JP7628067B2 - Fire-prevention cell unit, its manufacturing method, and battery - Google Patents

Description

The present invention relates to a fire-proof cell unit that includes a fire-proof sheet in a battery cell, a manufacturing method thereof, and a battery that includes the fire-proof cell unit.

Currently, there is a growing movement around the world to gradually replace conventional gasoline or diesel vehicles with electric vehicles in order to reduce the burden on the global environment. Electric vehicles are becoming more and more popular, particularly in European countries such as France, the Netherlands, and Germany, as well as in China.

Various batteries, such as the above-mentioned automobile batteries, may go into thermal runaway due to some reason, resulting in fire, smoke, etc. In recent years, automobile batteries in which multiple battery cells are arranged and mounted inside a housing have become known. In such batteries in which multiple battery cells are arranged and mounted, if one battery cell ignites or emits smoke, etc., there is a risk that the heat will be transferred to the surrounding battery cells, causing even more serious problems such as fire, smoke, and explosion. In order to minimize damage caused by such problems, methods have been considered that make it difficult for heat from abnormally hot battery cells to be transferred to the surrounding battery cells. For example, a method of providing a fire-prevention sheet such as a fire-resistant material or a heat-insulating layer between multiple battery cells has been known for some time (see Patent Document 1).

JP 2018-206604 A

Fire prevention sheets are required to have low hardness and be easily deformed in order to reduce damage to the sheet even if the battery cells expand due to overheating. In addition, it is preferable for the sheet to contain air in order to improve the heat insulating properties of the fire prevention sheet. In order to meet the above demand, the inventors came up with the idea of providing a porous rubber sheet on the side of the battery cell and sandwiching the sheet between the battery cells. The inventors carried out development to further improve the heat insulating properties of the porous rubber sheet and completed the present invention. The present invention also contributes to the achievement of the applicant's sustainable development goal of "ensuring access to affordable, reliable, sustainable and modern energy for all".

The present invention has been made in consideration of the above problems, and aims to provide a fire-prevention cell unit that is equipped with a fire-prevention sheet that is easily deformed in response to overheating expansion of the battery cell and has excellent thermal insulation properties, a manufacturing method thereof, and a battery.

(1) A fire spread prevention cell unit according to one embodiment for achieving the above object comprises:
A battery cell;
a fire prevention sheet attached to a side surface of the battery cell in a direction in which the battery cells are arranged;
Equipped with
The fire spread prevention sheet is a porous sponge sheet,
The holes in the fire prevention sheet are elongated and oriented with their length along the surface of the fire prevention sheet.
(2) In another embodiment of the fire spread prevention unit, the adhesion of the surface of the fire spread prevention sheet that is attached to the battery cell may preferably be higher than the adhesion of the outer surface that is located on the opposite side in the thickness direction of the fire spread prevention sheet to the adhesion surface.
(3) In the fire spread prevention unit according to another embodiment, preferably, the fire spread prevention sheet may further include a flame retardant material.
(4) In the fire prevention unit according to another embodiment, the fire prevention sheet may preferably be made primarily of silicone rubber.
(5) In order to achieve the above object, a method for manufacturing a fire spread prevention type cell unit according to one embodiment is a method for manufacturing any one of the fire spread prevention type cell units described above, comprising the steps of:
a clamping step of sandwiching the curable composition that becomes a fire spread prevention sheet after curing between plates;
a hardening step of producing a sponge-like hardened body by foaming the mixture after the clamping step so that the length direction of the holes is oriented in the clamping direction between the plates;
A sheet forming process in which the hardened body is formed into a sheet having a length direction of the hole along the surface of the fire spread prevention sheet;
a step of attaching the fire spread prevention sheet after the sheet forming step to a side surface located in a direction in which the battery cells are arranged;
Includes.
(6) In order to achieve the above object, a battery according to one embodiment includes a plurality of fire-spread prevention cell units as described above arranged in a row.

The present invention provides a fire-proof cell unit that is equipped with a fire-proof sheet that is easily deformed in response to the overheating expansion of the battery cell and has excellent thermal insulation properties, as well as a manufacturing method thereof and a battery.

