JP7832052B2 - Busbars and energy storage devices - Google Patents

Description

This invention relates to a busbar and an energy storage device in which multiple battery cells are connected by a busbar.

Various electronic devices, electric vehicles or hybrid vehicles driven by electric motors, and storage batteries are equipped with energy storage devices that connect multiple battery cells in series or parallel using busbars. Furthermore, lithium-ion secondary batteries, which offer higher capacity and output compared to lead-acid batteries and nickel-metal hydride batteries, are primarily used as battery cells.

However, during charging and discharging, if an overcurrent is passed through the battery cell, the busbars used for connection may overheat. Therefore, Patent Document 1 describes covering the busbars with a mica sheet.

Japanese Patent Publication No. 2020-528650

Incidentally, overcharging or other factors can cause a battery cell to overheat, reaching temperatures of several hundred degrees Celsius, and in some cases, even emitting flames. In such abnormal situations, the busbar is also exposed to similar high temperatures and flames, causing adjacent battery cells to become extremely hot via the busbar.

However, Patent Document 1 addresses measures to suppress the heat generation of the busbar itself, and does not focus on protecting the busbar from high temperatures or flames from the battery cell during abnormal conditions. Furthermore, because mica contains crystalline water, it expands or releases crystalline water when exposed to high temperatures or flames during abnormal conditions, becoming structurally unstable.

Therefore, the present invention aims to provide a busbar that can protect battery cells from high temperatures and flames during abnormal situations. Furthermore, the present invention aims to provide an energy storage device that connects battery cells using such a busbar, thereby demonstrating high safety even during abnormal situations.

The above objective of the present invention is achieved by the following configuration [1] relating to the busbar.

[1] A busbar used in an energy storage device including a battery cell,
A busbar in which the busbar body, made of a conductive material, is wound with an inorganic fiber sheet.

Furthermore, preferred embodiments of the present invention relating to busbars are described in the following [2] to [19].

[2] The bus bar according to [1], characterized in that the inorganic fiber sheet is an inorganic fiber cloth.
[3] The bus bar according to [1], characterized in that the inorganic fiber sheet is at least one selected from silica fiber, alumina fiber, glass fiber, rock wool fiber, and AES (alkali earth silicate) fiber.
[4] The bus bar according to [1], characterized in that the inorganic fiber sheet is wound in multiple layers.
[5] The busbar according to [2], characterized in that an inorganic heat insulating material is placed between the side of the inorganic fiber sheet facing the battery cell and the busbar body, and is wound together with the busbar body by the inorganic fiber sheet.
[6] The bus bar according to [5], characterized in that the inorganic thermal insulation material is a wet sheet or a dry sheet containing inorganic particles.
[7] The busbar according to [5], characterized in that the inorganic fiber cloth is not bonded to itself, nor to the inorganic fiber cloth, the inorganic heat insulating material, and the busbar body, except for the surface opposite to the surface facing the battery cell.
[8] The bus bar according to [5], characterized in that at least one between the inorganic fiber cloth, the inorganic insulation material, and the bus bar body is not bonded and an air layer exists.
[9] The bus bar according to [2], characterized in that the inorganic fiber cloths are bonded together on the side opposite to the side facing the battery cell.
[10] The bus bar according to [5], characterized in that the inorganic thermal insulation material includes inorganic fibers or infusible fibers.
[11] The bus bar according to [10], characterized in that the infusible fiber has a carbon content of 55 to 95% by mass.
[12] The bus bar according to [10], characterized in that the infusible fibers consist of short fibers.
[13] The bus bar according to [10], characterized in that the infusible fiber has a fiber diameter of 1 to 30 μm.
[14] The bus bar according to [5], characterized in that the inorganic heat insulating material contains organic fibers.
[15] The bus bar according to [5], characterized in that the inorganic heat insulating material contains inorganic particles.
[16] The bus bar according to [15], characterized in that the inorganic particles include first inorganic particles and second inorganic particles having different average particle diameters.
[17] The busbar according to [16], characterized in that the first inorganic particles consist of at least one selected from oxide particles, carbide particles, nitride particles and inorganic hydrate particles.
[18] The busbar according to [16] or [17], characterized in that the first inorganic particle consists of at least one selected from nanoparticles, hollow particles and porous particles.
[19] The bus bar according to [16], characterized in that the second inorganic particles are metal oxide particles.

Furthermore, the above-mentioned objective of the present invention is achieved by the configuration of the energy storage device described in [20] below.

