Insulating adhesive and secondary battery

Abstract

An insulating adhesive and a secondary battery. The insulating adhesive comprises a first insulating adhesive layer, a second insulating adhesive layer and a third insulating adhesive layer, which are stacked in sequence along a first direction. A degree of swelling of the insulating adhesive when soaked in dimethyl carbonate for 4 hours at room temperature is less than or equal to 5%. Packaging tension between the insulating adhesive and a packaging bag of the secondary battery is high, and a sealing effect is good.

Description

Insulation glue and secondary batteries Technical Field

[0001] The present application relates to the technical field of energy storage devices, and in particular to a second insulating adhesive 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 an insulating adhesive and a secondary battery using the insulating adhesive, wherein the insulating adhesive has a good sealing effect with the packaging bag of the secondary battery.

[0004] In a first aspect, the present 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 insulating adhesive has a swelling degree of less than or equal to 5% after being immersed in dimethyl carbonate for 4 hours at room temperature. When the swelling degree of the insulating adhesive is within the aforementioned range, the insulating adhesive has a high tensile strength, and the sealing tension between the insulating adhesive and the packaging bag of a secondary battery to which the insulating adhesive is applied is high, thereby improving the sealing effect.

[0005] According to some embodiments of the present application, the swelling degree of the insulating adhesive after being immersed in dimethyl carbonate at 85° C. for 4 hours is less than or equal to 5%.

[0006] According to some embodiments of the present application, the difference in swelling degree of the insulating adhesive after being immersed in dimethyl carbonate for 4 hours at room temperature and at 85° C. is less than or equal to 1%.

[0007] According to some embodiments of the present application, the first insulating adhesive layer includes a grafted polymer, and the grafting rate of the grafted polymer is 0.03%-0.5%. When the grafting rate is less than 0.03%, the polar groups introduced into the insulating adhesive are insufficient, resulting in insufficient adhesion between the insulating adhesive and the tabs of the secondary battery to which the insulating adhesive is applied. This may cause delamination at the tab-to-adhesive interface after the insulating adhesive 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, which in turn causes bloating in the secondary battery to which the insulating adhesive is applied.

[0008] According to some embodiments of the present application, the third insulating adhesive layer includes a grafted polymer with a grafting rate of 0.03% to 0.5%. When both the first insulating adhesive layer and the third insulating adhesive layer include the grafted polymer, when the insulating adhesive is applied to the tab of the secondary battery, adhesion failure of the insulating adhesive to the packaging bag and the tab due to the first and third insulating adhesive layers being applied reversely can be avoided.

[0009] According to some embodiments of the present application, the grafting rate of the grafted polymer is 0.03%-0.15%.

[0010] 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.

[0011] 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 140-200°C.

[0012] 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. 10.5% h1≤B1≤35% h1, C1≥0.9A1, 30% h1≤C1≤79% h1, and 10.5% h1≤A1≤35% 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.

[0013] 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.

[0014] According to some embodiments of the present application, the first insulating adhesive layer and / or the third insulating adhesive layer further include a toughening modifier. The toughening modifier can enhance the flexibility and impact resistance of the insulating adhesive, thereby increasing the packaging strength between the insulating adhesive and the secondary battery packaging bag in which it is applied.

[0015] 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.

[0016] According to some embodiments of the present application, the content of the toughening modifier is 4%-10%.

[0017] According to some embodiments of the present application, the swelling degree of the insulating adhesive after being immersed in dimethyl carbonate for 4 hours at room temperature is less than or equal to 3%.

[0018] According to some embodiments of the present application, the swelling degree of the insulating adhesive after being immersed in dimethyl carbonate for 4 hours at room temperature is less than or equal to 0.5%.

[0019] According to some embodiments of the present application, the difference in swelling degree of the insulating adhesive after immersion in dimethyl carbonate for 4 hours at room temperature and 85° C. is less than or equal to 0.4%.

