Composite current collector base film, and preparation method therefor and use thereof

Abstract

The present application provides a composite current collector base film, and a preparation method therefor and a use thereof. The composite current collector base film comprises a first polymer layer; and the first polymer layer comprises the following components by mass fraction: 20-60 wt% of a polyester material, and 40-80 wt% of a hydrocarbon polymer material. The present application introduces a specific content of a hydrocarbon polymer material, which can reduce the polarity of the base film and destroy the regular arrangement of polyester macromolecules, so that the surface roughness of the base film is higher, and the problem of film surface adhesion caused by the lack of silicon dioxide is solved; additionally, the crystallinity of the base film can be reduced, and the free volume and surface tension of the base film can be improved, solving the problem of low adhesion between a metal layer and the base film caused by the reduction of the polarity of the base film. Therefore, the composite current collector base film can solve the problem of poor high-temperature cycle performance of polyester film-based composite current collectors during use at the battery end.

Description

Composite current collector base film, preparation method and application thereof TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a composite current collector base film, a preparation method and application thereof. BACKGROUND

[0002] At present, the composite current collector based on the high polymer polymer film has been widely concerned and applied in the new energy industry. The preparation process of the composite current collector is generally as follows: a layer of metal (aluminum, copper, etc.) material is deposited on the high polymer thin film (such as polypropylene, polyethylene, polyester, etc.) by using the physical vapor deposition (PVD) method. The surface metallized thin film with certain conductive capacity prepared is the composite current collector. Compared with the traditional current collector, the composite current collector based on the high polymer polymer film has the characteristics of low cost, light weight, good internal insulation, etc. These characteristics enable the composite current collector to reduce the cost of the battery and improve the energy density and safety of the battery when the composite current collector is applied in the battery.

[0003] Among the many composite current collectors based on the high polymer polymer film, the composite current collector based on the polyester film is the most common. In the process of preparing the polyester film, in order to prevent the film surfaces from adhering to each other during the winding process, an anti-adhesion agent, silicon dioxide, is usually added. However, the silicon dioxide introduced in the polyester film will be eroded by the electrolyte and its electrochemical reaction products during the high-temperature charge-discharge cycle of the battery, thereby being dissolved out. The dissolution of silicon dioxide and the consumption of the electrolyte and its electrochemical reaction products will cause the high-temperature charge-discharge cycle performance of the battery to deteriorate.

[0004] Therefore, it is urgent to study a new current collector base film to solve the problems of the dissolution of silicon dioxide in the film and the consumption of the electrolyte and its electrochemical reaction products caused by the dissolution, which leads to the deterioration of the high-temperature cycle performance of the battery. SUMMARY

[0005] The application provides a composite current collector base film, a preparation method and application thereof. In the application, the composite current collector base film is prepared by using the first polyester material and the hydrocarbon polymer material with specific compositions in cooperation. On the one hand, the introduction of the hydrocarbon polymer material can reduce the polarity of the base film and at the same time destroy the regular arrangement of the polyester macromolecule, so as to make the surface roughness of the base film higher, thereby effectively solving the problem of the adhesion of the film surfaces during the winding process caused by the lack of silicon dioxide. On the other hand, the introduction of the hydrocarbon polymer material can reduce the crystallinity of the base film, improve the free volume and surface tension of the base film, and effectively solve the problem of the low adhesion between the metal layer and the base film in the composite current collector caused by the reduction of the polarity of the base film. Therefore, the composite current collector base film can solve the problem of the poor high-temperature cycle performance of the composite current collector based on the polyester film during the application in the battery end, and effectively promote the popularization of the composite current collector in the application end.

[0006] Further, the application provides a composite current collector base film comprising a second polymer layer and / or a third polymer layer which are sequentially stacked on the first polymer layer. Further, the application provides a composite current collector base film comprising a first polymer layer, a second polymer layer and a third polymer layer which are sequentially stacked, by introducing hydrocarbon polymer material into the first polymer layer and the third polymer layer without adding anti-adhesion silica, on the one hand, the polarity of the composite polymer film can be reduced, the surface roughness of the composite polymer film is improved, thereby solving the problem of film surface adhesion in the winding process caused by the absence of anti-adhesion; on the other hand, the problem of low adhesion between the metal layer and the composite polymer film in the prepared current collector is solved, the high temperature cycle performance of the current collector in the application process of the battery is effectively improved, and the three-layer structure composite polymer film constructed by the application has good mechanical properties.

[0007] In a first aspect, the application provides a composite current collector base film, which comprises a first polymer layer, and the first polymer layer comprises a first polyester material and a hydrocarbon polymer material, wherein the mass ratio of the first polyester material and the hydrocarbon polymer material is (20-60):(40-80).

[0008] Preferably, the raw materials for preparing the first polymer layer comprise the following components by mass fraction:

[0009] Polyester material 20-60wt%, hydrocarbon polymer material 40-80wt%.

[0010] The application prepares a composite current collector base film by synergistically cooperating the first polyester material and the hydrocarbon polymer material with a specific composition, on the one hand, the introduction of the hydrocarbon polymer material can reduce the polarity of the base film, and at the same time, destroy the regular arrangement of the polyester macromolecule, so that the surface roughness of the base film is higher, thereby effectively solving the problem of film surface adhesion in the winding process caused by the absence of silica; on the other hand, the introduction of the hydrocarbon polymer material can reduce the crystallinity of the base film, improve the free volume and surface tension of the base film, and effectively solve the problem of low adhesion between the metal layer and the base film in the composite current collector caused by the reduction of the polarity of the base film. Therefore, the composite current collector base film can solve the problem of poor high temperature cycle performance of the polyester film-based composite current collector in the application process of the battery, and effectively promote the popularization of the composite current collector in the application end.

[0011] In the first polymer layer of the application, the mass fraction of the first polyester material is 20-60wt%, for example, it can be 20wt%, 30wt%, 40wt%, 50wt% or 60wt% and the like, and the mass fraction of the hydrocarbon polymer material is 40-80wt%, for example, it can be 40wt%, 50wt%, 60wt%, 70wt% or 80wt% and the like.

[0012] In the present application, if the content of the hydrocarbon polymer material is too low, the prepared base film will be seriously sticky during the winding process and will be easily sticky during the unwinding use; and if the content of the hydrocarbon polymer material is too high, the surface tension of the prepared base film will decrease too much, which will lead to the poor adhesion between the metal layer and the base film in the prepared composite current collector, and further cause the poor charge-discharge cycle performance of the battery.

[0013] As a preferred embodiment of the present application, the mass ratio of the first polyester material and the hydrocarbon polymer material is (30-50):(50-70), wherein the selection range "30-50" of the first polyester material can be 30, 35, 40, 45 or 50, etc., and the selection range "50-70" of the polyolefin material can be 50, 55, 60, 65 or 70, etc.

[0014] In the present application, the mass ratio of the first polyester material and the hydrocarbon polymer material is (30-50):(50-70), which can better realize the synergistic effect of the polyester material and the hydrocarbon polymer material. If the mass ratio is too high, the prepared base film will be seriously sticky during the winding process and will be easily sticky during the unwinding use; and if the mass ratio is too low, the adhesion between the metal layer and the base film in the prepared composite current collector will be poor, which will further cause the poor charge-discharge cycle performance of the battery.

[0015] Preferably, the first polyester material comprises any one or a combination of at least two of polyethylene terephthalate, polyethylene 2,6-naphthalate, polybutylene terephthalate, poly-1,4-cyclohexane dimethanol terephthalate, polyethylene terephthalate-1,4-cyclohexane dimethanol terephthalate, polypropylene 2,6-naphthalate, polypropylene terephthalate, polybutylene 2,6-naphthalate, polybutylene 2,5-furandicarboxylate or polybutylene adipate terephthalate.

[0016] Preferably, the viscosity average molecular weight of the first polyester material is 15000-50000 Da, for example, it can be 15000 Da, 20000 Da, 25000 Da, 30000 Da, 35000 Da, 40000 Da, 45000 Da or 50000 Da, etc., preferably 18000-40000 Da.

[0017] In the present application, too low or too high viscosity average molecular weight of the polyester material will lead to poor film forming property.

[0018] Preferably, the hydrocarbon polymer material is a polyolefin material, including but not limited to a polyolefin homopolymer, a polyolefin copolymer, or a mixture thereof. The polyolefin material also includes but is not limited to polyethylene, polypropylene, polybutadiene, polyisoprene, polycyclopentadiene, polystyrene, and copolymers and mixtures of any combination of the above. Preferably, the polyolefin material includes an alkene-based polymer (homopolymer or copolymer) and / or a cycloalkene-based polymer (homopolymer or copolymer), preferably a mixture of alkene-based polymer and cycloalkene-based polymer.

[0019] Preferably, the alkene-based polymer includes any one of polyethylene, polypropylene, ethylene-propylene copolymer, or propylene-butylene copolymer, or ethylene-propylene-butylene copolymer, or a combination of at least two of them.

[0020] Preferably, the cycloalkene-based polymer includes polydicyclo[2.2.1]hepta-2-ene, polycyclopentene, polycyclopentadiene, polycyclohexene, dicyclo[2.2.1]hepta-2-ene-ethylene copolymer, or dicyclo[2.2.1]hepta-2-ene-propylene copolymer.

[0021] Preferably, the number average molecular weight of the hydrocarbon polymer material is 10,000-100,000 Da, for example, it can be 10,000 Da, 20,000 Da, 40,000 Da, 60,000 Da, 80,000 Da, or 100,000 Da, etc., preferably 15,000-80,000 Da.

[0022] In this application, too low or too high number average molecular weight of the hydrocarbon polymer material will result in poor film-forming properties and defects.

[0023] As a preferred embodiment of the present application, the thickness of the composite current collector base film is ≥1 μm, for example, it can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or 30 μm, etc., preferably 2-20 μm.

[0024] In this application, considering that the thinner the composite current collector base film, the more it can promote the improvement of the energy density of the composite current collector, while considering the production difficulty (the thinner the film, the greater the production difficulty, the lower the yield), it is preferred that the thickness of the composite current collector base film is 2-20 μm.

[0025] In a second aspect, the present application provides a composite current collector base film, wherein the composite current collector base film comprises a first polymer layer, a second polymer layer, and / or a third polymer layer stacked in sequence, the first polymer layer comprises a first polyester material and a hydrocarbon polymer material, the second polymer layer comprises a second polyester material, and the third polymer layer comprises a first polyester material and a hydrocarbon polymer material.

