Busbars and energy storage devices

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

Technical Field

[0001] 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.

Background Art

[0002] Power storage devices in which a plurality of battery cells or battery modules are connected in series or in parallel by a bus bar are mounted in various electronic devices, electric vehicles or hybrid vehicles driven by an electric motor, storage batteries, and the like. Further, as the battery cells, lithium ion secondary batteries capable of high capacity and high output are mainly used as compared with lead storage batteries, nickel metal hydride batteries, and the like.

[0003] [[ID=J15]] However, when an overcurrent is applied to a battery cell or a battery module during charging or discharging, the bus bar used for the connection may generate heat. Therefore, in Patent Document 1, the bus bar is covered with a mica sheet.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, due to overcharging or the like, a certain battery cell may cause thermal runaway and reach a high temperature of several hundred degrees Celsius, or in some cases, may emit flames. In such an abnormal situation of the battery, the bus bar is also exposed to the same high temperature or flames, and the adjacent battery cells via the bus bar become hot.

[0006] However, Patent Document 1 addresses measures to suppress the heat generated by the busbar itself and does not focus on protecting the busbar from high temperatures or flames from the battery cells during battery malfunctions. Moreover, because mica contains crystalline water, when exposed to high temperatures or flames during battery malfunctions, it expands or releases crystalline water, becoming structurally unstable.

[0007] Furthermore, Patent Document 1 requires the process of wrapping the mica sheet around the busbar. Due to spatial constraints at the battery cell installation location, the busbar may have a complex shape, and when the busbar has a complex shape, it is difficult to wrap the mica sheet around every corner of the busbar. If there are uneven wrapping or gaps in the mica sheet, the desired effects cannot be fully obtained. Moreover, it is conceivable that the adhesive surface of the mica sheet may peel off at high temperatures.

[0008] Therefore, the present invention aims to provide a busbar that can protect against high temperatures and flames emanating from battery cells in the event of a battery malfunction. Furthermore, the present invention aims to provide a method for manufacturing busbars that does not require winding work like with mica sheets, eliminates problems such as uneven winding or gaps in the sheet, and prevents the sheet from peeling off, and can easily accommodate complex shapes. Furthermore, the present invention aims to provide an energy storage device that connects battery cells or battery modules using such busbars, thereby demonstrating high safety even in the event of a battery malfunction. [Means for solving the problem]

[0009] The above objective of the present invention is achieved by the following configuration [1] relating to the busbar.

[0010] [1] A busbar used in an energy 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.

[0011] Furthermore, preferred embodiments of the present invention relating to busbars are described in the following [2] to

[16] .

[0012] [2] The bus bar according to [1], characterized in that the inorganic thermal insulation material includes both the inorganic fibers and the inorganic particles. [3] The bus bar according to [1] or [2], characterized in that the inorganic insulation material is a wet sheet or a dry sheet. [4] The bus bar according to [1] or [2], characterized in that an endothermic reaction layer is interposed between the bus bar body and the inorganic heat insulating material. [5] The bus bar according to [1] or [2], characterized in that an inorganic fiber cloth is arranged on the side of the inorganic heat insulating material facing the battery cell. [6] The busbar according to [5], characterized in that the laminate of the busbar body and the inorganic heat insulating material is wound with the inorganic fiber cloth. [7] The bus bar according to [1] or [2], characterized in that the inorganic thermal insulation material contains infusible fibers. [8] The bus bar according to [7], characterized in that the infusible fiber has a carbon content of 55 to 95% by mass. [9] The bus bar according to [7], characterized in that the infusible fibers consist of short fibers.

[10] The bus bar according to [7], characterized in that the infusible fiber has a fiber diameter of 1 to 30 μm.

[11] The bus bar according to [1] or [2], characterized in that the inorganic thermal insulation material contains organic fibers.

[12] The bus bar according to [1] or [2], characterized in that the inorganic thermal insulation material contains inorganic particles.

[13] The bus bar according to

[12] , characterized in that the inorganic particles include first inorganic particles and second inorganic particles having different average particle diameters from each other.

