JP7670513B2 - 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, the radiant heat from the first energy storage element toward the second energy storage element, or a portion of the radiant heat from the second energy storage element toward 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 diffuse heat generated during normal use to the outside, while suppressing the transfer of heat between the battery cells in the event of an abnormality, and 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 in contact with the battery cell;
At least one intermediate layer disposed between the pair of surface layers;
a heat insulating material disposed between the surface layer and the intermediate layer,
The thermal control sheet for a battery pack, wherein the surface layer and the intermediate layer each have 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 [16].

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

[3] The thermal control sheet for a battery pack according to [1] or [2], characterized in that the thermal conductivity of the insulating material is less than 1 (W/m·K).

[4] The thermal control sheet for a battery pack according to any one of [1] to [3], characterized in that the thermal conductivity of the surface layer and the thermal conductivity of the intermediate layer are both at least 10 times the thermal conductivity of the insulating material.

[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 intermediate layer is equal to or greater than the thermal conductivity of the surface layer.

[6] The thermal control sheet for a battery pack according to any one of [1] to [5], characterized in that the emissivity of the intermediate layer is equal to or higher than the emissivity of the surface layer.

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

[8] The thermal control sheet for a battery pack described in [7], characterized in that the surface layer is made of one metal selected from stainless steel, copper or a copper alloy, silver or a silver alloy, nickel or a nickel alloy, and titanium or a titanium alloy.

[9] The thermal control sheet for a battery pack according to [7], characterized in that the surface layer is a composite layer formed by laminating two or more metals selected from stainless steel, copper or a copper alloy, silver or a silver alloy, nickel or a nickel alloy, and titanium or a titanium alloy.

[10] The thermal control sheet for a battery pack described in [8], characterized in that the surface layer is made of one metal selected from stainless steel, silver, and a silver alloy.

[11] The thermal control sheet for a battery pack according to any one of [1] 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 [11], characterized in that the intermediate layer is made of one metal selected from 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.

[13] The thermal control sheet for a battery pack according to [11], characterized in that the intermediate layer is a composite layer in which two or more metals selected from 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 are laminated.

[14] The thermal control sheet for a battery pack according to [12], characterized in that the intermediate layer is made of one metal selected from aluminum or an aluminum alloy, copper or a copper alloy, and silver or a silver alloy.

[15] The thermal control sheet for a battery pack described in any one of [1] to [14], characterized in that the insulating material contains at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles.

[16] The thermal control sheet for a battery pack according to [15], characterized in that the heat insulating material contains at least one selected from alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite material, microporous particles, hollow silica particles, thermally expandable inorganic material, and aerogel.

The above object of the present invention is also achieved by the following configuration [17] relating to the battery pack.

[17] 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 [16] interposed between the plurality of battery cells;
A battery pack, wherein a surface layer of the thermal control sheet for the battery pack is in contact with the battery cells.

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 the surface layer and intermediate layer have a lower emissivity and a higher thermal conductivity than the insulating material disposed between them. Therefore, the heat generated from the battery cell is reduced through the surface layer and intermediate layer by the suppression effect of radiative heat transfer and the heat diffusion effect by conductive heat transfer, and can be gradually reduced through the insulating material. As a result, the heat generated from one battery cell can be suppressed from propagating 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 method for evaluating the effect of thermal control. FIG. 5 is a perspective view showing the size of the thermal control sheet used in this embodiment.

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

As a result, the inventors discovered that the above problem can be solved by configuring a thermal control sheet for a battery pack to be interposed between multiple battery cells, by disposing an intermediate layer between a pair of surface layers and disposing a thermal insulating material between each surface layer and the intermediate layer, and by making the emissivity of the surface layer and the intermediate layer lower than that of the insulating material and making the thermal conductivity higher than that of the insulating material.

That is, when the temperature of a battery cell rises, the surface layer in contact with the battery cell 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. Then, the amount of heat generated from the battery cell is reduced by the surface layer and the insulating material before it reaches the intermediate layer, and the intermediate layer further suppresses radiative heat transfer to the next layer and diffuses the heat that reaches the intermediate layer by conductive heat transfer.
In this way, by utilizing the surface layer and intermediate layer to suppress radiative heat transfer and to diffuse heat by conductive heat transfer, when a battery cell becomes hot, heat transfer is gradually suppressed before it reaches an adjacent battery cell, and the heat can be diffused to the outside, thereby suppressing a chain reaction of thermal runaway.

