Composite current collector based on pp-based film / pet-based film and production process

Abstract

The application discloses a composite current collector based on a PP-based film / PET-based film and a production process, which comprises the following steps: S1, base film pretreatment; S2, physical modification treatment; S3, double-layer intermediate transition layer preparation; and S4, metal layer preparation. The physical modification constructs a micro-nano rough structure on the surface of the base film through plasma etching, removes impurities in a weak boundary layer, increases the contact area by 3-5 times, provides a basis for the mechanical occlusion of the transition layer and the metal layer, and introduces a small amount of oxygen-containing polar groups to preliminarily increase the surface energy; and the transition layer is a composite structure of a silane coupling agent and a Cr layer, is combined with the polar groups of the base film through Si-O-C covalent bonds, is connected with the coupling agent and the Cr layer through Cr-N coordination bonds, and is embedded into rough pits through Cr atoms to form a dual action of mechanical anchoring and chemical bridging, so that the peeling strength of the metal layer and the base film is greatly increased through the cooperation of the two, and the mechanical requirement of long-term cycling of a lithium battery is met.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite current collectors, and particularly relates to a PP-based film / PET-based film composite current collector and a production process of the PP-based film / PET-based film composite current collector. BACKGROUND

[0002] The current collector is one of indispensable electrode materials of a lithium ion battery, and has important functions of bearing active substances (bearing property) and collecting micro-current (conductivity). The composite current collector is a "metal-polymer-metal" sandwich structure, the inner layer is a polymer polymer layer (such as a PET-based film, a PP-based film or PI), and the two sides are metal conductive layers, which realize lightweight, high safety and high performance by combining the characteristics of different materials. The core lies in that the middle layer uses a polymer-based film (such as a PET-based film, a PP-based film, etc.), and the outer layer is plated with a metal film (such as copper or aluminum), which not only retains the metal conductivity, but also has the lightweight, flexibility and insulation of the polymer material, so that the battery energy density can be significantly improved and the safety hazard can be reduced.

[0003] The PP-based film / PET-based film is a non-polar or weakly polar polymer, and as a base film, the surface energy is low, the compatibility with the polar metal layer (Cu / Al) is poor, the interfacial bonding force is insufficient, and the metal layer is prone to fall off during the charging and discharging process, thereby shortening the cycle life and working time of the battery. SUMMARY

[0004] The present application aims at the problem of poor compatibility of the base film with the polar metal layer, insufficient interfacial bonding force and easy metal layer falling off in the prior art, and proposes the following technical scheme:

[0005] The production process of the PP-based film / PET-based film composite current collector comprises the following steps:

[0006] S1, base film pretreatment;

[0007] A PP-based film or a PET-based film with a thickness of 3-12 μm is selected, and after being treated by a cleaning process, the oil stains and other impurities attached to the outer surface are removed;

[0008] S2, physical modification treatment;

[0009] The base film is placed in a plasma treatment device with Ar / O2 mixed gas as the working medium, high-energy ions continuously impact the surface of the base film after the device is started, the weak boundary layer on the surface of the base film is effectively removed, at the same time, a uniform 50-200 nm micro-nano rough structure is formed to provide a "mechanical anchoring space", and part of the chemical bonds are broken under the action of oxidation reaction to introduce oxygen-containing groups such as hydroxyl (-OH) and carboxyl (-COOH) on the surface of the base film;

[0010] S3, double-layer intermediate transition layer preparation;

[0011] a, preparation of coupling agent transition layer: immerse the base film into a mixture of silane coupling agent and ethanol, the volume ratio of silane coupling agent to ethanol in the mixture is 9:1, immerse the base film for 1-2 min and then take it out and dry at 60-70℃, a 5-10 nm coupling agent layer is formed on the surface of the dried base film, hydrolysis and condensation reaction occurs between -Si(OCH3)3 in the mixture and -OH on the surface of the base film to form Si-O-C covalent bond to achieve firm anchoring;

[0012] b, preparation of metal transition layer: select Cr target as sputtering source, use magnetic sputtering process for sputtering treatment, deposit a 5-10 nm thick Cr layer on the surface of the coupling agent transition layer, the Cr layer forms Cr-N chemical bond with the exposed -NH2 groups in the coupling agent transition layer, at the same time, Cr atoms embed into the micro-nano rough structure of the base film formed by physical modification through their own diffusion ability, and form a "mechanical interlocking" effect with the surface of the base film;

[0013] S4, metal layer preparation;

[0014] use Ar + ion bombardment on the surface of the transition layer to remove the oxide layer on the surface of the transition layer and activate the atomic activity, then select the target material according to the polarity of the current collector to perform sputtering treatment of the two metal layers in turn, metal atoms (Cu 2+ / Al 3+ ) form solid solution alloying with the Cr transition layer, at the same time, nucleate along the coupling agent layer to avoid "island growth" of the metal layer, and form a composite current collector after the preparation of the metal layer is completed.

