. In the sealing welding process, the battery casing 11 and the cover 12 are sealed using laser welding or similar methods. At this stage, the non-aqueous electrolyte 18 has not yet been injected, and the injection port of the cover 12 is open.

[0061] After the sealing and welding process is completed, the battery cell drying process is carried out. In the battery cell drying process, any remaining moisture in the battery casing is thoroughly dried, thus raising the temperature inside the battery to, for example, around 105°C.

[0062] At the end of the battery cell drying process, a liquid injection / sealing process is performed. During this process, non-aqueous electrolyte 18 is injected into the battery cell through the injection port on the cover 12. After injection, the injection port is sealed. This completes the assembly of the lithium-ion secondary battery 10, and a self-discharge check is performed as described below.

[0063] <Inspection Components of Lithium-ion Secondary Battery 10>

[0064] Next, refer to Figure 4 The configuration for inspecting the lithium-ion secondary battery 10 is explained.

[0065] like Figure 4 As shown, during the self-discharge test of the lithium-ion secondary battery 10, multiple lithium-ion secondary batteries 10 are arranged in a manner along the thickness direction D in an inspection fixture (not shown). In this embodiment, 25 lithium-ion secondary batteries 10 can be arranged in the inspection fixture, but it is not limited to this. In this embodiment, multiple lithium-ion secondary batteries 10 can be arranged such that a groove-shaped gap is formed between each of the multiple lithium-ion secondary batteries 10.

[0066] Multiple lithium-ion secondary batteries 10 are constrained along the thickness direction D, depending on the type of process. "Constraint" refers to applying pressure directly or indirectly along the thickness direction D to the electrode body 15, compressing the separator 40. In this embodiment, with multiple lithium-ion secondary batteries 10 disposed, the battery casing 11 is pressed along the thickness direction D. The pressing is not limited to a press; it can also be a configuration using a constraint frame and fastening with threads. The constraint includes strong constraint with a high applied pressure and weak constraint with a lower applied pressure. In this embodiment, the weak constraint is applied at approximately 0.5 kN, but it is not limited to this. In this embodiment, the strong constraint is applied at approximately 10 kN, but it is not limited to this.

[0067] Multiple lithium-ion secondary batteries 10 are cooled by contact with cold air in the cooling process detailed below. In this embodiment, the cold air is applied from below the multiple lithium-ion secondary batteries 10, but it is not limited to this. By allowing the cold air to pass through the gaps formed between the multiple lithium-ion secondary batteries 10, the cooling of the multiple lithium-ion secondary batteries 10 can be promoted.

[0068] <Inspection Methods for Lithium-ion Secondary Batteries>

[0069] Here, refer to Figure 5 The inspection method for lithium-ion secondary battery 10 is explained.

[0070] like Figure 5As shown, firstly, after the manufacturing of the lithium-ion secondary battery 10 is completed, a charging process is performed in step S11. During the charging process, an initial charge is performed for purposes such as forming an SEI (Solid Electrolyte Interphase) coating. The initial charge is performed at a low charge rate to suppress the temperature rise of the lithium-ion secondary battery 10. During the charging process, a full charge to 100% SOC (State of Charge) is performed, but it can also be, for example, 90% SOC. In this embodiment, the charging process is performed, for example, at room temperature of around 20°C. During the charging process, multiple lithium-ion secondary batteries 10 are strongly constrained.

[0071] After the charging process is completed, a high-temperature aging process is performed in step S12. The high-temperature aging process involves storing the lithium-ion secondary battery 10, which was charged during the charging process, in a high-temperature environment. In the high-temperature aging process, the lithium-ion secondary battery 10 is chemically stabilized / activated. One of its purposes is to accelerate the dissolution / precipitation of the metal in cases of micro-inter-electrode short circuits caused by fine metal particles present within the electrodes, thereby detecting these micro-short circuits. Therefore, in this embodiment, the high-temperature aging process is performed, for example, at a temperature of approximately 60°C. In this embodiment, multiple lithium-ion secondary batteries 10 are stored in a high-temperature environment for a predetermined time during the high-temperature aging process. In this embodiment, the time for performing the high-temperature aging process is, for example, 48 hours, but it is not limited to this. In this embodiment, the multiple lithium-ion secondary batteries 10 are not constrained during the high-temperature aging process, but they may also be weakly constrained.

