Composite current collector based on PP (Polypropylene) base film / PET (Polyethylene Terephthalate) base film and production process

Abstract

The invention discloses a composite current collector based on a PP (Polypropylene) base film / PET (Polyethylene Terephthalate) base film and a production process. The process comprises the following steps: S1, pre-treating a base film; s2, physical modification treatment; s3, preparing a double-layer middle transition layer; and S4, preparing a metal layer. According to the physical modification, a micro-nano rough structure is constructed on the surface of the base film through plasma etching, so that impurities in a weak boundary layer are removed, the contact area is increased by 3-5 times, a mechanical occlusion basis is provided for a transition layer and a metal layer, and meanwhile, a small amount of oxygen-containing polar groups are introduced to preliminarily improve the surface energy; the transition layer is of a composite structure of a silane coupling agent and a Cr layer, the coupling agent and the Cr layer are connected through Si-O-C covalent bonds and polar groups of the base film and Cr-N coordinate bonds, and Cr atoms are embedded into rough pits to form the dual effect of mechanical anchoring and chemical bridging, so that the peeling strength of the metal layer and the base film is greatly improved through the cooperation of the two; the mechanical requirement of long-term circulation of the lithium battery is met.

Description

Technical Field

[0001] This invention belongs to the field of composite current collector technology, and particularly relates to composite current collectors based on PP base film / PET base film and the production process of composite current collectors based on PP base film / PET base film. Background Technology

[0002] Current collectors are an indispensable electrode material in lithium-ion batteries, playing a crucial role in carrying active materials (carrying capacity) and collecting microcurrents (conductivity). Composite current collectors employ a "metal-polymer-metal" sandwich structure, with an inner polymer layer (such as PET, PP, or PI base film) and conductive metal layers on both sides. By combining the properties of different materials, lightweight, high safety, and high performance are achieved. The core lies in using a polymer base film (such as PET or PP base film) in the middle layer and a metal film (such as copper or aluminum) on the outer layer. This retains the conductivity of the metal while also possessing the lightweight, flexibility, and insulation properties of the polymer material, significantly improving battery energy density and reducing safety hazards.

[0003] PP / PET base film is a non-polar or weakly polar polymer. When used as a base film, it has low surface energy, poor compatibility with polar metal layers (Cu / Al), and insufficient interfacial bonding. During charging and discharging, the metal layer is prone to peeling off, which leads to a shortened battery cycle life and working time. Summary of the Invention

[0004] This invention addresses the problem in existing technologies where poor compatibility and insufficient interfacial adhesion between the base film and the polar metal layer easily lead to metal layer detachment, and proposes the following technical solution: The production process of composite current collectors based on PP / PET film includes the following steps: S1. Base film pretreatment; Select PP or PET base film with a thickness of 3-12μm, and remove oil and other impurities attached to the outer surface after cleaning process; S2, Physical modification treatment; The base film is placed in a plasma processing device with Ar / O2 mixed gas as the working medium. After the device is started, high-energy ions continuously bombard the surface of the base film. The weak boundary layer on the surface of the base film is effectively removed, while a uniform 50-200nm micro-nano rough structure is formed to provide "mechanical anchoring space". Under the action of oxidation reaction, some chemical bonds are broken to introduce oxygen-containing groups such as hydroxyl (-OH) and carboxyl (-COOH) on the surface of the base film. S3, Preparation of a double-layer intermediate transition layer; a. Preparation of coupling agent transition layer: Immerse the base film in a mixture of silane coupling agent and ethanol, with a volume ratio of silane coupling agent to ethanol of 9:1. After immersion for 1-2 minutes, remove the base film and dry it at 60-70℃. A 5-10 nm coupling agent layer is formed on the surface of the dried base film. The -Si(OCH3)3 in the mixture undergoes a hydrolysis and condensation reaction with the -OH on the surface of the base film to form Si-OC covalent bonds for strong anchoring. b. Preparation of metal transition layer: Cr target is selected as sputtering source and sputtering is performed by magnetron sputtering process to deposit a Cr layer with a thickness of 5-10 nm on the surface of the coupling agent transition layer. At the same time, the Cr layer forms Cr-N chemical bonds with the exposed -NH2 groups of the coupling agent transition layer, and the Cr atoms are embedded in the micro-nano rough structure formed by the physical modification of the base film by means of their own diffusion ability, forming a "mechanical interlocking" effect with the surface of the base film. S4. Metal layer preparation; Using Ar + Ion bombardment of the transition layer surface removes the oxide layer and activates atomic activity. Subsequently, based on the current collector polarity, two metal layers are sputtered sequentially. Metal atoms (Cu...) 2+ / Al 3+ While forming a solid solution alloy with the Cr transition layer, it uniformly nucleates along the coupling agent layer to avoid "island growth" of the metal layer. After the metal layer is prepared, a composite current collector is formed.

