JP7414928B2 - Method for manufacturing heat insulating sheet for assembled battery and method for manufacturing assembled battery - Google Patents

Description

The present invention relates to a heat insulating sheet for an assembled battery interposed between battery cells of an assembled battery, and an assembled battery in which a heat insulating sheet for an assembled battery is interposed between the battery cells.

2. Description of the Related Art Conventionally, in order to suppress heat transfer from a heat generating element to other objects, a heat insulating sheet has been used that is placed close to a heat generating element or is used with at least a portion thereof in contact with the heat generating element.

Furthermore, in recent years, from the viewpoint of environmental protection, the development of electric vehicles, hybrid vehicles, etc. driven by electric motors has been actively promoted. This electric vehicle, hybrid vehicle, etc. is equipped with an assembled battery in which a plurality of battery cells are connected in series or in parallel to serve as a power source for a driving electric motor.

Lithium ion secondary batteries, which are capable of higher capacity and higher output than lead-acid batteries, nickel-metal hydride batteries, etc., are mainly used for these battery cells. In a battery that is capable of high capacity and high output, if a certain battery cell suddenly rises in temperature due to an internal short circuit or overcharging of the battery, and a thermal runaway occurs in which it continues to generate heat, Heat from a battery cell that has experienced thermal runaway may propagate to other adjacent battery cells, potentially causing thermal runaway in the other battery cells.

In the field of assembled batteries as mentioned above, various heat insulating sheets are used between battery cells in order to suppress the propagation of heat from a battery cell that has experienced thermal runaway to adjacent battery cells, and to prevent a chain reaction of thermal runaway. is proposed. For example, Patent Document 1 discloses a power storage device in which two plates are arranged facing each other between two adjacent power storage elements, and a space formed between these plates functions as a low thermal conductivity layer. There is. Note that, in the above-mentioned power storage device, for example, a damper material made by collecting and bonding mica pieces is used as the plate material.

By the way, in an assembled battery, each battery cell causes thermal expansion by repeating charging and discharging, and pressing force repeatedly acts between adjacent battery cells. In the heat transfer suppressing sheet described in Patent Document 1, since the low thermal conductivity layer is an air layer, it cannot be said that the sheet has sufficient mechanical strength to withstand such repeated pressing forces.

In addition, since a battery cell that has experienced thermal runaway undergoes large thermal expansion, the pressing force on adjacent battery cells becomes excessive. There is also a concern that the plate material made of dammar material or the like may be damaged due to the large pressing force.

Therefore, Patent Document 2 proposes a heat insulating material having a composite layer of a fiber sheet and a silica airgel having a nano-sized porous structure as a heat insulating material installed between adjacent battery cells. In a battery unit using the above-mentioned heat insulating material, even if the battery cells repeatedly expand and contract and compressive stress is applied to the heat insulating material, the fiber sheet can absorb the stress. As a result, destruction of the silica airgel can be suppressed, and deterioration of the heat insulating properties of the silica airgel can be prevented.

JP 2015-211013 Publication JP2018-204708A

However, even when the heat insulating material described in Patent Document 2 is used, there is a problem in that sufficient heat insulation properties are not obtained in a high temperature region. If battery cells reach high temperatures and the insulation is not working properly, multiple cells will thermally expand and the insulation placed in the same battery case will be compressed even more, reducing the density of the insulation. may rise significantly. As a result, the thermal conductivity of the heat insulating material further increases, making it impossible to maintain desired heat insulation properties. Furthermore, if the heat insulation effect of the heat insulating material decreases, there is a risk that it will not be possible to suppress problems such as fire or explosion of the battery when the battery generates abnormal heat. Therefore, there is a need to develop a heat insulating sheet for assembled batteries that has excellent heat insulating properties even in a high temperature range of 500° C. or higher.

The present invention has been made in view of the above-mentioned situation, and it is possible to obtain excellent heat insulation properties in a wide temperature range from the temperature during normal use of batteries to high temperatures of 500°C or more, and preferably, Provided is a heat insulating sheet for an assembled battery that can maintain excellent heat insulation even when compressive stress on the heat insulating sheet for a battery increases, and an assembled battery in which the heat insulating sheet for an assembled battery is interposed between battery cells. The purpose is to

The above object is achieved by the following (1) heat insulating sheet for assembled batteries according to the present invention.
(1) A heat insulating sheet for a battery assembly interposed between the battery cells in a battery assembly in which a plurality of battery cells are connected in series or in parallel,
comprising first particles made of silica nanoparticles and second particles made of metal oxide,
A heat insulating sheet for an assembled battery, wherein the content of the first particles is 60% by mass or more and 95% by mass or less with respect to the total mass of the first particles and the second particles.

