An aluminum-plastic composite film for preventing copper diffusion in lithium batteries and a preparation method thereof

Abstract

The present invention relates to the technical field of aluminum-plastic composite films, and provides an aluminum-plastic composite film for preventing copper diffusion in lithium batteries and a preparation method thereof. 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 material film; the boron nitride / polyvinylidene fluoride composite material film includes a polyvinylidene fluoride base film and boron nitride dispersed in the polyvinylidene fluoride base film; the aluminum nitride / aluminum composite layer includes a metal aluminum layer and aluminum nitride layers on both surface sides of the metal aluminum layer. By optimizing the material composition and process, the present invention improves the chemical stability and mechanical properties of the composite film, effectively inhibits copper diffusion, is suitable for high-safety lithium battery packaging, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum-plastic composite films, and particularly 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 field of current 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 battery energy density, the safety requirements for battery packaging materials have become increasingly prominent. Among them, as the core packaging material for soft-pack lithium batteries, aluminum-plastic composite films directly affect the chemical stability and cycle life of 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 in the battery, 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 battery 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] At present, regarding the problem of copper diffusion-proof in 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 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, but there is no microstructural 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 technology of copper diffusion-proof aluminum-plastic composite films. Summary of the Invention

[0004] (1) Technical Problems to be Solved

[0005] 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, to solve the problem of insufficient copper diffusion-proof performance of current aluminum-plastic composite films.

[0006] (2) Technical Solutions

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] 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;

[0009] 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;

[0010] 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.

[0011] Preferably, the boron nitride nanosheets in the boron nitride / polyvinylidene fluoride composite film are in a sheet structure, and the orientation of the boron nitride nanosheets is arranged along the plane direction of the boron nitride / polyvinylidene fluoride composite film;

[0012] The average diameter of the boron nitride is 0.5~2 μm, and the average thickness is 10~100 nm.

[0013] 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 is used as the core conductive layer, and both its upper and lower surfaces contain nanoscale aluminum nitride layers, which not only enhance the interlayer bonding force, but also provide an additional diffusion barrier, improve the copper diffusion prevention ability, and at the same time rely on the high thermal conductivity of aluminum nitride to optimize the thermal management performance of the packaging film, reduce the heat accumulation during high-rate charging and discharging of the battery, and improve the overall safety.

[0014] The first adhesive resin layer and the second adhesive resin layer form a uniform and stable bonding interface between the multi-layer materials, enhancing the mechanical flexibility of the film material and effectively preventing 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, protecting the structural integrity. Its high toughness ensures that the encapsulation film is not easily damaged during processing, packaging, and use. At the same time, it has good moisture resistance and chemical resistance, providing additional guarantee for the diffusion prevention function.

[0015] Preferably, the method for preparing the boron nitride / polyvinylidene fluoride composite film comprises the following steps:

[0016] (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, and 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;

[0017] (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 film.

[0018] The present invention prepares a boron nitride porous preform by using a vacuum filtration process, 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, enabling the polymer solution to penetrate into the pore structure of the boron nitride, and forming a uniform composite film after the solvent volatilizes and solidifies. 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 material film, enabling it to form a continuous sheet arrangement in the barrier layer, thereby effectively extending the diffusion path of copper ions, improving the barrier effect, and avoiding the increase in film brittleness caused by excessive filling. Overall, through the synergistic design of boron nitride / polyvinylidene fluoride, the present invention achieves excellent mechanical stability and interfacial bonding strength while ensuring high-efficiency copper diffusion prevention performance, providing a new technical solution for the high-performance of lithium battery packaging materials.

[0019] 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;

[0020] In step (2), the mass ratio of polyvinylidene fluoride particles and N-methylpyrrolidone is 5.0-10.0:100.

