Lead tab with improved adhesion

Abstract

To provide a lead tab with improved adhesion.SOLUTION: According to an embodiment of the present invention, there is provided a lead tab including a metallic base including copper, a nickel plating layer stacked on both surfaces of the metallic base, and a metallic layer on the nickel plating layer, wherein the metallic layer includes 70 to 99. 9wt% of chromium and has an adhesion strength of 1. 4N / mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lead tab with improved adhesion. [Background technology]

[0002] The secondary battery industry is in the spotlight as a core component of IT equipment, along with semiconductors and displays. In recent years, the use of large-capacity batteries has been increasing for applications such as electric bicycles, hybrid electric vehicles (HEVs), electric vehicles (EVs), plug-in hybrid electric vehicles (PHEVs), and energy storage systems (ESSs).

[0003] Typical secondary batteries are equipped with lead tabs for extracting electricity. One end of the lead tab of a secondary battery is connected to the battery element and sandwiched between opposing films, and the other end protrudes outside the films.

[0004] In secondary batteries, surface treatment of the lead tab is required to facilitate adhesion between the lead tab and insulating film and to prevent defects such as corrosion and peeling due to stimuli inside and outside the battery in the actual usage environment after adhesion.

[0005] On the other hand, hexavalent chromium was used in the materials used in conventional surface treatment technologies. However, the use of surface treatment methods using hexavalent chromium is currently restricted or limited worldwide due to its toxicity to the human body and environmental issues.

[0006] To solve these problems, research into lead tabs with improved adhesion has been ongoing. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention relates to a lead tab with improved adhesion that can avoid the problems caused by the limitations and drawbacks of the related art as described above.

[0008] In addition to the above-mentioned aspects of the present invention, other features and advantages of the present invention will be described below or will be apparent to those skilled in the art from such description. [Means for solving the problem]

[0009] One embodiment of the present invention provides a lead tab including a metal substrate, nickel plating layers laminated on both sides of the metal substrate, and a metal layer on the nickel plating layer, the metal layer containing 70 to 99.9 wt% chromium and having an adhesion strength of 1.4 N / mm or more. [Effects of the Invention]

[0010] According to the present invention, a lead tab with improved adhesion can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a perspective view of a secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view of a lead tab according to an embodiment of the present invention. [Figure 3] FIG. 2 is a cross-sectional view taken along II' in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments described below are presented for illustrative purposes only to help a clear understanding of the present invention, and are not intended to limit the scope of the present invention.

[0013] The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are merely examples, and the present invention is not limited to the details shown in the drawings. The same components may be designated by the same reference numerals throughout the specification. In describing the present invention, if it is determined that a detailed description of related publicly known technology may unnecessarily obscure the gist of the present invention, such a detailed description will be omitted.

[0014] When terms such as "comprise," "have," and "consist of" are used in this specification, other parts may be added unless the expression "only" is used. When an element is expressed in the singular, it includes the plural unless otherwise expressly stated. In addition, when interpreting an element, it is interpreted as including a margin of error even if there is no other explicit statement.

[0015] When describing a positional relationship, for example, when the positional relationship of two parts is described using "above," "on top," "below," "next to," etc., one or more other parts may be located between the two parts, unless the words "immediately" or "directly" are used.

[0016] Spatially relative terms such as "below," "bottom," "above," and "top" can be used to easily describe the relationship between one element or component and another, as shown in the figures. Spatially relative terms should be understood to include different orientations of elements in use or operation in addition to the orientation shown in the figures. For example, if elements shown in the figures are inverted, an element described as "below" or "below" another element can be placed "above" the other element. Thus, the exemplary term "below" can encompass both an orientation of below and above. Similarly, the exemplary terms "above" or "above" can encompass both an orientation of above and below.

[0017] When describing a temporal relationship, for example, when the temporal precedence is described using "after," "following," "next," or "before," it can also include cases where the relationship is not consecutive, unless the words "immediately" or "directly" are used.

[0018] Although terms such as "first" and "second" are used to describe various components, these components are not limited by these terms. These terms are used to distinguish one component from another. Therefore, a first component referred to below may also be a second component within the technical concept of the present invention.