FIG. 1 is a perspective view for explaining the configuration of a fire spread prevention type cell unit according to an embodiment of the present invention. FIG. 2 shows a cross-sectional view of the fire spread prevention type cell unit taken along line AA of FIG. FIG. 3A shows the fire spread prevention cell unit of FIG. 1 as viewed from the outer surface side of the fire spread prevention sheet, and FIG. 3B shows a modified example of the fire spread prevention cell unit as viewed from the outer surface side. FIG. 4 shows a flow of a manufacturing process for a fire spread prevention cell unit according to an embodiment of the present invention, and cross-sectional views of a representative form in each process. FIG. 5 shows a diagram for explaining the method of the thermal conductivity test. FIG. 6 shows a diagram for explaining the results of the thermal conductivity test (5 minutes after the start of heating). FIG. 7 shows a diagram for explaining the results of the thermal conductivity test (30 minutes after the start of heating). FIG. 8 is a perspective view showing a state in which a fire spread prevention type cell unit is being loaded into a battery according to an embodiment, and a state after the loading is completed.

Next, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below does not limit the invention according to the claims, and not all of the elements and combinations thereof described in the embodiment are necessarily essential to the solution of the present invention.

1. Fire-Spread-Prevention Cell Unit First, a fire-spread-prevention cell unit according to an embodiment of the present invention will be described with reference to the drawings.

Figure 1 shows a perspective view for explaining the configuration of a fire spread prevention type cell unit according to an embodiment of the present invention. Figure 2 shows a cross-sectional view of the fire spread prevention type cell unit of Figure 1 along line A-A and an enlarged view of part B.

The fire-proof cell unit 1 according to this embodiment includes a battery cell 20 and a fire-proof sheet 10 attached to a side surface in the direction in which the battery cells 20 are arranged. More specifically, the fire-proof cell unit 1 is a unit formed by integrating the battery cell 20 with the fire-proof sheet 10 attached to at least one of the two sides in the direction in which the battery cells 20 are arranged. The fire-proof sheet 10 is disposed between a plurality of battery cells 20 inside the battery, and is a sheet capable of preventing fire spread by suppressing heat transfer to other battery cells 20 when the battery cell 20 is in an overheated state. The fire-proof sheet 10 is used by attaching its widest surface to the battery cell 20. A single structure in which the fire-proof sheet 10 is attached to the battery cell 20 is called the fire-proof cell unit 1. In this embodiment, the fire-proof sheet 10 is in close contact with the battery cell 20, and can be attached without an adhesive or other layer. There are no particular restrictions on the thickness of the fire prevention sheet 10, but it is preferably 1 to 20 mm, and more preferably 2 to 8 mm.

In the fire spread prevention sheet 10, the adhesion of the attachment surface 11 to the battery cell 20 is preferably higher than the adhesion of the outer surface 12 located on the opposite side of the thickness direction of the fire spread prevention sheet 10 from the attachment surface 11. As a result, each fire spread prevention cell unit 1 can be easily loaded into or removed from the battery. In this application, "adhesion" is interpreted as being different from "bonding" or "adhesion" and as being in a state that can be repeatedly attached.

In this embodiment, the attachment surface 11 where the fire spread prevention sheet 10 is attached to the battery cell 20 is a surface with high smoothness, and is a surface that can be adhered closely to the widest surface (side surface) of the battery cell 20 with almost no air intervening between it and the surface. The surface roughness of the attachment surface 11 is smaller than the surface roughness of the outer surface 12, when compared in terms of the arithmetic mean height (Sa) based on "ISO 25178 Surface Quality".

When using a standard other than Sa, it is preferable to use the maximum height (Sz) based on "ISO 25178 Surface Quality" as the standard. The surface roughness of the attachment surface 11 is smaller than the surface roughness of the outer surface 12 when compared in terms of the maximum height (Sz) value based on "ISO 25178 Surface Quality". Note that Sa and Sz are measured while avoiding open holes 15 on the attachment surface 11 and the outer surface 12.

