Insulating adhesive, tab assembly, and secondary battery

Abstract

An insulating adhesive, a tab assembly, and a secondary battery. The secondary battery comprises an electrode assembly, a tab assembly, and a packaging pouch; the electrode assembly is accommodated in the packaging pouch; the packaging pouch comprises a sealing part; the tab assembly comprises tabs and insulating adhesives respectively arranged on two sides of respective tabs; and the tabs are connected to the electrode assembly and pass through the sealing part to extend out of the packaging pouch. The insulating adhesive comprises a first insulating adhesive layer, a second insulating adhesive layer and a third insulating adhesive layer which are sequentially stacked in a first direction; the second insulating adhesive layer comprises a cross-linked polymer; and the degree of crosslinking of the cross-linked polymer ranges from 20% to 70%. The insulating adhesive of the secondary battery of the present application is not prone to warping, and has a good sealing effect.

Description

Insulation glue, tab components and secondary batteries Technical Field

[0001] The present application relates to the technical field of energy storage devices, and in particular to an insulating adhesive, a tab assembly, and a secondary battery. Background Art

[0002] Lithium-ion secondary batteries have the characteristics of high energy density, long cycle life, high nominal voltage, low self-discharge rate, small size and light weight. They are widely used in various fields such as energy storage, portable electronic devices and electric vehicles. In order to ensure the safety performance of secondary batteries, lithium-ion secondary batteries need to pass a series of tests before leaving the factory, including internal short-circuit tests, drop tests, puncture tests, etc. Among them, the drop test is a relatively stringent safety test for lithium-ion secondary batteries. After a lithium-ion secondary battery falls, the tab is prone to problems such as the top seal being broken open and leakage. It is usually improved by providing insulating glue at the tab packaging position. However, the sealing effect between the existing insulating glue and the shell still needs to be improved. Summary of the Invention

[0003] One object of the present application is to provide a secondary battery having a good sealing effect and an insulating adhesive that is not prone to warping.

[0004] In a first aspect, the present application provides a secondary battery comprising an electrode assembly, a tab assembly, and a packaging bag. The electrode assembly is housed in the packaging bag, the packaging bag comprising a sealing portion, and the tab assembly comprising tabs and insulating adhesive disposed on either side 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 comprises a first insulating adhesive layer, a second insulating adhesive layer, and a third insulating adhesive layer stacked in sequence along a first direction. The second insulating adhesive layer comprises a cross-linked polymer having a cross-linking degree of 20% to 70%.

[0005] In the secondary battery provided in the present application, the cross-linking degree of the cross-linked polymer of the second insulating adhesive layer of the insulating adhesive is 20% to 70%, so that the second insulating adhesive layer has suitable fluidity, which is beneficial to reducing the risk of warping of the insulating adhesive. When heated, the packaging bag and the insulating adhesive can be completely fused with no obvious interface, thereby improving the packaging 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 the present application, the melt index of the second insulating adhesive layer is A, where A is ≤ 7 g / 10 min. When the melt index of the second insulating adhesive layer is within the above range, the insulating adhesive does not flow at high temperatures, which helps reduce the risk of the insulating adhesive warping and improves the sealing effect.

[0007] According to some embodiments of the present application, the cross-linking degree of the cross-linked polymer is 36% to 45%. When the cross-linking degree of the cross-linked polymer is within the above range, the secondary battery has both low leakage rate and low insulating adhesive warping rate.

[0008] According to some embodiments of the present application, a cross-linked polymer is produced by cross-linking a polymer with a cross-linking agent and an auxiliary agent, where the mass of the cross-linking agent is W1, the total mass of the insulating adhesive is W2, and 0.1% ≤ W1 / W2 ≤ 0.6%. When the content of the cross-linking agent is within the above range, the cross-linked polymer can have an appropriate degree of cross-linking.

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

[0010] According to some embodiments of the present application, the cross-linked polymer is carbon-carbon cross-linked. Carbon-carbon cross-links are resistant to electrolytes, which helps improve the sealing of the secondary battery. Furthermore, the carbon-carbon bond energy is large and not easily broken, which improves the heat aging resistance and compression set of the second insulating adhesive layer. According to some embodiments of the present application, 4.2g / 10min≤A≤4.7g / 10min. When the melt index of the second insulating adhesive layer is within the above range, the secondary battery has both a low leakage rate and a low insulating adhesive separation rate.

[0011] According to some embodiments of the present application, the first insulating adhesive layer and the third insulating adhesive layer include grafted polymers, and the grafting rate of the grafted polymers is 0.03% to 0.5%, so that the insulating adhesive has sufficient adhesion to the tabs and the packaging bag, and the insulating adhesive has good water vapor barrier performance.