[0019] The term "at least one" should be understood to include all possible combinations of one or more associated items. For example, "at least one of the first, second, and third items" can mean each of the first, second, or third items, as well as all possible combinations of items that can be present from two or more of the first, second, and third items.

[0020] The features of the various embodiments of the present invention may be partially or wholly combined or combined with one another, may be technically interlocked and driven in various ways, and each embodiment may be implemented independently of the others or may be implemented together in relation to one another.

[0021] FIG. 1 is a perspective view of a secondary battery 1 according to an embodiment of the present invention.

[0022] FIG. 2 is a cross-sectional view of a lead tab 10 according to one embodiment of the present invention.

[0023] FIG. 3 is a cross-sectional view taken along II' in FIG.

[0024] The type of secondary battery 1 according to an embodiment of the present invention is not particularly limited, but may preferably be a lithium secondary battery.

[0025] 1 and 3, a secondary battery 1 according to an embodiment of the present invention includes a film-shaped anode 161 and a film-shaped cathode 162 stacked with a separator 163 interposed therebetween, and an electrolyte 164 disposed between the anode 161 and the cathode 162, enabling charging and discharging through the transfer of lithium ions. The secondary battery 1, including the anode 161, the cathode 162, and the electrolyte 164, is liquid-tightly covered with an exterior material 30. Specifically, the anode 161, the cathode 162, and the electrolyte 164 are enclosed within the exterior material 30 to protect them from the outside. The anode 161 is formed by coating anode active material slurry on a copper foil for secondary batteries as an anode current collector. The cathode 162 is also formed by coating a cathode active material slurry on a cathode current collector, such as aluminum.

[0026] Although not shown in the figure, the lead tab 10 may consist of a negative electrode lead tab and a positive electrode lead tab. More specifically, the lead tab 10 located on the left side of Fig. 1 may be the negative electrode lead tab, and the lead tab 10 located on the right side may be the positive electrode lead tab.

[0027] Referring to FIG. 1, a sealing tape 20 is disposed on one side of an outer casing 30 of a secondary battery 1. The sealing tape 20 further improves adhesion between the lead tab 10 and the outer casing 30. The sealing tape 20 is disposed on the lead tab 10, and a portion of the sealing tape 20 adheres to the inner surface of the outer casing 30 to seal the outer casing 30. The sealing tape 20 prevents leakage of the electrolyte 164 or the like sealed inside the outer casing 30. The sealing tape 20 is also disposed between the lead tab 10 and the outer casing 30 to ensure insulation between the lead tab 10 and the outer casing 30. A polypropylene film is used as the sealing tape 20. However, the present invention is not limited thereto and may be formed of a polymer composite.

[0028] Referring to FIG. 1, one end of the lead tab 10 is connected to either the positive electrode 161 or the negative electrode 162 , and the other end of the lead tab 10 is exposed to the outside of the exterior material 30 .

[0029] 2, the lead tab 10 of the present invention includes a metal substrate 110 containing copper (Cu), a nickel-plated layer 120 on the metal substrate 110, and a metal layer 130 on the nickel-plated layer 120. The metal substrate 110, the nickel-plated layer 120, and the metal layer 130 will be described in detail below.

[0030] Referring to FIG. 3, a plurality of electrode tabs 150 protruding from the negative electrode 161 are integrally joined to form a pre-welding portion 151, and a lead tab 10 is electrically connected to the upper end of the pre-welding portion 151 by welding.

[0031] For example, in the case of ultrasonic welding, when ultrasonic vibrations are applied, the lead tab 10 bites into and adheres to the pre-welded portion 151 formed by the electrode tab 150 being integrally bonded while being plastically deformed by frictional heat.

[0032] The material of the metal substrate 110 is not particularly limited, but may be aluminum or copper. According to an embodiment of the present invention, the metal substrate 110 may be a rolled copper foil.

[0033] According to an embodiment of the present invention, the metal substrate 110 may have a thickness of 100 to 1,000 μm, and preferably has a thickness of 100 to 500 μm.

[0034] A nickel plating layer 120 is disposed on the metal substrate 110 .

