Adhesive composition, adhesive layer containing adhesive composition and new energy automobile power battery assembly

Abstract

The invention provides an adhesive composition, an adhesive layer containing the adhesive composition and a new energy automobile power battery assembly. The adhesive composition comprises: 30-40 wt% of a thermoplastic polymer; 5-15 wt% of a thermally conductive filler; 3-8 wt% of a plasticizer; 1-4 wt% of a coupling agent; 0.5 to 3 wt% of a stabilizer; and an organic solvent, wherein the thermoplastic polymer is a blend of thermoplastic copolyester and thermoplastic polyacrylate in a weight ratio of 2: 1-1: 2. According to the technical scheme, the adhesive has high bonding strength at normal temperature and high-temperature disassembly easiness, a formed bonding layer has the characteristics of high heat conductivity and high insulation, and when the adhesive is applied to a power battery assembly, the volume fraction of a battery can be increased, the disassembly time can be shortened, the maintenance damage rate can be reduced, and the full-temperature-range use requirement can be met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy automobile power battery packaging, in particular to an adhesive composition, an adhesive layer comprising the adhesive composition, and a new energy automobile power battery assembly. BACKGROUND

[0002] With the acceleration of global energy transformation and the rapid expansion of the new energy automobile industry, as the core power source of new energy automobiles, the advancement of power battery packaging technology directly determines the vehicle's endurance, safety performance, and life cycle maintenance cost, and has become a key link restricting the high-quality development of the industry. Currently, the mainstream in the field of new energy automobile power battery packaging uses heat-conducting structural adhesives to replace traditional metal mechanical fasteners to integrate the battery module and the cooling plate. This scheme can significantly reduce the weight of the battery pack and improve the volume efficiency of the battery pack compared to mechanical fastening, and is therefore widely used in various new energy automobile power battery assemblies. However, the existing technical solutions gradually expose multiple insurmountable technical defects in actual application, and cannot meet the requirements of new energy automobiles for "high reliability, easy maintenance, and long life" of power batteries.

[0003] Firstly, the existing heat-conducting structural adhesives generally face the binary contradiction between "adhesion strength and disassembly convenience", which has become a core bottleneck restricting the efficiency of battery maintenance and recycling. To ensure the structural stability of the battery pack under complex working conditions, including continuous vibration during high-speed driving of the vehicle, instantaneous impact during emergency braking or collision, and long-term service environment under normal working conditions, the dynamic shear strength of the existing heat-conducting structural adhesives is generally high. However, this high adhesion strength makes it difficult to separate the battery module and the cooling plate when the battery needs to be repaired or recycled. The operator needs to use a "high-temperature heating + mechanical prying" composite process to achieve separation, which leads to complex and time-consuming disassembly of single modules, and seriously reduces the maintenance efficiency. More importantly, high-temperature disassembly above 120℃ can cause thermal decomposition of the positive electrode material of the battery, damaging the structure of the active material of the battery, and further reducing the recycling value.

[0004] Secondly, the "insufficient functional integration" of the existing packaging solution leads to complex structure and redundant weight, which is contrary to the development goal of "lightweight and high energy density" of new energy vehicles. The power battery packaging needs to meet multiple functional requirements such as heat conduction, insulation, weather resistance, and cushioning. However, the adhesive in the existing technology only has a single adhesive function, and other performances need to be achieved by stacking 3-4 independent functional films. For example, to meet the thermal conductivity requirement, a separate thermal filler layer is needed; to meet the insulation standard of volume resistivity, an additional epoxy resin insulation film is needed; to resist high temperature and humidity, salt spray and other harsh environmental erosion, a weather-resistant protective layer is also needed. This "multi-layer stacking" design mode increases the total thickness of the packaging structure and the overall weight of the battery pack, directly leading to a decrease in battery volume rate and indirectly affecting the vehicle's range. At the same time, the interface matching between the multi-layer structure is poor, and the difference in the thermal expansion coefficient of each layer is large.

[0005] Finally, the "low efficiency and high pollution" of the existing disassembly process does not meet the requirements of green development. During the current battery pack disassembly process, organic solvents (such as toluene and ethyl acetate) are needed to soften the structural glue, and solvent residues will cause the cycle life of the repaired battery to be shortened. At the same time, the volatilization of organic solvents not only harms the health of the operators, but also pollutes the environment. In addition, the existing packaging solution lacks consideration of the whole life cycle of the battery. After the disassembly of the retired battery, the adhesive and the battery material are difficult to completely separate, leading to an increase in the difficulty of recycling valuable resources such as positive materials and copper foil.

[0006] In summary, the existing adhesive and related assembly technology for packaging new energy vehicle power batteries have significant defects in key dimensions such as "strength-disassembly balance", "functional integration", "cost-performance matching", and "green recycling". Developing an adhesive composition that can balance normal temperature high reliability, high temperature easy disassembly, multi-functional integration, and low cost mass production has become a core technical problem that needs to be solved in the field. SUMMARY

[0007] From the above technical problems, one of the purposes of the present application is to solve the defects of the existing adhesive and assembly technology for packaging new energy vehicle power batteries, to ensure the normal temperature service reliability of new energy vehicle power batteries, to meet the requirements of 25°C high shear strength, 55°C high retention rate, and full temperature range use; to improve the convenience of high temperature disassembly, to reduce the shear strength and separation force at 80°C, and to shorten the disassembly time; to realize efficient functional integration, to balance high thermal conductivity, high insulation, and weather resistance, to reduce the number of functional films, and to build a simple structure, light weight, and high battery volume rate power battery assembly.

[0008] Specifically, according to one aspect of the present application, an adhesive composition is provided, which comprises, based on the total solid content thereof: 30-40% by weight of a thermoplastic polymer; 5-15 wt% of a thermally conductive filler; 3-8 wt% of a plasticizer; 1-4 wt% of a coupling agent; 0.5-3 wt% of a stabilizer; and an organic solvent, wherein: the thermoplastic polymer is a blend of a thermoplastic copolyester and a thermoplastic polyacrylate in a weight ratio of 2: 1-1:2; the thermoplastic copolyester is a butylene terephthalate-adipate block copolymer having a glass transition temperature of 53-58 °C and a number average molecular weight of 15000-21000 g / mol; and the thermoplastic polyacrylate is a methyl methacrylate-ethyl acrylate-butyl acrylate terpolymer having a glass transition temperature of 60-65 °C and a number average molecular weight of 20000-23000 g / mol.

