Polyester master batch, polyester film and preparation method and application thereof

Abstract

The invention relates to a polyester master batch, a polyester film as well as a preparation method and application of the polyester film. The polyester master batch is prepared from the following raw materials in parts by weight: 100 parts of binary acid, 40-60 parts of flexible dihydric alcohol, 0.5-5 parts of rigid dihydric alcohol, 0.5-5 parts of polar dihydric alcohol containing phosphonic acid group and / or phosphate group and 3-8 parts of reinforcing filler, and the reinforcing filler comprises aramid fiber nanowhiskers. The polyester master batch is subjected to formula design, the prepared polyester master batch is excellent in mechanical property, a polyester film prepared from the polyester master batch has excellent rigidity and surface energy, the composite current collector containing the polyester film solves the problem that the polyester film is prone to delaminating from a metal coating, and the composite current collector has the advantages that the composite current collector is simple in preparation process and low in cost. And the stability and the safety of the composite current collector in the use process are ensured by combining the high rigidity of the polyester film.

Description

Technical Field

[0001] This invention relates to the field of polyester materials technology, and in particular to a polyester masterbatch, a polyester film, a method for preparing the same, and their applications. Background Technology

[0002] Current collectors are a key component in lithium-ion batteries, supercapacitors, and some flexible electronic devices. Their main function is to conduct electrons between the electrode active material and the external circuitry, while also providing support, collecting electrons, and dissipating heat. Currently, commercial current collectors are mostly made of metal foil, such as copper foil for the negative electrode and aluminum foil for the positive electrode. Although traditional metal foils have good conductivity, they also have several shortcomings in practical applications: their thickness is usually 6-20 μm, which limits energy density; at the same time, metal foils have poor flexibility and are prone to pulverization, shedding, and bending cracking under high-rate charge-discharge and long-cycle conditions, which is detrimental to the development of high-performance batteries.

[0003] In recent years, with the increasing demand for lightweight, flexible, and high-energy-density energy storage devices, composite current collectors have gradually become a research hotspot. These materials are generally composed of a polymer film matrix (such as polyester, polypropylene, polyimide, etc.) and a metal coating or deposition layer. This "polymer base film + metal conductive layer" structure effectively reduces the overall mass of the current collector and improves mechanical flexibility to a certain extent, thereby significantly enhancing the energy density and safety of the battery. Among them, PET film is considered a composite current collector substrate with great application potential due to its wide availability of raw materials, moderate cost, good transparency, and dimensional stability.

[0004] However, using PET as a composite current collector substrate still presents two prominent problems: First, insufficient surface energy. The surface tension of ordinary PET films is typically around 38-40 mN / m, which is insufficient to ensure the firm adhesion of metal coatings (copper or aluminum) under high temperature, high humidity, or long-term cycling conditions, easily leading to interfacial peeling or even electrode failure. Therefore, how to endow PET with higher surface polarity through molecular structure design or process modification, increasing its surface energy to ≥42 mN / m, becomes the key to ensuring the adhesion of metal coatings. Second, limited bulk rigidity. The tensile modulus of conventional PET is between 3.5-4.0 GPa. For ultra-thin (≤5 μm) films, deformation or warping is easily generated during stretching, coating, and subsequent battery winding, affecting film formation accuracy and dimensional stability. At the same time, the relatively low glass transition temperature (approximately 75 ℃) limits its mechanical retention performance under high-temperature environments.

[0005] Therefore, the need to provide a polyester film with low surface energy and high modulus, which can help achieve thinner, more stable and more durable composite current collectors, has become an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a polyester masterbatch, a polyester film, a preparation method thereof, and its application. By designing the formulation of the polyester masterbatch, the resulting polyester masterbatch exhibits excellent mechanical properties. The polyester film prepared from this polyester masterbatch possesses both excellent rigidity and surface energy. The composite current collector containing the polyester film solves the problem of easy delamination between the polyester film and the metal coating. Furthermore, the high rigidity of the polyester film ensures the stability and safety of the composite current collector during use.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a polyester masterbatch, wherein the raw materials for preparing the polyester masterbatch include, by weight, 100 parts of diacid, 40-60 parts of flexible diol, 0.5-5 parts of rigid diol, 0.5-5 parts of polar diol containing phosphonic acid group and / or phosphate ester group, and 3-8 parts of reinforcing filler.