[0026] In the present application, the first polymer layer and the third polymer layer are composed of the same or different components.

[0027] In the present application, the first polymer layer and the third polymer layer comprise a first polyester material and a hydrocarbon polymer material.

[0028] In the present application, the first polymer layer and / or the third polymer layer are composed of a first polyester material and a hydrocarbon polymer material.

[0029] In the present application, the first polymer layer and / or the third polymer layer comprise a first polyester material and a hydrocarbon polymer material and any other suitable components.

[0030] In the present application, the second polymer layer comprises a second polyester material.

[0031] In the present application, the second polymer layer does not comprise inorganic particles.

[0032] Preferably, the second polymer layer does not comprise silicon dioxide.

[0033] In the present application, the second polymer layer is composed of a second polyester material.

[0034] In the present application, the second polymer layer comprises a second polyester material and any other suitable components.

[0035] In the present application, in the first polymer layer, the mass ratio of the first polyester material to the hydrocarbon polymer material is (20-60):(40-80).

[0036] In the present application, in the third polymer layer, the mass ratio of the first polyester material to the hydrocarbon polymer material is (20-60):(40-80).

[0037] In the present application, in the second polymer layer, the content of the second polyester material is greater than or equal to 95wt%, preferably greater than or equal to 98wt%, further preferably greater than or equal to 99wt%, and most preferably 100wt%.

[0038] In the present application, the introduction of the hydrocarbon polymer material in the first polymer layer and the third polymer layer and the absence of the anti-adhesion agent silicon dioxide can reduce the polarity of the film on the one hand, and on the other hand, due to the introduction of the hydrocarbon polymer (such as polyolefin), the regular arrangement of the polyester macromolecule is destroyed, thereby forming a higher roughness on the surface of the film and reducing the crystallinity of the film to improve the free volume of the film. Therefore, the introduction of the hydrocarbon polymer material not only can solve the problem of film surface adhesion in the winding process caused by the absence of the anti-adhesion agent, but also can solve the problem of low adhesion between the metal layer in the current collector and the composite polymer film caused by the reduction of the polarity of the film, thereby improving the high-temperature cycle performance of the current collector in the application process of the battery. In addition, the composite polymer film with a three-layer structure constructed in the present application has good mechanical properties.

[0039] In the first polymer layer of the present application, the mass ratio of the first polyester material and the hydrocarbon polymer material is (20-60):(40-80), wherein the selected range "20-60" of the first polyester material may be, for example, 20, 25, 30, 35, 40, 45, 50, 55, 58, or 60, etc., and the selected range "40-80" of the hydrocarbon polymer material may be, for example, 40, 45, 50, 55, 60, 65, 70, 75, or 80, etc.

[0040] In the present application, if the mass ratio of the first polyester material and the hydrocarbon polymer material is too large, i.e., the content of the hydrocarbon polymer material is too low, the prepared composite polymer film will have a serious film sticking problem during the winding process, and will be prone to film sticking when unwound for use. If the mass ratio of the first polyester material and the hydrocarbon polymer material is too small, i.e., the content of the hydrocarbon polymer material is too high, the surface tension of the prepared composite polymer film will decrease too much, resulting in poor adhesion between the metal layer and the composite polymer film in the subsequently prepared current collector, and further causing poor charge-discharge cycle performance of the battery.

[0041] In the third polymer layer of the present application, the mass ratio of the first polyester material and the hydrocarbon polymer material is (20-60):(40-80), wherein the selected range "20-60" of the first polyester material may be, for example, 20, 25, 30, 35, 40, 45, 50, 55, 58, or 60, etc., and the selected range "40-80" of the hydrocarbon polymer material may be, for example, 40, 45, 50, 55, 60, 65, 70, 75, or 80, etc.

[0042] In the present application, if the mass ratio of the first polyester material and the hydrocarbon polymer material is too large, i.e., the content of the hydrocarbon polymer material is too low, the prepared composite polymer film will have a serious film sticking problem during the winding process, and will be prone to film sticking when unwound for use. If the mass ratio of the first polyester material and the hydrocarbon polymer material is too small, i.e., the content of the hydrocarbon polymer material is too high, the surface tension of the prepared composite polymer film will decrease too much, resulting in poor adhesion between the metal layer and the composite polymer film in the subsequently prepared current collector, and further causing poor charge-discharge cycle performance of the battery.

[0043] As a preferred embodiment of the present application, the first polyester material and the second polyester material independently comprise any one or a combination of at least two of polyethylene terephthalate, polyethylene 2,6-naphthalate, polybutylene terephthalate, poly-1,4-cyclohexane dimethanol terephthalate, polyethylene terephthalate-1,4-cyclohexane dimethanol, polypropylene 2,6-naphthalate, polypropylene terephthalate, polybutylene 2,6-naphthalate, polybutylene 2,5-furandicarboxylate, or polybutylene adipate terephthalate.

[0044] In the present application, the first polyester material and the second polyester material can be the same or different.

[0045] Preferably, the viscosity average molecular weight of the first polyester material and the second polyester material is independently 15000-50000 Da, for example, can be 15000 Da, 20000 Da, 25000 Da, 30000 Da, 35000 Da, 40000 Da, 45000 Da or 50000 Da, etc.

[0046] In the present application, the viscosity average molecular weight of the first polyester material and the second polyester material can be the same or different.

[0047] In the present application, the viscosity average molecular weight of the polyester material is too low or too high, which will result in poor film-forming property.

[0048] Preferably, the hydrocarbon polymer material is a polyolefin material, a polydiene material (such as polybutadiene, polyisoprene, polycyclopentadiene), or a styrene-based polymer (polystyrene and its copolymer, styrene-butadiene block copolymer). Preferably, the hydrocarbon polymer material is a polyolefin material. Preferably, the polyolefin material includes an alkene-based polymer and / or a cycloalkene-based polymer, preferably an alkene-based copolymer and / or a cycloalkene-based copolymer, more preferably a mixture of an alkene-based copolymer and a cycloalkene-based copolymer.

[0049] Preferably, the hydrocarbon polymer material includes any one or a combination of at least two of polyethylene, polypropylene, polystyrene, ethylene-propylene copolymer, ethylene-propylene-butene copolymer or cycloalkene-based copolymer, preferably any one or a combination of at least two of random polypropylene, ethylene-propylene copolymer, ethylene-propylene-butene copolymer or cycloalkene-based copolymer.

[0050] Preferably, the number average molecular weight of the hydrocarbon polymer material is 10000-100000 Da, for example, can be 10000 Da, 20000 Da, 40000 Da, 60000 Da, 80000 Da or 100000 Da, etc.

[0051] In the present application, the number average molecular weight of the hydrocarbon polymer material is too low or too high, which will result in poor film-forming property.

[0052] As a preferred embodiment of the present application, the thicknesses of the first polymer layer, the second polymer layer and the third polymer layer are denoted as h1, h2 and h3 respectively, h1 = h3, h1 : h2 = (1-15) : (70-98), wherein the selected range of "1-15" of h1 may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15, etc., and the selected range of "70-98" of h2 may be 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96 or 98, etc.

[0053] It should be noted that the introduction of the hydrocarbon polymer during the preparation of the polymer film will cause the orientation degree and the crystallinity of the polyester macromolecule to decrease during the stretching process, thereby causing the mechanical properties to deteriorate. In order to solve this problem, the present application designs a three-layer composite polymer film, the thickness of the second polymer layer in the three layers dominates, and the second polymer layer only contains the second polyester material, so that a higher orientation degree and crystallinity can be obtained during the stretching process, and the prepared composite polymer film has good mechanical properties. If the ratio of h1 and h2 is too small, i.e. the thickness of the first polymer layer or the third polymer layer is too thin, the production difficulty is large, and it is not easy to control the uniformity of the thickness, the anti-bonding property is poor, which causes the film to be easy to stick and prone to breakage; if the ratio of h1 and h2 is too large, i.e. the thickness of the first polymer layer or the third polymer layer is too thick, the mechanical properties of the prepared composite polymer film deteriorate.

[0054] Preferably, the thickness of the composite polymer film is ≥1 μm, which may be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm, etc., and is preferably 2-20 μm.

[0055] In the present application, considering that the thinner the composite polymer film is, the more it can promote the improvement of the energy density of the composite current collector, while also considering the production difficulty (the thinner the film is, the greater the production difficulty is, and the lower the yield is), it is preferred that the thickness of the composite polymer film is 2-20 μm.

[0056] In a third aspect, the present application provides a preparation method of the composite current collector base film as described in the first aspect, and the preparation method comprises the following steps:

[0057] (1) The first polyester material and the hydrocarbon polymer material are pretreated respectively, and then mixed to obtain a mixed material;

[0058] (2) The mixed material is sequentially subjected to melt extrusion, chip forming, stretching treatment and heat treatment, and is wound to obtain the composite current collector base film.

[0059] The preparation method provided by the present application is simple and easy to implement, and is easy to scale up.

[0060] As a preferred embodiment of the present application, the step of pre-treating the first polyester material in step (1) comprises sequentially subjecting the first polyester material to a first crystallization treatment and a first drying treatment.

[0061] Preferably, the first crystallization treatment has a crystallization temperature of 130-200°C, such as 130°C, 150°C, 170°C, or 190°C, and a crystallization time of 20-130 minutes, such as 20 minutes, 40 minutes, 60 minutes, 80 minutes, 100 minutes, or 120 minutes.

[0062] In the present application, the crystallization temperature is 130-200°C and the crystallization time is 20-130 minutes, which can increase the crystallinity of the polymer and prevent sticking during drying.

[0063] Preferably, the first drying treatment has a drying temperature of 130-180°C, such as 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C, and a drying time of 110-300 minutes, such as 110 minutes, 150 minutes, 200 minutes, 250 minutes, or 300 minutes.

[0064] In the present application, the drying temperature is 130-180°C and the drying time is 110-300 minutes, which can effectively remove the moisture in the polyester raw material and prevent the polymer from being oxidized during melt extrusion.

[0065] Preferably, the step of pre-treating the hydrocarbon polymer material in step (1) comprises sequentially subjecting the hydrocarbon polymer material to a second crystallization treatment and a second drying treatment.