[0009] According to certain preferred embodiments of the present application, the thermally conductive filler is selected from one or more of alumina, silica, magnesia, beryllia, titania, aluminum nitride, silicon nitride, boron nitride, graphene, silicon carbide, and carbon fiber.

[0010] According to certain preferred embodiments of the present application, the thermally conductive filler is a compounding of nano-alumina and hexagonal boron nitride in a weight ratio of 1: 1-2: 1, wherein the nano-alumina has a particle size of 50-100 nm and the hexagonal boron nitride has a particle size of 1-5 μιη.

[0011] According to certain preferred embodiments of the present application, the plasticizer is selected from one or more of phthalate plasticizers, aliphatic dibasic acid ester plasticizers, polyester plasticizers, phosphate plasticizers, epoxy plasticizers, and citrate plasticizers.

[0012] According to certain preferred embodiments of the present application, the plasticizer is a compounding of dioctyl phthalate and polyethylene adipate in a weight ratio of 1: 1-2: 1.

[0013] According to certain preferred embodiments of the present application, the polyethylene adipate has a number average molecular weight of 500-2000 g / mol.

[0014] According to certain preferred embodiments of the present application, the coupling agent is selected from one or more of silane coupling agents, titanate coupling agents, and aluminate coupling agents.

[0015] According to certain preferred embodiments of the present application, the coupling agent is a compounding of γ-aminopropyl triethoxysilane and isopropyl tri(dioctyl pyrophosphato) titanate in a weight ratio of 2: 1-3: 1.

[0016] According to some preferred embodiments of the present application, the stabilizer is selected from one or more of an antioxidant, a light stabilizer, an anti-hydrolysis stabilizer, an anti-metal ion stabilizer, and an ultraviolet absorber.

[0017] According to some preferred embodiments of the present application, the stabilizer is a complex of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester and 2-(2H-benzotriazol-2-yl)-4,6-di-tert-amylphenol at a weight ratio of 2:1 to 3:1.

[0018] According to some preferred embodiments of the present application, the adhesive composition comprises 10 to 20% by weight of the organic solvent, based on the total weight thereof.

[0019] According to some preferred embodiments of the present application, the organic solvent is selected from one or more of methyl ethylene ketone, acetone, butanone, cyclohexanone, ethyl acetate, butyl acetate, isobutyl acetate, propylene glycol methyl ether acetate, toluene, and xylene.

[0020] According to another aspect of the present application, there is provided an adhesive layer comprising the adhesive composition described above.

[0021] According to some preferred embodiments of the present application, the adhesive layer has a thickness of 15 to 80 μm.

[0022] According to still another aspect of the present application, there is provided a new energy automobile power battery assembly comprising: a battery module; a thermally conductive structural adhesive layer in contact with the battery module; an adhesive layer in contact with the thermally conductive structural adhesive layer, the adhesive layer being cured from the adhesive composition described above; an insulating buffer layer in contact with the adhesive layer; and a cooling plate in contact with the insulating buffer layer.

[0023] According to some preferred embodiments of the present application, the thermally conductive structural adhesive layer has a thickness of 0.5 to 2 mm.

[0024] According to some preferred embodiments of the present application, the adhesive layer has a thickness of 15 to 80 μm.

[0025] According to some preferred embodiments of the present application, the insulating buffer layer is formed of an epoxy resin-based material and has a thickness of 25 to 50 μm.

[0026] According to some preferred embodiments of the present application, the cooling plate is a metal plate having a circulation pipe inside.

[0027] According to some preferred embodiments of the present application, the cooling plate is an aluminum alloy plate, and the diameter of the circulation pipe is 3-5 mm. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings are provided in the present specification to more clearly explain the technical solutions of the present application, however the present application is not limited thereto.

[0029] Figure 1 A partial surface structure schematic diagram of a new energy automobile power battery assembly according to one specific embodiment of the present application is shown. DETAILED DESCRIPTION

[0030] The present application will be further described in detail below in combination with the accompanying drawings and specific embodiments. It will be understood that other embodiments are considered, and can be implemented without departing from the scope or spirit of the present application. Therefore, the following detailed description is non-limiting.

[0031] Unless otherwise indicated, all numbers expressing features, quantities and physical characteristics in the present specification are to be understood as being modified in all instances by the term "about". Accordingly, unless otherwise indicated, the numerical parameters set forth in the specification are approximations that can vary depending upon the desired properties sought to be obtained by the teachings disclosed herein. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0032] As described herein, the term "formulation" has a similar or identical meaning as the terms "blend", "mixture", "composition" and "combination", unless otherwise specified, and denotes a combination of two or more components.

[0033] As described above, the existing heat-conducting structural adhesive for packaging new energy automobile power batteries has a contradiction between adhesion strength and disassembly convenience. Although high strength at room temperature ensures stable working conditions, the strength is still high at high temperature, which leads to difficult disassembly and high module damage rate. In addition, the traditional adhesive has single function, needs to be stacked with multiple functional films, increases the packaging thickness and weight, reduces the battery volume rate, and has poor interlayer interface matching, is prone to peeling after thermal cycling, and has a risk of thermal runaway. The present application aims to solve the above technical problems.

