A low-density high-performance heat-conducting structural adhesive for power batteries and a preparation method thereof

Abstract

The application belongs to the technical field of power battery manufacturing, and discloses a low-density high-performance heat-conducting structural adhesive for power batteries and a preparation method thereof. The heat-conducting structural adhesive is formed by mixing component A and component B, and modified hollow glass microbeads are included in both components. In the heat-conducting adhesive layer after the mixing and solidification of component A and component B, the enhanced and long-chain interpenetrating reticular macromolecular polyurethane polymers formed by the cross-linking reaction of isocyanate and polyhydric alcohol are involved, the micro network structure in the heat-conducting adhesive layer is constructed by taking the modified hollow glass microbeads as a skeleton, the large-particle-size modified hollow glass microbeads and small-particle-size aluminum hydroxide particles are uniformly and firmly coated, the aluminum hydroxide particles fill the pores around the modified hollow glass microbeads to form a short three-dimensional heat-conducting path, and the components form the nanometer-micron scale interpenetrating network in the heat-conducting adhesive layer after solidification, so that the heat-conducting adhesive layer has low density and high heat-conducting performance at the same time, and the requirements of weight reduction and efficiency improvement of electric vehicles are met at the same time.

Description

Technical Field

[0001] This invention belongs to the field of power battery manufacturing technology, specifically relating to a low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method. Background Technology

[0002] Thermally conductive adhesive, also known as thermally conductive structural adhesive or thermally conductive sealant, is a material with high thermal conductivity. It allows heat to be rapidly transferred from one surface to another, often serving as an efficient tool for heat transfer. It is typically composed of polymer materials and thermally conductive fillers, and its main function is to improve heat conduction efficiency for thermal management and heat dissipation. There are many types of thermally conductive adhesives commonly found in the market for power batteries. These adhesives can be synthesized from various materials and can be categorized based on their main materials, such as: silicone thermally conductive adhesives, epoxy thermally conductive adhesives, acrylic thermally conductive adhesives, and polyurethane thermally conductive adhesives.

[0003] The power battery is one of the core components of an electric vehicle, directly affecting its performance and driving range. As the electric vehicle market continues to grow, power battery technology is also constantly innovating and advancing. Lithium-ion batteries, with their advantages of small size, high energy density, long cycle life, and low environmental pollution, are gradually replacing lead-acid batteries. Their applications in consumer electronics, electric vehicles, and energy storage devices are deepening, with significant market demand and rapid growth. Currently, electric vehicles primarily use ternary lithium-ion battery technology. Ternary lithium-ion batteries offer advantages such as high energy density, long cycle life, and low self-discharge rate, making them widely used in the electric vehicle field. With the rapid development of electric vehicles, higher demands are being placed on the thermally conductive structural adhesives used in lithium batteries. On the one hand, they must support weight reduction and energy efficiency; on the other hand, they must possess high comprehensive performance, including good heat dissipation, mechanical properties, and resistance to environmental aging. However, existing thermally conductive structural adhesives cannot simultaneously meet all these requirements.

[0004] Existing polyurethane thermally conductive adhesives are frequently used for sealing and bonding between adjacent automotive lithium-ion battery module housings, as well as for effective sealing and bonding between the battery module housing and the casing. These adhesives must also possess good thermal conductivity, mechanical strength, and flame retardant properties. However, existing polyurethane thermally conductive adhesives generally suffer from several problems, including: increasing the amount of thermally conductive powder filler is necessary to improve thermal conductivity, leading to high material viscosity, high density, and overall weight gain; conversely, reducing the amount of thermally conductive powder filler results in decreased thermal conductivity and poor flame retardancy; adding nitrides to improve thermal conductivity results in high material viscosity and high cost; and existing low-density, high-thermal-conductivity polyurethane structural adhesives typically only reduce density to 1.6 g / cm³. 3The above limits cannot be further reduced. For example, Chinese invention patent document CN114316880A discloses a low-density, high-thermal-conductivity polyurethane structural adhesive, composed of component A and component B, with a weight ratio of 1:(0.8-1.2). Component A includes: castor oil-modified polyol, polyester polyol, polyether polyol, dispersant, yellow pigment, catalyst, aluminum hydroxide, dehydrating agent, silane coupling agent, fumed silica, and defoamer; component B includes: low-viscosity castor oil-modified polyol, isocyanate, molecular sieve, dispersant, monofunctional isocyanate, fumed silica, silane coupling agent, low-density filler, blue pigment, and thermally conductive filler. This potting compound has the characteristics of low density, low modulus, high strength, and high thermal conductivity, but its density is all around 1.6 g / cm³. 3 The thermal conductivity is 0.8~0.9 W / (m·K). It is particularly important to use high-performance thermally conductive fillers; replacing them with other fillers results in a significant decrease in thermal conductivity and a significant increase in product viscosity. For example, replacing them with (organic) expanded microspheres increases the system density. Therefore, the expanded microspheres selected in this invention can have a lower density; the lowest solid density described in the examples is 1.62 g / cm³. 3 However, the thermal conductivity at this point is only 0.82 W / (m·K), making it difficult to simultaneously meet the requirements of reducing material density and maintaining key properties such as thermal conductivity.

[0005] Chinese invention application CN 202311417045.4 discloses a low-density two-component polyurethane thermally conductive structural adhesive for power batteries and its preparation method. Example 1 describes a structural adhesive composed of component A and component B in a 1:1 volume ratio. Both component A and component B formulations utilize Saint-Lite HS28 glass microspheres (hollow glass microspheres, D50=45μm). =0.28g / cm 3 (Compressive strength 28MPa / 4000psi) 1.5 parts by weight, total addition amount 3wt%, corresponding to a cured density of 1.61g / cm³. 3 The thermal conductivity is 1.22 W / (m·K), and the tensile strength is 8.4 MPa. Examples 1-3 all reduce density by adding glass microspheres and compensate for the loss of thermal conductivity by appropriately increasing the content of thermally conductive powder, ultimately achieving a balance between density and thermal conductivity. Therefore, in this invention, the added glass microspheres mainly reduce density and achieve a balance between density and thermal conductivity, without possessing other functions or technical effects. Due to the relatively large diameter of the glass microspheres and the small addition ratio, the cured adhesive layer is 1 cm thick. 3 The number of microbeads contained within is 2.60. Each microbead occupies an area (calculated as a square) of [number missing]. 1cm 3The average number of microspheres per layer in the adhesive layer is 11,700. The minimum distance between the edges of two glass microspheres in the adhesive layer is 92.45-45=47.45μm, which is larger than the diameter of the glass microspheres. The large pores between adjacent glass microspheres make it difficult to form a skeleton for the adhesive layer. Therefore, a large amount of thermally conductive powder is needed to fill the pores, resulting in an overall addition of more than 70wt% of thermally conductive powder. This leads to a long thermal conduction path and an abnormal density trend: when the addition of glass microspheres is 2wt%, the density of the adhesive layer is 1.58g / cm³. 3 When the amount added was increased to 3wt%, the density was 1.61 g / cm³. 3 As the amount of hollow microspheres added increases, the density of the adhesive layer actually increases instead of decreasing; at the maximum addition amount of 6 wt%, the density is 1.60 g / cm³. 3 The density also increases with the addition of 2wt% material. In addition, hollow glass microspheres using HS28 (D50=45μm) have a higher risk of breakage and a relatively high breakage rate during production and use due to their low compressive strength. The increased breakage rate inevitably leads to an increase in the density of the adhesive layer and a decrease in thermal conductivity and mechanical strength.

