Busbar and method for manufacturing the same, and energy storage device
A thermally expandable and carbonizable insulating coating on busbars addresses the vulnerability of bus bars to high temperatures and flames, enhancing safety and ease of manufacturing in power storage devices.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- IBIDEN CO LTD
- Filing Date
- 2022-07-29
- Publication Date
- 2026-06-09
AI Technical Summary
Existing bus bars in power storage devices are vulnerable to damage and overheating from high temperatures and flames during battery abnormalities, and wrapping methods like using mica sheets are cumbersome and prone to gaps or peeling, compromising safety.
A busbar coated with an insulating material that expands and carbonizes at high temperatures to protect against heat and flames, using a coating process that ensures uniform coverage without gaps, even on complex shapes.
The coated busbar effectively insulates and prevents damage from high temperatures and flames, ensuring safety by expanding and forming a carbonized layer to maintain insulation and prevent short circuits, while simplifying the manufacturing process.
Smart Images
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Abstract
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 are connected in series or in parallel by a bus bar are mounted in various electronic devices, electric vehicles or hybrid hybrid vehicles driven by an electric motor, hybrid vehicles, storage batteries, etc. 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 hydrogen batteries, etc.
[0003] However, when an overcurrent is applied to the battery cell during charge and discharge, the bus bar used for connection may generate heat and, in some cases, emit flames. In such an abnormal situation of the battery, the bus bar is also exposed to the same high temperature and flames, and the bus bar itself may be damaged, or the adjacent battery cells via the bus bar may become overheated. 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] However, Patent Document 1 is a measure for suppressing the heat generation of the bus bar itself, and does not focus on protecting the bus bar against high temperature and flames from the battery cells in the event of battery abnormality. Moreover, since mica contains crystal water, when exposed to high temperature and flames in the event of battery abnormality, it expands or releases crystal water, becoming structurally unstable.
[0006] 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.
[0007] Therefore, the present invention aims to provide a busbar that can protect battery cells from high temperatures and flames in the event of a battery malfunction. Furthermore, it aims to provide a method for manufacturing a busbar that eliminates the need for winding work like with mica sheets, avoids problems such as uneven winding, gaps in the sheet, and sheet peeling, and can easily accommodate complex shapes. Finally, it aims to provide an energy storage device that connects multiple battery cells or battery modules using such a busbar, demonstrating high safety even in the event of a malfunction. [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 characterized in that the busbar body, which contains a conductive material, is covered with an insulating coating containing an insulating material whose expansion initiation temperature is 250°C or higher.
[0010] Furthermore, preferred embodiments of the present invention relating to busbars are described in the following [2] to [8].
[0011] [2] The bus bar according to [1], characterized in that the insulating material comprises a foaming agent and a binder. [3] The bus bar according to [2], characterized in that the foaming agent is at least one of an ammonium salt, an amino compound, and a chlorinated paraffin. [4] The bus bar according to [2] or [3], characterized in that the binder is at least one of a synthetic resin emulsion, alkyd, vinyl chloride resin, urethane resin, and epoxy resin. [5] The bus bar according to any one of [2] to [4], characterized in that the insulating material further contains a carbonizing agent. [6] The bus bar according to [5], characterized in that the carbonizing agent is at least one of a carbohydrate and a polyhydric alcohol. [7] The bus bar according to [5], characterized in that the foaming agent is ammonium polyphosphate, the binder is a urethane resin, and the carbonizing agent is a polyhydric alcohol. [8] The bus bar according to any one of [1] to [7], characterized in that the thickness of the insulating coating is 0.3 mm or more.
[0012] Furthermore, the above objective of the present invention is achieved by the configuration described below [9] relating to a method for manufacturing a busbar.
[0013] [9] A method for manufacturing a busbar used in an energy storage device including a battery cell, A method for manufacturing a busbar, characterized by applying a coating solution containing an insulating material having an expansion start temperature of 250°C or higher to a busbar body containing a conductive material, and then drying it.
[0014] Furthermore, preferred embodiments of the present invention relating to a method for manufacturing busbars are described in the following
[10] to
[12] .
