High-strength PET film for composite current collector and preparation method of high-strength PET film

Abstract

The invention discloses a high-strength PET film for a composite current collector and a preparation method of the high-strength PET film, and relates to the technical field of PET films.The preparation method comprises the following steps that modified PET resin, an antioxidant and a lubricating agent are evenly mixed, melt extrusion, film casting and two-way stretching are conducted, and a base film is obtained; the base film is sequentially subjected to ion irradiation, oxidation treatment, RAFT polymerization, washing and drying, and the high-strength PET film is obtained. The modified PET resin is prepared by carrying out copolymerization on dimethyl phthalate, a diester compound, 1, 4-cyclohexanedimethanol, ethylene glycol and 9, 9-bis [4-(2-hydroxyethoxy) phenyl] fluorene; the diester compound is prepared by carrying out a reaction on dimethyl itaconate and trans-1, 4-diaminocyclohexane.

Description

Technical Field

[0001] The present invention relates to the technical field of PET films, in particular to a high-strength PET film for a composite current collector and a preparation method thereof. Background Art

[0002] In the lithium-ion battery field, composite current collectors, as key components, place stringent demands on the comprehensive performance of PET film. Traditional PET film has gradually exposed issues with insufficient mechanical strength, making it difficult to maintain structural stability during battery cycling. Its high thermal shrinkage makes it prone to deformation at high temperatures, impacting battery safety and reliability. Furthermore, its poor electrolyte resistance leads to swelling after prolonged immersion in electrolyte, resulting in a decrease in current collector performance, which in turn affects the battery's lifespan and electrochemical performance.

[0003] To solve the above problems, although existing technologies have attempted to optimize the performance of PET films through chemical modification, physical treatment, etc., there are still limitations in molecular chain structure regulation and surface functional modification, 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 technical difficulty that urgently needs to be overcome in this field. Summary of the Invention

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

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a high-strength PET film for a composite current collector comprises the following steps: S1: uniformly mixing a modified PET resin, an antioxidant, and a lubricant, melt-extruding, casting into a film, and biaxially stretching to obtain a base film;

[0008] S2: The base film is sequentially subjected to ion irradiation, oxidation treatment, RAFT polymerization, washing, and drying 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-cyclohexanedimethanol, ethylene glycol, and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene;

[0010] Furthermore, the diester compound is prepared by reacting dimethyl itaconate and trans-1,4-diaminocyclohexane.

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

[0012] Add dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, zinc acetate, and antimony trioxide into a reaction vessel, heat to 180-210° C. under a nitrogen atmosphere, react for 4-6 hours, further heat to 260-280° C. while reducing the pressure to 10-20 Pa, react for 3-4 hours, and then introduce nitrogen to return to atmospheric pressure to obtain a modified PET resin;

[0013] Furthermore, in the preparation process of the modified PET resin, the total molar ratio of 1,4-cyclohexanedimethanol, 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-cyclohexanedimethanol: 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 diester compounds;

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

[0016] Furthermore, the preparation method of the diester compound comprises the following steps: adding dimethyl itaconate and trans-1,4-diaminocyclohexane to methanol, stirring evenly, heating to 70-75° C. to react for 15-16 hours, cooling, filtering, washing the product with methanol, and vacuum drying to obtain the diester compound;

[0017] Furthermore, during the preparation of the diester compound, the molar ratio of dimethyl itaconate to trans-1,4-diaminocyclohexane was 1:0.5.

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

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

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

[0021] Furthermore, the RAFT polymerization process comprises the following steps: placing the base film after oxidation treatment in an acrylate compound solution, adding a RAFT agent, and initiating ultraviolet light for 4-5 hours under a nitrogen atmosphere;

[0022] Furthermore, 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;

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

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

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

[0026] Furthermore, the preparation method of the acrylate compound comprises the following steps:

[0027] An oxazolidinone compound, 4-dimethylaminopyridine, and triethylamine were added to tetrahydrofuran, heated to 60-65°C and stirred evenly, and a tetrahydrofuran solution of methacrylic anhydride was added. The mixture was kept warm for 24 hours under a nitrogen atmosphere, and rotary evaporated to obtain a crude product. The crude product was added to dichloromethane and washed alternately with a saturated sodium bicarbonate solution, a 1 mol% hydrochloric acid solution, deionized water, and a saturated saline solution, dried over anhydrous magnesium sulfate, purified, and dried in vacuo to obtain an acrylate compound.