[0006] In summary, the glass microspheres added to the polyurethane thermal conductive adhesive in the prior art are mainly for adjusting the density. During the curing process of the adhesive layer, they cannot participate in the formation of specific microstructures or shorten the thermal conduction path. After curing, the density of the thermal conductive adhesive layer and its mechanical strength, high thermal conductivity, flame retardancy, and adhesion are still contradictory properties. Therefore, the existing technology is difficult to simultaneously achieve the above properties and cannot meet the requirements of weight reduction and efficiency improvement of electric vehicles. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this paper provides a low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method. Through synergistic improvements to raw materials and preparation methods, organic materials with unique components and proportions are polymerized into long-chain polymers. Hollow glass microspheres and aluminum hydroxide (both possessing microstructure shaping properties) with appropriate size, strength, and addition ratios are introduced, and the components work synergistically to construct the microstructure within the thermally conductive adhesive layer using a sufficient number of modified hollow glass microspheres as a framework. During curing, the hollow glass microspheres, aluminum hydroxide, and polymers together form a cross-linked, interpenetrating nanoscale network structure, enhancing cross-linking and allowing adjacent modified hollow microspheres to interact. The pore distance between the edges of the glass microspheres is smaller than the diameter of the modified hollow glass microspheres. The polymer material can effectively encapsulate the inorganic thermally conductive filler aluminum hydroxide powder particles and the modified hollow glass microspheres, shortening the length of the three-dimensional thermally conductive pathways around the modified hollow glass microspheres. This allows the cured thermally conductive adhesive layer to form an interpenetrating network and a three-dimensional thermally conductive structure at the nano- to micron scale. While significantly reducing the solid density of the thermally conductive adhesive layer, it maintains or improves other key properties. The thermally conductive adhesive layer can maintain thermal conductivity, insulation, flame retardancy, high strength, and excellent toughness, thereby overcoming the contradictory properties of density and mechanical strength, high thermal conductivity, flame retardancy, and adhesion of the thermally conductive adhesive layer, so as to simultaneously meet the needs of weight reduction and efficiency improvement of electric vehicles.

[0008] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0009] A low-density, high-performance thermally conductive structural adhesive for power batteries, comprising the following components in the following proportions by weight:

[0010] Component A: 20-40g polyol, 0.5-2.0g small molecule alcohol, 0.1-1g dehydrating agent, 60-75g aluminum hydroxide, 0.01-0.1g catalyst, 3-13g modified hollow glass microspheres;

[0011] Component B: Diol 5-15, Highly active polyisocyanate 10-30, Aluminum hydroxide 60-75, Modified hollow glass microspheres 3-13;

[0012] The modified hollow glass microspheres are prepared by surface modification of hollow glass microspheres with a particle size D50=40μm using a coupling agent.

[0013] Aluminum hydroxide is a solid particle with a particle size D50 of 5–30 μm;

[0014] When used in combination, the mass ratio of component A to component B is 1:(0.8~1.2).

[0015] In the thermally conductive adhesive layer after the mixture of components A and B has cured, a reinforced, long-chain interpenetrating network of polyurethane polymer, formed by the cross-linking reaction of small-molecule alcohols and diols with isocyanates and polyols, is constructed using modified hollow glass microspheres (hollow, low-density, but non-thermal conductive) as a framework. This network uniformly and firmly coats the large-diameter modified hollow glass microspheres with small-diameter aluminum hydroxide particles. The pore distance between the edges of two adjacent modified hollow glass microspheres is smaller than the diameter of the microsphere. The aluminum hydroxide particles fill the pores around the modified hollow glass microspheres, forming short three-dimensional thermally conductive pathways. Together, the components form a nano- to micron-scale interpenetrating network and a three-dimensional thermally conductive structure in the cured thermally conductive adhesive layer, resulting in a thermal conductivity of no more than 1.50 g / cm³. 3 It has low density and high thermal conductivity with a thermal conductivity of not less than 0.84 W / (m•k).

[0016] A method for preparing the aforementioned low-density, high-performance thermally conductive structural adhesive for power batteries, characterized by comprising the following steps:

[0017] S1: Preparation of component A

[0018] The measured polyol, small molecule alcohol, aluminum hydroxide thermally conductive filler, catalyst, and modified hollow glass microspheres are sequentially added to the reactor. The temperature is raised to 70-80℃ and stirred evenly. Then the temperature is raised to 100-130℃, and a vacuum below -90KPa is drawn while stirring for 2-4 hours. When the temperature drops below 60℃, a dehydrating agent is added. Then, stirring is continued for 0.5-1 hours under a vacuum below -90KPa before discharging. The product is then sealed and packaged to obtain component A.

[0019] S2: Preparation of component B

[0020] Diol is added to the reactor in proportion and dehydrated at 100-130℃ under vacuum below -90KPa for 2-4 hours. After the temperature drops to below 50℃, highly active polyisocyanate is added and stirred and heated to 65℃-85℃ for 2-2.5 hours. Then aluminum hydroxide thermally conductive filler and modified hollow glass microspheres are added and stirred under vacuum below -90KPa for 0.5-1 hours. The mixture is then discharged, sealed, and packaged to obtain component B.

[0021] S3: Preparation of Hybrid Thermally Conductive Structural Adhesive

[0022] The components A and B are packaged separately. When using, components A and B are mixed evenly at a mass ratio of 1:(0.8~1.2) and then coated on the connecting surface of the aluminum shell or plastic parts of the power lithium battery.

[0023] S4: Preparation of thermally conductive adhesive layer

[0024] Heating at room temperature or 80°C cures the thermally conductive adhesive layer to form a thermally conductive layer of a set thickness. The internal cross-linking reaction of the thermally conductive adhesive layer is enhanced, and the long-chain interpenetrating polyurethane polymer is used as a skeleton to construct the microstructure within the thermally conductive adhesive layer. This makes the pore distance between the edges of two adjacent modified hollow glass microspheres smaller than the diameter of the modified hollow glass microsphere. After aluminum hydroxide particles fill the pores around the modified hollow glass microspheres, a shorter three-dimensional thermally conductive pathway is formed. The polyurethane polymer uniformly and firmly coats the modified hollow glass microspheres and the thermally conductive filler aluminum hydroxide particles, forming a long-chain interpenetrating network and a three-dimensional thermally conductive structure adhesive layer at the nano-micro scale, which bonds and seals the joint surfaces. At this point, within the multiple nano- to micro-scale interpenetrating networks and three-dimensional thermally conductive microstructures of different scales, large-diameter hollow glass microspheres form a spatial porous framework, while small-diameter aluminum hydroxide particles fill the pores within this framework. These are then uniformly coated, networked, and positioned by macromolecular polymers. The aluminum hydroxide particles form reliable and relatively short three-dimensional thermally conductive pathways within the thermally conductive adhesive layer. This significantly reduces the solid density of the thermally conductive adhesive layer while maintaining key properties such as high thermal conductivity, high mechanical strength, high shear strength, high flame retardancy, and high weather resistance, resulting in a thermally conductive adhesive layer with a density not exceeding 1.50 g / cm³. 3 It has low density and high thermal conductivity with a thermal conductivity of not less than 0.84 W / (m•k).

[0025] The beneficial effects of the low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method provided by this invention include at least the following:

[0026] 1. This invention, through synergistic improvement of raw materials and preparation methods, introduces organic materials with unique components and proportions to polymerize into long-chain polymer materials. It also introduces modified hollow glass microspheres (low-density fillers and a framework for constructing the micro-network structure, shortening thermal conductivity pathways) with suitable shape, structure, size, strength, and dosage, and multiple functions, along with aluminum hydroxide. Furthermore, the components synergistically form a cross-linked, interpenetrating polyurethane polymer network during the curing process, using modified hollow glass as a framework to shape the internal microstructure. The polymer network effectively encapsulates inorganic thermally conductive filler aluminum hydroxide powder particles and modified hollow glass microspheres, ensuring that the pore distance between the edges of two adjacent modified hollow glass microspheres is smaller than the diameter of the microsphere. This results in a three-dimensional thermally conductive microstructure with multiple nano- to micron-scale interpenetrating networks and short thermally conductive pathways after curing. While significantly reducing the solid density of the thermally conductive adhesive layer (which has a significant effect on lightweighting automotive batteries), it maintains or improves other key properties, including thermal conductivity, insulation, flame retardancy, high strength, and excellent toughness. This overcomes the contradictory properties of density versus mechanical strength, high thermal conductivity, flame retardancy, and adhesion in thermally conductive adhesive layers. In particular, the thermal conductivity still meets design requirements, resulting in a thermally conductive adhesive layer with a density not exceeding 1.50 g / cm³. 3 Its low density and high thermal conductivity of not less than 0.84 W / (m•k) can simultaneously meet the needs of weight reduction and efficiency improvement in electric vehicles.

