Heat-conducting adhesive, heat-conducting bonding layer and new energy automobile power battery comprising heat-conducting bonding layer

Abstract

The invention provides a heat-conducting adhesive, a heat-conducting bonding layer and a new energy automobile power battery comprising the heat-conducting bonding layer. The thermally conductive adhesive comprises: 40-55 wt% of an epoxy resin; 5-12 wt% of a curing agent, wherein the curing agent is one or more of an aliphatic amine curing agent and an imidazole curing agent; 10-25 wt% of a thermally conductive filler; 3-8 wt% of a toughening agent; 2-6 wt% of a flame retardant; 1-3 wt% of a coupling agent; 0.5 to 2 wt% of an anti-aging agent; and an organic solvent. An adhesive layer formed by curing the heat-conducting adhesive has good mechanical strength and flexibility, can bear loads such as impact and vibration, resists thermal cycling and damp-heat aging, is good in heat conductivity and good in insulating property, is suitable for a new energy automobile power battery, and is particularly suitable for a CTP structure.

Description

TECHNICAL FIELD

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

[0002] With the rapid development of the new energy automobile industry, as a core component, the structural design and performance optimization of the power battery have become the focus of the industry. The CTP (Cell to Pack) structure directly integrates the battery cell into the battery pack by omitting the module shell, greatly improving the space utilization and energy density, and has become an important development direction of the power battery technology. However, the dense arrangement of the battery cell under the CTP structure leads to more complex heat dissipation paths, and the battery pack needs to withstand continuous vibration, impact and other dynamic loads during vehicle driving, which puts strict requirements on the internal connecting materials.

[0003] As a key material with both bonding and heat conduction functions in the CTP battery pack, the performance of the heat-conducting adhesive directly affects the safety and reliability of the battery. In the prior art, the traditional heat-conducting adhesive often has difficulty in balancing multiple performances: some products add a large amount of inorganic fillers to pursue high thermal conductivity, which increases the brittleness of the adhesive layer and reduces the mechanical strength, and interface peeling often occurs under vibration or impact conditions, which cannot achieve cohesive failure; while the adhesive with emphasis on flexibility often has low thermal conductivity due to insufficient filler ratio, which is difficult to meet the heat dissipation requirements of the CTP structure.

[0004] At the same time, the working environment of the power battery is complex and changeable, and it is subjected to temperature cycles of -40℃ to 80℃ for a long time, and faces aging factors such as high humidity and electrolyte evaporation. After long-term cold and hot cycles or humid heat aging, the existing adhesive is prone to problems such as degradation of the polymer chain, separation of the filler and the matrix interface, resulting in significant attenuation of the mechanical strength and thermal conductivity, and thus affecting the structural stability and thermal management efficiency of the battery pack.

[0005] In addition, the CTP structure has strict requirements on the insulation performance of the material to avoid the risk of short circuit between the battery cells. However, some existing heat-conducting adhesives introduce conductive fillers to improve thermal conductivity, which leads to a decrease in insulation performance and cannot meet the use standards of high dielectric strength and volume resistivity. Therefore, it is of great significance to develop a heat-conducting adhesive that can simultaneously meet the requirements of mechanical strength, flexibility, aging resistance, thermal conductivity and insulation performance, to promote the technical upgrading of the CTP structure power battery. SUMMARY

[0006] From the technical problems set forth above, the present application aims to provide a heat-conducting adhesive suitable for a car power battery pack (especially a CTP structure), which can simultaneously have good mechanical strength, flexibility, aging resistance, and suitable heat-conducting and insulating properties after curing to form an adhesive layer, thereby meeting the use requirements of the power battery.

[0007] Specifically, according to one aspect of the present application, a heat-conducting adhesive is provided, which comprises, based on the total weight thereof: 40-55 wt%, preferably 45-50 wt% of an epoxy resin having an epoxy value of 0.25-0.35 eq / 100 g and a viscosity of 2000-3500 mPa•s at 25°C; 5-12 wt%, preferably 8-10 wt% of a curing agent, which is one or more of a fatty amine curing agent and an imidazole curing agent; 10-25 wt%, preferably 15-22 wt% of a heat-conducting filler, which is a compound of nano-aluminum oxide and hexagonal boron nitride at a weight ratio of 1:1-2:1; 3-8 wt% of a toughening agent; 2-6 wt% of a flame retardant; 1-3 wt% of a coupling agent; 0.5-2 wt% of an anti-aging agent; and an organic solvent.

[0008] According to certain preferred embodiments of the present application, the epoxy resin is a modified epoxy resin obtained by grafting modification of a bisphenol A epoxy resin with a polyether polyol.

[0009] According to certain preferred embodiments of the present application, the bisphenol A epoxy resin has a number average molecular weight of 350-450 g / mol.

[0010] According to certain preferred embodiments of the present application, the polyether polyol is polyethylene glycol, polypropylene glycol, or a combination thereof, and the polyether polyol has a number average molecular weight of 400-1000 g / mol.

[0011] According to certain preferred embodiments of the present application, the fatty amine curing agent is selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, polyethylene polyamine, and isophorone diamine.

