Electrode lead, method for manufacturing electrode lead, and pouch type secondary battery

Abstract

An electrode lead according to one embodiment of the present invention for solving the problem 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 protrudes to the outside of 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. The connecting portion is formed by curing an adhesive applied between the first electrode lead and the second electrode lead, wherein the adhesive is formed by mixing a conductive material and a solvent. The solvent is formed by mixing a polymer and a diluent, and includes 5wt% to 15wt% of the diluent.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0042421, filed on Apr. 7, 2020, which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present invention relates to an electrode lead, a method for manufacturing the electrode lead, and a pouch-type secondary battery, and more particularly, to an electrode lead which is formed in two sections to discharge gas generated in a battery casing to the outside to ensure safety, and wherein the two-section electrode lead is reliably separated to completely cut off electrical connection, and the present invention also relates to a method for manufacturing the electrode lead and a pouch-type secondary battery. Background Art

[0004] Generally speaking, secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries and lithium-ion polymer batteries. Such secondary batteries are applied to and used in small products (such as digital cameras, P-DVDs, MP3Ps, mobile phones, PDAs, portable game devices, power tools, electric bicycles, etc.) and large products that require high power (such as electric vehicles and hybrid vehicles, power storage devices for storing surplus power or renewable energy, and backup power storage devices).

[0005] In order to manufacture an electrode assembly, a cathode (hereinafter referred to as a positive electrode), a separator and an anode (hereinafter referred to as a negative electrode) are manufactured and stacked. Specifically, a positive electrode active material slurry is applied to a positive current collector, and a negative electrode active material slurry is applied to a negative current collector to manufacture a positive electrode and a negative electrode. In addition, when the separator is inserted and stacked between the manufactured positive electrode and the manufactured negative electrode, a unit cell is formed. The unit cells are stacked on each other to form an electrode assembly. In addition, when the electrode assembly is housed in a specific housing and an electrolyte is injected, a secondary battery is manufactured.

[0006] Such secondary batteries are classified into pouch-type secondary batteries and can-type secondary batteries according to the material of the battery case that accommodates the electrode assembly. In the pouch-type secondary battery, the electrode assembly is accommodated in a pouch made of a flexible polymer material having a variable shape. In addition, in the can-type secondary battery, the electrode assembly is accommodated in a case made of a metal or plastic material having a predetermined shape.

[0007] The pouch-type battery case is manufactured by stretching a flexible pouch film to form a cup-shaped portion. When the cup-shaped portion is formed, the motor assembly is accommodated in the accommodation space of the cup-shaped portion, and then the battery case is folded to seal the sealing portion, thereby manufacturing a secondary battery.

[0008] In a secondary battery, gas in the secondary battery may be generated due to internal short circuit, overcharge, over discharge, etc. Here, the gas may increase the internal pressure of the secondary battery, thereby causing problems such as weakening of the bonding force between components, damage to the housing of the secondary battery, premature operation of the protection circuit, electrode deformation, internal short circuit, explosion, etc. Therefore, in the case of a can type secondary battery, a protective member such as a CID filter and a safety valve is provided so as to physically interrupt the electrical connection when the internal pressure of the housing increases. However, in the case of a pouch type secondary battery according to the prior art, a protective member is not adequately provided.

[0009] (Patent Document 1)

[0010] Korean Patent Gazette: 2019-0059677 Summary of the invention

[0011] Technical issues

[0012] An object of the present invention is to provide an electrode lead which is formed in two sections to discharge the gas generated in the battery casing to the outside to ensure safety, and wherein the two-section electrode lead is reliably separated to completely cut off the electrical connection, and an object of the present invention is also to provide a method for manufacturing the electrode lead and a pouch-type secondary battery.

[0013] The objects of the present invention are not limited to the above objects, but those skilled in the art will clearly understand other objects described herein from the following description.

[0014] Technical Solution

[0015] An electrode lead according to one embodiment of the present invention for achieving the above purpose includes: a first electrode lead, one end of which is connected to an electrode connector 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 the second electrode lead protrudes to the outside of a battery case accommodating the electrode assembly; and a connecting portion, the connecting portion being configured to connect the first electrode lead to the second electrode lead, wherein the connecting portion is formed by curing an adhesive applied between the first electrode lead and the second electrode lead, the adhesive being formed by mixing a conductor and a solvent, the solvent being formed by mixing a polymer and a diluent, and the solvent containing 5 wt % to 15 wt % of the diluent.

[0016] In addition, the solvent may contain 5 wt % to 10 wt % of the diluent.

[0017] Additionally, the diluent may include a glycidyl ester-based material.

[0018] In addition, the adhesive may contain 70 wt % to 85 wt % of the conductor and 15 wt % to 30 wt % of the solvent.

[0019] Furthermore, the conductor may include at least one of graphite, carbon black, conductive fibers, metal powders, conductive whiskers, conductive metal oxides, and conductive materials.

[0020] Furthermore, the conductor may include silver.

[0021] In addition, the polymer may include at least one of acrylic resin, epoxy resin, ethylene propylene diene monomer (EPDM) resin, chlorinated polyethylene (CPE) resin, silicone, polyurethane, urea resin, melamine resin, phenolic resin, unsaturated ester resin, polypropylene (PP), polyethylene (PE), polyimide and polyamide.

