Insulating adhesive, tab assembly, and secondary battery

Abstract

The application discloses an insulating adhesive, a tab assembly and a secondary battery. The secondary battery comprises an electrode assembly, a tab assembly and a packaging bag, the electrode assembly is accommodated in the packaging bag, the packaging bag comprises a sealing part, the tab assembly comprises a tab and insulating adhesives arranged on both sides of the tab respectively, the tab is connected with the electrode assembly and extends out of the packaging bag through the sealing part. The insulating adhesive comprises a first insulating adhesive layer, a second insulating adhesive layer and a third insulating adhesive layer arranged in sequence along a first direction, the second insulating adhesive layer comprises a cross-linked polymer, and the cross-linking degree of the cross-linked polymer is 20% to 70%. The insulating adhesive of the secondary battery is not easy to be warped, and the sealing effect is good.

Description

Technical Field

[0001] This application relates to the field of energy storage device technology, and in particular to an insulating adhesive, a tab assembly, and a secondary battery. Background Technology

[0002] Lithium-ion rechargeable batteries are characterized by high energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, and light weight, and are widely used in various fields such as energy storage, portable electronic devices, and electric vehicles. To ensure the safety performance of rechargeable batteries, they must undergo a series of tests before leaving the factory, including internal short-circuit tests, drop tests, and puncture tests. Among these, the drop test is one of the most stringent safety tests for lithium-ion rechargeable batteries. After a drop, the top seal at the electrode tabs is prone to breakage and leakage. Currently, insulating adhesive is typically used at the electrode tab sealing location to improve the sealing effect. However, the sealing effect between the existing insulating adhesive and the casing still needs improvement. Summary of the Invention

[0003] One object of this application is to provide a secondary battery with good sealing performance and whose insulating adhesive is not easily peeled off.

[0004] This application provides a secondary battery, including an electrode assembly, a tab assembly, and a packaging bag. The electrode assembly is housed in the packaging bag, which includes a sealing portion. The tab assembly includes tabs and insulating adhesive layers respectively disposed on both sides of the tabs. The tabs are connected to the electrode assembly and extend out of the packaging bag through the sealing portion. The insulating adhesive includes a first insulating adhesive layer, a second insulating adhesive layer, and a third insulating adhesive layer sequentially stacked along a first direction. The second insulating adhesive layer includes a cross-linked polymer with a cross-linking degree of 20% to 70%.

[0005] The secondary battery provided in this application has a cross-linking degree of 20% to 70% for the cross-linked polymer of the second insulating layer of the insulating adhesive, which gives the second insulating layer suitable fluidity, helps to reduce the risk of the insulating adhesive lifting, and when heated, the packaging bag and the insulating adhesive can be completely fused without obvious interface, thereby improving the sealing strength between the insulating adhesive and the packaging bag, improving the sealing effect, and reducing the risk of leakage.

[0006] According to some embodiments of this application, the melt index of the second insulating adhesive layer is A, where A ≤ 7 g / 10 min. When the melt index of the second insulating adhesive layer is within the above range, the insulating adhesive exhibits no flow behavior at high temperatures, which helps reduce the risk of adhesive lifting and improves the sealing effect.

[0007] According to some embodiments of this application, the degree of crosslinking of the crosslinked polymer is 36% to 45%. When the degree of crosslinking of the crosslinked polymer is within the above range, the secondary battery has both a low leakage rate and a low insulation adhesive peeling rate.

[0008] According to some embodiments of this application, the crosslinked polymer is produced by crosslinking the polymer with a crosslinking agent and an auxiliary agent, wherein the mass of the crosslinking agent is W1, the total mass of the insulating adhesive is W2, and 0.1% ≤ W1 / W2 ≤ 0.6%. When the content of the crosslinking agent is within the above range, the crosslinked polymer can have a suitable degree of crosslinking.

[0009] According to some embodiments of this application, the crosslinking agent includes one or more of silane coupling agents, hydrogen peroxide, triallyl isocyanurate, trimethylolpropane trimethacrylate, or tris(2-acryloyloxyethyl) isocyanurate.

[0010] According to some embodiments of this application, the crosslinked polymer is a carbon-carbon crosslink. Carbon-carbon crosslinks are resistant to electrolyte, which helps improve the sealing performance of the secondary battery; furthermore, the carbon-carbon bond energy is relatively high, making it less prone to breakage, resulting in better heat aging resistance and compression set resistance of the second insulating layer. According to some embodiments of this application, 4.2 g / 10 min ≤ A ≤ 4.7 g / 10 min. When the melt index of the second insulating layer is within the above range, the secondary battery exhibits both low leakage rate and low insulating adhesive separation rate.

[0011] According to some embodiments of this application, the first insulating layer and the third insulating layer include a grafted polymer with a grafting rate of 0.03% to 0.5%, which provides sufficient adhesion between the insulating adhesive and the tabs and the packaging bag, and the insulating adhesive has good moisture barrier properties.

[0012] According to some embodiments of this application, the second insulating layer includes a white colorant and the third insulating layer includes a gray colorant, which helps to distinguish the individual insulating layers of the insulating adhesive.

[0013] According to some embodiments of this application, the melting points of the first insulating adhesive layer and the third insulating adhesive layer are both 100-140°C, and the melting point of the second insulating adhesive layer is 140-400°C.

[0014] According to some embodiments of this application, the melting point of the second insulating layer differs from that of the first insulating layer or the third insulating layer by 40–300°C. The second insulating layer has a higher melting point, reducing the risk of short circuits between the packaging bag and the electrode tabs due to over-melting under heat. Furthermore, the first and third insulating layers have lower melting points, allowing the secondary battery to melt and release pressure at high temperatures, thus improving safety.

