Resin film for terminal

Abstract

To provide a resin film for a terminal which is excellent in openability under high temperature environment, and is excellent in adhesion between an exterior material and a metal terminal under room temperature environment, and can enhance safety of a power storage device.SOLUTION: A resin film for a terminal for covering the outer peripheral surface of a part of a metal terminal constituting a power storage device includes a resin layer containing (A) polyethylene, and (B) a compatibilizer having a part compatible with (A) the polyethylene and a part compatible with polypropylene.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a resin film for terminals and a power storage device using the same.

Background Art

[0002] In recent years, there has been an increasing demand for miniaturization of portable devices and effective utilization of natural power generation energy. Research and development of lithium-ion secondary batteries (a type of power storage device) that can obtain a higher voltage and have a high energy density have been carried out.

[0003] As a packaging material used for the above lithium-ion secondary battery, a metal can has been conventionally used in many cases. However, due to the low manufacturing cost, a packaging material in which a laminate of a metal layer (for example, aluminum foil) and a resin film is formed into a bag shape has been increasingly used in response to requirements such as thinning and diversification of products to be applied.

[0004] A laminated lithium-ion secondary battery in which a battery body is housed and sealed inside the above packaging material is provided with a current extraction terminal called a tab. The tab has a metal terminal (sometimes called a "tab lead") connected to the negative electrode or the positive electrode of the battery body and extending outside the packaging material (outer packaging material), and a resin film for terminals (sometimes called a "tab sealant") that covers a part of the outer peripheral surface of the metal terminal, respectively (see, for example, Patent Documents 1 to 3). Usually, the resin film for terminals is fused to the metal terminal.

[0005] Incidentally, high safety is required for power storage devices such as the above-mentioned lithium-ion secondary batteries. Generally, organic solvents are used as electrolytes in power storage devices. However, when the power storage device is exposed to high temperatures, the organic solvent may volatilize or decompose due to the temperature rise, generating flammable gases, and the pressure inside the packaging material may increase. If this temperature rise and the pressure increase inside the packaging material progress, it may cause excessive expansion of the packaging material, increasing the risk of problems such as rupture and explosion. Therefore, in order to prevent the occurrence of the above problems, power storage devices are provided with safety measures that can release gas to the outside when the pressure inside the packaging material rises excessively.

[0006] For example, Patent Document 4 proposes a battery case having an explosion-proof structure provided with a half-cut portion by laser light irradiation. Also, for example, Patent Document 5 proposes a battery packaging material that can be opened when a set temperature is reached by defining the melting point of the sealant layer in the packaging material, and can suppress excessive expansion and the runaway of the battery reaction.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the battery case described in Patent Document 4 has a problem of poor manufacturing efficiency because facilities and processes for forming an explosion-proof structure by laser light irradiation are required. Further, by providing a heart cut portion, there is also a problem that the barrier property and the impact resistance are likely to decrease. On the other hand, the battery packaging material described in Patent Document 5 has a problem that since the entire sealant layer can be cracked at a set temperature, the cracking range is wide and there is a risk that the organic solvent leaks out. Further, since the cracking range is wide, there is a problem that it is difficult to confirm whether the cracking has actually occurred.

[0009] The present disclosure has been made in view of the problems of the above prior art, and is excellent in peelability under a high temperature environment and adhesion between an exterior material and a metal terminal under a room temperature environment, and can improve the safety of an electric storage device. An object is to provide a resin film for a terminal and an electric storage device using the same.

Means for Solving the Problems

[0010] In order to achieve the above object, the present disclosure is a resin film for a terminal for covering a part of the outer peripheral surface of a metal terminal constituting an electric storage device, and includes (A) polyethylene and (B) a compatibilizer having a part compatible with the (A) polyethylene and a part compatible with polypropylene. A resin film for a terminal is provided.

[0011] Generally, as the resin film for terminals, a polypropylene (PP) film is widely used. However, since the resin film for terminals made of PP has a high melting point, it is difficult to open at high temperatures and it is difficult to function as a safety valve for preventing excessive expansion of the power storage device and runaway of the battery reaction in a high-temperature environment. On the other hand, polyethylene (PE) has a low melting point, so it has excellent openability in a high-temperature environment and is effective as a safety valve. However, it is difficult to sufficiently obtain the adhesion with the exterior material for the resin film for terminals made of PE, and it is difficult to satisfy the basic characteristics as the resin film for terminals. This is because a PP sealant layer is generally used as the sealant layer of the exterior material. Therefore, the inventors of the present invention studied a resin film for terminals using PE and PP in combination. However, the adhesion with the exterior material was still insufficient. The inventors presume that this is because PP and PE form a sea-island interface and are easily cracked between the interfaces, so sufficient strength cannot be obtained.

[0012] As a result of further intensive studies by the inventors, by including (A) polyethylene and (B) a compatibilizer having a site compatible with the above (A) polyethylene and a site compatible with polypropylene in the resin layer constituting the resin film for terminals, it was found that it is possible to achieve both the openability in a high-temperature environment and the adhesion with the exterior material and metal terminals in a room-temperature environment. Since the compatibilizer (B) has a site compatible with the polyethylene (A), the adhesion strength between the compatibilizer (B) and the polyethylene (A) can be increased, and since it has a site compatible with polypropylene, the adhesion strength between the resin film for terminals and the sealant layer of the exterior material can be increased through the compatibilizer (B). Therefore, the resin film for terminals can obtain excellent openability in a high-temperature environment and excellent adhesion with metal terminals in a room-temperature environment because the resin layer contains the polyethylene (A), and at the same time, since the resin layer further contains the compatibilizer (B), excellent adhesion with the exterior material in a room-temperature environment can be obtained without impairing the effect of the above (A) polyethylene, and the safety of the power storage device can be improved.

[0013] In the resin film for terminals, the (B) compatibilizer may be a block copolymer or a graft copolymer. By the (B) compatibilizer being a block copolymer or a graft copolymer, the compatibility with (A) polyethylene and the adhesion to the sealant layer of the exterior material can be further improved.

[0014] In the resin film for terminals, the (B) compatibilizer may have an amorphous unit. By the (B) compatibilizer having an amorphous unit, the unsealing property under a high-temperature environment can be further improved.

