Secondary battery

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 relating 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] JP 2022-148731 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the inventor's study, 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 the like. This makes it easier for heat inside the battery to be transferred to the battery case in the melted part of the insulating film, which may cause localized heat concentration. As a result, there is a risk of a hole being formed in the battery case. In addition, the contents of the secondary battery (e.g., fragments of the active material layer, etc.) may be discharged to the outside from the holed part and scattered around.

[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 holes are less likely to form in the battery case. [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 larger 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, since the linear expansion coefficient of the second metal layer is relatively large, 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 causes the heat to move, allowing the heat to be diffused over a wide area. As a result, localized heat concentration on the battery case is suppressed, and holes in the battery case can be prevented. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view illustrating a secondary battery according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of the secondary battery of FIG. 1 turned upside down. [Diagram 3] FIG. 3 is a vertical sectional view that typically illustrates the internal structure of the secondary battery of FIG. [Figure 4] FIG. 4 is a perspective view that shows a schematic view of an electrode body attached to a sealing plate. [Diagram 5] FIG. 5 is a cross-sectional view that illustrates a schematic 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 illustrating a cooling plate according to an embodiment. [Figure 8] FIG. 8 is a perspective view illustrating a schematic example of an arrangement of the cooling plates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, some embodiments of the technology disclosed herein will be described in detail with reference to the drawings. Note that matters other than those specifically mentioned in this specification and 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 the conventional technology in the field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the field. In addition, in the following drawings, the same reference numerals are used to denote members and parts that perform the same function.

[0010] In this specification, the term "secondary battery" refers to a general electricity storage device that can repeatedly be 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 the meaning of "greater than A" and "smaller than B" as well as the meaning of "A to B" and "B to A".

[0011] FIG. 1 is a perspective view of a secondary battery 100 according to an 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 determined for the convenience of description 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 similar to those of a conventional battery.

[0013] The battery case 10 is a housing that contains the electrode body 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 (square) outer shape. The battery case 10 is preferably square. 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 here 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 is in the shape of a square tube, and as shown in Fig. 1, includes a substantially rectangular bottom surface 12a, a pair of long side surfaces 12b extending from the long sides of the bottom surface 12a and facing each other, 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 (for example, welding) the seams. Here, the 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 exhaust valve 13 is configured to break when the pressure inside the battery case 10 reaches or exceeds a predetermined value, thereby discharging the gas inside the battery case 10 to the outside. In this embodiment, the number of gas exhaust valves 13 is one, but it may be two or more. In this embodiment, the gas exhaust valve 13 is provided on the bottom surface 12a, but in other embodiments, the gas exhaust valve 13 may be provided on a surface other than the bottom surface 12a, for example, on the long side surface 12b, the top surface 12c, the sealing plate 14, etc. In addition, the area of ​​the gas exhaust valve 13 is arbitrary.

[0017] In this embodiment, the gas release valve 13 is a cross-shaped cutout. 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 cutout (vertical or horizontal lines only), or may be a conventionally known elliptical valve (with a cutout therein) or circular valve (with a cutout therein). The dimensions (length, depth) of the cutout are arbitrary and may be appropriately determined taking into consideration, for example, the pressure resistance of the battery case 10, etc.

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

[0019] The positive electrode terminal 30 and the negative electrode terminal 40 are fixed to the battery case 10. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are 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 arranged on one side of the long side direction Y (the right side in FIG. 1 and FIG. 2). The negative electrode terminal 40 is attached to the sealing plate 14 arranged on the other side of the long side direction Y (the left side in FIG. 1 and FIG. 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 this embodiment, the positive electrode terminal 30 and the negative electrode terminal 40 are provided on a surface different from the gas exhaust 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 exhaust 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 shifted from the center of the sealing plate 14, for example, in the short side direction X. In addition, 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 shifted to one side in the short side direction X, and the other may be shifted to the other side in the short side direction X.

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

[0022] As shown in Fig. 3, the positive electrode terminal 30 is electrically connected to the positive electrode 23 of the electrode body 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 body 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 accommodated 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 arranged inside the battery case 10 while being covered with an insulating film 50 described below. In this embodiment, a plurality of electrode bodies 20 (two in Fig. 4) are accommodated inside one battery case 10. However, the number of electrode bodies 20 accommodated inside one battery case 10 is not particularly limited, and in other embodiments, it may be three or more, or may be one.

