High-strength pet film for composite current collector and method for manufacturing the same

Abstract

This invention discloses a high-strength PET film for composite current collectors and its preparation method, relating to the field of PET film technology. The preparation method includes the following steps: uniformly mixing modified PET resin, antioxidant, and lubricant; melt extruding; casting into a film; and biaxially stretching to obtain a base film; subjecting the base film to sequential ion irradiation, oxidation treatment, RAFT polymerization, washing, and drying to obtain a high-strength PET film; wherein the modified PET resin is prepared by copolymerization of dimethyl phthalate, a diester compound, 1,4-cyclohexanediethanol, ethylene glycol, and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene; and the diester compound is prepared by reaction of dimethyl itaconic acid and trans-1,4-diaminocyclohexane.

Description

Technical Field

[0001] This invention relates to the field of PET film technology, specifically a high-strength PET film for composite current collectors and its preparation method. Background Technology

[0002] In the field of lithium-ion batteries, composite current collectors are key components, placing stringent demands on the overall performance of PET films. Traditional PET films have gradually revealed insufficient mechanical strength in applications, making it difficult to meet the structural stability requirements during battery cycling; their high thermal shrinkage rate makes them prone to deformation at high temperatures, affecting battery safety and reliability; simultaneously, their poor electrolyte resistance leads to swelling after prolonged immersion in electrolyte, resulting in decreased current collector performance and consequently affecting battery life and electrochemical performance.

[0003] To address the aforementioned issues, existing technologies have attempted to optimize PET film performance through chemical modification and physical treatment. However, limitations remain in areas such as molecular chain structure regulation and surface functionalization, making it difficult to achieve a synergistic improvement in mechanical properties, thermal stability, and electrolyte resistance.

[0004] Therefore, developing a PET film with high strength, low shrinkage and excellent electrolyte resistance, and its preparation method, has become a key technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength PET film for composite current collectors and its preparation method, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a high-strength PET film for composite current collectors includes the following steps: S1: Mixing modified PET resin, antioxidant, and lubricant evenly, melting and extruding, casting into a film, and biaxially stretching to obtain a base film;

[0008] S2: The base film is subjected to ion irradiation, oxidation treatment, RAFT polymerization, washing and drying in sequence to obtain a high-strength PET film;

[0009] Furthermore, the modified PET resin is prepared by copolymerization of dimethyl phthalate, a diester compound, 1,4-cyclohexanediol, ethylene glycol, and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene;

[0010] Furthermore, the diester compound is prepared by reacting itaconic acid dimethyl ester with trans-1,4-diaminocyclohexane.

[0011] Furthermore, the preparation method of the modified PET resin includes the following steps:

[0012] Dimethyl phthalate, a diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, zinc acetate, and antimony trioxide were added to a reaction vessel. Under a nitrogen atmosphere, the mixture was heated to 180-210℃ and reacted for 4-6 hours. The mixture was then further heated to 260-280℃ while the pressure was reduced to 10-20 Pa and reacted for 3-4 hours. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0013] Furthermore, in the preparation process of the modified PET resin, the total molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and diester compound is (1.5-2.1):1; the mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1; and the mass ratio of dimethyl phthalate: diester compound is 1:1.

[0014] Furthermore, the amount of zinc acetate added is 0.2 mol% of the total molar amount of dimethyl phthalate and the diester compound.

[0015] Furthermore, the amount of antimony trioxide added is 0.1 mol% of the total molar amount of dimethyl phthalate and the diester compound.

[0016] Furthermore, the preparation method of the diester compound includes the following steps: adding dimethyl itaconic acid and trans-1,4-diaminocyclohexane to methanol, stirring evenly, heating to 70-75℃ and reacting for 15-16 hours, cooling, filtering, washing the product with methanol, and vacuum drying to obtain the diester compound.

[0017] Furthermore, in the preparation of the diester compound, the molar ratio of dimethyl itaconic acid to trans-1,4-diaminocyclohexane is 1:0.5.

