Battery pack

Abstract

Provided is a battery pack in which the chain of thermal runaway due to high-temperature gas from an abnormal battery cell generated during a thermal runaway can be prevented. The battery pack according to the present invention comprises: a module having a plurality of battery cells each provided with a safety valve; a case accommodating the module; and a heat insulating material provided between the module and the case. The battery pack is characterized in that: the heat insulating material includes a first heat insulating sheet; the first heat insulating sheet has a plurality of openings formed through the first heat insulating sheet; a cover piece is disposed at each of the plurality of openings, the cover piece covering at least a part of the opening; the cover piece is bonded to the first heat insulating sheet by an adhesive; and when the first heat insulating sheet is viewed in a planar transparent view, one of the openings is positioned so as to overlap at least a part 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, the first insulating sheet has a plurality of openings formed therein that penetrate the first insulating sheet, 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 with an adhesive, and when the first 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 insulating sheet having an opening formed therethrough. The opening is positioned so as to overlap at least a portion of the safety valve when viewed from above. Therefore, gas discharged from the safety valve reaches the vicinity of the opening in the first insulating sheet.

[0013] 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 with an adhesive. The high temperature of the gas that reaches the vicinity of the opening of the first insulating sheet causes the adhesive that adheres the covering piece to thermally decompose, thereby weakening the bond between the covering piece and the first insulating sheet. Gas pressure is also 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.

[0014] The gas then passes through the opening in the first insulating sheet and is released between the insulating material and the case. During this process, the temperature of the high-temperature gas drops and the gas pressure also decreases. Therefore, even if the gas is released from the opening and comes into contact with the case, the case is unlikely to be heated or damaged by the gas.

[0015] Furthermore, gas released from the opening in the first insulating sheet diffuses between the thermal insulation material and the case and reaches the other opening in the first insulating sheet. However, because a covering piece is placed inside the other opening in the first insulating sheet, even if the gas reaches the other opening in the first insulating sheet, it is possible to prevent backflow from the other opening in the first insulating sheet toward the module.

[0016] 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.

[0017] 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, because if the covering pieces are disposed inside the openings, the covering pieces are likely to peel off from the first insulating sheet.

[0018] 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.

[0019] 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.

[0020] In the battery pack of the present invention, it is preferable that at least a portion of the covering pieces are arranged so as to contact one another. In this case, the portions where the covering pieces contact one another are preferably formed linearly. Furthermore, in the battery pack of the present invention, it is preferable that the covering pieces are arranged so that at least a portion of the covering pieces contact the contour of the opening. When the covering pieces are arranged in this manner, it is easier to prevent backflow of gas from gaps between the covering pieces or gaps between the covering pieces and the opening.

[0021] 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.

[0022] 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.

[0023] In the battery pack of the present invention, the first heat insulating sheet may be a mica sheet or a heat-resistant resin sheet, which are suitable materials for the first heat insulating sheet.

[0024] In the battery pack of the present invention, the covering piece is preferably made of the same material as the first insulating sheet. The first insulating sheet and the covering piece can be simultaneously produced by punching out the monolithic sheet so as to form an opening.

[0025] In the battery pack of the present invention, the adhesive preferably includes an organic adhesive. If the adhesive includes an organic adhesive, the adhesive is more likely to thermally decompose when high-temperature gas from the abnormal battery cell reaches the covering piece, which makes the covering piece more likely to peel off from the first insulating sheet.

[0026] In the battery pack of the present invention, the thermal insulation material may further include a second insulating sheet, and the second insulating sheet may be laminated on the first insulating sheet so as 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 second 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 first insulating sheet and reaches the second insulating sheet. The gas is blocked by the second insulating sheet. As a result, the gas is prevented from contacting the case. The second insulating sheet is also pushed upward by the gas, away from the first insulating sheet. This allows the gas to diffuse through the gap formed between the second insulating sheet and the first insulating sheet. The temperature and pressure of the gas then decrease.

[0027] 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.

[0028] 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.