[0027] 2. The low-density, high-performance thermally conductive structural adhesive for power batteries provided by this invention introduces organic materials of polymers that can be enhanced through cross-linking reactions and have long-chain interpenetrating structures during polymerization, as well as inorganic thermally conductive fillers of appropriate size, addition ratio, and physicochemical properties, and modified hollow glass microspheres that can form multi-level (nano / micron) network structure frameworks at different scales. Through the synergistic effect of each component, the final thermally conductive adhesive layer after curing possesses a reasonable microstructure. The thermally conductive filler can fully fill the pores formed around the hollow glass microspheres, forming good three-dimensional thermal conductive pathways, thereby enabling the cured thermally conductive adhesive layer to have a low density (as low as 1.33 g / cm³). 3 It has a high thermal conductivity and a density that is more than 15% lower than that of similar products in the prior art, and the overall manufacturing cost is lower, thus meeting the needs of electric vehicles for weight reduction, efficiency improvement and cost reduction.

[0028] 3. This invention combines appropriate addition amounts, sizes, shapes, structures, and compressive strength of modified hollow glass microspheres to make them the core framework of the micro-network structure within the thermally conductive adhesive layer. This effectively shortens the three-dimensional thermal conduction pathways around the glass microspheres, improving the overall performance of the material, including thermal conductivity, mechanical properties, and toughness, while reducing density. The modified hollow glass microspheres used in this invention, after surface modification with a coupling agent, have reduced oil absorption values, significantly improving their interfacial adhesion to other components in component A and component B. Furthermore, the combination of long-chain polymers enhanced by cross-linking reactions and the size of the thermally conductive filler allows for the addition of modified hollow glass microspheres in a larger proportion (up to 10 wt% or more). By shaping the microstructure using modified hollow glass microspheres as the framework, the thermally conductive structural adhesive product achieves a lower solid density while meeting the requirements for thermal conductivity and adhesive strength. Compared to traditional products or CN114316880A, the density can be reduced by 15-20%, effectively overcoming the technical contradiction of a rapid decrease in thermal conductivity and mechanical strength with decreasing density.

[0029] 4. The modified hollow glass microspheres used in this invention have high compatibility with polyurethane materials. The cured thermally conductive adhesive layer has good adhesion to various substrates (including polar and non-polar substrates). Moreover, the modified hollow glass microspheres have high compressive strength and closed-cell rate, and are not easily broken during production and construction. This makes the cured thermally conductive adhesive layer more weather-resistant, acid and alkali-resistant, and anti-aging. Furthermore, there is no risk of bubbling during long-term use, which enables it to meet the various requirements of new energy vehicle lithium batteries for thermally conductive structural adhesives for structural bonding.

[0030] 5. The preparation method provided by the present invention uses fewer types of components, the raw materials are readily available, the operation is simple and the conditions are mild, the process steps are compact and easy to control, and it is easy to mass-produce and use in the industrial sector, with excellent prospects for industrial application; the thermally conductive structural adhesive after the two components are mixed can be cured at room temperature or heated to a temperature below 80°C, making it convenient to use. Attached Figure Description

[0031] Figure 1 This is a 200μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 1 of this invention;

[0032] Figure 2 This is a 50μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 1 of this invention;

[0033] Figure 3 This is a 20μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 1 of this invention;

[0034] Figure 4 This is a 10μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 1 of this invention.

[0035] Figure 5 This is a 4μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 1 of this invention.

[0036] Figure 6 This is a 500nm electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 1 of this invention.

[0037] Figure 7 This is a 200μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 2 of this invention;

[0038] Figure 8 This is a 50μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 2 of this invention;

[0039] Figure 9 This is a 10μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 2 of this invention.

[0040] Figure 10 This is a 4μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 2 of this invention.

[0041] Figure 11 This is a 500nm electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 2 of this invention.

[0042] Figure 12 This is a 200μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 3 of this invention.

[0043] Figure 13 This is a 100μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 3 of this invention.

[0044] Figure 14 This is a 40μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 3 of this invention.

[0045] Figure 15This is a 5μm-scale electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in Example 3 of this invention;

[0046] Figure 16 This is a 500nm electron microscope image of the vertical cross-section of the thermally conductive adhesive layer after curing of the low-density, high-performance thermally conductive structural adhesive for power batteries prepared in Example 3 of this invention. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. All raw materials used in the following embodiments of the present invention are commercially available products; wherein, cashew nut shell oil modified polyether polyol was purchased from Cardlä Company; isophorone diisocyanate was purchased from Wanhua Chemical; the small molecule alcohol is commercially available trimethylolpropane; aluminum hydroxide thermally conductive filler was purchased from Foshan Jingge; the dehydrating agent is vinyltrimethoxysilane, purchased from Guangzhou Yourun Chemical; the catalyst is an organozirconium catalyst, purchased from Guangzhou Yourun Chemical; the highly active polyisocyanate is diphenylmethane diisocyanate, purchased from Wanhua Chemical; and the diol is PPG polyether, purchased from Shanghai Jiahe.

[0048] Basic Implementation

[0049] The basic embodiment of this invention is a targeted research and development project aimed at addressing the fact that the 0.8W~1.2W polyurethane thermally conductive structural adhesive in the prior art cannot simultaneously meet the requirements of weight reduction, efficiency improvement and cost reduction in new energy vehicles.

[0050] The low-density, high-performance thermally conductive structural adhesive for power batteries provided in this embodiment is composed of the following components in the following proportions by weight:

[0051] Component A: 20-40g polyol, 0.5-2.0g small molecule alcohol, 0.1-1g dehydrating agent, 60-75g aluminum hydroxide, 0.01-0.1g catalyst, 3-13g modified hollow glass microspheres;

[0052] Component B: 5-15% diol, 10-30% highly active polyisocyanate, 60-75% aluminum hydroxide, and 3-13% modified hollow glass microspheres; wherein the relative molecular weight of the diol is 1000-6000.

[0053] The modified hollow glass microspheres are prepared by surface modification of hollow glass microspheres with a particle size D50=40μm using a coupling agent.

[0054] Aluminum hydroxide is a solid particle with a particle size D50 of 5–30 μm;

[0055] When used in combination, the mass ratio of component A to component B is 1:(0.8~1.2).

[0056] In the thermally conductive adhesive layer after the mixture of components A and B has cured, small-molecule alcohols and diols participate in the crosslinking reaction of isocyanate and polyols to form a reinforced, long-chain interpenetrating network of polyurethane polymers. Modified hollow glass microspheres serve as the framework to construct the microscopic network structure within the thermally conductive adhesive layer. This uniformly and firmly coats the large-diameter modified hollow glass microspheres with small-diameter aluminum hydroxide particles. The pore distance between the edges of two adjacent modified hollow glass microspheres is smaller than the diameter of the microsphere. The aluminum hydroxide particles fill the pores around the modified hollow glass microspheres, forming short three-dimensional thermally conductive pathways. All components together form a nano- to micron-scale interpenetrating network and a three-dimensional thermally conductive structure in the cured thermally conductive adhesive layer, resulting in a thermal conductivity of no more than 1.50 g / cm³. 3 It has low density and high thermal conductivity with a thermal conductivity of not less than 0.84 W / (m•k).

[0057] The polyol mentioned is one or more of polyolefin polyol, polyacrylate polyol, cashew nut shell oil bio-based modified polyol, and polymer polyol POP, with a hydroxyl value of 112-305 mg KOH / g.

[0058] The polyolefin polyols, polyacrylate polyols, cashew nut shell oil bio-based modified polyols, and polymer polyols (POPs) used in this invention are all oligomeric polyols. The main differences lie in the initiators and raw materials used in their synthesis. Representative products of polyolefin polyols include hydroxyl-terminated polybutadiene (butyl-hydroxy) and hydroxyl-terminated butadiene-acrylonitrile copolymer (butyl-acrylonitrile-hydroxy). Polyacrylate polyols are synthesized from hydroxyl-containing acrylates or allyl alcohols and hydroxyl-free acrylates. Polymer polyols (POPs), also known as vinyl polymer grafted polyether polyols or grafted polymer polyols, are produced by free radical grafting polymerization of vinyl monomers with a parent polyoxypropylene ether polyol in the presence of an initiator. They are generally white or light milky yellow in appearance and contain organic fillers. Cashew nut shell oil bio-based modified polyols, also known as modified cashew nut shell oil polyether polyols, are prepared by extracting cashew phenol from cashew trees and then reacting it with formaldehyde, diethanolamine, etc., via a Mannich reaction. These are liquids with a hydroxyl value of 225-305 mg. KOH / g.