[0022] Additionally, the polymer may include an epoxy resin.

[0023] A pouch-type secondary battery according to one embodiment of the present invention for achieving the above purpose includes: an electrode assembly, in which electrodes and separators are stacked, the electrodes including a positive electrode and a negative electrode; a pouch-shaped battery case, the battery case being configured to accommodate the electrode assembly; an electrode connector, the electrode connector being connected to the electrode and protruding from one side of the electrode assembly; a first electrode lead, one end of the first electrode lead being connected to the electrode connector; a second electrode lead, one end of the second electrode lead being connected to the other end of the first electrode lead, and the other end of the second electrode lead protruding to the outside of the battery case; and a connecting portion, the connecting portion being configured to connect the first electrode lead to the second electrode lead, wherein the connecting portion is formed by curing an adhesive applied between the first electrode lead and the second electrode lead, the adhesive being formed by mixing a conductive material and a solvent, the solvent being formed by mixing a polymer and a diluent, and the solvent containing 5 wt % to 15 wt % of the diluent.

[0024] In addition, the pouch type secondary battery may further include an insulating portion configured to surround a portion where the first and second electrode leads are connected to each other via the connecting portion and configured to combine the first and second electrode leads with the battery case.

[0025] In addition, a bonding force between each of the first electrode lead and the second electrode lead and the connection portion may be smaller than a bonding force between each of the first electrode lead and the second electrode lead and the insulation portion.

[0026] Furthermore, the insulating portion may be made of at least one of a thermoplastic resin, a thermosetting resin, and a photocurable resin, and the insulating portion has electrical insulating properties.

[0027] A method for manufacturing an electrode lead according to one embodiment of the present invention for achieving the above purpose includes: a step of manufacturing each of a first electrode lead and a second electrode lead; a step of applying an adhesive to at least one of the other end of the first electrode lead or one end of the second electrode lead; a step of combining the other end of the first electrode lead with the one end of the second electrode lead to form a lead stack; and a step of applying heat to the lead stack to cure the adhesive to form a connecting portion, wherein the adhesive is formed by mixing a conductive material and a solvent, the solvent is formed by mixing a polymer and a diluent, and the solvent contains 5wt% to 15wt% of the diluent.

[0028] Other implementation specifics are included in the detailed description and accompanying drawings.

[0029] Beneficial effects

[0030] According to the embodiments of the present invention, there are at least the following effects.

[0031] Since a two-stage electrode lead is provided, even if gas is generated in the battery case and the internal pressure increases, the gas can be discharged to the outside to ensure safety.

[0032] Furthermore, since the two-stage electrode lead is reliably separated, the electrical connection can be completely cut off.

[0033] In addition, while improving the electrolyte resistance of the adhesive bonding the two-segment electrode lead to each other, the contact resistance is not significantly increased.

[0034] The effects of the present invention are not limited to the above description, and therefore, more various effects are involved in this specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is an assembly diagram of a secondary battery according to one embodiment of the present invention.

[0036] Figure 2 is a perspective view of a secondary battery according to one embodiment of the present invention.

[0037] Figure 3 is a perspective view showing a state in which the volume of a pouch-type secondary battery according to one embodiment of the present invention is expanded.

[0038] Figure 4: is a flowchart showing a method of manufacturing an electrode lead according to one embodiment of the present invention.

[0039] Figure 5 The invention relates to a pouch-type secondary battery according to an embodiment of the present invention. Figure 2 A partial cross-sectional view taken along line A-A'.

[0040] Figure 6 The pouch-type secondary battery according to one embodiment of the present invention is expanded in volume. Figure 2 A partial cross-sectional view taken along line A-A'.

[0041] Figure 7 is a graph showing the weight reduction rate of each of the electrode lead samples of Manufacturing Example 1 and Comparative Example 1 according to the present invention. DETAILED DESCRIPTION

[0042] The advantages and features of the present invention and its implementation methods will be explained by the following embodiments described with reference to the accompanying drawings. However, the present invention can be embodied in different forms and should not be construed as being limited to the embodiments described herein. On the contrary, these embodiments are provided to make this disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art. In addition, the present invention is limited only by the scope of the claims. Similar reference numerals refer to all similar elements.

[0043] Unless the terms used in the present invention are defined differently, all terms used herein (including technical and scientific terms) have the same meanings as generally understood by those skilled in the art. In addition, unless clearly and obviously defined in this description, the terms defined in the commonly used dictionaries are not ideally or excessively interpreted as having a formal meaning.

[0044] In the following description, technical terms are only used to explain specific exemplary embodiments, but do not limit the present invention. In this specification, unless otherwise mentioned, terms in the singular may include plural forms. The meaning of "including" does not exclude other components other than the mentioned components.

[0045] Hereinafter, preferred embodiments will be described in detail with reference to the accompanying drawings.

[0046] Figure 1 is an assembly diagram of a secondary battery 1 according to one embodiment of the present invention, and Figure 2 is a perspective view of a secondary battery 1 according to one embodiment of the present invention.

[0047] like Figure 1As shown in , a pouch-type secondary battery 1 according to one embodiment of the present invention includes an electrode assembly 10 in which electrodes such as a positive electrode and a negative electrode and a separator are stacked, and a pouch-type battery case 13 in which the electrode assembly 10 is accommodated.

