Secondary batteries

Abstract

To provide a secondary battery which makes a hole less likely to occur in a battery case.SOLUTION: The invention provides a secondary battery 100 including a battery case 10, an electrode body 20 housed in the battery case 10, and an insulator film 50 disposed between the battery case 10 and the electrode body 20. The insulator film 50 includes: a first metal layer formed of a first metal; and a second metal layer disposed closer to the battery case 10 than the first metal layer and formed of a second metal having a linear expansion coefficient larger than that of the first metal. Further, in the insulator film 50, at least a surface facing the battery case 10 and a surface facing the electrode body 20 are covered with an insulation material.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] A secondary battery typically includes a battery case and an electrode assembly housed in the battery case. Prior art documents related to secondary batteries include Patent Documents 1 and 2. For example, Patent Document 1 discloses a secondary battery further including an insulating film made of synthetic resin and disposed between the battery case and the electrode assembly. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 027296 [Patent Document 2] Japanese Patent Publication No. 2022-148731 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the inventor's research, if the insulating film is made of a synthetic resin such as polypropylene (PP), the insulating film may partially melt when the temperature inside the battery rises due to overcharging or other reasons. This makes it easier for heat inside the battery to be transferred to the battery case in the melted area, which can cause localized heat concentration. This can result in a hole being created in the battery case. Furthermore, the contents of the secondary battery (e.g., fragments of the active material layer) may be ejected from the hole and scattered around the surrounding area.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a secondary battery in which localized heat concentration on the battery case is suppressed and the battery case is less likely to develop holes. [Means for solving the problem]

[0006] The present invention provides a secondary battery comprising a battery case, an electrode assembly housed in the battery case, and an insulating film disposed between the battery case and the electrode assembly. The insulating film includes a first metal layer made of a first metal, and a second metal layer disposed closer to the battery case than the first metal layer and made of a second metal having a linear expansion coefficient greater than that of the first metal, and at least a surface facing the battery case and a surface facing the electrode assembly are covered with an insulating material.

[0007] In the present invention, the second metal layer has a relatively large linear expansion coefficient. Therefore, when heat is transferred from the first metal layer on the electrode body side to the second metal layer on the battery case side, the second metal layer expands significantly. This expansion also transfers heat, allowing the heat to be diffused over a wide area. As a result, localized heat concentration on the battery case is suppressed, and the formation of holes in the battery case can be prevented. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view schematically showing a secondary battery according to one embodiment. [Figure 2] FIG. 2 is a perspective view of the secondary battery of FIG. 1 turned upside down. [Figure 3] FIG. 3 is a vertical cross-sectional view schematically showing the internal structure of the secondary battery of FIG. [Figure 4] FIG. 4 is a perspective view that schematically shows the electrode body attached to the sealing plate. [Figure 5] FIG. 5 is a cross-sectional view schematically illustrating the configuration of an insulating film according to an embodiment. [Figure 6] FIG. 6 is a development view of an insulating film according to an embodiment. [Figure 7] FIG. 7 is a perspective view schematically illustrating a cooling plate according to an embodiment. [Figure 8] FIG. 8 is a perspective view schematically showing an example of the arrangement of the cooling plates. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, several embodiments of the technology disclosed herein will be described in detail with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (for example, the general configuration and manufacturing process of a secondary battery that does not characterize the technology disclosed herein) can be understood as design matters of a person skilled in the art based on prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function are denoted by the same reference numerals.

[0010] In this specification, the term "secondary battery" refers to a general electricity storage device that can be repeatedly charged and discharged by the movement of charge carriers between a positive electrode and a negative electrode via an electrolyte. In this specification, the expression "A to B" indicating a range includes not only the meaning of A or more but also the meaning of "greater than A" and "smaller than B."

[0011] FIG. 1 is a perspective view of a secondary battery 100 according to one embodiment. FIG. 2 is a perspective view of the secondary battery 100 of FIG. 1 turned upside down. FIG. 3 shows the internal structure of the secondary battery 100 of FIG. 1. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent the short side direction of the secondary battery 100, the long side direction perpendicular to the short side direction, and the up-down direction perpendicular to the short side direction and the long side direction, respectively. However, these directions are defined for the sake of convenience and do not limit the installation mode of the secondary battery 100 in any way.

[0012] As shown in FIG. 3, the secondary battery 100 includes a battery case 10, an electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, and an insulating film 50. Although not shown, the secondary battery 100 further includes an electrolyte. The secondary battery 100 is a lithium-ion secondary battery. The secondary battery 100 is preferably a lithium-ion secondary battery. The secondary battery 100 is characterized by including the insulating film 50 disclosed herein, and other configurations may be the same as conventional ones.

[0013] The battery case 10 is a housing that houses the electrode assembly 20, the insulating film 50, and the electrolyte. As shown in FIGS. 1 and 2, the battery case 10 has a flat, bottomed, rectangular parallelepiped (rectangular) outer shape. The battery case 10 is preferably rectangular. The material of the battery case 10 may be the same as that conventionally used, and is not particularly limited. The battery case 10 is preferably made of metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like.

[0014] 3, the battery case 10 includes a case body 12 having a pair of openings 12h and two sealing plates 14 that close the pair of openings 12h. The battery case 10 is integrated by joining (for example, welding) the sealing plates 14 to the peripheries of the pair of openings 12h of the case body 12. The battery case 10 is hermetically sealed (sealed).