[20] A power storage device comprising multiple battery cells or modules connected by a busbar as described in any one of [1] to [19].

The busbar of this invention has its body wrapped in an inorganic fiber sheet, which protects it from high temperatures and flames from battery cells experiencing thermal runaway in the event of an abnormality.

Furthermore, because the energy storage device of this invention connects multiple battery cells and modules using such busbars, it exhibits high safety even in the event of a malfunction.

Figure 1A is a perspective view showing an example of the busbar of the present invention. Figure 1B is a perspective view showing another example of the busbar of the present invention. Figure 2 is a cross-sectional view of Embodiment 1, taken along the line A-A in Figure 1A. Figure 3 is a cross-sectional view of Embodiment 2, taken along the line A-A in Figure 1A. Figure 4A is a cross-sectional view showing a power storage device equipped with the busbars shown in Figure 1A. Figure 4B is a cross-sectional view showing a power storage device equipped with the busbars shown in Figure 1B.

The embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below, and can be modified and implemented as desired without departing from the spirit of the invention.

[Overall configuration of the bus bar]
Figure 1A is a perspective view showing an example of the busbar 1 of the present invention, showing it attached to a battery cell 110. As shown in the figure, the busbar body 5, made of a conductive material, is for example a metal plate member that is Z-shaped overall. The electrodes 111 of the battery cell 110 are inserted into the connection hole 6a at one end, and a terminal cap 112 is placed over it to secure it. The connection hole 6b at the other end of the busbar body 5 is connected to an adjacent battery cell (not shown) or an external device. The busbar 1 is constructed by winding an inorganic fiber sheet 10, which will be described later, around the part (surface) of the busbar body 5 excluding the connection holes 6a and 6b.

Furthermore, the busbar body 5 can be made entirely of an I-shaped flat plate, as shown in Figure 1B, and the portion excluding the connection holes 6a and 6b at both ends can be covered with an inorganic fiber sheet 10 to form the busbar 1.

Furthermore, the busbar 1 may be directly or indirectly connected to the electrodes 111 of the battery cell 110, or it may be electrically connected to the electrodes 111 of the battery cell 110.

<Embodiment 1>

Figure 2 is a cross-sectional view taken along the line A-A in Figure 1A. The battery cell 110 is located at the bottom of the figure. In the event of a malfunction, high temperatures and flames will be generated from the battery cell 110. Therefore, an inorganic fiber sheet 10 is wound around the busbar body 5. In the illustrated example, the inorganic fiber sheet 10 is wound around the busbar body 5 three times, but it may be wound once or multiple times. In all cases, the end portion 10a of the winding should be located on the side that does not face the battery cell 110.

In the event of an abnormality, in addition to the high temperature emanating from the battery cell 110, gas from the electrolyte and fragments of the battery cell 110 are generated along with flames. Therefore, it is preferable that the inorganic fiber sheet 10 has excellent heat resistance and barrier properties against gas and fragments. For this reason, an inorganic fiber cloth (woven fabric) is preferred as the inorganic fiber sheet 10, and at least one selected from silica fiber, alumina fiber, glass fiber, rock wool fiber, and AES (alkali earth silicate) fiber is preferred. AES fiber is an artificial mineral fiber made from high-purity silica, calcia, and magnesia.

Furthermore, during winding, the inorganic fiber sheets 10 do not need to be bonded to each other or to the busbar 1 and the inorganic fiber sheets 10 on the side facing the battery cell 110. By not bonding them, an air layer is formed between the inorganic fiber sheets 10 and adjacent inorganic fiber sheets 10, and between the inorganic fiber sheets 10 and the surface 5a of the busbar body 5 facing the battery cell 110, thereby improving heat insulation performance.

A heat-absorbing reaction layer 20 may be interposed between the surface 5b of the busbar body 5 (opposite to surface 5a) and the inorganic fiber sheet 10. The heat-absorbing reaction layer 40 has the effect of absorbing heat from the battery cell 110 that has experienced thermal runaway, thereby enhancing the heat insulation performance. Various resins can be used as the heat-absorbing reaction layer 40, but a double-sided tape with adhesive layers formed on both sides of a resin base material is preferred because it can bond and fix the busbar body 5 and the inorganic fiber sheet 10 together.

Furthermore, the endothermic reaction layer 20 may be interposed between the portion of the inorganic fiber sheet 10 that contacts the surface 5b of the busbar body 5 and the end portion 10a of the winding, further enhancing the thermal insulation performance.

