High-strength polyester base film, its manufacturing method and use in composite current collectors

Abstract

The present invention discloses a high strength polyester base film and its manufacturing method and use in a composite current collector, and relates to the technical field of current collectors. [Means] The raw materials for the high-strength polyester base film include polyethylene terephthalate white chips A and polyethylene terephthalate white chips B, and the manufacturing method includes (1) thoroughly mixing the two materials, (2) heating and melting the mixed materials to form a molten mixture, and then extruding the mixture to produce a slab, (3) longitudinally stretching the slab along the direction of travel of a mechanical transport mechanism, and (4) subsequently entering a transverse oven unit for transverse stretching. The high-strength polyester base film manufactured by this method has the characteristics of high strength and high elongation, and can significantly improve the puncture resistance of the composite current collector, thereby improving safety in extreme situations such as collisions and impacts of the battery.

Description

[Technical Field]

[0001] The present invention relates to the field of current collectors, and more particularly to a high strength polyester base film and its method of manufacture and use in composite current collectors. [Background technology]

[0002] Currently, composite current collectors based on polymer films are attracting widespread attention and application in the new energy industry. The manufacturing process for these composite current collectors typically involves depositing a layer of metal (e.g., aluminum, copper, etc.) on a polymer film (e.g., polypropylene, polyethylene, polyester, etc.) using physical vapor deposition (PVD) to produce a film with a metallized surface that has a certain degree of conductive ability, resulting in a composite current collector. Compared to existing current collectors, composite current collectors based on polymer films have advantages such as low cost, light weight, and good internal insulation. These features allow the application of composite current collectors in batteries to reduce battery costs while improving the battery's energy density and safety.

[0003] However, the polymer films used in composite current collectors in the prior art are not developed exclusively for battery material applications, but are instead mature films from other industries, such as packaging and capacitors. Due to different application needs in the packaging and capacitor industries, various requirements are placed on the film's light transmittance, food safety, insulation properties, etc. To meet these requirements, the use of additives has to be increased or restricted, or various incompatible technical indicators have to be selected and discarded in the manufacturing process.

[0004] Therefore, the mature films currently available in the industry are not ideal base film materials for composite current collectors, especially puncture-resistant composite current collectors. Furthermore, the addition of certain additives can result in composite current collectors made with these films, resulting in low strength, weak bonding, easy powder shedding, and slow melting. Meanwhile, while the polyester base films used in the industry today have tensile strengths of less than 300 MPa in both the machine direction (MD) and transverse direction (TD), the current collector industry requires that the tensile strength in each direction be greater than 300 MPa. In particular, at a certain deformation, e.g., 10%, the tensile strength in each direction of the film must be greater than 140 MPa. Furthermore, within the range of elastic deformation, e.g., 2.5%, the tensile strength in each direction of the film must be greater than 100 MPa.

[0005] In view of the above situation, there is an urgent need to develop polymer films suitable for composite current collectors in the battery industry. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to solve the problems presented in the background art by providing a high-strength polyester base film, a method for producing the same, and its use in a composite current collector. The polyester base film produced by the present invention has the characteristics of high strength and high elongation, which can significantly improve the puncture resistance of the composite current collector, thereby improving safety in extreme situations such as battery collisions and impacts. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides the following technical aspects.

[0008] In the present invention, first, a high-strength polyester base film is provided, and raw materials for the high-strength polyester base film include polyethylene terephthalate white chips A and polyethylene terephthalate white chips B, The polydispersity index of the polyethylene terephthalate white chip A is 1.7±0.5, and the following conditions are met: (1) Weight average molecular weight Mw=33000±2000, (2) Number average molecular weight Mn=19000±1000, (3) Z average molecular weight Mz=60000±3000, One of the following is satisfied: The polydispersity index of the polyethylene terephthalate white chip B is 1.9±0.5, and the following conditions are met: (1) Weight average molecular weight Mw=50000±5000, (2) Number average molecular weight Mn=30000±3000, (3) Z average molecular weight Mz=90000±3000, Satisfies one of the following: Provides a high strength polyester base film.