[0048] In order to manufacture the pouch-type secondary battery 1, first, a slurry in which an electrode active material, a binder and a plasticizer are mixed with each other is applied to a positive current collector and a negative current collector to manufacture electrodes such as a positive electrode and a negative electrode. The electrodes are stacked on both sides of a separator to manufacture an electrode assembly 10 having a predetermined shape. Then, the electrode assembly 10 is inserted into a battery case 13, and the battery case 13 is sealed after an electrolyte is injected into the battery case 13.

[0049] In particular, the electrode assembly 10 may be a stacked structure including two types of electrodes such as a positive electrode and a negative electrode and a separator, the separator being arranged between the electrodes to insulate the electrodes from each other, or arranged on the left or right side of one electrode. The stacked structure may have various shapes, without being limited by the shape. For example, a cathode and an anode each having a predetermined standard may be stacked with a separator therebetween, or the stacked structure may be wound in the form of a roll core. Each of the two types of electrodes (i.e., a positive electrode and a negative electrode) has a structure in which an active material slurry is applied to a current collector having a metal foil or metal mesh shape. The slurry may generally be formed by stirring a granular active material, an auxiliary conductor, a binder, and a plasticizer with an added solvent. The solvent may be removed in subsequent processing.

[0050] like Figure 1 As shown in , the electrode assembly 10 includes an electrode tap 11. The electrode tap 11 is respectively connected to the positive electrode and the negative electrode of the electrode assembly 10 so as to protrude to the outside of the electrode assembly 10, thereby providing a path for electrons to move between the inside and the outside of the electrode assembly 10. The current collectors of the electrode assembly 10 are each composed of a portion coated with an electrode active material and a distal portion (i.e., a non-coated portion) that is not coated with an electrode active material. In addition, each electrode tap 11 can be formed by cutting the non-coated portion or connecting a separate conductive member to the non-coated portion by ultrasonic welding. As shown in FIG. Figure 1 As shown in FIG. 1 , the electrode tabs 11 may protrude from one side of the electrode assembly 10 in the same direction, but the present invention is not limited thereto. For example, the electrode tabs 11 may protrude in different directions from each other.

[0051] In the electrode assembly 10, the electrode lead 12 for supplying power to the outside of the secondary battery 1 is connected to the electrode tab 11 by spot welding. The electrode lead 12 according to one embodiment of the present invention is provided in plurality to form a two-stage electrode lead 12. In addition, in the two-stage electrode lead 12, the first electrode lead 123 (see Figure 5) is connected to the electrode connector 11 of the electrode assembly 10, and the second electrode lead 124 (see Figure 5 ) protrudes to the outside of the battery case 13. A detailed description about the two-segment electrode lead 12 will be described later.

[0052] A portion of the electrode lead 12 is surrounded by the insulating portion 14. The insulating portion 14 may be arranged to be confined within the sealing portion 134, where the upper shell 131 and the lower shell 132 of the battery case 13 are heat-melted so that the electrode lead 12 is combined with the battery case 13. In addition, the power generated from the electrode assembly 10 can be prevented from flowing to the battery case 13 via the electrode lead 12, and the sealing of the battery case 13 can be maintained. Therefore, the insulating portion 14 may be a non-conductor with high viscosity and non-conductivity, with the aid of which electricity cannot be well conducted. In particular, the insulating portion 14 may include at least one of a thermoplastic resin, a thermosetting resin, and a photocurable resin, which has electrical insulation as a polymer resin. In general, although an insulating tape that is easily attached to the electrode lead 12 and has a relatively thin thickness is mainly used as the insulating portion 14, the present invention is not limited thereto. For example, various components can be used as the insulating portion 14 as long as these components can insulate the electrode lead 12.

[0053] The electrode lead 12 includes: a positive electrode lead 121, one end of which is connected to the positive electrode terminal 111 so as to extend in the direction in which the positive electrode terminal 111 protrudes; and a negative electrode lead 122, one end of which is connected to the negative electrode terminal 112 so as to extend in the direction in which the negative electrode terminal 112 protrudes. Figure 1 As shown in , all the other ends of the positive electrode lead 121 and the negative electrode lead 122 protrude to the outside of the battery case 13. Therefore, the power generated in the electrode assembly 10 can be supplied to the outside. In addition, since each of the positive electrode tab 111 and the negative electrode tab 112 is formed to protrude in different directions, each of the positive electrode lead 121 and the negative electrode lead 122 can extend in different directions.

[0054] The positive electrode lead 121 and the negative electrode lead 122 may be made of different materials from each other. That is, the cathode lead 121 may be made of the same material as the cathode current collector (i.e., aluminum (Al) material), and the anode lead 122 may be made of the same material as the anode current collector (i.e., copper (Cu) material or copper material coated with nickel (Ni)). In addition, the portion of the electrode lead 12 protruding to the outside of the battery case 13 may be set as a terminal portion and electrically connected to an external terminal.

