KR102833816B1 - The Electrode Lead, The Method For Manufacturing Thereof And The Pouch Type Secondary Battery - Google Patents

Abstract

According to an embodiment of the present invention for solving the above problem, an electrode lead includes: a first electrode lead, one end of which is connected to an electrode tab protruding from one side of an electrode assembly; a second electrode lead, one end of which is connected to the other end of the first electrode lead and the other end of which protrudes outside a battery case accommodating the electrode assembly; and a connecting portion that connects the first electrode lead and the second electrode lead to each other, wherein the connecting portion is formed by curing an adhesive applied between the first electrode lead and the second electrode lead, and the adhesive is applied in an amount of 2.3 mg to 2.7 mg.

Description

Electrode lead, method for manufacturing thereof and pouch type secondary battery {The Electrode Lead, The Method For Manufacturing Thereof And The Pouch Type Secondary Battery}

The present invention relates to an electrode lead, a method for manufacturing the same, and a pouch-type secondary battery, and more particularly, to an electrode lead in which a two-stage electrode lead is formed so as to discharge gas generated inside a battery case to the outside to ensure safety, and in which the two-stage electrode lead can be reliably detached so as to completely cut off electrical connection, a method for manufacturing the same, and a pouch-type secondary battery.

In general, types of secondary batteries include nickel cadmium batteries, nickel hydrogen batteries, lithium ion batteries, and lithium ion polymer batteries. These secondary batteries are used in not only small products such as digital cameras, P-DVDs, MP3Ps, mobile phones, PDAs, portable game devices, power tools, and e-bikes, but also large products requiring high output such as electric vehicles or hybrid vehicles, as well as power storage devices that store surplus generated power or renewable energy and backup power storage devices.

In order to manufacture an electrode assembly, a cathode, a separator, and an anode are manufactured and laminated. Specifically, a cathode active material slurry is applied to a cathode current collector, and an anode active material slurry is applied to an anode current collector to manufacture a cathode and an anode. Then, when a separator is interposed between the manufactured cathodes and anodes and they are laminated, unit cells are formed, and the unit cells are laminated to form an electrode assembly. Then, when this electrode assembly is accommodated in a specific case and an electrolyte is injected, a secondary battery is manufactured.

These secondary batteries are classified into pouch types and can types, depending on the material of the battery case that accommodates the electrode assembly. The pouch type accommodates the electrode assembly in a pouch made of a flexible polymer material with an irregular shape. The can type accommodates the electrode assembly in a case made of a material such as metal or plastic with a fixed shape.

A pouch-type battery case is manufactured by forming a cup portion by drawing on a flexible pouch film. Then, when the cup portion is formed, an electrode assembly is accommodated in the receiving space of the cup portion, the battery case is folded, and then the sealing portion is sealed to manufacture a secondary battery.

Meanwhile, secondary batteries may generate gas internally due to internal short circuits, overcharge, overdischarge, etc. These gases increase the internal pressure of the secondary battery, which may cause problems such as weakening of the bonding strength between components, damage to the secondary battery case, early operation of the protection circuit, deformation of the electrodes, internal short circuits, and explosion. In the case of can-type secondary batteries, protective members such as a CID filter and a safety vent are provided to physically block the electrical connection when the pressure inside the case increases. However, in the case of conventional pouch-type secondary batteries, such protective members are not sufficiently provided.

Korean Public Notice No. 2019-0059677

The problem to be solved by the present invention is to provide an electrode lead, a method for manufacturing the same, and a pouch-type secondary battery, in which a two-stage electrode lead is formed so as to ensure safety by discharging gas generated inside a battery case to the outside, and in which the two-stage electrode lead can be reliably detached so as to completely cut off electrical connection.

The tasks of the present invention are not limited to the tasks mentioned above, and other tasks not mentioned will be clearly understood by those skilled in the art from the description below.

According to an embodiment of the present invention for solving the above problem, an electrode lead includes: a first electrode lead, one end of which is connected to an electrode tab protruding from one side of an electrode assembly; a second electrode lead, one end of which is connected to the other end of the first electrode lead and the other end of which protrudes outside a battery case accommodating the electrode assembly; and a connecting portion that connects the first electrode lead and the second electrode lead to each other, wherein the connecting portion is formed by curing an adhesive applied between the first electrode lead and the second electrode lead, and the adhesive is applied in an amount of 2.3 mg to 2.7 mg.

Additionally, the adhesive may be applied along an upper line that is moved upward by a first length from a center line that bisects the width of the connection area where the connection portion is formed in the first electrode lead or the second electrode lead.

Additionally, the adhesive may be applied along a lower line that is parallel to a second length downward from a center line that bisects the width of the connection area where the connection portion is formed in the first electrode lead or the second electrode lead.

According to an embodiment of the present invention for solving the above problem, a pouch-type secondary battery comprises: an electrode assembly including a positive electrode and a negative electrode, and a separator laminated thereon; a battery case in the form of a pouch for accommodating the electrode assembly; an electrode tab connected to the electrode and protruding from one side of the electrode assembly; a first electrode lead having one end connected to the electrode tab; a second electrode lead having one end connected to the other end of the first electrode lead and the other end protruding outside the battery case; and a connecting portion connecting the first electrode lead and the second electrode lead to each other, wherein the connecting portion is formed by curing an adhesive applied between the first electrode lead and the second electrode lead, and the adhesive is applied in an amount of 2.3 mg to 2.7 mg.

According to an embodiment of the present invention for solving the above problem, a method for manufacturing an electrode lead includes the steps of manufacturing a first electrode lead and a second electrode lead respectively; applying an adhesive to at least one of the other end of the first electrode lead and one end of the second electrode lead; bonding the other end of the first electrode lead and one end of the second electrode lead to each other to form a lead laminate; and applying heat to the lead laminate to harden the adhesive, thereby forming a connecting portion, wherein in the step of applying the adhesive, the adhesive is applied in an amount of 2.3 mg to 2.7 mg.