[0035] According to one embodiment of the present invention, the nickel plating layer 120 contains nickel (Ni), and therefore the lead tab 10 according to the embodiment of the present invention has an anti-oxidation effect and can prevent corrosion caused by hydrofluoric acid generated by the reaction of the electrolyte with moisture.

[0036] According to an embodiment of the present invention, the nickel plating layer 120 may have a thickness of 0.5 to 10.0 μm.

[0037] On the other hand, if the nickel plating layer 120 has a thickness of less than 0.5 μm, the nickel plating layer 120 may be deposited unevenly, and as a result, the metal layer 130 disposed on the nickel plating layer 120 may be deposited unevenly, resulting in a problem that the lead tab 10 including the nickel plating layer 120 has uneven corrosion resistance.

[0038] Furthermore, if the nickel plating layer 120 has a thickness exceeding 10.0 μm, the internal stress in the nickel plating layer 120 increases, causing cracks. Therefore, the nickel plating layer 120 according to the present embodiment should have a thickness of 0.5 to 10.0 μm.

[0039] In this way, the corrosion resistance of the lead tab 10 can be significantly improved through the nickel plating layer 120, which has excellent corrosion resistance, and at the same time, the adhesion between the metal substrate 110 and the metal layer 130 can be increased, resulting in further improvement in corrosion resistance and sealing performance.

[0040] According to an embodiment of the present invention, the lead tab 10 may further include a metal layer 130 on the nickel plating layer 120 .

[0041] The metal layer 130 contains 70 to 99.9 wt % (w / w) of chromium (Cr).

[0042] Specifically, the metal layer 130 may be formed by a dry vacuum process. For example, the metal layer 130 may be formed by any one of a sputtering process, an evaporation process, an ion plating process, and a CVD process, as examples of the dry vacuum process. Preferably, the metal layer 130 may be formed by a sputtering process.

[0043] When the metal layer 130 is formed on the nickel plating layer 120 by a dry vacuum process, nickel (Ni) may be partially contained within the metal layer 130. Even in this case, the metal layer 130 may contain 70.0% or more of chromium (Cr).

[0044] Typically, lead tabs further include a protective layer containing a chromium compound to improve corrosion resistance. Here, the protective layer is formed by chromate treatment. However, a protective layer formed by chromate treatment may have a very high oxygen fraction within the protective layer. Here, the oxygen fraction refers to the ratio of oxygen to the total number of atoms in the protective layer. A protective layer with a very high oxygen fraction may cause excessive oxidation of the metal layer in contact with the protective layer, resulting in reduced adhesion between the lead tab and the insulating film.

[0045] In addition, in the case of a protective layer formed by chromate treatment, trivalent chromium (Cr 3+ ) or hexavalent chromium (Cr 6+ ) may be present in part. Here, hexavalent chromium (Cr 6+ ) can have a strong oxidizing power, which can result in excessive oxidation of the metal layer in contact with the protective layer, resulting in a decrease in the adhesion between the lead tab and the insulating film.

[0046] Therefore, according to one embodiment of the present invention, in order to increase the adhesive strength between the lead tab 10 and the sealing tape 20, the metal layer 130 needs to contain 70 to 99.9 wt % of chromium (Cr).

[0047] According to one embodiment of the present invention, when the metal layer 130 is deposited by a sputtering process and contains 70 to 99.9 wt% chromium (Cr), the oxygen fraction in the metal layer 130 is sufficiently low to achieve the intended purpose, thereby increasing the adhesion between the lead tab 10 and the sealing tape 20. As a result, defects such as corrosion and peeling due to stimuli inside and outside the battery may not occur in an actual usage environment.

[0048] According to an embodiment of the present invention, when the metal layer 130 is deposited by a sputtering process and contains 70 to 99.9 wt % of chromium (Cr), the hexavalent chromium (Cr 6+ ) is less harmful to humans and the environment, which can prevent the occurrence of harmful effects.

[0049] The lead tab 10 according to one embodiment of the present invention may have an adhesion strength of 1.4 N / mm or more. The adhesion strength of the lead tab 10 is measured by heat-sealing the lead tab 10 and the insulating film, immersing the fused lead tab 10 and insulating film in a moisture-containing electrolyte solution in an aluminum pouch, sealing the pouch, and then measuring the peel strength 21 days later. The measured peel strength is defined as the adhesion strength according to the present invention. A method for measuring adhesion strength according to one embodiment of the present invention will be described in detail below.