[0012] According to certain preferred embodiments of the present application, the imidazole curing agent is selected from the group consisting of imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenylimidazole.

[0013] According to some preferred embodiments of the present application, the curing agent is a complex of isophorone diamine and 2-methyl imidazole in a weight ratio of 3:1 to 2:1.

[0014] According to some preferred embodiments of the present application, the nano-aluminum oxide has a particle size of 50-100 nm and the hexagonal boron nitride has a particle size of 1-5 μm.

[0015] According to some preferred embodiments of the present application, the toughening agent is a core-shell structured acrylate elastomer.

[0016] According to some preferred embodiments of the present application, the flame retardant is a halogen-free phosphazene flame retardant, an inorganic nanoparticle flame retardant or a combination thereof.

[0017] According to some preferred embodiments of the present application, the flame retardant is a complex of hexaphenoxycyclotriphosphazene and nano-magnesium hydroxide in a weight ratio of 1:2 to 1:4.

[0018] According to some preferred embodiments of the present application, the nano-magnesium hydroxide has an average particle size of 50-100 nm.

[0019] According to some preferred embodiments of the present application, the coupling agent is selected from one or more of the group consisting of silane-based coupling agents, titanate-based coupling agents and aluminate-based coupling agents.

[0020] According to some preferred embodiments of the present application, the coupling agent is a complex of γ-aminopropyl triethoxysilane and isopropyl tri(dioctyl pyrophosphoryloxy) titanate in a weight ratio of 2:1 to 3:1.

[0021] According to some preferred embodiments of the present application, the anti-aging agent is tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester.

[0022] According to some preferred embodiments of the present application, the thermally conductive adhesive comprises 20-35 wt% of an organic solvent based on the total weight thereof.

[0023] According to some preferred embodiments of the present application, the organic solvent is selected from one or more of the group consisting of propylene glycol methyl ether acetate, methyl vinyl ketone, acetone, butanone, cyclohexanone, ethyl acetate, butyl acetate, isobutyl acetate, propylene glycol methyl ether acetate, toluene and xylene.

[0024] According to another aspect of the present application, there is provided a thermally conductive adhesive layer, which is cured from the thermally conductive adhesive described above.

[0025] According to some preferred embodiments of the present application, the thickness of the heat-conducting adhesive layer is 50-200 μm, preferably 80-150 μm.

[0026] According to yet another aspect of the present application, a new energy automobile power battery is provided, which comprises: an array of battery cells composed of a plurality of square or cylindrical battery cells in series or parallel connection; a heat-conducting adhesive layer; a cooling plate; and a housing, wherein: the heat-conducting adhesive layer is coated between the battery cells and between the battery cells and the cooling plate, and the housing accommodates the array of battery cells and the cooling plate.

[0027] According to some preferred embodiments of the present application, the thickness of the heat-conducting adhesive layer is 50-200 μm, preferably 80-150 μm.

[0028] According to some preferred embodiments of the present application, the new energy automobile power battery further comprises an insulating buffer layer disposed between the array of battery cells and the housing.

[0029] According to some preferred embodiments of the present application, the insulating buffer layer is formed of an epoxy resin-based material.

[0030] According to some preferred embodiments of the present application, the cooling plate is a metal plate with a circulating pipe inside.

[0031] According to some preferred embodiments of the present application, the cooling plate is an aluminum alloy plate, and the diameter of the circulating pipe is 3-5 mm. BRIEF DESCRIPTION OF DRAWINGS

[0032] In the present specification, the accompanying drawings are provided to more clearly explain the technical solutions of the present application, however, the present application is not limited thereto.

[0033] Figure 1 A schematic diagram of the packaging structure of a new energy automobile power battery according to one specific embodiment of the present application is shown. DETAILED DESCRIPTION

[0034] The present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It will be understood that other embodiments are contemplated, and can be practiced without departing from the scope or spirit of the present application. Therefore, the following detailed description is non-limiting.

[0035] All numbers expressing characteristics dimensions, quantities and ranges of values used in the specification are to be understood as being modified in all instances by the terms "about" unless otherwise indicated. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing 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.

[0036] 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.

[0037] As described above, existing thermal conductive adhesives are difficult to balance mechanical strength, flexibility, thermal conductivity and other properties. For example, high thermal conductivity products increase brittleness and decrease mechanical strength due to the addition of inorganic fillers, and are prone to interface peeling. Products focusing on flexibility have low thermal conductivity, which cannot meet the heat dissipation requirements of CTP structure. Moreover, existing adhesives have poor aging resistance, and their performance decays after cold and hot cycle, and some of them also have insufficient insulation performance due to the use of conductive fillers, which are difficult to adapt to CTP structure power batteries. The present application aims to solve the above technical problems.

