Secondary battery

Abstract

The secondary battery includes: a plurality of positive electrodes each having a positive electrode core and a positive electrode active material disposed on the positive electrode core; a plurality of negative electrodes each having a negative electrode core and a negative electrode active material disposed on the negative electrode core; one or more separator films; and an adhesive that is coated on at least one side surface in the thickness direction of the separator film so that the areal density becomes substantially constant. The secondary battery includes a stacked portion in which the positive electrodes and the negative electrodes are alternately stacked with the separator film interposed therebetween, and the area of the adhered portion of the adhesive on the outer side in the stacking direction of the stacked portion is larger than the area of the adhered portion of the adhesive on the inner side in the stacking direction of the stacked portion.

Description

Technical Field

[0001] The present invention relates to a secondary battery. Background Art

[0002] In recent years, the demand for secondary batteries has been increasing in various applications. Among them, lithium-ion secondary batteries using non-aqueous electrolytes have attracted attention due to their high energy density. As one of their forms, there is a secondary battery as described in Patent Document 1. In the secondary battery of this form, a flat electrode body formed by laminating a positive electrode plate and a negative electrode plate with a separator therebetween is inserted into an outer package. The positive electrode composite material layer of the positive electrode plate is provided on both sides of the positive electrode core body, and the negative electrode composite material layer of the negative electrode plate is provided on both sides of the negative electrode core body. The positive electrode active material and the negative electrode active material each have a structure capable of intercalating / deintercalating lithium ions. The separator is a porous material that allows lithium ions to pass through, and on the other hand, prevents short circuits caused by electrical contact between the positive electrode plate and the negative electrode plate.

[0003] The positive electrode plate and the negative electrode plate are respectively electrically connected to current collectors and inserted into the outer package. The outer package is sealed after injecting an electrolyte. For this secondary battery, in order to prevent direct contact between the positive and negative electrodes caused by shrinkage of the separator, an adhesive layer is provided on the surface of the separator, and the positive electrode plate and the separator and the negative electrode plate and the separator are bonded by thermocompression bonding.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-26943 Summary of the Invention

[0007] In the secondary battery of Patent Document 1, separators with different coating amounts and areas of the adhesive are used to prevent uneven melting of the adhesive layer and reduce poor ion permeability. However, since multiple separators with different coating amounts and areas of the adhesive are required, it is difficult to improve productivity.

[0008] Moreover, especially in the case of a secondary battery for vehicle use, high durability is required. Therefore, it is preferable that the electrolyte retention amount is uniform regardless of the position in the lamination direction of the electrode body.

[0009] In order to solve the above problems, the present invention provides a secondary battery, which includes: a positive electrode having a positive electrode core and a positive electrode active material disposed on the positive electrode core; a negative electrode having a negative electrode core and a negative electrode active material disposed on the negative electrode core; one or more separator films; and an adhesive coated on at least one side surface in the thickness direction of the separator film so that the areal density is substantially constant. The secondary battery includes a stacked portion in which the positive electrode and the negative electrode are alternately stacked with the separator film therebetween, and the area of the adhered portion of the adhesive on the outer side in the stacking direction of the stacked portion is larger than the area of the adhered portion of the adhesive on the inner side in the stacking direction of the stacked portion.

[0010] In addition, in the case where the secondary battery has a laminated electrode body, if the area of the adhered portion of the adhesive coated on the two outermost separator films in the stacked portion is larger than the area of the adhered portion of the adhesive coated on one or two separator films (one separator film when the number of stacked layers is odd; two separator films when the number of stacked layers is even) located in the center of the stacked portion, the requirement that "the area of the adhered portion of the adhesive on the outer side in the stacking direction of the stacked portion is larger than the area of the adhered portion of the adhesive on the inner side in the stacking direction of the stacked portion" is satisfied.

[0011] In addition, in the case where the secondary battery has a wound electrode body, if the area of the adhered portion of the adhesive coated on the outermost peripheral portion of the separator film is larger than the area of the adhered portion of the adhesive coated on the innermost peripheral portion of the separator film, the requirement that "the area of the adhered portion of the adhesive on the outer side in the stacking direction of the stacked portion is larger than the area of the adhered portion of the adhesive on the inner side in the stacking direction of the stacked portion" is satisfied.

[0012] In addition, in the case where the secondary battery has a laminated electrode body, the stacked portion may be a region where the positive electrode, the negative electrode, and the separator film all overlap when viewed from the stacking direction. Alternatively, the stacked portion may also be an electrode body or an electrode group. In addition, in the case where the secondary battery has a wound electrode body, when the electrode body is flat, a partial region in the direction parallel to the pressing plate that presses the electrode body into a flat shape has a structure in which the positive electrode, the negative electrode, and the separator film are stacked with the separator film disposed between the positive electrode and the negative electrode. Therefore, in the case where the secondary battery has a wound electrode body, a partial region in the circumferential direction can be used as the stacked portion, and in this case, the separator film located on the innermost peripheral side and the separator film located on the outermost peripheral side can be determined.

[0013] According to the present invention, it is possible to realize a secondary battery that is not easily deteriorated and has excellent mass productivity, and in which the electrolyte retention amount is easily made uniform regardless of the position in the stacking direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Is a perspective view of a prismatic secondary battery according to an embodiment of the present invention.

[0015] Figure 2 Is a perspective view of the electrode body and the sealing plate constituting the above-mentioned prismatic secondary battery.

[0016] Figure 3 Is an exploded perspective view of the electrode body of the above-mentioned prismatic secondary battery.

[0017] Figure 4 Is a schematic representation Figure 2 Of the cross-section taken along line A-A.

[0018] Figure 5A Is an enlarged schematic cross-sectional view after cutting a part of the outer side in the stacking direction of the first electrode group with a plane substantially orthogonal to the height direction.

[0019] Figure 5B Is a view showing the state where the positive electrode has been peeled off from a part of the first electrode group.

[0020] Figure 6A Is an enlarged schematic cross-sectional view after cutting a part of the inner side in the stacking direction of the first electrode group with a plane substantially orthogonal to the height direction.

[0021] Figure 6B Is a view showing the state where the positive electrode has been peeled off from a part of the first electrode group.

[0022] Figure 7A Is a schematic top view showing the adhesive part transferred to the peeled positive electrode in the secondary battery of one embodiment, and is a schematic top view showing the adhesive part transferred to the positive electrode on the outer side in the stacking direction.

[0023] Figure 7B Is a schematic top view showing the adhesive part transferred to the peeled positive electrode in the secondary battery of one embodiment, and is a schematic top view showing the adhesive part transferred to the positive electrode on the inner side in the stacking direction.

[0024] Figure 8 Is a graph showing the relationship between the number of layers in the stack group and the ratio of the transfer area to the area of one side of the positive electrode, and is a graph showing the adhesive transfer area ratio.

[0025] Figure 9 Is a graph showing Figure 8 Of the spline curve passing through all the measurement points.

[0026] Figure 10 Is a graph showing the relationship between the number of layers and the thickness of the separator, where the dots represent the thickness of the separator before pressing with a hot plate and the solid line represents the thickness of the separator after pressing with a hot plate.

[0027] Figure 11 It is a plan view of a wound-type rectangular secondary battery according to another embodiment.

[0028] Figure 12 It is a front view of a wound-type rectangular secondary battery.

[0029] Figure 13 (a) is Figure 1 A-A line partial cross-sectional view, Figure 13 (b) is Figure 13 Partial cross-sectional view of line BB of (a), Figure 13 (c) is Figure 13 (a) C-C line cross-sectional view.

[0030] Figure 14A It is a plan view of a positive electrode included in a wound-type rectangular secondary battery.

[0031] Figure 14B It is a plan view of a negative electrode included in a wound-type rectangular secondary battery.

[0032] Figure 15 This is a perspective view of a flat wound electrode body included in a wound prismatic secondary battery, with the winding end side thereof developed.

[0033] Figure 16A It is a schematic diagram for explaining the corresponding relationship between the stacked type electrode body and the wound type electrode body.

