Secondary battery manufacturing method

Abstract

To provide a method for manufacturing a secondary battery, with which the dimensional stability of an exposed portion in an electrode substrate can be improved.SOLUTION: Provided is a method for manufacturing a secondary battery, the method including: a coating step of forming a positive electrode mixture layer 23 and an insulating layer 24 adjacent to the positive electrode mixture layer 23 on a foil-like positive electrode substrate 22 having an edge 22E extending in a longitudinal direction so that a portion between the insulating layer 24 and the edge 22E of the positive electrode substrate 22 forms an exposed portion 22A where the positive electrode substrate 22 is exposed; and a stretching step of, after a pressing step of pressing the positive electrode mixture layer 23, stretching, in the longitudinal direction, the insulating layer 24 and an extension portion 22C located between the edge 22E and the positive electrode mixture layer 23 in the positive electrode substrate 22. In the stretching step, a stress greater than or equal to yield stress of the positive electrode substrate 22 or greater than or equal to 0.2% proof stress of the positive electrode substrate and less than tensile strength of the positive electrode substrate 22 is applied to the extension portion 22C, and a stress greater than or equal to yield stress of the insulating layer 24 or greater than or equal to 0.2% proof stress of the insulating layer is applied to the insulating layer 24.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a secondary battery. [Background technology]

[0002] Electric vehicles and hybrid vehicles use secondary batteries such as nonaqueous secondary batteries and nickel-metal hydride batteries as their power sources. A lithium-ion secondary battery, which is an example of a nonaqueous secondary battery, includes electrode plates (positive and negative electrode plates). The electrode plates include a long electrode base material and a mixture layer formed by applying a mixture paste to the electrode base material. The electrode base material includes exposed portions along its widthwise edges where the mixture paste is not applied and the electrode base material is exposed. The exposed portions are used as current collectors for connection to external terminals. In addition, an insulating layer made of insulating paste is formed at the boundary between the mixture layer and the exposed portion on either the positive or negative electrode plate (see, for example, Patent Document 1).

[0003] The method for manufacturing an electrode plate includes a pressing step in which a mixture paste and an insulating paste are applied to an electrode base material and dried to form a mixture layer and an insulating layer, and then the mixture layer is pressed to adjust the thickness of the mixture layer. In the pressing step, not only the mixture layer but also the mixture-coated portion of the electrode base material where the mixture layer is formed deforms. As a result, the electrode base material after the pressing step has a shape in which the side edges of the electrode base material are curved in the width direction due to partial differences in the amount of elongation in the width direction of the mixture-coated portion. Therefore, after the pressing step, a stretching step is performed to stretch the extension portions of the electrode base material that extend from the mixture layer to the side edges in order to correct the width direction curvature of the side edges of the electrode base material. The extension portions are portions where the mixture layer is not formed and are composed of exposed portions and portions of the electrode base material where the insulating layer is formed. In the stretching step, tension is applied to the extension portions along the longitudinal direction perpendicular to the width direction, thereby correcting the width direction curvature of the electrode base material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-072007 Summary of the Invention [Problem to be solved by the invention]

[0005] In the stretching process, the extended portion of the electrode substrate is stretched to an extent that takes into account deformation due to springback. If excessive plastic deformation, equivalent to the non-uniform plastic deformation region in the stress-strain curve, occurs in the extended portion, the extended portion deforms not only in the width direction but also in the thickness direction of the electrode substrate, resulting in a wavy shape in the thickness direction of the electrode substrate. In this case, when the exposed portions are welded together in an overlapping state to form an electrode terminal in a subsequent process, it becomes difficult to overlap the exposed portions in the correct position. This can result in a decrease in the dimensional stability of the electrode terminal or the exposed portions being bent. [Means for solving the problem]

[0006] A method for manufacturing a secondary battery that solves the above-mentioned problems includes a coating step of forming a composite layer and an insulating layer adjacent to the composite layer on a foil-shaped electrode base material having side edges extending in a specific direction, and forming an exposed portion in the electrode base material between the side edges and the insulating layer; and a pressing step of pressing the composite layer, followed by a stretching step of stretching an extended portion located in the electrode base material between the side edges and the composite layer and the insulating layer in the specific direction, wherein in the stretching step, a stress that is equal to or greater than the yield stress or 0.2% proof stress of the electrode base material and less than the tensile strength of the electrode base material is applied to the extended portion, and a stress that is equal to or greater than the yield stress or 0.2% proof stress of the insulating layer is applied to the insulating layer.

[0007] According to the above manufacturing method, in the stretching step following the pressing step, the extension portion located between the side edge and the electrode composite layer of the electrode base material and the insulating layer are stretched in a specific direction, thereby correcting the widthwise curvature of the electrode base material that occurs in the pressing step. Furthermore, by applying a stress to the extension portion that is equal to or greater than the yield stress or 0.2% proof stress of the electrode base material but less than the tensile strength of the electrode base material, the extension portion undergoes uniform plastic deformation throughout, without the non-uniform plastic deformation that occurs when a stress equivalent to the tensile strength is applied. Therefore, waviness in the thickness direction of the extension portion, including the exposed portion, can be suppressed. Furthermore, by applying a stress equal to or greater than the yield stress or 0.2% proof stress of the insulating layer to the insulating layer in the stretching step, plastic deformation occurs in the insulating layer. As a result, deformation due to springback in the extension portion after the stretching step is suppressed by the plastically deformed insulating layer, thereby improving the dimensional stability of the exposed portion, which is part of the extension portion.

