Pressurizing bag for secondary batteries

Abstract

To provide a pressurizing bag for secondary batteries capable of improving uniformity of pressurization.SOLUTION: A pressurizing bag 1 for secondary batteries is formed in a rectangular shape and a thin plate shape in a front view. The pressurizing bag 1 for secondary batteries is a bag in which air-tight and flexible sheet materials 11 and 12 are overlapped and peripheral edges of both the sheet materials are joined. In at least one side of sides where both the sheet materials 11 and 12 are joined, a boundary E between a junction region GR in which both the sheet materials are joined and a bag portion BR which becomes a hollow bag by separating both the sheet materials is made linear in parallel with an outer peripheral edge SE of the sheet material in a central portion (CE) of the one side, and in at least one of terminals (EE) of the one side, the boundary is made closer to the outer peripheral edge SE of the sheet material toward the terminal of the one side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a pressure bag for use with a secondary battery, that is, a pressure bag for a secondary battery. [Background technology]

[0002] Secondary batteries, which can be charged and discharged, are used in a variety of applications, including electric vehicles, home appliances, and mobile phones. A typical secondary battery consists of an electrode assembly in which a positive electrode and a negative electrode are stacked and wound with a separator between them, and the assembly is sealed in a container together with an electrolyte. For applications such as automobiles, it is common to electrically connect multiple such secondary batteries and use them as an integrated battery pack.

[0003] Secondary batteries are also pressurized using a pressure bag. If the secondary battery contains an electrolyte, the secondary battery is also pressurized using a pressure bag to remove the air from the secondary battery package and fill it with the electrolyte without any gaps. If the secondary battery is a so-called all-solid-state battery, the secondary battery is used in a pressurized environment using a pressure bag or the like to increase the adhesion between the solid electrolyte and the electrode body and prevent the formation of crystalline precipitates.

[0004] For example, Patent Document 1 discloses a technique in which a plurality of battery cells are stacked at equal intervals, spacers (pressure bags) that can be expanded by air pressure are arranged, and the spacers pressurize the battery cells in the thickness direction. Furthermore, for example, Patent Document 2 discloses a technology in which, in a battery module in which secondary batteries are stacked, a pressure adjustment member 60 (pressurized bag) having a liquid holding section and a liquid storage section is placed between the secondary batteries or at the end of the stacked secondary batteries, and it is disclosed that this technology allows the restraining pressure applied to the secondary batteries to be suitably controlled, thereby suppressing deterioration of battery performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. WO2015-141631 [Patent Document 2] Japanese Patent Application Publication No. 2019-128980 Summary of the Invention [Problem to be solved by the invention]

[0006] In technologies for pressurizing these secondary batteries, a pressure bag may be used, which is a flat bag made by overlapping flexible sheet materials and joining the periphery. Typically, a pressure bag such as a pouch bag made by overlapping laminate films is used. Such pressure bags can be made thin, which can contribute to the compactness of battery packs and the like.

[0007] However, the inventors have discovered that when such a pouch bag is used as a pressurized bag for a secondary battery, it is difficult to apply pressure uniformly. According to the inventors' investigation, when a pouch bag that is rectangular in front view is used as a pressurized bag, the pressure tends to be insufficient near the corners of the rectangle.

[0008] An object of the present invention is to provide a pressure bag for a secondary battery that can improve the uniformity of pressure application. [Means for solving the problem]

[0009] After careful consideration, the inventor discovered that in a rectangular bag made by overlapping flexible sheet material and joining the edges, if the shape of the joints at the corners of the rectangle is devised, the shape of the expanding bag will change, thereby improving the uniformity of pressure application, and thus completed the present invention.

[0010] The present invention is a pressure bag for a secondary battery that is rectangular and thin when viewed from the front, and is made by overlapping airtight and flexible sheet materials and joining the peripheral edges of both sheet materials, and on at least one of the sides where the two sheet materials are joined, the boundary between the joined area where the two sheet materials are joined and the bag part where the two sheet materials are separated to form a hollow bag is in a straight line parallel to the outer edge of the sheet material at the center of the one side, and at least one of the ends of the one side, the boundary approaches the outer edge of the sheet material as it moves towards the end of the one side (first invention).

[0011] In the first invention, preferably, the boundary is linear at least at one end of the one side, and the angle between the boundary at the end and the boundary at the center of the one side is between 20 degrees and 45 degrees (invention 2). Also, in the first invention, preferably, the pressurized bag is made by folding a single sheet material and joining its peripheral edges, and the one side is a side adjacent to the folded edge of the sheet material, and at the end of the folded edge side of the one side, the boundary approaches the outer peripheral edge of the sheet material as it moves toward the folded edge (invention 3).

