Electricity storage device and method for manufacturing the same

Abstract

To provide a technique capable of obtaining a power storage device including a wound electrode body with appropriately suppressed springback.SOLUTION: In a preferred embodiment of a manufacturing method of a wound electrode body disclosed herein, the manufacturing method includes: a preparation step (S1) of preparing a positive electrode sheet, a negative electrode sheet, and a separator sheet; a winding step (S2) of winding the positive electrode sheet and the negative electrode sheet via the separator sheet to manufacture a winding body; and a wrapping step (S3) of subjecting the separator sheet existing in a winding end area of the winding body to heat treatment and wrapping the separator sheet around the winding body. Herein, the manufacturing method further includes, after the wrapping step, a pressing step (S4) of pressing the winding body to mold the winding body into a flat shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electricity storage device and a method for manufacturing the electricity storage device. [Background technology]

[0002] For example, Patent Document 1 below discloses a method for manufacturing a secondary battery equipped with a wound electrode body, which includes a step of fabricating a wound electrode body by placing a separator sheet on which a heat-resistant layer is formed between positive and negative electrode sheets and winding them. It is described that this method for manufacturing a secondary battery suppresses loosening of the wound electrode body (hereinafter also referred to as "springback"). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-137985 Summary of the Invention [Problem to be solved by the invention]

[0004] However, according to the investigations of the present inventors, it has been found that there is still room for improvement in the manufacturing method of the secondary battery as described above in terms of suppressing springback of the wound electrode body. Furthermore, it has been found that when a wound electrode body in which springback has occurred as described above is inserted into a battery case, a load is likely to be applied to the joint between the wound electrode body and the sealing plate (for example, the electrode current collector terminal located between the wound electrode body and the sealing plate). In other words, there is a need for further development of a technology that can obtain an electricity storage device including a wound electrode body in which springback is suitably suppressed.

[0005] The present disclosure has been made in consideration of the above circumstances, and its main purpose is to provide a technology that can obtain an electricity storage device including a wound electrode body in which springback is suitably suppressed. [Means for solving the problem]

[0006] To achieve this object, the present disclosure provides a method for manufacturing an electricity storage device in which a positive electrode sheet and a negative electrode sheet are stacked with a separator sheet interposed therebetween and wound. The method for manufacturing such an electricity storage device preferably includes a preparation step of preparing the positive electrode sheet, the negative electrode sheet, and the separator sheet. The method for manufacturing such an electricity storage device preferably also includes a winding step of winding the positive electrode sheet and the negative electrode sheet with the separator sheet interposed therebetween to produce a wound body. The method for manufacturing such an electricity storage device preferably also includes a winding step of heat-treating the separator sheet present in the winding end region of the wound body and winding it around the wound body. Details will be described later, but the method for manufacturing an electricity storage device with such a configuration can provide an electricity storage device including a wound electrode body in which springback is suitably suppressed.