[0059] The small molecule alcohols are selected from ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 2,4-pentanediol, 2-methyl-1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, and 2-methyl-1,3-propanediol. One or more of the following: 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,4-butanediol, 1,2-octanediol, 3,6-octanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,7-dimethyl-3,6-octanediol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, hydroquinone-bis(β-hydroxyethyl) ether, trimethylolpropane, and trimethylolpropane monoallyl ether, with a relative molecular weight of 90 to 150.

[0060] The dehydrating agent is vinyltrimethoxysilane or methyltrimethoxysilane.

[0061] The aluminum hydroxide used as a thermally conductive filler is one or more of the following: D50 = 5-10 μm, D50 = 10-20 μm, and D50 = 20-30 μm.

[0062] The catalyst is selected from one or more of organotin catalysts, organobismuth catalysts, organozinc catalysts, and organozirconium catalysts.

[0063] The hollow glass microspheres have a particle size D50 of 40 μm, a compressive strength of 2000–6000 psi, and a density of 0.3–0.38 g / cm³. 3 And it undergoes surface modification treatment through the following steps:

[0064] (1) Dissolve 100 ml of titanate coupling agent in 900 ml of ethanol and stir well to obtain coupling agent solution;

[0065] (2) Take 100g of hollow glass microspheres and add them to the prepared coupling agent solution. Stir with an electric stirrer at 60r / min for 10min, and then sonicate for 10min.

[0066] (3) Filter out the hollow glass microspheres and put them into an oven at 120°C for 120 min to obtain the coupling agent surface modified hollow glass microspheres.

[0067] The diol is selected from one or more of polypropylene glycol (PPG), polytetrahydrofuran glycol, and modified cashew nut shell-derived polyether diol. Polytetrahydrofuran glycol (also known as polytetrahydrofuran ether diol, abbreviated as PTMEG, PTG, PTMG, PTMO, or PTHF) is an important polymer with the molecular formula HO[CH2CH2CH2CH2O]. n H. In specific embodiments of the present invention, commercially available products such as PTMG1000 (2 functionalities, molecular weight 1000±50, hydroxyl value 107~118mg KOH / g) from Mitsubishi Corporation of Japan can be selected.

[0068] The highly active polyisocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, naphthalene-1,5-diisocyanate, and polymeric MDI.

[0069] The aforementioned method for preparing low-density, high-performance thermally conductive structural adhesive for power batteries includes the following steps:

[0070] S1: Preparation of component A

[0071] The measured polyol, small molecule alcohol, aluminum hydroxide thermally conductive filler, catalyst, and modified hollow glass microspheres are sequentially added to the reactor. The temperature is raised to 70-80℃ and stirred evenly. Then the temperature is raised to 100-130℃, and a vacuum below -90KPa is drawn while stirring for 2-4 hours. When the temperature drops below 60℃, a dehydrating agent is added. Then, stirring is continued for 0.5-1 hours under a vacuum below -90KPa before discharging. The product is then sealed and packaged to obtain component A.

[0072] S2: Preparation of component B

[0073] Diol is added to the reactor in proportion and dehydrated at 100-130℃ under vacuum below -90KPa for 2-4 hours. After the temperature drops to below 50℃, highly active polyisocyanate is added and stirred and heated to 65℃-85℃ for 2-2.5 hours. Then aluminum hydroxide thermally conductive filler and modified hollow glass microspheres are added and stirred under vacuum below -90KPa for 0.5-1 hours. The mixture is then discharged, sealed, and packaged to obtain component B.

[0074] S3: Preparation of Hybrid Thermally Conductive Structural Adhesive

[0075] The components A and B are sealed and packaged separately. When using, the seals are removed, and the components A and B are mixed evenly at a mass ratio of 1:(0.8~1.2). The mixture is then coated onto the connecting surface of the aluminum shell or plastic parts of the power lithium battery.

[0076] S4: Preparation of thermally conductive adhesive layer

[0077] Heating at room temperature or 80°C cures the thermally conductive adhesive layer to form a thermally conductive layer of a set thickness. The internal cross-linking reaction of the thermally conductive adhesive layer is enhanced, and the long-chain interpenetrating polyurethane polymer is used as a skeleton to construct the microstructure within the thermally conductive adhesive layer. This makes the pore distance between the edges of two adjacent modified hollow glass microspheres smaller than the diameter of the modified hollow glass microsphere. After aluminum hydroxide particles fill the pores around the modified hollow glass microspheres, a shorter three-dimensional thermally conductive pathway is formed. The polyurethane polymer uniformly and firmly coats the modified hollow glass microspheres and the thermally conductive filler aluminum hydroxide particles, forming a long-chain interpenetrating network and a three-dimensional thermally conductive structure adhesive layer at the nano-micro scale, which bonds and seals the joint surfaces. At this point, within the multiple nano- to micro-scale interpenetrating networks and three-dimensional thermally conductive microstructures of different scales, large-diameter hollow glass microspheres form a spatial porous framework, while small-diameter aluminum hydroxide particles fill the pores within this framework. These are then uniformly coated, networked, and positioned by macromolecular polymers. The aluminum hydroxide particles form reliable and relatively short three-dimensional thermally conductive pathways within the thermally conductive adhesive layer. This significantly reduces the solid density of the thermally conductive adhesive layer while maintaining key properties such as high thermal conductivity, high mechanical strength, high shear strength, high flame retardancy, and high weather resistance, resulting in a thermally conductive adhesive layer with a density not exceeding 1.50 g / cm³. 3 It has low density and high thermal conductivity with a thermal conductivity of not less than 0.84 W / (m•k).

[0078] In the thermally conductive adhesive layer prepared in this embodiment of the invention, there are multiple scale levels (from tens of nanometers to hundreds of micrometers) of nano-micrometer scale interpenetrating networks and three-dimensional thermally conductive microstructures. Large-diameter (thermally insulating) hollow glass microspheres form a spatial pore skeleton, making the pore distance between the edges of two adjacent modified hollow glass microspheres smaller than the diameter of the modified hollow glass microsphere. Small-diameter (thermally conductive) aluminum hydroxide particles fill the pores in the skeleton, and then are uniformly coated, networked and fixed in position by a macromolecular polyurethane polymer. This allows the aluminum hydroxide particles to still form a relatively short (smaller than the diameter of the glass microspheres) and reliable three-dimensional thermally conductive pathway within the thermally conductive adhesive layer. While significantly reducing the solid density of the thermally conductive adhesive layer, it can still maintain key properties such as high thermal conductivity, high mechanical strength, high shear strength, high flame retardancy and high weather resistance, so that the thermally conductive adhesive layer has a density of no more than 1.50 g / cm³. 3 It has low density and high thermal conductivity of not less than 0.84 W / (m•k), and also possesses other key comprehensive properties such as shear strength and hardness.

[0079] The embodiments of this invention use appropriate addition amounts, particle size D50 = 40 μm, compressive strength of 2000–6000 psi, and density of 0.3–0.38 g / cm³. 3Modified hollow glass microspheres are an inorganic non-metallic material, primarily composed of SiO2, which lacks thermal conductivity, electrical conductivity, and electromagnetic shielding properties. This invention utilizes surface-modified hollow glass microspheres treated with a coupling agent, resulting in high strength, low density, and good material compatibility. In contrast, commercially available hollow glass microspheres suffer from insufficient compressive strength, low closed-cell ratio, and high oil absorption. Insufficient compressive strength leads to brittleness during production and application, contaminating the adhesive layer and increasing density. Low closed-cell ratio results in significant bubbling during adhesive curing, affecting the adhesive's performance. High oil absorption makes it difficult to add the microspheres or results in excessively high viscosity after addition, hindering application. Therefore, this invention specifies particular requirements for the type, dosage, particle size, compressive strength, and modification treatment of the hollow glass microspheres; the combination of these characteristics is crucial to achieving the desired technical effect.