[0021] Preferably, the preparation method of the boron nitride nanosheets is as follows:

[0022] 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;

[0023] 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;

[0024] 3) Transfer the centrifuged supernatant suspension to a container, then continue to add ethanol in an amount twice the volume of the suspension, and centrifuge at a rotation speed of 6000 - 8000 rpm for 10 - 20 min, and then continue to retain the centrifuged supernatant suspension;

[0025] 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 - 0.1 MPa for 6 - 12 h to obtain boron nitride nanosheets.

[0026] The boron nitride / polyvinylidene fluoride composite membrane of the present invention is mainly used to enhance the copper diffusion prevention performance of the aluminum-plastic composite membrane. The preparation of boron nitride nanosheets adopts an ultrasonic exfoliation technique. Using hexagonal boron nitride powder as a 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 through centrifugal purification and rotary evaporation drying.

[0027] Preferably, the preparation method of the aluminum nitride / aluminum composite layer is as follows: Place the 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 - 500 sccm and a pressure of MPa, and perform surface pretreatment using radio frequency plasma with an RF power of 300 - 500 W and a treatment time of 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 with a gas flow rate of 100 - 500 sccm and a pressure of MPa, then heat the obtained aluminum foil to 500 - 530 °C at a heating rate of 5 - 10 °C / min, and simultaneously perform plasma-enhanced nitriding treatment using radio frequency plasma with an RF power of 300 - 500 W and a treatment time of 120 - 360 min. After the nitriding treatment is completed, stop heating and introduce high-purity argon gas for protective cooling, controlling the cooling rate to be 5 - 20 °C / min until the temperature drops to room temperature, and finally obtain the aluminum nitride / aluminum composite layer.

[0028] The present invention uses an aluminum nitride / aluminum composite layer and a barrier layer mainly to enhance the copper diffusion prevention performance of lithium battery packaging materials, while taking into account mechanical stability, thermal management ability, and interfacial bonding performance. The aluminum nitride / aluminum composite layer is prepared by plasma-enhanced nitridation process. First, the aluminum foil is subjected to radio frequency plasma surface pretreatment to remove the natural aluminum oxide 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.

[0029] Preferably, the thickness of the barrier layer is 30 - 60 μm;

[0030] The thickness of the aluminum nitride / aluminum composite layer is 10.0 - 50.0 μm;

[0031] The thickness of the nylon layer is 10 - 30 μm.

[0032] Preferably, the heat-sealing layer is ethylene-methyl acrylate copolymer, and its thickness is 30 - 60 μm.

[0033] 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.

[0034] The present invention also provides a preparation method for a copper diffusion prevention aluminum-plastic composite film for lithium batteries, comprising the following steps:

[0035] S1. Uniformly coat a resin adhesive on the side of the nylon layer close to the aluminum nitride / aluminum composite layer. After coating, pre-dry it at 60 - 80 °C, then stack it with the aluminum nitride / aluminum composite layer, and then hot-press and compound it through a continuous roller press to obtain a first composite film;

[0036] S2. Uniformly coat a resin adhesive on the surface of the aluminum nitride / aluminum composite layer of the first composite film. After coating, pre-dry it at 60 - 80 °C, then stack it with the barrier layer, and then hot-press and compound it through a continuous roller press to obtain a second composite film;

[0037] S3. Uniformly coat the surface of the barrier layer of the second composite film with a resin adhesive. After coating, pre-dry it at 60-80 °C, then stack it with the heat-sealing layer, and then thermally press and laminate it through a continuous roller press, and then cure it to obtain the copper diffusion-proof aluminum-plastic composite film.

[0038] (3) Beneficial technical effects

[0039] 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 relying on the oriented arrangement of boron nitride flakes and a highly dense polymer matrix to ensure long-term stability. The aluminum nitride / aluminum composite layer strengthens the bonding force through nano-scale aluminum nitride interfaces, provides an additional diffusion barrier, and optimizes the thermal management performance to reduce 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.