[0009] Preferably, the Poly Ethylene terephthalate white chip A and Poly The mass ratio of the ethylene terephthalate white chips B ranges from 99:1 to 90:10.

[0010] Preferably, the Poly Ethylene terephthalate white chip A and Poly GPC measurement is performed on a mixture containing ethylene terephthalate white chip B, a molecular weight distribution curve of the mixture is obtained, and the part with a molecular weight Mw greater than 75,000 but less than 200,000 is integrated to obtain the integral area ΔS, and the proportion of the obtained ΔS to the total curve integral area is between 15% and 35%.

[0011] Furthermore, the thickness of the high-strength polyester base film is 2 to 6 μmand the ultimate stretch strength in the machine direction and the transverse direction is ≧300 MPa, where, when the deformation amount reaches 10%, the stretch strength in the machine direction and the transverse direction is both ≧140 MPa and the elongation at break is both ≧80%, and when the deformation amount reaches 2.5%, the stretch strength in the machine direction and the transverse direction is both ≧100 MPa and the elongation at break is both ≧80%.

[0012] In the present invention, there is provided a method for producing the high-strength polyester base film, (1) weighing polyethylene terephthalate white chips A and polyethylene terephthalate white chips B and thoroughly mixing them; (2) heating and melting the materials mixed in step (1) to form a molten mixture, and then extruding the mixture to produce a cast slab; (3) performing a longitudinal stretching process on the cast piece produced in step (2) at a longitudinal stretching ratio of 1:4 to 1:5; (4) performing a transverse stretching treatment on the cast piece produced in step (3) at a transverse stretching ratio of 1:4 to 1:5 to obtain the high-strength polyester base film; Further provided is a method for producing a high strength polyester base film.

[0013] Preferably, in the treatment process of step (2), the casting temperature is 220 to 270°C, the temperature of the chill roll is 20 to 35°C, the extrusion rate is 50 to 100 m / min, and the speed of the chill roll is 50 to 100 m / min.

[0014] Preferably, the temperature of the longitudinal stretching treatment described in step (3) is 115 to 130°C, and (4) The temperature for the transverse stretching treatment is 230 to 260°C.

[0015] In the present invention, the structure includes a support layer and a metal layer provided on each of the two surfaces of the support layer, the support layer being the high-strength polyester base film described above, and the thickness of the metal layer is 0.8 to 1.5 mm. μmThe present invention further provides a composite current collector,

[0016] Preferably, the metal layer is one of copper, a copper alloy, aluminum, or an aluminum alloy.

[0017] More preferably, a protective layer is provided on the surface of the metal layer away from the high-strength polyester base film, and the method for coating the protective layer includes the steps of: (1) uniformly dispersing carbon nanotubes in a solution of N-methylpyrrolidone (NMP) to prepare a coating solution; (2) The coating solution prepared in step (1) is mixed with 10 to 100 μm and coating the surface of the metal layer uniformly with a coating thickness of (3) Drying the composite current collector prepared in step (2) at 90 to 110°C.

[0018] The coating thickness is not the thickness after drying at 90 to 110°C; here, the thickness after drying at 90 to 110°C is the thickness of the protective layer, and the coating thickness is the thickness when the coating liquid is uniformly applied to the surface of the metal layer.

[0019] In step (1) of the method for applying the protective layer, the mass ratio of the carbon nanotubes to the N-methylpyrrolidone solution is 1:1000 to 1:500. [Effects of the Invention]

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The present invention meets the special requirements for polyester film in the composite current collector industry by producing a specialized polyester base film with high strength and high elongation at break. The invention selects polyester resin chips with specific molecular weight and molecular weight distribution, blends them with a small amount of high molecular weight polyester, and limits the polymer components that make up a small proportion of the total but have a significant impact on performance. Combined with a stretching process, the polyester base film is manufactured using a simple manufacturing process without the use of additives. This avoids problems such as low strength, weak bonding strength, easy powder shedding, and slow cutting due to the addition of additives.

