Secondary battery

Abstract

To provide a secondary battery that can simultaneously achieve both cooling performance during normal operation and fire resistance.SOLUTION: In a secondary battery 10, an electrode body 11 is sealed in a container 12 together with an electrolyte. The outer periphery of the electrode body 11 or the container 12 is covered with a nonwoven fabric 1. The nonwoven fabric 1 is permeable to gas or liquid. The nonwoven fabric 1 carries functional particles 4, 4 having thermal expansion properties, and the functional particles 4, 4 expand when heated, improving the heat insulating properties of the nonwoven fabric 1. The functional particles are, for example, aluminum hydrogen phosphite particles.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a secondary battery and a battery pack in which a plurality of secondary batteries are combined. [Background technology]

[0002] Secondary batteries, which can be charged and discharged, are used in a variety of applications, including electric vehicles, home appliances, and mobile phones. In general, secondary batteries are made by stacking positive and negative electrodes with a separator between them, and the wound electrode body is sealed in a container together with an electrolyte. In applications such as automobiles, it is common to electrically connect multiple such secondary batteries and use them as a battery pack.

[0003] When using secondary batteries, particularly large-capacity, high-output secondary batteries such as those used in electric vehicles, thermal management is required to maintain an appropriate battery temperature. For example, in a battery pack, even if one of the secondary batteries ignites due to some abnormality and becomes hot, it is required that the adjacent secondary batteries do not catch fire (fire spread resistance).Patent Document 1 discloses a secondary battery in which the electrode body is wrapped with a laminated sheet material having specific heat transfer properties, and discloses that this secondary battery has good fire spread resistance. Furthermore, during normal battery operation, secondary batteries generate heat as they are charged and discharged, and therefore, particularly in large-capacity, high-output secondary batteries, the secondary batteries must be cooled by air cooling, liquid cooling or other means. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-148731 A Summary of the Invention [Problem to be solved by the invention]

[0005] Proper thermal management of secondary batteries is not an easy task. From the viewpoint of preventing the spread of fire in a battery pack, it is necessary to properly insulate the secondary batteries from each other, i.e., to insulate the batteries themselves, but in order to effectively cool the secondary batteries, it is preferable to increase thermal conductivity without insulating the batteries, which is a trade-off that exists with regard to insulation.

[0006] An object of the present invention is to provide a secondary battery that can achieve both cooling performance during normal operation and fire resistance. [Means for solving the problem]

[0007] As a result of extensive research, the inventors discovered that if the electrode body and container of a secondary battery are covered with a nonwoven fabric through which fluid can pass, and if the nonwoven fabric is supported with functional particles having thermal expansion properties so that the functional particles expand when heated, improving the insulating properties of the nonwoven fabric, it is possible to achieve both the cooling ability and fire resistance of the secondary battery, and thus completed the present invention.

[0008] The present invention is a secondary battery in which an electrode body is sealed in a container together with an electrolyte, and the outer periphery of the electrode body or the container is covered with a nonwoven fabric, which allows gas or liquid to pass through and carries functional particles having thermal expansion properties, so that the functional particles expand when heated, improving the insulating properties of the nonwoven fabric (first invention).

[0009] In the first invention, preferably, the nonwoven fabric includes long fibers made of synthetic resin with the functional particles integrated therein, the long fibers having diameters that vary in the longitudinal direction of the fibers as if a plurality of large diameter portions and small diameter portions were alternately arranged and strung together, the small diameter portions being monofilaments formed from the synthetic resin, and the large diameter portions containing the functional particles (second invention). Furthermore, in the second invention, preferably, the fiber diameter of the small diameter portions of the long fibers is equal to or smaller than the diameter of the functional particles contained in the large diameter portions, and the functional particles are integrated with the large diameter portions by being wrapped in the synthetic resin in a membrane, net, or fiber bundle form, or by being bonded by the synthetic resin. (Third invention).

[0010] In the first invention, preferably, the functional particles are aluminum hydrogen phosphite particles (fourth invention). In the second invention, preferably, the fiber diameter of the small diameter portion is 100 nanometers or more and 10 micrometers or less, and the diameter of the functional particles is 300 nanometers or more and 200 micrometers or less (fifth invention). In the first invention, the nonwoven fabric is preferably in a bag shape (sixth invention).

[0011] The present invention also provides a battery pack in which a plurality of secondary batteries according to the first invention are electrically connected and integrated, the secondary batteries being flat plate-shaped batteries stacked one on top of the other (seventh invention). Effect of the Invention

[0012] According to the secondary battery (first invention) and the assembled battery (seventh invention) of the present invention, while the battery has excellent cooling properties during normal operation, when abnormal heat generation such as fire occurs, the functional particles expand due to heating, improving the heat insulating properties of the nonwoven fabric and suppressing the spread of fire. In other words, both cooling properties and fire resistance can be achieved.

