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

Abstract

A composite film for a current collector, a preparation method therefor, and the use thereof. The composite film comprises a base film (B) and a polyimide layer (A) provided on at least one surface of the base film (B). The base film (B) comprises a base film (B) hydrophilically modified by a modification compound, the molecular structure of the modification compound containing a carbon-carbon double bond and a functional group, and the functional group comprising at least one of an anhydride group, a carboxyl group, a hydroxyl group, an amide group, or an ester group; the polyimide layer is prepared by an aqueous phase monomer and an organic phase monomer undergoing an interfacial polymerization reaction on the surface of the base film. The composite film has excellent heat resistance and mechanical properties, exhibits high adhesion to metal conductive layers, so as to prevent metal conductive layers in composite current collectors from peeling off, and in addition, is not prone to film breakage during the preparation process , thus achieving high yield and low cost.

Description

Composite film for current collector and preparation method and application thereof TECHNICAL FIELD

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

[0002] The current collector is one of indispensable electrode materials of a lithium ion battery, has the important functions of bearing active substances and collecting micro-current, and can be divided into a traditional current collector and a composite current collector. The traditional current collector is mostly prepared by calendering, while the composite current collector has a "sandwich" structure, the inner layer of which is a polymer high molecular layer such as polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE) and the like, and the two sides are metal conductive layers (such as Al or Cu and the like). Compared with the traditional current collector, the composite current collector based on the polymer film has the characteristics of low cost, light weight and good internal insulation. 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 used in the battery.

[0003] Among the many composite current collectors, the composite current collector based on the polypropylene film or the polyethylene film is relatively common. However, in the process of preparing the composite current collector with the polypropylene film or the polyethylene film as the base film, the surface tension of the polypropylene film or the polyethylene film is weak due to the weak polarity of the material itself, which leads to poor bonding with the metal layer and easy peeling of the metal layer. In addition, the mechanical properties and heat resistance of the polypropylene film or the polyethylene film are poor, and the film is prone to breakage during the preparation of the composite current collector, which affects the yield; in addition, the mechanical properties of the prepared composite current collector are poor, which also affects the subsequent processing of the electrode sheet.

[0004] Therefore, it is an urgent problem to be solved in the field to develop a composite current collector material which has good adhesion with the metal layer, excellent mechanical properties and heat resistance, is not prone to film breakage during the preparation of the current collector, has high yield and does not affect the subsequent processing.

[0005] SUMMARY

[0006] The following is a summary of the subject matter of the detailed description. This summary is not intended to limit the scope of the claims.

[0007] In a first aspect, the present application relates to a composite film for current collector, comprising a base film and a polyimide layer arranged on at least one surface of the base film; the base film comprises a base film modified by a modified compound; the modified compound comprises a carbon-carbon double bond and a functional group in the molecular structure; the functional group comprises at least one of an acid anhydride, a carboxyl group, a hydroxyl group, an amide group or an ester group; the polyimide layer comprises a polyimide layer prepared by interfacial polymerization of an aqueous monomer and an organic monomer on the surface of the base film.

[0008] In a second aspect, the present application relates to a preparation method of the composite film for current collector according to the first aspect, comprising the following steps:

[0009] sequentially treating at least one surface of the base film with an aqueous monomer solution and an organic monomer solution to perform interfacial polymerization, thereby obtaining the composite film for current collector; the base film comprises a base film modified by a modified compound.

[0010] In a third aspect, the present application relates to a composite current collector, comprising a first protective layer, a first metal conductive layer, a base, a second metal conductive layer and a second protective layer arranged in sequence; the base comprises the composite film for current collector according to the first aspect.

[0011] In a fourth aspect, the present application relates to a lithium ion battery, comprising the composite film for current collector according to the first aspect and / or the composite current collector according to the third aspect.

[0012] Compared with the related art, the present application has the following beneficial effects:

[0013] In the present application, the base film is modified by hydrophilization, and then a polyimide layer is arranged on the surface of the base film by interfacial polymerization, so that the obtained composite film has excellent heat resistance and mechanical properties, high adhesion to metal, and avoids the problem of metal layer falling off of the current collector; and in the preparation process, film breakage is less likely to occur, the yield is high, the subsequent processing of the pole piece is not affected, and the cost is low.

[0014] Other aspects can be apparent after reading and understanding the drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1 is a structural schematic diagram of a composite film according to an embodiment of the present application;

[0016] In the drawings, A represents a polyimide layer; and B represents a base film.

[0017] FIG. 2 is a structural schematic diagram of a composite current collector according to an embodiment of the present application;

[0018] 1 - first protective layer; 2 - first metal conductive layer; 3 - substrate; 4 - second metal conductive layer; 5 - second protective layer. DETAILED DESCRIPTION

[0019] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be described in detail below. It should be noted that the various aspects, features, embodiments and advantages described in the present application can be compatible and / or combined together.