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

[0013] According to some embodiments of the present 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 the present application, 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 to 300°C. The higher melting point of the second insulating adhesive layer reduces the risk of over-melting of the second insulating adhesive layer under heat, which could cause a short circuit between the packaging bag and the tab. Furthermore, the lower melting points of the first and third insulating adhesive layers allow the secondary battery to melt and release pressure at high temperatures, thereby improving safety.

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

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

[0017] According to some embodiments of the present application, the toughening modifier includes one or more of EPDM rubber, EPDM rubber, styrene-butadiene rubber, low-density polyethylene, ethylene-vinyl acetate copolymer, linear low-density polyethylene, nylon, polyethylene terephthalate, polycarbonate, ultra-high molecular weight polyethylene, or POE plastic.

[0018] According to some embodiments of the present application, along a 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. 11% h1 ≤ B1 ≤ 34% h1, C1 ≥ 0.8 A1, and 30% h1 ≤ C1 ≤ 79% h1. When the insulating adhesive meets these conditions, the packaging bag and the insulating adhesive can be completely integrated without a noticeable interface, thereby improving the sealing 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 the present application, the secondary battery further includes an electrolyte comprising fluoroethylene carbonate, wherein the fluoroethylene carbonate content is 0.1 wt% to 7 wt% based on the total mass of the electrolyte. When the fluoroethylene carbonate content is within the above range, it helps reduce the swelling of the insulating adhesive, thereby reducing the risk of leakage of the secondary battery.

[0020] The second aspect of the present application provides an insulating adhesive, which includes a first insulating adhesive layer, a second insulating adhesive layer and a third insulating adhesive layer stacked in sequence along a first direction. The second insulating adhesive layer includes a cross-linked polymer, and the cross-linking degree of the cross-linked polymer is 20% to 70%.

[0021] A third aspect of the present application provides a tab assembly, which includes a tab and insulating glue respectively arranged on both sides of the tab, and the insulating glue is the insulating glue of the above embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0023] FIG1 is a schematic diagram of a secondary battery provided in one embodiment of the present application;

[0024] FIG2 is a schematic cross-sectional view of an insulating adhesive provided in one embodiment of the present application;

[0025] FIG3 is a schematic cross-sectional view of the battery shown in FIG1 along line III-III;

[0026] FIG4 is a schematic cross-sectional view of a packaging film provided in one embodiment of the present application;

[0027] FIG5 is a schematic diagram of an electronic device provided in an embodiment of the present application.

[0028] Description of Main Component Symbols Insulating adhesive 30 First insulating adhesive layer 31 Second insulating adhesive layer 32 Third insulating adhesive layer 33 Secondary battery 100 Electrode assembly 10 Packaging bag 40 Tab 20 First packaging film 41 Second packaging film 42 Accommodating cavity 410 Sealing portion 420 Packaging layer 401 Metal layer 402 Protective layer 403 First portion 303 Second portion 302 Third portion 301 First end portion 303a Second end portion 303b Adhesive region 201 Electronic device 200 Main body 210 DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0030] Below, embodiments of the present application will be described in detail. However, the present application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided to make the present application thorough and detailed for those skilled in the art.

[0031] In addition, for the sake of brevity and clarity, the size or thickness of various components or layers may be exaggerated in the accompanying drawings. Throughout the text, the same numerical value refers to the same element. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more related enumerated items. In addition, it should be understood that when element A is referred to as "connecting" element B, element A can be directly connected to element B, or there may be an intermediate element C and element A and element B can be indirectly connected to each other.

[0032] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0033] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit this application. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to 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.

[0034] Spatial related terms, such as "on" etc., can be used herein for convenient description, to describe the relationship between an element or feature and another element (multiple elements) or feature (multiple features) as illustrated in the figure. It should be understood that, in addition to the directions described in the figure, spatial related terms are intended to include different directions of equipment or devices in use or operation. For example, if the equipment in the figure is turned over, the elements described as "above" or "on" other elements or features will be oriented "below" or "below" other elements or features. Therefore, the exemplary term "on" can include the direction above and below. It should be understood that although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish an element, component, region, layer or part from another element, component, region, layer or part. Therefore, the first element, component, region, layer or part discussed below can be referred to as the second element, component, region, layer or part, without departing from the teachings of the exemplary embodiments.

[0035] 1 and 3 , an embodiment of the present application provides a secondary battery 100 comprising an electrode assembly 10, a tab assembly, a packaging bag 40, and an electrolyte contained within the packaging bag 40. The tab assembly comprises a tab 20 and insulating adhesive 30 disposed on either side of the tab. The tab 20 is connected to the electrode assembly 10. The packaging bag 40 encases the electrode assembly 10 and covers a portion of the tab 20. The insulating adhesive 30 is disposed between the packaging bag 40 and the tab 20 and connects the packaging bag 40 and the tab 20. In this embodiment, there are two tabs 20, namely a positive tab and a negative tab. The two tabs 20 are located on the same side of the secondary battery 100 and extend outside the packaging bag 40. There are four insulating adhesives 30, two of which are disposed on opposite surfaces of one tab 20, and two of which are disposed on opposite surfaces of the other tab 20. The two insulating adhesives 30 located on the same side of the two tabs 20 are 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 tabs 20 may be connected to form a single unit, or the two tabs 20 may be located on different sides of the secondary battery 100.