[0015] In the resin film for terminals, the mass ratio ((A) / (B)) of the (A) polyethylene and the (B) compatibilizer contained in the resin layer may be 0.15 to 30. If the ratio of the (B) compatibilizer to the (A) polyethylene is too small, the adhesion to the sealant layer of the exterior material tends to decrease, and if it is too large, the adhesion to the metal terminal tends to decrease. By setting the mass ratio ((A) / (B)) within the above range, the adhesion to the sealant layer of the exterior material and the adhesion to the metal terminal can be made compatible at a higher level.

[0016] In the resin film for terminals, the resin layer may further contain (C) polypropylene. By the resin layer further containing (C) polypropylene, the seal strength at a temperature lower than the target unsealing temperature (for example, 130 °C) (for example, 100 °C) can be improved, and the unsealing temperature can be controlled.

[0017] In the resin film for terminals, the resin layer may contain a resin having a polar group. Here, at least one of the (A) polyethylene, (B) compatibilizer, and (C) polypropylene may be a resin having a polar group, or a resin having a polar group different from these may be used. By the resin layer containing a resin having a polar group, the adhesion to the metal terminal can be further improved.

[0018] The resin film for terminals is composed of three or more layers, and the layers disposed on at least both surfaces of the resin film for terminals may be the resin layers. By having resin layers on both surfaces, excellent unsealing property in a high-temperature environment and excellent adhesion to the exterior material and the metal terminals in a room-temperature environment can be obtained. Also, by adopting a multi-layer structure of three or more layers, it becomes possible to dispose an intermediate layer having various functions between the resin layers on both surfaces. For example, by providing an insulating layer as the intermediate layer, the insulation property can be further improved. Further, by disposing the resin layers on both surfaces, the generation of curl of the resin film for terminals can be suppressed.

[0019] The present disclosure also provides a power storage device including a power storage device main body, a metal terminal electrically connected to the power storage device main body, an exterior material that sandwiches the metal terminal and houses the power storage device main body, and the resin film for terminals of the present disclosure disposed between the metal terminal and the exterior material so as to cover a part of the outer peripheral surface of the metal terminal. The exterior material has a sealant layer containing polypropylene on the surface in contact with the resin film for terminals. Such a power storage device is excellent in unsealing property in a high-temperature environment and in adhesion between the exterior material and the metal terminals and the resin film for terminals in a room-temperature environment, and has high safety.

Advantages of the Invention

[0020] According to the present disclosure, there are provided a resin film for terminals excellent in unsealing property in a high-temperature environment and in adhesion to the exterior material and the metal terminals in a room-temperature environment, and capable of enhancing the safety of a power storage device, and a power storage device using the same.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0022] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and duplicate descriptions are omitted. Also, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0023] FIG. 1 is a perspective view showing a schematic configuration of a power storage device according to an embodiment of the present disclosure. In FIG. 1, as an example of the power storage device 10, a lithium-ion secondary battery is illustrated as an example, and the following description will be given. Note that the lithium-ion secondary battery having the configuration shown in FIG. 1 may be referred to as a battery pack or a battery cell.

[0024] The power storage device 10 shown in FIG. 1 is a lithium-ion secondary battery, and includes a power storage device main body 11, an exterior material 13, a pair of metal terminals 14 (tab leads), and a resin film for terminals 16 (tab sealant).

[0025] The power storage device main body 11 is a battery main body that performs charge and discharge. The exterior material 13 covers the surface of the power storage device main body 11 and is arranged so as to be in contact with a part of the resin film for terminals 16.

[0026] FIG. 2 is a cross-sectional view showing an example of a cut surface of the exterior material shown in FIG. 1. In FIG. 2, the same reference numerals are given to the same components as those in the structure shown in FIG. 1.

[0027] Here, with reference to FIG. 2, an example of the configuration of the exterior material 13 will be described. The exterior material 13 has a seven-layer structure in which an inner layer 21, an inner layer side adhesive layer 22, a corrosion prevention treatment layer 23-1, a barrier layer 24 which is a metal layer, a corrosion prevention treatment layer 23-2, an outer layer side adhesive layer 25, and an outer layer 26 are sequentially laminated from the inside in contact with the power storage device main body 11.

[0028] The inner layer 21 is a sealant layer that imparts sealing properties by heat sealing to the exterior material 13, and is a layer that is disposed inside during the assembly of the power storage device 10 and is heat sealed (heat fused). As the base material of the inner layer (sealant layer) 21, for example, a polyolefin resin or an acid-modified polyolefin resin obtained by graft-modifying a polyolefin resin with maleic anhydride or the like can be used. As the above polyolefin resin, for example, low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymer; homo, block, or random polypropylene; propylene-α-olefin copolymer, etc. can be used. Among these, the above polyolefin resin preferably contains polypropylene. These polyolefin resins may be used alone or in combination of two or more.

[0029] Also, the inner layer 21 may be configured using a single-layer film or a multilayer film in which a plurality of layers are laminated according to the required functions. Specifically, for example, in order to impart moisture resistance, a multilayer film in which a resin such as ethylene-cyclic olefin copolymer or polymethylpentene is interposed may be used. Further, the inner layer 21 may contain various additives (for example, flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, tackifiers, etc.).

[0030] The thickness of the inner layer 21 is preferably set, for example, within the range of 10 to 150 μm, more preferably 30 to 80 μm. If the thickness of the inner layer 21 is less than 10 μm, the heat seal adhesion between the exterior materials 13 and the adhesion to the terminal resin film 16 may decrease. Also, if the thickness of the inner layer 21 is more than 150 μm, it becomes a factor for increasing the cost of the exterior material 13, which is not preferable.

[0031] As the inner layer side adhesive layer 22, for example, a known adhesive such as a general dry lamination adhesive or an acid-modified heat-fusible resin can be appropriately selected and used.

[0032] As shown in Fig. 2, it is preferably in terms of performance to form the corrosion prevention treatment layers 23-1 and 23-2 on both sides of the barrier layer 24. However, considering the cost, the corrosion prevention treatment layer 23-1 may be disposed only on the surface of the barrier layer 24 located on the inner layer side adhesive layer 22 side.

[0033] The barrier layer 24 is, for example, a metal layer having conductivity. Examples of the material of the barrier layer 24 include aluminum and stainless steel, etc. Aluminum is preferable from the viewpoints of cost, mass (density), etc.

[0034] As the outer layer side adhesive layer 25, for example, a general polyurethane-based adhesive mainly composed of polyester polyol, polyether polyol, acrylic polyol, etc. can be used.

