JP7670514B2 - Thermal control sheet for battery pack and battery pack - Google Patents

Description

The present invention relates to a thermal control sheet for a battery pack suitable for use in a battery pack that serves as a power source for an electric motor that drives an electric vehicle or hybrid vehicle, and to a battery pack using the thermal control sheet for a battery pack.

In recent years, from the perspective of environmental protection, there has been active development of electric vehicles and hybrid vehicles that are driven by electric motors. These electric vehicles and hybrid vehicles are equipped with a battery pack in which multiple battery cells are connected in series or parallel to serve as the power source for the driving electric motor.

These battery cells mainly use lithium-ion secondary batteries, which have higher capacity and power output than lead-acid batteries or nickel-metal hydride batteries. However, if thermal runaway occurs in one battery cell due to an internal short circuit or overcharging (i.e., in the event of an "abnormality"), heat may be transmitted to other adjacent battery cells, potentially causing thermal runaway in the other battery cells.

For example, Patent Document 1 discloses an electricity storage device that can provide effective insulation between multiple electricity storage elements such as lithium ion secondary batteries. The electricity storage device described in Patent Document 1 has a first plate material and a second plate material having thermal insulation properties arranged between a first electricity storage element and a second electricity storage element adjacent to each other. In addition, a low thermal conductivity layer, which is a layer of a material having a lower thermal conductivity than the first plate material and the second plate material, is formed between the first plate material and the second plate material.

In the energy storage device of Patent Document 1 configured in this manner, a portion of the radiant heat traveling from the first energy storage element to the second energy storage element, or a portion of the radiant heat traveling from the second energy storage element to the first energy storage element, is blocked by the first plate material and the second plate material. In addition, the transfer of heat from one of these two plate materials to the other is suppressed by the low thermal conductivity layer.

JP 2015-211013 A

Incidentally, when a charge/discharge cycle is performed on battery cells assembled into a battery pack (i.e., during "normal use"), in order to fully utilize the charge/discharge performance of the battery cells, it is necessary to maintain the temperature of the battery cell surface below a predetermined value (e.g., below 150°C).
Furthermore, in the event of an abnormal situation in which a battery cell reaches a temperature of, for example, 200° C. or higher, it is necessary to effectively cool the battery cell while suppressing the transfer of heat to adjacent battery cells and preventing thermal runaway.

However, the above-mentioned energy storage device only has a heat insulating member and a low thermal conductive layer between the first and second energy storage elements, and therefore cannot efficiently dissipate heat generated during charge and discharge cycles to the outside. Furthermore, when thermal runaway occurs in one battery cell, it is difficult to effectively suppress the chain reaction of thermal runaway with only the above-mentioned structure.
As such, there has been a demand in recent years for further improvements in heat control means that can efficiently diffuse generated heat to the outside during normal use and suppress a chain reaction of thermal runaway.

The present invention was made in consideration of the above problems, and aims to provide a thermal control sheet for a battery pack and a battery pack that can be used in a battery pack in which multiple battery cells are connected in series or parallel, and that can efficiently cool the battery cells by diffusing heat generated during normal use to the outside, while also suppressing the transfer of heat between the battery cells in the event of an abnormality, preventing a chain reaction of thermal runaway.

The above object of the present invention is achieved by the following configuration [1] relating to a thermal control sheet for a battery pack.

[1] A thermal control sheet for a battery assembly used in a battery assembly in which a plurality of battery cells are connected in series or parallel, the sheet being interposed between the battery cells,
A pair of surface layers;
a heat insulating material disposed between the pair of surface layers,
the surface layer has a plate-shaped portion having a surface facing the battery cell, and a plurality of protrusions protruding from the facing surface toward the battery cell,
The thermal control sheet for a battery pack, wherein the plate-shaped portion has a lower emissivity and a higher thermal conductivity than the insulating material.

Furthermore, preferred embodiments of the present invention relating to the thermal control sheet for a battery pack relate to the following [2] to [13].

[2] The thermal control sheet for a battery pack described in [1], characterized in that the surface layer is formed by adhering a plurality of convex parts to the surface of the plate member that constitutes the plate-shaped portion.

[3] The thermal control sheet for a battery pack described in [2], characterized in that the protrusions are adhesives fixed to the surface of the plate member.

[4] The thermal control sheet for a battery pack described in [1], characterized in that the surface layer is formed by integrally molding the plate-shaped portion and the protrusion.

[5] A thermal control sheet for a battery pack according to any one of [1] to [4], characterized in that the thermal conductivity of the insulating material is less than 1 (W/m·K).

[6] A thermal control sheet for a battery pack according to any one of [1] to [5], characterized in that the thermal conductivity of the plate-shaped portion is 10 times or more the thermal conductivity of the insulating material.

[7] The thermal control sheet for a battery pack described in any one of [1] to [6], characterized in that the plate-shaped portion is made of a metal having a melting point of 600°C or higher, or a ceramic.

[8] An intermediate layer is disposed between the pair of surface layers,
The heat insulating material is disposed between the pair of surface layers and the intermediate layer,
The thermal control sheet for a battery pack according to any one of [1] to [7], wherein the intermediate layer has a lower emissivity than the insulating material and a higher thermal conductivity than the insulating material.

[9] Two or more intermediate layers;
and a heat insulating material disposed between adjacent intermediate layers.