[0015] As a preferred embodiment of the above technical solution, it further comprises S5, post-processing;

[0016] low-temperature annealing and plasma passivation treatment are performed on the composite current collector, and the metal layer defects and peel strength of the composite current collector are detected by optical microscope and peel tester after the treatment is completed.

[0017] As a preferred embodiment of the above technical solution, the S2 and S3 steps further comprise chemical modification treatment:

[0018] when the base film is a PP base film, immerse the physically modified PP base film into a modification liquid, and perform water bath reaction at 60-70℃ for 2-3 h, then perform acetone ultrasonic cleaning and vacuum drying to complete the chemical modification treatment of the PP base film;

[0019] when the base film is a PET base film, coat the coating liquid on the surface of the physically modified PET base film by micro-gravure coating process, control the wet film thickness to be 50-100 nm, and then perform rapid drying at 100-120℃ for 30-60 s to form a 10-20 nm thick ultra-thin polar coating layer.

[0020] As the preferred technical scheme, the modified liquid component is maleic anhydride, benzoyl peroxide and toluene, the content of the maleic anhydride is 0.5-1wt% of the modified liquid, the content of the benzoyl peroxide is 0.1-0.2wt% of the modified liquid, the benzoyl peroxide is decomposed to generate free radicals as an initiator, attacks the C-H bond on the molecular chain of the PP base film to break it to form active sites, the maleic anhydride monomer is combined with the active sites by opening the double bond to form a polymer chain containing a large amount of carboxyl (-COOH) on the surface of the PP base film to improve the surface polarity.

[0021] As the preferred technical scheme, the coating liquid component is polyurethane and N,N-dimethylformamide solvent, the content of the polyurethane is 1-2wt% of the coating liquid, the polyurethane molecular chain is closely attached by forming hydrogen bonds with a small amount of hydroxyl (-OH) on the surface of the PET base film to form a large number of polar groups that improve the surface chemical activity.

[0022] As the preferred technical scheme, the cleaning process in the S1 step includes the following contents:

[0023] Ethanol ultrasonic cleaning: the base film is placed in an ultrasonic cleaning machine with ethanol as the medium, and cleaned for 10-15min to remove oil stains on the surface of the base film;

[0024] Deionized water rinsing: the cleaned base film is rinsed with deionized water to remove the surface ethanol residue, and then dried in a drying oven at 60-80℃ for 30-60min to remove the water.

[0025] As the preferred technical scheme, in the S2 step, the PP base film temperature is ≤60℃ and the PET base film temperature is ≤80℃ during the plasma treatment.

[0026] As the preferred technical scheme, in the S4 step, the PP base film temperature is ≤80℃ and the PET base film temperature is ≤120℃ during the sputtering treatment of the metal layer.

[0027] The PP base film / PET base film composite current collector prepared based on the production process of the PP base film / PET base film composite current collector has a cross-sectional structure from inside to outside: PP base film / PET base film→chemical modification layer→KH550 coupling agent layer→Cr transition layer→Cu / Al metal layer→oxidation passivation film.

[0028] The beneficial effects of the present application are:

[0029] 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.

[0030] 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

[0031] Figure 1 The diagram shown is a process flow chart of an embodiment. Detailed Implementation

[0032] 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.

[0033] Example 1

[0034] Figure 1 The production process of composite current collectors based on PP / PET film includes the following steps:

[0035] S1. Base film pretreatment;

[0036] 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;

[0037] The cleaning process in step S1 includes the following:

[0038] Ethanol ultrasonic cleaning: the base film is placed in an ultrasonic cleaning machine with ethanol as the medium, and cleaned for 10-15 min to remove oil stains on the surface of the base film. The ethanol ultrasonic cleaning power is 300-500 W, and the oil stains and particulate impurities are detached from the surface of the base film by the mechanical vibration of the ultrasonic waves and dissolved in ethanol;

[0039] Deionized water rinsing: deionized water is used to rinse the cleaned base film to remove surface ethanol residues, and then vacuum drying is performed at 60-80℃ in a drying box for 30-60 min to remove water. The vacuum drying degree is ≤-0.09 MPa. By reducing the air pressure, the evaporation of water or solvent is accelerated, and the interference of residual liquid on subsequent modification is avoided.