[0013] Furthermore, in the case of the second aspect of the invention, a large amount of functional particles can be supported on the nonwoven fabric, which further improves the fire resistance. Also, the functional particles are less likely to fall off the nonwoven fabric and contaminate the surroundings. Furthermore, in the case of the third aspect of the invention, the thermal expansion of the functional particles occurs quickly, and the fire spread resistance is further improved. Furthermore, in the case of the fourth aspect of the invention, the nonwoven fabric is transformed into a fire-resistant and insulating layer by the expanded functional particles, and the fire resistance is further improved. Furthermore, in the case of the fifth aspect of the invention, the thermal expansion of the functional particles occurs quickly, and the fire spread resistance is further improved. Furthermore, in the case of the sixth aspect of the invention, the secondary battery and the electrode assembly can be effectively covered with nonwoven fabric, facilitating assembly. [Brief description of the drawings]

[0014] [Figure 1] 1 is a perspective view showing the appearance of a secondary battery according to a first embodiment; [Diagram 2] XX cross-sectional view showing the structure of the secondary battery of the first embodiment. [Diagram 3] 1 is a schematic diagram showing a structure of a battery pack in which secondary batteries according to a first embodiment are stacked. [Figure 4] FIG. 6 is a cross-sectional view showing the structure of a secondary battery according to a second embodiment. [Diagram 5] FIG. 2 is a schematic diagram showing the structure of a nonwoven fabric used in the secondary battery of the first embodiment. [Figure 6] FIG. 2 is a schematic diagram showing the structure of a large diameter portion and a small diameter portion of a long fiber. [Figure 7] 1 is a micrograph showing the structure of an example of a nonwoven fabric. [Figure 8] 1 is a micrograph showing the structure of nonwoven fabric Example 2. [Figure 9] 1 is a micrograph showing the structure of nonwoven fabric Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, with reference to the drawings, an embodiment of the present invention will be described taking as an example a secondary battery used in the form of a battery pack in an electric vehicle. The present invention is not limited to the individual embodiments shown below, and the embodiments can be modified and carried out.

[0016] Figures 1 and 2 show the appearance and structure of a secondary battery 10 of a first embodiment. Figure 2 is a cross-sectional view taken along the line XX in Figure 1. Figure 3 shows a schematic structure of a battery pack 20 in which secondary batteries 10, 10 are stacked. Figure 3 is drawn as viewed from the same direction as Figure 2.

[0017] As shown in Figs. 1 and 2, the secondary battery 10 is configured by sealing an electrode body 11 together with an electrolyte (not shown) in a container 12. The electrode body 11 is one power generation unit. As in this embodiment, one electrode body 11 may be housed in the container 12, or multiple electrode bodies 11, 11 may be housed in the container 12. The secondary battery 10 is sometimes called a single cell or a battery element in contrast to a battery pack described later. The shape of the secondary battery 10 is not particularly limited, and may be cylindrical, but is preferably flat as in this embodiment. A flat secondary battery is sometimes called a rectangular battery.

[0018] As shown in FIG. 3, the battery pack 20 of this embodiment is configured by electrically connecting a plurality of the secondary batteries 10, 10 and integrating them with each other. The battery pack 20 is configured by stacking a plurality of flat plate-shaped secondary batteries 10, 10. Typically, but not necessarily, the positive electrode members 13 and the negative electrode members 14 of each secondary battery are connected by a bus bar 23 to establish electrical connection. Typically, but not necessarily, corrugated spacers 21, 21 are sandwiched between the individual secondary batteries 10, 10 to create a space between the secondary batteries at a predetermined interval, and cooling air is passed through this space to cool the secondary batteries when they are operated. Typically, but not necessarily, end plates 22, 22 are provided to sandwich the stacked structure of the secondary batteries 10, 10 and the spacers 21, 21, and the stacked structure of the battery pack 20 is maintained by fastening the end plates 22, 22 with fastening members such as bolts or bands. The bus bars 23, the end plates 22, and the spacers 21 may be made of known materials as appropriate.

[0019] The battery pack 20 can be housed in a battery case (not shown) or the like and mounted on a vehicle such as a hybrid car for use. Typically, a battery case or the like is used to send cooling air for cooling the battery pack 20 to the spaces between the spacers 21, 21, thereby cooling the individual secondary batteries 10, 10. Note that the means for cooling the batteries is not limited to an air-cooling type that uses cooling air, and may be a liquid-cooling type that uses a cooling liquid.

[0020] The secondary battery 10 of this embodiment will now be described in more detail. In the secondary battery 10 of this embodiment, known materials can be appropriately used as the electrode body 11, electrolyte, container 12, positive electrode member 13, and negative electrode member 14. These members can be assembled into the secondary battery 10 by a known method.

[0021] The electrode assembly 11 includes a positive electrode, a separator, and a negative electrode. The positive electrode, the separator, and the negative electrode are in a sheet form. The positive electrode and the negative electrode are laminated with the separator sandwiched between them, and the laminated state is wound to form the electrode assembly 11. In this embodiment, the electrode assembly is in a flat (plate) shape.

[0022] The positive electrode, negative electrode, and separator may be made of any known material. The positive electrode is conductive and includes a positive electrode active material (for example, a lithium transition metal complex oxide). The negative electrode is conductive and includes a negative electrode active material (for example, graphite). The separator may be a porous resin film.