Additionally, in the step of applying the adhesive, the adhesive can be applied in an application amount of 2.4 mg to 2.6 mg.

Additionally, the adhesive may be applied along an upper line that is moved upward by a first length from a center line that bisects the width of the connection area where the connection portion is formed in the first electrode lead or the second electrode lead.

Additionally, the adhesive may be further applied along the center line.

Additionally, the first length may be from 1.3 mm to 1.7 mm.

Additionally, the adhesive may be applied along a lower line that is parallel to a second length downward from a center line that bisects the width of the connection area where the connection portion is formed in the first electrode lead or the second electrode lead.

Additionally, the adhesive may be further applied along the center line.

Additionally, the second length may be from 0.8 mm to 1.2 mm.

Other specific details of the present invention are included in the detailed description and drawings.

According to embodiments of the present invention, at least the following effects are achieved.

By forming a two-stage electrode lead, even if gas is generated inside the battery case and the internal pressure increases, the gas can be discharged to the outside to ensure safety.

In addition, while maintaining the electrolyte resistance of the adhesive bonding the two-stage electrode leads, the two-stage electrode leads can be reliably detached, thereby completely disconnecting the electrical connection.

The effects according to the present invention are not limited to those exemplified above, and further diverse effects are included in the present specification.

Figure 1 is an assembly diagram of a secondary battery according to one embodiment of the present invention.
Figure 2 is a perspective view of a secondary battery according to one embodiment of the present invention.
FIG. 3 is a perspective view showing an expanded volume of a pouch-type secondary battery according to one embodiment of the present invention.
FIG. 4 is a flow chart showing a method for manufacturing an electrode lead according to one embodiment of the present invention.
FIG. 5 is a part of a cross-sectional view taken along line A-A' of FIG. 2 of a pouch-type secondary battery according to one embodiment of the present invention.
FIG. 6 is a part of a cross-sectional view taken along line A-A' of FIG. 2 showing an expanded volume of a pouch-type secondary battery according to one embodiment of the present invention.
Figure 7 is a schematic diagram showing the appearance of adhesive applied to a conventional connection area.
Figure 8 is a schematic diagram showing an appearance of applying an adhesive according to one embodiment of the present invention.
Figure 9 is a schematic diagram showing an adhesive applied according to a modified example of one embodiment of the present invention.
Figure 10 is a schematic diagram showing an adhesive applied according to another embodiment of the present invention.
Figure 11 is a schematic diagram showing an adhesive applied according to a modified example of another embodiment of the present invention.

The advantages and features of the present invention, and the methods for achieving them, will become clearer with reference to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and the present embodiments are provided only to make the disclosure of the present invention complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used with a meaning that can be commonly understood by a person of ordinary skill in the art to which the present invention belongs. In addition, terms defined in commonly used dictionaries shall not be ideally or excessively interpreted unless explicitly specifically defined.

The terminology used herein is for the purpose of describing embodiments only and is not intended to limit the invention. In this specification, the singular also includes the plural unless specifically stated otherwise. The terms "comprises" and/or "comprising" as used herein do not exclude the presence or addition of one or more other components in addition to the components mentioned.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

FIG. 1 is an assembly diagram of a secondary battery (1) according to one embodiment of the present invention, and FIG. 2 is a perspective view of a secondary battery (1) according to one embodiment of the present invention.

A pouch-type secondary battery (1) according to one embodiment of the present invention includes, as illustrated in FIG. 1, an electrode assembly (10) formed by stacking electrodes such as a positive electrode, a negative electrode, and a separator, and a pouch-type battery case (13) that accommodates the electrode assembly (10) inside.

In order to manufacture a pouch-type secondary battery (1), first, a slurry containing an electrode active material, a binder, and a plasticizer is applied to a positive electrode current collector and a negative electrode current collector to manufacture electrodes such as a positive electrode and a negative electrode. This is laminated on both sides of a separator to form an electrode assembly (10) of a predetermined shape, and then the electrode assembly (10) is inserted into a battery case (13), an electrolyte is injected, and then sealed.

Specifically, the electrode assembly (Electrode Assembly, 10) may be a laminated structure having two types of electrodes, a positive electrode and a negative electrode, and a separator interposed between the electrodes or arranged on the left or right side of one of the electrodes to mutually insulate the electrodes. The laminated structure may have various forms without limitation, such as a positive electrode and a negative electrode having a predetermined specification being laminated with a separator interposed therebetween, or being wound in the form of a jelly roll. The two types of electrodes, that is, the positive electrode and the negative electrode, each have a structure in which an active material slurry is applied to an electrode current collector in the form of a metal foil or metal mesh containing aluminum and copper, respectively. The slurry can be typically formed by stirring a granular active material, an auxiliary conductor, a binder, a plasticizer, etc. in a state in which a solvent is added. The solvent is removed in a subsequent process.

The electrode assembly (10) includes an electrode tab (11), as illustrated in FIG. 1. The electrode tab (11) is connected to the positive and negative electrodes of the electrode assembly (10), respectively, and protrudes to the outside of the electrode assembly (10) to serve as a path through which electrons can move between the inside and the outside of the electrode assembly (10). The electrode current collector of the electrode assembly (10) is composed of a portion where an electrode active material is applied and a terminal portion where the electrode active material is not applied, i.e., a non-coated portion. In addition, the electrode tab (11) may be formed by cutting the non-coated portion or by connecting a separate conductive member to the non-coated portion by ultrasonic welding, etc. As illustrated in FIG. 1, these electrode tabs (11) may protrude in parallel in the same direction from one side of the electrode assembly (10), but are not limited thereto and may protrude in different directions.

