JP2023171187A - Bus bar, method of manufacturing the same, and power storage device - Google Patents

Abstract

To provide a bus bar capable of achieving protection against high temperature or fire from battery cells at the time of abnormality of a battery, and to provide a power storage device that exhibits high safety even at the time of abnormality of the battery by connecting battery cells or battery modules by such the bus bar.SOLUTION: In a bus bar 1 used for a power storage device 100 that includes battery cells 110, an inorganic thermal insulation material 20 including at least one of an inorganic fiber and an inorganic particle is provided on a surface of a bus bar body 5 made of a conductive material. For the power storage device 100, a plurality of battery cells 110 or battery modules are connected by the bus bar 1 and accommodated in a battery case 120.SELECTED DRAWING: Figure 2

Description

The present invention relates to a bus bar, a method for manufacturing the same, and a power storage device in which a plurality of battery cells or battery modules are connected by a bus bar.

Various electronic devices, electric vehicles or hybrid vehicles driven by electric motors, storage batteries, and the like are equipped with power storage devices in which a plurality of battery cells or battery modules are connected in series or in parallel via bus bars. In addition, 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 as battery cells.

However, when an overcurrent is applied to a battery cell or battery module during charging and discharging, the bus bar used for connection may generate heat. Therefore, in Patent Document 1, the busbar is covered with a mica sheet.

Japanese Patent Application Publication No. 2020-528650

However, due to overcharging, some battery cells may undergo thermal runaway, reaching temperatures of several hundred degrees Celsius, or even emitting flames. When such a battery abnormality occurs, the bus bar is also exposed to similar high temperatures and flames, and adjacent battery cells become heated through the bus bar.

However, Patent Document 1 is a measure for suppressing the heat generation of the bus bar itself, and does not focus on protecting the bus bar from high temperatures and flames from the battery cells when the battery is abnormal. Furthermore, since mica contains water of crystallization, if the battery is exposed to high temperatures or flames during abnormal conditions, it will expand, release crystallized water, and become structurally unstable.

Further, in Patent Document 1, it is necessary to wrap the mica sheet around the bus bar. Busbars may have a complicated shape due to spatial restrictions on the location where battery cells are installed, and when the busbar has a complicated shape, it is difficult to wrap the mica sheet to every corner of the busbar. If the mica sheet has uneven winding or gaps, the desired effects described above cannot be sufficiently obtained. Furthermore, it is also assumed that the adhesive surface of the mica sheet may peel off at high temperatures.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a bus bar that can be protected from high temperatures and flames from battery cells when the battery is abnormal.
In addition, the present invention provides a bus bar that does not require wrapping work like mica sheets, causes uneven winding, gaps between sheets, and peeling of sheets, and can be easily manufactured to accommodate complex shapes. The purpose is to provide a manufacturing method.
A further object of the present invention is to provide a power storage device that connects battery cells or battery modules to each other using such a bus bar and exhibits high safety even in the event of battery abnormality.

The above object of the present invention is achieved by the following configuration [1] regarding the bus bar.

[1] A bus bar used in a power storage device including a battery cell,
A busbar comprising an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles on the surface of a busbar body made of a conductive material.

Further, preferred embodiments of the present invention relating to the bus bar relate to the following [2] to [16].

[2] The bus bar according to [1], wherein the inorganic heat insulating material includes both the inorganic fibers and the inorganic particles.
[3] The bus bar according to [1] or [2], wherein the inorganic heat insulating material is a wet sheet or a dry sheet.
[4] The busbar according to [1] or [2], wherein an endothermic reaction layer is interposed between the busbar main body and the inorganic heat insulating material.
[5] The bus bar according to [1] or [2], wherein an inorganic fiber cloth is arranged on a side of the inorganic heat insulating material facing the battery cells.
[6] The bus bar according to [5], wherein the laminate of the bus bar body and the inorganic heat insulating material is wound with the inorganic fiber cloth.
[7] The busbar according to [1] or [2], wherein the inorganic heat insulating material includes infusible fibers.
[8] The busbar according to [7], wherein the infusible fiber has a carbon content of 55 to 95% by mass.
[9] The busbar according to [7], wherein the infusible fibers are short fibers.
[10] The busbar according to [7], wherein the infusible fiber has a fiber diameter of 1 to 30 μm.
[11] The busbar according to [1] or [2], wherein the inorganic heat insulating material contains organic fibers.
[12] The bus bar according to [1] or [2], wherein the inorganic heat insulating material contains inorganic particles.
[13] The bus bar according to [12], wherein the inorganic particles include first inorganic particles and second inorganic particles that have different average particle diameters from each other.
[14] The bus bar according to [13], wherein the first inorganic particles are made of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.
[15] The bus bar according to [14], wherein the first inorganic particles are made of at least one selected from nanoparticles, hollow particles, and porous particles.
[16] The bus bar according to [13], wherein the second inorganic particles are metal oxide particles.

Moreover, the above-mentioned object of the present invention is achieved by the following structure [17] related to the method for manufacturing a bus bar.