[0015] The case body 12 has a rectangular cylindrical shape and, as shown in FIG. 1, includes a substantially rectangular bottom surface 12a, a pair of opposing long side surfaces 12b extending from the long sides of the bottom surface 12a, and a top surface 12c connecting the upper ends of the pair of long side surfaces 12b. The top surface 12c is substantially rectangular. The top surface 12c faces the bottom surface 12a. The case body 12 is formed, for example, by bending a single metal plate into a cylindrical shape and joining the seams (for example, by welding). Here, a welded joint 12d is located on the top surface 12c. A gas exhaust valve 13 is provided on the bottom surface 12a.

[0016] The gas release valve 13 is configured to break when the pressure inside the battery case 10 reaches or exceeds a predetermined value, thereby releasing the gas inside the battery case 10 to the outside. In this embodiment, there is one gas release valve 13, but there may be two or more. In this embodiment, the gas release valve 13 is provided on the bottom surface 12a, but in other embodiments, the gas release valve 13 may be provided on a surface other than the bottom surface 12a, such as the long side surface 12b, the top surface 12c, or the sealing plate 14. The area of ​​the gas release valve 13 is arbitrary.

[0017] In this embodiment, the gas release valve 13 is a cross-shaped notch. However, the shape of the gas release valve 13 is not particularly limited. In other embodiments, the gas release valve 13 may be, for example, a linear notch (vertical or horizontal only), or may be a conventionally known oval valve (with a notch therein) or a circular valve (with a notch therein). The dimensions of the notch (length, depth) are arbitrary and can be determined appropriately taking into consideration, for example, the pressure resistance of the battery case 10.

[0018] The sealing plate 14 is a plate-like member that seals the opening 12h. The sealing plate 14 has a substantially rectangular shape in a plan view. The area of ​​the sealing plate 14 is smaller than that of the long side surface 12b. The sealing plate 14 has a liquid inlet 15. The liquid inlet 15 is used to inject an electrolyte into the battery case 10 after the sealing plate 14 is assembled to the case body 12. The liquid inlet 15 is sealed with a sealing member 16 after the electrolyte is injected. Note that in the present embodiment, the liquid inlet 15 is provided in the sealing plate 14, but in other embodiments, the liquid inlet 15 may be provided in the case body 12. Also, in the present embodiment, the liquid inlet 15 is provided on a different surface from the gas release valve 13, but in other embodiments, the liquid inlet 15 may be provided on the same surface as the gas release valve 13.

[0019] The positive electrode terminal 30 and the negative electrode terminal 40 are each fixed to the battery case 10. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are each fixed to opposing surfaces of the battery case 10 (specifically, the sealing plate 14). More specifically, the positive electrode terminal 30 is attached to the sealing plate 14 located on one side in the long side direction Y (the right side in FIGS. 1 and 2). The negative electrode terminal 40 is attached to the sealing plate 14 located on the other side in the long side direction Y (the left side in FIGS. 1 and 2). In this embodiment, the positive electrode terminal 30 and the negative electrode terminal 40 are provided on the sealing plate 14, but in other embodiments, the positive electrode terminal 30 and the negative electrode terminal 40 may be provided on the case body 12. In addition, in this embodiment, the positive electrode terminal 30 and the negative electrode terminal 40 are provided on a surface different from the gas release valve 13, but in other embodiments, the positive electrode terminal 30 and the negative electrode terminal 40 may be provided on the same surface as the gas release valve 13.

[0020] The positive electrode terminal 30 and the negative electrode terminal 40 are each exposed on the outer surface of the sealing plate 14. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are arranged on an axis that extends in the long side direction Y and passes through the center of the sealing plate 14. However, in other embodiments, the axis may be offset from the center of the sealing plate 14, for example, in the short side direction X. Furthermore, the positive electrode terminal 30 and the negative electrode terminal 40 do not have to be arranged on the axis. For example, one of the positive electrode terminal 30 and the negative electrode terminal 40 may be offset to one side in the short side direction X, and the other may be offset to the other side in the short side direction X.

[0021] The positive electrode terminal 30 is preferably made of a metal, more preferably aluminum or an aluminum alloy, for example, and the negative electrode terminal 40 is preferably made of a metal, more preferably copper or a copper alloy, for example.

[0022] As shown in Fig. 3, the positive electrode terminal 30 is electrically connected to the positive electrode 23 of the electrode assembly 20 via a positive electrode current collector 32 inside the battery case 10. The negative electrode terminal 40 is electrically connected to the negative electrode 24 of the electrode assembly 20 via a negative electrode current collector 42 inside the battery case 10. The positive electrode terminal 30 and the negative electrode terminal 40 are insulated from the case body 12 by an insulating film 50. The positive electrode terminal 30 and the negative electrode terminal 40 are insulated from the sealing plate 14 by an insulating member 60 (see Fig. 4).

[0023] The electrode body 20 is housed inside the battery case 10. FIG. 4 is a perspective view of the electrode body 20 attached to the sealing plate 14. As shown in FIG. 4, the electrode body 20 is placed inside the battery case 10 while covered with an insulating film 50, which will be described later. In this embodiment, a plurality of electrode bodies 20 (two in FIG. 4) are housed inside one battery case 10. However, the number of electrode bodies 20 housed inside one battery case 10 is not particularly limited, and in other embodiments, there may be three or more electrode bodies 20, or there may be one electrode body.

