Methods for inspecting secondary batteries

Abstract

The goal is to identify the location of minute foreign objects causing minute short circuits without disassembling the coiled body. [Solution] Extract cells with abnormal OCV voltage from the target cells (S1). Disassemble the extracted cells and take out the electrode body, which is a flat wound body (S2). Cut off the central part of the current collector at the widthwise end of the electrode body, leaving a tab shape, to form a measurement section (S3). Cut off the other measurement sections, leaving the innermost and outermost foils (S4). Restrict the electrode body from the thickness direction (S5). Dry the electrode body to reduce the conductivity of the non-aqueous electrolyte (S6). In this state, measure the electrical resistance of the innermost and outermost foils of the electrode body (S7). Identify the position of minute foreign matter in the winding direction from the electrical resistance (S8). If necessary, unfold the electrode body to check the shape and type of minute foreign matter (S9).

Description

[Technical Field]

[0001] The present invention relates to a method for inspecting secondary batteries, and more particularly to a method for inspecting secondary batteries that can estimate the location of a short circuit without disassembling the wound electrode body. [Background technology]

[0002] Secondary batteries, such as lithium-ion secondary batteries used as power sources for vehicles like hybrid vehicles (HVs) and electric vehicles (BEVs), require high voltage and large input / output capabilities, as well as a high battery capacity per unit volume [Ah / l]. For this reason, battery packs equipped with battery assemblies made up of many individual cells are used. Such cells have an electrode body in which a positive electrode plate with a positive electrode composite layer formed on a positive electrode current collector and a negative electrode plate with a negative electrode composite layer formed on a negative electrode current collector are laminated and wound together with a separator in between, and impregnated with an electrolyte. In such secondary battery cells, the wound electrode body, in particular, is shaped into a flattened form so that it can be stacked to form a battery pack.

[0003] In such secondary batteries, minute metal fragments originating from metal foils such as current collectors, or minute foreign matter resulting from contamination of the composite layer composition, may be introduced during the manufacturing process. In addition, changes in potential during use may cause chemical deposition of metals such as Li in the non-aqueous electrolyte. Such minute foreign matter can cause conductivity between the positive and negative electrodes, which should be insulated by the separator, resulting in a minute short circuit. Such a minute short circuit causes self-discharge, leading to a decrease in battery capacity [Ah] and a decrease in open-circuit voltage (OCV) [V].

[0004] In secondary batteries, if an abnormal drop in the open-circuit voltage (OCV) occurs, self-discharge due to a minute short circuit caused by such minute foreign matter is suspected as the cause. Therefore, Patent Document 1 discloses a method for inspecting a battery consisting of a positive electrode, a negative electrode, a separator arranged to isolate the two, and an electrolyte. This method involves keeping the electrolyte in a solid state, measuring the AC impedance between the positive and negative electrodes, and determining the presence or absence of a short circuit based on the resistance value. With such a method, it is possible to detect changes in electrical resistance caused by minute short circuits.

[0005] The method described in Patent Document 1 makes it possible to determine whether a minute short circuit caused by such minute foreign matter is the cause of an abnormal decrease in the open-circuit voltage OCV [V] in a secondary battery. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2003-45500 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, it was impossible to know exactly where the minute short circuit caused by that tiny foreign object was occurring. Therefore, if an abnormality was found, it was ultimately necessary to dismantle the coil, peel off the laminate, and visually search and confirm the minute foreign object causing the minute short circuit across its entire surface.

[0008] The problem that the secondary battery inspection method of the present invention aims to solve is to identify the location of minute foreign matter causing a minute short circuit without disassembling the winding. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides a secondary battery inspection method comprising: a secondary battery having an electrode body in which a positive electrode plate having a positive electrode composite layer formed on a positive electrode current collector and a negative electrode plate having a negative electrode composite layer formed on a negative electrode current collector are wound flat with a separator in between and impregnated with an electrolyte, the method comprising: suppressing the conductivity of the electrolyte impregnated into the electrode body; removing the portions at both ends in the width direction W parallel to the winding axis direction of the electrode body in which the positive electrode current collectors and the negative electrode current collectors are electrically connected, thereby electrically separating the positive electrode current collectors and the negative electrode current collectors; and measuring the electrical resistance by applying a voltage at a plurality of measurement positions MP on the positive electrode plate and at measurement positions MP on the negative electrode plate.

[0010] The step of electrically separating the positive electrode current collectors from each other and the negative electrode current collectors from each other may be carried out by removing the connection portion on the outer side of the width direction W in the thickness direction D at both ends in the width direction W and the length direction L which is perpendicular to the width direction W and the thickness direction D, and at the center of the length direction L, thereby forming a tab-shaped measuring portion on the inside of the center of the length direction L that will be the measuring position MP of the electrically separated positive electrode current collector and the negative electrode current collector.

[0011] In the step of measuring the electrical resistance, a restraining force may be applied to the electrode body from the thickness direction D. The restraining force may be 4 to 9 kN. In the measurement step described above, the first measurement position MP of the positive electrode plate P-IN and the second measurement position MP of the negative electrode plate N-IN However, it is positioned at the inner end when wound, and furthermore, at the third measurement position MP of the positive electrode plate. P-OUT and the fourth measurement position MP of the negative electrode plate N-OUT It can be positioned at the outer end when it is wound up.

[0012] In this case, the first measurement position MP P-IN And, the measurement position MP of connected 2 N-IN Electrical resistance R IN And, the measurement position MP of the above 3 P-OUT And, the measurement position MP of configured 4N-OUT The electrical resistance R in OUT From the ratio with, it is possible to include a step of estimating the short - circuit position between the inner end portion and the outer end portion.

[0013] In the step of measurement, the measurement position MP of one of the positive electrode plate or the negative electrode plate may be fixed, and the other electrode plate may be measured a plurality of times at different positions between the inner end portion and the outer end portion in the winding direction.

[0014] In this case, in the step of measurement, it is possible to include a step of determining the short - circuit position, in which, as a result of a plurality of measurements, it is determined that a short - circuit has occurred at a position close to the measurement position MP of the other electrode plate where the lowest electrical resistance is measured.

[0015] In the step of suppressing the conductivity of the electrolytic solution impregnated in the electrode body, the conductivity of the electrolytic solution may be suppressed by drying the electrolytic solution. Also, in the step of suppressing the conductivity of the electrolytic solution impregnated in the electrode body, the conductivity of the electrolytic solution may be suppressed by freezing the electrolytic solution.

Advantages of the Invention

[0016] According to the inspection method of the secondary battery of the present invention, it is possible to specify the position of the minute foreign matter causing a minute short - circuit without disassembling the wound body.