[0023] The electrolyte can also be appropriately selected from known electrolytes, and may be a non-aqueous electrolyte solution containing a non-aqueous solvent (e.g., ethylene carbonate) and an electrolyte salt (e.g., an inorganic lithium salt).

[0024] There are no particular limitations on the container 12 as long as it can enclose the electrode body 11 and the electrolyte. The container 12 may be made of resin or metal.

[0025] The positive electrode of the electrode body 11 is connected to a positive electrode member 13, and the positive electrode member 13 is exposed to the outside of the container 12. The negative electrode of the electrode body 11 is connected to a negative electrode member 14, and the negative electrode member 14 is exposed to the outside of the container 12. The positive electrode member 13 and the negative electrode member 14 serve as external terminals of the secondary battery 10, and are electrically connected to a bus bar 23 or the like.

[0026] In the secondary battery 10 of this embodiment, the outer periphery of the electrode body 11 is covered with a nonwoven fabric 1. Preferably, as in this embodiment, the nonwoven fabric 1 is formed into a bag shape, and the electrode body 11 is housed in the bag. In this embodiment, the electrode body 11 and the nonwoven fabric 1 are housed in a container 12 with the outer periphery of the electrode body 11 covered with the nonwoven fabric 1.

[0027] For favorable thermal management of the secondary battery 10, it is preferable that the electrode body 11 and the nonwoven fabric 1 are in close contact with each other, and that the nonwoven fabric 1 is in close contact with the container 12. In addition, although not essential, when the electrode body 11 is in the form of a flat plate, it is preferable that both of the wide surfaces of the electrode body 11, that is, both the front and back surfaces of the plate when the electrode body 11 is regarded as a plate, are covered with the nonwoven fabric 1.

[0028] The secondary battery may be one in which the outer periphery of the container 12 is covered with the nonwoven fabric 1, as in a secondary battery 30 of a second embodiment shown in Fig. 4. As in the secondary battery 30 of the second embodiment, the nonwoven fabric 1 may be attached to both sides of the broad surface of the flat container 12, that is, to both the front and back surfaces of the plate when the electrode body 11 is regarded as a plate.

[0029] Furthermore, when flat secondary batteries 10, 10 are stacked to form an assembled battery 20, the nonwoven fabric 1 is arranged so as to partition the electrode bodies 11, 11 of adjacent secondary batteries, contributing to suppression of the spread of fire. Preferably, the nonwoven fabric 1 is arranged so as to cover the entire opposing surfaces of adjacent electrode bodies 11, 11. Also, preferably, the nonwoven fabric 1 is arranged on both of the adjacent secondary batteries. It is not necessary that the nonwoven fabric 1 is arranged on one secondary battery and the nonwoven fabric 1 is not arranged on the other secondary battery.

[0030] Regarding the extent to which nonwoven fabric 1 covers the outer periphery of electrode body 11 and container 12, nonwoven fabric 1 does not need to completely cover the outer periphery of electrode body 11 and container 12. It is sufficient that at least a part of the area where secondary batteries are adjacent to each other in the battery pack is covered by nonwoven fabric 1 so as to improve fire resistance. When the secondary battery or electrode body is flat, it is preferable that at least one of the front and back sides of the secondary battery or electrode body, when viewed as a plate, is entirely covered with nonwoven fabric 1, and it is particularly preferable that both sides are covered with nonwoven fabric 1. When the secondary battery or electrode body is cylindrical, it is preferable that nonwoven fabric 1 is wrapped around the side surface of the cylinder so that the entire side surface is covered with nonwoven fabric 1.

[0031] The nonwoven fabric 1 will be described in detail below. Gas or liquid can pass through the nonwoven fabric 1. For example, when the nonwoven fabric 1 is placed inside a container as in this embodiment, the nonwoven fabric 1 is configured to allow electrolyte liquid to pass through. When the nonwoven fabric 1 is placed outside a container, the nonwoven fabric 1 is configured to allow cooling air or cooling liquid to pass through.

[0032] The nonwoven fabric 1 also carries functional particles 4, 4 having thermal expansion properties. The functional particles 4, 4 having thermal expansion properties expand when heated, improving the heat insulating properties of the nonwoven fabric 1. The expansion start temperature at which the functional particles 4, 4 start to expand is set to be higher than the temperature during normal operation of the secondary battery 10, and is set so that the functional particles 4, 4 do not expand when the secondary battery is operating normally, but expand when the nonwoven fabric 1 is exposed to a high temperature due to abnormal heating of the secondary battery or the occurrence of a fire. For example, the preferred range of the expansion start temperature of the functional particles 4, 4 having thermal expansion properties can be set to 250°C to 400°C.

[0033] Examples of the thermally expandable functional particles 4,4 include thermally expandable graphite, aluminum phosphite, etc. The functional particles 4,4 are preferably inorganic particles that do not melt even when exposed to high temperatures and that maintain their function as a fire-resistant heat insulating layer for a predetermined period of time.

