Aluminum-carbon connection interface enhancing structure and method for battery shell

Abstract

The invention belongs to the technical field of battery pack processing, and relates to an aluminum-carbon connection interface reinforcing structure and method for a battery shell, and the aluminum-carbon connection interface reinforcing method comprises the following steps: (1) carrying out surface activation treatment on an aluminum alloy frame, and then coating a functional middle layer to obtain a frame to be bonded; the functional middle layer is prepared from the following raw materials: nano reinforced particles and a toughening agent; and (2) applying pressure to the carbon fiber upper cover subjected to surface modification treatment and the to-be-bonded frame obtained in the step (1) by adopting a structural adhesive, and curing to form the aluminum-carbon connection interface reinforcing structure. According to the invention, a multi-stage interface treatment mechanism with synergistic effects of corrosion protection, mechanical interlocking and chemical bonding is adopted, so that the interface strength, toughness and long-term durability of connection are remarkably improved, and the strict requirements of a high-performance electric vehicle battery pack on light weight, high safety and long service life are met.

Description

Technical Field

[0001] This invention belongs to the field of battery pack processing technology, and relates to an aluminum-carbon interface reinforcement structure and method for battery casing. Background Technology

[0002] As the heaviest single component of an electric vehicle, the battery pack's lightweight design is crucial for improving the vehicle's energy density and driving range. Carbon fiber reinforced composites, due to their superior specific strength, specific modulus, fatigue resistance, and corrosion resistance, are considered ideal materials for achieving battery pack lightweighting. Using carbon fiber composites to manufacture the battery pack cover not only significantly reduces weight but also reduces the number of parts through an integrated design, while effectively improving the battery pack's protection under extreme conditions such as collisions.

[0003] Currently, the industry generally adopts a hybrid structure of "carbon fiber top cover + metal frame". Achieving a high-performance and high-reliability connection between the carbon fiber top cover and the aluminum alloy frame is a key link to ensure the overall sealing, structural integrity and long-term durability of the battery pack.

[0004] For joining dissimilar materials such as carbon fiber composites and aluminum alloys, the mainstream methods include mechanical joining and adhesive bonding. Mechanical joining achieves connection through physical fastening, but this method disrupts fiber continuity, increases weight and cost, and the direct contact between carbon fiber and aluminum alloy makes them susceptible to galvanic corrosion in humid environments, accelerating joint failure. CN119634655A discloses a riveting and welding process that uses an improved riveting and welding technique to join ultra-high strength steel, aluminum plates, and carbon fiber to solve the problem of difficult multi-layer dissimilar plate joining, but it still does not completely avoid mechanical damage and potential corrosion problems to the composite material. Adhesive bonding can achieve surface bonding, avoid stress concentration, and provide good sealing and vibration damping performance, but ordinary adhesive bonding cannot overcome the weak interfacial bonding caused by the huge differences in physical and chemical properties between carbon fiber and aluminum. Existing improvement research mainly focuses on single-level optimization such as surface pretreatment and adhesive modification, with limited synergistic effects on improving interfacial strength, toughness, and long-term durability, especially in addressing problems such as thermal stress caused by mismatch in the coefficients of thermal expansion of the materials and interfacial degradation under long-term environmental aging.

[0005] In summary, to address the connection problem between the carbon fiber top cover and the aluminum alloy frame, there is an urgent need to develop a novel connection method that can synergistically enhance the interface bonding, effectively release thermal stress, and resist aging in complex environments. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an aluminum-carbon interface reinforcement structure and method for battery casings. It employs a multi-level interface treatment mechanism that combines corrosion protection, mechanical interlocking, and chemical bonding, which significantly improves the interface strength, toughness, and long-term durability of the connection, thereby meeting the stringent requirements of high-performance electric vehicle battery packs for lightweight, high safety, and long lifespan.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for enhancing the aluminum-carbon interface for a battery casing, the method comprising the following steps:

[0009] (1) The aluminum alloy frame is surface activated and then coated with a functionalized intermediate layer to obtain the frame to be bonded; the raw materials of the functionalized intermediate layer include nano-reinforcing particles and toughening agents.

[0010] (2) The surface-modified carbon fiber cover is pressed and bonded to the frame to be bonded in step (1) using structural adhesive. After curing, an aluminum-carbon interface reinforcement structure is formed.

[0011] The aluminum-carbon interface enhancement method for battery casings provided by this invention significantly improves the interface strength, toughness, and long-term durability of the connection through innovative surface activation, functionalized intermediate layer design, and multi-scale interface enhancement mechanism. By introducing a functionalized interlayer between the aluminum alloy frame and the structural adhesive layer, this interlayer simultaneously acts on three key interfaces: aluminum alloy / functionalized interlayer, functionalized interlayer / adhesive, and adhesive / carbon fiber. Part of this interlayer penetrates into the micropores of the activated layer on the aluminum alloy frame surface, forming an interlocking structure. The dispersed nano-reinforcing particles within this interlayer form microscopic interlocks with the polymer penetrating the micropores, and simultaneously form a dense reinforcing network in the functionalized interlayer body and the region near the adhesive layer. The dispersed toughening agent within this interlayer significantly improves the fracture toughness and impact resistance of the interface. The resulting aluminum-carbon interface reinforcement structure achieves a multi-scale synergistic reinforcement interface in the interface region, characterized by "mechanical interlocking (activated layer micropores / polymer penetration) - chemical bonding (structural adhesive / functionalized interlayer / activated aluminum alloy frame surface) - nano-reinforcement (nanoparticle network) - toughening (toughening agent phase)," thus solving the problems of thermal mismatch, weak interfaces, and easy aging.

[0012] It should be noted that the present invention does not limit the aluminum alloy grade of the aluminum alloy frame described in step (1). Those skilled in the art can make an adaptive selection according to the actual application scenario, such as 6061-T6, 7075, etc.

[0013] Preferably, the surface activation treatment in step (1) includes sequential alkaline washing and degreasing, acid washing and activation, and oxidation treatment.

[0014] Preferably, the alkaline washing and degreasing temperature is 60-70℃ and the time is 5-10 minutes.

[0015] The alkaline washing and degreasing process can remove surface oil stains from the aluminum alloy frame.

[0016] The alkaline washing and degreasing temperature is 60-70℃, for example, it can be 60℃, 62℃, 65℃, 68℃ or 70℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] The alkaline washing and degreasing time is 5-10 minutes, for example, it can be 5 minutes, 6 minutes, 8 minutes, 9 minutes or 10 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the alkaline solution used for alkaline washing and degreasing includes a NaOH solution with a concentration of 40-60 g / L, such as 40 g / L, 45 g / L, 50 g / L, 55 g / L or 60 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, after alkaline washing and degreasing and before acid washing and activation, the process further includes a step of rinsing with deionized water until the water film is continuous.

[0020] Preferably, the pickling activation temperature is 15-30℃ and the time is 30-60 min.

[0021] The pickling and activation step can remove the oxide layer and micro-etch the surface.

