Heat transfer suppression sheet and assembled battery

Abstract

To provide a heat transfer suppression sheet that is used in a battery pack in which a plurality of battery cells are connected in series or in parallel, efficiently diffuses heat generated in the battery cell to outside of the heat transfer suppression sheet during normal use, and suppresses propagation of heat between the battery cells at the time of abnormality, thereby being capable of preventing a chain of thermal runaway.SOLUTION: A heat transfer suppression sheet 10 has a heat insulation layer 11a and a high heat conductive layer 12a provided on both surfaces orthogonal to a thickness direction of the heat insulation layer 11a. Thermal conductivity of the high heat conductive layer 12a is higher than that of the heat insulation layer 11a. One end surface A12 in parallel to a thickness direction of the high heat conductive layer 12a extends at least to one end surface A10 side in parallel to a thickness direction of the heat transfer suppression sheet 10. With the heat insulating layer 11a, one end surface A10 side of the heat transfer suppression sheet 10 is thinner than the other end surface B10 side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat transfer suppression sheet suitably used as a power source for an electric motor that drives, for example, an electric vehicle or a hybrid vehicle, and a battery pack using the heat transfer suppression sheet.

Background Art

[0002] In recent years, from the perspective of environmental protection, the development of electric vehicles or hybrid vehicles driven by electric motors has been actively promoted. Such electric vehicles or hybrid vehicles are equipped with a battery pack in which a plurality of battery cells are connected in series or parallel to serve as a power source for the driving electric motor.

[0003] For this battery cell, a lithium-ion secondary battery that can achieve high capacity and high output is mainly used compared to lead-acid batteries and nickel-metal hydride batteries. However, when thermal runaway occurs in one battery cell due to internal short circuit or overcharging of the battery (i.e., in the case of "abnormal conditions"), heat may be propagated to adjacent other battery cells, causing thermal runaway of other battery cells.

[0004] For example, Patent Document 1 discloses a power storage device capable of achieving effective heat insulation between a plurality of power storage elements such as lithium-ion secondary batteries. The power storage device described in Patent Document 1 has a first plate material and a second plate material having heat insulation properties disposed between adjacent first and second power storage elements. Further, a low heat conduction layer, which is a layer of a substance having a lower thermal conductivity than these first and second plate materials, is formed between the first plate material and the second plate material.

[0005] In the power storage device according to Patent Document 1 configured as described above, radiant heat traveling from the first power storage element to the second power storage element or from the second power storage element to the first power storage element is blocked by the first plate material and the second plate material. Further, the transfer of heat from one of these two plate materials to the other is suppressed by the low heat conduction layer.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] By the way, when performing a charge-discharge cycle on a battery cell assembled into a battery pack (that is, in the case of "normal use"), in order to sufficiently exhibit the charge-discharge performance of the battery cell, it is necessary to maintain the temperature on the surface of the battery cell at a predetermined value or lower (for example, 150°C or lower). In addition, when an abnormal situation occurs where the temperature of the battery cell reaches, for example, 200°C or higher, it is necessary to effectively cool the battery cell, suppress the heat propagation to adjacent battery cells, and prevent thermal runaway.

[0008] However, in the structure in which a low thermal conductivity layer is provided between heat insulating plates of an electric storage device as shown in Patent Document 1, the heat generated during the charge-discharge cycle cannot be efficiently diffused to the outside. Further, when thermal runaway occurs in one battery cell, it is difficult to effectively suppress the chain reaction of thermal runaway only with the heat insulating performance of the above structure. As described above, in recent times, further improvement has been demanded for a heat control means that has excellent heat insulating performance capable of efficiently diffusing the heat generated in the battery cell to the outside during normal use and suppressing the chain reaction of thermal runaway during abnormal times.

[0009] The present invention has been made in view of the above problems, and is used in a battery pack in which a plurality of battery cells are connected in series or in parallel. During normal use, the heat generated in the battery cell is efficiently diffused to the outside of the heat transfer suppression sheet, and even during abnormal times, the heat propagation between the battery cells is suppressed to prevent the chain reaction of thermal runaway. An object is to provide a heat transfer suppression sheet and a battery pack.

Means for Solving the Problems

[0010] The above object of the present invention is achieved by the configuration of the following [1] related to the heat transfer suppression sheet.

[0011] [1] A heat transfer suppression sheet used for a battery pack in which a plurality of battery cells are connected in series or in parallel, a heat insulation layer, and a high heat conductivity layer provided on both surfaces orthogonal to the thickness direction of the heat insulation layer, and having, the thermal conductivity of the high heat conductivity layer is higher than the thermal conductivity of the heat insulation layer, one end surface parallel to the thickness direction of the high heat conductivity layer extends at least to one end surface side parallel to the thickness direction of the heat transfer suppression sheet, the heat insulation layer is thinner on the one end surface side of the heat transfer suppression sheet than on the other end surface side of the heat transfer suppression sheet facing the one end surface of the heat transfer suppression sheet, a heat transfer suppression sheet.

[0012] Further, a preferred embodiment of the present invention related to the heat transfer suppression sheet relates to the following [2] to

[12] .

[0013] [2] The heat transfer suppression sheet according to [1], wherein the high heat conductivity layer extends from the one end surface side to the other end surface side of the heat transfer suppression sheet.

[0014] [3] The heat transfer suppression sheet according to [1] or [2], wherein the thickness of the heat insulation layer continuously decreases toward the one end surface side of the heat transfer suppression sheet.

[0015] [4] The heat transfer suppression sheet according to [1] or [2], wherein the thickness of the heat insulation layer increases stepwise toward the one end surface side of the heat transfer suppression sheet.

[0016] [5] The heat transfer suppression sheet according to any one of [1] to [4], wherein the thickness of the heat insulation layer decreases toward the one end surface side of the heat transfer suppression sheet so that the rate of decrease in the thickness increases.

[0017] [6] The heat transfer suppression sheet according to any one of [1] to [5], wherein the high thermal conductivity layers provided on both surfaces of the heat insulation layer are connected on the one end face side of the heat transfer suppression sheet.

[0018] [7] The heat transfer suppression sheet according to any one of [1] to [6], wherein the high thermal conductivity layer is made of at least one material selected from metals, ceramics, and carbon.

[0019] [8] The heat transfer suppression sheet according to any one of [1] to [7], wherein the heat conductivity of the heat insulation layer is less than 1 (W / m·K).

[0020] [9] The heat transfer suppression sheet according to any one of [1] to [8], wherein the heat insulation layer contains at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles.

[0021]

[10] The heat insulation layer includes a first inorganic fiber, a second inorganic fiber, and inorganic particles, the first inorganic fiber is an amorphous fiber, the second inorganic fiber is composed of at least one selected from amorphous fibers having a glass transition point higher than that of the first inorganic fiber and crystalline fibers, the inorganic particles are composed of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, The heat transfer suppression sheet according to [9], wherein the inorganic particles include at least one selected from nanoparticles, hollow particles, and porous particles.

[0022]

[11] The heat insulation layer includes a first inorganic fiber, a second inorganic fiber, and inorganic particles, the average fiber diameter of the first inorganic fiber is larger than the average fiber diameter of the second inorganic fiber, the first inorganic fiber is linear or needle-shaped, The heat transfer suppression sheet according to [9], wherein the second inorganic fiber is dendritic or crumpled.

[0023]

[12] The heat insulation layer includes a first inorganic fiber, a second inorganic fiber, and inorganic particles. The first inorganic fiber is an amorphous fiber. The second inorganic fiber is composed of at least one selected from amorphous fibers having a glass transition point higher than that of the first inorganic fiber and crystalline fibers. The heat transfer suppression sheet according to [9], wherein an average fiber diameter of the first inorganic fiber is larger than an average fiber diameter of the second inorganic fiber.

[0024] The above object of the present invention is achieved by the configurations of the following

[13] and

[14] related to the assembled battery.