[0038] In particular, according to one aspect of the present application, a thermal conductive adhesive is provided, which comprises, based on its total weight: 40-55 wt%, preferably 45-50 wt% of an epoxy resin, the epoxy resin having an epoxy value of 0.25-0.35 eq / 100g and a viscosity of 2000-3500 mPa•s at 25℃; 5-12 wt%, preferably 8-10 wt% of a curing agent, the curing agent being one or more of a fatty amine curing agent and an imidazole curing agent; 10-25 wt%, preferably 15-22 wt% of a thermal conductive filler, the thermal conductive filler being a complex of nano-aluminum oxide and hexagonal boron nitride at a weight ratio of 1:1-2:1; 3-8 wt% of a toughening agent; 2-6 wt% of a flame retardant; 1-3 wt% of a coupling agent; 0.5-2 wt% of an anti-aging agent; and an organic solvent.

[0039] As described above, the present application aims to provide a thermal conductive adhesive suitable for new energy automobile power batteries (especially CTP structure), which realizes the synergistic optimization of mechanical strength, flexibility, thermal conductivity, insulation and aging resistance by adjusting the type, ratio and performance parameters of each component.

[0040] According to the technical scheme of the present application, the heat-conducting adhesive of the present application is composed of epoxy resin, curing agent, heat-conducting filler, toughening agent, flame retardant, coupling agent, anti-aging agent and organic solvent based on the total weight. The selection and ratio of each component are not simply superimposed, but form a composite system with multiple functions through intermolecular interaction, interface regulation and performance complementation.

[0041] Specifically, the content of the epoxy resin is 40-55% by weight (preferably 45-50% by weight), and needs to satisfy the epoxy value of 0.25-0.35 eq / 100g and the viscosity of 2000-3500 mPa•s at 25°C.

[0042] The regulation of the epoxy value is of great significance. The epoxy value reflects the concentration of epoxy groups in the epoxy resin and is a key parameter affecting the degree of curing reaction and crosslinking density. In the present application, the epoxy value of the epoxy resin is 0.25-0.35 eq / 100g, too low crosslinking density, the strength and aging resistance of the adhesive layer are reduced; too high, the reaction activity is too strong, easy to lead to the curing speed is too fast, the internal stress is concentrated, and the flexibility is reduced.

[0043] According to the technical scheme of the present application, the viscosity of 2000-3500 mPa•s at 25°C not only ensures the flowability of the adhesive during coating (easy to uniformly coat on the surface of the battery cell and the cooling plate), but also avoids the filler settling or the adhesive layer being too thin due to too low viscosity. In the research of the present application, it is found that if the epoxy resin with too high viscosity is used, bubbles and uneven thickness will appear during coating, which will eventually reduce the heat-conducting performance and mechanical strength.

[0044] According to the preferred embodiment of the present application, a bisphenol A epoxy resin grafted and modified by polyether polyol is preferably used. Without being bound by theory, the bisphenol A epoxy resin itself has high mechanical strength but high brittleness; and the flexible segment of polyethylene glycol or polypropylene glycol introduced into the epoxy resin molecule through grafting reaction can improve the impact resistance of the adhesive layer through the dual mechanisms of "molecular chain flexibility improvement" and "crosslinking network toughening".

[0045] Preferably, the epoxy resin is a modified epoxy resin obtained by grafting and modifying bisphenol A epoxy resin with polyether polyol. Preferably, the number average molecular weight of the bisphenol A epoxy resin is 350-450 g / mol. Preferably, the polyether polyol is polyethylene glycol, polypropylene glycol or a combination thereof, and the number average molecular weight of the polyether polyol is 400-1000 g / mol.

[0046] According to some preferred embodiments of the present application, the content of the curing agent is 5-12 wt% (preferably 8-10 wt%), and is one or more of a fatty amine curing agent and an imidazole curing agent. The role of the curing agent is to react with the epoxy groups of the epoxy resin to form a three-dimensional cross-linked structure, the type and amount of which directly affect the curing speed, cross-linking density and final performance. Preferably, the fatty amine curing agent is selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetramine, polyethylene polyamine and isophorone diamine. Preferably, the imidazole curing agent is selected from the group consisting of imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole and 2-phenylimidazole.

[0047] Fatty amine curing agents (such as ethylenediamine, isophorone diamine) have high reactivity and can be rapidly cured at low temperature, but their use alone can lead to a large brittleness of the adhesive layer; imidazole curing agents (such as 2-methylimidazole, 2-phenylimidazole) have latent curing properties, can extend the pot life of the adhesive, and the adhesive layer after curing has better flexibility. Most preferably, the present application uses isophorone diamine and 2-methylimidazole in a weight ratio of 3:1-2:1, which not only ensures the curing efficiency (complete curing at 80℃ for 2h), but also makes the cross-linked network more uniform through the intermolecular interaction of the two curing agents, significantly improving the strength retention rate after aging at 55℃.

[0048] It has been found in the research of the present application that an insufficient amount of curing agent (such as less than 5 wt%) can lead to incomplete cross-linking of the epoxy resin, resulting in a decrease in the strength and solvent resistance of the adhesive layer; an excessive amount of curing agent (such as more than 12 wt%) can cause unreacted curing agent to remain as defect points, reducing the insulation performance and aging resistance of the adhesive layer.