[0015] According to some embodiments of this application, the first insulating layer, the second insulating layer, and the third insulating layer all comprise polymers, including one or more of polypropylene, polyethylene, ethylene-based elastomers, propylene-based elastomers, styrene-based elastomers, ionomer resins, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol.

[0016] According to some embodiments of this application, the first insulating layer and / or the third insulating layer further include a toughening modifier. By configuring the toughening modifier, the flexibility and impact resistance of the insulating adhesive can be improved, thereby increasing the sealing strength between the insulating adhesive and the packaging bag.

[0017] According to some embodiments of this application, the toughening modifier includes one or more of ethylene propylene diene monomer (EPDM), ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), low-density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), linear low-density polyethylene (LDPE), nylon, polyethylene terephthalate (PET), polycarbonate, ultra-high molecular weight polyethylene (UHMWPE), or PO E plastic.

[0018] According to some embodiments of this application, along the first direction, the thickness of the insulating adhesive is h1, the thickness of the first insulating adhesive layer is A1, the thickness of the second insulating adhesive layer is B1, and the thickness of the third insulating adhesive layer is C1, where 11%h1≤B1≤34%h1, C1≥0.8A1, and 30%h1≤C1≤79%h1. Insulating adhesives meeting the above conditions can completely fuse with the packaging bag without a clear interface during encapsulation, thereby improving the encapsulation strength between the insulating adhesive and the packaging bag, enhancing the sealing effect, and reducing the risk of leakage.

[0019] According to some embodiments of this application, the secondary battery further includes an electrolyte comprising fluoroethylene carbonate, wherein the content of fluoroethylene carbonate is 0.1 wt% to 7 wt% based on the total mass of the electrolyte. When the content of fluoroethylene carbonate is within the above range, it helps to reduce the swelling degree of the insulating adhesive, thereby reducing the risk of leakage of the secondary battery.

[0020] A second aspect of this application provides an insulating adhesive comprising a first insulating adhesive layer, a second insulating adhesive layer, and a third insulating adhesive layer stacked sequentially along a first direction. The second insulating adhesive layer comprises a crosslinked polymer with a crosslinking degree of 20% to 70%.

[0021] A third aspect of this application provides a tab assembly, which includes a tab and insulating adhesive disposed on both sides of the tab, wherein the insulating adhesive is the insulating adhesive described in the above embodiment. Attached Figure Description

[0022] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0023] Figure 1 A schematic diagram of a secondary battery provided in an embodiment of this application;

[0024] Figure 2 A cross-sectional schematic diagram of the insulating adhesive provided in one embodiment of this application;

[0025] Figure 3 for Figure 1 A schematic diagram of the cross-section of the battery along line III-III;

[0026] Figure 4 This is a cross-sectional schematic diagram of an encapsulation film provided in an embodiment of this application;

[0027] Figure 5 A schematic diagram of an electronic device provided in an embodiment of this application.

[0028] Explanation of main component symbols

[0029] Insulating adhesive 30

[0030] First insulating adhesive layer 31

[0031] Second insulating adhesive layer 32

[0032] Third insulating adhesive layer 33

[0033] Secondary battery 100

[0034] Electrode assembly 10

[0035] Packaging bag 40

[0036] JE20

[0037] First encapsulation film 41

[0038] Second encapsulation film 42

[0039] Receiving cavity 410

[0040] Sealing part 420

[0041] Encapsulation layer 401

[0042] Metal layer 402

[0043] Protective layer 403

[0044] Part 1, 303

[0045] Part 2, 302

[0046] Part 301

[0047] First end 303a

[0048] Second end 303b

[0049] Adhesion area 201

[0050] Electronic devices 200

[0051] Main body 210 Detailed Implementation

[0052] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0053] The embodiments of this application will be described in detail below. However, this application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided to provide a thorough and detailed understanding of this application to those skilled in the art.

[0054] Additionally, for brevity and clarity, the dimensions or thicknesses of various components and layers may be enlarged in the accompanying drawings. Throughout the text, the same numerical values ​​refer to the same elements. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more of the associated enumerated items. Furthermore, it should be understood that when element A is referred to as "connecting" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0055] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0056] The technical terms used herein are for the purpose of describing particular embodiments and are not intended to limit this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. It should be further understood that the term "comprising," as used in this specification, means the presence of the described features, values, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof.

[0057] Spatial terms, such as "above," may be used herein for convenience in describing the relationship between one element or feature and another element (or feature) or feature (or feature) illustrated in the figures. It should be understood that, in addition to the directions depicted in the figures, spatial terms are intended to include different orientations of the device or apparatus during use or operation. For example, if the device in the figure is flipped, an element described as "above" or "on" other elements or features would be oriented "below" or "under" other elements or features. Therefore, the exemplary term "above" can include both above and below orientations. It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, a first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0058] Please see 1 and Figure 3 This application provides a secondary battery 100, including an electrode assembly 10, a tab assembly, a packaging bag 40, and an electrolyte contained within the packaging bag 40. The tab assembly includes tabs 20 and insulating adhesive 30 disposed on both sides of the tabs. The tabs 20 are connected to the electrode assembly 10. The packaging bag 40 covers the electrode assembly 10 and a portion of the tabs 20. The insulating adhesive 30 is disposed between the packaging bag 40 and the tabs 20, connecting the packaging bag 40 and the tabs 20. In this embodiment, there are two tabs 20, namely a positive tab and a negative tab, located on the same side of the secondary battery 100 and extending outside the packaging bag 40; there are four insulating adhesive 30s, with two insulating adhesive 30s disposed on opposite surfaces of one tab 20 and the other two insulating adhesive 30s disposed on opposite surfaces of the other tab 20, with the two insulating adhesive 30s on the same side of the two tabs 20 spaced apart. The material of the positive electrode tab may include at least one of Ni, Ti, Al, Ag, Au, Pt, Fe, and combinations thereof. The material of the negative electrode tab may include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, and combinations thereof. In other embodiments, the two first layers 50 located on the same side of the two electrodes 20 may be interconnected to form a whole, and the two electrodes 20 may also be located on different sides of the secondary battery 100.