[0020] Unless otherwise defined, the meanings of the scientific and technical terms in the present specification are the same as those generally understood by those skilled in the art.

[0021] The present application relates to a composite film for current collector, a preparation method thereof, a composite current collector comprising the same, and a lithium ion battery comprising the same or the composite current collector.

[0022] In a first aspect, the present application relates to a composite film for current collector, comprising a base film and a polyimide layer disposed on at least one surface of the base film; the base film comprises a base film modified by a hydrophilic modification compound; the molecular structure of the modification compound contains a carbon-carbon double bond and a functional group; the functional group comprises at least one of an acid anhydride, a carboxyl group, a hydroxyl group, an amide group or an ester group; the polyimide layer comprises a polyimide layer prepared by interfacial polymerization of water phase monomers and organic phase monomers on the surface of the base film.

[0023] In the present application, by using a modification compound with a specific structure to modify the base film, the adhesion of the base film and the polyimide layer is improved, and the polyimide layer is prevented from falling off; after the hydrophilic modification, the polyimide layer is disposed on at least one surface of the base film through interfacial polymerization, and the obtained composite film has excellent heat resistance and mechanical properties, high adhesion to the metal conductive layer, and is prevented from falling off; and during the preparation process, film breakage is less likely to occur, the yield is high, the subsequent processing of the pole piece is not affected, and the cost is low.

[0024] In the present application, the method for hydrophilic modification comprises one or more of plasma-induced graft polymerization, radiation (ultraviolet light and electron beam, ion beam, gamma ray) treatment, block copolymer modification or graft copolymer modification; in some embodiments, graft copolymer modification is preferred.

[0025] In some embodiments, the grafting rate of the modifying compound in the base film is 0.1-5%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.6%, 2.7%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, or a range defined by any two of them.

[0026] In the present application, the grafting rate is the ratio of the mass of the grafted compound to the total mass of the base film; when the grafting rate is too low, the surface tension is not improved significantly; when the grafting rate is too high, defects are easily formed, affecting the yield of the product.

[0027] In some embodiments, the modifying compound comprises any one or a combination of at least two of maleic anhydride, acrylic acid, polyvinyl alcohol, acrylamide, methyl methacrylate, or azo-methylene double acrylamide.

[0028] In some embodiments, the base film modified by the hydrophilic modification of the modifying compound is prepared by a method comprising:

[0029] (1) treating the unmodified base film with a hydroxylating agent to obtain a base film containing hydroxyl groups on the surface; and

[0030] (2) treating the base film obtained in step (1) with a modifying compound to obtain the base film modified by the hydrophilic modification.

[0031] In some embodiments, before the treatment with the hydroxylating agent, the method further comprises the steps of soaking the unmodified base film in an alcohol solvent for 0.5-1.5 h, soaking in water, replacing the alcohol in the film with water, and removing the excess water on the surface of the film.

[0032] In some embodiments, the treatment in step (1) is performed for 0.5-2 h, for example, it can be 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2 h, or a range defined by any two of them.

[0033] In the present application, the treatment time of the hydroxylating agent is within a specific range, which is beneficial to improve the mechanical properties and adhesion to metal of the composite film and reduce the thermal shrinkage of the composite film; if the treatment time is too short, the performance improvement is not obvious; if the treatment time is too long, the surface of the base film is damaged due to oxidative degradation, the bonding force with the polyimide layer is poor, thereby the mechanical properties of the composite film are significantly reduced and the defective rate during the preparation of the composite current collector is significantly increased.

[0034] In some embodiments, the temperature of the treatment in step (1) is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, 80°C or within a range defined by any two of them.

[0035] In some embodiments, the hydroxylating agent includes any one or a combination of at least two of sodium persulfate, ammonium persulfate, ammonium persulfate or ozone.

[0036] In some embodiments, the hydroxylating agent includes a hydroxylating agent solution, and the mass concentration of the hydroxylating agent in the hydroxylating agent solution is 10-20%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or within a range defined by any two of them.

[0037] In some embodiments, the modifying compound in step (2) includes a modifying compound solution.

[0038] In some embodiments, the mass concentration of the modifying compound in the modifying compound solution is 1-10%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or within a range defined by any two of them.

[0039] In some embodiments, the modifying compound solution further includes an initiator, and the concentration of the initiator is 0.6-1 g / L, for example, it can be 0.6 g / L, 0.62 g / L, 0.64 g / L, 0.66 g / L, 0.68 g / L, 0.7 g / L, 0.72 g / L, 0.74 g / L, 0.76 g / L, 0.78 g / L, 0.8 g / L, 0.82 g / L, 0.84 g / L, 0.86 g / L, 0.88 g / L, 0.9 g / L, 0.92 g / L, 0.94 g / L, 0.96 g / L, 0.98 g / L, 1 g / L or within a range defined by any two of them.