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

[0025] 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. The electrode body 20 is housed inside the battery case 10 with the winding axis oriented along the long side direction Y. The electrode body 20 is 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 be housed inside the battery case 10 with the winding axis oriented along the vertical direction Z, for example. The electrode body 20 may be a so-called vertically wound type. Each member (positive electrode, negative electrode, separator, etc.) constituting the electrode body 20 may be the same as that of a general secondary battery and is not particularly limited.

[0026] The positive electrode 23 typically includes a positive electrode current collector and a positive electrode active material layer fixed on at least one surface of the positive electrode current collector. The positive electrode current collector is in the form of a strip. The positive electrode current collector is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. 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 shape along the longitudinal direction of the strip-shaped positive electrode current collector. The positive electrode active material layer has 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, and examples thereof include lithium transition metal composite oxides such as lithium cobalt oxide, lithium manganate, 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, and includes a lithium nickel composite oxide in which the Ni content in the composite oxide is in the range of 70 to 100 mol% with respect to the total number of moles of the constituent elements in the composite oxide excluding Li and oxygen. The positive electrode active material also includes those in which a part of Ni, Co, and Mn is replaced with Al, Ti, Zr, P, B, Si, Nb, C, etc., and 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 on at least one surface of the negative electrode current collector. The negative electrode current collector is in the form of a strip. The negative electrode current collector is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. 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 has 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, 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. As the separator, for example, a porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) is suitable. A heat resistance layer (HRL) containing an inorganic filler may be provided on the surface of the separator. As the inorganic filler, for example, alumina, boehmite, aluminum hydroxide, titania, etc. may be used.

[0031] The electrolyte is accommodated in the battery case 10 together with the electrode body 20. The electrolyte may be the same as that in a general secondary battery, and is not particularly limited. The electrolyte is typically a non-aqueous liquid electrolyte (nonaqueous electrolyte) 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 the 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) called LiFSI, or a mixture thereof. The concentration of the supporting salt is preferably 0.6 to 1.8 mol per 1 L of the non-aqueous solvent.

[0032] The insulating film 50 is housed inside the battery case 10 together with the electrode body 20. The insulating film 50 is disposed between the battery case 10 and the electrode body 20. As shown in FIG. 4, the insulating film 50 covers the periphery of the electrode body 20. In particular, it is preferable that the insulating film 50 covers at least the curved portion facing the bottom surface 12a of the electrode body 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-like or bag-like shape.

[0033] 5 is a cross-sectional view showing a configuration of an insulating film 50 according to an 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 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 is a surface that faces the electrode body 20, and the second surface 50b is a surface that 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 body 20 are covered with an insulating material. More 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 ends of the insulating film 50 in the width direction W perpendicular to the stacking direction T are also covered with the substrate 58. However, in other embodiments, for example, in a portion where the insulating film 50 does not contact the battery case 10 or the electrode body 20, the first metal layer 51 and / or the second metal layer 52 may be exposed at the ends in the width direction W.

[0035] 5, the first metal layer 51 and the second metal layer 52 are in contact (direct contact) in the stacking direction T. However, in other embodiments, a base material 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 base material 58, an adhesive layer or the like different from the base material 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 effect of the technology disclosed herein can be exerted at 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 kinds 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 (eg, 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 exhibited 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, and in one example, 2000°C or lower. Specific examples of the first metal include, for example, copper, beryllium, nickel, iron, titanium, tungsten, stainless steel, carbon steel, nickel steel, duralumin, etc., and titanium is 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 (length in the stacking direction T) T2 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 effect of the technology disclosed herein can be exhibited at 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 larger 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 larger 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, 10×10 -6 / K or more is preferable, for example, 14 to 25 × 10 -6 / K. In addition, 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, 6×10 -6 / K or more is more preferable, and 7×10 -6 / K or more is particularly preferable. This allows the effects of the technology 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, carbon steel, etc., and among these, copper is preferable.