[0022] (2) The composite current collector of the present invention has a high adhesion between the surface metal and the polyester base film, which effectively prevents the metal layer from peeling or falling off from the polyester base film, thereby extending the service life of the composite current collector and batteries using the composite current collector. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a graph showing the molecular weight distribution of the mixed material obtained in step (1) of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will be described in detail below with reference to the drawings and examples. Of course, the described examples are only some of the examples of the present invention, and are not all of the examples. All other examples that a person skilled in the art can obtain based on the examples of the present invention without performing creative work are all within the scope of protection of the present invention.

[0025] Example 1 (1) In this embodiment, the high-strength polyester base film is a polyethylene terephthalate (PET) white chip A, which is the host material of the polyester base film, and has a weight-average molecular weight Mw of 33,000, a number-average molecular weight Mn of 19,000, a Z-average molecular weight Mz of 59,000, and a polydispersity index of 1.74. A high-strength polyester base film is provided, which satisfies the following requirements: weight average molecular weight Mw of 55,000, number average molecular weight Mn of 33,000, Z average molecular weight Mz of 93,000, and polydispersity index of 1.67, using polyethylene terephthalate (PET) white chip B, which is an assist material for the formulation of the polyester base film.

[0026] The method for producing the high-strength polyester base film includes: (1) Mix the host material (i.e., polyester chip A) and the assist material (i.e., polyester chip B) in a mass ratio of 92:8, and perform GPC measurement. As shown in Figure 1, ΔS=30%. (2) The materials mixed in step (1) are fed into a twin-screw extruder, heated and melted to form a melt, and then the melt is extruded into a coat hanger type single-pass die to produce a cast piece, where the casting temperature is 220°C, the temperature of the chill roll is 20°C, the extrusion rate is 50m / min, and the speed of the chill roll is 50m / min; (3) longitudinally stretching the slab obtained in step (2) along the moving direction of the mechanical transport mechanism, wherein the longitudinal stretching ratio is 1:4 and the longitudinal stretching temperature is 120°C; (4) Then, the film is transversely stretched in a transverse oven unit at a temperature of 240°C, where the transverse stretch ratio is 1:4 and the final thickness is 4.5 mm. μm and preparing a bidirectionally stretched polyester film,

[0027] Upon testing, the film's MD stretching strength was 380 MPa, its breaking elongation was 80%, its TD stretching strength was 350 MPa, its breaking elongation was 90%, its MD P10 stretching strength (when deformation reaches 10%) was 170 MPa, its P2.5 stretching strength (when deformation reaches 2.5%) was 130 MPa, and its TD P10 stretching strength (when deformation reaches 10%) was 170 MPa, and its TD P2.5 stretching strength (when deformation reaches 2.5%) was 130 MPa.

[0028] (2) This embodiment also provides a method for preparing a composite negative electrode current collector from a polyester base film.

[0029] A. First, the metal conductive layer is produced. The polyester base film with the surface cleaned as produced in Example 1 is placed in a vacuum deposition chamber, and high-purity copper wire (purity greater than 99.99%) is melt-evaporated in the metal evaporation chamber at a high temperature of 1400-2000°C. The evaporated metal atoms pass through the cooling system in the vacuum deposition chamber and are deposited on both surfaces of the polymer base film, forming a copper metal conductive layer with a thickness of 1.0 micrometer.

[0030] B. Next, the protective layer is produced. 1 g of graphene is uniformly dispersed in 999 g of N-methylpyrrolidone (NMP) solution using ultrasonic dispersion to prepare a coating solution with a solid content of 0.1 wt.%, which is then uniformly coated onto the surface of the metal conductive layer using a die coating process, with the coating weight controlled to 80 micrometers. Finally, the coating is dried at 100°C.

[0031] (3) This embodiment also provides a method for fabricating a composite positive electrode current collector from a polyester base film.