Furthermore, the heat insulating sheet for assembled batteries of the present invention preferably has the following properties (2) to (9).
(2) The heat insulating sheet for an assembled battery according to (1), wherein the first particles have an average particle diameter of 1 nm or more and 100 nm or less.
(3) The heat insulating sheet for an assembled battery according to (1) or (2), wherein the second particles are at least one selected from titania, zirconia, zircon, barium titanate, zinc oxide, and alumina.
(4) The heat insulating sheet for an assembled battery according to any one of (1) to (3), wherein the second particles are titania.
(5) The heat insulating sheet for an assembled battery according to any one of (1) to (4), wherein the second particles have an average particle diameter of 0.1 μm or more and 50 μm or less.
(6) Contains a binding material consisting of at least one selected from fibers, binders, and heat-resistant resins,
The heat insulating sheet for an assembled battery according to any one of (1) to (5), wherein the content of the binder is 10% by mass or more and 60% by mass or less based on the total mass of the heat insulating sheet for an assembled battery.
(7) The heat insulating sheet for assembled batteries according to any one of (1) to (6), which contains 60% by mass or less of inorganic balloons based on the total mass of the heat insulating sheet for assembled batteries.
(8) The heat insulating sheet for an assembled battery according to (7), wherein the inorganic balloon is at least one selected from a shirasu balloon, a silica balloon, a fly ash balloon, a barite balloon, and a glass balloon.
(9) The heat insulating sheet for an assembled battery according to (7) or (8), wherein the inorganic balloon has an average particle diameter of 1 μm or more and 100 μm or less.

The above object is achieved by the assembled battery (10) below according to the present invention.
(10) A battery assembly in which a plurality of battery cells are arranged through the battery insulation sheet according to any one of (1) to (9), and the plurality of battery cells are connected in series or in parallel. .

According to the present invention, it is possible to obtain excellent heat insulation properties in a wide temperature range from the temperature during normal use of the battery to a high temperature of 500°C or higher, and preferably, the compressive stress on the heat insulation sheet for assembled batteries is increased. Even in such cases, it is possible to provide a heat insulating sheet for assembled batteries that can maintain excellent heat insulation properties, and an assembled battery in which the heat insulating sheets for assembled batteries are interposed between battery cells.

FIG. 1 is a schematic diagram showing the structure of a heat insulating sheet for an assembled battery according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an embodiment of the assembled battery according to the present invention. FIG. 3 is a graph showing changes in thermal conductivity depending on the mass ratio of first particles and second particles in a heat insulating sheet for an assembled battery, where the vertical axis is thermal conductivity and the horizontal axis is temperature. FIG. 4 is a graph showing a change in thermal conductivity depending on the density of a heat insulating sheet for an assembled battery, where the vertical axis is thermal conductivity and the horizontal axis is temperature.

The inventors of the present application have developed a heat insulating sheet for assembled batteries (hereinafter also referred to as "insulating sheet") that can obtain excellent heat insulation properties in a wide temperature range from the temperature during normal use of the battery to high temperatures of 500°C or higher. We have conducted extensive research to provide the following. As a result, the heat insulating sheet contains first particles made of silica nanoparticles and second particles made of metal oxide, and by appropriately adjusting the mass ratio of the first particles and second particles, It has been found that excellent heat insulation properties can be obtained even in high temperature ranges.

The silica nanoparticles contained as the first particles in the heat insulating sheet have a low density, which suppresses conductive heat transfer, and furthermore, since voids are finely dispersed, they have excellent heat insulating properties that suppress convective heat transfer. Therefore, conduction of heat between adjacent silica nanoparticles can be suppressed during normal use of the battery in the normal temperature range. However, since the first particles have a low density and a small particle size, the light shielding effect is small, and the effect of suppressing radiant heat transfer is small. Therefore, by containing a metal oxide having a high refractive index and a strong effect of diffusely reflecting light as the second particles, it is possible to suppress radiant heat transfer particularly in a high temperature region such as abnormal heat generation. Therefore, by including silica nanoparticles and metal oxides in an appropriate ratio in a heat insulating sheet, it is possible to obtain excellent heat insulating properties over a wide temperature range from the temperature during normal battery use to high temperatures of 500°C or higher. can.

In addition, the inventors of the present application have found that when silica nanoparticles with a small average particle size are used in a heat insulating sheet, even if the heat insulating sheet is compressed due to the swelling of the battery and the density of the heat insulating sheet increases, the density of the heat insulating sheet increases. It has been found that the increase in conductive heat transfer can be suppressed.
This is thought to be because, since silica nanoparticles are insulators, fine voids are easily formed between the particles due to the repulsion caused by static electricity, and the particles are filled in such a way that they have a low bulk density and cushioning properties. In other words, if the heat insulating sheet contains silica nanoparticles with an average particle size of 1 nm or more and 100 nm or less, even if compressive stress is applied, the voids remaining between the silica nanoparticles and the contact points between many particles will cause conduction. It is possible to suppress heat transfer and maintain the heat insulating properties of the heat insulating sheet.