[0020] A second aspect of the present application provides a secondary battery, comprising an electrode assembly, a tab assembly and a packaging bag, wherein the electrode assembly is contained in the packaging bag, the packaging bag comprises a sealing portion, the tab assembly comprises a tab and insulating glue respectively arranged on both sides of the tab, the insulating glue being the insulating glue of any of the above-mentioned embodiments, the tab being connected to the electrode assembly and extending out of the packaging bag through the sealing portion, the first insulating glue layer being connected to the tab, and the third insulating glue layer being connected to the packaging bag. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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:

[0022] FIG1 is a schematic cross-sectional view of an insulating adhesive provided in one embodiment of the present application;

[0023] FIG2 is a schematic diagram of a secondary battery provided in one embodiment of the present application;

[0024] FIG3 is a schematic cross-sectional view of the battery shown in FIG2 along line III-III;

[0025] FIG4 is a schematic cross-sectional view of a packaging film provided in one embodiment of the present application;

[0026] FIG5 is a schematic diagram of an electronic device provided in an embodiment of the present application.

[0027] 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

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0032] 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.

[0033] 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.

[0034] Referring to Figure 1 , one embodiment of the present application provides an insulating adhesive 30 for use in a secondary battery, for bonding the battery's tabs to the packaging bag. The insulating adhesive 30 comprises a first insulating adhesive layer 31, a second insulating adhesive layer 32, and a third insulating adhesive layer 33 stacked sequentially along a first direction Z. The first insulating adhesive layer 31 is used to bond to the tab, while the third insulating adhesive layer 33 is used to bond to the packaging bag, providing a seal. The second insulating adhesive layer 32 provides support to reduce the risk of over-melting of the insulating adhesive 30, which could cause a short circuit between the packaging bag and the tab.

[0035] The insulating adhesive 30 will swell in dimethyl carbonate (DMC). At room temperature (e.g., 25°C) and high temperature (e.g., 85°C), the swelling degree of the insulating adhesive 30 in the DMC solvent is small and remains roughly stable as the immersion time increases, reducing the risk of secondary battery leakage. In this application, room temperature refers to the indoor ambient temperature of the insulating adhesive. Under normal circumstances, the indoor ambient temperature is defined as 25°C. In some embodiments, the swelling degree of the insulating adhesive 30 after immersion in the DMC solvent for 4 hours at room temperature is less than or equal to 5%, for example, the swelling degree is 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.8%, 1%, 2%, 3%, 4%, or 5%. When the swelling degree of the insulating adhesive 30 is greater than 5%, the cohesive force of the insulating adhesive 30 material is reduced, resulting in a rapid decrease in the elongation at break / fracture strength of the insulating adhesive 30, which in turn reduces the sealing strength between the insulating adhesive 30 and the tab and packaging bag, increasing the risk of secondary battery leakage. In some embodiments, the difference in swelling degree of the insulating adhesive 30 after being immersed in a DMC solvent for 4 hours and 48 hours at room temperature is less than or equal to 0.5%.

[0036] In some embodiments, the swelling degree of the insulating adhesive 30 after immersion in a DMC solvent at 85°C for 4 hours is less than or equal to 5%, for example, the swelling degree is 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.8%, 1%, 2%, 3%, 4%, or 5%. In some embodiments, the difference in swelling degree between the insulating adhesive 30 after immersion in a DMC solvent at 85°C for 4 hours and 48 hours is less than or equal to 3%. In some embodiments, the difference in swelling degree between the insulating adhesive 30 after immersion in a DMC solvent at room temperature and at 85°C for 4 hours is less than or equal to 1%. In this case, the insulating adhesive 30 has good swelling stability, which can further reduce the risk of leakage in the secondary battery.