[0049] According to the technical solution of the present application, the content of the heat-conducting filler is 10-25 wt% (preferably 15-22 wt%), and preferably a 1:1-2:1 weight ratio of nano-alumina and hexagonal boron nitride compound. The role of the heat-conducting filler is to form a continuous heat-conducting path in the adhesive layer, and the type, particle size and ratio thereof directly determine the thermal conductivity.

[0050] Without being bound by theory, nano-alumina has high thermal conductivity (thermal conductivity of 30 W / (m•K)) and good insulation, but the particles tend to agglomerate; hexagonal boron nitride has a layered structure and can inhibit the agglomeration of alumina. According to the research of the present application, when nano-alumina and hexagonal boron nitride are compounded in a weight ratio of 1:1-2:1, the nano-alumina is filled in the interlayer gaps of the hexagonal boron nitride, forming a "point-plane combined" heat-conducting network, which can significantly improve the thermal conductivity at 25℃.

[0051] According to the technical solutions of the present application, the content of the toughening agent is 3-8% by weight, preferably a core-shell structured acrylate elastomer. The core-shell structured acrylate elastomer (for example, a core layer of polybutadiene, a shell layer of polymethyl methacrylate, a particle size of 100-200 nm) has good compatibility with the epoxy resin, the polar groups of the shell layer can form hydrogen bonds with the epoxy resin, and the flexible chain segments of the core layer can absorb energy by deformation when impacted.

[0052] According to some technical solutions of the present application, the content of the flame retardant is 2-6% by weight, preferably a 1:2-1:4 weight ratio of hexaphenoxycyclotriphosphazene and nano-magnesium hydroxide compound. The flame retardant improves the flame retardant grade of the adhesive layer through the synergistic effect of inhibiting the combustion chain reaction (phosphazene type) and forming a flame retardant barrier (magnesium hydroxide). Specifically, hexaphenoxycyclotriphosphazene (phosphorus content 12%) decomposes to produce phosphate substances at high temperatures, which can inhibit the free radical chain reaction; nano-magnesium hydroxide (particle size 50-100 nm) decomposes to release water vapor upon heating, reducing the temperature of the combustion zone and forming a magnesium oxide protective layer. When the two are compounded at a ratio of 1:2 to 1:4, the limiting oxygen index (LOI) of the adhesive layer can reach 32% (difficult to burn), and no toxic gas is released during combustion (better than halogen-containing flame retardants).

[0053] According to some technical solutions of the present application, the content of the coupling agent is 1-3% by weight. Preferably, the coupling agent is selected from one or more of the group consisting of silane coupling agents, titanate coupling agents and aluminate coupling agents. More preferably, a 2:1-3:1 weight ratio of γ-aminopropyl triethoxysilane and isopropyl tri(dioctyl pyrophosphoryloxy) titanate compound. The coupling agent reacts with the surface of the thermally conductive filler (hydroxyl, carboxyl) and the epoxy resin matrix (epoxy group) through different functional groups at both ends of the molecule, improving the interfacial bonding force. Silane coupling agent (γ-aminopropyl triethoxysilane) has better modification effect on nano-alumina, and titanate coupling agent is more suitable for the layered structure of hexagonal boron nitride. The compound of the two can improve the dispersibility of the filler in the matrix, reduce the interfacial thermal resistance, thereby further improve the thermal conductivity and improve the tensile shear strength of the adhesive layer.

[0054] Critical value of the amount: insufficient coupling agent (such as less than 1% by weight) has limited modification effect; excessive amount (such as more than 3% by weight) can form a "weak boundary layer" at the interface, which can actually reduce the bonding force.

[0055] According to some technical solutions of the present application, the anti-aging agent is tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester (i.e., antioxidant 1010), with a content of 0.5-2% by weight. Its role is to capture free radicals and inhibit the oxidative degradation of the molecular chain of the epoxy resin, especially under high temperature (55°C) and humid heat environment.

[0056] According to some embodiments of the present application, the content of the organic solvent is 20-35 wt%. Preferably, the organic solvent is selected from one or more of the group consisting of propylene glycol methyl ether acetate, methyl vinyl ketone, acetone, butanone, cyclohexanone, ethyl acetate, butyl acetate, isobutyl acetate, propylene glycol methyl ether acetate, toluene and xylene. The role of the organic solvent is to reduce the viscosity of the adhesive, facilitate coating (such as spraying, scraping), and volatilize during the curing process without leaving residues in the adhesive layer. The present application preferably uses low-toxicity, high-boiling point (100-150°C) solvents (such as propylene glycol methyl ether acetate), which not only ensure the flowability during coating, but also slowly volatilize during hot air drying at 60°C, avoiding the generation of bubbles in the adhesive layer due to too fast volatilization.

[0057] According to another aspect of the present application, a thermally conductive adhesive layer is provided, which is formed by curing the thermally conductive adhesive described above, and has a thickness of 50-200 μm (preferably 80-150 μm). This thickness range can ensure sufficient mechanical strength and continuity of the thermal conduction path, and will not cause too large a gap between the battery cells (suitable for the compact design of the CTP structure) due to excessive thickness.