[0022] The pickling activation temperature is 15-30℃, for example, it can be 15℃, 18℃, 20℃, 25℃ or 30℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] The pickling and activation time is 30-60 min, for example, it can be 30 min, 35 min, 40 min, 50 min or 60 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the acid solution used for pickling and activation includes a mixture of nitric acid and hydrofluoric acid in a volume ratio of (9-11):1, for example, it can be 9:1, 9.5:1, 10:1, 10.5:1 or 11:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the step of washing and drying is included after the pickling activation and before the oxidation treatment, wherein the drying includes drying with compressed air or drying at 80°C for 10 minutes.

[0026] Preferably, the oxidation treatment includes micro-arc oxidation or anodic oxidation, with micro-arc oxidation being the preferred method.

[0027] The micro-arc oxidation can form a thicker, more porous, and harder activation layer that is metallurgically bonded to the substrate. This activation layer has an extremely high specific surface area and reactivity, laying the foundation for the subsequent formation of strong mechanical interlocking and providing anchoring points for nanoparticles.

[0028] Preferably, the electrolyte used in the micro-arc oxidation comprises a mixture of a Na2SiO3·9H2O solution with a concentration of 9-11 g / L and a KOH solution with a concentration of 1-3 g / L, with deionized water as the solvent and a temperature of 20-40°C.

[0029] The concentration of the Na2SiO3·9H2O solution is 9-11 g / L, for example, it can be 9 g / L, 9.5 g / L, 10 g / L, 10.5 g / L or 11 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] The concentration of the KOH solution is 1-3 g / L, for example, it can be 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L or 3 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The temperature is 20-40℃, for example, it can be 20℃, 25℃, 30℃, 35℃ or 40℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the micro-arc oxidation uses a bipolar pulse power supply with a positive voltage of 450V, a negative voltage of 80V, a frequency of 500Hz, and a duty cycle of 30%.

[0033] Preferably, the micro-arc oxidation time is 28-32 min, for example, it can be 28 min, 29 min, 30 min, 31 min or 32 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] The electrolyte needs to be circulated and cooled during the micro-arc oxidation process.

[0035] Preferably, the thickness of the film formed after micro-arc oxidation is 20-30 μm, the microhardness is >800 HV, the porosity is 30-45%, and the average pore size is 1-3 μm.

[0036] The thickness of the film formed after micro-arc oxidation is 20-30 μm, for example, it can be 20 μm, 22 μm, 25 μm, 28 μm or 30 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] The microhardness of the film formed after micro-arc oxidation is >800HV, for example, it can be 820HV, 850HV, 880HV, 900HV or 920HV, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] The porosity of the film formed after micro-arc oxidation is 30-45%, for example, it can be 30%, 35%, 38%, 40% or 45%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] The average pore size of the film formed after micro-arc oxidation is 1-3 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, by weight, the raw material components of the functionalized intermediate layer in step (1) include: 95-105 parts of polymer matrix, 7-9 parts of nano-reinforcing particles, 18-22 parts of toughening agent, 1-3 parts of coupling agent, 0.7-0.9 parts of dispersant, and 4-6 parts of curing agent.

[0041] In the raw material components of the functionalized intermediate layer, the polymer matrix plays a role in bonding and supporting the matrix, requiring the selection of a resin with good compatibility with subsequent structural adhesives. The core functions of the nano-reinforcing particles are: 1) Strengthening the network: uniformly dispersed in the matrix, forming a rigid reinforcing network, improving the modulus and strength of the functionalized intermediate layer itself, and constraining polymer deformation; 2) Stress transfer and redistribution: acting as a rigid "bridge," improving the transfer of stress from the high-modulus aluminum alloy to the low-modulus polymer / adhesive layer, and helping to homogenize the interfacial stress distribution and alleviate stress concentration; 3) Crack deflection and pinning: hindering crack propagation. 4) Reduce the coefficient of thermal expansion: The addition of high modulus particles can reduce the overall coefficient of thermal expansion of the functionalized intermediate layer, which can alleviate the mismatch between the coefficient of thermal expansion and that of aluminum alloy to a certain extent; The core role of toughening agent is: 1) Induce crazes / shear bands: Under stress, induce a large amount of energy dissipation mechanism, which significantly improves the interfacial toughness and impact resistance; 2) Reduce stress concentration: Improve the plastic deformation ability of polymer matrix and passivate the stress at the crack tip; 3) Improve low temperature performance; Coupling agent can further promote the chemical bonding between functionalized intermediate layer and active layer, and between functionalized intermediate layer and adhesive.

[0042] The polymer matrix in the raw material components of the functionalized intermediate layer is 95-105 parts by weight, for example, 95 parts, 98 parts, 100 parts, 102 parts or 105 parts, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] The weight percentage of nano-reinforcing particles in the raw material components of the functionalized intermediate layer is 7-9 parts, for example, 7 parts, 8 parts or 9 parts, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] The toughening agent in the raw material components of the functionalized intermediate layer is 18-22 parts by weight, for example, 18, 19, 20, 21 or 22 parts, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] The coupling agent in the raw material components of the functionalized intermediate layer is 1-3 parts by weight, for example, it can be 1 part, 2 parts or 3 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] The weight percentage of the dispersant in the raw material components of the functionalized intermediate layer is 0.7-0.9 parts, for example, it can be 0.7 parts, 0.8 parts or 0.9 parts, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] The curing agent in the raw material components of the functionalized intermediate layer is 4-6 parts by weight, for example, 4, 5 or 6 parts, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the polymer matrix comprises epoxy resin and / or polyurethane.

[0049] Preferably, the epoxy resin includes epoxy resin E51.

[0050] Preferably, the nano-reinforcing particles include any one or a combination of at least two of nano-silica, nano-alumina, carbon nanotubes or graphene sheets. Typical but non-limiting combinations include a combination of nano-silica and nano-alumina, a combination of nano-alumina, carbon nanotubes and graphene sheets, or a combination of nano-silica, nano-alumina, carbon nanotubes and graphene sheets.

[0051] Preferably, the particle size of the nano-reinforcing particles is 30 nm.

[0052] Preferably, the toughening agent comprises any one or a combination of at least two of liquid rubber, core-shell rubber particles, or hyperbranched polymers. Typical but non-limiting combinations include a combination of liquid rubber and core-shell rubber particles, a combination of core-shell rubber particles and hyperbranched polymers, or a combination of liquid rubber, core-shell rubber particles, and hyperbranched polymers.

[0053] The liquid rubber may be polysulfide rubber toughening agent JLY-124, the core-shell rubber particles may be methyl methacrylate-butadiene-styrene, and the hyperbranched polymer may be hyperbranched epoxy resin. This invention does not limit the specific types of liquid rubber, core-shell rubber particles, or hyperbranched polymers, and those skilled in the art can make adaptive adjustments according to actual application scenarios.

[0054] Preferably, the coupling agent includes any one or a combination of at least two of silane coupling agents, titanate coupling agents, or aluminate coupling agents. Typical but non-limiting combinations include combinations of silane coupling agents and titanate coupling agents, combinations of titanate coupling agents and aluminate coupling agents, or combinations of silane coupling agents, titanate coupling agents, and aluminate coupling agents.

