JP7566246B2 - Battery Tab Leads - Google Patents

Description

The present disclosure relates to a tab lead for a battery.
This application claims priority based on Japanese Application No. 2020-014715 filed on January 31, 2020, and incorporates by reference all of the contents of these Japanese applications.

As a lead wire used in a battery, a battery tab lead has been proposed, which is composed of a lead conductor connected to the positive electrode or negative electrode of the battery and an insulating resin layer covering the lead conductor.
Patent Document 1 discloses a lead member (tab lead) in which a pair of insulating films are attached to both surfaces of a heat-sealed portion of a lead conductor, the insulating film having a two-layer structure consisting of a cross-linking layer and an adhesive layer, the heat-sealed portion of the lead conductor being covered with the adhesive layer, and the outside of that being covered with the cross-linking layer.

Patent Document 2 discloses a lead wire (tab lead) for a non-aqueous electrolyte battery, which has a lead conductor, a first insulating layer that directly covers at least a portion of the lead conductor, and a second insulating layer that covers the first insulating layer, the second insulating layer being formed from a crosslinked body of a resin composition containing an olefin crystal-ethylene butene-olefin crystal block polymer and polypropylene in a mass ratio of 10:90 to 40:60.

JP 2011-103245 A WO2018/074090 publication

The present disclosure provides a battery tab lead including a lead conductor and a resin layer that covers a heat-sealed portion of the lead conductor,
the resin layer has a conductor adhesive layer provided on the lead conductor side, an intermediate layer, and a packaging adhesive layer provided on the intermediate layer on the opposite side to the conductor adhesive layer side,
The conductor adhesive layer contains a polyolefin resin,
the intermediate layer contains a crosslinked polyolefin resin, and the packaging material adhesive layer contains a polyolefin resin and has an elastic modulus at 200° C. of 0.1 MPa or more and 15 MPa or less.

FIG. 2 is a perspective view illustrating the vicinity of a heat-sealed portion of an example of a tab lead according to the present disclosure. 2 is a schematic cross-sectional view showing a cross section of a heat-sealed portion of the tab lead of the present disclosure. FIG. FIG. 11 is a schematic cross-sectional view showing a cross section of a heat-sealed portion of a conventional tab lead. 1 is a cross-sectional view showing a cross-sectional structure of an example of a nonaqueous electrolyte battery using a tab lead of the present disclosure. 1 is a cross-sectional view showing a schematic diagram of a heat-sealed portion using a tab lead according to the present disclosure. FIG. 11 is a cross-sectional view showing a schematic diagram of a heat-sealed portion using a conventional tab lead.

[Problem to be solved by the present disclosure]
As described in Patent Documents 1 and 2, by using a tab lead in which the heat-sealed portion of the lead conductor is covered with an adhesive layer and the outside of that is covered with a cross-linked layer made of a cross-linked resin, it is possible to obtain excellent adhesion to the lead conductor while preventing a short circuit between the lead conductor and the metal layer of the sealed container during heat fusion. As a result, the resulting battery can suppress leakage of electrolyte and infiltration of moisture from the outside.

However, it has been found that when such tab leads are used to seal the opening of a battery enclosure by heat sealing, there are cases where the cross-linked layer of the tab lead does not adhere to the laminate film of the enclosure, resulting in voids (areas where the gap between the cross-linked layer and the thermoplastic resin layer of the laminate film is not filled sufficiently, resulting in voids). This is particularly likely to occur when the lead conductor is flat and thick. If voids occur, electrolyte leakage and moisture entry into the battery are likely to occur, which is problematic in terms of battery reliability (the property of battery performance not easily degraded). There is therefore a need to develop a tab lead that prevents the occurrence of such voids during the process of heat sealing the opening (packaging sealing process).

The objective of the present disclosure is to provide a tab lead for use in batteries, particularly non-aqueous electrolyte batteries, which can adequately prevent short-circuiting between the lead conductor and the metal layer of the sealed container when the opening of the sealed container is heat-sealed during battery manufacture, and which ensures sufficient adhesion between the resin layer and the lead conductor, as well as sufficient adhesion between the tab lead and the laminate film of the sealed container, thereby suppressing the occurrence of voids between the resin layer and the thermoplastic resin layer of the laminate film.