[0058] According to still another aspect of the present application, a new energy vehicle power battery is provided, which comprises: an array of battery cells, which is composed of a plurality of square or cylindrical battery cells in series or parallel connection; the thermally conductive adhesive layer described above; a cooling plate; and a housing, wherein: the thermally conductive adhesive layer is coated between the battery cells and between the battery cells and the cooling plate, and the housing contains the array of battery cells and the cooling plate.

[0059] Figure 1 A schematic diagram of the packaging structure of a new energy vehicle power battery 100 according to one specific embodiment of the present application is shown. As shown in FIG. 1, Figure 1 the new energy vehicle power battery 100 comprises: an array of battery cells 1; a thermally conductive adhesive layer 2; a cooling plate 3; and a housing 4, the thermally conductive adhesive layer 2 is coated between the battery cells and between the battery cells and the cooling plate 3, and the housing 4 contains the array of battery cells 1 and the cooling plate 3. It should be noted that, Figure 1 The relative positions of the various components in the new energy vehicle power battery 100 are shown for illustrative purposes only, but by no means limit their relative sizes or proportions.

[0060] Specifically, the heat-conducting adhesive layer is coated between the battery cells and the cooling plate to conduct the heat generated by the battery cells during operation through the path of "battery cell-adhesive layer-cooling plate". Preferably, the cooling plate is an aluminum alloy plate with an internal diameter of 3-5 mm circulating pipeline, and the maximum temperature of the battery cell can be controlled below 45℃ when the flow rate of the cooling liquid is 1 L / min. Preferably, the thickness of the heat-conducting adhesive layer is 50-200 μm, preferably 80-150 μm. Preferably, the new energy vehicle power battery further comprises an insulating buffer layer arranged between the array of battery cells and the shell. Preferably, the insulating buffer layer is formed of an epoxy resin material.

[0061] Compared with the prior art, the heat-conducting adhesive, the heat-conducting adhesive layer and the new energy vehicle power battery comprising the heat-conducting adhesive layer according to the present application have the following advantages: 1. The epoxy resin is grafted and modified and matched with a specific curing agent to ensure good mechanical strength and flexibility. The heat-conducting filler composed of nano-aluminum oxide and hexagonal boron nitride significantly improves the heat conductivity.

[0062] 2. The heat-conducting adhesive layer cured from the above-mentioned adhesive has good mechanical strength, flexibility, aging resistance, heat conductivity and insulation, can effectively withstand impact, vibration and other loads, and is resistant to cold and hot cycles and damp heat aging, thereby ensuring the stability of the battery structure and the efficiency of thermal management.

[0063] 3. The new energy vehicle power battery according to the present application has high reliability. Specifically, the array of battery cells is connected to the cooling plate through the heat-conducting adhesive layer, which can efficiently dissipate heat, maintain the appropriate working temperature of the battery cells, and improve the safety, reliability and service life of the battery as a whole.

[0064] The present application will be described in more detail with reference to the following examples. It should be noted that these descriptions and examples are intended to facilitate the understanding of the present application, but not to limit the present application.

[0065] 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".

[0066] Performance test method The heat-conducting adhesive prepared in the following examples and comparative examples was respectively tested for normal temperature service reliability, heat-conducting performance, insulation performance and salt spray corrosion resistance by the following detailed description.

[0067] Normal temperature service reliability test 25℃ dynamic shear strength test: refer to GB / T 7124-2021 "Adhesives - Determination of tensile shear strength (rigid material to rigid material)", take the adhesive composition sample prepared by the following examples or comparative examples, coat between the aluminum alloy substrate for power battery (size 100mmx25mmx2mm) and the battery module simulation substrate (size 100mmx25mmx3mm), control the adhesive layer thickness to be 30μm, dry for 1h at 60℃ hot air, 30min at 100℃ vacuum curing. Using a universal testing machine, test the shear strength at a tensile rate of 5mm / min, test 5 times in each group, take the average value.

[0068] 55℃ strength retention rate test: place the above cured shear sample in a 55℃ constant temperature box, static for 1000h, take out and balance for 2h in a 25℃ environment, test the shear strength at the same tensile rate, calculate the ratio of the strength after 55℃ aging and the initial 25℃ strength (i.e. strength retention rate).

[0069] Full temperature range (-40℃-55℃) cycle stability test: place the shear sample in a high-low temperature cycle box, 1 cycle according to -40℃ (2h of heat preservation)→ heating to 55℃ (2h of heat preservation). A total of 500 cycles. After the cycle is completed, test the 25℃ dynamic shear strength, calculate the ratio with the initial strength.

[0070] 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 power battery normal temperature work.

[0071] Good: 25℃ dynamic shear strength is 2.5-3.1MPa, 55℃1000h strength retention rate is 75%-84%, 500 times full temperature range cycle strength retention rate is 70%-79%, can meet the requirements of power battery normal temperature service.

[0072] Poor: 25℃ dynamic shear strength<2.5MPa, 55℃1000h strength retention rate<75%, 500 times full temperature range cycle strength retention rate<70%, prone to module displacement, interface peeling, cannot meet the requirements of power battery normal temperature service.