Brief Description of the Drawings

[0017] [Figure 1] It is a perspective view showing an outline of the external configuration of the cell of the lithium - ion secondary battery of the present embodiment. [Figure 2] It is a schematic view showing the configuration of the wound electrode body. [Figure 3] It is a perspective view of the electrode body before being cut by the cutting line. [Figure 4] It is a view seen from the thickness direction D of the electrode body before being cut by the cutting line. [Figure 5]This is a flowchart showing the procedure for the inspection method of a lithium-ion secondary battery according to the first embodiment. [Figure 6] This is a perspective view of the unfolded electrode body of the first embodiment. [Figure 7] This is a cross-sectional view of the unfolded electrode body of the first embodiment. [Figure 8] This is a graph showing the relationship between the measurement position and electrical resistance in the first embodiment. [Figure 9] This is a perspective view of the unfolded electrode body of the second embodiment. [Figure 10] This is a cross-sectional view of the unfolded electrode body of the second embodiment. [Figure 11] This graph shows the relationship between the measurement location and electrical resistance in the second embodiment. [Modes for carrying out the invention]

[0018] (First Embodiment) Hereinafter, an example of a secondary battery inspection method of the present invention will be described with reference to Figures 1 to 8, using a first embodiment of the inspection method for cell 1 of a lithium-ion secondary battery.

[0019] <Outline of this embodiment> The lithium-ion secondary battery cell 1 of this embodiment exemplifies a single cell 1 that constitutes a battery pack for driving a vehicle. As shown in Figure 1, cell 1 has a flat appearance because multiple cells 1 are stacked to form a battery pack. Inside cell 1, as shown in Figure 2, a positive electrode plate 3 with a positive electrode composite layer 32 formed on a positive electrode current collector 31 and a negative electrode plate 2 with a negative electrode composite layer 22 formed on a negative electrode current collector 21 are stacked via a separator 4. This stacked body comprises an electrode body 12 that is flattened and wound. The electrode body 12 is housed in a battery case 11, filled with a non-aqueous electrolyte 13, and sealed.

[0020] Cell 1 of such lithium-ion secondary batteries may contain minute metal powder during manufacturing. Alternatively, metal ions in the non-aqueous electrolyte 13 may become metallic due to the potential of the positive electrode and precipitate. The negative electrode plate 2 and the positive electrode plate 3 are stacked with an insulating separator 4 in between, so in terms of design, there is no electrical conductivity without the non-aqueous electrolyte 13. However, due to the minute foreign matter MF described above, the current density [A / mm²] may decrease. 2 Unevenness in the ] can cause minute foreign matter MF to grow, pierce through separator 4, and cause a minute short circuit. When such a minute short circuit occurs, self-discharge can occur, causing an abnormal drop in the OCV (Open Circuit Voltage) of cell 1.

[0021] In such cases, the cause may be unknown from the outside. To investigate this, it was necessary to disassemble the lithium-ion secondary battery cell 1, remove the welds of the wound electrode body 12, and unfold the laminate by peeling off the negative electrode plate 2, positive electrode plate 3, and separator 4. Then, it was necessary to visually inspect the entire structure for any traces. Because the location of this minute short circuit is so small, finding any traces was a cumbersome process.

[0022] In the lithium-ion secondary battery cell 1 inspection method of this embodiment, the location of minute foreign matter MF causing a minute short circuit is identified by electrically measuring it without disassembling the electrode body 12. If necessary, the electrode body 12 can be unfolded and the identified location inspected, allowing the cause of the short circuit to be determined by directly inspecting the minute foreign matter MF that caused the short circuit.

[0023] Figure 5 is a flowchart illustrating the procedure for inspecting a lithium-ion secondary battery according to the first embodiment. Briefly explaining the specific procedure, in the first embodiment, first, the OCV voltage abnormal cell of the target cell 1 is extracted (S1). The extracted cell 1 is disassembled and the electrode body 12, which is a flat wound body, is removed (S2). The central parts of the positive electrode current collector 31 and negative electrode current collector 21 at the width direction W of the electrode body 12 are cut away, leaving a tab shape, to form a measurement section MT (S3). The other measurement sections MT are cut, leaving the innermost and outermost foils (S4). The electrode body 12 is restrained from the thickness direction D (S5). The electrode body 12 is dried to reduce the conductivity of the non-aqueous electrolyte 13 (S6). In this state, the electrical resistance R [mΩ] of the innermost and outermost foils of the electrode body 12 is measured (S7). The position of the winding direction of minute foreign matter MF is identified from the electrical resistance R [mΩ] (S8). If necessary, unfold the electrode body 12 to check the shape and type of the minute foreign matter MF (S9).

[0024] By following this procedure, the location of the minute foreign object MF causing the minute short circuit can be identified by electrically measuring it without disassembling the electrode body 12. <Configuration of this embodiment> <Lithium-ion rechargeable battery> Figure 1 is a perspective view showing a schematic representation of the external configuration of cell 1 of the lithium-ion secondary battery according to this embodiment. First, the configuration of cell 1 of the lithium-ion secondary battery, which is the premise for the inspection method of cell 1 of the lithium-ion secondary battery according to this embodiment, will be briefly explained. Note that cell 1 is an example for the purpose of explaining the present invention and does not limit the present invention.

[0025] As shown in Figure 1, the lithium-ion secondary battery is configured as a cell 1 that makes up a vehicle battery pack (not shown). Cell 1 comprises a battery case 11 having a plate-shaped rectangular parallelepiped body with an opening on the top and a lid. An electrode body 12 is housed inside the battery case 11. A non-aqueous electrolyte 13 is filled into the battery case 11 through an injection port 18. The battery case 11 is made of metal such as an aluminum alloy and forms a sealed battery case with a lid. The lithium-ion secondary battery also has a positive electrode external terminal 14 and a negative electrode external terminal 15 used for charging and discharging power. The positive electrode external terminal 14 is electrically connected to a positive electrode current collector terminal 16 inside the battery case 11 via the lid. The negative electrode external terminal 15 is electrically connected to a negative electrode current collector terminal 17 inside the battery case 11 via the lid. The positive electrode current collector terminal 16 is electrically connected to the positive electrode current collector portion 33 (see Figure 2) of the electrode body 12. Furthermore, the negative electrode current collector terminal 17 is electrically connected to the negative electrode current collector section 23 (see Figure 2) of the electrode body 12.

[0026] The lid has an injection port 18 for injecting the non-aqueous electrolyte 13. This injection port 18 is sealed after injection, and the cell case of cell 1 is completely sealed. <Electrode body 12> Figure 2 is a schematic diagram showing the configuration of the wound electrode body 12. It shows a part of the wound body unfolded. The electrode body 12 is made up of a number of negative electrode plates 2, positive electrode plates 3, and separators 4 placed between them, all stacked together. The stacked negative electrode plates 2, positive electrode plates 3, and separators 4 are wound together to form a flat shape. The negative electrode plate 2 has a negative electrode composite layer 22 formed on a negative electrode current collector 21 made of copper foil, which serves as the base material. A negative electrode current collector 23 is provided on one end in the width direction W (winding axis direction) perpendicular to the winding direction (length direction L). The negative electrode current collector 23 does not have the negative electrode composite layer 22 formed on it, and the metal of the negative electrode current collector 21 is exposed.