[14] The busbar according to

[13] , characterized in that the first inorganic particles consist 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 composed of at least one selected from nanoparticle, hollow particle, and porous particle.

[16] The bus bar according to

[13] , wherein the second inorganic particles are metal oxide particles.

[0013] Further, the above object of the present invention is achieved by the following configuration according to

[17] related to a method for manufacturing a bus bar.

[0014]

[17] A method for manufacturing a bus bar used in a power storage device including a battery cell, characterized in that after applying a coating liquid containing at least one of inorganic fiber and inorganic particles to a bus bar body containing a conductive material, it is dried.

[0015] Further, the above object of the present invention is achieved by the following configuration according to

[18] related to a power storage device.

[0016]

[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] .

Advantages of the Invention

[0017] The bus bar of the present invention is coated with an inorganic heat insulating material containing at least one of inorganic fiber and inorganic particles, and is protected from high temperature and flame from a battery cell that has caused thermal runaway in case of an abnormality of the battery.

[0018] Further, the method for manufacturing the bus bar of the present invention only needs to apply a coating liquid containing at least one of inorganic fiber and inorganic particles to the bus bar body, so the manufacturing process is simple, and an insulating film can be formed uniformly without gaps regardless of the shape of the bus bar body.

[0019] Further, the power storage device of the present invention connects battery cells or battery modules to each other by such a bus bar, so it shows high safety even in case of an abnormality of the battery.

Brief Description of the Drawings

[0020] [Figure 1A] Figure 1A is a perspective view showing an example of the bus bar of the present invention. [Figure 1B] Figure 1B is a perspective view showing another example of the bus bar of the present invention. [Figure 2] Figure 2 is a cross-sectional view showing Embodiment 1 along the line A-A of Figure 1A. [Figure 3] Figure 3 is a cross-sectional view showing Embodiment 2 along the line A-A of Figure 1A. [Figure 4A] Figure 4A is a cross-sectional view showing a power storage device including the bus bar of Figure 1A. [Figure 4B] Figure 4B is a cross-sectional view showing a power storage device including the bus bar of Figure 1B.

Embodiments for Carrying Out the Invention

[0021] 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 arbitrarily modified and implemented without departing from the gist of the present invention.

[0022] [Overall Configuration of Bus Bar] Figure 1A is a perspective view showing an example of the bus bar 1 of the present invention, showing the state of being mounted on the battery cell 110. As shown in the figure, the bus bar main body 5 made of a conductive material is, for example, a metal plate member having an overall Z shape. The electrode 111 of the battery cell 110 is inserted into the connection hole 6a at one tip, and the terminal cap 112 is put on and fixed. Also, an adjacent battery cell (not shown) or an external device is connected to the connection hole 6b at the other tip of the bus bar main body 5. Then, the portion (surface) of the bus bar main body 5 excluding the connection holes 6a and 6b is covered with an inorganic heat insulating material 20 described later, and the bus bar 1 is constituted.

[0023] Also, as shown in Figure 1B, the bus bar main body 5 can be made into an I-shaped flat plate as a whole, and the portion excluding the connection holes 6a and 6b at both ends can be covered with the inorganic heat insulating material 20 to form the bus bar 1.

[0024] 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.

[0025] <Embodiment 1> Figure 2 is a cross-sectional view of the busbar 1 of Embodiment 1, shown along the line AA in Figure 1A. The battery cell 110 is located on the lower side of the figure, and when the battery malfunctions, high temperatures and flames are generated from the battery cell 110. Therefore, an inorganic heat insulating material 20 is placed on the surface 5a of the busbar body 5 that faces the battery cell 110.

[0026] In addition to the inorganic insulation material 20, an inorganic fiber sheet 30 may be laminated on the side facing the battery cell 110. The inorganic insulation material 20 and the inorganic fiber sheet 30 may or may not be bonded. If they are not bonded, an air layer is formed between the inorganic insulation material 20 and the inorganic fiber sheet 30, thereby improving the insulation performance.

