A method for preparing a bopet film for composite current collectors

Abstract

The application discloses a preparation method of a BOPET film for a composite current collector, and belongs to the technical field of BOPET films. The method comprises the configuration of a water-based epoxy coating liquid and the preparation of an online coating BOPET film, and the composite current collector is a novel current collector material capable of replacing traditional copper / aluminum foils in lithium ion batteries. Compared with traditional single-layer metal foils, the composite current collector comprises a three-layer material structure, namely a metal layer, a polymer base material layer and a metal layer. The application of the composite material greatly expands the function of the current collector in the lithium battery, so that the current collector can block internal short circuits caused by mechanical damage, prevent the occurrence of battery thermal runaway, and further ensure human-machine safety. Meanwhile, the introduction of the polymer material as an intermediate support layer can reduce the weight of the battery, improve the energy density, further save metal raw materials, and reduce the cost of the battery cell and resource consumption.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of BOPET films, in particular to a preparation method of a BOPET film for composite current collectors. BACKGROUND

[0002] At present, PET / PP is the mainstream material of the composite current collector substrate, and the industrialization pace of PET is more rapid due to the outstanding mechanical properties and plating advantages, and has reached the initial mass production stage. However, the finished product of the battery cell based on the PET substrate has the problems of low high-temperature cycle number and fast capacity recession in the test use. The reason is that the pinholes existing in the plating film defects expose the PET substrate, and then the PET substrate cannot resist the corrosion of the electrolyte under the long-term high-temperature condition, which causes the capacity loss of the battery, especially the low negative electrode oxidation potential, and different from the positive electrode which has a dense aluminum oxide layer for protection, the corrosion problem is more serious, which greatly influences the industrialization process of the PET copper foil. Meanwhile, compared with the traditional pure metal, the PET material has the essential difference in the mechanical properties, electrical conductivity and thermal stability based on the battery cell manufacturing process and use conditions, which may cause the problems of coating broken belt, foil wrinkle and low cell rate in the production and use, and increases the product quality risk. Therefore, in order to better replace the traditional foil and be applied to the current collector field, it is urgent to study a method for improving the performance and corrosion resistance of the PET film. SUMMARY

[0003] In order to make the BOPET film have corrosion resistance and better apply to the application environment of the battery current collector, the application discloses a preparation method of a BOPET film for a composite current collector, which has the following steps:

[0004] A BOPET film for a composite current collector comprises, from top to bottom, an upper surface layer, a core layer and a lower surface layer, and further comprises a water-based epoxy coating liquid coated on the upper and lower surfaces of the film.

[0005] The upper surface layer, the core layer and the lower surface layer; further comprising a water-based epoxy coating liquid coated on the upper and lower surfaces of the film.

[0006] The upper surface layer comprises bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch and nano-CaCO3 modified anti-adhesion masterbatch; the raw material of the core layer comprises graphene modified bright polyester chips; and the lower surface layer comprises bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch and nano-CaCO3 modified anti-adhesion masterbatch.

[0007] Preferably, the graphene modified bright polyester chips comprise nano-graphene material and polyethylene terephthalate.

[0008] Preferably, the nano-CaCO3 modified anti-adhesion masterbatch comprises nano-CaCO3 particles, terephthalic acid, isophthalic acid and ethylene glycol.

[0009] Preferably, the nano-SiO2 modified anti-sticking masterbatch comprises nano-SiO2 particles, terephthalic acid, isophthalic acid and ethylene glycol.

[0010] Preferably, the mass fraction of the light polyester chip in the upper and lower surface layers is 60%.

[0011] Preferably, the mass fraction of the nano-SiO2 modified anti-sticking masterbatch in the upper and lower surface layers is 20%.

[0012] Preferably, the mass fraction of the nano-CaCO3 modified anti-sticking masterbatch in the upper and lower surface layers is 20%.

[0013] Preferably, the water-based epoxy coating liquid comprises a water-based epoxy emulsion, a water-based silica sol, a defoaming agent and a leveling agent.

[0014] A method for preparing a BOPET film for a composite current collector, the method comprising the following steps:

[0015] The water-based epoxy emulsion is added with deionized water and stirred, and at the same time, the water-based silica sol, the defoaming agent and the leveling agent are continuously added and stirred, and finally the curing agent is added and mixed to obtain a water-based epoxy coating liquid;

[0016] The core layer raw material is pre-crystallized, dried by blowing air, and impurities are removed, and then melted, extruded to a filter screen, and finally conveyed to a die head; the upper surface layer raw material is melted and extruded, and the melt is vacuum dried, and then conveyed to the die head; the lower surface layer and the upper surface layer share a single screw extruder, and are conveyed to each surface layer through a flow divider at the die head;

[0017] The core layer, the upper surface layer and the lower surface layer melt are conveyed to the three-layer die head through the melt pipeline and accurately metered by the melt pump, and then combined, cast and attached to the surface of the cold roller under the action of static electricity to form a polyester thick sheet with an upper surface layer, a core layer and a lower surface layer;

[0018] After the thick sheet is longitudinally stretched and subjected to double-sided corona treatment, the water-based epoxy coating liquid is coated on both sides of the film online, and then enters the transverse stretching section in sequence for preheating, stretching, setting and cooling treatment;

[0019] The finally formed film enters the traction section for flattening, thickness measurement, edge trimming and winding into a mother roll, and then the finished film is obtained by slitting.

[0020] The composite BOPET film for a current collector or the composite BOPET film for a current collector prepared by the above method is applied in manufacturing an electric core.