[0027] The positive electrode plate 3 has a positive electrode composite layer 32 formed on a positive electrode current collector 31 made of aluminum foil, which serves as the base material. As shown in Figure 2, the positive electrode current collector 33 is provided on the other end (opposite side from the negative electrode current collector 23) in the width direction W (winding axis direction) which is perpendicular to the winding direction (length direction L) of the positive electrode current collector 31. The positive electrode composite layer 32 is not formed on the positive electrode current collector 33, and the metal of the positive electrode current collector 31 is exposed.

[0028] <Laminated structure of electrode body 12> As shown in Figure 2, the basic configuration of the electrode body 12 of the lithium-ion secondary battery includes a negative electrode plate 2, a positive electrode plate 3, and a separator 4.

[0029] The negative electrode plate 2 has a negative electrode composite material layer 22 on both sides of the negative electrode current collector 21, which serves as the negative electrode base material. One end of the negative electrode current collector 21 is a negative electrode current collector portion 23 in which metal is exposed. The positive electrode plate 3 has a positive electrode composite material layer 32 on both sides of the positive electrode current collector 31, which serves as the positive electrode base material. The other end of the positive electrode current collector 31 is a positive electrode current collector portion 33 where metal is exposed.

[0030] A laminate is formed by stacking a negative electrode plate 2 and a positive electrode plate 3 with a separator 4 in between. As shown in Figure 2, this laminate is wound longitudinally around a winding axis to form a wound electrode body 12 that is shaped into a flattened form as shown in Figure 3.

[0031] <Nonaqueous electrolyte 13> The non-aqueous electrolyte 13 of cell 1 in this embodiment shown in Figure 1 is a composition obtained by dissolving a lithium salt in an organic solvent. Examples of lithium salts that can be used include LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butanesultone; or phosphorus compounds such as triethyl phosphate and trioctyl phosphate. One or more of these can be mixed and used as the non-aqueous electrolyte 13. However, the composition of the non-aqueous electrolyte 13 is not limited to these.

[0032] In this embodiment, EC (ethylene carbonate) is used as the organic solvent. Furthermore, a compound containing a lithium salt may be added as an additive for film formation. In this embodiment, lithium bisoxalate borate (LiBOB, LiB(C2O4)2) is added.

[0033] <Components of electrode body 12> Next, we will describe the components that make up the electrode body 12: the negative electrode plate 2, the positive electrode plate 3, and the separator 4.

[0034] <Negative electrode plate 2> As shown in Figure 2, the negative electrode plate 2 is constructed by forming a negative electrode composite material layer 22 on both sides of the negative electrode current collector 21, which is the negative electrode substrate. In the source process, the negative electrode composite material paste is applied to the negative electrode current collector 21. Subsequently, the negative electrode plate 2 is completed through drying, pressing, and cutting processes.

[0035] In this embodiment, the negative electrode current collector 21 is made of Cu foil. The negative electrode current collector 21 serves as the base material for the negative electrode composite layer 22 and also functions as a current collector that collects electricity from the negative electrode composite layer 22. One end of the negative electrode current collector 21 is a negative electrode current collector section 23 where the metal surface is exposed and the negative electrode composite layer 22 is not formed thereon. In other words, the negative electrode active material particles are electrically connected to the negative electrode external terminal 15 via the negative electrode current collector 21, the negative electrode current collector section 23, and the negative electrode current collector terminal 17.

[0036] The negative electrode composite layer 22 consists of a negative electrode active material as the raw material, and a binder (binding agent) and additives as auxiliary materials. The raw material and auxiliary materials are mixed with an organic solvent to produce a negative electrode composite paste. This negative electrode composite paste is applied to the negative electrode current collector 21. The applied negative electrode composite paste is dried and then shaped and pressed to complete the negative electrode plate 2.

[0037] In this embodiment, the negative electrode active material is powdered graphite particles GP, which consist of graphite having a layered structure, and lithium ions Li + It is a material capable of absorbing and releasing substances. <Positive plate 3> As shown in Figure 2, the positive electrode plate 3 consists of a positive electrode current collector 31, which is the positive electrode substrate, and a positive electrode composite layer 32 coated thereon. In the source process, the positive electrode composite layer 32 is applied to the positive electrode current collector 31 by coating it with a positive electrode composite paste. Subsequently, the positive electrode plate 3 is completed through drying, pressing, and cutting processes.

[0038] The positive electrode plate 3 is constructed by forming a positive electrode composite material layer 32 on both sides of a positive electrode current collector 31, which is a positive electrode substrate. In this embodiment, the positive electrode current collector 31 is made of aluminum foil. The positive electrode current collector 31 serves as a base material for the positive electrode composite material layer 32 and also functions as a current collector that collects electricity from the positive electrode composite material layer 32.

[0039] First, although Al foil was used as an example for the positive electrode substrate constituting the positive electrode current collector 31, it can be made of a conductive material consisting of a metal with good conductivity, for example. As a material with good conductivity, in addition to Al foil, materials containing Al alloys can be used. The composition of the positive electrode current collector 31 is not limited to this.

[0040] The positive electrode composite layer 32 is formed by coating the positive electrode composite paste onto the positive electrode current collector 31 and drying it. The positive electrode composite layer 32 contains positive electrode active material particles as well as additives such as conductive additives, binders, and dispersants.

[0041] The positive electrode active material particles contain a lithium transition metal oxide having a layered crystalline structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. Preferably, the transition metal elements contained in the lithium transition metal oxide are at least one of Ni, Co, and Mn. The positive electrode active material of this embodiment is exemplified by a ternary system called NCM, which has a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0042] Furthermore, the positive electrode active material in this embodiment is not limited to having a lithium transition metal oxide containing all of Ni, Co, and Mn. It may also have a composition containing, for example, Al.

[0043] <Separator 4> The separator 4 is a highly insulating nonwoven fabric, such as one made of porous resin, for holding the non-aqueous electrolyte 13 between the negative electrode plate 2 and the positive electrode plate 3. As the separator 4, porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, or lithium-ion or ion-conductive polymer electrolyte membranes can be used alone or in combination. In this embodiment, both outer surfaces are made of polypropylene (PP), which has high mechanical strength and excellent heat resistance. The interior is made of polyethylene (PE), which shuts down at high temperatures.

[0044] (Inspection procedure of this embodiment) Next, a method for inspecting the cell 1 of such a lithium-ion secondary battery will be described with reference to the flowchart of FIG. 5.