[0032] A. First, the metal conductive layer is produced. The polyester base film with the surface cleaned as produced in Example 1 is placed in a vacuum deposition chamber, and high-purity aluminum wire (purity greater than 99.99%) in the metal evaporation chamber is melt-evaporated at a high temperature of 1300-2000°C. The evaporated metal atoms pass through the cooling system in the vacuum deposition chamber and are deposited on both surfaces of the polymer base film, forming an aluminum metal conductive layer with a thickness of 1.0 micrometer.

[0033] B. Next, the protective layer is produced. 1 g of carbon nanotubes is uniformly dispersed in 999 g of N-methylpyrrolidone (NMP) solution using ultrasonic dispersion to prepare a coating solution with a solid content of 0.1 wt.%, which is then uniformly coated onto the surface of the metal conductive layer using a die coating process, with the coating amount controlled to 90 micrometers. Finally, the coating is dried at 100°C.

[0034] Example 2 (1) In this embodiment, the high-strength polyester base film is a polyethylene terephthalate (PET) white chip A, which is the host material of the polyester base film, and has a weight-average molecular weight Mw of 33,000, a number-average molecular weight Mn of 19,000, a Z-average molecular weight Mz of 59,000, and a polydispersity index of 1.74. A high-strength polyester base film is provided in which the polyethylene terephthalate (PET) white chip B, which is an assist material for the formulation of the polyester base film, has a weight-average molecular weight Mw of 50,000, a number-average molecular weight Mn of 30,000, a Z-average molecular weight Mz of 90,000, and a polydispersity index of 1.67.

[0035] The method for producing the high-strength polyester base film includes: (1) Mixing the host material (i.e., polyester chip A) and the assist material (i.e., polyester chip B) in a mass ratio of 95:5, and performing GPC measurement to find that ΔS=25%; (2) the premixed material of step (1) is fed into a twin-screw extruder, heated and melted to form a melt, and then the melt is extruded into a coat hanger type single-pass die to form a cast piece, wherein the casting temperature is 250°C, the temperature of the chill roll is 28°C, the extrusion rate is 75m / min, and the speed of the chill roll is 75m / min; (3) longitudinally stretching the slab obtained in step (2) along the moving direction of the mechanical transport mechanism, wherein the longitudinal stretching ratio is 1:4 and the longitudinal stretching temperature is 125°C; (4) Then, the film is transversely stretched in a transverse oven unit at a temperature of 250°C, where the transverse stretch ratio is 1:4 and the final thickness is 4.5 mm. μm and preparing a bidirectionally stretched polyester film,

[0036] Upon testing, the film's MD stretching strength was 350 MPa, its breaking elongation was 90%, its TD stretching strength was 330 MPa, its breaking elongation was 100%, its MD P10 stretching strength (when deformation reaches 10%) was 160 MPa, its P2.5 stretching strength (when deformation reaches 2.5%) was 120 MPa, and its TD P10 stretching strength (when deformation reaches 10%) was 160 MPa, and its TD P2.5 stretching strength (when deformation reaches 2.5%) was 120 MPa.

[0037] (2) This embodiment also provides a method for preparing a composite negative electrode current collector from a polyester base film.

[0038] A. First, the metal conductive layer is produced. The polyester base film with the surface cleaned as produced in Example 2 is placed in a vacuum deposition chamber, and high-purity copper wire (purity greater than 99.99%) is melt-evaporated in the metal evaporation chamber at a high temperature of 1400-2000°C. The evaporated metal atoms pass through the cooling system in the vacuum deposition chamber and are deposited on both surfaces of the polymer base film, forming a copper metal conductive layer with a thickness of 0.8 micrometers.

[0039] B. Next, the protective layer is produced. 1 g of graphene is uniformly dispersed in 599 g of N-methylpyrrolidone (NMP) solution using ultrasonic dispersion to prepare a coating solution with a solid content of 0.17 wt.%, which is then uniformly coated onto the surface of the metal conductive layer using a die coating process, with the coating weight controlled to 70 micrometers. Finally, the coating is dried at 90°C.