[0040] S2, physical modification treatment;

[0041] The base film is placed in a plasma treatment device with Ar / O2 mixed gas as the working medium, and the Ar / O2 mixed gas ratio is 3:1-5:1. High-energy ions continuously impact the surface of the base film after the device is started. The weak boundary layer on the surface of the base film is effectively removed, at the same time, a uniform 50-200 nm micro-nano rough structure is formed to provide a "mechanical anchoring space", and part of the chemical bonds are broken under the action of oxidation reaction to introduce hydroxyl (-OH), carboxyl (-COOH) and other oxygen-containing groups on the surface of the base film;

[0042] In the S2 step, the temperature of the PP base film is ≤60℃ and the temperature of the PET base film is ≤80℃ during plasma treatment.

[0043] During the physical modification treatment, based on physical etching, accompanied by mild oxidation reaction, "rough base" and "initial polar site" are provided for subsequent chemical modification. Among them, Ar + The plasma bombards the surface of the base film, destroys the intermolecular forces of the surface layer of the base film through momentum transfer, forms 50-200 nm micro-nano pits on the surface, and the active oxygen species (O + , O2 + ) in the O2 plasma reacts with the surface layer molecules (C-C bonds of PP base film and C-O bonds of PET base film) to break part of the covalent bonds and introduce hydroxyl (-OH), carboxyl (-COOH) and other oxygen-containing polar groups, forming a "polar-nonpolar transition zone".

[0044] S3, double-layer intermediate transition layer preparation;

[0045] a. Preparation of coupling agent transition layer: immerse the base film into a mixture of silane coupling agent and ethanol, the volume ratio of silane coupling agent and ethanol in the mixture is 9:1, the silane coupling agent is KH550 silane coupling agent, take out the base film after 1-2 min of immersion and dry at 60-70℃, a 5-10 nm coupling agent layer is formed on the surface of the dried base film, hydrolytic condensation reaction occurs between -Si(OCH3)3 in the mixture and -OH on the surface of the base film, forming Si-O-C covalent bond to achieve firm anchoring;

[0046] Hydrolytic condensation reaction occurs between -Si(OCH3)3 group of KH550 silane coupling agent and -OH on the surface of the base film, forming stable Si-O-C covalent bond to anchor the coupling agent on the surface of the base film, the hydrolytic condensation reaction equation is:

[0047] Si-O-CH3 + -OH → Si-O-C + CH3OH

[0048] The exposed -NH2 group provides a chemical bonding site for the upper metal transition layer, and at the same time, the coupling agent molecular chain penetrates into the micro-pits formed by physical modification of the base film, filling the fine gaps and further optimizing the surface flatness.

[0049] b. Preparation of metal transition layer: select Cr target as the sputtering source, and use magnetic sputtering process for sputtering treatment to deposit a 5-10 nm thick Cr layer on the surface of the coupling agent transition layer, the Cr layer forms Cr-N chemical bond with the exposed -NH2 group of the coupling agent transition layer, and at the same time, Cr atoms embed into the micro-nano rough structure formed by 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.

[0050] The Cr layer forms Cr-N chemical bond with the exposed -NH2 group of the coupling agent layer, and at the same time, Cr atoms embed into the micro-nano rough structure formed by physical modification of the base film by means of their own diffusion ability, forming a "mechanical interlocking" effect, and the excellent film continuity of Cr itself constructs a uniform primer layer without pinholes on the surface of the base film, blocking the influence of potential defects of the base film on the subsequent metal layer.

[0051] S4. Metal layer preparation

[0052] Ar + ions bombard the surface of the transition layer to remove the oxide layer on the surface of the transition layer and activate atomic activity, Ar + ions, the ion pretreatment power is 50-80 W, and the time is 30-40 s, and then according to the polarity of the current collector, the target material is selected to perform sputtering treatment of the two metal layers in turn, the metal atoms (Cu 2+ / Al 3+) and Cr transition layer at the same time, uniform nucleation along the coupling agent layer to avoid the "island growth" of the metal layer, and the composite current collector is formed after the preparation of the metal layer is completed.