[0073] Thermal conductivity test The adhesive compositions prepared in the following examples or comparative examples were coated on a polyimide film substrate to a thickness of 50 μm, dried at 60 °C by hot air for 1 h, and dried at 100 °C under vacuum for 30 min to form an adhesive layer sample. The thermal conductivity of the adhesive layer was measured at two temperature points of 25 °C and 55 °C according to GB / T 22588-2008 "Measurement of thermal diffusivity or thermal conductivity by flash method", using a laser flash thermal conductivity instrument, and each group was tested in triplicate, and the average value was taken.

[0074] Evaluation criteria: Excellent: thermal conductivity at 25 °C ≥ 2.3 W / (m•K), thermal conductivity at 55 °C ≥ 2.5 W / (m•K), which well meets the fast-charging heat dissipation requirements of power batteries; Good: thermal conductivity at 25 °C 1.8-2.2 W / (m•K), thermal conductivity at 55 °C 2.0-2.4 W / (m•K), which can meet the fast-charging heat dissipation requirements of power batteries; Poor: thermal conductivity at 25 °C < 1.8 W / (m•K), thermal conductivity at 55 °C < 2.0 W / (m•K), which easily leads to local overheating of the battery and cannot meet the heat dissipation requirements of the package.

[0075] Insulation performance test The heat-conducting adhesive prepared in the following examples or comparative examples was cured into a film sample with a thickness of 100 μm, and cut into a square of 100 mm x 100 mm. The dielectric strength was tested using a dielectric strength tester (compliant with GB / T 1408.1-2016 standard), in which the sample was placed between two circular copper electrodes (diameter 50 mm) with a spacing consistent with the thickness of the sample, an alternating current voltage of 50 Hz was applied at a voltage increasing rate of 1 kV / s, and the voltage value at the breakdown of the sample was recorded, and the average value of 5 tests was taken as the dielectric strength (kV / mm). In addition, the volume resistivity was tested using a high resistance meter (compliant with GB / T 1410-2006 standard), in which a three-electrode system was used, a direct current voltage of 500 V was applied to the surface of the sample, and the resistance value was measured after standing for 1 min, and the volume resistivity (Ω•cm) was calculated according to the size of the sample, and the average value of 3 tests was taken.

[0076] Evaluation criteria: Excellent: dielectric strength ≥ 20 kV / mm, volume resistivity ≥ 1 x 10 14 Ω•cm; Good: dielectric strength ≥ 15 kV / mm and < 20 kV / mm, volume resistivity ≥ 1 x 10 13 Ω•cm and < 1 x 10 14 Ω•cm; Poor: dielectric strength < 15 kV / mm, volume resistivity < 1 x 10 13 Ω•cm.

[0077] Salt fog 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 by hot air at 60°C for 1 h, vacuum dried at 100°C for 30 min, and cured 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 a 5% sodium chloride solution (pH 6.5-7.2), a constant temperature of 35°C, a spray amount of 1.5 mL / (h•cm²), and a salt spray test was performed for 1000 h. 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.

[0078] Evaluation criteria: Excellent: After 1000 h of salt spray, the adhesive layer has no blistering, peeling, discoloration, the grid test (grid spacing 1 mm) has an adhesion of 0 grade, and meets the outdoor and high humidity environment use requirements of power batteries; Good: After 1000 h of salt spray, the adhesive layer has slight discoloration at the edge, no blistering and peeling, and the grid adhesion is grade 1; Poor: After 1000 h of salt spray, the adhesive layer has blistering, peeling or obvious discoloration, and the grid adhesion is ≥ grade 2, which cannot meet the salt spray corrosion resistance requirements of power batteries.

[0079] Preparation Example 1 (Preparation of Epoxy Resin 1) A 500 mL four-necked flask equipped with a stirrer, thermometer and reflux condenser was charged with 100 g of bisphenol A epoxy resin (number average molecular weight about 390-400 g / mol, determined by gel permeation chromatography) and 50 g of ethyl acetate, and the temperature was raised to 80°C while stirring to completely dissolve the epoxy resin. 30 g of polyethylene glycol (number average molecular weight about 600 g / mol, determined by end group titration) and 1.5 g of boron trifluoride ether solution were added to the flask, and after stirring, the temperature was raised to 110°C and the reaction was carried out for 3 h. After the reaction was completed, the temperature was lowered to 60°C, 5 g of deionized water was added to terminate the reaction, and after stirring for 30 min, the layers were separated and the water phase was removed. The organic phase was distilled under reduced pressure (temperature 80°C, vacuum degree -0.09 MPa) to remove residual solvents and water, and a light yellow transparent epoxy resin 1 was obtained.

[0080] In addition, the epoxy value was tested by acid-base titration method. Specifically, 1.5 g of the epoxy resin 1 sample was weighed into a 250 mL conical flask, 25 mL of hydrochloric acid-acetone solution (hydrochloric acid to acetone in a volume ratio of 1:40) was added, and after sealing, it was left to stand for 1 h; 3 drops of phenolphthalein indicator were added, and titrated with 0.1 mol / L sodium hydroxide standard solution until the solution turned pink and remained colorless for 30 s, while a blank test was performed. The epoxy value was calculated to be 0.30 eq / 100 g.

