Battery pack

Abstract

Provided is a battery pack capable of preventing a chain of thermal runaway caused by a high-temperature gas generated from an abnormal battery cell during thermal runaway. This battery pack comprises a module that has a plurality of battery cells each provided with a safety valve, a case that accommodates the module, and a heat insulating material that is provided between the module and the case, the battery pack being characterized in that: the heat insulating material includes a first heat insulating sheet, and a second heat insulating sheet laminated on the first heat insulating sheet; the heat insulating material is disposed such that the first heat insulating sheet is positioned on the module side and the second heat insulating sheet is positioned on the case side; a plurality of openings penetrating the second heat insulating sheet are formed in the second heat insulating sheet; the plurality of openings each have a covering piece that covers at least a portion of the opening; the covering pieces are bonded to the first heat insulating sheet and / or the second heat insulating sheet by an adhesive layer; and when the second heat insulating sheet is seen in a perspective plan view, one of the openings is positioned so as to overlap at least a portion of one of the safety valves.

Description

Battery pack

[0001] The present invention relates to a battery pack.

[0002] In battery packs, which consist of modules containing multiple battery cells housed in a case, high-temperature gases and flames can be generated during thermal runaway. These gases and flames can spread to the surrounding area and potentially trigger further thermal runaway. To prevent a chain reaction of thermal runaway, a safety valve has traditionally been installed in the module to release the high-temperature gases generated during thermal runaway.

[0003] Furthermore, if the high-temperature gas released from the safety valve hits the case directly, the temperature of the case will rise, which may cause thermal damage to the area around the battery pack.To prevent this, it has been common practice to place a heat insulating material between the module and the case.

[0004] As such a battery pack, Patent Document 1 discloses a storage device comprising: a storage stack including a plurality of storage cells, each having an exhaust valve on its upper surface; an upper case covering the storage stack from above; and first and second heat-resistant sheets that are heat-resistant to exhaust gases discharged from the exhaust valves and are arranged between the upper case and the storage stack, wherein the first heat-resistant sheet has a plurality of holes formed in positions that overlap each of the exhaust valves in the vertical direction, and the second heat-resistant sheet is arranged above the first heat-resistant sheet so as to cover the plurality of holes.

[0005] JP 2023-59480 A

[0006] In the energy storage device (battery pack) described in Patent Document 1, during thermal runaway, high-temperature gas discharged from the exhaust valve of the abnormal battery cell passes through the hole in the first heat-resistant sheet and blows up onto the second heat-resistant sheet, pushing the second heat-resistant sheet upward and away from the first heat-resistant sheet, forming a gas flow path between the first and second heat-resistant sheets. Because the second heat-resistant sheet blocks the gas, it does not blow into the upper case, preventing damage to the upper case. Furthermore, the first heat-resistant sheet prevents the gas blocked by the second heat-resistant sheet from coming into contact with adjacent cells, preventing the temperature of the adjacent cells from rising.

[0007] However, in the energy storage device (battery pack) described in Patent Document 1, the high-temperature gas is blocked by the second heat-resistant sheet, which can cause the high-temperature gas to flow back through other holes in the first heat-resistant sheet and out the exhaust valve of a normal cell adjacent to the abnormal battery cell. If the high-temperature gas flows back, the normal cell may experience thermal runaway. In other words, the energy storage device (battery pack) described in Patent Document 1 has the problem of being unable to adequately prevent a chain reaction of thermal runaway.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide a battery pack that can prevent a chain reaction of thermal runaway caused by high-temperature gas from an abnormal battery cell that occurs during thermal runaway.

[0009] The battery pack of the present invention is a battery pack comprising a module having a plurality of battery cells, each having a safety valve, a case for accommodating the module, and an insulating material provided between the module and the case, wherein the insulating material includes a first insulating sheet and a second insulating sheet laminated on the first insulating sheet, the insulating material is arranged so that the first insulating sheet is located on the module side and the second insulating sheet is located on the case side, the second insulating sheet has a plurality of openings formed therethrough, each of the plurality of openings has a covering piece disposed therein that covers at least a portion of the opening, the covering piece is adhered to the first insulating sheet and / or the second insulating sheet by an adhesive layer, and when the second insulating sheet is viewed from above, one of the openings is positioned so as to overlap at least a portion of one of the safety valves.

[0010] The battery pack of the present invention can prevent a chain reaction of thermal runaway caused by high-temperature gas from an abnormal battery cell during thermal runaway. The principle behind this is explained below.

[0011] In the battery pack of the present invention, the module is provided with a safety valve. Therefore, when a battery cell experiences thermal runaway and generates high-temperature gas, the gas is released from the safety valve and reaches the insulating material.

[0012] The thermal insulation material includes a first thermal insulation sheet and a second thermal insulation sheet laminated on the first thermal insulation sheet. The thermal insulation material is arranged so that the first thermal insulation sheet is located on the module side and the second thermal insulation sheet is located on the case side. Therefore, gas that reaches the thermal insulation material first comes into contact with the first thermal insulation sheet. The gas passes through passages formed by melting the first thermal insulation sheet and gaps formed in the first thermal insulation sheet.

[0013] The second insulating sheet has an opening formed therethrough, and the opening is positioned so as to overlap at least a portion of the safety valve when viewed from above, so that gas passing through the first insulating sheet reaches the vicinity of the opening in the second insulating sheet.

[0014] A covering piece is placed in the opening, covering at least a portion of the opening, and the covering piece is adhered to the first insulating sheet and / or the second insulating sheet by an adhesive layer. The high temperature of the gas that reaches the vicinity of the opening of the second insulating sheet causes thermal decomposition of the adhesive layer that adheres the covering piece. This weakens the adhesion between the covering piece and the first insulating sheet and / or the second insulating sheet. Furthermore, gas pressure is applied to the covering piece from the module side toward the case side. As a result, the covering piece peels off from the first insulating sheet and / or the second insulating sheet.

[0015] The gas that passes through the first insulating sheet then passes through the opening in the second insulating sheet and is released between the insulating material and the case. In this case, the high-temperature gas cools down as it passes through the first insulating sheet, and the gas pressure also drops. Therefore, even if the gas is released from the opening and comes into contact with the case, the case is unlikely to heat up or be damaged by the gas.

[0016] Furthermore, gas released from the opening in the second insulating sheet diffuses between the thermal insulation material and the case and reaches the other opening in the second insulating sheet. However, because a covering piece is placed inside the other opening in the second insulating sheet, even if the gas reaches the other opening in the second insulating sheet, it is possible to prevent backflow from the other opening in the second insulating sheet toward the module.

[0017] Based on this principle, the present invention can prevent high-temperature gas generated from an abnormal battery cell during thermal runaway from reaching other battery cells, thereby preventing a chain reaction of thermal runaway.

[0018] In the battery pack of the present invention, it is preferable that at least one covering piece is disposed inside each of the plurality of openings, and it is preferable that a plurality of covering pieces are disposed inside each of the openings. If the covering pieces are disposed inside the openings, the covering pieces are likely to peel off from the first insulating sheet and / or the second insulating sheet.

[0019] In the battery pack of the present invention, it is preferable that a plurality of the covering pieces are arranged inside each of the plurality of openings.

[0020] In order to prevent backflow of high-temperature gas from the case side, it is preferable that there is no gap between the opening and the covering piece. When a covering piece is placed inside the opening so that no gap occurs between the opening and the covering piece, the size of each covering piece is smaller when multiple covering pieces are placed than when a monolith covering piece is placed. When a monolith covering piece is placed at the opening, if the monolith covering piece is peeled off by gas from the module side, the monolith covering piece is large, and therefore the monolith covering piece may block the gas flow path and inhibit gas diffusion. On the other hand, when multiple covering pieces are placed at the opening, if multiple covering pieces are peeled off by gas from the module side, each covering piece is small, and therefore each covering piece is less likely to inhibit gas diffusion.

[0021] In the battery pack of the present invention, it is preferable that the covering pieces are arranged so that at least a portion of each piece contacts one another. Also, in the battery pack of the present invention, it is preferable that the covering pieces are arranged so that at least a portion of each piece contacts the contour of the opening. When the covering pieces are arranged in this manner, it becomes easier to prevent backflow of gas from gaps between the covering pieces or gaps between the covering pieces and the opening.

[0022] In the battery pack of the present invention, the covering piece is preferably arranged so as to cover the outline of the opening from the case side, so that no gap is formed between the covering piece and the opening, making it easier to prevent gas from flowing back through the gap between the covering piece and the opening.

[0023] In the battery pack of the present invention, it is preferable that the first insulating sheet has a cut portion formed therein that continues from the main surface on which the second insulating sheet is laminated to the other main surface, and that at least a portion of the cut portion is located inside the opening when the insulating material is viewed in plan from the second insulating sheet side. When the cut portion is formed in the first insulating sheet, high-temperature gas from the module side can easily pass through the cut portion and reach the covering piece.

[0024] In the battery pack of the present invention, the cut portion may be formed in a linear shape when the heat insulating material is viewed in a plan view from the second heat insulating sheet side. The linear cut portion can be easily formed using a cutter or the like.

[0025] In the battery pack of the present invention, the cut portion may be formed so as to intersect the outline of the opening when the heat insulating material is viewed in a plan view from the second heat insulating sheet side. Furthermore, in the battery pack of the present invention, it is preferable that the first heat insulating sheet has a plurality of cut portions. Furthermore, in the battery pack of the present invention, it is preferable that the first heat insulating sheet has a plurality of linear cut portions formed therein when the heat insulating material is viewed in a plan view from the second heat insulating sheet side, and at least some of the cut portions are in contact with each other. When cut portions are formed in this manner, high-temperature gas from the module side can more easily pass through the first heat insulating sheet.