[0034] The form in which the nonwoven fabric 1 used in the secondary battery 10 carries the thermally expandable functional particles 4, 4 is not particularly limited, and the functional particles may be carried by the fibers constituting the nonwoven fabric with a binder or the like. Preferably, the thermally expandable functional particles 4, 4 are supported so as to be integrated with the long fibers made of synthetic resin, as in the nonwoven fabric 1 of the embodiment shown in Fig. 5. When integrated in this manner, the functional particles are less likely to fall off, and air and liquids can easily pass through the nonwoven fabric even if a large amount of functional particles are supported. The structure of the nonwoven fabric 1 according to the embodiment shown in FIG. 5 will now be described in detail.

[0035] The nonwoven fabric 1 of the embodiment shown in FIG. 5 is a nonwoven fabric containing long fibers made of synthetic resin with thermally expandable functional particles 4,4 integrated therein. Here, the long fibers are long fibers in contrast to the short fibers in the fibers constituting the nonwoven fabric. The long fibers are also called filament yarns. Short fibers are called staple fibers, etc., and their length is approximately several mm to several tens of cm, whereas the long fibers are fibers that are not cut short. The long fibers are typically spun by the meltblowing method, the electrospinning method, or the spunbonding method, and are stacked as they are to form a nonwoven fabric. Note that the nonwoven fabric 1 does not have to be composed of only long fibers, and may contain short fibers, or may be mixed so that the long fibers and the short fibers are intertwined.

[0036] Although not essential, the blending amount of the functional particles 4,4 relative to the nonwoven fabric 1 is preferably about 10 to 500 g / m2.

[0037] The nonwoven fabric may be a single layer, or may be a laminated nonwoven fabric in which multiple nonwoven fabric layers, films, sheets, woven fabrics, etc. are laminated. The nonwoven fabric may be a composite nonwoven fabric in which a layer of nonwoven long fibers is laminated on a woven fabric or mesh material. The synthetic resin long fibers integrated with the functional particles 4,4 may be contained in only one of the nonwoven fabric layers.

[0038] In addition, all of the long fibers contained in nonwoven fabric 1 may be long fibers made of synthetic resin with functional particles integrated therein, but nonwoven fabric 1 may also contain other long fibers, for example, long fibers that do not have functional particles integrated therein. Although not essential, the nonwoven fabric 1 of this embodiment is a single-layer nonwoven fabric obtained by electrospinning long fibers made of synthetic resin with functional particles integrated therein.

[0039] Fig. 5 shows a schematic structure of a nonwoven fabric 1 that can be used in the battery of the first embodiment. Fig. 7 shows a microscope photograph of an example of the nonwoven fabric of the embodiment of Fig. 5. In Fig. 5, the small diameter parts 3, 3 are represented by a single solid line. The long fibers contained in the nonwoven fabric 1 have diameters that change in the longitudinal direction of the fibers so that a plurality of large diameter portions 2, 2 and small diameter portions 3, 3 are arranged alternately. In other words, the long fibers are fibers that are structured like a string of large diameter portions 2, 2 and small diameter portions 3, 3. That is, the diameters of the long fibers change in the longitudinal direction of the fibers.

[0040] The small diameter parts 3, 3 of the long fibers are monofilaments formed from the synthetic resin. The synthetic resin is not particularly limited as long as it can be made into fibers, but it is preferable that the synthetic resin is suitable for producing long fibers by the melt-blowing method or the electrospinning method. In addition, it is preferable that the synthetic resin is a resin that adheres to the functional particles described later. For example, polyurethane resin or vinyl chloride resin can be used as the synthetic resin that is the raw material for the long fibers.

[0041] The monofilament that becomes the small diameter portion 3,3 may be composed only of the synthetic resin described above, but may also contain other compounding materials, such as particles having a diameter smaller than the diameter of the small diameter portion, such as reinforcing materials or bulking materials, or agents that improve the properties of the synthetic resin.

[0042] Although not essential, the fiber diameter of the small diameter parts 3,3 is preferably 100 nanometers or more and 10 micrometers or less. The fiber diameter of the small diameter parts 3,3 is particularly preferably 500 nanometers or more and 3 micrometers or less. Here, the fiber diameter means the diameter of the fiber measured in a direction perpendicular to the extending direction of the fiber, and is obtained by taking a microphotograph of the nonwoven fabric 1 and measuring the fiber diameter of the small diameter part on the photograph. Preferably, the fiber diameter is measured at 10 to 20 small diameter parts, and the average of these is treated as the fiber diameter of the small diameter part.

[0043] The large diameter portion 2,2 contains thermally expandable functional particles 4,4. Although not essential, at least a part of the large diameter portion 2,2 is formed by solidifying a plurality of functional particles 4,4 into a string-like or ball-like shape with the synthetic resin. Here, the string-like shape means that, with respect to the shape of the large diameter portion, the length in the extension direction of the fiber is greater than the length in the direction perpendicular to the extension direction of the fiber, preferably three times or more. Also, the ball-like shape means that, with respect to the shape of the large diameter portion, the length in the extension direction of the fiber is approximately the same as the length in the direction perpendicular to the extension direction of the fiber, preferably 1 / 2 or more and 2 times or less. Note that the long fiber may have a large diameter portion that does not contain functional particles or a large diameter portion that contains only one functional particle.

