JP7670516B2 - 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, in recent years, there has been a demand 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.

Furthermore, when thermal runaway occurs in a battery cell, gas is generated inside the battery, causing the internal pressure to rise, which can lead to deformation of the battery cell. Such deformation of the battery cell occurs slightly even during normal use, and if the internal pressure of the battery cell repeatedly rises and falls during charging and discharging, the battery cell is repeatedly pressed and released by the case, causing a decrease in battery performance.

Furthermore, battery packs used in electric or hybrid vehicles are in an environment where they are exposed to vibration for long periods of time. When external pressure is applied to the battery cells due to vibration, the exterior material of the battery cells can deteriorate and battery performance can decrease, similar to the case of the change in internal pressure mentioned above.

The present invention has been made in consideration of the above problems, and aims to provide a thermal control sheet for a battery assembly, and a battery assembly, which are used in a battery assembly in which multiple battery cells are connected in series or parallel, and which can efficiently cool the battery cells by diffusing heat generated from the battery cells to the outside, suppress the propagation of heat between the battery cells, prevent a chain reaction of thermal runaway, and suppress deterioration of battery performance due to changes in external pressure on the battery cells.

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 substantially uniform thickness and has a protrusion protruding toward the battery cell and a recess recessed in a direction away from the battery cell,
The thermal control sheet for a battery pack, wherein the surface layer 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 [12].

[2] The thermal control sheet for a battery pack described in [1], characterized in that the surface layer has a corrugated shape.

[3] The thermal control sheet for a battery pack described in [1], characterized in that the surface layer is made of an embossed plate material.

[4] A thermal control sheet for a battery pack according to any one of [1] to [3], characterized in that the thermal conductivity of the insulating material is less than 1 (W/m·K).

[5] The thermal control sheet for a battery pack described in any one of [1] to [4], characterized in that the thermal conductivity of the surface layer is 10 times or more the thermal conductivity of the insulating material.

[6] The thermal control sheet for a battery pack according to any one of [1] to [5], characterized in that the surface layer is made of a metal having a melting point of 600°C or higher, or a ceramic.

[7] 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 [6], wherein the intermediate layer has a lower emissivity than the insulating material and a higher thermal conductivity than the insulating material.

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

[9] The thermal control sheet for a battery pack according to [7] or [8], characterized in that the thermal conductivity of the intermediate layer is 10 times or more the thermal conductivity of the insulating material.

[10] A thermal control sheet for a battery pack according to any one of [7] to [9], characterized in that the thermal conductivity of the intermediate layer is equal to or greater than the thermal conductivity of the surface layer.

[11] The thermal control sheet for a battery pack according to any one of [7] to [10], characterized in that the intermediate layer is made of metal or ceramic.

[12] The thermal control sheet for a battery pack according to any one of [1] to [11], 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 [13] relating to the battery pack.

[13] 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 [12] interposed between the plurality of battery cells;
a gas flow path is provided between the recess in the surface layer and the battery cell.

The thermal control sheet for a battery pack of the present invention is a thermal control sheet used for a battery pack in which a plurality of battery cells are connected in series or parallel, and a pair of surface layers have convex and concave portions, and a gas flow path is formed between the battery cells, so that convective heat transfer toward the adjacent battery cells is suppressed and the battery cells can be cooled. 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 layers by the suppression effect of radiative heat transfer and the heat diffusion effect by conductive heat transfer, and can be reduced in stages through the insulating material. As a result, the heat generated from one battery cell can be suppressed from propagating to the adjacent battery cells, and a chain reaction of thermal runaway can be prevented.
Furthermore, the surface layer has a substantially uniform thickness and has protrusions and recesses, providing excellent cushioning properties, which allows it to absorb external pressure acting on the battery cell and suppress deterioration of battery performance.

The battery pack of the present invention has the above-mentioned thermal control sheet interposed between multiple battery cells, so that during normal use and in the event of an abnormality, heat can be efficiently diffused to suppress the transfer of heat between battery cells, preventing a chain reaction of thermal runaway, and suppressing the deterioration of battery performance due to vibrations, changes in external pressure, etc.