[0026] In the battery pack of the present invention, it is preferable that a plurality of the covering pieces are disposed inside the opening, at least a portion of the covering pieces are in contact with one another, and the cut portion is formed along the portion where the covering pieces are in contact with one another when the thermal insulating material is viewed in plan from the second insulating sheet side. Such covering pieces and the cut portion can be formed by punching out the monolith covering pieces and the first insulating sheet simultaneously.

[0027] In the battery pack of the present invention, when the insulating material is viewed from above from the second insulating sheet side, the covering pieces preferably have a linear contact portion, and the covering pieces and the cutout portion can be formed by simultaneously punching the covering pieces of the monolith and the first insulating sheet in a linear shape.

[0028] In the battery pack of the present invention, the opening preferably has a planar shape of at least one selected from the group consisting of a triangle, a rectangle, a hexagon, a circle, an ellipse, and a racetrack shape, and openings of such shapes can be easily formed.

[0029] In the battery pack of the present invention, the first insulating sheet is preferably an inorganic fiber mat, which can be easily molded and exhibits excellent performance as the first insulating sheet.

[0030] In the battery pack of the present invention, the inorganic fiber mat is preferably a mat-shaped inorganic fiber containing at least one fiber selected from the group consisting of silica fiber, glass fiber, alumina fiber, aluminosilicate fiber, basalt fiber, rock wool, and biosoluble fiber. Inorganic fiber mats made of such materials can be easily processed.

[0031] In the battery pack of the present invention, the inorganic fiber mat may be formed by processing inorganic fibers containing fibers with a melting point of 1000° C. or higher into a mat shape. When the inorganic fiber mat contains fibers with a melting point of 1000° C. or higher, the inorganic fibers have high heat resistance, so that the inorganic fiber mat is less likely to deteriorate even if high-temperature gas from an abnormal battery cell reaches the inorganic fiber mat.

[0032] In the battery pack of the present invention, the inorganic fiber mat may be formed into a mat from inorganic fibers containing fibers with a melting point of less than 1000° C. If the inorganic fiber mat contains fibers with a melting point of less than 1000° C., when high-temperature gas from an abnormal battery cell reaches the inorganic fiber mat, the inorganic fiber mat melts and a gas flow path is easily formed.

[0033] In the battery pack of the present invention, the second insulating sheet may be a mica sheet or a heat-resistant resin sheet, which are suitable as the second insulating sheet.

[0034] In the battery pack of the present invention, the covering piece is preferably made of the same material as the second insulating sheet. The second insulating sheet and the covering piece can be simultaneously produced by punching the monolith sheet so as to form an opening.

[0035] In the battery pack of the present invention, the adhesive layer preferably includes an organic adhesive layer. If the adhesive layer includes an organic adhesive layer, the adhesive layer is likely to be thermally decomposed when high-temperature gas from the abnormal battery cell passes through the inorganic fiber mat and reaches the covering piece, which makes the covering piece more likely to peel off from the inorganic fiber mat.

[0036] In the battery pack of the present invention, the thermal insulation material may further include a third insulating sheet, which may be laminated on the second insulating sheet to cover the opening from the case side. Such a battery pack is arranged so that the first insulating sheet is vertically lower and the third insulating sheet is vertically upper. In a battery pack arranged in this manner, the safety valve is vertically upper, so high-temperature gas from an abnormal battery cell is released vertically upward. The gas then passes through the opening formed in the second insulating sheet and reaches the third insulating sheet. The gas is blocked by the third insulating sheet. As a result, the gas is prevented from contacting the case. The third insulating sheet is also pushed upward by the gas, away from the second insulating sheet. This allows the gas to diffuse through the gap formed between the third insulating sheet and the second insulating sheet. The temperature and pressure of the gas then decrease.

[0037] In the battery pack of the present invention, the case includes a storage compartment consisting of a bottom and side walls, and a lid that covers the storage compartment, and the safety valve may be located on the bottom side or the lid side. When the battery pack of the present invention is arranged, the battery pack may be arranged so that the safety valve is located vertically upper or lower from the viewpoint of fail-safe. Since battery packs are often arranged so that the bottom or lid of the case is located lower, arranging the safety valve on the bottom or lid side of the case makes it easier to position the safety valve vertically upper or lower.

[0038] According to the present invention, it is possible to provide a battery pack that can prevent a chain reaction of thermal runaway caused by high-temperature gas from an abnormal battery cell that occurs during thermal runaway.

[0039] FIG. 1A is a perspective view schematically illustrating an example of a battery pack according to a first embodiment of the present invention. FIG. 1B is a cross-sectional view taken along line A-A in FIG. 1A. FIG. 1C is an exploded view of the battery pack shown in FIG. 1A. FIG. 2A is a cross-sectional view schematically illustrating an example of one safety valve and its vicinity in the battery pack according to the first embodiment of the present invention. FIG. 2B is a plan view of the safety valve shown in FIG. 2A as viewed from the insulating material side. FIG. 3A is an explanatory diagram sequentially illustrating the principle by which a chain reaction of thermal runaway is prevented when one battery cell experiences thermal runaway in the battery pack according to the first embodiment of the present invention. FIG. 3B is an explanatory diagram sequentially illustrating the principle by which a chain reaction of thermal runaway is prevented when one battery cell experiences thermal runaway in the battery pack according to the first embodiment of the present invention. FIG. 3C is an explanatory diagram sequentially illustrating the principle by which a chain reaction of thermal runaway is prevented when one battery cell experiences thermal runaway in the battery pack according to the first embodiment of the present invention. FIG. 4A is a plan view schematically illustrating another example of a shape of mica pieces in the battery pack according to the first embodiment of the present invention. FIG. 4B is a plan view schematically showing an example of another shape of the mica pieces in the battery pack according to the first embodiment of the present invention. FIG. 4C is a plan view schematically showing an example of another shape of the mica pieces in the battery pack according to the first embodiment of the present invention. FIG. 4D is a plan view schematically showing an example of another shape of the mica pieces in the battery pack according to the first embodiment of the present invention. FIG. 4E is a plan view schematically showing an example of another shape of the mica pieces in the battery pack according to the first embodiment of the present invention. FIG. 5A is an enlarged cross-sectional view schematically showing an example of a cross section of a heat insulating material provided in a battery pack according to a second embodiment of the present invention. FIG. 5B is a plan view of an example of a mica sheet included in the heat insulating material shown in FIG. 5A. FIG. 5C is a plan view of an example of an inorganic fiber mat included in the heat insulating material shown in FIG. 5A. FIG. 6A is a plan view schematically showing another example of a cut portion formed in the inorganic fiber mat of the battery pack according to the second embodiment of the present invention. FIG. 6B is a plan view schematically showing another example of an opening and mica pieces formed in the mica sheet of the battery pack according to the second embodiment of the present invention. FIG. 7A is a plan view schematically showing another example of a cut portion formed in an inorganic fiber mat of a battery pack according to a second embodiment of the present invention.FIG. 7B is a plan view schematically showing another example of openings and mica pieces formed in the mica sheet of the battery pack according to the second embodiment of the present invention. FIG. 8A is a plan view schematically showing another example of cuts formed in the inorganic fiber mat of the battery pack according to the second embodiment of the present invention. FIG. 8B is a plan view schematically showing another example of openings and mica pieces formed in the mica sheet of the battery pack according to the second embodiment of the present invention. FIG. 9A is an enlarged cross-sectional view schematically showing an example of a cross section of an insulating material provided in the battery pack according to the third embodiment of the present invention. FIG. 9B is an enlarged cross-sectional view schematically showing another example of a cross section of an insulating material provided in the battery pack according to the third embodiment of the present invention. FIG. 9C is an enlarged cross-sectional view schematically showing another example of a cross section of an insulating material provided in the battery pack according to the third embodiment of the present invention. FIG. 10 is an enlarged cross-sectional view schematically showing an example of a battery pack according to the fourth embodiment of the present invention. FIG. 11A is an explanatory diagram sequentially illustrating the principle by which a chain reaction of thermal runaway is prevented when one battery cell experiences thermal runaway in the battery pack according to the fourth embodiment of the present invention. FIG. 11B is an explanatory diagram sequentially showing the principle of preventing a chain reaction of thermal runaway when one battery cell experiences thermal runaway in a battery pack according to a fourth embodiment of the present invention. FIG. 11C is an explanatory diagram sequentially showing the principle of preventing a chain reaction of thermal runaway when one battery cell experiences thermal runaway in a battery pack according to a fourth embodiment of the present invention. FIG. 12 is a photograph taken from the mica sheet side of the insulating material according to Example 1-1 of the present invention. FIG. 13 is a photograph taken from the mica sheet side of the insulating material according to Example 1-2 of the present invention. FIG. 14 is an explanatory diagram schematically showing a gas pressure cleavage test 1. FIG. 15A is a photograph taken from the second jig side before the gas valve was released in a gas pressure cleavage test using the insulating material according to Example 1-1. FIG. 15B is a photograph taken from the second jig side after the gas valve was released in a gas pressure cleavage test using the insulating material according to Example 1-1. FIG. 16A is a photograph taken from the second jig side before the gas valve was released in a gas pressure cleavage test using the insulating material according to Example 1-2. Fig. 16B is a photograph taken from the second jig side after the gas valve is opened in a gas pressure cleavage test using the heat insulating material according to Example 1-2. Fig. 17A is a plan view schematically showing the inorganic fiber mat according to Example 2-1.FIG. 17B is a plan view schematically showing openings and mica pieces in the mica sheet according to Example 2-1. FIG. 18A is a plan view schematically showing cut portions in the inorganic fiber mat according to Example 2-2. FIG. 18B is a plan view schematically showing openings and mica pieces in the mica sheet according to Example 2-2. FIG. 19A is a plan view schematically showing cut portions in the inorganic fiber mat according to Example 2-3. FIG. 19B is a plan view schematically showing openings and mica pieces in the mica sheet according to Example 2-3. FIG. 20A is a plan view schematically showing an inorganic fiber mat according to Comparative Example 2-1. FIG. 20B is a plan view schematically showing a mica sheet according to Comparative Example 2-1. FIG. 21 is an explanatory diagram schematically showing cleavage test 2.