An electrode lead (12) for supplying electricity to the outside of a secondary battery (1) is connected to an electrode tab (11) of an electrode assembly (10) by spot welding or the like. According to one embodiment of the present invention, a plurality of electrode leads (12) are provided to form a two-stage electrode lead (12). And, among the two-stage electrode leads (12), a first electrode lead (123, illustrated in FIG. 5) is connected to the electrode tab (11) of the electrode assembly (10), and a second electrode lead (124, illustrated in FIG. 5) protrudes to the outside of a battery case (13). A detailed description of the two-stage electrode leads (12) will be described later.

A part of the electrode lead (12) is surrounded by an insulating portion (14). The insulating portion (14) is positioned limited to a sealing portion (134) where the upper case (131) and the lower case (132) of the battery case (13) are thermally fused, thereby bonding the electrode lead (12) to the battery case (13). In addition, it prevents electricity generated from the electrode assembly (10) from flowing to the battery case (13) through the electrode lead (12), and maintains the sealing of the battery case (13). Therefore, the insulating portion (14) may be made of a non-conductive material having high adhesiveness and poor electricity conductivity, particularly a polymer resin, and at least one of a thermoplastic, a thermosetting, and a photocurable resin having electrical insulation. In general, as the insulating part (14), an insulating tape that is easy to attach to the electrode lead (12) and has a relatively thin thickness is often used, but it is not limited thereto and various materials can be used as long as they can insulate the electrode lead (12).

The electrode lead (12) includes a positive lead (121) which has one end connected to the positive tab (111) and extends in the protruding direction of the positive tab (111), and a negative lead (122) which has one end connected to the negative tab (112) and extends in the protruding direction of the negative tab (112). Meanwhile, as shown in FIG. 1, both the positive lead (121) and the negative lead (122) have other ends that protrude to the outside of the battery case (13). As a result, electricity generated inside the electrode assembly (10) can be supplied to the outside. In addition, since the positive tab (111) and the negative tab (112) are formed to protrude in various directions, respectively, the positive lead (121) and the negative lead (122) can also extend in various directions, respectively.

The positive electrode lead (121) and the negative electrode lead (122) may be made of different materials. That is, the positive electrode lead (121) may be made of the same aluminum (Al) material as the positive electrode collector, and the negative electrode lead (122) may be made of the same copper (Cu) material as the negative electrode collector or a nickel (Ni)-coated copper material. In addition, a portion of the electrode lead (12) protruding outside the battery case (13) becomes a terminal portion and is electrically connected to an external terminal.

The battery case (13) is a pouch made of a flexible material that accommodates the electrode assembly (10) inside. Hereinafter, the battery case (13) will be described as a pouch. When a flexible pouch film (135) is drawn and formed using a punch or the like, a portion thereof is stretched to form a cup portion (133) including a pocket-shaped accommodation space (1331), thereby manufacturing the battery case (13). The battery case (13) accommodates and seals the electrode assembly (10) so that a portion of the electrode lead (12), i.e., a terminal portion, is exposed. This battery case (13) includes an upper case (131) and a lower case (132), as illustrated in FIG. 1. A cup portion (133) is formed in the lower case (132) to provide a receiving space (1331) capable of accommodating an electrode assembly (10), and the upper case (131) covers the receiving space (1331) from the top so that the electrode assembly (10) does not fall out of the battery case (13). In addition, the sealing portion (134) is sealed to seal the receiving space (1331). At this time, a cup portion (133) with a receiving space (1331) is formed in the upper case (131) so that the electrode assembly (10) can be received from the top. The upper case (131) and the lower case (132) may be manufactured so that one side is connected to each other as illustrated in FIG. 1, but are not limited thereto and may be manufactured in various ways, such as being manufactured separately from each other.

When the electrode lead (12) is connected to the electrode tab (11) of the electrode assembly (10) and the insulation portion (14) is formed on a part of the electrode lead (12), the electrode assembly (10) is accommodated in the accommodation space (1331) provided in the cup portion (133) of the lower case (132), and the upper case (131) covers the space from the top. Then, an electrolyte is injected inside, and a sealing portion (134) formed to extend outward from the edges of the upper case (131) and the lower case (132) is sealed. The electrolyte is for moving lithium ions generated by the electrochemical reaction of the electrode during charging and discharging of the secondary battery (1), and may include a non-aqueous organic electrolyte that is a mixture of a lithium salt and a high-purity organic solvent, or a polymer using a polymer electrolyte. Through this method, a pouch-type secondary battery (1) can be manufactured as shown in FIG. 2.

Figure 3 is a perspective view showing an expanded volume of a pouch-type secondary battery (1) according to one embodiment of the present invention.

In general, pouch-type secondary batteries (1) may generate an abnormally large amount of gas due to internal short circuits, overcharge, overdischarge, etc. caused by external impacts on the electrode assembly (10), heat generation, electrolyte decomposition, thermal runaway, etc. caused by these. Or, when stored or kept at a high temperature, the high temperature may rapidly promote the electrochemical reaction of the electrolyte and electrode active material, causing gas to be generated.

Meanwhile, in order to manufacture a pouch-type battery case (13), a flexible pouch film (135) is drawn and formed using a punch or the like. This drawing forming is performed by inserting the pouch film (135) into a press and applying pressure to the pouch film (135) with a punch to stretch the pouch film (135). By stretching the pouch film (135) in this way to form a cup portion (133) by recessing it, the battery case (13) is manufactured. This pouch film (135) is formed by laminating a surface protection layer mainly made of a polymer such as nylon resin or polyethylene terephthalate (PET), a gas barrier layer mainly made of an aluminum foil, and a sealant layer mainly made of a polymer such as polypropylene (PP) or polyethylene (PE).