[17] A method for manufacturing a bus bar used in a power storage device including a battery cell, comprising:
A method for manufacturing a busbar, comprising applying a coating liquid containing at least one of inorganic fibers and inorganic particles to a busbar body containing a conductive material, and then drying the coating liquid.

Further, the above object of the present invention is achieved by the following configuration [18] related to the power storage device.

[18] A power storage device in which a plurality of battery cells or battery modules are connected by the bus bar according to any one of [1] to [16].

The bus bar of the present invention is coated with an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles, and is protected from high temperatures and flames from battery cells that have undergone thermal runaway in the event of battery abnormality.

In addition, the method for manufacturing a busbar of the present invention simplifies the manufacturing process because it is only necessary to apply a coating liquid containing at least one of inorganic fibers and inorganic particles to the busbar body, and the manufacturing process is simple, regardless of the shape of the busbar body. An insulating film can be formed uniformly without any gaps.

Further, since the power storage device of the present invention connects battery cells or battery modules to each other using such a bus bar, it exhibits high safety even in the event of battery abnormality.

FIG. 1A is a perspective view showing an example of the bus bar of the present invention. FIG. 1B is a perspective view showing another example of the bus bar of the present invention. FIG. 2 is a cross-sectional view of Embodiment 1 taken along the line AA in FIG. 1A. FIG. 3 is a cross-sectional view of Embodiment 2 taken along the line AA in FIG. 1A. FIG. 4A is a sectional view showing a power storage device including the bus bar of FIG. 1A. FIG. 4B is a sectional view showing a power storage device including the bus bar of FIG. 1B.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be implemented with arbitrary changes within the scope of the gist of the present invention.

[Overall configuration of bus bar]
FIG. 1A is a perspective view showing an example of the bus bar 1 of the present invention, showing a state where it is attached to a battery cell 110. As shown in the figure, the busbar body 5 made of a conductive material is, for example, a Z-shaped metal plate member as a whole, and the electrode 111 of the battery cell 110 is inserted into the connection hole 6a at one end. It is fixed by covering with the terminal cap 112. Further, adjacent battery cells (not shown) and external equipment are connected to the connection hole 6b at the other end of the busbar body 5. Then, a portion (surface) of the busbar body 5 excluding the connection holes 6a and 6b is covered with an inorganic heat insulating material 20, which will be described later, to form the busbar 1.

Further, as shown in FIG. 1B, the busbar body 5 can be made into a flat plate with an I-shape as a whole, and the portions excluding the connection holes 6a and 6b at both ends can be covered with an inorganic heat insulating material 20 to form the busbar 1. You can also do it.

Note that the bus bar 1 may be directly or indirectly connected to the electrode 111 of the battery cell 110, or may be electrically connected to the electrode 111 of the battery cell 110.

<Embodiment 1>
FIG. 2 is a sectional view showing the bus bar 1 of Embodiment 1 along the AA arrow in FIG. High temperatures and flames occur from 110. Therefore, an inorganic heat insulating material 20 is placed on the surface 5a of the busbar body 5 facing the battery cells 110.

Further, in addition to the inorganic heat insulating material 20, an inorganic fiber sheet 30 may be laminated on the side facing the battery cell 110. The inorganic heat insulating material 20 and the inorganic fiber sheet 30 may or may not be bonded together. When not bonded, an air layer is formed between the inorganic heat insulating material 20 and the inorganic fiber sheet 30, so that the heat insulating performance is improved.

When a battery malfunctions, in addition to the high temperature from the battery cells 110, electrolyte gas and fragments of the battery cells 110 are generated along with flames. As the inorganic fiber sheet 30, inorganic fiber cloth, specifically woven cloth such as glass cloth, silica cloth, alumina cloth, etc., especially silica cloth (woven cloth) is preferable.

Furthermore, an endothermic reaction layer 40 may be interposed between the surface 5a of the busbar body 5 and the inorganic heat insulating material 20. The endothermic reaction layer 40 has a function of absorbing heat from the battery cell 110 that has caused thermal runaway, and improves heat insulation performance. Various resins can be used as the endothermic reaction layer 40, but since the busbar body 5 and the inorganic heat insulating material 20 can be bonded and fixed, double-sided tape with adhesive layers formed on both sides of the resin base material is preferable. preferable.

Furthermore, an insulating tape (insulating sheet) 50 may be wound (covered) so as to surround the bus bar 1, the endothermic reaction layer 40, the inorganic heat insulating material 20, and the inorganic fiber sheet 30. That is, the insulating tape 50 becomes the outermost layer. When winding the insulating tape 50, as shown in the figure, start winding from the surface 5b of the bus bar body 5 opposite to the battery cells 110, and wrap the endothermic reaction layer 40, inorganic heat insulating material 20, and inorganic fiber sheet 30. The winding end portion 50b is positioned on the surface 50a that contacts the busbar main body 5 as it rotates. Further, in consideration of the shape retention of the laminate consisting of the inorganic heat insulating material 20, the inorganic fiber sheet 30, and the endothermic reaction layer 40, the winding end portion 50b of the insulating tape 50 may be bonded with an adhesive.

Note that the insulating tape 50 only needs to have electrical insulation properties in order to come into contact with the battery cells 110, and for example, a resin tape can be used.