[Means for solving the problems]
As a result of research, the inventors have found that a tab lead that solves the above-mentioned problems can be obtained by making the resin layer covering the heat-sealed portion of the lead conductor include a conductor adhesive layer that can be adhered to the lead conductor and an intermediate layer made of crosslinked resin, as well as a packaging adhesive layer that is provided on the opposite side of the intermediate layer to the conductor adhesive layer, and the packaging adhesive layer is formed using a polyolefin resin and has an elastic modulus within a specific range, and have thus completed the tab lead for batteries of the present disclosure.

The aspects of the present disclosure made to solve the above problems are as follows:
A battery tab lead including a lead conductor and a resin layer covering a heat-sealed portion of the lead conductor,
the resin layer has a conductor adhesive layer provided on the lead conductor side, an intermediate layer, and a packaging adhesive layer provided on the intermediate layer on the opposite side to the conductor adhesive layer side,
The conductor adhesive layer contains a polyolefin resin,
The intermediate layer contains a crosslinked polyolefin resin, and the packaging material adhesive layer contains a polyolefin resin and has an elastic modulus at 200° C. of 0.1 MPa or more and 15 MPa or less.

In a more preferred aspect of the present disclosure, the packaging adhesive layer has an elastic modulus at 200°C of 1.0 MPa or more and 10 MPa or less.

[Effects of the present disclosure]
If a battery, for example a non-aqueous electrolyte battery, is manufactured using the battery tab lead of the present disclosure, the resin layer and the lead conductor are sufficiently adhered to each other when the opening of the sealed container is heat-sealed, and the occurrence of a short circuit between the lead conductor and the metal layer of the sealed container can be sufficiently prevented. Furthermore, the resin layer and the thermoplastic resin layer of the laminate film (sealed container) are adhered to each other, and the occurrence of voids between the layers is suppressed, so that problems such as leakage of electrolyte and intrusion of moisture from the outside into the battery can be suppressed, and a battery with excellent reliability can be easily manufactured.

[Mode for carrying out the present disclosure]
Hereinafter, the embodiments of the present disclosure will be described in detail. Note that the present invention is not limited to the following contents, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

An aspect of the present disclosure is
A battery tab lead including a lead conductor and a resin layer covering a heat-sealed portion of the lead conductor,
the resin layer has a conductor adhesive layer provided on the lead conductor side, an intermediate layer, and a packaging adhesive layer provided on the intermediate layer on the opposite side to the conductor adhesive layer side,
The conductor adhesive layer contains a polyolefin resin,
The intermediate layer contains a crosslinked polyolefin resin, and the packaging material adhesive layer contains a polyolefin resin and has an elastic modulus at 200° C. of 0.1 MPa or more and 15 MPa or less.

(Configuration of battery tab lead according to the present disclosure)
The tab lead for a battery (hereinafter also referred to simply as the tab lead) disclosed herein comprises a resin layer that covers the lead conductor and the heat-sealed portion of the lead conductor, and is characterized in that the resin layer has a packaging material adhesive layer in addition to a conductor adhesive layer and an intermediate layer.
Fig. 1 is a perspective view showing the vicinity of a heat-sealed portion of an example of a battery tab lead according to the present disclosure. In Fig. 1, reference numeral 1 denotes a lead conductor, and reference numeral 2 denotes a resin layer. As shown in Fig. 1, the surface of a heat-sealed portion A (a portion that is heat-sealed when sealing an enclosed container) of the lead conductor 1 is covered with a resin layer 2. The enclosed container and the lead conductor 1 are bonded (heat-sealed) via this resin layer 2.

Figure 2 is a schematic cross-sectional view showing a cross section of the heat-sealed portion of the battery tab lead of Figure 1. The resin layer 2 is composed of a conductor adhesive layer 3, an intermediate layer 4, and a packaging material adhesive layer 5. Figure 3 is a schematic cross-sectional view showing a cross section of a heat-sealed portion of a conventional battery tab lead. In Figure 3, 11 is a lead conductor, 21 is a resin layer, and the resin layer 21 is composed of a conductor adhesive layer 31 and a cross-linking layer 41. The battery tab lead of the present disclosure shown in Figure 2 differs from the conventional battery tab lead shown in Figure 3 in that it has a packaging material adhesive layer 5 in addition to the conductor adhesive layer 3 and intermediate layer 4.

