JP7756679B2 - Electricity storage device and method for manufacturing the same - Google Patents

Description

This disclosure relates to an electricity storage device and a method for manufacturing the electricity storage device.

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

JP 2014-137985 A

However, the inventors' investigations have revealed that there is still room for improvement in the manufacturing method of the above-described secondary battery from the perspective of suppressing springback of the wound electrode body. Furthermore, it has been found that a wound electrode body in which springback has occurred as described above is likely to impose a load on 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) when inserted into a battery case. In other words, there is a demand for further development of technology that can obtain an electricity storage device equipped with a wound electrode body in which springback is suitably suppressed.

This disclosure was made in light of these circumstances, and its main purpose is to provide technology that can obtain an energy storage device equipped with a wound electrode body in which springback is suitably suppressed.

To achieve this objective, 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 between them 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 includes a winding step of winding the positive electrode sheet and the negative electrode sheet with the separator sheet interposed between them to produce a wound body. The method for manufacturing such an electricity storage device preferably 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. Although details will be described later, a method for manufacturing an electricity storage device with such a configuration can produce an electricity storage device including a wound electrode body in which springback is suitably suppressed.

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, and in which, when the porosity of the separator sheet present in the end-of-winding region of the wound electrode body is P and the porosity of the separator sheet present in a region other than the end-of-winding region of the wound electrode body is Q, the ratio of P to Q (P/Q) is less 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.

1 is a flowchart showing each step of a battery manufacturing method according to one embodiment. 1 is a schematic diagram showing the configuration of a wound electrode body manufacturing apparatus according to one embodiment. FIG. 1A to 1C are schematic diagrams for explaining the production of a wound body according to an embodiment. 5A and 5B are schematic diagrams for explaining adjustment of the position of a separator sheet according to one embodiment. 5A and 5B are schematic diagrams for explaining adjustment of the position of a separator sheet according to one embodiment. 5A and 5B are schematic diagrams for explaining cutting of a separator sheet according to one embodiment. 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. 3A and 3B are schematic diagrams for explaining application of tape to a roll according to one embodiment. FIG. 2 is a schematic diagram illustrating a configuration of a winding body according to an embodiment. FIG. 2 is a schematic diagram illustrating a state of a wound body before pressing according to an embodiment. FIG. 2 is a schematic diagram illustrating a state of a rolled body after pressing according to an embodiment. FIG. 1 is a front view schematically illustrating the internal structure of a battery according to an embodiment. FIG. 1 is a perspective view schematically showing a wound electrode body according to one embodiment.

Below, several embodiments of the technology disclosed herein are described 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 not specifically mentioned in this specification but necessary for implementing the technology disclosed herein (for example, the general configuration and manufacturing process of an energy storage device that does not characterize this disclosure) can be understood as design matters of a person 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 forms. The battery manufacturing method disclosed herein may include additional processes at any stage, and if a process is not described as essential, it may be deleted as appropriate. Furthermore, the order of the processes may be changed as long as the effects of the technology disclosed herein are achieved.

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 (e.g., 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.

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

The first winding core 204 shown in FIG. 2 is a member that winds the positive electrode sheet 50 and the negative electrode sheet 60 via the separator sheet 70. The first winding core 204 has the function of holding each sheet wound around its circumferential surface. Also, 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 provided. Here, the third winding core 208 is a member that operates when adjusting the position of the separator sheet 70 (described below). 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 shown as two semicircular members with a bisected structure, but these winding cores may be cylindrical, or a flat winding core may be used when winding into a flat shape.

The adjustment roller 210 shown in Figure 5 is a roller that adjusts the position of the separator sheet 70 to an appropriate position when cutting the separator sheet 70, as described below. The cutter 212 shown in Figure 6 is a cutter that cuts the separator sheet 70 to the desired length. The chuck 214 shown in Figure 6 is a member for holding the separator sheet 70. The chuck 214 is, for example, an electrostatic chuck.

The heat applicator 216 shown in Figure 7 is a member for heat-treating the surface of the separator sheet 70A present in the winding end region of the winding body 20A. Examples of the heat applicator 216 include a hair dryer, an infrared heater (IR heater), an electromagnetic induction heater (IH heater), etc. Commercially available products can be used without any particular restrictions.

The tape application member 218 shown in Figure 8 is a member that applies a stop tape to the winding end of the separator sheet 70 of the winding body 20A. Any stop tape used for this type of winding body can be used as this tape, without any particular restrictions.