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

[0043] The insulating film 50 preferably has a through hole H (see FIG. 6) at a position facing the gas exhaust 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 exhaust valve 13. Furthermore, the size of the through hole H is arbitrary. When the gas exhaust valve 13 is an elliptical or circular valve, the size of the through hole H is preferably about ±10 mm from the outer edge of the gas exhaust valve 13. Furthermore, when the gas exhaust valve 13 is a notch as in this embodiment, it is preferable that the insulating film 50 covers a part of the notch at the portion facing the gas exhaust valve 13.

[0044] By having the insulating film 50, the secondary battery 100 is less likely to cause localized heat concentration on the battery case 10 even if an unsafe event occurs in the battery case 10 due to, for example, overcharging. In detail, since the linear expansion coefficient of the second metal constituting the second metal layer 52 is larger than that of the first metal constituting the first metal layer 51, when fragments of the active material layer generated from the electrode body 20 in 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, so that the heat can be diffused to the surroundings. As a result, localized heat concentration on the battery case 10 is suppressed, and holes in the battery case 10 can be suppressed.

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

[0046] In the preparation step S1, for example, a metal plate (sheet-shaped, thickness 0.5 to 3 mm) made of a first metal (including alloy) and a metal plate (sheet-shaped, thickness 0.5 to 3 mm) made of a second metal are prepared, and rolled into foils of a predetermined thickness by metal roll press processing. Next, the two obtained metal foils (including alloy foils) are cut into predetermined sizes. The cutting method is not particularly limited, and for example, cutting may be performed with a metal blade or a laser. It is preferable to remove burrs from the cut ends. This makes it difficult for the metal ends to penetrate the base material 58 in the insulating film 50.

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

[0048] Alternatively, as a second method, a film can be produced by first stacking two sheets of metal foil of a predetermined size, and then pressing a plastic film onto the non-facing surfaces of each foil in the same manner as above. In this case, the plastic film should be larger than the metal foil so as to cover the two sheets of metal foil. After that, unnecessary plastic film portions are removed by cutting. In this case, care should be taken not to expose the edge faces of the metal foil on the cut edge faces. The cutting method is not particularly limited, and may be performed using, for example, a metal blade or a laser.

[0049] Furthermore, as a third method, without using adhesive, a plastic film such as olefin resin or various engineering plastics (PET, PEN, PI, PPE, fluororesin film, etc.) is placed on a metal foil of a given size, and then heated at a high temperature of up to about 400°C to melt the plastic and press it together to produce an integrated product of the 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 product is heated and melted again to produce a film.

[0050] Alternatively, as a fourth method, it is possible to first stack two metal foils cut to different sizes, place a plastic film on each of the non-facing sides of each foil, and heat them at a high temperature of up to about 400°C to melt the plastic and press them together to produce a film. In this case, too, the plastic film is made large enough to cover the entire metal foil. Then, as in the second method, unnecessary plastic film portions are removed by cutting.

[0051] Next, in the processing step S2, for example, the film obtained above is cut into a shape and size according to the outer shape of the electrode body 20. FIG. 6 is a development 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 body 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 body 20 and a pair of long side surfaces 12b of the battery case 10. The cutout portions N1 and N2 correspond to the connection portion between the electrode body 20 and the positive electrode current collector 32 (see FIG. 3) and the connection portion between the electrode body 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 part of it faces the gas release valve 13. The through hole H can be formed by removing the insulating film 50 or the plastic film in the portion facing the gas release valve 13 by cutting. Additionally, the positions of the dashed lines may be provided with creases (for example, grooves or perforations) for folding molding. By folding a film of this shape along the dotted lines, insulating film 50 can be produced.

[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 body 20 so as to be in contact with a portion of the battery case 10 (e.g., the bottom surface 12a). 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) mainly made of aluminum or a metal material mainly 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 in the battery case 10 can be efficiently dissipated, and the safety of the secondary battery 100 can be improved. The cooling plate 70 is an example of a "gap forming portion".

[0053] 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 here) protrusions 72. The base portion 71 is rectangular. The protrusions 72 are provided on the surface facing the electrode body 20. The surface of the cooling plate 70 facing the electrode body 20 has an uneven shape. The protrusions 72 here are prismatic along the long side. However, the number and shape (height, length, etc.) of the protrusions 72 are not particularly limited and are arbitrary.