[0018] Furthermore, the parameters of the ion irradiation include: ion irradiation energy: 1.75-1.8 MeV, and ion irradiation flux: 4.2-4.3 × 10⁻⁶. 7 ion / cm 2 .

[0019] Furthermore, the oxidation process includes the following steps: placing the ion-irradiated base film in a 500mM hydrogen peroxide solution at pH=3 and subjecting it to ultraviolet radiation for 2-3 hours; washing the base film with deionized water and drying it; then placing the base film in a 5% w / v benzophenone dimethylformamide solution and shaking it at room temperature for 24 hours; washing the base film with deionized water and ethanol and drying it.

[0020] Furthermore, the parameters of the ultraviolet radiation include: wavelength: 254nm, power: 190W.

[0021] Furthermore, the RAFT polymerization process includes the following steps: placing the oxidized base film in an acrylate compound solution, adding RAFT reagent, and initiating the polymerization under a nitrogen atmosphere with ultraviolet light for 4-5 hours;

[0022] Furthermore, the concentration of the acrylate compound solution is 20-25% w / v, and the solvent is an aqueous solution of acetone with a volume ratio of 1:1.

[0023] Furthermore, the molar ratio of the acrylate compound to the RAFT reagent is (500-1000):1;

[0024] Furthermore, the RAFT reagent is O-ethyl-S-(1-methoxycarbonylethyl) dithiocarbonate;

[0025] Furthermore, the parameters for ultraviolet initiation include: wavelength: 295nm, power: 15W, and distance between the ultraviolet light and the substrate: 7-8cm.

[0026] Furthermore, the method for preparing the acrylate compound includes the following steps:

[0027] Oxazolidinone compound, 4-dimethylaminopyridine, and triethylamine were added to tetrahydrofuran and heated to 60-65°C with stirring until homogeneous. A tetrahydrofuran solution of methacrylic anhydride was added, and the reaction was maintained at this temperature for 24 hours under a nitrogen atmosphere. The mixture was then rotary evaporated to obtain a crude product. The crude product was added to dichloromethane and washed alternately with saturated sodium bicarbonate solution, 1 mol% hydrochloric acid solution, deionized water, and saturated brine. The mixture was dried over anhydrous magnesium sulfate, purified, and vacuum dried to obtain an acrylate compound.

[0028] Furthermore, in the preparation of the acrylate compound, the molar ratio of oxazolidinone compound: 4-dimethylaminopyridine: triethylamine: methacrylate is 2:0.6:3:2.1.

[0029] Furthermore, the method for preparing the oxazolidinone compound includes the following steps: adding phenyl isocyanate and glycidyl to dichloromethane and reacting at room temperature for 4-6 h to obtain phenyl glycidyl carbamate; adding phenyl glycidyl carbamate to acetone, adding 1,5,7-triazabicyclo[4.4.0]decene-5-ene, and heating to 35-40℃ for 2-2.5 h to obtain the oxazolidinone compound;

[0030] Furthermore, in the preparation of phenyl glycidyl carbamate, the molar ratio of phenyl isocyanate to glycidyl is 1:1; in the preparation of oxazolidinone compounds, the amount of 1,5,7-triazabicyclo[4.4.0]decene-5-ene added is 5 mol of the molar amount of phenyl glycidyl carbamate.

[0031] Furthermore, the components in the base film, by mass parts, include: 80-100 parts of modified PET resin, 0.8-1.6 parts of antioxidant, and 0.7-1.2 parts of lubricant.

[0032] Furthermore, the antioxidant includes at least one of antioxidant 1010, antioxidant 168, and antioxidant 1076; the lubricant is at least one of ethylene bis-stearamide and butyl stearate.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. This invention introduces a self-made diester compound and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene into the polymer segments of PET. The rigid tricyclic structure of the diester compound increases the steric hindrance of the molecular chain, raising the glass transition temperature of the copolyester. Its two pyrrolidone rings are symmetrically arranged around cyclohexane, which is beneficial for the orderly arrangement of the molecular chain during cooling, forming crystalline regions, improving crystallinity, and enhancing the mechanical properties and thermal stability of the material. The rigid ring structure of the fluorene group in 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene hinders the orderly arrangement of the molecular chain during copolymerization, inhibiting crystallization behavior. At the same time, the large steric hindrance reduces the attack sites of free radicals during thermo-oxidative degradation, and the conjugated structure of the rigid ring increases the thermal decomposition energy barrier of the molecular chain, further improving thermal stability. The two compounds synergistically regulate the molecular chain regularity and segment mobility of the copolyester, further enhancing the mechanical strength of the copolyester while improving thermal stability.