If gas is generated inside the battery case (13), since each layer of the battery case (13) is flexible, the generated gas increases the internal pressure of the secondary battery (1), causing the volume of the secondary battery (1) to expand as shown in Fig. 3. Then, problems such as weakening of the bonding strength between components, damage to the case of the secondary battery (1), early operation of the protection circuit, deformation of the electrode, internal short circuit, and explosion occur.

Figure 4 is a flow chart showing a method for manufacturing an electrode lead (12) according to one embodiment of the present invention.

According to one embodiment of the present invention, by forming a two-stage electrode lead (12), even if gas is generated inside the battery case (13) and the internal pressure increases, the gas can be discharged to the outside to ensure safety. In addition, while maintaining the electrolyte resistance of the adhesive (151, illustrated in FIG. 7) that bonds between the two-stage electrode leads (12), the two-stage electrode leads (12) can be reliably detached, so that the electrical connection can be completely cut off.

To this end, a method for manufacturing an electrode lead (12) according to one embodiment of the present invention comprises the steps of: manufacturing a first electrode lead (123) and a second electrode lead (124), respectively; applying an adhesive (151) to at least one of the other end of the first electrode lead (123) and one end of the second electrode lead (124); forming a lead laminate by bonding the other end of the first electrode lead (123) and one end of the second electrode lead (124) to each other; and forming a connecting portion (15) by applying heat to the lead laminate to harden the adhesive (151), wherein in the step of applying the adhesive (151), the adhesive (151) is applied in an amount of 2.3 mg to 2.7 mg.

An electrode lead (12) manufactured in this manner includes: a first electrode lead (123) having one end connected to an electrode tab (11) protruding from one side of an electrode assembly (10); a second electrode lead (124) having one end connected to the other end of the first electrode lead (123) and the other end protruding to the outside of a battery case (13) accommodating the electrode assembly (10); and a connecting portion (15) connecting the first electrode lead (123) and the second electrode lead (124) to each other, wherein the connecting portion (15) is formed by curing an adhesive (151) applied between the first electrode lead (123) and the second electrode lead (124), and the adhesive (151) is applied in an amount of 2.3 mg to 2.7 mg.

And according to one embodiment of the present invention including such an electrode lead (12), a pouch-type secondary battery (1) comprises: an electrode assembly (10) including a positive electrode and a negative electrode, and a separator laminated thereon; a pouch-shaped battery case (13) accommodating the electrode assembly (10); an electrode tab (11) connected to the electrode and protruding from one side of the electrode assembly (10); a first electrode lead (123) having one end connected to the electrode tab (11); a second electrode lead (124) having one end connected to the other end of the first electrode lead (123) and the other end protruding to the outside of the battery case (13); And a connecting portion (15) connecting the first electrode lead (123) and the second electrode lead (124) to each other, wherein the connecting portion (15) is formed by curing an adhesive (151) applied between the first electrode lead and the second electrode lead, and the adhesive (151) is applied in an amount of 2.3 mg to 2.7 mg.

Below, each step shown in the flow chart of Fig. 4 is specifically described with reference to Figs. 5 to 11.

FIG. 5 is a part of a cross-sectional view taken along line A-A' of FIG. 2 of a pouch-type secondary battery (1) according to one embodiment of the present invention.

According to one embodiment of the present invention, the electrode lead (12) is formed in two stages. That is, the electrode lead (12) includes a first electrode lead (123) whose end is connected to the electrode tab (11) of the electrode assembly (10), and a second electrode lead (124) whose end is connected to the other end of the first electrode lead (123) and whose other end protrudes outside the battery case (13). In addition, the other end of the first electrode lead (123) and one end of the second electrode lead (124) are connected to each other by bonding one surface thereof through a connecting portion (15).

In order to manufacture such electrode leads (12), first, the first electrode lead (123) and the second electrode lead (124) are manufactured separately (S401). It is preferable that both the first electrode lead (123) and the second electrode lead (124) have a rectangular shape. In addition, in order to be easily bonded to each other later, it is preferable that the widths are the same.

An adhesive (151) is applied to at least one of the other end of the first electrode lead (123) manufactured above and one end of the second electrode lead (124) (S402). At this time, according to one embodiment of the present invention, the adhesive (151) is applied in an amount of 2.3 mg to 2.7 mg, more preferably in an amount of 2.4 mg to 2.6 mg. If the amount of the adhesive (151) applied is less than 2.3 mg, the adhesive strength of the first electrode lead (123) and the second electrode lead (124) is reduced, and in particular, the electrolyte resistance is also reduced, so that the adhesive strength may be further reduced by the electrolyte. Therefore, the first electrode lead (123) and the second electrode lead (124) may be detached from each other in the initial stage when the secondary battery (1) has not expanded significantly. In addition, since the first electrode lead (123) and the second electrode lead (124) are not in close contact with each other, there is also a problem that power is not supplied smoothly. On the other hand, if the amount of adhesive (151) applied is more than 2.7 mg, even if the secondary battery (1) is sufficiently expanded, the first electrode lead (123) and the second electrode lead (124) are not detached from each other, which causes a safety problem.

Then, the other end of the first electrode lead (123) and one end of the second electrode lead (124) are bonded to each other to form a lead laminate (S403).

The adhesive (151) contains a conductive material. As a result, electricity generated from the electrode assembly (10) can be easily discharged to the outside. To this end, the adhesive (151) is formed by mixing a conductive material and a solvent, and it is preferable that the solvent is formed by mixing a polymer and a diluent.

The conductive material includes at least one of conductive materials such as natural or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorocarbon, aluminum, nickel, gold, silver, and copper powder; powders having a Core/Shell structure in which one type of metal is coated with another type of metal; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and silver is most preferably included in particular. The conductive material included in such adhesive (151) is preferably 70 to 85 wt%.