[10] The thermal control sheet for a battery pack according to [8] or [9], characterized in that the thermal conductivity of the intermediate layer is 10 times or more the thermal conductivity of the insulating material.

[11] A thermal control sheet for a battery pack according to any one of [8] to [10], characterized in that the thermal conductivity of the intermediate layer is equal to or greater than the thermal conductivity of the plate-shaped portion.

[12] The thermal control sheet for a battery pack according to any one of [8] to [11], characterized in that the intermediate layer is made of metal or ceramic.

[13] The thermal control sheet for a battery pack according to any one of [1] to [12], characterized in that the insulating material contains at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles.

The above object of the present invention is also achieved by the following configuration [14] relating to the battery pack.

[14] A battery case;
A plurality of battery cells housed inside the battery case and connected in series or parallel;
and a thermal control sheet for a battery pack according to any one of [1] to [13] interposed between the plurality of battery cells;
a gas flow path is provided between the battery cell and an area of the surface layer excluding the protrusions.

The thermal control sheet for a battery pack of the present invention is a thermal control sheet used in a battery pack in which multiple battery cells are connected in series or parallel, and a pair of surface layers have multiple protrusions that protrude toward the battery cells, and a gas flow path is formed between the surface layers and the battery cells, thereby suppressing convective heat transfer toward the adjacent battery cells and cooling the battery cells. In addition, the plate-shaped portions in the surface layers have a lower emissivity and a higher thermal conductivity than the insulating material disposed between them.
Therefore, the heat generated from the battery cells can be reduced through the surface layer by the suppression effect of radiative heat transfer and the heat diffusion effect of conductive heat transfer, and can also be gradually reduced through the insulating material. As a result, the heat generated from one battery cell can be prevented from being transmitted to an adjacent battery cell, and a chain reaction of thermal runaway can be prevented.

The battery pack of the present invention has the above-mentioned thermal control sheet interposed between multiple battery cells, which allows for efficient heat diffusion during normal use and in the event of an abnormality, while also suppressing the transfer of heat between battery cells, preventing a chain reaction of thermal runaway.

FIG. 1 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view that illustrates a schematic diagram of a battery pack to which the thermal control sheet for a battery pack according to the first embodiment is applied. FIG. 3 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a second embodiment of the present invention. FIG. 4 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a third embodiment of the present invention. FIG. 5 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a fourth embodiment of the present invention.

The inventors have conducted extensive research to provide a thermal control sheet for a battery pack that can efficiently diffuse heat generated from the battery cells to the outside and cool the battery cells, while suppressing the transfer of heat between the battery cells during abnormal conditions when high-temperature heat is generated, even during normal use when relatively low-temperature heat is generated.

As a result, the inventors discovered that the above problem can be solved by forming a thermal control sheet by disposing a pair of surface layers having multiple protrusions on the surface facing the battery cell and disposing a thermal insulating material between the pair of surface layers, and by making the plate-shaped portion of the surface layer facing the battery cell have a lower emissivity and a higher thermal conductivity than the thermal insulating material.

Specifically, the surface layer of the thermal control sheet for a battery pack according to the present invention has a convex portion on the surface facing the battery cell, so that a gas flow path is formed between the battery cell and the area excluding the convex portion. Therefore, when the temperature of a certain battery cell rises, the temperature of the gas in the vicinity of the battery cell also rises, and the gas moves to the outside of the thermal control sheet through the flow path, promoting heat dissipation. Therefore, convective heat transfer from the battery cell to the battery cell is suppressed. At the same time, low-temperature gas present outside the thermal control sheet flows into the surface of the battery cell through the flow path, so that the battery cell can be efficiently cooled.
The surface layer has a plate-like portion having a surface facing the battery cell, and this plate-like portion has the effect of suppressing radiative heat transfer from the battery cell and diffusing the heat that reaches the plate-like portion by conductive heat transfer. After the amount of heat generated from the battery cell is reduced by the surface layer and the insulating material, the other surface layer suppresses radiative heat transfer to the adjacent battery cell and allows the heat to be diffused by conductive heat transfer.
In this way, by utilizing the surface layer to suppress convective heat transfer and radiative heat transfer and to diffuse heat by conductive heat transfer, if a battery cell becomes hot, the heat can be diffused to the outside and the battery cell can be cooled. Since the heat transfer can be suppressed in stages before it reaches adjacent battery cells, a chain reaction of thermal runaway can be suppressed.

The following describes in detail an embodiment of the present invention with reference to the drawings. Note that the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the spirit of the present invention.

[1. Thermal control sheet for battery packs]
Hereinafter, the thermal control sheet for a battery pack according to the embodiment of the present invention will be described in order from the first embodiment to the fourth embodiment. After that, the surface layer having the convex portion, the insulating material, etc., which constitute the thermal control sheet for a battery pack according to the present embodiment will be described. Furthermore, the manufacturing method of the thermal control sheet for a battery pack according to the present embodiment will be described.

First Embodiment
1 is a cross-sectional view showing a schematic diagram of a thermal control sheet for a battery assembly according to a first embodiment of the present invention. Hereinafter, the thermal control sheet for a battery assembly may be simply referred to as a "thermal control sheet."
The thermal control sheet 10 for a battery pack according to the first embodiment has a pair of surface layers 11a and 11b, and a heat insulating material 13 is disposed between the surface layers 11a and 11b. The surface layer 11a has a plate-shaped portion 21a having a surface facing a battery cell, which will be described later, and a plurality of protrusions 14a are formed on the surface of the plate-shaped portion 21a opposite to the heat insulating material 13 side. Similarly, the surface layer 11b has a plate-shaped portion 21b, and a plurality of protrusions 14b are formed on the surface of the plate-shaped portion 21b opposite to the heat insulating material 13 side. In other words, the thermal control sheet 10 has a configuration in which a plurality of protrusions 14a and protrusions 14b are formed on the outer surface perpendicular to the stacking direction of the surface layers 11a and 11b and the heat insulating material 13.