[0034] In particular, according to one aspect of the present application, there is provided an adhesive composition comprising, based on the total solid content thereof: 30-40% by weight of a thermoplastic polymer; 5-15% by weight of a thermally conductive filler; 3-8% by weight of a plasticizer; 1-4% by weight of a coupling agent; 0.5-3% by weight of a stabilizer; and organic solvents, wherein: the thermoplastic polymer is a blend of a thermoplastic copolyester and a thermoplastic polyacrylate in a weight ratio of 2:1-1:2; the thermoplastic copolyester is a butylene terephthalate-adipate block copolymer with a glass transition temperature of 53-58℃ and a number average molecular weight of 15000-21000 g / mol; and the thermoplastic polyacrylate is a methyl methacrylate-ethyl acrylate-butyl acrylate terpolymer with a glass transition temperature of 60-65℃ and a number average molecular weight of 20000-23000 g / mol.

[0035] The thermoplastic polymer as the matrix skeleton of the adhesive composition determines the mechanical strength, temperature response characteristics and interfacial bonding capacity of the adhesive layer. Specifically, the thermoplastic copolyester selected by the present application is a butylene terephthalate-adipate block copolymer (PBAT), which contains both rigid butylene terephthalate (PBT) segments and flexible adipate butylene (PBA) segments in the molecular chain. By adjusting the block ratio of the two segments, the glass transition temperature (Tg), crystallinity and mechanical properties of the polymer can be adjusted.

[0036] Specifically, the Tg of the PBAT block copolymer of the present application is controlled at 53-58℃, which is of great significance. On the one hand, the Tg of 53-58℃ is higher than the normal working temperature of the power battery (25-55℃), which ensures that the polymer matrix remains rigid under normal working conditions such as vehicle driving and fast charging, providing stable shear strength and structural support for the adhesive layer, and avoiding module displacement or interfacial peeling caused by matrix softening; on the other hand, the Tg is lower than the high-temperature disassembly temperature (80℃), when the disassembly temperature reaches 80℃, the PBAT segment changes from glassy state to high-elastic state, the molecular chain movement ability is enhanced, and the matrix rigidity is reduced, thereby reducing the adhesion strength.

[0037] The number average molecular weight of the PBAT of the present application is 15000-21000 g / mol, which is selected based on the following considerations: if the molecular weight is lower than 15000 g / mol (such as 12000 g / mol), the polymer molecular chain is short and the degree of interchain entanglement is insufficient, resulting in a significant decrease in the tensile strength and interfacial bonding force of the adhesive layer, a low dynamic shear strength at 25℃, and an inability to meet the working condition requirements of power battery vibration resistance and impact resistance; if the molecular weight is higher than 21000 g / mol (such as 25000 g / mol), the molecular chain is too tightly entangled, and the molecular chain movement is hindered at high temperature (80℃), even in the high-elastic state, the adhesive layer still maintains a high cohesive strength, the shear strength at 80℃ is too high, resulting in a large separation force during disassembly and an increase in module damage rate.

[0038] In addition, according to the technical scheme of the present application, the thermoplastic polyacrylate selected by the present application is methyl methacrylate-ethyl acrylate-butyl acrylate terpolymer (MMA-EA-BA), and through synergistic copolymerization of the three monomers, the deficiencies of single acrylate polymer in rigidity, adhesion or weather resistance are solved, and a performance complementary blending system with PBAT is formed.

[0039] The present application controls the Tg of the terpolymer at 60-65℃ by regulating the weight ratio of MMA, EA and BA. This Tg design forms a reasonable gradient with the Tg of PBAT (53-58℃): the Tg of 60-65℃ further ensures the structural stability of the adhesive layer at a high temperature of 55℃, avoiding the strength attenuation caused by the softening of the matrix; at the same time, there is still a temperature difference of 15-20℃ between 60-65℃ and the disassembly temperature of 80℃, which ensures that the terpolymer can also change from glassy state to high-elastic state at high temperature, and cooperates with PBAT to reduce the adhesion strength.

[0040] According to the technical scheme of the present application, the number average molecular weight of the methyl methacrylate-ethyl acrylate-butyl acrylate terpolymer is 20000-23000 g / mol, and this range is selected based on the blending compatibility and mechanical property matching of PBAT. If the molecular weight is lower than 20000 g / mol (such as 18000 g / mol), the blending system of the terpolymer and PBAT is prone to phase separation, resulting in uneven internal structure of the adhesive layer and large fluctuation of mechanical properties; if the molecular weight is higher than 23000 g / mol (such as 25000 g / mol), the melt viscosity of the blending system is significantly increased, which is not conducive to the implementation of the subsequent coating process, and the molecular chain movement is difficult at high temperature, affecting the disassembly performance.

[0041] The present application realizes synergistic enhancement effect by blending PBAT and the terpolymer at a weight ratio of 2:1-1:2, and utilizing the structural complementarity of the two polymers. Specifically, without being bound by theory, the rigid segment (PBT) of PBAT and the MMA unit of the terpolymer synergistically enhance the room temperature rigidity and shear strength of the adhesive layer, and the flexible segment (PBA) of PBAT and the EA and BA units of the terpolymer synergistically improve the toughness and low-temperature anti-brittle fracture performance of the adhesive layer. In addition, the Tg of PBAT (53-58℃) and the Tg of the terpolymer (60-65℃) form a temperature response gradient, and within the working temperature range of 25-55℃, both polymers are in glassy state, and the adhesive layer maintains high rigidity and high adhesion strength; when the temperature rises to 60-70℃, PBAT first changes to high-elastic state, and the adhesion strength begins to decrease; when the temperature reaches 80℃, the terpolymer also changes to high-elastic state, and the adhesion strength rapidly decreases, realizing efficient disassembly.

[0042] The source of the thermoplastic copolyester and the thermoplastic polyacrylate that can be used in the present application is not particularly limited, and it can be commercially available or can be prepared according to known organic synthesis methods in the art.

[0043] According to certain preferred embodiments of the present application, the thermally conductive filler is selected from one or more of alumina, silica, magnesia, beryllia, titania, aluminum nitride, silicon nitride, boron nitride, graphene, silicon carbide, and carbon fiber.