When the fire spread prevention sheet 10 is manufactured by molding, the roughness of the attachment surface 11 and the outer surface 12 can be easily obtained by transferring the roughness of the inner surface of the mold or the resin sheet placed in the mold. In addition, if the surface roughness of the outer surface 12 is to be made larger, a blasting process in which fine particles are collided may be performed. In this way, when the surface roughness of the outer surface 12 is made larger than that of the attachment surface 11, it becomes easier to load or pull out one fire spread prevention cell unit 1 from among the multiple fire spread prevention cell units 1 into or from the battery housing. This is because when the fire spread prevention cell unit 1 is loaded or pulled out, the fire spread prevention cell unit 1 is unlikely to adhere to the adjacent fire spread prevention cell unit 1. In particular, the multiple fire spread prevention cell units 1 in the battery are often compressed from the outside in the column direction of the fire spread prevention cell unit 1 after being loaded into the battery. Even in such a case, if the surface roughness of the outer surface 12 is large, the situation in which the fire spread prevention cell units 1 adhere to each other can be reduced. Furthermore, making the attachment surface 11 smooth increases the adhesion between the fire spread prevention sheet 10 and the side of the battery cell 20, making it easier to load or pull out each fire spread prevention cell unit 1 into or from the battery.

The means for making the outer surface 12 less adhesive than the attachment surface 11 is not limited to providing a difference in surface roughness as described above, and other means may be used. For example, the fire spread prevention sheet 10 may be made up of two layers of sheets, with the sheet on the outer surface 12 side being harder than the sheet on the attachment surface 11 side.

In this embodiment, the fire spread prevention sheet 10 is approximately the same size as the widest surface (side surface) of the battery cell 20, but it may be larger or smaller than that side surface. However, to improve fire spread prevention, it is preferable that the fire spread prevention sheet 10 be the same size as or larger than the side surface of the battery cell 20.

In this embodiment, the fire spread prevention sheet 10 is a porous sponge sheet. This sponge sheet has holes 15 that are preferably 40 to 95 volume %, more preferably 60 to 90 volume %, of the total volume of the sheet. The air in the holes 15 of the sponge sheet gives the fire spread prevention sheet 10 excellent heat insulation. Therefore, the fire spread prevention sheet 10 contributes to low thermal conductivity between adjacent battery cells 20. The holes 15 have an elongated shape, that is, an anisotropic shape, and the length direction of the holes 15 is oriented along the surface of the fire spread prevention sheet 10. The length direction of the holes 15 is a direction that is approximately perpendicular (90 degrees ± 5 degrees) to the thickness direction of the fire spread prevention sheet 10. However, some of the multiple holes 15 may have a shape other than an elongated shape, or may have an elongated shape but not be oriented in a direction approximately perpendicular to the thickness direction. At least 50% of all holes 15, preferably at least 70%, and more preferably at least 90% should be elongated and have their length oriented in a direction that is approximately perpendicular to the thickness direction of the fire prevention sheet 10.

As shown in FIG. 2, in the fire spread prevention sheet 10, the elongated holes 15 are oriented so that the length of the holes 15 faces in the direction along the sheet surface. In this case, the thermal conductivity (S1) in the thickness direction of the fire spread prevention sheet 10 is lower than the thermal conductivity (S2) in the length direction of the holes 15 (the height direction of the battery cells 20 in FIG. 2). Therefore, the fire spread prevention sheet 10 can reduce thermal conduction between adjacent battery cells 20.

The fire spread prevention sheet 10 is mainly made of resin or rubber, and preferably made of rubber. Examples of rubber include thermosetting elastomers such as silicone rubber, urethane rubber, isoprene rubber, ethylene propylene rubber, natural rubber, ethylene propylene diene rubber, nitrile rubber (NBR), or styrene butadiene rubber (SBR); thermoplastic elastomers such as urethane-based, ester-based, styrene-based, olefin-based, butadiene-based, and fluorine-based elastomers, or composites thereof. Of rubbers, silicone rubber, which has relatively high heat resistance, is more preferably used. The fire spread prevention sheet 10 is preferably made mainly of silicone rubber. The fire spread prevention sheet 10 is more preferably a porous sponge sheet made of silicone rubber. In this application, "mainly" or "main material" is interpreted as being more than 50% by mass of the entire constituent materials.