<Embodiment 2>
As shown in Figure 3, an inorganic heat insulating material 30 may be interposed (placed) between the surface 5a of the busbar body 5 and the inorganic fiber sheet 10 before winding it. The inorganic heat insulating material 30 further enhances the heat insulating performance on the side facing the battery cell 110, and even if the battery cell 110 experiences thermal runaway, the chain reaction of thermal runaway can be prevented more reliably.

The side facing the battery cell 110, i.e., the space between the surface 5a of the busbar body 5 and the inorganic insulation material 30, and the space between the inorganic insulation material 30 and the portion 10b of the inorganic fiber sheet 10 facing the battery cell 110, do not need to be bonded. By not bonding them, an air layer is formed between them, improving the insulation performance.

Furthermore, similar to Embodiment 1, the endothermic reaction layer 20 may be interposed between the surface 5b of the busbar body 5 opposite to surface 5a and the inorganic fiber sheet 10, or between the portion of the inorganic fiber sheet 10 that contacts surface 5b of the busbar body 5 and the winding end portion 10a, thereby further enhancing the thermal insulation performance.

[Regarding inorganic insulation material 30]
In both Embodiment 1 and Embodiment 2 described above, there are no restrictions on the inorganic thermal insulation material 30, but it is preferable to include the following compound materials because they have excellent thermal insulation performance.

(Inorganic fibers)
The inorganic thermal insulation material 30 may contain inorganic fibers. Specifically, inorganic fibers having a melting point of less than 700°C are preferred, and many amorphous inorganic fibers can be used. Among these, fibers containing _SiO2 are preferred, and glass fibers are more preferred because they are inexpensive, readily available, and have excellent handling properties.

Furthermore, when the inorganic fiber is crystalline, specifically, ceramic fibers such as silica fibers, alumina fibers, alumina silicate fibers, zirconia fibers, carbon fibers, soluble fibers, refractory ceramic fibers, aerogel composites, magnesium silicate fibers, alkali earth silicate fibers, potassium titanate fibers, glass fibers, glass wool, and other glass-based fibers, as well as mineral fibers such as rock wool, basalt fibers, and wollastonite, can be used.

Furthermore, if the melting point exceeds 1000°C, the inorganic fiber will not melt or soften even if thermal runaway occurs in the battery cell, and will maintain its shape, making it suitable for use. Among the inorganic fibers listed above, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers, and alumina silicate fibers, as well as mineral fibers. Among these, it is even more preferable to use those with a melting point exceeding 1000°C.

(Other ingredients)
In addition to the inorganic fibers mentioned above, the inorganic insulation material 30 may also contain organic binders, organic fibers, and inorganic particles.

(Resin binder)
The inorganic fibers described above can also be bound together with a resin binder. The resin binder is not particularly limited as long as it has a glass transition temperature lower than that of the organic fibers described later. 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.

The glass transition temperature of the resin binder is not specifically defined, but it is preferably -10°C or higher. Furthermore, if the glass transition temperature of the resin binder is above room temperature, the strength of the inorganic insulation material 30 containing the resin binder can be further improved when used at room temperature. Therefore, the glass transition temperature of the resin binder is 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.

The resin binder content is preferably 0.5% by mass or more, more preferably 1% by mass or more, relative to the total mass of the inorganic insulation material 30. Furthermore, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

(Organic fibers)
In addition to the inorganic fibers mentioned above, organic fibers may also be included. As organic fibers, at least one selected from polyvinyl alcohol (PVA) fibers, polyethylene fibers, nylon fibers, polyurethane fibers, and ethylene-vinyl alcohol copolymer fibers can be used.

Furthermore, as will be described later, the inorganic insulation material 30 can also be manufactured by papermaking. However, since it is difficult to raise the heating temperature above 250°C in this process, the glass transition temperature of the organic fibers is preferably 250°C or lower, and more preferably 200°C or lower.

While there are no particular limitations on the lower limit of the glass transition temperature of the organic fibers, if the difference between the glass transition temperature of the organic fibers and that of the resin binder is 10°C or more, the resin binder will solidify after the semi-molten organic fibers have completely solidified during the cooling process in manufacturing. Therefore, the reinforcing effect of the resin binder on the skeleton can be fully obtained. Accordingly, the difference between the glass transition temperature of the resin binder and that of the organic fibers is preferably 10°C or more, and more preferably 30°C or more.