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.

The present inventors have conducted extensive research in order to provide a thermal control sheet for a battery pack that can solve the above problems.
As a result, the inventors discovered that the above problem can be solved by forming a thermal control sheet by arranging a pair of surface layers, each having convex and concave portions and of approximately uniform thickness, on the surface facing the battery cell, and disposing an insulating material between the pair of surface layers, and by making the surface layers have a lower emissivity and a higher thermal conductivity than the insulating material.

Specifically, the surface layer of the thermal control sheet for a battery pack according to the present invention has a convex portion protruding toward the battery cell and a concave portion recessed in a direction away from the battery cell, so that a gas flow path is formed between the concave portion and the battery cell. 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 also has the effect of suppressing radiative heat transfer from the battery cell and diffusing the heat that reaches the surface layer by conductive heat transfer. After the amount of heat generated from the battery cell is reduced by the surface layer and the thermal insulation material, the other surface layer suppresses radiative heat transfer to the adjacent battery cell and can diffuse the heat 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 third embodiment. After that, the surface layer, the heat insulating material, etc. constituting 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, 11b, and a heat insulating material 13 is disposed between the surface layers 11a, 11b. The surface layer 11a has a substantially uniform thickness, and has a protrusion 14a and a recess 16a formed therein. Similarly, the surface layer 11b has a substantially uniform thickness, and has a protrusion 14b and a recess 16b formed therein. That is, the thermal control sheet 10 has a configuration in which the protrusions 14a, 14b, and the recesses 16a, 16b are provided on the outer surface perpendicular to the lamination direction of the surface layers 11a, 11b and the heat insulating material 13.

In the first embodiment, the surface layers 11a and 11b are made of a material that has a lower emissivity and a higher thermal conductivity than the insulating material 13, for example, a stainless steel plate processed into a corrugated shape. 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.
The thermal control sheet 10 also has, on its outer surface, protrusions 14a and 14b that protrude toward the battery cells 20a, 20b, and 20c, and recesses 16a and 16b that recess in a direction away from the battery cells 20a, 20b, and 20c. Therefore, gas flow paths 18 are formed between the recesses 16a and 16b 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, in the thermal control sheet 10 according to the first embodiment, a surface layer 11a having protrusions 14a and recesses 16a is disposed in a position in contact with the battery cell 20a. This surface layer 11a is made of a corrugated stainless steel plate having a substantially uniform thickness, and has a lower emissivity and a higher thermal conductivity than the insulating material 13.
Similarly, surface layers 11a, 11b made of stainless steel plates having protrusions 14a, 14b and recesses 16a, 16b are disposed at positions in contact with the battery cells 20b, 20c.

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 surface layer 11a 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 surface layer 11a has a higher thermal conductivity than the insulating material 13, a portion of the heat propagated to the surface layer 11a 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 surface layer 11a refers to the direction of the main surface on which the protrusions 14a and the recesses 16a are formed.

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 suppress radiative heat transfer to the battery cell 20b, and because a portion of the heat is propagated in the planar direction of the surface layer 11b, 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.

Furthermore, since the surface layers 11a and 11b constituting the thermal control sheet 10 are made of corrugated stainless steel plates having a substantially uniform thickness, for example, when the surface layer 11a is pressed in the thickness direction of the thermal control sheet 10, it deforms so that the height of the convex portion 14a becomes lower. Similarly, the surface layer 11b also deforms so that the height of the convex portion 14b becomes lower by pressing. In this way, the deformation of the surface layers 11a and 11b gives the thermal control sheet 10 a cushioning property. As a result, even if the temperature of a certain battery cell rises and the internal pressure changes, causing the battery cell to deform, the thermal control sheet 10 in contact with the battery cell absorbs the deformation, so that it is possible to prevent pressure from being applied to the battery cell and other battery cells.
Furthermore, when a battery pack incorporating the thermal control sheet 10 of this embodiment is used in an electric vehicle or hybrid vehicle, the thermal control sheet 10 has cushioning properties, so that even if the battery cell is exposed to vibration for a long period of time, the impact and external pressure transmitted to the battery cell can be reduced, and deterioration of the exterior material of the battery cell and deterioration of battery performance can be suppressed.