Furthermore, the inventors of the present invention have discovered that the size of the voids between particles contained in the heat insulating sheet affects the heat insulating properties of the heat insulating sheet. That is, if the voids formed between the particles are, for example, several hundreds of nanometers or more, convection tends to occur in the voids, which may reduce the heat insulating properties of the heat insulating sheet.
However, in a heat insulating sheet that uses silica nanoparticles with a small particle size as the first particles, the voids between the particles are small, for example, several tens of nanometers, making it difficult for air to move in the voids, making it difficult for convective heat transfer to occur. It is thought that this can be suppressed and the heat insulation properties can be further improved.
Note that it is important to form many fine voids and increase the number of contact points between particles, and the silica nanoparticles may be contained in the form of primary particles or aggregated secondary particles.

The present invention is based on such knowledge, and below, a heat insulating sheet for a battery pack and a battery pack according to an embodiment (this embodiment) of the present invention will be described in detail with reference to the drawings.

<Basic composition of insulation sheet for assembled batteries>
FIG. 1 is a schematic diagram showing the configuration of a heat insulating sheet for assembled batteries according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view schematically showing an embodiment of an assembled battery using the heat insulating sheet for assembled batteries shown in FIG. It is a diagram. The heat insulating sheet 10 includes first particles 21 made of silica nanoparticles and second particles 22 made of titania (metal oxide).
In addition, as the above-mentioned silica nanoparticles, it is desirable to use particles whose primary particles have an average particle diameter of 1 nm or more and 100 nm or less.

As shown in FIG. 2, a specific usage form of this heat insulating sheet 10 for assembled batteries is such that a plurality of battery cells 20 are arranged with the heat insulating sheet 10 for assembled batteries interposed in between, and the plurality of battery cells 20 are connected in series. Alternatively, the assembled battery 100 is configured by being stored in the battery case 30 in a parallel connected state (the connected state is not shown).
Note that, for example, a lithium ion secondary battery is preferably used as the battery cell 20, but the present invention is not particularly limited thereto, and may be applied to other secondary batteries.

The following description assumes that a battery cell 20 that generates heat is present on one surface 10a of the heat insulating sheet 10. In the heat insulating sheet configured as described above, when the battery cell 20 generates heat, a part of the heat incident from the one surface 10a side of the heat insulating sheet 10 damages the first particles 21 that are in contact with each other, as shown by the arrow 15a. The heat is conducted (conductive heat transfer) toward the other surface 10b of the heat insulating sheet 10 via the media. At this time, since silica nanoparticles having heat insulating properties are used as the first particles 21, the heat resistance is high, and a high temperature difference can be ensured between the surface and the other surface 10b of the heat insulating sheet 10, reducing the amount of heat transfer. .

Furthermore, when the battery cell 20 generates heat and a part of the heat reaches the second particles 22 due to radiation, it is diffusely reflected by the second particles 22 which are metal oxides, as shown by the arrow 15b. 22 can suppress heat from being propagated to the other surface 10b of the heat insulating sheet 10.

As described above, when thermal runaway occurs in a certain battery cell 20, it is possible to effectively suppress the propagation of heat to other adjacent battery cells, thereby suppressing the occurrence of thermal runaway in other battery cells. be able to.

In addition, in this embodiment, silica nanoparticles are used as the first particles 21, and since the contact points between the particles are small, the amount of heat conducted by the silica nanoparticles is determined by using silica particles obtained by crushing with a large particle size. It will be smaller than if you did it. Furthermore, since commonly available silica nanoparticles have a bulk density of about 0.1 g/cm ³ , for example, the battery cells 20 placed on both sides of the heat insulating sheet 10 expand thermally, causing the heat insulating sheet 10 to Even when a large compressive stress is applied to the silica nanoparticles, the size (area) and number of contact points between the silica nanoparticles do not increase significantly, and the heat insulation properties can be maintained.

Furthermore, in this embodiment, even if the silica nanoparticles overlap and exist in the heat insulating sheet 10, the voids formed between the particles are only about several tens of nanometers, and small convection as shown by arrow 15c occurs. Even if convection occurs, the area occupied by the entire thickness is very small. Therefore, heat transfer that penetrates the front and back sides of the heat insulating sheet 10 is less likely to occur. Therefore, when silica nanoparticles are used as the first particles 21, the heat insulating properties of the heat insulating sheet 10 can be further improved.

<Details of insulation sheet for assembled batteries>
Next, the first particles and second particles constituting the heat insulating sheet for assembled battery will be explained in detail.

(Type of first particle)
In the present invention, silica nanoparticles are used as the first particles. As the silica nanoparticles, wet silica, dry silica, aerogel, etc. can be used.
Furthermore, in the present invention, silica nanoparticles are nanometer-order silica particles having a spherical or nearly spherical average particle diameter of less than 1 μm.

(Average particle diameter of first particles: 1 nm or more and 100 nm or less)
As mentioned above, the particle size of the first particles can affect the heat insulation properties of the heat insulation sheet, so if the average particle size of the first particles is limited to a predetermined range, even higher heat insulation properties can be obtained. can.
That is, when the average particle diameter of the first particles is set to 1 nm or more and 100 nm or less, it is possible to suppress convective heat transfer and conductive heat transfer within the heat insulating sheet, especially in a temperature range below 500°C, and improve the heat insulation properties. This can be further improved.
Note that the average particle diameter of the first particles is more preferably 2 nm or more, and even more preferably 3 nm or more. Further, the average particle diameter of the first particles is more preferably 50 nm or less, and even more preferably 10 nm or less.

