Copper diffusion prevention aluminum-plastic composite film for lithium battery and preparation method of copper diffusion prevention aluminum-plastic composite film

Abstract

The invention relates to the technical field of aluminum-plastic composite films, and provides a copper diffusion prevention aluminum-plastic composite film for a lithium battery and a preparation method thereof.The aluminum-plastic composite film sequentially comprises a nylon layer, a first adhesive resin layer, an aluminum nitride / aluminum composite layer, a second adhesive resin layer, a blocking layer, a third adhesive resin layer and a heat sealing layer from outside to inside; the barrier layer is a boron nitride / polyvinylidene fluoride composite material film; the boron nitride / polyvinylidene fluoride composite material film comprises a polyvinylidene fluoride base film and boron nitride dispersed in the polyvinylidene fluoride base film; the aluminum nitride / aluminum composite layer comprises a metal aluminum layer and aluminum nitride layers located on the surfaces of the two sides of the metal aluminum layer. By optimizing the material composition and process, the chemical stability and mechanical property of the composite film are improved, copper diffusion is effectively inhibited, and the composite film is suitable for high-safety lithium battery packaging and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum-plastic composite films, and particularly relates to a copper diffusion-proof aluminum-plastic composite film for lithium batteries and a preparation method thereof. Background Art

[0002] As an important technology in the current field of energy storage and conversion, lithium-ion batteries play a key role in various scenarios such as consumer electronics, electric vehicles, and energy storage systems. With the improvement of the battery energy density, the safety requirements for battery packaging materials have become increasingly prominent. Among them, as the core packaging material of soft-pack lithium batteries, aluminum-plastic composite films directly affect the chemical stability and cycle life of the batteries. Under high voltage, high temperature, or long-term use environments, copper current collectors may diffuse due to electrochemical corrosion or migration effects, resulting in internal short circuits of the batteries, and thus triggering safety hazards. Therefore, the packaging film needs to have excellent copper diffusion-proof ability to effectively block the migration of copper ions, while maintaining good gas and moisture barrier properties to prevent the influence of the external environment on the battery system. In addition, the packaging film also needs to have excellent mechanical strength to withstand the repeated charge and discharge processes of the batteries without structural failure, and at the same time have good processing adaptability to meet the needs of large-scale production. In this context, developing new aluminum-plastic composite films with high barrier properties, mechanical stability, and copper diffusion-proof ability is of great significance for improving the safety of lithium batteries, extending their service life, and expanding their application scope.

[0003] Currently, regarding the problem of copper diffusion-proof of lithium battery packaging films, some studies have proposed to improve their performance by introducing functional barrier layers or optimizing the composite structure in aluminum-plastic composite films. For example, Chinese Patent with the publication number CN106243551A discloses an aluminum-plastic composite film, which is sequentially provided with an outer protective layer, a first adhesive layer, an aluminum foil layer, a second adhesive layer, and a heat-sealing layer from the outside to the inside. However, it does not have a microstructure design for copper ion diffusion, so there are certain limitations in the blocking effect on copper ions. In addition, it is prone to interfacial peeling under thermal cycling or mechanical stress, reducing the overall stability. Therefore, how to optimize the interfacial stability and improve the mechanical strength while ensuring the blocking effect is still an urgent problem to be solved in the current copper diffusion-proof technology of aluminum-plastic composite films. Summary of the Invention

[0004] (1) Technical Problems to be Solved The purpose of the present invention is to provide a copper diffusion-proof aluminum-plastic composite film for lithium batteries and a preparation method thereof, so as to solve the problem of insufficient copper diffusion-proof performance of current aluminum-plastic composite films.

[0005] (2) Technical Solutions In order to achieve the above purpose, the present invention provides the following technical solutions: An aluminum-plastic composite film for preventing copper diffusion in lithium batteries, the aluminum-plastic composite film sequentially includes a nylon layer, a first adhesive resin layer, an aluminum nitride / aluminum composite layer, a second adhesive resin layer, a barrier layer, a third adhesive resin layer, and a heat-sealing layer from outside to inside; The barrier layer is a boron nitride / polyvinylidene fluoride composite film; the boron nitride / polyvinylidene fluoride composite film includes a polyvinylidene fluoride base film and boron nitride dispersed in the polyvinylidene fluoride base film; the mass ratio of boron nitride to the polyvinylidene fluoride base film is (0.8~1.2):1; The aluminum nitride / aluminum composite layer includes a metal aluminum layer and aluminum nitride layers on both side surfaces of the metal aluminum layer; the thickness of the aluminum nitride layer is 50~200 nm.

[0006] Preferably, the boron nitride nanosheets in the boron nitride / polyvinylidene fluoride composite film are in a flaky structure, and the orientation of the boron nitride nanosheets is arranged along the plane direction of the boron nitride / polyvinylidene fluoride composite film; The average diameter of the boron nitride is 0.5~2 μm, and the average thickness is 10~100 nm.

[0007] The aluminum-plastic composite film for preventing copper diffusion of the present invention adopts a multi-layer composite structure design to enhance the copper diffusion prevention performance of the lithium battery packaging material, while taking into account mechanical stability, chemical stability and thermal conductivity. Through the synergistic effect of each layer of materials, the diffusion of copper ions is effectively inhibited, and the safety and long-term reliability of battery packaging are improved. Among them, the barrier layer is composed of a boron nitride / polyvinylidene fluoride composite film. In the boron nitride / polyvinylidene fluoride composite film, the mass ratio of boron nitride to the polyvinylidene fluoride base film is reasonably controlled, and the boron nitride lamellae are arranged along the plane direction. Its high chemical inertness and layered structure form a physical barrier, while the high density and chemical resistance of polyvinylidene fluoride further strengthen the stability of the barrier layer, ensuring its long-term effectiveness in the electrolyte environment. The aluminum nitride / aluminum composite layer, as the core conductive layer, has nano-scale aluminum nitride layers on both its upper and lower surfaces, which not only enhances the interlayer bonding force, but also provides an additional diffusion barrier, improves the copper diffusion prevention ability, and at the same time optimizes the thermal management performance of the packaging film by relying on the high thermal conductivity of aluminum nitride, reduces the heat accumulation during high-rate charge and discharge of the battery, and improves the overall safety.

[0008] The first adhesive resin layer and the second adhesive resin layer form a uniform and stable bonding interface between the multi-layer materials, enhance the mechanical flexibility of the film material, and effectively prevent the formation of diffusion channels caused by interface defects, thereby further strengthening the copper diffusion prevention performance. The outermost nylon layer provides excellent mechanical impact resistance and environmental stability, protects the structural integrity, its high toughness ensures that the packaging film is not easily damaged during processing, packaging and use, and at the same time has good moisture resistance and chemical resistance, providing additional protection for the anti-diffusion function.