[0027] When a battery malfunctions, in addition to the high temperature from the battery cell 110, gas from the electrolyte and fragments of the battery cell 110 are generated along with flames. Therefore, for the inorganic fiber sheet 30, an inorganic fiber cloth, specifically a woven fabric such as glass cloth, silica cloth, or alumina cloth, and especially a silica cloth (woven fabric), is preferred due to its excellent heat resistance and barrier properties against gas and fragments.

[0028] Furthermore, an endothermic reaction layer 40 may be interposed between the surface 5a of the busbar body 5 and the inorganic insulation material 20. The endothermic reaction layer 40 has the effect of absorbing heat from the battery cell 110 that has experienced thermal runaway, thereby improving the insulation performance. Various resins can be used as the endothermic 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 insulation material 20 together.

[0029] Furthermore, an insulating tape (insulating sheet) 50 may be wrapped around (covered) the busbar 1, the endothermic reaction layer 40, the inorganic insulation material 20, and the inorganic fiber sheet 30. That is, the insulating tape 50 becomes the outermost layer. When wrapping the insulating tape 50, as shown in the figure, the wrapping should begin from the side 5b of the busbar body 5 opposite to the battery cell 110, and wrap around the endothermic reaction layer 40, the inorganic insulation material 20, and the inorganic fiber sheet 30, so that the end portion 50b is positioned on the surface 50a that is in contact with the busbar body 5. Also, considering the shape retention of the laminate consisting of the inorganic insulation material 20, the inorganic fiber sheet 30, and the endothermic reaction layer 40, the end portion 50b of the insulating tape 50 may be bonded with an adhesive.

[0030] Furthermore, since the insulating tape 50 comes into contact with the battery cell 110, it only needs to have electrical insulating properties, and for example, a resin tape can be used.

[0031] <Embodiment 2> Figure 3 is a cross-sectional view of the busbar 1 of Embodiment 2, following the view in Figure 2. As shown, an inorganic heat insulating material 20 is attached to the surface 5a of the busbar body 5 facing the battery cell 110, and an inorganic fiber sheet 30 is laminated around the busbar body 5, starting from the surface 5b opposite to the battery cell 110. Because the inorganic fiber sheet 30 is flexible, it can easily wrap around the busbar body 5, and furthermore, because it is electrically insulating, it does not short-circuit even when in contact with the battery cell 110.

[0032] Furthermore, the inorganic fiber sheet 30 is preferably a woven fabric such as silica cloth, glass cloth, or alumina cloth.

[0033] Furthermore, an endothermic reaction layer 40 may be interposed between the surface 5b of the busbar body 5 and the starting portion 30a of the inorganic fiber sheet 30. In addition, an endothermic reaction layer 40 may also be interposed between the starting portion 30a and the ending portion 30b of the inorganic fiber sheet 30.

[0034] The surface 5a of the busbar body 5 and the inorganic insulation material 20 may or may not be bonded.

[0035] Furthermore, if these are not bonded together, an air layer is formed between the surface 5a of the busbar body 5 and the inorganic insulation material 20, thereby improving the insulation performance.

[0036] [Regarding inorganic insulation material 20] In both Embodiment 1 and Embodiment 2 described above, there are no restrictions on the type of inorganic heat insulating material 20, but because it has excellent heat insulating performance, it is preferable to include at least one of inorganic fibers and inorganic particles, and preferably both inorganic fibers and inorganic particles. The busbar 1 of this embodiment is covered with an inorganic heat insulating material that includes at least one, preferably both, of inorganic fibers and inorganic particles, and is protected from high temperatures and flames from battery cells that have experienced thermal runaway in the event of a battery malfunction.

[0037] (Inorganic fibers) The inorganic insulation material 20 may contain inorganic fibers. Specifically, inorganic fibers with a melting point of less than 700°C are preferred, and many amorphous inorganic fibers can be used. There are no particular restrictions on the type of inorganic fiber, and various inorganic fibers such as glass fibers, glass wool, slag wool, rock wool, alkali earth silicate fibers, refractory ceramic fibers, basalt fibers, and sorbable fibers can be used. These fibers may be used individually or in combination of multiple types. 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, these fibers may be crystalline or amorphous, but amorphous is preferred from the viewpoint of flexibility.