[0029] 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. 4F 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 an insulating material provided in a battery pack according to a second embodiment of the present invention. FIG. 5B is an enlarged cross-sectional view schematically showing another example of a cross section of an insulating material provided in a battery pack according to the second embodiment of the present invention. FIG. 6 is an enlarged cross-sectional view schematically showing an example of a battery pack according to a third embodiment of the present invention. FIG. 7A is an explanatory diagram sequentially showing 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 third embodiment of the present invention. FIG. 7B is an explanatory diagram sequentially showing the principle of preventing a chain reaction of thermal runaway when one battery cell experiences thermal runaway in the battery pack according to the third embodiment of the present invention.FIG. 7C is an explanatory diagram sequentially showing the principle of preventing a chain reaction of thermal runaway when one battery cell experiences thermal runaway in the battery pack according to the third embodiment of the present invention.

[0030] 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.

[0031] First Embodiment A battery pack according to a first embodiment of the present invention will be described, in which the first insulating sheet and covering pieces constituting the insulating material are mica sheets 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. A 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.

[0032] 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).

[0033] 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.

[0034] 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.).

[0035] Examples of materials that can be used to form the case 30 include steel and aluminum. As the steel, stainless steel (SUS) is preferred.

[0036] 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.

[0037] As shown in Fig. 2A, the heat insulating material 40 is made of a mica sheet 42, which is a first heat insulating sheet. An opening 42a is formed in the mica sheet 42, and as shown in Fig. 2B, four mica pieces 50, which are covering pieces, are arranged inside the opening 42a. The mica pieces 50 are adhered to the mica sheet 42 with an adhesive (not shown). In other words, the mica pieces 50 are adhered to the inner wall of the opening 42a.

[0038] 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 .

[0039] 2B, the opening 42a is circular. The four mica pieces 50 are congruent sector shapes 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 a circle. The mica pieces 50 may be bonded to each other with an adhesive at the contacting portions.

[0040] 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.

[0041] 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 insulating material 40 (mica sheet 42).

[0042] 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 released from the safety valve 22a reaches the vicinity of the opening 42a of the mica sheet 42.

[0043] Mica pieces 50 are disposed inside the openings 42a of the mica sheet 42 and are adhered to the mica sheet 42 with an adhesive (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 that adheres the mica pieces 50 to thermally decompose. This weakens the adhesion between the mica pieces 50 and the mica sheet 42. Gas pressure is also applied to the mica pieces 50 from the module 20 toward the case 30. As a result, as shown in FIG. 3B , the mica pieces 50 peel off from the mica sheet 42. In the battery pack 10, the mica pieces 50 are separate from the mica sheet 42 and are adhered with an adhesive as separate components. In other words, the mica pieces 50 are not partially continuous with the mica sheet 42. Therefore, the thermal decomposition of the adhesive reliably peels the mica pieces 50 off the mica sheet 42.

[0044] The gas G then passes through the openings 42a of the mica sheet 42 and is released between the heat insulating material 40 and the case 30. In this process, the temperature of the gas G drops and the gas pressure also drops. Therefore, even if the gas G is released from the openings 42a and comes into contact with the case 30, the case 30 is unlikely to be heated or damaged by the gas G.

[0045] 3C, the gas G released from the opening 42a of the mica sheet 42 diffuses between the mica sheet 42 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.

[0046] 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.

[0047] 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.

[0048] (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.

[0049] 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.

[0050] 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 mica sheet when the gas reaches them, so mica pieces arranged in an area that the gas cannot reach are less likely to peel off.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Next, the shape of the mica pieces when multiple mica pieces are arranged inside the opening will be described below. Figures 4A to 4F 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.

[0057] 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.

[0058] 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.

[0059] 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. １ and 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 In this case, the mica piece 50c is a circle located inside the １ and mica pieces 50c ２ The mica pieces 50c are bonded together with an adhesive to form a contact area. ２ can be held without falling off.

[0060] 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.

[0061] 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.