[0037] The swelling degree of insulating adhesive 30 in DMC solvent is determined by the following method: First, weigh 0.5g of sample and dry it at 65°C for 2 hours. The sample weight is then measured (W0). Next, 200ml of DMC solvent is placed in the dried sample and soaked at room temperature (25°C) or 85°C for 4 hours or 48 hours. The sample is then cooled to room temperature, removed at room temperature, cleaned with alcohol, and the surface liquid wiped off. The sample weight is then measured (W1). Swelling degree = W0 / W1.

[0038] In some embodiments, 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 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.

[0039] In some embodiments, the first insulating adhesive layer 31 and the third insulating adhesive layer 33 both 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 insulating adhesive are insufficient, resulting in insufficient bonding between the insulating adhesive and the tabs, which may cause delamination at the tab-to-tab interface after the insulating adhesive comes into contact with the electrolyte, resulting in poor sealing performance. When the grafting rate is greater than 5%, the polar groups have strong water absorption, resulting in poor water vapor barrier performance of the insulating adhesive, which in turn causes flatulence in the secondary battery. Preferably, the grafting rate of the grafted polymer is 0.03% to 0.15%. Within this range, the packaging tension of the secondary battery using the insulating adhesive 30 remains stable. When both the first insulating adhesive layer 31 and the third insulating adhesive layer 33 include a graft polymer, when the insulating adhesive 30 is applied to the tab of the secondary battery, adhesion failure of the insulating adhesive 30 to the packaging bag and the tab due to the first insulating adhesive layer 31 and the third insulating adhesive layer 33 being applied upside down can be avoided. In other embodiments, only the first insulating adhesive layer 31 or the third insulating adhesive layer 33 includes a graft polymer.

[0040] 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):

[0041] Where GR is the grafting rate of the purified sample, △V is the volume of the consumed KOH-ethanol standard solution (mL), C is the concentration of the KOH-ethanol standard solution (mol / L), and m is the mass of the test sample (g).

[0042] 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.

[0043] 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. 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 POE plastic, which are 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.

[0044] 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 sealing strength between the insulating adhesive 30 and the packaging bag is high. When the toughening modifier content exceeds 10 wt%, the crystals may become integrated and delamination may occur.

[0045] In some embodiments, the second insulating adhesive layer 32 further includes a white colorant, and the third insulating adhesive layer 33 further includes a gray colorant. This facilitates identification of the insulating adhesive layers during production and prevents the third insulating adhesive layer 33 from adhering to the tab. Based on the mass of the second insulating adhesive layer 32, the white 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%. 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 white colorant may include at least one of titanium dioxide, zinc sulfide, lithopone, or zinc oxide. The gray colorant may include at least one of graphite, carbon black, or manganese iron black.

[0046] 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 200°C. When the melting points are within this range, the difference between the melting points of the three insulating adhesive layers is small, which reduces the possibility that the first insulating adhesive layer 31 or the second insulating adhesive layer 30 on the outside will overmelt while the second insulating adhesive layer 32 on the inside will not melt when the package is heated.

[0047] 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, 10.5% h1 ≤ B1 ≤ 35% h1, C1 ≥ 0.9A1, 30% h1 ≤ C1 ≤ 79% h1, and 10.5% h1 ≤ A1 ≤ 35% h1. Meeting the requirement of 10.5% h1 ≤ B1 ≤ 35% h1 ensures that the second insulating adhesive layer 32 does not overmelt or undermelt when the package is heated, thereby preventing the interface between the second insulating adhesive layer 32 and the first insulating adhesive layer 31 or the third insulating adhesive layer 33, causing delamination and reducing the package strength. Satisfy C1≥0.9A1, 30%h1≤C1≤79%h1, 10.5%h1≤A1≤35%h1, ensure that the third insulating adhesive layer 33 and the packaging bag can be completely fused and the first insulating adhesive layer 31 is fused and bonded to the tab. Since the third insulating adhesive layer 33 is heated and melted first relative to the first insulating adhesive layer 31 during packaging, this design can avoid the third insulating adhesive layer 33 from overmelting and causing the packaging bag and the second insulating adhesive layer 32 to fuse, resulting in a poor fusion interface problem, and can also avoid the first insulating adhesive layer 31 from melting. Insufficient fusion or over-melting results in poor adhesion to the tab 20, ensuring that the third insulating adhesive layer 33 and the packaging bag can be completely fused, and the first insulating adhesive layer 31 is fused and bonded to the tab, and the first insulating adhesive layer 31, the second insulating adhesive layer 32 and the third insulating adhesive layer 33 are asymmetric in thickness. The three-layer structure with asymmetric thickness is adopted, so that during packaging, the insulating adhesive 30 and the packaging bag can be completely fused without obvious interface, thereby improving the packaging strength between the insulating adhesive 30 and the packaging bag, improving the sealing effect, and reducing the risk of leakage.