<Embodiment 2>
FIG. 3 is a sectional view showing the bus bar 1 of the second embodiment according to FIG. 2. As shown in FIG. As shown in the figure, an inorganic heat insulating material 20 is attached to the surface 5a of the busbar body 5 facing the battery cells 110, and the winding begins on the surface 5b opposite to the battery cells 110 and goes around the busbar body 5. The inorganic fiber sheets 30 are laminated in this way. Since the inorganic fiber sheet 30 has flexibility, it can easily go around the bus bar body 5, and furthermore, since it is electrically insulating, it will not cause a short circuit even if it comes into contact with the battery cell 110.

Note that as the inorganic fiber sheet 30, woven fabrics such as silica cloth, glass cloth, alumina cloth, etc. are preferable.

Furthermore, an endothermic reaction layer 40 may be interposed between the surface 5b of the busbar body 5 and the winding start portion 30a of the inorganic fiber sheet 30. Furthermore, an endothermic reaction layer 40 may also be interposed between the winding start portion 30a and the winding end portion 30b of the inorganic fiber sheet 30.

The surface 5a of the bus bar body 5 and the inorganic heat insulating material 20 may or may not be bonded together.

Note that when these are not bonded, an air layer is formed between the surface 5a of the busbar body 5 and the inorganic heat insulating material 20, so that the heat insulating performance is improved.

[About inorganic insulation material 20]
In both Embodiment 1 and Embodiment 2 described above, the type of inorganic heat insulating material 20 is not limited, but since it has excellent heat insulating performance, it contains at least one of inorganic fibers and inorganic particles, and preferably contains inorganic fibers and inorganic particles. It is preferable to include both inorganic particles. The bus bar 1 of this embodiment is covered with an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles, and preferably both. protected from

(Inorganic fiber)
The inorganic heat insulating material 20 can include inorganic fibers. Specifically, as the inorganic fiber, an inorganic fiber having a melting point of less than 700° C. is preferable, and many amorphous inorganic fibers can be used. The type of inorganic fiber is not particularly limited, and various inorganic fibers can be used, such as glass fiber, glass wool, slag wool, rock wool, alkali earth silicate fiber, refractory ceramic fiber, basalt fiber, and soluble fiber. Note that these fibers may be used alone or in combination. Among these, fibers containing SiO ₂ are preferred, and glass fibers are more preferred because they are inexpensive, easily available, and have excellent handling properties. Further, these fibers may be crystalline or amorphous, but from the viewpoint of flexibility, amorphous is preferable.

In addition, when the inorganic fiber is crystalline, specifically, silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, airgel composite material, magnesium silicate fiber, Ceramic fibers such as alkali earth silicate fibers and potassium titanate fibers, glass fibers such as glass fibers and glass wool, mineral fibers such as rock wool, basalt fibers, and wollastonite can be used.

In addition, if the melting point exceeds 1000°C, the inorganic fibers will not melt or soften and can maintain their shape even if thermal runaway occurs in the battery cell, so they can be suitably used. . Among the above-mentioned fibers listed as inorganic fibers, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers and alumina silicate fibers, and mineral fibers, and among these, those with a melting point exceeding 1000 ° C. It is more preferable to use

(Inorganic particles)
The inorganic heat insulating material 20 can contain inorganic particles instead of or together with inorganic fibers. When the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are easily available and can suppress an increase in manufacturing costs. Further, when the thickness is 200 μm or less, a desired heat insulation effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

As the inorganic particles, a single inorganic particle may be used, or two or more types of inorganic particles (for example, first inorganic particles and second inorganic particles) may be used in combination. When two types of inorganic particles are included, the first inorganic particles and the second inorganic particles are selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles from the viewpoint of heat transfer suppressing effect. It is preferable to use particles made of at least one inorganic material, and it is more preferable to use oxide particles. Furthermore, the shapes of the first inorganic particles and the second inorganic particles are not particularly limited, but they preferably contain at least one selected from nanoparticles, hollow particles, and porous particles. Particles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of a thermally expandable inorganic material, particles made of a hydrous porous material, etc. can also be used.

Note that when two or more kinds of inorganic particles having different heat transfer suppressing effects are used together, cooling can be performed in multiple stages, and the endothermic effect can be exerted over a wider temperature range. Specifically, it is preferable to use a mixture of large diameter particles and small diameter particles. For example, when nanoparticles are used as one of the inorganic particles, it is preferable that the other inorganic particles include inorganic particles made of a metal oxide.
Hereinafter, the inorganic particles will be described in more detail, with small-diameter inorganic particles being referred to as first inorganic particles and large-diameter inorganic particles being referred to as second inorganic particles.

(First inorganic particles)
(oxide particles)
Oxide particles are preferred as the first inorganic particles. Oxide particles have a high refractive index and have a strong effect of diffusely reflecting light, so they can suppress radiant heat transfer, especially in high temperature regions such as abnormal heat generation. As the oxide particles, at least one particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. In particular, silica is a component with high heat insulation properties, and titania is a component with a high refractive index compared to other metal oxides, and is highly effective in diffusely reflecting light and blocking radiant heat in high temperature regions of 500 degrees Celsius or higher. Therefore, it is most preferable to use silica and titania as the oxide particles.