The resin layer 2 has the conductor adhesive layer 3, the intermediate layer 4, and the packaging material adhesive layer 5 as essential components, but may have other layers. For example, a layer for improving the adhesion between these layers may be provided between the conductor adhesive layer 3 and the intermediate layer 4 and/or between the intermediate layer 4 and the packaging material adhesive layer 5. Since polyolefin resin is used for the conductor adhesive layer 3, the intermediate layer 4, and the packaging material adhesive layer 5, when a layer for improving the adhesion between the layers is provided, it is preferable that the layer be a layer using a polyolefin resin.
In this way, the resin layer 2 may be composed of three or more layers.

Next, each component of the battery tab lead disclosed herein will be described.

(Conductor Adhesive Layer)
The conductor adhesive layer is a layer provided on the lead conductor side of the resin layer, and adheres to the lead conductor.
The conductor adhesive layer includes a thermoplastic polyolefin resin that can be adhered to the lead conductor. Examples of the polyolefin resin include polyethylene, polypropylene, ethylene-based elastomer, styrene-based elastomer, and ionomer resins obtained by crosslinking a copolymer of ethylene and methacrylic acid with Na, Mg, K, etc. The resin contained in the conductor adhesive layer is preferably a resin having a high adhesive strength to the lead conductor. As the resin contained in the conductor adhesive layer, resins obtained by modifying the above-mentioned polyolefin resins with maleic acid, acrylic acid, methacrylic acid, maleic anhydride, and epoxy groups are also preferably used because the adhesive strength to the lead conductor is improved by modification. In particular, maleic anhydride-modified polyolefin resins can be preferably used.

The conductor adhesive layer may be composed of only a thermoplastic polyolefin resin that can be adhered to the lead conductor, or may contain other components. The conductor adhesive layer can be mixed with various additives such as flame retardants, ultraviolet absorbers, light stabilizers, heat stabilizers, lubricants, and colorants. The conductor adhesive layer containing a thermoplastic polyolefin resin that can be adhered to the lead conductor and various additives can be produced by mixing the polyolefin resin and the additives using a known mixing device such as an open roll, a pressure kneader, a single-screw mixer, or a twin-screw mixer, and then extruding the mixture into a film-like layer by T-die molding, inflation molding, or other extrusion molding.
The optimum thickness of the conductor adhesive layer varies depending on the thickness of the lead conductor, but is usually preferably 20 μm or more and 250 μm or less.

(Middle class)
The intermediate layer includes a crosslinked polyolefin resin. By using a polyolefin resin as a forming material for the intermediate layer, excellent adhesion to the conductor adhesive layer formed of a polyolefin resin that can be adhered to the lead conductor can be obtained. In particular, by using a polyolefin resin having the same or similar chemical structure as the polyolefin resin constituting the conductor adhesive layer, even better adhesion to the conductor adhesive layer can be obtained.
Examples of the crosslinked polyolefin resin include a crosslinked polypropylene resin, or a crosslinked product of a resin composition containing a polypropylene resin and a thermoplastic elastomer in a mass ratio of 90: 10 to 60: 40. Since this resin composition has excellent crosslinking properties, by using this resin composition to form an intermediate layer, crosslinking is possible even if the amount of the crosslinking assistant described below is reduced, and adverse effects of the crosslinking assistant on molding equipment and products can be suppressed.
Examples of the thermoplastic elastomer include ethylene-butene copolymer resin, ethylene-octene copolymer resin, olefin crystal-ethylenebutene-olefin crystal block polymer, polypropylene-based elastomer such as Toughmer PN2070 manufactured by Mitsui Chemicals, Inc. At least one selected from these can be used as the thermoplastic elastomer.

By cross-linking polyolefin resin, its resistance to thermal deformation is improved, making it less susceptible to thermal deformation even when heated above the melting point of the resin. Therefore, by providing an intermediate layer containing cross-linked polyolefin resin on the surface of the heat-sealed portion of the lead conductor, thermal deformation and melting of the intermediate layer are suppressed even when the tab lead is heat-sealed to the opening of the sealed container, and short-circuiting between the lead conductor and the metal layer of the sealed container can be prevented.