[0036] The electrode assembly 10 includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive and negative electrode sheets. The electrode assembly 10 is formed by stacking or winding the positive electrode sheet, the separator, and the negative electrode sheet. The positive and negative electrode sheets are electrically connected to two tabs 20, respectively.

[0037] The packaging bag 40 includes a first packaging film 41 and a second packaging film 42 that are arranged opposite to each other, and the shape of the first packaging film 41 and the shape of the second packaging film 42 match each other. The first packaging film 41 and the second packaging film 42 are connected to each other and enclose to form a accommodating cavity 410, and the accommodating cavity 410 is used to accommodate the electrolyte, the electrode assembly 10, the tab 20 and at least a portion of the first layer 50. The edges of the first packaging film 41 and the second packaging film 42 are connected to form a sealing portion 420, and the sealing portion 420 extends from the outer side surface of the accommodating cavity 410 toward the side away from the accommodating cavity 410. The sealing portion 420 is the portion where the packaging bag 40 is sealed by a hot pressing process after accommodating the electrode assembly 10 and the electrolyte. The tab 20 is partially accommodated in the accommodating cavity 410 and extends out of the packaging bag 40 through the sealing portion 420.

[0038] Referring to Figures 3 and 4 , the first packaging film 41 and the second packaging film 42 each include an encapsulation layer 401, a metal layer 402, and a protective layer 403 stacked sequentially along a first direction Z. The encapsulation layer 401 is positioned adjacent to the electrode assembly 10, while the protective layer 403 is positioned further 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 and second packaging films 41 and 42 are connected to encapsulate the packaging bag 40, preventing the packaging bag 40 from being dissolved or swollen by the organic solvent in the electrolyte. The encapsulation layer 401 also prevents the electrolyte in the electrolyte from contacting the metal layer 402, which could corrode the metal layer 402. The protective layer 403 is made of a polymer resin and is used to protect the metal layer 402 from damage due to external forces. It also prevents air from penetrating the external environment, maintaining a water- and oxygen-free environment within the secondary battery 100. Metal layer 402 is made of metal, such as aluminum or steel, and is used to prevent moisture from penetrating the external environment and protect the secondary battery 100 from damage caused by external forces. When packaging the secondary battery 100 in packaging bag 40, the packaging film is folded in half. A heat seal head is then applied to the folded surface of the packaging film at a specific temperature (180-215°C) and pressure (0.3-0.6 MPa) for a specific time (1.5-3 seconds) to melt and connect the packaging layer 401 of the packaging film. At this point, the innermost layer of packaging bag 40 is the packaging layer 401.

[0039] Referring to Figure 1 , along 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 region of the insulating adhesive 30 that overlaps with the tab 20 in the first direction Z and is spaced apart from the sealing portion 420. The third portion 301 is the region 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 region 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.

[0040] The first portion 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 portions 301 located at the four corners. Two third portions 301 are located inside the packaging bag 40 and on either side of the first end 303a in the third direction Y. The other two third portions 301 are located outside the packaging bag 40 and on either side 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 of the tab 20. By providing the third portions 301 and the first portion 303, the insulating adhesive 30 extends inward from the sealing portion 420 into the accommodating cavity 410, thereby avoiding the risk of the effective seal width being narrowed due to the insulating adhesive 30 not extending from the sealing portion 420 into the packaging bag 40. Furthermore, the insulating adhesive 30 extends outward from the sealing portion 420 to the outside of the packaging bag 40, thereby preventing the risk of the edges of the packaging bag 40 being compressed during packaging and facilitating sealing.

[0041] Referring to Figures 3 and 2 , along a 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 in sequence. The first insulating adhesive layer 31 is connected to the tab 20, and the third insulating adhesive layer 33 is connected to the encapsulation layer 401 of the packaging bag 40. The first insulating adhesive layer 31 and the third insulating adhesive layer 33 provide sealing. The second insulating adhesive layer 32 provides support to reduce the risk of over-melting of the insulating adhesive 30 and a short circuit between the packaging bag and the tab.

[0042] In this application, the first portion 303, the third portion 301, and the second portion 302 all include a first insulating adhesive layer 31, a second insulating adhesive layer 32, and a third insulating adhesive layer 33. Before packaging, the thicknesses of the first insulating adhesive layer 31, the second insulating adhesive layer 32, and the third insulating adhesive layer 33 of the first portion 303, the second portion 302, and the third portion 301 are approximately equal. The insulating adhesive 30 is located in different regions and named differently. In the first portion 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 portion 302, the insulating adhesive 30 includes the first insulating adhesive layer of the second portion, the second insulating adhesive layer of the second portion, and the third insulating adhesive layer of the second portion; and in the third portion 301, the insulating adhesive 30 includes the first insulating adhesive layer of the third portion, the second insulating adhesive layer of the third portion, and the third insulating adhesive layer of the third portion. Since the first end portion 303a included in the first part 303 is not heat-melted during packaging, 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 portion 303a is roughly 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 packaging with the insulating adhesive 30.