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.

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

The thermal control sheet 40 for a battery pack according to the second embodiment has an intermediate layer 12 disposed between the surface layer 11a and the surface layer 11b. Insulating materials 13a and 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 and 11b is the same as that of the first embodiment. The intermediate layer 12, like the surface layers 11a and 11b, is made of a material that has a lower emissivity and a higher thermal conductivity than the insulating materials 13a and 13b, for example an aluminum plate.

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 surface layer 11a has a lower emissivity than the insulating material 13, and thus can suppress radiative heat transfer to the insulating material 13. Also, the surface layer 11a has a higher thermal conductivity than the insulating material 13, and the protrusions 14a are in contact with the battery cells 20a, so that heat generated from the battery cells 20a is easily propagated in the planar direction of the surface layer 11a via the protrusions 14a and released to the outside. In this way, the amount of heat generated from the battery cells 20a is reduced through the surface layer 11a, and heat transfer to the insulating material 13 is suppressed.

The remaining heat reduced by the surface layer 11a is further reduced by the heat insulating material 13a before reaching the intermediate layer 12. The intermediate layer 12, like the surface layer 11a, 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, and therefore 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 second embodiment, the battery cell 20a and the battery cell 20b are arranged via the thermal control sheet 40, 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 40 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 suppressing 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.

Furthermore, as in the first embodiment, the thermal control sheet 40 has cushioning properties, so it can absorb deformation of the battery cells and reduce the impact and external pressure transmitted to the battery cells, thereby preventing deterioration of battery performance, etc.

Third Embodiment
In the above-described second embodiment, the thermal control sheet 40 for the battery pack has a five-layer structure in which the surface layer 11a, the insulating material 13a, the intermediate layer 12, the insulating material 13b, and the surface layer 11b 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. 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.
The thermal control sheet 15 for a battery pack according to the third 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 second embodiment.

In the third 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.

Furthermore, as in the first and second embodiments, the thermal control sheet 15 has cushioning properties, which allows it to absorb deformation of the battery cells and reduce the impact and external pressure transmitted to the battery cells, thereby preventing deterioration of battery performance, etc.

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 pack according to this embodiment has a substantially uniform thickness, and has convex portions that protrude toward the battery cells and concave portions that are recessed in a direction away from the battery cells.
The surface layer may be in the form of a corrugated sheet, as shown in the first to third embodiments, or may have projections and recesses formed regularly or irregularly by embossing. In either form, the projections and recesses form a gas flow path between the thermal control sheet and the battery cell, thereby allowing the battery cell to be cooled efficiently. In addition, the surface layer is formed by processing a plate-like material having a substantially uniform thickness, so that the surface layer can absorb shock and pressure. Note that the substantially uniform thickness refers to the thickness when the material of the surface layer is processed into a sheet by a general manufacturing method. For example, even if the layer thickness is partially thickened for the purpose of reinforcing the sheet, the present invention is also included in the present invention.
Specifically, as a substantially uniform thickness, it is preferable that the maximum value of the thickness of the surface layer is 500% or less of the minimum value of the thickness of the surface layer, more preferably 300% or less, even more preferably 150% or less, and particularly preferably 110% or less.

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

The thermal conductivity of the surface layer 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 surface layer can be measured in accordance with "Method of measuring emissivity of fine ceramics and ceramic composite materials" described in JIS R 1693.

The surface layer is preferably made of, for example, a metal or ceramic. In order to prevent the surface layer from being damaged by melting or the like in the event of a significant increase in the temperature of the battery cell due to an abnormality, it is more preferable that the surface layer be made of a metal or ceramic with a melting point of 600°C or higher. It is even more preferable that the surface layer be made of a metal with a melting point of 900°C or higher.

Specifically, it is preferable to use 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 as the material for the surface layer. Of these materials, stainless steel and silver have melting points of approximately 1400°C and approximately 960°C, respectively, and there is no risk of them melting even if the battery cell becomes hot. In addition, stainless steel and silver are less likely to oxidize compared to 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 for the surface layer.