On the other hand, if the difference in the glass transition temperatures between the two is 130°C or less, the time between the complete solidification of the organic fibers and the start of solidification of the resin binder can be appropriately adjusted. Since the resin binder solidifies while maintaining a good dispersion state, an even greater reinforcement effect on the framework can be obtained. Therefore, the difference between the glass transition temperature of the resin binder and the glass transition temperature of the organic fibers is preferably 130°C or less, more preferably 120°C or less, even more preferably 100°C or less, even more preferably 80°C or less, and particularly preferably 70°C or less.

Furthermore, the mixture may contain two or more types of organic fibers. In this case, at least one of the organic fibers must act as a framework, i.e., an organic fiber having a glass transition temperature higher than that of the resin binder. The difference between the glass transition temperature of the resin binder and the glass transition temperature of at least one type of organic fiber is preferably 10°C or higher, more preferably 30°C or higher, preferably 130°C or lower, more preferably 120°C or lower, even more preferably 100°C or lower, even more preferably 80°C or lower, and particularly preferably 70°C or lower.

When the content of organic fibers and resin binder is appropriately controlled, the function of the organic fibers as a skeleton can be fully obtained, as can the reinforcing effect of the resin binder on the skeleton. The content of organic fibers is preferably 0.5% by mass or more, more preferably 1% by mass or more, relative to the total mass of the inorganic insulation material 30. Furthermore, it is preferably 12% by mass or less, and more preferably 8% by mass or less. When multiple organic fibers having a glass transition temperature higher than the glass transition temperature of the resin binder are included, it is preferable that the total amount of these multiple organic fibers is within the above-mentioned organic fiber content range.

As described above, when two or more types of organic fibers are included, it is sufficient if at least one type of organic fiber has a glass transition temperature higher than that of the resin binder. However, it is more preferable to include crystalline organic fibers that do not have a glass transition temperature as the other organic fibers.

It is also possible to include organic fibers in a crystalline state that do not have a glass transition temperature. Since these crystalline organic fibers do not have a softening point, the strength of the inorganic insulation material 30 can be maintained even when exposed to high temperatures that would cause the skeletal organic fibers to soften. Furthermore, by including organic fibers in a crystalline state, these organic fibers also act as the skeletal structure of the insulation material at room temperature (20°C). Therefore, the flexibility and handling properties of the inorganic insulation material 30 can be improved.

Polyester (PET) fibers are an example of organic fibers in a crystalline state.

Furthermore, when manufacturing the inorganic insulation material 30 using the papermaking method, it is preferable to use water as the dispersion liquid, but it is preferable that the organic fibers have low solubility in water. While the "water dissolution temperature" can be used as an indicator of solubility in water, the water dissolution temperature of the organic fibers is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

While there are no particular limitations on the fiber length of the organic fibers, it is preferable that the average fiber length be 10 mm or less from the viewpoint of ensuring moldability and processability. On the other hand, from the viewpoint of allowing the organic fibers to function as a framework and ensuring the compressive strength of the thermal insulation material, it is preferable that the average fiber length be 0.5 mm or more.

(Inorganic particles)
Furthermore, inorganic particles can also be included. If the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are readily available and the increase in manufacturing costs can be suppressed. Also, if it is 200 μm or less, the desired heat insulating 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, and more preferably 0.05 μm or more and 100 μm or less.

As inorganic particles, a single inorganic particle may be used, or two or more types of inorganic particles (first inorganic particles and second inorganic particles) may be used in combination. From the viewpoint of heat transfer suppression effect, it is preferable to use particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles as the first and second inorganic particles, and more preferably oxide particles. Furthermore, the shape of the first and second inorganic particles is not particularly limited, but it is preferable to include at least one selected from nanoparticles, hollow particles, and porous particles. Specifically, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, particles made of water-containing porous materials, etc., can also be used.

Furthermore, by using two or more inorganic particles with different heat transfer suppression effects, multi-stage cooling is possible, and the endothermic effect can be exhibited over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter and small-diameter particles. For example, when using nanoparticles as one type of inorganic particle, it is preferable to include inorganic particles made of metal oxides as the other type of inorganic particle. Below, the inorganic particles will be described in more detail, with small-diameter inorganic particles referred to as the first inorganic particles and large-diameter inorganic particles as the second inorganic particles.

(First inorganic particle)
(Oxide particles)
As the first inorganic particles, oxide particles are preferred. Oxide particles have a high refractive index and a strong effect of diffusely reflecting light, so they can suppress radiative heat transfer, especially in high-temperature regions such as abnormal heat generation. As 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 higher refractive index compared to other metal oxides, and has a high effect of diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher, so it is most preferable to use silica and titania as oxide particles.