[0034] Figure 16B It is a schematic diagram for explaining the corresponding relationship between the stacked type electrode body and the wound type electrode body. DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in the case where the following includes multiple embodiments, modified examples, etc., it is conceived from the beginning to appropriately combine their characteristic parts to construct a new embodiment. In addition, in the following embodiments, the same reference numerals are marked on the same structure in the drawings, and repeated descriptions are omitted. In addition, regarding the constituent elements described below, which are not recorded in the independent claims representing the highest concept, they are arbitrary constituent elements and are not essential constituent elements. In addition, in this specification, the description of "numerical value A to numerical value B" means "above numerical value A and below numerical value B". In addition, in the following description, the height direction of the outer can 14, 140 is set as the "upper and lower direction" of the secondary battery 10, 110, the sealing plate 15 side, 123 side is set as "up", and the bottom side of the outer can 14, 140 is set as "down". In addition, the direction along the long side direction of the sealing plate 15, 123 is set as the "lateral direction" of the secondary battery 10, 110.

[0036] Figure 1 is a perspective view of a square secondary battery 10 according to an embodiment of the present invention, Figure 2 and is a perspective view of an electrode body 11 and a sealing plate 15 constituting the square secondary battery 10 (a view showing a state in which the outer can 14 is removed). As Figure 1 and Figure 2 shown, the square secondary battery (hereinafter simply referred to as the secondary battery) 10 includes a square container including an outer can 14 and a sealing plate 15 as an outer package, but the outer package is not limited thereto.

[0037] As Figure 1 and Figure 2 shown, the secondary battery 10 includes: an electrode body 11; an electrolyte; a bottomed cylindrical outer can 14 that houses the electrode body 11 and the electrolyte; and a sealing plate 15 to which a positive electrode terminal 12 and a negative electrode terminal 13 are attached, and the sealing plate 15 closes the opening of the outer can 14. The electrode body 11 has a structure in which a positive electrode 20 and a negative electrode 30 are alternately stacked with a separator 40 therebetween, which will be described in detail later using Figure 3 . The outer can 14 is a flat, substantially rectangular parallelepiped-shaped metal square container that is open at one end in the height direction. The outer can 14 and the sealing plate 15 are made of, for example, a metal material mainly composed of aluminum.

[0038] The electrolyte may be an aqueous electrolyte, but a non-aqueous electrolyte is preferred, and a non-aqueous electrolyte solution is used in the present embodiment. The non-aqueous electrolyte solution includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and a mixed solvent of two or more of them can be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen in these solvents is substituted with a halogen atom such as fluorine. As the electrolyte salt, for example, a lithium salt such as LiPF6 can be used.

[0039] On the sealing plate 15, as described above, a positive electrode terminal 12 and a negative electrode terminal 13 are attached. The sealing plate 15 has an elongated rectangular shape, and the positive electrode terminal 12 is disposed on one end side in the long side direction of the sealing plate 15, and the negative electrode terminal 13 is disposed on the other end side in the long side direction of the sealing plate 15. The positive electrode terminal 12 and the negative electrode terminal 13 are external connection terminals that are electrically connected to other secondary batteries 10 and loads, and the positive electrode terminal 12 and the negative electrode terminal 13 are attached to the sealing plate 15 with an insulating member therebetween.

[0040] The positive electrode 20 includes a positive electrode tab 23 electrically connected to the positive electrode terminal 12, and the negative electrode 30 includes a negative electrode tab 33 electrically connected to the negative electrode terminal 13, which will be described in detail later. The positive electrode terminal 12 is electrically connected to a positive electrode tab group 24 formed by laminating a plurality of positive electrode tabs 23 via a positive electrode current collector plate 25, and the negative electrode terminal 13 is electrically connected to a negative electrode tab group 34 formed by laminating a plurality of negative electrode tabs 33 via a negative electrode current collector plate 35.

[0041] A current cut-off device 18 is provided as a functional component on the sealing plate 15. The current cut-off device 18 is configured to cut off the current path when an abnormality occurs in the battery. The functional component is, for example, a component that functions as a safety device or a control device for the secondary battery 10. The functional component is disposed on the inner surface of the sealing plate 15 close to the positive electrode terminal 12 or the negative electrode terminal 13. In the present embodiment, the current cut-off device 18 is attached to the positive electrode terminal 12 and disposed inside the positive electrode terminal 12.

[0042] The current cut-off device 18 is a pressure-sensing type safety device that cuts off the current path when an abnormality occurs in the secondary battery 10 and the internal pressure of the outer can 14 rises above a predetermined pressure. The current cut-off device 18 is, for example, disposed between the positive electrode terminal 12 and the positive electrode current collector plate 25 and is electrically connected to the positive electrode terminal 12 and the positive electrode current collector plate 25 during normal use. The structure of the current cut-off device 18 is not particularly limited. As an example, a device including a reversing plate can be cited. When the internal pressure rises, the reversing plate reverses in a direction away from the positive electrode current collector plate 25 to cut off the electrical connection with the positive electrode current collector plate 25, thereby cutting off the current path between the positive electrode terminal 12 and the positive electrode current collector plate 25.

[0043] In addition, the sealing plate 15 is provided with: a liquid injection portion 16 for injecting a non-aqueous electrolyte; and a gas discharge valve 17 for opening the valve to discharge gas when an abnormality occurs in the battery. The gas discharge valve 17 is disposed at the central portion in the long side direction of the sealing plate 15, and the liquid injection portion 16 is disposed between the positive electrode terminal 12 and the gas discharge valve 17.

[0044] As Figure 2 As illustrated, the electrode body 11 is divided into a first electrode group 11A and a second electrode group 11B. The electrode groups 11A and 11B, for example, have the same lamination structure and dimensions as each other and are laminated and disposed in the thickness direction of the electrode body 11. At the upper end portions of the respective electrode groups, a positive electrode tab group 24 formed by a plurality of positive electrode tabs 23 and a negative electrode tab group 34 formed by a plurality of negative electrode tabs 33 are formed. The positive electrode tab group 24 and the negative electrode tab group 34 are respectively connected to the current collector plates of the sealing plate 15. The outer peripheral surfaces of the electrode groups 11A and 11B are covered with a separator 40, and are configured to have independent battery reactions in the electrode groups 11A and 11B.

[0045] Figure 3is an exploded perspective view of the electrode body 11. As Figure 3 illustrated, the electrode body 11 includes a plurality of positive electrodes 20 and a plurality of negative electrodes 30. In the electrode groups 11A and 11B that make up the electrode body 11, for example, the negative electrode 30 includes one more sheet than the positive electrode 20, and the negative electrodes 30 are arranged on both sides in the thickness direction of the electrode groups 11A and 11B. Figure 3 In, a plurality of separator sheets 40 each arranged between the positive electrode 20 and the negative electrode 30 are illustrated, but the separator sheets 40 included in the electrode groups 11A and 11B may each be one sheet. In this case, the longitudinally long separator sheet 40 is bent and arranged between the positive electrode 20 and the negative electrode 30. In the present embodiment, the electrode groups 11A and 11B each contain an adhesive and are manufactured using a hot pressing process, which will be described in detail later. More specifically, the electrode groups 11A and 11B are manufactured as follows: A laminate formed by alternately laminating a plurality of positive electrodes 20 and a plurality of negative electrodes 30 with separator sheets 40 interposed therebetween one by one in the stacking direction is pressed using a pair of hot plates, thereby applying heat and pressure to the laminate to bring at least a part of the adhesive into a state where it exhibits adhesive force.

[0046] The electrode body 11 includes the electrode groups 11A and 11B manufactured in this way, and is a laminated electrode body in which a plurality of positive electrodes 20 and a plurality of negative electrodes 30 are alternately laminated one by one with separator sheets 40 interposed therebetween. The positive electrode 20 includes a positive electrode tab 23 protruding upward, and the negative electrode 30 includes a negative electrode tab 33 protruding upward. In other words, the positive electrode 20 and the negative electrode 30 are laminated and arranged such that the tabs face the same direction. In addition, the positive electrode tab 23 is located on one lateral end side of the electrode body 11, the negative electrode tab 33 is located on the other lateral end side of the electrode body 11, and the plurality of positive electrode tabs 23 are arranged in the thickness direction of the electrode body 11 and the plurality of negative electrode tabs 33 are arranged in the thickness direction of the electrode body 11.