[0035] 2. To further improve the service life of PET film and broaden its application scenarios, specifically by enhancing its electrolyte resistance, this invention grafts acrylate monomers onto the surface of a PET base film via UV initiation. The rigid heterocyclic structure of the oxazolidinone in the polymer side chains and the syndiotactic stereoregularity of the main chain enhance the interaction between molecular chains. When compounded with PET, the polymer acts as a reinforcing phase, improving the tensile strength and modulus of the PET film through chemical crosslinking, while reducing its swelling rate in the electrolyte. This prevents the current collector from experiencing performance degradation due to solvent erosion and forms a dense protective layer, enhancing the current collector's resistance to electrolytes and acid / alkali environments.

[0036] UV-initiated polymerization firmly fixes the acrylate polymer onto the PET base film surface, reducing interlayer delamination of the composite current collector during cycling. Furthermore, the polymer's high glass transition temperature suppresses molecular chain movement during electrochemical processes, reducing interfacial impedance fluctuations and improving battery cycle stability. The alternating structure formed by free radical copolymerization optimizes molecular chain arrangement, reduces defect sites, thereby lowering the probability of side reactions during charge-discharge processes and extending battery life. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The following examples illustrate a method for preparing acrylate compounds, comprising the following steps:

[0039] Step (1): Add 1 mmol of phenyl isocyanate and 1 mmol of glycidyl to dichloromethane and react at room temperature for 4 h to obtain phenyl glycidyl carbamate.

[0040] Step (2): Add 1 mmol of phenyl glycidyl carbamate to acetone, add 5 mol% of 1,5,7-triazabicyclo[4.4.0]decene-5-ene, heat to 35℃ and react for 2 h to obtain the oxazolidinone compound;

[0041] Step (3): 2 mmol of oxazolidinone compound, 0.6 mmol of 4-dimethylaminopyridine, and 3 mmol of triethylamine were added to tetrahydrofuran, heated to 60°C and stirred until homogeneous. Then, 2.1 mmol of tetrahydrofuran solution of methacrylic anhydride was added, and the reaction was carried out under a nitrogen atmosphere for 24 h. The mixture was then rotary evaporated to obtain the crude product. The crude product was added to dichloromethane and washed alternately with saturated sodium bicarbonate solution, 1 mol% hydrochloric acid solution, deionized water, and saturated brine. The mixture was dried over anhydrous magnesium sulfate, purified, and vacuum dried to obtain the acrylate compound.

[0042] The preparation method of the diester compound includes the following steps: adding dimethyl itaconic acid and 0.5 mmol of trans-1,4-diaminocyclohexane to methanol, stirring evenly, heating to 70°C and reacting for 15 h, cooling, filtering, washing the product with methanol, and drying under vacuum to obtain the diester compound.

[0043] Example 1: A method for preparing a high-strength PET film for composite current collectors, comprising the following steps:

[0044] S1: Dimethyl phthalate, diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 0.2 mol% zinc acetate, and 0.1 mol% antimony trioxide were added to a reaction vessel and heated to 180°C for 4 h under a nitrogen atmosphere. The mixture was then further heated to 260°C while the pressure was reduced to 1 Pa for 3 h. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0045] The molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is 1.5:1;

[0046] The mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1;

[0047] The mass ratio of dimethyl phthalate to diester compound is 1:1;

[0048] S2: Mix 100 parts of modified PET resin, 0.8 parts of antioxidant 1010 and 0.7 parts of butyl stearate evenly, melt extrude, cast into a film, and biaxially stretch to obtain a base film;