[0048] In some embodiments, 8.3A1 ≥ C1 ≥ 1.05A1. As the thickness of the third insulating adhesive layer 33 increases, the post-encapsulation tensile force increases, resulting in a better secondary battery sealing effect. When 8.3A1 < C1, during encapsulation, insufficient fusion and interface formation between the third insulating adhesive layer 33, the packaging bag, and the second insulating adhesive layer 32 may occur, resulting in a reduced encapsulation tensile force and an increased risk of secondary battery leakage.

[0049] 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.

[0050] 2 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 the other two 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Referring to Figure 2 , 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.

[0055] 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.

[0056] Please refer to Figure 3 and Figure 1. Along the first direction Z, the insulating glue 30 includes a first insulating glue layer 31, a second insulating glue layer 32 and a third insulating glue layer 33 stacked in sequence. The first insulating glue layer 31 is connected to the tab 20, and the third insulating glue layer 33 is connected to the packaging layer 401 of the packaging bag 40.

[0057] 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.

[0058] 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.

[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, 10.5% h1 ≤ B1 ≤ 35% h1, C1 ≥ 0.9A1, 30% h1 ≤ C1 ≤ 79% h1, and 10.5% h1 ≤ A1 ≤ 35% h1. Tab assemblies that meet these conditions, after sealing, have good sealing between the tab and the insulating adhesive 30, and good sealing between the tab assembly and the packaging bag 40. The packaging tension between the tab assembly and the packaging bag 40 meets the sealing requirements, effectively reducing leakage.

[0060] 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.

[0061] 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.

[0062] 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).

[0063] 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%.

[0064] 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%.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] The performance of the insulating adhesive and the secondary battery provided in this application are described below through specific examples and comparative examples.

[0070] Example 1-1

[0071] 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.

[0072] 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.

[0073] Preparation of isolation film: Polyethylene film is selected as the isolation film.

[0074] 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.

[0075] Preparation of the insulating adhesive: 99% of a polymer matrix and 1% of an additive are mixed, melted, and then extruded to form a first insulating adhesive layer. The polymer matrix is ​​polypropylene (PP), and the additive includes an antioxidant (2,6-di-tert-butyl-p-cresol). A second insulating adhesive layer is formed by mixing 99% of the polymer matrix and 1% of an additive, melted, and then extruded. The polymer matrix is ​​polypropylene (PP), and the additives include a white colorant (titanium dioxide) and an antioxidant (2,6-di-tert-butyl-p-cresol). A third insulating adhesive layer is formed by mixing 99% of the polymer matrix and 1% of an additive, melted, and then extruded. 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). The first, second, and third insulating adhesive layers are laminated together using a heat-bonding method to form the insulating adhesive shown in Figure 1. The swelling degree of the insulating glue is 0.04% when immersed for 4 hours at 25°C.

[0076] Preparation of secondary batteries: stack the positive electrode sheet, polyethylene separator, and negative electrode sheet in order, with the separator placed between the positive and negative electrode sheets, and wind them to obtain an electrode assembly; place the electrode assembly in a packaging bag, set insulating glue between the packaging bag and the tab, and obtain a secondary battery after liquid injection and formation.