[0044] Preferably, the thermally conductive filler is a compound of nano-alumina and hexagonal boron nitride at a weight ratio of 1:1-2:1, wherein the nano-alumina has a particle size of 50-100 nm, and the hexagonal boron nitride has a particle size of 1-5 μm. According to the above technical solution, the nano-alumina (particle size 50-100 nm) and the hexagonal boron nitride (particle size 1-5 μm) are compounded at a weight ratio of 1:1-2:1 to construct a "point-surface combined" dual thermal conduction network, which significantly improves the thermal conductivity of the adhesive layer. Without being bound by theory, the nano-alumina (50-100 nm) is a spherical or spherical-like particle with a large specific surface area, which can be uniformly dispersed in the adhesive matrix to form a primary thermal conduction path through the "point contact" between the particles. On the other hand, the hexagonal boron nitride (h-BN) has a flaky layered structure with excellent in-plane thermal conductivity, and the flaky structure will be oriented and arranged along the coating direction during the coating process to form a secondary thermal conduction network through "surface-surface stacking". It is found in the research of the present application that the layered structure of the flaky h-BN can span the gap between the nano-alumina particles, further reducing the thermal resistance and improving the thermal conductivity efficiency.

[0045] The plasticizer in the adhesive composition mainly plays a role in reducing the glass transition temperature of the polymer matrix, improving the flexibility and low-temperature anti- brittle performance of the adhesive layer, and can also optimize the dispersibility of the filler and the interfacial bonding capacity of the adhesive layer. According to some preferred embodiments of the present application, the plasticizer is selected from one or more of phthalate plasticizers, aliphatic dibasic acid ester plasticizers, polyester plasticizers, phosphate plasticizers, epoxy plasticizers and citrate plasticizers. More preferably, the plasticizer is a compound of dioctyl phthalate and polyethylene adipate with a weight ratio of 1:1 to 2:1. The present application uses a compound of dioctyl phthalate (DOP) and polyethylene adipate (PEA) with a weight ratio of 1:1 to 2:1, which utilizes the complementary properties of the two plasticizers to achieve a synergistic optimization of the "room temperature flexibility-low temperature anti-brittle performance-migration resistance" of the adhesive layer. Without being bound by theory, DOP is a small molecule phthalate plasticizer, which contains flexible octyl chains and polar ester groups in its molecular structure, and can quickly insert between the molecular chains of PBAT and the terpolymer, weaken the intermolecular force, and reduce the glass transition temperature (Tg) of the polymer matrix. In addition, PEA is a high molecular weight polyester plasticizer, which contains multiple ester groups and hydroxyl groups in its molecular chain. On the one hand, its flexible aliphatic segment can entangle with the polymer molecular chain to form a stable plasticizing structure, which has excellent migration resistance and can maintain the plasticizing effect for a long time; on the other hand, the hydroxyl groups at the end of the PEA molecular chain can form hydrogen bonds with the ester groups in the PBAT / terpolymer molecular chain, enhancing the intermolecular force and maintaining the flexibility of the molecular chain in a low temperature environment (-40°C), thereby avoiding brittle cracking of the adhesive layer.

[0046] Preferably, the number average molecular weight of the polyethylene adipate is 500-2000 g / mol.

[0047] According to some preferred embodiments of the present application, the coupling agent is selected from one or more of silane coupling agents, titanate coupling agents and aluminate coupling agents. Examples of coupling agents that can be used include but are not limited to: γ-aminopropyl triethoxysilane, γ-glycidoxypropyl trimethoxysilane, isopropyl tri(dioctyl pyrophosphoryloxy) titanate, isopropyl tristearoyl titanate and distearyloxyisopropyl aluminate. Preferably, the coupling agent is a compound of γ-aminopropyl triethoxysilane and isopropyl tri(dioctyl pyrophosphoryloxy) titanate with a weight ratio of 2:1 to 3:1. By selecting a specific ratio of a compound of γ-aminopropyl triethoxysilane and isopropyl tri(dioctyl pyrophosphoryloxy) titanate, the adhesion strength of the adhesive layer under working conditions can be greatly improved.

[0048] In addition, the power battery will face complex environments such as high temperature, high humidity, and ultraviolet radiation during long-term service, which can easily lead to degradation of the polymer matrix in the adhesive composition and breaking of chemical bonds, thereby causing the mechanical properties, thermal conductivity, and insulation performance of the adhesive layer to deteriorate. The adhesive composition according to the present application comprises a stabilizer to improve the relevant performance. According to certain preferred embodiments of the present application, the stabilizer is selected from one or more of an antioxidant, a light stabilizer, an anti-hydrolysis stabilizer, an anti-metal ion stabilizer, and an ultraviolet absorber. Preferably, the stabilizer is a complex of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester (i.e., antioxidant 1010) and 2-(2H-benzotriazol-2-yl)-4,6-di-tert-amylphenol at a weight ratio of 2:1 to 3:1. By selecting the above specific stabilizer complex system, the salt spray corrosion resistance of the obtained adhesive layer can be greatly improved.

[0049] The organic solvent mainly plays a role in dissolving the polymer matrix and dispersing the fillers and additives in the adhesive composition. Preferably, the adhesive composition comprises 30-55% by weight of the organic solvent based on the total weight thereof. Preferably, the organic solvent is selected from one or more of methyl ethylene ketone, acetone, butanone, cyclohexanone, ethyl acetate, butyl acetate, isobutyl acetate, propylene glycol methyl ether acetate, toluene, and xylene.

[0050] According to another aspect of the present application, there is provided an adhesive layer comprising the adhesive composition described above. Preferably, the thickness of the adhesive layer is 15-80 μm.

[0051] According to still another aspect of the present application, there is provided a new energy automobile power battery assembly comprising: a battery module; a thermally conductive structural adhesive layer in contact with the battery module; an adhesive layer in contact with the thermally conductive structural adhesive layer, the adhesive layer being cured from the adhesive composition described above; an insulating buffer layer in contact with the adhesive layer; and a cooling plate in contact with the insulating buffer layer.

[0052] The adhesive layer formed by curing the adhesive composition of the present application is ultimately applied to the new energy automobile power battery assembly, and through optimization of the layered structure of the assembly, the functions of "thermal conduction-insulation-buffering-adhesion" are integrated, thereby solving the problems of complex structure, large weight, and low volume ratio of the traditional assembly.