[0040] 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. Processes such as ultrasonic exfoliation, vacuum filtration and hot pressing treatment are used to ensure uniform distribution and high stability of the material, avoiding problems such as insufficient interfacial bonding force and increased brittleness of the barrier layer in traditional solutions, and providing a reliable solution for high-safety lithium battery packaging.

[0041] 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 uses 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 control the thickness of the composite layer to make it flexible while ensuring the barrier performance, avoiding the brittleness problem caused by the increase in layer thickness in traditional solutions, and providing a reliable solution for high-safety lithium battery packaging. Description of the drawings

[0042] Figure 1 It is a microstructural morphology diagram of the boron nitride porous preform prepared in Example 1 of the present invention.

[0043] Figure 2 It is a microstructural morphology diagram of the barrier layer prepared in Example 1 of the present invention.

[0044] Figure 3 This 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

[0045] 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.

[0046] Example 1

[0047] A copper diffusion-proof aluminum-plastic composite film for lithium batteries, which 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.

[0048] 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; 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 0.5 μm, and the average thickness is 10 nm.

[0049] 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.

[0050] 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 thickness of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer is 2.0 μm; the thickness of the nylon layer is 10 μm; the heat-sealing layer is an ethylene-methyl acrylate copolymer, and its thickness is 30 μm.

[0051] The preparation method of the boron nitride / polyvinylidene fluoride composite film in this example is as follows:

[0052] (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 sulfate are added continuously. 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.

[0053] (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 bubbles to 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.

[0054] The preparation method of the boron nitride nanosheets in this example is as follows:

[0055] 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 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;

[0056] 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;

[0057] 3) The centrifuged supernatant suspension is transferred to a clean container, and then ethanol twice the volume of the suspension is added continuously, and centrifuged at a speed of 6000 rpm for 10 min. Then, the centrifuged supernatant suspension is retained;

[0058] 4) Repeat step 3) three times. Finally, transfer the obtained supernatant suspension to a rotary evaporator and dry it at 60 °C under a vacuum of -0.08 MPa for 6 h to finally obtain boron nitride nanosheets.

[0059] 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 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, raise 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 to perform 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 at 5 °C / min until the temperature drops to room temperature to finally obtain the aluminum nitride / aluminum composite layer.

[0060] The preparation method of a copper diffusion-proof aluminum-plastic composite film for lithium batteries in this example includes the following steps:

[0061] 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 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;

[0062] 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;

[0063] 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 cure it to obtain the copper diffusion-proof aluminum-plastic composite film.

[0064] 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 diffusion inhibition ability of the barrier layer against copper ions. Figure 2Further 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 structure is dense and uniform. This indicates that the boron nitride / polyvinylidene fluoride composite film has successfully achieved a highly oriented sheet arrangement during the preparation process, thereby improving the anti-diffusion performance of the material. Figure 3 Shows the cross-sectional microstructure of the aluminum nitride / aluminum composite layer. A uniform and continuous aluminum nitride layer can be clearly observed, which indicates that the plasma-enhanced nitridation treatment effectively forms a high-quality aluminum nitride interface 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 efficient anti-copper diffusion performance and excellent mechanical stability by optimizing the orientation structure of the boron nitride nanosheets and the interface engineering of the aluminum nitride / aluminum layer.

[0065] Example 2

[0066] 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.

[0067] 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 sheet 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.

[0068] 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 95 nm; the thickness of the aluminum nitride / aluminum composite layer is 22 μm.

[0069] 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 thickness of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer is 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.

[0070] The preparation method of the boron nitride / polyvinylidene fluoride composite film in this example is as follows:

[0071] (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. Next, 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 porous boron nitride preform layer. Then, the porous boron nitride preform layer is dried at 72 °C for 2.6 h. Finally, in an air atmosphere, the porous boron nitride preform layer is calcined at 415 °C for 39 min to remove organic substances, and cooled to room temperature to obtain a porous boron nitride preform.