[0008] In the method for manufacturing a secondary battery, it is preferable that the electrode base material contains aluminum, the insulating layer contains a resin component and an inorganic component, and the mass ratio of the resin component to the mass of the insulating layer is 15% or more. According to the manufacturing method, when the electrode base material contains aluminum, by setting the mass ratio of the resin component contained in the insulating layer to the mass of the insulating layer to be 15% or more, when a specific elongation is imparted to the insulating layer and the extension portion, a stress of equal to or greater than 0.2% proof stress and equal to or less than the tensile strength of the aluminum can be applied to the extension portion, and a stress of equal to or greater than the yield stress or 0.2% proof stress of the insulating layer can be applied to the insulating layer.

[0009] In the method for manufacturing a secondary battery, the mass ratio of the resin component to the mass of the insulating layer is preferably 30% or less. According to the manufacturing method, by setting the mass ratio of the resin component contained in the insulating layer to 30% or less to the mass of the insulating layer, excessive reduction in the mechanical strength of the insulating layer can be suppressed. Therefore, the dimensional stability of the exposed portion can be improved without reducing the short-circuit prevention function of the insulating layer.

[0010] In the method for manufacturing a secondary battery described above, the coating step includes forming the composite layer between two side edges of the electrode base material extending in the specific direction, and forming one insulating layer between the composite layer and each side edge to form two exposed portions. The stretching step includes applying tension to the electrode base material along the specific direction while the exposed portions and the insulating layer are in contact with a roll, thereby stretching the extended portions and the insulating layer in the specific direction. The roll preferably includes a main body portion and enlarged-diameter portions located on both sides of the main body portion and having a diameter larger than that of the main body portion. In the stretching step, the enlarged-diameter portions preferably contact the exposed portions and the insulating layer. According to the manufacturing method described above, the enlarged-diameter portions can selectively apply tension only to the extended portions and the insulating layer in the stretching step. Therefore, the stretching step can effectively correct the widthwise curvature of the electrode base material that occurs in the pressing step.

[0011] In the method for manufacturing a secondary battery, the composite layer and the insulating layer are preferably provided on opposing first and second surfaces of the electrode base material, respectively. In the stretching step, a plurality of rolls are preferably used, with at least one first roll among the plurality of rolls contacting the insulating layer and the exposed portion provided on the first surface, and at least one second roll among the plurality of rolls, different from the first roll, contacting the insulating layer and the exposed portion provided on the second surface. According to the manufacturing method, in the stretching step, the electrode plate is supported from both the first and second surfaces of the electrode base material. This more reliably suppresses deformation in the thickness direction of the extension and the insulating layer. Therefore, the dimensional stability of the exposed portion, which is part of the extension, can be further improved. [Effects of the Invention]

[0012] According to the present invention, the dimensional stability of the exposed portion of the electrode base material can be improved. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view of a cell battery of a lithium ion secondary battery. [Figure 2] FIG. 2 is a partially developed view of the electrode assembly. [Figure 3] FIG. 3 is a cross-sectional view of the electrode assembly in an expanded state. [Figure 4] FIG. 4 is a process diagram showing the manufacturing procedure of the positive electrode plate. [Figure 5] FIG. 5 is a plan view showing a state in which a positive electrode material mixture layer and an insulating layer are formed on a positive electrode substrate. [Figure 6] FIG. 6 is an enlarged plan view of the side edge of the positive electrode substrate after the pressing step. [Figure 7] FIG. 7 is a schematic diagram showing the positive electrode plate and rolls in the stretching step. [Figure 8] FIG. 8 is a cross-sectional view showing the positive electrode plate and the roll in the stretching step. [Figure 9] FIG. 9 is a diagram showing stress-strain curves for insulating layers with different resin component contents. [Figure 10] FIG. 10 is a diagram showing the stress-strain curve of the positive electrode substrate and the stress-strain curve of the insulating layer. [Figure 11] FIG. 11 is a diagram showing, as a reference example, the shape of an extended portion of a positive electrode substrate when a stress equivalent to the tensile strength of the positive electrode substrate is applied to the extended portion in the stretching step. [Figure 12] FIG. 12 is a diagram showing the shape of the extended portion of the positive electrode substrate when a stress equal to or greater than the 0.2% proof stress and less than the tensile strength of the positive electrode substrate is applied to the extended portion in the stretching step of this embodiment. [Figure 13] FIG. 13 is a cross-sectional view of the positive electrode plate used in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, one embodiment of the present invention will be described with reference to FIGS. [Lithium-ion secondary battery] As shown in Figure 1, a lithium-ion secondary battery 10, which is an example of a secondary battery, is a cell battery that is combined with multiple lithium-ion secondary batteries 10 and sealed in a resin or metal case to form a battery pack. The battery pack is used in hybrid vehicles and electric vehicles.

[0015] The lithium-ion secondary battery 10 includes a battery case 11 and a lid 12. The battery case 11 has a rectangular parallelepiped shape with an opening on the upper side. The lid 12 seals the opening of the battery case 11. The battery case 11 and the lid 12 are made of a metal such as aluminum or an aluminum alloy. The lithium-ion secondary battery 10 forms a sealed battery container by attaching the lid 12 to the battery case 11.

[0016] Two external terminals 13A and 13B are provided on the lid 12. The external terminals 13A and 13B are used for charging and discharging power. An electrode assembly 20 is housed inside the battery case 11. A positive electrode side current collector 20A, which is the positive electrode side end of the electrode assembly 20, is electrically connected to the positive electrode external terminal 13A via a positive electrode side current collector 14A. A negative electrode side current collector 20B, which is the negative electrode side end of the electrode assembly 20, is electrically connected to the negative electrode external terminal 13B via a negative electrode side current collector 14B. A nonaqueous electrolyte is injected into the battery case 11 through an inlet (not shown). The shapes of the external terminals 13A and 13B are not limited to those shown in FIG. 1 and may be any shape.

