Power storage device

Abstract

To provide a power storage device with improved sealing performance of permeable membrane.SOLUTION: A power storage device includes: an electrode body; an electrolyte; and an exterior body that accommodates the electrode body and the electrolyte. An opening part 70 is provided on one surface of the exterior body, and a permeable membrane 80 that does not allow liquid disposed in the opening part 70 to pass therethrough and allows gas to pass therethrough is provided. In addition, the opening part 70 has an overhanging part 71 which overhangs from an inner wall surface of the opening part 70 in an opening center direction, a plurality of caulking claws 73 provided on the outer periphery of the opening part 70 so as to face the overhanging part 71, and a holding frame 90 for holding the permeable membrane 80. The permeable membrane 80 is disposed in the opening part 70 by holding the holding frame 90 in a state of being caulked between the plurality of caulking claws 73 and the overhanging portion 71.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to an electricity storage device. [Background technology]

[0002] In electricity storage devices such as lithium-ion secondary batteries, nickel-metal hydride batteries, and other secondary batteries, or capacitors, the electrolyte decomposes during charging and discharging, generating gases such as CO2. The generated gas can cause the exterior body of the electricity storage device (a case housing the electrode assembly, electrolyte, etc.) to expand, potentially resulting in deformation of the exterior body. In such cases, it is desirable to provide a permeable membrane to discharge the generated gas to the exterior body and reduce the internal pressure of the electricity storage device.

[0003] For example, Japanese Patent Application Laid-Open Publication No. 2016-46021 discloses a nonaqueous secondary battery in which a membrane capable of selectively releasing hydrogen gas is provided in a portion of the exterior body. The membrane is attached to a metal ring. The metal ring (membrane assembly) to which the membrane is attached is fitted into a through-hole in the exterior body and joined to the exterior body. This allows hydrogen gas generated inside the exterior body to be appropriately released.

[0004] There are also examples in which a membrane capable of releasing gas is integrated with an explosion-proof valve (safety valve). For example, Japanese Patent Application Laid-Open Publication No. 2013-168293 discloses a battery pack in which an explosion-proof valve functions as a vent. The battery pack includes a breathable membrane that selectively allows gas to pass through but not liquid, and that breaks or deforms as internal pressure increases. The battery pack also includes a plate-shaped protector that is positioned on the outside of the breathable membrane and is retained at its periphery so that it can be removed by bending and deforming due to a predetermined pressure difference. The battery pack also includes a vent that opens to the outside and allows a small amount of air to pass through the breathable membrane. This reduces the risk of rainwater or foreign objects entering the pack case. Furthermore, when internal pressure suddenly increases, the protector deforms, functioning as an explosion-proof valve. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-46021 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-168293 Summary of the Invention [Problem to be solved by the invention]

[0006] However, JP 2016-46021 A includes two steps: a step of attaching a membrane to a metal ring to prepare a membrane assembly, and a step of joining the membrane assembly to an exterior body. Furthermore, when joining the membrane assembly to the exterior body, there is a risk of the membrane being deformed due to heat input, etc. In JP 2013-168293 A, the gas-permeable membrane is sandwiched between an explosion-proof valve case and a protector. Furthermore, the protector is held to the explosion-proof valve case by a locking protrusion on the periphery of the protector. With this configuration, the gas-permeable membrane does not provide sufficient sealing, which may result in electrolyte leakage. Furthermore, applying a load to the protector to improve sealing may cause the gas-permeable membrane to break.

[0007] Therefore, an object of the present disclosure is to provide an electricity storage device in which the sealing properties of the permeable membrane of the electricity storage device are improved and leakage of the electrolyte is suppressed. [Means for solving the problem]

[0008] The electricity storage device disclosed herein includes an electrode assembly, an electrolyte, and an exterior housing that houses the electrode assembly and the electrolyte. The electricity storage device has an opening and a permeable membrane on one surface of the exterior housing that does not allow a liquid disposed in the opening to pass through but allows a gas to pass through. The electricity storage device also has a protruding portion that protrudes from the inner wall surface of the opening toward the center of the opening, a plurality of crimping claws provided on the outer periphery of the opening so as to face the protruding portion, and a holding frame that holds the permeable membrane. Here, the permeable membrane is positioned in the opening by the holding frame being crimped and held between the plurality of crimping claws and the protruding portion.

[0009] In this electricity storage device, the holding frame is crimped with the protruding portion and the crimping claws, thereby fixing the permeable membrane to the opening. By crimping the holding frame, the permeable membrane is pressed against the opening, thereby improving the sealing of the opening. Furthermore, since the permeable membrane can be assembled without applying heat, deformation of the permeable membrane can be prevented.

[0010] In one aspect of the electricity storage device disclosed herein, the protruding portion has a convex portion on a surface facing the crimping claws. Here, the permeable membrane is arranged so that the convex portion bites into the permeable membrane by crimping the holding frame between the multiple crimping claws and the protruding portion. This can further improve the sealing performance of the permeable membrane.

[0011] In one aspect of the electricity storage device disclosed herein, a convex portion is provided on the outer peripheral edge of the holding frame, facing the protruding portion. The convex portion of the holding frame is located on the outer periphery from the center of the opening, farther outward than the convex portion of the protruding portion. This allows the convex portion of the holding portion to fit into the convex portion of the protruding portion. This effect is that the permeable membrane is more firmly held, improving sealing performance.

[0012] In one aspect of the electricity storage device disclosed herein, the exterior body has a box-like shape. The crimping claws are provided more on the long sidewall side of the exterior body than on the short sidewall side. This makes it easier to maintain the sealing performance of the permeable membrane even when the exterior body expands due to a sudden increase in internal pressure. This effect stabilizes the operating pressure of the permeable membrane and reduces the increase in internal pressure.