In the first embodiment, the plate-like portions 21a and 21b of the surface layers 11a and 11b are made of a material with a lower emissivity and a higher thermal conductivity than the insulating material 13, for example, a stainless steel plate. The protrusions 14a and 14b are formed, for example, by adhering an adhesive to the plate members constituting the plate-like portions 21a and 21b. Furthermore, the insulating material 13 is, for example, an alumina fiber.

2 is a cross-sectional view showing a schematic diagram of a battery pack to which the thermal control 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, and 20c stored inside the battery case 30, and a thermal control sheet 10 interposed between the battery cells 20a and 20b and between the battery cells 20b and 20c. The plurality of battery cells 20a, 20b, and 20c are connected in series or in parallel by bus bars (not shown) or the like.
In addition, since the thermal control sheet 10 has a plurality of convex portions 14a and 14b that protrude toward the outer surface, i.e., the battery cells 20a, 20b, and 20c, a gas flow path 18 is formed between the thermal control sheet 10 and the battery cells 20a, 20b, and 20c.
The battery cells 20a, 20b, and 20c are preferably, for example, lithium ion secondary batteries, but are not limited thereto and may be other secondary batteries.

In a typical conventional battery pack, a sheet disposed between a plurality of battery cells has a heat insulating material disposed on the surface closest to the battery cells.
In contrast, the thermal control sheet 10 according to the first embodiment is provided with a surface layer 11a having protrusions 14a that protrude toward the battery cells 20a, for example. Also, a stainless steel plate with a lower emissivity and higher thermal conductivity than the insulating material 13 is used for the plate-like portion 21a having a surface facing the battery cells 20a.
Similarly, in each of the battery cells 20b and 20c, the thermal control sheet 10 is disposed between the adjacent battery cells, and a surface layer 11a having a protrusion 14a protruding toward each of the battery cells 20b and 20c or a surface layer 11b having a protrusion 14b is disposed.

In the first embodiment configured in this manner, for example, when the temperature of the battery cell 20a rises, the temperature of the gas in the flow path 18 between the battery cell 20a and the thermal control sheet 10 rises. The heated gas is then released to the outside from between the battery cell 20a and the thermal control sheet 10 via the flow path 18, so that convective heat transfer from the battery cell 20a to the battery cell 20b is suppressed.
Furthermore, as the heated gas moves, low-temperature gas that was present in other areas flows into the flow paths 18, making it possible to efficiently cool the battery cells 20a.
Furthermore, since the plate-shaped portion 21a has a lower emissivity than the insulating material 13, it is possible to suppress radiative heat transfer to the insulating material 13. Furthermore, since the plate-shaped portion 21a has a higher thermal conductivity than the insulating material 13, a portion of the heat propagated to the plate-shaped portion 21a is propagated in the planar direction. In this way, the amount of heat generated from the battery cell 20a is reduced through the surface layer 11a, and heat transfer to the insulating material 13 is suppressed.
The planar direction of the plate-like portion 21a refers to the direction of a surface perpendicular to the thickness direction of the plate-like portion 21a.

The remaining heat reduced by the surface layer 11a is further reduced by the heat insulating material 13 before reaching the other surface layer 11b. As in the case of the surface layer 11a, the heat that reaches the surface layer 11b can be suppressed from being radiated and transferred to the battery cell 20b by the plate-shaped portion 21b, and part of the heat is propagated in the planar direction of the plate-shaped portion 21b, so that the heat transfer to the battery cell 20b can be suppressed.

In this way, by arranging the battery cell 20a and the battery cell 20b via the thermal control sheet 10, when heat is generated from the battery cell 20a, the battery cell 20a can be cooled efficiently. In addition, conductive heat transfer to the battery cell 20b side is suppressed, and the heat can be diffused, while convective heat transfer and radiative heat transfer are suppressed, so the propagation of heat between the battery cells can be suppressed and a chain reaction of thermal runaway can be prevented.

The thermal control sheet 10 is configured symmetrically in the thickness direction with the insulating material 13 at the center. Therefore, even if heat is generated from the battery cell 20b, the heat is gradually reduced toward the battery cell 20a by passing through the surface layer 11b, the insulating material 13, and the surface layer 11a in this order, and the propagation of heat to the battery cell 20a can be suppressed.
Similarly, the heat generated from battery cell 20b is gradually reduced by passing through surface layer 11a, insulation material 13, and surface layer 11b, in that order, toward battery cell 20c, thereby suppressing the transmission of heat to battery cell 20c.

In addition, in this embodiment, the surface layers 11a, 11b can be obtained by placing a desired amount of adhesive on one side of the stainless steel plate and allowing the adhesive to solidify. Therefore, the surface layers 11a, 11b having the protrusions 14a, 14b can be produced very easily.