[0009] Preferably, the method for preparing the boron nitride / polyvinylidene fluoride composite membrane comprises the following steps: (1) Add boron nitride nanosheets and ethanol into a mixing container, add sodium dodecyl sulfonate, and obtain a suspension after ultrasonic treatment; pour the obtained suspension into a vacuum filtration device, filter under negative pressure to form a boron nitride porous preform; dry the boron nitride porous preform at 60-100 °C for 2-4 h, then calcine it at 400-450 °C for 30-60 min in an air atmosphere, and cool it to room temperature to obtain a boron nitride porous preform; (2) Stir and mix polyvinylidene fluoride and N-methylpyrrolidone, and obtain a polymer solution after standing; place the boron nitride porous preform in an impregnation tank, add the polymer solution and impregnate for 5-10 min, take it out and place it in a vacuum curing furnace, heat up to 80-120 °C for solvent evaporation and curing, the curing time is 2-6 h, then perform hot pressing treatment on the obtained preform at 120-150 °C, the pressure is 2-5 MPa, and the pressure holding time is 30-60 min. After the hot pressing is completed, cool it to room temperature to obtain the boron nitride / polyvinylidene fluoride composite membrane.

[0010] The present invention uses a vacuum filtration process to prepare a boron nitride porous preform, ensuring that the layered structure of the nanosheets forms a continuous barrier network at the microscale, and removing organic substances through high-temperature calcination to improve the stability and interfacial bonding performance of the material. During the preparation of the barrier layer, the boron nitride porous preform is impregnated in a uniformly dispersed polyvinylidene fluoride solution, so that the polymer solution penetrates into the pore structure of boron nitride, and a uniform composite film is formed after solvent evaporation and curing. Finally, the interfacial bonding force is optimized through hot pressing treatment to improve the overall mechanical strength and durability. In this system, the two-dimensional layered structure of boron nitride provides excellent copper ion barrier ability, while polyvinylidene fluoride as the matrix material endows the barrier layer with good flexibility and processing adaptability, enabling it to achieve stable structural integration in the aluminum-plastic composite film. Moreover, the boron nitride sheets in the present invention are arranged in an orderly orientation in the barrier layer, thereby constructing an efficient copper ion diffusion barrier at the molecular scale. In addition, the present invention combines reasonable control of the proportion and size parameters of boron nitride in the composite membrane, so that it forms a continuous sheet arrangement in the barrier layer, thereby effectively extending the diffusion path of copper ions, improving the barrier effect, and at the same time avoiding the increase in film brittleness caused by too high filling degree. Overall, through the synergistic design of boron nitride / polyvinylidene fluoride, the present invention ensures high-efficiency copper diffusion prevention performance while achieving excellent mechanical stability and interfacial bonding strength, providing a new technical solution for the high-performance of lithium battery packaging materials.

[0011] Preferably, in step (1), the mass ratio of the boron nitride nanosheets, sodium dodecyl sulfonate, and ethanol is 0.5-4.5:0.05-0.5:100-150; In step (2), the mass ratio of polyvinylidene fluoride particles to N-methylpyrrolidone is 5.0-10.0:100.

[0012] Preferably, the preparation method of the boron nitride nanosheets is as follows: 1) By weight, 0.5-2.5 parts of hexagonal boron nitride powder are placed in a mixing container, and then 200-300 parts of N-methylpyrrolidone and 1.0-3.5 parts of polyvinylpyrrolidone are added. Stir at a stirring rate of 300-600 rpm for 10-30 min, and then perform ultrasonic exfoliation treatment. Set the ultrasonic power to 300-500 W, the ultrasonic frequency to 40-60 kHz, the ultrasonic time to 120-360 min, and control the temperature at 30-40 °C; 2) After the ultrasonic exfoliation is completed, transfer the obtained suspension to a centrifuge tube and centrifuge at a rotation speed of 3000-6000 rpm for 10-30 min; 3) Transfer the supernatant suspension obtained by centrifugation to a container, then continue to add ethanol with a volume twice that of the suspension, and centrifuge at a rotation speed of 6000-8000 rpm for 10-20 min, and then continue to retain the supernatant suspension obtained by centrifugation; 4) Repeat step 3) 3-5 times. Finally, transfer the obtained supernatant suspension to a rotary evaporator and dry it at 60-100 °C and a vacuum degree of -0.08 to -0.1 MPa for 6-12 h to obtain boron nitride nanosheets.

[0013] The boron nitride / polyvinylidene fluoride composite membrane of the present invention is mainly used to enhance the anti-copper diffusion performance of the aluminum-plastic composite membrane. The preparation of the boron nitride nanosheets adopts the ultrasonic exfoliation technology. Using hexagonal boron nitride powder as the precursor, under the synergistic action of N-methylpyrrolidone and polyvinylpyrrolidone, high-quality boron nitride nanosheets are obtained through ultrasonic treatment, and their high dispersibility is ensured by centrifugal purification and rotary evaporation drying.

[0014] Preferably, the preparation method of the aluminum nitride / aluminum composite layer is: Place the aluminum foil in the reaction cavity of a plasma nitriding furnace, evacuate to Pa, then introduce high-purity argon gas, the gas flow rate is 100-500 sccm, and the pressure is MPa, perform surface pretreatment using radio frequency plasma, the RF power is 300-500 W, and the treatment time is 10-30 min to remove the natural aluminum oxide layer on the surface of the aluminum foil. After the pretreatment is completed, introduce high-purity nitrogen gas, the gas flow rate is 100-500 sccm, and the pressure is MPa, and then heat the obtained aluminum foil to 500 - 530 °C at a heating rate of 5 - 10 °C / min. At the same time, perform plasma-enhanced nitridation treatment using radio frequency plasma, with an RF power of 300 - 500 W and a treatment time of 120 - 360 min. After the nitridation treatment is completed, stop heating and introduce high-purity argon for protective cooling, controlling the cooling rate at 5 - 20 °C / min until the temperature drops to room temperature, finally obtaining an aluminum nitride / aluminum composite layer.

[0015] In the present invention, the aluminum nitride / aluminum composite layer and the barrier layer are mainly used to enhance the copper diffusion prevention performance of the lithium battery packaging material, while taking into account mechanical stability, thermal management ability, and interfacial bonding performance. The aluminum nitride / aluminum composite layer is prepared by a plasma-enhanced nitridation process. First, the aluminum foil is subjected to radio frequency plasma surface pretreatment to remove the natural alumina layer and improve the activity of aluminum. Subsequently, a plasma-enhanced nitridation reaction is carried out in a high-purity nitrogen environment, enabling nitrogen atoms to react with aluminum to form a dense and uniform aluminum nitride layer on the surface of the aluminum foil. This aluminum nitride layer not only provides chemical stability but also constructs an efficient diffusion barrier at the microscale to prevent the penetration of copper ions. At the same time, the interface between it and the aluminum substrate has good bonding, ensuring the structural integrity and thermal conductivity of the composite layer. In addition, the thickness of the aluminum nitride / aluminum composite layer is reasonably controlled to balance the barrier effect and mechanical flexibility, avoiding affecting the overall performance of the packaging film due to excessive layer thickness.

[0016] Preferably, the thickness of the barrier layer is 30 - 60 μm; The thickness of the aluminum nitride / aluminum composite layer is 10.0 - 50.0 μm; The thickness of the nylon layer is 10 - 30 μm.