The particle size of oxide particles can affect the effect of reflecting radiant heat; therefore, limiting the average primary particle size to a predetermined range can achieve even higher thermal insulation. Specifically, if the average primary particle size of the oxide particles is 0.001 μm or larger, it is sufficiently larger than the wavelength of light contributing to heating, efficiently scattering light. This suppresses radiative heat transfer in the inorganic thermal insulation material 30 in the high-temperature range of 500°C or higher, further improving thermal insulation. On the other hand, if the average primary particle size of the oxide particles is 50 μm or less, the number and contact points between particles do not increase even when compressed, making it difficult to form conduction heat transfer paths. Therefore, the impact on thermal insulation, especially in the normal temperature range where conduction heat transfer is dominant, can be reduced.

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

(Nanoparticles)
Nanoparticles are preferred as the first inorganic particles. Because nanoparticles have a low density, they suppress conductive heat transfer, and because the voids are finely dispersed, they suppress convective heat transfer, resulting in excellent thermal insulation. For this reason, it is preferable to use nanoparticles when using batteries at normal room temperature, as they can suppress heat conduction between adjacent nanoparticles.

Furthermore, nanoparticles refer to particles that are spherical or nearly spherical, with an average primary particle diameter of less than 1 μm, on the order of nanometers.

Furthermore, by using nanoparticles with a small average primary particle diameter as oxide particles, it is possible to suppress the increase in conductive heat transfer of the inorganic insulation material 30 even when the internal density of the inorganic insulation material 30 increases due to expansion associated with thermal runaway of the battery cell. This is thought to be because nanoparticles easily create fine voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed in a way that provides cushioning.

Furthermore, when nanoparticles are used as the first inorganic particles, the material is not particularly limited as long as it conforms to the above definition of nanoparticles. For example, silica nanoparticles are a material with high thermal insulation properties, and because the contact points between particles are small, the amount of heat conducted by silica nanoparticles is smaller compared to when silica particles with a larger particle size are used. In addition, since commonly available silica nanoparticles have a bulk density of about 0.1 (g/ ^cm³ ), even if a large compressive stress is applied to the inorganic thermal insulation material 30, for example, the size (area) and number of contact points between silica nanoparticles do not increase significantly, and thermal insulation properties can be maintained. Therefore, it is preferable to use silica nanoparticles as nanoparticles. As 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 thermal insulation can be obtained. Specifically, by setting the average primary particle diameter of the nanoparticles to 1 nm or more and 100 nm or less, convective and conductive heat transfer within the insulating material can be suppressed, particularly in the temperature range below 500°C, thereby further improving thermal insulation. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the numerous contact points between particles suppress conductive heat transfer, maintaining the thermal insulation properties of the inorganic insulating material 30. 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, when exposed to heat from a heat source and exceeding their decomposition start temperature, undergo thermal decomposition, releasing their crystalline water and lowering the temperature of the heat source and its surroundings—a phenomenon known as "endothermic action." After releasing the crystalline water, they become porous, exhibiting insulating properties through their numerous air pores.

Specific examples of inorganic hydrates include aluminum hydroxide (Al(OH) _₃ ), magnesium hydroxide (Mg(OH) _₂ ), calcium hydroxide (Ca(OH) _₂ ), zinc hydroxide (Zn(OH) _₂ ), iron hydroxide (Fe(OH) _₂ ), manganese hydroxide (Mn(OH) _₂ ), zirconium hydroxide (Zr(OH) _₂ ), and gallium hydroxide (Ga(OH) _₃ ).

For example, aluminum hydroxide contains approximately 35% crystal water, and as shown in the formula below, it undergoes thermal decomposition to release crystal water, exhibiting an endothermic effect. After releasing the crystal water _, it becomes a porous alumina ( _Al₂O₃ ) and functions as an insulating material.
2Al(OH) ₃ →Al ₂ O ₃ +3H ₂ O

Furthermore, in battery cells experiencing thermal runaway, the temperature rapidly rises to over 200°C and continues to rise to around 700°C. Therefore, it is preferable that the inorganic particles consist of inorganic hydrates whose thermal decomposition initiation temperature is 200°C or higher.