Second Embodiment
Fig. 3 is a cross-sectional view showing a thermal control sheet for a battery pack according to a second embodiment of the present invention. In the second embodiment shown in Fig. 3, the third embodiment shown in Fig. 4, and the fourth embodiment shown in Fig. 5, the same or equivalent parts as those in the first embodiment are given the same reference numerals in the drawings, and their description is omitted or simplified. In addition, since the second to fourth embodiments can be used in place of the thermal control sheet 10 described in the battery pack 100 shown in Fig. 2, the effects and the like will be described below assuming that the thermal control sheets according to the second to fourth embodiments are applied to the battery pack 100.

The thermal control sheet 40 for a battery pack according to the second embodiment has a pair of surface layers 41a and 41b, and a heat insulating material 13 is disposed between the surface layers 41a and 41b. The surface layer 41a has a plate-shaped portion 42a, and the plate-shaped portion 42a has a plurality of protrusions 43a that protrude toward the battery cell. Similarly, the surface layer 41b has a plate-shaped portion 42b, and the plate-shaped portion 42a has a plurality of protrusions 43b that protrude toward the battery cell. In this embodiment, the plate-shaped portion 42a and the protrusions 43a, and the plate-shaped portion 42b and the protrusions 43b are integrally molded from stainless steel, thereby forming the surface layer 41a and the surface layer 41b. That is, the plate-shaped portions 42a and 42b in the second embodiment refer to the portions of the surface layers 11a and 11b excluding the protrusions 43a and 43b.

Even in the second embodiment configured in this manner, for example, when the temperature of the battery cell 20a rises, the heated gas is released to the outside from between the battery cell 20a and the thermal control sheet 10 because a gas flow path exists between the battery cell 20a and the thermal control sheet 40. Therefore, convective heat transfer from the battery cell 20a to the battery cell 20b is suppressed.
Furthermore, as the heated gas moves, low-temperature gas that was present in other areas flows into the flow path, making it possible to efficiently cool the battery cells 20a.
Furthermore, in this embodiment, the plate-shaped portion 21a and the protruding portion 43a have a lower emissivity than the insulating material 13, so that radiative heat transfer to the insulating material 13 side can be suppressed. Also, the plate-shaped portion 21a and the protruding portion 43a have a higher thermal conductivity than the insulating material 13, and the protruding portion 43a is in contact with the battery cell 20a, so that the heat generated from the battery cell 20a is easily transferred to the plate-shaped portion 21a via the protruding portion 43a. Then, a part of the heat transferred to the plate-shaped portion 21a is transferred in the direction of its surface and released to the outside. In this way, the amount of heat generated from the battery cell 20a is reduced by passing through the surface layer 11a, and the heat transfer to the insulating material 13 side is suppressed.

As in the first embodiment, the remaining heat reduced by the surface layer 11a reaches the insulating material 13 and the other surface layer 11b, and the plate-shaped portion 21b can suppress radiative heat transfer to the battery cell 20b. At the same time, part of the heat is propagated in the planar direction of the plate-shaped portion 21b by conductive heat transfer, so that the heat transfer to the battery cell 20b can be suppressed and a chain reaction of thermal runaway can be prevented.

The thermal control sheet 10 is configured symmetrically in the thickness direction with the insulating material 13 at the center. Therefore, even if heat is generated from the battery cell 20b, the heat is gradually reduced toward the battery cell 20a by passing through the surface layer 11b, the insulating material 13, and the surface layer 11a in this order, and the propagation of heat to the battery cell 20a can be suppressed.
Similarly, the heat generated from battery cell 20b is gradually reduced by passing through surface layer 11a, insulation material 13, and surface layer 11b, in that order, toward battery cell 20c, thereby suppressing the transmission of heat to battery cell 20c.

As described above, in the second embodiment, the surface layers 11a, 11b having the convex portions 43a, 43b and the plate-shaped portions 42a, 42b are made of stainless steel, so that radiative heat transfer can be suppressed throughout the surface layers 11a, 11b, and heat can be released in the planar direction by conductive heat transfer.

Third Embodiment
FIG. 4 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a third embodiment of the present invention.
In the thermal control sheet 50 for a battery pack according to the third embodiment, an intermediate layer 12 is disposed between the surface layer 11a and the surface layer 11b. Insulating materials 13a, 13b are disposed between the surface layer 11a and the intermediate layer 12, and between the surface layer 11b and the intermediate layer 12, respectively. The configuration of the surface layers 11a, 11b is the same as that of the first embodiment. The intermediate layer 12, like the plate-shaped portions 21a, 21b, is made of a material having a lower emissivity and a higher thermal conductivity than the insulating materials 13a, 13b, for example, an aluminum plate.

In the third embodiment configured as described above, when the temperature of the battery cell 20a rises, the presence of the surface layer 11a provides the same effect as in the first embodiment. The remaining heat reduced by the surface layer 11a is further reduced by the heat insulating material 13a and then reaches the intermediate layer 12. The intermediate layer 12, like the plate-shaped portion 21a, has a lower emissivity than the heat insulating materials 13a and 13b, and therefore can suppress radiative heat transfer to the next layer, i.e., the heat insulating material 13b. Furthermore, the intermediate layer 12 has a higher thermal conductivity than the heat insulating materials 13a and 13b, so that a part of the heat that reaches the intermediate layer 12 is propagated in the surface direction of the intermediate layer 12 and diffused to the outside of the thermal control sheet 10. The surface direction of the intermediate layer 12 refers to the direction of the surface perpendicular to the thickness direction of the intermediate layer 12.
Similarly, the heat dissipated by the intermediate layer 12 is further dissipated through the insulating material 13b and the surface layer 11b.