[0080] The present invention uses materials with a D50 of 40 μm, a compressive strength of 2000–6000 psi, and a density of 0.3–0.38 g / cm³. 3 The modified hollow glass microspheres of this model are different from those of two other commercially available models, which have a D50 of 30μm, a compressive strength of 10,000–18,000 psi, and a density of 0.6 g / cm³. 3 With a D50 of 55–65 μm, a compressive strength of 250–300 psi, and a density of 0.125–0.15 g / cm³, it possesses the following properties: 3 This would fail to meet the requirements of the present invention and would not achieve the technical effects described herein. The modified hollow glass microspheres used in each embodiment are specifically 3M products with a D50=40μm, preferably S38 microspheres with a D50=40μm and a density ρ=0.38g / cm³. 3 .

[0081] The total amount of modified hollow glass microspheres added in each embodiment was 5%~10%, corresponding to a density of 1.33 g / cm³ for the product after curing of the adhesive layer. 3 ~1.50g / cm 3 The thermal conductivity remains around 0.9 W / (m•K), while the shear strength and tensile strength are significantly improved, and the elongation at break remains within a reasonable range. Based on an average addition of 7 wt%, the cured thermally conductive adhesive layer has a 1 cm depth of [missing value]. 3 The number of microbeads contained within is 7.95. If the glass micro-presses are arranged in an ideal manner, that is, layered on top of each other, then 1cm 3 The internal stackable layer count is 250 layers, 1cm. 3 Each inner layer contains an average of 31,800 microbeads, and the area occupied by each microbead (calculated as a square) is... It is equivalent to a square with a side length of 56μm; the minimum distance between the edges of two adjacent modified hollow glass microspheres is about 16μm, and the average distance is about 30μm, both of which are smaller than the diameter of the hollow glass microspheres themselves. This is beneficial for the formation of short-length three-dimensional thermal conductive pathways (less than 40μm) around the filling of thermal conductive powder, which is beneficial for improving the overall performance of the adhesive layer.

[0082] The present invention will be described in detail below with more specific embodiments, test data, electron micrographs, etc. Unless otherwise specified, all proportions are by weight.

[0083] Overview of Examples 1-6 and Comparative Examples 1-3

[0084] The low-density, high-performance thermally conductive structural adhesives for power batteries and their preparation methods provided in Examples 1-6 are specific selections based on the aforementioned basic examples. The difference lies in the specific components and proportions (by weight) of the low-density, high-performance thermally conductive structural adhesives for power batteries in each example, as shown in Table 1 below:

[0085] Table 1

[0086]

[0087] Example 1

[0088] Please see the appendix Figures 1-6 The low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method provided in this embodiment are specific selections based on the aforementioned basic embodiments. The difference lies in the specific components, proportions, and preparation methods of the low-density, high-performance thermally conductive structural adhesive for power batteries in this embodiment, as follows:

[0089] The pre-preparation of modified hollow glass microspheres includes the following steps:

[0090] (1) Dissolve 100 ml of titanate coupling agent in 900 ml of ethanol and stir well to obtain coupling agent solution;

[0091] (2) Take particles with a particle size D50 of 40 μm, a compressive strength of 2000–6000 psi, and a density of 0.3–0.5 g / cm³. 3 100g of hollow glass microspheres were added to the prepared coupling agent solution and stirred for 10min with an electric stirrer at 60r / min, followed by ultrasonic vibration for 10min.

[0092] (3) Filter out the hollow glass microspheres and put them into an oven at 120°C for 120 min to obtain the desired modified hollow glass microspheres;

[0093] (4) According to the proportions in Table 1, the measured polyolefin polyol, small molecule alcohol, aluminum hydroxide, catalyst, and modified hollow glass microspheres are added to the reactor in sequence, heated to 70-80℃, stirred evenly, then heated to 100-130℃, vacuumed below -90KPa and stirred for 2-4 hours, and when the temperature drops below 60℃, the dehydrating agent is added, and then stirred for 0.5-1 hours under vacuum below -90KPa before discharging, sealing and packaging to obtain component A;

[0094] Among them, the polyol is a cashew nut shell oil bio-based modified polyol with a hydroxyl value of 225 mg KOH / g; the small molecule alcohol is trimethylolpropane; the catalyst is CUCAT-GF02 from Guangzhou Yourun Chemical; the dehydrating agent is methyltrimethoxysilane; and the aluminum hydroxide is a mixture of two powder products with D50=5~10μm and D50=10~20μm in a mass ratio of 2:1.

[0095] (5) Add the diol to the reactor and dehydrate it at 100-130℃ under vacuum below -90KPa for 2-4 hours. When the temperature drops to below 50℃, add the highly active polyisocyanate, stir and heat to 65℃-85℃, react for 2-2.5 hours, then add the thermally conductive filler aluminum hydroxide and modified hollow glass microspheres, stir under vacuum below -90KPa for 0.5-1 hours, discharge the material, seal and package it to obtain component B.

[0096] Among them, the highly active polyisocyanate is diphenylmethane diisocyanate; the diol is polypropylene glycol with a relative molecular weight of 1000; and the aluminum hydroxide is a mixture of two powder products with particle sizes of D50=5~10μm and D50=10~20μm in a mass ratio of 2:1.

[0097] (6) When using, remove the packaging of the above components A and B, mix them evenly in a weight ratio of 1:1 to obtain low-density polyurethane thermally conductive structural adhesive, and apply it evenly to the connecting surface of the aluminum shell or plastic parts of the power lithium battery to achieve the set thickness.

[0098] (7) The thermally conductive adhesive layer is heated and cured at room temperature or 80°C to form a thermally conductive adhesive layer with a set thickness (generally 0.25-1 mm). The internal cross-linking reaction of the thermally conductive adhesive layer enhances the long-chain interpenetrating network of polyurethane polymer. The modified hollow glass microspheres serve as the skeleton to construct the microstructure within the thermally conductive adhesive layer. The thermally conductive filler aluminum hydroxide particles are uniformly and firmly coated. The aluminum hydroxide particles fill the pores around the modified hollow glass microspheres to form a long-chain interpenetrating network and a three-dimensional thermally conductive structure with nano-micron scale, which bonds and seals the connection surface.

[0099] This invention, through appropriate addition ratios (which can be further converted into particle number, layer number, and volume), size, type selection, and modification treatment of modified hollow glass microspheres, allows for their addition in a larger proportion. Furthermore, it enables the thermally conductive adhesive layer to achieve a lower density while meeting key performance requirements such as thermal conductivity and adhesive strength. Experimental results show that the low-density polyurethane thermally conductive structural adhesive provided in this invention has a cured thermal conductivity of 0.80–1.0 W / (m·K) and a density of 1.30–1.5 g / cm³. 3 The tensile shear strength was 10–16 MPa (23℃, 7d), and the tensile strength was 10.0–16.0 MPa (23℃, 7d). Specific test results are shown in Table 1.

[0100] The cross-sectional electron microscope image of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in this embodiment of the invention is attached. Figures 1-6 As shown in the microstructure diagrams at various scales, the interior of the cured thermally conductive adhesive layer's vertical cross-section is constructed from a network of large-molecule polyurethane polymers reinforced by cross-linking reactions and with large-particle modified hollow glass microspheres as the framework. The modified hollow glass microspheres serve as the local core, with aluminum hydroxide particles filling the pores around them. The polyurethane polymer then uniformly and firmly coats the heat-insulating low-density modified hollow glass microspheres and the thermally conductive filler aluminum hydroxide particles, forming a three-dimensional thermally conductive structure with a multi-scale nano-microscale long-chain interpenetrating network and relatively short pathways, thus bonding and sealing the connection surfaces. Polyurethane polymer materials are distributed on the surface, periphery, and pores of solid modified hollow glass microspheres and aluminum hydroxide particles. The components work together to form a dense three-dimensional thermally conductive microstructure with an interpenetrating network at the nano- to micron scale within the three-dimensional space of the adhesive layer. The polymer materials and solid particles complement each other to form a virtual-solid micro-network structure, which can significantly reduce the density of the thermally conductive adhesive layer while maintaining its thermal conductivity, hardness, mechanical strength, flame retardancy, and dielectric strength to meet design requirements. This effectively meets the needs of weight reduction and efficiency improvement in electric vehicles.