[0040] The battery pack of the present invention will be specifically described below. However, the present invention is not limited to the following configuration, and can be appropriately modified and applied within the scope of the present invention. Note that a combination of two or more of the individual preferred configurations of the present invention described below also constitutes the present invention.

[0041] First Embodiment A battery pack according to a first embodiment of the present invention will be described, in which the first insulating sheet, the second insulating sheet, and the covering piece constituting the insulating material are an inorganic fiber mat, a mica sheet, and mica pieces. FIG. 1A is a perspective view schematically illustrating an example of a battery pack according to the first embodiment of the present invention. FIG. 1B is a cross-sectional view taken along line A-A in FIG. 1A. FIG. 1C is an exploded view of the battery pack shown in FIG. 1A. The battery pack 10 shown in FIGS. 1A, 1B, and 1C includes a module 20 having a plurality of battery cells 21 and a case 30 that houses the module 20. As shown in FIG. 1B, in the battery pack 10, each battery cell 21 is provided with a safety valve 22. As shown in FIG. 1B, the case 30 includes a housing portion 31 formed of a bottom portion 31b and a sidewall 31s, and a lid portion 32 that covers the housing portion 31. The module 20 is housed in the housing portion 31. In addition, in the battery pack 10, a heat insulating material 40 is provided between the module 20 and the case 30.

[0042] The battery cells 21 store power and are preferably, for example, rechargeable so-called secondary batteries. Examples of secondary batteries include lithium ion batteries, nickel-metal hydride batteries, and sodium ion batteries. The battery cells 21 shown in Figures 1B and 1C are rectangular parallelepiped. However, in the battery pack of the present invention, the battery cells may have a three-dimensional shape other than a rectangular parallelepiped shape (for example, a cube or a modified shape).

[0043] 1B and 1C, in the module 20, a plurality of battery cells 21 are arranged in a row and fixed by a connecting module member 20a. Also, as shown in Fig. 1C, the battery cells 21 have terminals 23, and adjacent battery cells 21 are electrically connected by connecting each terminal 23 to a bus bar 20b arranged on the connecting module member 20a.

[0044] The bus bar 20b is a flat, electrically conductive metal member. Examples of materials for the bus bar 20b include copper, copper alloy, stainless steel (SUS), and aluminum. The bus bar 20b may be fixed to the terminal 23 by any fixing means (e.g., screwing, welding, etc.).

[0045] Examples of materials that can be used to form the case 30 include steel and aluminum. As the steel, stainless steel (SUS) is preferred.

[0046] Fig. 2A is a cross-sectional view schematically illustrating an example of one safety valve and its vicinity in the battery pack according to the first embodiment of the present invention, and Fig. 2B is a plan view of the safety valve shown in Fig. 2A as viewed from the heat insulating material side.

[0047] 2A, the heat insulating material 40 includes an inorganic fiber mat 41, which is a first heat insulating sheet, and a mica sheet 42, which is a second heat insulating sheet, laminated on the inorganic fiber mat 41. The heat insulating material 40 is arranged so that the inorganic fiber mat 41 is located on the module 20 side and the mica sheet 42 is located on the case 30 side.

[0048] As shown in Fig. 2A, an opening 42a is formed in the mica sheet 42, penetrating the mica sheet 42, and as shown in Fig. 2B, four covering pieces, that is, mica pieces 50, are arranged inside the opening 42a. The mica pieces 50 are adhered to the inorganic fiber mat 41 by an adhesive layer (not shown).

[0049] As shown in FIG. 2B , when the mica sheet 42 is viewed from above, one opening 42 a is positioned so as to overlap one safety valve 22 .

[0050] 2B, the opening 42a is circular. The four mica pieces 50 are congruent sectors that form a circle when combined. The four mica pieces 50 are in contact with the outline of the opening 42a and with each other to form the circle.

[0051] The battery pack 10 can prevent a chain reaction of thermal runaway caused by high-temperature gas from an abnormal battery cell that occurs during thermal runaway. The principle behind this is explained below.

[0052] 3A to 3C are explanatory diagrams sequentially illustrating the principle of preventing a chain reaction of thermal runaway when one battery cell experiences thermal runaway in the battery pack according to the first embodiment of the present invention. As shown in Fig. 3A, when one battery cell 21a experiences thermal runaway and generates high-temperature gas from the battery cell 21a, gas G (in Fig. 3A, the gas is indicated by the symbol "G" and the direction of gas flow is indicated by an arrow) is discharged from the safety valve 22a. The gas released from the safety valve 22a then reaches the thermal insulator 40.

[0053] The heat insulating material 40 includes an inorganic fiber mat 41 and a mica sheet 42 laminated on the inorganic fiber mat 41. The heat insulating material 40 is arranged so that the inorganic fiber mat 41 is located on the module 20 side and the mica sheet 42 is located on the case 30 side. Therefore, the gas G that reaches the heat insulating material 40 first comes into contact with the inorganic fiber mat 41. The inorganic fiber mat 41 is not dense and there are spaces between the inorganic fibers, so the gas G can pass through the inorganic fiber mat 41.

[0054] The mica sheet 42 has an opening 42a formed therethrough, and when the mica sheet 42 is viewed from above, the opening 42a is positioned so as to overlap with the safety valve 22. Therefore, the gas G that has passed through the inorganic fiber mat 41 reaches the vicinity of the opening 42a of the mica sheet 42.

[0055] Mica pieces 50 are arranged inside the openings 42a of the mica sheet 42, and the mica pieces 50 are adhered to the inorganic fiber mat 41 by an adhesive layer (not shown). The high temperature of the gas G that reaches the vicinity of the openings 42a of the mica sheet 42 causes the adhesive layer that adheres the mica pieces 50 to thermally decompose. This weakens the adhesion between the mica pieces 50 and the inorganic fiber mat 41. In addition, gas pressure is applied to the mica pieces 50 from the module 20 side toward the case 30 side. As a result, the mica pieces 50 peel off from the inorganic fiber mat 41, as shown in FIG. 3B .

[0056] Then, gas G that has passed through inorganic fiber mat 41 passes through openings 42a of mica sheet 42 and is released between heat insulating material 40 and case 30. In such a case, the temperature of high-temperature gas G decreases while passing through inorganic fiber mat 41, and the gas pressure also decreases. Therefore, even if gas G is released from openings 42a and comes into contact with case 30, case 30 is unlikely to be heated or damaged by gas G.

[0057] Furthermore, since the gas G is released from the openings 42 a of the mica sheet 42 , it is possible to prevent the gas G from passing through the inside of the inorganic fiber mat 41 and flowing back through other safety valves 22 .

[0058] 3C, the gas G released from the opening 42a of the mica sheet 42 diffuses between the heat insulating material 40 and the case 30, and reaches the other openings 42a of the mica sheet 42. However, because mica pieces 50 are arranged inside the other openings 42a of the mica sheet 42, even if the gas G reaches the other openings 42a of the mica sheet 42, it is possible to prevent the gas G from flowing back from the other openings 42a of the mica sheet 42 toward the module 20.

[0059] Based on this principle, the battery pack 10 can prevent high-temperature gas G generated from an abnormal battery cell 21a during thermal runaway from reaching other battery cells 21. This prevents a chain reaction of thermal runaway.

[0060] A preferred embodiment of the heat insulating material of the battery pack according to the first embodiment of the present invention will be described below.

[0061] (Inorganic Fiber Mat) The thickness of the inorganic fiber mat 41 is preferably 0.5 to 10 mm, and more preferably 1 to 4 mm. If the thickness of the inorganic fiber mat is less than 0.5 mm, the inorganic fiber mat is too thin, making it difficult for the temperature and pressure of the gas to decrease as it passes through the inorganic fiber mat. As a result, the gas reaches the case with great force while still hot, making the case more susceptible to deterioration. If the thickness of the inorganic fiber mat exceeds 10 mm, the inorganic fiber mat becomes too thick, making it difficult to miniaturize the entire battery pack.

[0062] The bulk density of the inorganic fiber mat 41 is 0.1 to 1.0 g / cm ３ is preferably 0.2 to 0.7 g / cm ３ It is more preferable that the bulk density of the inorganic fiber mat 41 is 0.1 g / cm ３ If the bulk density of the inorganic fiber mat 41 is less than 1.0 g / cm, the gaps between the inorganic fibers become large, and as the gas passes through the inorganic fiber mat, the temperature of the gas is less likely to decrease, and the gas pressure is less likely to decrease. As a result, the gas reaches the case with force while still at a high temperature, which makes the case more likely to deteriorate. ３ If the temperature exceeds this value, it becomes difficult for the gas to pass through the inorganic fiber mat, and the high-temperature gas remains inside the battery cell, making it difficult for the temperature inside the battery cell to decrease. This makes it more likely that a chain reaction of thermal runaway will occur.

[0063] The inorganic fiber mat 41 is preferably a mat-shaped inorganic fiber containing at least one type of fiber selected from silica fiber, glass fiber, alumina fiber, aluminosilicate fiber, basalt fiber, rock wool, and biosoluble fiber. Inorganic fiber mats made of such materials can be easily processed.

[0064] The inorganic fiber mat 41 may be formed by processing inorganic fibers containing fibers with a melting point of 1000° C. or higher into a mat shape. Examples of such inorganic fibers include silica fibers, alumina fibers, aluminosilicate fibers, and biosoluble fibers. When the inorganic fiber mat contains fibers with a melting point of 1000° C. or higher, the inorganic fibers have high heat resistance, making the inorganic fiber mat less susceptible to deterioration even if high-temperature gas from an abnormal battery cell reaches the inorganic fiber mat.