(Type of second particle)
In the present invention, a metal oxide is used as the second particle. As the metal oxide, titania, zirconia, zircon, barium titanate, zinc oxide, alumina, etc. can be used. In particular, titania is a component with a higher refractive index than other metal oxides, and it is most preferable to use titania because it has a high effect of diffusely reflecting light and blocking radiant heat in a high temperature region of 500° C. or higher.

(Average particle diameter of second particles: 0.1 μm or more and 50 μm or less)
Since the particle size of the second particles may affect the effect of reflecting radiant heat, even higher heat insulation properties can be obtained by limiting the average particle size of the second particles to a predetermined range.
That is, when the average particle diameter of the second particles is 0.1 μm or more, it is sufficiently larger than the wavelength of the light that contributes to heating, and the light is efficiently diffusely reflected. ), radiant heat transfer within the heat insulating sheet is suppressed in a high temperature range of 500° C. or higher, making it possible to further improve the heat insulating properties. On the other hand, if the average particle diameter of the second particles is 50 μm or less, the number of contact points between the particles will not increase even if the particles are compressed, making it difficult to form a path for conductive heat transfer, especially at normal temperatures where conductive heat transfer is dominant. The effect on the insulation properties of the area can be reduced.
Note that the average particle diameter of the second particles is more preferably 1 μm or more, and even more preferably 5 μm or more. Further, the average particle diameter of the second particles is more preferably 30 μm or less, and even more preferably 10 μm or less.
In the present invention, the average particle diameter can be determined by observing particles with a microscope, comparing them with a standard scale, and taking the average of 10 arbitrary particles.

(Content of first particles: 60% by mass or more and 95% by mass or less based on the total mass of first particles and second particles)
In the present invention, the heat insulating sheet contains second particles in order to improve heat insulation even in a high temperature range of 500°C or higher, but the amount of the second particles added to the first particles is small. Even if there is, the effect of suppressing radiant heat transfer can be obtained. Further, in order to obtain the effect of suppressing convective heat transfer and conductive heat transfer by the first particles, it is preferable to increase the amount of the first particles added to the second particles.
In addition, since the first particles are silica nanoparticles, their bulk density is low (about 0.1 g/ ^cm3 ), and the second particles have a larger average particle diameter than the first particles, so there are fewer voids, and the bulk density of the second particles is It is 10 times or more of the first particle, for example, if titania is selected, it is about 40 times (about 4 g/cm ³ ). Therefore, when expressed as a volume ratio (compared to when expressed as a mass ratio), the proportion of the second particles is very small, but the second particles only need to block light to suppress radiant heat transfer. It works effectively even in small amounts. As described above, since the mass ratio of the first particles and the second particles greatly affects the heat insulation properties in the range from normal temperature to high temperature of 500°C or more, in the present invention, the mass ratio of the first particles and the second particles It is necessary to appropriately adjust the mass ratio.

When the content of the first particles of the heat insulating sheet for assembled batteries of the present invention is 60% by mass or more with respect to the total mass of the first particles and the second particles, the first particles occupy most of the volume. This suppresses convective heat transfer or conductive heat transfer within the heat insulating sheet, resulting in high heat insulating properties even when compressed.
It is more preferable that the content of the first particles in the heat insulating sheet for an assembled battery of the present invention is 70% by mass or more based on the total mass of the first particles and the second particles. When the content of the first particles is 70% by mass or more with respect to the total mass of the first particles and the second particles, the first particles further occupy a large part of the volume, and the inside of the heat insulating sheet is This suppresses convective heat transfer or conductive heat transfer, resulting in even higher heat insulation properties.

On the other hand, when the content of the first particles is 95% by mass or less with respect to the total mass of the first particles and the second particles, the content of the second particles is 5% by mass or more, and the content of the second particles is It becomes possible to exhibit the effect of shielding radiant heat. Therefore, in a high temperature region of 500° C. or higher, radiant heat transfer within the heat insulating sheet can be suppressed and heat insulating properties can be exhibited.
It is more preferable that the content of the first particles in the heat insulating sheet for an assembled battery of the present invention is 90% by mass or less based on the total mass of the first particles and the second particles. When the content of the first particles is 90% by mass or less with respect to the total mass of the first particles and the second particles, the content of the second particles is 10% by mass or more, and the radiant heat due to the second particles is The shielding effect can be further demonstrated. Therefore, in a high temperature region of 500° C. or higher, radiant heat transfer within the heat insulating sheet can be suppressed, and even when compressed, the heat insulating property can be exhibited.