[0025]

[13] A battery case, A plurality of battery cells housed inside the battery case and connected in series or in parallel, An assembled battery having the heat transfer suppression sheet according to any one of [1] to

[12] interposed between the plurality of battery cells.

[0026]

[14] A battery case, A plurality of battery cells housed inside the battery case and connected in series or in parallel, The heat transfer suppression sheet according to any one of [1] to

[12] interposed between the plurality of battery cells, A heat transfer member disposed between the battery case and the heat transfer suppression sheet, An assembled battery, wherein one end face side of the heat transfer suppression sheet is in contact with the heat transfer member.

Advantages of the Invention

[0027] The heat transfer suppression sheet of the present invention has a heat insulation layer and high heat conduction layers provided on both surfaces orthogonal to the thickness direction of the heat insulation layer. One end face parallel to the thickness direction of the high heat conduction layer extends at least on one end face side parallel to the thickness direction of the heat transfer suppression sheet, and the heat insulation layer is thinner on the one end face side of the heat transfer suppression sheet than on the other end face side facing the one end face of the heat transfer suppression sheet. In such a heat transfer suppression sheet, when heat generated from a battery cell reaches the heat transfer suppression sheet, it immediately moves in the plane direction orthogonal to the thickness of the high heat conduction layer through the high heat conduction layer. Such a heat transfer suppression sheet efficiently diffuses the heat generated in the battery cell to the outside of the heat transfer suppression sheet during normal use, and suppresses the heat propagation between battery cells even in the event of an abnormality, thereby preventing the chain of thermal runaway.

[0028] Moreover, in the assembled battery of the present invention, since the above heat transfer suppression sheet is interposed between a plurality of battery cells, the heat generated in the battery cell is efficiently diffused to the outside of the heat transfer suppression sheet during normal use, and even in the event of an abnormality, the heat propagation between battery cells is suppressed, thereby preventing the chain of thermal runaway.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7A

Figure 7B

[0030] The present inventor has earnestly studied to provide a heat transfer suppression sheet for a battery pack that can efficiently diffuse heat generated from battery cells to the outside of the heat transfer suppression sheet during normal use and can suppress the propagation of heat between battery cells even during an abnormal situation where a large amount of heat is generated, thereby suppressing the chain of thermal runaway.

[0031] As a result, the present inventor has found that the problem can be solved in a heat transfer suppression sheet having a heat insulating layer and high heat conductive layers provided on both surfaces orthogonal to the thickness direction of the heat insulating layer, the heat conductivity of the high heat conductive layer being higher than that of the heat insulating layer, one end surface parallel to the thickness direction of the high heat conductive layer extending at least to one end surface side parallel to the thickness direction of the heat transfer suppression sheet, and the heat insulating layer being thinner on the one end surface side of the heat transfer suppression sheet than on the other end surface side facing the one end surface of the heat transfer suppression sheet.

[0032] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[0033] [1. Heat Transfer Suppression Sheet] Hereinafter, each of the first to sixth embodiments of the heat transfer suppression sheet for a battery pack according to the embodiments of the present invention will be described in order. Thereafter, the heat insulating layer, the high heat conductive layer, etc. constituting the heat transfer suppression sheet for a battery pack according to the present embodiment will be described. Further, a method for manufacturing the heat transfer suppression sheet for a battery pack according to the present embodiment will be described.

[0034] <First Embodiment> FIG. 1 is a cross-sectional view schematically showing a heat transfer suppression sheet for a battery pack according to a first embodiment of the present invention. Hereinafter, the heat transfer suppression sheet for a battery pack may be simply referred to as a "heat transfer suppression sheet". The heat transfer suppression sheet 10 for a battery pack according to the first embodiment includes a heat insulating layer 11a and a pair of high thermal conductivity layers 12a partially provided on both surfaces orthogonal to the thickness direction of the heat insulating layer 11a. The high thermal conductivity layer 12a has a higher thermal conductivity than the heat insulating layer 11a, and one end surface A12 parallel to the thickness direction of the high thermal conductivity layer 12a extends at least toward one end surface A10 side parallel to the thickness direction of the heat transfer suppression sheet 10. Further, the heat insulating layer 11a is thinner on the one end surface A10 side of the heat transfer suppression sheet 10 than on the other end surface B10 side of the heat transfer suppression sheet facing the one end surface A10. The high thermal conductivity layer 12a is provided, for example, in a space P formed by the thinning of the thickness of the heat insulating layer 11a. The space P is a region surrounded by a broken line in FIG. 1. Note that the pair of high thermal conductivity layers 12a provided on both surfaces orthogonal to the thickness direction of the heat insulating layer 11a are not limited to high thermal conductivity layers having the same shape and the same components as each other, and may be high thermal conductivity layers having different shapes and different materials from each other.

[0035] FIG. 2 is a cross-sectional view schematically showing a battery pack to which the heat transfer suppression sheet for a battery pack according to the first embodiment is applied. The battery pack 100 includes a battery case 30, a plurality of battery cells 20a, 20b, 20c housed inside the battery case 30, a heat transfer suppression sheet 10 interposed between the battery cell 20a and the battery cell 20b and between the battery cell 20b and the battery cell 20c, and a heat transfer member 40 disposed between these battery cells 20a, 20b, 20c and the heat transfer suppression sheet 10 and the battery case 30.

[0036] And the heat transfer suppression sheet 10 is arranged such that its one end surface A10 side is in contact with the heat transfer member 40. Further, the plurality of battery cells 20a, 20b, 20c are connected in series or in parallel by a bus bar or the like (not shown).

[0037] In this embodiment, the heat transfer member 40 means a member that transfers the heat of the battery cells 20a, 20b, 20c and the heat transfer suppression sheet 10 to the heat transfer member 40 to promote heat dissipation. As the heat transfer member 40, for example, in addition to a heat sink and a heat storage material, it also includes a heat dissipation material (TIM: Thermal Interface Material) disposed between the heat sink or the heat storage material and the battery cells 20a, 20b, 20c.

[0038] Note that the heat transfer member 40 does not necessarily need to be disposed on the entire bottom surface of the battery case 30 as shown in FIG. 2, and it is sufficient that it is installed at least between the heat transfer suppression sheet 10 and the battery case 30. For the battery cells 20a, 20b, 20c, for example, lithium ion secondary batteries are preferably used, but it is not particularly limited thereto, and it can also be applied to other secondary batteries.

[0039] In the first embodiment configured as described above, for example, when the heat generated from the battery cell 20a is transmitted to the high thermal conductivity layer 12a, since the high thermal conductivity layer 12a has a higher thermal conductivity than the heat insulation layer 11a, the heat of the high thermal conductivity layer 12a quickly moves along the surface direction in the high thermal conductivity layer 12a and is released to the outside of the heat transfer suppression sheet 10. Note that the "surface direction" in the high thermal conductivity layer 12a refers to the direction of the surface orthogonal to the thickness direction of the high thermal conductivity layer 12a (the vertical direction in FIG. 1).

[0040] Further, since one end face A12 parallel to the thickness direction of the high thermal conductivity layer 12a extends toward the one end face A10 side of the heat transfer suppression sheet 10, when the heat transfer member 40 is provided on the one end face A10 side of the heat transfer suppression sheet 10, the heat transmitted to the high thermal conductivity layer 12a is efficiently taken away by the heat transfer member 40 and diffuses to the outside of the heat transfer suppression sheet 10. That is, in the assembled battery 100 using the heat transfer suppression sheet 10 of this embodiment, when heat is generated from a certain battery cell, the heat transfer suppression sheet 10 efficiently diffuses the heat to the outside of the heat transfer suppression sheet 10 during normal use, and suppresses the propagation of heat to adjacent battery cells during abnormal times, and can prevent the chain of thermal runaway.