[0050] According to one embodiment of the present invention, when the lead tab 10 has an adhesion strength of 1.4 N / mm or more, the bonding strength between the lead tab 10 and the sealing tape 20 is improved, and defects such as corrosion and peeling due to stimuli inside and outside the battery may not occur in an actual usage environment.

[0051] On the other hand, if the lead tab 10 has an adhesion strength of less than 1.4 N / mm, the bonding strength between the lead tab 10 and the sealing tape 20 will be reduced, and defects such as corrosion or peeling may occur due to stimuli inside and outside the battery in the actual usage environment. Preferably, the lead tab 10 has an adhesion strength of 1.5 N / mm or more.

[0052] According to one embodiment of the present invention, the metal layer 130 may have a thickness of 10 to 500 nm.

[0053] If the metal layer 130 has a thickness of less than 10 nm, the metal layer 130 may be deposited unevenly, and as a result, when forming the secondary battery 1, the sealing tape 20 placed on the metal layer 130 may be deposited unevenly, which may cause a problem of leakage of the electrolyte 164 in the secondary battery 1.

[0054] Furthermore, if the thickness of the metal layer 130 exceeds 500 nm, the internal stress in the metal layer 130 increases, causing cracks. Therefore, the metal layer 130 according to the embodiment of the present invention should have a thickness of 10 to 500 nm, and preferably, a thickness of 10 to 200 nm.

[0055] A method for manufacturing the lead tab 10 according to an embodiment of the present invention will now be described in detail.

[0056] First, a metal substrate 110 is prepared.

[0057] The metal substrate 110 may have a thickness of 100 to 1,000 μm and may be made of, but is not limited to, aluminum or copper. According to one embodiment of the present invention, the metal substrate 110 may be a rolled copper foil.

[0058] Subsequently, a nickel plating layer 120 is formed on the metal substrate 110. The nickel plating layer 120 may be formed to a thickness of 0.5 to 10.0 μm through an electroplating process using a roll-to-roll device.

[0059] The electroplating process of the present invention for forming the nickel plating layer 120 will be described in more detail below.

[0060] The electroplating of the present invention is carried out by passing the metal substrate 110 through the electrolyte.

[0061] According to the present invention, the electrolytic solution is maintained at 40-60°C and pH 3.5-4.5 during the electroplating process, and contains 350-600 g / L of nickel sulfamate, 10-20 g / L of nickel chloride, 30-50 g / L of boric acid, and 0.01-0.02 g / L of a pitting inhibitor.

[0062] According to one embodiment of the present invention, the pitting prevention agent comprises NS-AP (MK Chem & Tech).

[0063] The electroplating process can be carried out at a speed of 2 to 3 m / min until the nickel plating layer 120 reaches a thickness of 0.5 to 10.0 μm.

[0064] The current density applied during the electroplating process is 5 to 12 A / dm 2 It could be.

[0065] The electroplating process may be vertical.

[0066] Subsequently, a metal layer 130 may be formed on the nickel plating layer 120 by a sputtering process using a DC sputtering device. The metal layer 130 may have a thickness of 10 to 500 nm.

[0067] Here, chromium (Cr) metal is used as the sputtering target.

[0068] The present invention will be described in detail below through examples and comparative examples, but the following examples are provided only to aid in understanding the present invention, and the scope of the present invention is not limited to these examples.

[0069] Example 1 After preparing rolled copper foil as the metal substrate, a nickel plating layer with a thickness of 2 μm was formed on both sides of the metal substrate using an electroplating process. Here, the concentration of nickel sulfamate in the electrolyte for forming the nickel plating layer was 600 g / L, the concentration of nickel chloride was 15 g / L, the concentration of boric acid was 40 g / L, and the concentration of pitting inhibitor was 0.02 g / L. The electrolyte concentration was 50°C, pH was 4.0, and the current density was 10 A / dm 2 The electroplating process was carried out at a speed of 2.5 m / min.

[0070] Here, NS-AP (MK Chem & Tech) was used as the pitting inhibitor.