[0024] As shown in Fig. 3, the electrode assembly 20 includes a positive electrode 23 and a negative electrode 24. Here, the electrode assembly 20 is a wound electrode assembly. Specifically, the electrode assembly 20 is formed by winding a laminate formed by stacking a strip-shaped positive electrode 23 and a strip-shaped negative electrode 24 with a strip-shaped separator interposed therebetween in the longitudinal direction around a winding axis. However, in other embodiments, the electrode assembly 20 may be a laminated electrode assembly formed by stacking a rectangular positive electrode and a rectangular negative electrode in an insulated state.

[0025] Here, the electrode body 20 has a flat outer shape. The electrode body 20 has a pair of curved portions and a pair of flat surfaces connecting the pair of curved portions. Here, the electrode body 20 is housed inside the battery case 10 with its winding axis oriented along the long side direction Y. The electrode body 20 is of a so-called horizontally wound type. The pair of curved portions of the electrode body 20 face the bottom surface 12a and the top surface 12c of the case body 12, respectively. The pair of flat surfaces of the electrode body 20 face the pair of long side surfaces 12b of the case body 12, respectively. However, the electrode body 20 may also be housed inside the battery case 10 with its winding axis oriented along the up-down direction Z, for example. The electrode body 20 may also be of a so-called vertically wound type. The components constituting the electrode body 20 (such as a positive electrode, a negative electrode, and a separator) may be similar to those of a general secondary battery and are not particularly limited.

[0026] The positive electrode 23 typically includes a positive electrode current collector and a positive electrode active material layer fixed to at least one surface of the positive electrode current collector. The positive electrode current collector is strip-shaped here. The positive electrode current collector is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. Here, the positive electrode current collector is a metal foil, specifically, an aluminum foil.

[0027] The positive electrode active material layer is provided in a strip-like shape along the longitudinal direction of the strip-shaped positive electrode current collector. The positive electrode active material layer contains a positive electrode active material capable of reversibly absorbing and releasing charge carriers. The positive electrode active material is preferably an oxide containing at least one of Ni, Co, and Mn, such as lithium transition metal composite oxides such as lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel manganese composite oxide, and lithium nickel cobalt composite oxide. The positive electrode active material is preferably, for example, a composite oxide containing Ni and Li, in which the Ni content in the composite oxide is in the range of 70 to 100 mol% relative to the total number of moles of the constituent elements excluding Li and oxygen in the composite oxide. Positive electrode active materials also include those in which a portion of the Ni, Co, and Mn is replaced with Al, Ti, Zr, P, B, Si, Nb, C, etc., or those in which the particle surface is covered with a compound containing Al, Ti, Zr, W, P, B, Si, Nb, C, etc. The total amount of substitution and addition is about 0.1 to 7%.

[0028] The negative electrode 24 typically includes a negative electrode current collector and a negative electrode active material layer fixed to at least one surface of the negative electrode current collector. The negative electrode current collector is strip-shaped here. The negative electrode current collector is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. Here, the negative electrode current collector is a metal foil, specifically a copper foil.

[0029] The negative electrode active material layer is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode current collector. The negative electrode active material layer contains a negative electrode active material capable of reversibly absorbing and releasing charge carriers. Examples of the negative electrode active material include carbon materials such as graphite and carbon, and metals capable of absorbing lithium such as Si, SiO, SiC, and Sn, and compounds thereof.

[0030] The separator is a member that insulates the positive electrode active material layer from the negative electrode active material layer. A porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) is suitable as the separator. A heat-resistant layer (HRL) containing an inorganic filler may be provided on the surface of the separator. Examples of inorganic fillers that can be used include alumina, boehmite, aluminum hydroxide, and titania.

[0031] The electrolyte solution is accommodated inside the battery case 10 together with the electrode assembly 20. The electrolyte solution may be the same as that used in general secondary batteries and is not particularly limited. The electrolyte solution is typically a non-aqueous liquid electrolyte (nonaqueous electrolyte solution) containing a non-aqueous solvent and a supporting salt. The non-aqueous solvent contains, for example, carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The non-aqueous solvent is preferably a mixture of EC, EMC, and DMC in a range of 1 to 99% so that the total ratio is 100%. The supporting salt is, for example, a fluorine-containing lithium salt. The fluorine-containing lithium salt preferably contains lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (F2LiNO4S2), also known as LiFSI, or a mixture thereof. The concentration of the supporting salt is preferably 0.6 to 1.8 mol per 1 L of non-aqueous solvent.

[0032] The insulating film 50 is housed inside the battery case 10 together with the electrode assembly 20. The insulating film 50 is disposed between the battery case 10 and the electrode assembly 20. As shown in FIG. 4, the insulating film 50 covers the periphery of the electrode assembly 20. Specifically, it is preferable that the insulating film 50 covers at least the curved portion facing the bottom surface 12a of the electrode assembly 20 and a pair of flat surfaces. The insulating film 50 is made of a single sheet-like member assembled into, for example, a box- or bag-like shape.