[0007] From another aspect, the present disclosure provides an electricity storage device obtained by any of the methods for manufacturing an electricity storage device disclosed herein. This electricity storage device includes a wound electrode body in which a positive electrode sheet and a negative electrode sheet are stacked with a separator sheet interposed therebetween and wound, in which, when the porosity of the separator sheet present in the winding end region of the wound electrode body is P and the porosity of the separator sheet present in a region other than the winding end region of the wound electrode body is Q, the ratio of P to Q (P / Q) is smaller than 1. Because this electricity storage device is obtained by any of the methods for manufacturing an electricity storage device disclosed herein, it can be said to be an electricity storage device including a wound electrode body in which springback is suitably suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a flowchart showing each step of a battery manufacturing method according to one embodiment. [Figure 2]1 is a schematic diagram showing the configuration of a wound electrode body manufacturing apparatus according to one embodiment. FIG. [Figure 3] 1A to 1C are schematic diagrams for explaining the production of a wound body according to an embodiment. [Figure 4] 5A and 5B are schematic diagrams for explaining adjustment of the position of a separator sheet according to one embodiment. [Figure 5] 5A and 5B are schematic diagrams for explaining adjustment of the position of a separator sheet according to one embodiment. [Figure 6] 5A and 5B are schematic diagrams for explaining cutting of a separator sheet according to one embodiment. [Figure 7] 10A and 10B are schematic diagrams for explaining the heat treatment of a separator sheet present in the winding end region of a winding body according to one embodiment. [Figure 8] 3A and 3B are schematic diagrams for explaining application of tape to a roll according to one embodiment. [Figure 9] FIG. 2 is a schematic diagram illustrating a configuration of a winding body according to an embodiment. [Figure 10] FIG. 2 is a schematic diagram illustrating a state of a wound body before pressing according to an embodiment. [Figure 11] FIG. 2 is a schematic diagram illustrating a state of a rolled body after pressing according to an embodiment. [Figure 12] FIG. 1 is a front view schematically illustrating the internal structure of a battery according to an embodiment. [Figure 13] FIG. 1 is a perspective view schematically showing a wound electrode body according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Several embodiments of the technology disclosed herein will be described below with reference to the drawings. In the following drawings, components and parts that perform the same function are denoted by the same reference numerals. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. Matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (e.g., the general configuration and manufacturing process of an energy storage device that does not characterize this disclosure) can be understood as design matters by those skilled in the art based on conventional technology in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. Furthermore, the following description is not intended to limit the present disclosure to the following embodiments. The battery manufacturing method disclosed herein may include additional steps at any stage, and steps that are not described as essential may be omitted as appropriate. Furthermore, the order of steps may be changed as long as the effects of the technology disclosed herein are achieved.

[0010] In this specification, the notation "A to B" indicating a range means "greater than A and less than B." It also encompasses the meanings of "greater than A" and "less than B." In addition, in this specification, the term "electricity storage device" refers to a device that can charge and discharge. Electricity storage devices include batteries such as primary batteries and secondary batteries (for example, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, and nickel-metal hydride batteries), and capacitors (physical batteries) such as electric double layer capacitors. The electrolyte may be any of a liquid electrolyte (electrolytic solution), a gel electrolyte, and a solid electrolyte. Hereinafter, a lithium ion secondary battery (hereinafter simply referred to as "battery 100"), which is one embodiment of the electricity storage device disclosed herein, will be described as an example.

[0011] <Battery manufacturing method> First, a method for manufacturing a battery according to this embodiment will be described with reference to a wound electrode assembly manufacturing apparatus 200. Before describing the method for manufacturing a battery according to this embodiment, the wound electrode assembly manufacturing apparatus 200 will be described. Here, FIG. 1 is a flowchart showing each step of the method for manufacturing a battery according to one embodiment. FIG. 2 is a schematic diagram showing the configuration of a wound electrode assembly manufacturing apparatus according to one embodiment. FIG. 3 is a schematic diagram for explaining the production of a wound body according to one embodiment. FIGS. 4 and 5 are schematic diagrams for explaining the adjustment of the position of a separator sheet according to one embodiment. FIG. 6 is a schematic diagram for explaining the cutting of a separator sheet according to one embodiment. FIG. 7 is a schematic diagram for explaining the heat treatment of a separator sheet present in the winding end region of a wound body according to one embodiment. FIG. 8 is a schematic diagram for explaining the application of tape to a wound body according to one embodiment. FIG. 9 is a schematic diagram showing the configuration of a wound body according to one embodiment. Note that in FIGS. 7 and 8, only the first winding core 204 is shown for ease of explanation. Below, each component of the wound electrode assembly manufacturing apparatus 200 according to this embodiment will be described.

[0012] The first winding core 204 shown in FIG. 2 is a member that winds up the positive electrode sheet 50 and the negative electrode sheet 60 with the separator sheet 70 interposed therebetween. The first winding core 204 has the function of holding each sheet that is wound around its circumferential surface. As shown in FIG. 2, in this embodiment, in addition to the first winding core 204, a second winding core 206 and a third winding core 208 are also provided. Here, the third winding core 208 is a member that operates when adjusting the position of the separator sheet 70, which will be described later. The first winding core 204, the second winding core 206, and the third winding core 208 are located within the index 202. Note that the first winding core 204, the second winding core 206, and the third winding core 208 are two semicircular members and have a two-part structure here, but these winding cores may have a cylindrical shape, or a flat winding core may be used when winding into a flat shape.