[0017] Preferably, the heat-sealing layer is ethylene-methyl acrylate copolymer, and its thickness is 30 - 60 μm.

[0018] Preferably, the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are all epoxy resin layers, and the thicknesses of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are 2.0 - 5.0 μm.

[0019] The present invention also provides a method for preparing a copper diffusion prevention aluminum-plastic composite film for lithium batteries, including the following steps: S1. Uniformly coat a resin adhesive on the side of the nylon layer close to the aluminum nitride / aluminum composite layer. After coating, perform pre-drying at 60 - 80 °C, then stack it with the aluminum nitride / aluminum composite layer, and then perform hot pressing and compounding through a continuous roller press to obtain a first composite film; S2. Uniformly coat the surface of the aluminum nitride / aluminum composite layer of the first composite film with a resin adhesive. After coating, perform pre-drying at 60 - 80 °C, then stack it with the barrier layer, and then perform hot pressing and compounding through a continuous roller press to obtain a second composite film; S3. Uniformly coat the surface of the barrier layer of the second composite film with a resin adhesive. After coating, perform pre-drying at 60 - 80 °C, then stack it with the heat-sealing layer, and then perform hot pressing and compounding through a continuous roller press, and then cure it to obtain the copper diffusion-proof aluminum-plastic composite film.

[0020] (3) Beneficial technical effects 1. Through the collaborative design of the multi-layer composite structure, the present invention significantly improves the copper diffusion-proof performance of the lithium battery packaging material, while taking into account mechanical strength, chemical stability, and thermal conductivity. The barrier layer (boron nitride / polyvinylidene fluoride composite film) constructs an efficient copper ion barrier by the oriented arrangement of boron nitride sheets and a highly dense polymer matrix, ensuring long-term stability. The aluminum nitride / aluminum composite layer strengthens the bonding force through the nano-scale aluminum nitride interface, provides an additional diffusion barrier, and optimizes the thermal management performance, reducing the risk of heat accumulation. The adhesive resin layer optimizes the interfacial bonding, prevents the formation of diffusion channels, and the nylon layer enhances the overall impact resistance and environmental adaptability, ensuring high reliability of the packaging film under complex working conditions.

[0021] 2. The boron nitride / polyvinylidene fluoride composite film of the present invention can achieve efficient copper diffusion-proof performance, improving the safety and reliability of the lithium battery packaging material. Compared with the prior art, this solution constructs an orderly arranged boron nitride layered structure to form an efficient physical barrier, effectively extending the diffusion path of copper ions, while the polyvinylidene fluoride matrix ensures overall flexibility and chemical resistance, optimizes the interfacial bonding force, and enhances mechanical stability. Adopting processes such as ultrasonic peeling, vacuum filtration, and hot pressing treatment ensures uniform distribution and high stability of the material, avoiding problems such as insufficient interfacial bonding force and increased brittleness of the barrier layer in the traditional solution, and providing a reliable solution for high-safety lithium battery packaging.

[0022] 3. Through the optimized design of the aluminum nitride / aluminum composite layer and the barrier layer, the present invention realizes the efficient copper diffusion-proof performance of the lithium battery packaging material, and improves mechanical stability, thermal management ability, and interfacial bonding performance. Compared with the prior art, the present invention adopts a plasma-enhanced nitriding process to uniformly form an aluminum nitride layer on the surface of the aluminum substrate, efficiently blocking the penetration of copper ions, while optimizing the interfacial bonding force to ensure the stability and thermal conductivity of the composite layer. Reasonably controlling the thickness of the composite layer enables it to have flexibility while ensuring the barrier performance, avoiding the brittleness problem caused by the increase in layer thickness in the traditional solution, and providing a reliable solution for high-safety lithium battery packaging. Description of the drawings

[0023] Figure 1It is the microstructural morphology diagram of the boron nitride porous preform prepared in Example 1 of the present invention.

[0024] Figure 2 It is the microstructural morphology diagram of the barrier layer prepared in Example 1 of the present invention.

[0025] Figure 3 It is the cross-sectional microstructure morphology diagram of the aluminum nitride / aluminum composite layer prepared in Example 1 of the present invention. Detailed implementation manners

[0026] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] Example 1

[0028] A copper diffusion-proof aluminum-plastic composite film for lithium batteries, which from outside to inside is successively a nylon layer, a first adhesive resin layer, an aluminum nitride / aluminum composite layer, a second adhesive resin layer, a barrier layer, a third adhesive resin layer, and a heat-sealing layer.

[0029] The barrier layer is a boron nitride / polyvinylidene fluoride composite film, and the thickness of the barrier layer is 30 μm. The boron nitride / polyvinylidene fluoride composite film includes a polyvinylidene fluoride base film and boron nitride dispersed in the polyvinylidene fluoride base film; the mass ratio of the boron nitride to the polyvinylidene fluoride base film is 1.2:1; in the boron nitride / polyvinylidene fluoride composite film, the boron nitride nanosheets are in a flake structure, and the orientation of the boron nitride nanosheets is arranged along the plane direction of the boron nitride / polyvinylidene fluoride composite film; the average diameter of the boron nitride nanosheets is 0.5 μm, and the average thickness is 10 nm.

[0030] The aluminum nitride / aluminum composite layer includes a metal aluminum layer and aluminum nitride layers on both surface sides of the metal aluminum layer; the thickness of the aluminum nitride layer is 50 nm; the thickness of the aluminum nitride / aluminum composite layer is 10.0 μm.

[0031] The first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are all epoxy resin layers with the same thickness. The thicknesses of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are 2.0 μm; the thickness of the nylon layer is 10 μm; the heat-sealing layer is an ethylene-methyl methacrylate copolymer, and its thickness is 30 μm.

[0032] The preparation method of the boron nitride / polyvinylidene fluoride composite film in this embodiment is as follows: (1) By weight, 0.5 parts of boron nitride nanosheets and 100 parts of ethanol are added to a mixing container. Then, 0.05 parts of sodium dodecyl sulfonate are continuously added. Next, ultrasonic treatment is carried out for 30 min to obtain a suspension. The obtained suspension is poured into a vacuum filtration device and filtered under a negative pressure of 0.01 MPa to form a porous boron nitride preform layer. Then, the porous boron nitride preform layer is dried at 60 °C for 2 h. Finally, in an air atmosphere, the porous boron nitride preform layer is calcined at 400 °C for 30 min to remove organic substances, and cooled to room temperature to obtain a porous boron nitride preform.

[0033] (2) By weight, 5.0 parts of polyvinylidene fluoride particles and 100 parts of N-methylpyrrolidone are added to a stirring container and stirred at a stirring rate of 300 rpm for 30 min to form a uniform and transparent polymer solution. After stirring, the polymer solution is allowed to stand for 60 min to remove air bubbles and obtain a uniform polymer solution for standby. The porous boron nitride preform is placed in an impregnation tank, and then the uniform polymer solution is slowly poured in and impregnated at 25 °C for 5 min. Then, the porous boron nitride preform impregnated with the polymer solution is taken out and placed horizontally in a vacuum curing furnace, and solvent evaporation curing is carried out at 80 °C. The curing time is 2 h, and the heating rate is 1 °C / min. During the curing process, after curing is completed, the preform is subjected to hot pressing treatment at 120 °C, the pressure is controlled at 2 MPa, and the pressure holding time is 30 min. After hot pressing, it is slowly cooled to room temperature to obtain a boron nitride / polyvinylidene fluoride composite membrane.

