LEAD MEMBER, PACKAGE OF SECONDARY BATTERY, AND METHOD FOR PRODUCING LEAD MEMBER

A lead member for a secondary battery includes a conductor, and a covering material. The conductor has an upper surface and a lower surface that extend in a length direction and a width direction and are opposite to each other, and a first side surface and a second side surface that extend in the length direction and a thickness direction, connect the upper surface to the lower surface, and are opposite to each other. The covering material is formed by sticking a plurality of insulating films together to surround the upper surface, the first side surface, the lower surface, and the second side surface. Each of the plurality of insulating films includes an inner layer and an outer layer, in an order from a side closer to the conductor. The lead member includes a first insulator and a second insulator on the first side surface and the second side surface of the conductor respectively, in an area surrounded by the covering material of the conductor. The first insulator and the second insulator have a lower melting point than the inner layer. The first insulator and the second insulator are placed to be separated from each other.

TECHNICAL FIELD

This application is based upon and claims priority to Japanese Patent Application No. 2020-024013, filed Feb. 17, 2020, the entire contents of which are incorporated herein by reference.

The present disclosure relates to a lead member, a package of a secondary battery, and a method for manufacturing the lead member.

BACKGROUND ART

A body of a secondary battery is accommodated and packaged in an enclosing casing and is used. Such a secondary battery package includes a lead member. The lead member is used to lead the terminals of the positive and negative electrodes of the secondary battery body accommodated in the enclosing casing to the outside of the enclosing casing. The lead member is configured such that an insulating film is bonded to a portion of a conductor to cover the periphery of the conductor.

In such a lead member, one end of the conductor is electrically connected to one electrode, and the other end of the conductor is led out from the enclosing casing, thereby allowing electrical connection with the electrode via the lead member (for example, Patent Document 1).

RELATED ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

In the present disclosure, a lead member for a secondary battery, including a conductor, and a covering material, is provided. The conductor has an upper surface and a lower surface that extend in a length direction and a width direction and are opposite to each other, and a first side surface and a second side surface that extend in the length direction and a thickness direction, connect the upper surface to the lower surface, and are opposite to each other. The covering material is formed by sticking a plurality of insulating films together to surround the upper surface, the first side surface, the lower surface, and the second side surface. Each of the plurality of insulating films includes an inner layer and an outer layer, in an order from a side closer to the conductor. The lead member includes a first insulator and a second insulator on the first side surface and the second side surface of the conductor respectively, in an area surrounded by the covering material of the conductor. The first insulator and the second insulator have a lower melting point than the inner layer. The first insulator and the second insulator are placed to be separated from each other.

Additionally, in the present disclosure, a method of manufacturing a lead member for a secondary battery is provided. The method includes:

a) a step of preparing a conductor having a first surface and a second surface that are opposite to each other, and a third surface and a fourth surface that are opposite to each other and are orthogonal to the first surface and the second surface;

b) a step of placing insulator materials on a portion of the first surface and a portion of the second surface, the insulator material having an insulating property;

c) a step of placing a first insulating film including a first inner layer and a first outer layer to cover the insulator materials when viewed from the third surface such that the first inner layer faces the third surface;

d) a step of placing a second insulating film including a second inner layer and a second outer layer to cover the insulator materials when viewed from the fourth surface such that the second inner layer faces the fourth surface; and

e) a step of welding the first insulating film and the second insulating film to each other on a first surface side and on a second surface side.

Additionally, in the present disclosure, a method of manufacturing a lead member for a secondary battery is provided. The method includes:

a) a step of preparing a first insulating film including a first inner layer and a first outer layer, and a second insulating film including a second inner layer and a second outer layer;

b) a step of placing first insulator materials on portions of the first inner layer in the first insulating film;

c) a step of preparing a conductor having a first surface and a second surface that are opposite to each other, and a third surface and a fourth surface that are opposite to each other and are orthogonal to the first surface and the second surface;

d) a step of placing the first insulating film such that the first inner layer faces the third surface of the conductor when viewed from the third surface, the first insulator materials being placed on a portion of the first surface of the conductor and a portion of the second surface of the conductor;

e) a step of placing the second insulating film such that the second inner layer faces the fourth surface of the conductor when viewed from the fourth surface; and

f) a step of welding the first insulating film and the second insulating film to each other on a first surface side and on a second surface side.

EMBODIMENT FOR CARRYING OUT THE INVENTION

Problems to be Solved by this Disclosure

There may be a gap between a conductor and an insulating film in a lead member for a secondary battery. To address such a problem, Patent Document 2 proposes a conductor that is processed to have a taper from the upper surface and the lower surface of the conductor to the side surfaces.

However, according to the inventors of the present application, it is often found that the above-described “gap” is still present even when the solution described in Patent Document 2 is adopted.

The present disclosure is made in view of such a background, and it is an object of the present disclosure to provide a lead member that significantly suppresses generation of the gap between the side surface of the conductor and an insulating film. Additionally, it is an object of the present disclosure to provide a package of a secondary battery including such a lead member, and a method of manufacturing such a lead member.

Effect of the Present Disclosure

In the present disclosure, a lead member that significantly suppresses generation of the gap between the side surface of the conductor and the insulating film can be provided. Additionally, in the present disclosure, a package of a secondary battery including such a lead member and a method of manufacturing such a lead member may be provided.

Description of Embodiments of the Present Disclosure

(Lead Member for Conventional Secondary Battery)

First, to better understand the features according to one embodiment of the present disclosure, a configuration of a lead member for a conventional secondary battery will be briefly described with reference toFIG.1.

FIG.1schematically illustrates a cross-section of the lead member for the conventional secondary battery. As illustrated inFIG.1, a lead member1for the conventional secondary battery includes a conductor20and insulating films42.

The insulating films42are placed over and under the conductor20. Additionally, a portion of the conductor20is enclosed between the upper insulating film42and the lower insulating film42by sticking the upper insulating film42and the lower insulating film42to each other.