The polymer is a thermosetting polymer resin, and includes at least one of epoxy resin, acrylic resin, EPDM (Ethylene Propylene Diene Monomer) resin, CPE (Chlorinated Polyethylene) resin, silicone, polyurethane, urea resin, melamine resin, phenol resin, and unsaturated ester resin, polypropylene, polyethylene, polyimide, and polyamide, and in particular, it is most preferable to include epoxy or acrylic resin. It is preferable that the polymer included in such adhesive (151) is 15 to 30 wt%.

Meanwhile, in order to reduce the viscosity of the adhesive (151) and increase the fluidity to enhance the user's convenience, a diluent is added to the polymer. Here, the diluent may be a glycidyl ester, and may include at least one of, for example, monoepoxides such as n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, styrene oxide, phenyl glycidyl ether, cresyl glycidyl ether, glycidyl methacrylate, tertiary carboxylic acid glycidyl ester, and vinyl cyclohexene monoepoxide, and diepoxides such as butanediol glycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and vinyl cyclohexene dioxide.

After forming the lead laminate, heat is applied to the lead laminate using an oven or the like (S404). Then, the adhesive (151) dries and hardens to form a connection part (15), and this connection part (15) also includes a conductive material and a conductive polymer. Accordingly, as shown in Fig. 5, the manufacture of a two-stage electrode lead (12) in which the first electrode lead (123) and the second electrode lead (124) are connected to each other is completed.

When the battery case (13) is normal, the first and second electrode leads (123, 124) should be stably connected to each other, and when the battery case (13) expands, the first and second electrode leads (123, 124) should be easily detached from each other. Therefore, it is preferable that the first and second electrode leads (123, 124) be located on different planes so that the upper and lower surfaces are connected to each other, rather than being located on the same plane so that the sides are connected.

It is preferable that the connecting portion (15) connecting the first electrode lead (123) and the second electrode lead (124) to each other be very thin, with a thickness of 1 to 500 μm. Accordingly, even if the first electrode lead (123) and the second electrode lead (124) form a step, the size of the step may not be excessively large.

Meanwhile, as described above, a portion of the electrode lead (12), particularly a portion where the first electrode lead (123) and the second electrode lead (124) are connected through the connection portion (15), is surrounded by an insulating portion (14). Then, the first and second electrode leads (123, 124) are bonded to the battery case (13) through the insulating portion (14). In the process of sealing the upper case (131) and the lower case (132), the portion in contact with the electrode lead (12) has relatively high pressure, so there is a high possibility that the sealant layer of the battery case (13) will be damaged. As described above, this sealant layer is insulative because it is in direct contact with the electrode assembly (10). However, if the sealant layer is damaged, electricity can flow to the battery case (13) through the electrode lead (12). In particular, since the gas barrier layer of the battery case (13) is made of a metal such as aluminum, if the sealant layer is damaged even a little and the gas barrier layer is exposed, it can easily flow electricity by coming into contact with the electrode lead (12).

Accordingly, the insulating portion (14) is manufactured as a non-conductive material that does not conduct electricity well. In addition, the insulating portion (14) has high mechanical strength and heat resistance. Accordingly, the insulating portion (14) may include, for example, a polyolefin resin such as polypropylene (PP) or polyethylene (PE). In particular, polypropylene (PP) has excellent mechanical properties such as tensile strength, rigidity, surface hardness, wear resistance, and heat resistance, and chemical properties such as corrosion resistance, and is therefore mainly used in manufacturing the insulating portion (14). Furthermore, in order to improve the adhesiveness of the insulating portion (14), acid-treated polypropylene may be included. For example, acid-treated polypropylene and normal polypropylene may be mixed, polyethylene may be further mixed, or only acid-treated polypropylene may be included. Here, the acid-treated polypropylene may be MAH PP (maleic anhydride polypropylene).

Therefore, when the upper case (131) and the lower case (132) are heat-sealed, the insulation (14) maintains its shape, thereby blocking contact between the electrode lead (12) and the gas barrier layer even if the sealant layer is partially damaged and the gas barrier layer is exposed. This prevents electricity generated from the electrode assembly (10) from flowing to the battery case (13) through the electrode lead (12).

As shown in Fig. 5, the insulation (14) surrounds all of the first electrode lead (123), the connection (15), and the second electrode lead (124). If the first electrode lead (123) or the connection (15) is not surrounded, even if the battery case (13) expands, a repulsive force cannot be applied to the first electrode lead (123) and the second electrode lead (124).

FIG. 6 is a part of a cross-sectional view taken along line A-A' of FIG. 2 showing an expanded volume of a pouch-type secondary battery (1) according to one embodiment of the present invention.

As described above, if the pressure inside the pouch-type battery case (13) increases, the volume of the pouch-type secondary battery (1) expands. Accordingly, as illustrated in FIG. 6, the outer wall of the battery case (13) moves toward the outside. At this time, among the outer walls of the battery case (13), the upper and lower walls have a large area and are not sealed, so that the ductility is greater. Accordingly, the upper wall of the battery case (13) moves upward (U), and the lower wall moves downward (D). Meanwhile, as the outer wall of the battery case (13) moves toward the outside, a repulsive force is applied to the first electrode lead (123) and the second electrode lead (124) connected through the insulating portion (14). Accordingly, as the internal pressure of the battery case (13) gradually increases, the force exerted on the outer wall of the battery case (13) to move becomes greater, and the magnitude of the repulsive force applied to the first electrode lead (123) and the second electrode lead (124) also increases.