[0013] In one aspect of the electricity storage device disclosed herein, the holding frame has beams connecting parts of the outer periphery of the holding frame, thereby improving the strength of the holding frame and suppressing deformation of the permeable membrane due to an increase in internal pressure.

[0014] In one aspect of the electricity storage device disclosed herein, the opening is located on the upper surface of the exterior body when the electricity storage device is installed, which allows generated gas to be efficiently discharged through the opening. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view of a lithium ion secondary battery according to one embodiment disclosed herein. [Figure 2] FIG. 2 is a longitudinal cross-sectional view of a lithium ion secondary battery according to one embodiment disclosed herein. [Figure 3] FIG. 3 is an exploded view that schematically shows the configuration of a wound electrode body of a lithium ion secondary battery according to one embodiment disclosed herein. [Figure 4] FIG. 4 is a diagram schematically illustrating the surface of a sealing plate of a lithium ion secondary battery according to one embodiment disclosed herein. [Figure 5] FIG. 5 is a perspective view of an opening of a lithium ion secondary battery according to one embodiment disclosed herein. [Figure 6] FIG. 6 is a cross-sectional view of an opening of a lithium ion secondary battery according to one embodiment disclosed herein. [Figure 7]FIG. 7 is a cross-sectional view of an opening of a lithium ion secondary battery according to one embodiment disclosed herein before crimping. [Figure 8] FIG. 8 is a cross-sectional view of an opening in the lithium ion secondary battery according to one embodiment disclosed herein during crimping. [Figure 9] FIG. 9 is a schematic plan view of a metal frame of an electricity accumulation device according to another embodiment. [Figure 10] FIG. 10 is a schematic plan view of a metal frame having four through-holes of an electricity storage device according to another embodiment. [Figure 11] FIG. 11 is a diagram schematically illustrating the back side of the sealing plate of an electricity storage device according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Terminology> A lithium-ion secondary battery, which is one typical embodiment of an energy storage device according to the present disclosure, will be described in detail below with reference to the drawings. Matters necessary for implementation other than those specifically mentioned in this specification (e.g., the general configuration and manufacturing process of an energy storage device that does not characterize the present disclosure) can be understood as design matters of a person skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. 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.

[0017] In this specification, the term "electricity storage device" refers to a concept that encompasses devices in which charge carriers move between a pair of electrodes (positive and negative electrodes), resulting in charge and discharge reactions. That is, electricity storage devices include batteries such as secondary batteries (e.g., lithium ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries), and capacitors (physical batteries) such as lithium ion capacitors and electric double layer capacitors. Furthermore, in this specification, the term "lithium ion secondary battery" refers to an electricity storage device that uses lithium ions as charge carriers and achieves repeated charging and discharging by the movement of charge associated with the lithium ions between the positive and negative electrodes.

[0018] In this specification, when a numerical range is described as "A to B (where A and B are any numerical values)," it means "A or more and B or less," and also encompasses the meanings of "greater than A and less than B," "greater than A and B or less," and "greater than A and less than B."

[0019] <Electricity storage device> The lithium-ion secondary battery 1 of this embodiment includes an electrode assembly, an electrolyte, and an exterior housing 10. FIG. 1 is a perspective view of the lithium-ion secondary battery 1 according to one embodiment. FIG. 2 is a schematic longitudinal cross-sectional view of the lithium-ion secondary battery 1 taken along line II-II in FIG. 1. In FIG. 2, a portion of the wound electrode assembly 20 is shown in a see-through manner so that the configuration of the wound electrode assembly 20 can be seen. In the following description, the symbols L, R, U, and D in the drawings represent the left, right, top, and bottom of the lithium-ion secondary battery 1. Furthermore, the symbol T in the drawings represents the thickness direction of the lithium-ion secondary battery 1. However, these directions are merely provided for the sake of convenience in the description and do not in any way limit the installation form of the lithium-ion secondary battery 1.

[0020] <Exterior body> The exterior body 10 is a case that mainly houses the wound electrode assembly 20, an electrolyte (not shown), and the like. As shown in FIG. 1 , in the lithium-ion secondary battery 1 according to this embodiment, the exterior body 10 has a hexahedral box shape. More specifically, the shape of the exterior body 10 is a rectangular parallelepiped, i.e., a flattened square. However, the shape of the exterior body 10 is not limited thereto and may be, for example, a cylindrical shape. The exterior body 10 includes a main body 11 of the exterior body 10 that houses the wound electrode assembly 20 and an electrolyte (not shown), and a sealing plate (lid) 60 that seals the opening of the main body 11. The main body 11 and the sealing plate 60 are welded and sealed by laser welding or the like. The material of the exterior body 10 is not particularly limited as long as it is the same as that used in conventional power storage devices of this type. As an example, the material of the exterior body 10 is a lightweight metal material with good thermal conductivity, such as aluminum. However, the configuration of the exterior body 10 can be modified. For example, a flexible laminate film may be used as the exterior body.

[0021] The exterior body 10 is provided with a safety valve 61, a liquid inlet 62, and an opening 70. The safety valve 61 is a thin-walled valve configured to release internal pressure when the internal pressure of the exterior body 10 rises above a predetermined level. The liquid inlet 62 is a hole for injecting the electrolyte. The liquid inlet 62 is no longer needed after the electrolyte is injected, and can be sealed by laser welding or the like. Alternatively, the liquid inlet 62 can be sealed by attaching a plug. The opening 70 is a hole for discharging gas generated inside the exterior body 10 to the outside of the exterior body 10. In this embodiment, the main body 11 of the exterior body 10 is composed of a bottom wall 11a, a pair of short side walls 11c1 and 11c2 extending from the bottom wall 11a and facing each other, and long side walls 11b1 and 11b2. Here, the safety valve 61, the liquid inlet 62, and the opening 70 are provided in the sealing plate 60.