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

Next, a method for manufacturing a battery according to this embodiment will be described with reference to the 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 and wound with a separator sheet 70 interposed therebetween. This method for manufacturing a battery includes a preparation step (step S1) in which the positive electrode sheet 50, the negative electrode sheet 60, and the separator sheet 70 are prepared. This method for manufacturing a battery also includes a winding step (step S2) in which the positive electrode sheet 50 and the negative electrode sheet 60 are wound with the separator sheet 70 interposed therebetween to produce a wound assembly 20A. This method for manufacturing a battery also includes a winding step (step S3) in which the separator sheet 70 present at the end of the winding of the wound assembly 20A is heat-treated and then wound around the wound assembly 20A. Furthermore, this embodiment further includes a pressing step (step S4) after the winding step, in which the wound body 20A is pressed to form a flat shape.

As described above, in the method for manufacturing 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 secured. This securing allows a load to be continuously applied to the wound body 20A (wound electrode body 20), thereby effectively suppressing springback of the wound electrode body 20. Each step is described below.

The "winding end region" may refer to, for example, the region of the outermost turn (corresponding to the region P1-P2 in FIG. 9 ) of the sheet constituting the winding body, extending from the outermost turn to within five, four, three, two, or one turns inward from the outermost turn. Alternatively, the "winding end region" may refer to only the outermost turn, or to within half a turn of the outermost turn. For example, in this embodiment, the winding end region is limited to the outermost turn (i.e., the region P1-P2 in FIG. 9 ), and the separator sheet 70 present only at the outermost turn is stretched during the winding process described below. Furthermore, from the perspective of facilitating heat treatment during the winding process described below, it is preferable that the winding end region of the winding body 20A, as in this embodiment, does not include the positive electrode sheet 50 and the negative electrode sheet 60, but is composed of only two separator sheets 70. However, the technology disclosed herein is not limited to the above description. The "winding end region" of the wound electrode body, which will be described later, can also be defined in a similar manner. In other words, the "winding body" in the above description can be replaced with the "wound electrode body."

(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, two separator sheets 70 are prepared. Each of these components will be described below.

The positive electrode current collector foil 52 that constitutes the positive electrode sheet 50 may be a known positive electrode current collector foil used in lithium-ion secondary batteries, such as aluminum foil or aluminum alloy foil. The thickness of the positive electrode current collector foil 52 is not particularly limited, but is, for example, 3 μm to 35 μm, and preferably 5 μm to 20 μm.

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. Specific examples of the positive electrode active material include lithium composite oxides and lithium transition metal phosphate compounds. 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 lithium nickel cobalt manganese composite oxide.

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 laser diffraction scattering.

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% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more.

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

The content of the conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.1% to 15% by mass, and more preferably 0.5% 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% to 15% by mass, and more preferably 1.5% 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 also 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.

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

The negative electrode active material layer 64 contains a negative electrode active material. Examples of the negative electrode active material that can be used include carbon materials such as graphite, hard carbon, and soft carbon. Graphite may be natural graphite or artificial graphite, or it may be amorphous carbon-coated graphite, in which graphite is coated with an amorphous carbon material.

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 laser diffraction scattering.

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, and 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, and 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, and 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.

Examples of the 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 standpoint of optimally performing 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 the separator sheet 70.

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 body 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 (similarly measured porosities 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 in accordance with 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 located in the winding end region of the winding body 20A.

(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.

Here, the number of windings (number of turns) of the winding body 20A (or the wound electrode body 20 described below) 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 may be, for example, 60 or less, or 50 or less.

(Winding process: step S3)
In this process, 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 a 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 the separator sheet 70A present in the winding end region of the winding body 20A after the heat treatment becomes smaller than A, where A is the porosity of the surface of the separator sheet 70A present in the winding end region of the winding body 20A before the heat treatment. From the viewpoint of more effectively obtaining the above-mentioned springback suppression effect, 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.

In addition, 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. 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 can thermally modify and harden the separator sheet 70A present in the end winding region of the wound body 20A. Then, by wrapping 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 effectively suppressing springback of the wound electrode body 20.

Next, as shown in Figure 8, a tape application member is used to apply a winding tape to the winding end of the winding body 20A prepared as described above.

(Pressing process: step S4)
In this embodiment, the method further includes a pressing step of pressing the wound electrode 20A to form a flat shape after the winding step. FIG. 10 is a schematic diagram illustrating the state of the wound electrode 20A according to one embodiment before pressing. FIG. 11 is a schematic diagram illustrating the state of the wound electrode 20A according to one embodiment after pressing. This pressing step can be performed by pressing the wound electrode 20A prepared 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 20 can be more effectively suppressed. In this manner, the wound electrode 20 can be prepared.