[0055] The silane coupling agent can be silane coupling agent KH-560, a copolymer of vinyltriethoxysilane, etc., and the aluminate coupling agent can be distearyloxyisopropyl aluminate. This invention does not limit the specific types of silane coupling agents, titanate coupling agents or aluminate coupling agents. Those skilled in the art can make adaptive adjustments according to actual application scenarios.

[0056] Preferably, the dispersant includes the polymeric dispersant BYK-163.

[0057] Preferably, the curing agent comprises low molecular weight polyamide 650 curing agent with an amine value of 200-240 mg KOH / g.

[0058] Preferably, the preparation method of the raw material for the functionalized intermediate layer in step (1) specifically includes: pretreating the nano-reinforcing particles with a coupling agent, mixing the pretreated nano-particles with a polymer matrix, toughening agent and dispersant and then vacuum degassing, adding a curing agent to the mixture and stirring to obtain the raw material for the functionalized intermediate layer.

[0059] Preferably, the pretreatment step specifically includes: drying the nano-reinforcing particles at 120°C for 2 hours, then taking 3% by weight of the coupling agent of the nano-reinforcing particles, hydrolyzing it with an ethanol-water solution at a mass ratio of 95:5, mixing it with the nano-reinforcing particles, reacting it at 80°C for 1 hour, and then drying it.

[0060] The pretreatment step can prevent the agglomeration of nano-reinforced particles.

[0061] Preferably, the mixing includes sequential stirring at 500 rpm for 5 min and dispersion at 2000 rpm for 30 min.

[0062] Preferably, water bath cooling is used during the mixing process to control the temperature to <60°C, for example, it can be 55°C, 50°C, 45°C, 40°C or 35°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] Preferably, the vacuum degassing is performed at -0.095 MPa for 15 minutes until no bubbles are visible to the naked eye.

[0064] Preferably, the stirring speed is 300 rpm and the time is 5-10 min, for example, it can be 5 min, 6 min, 8 min, 9 min or 10 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] Preferably, the viscosity of the functionalized intermediate layer in step (1) is 2500-5000 mPa·s, for example, it can be 2500 mPa·s, 3000 mPa·s, 3500 mPa·s, 4000 mPa·s or 5000 mPa·s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] The viscosity of the functionalized intermediate layer was measured using a rotational viscometer at 25°C and 20 rpm, with the viscosity controlled between 2500-5000 mPa·s, which facilitates coating and ensures good wetting of micropores.

[0067] Preferably, the coating thickness of the functionalized intermediate layer in step (1) is 30-40 μm, for example, it can be 30 μm, 32 μm, 35 μm, 38 μm or 40 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] Preferably, after applying the functionalized intermediate layer in step (1), the process further includes a step of standing at 21-25°C for 15-20 minutes and pre-curing at 55-65°C for 25-35 minutes.

[0069] The settling temperature is 21-25℃, for example, it can be 21℃, 22℃, 23℃, 24℃ or 25℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] The settling time is 15-20 minutes, for example, it can be 15 minutes, 16 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] The pre-curing temperature is 55-65℃, for example, it can be 55℃, 58℃, 60℃, 62℃ or 65℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] The pre-curing time is 25-35 minutes, for example, it can be 25 minutes, 28 minutes, 30 minutes, 32 minutes or 35 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0073] Preferably, the dry film thickness of the pre-cured functionalized intermediate layer is 15-25 μm, for example, it can be 15 μm, 18 μm, 20 μm, 22 μm or 25 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0074] Preferably, the carbon fiber cover in step (2) is a T700 carbon fiber / epoxy resin prepreg molded part.

[0075] Preferably, the surface modification treatment in step (2) includes sequential cleaning and oxygen plasma treatment.

[0076] Preferably, the cleaning involves wiping the surface of the carbon fiber cover with acetone.

[0077] During the cleaning process, non-woven fabric is dipped in analytical grade acetone and wiped three times in a single direction to remove weak boundary layers such as release agents, and then left to air dry at room temperature for 5 minutes.

[0078] Preferably, the specific steps of the oxygen plasma treatment include: evacuating the cavity to a vacuum level of <10Pa, then introducing high-purity oxygen at a flow rate of 100-150sccm, controlling the working pressure at 30-50Pa, the radio frequency power supply at 300W, the treatment time at 4-6min, and the sample stage rotation speed at 5-10rpm.

[0079] The oxygen plasma treatment effectively etches the epoxy resin matrix, exposing more carbon fibers and introducing oxygen-containing polar groups on the surface, significantly improving wettability and chemical bonding ability. Laser etching can also be used as an alternative to oxygen plasma treatment.

[0080] The vacuum level of the cavity is evacuated to <10Pa, for example, it can be 8Pa, 6Pa, 5Pa, 3Pa or 1Pa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] The flow rate of the high-purity oxygen is 100-150 sccm, for example, it can be 100 sccm, 110 sccm, 120 sccm, 130 sccm or 150 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] The working pressure is 30-50 Pa, for example, it can be 30 Pa, 35 Pa, 40 Pa, 45 Pa or 50 Pa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0083] The processing time is 4-6 minutes, for example, it can be 4 minutes, 4.5 minutes, 5 minutes, 5.5 minutes or 6 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0084] The rotation speed of the sample stage is 5-10 rpm, for example, it can be 5 rpm, 6 rpm, 8 rpm, 9 rpm or 10 rpm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0085] After the oxygen plasma treatment, the next pressure bonding process is carried out within 30 minutes to prevent the surface activity from decaying.

[0086] Preferably, the structural adhesive in step (2) comprises a two-component toughened epoxy structural adhesive.

[0087] Preferably, the two-component toughened epoxy structural adhesive comprises epoxy resin E51 and polysulfide rubber JLY-124 in a mass ratio of (4-6):1, for example, it can be 4:1, 4.5:1, 5:1, 5.5:1 or 6:1, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0088] Preferably, the structural adhesive described in step (2) is applied to the surface of the frame to be bonded, or simultaneously applied to the surface-modified carbon fiber cover and the surface of the frame to be bonded.

[0089] Preferably, the coating thickness of the structural adhesive in step (2) is 0.1-0.2 mm, for example, it can be 0.1 mm, 0.12 mm, 0.15 mm, 0.18 mm or 0.2 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0090] Preferably, the pressure applied in step (2) is 0.4-0.6 MPa, for example, it can be 0.4 MPa, 0.45 MPa, 0.5 MPa, 0.55 MPa or 0.6 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0091] Preferably, the specific steps of curing in step (2) include: heating to 75-85°C at a rate of 1-2°C / min, holding for 55-65 min, and then continuing to heat to 115-125°C and holding for 125-135 min.