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 of a first embodiment and a second embodiment. After that, the surface layer, intermediate layer, 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, an intermediate layer 12 disposed between the surface layers 11a and 11b, and insulating materials 13a, 13b disposed between the surface layer 11a and the intermediate layer 12, and between the surface layer 11b and the intermediate layer 12, respectively.
In the first embodiment, the surface layers 11a and 11b are made of a material having a lower emissivity and a higher thermal conductivity than the insulating materials 13a and 13b, such as a stainless steel plate. The intermediate layer 12 is also made of a material having a lower emissivity and a higher thermal conductivity than the insulating materials 13a and 13b, such as an aluminum plate. The insulating materials 13a and 13b are, for example, alumina fibers.

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 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, the surface layers 11a and 11b are disposed so as to be in contact with the battery cells 20a, 20b, and 20c. Furthermore, stainless steel plates having a lower emissivity and a higher thermal conductivity than the thermal insulating materials 13a and 13b are used as the surface layers 11a and 11b.

In the first embodiment configured as described above, for example, when the temperature of the battery cell 20a rises, the surface layer 11a provided at a position in contact with the battery cell 20a has a lower emissivity than the insulating materials 13a and 13b, and therefore can suppress radiative heat transfer to the insulating material 13a side. Also, since the surface layer 11a has a higher thermal conductivity than the insulating materials 13a and 13b, part of the heat propagated to the surface layer 11a is propagated in the planar direction of the surface layer 11a. 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 13a side is suppressed.
The surface direction of the surface layer 11a refers to the direction of a surface perpendicular to the thickness direction of the surface layer 11a. Similarly, the surface direction of the intermediate layer 12 described below refers to the direction of a surface perpendicular to the thickness direction of the intermediate layer 12.

The remaining heat reduced by the surface layer 11a is further reduced by passing through the insulating material 13a before reaching the intermediate layer 12. Like the surface layer 11a, the intermediate layer 12 has a lower emissivity than the insulating materials 13a and 13b, and therefore can suppress radiative heat transfer to the next layer, i.e., the insulating material 13b. In addition, the intermediate layer 12 has a higher thermal conductivity than the insulating materials 13a and 13b, and therefore some 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.

Similarly, the heat dissipated by the intermediate layer 12 is further dissipated through the insulating material 13b and the surface layer 11b.
Therefore, by arranging battery cell 20a and battery cell 20b via thermal control sheet 10, when heat is generated from battery cell 20a, the heat can be efficiently diffused and the transmission of heat between the battery cells can be suppressed, thereby preventing a chain reaction of thermal runaway.

The thermal control sheet 10 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.

Second Embodiment
In the above first embodiment, the thermal control sheet 10 for the battery pack has a five-layer structure in which a surface layer 11a, an insulating material 13a, an intermediate layer 12, an insulating material 13b, and a 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.

Figure 3 is a cross-sectional view showing a schematic diagram of a thermal control sheet for a battery pack according to a second embodiment of the present invention. In the second embodiment shown in Figure 3, parts that are the same as or equivalent to those in the first embodiment are given the same reference numerals in the drawing, and their description is omitted or simplified. In addition, since the second embodiment can be used in place of the thermal control sheet 10 described in the battery pack 100 shown in Figure 2, the effects and the like will be described assuming that the thermal control sheet according to the second embodiment is applied to the battery pack 100.

The thermal control sheet 15 for a battery pack according to the second 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 second embodiment, similarly to the first embodiment, the surface layers 11a and 11b are made of a material having a lower emissivity and a higher thermal conductivity than the thermal insulators 13a, 13b, and 13c, and the intermediate layers 12a and 12b are also made of a material having a lower emissivity and a higher thermal conductivity than the thermal insulators 13a, 13b, and 13c.

In the second embodiment configured as described above, when the temperature of the battery cell 20a rises, the surface layer 11a provided at the position in contact with the battery cell 20a has a lower emissivity than the insulating material, so that it is possible to suppress the radiative heat transfer to the insulating material 13a side. In addition, since the surface layer 11a has a higher thermal conductivity than the insulating material, a part of the heat transferred to the surface layer 11a is transferred in the planar direction of the surface layer 11a and diffused to the outside of the thermal control sheet 15.
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 13a side and also 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, radiative heat transfer is gradually suppressed between the adjacent battery cells 20b via the insulating material 13c, intermediate layer 12b, insulating material 13b, and surface layer 11b, and heat is diffused by conductive heat transfer. Therefore, the heat transfer between 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 pack according to this embodiment has the effect of suppressing radiative heat transfer from the battery cells in contact with it, and the effect of 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. In addition, 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 in contact with the battery cell 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 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 above-mentioned surface layer materials. When a composite layer is used as the surface layer, the above-mentioned 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 surface 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 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 surface layer is preferably 300 μm or less, and more preferably 200 μm or less.