[0035] As the outer layer 26, for example, a single layer film such as nylon or polyethylene terephthalate (PET), or a multilayer film can be used. Similar to the inner layer 21, the outer layer 26 may contain various additives (for example, flame retardants, slip agents, anti-blocking agents, antioxidants, light stabilizers, tackifiers, etc.). Further, the outer layer 26 may have a protective layer formed, for example, by laminating a resin insoluble in the electrolytic solution or coating a resin component insoluble in the electrolytic solution as a countermeasure against liquid leakage.

[0036] Fig. 3 is a cross-sectional view in the A-A line direction of the resin film for terminals and the metal terminal shown in Fig. 1. In Fig. 3, the same reference numerals are given to the same constituent parts as those of the structure shown in Fig. 1.

[0037] As shown in FIGS. 1 and 3, a pair (two in the case of FIG. 1) of metal terminals 14 has a metal terminal body 14-1 and a corrosion prevention layer 14-2. Among the pair of metal terminal bodies 14-1, one metal terminal body 14-1 is electrically connected to the positive electrode of the power storage device body 11, and the other metal terminal body 14-1 is electrically connected to the negative electrode of the power storage device body 11. The pair of metal terminal bodies 14-1 extends in a direction away from the power storage device body 11, and a part of it is exposed from the exterior material 13. The shape of the pair of metal terminal bodies 14-1 can be, for example, a flat plate shape.

[0038] As the material of the metal terminal body 14-1, a metal can be used. The metal that becomes the material of the metal terminal body 14-1 is preferably determined in consideration of the structure of the power storage device body 11 and the materials of the respective components of the power storage device body 11.

[0039] For example, when the power storage device 10 is a lithium-ion secondary battery, aluminum is used as the current collector for the positive electrode, and copper is used as the current collector for the negative electrode. In this case, as the material of the metal terminal body 14-1 connected to the positive electrode of the power storage device body 11, it is preferable to use aluminum. Also, considering the corrosion resistance to the electrolytic solution, as the material of the metal terminal body 14-1 connected to the positive electrode of the power storage device body 11, for example, it is preferable to use an aluminum material with a purity of 97% or more such as 1N30. Furthermore, when bending the metal terminal body 14-1, it is preferable to use an O material that has been tempered by sufficient annealing for the purpose of adding flexibility. As the material of the metal terminal body 14-1 connected to the negative electrode of the power storage device body 11, it is preferable to use copper with a nickel plating layer formed on the surface or nickel.

[0040] The thickness of the metal terminal body 14-1 depends on the size and capacity of the lithium-ion secondary battery. When the lithium-ion secondary battery is small, the thickness of the metal terminal body 14-1 may be, for example, 50 μm or more. Also, in the case of a large lithium-ion secondary battery for power storage and in-vehicle use, etc., the thickness of the metal terminal body 14-1 can be appropriately set within the range of, for example, 100 to 500 μm.

[0041] The corrosion prevention layer 14-2 is disposed so as to cover the surface of the metal terminal body 14-1. In the case of a lithium-ion secondary battery, the electrolytic solution contains corrosion components such as LiPF6. The corrosion prevention layer 14-2 is a layer for suppressing the corrosion of the metal terminal body 14-1 by the corrosion components such as LiPF6 contained in the electrolytic solution.

[0042] As shown in FIG. 3, the resin film 16 for terminals is disposed so as to cover a part of the outer peripheral surface of the metal terminal 14. In the present embodiment, the resin film 16 for terminals has a configuration in which a first resin layer 31 that contacts the outer peripheral side surface of the metal terminal 14, a second resin layer 32 that contacts the exterior material 13, and an intermediate layer 33 disposed between the first resin layer 31 and the second resin layer 32 are laminated. Note that the resin film 16 for terminals may be composed of one layer or two layers, or may be composed of four or more layers.

[0043] By being disposed so as to cover the outer peripheral surface of the metal terminal 14, the first resin layer 31 has a function of sealing the circumferential direction of the metal terminal 14 and bringing the resin film 16 for terminals into close contact with the metal terminal 14. Further, the second resin layer 32 has a function of sealing the inside of the exterior material 13 by being fused to the exterior material 13.

[0044] In the present embodiment, the first resin layer 31 and the second resin layer 32 contain (A) polyethylene (hereinafter also referred to as “component (A)”) and (B) a compatibilizer having a part compatible with the above (A) polyethylene and a part compatible with polypropylene (hereinafter also referred to as “component (B)”). Further, the first resin layer 31 and the second resin layer 32 may further contain (C) polypropylene (hereinafter also referred to as “component (C)”). Further, the first resin layer 31 and the second resin layer 32 may contain a resin having a polar group. Here, the resin having a polar group may be any of the components (A) to (C), or may be a resin (D) having a polar group (hereinafter also referred to as “component (D)”) that is a component different from the components (A) to (C).

[0045] (A) Examples of the polyethylene include ultra-low density polyethylene (VLDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), etc. Among these, from the viewpoint of further improving the heat sealability and heat seal strength, it is preferable to use LDPE and LLDPE.

[0046] (A) The polyethylene may include modified polyethylene having a polar group. By the polyethylene (A) having a polar group, the adhesion between the first resin layer 31 and the metal terminal 14 can be further improved. Examples of the polar group include a hydroxyl group, a glycidyl group, an amide group, an imino group, an oxazoline group, an acid anhydride group, a carboxyl group, an ester group, etc. From the viewpoint of reactivity, an acid anhydride group (particularly a group derived from maleic anhydride) is preferable as the polar group. The modified polyethylene may be an acid-modified polyethylene obtained by graft-modifying maleic anhydride or the like. Specific product examples of the modified polyethylene include, for example, "Admer" manufactured by Mitsui Chemicals, Inc., "Modic" manufactured by Mitsubishi Chemical Corporation, etc. (A) The polyethylene can be used alone or in combination of two or more.

[0047] (A) The melting point of the polyethylene is preferably 80 to 135 °C, more preferably 100 to 125 °C. By the melting point of the polyethylene (A) being 135 °C or lower, the unsealing property under a high temperature environment can be further improved, and by being 80 °C or higher, it can be prevented from being unsealed during the production of the power storage device.

[0048] In this specification, the melting point of the resin can be determined by measuring with a differential scanning calorimeter (DSC), taking the peak top with the largest heat of fusion as the main peak, and reading the peak temperature.