[0053] Figure 1 A partial surface structure schematic diagram of a new energy automobile power battery assembly 100 according to a specific embodiment of the present application is shown. As Figure 1As shown in the drawings, the new energy automobile power battery assembly 100 comprises: a battery module 1; a heat-conducting structural adhesive layer 2 in contact with the battery module 1; an adhesive layer 3 in contact with the heat-conducting structural adhesive layer 2; an insulating buffer layer 4 in contact with the adhesive layer 3; and a cooling plate 5 in contact with the insulating buffer layer 4. In Figure 1 The structure of the new energy automobile power battery assembly is shown in the drawings in the form of layer-by-layer lamination, however, it should be noted that the new energy automobile power battery assembly according to the present application is by no means limited to this, and the new energy automobile power battery assembly according to the present application can also have an encapsulation structure in which each layer completely covers the battery module.

[0054] Specifically, the thickness of the heat-conducting structural adhesive layer is 0.5-2 mm. The material of the heat-conducting structural adhesive layer is not particularly limited and can be selected from conventional conductive adhesives. Preferably, the thickness of the adhesive layer is 15-80 μm. According to certain preferred embodiments of the present application, the insulating buffer layer is formed of an epoxy resin-based material and has a thickness of 25-50 μm. According to certain preferred embodiments of the present application, the cooling plate is a metal plate with a circulating pipe inside.

[0055] Preferably, the cooling plate is an aluminum alloy plate and the diameter of the circulating pipe is 3-5 mm.

[0056] Compared with the prior art, the adhesive composition, the adhesive layer comprising the adhesive composition and the new energy automobile power battery assembly according to the present application have the following advantages: 1. The adhesive composition greatly increases the dynamic shear strength at 25℃ and the strength retention rate at 55℃ by precisely regulating the types of the components and their proportions, thereby meeting the stable requirements under driving vibration, collision and other working conditions; the disassembly time of a single module is greatly shortened, which is much better than the disassembly time length of the prior art, and the secondary damage rate to the module is reduced.

[0057] 2. The adhesive composition has high thermal conductivity, high insulation, salt mist corrosion resistance and other properties, and does not need to be overlaid with 3-4 functional films, thereby solving the problem of thick and heavy encapsulation of the traditional scheme, which is helpful to the lightweight of the battery pack.

[0058] 3. By synergistically designing the plasticizer and the polymer, the embrittlement temperature of the adhesive layer is reduced to below -40℃, and the adhesive layer can stably work in the full temperature range of -40℃-85℃, thereby avoiding the risk of high peeling rate and easy heat runaway after thermal cycling of the prior art.

[0059] 4. The battery volume ratio of the power battery assembly using the adhesive layer of the present application is greatly improved; the interface matching of the cooling plate and the adhesive layer is optimized, and the cooling power of the unit weight cooling plate is improved.

[0060] The application will be described in more detail below with reference to the embodiments. It should be noted that these descriptions and embodiments are intended to facilitate the understanding of the application, and are not limiting to the application.

[0061] Examples In the present application, unless otherwise specified, the reagents used are commercially available products, which are used directly without further purification treatment. In addition, the "%" mentioned is "wt%" and the "parts" mentioned is "wt parts".

[0062] Performance test method The adhesive compositions prepared in the following examples and comparative examples were respectively tested for normal temperature service reliability, high temperature disassembly convenience, thermal conductivity, salt spray corrosion resistance by the following detailed description.

[0063] Normal temperature service reliability test 25℃ dynamic shear strength test: according to GB / T 7124-2021 "Determination of tensile shear strength of adhesives (rigid material to rigid material)", the adhesive composition samples prepared in the following examples or comparative examples were coated between the aluminum alloy substrate for power battery (size 100mm×25mm×2mm) and the battery module simulation substrate (size 100mm×25mm×3mm), the adhesive layer thickness was controlled to be 30μm, and the curing was carried out by 60℃ hot air drying for 1h and 100℃ vacuum drying for 30min. A universal testing machine was used to test the shear strength at a tensile rate of 5mm / min, 5 parallel tests were performed for each group, and the average value was taken.

[0064] 55℃ strength retention rate test: the above cured shear sample was placed in a 55℃ constant temperature box, and statically placed for 1000h, then taken out and balanced at 25℃ environment for 2h, the shear strength was tested at the same tensile rate, and the ratio of the strength after 55℃ aging to the initial 25℃ strength (i.e. strength retention rate) was calculated.

[0065] Full temperature range (-40℃-55℃) cycle stability test: the shear sample was placed in a high and low temperature cycle box, and 1 cycle was carried out according to -40℃ (2h of heat preservation)→ heating to 55℃ (2h of heat preservation). A total of 500 cycles were carried out. After the cycle was completed, the 25℃ dynamic shear strength was tested, and the ratio to the initial strength was calculated.

[0066] Evaluation criteria: Excellent: 25℃ dynamic shear strength ≥3.2MPa, 55℃ 1000h strength retention rate ≥85%, 500 times full temperature range cycle strength retention rate ≥80%, excellent performance in normal temperature work of power battery.

[0067] Good: 2.5-3.1 MPa at 25℃, 75%-84% of strength retention at 55℃ for 1000h, 70%-79% of strength retention after 500 cycles in full temperature range, which can meet the requirements of power battery service at room temperature.

[0068] Poor: <2.5 MPa at 25℃, <75% of strength retention at 55℃ for 1000h, <70% of strength retention after 500 cycles in full temperature range, which is prone to module displacement and interface peeling, and cannot meet the requirements of power battery service at room temperature.

[0069] High-temperature disassembly convenience test The adhesive samples (aluminum alloy substrate-adhesive layer-battery module substrate, adhesive layer thickness 15-80 μm) formed by curing the adhesive compositions prepared in the following examples or comparative examples were taken out and placed in an 80℃ constant temperature environment box for 30min (simulating the actual disassembly preheating temperature). A universal testing machine was used to test the 80℃ dynamic shear strength of the samples at a rate of 10mm / min; at the same time, a digital push-pull force meter was used to measure the minimum separation force for separating the battery module from the substrate, and the average value was taken from 5 parallel tests in each group.