[0072] After the high-temperature aging process, a cooling process is performed in step S13. The cooling process cools the lithium-ion secondary batteries 10 that have been stored in a high-temperature environment in step S12. In the cooling process, to prevent the multiple lithium-ion secondary batteries 10 from being exposed to excessively high temperatures, the multiple lithium-ion secondary batteries 10 are exposed to cold air for a predetermined time, thereby cooling them and restoring them to room temperature. This shortens the self-discharge inspection time. The cooling process is performed, for example, at room temperature of around 20°C. In this embodiment, the cooling process is performed for example for 4 hours, but is not limited to this. In this embodiment, the multiple lithium-ion secondary batteries 10 are not constrained during the cooling process, but may be weakly constrained. Thus, the cooling process cools the lithium-ion secondary batteries 10 either directly or indirectly from the thickness direction D with a pressure less than that used in the inspection process described later, or without constraining the electrode body 15.

[0073] After the cooling process, an inspection process is performed in step S20. In this inspection process, after the charging, high-temperature aging, and cooling processes, the open-circuit voltage (OCV) of multiple lithium-ion secondary batteries 10 is measured. As a result, in this inspection process, the voltage drop ΔV per unit time of the open-circuit voltage (OCV) is used to check whether excessive self-discharge has occurred. That is, the inspection process is a process of checking whether the lithium-ion secondary batteries 10 are normal based on the voltage drop ΔV per unit time of the lithium-ion secondary batteries 10 after the cooling process. The inspection process is performed, for example, at room temperature of approximately 20°C. In this inspection process, multiple lithium-ion secondary batteries 10 are strongly constrained to detect fine short circuits between the electrodes. Thus, the inspection process is a process of checking whether the lithium-ion secondary batteries 10 are normal under a condition where the electrode body 15 is constrained by pressure applied directly or indirectly from the thickness direction D at a pressure greater than that of the cooling process.

[0074] like Figure 6 and Figure 7 As shown, the inspection process includes a first period P1 and a second period P2. The first period P1 is the period from symbol T0 to symbol T1, which is the period after the cooling process ends. The second period P2 is the period after symbol T1, which is the period after the first period P1 ends. In this embodiment, the first period P1 is, for example, 1 to 2 hours, but it is not limited to this.

[0075] <Inspection Procedure>

[0076] like Figure 5 As shown, at the start of the inspection process, in step S21, it is determined whether the first period P1 has ended. Before the first period P1 ends, the process does not proceed to step S22; when the first period P1 ends, the process proceeds to step S22. That is, during the inspection process, the open-circuit voltage (OCV) of the cell is not measured during the first period P1.

[0077] In the inspection process, when the first period P1 ends, the second period P2 is established. Furthermore, in step S22, the first measurement process is performed. The first measurement process is the process of measuring the first open voltage OCV1. Thus, the inspection process includes the first measurement process of measuring the voltage value of the lithium-ion secondary battery 10 during the second period P2.

[0078] After the first measurement process is completed, in step S23, it is determined whether a predetermined time has elapsed since the end of the first measurement process. In this embodiment, the predetermined time is, for example, 24 hours, but it is not limited to this. During the second period P2, the process does not proceed to step S24 until the predetermined time has elapsed since the end of the first measurement process. The process proceeds to step S24 only after the predetermined time has elapsed since the end of the first measurement process.

[0079] After a predetermined time has elapsed since the completion of the first measurement step, a second measurement step is performed in step S24. The second measurement step measures the second open voltage OCV2. Thus, the inspection process includes a second measurement step in which the voltage value of the lithium-ion secondary battery 10 is measured after a predetermined time has elapsed since the first measurement step was performed during the second period P2.

[0080] After the second measurement process is completed, in step S25, the voltage drop value ΔV per unit time is calculated based on the difference between the first open voltage OCV1 and the second open voltage OCV2 and a specified time. It is then determined whether the calculated voltage drop value ΔV per unit time is below a threshold value.

[0081] If the voltage drop value ΔV per unit time is determined to be below a threshold, the lithium-ion secondary battery 10 is determined to be normal in step S26. If the voltage drop value ΔV per unit time is determined to be not below the threshold, the lithium-ion secondary battery 10 is determined to be abnormal in step S27. That is, the inspection process includes a determination process (second determination process), where the lithium-ion secondary battery 10 is determined to be normal when the voltage drop value ΔV per unit time based on the voltage measured in the first measurement process and the voltage measured in the second measurement process is below the threshold.

[0082] <Inspect the status of each stage of the process>

[0083] Here, refer to Figure 6 and Figure 7 The status of each stage of the inspection process is described.

[0084] like Figure 6 and Figure 7 As shown, after the cooling process ends, the voltage drop ΔV of the open voltage OCV per unit time decreases over time. In other words, compared with period 2 P2, the open voltage OCV of period 1 P1 decreases sharply; compared with period 1 P1, the open voltage OCV of period 2 P2 decreases slowly.