[0041] <Second Embodiment> FIG. 3 is a cross-sectional view schematically showing a heat transfer suppression sheet for a battery pack according to the second embodiment of the present invention. Hereinafter, although the heat transfer suppression sheets, heat insulating layers, and high heat conductivity layers of the second to fifth embodiments shown in FIGS. 3 to 6 are given different reference numerals, the contents described in the first embodiment are similarly described in the second to fifth embodiments, and thus the description thereof is omitted in the second to fifth embodiments. Further, since the second to fifth embodiments can be used in place of the heat transfer suppression sheet 10 provided in the battery pack 100 shown in FIG. 2, the effects and the like will be described assuming that the heat transfer suppression sheets according to the second to fifth embodiments are applied to the battery pack 100.

[0042] The heat transfer suppression sheet 15 for a battery pack according to the second embodiment includes a heat insulating layer 11b and a pair of high heat conductivity layers 12b provided on both surfaces orthogonal to the thickness direction of the heat insulating layer 11b. The high heat conductivity layer 12b has a higher thermal conductivity than the heat insulating layer 11b, and one end face A12 parallel to the thickness direction of the high heat conductivity layer 12b extends at least toward one end face A15 side parallel to the thickness direction of the heat transfer suppression sheet 15. Further, the heat insulating layer 11b is thinner on the one end face A15 side of the heat transfer suppression sheet 15 than on the other end face B15 side of the heat transfer suppression sheet facing the one end face A15 of the heat transfer suppression sheet 15. As shown in FIG. 3, the high heat conductivity layer 12b according to the second embodiment extends wider from one end face A15 side of the heat transfer suppression sheet 15 toward the other end face B15 side of the heat transfer suppression sheet 15 facing the one end face A15 of the heat transfer suppression sheet 15 than the high heat conductivity layer 12a according to the first embodiment.

[0043] Also in the second embodiment configured as described above, the same effects as those of the first embodiment can be obtained. Further, the wider the high heat conductivity layer 12b is provided in the plane direction of the heat transfer suppression sheet 15 (that is, the direction of the plane orthogonal to the thickness direction of the high heat conductivity layer 12b), the more heat transmitted from the battery cell can be received and diffused to the outside of the heat transfer suppression sheet 15 through the high heat conductivity layer 12b. Therefore, in the second embodiment, heat can be more efficiently diffused to the outside of the heat transfer suppression sheet 15 during normal use, and the propagation of heat to adjacent battery cells can be more suppressed during abnormal times, further preventing the chain of thermal runaway.

[0044] In the above-described first and second embodiments, the high thermal conductivity layer is provided so as to be in contact with a part of both surfaces orthogonal to the thickness direction of the heat insulation layer. However, in the present invention, the high thermal conductivity layer may be provided on the entire surfaces of both sides orthogonal to the thickness direction of the heat insulation layer. Further, it is preferable that the thickness of the high thermal conductivity layer is formed to increase as it approaches from the other end face side to one end face side of the heat transfer suppression sheet. Hereinafter, an example in which the shape and the like of the high thermal conductivity layer are different from those of the first and second embodiments will be described.

[0045] <Third Embodiment> FIG. 4 is a cross-sectional view schematically showing a heat transfer suppression sheet for a laminated battery according to a third embodiment of the present invention.

[0046] The heat transfer suppression sheet 16 for a laminated battery according to the third embodiment includes a heat insulation layer 11c and a pair of high thermal conductivity layers 12c provided on both surfaces orthogonal to the thickness direction of the heat insulation layer 11c. The high thermal conductivity layer 12c has a higher thermal conductivity than the heat insulation layer 11c, and one end face A12 parallel to the thickness direction of the high thermal conductivity layer 12c extends toward one end face A16 side parallel to the thickness direction of the heat transfer suppression sheet 16. Further, the high thermal conductivity layer 12c also extends toward the other end face B16 side parallel to the thickness direction of the heat transfer suppression sheet 16. That is, the high thermal conductivity layer 12c extends from one end face A16 side to the other end face B16 side of the heat transfer suppression sheet 16 and is formed so as to cover the entire surfaces of both sides orthogonal to the thickness direction of the heat insulation layer 11c. Note that, similar to the first and second embodiments, the heat insulation layer 11c is thinner on the one end face A16 side of the heat transfer suppression sheet 16 than on the other end face B16 side of the heat transfer suppression sheet facing the one end face A16.

[0047] To elaborate on the shape of the high thermal conductivity layer 12c, as shown in FIG. 4, in the third embodiment, the thickness of the heat insulation layer 11c is formed to continuously decrease from the other end face B16 side to the one end face A16 side of the heat transfer suppression sheet 16. And similar to the first embodiment, in the heat transfer suppression sheet 16 of the third embodiment, the high thermal conductivity layer 12c is provided in the space formed by the decreasing thickness of the heat insulation layer 11c, and the high thermal conductivity layer 12c is formed to continuously (gradually) thicken toward the one end face A16 side of the heat transfer suppression sheet.

[0048] Even in the third embodiment configured as described above, the same effects as those of the first embodiment can be obtained. Also, since the high thermal conductivity layer 12c exists on the entire both surfaces of the heat insulation layer 11c, for example, heat generated from the battery cell 20a is likely to be transmitted to the high thermal conductivity layer 12c, and the heat transmitted to the high thermal conductivity layer 12c can be quickly moved along its surface direction. Further, since the thickness of the high thermal conductivity layer 12c continuously thickens toward the one end face A16 side, the amount of heat that can move through the high thermal conductivity layer 12c increases as it approaches the one end face A16 side. That is, the heat transfer in the surface direction toward the one end face A16 side is selectively promoted, and a more efficient heat dissipation effect is obtained.

[0049] In the above-described third embodiment, the high thermal conductivity layer 12c whose thickness continuously thickens as it approaches the one end face A16 side of the heat transfer suppression sheet 16 is arranged to cover the entire both surfaces of the heat insulation layer 11c, but a high thermal conductivity layer having a similar shape may be arranged to cover only a part of the both surfaces of the heat insulation layer 11c. However, even in this case, it is assumed that the one end face A12 of the high thermal conductivity layer extends toward the one end face A16 side of the heat transfer suppression sheet 16.

[0050] <Fourth Embodiment> FIG. 5 is a cross-sectional view schematically showing a heat transfer suppression sheet for a battery pack according to a fourth embodiment of the present invention. The heat transfer suppression sheet 17 for a battery pack according to the fourth embodiment includes a heat insulation layer 11d and a pair of high thermal conductivity layers 12d provided on both surfaces orthogonal to the thickness direction of the heat insulation layer 11d. Compared with the heat insulation layer 11d, the high thermal conductivity layer 12d has a higher thermal conductivity, and one end surface A12 parallel to the thickness direction of the high thermal conductivity layer 12d extends at least toward one end surface A17 side parallel to the thickness direction of the heat transfer suppression sheet 17. Further, the heat insulation layer 11d is thinner on the one end surface A17 side of the heat transfer suppression sheet 17 than on the other end surface B17 side of the heat transfer suppression sheet facing the one end surface A17.

[0051] To describe the shape of the high thermal conductivity layer 12d in detail, as shown in FIG. 5, in the fourth embodiment, the thickness of the heat insulation layer 11d becomes thinner stepwise toward the one end surface A17 side of the heat transfer suppression sheet. Similar to the first embodiment, in the heat transfer suppression sheet 17 of the fourth embodiment, the high thermal conductivity layer 12d is provided in a space formed by the thinning of the thickness of the heat insulation layer 11d, and the high thermal conductivity layer 12d becomes thicker stepwise toward the one end surface A17 side of the heat transfer suppression sheet.

[0052] Even in the fourth embodiment configured as described above, the same effects as those of the first embodiment can be obtained. Further, the stepwise thickened high thermal conductivity layer 12d in the fourth embodiment can be formed, for example, as shown in FIG. 5, by overlapping a plurality of sheets of different sizes, so that the high thermal conductivity layer 12d can be easily manufactured. However, the stepwise thickened high thermal conductivity layer 12d may be formed of a material made of a single metal or the like. In addition, the stepwise thickened high thermal conductivity layer 12d may create a space 21 between the high thermal conductivity layer 12d and the heat insulation layer 11d. By holding air in this space 21, the heat insulation performance of the heat transfer suppression sheet 17 is improved.