[0021] The preparation method of the composite current collector BOPET film has the following advantages: the resistivity of the film as a whole can be significantly reduced by adding graphene to the PET chip in the film core layer and blending modification, so that the obtained composite current collector has better electrical conductivity performance. The surface layer A and the surface layer C use different additive modified anti-sticking masterbatch (CaCO3 / SiO2) as the functional layer of the film by mixing in a specific ratio. Due to the characteristics of high specific surface area and surface activation energy of nano-CaCO3, the heat energy in the PET molecules can be effectively absorbed when the PET matrix is heated, and the CaCO3 interspersed in the PET molecular chain segment can further hinder the movement of the chain segment, increase the resin melting peak, and improve the overall heat shrinkage rate of the film. As a heterogeneous nucleating agent, nano-SiO2 can affect the crystallization behavior of PET molecules, especially at high temperatures, it can promote the formation of a crystal lattice of polymer molecules, and improve the overall mechanical properties of the film. Finally, a dense epoxy resin corrosion-resistant layer is coated on the surface of the film, so that the film surface has excellent chemical inertness, prevents the contact corrosion of electrolyte, and due to the existence of a large number of polar groups on the surface of the epoxy resin, it is more helpful for the adhesion of the metal foil on the surface of the base film.

[0022] The BOPET film prepared by the method has higher electrical conductivity efficiency, more excellent mechanical strength and heat resistance, and further has corrosion resistance by coating an anti-corrosion coating layer, which not only ensures the quality of the subsequent composite current collector processing process, but also avoids the capacity loss caused by electrolyte corrosion of the prepared battery cell, and reaches the level of traditional battery cells. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application are described clearly and completely, obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0024] The present application provides a preparation method of a composite current collector BOPET film. The present application will be further described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments.

[0025] In the following examples and comparative examples, the raw materials for preparing the BOPET film include bright polyester chips, graphene-modified polyester chips ① (effective component: ~5 nm, 1.2%), graphene-modified polyester chips ② (effective component: ~2 nm, 2.5%), graphene-modified polyester chips ③ (effective component: ~10 nm, 0.5%), nano-SiO2-modified anti-adhesion masterbatch (effective component: ~0.6 μm, 2%), nano-CaCO3-modified anti-adhesion masterbatch (effective component: ~0.65 μm, 1.5%), commercial anti-adhesion masterbatch K (SiO2, 3.0 μm, 3300 ppm), and commercial anti-adhesion masterbatch S (CaCO3, 3.5 μm, 3300 ppm). The graphene-modified polyester chips are prepared by melt blending nano-graphene material with polyethylene terephthalate, and the CaCO3 / SiO2-modified masterbatch is prepared by mixing the additives with terephthalic acid, isophthalic acid and ethylene glycol, followed by esterification and polycondensation.

[0026] Example 1

[0027] Example 1 describes a method for preparing a BOPET film for a composite current collector, which includes the following specific steps:

[0028] (1) Preparation of the aqueous epoxy coating solution

[0029] 20 parts by mass of the aqueous epoxy emulsion K-020 was added to a mixing tank, 75 parts by mass of deionized water was added, and stirring was performed at 500 rpm. Then, 2 parts by mass of the aqueous silica sol LS-50, 0.5 parts by mass of the defoaming agent BW-225, and 0.5 parts by mass of the leveling agent BW-404 were continuously added, and the stirring was continued for 30 min. Finally, 2 parts by mass of the curing agent K-62 was added and mixed thoroughly to obtain the aqueous epoxy coating solution.

[0030] (2) Preparation of the BOPET film by online coating

[0031] The BOPET film in this example is a typical three-layer co-extruded polyester film. The A layer (upper surface layer) contains bright polyester chips, nano-SiO2-modified anti-adhesion masterbatch and nano-CaCO3-modified anti-adhesion masterbatch, wherein the mass fraction of the bright polyester chips is 60%, the mass fraction of the nano-SiO2-modified anti-adhesion masterbatch is 20%, and the mass fraction of the nano-CaCO3-modified anti-adhesion masterbatch is 20%. The B layer (core layer) contains graphene-modified bright polyester chips ①. The C layer (lower surface layer) contains bright polyester chips, nano-SiO2-modified anti-adhesion masterbatch and nano-CaCO3-modified anti-adhesion masterbatch, wherein the mass fraction of the bright polyester chips is 60%, the mass fraction of the nano-SiO2-modified anti-adhesion masterbatch is 20%, and the mass fraction of the nano-CaCO3-modified anti-adhesion masterbatch is 20%.

[0032] The B layer raw material is pre-crystallized at 165°C and then sent into a fluidized bed, a drying tower for air drying and impurity removal, and then into single screw extruder 1 for melting and extrusion at 275°C to a filter screen, and finally metered by a melt pump and delivered to the die head; the A layer raw material is directly sent into single screw extruder 2 for melting and extrusion at 280°C, and the melt is vacuum dried to remove water, and then metered by a filter screen and a melt pump and delivered to the die head; the C layer shares the single screw extruder 2 with the A layer, and is delivered to each surface layer through a flow divider at the die head.

[0033] The melts of each layer are gathered at the die head to form a three-layer structure of the molten film sheet, and slowly flow down from the film lip at a uniform speed, and closely adhere to the surface of the cold roller at 29°C under the action of high voltage electrostatic field of 6.8 kV, and cast into a polyester thick sheet.

