JP7670515B2 - 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 achieve 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,
At least one composite layer;
At least one layer of insulation;
The composite layer includes a base layer made of ceramic or graphite and a metal layer disposed on both sides of the base layer;
The metal layer has a lower emissivity than the thermal insulation material,
A thermal control sheet for a battery pack, wherein one of the metal layer and the base layer has a thermal conductivity higher than that of 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 [14].

[2] Two or more layers of the insulating material;
The thermal control sheet for a battery pack according to [1], further comprising: the composite layer disposed between adjacent ones of the insulating materials.

[3] Two or more composite layers,
The thermal control sheet for a battery pack according to [1], further comprising: the insulating material disposed between adjacent ones of the composite layers.

[4] The thermal control sheet for a battery pack described in any one of [1] to [3], characterized in that the base layer is made of one material selected from AlN, SiC, TiN, and graphite.

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

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

[7] The thermal control sheet for a battery pack according to any one of [1] to [6], characterized in that the metal 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.

[8] Further, the device has at least one heat dissipation layer,
The heat insulating material is disposed between the heat dissipation layer and the composite layer,
The thermal control sheet for a battery pack according to any one of [1] to [7], wherein the heat dissipation layer has a lower emissivity than the insulating material and a higher thermal conductivity than the insulating material.

[9] A pair of the heat dissipation layers;
the composite layer disposed between the pair of heat dissipation layers;
The thermal control sheet for a battery pack according to [8], further comprising a heat insulating material disposed between the heat dissipation layer and the composite layer.

[10] A pair of the composite layers;
the heat dissipation layer disposed between the pair of composite layers;
The thermal control sheet for a battery pack according to [8], further comprising a heat insulating material disposed between the composite layer and the heat dissipation layer.

[11] The thermal control sheet for a battery pack according to any one of [8] to [10], characterized in that the heat dissipation 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.

[12] The thermal control sheet for a battery pack according to any one of [8] to [10], characterized in that the heat dissipation layer is a laminate of 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.

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

[14] The thermal control sheet for a battery pack according to [13], 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 [15] relating to the battery pack.

[15] 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 [14] interposed between the plurality of battery cells.

The thermal control sheet for battery packs of the present invention comprises a composite layer having a base layer and a metal layer, and since the metal layer has a lower emissivity than the insulating material and either the metal layer or the base layer has a high thermal conductivity, the heat generated from the battery cells is reduced by the suppression effect of radiative heat transfer through the composite layer and the heat diffusion effect of conductive heat transfer. As a result, the heat generated from one battery cell can be suppressed from propagating to an adjacent battery cell, preventing a chain reaction of thermal runaway.

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

FIG. 1 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view that illustrates a schematic diagram of a battery pack to which the thermal control sheet for a battery pack according to the first embodiment is applied. FIG. 3 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a second embodiment of the present invention. FIG. 4 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a third embodiment of the present invention. FIG. 5 is a cross-sectional view that illustrates a thermal control sheet for a battery pack according to a fourth embodiment of the present invention. FIG. 6 is a cross-sectional view that illustrates a method for evaluating the effect of thermal control. FIG. 7 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 problems can be solved by using a thermal control sheet for a battery pack, which is interposed between multiple battery cells, that uses a composite layer having a base layer made of ceramic or graphite and metal layers disposed on both sides of the base layer, and a thermal insulating material, and by making the metal layer have a lower emissivity than the thermal insulating material and making either the metal layer or the base layer have a high thermal conductivity.

That is, when the temperature of a battery cell rises and the heat reaches the thermal control sheet for a battery pack, the metal layer has a lower emissivity than the insulating material, and therefore suppresses radiative heat transfer from the battery cell. In addition, either the base layer or the metal layer has a higher thermal conductivity than the insulating material, and therefore has the effect of diffusing the heat that reaches the thermal control sheet for a battery pack by conductive heat transfer. In addition, the heat transfer is reduced by passing through the insulating material. In this way, the heat generated from a battery cell can be diffused by conductive heat transfer while suppressing radiative heat transfer by passing through the metal layer, base layer, and insulating material before reaching an adjacent battery cell.
Therefore, if a battery cell becomes too hot, heat transfer is gradually suppressed before it reaches an adjacent battery cell, and the heat can be diffused to the outside, thereby preventing 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 assembly according to the embodiment of the present invention will be described in order from the first to fourth embodiments. After that, the metal layer, base layer, insulating material, etc. constituting the thermal control sheet for a battery assembly according to the present embodiment will be described. Furthermore, the manufacturing method of the thermal control sheet for a battery assembly 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 includes a pair of heat insulating materials 13a, 13b, and a composite layer 12 disposed between the heat insulating materials 13a and 13b.
The composite layer 12 has a base layer 14 and metal layers 11a, 11b disposed on both sides of the base layer 14. Note that the two sides of the base layer 14 refer to two sides that are perpendicular to the thickness direction of the base layer 14.