[0015]
[10] The method for manufacturing a bus bar according to [9], characterized in that the insulating material includes a foaming agent and a binder.
[11] The method for manufacturing a bus bar according to
[10] , characterized in that the insulating material further contains a carbonizing agent.
[12] A method for manufacturing a bus bar according to any one of [9] to
[11] , characterized in that the coating liquid is applied such that the film thickness after drying is 0.3 mm or more.
[0016] Further, the above object of the present invention is achieved by the following configuration
[13] or
[14] related to the power storage device.
[0017]
[13] A power storage device in which a plurality of battery cells or battery modules are connected by the bus bar described in any one of [1] to [7].
[14] A power storage device in which a plurality of battery cells or battery modules are connected by the bus bar described in [8].
Effects of the Invention
[0018] The bus bar of the present invention is formed by coating a bus bar body containing a conductive material with an insulating film containing an insulating material having an initial expansion temperature of 250°C or higher. When an abnormality occurs in the battery, the insulating film expands, and more preferably, carbonizes, so that it is protected from the high temperature and flame from the battery cell that has caused thermal runaway.
[0019] Further, the manufacturing method of the bus bar of the present invention only needs to apply a coating liquid containing an insulating material having an initial expansion temperature of 250°C or higher to the bus bar body. Therefore, the manufacturing process is simple, and an insulating film can be formed uniformly without gaps regardless of the shape of the bus bar body.
[0020] Furthermore, since the power storage device of the present invention connects a plurality of battery cells and battery modules by such a bus bar, it exhibits high safety even in case of an abnormality.
Brief Description of the Drawings
[0021] [Figure 1] FIG. 1 is an exploded perspective view showing a state in which an example of the bus bar of the present invention is mounted on a battery cell. [Figure 2] FIG. 2 is a cross-sectional view showing an embodiment of the bus bar along the line A-A in FIG. 1. [Figure 3] FIG. 3 is a graph showing the back surface temperature (°C) during flame irradiation in the examples and comparative examples. [Figure 4] FIG. 4 is a graph showing the results of measuring the film thickness (mm) of the insulating film before and after flame irradiation in the examples and comparative examples. [Figure 5] Figure 5 shows photographs of the insulating coatings of each sample from Example 1 and Comparative Example 1, taken after flame irradiation, with Figure 5(A) showing that of Example 1 and Figure 5(B) showing that of Comparative Example 1. [Figure 6] Figure 6 is a photograph used as a substitute for a drawing, showing the side view of the sample from Example 1 after flame irradiation. [Figure 7] Figure 7 is a cross-sectional view showing an example of the energy storage device of the present invention. [Modes for carrying out the invention]
[0022] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below, and can be modified and implemented as desired without departing from the spirit of the invention.
[0023] [Bus bar] Figure 1 is an exploded perspective view showing the busbar 1 according to this embodiment attached to a battery cell 110. As shown in Figure 1, the busbar body 5, made of a conductive material, is, for example, a metal plate member that is Z-shaped overall. The electrodes 111 of the battery cell 110 are inserted into the connection hole 6a at one end, and a terminal cap 112 is placed over it to secure it. The connection hole 6b at the other end of the busbar body 5 is connected to an adjacent battery cell (not shown) or an external device (not shown). The portion of the busbar body 5 excluding the connection holes 6a and 6b (the surface) is covered with an insulating coating 10, which will be described later, to form the busbar 1.
[0024] Although not shown in the diagram, the busbar body 5 can be made into various shapes depending on the installation location of the battery cell 110, such as being entirely I-shaped or having an irregular shape with a curved section.
[0025] If the busbar body 5 has a shape such as the Z-shape 5a or curved portion (not shown) shown in Figure 1, then in the busbar described in Patent Document 1, the method of wrapping a mica sheet around it would require considerable effort to prevent uneven wrapping or gaps in the bent portion 5a or curved portion, or gaps may occur due to vibration, or the adhesive may peel off. However, as will be described later, in this embodiment, the insulating film 10 is formed by coating with a predetermined coating liquid, so such problems do not occur.