[0012] The present invention also provides a battery pack comprising a plurality of stacked flat secondary batteries, wherein a pressurizing bag for a secondary battery according to any one of the first to third inventions is stacked between adjacent secondary batteries (fourth invention).The present invention also provides a battery pack comprising a plurality of stacked flat secondary batteries, wherein a pressurizing bag for a secondary battery according to any one of the first to third inventions is stacked on at least one end surface of the assembly of stacked secondary batteries (fifth invention). [Effects of the Invention]

[0013] According to the pressurizing bag for a secondary battery of the present invention (first invention), the uniformity of pressurization is improved. When the second invention is used, the uniformity of pressurization is particularly improved. Furthermore, when the third invention is used, the uniformity of pressurization is improved even at the corners of the folded edge. Furthermore, in the battery packs of the fourth and fifth aspects of the invention, the secondary batteries, including their peripheral edges, are pressurized uniformly, thereby suppressing deterioration of battery performance. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing the structure of a battery pack incorporating a pressurizing bag for a secondary battery according to a first embodiment. [Figure 2] 1A and 1B are a front view and a cross-sectional view showing the structure of a pressurizing bag for a secondary battery according to a first embodiment. [Figure 3] 3 is an enlarged view of a joining region of the pressurizing bag for a secondary battery according to the first embodiment. FIG. [Figure 4] 10A and 10B are perspective views showing examples of shapes of penetrating members integrated into a pressurizing bag for a secondary battery. [Figure 5] 3 is a perspective view showing a deformation state in the vicinity of the joining region when the pressurizing bag for a secondary battery of the first embodiment is expanded. FIG. [Figure 6] 3 is a perspective view showing a deformation state in the vicinity of the joining region when the pressurizing bag for a secondary battery of the first embodiment is expanded. FIG. [Figure 7] 3 is a cross-sectional view showing a deformation state in the vicinity of a joining region when the pressurizing bag for a secondary battery of the first embodiment is expanded. FIG. [Figure 8] FIG. 1 is a front view showing the structure of a conventional pressure bag for a secondary battery. [Figure 9] 1 is a cross-sectional view showing a state of deformation near the joint area when a conventional pressurizing bag for a secondary battery is expanded. [Figure 10] 5 is a schematic diagram showing another structure of a battery pack incorporating the pressurizing bag for a secondary battery of the first embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, with reference to the drawings, an embodiment of the present invention will be described using as an example a pressurizing bag for a secondary battery that is stacked together with secondary batteries stacked together in a battery pack installed in an electric vehicle or a hybrid vehicle. The present invention is not limited to the individual embodiments shown below, and can be implemented by modifying the form.

[0016] FIG. 1 is a schematic diagram showing the structure of a battery pack 8 incorporating a pressurized bag 1 for a secondary battery according to the first embodiment. The secondary battery 81 is flat. A plurality of flat secondary batteries 81, 81 are stacked to form the battery pack 8. The secondary batteries 81, 81 are electrically connected to each other by bus bars (not shown) or the like to function as a battery pack (battery module). The secondary battery is not particularly limited, but is typically a lithium ion battery, and in particular an all-solid-state battery.

[0017] In the battery pack 8 of this embodiment, the pressurizing bags 1 are stacked between adjacent secondary batteries 81, 81. That is, in the battery pack 8 of this embodiment, the secondary batteries 81 and the pressurizing bags 1 are stacked alternately. In FIG. 1, the flat secondary batteries 81 and the pressurizing bags 1 are stacked so as to extend in the depth direction of the page. Furthermore, in the battery pack 8, end plates 85, 85 are provided to sandwich and tighten the stacked secondary batteries and pressure bags from both sides. The distance between the end plates is determined by tightening members or the like, and when pressure is applied to the pressure bags 1, 1, the plate-like secondary batteries 81, 81 are also compressed.

[0018] 1, the pressure bags 1, 1 are pressurized by feeding pressurized fluid pressurized to a predetermined pressure P into the pressure bags through injection paths provided in the pressure bags 1, 1 via a piping manifold 86 or the like. If the pressure bags are closed pressure bags without an injection path for the pressurized fluid, the pressure bags can be pressurized by sealing the fluid in them in advance and tightening the end plates 85, 85 to tighten the pressure bags.