[0022] A positive electrode external terminal 14 and a negative electrode external terminal 15 for external connection are provided in an exposed state on the outside of the exterior body 10. These electrode terminals are electrically connected to a wound electrode body 20 housed in the exterior body 10 via internal terminals 16 and 17. The external terminals 14 and 15 are made of metal. For example, aluminum or an aluminum alloy can be used as the positive electrode external terminal 14. For example, copper or a copper alloy can be used as the negative electrode external terminal 15.

[0023] The internal terminals 16, 17 are made of metal. For example, aluminum or an aluminum alloy may be used as the positive electrode internal terminal 16 from the viewpoint of improving the bonding strength with the positive electrode tab 31c (or the portion 31a where the positive electrode active material layer is not formed). For example, copper or a copper alloy may be used as the negative electrode internal terminal 17 from the viewpoint of improving the bonding strength with the negative electrode tab 41c (or the portion 41a where the negative electrode active material layer is not formed).

[0024] In this embodiment, the external terminals 14 and 15 are attached to a front surface 60a (outside) of the sealing plate 60 via a gasket 18. The internal terminals 16 and 17 are attached to a back surface 60b (inside) of the sealing plate 60 via an insulator 19. The materials of the gasket 18 and the insulator 19 are not particularly limited. Materials with excellent chemical resistance and weather resistance can be used for the gasket 18 and the insulator 19. For example, resins such as tetrafluoroethylene-polyfluoroalkyl vinyl ether copolymer (PFA), polyethylene (PE), polypropylene (PP), and polyphenylene sulfide (PPS) can be used for the gasket 18 and the insulator 19.

[0025] <Permeable membrane> The permeable membrane 80 is a membrane that can discharge gas (e.g., H2 or CO2) generated within the electricity storage device (or exterior body) to the outside. The permeable membrane 80 also does not allow liquids such as electrolyte and water to pass through. As a result, the permeable membrane 80 selectively allows only gas to pass through, and can suppress an increase in the internal pressure of the electricity storage device. The permeable membrane 80 generally has the role of discharging gas generated within the electricity storage device to the outside. The permeable membrane 80 also has the role of preventing the electrolyte within the electricity storage device from leaking to the outside and preventing liquids such as water from entering the electricity storage device from the outside.

[0026] The permeable membrane 80 is sandwiched between the protruding portion 71 and the crimping claws 73 of the opening 70, with the holding frame 90 interposed therebetween. The shape and size of the permeable membrane 80 are not particularly limited as long as they do not significantly impair the effects of the technology of the present disclosure. In this embodiment, the permeable membrane 80 is formed in a circular sheet shape. The diameter of the permeable membrane 80 is formed to be larger than the hole diameter of the ventilation hole 72. The permeable membrane 80 is pressed against the back surface 71b of the protruding portion 71 by crimping the holding frame 90 with the protruding portion 71 and the crimping claws 73. In this way, the permeable membrane 80 closes the opening 70 and separates the inside and outside of the exterior body 10.

[0027] The material of the permeable membrane 80 may be any material that selectively allows gas to pass through while not allowing liquid to pass through, and may be selected from known materials. Examples of materials for the permeable membrane 80 include porous membranes made of resins such as fluororesin, polyester resin, polyolefin resin, silicone resin, acrylic resin, polysulfone, polystyrene, polyimide, and polyamide. Examples of fluororesin include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer (ETFE), vinylidene fluoride (FKM), tetrafluoroethylene-propylene copolymer (FEPM), and tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (FFKM). Examples of polyolefin resins include PE, PP, and polymethylpentene (PMP). Examples of polyester resins include polyethylene terephthalate (PET). Examples of silicone resins include polydimethylsiloxane (PDMS). Examples of acrylic resins include polymethyl methacrylate (PMMA). The permeable membrane 80 may be made of one of these resins or a combination of two or more of them. Other examples include molecular sieve membranes such as zeolite and silica, and chemical separation membranes such as palladium and its alloys, niobium and its alloys, and amorphous alloys of zinc and nickel. Of these, the permeable membrane 80 is preferably made of fluororesin because of its high heat resistance, chemical resistance, and electrical insulation. Furthermore, from the viewpoint of ease of processing, PTFE or PFA is more preferable as the material for the permeable membrane 80.

[0028] Such a permeable membrane 80 may have a gas-selective function, for example, allowing certain gases to pass through while blocking other gases. For example, helium (He) is not a gas that can be generated later within an electricity storage device. Furthermore, He is smaller than hydrogen molecules and is chemically stable, so it contributes little to an increase in the internal pressure of the electricity storage device. Therefore, the permeable membrane 80 may be permeable to He, regardless of whether it is generated later. On the other hand, carbon dioxide gases such as carbon monoxide (CO) and carbon dioxide (CO2), hydrogen (H2), and hydrocarbons such as methane (CH4) and ethane (C2H5) can be generated by gradual decomposition of the electrolyte during charging and discharging of the electricity storage device. Alternatively, they can be generated by overcharging or overdischarging. Therefore, a membrane with good permeability to these gases is preferable. The gas permeability can be adjusted by the pore size or material of the permeable membrane 80. The pore size of the permeable membrane 80 is not particularly limited as long as it does not significantly impair the effects of the technology disclosed herein. The lower limit of the average pore size of the permeable membrane 80 may be 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more. The upper limit of the average pore size of the permeable membrane 80 may be 20 μm or less, 10 μm or less, or 2 μm or less.