In this way, even in the third embodiment, the battery cell 20a and the battery cell 20b are arranged via the thermal control sheet 50, so that when heat is generated from the battery cell 20a, the battery cell 20a can be efficiently cooled. In addition, since an intermediate layer 12 is provided between the pair of surface layers 11a, 11b via the insulating materials 13a, 13b, the radiative heat transfer to the battery cell 20b side is further suppressed, the heat can be diffused, and the heat propagation between the battery cells can be suppressed, so that the chain reaction of thermal runaway can be further suppressed.

The thermal control sheet 50 is configured symmetrically in the thickness direction with the intermediate layer 12 at the center. Therefore, even if heat is generated from the battery cell 20b, the heat is gradually reduced toward the battery cell 20a by passing through the surface layer 11b, the insulating material 13b, the intermediate layer 12, the insulating material 13a, and the surface layer 11a in this order, thereby making it possible to suppress the propagation of heat to the battery cell 20a.
Similarly, the heat generated from battery cell 20b is gradually reduced by passing through surface layer 11a, insulating material 13a, intermediate layer 12, insulating material 13b, and surface layer 11b, in that order, toward battery cell 20c, thereby suppressing the transmission of heat to battery cell 20c.

Fourth Embodiment
In the above third embodiment, the thermal control sheet 50 for the battery pack has a five-layer structure in which the surface layer 11a having the convex portion 14a, the insulating material 13a, the intermediate layer 12, the insulating material 13b, and the surface layer 11b having the convex portion 14b are arranged in this order, but the thermal control sheet for the battery pack of the present invention is not limited to five layers.
For example, it may have two intermediate layers and a thermal insulating material disposed between two adjacent intermediate layers.

FIG. 5 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a fourth embodiment of the present invention.
The thermal control sheet 15 for a battery pack according to the fourth embodiment has a pair of surface layers 11a, 11b, two intermediate layers 12a, 12b disposed between the surface layers 11a and 11b, and insulating materials 13a, 13b, 13c disposed between each of the layers.
In the fourth embodiment, the configuration of the surface layers 11a and 11b, the materials of the heat insulating materials 13a, 13b and 13c, and the materials of the intermediate layers 12a and 12b are the same as those in the third embodiment.

In the fourth embodiment configured as described above, the heat generated from the battery cells 20a can be prevented from being convectively transferred to the insulating material 13a by passing through the surface layer 11a, and the battery cells 20a can be efficiently cooled. In addition, the heat can be prevented from being radiatively transferred to the insulating material 13a, and the heat can be diffused to the outside by conductive heat transfer.
The heat that has reached the insulating material 13a is then further reduced by the insulating material 13a before reaching the intermediate layer 12a. The intermediate layer 12a suppresses radiative heat transfer to the insulating material 13c side and diffuses the heat that has reached the intermediate layer 12a in the surface direction of the intermediate layer 12a, thereby suppressing the transfer of heat to the insulating material 13c side.

In the same way, as the heat is transferred to the battery cell 20b through the insulating material 13c, the intermediate layer 12b, the insulating material 13b, and the surface layer 11b, the heat transfer is gradually suppressed and the heat is diffused by conductive heat transfer. Therefore, the heat transfer between the battery cells can be efficiently suppressed, and the chain reaction of thermal runaway can be suppressed.

The effects of the present invention can be obtained even if the intermediate layers are, for example, three or more layers, with insulating material disposed between each intermediate layer. However, since increasing the number of layers increases the overall thickness of the thermal control sheet and decreases the thickness of each insulating material, it is preferable to appropriately select the number of intermediate layers and the thickness of the insulating material, etc., depending on the required performance.

Next, we will explain in detail the surface layer, intermediate layer, insulating material, etc. that make up the thermal control sheet for battery packs according to the present invention.

<Surface layer>
The surface layer used in the thermal control sheet for a battery assembly according to this embodiment has a plate-like portion having a surface facing the battery cell, and a plurality of protrusions protruding from the plate-like portion toward the battery cell.
The form of the surface layer may be such that the convex material is adhered to a plate member as shown in the first, third and fourth embodiments, or such that the convex portion and the plate-like portion are integrally molded as shown in the second embodiment.

(Plate-shaped portion)
The plate-shaped portion in the surface layer has the effect of suppressing radiative heat transfer from the battery cell and the effect of diffusing heat that reaches the surface layer by conductive heat transfer. Therefore, at least the plate-shaped portion has a lower emissivity and a higher thermal conductivity than the insulating material described below. The specific value of the emissivity of the plate-shaped portion is preferably less than 0.5, and more preferably less than 0.2. In addition, the specific value of the thermal conductivity of the plate-shaped portion is preferably 5 (W/m·K) or more, and more preferably 15 (W/m·K) or more.

The thermal conductivity of the plate-shaped portion can be calculated by a laser flash method and a differential scanning calorimetry (DSC) method, as shown in the following (1) to (3).
(1) Thermal diffusivity is measured in accordance with the "Method for measuring thermal diffusivity of metals by laser flash method" described in JIS H 7801.
(2) The specific heat capacity is measured in accordance with "Method for measuring specific heat capacity of long fiber reinforced ceramic composite material by differential scanning calorimetry" described in JIS R 1672.
(3) Calculate the thermal conductivity based on the values obtained in (1) and (2).
The emissivity of the plate-shaped portion can be measured in accordance with "Method of measuring emissivity of fine ceramics and ceramic composite materials" described in JIS R 1693.