[0054] Fig. 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 body 20, that is, between the bottom surface 12a and the electrode body 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 body 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 so as to sandwich the gas exhaust valve 13. However, the number of cooling plates 70 arranged inside one battery case 10 is not particularly limited, and in other embodiments, it may be three or more, or it may be one. For example, when two gas exhaust valves 13 are provided on the bottom surface 12a, three cooling plates 70 may be arranged in the long side direction Y so as to sandwich the two gas exhaust valves 13. Alternatively, when one or two or more gas exhaust valves 13 are provided on a portion other than the bottom surface 12a of the battery case 10, for example, on the long side surface 12b, the top surface 12c, or the sealing plate 14, one large cooling plate 70 may be arranged on the bottom surface 12a.

[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, a truck, etc. The type of vehicle is not particularly limited, but examples thereof include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), a battery electric vehicle (BEV), etc.

[0057] Several examples of the present invention will be described below, 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 0.5-3 mm) made of the first metal and a metal plate (sheet-shaped, thickness 0.5-3 mm) made of the second metal shown in Table 1 were prepared, and rolled into foils with thicknesses shown in Table 1 by metal roll press processing. Next, the two metal foils were cut to a predetermined size, and then they were stacked, and a plastic film (PP) was placed on the non-facing side of each foil. The plastic film was sized to cover the entire metal foil (including the end). Next, this laminate was heated at a high temperature of up to about 400°C to melt the plastic, and further 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 shown in Table 1. The difference in linear expansion coefficient was calculated by (linear expansion coefficient of the second metal) - (linear expansion coefficient of the first metal). In Comparative Example 1, only a PP film was used.

[0059] Next, a rectangular parallelepiped battery case having a gas exhaust valve was prepared. The position and number of the gas exhaust valves are as shown in Table 1. Next, the film obtained above was cut to a predetermined size and folded to prepare an insulating film. At this time, for the examples in which a through hole is "present" in Table 1, a through hole was provided at a position facing the gas exhaust valve. Specifically, at least a part of the metal foil in the portion facing the gas exhaust valve was removed by cutting to provide a through hole. In addition, for the examples in which a cooling plate is "present" in Table 1, 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 was opposed to the electrode body, and the side of the second metal layer was opposed to the battery case. Then, the electrode body covered with the insulating film was housed in a battery case, and an electrolyte was further injected into the battery case to produce a rectangular secondary battery.

[0060] <Evaluation of secondary batteries> The prototype secondary battery was placed in a discharged state and sandwiched between 3 cm thick aluminum metal blocks from both long sides via heat insulating material and elastic body, and was constrained at a constant pressure of 0.1 to 1 MPa. A hole of several mm in diameter was drilled in the center of the metal block (the position of the center of gravity (center) of the long sides of the secondary battery) so that a nail could be inserted. The hole had a diameter of about +1 to 2 mm compared to the nail diameter. For example, if the nail diameter is 3 mm, the hole diameter is about 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 performed according to the following procedure.

[0061] In the nail penetration test, a specified nail was inserted through a hole in the center of a metal block, forcibly shorting the secondary battery and raising the temperature of the secondary battery. The test temperature was room temperature (approximately 25°C). The type of nail used was a round nail size N65 (φ3mm / no shape or angle specified) manufactured by Daido Hunt Co., Ltd. The nail penetration speed was 1mm / s, and was stopped when the secondary battery entered a thermal runaway state.