[0017] [Electrode body] 2 and 3, the electrode assembly 20 is a flat wound body obtained by winding a laminate in which long positive electrode plates 21 and negative electrode plates 25 are stacked with separators 28 interposed therebetween. The positive electrode plates 21 and negative electrode plates 25 are examples of electrode plates that make up the electrode assembly 20. In the laminate before winding, the positive electrode plates 21, separators 28, negative electrode plates 25, and separators 28 are stacked in this order in the thickness direction D3 (see FIG. 3). The positive electrode plates 21, negative electrode plates 25, and separators 28 are stacked such that their respective longitudinal directions coincide with the longitudinal direction D1.

[0018] [Positive electrode] As shown in Fig. 2, the positive electrode plate 21 includes a positive electrode substrate 22, a positive electrode mixture layer 23, and an insulating layer 24. The positive electrode substrate 22 is a foil-like electrode substrate formed in a long shape. The positive electrode mixture layer 23 is provided on each of a first surface 22S1 (see Fig. 3) and a second surface 22S2 (see Fig. 3) that face each other of the positive electrode substrate 22. The insulating layer 24 is provided on each of the first surface 22S1 and the second surface 22S2 of the positive electrode substrate 22 at a position adjacent to the positive electrode mixture layer 23.

[0019] 3, the positive electrode substrate 22 has one side edge 22E extending in a specific direction. For example, the specific direction is the longitudinal direction D1. The side edge 22E is located at one end of the positive electrode substrate 22 in the width direction D2, which is the shorter side of the positive electrode substrate 22. The width direction D2 is a direction that intersects with the longitudinal direction D1, and for example, is a direction that is perpendicular to the longitudinal direction D1.

[0020] An exposed portion 22A where the positive electrode substrate 22 is exposed and where neither the positive electrode mixture layer 23 nor the insulating layer 24 is formed is provided between the side edge 22E of the positive electrode substrate 22 and the insulating layer 24. The insulating layer 24 is provided in the positive electrode plate 21 at a position spaced apart from the side edge 22E of the positive electrode substrate 22. The positive electrode mixture layer 23 and the insulating layer 24 are in contact with each other at the boundary between them.

[0021] The positive electrode substrate 22 includes a mixture coated portion 22B and an extending portion 22C. The mixture coated portion 22B is a portion of the positive electrode substrate 22 on which the positive electrode mixture layer 23 is provided. The extending portion 22C is a portion of the positive electrode substrate 22 on which the positive electrode mixture layer 23 is not provided. In other words, the extending portion 22C is composed of the exposed portion 22A and a portion of the positive electrode substrate 22 on which the insulating layer 24 is provided.

[0022] The positive electrode substrate 22 is a metal foil made of aluminum or an alloy containing aluminum as a main component. The thickness of the positive electrode substrate 22 is, for example, 8 μm or more and 18 μm or less. The positive electrode substrate 22 functions as a current collector for the positive electrode. When the positive electrode substrate 22 is wound, opposing surfaces of the exposed portion 22A of the positive electrode substrate 22 are pressed against each other to form the positive electrode side current collecting portion 20A.

[0023] The positive electrode mixture layer 23 is a hardened body of a liquid positive electrode mixture paste. The thickness of the positive electrode mixture layer 23 is, for example, 15 μm or more and 250 μm or less. The positive electrode mixture paste is an example of a mixture paste, and includes a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder.

[0024] The positive electrode active material is a lithium-containing composite metal oxide capable of absorbing and releasing lithium ions. The lithium-containing composite oxide is an oxide containing lithium and a metal element other than lithium. The metal element other than lithium is at least one selected from the group consisting of nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained in the lithium-containing composite oxide as iron phosphate.

[0025] For example, the lithium-containing composite oxide is lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or lithium manganese oxide (LiMn2O4). For example, the lithium-containing composite oxide is a ternary lithium-containing composite oxide containing nickel, cobalt, and manganese, such as lithium nickel cobalt manganese oxide (LiNiCoMnO2). For example, the lithium-containing composite oxide is lithium iron phosphate (LiFePO4).

[0026] The positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent. The positive electrode conductive material may be, for example, carbon black such as acetylene black or ketjen black, carbon fiber such as carbon nanotube or carbon nanofiber, or graphite. The positive electrode binder is an example of a resin component contained in the positive electrode mixture paste. Examples of the positive electrode binder include polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA).

[0027] The insulating layer 24 is a hardened liquid insulating paste. The thickness of the insulating layer 24 is smaller than the thickness of the positive electrode mixture layer 23. The thickness of the insulating layer 24 is, for example, 2 μm or more and 40 μm or less. The insulating paste includes an inorganic component, an insulating paste solvent, and a resin component. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina, which are inorganic substances having insulating properties. An NMP solution, which is an example of an organic solvent, is used as the insulating paste solvent. The resin component functions as a binder in the insulating layer 24. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic, which are polymer materials soluble in NMP.

[0028] [Negative electrode] 2 and 3, the negative electrode plate 25 includes a negative electrode substrate 26, which is a foil-shaped electrode substrate formed in a long shape, and a negative electrode mixture layer 27 provided on both sides of the negative electrode substrate 26. The negative electrode plate 25 is produced by kneading materials that constitute the negative electrode mixture layer 27, applying the kneaded material to the negative electrode substrate 26, and drying the applied material.

[0029] The negative electrode substrate 26 functions as a current collector for the negative electrode. A thin film made of copper or an alloy mainly composed of copper is used as the negative electrode substrate 26. An exposed portion 26A where the negative electrode substrate 26 is exposed without the negative electrode mixture layer 27 formed is provided at an end of the negative electrode substrate 26 in the width direction D2 opposite the exposed portion 22A of the positive electrode plate 21. When the exposed portion 26A is wound, opposing surfaces of the exposed portion 26A are pressed against each other to form the negative electrode side current collecting part 20B.