[0081] In addition, viscosity determination was performed using a rotational viscometer. The epoxy resin 1 sample was placed in a 25°C constant temperature water bath for 30 min, and the viscosity was determined at a rotation speed of 12 r / min, and the viscosity was measured to be 2800 mPa•s.

[0082] Preparation Example 2 (Preparation of epoxy resin 2) In a 500 mL four-necked flask equipped with a stirrer, a thermometer, and a reflux condenser, 100 g of bisphenol A epoxy resin (number average molecular weight of about 380-390 g / mol, determined by gel permeation chromatography) and 50 g of ethyl acetate were added, and the temperature was raised to 80°C while stirring to completely dissolve the epoxy resin. 25 g of polyethylene glycol (number average molecular weight of about 800 g / mol, determined by end group titration) and 1.2 g of boron trifluoride ether solution were added to the flask, and after stirring, the temperature was raised to 110°C and the reaction was maintained for 3 h. After the reaction was completed, the temperature was lowered to 60°C, 5 g of ionized water was added to terminate the reaction, and after stirring for 30 min, the layers were separated, and the aqueous phase was removed. The organic phase was distilled under reduced pressure (temperature 80°C, vacuum degree -0.09 MPa) to remove residual solvents and moisture, and a light yellow transparent modified epoxy resin 2 was obtained. The epoxy value tested by the acid-base titration method described in Preparation Example 1 above was 0.28 eq / 100 g. The viscosity measured by the rotational viscometer method described in Preparation Example 1 above was 3200 mPa•s.

[0083] Example 1 (E1) In a stirred tank equipped with a high-speed disperser, 400 g of epoxy resin 1 and 220 g of propylene glycol methyl ether acetate were added, and stirring was started (800 r / min), and the system was uniformly dispersed for 10 min. 200 g of thermally conductive filler (nanometer alumina (average particle size about 100 nm) 133.3 g, hexagonal boron nitride (average particle size about 2 μm) 66.7 g) and 10 g of γ-aminopropyl triethoxysilane were sequentially added to the stirred tank, and the temperature was raised to 50°C, and high-speed dispersion was carried out at 1500 r / min for 30 min to fully wet and disperse the filler. The temperature was lowered to 30°C, 30 g of core-shell structured acrylate elastomer (core layer: polybutadiene, shell layer: polymethyl methacrylate, average particle size about 100-200 nm), 50 g of hexaphenoxy cyclotriphosphazene and 10 g of antioxidant 1010 (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester) were added, and stirring was carried out at 1000 r / min for 20 min, and the mixture was uniformly mixed. Finally, 80 g of 2-methylimidazole was added, and stirring was continued at 800 r / min for 15 min to obtain a uniform, non-precipitated viscous liquid, which was the thermally conductive adhesive 1.

[0084] The thermally conductive adhesives 1 were tested according to the methods of room temperature service reliability, thermal conductivity, insulation performance, and salt spray corrosion resistance described in detail above, and the test results are shown in Table 1 below.

[0085] Examples 2-8 (E2-E8) The operation was carried out in a similar manner to Example 1 to prepare thermally conductive adhesives 2-8, except that only the types and proportions of the various components were adjusted as shown in Table 1 below.

[0086] The thermally conductive adhesives 2-8 were tested according to the methods of room temperature service reliability, thermal conductivity, insulation performance, and salt spray corrosion resistance described in detail above, and the test results are shown in Table 1 below.

[0087] Comparative Example 1 (CE1) The operation was carried out in a similar manner to Example 1 to prepare comparative thermally conductive adhesive 1, except that JEf-0212 (epoxy value about 0.40-0.45 eq / 100 g, purchased from Changshu Jiafei Chemical Co., Ltd.) was used instead of epoxy resin 1.

[0088] Comparative Example 2 (CE2) The operation was carried out in a similar manner to Example 1 to prepare comparative thermally conductive adhesive 2, except that Araldite ® GY 260 (viscosity about 12000 mPa•s, purchased from Huntsman Advanced Materials) was used instead of epoxy resin 1.

[0089] Comparative Examples 3-5 (CE3-CE5) The operation was carried out in a similar manner as in Example 1 to prepare comparative thermal conductive adhesives CE3-CE5, except that the type and ratio of each component were adjusted as shown in Table 1 below.

[0090] According to the methods of normal temperature service reliability, thermal conductivity, insulation performance, and salt spray corrosion resistance described in detail above, the thermal conductive adhesives CE3-CE5 were tested and the test results are shown in Table 1 below.

[0091] Table 1 Formulation of thermal conductive adhesives of Examples 1-8 (E1-E8) and Comparative Examples 1-5 (CE1-CE5) and performance test results

[0092] As can be seen from the results of Table 1 above, the thermal conductive adhesives of Examples 1-8 within the scope of the present application all meet the requirements of new energy automobile power batteries on the normal temperature service reliability, thermal conductivity, insulation performance, and salt spray corrosion resistance of the thermal conductive adhesive (especially suitable for CTP structure).