[0053] <Fifth Embodiment> FIG. 6 is a cross-sectional view schematically showing a heat transfer suppression sheet for a battery pack according to a fifth embodiment of the present invention. The heat transfer suppression sheet 18 for a battery pack according to the fifth embodiment includes a heat insulation layer 11e and high thermal conductivity layers 12e provided on both surfaces orthogonal to the thickness direction of the heat insulation layer 11e. The high thermal conductivity layer 12e has a higher thermal conductivity than the heat insulation layer 11e, and one end face A12 parallel to the thickness direction of the high thermal conductivity layer 12e extends at least toward one end face A18 side parallel to the thickness direction of the heat transfer suppression sheet 18. Further, the heat insulation layer 11e is thinner on the one end face A18 side of the heat transfer suppression sheet 18 than on the other end face B18 side of the heat transfer suppression sheet facing the one end face A18.

[0054] To describe the shape of the high thermal conductivity layer 12e in detail, as shown in FIG. 6, in the heat transfer suppression sheet 18 according to the fifth embodiment, the thickness of the heat insulation layer e becomes thinner toward one end face A18 side of the heat transfer suppression sheet 18 so that the rate of decrease in the thickness of the heat insulation layer 11e increases. Similar to the first embodiment, in the heat transfer suppression sheet 18 of the fifth embodiment, the high thermal conductivity layer 12e is provided in a space formed by the thinning of the thickness of the heat insulation layer 11e, and the high thermal conductivity layer 12e becomes thicker toward one end face A18 side of the heat transfer suppression sheet 18 so that the rate of increase in the thickness of the high thermal conductivity layer 12e increases.

[0055] Even in the fifth embodiment configured as described above, the same effects as those of the first embodiment can be obtained. Further, since the thickness of the high thermal conductivity layer 12e becomes thicker toward one end face A18 side, the amount of heat that can move the high thermal conductivity layer 12e increases as it approaches the one end face A18 side. Therefore, in the region near the one end face A18, the heat transfer in the surface direction toward the one end face A18 side is selectively promoted, and a more efficient heat dissipation effect can be obtained. On the other hand, in the region away from the heat transfer member 40, heat tries to move toward the heat insulation layer 11e while heat moves in the surface direction toward the heat transfer member 40. However, in this embodiment, in the position away from the heat transfer member 40, that is, in the region near the other end face B18 side, since the heat insulation layer 11e is thick, the heat transfer in the thickness direction can be suppressed.

[0056] <Sixth Embodiment> FIGS. 7A and 7B are cross-sectional views schematically showing a heat transfer suppression sheet for a battery pack according to the sixth embodiment of the present invention. As shown in FIGS. 7A and 7B, the heat transfer suppression sheet 19 for a battery pack according to the sixth embodiment includes a heat insulation layer 11f and high thermal conductivity layers 12f provided on both surfaces orthogonal to the thickness direction of the heat insulation layer 11f. The high thermal conductivity layer 12f has a higher thermal conductivity than the heat insulation layer 11f, and one end face A12 parallel to the thickness direction of the high thermal conductivity layer 12f extends at least toward one end face A19 side parallel to the thickness direction of the heat transfer suppression sheet 19. Further, the heat insulation layer 11f is thinner on the one end face A19 side of the heat transfer suppression sheet 19 than on the other end face B19 side of the heat transfer suppression sheet facing the one end face A19.

[0057] As shown in FIGS. 7A and 7B, in the heat transfer suppression sheet 19 according to the sixth embodiment, a pair of high thermal conductivity layers 12f are connected on the one end face A19 side. More specifically, the high thermal conductivity layer 12f according to the sixth embodiment may be arranged such that a plurality of high thermal conductivity layers are only in contact with each other on the one end face A19 side, or may be joined at the contact positions. Further, it may be formed of one high thermal conductivity layer 12f.

[0058] Even in the sixth embodiment configured as described above, the same effects as those of the first embodiment can be obtained. In this embodiment, the high thermal conductivity layers 12f are in contact with each other on the one end face A19 side. For example, there is a possibility that heat generated from the battery cell 20a is easily transmitted to the adjacent battery cell 20b in the region where the high thermal conductivity layers 12f are in contact with each other. However, the heat transfer member 40 arranged on the one end face A19 side of the heat transfer suppression sheet 19 has a large heat capacity and is made of a material that easily releases heat even when water does not flow through a water-cooled jacket or the like, for example. Therefore, even when the high thermal conductivity layers 12f are in contact with each other on the one end face A19 side, the heat transmitted to the high thermal conductivity layers 12f can be released to the outside through the heat transfer member 40.

[0059] Next, the high thermal conductivity layer, heat insulation layer, and heat transfer member that constitute the heat transfer suppression sheet for the assembled battery according to the present invention will be described in detail.

[0060] <1-1. High thermal conductivity layer> The high thermal conductivity layer used in the heat transfer suppression sheet for the assembled battery according to the present embodiment has the effect of suppressing radiant heat transfer from being transmitted to adjacent battery cells, and the effect of moving the heat that has reached the high thermal conductivity layer in the direction of one end surface of the heat transfer suppression sheet and diffusing it to the outside of the heat transfer suppression sheet.

[0061] As the high thermal conductivity layer having a thermal conductivity higher than that of the heat insulation layer, it is preferable to select, for example, one made of at least one material selected from metals, ceramics, and carbon. Specifically, as the metal, it can be selected from aluminum or aluminum alloy, stainless steel, copper or copper alloy, silver or silver alloy, nickel or nickel alloy, titanium or titanium alloy, etc. Further, as the ceramic, it can be selected from silicon carbide, aluminum nitride, silicon nitride, boron nitride, titanium nitride, etc. Furthermore, as the carbon, it can be selected from carbon fiber, carbon nanotube, diamond, graphite, etc.

[0062] Note that a high thermal conductivity layer may be formed by laminating a plurality of metal layers made of different types of the above metals. Examples of such a high thermal conductivity layer include [aluminum / copper / aluminum] composite layer, [aluminum / silver / aluminum] composite layer, [nickel / stainless steel / nickel] composite layer, [silver / stainless steel / silver] composite layer, etc. The above composite layer can be obtained by forming a surface layer on both sides of the central base layer by a method such as wet plating or vapor deposition. Also, the high thermal conductivity layer may be composed of a combination of different types of materials selected from the above metals, ceramics, and carbon.

[0063] When the high thermal conductivity layer contains a metal, in order to ensure the insulation between the high thermal conductivity layer and the adjacent battery cell, it is preferable to perform an insulation treatment on the high thermal conductivity layer. Specifically, it is preferable to dispose an insulating material on the contact surface of the high thermal conductivity layer with the adjacent battery cell. For example, methods such as applying an insulating material to the above contact surface of the high thermal conductivity layer, interposing a sheet made of an insulating material, electrodeposition coating, anodizing treatment, etc. can be mentioned. In addition, examples of the insulating material include polyethylene, polypropylene, polystyrene, polycarbonate, acrylic resin, polyimide, polyethylene terephthalate, vinyl chloride resin, epoxy resin, nylon resin, silicone resin, fluororesin, etc.

[0064] The thermal conductivity of the high thermal conductivity layer is 5 to 450 (W / m·K), and since it is sufficiently larger than the thermal conductivity of the heat insulation layer described later (for example, 0.05 (W / m·K)), the heat reaching the high thermal conductivity layer can be efficiently diffused to the outside of the heat transfer suppression sheet. As a specific thermal conductivity when compared with the heat insulation layer, the thermal conductivity of the high thermal conductivity layer is preferably 10 times or more, and more preferably 100 times or more, the thermal conductivity of the heat insulation layer.

[0065] Note that the thermal conductivity of the high thermal conductivity layer can be calculated by the laser flash method and the differential scanning calorimetry (DSC) method as shown in the following (1) to (3). (1) Measure the thermal diffusivity in accordance with the "Method for Measuring Thermal Diffusivity of Metals by Laser Flash Method" described in JIS H 7801. (2) Measure the specific heat capacity in accordance with the "Method for Measuring Specific Heat Capacity of Long Fiber Reinforced Ceramic Matrix Composites by Differential Scanning Calorimetry" described in JIS R 1672. (3) Calculate the thermal conductivity based on the values obtained in (1) and (2).