[0040] In the present application, the initiator concentration is in a specific range, which is beneficial to improve the mechanical properties of the composite film and the adhesion to metal, reduce the thermal shrinkage of the composite film, and reduce the defective rate of the composite current collector; when the initiator concentration is too high, due to the limited grafting position on the surface of the base film, the self-polymerization tendency between monomers is intensified, the monomers are rapidly consumed, and the grafting rate will show a downward trend, thereby leading to performance reduction; when the initiator concentration is too low, the grafting rate is slow, the grafting rate is insufficient, and the hydrophilic modification of the base film is insufficient.

[0041] In some embodiments, the treatment time in step (2) is 5-15 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min or within a range defined by any two of them.

[0042] In the present application, the treatment time (i.e. the grafting modification time) in step (2) is in a specific range, which is beneficial to improve the mechanical properties of the composite film and the adhesion to metal, reduce the thermal shrinkage of the composite film, and reduce the defective rate of the composite current collector.

[0043] In some embodiments, the initiator includes any one or a combination of at least two of dibenzoyl peroxide, cerium ammonium nitrate or l,1-di-tert-butyl peroxy-3,3,5-trimethylcyclohexane.

[0044] In the present application, after the treatment in step (2) is completed, the obtained base film is further subjected to a washing step.

[0045] In some embodiments, after the treatment in step (2) is completed, a hydrolysis step is further included.

[0046] In some embodiments, the hydrolysis time is 5-15 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min or within a range defined by any two of them.

[0047] In the present application, the hydrolysis is carried out under alkaline conditions, specifically, the base film of the grafting modified compound is soaked in a 1 mol / L alkaline solution, hydrolyzed for 5-15 min, so that part of the amide group, acid anhydride group or ester group is hydrolyzed into carboxyl group with stronger hydrophilicity, and after pure water washing, a hydrophilic modified base film is obtained.

[0048] In the present application, the hydrolysis time is within a specific range, which is beneficial to improve the mechanical properties and adhesion to metal of the composite film, reduce the thermal shrinkage of the composite film, and reduce the defective rate of the composite current collector; if the hydrolysis time is too long, the base film will be damaged, and the mechanical properties, heat resistance, and adhesion will be poor, and the defective rate will increase.

[0049] In some embodiments, the mass ratio of the aqueous phase monomer to the organic phase monomer is 1:(1-3), for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3, or within a range defined by any two of them.

[0050] In the present application, the mass ratio of the aqueous phase monomer to the organic phase monomer is within a specific range, which is beneficial to improve the mechanical properties and adhesion to metal of the composite film, reduce the thermal shrinkage of the composite film, and reduce the defective rate of the composite current collector; if the mass of the organic phase monomer is too large, water will participate in the interfacial polymerization reaction, resulting in a loose interfacial polymerization layer, and thus leading to poor performance of the composite film.

[0051] In some embodiments, the aqueous phase monomer comprises an amine monomer.

[0052] Preferably, the amine monomer comprises any one of methylamine, isopropylamine, cyclohexylamine, dodecylamine, dimethyl ethylenediamine, triethylenetetramine, ethylenediamine, propylenediamine, hexylenediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, or piperazine, or a combination of at least two of them.

[0053] In some embodiments, the organic phase monomer comprises an acyl chloride compound and / or an acid anhydride compound.

[0054] In some embodiments, the acyl chloride compound comprises any one of trimesoyl chloride, pyromellitic acid chloride, isophthaloyl chloride, or terephthaloyl chloride, or a combination of at least two of them.

[0055] In some embodiments, the acid anhydride compound comprises pyromellitic dianhydride and / or 3,3',4,4'-diphenyl tetracarboxylic anhydride.

[0056] In some embodiments, the base film comprises a polypropylene film and / or a polyethylene film.

[0057] In some embodiments, the base film has a porosity of 10-50%, for example, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or a range defined by any two of them; a pore size of 10-300 nm, for example, 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm, or a range defined by any two of them; and further preferably, a porosity of 20-40% and a pore size of 50-200 nm.

[0058] In the present application, if the porosity of the base film is too low, the bonding with the polyimide layer is not strong enough; if the porosity is too high, the supporting performance of the base film is poor; if the pore size is too small, the resistance is increased; and if the pore size is too large, the base film is easily punctured during the subsequent rolling process of coating the electrode material.

[0059] In some embodiments, the thickness of the composite film is ≥2 μm, for example, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, or 32 μm, etc.

[0060] In the present application, considering both the energy density of the material and the difficulty of production (the thinner the film, the greater the difficulty of production, and the lower the yield), in some embodiments, the thickness of the composite film is preferably 2-20 μm.

[0061] In some embodiments, the thickness of the polyimide layer accounts for 5-10% of the total thickness of the composite film for current collector, for example, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a range defined by any two of them.

[0062] In some embodiments, the composite film for current collector comprises a base film and a polyimide layer arranged on one surface of the base film.