[0009] The reinforcing filler includes aramid nanofibers.

[0010] Among them, 40-60 portions can be 40 portions, 45 portions, 50 portions, 55 portions or 60 portions, etc.; 0.5-5 portions can be 0.5 portions, 1 portion, 2 portions, 3 portions, 4 portions or 5 portions, etc.; 3-8 portions can be 3 portions, 4 portions, 5 portions, 6 portions, 7 portions or 8 portions, etc.

[0011] This invention provides a polyester masterbatch that, by introducing polar diols containing phosphonic acid groups and / or phosphate ester groups and reinforcing fillers into the polyester chain segments, increases the surface energy and roughness of the polyester film made from the polyester masterbatch. This facilitates the further preparation of composite current collectors, enabling a stronger metal coating through chemical bonding and mechanical interlocking. Furthermore, by introducing rigid groups into the polyester chain segments, the modulus of the polyester film made from the polyester masterbatch is improved, enhancing the processing performance of the polyester film. This solves the problems of insufficient rigidity of the polyester film and poor adhesion between the polyester film and the metal coating, effectively improving the stability of the composite current collector under the working environment of lithium-ion batteries and enhancing the safety of lithium-ion batteries.

[0012] Preferably, the dicarboxylic acid includes terephthalic acid.

[0013] Preferably, the flexible diol comprises ethylene glycol.

[0014] Preferably, the rigid diol has carbon hydroxyl groups at both ends of its molecular chain.

[0015] Preferably, the rigid diol comprises neopentyl glycol and / or 1,4-cyclohexanediethanol.

[0016] Preferably, the polar diol containing phosphonic acid groups and / or phosphate ester groups has carboxyl groups and / or hydroxyl groups at both ends of its molecular chain.

[0017] Preferably, the polar diol containing phosphonic acid and / or phosphate groups includes diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonate and / or 2-hydroxyethyl methacrylate phosphate.

[0018] Preferably, the length of the aramid nanocrystals is ≤200 nm, for example, it can be 100 nm, 120 nm, 140 nm, 150 nm, 160 nm, 180 nm or 200 nm, etc.

[0019] Preferably, the raw materials for preparing the polyester masterbatch further include 0.02-0.06 parts of catalyst by weight, for example, 0.02, 0.03, 0.04, 0.05 or 0.06 parts.

[0020] Preferably, the catalyst comprises any one or a combination of at least two of antimony glycolate, tetrabutyl titanate, cobalt acetate tetrahydrate, or zinc acetate, and more preferably zinc acetate.

[0021] The preferred catalyst in this invention is zinc acetate. Zinc ions can coordinate with the end groups (carboxyl and hydroxyl groups) in the polyester film material, increasing the surface polarity of the polyester film, attracting coordination anchors for metal ions, preventing the metal coating from slipping or debonding at the interface, and improving the bonding strength between the polyester film and the metal coating in the composite current collector. Other commonly used catalysts, such as antimony glycolate and tetrabutyl titanate, tend to be dispersed throughout the polyester film material due to their large volume and alkoxide composition, and are not pushed to the surface. Therefore, they do not change the surface polarity of the polyester film and thus do not affect the metal coating. In addition, tetrabutyl titanate easily transforms into titanium oxide during polymerization. Titanium oxide has a water-carrying surface and can even hinder the adhesion of the metal coating.