[0047] The positive electrode 20 has a positive electrode core and a positive electrode composite layer provided on the surface of the positive electrode core. The positive electrode core can be made of a foil of a metal such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 20, a thin film having such a metal disposed on the surface layer, or the like. The positive electrode composite layer preferably contains a positive electrode active material, a conductive material, and a binder material, and is provided on both sides of the positive electrode core. The positive electrode 20 can be manufactured, for example, by coating a positive electrode composite slurry containing a positive electrode active material, a conductive material, and a binder material or the like on the positive electrode core, drying the coating film, and then compressing it to form the positive electrode composite layer on both sides of the positive electrode core.

[0048] The positive electrode 20 has a structure in which a positive electrode composite material layer made of a positive electrode composite material is disposed over the entire region of a portion (hereinafter referred to as "base") of the surface of the positive electrode core other than the positive electrode tab 23. The thickness of the positive electrode core is, for example, 5 μm to 20 μm, preferably 8 μm to 15 μm. The base of the positive electrode core has a quadrilateral shape in a front view, and the positive electrode tab 23 protrudes from one side of the quadrilateral. Usually, a positive electrode core integrally formed with the base and the positive electrode tab 23 is obtained by processing a single metal foil.

[0049] A lithium transition metal composite oxide is used as the positive electrode active material. Examples of the metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, etc. Among them, at least one of Ni, Co, and Mn is preferably contained. As an example of a preferred composite oxide, a lithium transition metal composite oxide containing Ni, Co, and Mn; a lithium transition metal composite oxide containing Ni, Co, and Al can be cited.

[0050] Examples of the conductive material contained in the positive electrode composite material layer include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of the binder material contained in the positive electrode composite material layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, etc. In addition, these resins can be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, poly(ethylene oxide) (PEO), etc.

[0051] The negative electrode 30 has a negative electrode core and a negative electrode composite material layer provided on the surface of the negative electrode core and made of a negative electrode composite material. As the negative electrode core, a foil of a metal stable within the potential range of the negative electrode 30 such as copper, or a thin film of the metal disposed on the surface layer can be used. The negative electrode composite material layer preferably contains a negative electrode active material and a binder material, and is provided on both sides of the negative electrode core. The negative electrode 30 can be produced, for example, by coating a negative electrode composite material slurry containing a negative electrode active material and a binder material, etc. on the surface of the negative electrode core, drying the coating film, and then compressing to form the negative electrode composite material layer on both sides of the negative electrode core.

[0052] The negative electrode 30 has a structure in which a negative electrode composite material layer is formed over the entire region of a base which is a portion of the surface of the negative electrode core other than the negative electrode tab 33. The thickness of the negative electrode core is, for example, 3 μm to 15 μm, preferably 5 μm to 10 μm. Similar to the case of the positive electrode 20, the base of the negative electrode core has a quadrilateral shape in a front view, and the negative electrode tab 33 protrudes from one side of the quadrilateral. Usually, a negative electrode core integrally formed with the base and the negative electrode tab 33 is obtained by processing a single metal foil.

[0053] As the negative electrode active material, a carbon-based active material that reversibly occludes and releases lithium ions, for example, is included. Suitable carbon-based active materials are natural graphite such as flake graphite, massive graphite, and earthy graphite; artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). In addition, as the negative electrode active material, an Si-based active material composed of at least one of Si and Si-containing compounds may be used, or a carbon-based active material and an Si-based active material may be used in combination.

[0054] Similar to the case of the positive electrode 20, as the binder material included in the negative electrode composite material layer, a fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc. can also be used, but styrene-butadiene rubber (SBR) is preferably used. In addition, the negative electrode composite material layer preferably further includes CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. Among them, it is suitable to use SBR in combination with CMC or its salt, and PAA or its salt.

[0055] Figure 4 is a schematic representation Figure 2 of the cross-sectional view taken along line A-A. Hereinafter, with reference to Figure 2 and Figure 4 the structures of the positive electrode tab group 24 and the negative electrode tab group 34 of the electrode body 11 will be described in detail. As shown in Figure 2 and Figure 4 the electrode body 11 has a positive electrode tab group 24 formed by laminating a plurality of positive electrode tabs 23 and a negative electrode tab group 34 formed by laminating a plurality of negative electrode tabs 33. The plurality of positive electrode tabs 23 of the positive electrode tab group 24 overlap in the stacking direction of the electrodes, and one positive electrode tab group 24 is formed for each of the electrode groups 11A and 11B. Similarly, the plurality of negative electrode tabs 33 of the negative electrode tab group 34 overlap in the stacking direction of the electrodes, and one negative electrode tab group 34 is formed for each of the electrode groups 11A and 11B.

[0056] The positive electrode tab group 24 is joined to the positive electrode current collector plate 25 mounted on the inner surface (lower surface) of the sealing plate 15 by welding or the like. As described above, the positive electrode current collector plate 25 is a plate-shaped conductive member electrically connected to the positive electrode terminal 12 via the current cut-off device 18. An insulating member 26 is interposed between the sealing plate 15 and the positive electrode current collector plate 25 to prevent contact between the two members. Similarly, the negative electrode tab group 34 is joined to the negative electrode current collector plate 35 mounted on the inner surface of the sealing plate 15 with an insulating member interposed therebetween by welding or the like.

[0057] The positive electrode tab group 24 and the negative electrode tab group 34 only need to function as a conduction path connecting the electrode body 11 and each terminal, and their shapes are not particularly limited. In Figure 2 and Figure 4In the example shown, a plurality of positive electrode tabs 23 and a plurality of negative electrode tabs 33 of the electrode group 11A are stacked in a state of being bent from the outside to the inside of the secondary battery 10, respectively, to form a positive electrode tab group 24 and a negative electrode tab group 34 having a substantially U-shaped cross section in a cross-sectional view. Similarly, a tab group having a substantially U-shaped cross section in a cross-sectional view is also formed in the electrode group 11B. In addition, each tab group may have a U shape that is bent from the inside to the outside of the secondary battery 10. And, as Figure 4 shown, the tab groups of the two stacked electrode groups may be arranged such that the cross-sectional shape of the tab group of one electrode group is substantially symmetric with respect to the cross-sectional shape of the tab group of the other electrode group with respect to the boundary line of the electrode groups.

[0058] The positive electrode tab group 24 may be welded to the upper surface of the positive electrode current collector plate 25 facing the sealing plate 15 side, but is preferably welded to the lower surface of the positive electrode current collector plate 25. In the present embodiment, both the positive electrode tab group 24 and the negative electrode tab group 34 are welded to the lower surface of the current collector plate. However, for example, the positive electrode tab group 24 may be welded to the lower surface of the positive electrode current collector plate 25, and the negative electrode tab group 34 may be welded to the upper surface of the negative electrode current collector plate 35. In addition, in the present embodiment, the case where the electrode body 11 includes the divided first electrode group 11A and second electrode group 11B has been described, but the electrode body may also have one undivided electrode group.

[0059] For example, the sealing plate 15 is fitted into the opening of the outer can 14, and the fitting portion of the sealing plate 15 on which the electrode body 11 is mounted and the outer can 14 is laser welded. Then, a non-aqueous electrolyte is injected into the outer can 14 using the liquid injection portion 16, and then the liquid injection portion 16 is sealed with a blind rivet, thereby forming the secondary battery 10.

[0060] Next, the structure of the first electrode group 11A and the separator 40 will be further described in detail. In addition, since the second electrode group 11B has the same structure as that of the first electrode group 11A, the description of its structure is omitted. Figure 5A is an enlarged schematic cross-sectional view after a part of the outer side in the stacking direction of the first electrode group 11A (hereinafter simply referred to as the electrode group 11A) is cut by a plane substantially orthogonal to the height direction, and is an enlarged schematic cross-sectional view including a part of the separator 40, a part of the positive electrode 20, and the bonded portion 50a bonded in the adhesive 50 described below.