[0063] In some embodiments, the composite film for current collector comprises a base film and a polyimide layer arranged on both surfaces of the base film.

[0064] In a second aspect, the present application relates to a preparation method of the composite film for current collector according to the first aspect, which comprises the following steps:

[0065] The at least one surface of the base film is treated with a water-phase monomer solution and an organic-phase monomer solution in sequence to perform an interfacial polymerization reaction, thereby obtaining the composite film for the current collector; the base film comprises a base film modified by a hydrophilic modification compound.

[0066] In some embodiments, the water-phase monomer solution is used to treat the base film for 20-30 min, for example, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, or a range defined by any two of them.

[0067] In some embodiments, the mass concentration of the water-phase monomer in the water-phase monomer solution is 0.5-3 g / L, for example, 0.5 g / L, 0.6 g / L, 0.8 g / L, 1 g / L, 1.2 g / L, 1.4 g / L, 1.6 g / L, 1.8 g / L, 2 g / L, 2.2 g / L, 2.4 g / L, 2.6 g / L, 2.8 g / L, 3 g / L, or a range defined by any two of them.

[0068] In some embodiments, the water-phase monomer solution further comprises at least one of an acid acceptor, a surfactant, or a phase transfer catalyst.

[0069] In some embodiments, the acid acceptor comprises at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, or potassium hydroxide.

[0070] In some embodiments, the surfactant comprises at least one of sodium dodecyl sulfate, hexadecyl trimethyl ammonium bromide, sodium dodecyl benzene sulfonate, sodium hexadecyl sulfate, dodecanol polyoxyethylene ether, dodecanol polyoxyethylene ether sulfate, sodium oleate diacetate, fatty alcohol polyoxyethylene ether, fatty acid triethanolamine salt, or alkyl phenol polyoxyethylene ether.

[0071] In some embodiments, the phase transfer catalyst comprises at least one of cyclodextrin, benzyl triethyl ammonium chloride, tetrabutyl ammonium bromide, tetrabutyl ammonium chloride, tetrabutyl ammonium hydrogen sulfate, trioctylmethyl ammonium chloride, dodecyl trimethyl ammonium chloride, or tributyl amine.

[0072] In some embodiments, the organic-phase monomer solution is used to treat the base film for 5-10 min, for example, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or a range defined by any two of them.

[0073] In some embodiments, the mass concentration of the organic phase monomer in the organic phase monomer solution is 1-5 g / L, for example, can be 1 g / L, 1.2 g / L, 1.4 g / L, 1.6 g / L, 1.8 g / L, 2 g / L, 2.2 g / L, 2.4 g / L, 2.6 g / L, 2.8 g / L, 3 g / L, 3.2 g / L, 3.4 g / L, 3.6 g / L, 3.8 g / L, 4 g / L, 4.2 g / L, 4.4 g / L, 4.6 g / L, 4.8 g / L, 5 g / L or within a range defined by any two of them.

[0074] In some embodiments, the solvent of the organic phase monomer solution comprises at least one of dimethylformamide, dimethylacetamide, dichloromethane, acetone, anhydrous methanol or tetrahydrofuran.

[0075] In some embodiments, the interface polymerization reaction further comprises the steps of treating with an imidization reagent and heat treatment after the interface polymerization reaction.

[0076] In some embodiments, the time of the imidization reagent treatment is 10-50 s, for example, can be 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s or within a range defined by any two of them.

[0077] In some embodiments, the imidization reagent comprises a dehydrating agent and a catalyst.

[0078] In the present application, the dehydrating agent comprises anhydride and / or tertiary amine compound; the catalyst comprises at least one of pyrrole imidazole, imidazole, triazole, triethylamine, pyridine or 2-methylpyridine.

[0079] In some embodiments, the temperature of the heat treatment is 130-150℃, for example, can be 130℃, 135℃, 140℃, 145℃, 150℃ or within a range defined by any two of them; the time is 2-4 h, for example, can be 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, 3 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h, 4 h or within a range defined by any two of them.

[0080] It should be noted that in the present application, the materials of the polyimide layers (such as water phase monomer, organic phase monomer) provided on the two surfaces of the base film can be the same or different; the thickness of the polyimide layers can be the same or different.

[0081] In a third aspect, the present application relates to a composite current collector, which comprises a first protective layer, a first metal conductive layer, a substrate, a second metal conductive layer and a second protective layer arranged in sequence; the substrate comprises the composite film for current collector according to the first aspect.

[0082] In some embodiments, the material of the first metal conductive layer and the second metal conductive layer each independently comprises any one or a combination of at least two of copper, copper alloy, aluminum or aluminum alloy.

[0083] In some embodiments, the total thickness of the first metal conductive layer and the second metal conductive layer is 700-1300 nm, for example, can be 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1050 nm, 1150 nm, 1200 nm, 1250 nm, 1300 nm or within a range defined by any two of them.