[0049] In the first resin layer 31 and the second resin layer 32, the content of (A) polyethylene is preferably 5 to 95% by mass, more preferably 10 to 75% by mass, based on the total amount of each layer. When the content of (A) polyethylene is 5% by mass or more, the peelability under high-temperature environments and the adhesion to metal terminals under room-temperature environments tend to be further improved. When the content is 95% by mass or less, the adhesion to the exterior material under room-temperature environments tends to be further improved.

[0050] (B) The compatibilizer has a site compatible with (A) polyethylene and a site compatible with polypropylene, and has a function of improving the adhesion between the second resin layer 32 and the exterior material 13. Further, when the first resin layer 31 and the second resin layer 32 contain (C) polypropylene, (B) the compatibilizer also has a function of improving the adhesion strength at the sea-island interface between (A) polyethylene and (C) polypropylene.

[0051] Examples of (B) the compatibilizer include ethylene-propylene rubber (EPR), ethylene-propylene-diene rubber (EPDM), a block copolymer having a site compatible with (A) polyethylene and a site compatible with polypropylene, and a graft copolymer having a site compatible with (A) polyethylene and a site compatible with polypropylene.

[0052] Examples of the block copolymer include a block copolymer composed of a crystalline polyethylene unit and an ethylene-butylene copolymer unit, a block copolymer composed of a polyethylene unit and an ethylene-1-octene copolymer unit, and a block copolymer composed of a polypropylene unit and a polyethylene unit. Examples of the graft copolymer include a graft copolymer in which a polyethylene unit is grafted onto polypropylene. Each unit constituting the copolymer may be a crystalline unit or an amorphous unit.

[0053] (B) As a compatibilizer, from the viewpoint of compatibility, it is preferable to use a block copolymer or a graft copolymer, and from the viewpoint of peelability, it is preferable to use one having an amorphous unit. (B) The compatibilizer can be used alone or in combination of two or more.

[0054] In the (B) compatibilizer, the content ratio of the part compatible with (A) polyethylene to the part compatible with polypropylene ((mass ratio of the part compatible with (A) polyethylene / the part compatible with polypropylene)) is preferably 1 / 9 to 9 / 1, more preferably 2 / 8 to 8 / 2, and even more preferably 3 / 7 to 7 / 3. When this content ratio is 1 / 9 or more, the adhesion strength between the (B) compatibilizer and (A) polyethylene can be further increased. On the other hand, when this content ratio is 9 / 1 or less, the adhesion strength between the terminal resin film and the sealant layer of the exterior material via the (B) compatibilizer can be further increased.

[0055] In the first resin layer 31 and the second resin layer 32, the mass ratio of (A) polyethylene to (B) compatibilizer ((A) / (B)) is preferably 0.15 to 30, more preferably 0.5 to 10, and even more preferably 1.0 to 5. When this mass ratio ((A) / (B)) is 0.15 or more, the peelability under high-temperature environment and the adhesion to the metal terminal under room-temperature environment tend to be further improved, and when it is 30 or less, the adhesion to the exterior material under room-temperature environment tends to be further improved.

[0056] As (C) polypropylene, homopolypropylene, random polypropylene, block polypropylene, etc. can be used. Among these, from the viewpoints of peelability and impact resistance under high-temperature environment, it is preferable to use random polypropylene having a melting point of 110 to 150°C.

[0057] (C) Polypropylene may contain modified polypropylene having a polar group. By (C) polypropylene having a polar group, the adhesion between the first resin layer 31 and the metal terminal 14 can be further improved. Examples of the polar group include a hydroxyl group, a glycidyl group, an amide group, an imino group, an oxazoline group, an acid anhydride group, a carboxyl group, an ester group, and the like. From the viewpoint of reactivity, an acid anhydride group (particularly a group derived from maleic anhydride) is preferable as the polar group. The modified polypropylene may be an acid-modified polypropylene obtained by graft-modifying maleic anhydride or the like. Specific product examples of the modified polypropylene include, for example, "Admer" manufactured by Mitsui Chemicals, Inc., "Modic" manufactured by Mitsubishi Chemical Corporation, "Toyotack" manufactured by Toyobo Co., Ltd., "Yumex Sansuck" manufactured by Sanyo Chemical Industries, Ltd., and the like. (C) Polypropylene can be used alone or in combination of two or more kinds.

[0058] (C) The melting point of polypropylene is preferably 110 to 165 ° C, more preferably 120 to 150 ° C. By the melting point of (C) polypropylene being 165 ° C or less, a decrease in the sealability under a high-temperature environment can be suppressed, and by being 110 ° C or more, the seal strength at a temperature (for example, 100 ° C) lower than the target opening temperature (for example, 130 ° C) can be further improved, and the opening temperature can be appropriately controlled.

[0059] When the first resin layer 31 and / or the second resin layer 32 contains (C) polypropylene, the content is preferably 5 to 95% by mass, more preferably 30 to 80% by mass, based on the total amount of each layer. When the content of (C) polypropylene is 5% by mass or more, the seal strength at a temperature (for example, 100 ° C) lower than the target opening temperature (for example, 130 ° C) can be further improved, and the opening temperature can be appropriately controlled. On the other hand, when the content of (C) polypropylene is 95% by mass or less, a decrease in the sealability under a high-temperature environment can be suppressed.

[0060] The first resin layer 31 and the second resin layer 32 may contain, in addition to the above components (A) to (C), a resin having a (D) polar group (hereinafter also referred to as "polar resin"). It is effective to add the (D) polar resin when none of the above components (A) to (C) has a polar group. However, it may be further added when one or more of the above components (A) to (C) has a polar group.

[0061] Examples of the polar group contained in the (D) polar resin include a hydroxyl group, a glycidyl group, an amide group, an imino group, an oxazoline group, an acid anhydride group, a carboxyl group, an ester group, etc. From the viewpoint of reactivity, an acid anhydride group (especially a group derived from maleic anhydride) is preferable as the polar group. Further, the (D) polar resin more preferably has a site that is partially compatible with (A) polyethylene.

[0062] The (D) polar resin other than the above components (A) to (C) is not particularly limited. For example, copolymers of olefins such as ethylene and propylene and other monomers copolymerizable with the olefins can be mentioned. For example, by using a monomer having a polar group as the other monomer, a resin having a polar group can be obtained. Examples of such (D) polar resins include ethylene / acrylic acid / glycidyl methacrylate copolymer, polyhydroxypolyolefin oligomer, etc. The (D) polar resin can be used alone or in combination of two or more.