[0044] The diameter of the large diameter portion 2,2 is larger than the fiber diameter of the small diameter portion 3,3. The diameter of the large diameter portion is the diameter measured in a direction perpendicular to the extending direction of the fiber. Preferably, the diameter is measured at 10 to 20 large diameter portions, and the average of the diameters is treated as the diameter of the large diameter portion. Although not essential, the diameter of the large diameter portion 2,2 is preferably 150 nanometers or more and 300 micrometers or less. Particularly preferably, the diameter of the large diameter portion 2,2 is 1 micrometer or more and 50 micrometers or less. Also, preferably, the diameter of the large diameter portion 2,2 is 3 to 20 times, and particularly preferably 4 to 10 times, the fiber diameter of the small diameter portion 3,3.

[0045] FIG. 6 shows a schematic structure of the large diameter portion 2,2 and the small diameter portion 3,3 in the long fiber. The large diameter portion 2 contains a plurality of thermally expandable functional particles 4,4. In the illustrated embodiment, these functional particles 4,4 are wrapped or bonded with the same synthetic resin as that constituting the small diameter portion, and are solidified into a string-like or ball-like shape. In the large diameter portion 2,2, the functional particles 4,4 may be bonded to each other by the synthetic resin, or the functional particles 4,4 may be wrapped with a synthetic resin in a film-like or net-like shape. In the large diameter portion 2,2, only one functional particle may be present in the radial direction of the fiber, or multiple functional particles may be present in the radial direction of the fiber. At the end of the large diameter portion 2,2, the large diameter portion 2 and the small diameter portion 3 are continuous so that the synthetic resin contained in the large diameter portion becomes the monofilament of the small diameter portion 3,3 as it is.

[0046] The functional particles 4,4 contained in the large diameter portion 2,2 have thermal expansion. That is, in the nonwoven fabric 1 of this embodiment, particles having thermal expansion are used as functional particles. Examples of particles having thermal expansion include thermally expandable microcapsules, thermally expandable graphite, and aluminum phosphite. Examples of aluminum phosphite particles having thermal expansion include "APA-100" from Taihei Chemical Industry Co., Ltd. Among aluminum phosphite particles, aluminum hydrogen phosphite particles (such as "NSF" from Taihei Chemical Industry Co., Ltd.) can be preferably used. These particles have the property of expanding when heated to a predetermined temperature. If the large diameter portion 2,2 contains particles having thermal expansion, when the nonwoven fabric is heated, the large diameter portion 2,2 expands and changes so that the voids of the nonwoven fabric become smaller and narrower, causing a change in which the breathability of the nonwoven fabric becomes smaller. Furthermore, as the functional particles 4, 4 expand, the particles themselves become foamed and hollow, making it difficult for heat to pass through, and the heat insulating properties of the nonwoven fabric 1 are improved.

[0047] Preferably, the fiber diameter Ds of the small diameter portion 3,3 is equal to or smaller than the diameter Dp of the functional particles 4,4 contained in the large diameter portion 2,2. The fiber diameter Ds of the small diameter portion 3,3 and the diameter Dp of the functional particles 4,4 may be substantially the same. In addition, the diameter Dp of the functional particles 4,4 in the present invention refers to the volume average diameter. The diameter Dp of the functional particles 4,4 contained in the large diameter portion is typically 300 nanometers or more and 200 micrometers or less. In addition, although not essential, the fiber diameter Ds of the small diameter portion 3,3 is preferably 1 / 100 or more of the diameter Dp of the functional particles 4,4.

[0048] An example of a method for producing the nonwoven fabric 1 of the above embodiment will be described below. The nonwoven fabric 1 can be produced by applying a melt-blowing method or an electrospinning method.

[0049] First, in the first step, a liquefied synthetic resin is mixed with thermally expandable functional particles. The synthetic resin is liquefied by heating to melt it or by dissolving it in a solvent. The functional particles 4,4 are mixed and dispersed in the liquefied synthetic resin. The functional particles may be kneaded into the synthetic resin in advance, which is then heated and melted to obtain a liquid synthetic resin in which the functional particles are dispersed, or the synthetic resin may be dissolved in a solvent or the like to liquefy it, and then the functional particles are mixed and dispersed.

[0050] In this embodiment, polyurethane resin is dissolved in a solvent to make it liquid, and aluminum hydrogen phosphite powder (manufactured by Taihei Chemical Industry Co., Ltd., NSF, volume average diameter 5 micrometers) is mixed therein as functional particles 4,4, and dispersed by stirring.

[0051] Next, in the second step following the first step, the liquid synthetic resin in which the functional particles 4,4 are dispersed is spun into long fibers by melt-blowing or electrospinning, and then deposited to form a nonwoven fabric.

[0052] The liquid synthetic resin discharged from the spinning nozzle is stretched by centrifugal force, gravity, electrostatic force, etc. to become thin fibers. These thin fibers become the small diameter parts 3,3 of the long fibers. At this time, when the functional particles 4,4 are discharged from the nozzle together with the liquid synthetic resin, the part where the functional particles 4,4 are gathered solidifies into a string-like or ball-like shape to become the large diameter parts 2,2, while the excess synthetic resin is stretched to form the small diameter parts 3,3, and the large diameter parts 2,2 and the small diameter parts 3,3 are alternately strung together to form a continuous long fiber. The long fibers thus formed are solidified as the solvent evaporates and the temperature drops, and are deposited on the base of the spinning device, producing the nonwoven fabric 1.

