Battery module cover and battery pack

Abstract

Provided is a module cover (41) capable of suppressing thermal diffusion when a battery cell undergoes thermal runaway. The module cover (41) is disposed between a battery module (21), in which multiple battery cells (11) are assembled, and a housing (30) which accommodates the battery module (21). The battery cells (11) each have a discharge valve (16) that opens when the internal pressure exceeds a set pressure. The module cover (41) has: a covering part (42) that covers the discharge valves (16) of the multiple battery cells (11); and a partition part (48) that partitions the space between adjacent ones of the discharge valves (16). An easily penetrable part (44) is provided to the covering part (42) facing the discharge valves (16) in the module cover (41).

Description

Battery module cover and battery pack

[0001] This invention relates to a battery module cover and a battery pack.

[0002] In recent years, with the advancement of research and development in electric and hybrid vehicles, efforts have been made to increase the energy density and reduce the weight of batteries. In batteries, for example, an internal short circuit in a battery cell can cause gas to be generated due to the decomposition and vaporization of the electrolyte, leading to an abnormal increase in internal pressure. In such cases, the discharge valve provided in the battery cell may open, causing the vaporized electrolyte and high-temperature components inside the battery to be ejected forcefully in a short period of time accompanied by flames, resulting in what is known as thermal runaway.

[0003] Patent Document 1 proposes a battery pack in which a battery module, which is an assembly of multiple battery cells, is housed in a casing made of a specific material that has excellent flame resistance and strength, in order to delay the spread of fire to automotive interior materials when a flame occurs due to thermal runaway of battery cells.

[0004] Japanese Patent Publication No. 2024-60540

[0005] In a battery pack containing modules with multiple battery cells housed in a casing, if one battery cell experiences thermal runaway, other battery cells may be heated by the high-temperature ejected material, potentially causing a chain reaction of thermal runaway. Suppressing such heat diffusion within the casing is desirable. This invention provides a module cover that can suppress heat diffusion when thermal runaway occurs in a battery cell.

[0006] The present invention has the following aspects: <1> A module cover disposed between a battery module, which is an assembly of a plurality of battery cells, and a housing that houses the battery module, wherein the battery cells have discharge valves that open when the internal pressure exceeds a set pressure, the module cover has a covering portion that covers the discharge valves of the plurality of battery cells, and a partition portion that partitions the space between adjacent discharge valves, and an easily penetrated portion is provided in the covering portion facing the discharge valve. <2> The module cover according to <1>, wherein the module cover has a resin layer containing a flame retardant. <3> The module cover according to <2>, wherein the module cover is made of a laminate having the resin layer and a fiber layer, and the fiber layer is located on the battery module side of the resin layer. <4> The module cover according to any one of <1> to <3>, wherein the easily penetrated portion is made thinner by providing recesses on one or both of the upper and lower surfaces of the covering portion. <5> The module cover according to any one of <1> to <3>, wherein the easily penetrated portion has a weakening line formed by cutting out the upper or lower surface of the covering portion. <6> The module cover according to any one of <1> to <5>, wherein the easily penetrated portion is made thinner by providing a recess on one of the upper and lower surfaces of the covering portion, and has a weakening line formed by cutting out the other of the upper and lower surfaces of the covering portion. <7> The module cover according to any one of <1> to <6>, wherein the covering portion and the partition portion are integrally molded. <8> A battery pack comprising a battery module in which a plurality of battery cells are assembled and housed in a housing, wherein the module cover according to any one of <1> to <7> is disposed between the housing and the battery module. <9> The battery pack according to <8>, wherein the housing has an exhaust hole.

[0007] By placing the module cover of the present invention between the housing and the battery module, heat diffusion can be suppressed in the event of thermal runaway of the battery cells.

[0008] This is a schematic cross-sectional view of a part of the first embodiment of the battery pack according to the present invention. This is a cross-sectional view showing an enlarged portion of Figure 1. This is a schematic cross-sectional view of a part of the main part of the second embodiment of the battery pack according to the present invention. This is a schematic cross-sectional view of a part of the main part of the third embodiment of the battery pack according to the present invention. This is a schematic cross-sectional view of a part of the main part of the fourth embodiment of the battery pack according to the present invention. This is a schematic cross-sectional view of a part of the main part of the fifth embodiment of the battery pack according to the present invention. This is a schematic cross-sectional view of a part of the main part of the sixth embodiment of the battery pack according to the present invention. This is a diagram for explaining the method for evaluating flame resistance. This is a perspective view showing the battery pack used in the evaluation of the temperature rise suppression effect, where Figure 9(A) is a perspective view of the battery pack of Example 1, Figure 9(B) is a perspective view of the battery pack of Comparative Example 1, and Figure 9(C) is a perspective view of the battery pack of Reference Example. This is a temperature distribution contour diagram, which is the simulation result in the evaluation of the temperature rise suppression effect.

[0009] The following description of a battery pack according to an embodiment of the present invention will be made with reference to the drawings. Note that the following diagrams are schematic diagrams intended to clearly illustrate the configuration, and the dimensional ratios of each component may differ from those of the actual components.

[0010] The battery used in the battery pack of this embodiment is not particularly limited. Examples include secondary batteries such as lithium-ion batteries, nickel-metal hydride batteries, lithium-sulfur batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, sodium-sulfur batteries, lead-acid batteries, and air batteries. Among these, lithium-ion batteries are preferred.

[0011] <First Embodiment> Figure 1 is a cross-sectional view of a battery pack according to the first embodiment. The battery pack 100 of this embodiment comprises a battery module 21 which is an assembly of a plurality of battery cells (individual batteries) 11, a housing 30 which houses these, and a module cover 41 which is disposed between the battery module 21 and the housing 30.

[0012] The housing 30 has a bottomed, hollow housing formed by a bottom plate 33 and four side plates 32, and a lid 31 that closes the opening of the housing. The battery module 21 is housed on the bottom plate 33 of the housing 30 via a cushioning material 35. The battery cells 11 that make up the battery module 21 have a cell body 12 and a discharge valve 16 that opens when the internal pressure of the cell body exceeds a set pressure. The cell body 12 is a rectangular parallelepiped having a height direction or vertical direction (H), a width direction (W), and a thickness direction (D), and the discharge valve 16 is provided on one end face 14 perpendicular to the height direction. In this embodiment, the side of the cell body 12 where the discharge valve 16 is located in the height direction (H) is considered the upper side, and the end face 14 is considered the upper surface 14. In the battery module 21, a plurality of battery cells 11 are arranged such that the position of the upper surface 14 of the cell body 12 in the height direction (H) is the same for all of them. A spacer 34 is sandwiched between adjacent battery cells 11.

[0013] The module cover 41 has a covering portion 42 that covers the discharge valves 16 of a plurality of battery cells 11, and a partition portion 48 that divides the space between adjacent discharge valves 16. In the module cover 41, the surface facing the lid 31 of the housing 30 is the upper surface, and the surface facing the battery module 21 is the lower surface.

[0014] The covering portion 42 is in the form of a sheet with its thickness in the height direction (H) of the battery cell 11, and a partition portion 48 protrudes from the covering portion 42 toward the battery module 21 side, forming a bottomed hollow housing portion 49 that houses the discharge valve 16.

[0015] As shown in Figure 2, the upper surface of the module cover 41 is the upper surface 42a of the covering portion 42 and has a weakening line 46. On the lower surface of the module cover 41, partition portions 48 and housing portions 49 are alternately present. That is, on the lower surface of the module cover 41, the lower surface 48a of the partition portion 48, the side surface 49a of the housing portion 49, the bottom surface 49b of the housing portion 49, and the side surface 49a of the housing portion 49 are continuously present. When the module cover 41 is placed between the battery module 21 and the housing 30, the lower surface 48a of the partition portion 48 may or may not be in contact with the cell body 12 of the battery cell 11. In the example shown in Figure 2, the lower surface 48a of the partition portion 48 is in contact with the cell body 12 of the battery cell 11, and the housing portion 49 airtightly houses the discharge valve 16.

[0016] If the lower surface 48a of the partition portion 48 is not in contact with the cell body 12 of the battery cell 11, the distance from the lower surface 48a of the partition portion 48 to the cell body 12 may be, for example, greater than 0 and 10 mm or less, greater than 0 and 5 mm or less, or greater than 0 and 1 mm or less. Also, if the lower surface 48a of the partition portion 48 is not in contact with the cell body 12 of the battery cell 11, the space between the module cover 41 and the battery cell 11 may be filled with another member (not shown), such as an O-ring.

[0017] The lower surface 48a of the partition portion 48 may or may not be in contact with the spacer 34 between adjacent cell bodies 12. In the example shown in Figure 2, the lower surface 48a of the partition portion 48 is in contact with the spacer 34, and the cell body 12 is airtightly surrounded by the side plate 32 of the housing 30, the spacer 34, the cushioning material 35, and the module cover 41. Although Figure 2 shows a battery pack 100 with a spacer 34, the spacer 34 is not required. Also, the lower surface 48a of the partition portion 48 may or may not be in contact with other components attached to the battery cell 11 (such as busbars, not shown). A space S exists between the upper surface 42a of the covering portion 42 and the lid 31 of the housing 30. Although not shown, the housing 30 may be provided with exhaust holes that communicate with the space S.

[0018] The covering portion 42 facing the discharge valve 16 is provided with an easily penetrated portion 44 surrounded by a weakening line 46. The weakening line 46 is formed by cutting out the upper surface 42a of the covering portion 42, locally thinning the covering portion 42. The "covering portion 42 facing the discharge valve 16" is the covering portion 42 that does not have the partition portion 48, and is also the upper surface 42a of the covering portion 42 at a position corresponding to the bottom surface 49b of the storage portion 49 or the bottom surface 49b (lower surface of the covering portion 42).

[0019] When the module cover 41 is viewed from above in a plan view, the easy-penetration portion 44 is located within the area where the housing portion 49 exists. The planar shape of the easy-penetration portion 44 and the planar shape of the housing portion 49 may be the same. In the height direction (H) of the battery cell 11, the distance from the tip of the discharge valve 16 to the module cover 41 may be, for example, 0 to 10 mm, 0.5 to 5 mm, or 1 to 3 mm.