[0045] <Extraction of cells with abnormal OCV voltage (S1)> First, the cell 1 of the target lithium-ion secondary battery is charged to a predetermined voltage, left under certain conditions, and the decrease in OCV [V] is measured. If there is a decrease in OCV [V] above a certain threshold, self-discharge due to a micro short circuit is suspected. Alternatively, the self-discharge [Ah / s] may be actually measured. If there is any abnormality, it may be the subject of inspection. In order to identify the cause of the abnormality of the cell 1 extracted in this way, the inspection of this embodiment is performed.

[0046] <Disassemble the cell 1 and take out the electrode body 12 which is the wound body (S2)> First, remove the welded lid of the battery case 11 of the cell 1 from the main body. At this time, the electrode body 12 is integrated with the lid together with the positive electrode current collector terminal 16 and the negative electrode current collector terminal 17. Separate this electrode body 12 from the positive electrode current collector terminal 16 and the negative electrode current collector terminal 17.

[0047] [[ID=IS]] <Cut and remove the central parts of the positive electrode current collector 31 and the negative electrode current collector 21 leaving them tab-shaped to form the measurement part MT (S3)> Subsequently, the measurement part MT is formed.<00OB335>

[0048] FIG. 3 is a perspective view of the electrode body 12 before a part of the positive electrode current collector 31 and the negative electrode current collector 21 are removed by the cutting line CL. FIG. 4 is a view seen from the thickness direction D of the electrode body 12 before a part of the positive electrode current collector 31 and the negative electrode current collector 21 are removed by the cutting line CL.

[0049] As shown in Figure 3, the wound body of the electrode body 12 is pressed in the thickness direction D at the center of both ends in the width direction W and welded at the welding point WP. Therefore, the positive electrode current collectors 31 and the negative electrode current collectors 21 are electrically connected from the inner end IN to the outer end OUT in the winding direction. In this embodiment, the positive electrode current collectors 31 and the negative electrode current collectors 21 are electrically separated by the following procedure. First, at both ends in the width direction W of the electrode body 12, both ends in the length direction L are cut along the cutting line CL in the thickness direction D. The outer ends of both ends in the width direction W of the electrode body 12 are pressed, and the positive electrode current collectors 31 and the negative electrode current collectors 21 are in contact and electrically conductive. When cut along the cutting line CL in the thickness direction D from this state, the electrically conductive portion is cut off, and the positive electrode current collectors 31 and the negative electrode current collectors 21 are electrically separated. Furthermore, the welded area WP, which is the outer welded area in the width direction W at the center of the length direction L, is removed in the thickness direction D. When the material is cut in the thickness direction D along the cut line CL from this state, the electrically conductive portion due to welding is removed, and the positive electrode current collectors 31 and the negative electrode current collectors 21 are electrically separated.

[0050] As a result of this excision, as shown in Figure 4, a rectangular tab-shaped measuring section MT is formed, which is the measurement position MP of the positive electrode current collector 31 and the negative electrode current collector 21, electrically separated on the inside of the central part in the length direction L in the width direction W. In this tab-shaped measuring section MT, the positive electrode current collectors 31 and the negative electrode current collectors 21 are electrically separated from each other.

[0051] <Cut the other measurement sections while leaving the innermost and outermost foils intact (S4)> In the first embodiment, the first measurement position MP of the positive electrode plate 3 is further specified. P-IN The innermost foil, the second measurement position MP of the negative electrode plate 2. N-IN The tab-shaped measuring portion MT that protrudes in a rectangular shape other than the innermost foil is removed. Similarly, the third measuring position MP of the positive electrode plate 3 is removed. P-OUT The outermost foil, the fourth measurement position MP of the negative electrode plate 2. N-OUTThe rectangular tab-shaped measuring sections MT, which protrude from the outermost foil, are also removed. As a result, only four measuring sections MT remain. Each of these four measuring sections MT is then positioned at its respective measurement location MP.

[0052] <The electrode body 12 is restrained from the thickness direction D (S5)> Although not shown in the diagram, the electrode body 12, consisting only of the wound material, is clamped from the thickness direction D with a restraint device and pressed with a force of 4 to 9 kN. This reproduces a minute short circuit caused by a minute foreign object MF under pressure inside the battery case 11.

[0053] <To reduce the conductivity of the non-aqueous electrolyte 13, the electrode body 12 is dried (S6)> When the non-aqueous electrolyte 13 is activated, it moves ions and exhibits conductivity. This results in conduction other than minute short circuits caused by minute foreign matter MF. Therefore, in this embodiment, the electrode body 12 is dried to deactivate the non-aqueous electrolyte 13 and suppress conduction other than minute short circuits caused by minute foreign matter MF. Drying is performed, for example, by using hot air to volatilize the volatile organic solvent EC (ethylene carbonate) in the non-aqueous electrolyte 13 impregnated in the separator 4.

[0054] Furthermore, to reduce the conductivity of the non-aqueous electrolyte 13 of the electrode body 12, drying is not the only method; freezing may also be used. Drying generally allows for measurement in a shorter time, but it is susceptible to the degree of drying and the humidity of the environment, which can alter conductivity and other properties. On the other hand, freezing is less affected by the degree of drying and the humidity of the environment, but it requires refrigeration equipment and time to freeze, which reduces the efficiency of the test.

[0055] Furthermore, the method for deactivating the non-aqueous electrolyte 13 is not limited to these methods; chemical methods, such as eliminating ions, may also be used. <Measurement of electrical resistance R [mΩ] at measurement position MP of the innermost and outermost foils of electrode body 12 (S7)> Figure 6 is a perspective view of the unfolded electrode body 12 of the first embodiment. The central parts of the positive electrode current collector 31 and the negative electrode current collector 21 are cut away, leaving a tab shape, to form the measurement section MT (S3). The other measurement sections MT are cut away, leaving the innermost and outermost foils, to form four measurement sections MT (S4). At this stage, the electrode body 12 maintains a wound state, but in Figure 6, it is shown unfolded for explanatory purposes. After the four measurement sections MT are formed (S4), the electrode body 12 is unfolded to form the state shown in Figure 6. The measurement section MT of the inner positive electrode plate 3 has a measurement position MP P-IN The negative electrode plate 2 on the inside IN has a measurement position MP. N-IN The measurement section MT of the positive electrode plate 3 on the outer OUT is located at the measurement position MP. P-OUT The negative electrode plate 2 on the outside OUT has a measurement section MT at the measurement position MP. N-OUT They are placed.

[0056] Figure 7 is a cross-sectional view of the unfolded electrode body 12 of the first embodiment. Measurement position MP P-IN , measurement position MP P-OUT It is connectable to a measuring section MT provided on the surface of the positive electrode current collector 31 of the positive electrode plate 3. Measurement position MP N-IN , measurement position MP N-OUT It is connectable to a measuring section MT provided on the surface of the negative electrode current collector 21 of the negative electrode plate 2. The minute foreign matter MF protrudes from the negative electrode composite layer 22 toward the positive electrode composite layer 32, penetrating the separator 4. As a result, it breaks the insulation provided by the separator 4, and the negative electrode composite layer 32 and the positive electrode composite layer 22 become electrically conductive.