[0062] The morphological changes of the secondary batteries after the thermal runaway were evaluated using six ranks from rank 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 occurred only from the gas exhaust valve, and there was no change in the battery case. Rank 1: The ejection occurred from the gas exhaust valve and its surrounding area, and there was no other change to the battery case. Rank 2: Ejected material was from the gas exhaust valve and its surrounding area, and up to three other locations were ruptured, but there was no rupture at either terminal. Rank 3: Ejected material was from the gas exhaust valve and its surrounding area, and from 4 to 9 other ruptures, but no ruptures at either terminal. Rank 4: Ejections were from the gas exhaust valve and its surroundings, and from 10 or more other ruptures. There were also ruptures in both terminals. Rank 5: The ejection was from the gas release valve and its surrounding area, and from 10 or more other cracks. The cracks were also on 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 smaller linear expansion coefficient than the first metal. All of Comparative Examples 1 to 3 showed the largest change in shape of the secondary battery after thermal runaway, and were in 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) having a thickness of 0.2 mm and a second metal layer made of aluminum (Al) having a linear expansion coefficient larger than that of the first metal. In Example 1, the change in shape of the secondary battery after thermal runaway was relatively suppressed compared to Comparative Examples 1 to 3, and the battery was ranked as rank 4. Although it is not intended to be interpreted in a particularly restrictive manner, the reason for this is that since the linear expansion coefficient of the second metal is larger than that of the first metal (alloy), when an ejection generated from the electrode body inside the battery hits the first metal layer, the second metal layer expands more than the first metal layer, and heat also moves with the expansion, allowing the heat to be diffused to the surroundings more, and as a result, heat concentration on the battery case in contact with that part is suppressed, and the battery case is less likely to be perforated.

[0066] Example 2 is an example using an insulating film having a first metal layer made of copper (Cu) having a thickness of 0.2 mm and a second metal layer made of an alloy made of brass (Cu 67%, Zn 33%) having a larger 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 was ranked as rank 3. Although it is not intended to be particularly limited, this is thought to be because the melting point of the first metal is higher than that of Example 1. In other words, if the melting point of the first metal is high, the time that heat can be diffused before melting is longer, and it is thought that the amount of heat concentrated in the battery case can be effectively reduced.

[0067] Example 3 is an example using an insulating film having a first metal layer made of beryllium (Be) having a thickness of 0.2 mm and a second metal layer made of copper (Cu) having a linear expansion coefficient larger than that of the first metal. In Example 3, the change in 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 was ranked as rank 2. Although it is not intended to be particularly limited, the reason for this is thought to be that the melting point of the first metal is higher than that of Example 1, and the difference in the linear expansion coefficient between the first metal and the second metal is large. In other words, when the difference in the linear expansion coefficient between the first metal and the second metal is large, the thermal diffusion effect of the second metal becomes larger, and therefore the concentration of heat on the battery case is more suppressed.

[0068] Examples 4 to 12 are examples in which the type of the first metal and / or the second metal is different. From the results of Examples 4 to 12, it was found 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 and tend to produce better results (tend 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 are different. When the thickness of each metal layer is thinner than 0.05 mm, the uniformity of the film thickness is poor, and fabrication is difficult. On the other hand, when the thickness of each metal layer is thicker than 1.5 mm, the total amount of the electrode body placed in the battery case is greatly reduced, leading to a decrease in the battery capacity. Therefore, the thickness of the first metal layer and the second metal layer is preferably in the range of 0.05 to 1.5 mm, and from the results of Examples 13 to 17, it was found that within this range, a thicker thickness suppresses the change in the shape of the secondary battery after thermal runaway, resulting in better results (improved rank).

[0070] Example 18 is similar to Example 9, except that a through hole was provided in the insulating film at a position opposite the gas exhaust 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 similar to 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 laying a cooling plate on the bottom surface to improve heat dissipation suppresses morphological changes in 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 changes to 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 larger linear expansion coefficient than 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 a metal constituting the battery case. Item 3: The secondary battery according to item 1 or 2, wherein the first metal has a melting point of 1250° C. or higher. Item 4: The secondary battery according to any one of Items 1 to 3, wherein the first metal has a melting point of 1400° C. or higher. Item 5: The secondary battery according to any one of Items 1 to 4, wherein a difference in linear expansion coefficient between the first metal and the second metal is 5 / 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 surface, a side surface, and an opening, and a sealing plate that seals the opening, and the gas release valve is provided on the bottom surface. 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 gap forming portion having an uneven surface on the side facing the electrode body. [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. 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 1250° C. or higher. The secondary battery according to claim 1 .

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

5. A difference in linear expansion coefficient between the first metal and the second metal is 5 / K or more. The secondary battery according to claim 1 .

6. 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 .

7. 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 .

8. the battery case has a gas release valve; the insulating film has a through hole at a position facing the gas exhaust valve; The secondary battery according to claim 1 .

9. 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 8.

10. 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 9.

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