[0026] Next, Figure 2 is a cross-sectional view of the busbar 1 along the line AA in Figure 1. Although not shown in the illustration, a battery cell 110 is located on the lower side in Figure 2, and in the event of a battery malfunction, high temperatures and flames may occur due to heat transfer from the battery cell 110. For this reason, the busbar body 5 is covered with a predetermined insulating coating 10. This insulating coating 10 can be formed on the sides (plate thickness portion) and top and bottom surfaces to cover the entire surface of the busbar body 5 as shown in the illustration, but it may also be formed only on the surface facing the battery cell 110 (in this case, the bottom surface).
[0027] The insulating coating 10 includes an insulating material whose expansion initiation temperature is 250°C or higher. Since the busbar 1 reaches approximately 100°C when energized (during normal battery use), even under normal conditions, it is preferable to set the expansion initiation temperature of the insulating coating 10 to 250°C or higher, or 300°C or higher, or 350°C or higher, or 400°C or higher, so that the insulating coating 10 does not expand during normal battery use.
[0028] When the insulating coating 10 begins to expand at a high temperature of 250°C or higher, air is drawn into its interior, forming an air layer. This suppresses the transfer of the generated high heat to the busbar 1, thereby improving its thermal insulation performance. Consequently, the melting of the busbar 1 itself (i.e., damage to the busbar 1 due to high heat) can be effectively suppressed. Furthermore, in order to effectively improve the thermal insulation performance, it is preferable that the expansion rate of the insulating coating 10 is large, and that the expansion rate is preferably 10% or more of the volume before expansion, more preferably 13% or more, and even more preferably 15% or more.
[0029] In this embodiment, the busbar 1 is covered with an insulating coating 10 containing an insulating material whose expansion start temperature is 250°C or higher, thereby covering the busbar body 5 which contains a conductive material. During normal use of the battery (at most approximately 100°C), the busbar 1 functions as an insulating material to ensure insulation from other parts and equipment around it. However, in the event of a battery malfunction (at least 250°C or higher), the insulating coating 10 expands, increasing the contact distance with the conductive part and reducing the risk of short circuits.
[0030] Furthermore, considering further improvement of insulation properties, it is preferable that the insulating material used in the insulating coating 10 contains a foaming agent and a binder, and more specifically, it is preferable that the insulating material used in the insulating coating 10 is a foamed resin. When the insulating material contains a foaming agent and a binder, air is effectively incorporated into the foamed bubbles, so effective heat insulation can be expected.
[0031] There are no particular restrictions on the type of insulating material whose expansion initiation temperature is 250°C or higher. However, if the insulating material contains a foaming agent, the foaming agent is preferably at least one of ammonium salts, amino compounds, and chlorinated paraffins, and may be a combination of at least some of these. Examples of ammonium salts include ammonium phosphate, ammonium polyphosphate, and melamine phosphate. Examples of amino compounds include dicyanamide, urea, and melamine.
[0032] Furthermore, when the insulating material contains a binder, the binder is preferably at least one of the following: synthetic resin emulsion (water-based), alkyd (solvent-based), vinyl chloride resin (solvent-based), urethane resin (solvent-based), and epoxy resin (solvent-based), and may be a combination of at least some of these.
[0033] Furthermore, urethane prepolymers can be cited as urethane resins used as binders. Urethane prepolymers are obtained by reacting a polyol compound with an excess of a polyisocyanate compound and have isocyanate groups at the molecular ends.
[0034] Examples of polyol compounds that constitute urethane prepolymers include polyether polyols and polyester polyols. Their weight-average molecular weight is typically 300 to 5000 (preferably 500 to 3000).
[0035] Furthermore, examples of polyisocyanate compounds include aliphatic, alicyclic, or aromatic polyisocyanates commonly used in the production of polyurethanes. Specifically, examples include tetramethylene diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, metaxylylene diisocyanate, and 4,4'-diphenylmethane diisocyanate.