[0029] <Opening> The exterior housing 10 of the power storage device disclosed herein has an opening 70 for discharging gas (e.g., H2 or CO2) generated inside the exterior housing 10 to the outside. The opening 70 is a hole that penetrates from the inside to the outside of the exterior housing 10. The shape of the opening 70 is not particularly limited as long as it does not significantly impair the effects of the technology disclosed herein. Considering the ease of crimping and the influence of deformation of the exterior housing 10 due to an increase in internal pressure, a circular shape of the opening 70 is preferable. FIG. 4 is a diagram schematically illustrating a surface 60a of a sealing plate 60 of a lithium-ion secondary battery 1 according to one embodiment disclosed herein. In this embodiment, as shown in FIG. 4, circular openings 70 are provided in the sealing plate 60. However, the number or arrangement of the openings 70 is not limited thereto. The openings 70 may be provided, for example, in a side wall 10c1 of the exterior housing 10. However, gas generated inside the exterior housing 10 has a smaller specific gravity than the electrolyte and therefore tends to move upward (here, in the U direction). Therefore, it is preferable to provide opening 70 on the top surface (here, sealing plate 60). By providing opening 70 on the top surface of exterior body 10, the generated gas can be efficiently discharged.

[0030] FIG. 5 is a perspective view of an opening 70 of a lithium-ion secondary battery 1 according to one embodiment disclosed herein. FIG. 5 is a view from the rear surface 60b side of the sealing plate 60 so that the configuration of the opening 70 can be seen. FIG. 6 is a schematic longitudinal cross-sectional view of the opening 70 taken along line VI-VI in FIG. 5. As shown in FIG. 6, the opening 70 according to this embodiment includes a protruding portion 71 and a plurality of crimping claws 73. FIG. 6 illustrates the relationship between the crimping claws 73, the holding frame 90, the permeable membrane 80, and the protruding portion 71 so that the crimping joint state in the opening 70 can be seen. Note that FIGS. 5 and 6 and FIGS. 7 and 8, which will be described later, are shown upside down relative to FIGS. 1 and 2, in accordance with the crimping process of this embodiment.

[0031] As shown in FIG. 6 , the opening 70 has a protruding portion 71 that protrudes from the inner wall surface of the opening 70 toward the center of the opening. The protruding portion 71 has a back surface 71b on which the permeable membrane 80 and the holding frame 90 can be disposed, and a front surface 71a facing the back surface 71b. The protruding portion 71 also forms a vent hole 72 that is smaller than the opening 70. The vent hole 72 is closed by the permeable membrane 80 to prevent electrolyte leakage. In this embodiment, the opening 70 is provided in the sealing plate 60. The back surface 71b of the protruding portion 71 is in the same direction as the back surface 60b of the sealing plate 60. The front surface 71a of the protruding portion 71 is directly connected to the front surface 60a of the sealing plate 60. Gas generated inside the exterior body 10 permeates the permeable membrane 80 and is then discharged to the outside through the vent hole 72.

[0032] The dimensions or shape of the protruding portion 71 are not particularly limited as long as they do not significantly impair the effects of the technology of the present disclosure. In this embodiment, as shown in FIG. 6 , the thickness of the protruding portion 71 is smaller than the thickness of the sealing plate 60. This creates a recess in the opening 70, allowing the permeable membrane 80 and the holding frame 90 to be positioned along the protruding portion 71 and the inner wall surface of the opening 70. The protruding portion 71 also has a protruding portion 71c on the surface facing the crimping claws 73 (here, the back surface 71b of the protruding portion 71). The protruding portion 71c is provided circumferentially along the inner wall of the opening 70. When the holding frame 90 is crimped by the crimping claws 73 and the protruding portion 71, the protruding portion 71c bites into the permeable membrane 80, thereby holding the permeable membrane 80. This further improves the sealing performance of the permeable membrane 80. Furthermore, by providing the protrusion 71 with the protrusion 71c, a larger reaction force is generated on the surface of the permeable membrane 80 facing the protrusion 71c. To counter this reaction force, it is preferable that the tip 73a of the crimping claw 73 is positioned closer to the center of the opening than the outer periphery of the protrusion 71c when crimped. This allows the permeable membrane 80 to be stably fixed, thereby improving the sealing performance of the opening 70.

[0033] As shown in FIG. 5 , the opening 70 has a plurality of crimping claws 73 provided on the outer periphery of the opening 70 so as to face the protruding portion 71. The crimping claws 73 can be formed by deforming the outer periphery of the opening 70 (or the sealing plate 60 or the main body 11 of the exterior body 10). Alternatively, the crimping claws 73 can be attached to the outer periphery of the opening 70 by adhesive, welding, or the like. In this embodiment, as shown in FIG. 5 , a flange 74 to which the crimping claws 73 are attached is welded to the outer periphery of the opening 70. As shown in FIG. 5 , the crimping claws 73 are attached in an upright position (approximately perpendicular to the back surface 60b of the sealing plate 60) to position the permeable membrane 80 and the holding frame 90 in the opening 70. The flange 74 becomes thinner toward the tip 73a of the crimping claw 73. In this embodiment, the crimping claws 73 are attached to the back surface 60b of the sealing plate 60 so that the crimping process can be easily performed and the crimping claws 73 are not exposed to the outside. However, this is not limiting, and the crimping claws 73 may be attached to the front surface 60a.

[0034] The number, arrangement, dimensions, shape, etc. of the crimping claws 73 are not particularly limited as long as the effects of the technology of the present disclosure are achieved. Furthermore, the material of the crimping claws 73 may be the same as that of the exterior body 10. The crimping claws 73 may typically be arranged intermittently around the outer periphery of the opening 70. In this embodiment, as shown in FIG. 5 , eight rectangular crimping claws 73 are arranged at regular intervals around the outer periphery of the opening 70. However, the shape of the crimping claws 73 may also be angular with a pointed tip, etc. Furthermore, the length of each crimping claw 73 may differ.