[0034] The preparation method of the boron nitride nanosheets in this example is as follows: 1) By weight, 0.5 parts of hexagonal boron nitride powder are placed in a clean and dry mixing container. Then, 200 parts of N-methylpyrrolidone and 1.0 part of polyvinylpyrrolidone are continuously added and stirred at a stirring rate of 300 rpm for 10 min. Next, ultrasonic exfoliation treatment is carried out. The ultrasonic power is set to 300 W, the ultrasonic frequency is 40 kHz, and the ultrasonic time is 120 min. The ultrasonic process is cooled by a water bath, and the temperature is controlled at 30 °C. 2) After ultrasonic exfoliation is completed, the obtained suspension is transferred to a centrifuge tube and centrifuged at a speed of 3000 rpm for 10 min. 3) The centrifuged supernatant suspension is transferred to a clean container, and then ethanol twice the volume of the suspension is continuously added and centrifuged at a speed of 6000 rpm for 10 min. Then, the centrifuged supernatant suspension is continuously retained. 4) Step 3) is repeated 3 times. Finally, the obtained supernatant suspension is transferred to a rotary evaporator and dried at 60 °C and a vacuum degree of -0.08 MPa for 6 h to finally obtain boron nitride nanosheets.

[0035] The preparation method of the aluminum nitride / aluminum composite layer in this embodiment is as follows: Place a clean aluminum foil in the reaction chamber of a plasma nitriding furnace, evacuate to Pa, then introduce high-purity argon gas with a gas flow rate of 100 sccm and a pressure of MPa. Perform surface pretreatment using radio frequency plasma with an RF power of 300 W and a treatment time of 10 min to remove the natural aluminum oxide layer on the aluminum foil surface and improve the activity of aluminum. After the pretreatment is completed, introduce high-purity nitrogen gas with a gas flow rate of 100 sccm and a pressure of MPa. Then heat the aluminum foil to 500 °C, increase the temperature at a rate of 5 °C / min, and at the same time turn on the radio frequency plasma with an RF power of 300 W for plasma-enhanced nitriding treatment for 120 min. After the nitriding reaction is completed, stop heating and introduce high-purity argon gas for protective cooling, controlling the cooling rate to 5 °C / min until the temperature drops to room temperature, and finally obtain the aluminum nitride / aluminum composite layer.

[0036] The preparation method of a copper diffusion-proof aluminum-plastic composite film for lithium batteries in this embodiment includes the following steps: S1. Uniformly coat an epoxy resin adhesive on one side of the nylon layer close to the aluminum nitride / aluminum composite layer. After coating, perform pre-drying at 65 °C, then stack it with the aluminum nitride / aluminum composite layer, and then perform hot pressing and compounding through a continuous roll press to obtain a first composite film; S2. Uniformly coat an epoxy resin adhesive on the surface of the aluminum nitride / aluminum composite layer of the first composite film. After coating, perform pre-drying at 65 °C, then stack it with the barrier layer, and then perform hot pressing and compounding through a continuous roll press to obtain a second composite film; S3. Uniformly coat an epoxy resin adhesive on the surface of the barrier layer of the second composite film. After coating, perform pre-drying at 65 °C, then stack it with the heat-sealing layer, and then perform hot pressing and compounding through a continuous roll press, and then perform curing to obtain the copper diffusion-proof aluminum-plastic composite film.

[0037] Through Figure 1 The microscopic structure of the boron nitride porous preform prepared in Example 1 can be clearly observed. Among them, the boron nitride nanosheets show obvious parallel layered arrangements, and this ordered structure helps to improve the ability of the barrier layer to inhibit the diffusion of copper ions. Figure 2 It further shows the overall microscopic morphology of the barrier layer. The parallel orientation of the boron nitride nanosheets is clearly visible, and at the same time, the film layer structure is dense and uniform, which indicates that the boron nitride / polyvinylidene fluoride composite material film has successfully achieved a highly oriented sheet-like arrangement during the preparation process, thereby improving the anti-diffusion performance of the material. Figure 3The cross-sectional microstructure of the aluminum nitride / aluminum composite layer is shown, and a uniform and continuous aluminum nitride layer can be clearly observed, indicating that the plasma-enhanced nitriding treatment effectively forms a high-quality aluminum nitride interfacial layer, providing better interfacial bonding force and thermal stability for the aluminum-plastic composite film. Based on the above results, it is proved that the present invention realizes high-efficiency copper diffusion prevention performance and excellent mechanical stability by optimizing the orientation structure of boron nitride nanosheets and the interfacial engineering of the aluminum nitride / aluminum layer.

[0038] Example 2

[0039] An aluminum-plastic composite film for preventing copper diffusion in lithium batteries, the aluminum-plastic composite film from outside to inside is successively a nylon layer, a first adhesive resin layer, an aluminum nitride / aluminum composite layer, a second adhesive resin layer, a barrier layer, a third adhesive resin layer, and a heat-sealing layer.

[0040] The barrier layer is a boron nitride / polyvinylidene fluoride composite film, and the thickness of the barrier layer is 42 μm. The boron nitride / polyvinylidene fluoride composite film includes a polyvinylidene fluoride base film and boron nitride dispersed in the polyvinylidene fluoride base film; the mass ratio of the boron nitride to the polyvinylidene fluoride base film is 1.06:1; the boron nitride nanosheets in the boron nitride / polyvinylidene fluoride composite film are in a flaky structure, and the orientation of the boron nitride nanosheets is arranged along the plane direction of the boron nitride / polyvinylidene fluoride composite film; the average diameter of the boron nitride nanosheets is 1.1 μm, and the average thickness is 37 nm.

[0041] The aluminum nitride / aluminum composite layer includes a metal aluminum layer and aluminum nitride layers on both side surfaces of the metal aluminum layer; the thickness of the aluminum nitride layer is 95 nm; the thickness of the aluminum nitride / aluminum composite layer is 22 μm.

[0042] The first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are all epoxy resin layers with the same thickness, and the thicknesses of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are 2.9 μm; the thickness of the nylon layer is 16 μm; the heat-sealing layer is an ethylene-methyl methacrylate copolymer, and its thickness is 38 μm.

[0043] The preparation method of the boron nitride / polyvinylidene fluoride composite film in this example is as follows: (1) By weight, 1.7 parts of boron nitride nanosheets and 115 parts of ethanol are added to a mixing container, then 0.18 part of sodium dodecyl sulfate is added continuously, and then ultrasonic treatment is carried out for 39 min to obtain a suspension. The obtained suspension is poured into a vacuum filtration device and filtered under a negative pressure of 0.037 MPa to form a boron nitride porous preform layer. Then the boron nitride porous preform layer is dried at 72°C for 2.6 h, and finally, in an air atmosphere, the boron nitride porous preform layer is calcined at 415°C for 39 min to remove organic substances, and cooled to room temperature to obtain a boron nitride porous preform.