[0005] As a preferred embodiment of the above technical solution, S5 and post-processing are also included; The composite current collector was subjected to low-temperature annealing and plasma passivation treatment. After the treatment, the defects in the metal layer and the peel strength of the composite current collector were detected by optical microscope and peel tester.

[0006] As a preferred embodiment of the above technical solution, steps S2 and S3 further include chemical modification treatment: When the base film is PP base film, the physically modified PP base film is immersed in the modification solution and reacted in a water bath at a constant temperature of 60-70℃ for 2-3 hours. After ultrasonic cleaning with acetone and vacuum drying, the chemical modification treatment of PP base film is completed. When the base film is a PET base film, the coating liquid is coated on the surface of the physically modified PET base film by micro-gravure coating process, and the wet film thickness is controlled to be 50-100nm. Then, it is quickly dried at 100-120℃ for 30-60s to form an ultra-thin polar coating of 10-20nm.

[0007] As a preferred embodiment of the above technical solution, the modified liquid consists of maleic anhydride, benzoyl peroxide, and toluene. The content of maleic anhydride is 0.5-1 wt% of the modified liquid, and the content of benzoyl peroxide is 0.1-0.2 wt% of the modified liquid. Benzoyl peroxide acts as an initiator, decomposing to generate free radicals that attack the CH bonds on the PP base film molecular chain, causing them to break and form active sites. The maleic anhydride monomer binds to the active sites through the opening of double bonds, grafting polymer chains containing a large number of carboxyl groups (-COOH) onto the surface of the PP base film to enhance surface polarity.

[0008] As a preferred embodiment of the above technical solution, the coating liquid is composed of polyurethane and N,N-dimethylformamide solvent, and the content of polyurethane is 1-2 wt% of the coating liquid. The polyurethane molecular chains are tightly attached to the PET base film by forming hydrogen bonds with a small number of hydroxyl groups (-OH) on the surface, forming a large number of polar groups that enhance the surface chemical activity.

[0009] As a preferred embodiment of the above technical solution, the cleaning process in step S1 includes the following: Ethanol ultrasonic cleaning: Place the base film in an ultrasonic cleaner with ethanol as the medium and clean for 10-15 minutes to remove oil and dirt from the surface of the base film; Rinse with deionized water: Rinse the cleaned base film with deionized water to remove surface ethanol residue, and then vacuum dry in a drying oven at 60-80℃ for 30-60 minutes to remove moisture.

[0010] As a preferred embodiment of the above technical solution, in step S2, during plasma treatment, the temperature of the PP base film is ≤60℃ and the temperature of the PET base film is ≤80℃.

[0011] As a preferred embodiment of the above technical solution, in step S4, during the sputtering treatment of the metal layer, the temperature of the PP base film is ≤80℃ and the temperature of the PET base film is ≤120℃.

[0012] The composite current collector based on PP / PET film is prepared by a production process. The cross-sectional structure of the composite current collector from the inside to the outside is as follows: PP / PET film → chemical modification layer → KH550 coupling agent layer → Cr transition layer → Cu / Al metal layer → oxide passivation film.