[0035] The holding frame 90 is a frame for holding the permeable membrane 80. The holding frame 90 can hold the permeable membrane 80 by being crimped between the crimping claws 73 and the protruding portion 71. In this embodiment, as shown in FIG. 6, the permeable membrane 80 is sandwiched between the holding frame 90 and the protruding portion 71. The permeable membrane 80 is supported by the crimped holding frame 90. The holding frame 90 may also have a protrusion 71c that protrudes toward the protruding portion 71. The protrusion 71c bites into the permeable membrane 80 when the holding frame 90 is crimped. This improves the sealing performance of the permeable membrane 80. In this embodiment, as shown in FIG. 6, a protrusion 90a is provided on the outer periphery of the holding frame 90, facing the protruding portion 71. The protrusion 90a of the holding frame 90 is located further outward from the center of the opening 70 than the protrusion 71c of the protruding portion 71. In other words, the convex portion 71c of the protruding portion 71 is located more inward of the opening 70 than the convex portion 90a of the holding frame 90. This allows the convex portion 90a of the holding frame 90 and the convex portion 71c of the protruding portion 71 to fit together, further improving the sealing performance of the permeable membrane 80. The positional relationship between the convex portion 90a of the holding frame 90 and the convex portion 71c of the protruding portion 71 is not particularly limited. The convex portion 90a of the holding frame 90 may be located more inward of the opening 70 than the convex portion 71c of the protruding portion 71. Alternatively, the convex portion a of the holding frame 90 and the convex portion 71c of the protruding portion 71 may be formed to face each other, thereby sandwiching the permeable membrane 80. However, as in this embodiment, it is preferable that the convex portion 90a of the holding frame 90 be located more outward from the center of the opening 70 than the convex portion 71c of the protruding portion 71. In this way, when the holding frame 90 is crimped, the permeable membrane 80 is also compressed by the inner wall surface of the opening 70. Therefore, the permeable membrane 80 can be fixed to the opening 70 without being deflected.

[0036] As shown in FIG. 6 , the holding frame 90 includes a frame portion 91 for covering and holding the permeable membrane 80. The holding frame 90 also includes through-holes 92 for passing generated gas. The through-holes 92 are surrounded by the frame portion 91. Gas generated inside the exterior body 10 passes through the through-holes 92 of the holding frame 90 and then permeates the permeable membrane 80. The gas is then discharged to the outside of the exterior body 10 through the ventilation opening 72. The material of the holding frame 90 is not particularly limited. The holding frame 90 may be made of, for example, resin or metal. However, from the standpoint of strength, the holding frame 90 is preferably made of metal. The material of the holding frame 90 may be the same as that of the exterior body 10. The shape of the holding frame 90 is not particularly limited as long as it does not significantly impair the effects of the technology of the present disclosure. In this embodiment, the holding frame 90 is a circular metal ring.

[0037] <Electrolyte> Any conventionally known electrolyte can be used without any particular limitation. In this embodiment, a liquid electrolyte (electrolytic solution) that is liquid at room temperature (25°C) is used. For example, a non-aqueous electrolyte solution prepared by adding a film-forming agent to an appropriate non-aqueous solvent can be used as the electrolyte. Any conventionally known non-aqueous electrolyte can be used without any particular limitation. Examples of non-aqueous solvents include carbonates, ethers, esters, sulfones, and lactones. Among these, carbonates are preferred from the viewpoint of improving the performance of the electricity storage device. Examples of carbonates that can be used include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). These solvents can be used alone or in combination of two or more. Note that this embodiment does not limit the electrolyte of the electricity storage device disclosed herein to an electrolytic solution. The electrolyte may be an electrolytic solution (liquid electrolyte) as described above, a polymer electrolyte in which an electrolytic solution is impregnated into a predetermined polymer and gelled (or soled), or a solid electrolyte in which the electrolyte is entirely solid.

[0038] <Electrode body> The positive electrode 30 and negative electrode 40 of the lithium ion secondary battery 1 according to this embodiment have active material layers 32, 42. FIG. 3 is an exploded view schematically showing the configuration of the wound electrode body 20 according to this embodiment. The positive electrode 30 has a positive electrode current collector foil 31 and a positive electrode active material layer 32. The negative electrode 40 has a negative electrode current collector foil 41 and a negative electrode active material layer 42. Separators 50a, 50b are interposed between the positive electrode 30 and the negative electrode 40.

[0039] In this embodiment, the electrode body is a wound electrode body 20 in which a rectangular positive electrode 30 and a negative electrode 40 are wound with rectangular separators 50a and 50b interposed therebetween. FIG. 2 is an exploded view schematically showing a cell unit constituting the wound electrode body 20, which is one of the embodiments. In the following description, the symbols LR, T, and UD in the drawings represent the width direction, thickness direction, and height direction of the wound electrode body 20. However, these directions are merely for the convenience of explanation and do not limit the installation form of the wound electrode body 20 in any way. Note that the electrode body is not limited to this, and may be a laminated electrode body in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween. Furthermore, the number of electrode bodies is not particularly limited. The exterior body 10 may house multiple electrode bodies (for example, by stacking multiple cell units in the thickness direction).