The surface layer may be a composite layer formed by laminating two or more metals selected from the materials usable as the surface layer. When a composite layer is used as the surface 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 composite layers 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 surface 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 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 surface layer and the effect of diffusing heat by conductive heat transfer, the thickness of the surface layer is preferably 30 μm or more, and more preferably 50 μm or more. On the other hand, taking into consideration the overall thickness of the thermal control sheet, the thickness of the surface layer is preferably 300 μm or less, and more preferably 200 μm or less.
The thickness of the surface layer refers to the thickness of a sheet on which no protrusions or recesses are formed.

Furthermore, the surface layer may consist of a single layer, or may be a laminate of multiple thin layers of the same material. When the surface layer is made up of laminated 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 surface layer consisting of a single layer. Therefore, even if the surface layer consists of multiple layers, it is preferable that the total thickness is within the above range.

<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.
In addition, 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 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 surface layer.

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 composite 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, like the surface layer, the intermediate layer may be a single layer or a laminate of multiple thin films made of the same material. When the intermediate layer is made of laminated thin films made 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 of a single layer. Therefore, even if the intermediate layer is made 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 surface in the 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 surface layer. For the same reason, it is preferable that the emissivity of the intermediate layer is equal to or higher than the emissivity of the surface layer.
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 preparing surface layers having convex portions and concave portions, 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 together, and when they are joined together, 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.

Furthermore, even if the temperature of the battery cell 20a rises and the internal pressure changes, causing the battery cell 20a to deform, the thermal control sheet 10 absorbs the deformation of the battery cell 20a, thereby preventing pressure from being applied to the battery cell 20a and the adjacent battery cell 20b.
Furthermore, when a battery pack incorporating the thermal control sheet 10 of this embodiment is used in an electric vehicle or hybrid vehicle, the thermal control sheet 10 has cushioning properties, so that even if the battery pack is exposed to vibration for a long period of time, the impact and external pressure transmitted to the battery cells 20a, 20b, and 20c can be reduced, thereby suppressing deterioration of the exterior materials of the battery cells 20a, 20b, and 20c and deterioration of the battery performance.

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 Thermal control sheet for battery pack 11a, 11b Surface layer 12, 12a, 12b Intermediate layer 13, 13a, 13b, 13c Heat insulating material 14a, 14b Convex portion 16a, 16b Concave portion 20a, 20b, 20c Battery cell 30 Battery case 100 Battery pack

Claims (12)

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 substantially uniform thickness and has a protrusion protruding toward the battery cell and a recess recessed in a direction away from the battery cell,
The surface layer has a lower emissivity and a higher thermal conductivity than the thermal insulation material,
The thermal control sheet for a battery pack, wherein the surface layer 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 substantially uniform thickness and has a protrusion protruding toward the battery cell and a recess recessed in a direction away from the battery cell,
The surface layer has a lower emissivity and a higher thermal conductivity than the thermal insulation 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;
3. The thermal control sheet for a battery pack according to claim 2 , further comprising a heat insulating material disposed between adjacent ones of the intermediate layers. The thermal control sheet for a battery pack according to claim 2 or 3 , 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) . 5. The thermal control sheet for a battery pack according to claim 2 , wherein the thermal conductivity of the intermediate layer is equal to or higher than the thermal conductivity of the surface layer. The thermal control sheet for a battery pack according to any one of claims 2 to 5 , wherein the intermediate layer is made of a metal or a ceramic. The thermal control sheet for a battery pack according to any one of claims 1 to 6 , wherein the surface layer has a corrugated shape. The thermal control sheet for a battery pack according to any one of claims 1 to 6 , characterized in that the surface layer is made of an embossed plate material. The thermal control sheet for a battery pack according to any one of claims 1 to 8 , 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 9 , characterized in that the thermal conductivity of the surface layer is 10 times or more higher than 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 10 , 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 11 interposed between the plurality of battery cells;
a gas flow path is provided between the recess in the surface layer and the battery cell.

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