[0063] When the first resin layer 31 and / or the second resin layer 32 contains the (D) polar resin, its content is preferably 1 to 20% by mass, more preferably 5 to 15% by mass, based on the total amount of each layer. When the content of the (D) polar resin is 1% by mass or more, the adhesion to the metal terminal at room temperature tends to be further improved. When it is 20% by mass or less, it tends to be easy to suppress the decrease in the peelability at high temperature and the adhesion to the exterior material at room temperature.

[0064] In the first resin layer 31 and the second resin layer 32, when one or more of the above components (A) to (C) are resins having polar groups, the proportion of the resin having polar groups in the total amount of the components (A) to (C) is preferably 40% by mass or more, more preferably 80% by mass or more, from the viewpoint of further improving the adhesion to the metal terminal under a room temperature environment.

[0065] Additives other than the above-described components may be added to the first resin layer 31 and the second resin layer 32. Examples of the additives include antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, and crystal nucleating agents. These can be used alone or in combination of two or more.

[0066] The thickness of the first resin layer 31 and the second resin layer 32 is preferably 10 to 100 μm, more preferably 15 to 50 μm. If the thickness of the first resin layer 31 and the second resin layer 32 is less than 10 μm, the adhesion to the metal terminal 14 may decrease. Also, if the thickness of the first resin layer 31 is more than 100 μm, it will cause an increase in the cost of the resin film 16 for terminals, which is not preferable.

[0067] The first resin layer 31 and the second resin layer 32 preferably have at least one peak top of the heat of solution measured by DSC, and the peak top is preferably in the range of 80 to 135°C, more preferably in the range of 100 to 125°C. By satisfying the above conditions, the sealability under a high temperature environment can be further improved. Furthermore, the first resin layer 31 and the second resin layer 32 preferably have a second peak top located at a temperature higher than the first peak top of the heat of solution, and the second peak top is preferably in the range of 110 to 165°C, more preferably in the range of 120 to 150°C. The appearance of this second peak top can further improve the non-sealability under a non-high temperature environment in addition to the sealability under a high temperature environment.

[0068] The intermediate layer 33 is disposed between the first resin layer 31 and the second resin layer 32. One surface of the intermediate layer 33 is covered by the first resin layer 31, and the other surface is covered by the second resin layer 32.

[0069] The intermediate layer 33 is preferably an insulating layer. The insulating layer is a layer for preventing insulation degradation caused by the sealant (the sealant layer of the exterior material and the first and second resin layers of the resin film for terminals) flowing out during heat sealing and the exposed metal layer of the exterior material coming into contact with the metal terminal. Therefore, the insulating layer is preferably formed using a resin having a high melting point or glass transition temperature that does not flow out during heat sealing.

[0070] As the resin constituting the insulating layer, for example, polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polymethylpentene, polyacetal, cyclic polyolefin, polyamide, polycarbonate, polyphenylene ether, polypropylene, etc. can be used. Among these, from the viewpoints of film-forming property, interlayer adhesion, impact resistance, etc., it is preferable to use polypropylene, and it is more preferable to use block polypropylene in particular. Also, when the insulating layer contains polypropylene, the (B) compatibilizer contained in the first resin layer 31 and the second resin layer 32 can improve not only the adhesion to the exterior material but also the adhesion to the insulating layer. These resins can be used alone or in combination of two or more.

[0071] Further, the insulating layer may be colored by adding a pigment to the insulating layer. By coloring the insulating layer, the visibility of the resin film 16 for terminals can be improved. Thereby, the accuracy of inspection of the resin film 16 for terminals (specifically, for example, inspection of whether the resin film 16 for terminals is attached to the metal terminal 14, inspection of the attachment position of the resin film 16 for terminals with respect to the metal terminal 14, etc.) can be improved. Examples of the pigment include copper oxide, cobalt oxide, zinc oxide, titanium oxide, carbon black, barium sulfate, quinacridone-based pigments, polyazo-based pigments, isoindolinone-based pigments, etc.

[0072] Further, the intermediate layer 33 may be a layer having a configuration other than the above-described insulating layer. The intermediate layer 33 may be, for example, a layer that satisfies one or more requirements among a layer containing a resin having a crosslinked structure (crosslinked layer) and a layer containing at least one selected from the group consisting of a filler and a fiber (reinforcing layer).

[0073] In the crosslinked layer, examples of the resin having a crosslinked structure include crosslinked acrylic resin, epoxy resin, phenolic resin, urea resin, melamine resin, polyurethane resin, and the like. These can be used alone or in combination of two or more.

[0074] In the reinforcing layer, examples of the filler include silica particles, alumina particles, barium sulfate particles, calcium carbonate particles, and the like. These can be used alone or in combination of two or more. The average particle size of the filler is preferably 0.1 to 10 μm, and the content of the filler is preferably 0.5 to 20% by mass based on the total amount of the reinforcing layer (intermediate layer 33).

[0075] In the reinforcing layer, examples of the fiber include fibers made of cellulose resin and resins having a melting point of 200°C or higher used in the above heat-resistant layer. These can be used alone or in combination of two or more. The fiber width of the fiber is preferably 10 nm to 10 μm, and the content of the fiber is preferably 0.5 to 70% by mass based on the total amount of the reinforcing layer (intermediate layer 33). Further, the fibers may form a nonwoven fabric.

[0076] The reinforcing layer can be a layer in which the above-described filler and / or fiber is dispersed in the above-described polyolefin resin, resin having a melting point of 200°C or higher, resin having a crosslinked structure, or the like.

[0077] The intermediate layer 33 does not necessarily have a single-layer structure, and may have, for example, a multilayer structure in which a plurality of resin layers are bonded together via an adhesive. Therefore, the intermediate layer 33 may have a multilayer structure composed of two or more of the insulating layer, crosslinked layer, and reinforcing layer.

[0078] The thickness of the intermediate layer 33 (or the overall thickness in the case of a multilayer structure) can be appropriately set within a range of, for example, 10 to 200 μm, and preferably 20 to 100 μm. Note that the balance between the thickness of the intermediate layer 33 and the thicknesses of the metal terminal 14 and the first resin layer 31 is important. When the thicknesses of the first resin layer 31 and the metal terminal 14 are large, the thickness of the intermediate layer 33 may be increased accordingly.