[0066] Preferably, the second crystallization treatment has a crystallization temperature of 60-100°C, such as 60°C, 70°C, 80°C, 90°C, or 100°C, and a crystallization time of 20-120 minutes, such as 20 minutes, 40 minutes, 60 minutes, 80 minutes, 100 minutes, or 120 minutes.

[0067] In the present application, the crystallization temperature is 60-100°C and the crystallization time is 20-120 minutes, which can increase the crystallinity of the polymer and prevent sticking during drying.

[0068] Preferably, the second drying treatment has a drying temperature of 60-80°C, such as 60°C, 65°C, 70°C, 75°C, or 80°C, and a drying time of 100-300 minutes, such as 100 minutes, 150 minutes, 200 minutes, 250 minutes, or 300 minutes.

[0069] In the present application, the temperature for drying is 60-80℃, and the time is 100-300min, which can effectively remove the moisture in the hydrocarbon polymer material and prevent the polymer from being oxidized during melt extrusion.

[0070] As a preferred embodiment of the present application, the temperature for heating and melting during the melt extrusion of step (2) is 270-300℃, for example, it can be 270℃, 280℃, 290℃ or 300℃, etc.

[0071] Preferably, the stretching treatment of step (2) includes longitudinal stretching and transverse stretching.

[0072] Preferably, the step of longitudinal stretching includes:

[0073] The formed cast sheet is preheated, then subjected to longitudinal stretching, and after the stretching is completed, it is cooled;

[0074] Preferably, the preheating temperature is 60-80℃, for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃, etc.

[0075] Preferably, the cooling temperature is 30-50℃, for example, it can be 30℃, 40℃ or 50℃, etc.

[0076] Preferably, the step of transverse stretching includes:

[0077] The longitudinally stretched film sheet is preheated, then subjected to transverse stretching, and after the stretching is completed, it is cooled;

[0078] Preferably, during the transverse stretching, the preheating temperature is 60-80℃, for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃, etc., and the cooling temperature is 40-70℃, for example, it can be 40℃, 50℃, 60℃ or 70℃, etc.

[0079] Preferably, the stretching ratio of the longitudinal stretching is (3-6):1, for example, it can be 3:1, 4:1, 5:1 or 6:1, etc., the stretching temperature of the longitudinal stretching is 80-110℃, for example, it can be 80℃, 90℃, 100℃ or 110℃, etc., the stretching ratio of the transverse stretching is (2-4):1, for example, it can be 2:1, 3:1 or 4:1, etc., and the stretching temperature of the transverse stretching is 80-110℃, for example, it can be 80℃, 90℃, 100℃ or 110℃, etc.

[0080] Preferably, the temperature for heat treatment of step (2) is 70-100℃, for example, it can be 70℃, 80℃, 90℃ or 100℃, etc.

[0081] As a preferred embodiment of the present application, the preparation method includes the following steps:

[0082] (1) conveying the first polyester material into a crystallizer, treating at 130-200°C for 20-130 min, and then conveying into a drying tower, drying treatment at 130-180°C for 110-300 min, to obtain a pretreated polyester material;

[0083] conveying the hydrocarbon polymer material into a crystallizer, treating at 60-100°C for 20-120 min, and then conveying into a drying tower, drying treatment at 60-80°C for 100-300 min, to obtain a pretreated hydrocarbon polymer material;

[0084] Preferably, the hydrocarbon polymer material is a mixture of an olefin-based polymer and a cyclic olefin-based polymer.

[0085] (2) mixing the pretreated first polyester material and the pretreated hydrocarbon polymer material to obtain a mixture, and then conveying the mixture into a twin-screw extruder, melting treatment at 270-300°C, filtering, and then extruding through a die to obtain a molten material;

[0086] (3) casting the molten material onto a casting roll, and then cooling treatment by the casting roll and water cooling to form a shaped casting, the cooling temperature being 20-60°C (for example, 20°C, 30°C, 40°C, 50°C, or 60°C, etc.), to obtain a shaped casting;

[0087] (4) preheating the shaped casting at 60-80°C, and then performing longitudinal stretching, the stretching ratio being (3-6):1, the stretching temperature being 80-110°C, and after the stretching, cooling treatment at 30-50°C;

[0088] preheating the cooled film at 60-80°C, and then performing transverse stretching, the stretching ratio being (2-4):1, the stretching temperature being 80-110°C, and after the stretching, cooling treatment at 40-70°C, to obtain a stretched film;

[0089] (5) performing heat treatment on the stretched film at a temperature of 70-100°C, and then cooling by air, and then winding the film by a winding system through a traction system, to obtain the composite current collector base film.

[0090] In a fourth aspect, the application provides a preparation method of the composite polymer film according to the first aspect, the preparation method comprising the following steps:

[0091] adding the preparation raw materials of the first polymer layer, the second polymer layer, and the third polymer layer into corresponding extrusion equipment respectively, melt co-extruding, and then sequentially performing casting, stretching treatment, and heat treatment, and winding to obtain the composite polymer film.

[0092] The preparation method provided by the application is simple and easy to implement, easy to scale up, and can effectively promote the popularization of the current collector at the application end.

[0093] It should be noted that the preparation raw materials of the first polymer layer, the second polymer layer and the third polymer layer are melted respectively and then extruded by one die.

[0094] As a preferred embodiment of the application, the preparation raw material of the first polymer layer is pretreated before being added to the corresponding extrusion equipment, and the specific steps include:

[0095] The first polyester material is crystallized and dried, and the hydrocarbon polymer material is crystallized and dried, and then the dried first polyester material and hydrocarbon polymer material are mixed.

[0096] Preferably, in the pretreatment process of the first polymer layer, the first polyester material is crystallized at a temperature of 130-200℃, for example, 130℃, 150℃, 170℃ or 190℃, etc., and the crystallization time is 20-130min, for example, 20min, 40min, 60min, 80min, 100min or 120min, etc.

[0097] In the application, the first polyester material is crystallized at 130-200℃ for 20-130min, which can improve the crystallinity of the polymer and prevent sticking during drying.

[0098] Preferably, in the pretreatment process of the first polymer layer, the first polyester material is dried at a temperature of 130-180℃, for example, 130℃, 140℃, 150℃, 160℃, 170℃ or 180℃, etc., and the drying time is 110-300min, for example, 110min, 150min, 200min, 250min or 300min, etc.

[0099] In the application, the first polyester material is dried at 130-180℃ for 110-130min, which can effectively remove the moisture in the first polyester material and prevent the polymer from being oxidized during melt extrusion.

[0100] Preferably, in the pretreatment process of the first polymer layer, the hydrocarbon polymer material is crystallized at a temperature of 60-100℃, for example, 60℃, 70℃, 80℃, 90℃ or 100℃, etc., and the crystallization time is 20-120min, for example, 20min, 40min, 60min, 80min, 100min or 120min, etc.

[0101] In the present application, the crystallization of the hydrocarbon polymer material at 60-80°C for 100-300 min can effectively remove the moisture in the hydrocarbon polymer material, preventing the polymer from being oxidized during melt extrusion.

[0102] Preferably, in the pretreatment process of the first polymer layer, the drying temperature of the hydrocarbon polymer material is 60-80°C, for example, it can be 60°C, 65°C, 70°C, 75°C or 80°C, etc., and the drying time is 100-300 min, for example, it can be 100 min, 150 min, 200 min, 250 min or 300 min, etc.

[0103] In the present application, the drying at 60-80°C for 100-300 min can effectively remove the moisture in the hydrocarbon polymer material, preventing the polymer from being oxidized during melt extrusion.

[0104] Preferably, before the raw materials for preparing the second polymer layer are added to the corresponding extrusion equipment, the raw materials for preparing the second polymer layer are pretreated, and the specific steps include:

[0105] The second polyester material is crystallized and dried.

[0106] Preferably, in the pretreatment process of the second polymer layer, the crystallization temperature of the second polyester material is 130-200°C, for example, it can be 130°C, 150°C, 170°C or 190°C, etc., and the crystallization time is 20-130 min, for example, it can be 20 min, 40 min, 60 min, 80 min, 100 min or 120 min, etc.

[0107] In the present application, the crystallization of the second polyester material at 130-200°C for 20-130 min can improve the crystallinity of the polymer and prevent sticking during drying.

[0108] Preferably, in the pretreatment process of the second polymer layer, the drying temperature of the second polyester material is 130-180°C, for example, it can be 130°C, 140°C, 150°C, 160°C, 170°C or 180°C, etc., and the drying time is 110-300 min, for example, it can be 110 min, 150 min, 200 min, 250 min or 300 min, etc.

[0109] In the present application, the drying at 130-180°C for 110-130 min can effectively remove the moisture in the second polyester material, preventing the polymer from being oxidized during melt extrusion.

[0110] Preferably, before the raw materials for preparing the third polymer layer are added to the corresponding extrusion equipment, the raw materials for preparing the third polymer layer are pretreated, and the specific steps include:

[0111] The first polyester material is crystallized and dried, and the hydrocarbon polymer material is crystallized and dried, and then the dried first polyester material and the dried hydrocarbon polymer material are mixed.

[0112] Preferably, during the pretreatment of the first polymer layer, the hydrocarbon polymer material is crystallized at a temperature of 60-100℃, such as 60℃, 70℃, 80℃, 90℃ or 100℃, and the crystallization time is 20-120min, such as 20min, 40min, 60min, 80min, 100min or 120min.

[0113] In this application, the crystallization of the hydrocarbon polymer material at 60-100℃ for 20-120min can improve the crystallinity of the polymer and prevent sticking during drying.

[0114] Preferably, during the pretreatment of the first polymer layer, the hydrocarbon polymer material is dried at a temperature of 60-80℃, such as 60℃, 65℃, 70℃, 75℃ or 80℃, and the drying time is 100-300min, such as 100min, 150min, 200min, 250min or 300min.

[0115] In this application, drying at 60-80℃ for 100-300min can effectively remove moisture from the hydrocarbon polymer material and prevent the polymer from being oxidized during melt extrusion.

[0116] Preferably, during the melt co-extrusion process, the temperature of the heated melt is 270-290℃, such as 270℃, 280℃ or 290℃.