It is preferable that the fire spread prevention sheet 10 contains a flame retardant material to further enhance the fire spread prevention performance. The flame retardant material is preferably one or more inorganic compounds such as carbon (including amorphous carbon and graphite), halides, phosphorus compounds, platinum, platinum complexes, magnesium hydroxide, and aluminum hydroxide. The flame retardant material is preferably contained in an amount of 0.5 to 20 mass %, more preferably 1 to 20 mass %, based on the total mass of the fire spread prevention sheet 10.

Figure 3 shows (A) the fire-spread-prevention cell unit of Figure 1 as viewed from the outer surface side of the fire-spread-prevention sheet, and (B) a view of a modified example of the fire-spread-prevention cell unit as viewed from its outer surface.

In this embodiment, the direction of the longest side, the direction of the second longest side, and the direction of the shortest side of the battery cell 20 are referred to as the height direction, the width direction, and the thickness direction, respectively. In A, the holes 15 are oriented along the surface of the fire prevention sheet 10 and such that the length direction of the holes 15 faces the height direction of the battery cell 20. On the other hand, in B, the holes 15 are oriented along the surface of the fire prevention sheet 10 and such that the length direction of the holes 15 faces the width direction of the battery cell 20. In both cases A and B, the length direction of the holes 15 is approximately perpendicular to the thickness direction of the fire prevention sheet 10. Therefore, in both cases A and B, the fire prevention sheet 10 effectively contributes to reducing the thermal conductivity between adjacent battery cells 20. In addition, the length direction of the holes 15 may be oriented between the height direction and the width direction of the battery cell 20, i.e., diagonally, in addition to the height direction and width direction of the battery cell 20.

2. Manufacturing Method of Fire-Spread-Resistant Cell Unit Next, a manufacturing method of a fire-spread-resistant cell unit according to an embodiment of the present invention will be described with reference to the drawings.

Figure 4 shows the flow of the manufacturing process for a fire-spread prevention cell unit according to an embodiment of the present invention, and cross-sectional views of representative forms at each step.

The method for manufacturing the fire-spread-prevention cell unit according to this embodiment is a method for manufacturing the above-mentioned fire-spread-prevention cell unit 1, and includes a clamping process (S101), a hardening process (S102), a sheet forming process (S103), and an attachment process (S104). Each process will be described in detail below.

(1) Clamping step (S101)
This step is a step of sandwiching the curable composition 26, which will become a fire spread prevention sheet after curing, between plates 25. The curable composition 26 is preferably capable of retaining its shape, and is, for example, in a semi-cured state that is not completely cured. The curable composition 26 sandwiched between plates 25 preferably has a cylindrical, rectangular column, or a similar shape. The curable composition 26 contains, for example, an organic foaming agent for foaming during curing. Examples of the foaming agent include azobisisobutyronitrile (AIBN) and azodicarbonamide (ADCA). As an example of a method that does not contain an organic foaming agent, a method of using a curable composition 26 in which thermally expandable resin beads are added to rubber can be mentioned. In this case, the resin beads become balloon-like during curing, and a sponge-like cured body can be obtained. As another example of a method that does not contain an organic foaming agent, a method of using a curable composition 26 in which air has been mixed into a non-foaming liquid rubber under high pressure can be mentioned. In this case, a sponge-like cured body can be obtained by curing the curable composition 26 under normal pressure. In any foaming method, in the clamping step, the foamable curable composition 26 is clamped from both sides by plates 25. There are no limitations on the material of the plates 25 as long as it is possible to maintain the shape of the curable composition 26 when it is cured, and for example, a metal plate, typically an aluminum plate, or a resin plate, typically a polyethylene terephthalate plate, can be used.

(2) Curing process (S102)
This step is a step of producing a sponge-like cured body 27 by foaming the composition 26 so that the length direction of the holes 15 faces the clamping direction of the plates 25 after the clamping step. The side of the curable composition 26 is not in contact with the plates 25. Therefore, heat is transferred to the side faster than the upper and lower surfaces in contact with the plates 25. Therefore, the side region is easily cured before foaming. As a result, inside the curable composition 26, the holes 15 are easily oriented toward the plate 25 and become elongated. In this way, a sponge-like cured body 27 having elongated holes 15 in the direction of the plate 25 is completed. When a curable silicone rubber composition is used as the curable composition 26, the composition is heated in this step.