In the first embodiment, the metal layers 11a and 11b are made of a material having a lower emissivity than the insulating materials 13a and 13b, for example, aluminum. Aluminum is also a material having a higher thermal conductivity than the insulating materials 13a and 13b. The base layer 14 is made of ceramic or graphite, for example, AlN. The insulating materials 13a and 13b are, for example, 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 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 the first embodiment configured as described above, for example, when the temperature of the battery cell 20a rises, the heat transfer is first reduced by passing through the heat insulating material 13a. Next, the heat reaches the metal layer 11a of the composite layer 12, but since the metal layer 11a has a lower emissivity than the heat insulating materials 13a and 13b, the heat transfer by radiation to the base layer 14 side can be suppressed. Furthermore, since the metal layer 11a has a higher thermal conductivity than the heat insulating materials 13a and 13b, a part of the heat transferred to the metal layer 11a is transferred in the surface direction of the metal layer 11a and diffused to the outside of the thermal control sheet 10. In this way, the amount of heat generated from the battery cell 20a is reduced by passing through the metal layer 11a.
The planar direction of the metal layer 11a refers to the direction of a plane perpendicular to the thickness direction of the metal layer 11a.

The heat reduced through the metal layer 11a then reaches the metal layer 11b through the base layer 14, where it is diffused in the surface direction of the metal layer 11b and released to the outside, suppressing heat transfer to the heat insulating material 13b. In this embodiment, the base layer 14 is made of AlN and has excellent thermal conductivity, so that it can obtain the effect of diffusing heat in the surface direction, similar to the metal layer 11a, and can reduce conductive heat transfer toward the metal layer 11b. In this way, the remaining heat reduced by the composite layer 12 is further reduced through the heat insulating material 13b.
Therefore, by arranging the battery cells 20a and 20b via a pair of insulating materials 13a, 13b and the composite layer 12, when heat is generated from the 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.

In addition, the base layer 14 made of AlN has excellent fire resistance, so even if a battery cell were to catch fire, the thermal control sheet 10 having the base layer 14 can be used to prevent the fire from affecting other areas.

The thermal control sheet 10 is configured symmetrically in the thickness direction with respect to the base layer 14 of the composite layer 12. Therefore, even if heat is generated from the battery cell 20b, this heat is gradually reduced toward the battery cell 20a by passing through the insulating material 13b, the metal layer 11b, the base layer 14, the metal layer 11a, and the insulating material 13a 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 insulation material 13a, metal layer 11a, base layer 14, metal layer 11b and insulation material 13b in this order toward battery cell 20c, thereby suppressing the transmission of heat to battery cell 20c.

In the first embodiment, one composite layer 12 is disposed between the insulating material 13a and the insulating material 13b, but the number of composite layers is not limited to one. Although not shown in the figures, the above effect can be obtained even if two or more composite layers are disposed between the insulating material 13a and the insulating material 13b, and insulating materials are disposed between adjacent composite layers.

Second Embodiment
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 to fourth embodiments shown below, the same or equivalent parts as those in the first embodiment are denoted by the same reference numerals in the drawings, and their description will be omitted or simplified. In addition, since the second to fourth embodiments can be used in place of the thermal control sheet 10 described in the battery 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 to fourth embodiments are applied to the battery assembly 100.

The thermal control sheet 40 for a battery pack according to the second embodiment has a pair of composite layers 12a, 12b, and a heat insulating material 13 disposed between the composite layers 12a and 12b.
The configuration of the composite layers 12a and 12b and the materials of the metal layers 11a and 11b and the base layer 14 are similar to those of the composite layer 12 according to the first embodiment.