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.

(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 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, as shown in Fig. 1, or may be a laminate of multiple thin layers 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 when 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.

(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.

<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>
The thermal control sheet according to the present embodiment can be obtained, for example, by preparing a pair of metal plates as surface layers, disposing a metal plate as an intermediate layer between the pair of surface layers, and disposing a heat insulating material between the surface layers and the intermediate layer. These layers may or may not be bonded to each other. When they are bonded, 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. 3, a 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.

Below, we will explain an example of the invention and a comparative example of the thermal control sheet for a battery pack according to this embodiment.

[Example 1: Effect of heat control on the presence or absence of a surface layer or intermediate layer, and on the type of intermediate layer]
A stainless steel plate or a silver plate was prepared as the surface layers 11a and 11b shown in FIG. 1, and an aluminum plate, a copper plate, a stainless steel plate, a silver plate, or an [aluminum/silver/aluminum] composite layer was prepared as the intermediate layer 12. An alumina fiber sheet, an aerogel blanket, or a glass fiber was prepared as the insulating materials 13a and 13b, and the surface layer, the intermediate layer, and the insulating material were laminated to produce a thermal control sheet 10 for a battery pack according to the invention. As a comparative example, a test piece was prepared in which either one or both of the surface layer 11a and the intermediate layer 12 was not laminated, in comparison with the above-mentioned invention example. Then, the effect of thermal control depending on the presence or absence of the surface layer or the intermediate layer was evaluated for the obtained thermal control sheet.

Fig. 4 is a cross-sectional view showing a typical method for evaluating the effect of thermal control, and Fig. 5 is a perspective view showing the size of the thermal control sheet used in this example.
As shown in FIG. 4, an Fe jig 16 heated to 800° C. in an electric furnace was placed on one side (surface of the surface layer 11a) of the thermal control sheet 10 so that it was moved from the electric furnace within 5 seconds. Then, the temperature 90 seconds after placement was measured by a thermocouple 17 placed on the other side (surface of the surface layer 11b) of the thermal control sheet 10 to evaluate the effect of thermal control. Similarly, for the comparative examples, the thermal control sheet 10 shown in FIG. 4 and FIG. 5 was replaced with the test piece of the comparative example to evaluate the effect of thermal control. However, for some comparative examples in which the surface layer was not laminated, the surface layer 11b was disposed on the other side for measurement by the thermocouple 17.

As shown in FIG. 5, the thermal control sheet 10 produced was a square with sides of 50 mm and a total thickness of 1.5 mm. On one side of the thermal control sheet 10, the width of the contact area A with the Fe jig 16 was 25 mm, and the length in the direction perpendicular to the width direction was 50 mm from one side of the thermal control sheet 10 to the opposing side.

Detailed measurement conditions are shown in Table 1 below, and lamination conditions and measurement results are shown in Table 2 below. In the tables shown below, "SUS" stands for stainless steel, and [Al/Ag/Al] stands for an [aluminum/silver/aluminum] composite layer. Also, "AF" stands for alumina fiber, and "AG-F" stands for an aerogel blanket, both trade names of SHENZHEN AEROGEL TECHNOLOGY CO., LTD. "GF" stands for glass fiber. "-" stands for no lamination.
The alumina fiber used had a thermal conductivity of 0.05 (W/m K) and an emissivity of 0.8. The aerogel blanket (AG-F) had a thermal conductivity of 0.02 (W/m K) and an emissivity of 0.8. The glass fiber (GF) had a thermal conductivity of 0.05 (W/m K) and an emissivity of 0.8.
Furthermore, the emissivity of the stainless steel plate as the surface layer, and the aluminum plate, copper plate, and stainless steel plate as the intermediate layer was all about 0.2.