[0062] As shown in FIG. 4F, the mica pieces in the battery pack according to the first embodiment of the present invention are six mica pieces 50f １ , mica pieces 50f ２ , mica pieces 50f ３ , mica pieces 50f ４ , mica pieces 50f ５ and mica pieces 50f ６ The mica pieces may be shaped so that, when combined, they form a racetrack shape. More specifically, the shape is obtained by cutting a single racetrack-shaped mica piece along a line segment L1 along the long axis and four line segments L2, L3, L4, and L5 that are tangent to line segment L1. The point where line segment L1 and line segment L2 meet is the same as the point where line segment L1 and line segment L3 meet, and the angle formed by line segment L1 and line segment L2 is the same as the angle formed by line segment L1 and line segment L3. Furthermore, the point where line segment L1 and line segment L4 meet is the same as the point where line segment L1 and line segment L5 meet, and the angle formed by line segment L1 and line segment L4 is the same as the angle formed by line segment L1 and line segment L5.

[0063] In the thermal insulation material 40, the mica pieces 50 are adhered to the mica sheet 42 with an adhesive (not shown). The adhesive preferably contains a material that thermally decomposes when gas reaches the mica pieces 50. If the adhesive contains such a material, the mica pieces 50 are likely to peel off when gas reaches the mica pieces 50.

[0064] 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, and more specifically, a polyamide-based organic material. If the adhesive contains a polyamide-based organic material, the adhesive is more likely to thermally decompose when the high-temperature gas G from the abnormal battery cell reaches the mica pieces 50. This makes it easier for the mica pieces 50 to peel off from the mica sheet 42.

[0065] In the battery pack 10, the mica sheet 42, which is the first 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 first insulating sheet, or may be made of a different material.

[0066] A method for manufacturing the insulating material included in the battery pack according to the first embodiment of the present invention will now be described. When manufacturing the insulating material, a mica sheet is prepared. Next, the mica sheet is punched to produce a mica sheet with an opening and mica pieces. Next, the mica pieces are adhered to the mica sheet (the inner wall of the opening) using an adhesive so that the prepared mica pieces fit inside the opening. This completes the manufacturing of the insulating material to be placed in the battery pack of the present invention.

[0067] 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.

[0068] Also, mica pieces other than punched mica pieces may be placed inside the opening.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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 mica pieces are arranged so as to cover the outline of the opening from the case side. The battery pack according to the second embodiment of the present invention will be described in detail below with reference to the drawings.

[0073] 5A and 5B are enlarged cross-sectional views schematically illustrating 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, respectively.

[0074] 5A includes a mica sheet 142 and mica pieces 150. An opening 142a is formed in the mica sheet 142, and the mica pieces 150 are arranged so as to cover the outline of the opening 142a from the case (not shown) side. The mica pieces 150 are adhered to the surface of the mica sheet 142 with an adhesive (not shown).

[0075] The heat insulating material 140b shown in FIG. 5B differs from the heat insulating material 140a in that a plurality of mica pieces 150 are arranged.

[0076] 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.

[0077] Other than the above differences, the preferred materials for each component of the battery pack according to the second 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.

[0078] (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 first embodiment of the present invention in that the heat insulating material further includes a second 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 third embodiment of the present invention will be described in detail below with reference to the drawings.

[0079] FIG. 6 is an enlarged cross-sectional view schematically illustrating an example of a battery pack according to a third embodiment of the present invention. The battery pack 210 shown in FIG. 6 includes a module 220 having a plurality of battery cells 221 and a connection module member 220a connecting the battery cells 221, and a case 230 that houses the module 220. In the battery pack 210, each battery cell 221 is provided with a safety valve 222. In addition, in the battery pack 210, a heat insulating material 240 is provided between the module 220 and the case 230. The battery pack 210 is arranged so that the safety valve 222 is located vertically upward. In other words, the battery pack 210 is arranged upside down compared to the battery pack 10 shown in FIG. 1B.