[0055] The battery case 13 is a bag made of a flexible material, in which the electrode assembly 10 is accommodated. Hereinafter, the case where the battery case 13 is a bag will be described. When a flexible bag film 135 is drawn using a punch or the like, a portion of the bag film 135 is stretched to form a cup-shaped portion 133 including a bag-shaped accommodation space 1331, thereby manufacturing the battery case 13. The battery case 13 accommodates the electrode assembly 10 so that a portion of the electrode lead 12 (i.e., the terminal portion) is exposed and then sealed. Figure 1 As shown in , the battery case 13 includes an upper case 131 and a lower case 132. A receiving space 1331 may be provided in the lower case 132, in which a cup-shaped portion 133 is formed to receive the electrode assembly 10, and the upper case 131 may cover the upper side of the receiving space 1331 so that the electrode assembly 10 is not separated to the outside of the battery case 13. In addition, the sealing portion 134 is sealed to seal the receiving space 1331. Here, the cup-shaped portion 133 having the receiving portion 1331 may be formed in the upper case 131 to receive the electrode assembly 10 in the upper portion. As shown in FIG. Figure 1 As shown in FIG. 1 , one side of the upper housing 131 and one side of the lower housing 132 may be connected to each other. However, the present invention is not limited thereto. For example, the upper housing 131 and the lower housing 132 may be manufactured separately to be separated from each other.

[0056] When the electrode lead 12 is connected to the electrode connector 11 of the electrode assembly 10 and an insulating portion 14 is provided on a portion of the electrode lead 12, the electrode assembly 10 can be accommodated in a accommodating space 1331 provided in the cup-shaped portion 133 of the lower shell 132, and the upper shell 131 can cover the accommodating space from the upper side. In addition, an electrolyte is injected, and a sealing portion 134 extending outward from the edges of the upper shell 131 and the lower shell 132 is sealed. The electrolyte can move lithium ions generated by the electrochemical reaction of the electrodes during charging and discharging of the secondary battery 1. The electrolyte 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. As Figure 2 As shown in , the pouch type secondary battery 1 may be manufactured by the above method.

[0057] Figure 3 1 is a perspective view showing a state in which the volume of the pouch-type secondary battery 1 is expanded according to one embodiment of the present invention.

[0058] In general, the pouch-type secondary battery 1 may abnormally generate a large amount of gas due to heat caused by internal short circuit, overcharge, overdischarge, etc., external impact on the electrode assembly 10, and electrolyte decomposition and thermal runaway caused by heat. In addition, when the secondary battery is stored at high temperature, the electrochemical reaction between the electrolyte and the electrode active material is rapidly promoted by the high temperature, thereby generating gas.

[0059] In order to manufacture the pouch type battery case 13, a flexible pouch film 135 is drawn using a punch or the like. Drawing is performed by inserting the pouch film 135 into a punch and applying pressure to the pouch film 135 via the punch to stretch the pouch film 135. As described above, the pouch film 135 is stretched to form a recessed cup-shaped portion 133, thereby manufacturing the battery case 13. The pouch film 135 is formed by stacking a surface protective layer made of nylon resin or polyethylene terephthalate (PET), a gas barrier layer mainly made of an aluminum film (Al foil), and a sealant layer mainly made of a polymer such as polypropylene (PP) or polyethylene (PE).

[0060] However, if gas is generated in the battery case 13, since all layers have flexibility in the battery case 13, as shown in FIG. Figure 3 As shown in , the internal pressure of the secondary battery 1 increases due to the generated gas, thereby expanding the volume of the secondary battery 1. In addition, there are problems such as weakening of the bonding force between components, damage to the case of the secondary battery 1, premature operation of the protection circuit, electrode deformation, internal short circuit, explosion, etc.

[0061] Figure 4 is a flowchart illustrating a method of manufacturing the electrode lead 12 according to one embodiment of the present invention.

[0062] According to one embodiment of the present invention, since the two-stage electrode lead 12 is formed, even if gas is generated in the battery case to increase the internal pressure, the gas can be discharged to the outside to ensure safety. In addition, since the two-stage electrode lead 12 is reliably separated, the electrical connection can be completely cut off. In addition, while improving the electrolyte resistance of the adhesive that bonds the two-stage electrode lead 12 to each other, the contact resistance does not increase significantly.

[0063] To this end, the method of manufacturing the electrode lead 12 according to one embodiment of the present invention includes: a step of manufacturing each of the first electrode lead 123 and the second electrode 12; a step of applying an adhesive to at least one of the other end of the first electrode lead 123 and one end of the second electrode lead 124; a step of combining the other end of the first electrode lead 123 with one end of the second electrode lead 124 to form a lead stack; and a step of applying heat to the lead stack to cure the adhesive, thereby forming the connection portion 15. Here, the adhesive is formed by mixing a conductor and a solvent, the solvent is formed by mixing a polymer and a diluent, and the solvent contains 5wt% to 15wt% of the diluent.

[0064] The electrode lead 12 manufactured in this manner includes: a first electrode lead 123, one end of which is connected to the electrode tab 11 protruding from one side of the electrode assembly 10; a second electrode lead 124, one end of which is connected to the other end of the first electrode lead 123, and the other end protrudes to the outside of the battery case 13 accommodating the electrode assembly 10; and a connecting portion 15 configured to connect the first electrode lead 123 to the second electrode lead 124. Here, the connecting portion 15 is formed by curing an adhesive applied between the first electrode lead 123 and the second electrode lead 124, the adhesive being formed by mixing a conductor and a solvent, the solvent being formed by mixing a polymer and a diluent, the solvent containing 5wt% to 15wt% of the diluent.