[0072] (2) By weight, 6.5 parts of polyvinylidene fluoride particles and 100 parts of N-methylpyrrolidone are added to a stirring container and stirred at a stirring rate of 390 rpm for 39 min to form a uniform and transparent polymer solution. After stirring, the polymer solution is allowed to stand for 78 min to remove 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 30 °C for 7 min. Then, the porous boron nitride preform impregnated with the polymer solution is taken out, placed horizontally in a vacuum curing furnace, and solvent volatilization curing is carried out at 92 °C. The curing time is 3.2 h, and the heating rate is 2.2 °C / min. During the curing process, after curing is completed, the preform is subjected to hot pressing treatment at 129 °C, the pressure is controlled at 2.9 MPa, and the pressure holding time is 39 min. After hot pressing, it is slowly cooled to room temperature to obtain a boron nitride / polyvinylidene fluoride composite membrane.

[0073] The preparation method of the boron nitride nanosheets in this example is as follows:

[0074] 1) By weight, 1.1 parts of hexagonal boron nitride powder are placed in a clean and dry mixing container. Then, 230 parts of N-methylpyrrolidone and 1.8 parts of polyvinylpyrrolidone are added, and stirred at a stirring rate of 390 rpm for 16 min. Next, ultrasonic exfoliation treatment is carried out. The ultrasonic power is set to 360 W, the ultrasonic frequency is 46 kHz, and the ultrasonic time is 192 min. The ultrasonic process is cooled by a water bath, and the temperature is controlled at 33 °C;

[0075] 2) After ultrasonic exfoliation is completed, the obtained suspension is transferred to a centrifuge tube and centrifuged at a rotation speed of 3900 rpm for 16 min;

[0076] 3) The centrifuged supernatant suspension is transferred to a clean container, and then ethanol twice the volume of the suspension is added continuously, and centrifuged at a rotation speed of 6600 rpm for 13 min. Then, the centrifuged supernatant suspension is continuously retained;

[0077] 4) Repeat step 3) four times. Finally, transfer the obtained supernatant suspension to a rotary evaporator and dry it at 72 °C under a vacuum of -0.087 MPa for 7.8 h to finally obtain boron nitride nanosheets.

[0078] 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 220 sccm and a pressure of 0.028 MPa. Perform surface pretreatment using radio frequency plasma with an RF power of 360 W and a treatment time of 16 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 220 sccm and a pressure of 0.028 MPa. Then heat the aluminum foil 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 nitriding treatment for 192 min. After the nitriding reaction is completed, stop heating and introduce high-purity argon gas for protective cooling, controlling the cooling rate at 9.5 °C / min until the temperature drops to room temperature to finally obtain the aluminum nitride / aluminum composite layer.

[0079] A preparation method of a copper diffusion-proof aluminum-plastic composite film for lithium batteries in this example includes the following steps:

[0080] 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 70 °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;

[0081] 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 70 °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;

[0082] 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 70 °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.

[0083] Example 3

[0084] A copper diffusion-proof aluminum-plastic composite film for lithium batteries, 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.

[0085] The barrier layer is a boron nitride / polyvinylidene fluoride composite membrane, and the thickness of the barrier layer is 50 μm. The boron nitride / polyvinylidene fluoride composite membrane 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 0.95:1; the boron nitride nanosheets in the boron nitride / polyvinylidene fluoride composite membrane 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 membrane; the average diameter of the boron nitride nanosheets is 1.7 μm, and the average thickness is 64 nm.

[0086] 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 140 nm; the thickness of the aluminum nitride / aluminum composite layer is 34.0 μm.

[0087] 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 thickness of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer is 3.8 μm; the thickness of the nylon layer is 22 μm; the heat-sealing layer is an ethylene-methyl methacrylate copolymer, and its thickness is 53 μm.