[0077] Examples 1-2 to 1-8 and Comparative Example 1

[0078] The differences from Example 1-1 lie in the composition and content of the polymer matrix of the third insulating adhesive layer, and the swelling degree of the insulating adhesive after immersion in DMC for 4 hours at room temperature. For specific parameters, see Table 1. In each Example and Comparative Example, the total content of the polymer matrix in each insulating adhesive layer was 99%, and the total content of the additive in each insulating adhesive layer was 1%.

[0079] The secondary batteries prepared in the embodiments and comparative examples were subjected to packaging tensile tests, and the test results are shown in Table 1.

[0080] First, weigh 0.5g of sample and dry it at 65°C for 2 hours. The sample weight is then measured (W0). Then, soak the dried sample in 200ml of DMC solvent at room temperature (25°C) for 4 hours. The sample is then cooled to room temperature, removed from the sample, cleaned with alcohol, and the surface liquid wiped away. The sample weight is then measured (W1). Swelling degree = W0 / W1.

[0081] Secondary battery packaging tensile test:

[0082] Cut the portion of the battery corresponding to the tab, insulating adhesive, and seal along the width of the tab to obtain a sample with a width of 5 mm and a length of 5 cm. Clamp the sample on a high-speed rail tensile testing machine, with the tab fixed to the upper clamp and the packaging bag fixed to the lower clamp. Set the tensile speed to 175±5 mm / min, and pull the sample upward in a 180-degree direction to separate the insulating adhesive from the packaging bag, or separate the insulating adhesive from the tab. Read the peel force of the insulating adhesive from the packaging bag or tab. Divide the peel force value (unit: N) by the sample width to calculate the packaging tension F (N / mm) between the insulating adhesive sample and the packaging bag or tab.

[0083] Table 1

[0084] Table 1 shows that when the insulating adhesive's swelling is less than or equal to 5% after immersion in DMC solvent at room temperature for 4 hours, the insulating adhesive and the packaging bag fuse well, resulting in a greater sealing force between the insulating adhesive and the packaging bag, which improves the sealing effect. When the insulating adhesive's swelling is greater than 0.04% after immersion in DMC solvent at room temperature for 4 hours, the sealing force tends to decrease as the swelling increases.

[0085] Examples 2-1 to 2-8 differ from Example 1-1 in the composition of the polymer matrix of the first insulating adhesive layer and the swelling degree of the insulating adhesive after immersion in DMC at 85°C for 4 hours. For specific parameters, see Table 2. In each example, the composition and content of the second insulating adhesive layer are the same, the composition and content of the third insulating adhesive layer are the same, the additives of the first insulating adhesive layer are the same, and the content of the polymer matrix of the first insulating adhesive layer is the same.

[0086] The secondary batteries prepared in each embodiment were subjected to packaging tensile test and water vapor content test. The test results are shown in Table 2.

[0087] Water vapor content test:

[0088] The electrode assembly was placed in a packaging bag, insulating glue was set between the packaging bag and the tab, the packaging bag was sealed, and then dried at 80°C for 6 hours. Then 1-2g DMC was injected into the packaging bag, and then the electrolyte was injected and packaged to obtain a test sample.

[0089] The electrode assembly was placed in a packaging bag, insulating glue was set between the packaging bag and the tab, the packaging bag was sealed, and then dried at 80°C for 6 hours, and then the electrolyte was injected and packaged to obtain a test sample.

[0090] Litmus paper was placed on the test sample and blank test sample, and each was placed in an oven at 60°C and 90% RH. At regular intervals (e.g., on days 7, 14, 21, 28, and 35), five cells from each group were removed for DMC water content testing. Specifically, the battery was removed and placed in a dry room in the water content testing equipment. A needle was inserted through the injection port to remove an appropriate amount of DMC and test the water content.