[0033] 5 is a cross-sectional view showing the configuration of an insulating film 50 according to one embodiment. The insulating film 50 has an insulating base portion 58, and a first metal layer 51 and a second metal layer 52 embedded in the base portion 58. The first metal layer 51 and the second metal layer 52 are stacked in a stacking direction T extending from the electrode body 20 toward the battery case 10. The insulating film 50 has a first surface 50a and a second surface 50b that are perpendicular to the stacking direction T. The first surface 50a faces the electrode body 20, and the second surface 50b faces the battery case 10.

[0034] At least the surface of the insulating film 50 facing the battery case 10 and the surface facing the electrode assembly 20 are covered with an insulating material. Specifically, at least the first surface 50a and the second surface 50b of the insulating film 50 are each composed of a substrate 58. The first metal layer 51 and the second metal layer 52 are not exposed on the first surface 50a and the second surface 50b. In this embodiment, both end portions of the insulating film 50 in the width direction W, which is perpendicular to the stacking direction T, are also covered with the substrate 58. However, in other embodiments, for example, in portions of the insulating film 50 that do not contact the battery case 10 or the electrode assembly 20, the first metal layer 51 and / or the second metal layer 52 may be exposed at the end portions in the width direction W.

[0035] 5, the first metal layer 51 and the second metal layer 52 are in direct contact with each other in the stacking direction T. However, in other embodiments, a substrate 58 may be interposed between the first metal layer 51 and the second metal layer 52. Furthermore, for example, instead of or in addition to the substrate 58, an adhesive layer or the like different from the substrate 58 may be interposed between the first metal layer 51 and the second metal layer 52.

[0036] The first metal layer 51 is disposed closer to the electrode body 20 than the second metal layer 52. Although not particularly limited, the thickness T1 (length in the stacking direction T) of the first metal layer 51 is preferably 0.05 to 1.5 mm, more preferably 0.1 to 1 mm, and even more preferably 0.2 to 0.5 mm. By setting the thickness to a predetermined value or more, the effects of the technology disclosed herein can be exerted to a high level. By setting the thickness to a predetermined value or less, the volumetric energy density can be improved.

[0037] The first metal layer 51 is made of a first metal. The first metal is a metal or an alloy (two or more types of metals). The type of the first metal is not particularly limited as long as it has a smaller linear expansion coefficient than the second metal described below. Although not particularly limited, the linear expansion coefficient of the first metal is preferably 23×10 -6 / K or less, for example, 0.1 to 22 × 10 -6 / K. The linear expansion coefficient of the first metal is preferably smaller than the linear expansion coefficient of the metal (for example, aluminum) that constitutes the battery case 10.

[0038] The melting point of the first metal is preferably higher than the melting point of the metal (e.g., aluminum or aluminum alloy) constituting the battery case 10. Although not particularly limited, the melting point of the first metal is preferably 1000°C or higher, more preferably 1250°C or higher, and even more preferably 1400°C or higher. This allows the effects of the technology disclosed herein to be exerted at a high level. From the viewpoint of cost, etc., the melting point of the first metal may be 5000°C or lower, 4000°C or lower, or, for example, 2000°C or lower. Specific examples of the first metal include copper, beryllium, nickel, iron, titanium, tungsten, stainless steel, carbon steel, nickel steel, and duralumin, with titanium being particularly preferred.

[0039] The second metal layer 52 is disposed closer to the battery case 10 than the first metal layer 51. Although not particularly limited, the thickness T2 (length in the stacking direction T) of the second metal layer 52 is preferably 0.05 to 1.5 mm, more preferably 0.1 to 1 mm, and even more preferably 0.2 to 0.5 mm. By setting the thickness to a predetermined value or more, the effects of the technology disclosed herein can be exerted to a high level. By setting the thickness to a predetermined value or less, the volumetric energy density can be improved. Here, the thickness T2 of the second metal layer 52 is the same as the thickness T1 of the first metal layer 51, but in other embodiments, the thicknesses of the first metal layer 51 and the second metal layer 52 may be different.

[0040] The second metal layer 52 is made of a second metal having a linear expansion coefficient greater than that of the first metal. The second metal is typically a metal or alloy (two or more metals) different from the first metal. The type of the second metal is not particularly limited as long as it has a linear expansion coefficient greater than that of the first metal. Although not particularly limited, the linear expansion coefficient of the second metal is preferably 5×10 -6 / K or more is preferable, and 10 × 10 -6 / K or more is preferable, for example, 14 to 25 × 10 -6 / K. Although not particularly limited, the difference in the linear expansion coefficient between the first metal and the second metal ((linear expansion coefficient of the second metal) - (linear expansion coefficient of the first metal)) may be 1 x 10 -6 / K or more is preferable, 5×10 -6 / K or more is preferable, and 6×10 -6 / K or more is more preferable, and 7×10 -6 This allows the effects of the techniques disclosed herein to be exerted at a high level.

[0041] The second metal is a metal whose melting point is typically lower than that of the first metal. Although not particularly limited, the melting point of the second metal is preferably 500°C or higher, more preferably 800°C or higher. This allows the effects of the technology disclosed herein to be exerted at a high level. The melting point of the second metal may be 2000°C or lower, or 1500°C or lower. Specific examples of the second metal include aluminum, copper, brass, stainless steel, and carbon steel, with copper being particularly preferred.