[0061] As Figure 5AAs shown, the separator 40 has a base material 40a and a heat-resistant layer 40b provided on one side in the thickness direction of the base material 40a. The base material 40a is composed of a porous sheet having ion permeability and insulation. The separator 40 can be composed of a porous substrate mainly composed of at least one selected from polyolefin, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyethersulfone, polyetherimide, and aromatic polyamide, preferably polyolefin, and particularly preferably composed of polyethylene and polypropylene. The heat-resistant layer 40b is provided for the purpose of protecting the separator 40 when heat is generated due to a short circuit between the positive electrode 20 and the negative electrode 30, etc. The heat-resistant layer 40b contains inorganic particles such as aluminum oxide, etc., and is composed of a ceramic heat-resistant layer, etc., for example.

[0062] The electrode group 11A further includes an adhesive 50. Specifically, after the heat-resistant layer 40b is provided on the entire surface of one side in the thickness direction of the base material 40a by an existing method such as vapor deposition, a plurality of dot-shaped adhesives (dot-shaped portions) are arranged in a manner such that the area density is substantially constant in the entire region of the side surface of the separator 40 where the heat-resistant layer 40b is provided and the entire region of the other side surface of the separator 40 where the heat-resistant layer 40b is not provided, by printing or the like. Here, among the plurality of dot-shaped adhesives, the amount of each dot-shaped adhesive is substantially the same. In addition, in the entire region of one side surface and the entire region of the other side surface of the separator 40, the number density of the dot-shaped adhesives is substantially constant. In addition, the coating form of the adhesive 50 may not be a dot-shaped form, but a form coated on the entire surface of the separator. That is, it may also be a structure in which the adhesive is arranged in a manner such that the area density is substantially constant on at least one of the entire surface of one side surface and the entire surface of the other side surface of the separator, and an adhesive layer is provided on at least one side surface of the separator. As the adhesive 50, an acrylic resin-based adhesive, a polyurethane resin-based adhesive, an ethylene-vinyl acetate resin-based adhesive, or an epoxy resin-based adhesive can be used.

[0063] In this embodiment, the positive electrode 20 and the negative electrode 30 are alternately laminated with the separator 40 interposed therebetween such that the side surface of the separator 40 on which the adhesive is arranged faces the positive electrode 20, and then pressure and heat are applied to the laminate from both sides in the lamination direction by hot plates arranged on one side and the other side in the lamination direction, so that a part of the adhesive melts. In this way, the separator 40 and the positive electrode 20 are bonded with the adhesive, and the separator 40 and the negative electrode 30 are bonded with the adhesive, thereby preventing the situation where the power generation performance is reduced due to the displacement of the separator 40 relative to the positive electrode 20 and the negative electrode 30.

[0064] As the temperature of the hot plate, any temperature can be used as long as it is above the temperature at which the adhesive used melts. In addition, as the pressure applied to the stack by the two hot plates, it is preferred to use a pressure lower than the pressure used in the past. In detail, in the secondary battery 10 of the present invention, as a set of temperature and pressure applied to the stack, a set of temperature and pressure is intentionally used in which a portion of the adhesive applied on the diaphragm (or diaphragm portion (in the case of a bent diaphragm)) located in the central part of the stacking direction in the stack is not melted and the bonding area does not increase.

[0065] Figure 6A This is an enlarged schematic cross-sectional view of a portion of the inner side of the electrode group 11A in the stacking direction when the stack is pressed using such a combination of temperature and pressure, and includes a portion of the separator 40, a portion of the positive electrode 20, and a bonded portion 50b of the adhesive 50. Figure 5A , Figure 6A , the following description Figure 5B and the following description Figure 6B In the figure, for easy understanding, the portion of the adhesive 50 that does not contribute to the bonding is omitted from illustration.

[0066] like Figure 5A and Figure 6A As shown, the result of pressing the stack using such a combination of temperature and pressure is that, in the case of the secondary battery 10 of the present invention, the volume (area) of the bonding portion 50b contributing to the bonding in the adhesive 50 on the inner diaphragm in the stacking direction (or the diaphragm portion on the inner side in the stacking direction) is smaller than the volume (area) of the bonding portion 50a contributing to the bonding in the adhesive 50 on the outer diaphragm in the stacking direction (or the diaphragm portion on the outer side in the stacking direction).

[0067] In the past, if the physical condition is that part of the adhesive applied to the separator does not melt, part of the adhesive applied with great difficulty will not show its effectiveness, resulting in an increase in material costs, so there is no situation where the pressing process is performed under such physical conditions. However, the inventors have found that if a structure that was previously avoided is intentionally adopted, a significant effect that far exceeds the problem of increased material costs can be obtained. Below, a method for confirming that a secondary battery is in such a state and a significant effect are described using a non-aqueous electrolyte secondary battery as an embodiment of a secondary battery.

[0068] [One Example of Secondary Battery]

[0069] The present inventor fabricated a secondary battery of one embodiment. For the secondary battery of one embodiment, a positive electrode, a negative electrode, and a separator were fabricated as follows, and a non-aqueous electrolyte was prepared. In addition, using the fabricated positive electrode, negative electrode, and separator, an electrode body was fabricated as follows, and the battery was assembled.

[0070] <Fabrication of Positive Electrode>

[0071] A positive electrode composite layer was formed on both sides of an aluminum foil with a thickness of 13 μm. After compression treatment, the thickness of the positive electrode composite layer on one side was 62 μm. The length of the positive electrode plate in the short side direction was 76.5 mm. The width (length in the short side direction) of the current collector ear where the positive electrode core was exposed was 19.6 mm. The length of the positive electrode plate in the long side direction was 138.9 mm. The positive electrode composite layer contained lithium nickel cobalt manganese composite oxide as the positive electrode active material, acetylene black as the conductive material, and polyvinylidene fluoride (PVDF) as the binder material in a mass ratio of 97:2:1.

[0072] <Fabrication of Negative Electrode>

[0073] A negative electrode composite layer was formed on both sides of a copper foil with a thickness of 8 μm. After compression treatment, the thickness of the negative electrode composite layer on one side was 76 μm. In addition, the length of the negative electrode plate in the short side direction was 78.2 mm. The width (length in the short side direction) of the current collector ear where the negative electrode core was exposed was 18.2 mm. In addition, the length of the negative electrode plate in the long side direction was 142.8 mm. In addition, the negative electrode composite layer contained graphite as the negative electrode active material, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) as the binder material in a mass ratio of 98:1:1.

[0074] <Separator>

[0075] For the separator, a separator was used in which a ceramic heat-resistant layer was coated on one side of a polyethylene single-layer substrate and an adhesive layer made of an acrylic resin was dot-coated on both sides. The thickness of the substrate layer of the separator was 12 μm, the thickness of the heat-resistant layer was 4 μm, and the width was 80.7 mm. Here, the amount of one dot-shaped adhesive was made substantially the same. All the dot-shaped adhesives were made substantially the same. In addition, in the entire area of one side surface and the entire area of the other side surface of the separator, the number density of the dot-shaped adhesives was made substantially constant.

[0076] <Preparation of Non-aqueous Electrolyte>

[0077] Prepare a mixed solvent by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio (at 25°C and 1 atmosphere) of 30:30:40. Add LiPF6 to this mixed solvent to make it 1.15 mol / L, thereby preparing a non-aqueous electrolyte.

[0078] <Fabrication of the electrode body>

[0079] Set the number of stacked positive electrode plates to 35 layers and the number of stacked negative electrode plates to 36 layers. Stack the positive electrode and the negative electrode with a bent separator interposed therebetween to insulate them and with the collector ears of the positive electrode and the collector ears of the negative electrode not overlapping each other to fabricate a stacked body. Then, apply a pressure of 2 MPa to the stacked body from both sides in the stacking direction of the stacked body using a hot plate set at 100°C to fabricate one electrode group. Another electrode group was fabricated using the same method.