[0065] The pouch-type secondary battery 1 including such an electrode lead 12 according to one embodiment of the present invention includes: an electrode assembly 10 in which electrodes including a positive electrode and a negative electrode and a separator are stacked; a pouch-shaped battery case 13 configured to accommodate 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, one end of which is connected to the electrode tab 11; a second electrode lead 124, one end of which is 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 configured to connect the first electrode lead 123 to the second electrode lead 124. Here, the connecting portion 15 is formed by curing an adhesive applied between the first electrode lead and the second electrode lead, the adhesive being formed by mixing a conductor and a solvent, the solvent being formed by mixing a polymer and a diluent, and the solvent containing 5 wt % to 15 wt % of the diluent.

[0066] In the following, reference will be made to Figure 5 and Figure 6 describe Figure 4 Each step is shown in the flow chart.

[0067] Figure 5 The invention relates to a pouch-type secondary battery according to an embodiment of the present invention. Figure 2 A partial cross-sectional view taken along line A-A'.

[0068] According to one embodiment of the present invention, the electrode lead 12 is formed in two sections. That is, the electrode lead 12 includes: a first electrode lead 123, one end of which is connected to the electrode connector 11 of the electrode assembly 10; and a second electrode 124, one end of which is connected to the other end of the first electrode lead 123, and the other end protrudes to the outside of the battery case 13. In addition, one surface of the other end of the first electrode lead 123 and one surface of one end of the second electrode lead 124 can be adhered to each other by means of a connecting member 15, so as to be connected to each other.

[0069] In order to manufacture the electrode lead 12, first, the first electrode lead 123 and the second electrode lead 124 are manufactured separately (S401). Preferably, each of the first electrode lead 123 and the second electrode lead 124 has a rectangular shape. In addition, in order to easily combine with each other later, it is preferred that the first electrode lead 123 and the second electrode lead 124 have the same width.

[0070] An adhesive is applied to at least one of the other end of the manufactured first electrode lead 123 and one end of the manufactured second electrode lead 124 (S402). 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 stack (S403).

[0071] The binder includes a material having conductivity. Therefore, electricity generated from the electrode assembly 10 can be easily discharged to the outside. To this end, it is preferred that the binder is formed by mixing a conductor and a solvent, and the solvent is formed by mixing a polymer and a diluent.

[0072] The conductor may include at least one of the following: natural or artificial graphite; carbon black, such as acetylene black, Kerner black, channel black, furnace black, lamp black and summer black; conductive fiber, such as carbon fiber or metal fiber; metal powder, such as fluorinated carbon, aluminum, nickel, gold, silver and copper powder; core / shell structure powder coated with different kinds of metals on one metal; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenyl derivatives, and the conductor, in particular, the conductor may most preferably include silver. Preferably, the content of the conductor contained in the binder is 70wt% to 85wt%.

[0073] The polymer may include at least one of acrylic resin, epoxy resin, ethylene propylene diene monomer (EPDM) resin, chlorinated polyethylene (CPE) resin, silicone, polyurethane, urea resin, melamine resin, phenolic resin, unsaturated ester resin, polypropylene (PP), polyethylene (PE), polyimide and polyamide, and the polymer may most preferably include epoxy resin or acrylic resin. Preferably, the content of the polymer contained in the adhesive is 15wt% to 30wt%.

[0074] In order to increase the convenience of users by reducing the viscosity of the adhesive and improving the fluidity, a diluent is added to the polymer. Here, the diluent can be a glycidyl ester material, for example, it can include n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, styrene oxide, phenyl glycidyl ether, cresyl glycidyl ether, methacrylate glycidyl ester, tertiary carboxylic acid glycidyl ester, monoepoxides such as vinyl cyclohexene monoepoxide, butanediol glycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether or diepoxides such as vinyl cyclohexene dioxide.

[0075] In addition, the addition ratio of the diluent is 5wt% to 15wt%, preferably 5wt% to 10wt%. If the addition ratio of the diluent is less than 5wt%, the viscosity is too high, so it is almost impossible to apply the adhesive, or even if the adhesive can be applied, there is a problem that it takes too much time and effort to apply the adhesive. On the contrary, if the addition ratio of the diluent is greater than 15wt%, the electrolyte resistance of the connecting portion 15 formed by curing the adhesive will decrease. Therefore, there is a problem that after the secondary battery 1 is manufactured, the two-stage electrode lead 12 is separated due to the electrolyte.

[0076] After forming the lead stack, heat is applied to the lead stack using an oven or the like (S404). Then, the adhesive is dried and cured to form the connection portion 15, and the connection portion 15 also includes a conductor and a conductive polymer. Figure 5 As shown in , the two-section electrode lead 12 in which the first electrode lead 123 and the second electrode lead 124 are connected to each other can be completely manufactured.

[0077] When the battery case 13 is normal, the first electrode lead 123 and the second electrode lead 124 must be stably connected to each other. When the secondary battery 13 expands, the first electrode lead 123 and the second electrode lead 124 must be easily separated from each other. Therefore, it is preferred that the first electrode lead 123 and the second electrode lead 124 are arranged on different planes so that the upper surface and the lower surface thereof are connected to each other, rather than the first electrode lead 123 and the second electrode lead 124 being arranged on the same plane so that the side surfaces thereof are connected to each other.