[0079] The total thickness of the first resin layer 31, the second resin layer 32, and the intermediate layer 33 (the thickness of the resin film 16 for terminals) is preferably 10 to 500 μm, more preferably 15 to 300 μm, and even more preferably 30 to 200 μm, from the viewpoints of heat sealability, embeddability of the metal terminal, and insulation.

[0080] When the intermediate layer 33 is an insulating layer, the ratio of the thicknesses of the first resin layer 31, the intermediate layer 33, and the second resin layer 32 (first resin layer 31: intermediate layer 33: second resin layer 32) may be, for example, 2:1:2, 1:2:1, 1:1:1, etc., to make the thicknesses of the first resin layer 31 and the second resin layer 32 uniform. From the viewpoint of embeddability of the metal terminal, the thickness of the first resin layer 31 in contact with the metal terminal may be made greater than the thickness of the second resin layer 32, such as 3:1:1, 2:2:1, 5:3:2.

[0081] When the thicknesses of the first resin layer 31 and the second resin layer 32 are the same, the ratio of their thicknesses to the thickness of the intermediate layer 33 (first resin layer 31 or second resin layer 32: intermediate layer 33) may be 1:3 to 3:1, or may be 1:2 to 2:1. When the thickness of the first resin layer 31 is greater than the thickness of the second resin layer 32, the ratio of the thickness of the first resin layer 31 to the thickness of the intermediate layer 33 (first resin layer 31: intermediate layer 33) may be 4:1 to 1:1, or may be 3:1 to 1:1, and the ratio of the thickness of the second resin layer 32 to the thickness of the intermediate layer 33 (second resin layer 32: intermediate layer 33) may be 1:3 to 3:1, or may be 1:2 to 2:1.

[0082] As described above, the preferred embodiments of the present disclosure have been described in detail. However, the present disclosure is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present disclosure described in the claims.

[0083] For example, in FIG. 3, the resin film 16 for terminals having a three-layer structure has been described as an example. However, a second intermediate layer made of an insulating resin or the like may be disposed between the intermediate layer 33 and the first resin layer 31, and between the intermediate layer 33 and the second resin layer 32, respectively.

[0084] In this way, by disposing second intermediate layers between the intermediate layer 33 and the first resin layer 31, and between the intermediate layer 33 and the second resin layer 32, respectively, to form a multilayer structure of four or more layers, the insulation between the intermediate layer 33 and the barrier layer 24 (metal layer) constituting the exterior material 13, and the insulation between the intermediate layer 33 and the metal terminal 14 can be improved. Note that the second intermediate layer may be the crosslinked layer or the reinforcing layer described above.

[0085] Further, the resin film 16 for terminals may be composed of one layer or two layers.

[0086] When the resin film 16 for terminals has a single-layer structure, the single layer may have the same configuration as the first resin layer 31 described above. In this case, the thickness of the first resin layer 31 is preferably 10 to 500 μm, more preferably 15 to 300 μm, and still more preferably 30 to 200 μm from the viewpoints of heat sealability, embeddability of the metal terminal, and insulation.

[0087] When the resin film 16 for terminals has a two-layer structure, at least one layer may have the same configuration as the first resin layer 31 described above, with the side in contact with the metal terminal 14 being the first resin layer and the side in contact with the exterior material 13 being the second resin layer, and the other layer may have the same configuration as the second resin layer 32 or the intermediate layer 33 described above. Further, the other layer may have a configuration different from that of the second resin layer 32 or the intermediate layer 33 described above.

[0088] Further, the first resin layer 31 and the second resin layer 32 may have the same configuration or different configurations. In the resin film for terminals of the present disclosure, when having a plurality of layers, at least one layer may be a resin layer containing (A) polyethylene and (B) a compatibilizer, and the other layers do not have to satisfy the requirements of the above resin layer. Therefore, one of the first resin layer 31 and the second resin layer 32 may be a layer containing (A) polyethylene and (B) a compatibilizer, and the other may be a layer not containing one or both of (A) polyethylene and (B) a compatibilizer. However, from the viewpoint of more sufficiently obtaining the effects of the present disclosure and suppressing the occurrence of curl of the resin film for terminals, the two layers on both surfaces of the resin film for terminals are preferably resin layers containing (A) polyethylene and (B) a compatibilizer, and more preferably layers having substantially the same material composition.

[0089] Next, a method for manufacturing the resin film 16 for terminals of the present embodiment will be briefly described. There is no particular limitation on the method for manufacturing the resin film 16 for terminals. The resin film 16 for terminals can be manufactured using, for example, a film extrusion manufacturing apparatus having a die such as a round die used when using an inflation molding method or a T-die used when using a push die method. However, from the viewpoint of film forming stability, a multi-layer inflation molding method is preferable.

[0090] In the following description, as an example of the method for manufacturing the resin film 16 for terminals, the case where the resin film 16 for terminals is manufactured using an inflation molding method (in other words, an inflation molding apparatus) will be described.

[0091] First, the base materials of the first resin layer 31, the second resin layer 32, and the intermediate layer 33 are prepared. Next, the base materials of the first resin layer 31, the second resin layer 32, and the intermediate layer 33 are supplied to an inflation molding apparatus. Next, while extruding the three base materials so as to form a three-layer structure (a structure in which the first resin layer 31, the second resin layer 32, and the intermediate layer 33 are laminated) from the extrusion part of the inflation molding apparatus, air is supplied from the inside of the extruded three-layer structure laminate.

[0092] While transporting the cylindrically inflated resin film 16 for terminals in a cylindrical shape, after deforming it into a flat shape by a guide part, the resin film 16 for terminals is folded into a sheet shape by a pair of pinch rollers. Both ends of the woven tube are slit, and by winding a pair (two strips) of films around a winding core in a roll shape, the resin film 16 for terminals in a roll shape is manufactured.

[0093] When manufacturing the resin film 16 for terminals, the extrusion temperature is preferably in the range of, for example, 130 to 300°C, more preferably 130 to 250°C. When the extrusion temperature is less than 130°C, the melting of the resin constituting each layer becomes insufficient, so that the melt viscosity becomes considerably large, and there is a risk that the extrusion from the screw becomes unstable. On the other hand, when the extrusion temperature exceeds 300°C, the oxidation and deterioration of the resin constituting each layer become intense, so that the quality of the resin film 16 for terminals deteriorates.