[0080] <Assembly of the battery>

[0081] The exposed portions of multiple stacked positive electrode cores are electrically connected to the positive electrode terminal via the positive electrode current collector. In addition, the exposed portions of multiple stacked negative electrode cores are electrically connected to the negative electrode terminal via the negative electrode current collector. The positive electrode terminal and the negative electrode terminal are respectively fixed to the sealing body with an insulating member interposed therebetween. The sealing body is provided with a gas discharge valve that opens when a predetermined pressure is applied. The positive electrode current collector, the positive electrode terminal, and the sealing body are respectively made of aluminum or aluminum alloy components. The negative electrode current collector and the negative electrode terminal are respectively made of copper or copper alloy components. After joining the electrode body in a state where two electrode groups are overlapped to the sealing body, the electrode body is inserted into an outer can with an open side in a state where an insulating sheet formed of a resin material exists around it. The outer can is, for example, an outer can made of aluminum or aluminum alloy. The sealing body is fitted into the opening of the outer can, and the fitting portion of the sealing body and the outer can is laser welded. The sealing body is a sealing body made of aluminum or aluminum alloy. The above non-aqueous electrolyte is injected into the outer can from the electrolyte injection port, and then the electrolyte injection port is sealed with a blind rivet, thereby fabricating a rectangular non-aqueous electrolyte secondary battery with an external dimension of width 148 mm × height 91 mm × thickness 26.5 mm.

[0082] <Test content>

[0083] Regarding the electrode group used in the secondary battery of the above one embodiment, the following tests were conducted. Specifically, each positive electrode was peeled off from the separator after the pressing process using the hot plate, and the adhesive transfer rate in the stacking direction was measured. The adhesive force between the heat-resistant layer and the base material of the separator is a relatively weak force of about 5 N / m to 7 N / m. Therefore, when the positive electrode is peeled off from the separator, the adhered adhesive portion in the adhesive does not peel off from the positive electrode and the heat-resistant layer, but the heat-resistant layer peels off from the base material. That is, in Figure 5B andFigure 6B In the electrode group shown, when the positive electrode 20 is peeled off from the separator 40, as Figure 5B and Figure 6B shown, the bonding portions 50a, 50b are not peeled off from the positive electrode 20 and the heat-resistant layer 40b. Instead, the portions of the heat-resistant layer 40b bonded to the bonding portions 50a, 50b are separated from the separator 40 and separated from the separator 40 together with the bonding portions 50a, 50b.

[0084] That is, the bonding portions 50a, 50b of the adhesive 50 are transferred to the positive electrode. Therefore, by measuring the area of the bonding portions 50a, 50b transferred to the peeled positive electrode 20, the area of the bonding portions 50a, 50b on each positive electrode 20 can be determined. Use Figure 7A and Figure 7B to illustrate this. Figure 7A , Figure 7B is a schematic plan view showing the bonding portions transferred to the peeled positive electrode 20 in a secondary battery of one embodiment, Figure 7A is a schematic plan view showing the bonding portions transferred to the positive electrode 20 on the outer side in the stacking direction, Figure 7B is a schematic plan view showing the bonding portions transferred to the positive electrode 20 on the inner side in the stacking direction. In the electrode group of the secondary battery of the present invention, in the pressing process using a hot plate, the pressing pressure is reduced, so the adhesive on the inner side in the stacking direction is not easily melted, and the proportion of the non-bonding portion where the bonding force is not exhibited in the bonding material is large. That is, as Figure 7A , Figure 7B shown, the areas of the bonding portions 50a, 50b transferred to the positive electrode 20 vary on the inner and outer sides in the stacking direction. Thus, by only measuring the area of the bonding portions transferred to the peeled positive electrode 20, it is possible to determine whether the secondary battery of the present invention has been manufactured.

[0085] <Test Results>

[0086] Figures 8 - 10 is a graph showing the test results. Specifically, Figure 8 is a graph showing the relationship between the number of layers in the stacked group (indicating the number of the positive electrode starting from one side in the stacking direction) and the ratio of the transfer area to the area of one side of the positive electrode, and is a graph showing the adhesive transfer area ratio. In addition, Figure 9 is shown by Figure 8A chart of the spline curves for all measurement points. Here, a spline curve is a smooth curve passing through a given finite set of points and is a curve widely used in shape design such as CAD. In addition, the function representing the spline curve is called a spline function. Further, hereinafter, sometimes a spline curve is used to define the technical scope of the technology of the present invention, but as long as there is at least one spline curve satisfying the definition, it is regarded as satisfying the definition. That is, there are multiple types of spline functions for defining spline curves, such as B-spline (basis spline), C-spline (cardinal spline), and N-spline (natural spline). Against this background, in this specification, for the judgment of whether the regulations related to spline curves described below are satisfied, as long as there is at least one spline curve satisfying the regulations related to the spline curve and being differentiable and smooth from one end to the other end, it is regarded as satisfying the regulations. Here, for the judgment of whether it is differentiable at one end and the other end, if one of right differentiation and left differentiation can be performed at each of the said ends, it is regarded as differentiable. In addition, Figure 10 is a chart showing the relationship between the number of layers (a number indicating which part between the electrodes from one side in the stacking direction) and the thickness of the separator. The dots represent the thickness of the separator before pressing with a hot plate, and the solid line represents the thickness of the separator after pressing with a hot plate.

[0087] In addition, Figures 8 - 10 As a result of a test example, an electrode group capable of easily obtaining a result similar to this result can be fabricated. Specifically, for such an electrode group, as long as the temperature and pressure are given during pressing with a hot plate such that a part of the adhesive coated on the separator (or separator part in the case of a bent separator) located at the central part in the stacking direction of the laminate does not melt and the bonding area does not increase, it can be easily fabricated, and it can be easily fabricated with countless combinations of the temperature and pressure given during pressing with a hot plate. Further elaborating, such an electrode group can be easily fabricated by pressing at a temperature near the lower limit temperature at which the used adhesive melts, and in addition, can be easily fabricated by performing the pressing process at a pressure of 90% or less of the pressure given when all the adhesive melts.

[0088] In one embodiment, as Figure 8 shown, the area of the bonded part of the adhesive coated on each of the two outermost separators in the stacking part is larger than the area of the bonded part of the adhesive coated on the separator located at the center in the stacking part.

[0089] In addition, as Figure 9As shown, in the case where the spline curve trisects the electrode group into a first region A1 with a smaller number of stacked layers (the part close to the start of stacking), a second region A2 with a larger number of stacked layers (the part close to the end of stacking), and a third region A3 with a number of stacked layers between the first region A1 and the second region A2, the third region A3 has a portion P, and this portion P has a minimum value of the area of the bonding part.

[0090] In addition, as Figure 9 shown, there are a fourth region A4 and a fifth region A5 that satisfy the following condition: the maximum change rate of the spline curve in the fourth region A4 is less than 1 / 3 of the minimum change rate of the fifth region A5 in the inner region of the number of stacked layers compared to the fourth region A4.

[0091] In addition, in one embodiment, as Figure 10 shown, the outermost two separator films respectively have a thickness of 80% or more of the thickness of the separator film with the middle number of stacked layers in the stacked group. In addition, compared with the thickness of the separator film before the pressing process, the maximum amount of flattening in the thickness direction of the separator film after the pressing process is about 1.0 μm (the amount of flattening in the thickness direction after the pressing process is 7% or less of the thickness of the separator film before the pressing process). In addition, in other test examples conducted by the inventors, the outermost two separator films can respectively have a thickness of 90% or more of the thickness of the separator film with the middle number of stacked layers in the stacked group. And the maximum amount of flattening in the thickness direction of the separator film after the pressing process can also be 5% or less of the thickness of the separator film before the pressing process. In addition, the amount of flattening of the separator film can be obtained from the difference between the thickness of the separator film in the stacked portion before being subjected to pressure in the pressing process and the thickness of the separator film after being subjected to pressure. Specifically, the separator film can be taken out from each electrode group before and after the pressing process, and the amount of flattening of the separator film can be obtained from the difference in thickness of the separator film. In addition, even for the stacked group after the pressing process, the thickness of the separator film outside the stacked portion can be regarded as the thickness before the pressing process, and the amount of flattening of the separator film can be obtained from the difference in thickness from the separator film in the stacked portion.