[0013] The adjustment roller 210 shown in Fig. 5 is a roller that adjusts the position of the separator sheet 70 to an appropriate position when cutting the separator sheet 70, which will be described later. The cutter 212 shown in Fig. 6 is a cutter that cuts the separator sheet 70 to a desired length. The chuck 214 shown in Fig. 6 is a member for holding the separator sheet 70. The chuck 214 is, for example, an electrostatic chuck.

[0014] 7 is a member for heat-treating the surface of the separator sheet 70A present in the winding end region of the wound body 20A. Examples of the heat-providing device 216 include a dryer, an infrared heater (IR heater), and an electromagnetic induction heater (IH heater). Commercially available products can be used as these without any particular restrictions.

[0015] 8 is a member that applies a stop tape to the winding end of the separator sheet 70 of the winding body 20A. As such a tape, any stop tape used for this type of winding body can be used without any particular restrictions.

[0016] It is preferable that each component of the wound electrode manufacturing apparatus 200 has a required actuator as appropriate. The control device is configured to control each component of the wound electrode manufacturing apparatus 200 so that required operations are performed at predetermined timings in accordance with a preset program. The control device can be embodied by a computer such as a microcontroller, for example.

[0017] Next, a method for manufacturing a battery according to this embodiment will be described with reference to a wound electrode assembly manufacturing apparatus 200. As shown in FIG. 1 , the method for manufacturing a battery according to this embodiment is a method for manufacturing a battery 100 including a wound electrode assembly 20 in which a positive electrode sheet 50 and a negative electrode sheet 60 are stacked with a separator sheet 70 interposed therebetween and wound. This battery manufacturing method includes a preparation step (step S1) of preparing the positive electrode sheet 50, the negative electrode sheet 60, and the separator sheet 70. This battery manufacturing method also includes a winding step (step S2) of winding the positive electrode sheet 50 and the negative electrode sheet 60 with the separator sheet 70 interposed therebetween to produce a wound assembly 20A. This battery manufacturing method also includes a winding step (step S3) of heat-treating the separator sheet 70 present in the winding end region of the wound assembly 20A and winding it around the wound assembly 20A. In addition, this embodiment further includes a pressing step (step S4) after the winding step, in which the wound body 20A is pressed to form it into a flat shape.

[0018] As described above, in the manufacturing method of the wound electrode body, in the winding step (step S3), the separator sheet 70A present in the winding end region of the wound body 20A is heat-treated and then wound around the wound body 20A. This heat treatment thermally modifies and hardens the separator sheet 70A present in the winding end region of the wound body 20A. By winding the hardened separator sheet 70A around the wound body 20A, the wound body 20A can be fastened. This fastening allows a load to be continuously applied to the wound body 20A (wound electrode body 20), thereby suitably suppressing springback of the wound electrode body 20. Each step is described below.

[0019] The "winding end region" may be, for example, a region from the outermost periphery (corresponding to the region P1-P2 in FIG. 9 ) to within five peripheries, four peripheries, three peripheries, two peripheries, or one periphery, among the turns (turns) of the sheet constituting the wound body. Alternatively, the "winding end region" may be only the outermost periphery, or may be a region within half a periphery of the outermost periphery, among the turns (turns) of the sheet constituting the wound body. For example, in this embodiment, the winding end region is only the outermost periphery (i.e., the region P1-P2 in FIG. 9 ), and the separator sheet 70 present only in the outermost periphery is stretched in the winding process described below. Furthermore, from the viewpoint of facilitating heat treatment in the winding process described below, it is preferable that the winding end region of the wound body 20A does not include the positive electrode sheet 50 and the negative electrode sheet 60, and is composed of only two separator sheets 70, as in this embodiment. However, the technology disclosed herein is not limited to the above description. The "winding end region" of a wound electrode body, which will be described later, can also be defined in the same way. That is, the "winding body" in the above description can be replaced with the "wound electrode body."