[0019] 2 is a front view and a cross-sectional view showing the structure of a pressurizing bag for a secondary battery (also simply referred to as a "pressurizing bag") 1 of the first embodiment. The cross-sectional view shows the bag in a slightly expanded state, with the sheet material separated at the center of the bag. The pressurizing bag 1 is a thin, rectangular plate when viewed from the front. The shape of the pressurizing bag 1 corresponds to the shape of the secondary battery 81 to be combined with it, and typically, the shape of the pressurizing bag 1 is determined so that the flat-plate-shaped secondary battery 81 fits into the bulging portion (bag portion BR) of the pressurizing bag 1 when viewed from the front (the left side of FIG. 1).

[0020] The pressurized bag 1 is a bag formed by overlapping airtight and flexible sheet materials 11 and 12 and joining the peripheral edges of both sheet materials. Sheet material 11 is located on the front side of the bag, and sheet material 12 is located on the back side of the bag. Sheet materials 11 and 12 are joined in a sealed state so that a fluid can be sealed in the pressurized bag. The area where sheet materials 11 and 12 are joined to each other is called the joining area GR. On the other hand, when a fluid is injected into the pressurized bag, the sheet materials separate to form a hollow bag, and the part where the bag expands is called the bag portion BR.

[0021] The airtight and flexible sheet materials 11 and 12 constituting the pressurized bag 1 are not particularly limited, but any sheet material that can withstand the pressure applied to the bag, has airtightness or liquid-tightness sufficient to prevent the passage of pressurized fluids such as gases or liquids, and has appropriate stretchability and flexibility can be used. Preferred examples include a laminate film in which aluminum foil is coated and laminated with a thermoplastic resin (preferably, but not necessarily, polypropylene (PP) resin or polyethylene terephthalate (PET) resin), a rubber sheet, or a thermoplastic elastomer sheet. The sheet materials 11 and 12 may be made of a resin composition containing reinforcing fibers. Furthermore, the sheet materials 11 and 12 may also be sheet materials that include a reinforcing layer containing reinforcing fibers, reinforcing yarns, reinforcing cloth, nonwoven fabric, or the like.

[0022] There are no particular limitations on the specific form in which sheet materials 11 and 12 are arranged on the front and back sides of pressurized bag 1. Two independent sheet materials may be prepared and overlapped to form sheet materials 11 and 12. Alternatively, as in the pressurized bag 1 of the embodiment shown in FIG. 2, one sheet material may be folded in half and overlapped to form sheet materials 11 and 12. Alternatively, sheet materials may be formed into a cylindrical shape in advance, and the cylinder may be flattened and overlapped to form sheet materials 11 and 12.

[0023] The sheet materials 11 and 12 are joined together so that the rectangular pressurized bag 1 is closed all around. The joining can be performed by various methods depending on the material of the sheet materials. The joining may be performed by adhesion using an adhesive, cross-linking adhesion using cross-linking of rubber or the like, or by welding if the sheet material is a sheet material in which a thermoplastic resin is laminated on the surface of the sheet material. Examples of welding methods include so-called hot plate welding, ultrasonic welding, high-frequency welding, laser welding, and infrared welding.

[0024] Although not required, the pressurized bag 1 may be provided with a penetrating member 14. The penetrating member 14 may be provided with a through hole that allows pressurized fluid to pass in and out of the bag. The specific form of the penetrating member 14 is not particularly limited, but in this embodiment, as shown in FIG. 4, a penetrating member 14 having a joint 14a and a nipple 14b is used. The joint 14a is sandwiched between flexible sheet materials 11 and 12 in the joint region GR of the pressurized bag 1, and the joint 14a and the flexible sheet materials 11 and 12 are joined together to seal the joint. A pipe that supplies pressurized fluid can be connected to the nipple 14b, and the pressurized bag 1 can be pressurized through the through hole.

[0025] The boundary E (EE, CE) between the joining region GR and the bag portion BR in the pressurized bag 1 of this embodiment will be described in more detail. As shown in Figure 3, in the joining region GR of the top side, the boundary E (CE) is a straight line parallel to the outer edge SE of the sheet material at the center of the side. In this portion, the width of the joining region is constant. Here, the side refers to the side when the pressurized bag is viewed as a rectangle. Furthermore, the width of the joining region refers to the distance between the outer edge SE and the boundary E on each side, and in the joining region GR of the top side shown in Figure 3, this is the distance measured in the vertical direction of the figure. In Figure 3, the boundary at the center of the side is shown as boundary CE.