[0043] The tab assembly also includes a bonding region 201, which is the portion where the insulating adhesive 30 on both sides of the tab 20 along the first direction Z adheres to each other. The bonding region 201 is composed of 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 bonding region 201, the first insulating adhesive layers 31 of the two insulating adhesives 30 adhere to each other to form a first insulating adhesive bonding layer.

[0044] The first insulating adhesive layer 31, the second insulating adhesive layer 32, and the third insulating adhesive layer 33 all include a polymer. The polymer may include one or more of polypropylene, polyethylene, an ethylene-based elastomer, a propylene-based elastomer, a styrene-based elastomer, an ionomer resin, polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol. These polymers have excellent adhesive properties.

[0045] The second insulating adhesive layer 32 includes a cross-linked polymer. In some embodiments, the cross-linked polymer is produced by cross-linking the polymer with a cross-linking agent and irradiation. The cross-linking agent may include one or more of a silane coupling agent, hydrogen peroxide, triallyl isocyanurate, trimethylolpropane trimethacrylate, and tris(2-acryloyloxyethyl) isocyanurate. The cross-linking agent reacts with the polymer to form a carbon-carbon double bond addition reaction to achieve cross-linking, so the cross-linking point of the cross-linked polymer is a carbon-carbon cross-link. The carbon-carbon cross-link is resistant to electrolyte and is used to improve the sealing of the secondary battery 100; and the carbon-carbon cross-link has a large bond energy and is not easy to break, so that the second insulating adhesive layer 32 has better heat aging resistance and compression permanent deformation.

[0046] In some embodiments, the second insulating adhesive layer 32 further includes an additive. The cross-linked polymer is produced by cross-linking a polymer with the cross-linking agent and the additive. The mass of the cross-linking agent is W1, the total mass of the insulating adhesive is W2, and 0.1% ≤ W1 / W2 ≤ 0.6%. When the cross-linking agent content is within the above range, the cross-linked polymer in the second insulating adhesive layer 32 can have an appropriate degree of cross-linking.

[0047] Additives may include colorants, antioxidants, and the like. The colorant may be white or gray. The antioxidant may include 2,6-di-tert-butyl-p-cresol. In some embodiments, the second insulating adhesive layer 32 also includes a white colorant to facilitate identification during production. Based on the mass of the second insulating adhesive layer 32, the content of the white 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 white colorant may include at least one of titanium dioxide, zinc sulfide, lithopone, or zinc oxide.

[0048] In some embodiments, the cross-linking degree of the cross-linked polymer of the second insulating adhesive layer 32 is 20% to 70%. When the cross-linking degree of the cross-linked polymer is within the above range, the second insulating adhesive layer 32 exhibits a highly elastic state at high temperatures (e.g., 200°C), which helps reduce the risk of the second insulating adhesive layer 32 over-melting when heated, resulting in a short circuit between the packaging bag and the tab, and helps reduce the detachment rate of the insulating adhesive, improve the sealing effect, and reduce the risk of leakage. When the cross-linking degree is lower than 20%, the high-temperature resistance effect cannot be achieved; when the cross-linking degree exceeds 70%, the fluidity of the second insulating adhesive layer 32 deteriorates, which deteriorates the sealing effect of the secondary battery 100. Preferably, the cross-linking degree of the cross-linked polymer is 36% to 45%. When the cross-linking degree of the cross-linked polymer is within the above preferred range, the secondary battery 100 has both a low leakage rate and a low insulating adhesive detachment rate.

[0049] In the present application, the cross-linking degree of the cross-linked 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, so that the non-cross-linked part of the sample is fully dissolved in xylene, filter out the insoluble matter, and weigh the mass of the insoluble matter after drying as M1. The weight ratio M1 / M2 is the cross-linking degree.

[0050] In some embodiments, the melt index of the second insulating adhesive layer 32 is A, A≤7g / 10min. When the melt index of the second insulating adhesive layer 32 is within the above range, the second insulating adhesive layer 32 has no flow state at high temperatures (such as 200°C), has high heat resistance, and helps reduce the risk of over-melting of the second insulating adhesive layer 32 when heated. Preferably, 4.2g / 10min≤A≤4.7g / 10min. When the melt index of the second insulating adhesive layer 32 is within the above preferred range, the secondary battery 100 has both a low leakage rate and a low insulating adhesive warping rate.