[0036] The reaction ratio between the polyol compound and the polyisocyanate compound should be set so that there is an excess of isocyanate groups in the polyisocyanate compound compared to the hydroxyl groups in the polyol compound, and it is preferable to set it so that (NCO / OH) is approximately 1.2 to 2.2.
[0037] The foaming agent described above can also function as a carbon layer forming agent. The carbon layer forming agent referred to here is a component that promotes the carbonization of the foamed resin, which is the carbon component. After the foamed resin has foamed, it carbonizes the carbon in the resin by creating an inert gas atmosphere, forming a carbon layer and stopping further combustion. As a compound having such an effect, ammonium polyphosphate is preferred, which is one of the ammonium salts described above and has a large inert gas generation effect. Nitrogen gas is generated from the ammonium groups in ammonium polyphosphate, effectively blocking contact with oxygen in the air.
[0038] As stated above, the expansion start temperature of the insulating material contained in the insulating coating 10 is 250°C or higher. However, in order to further enhance the flame retardant effect against high temperatures and flames from battery cells that have experienced thermal runaway, it is preferable that the expansion start temperature be 550°C or lower, 540°C or lower, or 530°C or lower. In particular, when the insulating material contains a foaming agent, a more effective flame retardant effect can be expected by forming the carbonized layer as described above. However, if the expansion start temperature is too high, it may not be possible to properly form the carbonized layer on the sufficiently foamed surface, and a more effective flame retardant effect may not be obtained. Therefore, it is preferable that the expansion start temperature of the insulating material contained in the insulating coating 10 be in the range of 250°C to 550°C.
[0039] Furthermore, as will be described later, a coating solution is used to form the insulating film 10. However, if ammonium polyphosphate is left for a long time, it may decompose in the coating solution, generating ammonia gas and potentially degrading over time, leading to a decrease in the carbonized layer formation performance. Therefore, to prevent this deterioration over time, it is preferable to thinly coat it with a water-resistant resin and microencapsulate it.
[0040] Furthermore, it is preferable that the insulating film 10 further contains a carbonizing agent. The carbonizing agent is preferably at least one of carbohydrates and polyhydric alcohols, and may be a combination of at least some of these. By further containing a carbonizing agent in addition to the foaming agent and binder described above, the insulating film 10 can, for example, when the foaming agent (and carbonizing agent) is ammonium polyphosphate and the carbonizing agent is a polyhydric alcohol, when the temperature of the insulating film 10 reaches 250-300°C, the ammonium polyphosphate acting as a reaction catalyst decomposes, and the resulting phosphate decomposes the polyhydric alcohol, which is the carbonizing agent, and further dehydration can more effectively form a carbonized layer.
[0041] In parallel with this reaction, the foaming agent, ammonium polyphosphate, further decomposes, generating ammonia gas, water vapor, carbon dioxide, etc., which significantly expand the formed carbonized layer, thereby creating an insulating layer.
[0042] Furthermore, in addition to the foaming agent, binder (resin), and carbonizing agent mentioned above, the insulating coating 10 may also contain various additives (for example, inorganic particles, organic polymers, etc.) that have been conventionally found in heat-resistant and flame-retardant coatings. Examples of other additives include flame retardants, dispersants, coloring pigments (such as titanium dioxide), and extender pigments.
[0043] Next, the total content of foaming agent and binder in the insulating coating 10 is 0.5 to 1.8 kg / m² of the total coating weight. 2 Preferably, it is 0.5 to 0.7 kg / m 2 It is more preferable that the total content of the foaming agent and binder, as well as the carbonizing agent, are below the respective lower limits mentioned above, insufficient heat resistance against abnormally high temperatures and flames cannot be obtained. Even if they exceed the respective upper limits mentioned above, no further improvement in heat resistance can be expected.
[0044] Furthermore, the thickness of the insulating coating 10 is preferably 0.3 mm or more, and more preferably 0.4 mm or more. As shown in the test examples described later, if the thickness is less than 0.3 mm, sufficient heat resistance cannot be obtained against high temperatures and flames in the event of a battery malfunction. There is no upper limit on the thickness, but if it becomes thicker than necessary, further improvement in heat resistance cannot be expected, and rather defects in the film quality, such as cracks appearing in the insulating coating 10, may occur, so an upper limit of 2.0 mm is appropriate for the thickness.