Further, the average particle diameter of the second particles is preferably 100 to 10,000 times the particle diameter of the first particles. Since both the first particles and the second particles are insulators, a repulsive force due to static electricity acts between the individual particles, and certain voids are formed. As the particle size becomes finer, the ratio of voids increases due to the effect of repulsive force due to static electricity, and the bulk density decreases. When the average particle diameter of the second particles is 100 times or more the particle diameter of the first particles, the first particles contain many voids to ensure cushioning and heat insulation properties, and the second particles absorb light due to diffuse reflection. It has a sufficient particle size for shielding and can maintain heat insulation over a wide temperature range even when compressed from the outside.
In addition, if the average particle diameter of the second particles is 10,000 times or less than the particle diameter of the first particles, it will be difficult to form a path for conductive heat transfer, especially in the normal temperature range where conductive heat transfer is dominant. The impact of this can be reduced.

In the heat insulating sheet for assembled batteries of the present invention, it is preferable that the first particles have an average particle diameter of 1 nm or more and 100 nm or less, and the second particles have an average particle diameter of 0.1 μm or more and 50 μm or less.
When the average particle diameter of the first particles is 1 nm or more and 100 nm or less, many voids are formed and it also has cushioning properties, so even if compressive force is applied from the outside, it can be applied over a wide temperature range centered on the normal temperature range. It is possible to efficiently suppress convective heat transfer and conductive heat transfer over the entire range.
Moreover, when the average particle diameter of the second particles is 0.1 μm or more and 50 μm or less, radiant heat transfer can be efficiently suppressed in a high temperature region of 500° C. or higher. As a result, it is thought that high heat insulation properties can be obtained over a wide temperature range from the temperature during normal use of the battery to high temperatures of 500° C. or higher, even when compressive force is applied from the outside.

In the heat insulating sheet for assembled batteries of the present invention, the content of the first particles is 60% by mass or more and 95% by mass or less based on the total mass of the first particles and the second particles, and It is desirable that the average particle diameter is 1 nm or more and 100 nm or less, and the average particle diameter of the second particles is 0.1 μm or more and 50 μm or less.
When the average particle diameter of the first particles is 1 nm or more and 100 nm or less, many voids are formed and it also has cushioning properties, so even if compressive force is applied from the outside, it can be applied over a wide temperature range centered on the normal temperature range. It is possible to efficiently suppress convective heat transfer and conductive heat transfer over the entire range.
When the average particle diameter of the second particles is 0.1 μm or more and 50 μm or less, radiant heat transfer can be efficiently suppressed in a high temperature region of 500° C. or higher.
When the content of the first particles is 60% by mass or more and 95% by mass or less with respect to the total mass of the first particles and the second particles, the amount of the second particles necessary for suppressing radiant heat transfer , it is possible to optimize the amount of the first particles necessary for suppressing conduction/convection heat transfer and providing cushioning properties.
As a result, it is thought that well-balanced and high heat insulation properties can be obtained over a wide temperature range from the temperature at which the battery is normally used to high temperatures of 500° C. or higher, even when compressive force is applied from the outside.

In addition to the first particles and second particles, the heat insulating sheet for assembled batteries may contain an inorganic balloon as a component that further enhances the heat insulating effect, and further includes a binder, a coloring agent, etc. It may also contain components necessary for forming into a heat insulating material. Other components will also be explained in detail below.

(Inorganic balloon: 60% by mass or less)
The heat insulating sheet for assembled batteries according to the present invention may contain 60% by mass or less of inorganic balloons based on the total mass of the heat insulating sheet.
When the inorganic balloon is included in the heat insulating sheet in a range of 60% by mass or less, convection heat transfer or conductive heat transfer within the heat insulating sheet can be suppressed in the temperature range below 500°C, and the heat insulation properties of the heat insulating sheet are improved. can be further improved.
The mass of the inorganic balloon relative to the total mass of the heat insulating sheet is more preferably 50% by mass or less. As the inorganic balloon, at least one selected from a shirasu balloon, a silica balloon, a fly ash balloon, a barite balloon, and a glass balloon can be used.

(Average particle size of inorganic balloon: 1 μm or more and 100 μm or less)
When the heat insulating sheet for assembled batteries according to the present invention includes inorganic balloons, if the average particle diameter of the inorganic balloons is appropriately adjusted, the battery cells may thermally expand and compressive stress is applied to the heat insulating sheet. Even in this case, it is possible to reduce the influence of changes in density on thermal insulation properties.
That is, when the average particle diameter of the inorganic balloon is 1 μm or more and 100 μm or less, even if the density of the first particles and the second particles in the heat insulation sheet changes, it is possible to further suppress the deterioration of the heat insulation properties. . Further, the average particle diameter of the inorganic balloon is more preferably 3 μm or more and 70 μm or less.

In addition, in the heat insulating sheet for assembled batteries according to the present invention, the total amount of the first particles, second particles, and inorganic balloons that function as a heat insulating material is 40% by mass or more and 95% by mass with respect to the total mass of the heat insulating sheet for assembled batteries. It is preferable that it is below. By setting it within this range, it is possible to easily obtain heat insulation properties, ensure strength as a sheet, and suppress scattering of particles. Furthermore, the total amount of the first particles, the second particles, and the inorganic balloon that function as a heat insulating material is more preferably 50% by mass or more and 80% by mass or less based on the total mass of the heat insulating sheet for assembled battery.