[0059] The electrode assembly 10 includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The electrode assembly 10 is formed by stacking or winding the positive electrode, separator, and negative electrode. The positive and negative electrode are electrically connected to two tabs 20, respectively.

[0060] The packaging bag 40 includes a first sealing film 41 and a second sealing film 42 disposed opposite to each other, the shapes of the first sealing film 41 and the second sealing film 42 being mutually compatible. The first sealing film 41 and the second sealing film 42 are interconnected and enclose to form a receiving cavity 410, which is used to receive at least a portion of the electrolyte, the electrode assembly 10, the tab 20, and the first layer 50. The edges of the first sealing film 41 and the second sealing film 42 are connected to form a sealing portion 420, which extends from the outer side of the receiving cavity 410 toward a side opposite to the receiving cavity 410. The sealing portion 420 is the part of the packaging bag 40 that is sealed by a hot-pressing process after the electrode assembly 10 and the electrolyte are contained. The tab 20 is partially received in the receiving cavity 410 and extends out of the packaging bag 40 through the sealing portion 420.

[0061] Please see Figure 3 and Figure 4 Both the first encapsulation film 41 and the second encapsulation film 42 include an encapsulation layer 401, a metal layer 402, and a protective layer 403 sequentially stacked along the first direction Z. The encapsulation layer 401 is disposed close to the electrode assembly 10, while the protective layer 403 is disposed away from the electrode assembly 10. The encapsulation layer 401 is made of a polymer, such as polypropylene or polyamide. The encapsulation layers 401 of the first encapsulation film 41 and the second encapsulation film 42 are connected to encapsulate the packaging bag 40, preventing the packaging bag 40 from being dissolved or swollen by organic solvents in the electrolyte. The encapsulation layer 401 also prevents the electrolyte in the electrolyte from contacting the metal layer 402, thus preventing corrosion of the metal layer 402. The protective layer 403 is made of a polymer resin and is used to protect the metal layer 402, preventing the metal layer 402 from being damaged by external forces. It also prevents air from penetrating from the external environment, maintaining an anhydrous and oxygen-free environment inside the secondary battery 100. The metal layer 402 is made of metal, such as aluminum or steel, and is used to prevent moisture from penetrating and to prevent external forces from damaging the secondary battery 100. When packaging the secondary battery 100 with the packaging bag 40, the packaging film can be folded in half, and then a heat-sealing head is used to apply a certain temperature (180-215℃) and pressure (0.3-0.6MPa) to the surface of the folded packaging film for a certain time (1.5-3S) to heat-seal it, so that the packaging layer 401 of the packaging film melts and connects. At this time, the innermost layer of the packaging bag 40 is the packaging layer 401.

[0062] Please see Figure 1Along the second direction X, the insulating adhesive 30 includes a first portion 303, a third portion 301, and a second portion 302 that are interconnected. The first portion 303 is the area of ​​the insulating adhesive 30 that overlaps with the tab 20 and is spaced apart from the sealing portion 420 in the first direction Z. The third portion 301 is the area of ​​the insulating adhesive 30 that does not overlap with either the tab 20 or the sealing portion 420 in the first direction Z. The second portion 302 is the area of ​​the insulating adhesive 30 that overlaps with the sealing portion 420 in the first direction Z. The second direction X is perpendicular to the first direction Z. In this embodiment, the first direction Z is the thickness direction of the tab 20, and the second direction X is the length direction of the tab 20.

[0063] The first part 303 includes a first end 303a located inside the packaging bag 40 and a second end 303b located outside the packaging bag 40. The insulating adhesive 30 includes four third parts 301 distributed at the four corners, wherein two third parts 301 are located inside the packaging bag 40 and on both sides of the first end 303a in the third direction Y, and the other two third parts 301 are located outside the packaging bag 40 and on both sides of the second end 303b in the third direction Y. The third direction Y is perpendicular to the first direction Z and the second direction X. In this embodiment, the third direction Y is the width direction of the tab 20. By setting the third parts 301 and the first parts 303, the insulating adhesive 30 extends inward from the sealing part 420 into the receiving cavity 410, thereby avoiding the risk of narrowing of the effective seal width due to the insulating adhesive 30 not extending from the sealing part 420 into the packaging bag 40; and the insulating adhesive 30 extends outward from the sealing part 420 to the outside of the packaging bag 40, thereby avoiding the risk of the edge of the packaging bag 40 being compressed during sealing, which is beneficial for sealing.

[0064] Please see Figure 3 and Figure 2 Along the first direction Z, the insulating adhesive 30 includes a first insulating adhesive layer 31, a second insulating adhesive layer 32, and a third insulating adhesive layer 33 stacked sequentially. The first insulating adhesive layer 31 is connected to the tab 20, and the third insulating adhesive layer 33 is connected to the sealing layer 401 of the packaging bag 40. The first insulating adhesive layer 31 and the third insulating adhesive layer 33 provide a sealing function. The second insulating adhesive layer 32 provides support to reduce the risk of short circuit between the packaging bag and the tab due to over-melting of the insulating adhesive 30.