[0078] Preferably, the connection portion 15 connecting the first electrode lead 123 and the second electrode lead 124 has an extremely thin thickness of 1 μm to 500 μm. Therefore, even if a step portion is formed between the first electrode lead 123 and the second electrode lead 124, the size of the step portion is not too large.

[0079] As described above, a portion of the electrode lead 12 is surrounded by the insulating portion 14, and in particular, a portion where the first electrode lead 123 and the second electrode lead 124 are connected to each other by means of the connecting portion 15 is surrounded by the insulating portion 14. Moreover, the first electrode lead 123 and the second electrode lead 124 are combined with the battery case 13 via the insulating portion 14. In the process of sealing the upper case 131 and the lower case 132, a relatively high pressure may be applied to the portion in contact with the electrode lead 12, thereby damaging the sealant layer of the battery case 13. Since the sealant layer is directly in contact with the electrode assembly 10 as described above, the sealant layer may have insulating properties. However, if the sealant layer is damaged, electricity may flow to the battery case 13 via 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 partially damaged to expose the gas barrier layer, electricity may easily flow due to contact with the electrode lead 12.

[0080] Therefore, the insulating part 14 can be made of a non-conductor with non-conductivity, which is non-conductive. In addition, the insulating part 14 has high mechanical strength and heat resistance. Therefore, the insulating part 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, heat resistance, and chemical properties such as corrosion resistance, and is therefore mainly used to manufacture the insulating part 14. In addition, acid-treated polypropylene can be provided to improve the bonding force of the insulating part 14. For example, acid-treated polypropylene and ordinary polypropylene can be mixed with each other, and polypropylene can be further mixed or only acid-treated polypropylene can be provided. Here, the acid-treated polypropylene can be maleic anhydride polypropylene (MAH PP).

[0081] Therefore, when the upper shell 131 and the lower shell 132 are thermally fused, the insulating portion 14 can maintain its shape, thereby preventing the electrode lead 12 and the gas barrier layer from contacting each other even if a portion of the sealant layer is damaged. Therefore, the power generated from the electrode assembly 10 can be prevented from flowing to the battery case 13 via the electrode lead 12.

[0082] like Figure 5 As shown in , the insulating portion 14 may surround all of the first electrode lead 123, the connecting portion 15, and the second electrode lead 124. If the first electrode lead 123 or the connecting portion 15 is not surrounded by the insulating portion 14, even if the battery case 13 expands, repulsive force may not be applied to the first electrode lead 123 and the second electrode 124.

[0083] Figure 6 The pouch-type secondary battery according to one embodiment of the present invention is expanded in volume. Figure 2A partial cross-sectional view taken along line A-A'.

[0084] As described above, when the internal pressure of the pouch type secondary battery 13 increases, the volume of the pouch type secondary battery 1 expands. Figure 6 As shown in , the outer wall of the battery housing 13 moves outward. Here, the upper wall and the lower wall of the outer wall of the battery housing 13 may have a large area and are not sealed, resulting in higher flexibility. Therefore, the upper wall of the battery housing 13 may move upward, and the lower wall of the battery housing 13 may move downward. The outer wall of the battery housing 13 may move outward to apply a repulsive force to the first electrode lead 123 and the second electrode 124 connected by means of the insulating portion 14. Therefore, as the internal pressure of the battery housing 13 gradually increases, the moving force of the outer wall of the battery housing 13 may be greater, and the repulsive force applied to the first electrode lead 123 and the second electrode lead 124 may be greater.

[0085] When the binding force between the first electrode lead 123 and the second electrode lead 124 is greater than the repulsive force, as shown in FIG. Figure 6 As shown in , the first electrode lead 123 and the second electrode lead 124 can be separated from each other. Therefore, the electrical connection can be physically interrupted so that electricity no longer flows. Here, the separation may mean that the adsorption or attachment parts are separated from each other. However, the bonding force between the first electrode lead 123 and the second electrode lead 124 and the connecting portion 15 may be less than the bonding 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 bonding force between the first electrode lead 123 and the second electrode lead 124 and the insulating portion 14 can be maintained to maintain the sealing of the battery case 13, but the first electrode lead 123 and the second electrode lead 124 can be separated from each other.

[0086] Manufacturing Example 1

[0087] A nickel-plated copper plate having a thickness of 200 μm was cut to produce each of a first electrode lead having a length of 40 mm and a width of 45 mm and a second electrode lead having a length of 10 mm and a width of 45 mm.

[0088] 30 g of a first silver powder having a particle size of 5 μm or less and 30 g of a second silver powder having a particle size of 2 μm or less were mixed in a weight ratio of 1:1. In addition, 1 g of glycidyl ester was added as a diluent to 9 g of liquid epoxy resin to prepare a solvent. In addition, 7.8 g of the mixed silver powder was dissolved in 2.2 g of the solvent to prepare an adhesive containing 78 wt % of silver and 22 wt % of the solvent. Here, glycidyl ester as a diluent was applied to the epoxy resin at a ratio of 10 wt %, thus accounting for 2.2 wt % of the total adhesive.

[0089] The prepared adhesive was applied to an area from one end of the second electrode lead to a distance of 5 mm, and the other end of the first electrode lead was bonded to form a lead stack. In addition, the lead stack was placed in an oven, and the adhesive was dried and cured at a temperature of 180° C. for 1 hour to manufacture a two-segment electrode lead.