[0088] The preparation method of the boron nitride / polyvinylidene fluoride composite membrane in this embodiment is as follows:

[0089] (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 porous boron nitride preform layer. Then dry the porous boron nitride preform layer at 84°C for 3.2 h, and finally, in an air atmosphere, calcine the porous boron nitride preform layer at 430°C for 48 min to remove organic substances, and cool it to room temperature to obtain a porous boron nitride preform.

[0090] (2) Add 8.0 parts by weight of polyvinylidene fluoride particles and 100 parts of N-methylpyrrolidone into 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 and 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 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 carry out 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 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 hot pressing is completed, slowly cool down to room temperature to obtain the boron nitride / polyvinylidene fluoride composite membrane.

[0091] The preparation method of the boron nitride nanosheets in this example is as follows:

[0092] (1) Place 1.7 parts by weight of hexagonal boron nitride powder in a clean and dry mixing container, and 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.

[0093] (2) After the ultrasonic exfoliation is completed, transfer the obtained suspension to a centrifuge tube and centrifuge at a rotation speed of 4800 rpm for 22 min.

[0094] (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 rotation speed of 7200 rpm for 16 min. Then continue to retain the supernatant suspension obtained by centrifugation.

[0095] (4) Repeat step (3) 4 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.

[0096] 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 340 sccm and a pressure of 0.046 MPa. Radio-frequency plasma was used for surface pretreatment with an RF power of 420 W and a treatment time of 22 min to remove the natural alumina 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 340 sccm and a pressure of 0.046 MPa. Then, the aluminum foil was heated to 525 °C at a heating rate of 8.0 °C / min while the radio-frequency plasma was turned on with an RF power of 420 W for plasma-enhanced nitridation treatment for 264 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 14.0 °C / min until the temperature dropped to room temperature, and finally an aluminum nitride / aluminum composite layer was obtained.

[0097] A method for preparing a copper diffusion-proof aluminum-plastic composite film for a lithium battery according to this embodiment includes the following steps:

[0098] 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 80 °C, and then it was superimposed on the aluminum nitride / aluminum composite layer, and then hot-pressed and compounded through a continuous roller press to obtain a first composite film;

[0099] 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 80 °C, and then it was superimposed on the barrier layer, and then hot-pressed and compounded through a continuous roller press to obtain a second composite film;

[0100] 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 80 °C, and then it was superimposed on the heat-sealing layer, and then hot-pressed and compounded through a continuous roller press and then cured to obtain the copper diffusion-proof aluminum-plastic composite film.

[0101] Example 4

[0102] A copper diffusion-proof aluminum-plastic composite film for a lithium battery, where 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 the outside to the inside.

[0103] 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; in the boron nitride / polyvinylidene fluoride composite film, the boron nitride nanosheets 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 2 μm, and the average thickness is 100 nm.

[0104] 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 200 nm; the thickness of the aluminum nitride / aluminum composite layer is 50.0 μm.

[0105] 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 thickness of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer is 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.

[0106] The preparation method of the boron nitride / polyvinylidene fluoride composite film in this embodiment is as follows:

[0107] (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 further added, 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 preform layer. Then, the boron nitride porous preform layer is dried at 100°C for 4 h, and finally, in an air atmosphere, the boron nitride porous preform 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.

[0108] (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 stirring, 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 for 6 h, and the heating rate is 5 °C / min. During the curing process, after 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 hot pressing, it is slowly cooled to room temperature to obtain a boron nitride / polyvinylidene fluoride composite film.

[0109] The preparation method of the boron nitride nanosheets in this example is as follows:

[0110] 1) By weight, 2.5 parts of hexagonal boron nitride powder are placed in a clean and dry mixing container, and 300 parts of N-methylpyrrolidone and 3.5 parts of polyvinylpyrrolidone are further added, 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;

[0111] 2) After the ultrasonic exfoliation is completed, the obtained suspension is transferred to a centrifuge tube and centrifuged at a rotation speed of 6000 rpm for 30 min;

[0112] 3) The centrifuged supernatant suspension is transferred to a clean container, and then ethanol twice the volume of the suspension is further added, and centrifuged at a rotation speed of 8000 rpm for 20 min, and then the centrifuged supernatant suspension is continuously retained;

[0113] 4) Step 3) is repeated 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.