[0066] Of the high thermal conductivity layers provided on both surfaces orthogonal to the thickness direction of the heat insulating layer, the thickness of one of the high thermal conductivity layers preferably exceeds 0 μm, more preferably 5 μm or more, still more preferably 10 μm or more, still more preferably 15 μm or more, and particularly preferably 25 μm or more at the thinnest part of the high thermal conductivity layer in order to sufficiently obtain the heat diffusion effect due to conduction heat transfer. On the other hand, from the viewpoint of the thickness of the entire heat transfer suppression sheet, the thickness of one of the high thermal conductivity layers is preferably 150 μm or less, more preferably 100 μm or less at the thickest part.

[0067] Furthermore, as described above, the high thermal conductivity layer may be composed of a single layer or may be a laminate of a plurality of layers made of various materials. When a layer made of the same material is laminated to form the high thermal conductivity layer, the same effect can be obtained if the total thickness of the plurality of layers is the same as the thickness of the high thermal conductivity layer composed of a single layer. Therefore, even when the high thermal conductivity layer is composed of a plurality of layers, the total thickness thereof is preferably within the above range.

[0068] <1-2. Heat insulating layer> The heat insulating layer used in the heat transfer suppression sheet according to the present embodiment is not particularly limited as long as it has a heat insulating effect. As an index representing the heat insulating effect, the thermal conductivity can be mentioned. In the present embodiment, the thermal conductivity of the heat insulating layer is preferably less than 1 (W / m·K), more preferably less than 0.5 (W / m·K), and still more preferably less than 0.2 (W / m·K). Furthermore, the thermal conductivity of the heat insulating layer is more preferably less than 0.1 (W / m·K), more preferably less than 0.05 (W / m·K), and particularly preferably less than 0.02 (W / m·K). Note that the thermal conductivity of the heat insulating layer can be measured in accordance with the "Test Method for Thermal Conductivity of Refractory Materials" described in JIS R 2251.

[0069] As such a heat insulating layer, for example, one containing at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles can be used. As the inorganic fibers, alumina fiber, carbon fiber, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite material, etc. can be used. As the organic fibers, cellulose fiber, etc. can be used. In addition, for these fibers, a single fiber may be used, or two or more kinds of fibers may be used in combination.

[0070] As the inorganic particles, mica, microporous particles, hollow silica particles, thermally expandable inorganic materials, and aerogel can be used. Examples of the thermally expandable inorganic materials include vermiculite, bentonite, mica, perlite, etc. As the organic particles, hollow polystyrene particles, etc. can be used.

[0071] Among these materials for the heat insulation layer, alumina fiber, glass fiber, aerogel composite material, etc. can be preferably used.

[0072] Also, as another example of the heat insulation layer, specifically, it includes inorganic particles, a first inorganic fiber, and a second inorganic fiber, the first inorganic fiber is an amorphous fiber, and the second inorganic fiber is at least one selected from amorphous fibers having a glass transition point higher than that of the first inorganic fiber and crystalline fibers. The inorganic particles, the first inorganic fiber, and the second inorganic fiber are all heat-resistant materials. Furthermore, innumerable minute spaces are formed between the particles, between the particles and the fibers, and between the fibers, and the heat insulation effect by air is also exerted, so it has excellent heat transfer suppression performance. Hereinafter, the inorganic particles, the first inorganic fiber, and the second inorganic fiber that may be contained in the heat insulation layer will be described in detail below.

[0073] <1-2-1. Inorganic Particles> The material of the inorganic particles is not particularly limited. From the perspective of the heat transfer suppression effect, it is preferable that the inorganic particles are composed of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and more preferably include oxide particles. Also, the shape and size of the inorganic particles are not particularly limited, but it is preferable to include at least one selected from nanoparticles, hollow particles, and porous particles, and more preferably include nanoparticles.

[0074] Note that as the inorganic particles, a single type of inorganic particle may be used, or a combination of two or more types of inorganic particles may be used. When two or more types of inorganic particles with different heat transfer suppression effects are used in combination, the heating element can be cooled in multiple stages, and the endothermic effect can be manifested in a wider temperature range. Also, it is preferable to use a mixture of large-diameter particles and small-diameter particles as the inorganic particles. When small-diameter inorganic particles enter the gaps between large-diameter inorganic particles, a denser structure can be formed, and the heat transfer suppression effect can be improved.

[0075] When the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are easy to obtain, and an increase in manufacturing cost can be suppressed. Also, when it is 200 μm or less, a desired heat insulation effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0076] Subsequently, an example of the material or shape of the particles that can be used as the inorganic particles will be described in detail below.

[0077] (1-2-1-1. Oxide Particles) Since oxide particles have a high refractive index and a strong effect of diffusely reflecting light, using oxide particles as inorganic particles can suppress radiative heat transfer, particularly in high-temperature regions such as abnormal heat generation. As the oxide particles, at least one kind of particles selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. That is, among the above-mentioned oxide particles that can be used as inorganic particles, only one kind may be used, or two or more kinds of oxide particles may be used. In particular, silica is a component with high heat insulation properties, and titania is a component with a high refractive index compared to other metal oxides and has a high effect of diffusely reflecting light and blocking radiative heat in a high-temperature region of 500 °C or higher. Therefore, it is most preferable to use silica and titania as the oxide particles.

[0078] (Average primary particle diameter of oxide particles: 0.001 μm or more and 50 μm or less) Since the particle diameter of the oxide particles may affect the effect of reflecting radiative heat, limiting the average primary particle diameter to a predetermined range can obtain even higher heat insulation properties. That is, when the average primary particle diameter of the oxide particles is 0.001 μm or more, it is sufficiently larger than the wavelength of light contributing to heating, and light is efficiently diffusely reflected. Therefore, radiative heat transfer of heat in the heat insulation layer is suppressed in a high-temperature region of 500 °C or higher, and the heat insulation properties can be further improved. On the other hand, when the average primary particle diameter of the oxide particles is 50 μm or less, even if compressed, the number of contacts between particles does not increase, and it is difficult to form a path for conductive heat transfer. Therefore, the influence on the heat insulation properties in the normal temperature range where conductive heat transfer is dominant can be particularly reduced.

[0079] When using two or more kinds of oxide particles, it is also preferable to use a mixture of large-diameter particles and small-diameter particles (nanoparticles). In this case, the average primary particle diameter of the large-diameter particles is more preferably 1 μm or more and 50 μm or less, even more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less. In the present invention, the average primary particle diameter can be determined by observing the particles with a microscope, comparing them with a standard scale, and taking the average of any 10 particles.

[0080] (1-2-1-2. Nanoparticles) In the present invention, the term "nanoparticle" refers to particles on the nanometer order with an average primary particle diameter of less than 1 μm that are spherical or nearly spherical. Since nanoparticles have a low density, they suppress conductive heat transfer. When nanoparticles are used as inorganic particles, the voids are more finely dispersed, and thus excellent heat insulation properties for suppressing convective heat transfer can be obtained. Therefore, it is preferable to use nanoparticles in that heat conduction between adjacent nanoparticles can be suppressed during normal use of the battery at room temperature.

[0081] Also, in the present invention, among the oxide particles, carbide particles, nitride particles, and inorganic hydrate particles selected as inorganic particles, it is preferable that at least one kind is a nanoparticle. Furthermore, when using nanoparticles with a small average primary particle diameter as oxide particles, even when the heat transfer suppression sheet is compressed due to the expansion accompanying thermal runaway of the battery cell and the internal density increases, an increase in conductive heat transfer of the heat insulation layer can be suppressed. This is presumably because nanoparticles easily form fine voids between particles due to the repulsive force caused by static electricity and have a low bulk density, so that the particles are filled in a cushioned manner.