[0117] Preferably, during the melt co-extrusion process, the volume ratio of the extrusion amount of the raw materials for preparing the first polymer layer, the second polymer layer and the third polymer layer is (1-15):(70-98):(1-15), wherein the selection range of the extrusion amount of the first polymer layer "1-15" can be 1, 3, 5, 7, 9, 11, 13 or 15, the selection range of the extrusion amount of the second polymer layer "70-98" can be 70, 75, 80, 85, 90, 95 or 98, and the selection range of the extrusion amount of the third polymer layer "1-15" can be 1, 3, 5, 7, 9, 11, 13 or 15.

[0118] Preferably, the stretching treatment includes longitudinal stretching and transverse stretching.

[0119] Preferably, the longitudinal stretching step includes:

[0120] Preheating, then longitudinal stretching, and cooling after the end of the stretching.

[0121] Preferably, the preheating temperature is 60-80℃, for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃, etc.

[0122] Preferably, the cooling temperature is 30-50℃, for example, it can be 30℃, 40℃ or 50℃, etc.

[0123] Preferably, the longitudinal stretching ratio is (3-6):1, for example, it can be 3:1, 4:1, 5:1 or 6:1, etc., the longitudinal stretching temperature is 80-110℃, for example, it can be 80℃, 90℃, 100℃ or 110℃, etc., the transverse stretching ratio is (2-4):1, for example, it can be 2:1, 3:1 or 4:1, etc., the transverse stretching temperature is 80-110℃, for example, it can be 80℃, 90℃, 100℃ or 110℃, etc.

[0124] Preferably, in the process of transverse stretching, the preheating temperature is 60-80℃, for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃, etc., and the cooling temperature is 40-70℃, for example, it can be 40℃, 50℃, 60℃ or 70℃, etc.

[0125] Preferably, the heat treatment temperature is 70-100℃, for example, it can be 70℃, 80℃, 90℃ or 100℃, etc.

[0126] As a preferred embodiment of the present application, the preparation method comprises the following steps:

[0127] (1) Pre-treating the raw material for preparing the first polymer layer, the specific steps comprising: crystallizing the first polyester material at 130-200℃ for 20-130min, then drying at 130-180℃ for 110-300min, crystallizing the hydrocarbon polymer material at 60-100℃ for 20-120min, then drying at 60-80℃ for 100-300min, then mixing the dried first polyester material and hydrocarbon polymer material to obtain the first material;

[0128] Pre-treating the raw material for preparing the second polymer layer, the specific steps comprising: crystallizing the second polyester material at 130-200℃ for 20-130min, then drying at 130-180℃ for 110-300min to obtain the second material;

[0129] The raw material for preparing the third polymer layer is pretreated, and the specific steps include: crystallizing the first polyester material at 130-200℃ for 20-130min, and then drying at 130-180℃ for 110-300min; crystallizing the hydrocarbon polymer material at 60-100℃ for 20-120min, and then drying at 60-80℃ for 100-300min; and then mixing the dried first polyester material and hydrocarbon polymer material to obtain the third material;

[0130] (2) The first material, the second material and the third material are respectively transported into corresponding double-screw extruders, heated and melted at 270-290℃, filtered and then co-extruded through a die to obtain a molten material;

[0131] The volume ratio of the extrusion amounts of the first material, the second material and the third material is (1-15):(70-98):(1-15);

[0132] (3) The molten material is cast onto a casting roller, and then cooled at 20-60℃ (for example, 20℃, 30℃, 40℃, 50℃ or 60℃, etc.) to obtain a shaped casting sheet;

[0133] (4) The shaped casting sheet is preheated at 60-80℃, and then stretched in the longitudinal direction with a stretching ratio of (3-6):1 and a stretching temperature of 80-110℃, and then cooled at 30-50℃ after the stretching;

[0134] The cooled film sheet is preheated at 60-80℃, and then stretched in the transverse direction with a stretching ratio of (2-4):1 and a stretching temperature of 80-110℃, and then cooled at 40-70℃ after the stretching;

[0135] (5) The film sheet after step (4) is treated is heat-treated at a temperature of 70-100℃, and then cooled by air, enters a winding system through a traction system to wind the film sheet, and thus the composite polymer film is obtained.

[0136] In a fifth aspect, the application provides a composite current collector, which comprises the composite current collector base film according to the first aspect or the second aspect or the composite current collector base film prepared by the preparation method according to the third aspect or the fourth aspect, and a metal layer arranged on at least one side surface of the composite current collector base film.

[0137] In the application, the metal layer serves as an electric conductor.

[0138] As a preferred embodiment of the application, the material of the metal layer comprises a metal element and / or a metal alloy.

[0139] As a preferred embodiment of the present application, the metal element includes any one or a combination of at least two of elemental copper, elemental aluminum, elemental nickel, elemental titanium, or elemental silver.

[0140] Preferably, the metal alloy includes any one or a combination of at least two of a copper alloy, an aluminum alloy, or a nickel alloy.

[0141] Preferably, the thickness of the metal layer is 500-2000 nm, for example, 500 nm, 1000 nm, 1500 nm, or 2000 nm, etc., preferably 700-1200 nm.

[0142] Preferably, the preparation method of the metal layer includes any one or a combination of at least two of physical vapor deposition, electroplating, or chemical plating.

[0143] Preferably, the physical vapor deposition includes any one or a combination of at least two of resistance heating vacuum evaporation, electron beam heating vacuum evaporation, laser heating vacuum evaporation, or magnetron sputtering.

[0144] Preferably, the metal layer is provided with a protective layer on the side surface away from the composite current collector base film.

[0145] It should be noted that when the composite current collector base film is provided with a protective layer on both side surfaces, the materials of the two side protective layers can be consistent or inconsistent, and the thicknesses can be consistent or inconsistent.

[0146] In the present application, the protective layer is provided to prevent the metal conductive layer from being chemically corroded or physically damaged.

[0147] Preferably, the material of the protective layer includes any one or a combination of at least two of elemental nickel, elemental chromium, a nickel-based alloy, a copper-based alloy, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper chromate, copper chromite, chromium chromate, graphite, carbon black, acetylene black, ketjen black, carbon nanometer quantum dots, carbon nanotubes, carbon nanofibers, or graphene.

[0148] Preferably, the thickness of the protective layer is 5-100 nm, for example, 5 nm, 10 nm, 50 nm, or 100 nm, etc.

[0149] Preferably, the thickness of the protective layer is ≤1 / 10 of the thickness of the metal layer.

[0150] Preferably, the preparation method of the protective layer includes any one or a combination of at least two of physical vapor deposition, chemical vapor deposition, in-situ forming, or coating.

[0151] Preferably, the physical vapor deposition includes vacuum evaporation and / or magnetron sputtering.

[0152] Preferably, the chemical vapor deposition method comprises atmospheric pressure chemical vapor deposition and / or plasma enhanced chemical vapor deposition.

[0153] Preferably, the coating method comprises any one of die coating, blade coating or extrusion coating.

[0154] In a sixth aspect, the present application provides a lithium ion battery, wherein the electrode tab of the lithium ion battery comprises the composite current collector according to the fifth aspect, or comprises a composite current collector made of the composite current collector base film according to the first or second aspect.

[0155] The numerical ranges recited herein are inclusive of the endpoints and also include any ranges that would be formed by limiting the upper or lower end of the range. For the sake of brevity, the precise numerical values of the upper and lower limits of the ranges are not listed herein.

[0156] Compared with the prior art, the present application has the following beneficial effects:

[0157] (1) The present application prepares a composite current collector base film by synergistically using a polyester material and a hydrocarbon polymer material with a specific composition. On the one hand, the introduction of the hydrocarbon polymer material can reduce the polarity of the base film, and at the same time, destroy the regular arrangement of the polyester macromolecule, so as to make the surface roughness of the base film higher, and effectively solve the problem of film surface adhesion in the winding process caused by the absence of silica. On the other hand, the introduction of the hydrocarbon polymer material can reduce the crystallinity of the base film, and improve the free volume and surface tension of the base film, effectively solving the problem of low adhesion between the metal layer and the base film in the composite current collector caused by the reduction of the polarity of the base film. Therefore, the composite current collector base film can solve the problem of poor high-temperature cycle performance of the polyester film-based composite current collector in the application end of the battery, and effectively promote the popularization of the composite current collector in the application end.

[0158] (2) The introduction of the hydrocarbon polymer material in the first polymer layer and the third polymer layer without adding the anti-adhesion agent silica can reduce the polarity of the film, and on the other hand, due to the introduction of the polyolefin, the regular arrangement of the polyester macromolecule is destroyed, so as to form higher roughness on the film surface, and reduce the crystallinity of the film and improve the free volume of the film. Therefore, the introduction of the hydrocarbon polymer material can not only solve the problem of film surface adhesion in the winding process caused by the absence of the anti-adhesion agent, but also solve the problem of low adhesion between the metal layer and the composite polymer film in the current collector caused by the reduction of the polarity of the film, thereby improving the high-temperature cycle performance of the current collector in the application end of the battery. In addition, the composite polymer film with a three-layer structure constructed by the present application has good mechanical properties.

[0159] (3) The preparation method provided by the present application is simple and easy to scale up. DETAILED DESCRIPTION

[0160] The technical solutions of the present application are further illustrated below by specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0161] Embodiment 1

[0162] The present embodiment provides a composite current collector base film, and raw materials for preparing the composite current collector base film include the following components by mass fraction:

[0163] 50 wt% of polyethylene terephthalate and 50 wt% of polypropylene, and the mass ratio of the two is 50:50;

[0164] The viscosity average molecular weight of the polyethylene terephthalate is 30,000 Da, and the number average molecular weight of the polypropylene is 60,000 Da;

[0165] The thickness of the composite current collector base film is 4.5 μm.