[0101] The test data of the main properties and parameters of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in this embodiment are shown in Table 2.

[0102] The test methods used in Table 2 are as follows:

[0103] Tensile strength and elongation at break: tested according to the methods in GB / T 528-2009;

[0104] Shear strength: Tested according to the method in GB / T 7124-2008;

[0105] Thermal conductivity: tested according to the method in ASTM D 5470;

[0106] Hardness: Tested according to the method in GB / T 531.1—2008;

[0107] Density: Tested using the method in GB / T 533—2008.

[0108] Example 2

[0109] Please see the appendix Figure 7-11 The low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method provided in this embodiment are basically the same as those in Example 1. The difference lies in the specific components, proportions, and preparation methods of the low-density, high-performance thermally conductive structural adhesive for power batteries in this embodiment, which are as follows:

[0110] (1) According to the proportions in Table 1, the measured polyols, small molecule alcohols, aluminum hydroxide thermally conductive fillers, catalysts, and modified hollow glass microspheres are sequentially added to the reactor. The temperature is raised to 70-80℃ and stirred evenly. Then the temperature is raised to 100-120℃, and the vacuum is drawn below -90KPa while stirring for 2.5h. When the temperature drops below 60℃, the dehydrating agent is added. Then the stirring is continued for 0.5h under a vacuum below -90KPa before the material is discharged, sealed and packaged to obtain component A.

[0111] (2) Add the diol to the reactor and dehydrate it under vacuum below -90 kPa for 2 hours at 100-120°C. When the temperature drops to below 50°C, add the highly active polyisocyanate and stir and heat to 70-80°C. React for 2-2.5 hours. Then add aluminum hydroxide thermally conductive filler and hollow glass microspheres. Stir for 0.5 hours under vacuum below -90 kPa and discharge the material. Seal and package to obtain component B.

[0112] (3) Mix the above components A and B at a mass ratio of 1:0.8 to obtain a low-density polyurethane thermally conductive structural adhesive.

[0113] Among them, the polyol is a polyolefin polyol with a hydroxyl value of 180 mg KOH / g; the small molecule alcohol is 1,4-butanediol; the catalyst is CUCAT-GF02 from Guangzhou Yourun Chemical; the dehydrating agent is methyltrimethoxysilane; the highly active polyisocyanate is diphenylmethane diisocyanate; the diol is modified cashew shell-infused polyether diol with a hydroxyl value of 170 mg KOH / g; and the aluminum hydroxide is a powder product with a D50 of 10-20 μm.

[0114] The low-density, high-performance thermally conductive structural adhesive for power batteries prepared in this embodiment of the invention has a cross-sectional electron microscope image of the cured thermally conductive adhesive layer, as shown in the attached figure. Figures 7-11As shown in the microstructure diagrams at various scales, the interior of the cured thermally conductive adhesive layer is formed by the interweaving of high-molecular-weight materials with enhanced cross-linking reaction and long interpenetrating chains, creating a multi-level nano- to micro-scale network structure. Moreover, the long chains formed by these high-molecular-weight materials can also span the pores between solid particles, thereby reducing the material density and shortening the length of the thermal conductivity path, enabling the material to possess key properties such as high thermal conductivity and high mechanical strength.

[0115] The performance parameter test data of the thermally conductive adhesive layer after curing of the low-density high-performance thermally conductive structural adhesive for power batteries prepared in this embodiment are shown in Table 2.

[0116] Example 3

[0117] Please see the appendix Figure 12-15 The low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method provided in this embodiment are basically the same as those in Examples 1-2. The difference lies in the specific components, proportions, and preparation methods of the low-density, high-performance thermally conductive structural adhesive for power batteries in this embodiment, which are as follows:

[0118] (1) According to the proportions in Table 1, the measured polyols, small molecule alcohols, aluminum hydroxide thermally conductive fillers, catalysts, and modified hollow glass microspheres are sequentially added to the reactor. The temperature is raised to 70-80℃ and stirred evenly. Then the temperature is raised to 100-120℃, and the vacuum is drawn below -90KPa while stirring for 2.5h. When the temperature drops below 60℃, the dehydrating agent is added. Then the stirring is continued for 0.5h under a vacuum below -90KPa before the material is discharged, sealed and packaged to obtain component A.

[0119] (2) Add the diol to the reactor and dehydrate it under vacuum below -90 kPa for 2 hours at 100-120°C. When the temperature drops to below 50°C, add the highly active polyisocyanate and stir and heat to 70-80°C. React for 2-2.5 hours. Then add aluminum hydroxide thermally conductive filler and hollow glass microspheres. Stir for 0.5 hours under vacuum below -90 kPa and discharge the material. Seal and package to obtain component B.

[0120] (3) Mix the above components A and B at a mass ratio of 1:1.2 to obtain a low-density polyurethane thermally conductive structural adhesive.

[0121] Among them, the polyol is polyacrylate polyol with a hydroxyl value of 225 mg KOH / g; the small molecule alcohol is 1,4-butanediol; the catalyst is CUCAT-S1015 from Guangzhou Yourun Chemical; the dehydrating agent is vinyltrimethoxysilane; the highly active polyisocyanate is isophorone diisocyanate; the diol is modified cashew nut shell-infused polyether diol with a hydroxyl value of 170 mg KOH / g; and the aluminum hydroxide is a powder product with a particle size D50 of 20-30 μm.

[0122] The low-density, high-performance thermally conductive structural adhesive for power batteries prepared in this embodiment of the invention has a cross-sectional electron microscope image of the cured thermally conductive adhesive layer, as shown in the attached figure. Figures 12-15 As shown in the diagrams, the microstructure at various scales reveals that the vertical cross-section of the cured thermally conductive adhesive layer is composed of a multi-level nano-micro network structure formed by the interweaving of polymer materials with enhanced cross-linking reaction and long interpenetrating chains. Moreover, the long chains formed by these polymer materials can also span the pores between solid particles, thereby reducing the material density while still enabling the material to possess key properties such as high thermal conductivity.

[0123] Example 4

[0124] The low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method provided in this embodiment are basically the same as those in Examples 1-2. The difference lies in the specific components, proportions, and preparation methods of the low-density, high-performance thermally conductive structural adhesive for power batteries in this embodiment, which are as follows:

[0125] (1) According to the proportions in Table 1, the measured polyols, small molecule alcohols, aluminum hydroxide thermally conductive fillers, catalysts, and modified hollow glass microspheres are sequentially added to the reactor. The temperature is raised to 70-80℃ and stirred evenly. Then the temperature is raised to 100-120℃, and the vacuum is drawn below -90KPa while stirring for 2.5h. When the temperature drops below 60℃, the dehydrating agent is added. Then the stirring is continued for 0.5h under a vacuum below -90KPa before the material is discharged, sealed and packaged to obtain component A.

[0126] (2) Add the diol to the reactor and dehydrate it under vacuum below -90 kPa for 2 hours at 100-120°C. When the temperature drops to below 50°C, add the highly active polyisocyanate and stir and heat to 70-80°C. React for 2-2.5 hours. Then add aluminum hydroxide thermally conductive filler and hollow glass microspheres. Stir for 0.5 hours under vacuum below -90 kPa and discharge the material. Seal and package to obtain component B.

[0127] (3) Mix the above components A and B at a mass ratio of 1:0.9 to obtain a low-density polyurethane thermally conductive structural adhesive.

[0128] Among them, the polyol is a cashew nut shell oil bio-based modified polyol with a hydroxyl value of 305 mg KOH / g; the small molecule alcohol is trimethylolpropane; the catalyst is CUCAT-GF02 from Guangzhou Yourun Chemical; the dehydrating agent is vinyltrimethoxysilane; the highly active polyisocyanate is diphenylmethane diisocyanate; the diol is a modified cashew nut shell-infused polyether diol with a hydroxyl value of 170 mg KOH / g; and the aluminum hydroxide is a powder product with a particle size D50 of 10-20 μm.