[0085] like Figure 7As shown, in a specific example, at the moment T1, the end of the first period P1, the voltage drop value ΔV per unit time becomes the reference voltage drop value ΔV0. Furthermore, before the moment T1, the voltage drop value ΔV per unit time is greater than the reference voltage drop value ΔV0. On the other hand, after the moment T1, the voltage drop value ΔV per unit time is less than the reference voltage drop value ΔV0. That is, the second period P2 is the period during which the voltage drop value ΔV per unit time of the open voltage OCV is less than that of the first period P1. In this case, unlike the second determination process, the voltage drop value ΔV per unit time of the open voltage OCV is calculated as the voltage drop value within a time shorter than the specified time, but it is not limited to this.

[0086] In addition, after the cooling process is completed, as time passes, the standard deviation ΔVσ of the voltage drop ΔV per unit time of the open voltage OCV in the multiple lithium-ion secondary batteries 10 decreases.

[0087] To give a specific example, at the time T1, the end of the first period P1, the standard deviation ΔVσ of the voltage drop per unit time ΔV becomes the reference standard deviation ΔVσ0. The reference standard deviation ΔVσ0 is used to determine the permissible standard deviation of the voltage drop per unit time ΔV. Furthermore, before the time sign T1, the standard deviation ΔVσ of the voltage drop per unit time ΔV is greater than the reference standard deviation ΔVσ0. On the other hand, after the time sign T1, the standard deviation ΔVσ of the voltage drop per unit time ΔV is less than the reference standard deviation ΔVσ0. That is, the second period P2 is the period in which the deviation of the voltage drop per unit time ΔV in the lithium-ion secondary battery 10 is less than that in the first period P1. Additionally, the second period P2 can also be described as the period in which the slope of the voltage drop in the lithium-ion secondary battery 10 is less than that in the first period P1.

[0088] This has been found to be due to the lithium-ion secondary battery 10 failing to return to room temperature after the high-temperature aging and cooling processes. For example, multiple lithium-ion secondary batteries 10 were stored in a high-temperature environment during the high-temperature aging process.

[0089] Subsequently, multiple lithium-ion secondary batteries 10 are configured at room temperature, but these batteries have a temperature difference with the external gas. Furthermore, the configurations of each lithium-ion secondary battery 10 may differ, resulting in varying heat transfer rates. Consequently, the temperatures of each lithium-ion secondary battery 10 deviate from their respective configurations.

[0090] In particular, during the cooling process, multiple lithium-ion secondary batteries 10 are cooled by contacting cold air. However, the configurations of the multiple lithium-ion secondary batteries 10 may be different, and the airflow of the cold air contacted by each of the multiple lithium-ion secondary batteries 10 may be different. As a result, the temperatures of the multiple lithium-ion secondary batteries 10 will vary.

[0091] To give a specific example, among the multiple lithium-ion secondary batteries 10 arranged in a manner along the thickness direction D, the outermost lithium-ion secondary battery 10 and the innermost lithium-ion secondary battery 10 have different ways of transferring heat to the external gas, and the air volume of the cold air is also different.

[0092] When the temperature in the lithium-ion secondary battery 10 is high, the voltage drop ΔV of the open-circuit voltage OCV tends to increase compared to when the temperature is low. Therefore, when the individual temperatures of the multiple lithium-ion secondary batteries 10 deviate, the voltage drop ΔV of the open-circuit voltage OCV also deviates. Thus, by not measuring the first open-circuit voltage OCV1 in the first period P1 and measuring the first open-circuit voltage OCV1 in the second period P2, the deviation of the open-circuit voltage OCV of the multiple lithium-ion secondary batteries 10 can be suppressed.

[0093] <Constraint strength in the cooling process>

[0094] Next, refer to Figure 8 The constraint strength in the cooling process is explained.

[0095] like Figure 8 As shown, if the constraint strength in the cooling process decreases, the standard deviation ΔVσ of the voltage drop ΔV per unit time of the open voltage OCV in the multiple lithium-ion secondary batteries 10 decreases.

[0096] To give a specific example, when the constraint strength in the cooling process is the reference strength G0, the standard deviation ΔVσ of the voltage drop per unit time ΔV becomes the reference standard deviation ΔVε0. Furthermore, when the constraint strength is greater than the reference strength G0, the standard deviation ΔVσ of the voltage drop per unit time ΔV is greater than the reference standard deviation ΔVσ0. On the other hand, when the constraint strength is less than the reference strength G0, the standard deviation ΔVσ of the voltage drop per unit time ΔV is less than the reference standard deviation ΔVσ0. Additionally, the reference strength G0 is a strength that is less than the constraint strength based on a strong constraint and greater than the constraint strength based on a weak constraint.