[0114] 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 500 sccm and a pressure of 0.1 MPa. Radio-frequency plasma was used for surface pretreatment 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 was completed, high-purity nitrogen gas was introduced with a gas flow rate of 500 sccm and a pressure of 0.1 MPa. Then, the aluminum foil was heated to 530 °C at a heating rate of 10 °C / min while starting the radio-frequency plasma with an RF power of 500 W for plasma-enhanced nitridation treatment with a treatment time of 360 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 20 °C / min until the temperature dropped to room temperature, and finally an aluminum nitride / aluminum composite layer was obtained.

[0115] A preparation method of a copper diffusion-proof aluminum-plastic composite film for lithium batteries in this embodiment includes the following steps:

[0116] 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 80 °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 the first composite film;

[0117] 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 80 °C, and then it was superposed with the barrier layer, and then hot-pressed and compounded through a continuous roll press to obtain the second composite film;

[0118] 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 80 °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.

[0119] Comparative Example 1:

[0120] It was basically the same as Example 1, except that the barrier layer did not use a boron nitride / polyvinylidene fluoride composite film but a single polyvinylidene fluoride film.

[0121] Comparative Example 2:

[0122] It was basically the same as Example 1, except that the aluminum nitride / aluminum composite layer was replaced with an aluminum foil.

[0123] Comparative Example 3:

[0124] It was basically the same as Example 1, except that the mass ratio of boron nitride to polyvinylidene fluoride in the barrier layer was 1.5:1.

[0125] Comparative Example 4:

[0126] It is basically the same as Example 1, except that when preparing the boron nitride / polyvinylidene fluoride composite membrane, the boron nitride nanosheets are replaced with hexagonal boron nitride powder.

[0127] Performance test:

[0128] Copper diffusion prevention performance test: The prepared aluminum-plastic composite membrane was cut into test samples of 2 cm×2 cm and clamped between a copper foil and an electrolyte solution ( solution), and a diffusion experiment was carried out at 60°C. Inductively coupled plasma mass spectrometry (ICP-MS) was used to measure the concentration of copper ions in the immersion solution and compared with the samples of the comparative example to evaluate the inhibitory effect of the boron nitride / polyvinylidene fluoride barrier layer on copper ion diffusion.

[0129] Mechanical property test: A tensile testing machine was used to test the tensile strength and elongation at break of the aluminum-plastic composite membrane. The test rate was set at 5 mm / min, and the sample size was 10 mm×50 mm.

[0130] The performances of the aluminum-plastic composite membranes of Examples 1-4 and Comparative Examples 1-4 are summarized in Table 1.

[0131] Table 1 Summary of the performances of the aluminum-plastic composite membranes of Examples 1-4 and Comparative Examples 1-4

[0132]

[0133] Compared with the comparative examples, the aluminum-plastic composite membranes 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 membranes of the examples is much lower than that of the comparative examples, with the lowest value reaching 0.01 μg / cm²·h, while the highest value of the aluminum-plastic composite membranes of the comparative examples is as high as 0.30 μg / cm²·h, indicating that the aluminum-plastic composite membranes of the examples have a more excellent barrier effect in inhibiting copper ion penetration. In terms of tensile strength, the values of the aluminum-plastic composite membranes of the examples are all higher than those of the comparative examples, with the highest value reaching 134 MPa, while the lowest value of the comparative examples is only 80 MPa, indicating that the aluminum-plastic composite membrane 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 membranes 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 membranes 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.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. 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. An aluminum-plastic composite film for preventing copper diffusion in lithium batteries, characterized in that, 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; In the boron nitride / polyvinylidene fluoride composite film, the boron nitride nanosheets 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 0.5~2 μm, and the average thickness is 10~100 nm.