[0166] The present embodiment also provides a preparation method of the above-mentioned composite current collector base film, and the preparation method includes the following steps:

[0167] (1) polyethylene terephthalate is transported into a crystallizer, treated at 150°C for 60 min, then transported into a drying tower, and dried at 160°C for 160 min to obtain pretreated polyethylene terephthalate;

[0168] Polypropylene is transported into a crystallizer, treated at 80°C for 100 min, then transported into a drying tower, and dried at 70°C for 100 min to obtain pretreated polypropylene;

[0169] (2) the pretreated polyethylene terephthalate and the pretreated polypropylene are mixed to obtain a mixture, and then the mixture is transported into a twin-screw extruder, subjected to melt treatment at 280°C, filtered by a metering pump, and extruded through a die to obtain a melt;

[0170] (3) the melt is cast onto a casting roll, and subjected to cooling treatment by the casting roll and water cooling to form a shaped casting, and the cooling temperature is 30°C;

[0171] (4) the shaped casting is preheated at 70°C, then subjected to longitudinal stretching, the stretching ratio is 3:1, the stretching temperature is 110°C, and after the stretching, the film is subjected to cooling treatment at 40°C;

[0172] The film after the cooling treatment is preheated at 80°C, then subjected to transverse stretching, the stretching ratio is 3:1, the stretching temperature is 110°C, and after the stretching, the film is subjected to cooling treatment at 40°C to obtain a stretched film;

[0173] (5) The stretched film is heat treated in an oven at a temperature of 80°C, followed by air cooling, and then wound into a roll by a winding system to obtain a composite current collector base film.

[0174] The embodiment also provides a composite current collector, comprising the composite current collector base film as described above, and a copper layer arranged on both sides of the composite current collector base film, the thickness of the copper layer on one side being 1000 nm;

[0175] The copper layer is provided with a protective layer on the side away from the composite current collector base film, the material of the protective layer being a mixture of copper chromate, copper chromite and chromium chromate, the thickness of the protective layer on one side being 10 nm.

[0176] The embodiment also provides a preparation method of the composite current collector, comprising the following steps:

[0177] (a) The composite current collector base film is placed in a vacuum evaporation cabin, and a high-purity copper wire (purity greater than 99.99%) in an evaporation chamber is melted and evaporated at a high temperature of 1600°C, and the metal atoms after evaporation are deposited on both surfaces of the composite current collector base film through a cooling system in the vacuum evaporation chamber to form a copper layer;

[0178] (b) The composite current collector base film with the copper layer prepared above is placed in a dip coating liquid, the dip coating liquid is a potassium dichromate aqueous solution with a concentration of 0.5 g / L, the dip coating time is 30 s, after the dip coating is completed, the liquid is removed by extrusion, and then the composite current collector is obtained by drying in a 60°C oven.

[0179] Embodiment 2

[0180] The difference between the embodiment and embodiment 1 is that the polypropylene is replaced by polyethylene.

[0181] The rest of the preparation method and parameters remain the same as those in embodiment 1.

[0182] Embodiment 3

[0183] The difference between the embodiment and embodiment 1 is that the polypropylene is replaced by an ethylene-propylene copolymer.

[0184] The rest of the preparation method and parameters remain the same as those in embodiment 1.

[0185] Embodiment 4

[0186] The difference between the embodiment and embodiment 1 is that the polypropylene is replaced by a mixture of polypropylene and a polymer of dicyclo[2,2,1]hept-2-ene and ethylene (CAS: 26007-43-2) in a mass ratio of 1:1.

[0187] The rest of the preparation method and parameters are consistent with Example 1.

[0188] Example 5

[0189] The difference between this example and Example 1 is that polyethylene terephthalate is replaced by polybutylene terephthalate.

[0190] The rest of the preparation method and parameters are consistent with Example 1.

[0191] Example 6

[0192] The difference between this example and Example 1 is that polyethylene terephthalate is replaced by polyethylene 2,6-naphthalate.

[0193] The rest of the preparation method and parameters are consistent with Example 1.

[0194] Example 7

[0195] The difference between this example and Example 1 is that the mass fraction of polypropylene is 40wt%, and the mass fraction of polyethylene terephthalate is adjusted to 60wt%.

[0196] The rest of the preparation method and parameters are consistent with Example 1.

[0197] Example 8

[0198] The difference between this example and Example 1 is that the mass fraction of polypropylene is 80wt%, and the mass fraction of polyethylene terephthalate is adjusted to 20wt%.

[0199] The rest of the preparation method and parameters are consistent with Example 1.

[0200] Example 9

[0201] The difference between this example and Example 1 is that the viscosity average molecular weight of polyethylene terephthalate is 15000Da.

[0202] The rest of the preparation method and parameters are consistent with Example 1.

[0203] Example 10

[0204] The difference between this example and Example 1 is that the viscosity average molecular weight of polyethylene terephthalate is 50000Da.

[0205] The rest of the preparation method and parameters are consistent with Example 1.

[0206] Example 11

[0207] The difference between this example and Example 1 is that the number average molecular weight of polypropylene is 10000Da.

[0208] The remaining preparation method and parameters are consistent with Example 1.

[0209] Example 12

[0210] The difference between this example and Example 1 is that the number average molecular weight of the polypropylene is 100000 Da.

[0211] The remaining preparation method and parameters are consistent with Example 1.

[0212] Example 13

[0213] The difference between this example and Example 1 is that the viscosity average molecular weight of the polyethylene terephthalate is 13000 Da.

[0214] The remaining preparation method and parameters are consistent with Example 1.

[0215] Example 14

[0216] The difference between this example and Example 1 is that the viscosity average molecular weight of the polyethylene terephthalate is 52000 Da.

[0217] The remaining preparation method and parameters are consistent with Example 1.

[0218] Example 15

[0219] The difference between this example and Example 1 is that the number average molecular weight of the polypropylene is 9000 Da.

[0220] The remaining preparation method and parameters are consistent with Example 1.

[0221] Example 16

[0222] The difference between this example and Example 1 is that the number average molecular weight of the polypropylene is 110000 Da.

[0223] The remaining preparation method and parameters are consistent with Example 1.

[0224] Example 17

[0225] The present example provides a composite polymer film for a current collector, the composite polymer film comprising a first polymer layer, a second polymer layer and a third polymer layer stacked in sequence;

[0226] The material of the first polymer layer and the third polymer layer is a combination of a first polyester material and a polyolefin material, and the material of the second polymer layer is a second polyester material.

[0227] The first polyester material and the second polyester material are both polyethylene terephthalate with a viscosity average molecular weight of 30000 Da; the polyolefin material is polypropylene with a isotacticity of 97% and a number average molecular weight of 60000 Da;

[0228] In the first polymer layer, the mass ratio of the first polyester material and the polyolefin material is 40:60; in the third polymer layer, the mass ratio of the first polyester material and the polyolefin material is 40:60;

[0229] In the second polymer layer, the content of the second polyester material is 100wt%;

[0230] The thicknesses of the first polymer layer, the second polymer layer and the third polymer layer are denoted as h1, h2 and h3 respectively, h1=h3, h1:h2:h3=8:84:8;

[0231] The thickness of the composite polymer film is 4.5μm.

[0232] The embodiment also provides a preparation method of the composite polymer film, which comprises the following steps:

[0233] (1) The preparation raw material of the first polymer layer is pretreated, and the specific steps include: the first polyester material is placed in a crystallizer and crystallized at 150℃ for 60min, and then placed in a drying tower and dried at 160℃ for 160min; the polyolefin material is placed in a crystallizer and crystallized at 80℃ for 100min, and then placed in a drying tower and dried at 70℃ for 100min; then the dried first polyester material and polyolefin material are mixed according to a mass ratio of 40:60 to obtain a first material;

[0234] The preparation raw material of the second polymer layer is pretreated, and the specific steps include: the second polyester material is placed in a crystallizer and crystallized at 150℃ for 60min, and then placed in a drying tower and dried at 160℃ for 160min to obtain a second material;

[0235] The preparation raw material of the third polymer layer is pretreated, and the specific steps include: the first polyester material is placed in a crystallizer and crystallized at 150℃ for 60min, and then placed in a drying tower and dried at 160℃ for 160min; the polyolefin material is placed in a crystallizer and crystallized at 80℃ for 100min, and then placed in a drying tower and dried at 70℃ for 100min; then the dried first polyester material and polyolefin material are mixed according to a mass ratio of 40:60 to obtain a third material;

[0236] (2) the first material, the second material and the third material are respectively transported into corresponding double screw extruders, melted at 280℃, and then filtered by a metering pump and co-extruded through a die to obtain a molten material;

[0237] The volume ratio of the extrusion amounts of the first material, the second material and the third material is 8:84:8.

[0238] (3) the molten material is cast onto a casting roller and cooled at 30℃ to obtain a shaped casting sheet;

[0239] (4) the shaped casting sheet is preheated at 70℃, then stretched in the longitudinal direction with a stretching ratio of 4:1 at a stretching temperature of 110℃, and cooled at 40℃ after the stretching;

[0240] The cooled film is preheated at 80℃, then stretched in the transverse direction with a stretching ratio of 3:1 at a stretching temperature of 110℃, and cooled at 40℃ after the stretching;

[0241] (5) the film after step (4) is heat treated at a temperature of 80℃, then cooled by air, enters a take-up system through a traction system to wind the film, and the composite polymer film is obtained.

[0242] The embodiment also provides a current collector, which comprises the composite polymer film and a copper layer arranged on both surfaces of the composite polymer film, and a protective layer arranged on the surface of the copper layer away from the composite polymer film.

[0243] The single-sided thickness of the copper layer is 1000nm, the material of the protective layer is chromium oxide, and the single-sided thickness of the protective layer is 10nm.

[0244] The embodiment also provides a preparation method of the current collector, which comprises the following steps:

[0245] (a) the composite polymer film is placed in a vacuum evaporation cabin, high-purity copper wire (purity greater than 99.99%) in a metal evaporation chamber is melted and evaporated at a high temperature of 1600℃, and the evaporated metal atoms are deposited on both surfaces of the composite polymer film through a cooling system in the vacuum coating chamber to form a copper layer;

[0246] (b) the composite film containing the copper layer is placed in a dip coating liquid, the dip coating liquid is a potassium dichromate aqueous solution (mass concentration is 0.5g / L), the dip coating time is 30s, the dip coating is completed, then the liquid is removed by extrusion, and then the current collector is obtained by drying in a 60℃ oven.

[0247] Example 18

[0248] The difference between this example and example 17 is that the polyolefin material is an ethylene-propylene-butene copolymer.

[0249] The remaining preparation method and parameters are consistent with example 17.

[0250] Example 19

[0251] The difference between this example and example 17 is that the polyolefin material is a polymer of bicyclo[2,2,1]hept-2-ene and ethylene (CAS: 26007-43-2).

[0252] The remaining preparation method and parameters are consistent with example 1.

[0253] Example 20

[0254] The difference between this example and example 17 is that the first polyester material and the second polyester material are both polybutylene terephthalate.