[0097] Regarding this point, after the high-temperature aging process, when cooling multiple lithium-ion secondary batteries 10 during the cooling process, compared to the case of low constraint strength, the temperature of the lithium-ion secondary batteries 10 is less likely to drop from high temperature to room temperature when the constraint strength is high. Therefore, during the cooling process, by not constraining or weakly constraining multiple lithium-ion secondary batteries 10, the deviation of the open voltage (OCV) of each of the multiple lithium-ion secondary batteries 10 can be suppressed.

[0098] <Function of the first implementation method>

[0099] The function of the first embodiment will be explained.

[0100] First, when the lithium-ion secondary battery 10 is manufactured, it undergoes an initial charge during the charging process. Then, during the high-temperature aging process, the lithium-ion secondary battery 10 is stored in a high-temperature environment. Therefore, the initial charge capacity and high-temperature aging conditions can be defined as inspection criteria for the lithium-ion secondary battery 10.

[0101] Next, in the cooling process, the lithium-ion secondary batteries 10 are cooled. In this cooling process, the multiple lithium-ion secondary batteries 10 are not constrained or are only weakly constrained. As a result, temperature deviations among the multiple lithium-ion secondary batteries 10 can be suppressed.

[0102] Next, during the inspection process, the first open-circuit voltage OCV1 was not measured during period 1 (P1). After period 1 (P1) ended, the first open-circuit voltage OCV1 was measured during period 2 (P2). During period 2 (P2), after a predetermined time had elapsed following the measurement of the first open-circuit voltage OCV1, the second open-circuit voltage OCV2 was measured. Based on the first open-circuit voltage OCV1, the second open-circuit voltage OCV2, and the predetermined time, the voltage drop ΔV per unit time of the open-circuit voltage OCV was calculated. If the calculated voltage drop ΔV per unit time of the open-circuit voltage OCV was determined to be below a threshold, the lithium-ion secondary battery 10 was deemed normal as a self-discharge check.

[0103] In this way, by not measuring the first open voltage OCV1 during the first period P1 and measuring the first open voltage OCV1 during the second period P2, the deviation of the voltage drop value ΔV per unit time in the multiple lithium-ion secondary batteries 10 can be suppressed. In addition, the predetermined time from measuring the first open voltage OCV1 to measuring the second open voltage OCV2 can be shortened, and as a result, the inspection time for self-discharge testing can be shortened.

[0104] <Effects of the first implementation method>

[0105] The effects of the first embodiment will be explained.

[0106] (1) According to the inspection method of the lithium-ion secondary battery 10 of this embodiment, the first open voltage OCV1 of the lithium-ion secondary battery 10 is measured during the second period P2, and the second open voltage OCV2 is measured after a predetermined time has elapsed after the measurement of the first open voltage OCV1. The second period P2 is the period during which the deviation of the voltage drop value ΔV per unit time among the plurality of lithium-ion secondary batteries 10 is less than that during the first period P1. Therefore, by measuring the first open voltage OCV1 during the second period P2, compared with measuring the first open voltage OCV1 during the first period P1, the time from the end of the cooling process to the measurement of the second open voltage OCV2 can be shortened. Therefore, the deviation of the voltage drop value ΔV per unit time among the plurality of lithium-ion secondary batteries 10 can be suppressed, and the inspection time of the self-discharge inspection can be shortened without reducing the inspection accuracy of the self-discharge inspection.

[0107] (2) The cooling process involves cooling multiple lithium-ion secondary batteries 10 by applying a small pressure to the electrode body 15 directly or indirectly along the thickness direction D, or without constraining the electrode body 15. Therefore, the cooling efficiency of the multiple lithium-ion secondary batteries 10 can be improved, and temperature deviations within the multiple lithium-ion secondary batteries 10 can be suppressed. Consequently, deviations in the voltage drop ΔV per unit time within the multiple lithium-ion secondary batteries 10 can be suppressed, and the inspection time for self-discharge testing can be shortened without reducing the inspection accuracy of the self-discharge test.

[0108] [Second Implementation]

[0109] Next, the second embodiment will be described.

[0110] In the first embodiment, the normality of the lithium-ion secondary battery 10 is determined based on the first open voltage OCV1 and the second open voltage OCV2 after a predetermined time. In the second embodiment, the normality of the lithium-ion secondary battery 10 can be determined based on the first open voltage OCV1 and the third open voltage OCV3 after a time shorter than the predetermined time. In the following description, the same reference numerals are used for the same configurations and control elements as in the previously described embodiments, and repeated descriptions are omitted or simplified.