[0042] The substrate 58 is made of an insulating material. The substrate 58 is typically made of a material with a lower melting point than the first metal and the second metal. The substrate 58 is preferably made of a resin, such as an olefin resin such as polyethylene (PE), polypropylene (PP / OPP), or polymethylpentene (PMP / TPX™), a polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), or a fluororesin resin such as acrylic resin (PMMA), polyimide (PI), polyphenylene ether (PPE), triacetate (TAC), polyphenylene sulfide resin (PPS), polycarbonate (PC), nylon, or polytetrafluoroethylene (PTFE). Of these, an olefin resin or an engineering plastic (engineering plastic) having a heat resistance of 100°C or higher is preferred.

[0043] The insulating film 50 preferably has a through-hole H (see FIG. 6) at a position facing the gas release valve 13. However, in other embodiments, the insulating film 50 may not have the through-hole H. Alternatively, the insulating film 50 may be made of only a plastic film such as PP only at the portion facing the gas release valve 13. Furthermore, the size of the through-hole H is arbitrary. If the gas release valve 13 is an oval or circular valve, the size of the through-hole H is preferably about ±10 mm from the outer edge of the gas release valve 13. Furthermore, if the gas release valve 13 is a notch as in this embodiment, it is preferable that the insulating film 50 cover a part of the notch at the portion facing the gas release valve 13.

[0044] The secondary battery 100 includes the insulating film 50, which reduces the likelihood of localized heat concentration in the battery case 10 even if an unsafe event occurs inside the battery case 10 due to, for example, overcharging. Specifically, the linear expansion coefficient of the second metal constituting the second metal layer 52 is greater than that of the first metal constituting the first metal layer 51. Therefore, when fragments of the active material layer generated from the electrode body 20 inside the battery case 10 come into contact with the first metal layer 51 and heat is transferred to the second metal layer 52, the second metal layer 52 expands more than the first metal layer 51. At this time, heat also moves with the expansion, allowing the heat to be diffused to the surroundings. As a result, localized heat concentration in the battery case 10 is reduced, and the battery case 10 is prevented from being perforated.

[0045] Such an insulating film 50 can be produced, for example, by a manufacturing method including a preparation step S1 of preparing a film as a raw material, and a processing step S2 of processing the prepared film.

[0046] In the preparation step S1, for example, a metal plate (sheet-shaped, approximately 0.5 to 3 mm thick) made of a first metal (including alloy) and a metal plate (sheet-shaped, 0.5 to 3 mm thick) made of a second metal are prepared, and then rolled into foils of predetermined thicknesses using a metal roll press. Next, the two obtained metal foils (including alloy foils) are cut into predetermined sizes. The cutting method is not particularly limited, and may be, for example, cutting with a metal blade or using a laser. It is preferable to deburr the cut edges. This makes it less likely that the metal edges of the insulating film 50 will penetrate the base material 58.

[0047] Next, adhesive is applied to each of two pieces of metal foil cut to a predetermined size, and a plastic film made of the material described above is pressed onto both sides. After that, the metal foils covered with the plastic film are stacked with the adhesive interposed therebetween and pressed together again, thereby producing a film having a first metal layer 51 and a second metal layer 52.

[0048] Alternatively, as a second method, two sheets of metal foil of a predetermined size can be first stacked together, and then a plastic film can be pressed onto the non-facing sides of each foil in a manner similar to that described above to produce a film. In this case, the plastic film should be larger than the metal foil so that it covers the two sheets of metal foil. The unnecessary plastic film is then removed by cutting, taking care not to expose the edge of the metal foil at the cut edge. The cutting method is not particularly limited; for example, cutting can be done with a metal blade or a laser.

[0049] Furthermore, as a third method, without using adhesive, a plastic film such as an olefin resin or various engineering plastics (PET, PEN, PI, PPE, fluororesin film, etc.) is placed on a metal foil of a predetermined size, and heated to a high temperature of up to approximately 400°C to melt the plastic and press it together to produce an integrated product of metal foil and plastic. Then, a metal foil covered with a plastic film is placed on the surface of the integrated product, and the resulting film can be produced by heating and melting it again.

[0050] Alternatively, as a fourth method, two pieces of metal foil cut to different predetermined sizes are first stacked together, and a plastic film is placed on each of the opposing sides of each foil. The resulting film can then be produced by heating the resulting film at a high temperature of up to approximately 400°C to melt the plastic and press the resulting film together. In this case, the plastic film should also be large enough to cover the entire metal foil. Then, as in the second method, any unnecessary plastic film is removed by cutting.

[0051] Next, in the processing step S2, for example, the film obtained as described above is first cut to a shape and size that matches the outer shape of the electrode assembly 20. FIG. 6 is a developed view of an insulating film 50 according to one embodiment. In FIG. 6, the bottom surface portion BP is a portion facing the lower end of the electrode assembly 20 and the bottom surface 12a of the battery case 10, and the side surface portion SP is a portion facing a pair of flat surfaces of the electrode assembly 20 and a pair of long side surfaces 12b of the battery case 10. Furthermore, the cutout portions N1 and N2 correspond to the connection portion between the electrode assembly 20 and the positive electrode current collector 32 (see FIG. 3) and the connection portion between the electrode assembly 20 and the negative electrode current collector 42 (see FIG. 3), respectively. Here, the insulating film 50 has a through-hole H in the bottom surface portion BP. The through-hole H is provided so that at least a portion thereof faces the gas release valve 13. The through-hole H can be formed by cutting and removing the portion of the insulating film 50 or plastic film facing the gas release valve 13. Additionally, the positions of the dashed lines may be provided with creases (for example, grooves or perforations) for folding. Insulating film 50 can be produced by folding a film of this shape along the dotted lines.