[0022] In a second aspect, the present invention provides a method for preparing polyester masterbatch as described in the first aspect, the method comprising the following steps:

[0023] (1) The esterification reaction is carried out by mixing the dicarboxylic acid, flexible diol, rigid diol and reinforcing filler;

[0024] (2) The catalyst, a polar diol containing phosphonic acid group and / or phosphate ester group is optionally mixed with the reaction system obtained in step (1) and subjected to polycondensation reaction to obtain the polyester masterbatch.

[0025] Preferably, both the esterification reaction and the polycondensation reaction are carried out in a special polyester reactor.

[0026] Preferably, the polyester special reactor is equipped with a device for monitoring the temperature of the steam generated by the reaction.

[0027] Preferably, the temperature of the esterification reaction in step (1) is 220-250℃, for example, it can be 220℃, 225℃, 230℃, 235℃, 240℃, 245℃ or 250℃.

[0028] Preferably, the esterification reaction in step (1) continues until the temperature of the vapor generated by the reaction is <100°C, for example, it can be 90°C, 92°C, 94°C, 95°C, 96°C or 98°C.

[0029] Preferably, the esterification reaction in step (1) is carried out under pressure.

[0030] Preferably, the pressure of the esterification reaction in step (1) is depressurized from 340-360 kPa (e.g., 340 kPa, 345 kPa, 350 kPa, 355 kPa, or 360 kPa) to 0 kPa within 100-110 min from the start of the reaction (e.g., 100 min, 102 min, 104 min, 105 min, 106 min, 108 min, or 110 min, etc.) at a rate of -3 to -3.6 kPa / min (e.g., -3 kPa / min, -3.2 kPa / min, -3.4 kPa / min, -3.5 kPa / min, or -3.6 kPa / min, etc.).

[0031] Preferably, the esterification reaction in step (1) is carried out under an inert gas.

[0032] Preferably, the inert gas includes nitrogen.

[0033] Preferably, the temperature of the polycondensation reaction in step (2) is 270-290°C, for example, it can be 270°C, 275°C, 280°C, 285°C or 290°C.

[0034] Preferably, the polycondensation reaction in step (2) is carried out under vacuum.

[0035] Preferably, the vacuum degree of the polycondensation reaction in step (2) is evacuated from 0 kPa to -90 to -110 kPa at a rate of -1.2 to -2.2 kPa / min (e.g., -1.2 kPa / min, -1.4 kPa / min, -1.6 kPa / min, -1.5 kPa / min, -1.8 kPa / min, 2 kPa / min, or -2.2 kPa / min) within 50-70 min from the start of the reaction (e.g., 50 min, 55 min, 60 min, 65 min, or 70 min).

[0036] Preferably, the polycondensation reaction in step (2) continues until the intrinsic viscosity of the reaction system is ≥0.7 dL / g, for example, it can be 0.7 dL / g, 0.8 dL / g, 0.9 dL / g or 1 dL / g, etc.

[0037] Preferably, after the polycondensation reaction in step (2), the process further includes the steps of feeding, cooling, drawing, granulation and drying.

[0038] Thirdly, the present invention provides a polyester film obtained by molding polyester masterbatch as described in the first aspect.

[0039] Preferably, the molding process includes biaxial stretching molding.

[0040] Preferably, the molding temperature is 130-170℃, for example, it can be 130℃, 140℃, 150℃, 160℃ or 170℃.

[0041] Preferably, the thickness of the polyester film is ≤4 μm, for example, it can be 1 μm, 2 μm, 3 μm or 4 μm, etc.

[0042] Fourthly, the present invention provides a composite current collector comprising a polyester film and a metal coating as described in the third aspect.

[0043] Preferably, the thickness of the metal coating is ≤1 μm, for example, it can be 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm or 1 μm, etc.

[0044] Preferably, the composite current collector is prepared by the following method, the preparation method comprising:

[0045] The composite current collector is obtained by vacuum evaporating metal onto a polyester film as described in the third aspect to form a metal coating.