2. The aluminum-plastic composite film for preventing copper diffusion in a lithium battery according to claim 1, wherein The preparation method of the boron nitride / polyvinylidene fluoride composite film includes the following steps: (1) Add boron nitride nanosheets and ethanol into a mixing container, add sodium dodecyl sulfate, 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, and 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 volatilization 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 film.

3. The aluminum-plastic composite film for preventing copper diffusion in a lithium battery according to claim 2, wherein 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 and N-methylpyrrolidone is 5.0~10.0:

100.

4. The aluminum-plastic composite film for preventing copper diffusion in a lithium battery according to claim 2, wherein The preparation method of the boron nitride nanosheets is: 1) By weight, place 0.5~2.5 parts of hexagonal boron nitride powder in a mixing container, continue to add 200~300 parts of N-methylpyrrolidone and 1.0~3.5 parts of polyvinylpyrrolidone, 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 to 30~40 °C; 2) After ultrasonic exfoliation, transfer the obtained suspension to a centrifuge tube and centrifuge at a rotational 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 twice the volume of the suspension, and centrifuge at a rotational speed of 6000 - 8000 rpm for 10 - 20 min, 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 under a vacuum of -0.08 - 0.1 MPa for 6 - 12 h to obtain boron nitride nanosheets.

5. The aluminum-plastic composite film for preventing copper diffusion in a lithium battery according to claim 1, wherein The preparation method of the aluminum nitride / aluminum composite layer is as follows: Place the aluminum foil in the reaction chamber of the plasma nitriding furnace and evacuate to , then introduce high-purity argon gas with a gas flow rate of 100 - 500 sccm and a pressure of . Perform surface pretreatment using radio frequency plasma with an RF power of 300 - 500 W and a treatment time of 10 - 30 min. After the pretreatment, introduce high-purity nitrogen gas with a gas flow rate of 100 - 500 sccm and a pressure of . Then heat the obtained aluminum foil to 500 - 530 °C at a heating rate of 5 - 10 °C / min, and simultaneously perform plasma enhanced nitriding treatment using radio frequency plasma with an RF power of 300 - 500 W and a treatment time of 120 - 360 min. After the nitriding treatment is completed, stop heating and introduce high-purity argon gas for protective cooling, controlling the cooling rate to be 5 - 20 °C / min until the temperature drops to room temperature, and finally obtain an aluminum nitride / aluminum composite layer.

6. The aluminum-plastic composite film for preventing copper diffusion in a lithium battery according to claim 1, wherein 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.

7. The aluminum-plastic composite film for preventing copper diffusion in a lithium battery according to claim 1, wherein The heat-sealing layer is ethylene-methacrylic acid copolymer, and its thickness is 30 - 60 μm.

8. The aluminum-plastic composite film for preventing copper diffusion in a lithium battery 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 thicknesses of the first adhesive resin layer, the second adhesive resin layer, and the third adhesive resin layer are 2.0 - 5.0 μm.

9. A method for preparing a copper diffusion-proof aluminum-plastic composite film for a lithium battery according to any one of claims 1 to 8, characterized in that, It includes 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, pre-dry it at 60 - 80 °C, then stack it with the aluminum nitride / aluminum composite layer, and then hot-press and laminate it through a continuous roller press to obtain a first composite film; S2. Uniformly coat a resin adhesive on the surface of the aluminum nitride / aluminum composite layer of the first composite film. After coating, pre-dry it at 60 - 80 °C, then stack it with the barrier layer, and then hot-press and laminate it through a continuous roller press to obtain a second composite film; S3. Uniformly coat a resin adhesive on the surface of the barrier layer of the second composite film. After coating, pre-dry it at 60 - 80 °C, then stack it with the heat-sealing layer, and then hot-press and laminate it through a continuous roller press, and then cure it to obtain the copper diffusion-proof aluminum-plastic composite film.

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