[0049] S3: The base film was subjected to 1.75 MeV and 4.2 × 10⁻⁶ mV sequentially. 7 ion / cm 2 Ion irradiation was performed on the substrate film. After ion irradiation, the substrate film was placed in a 500mM hydrogen peroxide solution at pH 3 and subjected to UV irradiation at 254nm and 190W for 2 hours. The substrate film was then washed with deionized water and dried. The substrate film was then placed in a 5% w / v benzophenone-dimethylformamide solution and shaken at room temperature for 24 hours. The substrate film was then washed with deionized water and ethanol and dried. The oxidized substrate film was then placed in a 20% w / v acrylate compound solution, RAFT reagent was added, and UV initiation was performed at 295nm and 15W under a nitrogen atmosphere, with a distance of 7cm between the UV light and the substrate film, for 4 hours. After washing and drying, a high-strength PET film was obtained.

[0050] The molar ratio of the acrylate compound to the RAFT reagent is 500:1.

[0051] Example 2: A method for preparing a high-strength PET film for composite current collectors, comprising the following steps:

[0052] S1: Dimethyl phthalate, diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 0.2 mol% zinc acetate, and 0.1 mol% antimony trioxide were added to a reaction vessel and heated to 180°C for 4 h under a nitrogen atmosphere. The mixture was then further heated to 260°C while the pressure was reduced to 1 Pa for 3 h. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0053] The molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is 2.1:1;

[0054] The mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1;

[0055] The mass ratio of dimethyl phthalate to diester compound is 1:1;

[0056] S2: Mix 100 parts of modified PET resin, 0.8 parts of antioxidant 1010 and 0.7 parts of butyl stearate evenly, melt extrude, cast into a film, and biaxially stretch to obtain a base film;

[0057] S3: The base film was subjected to 1.75 MeV and 4.2 × 10⁻⁶ mV sequentially. 7 ion / cm 2 Ion irradiation was performed on the substrate film. After ion irradiation, the substrate film was placed in a 500mM hydrogen peroxide solution at pH 3 and subjected to UV irradiation at 254nm and 190W for 2 hours. The substrate film was then washed with deionized water and dried. The substrate film was then placed in a 5% w / v benzophenone-dimethylformamide solution and shaken at room temperature for 24 hours. The substrate film was then washed with deionized water and ethanol and dried. The oxidized substrate film was then placed in a 20% w / v acrylate compound solution, RAFT reagent was added, and UV initiation was performed at 295nm and 15W under a nitrogen atmosphere, with a distance of 7cm between the UV light and the substrate film, for 4 hours. After washing and drying, a high-strength PET film was obtained.

[0058] The molar ratio of the acrylate compound to the RAFT reagent is 500:1.

[0059] Example 3: A method for preparing a high-strength PET film for composite current collectors, comprising the following steps:

[0060] S1: Dimethyl phthalate, diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 0.2 mol% zinc acetate, and 0.1 mol% antimony trioxide were added to a reaction vessel and heated to 180°C for 4 h under a nitrogen atmosphere. The mixture was then further heated to 260°C while the pressure was reduced to 1 Pa for 3 h. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0061] The molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is 2.1:1;

[0062] The mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1;

[0063] The mass ratio of dimethyl phthalate to diester compound is 1:1;

[0064] S2: Mix 100 parts of modified PET resin, 0.8 parts of antioxidant 1010 and 0.7 parts of butyl stearate evenly, melt extrude, cast into a film, and biaxially stretch to obtain a base film;

[0065] S3: The base film was subjected to 1.75 MeV and 4.2 × 10⁻⁶ mV sequentially. 7 ion / cm 2 Ion irradiation was performed on the substrate film. After ion irradiation, the substrate film was placed in a 500 mM hydrogen peroxide solution at pH 3 and subjected to UV irradiation at 254 nm and 190 W for 2 h. The substrate film was then washed with deionized water and dried. The substrate film was then placed in a 5% w / v benzophenone dimethylformamide solution and shaken at room temperature for 24 h. The substrate film was then washed with deionized water and ethanol and dried. The oxidized substrate film was then placed in a 25% w / v acrylate compound solution, RAFT reagent was added, and UV initiation was performed at 295 nm and 15 W under a nitrogen atmosphere, with a distance of 7 cm between the UV light and the substrate film, for 4 h. After washing and drying, a high-strength PET film was obtained.