[0038] Furthermore, when the inorganic fibers are 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 mineral fibers such as rock wool, basalt fibers, and wollastonite can be used.

[0039] 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 be able to 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 aluminasilicate fibers, as well as mineral fibers, and among these, it is even more preferable to use those with a melting point exceeding 1000°C.

[0040] (Inorganic particles) The inorganic thermal insulation material 20 may include inorganic particles in place of or together with inorganic fibers. If the average secondary particle diameter of the inorganic particles is 0.01 μm or more, it is readily available and the increase in manufacturing costs can be suppressed. Furthermore, if it is 200 μm or less, the desired thermal 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, and more preferably 0.05 μm or more and 100 μm or less.

[0041] As inorganic particles, a single inorganic particle may be used, or two or more types of inorganic particles (for example, a first inorganic particle and a second inorganic particle) may be used in combination. When two types of inorganic particles are included, 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 it is more preferable to use oxide particles. Furthermore, there are no particular limitations on the shape of the first and second inorganic particles, 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.

[0042] 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, we will describe inorganic particles in more detail, referring to small-diameter inorganic particles as the first inorganic particles and large-diameter inorganic particles as the second inorganic particles.

[0043] (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 thermal 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.

[0044] 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 result in even higher thermal insulation. Specifically, if the average primary particle size of oxide particles is 0.001 μm or larger, it is sufficiently larger than the wavelength of light that contributes to heating, and efficiently diffusely reflects light. As a result, radiative heat transfer in the inorganic thermal insulation material 20 is suppressed in the high-temperature region of 500°C or higher, further improving thermal insulation. On the other hand, if the average primary particle size of 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.

[0045] 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.

[0046] (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, when using a battery in the normal room temperature range, it is preferable to use nanoparticles because they can suppress heat conduction between adjacent nanoparticles.

[0047] Note that nanoparticles refer to particles that are spherical or nearly spherical, with an average primary particle diameter of less than 1 μm and on the order of nanometers.

[0048] 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 20 even when the internal density of the inorganic insulation material 20 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 the repulsive force caused by static electricity, and because their bulk density is low, the particles are packed in a way that provides cushioning.

[0049] Furthermore, when using nanoparticles 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 using silica particles with a larger particle size. Also, commonly available silica nanoparticles have a bulk density of 0.1 g / cm³. 3 Therefore, even if a large compressive stress is applied to the inorganic insulation material 20, for example, the size (area) and number of contact points between silica nanoparticles do not increase significantly, and the insulation properties can be maintained. For this reason, it is preferable to use silica nanoparticles. As silica nanoparticles, wet silica, dry silica, aerogel, etc. can be used.

[0050] 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 20. Moreover, 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.

[0051] (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.

[0052] 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).

[0053] 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 → Al2O3 + 3H2O

[0054] 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.

[0055] 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 range of rapid temperature increases in battery cells experiencing thermal runaway, and can effectively suppress temperature rise, making them desirable inorganic hydrates.

[0056] 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 20 to reach their thermal decomposition temperature, and thus the inorganic hydrate particles near the center of the inorganic insulation material 20 may not be completely decomposed. For this reason, 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.

[0057] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, and perlite.

[0058] (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.

[0059] (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 20.

[0060] As the inorganic balloon, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barlite balloons, and glass balloons can be used.

[0061] The inorganic balloon content is preferably 60% by mass or less relative to the total mass of the inorganic insulation material 20.

[0062] Furthermore, the average particle size of the inorganic balloons is preferably between 1 μm and 100 μm.

[0063] (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.

[0064] 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 20. In addition, metal oxide particles such as titania have a high effect in blocking radiant heat. Moreover, by using both large-diameter and small-diameter inorganic particles, the small-diameter inorganic particles can fill the gaps between the large-diameter inorganic 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 include particles made of metal oxides, which are larger in diameter than the first inorganic particles, as second inorganic particles in the inorganic thermal insulation material 20.

[0065] 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 in scattering light and blocking radiant heat in the high-temperature range of 500°C or higher, so using titania is most preferable.