[0080] The heat insulating material 240 is formed by laminating a mica sheet 242 as a first heat insulating sheet and a second heat insulating sheet 243 in this order from the bottom.

[0081] The mica sheet 242 has an opening 242a formed therethrough, and a mica piece 250 is disposed inside the opening 242a.

[0082] The mica pieces 250 are adhered to the mica sheet 242 (the inner wall of the opening 242a) by an adhesive (not shown).

[0083] The second heat insulating sheet 243 is laminated on the mica sheet 242 so as to cover the opening 242a from the case 230 side.

[0084] Next, the function of the second insulating sheet 243 will be described using the drawings. Figures 7A to 7C are explanatory diagrams 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 third embodiment of the present invention. As shown in Figure 7A, when one battery cell 221a experiences thermal runaway and generates high-temperature gas from the battery cell 221a, gas G (in Figure 7A, 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 222a. The gas released from the safety valve 222a then reaches the insulating material 240.

[0085] The gas G that has reached the heat insulating material 240 reaches the mica sheet 242. The mica sheet 242 has an opening 242a formed therethrough, and the opening 242a is positioned so as to overlap with the safety valve 222 when the mica sheet 242 is viewed from above.

[0086] Mica pieces 250 are arranged inside openings 242a of the mica sheet 242, and are adhered to the mica sheet 242 with an adhesive (not shown). The high temperature of the gas G that reaches the vicinity of openings 242a of the mica sheet 242 causes the adhesive that adheres the mica pieces 250 to thermally decompose. This weakens the adhesion between the mica pieces 250 and the mica sheet 242. In addition, gas pressure is applied to the mica pieces 250 from the module 220 side toward the case 230 side. As a result, the mica pieces 250 peel off from the mica sheet 242, as shown in FIG. 7B .

[0087] The gas G then passes through the openings 242a of the mica sheet 242 and reaches the second insulating sheet 243. The gas G is blocked by the second insulating sheet 243. The gas G also pushes the second insulating sheet 243 upward so as to move away from the mica sheet 242. As a result, the gas G can be prevented from coming into contact with the case 230.

[0088] 7C, the gas G is diffused through the gap S formed between the second insulating sheet 243 and the mica sheet 242. Then, the temperature and pressure of the gas G decrease.

[0089] 7C, the second insulating sheet 243 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 242, thereby forming a gap S. For example, the second insulating sheet 243 may be disposed on the mica sheet 242 without being fixed, or may be disposed on the mica sheet 242 so that a portion of it is fixed.

[0090] The second heat insulating sheet 243 may be made of a sheet member whose main ingredient is magnesium silicate (containing approximately 75% to 85% by weight of magnesium silicate), or a sheet member whose main ingredient is silica.

[0091] In the above description of the battery pack according to the first embodiment of the present invention, 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 portion that does not overlap.

[0092] Furthermore, in the above description of the battery pack according to the first embodiment of the present invention, when the mica sheet is viewed in plan view, one opening 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.

[0093] In the above description of the first to third embodiments of the present invention, the first insulating sheet is a mica sheet and the covering pieces are mica pieces. However, in the battery pack of the present invention, the first insulating sheet may be a heat-resistant resin sheet. Also, the covering pieces may be heat-resistant resin pieces. Also, the heat-resistant resin sheet or the heat-resistant resin pieces may be made of polyamide resin, polybutylene terephthalate resin, or polypropylene resin.

[0094] The present specification discloses the following:

[0095] 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, the first insulating sheet has a plurality of openings formed therein that penetrate the first insulating sheet, 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 with an adhesive, and when the first insulating sheet is viewed in plan view, one of the openings is positioned so as to overlap at least a portion of one of the safety valves.

[0096] 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.

[0097] 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.

[0098] The present disclosure (4) is a battery pack according to the present disclosure (3), in which at least some of the plurality of covering pieces are arranged so as to be in contact with each other, and the plurality of covering pieces are adhered to each other with an adhesive.