[0082] In the present invention, when using nanoparticles as inorganic particles, as long as they conform to the above definition of nanoparticles, the material is not particularly limited. For example, silica nanoparticles In addition to being a material with high heat insulation properties, since the contact points between particles are small, the amount of heat conducted by silica nanoparticles is smaller compared to the case of using silica particles with a large particle diameter. Also, generally available silica nanoparticles have a bulk density of 0.1 g / cm 3Since it is at such a level, for example, even when the battery cells arranged on both sides of the heat transfer suppression sheet thermally expand and a large compressive stress is applied to the heat transfer suppression sheet, the size (area) and number of contacts between silica nanoparticles do not increase significantly, and the heat insulation property can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. As the silica nanoparticles, wet silica, dry silica, aerogel, etc. can be used.

[0083] As described above, titania has a high effect of blocking radiant heat, silica nanoparticles have extremely low conductive heat transfer, and excellent heat insulation can be maintained even when compressive stress is applied to the heat insulation layer. Therefore, it is most preferable to use both titania and silica nanoparticles as the inorganic particles.

[0084] (Average primary particle diameter of nanoparticles: 1 nm or more and 100 nm or less) Limiting the average primary particle diameter of the nanoparticles to a predetermined range can obtain even higher heat insulation performance. That is, when the average primary particle diameter of the nanoparticles is 1 nm or more and 100 nm or less, in particular, in the temperature range below 500 °C, convective heat transfer and conductive heat transfer of heat in the heat insulation layer can be suppressed, and the heat insulation property can be further improved. Also, even when compressive stress is applied, the voids remaining between the nanoparticles and the contacts between many particles suppress conductive heat transfer, and the heat insulation property of the heat insulation layer can be maintained. In addition, the average primary particle diameter of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. On the other hand, the average primary particle diameter of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0085] (1-2-1-3. Inorganic hydrate particles) When the inorganic hydrate particles receive heat from the heating element and reach a temperature equal to or higher than the thermal decomposition start temperature, they thermally decompose, release the crystal water they possess, and exhibit a so-called "endothermic effect" of lowering the temperature of the heating element and its surroundings. Also, after releasing the crystal water, they become a porous body and exhibit a heat insulation effect due to innumerable air holes. Specific examples of inorganic hydrates include aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), zinc hydroxide (Zn(OH)2), iron hydroxide (Fe(OH)2), manganese hydroxide (Mn(OH)2), zirconium hydroxide (Zr(OH)2), gallium hydroxide (Ga(OH)3), and the like.

[0086] For example, aluminum hydroxide has about 35% water of crystallization and, as shown in the following formula, undergoes thermal decomposition to release water of crystallization and exhibits an endothermic effect. After releasing the water of crystallization, it becomes alumina (Al2O3), which is a porous body and functions as a heat insulation layer. 2Al(OH)3 → Al2O3 + 3H2O

[0087] In addition, as will be described later, the assembled battery of the present invention has a heat transfer suppression sheet interposed between battery cells. However, in a battery cell that has experienced thermal runaway, the temperature rapidly rises to over 200°C and continues to rise to around 700°C. Therefore, it is preferable that the inorganic particles are composed of an inorganic hydrate whose thermal decomposition start temperature is 200°C or higher. The thermal decomposition start temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide. All of these substantially overlap with the temperature range of the rapid temperature rise of a battery cell that has experienced thermal runaway, and it can be said that they are preferable inorganic hydrates because they can efficiently suppress the temperature rise.

[0088] Further, when inorganic hydrate particles are used as the inorganic particles, if the average particle diameter is too large, the inorganic particles (inorganic hydrates) near the center of the heat insulation layer require a certain amount of time to reach their thermal decomposition temperature, and thus the inorganic particles near the center of the heat insulation layer may not be completely thermally decomposed. For this reason, the average secondary particle diameter of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0089] <1-2-2. First inorganic fiber> The first inorganic fiber is an amorphous fiber, and the second inorganic fiber is a fiber composed of at least one selected from amorphous fibers having a glass transition point higher than that of the first inorganic fiber and crystalline fibers. Note that the melting point of the crystalline inorganic fiber is usually higher than the glass transition point of the amorphous inorganic fiber. Therefore, when the first inorganic fiber is exposed to a high temperature, its surface softens earlier than the second inorganic fiber, and binds inorganic particles and the second inorganic fiber, so that the mechanical strength of the heat insulation layer can be improved. Specifically, as the first inorganic fiber, an inorganic fiber having a melting point of less than 700 °C is preferable, and many amorphous inorganic fibers can be used. Among them, a fiber containing SiO2 is preferable, and since it is inexpensive, easily available, and excellent in handleability and the like, glass fiber is more preferable.

[0090] <1-2-3. Second inorganic fiber> As described above, the second inorganic fiber is a fiber composed of at least one selected from amorphous fibers having a glass transition point higher than that of the first inorganic fiber and crystalline fibers. As the second inorganic fiber, many crystalline inorganic fibers can be used. When the second inorganic fiber is composed of a crystalline fiber or has a glass transition point higher than that of the first inorganic fiber, even when the first inorganic fiber softens when exposed to a high temperature, the second inorganic fiber does not melt or soften. Therefore, even during thermal runaway of the battery cell, its shape can be maintained and it can continue to exist between the battery cells. In addition, when the second inorganic fiber does not melt or soften, minute spaces between inorganic particles, between inorganic particles and the first and second inorganic fibers, and between the first and second inorganic fibers are maintained, so that a heat insulation effect by air is exhibited and excellent heat transfer suppression performance can be maintained.

[0091] When the second inorganic fiber is crystalline, examples of the second inorganic fiber include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, and zirconia fiber, and mineral fibers such as rock wool, alkali earth silicate fiber, zirconia fiber, potassium titanate fiber, and wollastonite. Among the fibers listed as the second inorganic fiber, if the melting point exceeds 1000 °C, even if thermal runaway of the battery cell occurs, the second inorganic fiber will not melt or soften and can maintain its shape, so it can be preferably used. Among the fibers listed as the second inorganic fiber, for example, it is more preferable to use ceramic fibers such as silica fiber, alumina fiber, and alumina silicate fiber, and mineral fibers, and among these, it is even more preferable to use those with a melting point exceeding 1000 °C. Also, even when the second inorganic fiber is amorphous, if it is a fiber with a glass transition point higher than that of the first inorganic fiber, it can be used. For example, glass fiber with a glass transition point higher than that of the first inorganic fiber may be used as the second inorganic fiber. Note that as the second inorganic fiber, various exemplified inorganic fibers may be used alone, or two or more kinds may be used in combination.

[0092] As described above, the glass transition point of the first inorganic fiber is lower than that of the second inorganic fiber, and when exposed to high temperature, the first inorganic fiber softens first, so the first inorganic fiber can bind the inorganic particles and the second inorganic fiber. However, for example, when the second inorganic fiber is amorphous and its fiber diameter is thinner than that of the first inorganic fiber, if the glass transition points of the first inorganic fiber and the second inorganic fiber are close, the second inorganic fiber may soften first. Therefore, when the second inorganic fiber is an amorphous fiber, the glass transition point of the second inorganic fiber is preferably 100 °C or more higher than that of the first inorganic fiber, and more preferably 300 °C or more higher.

[0093] (Average Fiber Diameter of Inorganic Fibers) In the present invention, inorganic fibers with a large average fiber diameter (thick fibers) have the effect of improving the mechanical strength and shape retention of the heat insulation layer. By making either the first inorganic fiber or the second inorganic fiber thick, the above effect can be obtained. Since an external impact may act on the heat transfer suppression sheet, the inclusion of thick inorganic fibers in the heat insulation layer increases the impact resistance. Examples of the external impact include the pressing force due to the expansion of the battery cell and the wind pressure due to the ignition of the battery cell. Further, in order to improve the mechanical strength and shape retention of the heat insulation layer, it is particularly preferable that the thick inorganic fibers are linear or needle-shaped. Note that the linear or needle-shaped fibers refer to fibers having a crimp ratio of, for example, less than 10%, preferably 5% or less, which will be described later.