[0071] Subsequently, a 20 nm thick metal layer was formed on the nickel plating layer using a sputtering process, completing a 300 μm lead tab. Chromium (Cr) metal was used as the target during the sputtering process.

[0072] Example 2 A lead tab was completed in the same manner as in Example 1, except that when forming the nickel plating layer, the concentration of nickel sulfamate in the electrolyte was 500 g / L.

[0073] Example 3 A lead tab was completed in the same manner as in Example 1, except that when forming the nickel plating layer, the electrolytic solution contained nickel chloride at a concentration of 20 g / L.

[0074] Example 4 A lead tab was completed in the same manner as in Example 1, except that the concentration of boric acid in the electrolyte was 35 g / L when the nickel plating layer was formed.

[0075] Example 5 A lead tab was completed in the same manner as in Example 1, except that the concentration of the pitting inhibitor was 0.15 g / L in the electrolyte when forming the nickel plating layer.

[0076] Comparative Example 1 After preparing rolled copper foil as the metal substrate, a nickel plating layer with a thickness of 2 μm was formed on both sides of the metal substrate using an electroplating process. Here, the concentration of nickel sulfamate in the electrolyte for forming the nickel plating layer was 600 g / L, the concentration of nickel chloride was 15 g / L, the concentration of boric acid was 40 g / L, and the concentration of pitting inhibitor was 0.02 g / L. The electrolyte concentration was 50°C, pH was 4.0, and the current density was 10 A / dm 2The electroplating process was carried out at a speed of 2.5 m / min.

[0077] Here, NS-AP (MK Chem & Tech) was used as the pitting inhibitor.

[0078] Next, the metal substrate having nickel plating layers formed on both sides was immersed in a 0.06 M chromate solution at room temperature for 20 seconds, dried at room temperature for 10 seconds, rinsed with distilled water for 10 seconds, immersed in a 0.06 M chromate solution at room temperature for 10 seconds, dried for 10 seconds, rinsed with distilled water for 10 seconds, and dried for 15 seconds to form a protective layer with a thickness of 20 nm. A 300 μm lead tab was completed using the same method as in Example 1, except for this.

[0079] Comparative Example 2 A lead tab was completed in the same manner as in Comparative Example 1, except that when forming the nickel plating layer, the concentration of nickel sulfamate in the electrolyte was 500 g / L.

[0080] Comparative Example 3 A lead tab was completed in the same manner as in Comparative Example 1, except that when forming the nickel plating layer, the concentration of nickel chloride in the electrolyte was 20 g / L.

[0081] Comparative Example 4 A lead tab was completed in the same manner as in Comparative Example 1, except that the concentration of boric acid in the electrolyte was 35 g / L when the nickel plating layer was formed.

[0082] Comparative Example 5 A lead tab was completed in the same manner as in Comparative Example 1, except that the concentration of the pitting inhibitor in the electrolyte was 0.15 g / L when the nickel plating layer was formed.

[0083] The adhesive strength of the lead tabs in Examples 1 to 5 and Comparative Examples 1 to 5, depending on whether or not a metal layer was formed by the sputtering process, is shown in Tables 1 and 2 below.

[0084] [Table 1]

[0085] [Table 2]

[0086] i) Adhesion strength measurement Ten lead tab samples manufactured in each of Examples 1 to 5 and Comparative Examples 1 to 5 were heat-sealed to an insulating film, and the fused samples and insulating film were then immersed in a moisture-containing electrolyte solution in an aluminum pouch, and the pouch was sealed. After 2, 7, 12, 17, 21, 25, and 28 days had passed, the 10 lead tab samples were removed from the pouches and dried, and their peel strengths were measured. The measured peel strengths were the adhesion strength after 2 days, 7 days, 12 days, 17 days, 21 days, 25 days, and 28 days. In the present invention, when "adhesion strength" is mentioned without any reference to the passage of time, it refers to the peel strength measured after 21 days.

[0087] In Table 1, NG means that the adhesion between the lead tab sample and the insulating film was so weak that peel strength measurement was impossible.