[0034] The obtained thick sheet is sent to the longitudinal stretching section, and stretched longitudinally under the conditions of preheating temperature 85°C, stretching temperature 101°C, and stretching ratio 3.1, and then the outlet film A and C surfaces are treated by corona treatment in sequence, and then a uniform layer of water-based epoxy coating liquid is coated on both surfaces of the film through a network roller online coating equipment, and the coating amount on each surface is 2.5 g / m 2 , and then the film enters the transverse stretching section, and stretched transversely under the conditions of preheating temperature 90°C, stretching temperature 105°C, setting temperature 225°C, and stretching ratio 3.2, and cooled at 25°C to obtain a biaxially stretched polyester film.

[0035] The finally formed film enters the traction section for flattening, thickness measurement, edge trimming, and winding into a mother roll, and then the finished film is obtained by slitting.

[0036] Example 2

[0037] Example 2 describes a preparation method of a BOPET film for a composite current collector, and the specific steps include (the type of graphene modified polyester chip in the B layer is replaced compared with Example 1):

[0038] (1) Preparation of water-based epoxy coating liquid

[0039] 20 parts by mass of water-based epoxy emulsion K-020 is added into a mixing tank, 75 parts by mass of deionized water is added, stirring is carried out at 500 rpm, 2 parts by mass of water-based silica sol LS-50, 0.5 parts by mass of defoaming agent BW-225, and 0.5 parts of leveling agent BW-404 are continuously added, stirring is continued for 30 min, and finally 2 parts by mass of curing agent K-62 is added for thorough mixing to obtain the water-based epoxy coating liquid.

[0040] (2) Preparation of online coated BOPET film

[0041] The BOPET film in this embodiment is a typical three-layer co-extrusion polyester film. The A layer (upper surface layer) contains large-gloss polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of large-gloss polyester chips is 60%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 20%. The B layer (core layer) contains large-gloss graphene modified polyester chips ②. The C layer (lower surface layer) contains large-gloss polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of large-gloss polyester chips is 60%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 20%.

[0042] The B layer raw material is pre-crystallized at 165°C and then sent to a fluidized bed and a drying tower for air drying and impurity removal, and then enters a single screw extruder 1, melts and extrudes to a filter screen at 275°C, and finally is conveyed to a die head after metering by a melt pump. The A layer raw material is directly sent to a single screw extruder 2, melts and extrudes at 280°C, and the melt is vacuum dried to remove water, and then is conveyed to the die head after metering by a filter screen and a melt pump. The C layer shares the single screw extruder 2 with the A layer, and is conveyed to each surface layer through a flow divider at the die head.

[0043] The melts of each layer are gathered at the die head to form a three-layer structure of the molten film sheet, which is slowly and uniformly cast from the film lip under the action of 6.8kV high voltage static electricity, and is tightly attached to the surface of a 29°C cold roller to form a polyester thick sheet.

[0044] The obtained thick sheet is put into a longitudinal stretching section, and is stretched longitudinally under the conditions of a preheating temperature of 85°C, a stretching temperature of 101°C, and a stretching ratio of 3.1. Then, the A and C surfaces of the outlet film are sequentially subjected to corona treatment, and then a uniform layer of water-based epoxy coating liquid is coated on both surfaces of the film through a network roller online coating equipment, with a coating amount of 2.5g / m 2 After that, the film enters a transverse stretching section, and is stretched transversely under the conditions of a preheating temperature of 90°C, a stretching temperature of 105°C, a setting temperature of 225°C, and a stretching ratio of 3.2, and is cooled at 25°C to obtain a biaxially stretched polyester film.

[0045] The finally formed film enters a traction section to be flattened, thickness measured, edges trimmed, and collected into a mother roll, and then the finished film is obtained by slitting.

[0046] Example 3

[0047] Example 3 describes a method for preparing a BOPET film for a composite current collector, and the specific steps include: replacing the type of graphene modified polyester chips in the B layer compared with Example 1.

[0048] (1) Preparation of aqueous epoxy coating solution

[0049] An aqueous epoxy emulsion K-020 of 20 parts by mass was added into a mixing tank, 75 parts by mass of deionized water was added, stirring was carried out at 500 rpm, and then 2 parts by mass of aqueous silica sol LS-50, 0.5 parts by mass of defoaming agent BW-225, and 0.5 parts of leveling agent BW-404 were continuously added thereto, stirring was continued for 30 min, and finally 2 parts by mass of curing agent K-62 was added for thorough mixing, to obtain an aqueous epoxy coating solution.

[0050] (2) Preparation of BOPET film coated online

[0051] The BOPET film in this embodiment is a typical three-layer co-extruded polyester film, the A layer (upper surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 60%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 20%; the B layer (core layer) contains graphene modified bright polyester chips ③; and the C layer (lower surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 60%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 20%.

[0052] The B layer raw material was pre-crystallized at 165°C, then sent into a fluidized bed and a drying tower for air blowing drying and impurity removal, and then into single-screw extruder 1 for melting and extrusion onto a filter screen at 275°C, and finally metered by a melt pump and delivered to a die head; the A layer raw material was directly sent into single-screw extruder 2 for melting and extrusion at 280°C, and the melt was vacuum dried to remove water, and then metered by a filter screen and a melt pump and delivered to a die head; the C layer and the A layer shared single-screw extruder 2, and were delivered to each surface layer through a flow divider at the die head.

[0053] The melts of each layer were gathered at the die head to form a three-layer molten film sheet, which was slowly and uniformly cast from the film lip under the action of 6.8 kV high voltage static electricity, and tightly attached to the surface of a 29°C cold roller to form a polyester thick sheet.