[0040] (3) This embodiment also provides a method for fabricating a composite positive electrode current collector from a polyester base film.

[0041] A. First, the metal conductive layer is produced. The polyester base film with the surface cleaned as produced in Example 2 is placed in a vacuum deposition chamber, and high-purity aluminum wire (purity greater than 99.99%) in the metal evaporation chamber is melt-evaporated at a high temperature of 1300-2000°C. The evaporated metal atoms pass through the cooling system in the vacuum deposition chamber and are deposited on both surfaces of the polymer base film, forming an aluminum metal conductive layer with a thickness of 0.8 micrometers.

[0042] B. Next, the protective layer is produced. 1 g of carbon nanotubes is uniformly dispersed in 599 g of N-methylpyrrolidone (NMP) solution using ultrasonic dispersion to prepare a coating solution with a solid content of 0.17 wt.%, which is then uniformly coated onto the surface of the metal conductive layer using a die coating process, with the coating weight controlled to 80 micrometers. Finally, the coating is dried at 90°C.

[0043] Example 3 (1) In this embodiment, the high-strength polyester base film is a polyethylene terephthalate (PET) white chip A, which is the host material of the polyester base film, and has a weight-average molecular weight Mw of 33,000, a number-average molecular weight Mn of 19,000, a Z-average molecular weight Mz of 59,000, and a polydispersity index of 1.74. A high-strength polyester base film is provided in which polyethylene terephthalate (PET) white chip B, which is an assist material for the formulation of the polyester base film, has a weight-average molecular weight Mw of 45,000, a number-average molecular weight Mn of 27,000, a Z-average molecular weight Mz of 87,000, and a polydispersity index of 1.67.

[0044] The method for producing the high-strength polyester base film includes: (1) Mixing the host material (i.e., polyester chip A) and the assist material (i.e., polyester chip B) in a mass ratio of 97:3, and performing GPC measurement to find that ΔS=15%; (2) the premixed material of step (1) is fed into a twin-screw extruder, heated and melted to form a melt, and then the melt is extruded into a coat hanger type single-pass die to form a cast piece, the casting temperature is 270°C, the temperature of the chill roll is 35°C, the extrusion rate is 100m / min, and the speed of the chill roll is 100m / min; (3) longitudinally stretching the slab obtained in step (2) along the moving direction of the mechanical transport mechanism, wherein the longitudinal stretching ratio is 1:4 and the longitudinal stretching temperature is 130°C; (4) Then, the film is transversely stretched in a transverse oven unit at a temperature of 260°C, where the transverse stretch ratio is 1:4 and the final thickness is 4.5 mm. μm and preparing a bidirectionally stretched polyester film,

[0045] Upon testing, the film's MD stretching strength was 310 MPa, its breaking elongation was 100%, its TD stretching strength was 300 MPa, its breaking elongation was 110%, its MD P10 stretching strength (when deformation reaches 10%) was 140 MPa, its P2.5 stretching strength was 100 MPa, and its TD P10 stretching strength (when deformation reaches 10%) was 140 MPa, its P2.5 stretching strength was 100 MPa.

[0046] (2) This embodiment also provides a method for preparing a composite negative electrode current collector from a polyester base film.

[0047] A. First, the metal conductive layer is produced. The polyester base film with the surface cleaned as produced in Example 3 is placed in a vacuum deposition chamber, and high-purity copper wire (purity greater than 99.99%) is melt-evaporated in the metal evaporation chamber at a high temperature of 1400-2000°C. The evaporated metal atoms pass through the cooling system in the vacuum deposition chamber and are deposited on both surfaces of the polymer base film, forming a copper metal conductive layer with a thickness of 1.5 micrometers.

[0048] B. Next, the protective layer is produced. 1 g of graphene is uniformly dispersed in 799 g of N-methylpyrrolidone (NMP) solution using ultrasonic dispersion to prepare a coating solution with a solid content of 0.125 wt.%, which is then uniformly coated onto the surface of the metal conductive layer using a die coating process, with the coating weight controlled to 90 micrometers. Finally, the coating is dried at 110°C.