[0129] Example 5

[0130] The low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method provided in this embodiment are basically the same as those in Examples 1-2. The difference lies in the specific components, proportions, and preparation methods of the low-density, high-performance thermally conductive structural adhesive for power batteries in this embodiment, which are as follows:

[0131] (1) According to the proportions in Table 1, the measured polyols, small molecule alcohols, aluminum hydroxide thermally conductive fillers, catalysts, and modified hollow glass microspheres are sequentially added to the reactor. The temperature is raised to 70-80℃ and stirred evenly. Then the temperature is raised to 100-120℃, and the vacuum is drawn below -90KPa while stirring for 2.5h. When the temperature drops below 60℃, the dehydrating agent is added. Then the stirring is continued for 0.5h under a vacuum below -90KPa before the material is discharged, sealed and packaged to obtain component A.

[0132] (2) Add the diol to the reactor and dehydrate it under vacuum below -90 kPa for 2 hours at 100-120°C. When the temperature drops to below 50°C, add the highly active polyisocyanate and stir and heat to 70-80°C. React for 2-2.5 hours. Then add aluminum hydroxide thermally conductive filler and hollow glass microspheres. Stir for 0.5 hours under vacuum below -90 kPa and discharge the material. Seal and package to obtain component B.

[0133] (3) Mix the above components A and B at a mass ratio of 1:0.95 to obtain a low-density polyurethane thermally conductive structural adhesive.

[0134] The polyol is a mixture of cashew nut shell oil bio-based modified polyol and polyacrylate polyol in a 1:1 mass ratio, with a mixed hydroxyl value of 225 mg KOH / g; the small molecule alcohol is 1,4-butanediol; the catalyst is CUCAT-GF02 from Guangzhou Yourun Chemical; the dehydrating agent is vinyltrimethoxysilane; the highly active polyisocyanate is toluene diisocyanate; the polyoxypropylene glycol and modified cashew nut shell-derived polyether diol are mixed in a 2:1 mass ratio, with a hydroxyl value of 132 mg KOH / g; and the aluminum hydroxide is a powder product with a D50 of 5-10 μm.

[0135] Example 6

[0136] The low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method provided in this embodiment are basically the same as those in Examples 1-2. The difference lies in the specific components, proportions, and preparation methods of the low-density, high-performance thermally conductive structural adhesive for power batteries in this embodiment, which are as follows:

[0137] (1) According to the proportions in Table 1, the measured polyols, small molecule alcohols, aluminum hydroxide thermally conductive fillers, catalysts, and modified hollow glass microspheres are sequentially added to the reactor. The temperature is raised to 70-80℃ and stirred evenly. Then the temperature is raised to 100-120℃, and the vacuum is drawn below -90KPa while stirring for 2.5h. When the temperature drops below 60℃, the dehydrating agent is added. Then the stirring is continued for 0.5h under a vacuum below -90KPa before the material is discharged, sealed and packaged to obtain component A.

[0138] (2) Add the diol to the reactor and dehydrate it under vacuum below -90 kPa for 2 hours at 100-120°C. When the temperature drops to below 50°C, add the highly active polyisocyanate and stir and heat to 70-80°C. React for 2-2.5 hours. Then add aluminum hydroxide thermally conductive filler and hollow glass microspheres. Stir for 0.5 hours under vacuum below -90 kPa and discharge the material. Seal and package to obtain component B.

[0139] (3) Mix the above components A and B at a mass ratio of 1:1.2 to obtain a low-density polyurethane thermally conductive structural adhesive.

[0140] Among them, the polyol is a polyolefin polyol with a hydroxyl value of 180 mg KOH / g; the small molecule alcohol is hydroquinone-bis(β-hydroxyethyl) ether; the catalyst is CUCAT-GF02 from Guangzhou Yourun Chemical; the dehydrating agent is methyltrimethoxysilane; the highly active polyisocyanate is diphenylmethane diisocyanate; the diol is a mixture of polypropylene glycol and modified cashew nut shell-soaked polyether diol in a mass ratio of 2:1, with a hydroxyl value of 132 mg KOH / g; and the aluminum hydroxide is a mixture of two specifications with particle sizes of D50=5~10μm and D50=10~20μm in a mass ratio of 2:1.

[0141] Comparative Example

[0142] The selection and proportion of components for Comparative Examples 1 to 4 are shown in Table 1. The specific selection of each component and preparation process is the same as that in Example 1.

[0143] In Comparative Examples 1 to 4, compared to Example 1, the other raw materials remained unchanged in Comparative Example 1, but component A did not contain hollow glass microspheres;

[0144] Compared to Example 1, in Comparative Example 2, other raw materials remained unchanged, but the amount of modified hollow glass microspheres in component B was increased;

[0145] Comparative Example 3, compared to Example 1, used unmodified hollow glass microspheres with a particle size of D50=30μm, with other raw materials remaining unchanged.

[0146] Compared to Example 1, Comparative Example 4 used unmodified hollow glass microspheres with a particle size of D50=60μm, with other raw materials remaining unchanged.

[0147] The test results of various performance data of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 2 below.

[0148] Table 2

[0149]

[0150] As shown in Table 2, the density of the thermally conductive adhesive layer in each embodiment decreased significantly while maintaining good thermal conductivity, shear strength, and tensile strength, thus meeting various design requirements. Performance test results of the above embodiments of the present invention show that the overall performance of the thermally conductive adhesive layer is superior when the total amount of modified hollow glass microspheres added is 5-8 wt%; the maximum total addition should not exceed 10 wt%, while the overall performance of the thermally conductive adhesive layer is optimal at around 5 wt%.

[0151] The density of the thermally conductive adhesive layer in Comparative Example 1 increased significantly; the thermal conductivity and elongation at break of the thermally conductive adhesive layer in Comparative Example 2 decreased significantly; the density of the thermally conductive adhesive layer in Comparative Example 3 did not decrease significantly; and the thermal conductivity, shear strength, and tensile strength of the thermally conductive adhesive layer in Comparative Example 4 all decreased significantly.

[0152] Commercially available hollow glass microspheres cannot be directly applied to the embodiments of this invention. Conventional hollow glass microspheres have a hollow structure and low density, but they are not thermally conductive. Therefore, when directly added to the thermally conductive adhesive layer, although the material density decreases, the thermal conductivity also decreases rapidly; the addition amount cannot exceed 5 wt%, otherwise the thermal conductivity and other properties will not meet the design requirements. Furthermore, since conventional hollow glass microspheres (and other similar organic material particles) are thermal insulation materials and have high oil absorption values, the viscosity of the components increases significantly when the addition amount is large. Although the density of the thermally conductive adhesive layer decreases, due to the poor compatibility between the resin and the glass microspheres, the thermal conductivity, shear strength, tensile strength, and elongation at break all decrease significantly with increasing addition amount. When the addition amount is greater than 5 wt%, these key properties cannot meet the design requirements, let alone an addition amount of 10 wt% or more.

[0153] Therefore, the amount, particle size, strength, and material compatibility of hollow glass microspheres have a crucial impact on the microstructure, processing technology, and final performance of the adhesive layer. If smaller hollow glass microspheres are used, their smaller hollow volume and higher density result in less effect on reducing the density of the adhesive layer. While larger hollow glass microspheres have lower density, allowing for a significant reduction in density with smaller additions, their structural characteristics (larger particle size and lower strength) result in a less dense distribution of the thermally conductive filler particles in the surrounding space, leaving numerous pores and failing to form effective three-dimensional thermal conductivity pathways, thus significantly decreasing the thermal conductivity. Furthermore, the lower compressive strength of larger hollow glass microspheres during production and use may cause breakage under strong external forces, potentially damaging equipment and degrading the performance of the thermally conductive adhesive.

[0154] The thermally conductive adhesive samples prepared in the above embodiments of the present invention have been tested under confidentiality and used in the manufacture of ternary lithium-ion battery modules, specifically for connecting and sealing the gap between two lithium-ion battery aluminum casings. Actual testing shows that this thermally conductive adhesive is superior to commercially available conventional 0.8W polyurethane thermally conductive structural adhesive (density 1.65–1.75 g / cm³). 3 With a thermal conductivity of 0.9~1.1W / (m•k), its density decreased by 15~20%, while the thermal conductivity remained at around 0.9W / (m•k), which effectively overcame the technical contradiction that the thermal conductivity and mechanical strength would rapidly decrease as the material density decreased.