[0054] The obtained thick sheet was put into a longitudinal stretching section, and stretched longitudinally under the conditions of preheating temperature 85°C, stretching temperature 101°C, and stretching ratio 3.1, and then the outlet film A and C surfaces were sequentially subjected to corona treatment, and then a uniform layer of aqueous epoxy coating solution was coated on both surfaces of the film by a screen roller online coating equipment, with a coating amount of 2.5 g / m 2After that, the film enters the transverse stretching section, and is stretched in the transverse direction under the conditions of a preheating temperature of 90°C, a stretching temperature of 105°C, a setting temperature of 225°C, and a stretching ratio of 3.2, and is cooled at 25°C to obtain a biaxially stretched polyester film.

[0055] The finally shaped film enters the traction section to be flattened, measured in thickness, trimmed, and collected into a mother roll, and then cut into finished film.

[0056] Example 4

[0057] Example 4 describes a method for preparing a BOPET film for a composite current collector, which includes the following specific steps: (compared with Example 1, the ratio of the water-based epoxy coating solution is changed)

[0058] (1) Preparation of the water-based epoxy coating solution

[0059] 15 parts by mass of a water-based epoxy emulsion K-020 is added into a mixing tank, 81.4 parts by mass of deionized water is added, stirring is performed at 500 rpm, 1.5 parts by mass of a water-based silica sol LS-50, 0.3 parts by mass of a defoaming agent BW-225, and 0.3 parts of a leveling agent BW-404 are continuously added thereto, stirring is continued for 30 min, and finally 1.5 parts by mass of a curing agent K-62 is added for thorough mixing to obtain the water-based epoxy coating solution.

[0060] (2) Preparation of the on-line coated BOPET film

[0061] The BOPET film in this example is a typical three-layer co-extruded polyester film, the A layer (upper surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of the bright polyester chips is 60%, the mass fraction of the nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of the nano-CaCO3 modified anti-adhesion masterbatch is 20%; the B layer (core layer) contains graphene modified bright polyester chips ①; and the C layer (lower surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of the bright polyester chips is 60%, the mass fraction of the nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of the nano-CaCO3 modified anti-adhesion masterbatch is 20%.

[0062] The B layer raw material is pre-crystallized at 165°C, then sent into a fluidized bed, a drying tower for air drying and impurity removal, and then into single screw extruder 1 for melting and extrusion at 275°C to a filter screen, and finally metered by a melt pump and delivered to the die head; the A layer raw material is directly sent into single screw extruder 2 for melting and extrusion at 280°C, and the melt is vacuum dried to remove water, and then metered by a filter screen and a melt pump and delivered to the die head; the C layer shares the single screw extruder 2 with the A layer, and is delivered to each surface layer through a flow divider at the die head.

[0063] The melts of each layer are gathered at the die head to form a three-layer structure of the molten film sheet, and slowly flow down from the film lip at a uniform speed, and closely adhere to the surface of the cold roller at 29°C under the action of high voltage electrostatic field of 6.8 kV, and cast into a polyester thick sheet.

[0064] The obtained thick sheet is sent to the longitudinal stretching section, and stretched longitudinally under the conditions of preheating temperature 85°C, stretching temperature 101°C, and stretching ratio 3.1, and then the outlet film A and C surfaces are treated by corona treatment in sequence, and then a uniform layer of water-based epoxy coating liquid is coated on both surfaces of the film through a network roller online coating equipment, and the coating amount on each surface is 2.5 g / m 2 , and then the film enters the transverse stretching section, and stretched transversely under the conditions of preheating temperature 90°C, stretching temperature 105°C, setting temperature 225°C, and stretching ratio 3.2, and cooled at 25°C to obtain a biaxially stretched polyester film.

[0065] The finally shaped film enters the traction section for flattening, thickness measurement, edge trimming, and winding into a mother roll, and then the finished film is obtained by slitting.

[0066] Example 5

[0067] Example 5 describes a preparation method of a BOPET film for a composite current collector, and the specific steps include: (compared with Example 1, the ratio of the water-based epoxy coating liquid is changed)

[0068] (1) Preparation of water-based epoxy coating liquid

[0069] 25 parts by mass of water-based epoxy emulsion K-020 is added into a mixing tank, 68.6 parts by mass of deionized water is added, stirring is carried out at 500 rpm, and then 2.5 parts by mass of water-based silica sol LS-50, 0.7 parts by mass of defoaming agent BW-225, and 0.7 parts of leveling agent BW-404 are continuously added, and the stirring is continued for 30 min, and finally 2.5 parts by mass of curing agent K-62 is added for thorough mixing, and the water-based epoxy coating liquid is obtained.

[0070] (2) Preparation of online coated BOPET film

[0071] The BOPET film in this embodiment is a typical three-layer co-extrusion polyester film. The A layer (upper surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of the bright polyester chips is 60%, the mass fraction of the nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of the nano-CaCO3 modified anti-adhesion masterbatch is 20%. The B layer (core layer) contains graphene modified bright polyester chips ①. The C layer (lower surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of the bright polyester chips is 60%, the mass fraction of the nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of the nano-CaCO3 modified anti-adhesion masterbatch is 20%.

[0072] The B layer raw material is pre-crystallized at 165°C, then sent to a fluidized bed and a drying tower for air drying and impurity removal, and then enters a single screw extruder 1, melts and extrudes at 275°C to a filter screen, and finally transported to the die head after metering by a melt pump. The A layer raw material is directly sent to a single screw extruder 2, melts and extrudes at 280°C, and the melt is vacuum dried to remove water, then transported to the die head after metering by a filter screen and a melt pump. The C layer and the A layer share a single screw extruder 2, and are transported to each surface layer through a flow divider at the die head.