[0045] [How to manufacture a busbar] To manufacture the busbar 1, first, an insulating material having an expansion onset temperature of at least 250°C, preferably a foaming agent and a binder, more preferably a carbonizing agent, and other additives as needed are weighed, 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 insulating film 10 according to this embodiment. There are no restrictions on the application method; 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 insulating film 10, a rust-preventive primer may be applied to the surface of the busbar body 5 using a brush to a predetermined thickness, the coating may be dried to form a primer film, and the insulating film 10 may be formed on top of the primer film.
[0046] The amount applied should be adjusted so that the film thickness after drying is 0.3 mm or more, preferably 0.4 mm or more.
[0047] 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, during drying, the temperature may be raised to a level that does not cause the insulating material to foam and expand, for example, to around 100°C to accelerate the hardening process.
[0048] 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 the present invention, since the insulating film 10 is formed by coating, such problems do not occur.
[0049] Furthermore, since the conductivity of the busbar 1 decreases when it generates heat, there is a risk that it may degrade the performance of the battery cells or battery packs (battery modules) to which it is applied. However, in a method of forming an insulating film 10 by applying the above-mentioned coating liquid, such as the manufacturing method of the busbar 1 according to this embodiment, it is possible to form a thin insulating film 10, and the effective heat dissipation of the busbar 1 during normal use of the battery can reduce the degradation of the overall performance of the battery cells or battery modules.
[0050] Furthermore, because the insulating coating 10 can be made thin, the overall volume occupied by the busbar 1 does not become too large, allowing for effective use of the battery space within the battery pack and potentially contributing to an increase in the battery pack's capacity.
[0051] [Energy storage device] As shown in Figure 7, the energy storage device 100 houses multiple battery cells 110 in a battery case 120. Adjacent battery cells 110 are connected to each other by the busbar 1.
[0052] The busbar 1 is covered with the insulating coating 10 described above, which protects the busbar 1 even if a battery cell 110 experiences thermal runaway, and prevents a chain reaction of thermal runaway to adjacent battery cells 110 via the busbar 1. Therefore, since the energy storage device of this embodiment connects multiple battery cells 110 and modules (not shown) via such a busbar 1, it exhibits high safety even in the event of an abnormality. [Examples]
[0053] (Examples 1-4) A 2mm thick aluminum plate, with sides of 100mm, was used to represent the busbar body. SK Taikacoat primer (for rust prevention) was applied to one side of the plate using a brush to a thickness of approximately 0.05mm and allowed to dry. Then, on top of the formed primer film, SK Taikacoat Main Material HS, manufactured by SK Kaken Co., Ltd., was applied as an insulating film using a scraper to the thickness shown in Table 1 (refer to "Before Flame Irradiation" in the "Thickness of Insulating Film (mm)" column) to create samples.
[0054] (Comparative Examples 1-3) In Comparative Example 1, a sample was prepared by applying two layers of 0.11 mm thick mica tape manufactured by Nippon Mica Manufacturing Co., Ltd. to one side of the same aluminum plate as in the example, thereby forming an insulating film with a total thickness of 0.22 mm. In Comparative Example 2, a sample was prepared by layering two sheets of Okabe Mica Co., Ltd.'s "D680A" (0.3 mm thick) as the lower layer and two layers of the same mica tape (0.11 mm thick) as the upper layer, and then bonding them together to form an insulating film with a total thickness of 0.52 mm. In Comparative Example 3, a sample was prepared by layering a 0.5 mm thick sheet of Okabe Mica Co., Ltd.'s "D680A" and a 0.11 mm thick mica tape of the same product as an upper layer, and then bonding them together to form an insulating film with a total thickness of 0.72 mm.