Although not clearly illustrated inFIG.1, the conductor20has a plate shape. That is, the conductor20has an upper surface22and a lower surface24that are rectangular and opposite to each other, a first side surface26aand a second side surface26bthat are opposite to each other, and a first end surface and a second end surface that are opposite to each other. Here, inFIG.1, the first end and second end surfaces of the conductor20cannot be recognized.

The first side surface26aand the second side surface26b, as well as the first end surface and the second end surface are surfaces connecting the upper surface22to the lower surface24.

FIG.1illustrates a cross-section of lead member1in a direction parallel to the first end surface and the second end surface of the conductor20. InFIG.1, the left and right sides of the conductor20correspond to the first side surface26aand the second side surface26b, respectively.

The upper and lower insulating films42each are formed of two layers and have an inner layer44and an outer layer46. The inner layer44of the insulating film42is formed of a resin material. The outer layer46of the insulating film42is formed of a resin material having a higher melting point than that of the inner layer44and having heat resistance.

When manufacturing such a lead member1, first, the rectangular insulating films42are aligned with each other and placed at predetermined positions on the upper surface22side and the lower surface24side of the conductor20.

InFIG.1, when the right and left direction is referred to as the width direction, the size of each insulating film42in the width direction is selected to be longer than the size of the conductor20in the width direction. Thus, when the insulating films42are placed over and under the conductor20, each insulating film42protrudes from the first side surface26aand the second side surface26bof the conductor20.

Next, in this state, a hot press process is performed on the insulating films42. That is, the insulating films42are pressed from the upper and lower sides (or from the upper side) with heat being applied to the insulating films42.

The hot press process is pertained at a temperature at which the inner layer44of the insulating film42melts but the outer layer46does not melt. Thus, during performing the hot press process, only the inner layer44of each insulating film42melts. Thus, the protruding ends of the inner layers44of the respective insulating films42are welded together with the conductor20being enclosed therebetween.

As a result, as illustrated inFIG.1, protrusions33of the insulating films42are respectively formed on the first side surface26aside and the second side surface26bside of the conductor20. This forms the lead member1.

Here, in the method of manufacturing the conventional lead member1, there may be a case in which the inner layers44do not expand sufficiently during performing the hot press process, and the inner layers44of the insulating films42do not properly contact the desired locations closely on the first side surface26aand the second side surface26bof the conductor20. In this case, as illustrated inFIG.1, gaps55are generated between the first side surface26aof the conductor20and the inner layer44and between the second side surface26bof the conductor20and the inner layer44in the lead member1.

When the lead member1is applied to a package accommodating a secondary battery, such gaps55may cause leakage of the electrolyte from the secondary battery side, leakage of the reaction product generated in the outer package, or the like. Therefore, it is necessary to suppress such gaps55as much as possible.

Especially in recent years, with the increase in the capacity and output of the secondary battery, the increase in the temperature of each member used for the package of the secondary battery is considered as a problem. Additionally, as part of a solution to this, it is examined that the conductor20used in the lead member1is thickened so as to facilitate heat radiation from the secondary battery.

However, in the conventional lead member1, when the conductor20is thickened, the problem of the gap55described above is expected to become more pronounced.

In order to suppress the above-described gap55in the conventional lead member1, it is conceivable that pressing pressure to the insulating sheet40from the upper and lower sides is increased or the temperature of the hot press process is increased so that the inner layer44sufficiently expands to the first and second side surfaces26aand26bof the conductor20during performing the hot press process.

However, such a process may lead to a longer manufacturing process of the lead member1and may cause a decrease in the production efficiency. Additionally, in this case, after the production of the lead member1, a problem that the inner layer44significantly spreads from the outer layer46in a direction from the first end surface to the second end surface of the conductor20or vice versa may occur.

Additionally, as an alternative solution, it is conceivable that the first side surface26aand the second side surface26bof the conductor20are processed to have a taper. However, according to the inventors of the present application, it is often found that even with such processing to have a taper, the gap55is still present in the manufactured lead member1. Further, when the conductor20is thicker, the solution of the taper may obtain insufficient effect.

With respect to the above, in one embodiment of the present disclosure, a lead member for a secondary battery, including a conductor and a covering material, is provided. The conductor has an upper surface and a lower surface that extend in a length direction and a width direction and that are opposite to each other, and a first side surface and a second side surface that extend in the length direction and a thickness direction, connect the upper surface to the lower surface, and are opposite to each other. The covering material is famed by sticking a plurality of insulating films together to surround the upper surface, the first side surface, the lower surface, and the second side surface. Each of the plurality of insulating films includes an inner layer and an outer layer, in an order from a side closer to the conductor. The lead member includes a first insulator and a second insulator on the first side surface and the second side surface of the conductor respectively, in an area surrounded by the covering material of the conductor. The first insulator and the second insulator have a lower melting point than the inner layer. The first insulator and the second insulator are placed to be separated from each other.

Here, in the present application, a term “placed to be separated from each other” with respect to the first and second insulators indicates that the first insulator and the second insulator are not in contact with each other on either the upper surface or the lower surface of the conductor.

Additionally, in one embodiment of the present disclosure, a method of manufacturing a lead member for a secondary battery is provided. The method includes:

a) a step of preparing a conductor having a first surface and a second surface that are opposite to each other, and a third surface and a fourth surface that are opposite to each other and are orthogonal to the first surface and the second surface;

b) a step of placing insulator materials on a portion of the first surface and a portion of the second surface, the insulator material having an insulating property;

c) a step of placing a first insulating film including a first inner layer and a first outer layer s to cover the insulator materials when viewed from the third surface such that the first inner layer faces the third surface;

d) a step of placing a second insulating film including a second inner layer and a second outer layer to cover the insulator materials when viewed from the fourth surface such that the second inner layer faces the fourth surface; and

e) a step of welding the first insulating film and the second insulating film to each other on a first surface side and on a second surface side.