The thermal decomposition initiation temperatures for the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, 330°C for magnesium hydroxide, 580°C for calcium hydroxide, 200°C for zinc hydroxide, 350°C for iron hydroxide, 300°C for manganese hydroxide, 300°C for zirconium hydroxide, and 300°C for gallium hydroxide. These temperatures largely overlap with the temperature ranges at which battery cells undergo thermal runaway rapidly increase in temperature. Therefore, these inorganic hydrates are considered desirable because they can efficiently suppress temperature rise.

Furthermore, if the average particle size of the inorganic hydrate particles is too large, it may take a certain amount of time for the inorganic hydrate particles near the center of the inorganic insulation material 30 to reach their thermal decomposition temperature, resulting in the inorganic hydrate particles near the center of the inorganic insulation material 30 not being completely decomposed. Therefore, the average secondary particle size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and 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, mica, and perlite.

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

(Inorganic balloon)
The inclusion of inorganic balloons can suppress convective or conductive heat transfer within the insulating material in the temperature range below 500°C, thereby further improving the thermal insulation performance of the inorganic insulating material 30.

As the inorganic balloon, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barlite balloons, and glass balloons can be used.

The inorganic balloon content is preferably 60% by mass or less relative to the total mass of the inorganic insulation material 30.

Furthermore, the average particle size of the inorganic balloons is preferably between 1 μm and 100 μm.

(Second inorganic particle)
The second inorganic particles are not particularly limited as long as they differ from the first inorganic particles in terms of material, particle size, etc. Examples of 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, particles made of thermally expandable inorganic materials, and particles made of water-containing porous materials. Details of these are as described above.

Furthermore, nanoparticles exhibit extremely low conductive heat transfer and can maintain excellent thermal insulation even when compressive stress is applied to the inorganic thermal insulation material 30. Additionally, metal oxide particles such as titania have a high effect in blocking radiant heat. Moreover, using both large-diameter and small-diameter inorganic particles allows the small-diameter particles to fill the gaps between the large-diameter particles, resulting in a denser structure and improving the heat transfer suppression effect. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further incorporate metal oxide particles, which are larger in diameter than the first inorganic particles, into the inorganic thermal insulation material 30 as the second inorganic particles.

Examples of metal oxides include silicon dioxide, titanium dioxide, aluminum oxide, barium titanate, zinc oxide, zircon, and zirconium oxide. In particular, titanium dioxide (titania) has a higher refractive index compared to other metal oxides, and is highly effective at diffusely reflecting light and blocking radiant heat in high-temperature regions above 500°C; therefore, using titania is most preferable.

If the average primary particle diameter of the second inorganic particles is between 1 μm and 50 μm, radiative heat transfer can be efficiently suppressed in the high-temperature region of 500°C or higher. More preferably, the average primary particle diameter of the second inorganic particles is between 5 μm and 30 μm, and most preferably 10 μm or less.

(Infusible fibers)
In lieu of, or in part thereof, the inorganic fibers mentioned above may be replaced with infusible fibers. Examples of infusible fibers include fibers obtained by infusifying thermoplastic resins such as polyacrylonitrile, cellulose, and pitch. Infusible fibers are, for example, fibers that have been treated to be infusible. Infusible treatment methods include irradiating with radiation or electron beams to cause crosslinking, or exposing to high temperatures in oxygen or water vapor to cause infusibility through the action of oxygen.

(Carbon content)
The infusible fibers preferably have a carbon content of 55 to 95% by mass. If the carbon content is 55% by mass or more, weight loss due to thermal decomposition has already begun, so shrinkage due to thermal decomposition is small, and even when directly exposed to flames during runaway thermal activity, the original shape can be retained and the insulating properties can be maintained. If the carbon content is 95% by mass or less, an endothermic reaction occurs as components other than carbon are removed and the structure changes to one consisting only of carbon, so the time it takes for heat to reach the back surface of the inorganic insulating material 30 can be delayed.

The desirable lower limit for carbon content is 60% by mass or more. Furthermore, the desirable upper limit for carbon content is 90% by mass or less, and the even more desirable upper limit for carbon content is 85% by mass or less.

The carbon content can be adjusted by heat treatment. For example, heat treatment in air or oxygen within the range of 150 to 300°C further promotes infusibility and removes components other than carbon, thereby increasing the carbon content. For example, heat treatment within the range of 300 to 1000°C promotes the formation of condensed polycyclic aromatic structures and generates decomposition gases, thereby increasing the carbon content.

Furthermore, infusible fibers are not limited to thermoplastic fibers that have been made infusible. Inorganic fibers may also be used, as long as they fall within the carbon content range mentioned above.