[0020] The easily penetrated portion 44 is easily destroyed and becomes a through-hole when the discharge valve 16 opens due to an increase in the internal pressure of the battery cell 11, causing the pressure inside the housing portion 49 to rise. As a result, when thermal runaway occurs in the battery cell 11, the high-temperature gas generated moves through the through-hole formed in the covering portion 42 into the space S between the covering portion 42 and the lid 31. It may also be discharged from the exhaust hole (not shown) of the housing 30. This prevents the high-temperature gas generated from one battery cell 11 from coming into contact with other cells.

[0021] The module cover 41 is made of a material that has flame-retardant properties and can form an easily penetrated portion 44. For example, the module cover 41 preferably has a resin layer containing a flame retardant. Flame-retardant properties are obtained by including a flame retardant. The resin constituting the resin layer is preferably a thermoplastic resin because of its excellent processability. The resin layer may further contain fibers. The fibers contribute to improving the strength, rigidity, and impact resistance of the resin layer. The thermoplastic resin, flame retardant, and fibers of the resin layer will be described later.

[0022] It is more preferable that the module cover 41 is made of a laminate having a resin layer and a fiber layer. The presence of a fiber layer further enhances flame resistance. When the module cover 41 is made of a laminate, it is preferable that the fiber layer is located closer to the battery module 21 than the resin layer. Specifically, it is preferable that the upper surface of the module cover 41, i.e., the upper surface 42a of the covering portion 42, is made of a resin layer, and the lower surface of the module cover 41, i.e., the lower surface 48a of the partition portion 48, the side surface 49a of the housing portion 49, and the bottom surface 49b of the housing portion 49, are made of a fiber layer.

[0023] It is preferable that the covering portion 42 and the partition portion 48 of the module cover 41 are integrally molded. If the integrally molded module cover 41 is made of a laminate, it is preferable that there is a continuous fiber layer along the lower surface of the module cover 41, and that the partition portion 48 and covering portion 42 above that layer are made of resin layers. Any layer may be present between the resin layer and the fiber layer.

[0024] If the module cover 41 is made of a laminate, and there is a continuous fiber layer along the lower surface of the module cover 41, and the partition portion 48 and covering portion 42 above it are made of resin layers, then the thickness H1 of the covering portion 42, that is, the distance from the upper surface 42a of the covering portion 42 to the bottom surface 49b of the housing portion 49, may be, for example, 0.5 to 3 mm. The maximum thickness H2 of the module cover 41, that is, the distance from the upper surface 42a of the covering portion 42 to the lower surface 48a of the partition portion 48, may be, for example, 1 to 5 mm.

[0025] If the module cover 41 is made of a laminate having a resin layer and a fiber layer, and the fiber layer is present along the lower surface of the module cover 41, it is preferable that the thickness of the fiber layer be uniform. When the thickness of the fiber layer is uniform, there are no particular restrictions on the thickness of the fiber layer as long as the thickness of the covering portion 42 can be within the above range, but it is preferable that it be 0.01 mm or more. If it is 0.01 mm or more, the bonding between the fiber layer and the resin layer will be good, and the fiber layer will be able to support the resin layer even if the resin layer melts due to heat. It is more preferable that the thickness of the fiber layer be 0.05 mm or more, and even more preferable that it be 0.1 mm or more. On the other hand, as an upper limit for the thickness of the fiber layer, from the viewpoint of suppressing the weight of the module cover 41 and cost, it is preferable that it be 5 mm or less, more preferable that it be 2 mm or less, even more preferable that it be 1 mm or less, and particularly preferable that it be 0.5 mm or less.

[0026] Furthermore, the thickness of the resin layer in the region where the easily penetrated portion 44 does not exist is preferably twice or more the thickness of the fiber layer. When the thickness of the resin layer is twice or more the thickness of the fiber layer, the flame-retardant properties of the laminate are further enhanced. The thickness of the resin layer is more preferably 2.5 times or more the thickness of the fiber layer, even more preferably 5 times or more, particularly preferably 8 times or more, and most preferably 10 times or more. On the other hand, the upper limit of the thickness of the resin layer in the region where the easily penetrated portion 44 does not exist may be, for example, 50 times or less, 45 times or less, 30 times or less, 20 times or less, or 15 times or less the thickness of the fiber layer.

[0027] From the viewpoint of providing the laminate with even better flame-retardant properties, it is also preferable that the thickness of the resin layer in the region where there are no easily penetrated portions 44 is 70% or more of the total thickness of the resin layer and the fiber layer. From the same viewpoint, it is more preferable that the thickness of the resin layer be 75% or more, even more preferable that it be 80% or more, and particularly preferable that it be 85% or more, relative to the total thickness of the resin layer and the fiber layer. There is no particular upper limit, and for example it may be 98% or less, or 95% or less.

[0028] In the module cover 41 of this embodiment, a continuous fiber layer exists along the lower surface, and the partition portion 48 and covering portion 42 above it are formed of a resin layer. When a weakening line 46 is provided on the upper surface 42a of the covering portion 42, causing the covering portion 42 to be locally thinned and providing an easily penetrated portion 44, the depth of the weakening line 46 is preferably in the range of 0.01 to 0.1 mm.

[0029] If the module cover 41 is made of a laminate, an adhesive layer may be provided between the resin layer and the fiber layer. From the viewpoint of improving flame resistance, it is preferable that the resin layer and the fiber layer are directly bonded together without any other layers in between. From a similar viewpoint, it is more preferable that the laminate is directly bonded to the resin layer and the fiber layer by melting and impregnating the fiber layer with at least a portion of the resin composition contained in the resin layer. It is particularly preferable that the laminate is directly bonded to the fiber layer by melting and impregnating the fiber layer with at least a portion of the resin composition contained in the resin layer.

[0030] The shape of the module cover differs between the following embodiments and the first embodiment. In the figures showing the following embodiments, the housing 30 that houses the battery module is not shown. Also, the same reference numerals are used for the same components as in Figure 1, and their descriptions are omitted.

[0031] <Second Embodiment> Figure 3 is a cross-sectional view of the main part of the battery pack of the second embodiment. In this embodiment, the module cover 51 has a covering portion 52 that covers the discharge valves 16 of a plurality of battery cells 11, and a partition portion 58 that partitions the space between adjacent discharge valves 16. The covering portion 52 is in the shape of a sheet with the height direction (H) of the battery cell 11 as its thickness direction, and rib-shaped partition portions 58 protrude from the covering portion 52 toward the battery module 21 side.

[0032] In this embodiment, the upper surface of the module cover 51 is the upper surface 52a of the covering portion 52 and has a recess 53. On the lower surface of the module cover 51, the lower surface 52b of the covering portion 52 and the partition portion 58 are continuous. When the module cover 51 is placed between the battery module 21 and the housing 30, the tip of the partition portion 58 may or may not be in contact with the cell body 12 of the battery cell 11. In the example shown in Figure 3, the tip of the partition portion 58 is in contact with the cell body 12 of the battery cell 11, forming a bottomed hollow housing portion 59 that airtightly houses the discharge valve 16.

[0033] If the tip of the partition portion 58 is not in contact with the cell body 12 of the battery cell 11, the distance from the tip of the partition portion 58 to the cell body 12 may be, for example, 0.01 to 10 mm, 0.1 to 5 mm, or 0.5 to 3 mm. Also, if the tip of the partition portion 58 is not in contact with the cell body 12 of the battery cell 11, the space between the module cover 51 and the battery cell 11 may be filled with another component (not shown), such as an O-ring.

[0034] In this embodiment, the partition portion 58 may or may not be in contact with the spacer 34. In the example shown in Figure 3, the partition portion 58 is not in contact with the spacer 34, and a space surrounding the upper part of the spacer 34 exists between adjacent housing portions 59. The partition portion 58 may or may not be in contact with other members attached to the battery cell 11 (such as busbars, not shown). A space S exists between the upper surface 52a of the covering portion 52 and the lid 31 of the housing 30. The housing 30 may be provided with an exhaust hole that communicates with the space S.

[0035] The covering portion facing the discharge valve 16 is provided with a thinned, easily penetrated portion 54. In this embodiment, the easily penetrated portion 54 is a thinned area on the upper surface 52a of the covering portion 52, where a recess 53 is provided. When the module cover 51 is viewed from above in plan view, the easily penetrated portion 54 is located within the area where the housing portion 59 exists. The planar shape of the easily penetrated portion 54 and the planar shape of the housing portion 59 may be the same. In this embodiment, in the height direction (H) of the battery cell 11, the distance from the tip of the discharge valve 16 to the module cover 51 may be, for example, 0 to 10 mm, 0.5 to 5 mm, or 1 to 3 mm.

[0036] The easily penetrated portion 54 is easily destroyed and becomes a through-hole when the discharge valve 16 opens due to an increase in the internal pressure of the battery cell 11, causing the pressure inside the housing portion 59 to rise. Therefore, when thermal runaway occurs in the battery cell 11, the high-temperature gas generated moves through the through-hole formed in the covering portion 52 into the space S between the covering portion 52 and the lid 31. It may also be discharged from the exhaust hole (not shown) of the housing 30. This prevents the high-temperature gas generated from one battery cell 11 from coming into contact with other cells.

[0037] The module cover 51 is made of a material that has flame-retardant properties and can form rib-shaped partitions 58 and easily penetrated portions 54. For example, the module cover 51 preferably has a resin layer containing a flame retardant. Flame-retardant properties are obtained by including a flame retardant. The resin constituting the resin layer is preferably a thermoplastic resin because of its excellent processability. The resin layer may further contain fibers. The fibers contribute to improving the strength, rigidity, and impact resistance of the resin layer. The thermoplastic resin, flame retardant, and fibers of the resin layer will be described later.

[0038] The module cover 51 preferably comprises a laminate having a resin layer and a fiber layer. Having a fiber layer further enhances the flame shielding property. When the module cover 51 comprises a laminate, the fiber layer is preferably positioned closer to the battery module 21 side than the resin layer. Specifically, the upper surface of the module cover 51, that is, the upper surface 52a of the covering portion 52 preferably consists of a resin layer, and the lower surface of the module cover 51, that is, the lower surface 52b of the covering portion 52, and the upper surface of the partition portion 58 preferably consist of a fiber layer.