[0053] In the S4 step, the temperature of the PP base film during sputtering treatment of the metal layer is ≤80°C, the temperature of the PET base film is ≤120°C, the sputtering power of the Cr transition layer is 100-150 W, the vacuum degree is 5x10 -3 -1x10 -2 Pa.

[0054] Metal ions and Cr transition layer atoms diffuse into each other, forming a Cu-Cr or Al-Cr solid solution (alloying reaction) to strengthen the interface bonding.

[0055] Physical modification builds a micro-nano rough structure on the surface of the base film through plasma etching, which not only removes impurities in the weak boundary layer, but also increases the contact area by 3-5 times, providing a basis for the "mechanical engagement" of the transition layer and the metal layer, while introducing a small amount of oxygen-containing polar groups to initially improve the surface energy. The transition layer is a composite structure of silane coupling agent and Cr layer, which is combined with the polar groups of the base film through Si-O-C covalent bonds, connected with the coupling agent and Cr layer through Cr-N coordination bonds, and also forms a "mechanical anchoring + chemical bridging" dual effect through the embedding of Cr atoms into rough pits. The two synergistically greatly improve the peeling strength of the metal layer and the base film, meeting the mechanical requirements of long-term cycling of lithium batteries. At the same time, physical modification eliminates impurities from the source to avoid the causes of metal layer holes, and the transition layer forms a continuous pinhole-free primer layer to provide uniform nucleation sites, inhibit "island growth" and local aggregation of metal atoms, and reduce the density of metal tumors to <3 / mm 2 , the hole rate is <1%, and the physical modification and transition layer process parameters are precisely matched according to the differences in the characteristics of the PP base film (temperature resistance ≤80°C) and the PET base film (temperature resistance ≤120°C), ensuring that the base film does not deform and the thickness deviation of the metal layer is ≤±5%. This synergy breaks through the limitations of traditional single physical roughening or transition layer, and innovatively constructs a multi-level interface effect of "macroscopic mechanical engagement-microscopic chemical bonding", forming a defect suppression closed loop of "source impurity removal-process nucleation regulation", and solves the core problems of poor compatibility and high defect rate between high polymers and metals.

[0056] It also includes S5, post-processing;

[0057] The composite current collector is low-temperature annealed and plasma passivated, and the metal layer defects and peeling strength of the composite current collector are detected by optical microscope and peeling tester after the treatment; when the composite current collector is low-temperature annealed, Ar gas annealing is carried out at 80-130℃, the annealing temperature of the PP-based film composite current collector is 80-90℃, the time is 1-1.5h, the annealing temperature of the PET-based film composite current collector is 120-130℃, and the time is 0.5-1h; when the composite current collector is plasma passivated, O2 plasma passivation is adopted, the plasma passivation power is 50-100W, and the time is 10-20s, so that an oxidation passivation film of 2-5nm is formed on the surface of the composite current collector.

[0058] The S2 and S3 steps further include chemical modification treatment:

[0059] When the base film is a PP-based film, the physically modified PP-based film is immersed in a modification liquid, and the water bath reaction is carried out at a constant temperature of 60-70℃ for 2-3h, and then the chemical modification treatment of the PP-based film is completed after acetone ultrasonic cleaning and vacuum drying;

[0060] The modification liquid components are maleic anhydride, benzoyl peroxide and toluene, the content of maleic anhydride is 0.5-1wt% of the modification liquid, and the content of benzoyl peroxide is 0.1-0.2wt% of the modification liquid; benzoyl peroxide is used as an initiator to decompose free radicals, attack C-H bonds on the molecular chain of the PP-based film to form active sites, and maleic anhydride monomers are combined with the active sites by opening the double bond to form polymer chains containing a large number of carboxyl groups (-COOH) on the surface of the PP-based film to improve the surface polarity.

[0061] Benzoyl peroxide is used as an initiator to decompose free radicals, attack C-H bonds on the surface of the PP-based film to form active free radicals, and addition reaction (graft copolymerization) occurs between the active free radicals and maleic anhydride monomers (containing -COOH) to form C-C covalent bonds, "anchor" -COOH on the surface of the PP-based film, and the generated grafting chain fills the physical modification micro-pits to improve the surface flatness of the base film.

[0062] Preparation process of PP-based film example 1:

[0063] Pretreatment of base film: select a PP-based film with a thickness of 8μm (surface flatness ≤1μm), ultrasonic cleaning with 300W ethanol for 15min→deionized water flushing for 2 times→80℃ vacuum drying for 30min, and control the water content to be ≤0.1wt%.