[0070] Evaluation criteria: Excellent: ≤0.8 MPa at 80℃, ≤0.5 MPa of separation force, ≤10min of single module disassembly time, no secondary damage to the module, meeting the requirements of rapid repair and recycling; Good: 0.9-1.2 MPa at 80℃, 0.6-0.8 MPa of separation force, 11-20min of single module disassembly time, slight damage rate ≤10%; Poor: >1.2 MPa at 80℃, >0.8 MPa of separation force, >20min of single module disassembly time, damage rate >10%, which cannot meet the requirements of efficient disassembly and recycling.

[0071] Thermal conductivity test The adhesive compositions prepared in the following examples or comparative examples were coated on a polyimide film substrate with a thickness of 50μm, dried at 60℃ for 1h and at 100℃ for 30min to form an adhesive layer sample. Referring to GB / T 22588-2008 "Flash method for measuring thermal diffusivity or thermal conductivity", a laser flash thermal conductivity instrument was used to test the thermal conductivity of the adhesive layer at 25℃ and 55℃, and the average value was taken from 3 parallel tests in each group.

[0072] Evaluation criteria: Excellent: ≥2.3 W / (m•K) at 25℃, ≥2.5 W / (m•K) at 55℃, which can well meet the requirements of power battery fast charging and heat dissipation; Good: thermal conductivity 1.8-2.2 W / (m•K) at 25℃, thermal conductivity 2.0-2.4 W / (m•K) at 55℃, which can meet the fast charging and heat dissipation requirements of power batteries; Poor: thermal conductivity <1.8 W / (m•K) at 25℃, thermal conductivity <2.0 W / (m•K) at 55℃, which is easy to cause local overheating of the battery and cannot meet the packaging heat dissipation requirements.

[0073] Salt spray corrosion resistance test The adhesive composition prepared in the following examples or comparative examples was coated on the surface of an aluminum alloy substrate (size 100 mm x 50 mm x 2 mm) for power batteries, with a thickness of 50 μm, dried at 60℃ for 1h and vacuum dried at 100℃ for 30min to form an adhesive layer sample. According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test-Salt Spray Test", a neutral salt spray test chamber was used, with 5% sodium chloride solution (pH 6.5-7.2), constant temperature at 35℃, spray amount of 1.5 mL / (h•cm²), salt spray test was carried out for 1000h. After the test, the sample was taken out, washed with water and dried, and the appearance of the adhesive layer and the bonding state with the substrate were observed.

[0074] Evaluation criteria: Good: after 1000h of salt spray, the adhesive layer has no blistering, peeling, discoloration, the adhesion of the grid test (grid spacing 1mm) reaches 0 level, which meets the outdoor and high humidity environment use requirements of power batteries; Good: after 1000h of salt spray, the adhesive layer has no blistering, peeling, discoloration, the adhesion of the grid test (grid spacing 1mm) reaches 0 level, which meets the outdoor and high humidity environment use requirements of power batteries; Poor: after 1000h of salt spray, the adhesive layer has blistering, peeling or obvious discoloration, the adhesion of the grid test is ≥2 level, which cannot meet the salt spray corrosion resistance requirements of power batteries.

[0075] Preparation Example 1 (preparation of thermoplastic copolyester 1) In a 500 mL four-necked flask equipped with a stirrer, thermometer, condenser and nitrogen inlet, 100 parts by weight of terephthalic acid, 65 parts by weight of adipic acid, 92 parts by weight of 1,4-butanediol were sequentially added, and then 0.05 parts by weight of tetrabutyl titanate (catalyst) and 0.02 parts by weight of triphenyl phosphate (stabilizer) were added. The flask was purged with nitrogen three times to ensure that the system was free of oxygen. The temperature was raised to 160°C, and the ester exchange reaction was carried out for 2 hours under stirring. During the reaction, the generated methanol was collected. Then the temperature was raised to 220°C, and the absolute pressure was gradually reduced to 50 Pa. The polycondensation reaction was carried out for 4 hours, and the viscosity change of the system was monitored in real time. After the reaction was completed, the heating was stopped, and nitrogen was introduced to release the vacuum. The product was extruded through a spinneret and cut into particles to obtain a thermoplastic copolyester 1. The glass transition temperature of the thermoplastic copolyester 1 was 55°C, as determined by differential scanning calorimetry (DSC), and the number average molecular weight was 18000 g / mol, as determined by gel permeation chromatography (GPC).

[0076] Preparation Example 2 (Preparation of thermoplastic copolyester 2) In a 1000 mL reactor with mechanical stirring, rectification column and nitrogen interface, 120 parts by weight of terephthalic acid, 70 parts by weight of adipic acid, 105 parts by weight of 1,4-butanediol were added, and then 0.06 parts by weight of antimony oxide (catalyst) and 0.03 parts by weight of triphenyl phosphite (antioxidant) were added. High-purity nitrogen (purity ≥ 99.99%) was introduced to exclude air in the reactor and maintain a slight positive pressure of nitrogen. The temperature was first raised to 180°C, and the esterification reaction was carried out for 3 hours. The generated water (about 32 mL of distillate) was collected. Then the temperature was raised to 240°C, and the absolute pressure was slowly reduced to 30 Pa. The polycondensation reaction was continued for 5 hours, and the melt viscosity was monitored by an Ubbelohde viscometer during the reaction. After the reaction was completed, nitrogen was introduced into the reactor to reach atmospheric pressure. The molten product was extruded through a spinneret, water-cooled and cut into particles to obtain a thermoplastic copolyester 2. The glass transition temperature of the thermoplastic copolyester 2 was 57°C, as determined by differential scanning calorimetry (DSC), and the number average molecular weight was 20000 g / mol, as determined by gel permeation chromatography (GPC).