[0088] Here, the lead tab samples were cut from the lead tabs manufactured in Examples 1 to 5 and Comparative Examples 1 to 5 to a size of 45 mm x 43 mm (width: 45 mm, length: 43 mm) and formed to a thickness of 300 μm.

[0089] The insulating film used was a Ppa-H3 polypropylene film (DNP), which had a length of 55 mm, a width of 10 mm, and a thickness of 150 μm.

[0090] The heat fusion conditions, electrolyte conditions, drying conditions and peel strength measurement conditions are as follows.

[0091] <Heat fusion conditions> One-step heat fusion conditions Temperature: 164℃ Time: 5 seconds Pressure: 0.6 MPa Two-stage heat fusion conditions Temperature: 230℃ Time: 3 seconds Pressure: 0.6 MPa 3-stage heat fusion conditions Temperature: 164℃ Time: 2 seconds Pressure: 0.6 MPa Heat fusion area: 100mmx25mm

[0092] Since the heat sealing proceeds by transferring heat not only to the insulating film but also to the surrounding area of ​​the insulating film, the heat sealing area must be able to cover the entire area of ​​the insulating film.

[0093] The heat fusion for measuring the adhesion strength is carried out three times.

[0094] <Electrolyte conditions> Electrolyte type: LiPF61.0M, EC:EMC=25:75vol%, FEC 3wt EC: Ethylene carbonate EMC: Ethyl methyl carbonate FEC: Fluoroethylene carbonate LiPF6: Lithium hexafluorophosphate Temperature: 80℃ Amount of water added to the electrolyte: 10,000 ppm Immersion time: 2 days, 7 days, 12 days, 17 days, 21 days, 25 days, 28 days after immersion The sample immersed in the pouch was placed in a dry oven at 80°C for the above period.

[0095] <Drying conditions> After evaluation, remove the sample from the pouch, rinse with running water for 5 seconds, and then dry at room temperature for 30 minutes.

[0096] <Peel strength measurement conditions> Measuring equipment: UTM (Shimadzu, AGS-X model) Peeling speed: 20mm / min Peeling angle: 180° Temperature: 23±5℃

[0097] Referring to Table 1, the following results can be seen.

[0098] In the case of the lead tabs of Examples 1 to 5 in which a metal layer was formed on the nickel plating layer by a sputtering process, it was found that the adhesion strength measured after immersion in an electrolyte for 21 days was 1.4 N / mm or more.

[0099] On the other hand, in the case of the lead tabs of Comparative Examples 1 to 5 in which a metal layer was not formed by the sputtering process but a protective layer was formed on the nickel plating layer by chromate treatment, it is clear that the adhesion strength was less than 1.4 N / mm.

[0100] The present specification described above is not limited by the above-mentioned examples and the attached drawings, and various substitutions, modifications, and alterations are possible within the scope of the technical subject matter of the present specification, which will be apparent to those skilled in the art to which the present specification pertains. Therefore, the scope of the present specification is defined by the claims below, and all modifications and alterations derived from the meaning, scope, and equivalent concepts of the claims should be construed as being included in the scope of the present specification. [Explanation of symbols]

[0101] 1: Secondary battery 10: Lead tab 20: Sealing tape 30: Exterior agent 110: Metal base material 120: Nickel plating layer 130: Metal layer

Claims

1. a metal substrate containing copper; a nickel plating layer laminated on both sides of the metal substrate; and a metal layer on the nickel plating layer, the metal layer comprises 70 to 99.9 wt % chromium; A lead tab with an adhesive strength of 1.4 N / mm or more.

2. The lead tab of claim 1 , wherein the metal substrate is a rolled copper foil.

3. 2. The lead tab according to claim 1, wherein the metal substrate has a thickness of 100 to 1,000 μm.

4. 2. The lead tab according to claim 1, wherein the nickel plating layer has a thickness of 0.5 to 10.0 μm.

5. The lead tab according to claim 1, wherein the metal layer has a thickness of 10 to 500 nm.

6. The lead tab of claim 1 , wherein the metal layer is formed by a dry vacuum process.

7. The lead tab of claim 6 , wherein the dry vacuum process includes at least one of a sputtering process, an evaporation process, an ion plating process, and a CVD process.

8. A secondary battery comprising the lead tab according to any one of claims 1 to 7.

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