[0090] Manufacturing Example 2

[0091] The two-segment electrode lead was manufactured in the same manner as in Manufacturing Example 1, except that 0.5 g of glycidyl ester was added as a diluent to 9.5 g of liquid epoxy resin to prepare a solvent. Here, glycidyl ester as a diluent was added to the epoxy resin at a ratio of 5 wt %, thus accounting for 1.1 wt % in the total binder.

[0092] Comparative Example 1

[0093] The two-segment electrode lead was manufactured in the same manner as in Manufacturing Example 1, except that 3 g of glycidyl ester was added as a diluent to 7 g of liquid epoxy resin to prepare a solvent. Here, glycidyl ester as a diluent was added to the epoxy resin at a ratio of 30 wt %, thus accounting for 6.6 wt % in the total binder.

[0094] Comparative Example 2

[0095] The two-segment electrode lead was manufactured in the same manner as in Manufacturing Example 1, except that 5 g of glycidyl ester was added as a diluent to 5 g of liquid epoxy resin to prepare a solvent. Here, glycidyl ester as a diluent was added to the epoxy resin at a ratio of 50 wt %, thus accounting for 11 wt % in the total binder.

[0096] [Table 1]

[0097]

[0098] Methods for measuring physical properties 1. Long-term reliability

[0099] First, the two-segment electrode lead samples manufactured in Manufacturing Example 1, Manufacturing Example 2, Comparative Example 1 and Comparative Example 2 were each contained in a 125 ml polyethylene (PE) bottle together with 30 ml of electrolyte (prepared by dissolving 1 M of lithium salt (LiPF6) and ethylene carbonate (EC), ethyl carbonate (EMC), and dimethyl carbonate (DMC), and ethylene carbonate (EC): ethyl carbonate (EMC): dimethyl carbonate (DMC) was 3:3:4), and then the inlet was sealed with paraffin. Then, each bottle was sealed with aluminum wrapping paper and stored in a room at a temperature of 60°C and a relative humidity of 90%RH for 16 weeks. After every 1, 2, 4, 8 and 16 weeks, the two-segment electrode lead samples were taken out, the electrolyte was completely removed, and a terminal was connected at each of the two ends to measure the resistance using an ohmmeter (model: HIOKI 3560).

[0100] Results obtained by measuring physical properties -1. Long-term reliability

[0101] [Table 2]

[0102]

[0103] As described in [Table 2], when Manufacturing Examples 1 and 2 are compared with Comparative Examples 1 and 2 according to the present invention, the electrode leads according to Manufacturing Examples 1 and 2 were not separated into the first electrode lead and the second electrode lead even after 16 weeks. On the other hand, in the electrode leads according to Comparative Examples 1 and 2, the first electrode lead and the second electrode lead were separated from each other due to the electrolyte after only two weeks.

[0104] As described above, in the case of the electrode leads according to Manufacturing Examples 1 and 2, the bonding force of the connection portion was not significantly reduced by the electrolyte, but in the case of the electrode leads according to Comparative Examples 1 and 2, the bonding force of the connection portion was significantly reduced. That is, it can be seen that the electrode leads according to Manufacturing Examples 1 and 2 have an electrolyte resistance superior to that of the electrode leads according to Comparative Examples 1 and 2.

[0105] In the electrode lead according to Manufacturing Example 1, the resistance increased from 0.150 mΩ as the initial resistance to 0.169 mΩ after 16 weeks, an increase of 12.7%. On the other hand, in the electrode lead according to Manufacturing Example 2, the resistance increased from 0.136 mΩ as the initial resistance to 0.137 mΩ after 16 weeks, an increase of only 0.74%.

[0106] As described above, it can be seen that the electrode lead according to Manufacturing Example 2 does not have a greater increase in resistance than the electrode lead according to Manufacturing Example 1.

[0107] Methods for measuring physical properties -2.Weight reduction rate

[0108] The two-segment electrode lead samples manufactured in Manufacturing Example 1 and Comparative Example 1 were placed in a synchronous thermogravimetric analyzer (manufacturer: HITACHI, model: STA7200). Then, heat was applied at a temperature from 30°C to 400°C at a heating rate of 4°C / min in a nitrogen (N2) atmosphere. Then, the change in mass compared to the initial mass was calculated to calculate the weight reduction rate.

[0109] Results obtained by measuring physical properties -2.Weight reduction rate

[0110] [Table 3]

[0111]

[0112] Figure 7 is a graph showing the weight reduction rate of each of the electrode lead samples of Manufacturing Example 1 and Comparative Example 1 according to the present invention.

[0113] like Figure 7 As shown in , as the temperature increases, the weight of the electrode lead according to Comparative Example 1 decreases faster than that of the electrode lead according to Manufacturing Example 1. In particular, as described in [Table 3], the weight reduction rate of the electrode lead manufactured at a temperature of 300°C according to Manufacturing Example 1 is only -0.4wt%, but the weight reduction rate of the electrode lead according to Comparative Example 1 is -1.4wt%. A high weight reduction rate means that the content of the diluent and the residual amount of moisture contained in the diluent itself are large. However, when the adhesive is dried and cured, the diluent and the moisture contained in the diluent itself are not fully evaporated in the electrode lead according to Comparative Example 1 (while being fully evaporated in the electrode lead according to Manufacturing Example 1), so the amount of the diluent and the residual amount of moisture are large. If the amount of the diluent and the residual amount of moisture are large, the reactivity with the electrolyte is high, and when the amount of the diluent and the residual amount of moisture are small, the reactivity with the electrolyte is low.