[0040] <Positive electrode and positive electrode active material layer> As shown in FIG. 3 , the positive electrode 30 includes a rectangular positive electrode current collector foil 31 and a positive electrode active material layer 32 formed on the surface of the positive electrode current collector foil 31. The positive electrode active material layer 32 contains a positive electrode active material that can reversibly store and release charge carriers (here, lithium ions), i.e., release charge carriers during charging and store charge carriers during discharging. The positive electrode active material layer 32 may be formed on one or both sides (here, both sides) of the positive electrode current collector foil 31. As shown in FIGS. 2 and 3 , the positive electrode 30 may have a positive electrode active material layer-free portion 31a where the positive electrode active material layer 32 is not formed and the positive electrode current collector foil 31 is exposed. The positive electrode active material layer-free portion 31a is provided at one end of the wound electrode body 20. In this embodiment, a plurality of positive electrode tabs 31c are provided intermittently at predetermined positions along the longitudinal direction of the positive electrode 30 in the portion 31a where the positive electrode active material layer is not formed. Each of the positive electrode tabs 31c protrudes in the width direction of the wound electrode body 20. The positive electrode tabs 31c are provided at predetermined positions so that they are aligned in the wound state. A positive electrode internal terminal 16 can be joined to the positive electrode tabs 31c. Also, in this embodiment, a positive electrode protective layer 31b is provided on the edge of the positive electrode active material layer 32 on the positive electrode current collector foil 31 (more specifically, on the portion 31a where the positive electrode active material layer is not formed). The positive electrode protective layer 31b is a layer that protects the portion 31a where the positive electrode active material layer is not formed and may be a layer containing an inorganic filler (e.g., alumina, etc.).

[0041] The material of the positive electrode current collector foil 31 is not particularly limited and may be any known positive electrode current collector foil 31 used in an electricity storage device (here, a lithium ion secondary battery). The material of the positive electrode current collector foil 31 is, for example, aluminum or an aluminum alloy. The positive electrode active material of the positive electrode active material layer 32 may be any positive electrode active material used in the positive electrodes of general electricity storage devices. Specifically, the positive electrode active material is a lithium composite metal oxide having a layered rock salt structure, a spinel structure, an olivine structure, or the like. Examples of lithium composite metal oxides include LiCoO2, LiNiO2, LiFeO2, and LiNi x Co y Mn 1-x-y O2(NCM), LiNi 0.5 Mn1.5 O4, LiNi 0.8 Co 0.15 Al 0.05 Examples of the positive electrode active material include LiCrO2 (NCA), LiCrMO4, LiMn2O4, and LiFePO4 (LFP). These positive electrode active materials may be used singly or in combination of two or more. Of these, NCM is preferred as the positive electrode active material from the viewpoint of improving the cycle characteristics of the power storage device. The positive electrode active material layer 32 may contain various additives such as a binder, a conductive additive, an inorganic filler, or a thickener.

[0042] <Negative electrode and negative electrode active material layer> As shown in FIG. 3 , the negative electrode 40 includes a rectangular negative electrode current collector foil 41 and a negative electrode active material layer 42 formed on the surface of the negative electrode current collector foil 41. The negative electrode active material layer 42 contains a negative electrode active material that can reversibly store and release charge carriers (e.g., lithium ions), i.e., that can store charge carriers during charging and release charge carriers during discharging. The negative electrode active material layer 42 may be formed on one or both sides (both sides in this example) of the negative electrode current collector foil 41. As shown in FIGS. 2 and 3 , the negative electrode 40 may have a negative electrode active material layer-free portion 41a where the negative electrode active material layer 42 is not formed and the negative electrode current collector foil 41 is exposed. The negative electrode active material layer-free portion 41a is provided at one end of the wound electrode body 20. In this embodiment, a plurality of negative electrode tabs 41c are provided intermittently at predetermined positions along the longitudinal direction of the negative electrode 40 in the negative electrode active material layer non-forming portion 41a. Each of the plurality of negative electrode tabs 41c protrudes in the width direction of the wound electrode body 20. The plurality of negative electrode tabs 41c are provided at predetermined positions so that they are aligned in a wound state. A negative electrode internal terminal 17 can be joined to the negative electrode tabs 41c.

[0043] The material of the negative electrode current collector foil 41 may be any known negative electrode current collector foil used in electricity storage devices (here, lithium ion secondary batteries), and is not particularly limited. The material of the negative electrode current collector foil 41 is, for example, copper or a copper alloy. The negative electrode active material of the negative electrode active material layer 42 may be any negative electrode active material used in the negative electrodes of general electricity storage devices. Specific examples of the negative electrode active material include carbon materials such as soft carbon (easily graphitizable carbon), amorphous carbon materials, graphite, hard carbon (non-graphitizable carbon), and carbon nanotubes; metal oxide materials such as silicon oxide, titanium oxide, vanadium oxide, and lithium-titanium composite oxide; metal nitride materials such as lithium nitride and lithium-cobalt composite nitride; and silicon compounds. These negative electrode active materials may be used alone or in combination of two or more. Of these, graphite is preferred as the negative electrode active material from the viewpoint of improving energy density. The negative electrode active material layer 42 may contain various additives such as a binder, a conductive additive, an inorganic filler, or a thickener.

[0044] <Separator> The separators 50a and 50b according to this embodiment are insulating porous sheets. However, the shape and dimensions of the separators 50a and 50b are not particularly limited and may be determined appropriately depending on the design of the power storage device. Typically, the separators 50a and 50b insulate the positive electrode 30 and the negative electrode 40, and therefore the dimensions of the separators 50a and 50b are larger than those of the positive electrode 30 and the negative electrode 40. The material of the separators 50a and 50b may be any known separator used in power storage devices and is not particularly limited. For example, resins such as polyolefins (e.g., polyethylene or polypropylene), polyesters, cellulose, or polyamides are preferably used as the material for the separators 50a and 50b. Furthermore, the surfaces of the separators 50a and 50b may be provided with a heat-resistant layer as long as it does not significantly impair the effects of the technology disclosed herein.