[0073] The melts of each layer are collected at the die head to form a three-layer structure of the molten film, and slowly flow down from the film lip at the same time, and tightly adhere to the surface of the 29°C cold roller under the action of 6.8kV high voltage static electricity, and cast into a polyester thick sheet.

[0074] The obtained thick sheet is put into the longitudinal stretching section, and stretched longitudinally under the conditions of preheating temperature 85°C, stretching temperature 101°C, and stretching ratio 3.1, and then the outlet film A and C surfaces are sequentially subjected to corona treatment, and then a uniform layer of water-based epoxy coating liquid is coated on both surfaces of the film through a network roller online coating equipment, with a coating amount of 2.5g / m 2 After that, the film enters the transverse stretching section, and stretched transversely under the conditions of preheating temperature 90°C, stretching temperature 105°C, setting temperature 225°C, and stretching ratio 3.2, and cooled at 25°C to obtain a biaxially stretched polyester film.

[0075] The finally formed film enters the traction section to be flattened, measured in thickness, trimmed, and collected into a mother roll, and then the finished film is obtained by slitting.

[0076] Example 6

[0077] Example 6 describes a method for preparing a BOPET film for composite current collector, and the specific steps include: (compared with Example 1, the A / C layer raw material ratio is changed)

[0078] (1) Preparation of aqueous epoxy coating solution

[0079] An aqueous epoxy emulsion K-020 of 20 parts by mass was added into a mixing tank, 75 parts by mass of deionized water was added, stirring was carried out at 500 rpm, and then 2 parts by mass of aqueous silica sol LS-50, 0.5 parts by mass of defoaming agent BW-225, and 0.5 parts of leveling agent BW-404 were continuously added thereto, stirring was continued for 30 min, and finally 2 parts by mass of curing agent K-62 was added for thorough mixing, to obtain an aqueous epoxy coating solution.

[0080] (2) Preparation of BOPET film by online coating

[0081] The BOPET film in this embodiment is a typical three-layer co-extruded polyester film, the A layer (upper surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 70%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 15%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 15%; the B layer (core layer) contains graphene modified bright polyester chips ①; and the C layer (lower surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 70%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 15%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 15%.

[0082] The B layer raw material was pre-crystallized at 165℃, then sent into a fluidized bed and a drying tower for air blowing drying and impurity removal, and then into single screw extruder 1 for melting and extrusion onto a filter screen at 275℃, and finally metered by a melt pump and delivered to a die head; the A layer raw material was directly sent into single screw extruder 2 for melting and extrusion at 280℃, and the melt was vacuum dried to remove water, and then metered by a filter screen and a melt pump and delivered to a die head; the C layer and the A layer shared single screw extruder 2, and were delivered to each surface layer through a flow divider at the die head.

[0083] The melts of each layer were gathered at the die head to form a three-layer molten film sheet, which was slowly and uniformly cast from the film lip under the action of 6.8kV high voltage static electricity, and tightly attached to the surface of a 29℃ cold roller to form a polyester thick sheet.

[0084] The obtained thick sheet was passed to a longitudinal stretching section, and stretched longitudinally under the conditions of preheating temperature 85℃, stretching temperature 101℃, and stretching ratio 3.1, and then the outlet film A and C surfaces were sequentially subjected to corona treatment, and then a uniform layer of aqueous epoxy coating solution was coated on both surfaces of the film by an online coating equipment with a coating amount of 2.5g / m 2After that, the film enters the transverse stretching section, and is stretched in the transverse direction under the conditions of a preheating temperature of 90°C, a stretching temperature of 105°C, a setting temperature of 225°C, and a stretching ratio of 3.2, and is cooled at 25°C to obtain a biaxially stretched polyester film.

[0085] The finally shaped film enters the traction section to be flattened, measured in thickness, trimmed, and collected into a mother roll, and then cut into finished film.

[0086] Example 7

[0087] Example 7 describes a method for preparing a BOPET film for a composite current collector, which includes the following specific steps: (compared with Example 1, the A / C layer raw material ratio is changed)

[0088] (1) Preparation of water-based epoxy coating solution

[0089] 20 parts by mass of water-based epoxy emulsion K-020 was added into a mixing tank, 75 parts by mass of deionized water was added, stirring was carried out at 500 rpm, and then 2 parts by mass of water-based silica sol LS-50, 0.5 parts by mass of defoaming agent BW-225, and 0.5 parts of leveling agent BW-404 were continuously added, stirring was continued for 30 min, and finally 2 parts by mass of curing agent K-62 was added for thorough mixing to obtain a water-based epoxy coating solution.

[0090] (2) Preparation of on-line coated BOPET film

[0091] The BOPET film in this example is a typical three-layer co-extruded polyester film, which includes an A layer (upper surface layer) containing bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 50%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 25%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 25%; a B layer (core layer) containing graphene modified bright polyester chips ①; and a C layer (lower surface layer) containing bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 50%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 25%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 25%.

[0092] The B layer raw material is pre-crystallized at 165°C and then sent into a fluidized bed, drying tower for air drying and impurity removal, and then into single screw extruder 1 for melting and extrusion at 275°C to a filter screen, and finally conveyed to the die head after metering by a melt pump; the A layer raw material is directly sent into single screw extruder 2 for melting and extrusion at 280°C, and the melt is vacuum dried to remove water, and then conveyed to the die head after metering by a filter screen and a melt pump; the C layer shares the single screw extruder 2 with the A layer, and is conveyed to each surface layer through a flow divider at the die head.