[0064] Physical modification: Ar / O2=3:1 mixed gas plasma treatment, power 150W, time 90s, vacuum degree 10 - 1Pa, base film temperature 60°C, micro-nano rough structure with Ra=100 nm formed, surface energy increased to 50 mN / m.

[0065] Chemical modification: 0.5wt% maleic anhydride + 0.1wt% benzoyl peroxide + toluene modification liquid was prepared, grafted for 2h in 60°C constant temperature water bath → acetone ultrasonic cleaning for 10min → 80°C vacuum drying for 1h, the density of polar groups increased 4 times.

[0066] Transition layer preparation: 1wt% KH550 coupling agent solution (ethanol / water=9:1) coating → 60°C drying for 15min (8nm coupling agent layer formed) → Cr target magnetron sputtering (power 100W, vacuum degree 5x10 -3 Pa, thickness 8nm), base film temperature 80°C.

[0067] Magnetron sputtering Cu layer: Ar + Ion pre-treatment (50W, 40s) → Cu target sputtering (power 200W, vacuum degree 3x10 - 3 Pa, deposition rate 0.8nm / s, thickness 1.5μm), base film temperature 80°C.

[0068] Post-processing: 80°C Ar annealing for 1.5h → O2 plasma passivation (50W, 20s), forming 3nm CuO passivation film.

[0069] PP base film comparative example 1 preparation process:

[0070] Base film pretreatment: consistent with PP base film example (8μm PP base film, ethanol ultrasonic cleaning → vacuum drying).

[0071] Direct magnetron sputtering Cu layer: skip physical modification, chemical modification, transition layer step, directly put the pretreated PP base film into the magnetron sputtering equipment → Ar + Ion pre-treatment (50W, 40s) → Cu target sputtering (parameters consistent with example: power 200W, vacuum degree 3x10 -3 Pa, thickness 1.5μm), base film temperature 80°C.

[0072] Post-processing: consistent with PP base film example (80°C Ar annealing + O2 plasma passivation).

[0073] Table 1 PP base film example 1 and PP base film comparative example 1 experimental data

[0074] Test index PP base film example 1 PP base film comparative example 1 Performance improvement range 90° metal layer peeling strength 3.2 N / m 0.4 N / m 7 times improvement Metal layer porosity 0.8% 8.5% 90.6% reduction Metal tumor density (>1 μm) 2 / mm 2 ]] 18 per mm 2 ]] 88.9% reduction Metal layer surface resistance 8.5 mΩ / □ 15.2 mΩ / □ 44.1% reduction Bonding force retention rate after 1000 cycles 82% 23% 2.6 times improvement

[0075] Example 2

[0076] When the base film is PET base film, the coating liquid is coated on the surface of the physically modified PET base film by micro-gravure coating process, the wet film thickness is controlled to be 50-100 nm, and then rapid drying is performed at 100-120°C for 30-60s to form an ultra-thin polar coating layer of 10-20 nm.

[0077] The coating liquid composition is polyurethane and N,N-dimethylformamide solvent, the content of the polyurethane is 1-2wt% of the coating liquid, the polyurethane molecular chain is closely attached by forming hydrogen bonds with a small amount of hydroxyl (-OH) on the surface of the PET base film, and a large number of polar groups that improve the surface chemical activity are formed.

[0078] The polyurethane coating liquid (containing -NH2 and -OH) penetrates into the physically modified micro-nano defects under capillary action, fills the micro pinholes and scratches, and forms a thin film after the solvent is volatilized. The -NH2 and -OH of the polyurethane form hydrogen bonds with the residual -OH on the surface of the PET base film, enhancing the adhesion of the coating to the base film, retaining the flexibility of the base film, and improving the surface chemical activity through a large number of polar groups.