Additionally, in one embodiment of the present disclosure, a method of manufacturing a lead member for a secondary battery is provided. The method includes:

a) a step of preparing a first insulating film including a first inner layer and a first outer layer, and a second insulating film including a second inner layer and a second outer layer;

b) a step of placing first insulator materials on portions of the first inner layer in the first insulating film;

c) a step of preparing a conductor having a first surface and a second surface that are opposite to each other, and a third surface and a fourth surface that are opposite to each other and are orthogonal to the first surface and the second surface;

d) a step of placing the first insulating film such that the first inner layer faces the third surface of the conductor when viewed from the third surface, the first insulator materials being placed on a portion of the first surface of the conductor and a portion of the second surface of the conductor;

e) a step of placing the second insulating film such that the second inner layer faces the fourth surface of the conductor when viewed from the fourth surface; and

f) a step of welding the first insulating film and the second insulating film to each other on a first surface side and on a second surface side.

In one embodiment of the disclosure, the first and second insulators are placed on the first and second side surfaces, respectively, in an area surrounded by the covering material of the conductor. Such a lead member configuration significantly reduces the possibility of generation of the above-described gap55on the first and second side surfaces of the conductor.

Therefore, in one embodiment of the present disclosure, the problem of the gap55that may occur in the conventional lead member1can be significantly reduced or eliminated.

(Lead Member for the Secondary Battery According to One Embodiment of the Disclosure)

Next, a specific configuration example of a lead member for a secondary battery according to one embodiment of the present disclosure will be described with reference toFIG.2andFIG.3.

FIG.2illustrates a schematic top view of the lead member for the secondary battery according to one embodiment of the present disclosure.FIG.3schematically illustrates a cross-section along the I-I line of the lead member for the secondary battery according to one embodiment of the present disclosure illustrated inFIG.2.

As illustrated inFIG.2andFIG.3, a lead member100for the secondary battery (hereinafter referred to as a “first lead member”) according to one embodiment of the present disclosure includes a conductor120and a covering material140.

As illustrated inFIG.2, the conductor120has a plate shape. The conductor120has an upper surface122and a lower surface124that are rectangular and opposite to each other, a first side surface126aand a second side surface126bthat are opposite to each other, and a first end surface128aand a second end surface128bthat are opposite to each other. The first side surface126aand the second side surface126b, and the first end surface128aand the second end surface128bare surfaces connecting the upper surface122to the lower surface124.

Here, for the purpose of clarification of the description, in the present application, hereinafter, the X direction inFIG.2andFIG.3is referred to as the “length direction,” the Y direction is referred to as the “width direction,” and the Z direction is referred to as the “thickness direction”. Thus, for example, the “width direction” (the Y direction) of the conductor120is perpendicular to the “length direction” (the X direction) and the “thickness direction” (the Z direction).

Additionally, in the present application, the distance from the first end surface128ato the second end surface128bin the length direction of the conductor120is referred to as the “length L” of the conductor120. The distance from the first side surface126ato the second side surface126bof the conductor120is referred to as the “width W” of the conductor120. Furthermore, the distance from the upper surface122to the lower surface124of the conductor120is referred to as the “thickness t” of the conductor120.

Here, when the distance from the first end surface128ato the second end surface128bin the conductor120is not constant, the “length L” of the conductor120represents the maximum size. The same applies to the “width W” and the “thickness t” of the conductor120.

The covering material140is placed to surround the periphery of the conductor120in a portion in the length direction (in the X direction), except for the first end surface128aand the second end surface128bof the conductor120. Here, in the present application, the area surrounded by the covering material140of the conductor120is also referred to as the “covered portion”.

In practice, the covering material140is formed by welding multiple insulating films together with the conductor120being interposed therebetween.

For example, in the example illustrated inFIG.2andFIG.3, the covering material140is famed of two insulating films142, each including an inner layer144and an outer layer146.

That is, the covering material140is formed by placing two insulating films142on the upper surface122side and the lower surface124side of the conductor120such that the inner layers144are placed inward and welding the inner layers144of both of the insulating films142to each other.

In the example illustrated inFIG.2andFIG.3, two insulating films142are joined on the first side surface126aside and the second side surface126bside of the conductor120. Thus, protrusions133of the covering material140are formed on the first side surface126aside and the second side surface126bside of the conductor120.

Here, as illustrated inFIG.3, in the first lead member100, a first additional layer156a(also referred to as a “first insulator”) is placed on the first side surface126aof the conductor120. Additionally, a second additional layer156b(also referred to as a “second insulator”) is placed on the second side surface126bof the conductor120.

Because of the presence of such a first additional layer156a, in the first lead member100, a gap is unlikely to exist between the first side surface126aof the conductor120and the inner layers144of the upper and lower insulating film142that are close to the first side surface126a. Similarly, because of the presence of the second additional layer156b, a gap is unlikely to exist between the second side surface126bof the conductor120and the inner layers144of the upper and lower insulating films142that are close to the second side surface126b.

As a result, the first lead member100can significantly suppress the problem of the gap55in the conventional lead member1.

Next, each component used in the lead member according to one embodiment of the present disclosure will be described in more detail. Here, for the purpose of clarification, the first lead member100illustrated inFIG.2andFIG.3will be used as an example to describe the components. Accordingly, the reference sins illustrated inFIG.2andFIG.3are used to represent respective components.

The conductor120may be formed of any material as long as a good electrical connection is formed between electrode of the secondary battery or leads of the secondary battery.

The conductor120may be formed of a metal, such as aluminum or copper, for example. Additionally, the conductor120may be formed by placing various coating films on a surface of a base material. Such coating films include, for example, metal plating films. In this case, the base material may be electrically conductive or have an insulating property.

The length of the conductor120(see the length L inFIG.2) may be in the range of, although not limited to, 20 mm to 90 mm, for example. Additionally, the width of the conductor120(see the width W inFIG.2) may be in the range of, although not limited to, 10 mm to 100 mm, for example. Further, the thickness t of the conductor120may be in the range of, although not limited to, 0.1 mm to 3 mm, for example.

Particularly, the first lead member100can significantly suppress generation of the gap55that may occur in the conventional lead member1even if the conductor120is thickened.

Additionally, at least either the first side surface126aor the second side surface126bof the conductor120may be tapered. In this case, generation of the gap can be further suppressed at the first side surface126aand the second side surface126bof the conductor120.