[0093] The melts of each layer are gathered at the die head to form a three-layer structure of the molten film sheet, and slowly flow down uniformly from the film lip, and closely adhere to the surface of the 29°C cold roller under the action of 6.8kV high voltage static electricity, and cast into a polyester thick sheet.

[0094] The obtained thick sheet is sent to the longitudinal stretching section, and stretched longitudinally under the conditions of preheating temperature 85°C, stretching temperature 101°C, and stretching ratio 3.1, and then the outlet film A and C surfaces are treated by corona treatment in sequence, and then a uniform layer of water-based epoxy coating liquid is coated on both surfaces of the film by a screen roller online coating device, with a coating amount of 2.5g / m 2 , and then the film enters the transverse stretching section, and stretched transversely under the conditions of preheating temperature 90°C, stretching temperature 105°C, setting temperature 225°C, and stretching ratio 3.2, and cooled at 25°C to obtain a biaxially stretched polyester film.

[0095] The finally formed film enters the traction section for flattening, thickness measurement, edge trimming, and is collected into a mother roll, and then the finished film is obtained by slitting.

[0096] Comparative Example 1

[0097] Comparative Example 1 describes a preparation method of a BOPET film for a composite current collector, which includes the following specific steps: (the film is not coated with an anticorrosion functional layer compared with Example 1)

[0098] (1) Preparation of non-online coated BOPET film

[0099] The BOPET film in this embodiment is a typical three-layer co-extrusion polyester film. The A layer (upper surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 60%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 20%. The B layer (core layer) contains graphene modified bright polyester chips ①. The C layer (lower surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 60%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 20%.

[0100] The B layer raw material is pre-crystallized at 165°C and then sent to a fluidized bed and a drying tower for air drying and impurity removal, and then enters single screw extruder 1, melts and extrudes to a filter screen at 275°C, and finally is conveyed to the die head after metering by a melt pump. The A layer raw material is directly sent to single screw extruder 2, melts and extrudes at 280°C, and the melt is vacuum dried to remove water, and then is conveyed to the die head after metering by a filter screen and a melt pump. The C layer shares single screw extruder 2 with the A layer, and is conveyed to each surface layer through a flow divider at the die head.

[0101] The melts of each layer are gathered at the die head to form a three-layer structure of the molten film sheet, and are slowly and uniformly cast from the film lip under the action of 6.8kV high voltage static electricity, and are tightly attached to the surface of the 29°C cold roller to form a polyester thick sheet.

[0102] The obtained thick sheet is put into the longitudinal stretching section, and is stretched longitudinally under the conditions of preheating temperature 85°C, stretching temperature 101°C, and stretching ratio 3.1, and then the outlet film A and C surfaces are sequentially subjected to corona treatment, and then a uniform layer of water-based epoxy coating liquid is coated on both surfaces of the film through a network roller online coating equipment, with a coating amount of 2.5g / m 2 After that, the film enters the transverse stretching section, and is stretched transversely under the conditions of preheating temperature 90°C, stretching temperature 105°C, setting temperature 225°C, and stretching ratio 3.2, and is cooled at 25°C to obtain a biaxially stretched polyester film.

[0103] The finally formed film enters the traction section to be flattened, thickness measured, edges trimmed, and collected into a mother roll, and then the finished film is obtained by slitting.

[0104] Comparative Example 2

[0105] Comparative Example 2 describes a method for preparing a BOPET film for composite current collector, which includes the following specific steps: (compared with Example 1, the B layer raw material of the film is changed)

[0106] (1) Preparation of aqueous epoxy coating solution

[0107] An aqueous epoxy emulsion K-020 of 20 parts by mass was added into a mixing tank, 75 parts by mass of deionized water was added, stirring was carried out at 500 rpm, and then 2 parts by mass of aqueous silica sol LS-50, 0.5 parts by mass of defoaming agent BW-225, and 0.5 parts of leveling agent BW-404 were continuously added thereto, stirring was continued for 30 min, and finally 2 parts by mass of curing agent K-62 was added for thorough mixing, to obtain an aqueous epoxy coating solution.

[0108] (2) Preparation of online coated BOPET film

[0109] The BOPET film in this embodiment is a typical three-layer co-extruded polyester film, the A layer (upper surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 60%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 20%; the B layer (core layer) is 100% bright polyester chips; and the C layer (lower surface layer) contains bright polyester chips, nano-SiO2 modified anti-adhesion masterbatch, and nano-CaCO3 modified anti-adhesion masterbatch, wherein the mass fraction of bright polyester chips is 60%, the mass fraction of nano-SiO2 modified anti-adhesion masterbatch is 20%, and the mass fraction of nano-CaCO3 modified anti-adhesion masterbatch is 20%.

[0110] The B layer raw material was pre-crystallized at 165°C, then sent into a fluidized bed and a drying tower for air blowing drying and impurity removal, and then into single-screw extruder 1 for melting and extrusion onto a filter screen at 275°C, and finally metered by a melt pump and delivered to a die head; the A layer raw material was directly sent into single-screw extruder 2 for melting and extrusion at 280°C, and the melt was vacuum dried to remove water, and then metered by a filter screen and a melt pump and delivered to a die head; the C layer and the A layer shared single-screw extruder 2, and were delivered to each surface layer through a flow divider at the die head.