(Binding material: 10% by mass or more and 60% by mass or less)
The heat insulating sheet for assembled batteries according to the present invention can be formed by sintering etc. even if it does not contain a binder, but especially when the heat insulating sheet for assembled batteries contains silica nanoparticles as the first particles. It is preferable to add a binder in an appropriate amount to maintain the shape of the heat insulating sheet. In the present invention, the binding material may be anything that binds the first particles and the second particles together to hold them, such as a binder with adhesion, a fiber that physically entangles the particles, and an adhesive agent. It does not matter what form it takes, such as heat-resistant resin that adheres to it.

Note that as the binder, organic binders, inorganic binders, etc. can be used. Although the present invention does not particularly limit these types, as the organic binder, polymer aggregates, acrylic emulsions, etc. can be used, and as the inorganic binder, for example, silica sol, alumina sol, sulfuric acid band, etc. can be used. can. These act as adhesives once the solvent such as water is removed.

As the fibers, organic fibers, inorganic fibers, etc. can be used. The organic fibers are not particularly limited, but synthetic fibers, natural fibers, pulp, etc. can be used. The inorganic fibers are not particularly limited, but it is preferable to use alumina fibers, silica-alumina fibers, silica fibers, glass fibers, glass wool, rock wool, and the like.

On the other hand, since the binder is made of a component with higher thermal conductivity than the first particles, second particles, etc., the binder exists in the voids formed within the heat insulating sheet to the extent that no convective heat transfer occurs. This will have an effect on suppressing convective heat transfer and conductive heat transfer by the first particles. Therefore, in the heat insulating sheet for assembled batteries of the present invention, the content of the binder is preferably 60% by mass or less, more preferably 50% by mass or less, based on the total mass of the heat insulating sheet. In the heat insulating sheet for assembled batteries of the present invention, the content of the binder is preferably 10% by mass or more, more preferably 20% by mass or more, based on the total mass of the heat insulating sheet.

(Average fiber diameter of inorganic fiber: 0.1 μm or more and 20 μm or less)
The inorganic fibers are linear or acicular fibers, and contribute to improving the mechanical strength and shape retention of the heat insulating sheet against compressive stress from the battery cells.
In order to obtain such an effect, when inorganic fibers are used as a binder, the average fiber diameter is preferably 0.1 μm or more, more preferably 2 μm or more. However, if the inorganic fibers are too thick, the moldability and processability into a heat insulating sheet may deteriorate, so the thickness is preferably 20 μm or less, more preferably 15 μm or less.

(Average fiber length of inorganic fiber: 0.1 mm or more and 20 mm or less)
When inorganic fibers are used as the binding material, the fibers are suitably entangled with each other when formed into a heat insulating sheet, and sufficient surface pressure can be obtained.
In order to obtain such effects, when inorganic fibers are used, the average fiber length is preferably 0.1 mm or more, more preferably 0.5 mm or more. However, if the average fiber length of the inorganic fibers is too long, the inorganic fibers may become too entangled with each other when preparing a slurry solution in which the inorganic fibers are dispersed in water in the papermaking process. may tend to accumulate unevenly.
Therefore, the average fiber length of the inorganic fibers is preferably 20 mm or less, more preferably 10 mm or less.
The fiber diameter and fiber length of the inorganic fibers can be measured by using tweezers to extract the inorganic fibers from the formed sheet without breaking them, observing them with a microscope, and comparing them with a standard scale. The fiber diameter and fiber length of the inorganic fibers are obtained from the average value of ten arbitrary fibers.

(Thickness of insulation sheet: 0.1 mm or more and 30 mm or less)
The thickness of the heat insulating sheet for assembled batteries according to the present invention is not particularly limited, but is preferably in the range of 0.1 mm or more and 30 mm or less. When the thickness of the heat insulating sheet is within the above range, sufficient mechanical strength can be obtained and it can be easily molded.

(Manufacturing method of heat insulating sheet for assembled battery)
Next, a method for manufacturing a heat insulating sheet for assembled batteries according to the present invention will be explained in detail.

The heat insulating sheet according to the present embodiment can be manufactured by molding a heat insulating sheet material containing first particles and second particles by a wet paper forming method, a dry molding method, or a wet molding method, or by an extrusion molding method. It may be manufactured by The manufacturing method for obtaining the heat insulating sheet by each molding method will be explained below.

[Manufacturing method of heat insulating sheet by wet paper forming method]
In the wet papermaking method, first particles and second particles, and if necessary, a binder such as inorganic fibers, organic fibers, or organic binders are mixed in water, and the mixture is stirred with a stirrer. Prepare. Thereafter, the obtained liquid mixture is poured into a molding machine having a mesh for filtration formed on the bottom surface, and the liquid mixture is dehydrated through the mesh, thereby producing a wet sheet. Thereafter, a heat insulating sheet can be obtained by heating and pressurizing the obtained wet sheet. Note that before the heating and pressurizing process, an aeration drying process may be performed in which hot air is aerated through the wet sheet to dry the sheet; however, this aeration drying process is not performed and the sheet is heated and Pressure may be applied.