[0052] In some embodiments, the secondary battery 100 preferably further includes a cooling plate 70 (see FIG. 7 ) disposed between the battery case 10 and the electrode assembly 20 so as to be in contact with a portion of the battery case 10 (e.g., the bottom surface 12 a). The cooling plate 70 is preferably made of a material with high thermal conductivity, and more preferably made of, for example, a metal material (including an alloy material) primarily made of aluminum or a metal material primarily made of copper. The surface of the cooling plate 70 is preferably coated with a resin such as polypropylene. By including the cooling plate 70, heat generated within the battery case 10 can be efficiently dissipated, improving the safety of the secondary battery 100. The cooling plate 70 is an example of a “gap-forming portion.”

[0053] FIG. 7 is a perspective view of a cooling plate 70 according to one embodiment. The cooling plate 70 of this embodiment has a base portion 71 and a plurality of (three in this example) protrusions 72. The base portion 71 is rectangular. The protrusions 72 are provided on the surface facing the electrode assembly 20. The surface of the cooling plate 70 facing the electrode assembly 20 has an uneven shape. Here, the protrusions 72 are prismatic along the long side. However, the number and shape (height, length, etc.) of the protrusions 72 are not particularly limited and can be any.

[0054] 8 is a perspective view showing an example of the arrangement of the cooling plate 70. In this embodiment, the cooling plate 70 is in contact with the bottom surface 12a. The cooling plate 70 is arranged on the bottom surface 12a side of the electrode assembly 20, i.e., between the bottom surface 12a and the electrode assembly 20 (not shown in FIG. 8). However, in other embodiments, the cooling plate 70 may be arranged on the long side surface 12b side, the top surface 12c side, or the sealing plate 14 side of the electrode assembly 20.

[0055] In this embodiment, a plurality of cooling plates 70 (two in FIG. 8 ) are arranged inside one battery case 10. The two cooling plates 70 are arranged side by side in the long side direction Y, sandwiching the gas release valve 13 therebetween. However, the number of cooling plates 70 arranged inside one battery case 10 is not particularly limited, and in other embodiments, there may be three or more cooling plates 70, or just one cooling plate. For example, if two gas release valves 13 are provided on the bottom surface 12 a, three cooling plates 70 may be arranged side by side in the long side direction Y, sandwiching the two gas release valves 13 therebetween. Alternatively, if one or more gas release valves 13 are provided on a portion of the battery case 10 other than the bottom surface 12 a, such as on the long side surface 12 b, the top surface 12 c, or the sealing plate 14, one larger cooling plate 70 may be arranged on the bottom surface 12 a.

[0056] The secondary battery 100 can be used for various purposes, but can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car, truck, etc. The type of vehicle is not particularly limited, but examples include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

[0057] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to these examples.

[0058] <Construction of secondary batteries> A metal plate (sheet-shaped, thickness 0.5 to 3 mm) made of the first metal and a metal plate (sheet-shaped, thickness 0.5 to 3 mm) made of the second metal listed in Table 1 were prepared and rolled into foils with the thicknesses listed in Table 1 using a metal roll press. Next, two metal foils were cut to a predetermined size and then stacked together. A plastic film (PP) was placed on each of the opposing surfaces of the foils. The plastic film was sized to cover the entire metal foil (including the edges). Next, this laminate was heated to a high temperature of approximately 400°C at maximum to melt the plastic, and then pressure-bonded to obtain a film having a first metal layer and a second metal layer. The properties (melting point, linear expansion coefficient) of the first metal and the second metal are as listed in Table 1. The difference in linear expansion coefficient was calculated by subtracting the linear expansion coefficient of the first metal from the linear expansion coefficient of the second metal. Comparative Example 1 used only a PP film.

[0059] Next, a rectangular parallelepiped battery case with a gas release valve was prepared. The position and number of the gas release valves were as shown in Table 1. Next, the film obtained above was cut to a predetermined size and folded to prepare an insulating film. Note that, for examples in Table 1 marked with "through holes," a through hole was provided at a position opposite the gas release valve. Specifically, at least a portion of the metal foil facing the gas release valve was cut away to provide a through hole. In addition, for examples in Table 1 marked with "cooling plate," a cooling plate was also prepared. Next, the electrode body was covered with the prepared insulating film. At this time, the side of the first metal layer faced the electrode body, and the side of the second metal layer faced the battery case. The electrode body covered with the insulating film was then placed in a battery case, and an electrolyte was further injected into the battery case to produce a rectangular secondary battery prototype.

[0060] <Evaluation of secondary batteries> The prototype secondary battery was placed in a discharged state and sandwiched between 3 cm thick aluminum metal blocks on both long sides with heat insulating material and elastic material interposed between them, and then restrained under a constant pressure of 0.1 to 1 MPa. A hole with a diameter of several mm was drilled in the center of the metal block (the center of gravity (center) of the long sides of the secondary battery), allowing a nail to be inserted. The diameter of this hole was approximately +1 to 2 mm compared to the nail diameter. For example, if the nail diameter was 3 mm, the hole diameter would be approximately 3.1 to 3.2 mm. Next, the secondary battery sandwiched between the metal blocks was charged to full charge (SOC 100%). A nail penetration test was then conducted using the following procedure.