[0077] Preparation Example 3 (Preparation of thermoplastic polyacrylate 1) Methyl methacrylate 60 parts by weight, ethyl acrylate 25 parts by weight, butyl acrylate 15 parts by weight (total weight of monomers 100 parts) and azobisisobutyronitrile 2 parts by weight (initiator) were mixed uniformly to form a prepolymer solution. The prepolymer solution was dropped into a flask at a rate of 2 drops per second through a constant pressure dropping funnel, and after the dropping was completed, the reaction was continued for 4 hours. After the reaction was completed, the reaction solution was slowly poured into 1500 parts by weight of deionized water for precipitation, and a white solid was collected by filtration and dried in a vacuum drying oven at 80°C for 12 hours to obtain a methyl methacrylate-ethyl acrylate-butyl acrylate terpolymer 1. The glass transition temperature thereof was 62°C as measured by a differential scanning calorimeter (DSC), and the number average molecular weight thereof was 21000 g / mol as measured by gel permeation chromatography (GPC).

[0078] Preparation Example 4 (Preparation of thermoplastic polyacrylate 2) In a 500 mL four-necked flask equipped with a mechanical stirrer, a reflux condenser, a nitrogen inlet tube, and a constant pressure dropping device, 180 parts by weight of butanone (solvent) was added, and high purity nitrogen gas (purity ≥ 99.99%) was introduced to replace the air in the system three times, and the temperature was raised to 80°C and kept constant. Methyl methacrylate 55 parts by weight, ethyl acrylate 30 parts by weight, butyl acrylate 15 parts by weight (total mass of monomers 100 parts) and dibenzoyl peroxide 1.5 parts by weight (initiator) were mixed to prepare a uniform prepolymer solution. The prepolymer solution was dropped into the flask at a rate of 1.5 drops per second through the constant pressure dropping device, and after the dropping was completed, the reaction was continued for 5 hours. After the reaction was completed, the reaction solution was slowly dropped into 1200 parts by weight of ethanol for precipitation, and a light yellow solid was collected by filtration and dried in a vacuum drying oven (vacuum degree ≤ -0.09 MPa) at 85°C for 10 hours to obtain a methyl methacrylate-ethyl acrylate-butyl acrylate terpolymer 2. The glass transition temperature thereof was 64°C as measured by a differential scanning calorimeter (DSC), and the number average molecular weight thereof was 22500 g / mol as measured by gel permeation chromatography (GPC).

[0079] Example 1 (E1) In a 2000mL stirring tank equipped with a high-speed disperser (speed 2000r / min) and a constant temperature water bath, 840g of ethyl acetate was first added, stirring was started and the water bath temperature was controlled at 30°C to ensure that the solvent was stably dispersed. Subsequently, 600g of thermoplastic polymer was added. The thermoplastic polymer was a premix of thermoplastic copolyester 1 (product of Preparation Example 1, 400g) and thermoplastic polyacrylate 1 (product of Preparation Example 3, 200g) with a weight ratio of 2:1. The speed was maintained and stirred for 60 minutes until the polymer was completely dissolved to form a transparent and uniform resin solution. Then, 300g of silica particles (particle size of about 100μm, pre-treated and dried to a water content of ≤0.1%) and 160g of plasticizer dioctyl phthalate were added in sequence, the speed was increased to 3000r / min, and stirred for 90 minutes to ensure that the filler was evenly dispersed without agglomeration. 80 g of the coupling agent γ-aminopropyltriethoxysilane and 20 g of the stabilizer pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] were then added, and stirring was continued for 45 minutes. During this time, the filler dispersion was monitored using a laser particle size analyzer to ensure that the particle size distribution D90 was ≤ 200 μm. After the stirring was completed, adhesive composition 1 was obtained.

[0080] According to the above-described methods for testing the normal temperature service reliability, high temperature disassembly convenience, thermal conductivity, and salt spray corrosion resistance, the adhesive composition 1 was tested and the test results are shown in Table 1 below.

[0081] Examples 2-10 (E2-E10) and Comparative Examples 1-4 (CE1-CE4) Adhesive compositions 2 to 10 and comparative adhesive compositions 1 to 4 were prepared in a similar manner to Example 1, except that the types and ratios of the components were adjusted as shown in Table 1 below.

[0082] According to the above-described methods for testing room temperature service reliability, high temperature disassembly convenience, thermal conductivity, and salt spray corrosion resistance, adhesive compositions 2-10 and comparative adhesive compositions 1-4 were tested and the test results are shown in Table 1 below.