[0039] The covering portion 52 and the partition portion 58 of the module cover 51 are preferably integrally formed. When the integrally formed module cover 51 comprises a laminate, it is preferable that there is a continuous fiber layer along the lower surface of the module cover 51, and the partition portion 58 and the covering portion 52 above it consist of a resin layer. An arbitrary layer may exist between the resin layer and the fiber layer.

[0040] In the module cover 51, the thickness H1 of the covering portion 52, that is, the distance from the upper surface 52a of the covering portion to the bottom surface 59b of the accommodating portion 59 may be, for example, 0.5 to 3 mm. The maximum thickness H2 of the module cover 51, that is, the distance from the upper surface 52a of the covering portion 52 to the lower surface of the partition portion 58 may be, for example, 1 to 5 mm. The thickness H3 at the easily penetrable portion 54 of the module cover 51 may be, for example, 0.1 to 1 mm.

[0041] The module cover 51 is made of a laminate having a resin layer and a fiber layer. When the fiber layer exists along the lower surface of the module cover 51, the thickness of the fiber layer is preferably uniform. When the thickness of the fiber layer is uniform, the thickness of the fiber layer is not particularly limited as long as the thickness H1 of the covering portion 52 can be within the above range, but it is preferably 0.01 mm or more. If it is 0.01 mm or more, the binding property between the fiber layer and the resin layer becomes good, and the fiber layer can support the resin layer even when the resin layer is melted by heat. The thickness of the fiber layer is more preferably 0.05 mm or more, and even more preferably 0.1 mm or more. On the other hand, as the upper limit value of the thickness of the fiber layer, from the viewpoint of suppressing the weight of the module cover 51 and cost, it is preferably 5 mm or less, more preferably 2 mm or less, even more preferably 1 mm or less, and particularly preferably 0.5 mm or less.

[0042] Also, the thickness of the resin layer in the region where the easily penetrating portion 54 does not exist is preferably at least twice the thickness of the fiber layer. When the thickness of the resin layer is at least twice the thickness of the fiber layer, the shielding property of the laminate is further enhanced. The thickness of the resin layer is more preferably at least 2.5 times the thickness of the fiber layer, even more preferably at least 5 times, particularly preferably at least 8 times, and most preferably at least 10 times. On the other hand, the upper limit of the thickness of the resin layer in the region where the easily penetrating portion 54 does not exist may be, for example, 50 times or less, 45 times or less, 30 times or less, 20 times or less, or 15 times or less the thickness of the fiber layer.

[0043] The thickness of the resin layer in the region where the easily penetrating portion 54 does not exist is also preferably 70% or more with respect to the total thickness of the resin layer and the fiber layer from the viewpoint of imparting even better shielding property to the laminate. From the same viewpoint, the thickness of the resin layer is more preferably 75% or more, even more preferably 80% or more, and particularly preferably 85% or more with respect to the total thickness of the resin layer and the fiber layer. The upper limit is not particularly limited and may be, for example, 98% or less, or 95% or less.

[0044] In the module cover 51 of this embodiment, a continuous fiber layer exists along the lower surface, and the partition portion 58 and covering portion 52 above it are formed of a resin layer. When a recess 53 is provided on the upper surface 52a of the covering portion 52 to locally thin the wall and provide an easily penetrated portion 54, the depth of the recess 53 is preferably in the range of 0.01 to 0.1 mm.

[0045] If the module cover 51 is made of a laminate, an adhesive layer may be provided between the resin layer and the fiber layer. From the viewpoint of improving flame resistance, it is preferable that the resin layer and the fiber layer are directly bonded together without any other layers in between. From a similar viewpoint, it is more preferable that at least a portion of the resin composition contained in the resin layer melts and directly bonds with the fiber layer. It is particularly preferable that at least a portion of the resin composition contained in the resin layer melts and impregnates the fiber layer, thereby directly bonding the resin layer and the fiber layer. The same applies to the following embodiments.

[0046] <Third Embodiment> Figure 4 is a cross-sectional view of the main part of the battery pack of the third embodiment. In the second embodiment, a recess 53 is provided on the upper surface 52a of the covering portion 52 to form an easy-penetration portion 54, whereas in this embodiment, a recess 63 is provided on the lower surface 62b of the covering portion 62 to form an easy-penetration portion 64. In this embodiment, the module cover 61 has a covering portion 62 that covers the discharge valves 16 of a plurality of battery cells 11, and a partition portion 68 that partitions the space between adjacent discharge valves 16. The covering portion 62 is sheet-like with the height direction (H) of the battery cell 11 as its thickness direction, and rib-shaped partition portions 68 protrude from the covering portion 62 toward the battery module 21 side.

[0047] In this embodiment, the upper surface of the module cover 61 is the upper surface 62a of the covering portion 62 and is a flat surface. On the lower surface of the module cover 61, the lower surface 62b of the covering portion 62 and the partition portion 68 are continuous, and the lower surface 62b of the covering portion 62 has a recess 63. When the module cover 61 is placed between the battery module 21 and the housing 30, the tip of the partition portion 68 may or may not be in contact with the cell body 12 of the battery cell 11. In the example shown in Figure 4, the tip of the partition portion 68 is in contact with the cell body 12 of the battery cell 11, forming a bottomed hollow housing portion 69 that airtightly houses the discharge valve 16.

[0048] If the tip of the partition portion 68 is not in contact with the cell body 12 of the battery cell 11, the distance from the tip of the partition portion 68 to the cell body 12 may be, for example, 0.01 to 10 mm, 0.1 to 5 mm, or 0.5 to 3 mm. Also, if the tip of the partition portion 68 is not in contact with the cell body 12 of the battery cell 11, the space between the module cover 61 and the battery cell 11 may be filled with another component (not shown), such as an O-ring.

[0049] In this embodiment, the partition portion 68 may or may not be in contact with the spacer 34. In the example shown in Figure 4, the partition portion 68 is not in contact with the spacer 34, and there is a space between adjacent housing portions 69 surrounding the upper part of the spacer 34. Furthermore, the partition portion 68 may or may not be in contact with other members attached to the battery cell 11 (such as busbars, not shown).

[0050] The covering portion 62 facing the discharge valve 16 is provided with an easily penetrated portion 64 in which the covering portion 62 is thinned. In this embodiment, the easily penetrated portion 64 is a region in which the lower surface 62b of the covering portion 62 is thinned by providing a recess 63. When the module cover 61 is viewed from above in plan view, the easily penetrated portion 64 is located within the region where the housing portion 69 exists. The planar shape of the easily penetrated portion 64 and the planar shape of the housing portion 69 may be the same. In this embodiment, in the height direction (H) of the battery cell 11, the distance from the tip of the discharge valve 16 to the module cover 61 may be, for example, 0 to 10 mm, 0.5 to 5 mm, or 1 to 3 mm.

[0051] In the module cover 61 of this embodiment, a continuous fiber layer exists along the lower surface, and the partition portion 68 and covering portion 62 above it are formed of a resin layer. When a recess 63 is provided on the lower surface 62b of the covering portion 62 to locally thin the wall and provide an easily penetrated portion 64, the depth of the recess 63 is preferably in the range of 0.01 to 0.1 mm.

[0052] According to this embodiment, in the same manner as in the second embodiment, it is possible to prevent high-temperature gas generated from one battery cell 11 from coming into contact with other cells. The material of the module cover 61 is the same as in the second embodiment. As in the second embodiment, it is preferable that the covering portion 62 and the partition portion 68 of the module cover 61 are integrally molded. In the module cover 61, the thickness H1 of the covering portion 62, the maximum thickness H2 of the module cover 61, and the thickness H3 of the easily penetrated portion 64 are the same as in the second embodiment. When the module cover 61 is made of a laminate having a resin layer and a fiber layer, the thickness of the fiber layer and the thickness of the resin layer are the same as in the second embodiment.

[0053] <Fourth Embodiment> Figure 5 is a cross-sectional view of the main part of the battery pack of the fourth embodiment. This embodiment differs from the second embodiment in that, in addition to the configuration of the second embodiment, a weakening line 56 is provided in the easily penetrated portion 54. In this embodiment, the easily penetrated portion 54 is made thinner by providing a recess 53 in the upper surface 52a of the covering portion 52, and a weakening line 56 is provided. The weakening line 56 is provided on the surface opposite to the surface on which the recess 53 is provided. That is, the weakening line 56 is formed by cutting out the lower surface 52b of the covering portion 52, thereby locally thinning the covering portion 52. When the module cover 51 is viewed from above in plan view, the weakening line 56 is located within the area where the easily penetrated portion 54 exists. The planar shape of the easily penetrated portion 54 and the planar shape of the area surrounded by the weakening line 56 may be the same. According to this embodiment, in the same way as in the second embodiment, it is possible to prevent high-temperature gas generated from one battery cell 11 from coming into contact with other cells.

[0054] <Fifth Embodiment> Figure 6 is a cross-sectional view of the main part of the battery pack of the fifth embodiment. This embodiment differs from the third embodiment in that, in addition to the configuration of the third embodiment, a weakening line 66 is provided in the easily penetrated portion 64. In this embodiment, the easily penetrated portion 64 is thinned by providing a recess 63 in the lower surface 62b of the covering portion 62, and a weakening line 66 is provided in the upper surface 62a of the covering portion 62. The weakening line 66 is provided on the surface opposite to the surface where the recess 63 is provided. That is, the weakening line 66 is formed by cutting out the upper surface 62a of the covering portion 62, locally thinning the covering portion 62. When the module cover 61 is viewed from above in plan view, the weakening line 66 is located within the area where the easily penetrated portion 64 exists. The planar shape of the easily penetrated portion 64 and the planar shape of the area surrounded by the weakening line 66 may be the same. According to this embodiment, in the same way as in the third embodiment, it is possible to prevent high-temperature gas generated from one battery cell 11 from coming into contact with other cells.