[0053] (Example) In the embodiment, aluminum hydrogen phosphite "NSF" (average particle diameter 5 micrometers) was used as the functional particle, and a nonwoven fabric 1 was obtained in which the diameter of the large diameter portion 2,2 was about 2 to 10 micrometers (average diameter 6 micrometers) and the diameter of the small diameter portion 3,3 was about 0.5 to 1.5 micrometers (average diameter 0.9 micrometers). The amount of functional particles 4,4 blended into the obtained nonwoven fabric 1 was about 100 g / m2. If a large number of long fibers are laminated, the amount of functional particles 4,4 blended per unit area in the nonwoven fabric 1 can be increased. FIG. 7 shows a micrograph of the nonwoven fabric of the embodiment. In FIG. 7, only a small portion of the layers in the thickness direction of the nonwoven fabric is photographed so that the form of the fibers can be clearly seen. The same is true for FIG. 8 and FIG. 9.

[0054] By adjusting the amount of functional particles, the viscosity and discharge speed of the liquid synthetic resin, the nozzle diameter, the applied voltage of static electricity, the distance from the nozzle to the base, the atmospheric temperature, etc., it is possible to adjust the size, length, diameter, and ratio of the large diameter portion 2,2 and the small diameter portion 3,3.

[0055] When the nonwoven fabric 1 is manufactured using the melt-blowing method or the electrospinning method, the synthetic resin is drawn from the large diameter portion to the small diameter portion during spinning, so that less synthetic resin remains in the large diameter portion. This causes the synthetic resin coating covering the functional resin in the large diameter portion to become thin or reticulated. The thin or reticulated synthetic resin coating is preferable because it allows the thermal expansion of the functional particles to be exerted more quickly and effectively.

[0056] The function and effect of the secondary battery 10 provided with the nonwoven fabric 1 will be described. The nonwoven fabric 1 used in the secondary battery 10 of the above embodiment is a nonwoven fabric that supports functional particles having thermal expansion properties, and the functional particles expand when heated, improving the heat insulating property of the nonwoven fabric. That is, the heat insulating property of the nonwoven fabric 1 is improved when the battery generates abnormal heat or catches fire, compared to when the battery is in normal operation. Therefore, in the secondary battery 10 of the above embodiment, the heat insulating property of the nonwoven fabric is relatively low and the cooling property is excellent when the battery is in normal operation, while when abnormal heat generation such as ignition occurs, the functional particles expand when heated, improving the heat insulating property of the nonwoven fabric, and the effect of preventing or suppressing ignition is obtained. That is, the secondary battery can achieve both cooling property and ignition resistance.

[0057] Furthermore, because the nonwoven fabric of the secondary battery 10 allows gas or liquid to pass through, when high-temperature air reaches the nonwoven fabric in the event of a fire, the high-temperature air easily penetrates into the nonwoven fabric, and the functional particles inside the nonwoven fabric also quickly expand, turning the entire nonwoven fabric 1 into a fire-resistant insulating layer and improving fire resistance. Furthermore, since the nonwoven fabric of the secondary battery 10 is permeable to gas or liquid, the following effects can be obtained.

[0058] When the nonwoven fabric 1 is used inside the container 12 of the secondary battery, if gas or liquid can pass through the nonwoven fabric, the electrolyte filling is prevented from being hindered, and the quality of the battery is improved. If the nonwoven fabric is permeable to gas or liquid, air is less likely to remain between the electrode body 11 and the nonwoven fabric 1, in the gaps of the nonwoven fabric 1, or between the nonwoven fabric 1 and the container 12. If air remains, the electrolyte cannot be distributed, the efficiency of the secondary battery 10 decreases, heat dissipation is impaired, and other problems occur that degrade the quality of the battery. From the viewpoint of improving the filling property of the electrolyte solution and improving the quality of the battery, it is preferable that the nonwoven fabric 1 is a nonwoven fabric that has a high affinity for the electrolyte solution, and it is preferable that the nonwoven fabric 1 is subjected to a treatment to increase its affinity for the electrolyte solution.

[0059] Furthermore, when nonwoven fabric 1 is used on the outside of container 12 of a secondary battery, if gas or liquid can pass through the nonwoven fabric, the battery can be efficiently cooled. If the nonwoven fabric is permeable to gas or liquid, the cooling air or cooling liquid is not prevented from reaching the surface of battery container 12, and heat transfer is efficiently performed. Furthermore, when nonwoven fabric 1 is used on the outside of container 12 of a secondary battery, if liquid can pass through the nonwoven fabric, it is possible to supply liquid to nonwoven fabric 1 to permeate it, and then send cooling air to vaporize the permeated liquid, thereby performing highly efficient cooling using the heat of vaporization.