[0066] If the average primary particle diameter of the second inorganic particles is 1 μm or more and 50 μm or less, 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 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0067] (Other ingredients) In addition to the inorganic fibers and inorganic particles mentioned above, the inorganic insulation material 20 may also contain an organic binder (resin binder) or organic fibers.

[0068] (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.

[0069] 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 thermal insulation material 20 can be further improved when the inorganic thermal insulation material 20 containing the resin binder is 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.

[0070] The resin binder content is preferably 0.5% by mass or more, and more preferably 1% by mass or more, relative to the total mass of the inorganic insulation material 20. Furthermore, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

[0071] (Organic fibers) In addition to the inorganic fibers mentioned above, organic fibers may also be included. Examples of organic fibers include at least one selected from 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-based fibers. Among these, those with excellent heat resistance and a high Young's modulus are preferred; specifically, polyphenylene sulfide-based and polyacrylonitrile-based fibers are preferred. These fibers may be used individually or in combination.

[0072] As will be described later, the inorganic insulation material 20 can also be manufactured by papermaking, but since it is difficult to raise the heating temperature above 250°C in that case, the glass transition temperature of the organic fibers is preferably 250°C or lower, and more preferably 200°C or lower.

[0073] While there are no particular limitations on the lower limit of the glass transition temperature of the organic fibers, if the difference between it and the glass transition temperature 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, thus allowing for sufficient reinforcement of the framework by the resin binder. Therefore, the difference between the glass transition temperature of the resin binder and the glass transition temperature of the organic fibers is preferably 10°C or more, and more preferably 30°C or more.

[0074] On the other hand, if the difference between the glass transition temperatures of the two is 130°C or less, the time from when the organic fibers are completely solidified until the resin binder begins to solidify can be appropriately adjusted, and the resin binder solidifies while maintaining a good dispersion state, thus further enhancing the reinforcing effect on the skeleton. 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.

[0075] Furthermore, the mixture may contain two or more types of organic fibers, in which case at least one of the organic fibers must act as a skeleton, 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.

[0076] 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, and the reinforcing effect of the resin binder on the skeleton can be fully obtained. 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 20. 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 range of the above-mentioned organic fiber content.

[0077] As described 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 temperature higher than that of the resin binder, but it is more preferable that the other organic fibers include crystalline organic fibers that do not have a glass transition temperature.

[0078] The inorganic insulation material 20 can also contain 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 20 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 of the inorganic insulation material 20 can be improved.

[0079] Polyester (PET) fibers are an example of organic fibers in a crystalline state.

[0080] Furthermore, when manufacturing the inorganic insulation material 20 using a 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. The "water dissolution temperature" can be used as an indicator of solubility in water, and it is preferable that the water dissolution temperature of the organic fibers be 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

[0081] 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, it is preferable that the average fiber length be 0.5 mm or more from the viewpoint of allowing the organic fibers to function as a skeleton and ensuring the compressive strength of the thermal insulation material.

[0082] Furthermore, as the organic fiber, a binder fiber with a core-sheath structure having a high-melting-point core and a low-melting-point sheath may be used. In the event of a battery malfunction, in addition to flames, debris may be scattered from the battery cell and collide with the busbar, causing damage. However, by using a binder fiber with a core-sheath structure having a high-melting-point core and a low-melting-point sheath, high strength can be obtained using the core as a framework. Moreover, in the event of a battery malfunction, the sheath melts and softens in response to high temperatures and flames, forming a network that is expected to mitigate the impact of debris.

[0083] The binder fiber having such a core-sheath structure is not particularly limited, as long as it 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. The first organic material that forms the core can be selected from at least one of polyethylene terephthalate, polypropylene, and nylon. The second organic material that forms the sheath can be selected from at least one of polyethylene terephthalate, polyethylene, polypropylene, and nylon.