(Fiber shape)
Infusible fibers consist of short fibers, and it is preferable that these fibers are aggregated to form a mat, paper-formed body, or blanket as an overall structure.

The term "short fiber" indicates that the fibers are not continuous fibers. In continuous fibers, the fiber orientation is aligned to form a fiber bundle, as in cross-filament winding. However, using short fibers results in an aggregate (mat, blanket, or paper-formed material) where the fibers are randomly oriented. Furthermore, because the inorganic insulation material 30 using short fibers has short conductive paths, its conductivity can be kept low even if carbonization progresses through carbonization due to thermal runaway or if the fibers undergo significant carbonization. Additionally, the random orientation of the fibers makes point contact between them more likely, further reducing thermal conductivity.

Paper-formed materials can be obtained by dispersing milled or chopped infusible fibers (fiber length approximately 0.01 to 10 mm) in water and then forming the paper. Mats and blankets can be obtained by laminating and compressing infusible fibers with a fiber length of approximately 10 to 1000 mm. A binder may be added to maintain overall strength and shape. Suitable binders include organic binders such as resins and inorganic binders such as ceramic precursors.

Furthermore, the infusible fibers preferably have a fiber diameter of 1 to 30 μm. If the fiber diameter of the infusible fibers is 1 μm or larger, the rate of air oxidation and sublimation is suppressed even when exposed to high temperatures, allowing the flame-retardant effect to be maintained for a long period. On the other hand, if the fiber diameter of the infusible fibers is 30 μm or less, a certain degree of flexibility is maintained even when carbonized by exposure to high temperatures, making them less susceptible to damage even when deformed or impacted.

In addition to infusible fibers, the material may also contain the organic fibers and inorganic particles mentioned above.

Furthermore, the inorganic insulation material 30 may be a dry sheet or a wet sheet. The manufacturing method is described below.

(Method for manufacturing inorganic thermal insulation material 30)
The inorganic thermal insulation material 30 is manufactured by molding fibrous components, particulate components, and other compounding materials using a dry molding method or a wet molding method. 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)
In the dry press molding method, fiber components, particle components, and other compounding materials are put into a mixer such as a V-type mixer in predetermined proportions. After the materials put into the mixer are thoroughly mixed, this mixture is put into a predetermined mold and press-molded to obtain the inorganic heat insulating material 30. Heating may be performed during press molding as needed.

Furthermore, the press pressure during press forming is preferably in the range of 0.98 MPa to 9.80 MPa. If the press pressure is less than 0.98 MPa, the resulting inorganic thermal insulation material 30 may collapse due to insufficient strength. On the other hand, if the press pressure exceeds 9.80 MPa, excessive compression may reduce processability, and the increased bulk density may lead to increased solid heat transfer and a decrease in thermal insulation performance.

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

(Manufacturing method using dry extrusion molding)
In the dry extrusion molding method, a paste is prepared by adding fiber components, particle components, and other compounding materials to water in predetermined proportions and kneading them in a kneader. Then, the obtained paste is extruded through a slit-shaped nozzle using an extruder and further dried to obtain the inorganic heat insulating material 30. When using the dry extrusion molding method, it is preferable to use methylcellulose and water-soluble cellulose ether as the organic binder, but any organic binder commonly used in the dry extrusion molding method can be used without particular limitation.

(Manufacturing method using wet molding)
In the wet molding method, fiber components, particle components, and other compounding materials are added to water in predetermined proportions, mixed in the water, and stirred with a stirrer to prepare a mixture. Then, the resulting mixture is dewatered through a filtration mesh to produce a wet sheet. Subsequently, the obtained wet sheet is heated and pressurized to obtain the inorganic heat insulating material 30.

Furthermore, before the heating and pressurizing process, a ventilated drying treatment may be performed by passing hot air through the wet sheet to dry it. However, this ventilated drying treatment may be omitted, and heating and pressurizing may be performed while the sheet remains wet. Also, when using a wet molding method, cationized starch or acrylic resin can be selected as the organic binder.

[Energy storage device]
Figure 4A shows the case using the busbar 1 shown in Figure 1A. As shown, the energy storage device 100 houses multiple battery cells 110 in a battery case 120. Adjacent battery cells 110 are connected by the busbar 1 shown in Figure 1A.

Figure 4B shows the case using the busbar 1 shown in Figure 1B. As illustrated, the energy storage device 100 houses multiple battery cells 110 in a battery case 120. Adjacent battery cells 110 are connected by the busbar 1 shown in Figure 1B.