[0111] The melts of each layer were gathered at the die head to form a three-layer structure of the molten film sheet, and were slowly and uniformly cast from the film lip, and were closely attached to the surface of a cold roller at 29°C under the action of high-voltage electrostaticity at 6.8 kV, to form a polyester thick sheet.

[0112] The obtained thick sheet was passed to a longitudinal stretching section, and was stretched longitudinally under the conditions of a preheating temperature of 85°C, a stretching temperature of 101°C, and a stretching ratio of 3.1, and then the A and C surfaces of the outlet film were sequentially subjected to corona treatment, and then a uniform layer of aqueous epoxy coating solution was coated on both surfaces of the film through a network roller online coating equipment, and the coating amount on each surface was 2.5 g / m 2Afterwards, the film enters the transverse stretching section, and is stretched in the transverse direction under the conditions of preheating temperature 90℃, stretching temperature 105℃, setting temperature 225℃, and stretching ratio 3.2, and is cooled at 25℃ to obtain the biaxially stretched polyester film.

[0113] The finally shaped film enters the traction section to be flattened, measured in thickness, trimmed, and collected into a mother roll, and then the finished film is obtained by slitting.

[0114] Comparative Example 3

[0115] Comparative Example 3 describes a method for preparing a BOPET film for composite current collector, which comprises the following specific steps: (compared with Example 1, the raw materials of the A / C layers of the film are changed)

[0116] (1) Preparation of the aqueous epoxy coating solution

[0117] 20 parts by mass of the aqueous epoxy emulsion K-020 was added into a mixing tank, 75 parts by mass of deionized water was added, and stirring was carried out at 500 rpm, while 2 parts by mass of the aqueous silica sol LS-50, 0.5 parts by mass of the defoaming agent BW-225, and 0.5 parts by mass of the leveling agent BW-404 were continuously added, and the stirring was continued for 30 min, and finally 2 parts by mass of the curing agent K-62 was added for thorough mixing, to obtain the aqueous epoxy coating solution.

[0118] (2) Preparation of the BOPET film coated online

[0119] The BOPET film in this example is a typical three-layer co-extruded polyester film, the A layer (upper surface layer) contains bright polyester chips, commercial anti-adhesion masterbatch K, and commercial anti-adhesion masterbatch S, wherein the mass fraction of the bright polyester chips is 60%, the mass fraction of the commercial anti-adhesion masterbatch K is 20%, and the mass fraction of the commercial anti-adhesion masterbatch S is 20%; the B layer (core layer) contains graphene-modified bright polyester chips ①; and the C layer (lower surface layer) contains bright polyester chips, commercial anti-adhesion masterbatch K, and commercial anti-adhesion masterbatch S, wherein the mass fraction of the bright polyester chips is 60%, the mass fraction of the commercial anti-adhesion masterbatch K is 20%, and the mass fraction of the commercial anti-adhesion masterbatch S is 20%.

[0120] The B layer raw material was pre-crystallized at 165℃, and then was sent into a fluidized bed and a drying tower for air blowing drying and impurity removal, and then was sent into a single-screw extruder 1 for melting and extrusion onto a filter screen at 275℃, and finally was sent to the die head through a melt pump for metering and conveying; the A layer raw material was directly sent into a single-screw extruder 2 for melting and extrusion at 280℃, and the melt was vacuum dried to remove water, and then was sent to the die head through a filter screen and a melt pump for metering and conveying; the C layer and the A layer shared the single-screw extruder 2, and were sent to each surface layer through a flow divider at the die head.

[0121] The melt of each layer converges at the die head to form a molten film sheet of three-layer structure, and is slowly and uniformly cast from the film lip, while being closely attached to the surface of a cold roller at 29℃ under the action of high voltage electrostatic field of 6.8kV, and is cast into a polyester thick sheet.

[0122] The obtained thick sheet is passed to a longitudinal stretching section, and is stretched longitudinally under the conditions of a preheating temperature of 85℃, a stretching temperature of 101℃ and a stretching ratio of 3.1, and then the outlet film is subjected to corona treatment in sequence on the A and C surfaces, and then a uniform layer of water-based epoxy coating liquid is coated on both surfaces of the film through a network roller on-line coating device, with a coating amount of 2.5g / m 2 After that, the film enters a transverse stretching section, and is stretched transversely under the conditions of a preheating temperature of 90℃, a stretching temperature of 105℃, a setting temperature of 225℃ and a stretching ratio of 3.2, and is cooled at 25℃ to obtain a biaxially stretched polyester film.

[0123] The finally shaped film enters a traction section to be flattened, thickness measured, trimmed and collected into a mother roll, and then the finished film is obtained by slitting.

[0124] Film performance test:

[0125] The finished films in Examples 1-7 and Comparative Examples 1-3 are subjected to performance tests, in which the test items include biaxial tensile strength, Young's modulus, heat shrinkage, resistivity, electrolyte immersion, and the specific test process is as follows:

[0126] Tensile strength / Young's modulus: a strip-shaped sample with a length of 150mm and a width of 15mm is cut from the film sample, and the short edges of the sample are clamped by the upper and lower clamps of the tensile tester with a distance of 100mm. The instrument is started, and the sample is stretched at a constant speed of 100mm / min until the sample is broken. Finally, the tensile strength value and the Young's modulus value are read in the matching analysis software, and each film sample is tested in three groups in the horizontal and vertical directions, and the average value is taken.