[0084] In some embodiments, the total thickness of the first protective layer and the second protective layer is 5-10% of the total thickness of the first metal conductive layer and the second metal conductive layer, for example, can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or within a range defined by any two of them.

[0085] In some embodiments, the material of the protective layer comprises at least one of a metal material (such as copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, etc.), a conductive polymer material (such as polyaniline, polycarbazole, polythiophene, polybenzothiadiazole, polystyrene mercaptan, polypyrrine, polystyrene, etc.) or an antioxidant material.

[0086] In some embodiments, the antioxidant material comprises benzotriazole, a substance generated by reaction of a metal with a passivator (such as basic chromium chromate), etc.

[0087] In this application, the purpose of the protective layer is to prevent the metal conductive layer from being chemically corroded.

[0088] In this application, the method for preparing the composite current collector comprises depositing metal on both surfaces of the substrate to obtain the first metal conductive layer and the second metal conductive layer arranged on both surfaces of the substrate; then coating the metal conductive layer with a protective layer material and drying to obtain the composite current collector.

[0089] In this application, the method for depositing metal comprises one or more of magnetron sputtering, vacuum evaporation, electroplating or chemical plating.

[0090] In a fourth aspect, the present application relates to a lithium ion battery comprising the composite film for current collector according to the first aspect and / or the composite current collector according to the third aspect.

[0091] The numerical ranges recited herein are inclusive of the endpoints and of any range that would be formed, even though that range would not explicitly be recited. Where a range of values is recited, it is meant to include all stated, interpolated, and extrapolated values, including the endpoints. To the extent that any numerical range is stated herein to include endpoints, those endpoints are also included to the exclusion of any intervening values that would not be included in the range.

[0092] For the purposes of the present application, the technical solutions and advantages thereof are more clearly apparent, the following further describes the present application with reference to the embodiments. It should be understood that the specific embodiments described herein are merely intended to explain the present application and are not intended to limit the present application.

[0093] The materials used in the present application are as follows:

[0094] Polypropylene-based film: purchased from Jiangsu Houshen New Energy Technology Co., Ltd., porosity 40%, pore size 20-30 nm, thickness 5 μm.

[0095] Preparation Example 1

[0096] The present preparation example provides a hydrophilic modified polypropylene film, which is prepared by the following method, and the preparation method comprises the following steps:

[0097] (1) after immersing the polypropylene-based film into methanol for 1 h, immersing it into pure water, replacing the methanol in the film with pure water, and removing the excess water on the surface of the film, immersing the PP-based film into a sodium persulfate solution with a mass concentration of 10%, controlling the solution temperature to be 70°C, and treating for 0.5 h to obtain a polypropylene-based film containing hydroxyl groups on the surface; and

[0098] (2) immersing the base film obtained in step (1) into an aqueous acrylamide solution with a mass concentration of 3%, adding an initiator cerium nitrate ammonium, controlling the concentration of cerium nitrate ammonium in the solution to be 0.6 g / L, treating for 5 min, and then washing the surface of the film with pure water to remove the excess grafted monomer aqueous solution; then immersing the obtained base film into a 1 mol / L sodium hydroxide solution for 5 min, and washing with pure water to obtain the hydrophilic modified polypropylene film.

[0099] Preparation Example 2

[0100] The present preparation example provides a hydrophilic modified polypropylene film, which is different from the preparation example 1 only in that the treatment time of the sodium persulfate solution in step (1) is 1 h, and the other raw materials, amounts and process parameters are the same as those of the preparation example 1.

[0101] Preparation Example 3

[0102] The present preparation example provides a hydrophilic modified polypropylene film, which is different from the preparation example 1 only in that the treatment time of the sodium persulfate solution in step (1) is 2 h, and the other raw materials, amounts and process parameters are the same as those of the preparation example 1.

[0103] Preparation Example 4

[0104] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 2 in that the concentration of cerium ammonium nitrate in step (2) is 0.8 g / L in the preparation method, and other raw materials, dosages and process parameters are the same as those in the preparation example 2.

[0105] Preparation Example 5

[0106] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 2 in that the concentration of cerium ammonium nitrate in step (2) is 1 g / L in the preparation method, and other raw materials, dosages and process parameters are the same as those in the preparation example 2.

[0107] Preparation Example 6

[0108] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 4 in that the grafting treatment time in step (2) is 10 min in the preparation method, and other raw materials, dosages and process parameters are the same as those in the preparation example 4.

[0109] Preparation Example 7

[0110] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 4 in that the grafting treatment time in step (2) is 15 min in the preparation method, and other raw materials, dosages and process parameters are the same as those in the preparation example 4.

[0111] Preparation Example 8

[0112] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 6 in that the soaking time in sodium hydroxide solution in step (2) is 10 min in the preparation method, and other raw materials, dosages and process parameters are the same as those in the preparation example 6.