[0255] The remaining preparation method and parameters are consistent with example 17.

[0256] Example 21

[0257] The difference between this example and example 17 is that the first polyester material and the second polyester material are both polyethylene 2,6-naphthalate.

[0258] The remaining preparation method and parameters are consistent with example 17.

[0259] Example 22

[0260] The difference between this example and example 17 is that in the first polymer layer, the mass ratio of the first polyester material and the polyolefin material is 60:40; in the third polymer layer, the mass ratio of the first polyester material and the polyolefin material is 60:40.

[0261] The remaining preparation method and parameters are consistent with example 17.

[0262] Example 23

[0263] The difference between this example and example 17 is that in the first polymer layer, the mass ratio of the first polyester material and the polyolefin material is 20:80; in the third polymer layer, the mass ratio of the first polyester material and the polyolefin material is 20:80.

[0264] The remaining preparation method and parameters are consistent with example 17.

[0265] Example 24

[0266] The difference between this example and example 17 is that the polyethylene terephthalate has a viscosity average molecular weight of 15000 Da.

[0267] The remaining preparation methods and parameters remain consistent with example 17.

[0268] Example 25

[0269] The difference between this example and example 1 is that the polyethylene terephthalate has a viscosity average molecular weight of 50000 Da.

[0270] The remaining preparation methods and parameters remain consistent with example 17.

[0271] Example 26

[0272] The difference between this example and example 17 is that the polypropylene has a number average molecular weight of 10000 Da.

[0273] The remaining preparation methods and parameters remain consistent with example 17.

[0274] Example 27

[0275] The difference between this example and example 17 is that the polypropylene has a number average molecular weight of 100000 Da.

[0276] The remaining preparation methods and parameters remain consistent with example 17.

[0277] Example 28

[0278] The difference between this example and example 17 is that h1 :h2:h3 = 1 :98:1.

[0279] The remaining preparation methods and parameters remain consistent with example 17.

[0280] Example 29

[0281] The difference between this example and example 17 is that h1 :h2:h3 = 15:70:15.

[0282] The remaining preparation methods and parameters remain consistent with example 17.

[0283] Example 30

[0284] The difference between this example and example 17 is that in the first polymer layer, the mass ratio of the first polyester material and the polyolefin material is 65:35; in the third polymer layer, the mass ratio of the first polyester material and the polyolefin material is 65:35.

[0285] The remaining preparation methods and parameters remain consistent with example 17.

[0286] Example 31

[0287] The difference between this example and Example 17 is that the mass ratio of the first polyester material and the polyolefin material in the first polymer layer is 15:85; and the mass ratio of the first polyester material and the polyolefin material in the third polymer layer is 15:85.

[0288] The rest of the preparation method and parameters remain consistent with Example 17.

[0289] Example 32

[0290] The difference between this example and Example 17 is that the viscosity average molecular weight of the polyethylene terephthalate is 13000 Da.

[0291] The rest of the preparation method and parameters remain consistent with Example 17.

[0292] Example 33

[0293] The difference between this example and Example 17 is that the viscosity average molecular weight of the polyethylene terephthalate is 52000 Da.

[0294] The rest of the preparation method and parameters remain consistent with Example 17.

[0295] Example 34

[0296] The difference between this example and Example 17 is that the number average molecular weight of the polypropylene is 9000 Da.

[0297] The rest of the preparation method and parameters remain consistent with Example 17.

[0298] Example 35

[0299] The difference between this example and Example 17 is that the number average molecular weight of the polypropylene is 110000 Da.

[0300] The rest of the preparation method and parameters remain consistent with Example 17.

[0301] Example 36

[0302] The difference between this example and Example 17 is that h1:h2:h3 = 0.5:99:0.5.

[0303] The rest of the preparation method and parameters remain consistent with Example 17.

[0304] Example 37

[0305] The difference between this example and Example 17 is that h1:h2:h3 = 17:66:17.

[0306] The rest of the preparation method and parameters are consistent with Example 17.

[0307] Example 38

[0308] The difference between this example and Example 17 is that the polypropylene is random polypropylene.

[0309] The rest of the preparation method and parameters are consistent with Example 17.

[0310] Comparative Example 1

[0311] The difference between this comparative example and Example 1 is that the mass fraction of polypropylene is 30wt%, and the mass fraction of polyethylene terephthalate is adjusted to 70wt%.

[0312] The rest of the preparation method and parameters are consistent with Example 1.

[0313] Comparative Example 2

[0314] The difference between this comparative example and Example 1 is that the mass fraction of polypropylene is 85wt%, and the mass fraction of polyethylene terephthalate is adjusted to 15wt%.

[0315] The rest of the preparation method and parameters are consistent with Example 1.

[0316] Comparative Example 3

[0317] The difference between this comparative example and Example 1 is that no polypropylene is added as a raw material for preparing the composite current collector base film.

[0318] The rest of the preparation method and parameters are consistent with Example 1.

[0319] Comparative Example 4

[0320] The difference between this comparative example and Example 7 is that polypropylene is replaced by silicon dioxide, and the content is adjusted to 1wt%, and the mass fraction of polyethylene terephthalate is adjusted to 99wt%.

[0321] The rest of the preparation method and parameters are consistent with Example 7.

[0322] Comparative Example 5

[0323] The difference between this comparative example and Example 17 is that the composite polymer film is a single-layer film, and the material is only polyethylene terephthalate.

[0324] The rest of the preparation method and parameters are consistent with Example 17.

[0325] Comparative Example 6

[0326] The difference between the present comparative example and Example 17 is that the composite polymer film is a single layer film, and the material is a combination of polyethylene terephthalate glycol and silica, the content of which is 99wt%, 1wt% respectively.

[0327] The rest of the preparation method and parameters remain the same as Example 17.

[0328] Comparative Example 7

[0329] The difference between the present comparative example and Example 17 is that the composite polymer film is a single layer film, and the material is a combination of polyethylene terephthalate glycol and polypropylene, the content of which is 40wt%, 60wt% respectively.

[0330] The rest of the preparation method and parameters remain the same as Example 17.

[0331] Performance test

[0332] I. The test of the defective rate of the composite current collector base film prepared in the above examples and comparative examples due to film breakage caused by sticking film during unwinding, the defective rate of the composite current collector base film caused by film breakage during film preparation, and the surface tension and surface roughness of the composite current collector base film is as follows:

[0333] ①Defective rate: the defective rate of the composite current collector base film caused by film breakage due to sticking film during unwinding, that is, the percentage of the number of unqualified products (in area) to the total product quantity (in area) caused by film breakage due to sticking film during unwinding; the defective rate of the composite current collector base film caused by film breakage during film preparation, that is, the percentage of the number of unqualified products (in area) caused by film breakage during film preparation to the total product quantity (in area).

[0334] ②Surface tension: determined according to standard GB / T 14216-2008.

[0335] ③Surface roughness: determined according to standard GB / T 31227-2014.

[0336] ④The tensile strength of the composite polymer film is tested according to standard GB / T 1040.3-2006.

[0337] II. The test of the adhesion between the composite current collector base film and the copper layer in the composite current collector prepared in the above examples and comparative examples, and the high temperature cycle performance of the battery prepared based on the composite current collector is as follows:

[0338] ①Adhesion: A 1 mm thick aluminum foil was bonded with a layer of Permacel P-94 double-sided tape, a composite current collector was bonded on top of the double-sided tape, and a layer of ethylene acrylic acid copolymer film (DuPont Nurcel 0903, thickness of 50 μm) was covered on top of the composite current collector, and then the sample was hot-pressed at 1.3 x 10 5 N / m 2 , 120°C for 10 s, cooled to room temperature (25°C), and cut into a small strip of 150 mm x 15 mm; finally, the ethylene acrylic acid copolymer film of the sample strip was fixed to the upper clamp of the tensile testing machine, and the rest was fixed to the lower clamp, and after being fixed, the two were peeled at an angle of 180° at a speed of 100 mm / min, and the peeling force, i.e., the adhesion of the composite current collector film and the copper layer, was tested.

[0339] ②High temperature cycle performance:

[0340] i. Assembling of lithium ion battery: for the positive electrode, the positive electrode current collector was a conventional aluminum foil (thickness of 12 μm), and the positive electrode material was LiNi 0.8 Mn 0.1 Co 0.1 O2(NCM811); for the negative electrode, the negative electrode current collector was the composite current collector prepared in the present application, and the negative electrode material was artificial graphite; for the separator, an aluminum oxide ceramic coated polyethylene separator (thickness of 25 μm) was used; for the electrolyte, a carbonate solution of 1 mol·L -1 LiPF6, including propylene carbonate, ethylene carbonate and methyl ethyl carbonate in a mass ratio of 1:1:1; using the above materials, a lithium ion battery was assembled according to the relevant process;

[0341] ii. Test conditions: the battery was cycled at 1C charge-discharge rate at 45°C, in a voltage range of 3V to 4.2V, for 800 times, and the capacity retention rate of the battery after cycle charge-discharge was recorded.

[0342] The above test results are shown in Tables 1 and 2.

[0343] Table 1

[0344] Table 2

[0345] Analysis:

[0346] As can be seen from the above table, the composite current collector base film prepared in the application solves the problem of polyester film sticking to the film during unwinding without adding an anti-adhesion agent, and compared with the traditional polyester film with an anti-adhesion agent, the high-temperature charge-discharge performance of the battery prepared from the composite current collector based on the composite current collector base film is improved under the premise of ensuring that the film does not stick during unwinding. This is because the anti-adhesion agent silicon dioxide is not introduced into the polyester film, avoiding the problem of poor high-temperature charge-discharge cycle performance of the battery caused by the dissolution of silicon dioxide and the consumption of electrolyte and its electrochemical reaction products.

[0347] As can be seen from Example 1 and Example 4, if a mixture of polypropylene and cyclic olefin copolymer is used as a hydrocarbon polymer material, the regular arrangement of polyester can be better inhibited, the surface roughness and free volume of the prepared polymer film are improved, and thus the adhesion between the copper layer and the base film in the prepared composite current collector is improved.

[0348] As can be seen from Examples 1-3 and Examples 5-6, replacing polyethylene terephthalate and polypropylene in the raw materials with other types of polyester and polyolefin can still achieve good technical effects.