As shown in Figure 13, the wound electrode body 20 has a configuration in which a long positive electrode sheet 50 and a long negative electrode sheet 60 are stacked with two long separator sheets 70 in between, and the stack is wound longitudinally. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed longitudinally 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 longitudinally 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 portions 52a (i.e., portions 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 portions 62a (i.e., portions 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 of the wound electrode body 20 in the winding axis direction (i.e., the width direction perpendicular to the longitudinal direction). Furthermore, a core portion 20a, where the positive electrode active material layer 54 and the negative electrode active material layer 64 face each other, is located in the center in the winding axis direction. WL in FIG. 13 indicates the winding axis.

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 laminate portion 52A and the negative electrode current collector foil laminate 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. This connects the electrode body 20 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.

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, with one of its faces (the top face in the figure) forming 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 internal pressure when the internal pressure of the battery case 30 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 the positive electrode current collector terminal 42a. The negative electrode terminal 44 is electrically connected to the 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.

Next, nonaqueous electrolyte 80 is prepared according to a known method. Nonaqueous electrolyte 80 typically contains a nonaqueous solvent and a supporting salt (electrolyte salt). The nonaqueous solvent can be any organic solvent commonly used in electrolytes for lithium-ion secondary batteries, including various carbonates, ethers, esters, nitriles, sulfones, and lactones. Of these, carbonates and esters are preferred, and specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl acetate, and methyl propionate. These nonaqueous solvents can be used alone or in combination of two or more.

As the supporting salt, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , or lithium bis(fluorosulfonyl)imide (LiFSI) (preferably LiPF ₆ ) can be suitably used. The concentration of the supporting salt is preferably 0.7 mol/L to 1.3 mol/L.

In addition, the non-aqueous electrolyte 80 may contain various additives other than those described above, 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.

Then, 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 way, the battery 100 can be obtained.

Next, we will explain the battery 100 obtained by the battery manufacturing method described above. Here, Figure 12 is a front view schematically showing the internal structure of a battery according to one embodiment. Figure 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 end-of-winding region of the wound electrode body 20 in Figure 13 indicates that it has been thermally denatured and hardened by heat treatment. First, the battery 100 according to this embodiment is a battery comprising 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 less than 1. That is, the porosity of separator sheet 70A heat-treated in the winding step (step S4) described above is lower than the porosity of separator sheet 70 not heat-treated. Because battery 100 is obtained by any of the battery manufacturing methods disclosed herein, it can be said to be a battery including a wound electrode body in which springback is suitably suppressed.

From the viewpoint of effectively 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, for example, within the range of 0 to 0.1.

Furthermore, it is preferable that the wound electrode body 20 includes a separator sheet 70 made of a polyolefin resin.

Battery 100 can be used for a variety of purposes. Specific applications include portable power sources for personal computers, portable electronic devices, mobile 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 power storage devices, with battery 100 being preferred as a power source for driving vehicles. Battery 100 can also be used in the form of a battery pack, typically consisting of multiple batteries connected in series and/or parallel.

The above describes one embodiment of the present disclosure, but the above embodiment is merely one example. The present disclosure can be implemented in various other forms. The present disclosure can be implemented based on the content disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and variations 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 may be deleted as appropriate.

For example, in the above embodiment, the wound electrode body 20 has a flat shape, but this is not limited to this. In other embodiments, the wound electrode body may have a cylindrical shape, etc.

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

The above describes embodiments of the present disclosure, but 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 content disclosed in this specification and common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and variations of the embodiments exemplified above.

20 Wound electrode body 30 Battery case 32 Case body 34 Lid 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector terminal 44 Negative electrode terminal 44a Negative electrode current collector terminal 50 Positive electrode sheet (positive electrode)
52 Positive electrode current collector foil 52a Positive electrode active material layer non-forming portion 52A Positive electrode current collector foil laminated portion 54 Positive electrode active material layer 60 Negative electrode sheet (positive electrode)
62 Negative electrode current collector foil 62a Negative electrode active material layer non-forming portion 62A Negative electrode current collector foil laminated portion 64 Negative electrode active material layer 70 Separator sheet (separator)
80 Non-aqueous electrolyte 100 Battery 200 Wound electrode body manufacturing apparatus 202 Index 204 First winding core 206 Second winding core 208 Third winding core 210 Adjustment roller 212 Cutter 214 Chuck 216 Heat applicator 218 Tape application member 300 Press machine

Claims (3)

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 produce a wound body; and a winding step of heat-treating the surface of the separator sheet present in a winding end region of the wound body at a temperature of 60°C to 130°C using a heat applicator, and winding the separator sheet around the wound body, wherein the heat applicator is at least one of a dryer, an infrared heater, and an electromagnetic induction heater . The method for manufacturing an electricity storage device according to claim 1, wherein in the preparation step, a separator sheet made of a polyolefin resin is prepared as the separator sheet. The method for manufacturing an electricity storage device according to claim 1 or 2 further comprises, after the winding step, a pressing step of pressing the wound body to form it into a flat shape.