[0013] The beneficial effects of this invention are as follows: 1. Physical modification involves constructing a micro-nano rough structure on the surface of the base film through plasma etching. This removes weak boundary layer impurities and increases the contact area by 3-5 times, providing a basis for "mechanical interlocking" between the transition layer and the metal layer. At the same time, a small amount of oxygen-containing polar groups are introduced to initially improve the surface energy. The transition layer is a composite structure of silane coupling agent and Cr layer. It is connected to the polar groups of the base film through Si-OC covalent bonds and Cr-N coordination bonds. Furthermore, the Cr atoms are embedded in the rough pits to form a dual effect of "mechanical anchoring + chemical bridging". The two work together to significantly improve the peel strength between the metal layer and the base film, meeting the mechanical requirements of long-term cycling of lithium batteries. 2. Chemical modification introduces a large number of -COOH groups by grafting maleic anhydride onto the PP base film and introduces -NH2 and -OH groups by coating the PET base film with polyurethane. This significantly increases the density of polar groups and surface energy, providing more active sites for the Si-OC covalent bonds of the silane coupling agent in the transition layer. This effectively enhances the bonding force between the transition layer and the base film, indirectly strengthening the overall bonding of the metal layer. The supplementary role of chemical modification can overcome the limitations of the shallow distribution of polar groups in physical modification, constructing a micron-scale "polar group enrichment region." This ensures the long-term stability of the bonding sites in the transition layer and forms a multi-scale synergistic interface of "base film-chemically modified layer-transition layer-metal layer." This allows for gradient transmission of bonding force between layers rather than layer-by-layer attenuation, breaking through the bottleneck of the traditional layer-by-layer decrease in interfacial bonding force. Ultimately, this achieves comprehensive optimization of the bonding strength, integrity, and stability of the metal layer. Attached Figure Description

[0014] Figure 1 The diagram shown is a process flow chart of an embodiment. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments and the accompanying drawings.

[0016] Example 1 Figure 1 The production process of composite current collectors based on PP / PET film includes the following steps: S1. Base film pretreatment; Select PP or PET base film with a thickness of 3-12μm, and remove oil and other impurities attached to the outer surface after cleaning process; The cleaning process in step S1 includes the following: Ethanol ultrasonic cleaning: Place the base film in an ultrasonic cleaner with ethanol as the medium and clean for 10-15 minutes to remove oil stains from the surface of the base film. The ethanol ultrasonic cleaning power is 300-500W. The mechanical vibration of the ultrasonic waves causes the oil stains and particulate impurities to detach from the surface of the base film and dissolve in the ethanol. Rinsing with deionized water: Rinse the cleaned base film with deionized water to remove surface ethanol residue, and then vacuum dry it in a drying oven at 60-80℃ for 30-60 minutes to remove moisture. The vacuum degree of vacuum drying is ≤-0.09MPa. By reducing the air pressure, the evaporation of moisture or solvent is accelerated, and the residual liquid is avoided from interfering with subsequent modification.

[0017] S2, Physical modification treatment; The base film is placed in a plasma processing device with an Ar / O2 mixed gas as the working medium. The ratio of Ar to O2 mixed gas is 3:1-5:1. After the device is started, high-energy ions continuously bombard the surface of the base film. The weak boundary layer on the surface of the base film is effectively removed, and a uniform 50-200nm micro-nano rough structure is formed to provide a "mechanical anchoring space". Under the action of oxidation reaction, some chemical bonds are broken to introduce oxygen-containing groups such as hydroxyl (-OH) and carboxyl (-COOH) on the surface of the base film. In step S2, during plasma treatment, the temperature of the PP base film is ≤60℃ and the temperature of the PET base film is ≤80℃.

[0018] During physical modification, physical etching is used as a basis, accompanied by a mild oxidation reaction, to provide a "rough substrate" and "initial polarity sites" for subsequent chemical modification. Among these, Ar... + Plasma bombardment of the substrate surface disrupts the intermolecular forces on the substrate surface through momentum transfer, creating micro- and nano-depressions of 50-200 nm. The reactive oxygen species (O2) in the O2 plasma... + O2 + It reacts with the surface molecules of the base film (CC bonds in PP base film and CO bonds in PET base film), breaking some covalent bonds and introducing oxygen-containing polar groups such as hydroxyl (-OH) and carboxyl (-COOH) groups to form a "polar-nonpolar transition region".