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

[0029] Furthermore, the preparation method of the oxazolidinone compound comprises the following steps: adding phenyl isocyanate and glycidol to dichloromethane, reacting at room temperature for 4-6 hours to obtain phenyl glycidyl carbamate; adding phenyl glycidyl carbamate to acetone, adding 1,5,7-triazabicyclo[4.4.0]decene-5-ene, heating to 35-40°C and reacting for 2-2.5 hours to obtain the oxazolidinone compound;

[0030] Furthermore, in the preparation process of phenyl glycidyl carbamate, the molar ratio of phenyl isocyanate: glycidol is 1:1; in the preparation process of the oxazolidinone compound, 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 proportions of the components in the base film, by mass, 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; and the lubricant is at least one of ethylene bisstearamide and butyl stearate.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

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

[0035] 2. To further extend the service life of PET film and expand its application scenarios, specifically to enhance its electrolyte resistance, the present invention grafts acrylate monomers onto the surface of the PET base film through UV initiation. The rigid oxazolidinone heterocyclic structure of the polymer side chain and the syndiotactic stereoregularity of the main chain enhance the interaction between the molecular chains. When compounded with PET, the polymer acts as a reinforcing phase, increasing the tensile strength and modulus of the PET film through chemical crosslinking. It also reduces its swelling rate in the electrolyte, preventing the performance degradation of the current collector due to solvent erosion. Furthermore, it forms a dense protective layer, enhancing the current collector's tolerance to electrolytes and acidic and alkaline environments.

[0036] The acrylate polymer is firmly fixed to the PET base film surface through UV-initiated polymerization, reducing interlayer delamination of the composite current collector during cycling. Furthermore, the polymer's high glass transition temperature inhibits molecular chain motion during electrochemical processes, reducing interfacial impedance fluctuations and improving battery cycling stability. The alternating structure formed by free radical copolymerization optimizes molecular chain alignment and reduces defect sites, thereby reducing the probability of side reactions in the current collector during charge and discharge, thereby extending battery life. DETAILED DESCRIPTION

[0037] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0038] In the following examples, the preparation method of the acrylate compound comprises the following steps:

[0039] Step (1): Add 1 mmol of phenyl isocyanate and 1 mmol of glycidol to dichloromethane and react at room temperature for 4 hours 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°C and react for 2 hours to obtain an 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 evenly, 2.1 mmol of methacrylic anhydride in tetrahydrofuran was added, and the mixture was kept warm for 24 hours under a nitrogen atmosphere, and 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, dried over anhydrous magnesium sulfate, purified, and vacuum dried to obtain an acrylate compound;

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

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

[0044] S1: dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, 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, heated to 180°C under a nitrogen atmosphere for 4 h, further heated to 260°C while reducing the pressure to 1 Pa for 3 h, and then nitrogen was introduced to return the pressure to atmospheric pressure to obtain a modified PET resin;

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

[0046] The mass ratio of the 1,4-cyclohexanedimethanol: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: 100 parts of modified PET resin, 0.8 parts of antioxidant 1010, and 0.7 parts of butyl stearate were mixed evenly, melt-extruded, cast into a film, and biaxially stretched to obtain a base film;

[0049] S3: The base film was subjected to 1.75 MeV, 4.2×10 7 ion / cm 2 Ion irradiation, placing the ion-irradiated base film in a pH = 3, 500mM hydrogen peroxide solution, 254nm, 190W ultraviolet radiation for 2h, washing the base film with deionized water, drying, and then placing the base film in a 5% w / v dimethylformamide solution of benzophenone, shaking at room temperature for 24h, washing the base film with deionized water and ethanol, drying, placing the oxidized base film in a 20% w / v acrylate compound solution, adding a RAFT agent, under a nitrogen atmosphere, 295nm, 15W, the distance between the ultraviolet light and the base film is 7cm, ultraviolet initiation for 4h, washing, and drying to obtain a high-strength PET film.