[0094] The rotation speed of the screw, the blow ratio, the take-up speed, etc. can be appropriately set in consideration of the set film thickness. In addition, the film thickness ratio of each layer of the resin film 16 for terminals can be easily adjusted by changing the rotation speed of each screw.

[0095] Note that the resin film 16 for terminals of the present embodiment may be manufactured using a method such as dry lamination using an adhesive or sandwich lamination of the formed insulating layers (insulating films).

[0096] Here, with reference to FIG. 3, a fusion bonding process for fusion bonding the resin film 16 for terminals of the present embodiment and the metal terminal 14 will be described. In the fusion bonding process, while simultaneously performing the melting of the first resin layer 31 by heating and the adhesion of the first resin layer 31 and the metal terminal 14 by pressurization, the resin film 16 for terminals and the metal terminal 14 are thermally fused.

[0097] In addition, in the above-mentioned fusion process, in order to obtain sufficient adhesion and sealing properties between the resin film 16 for terminals and the metal terminal 14, heating is performed up to a temperature equal to or higher than the melting point of the resin constituting the first resin layer 31.

[0098] Specifically, as the heating temperature of the resin film 16 for terminals, for example, 140 to 170 °C can be used. Also, the processing time (total time of heating time and pressurization time) needs to be determined in consideration of peel strength and productivity. The processing time can be appropriately set within the range of, for example, 1 to 60 seconds.

[0099] In addition, when giving priority to the production tact (productivity) of the resin film 16 for terminals, heat fusion may be performed by shortening the pressurization time at a temperature exceeding 170 °C. In this case, as the heating temperature, for example, 170 to 230 °C can be used, and as the pressurization time, for example, 3 to 20 seconds can be used.

Examples

[0100] Hereinafter, the present disclosure will be described more specifically based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0101] [Materials Used] The materials used in the examples and comparative examples are shown in Table 1 below.

Table 1

[0102] [Production of Resin Film for Terminals] (Examples 1 to 16 and Comparative Examples 1 to 4) Each component of the resin layer shown in Table 2 was blended in the blending amounts (unit: mass%, abbreviated as “%” in the table) shown in the same table, and dry-blended to prepare a base material for the resin layer. Next, using an inflation-type film extrusion manufacturing apparatus (Co-OI type) manufactured by Sumitomo Heavy Industries Modern Co., Ltd., the base material was extruded and molded at a melting temperature of 210°C to obtain a resin film for terminals composed of a single layer of resin layer with a thickness of 100 μm. When the heat of fusion of each film was measured by DSC, peaks corresponding to the melting points of the respective resin components were detected.

[0103] (Examples 17 to 22) Each component of the resin layer and the insulating layer shown in Table 2 was blended in the blending amounts (unit: mass%, abbreviated as “%” in the table) shown in the same table, and dry-blended to prepare a base material for the resin layer and a base material for the insulating layer, respectively. When preparing the base material for the insulating layer, a masterbatch was prepared by premixing a part of the block PP as the base resin and a black pigment, and then the masterbatch was dry-blended with the remaining base resin. When the heat of fusion of each film was measured by DSC, peaks corresponding to the melting points of the respective resin components were detected.

[0104] Next, a base material for the resin layer (first resin layer), a base material for the insulating layer (intermediate layer), and a base material for the resin layer (second resin layer) were set in an inflation-type film extrusion manufacturing apparatus (Co-OI type) manufactured by Sumitomo Heavy Industries Modern Co., Ltd., and the three base materials were extruded by the film extrusion manufacturing apparatus to produce a resin film for terminals having a three-layer structure of the first resin layer / insulating layer / second resin layer. The melting temperature of each base material was 210°C. In each example, the thicknesses of the first resin layer (lead side) / insulating layer / second resin layer (outer packaging material side) were as follows. Examples 17, 20: 25 μm / 50 μm / 25 μm Examples 18, 21: 40 μm / 40 μm / 20 μm Examples 19, 22: 50 μm / 30 μm / 20 μm

[0105] [Measurement of Initial (Room Temperature) Heat Seal Strength against Outer Packaging Material] A sample of the resin film for terminals cut to a size of 50 mm (TD) × 100 mm (MD) was folded in half so as to sandwich a formed aluminum foil cut to a size of 50 mm × 50 mm, and the end on the side opposite to the folded part was heat-sealed over a width of 10 mm at 165 °C / 0.6 MPa / 10 seconds. Then, it was folded in half so that the sealant layer of the exterior material having a laminated structure of nylon film (thickness 25 μm) / adhesive / aluminum foil (thickness 40 μm) / polypropylene sealant layer (thickness 80 μm) contacted the resin film for terminals, and the end on the side opposite to the folded part (the same location as the location where the resin film for terminals and the aluminum foil were heat-sealed) was heat-sealed over a width of 10 mm at 190 °C / 0.5 MPa / 5 seconds. Then, the central part in the longitudinal direction of the heat-sealed part was cut out with a width of 15 mm (see Fig. 4), and a sample for measuring the heat-seal strength was prepared. In this evaluation, the laminate 100 in Fig. 4 is a laminate composed of exterior material / resin film for terminals / aluminum foil / resin film for terminals / exterior material. For the heat-sealed part of this sample, a T-peel test between the exterior material and the resin film for terminals was conducted using a tensile testing machine (manufactured by Shimadzu Corporation) under the conditions of a room temperature (25 °C) environment and a tensile speed of 50 mm / min. Based on the obtained results, the initial heat-seal strength of the exterior material was evaluated according to the following evaluation criteria. If the evaluation is A, B, or C, it is qualified; if it is D, it is unqualified. The results are shown in Table 2. A: The heat-seal strength is 100 N / 15 mm or more B: The heat-seal strength is 90 N / 15 mm or more and less than 100 N / 15 mm C: The heat-seal strength is 80 N / 15 mm or more and less than 90 N / 15 mm D: The heat-seal strength is less than 80 N / 15 mm