[0079] Chemical modification introduces a large number of -COOH through grafting maleic anhydride on the PP base film and -NH2 and -OH through coating polyurethane on the PET base film, greatly improving the density of polar groups and surface energy, providing more active sites for the Si-O-C covalent bond of the silane coupling agent in the transition layer, effectively improving the adhesion of the transition layer to the base film, and indirectly strengthening the overall adhesion of the metal layer. The nano-scale pinholes or scratches left by physical modification can also be filled by capillary penetration of the grafted chains or coating molecules in chemical modification, forming a smooth pre-supporting surface to avoid penetrating holes in the metal layer. The uniform chemical activity area constructed by 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 effect of chemical modification can break through the limitation of the shallow surface distribution of polar groups in physical modification, construct a micron-level "polar group enrichment area", ensure the long-term stability of the transition layer bonding sites, and make the metal layer retain more than 80% of the adhesion after 1000 cycles. Through precise repair of micro-defects by high molecular chains, the damage to the flexibility of the base film caused by physical polishing is avoided. Moreover, a multi-scale cooperative interface of "base film-chemical modification layer-transition layer-metal layer" is formed, which allows the adhesion gradient to be transferred rather than attenuated in layers, breaks through the bottleneck of traditional interface adhesion decreasing layer by layer, and finally realizes the overall optimization of the adhesion strength, integrity and stability of the metal layer.

[0080] Preparation process of PET base film example 2:

[0081] Base film pretreatment: select a PET base film with a thickness of 5μm (surface flatness ≤1μm), ultrasonic cleaning with 500W ethanol for 10min → rinse with deionized water for 3 times → vacuum drying at 60°C for 60min, water content ≤0.1wt%.

[0082] Physical modification: Ar / O2=5:1 mixed gas plasma treatment, power 200W, time 60s, vacuum degree 10 - 2 Pa, base film temperature 80℃, micro-nano rough structure with Ra=80nm formed, surface energy improved to 55mN / m.

[0083] Chemical modification: prepare 1.5wt% polyurethane + N,N-dimethylformamide coating solution → micro-gravure coating (wet film 80nm) → 120℃ drying for 30s, form 15nm polar coating, micro defect filling rate 92%.

[0084] Transition layer preparation: 1.2wt% KH550 coupling agent solution (ethanol / water=9:1) coating → 70℃ drying for 10min (form 6nm coupling agent layer) → Cr target magnetron sputtering (power 150W, vacuum degree 1×10 -2 Pa, thickness 5nm), base film temperature 120℃.

[0085] Magnetron sputtering Al layer: Ar + Ion pre-treatment (80W, 30s) → Al target sputtering (power 300W, vacuum degree 5×10 - 3 Pa, deposition rate 0.5nm / s, thickness 2μm), base film temperature 120℃.

[0086] Post-processing: 120℃ Ar annealing for 1h → O2 plasma passivation (100W, 10s), form 2nm Al2O3 passivation film.

[0087] PET base film comparative example 2 preparation process:

[0088] Base film pre-treatment: consistent with PET base film example (5μm PET base film, ethanol ultrasonic cleaning → vacuum drying).

[0089] Direct magnetron sputtering Al layer: skip physical modification, chemical modification, transition layer steps, directly put the pre-treated PET base film into the magnetron sputtering equipment → Ar+ ion pre-treatment (80W, 30s) → Al target sputtering (parameters consistent with example: power 300W, vacuum degree 5×10 -3 Pa, thickness 2μm), base film temperature 120℃.

[0090] Post-processing: consistent with PET base film example (120℃ Ar annealing + O2 plasma passivation).

[0091] Table 2 PET base film example 2 and PET comparative example 2 experimental data

[0092] Test index PET base film example 2 PET base film comparative example 2 Performance improvement range 90° metal layer peeling strength 2.8 N / m 0.5 N / m 4.6 times improvement Metal layer porosity 0.5% 7.2% 93.1% reduction Metal tumor density (>1 μm) 1 mm 2 ]] 15 / mm 2 ]] 93.3% reduction Metal layer surface resistance 9.2 mΩ / □ 16.8 mΩ / □ 45.2% reduction Bonding force retention rate after 1000 cycles 85% 28% 2.0 times improvement

[0093] Example 3

[0094] A PP-based film / PET-based film composite current collector prepared by a production process of a PP-based film / PET-based film composite current collector, the cross-sectional structure of the composite current collector is in order from inside to outside: PP-based film / PET-based film→ chemically modified layer→ KH550 coupling agent layer→ Cr transition layer→ Cu / Al metal layer→ oxidation passivation film.

[0095] The above examples are only used to illustrate the technical solutions of the present application, and not to limit them.

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 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 hydroxyl (-OH) and carboxyl (-COOH) oxygen-containing groups 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. (Cu ions...) 2+ / Al 3+ While forming a solid solution alloy with the Cr transition layer, uniform nucleation occurs 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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