[0051] In some embodiments, both the first insulating adhesive layer 31 and the third insulating adhesive layer 33 include a grafted polymer, and the grafting rate of the grafted polymer is 0.03% to 0.5%. When the grafting rate is less than 0.03%, the polar groups introduced into the first insulating adhesive layer 31 are insufficient, resulting in insufficient adhesion between the first insulating adhesive layer 31 and the tab 20. This may cause delamination at the interface between the tab 20 and the first insulating adhesive layer 31 after the first insulating adhesive layer 31 comes into contact with the electrolyte, resulting in poor sealing performance. When the grafting rate is greater than 0.5%, the polar groups have strong water absorption, resulting in poor water vapor barrier performance of the insulating adhesive 30, which in turn causes flatulence in the secondary battery 100. Preferably, the grafting rate of the grafted polymer is 0.03% to 0.15%. Within this range, the packaging tension of the secondary battery 100 remains stable.

[0052] The grafting rate of the grafted polymer is determined by the following method: First, according to the grafting rate of the grafted polymer to be measured, a 0.1 mol / L KOH-ethanol standard solution is prepared and calibrated with potassium hydrogen phthalate; secondly, 10 g of the purified sample is weighed and dissolved in xylene to obtain a solution, the solution is slowly added to a sufficient amount of acetone solution, and filtered to obtain a precipitate; then, the precipitate is placed in a Soxhlet extractor for extraction (the extractant is xylene, and the extraction time is 3 h), and the precipitate is dried to constant weight; then, 2 g of the purified sample and 100 ml of xylene are added to a three-necked flask, 6 drops of deionized water and 6 drops of pyridine are added, and the solution is refluxed at the boiling temperature of xylene for 1 h, 5 drops of phenolphthalein indicator reagent are added, and the solution is titrated with a KOH-ethanol standard solution. After the red color of the solution does not fade for 10 minutes, the volume of the consumed standard solution is recorded and the grafting rate is calculated; three experiments are performed in parallel, and the average of the grafting rates measured in the three experiments is taken. The calculation formula of the grafting rate is shown in formula (1):

[0053] Where GR is the grafting rate of the purified sample, ΔV is the volume of the KOH-ethanol standard solution consumed (mL), C is the concentration of the KOH-ethanol standard solution (mol / L), and m is the mass of the sample (g). The grafting rate test method is not limited to the above test method.

[0054] In some embodiments, the graft polymer is produced by grafting the above-mentioned polymer with a polar group. The polar group includes at least one of maleic anhydride, maleic acid, acrylic acid, methacrylic acid, maleic anhydride, or an epoxy group. These graft polymers have strong adhesion to the tabs and packaging bags. Preferably, the graft polymer is maleic anhydride grafted polypropylene.

[0055] In some embodiments, the third insulating adhesive layer 33 also includes a gray colorant to facilitate identification of the various insulating adhesive layers during production and prevent adhesion between the third insulating adhesive layer 33 and the tab. Based on the mass of the third insulating adhesive layer 33, the gray colorant content 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 can include at least one of graphite, carbon black, or manganese iron black.

[0056] In some embodiments, the melting points of the first insulating adhesive layer 31 and the third insulating adhesive layer 33 are both between 100°C and 140°C, and the melting point of the second insulating adhesive layer 32 is between 140°C and 400°C. The difference between the melting point of the second insulating adhesive layer 32 and the melting point of the first insulating adhesive layer 31 or the melting point of the third insulating adhesive layer 33 is between 40°C and 300°C. The higher melting point of the second insulating adhesive layer 32 reduces the risk of over-melting of the second insulating adhesive layer 32 under heat, thereby causing a short circuit between the packaging bag 40 and the tab 20. Furthermore, the lower melting points of the first insulating adhesive layer 31 and the third insulating adhesive layer 33 allow the secondary battery 100 to melt and release pressure at high temperatures, thereby improving safety.

[0057] In some embodiments, the first insulating adhesive layer 31 and / or the third insulating adhesive layer 33 further include a toughening modifier for improving flexibility and impact resistance to improve the packaging strength of 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), styrene butadiene rubber, etc., which are used to prevent crack propagation. The toughening modifier may also include one or more of a flexible polymer, a rigid polymer, an ultra-high molecular weight polyethylene (UHMWPE), or a POE plastic, which is used to enhance the connection between crystals and blur the intercrystalline interface. The flexible polymer may be low-density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), linear low-density polyethylene (LLDPE), etc. The rigid polymer may be nylon (PA6), polyethylene terephthalate (PET), polycarbonate (PC), etc.

[0058] In some embodiments, the toughening modifier content in the first insulating adhesive layer 31 is 3 wt% to 10 wt%, and / or the toughening modifier content in the third insulating adhesive layer 33 is 3 wt% to 10 wt%. When the toughening modifier content is within the above range, the packaging strength between the insulating adhesive 30 and the packaging bag 40 is high. When the toughening modifier content exceeds 10 wt%, the crystals may become integrated and delamination may occur.