[0111] like Figure 9 As shown, after the first measurement process is completed, step S31 determines whether the opposing capacity ratio is within the allowable range. The opposing capacity ratio is the ratio of the positive electrode capacity to the negative electrode capacity of the opposing portions of the negative electrode plate 20 and the positive electrode plate 30.

[0112] The positive electrode capacity can be calculated, for example, based on the manufacturing and inspection conditions of the lithium-ion secondary battery 10. The manufacturing conditions of the lithium-ion secondary battery 10 may include, for example, the electrode conditions of the lithium-ion secondary battery 10. The electrode conditions of the lithium-ion secondary battery 10 may include, for example, the material properties of the positive electrode and the weight per unit area (approximate weight). The material properties of the positive electrode are the material properties of the positive electrode substrate 31 and the positive electrode composite material layer 32. The weight per unit area of ​​the positive electrode is the weight per unit area of ​​the positive electrode composite material layer 32 relative to the positive electrode substrate 31. The inspection conditions of the lithium-ion secondary battery 10 can, for example, be predicted based on the initial charge capacity. The initial charge capacity is the capacity of the initial charge performed in the charging process of step S11.

[0113] The negative electrode capacity can be calculated, for example, based on the manufacturing conditions of the lithium-ion secondary battery 10. The manufacturing conditions of the lithium-ion secondary battery 10 may include, for example, the electrode conditions of the lithium-ion secondary battery 10. The electrode conditions of the lithium-ion secondary battery 10 may include, for example, the weight per unit area of ​​the negative electrode. The weight per unit area of ​​the negative electrode is the weight per unit area of ​​the negative electrode composite material layer 22 relative to the negative electrode substrate 21.

[0114] The manufacturing and inspection conditions for such a lithium-ion secondary battery 10 can be measured values ​​from the lithium-ion secondary battery 10 being inspected, or they can be design values ​​based on the designer of the lithium-ion secondary battery 10.

[0115] The allowable range is calculated based on a reference capacity ratio R0, which serves as the benchmark for the capacity ratio. Specifically, the allowable range is a pre-defined tolerance range for the reference capacity ratio R0. In particular, the allowable range is the range within which the lithium-ion secondary battery 10 can be determined to be normal by whether the voltage drop ΔV per unit time in a short time shorter than a specified time is below a threshold value.

[0116] If it is determined that the opposing capacity ratio is not within the allowable range, proceed to step S23. On the other hand, if it is determined that the opposing capacity ratio is within the allowable range, proceed to step S32.

[0117] If the capacity ratio is determined to be within the acceptable range, in step S32, it is determined whether a predetermined short time has elapsed since the end of the first measurement process. This short time is shorter than a specified time, for example, approximately 10 minutes. During the second period P2, the process does not proceed to step S33 until the short time has elapsed since the end of the first measurement process; however, it proceeds to step S33 once the short time has elapsed since the end of the first measurement process.

[0118] When a short time has elapsed after the first measurement process ends, the third measurement process is performed in step S33. The third measurement process measures the third open-circuit voltage OCV3. Thus, the inspection process includes the third measurement process. During the second period P2, after the first measurement process is performed, when a time shorter than a specified time has elapsed, the voltage value of the lithium-ion secondary battery 10 is measured.

[0119] After the third measurement process ends, in step S34, based on the difference between the first open-circuit voltage OCV1 and the third open-circuit voltage OCV3 and the short time, the voltage decrease value ΔV per unit time is calculated. It is determined whether the calculated voltage decrease value ΔV per unit time is below the threshold value.

[0120] When it is determined that the voltage decrease value ΔV per unit time is below the threshold value, in step S26, the lithium-ion secondary battery 10 is determined to be normal. When it is determined that the voltage decrease value ΔV per unit time is not below the threshold value, the process proceeds to step S23. That is, the inspection process includes a determination process. Based on the voltage measured in the first measurement process and the voltage measured in the third measurement process, when the voltage decrease value ΔV per unit time is below the threshold value, the lithium-ion secondary battery 10 is determined to be normal.

[0121] Thus, in the present embodiment, the determination process for determining the voltage decrease value ΔV per unit time based on the first open-circuit voltage OCV1 and the third open-circuit voltage OCV3 is an example of the first determination process. In addition, in the present embodiment, the determination process for determining the voltage decrease value ΔV per unit time based on the first open-circuit voltage OCV1 and the second open-circuit voltage OCV2 is an example of the second determination process.