[0093] Comparative Example 1 uses JEf-0212 epoxy resin with an epoxy value of 0.40-0.45 eq / 100g, and after curing, the crosslinking density is too large, the adhesive layer is brittle, the shear strength at 25°C is only 2.0 MPa, and the strength retention rate after cold and hot cycles decreases to 60%, which cannot meet the dynamic load requirements.

[0094] Comparative Example 2 uses Araldite GY 260 with a viscosity of 12000 mPa•s, and after coating, the adhesive layer thickness is uneven (locally up to 300 μm), the thermal conduction path is blocked, the thermal conductivity coefficient at 25°C is only 1.5 W / (m•K), which leads to local overheating of the battery cell. ® GY 260 with a viscosity of 12000 mPa•s, and after coating, the adhesive layer thickness is uneven (locally up to 300 μm), the thermal conduction path is blocked, the thermal conductivity coefficient at 25°C is only 1.5 W / (m•K), which leads to local overheating of the battery cell.

[0095] The epoxy resin content of Comparative Example 3 is 30% by weight, the matrix cannot completely wrap the thermal conductive filler, the interface defects increase, the strength retention rate after 55°C aging is only 65%, and adhesive layer peeling occurs in the salt spray test.

[0096] When the epoxy resin content of Comparative Example 4 is 60% by weight, the proportion of thermal conductive filler is relatively insufficient, the thermal conductivity coefficient decreases to 1.7 W / (m•K), which cannot meet the heat dissipation requirements of CTP structure.

[0097] The curing agent content of Comparative Example 5 is 20%, the residual free amine leads to a decrease in the volume resistivity of the adhesive layer to 1×10¹² Ω•cm, the insulation performance is not up to standard, and there is a risk of short circuit.

[0098] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the spirit or scope of the disclosure. Thus, it is intended that the present disclosure cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.

Claims

1. A thermally conductive adhesive, characterized in that, The thermally conductive adhesive comprises, based on its total weight: 40-55% by weight of epoxy resin, wherein the epoxy value of the epoxy resin is 0.25-0.35 eq / 100g and the viscosity at 25°C is 2000-3500 mPa•s; 5-12% by weight of curing agent, wherein the curing agent is one or more of fatty amine curing agents and imidazole curing agents; 10-25% by weight of thermally conductive filler, wherein the thermally conductive filler is a compound of nano-alumina and hexagonal boron nitride in a weight ratio of 1:1-2:1; 3-8% by weight toughening agent; 2-6% by weight of flame retardant; 1-3% by weight of coupling agent; 0.5-2% by weight of anti-aging agent; and Organic solvents.

2. The thermally conductive adhesive according to claim 1, characterized in that, The epoxy resin is a modified epoxy resin obtained by grafting bisphenol A epoxy resin with polyether polyol, wherein the number average molecular weight of the bisphenol A epoxy resin is 350-450 g / mol; the polyether polyol is polyethylene glycol, polypropylene glycol or a combination thereof, and the number average molecular weight of the polyether polyol is 400-1000 g / mol.

3. The thermally conductive adhesive according to claim 1, characterized in that, The fatty amine curing agent is selected from the group consisting of: ethylenediamine, diethylenetriamine, triethylenetetramine, polyethylenepolyamine, and isophoronediamine, and the imidazole curing agent is selected from the group consisting of: imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenylimidazole.

4. The thermally conductive adhesive according to claim 1, characterized in that, The toughening agent is a core-shell structured acrylate elastomer.

5. The thermally conductive adhesive according to claim 1, characterized in that, The flame retardant is a halogen-free phosphazene flame retardant, an inorganic nanoparticle flame retardant, or a combination thereof.

6. The thermally conductive adhesive according to claim 1, characterized in that, The coupling agent is selected from one or more of the following groups: silane coupling agents, titanate coupling agents, and aluminate coupling agents.

7. The thermally conductive adhesive according to claim 1, characterized in that, The anti-aging agent is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid].

8. The thermally conductive adhesive according to claim 1, characterized in that, The thermally conductive adhesive contains 20-35% by weight of organic solvent based on its total weight.

9. A thermally conductive adhesive layer, characterized in that, The thermally conductive adhesive layer is formed by curing the thermally conductive adhesive according to any one of claims 1-8, wherein the thickness of the thermally conductive adhesive layer is 50-200 μm.

10. A power battery for new energy vehicles, characterized in that, The new energy vehicle power battery includes: A cell array, wherein the cell array is composed of multiple square or cylindrical cells connected in series or in parallel; A thermally conductive adhesive layer, wherein the thermally conductive adhesive layer is cured from the thermally conductive adhesive according to any one of claims 1-8; Cooling plate; and The shell, wherein: The thermally conductive adhesive layer is coated between the cells and between the cells and the cooling plate, and the housing accommodates the cell array and the cooling plate.

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