[0066] The molar ratio of the acrylate compound to the RAFT reagent is 500:1.

[0067] Example 4: A method for preparing a high-strength PET film for composite current collectors, comprising the following steps:

[0068] S1: Dimethyl phthalate, diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 0.2 mol% zinc acetate, and 0.1 mol% antimony trioxide were added to a reaction vessel and heated to 180°C for 4 h under a nitrogen atmosphere. The mixture was then further heated to 260°C while the pressure was reduced to 1 Pa for 3 h. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0069] The molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is 2.1:1;

[0070] The mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1;

[0071] The mass ratio of dimethyl phthalate to diester compound is 1:1;

[0072] S2: Mix 100 parts of modified PET resin, 0.8 parts of antioxidant 1010 and 0.7 parts of butyl stearate evenly, melt extrude, cast into a film, and biaxially stretch to obtain a base film;

[0073] S3: The base film was subjected to 1.75 MeV and 4.2 × 10⁻⁶ mV sequentially. 7 ion / cm 2 Ion irradiation was performed on the substrate film. After ion irradiation, the substrate film was placed in a 500 mM hydrogen peroxide solution at pH 3 and subjected to UV irradiation at 254 nm and 190 W for 2 h. The substrate film was then washed with deionized water and dried. The substrate film was then placed in a 5% w / v benzophenone dimethylformamide solution and shaken at room temperature for 24 h. The substrate film was then washed with deionized water and ethanol and dried. The oxidized substrate film was then placed in a 25% w / v acrylate compound solution, RAFT reagent was added, and UV initiation was performed at 295 nm and 15 W under a nitrogen atmosphere, with a distance of 7 cm between the UV light and the substrate film, for 4 h. After washing and drying, a high-strength PET film was obtained.

[0074] The molar ratio of the acrylate compound to the RAFT reagent is 1000:1.

[0075] Comparative Example 1: A method for preparing a high-strength PET film for composite current collectors, comprising the following steps:

[0076] S1: Dimethyl phthalate, diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 0.2 mol% zinc acetate, and 0.1 mol% antimony trioxide were added to a reaction vessel and heated to 180°C for 4 h under a nitrogen atmosphere. The mixture was then further heated to 260°C while the pressure was reduced to 1 Pa for 3 h. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0077] The molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is 1.5:1;

[0078] The mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1;

[0079] The mass ratio of dimethyl phthalate to diester compound is 1:1;

[0080] S2: Mix 100 parts of modified PET resin, 0.8 parts of antioxidant 1010 and 0.7 parts of butyl stearate evenly, melt extrude, cast into a film, and biaxially stretch to obtain a base film;

[0081] S3: The base film was subjected to 1.75 MeV and 4.2 × 10⁻⁶ mV sequentially. 7 ion / cm 2 Ion irradiation was performed on the substrate film. After ion irradiation, the substrate film was placed in a 500 mM hydrogen peroxide solution at pH 3 and subjected to 254 nm, 190 W ultraviolet radiation for 2 h. The substrate film was then washed with deionized water and dried. The substrate film was then placed in a 5% w / v benzophenone dimethylformamide solution and shaken at room temperature for 24 h. The substrate film was then washed with deionized water and ethanol and dried. The oxidized substrate film was then placed in a 20% w / v acrylate compound solution, and the hydrothermal initiator 4,4'-azobis-4-cyanopentanoic acid was added. The mixture was heated to 70 °C and reacted for 24 h. After washing and drying, a high-strength PET film was obtained.

[0082] The molar ratio of the acrylate compound to the RAFT reagent is 500:1.