Methods for crosslinking polyolefin resins include crosslinking by irradiation with ionizing radiation such as electron beams and gamma rays, chemical crosslinking with peroxides, silane crosslinking, etc. Among these, the method by irradiation with ionizing radiation is preferred from the viewpoints of productivity, ease of control, etc.
When crosslinking is performed by irradiation with ionizing radiation, a crosslinking aid may be added to the material for forming the intermediate layer, together with the polyolefin resin before crosslinking, as necessary. Examples of the crosslinking aid include compounds containing at least two unsaturated groups in the molecule, and specific examples thereof include triallyl isocyanurate, triallyl cyanurate, tris(2-acryloyloxyethyl)isocyanurate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, and ethyn glycol dimethacrylate.

Whether the olefin resin constituting the intermediate layer is crosslinked can be confirmed, for example, by the presence of insoluble matter remaining after immersing a sample in xylene at 120° C. for 24 hours.
The degree of crosslinking in the crosslinked polyolefin resin is preferably such that the gel fraction is about 20% to 90%. The gel fraction here is a value measured by the method described below.
(Method of Measuring Gel Fraction)
Approximately 1.0 g (this weight is W1) of a sample (crosslinked polyolefin resin (intermediate layer)) is immersed in xylene at 120° C. for 24 hours, after which the liquid portion is discarded and the solid portion is heated at 120° C. for 3 hours to dry and remove the xylene component. Thereafter, the weight of the solid portion (W2) is measured, and the gel fraction is calculated as (W2/W1)×100(%).

If the gel fraction is less than 20%, cross-linking is insufficient and there is a tendency for short-circuiting between the lead conductor and the metal layer of the sealed container to be insufficiently prevented. On the other hand, if the gel fraction exceeds 90%, adhesion to the packaging adhesive layer decreases and electrolyte leakage, etc. tends to occur more easily. It is preferable to select the amount of cross-linking aid and the amount of ionizing radiation exposure from a range that results in a degree of cross-linking within the above range and does not cause deterioration of the resin, etc.

In addition to the above-mentioned methods, the fact that the olefin resin constituting the intermediate layer is crosslinked can also be confirmed by the thermal deformation residual rate of the intermediate layer. In this case, the thermal deformation residual rate of the intermediate layer is measured by a thermomechanical analysis (TMA (Thermal Mechanical Analysis)) method, and if the thermal deformation residual rate is 20% or more, it is determined that the olefin resin is crosslinked.

In addition to the above-mentioned polyolefin resin and crosslinking aid, various additives such as flame retardants, ultraviolet absorbers, light stabilizers, heat stabilizers, lubricants, and colorants can be mixed into the material for forming the intermediate layer. When the material for forming the intermediate layer contains a polyolefin resin and an optional crosslinking aid and additives, the intermediate layer can be prepared by mixing the polyolefin resin before crosslinking, the crosslinking aid and additives using a known mixing device such as an open roll, a pressure kneader, a single-screw mixer, or a twin-screw mixer, and then extruding the mixture with a T-die or an inflation extruder to form a film-like layer, and then crosslinking the olefin resin contained in the obtained film-like layer by the above-mentioned method. The intermediate layer may be composed of only a crosslinked polyolefin resin, or may be composed of a crosslinked polyolefin resin and other components such as a crosslinking aid and an antioxidant.
The optimum thickness of the intermediate layer varies depending on the thickness of the lead conductor, but is usually preferably from 10 μm to 200 μm.

(Packaging Adhesive Layer)
The packaging adhesive layer is a layer containing a polyolefin resin and has an elastic modulus of 0.1 MPa or more and 15 MPa or less at 200°C measured by the method shown below. The packaging adhesive layer is provided on the opposite side of the intermediate layer from the conductor adhesive layer. By providing a packaging adhesive layer having an elastic modulus in the above range and containing a polyolefin resin, it is possible to suppress the occurrence of voids (areas where the gap between the resin layer and the thermoplastic resin layer of the laminate film is not sufficiently filled and becomes a gap) between the resin layer and the laminate film (enclosure container) (hereinafter, the property of suppressing the occurrence of voids may be referred to as "fillability"). Therefore, problems such as leakage of the electrolyte and intrusion of moisture from the outside are suppressed, and a nonaqueous electrolyte battery with excellent reliability (deterioration of the battery performance is suppressed) can be manufactured.