[0049] (3) This embodiment also provides a method for fabricating a composite positive electrode current collector from a polyester base film.

[0050] A. First, the metal conductive layer is produced. The polyester base film with the surface cleaned as produced in Example 3 is placed in a vacuum deposition chamber, and high-purity aluminum wire (purity greater than 99.99%) in the metal evaporation chamber is melt-evaporated at a high temperature of 1300-2000°C. The evaporated metal atoms pass through the cooling system in the vacuum deposition chamber and are deposited on both surfaces of the polymer base film, forming an aluminum metal conductive layer with a thickness of 1.5 micrometers.

[0051] B. Next, the protective layer is produced. 1 g of carbon nanotubes is uniformly dispersed in 799 g of N-methylpyrrolidone (NMP) solution using ultrasonic dispersion to prepare a coating solution with a solid content of 0.125 wt.%, which is then uniformly coated onto the surface of the metal conductive layer using a die coating process, with the coating amount controlled to 100 micrometers. Finally, the coating is dried at 110°C.

[0052] Comparative Example 1 This comparative example is almost the same as the manufacturing method of the composite current collector in Example 1, except that the polyethylene terephthalate (PET) white chips, which are the assist material for blending the polyester base film, have a weight average molecular weight Mw of 25,000, a number average molecular weight Mn of 13,000, a Z average molecular weight Mz of 57,000, and a polydispersity index of 1.92. In addition, the host material and the assist material described in Example 2 were mixed in a mass ratio of 92:8, and when measured by GPC, ΔS was 12%.

[0053] Stretch ratio in MD direction is 1:4, stretch ratio in TD direction is 1:4, final thickness is 4.5 μm A bidirectionally stretched polyester film was produced, and the film's MD stretch strength was 260 MPa, the breaking elongation was 120%, the TD stretch strength was 220 MPa, the breaking elongation was 130%, the MD P10 stretch strength (when the deformation amount reached 10%) was 125 MPa, the P2.5 stretch strength was 92 MPa, and the TD P10 stretch strength (when the deformation amount reached 10%) was 118 MPa, and the P2.5 stretch strength was 90 MPa.

[0054] As can be seen from the above data, the stretch strength in the transverse and longitudinal directions of the polyester base film is much lower than that of the base film obtained in Example 1, and the stretch strength of P10 and P2.5 is also significantly lower than that of Example 1.

[0055] Comparative Example 2 Commercially available 6 μm The pure copper foil is used as the current collector.

[0056] Comparative Example 3 Commercially available 13 μm Pure aluminum foil is used as the current collector.

[0057] Test Example (1) Referring to GB / T10004-2008, the current collectors obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to a puncture resistance test. The test results are shown in Table 1.

[0058] [Table 1]

[0059] As can be seen from the data in Table 1, the composite current collector manufactured with a polyester base film with high strength and high elongation at break has a puncture resistance that is far greater than that of conventional pure copper foil current collectors and pure aluminum foil current collectors.

[0060] As can be seen from the above, the polyester base film obtained by the manufacturing method of the present invention is characterized by high strength and high elongation at break. In addition, the composite current collector manufactured using this polyester base film has a puncture resistance that is far greater than that of conventional pure copper foil current collectors and pure aluminum foil current collectors, thereby improving safety in extreme situations such as battery collisions and impacts. Furthermore, the adhesion between the polyester base film and the metal conductive layer is strong, effectively preventing the metal layer from peeling or falling off from the polyester base film, thereby extending the service life of the composite current collector and batteries using the composite current collector.

[0061] Although the embodiments of the present invention have been disclosed as above, they are not limited to the operations described in the specification and embodiments, but are fully applicable to various fields suitable for the present invention, and a person skilled in the art can make various changes, modifications, substitutions and variations to these examples without departing from the principle and spirit of the present invention. Therefore, the present invention is not limited to specific details unless it deviates from the general concept limited by the claims and their equivalents.