[0084] Binder fibers having the core-sheath structure described above are generally available on the market, and the materials constituting the core and sheath may be the same or different. Examples of binder fibers in which the core and sheath are made of the same material but have different melting points include those in which the core and sheath are made of polyethylene terephthalate, polypropylene, or nylon. Examples of binder fibers in which the core and sheath are made of different materials include those in which the core is made of polyethylene terephthalate and the sheath is made of polyethylene, or those in which the core is made of polypropylene and the sheath is made of polyethylene.

[0085] (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.

[0086] (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 minimal, 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 20 can be delayed.

[0087] 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.

[0088] The carbon content can be adjusted by heat treatment. For example, heat treatment in air or oxygen within the range of 150-300°C further promotes infusibility and removes components other than carbon, thereby increasing the carbon content. For example, heat treatment within the range of 300-1000°C promotes the formation of condensed polycyclic aromatic structures and generates decomposition gases, thereby increasing the carbon content.

[0089] 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 above carbon content range.

[0090] (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.

[0091] Being a short fiber indicates that it is not a continuous fiber. In continuous fibers, the orientation direction of the fibers is aligned to form a fiber bundle, as in cross or filament winding. In contrast, using short fibers results in an aggregate (mat, blanket, or paper-formed body) where the fibers are oriented in random directions. Furthermore, inorganic insulation material 20 using short fibers has short conductive paths, so even if carbonization progresses in the fibers or due to thermal runaway, the conductivity can be kept low. In addition, the random orientation of the fibers makes it easier for them to make point contact with each other, which can reduce thermal conductivity.

[0092] Paper-formed materials can be obtained by dispersing milled or chopped infusible fibers (fiber length approximately 0.01 to 10 mm) in water and 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. In this process, a binder may be added to maintain the overall strength and shape. Organic binders such as resins and inorganic binders such as ceramic precursors can be used.

[0093] 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 more, the rate of air oxidation and sublimation can be suppressed even when exposed to high temperatures, and the flame-retardant effect can be maintained for a long time. On the other hand, if the fiber diameter of the infusible fibers is 30 μm or less, a certain degree of flexibility can be maintained even when carbonized by exposure to high temperatures, and it can be made less susceptible to damage even when deformation or impact occurs.

[0094] In addition to infusible fibers, the above-mentioned organic fibers and inorganic particles may also be included.

[0095] Furthermore, the inorganic insulation material 20 may be a dry sheet or a wet sheet. The method for manufacturing the inorganic insulation material 20 will be described below.

[0096] (Method for manufacturing inorganic insulation material 20) The inorganic thermal insulation material 20 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, press molding (dry press molding) and extrusion molding (dry extrusion molding) can be used.

[0097] (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 20. Heating may be performed during press molding as needed.

[0098] 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 20 may not be able to maintain its strength and may collapse. 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.

[0099] 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 can be used without particular limitation.

[0100] (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. The resulting paste is then extruded through a slit-shaped nozzle using an extrusion molding machine and further dried to obtain the inorganic heat insulating material 20. 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.

[0101] (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 20.

[0102] Furthermore, before the heating and pressurizing process, a ventilated drying treatment may be performed in which hot air is passed through the wet sheet to dry it. However, this ventilated drying treatment may be omitted, and the sheet may be heated and pressurized while still wet. In addition, when using a wet molding method, cationized starch or acrylic resin can be selected as the organic binder.

[0103] (How to manufacture a bus bar) As described above, the busbar 1 can be manufactured by covering the parts (surfaces) of the busbar body 5, excluding the connection holes 6a and 6b (see Figure 1), with the inorganic insulation material 20 manufactured by the manufacturing method described above.

[0104] Alternatively, the busbar 1 may be manufactured by applying a coating solution containing at least one of inorganic fibers and inorganic particles to the busbar body 5, and then drying it. Specifically, it is manufactured as follows. First, at least one of inorganic fibers and inorganic particles, and optionally a resin binder and other additives, are weighed and added to thinner as a dispersion medium, and thoroughly mixed to prepare a coating solution. Next, the area around the connection holes 6a and 6b (see Figure 1) in the busbar body 5 is masked, the coating solution is applied, and the coating film is dried to form the inorganic heat insulating material 20 according to this embodiment. There are no restrictions on the application method, and various methods are possible, such as applying with a brush, roll coater, spray, etc., or immersing the busbar body 5 in the coating solution. Alternatively, before forming the inorganic insulation material 20, a rust-preventive primer may be applied to the surface of the busbar body 5 to a predetermined thickness using a brush, the coating film may be dried to form a primer film, and the inorganic insulation material 20 may then be formed on top of the primer film.