[0113] Preparation Example 9

[0114] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 6 in that the soaking time in sodium hydroxide solution in step (2) is 15 min in the preparation method, and other raw materials, dosages and process parameters are the same as those in the preparation example 6.

[0115] Preparation Example 10

[0116] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 8 in that the acrylamide in step (2) is replaced by an equal mass of a 3% mass concentration maleic anhydride aqueous solution in the preparation method, and other raw materials, dosages and process parameters are the same as those in the preparation example 8.

[0117] Preparation Example 11

[0118] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 1 in that the time for the sodium persulfate solution treatment in the preparation method is 3h, and the other raw materials, dosages and process parameters are the same as those in the preparation example 1.

[0119] Preparation Example 12

[0120] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 4 in that the concentration of the cerium ammonium nitrate in the step (2) in the preparation method is 2g / L, and the other raw materials, dosages and process parameters are the same as those in the preparation example 4.

[0121] Preparation Example 13

[0122] The present preparation example provides a hydrophilic modified polypropylene film, which is only different from the preparation example 6 in that the time for the immersion in the sodium hydroxide solution in the step (2) in the preparation method is 40min, and the other raw materials, dosages and process parameters are the same as those in the preparation example 6.

[0123] Comparative Preparation Example 1

[0124] The present comparative preparation example provides a hydrophilic modified polypropylene film, which is prepared by the following method, and the preparation method comprises the following steps:

[0125] (1) preparing a mixed solution of gallic acid and 3-aminopropyl triethoxysilane, wherein the mass concentration of gallic acid is 2wt%, the mass concentration of 3-aminopropyl triethoxysilane is 6wt%, and the rest is solvent, which is obtained by mixing Tris-HCl (pH=8.5, 50mM) buffer and anhydrous ethanol in a volume ratio of 5:1; and

[0126] (2) immersing the polypropylene-based film into methanol for 1h, then immersing it into pure water, replacing the methanol in the film with pure water, and removing the excess water on the surface of the film; then immersing the PP-based film into the solution obtained in step (1) for 2h to obtain the hydrophilic modified polypropylene film.

[0127] Example 1

[0128] The present example provides a composite film, the structural schematic diagram of which is shown in Figure 1, which comprises a base film B (the hydrophilic modified polypropylene film provided in the preparation example 1) and a polyimide layer A arranged on both surfaces of the base film; and the preparation method of the composite film comprises the following steps:

[0129] (1) Dissolve the propylene diamine in pure water to prepare a propylene diamine aqueous solution with a mass concentration of 1 g / L, and add sodium hydroxide and sodium carbonate to prepare 0.4 g / L of sodium hydroxide and 0.8 g / L of sodium carbonate as an acid receiving agent, then add a surfactant, sodium dodecyl sulfate, to make the concentration of the surfactant 1.6 g / L; dissolve the pyromellitic acid chloride in dichloromethane to prepare an organic phase solution with a mass concentration of 1 g / L; the mass ratio of the aqueous phase monomer to the organic phase monomer is 1:1; and

[0130] (2) After the hydrophilic modified polypropylene film is soaked in the aqueous phase solution for 20 min, the excess aqueous phase solution is removed, and the film is immersed in the organic phase solution for 10 min; then the excess organic monomer is removed by washing with dichloromethane, and the film is immediately immersed in an imidization reagent composed of 1 mol / L of acetic anhydride and 1 mol / L of 2-methylpyridine for 30 s, dried, and then placed in an oven for baking at 130°C for 4 h to obtain the composite film.

[0131] Examples 2-10

[0132] Examples 2-10 each provide a composite film, which differs from Example 1 only in that the base film is the hydrophilic modified polypropylene film provided in Preparation Examples 2-10, respectively, and the other structures and preparation methods are the same as those of Example 1.

[0133] Example 11

[0134] This example provides a composite film, which differs from Example 8 only in that the mass ratio of the aqueous phase monomer to the organic phase monomer is 1:2, and the other structures and preparation methods are the same as those of Example 8.

[0135] Example 12

[0136] This example provides a composite film, which differs from Example 8 only in that the aqueous phase monomer is m-phenylenediamine, and the other structures and preparation methods are the same as those of Example 8.

[0137] Example 13

[0138] This example provides a composite film, which differs from Example 6 only in that the aqueous phase monomer is hexanediamine, and the other structures and preparation methods are the same as those of Example 6.

[0139] Examples 14-16

[0140] Examples 14-16 each provide a composite film, which differs from Example 1 only in that the base film is the hydrophilic modified polypropylene film provided in Preparation Examples 11-13, respectively, and the other structures and preparation methods are the same as those of Example 1.

[0141] Example 17

[0142] The present example provides a composite film, which is only different from Example 8 in that the mass ratio of the water phase monomer to the organic phase monomer is 1:4, and the other structures and preparation methods are the same as those of Example 8.

[0143] Comparative Example 1

[0144] The present comparative example provides a composite film, which is only different from Example 1 in that the base film is the hydrophilic modified polypropylene film provided in Comparative Preparation Example 1, and the other structures and preparation methods are the same as those of Example 1.