When the magnitude of the repulsive force becomes greater than the adhesive force between the first electrode lead (123) and the second electrode lead (124), the first electrode lead (123) and the second electrode lead (124) are eventually detached, as illustrated in FIG. 6. Therefore, the electrical connection is physically cut off, and electricity can no longer flow. Here, detachment means that what is adsorbed or attached is separated. However, at this time, the adhesive force between the first electrode lead (123) and the second electrode lead (124) and the connecting portion (15) is weaker than the adhesive force between the first electrode lead (123) and the second electrode lead (124) and the insulating portion (14). Therefore, when a repulsive force is applied to the first electrode lead (123) and the second electrode lead (124), the adhesive force between the first electrode lead (123) and the second electrode lead (124) and the insulating portion (14) is maintained, so that the sealing of the battery case (13) is maintained, and the first electrode lead (123) and the second electrode lead (124) are detached from each other.

Figure 7 is a schematic diagram showing an adhesive (151) applied to a conventional connection area (1241).

In the step (S40) of applying an adhesive (151) to at least one of the other end of the first electrode lead (123) and one end of the second electrode lead (124), conventionally, the adhesive (151) was simply applied to the center of the connection area (1241) where the connection portion (15) is formed. Specifically, as illustrated in FIG. 7, a center line (L1) that bisects the width (W) of the connection area (1241) where the connection portion (15) is formed in the first electrode lead (123) or the second electrode lead (124) was first set, and the adhesive (151) was simply applied only along this center line (L1).

However, since the size and capacity are different depending on the model of the secondary battery (1), it is necessary to control the timing of detachment of the first electrode lead (123) and the second electrode lead (124). That is, if detachment occurs too quickly, the adhesive strength needs to be further increased, and if detachment occurs too late, the adhesive strength needs to be further reduced. However, the conventional method had a problem in that it could not control the timing of detachment. Of course, the timing of detachment can be controlled by simply replacing and applying adhesives (151) having different adhesive strengths. However, since all of the equipment such as the adhesive (151), dispenser, and nozzle must be replaced depending on the model of the electrode lead (12) being manufactured, the replacement work is cumbersome, the processability and productivity are reduced, and the cost is excessively high.

FIG. 8 is a schematic diagram showing an appearance of applying an adhesive (151) according to one embodiment of the present invention, and FIG. 9 is a schematic diagram showing an appearance of applying an adhesive (151) according to a modified example of one embodiment of the present invention.

According to one embodiment of the present invention, as illustrated in FIG. 8, an adhesive (151) may be applied along an upper line (L2) that is moved upward (F) by a first length (t1) parallel to a center line (L1) that bisects the width (W) of a connection area (1241) where a connection portion (15) is formed in the first electrode lead (123) or the second electrode lead (124). Here, the first length (t1) may be 1.3 mm to 1.7 mm, and particularly preferably 1.4 mm to 1.6 mm.

According to one embodiment of the present invention, since the adhesive (151) is applied to the upper line (L2), the point where the first electrode lead (123) and the second electrode lead (124) are bonded is located further inward from the secondary battery (1) than in the past. Therefore, when the secondary battery (1) expands and a repulsive force is applied to the first electrode lead (123) and the second electrode lead (124), the distance between the point where the repulsive force is applied and the point where the repulsive force is bonded becomes closer than in the past. Therefore, a greater repulsive force is required to detach the first electrode lead (123) and the second electrode lead (124). In other words, the bonding strength is further increased.

Therefore, if the detachment of the first electrode lead (123) and the second electrode lead (124) occurs too quickly, the adhesive strength can be increased by applying the adhesive (151) along the upper line (L2) in the connection area (1241), as shown in FIG. 8. And, if, in order to further increase the adhesive strength, the adhesive (151) can be applied further along the center line (L1) as well as along the upper line (L2), as shown in FIG. 9.

In Fig. 8, the connection area (1241) is illustrated as being formed at one end of the second electrode lead (124), but the connection area (not shown) may also be formed at the other end of the first electrode lead (123). In this case, the other end of the first electrode lead (123) where the connection area is formed is positioned so that it faces downward, and one end of the first electrode lead (123) faces upward. Then, after adhesive (151) is applied along the upper line (not shown) of the connection area formed at the other end of the first electrode lead (123), the other end of the first electrode lead (123) and one end of the second electrode lead (124) are adhered to each other. As a result, the same effect as applying adhesive (151) to the upper line (L2) of the connection area (1241) formed at one end of the second electrode lead (124) is achieved.

FIG. 10 is a schematic diagram showing an appearance of applying an adhesive (151) according to another embodiment of the present invention, and FIG. 11 is a schematic diagram showing an appearance of applying an adhesive (151) according to a modified example of another embodiment of the present invention.

According to another embodiment of the present invention, as illustrated in FIG. 10, an adhesive (151) may be applied along a lower line (L3) that is parallel to a second length (t2) shifted downward (R) from a center line (L1) that bisects the width (W) of a connection area (1241) where a connection portion (15) is formed in the first electrode lead (123) or the second electrode lead (124). Here, the second length (t2) may be 0.8 mm to 1.2 mm, and particularly preferably 0.9 mm to 1.1 mm.

According to another embodiment of the present invention, since the adhesive (151) is applied to the lower line (L3), the point where the first electrode lead (123) and the second electrode lead (124) are bonded is located further outside the secondary battery (1) than in the past. Therefore, when the secondary battery (1) expands and a repulsive force is applied to the first electrode lead (123) and the second electrode lead (124), the distance between the point where the repulsive force is applied and the point where the repulsive force is bonded becomes further than in the past. Therefore, the first electrode lead (123) and the second electrode lead (124) are detached even with a smaller repulsive force. In other words, the bonding strength is further reduced.

Therefore, if the detachment of the first electrode lead (123) and the second electrode lead (124) occurs too late, the adhesive strength can be reduced by applying the adhesive (151) along the lower line (L3) in the connection area (1241), as illustrated in FIG. 10. If the adhesive strength is excessively reduced and needs to be increased to some extent, the adhesive (151) can be further applied along the center line (L1) as well as along the lower line (L3), as illustrated in FIG. 11.