The covering material140is formed of multiple insulating films142as described above. In the example illustrated inFIG.2andFIG.3, the covering material140is formed by sticking two upper and lower insulating films142together at the first side surface126aand the second side surface126bof the conductor120.

However, this is only one example, and the joints of the two insulating films142are not particularly limited. Additionally, the covering material140may be formed of three or more insulating films142. In the covering material140, the length of the protrusion133in the width direction, i.e., the size of the protrusion from the first side surface126aor the second side surface126bof the conductor120(see the size E illustrated inFIG.2), is not particularly limited, but is, for example, in the range of 2 mm to 25 mm. Additionally, the size of the covering material140in the length direction, i.e., the size B illustrated inFIG.2, is not particularly limited, but is, for example, in the range of 5 mm to 20 mm.

The insulating film142has a multi-layer structure and includes at least two layers of the inner layer144and the outer layer146. However, the insulating film142may include three or more layers.

The thickness of the insulating film142may be appropriately selected. Particularly, it is preferable that the thickness of the insulating film142is 20 μm or greater because a failure such as breakage caused by excessive thickness is unlikely to occur. However, if the insulating film142is too thick, this causes the first lead member100to become thicker. Therefore, the thickness of the insulating film142is preferably 20 μm or greater and 100 μm or less, and more preferably 30 μm or greater and 60 μm or less.

The inner layer144of insulating film142is typically formed of an insulating resin.

The inner layer144may contain, for example, 40 wt % or greater of polyolefin resin.

Examples of the polyolefin resin include polyethylene, polypropylene, ionomer resins, modified polyolefins, and the like. Particularly, adhesive polyolefin resins are preferable, from the viewpoint of the adhesion to the conductor120.

The adhesive polyolefin resins refer to polyolefin resins that are modified with carboxylic acid, such as maleic acid, acrylic acid, methacrylic acid and maleic anhydride, epoxy, or the like to have an adhesive functional group. Particularly, maleic anhydride-modified polyolefin resins are preferable because of its excellent adhesion to the conductor120and a sealing property.

The resin component contains an acid-containing polyolefin resin obtained by incorporating an acid-containing group into the polyolefin resin.

The polyolefin resin is a synthetic resin made by polymerizing or copolymerizing olefin-based monomers having radical polymerizable unsaturated double bonds. The olefinic monomers are not particularly limited, but examples of the olefinic monomers include alpha-olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methyl-1-pentene, conjugated dienes such as butadiene, isoprene, and the like. The olefinic monomers may be used singly or in combination of two or more species.

Examples of the polyolefin resin include polyethylene, such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene; polypropylene, such as homo polypropylene, a block copolymer of polypropylene, a random copolymer of polypropylene; terpolymers of ethylene-butene-propylene, and the like. Among these polyolefins, polyethylene and polypropylene are preferable.

Particularly, the inner layer144preferably contains 40 wt % or greater of an acid-modified polypropylene component, such as maleic anhydride-modified polypropylene.

The outer layer146of the insulating film142is also typically formed of an insulating resin. However, the outer layer146has a higher melting point than the inner layer144and is formed of a resin having heat resistance when a process of sticking the insulating films together is performed.

The outer layer146may include, for example, polyethylene terephthalate (PET) or may be formed of PET.

The thickness of the inner layer144normally changes in accordance with locations. While the inner layer144is relatively thick on sides facing the upper surface122and the lower surface124of the conductor120(hereinafter referred to as the “upper and lower sides”), the inner layer144tends to be relatively thin on sides facing the first side surface126aand the second side surface126bof the conductor120(hereinafter referred to as the “lateral sides”).

The thickness of the inner layer144on the upper and lower sides may be in the range of, for example, 1 μm to 10 μm, and preferably in the range of 2 μm to 5 μm. Also, the thickness of the inner layer144may be thinner on the lateral sides than the thickness on the upper and lower sides.

With respect to the above, the outer layer146tends to change less in thickness in accordance with locations than the inner layer144. The thickness of the outer layer146is in the range of, for example, 30 mm to 60 mm, on the upper and lower sides and the lateral sides.

The inner layer144has a higher melting point than the first additional layer156aand the second additional layer156b. The inner layer144preferably has a melting point in the range of 135° C. to 160° C., and more preferably has a melting point in the range of 140° C. to 160° C.

The melting point of the inner layer144is equal to or greater than 135° C., so that the resin component of the inner layer144flows, during heating for the formation of the covering material140, thereby sufficiently increasing the adhesion between the conductor120and the insulating film142. When the melting point of the inner layer144is 160° C. or greater, it is necessary to apply a corresponding amount of heat to obtain fluidity. Therefore, it is desirable that the melting point of the inner layer144is 160° C. or less.

Here, the melting point of the inner layer144is measured by a differential scanning calorimetry (DSC).

In general, in the first lead member100, with respect to the size of the insulating film142in the length direction (the X direction), the size of the inner layer144tends to be longer in than the size of the outer layer146.

This is because the inner layer144melts during sticking together of the insulating films142in the hot press process and tends to stretch in the length direction (the X direction).

Due to such a difference in the properties of the inner layer144and the outer layer146, what is called a “spread” phenomenon, in which the inner layer144protrudes from the outer layer146along the length direction (the X direction) in the covering material140of the manufactured first lead member100, may occur.

Particularly, in the conventional lead member1, in order to reduce the risk of generation of the gap55, the pressing pressure to the insulating film42from the upper and lower sides may be increased more than necessary, or the temperature of the hot press process may be increased more than necessary, during the hot press process in the manufacturing process.

However, when such a processing condition is employed, in the obtained lead member1, the “spread” of the inner layer44with respect to the outer layer46becomes more pronounced. Additionally, when such a high temperature and high pressure condition is employed, a longer time is required to manufacture the lead member1, which may cause a decrease in the production efficiency.

With respect to the above, in the first lead member100, the first additional layer156aand the second additional layer156bare respectively placed on the first side surface126aand the second side surface126bof the conductor120. Thus, the conventional gap55is unlikely occur at the first side surface126aand the second side surface126bof the conductor120.