As shown in Table 2 above, since invention examples No. 1 to 9 are thermal control sheets according to the embodiments of the present invention, the surface layer and intermediate layer can provide a suppression effect of radiative heat transfer and a diffusion effect due to conductive heat transfer, and all of them have excellent heat insulation effects.
In contrast, in Comparative Examples Nos. 1 to 6, either one or both of the surface layer and the intermediate layer were not laminated, and therefore the heat insulating effect was lower than that of the invention examples.

In addition, when comparing Inventive Examples Nos. 1 to 4 and 7 with Comparative Example No. 2, the surface layer and the heat insulating material are all the same, and the only difference is the presence or absence of an intermediate layer, but Inventive Examples Nos. 1 to 4 and 7 showed superior heat insulating effects. This shows that, regardless of the type of intermediate layer, having the intermediate layer described in the present invention is effective in obtaining superior heat insulating effects.
In addition, when comparing Example No. 3 and Comparative Example No. 3, both of which share the same insulating material and intermediate layer, and differ only in the presence or absence of one surface layer, Example No. 3 showed superior insulating effect. This shows that having the surface layer according to the present invention at the position in contact with the heated battery cell is effective in obtaining superior insulating effect.

[Example 2: Effect of thermal control on total number of layers and thickness of intermediate layer]

A thermal control sheet 15 according to the second embodiment of the present invention was produced by preparing stainless steel plates as the surface layers 11a and 11b, aluminum plates as the intermediate layers 12a and 12b, and alumina fiber sheets as the heat insulating materials 13a, 13b, and 13c shown in Fig. 3, and laminating the surface layers, intermediate layers, and heat insulating materials. A thermal control sheet with a total of nine layers was also produced by adding one intermediate layer and one heat insulating material. Note that for the nine-layer structure, thermal control sheets with different thicknesses of the intermediate layer were also produced.
Thereafter, in the same manner as in Example 1 above, the temperature of the surface of the thermal control sheet opposite to the surface on which the Fe jig was placed was measured to evaluate the effect of thermal control due to the total number of layers or the thickness of the intermediate layer.

The size of the thermal control sheet produced was the same as in Example 1 above. The lamination conditions and measurement results are shown in Table 3 below. For comparison, the results of Invention Example No. 1 in Example 1 above are also shown in Table 3.

As shown in Table 3 above, in invention examples 10 to 12, which had two or more intermediate layers, the surface layer and intermediate layer were able to provide a radiative heat transfer suppression effect and a conductive heat transfer diffusion effect, and were able to provide superior heat insulation effects compared to comparative examples 1 to 6 shown in Table 2 above.

In comparison with invention sample No. 1, invention sample No. 10 exhibits superior heat insulating effect. This is believed to be due to the fact that the number of intermediate layers has been increased from one to two, enhancing the heat diffusion effect. In invention sample No. 11, the number of intermediate layers has been further increased, but since the basis weight of the insulating material needs to be reduced as the number of layers is increased, invention sample No. 11 has the same heat insulating effect as invention sample No. 1.
In addition, in Example No. 11, the thickness of each intermediate layer was thicker than in Example No. 12, so the heat diffusion effect of the intermediate layer was high and excellent heat insulation effect was obtained.

[Example 3: Effect of thermal control on the thickness of each layer]

A five-layered thermal control sheet 10 for a battery pack was produced as an example of the invention, using stainless steel plates as the surface layers 11a and 11b, an aluminum plate as the intermediate layer 12, and an alumina fiber sheet or an aerogel blanket (AG-F) as the heat insulating materials 13a and 13b, and varying the thickness of the surface layer 11a and the intermediate layer 12, or the type and basis weight of the heat insulating materials 13a and 13b. The thickness of each surface layer 11b was 50 μm, and the total thickness was 1.5 mm.
Thereafter, in the same manner as in Example 1 above, the temperature of the surface of the thermal control sheet opposite to the surface on which the Fe jig was placed was measured to evaluate the effect of thermal control due to the thickness of each layer.

The size of the thermal control sheet produced was the same as in Example 1 above. The lamination conditions and measurement results are shown in Table 4 below. For comparison, the results of invention example No. 1 in Example 1 above are also shown in Table 4.