[0019] S3, Preparation of a double-layer intermediate transition layer; a. Preparation of coupling agent transition layer: The base film is immersed in a mixture of silane coupling agent and ethanol, with a volume ratio of silane coupling agent to ethanol of 9:1. The silane coupling agent is KH550 silane coupling agent. After immersion for 1-2 minutes, the base film is taken out and dried at 60-70℃. A 5-10 nm coupling agent layer is formed on the surface of the dried base film. The -Si(OCH3)3 in the mixture undergoes a hydrolysis and condensation reaction with the -OH on the surface of the base film to form Si-OC covalent bonds for strong anchoring. The -Si(OCH3)3 group of the KH550 silane coupling agent undergoes a hydrolytic condensation reaction with the -OH group on the substrate surface to form a stable Si-OC covalent bond, anchoring the coupling agent to the substrate surface. The hydrolytic condensation reaction equation is as follows: Si-O-CH3+ -OH→Si-OC + CH3OH; The exposed -NH2 groups provide chemical bonding sites for the upper metal transition layer, while the coupling agent molecular chains penetrate into the micro-pits formed by the physical modification of the base film, filling the tiny gaps and further optimizing the surface smoothness.

[0020] b. Preparation of metal transition layer: Cr target is selected as sputtering source and sputtering is performed by magnetron sputtering process to deposit a Cr layer with a thickness of 5-10 nm on the surface of the coupling agent transition layer. At the same time, the Cr layer forms Cr-N chemical bonds with the exposed -NH2 groups of the coupling agent transition layer, and the Cr atoms are embedded in the micro-nano rough structure formed by the physical modification of the base film by means of their own diffusion ability, forming a "mechanical interlocking" effect with the surface of the base film.

[0021] The Cr layer forms Cr-N chemical bonds with the exposed -NH2 groups of the coupling agent layer. At the same time, Cr atoms are embedded in the micro-nano rough structure formed by the physical modification of the base film through their own diffusion ability, forming a "mechanical interlocking" effect. The excellent film-forming continuity of Cr itself builds a uniform base layer without pinholes on the surface of the base film, blocking the influence of potential defects in the base film on the subsequent metal layer.

[0022] S4. Metal layer preparation; Using Ar + Ion bombardment of the transition layer surface removes the oxide layer and activates atomic activity. + Ion pretreatment power 50-80W, time 30-40s, followed by sputtering of two metal layers sequentially according to the target material selected based on the current collector polarity, metal atoms (Cu) 2+ / Al 3+ While forming a solid solution alloy with the Cr transition layer, it uniformly nucleates along the coupling agent layer to avoid "island growth" of the metal layer. After the metal layer is prepared, a composite current collector is formed.

[0023] In step S4, during the sputtering treatment of the metal layer, the temperature of the PP base film is ≤80℃, the temperature of the PET base film is ≤120℃, the sputtering power of the Cr transition layer is 100-150W, and the vacuum degree is 5×10⁻⁶. -3 -1×10 -2 Pa.

[0024] Metal ions diffuse with Cr transition layer atoms to form Cu-Cr or Al-Cr solid solutions (alloying reaction), which strengthens the interfacial bonding.

[0025] Physical modification involves constructing a micro-nano rough structure on the base film surface through plasma etching. This removes weak boundary layer impurities and increases the contact area by 3-5 times, providing a basis for the "mechanical interlocking" between the transition layer and the metal layer. Simultaneously, a small amount of oxygen-containing polar groups are introduced to initially enhance surface energy. The transition layer, a composite structure of silane coupling agent and Cr layer, combines Si-OC covalent bonds with polar groups on the base film and Cr-N coordination bonds with the coupling agent and Cr layer. Furthermore, the embedding of Cr atoms into rough pits creates a dual effect of "mechanical anchoring + chemical bridging," significantly improving the peel strength between the metal layer and the base film, meeting the mechanical requirements of long-term cycling in lithium batteries. Simultaneously, physical modification removes impurities at the source to avoid the causes of porosity in the metal layer. The transition layer forms a continuous, pinhole-free bottom layer providing uniform nucleation sites, inhibiting "island growth" and local aggregation of metal atoms, reducing the metal nodule density to <3 nodules / mm². 2 With a porosity of <1%, and considering the differences in characteristics between PP base film (temperature resistance ≤80℃) and PET base film (temperature resistance ≤120℃), the physical modification and transition layer process parameters are precisely matched to ensure that the base film does not deform and the metal layer thickness deviation is ≤±5%. This synergistic approach breaks through the limitations of traditional single physical roughening or transition layers, innovatively constructing a multi-level interface effect of "macroscopic mechanical interlocking - microscopic chemical bonding", forming a defect suppression closed loop of "source impurity removal - process nucleation regulation", solving the core problem of poor compatibility and high defect rate between polymer and metal interfaces.