[0055] <Sixth Embodiment> Figure 7 is a cross-sectional view of the main part of the battery pack of the sixth embodiment. This embodiment differs from the first embodiment in that, in the easy-penetration portion 44 of the first embodiment, a recess 43 is provided on the upper surface 42a of the covering portion 42 instead of a weakening line 46. In this embodiment, the covering portion 42 facing the discharge valve 16 is provided with an easy-penetration portion 44 in which the covering portion 42 is thinned. In this embodiment, the easy-penetration portion 44 is the thinned area in which the recess 43 is provided on the upper surface 42a of the covering portion 42. When the module cover 41 is viewed from above in plan view, the easy-penetration portion 44 is located within the area in which the housing portion 49 exists. The planar shape of the easy-penetration portion 44 and the planar shape of the housing portion 49 may be the same. According to this embodiment, in the same way as in the first embodiment, it is possible to prevent high-temperature gas generated from one battery cell 11 from coming into contact with other cells. In the module cover 41 of this embodiment, the thickness H1 of the covering portion 42 may be, for example, 0.5 to 5 mm. The maximum thickness H2 of the module cover 41 may be, for example, 1 to 5 mm. The thickness H3 of the easily penetrated portion 44 may be, for example, 0.1 to 1 mm.

[0056] <Modification> In the above embodiment, the side of the battery cell 11 where the discharge valve 16 is located was set to the upper side in the height direction (H), but this is not limited to this. For example, with the battery pack 100 installed in a predetermined position, the height direction (H) of the battery cell 11 may be vertical, horizontal, or any other method.

[0057] In the above embodiment, the shape of the battery cell body is a rectangular parallelepiped having a height direction (H), a width direction (W), and a thickness direction (D), but it is not limited to this. For example, it may be cylindrical with H being the height direction and D being the diameter direction. The shape of the discharge valve of the battery cell is not particularly limited and any shape can be adopted. The shape of the partition portion is not limited to the above embodiment. The tip of the partition portion may be in contact with the cell body to airtightly house the exhaust valve, or the tip of the partition portion may not be in contact with the cell body. As an example of a shape in which the tip of the partition portion is in contact with the cell body to airtightly house the exhaust valve, the lower surface of the partition portion may be a curved surface that follows the cell body.

[0058] The shape of the easily penetrated portion is not limited to the above embodiment. The easily penetrated portion only needs to have enough strength to break easily and become a through-hole when the pressure inside the housing portion that airtightly houses the discharge valve increases. For example, in the first embodiment, the weakening line 46 may not be provided, and the thickness H1 of the covering portion 42 may be made thinner so that the area surrounded by the partition portion 48 (housing portion 49) when viewed from above in plan view becomes the easily penetrated portion 44.

[0059] <Method for Manufacturing Module Covers> Module covers can be manufactured by a molding method using a mold (for example, injection molding). If the module cover consists of a resin layer, the covering portion and the partition portion can be integrally molded by filling a mold designed to correspond to the outer shape of the module cover with resin and curing it. If the module cover consists of a laminate having a resin layer and a fiber layer, the covering portion and the partition portion can be integrally molded by inserting a fiber sheet that will become the fiber layer (for example, a glass fiber nonwoven fabric sheet described later) into the mold, and then filling and curing the resin.

[0060] If the easily penetrated portion has a weakening line formed by a notch, the mold should be designed with corresponding irregular shapes. If such a weakening line is provided in a portion where a fiber layer exists, a fiber sheet with pre-made through holes corresponding to the notch may be inserted. If the easily penetrated portion is thinned by providing a recess, the mold should be designed with corresponding convex shapes. If a recess is provided in a portion where a fiber layer exists, the fiber sheet may be inserted along the convex shape corresponding to the recess. If the partition portion protrudes in a rib-like manner, the mold should be designed with corresponding recesses. If a rib-like partition portion is provided in a portion where a fiber layer exists, the fiber sheet may be inserted along the convex shape corresponding to the partition portion.

[0061] ≪Resin Layer≫ The resin layer constituting the module cover consists of a resin composition comprising (A) a thermoplastic resin and (B) a flame retardant. The resin composition may further contain (C) fibers. The (A) thermoplastic resin, (B) flame retardant, and (C) fibers constituting the resin composition will be described in detail below.

[0062] <(A) Thermoplastic Resin> In this embodiment, there are no particular restrictions on the thermoplastic resin (A) included in the resin composition constituting the resin layer, and examples include polyolefin resin, polycarbonate resin, polyester resin, acrylonitrile styrene resin, ABS resin, polyamide resin, modified polyphenylene oxide, polyvinyl chloride, polystyrene, polyvinyl acetate, polyurethane, etc. One of these may be used, or two or more may be used in combination. For example, the thermoplastic resin (A) may be a composite resin of two or more of the above thermoplastic resins. Of these, polyolefin resin is preferred from the viewpoint of resin properties, versatility, cost, etc., and polypropylene resin is particularly preferred. Furthermore, from the viewpoint of protecting the wiring of the cell with its insulating properties, it is also preferable to use a polybutylene terephthalate resin among the polyester resins.

[0063] There are no particular restrictions on the polyolefin resin, and examples include those described below. There are no particular restrictions on the polyester resin, and examples include polybutylene terephthalate. There are no particular restrictions on the polyamide resin, and examples include nylon 66 and nylon 6. In particular, this embodiment is especially useful when (A) the thermoplastic resin contains at least a polyolefin resin. In this specification, "polyolefin resin" means a resin in which the proportion of olefin units or cycloolefin units is 90 mol% or more of all constituent units that make up the resin. The proportion of olefin units or cycloolefin units is preferably 95 mol% or more, and particularly preferably 98 mol% or more, of all constituent units that make up the polyolefin resin.

[0064] Examples of polyolefin resins include polyethylene, polypropylene, and α-olefin-propylene blocks or random copolymers having four or more carbon atoms. Examples of polyethylene include low-density polyethylene, linear low-density polyethylene, and high-density polyethylene. Examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, hemiisotactic polypropylene, and stereoblock polypropylene. In α-olefin-propylene blocks or random copolymers having four or more carbon atoms, examples of α-olefins having four or more carbon atoms include butene, 3-methyl-1-butene, 3-methyl-1-pentene, and 4-methyl-1-pentene. Of these, it is particularly preferable that (A) the thermoplastic resin is a polypropylene-based resin. Polypropylene-based resins will be described in detail later. Note that one type of polyolefin resin may be used alone, or two or more types may be used in combination.

[0065] (Melt Flow Rate (MFR)) In this embodiment, the melt flow rate (hereinafter also referred to as "MFR") (230°C, 2.16 kg load) of the thermoplastic resin (A) contained in the resin layer is preferably 5 to 500 g / 10 min. If the MFR is 5 g / 10 min or more, good fluidity is obtained when manufacturing a module cover by injection molding, for example, and the processability is good. On the other hand, if it is 500 g / 10 min or less, the strength of the module cover is sufficient. From the above viewpoint, the MFR is preferably in the range of 10 to 300 g / 10 min, more preferably 20 to 200 g / 10 min, and even more preferably 25 to 100 g / 10 min. The MFR of the thermoplastic resin (A) can be adjusted by controlling, for example, the hydrogen concentration during polymerization. The MFR is a value measured in accordance with JIS K7210-1.

[0066] (Content of (A) Thermoplastic Resin) In this embodiment, the content of (A) thermoplastic resin in the resin composition is not particularly limited, but is preferably 15 to 80% by mass. When the content of (A) thermoplastic resin is 15% by mass or more, the moldability is particularly good, and the molding of the module cover becomes easy. On the other hand, when it is 80% by mass or less, a sufficient amount of (B) flame retardant, (C) fibers, etc. can be included, and good flame resistance can be obtained. From the above viewpoint, the content of (A) thermoplastic resin in the resin composition is preferably 35 to 70% by mass, and more preferably 40 to 60% by mass. The preferred content is the same when (A) thermoplastic resin is the preferred polypropylene resin described above.

[0067] <(A-1) Polypropylene Resin> In this embodiment, the (A) thermoplastic resin constituting the resin composition preferably includes the (A-1) polypropylene resin, as described above. Examples of the (A-1) polypropylene resin include propylene homopolymer or propylene-α-olefin copolymer. Here, the propylene-α-olefin copolymer may be either a random copolymer or a block copolymer.

[0068] (α-olefins) Examples of α-olefins constituting the above copolymer include ethylene, 1-butene, 2-methyl-1-propene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 1-heptene, methyl-1-hexene, dimethyl-1-pentene, ethyl-1-pentene, trimethyl-1-butene, 1-octene, etc. These may be copolymerized with propylene using one type, or two or more types may be copolymerized with propylene. Among these, ethylene or 1-butene is preferred from the viewpoint of improving the impact strength of the module cover, and ethylene is the most preferred.

[0069] (Propylene-ethylene random copolymer) In the case of a random copolymer of propylene and ethylene, it is preferable that it contains 90 to 99.5% by mass of propylene units, more preferably 92 to 99% by mass, and 0.5 to 10% by mass of ethylene units, more preferably 1 to 8% by mass. If the amount of ethylene units is above the lower limit, sufficient impact resistance of the module cover can be obtained, and if it is below the upper limit, sufficient rigidity can be maintained. The content of propylene units and ethylene units in a random copolymer of propylene and ethylene can be adjusted by controlling the composition ratio of propylene and ethylene during polymerization of the random copolymer of propylene and ethylene. Furthermore, the propylene content of a random copolymer of propylene and ethylene is a value measured using a cross-separation device or FT-IR, and the measurement conditions can be, for example, the method described in Japanese Patent Application Publication No. 2008-189893.

[0070] <Modified Polyolefin Resin> In this embodiment, the resin composition may further include a modified polyolefin resin in addition to the (A-1) polypropylene resin. Specifically, examples of modified polyolefin resins include acid-modified polyolefin resins and hydroxy-modified polyolefin resins, which may be used individually or in combination. There are no particular restrictions on the type of acid-modified polyolefin resin and hydroxy-modified polyolefin resin used as the modified polyolefin resin, and conventionally known resins may be used.

[0071] (Acid-modified polyolefin resins) Examples of acid-modified polyolefin resins include those obtained by chemically modifying polyolefins such as polyethylene, polypropylene, ethylene-α-olefin copolymers, ethylene-α-olefin-non-conjugated diene compound copolymers (EPDM, etc.), and ethylene-aromatic monovinyl compound-conjugated diene compound copolymer elastomers by graft copolymerization with an unsaturated carboxylic acid such as maleic acid or maleic anhydride. This graft copolymerization is carried out, for example, by reacting the above polyolefin with an unsaturated carboxylic acid in a suitable solvent using a radical generating agent such as benzoyl peroxide. In addition, the unsaturated carboxylic acid or its derivative component can also be introduced into the polymer chain by random or block copolymerization with a monomer for polyolefins.