[0105] Here, the term "drying" as used above includes not only the hardening of the coating film by heat treatment, but also the hardening of the coating film by natural drying at room temperature. Furthermore, heating to around 100°C may be used to accelerate the hardening process.

[0106] Furthermore, in the method of wrapping the mica sheet as described in Patent Document 1 above, wrapping work is required, and in particular, the wrapping work is time-consuming in order to prevent uneven wrapping or gaps from occurring in the bent portion 5a and curved portion. In addition, it is conceivable that gaps may occur due to vibration or the adhesive may peel off. However, in this embodiment, the inorganic heat insulating material 20 is formed by coating, so such problems do not occur.

[0107] [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.

[0108] Figure 4B shows the case using the busbar 1 shown in Figure 1B. 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 1B.

[0109] Since the busbar 1 is equipped with an inorganic heat insulating material 20, even if one battery cell 110 experiences thermal runaway, the busbar 1 can be protected, and a chain reaction of thermal runaway to adjacent battery cells 110 can be prevented via the busbar 1.

[0110] Although not shown in the diagram, multiple battery modules may be connected to each other by busbar 1, or at least one battery cell may be connected to at least one battery module by busbar 1. [Explanation of symbols]

[0111] 1 Bus bar 5 Busbar body 6a, 6b connection holes 20 Inorganic insulation materials 30 Inorganic fiber sheets 40 Endothermic reaction layer 50 Insulating Tapes 100 Energy storage devices 110 battery cells 111 Electrode 120 Battery Case

Claims

1. A busbar used in an energy storage device including a battery cell, The surface of the busbar body, which is made of a conductive material, is provided with an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles. A busbar characterized in that an inorganic fiber cloth is arranged on the side of the inorganic heat insulating material facing the battery cell.

2. The busbar according to claim 1, characterized in that the laminate of the busbar body and the inorganic heat insulating material is wrapped with the inorganic fiber cloth.

3. A busbar used in an energy storage device including a battery cell, The surface of the busbar body, which is made of a conductive material, is provided with an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles. The inorganic thermal insulation material contains infusible fibers, The aforementioned infusible fiber is characterized by having a carbon content of 55 to 95% by mass.

4. A busbar used in an energy storage device including a battery cell, The surface of the busbar body, which is made of a conductive material, is provided with an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles. The inorganic thermal insulation material contains infusible fibers, The bus bar is characterized in that the infusible fibers consist of short fibers having a fiber length of 0.01 to 1000 mm.

5. A busbar used in an energy storage device including a battery cell, The surface of the busbar body, which is made of a conductive material, is provided with an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles. The inorganic thermal insulation material contains infusible fibers, The bus bar is characterized in that the infusible fiber has a fiber diameter of 1 to 30 μm.

6. A busbar used in an energy storage device including a battery cell, The surface of the busbar body, which is made of a conductive material, is provided with an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles. The aforementioned inorganic insulation material is characterized by containing organic fibers.

7. A busbar used in an energy storage device including a battery cell, The surface of the busbar body, which is made of a conductive material, is provided with an inorganic heat insulating material containing at least one of inorganic fibers and inorganic particles. The aforementioned inorganic thermal insulation material contains inorganic particles, The inorganic particles include first inorganic particles and second inorganic particles having different average particle diameters from each other. The busbar is characterized in that the first inorganic particles consist of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

8. The bus bar according to claim 7, characterized in that the first inorganic particle consists of at least one selected from nanoparticles, hollow particles, and porous particles.

9. The bus bar according to claim 7, characterized in that the second inorganic particles are metal oxide particles.

10. A power storage device comprising multiple battery cells or battery modules connected by a busbar as described in any one of claims 1 to 9.

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