[0092] During the curing process, the following key processes occur, ultimately forming a composite reinforced interface: 1) Mechanical interlocking: The incompletely cured functionalized intermediate layer polymer penetrates into the micropores and pits of the aluminum alloy activated layer under pressure. After curing, these penetrated polymers are "anchored" within the micropores, forming a strong mechanical locking structure, which is the first line of defense against interfacial peeling stress; 2) Chemical bonding: The functionalized intermediate layer polymer forms chemical bonds with the surface of the activated layer rich in -OH groups, between the functionalized intermediate layer and the structural adhesive, and between the structural adhesive and the surface-modified carbon fibers rich in active groups through physical adsorption and chemical reactions such as hydroxyl and epoxy groups; 3) Nano-reinforcement: The nano-reinforcing particles uniformly dispersed in the functionalized intermediate layer form microscopic interlocks with the polymers penetrating the micropores on the one hand, and form a dense reinforcing network in the functionalized intermediate layer body and the area near the adhesive layer on the other hand. This network has multiple functions: a) significantly enhances the strength and modulus of the functionalized interlayer itself, making it an effective stress transfer layer; b) acts as a "microskeleton" to support the interface and resist compressive and shear deformation; c) hinders crack propagation paths and consumes fracture energy; d) through its high modulus characteristics, it partially coordinates the differences in modulus and thermal expansion coefficients between aluminum alloys and polymer materials, reducing the peak value of interfacial stress; 4) Toughening mechanism: The toughening agent phase in the functionalized interlayer induces a large amount of crimping, voiding, or shear yielding in the stress concentration area of ​​the interface. These plastic deformation processes absorb a large amount of energy, significantly improving the fracture toughness and impact resistance of the interface and preventing brittle fracture. These four interlocking, bonding, nano-strengthening, and toughening mechanisms work synergistically to construct a "mechanical-chemical-nano-reinforced" composite interface with high strength, high toughness, resistance to thermal cycling, and resistance to damp heat aging.

[0093] The heating rate is 1-2℃ / min, for example, it can be 1℃ / min, 1.2℃ / min, 1.5℃ / min, 1.8℃ / min or 2℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0094] The endpoint of the temperature rise is 75-85℃, for example, it can be 75℃, 78℃, 80℃, 82℃ or 85℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0095] The heat preservation time is 55-65 minutes, for example, it can be 55 minutes, 58 minutes, 60 minutes, 62 minutes or 65 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0096] The endpoint for further heating is 115-125℃, for example, it can be 115℃, 118℃, 120℃, 122℃ or 125℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0097] The heat preservation time is 125-135 minutes, for example, it can be 125 minutes, 128 minutes, 130 minutes, 132 minutes or 135 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0098] Preferably, after curing in step (2), the pressure is released after the furnace is cooled to below 60°C. For example, the temperature can be 60°C, 50°C, 40°C, 30°C or 20°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0099] In a second aspect, the present invention provides an aluminum-carbon interface reinforcement structure for a battery casing, comprising:

[0100] An aluminum alloy frame, the surface of which has an activation layer and a microporous structure formed by the activation layer;

[0101] The carbon fiber top cover has undergone surface modification treatment;

[0102] A functionalized intermediate layer is disposed on the surface of the aluminum alloy frame, and part of it penetrates into the microporous structure of the alloy frame surface to form a mechanical interlock. The interior of the functionalized intermediate layer contains nano-reinforcing particles and toughening agent phases.

[0103] A structural adhesive layer is disposed between the functionalized intermediate layer and the carbon fiber top cover to bond the two together.

[0104] The aluminum alloy frame, functionalized intermediate layer, structural adhesive layer and carbon fiber top cover are connected in sequence and form a composite reinforced interface in the interface area.

[0105] In this invention, a "mechanical-chemical-nano-reinforced" aluminum-carbon interface reinforcement structure with high strength, high toughness, heat cycle resistance, and resistance to damp heat aging is constructed through the synergistic effect of mechanical interlocking, chemical bonding, nano-reinforcement, and toughening mechanisms.

[0106] As a preferred embodiment of the present invention, the aluminum-carbon interface reinforcement structure for the battery casing is prepared by the aluminum-carbon interface reinforcement method for the battery casing described in the first aspect.

[0107] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0108] Compared with the prior art, the present invention has the following beneficial effects:

[0109] (1) Significantly improved interface strength: Mechanical interlocking and nano-reinforced network significantly improve the interface's ability to resist shear and tensile loads. Compared with direct bonding after only conventional surface treatment, the interface shear strength of the aluminum-carbon bonding interface enhancement method provided by this invention can reach more than 40.8 MPa.

[0110] (2) Significantly enhanced interfacial toughness: The combined effect of toughening agent and nano-reinforcing particles greatly increases the interfacial fracture energy, reaching 1050 J / m. 2 In summary, the connection structure exhibits excellent impact resistance, fatigue resistance, and crack arrest properties, thus preventing brittle failure.

[0111] (3) Excellent thermal stability and thermal cycling resistance: The functionalized intermediate layer has good high temperature stability and low thermal expansion coefficient. The nano-reinforced network can effectively constrain the thermal expansion of the polymer. The synergistic effect significantly alleviates the thermal mismatch stress between aluminum alloy and carbon fiber materials, improves the reliability of the connector under temperature alternation environment, and the thermal cycling strength retention rate can reach more than 95%.

[0112] (4) Excellent resistance to environmental aging: The dense micro-arc oxidation / anodic oxidation layer and functionalized intermediate layer provide a good physical barrier, preventing the intrusion of moisture and corrosive media. The reinforced mechanical interlocking and chemical bonding interface have stronger resistance to hydrolysis and corrosion. Nanoparticles can also improve the moisture resistance of the polymer matrix. After aging for 500 hours at 85°C / 85% humidity, the strength retention rate of the bond of the present invention can reach more than 88%, which is far superior to ordinary adhesive bonding.

[0113] (5) High process feasibility: The surface treatment, coating, bonding and curing involved are all mature or industrialized processes, which are easy to implement and promote.

[0114] (6) Strong versatility: The core idea of ​​the aluminum-carbon bonding interface enhancement method provided by the present invention can be extended to the bonding of other dissimilar materials with significant differences in thermal expansion coefficients or interface compatibility problems, such as magnesium alloy / carbon fiber reinforced composite materials, metal / thermoplastic composite materials, etc. Detailed Implementation

[0115] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0116] Example 1

[0117] This embodiment provides a method for enhancing the aluminum-carbon interface for a battery casing, the method comprising the following steps:

[0118] (1) The 6061-T6 aluminum alloy frame was degreased by alkaline washing at 65℃ for 8 min with a NaOH solution of 50 g / L. It was then rinsed with deionized water until the water film was continuous. Then, the aluminum alloy frame was activated by acid washing at 20℃ for 40 min with a mixture of nitric acid and hydrofluoric acid with a volume ratio of 10:1. After that, it was washed with water and dried at 80℃ for 10 min. Then, the aluminum alloy frame was subjected to micro-arc oxidation. The electrolyte used included a mixture of Na2SiO3·9H2O solution of 10 g / L and KOH solution of 2 g / L. The solvent was deionized water and the temperature was 30℃. The micro-arc oxidation was carried out using a bipolar pulse power supply with a positive voltage of 450V, a negative voltage of 80V, a frequency of 500Hz, a duty cycle of 30%, and a micro-arc oxidation time of 30 min. The thickness of the film formed after micro-arc oxidation was 25 μm, the microhardness was 900 HV, the porosity was 40%, and the average pore size was 2 μm.