[0072] Examples of unsaturated carboxylic acids used for modification include compounds having polymerizable double bonds into which carboxyl groups and, if necessary, functional groups such as hydroxyl groups or amino groups have been introduced, such as maleic acid, fumaric acid, itaconic acid, acrylic acid, and methacrylic acid. Derivatives of unsaturated carboxylic acids include their acid anhydrides, esters, amides, imides, and metal salts. Specific examples include maleic anhydride, itaconic anhydride, methyl acrylate, ethyl acrylate, butyl acrylate, and methyl methacrylate. Of these, maleic anhydride is preferred.

[0073] Preferred acid-modified polyolefin resins include those obtained by graft polymerization of maleic anhydride onto an olefin polymer whose main polymer constituent units are ethylene and / or propylene, and those obtained by copolymerizing an olefin mainly composed of ethylene and / or propylene with maleic anhydride. Specifically, examples include combinations of polyethylene / maleic anhydride-grafted ethylene-butene-1 copolymer, or polypropylene / maleic anhydride-grafted polypropylene.

[0074] (Hydroxy-modified polyolefin resins) Hydroxy-modified polyolefin resins are modified polyolefin resins that contain hydroxyl groups. Hydroxy-modified polyolefin resins may have hydroxyl groups at appropriate locations, for example, at the ends of the main chain or in side chains. Examples of olefin resins constituting hydroxy-modified polyolefin resins include α-olefins alone or copolymers such as ethylene, propylene, butene, 4-methylpentene-1, hexene, octene, nonene, decene, and dodecene, as well as copolymers of the α-olefins with copolymerizable monomers. Examples of preferred hydroxy-modified polyolefin resins include hydroxy-modified polyethylene resins such as low-density, medium-density, or high-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, ethylene-(meth)acrylic acid ester copolymers, and ethylene-vinyl acetate copolymers; hydroxy-modified polypropylene resins such as polypropylene homopolymers like isotactic polypropylene, random copolymers of propylene and α-olefins (e.g., ethylene, butene, hexane, etc.), and propylene-α-olefin block copolymers, as well as hydroxy-modified poly(4-methylpentene-1).

[0075] <(B) Flame retardant> In this embodiment, the resin composition constituting the resin layer contains (B) a flame retardant. The (B) flame retardant is not particularly limited and examples include phosphorus-based flame retardants, bromine-based flame retardants, antimony-based flame retardants, etc. Among these, phosphorus-based flame retardants are preferred from the viewpoint of improving flame resistance. Furthermore, in a classification focusing on the mechanism of action of the flame retardant, it is preferable that the (B) flame retardant is an intomessecent flame retardant from the viewpoint of improving flame resistance.

[0076] (Phosphorus-based flame retardants) Phosphorus-based flame retardants are phosphorus compounds, that is, compounds containing a phosphorus atom in their molecule. Phosphorus-based flame retardants exert their flame-retardant effect by forming a char (carbonized film) when the resin composition is burned. Phosphorus-based flame retardants may be known substances, such as (poly)phosphates and (poly)phosphate esters. Here, "(poly)phosphate" refers to a phosphate or polyphosphate, and "(poly)phosphate ester" refers to a phosphate ester or polyphosphate ester. It is preferable that the phosphorus-based flame retardant is solid at 80°C.

[0077] As a phosphorus-based flame retardant, (poly)phosphates are preferred in terms of flame retardancy. Examples of (poly)phosphates include ammonium polyphosphate, melamine polyphosphate, piperazine polyphosphate, piperazine orthophosphate, melamine pyrophosphate, piperazine pyrophosphate, melamine orthophosphate, calcium phosphate, magnesium phosphate, etc. Compounds in which melamine or piperazine is replaced with other nitrogen compounds in the above examples can also be used in the same way. Examples of other nitrogen compounds include N,N,N',N'-tetramethyldiaminomethane, ethylenediamine, N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, 1,2-propanediamine, 1,3-propanediamine, and Tramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, trans-2,5-dimethylpiperazine, 1,4-bis(2-aminoethyl)piperazine, 1,4-bis(3-aminopropyl)piperazine, acetoguanamine, benzoguanamine, acrylicguanamine, 2,4-diamino-6-nonyl-1,3 ,5-triazine, 2,4-diamino-6-hydroxy-1,3,5-triazine, 2-amino-4,6-dihydroxy-1,3,5-triazine, 2,4-diamino-6-methoxy-1,3,5-triazine, 2,4-diamino-6-ethoxy-1,3,5-triazine, 2,4-diamino-6-propoxy-1,3,5-triazine, 2,4-diamino-6-isopropoxy-1,3,5-triazine, 2,4-diamino-6- Examples include mercapto-1,3,5-triazine, 2-amino-4,6-dimercapto-1,3,5-triazine, ammeline, benzguanamine, acetoguanamine, phthalodiguanamine, melamine cyanurate, butylenediguanamine, norbornenediguanamine, methylenediguanamine, ethylenedimelamine, trimethylenedimelamine, tetramethylenedimelamine, hexamethylenedimelamine, and 1,3-hexylenedimelamine.These (poly)phosphates may be used individually or in combination of two or more.

[0078] Among the phosphorus-based flame retardants mentioned above, a salt of (poly)phosphoric acid and a nitrogen compound (hereinafter also referred to as "compound (B1)") is preferred. Compound (B1) is an intomessent flame retardant. Intomessent flame retardants are flame retardants that suppress the combustion of materials by forming an intumessent, which prevents radiant heat from the combustion source and the diffusion of combustion gases and smoke from the burning material to the outside. The formation of the intumessent suppresses the diffusion of decomposition products and heat transfer, resulting in excellent flame retardancy. Examples of nitrogen compounds in compound (B1) include ammonia, melamine, piperazine, and the other nitrogen compounds mentioned above. Specifically, examples include ammonium salts and amine salts of (poly)phosphoric acid such as ammonium polyphosphate, melamine polyphosphate, piperazine polyphosphate, ammonium pyrophosphate, melamine pyrophosphate, and piperazine pyrophosphate. Zinc oxide can also be included as a flame retardant aid. This is preferable because it further improves flame retardancy. Examples of commercially available phosphorus-based flame retardants include ADEKA stub FP-2100J, FP-2200, and FP-2500S (manufactured by ADEKA Corporation).

[0079] (Bromine-based flame retardants) Examples of bromine-based flame retardants include decabromodiphenyl ether, tetrabromobisphenol A, tetrabromobisphenol S, 1,2-bis(2',3',4',5',6'-pentabromophenyl)ethane, 1,2-bis(2,4,6-tribromophenoxy)ethane, 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine, 2,6-dibromophenol, 2,4-dibromophenol, Examples include brominated polystyrene, ethylene bistetrabromophthalimide, hexabromocyclododecane, hexabromobenzene, pentabromobenzyl acrylate, 2,2-bis[4'(2'',3''-dibromopropoxy)-3',5'-dibromophenyl]-propane, bis[3,5-dibromo-4-(2,3-dibromopropoxy)phenyl]sulfone, and tris(2,3-dibromopropyl) isocyanurate.

[0080] (Antimony-based flame retardants) Examples of antimony-based flame retardants include antimony trioxide, antimony tetroxide, antimony pentoxide, sodium pyroantimonate, antimony trichloride, antimony trisulfide, antimony oxychloride, antimony perchloropentane dichloride, and potassium antimonate, with antimony trioxide and antimony pentoxide being particularly preferred.

[0081] Of the above (B) flame retardants, phosphorus-based flame retardants are preferred because they have no biological residue and excellent flame retardancy, and non-halogen-based flame retardants are preferred from an environmental standpoint. Furthermore, intomessent flame retardants are preferred from the viewpoint of improving the flame-retardant properties of the resulting module cover. Note that the above (B) flame retardants can be used individually or in combination of two or more types.

[0082] (Content of (B) Flame retardant) In this embodiment, the content of (B) flame retardant in the resin composition is not particularly limited, but is preferably in the range of 1 to 40% by mass. If it is 1% by mass or more, good flame retardancy can be imparted to the module cover and good flame shielding properties can be obtained. On the other hand, if the content of (B) flame retardant is 40% by mass or less, (A) thermoplastic resin can be included in a sufficient content ratio, so the moldability is better. From the above viewpoint, the content of (B) flame retardant in the resin composition in this embodiment is more preferably in the range of 1 to 35% by mass, even more preferably in the range of 3 to 30% by mass, and particularly preferably in the range of 5 to 25% by mass.

[0083] <(C) Fibers> In this embodiment, the resin composition constituting the resin layer may contain (C) fibers. The (C) fibers may be organic or inorganic fibers, but inorganic fibers are preferred from the viewpoint of heat resistance. Examples include glass fibers, rock wool, basalt fibers, alumina fibers, silica alumina fibers, potassium titanate fibers, calcium silicate (wollastonite) fibers, alkali earth silicate fibers (biosoluble), silica fibers, and other ceramic fibers or metal oxide fibers, carbon fibers, stainless steel fibers, tungsten fibers, and other metal fibers. These inorganic fibers may be used individually or in combination of two or more. Among these inorganic fibers, at least one selected from the group consisting of glass fibers, ceramic fibers such as alumina fibers, metal oxide fibers, and carbon fibers is preferred from the viewpoint of improving heat resistance and flame resistance.

[0084] The (C) fiber described above preferably has an average fiber diameter of 3 to 25 μm. Furthermore, the average fiber length is preferably in the range of 0.05 to 100 mm, more preferably in the range of 0.5 to 50 mm, even more preferably in the range of 1 to 25 mm, and particularly preferably in the range of 2 to 15 mm. When the average fiber length is within the above range, the module cover having a resin layer containing the resin composition exhibits superior mechanical strength (such as bending strength) and superior heat resistance. While not bound by any particular theory, it is believed that when the average fiber length is within the above range, the (C) fiber tends to orient in the resin layer, thus providing the above advantages. Within the above range, the longer the average fiber length, the greater the mechanical strength and heat resistance tend to be. If there are multiple types of fibers, it is sufficient that the average fiber diameter and average fiber length of at least one type of fiber are within the above range.