[0026] Furthermore, at least one of the ends of the side, the boundary E approaches the outer peripheral edge SE of the sheet material (the outer peripheral edge on the upper side in the figure) as it approaches the end of the side. In other words, at the end of the side, the width of the joining region GR narrows as it approaches the end of the side. In Figure 3, the boundary at the end of the side is shown as boundary EE.

[0027] Although not essential, preferably, as in this embodiment, the boundary EE at the end of the side is linear at at least one of the ends of the side, and the angle formed between the boundary EE at the end and the boundary CE at the center of the side is between 20 degrees and 45 degrees. Also, in this embodiment, the boundary EE at the end of the side is linear, but this is not essential, and the boundary CE at the center of the side and the boundary EE at the end of the side may have a shape such that a rounded radius is formed between them.

[0028] 2 and 3, the right side of the rectangular pressurized bag 1 is the folded edge B, and the remaining three sides are the joining region GR. In the pressurized bag 1 of this embodiment, in all of the joining regions GR on the three sides, the boundary E between the joining region GR and the bag portion BR has a portion EE that approaches the outer edge SE of the sheet material toward the end of the side. The boundary E at all ends of all sides does not have to be such a boundary EE; as long as the boundary E at at least one end of at least one side has the above-mentioned shape, the uniformity of pressure in that portion will be improved.

[0029] Furthermore, although not essential, preferably, when one side of the rectangular pressurized bag 1 is formed as a folded edge B, as in this embodiment, the pressurized bag 1 is configured so that, in the joining region GR of the side adjacent to the folded edge B, the boundary EE at the end of the side on the folded edge B side approaches the outer peripheral edge of the sheet material as it moves toward the folded edge B.

[0030] Furthermore, in the case of a pressurized bag 1 in which a single sheet material is folded and the peripheral edges are joined, and two opposing sides of the rectangular pressurized bag 1 are folded edges B, it is preferable, although not essential, that in the joining region GR of the side adjacent to the folded edge B, the boundary EE at both ends of the side approaches the outer peripheral edge of the sheet material as it moves toward the folded edge B.

[0031] The above-described pressurized bag for a secondary battery can be manufactured by a known manufacturing technique. Specifically, flexible sheet materials 11 and 12 are prepared, stacked, and then the penetrating member 14 is appropriately positioned between the peripheral edges of the sheets 11 and 12, and the peripheral edges of the sheets 11 and 12 are joined by adhesive, welding, or other means. The shape of the boundary E (boundary CE, boundary EE) between the joining region GR and the bag portion BR can be formed by adjusting the adhesive application area or the shape of the heat and pressure head used for welding.

[0032] The secondary battery 81 will now be described in more detail. The secondary battery 81 is configured by sealing an electrode body together with an electrolyte in a container. The electrode body is a single power generation unit. Usually, one electrode body is housed in a container, but multiple electrode bodies may be housed in a container. In contrast to the battery pack 8, the secondary battery 81 is sometimes called a single cell, battery element, battery cell, etc. The shape of the secondary battery 81 is not particularly limited, but is typically flat. A flat-plate-shaped secondary battery 81 is sometimes called a prismatic battery.

[0033] Known materials can be used as appropriate for the electrode body, electrolyte, and container that make up the secondary battery 81. These components can be assembled into the secondary battery 81 by known methods. Secondary batteries in which the electrolyte is solid are called all-solid-state batteries, etc. In all-solid-state batteries, pressure is applied in the thickness direction of the electrode body and battery to improve contact between the electrolyte and the electrode body.

[0034] The electrode assembly includes a positive electrode, a negative electrode, and, if necessary, a separator. The positive electrode, separator, and negative electrode are in sheet form. The positive electrode and negative electrode are stacked with the separator sandwiched between them, and if necessary, wound in this stacked state to form the electrode assembly. In this embodiment, the electrode assembly is flat (plate-shaped). If the electrolyte is solid, the solid electrolyte is sandwiched between the positive electrode and the negative electrode.

[0035] The positive electrode, negative electrode, separator, and solid electrolyte may be any known material. The positive electrode is conductive and includes a positive electrode active material (e.g., a lithium transition metal composite oxide). The negative electrode is conductive and includes a negative electrode active material (e.g., graphite). The separator may be, for example, a porous resin film.