[0119] Nano-silica with a particle size of 30 nm was dried at 120°C for 2 h. Then, 3% by weight of silane coupling agent KH-560 (by mass of nano-silica) was hydrolyzed with an ethanol-water solution at a mass ratio of 95:5. The solution was then stirred with nano-silica at 500 rpm for 5 min and dispersed at 2000 rpm for 30 min, with water bath cooling at 50°C. The mixture was then reacted at 80°C for 1 h and dried. The resulting pretreated nano-silica was mixed with epoxy resin E51, polysulfide rubber toughening agent JLY-124, and polymeric dispersant BYK-163 and degassed under vacuum at -0.095 MPa for 15 min until no visible bubbles were observed. Low molecular weight polyamide 650 curing agent was added to the mixture and stirred at 300 rpm for 8 min. The curing agent had an amine value of 220 mg KOH / g, resulting in a functionalized intermediate layer with a viscosity of 3500 mPa·s.

[0120] The raw material components of the functionalized intermediate layer include: 100 parts of epoxy resin E51, 8 parts of nano silica, 20 parts of polysulfide rubber toughening agent JLY-124, 2 parts of silane coupling agent KH-560, 0.8 parts of polymeric dispersant BYK-163, and 5 parts of low molecular weight polyamide 650 curing agent.

[0121] Then, a functionalized intermediate layer with a thickness of 35μm was coated on the surface of the aluminum alloy frame after micro-arc oxidation. The layer was left to stand at 23℃ for 18min and pre-cured at 60℃ for 30min. The dry film thickness of the functionalized intermediate layer was 20μm, thus obtaining the frame to be bonded.

[0122] (2) Use non-woven fabric dipped in analytical grade acetone to wipe the surface of the carbon fiber cover three times in one direction, and let it air dry at room temperature for 5 minutes. The carbon fiber cover is a T700 carbon fiber / epoxy resin prepreg molded part. Then oxygen plasma treatment is performed. The specific steps include: evacuating the cavity to 8 Pa, then introducing high-purity oxygen with a flow rate of 120 sccm, controlling the working pressure at 40 Pa, the RF power supply power at 300 W, the treatment time at 5 minutes, and the sample stage rotation speed at 8 rpm.

[0123] Epoxy resin E51 and polysulfide rubber JLY-124 with a mass ratio of 5:1 were simultaneously coated on the surface of the carbon fiber cover after oxygen plasma treatment and the frame to be bonded obtained in step (1). The coating thickness was 0.15 mm. The carbon fiber cover and the frame to be bonded were pressed together with a pressure of 0.5 MPa. Then, the temperature was raised to 80°C at a rate of 1.5°C / min and held for 60 min. The temperature was then raised to 120°C and held for 130 min. After curing, the temperature was cooled to 60°C in the furnace and the pressure was released to form an aluminum-carbon bonding interface reinforcement structure.

[0124] The aluminum-carbon interface reinforcement structure includes:

[0125] A 6061-T6 aluminum alloy frame has an activation layer and a microporous structure formed by the activation layer on its surface; a carbon fiber top cover has undergone surface modification treatment in step (2); a functionalized intermediate layer is disposed on the surface of the 6061-T6 aluminum alloy frame, which partially penetrates into the microporous structure on the surface of the 6061-T6 alloy frame to form a mechanical interlock, and the interior of the functionalized intermediate layer contains nano-silica and polysulfide rubber toughening agent JLY-124; a structural adhesive layer is composed of epoxy resin E51 and polysulfide rubber JLY-124, and is disposed between the functionalized intermediate layer and the carbon fiber top cover to bond the two together; wherein, the 6061-T6 aluminum alloy frame, the functionalized intermediate layer, the structural adhesive layer and the carbon fiber top cover are connected in sequence and form a composite reinforced interface in the interface area.

[0126] Example 2

[0127] This embodiment provides a method for enhancing the aluminum-carbon interface for a battery casing, the method comprising the following steps:

[0128] (1) The 6061-T6 aluminum alloy frame was degreased by alkaline washing at 60℃ for 10 min with a NaOH solution of 40 g / L. It was then rinsed with deionized water until the water film was continuous. Then, the aluminum alloy frame was activated by acid washing at 15℃ for 60 min with a mixture of nitric acid and hydrofluoric acid with a volume ratio of 9:1. After that, it was washed with water and dried at 80℃ for 10 min. Then, the aluminum alloy frame was subjected to micro-arc oxidation. The electrolyte used included a mixture of Na2SiO3·9H2O solution of 9 g / L and KOH solution of 1 g / L. The solvent was deionized water and the temperature was 40℃. The micro-arc oxidation was carried out using a bipolar pulse power supply with a positive voltage of 450V, a negative voltage of 80V, a frequency of 500Hz, a duty cycle of 30%, and a micro-arc oxidation time of 28 min. The thickness of the film formed after micro-arc oxidation was 20 μm, the microhardness was 880 HV, the porosity was 30%, and the average pore size was 1 μm.

[0129] Nano-alumina with a particle size of 30 nm was dried at 120°C for 2 h. Then, 3% of the nano-alumina mass of distearyloxyisopropyl aluminate was hydrolyzed with an ethanol-water solution at a mass ratio of 95:5. The solution was then stirred with the nano-alumina at 500 rpm for 5 min and dispersed at 2000 rpm for 30 min, with water bath cooling controlled at 55°C. The mixture was then reacted at 80°C for 1 h and dried. The resulting pretreated nano-alumina was mixed with epoxy resin E51, methyl methacrylate-butadiene-styrene and high molecular weight dispersant BYK-163 and degassed under vacuum at -0.095 MPa for 15 min until no visible bubbles were observed. Low molecular weight polyamide 650 curing agent was added to the mixture and stirred at 300 rpm for 5 min. The curing agent had an amine value of 200 mg KOH / g, resulting in a functionalized intermediate layer with a viscosity of 2500 mPa·s.

[0130] The raw material components of the functionalized intermediate layer include: 95 parts of epoxy resin E51, 7 parts of nano alumina, 18 parts of methyl methacrylate-butadiene-styrene, 1 part of distearate-isopropyl aluminate, 0.7 parts of high molecular weight dispersant BYK-1630, and 4 parts of low molecular weight polyamide 650 curing agent.

[0131] Then, a functionalized intermediate layer with a thickness of 30 μm was coated on the surface of the aluminum alloy frame after micro-arc oxidation. The layer was left to stand at 21℃ for 20 min and pre-cured at 55℃ for 35 min. The dry film thickness of the functionalized intermediate layer was 15 μm, thus obtaining the frame to be bonded.