As shown in Table 4 above, in invention examples Nos. 13 to 18 in which the thickness of the surface layer was 50 μm or 150 μm, the thickness of the intermediate layer was 11 μm, 50 μm or 165 μm, and the basis weight of the heat insulating material was 150 (g/m ² ), 190 (g/m ² ), or 280 (g/m ² ), the surface layer and the intermediate layer were able to obtain a suppression effect of radiative heat transfer and a diffusion effect by conductive heat transfer, and a superior heat insulating effect was obtained compared to comparative examples Nos. 1 to 6 shown in Table 2 above.
In addition, since the thickness of the intermediate layer per layer is different among the invention samples No. 1, 13, and 14, the thicker the intermediate layer is, the higher the heat insulating effect is, and the invention sample No. 14 was able to obtain the best heat insulating effect.

In addition, since the thickness of the surface layer per layer is different between the invention samples No. 1 and No. 15, the invention sample No. 15 having a thicker surface layer exhibited a superior heat insulating effect.
Similarly, in the case of the invention samples No. 14 and No. 16, the thickness of the surface layer per layer is different from each other, and the invention sample No. 16 having the thicker surface layer exhibited a superior heat insulating effect.
Furthermore, inventive examples 13, 17, and 18, the type and basis weight of the insulating material were different from one another, and the intermediate layer was the thinnest, but no matter which insulating material was used, a superior insulating effect was obtained compared to comparative examples 1 to 6 shown in Table 2 above.

As described above, the thermal insulation effect of the thermal control sheet of the present invention varies depending on the total number of layers, the basis weight of the insulating material, and the thickness of the intermediate layer, so by appropriately controlling these, it is possible to obtain an even better insulating effect.

Reference Signs List 10, 15: Thermal control sheet for battery pack 11a, 11b: Surface layer 12, 12a, 12b: Intermediate layer 13a, 13b, 13c: Insulating material 17: Thermocouple 20a, 20b, 20c: Battery cell 30: Battery case 100: Battery pack

Claims (17)

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 in contact with the battery cell;
At least one intermediate layer disposed between the pair of surface layers;
a heat insulating material disposed between the surface layer and the intermediate layer,
The thermal control sheet for a battery pack, wherein the surface layer and the intermediate layer each have a lower emissivity and a higher thermal conductivity than the insulating material. Two or more intermediate layers;
2. The thermal control sheet for a battery pack according to claim 1, 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 1 or 2, characterized in that the thermal conductivity of the insulating material is less than 1 (W/m·K). The thermal control sheet for a battery pack according to any one of claims 1 to 3, characterized in that the thermal conductivity of the surface layer and the thermal conductivity of the intermediate layer are both 10 times or more higher than the thermal conductivity of the insulating material and are in the range of 5 to 450 (W/m K) . The thermal control sheet for a battery pack according to any one of claims 1 to 4, characterized in that 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 1 to 5, characterized in that the emissivity of the intermediate layer is equal to or higher than the emissivity of the surface layer. 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 a metal with a melting point of 600°C or higher, or a ceramic. The thermal control sheet for a battery pack according to claim 7, characterized in that the surface layer is made of one metal selected from stainless steel, copper or a copper alloy, silver or a silver alloy, nickel or a nickel alloy, and titanium or a titanium alloy. The thermal control sheet for a battery pack according to claim 7, characterized in that the surface layer is a composite layer in which two or more metals selected from stainless steel, copper or a copper alloy, silver or a silver alloy, nickel or a nickel alloy, and titanium or a titanium alloy are laminated. The thermal control sheet for a battery pack according to claim 8, characterized in that the surface layer is made of one metal selected from stainless steel, silver, and a silver alloy. The thermal control sheet for a battery pack according to any one of claims 1 to 10, characterized in that the intermediate layer is made of metal or ceramic. The thermal control sheet for a battery pack according to claim 11, characterized in that the intermediate layer is made of one metal selected from 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 thermal control sheet for a battery pack according to claim 11, characterized in that the intermediate layer is a composite layer in which two or more metals selected from 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 are laminated. The thermal control sheet for a battery pack according to claim 12, characterized in that the intermediate layer is made of one metal selected from aluminum or an aluminum alloy, copper or a copper alloy, and silver or a silver alloy. The thermal control sheet for a battery pack according to any one of claims 1 to 14, characterized in that the insulating material contains at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles. The thermal control sheet for a battery pack according to claim 15, characterized in that the heat insulating material contains at least one selected from alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite material, microporous particles, hollow silica particles, thermally expandable inorganic material, and aerogel. 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 16, which is interposed between the plurality of battery cells;
A battery pack, wherein a surface layer of the thermal control sheet for the battery pack is in contact with the battery cells.

Images