[0020] (Preparation process: Step S1) In this step, there are prepared a positive electrode sheet 50, a negative electrode sheet 60, and a separator sheet 70. In this embodiment, there are prepared two separator sheets 70. Each of these components will be described below.

[0021] The positive electrode current collector foil 52 constituting the positive electrode sheet 50 may be a known positive electrode current collector foil used in lithium ion secondary batteries, examples of which include aluminum foil, aluminum alloy foil, etc. The thickness of the positive electrode current collector foil 52 is not particularly limited and is, for example, 3 μm to 35 μm, and preferably 5 μm to 20 μm.

[0022] The positive electrode active material layer 54 contains a positive electrode active material. The positive electrode active material may be a known positive electrode active material used in lithium-ion secondary batteries. Specifically, for example, a lithium composite oxide, a lithium transition metal phosphate compound, or the like may be used as the positive electrode active material. The crystal structure of the positive electrode active material is not particularly limited and may be a layered structure, a spinel structure, an olivine structure, or the like. Examples of lithium composite oxides include lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium iron nickel manganese composite oxides. These positive electrode active materials may be used alone or in combination of two or more. A preferred positive electrode active material is a lithium nickel cobalt manganese composite oxide.

[0023] The average particle diameter (median diameter: D50) of the positive electrode active material is not particularly limited, but is, for example, 0.05 μm to 25 μm, preferably 1 μm to 20 μm, and more preferably 3 μm to 15 μm. The average particle diameter (D50) of the positive electrode active material can be determined, for example, by a laser diffraction scattering method.

[0024] The content of the positive electrode active material in the positive electrode active material layer 54 (i.e., the content of the positive electrode active material relative to the total mass of the positive electrode active material layer 54) is not particularly limited, but is, for example, 80 mass % or more, preferably 85 mass % or more, and more preferably 90 mass % or more.

[0025] The positive electrode active material layer 54 may contain components other than the positive electrode active material (i.e., optional components). Examples of the optional components include a conductive material, a binder, etc. Suitable conductive materials include carbon materials such as carbon black (e.g., acetylene black), carbon nanotubes (CNTs), and graphite. Suitable binders include polyvinylidene fluoride (PVDF), etc. When CNTs are used as the conductive material, the positive electrode active material layer 54 may further contain a dispersant for the CNTs.

[0026] The content of the conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.1% by mass to 15% by mass, and more preferably 0.5% by mass to 13% by mass. The content of the binder in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass to 15% by mass, and more preferably 1.5% by mass to 10% by mass. The thickness of the positive electrode active material layer 54 is not particularly limited, but is, for example, 10 μm to 300 μm, and preferably 20 μm to 200 μm. The positive electrode sheet 50 may contain an insulating layer (not shown) at the boundary between the positive electrode active material layer non-forming portion 52a and the positive electrode active material layer 54. The insulating layer may contain, for example, ceramic particles.

[0027] A known negative electrode current collector foil used in lithium ion secondary batteries, such as copper foil, may be used as the negative electrode current collector foil 62 that constitutes the negative electrode sheet 60. The thickness of the negative electrode current collector foil 62 is not particularly limited and is, for example, 3 μm to 35 μm, and preferably 5 μm to 20 μm.

[0028] The negative electrode active material layer 64 contains a negative electrode active material. As the negative electrode active material, for example, a carbon material such as graphite, hard carbon, or soft carbon can be used. The graphite may be natural graphite or artificial graphite, or may be amorphous carbon-coated graphite in which graphite is coated with an amorphous carbon material.

[0029] The average particle diameter (median diameter: D50) of the negative electrode active material is not particularly limited, but is, for example, 0.1 μm to 50 μm, preferably 1 μm to 25 μm, and more preferably 5 μm to 20 μm. The average particle diameter (D50) of the negative electrode active material can be determined, for example, by a laser diffraction scattering method.