[0083] Comparative Example 2: A method for preparing a high-strength PET film for composite current collectors, comprising the following steps:

[0084] S1: Dimethyl phthalate, diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 0.2 mol% zinc acetate, and 0.1 mol% antimony trioxide were added to a reaction vessel and heated to 180°C for 4 h under a nitrogen atmosphere. The mixture was then further heated to 260°C while the pressure was reduced to 1 Pa for 3 h. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0085] The molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is 1.5:1;

[0086] The mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1;

[0087] The mass ratio of dimethyl phthalate to diester compound is 1:1;

[0088] S2: Mix 100 parts of modified PET resin, 0.8 parts of antioxidant 1010 and 0.7 parts of butyl stearate evenly, melt extrude, cast into a film, and biaxially stretch to obtain a base film;

[0089] S3: The base film was subjected to 1.75 MeV and 4.2 × 10⁻⁶ mV sequentially. 7 ion / cm 2 Ion irradiation was performed on the substrate film. After ion irradiation, the substrate film was placed in a 500 mM hydrogen peroxide solution at pH 3 and subjected to UV irradiation at 254 nm and 190 W for 2 h. The substrate film was then washed with deionized water and dried. The substrate film was then placed in a 5% w / v benzophenone-dimethylformamide solution and shaken at room temperature for 24 h. The substrate film was then washed with deionized water and ethanol and dried. The oxidized substrate film was then placed in a 30% w / v acrylate compound solution, RAFT reagent was added, and UV initiation was performed at 295 nm and 15 W under a nitrogen atmosphere, with a distance of 7 cm between the UV light and the substrate film, for 4 h. After washing and drying, a high-strength PET film was obtained.

[0090] The molar ratio of the acrylate compound to the RAFT reagent is 500:1.

[0091] Comparative Example 3: A method for preparing a high-strength PET film for composite current collectors, comprising the following steps:

[0092] S1: Dimethyl phthalate, diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 0.2 mol% zinc acetate, and 0.1 mol% antimony trioxide were added to a reaction vessel and heated to 180°C for 4 h under a nitrogen atmosphere. The mixture was then further heated to 260°C while the pressure was reduced to 1 Pa for 3 h. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0093] The molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is 1.5:1;

[0094] The mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1;

[0095] The mass ratio of dimethyl phthalate to diester compound is 1:1;

[0096] S2: Mix 100 parts of modified PET resin, 0.8 parts of antioxidant 1010 and 0.7 parts of butyl stearate evenly, melt extrude, cast into a film, and biaxially stretch to obtain a base film;

[0097] S3: The base film was subjected to 1.75 MeV and 4.2 × 10⁻⁶ mV sequentially. 7 ion / cm 2 Ion irradiation was performed on the substrate film. After ion irradiation, the substrate film was placed in a 500mM hydrogen peroxide solution at pH 3 and subjected to UV irradiation at 254nm and 190W for 2 hours. The substrate film was then washed with deionized water and dried. The substrate film was then placed in a 5% w / v benzophenone-dimethylformamide solution and shaken at room temperature for 24 hours. The substrate film was then washed with deionized water and ethanol and dried. The oxidized substrate film was then placed in a 20% w / v acrylate compound solution, RAFT reagent was added, and UV initiation was performed at 295nm and 15W under a nitrogen atmosphere, with a distance of 7cm between the UV light and the substrate film, for 4 hours. After washing and drying, a high-strength PET film was obtained.

[0098] The molar ratio of the acrylate compound to the RAFT reagent is 1500:1.

[0099] Comparative Example 4: A method for preparing a high-strength PET film for composite current collectors, comprising the following steps:

[0100] S1: Dimethyl phthalate, diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 0.2 mol% zinc acetate, and 0.1 mol% antimony trioxide were added to a reaction vessel and heated to 180°C for 4 h under a nitrogen atmosphere. The mixture was then further heated to 260°C while the pressure was reduced to 1 Pa for 3 h. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin.