[0132] (2) Use non-woven fabric dipped in analytical grade acetone to wipe the surface of the carbon fiber cover three times in one direction, and let it air dry at room temperature for 5 minutes. The carbon fiber cover is a T700 carbon fiber / epoxy resin prepreg molded part. Then oxygen plasma treatment is performed. The specific steps include: evacuating the cavity to 5 Pa, then introducing high-purity oxygen with a flow rate of 100 sccm, controlling the working pressure at 30 Pa, the RF power supply power at 300 W, the treatment time at 6 minutes, and the sample stage rotation speed at 5 rpm.

[0133] Epoxy resin E51 and polysulfide rubber JLY-124 with a mass ratio of 4:1 were simultaneously coated on the surface of the carbon fiber cover after oxygen plasma treatment and the frame to be bonded obtained in step (1). The coating thickness was 0.1 mm. The carbon fiber cover and the frame to be bonded were pressed together with a pressure of 0.4 MPa. Then, the temperature was raised to 75°C at a rate of 1°C / min and held for 65 min. The temperature was then raised to 115°C and held for 135 min. After curing, the pressure was released after the furnace cooled to 50°C, forming an aluminum-carbon bonding interface reinforcement structure.

[0134] The aluminum-carbon interface reinforcement structure includes:

[0135] A 6061-T6 aluminum alloy frame has an activation layer and a microporous structure formed by the activation layer on its surface; a carbon fiber top cover has undergone surface modification treatment in step (2); a functionalized intermediate layer is disposed on the surface of the 6061-T6 aluminum alloy frame, which partially penetrates into the microporous structure on the surface of the 6061-T6 alloy frame to form a mechanical interlock, and nano-alumina and methyl methacrylate-butadiene-styrene are dispersed inside the functionalized intermediate layer; a structural adhesive layer is composed of epoxy resin E51 and polysulfide rubber JLY-124, and is disposed between the functionalized intermediate layer and the carbon fiber top cover to bond the two together; wherein, the 6061-T6 aluminum alloy frame, the functionalized intermediate layer, the structural adhesive layer and the carbon fiber top cover are connected in sequence and form a composite reinforced interface in the interface area.

[0136] Example 3

[0137] This embodiment provides a method for enhancing the aluminum-carbon interface for a battery casing, the method comprising the following steps:

[0138] (1) The 6061-T6 aluminum alloy frame was degreased by alkaline washing at 70℃ for 5 min with a NaOH solution of 60 g / L. It was then rinsed with deionized water until the water film was continuous. Then, the aluminum alloy frame was activated by acid washing at 30℃ for 30 min with a mixture of nitric acid and hydrofluoric acid with a volume ratio of 11:1. Then, it was washed with water and dried at 80℃ for 10 min. Then, the aluminum alloy frame was subjected to micro-arc oxidation. The electrolyte used included a mixture of Na2SiO3·9H2O solution of 11 g / L and KOH solution of 3 g / L. The solvent was deionized water and the temperature was 20℃. The micro-arc oxidation was carried out using a bipolar pulse power supply with a positive voltage of 450V, a negative voltage of 80V, a frequency of 500Hz, a duty cycle of 30%, and a micro-arc oxidation time of 28 min. The thickness of the film formed after micro-arc oxidation was 30 μm, the microhardness was 850 HV, the porosity was 45%, and the average pore size was 3 μm.

[0139] Nano-silica with a particle size of 30 nm was dried at 120°C for 2 h. Then, 3% by weight of silane coupling agent KH-560 (by mass of nano-silica) was hydrolyzed with an ethanol-water solution at a mass ratio of 95:5. The solution was then stirred with nano-silica at 500 rpm for 5 min and dispersed at 2000 rpm for 30 min, with water bath cooling at 40°C. The mixture was then reacted at 80°C for 1 h and dried. The resulting pretreated nano-silica was mixed with epoxy resin E51, hyperbranched epoxy resin, and polymeric dispersant BYK-163 and degassed under vacuum at -0.095 MPa for 15 min until no visible bubbles were observed. Low molecular weight polyamide 650 curing agent was added to the mixture and stirred at 300 rpm for 10 min. The curing agent had an amine value of 240 mg KOH / g, resulting in a functionalized intermediate layer with a viscosity of 5000 mPa·s.

[0140] The raw material components of the functionalized intermediate layer include: 105 parts of epoxy resin E51, 9 parts of nano silica, 22 parts of hyperbranched epoxy resin, 3 parts of silane coupling agent KH-560, 0.9 parts of polymeric dispersant BYK-163, and 6 parts of low molecular weight polyamide 650 curing agent.

[0141] Then, a functionalized intermediate layer with a thickness of 40 μm was coated on the surface of the aluminum alloy frame after micro-arc oxidation. The layer was left to stand at 25°C for 15 min and pre-cured at 65°C for 25 min. The dry film thickness of the functionalized intermediate layer was 25 μm, thus obtaining the frame to be bonded.

[0142] (2) Use non-woven fabric dipped in analytical grade acetone to wipe the surface of the carbon fiber cover three times in one direction, and let it air dry at room temperature for 5 minutes. The carbon fiber cover is a T700 carbon fiber / epoxy resin prepreg molded part. Then oxygen plasma treatment is performed. The specific steps include: evacuating the cavity to 3Pa, then introducing high-purity oxygen with a flow rate of 150sccm, controlling the working pressure at 30Pa, the RF power supply power at 300W, the treatment time at 4 minutes, and the sample stage rotation speed at 10rpm.

[0143] Epoxy resin E51 and polysulfide rubber JLY-124 with a mass ratio of 6:1 were simultaneously coated on the surface of the carbon fiber cover after oxygen plasma treatment and the frame to be bonded obtained in step (1). The coating thickness was 0.2 mm. The carbon fiber cover and the frame to be bonded were pressed together with a pressure of 0.6 MPa. Then, the temperature was raised to 85°C at a rate of 2°C / min and held for 55 min. The temperature was then raised to 125°C and held for 125 min. After curing, the pressure was released after the furnace cooled to 40°C, forming an aluminum-carbon bonding interface reinforcement structure.

[0144] The aluminum-carbon interface reinforcement structure includes:

[0145] A 6061-T6 aluminum alloy frame has an activation layer and a microporous structure formed by the activation layer on its surface; a carbon fiber top cover has undergone surface modification treatment in step (2); a functionalized intermediate layer is disposed on the surface of the 6061-T6 aluminum alloy frame, which partially penetrates into the microporous structure on the surface of the 6061-T6 alloy frame to form a mechanical interlock, and the interior of the functionalized intermediate layer contains dispersed nano-silica and hyperbranched epoxy resin; a structural adhesive layer is composed of epoxy resin E51 and polysulfide rubber JLY-124 and is disposed between the functionalized intermediate layer and the carbon fiber top cover to bond the two together; wherein, the 6061-T6 aluminum alloy frame, the functionalized intermediate layer, the structural adhesive layer and the carbon fiber top cover are connected in sequence and form a composite reinforced interface in the interface area.

[0146] Example 4

[0147] This embodiment provides a method for enhancing the aluminum-carbon interface for battery casings. The difference from Embodiment 1 is that nano-silica is not added to the raw material components of the functionalized intermediate layer in step (1), while the rest are the same as in Embodiment 1.