[0045] As shown in FIG. 3, the width Ln of the negative electrode active material layer 42 is formed wider than, for example, the width Lp of the positive electrode active material layer 32. The widths Ls of the separators 50a and 50b are formed wider than the negative electrode active material layer 42. That is, as shown in FIG. 3, Lp < Ln < Ls. The positive electrode 30, the first separator 50a, the negative electrode 40, and the second separator 50b are aligned in the length direction and are sequentially stacked and wound. Here, the negative electrode active material layer 42 covers the positive electrode active material layer 32 with the separators 50a and 50b interposed therebetween. The negative electrode active material layer 42 is covered with the separators 50a and 50b. The positive electrode tab 31c of the positive electrode current collector foil 31 and the negative electrode tab 41c of the negative electrode current collector foil 41 are provided so as to protrude from the separators 50a and 50b toward opposite sides in the width direction. The positive electrode protective layer 31b faces the edge of the negative electrode 40 on the side opposite to the side where the negative electrode tab 41c is provided through the separators 50a and 50b. As shown in FIG. 2, the wound electrode body 20 is in a flat state along a plane including the winding axis WL (see FIG. 3) so as to be accommodated in the exterior body 10. Along the winding axis WL, the positive electrode tab 31c is disposed on one side and the negative electrode tab 41c is disposed on the opposite side.

[0046] <Assembly of the permeable membrane (crimping)> In the electricity storage device of the present disclosure, as shown in FIG. 6 , the permeable membrane 80 is fixed by crimping the holding frame 90 between the crimping claws 73 of the opening 70 and the protruding portion 71. The crimping process can be performed by a conventionally known method. In this embodiment, first, as shown in FIG. 7 , the permeable membrane 80 and the holding frame 90 are placed inside the opening 70. The permeable membrane 80 is placed so as to abut against the protruding portion 71 and is sandwiched between the holding frame 90 and the protruding portion 71. As indicated by arrow A in FIG. 7 , the crimping claws 73 formed on the outer periphery of the opening 70 are pressed obliquely toward the center of the opening 70 using a servo press (e.g., Janome Electra Press JP-5004) or the like. This causes the crimping claws 73 to be bent at an angle. In FIG. 8 , the crimping claws 73 are bent partway to show an intermediate stage of the crimping process in this embodiment. Next, as shown in Fig. 8, the holding frame 90 is pushed into the opening 70 by pressing the crimping claws 73 in the direction of arrow B. This causes the holding frame 90 to be crimped to the crimping claws 73 and the protruding portion 71, thereby fixing the permeable membrane 80. Note that the pressing may be done once or multiple times.

[0047] An electricity storage device having the opening 70 as described above can prevent electrolyte leakage during assembly of the permeable membrane 80. In an electricity storage device, gas (e.g., H2 or CO2) may be generated inside the device due to charging and discharging. In such a case, the internal pressure of the electricity storage device increases, causing the exterior (case) of the electricity storage device to expand. This expansion of the electricity storage device may result in a decrease in volumetric energy density and deformation of the exterior. Therefore, a permeable membrane that does not allow liquids to pass through but allows gases to pass through may be attached to the electricity storage device. The permeable membrane discharges gas from the electricity storage device to the outside, thereby suppressing an increase in internal pressure and suppressing expansion of the electricity storage device. Such a permeable membrane is assembled, for example, to the exterior of the electricity storage device. When the permeable membrane is assembled to the exterior by welding or other methods involving heat input, the difference in thermal expansion coefficients between the permeable membrane and the exterior may cause distortion around the joint, resulting in electrolyte leakage. Furthermore, since the permeable membrane is formed in a sheet shape, there is a risk of scratches. Such scratches on the permeable membrane may cause leakage of the electrolyte. Therefore, the inventors have devised a configuration for the opening 70 in which the permeable membrane 80 is placed so as to prevent leakage of the electrolyte when the permeable membrane 80 is assembled.

[0048] The electricity storage device of the present disclosure has a protruding portion 71 that protrudes from the inner wall surface of the opening 70 toward the center of the opening, and multiple crimping claws 73 provided on the outer periphery of the opening 70 so as to face the protruding portion 71. The holding frame 90 and the permeable membrane 80 can be crimped and fixed to the opening 70 using the protruding portion 71 and the multiple crimping claws 73. The crimping claws 73 allow the permeable membrane 80 to be fixed without applying heat during assembly. This prevents distortion from occurring around the permeable membrane 80 and the exterior body 10, thereby suppressing electrolyte leakage. Furthermore, by fitting the holding frame 90, the permeable membrane 80 is pressed against the protruding portion 71. This allows the permeable membrane 80 to be firmly fixed. Furthermore, the opening 70 can be reliably sealed simultaneously with the assembly of the permeable membrane 80. Furthermore, because the permeable membrane 80 is directly fixed to the opening 70, the number of assembly steps can be reduced.

[0049] <Other embodiments> While the preferred embodiments of the present disclosure have been described above with reference to the accompanying drawings, such descriptions are not intended to be limiting and various modifications are possible.

[0050] <Other shapes of the holding frame> In another embodiment of the electricity storage device disclosed herein, the holding frame 90 has beam portions 93 connecting portions of the frame portion 91 (outer peripheral portion) of the holding frame 90. FIGS. 9 and 10 are schematic plan views of the holding frame 90 of one embodiment disclosed herein. As shown in FIGS. 9 and 10, the beam portions 93 divide the through-hole 92 of the holding frame 90 into several sections. The provision of the beam portions 93 improves the strength of the holding frame 90. This makes it possible to suppress deformation of the permeable membrane 80 due to crimping or an increase in internal pressure. Furthermore, as shown in FIG. 10, by providing a protrusion 90a on the frame portion 91 of the holding frame 90, it is possible to suppress adhesion of the beam portions 93 to the permeable membrane 80 when the holding frame 90 is crimped to the opening 70. This prevents gas from being prevented from being discharged from the electricity storage device, and stabilizes the operating pressure of the permeable membrane 80.