[0036] The electrolyte can also be appropriately selected from known electrolytes. The electrolyte may be a non-aqueous electrolytic solution containing a non-aqueous solvent (e.g., ethylene carbonate) and an electrolyte salt (e.g., an inorganic lithium salt). The solid electrolyte may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0037] The container of the secondary battery is not particularly limited as long as it can seal the electrode body and the electrolyte in. The container may be made of resin, metal, or a laminate film.

[0038] The operation and effect of the pressurizing bag 1 for a secondary battery according to the above embodiment will be described. According to the pressurizing bag 1, the uniformity of the pressurization is improved.

[0039] Figure 8 shows a prior art pressure bag 9. In the prior art pressure bag 9, the boundary E between the joining region GR and the bag portion BR is a straight line parallel to the outer edge SE of the pressure bag 9. In other words, the boundary is not designed to approach the outer edge SE as it approaches the end of the side. In the prior art pressure bag 9, deformation of the bag due to pressure tends to result in insufficient expansion near the corners of the rectangular pressure bag. This is because deformation of the bag portion BR in these areas is restricted by the joining region GR and folded edges B on the two sides surrounding the corner.

[0040] As a result, when conventional pressure bag 9 is pressurized with pressure P, as shown in Figure 9, areas (areas indicated by white arrows in Figure 9) where the bag is likely to expand insufficiently are created near the corners of the rectangular pressure bag, and in those areas, adjacent secondary batteries 81, 81 are not pressurized sufficiently. If there are areas where the battery is not pressurized sufficiently, battery deterioration is likely to begin from those areas, which is undesirable.

[0041] On the other hand, in the pressurized bag 1 for a secondary battery according to the above embodiment, the boundary E between the joining region GR and the bag portion BR is configured such that the boundary CE at the center of the side is a straight line parallel to the outer edge SE of the sheet material, and the boundary EE at the end of the side approaches the outer edge of the sheet material toward the end of the side, which changes the shape of the expanding bag portion BR. That is, the boundary EE is provided so that it approaches the outer edge of the sheet material toward the end of the side, and the bag portion BR is configured to be wedged toward the joining region GR, so that this portion deforms into a "gusset" shape, and the bag portion BR is more likely to expand in the thickness direction of the sheet material.

[0042] Figure 5 shows a schematic diagram of the deformation of the pressure bag 1 at the corner between the folded edge B and the joining area GR. As the edge of the side approaches the outer edge of the sheet material, the boundary EE is folded into a triangular shape, and the pressure bag 1 expands up to the corner. 6 shows a schematic diagram of the deformation of the pressure bag 1 at the corner between the two joining regions GR, GR. Similarly, the portion where the boundary EE was provided so as to approach the outer edge of the sheet material toward the end of the side is folded into a triangular shape, and the pressure bag 1 expands up to the corner.

[0043] In this way, in the pressurization bag 1 for secondary batteries of the above embodiment, when pressurized with pressure P, the bag expands sufficiently even near the corners of the rectangular pressurization bag, and therefore, as shown in Fig. 7, the area where the expansion of the bag is likely to be insufficient (the area indicated by the white arrow in Fig. 7) is reduced, and the appearance of an area where the pressurization of the battery 81 is insufficient is suppressed. This improves the uniformity of the pressurization, and prevents and suppresses deterioration of battery performance due to partial insufficient pressurization.

[0044] Preferably, the boundary EE is linear at at least one end of the one side, and the angle formed by the boundary EE at the end and the boundary CE at the center of the one side is between 20 degrees and 45 degrees, thereby ensuring the formation of a "gusset" portion as shown in Figures 5 and 6, and further improving the uniformity of pressurization. Furthermore, although not essential, in order to form a "gusset," it is preferable that the length of the boundary EE portion be 0.5 to 2 times the thickness of the pressure bag 1 when inflated (i.e., the size of the gap between the secondary batteries).

[0045] Preferably, the pressurized bag 1 is made by folding a single sheet material and joining the peripheral edges, and at the edge adjacent to the folded edge B of the sheet material, the boundary EE at the end of the edge on the folded edge B side is configured to approach the outer peripheral edge of the sheet material as it moves toward the folded edge B, thereby creating a larger ``gusset'' portion as shown in Figures 5 and 6, reducing the area in the pressurized bag where expansion is insufficient and further improving the uniformity of pressurization.

[0046] Furthermore, if the pressurizing bag 1 for secondary batteries of the above embodiment is incorporated into the battery pack, the corners of the rectangular flat batteries are more likely to be pressurized uniformly, thereby suppressing deterioration of the battery pack.