[0057] In Figure 7, the measurement position MP of the positive electrode plate 3, which is close to the inner IN side of the electrode body 12. P-IN And the measurement position MP of the negative electrode plate 2 N-IN However, this shows the state in which the probe is connected to the resistance meter 100.

[0058] At this time, the current measured from the resistance meter 100 flows through the conduction path EP. Measurement position MP of the positive electrode plate 3. P-INThe current from the probe of the connected resistance measuring instrument 100 flows from the positive electrode current collector 31 through minute foreign matter MF to the negative electrode current collector 21, and to the measurement position MP of the negative electrode plate 2. N-IN The probe connected to the resistor returns to the resistance measuring instrument 100. Then, the electrical resistance R [mΩ] of this conduction path EP is measured. At this time, the length of the conduction path EP is measured at the measurement position MP. P-IN The length L1 from the micro-foreign object MF, and the measurement position MP from the micro-foreign object MF. N-IN The total length L1' of the positive electrode current collector 31 up to this point is L1 + L1'. The total electrical resistance R [mΩ] of the conduction path EP is this electrical resistance R L1 [mΩ], electrical resistance R L1´ [mΩ] and the electrical resistance R at the minute foreign matter MF. MF This is the sum of [mΩ].

[0059] On the other hand, the measurement position MP of the positive electrode plate 3, which is closer to the outer OUT of the electrode body 12 P-OUT And the measurement position MP of the negative electrode plate 2 N-OUT When the probe of the resistance meter 100 is connected, the following is shown (not shown in the diagram). The current measured from the probe of the resistance meter 100 is at the measurement position MP of the positive plate 3. P-OUT Current flows from the connected probe to the positive electrode current collector 31, through minute foreign matter MF, to the negative electrode current collector 21, and to the measurement position MP of the negative electrode plate 2. N-OUT The probe connected to the resistor returns to the resistance measuring instrument 100. Then, the electrical resistance R [mΩ] of this conduction path EP is measured. At this time, the length of the conduction path EP is measured at the measurement position MP. P-OUT The length L2 from the micro-foreign object MF, and the measurement position MP from the micro-foreign object MF. N-OUT This is the sum of the lengths L2' of the positive electrode current collector 31 up to this point. The electrical resistance R[mΩ] of the portion including this length L2+L2' is equal to the electrical resistance R L2 [mΩ], electrical resistance R L2´ [mΩ] and the electrical resistance R at the minute foreign matter MF. MF This is the sum of [mΩ].

[0060] <The position of the winding direction of the minute foreign matter MF is determined from the electrical resistance R [mΩ] (S8)> Figure 8 is a graph showing the relationship between the measurement position MP and the electrical resistance R [mΩ] in the first embodiment. Here, the electrical resistance R [mΩ] is measured by moving the probe of the resistance measuring instrument 100 to the measurement position MP. P-IN and measurement position MP N-IN This shows the case when connected to [the specified location].

[0061] Here are two methods for determining the position in the winding direction, as illustrated here. First, as the first method, we consider the electrical resistance R of the minute foreign matter MF. MF [mΩ] is R min Let's explain the case where it is known to be [mΩ]. In this case, the minute foreign matter MF is at the measurement position MP P-IN and measurement position MP N-IN If it is located at the inner IN position very close to the minimum electrical resistance R[mΩ], then measuring its electrical resistance R min It shows [mΩ]. On the other hand, when it is located at the outermost OUT position, its electrical resistance R [mΩ] is the maximum electrical resistance R max [mΩ] is shown. Note that the maximum electrical resistance R max [mΩ] is measured at MP P-IN and measurement position MP P-OUT The electrical resistance R [mΩ] is measured, and the minimum electrical resistance R min It can also be calculated by adding to [mΩ]. The minimum electrical resistance R is calculated using the procedure described above. min [mΩ] and maximum electrical resistance R max Assume the value is [mΩ] and measure accordingly. In this case, the probe of the resistance meter 100 is placed at the measurement position MP P-IN and measurement position MP N-IN If the measured electrical resistance R [mΩ] when connected to is known, then, as shown in Figure 8, the measurement position MP can be measured from the inside IN. P-IN From the position P of the minute foreign body MF MF The distance L1 to the point is known. Here, the measured electrical resistance is R. m [mΩ], measurement position MP P-IN Measurement position MP P-OUT Let L be the total distance to the measurement point, and MP be the measurement point. P-IN From the position P of the minute foreign body MF MF Let L1 be the distance to that point. Then, L1 = L × (R m -Rmin ) / (R max -R min )...Formula 1 This is how the location of a tiny short circuit is estimated.

[0062] Next, as a second method, the electrical resistance R [mΩ] of the minute foreign matter MF, i.e., R min Let's explain the case where we can consider it to be =0 [mΩ]. In this case, the electrical resistance R [mΩ] of the minute foreign object MF can be ignored, so the electrical resistance R [mΩ] is proportional to the distance L1 to the minute foreign object MF. The probe of the resistance measuring instrument 100 is at the measurement position MP. P-IN and measurement position MP N-IN The electrical resistance measured when connected to the device is defined as Ra [mΩ]. The probe of the resistance meter 100 is placed at the measurement position MP P-OUT and measurement position MP N-OUT Let Rb [mΩ] be the electrical resistance measured when connected to the other.

[0063] In this case, the measurement position MP P-IN Distance L1 from the minute foreign object MF, measurement position MP P-OUT The distance L2 from the minute foreign object MF is L2=L1×Ra / Rb…Equation 2 From this, the location of minute foreign objects (MF) can be identified. The location of minute short circuits can be estimated using this method.

[0064] The first method requires prerequisite steps, such as the need to measure the electrode body 12 of the cell 1 beforehand, but the electrical resistance R of the minute foreign matter MF is... MF By considering [mΩ], a more accurate location can be estimated. Conversely, the electrical resistance R of the minute foreign object MF... MF There is a problem in that it is affected by [mΩ].

[0065] The second method does not require high accuracy because it ignores the electrical resistance R [mΩ] of the minute foreign matter MF. However, it does not require preliminary measurements, and the position of the minute foreign matter MF can be estimated using only the Ra / Rb ratio for an electrode body 12 whose electrical resistance R [mΩ] is unknown. Furthermore, because the electrical resistance R [mΩ] of the minute foreign matter MF is ignored, it is not affected by it. The purpose of this embodiment is to estimate the position of the minute foreign matter MF prior to visual inspection, so high accuracy is not required. From this viewpoint, this embodiment uses the second method, which is easy to prepare and is not affected by the electrical resistance R [mΩ] of the minute foreign matter MF.