In Fig. 10, the connection area (1241) is illustrated as being formed at one end of the second electrode lead (124), but the connection area (not shown) may also be formed at the other end of the first electrode lead (123). In this case, the other end of the first electrode lead (123) where the connection area is formed is positioned so that it faces downward, and one end of the first electrode lead (123) faces upward. Then, after adhesive (151) is applied along the lower line (not shown) of the connection area formed at the other end of the first electrode lead (123), the other end of the first electrode lead (123) and one end of the second electrode lead (124) are adhered to each other. As a result, the same effect as applying adhesive (151) to the lower line (L3) of the connection area (1241) formed at one end of the second electrode lead (124) is achieved.

Manufacturing example 1

A first electrode lead having a length of 11.0 mm and a width of 45.0 mm and a second electrode lead having a length of 40.5 mm and a width of 45.0 mm were manufactured by cutting a 0.2 mm thick copper (Cu) plate partially plated with nickel (Ni).

Meanwhile, an epoxy resin adhesive containing 78 wt% silver powder (Ag) with particle sizes of 5 μm and 2 μm and 22 wt% liquid epoxy was used as a conductive adhesive.

The conductive adhesive was applied lengthwise in the width direction at a coating amount of 2.5 mg at a point 1.0 mm from one end of the second electrode lead, and the other end of the first electrode lead was adhered to form a lead laminate. At this time, the length of the connection region where the first electrode lead and the second electrode lead overlap was 5.0 mm. Therefore, the adhesive was applied along an upper line that was moved upward by 1.5 mm in parallel from the center line of the connection region.

Then, a two-stage electrode lead was manufactured by placing the lead laminate on a jig and hardening the adhesive by heat-pressing at a temperature of 180°C for 2 minutes.

Manufacturing example 2

A two-stage electrode lead was manufactured in the same manner as in Manufacturing Example 1, except that the adhesive was applied in an amount of 2.5 mg at a point 3.5 mm from one end of the second electrode lead. Accordingly, the adhesive was applied along a lower line that was shifted 1.0 mm downward from the center line of the connection area.

Comparative Example 1

A two-stage electrode lead was manufactured in the same manner as in Manufacturing Example 1, except that 2.0 mg of adhesive was applied at a point 1.0 mm from one end of the second electrode lead.

Comparative Example 2

A two-stage electrode lead was manufactured in the same manner as in Manufacturing Example 1, except that 3.5 mg of adhesive was applied at a point 1.0 mm from one end of the second electrode lead.

Comparative Example 3

A two-stage electrode lead was manufactured in the same manner as in Manufacturing Example 1, except that the manufactured adhesive was applied at a point 2.5 mm from one end of the second electrode lead. Accordingly, the adhesive was applied along a center line that bisects the width of the connection area.

Measuring method of physical properties - 1. Adhesive strength according to application amount

First, six each of the two-stage electrode lead samples manufactured in Manufacturing Example 1, Comparative Example 1, and Comparative Example 2 were prepared. Then, each was placed in a 125 ml polyethylene (PE) bottle together with an electrolyte (lithium salt LiPF6 1 M, and ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) dissolved in a ratio of 3:3:4, respectively), and the inlet was sealed with paraffin. Then, each of the bottles was sealed with aluminum packaging paper, and stored in a space having a temperature of 60° C. and a relative humidity of 90% RH for 16 weeks. Thereafter, the two-stage electrode lead samples were taken out, and the electrolyte was completely removed.

In the above two-stage electrode lead samples, the second electrode lead located further outside the battery case was each bent. In particular, the point where the connection area of the second electrode lead starts was bent at a right angle. Then, the first electrode lead was fixed by bonding it to a flat jig, and the jig was fixed to the lower part of the tensile strength measuring device and the other end of the second electrode lead was fixed to the upper part. Then, while the lower part of the tensile strength measuring device was fixed, the upper part was moved in the opposite direction to the lower part, and a repulsive force was applied to the two-stage electrode lead samples. Then, the adhesive strength was measured by measuring the magnitude of the repulsive force when the first electrode lead and the second electrode lead were detached.

Physical property measurement results - 1. Adhesive strength according to application amount

Adhesive strength [N/45 mm] Comparative Example 1 (2.0 mg) Manufacturing Example 1 (2.5 mg) Comparative Example 2 (3.5 mg) 1 6.01 16.97 21.09 2 6.43 19.24 22.86 3 11.57 19.31 23.13 4 14.96 20.11 24.95 5 16.37 20.33 25.09 6 16.98 22.24 25.16 medium 12.05 19.70 23.71

The above [Table 1] shows the results of the experiment on each of the two-stage electrode lead samples manufactured in Manufacturing Example 1, Comparative Example 1, and Comparative Example 2, and the adhesive strengths are arranged in ascending order. As described in the above [Table 1], when Manufacturing Example 1 and Comparative Example 1 of the present invention are compared, there were samples in which the adhesive strength of the electrode leads according to Comparative Example 1 was significantly reduced to 7 N/45 mm or less. That is, when 2.0 mg was applied, the electrolyte resistance was reduced, and there was a high possibility that such a defect would occur. On the other hand, there were no samples in which the adhesive strength was significantly reduced in the electrode leads according to Manufacturing Example 1. That is, it can be seen that the electrode lead according to Manufacturing Example 1 has better electrolyte resistance than the electrode lead according to Comparative Example 1.

Meanwhile, when comparing Manufacturing Example 1 of the present invention with Comparative Example 2, the average value of the adhesive strength of the electrode lead according to Manufacturing Example 1 was 19.70 N/45 mm, and the average value of the adhesive strength of the electrode lead according to Comparative Example 2 was 23.71 N/45 mm. That is, it can be seen that the electrode lead according to Manufacturing Example 1 is more suitable for the two-stage electrode lead to be reliably detached and the electrical connection to be completely cut off.