[0026] It also includes S5 and post-processing; The composite current collector was subjected to low-temperature annealing and plasma passivation treatment. After the treatment, the metal layer defects and peel strength of the composite current collector were detected by optical microscope and peel tester. During the low-temperature annealing treatment of the composite current collector, Ar gas was used for annealing at 80-130℃. The annealing temperature of PP base film composite current collector was 80-90℃ for 1-1.5h, and the annealing temperature of PET base film composite current collector was 120-130℃ for 0.5-1h. During the plasma passivation treatment of the composite current collector, O2 plasma passivation was used with a plasma passivation power of 50-100W for 10-20s, so that a 2-5nm oxide passivation film was formed on the surface of the composite current collector.

[0027] Steps S2 and S3 also include chemical modification treatment: When the base film is PP base film, the physically modified PP base film is immersed in the modification solution and reacted in a water bath at a constant temperature of 60-70℃ for 2-3 hours. After ultrasonic cleaning with acetone and vacuum drying, the chemical modification treatment of PP base film is completed. The modified liquid consists of maleic anhydride, benzoyl peroxide, and toluene. The content of maleic anhydride is 0.5-1 wt% of the modified liquid, and the content of benzoyl peroxide is 0.1-0.2 wt%. Benzoyl peroxide acts as an initiator, decomposing to generate free radicals that attack the CH bonds on the PP base film molecular chain, causing them to break and form active sites. Maleic anhydride monomers bind to the active sites through the opening of double bonds, grafting polymer chains containing a large number of carboxyl groups (-COOH) onto the surface of the PP base film to enhance surface polarity.

[0028] Benzoyl peroxide, acting as an initiator, decomposes to generate free radicals, which attack the CH bonds on the surface of the PP base film to form active free radicals. These free radicals then undergo an addition reaction (graft copolymerization) with maleic anhydride monomers (containing -COOH) to form C-C covalent bonds, "anchoring" the -COOH to the surface of the PP base film. Furthermore, the resulting grafted chains fill the physically modified micro-pits, improving the smoothness of the base film surface.

[0029] Preparation process of PP base film in Example 1: Base film pretreatment: Select PP base film with a thickness of 8μm (surface flatness ≤1μm), ultrasonically clean it with 300W ethanol for 15min, rinse it twice with deionized water, and vacuum dry it at 80℃ for 30min, controlling the water content to ≤0.1wt%.

[0030] Physical modification: Treatment was performed using an Ar / O2 mixed gas plasma at a ratio of 3:1, with a power of 150W, a duration of 90s, and a vacuum level of 10. - 1 Pa, base film temperature 60℃, forming a micro-nano rough structure with Ra=100nm, the surface energy is increased to 50mN / m.

[0031] Chemical modification: Prepare a modification solution of 0.5wt% maleic anhydride + 0.1wt% benzoyl peroxide + toluene, and perform grafting reaction in a constant temperature water bath at 60℃ for 2h → ultrasonic cleaning with acetone for 10min → vacuum drying at 80℃ for 1h, which increases the density of polar groups by 4 times.

[0032] Transition layer preparation: Coating with 1wt% KH550 coupling agent solution (ethanol / water = 9:1) → Drying at 60℃ for 15 min (forming an 8nm coupling agent layer) → Cr target magnetron sputtering (power 100W, vacuum degree 5×10⁻⁶). -3 Pa (thickness 8 nm), base film temperature 80℃.

[0033] Magnetron sputtered Cu layer: Ar + Ion pretreatment (50W, 40s) → Cu target sputtering (power 200W, vacuum 3×10⁻⁶) - 3 Pa (deposition rate 0.8 nm / s, thickness 1.5 μm), base film temperature 80 °C.

[0034] Post-treatment: Ar annealing at 80℃ for 1.5h → O2 plasma passivation (50W, 20s) to form a 3nm CuO passivation film.

[0035] Preparation process of PP base film comparative example 1: Base film pretreatment: Same as the PP base film example (8μm PP base film, ultrasonic cleaning with ethanol → vacuum drying).