[0092] <Preferred Structures and Effects Derived from Each Structure>

[0093] As described above, according to the present invention, different from the secondary battery using separators with different coating amounts and areas of the adhesive in Patent Document 1, the adhesive is coated on one side surface in the thickness direction of the separator in such a way that the area density is substantially constant. Therefore, a secondary battery can be manufactured using only one type of separator instead of using multiple types of separators, and mass production of secondary batteries is possible.

[0094] In addition, in the hot pressing process for manufacturing the electrode groups 11A and 11B, which are an example of the stacked portion, conditions that were previously avoided due to increased material costs are intentionally used, namely, conditions of temperature and pressure under which a part of the adhesive coated on the separator (or separator portion in the case of a bent separator) on the inner side in the stacking direction does not melt and the bonding area does not increase. Therefore, compared with the outer side in the stacking direction, the gap between the electrodes in the region on the inner side in the stacking direction where the electrolyte (e.g., electrolyte solution) is difficult to penetrate can be enlarged, and the electrolyte permeability on the inner side in the stacking direction of the electrode groups 11A and 11B can be improved, and the retention amount of the electrolyte can be made closer to a uniform value regardless of the position in the stacking direction. Therefore, not only can the power generation performance of the secondary battery be improved, but also the reaction rate difference caused by the position in the stacking direction can be suppressed. As a result, the durability of the secondary battery can be improved.

[0095] Moreover, when manufacturing a secondary battery using such conditions of temperature and pressure under which a part of the adhesive coated on the separator on the inner side in the stacking direction does not melt and the bonding area does not increase, as a result, the degree of flattening (flattening in the thickness direction) of the outer separator, which was prone to being flattened due to the hot pressing structure in the past, can be suppressed. Therefore, the thickness difference between the outer separator and the inner separator in the stacking direction can also be suppressed, and the increase in air permeability caused by the flattening of the outer separator can also be suppressed. From this point of view, the reaction rate difference caused by the position in the stacking direction can be suppressed. Therefore, from this point of view, the durability of the secondary battery can also be improved.

[0096] In addition, the adhesive 50 may also be composed of a plurality of dot-like portions. Moreover, the number density of the dot-like portions coated on the separator 40 may also be substantially constant.

[0097] According to this structure, the adhesive 50 can be easily arranged on the separator 40 with a substantially constant area density.

[0098] In addition, it may be that when the vertical axis is the area of the bonded portion of the adhesive 50 and the horizontal axis is the number of layers, and the area of the bonded portion of the adhesive and the number of layers are plotted in a two-dimensional coordinate formed by separating adjacent numbers of layers on the horizontal axis at the same interval, the spline curve obtained by smoothly connecting the plotted multiple points has a minimum value of the area of the bonded portion in the third region A3 when the electrode group (stacked portion) is divided into three equal parts: the first region A1 with a smaller number of layers (close to the start of stacking), the second region A2 with a larger number of layers (close to the end of stacking), and the third region A3 with the number of layers between the first region A1 and the second region A2.

[0099] According to this structure, it is possible to increase the gap in a wide range of regions in the inner region, and regardless of the position in the stacking direction, the amount of electrolyte held can be made closer to a more uniform value.

[0100] In addition, there may be a fourth region A4 and a fifth region A5 that satisfy the following condition: the maximum change rate of the fourth region A4 of the spline curve is less than 1 / 3 of the minimum change rate of the fifth region A5 in the inner region located closer to the stacking number than the fourth region A4.

[0101] In the inner region in the stacking direction, the electrolyte permeability of the electrolyte has a tendency to deteriorate rapidly as it goes inward.

[0102] According to this structure, in the inner region in the stacking direction, it is possible to rapidly increase the inter-electrode gap as it goes toward the inner region in the stacking direction. Therefore, it is possible to form an inter-electrode gap that cancels out the rapidly deteriorating electrolyte permeability as it goes inward. Thus, regardless of the position in the stacking direction, the amount of electrolyte held can be made to accurately approach a uniform value.

[0103] In addition, it may be that when the number of stacked separators (separator portions) in the stacked portion (which can be composed of an electrode group, an electrode body, etc.) is odd, the thicknesses of the outermost two separators (separator portions) are each 90% or more of the thickness of the separator (separator portion) in the stacked portion that is in the middle of the stacking number. When the number of stacked separators in the stacked portion is even, the thicknesses of the outermost two separators (separator portions) are each 90% or more of the corresponding thickness of the separator (separator portion) with the larger thickness among the two separators (separator portions) in the middle of the stacking number in the stacked portion.

[0104] According to this structure, since the thickness difference between the separator on the outer side and the separator on the inner side in the stacking direction is small, it is possible to suppress the increase in air permeability caused by the flattening of the outer separator, and the durability of the secondary battery can be improved.

[0105] In addition, the amount of flattening in the thickness direction of the separator obtained based on the difference between the thickness of the separator in the stacked portion and the thickness of the separator outside the stacked portion may be 5% or less of the thickness of the separator outside the stacked portion.

[0106] In this structure, the thickness difference between the separator on the outer side and the separator on the inner side in the stacking direction is also small. Therefore, it is possible to suppress the increase in air permeability caused by the flattening of the outer separator, and the durability of the secondary battery can be improved.

[0107] In addition, it may be that the separator 40 has a heat-resistant layer 40b at least on one side in the thickness direction, and one side surface of the separator 40 is composed of the heat-resistant layer 40b.

[0108] According to this structure, the area of the bonding portion transferred to the separator 40 can be easily measured by the above method. In addition, when determining the bonding area of the adhesive on the separator without the heat-resistant layer included in the electrode body and the electrode group, electrode bodies and electrode groups are produced which are different only in that a heat-resistant layer is added and are pressed under the same temperature and the same pressure. And, in the produced electrode bodies and electrode groups, the method described in this specification is used to determine the bonding area.

[0109] In addition, in the above electrode groups 11A and 11B, the heat-resistant layer 40b is provided only on one side surface of the separator 40, but the heat-resistant layer may also be provided on the other side surface in addition to one side surface of the separator. Or, the separator may not have a heat-resistant layer.

[0110] Further, in the above electrode groups 11A and 11B, the adhesive is coated on both the one side surface and the other side surface of the separator 40, but the adhesive may also be coated only on one side surface of the separator.

[0111] Further, a plurality of dot-like regions made of an adhesive are provided on one side surface of the separator 40, but the adhesive may also be coated on the entire surface of at least one side surface of the separator in such a manner that the areal density is substantially constant.

[0112] Further, it may be that the above spline curve does not have a minimum value of the area of the bonding portion in the above third region. Or, it may be that the above spline curve has a portion in the central region in the middle when divided into five equal parts in the stacking direction, and this portion has a minimum value of the area of the bonding portion. Further, it may be that there is no fourth region and fifth region such that the maximum change rate of the fourth region is less than 1 / 3 of the minimum change rate of the fifth region located in the region inside the stacking number compared to the fourth region.

[0113] Further, the thickness of the separator on the outer side in the stacking direction may be less than 90% of the thickness of the separator in the center in the stacking direction, and the amount of flattening in the thickness direction of the separator obtained from the difference between the thickness of the separator in the stacking portion and the thickness of the separator outside the stacking portion may be 5% or less of the thickness of the separator outside the stacking portion.

[0114] Above, the case where the secondary battery includes a stacked electrode body has been described. Next, the case where the secondary battery includes a wound electrode body will be described. Figure 11 is a plan view of a square secondary battery 110 of the wound type, Figure 12 is a front view of the square secondary battery 110. Further, Figure 13 (a) of Figure 11 is a partial cross-sectional view taken along line A - A of Figure 13 (b) of Figure 13 is a partial cross-sectional view taken along line B - B of (a) of Figure 13 (c) ofFigure 13 Cross-sectional view of the C-C line of (a). In addition, Figure 14A is a top view of the positive electrode included in the square secondary battery 110, Figure 14B is a top view of the negative electrode included in the square secondary battery 110. In addition, Figure 15 is a perspective view of the winding end side of the flat wound electrode body included in the square secondary battery 110 unfolded. In addition, as the materials of the respective components of the wound type square secondary battery 110, the same materials as those of the corresponding components of the above-described laminated type square secondary battery 10 can be used. Therefore, in the following description, the materials of the respective components are simply described or the description is omitted.

