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, and to provide a power storage device that is high in safety even at the time of abnormality.SOLUTION: In a bus bar 1 used for a power storage device 100 that includes battery cells 110, a bus bar body 5 made of a conductive material is covered with a sleeve 10 consisting of an inorganic fiber sheet. For the power storage device 100, a plurality of battery cells 110 or 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 and a power storage device in which a plurality of battery cells are connected by the bus bar.

Background Art

[0002] [[ID=I2]]Power storage devices in which a plurality of battery cells 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 cell, a lithium ion secondary battery capable of high capacity and high output is mainly used as compared with a lead storage battery, a nickel hydrogen battery, or the like.

[0003] However, when an overcurrent is applied to the battery cell during charge and discharge, the bus bar used for 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 may emit flames in some cases. In such an abnormal situation, the bus bar is also exposed to the same high temperature and flames, and the adjacent battery cells become hot through the bus bar.

[0006] However, Patent Document 1 is a measure for suppressing heat generation of the bus bar itself, and does not focus on protecting the bus bar against high temperature and flames from the battery cell during abnormal times. Moreover, since mica contains crystal water, when it is exposed to high temperature and flames during abnormal times, it expands or releases crystal water and becomes structurally unstable.

[0007] 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 and exhibits high safety even during abnormal situations. [Means for solving the problem]

[0008] The above objective of the present invention is achieved by the following configuration [1] relating to the busbar.

[0009] [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 covered by a sleeve made of an inorganic fiber sheet.

[0010] Furthermore, preferred embodiments of the present invention relating to busbars are described in the following [2] to

[18] .

[0011] [2] The bus bar according to [1], characterized in that the sleeve and the bus bar body are partially bonded together. [3] The bus bar according to [1], characterized in that the sleeve and the bus bar body are partially separated. [4] The bus bar according to [1], characterized in that the sleeve is wound multiple times. [5] The bus bar according to [4], characterized in that the sleeve is bonded on the side opposite to the side facing the battery cell. [6] The bus bar according to [1], characterized in that the inorganic fiber sheet is an inorganic fiber cloth. [7] The bus bar according to [1], characterized in that an inorganic heat insulating material is interposed between the bus bar body and the sleeve on the side facing the battery cell. [8] The bus bar according to [7], characterized in that the inorganic thermal insulation material is a wet sheet or a dry sheet containing inorganic particles. [9] The bus bar according to [8], characterized in that the inorganic thermal insulation material includes inorganic fibers or infusible fibers.

[10] The bus bar according to [9], characterized in that the infusible fiber has a carbon content of 55 to 95% by mass.

[11] The bus bar according to [9], characterized in that the infusible fibers consist of short fibers.

[12] The bus bar according to [9], characterized in that the infusible fiber has a fiber diameter of 1 to 30 μm.

[13] The bus bar according to [7], characterized in that the inorganic thermal insulation material includes organic fibers.

[14] The bus bar according to [7], characterized in that the inorganic thermal insulation material contains inorganic particles.

[15] The bus bar according to

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

[16] The busbar according to

[15] , characterized in that the first inorganic particles consist of at least one selected from oxide particles, carbide particles, nitride particles and inorganic hydrate particles.

[17] The bus bar according to

[15] or

[16] , characterized in that the first inorganic particles consist of at least one selected from nanoparticles, hollow particles and porous particles.

[18] The busbar according to

[15] , characterized in that the second inorganic particles are metal oxide particles.

[0012] Furthermore, the above-mentioned objective of the present invention is achieved by the configuration of the energy storage device described below

[19] .

[0013]

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

[18] . [Effects of the Invention]

[0014] The busbar of the present invention is covered with a sleeve made of an inorganic fiber sheet, which protects it from high temperatures and flames from a battery cell that has experienced thermal runaway in the event of an abnormality.

[0015] In addition, since the power storage device of the present invention connects battery cells to each other by such a bus bar, it exhibits high safety even in case of an abnormality.

Brief Description of the Drawings

[0016] [Figure 1A] FIG. 1A is a perspective view showing an example of the bus bar of the present invention. [Figure 1B] FIG. 1B is a perspective view showing another example of the bus bar of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1A for Embodiment 1. [Figure 3] FIG. 3 is a cross-sectional view taken along the line A-A of FIG. 1A for Embodiment 2. [Figure 4A] FIG. 4A is a cross-sectional view showing a power storage device including the bus bar of FIG. 1A. [Figure 4B] FIG. 4B is a cross-sectional view showing a power storage device including the bus bar of FIG. 1B.

Modes for Carrying Out the Invention

[0017] 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.