[0030] The negative electrode mixture layer 27 is a hardened product of a liquid negative electrode mixture paste. The negative electrode mixture layer 27 includes a negative electrode active material that is a material capable of absorbing and releasing lithium ions. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, and easily graphitizable carbon. In addition to the negative electrode active material, the negative electrode mixture also includes a conductive agent, a binder, and the like.

[0031] [Separator] The separator 28 prevents contact between the positive electrode plate 21 and the negative electrode plate 25, and also holds the non-aqueous electrolyte between the positive electrode plate 21 and the negative electrode plate 25. When the electrode assembly 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte permeates from the ends of the separator 28 toward the center.

[0032] The separator 28 is a nonwoven fabric made of polypropylene, etc. As the separator 28, for example, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, an ion-conductive polymer electrolyte membrane, etc. can be used.

[0033] [Nonaqueous electrolyte] The non-aqueous electrolyte is a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent can be one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. The supporting salt can be one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc.

[0034] In this embodiment, ethylene carbonate is used as the nonaqueous solvent. Lithium bis(oxalato)borate (LiBOB) is added as a lithium salt to the nonaqueous electrolyte solution. For example, LiBOB is added to the nonaqueous electrolyte solution so that the concentration of LiBOB in the nonaqueous electrolyte solution is 0.001 to 0.1 mol / L.

[0035] [Positive electrode plate manufacturing process] The manufacturing process of the positive electrode plate 21 will be described below with reference to FIGS. As shown in FIG. 4, the manufacturing process of the positive electrode plate 21 includes steps S1 to S4.

[0036] [Coating process and drying process] Step S1 is a coating and drying step in which a positive electrode mixture paste and an insulating paste are applied to the positive electrode substrate 22 and dried to form a positive electrode mixture layer 23 and an insulating layer 24. In step S1, first, one strip of the positive electrode mixture paste and two strips of the insulating paste are applied to the first surface 22S1 of the positive electrode substrate 22 and dried. Thereafter, one strip of the positive electrode mixture paste and two strips of the insulating paste are also applied to the second surface 22S2 of the positive electrode substrate 22 and dried to form the positive electrode mixture layer 23 and the insulating layer 24 on both surfaces of the positive electrode substrate 22. The positive electrode mixture layer 23 contains a positive electrode active material, a positive electrode conductive material, and a positive electrode binder because the positive electrode solvent evaporates when the positive electrode mixture paste is dried. The insulating layer 24 contains an inorganic component and a resin component because the solvent for the insulating paste evaporates when the insulating paste is dried.

[0037] As shown in FIG. 5 , the positive electrode mixture paste is applied to the center of the positive electrode substrate 22 in the width direction D2 at positions spaced apart from two side edges 22E of the positive electrode substrate 22 located at both ends of the positive electrode substrate 22 in the width direction D2. Two strips of insulating paste are applied, one at a time, between the two side edges 22E of the positive electrode substrate 22 and the positive electrode mixture paste, at positions spaced apart from the two side edges 22E of the positive electrode substrate 22. The two strips of insulating paste are applied so as to sandwich the positive electrode mixture paste between them and so as to be in contact with the positive electrode mixture paste. Therefore, each insulating paste defines an exposed portion 22A in the positive electrode substrate 22 where the positive electrode substrate 22 is exposed, between the positive electrode mixture paste and the side edges 22E. Note that FIG. 5 illustrates a state in which the positive electrode mixture paste and the insulator paste are dried to form a positive electrode mixture layer 23 and an insulating layer 24.

[0038] [Pressing process] Step S2 is a pressing step in which the thickness of the positive electrode mixture layer 23 formed on both sides of the positive electrode substrate 22 is adjusted by pressing the positive electrode mixture layer 23. In step S2, the positive electrode plate 21 that has been subjected to the coating step and the drying step is conveyed in a conveyance direction D4 (see FIG. 6 ) along the longitudinal direction D1, while the positive electrode mixture layer 23 is pressed using a rolling roll (not shown). In step S2, the positive electrode mixture layer 23 and the mixture-coated portion 22B of the positive electrode substrate 22 on which the positive electrode mixture layer 23 is coated are pressed. On the other hand, in step S2, the insulating layer 24 and the extending portion 22C of the positive electrode substrate 22 on which the positive electrode mixture layer 23 is not coated are not pressed.

[0039] As shown in Fig. 6, in the positive electrode plate 21 after the pressing process in step S2, the side edge 22E of the positive electrode substrate 22 may have a shape that curves in the width direction D2 due to a partial difference in the amount of elongation in the composite-coated portion 22B of the positive electrode substrate 22. The amount of curvature W shown in Fig. 6 represents the amount of deviation in the width direction D2 of the side edge 22E. If the positive electrode plate 21 is wound together with the negative electrode plate 25 while the side edge 22E remains curved in the width direction D2, the positive electrode plate 21 will meander along the curved shape of the side edge 22E, making it difficult to maintain a desired positive-negative phase difference in the electrode body 20.

[0040] [Stretching process] As shown in FIG. 7 , step S3 is a stretching step for correcting the curved shape of the side edge 22E in the width direction D2. In the stretching step of step S3, tension T is applied along the longitudinal direction D1 of the positive electrode plate 21 to the positive electrode substrate 22 that has undergone the pressing step, with one or more rolls 30 in contact with each of the first surface 22S1 and the second surface 22S2. Hereinafter, the roll 30 in contact with the first surface 22S1 side of the positive electrode plate 21 will be referred to as the first roll 30A, and the roll 30 in contact with the second surface 22S2 side of the positive electrode plate 21 will be referred to as the second roll 30B. The positive electrode plate 21 is supported by the first roll 30A and the second roll 30B from each of the first surface 22S1 and the second surface 22S2 side of the positive electrode substrate 22.