[0065] In this application, the first part 303, the third part 301, and the second part 302 all include a first insulating adhesive layer 31, a second insulating adhesive layer 32, and a third insulating adhesive layer 33. Before encapsulation, the thicknesses of the first insulating adhesive layer 31, the second insulating adhesive layer 32, and the third insulating adhesive layer 33 in the first part 303, the second part 302, and the third part 301 are approximately equal, but the insulating adhesive 30 is located in different areas and has different names. In the first part 303, the insulating adhesive 30 includes the first insulating adhesive layer 31, the second insulating adhesive layer 32, and the third insulating adhesive layer 33; in the second part 302, the insulating adhesive 30 includes a second part first insulating adhesive layer, a second part second insulating adhesive layer, and a second part third insulating adhesive layer; in the third part 301, the insulating adhesive 30 includes a third part first insulating adhesive layer, a third part second insulating adhesive layer, and a third part third insulating adhesive layer. Since the first end 303a of the first part 303 was not heat-melted during encapsulation, the thickness of the first insulating adhesive layer 31, the second insulating adhesive layer 32 and the third insulating adhesive layer 33 of the first end 303a is approximately equal to the thickness of the first insulating adhesive layer 31, the second insulating adhesive layer 32 and the third insulating adhesive layer 33 before the insulating adhesive 30 was encapsulated.

[0066] The tab assembly also includes an adhesive region 201, which is the portion where insulating adhesive 30 located on both sides of the tab 20 are bonded together along the first direction Z. The adhesive region 201 is formed by a second portion 302 and a third portion 301 of the insulating adhesive 30 located on the same side of the tab 20 in the third direction Y. In the adhesive region 201, the first insulating adhesive layers 31 of the two insulating adhesives 30 are bonded together to form a first insulating adhesive layer.

[0067] The first insulating layer 31, the second insulating layer 32, and the third insulating layer 33 all comprise polymers. These polymers may include one or more of polypropylene, polyethylene, ethylene-based elastomers, propylene-based elastomers, styrene-based elastomers, ionomer resins, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol. These polymers possess excellent adhesive properties.

[0068] The second insulating layer 32 comprises a crosslinked polymer. In some embodiments, the crosslinked polymer is produced by crosslinking the polymer with a crosslinking agent and by irradiation. The crosslinking agent may include one or more of silane coupling agents, hydrogen peroxide, triallyl isocyanurate, trimethylolpropane trimethacrylate, and tris(2-acryloyloxyethyl) isocyanurate. The crosslinking agent reacts with the polymer via a carbon-carbon double bond addition reaction to achieve crosslinking, thus the crosslinking points of the crosslinked polymer are carbon-carbon crosslinks. The carbon-carbon crosslinks are resistant to electrolytes, which improves the sealing performance of the secondary battery 100; and the carbon-carbon crosslinks have a relatively high bond energy, making them less prone to breakage, resulting in better heat aging resistance and compression set resistance of the second insulating layer 32.

[0069] In some embodiments, the second insulating layer 32 further includes additives. The crosslinked polymer is produced by crosslinking the polymer with a crosslinking agent and additives. The mass of the crosslinking agent is W1, the total mass of the insulating adhesive is W2, and 0.1% ≤ W1 / W2 ≤ 0.6%. When the content of the crosslinking agent is within the above range, the crosslinked polymer of the second insulating layer 32 can have a suitable degree of crosslinking.

[0070] Additives may include colorants, antioxidants, etc. Colorants may be white or gray colorants. Antioxidants may include 2,6-di-tert-butyl-p-cresol. In some embodiments, the second insulating layer 32 also includes a white colorant to facilitate identification of the second insulating layer 32 during production. Based on the mass of the second insulating layer 32, the content of the white colorant is greater than 0 and less than 3%, for example, the content of the white colorant is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, or 2.8%. The white colorant may include at least one of titanium dioxide, zinc sulfide, zinc barium white, or zinc oxide.

[0071] In some embodiments, the degree of crosslinking of the crosslinked polymer in the second insulating layer 32 is 20% to 70%. When the degree of crosslinking of the crosslinked polymer is within the above range, the second insulating layer 32 exhibits a highly elastic state at high temperatures (e.g., 200°C), which helps reduce the risk of short circuit between the packaging bag and the electrode tab due to over-melting of the second insulating layer 32 when heated, and also helps reduce the separation rate of the insulating adhesive, improve the sealing effect, and reduce the risk of leakage. When the degree of crosslinking is less than 20%, it cannot achieve high-temperature resistance; when the degree of crosslinking exceeds 70%, the fluidity of the second insulating layer 32 deteriorates, resulting in a poor sealing effect of the secondary battery 100. Preferably, the degree of crosslinking of the crosslinked polymer is 36% to 45%. When the degree of crosslinking of the crosslinked polymer is within the above preferred range, the secondary battery 100 has both a low leakage rate and a low insulation adhesive separation rate.

[0072] In this application, the degree of crosslinking of the crosslinked polymer of the second insulating adhesive layer 32 can be measured by the following method: take an insulating adhesive sample with a mass of M2, dissolve the sample in hot xylene, reflux at high temperature to make the non-crosslinked part of the sample fully dissolve in xylene, filter out the insoluble matter, dry it and weigh the mass of the insoluble matter as M1, and the weight ratio M1 / M2 is the degree of crosslinking.

[0073] In some embodiments, the melt index of the second insulating adhesive layer 32 is A, where A ≤ 7 g / 10 min. When the melt index of the second insulating adhesive layer 32 is within the above range, the second insulating adhesive layer 32 exhibits no flow dynamics at high temperatures (e.g., 200°C), possessing high heat resistance and reducing the risk of over-melting when heated. Preferably, 4.2 g / 10 min ≤ A ≤ 4.7 g / 10 min. When the melt index of the second insulating adhesive layer 32 is within the above preferred range, the secondary battery 100 exhibits both low leakage rate and low insulating adhesive warping rate.