[0046] Preferably, the vacuum evaporation includes placing the polyester film as described in the third aspect in a vacuum chamber and performing a vacuum thermal evaporation reaction.

[0047] Preferably, the vacuum degree of the vacuum evaporation is 1×10⁻⁶. -5 ~1×10 -6 Torr, for example, could be 1×10 -5 Torr, 2×10 -5 Torr, 4×10 -5 Torr, 5×10 -5 Torr, 6×10 -5 Torr, 8×10 -5 Torr or 1×10-6 Torr.

[0048] Preferably, the deposition rate of the vacuum evaporation is 0.5-1.5 nm / s, for example, it can be 0.5 nm / s, 0.6 nm / s, 0.8 nm / s, 1 nm / s, 1.2 nm / s, 1.4 nm / s or 1.5 nm / s, etc.

[0049] Preferably, the deposition temperature of the vacuum evaporation is 80-100℃, such as 80℃, 85℃, 90℃, 95℃ or 100℃, and the deposition time of the vacuum evaporation is 12-17 min, such as 12 min, 13 min, 14 min, 15 min, 16 min or 17 min.

[0050] Preferably, the polyester film is pre-treated with surface activation, washing, and drying.

[0051] Preferably, the surface activation treatment includes placing the polyester film as described in the third aspect in an alkaline solution.

[0052] Preferably, the alkaline solution comprises an aqueous solution of sodium hydroxide.

[0053] Preferably, the sodium hydroxide aqueous solution contains 0.5-2 wt% sodium hydroxide, for example, 0.5 wt%, 1 wt%, 1.5 wt%, or 2 wt%.

[0054] Preferably, the surface activation treatment temperature is 50-60℃, for example, 50℃, 52℃, 54℃, 55℃, 60℃, 58℃ or 60℃, and the surface activation treatment time is 1-5 min, for example, 1 min, 2 min, 3 min, 4 min or 5 min.

[0055] Compared with the prior art, the present invention has at least the following beneficial effects:

[0056] (1) The present invention has made polyester masterbatch with excellent mechanical properties by formula design, and the polyester film made from the polyester masterbatch has both excellent rigidity and surface energy, and can be used as a composite current collector base film.

[0057] (2) The present invention provides a polyester film with excellent surface energy and rigidity. The film does not deform or warp during the preparation process. Compared with ordinary composite current collector base film, it solves the problem that the metal coating in the composite current collector is easy to separate from the base film. Combined with the high rigidity of the polyester film, it ensures the stability and safety of the composite current collector during use and improves the performance of lithium-ion batteries.

[0058] (3) The present invention provides a composite current collector, which reduces the overall mass of the current collector and effectively increases the energy density compared with the pure copper current collector. It does not delaminate under the high temperature working environment of lithium battery immersed in electrolyte, and meets the requirements for thinner, more stable and more durable composite current collectors. It is suitable for the field of lithium-ion batteries. Detailed Implementation

[0059] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0060] The specific information of the materials used in the following specific embodiments of the present invention is as follows:

[0061] Dicarboxylic acid, terephthalic acid;

[0062] Flexible diols, ethylene glycol;

[0063] Rigid diols, neopentyl glycol;

[0064] Rigid diol, 1,4-cyclohexanediethanol (CHDM).

[0065] Polar diols containing phosphonic acid groups and / or phosphate ester groups, N,N-bis(2-hydroxyethyl)aminomethylenephosphonate diethyl ester (DEHPA).

[0066] Polar diols containing phosphonic acid groups and / or phosphate groups, 2-hydroxyethyl methacrylate phosphate (HEMAP).

[0067] Catalyst, zinc acetate;

[0068] The reinforcing filler is aramid nanofibers with a length of 40-80 nm.