(3) Sheet forming process (S103)
This step is a step of shaping the hardened body 27 after the hardening step into a sheet having a shape in which the length direction of the holes 15 is oriented along the surface of the fire spread prevention sheet 10. An exemplary shaping method is a method of cutting out a sheet from the hardened body 27. Instead of cutting out, a cutting and/or polishing technique may be used. In addition, a step of making the adhesion of the attachment surface 11 and the outer surface 12 of the fire spread prevention sheet 10 different may be performed during this step or immediately after this step. When the outer surface 12 is processed to have a rougher surface than the attachment surface 11, the outer surface 12 may be subjected to a blasting treatment. When the attachment surface 11 is processed to have a smoother surface than the outer surface 12, the attachment surface 11 may be mirror-polished.

(4) Attachment process (S104)
This step is a step of attaching the fire spread prevention sheet 10 after the sheet forming step to the side located in the arrangement direction of the battery cells 20. A typical attachment method is attachment without using any adhesive, but an adhesive or double-sided tape can also be interposed between the fire spread prevention sheet 10 and the side of the battery cells 20.

3. Thermal Conduction Test Next, the method and results of the thermal conduction test with different hole directions will be described.

Figure 5 shows a diagram to explain the thermal conductivity test method.

First, a foamed silicone rubber test piece V (30 mm diameter x 10 mm thickness) with holes 15 long in the vertical direction and a foamed silicone rubber test piece H (30 mm diameter x 10 mm thickness) with holes 15 long in the horizontal direction were prepared, and cut vertically to expose the cross section. A digital microscope (manufactured by Keyence Corporation) was used for cross-sectional observation. Measurements were also performed using a specific gravity meter (manufactured by Alpha Mirage Corporation), and it was confirmed that both test pieces V and H had a specific gravity of 0.23 g/cm ^3. From this result, it was determined that both test pieces V and H had almost the same porosity. FIG. 5 shows cross-sectional photographs of both test pieces V and H and diagrams showing them diagrammatically. From the photograph and diagram of FIG. 5, it can be seen that test piece V has holes 15 long in the vertical direction, and test piece H has holes 15 long in the horizontal direction.

Figure 6 shows a diagram to explain the results of the thermal conductivity test (5 min after the start of heating). Figure 7 shows a diagram to explain the results of the thermal conductivity test (30 min after the start of heating).

Both test pieces V and H were placed on the hot plate 30 and heated to about 150°C. In this test, both test pieces V and H were heated from the bottom. Figures 6 and 7 show the temperature distributions of both test pieces V and H photographed with a thermography camera 5 minutes (a) and 30 minutes (b) after the start of heating. Note that different test pieces were photographed in (a) and (b). The temperature distributions were observed using a thermography camera (manufactured by Nippon Avionics Co., Ltd.). The "cell grain direction" in Figures 6 and 7 refers to the long direction of the holes 15. The horizontal stripes in both test pieces V and H show the temperature distribution, with the zones closer to the hot plate 30 having higher temperatures.

Comparing the temperature distributions of both test pieces V and H, it was found that the temperature line of approximately 70°C (position indicated by the white arrow) was lower for test piece H under both conditions, 5 minutes and 30 minutes after the start of heating (see the white line at the position indicated by the arrow). Similarly, when looking at the line of temperatures higher than 70°C, it was found that test piece H was in a lower position. From these results, it was found that test piece H, which has holes 15 that are longer in the horizontal direction, has a lower thermal conduction rate than test piece V, which has holes 15 that are longer in the vertical direction.

4. Battery Next, a battery according to an embodiment of the present invention will be described with reference to the drawings. The fire spread prevention type cell unit 1 according to the embodiment described above is loaded inside the battery.

Figure 8 shows an oblique view of the situation in which a fire-prevention cell unit is loaded into a battery according to an embodiment, and the situation after loading is complete.