(Method for measuring elastic modulus at 200°C)
The method for measuring the elastic modulus at 200° C. will be described below.
A microtome is used to cut the insulating film of the tab lead so that each layer can be observed. An atomic microscope (Oxford Instruments, Asylum Research Cypher ES) is used to measure and map the force curves at 20 points parallel to the film thickness and 20 points perpendicular to the film thickness, totaling about 400 points, using a silicon indenter with a nominal tip diameter of 20 nm at 1 μm intervals and a speed of 1 Hz in a 200°C environment. A histogram is created at 1 MPa intervals based on the obtained data, and the most frequent value is defined as the "elastic modulus at 200°C".

If the elastic modulus of the packaging adhesive layer at 200° C. is less than 0.1 MPa, the resin will flow out significantly during heat fusion, which can easily cause problems such as the resin spreading widely over the surfaces and ends of the lead conductors.
On the other hand, if the elastic modulus of the packaging adhesive layer at 200°C exceeds 15 MPa, it becomes difficult to sufficiently fill the gap between the resin layer near the end of the lead conductor and the thermoplastic resin layer of the laminate film, and voids are likely to occur. As a result, problems such as electrolyte leakage and moisture intrusion from the outside are likely to occur. The elastic modulus at 200°C is preferably in the range of 1.0 MPa to 10.0 MPa.
The elastic modulus at 200° C. of the polyolefin resin for forming the packaging material adhesive layer is preferably 0.1 MPa or more and 15 MPa or less, and more preferably 1.0 MPa or more and 10 MPa or less.

In addition to the elastic modulus in the above range, the packaging adhesive layer is required to have excellent adhesion to the intermediate layer and the thermoplastic resin layer of the laminate film of the enclosed container. Therefore, the polyolefin resin forming the packaging adhesive layer is preferably a polyolefin resin with the same or similar chemical structure as the uncrosslinked polyolefin resin that is the material forming the intermediate layer.

The thickness of the packaging adhesive layer is usually preferably 10 μm or more and 200 μm or less, but this preferred range varies depending on the thickness of the lead conductor, and is preferably 0.1 times or more and 1.0 times or less the thickness of the lead conductor. If the thickness of the packaging adhesive layer is thinner than the above range, it becomes difficult to fill the gap between the resin layer near the end of the lead conductor and the thermoplastic resin layer of the laminate film with resin, and voids are likely to occur (filling ability is reduced). On the other hand, if the packaging adhesive layer is thicker than the above range, a large amount of heat is required to melt the packaging adhesive layer, so that the resin is likely to melt insufficiently and the filling ability is reduced.
However, when the thickness of the thermoplastic resin layer (sealant layer) of the laminate film (on the side to be heat-sealed with the resin layer of the tab lead) is thin, it is desirable to make the packaging adhesive layer thick in order to sufficiently fill the gap between the resin layer and the thermoplastic resin layer of the laminate film and to suppress the occurrence of voids. When the sealant layer of the laminate film is made of a polyolefin resin, it is usually preferable that the total thickness of the sealant layer (the thermoplastic resin layer) and the packaging adhesive layer of the laminate film is 80 μm or more.

The packaging adhesive layer may be composed of only polyolefin resin, or may contain other components. Various additives such as flame retardants, ultraviolet absorbers, light stabilizers, heat stabilizers, lubricants, and colorants can be mixed into the packaging adhesive layer. The packaging adhesive layer containing polyolefin resin and various additives can be produced by mixing the polyolefin resin and the additives using a known mixing device such as an open roll, a pressure kneader, a single-screw mixer, or a twin-screw mixer, and then extruding the mixture into a film using a T-die or an inflation extruder.

(Lead conductor)
The shape of the lead conductor is not particularly limited, but in many cases, a metal having a flat plate shape with a thickness of 50 μm to 2 mm and a width of about 1 mm to 200 mm is preferable for the lead conductor used in a lithium ion battery, which is a non-aqueous electrolyte battery. Examples of metals used as the lead conductor include aluminum, titanium, nickel, copper, and nickel-plated copper. When the lead conductor is used in a lithium ion battery, in many cases, aluminum, titanium, or an alloy thereof is preferable for the lead conductor connected to the positive electrode plate, and in many cases, nickel, copper, or an alloy thereof is preferable for the lead conductor connected to the negative electrode plate.