[0066] <The electrode body 12 is unfolded to confirm the shape and type of the minute foreign matter MF (S9)> After determining the winding direction of the minute foreign matter MF from the electrical resistance R [mΩ] (S8), the wound electrode body 12 is unfolded and the shape and type of the minute foreign matter MF are visually confirmed (S9). Minute short circuits caused by minute foreign matter MF are often very small and difficult to detect visually. However, in the inspection method of this embodiment, the approximate winding direction of the minute foreign matter MF is determined in advance from the electrical resistance R [mΩ] (S8). Therefore, the range in which the minute short circuit is actually searched is limited to an extremely narrow range, making the cumbersome task of searching for minute short circuits significantly easier.

[0067] Furthermore, the high-voltage current does not melt or burn away the minute foreign matter MF at high temperatures, and it is possible to determine whether the minute foreign matter MF is a tiny fragment of metal introduced from the outside or Li or other metals deposited on the electrode plate. Therefore, the origin of the minute foreign matter MF can be estimated, and recurrence can be prevented by eliminating the cause of the minute short circuit.

[0068] (Operation of the first embodiment) According to the inspection method for the lithium-ion secondary battery cell 1 of the first embodiment, the location of minute foreign matter MF causing a minute short circuit can be identified simply by measuring its electrical resistance R [mΩ] without disassembling the electrode body 12, which is a wound body.

[0069] (Effects of the first embodiment) (1-1) According to the inspection method for the lithium-ion secondary battery cell 1 of this embodiment, the location of minute foreign matter MF causing a minute short circuit can be identified without disassembling the electrode body 12, which is a wound body.

[0070] (1-2) The method includes a step of suppressing the conductivity of the non-aqueous electrolyte 13 impregnated in the electrode body 12. This has the effect of suppressing the influence of the non-aqueous electrolyte 13 by the resistance measuring instrument 100, thereby enabling the precise location to be determined.

[0071] (1-3) At both ends of the electrode body 12 in the width direction W, the electrically connected portions of the positive electrode current collectors 31 and the negative electrode current collectors 21 are removed, thereby electrically separating the positive electrode current collectors 31 and the negative electrode current collectors 21. This has the effect of allowing the electrical resistance R [mΩ] to be measured from different measurement positions MP of the positive electrode current collector 31 and the negative electrode current collector 21 while the coiled body remains intact.

[0072] (1-4) At measurement positions MP on the positive electrode plate 3 and negative electrode plate 2, voltage is applied at different measurement positions MP to measure the electrical resistance R [mΩ]. Therefore, by measuring the electrical resistance R [mΩ] from different measurement positions MP, it is possible to estimate the location of minute foreign matter MF.

[0073] (1-5) The step of electrically isolating the positive electrode current collectors 31 and the negative electrode current collectors 21 involves removing the connection portion in the thickness direction D at both ends in the width direction W, at both ends in the length direction L which is perpendicular to the width direction W and the thickness direction D, and at the center of the length direction L which is outside the width direction W. Then, a tab-shaped measuring section MT is formed inside the center of the length direction L which will be the measurement position MP for the electrically isolated positive electrode current collector 31 and negative electrode current collector 21. This has the effect of making it easy to measure the electrical resistance R [mΩ] from different measurement positions MP.

[0074] (1-6) In the step of measuring electrical resistance, a restraining force of 4 to 9 [kN] is applied to the electrode body 12 from the thickness direction D. This has the effect of reproducing the conditions inside the battery case 11 and reproducing a minute short circuit in the electrode body 12 that has been removed from the battery case 11 and released from the restraining force.

[0075] (1-7) In the measurement step, the first measurement position MP of the positive electrode plate 3 P-IN And the second measurement position MP of the negative electrode plate 2. N-IN However, it is positioned at the inner end when wound. Furthermore, the third measurement position MP of the positive electrode plate 3. P-OUT And the fourth measurement position MP of the negative electrode plate 2 N-OUT It is positioned at the outer end when the coil is wound. Therefore, it has the effect of being able to identify the minute foreign matter MF regardless of its position from the inner end to the outer end when the coil is wound.

[0076] (1-8) First measurement position MP P-IN And the second measurement position MP N-IN Electrical resistance R IN [mΩ] and the third measurement position MP P-OUT And the fourth measurement position MP N-OUT Electrical resistance R OUT The ratio to [mΩ] is determined. From this ratio, the short-circuit location between the inner and outer ends is estimated. This has the advantage of allowing the short-circuit location to be estimated without unfolding the coil and peeling off the laminate.

[0077] (Second embodiment) Hereinafter, another example of the secondary battery inspection method of the present invention will be described with reference to Figures 9 to 11, using a second embodiment of the inspection method for cell 1 of a lithium-ion secondary battery.

[0078] <Outline of the second embodiment> The second embodiment shares the same basic configuration as the first embodiment, differing only in the procedure shown in Figure 5. First, the procedure of cutting the other measurement sections MT while leaving the innermost and outermost foils intact (S4) differs from the first embodiment. Also, the procedure of measuring the electrical resistance R [mΩ] at the measurement positions MP of the innermost and outermost foils of the electrode body 12 (S7) and the procedure of identifying the winding direction of minute foreign matter MF from the electrical resistance R [mΩ] (S8) differ from the first embodiment.

[0079] The description of the configuration common to the first embodiment will be omitted, and only the configuration of the measurement unit MT and the measurement position MP, and the method for determining the position of the minute foreign matter MF in the winding direction will be described. Figure 9 is a perspective view of the unfolded electrode body 12 in the second embodiment. In the first embodiment, in the procedure (S4) of cutting the other measuring parts MT while leaving the innermost and outermost foils intact, the other measuring parts MT are cut while leaving the innermost and outermost foils intact. In contrast, in the second embodiment, as shown in Figure 9, the measuring part MT (S3) formed by cutting away the central part of the current collector foil, leaving a tab shape, is left as is without performing the procedure in S4.

[0080] In the second embodiment, there is only one measurement position MP on the negative electrode plate 2 side, so for example, measurement position MP N-IN All measurement sections MT other than the one being set are cut off. Alternatively, they may be left as they are without being cut. Furthermore, on the negative electrode side, the procedure of forming the measurement section MT by cutting off the central part of the negative electrode current collector 21, leaving a tab shape (S3), may be omitted. In other words, the negative electrode current collector 21 itself may be used as the measurement section MT.

[0081] Furthermore, on the positive electrode plate 3 side, twice the number of windings are formed as measurement sections MT, but the number of measurement sections MT may be reduced by thinning them out at equal intervals, for example, every other section or every two sections.

[0082] Furthermore, since the numerous measurement points MT on the positive electrode plate 3 need to be insulated from each other, it is desirable to insert insulating sheets or similar materials between the numerous measurement points MT to ensure mutual insulation. Next, the method for measuring the electrical resistance R [mΩ] of the electrode body 12 of the second embodiment will be described. As described above, on the positive electrode plate 3, tabular measurement portions MT are formed in a number twice the circumference wound around the central portion of the positive electrode current collector 31. In FIG. 9, the actual wound body is simplified, and the case where nine measurement portions MT are provided is shown. A measurement position MP is set for each of them. The innermost one is provided with the measurement position MP P-IN is provided. One outside of that, the measurement position MP P-1 is provided. Further one outside of that, the measurement position MP P-2 is provided. Sequentially, the measurement positions MP P-3 ~ the measurement position MP P-7 are provided, and the measurement position MP P-OUT is provided on the outermost side.