[0018] [Overall Configuration of the Bus Bar] FIG. 1A is a perspective view showing an example of the bus bar 1 of the present invention, showing a state of being mounted on a battery cell 110. As shown in the figure, a bus bar main body 5 made of a conductive material is, for example, a metal plate member having an overall Z shape. An electrode 111 of the battery cell 110 is inserted into a connection hole 6a at one tip, and a terminal cap 112 is put on and fixed. Further, an adjacent battery cell (not shown) or an external device is connected to a connection hole 6b at the other tip of the bus bar main body 5. Then, a portion of the bus bar main body 5 excluding the connection holes 6a and 6b is covered with a sleeve 10 made of an inorganic fiber sheet described later, and the bus bar 1 is constituted.

[0019] Furthermore, the busbar body 5 can be made entirely of an I-shaped flat plate, as shown in Figure 1B, and the portion (surface) excluding the connection holes 6a and 6b at both ends can be covered with a sleeve 10 to form the busbar 1.

[0020] 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.

[0021] <Embodiment 1> Figure 2 is a cross-sectional view of the busbar 1 along the line AA in Figure 1A. The battery cell 110 is located at the bottom of the figure, and in the event of a malfunction, high temperatures or flames may be generated from the battery cell 110. Therefore, a sleeve 10 made of inorganic fiber sheet is wound around the busbar body 5. In the illustrated example, the sleeve 10 is wound around the busbar body 5 three times, but it may be wound once or multiple times.

[0022] In the event of an abnormality, 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, it is preferable that the sleeve 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 material for the sleeve 10, and an inorganic fiber cloth made of silica fibers, alumina fibers, glass fibers, rock wool fibers, or AES (alkali earth silicate) fibers is preferred. AES fibers are artificial mineral fibers made from high-purity silica, calcia, and magnesia.

[0023] Furthermore, the sleeve 10 and the busbar body 5 may be partially bonded together, or they may be partially separated.

[0024] When partially bonding, an endothermic reaction layer 20 is interposed between the busbar body 5's surface 5b (opposite to the surface 5a facing the battery cell 110) and the sleeve 10. An example of an endothermic reaction layer 20 is a double-sided tape with adhesive layers formed on both sides of a resin substrate. Furthermore, the endothermic reaction layer 20 absorbs heat from the battery cell 110 that has experienced thermal runaway, thereby improving the heat insulation performance.

[0025] Furthermore, if the sleeve 10 is wound in multiple layers, the upper sleeve 10 and the lower sleeve 10 may be bonded together by the endothermic reaction layer 20 on the side opposite to the side facing the battery cell 110 (the upper side in the figure).

[0026] On the other hand, if the busbar body 5 is partially separated, the surface 5a facing the battery cell 110 and the sleeve 10 are not bonded together, and an air layer is formed between them, thereby improving the heat insulation performance. Furthermore, if the sleeve 10 is wound in multiple layers, the upper sleeve 10 and the lower sleeve 10 are also not bonded together on the side facing the battery cell 110 (the lower side in the figure), and an air layer is formed between them.

[0027] <Embodiment 2> As shown in Figure 3, an inorganic heat insulating material 30 may be interposed between the sleeve 10 and the surface 5a of the busbar body 5. 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.

[0028] Furthermore, by not bonding the surface 5a of the busbar body 5 to the inorganic insulation material 30 and instead forming an air layer, the insulation performance can be improved. Also, by not bonding the surface 10a of the sleeve 10 facing the battery cell 110 to the surface 5a of the busbar body 5 and instead forming an air layer, the insulation performance can be improved.

[0029] Furthermore, on the side opposite to the side facing the battery cell 110 (the upper side in the figure), the space between the surface 5b of the busbar body 5 and the sleeve 10, and the space between the upper sleeve 10 and the lower sleeve 10, may be bonded by the endothermic reaction layer 20.

[0030] [Regarding inorganic insulation material 30] In both Embodiment 1 and Embodiment 2 described above, there are no restrictions on the inorganic insulation material 30, but it is preferable to include the following compound materials because they have excellent insulation performance.

[0031] (Inorganic fibers) The inorganic 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.

[0032] 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.

[0033] 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.

[0034] (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.

[0035] (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.

[0036] 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 30 can be further improved when the inorganic thermal insulation material 30 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.

[0037] 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 30. Furthermore, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

[0038] (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.

[0039] As will be described later, the inorganic insulation material 30 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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, based on 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 range of the above-mentioned organic fiber content.

[0044] 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.

[0045] The inorganic insulation material 30 can also contain organic fibers in a crystalline state that do not have a glass transition temperature. Since these organic fibers in a crystalline state 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 organic fibers forming the skeleton to soften. Furthermore, by including organic fibers in a crystalline state, these organic fibers also act as the skeleton of the insulation material at room temperature (20°C). Therefore, the flexibility and handling of the inorganic insulation material 30 can be improved.