In the second embodiment configured as described above, for example, when the temperature of the battery cell 20a rises, the metal layer 11a of the composite layer 12a can suppress the radiative heat transfer to the base layer 14 side, and the heat is propagated in the surface direction of the metal layer 11a and released to the outside of the thermal control sheet 40. Then, the heat is propagated in the surface direction of the base layer 14 through the base layer 14 in the same manner as in the case of the metal layer 11a, and is released to the outside of the thermal control sheet 40, and reaches the metal layer 11b. Then, the metal layer 11b can suppress the radiative heat transfer to the heat insulating material 13 side, and the heat is propagated in the surface direction of the metal layer 11b, and the heat is released to the outside of the thermal control sheet 40. In this way, the heat generated from the battery cell 20a is reduced through the composite layer 12a and reaches the heat insulating material 13.
The heat is then further reduced through the heat insulating material 13 and reaches the composite layer 12b. In the composite layer 12b, similar to the composite layer 12a, the metal layer 11a, the base layer 14, and the metal layer 11b suppress radiative heat transfer, and the heat is released to the outside of the thermal control sheet 40 by conductive heat transfer.

Therefore, by arranging the battery cells 20a and 20b via a pair of composite layers 12a, 12b and the insulating material 13, when heat is generated from the battery cell 20a, the heat can be efficiently diffused and the transfer of heat between the battery cells can be suppressed, preventing a chain reaction of thermal runaway.

The thermal control sheet 40 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, this heat is gradually reduced toward the battery cell 20a by passing through the composite layer 12b, the insulating material 13b, and the composite layer 12a 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 composite layer 12a, insulation material 13, and composite layer 12b, in that order, toward battery cell 20c, thereby suppressing the transmission of heat to battery cell 20c.

In the second embodiment, one layer of insulating material 13 is disposed between composite layer 12a and composite layer 12b, but the present invention is not limited to this. Although not shown in the figures, the above effect can be obtained even if three or more composite layers are prepared and insulating material is disposed between adjacent composite layers.

Third Embodiment
Fig. 4 is a cross-sectional view showing a schematic diagram of a thermal control sheet for a battery pack according to a third embodiment of the present invention. In the thermal control sheet 50 shown in Fig. 4, a heat dissipation layer 15 is disposed between a pair of composite layers 12a and 12b. Insulating materials 13a and 13b are disposed between the composite layer 12a and the heat dissipation layer 15, and between the composite layer 12b and the heat dissipation layer 15, respectively. The configuration and material of the composite layers 12a and 12b are the same as those of the second embodiment shown in Fig. 3.
The heat dissipation layer 15 is made of a material having a lower emissivity and a higher thermal conductivity than the heat insulating materials 13a and 13b, for example a stainless steel plate.

In the third embodiment configured in this manner, for example, if the temperature of the battery cell 20a rises, radiative heat transfer is suppressed through the composite layer 12a, as in the second embodiment, and heat is transferred in the planar direction by the metal layers 11a, 11b and the base layer 14, and the heat is released to the outside of the thermal control sheet 50.

The remaining heat reduced by the composite layer 12a is further reduced by passing through the insulating material 13a before reaching the heat dissipation layer 15. The heat dissipation layer 15 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 heat dissipation layer 15 has a higher thermal conductivity than the insulating materials 13a and 13b, and therefore some of the heat that reaches the heat dissipation layer 15 is propagated in the surface direction of the heat dissipation layer 15 and diffused to the outside of the thermal control sheet 50.

Similarly, the heat dissipated by the heat dissipation layer 15 is further reduced by the heat insulating material 13b and the composite layer 12b.
In this way, by arranging battery cell 20a and battery cell 20b via thermal control sheet 50, 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 50 is configured symmetrically in the thickness direction with respect to the heat dissipation layer 15. Therefore, even if heat is generated from the battery cell 20b, this heat is gradually reduced toward the battery cell 20a by passing through the composite layer 12b, the insulating material 13b, the heat dissipation layer 15, the insulating material 13a, and the composite layer 12a in this order, thereby making it possible to suppress the propagation of heat to the battery cell 20a.
Similarly, the heat generated from battery cell 20b is gradually reduced by passing through composite layer 12a, insulating material 13a, heat dissipation layer 15, insulating material 13b, and composite layer 12b, in that order, toward battery cell 20c, thereby suppressing the transmission of heat to battery cell 20c.