[0349] As can be seen from Example 1, Examples 7-8 and Comparative Examples 1-2, increasing the content of polypropylene reduces the adverse rate of the prepared base film due to sticking to the film during unwinding, increases the surface roughness and reduces the surface tension. This is because the increase in the content of polypropylene reduces the polarity of the prepared base film, resulting in a decrease in surface tension, and the increase in the content of polypropylene disrupts the regular arrangement of polyester macromolecules, thereby forming a higher roughness on the surface of the base film. Furthermore, the adhesion between the copper layer and the base film of the composite current collector prepared from the base film first increases and then decreases, which is because the increase in the content of polypropylene reduces the surface tension of the prepared base film, which will lead to a decrease in adhesion, but the increase in surface roughness will cause the adhesion to first increase and then decrease. In addition, the increase in the free volume of the macromolecules of the base film will also lead to an increase in adhesion, and the mutual restriction of the three will jointly lead to the change trend of the adhesion first increasing and then decreasing. Furthermore, the high-temperature charge-discharge cycle performance of the battery prepared from the composite current collector first increases and then decreases, which is due to the adhesion between the copper layer and the base film in the composite current collector first increasing and then decreasing.

[0350] As can be seen from Example 1, Examples 9-10 and Examples 13-14, increasing the viscosity-average molecular weight of the polyester material first reduces and then increases the film breakage rate during the preparation of the base film, which is caused by the fact that too high or too low molecular weight of the polyester polymer leads to poor film-forming property; the surface tension of the prepared base film slightly decreases, which is caused by the fact that the increase of the molecular weight of the polyester slightly reduces the content of the terminal carboxyl group of the polyester polymer; the surface roughness of the prepared base film increases, which is caused by the fact that the increase of the molecular weight leads to poor regular arrangement of the polymer molecules during the stretching process and reduces the crystallinity. Moreover, the adhesion between the base film and the copper layer of the composite current collector prepared based on the base film first increases and then decreases, which is caused by the fact that the surface tension of the base film decreases and the surface roughness of the base film increases. In addition, the high-temperature charge-discharge cycle performance of the battery prepared using the composite current collector first increases and then decreases, which is caused by the fact that the adhesion between the copper layer and the base film in the composite current collector first increases and then decreases.

[0351] As can be seen from Example 1, Examples 11-12 and Examples 15-16, increasing the number-average molecular weight of the hydrocarbon polymer material first reduces and then increases the film breakage rate during the preparation of the base film, which is caused by the fact that too high or too low molecular weight of the polyolefin polymer leads to poor film-forming property; the surface tension of the prepared base film remains unchanged, which is caused by the fact that the surface tension of the base film mainly depends on the properties of the polyester polymer; the surface roughness of the prepared base film increases, which is caused by the fact that the increase of the molecular weight leads to poor regular arrangement of the polymer molecules during the stretching process and reduces the crystallinity. Moreover, the adhesion between the base film and the copper layer of the composite current collector prepared based on the base film increases, which is caused by the fact that the surface roughness of the base film increases. In addition, the high-temperature charge-discharge cycle performance of the battery prepared using the composite current collector increases, which is caused by the fact that the adhesion between the copper layer and the base film in the composite current collector increases.

[0352] As can be seen from Example 1 and Comparative Example 3, if no polypropylene is added, the prepared base films are seriously adhered to each other, which leads to film breakage during the preparation of the composite current collector, thereby increasing the unwinding failure rate.

[0353] As can be seen from Example 1 and Comparative Example 4, if the polypropylene is replaced by silicon dioxide, the silicon dioxide will be eroded by the electrolyte and its electrochemical reaction products during the high-temperature charge-discharge cycle of the battery, thereby being dissolved out. The dissolution of the silicon dioxide and the consumption of the electrolyte and its electrochemical reaction products will lead to poor high-temperature charge-discharge cycle performance of the battery.

[0354] As can be seen from Examples 17-29, Comparative Example 5 and Comparative Example 6, the composite polymer film prepared in the application solves the problem of poor unwinding adhesion of the film without adding an anti-adhesion agent, and compared with the conventional polymer film added with an anti-adhesion agent, under the premise of ensuring the unwinding non-adhesion of the film and the tensile strength of the prepared polymer film, the high-temperature charge-discharge performance of the battery prepared from the composite current collector based on the composite polymer film is improved, which is because the composite polymer film does not introduce anti-adhesion agent silicon dioxide, and the problem of poor high-temperature charge-discharge cycle performance of the battery caused by the dissolution of silicon dioxide and the consumption of electrolyte and its electrochemical reaction products does not occur.

[0355] As can be seen from Example 17 and Comparative Example 7, compared with the single-layer structure polymer film, the tensile strength of the three-layer structure composite polymer film prepared in the application is obviously improved, and the high-temperature charge-discharge cycle performance of the battery based on the composite polymer film is improved, which is because the thickness of the second polymer layer in the three layers occupies a dominant position, and the second polymer layer only contains polyester material, which can achieve higher orientation and crystallinity during the biaxial stretching process, so as to ensure that the prepared composite polymer film has good mechanical properties. Moreover, the improvement of the tensile strength can reduce the generation of internal defects of the material during the preparation of the battery electrode sheet from the current collector, thereby further improving the high-temperature charge-discharge cycle performance of the battery.

[0356] As can be seen from Examples 17-21, replacing polyethylene terephthalate and polypropylene with other types of polyester materials and hydrocarbon polymer materials can still achieve good technical effects.

[0357] As can be seen from Example 17, Examples 22-23 and Examples 30-31: a. Increasing the content of polyolefin can reduce the adverse rate of the prepared polymer film caused by adhesion during the unwinding process, which is because the increase of the polyolefin content reduces the polarity of the film, resulting in a decrease in surface tension, and the increase of the polyolefin content destroys the regular arrangement of the polyester macromolecule, thereby forming a higher roughness on the surface of the film, and the decrease of the surface tension and the increase of the roughness jointly alleviate the adhesion; b. The adhesion between the copper layer in the current collector prepared from the composite polymer film and the composite polymer film first increases and then decreases, which is because the decrease of the surface tension of the film caused by the increase of the polyolefin content will lead to a decrease in adhesion, but the increase of the surface roughness caused by the increase of the polyolefin content will make the adhesion first increase and then decrease, in addition, the increase of the macromolecular free volume in the film caused by the increase of the polyolefin content will also lead to an increase in adhesion, and the mutual restriction of the three leads to the change trend that the adhesion first increases and then decreases; c. The high-temperature charge-discharge cycle performance of the battery prepared from the current collector first increases and then decreases, which is mainly caused by the adhesion between the copper layer in the current collector and the composite polymer film first increasing and then decreasing.

[0358] From Example 17, Example 24-25 and Example 32-33, it can be seen that: a. increasing the molecular weight of the polyester material, the first decrease and then increase the rate of film breakage in the preparation process of the composite polymer film, which is caused by the polyester high molecular weight too high or too low, the film-forming property is poor; b. in the current collector prepared by the base film of the composite polymer film, the adhesion between the composite polymer film and the copper layer first increases and then decreases, which is the result of the mutual restriction of the increase of the molecular weight of the polyester, the decrease of the surface tension of the film and the increase of the surface roughness; c. the high temperature charge-discharge cycle performance of the battery prepared by the current collector first increases and then decreases, which is mainly caused by the adhesion between the copper layer and the composite polymer film in the current collector first increases and then decreases.

[0359] From Example 17, Example 26-27 and Example 34-35, it can be seen that: a. increasing the molecular weight of the polyester material, the first decrease and then increase the rate of film breakage in the preparation process of the composite polymer film, which is caused by the polyester high molecular weight too high or too low, the film-forming property is poor; the surface tension of the prepared composite polymer film is unchanged, which is because the surface tension of the film mainly depends on the properties of the polyester high molecular; the surface roughness of the prepared composite polymer film increases, which is because the molecular weight increases, the regular arrangement of the high molecular in the stretching process is poor, the crystallinity decreases, thus leading to the increase of the roughness; b. in the composite current collector prepared by the base film of the composite polymer film, the adhesion between the composite polymer film and the copper layer increases, which is because the molecular weight of the polyolefin increases, the regular arrangement of the high molecular in the stretching process is poor, thus leading to the increase of the surface roughness of the prepared composite polymer film, which is beneficial to the adhesion between the composite polymer film and the copper layer; c. the high temperature charge-discharge cycle performance of the battery prepared by the current collector increases, which is mainly caused by the adhesion between the copper layer and the composite polymer film in the current collector.

[0360] From Example 17, Example 28-29 and Example 36-37, it can be seen that a. increasing the thickness of the first polymer layer and the third polymer layer can first reduce and then remain unchanged the adverse rate of the composite polymer film caused by sticking film during unwinding, because the thickness of the first polymer layer and the third polymer layer is too thin to create a good low surface tension and high roughness surface, resulting in the occurrence of winding sticking film; b. increasing the thickness of the first polymer layer and the third polymer layer can reduce the tensile strength of the composite polymer film, because the tensile strength of the polyester film mainly depends on the tensile strength of the second polymer layer, and the thickness ratio of the second polymer layer decreases with the increase of the thickness of the first polymer layer and the third polymer layer, resulting in the decrease of the tensile strength; c. in the current composite polymer film as the base film to prepare the current current collector, the adhesion between the composite polymer film and the copper layer first increases and then remains unchanged, which is caused by the increase of the surface tension and roughness of the film first increasing and then remaining unchanged; d. the high-temperature charge-discharge cycling performance of the battery prepared by the current current collector first increases and then decreases, which is caused by the decrease of the adhesion between the copper layer and the composite polymer film in the current collector and the tensile strength of the film.

[0361] From Example 17 and Example 38, it can be seen that random polypropylene is beneficial on the one hand to reduce the crystallinity of the first polymer layer and the third polymer layer, thereby improving the surface roughness of the prepared polymer film, and on the other hand to improve the free volume of the polymer, thereby improving the adhesion between the polymer film and the metal layer in the prepared composite current collector, and further improving the cycle performance of the battery.

[0362] The applicant declares that the present application illustrates the process method of the present application through the above examples, but the present application is not limited to the above process steps, that is, it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the raw materials selected by the present application and addition of auxiliary ingredients, selection of specific methods, etc. fall within the scope of protection and disclosure of the present application.