[0127] Heat shrinkage: a strip-shaped sample with a length of 150mm and a width of 20mm is cut from the film sample, and a line is drawn at each end of the sample with a distance of 25mm, so that the distance between the lines is 100mm. Then the oven temperature is set to 150℃, and the sample is placed in the oven and heated for 30min, then taken out and cooled. The distance between the two lines is measured with a scale, and the heat shrinkage of the sample is calculated, and the calculation method is shown in formula (1). Each film sample is tested in three groups in the horizontal and vertical directions, and the average value is taken.

[0128]

[0129] In the formula: S is the heat shrinkage, %;

[0130] L0 is the distance between the lines before heating, mm;

[0131] L1 is the distance between the marks after heating, mm.

[0132] Resistivity: A 100 mm x 100 mm square sample was cut from the film sample, connected to the input button and high voltage button of the high resistance meter respectively, and then the test voltage was adjusted to 500 V. The surface resistance value of the sample was measured and recorded. Each film sample was tested in parallel for 3 groups, and the average value was taken.

[0133] Electrolyte immersion: A 50 mm x 50 mm square sample was cut from the film sample and placed in a jar, 20 mL of lithium hexafluorophosphate (LiPF6) electrolyte was added, the jar was sealed with a plug and sealed with a sealing film to isolate air, then placed in a vacuum drying oven, vacuumed (equipment vacuum degree ~ 133 pa), heated to 80℃, kept for 7h, then taken out, and the film appearance corrosion degree was observed.

[0134] The test results of Examples 1-7 and Comparative Examples 1-3 are as follows:

[0135]

[0136] Results and analysis

[0137] According to the above test results, it can be seen that the film surface coated with a water-based epoxy anticorrosive layer has good chemical inertness, and the corrosion resistance to electrolyte at high temperature is significantly improved, which can better meet the use requirements of the prepared battery under harsh working conditions. At the same time, it is found that the mixing of graphene in the core layer of the film can effectively reduce the resistivity, which not only helps to eliminate the adverse effects of static electricity in the production process, but also makes the film itself have certain electronic transmission function, making up for the defect of low electronic transmission efficiency of the composite current collector battery. The addition of the same nano functional masterbatch further improves the mechanical properties of the film, and the corresponding thermal shrinkage rate is effectively controlled, indicating that the presence of nano anti-adhesion particles can play a positive role in the behavior characteristics of the resin molecule stretching process. It is worth noting that when the core layer does not add graphene, the mechanical properties of the film also decrease to a certain extent. Considering the high-strength structure of graphene itself, when it is blended with resin molecules, a special interface effect may be produced, which helps to improve the mechanical properties of the formed film.

[0138] In the description of the present specification, the description referring to the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0139] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A BOPET film for composite current collector, comprising from top to bottom: an upper surface layer, a core layer, and a lower surface layer; and a water-based epoxy coating solution coated on the upper and lower surfaces of the film. The graphene-modified bright polyester chip comprises nanographene material and polyethylene terephthalate. The upper surface layer comprises: large light polyester chips, nano Modified anti-sticking masterbatch, nano Modified anti-sticking masterbatch The raw material of the core layer comprises: graphene modified large-draft polyester chip; the lower surface layer comprises: large-draft polyester chip, nano modified anti-adhesion master batch, nano modified anti-adhesion master batch; The nanos The modified anti-sticking masterbatch includes nanos particles, terephthalic acid, isophthalic acid, and ethylene glycol; The nanos The modified anti-sticking masterbatch includes nanos particles, terephthalic acid, isophthalic acid, and ethylene glycol; The mass fraction of the upper and lower surface layers of the light polyester chip is 60%, and the upper and lower surface layers of the nano The mass fraction of the modified anti-adhesion masterbatch is 20%, and the upper and lower surface layers of the nano The mass fraction of the modified anti-adhesion masterbatch is 20%.

2. The BOPET film for composite current collector according to claim 1, characterized in that, The water-based epoxy coating solution comprises a water-based epoxy emulsion, a water-based silica sol, a defoaming agent, and a leveling agent.

3. The BOPET film for composite current collector according to claim 1, characterized in that, The method comprises the following steps:

4. The process for the preparation of BOPET film for composite current collector according to any one of claims 1-3, characterized by the fact that, The water-based epoxy emulsion is added with deionized water and stirred, and then the water-based silica sol, the defoaming agent, and the leveling agent are continuously added and stirred, and finally the curing agent is added and mixed to obtain the water-based epoxy coating solution. The core layer raw material is pre-crystallized, air-dried, and impurity-removed, and then melted, extruded to a filter screen, and finally conveyed to a die head; the upper surface layer raw material is melted and extruded, and the melt is vacuum-dried, and then conveyed to the die head; the lower surface layer and the upper surface layer share a single screw extruder, and are conveyed to the respective surface layers through a flow divider at the die head; The core layer, the upper surface layer, and the lower surface layer melts are conveyed to the three-layer die head through a melt pipe and a melt pump for accurate metering, and then combined, cast, and attached to the surface of a cold roller under the action of static electricity to form a polyester thick sheet having the upper surface layer, the core layer, and the lower surface layer. The thick sheet is longitudinally stretched, and then subjected to double-sided corona treatment, and then the water-based epoxy coating solution is coated on both surfaces of the film, and then the film enters a transverse stretching section for preheating, stretching, setting, and cooling in sequence. The finally formed film enters a traction section for flattening, thickness measuring, edge trimming, and winding into a mother roll, and then cut into finished film. 5.Use of the BOPET film for composite current collector according to any one of claims 1-3 or prepared by the preparation method of claim 4 in manufacturing an electric cell. ​

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