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

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

[0052] S1: dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, 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, heated to 180°C under a nitrogen atmosphere for 4 h, further heated to 260°C while reducing the pressure to 1 Pa for 3 h, and then nitrogen was introduced to return the pressure to atmospheric pressure to obtain a modified PET resin;

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

[0054] The mass ratio of the 1,4-cyclohexanedimethanol: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: 100 parts of modified PET resin, 0.8 parts of antioxidant 1010, and 0.7 parts of butyl stearate were mixed evenly, melt-extruded, cast into a film, and biaxially stretched to obtain a base film;

[0057] S3: The base film was subjected to 1.75 MeV, 4.2×10 7 ion / cm 2 Ion irradiation, placing the ion-irradiated base film in a pH = 3, 500mM hydrogen peroxide solution, 254nm, 190W ultraviolet radiation for 2h, washing the base film with deionized water, drying, and then placing the base film in a 5% w / v dimethylformamide solution of benzophenone, shaking at room temperature for 24h, washing the base film with deionized water and ethanol, drying, placing the oxidized base film in a 20% w / v acrylate compound solution, adding a RAFT agent, under a nitrogen atmosphere, 295nm, 15W, the distance between the ultraviolet light and the base film is 7cm, ultraviolet initiation for 4h, washing, and drying to obtain a high-strength PET film.

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

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

[0060] S1: dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, 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, heated to 180°C under a nitrogen atmosphere for 4 h, further heated to 260°C while reducing the pressure to 1 Pa for 3 h, and then nitrogen was introduced to return the pressure to atmospheric pressure to obtain a modified PET resin;

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

[0062] The mass ratio of the 1,4-cyclohexanedimethanol: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: 100 parts of modified PET resin, 0.8 parts of antioxidant 1010, and 0.7 parts of butyl stearate were mixed evenly, melt-extruded, cast into a film, and biaxially stretched to obtain a base film;

[0065] S3: The base film was subjected to 1.75 MeV, 4.2×10 7 ion / cm 2 Ion irradiation, placing the ion-irradiated base film in a pH = 3, 500mM hydrogen peroxide solution, 254nm, 190W ultraviolet radiation for 2h, washing the base film with deionized water, drying, and then placing the base film in a 5% w / v dimethylformamide solution of benzophenone, oscillating at room temperature for 24h, washing the base film with deionized water and ethanol, drying, placing the oxidized base film in a 25% w / v acrylate compound solution, adding a RAFT agent, under a nitrogen atmosphere, 295nm, 15W, the distance between the ultraviolet light and the base film is 7cm, ultraviolet initiation for 4h, washing, and drying to obtain a high-strength PET film.

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

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

[0068] S1: dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, 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, heated to 180°C under a nitrogen atmosphere for 4 h, further heated to 260°C while reducing the pressure to 1 Pa for 3 h, and then nitrogen was introduced to return the pressure to atmospheric pressure to obtain a modified PET resin;

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

[0070] The mass ratio of the 1,4-cyclohexanedimethanol: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: 100 parts of modified PET resin, 0.8 parts of antioxidant 1010, and 0.7 parts of butyl stearate were mixed evenly, melt-extruded, cast into a film, and biaxially stretched to obtain a base film;

[0073] S3: The base film was subjected to 1.75 MeV, 4.2×10 7 ion / cm 2 Ion irradiation, placing the ion-irradiated base film in a pH = 3, 500mM hydrogen peroxide solution, 254nm, 190W ultraviolet radiation for 2h, washing the base film with deionized water, drying, and then placing the base film in a 5% w / v dimethylformamide solution of benzophenone, oscillating at room temperature for 24h, washing the base film with deionized water and ethanol, drying, placing the oxidized base film in a 25% w / v acrylate compound solution, adding a RAFT agent, under a nitrogen atmosphere, 295nm, 15W, the distance between the ultraviolet light and the base film is 7cm, ultraviolet initiation for 4h, washing, and drying to obtain a high-strength PET film.