Thus, in the case of the first lead member100, it is not necessary to press or heat the inner layer144more than necessary during the formation of the covering material140, and thus the insulating films142can be joined at lower pressing pressure and/or a lower temperature.

Therefore, in the first lead member100, the “spread” of the inner layer144in the length direction (the X direction) can be significantly suppressed in comparison with the conventional lead member1.

For example, the spread amount P of the inner layer144represented by “P” inFIG.2can be 2 mm or less.

Additionally, in this case, when the insulating films142are joined, an extreme high temperature and high pressure condition is not required, and the time for manufacturing the first lead member100is shortened, so that the first lead member100can be manufactured more efficiently.

In the first lead member100, the size of the inner layer144of the insulating film142in the length direction (the X direction) is in the range of, for example, 5 mm to 20 mm. With respect to this, the size of the outer layer146of insulating film142in the length direction (X direction) is in the range of, for example, 5 mm to 22 mm.

The first additional layer156ais famed of a material having a lower melting point than that of the inner layer144. This allows the first additional layer156ato be more fluidized than the inner layer144when sticking two insulating films142together. As a result, the first additional layer156acan be more uniformly and rapidly distributed on the first side surface126aof the conductor120.

For example, the first additional layer156ahas a melting point in the range of 110° C. to 140° C. and preferably has a melting point in the range of 120° C. to 135° C.

The melting point of the first additional layer156ais measured by a differential scanning calorimetry (DSC).

The first additional layer156amay be formed of, for example, an insulating resin. Examples of the resin included in the first additional layer156ainclude, although not limited to, a polyolefin resin.

Examples of the polyolefin resin include polyolefins, cyclic polyolefins, acid modified polyolefins, and acid modified cyclic polyolefins. That is, the resin forming the first additional layer156amay or may not contain a polyolefin backbone, and preferably contain a polyolefin backbone.

It can be found whether the resin forming the first additional layer156acontains the polyolefin backbone, by infrared spectroscopy, gas chromatography mass spectrometry, or the like, for example.

For example, when maleic anhydride-modified polyolefins are measured by infrared spectroscopy, peaks derived from maleic anhydride are detected at wave numbers in vicinity of 1760 cm−1and 1780 cm−1. However, peaks may not be detected if the degree of acid modification is low. In this case, the presence or absence of the polyolefin backbone is analyzed by nuclear magnetic resonance spectroscopy.

Specific Examples of such polyolefins include polyethylene, such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene; polypropylene, such as homo polypropylene, a block copolymer of polypropylene (e.g., a block copolymer of propylene and ethylene), a random copolymer of polypropylene (e.g., a random copolymer of propylene and ethylene); a terpolymer of ethylene-butene-propylene, and the like. Among these polyolefins, polyethylene and polypropylene are preferable.

The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer. Examples of the olefin being a constituent monomer of the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, isoprene, and the like. Examples of the cyclic monomer being a constituent monomer of the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic dienes, such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, norbornadiene and the like. Among these polyolefins, cyclic alkenes are preferable and norbornenes are more preferable. The acid-modified polyolefin is a polymer modified by performing block or graft polymerization on the polyolefin with an acid component such as a carboxylic acid. Examples of the acid component used for the modification include carboxylic acids such as maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, itaconic anhydride, and the like, or anhydrides thereof.

The acid-modified cyclic polyolefin is a polymer obtained by performing copolymerization by replacing a portion of the monomers constituting the cyclic polyolefin with an α,β-unsaturated carboxylic acid or its anhydride, or by performing block or graft polymerization on the cyclic polyolefin with an α,β-unsaturated carboxylic acid or its anhydride. The carboxylic acid modified cyclic polyolefin is substantially the same, as described above. The carboxylic acid used for the modification is substantially the same as that used for the modification of the acid-modified polyolefin.

Among these resin components, polyolefins such as polypropylene and carboxylic acid modified polyolefins are preferable, and polypropylene and acid modified polypropylene are more preferable.

The first additional layer156amay contain, for example, 40 wt % or greater of a polyolefin resin, such as an acid modified polyolefin.

Other materials contained in the first additional layer156aare not particularly limited. The first additional layer156amay contain, for example, a thermoplastic resin having a lower melting point than that of a polypropylene resin, such as a low density polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-acrylate ester copolymer, or the like, a copolymer of polybutene and ethylene and/or butene and alpha-olefin; a low melting point polypropylene, such as a block copolymer, a random copolymer, a graft copolymer, or the like known as a copolymer of propylene and alpha-olefin; a resin such as a low melting point polyester in which at least one portion of a terephthalic acid unit is substituted with a dicarboxylic acid, such as isophthalic acid, adipic acid, phthalic acid, or the like in polyethylene terephthalate or polybutylene terephthalate, a synthetic rubber, such as ethylene-propylene rubber, ethylene-propylene-diene rubber, styrene-butadiene rubber, polybutadiene rubber, chlorinated polyethylene, polyisobutylene, or mixtures thereof; or thermosetting adhesives such as isocyanate-based adhesives or the like.

The second additional layer156bis substantially the same as the first additional layer156a.

Here, the first additional layer156aand the second additional layer156bare not necessarily formed of the same material. However, from the viewpoint of process simplification, it is preferable that the first additional layer156aand the second additional layer156bare formed of the same material.

(Application Example of the Lead Member According to One Embodiment of the Disclosure)

Next, an application example of the lead member according to one embodiment of the present disclosure will be described. Here, as the application example of the lead member according to one embodiment of the present disclosure, a package of a secondary battery is used, and a configuration thereof will be described. Additionally, the configuration of the package of the secondary battery will be described herein by using the first lead member100as an example of the lead member according to one embodiment of the present disclosure.

FIG.4andFIG.5schematically illustrate a configuration example of the package of the secondary battery including the lead member according to one embodiment of the present disclosure.FIG.4is a schematic perspective view of the package of the secondary battery including the lead member according to one embodiment of the present disclosure.FIG.5is a cross-sectional view of the package illustrated inFIG.4along the line II-II.