[0099] The present disclosure (5) is a battery pack described in the present disclosure (4) in which, when the insulating material is viewed in a plane from the first insulating sheet side, the portions where the covering pieces contact each other are formed in a straight line.

[0100] The present disclosure (6) is the battery pack according to any one of the present disclosures (1) to (5), wherein the covering piece is arranged so that at least a portion thereof contacts the contour of the opening.

[0101] The present disclosure (7) is a battery pack according to any one of the present disclosures (1) to (5), in which the covering piece is arranged so as to cover the opening from the case side.

[0102] The present disclosure (8) is the battery pack according to any one of the present disclosures (1) to (7), 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.

[0103] The present disclosure (9) is the battery pack according to any one of the present disclosures (1) to (8), wherein the first insulating sheet is a mica sheet.

[0104] The present disclosure (10) is the battery pack according to any one of the present disclosures (1) to (8), wherein the first heat insulating sheet is a heat-resistant resin sheet.

[0105] The present disclosure (11) is the battery pack according to any one of the present disclosures (1) to (10), wherein the covering piece is made of the same material as the first insulating sheet.

[0106] The present disclosure (12) is the battery pack according to any one of the present disclosures (1) to (11), wherein the adhesive includes an organic adhesive.

[0107] The present disclosure (13) is a battery pack according to any one of the present disclosures (1) to (12), wherein the heat insulating material further includes a second heat insulating sheet, and the second heat insulating sheet is laminated on the first heat insulating sheet so as to cover the opening from the case side.

[0108] The present disclosure (14) is a battery pack according to any one of the present disclosures (1) to (13), in which the case includes 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.

[0109] 10, 210 Battery pack 20, 220 Module 20a, 220a Connection module member 20b Bus bar 21, 21a, 221, 221a Battery cell 22, 22a, 222, 222a Safety valve 23 Terminal 30, 230 Case 31 Storage section 31b Bottom 31s Side wall 32 Lid 40, 140a, 140b, 240 Heat insulating material 42, 142, 242 Mica sheet 42a, 142a, 242a Opening 50, 50a, 50b １ , 50b ２ , 50b ３ , 50b ４ , 50c １ , 50c ２ , 50d, 50e, 50f １ , 50f ２ , 50f ３ , 50f ４ , 50f ５ , 50f ６ , 150, 250 Mica pieces 243 Second heat insulating sheet

Claims

1. A battery pack comprising: a module having a plurality of battery cells, each having a safety valve, a case that houses the module, and an insulating material provided between the module and the case, wherein the insulating material includes a first insulating sheet, the first insulating sheet has a plurality of openings formed therein that penetrate the first insulating sheet, 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 by an adhesive, and when the first insulating sheet is viewed in plan view, one of the openings is positioned so as to overlap at least a portion of one of the safety valves.

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

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

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

5. The battery pack according to claim 4, wherein when the heat insulating material is viewed in a plan view from the first heat insulating sheet side, the portions where the covering pieces come into contact with each other are formed in straight lines.

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

7. A battery pack according to any one of claims 1 to 5, wherein the covering piece is disposed so as to cover the opening from the case side.

8. The battery pack according to any one of claims 1 to 7, wherein the opening 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.

9. The battery pack according to any one of claims 1 to 8, wherein the first insulating sheet is a mica sheet.

10. The battery pack according to any one of claims 1 to 8, wherein the first heat insulating sheet is a heat-resistant resin sheet.

11. The battery pack according to any one of claims 1 to 10, wherein the covering piece is made of the same material as the first insulating sheet.

12. The battery pack according to any one of claims 1 to 11, wherein the adhesive includes an organic adhesive.

13. A battery pack as described in any one of claims 1 to 12, wherein the insulating material further includes a second insulating sheet, and the second insulating sheet is laminated on the first insulating sheet so as to cover the opening from the case side.

14. A battery pack as described in any one of claims 1 to 13, wherein the case comprises a storage section consisting of a bottom and side walls, and a lid section covering the storage section, and the safety valve is arranged so as to be located on the bottom side or on the lid side.

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