[0041] 8, the roll 30 includes a main body 31 and expanded diameter portions 32 located on both sides of the main body 31. The main body 31 has a first diameter OD1. The expanded diameter portions 32 have a second diameter OD2 that is larger than the first diameter OD1. The main body 31 is located opposite the positive electrode mixture layer 23 and spaced apart from the positive electrode mixture layer 23.

[0042] The expanded diameter portion 32 is a portion of the roll 30 that has a larger diameter than the main body portion 31. The expanded diameter portion 32 abuts against the exposed portion 22A and the insulating layer 24. The expanded diameter portion 32 of the first roll 30A is abutted by the exposed portion 22A and the insulating layer 24 formed on the first surface 22S1. The expanded diameter portion 32 of the second roll 30B is abutted by the exposed portion 22A and the insulating layer 24 formed on the second surface 22S2. The exposed portion 22A abuts against the expanded diameter portion 32 while being slightly deflected by the thickness of the insulating layer 24.

[0043] In the stretching step, tension T is applied to the positive electrode substrate 22 along the longitudinal direction D1 with the exposed portion 22A and the insulating layer 24 in contact with the expanded diameter portion 32 of the roll 30. At this time, the main body portion 31 is separated from the positive electrode mixture layer 23, so that tension T acts only on the extending portion 22C and the insulating layer 24. As the extending portion 22C and the insulating layer 24 are stretched along the longitudinal direction D1, an internal force acting outward in the width direction D2 acts on a portion of the side edge 22E that is recessed in the width direction D2 toward the center of the positive electrode substrate 22. This corrects the curved shape of the side edge 22E in the width direction D2 that was caused in the pressing step.

[0044] The stress acting on the extension portion 22C and the insulating layer 24 depends on the magnitude of the tension T, the cross-sectional areas of the extension portion 22C and the insulating layer 24 in a cross-sectional view of the positive electrode plate 21 cut along the width direction D2, and the stress-strain curves of the extension portion 22C and the insulating layer 24. In the stretching process, the insulating layer 24 and the portion of the extension portion 22C where the insulating layer 24 is formed are in close contact with each other, and therefore the amounts of deformation thereof are equal.

[0045] [Stress-strain curve of insulating layer] Here, with reference to FIG. 9, the relationship between the content of the resin component in the insulating layer 24 and the stress-strain curve of the insulating layer 24 will be described.

[0046] 9, in graph 40, the vertical axis represents the stress [MPa] acting on insulating layer 24, and the horizontal axis represents the elongation (strain) [%] of insulating layer 24. Curves 41 to 44 shown in graph 40 are stress-strain curves for insulating layer 24 at four levels of resin component content. Curves 41, 42, 43, and 44 correspond to the levels, in order from smallest to largest, of the resin component content.

[0047] The lower the resin content of the insulating layer 24, the harder and more brittle it becomes. Therefore, when the resin content of the insulating layer 24 is very low, as shown in curve 41, the insulating layer 24 breaks with almost no plastic deformation. Furthermore, when the resin content is higher than that of curve 41, as shown in curves 42 and 43, the elongation to break increases and a yield point appears. Furthermore, when the resin content is higher than that of curve 43, as shown in curve 44, the elongation to break increases further and the yield point disappears. Thus, by changing the resin content of the insulating layer 24, the elongation characteristics of the insulating layer 24 relative to stress can be controlled.

[0048] [Relationship between the stress-strain curve of the positive electrode mixture and the stress-strain curve of the insulating layer] Next, with reference to FIG. 10, the relationship between the stress-strain curve of the positive electrode substrate 22 and the stress-strain curve of the insulating layer 24 will be described.

[0049] 10 , in a graph 50, the vertical axis represents the stress [MPa] acting on each of the positive electrode substrate 22 and the insulating layer 24, and the horizontal axis represents the elongation (strain) [%] of each of the positive electrode substrate 22 and the insulating layer 24. A curve 51 shown in the graph 50 is an example of a stress-strain curve of the positive electrode substrate 22 when the positive electrode substrate 22 is made of aluminum. A curve 52 shown in the graph 50 is an example of a stress-strain curve of the insulating layer 24.

[0050] In graph 50, the stress-strain curve of positive electrode substrate 22 is roughly divided into three regions according to deformation behavior: elastic deformation region 51A, uniform plastic deformation region 51B, and non-uniform plastic deformation region 51C. In elastic deformation region 51A, elastic deformation occurs in positive electrode substrate 22. In uniform plastic deformation region 51B, uniform plastic deformation occurs in positive electrode substrate 22. In non-uniform plastic deformation region 51C, locally non-uniform plastic deformation occurs in positive electrode substrate 22.

[0051] In the case of aluminum, the stress at the boundary between the elastic deformation region 51A and the uniform plastic deformation region 51B is the 0.2% proof stress, which is the stress at which the permanent strain remaining after unloading is 0.2%. The 0.2% proof stress of aluminum is, for example, 327 MPa. The stress at the boundary between the uniform plastic deformation region 51B and the non-uniform plastic deformation region 51C is the tensile strength, which is the maximum value of stress. The tensile strength of aluminum is, for example, 392 MPa. Note that when a metal with a clear yield point in the stress-strain curve (for example, a metal containing a large amount of interstitial elements) is used as the material for the positive electrode substrate 22, the yield point becomes the stress at the boundary between the elastic deformation region 51A and the uniform plastic deformation region 51B.