[0069] Examples 1-10 and Comparative Examples 1-6

[0070] Examples 1-10 and Comparative Examples 1-6 respectively provide a polyester masterbatch and its preparation method. The raw materials for preparing the polyester masterbatch are shown in Table 1-2 (the amounts of each component in Table 1-2 are all by weight), where "--" indicates that the component was not added.

[0071] The preparation method includes:

[0072] (1) Mix terephthalic acid, ethylene glycol, rigid diol and aramid nanofibers and place them in a special polyester reactor. Purge nitrogen three times to remove air. Add nitrogen until the pressure inside the reactor reaches 120 kPa. Under stirring, heat the reaction system to 220°C and pressurize it to 350 kPa for esterification. During the reaction from the start to 120 min, release the pressure to 0 kPa at a rate of -3.5 kPa / min. Maintain the reaction temperature until the temperature of the gas generated by the reaction is <100°C when monitored in the special reactor. The esterification reaction ends.

[0073] (2) After the esterification reaction is completed, zinc acetate and a polar diol containing phosphonic acid group and / or phosphate ester group are added to the reaction system obtained in step (1) under a nitrogen atmosphere, and the temperature is rapidly raised to 280°C to carry out the polycondensation reaction. The vacuum degree of the polycondensation reaction is evacuated from 0 kPa to -100 kPa at a rate of -1.7 kPa / min from the start of the reaction to 60 min of the reaction. The reaction temperature and vacuum degree are maintained until the intrinsic viscosity of the system is ≥0.7, and the polycondensation reaction ends.

[0074] (3) After the polycondensation reaction is completed, the product is discharged, flowed into 10°C water for cooling and drawing, and the drawn yarn is granulated and dried to obtain the polyester masterbatch.

[0075] Table 1

[0076]

[0077] Table 2

[0078]

[0079] Comparative Example 7

[0080] This comparative example provides a polyester masterbatch and its preparation method. The raw materials for preparing the polyester masterbatch include 100 parts by weight of terephthalic acid, 50 parts by weight of ethylene glycol, and 0.02 parts by weight of antimony glycol.

[0081] The preparation method includes:

[0082] (1) Mix terephthalic acid, ethylene glycol, and antimony glycol, and place them in a special polyester reactor. Purge nitrogen three times to remove air. Add nitrogen until the pressure inside the reactor reaches 120 kPa. Under stirring, heat the reaction system to 220°C and pressurize it to 350 kPa for esterification. During the reaction from the start to 120 min, release the pressure to 0 kPa at a rate of -3.5 kPa / min. Maintain the reaction temperature until the temperature of the gas generated by the reaction is <100°C when monitored in the special ester reactor. The esterification reaction ends.

[0083] (2) After the esterification reaction is completed, the temperature is rapidly raised to 280°C to carry out the polycondensation reaction. The vacuum degree of the polycondensation reaction is reduced from 0 kPa to -100 kPa at a rate of -1.7 kPa / min from the start of the reaction to 60 min of the reaction. The reaction temperature and vacuum degree are maintained until the intrinsic viscosity of the system is ≥0.7. After the polycondensation reaction is completed.

[0084] (3) After the polycondensation reaction is completed, the product is discharged and cooled in 10°C water and drawn into fibers. The fibers obtained are then granulated and dried to obtain the polyester masterbatch.

[0085] Application Example 1

[0086] This application example provides a polyester film and a composite current collector, wherein the preparation method of the polyester film includes:

[0087] The polyester masterbatch obtained in Example 1 was biaxially stretched (150°C) to form a polyester film with a thickness of 4 μm.

[0088] The method for preparing the composite current collector includes:

[0089] (1) Surface activation treatment:

[0090] The polyester film was placed in a 1 wt% NaOH solution and surface activated at 50 °C for 3 min. After washing the polyester film with water to remove the alkaline solution, it was dried at 100 °C to obtain a surface-activated polyester film.