[0060] Furthermore, when the nonwoven fabric 1 used in the secondary battery 10 includes long fibers made of synthetic resin with functional particles 4, 4 integrated therein, the long fibers have diameters that change in the longitudinal direction of the fibers as if a plurality of large diameter portions 2, 2 and small diameter portions 3, 3 were alternately arranged and strung together, the small diameter portions 3, 3 are monofilaments formed from the synthetic resin, and the large diameter portions 2, 2 contain the functional particles 4, 4, a large amount of functional particles can be supported on the nonwoven fabric while maintaining breathability, and the fire resistance is further improved. Also, the functional particles are less likely to fall off the nonwoven fabric, and the functional particles are less likely to contaminate the surroundings.

[0061] Furthermore, when the fiber diameter of the small diameter portions 3,3 of the long fibers is equal to or smaller than the diameter of the functional particles 4,4 contained in the large diameter portions 2,2, and the functional particles 4,4 are wrapped in a membrane-like, mesh-like, or fiber-bundle-like synthetic resin, or are bonded with the synthetic resin to be integrated with the large diameter portions 2,2, the synthetic resin covering the functional particles becomes very thin, so that the thermal expansion and improvement of the insulating properties of the functional particles occur quickly, and the fire resistance is further improved.

[0062] Furthermore, when the functional particles are aluminum hydrogen phosphite particles, the expanded functional particles change the nonwoven fabric 1 into a fire-resistant and insulating heat insulating layer when heated, and the fire spread resistance is further improved. If the functional particles are insulating, there is no risk of the expanded functional particles causing a short circuit between the positive and negative electrodes of the battery, which is preferable. Furthermore, if the functional particles are aluminum hydrogen phosphite particles, the particles can reliably maintain their expanded form even when exposed to high temperatures during a battery fire, and the fire spread resistance is further improved.

[0063] Furthermore, when the fiber diameter of the small diameter parts 3,3 is 100 nanometers or more and 10 micrometers or less, and the diameter of the functional particles 4,4 is 300 nanometers or more and 200 micrometers or less, the thermal expansion of the functional particles 4,4 occurs quickly, and the fire resistance is further improved. In addition, such a nonwoven fabric 1 can improve the air permeability and liquid permeability, which contributes to improving the cooling performance during normal operation of the battery.

[0064] Furthermore, when the nonwoven fabric is bag-shaped, the secondary battery and the electrode body can be effectively covered with the nonwoven fabric, facilitating assembly. In particular, when a plurality of plate-shaped secondary batteries are stacked to form an assembled battery, the entire mutually facing surfaces of adjacent batteries can be effectively covered with the nonwoven fabric, allowing efficient production of the secondary battery 10 and the assembled battery 20.

[0065] The invention is not limited to the above-mentioned embodiment, and can be practiced with various modifications. Other embodiments of the invention will be described below, but in the following description, the differences from the above-mentioned embodiment will be mainly described, and detailed descriptions of similar parts will be omitted. In addition, these embodiments can be practiced by combining parts with each other or by replacing parts.

[0066] Although the nonwoven fabric 1 is exemplified as a bag-like shape when attached to a secondary battery, the shape is not limited to a bag-like shape. In the case of a flat secondary battery, the nonwoven fabric 1 may be attached to the secondary battery in a U-shaped folded form so as to cover two sides corresponding to both sides of the flat plate. Alternatively, the nonwoven fabric 1 may be attached by wrapping it around a container or an electrode body. Alternatively, the nonwoven fabric 1 may be folded and attached to the secondary battery by wrapping the electrode body 11 or the container 12 with the nonwoven fabric 1.

[0067] There is no particular limitation on the technical field in which the secondary battery 10 is used, and the secondary battery 10 can be applied to technical fields other than those exemplified in the above embodiment. For example, the secondary battery 10 can be used in electric vehicles and hybrid vehicles, but the use of the battery or battery pack is not limited to automobiles. For example, the secondary battery can also be used in electric bicycles. The secondary battery or battery pack may be used as a power source for trains, ships, or aircraft. The secondary battery or battery pack may also be used as a backup power source for computers, an auxiliary storage battery for wind power generation equipment or solar power generation equipment, or an auxiliary power source or backup power source for industrial equipment.

[0068] In addition, for example, in the above embodiment, the long fibers in the nonwoven fabric 1 are simply in contact with each other at the entangled portions, but the long fibers may be bonded to each other at the entangled portions. For example, the large diameter portions 2, 2 may be stuck together at the entangled portions, or three or more (preferably four or more) small diameter portions 3, 3 may be connected to one large diameter portion in appearance. In such a structure, the small diameter portions 3, 3 are connected between the large diameter portions 2, 2 in a network shape, which makes it easier to maintain the three-dimensional structure of the nonwoven fabric 1 and also provides good breathability.

[0069] Other examples of the nonwoven fabric 1 produced under different production conditions will be described below. Example 2 Figure 8 is a microscope photograph showing the structure of the nonwoven fabric of Example 2, which was manufactured by changing the manufacturing conditions. The manufacturing conditions were adjusted so that the long fibers were thicker overall, as compared to the above-mentioned Examples. The synthetic resin is thermoplastic polyurethane resin (TPU), the functional particles are "NSF" (average particle size 5 micrometers), and the fabrication is performed by electrospinning, as in the above-mentioned Examples.