[0085] The average fiber length of (C) fibers in a resin composition may vary depending on the manufacturing method of the resin layer. For example, when using injection molding, as described later, the resin composition containing (C) fibers is heated and melted, causing the (C) fibers to break and tending to shorten the average fiber length. The above average fiber length refers to the average fiber length in the resin composition and is the fiber length before heat treatment. Therefore, the average fiber length of (C) fibers in a resin layer manufactured by methods such as injection molding is preferably in the range of 0.05 to 50 mm, more preferably in the range of 0.25 to 25 mm, even more preferably in the range of 0.5 to 15 mm, and particularly preferably in the range of 1 to 10 mm. On the other hand, when a laminate having a resin layer is manufactured by lamination, the average fiber length of (C) fibers in the resin composition and the average fiber length of (C) fibers in the resin layer do not change. The fiber diameter can be measured using an optical microscope or the like, and the average fiber diameter can be obtained, for example, by measuring the fiber diameter of 10 randomly selected fibers and calculating the average value. Furthermore, fiber length can be measured using a ruler, calipers, etc., from magnified images obtained with a microscope, etc., as needed. The average fiber length can be obtained, for example, by measuring the fiber length of 10 randomly selected fibers and calculating the average value.

[0086] (Content of (C) fibers) In this embodiment, the content of (C) fibers in the resin composition is not particularly limited, but is preferably in the range of 3 to 60% by mass. When the content of (C) fibers is 3% by mass or more, the strength, rigidity, and impact resistance of the module cover can be ensured. On the other hand, when it is 60% by mass or less, the manufacturing and processing of the module cover can be easily carried out. In addition, when the content of (C) fibers is 60% by mass or less, the specific gravity becomes low, which has the advantage of a greater weight reduction effect as a metal substitute. From the above viewpoint, the content of (C) fibers in the resin composition in this embodiment is more preferably 10 to 50% by mass, even more preferably 20 to 45% by mass, and still more preferably 25 to 40% by mass.

[0087] (Glass Fibers) Glass fibers are one of the inorganic fibers suitable as (C) fibers in the resin composition. The glass fibers may be long fibers with an average fiber length of 30 mm or more, or short fibers (chopped strands) with an average fiber length. More specifically, the average fiber length is preferably in the range of 0.05 to 100 mm. When the average fiber length is within the above range, the strength and impact resistance of the module cover are good. From the above viewpoint, it is more preferable that the range is 0.5 to 50 mm, even more preferable that it is in the range of 1 to 25 mm, and particularly preferable that it is in the range of 2 to 15 mm. In the case of glass fibers as (C) fibers in a resin layer manufactured by methods such as injection molding, the average fiber length is preferably in the range of 0.05 to 50 mm, more preferably in the range of 0.25 to 25 mm, even more preferable that it is in the range of 0.5 to 15 mm, and particularly preferable that it is in the range of 1 to 10 mm.

[0088] There is no particular upper limit on the average fiber length of the glass fibers. For example, when using pellets manufactured by the plutonization method using glass fibers, the length of the pellet becomes the fiber length of the glass fiber, which is approximately 20 mm at most. In the case of swirl mat systems using long glass fibers, the length of the glass fibers in the roving used for manufacturing becomes the maximum fiber length, which can be as long as 17,000 m (17 km). However, if the fibers are cut to fit the size of the laminate, the cut length becomes the maximum fiber length. The average fiber diameter of the glass fibers is preferably in the range of 9 to 25 μm. If the average fiber diameter is 9 μm or more, the rigidity and impact resistance of the module cover will be sufficient, while if the average fiber diameter is 25 μm or less, the strength of the module cover will be good. From the above viewpoint, it is even more preferable that the average fiber diameter of the glass fibers be in the range of 10 to 15 μm.

[0089] The average fiber diameter and average fiber length of the glass fibers can be measured by the method described above. There are no special restrictions on the material of the glass fibers used in this embodiment; alkali-free glass, low-alkali glass, or alkali-containing glass may be used, and various compositions that have been conventionally used as glass fibers can be used.

[0090] <Optional Additives> In this embodiment, in addition to the above components, the resin composition may contain optional additives for purposes such as further improving the effects of the invention or providing other effects, as long as they do not significantly impair the effects of the present invention. Specifically, examples include colorants, light stabilizers, ultraviolet absorbers, nucleating agents such as sorbitol, antioxidants, antistatic agents, neutralizing agents such as inorganic compounds, antibacterial and antifungal agents such as thiazole, flame retardants and flame retardant aids such as halogen compounds and lignophenol, plasticizers, dispersants such as organometallic salts, dispersants that help (B) the flame retardant to disperse well in (A) the thermoplastic resin, lubricants such as fatty acid amides, metal deactivators such as nitrogen compounds, polyolefin resins other than the polypropylene resin, thermoplastic resins such as polyamide resins and polyester resins, elastomers (rubber components) such as olefin elastomers and styrene elastomers. Two or more of these optional additives may be used in combination.

[0091] As colorants, inorganic and organic pigments, for example, are effective in imparting and improving the colored appearance, aesthetics, texture, commercial value, weather resistance, and durability of the resin composition and the module cover having a resin layer composed of the resin composition. Specific examples of inorganic pigments include carbon black such as furnace carbon and Ketjencarbon; titanium dioxide; iron oxide (such as red iron oxide); chromic acid (such as yellow lead); molybdic acid; selenides; ferrocyanides; and organic pigments include azo pigments such as sparingly soluble azo lakes, soluble azo lakes, insoluble azo chelates; condensable azo chelates; and other azo chelates; phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green; slene pigments such as anthraquinone, perinone, perylene, and thioindigo; dye lakes; quinacridone-based pigments; dioxazine-based pigments; and isoindolinone-based pigments. Furthermore, to achieve a metallic or pearlescent finish, aluminum flakes or pearl pigments can be incorporated. Dyes can also be included.

[0092] For example, hindered amine compounds, benzotriazole compounds, benzophenone compounds, and salicylate compounds are effective in providing and improving the weather resistance and durability of the above-mentioned resin composition and the module cover having a resin layer composed of the resin composition, and are effective in further improving weather resistance and discoloration. Specific examples of hindered amine compounds include the condensate of dimethyl succinate and 1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine; poly[[6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]]; tetrakis(2,2,6,6-tetramethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate; tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate; bis(1,2,2,6,6-pentamethyl Examples of light stabilizers include tyl-4-piperidyl sebacate and bis-2,2,6,6-tetramethyl-4-piperidyl sebacate. Benzotriazole-based light stabilizers include 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole and 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole. Benzophenone-based light stabilizers include 2-hydroxy-4-methoxybenzophenone and 2-hydroxy-4-n-octoxybenzophenone. Salicylate-based light stabilizers include 4-t-butylphenyl salicylate and 2,4-di-t-butylphenyl 3',5'-di-t-butyl-4'-hydroxybenzoate. The method of using the above-mentioned light stabilizer and ultraviolet absorber in combination is preferable because it greatly improves weather resistance, durability, and weather-induced discoloration resistance.

[0093] As antioxidants, for example, phenolic, phosphorus-based, and sulfur-based antioxidants are effective in imparting and improving the heat resistance, processing stability, and heat aging resistance of polypropylene resin compositions and their molded articles. Furthermore, as antistatic agents, for example, nonionic and cationic antistatic agents are effective in imparting and improving the antistatic properties of the above-mentioned resin compositions and the resin layers composed of said resin compositions.

[0094] Examples of olefin-based elastomers include ethylene-α-olefin copolymer elastomers such as ethylene-propylene copolymer elastomer (EPR), ethylene-butene copolymer elastomer (EBR), ethylene-hexene copolymer elastomer (EHR), and ethylene-octene copolymer elastomer (EOR); ethylene-α-olefin-diene terpolymer elastomers such as ethylene-propylene-ethylidene norbornene copolymer, ethylene-propylene-butadiene copolymer, and ethylene-propylene-isoprene copolymer; and styrene-butadiene-styrene triblock copolymer elastomer (SBS). Examples of styrene-based elastomers include styrene-isoprene-styrene triblock copolymer elastomer (SIS), styrene-ethylene-butylene copolymer elastomer (SEB), styrene-ethylene-propylene copolymer elastomer (SEP), styrene-ethylene-butylene-styrene copolymer elastomer (SEBS), styrene-ethylene-butylene-ethylene copolymer elastomer (SEBC), hydrogenated styrene-butadiene elastomer (HSBR), styrene-ethylene-propylene-styrene copolymer elastomer (SEPS), styrene-ethylene-ethylene-propylene-styrene copolymer elastomer (SEEPS), styrene-butadiene-butylene-styrene copolymer elastomer (SBBS), partially hydrogenated styrene-isoprene-styrene copolymer elastomer, partially hydrogenated styrene-isoprene-butadiene-styrene copolymer elastomer, and hydrogenated polymer elastomers such as ethylene-ethylene-butylene-ethylene copolymer elastomer (CEBC). In particular, the use of ethylene-octene copolymer elastomer (EOR) and / or ethylene-butene copolymer elastomer (EBR) is preferred because it is easy to impart appropriate flexibility to the module cover according to this embodiment, and it tends to have excellent impact resistance.

[0095] <Method for Manufacturing the Resin Composition> In this embodiment, a conventionally known method can be used to manufacture the above resin composition, and it can be manufactured by blending, mixing, and melt-kneading the above components. Mixing is performed using a mixer such as a tumbler, V-blender, or ribbon blender, and melt-kneading is performed using equipment such as a single-screw extruder, twin-screw extruder, Banbury mixer, roll mixer, Brabender plastograph, or kneader, and the mixture is melt-kneaded and granulated.

[0096] ≪Fiber Layer≫ The module cover according to this embodiment preferably consists of a laminate having a resin layer and a fiber layer. The fiber layer, together with the resin layer, gives the laminate flame retardancy and flame shielding properties. From the viewpoint of achieving these effects, it is preferable that the fiber layer is made of fibers (X), and among these, it is preferable that it is a nonwoven fabric layer made of nonwoven fabric, a woven fabric layer made of woven fabric, or a knitted fabric layer made of knitted fabric. Nonwoven fabric is particularly preferable compared to woven fabric or knitted fabric because a part of the resin layer penetrates more easily into the surface of the fiber layer, resulting in higher bonding properties. Nonwoven fabric is also preferable because, since the orientation direction of the fibers is not fixed, there is no directional dependence of mechanical strength.