The plate-shaped portion is preferably made of, for example, metal or ceramic. Note that, in the event of an abnormality in which the temperature of the battery cell rises significantly, in order to prevent the plate-shaped portion located near the battery cell from being damaged by melting or the like, it is more preferable that the plate-shaped portion be made of a metal with a melting point of 600°C or higher, or ceramic. It is even more preferable that the plate-shaped portion be made of a metal with a melting point of 900°C or higher.

Specifically, the material of the plate-shaped portion is preferably at least one metal selected from stainless steel, copper or copper alloy, silver or silver alloy, nickel or nickel alloy, and titanium or titanium alloy, or one ceramic selected from AlN, SiC, and TiN. Of these materials, stainless steel and silver have melting points of approximately 1400°C and approximately 960°C, respectively, and are not likely to melt even if the battery cell becomes hot. In addition, stainless steel and silver are less likely to oxidize than other metals, and their emissivity increases less even when exposed to high temperatures. Therefore, in this embodiment, stainless steel, silver, or a silver alloy can be preferably used as the material of the surface layer.

The plate-shaped portion may be a composite layer formed by laminating two or more metals selected from the materials of the plate-shaped portion. When a composite layer is used as the plate-shaped portion, the two or more metal layers are selected to have a lower emissivity than the insulating material and a higher thermal conductivity than the insulating material. Examples of such plate-shaped portions include a [silver/copper/silver] composite layer, a [nickel/copper/nickel] composite layer, a [nickel/stainless steel/nickel] composite layer, and a [silver/stainless steel/silver] composite layer. The silver, copper, and nickel in the composite layer may each be in the form of an alloy.
The composite layer can be obtained by forming metal layers on both sides of a central base layer by wet plating or vapor deposition, or by laminating metal foils made of different materials.

The thermal conductivity of the metals mentioned above as the material for the plate-shaped portion is 5 to 450 (W/m·K), which is sufficiently greater than the thermal conductivity of the insulating material described below (e.g., 0.05 (W/m·K)), and therefore the heat that reaches the surface layer can be efficiently diffused. In terms of specific thermal conductivity compared to the insulating material, the thermal conductivity of the surface layer is preferably 10 times or more, and more preferably 100 times or more, the thermal conductivity of the insulating material.

In order to fully obtain the effect of suppressing radiative heat transfer by the plate-shaped portion and the effect of diffusing heat by conductive heat transfer, the thickness of the plate-shaped portion is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, even more preferably 30 μm or more, and particularly preferably 50 μm or more. On the other hand, taking into consideration the overall thickness of the thermal control sheet, the thickness of the plate-shaped portion is preferably 300 μm or less, and more preferably 200 μm or less.

Furthermore, the plate-shaped portion may consist of a single layer, or may be a laminate of multiple thin layers of the same material. When the plate-shaped portion is formed by laminating thin films of the same material, the same effect can be obtained as long as the total thickness of the multiple layers is the same as the thickness of the plate-shaped portion consisting of a single layer. Therefore, even if the plate-shaped portion consists of multiple layers, it is preferable that the total thickness is within the above range.

(Convex part)
As described above, the protrusions may be formed by adhering a protrusion material such as an adhesive to a plate member, or may be molded integrally with the plate-shaped portion.
The adhesive that can be used as the convex portion material may be, for example, a mixture mainly containing silicon dioxide.
Furthermore, when the convex portion and the plate-shaped portion are formed from different materials, the convex portion material is preferably a material that does not melt when the temperature of the battery cell to which the convex portion is in contact increases significantly. Specifically, the melting point of the convex portion material is preferably 600° C. or higher, and more preferably 900° C. or higher. In addition to the adhesive, silica sol, crushed ceramic fiber, glass, etc. can also be used as such a material, and the surface layer can be formed by bonding such a convex portion material and the plate member by any method.

The thermal control sheet according to the present invention can suppress convection heat transfer and cool the battery cells as long as a gas flow path is formed between the thermal control sheet and the battery cells, so the shape of the protrusions is not particularly limited. Specific shapes of the protrusions include cylindrical, prismatic, and hemispherical shapes, as well as ridge-like shapes.

<Thermal insulation>
The heat insulating material used in the thermal control sheet for a battery pack according to the present embodiment is not particularly limited as long as it has a heat insulating effect. Thermal conductivity can be cited as an index showing the heat insulating effect, and in the present embodiment, the heat conductivity of the heat insulating material is preferably less than 1 (W/m·K), more preferably less than 0.5 (W/m·K), and even more preferably less than 0.2 (W/m·K). Furthermore, the heat conductivity of the heat insulating material 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).
As such a heat insulating material, for example, a material containing at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles can be used.

The thermal conductivity of the insulating material can be measured in accordance with the "Test method for thermal conductivity of refractories" described in JIS R 2251.

As the inorganic fiber, alumina fiber, carbon fiber, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite material, and the like can be used.
As the organic fiber, cellulose fiber or the like can be used.
These fibers may be used alone or in combination of two or more kinds.

As inorganic particles, mica, microporous particles, hollow silica particles, thermally expandable inorganic materials, and aerogels can be used.
Examples of the thermally expandable inorganic material include vermiculite, bentonite, mica, and perlite.
As the organic particles, hollow polystyrene particles or the like can be used.