Similar to the composite layer shown in the first and second embodiments, the heat dissipation layer 15 of the thermal control sheet 50 may be two or more layers. For example, the thermal control sheet 50 shown in Fig. 4 may have two or more heat dissipation layers and a heat insulating material disposed between adjacent heat dissipation layers between the composite layer 12a and the composite layer 12b.
Further, the thermal control sheet 50 may further include a heat insulating material on the outer side of the composite layers 12a, 12b, that is, on the side opposite to the heat insulating materials 13a, 13b.

Fourth Embodiment
5 is a cross-sectional view showing a schematic diagram of a thermal control sheet for a battery pack according to a fourth embodiment of the present invention. In a thermal control sheet for a battery pack 60 according to the fourth embodiment, a composite layer 12 is disposed between a pair of heat dissipation layers 15a, 15b. Insulating materials 13a, 13b are disposed between the heat dissipation layer 15a and the composite layer 12, and between the heat dissipation layer 15b and the composite layer 12, respectively. The configuration and material of the composite layer 12, and the material of the heat dissipation layers 15a, 15b are the same as those in the third embodiment shown in FIG. 4.

Even in the fourth embodiment configured in this way, when the temperature of the battery cell 20a rises, the heat can be prevented from radiating heat toward the battery cell 20b by passing through the heat dissipation layer 15a, the insulation material 13a, the composite layer 12, the insulation material 13b, and the heat dissipation layer 15b in this order. In addition, the heat dissipation layers 15a, 15b and the metal layers 11a, 11b have a higher thermal conductivity than the insulation material, so the heat that reaches them is propagated in the planar direction and diffused to the outside of the thermal control sheet 60.

The heat generated from the battery cell 20a is gradually suppressed by radiation heat transfer through the thermal control sheet 60 to the adjacent battery cell 20b, and is thermally diffused by conductive heat transfer. This makes it possible to efficiently suppress the transfer of heat between battery cells and to suppress a chain reaction of thermal runaway.

The effects of the present invention can be obtained even if the composite layer 12 is made up of two or more layers and a heat insulating material is disposed between adjacent composite layers 12. Furthermore, a heat dissipation layer may be disposed between adjacent composite layers 12, and a heat insulating material may be disposed on the outermost surface of these.
However, increasing the number of layers will increase the overall thickness of the thermal control sheet and decrease the thickness of each sheet of insulation, so it is preferable to appropriately select the number of composite layers and heat dissipation layers, as well as the thickness of the insulation, etc., depending on the required performance.

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

<Composite layer>
The composite layer used in the thermal control sheet for a battery pack according to this embodiment has a base layer made of ceramic or graphite, and metal layers disposed on both sides of the base layer.

(Base layer)
When the base layer is made of ceramic, ceramic has high fire resistance, and even if the temperature of the battery cell rises significantly, it is possible to suppress the influence on other regions due to melting or the like.
Furthermore, when the base layer is made of graphite, particularly when a graphite sheet having a layered crystal structure is used, the graphite sheet has extremely high thermal conductivity in the plane direction, so that the heat that reaches the composite layer can be diffused to the outside more efficiently.
In addition, the fire resistance of graphite in an air atmosphere is 200° C. to 450° C., which is lower than that of ceramics. However, in this embodiment, the base layer is sandwiched between a pair of metal layers and can be considered to be placed in a non-oxidizing atmosphere, so the fire resistance is about 3000° C., and graphite can be used as a base layer in the same manner as ceramics.

In this embodiment, in order to obtain the effect of diffusing the heat that reaches the composite layer by conductive heat transfer, either the metal layer or the base layer has a higher thermal conductivity than the insulating material. When the base layer has a higher thermal conductivity than the insulating material, the specific value of the thermal conductivity of the base layer is preferably 10 (W/m·K) or more, and more preferably 100 (W/m·K) or more.

Examples of ceramics that can be used as the base layer include AlN, SiC, TiN, etc. Among these, AlN and SiC have high thermal conductivity, and therefore are highly effective in propagating heat that reaches the base layer in the planar direction, and can further suppress heat transfer.
As described above, in this embodiment, graphite can also be suitably used as the material for the base layer.