Since the particle size of the oxide particles may affect the effect of reflecting radiant heat, even higher heat insulation properties can be obtained by limiting the average primary particle size to a predetermined range. In other words, when the average primary particle diameter of the oxide particles is 0.001 μm or more, it is sufficiently larger than the wavelength of the light that contributes to heating, and in order to efficiently reflect light diffusely, the inorganic insulation is Radiation heat transfer in the material 20 is suppressed, and the heat insulation properties can be further improved. On the other hand, if the average primary particle diameter of the oxide particles is 50 μm or less, the number of contact points between the particles does not increase even when the particles are compressed, and it is difficult to form a path for conductive heat transfer, so conductive heat transfer is particularly dominant. The influence on the heat insulation properties in the normal temperature range can be reduced.

In this embodiment, the average primary particle diameter can be determined by observing the particles with a microscope, comparing them with a standard scale, and taking the average of 10 arbitrary particles.

(nanoparticles)
Nanoparticles are preferable as the first inorganic particles, and because nanoparticles have a low density, they suppress conductive heat transfer, and since the voids are finely dispersed, excellent heat insulation properties that suppress convective heat transfer can be obtained. For this reason, it is preferable to use nanoparticles because they can suppress the conduction of heat between adjacent nanoparticles when the battery is used in a normal temperature range.

Note that nanoparticles refer to nanometer-order particles having a spherical or nearly spherical shape and an average primary particle diameter of less than 1 μm.

Furthermore, if nanoparticles with a small average primary particle diameter are used as the oxide particles, even if the internal density of the inorganic heat insulating material 20 increases due to expansion due to thermal runaway of the battery cell, the conductivity of the inorganic heat insulating material 20 will increase. It is possible to suppress an increase in heat transfer. This is thought to be because nanoparticles tend to form fine voids between particles due to the repulsive force caused by static electricity, and because their bulk density is low, the particles are filled so as to provide cushioning properties.

In addition, when using nanoparticles as the first inorganic particles, the material is not particularly limited as long as it meets the above definition of nanoparticles. For example, in addition to being a highly insulating material, silica nanoparticles have small contact points between particles, so the amount of heat conducted by silica nanoparticles is smaller than when using silica particles with a large particle size. Become. Furthermore, since commonly available silica nanoparticles have a bulk density of about 0.1 (g/cm ³ ), for example, even when a large compressive stress is applied to the inorganic heat insulating material 20, The size (area) and number of contact points between silica nanoparticles do not increase significantly, and heat insulation properties can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. As the silica nanoparticles, wet silica, dry silica, aerogel, etc. can be used.

By limiting the average primary particle diameter of the nanoparticles to a predetermined range, even higher heat insulation properties can be obtained. In other words, when the average primary particle diameter of nanoparticles 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 material, especially in the temperature range below 500°C, and improve the heat insulation properties. This can be further improved. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the many contact points between the particles suppress conductive heat transfer, and the insulating properties of the inorganic heat insulating material 20 can be maintained. . Further, the average primary particle diameter of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. On the other hand, the average primary particle diameter of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

(Inorganic hydrate particles)
Inorganic hydrate particles thermally decompose when they receive heat from a heating element and reach a thermal decomposition start temperature, releasing their own water of crystallization and lowering the temperature of the heating element and its surroundings, a so-called "endothermic action." Express. Furthermore, after releasing the crystal water, it becomes a porous body and exhibits a heat insulating effect due to its countless air holes.

Specific examples of inorganic hydrates include aluminum hydroxide (Al(OH) ₃ ), magnesium hydroxide (Mg(OH) ₂ ), calcium hydroxide (Ca(OH) ₂ ), and zinc hydroxide (Zn(OH)). ₂ ), iron hydroxide (Fe(OH) ₂ ), manganese hydroxide (Mn(OH) ₂ ), zirconium hydroxide (Zr(OH) ₂ ), gallium hydroxide (Ga(OH) ₃ ), etc. .

For example, aluminum hydroxide has about 35% water of crystallization, and as shown in the following formula, it thermally decomposes to release water of crystallization and exhibits an endothermic action. After releasing the crystal water, it becomes porous alumina (Al ₂ O ₃ ), which functions as a heat insulator.
2Al(OH) ₃ →Al ₂ O ₃ +3H ₂ O

Note that in a battery cell that has experienced thermal runaway, the temperature rapidly rises to over 200°C and continues to rise to around 700°C. Therefore, the inorganic particles are preferably composed of inorganic hydrates whose thermal decomposition initiation temperature is 200° C. or higher.

The thermal decomposition starting temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, and approximately 200°C for iron hydroxide. is approximately 350°C, manganese hydroxide is approximately 300°C, zirconium hydroxide is approximately 300°C, and gallium hydroxide is approximately 300°C, all of which are approximately the same temperature range as the rapid temperature rise of battery cells that have experienced thermal runaway. It can be said that it is a preferable inorganic hydrate because it can efficiently suppress the temperature rise.