[Method for producing heat insulating sheet using dry molding method]
In the dry molding method, first particles and second particles, and if necessary, a binder such as an inorganic fiber, an organic fiber, or an organic binder are placed in a predetermined ratio into a mixer such as a V-type mixer. After thoroughly mixing the materials put into the mixer, the mixture is put into a predetermined mold and pressed to obtain a heat insulating sheet. During pressing, heating may be applied if necessary.

The press pressure is preferably in the range of 0.98 to 9.80 MPa. If the press pressure is less than 0.98 MPa, the obtained heat insulating sheet may not be able to maintain its strength and may collapse. On the other hand, if the press pressure exceeds 9.80 MPa, there is a risk that workability will be reduced due to excessive compression, and that solid heat transfer will increase due to the increased bulk density, resulting in a decrease in heat insulation properties.

[Method for producing heat insulating sheet by extrusion molding method]
In the extrusion molding method, first, water is added to the first particles and the second particles, and if necessary, a binder such as inorganic fibers, organic fibers, or organic binders, and the mixture is kneaded with a kneader to prepare a paste. . Thereafter, the obtained paste is extruded from a slit-shaped nozzle using an extrusion molding machine, and further dried to obtain a heat insulating sheet for assembled batteries. As the organic binder, it is preferable to use methyl cellulose, water-soluble cellulose ether, etc., but any organic binder commonly used when extrusion molding is used can be used without particular limitation.

[Assembled battery]
In the assembled battery according to the present invention, as illustrated in FIG. 2, a plurality of battery cells are arranged through the above-mentioned heat insulating sheet for assembled battery, and the plurality of battery cells are connected in series or in parallel. .

Examples of the heat insulating sheet for assembled batteries according to the present embodiment will be described below, but the present invention is not limited to these examples.

The following first particles, second particles, and binder were prepared, and these materials were sufficiently stirred and mixed to prepare a slurry. Using the obtained slurry, a heat insulating sheet was formed by a papermaking method.

The first particle contains 56% by mass of silica nanoparticles (average particle diameter 5 nm), and the second particle contains 24% by mass of titania (average particle diameter 8 μm) (first particle: second particle = 70 mass%: 30 mass% ) As binders, 11% by mass of glass fibers (average fiber diameter 10 μm, average fiber length 5mm), 8% by mass of pulp fibers, and 1% by mass of polymer aggregate were added, and the slurry was prepared by thoroughly stirring and mixing. did. The slurry was made into a paper sheet to obtain a heat transfer suppressing sheet (insulating sheet No. 1).
Note that drying was carried out at 110° C., and the size of the obtained heat insulating sheet was 80 mm in width, 80 mm in length, and 1 mm in thickness.

For insulation sheets with various mass ratios of first particles and second particles, multiple points ranging from the temperature during normal battery use (approximately 30 degrees Celsius) to high temperatures of 500 degrees Celsius or higher (approximately 850 degrees Celsius) The thermal conductivity was measured. The thermal conductivity was measured by an unsteady hot wire method in accordance with JIS method (R2616).

The content of the first particles (% by mass relative to the total amount of first particles and second particles) in each heat insulating sheet is shown in Table 1 below, and the thermal conductivity of the heat insulating sheet at each temperature is shown in FIG. Note that numbers 1 to 6 in FIG. 3 refer to insulation sheet No. 1 shown in Table 1. They correspond to numbers 1 to 6, respectively. Also, in Table 1 and FIG. 3 below, heat insulation sheet No. No. 6 is an example in which silica airgel was used as the first particles, and the binder shown in Table 1 above was not contained.

Insulation sheet for assembled batteries No. In Nos. 1 to 4, metal oxide (titania) is contained as the second particles, and the content of the first particles relative to the total mass of the first particles and the second particles is within the range of the present invention. Therefore, excellent heat insulation properties could be obtained in the temperature range from the temperature during normal use of the battery (approximately 30° C.) to a high temperature of 500° C. or higher (approximately 850° C.). In particular, as the content of the second particles increases, the thermal conductivity in the high temperature region of 500° C. or higher decreases, and the heat insulation improves.

On the other hand, insulation sheet No. Samples Nos. 5 and 6 did not contain the second particles, and therefore had high thermal conductivity in the high temperature range of 500° C. or higher. In addition, heat insulation sheet No. Both No. 5 and No. 6 do not contain the second particles, but insulation sheet No. Due to the influence of the magnesium silicate fiber contained in No. 5, insulation sheet No. It is thought that the thermal conductivity in the high temperature range of 500° C. or higher was lower than that of Sample No. 6.