The battery 40 according to this embodiment is, for example, a battery for an electric vehicle, and includes a plurality of battery cells 20 arranged side by side. The number of battery cells 20 is 12 in this embodiment, but may be 2 to 11 or 13 or more. The battery 40 is a storage battery, preferably a lithium ion battery. The battery 40 includes a bottomed housing 41 that opens on one side. The battery cells 20 are arranged inside 44 of the housing 41. The plurality of battery cells 20 are preferably applied with a force in a compressive direction from both sides of the housing 41 using a screw or the like, so that they are in close contact with each other (not shown). The bottom 42 (an example of a cooling portion) of the housing 41 is provided with one or more water-cooled pipes 43 for flowing cooling water, which is an example of a coolant 45. The coolant 45 may be referred to as a cooling medium or a coolant. The battery cells 20 are arranged in the housing 41 with a fire prevention sheet 10 sandwiched between adjacent battery cells 20. The fire-prevention sheet 10 is attached to the battery cell 20 to form a single fire-prevention cell unit 1. The fire-prevention cell unit 1 is loaded toward the inside 44 of the housing 41 (see the direction of arrow C).

The fire prevention sheet 10 arranged between the battery cells 20 is a porous sheet with the length direction of the holes 15 oriented in a direction parallel to the plane of the fire prevention sheet 10 and approximately perpendicular to the thickness direction of the fire prevention sheet 10. Therefore, the fire prevention sheet 10 can reduce thermal conduction when heat from an overheated battery cell 20 is conducted to an adjacent battery cell 20. As a result, the fire prevention sheet 10 is a sheet with a high fire spread prevention effect between the battery cells 20.

5. Other Embodiments Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and can be practiced in various modifications.

In the above embodiment, the comparison of the surface roughness of the attachment surface 11 and the outer surface 12 is performed using the arithmetic mean height (Sa) or maximum height (Sz) based on "ISO 25178 Surface Quality". However, instead of this, a similar comparison can be performed using the calculated mean roughness (Ra) or maximum height (Rz) based on JIS B 0601. In this case, the Ra (or Rz) of the attachment surface 11 is smaller than the Ra (or Rz) of the outer surface 12.

There are no particular restrictions on the length-to-short ratio (aspect ratio) of the hole 15 as long as it exceeds 1, but it is preferably 2 or more, and more preferably 3 or more.

It is preferable that the fire prevention sheet 10 can be repeatedly attached to the side of the battery cell 20. However, the fire prevention sheet 10 may be fixed to the side of the battery cell 20 so that it cannot be repeatedly attached.

The components of each of the above-described embodiments can be freely combined, except in cases where they cannot be combined with each other.

The present invention can be used in the field of batteries.

1: Fire-proof cell unit, 10: Fire-proof sheet, 11: Application surface, 12: Outer surface, 15: Hole, 20: Battery cell, 25: Plate, 26: Curable composition, 27: Cured body, 40: Battery.

Claims (6)

A battery cell;
a fire prevention sheet attached to a side surface of the battery cell in a direction in which the battery cells are arranged;
Equipped with
The fire spread prevention sheet is a porous sponge sheet,
The porous sponge sheet has a plurality of holes containing air inside the sheet,
A fire-spread-preventive cell unit, wherein the holes have an elongated shape and are oriented with their length direction along the surface of the fire-spread-preventive sheet. The fire spread prevention cell unit according to claim 1, characterized in that the adhesion of the surface of the fire spread prevention sheet that is attached to the battery cell is higher than the adhesion of the outer surface located on the opposite side of the fire spread prevention sheet in the thickness direction from the adhesion surface. The fire-prevention cell unit according to claim 1 or 2, characterized in that the fire-prevention sheet further contains a flame-retardant material. A fire-proof cell unit according to any one of claims 1 to 3, characterized in that the fire-proof sheet is made primarily of silicone rubber. A method for producing the fire spread prevention type cell unit according to any one of claims 1 to 4, comprising the steps of:
a clamping step of sandwiching the curable composition that becomes a fire spread prevention sheet after curing between plates;
a hardening step of producing a sponge-like hardened body by foaming the mixture after the clamping step so that the length direction of the holes is oriented in the clamping direction between the plates;
A sheet forming process in which the hardened body is formed into a sheet having a length direction of the hole along the surface of the fire spread prevention sheet;
a step of attaching the fire spread prevention sheet after the sheet forming step to a side surface located in a direction in which the battery cells are arranged;
A method for manufacturing a fire-spread prevention cell unit, comprising: A battery comprising a plurality of fire-prevention cell units according to any one of claims 1 to 4 arranged side by side.