Furthermore, if the average particle diameter of the inorganic hydrate particles is too large, it will take some time for the inorganic hydrate particles near the center of the inorganic heat insulating material 20 to reach their thermal decomposition temperature. The inorganic hydrate particles near the center of No. 20 may not be completely thermally decomposed. Therefore, the average secondary particle diameter of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

(Particles made of thermally expandable inorganic material)
Examples of thermally expandable inorganic materials include vermiculite, bentonite, pearlite, and the like.

(Particles made of water-containing porous material)
Specific examples of the water-containing porous material include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

(Inorganic balloon)
When the inorganic balloon is included, convection heat transfer or conductive heat transfer within the heat insulating material can be suppressed in a temperature range of less than 500° C., and the heat insulating properties of the inorganic heat insulating material 20 can be further improved. .

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.

The content of the inorganic balloon is preferably 60% by mass or less based on the total mass of the inorganic heat insulating material 20.

Further, the average particle diameter of the inorganic balloon is preferably 1 μm or more and 100 μm or less.

(Second inorganic particles)
The second inorganic particles are not particularly limited as long as they are different in material, particle size, etc. from the first inorganic particles. The second inorganic particles include oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, and thermally expandable inorganic materials. Particles made of a water-containing porous material, particles made of a water-containing porous material, etc. can be used, and the details thereof are as described above.

Note that nanoparticles have extremely low conductive heat transfer, and can maintain excellent heat insulation properties even when compressive stress is applied to the inorganic heat insulation material 20. Furthermore, metal oxide particles such as titania are highly effective in blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles enter the gaps between the large-diameter inorganic particles, resulting in a more dense structure and improving the heat transfer suppression effect. can. Therefore, when nanoparticles are used as the first inorganic particles, particles made of a metal oxide having a larger diameter than the first inorganic particles are further added to the inorganic heat insulating material 20 as the second inorganic particles. It is preferable to contain it.

Examples of metal oxides include silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zircon, and zirconium oxide. In particular, titanium oxide (titania) is a component with a high refractive index compared to other metal oxides, and is highly effective in diffusely reflecting light and blocking radiant heat in the high temperature range of 500°C or higher, so titania can be used. Most preferred.

When the average primary particle diameter of the second inorganic particles is 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. The average primary particle diameter of the second inorganic particles is more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

(Other blended materials)
In addition to the inorganic fibers and inorganic particles described above, the inorganic heat insulating material 20 may further contain an organic binder (resin binder) and organic fibers.

(resin binder)
The above-mentioned inorganic fibers can also be bound with a resin binder. The resin binder is not particularly limited as long as it has a glass transition point lower than the glass transition point of the organic fiber described below. For example, a resin binder containing at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin can be used.

Although the glass transition point of the resin binder is not particularly defined, it is preferably −10° C. or higher. Note that when the glass transition point of the resin binder is higher than room temperature, the strength of the inorganic heat insulating material 20 can be further improved when the inorganic heat insulating material 20 having the resin binder is used at room temperature. Therefore, the glass transition point of the resin binder is, for example, more preferably 20°C or higher, even more preferably 30°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher. preferable.

The content of the resin binder is preferably 0.5% by mass or more, and more preferably 1% by mass or more, based on the total mass of the inorganic heat insulating material 20. Moreover, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

(organic fiber)
In addition to the above-mentioned inorganic fibers, organic fibers may also be contained. The organic fibers are selected from, for example, polyvinyl alcohol (PVA) fibers, polyethylene fibers, nylon fibers, polyurethane fibers, ethylene-vinyl alcohol copolymer fibers, polypropylene fibers, polyester fibers, polyacrylic fibers, polyamide fibers, and fluorine fibers. At least one of these can be used. Among these, those having excellent heat resistance and high Young's modulus are preferable, and specifically, it is preferable to use polyphenylene sulfide type and polyacrylonitrile type. Note that these fibers may be used alone or in combination.

As will be described later, the inorganic heat insulating material 20 can also be manufactured by a paper forming method, but in that case it is difficult to increase the heating temperature higher than 250°C, so the glass transition point of the organic fiber is The temperature is preferably 250°C or lower, more preferably 200°C or lower.

The lower limit of the glass transition point of the organic fiber is also not particularly limited, but if the difference from the glass transition point of the resin binder is 10°C or more, the organic fiber, which was in a semi-molten state, will completely melt in the cooling process during manufacturing. Since the resin binder is solidified after the resin binder is solidified, it is possible to sufficiently obtain the effect of reinforcing the skeleton by the resin binder. Therefore, the difference between the glass transition point of the resin binder and the glass transition point of the organic fiber is preferably 10°C or more, more preferably 30°C or more.

On the other hand, if the difference in glass transition point between the two is 130°C or less, the time from when the organic fibers are completely solidified to when the resin binder begins to solidify can be appropriately adjusted, and the resin binder is in good condition. Since it solidifies while remaining in a dispersed state, it is possible to obtain an even stronger reinforcing effect on the skeleton. Therefore, the difference between the glass transition point of the resin binder and the glass transition point of the organic fiber is preferably 130°C or less, more preferably 120°C or less, even more preferably 100°C or less, The temperature is even more preferably 80°C or lower, particularly preferably 70°C or lower.