Next, the above heat insulation sheet No. Insulating sheets of various densities were formed using the same components and contents as in Example 1 using the paper-making method, and changes in thermal conductivity depending on the density of the insulating sheets were measured using the unsteady hot wire method described above. The type and density of each heat insulating sheet are shown in Table 2 below, and the thermal conductivity at each temperature of the heat insulating sheets having different densities is shown in FIG. Numbers 11 to 15 in FIG. 4 are the insulation sheet numbers shown in Table 2. 11 to 15, respectively. In addition, heat insulation sheet No. Nos. 11 and 12 are examples in which the content of the first particles (silica nanoparticles) was 70% by mass based on the total mass of the first particles and the second particles. In addition, heat insulation sheet No. 13 and 14 are examples in which aluminum hydroxide powder was used instead of silica nanoparticles and titania, and heat insulation sheet No. No. 15 is an example using airgel.

As shown in Table 2 and FIG. 4 above, insulation sheet No. Insulation sheets No. 11 and 12 contain silica and titania in an appropriate ratio and use aluminum hydroxide powder. Compared to No. 13 and No. 14, the thermal conductivity was lower in all temperature ranges. In addition, heat insulation sheet No. 1 using airgel. Compared to No. 15, excellent heat insulation properties could be obtained, especially in the temperature range of about 400° C. or higher. Furthermore, insulation sheet No. 11 and 12 use silica nanoparticles with an extremely small particle size as the first particles, so even if the compressive stress on the heat insulating sheet increases and the density increases, it is not easily affected by the increase in density. In both cases, excellent heat insulation properties were obtained.

On the other hand, insulation sheet No. As shown in 13 and 14, the thermal conductivity increased significantly in all temperature ranges as the density increased from 1.00 (g/cm ³ ) to 1.50 (g/cm ³ ). From these facts, even if the battery cells placed on both sides of the heat insulating sheet thermally expand and compressive stress is applied to the heat insulating sheet, silica nano particles with an average particle size of 1 nm to 100 nm can be used as the first particles. It has been shown that by using particles, it is possible to maintain excellent thermal insulation properties.

10 Heat insulation sheets 10a, 10b Surface 20 Battery cell 21 First particle 22 Second particle 30 Battery case 100 Assembled battery

Claims (12)

A method for producing a heat insulating sheet for an assembled battery , comprising molding a heat insulating sheet material containing first particles made of wet silica and second particles made of a metal oxide using a wet paper forming method. hand ,
The wet silica forms fine voids between the wet silica,
The method for producing a heat insulating sheet for an assembled battery, wherein the content of the first particles is 60% by mass or more and 95% by mass or less with respect to the total mass of the first particles and the second particles. A step of mixing and stirring a heat insulating sheet material containing first particles made of wet silica and second particles made of a metal oxide in water to prepare a mixed liquid;
Dehydrating the liquid mixture to produce a wet sheet;
heating and pressurizing the wet sheet;
A method for manufacturing a heat insulating sheet for assembled batteries by a wet paper forming method, comprising:
The wet silica forms fine voids between the wet silica,
The method for producing a heat insulating sheet for an assembled battery, wherein the content of the first particles is 60% by mass or more and 95% by mass or less with respect to the total mass of the first particles and the second particles. The method for manufacturing a heat insulating sheet for an assembled battery according to claim 1 or 2, wherein the heat insulating sheet material further includes at least one of organic fibers and an organic binder. The method for producing a heat insulating sheet for an assembled battery according to any one of claims 1 to 3 , wherein the first particles have an average particle diameter of 1 nm or more and 100 nm or less. The heat insulating sheet for assembled battery according to any one of claims 1 to 4 , wherein the second particles are at least one selected from titania, zirconia, zircon, barium titanate, zinc oxide, and alumina. Production method . The method for producing a heat insulating sheet for an assembled battery according to any one of claims 1 to 5 , wherein the second particles are titania. The method for producing a heat insulating sheet for an assembled battery according to any one of claims 1 to 6 , wherein the second particles have an average particle diameter of 0.1 μm or more and 50 μm or less. Contains a binding material consisting of at least one selected from fibers, binders and heat-resistant resins,
The method for producing a heat insulating sheet for an assembled battery according to any one of claims 1 to 7 , wherein the content of the binder is 10% by mass or more and 60% by mass or less based on the total mass of the heat insulating sheet for an assembled battery. The method for producing a heat insulating sheet for assembled batteries according to any one of claims 1 to 8 , comprising 60% by mass or less of inorganic balloons based on the total mass of the heat insulating sheets for assembled batteries. The method for manufacturing a heat insulating sheet for an assembled battery according to claim 9 , wherein the inorganic balloon is at least one selected from a shirasu balloon, a silica balloon, a fly ash balloon, a barite balloon, and a glass balloon. The method for manufacturing a heat insulating sheet for assembled batteries according to claim 9 or 10 , wherein the inorganic balloon has an average particle diameter of 1 μm or more and 100 μm or less. A plurality of battery cells are arranged via a heat insulating sheet for assembled batteries obtained by the method for producing a heat insulating sheet for assembled batteries according to any one of claims 1 to 11 , and the plurality of battery cells are arranged in series or in parallel. A method for manufacturing an assembled battery that connects to.

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