[0115] As Figures 11 - 13 and Figure 15 shown, the square secondary battery 110 includes an outer can (square outer can) 125 (refer to Figures 11 - 13 ), a sealing plate 123 (refer to Figure 11 , Figure 13 (a) of, Figure 13 (c) of) and a flat wound electrode body 114 (refer to Figure 13 , Figure 15 ). The outer can 125 is made of, for example, aluminum or an aluminum alloy, and has an opening on one side in the height direction. As Figure 12 shown, the outer can 125 has a bottom 140, a pair of first side surfaces 141 and a pair of second side surfaces 142, and the second side surface 142 is larger than the first side surface 141. As Figure 13 (a) of shown, the sealing plate 123 is fitted into the opening of the outer can 125. By joining the fitting portion of the sealing plate 123 and the outer can 125, a square battery case 145 is formed. In addition, as the materials of the respective components in the wound type square secondary battery, the same materials as those of the corresponding components in the laminated type square secondary battery can be adopted. Therefore, in the following description of the wound type square secondary battery, the materials of the respective components are simply described or the description is omitted.

[0116] As Figure 15 shown, the wound electrode body 114 has a structure in which a positive electrode 111 and a negative electrode 112 are wound in a state of being insulated from each other with a separator 113 interposed therebetween. The outermost surface side of the wound electrode body 114 is covered with the separator 113, and the negative electrode 112 is disposed at a position closer to the outer peripheral side than the positive electrode 111. As Figure 14AAs shown, the positive electrode 111 is manufactured as follows: A positive electrode composite material slurry is coated on both sides of a strip-shaped positive electrode core 115 made of aluminum or aluminum alloy foil with a thickness of about 10 μm to 20 μm. After drying and rolling, it is cut into strips of a predetermined size. The positive electrode composite material slurry contains a positive electrode active material, a conductive agent, a binder, and the like. At this time, at one end in the width direction, a positive electrode core exposed portion 115a is formed along the long side direction. The positive electrode composite material layer 111a is not formed on both sides of the positive electrode core exposed portion 115a. Preferably, on at least one side surface of the positive electrode core exposed portion 115a, for example, a positive electrode protective layer 111b is formed along the length direction of the positive electrode core exposed portion 115a adjacent to the positive electrode composite material layer 111a. The positive electrode protective layer 111b contains insulating inorganic particles and a binder. The conductivity of the positive electrode protective layer 111b is lower than that of the positive electrode composite material layer 111a. By providing the positive electrode protective layer 111b, it is possible to prevent the negative electrode composite material layer 112a from short-circuiting with the positive electrode core 115 due to foreign matters or the like. In addition, the positive electrode protective layer 111b can contain conductive inorganic particles. Furthermore, the positive electrode protective layer 111b may not be provided.

[0117] On the other hand, as Figure 14B shown, the negative electrode 112 is manufactured as follows: A negative electrode composite material slurry is coated on both sides of a strip-shaped negative electrode core 116 made of copper or copper alloy foil with a thickness of about 5 μm to 15 μm. After drying and rolling, it is cut into strips of a predetermined size. The negative electrode composite material slurry contains a negative electrode active material, a binder, and the like. At this time, a negative electrode core exposed portion 116a is formed along the long side direction. The negative electrode composite material layer 112a is not formed on both sides of the negative electrode core exposed portion 116a. In addition, the positive electrode core exposed portion 115a or the negative electrode core exposed portion 116a may also be formed respectively at both ends in the width direction of the positive electrode 111 or both ends in the width direction of the negative electrode 112.

[0118] As Figure 15As shown, the positive electrode 111 and the negative electrode 112 are arranged offset in the width direction of the wound electrode body 114 (the width direction of the positive electrode 111 and the negative electrode 112) in such a manner that the exposed portion 115a of the positive electrode core body and the negative composite material layer 112a do not overlap, and the exposed portion 116a of the negative electrode core body and the positive composite material layer 111a do not overlap. Then, the positive electrode 111 and the negative electrode 112 are wound in a state of being insulated from each other with a separator 113 coated with an adhesive having a substantially constant areal density on at least one side surface in the thickness direction, thereby forming a wound body. Then, the formed wound body is sandwiched between a pair of hot plates and pressed under temperature and pressure conditions such that a part of the adhesive on the inner peripheral side does not melt and the bonding area does not increase, and formed into a flat shape, thereby manufacturing a flat wound electrode body 114. The wound electrode body 114 has a plurality of stacked exposed portions 115a of the positive electrode core body at one end in the direction in which the winding axis extends (coinciding with the width direction when the strip-shaped positive electrode 111, the strip-shaped negative electrode 112, and the strip-shaped separator 113 are unfolded in a rectangular shape), and a plurality of stacked exposed portions 116a of the negative electrode core body at the other end in the direction in which the winding axis extends. As the separator 113, it is preferable to use a porous sheet made of polyolefin. The width of the separator 113 is preferably a width that can cover the positive composite material layer 111a and the positive electrode protective layer 111b and is larger than the width of the negative composite material layer 112a.

[0119] The plurality of stacked exposed portions 115a of the positive electrode core body are electrically connected to the positive electrode terminal 118 via the positive electrode current collector 117 (refer to Figure 13 (a)), and the plurality of stacked exposed portions 116a of the negative electrode core body are electrically connected to the negative electrode terminal 120 via the negative electrode current collector 119 (refer to Figure 13 (a)), which will be described in detail later. In addition, although not described in detail, as shown in Figure 13 (a), a current cut-off mechanism 127 that operates when the air pressure inside the battery case 145 becomes a predetermined value or more is preferably provided between the positive electrode current collector 117 and the positive electrode terminal 118.

[0120] As shown in Figure 11 , Figure 12 and Figure 13 (a), the positive electrode terminal 118 and the negative electrode terminal 120 are respectively fixed to the sealing plate 123 with insulating members 121, 122 interposed therebetween. The sealing plate 123 has a gas discharge valve 128 that opens when the air pressure inside the battery case 145 is higher than the operating pressure of the current cut-off mechanism 127. The positive electrode current collector 117, the positive electrode terminal 118, and the sealing plate 123 are each formed of aluminum or an aluminum alloy, and the negative electrode current collector 119 and the negative electrode terminal 120 are each formed of copper or a copper alloy. As shown in Figure 13As shown in (c), the flat wound electrode body 114 is inserted into the open-sided outer can 125 in a state where an insulating sheet (resin sheet) 124 is present around it except on the side of the sealing plate 123.

[0121] As Figure 13 shown in (b) and Figure 13 (c), on the positive electrode 111 side, a plurality of wound and laminated positive electrode core body exposed portions 115a are bundled toward the central portion in the thickness direction and further divided into two. The positive electrode core body exposed portions 115a are bundled, and a positive electrode intermediate member 130 is disposed between the positive electrode core body exposed portions 115a. The positive electrode intermediate member 130 is made of a resin material, and one or more, for example, two conductive positive electrode conductive members 129 are held in the positive electrode intermediate member 130. For the positive electrode conductive member 129, for example, a cylindrical positive electrode conductive member is used, and frustum-shaped protrusions that function as protrusions (Japanese: プロジェクション) are formed at both end portions of the positive electrode conductive member 129 that face the laminated positive electrode core body exposed portions 115a.