It can also contain two or more types of organic fibers, but in that case, at least one type of organic fiber is an organic fiber that acts as a skeleton, that is, an organic fiber that has a glass transition point higher than that of the resin binder. Any fiber is fine. Note that the difference between the glass transition point of the resin binder and the glass transition point of at least one organic fiber is preferably 10° C. or higher, more preferably 30° C. or higher, and 130° C. or higher, as described above. It is preferably at most 120°C, more preferably at most 100°C, even more preferably at most 80°C, particularly preferably at most 70°C.

When the contents of the organic fibers and the resin binder are appropriately controlled, the organic fibers can sufficiently function as a skeleton, and the resin binder can sufficiently strengthen the skeleton. The content of organic fibers is preferably 0.5% by mass or more, and more preferably 1% by mass or more, based on the total mass of the inorganic heat insulating material 20. Moreover, it is preferably 12% by mass or less, and more preferably 8% by mass or less. In addition, when a plurality of organic fibers having a glass transition point higher than the glass transition point of the resin binder are included, the total amount of these plurality of organic fibers is preferably within the range of the content of the organic fibers.

As mentioned above, when two or more types of organic fibers are included, it is sufficient that at least one type of organic fiber has a glass transition point higher than that of the resin binder, but as other organic fibers, It is more preferable to contain organic fibers in a crystalline state that do not have a glass transition point.

It is also possible to contain organic fibers in a crystalline state that do not have a glass transition point, but since these organic fibers in a crystalline state do not have a softening point, if they are exposed to high temperatures that would soften the organic fibers that form the skeleton. Even in this case, the strength of the inorganic heat insulating material 20 can be maintained. Moreover, by containing organic fibers in a crystalline state, these organic fibers also act as a skeleton of the heat insulating material at room temperature (20° C.). Therefore, the flexibility and handleability of the inorganic heat insulating material 20 can be improved.

In addition, polyester (PET) fiber is mentioned as an organic fiber in a crystalline state.

Further, when performing the papermaking method in manufacturing the inorganic heat insulating material 20, it is preferable to use water as a dispersion liquid, but it is preferable that the organic fiber has low solubility in water. "Solubility temperature in water" can be used as an indicator of solubility in water, but the dissolution temperature in water of organic fibers is preferably 60°C or higher, more preferably 70°C or higher, and 80°C or higher. is even more preferable.

The fiber length of the organic fibers is not particularly limited either, but from the viewpoint of ensuring moldability and processability, the average fiber length is preferably 10 mm or less. On the other hand, from the viewpoint of making the organic fibers function as a skeleton and ensuring the compressive strength of the heat insulating material, the average fiber length is preferably 0.5 mm or more.

Further, as the organic fiber, a binder fiber having a core-sheath structure having a core portion with a high melting point and a sheath portion with a low melting point may be used. When a battery malfunctions, in addition to flames, damaged objects may scatter from the battery cell and collide with the bus bar, causing damage. By using binder fibers with a core-sheath structure, it is possible to obtain high strength using the core as a skeleton, and the sheath melts and softens in response to high temperatures and flames during battery abnormalities, which strengthens the network. is expected to have the effect of mitigating collisions with damaged objects.

Such a binder fiber with a core-sheath structure has a core-sheath structure, and the melting point of the first organic material constituting the core is higher than the melting point of the second organic material constituting the sheath. If so, there are no particular limitations. As the first organic material serving as the core, at least one selected from polyethylene terephthalate, polypropylene, and nylon can be selected. Further, as the second organic material that becomes the sheath, at least one selected from polyethylene terephthalate, polyethylene, polypropylene, and nylon can be selected.

Note that binder fibers having a core-sheath structure as described above are generally commercially available, and the materials constituting the core portion and the sheath portion may be the same or different from each other. Examples of binder fibers in which the core and sheath are made of the same material and have different melting points include those in which the core and sheath are made of polyethylene terephthalate, polypropylene, nylon, etc. It will be done. Examples of binder fibers in which the core and sheath parts are made of different materials include those in which the core part is made of polyethylene terephthalate and the sheath part is made of polyethylene, and those in which the core part is made of polypropylene and the sheath part is made of polyethylene. Can be mentioned.

(Infusible fiber)
Infusible fibers may be used instead of the inorganic fibers or a portion thereof. Examples of the infusible fibers include fibers made of thermoplastic resins such as polyacrylonitrile, cellulose, and pitch that have been infusible. Infusible fibers are, for example, fibers that have been treated to make them infusible. Examples of infusible treatment include crosslinking by irradiating with radiation or electron beams, exposing them to high temperatures in oxygen or water vapor, and making them infusible by the action of oxygen. There are methods of melting.

(carbon content)
The carbon content of the infusible fiber is preferably 55 to 95% by mass. When the carbon content is 55% by mass or more, the weight loss due to thermal decomposition has already progressed, so there is little shrinkage due to thermal decomposition, and even when directly exposed to flame during thermal runaway, it retains its original shape and has good insulation properties. can be maintained. If the carbon content is 95% by mass or less, components other than carbon are eliminated and the structure changes to a structure consisting only of carbon, causing an endothermic reaction, which delays the time for heat to reach the back surface of the inorganic heat insulating material 20. be able to.