[0148] Example 5

[0149] This embodiment provides a method for enhancing the aluminum-carbon interface of a battery casing. The difference from Embodiment 1 is that the raw material components of the functionalized intermediate layer in step (1) do not contain polysulfide rubber toughening agent JLY-124, while the rest are the same as in Embodiment 1.

[0150] Example 6

[0151] This embodiment provides a method for enhancing the aluminum-carbon interface for battery casings. The difference from Embodiment 1 is that the viscosity of the functionalized intermediate layer described in step (1) is adjusted to 2000 mPa·s, while the rest is the same as in Embodiment 1.

[0152] Example 7

[0153] This embodiment provides a method for enhancing the aluminum-carbon interface for battery casings. The difference from Embodiment 1 is that the viscosity of the functionalized intermediate layer described in step (1) is adjusted to 5500 mPa·s, while the rest is the same as in Embodiment 1.

[0154] Example 8

[0155] This embodiment provides a method for enhancing the aluminum-carbon interface for battery casings. The difference from Embodiment 1 is that step (1) does not include the micro-arc oxidation step, while the rest is the same as in Embodiment 1.

[0156] Comparative Example 1

[0157] This comparative example provides a method for enhancing the aluminum-carbon interface for battery casings. The difference from Example 1 is that the 6061-T6 aluminum alloy frame is not subjected to alkaline washing and degreasing, acid washing and activation, and micro-arc oxidation in step (1). The rest is the same as in Example 1.

[0158] Comparative Example 2

[0159] This comparative example provides a method for enhancing the aluminum-carbon interface for a battery casing. The difference from Example 1 is that in step (1), no functionalized intermediate layer is coated on the surface of the aluminum alloy frame. All other steps are the same as in Example 1.

[0160] Comparative Example 3

[0161] This comparative example provides a method for enhancing the aluminum-carbon interface for battery casings. The difference from Example 1 is that the carbon fiber cover is not wiped and treated with oxygen plasma in step (2), while the rest is the same as in Example 1.

[0162] The aluminum-carbon interface reinforcement method for battery casings provided in Examples 1-8 and Comparative Examples 1-3 was used to obtain aluminum-carbon interface reinforcement structures. The interface shear strength and toughness were tested using a universal testing machine, and the results are shown in Table 1. A high-low temperature alternating damp heat test chamber was used for thermal cycling tests. The test conditions were: -40°C for 30 min, then switching to +125°C within 5 min and holding for 30 min; this constituted one cycle, and a total of 100 cycles were performed. The strength retention rate (%) was calculated as (interface shear strength after cycling / interface shear strength before cycling) × 100%, and the results are shown in Table 1. A damp heat aging performance test was conducted after aging at 85°C / 85%RH for 500 hours. The strength retention rate (%) was calculated as (interface shear strength after aging / interface shear strength before aging) × 100%, and the results are shown in Table 1.

[0163] Table 1

[0164]

[0165] As can be seen from Table 1, the aluminum-carbon bonding interface enhancement method for battery casing provided by the present invention adopts a multi-level interface treatment mechanism of "corrosion protection-mechanical interlocking-chemical bonding", which significantly improves the interface strength, toughness and long-term durability of the connection, thereby meeting the stringent requirements of high-performance electric vehicle battery packs for lightweight, high safety and long life.

[0166] A comparison between Examples 1 and 4 shows that the absence of nanoparticles in the functionalized interlayer leads to a significant decrease in interfacial shear strength (from 42.5 MPa to 35.1 MPa). This is because the increased rigidity of the nanoparticles and weakened particle bridging effect result in a reduced interlayer modulus, which fails to effectively transfer and homogenize interfacial stress, leading to increased stress concentration. A comparison between Examples 1 and 5 shows that the absence of a toughening agent in the functionalized interlayer leads to a sharp decrease in interfacial fracture energy (from 1150 J / m). 2 Reduced to 620J / m 2This is the most direct adverse effect. The interface changes from ductile fracture to brittle fracture, losing the ability to absorb energy through plastic deformation, and becoming abnormally sensitive to impact, vibration, and stress concentration. As can be seen from the comparison between Examples 1 and Examples 6 and 7, if the viscosity of the functionalized intermediate layer is too low, it will result in excessive fluidity, which may cause it to flow before coating and curing, resulting in uneven film thickness in some areas, or even failing to effectively support the adhesive layer. If the viscosity is too high, it will result in poor leveling and wettability, making it difficult to penetrate into the micropores of the micro-arc oxidation layer to form strong mechanical interlocking. At the same time, it may form a weak interface with the structural adhesive layer that is not fully bonded, introducing defects, thereby comprehensively weakening the connection strength and durability. As can be seen from the comparison between Examples 1 and 8, if the aluminum alloy frame is not micro-arc oxidized, the aluminum alloy surface will only have a flat chemical oxide layer, losing the macroscopic mechanical interlocking ability provided by the porous ceramic structure with high specific surface area.

[0167] As can be seen from the comparison between Example 1 and Comparative Example 1, without surface activation treatment of the aluminum alloy frame, the oxide layer, oil stains and low surface energy state of the original aluminum alloy surface are retained, which seriously hinders the effective wetting and adhesion of the functionalized intermediate layer or adhesive. As can be seen from the comparison between Example 1 and Comparative Example 2, without the introduction of a functionalized intermediate layer, the structural adhesive is directly bonded to the micro-arc oxide layer, and the "flexible-rigid" gradient transition layer constructed by nanoparticle reinforcement and toughening agent is missing. As can be seen from the comparison between Example 1 and Comparative Example 3, without surface modification treatment of the carbon fiber cover, the residual mold release agent and low chemical activity state on its surface result in low surface energy, and weak chemical bonding and physical adsorption with the adhesive.

[0168] In summary, the aluminum-carbon bonding interface reinforcement method for battery casings provided by this invention can significantly improve interface strength: mechanical interlocking and nano-reinforcing networks significantly enhance the interface's resistance to shear and tensile loads. Compared to direct bonding after conventional surface treatment, the interface shear strength of the aluminum-carbon bonding interface reinforcement method provided by this invention can be increased by 30-100%; it can also significantly enhance interface toughness: the combined effect of toughening agents and nano-reinforcing particles greatly increases the interface fracture energy, and the bonding structure has excellent impact resistance, fatigue resistance, and crack arrest performance, avoiding brittle failure; the bonding structure has excellent thermal stability and thermal cycling resistance: the functionalized intermediate layer has good high-temperature stability and a low coefficient of thermal expansion, and the nano-reinforcing network can effectively constrain the thermal expansion of the polymer, and the synergistic effect significantly alleviates the thermal mismatch stress between the aluminum alloy and carbon fiber materials, improving the reliability of the connector in temperature alternating environments; the bonding structure has excellent resistance to environmental aging: the dense micro-arc oxidation / anodic oxidation layer and the functionalized intermediate layer themselves provide a good physical barrier, preventing the intrusion of moisture and corrosive media. The reinforced mechanical interlocking and chemical bonding interface have stronger resistance to hydrolysis and corrosion. Nanoparticles can also improve the moisture resistance of the polymer matrix. After aging for 500 hours at 85℃ / 85% humidity, the strength retention rate of the bond of the present invention can be greater than 85%, which is far superior to ordinary adhesive bonding; the process is highly feasible: the surface treatment, coating, bonding and curing involved are all mature or industrially feasible processes, which are easy to implement and promote; it has strong versatility: the core idea of ​​the aluminum-carbon bonding interface enhancement method provided by the present invention can be extended to the bonding of other dissimilar materials with significant differences in thermal expansion coefficients or interface compatibility problems.