[0074] In some embodiments, both the first insulating layer 31 and the third insulating layer 33 comprise a grafted polymer, with a grafting rate of 0.03% to 0.5%. When the grafting rate is less than 0.03%, the polar groups introduced into the first insulating layer 31 are insufficient, resulting in insufficient adhesion between the first insulating layer 31 and the tab 20. This may cause delamination at the interface between the tab 20 and the first insulating layer 31 after contact with the electrolyte, leading to poor sealing performance. When the grafting rate is greater than 0.5%, the strong water absorption of the polar groups results in poor moisture barrier performance of the insulating adhesive 30, leading to gas expansion in the secondary battery 100. Preferably, the grafting rate of the grafted polymer is 0.03% to 0.15%, within which the encapsulation pull force of the secondary battery 100 remains stable.

[0075] The grafting rate of the grafted polymer was determined by the following method: First, according to the grafting rate of the grafted polymer to be tested, a 0.1 mol / L KOH-ethanol standard solution was prepared and standardized with potassium hydrogen phthalate; second, 10 g of purified sample was weighed and dissolved in xylene to obtain a solution, and the solution was slowly added to a sufficient amount of acetone solution and filtered to obtain a precipitate; then, the precipitate was placed in a Soxhlet extractor for extraction (extractant was xylene, extraction time was 3 h), and the precipitate was dried to constant weight; then, 2 g of purified sample and 100 ml of xylene were added to a three-necked flask, 6 drops of deionized water and 6 drops of pyridine were added, and the mixture was refluxed at the boiling temperature of xylene for 1 h, 5 drops of phenolphthalein indicator were added, and titrated with KOH-ethanol standard solution. After the red color of the solution did not fade for 10 min, the volume of standard solution consumed was recorded and the grafting rate was calculated; three parallel experiments were performed, and the average value of the grafting rate measured in the three experiments was taken. The formula for calculating the grafting rate is shown in formula (1):

[0076]

[0077] In the formula, GR represents the grafting rate of the purified sample, ΔV represents the volume (mL) of KOH-ethanol standard solution consumed, C represents the concentration (mol / L) of the KOH-ethanol standard solution, and m represents the mass (g) of the test sample. The grafting rate test method is not limited to the above method.

[0078] In some embodiments, the grafted polymer is produced by grafting the polymer with polar groups. The polar groups include at least one of maleic anhydride, maleic acid, acrylic acid, methacrylic acid, maleic anhydride, or epoxy groups. These grafted polymers exhibit strong adhesion to the tabs and packaging bags. Preferably, the grafted polymer is maleic anhydride-grafted polypropylene.

[0079] In some embodiments, the third insulating layer 33 further includes a gray colorant to facilitate identification of individual insulating layers during production and prevent adhesion between the third insulating layer 33 and the tabs. Based on the mass of the third insulating layer 33, the content of the gray colorant is greater than 0 and less than 3%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, or 2.8%. The gray colorant may include at least one of graphite, carbon black, or manganese iron black.

[0080] In some embodiments, the melting points of the first insulating layer 31 and the third insulating layer 33 are both 100°C to 140°C, and the melting point of the second insulating layer 32 is 140°C to 400°C. The difference between the melting point of the second insulating layer 32 and the melting point of the first insulating layer 31 or the third insulating layer 33 is 40°C to 300°C. The second insulating layer 32 has a higher melting point, reducing the risk of short circuit between the packaging bag 40 and the tab 20 due to over-melting of the second insulating layer 32 when heated; and the first insulating layer 31 and the third insulating layer 33 have lower melting points, allowing the secondary battery 100 to melt and release pressure at high temperatures, thus improving safety.

[0081] In some embodiments, the first insulating layer 31 and / or the third insulating layer 33 further include a toughening modifier to improve flexibility and impact resistance, thereby enhancing the sealing strength between the insulating adhesive 30 and the packaging bag 40. The toughening modifier may include rubber particles such as ethylene propylene diene monomer (EPR), ethylene propylene diene monomer (EPDM), and styrene-butadiene rubber to prevent crack propagation. The toughening modifier may also include one or more of flexible polymers, rigid polymers, ultra-high molecular weight polyethylene (UHMWPE), or POE plastics to enhance intercrystalline bonding and blur the intercrystalline interfaces. Flexible polymers may be low-density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), linear low-density polyethylene (LLDPE), etc. Rigid polymers may be nylon (PA6), polyethylene terephthalate (PET), polycarbonate (PC), etc.

[0082] In some embodiments, the content of the toughening modifier in the first insulating adhesive layer 31 is 3 wt% to 10 wt%, and / or the content of the toughening modifier in the third insulating adhesive layer 33 is 3 wt% to 10 wt%. When the content of the toughening modifier is within the above range, the sealing strength between the insulating adhesive 30 and the packaging bag 40 is high. When the content of the toughening modifier is greater than 10 wt%, it will cause the crystals to separate and delamination to occur.