[0155] In summary, the low-density, high-performance thermally conductive structural adhesive for power batteries and its preparation method provided in the above embodiments of the present invention, by selecting components and fillers of appropriate scale, form a unique three-dimensional thermally conductive microstructure with modified glass microspheres as the framework, long interpenetrating chains, multiple scales, and short pathways. This significantly reduces density by increasing the amount of modified glass microspheres used, while simultaneously maintaining many key properties of the thermally conductive structural adhesive, resulting in a thermally conductive adhesive layer with a density not exceeding 1.50 g / cm³. 3 Its low density and high thermal conductivity of not less than 0.84 W / (m•k) can meet the requirements of new energy vehicle lithium batteries for structural adhesives in terms of weight reduction, efficiency improvement and cost reduction.

[0156] It should be noted that the components, proportions, particle sizes and process parameters used in the above specific embodiments of the present invention are only examples. Other different implementation schemes obtained by making specific selections within the scope of the embodiments of the present invention can achieve the technical effects described in the present invention. Therefore, the present invention will not list them one by one.

[0157] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention using the methods and techniques disclosed above, or modify it into equivalent embodiments with equivalent changes, without departing from the scope of the present invention. All equivalent changes made to the components, proportions, and processes of the present invention should be covered within the protection scope of the present invention.

Claims

1. A low-density, high-performance thermally conductive structural adhesive for power batteries, characterized in that, It is made of the following components in the following proportions by weight: Component A: 20-40g polyol, 0.5-2.0g small molecule alcohol, 0.1-1g dehydrating agent, 60-75g aluminum hydroxide, 0.01-0.1g catalyst, 5-10g modified hollow glass microspheres; Component B: Diol 5-15, Highly active polyisocyanate 10-30, Aluminum hydroxide 60-75, Modified hollow glass microspheres 5-10; The highly active polyisocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, naphthalene-1,5-diisocyanate, and polymeric MDI; The modified hollow glass microspheres are prepared by surface modification of hollow glass microspheres with a particle size D50 = 40 μm using a coupling agent. The modification includes the following steps: (1) Dissolve 100 ml of titanate coupling agent in 900 ml of ethanol and stir until homogeneous to obtain coupling agent solution; (2) Take 100g of hollow glass microspheres and add them to the prepared coupling agent solution. Stir with an electric stirrer at 60r / min for 10min, and then sonicate for 10min. (3) Filter out the hollow glass microspheres and put them into an oven at 120°C for 120 min to obtain coupling agent surface modified hollow glass microspheres. The aluminum hydroxide is a solid particle with a particle size D50 of 5~30μm, which is one or a mixture of D50 = 5-10μm, 10-20μm, and 20-30μm; When used in combination, the mass ratio of component A to component B is 1:(0.8~1.2). In the thermally conductive adhesive layer after the mixture of components A and B has cured, small-molecule alcohols and diols participate in the crosslinking reaction of isocyanate and polyols to form a reinforced, long-chain interpenetrating network of polyurethane polymers. Modified hollow glass microspheres serve as the framework to construct the microscopic network structure within the thermally conductive adhesive layer. This uniformly and firmly coats the large-diameter modified hollow glass microspheres with small-diameter aluminum hydroxide particles. The pore distance between the edges of two adjacent modified hollow glass microspheres is smaller than the diameter of the microsphere. The aluminum hydroxide particles fill the pores around the modified hollow glass microspheres, forming short three-dimensional thermally conductive pathways. All components together form a nano- to micron-scale interpenetrating network and a three-dimensional thermally conductive structure in the cured thermally conductive adhesive layer, resulting in a thermal conductivity of no more than 1.50 g / cm³. 3 It has low density and high thermal conductivity with a thermal conductivity of not less than 0.84 W / (m•k).

2. The low-density, high-performance thermally conductive structural adhesive for power batteries according to claim 1, characterized in that: The polyol mentioned is one or more of polyolefin polyol, polyacrylate polyol, cashew nut shell oil bio-based modified polyol, and polymer polyol POP.

3. The low-density, high-performance thermally conductive structural adhesive for power batteries according to claim 1, characterized in that: The small molecule alcohols are selected from ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 2,4-pentanediol, 2-methyl-1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, etc. One or more of the following: alcohol, 2-methyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,4-butanediol, 1,2-octanediol, 3,6-octanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,7-dimethyl-3,6-octanediol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, hydroquinone-bis(β-hydroxyethyl) ether, trimethylolpropane, and trimethylolpropane monoallyl ether.

4. The low-density, high-performance thermally conductive structural adhesive for power batteries according to claim 1, characterized in that: The dehydrating agent is vinyltrimethoxysilane or methyltrimethoxysilane.

5. The low-density, high-performance thermally conductive structural adhesive for power batteries according to claim 1, characterized in that: Aluminum hydroxide is a thermally conductive filler, and it has one or more of the following particle sizes: D50 = 5-10 μm, D50 = 10-20 μm, and D50 = 20-30 μm.

6. The low-density, high-performance thermally conductive structural adhesive for power batteries according to claim 1, characterized in that: The catalyst is selected from one or more of organotin catalysts, organobismuth catalysts, organozinc catalysts, and organozirconium catalysts.

7. The low-density, high-performance thermally conductive structural adhesive for power batteries according to claim 1, characterized in that: The hollow glass microspheres have a particle size D50 of 40 μm, a compressive strength of 2000–6000 psi, and a density of 0.3–0.38 g / cm³. 3 .

8. The low-density, high-performance thermally conductive structural adhesive for power batteries according to claim 1, characterized in that: The diol is selected from one or more of polypropylene glycol, polytetrahydrofuran glycol, and modified cashew nut shell-soaked polyether diol.

9. A method for preparing the low-density, high-performance thermally conductive structural adhesive for power batteries according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Preparation of component A The measured polyol, small molecule alcohol, aluminum hydroxide, catalyst, and modified hollow glass microspheres are sequentially added to the reactor. The temperature is raised to 70-80℃ and stirred evenly. Then the temperature is raised to 100-130℃, and a vacuum below -90 kPa is drawn while stirring for 2-4 hours. When the temperature drops below 60℃, a dehydrating agent is added. Then, stirring is continued for 0.5-1 hours under a vacuum below -90 kPa before discharging. The product is then sealed and packaged to obtain component A. S2: Preparation of component B Diol is added to the reactor in proportion and dehydrated at 100-130℃ under vacuum below -90 kPa for 2-4 hours. After the temperature drops to below 50℃, highly active polyisocyanate is added and stirred and heated to 65-85℃. The reaction is carried out for 2-2.5 hours. Then aluminum hydroxide and modified hollow glass microspheres are added and stirred under vacuum below -90 kPa for 0.5-1 hours. The mixture is then discharged, sealed, and packaged to obtain component B. S3: Preparation of Hybrid Thermally Conductive Structural Adhesive The components A and B are packaged separately. When using, components A and B are mixed evenly at a mass ratio of 1:(0.8~1.2) and then coated on the connecting surface of the aluminum shell or plastic parts of the power lithium battery. S4: Preparation of thermally conductive adhesive layer The adhesive is cured at room temperature or 80°C to form a thermally conductive adhesive layer of a set thickness. The internal cross-linking reaction of the thermally conductive adhesive layer is enhanced by long-chain interpenetrating polyurethane polymer, which uses modified hollow glass microspheres as a framework to construct the microstructure within the thermally conductive adhesive layer. This ensures that the pore distance between the edges of two adjacent modified hollow glass microspheres is smaller than the diameter of the modified hollow glass microspheres. Aluminum hydroxide particles fill the pores around the modified hollow glass microspheres to form shorter three-dimensional thermally conductive pathways. The polyurethane polymer uniformly and firmly coats the modified hollow glass microspheres and the thermally conductive filler aluminum hydroxide particles, forming a long-chain interpenetrating network and a three-dimensional thermally conductive structure adhesive layer at the nano-micro scale. This bonds and seals the connecting surfaces, giving the thermally conductive adhesive layer both a low density of no more than 1.50 g / cm³ and a high thermal conductivity of no less than 0.84 W / (m·k).

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