[0044] (2) Add 6.5 parts by weight of polyvinylidene fluoride particles and 100 parts of N-methylpyrrolidone into a stirring container, stir at a stirring rate of 390 rpm for 39 min to form a uniform and transparent polymer solution. After the stirring is completed, let the polymer solution stand for 78 min to remove air bubbles and obtain a uniform polymer solution for standby; place the boron nitride porous preform into an impregnation tank, then slowly pour in the uniform polymer solution, and impregnate at 30 °C for 7 min. Then take out the boron nitride porous preform impregnated with the polymer solution, place it horizontally in a vacuum curing furnace, and carry out solvent evaporation curing at 92 °C for 3.2 h, with a heating rate of 2.2 °C / min. During the curing process, after curing is completed, perform hot pressing treatment on the preform at 129 °C, control the pressure at 2.9 MPa, and keep the pressure for 39 min. After the hot pressing is completed, slowly cool down to room temperature to obtain the boron nitride / polyvinylidene fluoride composite membrane.

[0045] The preparation method of the boron nitride nanosheets in this example is as follows: (1) Add 1.1 parts by weight of hexagonal boron nitride powder into a clean and dry mixing container, then continue to add 230 parts of N-methylpyrrolidone and 1.8 parts of polyvinylpyrrolidone, stir at a stirring rate of 390 rpm for 16 min, and then perform ultrasonic exfoliation treatment. Set the ultrasonic power to 360 W, the ultrasonic frequency to 46 kHz, and the ultrasonic time to 192 min. Cool the ultrasonic process through a water bath and control the temperature at 33 °C; (2) After the ultrasonic exfoliation is completed, transfer the obtained suspension to a centrifuge tube and centrifuge at a speed of 3900 rpm for 16 min; (3) Transfer the supernatant suspension obtained by centrifugation to a clean container, then continue to add ethanol with a volume twice that of the suspension, and centrifuge at a speed of 6600 rpm for 13 min, and then continue to retain the supernatant suspension obtained by centrifugation; (4) Repeat step (3) 4 times, and finally transfer the obtained supernatant suspension to a rotary evaporator, dry it at 72 °C and a vacuum degree of -0.087 MPa for 7.8 h to finally obtain boron nitride nanosheets.

[0046] The preparation method of the aluminum nitride / aluminum composite layer in this example is as follows: Place a clean aluminum foil in the reaction chamber of a plasma nitriding furnace, evacuate to Pa, and then high-purity argon gas was introduced with a gas flow rate of 220 sccm and a pressure of 0.028 MPa. Radio-frequency plasma was used for surface pretreatment with an RF power of 360 W and a treatment time of 16 min to remove the natural aluminum oxide layer on the aluminum foil surface and improve the activity of aluminum. After the pretreatment was completed, high-purity nitrogen gas was introduced with a gas flow rate of 220 sccm and a pressure of 0.028 MPa. Then the aluminum foil was heated to 510 °C at a heating rate of 6.5 °C / min while turning on the radio-frequency plasma with an RF power of 360 W for plasma-enhanced nitridation treatment with a treatment time of 192 min. After the nitridation reaction was completed, the heating was stopped, and high-purity argon gas was introduced for protective cooling, controlling the cooling rate at 9.5 °C / min until the temperature dropped to room temperature, and finally an aluminum nitride / aluminum composite layer was obtained.

[0047] A method for preparing a copper diffusion-proof aluminum-plastic composite film for a lithium battery according to this embodiment includes the following steps: S1. Epoxy resin adhesive was evenly coated on one side of the nylon layer close to the aluminum nitride / aluminum composite layer. After coating, pre-drying was carried out at 70 °C, and then it was superposed with the aluminum nitride / aluminum composite layer, and then hot-pressed and compounded through a continuous roll press to obtain a first composite film; S2. Epoxy resin adhesive was evenly coated on the surface of the aluminum nitride / aluminum composite layer of the first composite film. After coating, pre-drying was carried out at 70 °C, and then it was superposed with the barrier layer, and then hot-pressed and compounded through a continuous roll press to obtain a second composite film; S3. Epoxy resin adhesive was evenly coated on the surface of the barrier layer of the second composite film. After coating, pre-drying was carried out at 70 °C, and then it was superposed with the heat-sealing layer, and then hot-pressed and compounded through a continuous roll press and then cured to obtain the copper diffusion-proof aluminum-plastic composite film.

[0048] Example 3

[0049] A copper diffusion-proof aluminum-plastic composite film for a lithium battery, from the outside to the inside, is successively a nylon layer, a first adhesive resin layer, an aluminum nitride / aluminum composite layer, a second adhesive resin layer, a barrier layer, a third adhesive resin layer, and a heat-sealing layer.

[0050] The barrier layer is a boron nitride / polyvinylidene fluoride composite film with a thickness of 50 μm. The boron nitride / polyvinylidene fluoride composite film includes a polyvinylidene fluoride base film and boron nitride dispersed in the polyvinylidene fluoride base film; the mass ratio of boron nitride to the polyvinylidene fluoride base film is 0.95:1; the boron nitride nanosheets in the boron nitride / polyvinylidene fluoride composite film are in a flake structure, and the orientation of the boron nitride nanosheets is arranged along the plane direction of the boron nitride / polyvinylidene fluoride composite film; the average diameter of the boron nitride nanosheets is 1.7 μm, and the average thickness is 64 nm.

[0051] The aluminum nitride / aluminum composite layer includes a metallic aluminum layer and aluminum nitride layers on both surface sides of the metallic aluminum layer; the thickness of the aluminum nitride layer is 140 nm; the thickness of the aluminum nitride / aluminum composite layer is 34.0 μm.

[0052] The first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are all epoxy resin layers of the same thickness, and the thicknesses of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are 3.8 μm; the thickness of the nylon layer is 22 μm; the heat-sealing layer is an ethylene-methacrylic acid copolymer, and its thickness is 53 μm.

[0053] The preparation method of the boron nitride / polyvinylidene fluoride composite material film in this embodiment is as follows: (1) By weight, add 2.9 parts of boron nitride nanosheets and 130 parts of ethanol to a mixing container, then continue to add 0.32 part of sodium dodecyl sulfate, and then perform ultrasonic treatment for 48 min to obtain a suspension. Pour the obtained suspension into a vacuum filtration device and filter it under a negative pressure of 0.064 MPa to form a boron nitride porous preform. Then dry the boron nitride porous preform at 84°C for 3.2 h, and finally calcine the boron nitride porous preform at 430°C for 48 min in an air atmosphere to remove organic substances, and cool it to room temperature to obtain a boron nitride porous preform.