[0036] Direct magnetron sputtering of Cu layers: Skipping physical modification, chemical modification, and transition layer steps, the pretreated PP base film is directly placed into the magnetron sputtering equipment → Ar + Ion pretreatment (50W, 40s) → Cu target sputtering (parameters consistent with the example: power 200W, vacuum degree 3×10) -3 Pa (thickness 1.5 μm), base film temperature 80℃.

[0037] Post-treatment: Same as the PP base film example (80℃ Ar annealing + O2 plasma passivation).

[0038] Table 1. Experimental data of PP base film Example 1 and PP base film Comparative Example 1 detection indicators Example 1 of PP base film PP base film comparative example 1 Performance improvement 90° metal layer peel strength 3.2 N / m 0.4N / m 7 times Porosity of metal layer 0.8% 8.5% Reduced by 90.6% Metal nodule density (>1μm) <![CDATA[2 per mm 2 > <![CDATA[18 per mm 2 > Reduced by 88.9% Metal-level resistance 8.5mΩ / □ 15.2mΩ / □ Reduced by 44.1% Bonding strength retention rate after 1000 cycles 82% 23% Increased by 2.6 times Example 2 When the base film is a PET base film, the coating liquid is coated on the surface of the physically modified PET base film by micro-gravure coating process, and the wet film thickness is controlled to be 50-100nm. Then, it is quickly dried at 100-120℃ for 30-60s to form an ultra-thin polar coating of 10-20nm.

[0039] The coating liquid is composed of polyurethane and N,N-dimethylformamide solvent. The polyurethane content is 1-2 wt% of the coating liquid. The polyurethane molecular chains are tightly attached to the PET base film surface by forming hydrogen bonds with a small number of hydroxyl groups (-OH), forming a large number of polar groups that enhance the surface chemical activity.

[0040] The polyurethane coating liquid (containing -NH2 and -OH) penetrates into the physically modified micro-nano defects under capillary action, filling micro-pinholes and scratches. After the solvent evaporates, a thin film is formed. The -NH2 and -OH of the polyurethane form hydrogen bonds with the -OH remaining on the surface of the PET base film, enhancing the bonding between the coating and the base film. This not only preserves the flexibility of the base film but also enhances the surface chemical activity through a large number of polar groups.

[0041] Chemical modification introduces a large number of -COOH groups by grafting maleic anhydride onto the PP base film and introduces -NH2 and -OH groups by coating the PET base film with polyurethane. This significantly increases the density of polar groups and surface energy, providing more active sites for the Si-OC covalent bonds of the silane coupling agent in the transition layer. This effectively enhances the bonding force between the transition layer and the base film, indirectly strengthening the overall bonding of the metal layer. Furthermore, the nanoscale pinholes or scratches remaining from physical modification can be filled through the capillary penetration of grafted chains or coating molecules in chemical modification, forming a smooth pre-supported surface and preventing penetrating pores in the metal layer. Moreover, the uniform chemically active region constructed by the high-density polar groups increases the nucleation density of Cr atoms in the transition layer by 2-3 times, guiding the uniform growth of metal atoms and reducing the thickness deviation of the metal layer. The supplementary role of chemical modification can overcome the limitations of the shallow distribution of polar groups in physical modification, constructing a micron-level "polar group enrichment zone" to ensure the long-term stability of the transition layer binding sites, resulting in a binding force retention rate of >80% after 1000 cycles of the metal layer; it can precisely repair microscopic defects through polymer chains, avoiding damage to the flexibility of the base film caused by physical polishing; and it can form a multi-scale synergistic interface of "base film-chemically modified layer-transition layer-metal layer", allowing the binding force of each layer to be gradient transmitted rather than attenuated layer by layer, breaking through the bottleneck of the traditional interface binding force decreasing layer by layer, and finally achieving comprehensive optimization of the binding strength, integrity and stability of the metal layer.

[0042] Preparation process of PET base film in Example 2: Base film pretreatment: Select a PET base film with a thickness of 5μm (surface flatness ≤1μm), ultrasonically clean it with 500W ethanol for 10min, rinse it with deionized water 3 times, and vacuum dry it at 60℃ for 60min, with a water content ≤0.1wt%.