Claims

1. A composite current collector base film comprising a first polymer layer, the first polymer layer comprising a first polyester material and a hydrocarbon polymer material, wherein the mass ratio of the first polyester material and the hydrocarbon polymer material is (20-60):(40-80), preferably (30-50):(50-70).

2. The composite current collector base film of claim 1, wherein, The composite current collector base film further comprises a second polymer layer, the second polymer layer comprising a second polyester material, the content of the second polyester material in the second polymer layer being greater than or equal to 95wt%, preferably greater than or equal to 98wt%, further preferably greater than or equal to 99wt%, most preferably 100wt%.

3. The composite current collector base film of claim 1 or 2, wherein, The composite current collector base film further comprises a third polymer layer, the third polymer layer comprising a first polyester material and a hydrocarbon polymer material, wherein the mass ratio of the first polyester material and the hydrocarbon polymer material is (20-60):(40-80).

4. The composite current collector base film of any one of claims 1-3, wherein, The composite current collector base film comprises the composite polymer film comprising a first polymer layer, a second polymer layer and a third polymer layer stacked in sequence, the first polymer layer comprising a first polyester material and a hydrocarbon polymer material, wherein the mass ratio of the first polyester material and the hydrocarbon polymer material is (20-60):(40-80); the second polymer layer comprising a second polyester material, the content of the second polyester material in the second polymer layer being greater than or equal to 95wt%, preferably greater than or equal to 98wt%, further preferably greater than or equal to 99wt%, most preferably 100wt%; the third polymer layer comprising a first polyester material and a hydrocarbon polymer material, wherein the mass ratio of the first polyester material and the hydrocarbon polymer material is (20-60):(40-80).

5. The composite current collector base film of any one of claims 2-4, wherein, The second polyester material comprises any one or a combination of at least two of polyethylene terephthalate, polyethylene 2,6-naphthalate, polybutylene terephthalate, poly-l,4-cyclohexane dimethylene terephthalate, polyethylene terephthalate-1,4-cyclohexane dimethylene terephthalate, polypropylene 2,6-naphthalate, polypropylene terephthalate, polybutylene 2,6-naphthalate, polybutylene 2,5-furandicarboxylate or polybutylene adipate terephthalate; Preferably, the second polyester material has a viscosity average molecular weight of 15000-50000 Da, preferably 18000-40000 Da.

6. The composite current collector base film of any one of claims 1-5, wherein, The first polyester material comprises any one or a combination of at least two of polyethylene terephthalate, polyethylene 2,6-naphthalate, polybutylene terephthalate, poly-l,4-cyclohexane dimethylene terephthalate, polyethylene terephthalate-1,4-cyclohexane dimethylene terephthalate, polypropylene 2,6-naphthalate, polypropylene terephthalate, polybutylene 2,6-naphthalate, polybutylene 2,5-furandicarboxylate or polybutylene adipate terephthalate; Preferably, the first polyester material has a viscosity average molecular weight of 15000-50000 Da, preferably 18000-40000 Da.

7. The composite current collector base film of any one of claims 1-6, wherein, The hydrocarbon polymer material comprises a polyolefin material; Preferably, the polyolefin material comprises an olefin-based polymer and / or a cycloolefin-based polymer, preferably an olefin-based copolymer and / or a cycloolefin-based copolymer, more preferably a mixture of an olefin-based copolymer and a cycloolefin-based copolymer; Preferably, the olefin-based polymer comprises any one or a combination of at least two of polyethylene, polypropylene, ethylene-propylene copolymer, propylene-butylene copolymer or ethylene-propylene-butylene copolymer; Preferably, the cycloolefin-based polymer comprises polydicyclo[2.2.1]hepta-2-ene, polycyclopentene, polycyclopentadiene, polycyclohexene, dicyclo[2.2.1]hepta-2-ene-ethylene copolymer or dicyclo[2.2.1]hepta-2-ene-propylene copolymer; Preferably, the hydrocarbon polymer material has a number average molecular weight of 10,000-100,000 Da, preferably 15,000-80,000 Da.

8. The composite current collector base film of any one of claims 1-7, wherein, The thickness of the composite current collector base film is ≥1 μm, preferably 2-20 μm.

9. The composite current collector base film of claim 4, wherein, The thicknesses of the first, second and third polymer layers are denoted as h1, h2 and h3, respectively, h1=h3, and h1:h2=(1-15):(70-98).

10. A method for preparing the composite current collector base film according to any one of claims 1-9, comprising the following steps: (1) separately pre-treating a first polyester material and a hydrocarbon polymer material, and then mixing them to obtain a mixture; (2) sequentially subjecting the mixture to melt extrusion, sheet casting, stretching treatment and heat treatment, and then winding to obtain the composite current collector base film.

11. The production method according to claim 10, wherein The pre-treatment of the first polyester material in step (1) comprises sequentially subjecting the first polyester material to first crystallization treatment and first drying treatment; Preferably, the first crystallization treatment has a crystallization temperature of 130-200°C and a crystallization time of 20-130 min; Preferably, the first drying treatment has a drying temperature of 130-180°C and a drying time of 110-300 min; Preferably, the pre-treatment of the hydrocarbon polymer material in step (1) comprises sequentially subjecting the hydrocarbon polymer material to second crystallization treatment and second drying treatment; Preferably, the second crystallization treatment has a crystallization temperature of 60-100°C and a crystallization time of 20-120 min; Preferably, the second drying treatment has a drying temperature of 60-80°C and a drying time of 100-300 min.

12. The production method according to claim 10 or 11, wherein, In the melt extrusion in step (2), the temperature for heating and melting is 270-300°C; Preferably, the stretching treatment in step (2) comprises longitudinal stretching and transverse stretching; Preferably, the longitudinal stretching has a stretching ratio of (3-6):1, a stretching temperature of 80-110°C, and the transverse stretching has a stretching ratio of (2-4):1, a stretching temperature of 80-110°C; Preferably, the heat treatment in step (2) has a temperature of 70-100°C.

13. The production process according to any one of claims 10 to 12, wherein, The method comprises the following steps: (1) the first polyester material is transported into a crystallizer, treated at 130-200°C for 20-130 min, and then transported into a drying tower, dried at 130-180°C for 110-300 min to obtain a pretreated first polyester material; the hydrocarbon polymer material is transported into a crystallizer, treated at 60-100°C for 20-120 min, and then transported into a drying tower, dried at 60-80°C for 100-300 min to obtain a pretreated hydrocarbon polymer material; wherein the hydrocarbon polymer material is a mixture of an olefin-based polymer and a cyclic olefin-based polymer; (2) the pretreated first polyester material and the pretreated hydrocarbon polymer material are mixed to obtain a mixture, and then the mixture is transported into a twin-screw extruder, subjected to melt treatment at 270-300°C, filtered, and extruded through a die to obtain a melt; (3) the melt obtained by melt co-extrusion is cast onto a casting roll, and subjected to cooling treatment by the casting roll and water cooling to form a cast sheet, wherein the cooling temperature is 20-60°C, and the cast sheet is obtained; (4) the cast sheet is preheated at 60-80°C, and then subjected to longitudinal stretching with a stretching ratio of (3-6):1 and a stretching temperature of 80-110°C, and after the stretching, the cast sheet is subjected to cooling treatment at 30-50°C; the cast sheet after the cooling treatment is preheated at 60-80°C, and then subjected to transverse stretching with a stretching ratio of (2-4):1 and a stretching temperature of 80-110°C, and after the stretching, the cast sheet is subjected to cooling treatment at 40-70°C to obtain a stretched film sheet; (5) the stretched film sheet is subjected to heat treatment at a temperature of 70-100°C, and then cooled by air, drawn by a drawing system, and wound by a winding system to obtain the composite current collector base film.

14. The method of making according to claim 10, wherein, The preparation method further comprises adding the preparation raw materials of the second polymer layer and / or the third polymer layer into corresponding extrusion equipment respectively, melt co-extruding the preparation raw materials of the first polymer layer together to obtain a melt, and then sequentially performing cast sheet forming, stretching treatment, and heat treatment, and winding to obtain the composite polymer film.

15. The method of making according to claim 14, wherein, The preparation method further comprises pretreating the preparation raw materials of the second polymer layer before adding the preparation raw materials of the second polymer layer into corresponding extrusion equipment, including: the second polyester material is crystallized and dried, preferably, the second polyester material is crystallized at 130-200°C for 20-130 min, and then dried at 130-180°C for 110-300 min to obtain a second material; preferably, the preparation raw materials of the third polymer layer are pretreated before adding the preparation raw materials of the third polymer layer into corresponding extrusion equipment, including: The first polyester material is crystallized and dried, and the hydrocarbon polymer material is crystallized and dried, and then the dried first polyester material and the hydrocarbon polymer material are mixed, preferably, the first polyester material is crystallized at 130-200℃ for 20-130min, and then dried at 130-180℃ for 110-300min, the hydrocarbon polymer material is crystallized at 60-100℃ for 20-120min, and then dried at 60-80℃ for 100-300min, and then the dried first polyester material and the hydrocarbon polymer material are mixed to obtain a third material.

16. A composite current collector comprising the composite current collector base film according to any one of claims 1-9 or the composite current collector base film prepared according to the method of any one of claims 10-15, and a metal layer disposed on at least one side surface of the composite current collector base film.

17. The composite current collector of claim 16, wherein, The material of the metal layer comprises a metal element and / or a metal alloy; Preferably, the thickness of the metal layer is 500-2000nm, preferably 700-1200nm; Preferably, the method for preparing the metal layer comprises any one or a combination of at least two of physical vapor deposition, electroplating or electroless plating; Preferably, the metal layer is provided with a protective layer on the side surface away from the composite current collector base film; Preferably, the material of the protective layer comprises any one or a combination of at least two of elemental nickel, elemental chromium, a nickel-based alloy, a copper-based alloy, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper chromate, copper chromite, chromium chromate, graphite, carbon black, acetylene black, ketjen black, carbon nanometer quantum dots, carbon nanotubes, carbon nanofibers or graphene; Preferably, the thickness of the protective layer is 5-100nm; Preferably, the method for preparing the protective layer comprises any one or a combination of at least two of physical vapor deposition, chemical vapor deposition, in-situ forming or coating.

18. A lithium ion battery comprising the composite current collector according to claim 16 or 17, or comprising a composite current collector prepared based on the composite current collector base film according to any one of claims 1-9, in the electrode tab of the lithium ion battery.

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