[0101] The molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is 2.5:1;

[0102] The mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1;

[0103] The mass ratio of dimethyl phthalate to diester compound is 1:1;

[0104] S2: Mix 100 parts of modified PET resin, 0.8 parts of antioxidant 1010 and 0.7 parts of butyl stearate evenly, melt extrude, cast into a film, and biaxially stretch to obtain a base film;

[0105] S3: The base film was subjected to 1.75 MeV and 4.2 × 10⁻⁶ mV sequentially. 7 ion / cm 2 Ion irradiation was performed on the substrate film. After ion irradiation, the substrate film was placed in a 500mM hydrogen peroxide solution at pH 3 and subjected to UV irradiation at 254nm and 190W for 2 hours. The substrate film was then washed with deionized water and dried. The substrate film was then placed in a 5% w / v benzophenone-dimethylformamide solution and shaken at room temperature for 24 hours. The substrate film was then washed with deionized water and ethanol and dried. The oxidized substrate film was then placed in a 20% w / v acrylate compound solution, RAFT reagent was added, and UV initiation was performed at 295nm and 15W under a nitrogen atmosphere, with a distance of 7cm between the UV light and the substrate film, for 4 hours. After washing and drying, a high-strength PET film was obtained.

[0106] The molar ratio of the acrylate compound to the RAFT reagent is 500:1.

[0107] Experiment: Tensile strength: Tensile strength test was conducted according to GB / T 1040.1-2018;

[0108] Heat shrinkage rate: The heat shrinkage rate of high-strength PET film is tested according to ASTM D 1204. The smaller the value, the higher the heat resistance stability. The test is the heat shrinkage rate of the film after it is placed at 150°C for 30 minutes.

[0109] Electrolyte tolerance: Cut high-strength PET film into 20cm×20cm samples, record the perimeter C1, and then immerse them in electrolyte at 65℃ for 48h. Record the perimeter of the sample after immersion as C2 and calculate the degree of swelling.

[0110] Swelling degree = (C2-C1) / C1×100%.

[0111] The experimental data are shown in Table 1 below.

[0112] Table 1 Performance Tests of High-Strength PET Film

[0113]

[0114] Conclusion: The high-strength PET film for composite current collectors prepared by this invention has excellent mechanical properties, thermal stability, and electrolyte resistance.

[0115] Comparative Example 1 replaced the UV-initiated polymerization method with a traditional thermal initiation method. The water-soluble initiator has poor thermal stability, which easily leads to a decrease in chain transfer efficiency and makes it difficult to control the growth of polymer chains, resulting in a decrease in grafting efficiency. At the same time, it is prone to gelation and precipitation in aqueous solution, which leads to blockage of nanochannel inlets, affecting grafting uniformity and material properties.

[0116] In Comparative Example 2, excessively high concentrations of acrylate compounds can exacerbate the exothermic polymerization process, leading to localized gelation, blockage of nanochannel inlets, and affecting grafting uniformity and material properties.

[0117] In the comparative example 3, the concentration of RAFT reagent was too low, which led to a decrease in the chain reaction rate, an easy occurrence of chain termination, a decrease in chain transfer efficiency, difficulty in controlling polymer chain growth, and a decrease in grafting efficiency.

[0118] In Comparative Example 4, an excessively high molar ratio of diol to diacid leads to an excess of hydroxyl functional groups in the reaction system, initiating chain termination, limiting chain growth, and potentially increasing the polarity of the polymer, thus affecting crystallinity, solvent resistance, and mechanical properties.