[0065] The inorganic fiber mat 41 may be formed by processing inorganic fibers containing fibers with a melting point of less than 1000° C. Examples of such inorganic fibers include glass fiber, basalt fiber, and rock wool. If the inorganic fiber mat contains fibers with a melting point of less than 1000° C., when high-temperature gas from an abnormal battery cell reaches the inorganic fiber mat, the inorganic fiber mat melts, making it more likely that a gas flow path will be formed.

[0066] (Mica Sheet) The thickness of the mica sheet 42 is preferably 0.05 to 2.0 mm, more preferably 0.1 to 1.0 mm, and even more preferably 0.1 to 0.5 mm. If the thickness of the mica sheet is less than 0.05 mm, the strength of the mica sheet is low and it becomes easily damaged. If the thickness of the mica sheet exceeds 2.0 mm, the mica sheet becomes too thick, making it difficult to miniaturize the entire battery pack.

[0067] 2B, the shape of the opening 42a formed in the mica sheet 42 in a plan view is circular, but in the battery pack according to the first embodiment of the present invention, the shape of the opening formed in the mica sheet in a plan view may be triangular, rectangular, hexagonal, elliptical, racetrack, etc. Openings of such shapes can be easily formed.

[0068] The area of ​​the opening 42a in plan view is 1.0 to 18 cm ２ It is preferable that the length is 3 to 12 cm. ２ It is more preferable that the area of ​​the opening in plan view is 1.0 cm ２ If the area of ​​the opening in plan view is less than 18 cm, the gas will not easily pass through the opening.２ If the opening exceeds this value, the opening tends to be wider than the area of ​​the mica sheet that the gas can reach. As will be described in detail later, mica pieces arranged inside the opening are peeled off from the inorganic fiber mat when the gas reaches them, so mica pieces arranged in an area that the gas cannot reach are less likely to peel off.

[0069] In the battery pack 10, when the mica sheet 42 is viewed from above, it is sufficient that each opening is positioned so as to overlap at least a portion of each safety valve, but it is preferable that each opening is positioned so as to fit within the outline of each safety valve. When the opening is positioned in this manner, gas released from the safety valve can easily reach the opening.

[0070] 2B, the mica pieces 50 are arranged so that they are in contact with each other and are in contact with the contour of the opening 42a. In other words, the opening 42a is completely covered with the mica pieces 50. Therefore, in the battery pack 10, it is possible to prevent backflow of high-temperature gas G from the case 30 side.

[0071] In the heat insulating material 40 shown in FIG. 2B , four mica pieces 50 are arranged inside one opening 42 a. When arranging the mica pieces 50 inside the opening 42 a so as not to create a gap between the opening 42 a and the mica pieces 50, arranging multiple mica pieces results in a smaller size per mica piece than arranging monolithic (integral) mica pieces. When monolithic (integral) mica pieces are arranged in the opening 42 a, if the monolithic (integral) mica pieces are peeled off by gas G from the module 20 side, the monolithic (integral) mica pieces are large, and therefore may block the flow path of gas G and inhibit the diffusion of gas. On the other hand, when multiple mica pieces 50 are arranged in the opening 42 a, if the multiple mica pieces 50 are peeled off by gas G from the module 20 side, each mica piece 50 is small, and therefore each mica piece 50 is less likely to inhibit the diffusion of gas G.

[0072] 2B, the mica pieces 50 are arranged without gaps in one opening 42a. However, in the battery pack according to the first embodiment of the present invention, there may be a gap between one opening and the mica pieces arranged therein, or there may be gaps between the mica pieces themselves.

[0073] Furthermore, in the battery pack according to the first embodiment of the present invention, a monolithic mica piece may be disposed in one opening. In this configuration, the number of mica pieces disposed in the entire battery pack is reduced, allowing for efficient manufacturing of the battery pack.

[0074] Next, the shape of the mica pieces when multiple mica pieces are arranged inside the opening will be described below. Figures 4A to 4E are plan views schematically showing examples of other shapes of the mica pieces in the battery pack according to the first embodiment of the present invention.

[0075] 4A, the mica pieces in the battery pack according to the first embodiment of the present invention may be two mica pieces 50a. The mica pieces 50a are semicircular, and when the two mica pieces 50a are combined together, they form a circle.

[0076] As shown in FIG. 4B, the mica pieces in the battery pack according to the first embodiment of the present invention are four mica pieces 50b. １ , mica pieces 50b ２ , mica pieces 50b ３ and mica pieces 50b ４ The mica pieces 50b may be １ , mica pieces 50b ２ , mica pieces 50b ３ and mica pieces 50b ４ The mica pieces 50b are arranged in order from the left to form a circle. １ , mica pieces 50b ２ , mica pieces 50b ３ and mica pieces 50b ４ is a shape obtained by dividing a circle into four equal parts by lines perpendicular to the horizontal direction.

[0077] As shown in FIG. 4C, the mica pieces in the battery pack according to the first embodiment of the present invention are two mica pieces 50c. １and mica pieces 50c ２ The mica pieces 50c may be １ is a circular ring, and the mica piece 50c ２ 50cm mica piece １ It is a circle located inside the

[0078] 4D, the mica pieces in the battery pack according to the first embodiment of the present invention may be four mica pieces 50d. Each mica piece 50d is a right-angled isosceles triangle that forms a square when combined.

[0079] As shown in Fig. 4E, the mica pieces in the battery pack according to the first embodiment of the present invention may be four mica pieces 50e. The mica pieces 50e are congruent rectangles that form a square when arranged from left to right. In other words, each mica piece 50e has a shape obtained by dividing a square into four equal parts by lines perpendicular to the horizontal direction.

[0080] In the heat insulating material 40, the mica pieces 50 are adhered to the inorganic fiber mat 41 by an adhesive layer (not shown). The adhesive layer preferably contains a material that thermally decomposes when gas reaches it. If the adhesive layer contains such a material, the mica pieces 50 are more likely to peel off when gas reaches them.

[0081] The material that thermally decomposes when gas reaches it is, for example, an organic material with a thermal decomposition temperature of 80°C or higher, more specifically, a polyamide-based organic material. If the adhesive layer (not shown) contains a polyamide-based organic material, the adhesive layer is more likely to thermally decompose when the high-temperature gas G from the abnormal battery cell passes through the inorganic fiber mat 41 and reaches the mica pieces 50. This makes it easier for the mica pieces 50 to peel off from the inorganic fiber mat 41.

[0082] In the heat insulating material 40, the mica sheet 42 may also be adhered to the inorganic fiber mat 41 by an adhesive layer.

[0083] In the heat insulating material 40, the mica pieces 50 may be adhered by an adhesive layer to the inner wall of the opening 42a of the mica sheet 42, rather than to the inorganic fiber mat 41. Furthermore, the mica pieces 50 may be adhered by an adhesive layer to both the inorganic fiber mat 41 and the inner wall of the opening 42a of the mica sheet 42. Furthermore, when a plurality of mica pieces 50 are arranged, the mica pieces may be adhered to each other by an adhesive layer.

[0084] In the battery pack 10, the mica sheet 42, which is the second insulating sheet, and the mica pieces 50, which are the covering pieces, are made of the same material, mica. As will be described in detail later, the mica sheet 42 and the mica pieces 50 can be produced simultaneously by punching out a monolithic mica sheet so as to form openings. In the battery pack of the present invention, the covering pieces may be made of the same material as the second insulating sheet, or may be made of a different material.

[0085] A method for manufacturing the insulating material included in the battery pack according to the first embodiment of the present invention will be described. When manufacturing the insulating material, an inorganic fiber mat and a mica sheet are prepared. Next, the mica sheet is punched to produce a mica sheet with openings and mica pieces. Next, the mica sheet with openings is adhered to the main surface of the inorganic fiber mat with an adhesive layer. Furthermore, the mica pieces are adhered to the main surface of the inorganic fiber mat with an adhesive layer so that the prepared mica pieces fit inside the openings. This allows the insulating material to be disposed in the battery pack of the present invention to be manufactured.

[0086] When arranging multiple mica pieces, they may be cut and divided with a cutter or the like before being adhered. Alternatively, multiple mica pieces may be formed by making cuts in the mica sheet beforehand and punching the mica sheet to include the cuts. In this case, the mica sheet may be punched so that the cuts made in the mica sheet intersect with the outline of the punched portion. In this case, the cuts remain in the mica sheet. In other words, the mica sheet has a shape in which the cuts are formed so as to contact the outline of the opening.

[0087] Also, mica pieces other than punched mica pieces may be placed inside the opening.

[0088] Next, the use and arrangement method of the battery pack according to the first embodiment of the present invention will be described. The use of the battery pack according to the first embodiment of the present invention is not particularly limited, but it may be used as a power source for an electric vehicle, for example.

[0089] Furthermore, the battery pack according to the first embodiment of the present invention is preferably arranged so that the safety valves provided on the battery cells are located vertically either on the upper or lower side. When the battery pack is arranged so that the safety valves are located in this way, high-temperature gas from an abnormal battery cell is naturally and quickly dispersed, making it less likely that a chain reaction of thermal runaway will occur. In other words, this is a preferable battery pack arrangement from the viewpoint of fail-safety.

[0090] In the battery pack according to the first embodiment of the present invention, the safety valve may be disposed on the bottom side or the lid side. As described above, when the battery pack according to the first embodiment of the present invention is disposed, from the viewpoint of fail-safe, the battery pack may be disposed so that the safety valve is disposed on the vertically upper side or the vertically lower side. Since battery packs are often disposed so that the bottom or the lid of the case is disposed on the lower side, disposing the safety valve on the bottom side or the lid side of the case makes it easier to position the safety valve on the vertically upper side or the vertically lower side.