[0122] In addition, in the inspection process, when the counter capacity ratio of the positive electrode capacity to the negative electrode capacity is within a preset allowable range, the third measurement process and the first determination process of steps S32 to S34 are performed. In addition, when the lithium-ion secondary battery 10 is not determined to be normal in the first determination process, the second measurement process and the second determination process of steps S23 to S25 are performed.

[0123] <SOC, counter capacity ratio, open-circuit voltage OCV, and negative electrode potential Vnp>

[0124] Here, refer to Figures 10-13 The relationship between SOC, counter capacity ratio, open-circuit voltage OCV, and negative electrode potential Vnp will be described. Figures 10-12 In, the open-circuit voltage OCV and the negative electrode potential Vnp when the counter capacity ratio is the reference counter capacity ratio R0 are shown by solid lines. Figures 10-12 In, the open-circuit voltage OCV and the negative electrode potential Vnp when the counter capacity ratio is the first counter capacity ratio R1 are shown by dashed lines. Figures 10-12In the diagram, the open voltage OCV and negative electrode potential Vnp when the capacitance ratio is the second capacitance ratio R2 are represented by a double-dotted line.

[0125] like Figure 10 As shown, when the State of Charge (SOC) decreases, the open-circuit voltage (OCV) of the lithium-ion secondary battery 10 decreases. When the SOC increases, the open-circuit voltage (OCV) of the lithium-ion secondary battery 10 increases. When the SOC decreases, the negative electrode potential (Vnp) of the lithium-ion secondary battery 10 increases. When the SOC increases, the negative electrode potential (Vnp) of the lithium-ion secondary battery 10 decreases.

[0126] Especially as Figure 11 As shown, when the SOC obtainable in the self-discharge test is 80%–90%, the negative electrode potential Vnp varies depending on the capacitance ratio. Specifically, when the SOC obtainable in the self-discharge test is 80%–90%, compared to the first capacitance ratio R1, the negative electrode potential Vnp decreases sharply when it is the reference capacitance ratio R0. Furthermore, when the SOC obtainable in the self-discharge test is 80%–90%, compared to the reference capacitance ratio R0, the negative electrode potential Vnp decreases sharply when it is the second capacitance ratio R2.

[0127] like Figure 12 As shown, when the SOC obtainable during self-discharge testing is 80%–90%, the voltage drop ΔV of the open voltage OCV per unit SOC varies depending on the capacitance ratio. This is because, when the SOC obtainable during self-discharge testing is 80%–90%, the negative electrode potential Vnp varies depending on the capacitance ratio.

[0128] Specifically, such as Figure 12 and Figure 13 As shown, when the SOC achievable in the self-discharge test is 80%–90%, compared to the reference capacitance ratio R0, the voltage drop ΔV of the open-circuit voltage OCV per unit SOC decreases when the capacitance ratio is the first capacitance ratio R1. Conversely, when the SOC achievable in the self-discharge test is 80%–90%, compared to the reference capacitance ratio R0, the voltage drop ΔV of the open-circuit voltage OCV per unit SOC increases when the capacitance ratio is the second capacitance ratio R2.

[0129] Therefore, in step S31, the third measurement step and the first judgment step in steps S32 to S34 are performed under the condition that the opposing capacity ratio is within the allowable range. The allowable range is the range based on the reference opposing capacity ratio R0, and can be the range excluding the first opposing capacity ratio R1 and the second opposing capacity ratio R2.

[0130] <Function of the second implementation method>

[0131] The function of the second embodiment will be explained.

[0132] When the capacity ratio is within the allowable range, during the second period P2, after measuring the first open voltage OCV1, the third open voltage OCV3 is measured after a short time shorter than the specified time. The voltage drop ΔV per unit time of the open voltage OCV is calculated based on the first open voltage OCV1, the third open voltage OCV3, and the short time. If the calculated voltage drop ΔV per unit time of the open voltage OCV is determined to be below the threshold, the lithium-ion secondary battery 10 is judged to be normal as a self-discharge check. Even if the calculated voltage drop ΔV per unit time of the open voltage OCV is determined not to be below the threshold, a judgment can be made again based on the second open voltage OCV2.

[0133] In this way, even if a specified time has elapsed after measuring the first open voltage OCV1, the voltage drop ΔV per unit time can be determined based on the third open voltage OCV3. This shortens the self-discharge check time. It is particularly suitable for situations where the capacitance ratio is within the allowable range.

[0134] <Effects of the second implementation method>

[0135] The effects of the second embodiment will be explained.