[0083] In the first end 303a and the second end 303b, along the first direction Z, the thickness of the insulating adhesive 30 is h1, the thickness of the first insulating adhesive layer 31 is A1, the thickness of the second insulating adhesive layer 32 is B1, and the thickness of the third insulating adhesive layer 33 is C1, wherein 11%h1≤B1≤34%h1, C1≥0.8A1, and 30%h1≤C1≤79%h1. When the insulating adhesive 30 meets the above thickness requirements, during encapsulation, the packaging bag 40 and the insulating adhesive 30 can be completely fused without a clear interface, thereby improving the encapsulation strength between the insulating adhesive 30 and the packaging bag 40, improving the sealing effect, and reducing the risk of leakage. Specifically, satisfying 11%h1≤B1≤34%h1 ensures that the second insulating adhesive layer 32 is not over-melted or insufficiently fused when heated during encapsulation, preventing interface formation or delamination between the second insulating adhesive layer 32 and the first insulating adhesive layer 31 and the third insulating adhesive layer 33, which would reduce the encapsulation strength. The design satisfies C1 ≥ 0.8A1 and 30%h1 ≤ C1 ≤ 79%h1, ensuring complete fusion between the third insulating layer 33 and the packaging bag 40. Since the third insulating layer 33 is heated and melted before the first insulating layer 31 during encapsulation, this design avoids over-melting of the third insulating layer 33, which could lead to poor fusion interface between the packaging bag and the second insulating layer 32. This ensures complete fusion between the third insulating layer 33 and the packaging bag 40. Furthermore, the asymmetrical thickness of the first, second, and third insulating layers 31 and 32, along with this asymmetrical three-layer structure, allows for complete fusion of the insulating adhesive 30 and the packaging bag 40 without a noticeable interface during encapsulation. This improves the sealing strength between the insulating adhesive 30 and the packaging bag 40, enhances the sealing effect, and reduces the risk of leakage.

[0084] In some embodiments, 10.5%h1 ≤ A1 ≤ 35%h1. This design can prevent the first insulating adhesive layer 31 from being insufficiently fused or over-melted, resulting in poor adhesion to the tab 20, and ensure that the first insulating adhesive layer 31 is fused and bonded to the tab 20.

[0085] In some implementations, h1 is 30–160 μm. For example, h1 is 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, or 160 μm.

[0086] In some embodiments, when the thickness C1 of the third insulating adhesive layer 33 is within the above range, the secondary battery 100 can have high encapsulation strength while also having high insulation and corrosion resistance.

[0087] In the second part 302, along the first direction Z, the thickness of the third insulating layer in the second part is C2. In some embodiments, 92%C1≤C2≤98%C1, which minimizes the thickness change of the third insulating layer before and after heat sealing, thus improving the encapsulation strength. In some embodiments, 7μm≥C1-C2≥1μm.

[0088] The thickness of the sealing layer 401 in the area where the packaging bag 40 and the sealing part 420 do not overlap in the first direction Z is P. That is, before sealing, the thickness of the sealing layer 401 of the packaging bag 40 in the first direction Z is P. In the second part 302, the sealing layer 401 of the packaging bag 40 and the second part of the third insulating adhesive layer of the insulating adhesive 30 are fused together due to heat sealing, and the total thickness of the sealing layer 401 and the second part of the third insulating adhesive layer in the first direction Z is H. In some embodiments, 0.25(C2+P)≤H≤0.75(C2+P), which allows the sealing layer 401 of the packaging bag 40 and the second part of the third insulating adhesive layer of the insulating adhesive 30 to be completely fused together, thereby improving the sealing strength. Preferably, 0.29(C2+P)≤H≤0.5(C2+P).

[0089] In some embodiments, along the first direction Z, the thickness of the portion of the tab assembly corresponding to the second portion 302 of the insulating adhesive 30 is G. The thickness of the packaging bag 40 in the first direction Z is T. In this application, the thickness of the first encapsulation film 41 and the second encapsulation film 42 in the first direction Z is both T. Along the first direction Z, the thickness of the portion of the secondary battery 100 corresponding to the tab 20 and the second portion 302 is K, where 2T+G-(2P+2t)×75%<K<2T+G-(2P+2t)×15%.

[0090] In the bonding region 201, along the first direction Z, the thickness of the bonding region 201 is Q, the thickness of the first insulating adhesive layer in the bonding region is D, the thickness of the second insulating adhesive layer in the bonding region is B4, and the thickness of the third insulating adhesive layer in the bonding region is C4, wherein 10.5% (Q×0.5)≤B4≤35% (Q×0.5), C4>0.5D, 90%B4≤C4≤500%B4, and 120%B4≤D≤800B4.

[0091] The electrolyte comprises an organic solvent, a lithium salt, and electrolyte additives. The electrolyte additives include at least fluoroethylene carbonate (FEC). Based on the total mass of the electrolyte, the content of fluoroethylene carbonate is 0.1 wt% to 7 wt%. When the content of fluoroethylene carbonate is within this range, it helps reduce the swelling degree of the insulating adhesive 30, thereby reducing the risk of leakage in the secondary battery 100; it also achieves excellent cycle retention. Fluoroethylene carbonate affects the film formation of the negative electrode; when the content of fluoroethylene carbonate is within the above range, it helps reduce impedance. Electrolyte additives may also include lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorooxalate borate, fluoroethylene carbonate, lithium difluorophosphate, 1,2-bis(cyanoethoxy)ethane, or 1,2,3-tris(2-cyanoethoxy)propane, etc.

[0092] The organic solvent can be a conventional organic solvent in the art, such as at least one selected from carbonates, carboxylic acid esters, or fluoroethers. The carbonate is, for example, selected from one or more combinations of ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and methyl propyl carbonate. The carboxylic acid ester is, for example, selected from one or more combinations of ethyl propionate and propyl propionate. The fluoroether is, for example, selected from 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. The lithium salt is selected from at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium hexafluorophosphate.

[0093] Please see Figure 5 Embodiments of this application also provide an electronic device 200, which includes a main body 210 and a secondary battery 100. The secondary battery 100 is housed within the main body 210. The electronic device 200 may be one of a mobile phone, a tablet, or an e-reader.