(Fabrication of the Tab Lead of the Present Disclosure)
The tab lead of the present disclosure can be produced, for example, by a method in which a resin layer including a conductor adhesive layer, an intermediate layer, and a packaging material adhesive layer, in that order, is adhered to both surfaces of a position corresponding to the heat-sealed portion of a flat-shaped lead conductor (part A in Figure 1), with the conductor adhesive layer facing the lead conductor, and then heated to heat-seal the conductor adhesive layer (resin layer) and the lead conductor.
The resin layer including the conductor adhesive layer, intermediate layer and packaging adhesive layer can be prepared by overlapping each film-like layer prepared by the above-mentioned method and bonding them together by thermal lamination.
The heating temperature, pressure and heating time during the heat fusion and heat lamination are similar to those in the manufacture of conventional tab leads, and can be determined by referring to conventionally known conditions and making appropriate adjustments, if necessary, by conducting simple preliminary experiments.

(Manufacture of non-aqueous electrolyte battery)
The laminate film forming the battery enclosure is composed of a metal layer and thermoplastic resin layers (sealant layers) that insulate both surfaces of the metal layer.
The container for the nonaqueous electrolyte battery can be produced, for example, by preparing a pair of rectangular laminate films of a predetermined size, stacking them so that they face each other, and heat-sealing the three peripheral sides of the rectangle to a desired seal width using a sealing machine under predetermined heating conditions. In this way, a bag-shaped container having an opening on one side can be produced.
Other examples of the method for producing the sealed container include deep drawing of the laminate film, etc. The method for producing the sealed container is not particularly limited as long as it can produce a bag-shaped sealed container having an opening on one side and can provide a volume inside for storing the battery components.

The positive and negative electrode plates, each having the tab lead of the present disclosure connected to one end thereof, and an electrolyte solution are placed in the sealed container prepared as described above. The other end of the tab lead is extended to the outside of the sealed container so that the heat-sealed portion of the tab lead, i.e., the resin layer covering the surface of the lead conductor, is positioned at the opening of the sealed container, and the opening is then heated and pressurized for heat fusion (packaging sealing), thereby producing a nonaqueous electrolyte battery.
The heating temperature, pressure and time for heating and pressurizing during the heat fusion (packaging sealing) can be easily selected by referring to conditions conventionally employed in the manufacture of nonaqueous electrolyte batteries and, if necessary, by appropriately adjusting the conditions through simple preliminary experiments.

Figure 4 is a cross-sectional view showing the structure of a nonaqueous electrolyte battery manufactured as described above. In Figure 4, 6 is a positive electrode plate, 7 is a negative electrode plate, 8 is a tab lead of the present disclosure, one end of which is connected to the positive electrode plate 6 or the negative electrode plate 7, and 9 is a resin layer covering the surface of the heat-sealed portion of the lead conductor. In Figure 4, 52 is a nonaqueous electrolyte, and 53 is a seal portion of the sealed container 51. As shown in Figure 4, the resin layer 9 of the tab lead 8 is located at the heat-sealed portion 10 (opening) of the sealed container 51.

The heat-sealed portion 10 of the sealed container 51 is heat-sealed (packaging sealed) by heating and pressurization. Figures 5 and 6 are diagrams showing the state of the heat-sealed portion after heat-sealing. Figure 5 is a schematic cross-sectional view showing a cross-section of a heat-sealed portion using the tab lead of the present disclosure, and Figure 6 is a schematic cross-sectional view showing a cross-section of a heat-sealed portion using a conventional tab lead.

5 and 6, the laminate film 101 is composed of a metal layer 102 made of aluminum foil, a polyamide resin layer 103 covering the first surface of the metal layer 102, and a sealant layer 104 made of polypropylene resin covering the second surface of the metal layer 102. In the example of FIG. 5, the resin layer 2 includes a conductor adhesive layer 3, an intermediate layer 4, and a packaging adhesive layer 5. In the example of FIG. 6, the resin layer 21 includes a conductor adhesive layer 31 and a cross-linking layer 41. The intermediate layer 4 included in the resin layer 2 in the example of FIG. 5 and the cross-linking layer 41 included in the resin layer 21 in the example of FIG. 6 are both layers containing cross-linked resin, and layers containing cross-linked resin are not easily deformed by heating during heat fusion. Therefore, in the examples of FIG. 5 and 6, a short circuit between the metal layer 102 and the lead conductor 1 or the lead conductor 11 is prevented.