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

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

[0076] S1: dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, 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, heated to 180°C under a nitrogen atmosphere for 4 h, further heated to 260°C while reducing the pressure to 1 Pa for 3 h, and then nitrogen was introduced to return the pressure to atmospheric pressure to obtain a modified PET resin;

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

[0078] The mass ratio of the 1,4-cyclohexanedimethanol: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: 100 parts of modified PET resin, 0.8 parts of antioxidant 1010, and 0.7 parts of butyl stearate were mixed evenly, melt-extruded, cast into a film, and biaxially stretched to obtain a base film;

[0081] S3: The base film was subjected to 1.75 MeV, 4.2×10 7 ion / cm 2 Ion irradiation, placing the ion-irradiated base film in a pH=3, 500mM hydrogen peroxide solution, 254nm, 190W ultraviolet radiation for 2h, washing the base film with deionized water, drying, and then placing the base film in a 5% w / v dimethylformamide solution of benzophenone, oscillating at room temperature for 24h, washing the base film with deionized water and ethanol, drying, placing the oxidized base film in a 20% w / v acrylate compound solution, adding hydrothermal initiator 4,4'-azobis-4-cyanovaleric acid, heating to 70°C for reaction for 24h, washing, and drying to obtain a high-strength PET film.

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

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

[0084] S1: dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, 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, heated to 180°C under a nitrogen atmosphere for 4 h, further heated to 260°C while reducing the pressure to 1 Pa for 3 h, and then nitrogen was introduced to return the pressure to atmospheric pressure to obtain a modified PET resin;

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

[0086] The mass ratio of the 1,4-cyclohexanedimethanol: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: 100 parts of modified PET resin, 0.8 parts of antioxidant 1010, and 0.7 parts of butyl stearate were mixed evenly, melt-extruded, cast into a film, and biaxially stretched to obtain a base film;

[0089] S3: The base film was subjected to 1.75 MeV, 4.2×10 7 ion / cm 2 Ion irradiation, placing the ion-irradiated base film in a pH = 3, 500mM hydrogen peroxide solution, 254nm, 190W ultraviolet radiation for 2h, washing the base film with deionized water, drying, and then placing the base film in a 5% w / v dimethylformamide solution of benzophenone, oscillating at room temperature for 24h, washing the base film with deionized water and ethanol, drying, placing the oxidized base film in a 30% w / v acrylate compound solution, adding a RAFT agent, under a nitrogen atmosphere, 295nm, 15W, the distance between the ultraviolet light and the base film is 7cm, ultraviolet initiation for 4h, washing, and drying to obtain a high-strength PET film.

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

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

[0092] S1: dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, 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, heated to 180°C under a nitrogen atmosphere for 4 h, further heated to 260°C while reducing the pressure to 1 Pa for 3 h, and then nitrogen was introduced to return the pressure to atmospheric pressure to obtain a modified PET resin;

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

[0094] The mass ratio of the 1,4-cyclohexanedimethanol: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: 100 parts of modified PET resin, 0.8 parts of antioxidant 1010, and 0.7 parts of butyl stearate were mixed evenly, melt-extruded, cast into a film, and biaxially stretched to obtain a base film;

[0097] S3: The base film was subjected to 1.75 MeV, 4.2×10 7 ion / cm 2 Ion irradiation, placing the ion-irradiated base film in a pH = 3, 500mM hydrogen peroxide solution, 254nm, 190W ultraviolet radiation for 2h, washing the base film with deionized water, drying, and then placing the base film in a 5% w / v dimethylformamide solution of benzophenone, shaking at room temperature for 24h, washing the base film with deionized water and ethanol, drying, placing the oxidized base film in a 20% w / v acrylate compound solution, adding a RAFT agent, under a nitrogen atmosphere, 295nm, 15W, the distance between the ultraviolet light and the base film is 7cm, ultraviolet initiation for 4h, washing, and drying to obtain a high-strength PET film.