[0094] In this application, the electronic device 200 is taken as a mobile phone, with a secondary battery 100 disposed inside the phone to provide power for its use, and the main body 210 being the structure of a mobile phone. It is understood that in other embodiments, the electronic device 200 may have other structures, not limited to the above-mentioned mobile phone, tablet, or e-reader.

[0095] The performance of the insulating adhesive and secondary battery provided in this application will be described below through specific embodiments and comparative examples.

[0096] Example 1

[0097] Preparation of the positive electrode sheet: Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were dissolved in an N-methylpyrrolidone solution at a weight ratio of 97.5:1.0:1.5 to form a positive electrode slurry with a solid content of 75%. Aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated onto the surface of the current collector to obtain the positive electrode active material layer. After drying, cold pressing, and cutting, the positive electrode sheet was obtained.

[0098] Preparation of the negative electrode sheet: A coating slurry is formed by mixing 80 wt% of an inorganic conductive agent (single-walled carbon nanotubes with a G / D ratio of 65), 10 wt% of a conductive polymer (polypyrrole), 10 wt% of a binder (5 wt% CMC-Li and 5 wt% PVDF), and an appropriate amount of water. A negative electrode slurry is formed by mixing 97.7 wt% graphite, 1.3 wt% sodium carboxymethyl cellulose, 1.0 wt% styrene-butadiene rubber, and an appropriate amount of deionized water. Copper foil is used as the negative electrode current collector, and the negative electrode slurry is coated onto the surface of the current collector. After drying, a negative electrode active material layer is obtained. Subsequently, the negative electrode sheet is obtained through cold pressing and cutting.

[0099] Preparation of the separator membrane: Polyethylene film was selected as the separator membrane.

[0100] Preparation of electrolyte: Ethyl carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propylene propionate (PP), and vinylene carbonate (VC) were mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 and the organic solvent were mixed in a weight ratio of 8:92 to obtain the electrolyte.

[0101] Preparation of insulating adhesive:

[0102] The first insulating adhesive layer is obtained by mixing and melting 99% polymer matrix and 1% additives and then extruding. The polymer matrix is ​​polypropylene (PP), and the additives include an antioxidant (2,6-di-tert-butyl-p-cresol).

[0103] The second insulating adhesive layer is obtained by mixing and melting 99% polymer matrix, 0.1% crosslinking agent, and 0.9% additives, followed by extrusion molding. The polymer matrix is ​​polypropylene (PP), the crosslinking agent is hydrogen peroxide, and the additives include a white colorant (titanium dioxide) and an antioxidant (2,6-di-tert-butyl-p-cresol).

[0104] The third insulating layer is obtained by mixing and melting 99% polymer matrix and 1% additives and then extruding. The polymer matrix consists of 94% polypropylene (PP) and 5% polyethylene (PE), and the additives include a gray colorant (carbon black) and an antioxidant (2,6-di-tert-butyl-p-cresol).

[0105] The first insulating layer, the second insulating layer, and the third insulating layer are bonded together using a heat-bonding method to obtain the following: Figure 2 The insulating adhesive shown is subjected to gamma ray irradiation, resulting in the formation of a cross-linked polymer in the second insulating adhesive layer. The degree of cross-linking of the cross-linked polymer in the second insulating adhesive layer is 20%, and the melt index of the second insulating adhesive layer is 7 g / 10 min.

[0106] Preparation of a secondary battery: The positive electrode, polyethylene separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes, and then wound to obtain an electrode assembly. The electrode assembly is placed in a packaging bag, and insulating adhesive is applied between the packaging bag and the electrode tabs. Finally, a 1.5mm wide heat-sealing end cap is used for heat sealing to obtain the desired result. Figure 2 The secondary battery shown has a heat-sealing temperature of 205℃, a heat-sealing pressure of 0.4MPa, and a heat-sealing time of 1.5S. The thickness h1 of the insulating adhesive 30 is μm. In the first part 303, the thickness A1 of the first insulating adhesive layer 31 is μm, the thickness B1 of the second insulating adhesive layer 32 is μm, and the thickness C1 of the third insulating adhesive layer 33 is μm, where B1 = %h1, A1 = %C1, and C1 = %h1.

[0107] Examples 2-10 and Comparative Examples 1-3

[0108] The difference from Example 1 is that at least one of the following is different: the content of the crosslinking agent, the degree of crosslinking of the crosslinking polymer, and the melt index of the second insulating adhesive layer. The total content of crosslinking agent and additives in each example and comparative example is 1%. See Table 1 for specific parameters.

[0109] Drop tests were conducted on the secondary batteries prepared in each embodiment and comparative example, and the peeling rate of the insulating adhesive was measured. The test results are shown in Table 1.

[0110] Insulating adhesive peeling rate test:

[0111] Observe whether the insulating adhesive curls up relative to the direction in which the tabs extend. If the insulating adhesive curls up more than 10° relative to the direction in which the tabs extend, it is considered to have curled up. The ratio of the number of secondary batteries with curled insulating adhesive to the total number of test samples is the insulating adhesive curling rate.

[0112] Drop test:

[0113] The secondary battery was charged at a constant current of 0.5C to 4.2V at 20±5℃, and then charged at a constant voltage of 0.05C at 4.2V. It was then dropped freely from a height of 1.5 meters onto a smooth marble surface. The drop sequence was: front-back-bottom-top-left-right-top-left-top-right-bottom-left-bottom-right. Each side / corner was dropped once consecutively, constituting one round. The secondary battery was checked, and a total of 10 rounds were performed. The battery was recorded for any leakage.