[0055] (Heat resistance test) The sample was placed upright, and a flame from a burner was shone onto the surface (front) where the insulating coating was formed, from a distance of 100 mm. The flame size was adjusted to reach 1100°C. Then, the temperature (°C) of the surface (back) opposite to the surface where the insulating coating was formed was measured.
[0056] Furthermore, the thickness (mm) of the insulating coating before and after flame irradiation was measured using a dial gauge, and the expansion rate (%) was determined.
[0057] Table 1 summarizes the composition of the insulating coatings for each sample in the examples and comparative examples, along with the measurement results of the expansion coefficient and back surface temperature. Figure 3 graphs the back surface temperature (°C) during flame irradiation, and Figure 4 graphs the film thickness (mm) of the insulating coating before and after flame irradiation.
[0058] [Table 1]
[0059] As shown in Table 1, Figures 3 and 4, each sample in Examples 1 to 4 exhibits superior heat insulation compared to each sample in Comparative Examples 1 to 3, with a greater change in film thickness before and after flame irradiation, i.e., a larger coefficient of thermal expansion, and a lower back surface temperature. Furthermore, a film thickness of 0.3 mm or more is preferred for the insulating coating, and 0.4 mm or more is more preferred.
[0060] Furthermore, Figure 5 shows photographs of the insulating coatings of each sample from Example 1 (Figure 5(A)) and Comparative Example 1 (Figure 5(B)) taken after flame irradiation. As shown in Figure 5(A), in the sample from Example 1, the insulating coating foamed and then carbonized, turning the entire surface black.
[0061] Figure 6 is a photograph of the side view of the sample from Example 1 after flame irradiation. An insulating film remains on the surface of the aluminum plate, and the black area on top of it has foamed and carbonized, resulting in a layered structure. [Explanation of Symbols]
[0062] 1 Bus bar 5 Busbar body 6a, 6b connection holes 10 Insulating coating 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, which contains a conductive material, is covered with an insulating coating containing an insulating material whose expansion initiation temperature is 250°C or higher. The aforementioned insulating material comprises a foaming agent and a carbonizing agent, wherein the foaming agent comprises ammonium polyphosphate and the carbonizing agent comprises a polyhydric alcohol, characterized in that the busbar is otherwise made of an insulating material.
2. The busbar according to claim 1, characterized in that the insulating material includes a binder.
3. The bus bar according to claim 1, characterized in that the insulating material further comprises at least one of an amino compound and a chlorinated paraffin as the foaming agent.
4. The bus bar according to claim 2, characterized in that the binder is at least one of a synthetic resin emulsion, alkyd resin, vinyl chloride resin, urethane resin, and epoxy resin.
5. The bus bar according to claim 1, characterized in that the insulating material further comprises a carbohydrate as the carbonizing agent.
6. The bus bar according to claim 4, characterized in that the binder is a urethane resin.
7. The bus bar according to claim 1, characterized in that the ammonium polyphosphate is coated with a water-resistant resin and microencapsulated.
8. The busbar according to any one of claims 1 to 7, characterized in that the thickness of the insulating coating is 0.3 mm or more.
9. A method for manufacturing busbars used in energy storage devices including battery cells, The busbar body, which contains a conductive material, is coated with a coating solution containing an insulating material whose expansion initiation temperature is 250°C or higher, and then dried. A method for producing a busbar, characterized in that the insulating material comprises a foaming agent and a carbonizing agent, wherein the foaming agent comprises ammonium polyphosphate and the carbonizing agent comprises a polyhydric alcohol.
10. The method for manufacturing a busbar according to claim 9, characterized in that the insulating material includes a binder.
11. The method for producing a bus bar according to claim 9, characterized in that the ammonium polyphosphate is coated with a water-resistant resin and microencapsulated.
12. A method for manufacturing a bus bar according to any one of claims 9 to 11, characterized in that the coating liquid is applied such that the film thickness after drying is 0.3 mm or more.
13. A power storage device comprising multiple battery cells or battery modules connected by a busbar as described in any one of claims 1 to 7.
14. A power storage device comprising multiple battery cells or battery modules connected by the busbar described in claim 8.