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

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

[0100] S1: dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, 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, heated to 180°C under a nitrogen atmosphere for 4 h, further heated to 260°C while reducing the pressure to 1 Pa for 3 h, and then nitrogen was introduced to return the pressure to atmospheric pressure to obtain a modified PET resin;

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

[0102] The mass ratio of the 1,4-cyclohexanedimethanol: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: 100 parts of modified PET resin, 0.8 parts of antioxidant 1010, and 0.7 parts of butyl stearate were mixed evenly, melt-extruded, cast into a film, and biaxially stretched to obtain a base film;

[0105] S3: The base film was subjected to 1.75 MeV, 4.2×10 7 ion / cm 2 Ion irradiation, placing the ion-irradiated base film in a pH = 3, 500mM hydrogen peroxide solution, 254nm, 190W ultraviolet radiation for 2h, washing the base film with deionized water, drying, and then placing the base film in a 5% w / v dimethylformamide solution of benzophenone, shaking at room temperature for 24h, washing the base film with deionized water and ethanol, drying, placing the oxidized base film in a 20% w / v acrylate compound solution, adding a RAFT agent, under a nitrogen atmosphere, 295nm, 15W, the distance between the ultraviolet light and the base film is 7cm, ultraviolet initiation for 4h, washing, and drying to obtain a high-strength PET film.

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

[0107] Experiment: Tensile strength: Tensile strength test is carried out according to GB / T 1040.1-2018;

[0108] Thermal shrinkage: The thermal shrinkage of high-strength PET film is tested according to ASTM D 1204. The smaller the value, the higher the thermal stability. The test is based on the thermal shrinkage of the film after being placed at 150°C for 30 minutes.

[0109] Electrolyte tolerance: Cut high-strength PET film into 20cm x 20cm samples, record the circumference C1, and then soak it in a 65°C electrolyte for 48 hours. Record the circumference of the sample after soaking as C2, and calculate the swelling degree.

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

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

[0112] Table 1 High-strength PET film performance test

[0113]

[0114] Conclusion: The high-strength PET film for composite current collector prepared by the present invention has excellent mechanical properties, thermal stability and electrolyte tolerance.

[0115] Comparative Example 1 replaced the UV-initiated polymerization method with the traditional thermal initiation method. The water-soluble initiator has poor thermal stability, which easily leads to reduced chain transfer efficiency and difficulty in controlling the growth of the polymer chain, resulting in reduced grafting efficiency. At the same time, gelation and precipitation are prone to occur in aqueous solution, resulting in blockage of the nanochannel entrance, affecting the grafting uniformity and material properties.

[0116] In Comparative Example 2, the concentration of the acrylate compound is too high, which can easily lead to increased polymerization exotherm, trigger local gelation, and cause blockage of the nanochannel entrance, affecting the grafting uniformity and material properties.

[0117] In Comparative Example 3, the RAFT agent concentration was too low, which resulted in a reduced chain reaction rate, easy chain termination, and reduced chain transfer efficiency. It was difficult to control the growth of the polymer chain, resulting in reduced grafting efficiency.

[0118] In Comparative Example 4, the diol molar ratio of the diol to diacid molar ratio is too large, resulting in excessive hydroxyl functional groups in the reaction system, initiating chain termination, limiting chain growth, and possibly increasing the polarity of the polymer, 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 embodied 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 illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for preparing a high-strength PET film for a composite current collector, characterized in that: The following steps are involved: S1: uniformly mixing the modified PET resin, antioxidant, and lubricant, melt-extruding, casting into a film, and biaxially stretching to obtain a base film; S2: The base film is sequentially subjected to ion irradiation, oxidation treatment, RAFT polymerization, washing, and drying to obtain a high-strength PET film; The modified PET resin is prepared by copolymerization of dimethyl phthalate, a diester compound, 1,4-cyclohexanedimethanol, ethylene glycol, and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene; The diester compound is prepared by reacting dimethyl itaconate and trans-1,4-diaminocyclohexane.