[0059] At 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. Here, 11% h1 ≤ B1 ≤ 34% h1, C1 ≥ 0.8A1, and 30% h1 ≤ C1 ≤ 79% h1. When the insulating adhesive 30 meets these thicknesses, during packaging, the packaging bag 40 and the insulating adhesive 30 can completely fuse together, leaving no noticeable interface. 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. The requirement of 11% h1 ≤ B1 ≤ 34% h1 ensures that the second insulating adhesive layer 32 does not overmelt or under-fuse during packaging heat, preventing the second insulating adhesive layer 32 from forming an interface or delamination with the first and third insulating adhesive layers 31, 33, thereby reducing packaging strength. Meeting the requirements of C1 ≥ 0.8A1 and 30% h1 ≤ C1 ≤ 79% h1 ensures complete fusion of the third insulating adhesive layer 33 with the packaging bag 40. Since the third insulating adhesive layer 33 is heated and melted before the first insulating adhesive layer 31 during packaging, this design prevents overmelting of the third insulating adhesive layer 33, which could cause fusion between the packaging bag and the second insulating adhesive layer 32 and lead to a poor fusion interface. This ensures complete fusion of the third insulating adhesive layer 33 with the packaging bag 40. Furthermore, the asymmetric thicknesses of the first, second, and third insulating adhesive layers 31, 32, and 33 ensure complete fusion of the insulating adhesive 30 and the packaging bag 40 during packaging, eliminating a noticeable interface. 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.

[0060] 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 and thus poorly bonded to the tab 20, thereby ensuring that the first insulating adhesive layer 31 is fused and bonded to the tab 20.

[0061] In some embodiments, h1 is 30 to 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.

[0062] In some embodiments, 8.3A1≥C1≥1.05A1, when the thickness C1 of the third insulating adhesive layer 33 is within the above range, the secondary battery 100 can have high packaging strength while also having high insulation and corrosion resistance.

[0063] In the second portion 302, along the first direction Z, the thickness of the third insulating adhesive layer of the second portion is C2. In some embodiments, 92% C1 ≤ C2 ≤ 98% C1. This arrangement minimizes the thickness change of the third insulating adhesive layer of the second portion before and after heat sealing, thereby improving the packaging strength. In some embodiments, 7 μm ≥ C1 - C2 ≥ 1 μm.

[0064] The thickness of the encapsulation layer 401 in the first direction Z of the packaging bag 40 in the area where it does not overlap with the sealing portion 420 is P. That is, before packaging, the thickness of the encapsulation layer 401 of the packaging bag 40 in the first direction Z is P. In the second portion 302, the encapsulation layer 401 of the packaging bag 40 fuses with the second and third insulating adhesive layers of the insulating adhesive 30 due to heat sealing, resulting in a total thickness of the encapsulation layer 401 and the second and third insulating adhesive layers in the first direction Z of H. In some embodiments, 0.25(C2+P)≤H≤0.75(C2+P). This configuration allows the encapsulation layer 401 of the packaging bag 40 to completely fuse with the second and third insulating adhesive layers of the insulating adhesive 30, thereby improving packaging strength. Preferably, 0.29(C2+P)≤H≤0.5(C2+P).

[0065] 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 the present application, the thickness of the first packaging film 41 and the second packaging film 42 in the first direction Z is 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%.

[0066] In the bonding area 201, along the first direction Z, the thickness of the bonding area 201 is Q, the thickness of the first insulating adhesive layer in the bonding area is D, the thickness of the second insulating adhesive layer in the bonding area is B4, and the thickness of the third insulating adhesive layer in the bonding area is C4, wherein 10.5% (Q×0.5)≤B4≤35% (Q×0.5), C4>0.5D, 90% B4≤C4≤500% B4, 120% B4≤D≤800B4%.

[0067] The electrolyte includes an organic solvent, a lithium salt and an electrolyte additive. The electrolyte additive includes at least fluoroethylene carbonate (FEC). Based on the total mass of the electrolyte, the content of fluoroethylene carbonate is 0.1wt% to 7wt%. When the content of fluoroethylene carbonate is within the above range, it helps to reduce the swelling degree of the insulating glue 30, thereby reducing the risk of leakage of the secondary battery 100; at the same time, it can also obtain an excellent cycle retention rate. Fluoroethylene carbonate affects the film formation of the negative electrode. When the content of fluoroethylene carbonate is within the above range, it helps to reduce the impedance. The electrolyte additive may also include lithium difluorooxalatoborate, lithium difluorophosphate, lithium difluorooxalatoborate, fluoroethylene carbonate, lithium difluorophosphate, 1,2-bis(cyanoethoxy)ethane, or 1,2,3-tris(2-cyanoethoxy)propane, etc.