[0030] The negative electrode active material layer 64 may contain components other than the active material, such as a binder or a thickener. Examples of binders that can be used include styrene butadiene rubber (SBR) and polyvinylidene fluoride (PVDF). Examples of thickeners that can be used include carboxymethyl cellulose (CMC). The content of the negative electrode active material in the negative electrode active material layer 64 is preferably 90% by mass or more, more preferably 95% to 99% by mass. The content of the binder in the negative electrode active material layer 64 is preferably 0.1% to 8% by mass, more preferably 0.5% to 3% by mass. The content of the thickener in the negative electrode active material layer 64 is preferably 0.3% to 3% by mass, more preferably 0.5% to 2% by mass. The thickness of the negative electrode active material layer 64 is not particularly limited, but is, for example, 10 μm to 300 μm, and preferably 20 μm to 200 μm.

[0031] Examples of separator sheet 70 include porous sheets (films) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Among these, separator sheets made of polyolefin resins such as PE and PP are preferred from the viewpoint of favorably carrying out the heat treatments (e.g., thermal modification and hardening) described above. Furthermore, such porous sheets may have a single-layer structure or a laminated structure of two or more layers (e.g., a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of separator sheet 70.

[0032] The thickness of the separator sheet 70 is not particularly limited, but is, for example, 5 μm to 50 μm, and preferably 10 μm to 30 μm. In this embodiment, the wound electrode assembly 20 includes two separator sheets 70. The porosity of the separator sheet 70 is generally 20 to 60%, and may be, for example, 30 to 50%. Here, the "porosity" can be a value calculated from the pore volume measured using, for example, mercury intrusion porosimetry (porosities measured in a similar manner can also be used for the porosities A, B, P, and Q described below). The porosity can be measured using, for example, a commercially available mercury intrusion porosimeter. The porosity can be measured according to the method described in the catalog. The air permeability of the separator sheet 70 is, for example, 30 sec / 100 cc to 500 sec / 100 cc, and may be 30 sec / 100 cc to 300 sec / 100 cc or 50 sec / 100 cc to 200 sec / 100 cc. In this embodiment, the two separators have the same configuration, but in other embodiments, they may have different configurations. In other embodiments, there may be only one separator sheet 70. As in this embodiment, it is preferable to prepare a separator sheet 70 that is longer than the positive electrode sheet 50 and the negative electrode sheet 60 so that the separator sheet 70 is present in the winding end region of the wound body 20A.

[0033] (Winding process: step S2) In this process, the positive electrode sheet 50 and the negative electrode sheet 60 are wound with the separator sheet 70 interposed therebetween to produce the wound body 20A. In this embodiment, as shown in FIG. 9, the wound body 20A is produced so that only the separator sheet 70 is present in the winding end region. Specifically, as shown in FIG. 3, the positive electrode sheet 50, the negative electrode sheet 60, and the separator sheet 70 are first wound around the first winding core 204. At this time, the third winding core is moved to the rear so as not to interfere with the position adjustment of the separator sheet 70. Next, as shown in FIGS. 3 and 4, the index 202 is rotated 120° in the direction of arrow S. Next, as shown in FIG. 5, the third winding core 208 is rotated by an angle sufficient to sandwich the separator sheet 70. The position of the separator sheet 70 is adjusted by the adjustment roller 210 so that the third winding core 208 can sandwich the separator sheet 70. Then, the third winding core 208 is advanced onto the surface of the index 202. Next, as shown in Figure 6, the separator sheet 70 is cut to the desired length by a cutter 212. At this time, it is preferable that the separator sheet 70 on both sides of the cutter 212 is held down by a chuck 214.

[0034] Here, the number of windings (number of turns) of the wound body 20A (or the wound electrode body 20 described later) is not particularly limited, but may be, for example, 10 or more, 20 or more, 30 or more, or 40 or more. The upper limit of the number of windings is, for example, 60 or less, or may be 50 or less.