[0122] On the negative electrode 112 side, similarly, a plurality of wound and laminated negative electrode core body exposed portions 116a are bundled toward the central side in the thickness direction and further divided into two. The negative electrode core body exposed portions 116a are bundled, and a negative electrode intermediate member 132 is disposed between the negative electrode core body exposed portions 116a. The negative electrode intermediate member 132 is made of a resin material, and one or more, for example, two negative electrode conductive members 131 are held in the negative electrode intermediate member 132. For the negative electrode conductive member 131, for example, a cylindrical negative electrode conductive member is used, and frustum-shaped protrusions that function as protrusions are formed at both end portions of the negative electrode conductive member 131 that face the laminated negative electrode core body exposed portions 116a.

[0123] The positive electrode conductive member 129 and the bundled positive electrode core body exposed portions 115a disposed on both sides in its extending direction are joined, and the bundled positive electrode core body exposed portions 115a and the positive electrode current collector 117 disposed outside the depth direction of the battery case 145 are also joined and electrically connected. Similarly, the negative electrode conductive member 131 and the bundled negative electrode core body exposed portions 116a disposed on both sides of it are joined, and the bundled negative electrode core body exposed portions 116a and the negative electrode current collector 119 disposed outside the depth direction of the battery case 145 are also joined and electrically connected. One end portion of the positive electrode current collector 117 on the side opposite to the positive electrode core body exposed portion 115a side is electrically connected to the positive terminal 118, and one end portion of the negative electrode current collector 119 on the side opposite to the negative electrode core body exposed portion 116a side is electrically connected to the negative terminal 120. As a result, the positive electrode core body exposed portion 115a is electrically connected to the positive terminal 118, and the negative electrode core body exposed portion 116a is electrically connected to the negative terminal 120.

[0124] The wound electrode body 114, the intermediate member 130 for the positive electrode and the intermediate member 132 for the negative electrode, and the conductive member 129 for the positive electrode and the conductive member 131 for the negative electrode are joined together to form an integral structure. The conductive member 129 for the positive electrode is preferably a member made of aluminum or an aluminum alloy, which is the same material as the positive electrode core 115, and the conductive member 131 for the negative electrode is preferably a member made of copper or a copper alloy, which is the same material as the negative electrode core 116. The shapes of the conductive member 129 for the positive electrode and the conductive member 131 for the negative electrode may be the same or different.

[0125] For the connection between the positive electrode core exposed portion 115a and the positive electrode current collector 117, and the connection between the negative electrode core exposed portion 116a and the negative electrode current collector 119, resistance welding, laser welding, ultrasonic welding, etc. can be used. In addition, the intermediate member 130 for the positive electrode and the intermediate member 132 for the negative electrode may not be used.

[0126] As Figure 11 shown, an electrolyte injection hole 126 is provided in the sealing plate 123. The wound electrode body 114 equipped with the positive electrode current collector 117, the negative electrode current collector 119, the sealing plate 123, etc. is disposed in the outer can 125. At this time, preferably, in a state where the wound electrode body 114 is disposed in the insulating sheet 124 formed in a box shape or a bag shape, the wound electrode body 114 is inserted into the outer can 125. After that, the fitting portion between the sealing plate 123 and the outer can 125 is laser welded, and then a non-aqueous electrolyte is injected from the electrolyte injection hole 126. After that, a prismatic secondary battery 110 is manufactured by sealing the electrolyte injection hole 126. The sealing of the electrolyte injection hole 126 is performed, for example, by a blind rivet, welding, etc.

[0127] In addition, the case where the winding axis of the wound electrode body 114 is arranged parallel to the bottom 140 of the outer can 125 has been described, but the structure may also be such that the winding axis of the wound electrode body is arranged perpendicular to the bottom 140 of the outer can 125.

[0128] As mentioned above, an example of the prismatic wound secondary battery 110 has been illustrated, but it is not limited to the above-mentioned prismatic wound secondary battery 110. In any prismatic wound secondary battery, there is a problem that it is difficult for the electrolyte (electrolyte solution) to penetrate to the central hollow side.

[0129] That is, as in Figure 16A , Figure 16BAs shown in comparison, the lamination direction A of the laminated electrode body (which is the same as the pressing direction using a hot plate) corresponds to the pressing direction B of the wound electrode body using a hot plate. Further, in the wound electrode body, if the area of the bonded portion of the adhesive on the separator on the cavity side (inner peripheral side) is made smaller than the area of the bonded portion of the adhesive on the separator on the outer peripheral side, the above-described remarkable effects described for the laminated electrode group can also be obtained.

[0130] Here, such a wound electrode body can be easily manufactured in the following manner as described in detail for the laminated electrode group: on at least one of the one side surface and the other side surface in the thickness direction of the separator, an adhesive is applied so that the areal density becomes uniform (for example, as described above, a plurality of identical dot regions composed of an adhesive are printed on the separator so that the areal density becomes uniform), and a pressing process using a hot plate is performed under temperature and pressure conditions in which a part of the adhesive on the inner peripheral side does not melt and does not exhibit an adhesive effect.

[0131] Description of Reference Numerals

[0132] 10, secondary battery; 11, electrode body; 11A, 11B, electrode group; 20, 111, positive electrode; 21, 115, positive electrode core; 30, 112, negative electrode; 31, 116, negative electrode core; 40, 113, separator; 40a, base material; 40b, heat-resistant layer; 50, adhesive; 50a, 50b, bonded portions of the adhesive; 110, square secondary battery; 111a, positive electrode composite layer; 112a, negative electrode composite layer; 114, wound electrode body; A1, first region; A2, second region; A3, third region; A4, fourth region; A5, fifth region.

Claims

1. A secondary battery, wherein, the secondary battery includes: a plurality of positive electrodes, each positive electrode having a positive electrode core and a positive electrode active material disposed on the positive electrode core; a plurality of negative electrodes, each negative electrode having a negative electrode core and a negative electrode active material disposed on the negative electrode core; one or more separator membranes; and an adhesive, which is coated on at least one side surface in the thickness direction of the separator membrane so that the areal density becomes substantially constant, the secondary battery includes a stacked portion in which the positive electrodes and the negative electrodes are alternately stacked with the separator membrane therebetween, the area of the adhered portion of the adhesive on the outer side in the stacking direction of the stacked portion is larger than the area of the adhered portion of the adhesive on the inner side in the stacking direction of the stacked portion, the adhesive is composed of a plurality of dot-like portions, the number density of the dot-like portions coated on the separator membrane is substantially constant.

2. The secondary battery according to claim 1, wherein, when the vertical axis is set to the area of the adhered adhesive portion in the adhesive and the horizontal axis is set to the number of layers, and the area of the adhered adhesive portion in the adhesive and the number of layers are plotted in a two-dimensional coordinate formed by separating adjacent layers on the horizontal axis at the same interval, the spline curve formed by smoothly connecting the plotted plurality of points has a minimum value of the area of the adhered portion in the third region when the stacked portion is trisected into a first region with a smaller number of layers, a second region with a larger number of layers, and a third region with a number of layers between the first region and the second region.

3. The secondary battery according to claim 2, wherein, there are a fourth region and a fifth region that satisfy the following condition: the maximum change rate of the spline curve in the fourth region is less than 1 / 3 of the minimum change rate of the fifth region in the inner region of the number of layers compared to the fourth region.

4. The secondary battery according to any one of claims 1 to 3, wherein, when the number of layers of the separator membrane in the stacked portion is odd, the thicknesses of the outermost two separator membranes are each 90% or more of the thickness of the separator membrane in the stacked portion having the middle number of layers, when the number of layers of the separator membrane in the stacked portion is even, the thicknesses of the outermost two separator membranes are each 90% or more of the corresponding thickness of the separator membrane with the larger thickness among the two separator membranes having the middle number of layers in the stacked portion.

5. The secondary battery according to any one of claims 1 to 3, wherein, the amount of flattening in the thickness direction of the separator membrane, calculated based on the difference between the thickness of the separator membrane in the stacked portion and the thickness of the separator membrane outside the stacked portion, is 5% or less of the thickness of the separator membrane outside the stacked portion.

6. The secondary battery according to any one of claims 1 to 3, wherein, the separator membrane has a heat-resistant layer at least on one side in the thickness direction, the one side surface is composed of the heat-resistant layer.

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