[0068] The organic solvent may be any conventional organic solvent in the art, for example, at least one selected from carbonates, carboxylates, or fluoroethers. Carbonates may be selected from one or more combinations of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methylpropyl carbonate. Carboxylates may be selected from one or more combinations of ethyl propionate and propyl propionate. Fluoroethers may be selected from 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. Lithium salts may be selected from at least one of lithium bis(trifluoromethylsulfonyl imide), lithium bis(fluorosulfonyl imide), and lithium hexafluorophosphate.

[0069] 5 , an embodiment of the present application further provides an electronic device 200, which includes a main body 210 and a secondary battery 100. The secondary battery 100 is housed in the main body 210. The electronic device 200 may be a mobile phone, a tablet, or an e-reader.

[0070] In this application, the electronic device 200 is exemplified by a mobile phone. The secondary battery 100 is disposed within the mobile phone to provide power to the mobile phone. The main body 210 is a mobile phone structure. It is understood that in other embodiments, the electronic device 200 may also have other structures, not limited to the aforementioned mobile phones, tablets, and e-readers.

[0071] The performance of the insulating adhesive and the secondary battery provided in this application are described below through specific examples and comparative examples.

[0072] Example 1

[0073] Preparation of the positive electrode sheet: Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were dissolved in N-methylpyrrolidone 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 applied to the surface of the positive electrode current collector to form a positive electrode active material layer. After drying, cold pressing, and cutting, the positive electrode sheet was obtained.

[0074] Preparation of the negative electrode: 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 are mixed to form a coating slurry. 97.7 wt% of graphite, 1.3 wt% of sodium carboxymethyl cellulose, 1.0 wt% of styrene-butadiene rubber, and an appropriate amount of deionized water are mixed to form a negative electrode slurry. Copper foil is used as the negative electrode current collector. The negative electrode slurry is applied to the surface of the negative electrode current collector and dried to form the negative electrode active material layer. The negative electrode sheets are then cold pressed and cut.

[0075] Preparation of isolation film: Polyethylene film is selected as the isolation film.

[0076] Preparation of electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) are mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 and the organic solvent are mixed in a weight ratio of 8:92 to obtain an electrolyte.

[0077] Preparation of insulating glue:

[0078] The first insulating adhesive layer is obtained by mixing 99% of a polymer matrix and 1% of an additive, melting, and then extruding. The polymer matrix is ​​polypropylene (PP), and the additive includes an antioxidant (2,6-di-tert-butyl-p-cresol).

[0079] The second insulating adhesive layer is formed by mixing 99% polymer matrix, 0.1% crosslinking agent, and 0.9% additives, melting, and then extruding. 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).

[0080] The third insulating adhesive layer is formed by mixing 99% of a polymer matrix and 1% of an additive, melting, and then extruding. The polymer matrix is ​​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).

[0081] The first, second, and third insulating adhesive layers were laminated together using a thermal bonding process to produce the insulating adhesive shown in Figure 2. The insulating adhesive was irradiated with gamma rays to form a cross-linked polymer in the second insulating adhesive layer. The cross-linking degree of the cross-linked polymer in the second insulating adhesive layer was 20%, and the melt index of the second insulating adhesive layer was 7 g / 10 min.

[0082] Preparation of a secondary battery: The positive electrode sheet, polyethylene separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets, and then wound to form an electrode assembly. The electrode assembly is placed in a packaging bag, and insulating adhesive is applied between the packaging bag and the tabs. The assembly is then heat-sealed using a 1.5 mm wide heat seal head to form the secondary battery shown in Figure 2. The heat sealing temperature is 205°C, the heat sealing pressure is 0.4 MPa, and the heat sealing time is 1.5 seconds. The thickness h1 of the insulating adhesive 30 is μm. In the first portion 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.

[0083] Examples 2-10 and Comparative Examples 1-3

[0084] The difference from Example 1 is that at least one of the crosslinking agent content, the crosslinking degree of the crosslinked polymer, and the melt index of the second insulating adhesive layer is different. The total content of the crosslinking agent and auxiliary agent in each example and comparative example is 1%. Specific parameters are shown in Table 1.

[0085] The secondary batteries prepared in each embodiment and comparative example were subjected to a drop test and the insulating adhesive warping rate of the secondary batteries was measured. The test results are shown in Table 1.

[0086] Insulation adhesive warping rate test:

[0087] Observe whether the insulating adhesive is warping relative to the tab extension direction. If the insulating adhesive warps more than 10° relative to the tab extension direction, it is considered warping. The ratio of the number of secondary batteries with warped insulating adhesive to the total number of test samples is the insulating adhesive warping rate.

[0088] Drop test:

[0089] Charge the secondary battery at 0.5C constant current to 4.2V at 20±5°C, then charge it at 4.2V to 0.05C constant voltage. Then drop it from a height of 1.5 meters onto a smooth marble surface. Drop in the following order: front-back-bottom-top-left-right-upper-left-upper-right-lower-left-lower-right. Each side / corner is dropped once in a row, forming one cycle. Inspect the secondary battery for a total of 10 cycles. Record any leakage.