In the example of Figure 6, a gap 105 occurs between the sealant layer 104 and the cross-linking layer 41 near the end of the lead conductor 11, while in the example of Figure 5, the space between the sealant layer 104 and the intermediate layer 4 near the end of the lead conductor 1 (the portion indicated by (105)) is filled with the packaging adhesive layer 5.
By forming the packaging adhesive layer 5 using a polyolefin resin (such as polypropylene resin) that melts when heated during thermal melting, the polyolefin resin (such as polypropylene resin) melts during thermal melting, and can fill the gap that occurs between the sealant layer 104 and the intermediate layer 4 near the end of the lead conductor 1. As a result, problems such as leakage of electrolyte and infiltration of moisture from the outside can be suppressed.

The battery to which the tab lead of the present invention is applicable is not limited to the nonaqueous electrolyte battery described above, but is not particularly limited as long as the enclosed container is formed from a laminate film or laminate material containing a metal foil or a metal layer.

(Preparation of Lead Conductors)
Conductive plates made of the materials shown in the "Conductor: Material" column in Tables 1 and 2 and having the thicknesses shown in the same tables, with a width of 50 mm and a length of 45 mm, were prepared as lead conductors.

(Resin Layer)
1) Using the following resin a), b), or c), a film (layer) having the material and thickness shown in Tables 1 and 2 was formed using a single-layer T-die film molding machine under conditions of an extrusion temperature of 220° C. and a take-up speed of 10 m/min.
a) Admer QE060: Maleic anhydride modified polypropylene, elastic modulus at 200°C: 3.2 MPa, manufactured by Mitsui Chemicals (referred to as "metal adhesive PP" in the table).
b) Noblen FL6747: Polypropylene, elastic modulus at 200°C 4.4 MPa, manufactured by Sumitomo Chemical Co., Ltd. (referred to as "PP" in the table).
c) Noblen S131: Polypropylene, elastic modulus at 200°C: 32 MPa, manufactured by Sumitomo Chemical Co., Ltd. (polypropylene with low fluidity: shown as "PP2" in the table)
The layer indicated as "crosslinked PP" in the table is a layer b) of Noblen FL6747 ("PP"), which was crosslinked by irradiating a layer of Noblen FL6747 ("PP") with an electron beam irradiation device at an acceleration voltage of 120 kV to a dose of 120 kGy. The elastic modulus of the resin crosslinked under the same conditions at 200°C is 19 MPa.
Each layer of film was 10 mm wide and was stacked in the order shown in Tables 1 and 2 (from the first layer to the fifth layer in the table), and heat-pressed using a laminator to prepare a resin layer (laminated film).

(Making tab leads)
The resin layers prepared by the above-mentioned method were laminated on both surfaces of the lead conductor so that the first layer was on the laminate film side (outermost layer: packaging adhesive layer), and then thermocompression bonding (heat pressing) was performed to prepare a tab lead.

(Preparation of Laminate Film)
A sealant (sealant layer of a laminate film) made of the material (PP with a melting point of 135°C) shown in Tables 1 and 2 and having a thickness shown in the same tables is attached to an aluminum foil having a thickness shown in Tables 1 and 2 by extrusion lamination molding (an adhesive PP resin is applied to the interface with the aluminum foil).
Thereafter, a solvent adhesive was applied to the aluminum foil side, and a polyamide film having a thickness shown in Tables 1 and 2, which was produced by extrusion molding, was laminated thereon, and the polyamide film was then attached by roll compression at room temperature. Thereafter, the laminate film was cut into an A3 size rectangle to produce a laminate film.

The laminate film obtained above was placed on both surfaces of the tab lead obtained above, with the sealant facing the tab lead side, and then thermocompression bonding (hot pressing) was performed. The embeddability of the obtained samples near the ends of the conductor was evaluated using the following method. The results are shown in the "Embeddability" column of Tables 1 and 2.

(Method of determining filling ability)
The conductor end of the sample was cut out, embedded in epoxy resin, and polished with a polishing machine. The polished cross section was observed under an optical microscope at 10 to 100 times magnification to check for the presence or absence of voids of 1 μm or more in diameter. As a result of the observation, if no voids were found, it was rated as good, and if voids were found, it was rated as bad, and these are shown in the "Fillability" column of Tables 1 and 2.