[0136] (3) According to the inspection method of the lithium-ion secondary battery 10 of this embodiment, even before measuring the second open voltage OCV2, it is possible to determine whether the lithium-ion secondary battery 10 is normal based on the third open voltage OCV3. This can further shorten the inspection time for self-discharge testing.

[0137] (4) In particular, when the capacity ratio is within the preset allowable range, it is possible to determine whether the lithium-ion secondary battery 10 is normal based on the third open voltage OCV3. This can suppress the deviation of the voltage drop value ΔV per unit time and improve the inspection accuracy as the inspection time of the self-discharge test is shortened.

[0138] [Example of Change]

[0139] This implementation method can be modified as follows. This implementation method and the following modifications can be combined with each other to implement the same method within the scope of technical inconsistency.

[0140] In the second embodiment, the manufacturing conditions of the lithium-ion secondary battery 10, such as parameters used to calculate the positive electrode capacity, may include other parameters such as the thickness of the electrode body 15 after winding in the winding process. Furthermore, it is preferable, for example, that the positive electrode substrate 31, the positive electrode composite layer 32, the negative electrode substrate 21, and the negative electrode composite layer 22 have the same material properties. In this way, by suppressing deviations in parameters affecting the positive electrode capacity of the lithium-ion secondary battery 10, deviations in the plenum capacity ratio of the lithium-ion secondary battery 10 can be suppressed. Similarly, by suppressing deviations in parameters affecting the negative electrode capacity of the lithium-ion secondary battery 10, deviations in the plenum capacity ratio of the lithium-ion secondary battery 10 can be suppressed.

[0141] In the second embodiment, for example, the allowable range of the relative capacity ratio of the lithium-ion secondary battery 10 can be a range including the first relative capacity ratio R1 and the second relative capacity ratio R2. Alternatively, for example, the allowable range of the relative capacity ratio of the lithium-ion secondary battery 10 can be any range based on a reference relative capacity ratio R0. In this case, the threshold value of the voltage drop ΔV per unit time can be set to a large threshold value.

[0142] • In the second embodiment, for example, the threshold value of voltage drop ΔV per unit time can be set according to the reference counter-capacity ratio R0 of the lithium-ion secondary battery 10.

[0143] In the second embodiment, for example, the threshold values ​​can be different in the determination based on the first open voltage OCV1 and the second open voltage OCV2, and in the determination based on the first open voltage OCV1 and the third open voltage OCV3. That is, a first threshold value can be set for the voltage drop value ΔV per unit time based on the first open voltage OCV1 and the second open voltage OCV2, and a second threshold value can be set for the voltage drop value ΔV per unit time based on the first open voltage OCV1 and the third open voltage OCV3. In addition, for example, the second threshold value can be smaller than the first threshold value. Thus, the determination based on the first open voltage OCV1 and the third open voltage OCV3 can be performed based on a strict reference.

[0144] In this embodiment, the length of the first period P1 can be changed, for example, based on the time of the high-temperature aging process. The length of the first period P1 can be changed, for example, based on the temperature of the high-temperature aging process. The length of the first period P1 can be changed, for example, based on the time of the cooling process. The length of the first period P1 can be changed, for example, based on the airflow rate of the cold air in the cooling process. The length of the first period P1 can be changed, for example, based on the number of lithium-ion secondary batteries 10 to be inspected. The length of the first period P1 can be changed, for example, based on the configuration of the lithium-ion secondary batteries 10 to be inspected.

[0145] In this embodiment, the first, second, and third measurement steps are performed when the SOC of the lithium-ion secondary battery 10 is 80% to 90%, but the method is not limited to this. For example, the first, second, and third measurement steps can be performed when the SOC of the lithium-ion secondary battery 10 is 80% to 100%, or for example, when the SOC of the lithium-ion secondary battery 10 is 90% to 100%.

[0146] · Figure 5 , Figure 9 The flowchart shown is an example; those skilled in the art can add to, remove from, modify, or change the order of the process to implement it.

[0147] • In this embodiment, the invention is described using a lithium-ion secondary battery 10 as an example, but it can also be applied to other non-aqueous electrolyte secondary batteries.

[0148] This embodiment illustrates a thin-plate lithium-ion secondary battery 10 for automotive use, but it can also be applied to cylindrical batteries, etc. Furthermore, it is not limited to automotive batteries; it can also be applied to marine batteries, aircraft batteries, and stationary batteries.

[0149] The present invention may, of course, be implemented by those skilled in the art by adding, removing, altering, or changing the order of its components without departing from the scope of the claims.