[0043] Physical modification: Treatment was performed using an Ar / O2 mixed gas plasma at a ratio of 5:1, with a power of 200W, a duration of 60s, and a vacuum level of 10. - 2 Pa, base film temperature 80℃, forming a micro-nano rough structure Ra=80nm, surface energy increased to 55mN / m.

[0044] Chemical modification: Prepare a 1.5wt% polyurethane + N,N-dimethylformamide coating solution → microgravure coating (wet film 80nm) → dry at 120℃ for 30s to form a 15nm polar coating with a micro-defect filling rate of 92%.

[0045] Transition layer preparation: Coating with 1.2wt% KH550 coupling agent solution (ethanol / water = 9:1) → Drying at 70℃ for 10 min (forming a 6nm coupling agent layer) → Cr target magnetron sputtering (power 150W, vacuum degree 1×10⁻⁶). -2 Pa (thickness 5 nm), base film temperature 120℃.

[0046] Magnetron sputtering Al layer: Ar+ Ion pretreatment (80W, 30s) → Al target sputtering (power 300W, vacuum 5×10⁻⁶) - 3 Pa (deposition rate 0.5 nm / s, thickness 2 μm), base film temperature 120 °C.

[0047] Post-treatment: Ar annealing at 120℃ for 1 h → O2 plasma passivation (100 W, 10 s) to form a 2 nm Al2O3 passivation film.

[0048] Preparation process of PET base film (Comparative Example 2): Base film pretreatment: Same as the PET base film example (5μm PET base film, ultrasonic cleaning with ethanol → vacuum drying).

[0049] Direct magnetron sputtering of Al layer: Skipping physical modification, chemical modification, and transition layer steps, the pretreated PET base film is directly placed into the magnetron sputtering equipment → Ar⁺ ion pretreatment (80W, 30s) → Al target sputtering (parameters consistent with the example: power 300W, vacuum degree 5×10). -3 Pa (thickness 2 μm), base film temperature 120℃.

[0050] Post-treatment: Same as the PET base film example (120℃ Ar annealing + O2 plasma passivation).

[0051] Table 2 Experimental data of PET base film Example 2 and PET comparative example 2 detection indicators Example 2 of PET base film PET base film comparative example 2 Performance improvement 90° metal layer peel strength 2.8N / m 0.5N / m 4.6 times increase Porosity of metal layer 0.5% 7.2% Reduced by 93.1% Metal nodule density (>1μm) <![CDATA[1 per mm 2 > <![CDATA[15 per mm 2 > Reduced by 93.3% Metal-level resistance 9.2mΩ / □ 16.8mΩ / □ Reduced by 45.2% Bonding strength retention rate after 1000 cycles 85% 28% Improved by 2.0 times Example 3 The composite current collector based on PP / PET film is prepared by a production process. The cross-sectional structure of the composite current collector from the inside to the outside is as follows: PP / PET film → chemical modification layer → KH550 coupling agent layer → Cr transition layer → Cu / Al metal layer → oxide passivation film.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A production process for a composite current collector based on PP / PET film, characterized in that, Includes the following steps: S1. Base film pretreatment; Select PP or PET base film with a thickness of 3-12μm, and remove oil and other impurities attached to the outer surface after cleaning process; S2, Physical modification treatment; The base film is placed in a plasma processing device with Ar / O2 mixed gas as the working medium. After the device is started, high-energy ions continuously bombard the surface of the base film. The weak boundary layer on the surface of the base film is effectively removed, and a uniform 50-200nm micro-nano rough structure is formed to provide "mechanical anchoring space". Under the action of oxidation reaction, some chemical bonds are broken to introduce oxygen-containing groups such as hydroxyl (-OH) and carboxyl (-COOH) on the surface of the base film. S3, Preparation of a double-layer intermediate transition layer; a. Preparation of coupling agent transition layer: Immerse the base film in a mixture of silane coupling agent and ethanol, with a volume ratio of silane coupling agent to ethanol of 9:

1. After immersion for 1-2 minutes, remove the base film and dry it at 60-70℃. A 5-10 nm coupling agent layer is formed on the surface of the dried base film. The -Si(OCH3)3 in the mixture undergoes a hydrolysis and condensation reaction with the -OH on the surface of the base film to form Si-OC covalent bonds for strong anchoring. b. Preparation of metal transition layer: Cr target is selected as sputtering source and sputtering is performed by magnetron sputtering process to deposit a Cr layer with a thickness of 5-10 nm on the surface of the coupling agent transition layer. At the same time, the Cr layer forms Cr-N chemical bonds with the exposed -NH2 groups of the coupling agent transition layer, and the Cr atoms are embedded in the micro-nano rough structure formed by the physical modification of the base film by means of their own diffusion ability, forming a "mechanical interlocking" effect with the surface of the base film. S4. Metal layer preparation; Using Ar + Ion bombardment of the transition layer surface removes the oxide layer and activates atomic activity. Subsequently, based on the current collector polarity, two metal layers are sputtered sequentially. Metal atoms (Cu...) 2+ / Al 3+ While forming a solid solution alloy with the Cr transition layer, it uniformly nucleates along the coupling agent layer to avoid "island growth" of the metal layer. After the metal layer is prepared, a composite current collector is formed.

2. The production process of the composite current collector based on PP base film / PET base film according to claim 1, characterized in that, It also includes S5 and post-processing; The composite current collector was subjected to low-temperature annealing and plasma passivation treatment. After the treatment, the defects in the metal layer and the peel strength of the composite current collector were detected by optical microscope and peel tester.

3. The production process of the composite current collector based on PP base film / PET base film according to claim 1, characterized in that, Steps S2 and S3 also include chemical modification treatment: When the base film is PP base film, the physically modified PP base film is immersed in the modification solution and reacted in a water bath at a constant temperature of 60-70℃ for 2-3 hours. After ultrasonic cleaning with acetone and vacuum drying, the chemical modification treatment of PP base film is completed. When the base film is a PET base film, the coating liquid is coated on the surface of the physically modified PET base film by micro-gravure coating process, and the wet film thickness is controlled to be 50-100nm. Then, it is quickly dried at 100-120℃ for 30-60s to form an ultra-thin polar coating of 10-20nm.

4. The production process of the composite current collector based on PP base film / PET base film according to claim 3, characterized in that, The modified liquid consists of maleic anhydride, benzoyl peroxide, and toluene. The content of maleic anhydride is 0.5-1 wt% of the modified liquid, and the content of benzoyl peroxide is 0.1-0.2 wt%. Benzoyl peroxide acts as an initiator, decomposing to generate free radicals that attack the CH bonds on the PP base film molecular chain, causing them to break and form active sites. Maleic anhydride monomers bind to the active sites through the opening of double bonds, grafting polymer chains containing a large number of carboxyl groups (-COOH) onto the surface of the PP base film to enhance surface polarity.

5. The production process of the composite current collector based on PP base film / PET base film according to claim 4, characterized in that, The coating liquid is composed of polyurethane and N,N-dimethylformamide solvent. The polyurethane content is 1-2 wt% of the coating liquid. The polyurethane molecular chains are tightly attached to the PET base film surface by forming hydrogen bonds with a small number of hydroxyl groups (-OH), forming a large number of polar groups that enhance the surface chemical activity.

6. The production process of the composite current collector based on PP base film / PET base film according to claim 2, characterized in that, The cleaning process in step S1 includes the following: Ethanol ultrasonic cleaning: Place the base film in an ultrasonic cleaner with ethanol as the medium and clean for 10-15 minutes to remove oil and dirt from the surface of the base film; Rinse with deionized water: Rinse the cleaned base film with deionized water to remove surface ethanol residue, and then vacuum dry in a drying oven at 60-80℃ for 30-60 minutes to remove moisture.

7. The production process of the composite current collector based on PP base film / PET base film according to claim 1, characterized in that, In step S2, during plasma treatment, the temperature of the PP base film is ≤60℃ and the temperature of the PET base film is ≤80℃.

8. The production process of the composite current collector based on PP base film / PET base film according to claim 1, characterized in that, In step S4, during the sputtering treatment of the metal layer, the temperature of the PP base film is ≤80℃ and the temperature of the PET base film is ≤120℃.

9. A composite current collector based on PP / PET film, prepared by the production process of the composite current collector based on PP / PET film according to any one of claims 1-8, characterized in that, The cross-sectional structure of the composite current collector, from the inside out, is as follows: PP base film / PET base film → chemically modified layer → KH550 coupling agent layer → Cr transition layer → Cu / Al metal layer → oxide passivation film.

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