[0091] Second Embodiment Next, a battery pack according to a second embodiment of the present invention will be described. The battery pack according to the second embodiment of the present invention differs from the battery pack according to the first embodiment of the present invention in that the inorganic fiber mat has a continuous cut portion formed therein that extends from the main surface on which the mica sheet is laminated to the other main surface, and that at least a portion of the cut portion is located inside the opening when the thermal insulation material is viewed from above from the mica sheet side.

[0092] Fig. 5A is an enlarged cross-sectional view schematically showing an example of a cross section of a heat insulating material provided in a battery pack according to a second embodiment of the present invention. Fig. 5B is a plan view of an example of a mica sheet included in the heat insulating material shown in Fig. 5A. Fig. 5C is a plan view of an example of an inorganic fiber mat included in the heat insulating material shown in Fig. 5A.

[0093] 5A includes an inorganic fiber mat 141 and a mica sheet 142 laminated on the inorganic fiber mat 141. The inorganic fiber mat 141 has a cut portion 141a formed therein that continues from the main surface on which the mica sheet 142 is laminated to the other main surface.

[0094] 5B, the mica sheet 142 has a plurality of openings 142a formed therethrough, and four mica pieces 150 are disposed inside the openings 142a. The mica sheet 142 and the mica pieces 150 are adhered to the inorganic fiber mat 141 by an adhesive layer (not shown).

[0095] As shown in Figure 5B, the opening 142a is circular. The four mica pieces 150 are congruent sectors that form a circle when combined. The four mica pieces 150 are in contact with the outline of the opening 142a and with each other to form the circle.

[0096] As shown in FIG. 5C, the cut portion 141a is formed on the main surface of the inorganic fiber mat 141 so that two line segments intersect at right angles.

[0097] Furthermore, when the heat insulating material 140 is viewed from above from the mica sheet 142 side, the notch 141a is located inside the opening 142a.

[0098] When the cuts 141a are formed in the inorganic fiber mat 141, high-temperature gas from the module (not shown) can easily pass through the cuts 141a and reach the mica pieces 150. This prevents the gas from passing through the inside of the inorganic fiber mat 141 and flowing back through other safety valves.

[0099] In the heat insulating material 140, when the inorganic fiber mat 141 is viewed in plan, the cut portions 141 a may be formed in a linear shape, a straight line, or a curved line. The linear cut portions can be easily formed using a cutter or the like.

[0100] The heat insulating material 140 may have a single cut 141a or multiple cuts 141a. When multiple cuts 141a are formed, the cuts 141a may be in contact with each other or may intersect with each other. When cuts 141a are formed in this manner, high-temperature gas from the module side can easily pass through the inorganic fiber mat 141.

[0101] Furthermore, the cuts 141a may be formed along the portions where the mica pieces 150 contact each other. It is also preferable that the cuts 141a and the portions where the mica pieces 150 contact each other are formed linearly. Such mica pieces 150 and cuts 141a can be formed by punching out the monolithic mica sheet 142 and inorganic fiber mat 141 simultaneously.

[0102] Other preferred shapes of the cuts, openings, and mica pieces will be described below with reference to the drawings. Fig. 6A is a plan view schematically showing another example of a cut formed in an inorganic fiber mat of a battery pack according to a second embodiment of the present invention. Fig. 6B is a plan view schematically showing another example of an opening and mica pieces formed in a mica sheet of a battery pack according to the second embodiment of the present invention. Fig. 7A is a plan view schematically showing another example of a cut formed in an inorganic fiber mat of a battery pack according to the second embodiment of the present invention. Fig. 7B is a plan view schematically showing another example of an opening and mica pieces formed in a mica sheet of a battery pack according to the second embodiment of the present invention. Fig. 8A is a plan view schematically showing another example of a cut formed in an inorganic fiber mat of a battery pack according to the second embodiment of the present invention. Fig. 8B is a plan view schematically showing another example of an opening and mica pieces formed in a mica sheet of a battery pack according to the second embodiment of the present invention.

[0103] The notch 141a shown in FIG. １ The opening 142a shown in FIG. 6B is formed in the inorganic fiber mat 141 so that two line segments intersect at right angles. １ The opening 142a is circular. １ An opening 142a is formed on the inside of the １ A circular monolithic mica piece 150a is placed so as to fill the gap. １ are placed.

[0104] The notch 141a shown in FIG. ２ is formed in the inorganic fiber mat 141 so as to consist of one line segment. ２ The opening 142a is circular. ２ An opening 142a is formed on the inside of the ２ The semicircular mica pieces 150a are placed so as to fill the gap. ２ Two notches 141a are arranged. ２ is a mica piece 150a ２ It is formed along the contact area between them.

[0105] The notch 141a shown in FIG. ３ The cut portion 141a is formed in the inorganic fiber mat 141 by one line segment L1 and four line segments L2, L3, L4, and L5 that are in contact with the line segment L1. The point where the line segment L1 and the line segment L2 are in contact is the same as the point where the line segment L1 and the line segment L3 are in contact, and the angle formed by the line segment L1 and the line segment L2 and the angle formed by the line segment L1 and the line segment L3 are the same. Furthermore, the point where the line segment L1 and the line segment L4 are in contact is the same as the point where the line segment L1 and the line segment L5 are in contact, and the angle formed by the line segment L1 and the line segment L4 and the angle formed by the line segment L1 and the line segment L5 are the same. In other words, the cut portion 141a ３ The opening 142a shown in FIG. ３ The opening 142a is racetrack shaped. ３ An opening 142a is formed on the inside of the ３ The mica pieces 150a are placed so as to fill the gap. ３ Six mica pieces 150a are arranged. ３The shape of the mica pieces 150a is a shape that forms a racetrack when combined. ３ The contact portion is a notch 141a ３ It is formed along the

[0106] 7A and 7B and 8A and 8B, the cuts are formed along the contact points between the mica pieces. That is, the cuts and the contact points between the mica pieces are aligned. However, in the battery pack according to the second embodiment of the present invention, when the thermal insulating material is viewed in plan from the mica sheet side, the cuts and the contact points between the mica pieces do not have to be aligned.

[0107] In the above description, the end of the cut 141 a is in contact with the outline of the opening 142 a, but in the battery pack according to the second embodiment of the present invention, the cut may be formed so as to intersect with the outline of the opening when the thermal insulation material is viewed from the mica sheet side in a plan view. When the cut is formed in this manner, high-temperature gas from the module side can easily pass through the inorganic fiber mat 141.

[0108] The inorganic fiber mat 141 is preferably a mat made of inorganic fibers containing fibers with a melting point of 1000°C or higher. Examples of inorganic fibers include silica fibers, alumina fibers, aluminosilicate fibers, and biosoluble fibers. When the inorganic fiber mat 141 is made of such materials, the inorganic fibers have heat resistance, making it less likely for the inorganic fibers to melt and form holes due to the heat of the gas. This allows the gas to be appropriately dispersed as it passes through the inorganic fiber mat, preventing the gas from reaching the case at a high temperature. Furthermore, because the inorganic fiber mat 141 has cuts 141a, sufficient gas flow paths can be ensured even if the inorganic fibers do not melt.

[0109] The preferred materials for the mica sheet 142 and the adhesive layer are the same as those for the mica sheet 42 and the adhesive layer described above in connection with the battery pack according to the first embodiment of the present invention.

[0110] Next, a method for manufacturing the insulating material included in the battery pack according to the second embodiment of the present invention will be described. To manufacture the insulating material, an inorganic fiber mat and a mica sheet are prepared. Next, the mica sheet is punched to produce a mica sheet and mica pieces with openings formed therein. Note that the mica sheet may be punched to produce a single mica piece, or multiple mica pieces. After punching to produce a single mica piece, the single mica piece may be further cut into multiple mica pieces. Also, a cutout is formed in the inorganic fiber mat. Next, a mica sheet with an opening formed therein is bonded to the main surface of the inorganic fiber mat with an adhesive layer. At this time, the mica sheet is positioned so that the cutout in the inorganic fiber mat is positioned inside the opening in the mica sheet. Then, the mica pieces are bonded to the main surface of the inorganic fiber mat with an adhesive layer so that the fabricated mica pieces fit inside the opening. This completes the manufacturing of the insulating material to be disposed in the battery pack according to the second embodiment of the present invention.

[0111] The heat insulating material included in the battery pack according to the second embodiment of the present invention may also be manufactured by the following method. When manufacturing the heat insulating material, first, an inorganic fiber mat and a mica sheet are prepared. Next, the mica sheet is punched to produce a mica sheet and mica pieces with openings formed therein. Next, the mica sheet with openings formed therein is adhered to the main surface of the inorganic fiber mat with an adhesive layer. The mica pieces are also adhered to the main surface of the inorganic fiber mat with an adhesive layer so that the prepared mica pieces fit inside the openings. Then, a cut is formed in the inorganic fiber mat together with the mica pieces. At this time, the mica pieces are divided. This allows the heat insulating material to be disposed in the battery pack according to the second embodiment of the present invention to be manufactured. In the above method, the cut may be formed so that the cut intersects with the outline of the opening. In this case, the mica sheet has a shape in which the cut is formed so as to contact the outline of the opening.