[0114] Table 1

[0115]

[0116]

[0117] Note: X / 500 indicates that X samples out of 500 tested showed leakage.

[0118] As shown in Table 1, the curling rate of the insulating adhesive decreases with increasing crosslinking degree; and when the crosslinking degree is greater than 45%, the leakage rate increases with increasing crosslinking degree. When the crosslinking degree is between 20% and 70%, the curling rate and leakage rate of the insulating adhesive are both low; when the crosslinking degree is less than 20%, the curling rate of the insulating adhesive is too high; and when the crosslinking degree is greater than 70%, the leakage rate is too high.

[0119] Lithium-ion battery thermal chamber test: Lithium-ion batteries are charged to SOC% at a constant current of 0.5C (CC), and then placed in thermal shock chambers at 130℃ and 150℃ respectively. The test is stopped after 1 hour, or immediately after thermal runaway. Voltage and surface temperature changes are collected and experimental phenomena are recorded. A battery that does not catch fire, explode, or emit smoke is considered to have passed the test. Ten lithium-ion batteries are used for each test condition.

[0120] Lithium-ion battery hot box test: First, the lithium-ion battery is fully charged at 1.5C; second, the fully charged lithium-ion battery is placed in an oven, heated to 135℃ at a rate of 5℃ / min and held at that temperature for 1 hour. The lithium-ion battery passes the test if it does not catch fire or explode. Each embodiment and comparative example uses 100 lithium-ion batteries for testing. The hot box test pass rate = (number of batteries passing the test / 100) × 100%. The hot box test pass rate characterizes the thermal safety performance of the lithium-ion battery; a higher pass rate indicates better thermal safety performance.

[0121] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with this application are still within the scope of this application.

Claims

1. A secondary battery, comprising an electrode assembly, a tab assembly, and a packaging bag, wherein the electrode assembly is housed in the packaging bag, the packaging bag includes a sealing portion, the tab assembly includes tabs and insulating adhesive respectively disposed on both sides of the tabs, the tabs are connected to the electrode assembly and extend out of the packaging bag through the sealing portion, characterized in that, The insulating adhesive includes a first insulating adhesive layer, a second insulating adhesive layer, and a third insulating adhesive layer stacked sequentially along a first direction. The second insulating adhesive layer includes a cross-linked polymer with a cross-linking degree of 20% to 70% and a melt index of A, where A ≤ 7 g / 10 min. The first and third insulating adhesive layers include a grafted polymer with a grafting rate of 0.03% to 0.5%.

2. The secondary battery as described in claim 1, wherein, The degree of crosslinking of the crosslinked polymer is 36% to 45%.

3. The secondary battery as described in claim 1, wherein, 4.2g / 10min≤A≤4.7g / 10min.

4. The secondary battery as described in claim 1, wherein, The crosslinked polymer is a carbon-carbon crosslinked polymer.

5. The secondary battery according to any one of claims 1-4, wherein, The second insulating layer includes a white colorant, and the third insulating layer includes a gray colorant.

6. The secondary battery according to any one of claims 1-4, wherein, The melting points of the first insulating adhesive layer and the third insulating adhesive layer are both 100℃~140℃, and the melting point of the second insulating adhesive layer is 140℃~400℃.

7. The secondary battery as described in claim 6, wherein, The difference between the melting point of the second insulating adhesive layer and the melting point of the first insulating adhesive layer or the melting point of the third insulating adhesive layer is 40~300℃.

8. The secondary battery according to any one of claims 1-4, wherein, The first insulating layer, the second insulating layer, and the third insulating layer all comprise polymers, which include one or more of polypropylene, polyethylene, ethylene-based elastomers, propylene-based elastomers, styrene-based elastomers, ionomer resins, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol.

9. The secondary battery as described in claim 8, wherein, The first insulating layer and / or the third insulating layer further include a toughening modifier.

10. The secondary battery as claimed in claim 9, wherein, The toughening modifier includes one or more of the following: ethylene propylene diene monomer (EPDM) rubber, ethylene propylene diene monomer (EPDM) rubber, styrene-butadiene rubber (SBR), low-density polyethylene (LDPE), ethylene-vinyl acetate copolymer, linear low-density polyethylene (LDPE), nylon, polyethylene terephthalate (PET), polycarbonate, ultra-high molecular weight polyethylene (UHMWPE), or POE plastic.

11. The secondary battery according to any one of claims 1-4, wherein, Along the first direction, the thickness of the insulating adhesive is h1, the thickness of the first insulating adhesive layer is A1, the thickness of the second insulating adhesive layer is B1, and the thickness of the third insulating adhesive layer is C1, where 11%h1≤B1≤34%h1, C1≥0.8A1, and 30%h1≤C1≤79%h1.

12. The secondary battery according to any one of claims 1-4, wherein, The secondary battery also includes an electrolyte comprising fluoroethylene carbonate, wherein the content of fluoroethylene carbonate is 0.1 wt% to 7 wt% based on the total mass of the electrolyte.

13. An insulating adhesive, characterized in that, The insulating adhesive includes a first insulating adhesive layer, a second insulating adhesive layer, and a third insulating adhesive layer stacked sequentially along a first direction. The second insulating adhesive layer includes a cross-linked polymer with a cross-linking degree of 20% to 70% and a melt index of A, where A ≤ 7 g / 10 min. The first and third insulating adhesive layers include a grafted polymer with a grafting rate of 0.03% to 0.5%.

14. A tab assembly, characterized in that, The electrode assembly includes electrode tabs and insulating adhesives respectively disposed on both sides of the electrode tabs, wherein the insulating adhesives are the insulating adhesives as described in claim 13.

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