2. The method for preparing a high-strength PET film for a composite current collector according to claim 1, wherein: The preparation method of the modified PET resin comprises the following steps: Add dimethyl phthalate, diester compound, 1,4-cyclohexanedimethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, zinc acetate, and antimony trioxide into a reaction vessel, heat to 180-210° C. under a nitrogen atmosphere, react for 4-6 hours, further heat to 260-280° C. while reducing the pressure to 10-20 Pa, react for 3-4 hours, and then introduce nitrogen to return to atmospheric pressure to obtain a modified PET resin; During the preparation of the modified PET resin, the total molar ratio of 1,4-cyclohexanedimethanol, ethylene glycol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene: dimethyl phthalate, and the diester compound is (1.5-2.1):1; the mass ratio of 1,4-cyclohexanedimethanol: ethylene glycol: 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is 1:2:1; and the mass ratio of dimethyl phthalate: the diester compound is 1:

1.

3. The method for preparing a high-strength PET film for a composite current collector according to claim 1, wherein: The method for preparing the diester compound comprises the following steps: adding dimethyl itaconate and trans-1,4-diaminocyclohexane to methanol, stirring evenly, heating to 70-75° C. for reaction for 15-16 hours, cooling, filtering, washing the product with methanol, and vacuum drying to obtain the diester compound; During the preparation of the diester compound, the molar ratio of dimethyl itaconate to trans-1,4-diaminocyclohexane is 1:0.

5.

4. The method for preparing a high-strength PET film for a composite current collector according to claim 1, wherein: The parameters of the ion irradiation include: ion irradiation energy: 1.75-1.8 MeV, ion irradiation flux: 4.2-4.3×10 7 ion / cm 2 .

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

6. The method for preparing a high-strength PET film for a composite current collector according to claim 1, wherein: The RAFT polymerization process comprises the following steps: placing the oxidized base film in an acrylate compound solution, adding a RAFT agent, and initiating ultraviolet light for 4-5 hours under a nitrogen atmosphere; 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 agent is (500-1000):1; The parameters of the ultraviolet initiation include: wavelength: 295nm, power: 15W, and distance between the ultraviolet light and the base film: 7-8cm.

7. The method for preparing a high-strength PET film for a composite current collector according to claim 6, wherein: The preparation method of the acrylate compound comprises the following steps: An oxazolidinone compound, 4-dimethylaminopyridine, and triethylamine were added to tetrahydrofuran, heated to 60-65°C and stirred evenly, and a tetrahydrofuran solution of methacrylic anhydride was added. The mixture was kept warm for 24 hours under a nitrogen atmosphere, and then rotary evaporated, purified, and vacuum dried to obtain an acrylate compound. In the preparation process of the acrylate compound, the molar ratio of the oxazolidinone compound: 4-dimethylaminopyridine: triethylamine: methacrylic acid liver is 2:0.6:3:2.

1.

8. The method for preparing a high-strength PET film for a composite current collector according to claim 7, wherein: The preparation method of the oxazolidinone compound comprises the following steps: adding phenyl isocyanate and glycidol to dichloromethane, reacting at room temperature for 4-6 hours to obtain phenyl glycidyl carbamate; adding phenyl glycidyl carbamate to acetone, adding 1,5,7-triazabicyclo[4.4.0]decene-5-ene, heating to 35-40° C. and reacting for 2-2.5 hours to obtain the oxazolidinone compound; During the preparation of phenyl glycidyl carbamate, the molar ratio of phenyl isocyanate to glycidol is 1:1; during the preparation of the oxazolidinone compound, 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.

9. The method for preparing a high-strength PET film for a composite current collector according to claim 1, wherein: The components in the base film include, by mass, 80-100 parts of modified PET resin, 0.8-1.6 parts of antioxidant, and 0.7-1.2 parts of lubricant. 10 . A high-strength PET film prepared according to the method for preparing a high-strength PET film for a composite current collector according to any one of claims 1 to 9 .

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