[0054] (2) By weight, add 8.0 parts of polyvinylidene fluoride particles and 100 parts of N-methylpyrrolidone to a stirring container, stir at a stirring rate of 480 rpm for 48 min to form a uniform and transparent polymer solution. After the stirring is completed, let the polymer solution stand for 96 min to remove bubbles to obtain a uniform polymer solution for standby; place the boron nitride porous preform in an impregnation tank, then slowly pour in the uniform polymer solution, and impregnate it at 34°C for 8 min. Then take out the boron nitride porous preform impregnated with the polymer solution, place it horizontally in a vacuum curing furnace, and perform solvent evaporation curing at 104°C. The curing time is 4.4 h, and the heating rate is 3.4°C / min. During the curing process, after the curing is completed, perform hot pressing treatment on the preform at 138°C, control the pressure at 3.8 MPa, and the pressure holding time is 48 min. After the hot pressing is completed, slowly cool it to room temperature to obtain a boron nitride / polyvinylidene fluoride composite material film.

[0055] The preparation method of the boron nitride nanosheets in this embodiment is as follows: 1) Weigh 1.7 parts by weight of hexagonal boron nitride powder and place it in a clean and dry mixing container. Then, add 260 parts of N-methylpyrrolidone and 2.5 parts of polyvinylpyrrolidone. Stir at a stirring rate of 480 rpm for 22 min. Next, perform ultrasonic exfoliation treatment. Set the ultrasonic power to 420 W, the ultrasonic frequency to 52 kHz, and the ultrasonic time to 264 min. Cool the ultrasonic process through a water bath and control the temperature at 36 °C. 2) After the ultrasonic exfoliation is completed, transfer the obtained suspension to a centrifuge tube and centrifuge at a speed of 4800 rpm for 22 min. 3) Transfer the supernatant suspension obtained by centrifugation to a clean container. Then, continue to add ethanol with a volume twice that of the suspension and centrifuge at a speed of 7200 rpm for 16 min. Then, continue to retain the supernatant suspension obtained by centrifugation. 4) Repeat step 3) four times. Finally, transfer the obtained supernatant suspension to a rotary evaporator and dry it at 84 °C and a vacuum degree of -0.093 MPa for 9.6 h to finally obtain boron nitride nanosheets.

[0056] The preparation method of the aluminum nitride / aluminum composite layer in this example is as follows: Place a clean aluminum foil in the reaction chamber of a plasma nitriding furnace, evacuate to Pa, then introduce high-purity argon gas with a gas flow rate of 340 sccm and a pressure of 0.046 MPa. Perform surface pretreatment using radio frequency plasma with an RF power of 420 W and a treatment time of 22 min to remove the natural aluminum oxide layer on the surface of the aluminum foil and improve the activity of aluminum. After the pretreatment is completed, introduce high-purity nitrogen gas with a gas flow rate of 340 sccm and a pressure of 0.046 MPa. Then, heat the aluminum foil to 525 °C at a heating rate of 8.0 °C / min while turning on the radio frequency plasma with an RF power of 420 W for plasma-enhanced nitriding treatment with a treatment time of 264 min. After the nitriding reaction is completed, stop heating and introduce high-purity argon gas for protective cooling, controlling the cooling rate at 14.0 °C / min until the temperature drops to room temperature to finally obtain the aluminum nitride / aluminum composite layer.

[0057] The preparation method of a copper diffusion-proof aluminum-plastic composite film for a lithium battery in this example includes the following steps: S1. Uniformly coat an epoxy resin adhesive on the side of the nylon layer close to the aluminum nitride / aluminum composite layer. After coating, perform pre-drying at 80 °C, then stack it with the aluminum nitride / aluminum composite layer, and then perform hot pressing and compounding through a continuous roll press to obtain a first composite film. S2. Uniformly coat the surface of the aluminum nitride / aluminum composite layer of the first composite film with epoxy resin adhesive. After coating, conduct pre-drying at 80 °C, then stack it with the barrier layer, and then perform hot pressing and compounding through a continuous roll press to obtain the second composite film; S3. Uniformly coat the surface of the barrier layer of the second composite film with epoxy resin adhesive. After coating, conduct pre-drying at 80 °C, then stack it with the heat-sealing layer, and then perform hot pressing and compounding through a continuous roll press, and then cure to obtain the copper diffusion-proof aluminum-plastic composite film.

[0058] Example 4

[0059] A copper diffusion-proof aluminum-plastic composite film for lithium batteries, the aluminum-plastic composite film from outside to inside is successively a nylon layer, a first adhesive resin layer, an aluminum nitride / aluminum composite layer, a second adhesive resin layer, a barrier layer, a third adhesive resin layer, and a heat-sealing layer.

[0060] The barrier layer is a boron nitride / polyvinylidene fluoride composite film, and the thickness of the barrier layer is 60 μm. The boron nitride / polyvinylidene fluoride composite film includes a polyvinylidene fluoride base film and boron nitride dispersed in the polyvinylidene fluoride base film; the mass ratio of the boron nitride to the polyvinylidene fluoride base film is 0.8:1; the boron nitride nanosheets in the boron nitride / polyvinylidene fluoride composite film are in a flake structure, and the orientation of the boron nitride nanosheets is arranged along the plane direction of the boron nitride / polyvinylidene fluoride composite film; the average diameter of the boron nitride nanosheets is 2 μm, and the average thickness is 100 nm.

[0061] The aluminum nitride / aluminum composite layer includes a metal aluminum layer and aluminum nitride layers on both side surfaces of the metal aluminum layer; the thickness of the aluminum nitride layer is 200 nm; the thickness of the aluminum nitride / aluminum composite layer is 50.0 μm.

[0062] The first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are all epoxy resin layers with the same thickness. The thicknesses of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are 5.0 μm; the thickness of the nylon layer is 30 μm; the heat-sealing layer is an ethylene-methyl methacrylate copolymer, and its thickness is 60 μm.

[0063] The preparation method of the boron nitride / polyvinylidene fluoride composite film in this example is: (1) The preparation method of the boron nitride porous preform in this embodiment is as follows: By weight, 4.5 parts of boron nitride nanosheets and 150 parts of ethanol are added to a mixing container, then 0.5 part of sodium dodecyl sulfate is added continuously, and then ultrasonic treatment is carried out for 60 min to obtain a suspension. The obtained suspension is poured into a vacuum filtration device and filtered under a negative pressure of 0.1 MPa to form a boron nitride porous prefabricated layer. Then, the boron nitride porous prefabricated layer is dried at 100 °C for 4 h. Finally, in an air atmosphere, the boron nitride porous prefabricated layer is calcined at 450 °C for 60 min to remove organic substances, and cooled to room temperature to obtain the boron nitride porous preform.

[0064] (2) By weight, 10.0 parts of polyvinylidene fluoride particles and 100 parts of N-methylpyrrolidone are added to a stirring container and stirred at a stirring rate of 600 rpm for 60 min to form a uniform and transparent polymer solution. After the stirring is completed, the polymer solution is allowed to stand for 120 min to remove bubbles and obtain a uniform polymer solution for standby; the boron nitride porous preform is placed in an impregnation tank, and then the uniform polymer solution is slowly poured in and impregnated at 40 °C for 10 min. Then, the boron nitride porous preform impregnated with the polymer solution is taken out and placed horizontally in a vacuum curing furnace, and solvent evaporation curing is carried out at 120 °C. The curing time is 6 h, and the heating rate is 5 °C / min. During the curing process, after the curing is completed, the preform is subjected to hot pressing treatment at 150 °C, the pressure is controlled at 5 MPa, and the pressure holding time is 60 min. After the hot pressing is completed, it is slowly cooled to room temperature to obtain the boron nitride / polyvinylidene fluoride composite membrane.