[0091] Table 2

[0092] As shown in Table 2, when the grafting rate of the polymer matrix (maleic anhydride grafted polypropylene) of the first insulating adhesive layer is 0.03% to 0.05%, the maleic anhydride-containing first insulating adhesive layer can bond to the tab. As the grafting rate increases, the packaging tension between the insulating adhesive, the tab, and the packaging bag increases. However, as the grafted polymer increases, the insulating adhesive's water absorption increases, and its water vapor barrier performance decreases. The packaging tension of Example 2-7 is 0, which is due to insufficient introduced polar groups, resulting in insufficient adhesion between the tab and the insulating adhesive. Example 2-8 has the highest water vapor content, which is due to excessive introduction of polar groups, resulting in poor water vapor barrier performance.

[0093] 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. An insulating adhesive, comprising a first insulating adhesive layer, a second insulating adhesive layer, and a third insulating adhesive layer stacked in sequence along a first direction, characterized in that, The swelling degree of the insulating glue when soaked in dimethyl carbonate at room temperature for 4 hours is less than or equal to 5%.

2. The insulating adhesive according to claim 1, wherein, The swelling degree of the insulating glue when soaked in dimethyl carbonate at 85 °C for 4 hours is less than or equal to 5%.

3. The insulating adhesive according to claim 1, wherein, The first insulating glue layer includes a graft polymer, and the grafting rate of the graft polymer is 0.03% - 0.5%.

4. The insulating adhesive according to claim 3, wherein, The third insulating glue layer includes a graft polymer, and the grafting rate of the graft polymer is 0.03% - 0.5%.

5. The insulating adhesive according to claim 4, wherein, The grafting rate of the graft polymer is less than or equal to 0.03% - 0.15%.

6. The insulating glue according to claim 1, wherein, The swelling degree of the insulating glue when soaked in dimethyl carbonate at room temperature for 4 hours is less than or equal to 3%.

7. The insulating glue according to claim 6, wherein, The swelling degree of the insulating glue when soaked in dimethyl carbonate at room temperature for 4 hours is less than or equal to 0.5%.

8. The insulating adhesive according to claim 1, wherein, The difference in the swelling degree of the insulating glue when soaked in dimethyl carbonate at room temperature and 85 °C for 4 hours is less than or equal to 0.4%.

9. The insulating adhesive according to any one of claims 1-8, wherein, The second insulating glue layer includes a white colorant, and the third insulating glue layer includes a gray colorant.

10. The insulating adhesive according to any one of claims 1-8, wherein, The melting points of the first insulating glue layer and the third insulating glue layer are both 100 - 140 °C, and the melting point of the second insulating glue layer is 140 - 200 °C.

11. The insulating adhesive according to any one of claims 1-8, wherein, Along the first direction, the thickness of the insulating glue is h1, the thickness of the first insulating glue layer is A1, the thickness of the second insulating glue layer is B1, and the thickness of the third insulating glue layer is C1. 10.5%h1 ≤ B1 ≤ 35%h1, C1 ≥ 0.9A1, 30%h1 ≤ C1 ≤ 79%h1, 10.5%h1 ≤ A1 ≤ 35%h1.

12. The insulating adhesive according to any one of claims 1-8, wherein, The first insulating glue layer, the second insulating glue layer, and the third insulating glue layer all include a polymer, and the polymer includes one or more of polypropylene, acid-modified polypropylene, polyethylene, ethylene-based elastomer, propylene-based elastomer, styrene-based elastomer, ionomer resin, polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol.

13. The insulating adhesive according to any one of claims 1-8, wherein, The first insulating glue layer and / or the third insulating glue layer further includes a toughening modifier.

14. The insulating adhesive according to claim 13, wherein, The toughening modifier includes one or more of ethylene propylene diene monomer rubber, ethylene propylene diene monomer 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.

15. The insulating glue according to claim 13, wherein, The content of the toughening modifier is 4% - 10%.

16. 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, characterized in that, The insulating glue is the insulating glue according to any one of claims 1 - 15. The first insulating glue layer is connected to the tab, and the third insulating glue layer is connected to the packaging bag.

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