[0094] More specifically, in order to improve the mechanical strength and shape retention of the heat insulation layer, the average fiber diameter of the thick inorganic fibers is preferably 1 μm or more, more preferably 3 μm or more. However, if the thick inorganic fibers are too thick, the formability and processability of the heat insulation layer may decrease. Therefore, the average fiber diameter is preferably 20 μm or less, more preferably 15 μm or less. Regarding the method for measuring the average fiber diameter, the inorganic fibers are placed in a cylinder and pressure-crushed at 20.6 MPa. Next, this sample is placed on a sieve mesh, and the sample that has passed through the sieve is used as a test specimen for electron microscope observation. After depositing gold or the like on the surface of this test specimen, an electron micrograph with a magnification of about 1500 times is taken. The diameters of at least 40 fibers are measured from the obtained photograph, and the arithmetic mean value is taken as the average fiber diameter.

[0095] Note that if the thick inorganic fibers are too long, the formability and processability may decrease. Therefore, the fiber length is preferably 100 mm or less. Further, if the thick inorganic fibers are too short, the shape retention and mechanical strength may decrease. Therefore, the fiber length is preferably 0.1 mm or more. The fiber length can be measured using an image processing device capable of measuring the length from the electron micrograph obtained by an electron microscope.

[0096] On the one hand, inorganic fibers with a small average fiber diameter (thin-diameter) have the effect of improving the retention of inorganic particles and enhancing the flexibility of the heat insulation layer. Therefore, among the first inorganic fiber and the second inorganic fiber, by making the other one have a thin diameter, the above effects can be obtained.

[0097] More specifically, in order to improve the retention of inorganic particles, it is preferable that the thin-diameter inorganic fibers are easily deformable and have flexibility. Therefore, the thin-diameter inorganic fibers preferably have an average fiber diameter of less than 1 μm, and more preferably 0.1 μm or less. However, if the thin-diameter inorganic fibers are too thin, they are likely to break, and the retention ability of inorganic particles decreases. In addition, the proportion of fibers remaining entangled without holding inorganic particles in the heat insulation layer increases, and in addition to the decrease in the retention ability of inorganic particles, the moldability and shape retention also deteriorate. Therefore, the average fiber diameter of the thin-diameter inorganic fibers is preferably 1 nm or more, and more preferably 10 nm or more. In addition, since the moldability and shape retention of the thin-diameter inorganic fibers decrease if they are too long, the fiber length is preferably 0.1 mm or less.

[0098] Also, the thin-diameter inorganic fibers are preferably dendritic or crumpled. When the thin-diameter inorganic fibers have such a shape, they entangle with the thick-diameter inorganic fibers and inorganic particles in the heat insulation layer. Therefore, the retention ability of inorganic particles is improved. In addition, when the heat insulation layer is subjected to a pressing force or a wind pressure, the movement of the thin-diameter inorganic fibers by slipping is suppressed, and thereby, the mechanical strength against an external pressing force or impact is particularly improved.

[0099] Note that the dendritic shape is a two-dimensional or three-dimensional branched structure, for example, feather-shaped, tetrapod-shaped, radial-shaped, or three-dimensional network-shaped. When the thin-diameter inorganic fibers are dendritic, the average fiber diameter can be obtained by measuring the diameters of the trunk and branches at several points by SEM and calculating the average value thereof.

[0100] In addition, the crimped state refers to a structure in which the fibers are bent in various directions. As one method of quantifying the crimped form, it is known to calculate the crimp degree from an electron micrograph, and it can be calculated, for example, from the following formula. Crimp degree (%) = (fiber length - distance between fiber ends) / (fiber length) × 100 Here, both the fiber length and the distance between fiber ends are measured values on the electron micrograph. That is, they are the fiber length and the distance between fiber ends projected onto a two-dimensional plane, and are shorter than the actual values. Based on this formula, the crimp degree of the inorganic fibers with a small diameter is preferably 10% or more, and more preferably 30% or more. If the crimp degree is small, it becomes difficult to form the holding ability of the inorganic particles and the entanglement (network) between the inorganic fibers with a large diameter and between the inorganic fibers with a large diameter.

[0101] As described above, it is preferable that the average fiber diameter of either the first inorganic fiber or the second inorganic fiber is larger than the average fiber diameter of the other. However, in the present invention, it is more preferable that the average fiber diameter of the first inorganic fiber is larger than the average fiber diameter of the second inorganic fiber. When the average fiber diameter of the first inorganic fiber is large, the glass transition point of the first inorganic fiber is low and it softens early, so it becomes film-like and hardens as the temperature rises. On the other hand, when the average fiber diameter of the second inorganic fiber is small, the second inorganic fiber with a small diameter remains in the shape of a fiber even when the temperature rises, so the structure of the heat insulation layer can be maintained and powder falling can be prevented.

[0102] Note that as the first inorganic fiber, both an inorganic fiber with a large diameter and linear or needle-like shape and an inorganic fiber with a small diameter and dendritic or crimped shape are used. As the second inorganic fiber, both an inorganic fiber with a large diameter and linear or needle-like shape and an inorganic fiber with a small diameter and dendritic or crimped shape are used. This is most preferable because the holding effect of the inorganic particles, the mechanical strength, and the shape retention can be further enhanced.

[0103] (Contents of inorganic particles, first inorganic fiber, and second inorganic fiber) The content of the inorganic particles described above is preferably 30% by mass or more and 94% by mass or less based on the total mass of the heat insulation layer. The content of the first inorganic fiber is preferably 3% by mass or more and 30% by mass or less based on the total mass of the heat insulation layer. The content of the second inorganic fiber is preferably 3% by mass or more and 30% by mass or less based on the total mass of the heat insulation layer.

[0104] More preferably, based on the total mass of the heat insulation layer, the content of the inorganic particles is 60% by mass or more and 90% by mass or less, the content of the first inorganic fiber is 5% by mass or more and 15% by mass or less, and the content of the second inorganic fiber is 5% by mass or more and 15% by mass or less. By setting the content in this way, the heat absorption and heat insulation effect by the inorganic particles, the shape retention, pressure resistance, and wind pressure resistance by the first inorganic fiber, and the ability to hold the inorganic particles by the second inorganic fiber are expressed in a well-balanced manner.

[0105] <1-2-4. Other compounding materials> In the heat insulation layer, organic fibers, organic binders, etc. can be blended as necessary. All of these are useful for the purpose of reinforcing the heat insulation layer and improving the moldability, and it is preferable that the total amount is 10% by mass or less based on the total mass of the heat insulation layer.

[0106] <Thickness of the heat transfer suppression sheet> In this embodiment, the thickness of the heat transfer suppression sheet is not particularly limited, but it is preferably in the range of 0.05 to 6 mm. If the thickness of the heat transfer suppression sheet is less than 0.05 mm, sufficient mechanical strength cannot be imparted to the heat transfer suppression sheet. On the other hand, if the thickness of the heat transfer suppression sheet exceeds 6 mm, there is a possibility that the molding of the heat transfer suppression sheet itself becomes difficult.

[0107] Subsequently, the manufacturing method of the heat transfer suppression sheet for the assembled battery according to this embodiment will be described.

[0108] <Manufacturing method of the heat transfer suppression sheet> The heat transfer suppression sheet according to this embodiment can be obtained, for example, by disposing a heat insulation layer between high heat conduction layers. These may or may not be joined. When joining, for example, a method of fixing the peripheral edge of the laminated sheet by adhesion, welding, or the like can be used.

[0109] Note that the heat transfer suppression sheet according to this embodiment can be easily bent depending on the selection of the types and thicknesses of the high heat conduction layer and the heat insulation layer. Therefore, it is not affected by the shapes of the battery cells 20a, 20b, 20c and the battery case 30, and can be adapted to any shape. Specifically, in addition to square batteries, it can also be applied to cylindrical batteries, flat plate batteries, and the like.