The busbar 1 is surrounded by a laminate comprising an inorganic heat insulating material 30 and an inorganic fiber sheet 10. This protects the busbar 1 even if a battery cell 110 experiences thermal runaway, and prevents a chain reaction of thermal runaway to adjacent battery cells 110 via the busbar 1.

Although not shown in the diagram, multiple modules may be connected via busbar 1.

1 Busbar 5 Busbar body 6a, 6b Connection hole 10 Inorganic fiber sheet 20 Endothermic reaction layer 30 Inorganic insulation material 100 Energy storage device 110 Battery cell 111 Electrode 120 Battery case

Claims (14)

A busbar used in an energy storage device including a battery cell,
The busbar body, made of conductive material, is wound with an inorganic fiber sheet.
The aforementioned inorganic fiber sheet is an inorganic fiber cloth,
An inorganic heat insulating material is placed between the side of the inorganic fiber sheet facing the battery cell and the busbar body, and is wound together with the busbar body by the inorganic fiber sheet.
The aforementioned inorganic thermal insulation material is a wet sheet or a dry sheet containing inorganic particles, and is characterized by this busbar . A busbar used in an energy storage device including a battery cell,
The busbar body, made of conductive material, is wound with an inorganic fiber sheet.
The aforementioned inorganic fiber sheet is an inorganic fiber cloth,
An inorganic heat insulating material is placed between the side of the inorganic fiber sheet facing the battery cell and the busbar body, and is wound together with the busbar body by the inorganic fiber sheet.
The busbar is characterized in that, except for the surface opposite to the surface facing the battery cell, the inorganic fiber cloths are not bonded to each other, nor to the inorganic fiber cloths, the inorganic insulation material, and the busbar body. A busbar used in an energy storage device including a battery cell,
The busbar body, made of conductive material, is wound with an inorganic fiber sheet.
The aforementioned inorganic fiber sheet is an inorganic fiber cloth,
An inorganic heat insulating material is placed between the side of the inorganic fiber sheet facing the battery cell and the busbar body, and is wound together with the busbar body by the inorganic fiber sheet.
A busbar characterized in that at least one of the inorganic fiber cloth, the inorganic insulation material, and the busbar body is not bonded together, and an air layer exists between them. A busbar used in an energy storage device including a battery cell,
The busbar body, made of conductive material, is wound with an inorganic fiber sheet.
The aforementioned inorganic fiber sheet is an inorganic fiber cloth,
An inorganic heat insulating material is placed between the side of the inorganic fiber sheet facing the battery cell and the busbar body, and is wound together with the busbar body by the inorganic fiber sheet.
The aforementioned inorganic thermal insulation material is characterized by containing inorganic fibers or infusible fibers. The bus bar according to claim 4 , characterized in that the infusible fiber has a carbon content of 55 to 95% by mass. The bus bar according to claim 4 , characterized in that the infusible fibers consist of short fibers. The bus bar according to claim 4 , characterized in that the infusible fiber has a fiber diameter of 1 to 30 μm. A busbar used in an energy storage device including a battery cell,
The busbar body, made of conductive material, is wound with an inorganic fiber sheet.
The aforementioned inorganic fiber sheet is an inorganic fiber cloth,
An inorganic heat insulating material is placed between the side of the inorganic fiber sheet facing the battery cell and the busbar body, and is wound together with the busbar body by the inorganic fiber sheet.
The aforementioned inorganic insulation material is characterized by containing organic fibers. A busbar used in an energy storage device including a battery cell,
The busbar body, made of conductive material, is wound with an inorganic fiber sheet.
The aforementioned inorganic fiber sheet is an inorganic fiber cloth,
An inorganic heat insulating material is placed between the side of the inorganic fiber sheet facing the battery cell and the busbar body, and is wound together with the busbar body by the inorganic fiber sheet.
The aforementioned inorganic thermal insulation material is a bus bar characterized by containing inorganic particles. The bus bar according to claim 9 , characterized in that the inorganic particles include first inorganic particles and second inorganic particles having different average particle diameters from each other. The busbar according to claim 10 , characterized in that the first inorganic particles consist of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles. The bus bar according to claim 10 , characterized in that the first inorganic particle consists of at least one selected from nanoparticles, hollow particles, and porous particles. The bus bar according to claim 10 , characterized in that the second inorganic particles are metal oxide particles. A power storage device comprising multiple battery cells or modules connected by a busbar as described in any one of claims 1 to 13 .