As illustrated inFIG.4andFIG.5, a secondary battery package200includes a secondary battery (not illustrated), such as a lithium-ion secondary battery, an enclosing casing210accommodating the secondary battery, and two first lead members100.

The enclosing casing210serves to hermetically accommodate the secondary battery inside. Each lead member100is electrically connected to one of the electrodes of the secondary battery and serves to lead the two electrode terminals to the outside.

As illustrated inFIG.5, the first lead member100is electrically connected, near a second end surface128b, to a lead204extending from the secondary battery side. Although not apparent fromFIG.5, the lead204is electrically connected to one electrode of the secondary battery. Thus, the conductor120of each first lead member100can be utilized as an electrical connection terminal to a corresponding electrode of the secondary battery.

As illustrated inFIG.5, the enclosing casing210includes at least three layers: an innermost layer212, an intermediate layer214, and an outermost layer216. Among these, the innermost layer212is formed of a material that is resistant to the electrolyte of the secondary battery, such as a polyolefin resin. Additionally, the intermediate layer214is formed of metal such as, aluminum, copper, and stainless steel. Further, the outermost layer216is formed of a resin, such as, polyethylene terephthalate (PET), to protect the intermediate layer214.

The enclosing casing210is foamed by, for example, performing heat fusion on two multilayered films arranged to cover the secondary battery from above and below along the outer periphery. This forms a seal region211along the periphery of the enclosing casing210, as illustrated inFIG.4.

Additionally, the second end surface128bside of the first lead member100is inserted in advance between the multilayer films before the heat fusion is performed on the two multilayer films, so that the first lead member100is joined with the respective multilayer films during the heat fusion of the multilayer films. In this case, the first lead member100is placed with respect to the two multilayered films such that the first lead member100is bonded to the multilayer films at the position of the covering material140.

Thus, as illustrated inFIG.5, each of the first lead members100can be placed with respect to the enclosing casing210such that the first end surface128ais led out of the enclosing casing210and the second end surface128bis introduced into the enclosing casing210. Additionally, the enclosing casing210can be bonded at the position of the covering material140of the first lead member100.

In such a secondary battery package200, the first lead member100is applied as the lead member. Thus, in the secondary battery package200, the possibility of leakage of the electrolyte of the secondary battery from the side of the conductor of the lead member or leakage of reaction products generated inside the enclosing casing210through the gap in the lead member can be significantly suppressed.

(Method of Manufacturing the Lead Member According to One Embodiment of the Disclosure)

Next, an example of a method of manufacturing the lead member according to one embodiment of the present disclosure will be described with reference toFIGS.6to11.FIG.6schematically illustrates a flow of the method of manufacturing the lead member) according to one embodiment of the present disclosure (hereinafter, referred to as a “first manufacturing method”. Additionally,FIGS.7to11each schematically illustrate one step of the first manufacturing method.

As illustrated inFIG.6, the first manufacturing method includes:

(1) a step of preparing a conductor having an upper surface and a lower surface that are opposite to each other and a first side surface and a second side surface that are opposite to each other (step S110);

(2) a step of placing additional layer materials having an insulating property on a portion of the first side surface and a portion of the second side surface (step S120);

(3) a step of placing a first insulating film including a first inner layer and a first outer layer such that the additional layer materials are covered when viewed from the upper surface and the first inner layer faces the upper surface (step S130);

(4) a step of placing a second insulating film including a second inner layer and a second outer layer such that the additional layer materials are covered when viewed from the lower surface and the second inner layer faces the lower surface (step S140); and

(5) a step of welding the first insulating film and the second insulating film to each other on the first side surface side and on the second side surface side (step S150).

Each step will be described below. For the purpose of clarification, the first manufacturing method will be described by using the first lead member100illustrated inFIG.2andFIG.3as an example of the lead member. Accordingly, the reference signs illustrated inFIG.2andFIG.3are used to represent respective members.

First, the conductor120is prepared. The conductor120has a plate form. As described above, the conductor120has the upper surface122, the lower surface124, the first side surface126a, the second side surface126b, the first end surface128a, and the second end surface128b.

The thickness of the conductor120is in the range of, for example, 0.1 mm to 3 mm, but is not particularly limited. Particularly, it should be noted that the first manufacturing method is also applicable to the relatively thick conductor120.

The first side surface126aand/or the second side surface126bmay be processed to have a taper. However, the tapering process is not required for the first manufacturing method.

Next, additional layer materials (also referred to as “insulator materials”), which will be the first additional layer156aand the second additional layer156blater, are prepared.

The additional layer materials include an insulating resin. The examples of the insulating resin include resins described in the above section (the first additional layer156aand the second additional layer156b). Particularly, the additional layer material preferably contains 40 wt % or greater of polyolefin.

Here, it is preferable that the additional layer material is formed of a resin having a melting point lower than that of the resin forming the inner layer of the insulating film, which will be described later. In this case, the additional layer material can be sufficiently fluidized during performing the hot press process in the subsequent process. As a result, the additional layer material can be more uniformly and rapidly distributed to the first side surface126aand the second side surface126bof the conductor120.

Next, the additional layer material is placed on each of the first side surface126aand second side surface126bof the conductor120(hereinafter collectively referred to as “side surfaces126aand126b”).

FIG.7andFIG.8schematically illustrate a state in which an additional layer material152is placed on each of the first side surface126aand the second side surface126bof the conductor120. Here,FIG.7is a top view of the conductor120.FIG.8is a cross-sectional view along the III-III line ofFIG.7.

A method of placing the additional layer material152is not particularly limited. The additional layer materials152may be placed on the side surfaces126aand126bof the conductor120, for example, by a method of applying paste with a brush or the like, a method of spraying a liquid or a dispersion liquid containing a liquid and a solid, a method of printing ink with ink jet printing, or the like. In these methods, the additional layer material152can be placed relatively easily.

Next, a first insulating film142aand a second insulating film142bare prepared. The first insulating film142aand the second insulating film142beach include the inner layer144and the outer layer146.