[0046] Polyester (PET) fibers are an example of organic fibers in a crystalline state.

[0047] Furthermore, when manufacturing the inorganic insulation material 30 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.

[0048] 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.

[0049] (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.

[0050] 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 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.

[0051] 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 nanoparticles are used 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.

[0052] (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.

[0053] 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 30 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.

[0054] 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.

[0055] (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.

[0056] 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.

[0057] 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 the repulsive force caused by static electricity, and because their bulk density is low, the particles are packed in a way that provides cushioning.

[0058] 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 30, 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.

[0059] 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. 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.

[0060] (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.

[0061] 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).

[0062] 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

[0063] 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.

[0064] 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.

[0065] 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, and thus the inorganic hydrate particles near the center of the inorganic insulation material 30 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.

[0066] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0067] (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.

[0068] (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.

[0069] As the inorganic balloon, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barlite balloons, and glass balloons can be used.

[0070] The inorganic balloon content is preferably 60% by mass or less relative to the total mass of the inorganic insulation material 30.

[0071] Furthermore, the average particle size of the inorganic balloons is preferably between 1 μm and 100 μm.

[0072] (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.

[0073] 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. 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 30.

[0074] 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.

[0075] 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.

[0076] (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.

[0077] (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 30 can be delayed.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] (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.

[0082] 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, because the inorganic insulation material 30 using short fibers has short conductive paths, its conductivity can be kept low even if the fibers are highly carbonized or if carbonization progresses due to thermal runaway. 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.

[0083] 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.

[0084] 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.

[0085] In addition to infusible fibers, the above-mentioned organic fibers and inorganic particles may also be included.

[0086] Furthermore, the inorganic insulation material 30 may be a dry sheet or a wet sheet. The manufacturing method is described below.

[0087] (Method for manufacturing inorganic 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, press molding (dry press molding) and extrusion molding (dry extrusion molding) can be used.

[0088] (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.

[0089] 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 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.

[0090] 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.

[0091] (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 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; however, any organic binder commonly used in the dry extrusion molding method can be used without particular limitation.

[0092] (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.

[0093] 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.

[0094] [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.

[0095] 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.

[0096] The busbar 1 is covered with a sleeve 10 made of an inorganic fiber sheet, which protects the busbar 1 even if one battery cell 110 experiences thermal runaway, and prevents a chain reaction of thermal runaway to adjacent battery cells 110 via the busbar 1.

[0097] Although not shown in the diagram, multiple modules may be connected via busbar 1. [Explanation of symbols]

[0098] 1 Bus bar 5 Busbar body 6a, 6b connection holes 10 sleeves 20 Endothermic reaction layer 30 Inorganic insulation material 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 busbar body, made of a conductive material, is covered by a sleeve made of an inorganic fiber sheet. A busbar having an inorganic heat insulating material interposed between the busbar body and the sleeve on the side facing the battery cell.

2. The bus bar according to claim 1, characterized in that the inorganic thermal insulation material is a wet sheet or a dry sheet containing inorganic particles.

3. The bus bar according to claim 2, characterized in that the inorganic thermal insulation material includes inorganic fibers or infusible fibers.

4. The bus bar according to claim 3, characterized in that the infusible fiber has a carbon content of 55 to 95% by mass.

5. The bus bar according to claim 3, characterized in that the infusible fibers consist of short fibers.

6. The bus bar according to claim 3, characterized in that the infusible fiber has a fiber diameter of 1 to 30 μm.

7. The bus bar according to claim 1, characterized in that the inorganic insulation material includes organic fibers.

8. The bus bar according to claim 1, characterized in that the inorganic heat insulating material contains inorganic particles.

9. The bus bar according to claim 8, characterized in that the inorganic particles include first inorganic particles and second inorganic particles having different average particle diameters from each other.

10. The busbar according to claim 9, characterized in that the first inorganic particles consist of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

11. The bus bar according to claim 9 or 10, characterized in that the first inorganic particle consists of at least one selected from nanoparticles, hollow particles, and porous particles.

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

13. The busbar according to claim 1, characterized in that the sleeve and the busbar body are partially bonded together.

14. The bus bar according to claim 1, characterized in that the sleeve and the bus bar body are partially separated.

15. The bus bar according to claim 1, characterized in that the sleeve is wound multiple times.

16. The bus bar according to claim 15, characterized in that the sleeve is bonded on the side opposite to the side facing the battery cell.

17. The bus bar according to claim 1, characterized in that the inorganic fiber sheet is an inorganic fiber cloth.

18. A power storage device comprising multiple battery cells or modules connected by a busbar as described in claim 1 or 2.

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