The lower limit of the desirable carbon content is 60% by mass or more. Further, a desirable upper limit of the carbon content is 90% by mass or less, and a more desirable upper limit of the carbon content is 85% by mass or less.

Carbon content can be adjusted by heat treatment. For example, heat treatment in the air or in oxygen within the range of 150 to 300° C. can further promote infusibility and remove components other than carbon to increase the carbon content. For example, heat treatment within the range of 300 to 1000° C. can advance the formation of a condensed polycyclic aromatic structure, generate decomposition gas, and increase the carbon content.

Note that the infusible fibers are not limited to fibers obtained by infusible thermoplastic fibers. Inorganic fibers may be used as long as the carbon content is within the above range.

(fiber shape)
The infusible fibers are composed of short fibers, and it is preferable that these fibers are aggregated to form a mat, paper product, or blanket as a whole.

Being short fibers means that they are not continuous fibers. Continuous fibers form fiber bundles with the fibers aligned in the same direction as in cross or filament winding, but by using fibers, fibers are oriented in random directions to form aggregates (mats, blankets, paper products). ). Since the inorganic heat insulating material 20 using short fibers has a short conductive path, the conductivity can be lowered even if the fibers are highly carbonized or carbonization progresses due to thermal runaway. In addition, the fibers are randomly oriented, and the fibers tend to come into point contact with each other, making it possible to lower heat conduction.

The paper product can be obtained by dispersing infusible milled fibers or chopped fibers (fiber length of about 0.01 to 10 mm) in water, and then papermaking. Mats and blankets can be obtained by laminating infusible fibers with a fiber length of about 10 to 1000 mm and compressing them. At that time, a binder may be added to maintain the overall strength and shape. Note that as the binder, organic binders such as resins, inorganic binders such as ceramic precursors, etc. can be used.

Further, it is preferable that the infusible fiber has a fiber diameter of 1 to 30 μm. When the fiber diameter of the infusible fiber is 1 μm or more, the rate of air oxidation and sublimation can be suppressed even when exposed to high temperatures, and the flameproof effect can be maintained for a long time. On the other hand, when the fiber diameter of the infusible fiber is 30 μm or less, it can maintain a certain degree of flexibility even when exposed to high temperatures and carbonized, and can be made difficult to break even when deformed or impacted.

In addition to the infusible fibers, the above-mentioned organic fibers and inorganic particles can also be included.

Further, the inorganic heat insulating material 20 may be a dry sheet or a wet sheet. Below, a method for manufacturing the inorganic heat insulating material 20 will be explained.

(Method for manufacturing inorganic heat insulating material 20)
The inorganic heat insulating material 20 is manufactured by molding fiber components, particle components, and other compounded materials using a dry molding method or a wet molding method. As for the dry molding method, for example, a press molding method (dry press molding method) and an extrusion molding method (dry extrusion molding method) can be used.

(Manufacturing method using dry press molding method)
In the dry press molding method, fiber components, particle components, and other compounding materials are charged into a mixer such as a V-type mixer at predetermined ratios. Then, after sufficiently mixing the materials put into the mixer, the mixture is put into a predetermined mold and press-molded, whereby the inorganic heat insulating material 20 can be obtained. During press molding, heating may be performed if necessary.

Note that the press pressure during press molding is preferably in the range of 0.98 MPa or more and 9.80 MPa or less. If the press pressure is less than 0.98 MPa, the obtained inorganic heat insulating material 20 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 may be reduced due to excessive compression, or that solid heat transfer may increase due to increased bulk density, resulting in a reduction in heat insulation properties.

Furthermore, when using the dry press molding method, it is preferable to use polyvinyl alcohol (PVA) as the organic binder, but any organic binder commonly used when using the dry press molding method may be used. For example, it can be used without particular limitation.

(Manufacturing method using dry extrusion molding method)
In the dry extrusion method, a paste is prepared by adding fiber components, particle components, and other compounding materials to water in predetermined proportions and kneading with a kneader. Thereafter, the inorganic heat insulating material 20 can be obtained by extruding the obtained paste through a slit-shaped nozzle using an extrusion molding machine and drying it. When using the dry extrusion method, it is preferable to use methyl cellulose, water-soluble cellulose ether, etc. as the organic binder, but if it is an organic binder commonly used when using the dry extrusion method, there are no particular limitations. It can be used without.

(Manufacturing method using wet molding method)
In the wet molding method, a mixed liquid is prepared by adding fiber components, particle components, and other compounding materials to water at predetermined ratios, mixing in water, and stirring with a stirrer. Thereafter, a wet sheet is produced by dehydrating the obtained liquid mixture through a filtration mesh. Thereafter, the inorganic heat insulating material 20 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, but this aeration drying process is not performed and the sheet is heated and Pressure may be applied. Furthermore, when using a wet molding method, cationized starch or acrylic resin can be selected as the organic binder.

(Busbar manufacturing method)
As described above, the bus bar 1 is manufactured by covering the portion (surface) of the bus bar body 5 excluding the connection holes 6a and 6b (see FIG. 1) with the inorganic heat insulating material 20 manufactured by the manufacturing method described above. can do.