[0083] FIG. 10 is a cross-sectional view of the developed electrode body 12 of the second embodiment. In the second embodiment, the measurement position MP of either the positive electrode plate 3 or the negative electrode plate 2 is fixed at one location. In this embodiment, the measurement position MP on the negative electrode plate 2 side is set as the innermost measurement position MP N-IN . The other measurement portions MT of the negative electrode plate 2 are not used. As shown in FIG. 10, by setting the measurement position MP N-IN at one location like this, the distance between the measurement position MP N-IN and the minute foreign matter MF always becomes constant.

[0084] On the other electrode plate, in the positive electrode plate 3 in the second embodiment, the measurement positions MP P-IN , the measurement position MP P-1 ~ the measurement position MP P-7 , the measurement position MP P-OUT nine measurement positions MP are provided.

[0085] Next, the method for specifying the position of the minute foreign matter MF in the length direction L in the second embodiment will be described. For the measurement, one probe of the resistance measuring device 100 is connected to the measurement position MP N-IN on the negative electrode plate 2 side. This connection is not changed until all the measurements are completed.

[0086] The other probe first measures the innermost measurement position MP P-IN of the positive electrode plate 3.Connect to the following. At this time, when the electrical resistance R [mΩ] is measured by the resistance measuring instrument 100, the conductive path EP is at the measurement position MP. N-IN The distance between the microscopic foreign object MF and the electrode remains constant. The distance of the conductive path EP at the microscopic foreign object MF also remains constant. The conductive path EP on the positive electrode side is between the microscopic foreign object MF and the measurement position MP. P-IN Conductive path EP having distance from IN This is the result.

[0087] Next, the measurement position MP on the positive electrode plate 3 side is the second measurement position MP from the inside. P-1 Switch the connection and measure the electrical resistance R [mΩ]. In this case, the conductive path EP on the positive side is connected to the minute foreign matter MF and the measurement position MP. P-1 This results in a conductive path EP1 having a distance from the positive electrode plate 3. In this way, the measurement position MP on the positive electrode plate 3 side is measured at the measurement position MP P-2 ~Measurement position MP P-7 , measurement position MP P-OUT The process is then sequentially switched to the next setting, and the measurement is repeated.

[0088] Figure 11 is a graph showing the relationship between the measurement position MP and the electrical resistance R [mΩ] in the second embodiment. The horizontal axis, from left to right, shows the position from the inside IN to the outside OUT on the positive electrode plate 3, and the measurement position MP P-IN , measurement position MP P-1 ~Measurement position MP P-7 , measurement position MP P-OUT The nine measurement locations MP are shown. The vertical axis shows the electrical resistance R [mΩ] at each location. First, the measurement locations MP P-IN The electrical resistance R [mΩ] connected to the pin is plotted on the graph. Similarly, at the measurement position MP P-IN Plot the electrical resistance R [mΩ] connected to the pin on a graph. Similarly, at measurement position MP P-1 ~Measurement position MP P-7 , measurement position MP P-OUT The electrical resistance R [mΩ] at nine locations was plotted. As a result, the measurement position MP P-2The value of electrical resistance R [mΩ] was smallest at this point. In other words, among the conductive paths EP shown in Figure 10, conductive path EP2 has the lowest electrical resistance R [mΩ], meaning it is the shortest conductive path EP. Therefore, the position of the minute foreign matter MF is among the measurement positions MP, at measurement position MP P-2 It can be determined that this is the closest position.

[0089] (Operation of the second embodiment) Since the electrical resistance R [mΩ] is measured at multiple measurement locations MP, it is possible to reliably identify that minute foreign matter MF is located near the measurement location MP with the lowest electrical resistance R [mΩ] without having to calculate the electrical resistance R [mΩ].

[0090] (Effects of the second embodiment) In the second embodiment, in addition to the effects of the first embodiment, or different from those of the first embodiment, the following effects are achieved.

[0091] (2-1) Since the electrical resistance R [mΩ] is measured at multiple measurement locations MP, it has the effect of being able to pinpoint the location of minute foreign matter MF without having to calculate the electrical resistance R [mΩ].

[0092] (2-2) Since the electrical resistance R [mΩ] is measured at multiple measurement locations MP, it is possible to reliably identify that the minute foreign matter MF is located near the measurement location MP with the lowest electrical resistance R [mΩ].

[0093] (2-3) In particular, when the electrical resistance R [mΩ] of the minute foreign matter MF is large, the method of the second embodiment is not affected by the electrical resistance R [mΩ] of the minute foreign matter MF. For this reason, the position of the minute foreign matter MF can be estimated more accurately than in the first embodiment.

[0094] (2-4) Furthermore, even when multiple minute foreign matter MFs are present, multiple bottoms are formed, so the location of each can be detected. (Another example) The present invention is not limited to the embodiments described above, and can be implemented as follows.

[0095] ○This invention can be implemented by essentially reversing the positive and negative electrodes, and the internal and external components. ○In this embodiment, an example was shown in which the ends of the central part in the width direction W are welded, but even when the ends in the width direction W are welded, it is sufficient if the parts where the positive electrode current collectors 31 and the negative electrode current collectors 21 are in electrical contact can be removed.

[0096] ○Furthermore, this can also be implemented in cell 1 where the positive electrode current collector terminal 16 and the negative electrode current collector terminal 17 are crimped rather than welded. In short, it is sufficient that the positive electrode current collector 31 and the negative electrode current collector 21 can be electrically separated from each other.

[0097] ○The secondary battery of the present invention has been described using cell 1, which constitutes a battery pack for vehicle drive, as an example. However, it is sufficient to have an electrode body 12 in which a positive electrode plate 3, on which a positive electrode composite layer 32 is formed on a positive electrode current collector 31, and a negative electrode plate 2, on which a negative electrode composite layer 22 is formed on a negative electrode current collector 21, are wound flat with a separator 4 in between, and impregnated with a non-aqueous electrolyte 13. For example, it can also be implemented in other non-aqueous electrolyte secondary batteries or alkaline secondary batteries such as nickel-metal hydride secondary batteries.

[0098] ○In this embodiment, the non-aqueous electrolyte 13 was deactivated by drying, but it may also be deactivated chemically. ○The measuring section MT is exemplified as a rectangular tab shape, but its shape, size, and number are not limited to the embodiment.

[0099] ○In this embodiment, the measurement position MP is provided on the tab-shaped measurement section MT. However, if the positive electrode current collector 31 and the negative electrode current collector 21 can be electrically isolated from each other and the electrical resistance R [mΩ] can be measured at a predetermined position, the tab-shaped measurement section MT is not an essential configuration.