[0035] (Winding process: step S3) In this step, the separator sheet 70A present in the winding end region of the winding body 20A (i.e., the region P1-P2 in FIG. 9) is heat-treated and then wound around the winding body 20A. Specifically, as shown in FIG. 7, the surface of the separator sheet 70 present in the winding end region of the winding body 20A is first heat-treated (heated) by the heat applicator 216. The heat treatment temperature is preferably varied depending on the type of resin constituting the separator sheet 70, but can be approximately 50°C to 150°C (e.g., 60°C to 130°C). The heat treatment time is preferably varied depending on the type of resin constituting the separator sheet 70, but can be approximately 0.3 seconds to 1 hour (e.g., 0.5 seconds to 30 minutes). After the heat treatment, the separator sheet 70 may be cooled to room temperature (e.g., 20°C ± 5°C). Although not particularly limited, the heat treatment is preferably carried out until the porosity B of the surface of separator sheet 70A present in the winding end region of winding body 20A after the heat treatment becomes smaller than A, where A is the porosity of the surface of separator sheet 70A present in the winding end region of winding body 20A before the heat treatment. From the viewpoint of more effectively obtaining the above-mentioned effect of suppressing springback, the heat treatment is preferably carried out until the porosity B becomes 0.8 A or less, more preferably 0.5 A or less, and even more preferably 0.2 A or less or 0.1 A or less (for example, it may be 0). The B can be, for example, within the range of 0 to 0.1 A.

[0036] Furthermore, in this embodiment, only one side of the separator sheet 70A is heat-treated, but in other embodiments, both sides of the separator sheet 70A may be heat-treated. Furthermore, in this embodiment, the surfaces of both of the two separator sheets 70 are heat-treated, but in other embodiments, only the surface of one separator sheet 70 may be heat-treated. This heat treatment thermally modifies and hardens the separator sheet 70A present in the winding end region of the wound body 20A. Then, by winding the hardened separator sheet 70A after this heat treatment around the wound body 20A and fastening the wound body 20A, a load can be continuously applied to the wound body 20A (wound electrode body 20), thereby suitably suppressing springback of the wound electrode body 20.

[0037] Next, as shown in FIG. 8, a take-up tape is applied to the take-up end of the wound body 20A produced as described above using a tape applying member.

[0038] (Pressing process: Step S4) In this embodiment, the method further includes a pressing step of pressing the wound electrode body 20A to form a flat shape after the winding step. FIG. 10 is a schematic diagram showing the wound electrode body according to one embodiment before pressing. FIG. 11 is a schematic diagram showing the wound electrode body according to one embodiment after pressing. This pressing step can be performed by pressing the wound electrode body 20A produced as described above in the direction of the outline arrow using a press 300. While not particularly limited, the pressing pressure can be, for example, 20 N to 200 kN (preferably, 50 N to 120 kN). This pressing may be a heated press or a non-heated press. By performing this pressing step, springback of the wound electrode body 20 can be more effectively suppressed. In this manner, the wound electrode body 20 can be produced.

[0039] As shown in Fig. 13, the wound electrode body 20 has a configuration in which a laminate, in which a long positive electrode sheet 50 and a long negative electrode sheet 60 are stacked with two long separator sheets 70 interposed therebetween, is wound in the longitudinal direction. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (both sides in this case) of a long positive electrode current collector foil 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (both sides in this case) of a long negative electrode current collector foil 62. The positive electrode active material layer-free portion 52a (i.e., a portion where the positive electrode active material layer 54 is not formed and the positive electrode current collector foil 52 is exposed) and the negative electrode active material layer-free portion 62a (i.e., a portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector foil 62 is exposed) are formed so as to protrude outward from both ends in the winding axis direction (i.e., the width direction perpendicular to the longitudinal direction) of the wound electrode body 20. In addition, a core portion 20a where the positive electrode active material layer 54 and the negative electrode active material layer 64 face each other is present in the center in the winding axis direction. Note that WL in FIG. 13 indicates the winding axis.