[0145] Application Example

[0146] The present application example provides a composite current collector, the structural schematic diagram of which is shown in FIG. 2, which comprises a first protective layer 1, a first metal conductive layer 2, a substrate 3, a second metal conductive layer 4 and a second protective layer 5 which are sequentially stacked; the substrate comprises the composite film provided in Examples 1-17 and Comparative Example 1.

[0147] The preparation method of the composite current collector comprises:

[0148] The composite film prepared in the present application is placed in the cabin of a vacuum magnetron sputtering, and the sputtered copper atoms are deposited on the two surfaces of the composite film through the cooling system in the vacuum coating chamber to form a metal layer with a thickness of about 700 nm. Subsequently, the two metal layers are further thickened by water medium electroplating to form metal conductive layers with a thickness of about 1 μm. Then, a solution containing a benzotriazole antioxidant is coated on the surface of the obtained metal conductive layer to form a stable oxidation film protective layer with a thickness of 50 nm, and then dried at 100°C to obtain the composite current collector.

[0149] Performance test

[0150] The mechanical properties and heat resistance of the composite film obtained by testing, and the mechanical properties, defect rate and adhesion of the composite current collector and the metal conductive layer are tested by the following methods:

[0151] 1. The mechanical properties are characterized by tensile strength and elongation at break, and the reference standard is GB / T 1040.3-2006; the heat resistance is characterized by heat shrinkage, and the reference standard is GB / T 10003-2008; in the test results of the present application, the test data are in the MD direction (longitudinal direction), and the elongation at break of the composite current collector is based on the fracture of the metal layer.

[0152] 2. Defect rate: the percentage of the number of unqualified products caused by film breakage in the total product number during the preparation of the composite current collector.

[0153] 3. Adhesion: 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, 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 10 s at 120 °C, cooled to room temperature, cut into a 150 mm x 15 mm strip, and finally the ethylene acrylic acid copolymer film of the sample strip was fixed to the upper clamp of the tensile tester, and the rest was fixed to the lower clamp. After being fixed, the two were peeled at an angle of 180° at a speed of 100 mm / min, and the peeling force was tested.

[0154] The specific test results are shown in Table 1:

[0155] Table 1

[0156] As can be seen from Table 1, the composite film provided by the application is hydrophilically modified by using a modified compound with a specific structure on the base film, which is beneficial to improve the adhesion of the base film and the polyimide layer and avoid the polyimide layer from falling off. After hydrophilic modification, a polyimide layer is arranged on the surface of the base film through interfacial polymerization, and the composite film with a three-layer structure obtained has excellent heat resistance and mechanical properties, high adhesion to the metal conductive layer, and avoids the falling off of the current collector metal conductive layer. In the preparation process, film breakage is less likely to occur, the yield is high, and the subsequent processing of the pole piece is not affected, and the cost is low.

[0157] As can be seen from Examples 1-13, the tensile strength of the composite film provided by the application is 210-254 MPa, the elongation at break is 109-138%, and the heat shrinkage rate is 0.4-1.8%; the tensile strength of the composite current collector is 178-202 MPa, the elongation at break is 7.8-10.5%, the adhesion of the composite film to the metal conductive layer is 1.6-2.5 N / cm; and the defect rate of the composite current collector is less than or equal to 4%.

[0158] As can be seen from Examples 1 and Examples 14-17, the base film hydrophilically modified without using the specific method of the application has poor mechanical properties, heat resistance, and mechanical properties of the composite current collector of the composite film obtained, the defect rate increases, and the adhesion of the composite film to the metal conductive layer decreases.

[0159] As can be seen from the comparison of Example 1 and Comparative Example 1, the base film hydrophilically modified without using the specific method of the application has poor mechanical properties of the composite film and the composite current collector, and the adhesion of the composite current collector is significantly reduced.

[0160] The applicant states that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application, which can be easily thought of by any person skilled in the art, falls within the protection scope and disclosure scope of the present application.

Claims

1. A composite film for a current collector, comprising a base film and a polyimide layer disposed on at least one surface of the base film; the base film comprises a base film modified by a modifying compound; the modifying compound comprises a carbon-carbon double bond and a functional group in its molecular structure; the functional group comprises at least one of an anhydride, a carboxyl group, a hydroxyl group, an amide group or an ester group; the polyimide layer comprises a polyimide layer prepared by interfacial polymerization of a water phase monomer and an organic phase monomer on the surface of the base film.

2. The composite film for current collectors according to claim 1, wherein The grafting rate of the modifying compound in the base film is 0.1-5%.

3. The composite film for current collectors according to claim 1 or 2, wherein The modifying compound comprises any one or a combination of at least two of maleic anhydride, acrylic acid, polyvinyl alcohol, acrylamide, methyl methacrylate or azobis-acrylamide.