[0119] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a high-strength PET film for composite current collectors, characterized in that: Includes the following steps: S1: Mix the modified PET resin, antioxidant, and lubricant evenly, melt extrude, cast into a film, and biaxially stretch to obtain the base film; S2: The base film is subjected to ion irradiation, oxidation treatment, RAFT polymerization, washing and drying in sequence to obtain a high-strength PET film; The modified PET resin was prepared by copolymerization of dimethyl phthalate, a diester compound, 1,4-cyclohexanediol, ethylene glycol, and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene. The preparation method of the diester compound includes the following steps: adding dimethyl itaconic acid and trans-1,4-diaminocyclohexane to methanol, stirring evenly, heating to 70-75℃ and reacting for 15-16 hours, cooling, filtering, washing the product with methanol, and vacuum drying to obtain the diester compound; in the preparation of the diester compound, the molar ratio of dimethyl itaconic acid to trans-1,4-diaminocyclohexane is 1:0.5; The RAFT polymerization process includes the following steps: placing the oxidized base film in an acrylate compound solution, adding RAFT reagent, and initiating the polymerization under a nitrogen atmosphere using ultraviolet light for 4-5 hours; the concentration of the acrylate compound solution is 20-25% w / v, and the solvent is an acetone aqueous solution with a volume ratio of 1:1; the molar ratio of the acrylate compound to the RAFT reagent is (500-1000):1; the parameters for ultraviolet initiation include: wavelength: 295nm, power: 15W, and distance between the ultraviolet light and the base film: 7-8cm. The method for preparing the acrylate compound includes the following steps: adding an oxazolidinone compound, 4-dimethylaminopyridine, and triethylamine to tetrahydrofuran, heating to 60-65°C and stirring until homogeneous, adding a tetrahydrofuran solution of methacrylic anhydride, reacting under a nitrogen atmosphere for 24 hours, rotary evaporation, purification, and vacuum drying to obtain the acrylate compound; in the preparation of the acrylate compound, the molar ratio of oxazolidinone compound: 4-dimethylaminopyridine: triethylamine: methacrylic anhydride is 2:0.6:3:2.1; The method for preparing the oxazolidinone compound includes the following steps: adding phenyl isocyanate and glycidyl to dichloromethane and reacting at room temperature for 4-6 h to obtain phenyl glycidyl carbamate; adding phenyl glycidyl carbamate to acetone, adding 1,5,7-triazabicyclo[4.4.0]decene-5-ene, and heating to 35-40℃ for 2-2.5 h to obtain the oxazolidinone compound; In the preparation of phenyl glycidyl carbamate, the molar ratio of phenyl isocyanate to glycidyl is 1:1; in the preparation of oxazolidinone compounds, the amount of 1,5,7-triazabicyclo[4.4.0]decene-5-ene added is 5 mol of the molar amount of phenyl glycidyl carbamate.

2. The method for preparing a high-strength PET film for composite current collectors according to claim 1, characterized in that: The method for preparing the modified PET resin includes the following steps: Dimethyl phthalate, a diester compound, 1,4-cyclohexanediol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, zinc acetate, and antimony trioxide were added to a reaction vessel. Under a nitrogen atmosphere, the mixture was heated to 180-210℃ and reacted for 4-6 hours. The mixture was then further heated to 260-280℃ while the pressure was reduced to 10-20 Pa and reacted for 3-4 hours. Nitrogen gas was then introduced to restore the pressure to atmospheric pressure, yielding the modified PET resin. In the preparation of modified PET resin, the total molar ratio of 1,4-cyclohexanediethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and diester compound is (1.5-2.1):1; the mass ratio of 1,4-cyclohexanediethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1; and the mass ratio of dimethyl phthalate: diester compound is 1:

1.

3. The method for preparing a high-strength PET film for composite current collectors according to claim 1, characterized in that: The parameters of the ion irradiation include: ion irradiation energy: 1.75-1.8 MeV, and ion irradiation flux: 4.2-4.3 × 10⁻⁶. 7 ion / cm 2 .

4. The method for preparing a high-strength PET film for composite current collectors according to claim 1, characterized in that: The oxidation process includes the following steps: placing the ion-irradiated base film in a 500mM hydrogen peroxide solution at pH=3 and subjecting it to ultraviolet radiation for 2-3 hours; washing the base film with deionized water and drying it; then placing the base film in a 5% w / v benzophenone dimethylformamide solution and shaking it at room temperature for 24 hours; washing the base film with deionized water and ethanol and drying it. The parameters of the ultraviolet radiation include: wavelength: 254nm, power: 190W.

5. The method for preparing a high-strength PET film for composite current collectors according to claim 1, characterized in that: The components in the base film, by mass, include: 80-100 parts modified PET resin, 0.8-1.6 parts antioxidant, and 0.7-1.2 parts lubricant.

6. The high-strength PET film prepared by the method for preparing a composite current collector according to any one of claims 1-5.

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