[0091] (2) Vacuum evaporation of aluminum:

[0092] The surface-activated polyester film is fixed onto the substrate fixture of the vacuum evaporation apparatus, and then the vacuum chamber is evacuated to 5×10⁻⁶. -5 Torr;

[0093] High-purity aluminum (purity ≥99.99%) was placed in an electron beam evaporation source and vacuum evaporation was performed. The deposition rate of vacuum evaporation was controlled at 1 nm / s, the time was 15 min, the temperature was 100 ℃, and the aluminum layer thickness was 1.0 μm. After cooling, the composite current collector was obtained.

[0094] Application Example 2-10 and Comparative Application Example 1-7

[0095] Application Examples 2-10 and Comparative Application Examples 1-7 respectively provide a polyester film and a composite current collector. The difference from Application Example 1 is that the polyester masterbatch obtained in Example 1 is replaced with the polyester masterbatch provided in Examples 2-19 and Comparative Examples 1-9 to obtain the corresponding polyester film and further prepare the composite current collector. The rest is the same as in Example 1.

[0096] Test methods

[0097] (1) Surface energy test

[0098] The polyester masterbatch provided in the examples and comparative examples was dissolved in a mixed solution of 1.1.2.2-tetrachloroethane and phenol (mass ratio 1:1) at a concentration of 5 g / L. The mixture was coated onto a glass slide with a diameter of 2.5 cm using a dropper to prepare the sample by coating. The sample was then dried in a vacuum oven at 170°C for 48 h to remove the solvent and obtain a membrane sample. The contact angle of water and diiodomethane on the membrane sample was tested using a Dataphysics OCA20 contact angle meter (Germany) by the droplet method.

[0099] (2) Modulus test

[0100] Tensile strength and elongation at break were tested according to the national standard GB1040-2006. The polyester masterbatch provided in the examples and comparative examples was hot-pressed and quenched to obtain an amorphous film, which was then cut into dumbbell-shaped strips of 25 mm × 4 mm. The tensile properties were then tested using an Instron E44 universal tensile testing machine at a speed of 10 mm / min.

[0101] (3) Bonding strength test

[0102] Peel force tests were conducted on composite current collectors provided by corresponding use cases and comparative application examples after EAA heat sealing, with the test standard referring to GB / T25256-2010.

[0103] (4) Conductivity test

[0104] The surface resistance of the composite current collector was measured using a four-probe sheet resistance meter (Suzhou Jinglü ST2258C four-probe bulk resistivity meter) in the corresponding use case and comparative application example.

[0105] The test results are shown in Table 3:

[0106] Table 3

[0107]

[0108] The test results show that:

[0109] (1) As can be seen from Examples 1 to 10, the polyester masterbatch prepared by the present invention has excellent mechanical properties through formulation design, and the polyester film made from the polyester masterbatch has both excellent rigidity and surface energy, and can be used as a base film for composite current collectors. The obtained polyester masterbatch has a water contact angle of 39.0-41.7° and a diiodomethane contact angle of 31.0-32.5°, with high surface energy; the tensile strength can reach 150-176 MPa, with excellent mechanical properties. The bonding force between the polyester film and the metal coating in the obtained composite current collector can reach 3.9-4.55 N, solving the problem of easy delamination between the polyester film and the metal coating; the surface resistivity is only 45.6-47.8 Ω·cm, with excellent electrical properties.

[0110] (2) As can be seen from Examples 4-5 and Comparative Examples 1-6, the introduction of polar diols containing phosphonic acid groups and / or phosphate ester groups can effectively improve the surface energy of the polyester film, which is more conducive to the adhesion of the metal coating during the vapor deposition process and improves the bonding force between the film and the metal coating. The introduction of rigid diols effectively improves the modulus of the polyester film and improves the processing performance of the polyester film. The introduction of aramid nanofibers improves the mechanical interlocking effect between the polyester film and the metal interface and the rigidity of the polyester film itself, effectively improving the bonding ability between the film and the metal coating. If any component is missing, the technical effect of having excellent rigidity, surface energy and bonding ability and reducing surface resistance that this invention aims to achieve cannot be achieved.