[0047] The invention is not limited to the above-described embodiment, and various modifications can be made to the invention. Other embodiments of the invention will be described below, focusing on differences from the above-described embodiment, and detailed descriptions of similarities will be omitted. Furthermore, these embodiments can be implemented by combining parts of them with each other or by substituting parts of them.

[0048] In the above embodiment, an example has been shown in which the pressurizing bag 1 for secondary batteries is stacked together with an all-solid-state battery to form a battery pack, but the type of secondary battery is not limited to an all-solid-state battery, and the secondary battery may be a secondary battery using an electrolytic solution as long as it requires pressurization.

[0049] Furthermore, when the pressure bag 1 is used in an all-solid-state battery, pressure is usually applied when the battery is in use (during charging and discharging), but the timing and purpose of pressure application are not limited to this. For example, even when the pressure bag 1 for secondary batteries of the above embodiment is used in a manufacturing process for secondary batteries or battery packs that uses an electrolyte solution as in Patent Document 1, the pressure bag 1 for secondary batteries improves the uniformity of pressure application, thereby improving the quality of the manufactured secondary batteries or battery packs.

[0050] 10 shows another example of a battery pack using the pressurizing bag 1 for secondary batteries of the above embodiment, in which secondary batteries 81, 81 are stacked adjacent to each other to form a roughly rectangular parallelepiped battery assembly, and the pressurizing bag 1 is stacked at the end of the assembly of stacked secondary batteries 81, 81. In FIG. 10, the flat plate-shaped secondary batteries 81 and the pressurizing bag 1 are stacked so as to extend in the depth direction of the page. Furthermore, in this battery pack, end plates 85, 85 are provided to sandwich and tighten the stacked secondary batteries and pressure bag from both sides. The distance between the end plates is determined by tightening members or the like, and when pressure is applied to the pressure bag 1, the plate-like secondary batteries 81, 81 are also compressed. Even in such a battery pack, the secondary battery pressure bag 1 of the above embodiment improves the uniformity of the pressure applied to the batteries.

[0051] In the explanation of the battery pack above, the use form in which the pressurized bag 1 for secondary batteries of the above embodiment is stacked together with secondary batteries has been mainly explained, but the pressurized bag 1 for secondary batteries can also be used as a container for secondary batteries that require pressurization, i.e., an outer casing that houses the electrode body. [Industrial Applicability]

[0052] The pressurized bag 1 for secondary batteries can be used in, for example, assembled batteries, and is highly useful in industry. [Explanation of symbols]

[0053] 1. Pressurized bag for secondary batteries 11, 12 Sheet material GR junction area BR bag part B Broken edge E, CE, EE boundary SE outer edge 14 Penetrating member 8 battery packs 81 Secondary battery (battery cell) 85 End Plate 86 Piping manifold

Claims

1. A pressurizing bag for a secondary battery that is rectangular and thin-plate-shaped when viewed from the front, The pressurized bag is a bag made by overlapping airtight and flexible sheet materials and joining the peripheral edges of both sheet materials. At least one of the edges where the two sheet materials are joined is The boundary between the joined area where the two sheet materials are joined and the bag portion where the two sheet materials are separated to form a hollow bag is The center of the one side is formed into a straight line parallel to the outer periphery of the sheet material, At least one of the ends of the one side, the boundary approaches the outer periphery of the sheet material as it moves toward the end of the one side. Pressurized bag for secondary batteries.

2. the boundary is linear at least at one end of the one side, the angle formed by the boundary at the end and the boundary at the center of the one side is 20 degrees or more and 45 degrees or less; The pressure bag for a secondary battery according to claim 1 .

3. A pressurized bag in which a single sheet material is folded and the peripheral edges are joined, the one side is a side adjacent to the folded edge of the sheet material, At the end of the folded edge of the one side, the boundary approaches the outer circumferential edge of the sheet material as it moves toward the folded edge. The pressure bag for a secondary battery according to claim 1 .

4. A battery pack in which a plurality of flat secondary batteries are stacked, The pressure bag for a secondary battery according to any one of claims 1 to 3 is stacked and disposed between adjacent secondary batteries. Battery pack.

5. A battery pack in which a plurality of flat secondary batteries are stacked, a pressure bag for a secondary battery according to any one of claims 1 to 3 stacked and disposed on at least one end surface of an assembly of stacked secondary batteries; Battery pack.

Images