The thickness of the base layer is preferably 30 μm or more, and more preferably 100 μm or more. On the other hand, taking into consideration the overall thickness of the thermal control sheet, the thickness of the metal layer is preferably 300 μm or less, and more preferably 200 μm or less.

(Metal Layer)
Since the metal layer has the effect of suppressing radiative heat transfer from the battery cell, the metal layer is assumed to have a lower emissivity than the insulating material described below. The specific value of the emissivity of the metal layer is preferably less than 0.5, and more preferably less than 0.2.
In this embodiment, in order to have the effect of diffusing the heat that reaches the composite layer by conductive heat transfer, one of the metal layer and the base layer is made to have a higher thermal conductivity than the insulating material. When the metal layer has a higher thermal conductivity than the insulating material, the specific value of the thermal conductivity of the metal layer is preferably 10 (W/m·K) or more, and more preferably 100 (W/m·K) or more.

When the metal layer is disposed near the battery cell, in order to prevent the metal layer from being damaged by melting, etc., even if the temperature of the battery cell rises significantly in the event of an abnormality, the material constituting the metal layer is preferably a metal with a melting point of 600°C or higher. Furthermore, it is more preferable that the material constituting the metal layer is a metal with a melting point of 900°C or higher.

As the material for the metal layer, it is preferable to use 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. Of these materials, stainless steel and silver have melting points of approximately 1400°C and approximately 960°C, respectively, and are unlikely to melt even if the battery cell becomes hot, so they can be used near the battery cell. Furthermore, stainless steel and silver are less likely to oxidize than other metals, and their emissivity increases less even when exposed to high temperatures. Therefore, when the composite layer is placed near the battery cell, stainless steel, silver, or a silver alloy can be preferably used as the material for the metal layer.

On the other hand, when the composite layer is disposed at a position away from the battery cell, there is no need to consider the effects of oxidation and melting due to heat, so aluminum or aluminum alloys, copper or copper alloys, and silver or silver alloys, which have excellent thermal conductivity, can be suitably used as materials for the metal layer.

The thermal conductivity of the metals mentioned above as materials for the metal layer is 10 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 metal layer can be efficiently diffused. In terms of specific thermal conductivity compared to the insulating material, the thermal conductivity of the metal layer is preferably 10 times or more, and more preferably 100 times or more, of the thermal conductivity of the insulating material.

In order to fully obtain the effect of suppressing radiative heat transfer by the metal layer and the effect of diffusing heat by conductive heat transfer, the thickness of the metal 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 metal layer is preferably 300 μm or less, and more preferably 200 μm or less.

The above composite layer can be obtained, for example, by forming a metal layer on both sides of a central base layer by wet plating or vapor deposition, or by laminating metal foil on both sides of the base layer.

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

<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.

<Heat dissipation layer>
The thermal control sheet for a battery pack according to this embodiment may have a heat dissipation layer in addition to the composite layer and the heat insulating material. The heat dissipation layer has the effect of suppressing radiative heat transfer to the next layer and the effect of diffusing heat that has reached the heat dissipation layer by conductive heat transfer. Therefore, the heat dissipation layer has a lower emissivity and a higher thermal conductivity than the heat insulating material. The specific value of the emissivity of the heat dissipation 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 heat dissipation layer is preferably 5 (W/m·K) or more, and more preferably 15 (W/m·K) or more.
The thermal conductivity and emissivity of the heat dissipation layer can be calculated in the same manner as for the composite layer.

The heat dissipation layer is preferably made of, for example, a metal or ceramic. When a metal is used as the material for the heat dissipation 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 heat dissipation layer may be a laminated material obtained by laminating two or more metals selected from the materials of the heat dissipation layer. When a laminated material is used as the heat dissipation 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 heat dissipation layers include an aluminum/copper/aluminum heat dissipation layer, an aluminum/silver/aluminum heat dissipation layer, a nickel/stainless steel/nickel heat dissipation layer, and a silver/stainless steel/silver heat dissipation layer. The aluminum, copper, and silver in the heat dissipation layer may each be in the form of an alloy.
The laminated material can be obtained by forming metal films on both sides of a central metal plate by wet plating or vapor deposition, or by laminating metal foils made of different materials.