[0083] Table 1 Formulations and performance test results of the adhesive compositions of Examples 1-10 (E1-E10) and Comparative Examples 1-4 (CE1-CE4) Thermoplastic polymer Thermally conductive filler Plasticizer Coupling agent Stabilizer Organic solvent Service reliability Disassembly convenience Thermal conductivity Salt spray corrosion resistance E1 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 15 wt%: SiO2particles 8 wt%: dioctyl phthalate 4 wt%: γ-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Good Good E2 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 2 (2:1) 15 wt%: SiO2particles 8 wt%: dioctyl phthalate 4 wt%: γ-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Good Good E3 30 wt%: thermoplastic copolyester 2 and thermoplastic polyacrylate 1 (2:1) <![CDATA[15重量%:SiO2颗粒]]> 8 wt%: dioctyl phthalate 4 wt%: γ-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Good Good E4 40 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 5 wt%: SiO2particles 3 wt%: dioctyl phthalate 4 wt%: γ-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Good Good E5 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 15 wt%: SiO2particles 8 wt%: dioctyl phthalate 1 wt%: γ-aminopropyl triethoxysilane 3 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Good Good E6 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (1:2) 15 wt%: SiO2particles 8 wt%: dioctyl phthalate 4 wt%: γ-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Good Good E7 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 15 wt%: alumina (50 nm) + hexagonal boron nitride (2 μm) (2:1) 8 wt%: dioctyl phthalate 4 wt%: γ-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Excellent Good E8 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 15 wt%: alumina (50 nm) + hexagonal boron nitride (2 μm) (2:1) 8 wt%: dioctyl phthalate + polyethylene adipate (2:1) 4 wt%: γ-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Excellent Good E9 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 15 wt%: alumina (50 nm) + hexagonal boron nitride (2 μm) (2:1) 8 wt%: dioctyl phthalate + polyethylene adipate (2:1) 4 wt%: γ-aminopropyl triethoxysilane + isopropyl tri(dioctyl pyrophosphato) titanate (3:1) 1 wt%: antioxidant 1010 Balance: ethyl acetate Excellent Excellent Excellent Good E10 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 15 wt%: alumina (50 nm) + hexagonal boron nitride (2 μm) (2:1) 8 wt%: dioctyl phthalate + polyethylene adipate glycol (2:1) 4 wt%: gamma-aminopropyl triethoxysilane + isopropyl tri(dioctyl pyrophosphoryloxy) titanate (3:1) 1 wt%: antioxidant 1010 + 2-(2H-benzotriazol-2-yl)-4,6-di-tert-amylphenol (2:1) balance: ethyl acetate very good very good very good very good CE1 25 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 15 wt%: SiO2particles 8 wt%: dioctyl phthalate 4 wt%: gamma-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 balance: ethyl acetate poor good good good CE2 45 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 15 wt%: SiO2particles 8 wt%: dioctyl phthalate 4 wt%: gamma-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 balance: ethyl acetate good poor good good CE3 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 3 wt%: SiO2particles 8 wt%: dioctyl phthalate 4 wt%: gamma-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 balance: ethyl acetate good good poor good CE4 30 wt%: thermoplastic copolyester 1 and thermoplastic polyacrylate 1 (2:1) 20 wt%: SiO2particles 8 wt%: dioctyl phthalate 4 wt%: gamma-aminopropyl triethoxysilane 1 wt%: antioxidant 1010 balance: ethyl acetate poor poor good poor From the results in Table 1 above, it can be seen that the adhesive compositions of Examples 1-10 within the scope of the present invention all meet the requirements of new energy vehicle power batteries regarding the adhesive layer's reliability at room temperature service, ease of high-temperature disassembly, thermal conductivity, and salt spray corrosion resistance.

[0084] In Comparative Example 1, the thermoplastic polymer accounts for 25% (lower than 30% of the present application), and the normal temperature service reliability is poor, and the remaining performance is good, and the normal temperature strength is insufficient due to insufficient polymer.

[0085] In Comparative Example 2, the thermoplastic polymer accounts for 45% (higher than 40% of the present application), and the high-temperature disassembly convenience is poor, and the high-temperature strength is difficult to reduce due to excessive polymer.

[0086] In Comparative Example 3, the thermally conductive filler accounts for 3% (lower than 5% of the present application), and the thermal conductivity is poor, and the effective thermal conductivity network cannot be formed due to insufficient filler.

[0087] In Comparative Example 4, the thermally conductive filler accounts for 20% (higher than 15% of the present application), and the normal temperature service reliability, disassembly convenience and salt spray resistance are poor, and the structural stability is destroyed due to excessive filler.

[0088] Obviously, those skilled in the art can make various modifications and variations to the present disclosure without departing from the spirit and scope of the present disclosure. Thus, if these modifications and variations of the present disclosure fall within the scope of the claims of the present application and their equivalents, the present disclosure also intends to include these modifications and variations.

Claims

1. An adhesive composition, characterized in that The adhesive composition comprises, based on its total weight: 30-40% by weight of a thermoplastic polymer; 5-15 wt% thermally conductive filler; 3-8% by weight of a plasticizer; 1-4 wt% of a coupling agent; 0.5-3 wt% of a stabilizer; and Organic solvents, wherein: The thermoplastic polymer is a blend of a thermoplastic copolyester and a thermoplastic polyacrylate in a weight ratio of 2:1-1:2; the thermoplastic copolyester is a butylene terephthalate-butylene adipate block copolymer, having a glass transition temperature of 53-58°C and a number average molecular weight of 15,000-21,000 g / mol; and the thermoplastic polyacrylate is a methyl methacrylate-ethyl acrylate-butyl acrylate terpolymer, having a glass transition temperature of 60-65°C and a number average molecular weight of 20,000-23,000 g / mol.

2. The adhesive composition according to claim 1, wherein The thermally conductive filler is selected from one or more of aluminum oxide, silicon dioxide, magnesium oxide, beryllium oxide, titanium dioxide, aluminum nitride, silicon nitride, boron nitride, graphene, silicon carbide and carbon fiber.

3. The adhesive composition according to claim 1, wherein The plasticizer is selected from one or more of phthalate plasticizers, aliphatic dibasic acid ester plasticizers, polyester plasticizers, phosphate plasticizers, epoxy plasticizers and citrate plasticizers.

4. The adhesive composition according to claim 1, wherein The coupling agent is selected from one or more of silane coupling agents, titanate coupling agents and aluminate coupling agents.

5. The adhesive composition according to claim 1, wherein The stabilizer is selected from one or more of antioxidants, light stabilizers, anti-hydrolysis stabilizers, anti-metal ion stabilizers and ultraviolet absorbers.

6. The adhesive composition according to claim 1, characterized in that The adhesive composition includes 30-55 wt % of an organic solvent based on the total weight of the adhesive composition.

7. An adhesive layer, characterized in that The adhesive layer comprises the adhesive composition according to any one of claims 1 to 6.

8. A new energy vehicle power battery assembly, characterized in that: The new energy vehicle power battery assembly comprises: Battery modules; a thermally conductive structural adhesive layer in contact with the battery module; an adhesive layer in contact with the thermally conductive structural adhesive layer, wherein the adhesive layer is formed by curing the adhesive composition according to any one of claims 1 to 6; an insulating buffer layer in contact with the adhesive layer; and A cooling plate is in contact with the insulating buffer layer.

9. The new energy vehicle power battery assembly according to claim 8, characterized in that: The thickness of the adhesive layer is 15-80 μm.

10. The new energy vehicle power battery assembly according to claim 8, characterized in that: The cooling plate is a metal plate with a circulation pipe inside.

Images