[0051] <Arrangement of rivet claws> In another embodiment of the electricity storage device disclosed herein, more crimping claws 73 are provided on the long side walls 11b1 and 11b2 of the exterior body 10 than on the short side walls 11c1 and 11c2. FIG. 11 is a schematic diagram illustrating the back side of the sealing plate 60 of another embodiment of the electricity storage device. FIG. 11 shows a view from the inside of the electricity storage device so that the arrangement of the crimping claws 73 and their positional relationship with the long side wall 11b1 can be seen. In an electricity storage device having a hexahedral box-shaped exterior body 10 as shown in FIG. 11, the long side walls 11b1 and 11b2 are likely to bulge due to an increase in internal pressure. In such a case, since tensile force is likely to be applied to the long side walls 11b1 and 11b2, it is preferable to provide more crimping claws 73 on the long side walls 11b1 and 11b2 than on the short side walls 11c1 and 11c2. This configuration can prevent deformation of the permeable membrane 80. This makes it easier to maintain the sealing of the opening 70, so that when the internal pressure suddenly rises due to, for example, an internal short circuit, the operating pressure of the safety valve can be stabilized without causing the seal of the permeable membrane 80 to break down.

[0052] In the technology disclosed herein, each component and each process described herein may be omitted or combined as appropriate, unless a particular problem arises. This specification also includes the disclosures described in the following sections.

[0053] Item 1: An electricity storage device comprising an electrode assembly, an electrolyte, and an exterior body that accommodates the electrode assembly and the electrolyte, One surface of the exterior body has an opening and a permeable membrane that does not allow liquid placed in the opening to pass through but allows gas to pass through, a protruding portion protruding from an inner wall surface of the opening toward the center of the opening; a plurality of crimping claws provided on the outer periphery of the opening so as to face the protruding portion; a holding frame that holds the permeable membrane, Here, the permeable membrane is disposed in the opening by the holding frame being held in a crimped state between the plurality of crimping claws and the protruding portion.

[0054] Item 2: The protruding portion has a convex portion on a surface facing the crimping claw, Here, the permeable membrane is arranged so that the convex portions bite into the permeable membrane by crimping the holding frame between the plurality of crimping claws and the protruding portions.

[0055] Item 3: A convex portion is provided on the outer peripheral portion of the holding frame so as to face the protruding portion, Item 3. The electricity storage device according to item 2, wherein the convex portion of the holding frame is located further from the center of the opening toward the outer periphery than the convex portion of the protruding portion.

[0056] Item 4: The exterior body has a box shape, 4. The power storage device according to claim 1, wherein the number of said crimping claws provided on said long side wall of said exterior body is greater than the number of said crimping claws provided on said short side wall of said exterior body.

[0057] Item 5: The electricity storage device according to any one of items 1 to 4, wherein the holding frame has beam portions connecting parts of the outer periphery of the holding frame.

[0058] Item 6: The electricity storage device according to any one of items 1 to 5, wherein the opening is provided on an upper surface of the exterior body when the electricity storage device is installed. [Explanation of symbols]

[0059] 1. Lithium-ion secondary battery 10. Exterior body 11 Main unit 11a Bottom wall 11b1, 11b2 long side wall 11c1, 11c2 Short side wall 14 Positive external terminal 15 Negative external terminal 16 Positive internal terminal 17 Negative internal terminal 18 Gasket 19 Insulator 20 Electrode body 30 positive electrode 31 Positive electrode current collector foil 31a Portion where positive electrode active material layer is not formed 31b Positive electrode protective layer 31c Positive electrode tab 32 Positive electrode active material layer 40 negative electrode 41 Negative electrode current collecting foil 41a Part where negative electrode active material layer is not formed 41c Negative electrode tab 42 Negative electrode active material layer 50a, 50b Separator 60 Sealing plate 60a Surface of sealing plate 60b Back side of sealing plate 61 Safety valve 62 Liquid injection hole 70 Opening 71 Overhang 71a Surface of the protruding part 71b Back side of protruding part 71c Convex part of the protruding part 72 Ventilation hole 73 Crimping Claw 73a Tip of rivet claw 74 flange 80 Permeable membrane 90 Retaining frame 90a Protrusion of the holding frame 91 Frame 92 Through hole 93 Beam section A arrow (diagonal) B Arrow (vertical)

Claims

1. An electricity storage device comprising an electrode assembly, an electrolyte, and an exterior body that accommodates the electrode assembly and the electrolyte, One surface of the exterior body has an opening and a permeable membrane disposed in the opening that does not allow liquid to pass through but allows gas to pass through, a protruding portion protruding from an inner wall surface of the opening toward the center of the opening; a plurality of crimping claws provided on the outer periphery of the opening so as to face the protruding portion; a holding frame that holds the permeable membrane, Here, the permeable membrane is disposed in the opening by the holding frame being held in a crimped state between the plurality of crimping claws and the protruding portion.

2. The protruding portion has a convex portion on a surface facing the crimping claw, The power storage device according to claim 1 , wherein the permeable membrane is arranged such that the convex portions bite into the permeable membrane by crimping the holding frame between the plurality of crimping claws and the protruding portions.

3. a convex portion is provided on the outer peripheral edge of the holding frame so as to face the protruding portion, The electricity storage device according to claim 2 , wherein the convex portion of the holding frame is located further outward from the center of the opening than the convex portion of the protruding portion.

4. The exterior body has a box-like shape, The power storage device according to claim 1 , wherein the number of the crimping claws provided on the long side wall of the exterior body is greater than the number of the crimping claws provided on the short side wall of the exterior body.

5. The power storage device according to claim 1 , wherein the holding frame has beam portions connecting parts of an outer peripheral portion of the holding frame.

6. The electricity storage device according to claim 1 , wherein the opening is provided on an upper surface of the exterior body when the electricity storage device is installed.

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