When ceramic is used as the material for the heat dissipation layer, AlN, SiC, TiN, etc., which are suitable as the base layer in the above composite layer, can be used.

As shown in FIG. 5, when the heat dissipation layer is disposed near the battery cell, in order to prevent the heat dissipation layer from being damaged by melting, etc., even if the temperature of the battery cell rises significantly in the event of an abnormality, the material constituting the metal layer is preferably a metal with a melting point of 600°C or higher. Furthermore, it is more preferable that the material constituting the metal layer is a metal with a melting point of 900°C or higher.

When the heat dissipation layer is disposed near the battery cell, stainless steel, silver, or a silver alloy can be suitably used as the material for the heat dissipation layer for the same reasons as for the metal layer. For the same reasons, ceramics such as AlN, SiC, and TiN can also be suitably used.

On the other hand, when the heat dissipation layer is positioned at a position separated from the battery cell, for the same reasons as for the metal layer, aluminum or an aluminum alloy, copper or a copper alloy, or silver or a silver alloy can be suitably used as the material for the heat dissipation layer.
However, since the emissivity varies depending on the type of material and the surface condition, in order to further improve the effect of suppressing radiative heat transfer, it is preferable to select the material of the heat dissipation layer taking into consideration the surface condition, etc.

As with the metal layer, the thermal conductivity of the heat dissipation layer is preferably at least 10 times, and more preferably at least 100 times, the thermal conductivity of the insulating material.

In order to obtain a sufficient heat diffusion effect by conductive heat transfer, the thickness of the heat dissipation 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 heat dissipation layer is preferably 300 μm or less, and more preferably 200 μm or less.
Furthermore, the heat dissipation layer may be a single layer or may be a laminate of multiple thin films made of the same material, as shown in Figures 4 and 5. When the heat dissipation 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 heat dissipation layer made of a single layer. Therefore, even if the heat dissipation layer is made of multiple layers, it is preferable that the total thickness is within the above range.

<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 composite layer by the above-mentioned method, preparing a heat insulating material and, if necessary, a heat dissipation layer, and arranging them in a desired order. These layers may or may not be bonded to each other. If 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 composite layer and the insulating material. Therefore, it can be adapted to any shape, regardless of 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.

The composite layer 12 was prepared by forming metal layers 11a and 11b made of aluminum on both sides of a base layer 14 made of AlN, and stainless steel plates were prepared as heat dissipation layers 15a and 15b. In addition, alumina fiber sheets were prepared as heat insulating materials 13a and 13b, and a thermal control sheet for a battery pack 60 was prepared as an example of the invention by laminating the composite layer 12, the heat dissipation layers 15a and 15b, and the heat insulating materials 13a and 13b as shown in FIG. 5. In addition, as a comparative example, a thermal control sheet excluding the composite layer 12 of the example of the invention and a thermal control sheet made only of a thermal insulating material were prepared. As a thermal insulating material, in addition to the alumina fiber sheet, a thermal insulating material made of an aerogel blanket and a thermal insulating material made of glass fiber were prepared. After that, the effect of thermal control on the presence or absence of a metal layer or a heat dissipation layer was evaluated for the obtained thermal control sheet.

Fig. 6 is a cross-sectional view showing a typical method for evaluating the effect of thermal control, and Fig. 7 is a perspective view showing the size of the thermal control sheet used in this example.
As shown in Fig. 6, an Fe jig 16 heated to 800 ° C. in an electric furnace was placed on one side (surface of the heat dissipation layer 15a) of the thermal control sheet 60 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 heat dissipation layer 15b) of the thermal control sheet 60, and the effect of thermal control was evaluated. Similarly, for the comparative example, the thermal control sheet 60 shown in Figs. 6 and 7 was replaced with a test piece of the comparative example to evaluate the effect of thermal control.

As shown in FIG. 7, the thermal control sheet 60 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 60, 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 60 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 table below, "SUS" stands for stainless steel, and [Al/AlN/Al] stands for [aluminum/aluminum nitride (ceramic)/aluminum] composite layer. Also, "AF" stands for alumina fiber, and "AG-F" stands for aerogel blanket, both trade names of SHENZHEN AEROGEL TECHNOLOGY CO., LTD. "GF" stands for glass fiber. Furthermore, "-" in the thickness column indicates that the target layer was not formed.