Claims

1. A method for inspecting a non-aqueous electrolyte secondary battery, comprising an electrode body, a non-aqueous electrolyte, and a battery casing housing the electrode body and the non-aqueous electrolyte, the method comprising the following steps: The high-temperature aging process involves storing the charged non-aqueous electrolyte secondary batteries in a high-temperature environment. The cooling process involves cooling the non-aqueous electrolyte secondary battery that has been stored at a high temperature during the high-temperature aging process. as well as In the inspection process, after the cooling process is completed, the non-aqueous electrolyte secondary battery is checked for normal operation based on the voltage drop per unit time. The inspection process includes a first period after the cooling process ends and a second period after the first period ends. The second period is the period during which the deviation of the voltage drop per unit time in the non-aqueous electrolyte secondary battery is smaller than that in the first period. The inspection process involves checking whether the non-aqueous electrolyte secondary battery is functioning properly while the electrode body is constrained by pressure applied directly or indirectly in the thickness direction. The cooling process is a process of cooling the non-aqueous electrolyte secondary battery by directly or indirectly applying pressure to the electrode body in the thickness direction at a pressure lower than that of the inspection process, or by not constraining the electrode body. The inspection process includes the following steps: The first measurement step involves measuring the voltage value of the non-aqueous electrolyte secondary battery during the second period. In the second measurement step, during the second period, after a predetermined time has elapsed since the first measurement step, the voltage value of the non-aqueous electrolyte secondary battery is measured. as well as In the determination process, if the voltage drop per unit time based on the voltage values ​​measured in the first measurement step and the voltage values ​​measured in the second measurement step is below a threshold, the non-aqueous electrolyte secondary battery is determined to be normal. The inspection process includes the following steps: In the third measurement step, during the second period, when a time shorter than the specified time has elapsed after the first measurement step, the voltage value of the non-aqueous electrolyte secondary battery is measured. as well as In the first determination step, if the voltage drop per unit time based on the voltage value measured in the first measurement step and the voltage value measured in the third measurement step is below a threshold, the non-aqueous electrolyte secondary battery is determined to be normal. The determination process is the second determination process. The second measurement step and the second determination step are performed when the second determination step did not determine that the non-aqueous electrolyte secondary battery is normal.

2. The method of inspecting a nonaqueous electrolyte secondary battery according to claim 1, wherein If the second determination step is determined to be normal in the first determination step, the second determination step and the second determination step are not performed.

3. The inspection method for non-aqueous electrolyte secondary batteries according to claim 1 or 2, wherein, The electrode body has a positive electrode, a negative electrode, and a separator. The electrode body is constructed by laminating the positive electrode and the negative electrode with the spacer in between. In the inspection process, the third measurement process and the first judgment process are performed when the ratio of the opposing capacity of the positive electrode to the negative electrode is within a predetermined allowable range.

4. The inspection method for non-aqueous electrolyte secondary batteries according to claim 1 or 2, wherein, The first and second measurement steps are performed when the SOC of the non-aqueous electrolyte secondary battery is 80% to 90%.

5. A method for inspecting a non-aqueous electrolyte secondary battery, comprising an electrode body, a non-aqueous electrolyte, and a battery casing housing the electrode body and the non-aqueous electrolyte, the method comprising the following steps: The high-temperature aging process involves storing the charged non-aqueous electrolyte secondary batteries in a high-temperature environment. The cooling process involves cooling the non-aqueous electrolyte secondary battery that has been stored at a high temperature during the high-temperature aging process. as well as In the inspection process, after the cooling process is completed, the non-aqueous electrolyte secondary battery is checked for normal operation based on the voltage drop per unit time. The inspection process includes a first period after the cooling process ends and a second period after the first period ends. The second period is the period during which the deviation of the voltage drop per unit time in the non-aqueous electrolyte secondary battery is smaller than that in the first period. The inspection process includes the following steps: The first measurement step involves measuring the voltage value of the non-aqueous electrolyte secondary battery during the second period. The third measurement step involves measuring the voltage value of the non-aqueous electrolyte secondary battery during the second period, after a time shorter than a predetermined time has elapsed since the first measurement step. In the first determination step, when the voltage drop per unit time based on the voltage value measured in the first measurement step and the voltage value measured in the third measurement step is below a threshold, the non-aqueous electrolyte secondary battery is determined to be normal. In the second measurement step, if the non-aqueous electrolyte secondary battery was not determined to be normal in the first determination step, the voltage value of the non-aqueous electrolyte secondary battery is measured during the second period after the specified time has elapsed since the first measurement step was performed. as well as In the second determination step, when the voltage drop per unit time based on the voltage value measured in the first determination step and the voltage value measured in the second determination step is below a threshold, the non-aqueous electrolyte secondary battery is determined to be normal.

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