[0090] Table 1 Note: X / 500 means that the number of leaks among the 500 samples tested is X.

[0091] Table 1 shows that as the crosslinking degree increases, the insulating adhesive's warping rate decreases. Furthermore, when the crosslinking degree exceeds 45%, the leakage rate increases. When the crosslinking degree is between 20% and 70%, the insulating adhesive has a low warping rate and a low leakage rate. When the crosslinking degree is less than 20%, the insulating adhesive's warping rate is too high, and when the crosslinking degree exceeds 70%, the leakage rate is too high.

[0092] Lithium-ion battery hot box test: The lithium-ion battery is charged at a constant current (CC) of 0.5C to a state of charge (SOC%). The battery is then placed in a 130°C or 150°C thermal shock chamber, respectively. The battery is stored for one hour, or immediately after thermal runaway. The voltage and surface temperature changes are recorded. The battery passes the test if it does not catch fire, explode, or emit smoke. Ten lithium-ion batteries are tested for each test condition.

[0093] 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 and heated at 5°C / min to 135°C and held there for 1 hour. The lithium-ion battery passes the test if it does not catch fire or explode. Each example 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 indicates the thermal safety performance of the lithium-ion battery. A higher hot box test pass rate indicates better thermal safety performance.

[0094] The above disclosure is only a preferred embodiment of the present application and certainly cannot be used to limit the present application. Therefore, equivalent changes made based on the present application are still within the scope covered by the present application.

Claims

1. A secondary battery, comprising an electrode assembly, a tab assembly, and a packaging bag. The electrode assembly is accommodated in the packaging bag. The packaging bag includes a sealing portion. The tab assembly includes a tab and insulating adhesives respectively disposed on both sides of the tab. The tab is connected to the electrode assembly and extends out of the packaging bag through the sealing portion, and is characterized in that, The insulating adhesive includes a first insulating adhesive layer, a second insulating adhesive layer, and a third insulating adhesive layer that are sequentially stacked in a first direction. The second insulating adhesive layer includes a crosslinked polymer, and the crosslinking degree of the crosslinked polymer is 20% to 70%.

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

3. The secondary battery according to claim 1, wherein, The melt index of the second insulating adhesive layer is A, and A ≤ 7 g / 10 min.

4. The secondary battery according to claim 3, wherein, 4.2 g / 10 min ≤ A ≤ 4.7 g / 10 min.

5. The secondary battery according to claim 1, wherein, The crosslinked polymer is carbon-carbon crosslinked.

6. The secondary battery according to any one of claims 1 to 5, wherein, The first insulating adhesive layer and the third insulating adhesive layer include a graft polymer, and the grafting rate of the graft polymer is 0.03% to 0.5%.

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

8. The secondary battery according to any one of claims 1 to 5, wherein, The melting points of the first insulating adhesive layer and the third insulating adhesive layer are both 100°C to 140°C, and the melting point of the second insulating adhesive layer is 140°C to 400°C.

9. The secondary battery according to claim 8, 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 to 300°C.

10. The secondary battery according to any one of claims 1-5, wherein, The first insulating adhesive layer, the second insulating adhesive layer, and the third insulating adhesive layer all include a polymer, and the polymer includes one or more of polypropylene, polyethylene, ethylene-based elastomer, propylene-based elastomer, styrene-based elastomer, ionomer resin, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol.

11. The secondary battery according to claim 10, wherein, The first insulating adhesive layer and / or the third insulating adhesive layer further includes a toughening modifier.

12. The secondary battery according to claim 11, wherein, The toughening modifier includes one or more of ethylene propylene diene monomer (EPDM), ethylene propylene rubber (EPR), styrene-butadiene rubber (SBR), low density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), linear low density polyethylene (LLDPE), nylon, polyethylene terephthalate (PET), polycarbonate (PC), ultra-high molecular weight polyethylene (UHMWPE), or POE plastic.

13. The secondary battery according to any one of claims 1-5, 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. 11%h1 ≤ B1 ≤ 34%h1, C1 ≥ 0.8A1, 30%h1 ≤ C1 ≤ 79%h1.

14. The secondary battery according to any one of claims 1 to 5, wherein, The secondary battery further includes an electrolyte, and the electrolyte includes fluoroethylene carbonate. Based on the total mass of the electrolyte, the content of fluoroethylene carbonate is 0.1 wt% to 7 wt%.

15. 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 that are sequentially stacked in a first direction. The second insulating adhesive layer includes a crosslinked polymer, and the crosslinking degree of the crosslinked polymer is 20% to 70%.

16. An electrode tab assembly, characterized in that, The tab assembly includes a tab and insulating adhesives respectively disposed on both sides of the tab. The insulating adhesive is the insulating adhesive as described in claim 15.

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