4. The composite film for current collectors according to any one of claims 1 to 3, wherein The base film modified by the modifying compound is prepared by a method comprising: (1) treating an unmodified base film with a hydroxylation reagent to obtain a base film with a hydroxyl group on its surface; and (2) treating the base film obtained in step (1) with a modifying compound to obtain the base film modified by the modifying compound.

5. The composite film for current collectors according to claim 4, wherein The treatment in step (1) is performed for 0.5-2 hours. Preferably, the treatment in step (1) is performed at a temperature of 60-80℃. Preferably, the hydroxylation reagent comprises any one or a combination of at least two of sodium persulfate, ammonium persulfate, ammonium persulfate or ozone. Preferably, the hydroxylation reagent comprises a hydroxylation reagent solution with a mass concentration of the hydroxylation reagent of 10-20%. The modifying compound in step (2) comprises a modifying compound solution.

6. The composite film for current collectors according to claim 4 or 5, wherein Preferably, the mass concentration of the modifying compound in the modifying compound solution is 1-10%. Preferably, the modifying compound solution further comprises an initiator with a concentration of 0.6-1 g / L. Preferably, the treatment in step (2) is performed for 5-15 minutes. Preferably, the initiator comprises any one or a combination of at least two of dibenzoyl peroxide, cerium ammonium nitrate or l,1-di-tert-butyl peroxy-3,3,5-trimethylcyclohexane. After the treatment in step (2), a hydrolysis step is further included.

7. The composite film for current collectors according to any one of claims 4 to 6, wherein Preferably, the hydrolysis is performed for 5-15 minutes. The mass ratio of the water phase monomer to the organic phase monomer is 1: (1-3).

8. The composite film for current collectors according to any one of claims 1 to 7, wherein Preferably, the water phase monomer comprises an amine monomer. Preferably, the amine monomer comprises any one or a combination of at least two of methylamine, isopropylamine, cyclohexylamine, dodecylamine, dimethyl ethylenediamine, triethylenetetramine, ethylenediamine, propylenediamine, hexamethylenediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine or piperazine. Preferably, the organic phase monomer comprises an acid chloride compound and / or an anhydride compound. Preferably, the acid chloride compound comprises any one or a combination of at least two of trimesoyl chloride, pyromellitic acid dichloride, isophthaloyl dichloride or terephthaloyl dichloride. Preferably, the anhydride compound comprises pyromellitic acid dianhydride and / or 3,3',4,4'-diphenyl terephthalic anhydride. The base film comprises a polypropylene film and / or a polyethylene film.

9. The composite film for current collectors according to any one of claims 1 to 8, wherein ​ Preferably, the porosity of the base film is 10-50%, and the pore size is 10-300 nm, further preferably, the porosity is 20-40%, and the pore size is 50-200 nm; Preferably, the thickness of the composite film is ≥2 μm; Preferably, the thickness of the polyimide layer accounts for 5-10% of the total thickness of the composite film for current collector.

10. A method for preparing the composite film for current collector according to any one of claims 1-9, comprising the following steps: treating at least one surface of the base film with an aqueous monomer solution and an organic monomer solution in sequence to perform an interfacial polymerization reaction, thereby obtaining the composite film for current collector; the base film comprises a base film modified by a hydrophilic modification compound.

11. The production method according to claim 10, wherein The base film is treated with the aqueous monomer solution for 20-30 min; Preferably, the mass concentration of the aqueous monomer in the aqueous monomer solution is 0.5-3 g / L; Preferably, the aqueous monomer solution further comprises at least one of an acid acceptor, a surfactant or a phase transfer catalyst; Preferably, the base film is treated with the organic monomer solution for 5-10 min; Preferably, the mass concentration of the organic monomer in the organic monomer solution is 1-5 g / L.

12. The production method according to claim 10 or 11, wherein The interfacial polymerization reaction is further followed by steps of treating with an imidization reagent and heat treatment; Preferably, the treatment with the imidization reagent is performed for 10-50 s; Preferably, the imidization reagent comprises a dehydrating agent and a catalyst; Preferably, the heat treatment is performed at a temperature of 130-150 °C for 2-4 h.

13. A composite current collector comprising a first protective layer, a first metal conductive layer, a base film, a second metal conductive layer and a second protective layer arranged in sequence; the base film comprises the composite film for current collector according to any one of claims 1-9; Preferably, the material of the first metal conductive layer and the second metal conductive layer each independently comprises any one or a combination of at least two of copper, copper alloy, aluminum or aluminum alloy; Preferably, the total thickness of the first metal conductive layer and the second metal conductive layer is 700-1300 nm; Preferably, the total thickness of the first protective layer and the second protective layer accounts for 5-10% of the total thickness of the first metal conductive layer and the second metal conductive layer.

14. A lithium ion battery comprising the composite film for current collector according to any one of claims 1-9 and / or the composite current collector according to claim 13.

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