[0040] Next, the positive electrode current collector terminal 42a and the negative electrode current collector terminal 44a are attached to the positive electrode current collector foil laminated portion 52A and the negative electrode current collector foil laminated portion 62A of the wound electrode body 20 fabricated as described above by resistance welding, ultrasonic welding, or the like. Here, it is assumed that the positive electrode terminal 42, the negative electrode terminal 44, the positive electrode current collector terminal 42a, and the negative electrode current collector terminal 44a are attached to the lid 34 of the battery case 30. In this manner, the electrode body 20 is connected to the lid 34 of the battery case 30. The electrode body 20 is then inserted into the case body 32 through the opening of the case body 32. The case body 32 and the lid 34 are then sealed together by laser welding or the like.

[0041] Here, the battery case 30 is made of, for example, a metal (e.g., aluminum, stainless steel, nickel-plated steel, etc.). Aluminum is preferably used for the battery case 30 because it has good electrical conductivity, thermal conductivity, strength, and light weight. The case body 32 has a flattened rectangular parallelepiped shape, one of whose faces (the top face in the figure) is an opening. The lid 34 has a generally rectangular shape that fits the shape of the opening. The lid 34 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, as well as a thin-walled safety valve 36 that is designed to release the internal pressure of the battery case 30 when the internal pressure rises above a predetermined level. The lid also has a liquid injection hole (not shown) for injecting the nonaqueous electrolyte 80. The positive electrode terminal 42 is electrically connected to a positive electrode current collector terminal 42a. The negative electrode terminal 44 is electrically connected to a negative electrode current collector terminal 44a. The positive electrode terminal 42 and the positive electrode current collector terminal 42a are made of, for example, aluminum or an aluminum alloy. The negative electrode terminal 44 and the negative electrode current collector terminal 44a are made of, for example, copper or a copper alloy.

[0042] Next, a nonaqueous electrolyte 80 is prepared according to a known method. The nonaqueous electrolyte 80 typically contains a nonaqueous solvent and a supporting salt (electrolyte salt). As the nonaqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones commonly used in electrolyte solutions for lithium-ion secondary batteries can be used without any particular limitation. Of these, carbonates and esters are preferred, and specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl acetate, and methyl propionate. Such nonaqueous solvents can be used singly or in appropriate combinations of two or more.

[0043] As the supporting salt, for example, lithium salts such as LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI) (preferably LiPF6) can be suitably used. The concentration of the supporting salt is preferably 0.7 mol / L to 1.3 mol / L.

[0044] The nonaqueous electrolyte 80 may contain various additives other than the above-mentioned components, such as film-forming agents such as vinylene carbonate (VC) and oxalate complexes; gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); and thickeners, as long as the effects of the present disclosure are not significantly impaired.

[0045] Then, the non-aqueous electrolyte 80 is poured into the battery case 30 through the pouring hole in the lid 34 of the battery case 30, and the pouring hole is sealed. In this manner, the battery 100 can be obtained.

[0046] Next, a battery 100 obtained by the battery manufacturing method described above will be described. Here, FIG. 12 is a front view schematically showing the internal structure of a battery according to one embodiment. FIG. 13 is a perspective view schematically showing a wound electrode body according to one embodiment. The hatched portion of the separator sheet 70A present in the winding end region of the wound electrode body 20 in FIG. 13 indicates that the separator sheet 70A has been thermally denatured by heat treatment and has been hardened. First, the battery 100 according to this embodiment is a battery including a wound electrode body 20 in which a positive electrode sheet 50 and a negative electrode sheet 60 are stacked with a separator sheet 70 interposed therebetween and wound. Furthermore, when the porosity of separator sheet 70A present in the end-of-winding region of wound electrode body 20 is P and the porosity of separator sheet 70 present in the other region of wound electrode body 20 (in other words, the region of separator sheet 70 present in wound electrode body 20 other than separator sheet 70A) is Q, the ratio of P to Q (P / Q) is smaller than 1. That is, the porosity of separator sheet 70A heat-treated in the winding step (step S4) as described above is smaller than the porosity of separator sheet 70 not heat-treated. Such battery 100 is a battery obtained by any of the battery manufacturing methods disclosed herein, and can therefore be said to be a battery including a wound electrode body in which springback is suitably suppressed.