[0065] The preparation method of the boron nitride nanosheets in this embodiment is as follows: 1) By weight, 2.5 parts of hexagonal boron nitride powder are placed in a clean and dry mixing container, 300 parts of N-methylpyrrolidone and 3.5 parts of polyvinylpyrrolidone are added continuously, and stirred at a stirring rate of 600 rpm for 30 min. Next, ultrasonic exfoliation treatment is carried out. The ultrasonic power is set to 500 W, the ultrasonic frequency is 60 kHz, and the ultrasonic time is 360 min. The ultrasonic process is cooled by a water bath, and the temperature is controlled at 40 °C; 2) After the ultrasonic exfoliation is completed, the obtained suspension is transferred to a centrifuge tube and centrifuged at a speed of 6000 rpm for 30 min; 3) The supernatant suspension obtained by centrifugation is transferred to a clean container, then ethanol twice the volume of the suspension is added continuously, and centrifuged at a speed of 8000 rpm for 20 min, and then the supernatant suspension obtained by centrifugation is retained; 4) Repeat step 3) 5 times. Finally, the obtained supernatant suspension is transferred to a rotary evaporator and dried at 100 °C and a vacuum degree of -0.1 MPa for 12 h to finally obtain boron nitride nanosheets.

[0066] The preparation method of the aluminum nitride / aluminum composite layer in this embodiment is as follows: Place a clean aluminum foil in the reaction chamber of a plasma nitriding furnace, evacuate to Pa, then introduce high-purity argon gas with a gas flow rate of 500 sccm and a pressure of 0.1 MPa. Perform surface pretreatment using radio frequency plasma with an RF power of 500 W and a treatment time of 30 min to remove the natural aluminum oxide layer on the aluminum foil surface and improve the activity of aluminum. After the pretreatment is completed, introduce high-purity nitrogen gas with a gas flow rate of 500 sccm and a pressure of 0.1 MPa. Then heat the aluminum foil to 530 °C at a heating rate of 10 °C / min while turning on the radio frequency plasma with an RF power of 500 W for plasma-enhanced nitriding treatment for 360 min. After the nitriding reaction is completed, stop heating and introduce high-purity argon gas for protective cooling, controlling the cooling rate at 20 °C / min until the temperature drops to room temperature, and finally obtain the aluminum nitride / aluminum composite layer.

[0067] The preparation method of a copper diffusion-proof aluminum-plastic composite film for lithium batteries in this embodiment includes the following steps: S1. Uniformly coat an epoxy resin adhesive on the side of the nylon layer close to the aluminum nitride / aluminum composite layer. After coating, perform pre-drying at 80 °C, then stack it with the aluminum nitride / aluminum composite layer, and then perform hot pressing and compounding through a continuous roll press to obtain a first composite film; S2. Uniformly coat an epoxy resin adhesive on the surface of the aluminum nitride / aluminum composite layer of the first composite film. After coating, perform pre-drying at 80 °C, then stack it with the barrier layer, and then perform hot pressing and compounding through a continuous roll press to obtain a second composite film; S3. Uniformly coat an epoxy resin adhesive on the surface of the barrier layer of the second composite film. After coating, perform pre-drying at 80 °C, then stack it with the heat-sealing layer, and then perform hot pressing and compounding through a continuous roll press, and then cure to obtain the copper diffusion-proof aluminum-plastic composite film.

[0068] Comparative Example 1: It is basically the same as Example 1, except that the barrier layer does not use a boron nitride / polyvinylidene fluoride composite film, but uses a single polyvinylidene fluoride film.

[0069] Comparative Example 2: It is basically the same as Example 1, except that the aluminum nitride / aluminum composite layer is replaced with an aluminum foil.

[0070] Comparative Example 3: It is basically the same as Example 1, except that the mass ratio of boron nitride to polyvinylidene fluoride in the barrier layer is 1.5:1.

[0071] Comparative Example 4: It is basically the same as Example 1, except that when preparing the boron nitride / polyvinylidene fluoride composite film, the boron nitride nanosheets are replaced with hexagonal boron nitride powder.

[0072] Performance testing: Copper diffusion prevention performance testing: Cut the prepared aluminum-plastic composite film into test samples of 2 cm × 2 cm, and clamp it between a copper foil and an electrolyte solution for a diffusion experiment at 60°C. Use ICP-MS (Inductively Coupled Plasma Mass Spectrometry) to measure the concentration of copper ions in the immersion solution, and compare it with the samples of the comparative examples to evaluate the inhibitory effect of the boron nitride / polyvinylidene fluoride barrier layer on the diffusion of copper ions.

[0073] Mechanical property testing: Use a tensile testing machine to test the tensile strength and elongation at break of the aluminum-plastic composite film. The test rate is set at 5 mm / min, and the sample size is 10 mm × 50 mm.

[0074] The performance of the aluminum-plastic composite films of Examples 1 to 4 and Comparative Examples 1 to 4 is summarized in Table 1.

[0075] Table 1 Summary of the performance of the aluminum-plastic composite films of Examples 1 to 4 and Comparative Examples 1 to 4

[0076] Compared with the comparative examples, the aluminum-plastic composite films of the examples show significant advantages in terms of copper diffusion prevention performance, tensile strength, and elongation at break. In terms of copper diffusion prevention performance, the permeability of the aluminum-plastic composite films of the examples is much lower than that of the comparative examples. The lowest value reaches 0.01 μg / cm²·h, while the highest value of the aluminum-plastic composite films of the comparative examples is as high as 0.30 μg / cm²·h, indicating that the aluminum-plastic composite films of the examples have a more excellent barrier effect in inhibiting the penetration of copper ions. In terms of tensile strength, the values of the aluminum-plastic composite films of the examples are all higher than those of the comparative examples. The highest value reaches 134 MPa, while the lowest value of the comparative examples is only 80 MPa, indicating that the aluminum-plastic composite film materials of the examples are more superior in mechanical strength. In addition, in terms of elongation at break, although the values of the aluminum-plastic composite films of the examples are relatively low, their balanced mechanical properties ensure that the packaging materials still have a certain ductility while maintaining high strength, while the elongation at break of some samples in the comparative examples is relatively low, which may affect the practical application adaptability of the materials. Generally speaking, the aluminum-plastic composite films of the examples are superior to the comparative examples in terms of copper diffusion prevention ability, mechanical properties, and structural stability, and are more suitable for the requirements of high-performance lithium battery packaging.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that any equivalent structural transformation made under the concept of the present invention by using the content of the specification and drawings of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A copper diffusion-proof aluminum-plastic composite film for lithium batteries, characterized in that: The aluminum-plastic composite film includes, from outside to inside, a nylon layer, a first adhesive resin layer, an aluminum nitride / aluminum composite layer, a second adhesive resin layer, a barrier layer, a third adhesive resin layer, and a heat-sealing layer; The barrier layer is a boron nitride / polyvinylidene fluoride composite film; the boron nitride / polyvinylidene fluoride composite film includes a polyvinylidene fluoride based film and boron nitride dispersed in the polyvinylidene fluoride based film; the mass ratio of the boron nitride to the polyvinylidene fluoride based film is (0.8-1.2):1; The aluminum nitride / aluminum composite layer includes a metal aluminum layer and an aluminum nitride layer located on both sides of the metal aluminum layer; the thickness of the aluminum nitride layer is 50-200 nm.