[0052] In the stretching process, an elongation EL is imparted to the extending portion 22C of the positive electrode substrate 22, thereby applying a stress equal to or greater than the 0.2% yield strength of the positive electrode substrate 22 and less than the tensile strength of the positive electrode substrate 22. At the same time, a stress equal to or greater than the yield stress or 0.2% yield strength of the insulating layer 24 is applied to the insulating layer 24. The insulating layer 24 is also applied with an elongation EL that is the same as the elongation EL imparted to the extending portion 22C. Therefore, the resin content of the insulating layer 24 is determined so that when the extending portion 22C and the insulating layer 24 are applied with an elongation EL, a stress equal to or greater than the yield stress or 0.2% yield strength of the insulating layer 24 acts on the insulating layer 24.

[0053] For example, when the material of the positive electrode substrate 22 is aluminum, the mass ratio of the resin component in the insulating layer 24 is preferably 15% or more and 30% or less with respect to the mass of the insulating layer 24. If the mass ratio of the resin component in the insulating layer 24 is 15% or more, when an elongation EL is imparted to the extension portion 22C and the insulating layer 24, a stress equal to or greater than the yield stress or 0.2% proof stress of the insulating layer 24 acts on the insulating layer 24. Furthermore, if the mass ratio of the resin component in the insulating layer 24 is 30% or less, an excessive decrease in the mechanical strength of the insulating layer 24 can be suppressed.

[0054] [Deformation through the thickness of the exposed part] 11, as a reference example for illustrating the effects of this embodiment, the shape of the extended portion 22C of the positive electrode substrate 22 when a stress equivalent to the tensile strength of the positive electrode substrate 22 is applied to the extended portion 22C of the positive electrode substrate 22 in the stretching step will be described. For ease of explanation, the insulating layer 24 is not shown in FIG.

[0055] As shown in FIG. 11 , when stress equivalent to the tensile strength of the positive electrode substrate 22 acts on the extension portion 22C during the stretching process, non-uniform plastic deformation occurs in the extension portion 22C, corresponding to the non-uniform plastic deformation region 51C in the stress-strain curve. In the non-uniform plastic deformation region 51C, localized excessive deformation is likely to occur. When excessive plastic deformation occurs in the extension portion 22C during the stretching process, the extension portion 22C deforms not only along the longitudinal direction D1 and the width direction D2, but also in the thickness direction D3 of the positive electrode substrate 22. In this case, the extension portion 22C, including the exposed portion 22A, assumes a wavy shape in the thickness direction D3.

[0056] If the extension portion 22C is significantly deformed in the thickness direction D3, it becomes difficult to align the exposed portions 22A in the correct position when the exposed portions 22A are welded together in an overlapping state to form the positive current collecting portion 20A in a later process. As a result, the dimensional stability of the positive current collecting portion 20A may be reduced, and the exposed portions 22A may be bent or deformed when the positive current collecting portion 20A is formed.

[0057] Next, referring to Figure 12, we will explain the shape of the extension portion 22C when a stress that is equal to or greater than the 0.2% yield strength of the positive electrode substrate 22 and less than the tensile strength of the positive electrode substrate 22 is applied to the extension portion 22C, as in the stretching process of this embodiment.

[0058] 12, when a stress equal to or greater than the 0.2% yield strength of the positive electrode substrate 22 but less than the tensile strength of the positive electrode substrate 22 acts on the extension portion 22C during the stretching process, the extension portion 22C undergoes uniform plastic deformation corresponding to the uniform plastic deformation region 51B in the stress-strain curve. Such uniform plastic deformation can suppress wavy deformation in the thickness direction D3 that occurs in the non-uniform plastic deformation region 51C in the extension portion 22C. This improves the dimensional stability of the exposed portion 22A.

[0059] Furthermore, in the stretching process, a stress equal to or greater than the yield stress or 0.2% proof stress of insulating layer 24 acts on insulating layer 24, causing plastic deformation in insulating layer 24. Because plastically deformed insulating layer 24 is in close contact with extension portion 22C, deformation due to springback in extension portion 22C after the stretching process is suppressed by plastically deformed insulating layer 24. This also improves the dimensional stability of exposed portion 22A, which is part of extension portion 22C.

[0060] [Cutting process] Step S4 is a cutting step in which the positive electrode plate 21 that has been subjected to the stretching step of step S3 is cut at the center in the width direction D2. By the cutting step, the positive electrode plate 21 is divided into two along the longitudinal direction D1. By the above steps S1 to S4, the positive electrode plate 21 is manufactured.

[0061] [Effects of the embodiment] According to the above embodiment, the following effects can be obtained. (1) In the stretching step, the extension portion 22C and the insulating layer 24 are stretched in the longitudinal direction D1, and an internal force acting outward in the width direction D2 acts on the portion of the side edge 22E that is recessed in the width direction D2 toward the center of the positive electrode substrate 22. This makes it possible to correct the curved shape of the side edge 22E in the width direction D2 that was caused in the pressing step.

[0062] (2) In the stretching process, a stress equal to or greater than the yield stress or 0.2% proof stress of the positive electrode substrate 22 and less than the tensile strength of the positive electrode substrate 22 is applied to the extending portion 22C, thereby causing uniform plastic deformation in the extending portion 22C. This makes it possible to suppress wavy deformation in the thickness direction D3 that occurs in the non-uniform plastic deformation region 51C in the extending portion 22C. This improves the dimensional stability of the exposed portion 22A.

[0063] (3) In the stretching process, a stress equal to or greater than the yield stress or 0.2% proof stress of the insulating layer 24 is applied to the insulating layer 24, thereby causing plastic deformation in the insulating layer 24. As a result, deformation due to springback in the extended portion 22C after the stretching process is suppressed by the plastically deformed insulating layer 24. This can improve the dimensional stability of the exposed portion 22A.