[0047] From the viewpoint of suitably suppressing springback of the wound electrode body 20, the ratio (P / Q) is preferably 0.8 or less, more preferably 0.5 or less, and even more preferably 0.2 or less or 0.1 or less (for example, it may be 0. In this case, P is 0). The ratio (P / Q) can be set within the range of 0 to 0.1, for example.

[0048] Furthermore, the wound electrode body 20 preferably includes, as the separator sheet 70, a separator sheet made of a polyolefin resin.

[0049] Battery 100 can be used for a variety of purposes. Specific applications include portable power sources for personal computers, portable electronic devices, portable terminals, etc.; power sources for driving vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); and storage batteries for small-sized power storage devices, with battery 100 being particularly preferred as a power source for driving vehicles. Battery 100 can also be used in the form of a battery pack, typically consisting of a plurality of batteries connected in series and / or parallel.

[0050] Although one embodiment of the present disclosure has been described above, the above embodiment is merely an example. The present disclosure can be implemented in various other forms. The present disclosure can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiment. For example, it is possible to replace part of the above-described embodiment with other modified embodiments, and it is also possible to add other modified embodiments to the above-described embodiment. Furthermore, if a technical feature is not described as essential, it can be deleted as appropriate.

[0051] For example, in the above embodiment, the shape of the wound electrode body 20 is flat, but is not limited to this. In other embodiments, the shape of the wound electrode body may be cylindrical or the like.

[0052] For example, in the above embodiment, the method for manufacturing the wound electrode body includes the pressing step (step S4), but is not limited to this. For example, if the wound electrode body is cylindrical, the pressing step can be omitted.

[0053] Although the embodiments of the present disclosure have been described above, the above embodiments are merely examples. The present disclosure can be implemented in various other forms. The present disclosure can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiments. [Explanation of symbols]

[0054] 20 Wound electrode body 30 Battery case 32 Case body 34 Lid 36 Safety valve 42 Positive terminal 42a Positive current collecting terminal 44 Negative terminal 44a Negative electrode current collector terminal 50 Positive electrode sheet (positive electrode) 52 Positive electrode current collector foil 52a Portion where positive electrode active material layer is not formed 52A Positive current collector foil laminate 54 Cathode active material layer 60 negative electrode sheet (positive electrode) 62 Negative electrode current collecting foil 62a Part where negative electrode active material layer is not formed 62A negative electrode current collector foil laminate 64 Negative electrode active material layer 70 Separator sheet (separator) 80 Non-aqueous electrolyte 100 batteries 200 Wound electrode manufacturing equipment 202 Index 204 First winding core 206 Second winding core 208 Third winding core 210 Adjustment roller 212 Cutter 214 Zipper 216 Heat Applicator 218 Tape-attached parts 300 press machine

Claims

1. A method for manufacturing an electricity storage device including a wound electrode body in which a positive electrode sheet and a negative electrode sheet are stacked with a separator sheet interposed therebetween and wound, the method comprising the steps of: a preparation step of preparing the positive electrode sheet, the negative electrode sheet, and the separator sheet; a winding step of winding the positive electrode sheet and the negative electrode sheet with the separator sheet interposed therebetween to prepare a wound body; and a winding step of heat-treating a surface of the separator sheet present in the winding end region of the winding body at a temperature of 60°C to 130°C using a heat applicator, and then winding the separator sheet around the winding body, wherein the heat applicator is at least one of a dryer, an infrared heater, and an electromagnetic induction heater.

2. The method for producing an electricity storage device according to claim 1 , wherein in the preparing step, a separator sheet made of a polyolefin resin is prepared as the separator sheet.

3. The method for manufacturing an electricity storage device according to claim 1 or 2, further comprising, after the winding step, a pressing step of pressing the wound body to form it into a flat shape.

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