[0061] In the nail penetration test, a specified nail was inserted through a hole in the center of a metal block, forcing the secondary battery to short-circuit and raise the temperature of the secondary battery. The test temperature was room temperature (approximately 25°C). The nail used was a round nail manufactured by Daido Hunt Co., Ltd., size N65 (φ3 mm / no specified angle for the shape). The nail penetration speed was 1 mm / s, and the test was stopped when the secondary battery entered a thermal runaway state.

[0062] The morphological changes of the secondary batteries after thermal runaway were evaluated using six ranks from 0 to 5. The morphological changes of the secondary batteries for each rank are as follows. The results are shown in Table 1. Rank 0: The ejection was only from the gas release valve, and there was no change in the battery case. Rank 1: The ejected material was found to have split the gas release valve and its surrounding area, and there was no other change to the battery case. Rank 2: Ejected material was found from the gas release valve and its surrounding area, and from ruptures in up to three other locations, but there was no rupture at either terminal. Rank 3: Ejected material was found from the gas exhaust valve and its surrounding area, and from 4 to 9 other cracks, but there were no cracks in either terminal area. Rank 4: Ejections were found from the gas exhaust valve and its surrounding area, as well as from 10 or more other cracks, and cracks were also found in both terminals. Rank 5: Ejected material was found in the gas release valve and its surrounding area, and in 10 or more other locations. Cracks were also found in both terminals, and the terminal surfaces were separated from the battery case.

[0063] [Table 1]

[0064] As shown in Table 1, Comparative Example 1 is an example using an insulating film made of a polypropylene (PP) film with a thickness of about 0.4 mm. Comparative Example 2 is an example using an insulating film having two metal layers made of aluminum (Al) with a thickness of 0.2 mm. Comparative Example 3 is an example using an insulating film having a first metal layer made of aluminum (Al) with a thickness of 0.2 mm and a second metal layer made of an alloy made of duralumin (A2017) with a linear expansion coefficient smaller than that of the first metal. In all of Comparative Examples 1 to 3, the secondary batteries showed the greatest change in shape after thermal runaway, exhibiting a state of rank 5.

[0065] On the other hand, Example 1 is an example using an insulating film having a first metal layer made of an alloy of duralumin (A2017) with a thickness of 0.2 mm and a second metal layer made of aluminum (Al) with a linear expansion coefficient larger than that of the first metal. In Example 1, the secondary battery showed relatively less change in shape after thermal runaway compared to Comparative Examples 1 to 3, and exhibited a condition of Rank 4. While not intended to be particularly restrictive, it is believed that the reason for this is that, because the linear expansion coefficient of the second metal is larger than that of the first metal (alloy), when ejected material generated from the electrode body inside the battery hits the first metal layer, the second metal layer expands more than the first metal layer. This expansion also transfers heat, allowing the heat to be more widely dispersed. As a result, heat concentration on the battery case in contact with that area is suppressed, making the battery case less likely to develop a hole.

[0066] Example 2 is an example using an insulating film having a first metal layer made of copper (Cu) with a thickness of 0.2 mm and a second metal layer made of an alloy of brass (Cu 67%, Zn 33%), which has a higher linear expansion coefficient than the first metal. In Example 1, the change in shape of the secondary battery after thermal runaway was more suppressed than in Comparative Examples 1 to 3 and Example 1, and the battery exhibited a condition of Rank 3. Although no particular restriction is intended, this is thought to be because the melting point of the first metal was higher than in Example 1. In other words, if the melting point of the first metal is high, the time available for heat diffusion before melting is longer, which is thought to have effectively reduced the amount of heat concentrated in the battery case.

[0067] Example 3 is an example using an insulating film having a first metal layer made of beryllium (Be) with a thickness of 0.2 mm and a second metal layer made of copper (Cu) with a linear expansion coefficient greater than that of the first metal. In Example 3, the change in the shape of the secondary battery after thermal runaway was further suppressed compared to Comparative Examples 1 to 3 and Examples 1 and 2, and the battery exhibited a condition of Rank 2. While not intended to be particularly restrictive, this is thought to be due to the fact that the melting point of the first metal was higher than that of Example 1, and the difference in the linear expansion coefficient between the first metal and the second metal was greater. In other words, when the difference in the linear expansion coefficient between the first metal and the second metal was greater, the thermal diffusion effect of the second metal was greater, which is thought to have further suppressed heat concentration in the battery case.

[0068] Examples 4 to 12 are examples in which the type of the first metal and / or the second metal was varied. The results of Examples 4 to 12 show that a higher melting point of the first metal and a larger difference in the linear expansion coefficient between the first metal and the second metal tend to suppress morphological changes in the secondary battery after thermal runaway, resulting in better results (a tendency to improve the rank).