[0114] As described above, since the electrode lead according to Manufacturing Example 1 of the present invention has a smaller weight at high temperature than the electrode lead according to Comparative Example 1, it can be seen that the amount of diluent and the residual amount of moisture are small, and therefore, the electrolyte resistance is more excellent.

[0115] Those skilled in the art to which the present invention relates will appreciate that the present invention may be implemented in other specific forms without changing the technical ideas or essential features. Therefore, the embodiments disclosed above should be considered illustrative rather than restrictive. Therefore, the scope of the present invention is defined by the appended claims rather than the preceding description and the exemplary embodiments described therein. Various modifications made within the equivalent meanings of the claims of the present invention and within the claims should be considered to be within the scope of the present invention.

[0116] Reference numerals

[0117] 1: Secondary battery 10: Electrode assembly

[0118] 11: Electrode connector 12: Electrode lead

[0119] 13: Battery housing 14: Insulation part

[0120] 15: Connection part 111: Positive terminal

[0121] 112: Negative electrode connector 121: Positive electrode lead

[0122] 122: negative electrode lead 123: first electrode lead

[0123] 124: second electrode lead 131: upper shell

[0124] 132: Lower shell 133: Cup-shaped part

[0125] 134: Sealing part 135: Bag film

[0126] 1331: Accommodation Space

Claims

1. An electrode lead, comprising: a first electrode lead having one end 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 of the second electrode lead protruding to the outside of a battery case accommodating the electrode assembly; as well as a connecting portion configured to connect the first electrode lead to the second electrode lead, wherein the connection portion is formed by curing an adhesive applied between the first electrode lead and the second electrode lead using heat, The adhesive is formed by mixing a conductor and a solvent, The solvent is formed simply by mixing the polymer and the diluent, and The solvent contains 5 wt % to 15 wt % of the diluent.

2. The electrode lead according to claim 1, wherein: The solvent contains 5 wt % to 10 wt % of the diluent.

3. The electrode lead according to claim 1, wherein: The diluent includes glycidyl ester materials.

4. The electrode lead according to claim 1, wherein: The adhesive contains 70 wt % to 85 wt % of the conductor and 15 wt % to 30 wt % of the solvent.

5. The electrode lead according to claim 1, wherein: The conductor includes at least one of graphite, carbon black, conductive fiber, metal powder, powder of a core / shell structure in which one metal is coated with different kinds of metals, conductive whiskers, conductive metal oxides and conductive materials.

6. The electrode lead according to claim 5, wherein: The conductor includes silver.

7. The electrode lead according to claim 1, wherein: The polymer includes at least one of acrylic resin, epoxy resin, ethylene propylene diene monomer (EPDM) resin, chlorinated polyethylene (CPE) resin, silicone, polyurethane, urea resin, melamine resin, phenolic resin, unsaturated ester resin, polypropylene (PP), polyethylene (PE), polyimide and polyamide.

8. The electrode lead according to claim 7, wherein: The polymer includes epoxy resin or acrylic resin.

9. A pouch-type secondary battery, comprising: An electrode assembly, in which electrodes and a separator are stacked, wherein the electrodes include a positive electrode and a negative electrode; a pouch-shaped battery case configured to accommodate the electrode assembly; an electrode connector connected to the electrode and protruding from one side of the electrode assembly; a first electrode lead, one end of which is connected to the electrode connector; 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 the battery case; as well as a connecting portion configured to connect the first electrode lead to the second electrode lead, wherein the connection portion is formed by curing an adhesive applied between the first electrode lead and the second electrode lead using heat, The adhesive is formed by simply mixing a conductive material and a solvent, The solvent is formed by mixing the polymer and the diluent, and The solvent contains 5 wt % to 15 wt % of the diluent.

10. The pouch-type secondary battery according to claim 9, further comprising an insulating portion configured to surround a portion where the first electrode lead and the second electrode lead are connected to each other via the connecting portion, and configured to combine the first electrode lead and the second electrode lead with the battery case.

11. The pouch type secondary battery according to claim 10, wherein: A bonding force between each of the first electrode lead and the second electrode lead and the connection portion is smaller than a bonding force between each of the first electrode lead and the second electrode lead and the insulation portion.

12. The pouch type secondary battery according to claim 10, wherein: The insulating portion is made of at least one of a thermoplastic resin, a thermosetting resin, and a photocurable resin, and has electrical insulating properties.

13. A method for manufacturing an electrode lead, the method comprising: a step of manufacturing each of a first electrode lead and a second electrode lead; applying an adhesive to at least one of the other end of the first electrode lead or one end of the second electrode lead; combining the other end of the first electrode lead with the one end of the second electrode lead to form a lead stack; as well as applying heat to the lead stack to cure the adhesive to form a connection portion, wherein the adhesive is formed by mixing a conductive material and a solvent, The solvent is formed simply by mixing the polymer and the diluent, and The solvent contains 5 wt % to 15 wt % of the diluent.

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