Among these insulating materials, alumina fiber, glass fiber, aerogel composites, etc. can be preferably used.

(Middle class)
The intermediate layer used in the thermal control sheet for a battery pack according to this embodiment has the effect of suppressing radiation heat transfer to the next layer and diffusing the heat that reaches the intermediate layer by conductive heat transfer. Therefore, like the plate-shaped portion in the surface layer, it is important that the intermediate layer has a lower emissivity and a higher thermal conductivity than the insulating material described below. The specific value of the emissivity of the intermediate layer is preferably less than 0.5, and more preferably less than 0.2. In addition, the specific value of the thermal conductivity of the intermediate layer is preferably 10 (W/m·K) or more, and more preferably 100 (W/m·K) or more.
The intermediate layer is preferably made of, for example, a metal or a ceramic.

The thermal conductivity and emissivity of the intermediate layer can be calculated in the same manner as the thermal conductivity and emissivity of the plate-shaped portion.

When a metal is used as the material for the intermediate layer, it is preferable to use at least one metal selected from, for example, aluminum or an aluminum alloy, stainless steel, copper or a copper alloy, silver or a silver alloy, nickel or a nickel alloy, and titanium or a titanium alloy.

The intermediate layer may be a composite layer formed by laminating two or more metals selected from the materials for the intermediate layer. When a composite layer is used as the intermediate layer, the two or more metal layers are selected to have a lower emissivity than the insulating material and a higher thermal conductivity than the insulating material. Examples of such intermediate layers include an aluminum/copper/aluminum composite layer, an aluminum/silver/aluminum composite layer, a nickel/stainless steel/nickel composite layer, and a silver/stainless steel/silver composite layer. The aluminum, copper, and silver in the composite layer may each be in the form of an alloy.
The composite layer can be obtained by forming metal layers on both sides of a central base layer by wet plating or vapor deposition, or by laminating metal foils made of different materials.

When ceramic is used as the material for the intermediate layer, one type of ceramic selected from AlN, SiC, and TiN can be used.

As with the surface layer, the thermal conductivity of the metals mentioned above as materials for the intermediate layer is 5 to 450 (W/m·K), which is sufficiently greater than the thermal conductivity of the insulating material described below (e.g., 0.05 (W/m·K)), and therefore heat that reaches the intermediate layer can be efficiently diffused. In terms of specific thermal conductivity compared to the insulating material, the thermal conductivity of the intermediate layer is preferably 10 times or more, and more preferably 100 times or more, the thermal conductivity of the insulating material.

In addition, when the intermediate layer is made of metal, in order to obtain a sufficient heat diffusion effect by conductive heat transfer, the thickness of the intermediate layer is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, even more preferably 30 μm or more, and particularly preferably 50 μm or more. On the other hand, in consideration of the overall thickness of the thermal control sheet, the thickness of the intermediate layer is preferably 300 μm or less, and more preferably 200 μm or less.
Furthermore, the intermediate layer may be a single layer, or may be a laminate of multiple thin layers of the same material, as shown in Fig. 4. When the intermediate layer is made up of multiple thin layers of the same material, the same effect can be obtained as long as the total thickness of the multiple layers is the same as the thickness of the intermediate layer made up of a single layer. Therefore, even when the intermediate layer is made up of multiple layers, it is preferable that the total thickness is within the above range.

In addition, it is preferable that the intermediate layer has a high effect of transmitting heat that has reached one side in a planar direction and diffusing it to the outside of the thermal control sheet. Therefore, it is preferable that the thermal conductivity of the intermediate layer is equal to or higher than the thermal conductivity of the plate-shaped portion. For the same reason, it is preferable that the emissivity of the intermediate layer is equal to or higher than the emissivity of the plate-shaped portion.
Therefore, among the above-mentioned intermediate layer materials, aluminum or aluminum alloy, and copper or copper alloy are more suitable for use because they have higher thermal conductivity than stainless steel, which is a suitable material for the surface layer. However, since emissivity varies depending on the type of material and the surface condition, it is preferable to select a material taking into consideration the surface condition, etc.

<Thickness of thermal control sheet>
In this embodiment, the thickness of the thermal control sheet is not particularly limited, but is preferably in the range of 0.05 to 6 mm. If the thickness of the thermal control sheet is 0.05 mm or more, sufficient mechanical strength can be imparted to the thermal control sheet. On the other hand, if the thickness of the thermal control sheet is 6 mm or less, good assembly properties can be obtained.

Next, we will explain the manufacturing method of the thermal control sheet for the battery pack according to this embodiment.

<Method of manufacturing the thermal control sheet>
As described above, the thermal control sheet according to this embodiment can be obtained by bonding a convex material to a plate member or by preparing a surface layer having convex portions by integral molding, and disposing a heat insulating material between a pair of surface layers. When an intermediate layer is provided, the thermal control sheet can be obtained by disposing a pair of heat insulating materials between a pair of surface layers and disposing an intermediate layer therebetween. These may or may not be joined, and when they are joined, for example, a method of fixing the peripheral portions of the laminated sheets by adhesion or welding can be used.