[0111] (3) As can be seen from Examples 1-10 and Comparative Example 7, compared with traditional polyester film, the polyester film and composite current collector provided by the present invention effectively improve the bonding force between the polyester base film and the metal coating, and can meet the working and use requirements of lithium-ion batteries.

[0112] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A polyester masterbatch, characterized in that, The raw materials for preparing the polyester masterbatch include, by weight, 100 parts of dicarboxylic acid, 40-60 parts of flexible diol, 0.5-5 parts of rigid diol, 0.5-5 parts of polar diol containing phosphonic acid groups and / or phosphate ester groups, and 3-8 parts of reinforcing filler. The reinforcing filler includes aramid nanofibers.

2. The polyester masterbatch according to claim 1, characterized in that, The dicarboxylic acid includes terephthalic acid; Preferably, the flexible diol comprises ethylene glycol; Preferably, the rigid diol has carbon hydroxyl groups at both ends of its molecular chain; Preferably, the rigid diol comprises neopentyl glycol and / or 1,4-cyclohexanediethanol.

3. The polyester masterbatch according to claim 1 or 2, characterized in that, The polar diol containing phosphonic acid groups and / or phosphate ester groups has carboxyl groups and / or hydroxyl groups at both ends of its molecular chain; Preferably, the polar diol containing phosphonic acid and / or phosphate groups includes diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonate and / or 2-hydroxyethyl methacrylate phosphate.

4. The polyester masterbatch according to any one of claims 1-3, characterized in that, The length of the aramid nanocrystals is ≤200 nm.

5. The polyester masterbatch according to any one of claims 1-4, characterized in that, The raw materials for preparing the polyester masterbatch also include 0.02-0.06 parts by weight of catalyst; Preferably, the catalyst comprises any one or a combination of at least two of antimony glycolate, tetrabutyl titanate, cobalt acetate tetrahydrate, or zinc acetate, and more preferably zinc acetate.

6. A method for preparing polyester masterbatch as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) The esterification reaction is carried out by mixing the dicarboxylic acid, flexible diol, rigid diol and reinforcing filler; (2) The catalyst, a polar diol containing phosphonic acid group and / or phosphate ester group is optionally mixed with the reaction system obtained in step (1) and subjected to polycondensation reaction to obtain the polyester masterbatch.

7. The method for preparing polyester masterbatch according to claim 6, characterized in that, The temperature of the esterification reaction in step (1) is 220-250℃; Preferably, the esterification reaction in step (1) continues until the temperature of the vapor generated by the reaction is <100°C; Preferably, the esterification reaction in step (1) is carried out under pressure; Preferably, the pressure of the esterification reaction in step (1) is released from 340-360 kPa to 0 kPa at a rate of -3 to -3.6 kPa / min from the start of the reaction to 100-110 min of the reaction. Preferably, the esterification reaction in step (1) is carried out under an inert gas; Preferably, the inert gas includes nitrogen.

8. The method for preparing polyester masterbatch according to claim 6 or 7, characterized in that, The temperature of the polycondensation reaction in step (2) is 270-290℃; Preferably, the polycondensation reaction in step (2) is carried out under vacuum; Preferably, the vacuum degree of the polycondensation reaction in step (2) is evacuated from 0 kPa to -90 to -110 kPa at a rate of -1.2 to -2.2 kPa / min within 50-70 min from the start of the reaction. Preferably, the polycondensation reaction in step (2) continues until the intrinsic viscosity of the reaction system is ≥0.7 dL / g.

9. A polyester film, characterized in that, The polyester film is obtained by molding the polyester masterbatch as described in any one of claims 1-5.

10. A composite current collector, characterized in that, The composite current collector includes the polyester film and metal coating as described in claim 9.

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