[0112] The thermal insulator included in the battery pack according to the second embodiment of the present invention may also be manufactured by the following method. When manufacturing the thermal insulator, first, an inorganic fiber mat and a mica sheet are prepared, and the mica sheet is bonded to the main surface of the inorganic fiber mat with an adhesive layer. Next, a punching die is prepared, which has a first blade long enough to punch only the mica sheet and form the outline of the opening and mica pieces, and a second blade long enough to punch both the mica sheet and the inorganic fiber mat, divide the mica pieces, and form incisions in the inorganic fiber mat. In other words, a punching die having two blades of different lengths, with the second blade being longer than the first blade, is prepared. The punching die is then used to punch the mica sheet and the inorganic fiber mat from the mica sheet side, thereby simultaneously forming the opening in the mica sheet, the mica pieces, and the incisions in the inorganic fiber mat in a single operation.

[0113] The heat insulating material included in the battery pack according to the second embodiment of the present invention may also be manufactured by the following method. When manufacturing the heat insulating material, first, an inorganic fiber mat and a mica sheet are prepared, and the mica sheet is bonded to the main surface of the inorganic fiber mat with an adhesive layer. Next, a blade having a length sufficient to punch only the inorganic fiber mat is used to punch the inorganic fiber mat from the inorganic fiber mat side to form a cut portion. Next, a blade having a length sufficient to punch only the mica sheet is used to punch the mica sheet from the mica sheet side to form an opening and mica pieces. The number of mica pieces formed may be one or more. Note that one mica piece may be punched out and then further cut to form multiple mica pieces.

[0114] (Third embodiment) Next, a battery pack according to a third embodiment of the present invention will be described. The battery pack according to the third embodiment of the present invention differs from the battery pack according to the first embodiment and the battery pack according to the second embodiment of the present invention in that the mica pieces are arranged so as to cover the outline of the opening from the case side. The battery pack according to the third embodiment of the present invention will be described in detail below with reference to the drawings.

[0115] Fig. 9A is an enlarged cross-sectional view schematically showing an example of a cross section of a heat insulating material provided in a battery pack according to a third embodiment of the present invention. Fig. 9B is an enlarged cross-sectional view schematically showing another example of a cross section of a heat insulating material provided in a battery pack according to the third embodiment of the present invention. Fig. 9C is an enlarged cross-sectional view schematically showing another example of a cross section of a heat insulating material provided in a battery pack according to the third embodiment of the present invention.

[0116] 9A includes an inorganic fiber mat 241 and a mica sheet 242 laminated on the inorganic fiber mat 241. An opening 242a is formed in the mica sheet 242, and mica pieces 250 are arranged to cover the outline of the opening 242a from the case (not shown) side. The mica pieces 250 are adhered to the surface of the mica sheet 242 by an adhesive layer (not shown).

[0117] The heat insulating material 240b shown in FIG. 9B differs from the heat insulating material 240a in that the inorganic fiber mat 241 has a cut portion 241a formed therein that continues from the main surface on which the mica sheet 242 is laminated to the other main surface.

[0118] A heat insulating material 240c shown in FIG. 9C differs from the heat insulating material 240b in that a plurality of mica pieces 250 are arranged.

[0119] When the mica pieces are arranged in this manner, no gaps are formed between the mica pieces and the openings, making it easier to prevent gas from flowing back through between the mica pieces and the openings.

[0120] Other than the above differences, the preferred materials for each component of the battery pack according to the third embodiment of the present invention are the same as those described above in the description of the battery pack according to the first embodiment of the present invention.

[0121] (Fourth Embodiment) Next, a battery pack according to a fourth embodiment of the present invention will be described. The battery pack according to the fourth embodiment of the present invention differs from the first to third embodiments of the present invention in that the heat insulating material further includes a third heat insulating sheet, which is laminated on the mica sheet so as to cover the opening from the case side. The battery pack according to the fourth embodiment of the present invention will be described in detail below with reference to the drawings.

[0122] Fig. 10 is an enlarged cross-sectional view schematically illustrating an example of a battery pack according to a fourth embodiment of the present invention. The battery pack 310 shown in Fig. 10 includes a module 320 having a plurality of battery cells 321 and a connection module member 320a connecting the battery cells 321, and a case 330 that houses the module 320. In the battery pack 310, each battery cell 321 is provided with a safety valve 322. In addition, in the battery pack 310, a heat insulating material 340 is provided between the module 320 and the case 330. The battery pack 310 is arranged so that the safety valve 322 is located vertically upward. In other words, the battery pack 310 is arranged upside down compared to the battery pack 10 shown in Fig. 1B.

[0123] The heat insulating material 340 is formed by laminating an inorganic fiber mat 341 as a first heat insulating sheet, a mica sheet 342 as a second heat insulating sheet, and a third heat insulating sheet 343 in this order from the bottom.

[0124] The mica sheet 342 has an opening 342a formed therethrough, and a mica piece 350 is disposed inside the opening 342a.

[0125] The mica sheet 342 and the mica pieces 350 are adhered to the main surface of the inorganic fiber mat 341 by an adhesive layer (not shown).

[0126] The third heat insulating sheet 343 is laminated on the mica sheet 342 so as to cover the opening 342a from the case 330 side.

[0127] Next, the function of the third insulating sheet 343 will be described using the drawings. Figures 11A to 11C are explanatory diagrams sequentially illustrating the principle by which a chain reaction of thermal runaway is prevented when one battery cell experiences thermal runaway in a battery pack according to the fourth embodiment of the present invention. As shown in Figure 11A, when one battery cell 321a experiences thermal runaway and generates high-temperature gas from the battery cell 321a, gas G (in Figure 11A, the gas is indicated by the symbol "G" and the direction of gas flow is indicated by an arrow) is discharged from the safety valve 322a. The gas released from the safety valve 322a then reaches the insulating material 340.

[0128] The gas G that reaches the heat insulating material 340 first comes into contact with the inorganic fiber mat 341. The inorganic fiber mat 341 is not dense and there are spaces between the inorganic fibers, so the gas G can pass through the inorganic fiber mat 341.

[0129] The mica sheet 342 has an opening 342a formed therethrough, and when the mica sheet 342 is viewed from above, the opening 342a is positioned so as to overlap with the safety valve 322. Therefore, the gas G that has passed through the inorganic fiber mat 341 reaches the vicinity of the opening 342a of the mica sheet 342.

[0130] Mica pieces 350 are arranged inside openings 342a of mica sheet 342, and mica pieces 350 are adhered to inorganic fiber mat 341 by an adhesive layer (not shown). The high temperature of gas G that reaches the vicinity of openings 342a of mica sheet 342 causes thermal decomposition of the adhesive layer adhering mica pieces 350. This weakens the adhesion between mica pieces 350 and inorganic fiber mat 341. In addition, gas pressure is applied to mica pieces 350 from the module 320 side toward the case 330 side. As a result, mica pieces 350 peel off from inorganic fiber mat 341, as shown in FIG. 11B .

[0131] The gas G then passes through the openings 342a of the mica sheet 342 and reaches the third insulating sheet 343. The gas G is blocked by the third insulating sheet 343. The gas G also pushes the third insulating sheet 343 upward so as to move away from the mica sheet 342. As a result, the gas G can be prevented from coming into contact with the case 330.

[0132] 11C, the gas G is diffused through the gap S formed between the third insulating sheet 343 and the mica sheet 342. Then, the temperature and pressure of the gas G decrease.

[0133] 11C, the third insulating sheet 343 may be disposed in any manner as long as it can be pushed upward by the gas G so as to separate from the mica sheet 342, thereby forming a gap S. For example, the third insulating sheet 343 may be disposed on the mica sheet 342 without being fixed, or may be disposed on the mica sheet 342 so that a portion of it is fixed.

[0134] The third heat insulating sheet 343 may be made of a sheet member whose main raw material is magnesium silicate (containing approximately 75% to 85% by weight of magnesium silicate), or a sheet member whose main raw material is silica.

[0135] In the above descriptions of the first to fourth embodiments of the present invention, in the battery pack, when the mica sheet is viewed from above, one opening is positioned to overlap one safety valve. In the battery pack of the present invention, when the mica sheet is viewed from above, as long as one opening is positioned to overlap at least a portion of one safety valve, there may be a non-overlapping portion.

[0136] Furthermore, in the above description of the first to fourth embodiments of the present invention, when the mica sheet is viewed from above in a perspective view, one opening in the battery pack is positioned so as to overlap one safety valve, but multiple openings may each be positioned so as to overlap at least a portion of one safety valve.

[0137] In the above description of the first to fourth embodiments of the present invention, the first insulating sheet is an inorganic fiber mat. However, in the battery pack of the present invention, the first insulating sheet may be made of, for example, a sheet, paper, board, or the like formed using inorganic particles or a mixture of inorganic particles and inorganic fibers.

[0138] In the above description of the first to fourth embodiments of the present invention, the second insulating sheet is a mica sheet and the covering piece is a mica piece. However, in the battery pack of the present invention, the second insulating sheet may be a heat-resistant resin sheet. Also, the covering piece may be a heat-resistant resin piece. Also, the heat-resistant resin sheet or the heat-resistant resin piece may be made of polyamide resin, polybutylene terephthalate resin, or polypropylene resin.

[0139] The present specification discloses the following:

[0140] The present disclosure (1) is a battery pack comprising a module having a plurality of battery cells, each having a safety valve, a case for accommodating the module, and an insulating material provided between the module and the case, wherein the insulating material includes a first insulating sheet and a second insulating sheet laminated on the first insulating sheet, the insulating material is arranged so that the first insulating sheet is located on the module side and the second insulating sheet is located on the case side, the second insulating sheet has a plurality of openings formed therethrough, each of the plurality of openings has a covering piece disposed therein that covers at least a portion of the opening, the covering piece is adhered to the first insulating sheet and / or the second insulating sheet by an adhesive layer, and when the second insulating sheet is viewed from above in a perspective view, one of the openings is positioned so as to overlap at least a portion of one of the safety valves.

[0141] The present disclosure (2) is the battery pack according to the present disclosure (1), wherein at least one of the covering pieces is disposed inside each of the plurality of openings.