In the composite layer, the thermal conductivity of the aluminum plate used as the material of the metal layer was 200 (W/m·K), and the thermal conductivity of the stainless steel plate used as the material of the heat dissipation layer was 16 (W/m·K). The emissivity of both the aluminum plate and the stainless steel plate was approximately 0.2.
Furthermore, the thermal conductivity of the alumina fiber used was 0.05 (W/m K) and the emissivity was 0.8. The thermal conductivity of the aerogel blanket (AG-F) was 0.02 (W/m K) and the emissivity was 0.8. The thermal conductivity of the glass fiber (GF) was 0.05 (W/m K) and the emissivity was 0.8.

As shown in Table 2 above, since Example No. 1 is a thermal control sheet according to an embodiment of the present invention, the composite layer and the heat dissipation layer can suppress radiative heat transfer and provide a diffusion effect through conductive heat transfer, resulting in excellent heat insulation.
In contrast, Comparative Examples Nos. 1 to 4 did not have a composite layer or were made of only a heat insulating material, and therefore had a lower heat insulating effect than the invention examples.

When comparing Example No. 1 and Comparative Example No. 1, the total basis weight of the insulating material is the same, the heat dissipation layer is also the same, and the only difference is the presence or absence of a composite layer, but Example No. 1 showed a significantly better insulating effect. This shows that the composite layer has a significant impact on the insulating effect.

10, 40, 50, 60 Thermal control sheet for assembled battery 11a, 11b Metal layer 12, 12a, 12b Composite layer 13a, 13b Heat insulating material 14 Base layer 15, 15a, 15b Heat dissipation layer 17 Thermocouple 20a, 20b, 20c Battery cell 30 Battery case 100 Battery assembly

Claims (15)

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,
At least one composite layer;
At least one layer of insulation;
The composite layer includes a base layer made of ceramic or graphite and a metal layer disposed on both sides of the base layer;
The metal layer has a lower emissivity than the thermal insulation material,
A thermal control sheet for a battery pack, characterized in that both the metal layer and the base layer have a thermal conductivity higher than that of the insulating material. Two or more layers of the insulation material;
2. The thermal control sheet for a battery pack according to claim 1, further comprising: the composite layer disposed between adjacent ones of the insulating materials. Two or more of the composite layers;
2. The thermal control sheet for a battery pack according to claim 1, further comprising: the heat insulating material disposed between adjacent ones of the composite layers. The thermal control sheet for a battery pack according to any one of claims 1 to 3, characterized in that the base layer is made of one material selected from AlN, SiC, TiN, and graphite. 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 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 5, characterized in that the thermal conductivity of the metal layer is 10 times or more the thermal conductivity of the insulating material and is 10 to 450 (W/m·K) . The thermal control sheet for a battery pack according to any one of claims 1 to 6, characterized in that the metal 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. Further, the device has at least one heat dissipation layer,
The heat insulating material is disposed between the heat dissipation layer and the composite layer,
The thermal control sheet for a battery pack according to any one of claims 1 to 7, wherein the heat dissipation layer has a lower emissivity than the insulating material and a higher thermal conductivity than the insulating material. A pair of the heat dissipation layers;
the composite layer disposed between the pair of heat dissipation layers;
9. The thermal control sheet for a battery pack according to claim 8, further comprising a heat insulating material disposed between the heat dissipation layer and the composite layer. A pair of the composite layers;
the heat dissipation layer disposed between the pair of composite layers;
9. The thermal control sheet for a battery pack according to claim 8, further comprising a heat insulating material disposed between the composite layer and the heat dissipation layer. The thermal control sheet for a battery pack according to any one of claims 8 to 10, characterized in that the heat dissipation 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 any one of claims 8 to 10, characterized in that the heat dissipation layer is a laminate of 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. The thermal control sheet for a battery pack according to any one of claims 1 to 12, characterized in that the insulating material contains at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles. The thermal control sheet for a battery pack according to claim 13, 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;
A battery pack comprising: the thermal control sheet for a battery pack according to any one of claims 1 to 14, which is interposed between the plurality of battery cells.

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