Additionally, as illustrated inFIG.9andFIG.10, the first insulating film142ais placed on the upper side of the conductor120to be opposite to the upper surface122of the conductor120, and the second insulating film142bis placed on the lower side of the conductor120to be opposite to the lower surface124of the conductor120. The first insulating film142aand the second insulating film142bare placed such that the respective inner layers144are on the conductor120side.

Here,FIG.9is a schematic view of the conductor120sandwiched between the first insulating film142aand the second insulating film142b, viewed from the upper surface122side. Additionally,FIG.10is a virtual cross-sectional view of the assembly ofFIG.9along the IV-IV line.

As illustrated inFIG.9, the first insulating film142aand the second insulating film142bare arranged to include the portions of the side surfaces126aand126bwhere the additional layer materials152are placed when viewed from the upper surface122side of the conductor120. Additionally, the first insulating film142aand the second insulating film142bare placed such that the first insulating film142aand the second insulating film142boverlap each other when viewed from the upper surface122side of the conductor120.

Next, the hot press process is performed on the first insulating film142aand the second insulating film142bin the directions indicated by the arrows F ofFIG.10.

The hot press process causes the first insulating film142ato tightly contact the upper surface122of the conductor120. Additionally, the second insulating film142bis caused to tightly contact the lower surface124of the conductor120.

Additionally, the inner layer144of the first insulating film142aand the inner layer144of the second insulating film142bare welded on sides of the side surfaces126aand126bof the conductors120. As a result, the first insulating film142aand the second insulating film142bare joined to form the covering material140so as to surround a portion of the conductor120.

Here, the additional layer materials152are placed on the side surfaces126aand126bof the conductor120. These additional layer materials152are melted or are fluidized during performing the hot press process. Thus, after performing the hot press process, the first additional layer156acan be formed between the first side surface126aof the conductor120and the inner layers144. The second additional layer156bcan also be formed between the second side surface126bof the conductor120and the inner layers144.

This produces the first lead member100having a cross-sectional configuration as illustrated inFIG.11.

As illustrated inFIG.11, the first lead member100manufactured by the first manufacturing method can significantly reduce the gaps between the side surfaces126aand126bof the conductor120and the inner layers144of the covering material140, which may be generated in the conventional lead member1.

Additionally, as described above, in the conventional lead member1, in order to reduce the risk of generating the gap55, pressing pressure to the insulating film42from the upper and lower sides may be increased more than necessary, or the temperature of the hot press process may be increased more than necessary during the hot press process in the manufacturing process.

However, when such a processing condition is employed, in the obtained lead member1, the “spread” of the inner layer44with respect to the outer layer46becomes more pronounced. Additionally, when such a high temperature and high pressure condition is employed, a longer time is required to manufacture the lead member1, which may cause a decrease in the production efficiency.

In contrast, in the first manufacturing method, in step S150, during the hot press process, there is no need to apply pressing pressure or heat to the inner layer144more than necessary, and the first and second insulating films142aand142bcan be stuck together at lower pressing pressure and/or lower temperature. Thus, in the first manufacturing method, the first lead member100, in which the “spread” of the inner layer144in the length direction (the X direction) is significantly suppressed in comparison with the conventional lead member1, can be manufactured.

Additionally, in the first manufacturing method, when the first and second insulating films142aand142bare joined, the high temperature and high pressure conditions are not required, and thus the production time is shortened, so that the first lead member100can be manufactured more efficiently.

(Method of Manufacturing a Lead Member According to Another Embodiment of the Disclosure)

Next, a method of manufacturing a lead member according to another embodiment of the present disclosure will be described with reference toFIGS.12to14.

FIG.12schematically illustrates a flow of the method of manufacturing the lead member according to another embodiment of the present disclosure (hereinafter referred to as a “second manufacturing method”). Additionally,FIG.13andFIG.14each schematically illustrate one step of the second manufacturing method.

As illustrated inFIG.12, the second manufacturing method includes:

(1) a step of preparing a first insulating film including a first inner layer and a first outer layer, and a second insulating film including a second inner layer and a second outer layer (step S210);

(2) a step of placing additional layer materials at two predetermined positions of the first inner layer in the first insulating film (step S220);

(3) a step of preparing a conductor having an upper surface and a lower surface that are opposite to each other and a first side surface and a second side surface that are opposite to each other (step S230);

(4) a step of placing the first insulating film such that the first inner layer faces the upper surface of the conductor when viewed from the upper surface, the additional layer materials being placed on a portion of the first side surface and a portion of the second side surface of the conductor (step S240);

(5) a step of placing the second insulating film such that the second inner layer faces the lower surface of the conductor when viewed from the lower surface (step S250); and

(6) a step of welding the first insulating film and the second insulating film to each other on the first side surface side and the second side surface side (step S260).

Each step will be described below. For the purpose of clarification, the second manufacturing method will be described by using the first lead member100illustrated inFIG.2andFIG.3as an example of the lead member. Accordingly, reference signs illustrated inFIG.2andFIG.3are used to represent respective members.

First, the first insulating film142aand the second insulating film142b, which will later become the covering material140, are prepared. The first insulating film142aand the second insulating film142beach include the inner layer144and the outer layer146.

The first insulating film142aand the second insulating film142bmay have the same configuration as the first insulating film142aand the second insulating film142bin the first manufacturing method described above, respectively.

Next, the additional layer materials are placed at two positions on the inner layer144of the first insulating film142a.

FIG.13illustrates a top view of the first insulating film142a.FIG.13is a drawing of the first insulating film142aviewed from the inner layer144side.

As illustrated inFIG.13, the first insulating film142ahas additional portions formed in stripes and arranged perpendicular to an extending axial direction (the Y direction) of the first insulating film142aat two positions along the extending axial direction. These additional portions formed in stripes are referred to as a first additional layer material162caand a second additional layer material162cbin order from the left side ofFIG.13.

The first additional layer material162caand the second additional layer material162cbare formed of a material substantially the same as that of the additional layer material152used for the side surfaces126aand126bof the conductor120in the above-described first manufacturing method.