[0142] The present disclosure (3) is the battery pack according to the present disclosure (2), wherein a plurality of the covering pieces are arranged inside each of the plurality of openings.

[0143] The present disclosure (4) is the battery pack according to the present disclosure (3), wherein at least some of the covering pieces are arranged to be in contact with each other.

[0144] The present disclosure (5) is a battery pack in any combination with any of the present disclosures (1) to (4), in which the covering piece is arranged so that at least a portion thereof contacts the outline of the opening.

[0145] The present disclosure (6) is a battery pack in any combination with any of the present disclosures (1) to (4), in which the covering piece is arranged so as to cover the outline of the opening from the case side.

[0146] The present disclosure (7) is a battery pack according to any one of the present disclosures (1) to (6), in which the first insulating sheet has a cutout portion formed therein that continues from the main surface on which the second insulating sheet is laminated to the other main surface, and when the insulating material is viewed in a plan view from the second insulating sheet side, at least a portion of the cutout portion is located inside the opening.

[0147] The present disclosure (8) is a battery pack according to the present disclosure (7), in which the cut portion is formed linearly when the insulating material is viewed in a plan view from the second insulating sheet side.

[0148] The present disclosure (9) is a battery pack described in the present disclosure (8) in which, when the insulating material is viewed in a plane from the second insulating sheet side, the cut portion is formed so as to intersect with the outline of the opening.

[0149] The present disclosure (10) is the battery pack according to any one of the present disclosures (7) to (9), wherein the first insulating sheet has a plurality of the cut portions formed therein.

[0150] The present disclosure (11) is a battery pack described in any one of (7) to (10) in which, when the insulating material is viewed in a plane from the second insulating sheet side, a plurality of linear cut portions are formed in the first insulating sheet, and at least some of the cut portions are in contact with each other.

[0151] The present disclosure (12) is a battery pack according to any one of the present disclosures (7) to (11), in which a plurality of the covering pieces are arranged inside the opening, at least a portion of the covering pieces are in contact with each other, and when the insulating material is viewed in a plan view from the second insulating sheet side, the cut portion is formed along the portion where the covering pieces are in contact with each other.

[0152] The present disclosure (13) is a battery pack according to the present disclosure (12), in which, when the insulating material is viewed in a plane from the second insulating sheet side, the portions where the covering pieces come into contact with each other are formed in a straight line.

[0153] The present disclosure (14) is the battery pack according to any one of the present disclosures (1) to (13), wherein the planar shape of the opening is at least one selected from the group consisting of a triangle, a rectangle, a hexagon, a circle, an ellipse, and a racetrack shape.

[0154] The present disclosure (15) is the battery pack according to any one of the present disclosures (1) to (14), wherein the first heat insulating sheet is an inorganic fiber mat.

[0155] The present disclosure (16) is the battery pack according to the present disclosure (15), wherein the inorganic fiber mat is a mat-shaped inorganic fiber including at least one type of fiber selected from silica fiber, glass fiber, alumina fiber, aluminosilicate fiber, basalt fiber, rock wool, and biosoluble fiber.

[0156] The present disclosure (17) is the battery pack according to the present disclosure (15) or (16), wherein the inorganic fiber mat is a mat-shaped inorganic fiber including fibers having a melting point of 1000°C or higher.

[0157] The present disclosure (18) is a battery pack according to any one of the present disclosures (15) to (17), wherein the inorganic fiber mat is a mat-shaped inorganic fiber including fibers having a melting point of less than 1000°C.

[0158] The present disclosure (19) is the battery pack according to any one of the present disclosures (1) to (18), wherein the second insulating sheet is a mica sheet.

[0159] The present disclosure (20) is the battery pack according to any one of the present disclosures (1) to (18), wherein the second heat insulating sheet is a heat-resistant resin sheet.

[0160] The present disclosure (21) is the battery pack according to any one of the present disclosures (1) to (20), wherein the covering piece is made of the same material as the second insulating sheet.

[0161] The present disclosure (22) is the battery pack according to any one of the present disclosures (1) to (21), wherein the adhesive layer includes an organic adhesive layer.

[0162] The present disclosure (23) is a battery pack according to any one of the present disclosures (1) to (22), wherein the insulating material further includes a third insulating sheet, and the third insulating sheet is laminated on the second insulating sheet so as to cover the opening from the case side.

[0163] The present disclosure (24) is a battery pack according to any one of the present disclosures (1) to (23), in which the case has a storage section consisting of a bottom and a side wall section, and a lid section that covers the storage section, and the safety valve is arranged to be located on the bottom side or on the lid side.

[0164] <Cleavage Test 1> (Example 1-1) An inorganic fiber mat made of silica fiber and having a thickness of 5 mm was prepared. Also, a mica sheet having a thickness of 0.1 mm was prepared, and the mica sheet was punched out so as to form a circular opening having a diameter of 8 mm.

[0165] The mica sheet with the openings formed therein was adhered to the main surface of the inorganic fiber mat using a polyamide-based organic material (heat-resistant temperature 100°C). Also, the punched circular fragments (mica pieces) were adhered to the main surface of the inorganic fiber mat using a polyamide-based organic material (heat-resistant temperature 100°C) so as to fit inside the openings.

[0166] Next, the mica sheet, the mica piece, and the inorganic fiber mat were punched out so that two 30 mm line segments intersected at right angles and the intersection point coincided with the center of the mica piece.

[0167] The heat insulating material according to Example 1-1 was produced through the above steps. The obtained heat insulating material is shown in Fig. 12. Fig. 12 is a photograph of the heat insulating material according to Example 1-1 of the present invention taken from the mica sheet side.

[0168] (Example 1-2) A 5 mm thick inorganic fiber mat made of silica fiber was prepared. A 0.1 mm thick mica sheet was also prepared, and the mica sheet was punched out to form a circular opening with a diameter of 8 mm. Then, the punched circular fragments (mica pieces) were removed.

[0169] The mica sheet with the openings formed therein was adhered to the main surface of the inorganic fiber mat using a polyamide-based organic material (heat-resistant temperature 100°C). Next, the mica sheet and the inorganic fiber mat were punched out so that two 30 mm line segments intersected at right angles and the intersection point coincided with the center of the opening. After that, the mica piece was adhered to the main surface of the inorganic fiber mat using a polyamide-based organic material (heat-resistant temperature 100°C) so that it fit inside the opening.

[0170] The heat insulating material according to Example 1-2 was produced through the above steps. The obtained heat insulating material is shown in Fig. 13. Fig. 13 is a photograph of the heat insulating material according to Example 1-2 of the present invention taken from the mica sheet side.

[0171] Using the thermal insulating materials according to Examples 1-1 and 1-2, a cleavage test 1 was conducted, simulating the case where gas is ejected from a safety valve of a battery cell. FIG. 14 is an explanatory diagram schematically illustrating the cleavage test 1. As shown in FIG. 14, each thermal insulating material 40 was sandwiched and fixed between a first jig having a first opening 61a and a second jig 62 having a second opening 62a. The first opening 61a and the second opening 62a were circular with a radius of 10 mm. The thermal insulating material 40 was positioned so that the mica sheet 42 was located on the second jig 62 side. Furthermore, when viewed from the second jig 62 side, the center of gravity of the first opening 61a, the center of gravity of the opening 42a of the mica sheet 42, and the center of gravity of the second opening 62a were aligned. The thermal insulating material 40 was then compressed to a thickness of 3 mm. Next, the thermal insulating material 40 was heated at 250°C. This weakened the adhesive strength of the polyamide organic material, making it easier for the mica pieces to separate from the inorganic fiber mat. Next, a gas pipe 70 having a gas valve 71 was connected to the first opening 61a. Air at 25°C was then sent into the gas pipe so that the gas pressure before opening the gas valve 71 was 200 kPa. The gas valve 71 was then opened, and the air was sprayed onto the insulation material 40.

[0172] The gas pressure was measured after the gas valve 71 was opened. In the test using the heat insulating material according to Example 1-1, the gas pressure after the gas valve was opened was 90 kPa. In the test using the heat insulating material according to Example 1-2, the gas pressure after the gas valve was opened was 94 kPa.

[0173] Further, in each example, it was observed whether mica pieces had peeled off from the inorganic fiber mat. The results are shown in Figures 15A, 15B, 16A, and 16B. Figure 15A is a photograph taken from the second jig side before the gas valve was released in a gas pressure cleavage test using the insulating material according to Example 1-1. Figure 15B is a photograph taken from the second jig side after the gas valve was released in a gas pressure cleavage test using the insulating material according to Example 1-1. Figure 16A is a photograph taken from the second jig side before the gas valve was released in a gas pressure cleavage test using the insulating material according to Example 1-2. Figure 16B is a photograph taken from the second jig side after the gas valve was released in a gas pressure cleavage test using the insulating material according to Example 1-2.

[0174] 15A, 15B, 16A, and 16B, it was observed that mica pieces peeled off from the inorganic fiber mat when the insulating material of Example 1-1 or the insulating material of Example 1-2 was used. This result suggests that in the battery packs using the insulating material of Example 1-1 or the insulating material of Example 1-2, when high-temperature gas was ejected from the safety valve due to thermal runaway, the mica pieces peeled off from the inorganic fiber mat and the gas was dispersed between the insulating material and the case.