The results shown in Tables 1 and 2 show that in Experiments 2 to 4 and 6 to 10, in which a layer made of a non-crosslinked resin (PP) and having an elastic modulus at 200°C in the range of 0.1 MPa or more and 15 MPa or less was provided on the outside (the laminate film side to be heat-sealed) of the layer made of a crosslinked resin (PP), the generation of voids between the laminate film and the tab lead when the laminate film and the tab lead are heat-sealed was suppressed, and the filling ability was improved.
On the other hand, in Experiments 1 and 5 in which a layer made of a non-crosslinked resin (PP) and having an elastic modulus at 200°C in the range of 0.1 MPa to 15 MPa was not provided and a layer made of a crosslinked resin (PP) was the outermost layer (the layer in contact with the laminate film to be heat-sealed: packaging adhesive layer), and in Experiment 11 in which the outermost layer side was made of a non-crosslinked resin (PP) but had a layer with an elastic modulus at 200°C exceeding 15 MPa, voids were observed and filling properties were poor.

In other words, in order to obtain excellent embedding properties, it is necessary to provide a layer made of a non-crosslinked resin (PP) having an elastic modulus of 0.1 MPa or more and 15 MPa or less at 200°C on the outside of the layer made of crosslinked resin (PP).

However, even among Experiments 2-4 and 6-10 in which filling ability was improved, in Experiment 8, in which the sum of the thickness of the non-crosslinked layer (packaging adhesive layer) on the outside of the layer (middle layer) made of crosslinked resin (PP) and the thickness of the sealant layer was less than 80 μm (packaging adhesive layer (outermost layer: PP) thickness 25 μm, sealant layer thickness 50 μm, totalling 75 μm), filling ability was inferior to the other cases, and the occurrence of gaps between the laminate film and the tab lead was suppressed but not sufficiently prevented. These results show that a total thickness of 80 μm or more for the packaging adhesive layer and the sealant layer of the laminate film is preferable.

Reference Signs List 1, 11 Lead conductor 2, 21 Resin layer 3, 31 Conductor adhesive layer 4 Intermediate layer 41 Cross-linked layer 5 Packaging adhesive layer A Heat-sealed portion 6 Positive electrode plate 7 Negative electrode plate 8 Tab lead 9 Resin layer 10 Heat-sealed portion 51 Enclosed container 52 Non-aqueous electrolyte 53 Sealed portion 101 Laminate film 102 Metal layer (aluminum foil)
103 Polyamide resin layer 104 Sealant layer (polypropylene resin)
105 Void

Claims (9)

A battery tab lead including a lead conductor and a resin layer covering a heat-sealed portion of the lead conductor,
the resin layer has a conductor adhesive layer provided on the lead conductor side, an intermediate layer, and a packaging adhesive layer provided on the intermediate layer on the opposite side to the conductor adhesive layer side,
The conductor adhesive layer contains a polyolefin resin,
the intermediate layer contains a crosslinked polyolefin resin, and the packaging material adhesive layer contains a polyolefin resin and has an elastic modulus at 200° C. of 0.1 MPa or more and 15 MPa or less. The battery tab lead according to claim 1, wherein the packaging adhesive layer has an elastic modulus of 1.0 MPa or more and 10 MPa or less at 200°C. The battery tab lead according to claim 1 or 2, wherein the polyolefin resin forming the intermediate layer is a polypropylene resin or a resin composition containing a polypropylene resin and a thermoplastic elastomer in a mass ratio of 90:10 to 60:40. The battery tab lead according to claim 3, wherein the thermoplastic elastomer is at least one resin selected from ethylene-butene copolymer resin, ethylene-octene copolymer resin, olefin crystalline-ethylene-butene-olefin crystalline block polymer, and PP-based elastomer. A battery tab lead according to any one of claims 1 to 4, wherein the polyolefin resin contained in the conductor adhesive layer is a maleic anhydride modified polyolefin. A battery tab lead according to any one of claims 1 to 5, wherein the thickness of the conductor adhesive layer is 20 μm or more and 250 μm or less. A battery tab lead according to any one of claims 1 to 6, wherein the thickness of the packaging adhesive layer is 0.1 to 1.0 times the thickness of the lead conductor. The battery tab lead according to claim 7, wherein the thickness of the packaging adhesive layer is 10 μm or more and 200 μm or less. The battery tab lead according to claim 1 , wherein the resin layer comprises three or more layers.