[0106] [Measurement of the initial (room temperature) heat-seal strength for the leads] A sample of the resin film for terminals cut to a size of 50 mm (TD) × 100 mm (MD) was folded in half so as to sandwich the formed aluminum foil cut to a size of 50 mm × 50 mm, and the end opposite to the folded portion was heat-sealed over a width of 10 mm at 165 °C / 0.6 MPa / 10 seconds. Then, a 15-mm-wide central portion in the longitudinal direction of the heat-sealed portion was cut out (see Fig. 4), and a sample for measuring the heat-seal strength was prepared. In this evaluation, the laminate 100 in Fig. 4 is a laminate composed of a resin film for terminals / aluminum foil / resin film for terminals. With respect to the heat-sealed portion of this sample, a T-peel test was conducted between the aluminum foil (lead) and the resin film for terminals using a tensile testing machine (manufactured by Shimadzu Corporation) under the conditions of a room temperature (25 °C) environment and a tensile speed of 50 mm / min. Based on the obtained results, the initial heat-seal strength against the lead was evaluated according to the following evaluation criteria. If the evaluation is A, B, or C, it is considered qualified; if it is D, it is considered unqualified. The results are shown in Table 2. A: The heat-seal strength is 25 N / 15 mm or more B: The heat-seal strength is 20 N / 15 mm or more and less than 25 N / 15 mm C: The heat-seal strength is 15 N / 15 mm or more and less than 20 N / 15 mm D: The heat-seal strength is less than 15 N / 15 mm

[0107] [Measurement of Heat-Seal Strength in a 100 °C Environment] In the same manner as the measurement of the initial heat-seal strength against the lead, a sample for measuring the heat-seal strength was prepared. After this sample was allowed to stand in a 100 °C environment for 5 minutes, a T-peel test was conducted between the aluminum foil (lead) and the resin film for terminals using a tensile testing machine (manufactured by Shimadzu Corporation) under the conditions of a 100 °C environment and a tensile speed of 50 mm / min with respect to the heat-sealed portion of the sample. Based on the obtained results, the heat-seal strength in a 100 °C environment was evaluated according to the following evaluation criteria. Since the battery may be stored in an environment of 60 to 100 °C for aging, it is desirable to have a heat-seal strength of a certain level or more in a 100 °C environment. The results are shown in Table 2. A: The heat-seal strength is 4 N / 15 mm or more B: Heat seal strength is 3 N / 15 mm or more and less than 4 N / 15 mm C: Heat seal strength is 2 N / 15 mm or more and less than 3 N / 15 mm D: Heat seal strength is less than 2 N / 15 mm

[0108] [Measurement of heat seal strength under 130°C environment (evaluation of unsealing property)] In the same manner as the measurement of the initial heat seal strength of the pair of leads, a sample for heat seal strength measurement was prepared. After leaving this sample standing in a 130°C environment for 5 minutes, a T-peel test was conducted between the aluminum foil (lead) and the terminal resin film using a tensile testing machine (manufactured by Shimadzu Corporation) under the conditions of a 130°C environment and a tensile speed of 50 mm / min with respect to the heat seal portion of the sample. Based on the following evaluation criteria, the heat seal strength under a 130°C environment was evaluated from the obtained results. 130°C is the temperature at which the organic solvent volatilizes or decomposes and the inside of the exterior material begins to expand. The lower the heat seal strength at this temperature, the better the unsealing property under a high-temperature environment and the higher the safety. When the evaluation is A, B, or C, it is a pass; when it is D, it is a fail. The results are shown in Table 2. A: Heat seal strength is less than 2 N / 15 mm B: Heat seal strength is 2 N / 15 mm or more and less than 3 N / 15 mm C: Heat seal strength is 3 N / 15 mm or more and less than 5 N / 15 mm D: Heat seal strength is 5 N / 15 mm or more

[0109] [Evaluation of insulation property] (1) Production of tabs As the leads, those with a width of 5 mm, a length of 30 mm, and a thickness of 100 μm were used. The material had aluminum for the positive electrode and nickel for the negative electrode. Non-chromium-based surface treatment was performed on both the positive and negative electrodes. As the terminal resin film, that cut to a width of 15 mm and a length of 10 mm was used. Lamination was performed in the order of terminal resin film / lead / terminal resin film, and fusion was carried out at a fusion temperature of 150°C and a fusion time of 10 seconds. Thereby, positive and negative tabs were obtained.

[0110] (2) Fabrication of the battery pack As the exterior material, a laminated structure of nylon film (thickness 25 μm) / polyester polyol-based adhesive (thickness 5 μm) / aluminum foil (thickness 40 μm, A8079-O material) / acid-modified polypropylene (thickness 30 μm) / polypropylene (thickness 40 μm) was used. Non-chromium surface treatment was performed on both sides of the aluminum foil. The size of the exterior material was set to 50 mm × 90 mm, folded in half along the long side, and heat sealing was performed on one side of the side with a width of 45 mm with the positive electrode tab and the negative electrode tab sandwiched. The heat sealing was performed at 190°C for 5 seconds. The heat sealing of the sides without tabs at the remaining two locations was performed at 190°C for 3 seconds. First, heat sealing was performed on the opposite side of the folded side, and then 2 ml of an electrolyte solution in which LiPF6 (lithium hexafluorophosphate) was added to a mixed solution of diethyl carbonate and ethylene carbonate was filled, and finally heat sealing was performed on the opposite side of the tab. Thus, a battery pack for tab evaluation in which battery elements such as current collectors were not encapsulated was fabricated. Note that the fabrication conditions of the battery pack described above were made more severe in terms of heating temperature and heat sealing time than the conditions of the actual battery production process.

[0111] (3) Insulation evaluation The insulation between the negative electrode lead of the battery pack fabricated above and the exterior material was measured with a tester. Based on the following evaluation criteria, the insulation was evaluated from the number of specimens in which a short circuit occurred among 200 specimens. The results are shown in Table 2. A: Less than 2 short-circuited specimens B: 2 or more and less than 4 short-circuited specimens C: 4 or more and less than 6 short-circuited specimens D: 6 or more short-circuited specimens

[0112]

Table 2

Explanation of symbols

[0113] 10…Power storage device, 11…Power storage device main body, 13…Exterior material, 14…Metal terminal, 14-1…Metal terminal main body, 14-2…Corrosion prevention layer, 16…Resin film for terminal, 21…Inner layer, 22…Inner layer side adhesive layer, 23-1, 23-2…Corrosion prevention treatment layer, 24…Barrier layer, 25…Outer layer side adhesive layer, 26…Outer layer, 31…First resin layer, 32…Second resin layer, 33…Intermediate layer.

Claims

【Claim 1】 A resin film for a terminal for covering a part of the outer peripheral surface of a metal terminal constituting a power storage device, the resin film for a terminal comprising a resin layer containing (A) polyethylene and (B) a compatibilizer having a site compatible with the (A) polyethylene and a site compatible with polypropylene.

Images