[0169] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An aluminum carbon joint interface enhancement method for a battery housing, characterized by, The aluminum-carbon connecting interface reinforcing method comprises the following steps: (1) performing surface activation treatment on an aluminum alloy frame, and then coating a functionalized intermediate layer to obtain a frame to be bonded; the raw material of the functionalized intermediate layer comprises nano-enhanced particles and a toughening agent; (2) using a structural adhesive to press and adhere the carbon fiber upper cover subjected to surface modification treatment to the frame to be bonded obtained in step (1), and forming an aluminum-carbon connecting interface reinforcing structure after curing.

2. The aluminum-carbon joint interface enhancement method of claim 1, wherein, The surface activation treatment in step (1) comprises alkaline degreasing, acid activation and oxidation treatment in sequence; Preferably, the alkaline degreasing is performed at a temperature of 60-70°C for 5-10 min; Preferably, the alkaline solution used in the alkaline degreasing comprises a NaOH solution with a concentration of 40-60 g / L; Preferably, the acid activation is performed at a temperature of 15-30°C for 30-60 min; Preferably, the acid solution used in the acid activation comprises a mixed solution of nitric acid and hydrofluoric acid with a volume ratio of (9-11):

1.

3. The aluminum-carbon joint interface enhancement method of claim 2, wherein, The oxidation treatment comprises micro-arc oxidation or anodic oxidation, and preferably micro-arc oxidation; Preferably, the electrolyte used in the micro-arc oxidation comprises a mixed solution of a Na2SiO3·9H2O solution with a concentration of 9-11 g / L and a KOH solution with a concentration of 1-3 g / L, the solvent is deionized water, and the temperature is 20-40°C; Preferably, the micro-arc oxidation uses a bipolar pulse power source, and the positive voltage is set to 450 V, the negative voltage is set to 80 V, the frequency is set to 500 Hz, and the duty cycle is set to 30%; Preferably, the micro-arc oxidation is performed for 28-32 min; Preferably, the film layer formed after the micro-arc oxidation has a thickness of 20-30 μm, a microhardness of >800 HV, a porosity of 30-45%, and an average pore size of 1-3 μm.

4. The aluminum-carbon joint interface enhancement method according to any one of claims 1 to 3, characterized by, The raw material components of the functionalized intermediate layer in step (1) comprise, in terms of weight parts, 95-105 parts of a polymer matrix, 7-9 parts of nano-enhanced particles, 18-22 parts of a toughening agent, 1-3 parts of a coupling agent, 0.7-0.9 parts of a dispersing agent, and 4-6 parts of a curing agent.

5. The aluminum-carbon joint interface enhancement method of claim 4, wherein, The polymer matrix comprises an epoxy resin and / or a polyurethane; Preferably, the nano-enhanced particles comprise any one or a combination of at least two of nano-silicon dioxide, nano-aluminum oxide, carbon nanotubes or graphene sheets; Preferably, the toughening agent comprises any one or a combination of at least two of liquid rubber, core-shell rubber particles or hyperbranched polymers; Preferably, the coupling agent comprises any one or a combination of at least two of a silane coupling agent, a titanate coupling agent or an aluminate coupling agent.

6. The aluminum-carbon joint interface enhancement method according to claim 4 or 5, characterized by, The raw material preparation method of the functionalized intermediate layer in step (1) specifically comprises: pretreating the nano-enhanced particles with a coupling agent, mixing the obtained pretreated nano particles with a polymer matrix, a toughening agent and a dispersing agent to perform vacuum degassing, adding a curing agent to the obtained mixture to perform stirring, and obtaining the raw material of the functionalized intermediate layer.

7. The aluminum-carbon joint interface enhancement method according to any one of claims 1 to 6, characterized by, The viscosity of the functionalized intermediate layer in step (1) is 2500-5000 mPa·s; Preferably, the coating thickness of the functionalized intermediate layer in step (1) is 30-40 μm; Preferably, the functionalized intermediate layer coating in step (1) is followed by a step of standing for 15-20 min at 21-25℃ and pre-curing for 25-35 min at 55-65℃; Preferably, the dry film thickness of the functionalized intermediate layer after pre-curing is 15-25μm.

8. The aluminum-carbon joint interface enhancement method according to any one of claims 1 to 7, characterized by, The surface modification treatment in step (2) comprises cleaning and oxygen plasma treatment in sequence; Preferably, the cleaning is wiping the surface of the carbon fiber upper cover with acetone; Preferably, the specific steps of the oxygen plasma treatment include: vacuuming the cavity to <10Pa, then introducing high-purity oxygen with a flow rate of 100-150sccm, controlling the working pressure at 30-50Pa, the radio frequency power at 300W, the processing time at 4-6min, and the sample table rotation speed at 5-10rpm.

9. The aluminum-carbon joint interface enhancement method according to any one of claims 1 to 8, characterized by, The structural adhesive in step (2) comprises a two-component toughened epoxy structural adhesive; Preferably, the two-component toughened epoxy structural adhesive comprises epoxy resin E51 and polythiourethane rubber JLY-124 with a mass ratio of (4-6):1; Preferably, the structural adhesive in step (2) is coated on the surface of the frame to be bonded, or simultaneously coated on the surface of the carbon fiber upper cover and the surface of the frame to be bonded after surface modification treatment; Preferably, the coating thickness of the structural adhesive in step (2) is 0.1-0.2mm; Preferably, the pressure for pressing and fitting in step (2) is 0.4-0.6MPa; Preferably, the specific steps of the curing in step (2) include: heating at a rate of 1-2℃ / min to 75-85℃, maintaining for 55-65min, then continuing to heat to 115-125℃, maintaining for 125-135min; Preferably, the curing in step (2) is further followed by a step of removing the pressure after furnace cooling to below 60℃.

10. An aluminum-carbon joint interface enhancement structure for a battery case, characterized by, Comprise: an aluminum alloy frame having an activation layer and a microporous structure formed by the activation layer on the surface thereof; a carbon fiber upper cover subjected to surface modification treatment; a functionalized intermediate layer disposed on the surface of the aluminum alloy frame, partially penetrating into the microporous structure of the surface of the alloy frame to form mechanical interlocking, and having nano-reinforcing particles and a toughening agent phase dispersed therein; a structural adhesive layer disposed between the functionalized intermediate layer and the carbon fiber upper cover for bonding the two; wherein the aluminum alloy frame, the functionalized intermediate layer, the structural adhesive layer, and the carbon fiber upper cover are sequentially connected, and a composite reinforced interface is formed at the interface region.

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