[0100] ○The measurement position MP at the outer end may be set at the end in the winding direction. In this embodiment, "end" refers to any end within the feasible range. ○The voltage [V] applied to measure the electrical resistance R [mΩ] may be gradually increased, and the applied voltage [V] may be determined when a minute short circuit occurs. By doing so, the melting or burning of minute foreign matter MF can be suppressed, making it easier to pinpoint the cause of the minute short circuit.

[0101] ○Alternatively, a high-voltage spike may be applied to detect potential minute short circuits. ○In this embodiment, the description shows the probe of the resistance measuring instrument 100 being brought into contact with the measurement position MP, but it is also possible to make an electrical connection using methods such as clipping, attaching, or welding.

[0102] ○In this embodiment, the position of minute foreign matter MF was detected in the winding direction (longitudinal direction) of the positive electrode current collector 31 and the negative electrode current collector 21. Furthermore, once the position in the winding direction is determined, the position of minute foreign matter MF in the width direction W can also be detected by setting a measurement position MP so as to sandwich the minute foreign matter MF in the width direction W and measuring the electrical resistance R [mΩ].

[0103] ○In this embodiment, as an example of a lithium-ion secondary battery, cell 1 constituting a drive battery pack mounted on a vehicle shown in Figures 1 and 2 was given. However, as long as the present invention can be implemented, its purpose, shape, etc., are not limited. For example, even a cylindrical cell can be implemented as long as a measurement position MP can be provided.

[0104] ○The flowchart shown in Figure 5 is an example, and those skilled in the art can change the order of the steps, add or delete steps, or modify it as appropriate for implementation. ○The drawings are for illustrative purposes only and are not intended to limit the scope of this invention in terms of size, thickness, shape, quantity, etc.

[0105] ○The numerical values, numerical ranges, thresholds, etc., mentioned in this embodiment can be appropriately optimized and implemented by those skilled in the art. The graphs shown in Figures 8 and 11 are merely examples of implementation and are not necessarily limited to graphs. The desired relationship may also be processed as a relational expression, a table, or other means.

[0106] ○This embodiment is merely one example for explaining the present invention, and it goes without saying that those skilled in the art can add, delete, or modify its configuration to implement it. [Explanation of symbols]

[0107] MF...Micronized foreign body MP…Measurement position MP P-IN ... (Measurement position of the inner edge of the positive plate) MP N-IN ... (Measurement position at the inner edge of the negative electrode plate) MP P-OUT ... (Measurement position of the outer edge of the positive plate) MP N-OUT ... (Measurement position at the outer edge of the negative electrode plate) CL…Resection line MT…Measurement part WP... Welding point IN...inside OUT…outside EP… Conduction path R[mΩ]...Electrical resistance 1…Cell (Lithium-ion secondary battery) 11…Battery case 12...Electrode body 13...Nonaqueous electrolyte 14…Positive external terminal 15…Negative external terminal 16…Positive current collection terminal 17... Negative current collection terminal 18... Injection port 2… Negative plate 21...Negative electrode current collector 22...Negative electrode composite material layer 23... Negative electrode current collector 3…Positive plate 31...Positive electrode current collector 32…Positive electrode composite layer 33…Positive electrode current collector 4... Separator 100...Resistance measuring device

Claims

1. In a secondary battery comprising an electrode body in which a positive electrode plate having a positive electrode composite layer formed on a positive electrode current collector and a negative electrode plate having a negative electrode composite layer formed on a negative electrode current collector are flatly wound with a separator in between, and impregnated with an electrolyte, A step of suppressing the conductivity of the electrolyte impregnated in the electrode body, The steps include removing the portions at both ends of the electrode body in the width direction W parallel to the winding axis direction where the positive electrode current collectors and the negative electrode current collectors are electrically connected, thereby electrically separating the positive electrode current collectors and the negative electrode current collectors, The steps include: measuring electrical resistance by applying voltage at multiple measurement positions MP on the positive electrode plate and at measurement positions MP on the negative electrode plate; A method for inspecting a secondary battery, characterized by comprising the following features.

2. The step of electrically separating the positive electrode current collectors from each other and the negative electrode current collectors from each other is, At both ends of the width direction W, The method for inspecting a secondary battery according to claim 1, characterized in that both ends of the length direction L, which is perpendicular to the width direction W and the thickness direction D, and the connection portion on the outside of the width direction W in the central part of the length direction L are removed in the thickness direction D, and a tab-shaped measuring portion which is the measuring position MP of the electrically separated positive electrode current collector and the negative electrode current collector is formed on the inside of the central part of the length direction L.

3. In the step of measuring the electrical resistance, The method for inspecting a secondary battery according to claim 1, characterized in that a restraining force is applied to the electrode body from the thickness direction D.

4. The method for inspecting a secondary battery according to claim 3, characterized in that the restraining force is 4 to 9 [kN].

5. In the measurement step described above, The first measurement position MP of the positive electrode plate Ｐ-ＩＮ and the second measurement position MP of the negative electrode plate Ｎ-ＩＮ However, it is positioned at the inner end when it is wound up. Furthermore, the third measurement position MP on the positive electrode plate Ｐ-ＯＵＴ and the fourth measurement position MP of the negative electrode plate Ｎ-ＯＵＴ The method for inspecting a secondary battery according to claim 1, characterized in that the two are located at the outer end when the battery is wound.

6. the first measurement position MP Ｐ-ＩＮ and the electrical resistance R Ｎ-ＩＮ at the second measurement position MP ＩＮ and the third measurement position MP Ｐ-ＯＵＴ and the fourth measurement position MP Ｎ-ＯＵＴ and the electrical resistance R ＯＵＴ The method for inspecting a secondary battery according to claim 5, further comprising a step of estimating a short-circuit position between the inner end portion and the outer end portion from a ratio therewith.

7. In the measurement step described above, The method for inspecting a secondary battery according to claim 1, characterized in that the measurement position MP of one of the positive electrode plate or the negative electrode plate is fixed, and the other electrode plate is measured multiple times at different positions between the inner end and the outer end in the winding direction.

8. The method for inspecting a secondary battery according to claim 7, characterized in that the measurement step includes a step of determining the location of a short circuit, in which, as a result of multiple measurements, it is determined that a short circuit has occurred at a location close to the measurement location MP of the other electrode plate where the lowest electrical resistance is measured.

9. In the step of suppressing the conductivity of the electrolyte impregnated in the electrode body, The method for inspecting a secondary battery according to claim 1, characterized in that the conductivity of the electrolyte is suppressed by drying the electrolyte.

10. In the step of suppressing the conductivity of the electrolyte impregnated in the electrode body, The method for inspecting a secondary battery according to claim 1, characterized in that the conductivity of the electrolyte is suppressed by freezing the electrolyte.

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