[0069] Examples 13 to 17 are examples in which the thicknesses of the first metal layer and the second metal layer were different. When the thickness of each metal layer was thinner than 0.05 mm, the film thickness uniformity was poor, making production difficult. On the other hand, when the thickness of each metal layer was thicker than 1.5 mm, the total amount of electrode bodies placed in the battery case was reduced significantly, leading to a decrease in battery capacity. Therefore, the thicknesses of the first metal layer and the second metal layer are preferably in the range of 0.05 to 1.5 mm. The results of Examples 13 to 17 showed that, within this range, thicker thicknesses suppressed morphological changes in the secondary battery after thermal runaway, resulting in better results (improved ranking).

[0070] Example 18 is the same as Example 9, except that a through-hole was provided in the insulating film at a position opposite the gas release valve. In both Examples 9 and 18, it was found that the morphological change of the secondary battery after thermal runaway was suppressed to a high level, resulting in good results (rank 1).

[0071] Example 20 is the same as Example 19, except that a cooling plate was provided between the bottom surface of the battery case and the electrode body. Comparing Examples 19 and 20, it was found that placing a cooling plate on the bottom surface to improve heat dissipation suppressed the morphological change of the secondary battery after thermal runaway, resulting in better results (improving the rank from 1 to 0).

[0072] The embodiments of the technology disclosed herein have been described above. However, the above description is merely an example and does not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified in the above description.

[0073] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A secondary battery comprising a battery case, an electrode assembly housed in the battery case, and an insulating film disposed between the battery case and the electrode assembly, wherein the insulating film includes a first metal layer made of a first metal, and a second metal layer made of a second metal that is disposed closer to the battery case than the first metal layer and has a linear expansion coefficient greater than that of the first metal, and at least a surface facing the battery case and a surface facing the electrode assembly are covered with an insulating material. Item 2: The secondary battery according to item 1, wherein the battery case is made of metal, and the melting point of the first metal is higher than the melting point of the metal that constitutes the battery case. Item 3: The secondary battery according to Item 1 or 2, wherein the melting point of the first metal is 1250° C. or higher. Item 4: The secondary battery according to any one of Items 1 to 3, wherein the melting point of the first metal is 1400° C. or higher. Item 5: Linear expansion of the first metal and the second metal coefficient The difference is 5 ×10 -6 5. The secondary battery according to any one of items 1 to 4, wherein the .lambda. / K or more. Item 6: The secondary battery according to any one of Items 1 to 5, wherein the first metal layer has a thickness of 0.05 mm or more and 1.5 mm or less. Item 7: The secondary battery according to any one of Items 1 to 6, wherein the second metal layer has a thickness of 0.05 mm or more and 1.5 mm or less. Item 8: The secondary battery according to any one of items 1 to 7, wherein the battery case has a gas release valve, and the insulating film has a through-hole at a position facing the gas release valve. Item 9: The secondary battery according to item 8, wherein the battery case comprises a case body having a bottom, a side, and an opening, and a sealing plate that seals the opening, and the gas release valve is provided on the bottom. Item 10: The secondary battery according to item 9, further comprising a gap forming portion disposed between the bottom surface and the electrode body, the surface of which facing the electrode body has an uneven shape. [Explanation of symbols]

[0074] 10 Battery case 12 Case body 12a Bottom 13 Gas exhaust valve 14 Sealing plate 20 Electrode body 50 insulating film 51 1st metal layer 52 Second metal layer 58 Base material part 70 Cooling plate (gap forming part) 100 Secondary battery

Claims

1. A secondary battery comprising: a battery case; an electrode assembly housed in the battery case; and an insulating film disposed between the battery case and the electrode assembly, the insulating film includes a first metal layer made of a first metal, and a second metal layer arranged closer to the battery case than the first metal layer and made of a second metal having a linear expansion coefficient larger than that of the first metal, and at least a surface facing the battery case and a surface facing the electrode body are covered with an insulating material; The melting point of the first metal is 1250°C or higher. Secondary battery.

2. the battery case is made of metal, The melting point of the first metal is higher than the melting point of the metal constituting the battery case. The secondary battery according to claim 1 .

3. The melting point of the first metal is 1400°C or higher. The secondary battery according to claim 1 or 2.

4. The difference in linear expansion coefficient between the first metal and the second metal is 5×10 −6 / K or more. The secondary battery according to claim 1 or 2.

5. The thickness of the first metal layer is 0.05 mm or more and 1.5 mm or less. The secondary battery according to claim 1 or 2.

6. The thickness of the second metal layer is 0.05 mm or more and 1.5 mm or less. The secondary battery according to claim 1 or 2.

7. A secondary battery comprising: a battery case; an electrode assembly housed in the battery case; and an insulating film disposed between the battery case and the electrode assembly, the insulating film includes a first metal layer made of a first metal, and a second metal layer arranged closer to the battery case than the first metal layer and made of a second metal having a linear expansion coefficient larger than that of the first metal, and at least a surface facing the battery case and a surface facing the electrode body are covered with an insulating material; the battery case has a gas release valve; the insulating film has a through-hole at a position facing the gas exhaust valve; Secondary battery.

8. the battery case includes a case body having a bottom surface, a side surface, and an opening, and a sealing plate that seals the opening; The gas exhaust valve is provided on the bottom surface. The secondary battery according to claim 7 .

9. The electrode assembly further includes a gap forming portion disposed between the bottom surface and the electrode assembly, the gap forming portion having an uneven surface facing the electrode assembly. The secondary battery according to claim 8.

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