[0064] (4) When the positive electrode substrate 22 contains aluminum, by setting the mass ratio of the resin component in the insulating layer 24 to 15% or more, a stress equal to or greater than the yield stress or 0.2% proof stress of the insulating layer 24 can be applied to the insulating layer 24 in the stretching process. In other words, when a specific elongation EL is applied to the extension portion 22C and the insulating layer 24, a stress equal to or greater than the 0.2% proof stress and equal to or less than the tensile strength of aluminum acts on the extension portion 22C, and a stress equal to or greater than the yield stress or 0.2% proof stress of the insulating layer 24 can be applied to the insulating layer 24.

[0065] (5) When the mass ratio of the resin component in the insulating layer 24 is 30% or less, it is possible to prevent an excessive decrease in the mechanical strength of the insulating layer 24. Therefore, it is possible to improve the dimensional stability of the exposed portion 22A without reducing the short-circuit prevention function of the insulating layer 24.

[0066] (6) In the stretching process, the extending portion 22C and the insulating layer 24 are brought into contact with the expanded diameter portion 32 of the roll 30, so that the tension T can be selectively applied only to the extending portion 22C and the insulating layer 24. Therefore, in the stretching process, the curvature in the width direction D2 of the positive electrode substrate 22 that occurs in the pressing process can be suitably corrected.

[0067] (7) In the stretching step, the positive electrode plate 21 is supported by the first roll 30A and the second roll 30B from each of the first surface 22S1 and the second surface 22S2 of the positive electrode base material 22. This more reliably suppresses deformation of the extension portion 22C and the insulating layer 24 in the thickness direction D3. This further improves the dimensional stability of the exposed portion 22A.

[0068] [Example] Hereinafter, an example 1 and comparative examples 1 and 2 of the positive electrode plate 21 will be described. Note that these examples do not limit the above embodiment.

[0069] [Example 1] In Example 1, aluminum having a thickness of 12 μm was used as the positive electrode substrate 22. One positive electrode mixture layer 23 and two insulating layers 24 were formed on each of the first surface 22S1 and the second surface 22S2 of the positive electrode substrate 22. The insulating layer 24 contained boehmite as an inorganic component and PVDF, an example of a binder, as a resin component. In the insulating layer 24, the ratio of the mass of the inorganic component to the mass of the resin component was inorganic component:resin component=80%:20%. The thickness of the insulating layer 24 was 10 μm.

[0070] As shown in FIG. 13 , in Example 1, the width W1 in the width direction D2 from the center line CL of the positive electrode substrate 22, indicated by the dashed dotted line, to the side edge 22E was 103.5 mm. The width W2 in the width direction D2 from the center line CL to the end of the positive electrode mixture layer 23 was 89.6 mm. The width W3 of the insulating layer 24 in the width direction D2 was 4.1 mm. The width W4 of the exposed portion 22A in the width direction D2 was 9.8 mm. A positive electrode plate 21 having the above-described components and dimensions was manufactured through a coating process and a drying process, and then subjected to a pressing process, a stretching process, and a cutting process.

[0071] In the stretching step, tension T was set to 100 N so that a stress equivalent to the 0.2% proof stress of aluminum was applied to extension portion 22C. The 0.2% proof stress of the aluminum used in Example 1 and Comparative Examples 1 and 2 was 327 MPa. At this time, a stress equal to or greater than the 0.2% proof stress or yield stress of insulating layer 24 acted on insulating layer 24, causing plastic deformation of insulating layer 24.

[0072] [Comparative Example 1] In Comparative Example 1, the coating step, drying step, pressing step, stretching step, and cutting step were performed in the same manner as in Example 1, except that the insulating layer 24 was not formed on the positive electrode substrate 22.

[0073] Comparative Example 2 In Comparative Example 2, the coating, drying, pressing, and stretching steps were performed in the same manner as in Comparative Example 1, except that in the stretching step, tension T was set to 120 N so that a stress equivalent to the tensile strength of aluminum was applied to the extended portion 22C. The tensile strength of the aluminum used in Example 1 and Comparative Examples 1 and 2 was 392 MPa.

[0074] [Rating 1] In Evaluation 1, the positive electrode plates 21 of Example 1 and Comparative Examples 1 and 2 were evaluated for whether or not the curvature in the width direction D2 that occurs in the pressing process was corrected at the stage when the stretching process was completed. In Evaluation 1, those in which the curvature in the width direction D2 was corrected were evaluated as good (◯), and those in which the curvature in the width direction D2 was not corrected were evaluated as poor (×).

[0075] [Rating 2] In Evaluation 2, the positive electrode plates 21 of Example 1 and Comparative Examples 1 and 2 were evaluated for waviness in the thickness direction D3 that occurs during the stretching process after the stretching process was completed. In Evaluation 2, those without waviness in the thickness direction D3 were evaluated as good (◯), and those with waviness in the thickness direction D3 were evaluated as poor (×).

[0076] [Table 1]

[0077] As shown in Table 1, in Example 1, the curvature in the width direction D2 was corrected. In contrast, in Comparative Example 1, the curvature in the width direction D2 remained partially. This is thought to be because Comparative Example 1 does not include the insulating layer 24, and therefore the amount of deformation in the width direction D2 was reduced due to springback of the extension portion 22C after the stretching process. In Comparative Example 2, although the insulating layer 24 is not included, the extension portion 22C deforms to a degree that causes non-uniform plastic deformation. This is thought to ensure the amount of deformation in the width direction D2 even if springback of the extension portion 22C occurs after the stretching process.

[0078] In Example 1 and Comparative Example 1, waviness in the thickness direction D3 was not observed in the extending portion 22C. In Comparative Example 2, waviness in the thickness direction D3 was observed in the extending portion 22C. In Comparative Example 2, it is believed that the extending portion 22C was deformed to such an extent that non-uniform plastic deformation occurred, which made it easy for localized and excessive plastic deformation to occur in the extending portion 22C, causing waviness in the thickness direction D3 in the extending portion 22C.