[2. Battery pack]
The battery pack according to the present embodiment is a battery pack in which a plurality of battery cells are connected in series or parallel, and the thermal control sheet for a battery pack according to the present embodiment is interposed between the battery cells. Specifically, for example, as shown in Fig. 2, the battery pack 100 is a battery pack in which a plurality of battery cells 20a, 20b, 20c are arranged side by side, connected in series or parallel, and stored in a battery case 30, and the thermal control sheet 10 is interposed between the battery cells 20a, 20b, 20c.

In such a battery pack 100, the thermal control sheet 10 is interposed between each of the battery cells 20a, 20b, and 20c, so that during normal use, the transfer of heat between each of the battery cells 20a, 20b, and 20c can be suppressed.
Furthermore, even if one of the multiple battery cells 20a, 20b, and 20c experiences thermal runaway, becomes too hot, expands, or catches fire, the presence of the thermal control sheet 10 according to this embodiment can suppress the transfer of heat between the battery cells 20a, 20b, and 20c, thereby preventing a chain reaction of thermal runaway and minimizing adverse effects on other battery cells.

The thermal control sheet according to this embodiment can be easily bent depending on the type and thickness of the surface layer, intermediate layer, and insulating material. Therefore, it can be adapted to any shape without being affected by the shape of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, it can be applied to cylindrical batteries, flat batteries, etc. in addition to square batteries.

10, 15, 40, 50 Thermal control sheet for battery pack 11a, 11b, 41a, 41b Surface layer 12, 12a, 12b Intermediate layer 13, 13a, 13b, 13c Heat insulating material 14a, 14b, 43a, 43b Convex portion 20a, 20b, 20c Battery cell 21a, 21b, 42a, 42b Plate-shaped portion 30 Battery case 100 Battery pack

Claims (13)

A thermal control sheet for a battery assembly used in a battery assembly in which a plurality of battery cells are connected in series or parallel, the thermal control sheet being interposed between the battery cells,
A pair of surface layers;
a heat insulating material disposed between the pair of surface layers,
the surface layer has a plate-shaped portion having a surface facing the battery cell, and a plurality of protrusions protruding from the facing surface toward the battery cell,
The plate-shaped portion has a lower emissivity than the heat insulating material and a higher thermal conductivity than the heat insulating material,
The thermal control sheet for a battery pack , wherein the surface layer is formed by adhering a plurality of protrusion materials to the surface of a plate member constituting the plate-shaped portion . 2. The thermal control sheet for a battery pack according to claim 1 , wherein the protrusions are made of an adhesive that is fixed to the surface of the plate member. A thermal control sheet for a battery assembly used in a battery assembly in which a plurality of battery cells are connected in series or parallel, the thermal control sheet being interposed between the battery cells,
A pair of surface layers;
a heat insulating material disposed between the pair of surface layers,
the surface layer has a plate-shaped portion having a surface facing the battery cell, and a plurality of protrusions protruding from the facing surface toward the battery cell,
The plate-shaped portion has a lower emissivity than the heat insulating material and a higher thermal conductivity than the heat insulating material,
The thermal control sheet for a battery pack, wherein the plate-shaped portion is made of a metal having a melting point of 600° C. or higher, or a ceramic . A thermal control sheet for a battery assembly used in a battery assembly in which a plurality of battery cells are connected in series or parallel, the thermal control sheet being interposed between the battery cells,
A pair of surface layers;
a heat insulating material disposed between the pair of surface layers,
the surface layer has a plate-shaped portion having a surface facing the battery cell, and a plurality of protrusions protruding from the facing surface toward the battery cell,
The plate-shaped portion has a lower emissivity than the heat insulating material and a higher thermal conductivity than the heat insulating material,
An intermediate layer is disposed between the pair of surface layers,
The heat insulating material is disposed between the pair of surface layers and the intermediate layer,
The thermal control sheet for a battery pack , wherein the intermediate layer has a lower emissivity and a higher thermal conductivity than the insulating material . Two or more intermediate layers;
5. The thermal control sheet for a battery pack according to claim 4 , further comprising a heat insulating material disposed between adjacent intermediate layers. The thermal control sheet for a battery pack according to claim 4 or 5 , characterized in that the thermal conductivity of the intermediate layer is 10 times or more higher than the thermal conductivity of the insulating material and is 5 to 450 (W/m·K) . 7. The thermal control sheet for a battery pack according to claim 4 , wherein the thermal conductivity of the intermediate layer is equal to or higher than the thermal conductivity of the plate-shaped portion. The thermal control sheet for a battery pack according to any one of claims 4 to 7 , wherein the intermediate layer is made of a metal or a ceramic. 9. The thermal control sheet for a battery pack according to claim 3 , wherein the surface layer is formed by integrally forming the plate-like portion and the protrusion. The thermal control sheet for a battery pack according to any one of claims 1 to 9 , characterized in that the thermal insulation material has a thermal conductivity of less than 1 (W/m·K). The thermal control sheet for a battery pack according to any one of claims 1 to 10 , characterized in that the thermal conductivity of the plate-shaped portion is 10 times or more the thermal conductivity of the insulating material and is 5 to 450 (W/m·K) . The thermal control sheet for a battery pack according to any one of claims 1 to 11 , characterized in that the heat insulating material contains at least one material selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles. A battery case;
A plurality of battery cells housed inside the battery case and connected in series or parallel;
and a thermal control sheet for a battery pack according to any one of claims 1 to 12 , which is interposed between the plurality of battery cells;
a gas flow path is provided between the battery cell and an area of the surface layer excluding the protrusions.

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