Alternatively, the busbar 1 may be manufactured by applying a coating liquid containing at least one of inorganic fibers and inorganic particles to the busbar body 5 and then drying the coating liquid.
Specifically, it is manufactured as follows. First, at least one of inorganic fibers and inorganic particles, and if necessary, a resin binder and other additives are weighed, added to thinner as a dispersion medium, and thoroughly mixed to prepare a coating liquid. . Subsequently, the area around the connection holes 6a and 6b (see FIG. 1) in the busbar body 5 is masked, and the coating liquid is applied, and then the coating film is dried to form the inorganic heat insulating material 20 according to the present embodiment. . Note that there are no restrictions on the coating method, and various methods are possible, such as coating using a brush, roll coater, spray, etc., or immersing the bus bar body 5 in a coating liquid.
In addition, before forming the inorganic heat insulating material 20, an undercoat material for rust prevention is applied to the surface of the bus bar body 5 using a brush to a predetermined thickness, and then the coating is dried and an undercoat is applied. A coating film may be formed, and the inorganic heat insulating material 20 may be formed on the undercoat coating film.

Here, the above-mentioned drying includes not only the hardening treatment of the coating film by heat treatment, but also the hardening treatment of the coating film by natural drying at room temperature. Further, it may be heated to about 100° C. to accelerate the hardening process.

In addition, the method of winding the mica sheet as in Patent Document 1 requires a winding operation, and the winding operation is particularly time-consuming in order to prevent uneven winding or gaps from occurring at the bent portion 5a or the curved portion. . Furthermore, it is assumed that a gap may be created due to vibration or the like, or that the adhesive may peel off. However, in this embodiment, such a problem does not occur because the inorganic heat insulating material 20 is formed by coating.

[Power storage device]
4A shows a case where the bus bar 1 shown in FIG. 1A is used, and as shown, the power storage device 100 has a plurality of battery cells 110 housed in a battery case 120. Adjacent battery cells 110 are connected by bus bars 1 in FIG. 1A.

FIG. 4B shows a case where the bus bar 1 shown in FIG. 1B is used, and as shown, the power storage device 100 has a plurality of battery cells 110 housed in a battery case 120. Adjacent battery cells 110 are connected by bus bars 1 in FIG. 1B.

Since the bus bar 1 includes the inorganic heat insulating material 20, even if a certain battery cell 110 causes thermal runaway, the bus bar 1 can be protected, and a chain of thermal runaway to the adjacent battery cell 110 via the bus bar 1 can be prevented. Can be done.

Although not shown, a plurality of battery modules may be connected to each other by the bus bar 1, or at least one battery cell and at least one battery module may be connected by the bus bar 1.

1 Busbar 5 Busbar bodies 6a, 6b Connection hole 20 Inorganic heat insulating material 30 Inorganic fiber sheet 40 Endothermic reaction layer 50 Insulating tape 100 Power storage device 110 Battery cell 111 Electrode 120 Battery case

Claims (18)

A bus bar used in a power storage device including a battery cell,
A busbar comprising an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles on the surface of a busbar body made of a conductive material. The bus bar according to claim 1, wherein the inorganic heat insulating material includes both the inorganic fibers and the inorganic particles. The bus bar according to claim 1 or 2, wherein the inorganic heat insulating material is a wet sheet or a dry sheet. The busbar according to claim 1 or 2, wherein an endothermic reaction layer is interposed between the busbar main body and the inorganic heat insulating material. The bus bar according to claim 1 or 2, wherein an inorganic fiber cloth is arranged on a side of the inorganic heat insulating material facing the battery cells. 6. The bus bar according to claim 5, wherein the laminate of the bus bar body and the inorganic heat insulating material is wound with the inorganic fiber cloth. The bus bar according to claim 1 or 2, wherein the inorganic heat insulating material includes infusible fibers. The busbar according to claim 7, wherein the infusible fiber has a carbon content of 55 to 95% by mass. 8. The busbar according to claim 7, wherein the infusible fibers are short fibers. The bus bar according to claim 7, wherein the infusible fiber has a fiber diameter of 1 to 30 μm. The bus bar according to claim 1 or 2, wherein the inorganic heat insulating material contains organic fiber. The bus bar according to claim 1 or 2, wherein the inorganic heat insulating material contains inorganic particles. The bus bar according to claim 12, wherein the inorganic particles include first inorganic particles and second inorganic particles having different average particle diameters. The bus bar according to claim 13, wherein the first inorganic particles are made of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles. The bus bar according to claim 14, wherein the first inorganic particles are made of at least one selected from nanoparticles, hollow particles, and porous particles. The bus bar according to claim 13, wherein the second inorganic particles are metal oxide particles. A method for manufacturing a bus bar used in a power storage device including a battery cell, the method comprising:
A method for manufacturing a busbar, comprising applying a coating liquid containing at least one of inorganic fibers and inorganic particles to a busbar body containing a conductive material, and then drying the coating liquid. A power storage device comprising a plurality of battery cells or battery modules connected by the bus bar according to claim 1 or 2.

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