[0070] In the nonwoven fabric of Example 2, the diameter of the large diameter parts 2,2 was about 2 to 15 micrometers (average diameter 8 micrometers), and the diameter of the small diameter parts 3,3 was about 0.5 to 1.8 micrometers (average diameter 1.0 micrometer). Also, in the nonwoven fabric of Example 2, there were some parts where three or more small diameter parts extended so as to branch out from the large diameter parts.

[0071] Example 3 Figure 9 is a micrograph showing the structure of the nonwoven fabric of Example 3, which was manufactured by changing the manufacturing conditions. Compared to the above-mentioned Examples, the amount of functional particles blended was reduced, and the manufacturing conditions were adjusted. The synthetic resin is thermoplastic polyurethane resin (TPU), the functional particles are "NSF" (average particle size 5 micrometers), and the fabrication is performed by electrospinning, which are the same as the above-mentioned Examples.

[0072] In the nonwoven fabric of Example 3, the diameter of the large diameter parts 2,2 was about 3 to 8 micrometers (average diameter 5 micrometers), and the diameter of the small diameter parts 3,3 was about 0.3 to 1.0 micrometers (average diameter 0.6 micrometers). Also, in the nonwoven fabric of Example 3, there were parts where three or more small diameter parts extended so as to branch out from a large diameter part.

[0073] The nonwoven fabrics of Examples 1, 2, and 3 all had moderate breathability, and when exposed to hot air (approximately 800°C), the functional particles expanded to form a fire-resistant, insulating layer with almost no breathability, thereby improving the insulating properties.

[0074] In addition, in the above embodiment, a single-layer nonwoven fabric containing thermally expandable functional particles is exemplified, but the nonwoven fabric may be a multi-layer nonwoven fabric having a layer that does not contain functional particles. For example, a two-layer nonwoven fabric may be formed by laminating an aramid fiber mesh material as a support layer on the above nonwoven fabric.

[0075] The support layer is effective in improving the mechanical properties of the nonwoven fabric layer containing the thermally expandable particles. In particular, if the support layer is made of fibers made of a material that is more heat resistant than the synthetic resin that is the material of the long fibers of the nonwoven fabric, such as aramid fibers or metal fibers, the functional particles can be prevented from being easily released from the restraint of the functional particles by the long fibers when the functional particles expand due to exposure to high temperatures. When providing a support layer, it is particularly preferable to provide the support layer downstream of the expected air flow.

[0076] In the above embodiment, the functional particles have been described as having thermal expansion, but the function of the functional particles is not limited to thermal expansion. For example, the functional particles may be particles that have water retention and water absorption properties in addition to thermal expansion. In this case, the functional particles can increase the water absorption properties of the nonwoven fabric, or can produce a cooling effect by evaporating the absorbed moisture. [Industrial Applicability]

[0077] The secondary battery of the above embodiment can be used as a power source for electric vehicles, and can prevent the battery from catching fire, making it highly valuable in industry. [Explanation of symbols]

[0078] 1. Nonwoven fabric 2 Large diameter section 3 Small diameter section 4 Functional particles 10 Secondary battery 11 Electrode body 12 containers 13 Positive electrode material 14 Negative electrode material 20 Battery pack 21 Spacer 22 End plate 23 Busbar 30 Secondary battery

Claims

1. A secondary battery in which an electrode body is sealed in a container together with an electrolyte, The outer periphery of the electrode body or the container is covered with a nonwoven fabric, The nonwoven fabric is permeable to gas or liquid, The nonwoven fabric supports functional particles having thermal expansion properties, and the functional particles expand when heated, thereby improving the heat insulating properties of the nonwoven fabric. Secondary battery.

2. The nonwoven fabric is The functional particles are integrated into long fibers made of a synthetic resin, The long fibers have diameters that vary in the longitudinal direction of the fibers, as if a plurality of large diameter portions and small diameter portions were alternately arranged and strung together, the small diameter portion is a monofilament formed from the synthetic resin, The large diameter portion contains the functional particles.

2. The secondary battery according to claim 1.

3. a fiber diameter of the small diameter portion of the long fiber is equal to or smaller than a diameter of the functional particle included in the large diameter portion, the functional particles are wrapped in the synthetic resin in a film-like, net-like, or fiber-bundle-like form, or are bonded by the synthetic resin, and are integrated with the large diameter portion; 3. The secondary battery according to claim 2.

4. The functional particles are aluminum hydrogen phosphite particles.

2. The secondary battery according to claim 1.

5. The fiber diameter of the small diameter portion is 100 nanometers or more and 10 micrometers or less, and the diameter of the functional particle is 300 nanometers or more and 200 micrometers or less.

3. The secondary battery according to claim 2.

6. The nonwoven fabric is bag-shaped.

2. The secondary battery according to claim 1.

7. A battery pack comprising a plurality of secondary batteries according to claim 1 electrically connected and integrated together, The secondary battery is a flat plate-shaped secondary battery, A plurality of secondary batteries are stacked. Battery pack.

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