[0097] The size of the fibers (X) constituting the fiber layer is not limited within the range that achieves the effects of the present invention, but the average diameter of the fibers is preferably in the range of 3 to 25 μm, and the average fiber length is preferably in the range of 5 to 100 mm. If the average fiber diameter is 3 μm or more, handling during the manufacturing process of the fiber layer is easy, and if it is 25 μm or less, breakage is less likely to occur. Furthermore, if the average fiber length is 5 mm or more, the effect of imparting flame resistance to the laminate is excellent, and sufficient strength can be provided. On the other hand, if the average fiber length is 100 mm or less, breakage is less likely to occur. The fiber length can be measured using a ruler, caliper, etc., from an image magnified with a microscope, etc., as needed, and the average fiber length can be obtained, for example, by measuring the fiber length of 10 random fibers and calculating the average value.

[0098] The fibers (X) constituting the fiber layer are not particularly limited as long as they achieve the effects of the present invention, and include inorganic fibers such as glass fibers, carbon fibers, boron fibers, ceramic fibers, metal fibers, and metal oxide fibers, and organic fibers such as aramid fibers and aromatic polyester fibers. Of these, inorganic fibers are preferred in that they provide excellent flame resistance, and among them, glass fibers, ceramic fibers, metal fibers, and metal oxide fibers are preferred, with glass fibers being particularly preferred. As described above, among the fibers (X), at least one selected from the group consisting of glass fibers and aramid fibers is preferred. It is desirable that the laminate used in the module cover has excellent flame resistance. In particular, glass fibers are more preferred as the fibers (X) constituting the fiber layer in that they can withstand flame contact from the fiber layer side constituting the laminate.

[0099] <Nonwoven Fabric Layer> The nonwoven fabric layer is composed of nonwoven fabric. The fibers constituting the nonwoven fabric are not particularly limited as long as they achieve the effects of the present invention, and include inorganic fibers such as glass fibers, carbon fibers, boron fibers, ceramic fibers, metal fibers, and metal oxide fibers, and organic fibers such as aramid fibers and aromatic polyester fibers. Of these, inorganic fibers are preferred because they provide excellent flame resistance, and among them, glass fibers, ceramic fibers, metal fibers, and metal oxide fibers are preferred, with glass fibers being particularly preferred.

[0100] (Glass Fiber Nonwoven Fabric) Examples of glass fiber nonwoven fabrics include felt and blankets processed from short-fiber glass cotton, chopped strand mats processed from continuous glass fibers, swirl mats of continuous glass fibers, and unidirectional aligned mats. Among these, using a glass fiber mat made by needle-punching a swirl mat of continuous glass fibers is preferable because it provides excellent strength and impact resistance to the laminate. The glass fibers are the same as those described above in (C) Fiber.

[0101] The ceramic fiber is preferably composed mainly of silica and alumina, for example, in the range of silica:alumina = 40:60 to 0:100. Specifically, silica-alumina fibers, mullite fibers, and alumina fibers can be used.

[0102] Preferred materials for the metal fibers include those primarily composed of iron, copper, aluminum, nickel, tungsten, titanium, molybdenum, beryllium, platinum, etc. Furthermore, one or more alloying elements other than the above metals, such as carbon, nitrogen, chromium, cobalt, gold, and silver, may also be included. Due to their excellent strength and corrosion resistance, fibers primarily composed of stainless steel, nickel, or titanium are particularly preferred.

[0103] Suitable materials for metal oxide fibers include, for example, alkaline earth metal oxides such as magnesium oxide and calcium oxide; Group 4 metal oxides such as titanium oxide and zirconium oxide; Group 13 element oxides such as alumina and indium oxide; Group 14 element oxides such as silica, tin oxide, and lead oxide; and Group 15 element oxides such as antimony oxide. Among these, Group 13 to Group 15 element oxide fibers are preferred in that they effectively provide a high level of heat resistance, more preferably Group 13 element oxide fibers, and particularly preferably alumina fibers.

[0104] While there are no restrictions on the size of the fibers constituting the nonwoven fabric as long as the effects of the present invention are achieved, the average fiber diameter is preferably in the range of 3 to 25 μm, and the average fiber length is preferably in the range of 5 to 100 mm. If the average fiber diameter is 3 μm or more, handling during the manufacturing process of the nonwoven fabric is easy, and if it is 25 μm or less, breakage is less likely to occur. Furthermore, if the average fiber length is 5 mm or more, flame resistance can be imparted to the laminate, and sufficient strength can be provided. On the other hand, if the average fiber length is 100 mm or less, breakage is less likely to occur. From the above viewpoint, the average fiber length is more preferably in the range of 10 to 50 mm, and even more preferably in the range of 15 to 30 mm. The average fiber length can be measured by the method described above.

[0105] The basis weight (amount of fibers per unit area) of the non-woven fabric is preferably in the range of 10 to 500 g / m ２ ². When the basis weight is 10 g / m ２ ² or more, the flame shielding property of the laminate and sufficient strength of the laminate can be obtained. On the other hand, when it is 500 g / m ２ ² or less, the adhesiveness with the resin layer becomes good, sufficient flame shielding property of the laminate can be obtained, and the weight does not become excessively large. From the above viewpoints, the basis weight is more preferably in the range of 20 to 300 g / m ２ ², still more preferably in the range of 30 to 150 g / m ２ ², and particularly preferably in the range of 35 to 100 g / m ２ ². Among the above ranges of 35 to 100 g / m ２ ², the basis weight is preferably 35 to 75 g / m ２ ², more preferably 35 to 70 g / m ２ ², and still more preferably 35 to 45 g / m ２ ². Without being bound by a specific theory, it is considered that the lower the basis weight is, the easier it is for the resin composition containing the flame retardant to penetrate from the resin layer, leading to better overall flame shielding property.

[0106] As a method for manufacturing the non-woven fabric, conventionally known methods can be used. For example, a dry method, a wet method, a spunbond method, a melt blown method, an airlaid method, etc. can be used. Further, as a method for bonding the fibers of the non-woven fabric obtained by these manufacturing methods, known methods such as a chemical bond method, a thermal bond method, a needle punch method, a water jet entanglement method, etc. can be used.

[0107] <Woven fabric layer> The woven fabric layer is composed of a woven fabric. The fibers constituting the woven fabric are not particularly limited as long as they exhibit the effects of the present invention, and the same ones as those exemplified in the above non-woven fabric layer can be used. Note that, similar to the non-woven fabric layer, inorganic fibers are preferable, and particularly glass fibers are preferable. Regarding the size (average fiber diameter, average fiber length) and basis weight of the fibers constituting the woven fabric, they are the same as those described in the non-woven fabric layer. The fabric texture of the woven fabric made of the above fibers is not particularly limited, and any of plain weave, twill weave, satin weave, etc. may be used.

[0108] <Knitted Layer> The knitted layer is composed of knitted fabric. The fibers constituting the knitted fabric are not particularly limited as long as they achieve the effects of the present invention, and the same fibers as those exemplified in the nonwoven fabric layer above can be used. As with the nonwoven fabric layer, inorganic fibers are preferred, and glass fibers are particularly preferred. The size (average fiber diameter, average fiber length) and basis weight of the fibers constituting the knitted fabric are the same as those described for the nonwoven fabric layer. The structure of the knitted fabric made of the above fibers is not particularly limited and may be rib knit, garter stitch, stockinette stitch, etc.

[0109] <Method for Manufacturing the Laminate> The method for manufacturing the laminate according to this embodiment is not particularly limited and various known methods can be used. Specifically, examples include a method in which a resin layer and a fiber layer are formed in advance and then bonded together, or a method in which a fiber layer is set in a mold and a resin composition for forming the resin layer is injected and then injection molded.

[0110] One method of bonding involves preparing a resin sheet to form the resin layer and a glass fiber nonwoven fabric sheet to form the fiber layer, laminating them, and then heating and pressurizing them. More specifically, this method involves press-molding the resin sheet and the glass fiber nonwoven fabric sheet in a mold equipped with a heating device. The heating temperature is preferably 170 to 300°C. If the heating temperature is 170°C or higher, sufficient bonding between the resin layer and the fiber layer is achieved, improving the flame resistance of the laminate. On the other hand, if the heating temperature is 300°C or lower, the resin composition constituting the resin layer does not deteriorate. The pressurizing pressure is preferably 0.1 to 1 MPa. If the pressurizing pressure is 0.1 MPa or higher, sufficient bonding between the resin layer and the fiber layer is achieved, improving the flame resistance of the laminate. On the other hand, if the pressure is 1 MPa or lower, burrs do not form on the resin layer. When bonding the resin layer and the fiber layer, an adhesive layer can also be placed between the resin layer and the fiber layer. However, in this embodiment, since the bonding between the resin layer and the fiber layer is important, it is preferable that the resin layer and the fiber layer are directly bonded without any other layers in between. The cooling temperature is not particularly limited as long as it is below the freezing point of the thermoplastic resin, but if the cooling temperature is 80°C or lower, the resulting molded body (module cover) will not deform when removed. From this viewpoint, the cooling temperature is preferably room temperature to 80°C. A laminated sheet may be manufactured by lamination, in which a resin sheet and a glass fiber nonwoven fabric sheet are heated and pressurized by passing them between two pairs of rollers equipped with a heating device, and this laminated sheet may be used as part of the module cover. Lamination is preferable because it allows for continuous production and has good productivity.

[0111] As a method for manufacturing a laminate by injection molding, for example, a method may be used in which a glass nonwoven fabric, which will become the fiber layer, is set in a movable mold, the movable mold is fitted into a fixed mold to form a cavity, and a resin composition is injected into the cavity to integrally mold the resin composition and the glass nonwoven fabric (fiber layer). By this method, a laminate can be obtained in which the fiber layer is laminated on one side of the resin layer. When this injection molding method is used, the long fibers in the glass nonwoven fabric are less likely to break, so the flame-retardant properties of the laminate can be further improved.

[0112] The effects of the present invention will be explained below with reference to examples, but the present invention is not limited to the configurations of the examples.