2. The copper diffusion-proof aluminum-plastic composite film for lithium batteries according to claim 1, characterized in that: The boron nitride nanosheets in the boron nitride / polyvinylidene fluoride composite film are in a sheet-like structure, and the boron nitride nanosheets are oriented along the plane direction of the boron nitride / polyvinylidene fluoride composite film; The average diameter of the boron nitride nanosheets is 0.5-2 μm, and the average thickness is 10-100 nm.

3. The copper diffusion-proof aluminum-plastic composite film for lithium batteries according to claim 1, characterized in that: The method for preparing the boron nitride / polyvinylidene fluoride composite film comprises the following steps: (1) Adding boron nitride nanosheets and ethanol into a mixing container, adding sodium dodecyl sulfate, and obtaining a suspension after ultrasonic treatment; pouring the obtained suspension into a vacuum filtration device, filtering under negative pressure to form a porous boron nitride prefabricated layer; drying the porous boron nitride prefabricated layer at 60-100° C. for 2-4 hours, and then calcining it at 400-450° C. for 30-60 minutes in an air atmosphere, and cooling it to room temperature to obtain a porous boron nitride preform; (2) Stirring and mixing polyvinylidene fluoride and N-methylpyrrolidone, and obtaining a polymer solution after standing; placing a porous boron nitride preform in an impregnation tank, adding the polymer solution and impregnating for 5 to 10 minutes, taking it out and placing it in a vacuum curing furnace, heating it to 80 to 120° C. for solvent volatilization and curing for 2 to 6 hours, and then hot pressing the obtained preform at 120 to 150° C., the pressure is 2 to 5 MPa, and the pressure holding time is 30 to 60 minutes. After the hot pressing is completed, the temperature is lowered to room temperature to obtain the boron nitride / polyvinylidene fluoride composite film.

4. The copper diffusion-proof aluminum-plastic composite film for lithium batteries according to claim 3, characterized in that: In step (1), the mass ratio of the boron nitride nanosheets, sodium dodecyl sulfate, and ethanol is 0.5-4.5:0.05-0.5:100-150; In step (2), the mass ratio of polyvinylidene fluoride particles to N-methylpyrrolidone is 5.0-10.0:

100.

5. The copper diffusion-proof aluminum-plastic composite film for lithium batteries according to claim 3, characterized in that: The preparation method of the boron nitride nanosheets is: 1) By weight, 0.5-2.5 parts of hexagonal boron nitride powder are placed in a mixing container, and 200-300 parts of N-methylpyrrolidone and 1.0-3.5 parts of polyvinylpyrrolidone are added, and stirred at a stirring rate of 300-600 rpm for 10-30 minutes, and then ultrasonic stripping is performed, and the ultrasonic power is set to 300-500 W, the ultrasonic frequency is 40-60 kHz, the ultrasonic time is 120-360 minutes, and the temperature is controlled at 30-40 ° C; 2) After ultrasonic stripping is completed, the resulting suspension is transferred to a centrifuge tube and centrifuged at 3000-6000 rpm for 10-30 min; 3) Transfer the supernatant suspension obtained by centrifugation to a container, then continue to add ethanol twice the volume of the suspension, and centrifuge at a speed of 6000-8000 rpm for 10-20 minutes, and then continue to retain the supernatant suspension obtained by centrifugation; 4) Repeat step 3) 3 to 5 times, and finally transfer the obtained supernatant suspension to a rotary evaporator, and dry it at 60 to 100° C. and vacuum degree of -0.08 to -0.1 MPa for 6 to 12 hours to obtain boron nitride nanosheets.

6. The copper diffusion-proof aluminum-plastic composite film for lithium batteries according to claim 1, characterized in that: The preparation method of the aluminum nitride / aluminum composite layer is: Place the aluminum foil in the reaction chamber of the plasma nitriding furnace and evacuate to Pa, and then high-purity argon gas is introduced with a gas flow rate of 100~500sccm and a pressure of MPa, radio frequency plasma is used for surface pretreatment, the RF power is 300~500W, and the treatment time is 10~30min; after the pretreatment, high-purity nitrogen is introduced, the gas flow rate is 100~500sccm, and the pressure is MPa, and then the obtained aluminum foil is heated to 500-530°C at a heating rate of 5-10°C / min, and a radio frequency plasma is used for plasma enhanced nitridation treatment, the RF power is 300-500W, and the treatment time is 120-360min. After the nitridation treatment is completed, the heating is stopped, and high-purity argon gas is introduced for protective cooling, and the cooling rate is controlled to be 5-20°C / min until the temperature drops to room temperature, and finally an aluminum nitride / aluminum composite layer is obtained.

7. The copper diffusion-proof aluminum-plastic composite film for lithium batteries according to claim 1, characterized in that: The thickness of the barrier layer is 30-60 μm; The thickness of the aluminum nitride / aluminum composite layer is 10.0-50.0 μm; The thickness of the nylon layer is 10-30 μm.

8. The copper diffusion-proof aluminum-plastic composite film for lithium batteries according to claim 1, characterized in that: The heat sealing layer is ethylene-methacrylic acid copolymer, and its thickness is 30-60 μm.

9. The copper diffusion-proof aluminum-plastic composite film for lithium batteries according to claim 1, characterized in that: The first adhesive resin layer, the second adhesive resin layer and the third adhesive resin layer are all epoxy resin layers, and the thickness of the first adhesive resin layer, the second adhesive resin layer and the third adhesive resin layer is 2.0-5.0 μm.

10. A method for preparing the copper diffusion-proof aluminum-plastic composite film for lithium batteries according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. A resin adhesive is evenly applied to one side of the nylon layer close to the aluminum nitride / aluminum composite layer. After the coating is completed, it is pre-dried at 60 to 80 ° C and then superimposed with the aluminum nitride / aluminum composite layer, and then hot-pressed by a continuous roller press to obtain a first composite film; S2. The surface of the aluminum nitride / aluminum composite layer of the first composite film is uniformly coated with a resin adhesive. After the coating is completed, it is pre-dried at 60 to 80 ° C, and then superimposed with the barrier layer, and then hot-pressed by a continuous roller press to obtain a second composite film; S3. The surface of the barrier layer of the second composite film is uniformly coated with a resin adhesive. After coating, it is pre-dried at 60-80°C, and then superimposed with a heat sealing layer, and then hot-pressed and laminated by a continuous roller press, and then aged to obtain the anti-copper diffusion aluminum-plastic composite film.

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