Claims

1. A high-strength polyester base film, the raw material of which includes polyethylene terephthalate white chips A and polyethylene terephthalate white chips B; The polydispersity index of the polyethylene terephthalate white chip A is 1.7±0.5, and the following conditions are met: (1) Weight average molecular weight Mw=33000±2000, (2) Number average molecular weight Mn=19000±1000, (3) Z average molecular weight Mz=60000±3000, One of the following is satisfied: The polydispersity index of the polyethylene terephthalate white chip B is 1.9±0.5, and the following conditions are met: (1) Weight average molecular weight Mw=50000±5000, (2) Number average molecular weight Mn=30000±3000, (3) Z average molecular weight Mz=90000±3000, Satisfies one of the following: A high-strength polyester base film.

2. The mass ratio of the ethylene terephthalate white chips A to the ethylene terephthalate white chips B is in the range of 99:1 to 90:

10.

2. The high strength polyester base film according to claim 1.

3. GPC measurement is performed on a mixture obtained by mixing the ethylene terephthalate white chips A and the ethylene terephthalate white chips B, a molecular weight distribution curve of the mixture is obtained, and the part of the molecular weight Mw greater than 75,000 but less than 200,000 is integrated to obtain an integrated area ΔS, and the proportion of the obtained ΔS to the total curve integrated area is between 15% and 35%.

3. The high-strength polyester base film according to claim 1 or 2.

4. The high-strength polyester base film has a thickness of 2-6 μm and an ultimate stretch strength in both the longitudinal and transverse directions of ≧300 MPa, where, when the deformation reaches 10%, the stretch strength in both the longitudinal and transverse directions is ≧140 MPa and the elongation at break is ≧80%; when the deformation reaches 2.5%, the stretch strength in both the longitudinal and transverse directions is ≧100 MPa and the elongation at break is ≧80%.

4. The high strength polyester base film according to claim 3.

5. A method for producing the high-strength polyester base film according to any one of claims 1 to 4, (1) weighing polyethylene terephthalate white chips A and polyethylene terephthalate white chips B and thoroughly mixing them; (2) heating and melting the materials mixed in step (1) to form a molten mixture, and then extruding the mixture to produce a cast piece; (3) performing a longitudinal stretching process on the cast piece produced in step (2) at a longitudinal stretching ratio of 1:4 to 1:5; (4) performing a transverse stretching treatment on the cast piece produced in step (3) at a transverse stretching ratio of 1:4 to 1:5 to obtain the high-strength polyester base film; A method for producing a high-strength polyester base film.

6. The temperature of the longitudinal stretching treatment described in step (3) is 115 to 130°C, and the temperature of the transverse stretching treatment described in step (4) is 230 to 260°C.

6. The method for producing a high-strength polyester base film according to claim 5.

7. The structure comprises a support layer and a metal layer provided on each of the surfaces of both sides of the support layer, the support layer being the high-strength polyester base film according to any one of claims 1 to 4, and the thickness of the metal layer is 0.8 to 1.5 μm. A composite current collector characterized by:

8. The metal layer is one of copper, a copper alloy, aluminum, or an aluminum alloy.

8. The composite current collector according to claim 7.

9. A protective layer is provided on the surface of the metal layer away from the high-strength polyester base film, and a coating method for the protective layer includes the steps of: (1) uniformly dispersing carbon nanotubes in a solution of N-methylpyrrolidone (NMP) to prepare a coating solution; (2) uniformly applying the coating solution prepared in step (1) to the surface of the metal layer to a coating thickness of 10 to 100 μm; (3) drying the composite current collector prepared in step (2) at 90 to 110°C; 9. The composite current collector according to claim 7 or 8.

10. In step (1) of the method for coating the protective layer, the mass ratio of the carbon nanotubes to the N-methylpyrrolidone solution is 1:1000 to 1:500; 10. The composite current collector according to claim 9.

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