[0113] Example 1: A module cover as shown in Figure 4 was fabricated. The covering portion and the partition portion are composed of a laminate having a resin layer and a fiber layer.

[0114] (Resin layer) The resin composition forming the resin layer was obtained with the following composition. • Polypropylene resin ((A) Thermoplastic resin) Manufactured by Nippon Polypropylene Co., Ltd., "Novatec® BC03B" (Melt flow rate: 30g / 10min) • Flame retardant ((B) Flame retardant) Phosphorus-based flame retardant (Manufactured by ADEKA Corporation, Adeka Stab FP-2500S, non-halogen intomescent flame retardant) • Dispersant α-olefin / maleic anhydride copolymer (Manufactured by Mitsubishi Chemical Corporation, Diacarna 30M, weight-average molecular weight 7,800) • Glass fiber reinforced thermoplastic resin (Polypropylene resin ((A) Thermoplastic resin) / Glass fiber ((C) Fiber)) = 50 / 50, Pellet length 10mm, Manufactured by Nippon Polypropylene Co., Ltd., "Funkstar®") • Antioxidant / Phenol-based antioxidant (Manufactured by ADEKA Corporation, Adeka Stab AO-60) - Phosphate-based antioxidant (ADEKA Corporation, ADEKA Stab 2112) The above components were mixed in the ratios shown in Table 1 below to prepare the resin composition.

[0115] The ratio of the antioxidants, specifically the phenolic antioxidant and the phosphite antioxidant, was 0.007 parts by mass per 100 parts by mass of the resin composition.

[0116] (Fiber layer) Glass nonwoven fabric (manufactured by Olivest Co., Ltd., FAP-110, basis weight 110 g / m²) ２ (A thickness of 0.77 mm was used.)

[0117] (Manufacturing of Laminate) A resin composition having the above composition was laminated onto the fiber layer using a FANUC ROBOSHOT α-S300iA injection molding machine manufactured by FANUC Corporation to produce a laminate. (Manufacturing of Module Cover) A SUS spacer measuring 20 mm (D) x 20 mm (W) x 1 mm (H) was placed in the mold, a glass nonwoven fabric with a thickness of 0.77 mm was placed on top of it, and then a resin composition with the formulation shown in Table 1 was injection molded on top of that to secure a space for a recess 63 and a space for housing the discharge valve 16 of the battery cell 11, thereby obtaining a module cover measuring 200 mm in length x 200 mm in width x 2.0 mm in thickness. The molding conditions were as follows. 1) Temperature conditions: Cylinder temperature (220°C), mold temperature (60°C) 2) Injection conditions: Injection pressure (200 MPa), holding pressure (82 MPa) 3) Metering conditions: Screw rotation speed (50 rpm), back pressure (15 MPa)

[0118] Comparative Example 1 A module cover without easily penetrated sections, measuring 200 mm in length, 200 mm in width, and 2.0 mm in thickness, was obtained by placing a glass nonwoven fabric with a thickness of 0.77 mm inside a mold and then injection molding a resin composition with the formulation shown in Table 1 onto it.

[0119] For the evaluation of flame resistance, the module covers obtained in Example 1 and Comparative Example 1 were exposed to a 1200°C burner flame, and as shown in Figure 8, the time it took for the surface temperature of the module cover 61 on the lid 31 side to reach 100°C, 200°C, 300°C, and 400°C was measured. The results are shown in Table 2 below.

[0120] The maximum surface temperature reached in Example 1 was 200°C. The maximum surface temperature reached in Comparative Example 1 was 400°C. The combined composition (in mass%) of the module cover, including the resin layer and fiber layer, is shown in Table 2.

[0121] In Table 2, "-" indicates that the surface temperature of the module cover did not reach that temperature.

[0122] The following simulations were performed to evaluate the temperature rise suppression effect of the module cover on the top surface of the cell, as obtained in Example 1 and Comparative Example 1. As a reference example, the temperature change during thermal runaway of a battery pack without a module cover was also simulated.

[0123] <Battery Cell> The simulation targeted a fluid domain consisting of air composition and a solid domain consisting of components constituting the battery module (case / jelly roll / terminals / terminal cover / bus bar / tension plate / end plate / inter-cell spacer / module cover). Using a fluid-solid coupled scheme, the transient temperature changes of the fluid and solid domains during high-temperature gas ejection due to cell thermal runaway were calculated. The simulation was performed using computational fluid dynamics software (product name: STAR-CCM+ Ver. 2410, Siemens).

[0124] <Battery Cell and High-Temperature Gas Ejection Conditions> The cell dimensions were set to a height of 122 mm, a width of 26.9 mm, and a depth of 148.2 mm, including the case thickness of 1.0 mm. An anisotropic thermal conductivity derived from the electrode stacking structure was set for the jelly roll portion inside the cell, and calculations were performed assuming a battery cell with a half-cut model jelly roll portion as shown in Figures 9(A) to 9(C). Figure 9(A) is a perspective view of the battery pack of Example 1 (with module cover and easy-penetration portion), Figure 9(B) is a perspective view of the battery pack of Comparative Example 1 (with module cover and no easy-penetration portion), and Figure 9(C) is a perspective view of the battery pack of the reference example (without module cover).

[0125] The calculation was performed assuming that during thermal runaway, a high-temperature gas at 727°C and a flow rate of 0.02 kg / s is ejected for 10 seconds from the left end vent of the battery pack shown in Figures 9(A) to 9(C). The initial temperature of each component constituting the module and the gas inside the pack was assumed to be 23°C. An outlet pressure boundary was set at the right end of the battery pack shown in Figures 9(A) to 9(C) so that the gas inside the pack is discharged from the system according to the pressure difference created by the ejection of the high-temperature gas. Note that these conditions are intended to analyze heat transfer via the high-temperature gas generated during cell thermal runaway, and internal heat generation of the thermal runaway cell is omitted. It was assumed that the air inside the pack is separated from the outside air by the pack, and the air inside the pack / pack interface has an outside air temperature of 20°C and a heat transfer coefficient of 10 W / m ２ - The natural convection boundary condition for K was used. The half-cut surface was assumed to be a symmetric boundary.

[0126] The physical properties used for each component in the calculations are shown in Table 3. Note that x in the table represents temperature [K].

[0127]

[0128] Table 4 below shows the results of calculations assuming that the battery packs obtained in Example 1, Comparative Example 1, and Reference Example, as shown in Figures 9(A) to 9(C), experience thermal runaway. The "maximum temperature of cases other than the thermal runaway cell" under each condition was calculated.

[0129]

[0130] Furthermore, Figure 10 shows the temperature distribution contour plot obtained as a calculation result 10 seconds after high-temperature gas ejection. Figure 10(A) is the temperature distribution contour plot under the conditions used in Example 1, Figure 10(B) is the temperature distribution contour plot under the conditions used in Comparative Example 1, and Figure 10(C) is the temperature distribution contour plot under the conditions used in the Reference Example.

[0131] In the battery pack using the module cover of Example 1, the temperature rise of the case can was suppressed. This is thought to be because the high-temperature gas was released into the pack from the vent, and the module cover inhibited heat transfer from the high-temperature gas inside the pack to the top surface of the case cans of cells other than the thermally runaway cells. In the battery pack using the module cover of Comparative Example 1, the case can became hotter. This is thought to be because the high-temperature gas filled the narrow space between the module cover and the top surface of the cells, resulting in higher temperature and higher flow rate gas coming into contact with the top surface of the cells and exchanging heat. In the reference example without the module cover, the case cans of cells other than the thermally runaway cells became hot. This is thought to be because the top surface of the cells was heated by the high-temperature gas.

[0132] In the temperature distribution contour diagram of Figure 10, black areas represent high temperatures and white areas represent low temperatures. In Comparative Example 1 (Figure 10(B)) and Reference Example (Figure 10(C)), the upper part of the cell is black and represents a high temperature, while in Example 1 (Figure 10(A)), the upper part of the cell is white to gray and represents a low temperature. From the evaluation of the temperature rise suppression effect, it is clear that the module cover of the present invention provides an effect of suppressing heat transfer from the top surface of the cell when high-temperature gas is ejected due to cell thermal runaway.

[0133] 11 Battery cell 12 Cell body 14 Top surface (end face) 16 Discharge valve 21 Battery module 30 Housing 31 Cover 31a Inner surface of cover 32 Side plate 33 Bottom plate 34 Spacer 35 Cushioning material 41, 51, 61 Module cover 42, 52, 62 Covering part 42a, 52a, 62a Top surface of covering part 52b, 62b Bottom surface of covering part 43, 53, 63 Recess 44, 54, 64 Easy-penetration part 46, 56, 66 Weakening wire 48, 58, 68 Partition part 48a Bottom surface of partition part 49, 59, 69 Storage part 49a Side surface of storage part 49b, 59b Bottom surface of storage part 100 Battery pack

Claims

1. A module cover disposed between a battery module, which is an assembly of multiple battery cells, and a housing that houses the battery module, wherein the battery cells have discharge valves that open when the internal pressure exceeds a set pressure, the module cover has a covering portion that covers the discharge valves of the multiple battery cells, and a partition portion that divides the space between adjacent discharge valves, and an easily penetrated portion is provided in the covering portion facing the discharge valves.

2. The module cover according to claim 1, wherein the module cover has a resin layer containing a flame retardant.

3. The module cover according to claim 2, wherein the module cover is made of a laminate having the resin layer and the fiber layer, and the fiber layer is located on the battery module side of the resin layer.

4. The module cover according to claim 1, wherein the easily penetrated portion is made thinner by providing recesses on one or both of the upper and lower surfaces of the covering portion.

5. The module cover according to claim 1, wherein the easily penetrated portion has a weakening line formed by cutting out the upper or lower surface of the covering portion.

6. The module cover according to claim 1, wherein the easily penetrated portion is made thinner by providing a recess on one of the upper and lower surfaces of the covering portion, and has a weakening line formed by cutting out the other of the upper and lower surfaces of the covering portion.

7. The module cover according to claim 1, wherein the covering portion and the partition portion are integrally molded.

8. A battery pack comprising a battery module in which a plurality of battery cells are assembled, housed in a housing, wherein a module cover according to any one of claims 1 to 7 is disposed between the housing and the battery module.

9. The battery pack according to claim 8, wherein the housing has an exhaust port.

Images