[0175] <Cleaving Test 2> (Examples 2-1) to 2-3) and (Comparative Example 2-1) A 5 mm thick inorganic fiber mat made of silica fiber and a 0.1 mm thick mica sheet were prepared. Next, as shown in FIGS. 17A and 17B, 18A and 18B, 19A and 19B, and 20A and 20B, the inorganic fiber mat and the mica sheet were punched out to form incisions 41a, openings 42a, and mica pieces 50 (note that in FIGS. 17A and 20A, no incisions were made in the inorganic fiber mat, and in FIG. 20B, no openings were made in the mica sheet). FIG. 17A is a plan view schematically showing the inorganic fiber mat according to Example 2-1. FIG. 17B is a plan view schematically showing the openings and mica pieces of the mica sheet according to Example 2-1. FIG. 18A is a plan view schematically showing incisions of the inorganic fiber mat according to Example 2-2. Fig. 18B is a plan view schematically showing openings and mica pieces in the mica sheet according to Example 2-2. Fig. 19A is a plan view schematically showing cut portions in the inorganic fiber mat according to Example 2-3. Fig. 19B is a plan view schematically showing openings and mica pieces in the mica sheet according to Example 2-3. Fig. 20A is a plan view schematically showing the inorganic fiber mat according to Comparative Example 2-1. Fig. 20B is a plan view schematically showing the mica sheet according to Comparative Example 2-1.

[0176] The inorganic fiber mat shown in Figure 17A and the mica sheet and mica pieces shown in Figure 17B were combined, and the mica sheet with openings formed therein was adhered to the main surface of the inorganic fiber mat using a polyamide-based organic material (heat-resistant temperature 100°C). Furthermore, the punched circular fragments (mica pieces) were adhered to the main surface of the inorganic fiber mat using a polyamide-based organic material (heat-resistant temperature 100°C) so as to fit inside the openings. Through the above steps, the heat insulating material of Example 2-1 was produced.

[0177] Similarly, the inorganic fiber mat shown in Fig. 18A and the mica sheet and mica pieces shown in Fig. 18B were combined to produce a heat insulating material according to Example 2-2. Similarly, the inorganic fiber mat shown in Fig. 19A and the mica sheet and mica pieces shown in Fig. 19B were combined to produce a heat insulating material according to Example 2-3. Similarly, the inorganic fiber mat shown in Fig. 20A and the mica sheet shown in Fig. 20B were combined to produce a heat insulating material according to Comparative Example 2-1.

[0178] Using the thermal insulation materials according to Examples 2-1 to 2-3 and Comparative Example 2-1, a cleavage test 2 simulating a case in which gas is ejected from a safety valve of a battery cell was conducted. FIG. 21 is an explanatory diagram schematically illustrating the cleavage test 2. As shown in FIG. 21 , in the cleavage test 2, each thermal insulation material 40 was sandwiched and fixed between a first jig having a first opening 61a and a second jig 62 having a second opening 62a. The inorganic fiber mat 41 was placed on the first jig 61 side, and the mica sheet 42 was placed on the second jig 62 side. Furthermore, when viewed from the second jig 62 side, the centers of gravity of the first opening 61a, the opening 42a of the mica sheet 42, and the second opening 62a were aligned. The thermal insulation material 40 was then compressed so that its thickness was 3 mm. Thereafter, heated alumina particles were sprayed from the blasting device 80 so that the heated alumina particles would pass through the first opening 61a and reach the heat insulating material.

[0179] The thermal spraying conditions were as follows: <Thermal spraying conditions> Carrier gas: acetylene gas Carrier gas temperature: 3000°C Blasting particles: alumina particles Spraying distance: 150 mm Spraying time: 30 seconds

[0180] The surface temperature of the inorganic fiber mat when the heated alumina particles reached the inorganic fiber mat was 1300°C.

[0181] After the thermal spraying, the mica pieces 50 were observed to see if they had peeled off from the inorganic fiber mat 41 (whether the sprayed material had passed through the heat insulating material). The evaluation criteria were as follows. The evaluation results are shown in Table 1.

[0182] <Evaluation criteria> ⊚: Mica pieces peeled off from the inorganic fiber mat, and the sprayed material was able to pass through the insulation material sufficiently. ◯: Mica pieces peeled off from the inorganic fiber mat, and the sprayed material was able to pass through the insulation material, but there were signs that some of the sprayed material was retained (reflected). ×: The sprayed material was reflected by the insulation material and did not pass through the insulation material.

[0183]

[0184] As shown in Table 1, it was found that the sprayed material passed through the thermal insulation in each example in which openings were provided in the mica sheet. This result suggests that in the battery packs using the thermal insulation materials of Examples 2-1 to 2-3, when high-temperature gas was ejected from the safety valve due to thermal runaway, the gas passed through the thermal insulation and was dispersed between the thermal insulation and the case.

[0185] 10, 310 Battery pack 20, 320 Module 20a, 320a Connection module member 20b Bus bar 21, 21a, 321, 321a Battery cell 22, 22a, 322, 322a Safety valve 23 Terminal 30, 330 Case 31 Storage section 31b Bottom 31s Side wall 32 Lid 40, 140, 240a, 240b, 240c, 340 Heat insulating material 41, 141, 241, 341 Inorganic fiber mat 42, 142, 242, 342 Mica sheet 42a, 142a, 142a １ , 142a ２ , 142a ３、 242a, 342a opening 50, 50a, 50b １ , 50b ２ , 50b ３ , 50b ４ , 50c １ , 50c ２ , 50d, 50e, 150, 150a １ , 150a ２ , 150a ３ , 250, 350 Mica pieces 61 First jig 61a First opening 62 Second jig 62a Second opening 70 Gas pipe 71 Gas valve 80 Blasting device 141a, 141a １ , 141a ２ , 141a ３, 241a Cutout portion 343 Third heat insulating sheet

Claims

1. A module having multiple battery cells, each equipped with a safety valve, A case for housing the aforementioned module, A battery pack comprising an insulating material provided between the module and the case, The aforementioned insulation material includes a first insulation sheet and a second insulation sheet laminated on the first insulation sheet. The insulation material is arranged such that the first insulation sheet is located on the module side and the second insulation sheet is located on the case side. The second insulation sheet has a plurality of openings that penetrate it, Each of the aforementioned multiple openings is provided with a covering piece that covers at least a portion of the opening. The covering piece is bonded to the first insulation sheet and / or the second insulation sheet by an adhesive layer. A battery pack characterized in that, when the second heat insulating sheet is viewed through from above, one of the openings is positioned to overlap with at least a portion of one of the safety valves.

2. The battery pack according to claim 1, wherein at least one of the covering pieces is arranged inside each of the plurality of openings.

3. The battery pack according to claim 2, wherein a plurality of covering pieces are arranged inside each of the plurality of openings.

4. The battery pack according to claim 3, wherein at least some of the plurality of covering pieces are arranged to be in contact with each other.

5. The battery pack according to any one of claims 1 to 4, wherein at least a portion of the covering piece is arranged to contact the contour of the opening.

6. The battery pack according to any one of claims 1 to 4, wherein the covering piece is arranged to cover the contour of the opening from the case side.

7. The first insulation sheet has a continuous cut portion formed from the main surface on which the second insulation sheet is laminated to the other main surface. The battery pack according to any one of claims 1 to 4, wherein when the insulating material is viewed in plan from the second insulating sheet side, at least a portion of the cut portion is located inside the opening.

8. The battery pack according to claim 7, wherein the notch is formed in a linear shape when the insulating material is viewed in plan view from the second insulating sheet side.

9. The battery pack according to claim 8, wherein when the insulating material is viewed in plan from the second insulating sheet side, the notch is formed to intersect with the contour of the opening.

10. The battery pack according to claim 7, wherein the first heat insulating sheet has a plurality of cut portions formed therein.

11. When the aforementioned insulation material is viewed in plan view from the side of the second insulation sheet, The first heat insulating sheet has a plurality of linear cuts formed therein. The battery pack according to claim 7, wherein at least some of the multiple notches are in contact with each other.

12. Multiple covering pieces are arranged inside the opening. At least some of the multiple covering pieces are in contact with each other. The battery pack according to claim 7, wherein, when the insulating material is viewed in plan view from the second insulating sheet side, the notches are formed along the portions where the covering pieces come into contact with each other.

13. The battery pack according to claim 12, wherein when the insulating material is viewed in plan view from the second insulating sheet side, the portion where the covering pieces come into contact with each other is formed in a straight line.

14. The battery pack according to any one of claims 1 to 4, wherein the plan view shape of the opening is at least one selected from the group consisting of a triangle, a square, a hexagon, a circle, an ellipse, and a racetrack shape.

15. The battery pack according to any one of claims 1 to 4, wherein the first heat insulating sheet is an inorganic fiber mat.

16. The battery pack according to claim 15, wherein the inorganic fiber mat is made by processing inorganic fibers into a mat shape, comprising at least one fiber selected from silica fibers, glass fibers, alumina fibers, aluminosilicate fibers, basalt fibers, rock wool, and biosoluble fibers.

17. The battery pack according to claim 15, wherein the inorganic fiber mat is made by processing inorganic fibers containing fibers with a melting point of 1000°C or higher into a mat shape.

18. The battery pack according to claim 15, wherein the inorganic fiber mat is made by processing inorganic fibers, including fibers with a melting point of less than 1000°C, into a mat shape.

19. The battery pack according to any one of claims 1 to 4, wherein the second heat insulating sheet is a mica sheet.

20. The battery pack according to any one of claims 1 to 4, wherein the second heat insulating sheet is a heat-resistant resin sheet.

21. The battery pack according to any one of claims 1 to 4, wherein the covering piece is made of the same material as the second heat insulating sheet.

22. The battery pack according to any one of claims 1 to 4, wherein the adhesive layer comprises an organic adhesive layer.

23. The aforementioned insulation material further includes a third insulation sheet, The battery pack according to any one of claims 1 to 4, wherein the third heat insulating sheet is laminated on the second heat insulating sheet so as to cover the opening from the case side.

24. The case comprises a storage section consisting of a bottom and side walls, and a lid that covers the storage section. The battery pack according to any one of claims 1 to 4, wherein the safety valve is positioned on the bottom side or on the lid side.