Particularly, it is preferable that the first additional layer material162caand the second additional layer material162cbare formed of a resin having a melting point lower than that of the inner layer144. In this case, the first additional layer material162caand the second additional layer material162cbcan be sufficiently fluidized during performing the hot press process in subsequent steps.

Such a first additional layer material162caand a second additional layer material162cbmay be placed on the inner layer144of the first insulating film142aby, for example, coating or ink jet printing.

The positions where the first additional layer material162caand the second additional layer material162cbare placed in the first insulating film142aare selected to correspond to the width and relative position of the conductor120used in the subsequent step S230. For example, when the width of the conductor120is W, the distance between the first additional layer material162caand the second additional layer material162cbmay be set in the range of W±1 mm.

Additionally, for example, in step S220, when the conductor120is placed substantially in the center of the first insulating film142ain the width direction (the Y direction inFIG.13), the first additional layer material162caand the second additional layer material162cbmay be placed approximately at an equal distance from the center of the first insulating film142ain the width direction (the Y direction inFIG.13).

Here, similarly in the second insulating film142b, a third additional layer material162daand a fourth additional layer material162dbmay be placed at two positions on the inner layer144(seeFIG.14).

In this case, even when the first side surface126aand the second side surface126bof the conductor120are relatively thick, the additional layer materials can be securely placed on the first side surface126aand the second side surface126bin subsequent steps S240to S250.

In the following, step S230and later will be described by using the case where the third additional layer material162daand the fourth additional layer material162dbare also placed on the inner layer144of the second insulating film142bas an example.

Next, the conductor120is prepared. The conductor120has a plate form. As described above, the conductor120has the upper surface122, the lower surface124, the first side surface126a, the second side surface126b, and the like.

Next, as illustrated inFIG.14, the first insulating film142ais placed on the upper side of the conductor120to be opposite to the upper surface122of the conductor120, and the second insulating film142bis placed on the lower side of the conductor120to be opposite to the lower surface124of the conductor120.

The first insulating film142aand the second insulating film142bare placed such that the respective inner layers144are on the conductor120side. Additionally, as illustrated inFIG.14, the first insulating film142ais placed such that the first insulating film142aand the second insulating film142boverlap each other when viewed from the upper surface122side of the conductor120.

Here, as described above, in the first insulating film142a, the first additional layer material162caand the second additional layer material162cbare placed at the predetermined positions on the inner layer144. Additionally, in the second insulating film142b, the third additional layer material162daand the fourth additional layer material162dbare placed at the predetermined positions on the inner layer144.

Thus, as illustrated inFIG.14, when the first insulating film142aand the second insulating film142bare placed with respect to the conductor120, both the first and third additional layer materials162caand162daare placed such that the first and third additional layers162caand162daare on or near the first side surface126aof the conductor120when viewed from the upper surface122of the conductor120. Similarly, both the second and fourth additional layer materials162cband162dbare placed such that the second and fourth additional layer materials162cband162dbare on or near the second side surface126bof the conductor120when viewed from the lower surface124of the conductor120.

Next, the hot press process is performed on the first insulating film142aand the second insulating film142bin the directions indicated by the arrows F ofFIG.14. The hot press process causes the first insulating film142ato tightly contact the upper surface122of the conductor120. The second insulating film142bis also caused to tightly contact the lower surface124of the conductor120.

Additionally, the inner layer144of the first insulating film142aand the inner layer144of the second insulating film142bare welded on the sides of the side surfaces126aand126bof the conductor120. As a result, the first insulating film142aand the second insulating film142bare joined to form the covering material140to surround a portion of the conductor120.

At this time, the first and third additional layer materials162caand162dain the molten or fluidized state are pressed from the upper side and the lower side against the first side surface126aof the conductor120. Similarly, the second and fourth additional layer materials162cband162dbin the molten or fluidized state are pressed from the upper side and the lower side against the second side surface126bof the conductor120.

As a result, after the hot press process is performed, the first additional layer156acan be formed between the first side surface126aof the conductor120and the inner layers144. Additionally, the second additional layer156bcan be formed between the second side surface126bof the conductor120and the inner layers144.

This produces the first lead member100having a cross-sectional configuration as illustrated inFIG.11described above.

As illustrated inFIG.11, the first lead member100manufactured in the second manufacturing method can significantly suppress the gaps between the side surfaces126aand126bof the conductor120and the inner layers144of the covering material140, which may be generated in the conventional lead member1.

Additionally, in the second manufacturing method, as in the first manufacturing method, the first lead member100, in which the “spread” of the inner layer144in the length direction (the X direction) is significantly suppressed, can be manufactured in comparison with the conventional lead member1.

Additionally, in the second manufacturing method, when the first and second insulating films142aand142bare joined, the high temperature and high pressure conditions are not required, and thus the production time is shortened, so that the first lead member100can be manufactured more efficiently.

As described above, the method of manufacturing the lead member according to one embodiment of the present disclosure has been described by using the first and second manufacturing methods as examples. However, these are merely examples, and the lead member according to one embodiment of the present disclosure may be manufactured by another method.

For example, in the second manufacturing method described above, in step S220, the additional layer materials162caand162cbare placed at two positions of the first insulating film142a, and the additional layer materials162daand162dbare placed at two positions of the second insulating film142b.

Alternatively, however, the additional layer materials162daand162dbneed not be placed on the second insulating film142bside. Such an embodiment is beneficial, particularly when the conductor120is relatively thin.

Alternatively, only the first additional layer material162ca(or the second additional layer material162cb) may be placed on the first insulating film142aside and only the fourth additional layer material162db(or the third additional layer material162da) may be placed on the second insulating film142bside. Such an embodiment is also beneficial, particularly when the conductor120is relatively thin.

Various other modifications can be considered by a person skilled in the art. Accordingly, the scope of the present disclosure is defined by the description of the claims, and it is intended that the present disclosure include all modifications within the meaning and scope of the description and equivalents of the claims.

DESCRIPTION OF THE REFERENCE NUMERALS