Measuring method of physical properties - 2. Adhesive strength according to application location

First, in the two-stage electrode lead samples manufactured in Manufacturing Example 1, Manufacturing Example 2, and Comparative Example 3, the first electrode lead positioned further inside the battery case was each bent. In particular, the point where the connection area of the first electrode lead starts was bent at a right angle. Then, the second electrode lead was fixed by bonding it to a flat jig, and the jig was fixed to the lower part of the tensile strength measuring device and the other end of the first electrode lead was fixed to the upper part. Then, while the lower part of the tensile strength measuring device was fixed, the upper part was moved in the opposite direction of the lower part, and a repulsive force was applied to the two-stage electrode lead samples. Then, the adhesive strength was measured by measuring the magnitude of the repulsive force when the first electrode lead and the second electrode lead were detached.

Physical property measurement results - 2. Adhesive strength according to application location

Manufacturing Example 1 (Upper Line) Comparative Example 3 (Center Line) Manufacturing Example 2 (Lower Line) Adhesive strength [N/45 mm] 58.31 55.26 42.96

As described in the above [Table 2], when comparing Manufacturing Example 1 and Comparative Example 3 of the present invention, the adhesive strength of the electrode lead according to Manufacturing Example 1 was 58.31 N/45 mm, and the adhesive strength of the electrode lead according to Comparative Example 3 was 55.26 N/45 mm. That is, it can be seen that the adhesive strength increases further when the adhesive is applied to the upper line rather than the center line.

Therefore, if the detachment of the first electrode lead and the second electrode lead occurs too quickly, the bonding strength can be increased by applying the adhesive along the upper line in the connection area.

Meanwhile, when comparing Manufacturing Example 2 and Comparative Example 3 of the present invention, the adhesive strength of the electrode lead according to Manufacturing Example 2 was 42.96 N/45 mm, and the adhesive strength of the electrode lead according to Comparative Example 3 was 55.26 N/45 mm. That is, it can be seen that the adhesive strength decreases further when the adhesive is applied to the lower line rather than the center line.

Therefore, if the detachment of the first electrode lead and the second electrode lead occurs too late, the bonding strength can be reduced by applying the adhesive along the lower line in the connection area.

Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without changing the technical idea or essential characteristics thereof. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive. The scope of the present invention is indicated by the claims described below rather than the detailed description above, and various embodiments derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

1: Secondary battery 10: Electrode assembly
11: Electrode tab 12: Electrode lead
13: Battery case 14: Insulator
15: Connector 111: Positive tab
112: Negative tab 121: Positive lead
122: Negative lead 123: First electrode lead
124: Second electrode lead 131: Upper case
132: Lower case 133: Cup part
134: Sealing part 135: Pouch film
151: Adhesive 1241: Joint area
1331: Reception space

Claims (12)

A first electrode lead connected to an electrode tab protruding from one side of the electrode assembly;
A second electrode lead having one end connected to the other end of the first electrode lead and the other end protruding outward from the battery case accommodating the electrode assembly; and
Including a connecting portion connecting the first electrode lead and the second electrode lead to each other,
The above connecting part,
The adhesive applied between the first electrode lead and the second electrode lead is hardened and formed,
The above adhesive,
It is applied in an amount of 2.3 mg to 2.7 mg,
An electrode lead applied along an upper line parallel to a first length upwardly or a lower line parallel to a second length downwardly from a center line that bisects the width of a connection area where the connection portion is formed in the first electrode lead or the second electrode lead. delete delete An electrode assembly comprising an electrode including an anode and a cathode, and a separator laminated thereon;
A battery case in the form of a pouch for accommodating the above electrode assembly;
An electrode tab connected to the electrode and protruding from one side of the electrode assembly;
A first electrode lead connected to the above electrode tab;
A second electrode lead having one end connected to the other end of the first electrode lead and the other end protruding outside the battery case; and
Including a connecting portion connecting the first electrode lead and the second electrode lead to each other,
The above connecting part,
It is formed by curing the adhesive applied between the first electrode lead and the second electrode lead,
The above adhesive,
It is applied in an amount of 2.3 mg to 2.7 mg,
A pouch-type secondary battery, wherein the pouch-type secondary battery is applied along an upper line that is moved upward by a first length or a lower line that is moved downward by a second length from a center line that bisects the width of a connection area where the connection portion is formed in the first electrode lead or the second electrode lead. A step of manufacturing a first electrode lead and a second electrode lead, respectively;
A step of applying an adhesive to at least one of the other end of the first electrode lead and one end of the second electrode lead;
A step of forming a lead laminate by bonding the other end of the first electrode lead and one end of the second electrode lead to each other; and
Comprising a step of forming a connection by applying heat to the lead laminate to harden the adhesive,
In the step of applying the above adhesive,
The above adhesive,
It is applied in an amount of 2.3 mg to 2.7 mg,
A method for manufacturing an electrode lead, wherein the electrode lead is applied along an upper line parallel to a first length upwardly or a lower line parallel to a second length downwardly from a center line that bisects the width of a connection area where the connection portion is formed in the first electrode lead or the second electrode lead. In paragraph 5,
In the step of applying the above adhesive,
The above adhesive,
A method for manufacturing an electrode lead, wherein the electrode lead is applied in an amount of 2.4 mg to 2.6 mg. delete In paragraph 5,
The above adhesive,
A method for manufacturing an electrode lead, wherein the electrode lead is further applied along the center line. In paragraph 5,
The above first length is,
A method for manufacturing an electrode lead having a diameter of 1.3 mm to 1.7 mm. delete delete In paragraph 5,
The above second length is,
A method for manufacturing an electrode lead having a size of 0.8 mm to 1.2 mm.