[0079] [Example of change] The above embodiment can be modified as follows. In the stretching step, the number of rolls 30 may be one or three or more. For example, either the first roll 30A or the second roll 30B may be used, or other rolls 30 may be used in addition to the first roll 30A and the second roll 30B.

[0080] In the stretching step, if tension T can be selectively applied only to the extension portion 22C and the insulating layer 24, it is not necessary to use the roll 30 including the main body portion 31 and the expanded diameter portion 32. For example, two cylindrical rolling rolls may be brought into contact with the extension portion 22C and the insulating layer 24 located on both sides of the positive electrode plate 21 in the width direction D2, respectively.

[0081] The mass ratio of the resin component in the insulating layer 24 is not limited as long as a stress of yield stress or 0.2% proof stress or more acts on the insulating layer 24 in the stretching process. For example, the mass ratio of the resin component in the insulating layer 24 may be more than 30% as long as the mechanical strength of the insulating layer 24 can be ensured. In this case, the insulating layer 24 can exhibit a tendency for plastic deformation to occur at a lower stress and for the elongation to break to increase as a characteristic of the elongation to stress.

[0082] Although the positive electrode plate 21 has been illustrated as having an insulating layer 24, the negative electrode plate 25 may have an insulating layer at the boundary between the exposed portion 26A and the negative electrode mixture layer 27. In this case, the same manufacturing process as that for the positive electrode plate 21 is applied as a manufacturing process for the negative electrode plate 25. That is, in the stretching process, a stress equal to or greater than 0.2% yield strength and equal to or less than the tensile strength of the negative electrode substrate 26 (e.g., copper) is applied to the exposed portion 26A, and a stress equal to or greater than the yield stress or 0.2% yield strength of the insulating layer is applied to the insulating layer of the negative electrode plate 25.

[0083] Although the lithium-ion secondary battery 10 is shown as an example of a secondary battery, the manufacturing method of the above embodiment can be applied to any secondary battery that includes an electrode plate that includes an electrode substrate, a mixture layer, an insulating layer, and an exposed portion. Therefore, the secondary battery is not limited to a nonaqueous secondary battery such as the lithium-ion secondary battery 10, and may be, for example, a nickel-metal hydride storage battery.

[0084] The electrode body 20 is exemplified as a wound body formed by winding a laminate in which a positive electrode plate 21 and a negative electrode plate 25 are stacked with a separator 28 interposed therebetween. However, the electrode body 20 may be, for example, a laminate in which a plurality of positive electrode plates 21 and a plurality of negative electrode plates 25 are alternately stacked with a separator 28 interposed therebetween.

[0085] The lithium-ion secondary battery 10 may be installed in an automatic transport vehicle, a special-purpose vehicle for loading and unloading, an electric vehicle, a hybrid vehicle, a computer, or other electronic device, or may be part of other systems. For example, it may be installed in a moving object such as a ship or an aircraft, or it may be a power supply system that supplies power from a power plant via a substation to a building or home where a secondary battery is installed. [Explanation of symbols]

[0086] T…Tension 10...Lithium-ion secondary battery 20...Electrode body 21...Positive electrode plate 22...Positive electrode substrate 22A…Exposed part 22B...Compound coating section 22C...Extension part 22E…Side edge 22S1…Side 1 22S2…Second side 23...Positive electrode mixture layer 24...Insulating layer 25...Negative electrode plate 26...Anode substrate 27...Negative electrode mixture layer 28...Separator 30...roll 30A...1st roll 30B...2nd roll 31...Main body 32…Expanded diameter part

Claims

1. a coating step of forming a mixture layer and an insulating layer adjacent to the mixture layer on a foil-shaped electrode base material having side edges extending in a specific direction, and forming a portion of the electrode base material between the side edges and the insulating layer as an exposed portion in which the electrode base material is exposed; a stretching step of stretching an extending portion of the electrode base material located between the side edge and the mixture layer and the insulating layer in the specific direction after a pressing step of pressing the mixture layer, In the stretching step, a stress equal to or greater than the yield stress or 0.2% proof stress of the electrode base material and less than the tensile strength of the electrode base material is applied to the extended portion so that uniform plastic deformation occurs in the extended portion, and a stress equal to or greater than the yield stress or 0.2% proof stress of the insulating layer is applied to the insulating layer so that plastic deformation occurs in the insulating layer; the electrode substrate contains aluminum, the insulating layer contains a resin component and an inorganic component, The mass ratio of the resin component to the mass of the insulating layer is 15% or more and 30% or less. A method for manufacturing a secondary battery comprising the steps of:

2. the coating step includes forming the mixture layer between the two side edges extending in the specific direction in the electrode base material, and forming the insulating layer between the mixture layer and each of the side edges, one by one, to form two of the exposed portions; the stretching step includes applying tension to the electrode base material along the specific direction while the exposed portion and the insulating layer are in contact with a roll, thereby stretching the extended portion and the insulating layer in the specific direction; The roll includes a main body portion and enlarged diameter portions located on both sides of the main body portion and having a larger diameter than the main body portion, In the stretching step, the expanded diameter portion abuts against the exposed portion and the insulating layer. The method for manufacturing a secondary battery according to claim 1 .

3. the mixture layer and the insulating layer are provided on a first surface and a second surface facing each other of the electrode base material, respectively; In the stretching step, a plurality of the rolls are used, At least one first roll among the plurality of rolls abuts against the insulating layer provided on the first surface and the exposed portion, At least one second roll, which is different from the first roll, among the plurality of rolls is in contact with the insulating layer provided on the second surface and the exposed portion.

3. The method for manufacturing a secondary battery according to claim 2.

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