[0110] Also, as shown in FIG. 2, the heat transfer suppression sheet according to this embodiment does not necessarily need to be provided with the heat transfer member 40. For example, a configuration can be adopted in which heat is diffused from the high heat conduction layer 12a heated by the heat-generating battery cell to the space inside the battery case 30 or the battery case 30, which is used as a heat transfer member, and the space inside the battery case 30 with a lower temperature.

[0111] [2. Battery pack] The battery pack according to this embodiment is a battery pack in which a plurality of battery cells are connected in series or in parallel, and the heat transfer suppression sheet for the battery pack according to this embodiment is interposed between the battery cells. Specifically, for example, as shown in FIG. 2, the battery pack 100 is formed by arranging a plurality of battery cells 20a, 20b, 20c in parallel, connecting them in series or in parallel, and housing them in a battery case 30. A heat transfer suppression sheet 10 is interposed between the battery cells 20a, 20b, 20c. Further, a heat transfer member 40 is disposed between the battery case 30 and the heat transfer suppression sheet 10, and one end surface A10 side of the heat transfer suppression sheet 10 is disposed in contact with the heat transfer member 40.

[0112] In such a battery pack 100, since the heat transfer suppression sheet 10 according to the present embodiment is interposed between the battery cells 20a, 20b, and 20c, during normal use, the heat transfer suppression sheet 10 selectively transfers heat to one end surface of the heat transfer suppression sheet and diffuses it to the outside of the heat transfer suppression sheet. Therefore, the propagation of heat between the battery cells 20a, 20b, and 20c can be suppressed. Also, even when one of the plurality of battery cells 20a, 20b, and 20c undergoes thermal runaway and becomes high temperature, expands, or catches fire, due to the presence of the heat transfer suppression sheet 10 according to the present embodiment, the propagation of heat between the battery cells 20a, 20b, and 20c is suppressed, and the chain reaction of thermal runaway is blocked. Thereby, the adverse effect on other battery cells can be minimized.

[0113] (Heat transfer member) In the battery pack according to the present embodiment, examples of the heat transfer member include those configured to circulate a gaseous or liquid refrigerant, those with the refrigerant sealed, cooling plates, heat dissipation sheets, heat dissipation gels, TIMs, etc. However, in the present invention, the structure and material of the heat transfer member are not particularly limited.

[0114] In the present invention, the heat transfer member 40 is not necessarily required, and the plurality of battery cells 20a, 20b, and 20c and the heat transfer suppression sheet 10 may be directly placed on the inner bottom surface of the battery case 30. Even in such a case, since the heat transfer suppression sheet 10 has a high thermal conductivity layer, the heat reaching the high thermal conductivity layer is diffused in the plane direction and released from the end surface. Therefore, an excellent effect of suppressing the propagation of heat between the battery cells can be obtained, and the adverse effect on other battery cells can be minimized.

[0115] Although illustration is omitted, the heat transfer suppression sheet described in the above [1. Heat Transfer Suppression Sheet] can be disposed not only between a plurality of battery cells but also at the outermost side of a plurality of adjacent battery cells, that is, as shown in FIG. 2, assuming that the heat transfer member 40 is disposed at the bottom of the battery case 30, it can be disposed between the wall portion of the battery case 30 and the battery cell. Therefore, high versatility can be obtained, and it not only has the effect of preventing the chain reaction of thermal runaway due to heat propagation between adjacent battery cells, but also can suppress the spread of flames outside the battery case when a certain battery cell catches fire.

[0116] For example, the assembled battery according to the present embodiment is used in an electric vehicle (EV: Electric Vehicle) or the like and may be disposed under the floor of a passenger. In this case, even if a battery cell catches fire, the safety of the passenger can be ensured. Also, in this case, since a heat transfer suppression sheet or the like interposed between each battery cell can also be disposed between the battery cell and the battery case, there is no need to newly produce a flameproof material or the like, and an assembled battery that is easily safe and low-cost can be configured.

Explanation of Reference Numerals

[0117] 10, 15, 16, 17, 18, 19 Heat transfer suppression sheet (for assembled battery) 11a, 11b, 11c, 11d, 11e, 11f Heat insulation layer 12a, 12b, 12c, 12d, 12e, 12f High heat conduction layer 20a, 20b, 20c Battery cell 21 Space 30 Battery case 40 Heat transfer member 100 Assembled battery

Claims

1. A heat transfer suppression sheet used for a battery pack in which a plurality of battery cells are connected in series or in parallel, comprising: a heat insulation layer; and high thermal conductivity layers provided on both surfaces orthogonal to the thickness direction of the heat insulation layer, wherein the thermal conductivity of the high thermal conductivity layer is higher than that of the heat insulation layer, one end face parallel to the thickness direction of the high thermal conductivity layer extends at least to one end face side parallel to the thickness direction of the heat transfer suppression sheet, the heat insulation layer is thinner on the one end face side of the heat transfer suppression sheet than on the other end face side of the heat transfer suppression sheet facing the one end face of the heat transfer suppression sheet.

2. The heat transfer suppression sheet according to claim 1, wherein the high thermal conductivity layer extends from the one end face side to the other end face side of the heat transfer suppression sheet.

3. The heat transfer suppression sheet according to claim 1 or 2, wherein the thickness of the heat insulation layer continuously decreases toward the one end face side of the heat transfer suppression sheet.

4. The heat transfer suppression sheet according to claim 1 or 2, wherein the thickness of the heat insulation layer increases stepwise toward the one end face side of the heat transfer suppression sheet.

5. The heat transfer suppression sheet according to any one of claims 1 to 4, wherein the thickness of the heat insulation layer decreases toward the one end face side of the heat transfer suppression sheet such that the rate of decrease in thickness increases.

6. The heat transfer suppression sheet according to any one of claims 1 to 5, wherein the high thermal conductivity layers provided on both surfaces of the heat insulation layer are connected on the one end face side of the heat transfer suppression sheet.

7. The heat transfer suppression sheet according to any one of claims 1 to 6, wherein the high thermal conductivity layer is made of at least one material selected from metals, ceramics, and carbon.

8. The heat transfer suppression sheet according to any one of claims 1 to 7, wherein the thermal conductivity of the heat insulation layer is less than 1 (W / m·K).

9. The heat transfer suppression sheet according to any one of claims 1 to 8, wherein the heat insulation layer contains at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles.

10. The heat insulation layer includes a first inorganic fiber, a second inorganic fiber, and inorganic particles, the first inorganic fiber is an amorphous fiber, the second inorganic fiber is at least one selected from amorphous fibers having a glass transition point higher than that of the first inorganic fiber and crystalline fibers. The inorganic particles are composed of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, The heat transfer suppression sheet according to claim 9, wherein the inorganic particles include at least one selected from nanoparticles, hollow particles, and porous particles.

11. The heat insulation layer includes a first inorganic fiber, a second inorganic fiber, and inorganic particles, The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber, The first inorganic fiber is linear or needle-shaped, The heat transfer suppression sheet according to claim 9, wherein the second inorganic fiber is dendritic or crumpled.

12. The heat insulation layer includes a first inorganic fiber, a second inorganic fiber, and inorganic particles, The first inorganic fiber is an amorphous fiber, The second inorganic fiber is composed of at least one selected from amorphous fibers having a glass transition point higher than that of the first inorganic fiber and crystalline fibers, The heat transfer suppression sheet according to claim 9, wherein the average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber.

13. A battery case, A plurality of battery cells housed inside the battery case and connected in series or in parallel, A battery pack having the heat transfer suppression sheet according to any one of claims 1 to 12 interposed between the plurality of battery cells.

14. A battery case, A plurality of battery cells housed inside the battery case and connected in series or in parallel, The heat transfer suppression sheet according to any one of claims 1 to 12 interposed between the plurality of battery cells, A heat transfer member disposed between the battery case and the heat transfer suppression sheet, A battery pack, wherein one end face side of the heat transfer suppression sheet is in contact with the heat transfer member.

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