High-strength PP film for composite current collector and preparation method of high-strength PP film

Abstract

The invention discloses a high-strength PP film for a composite current collector and a preparation method thereof.The preparation method comprises the following steps that 1, PP resin particles and functional filler with the weight being 0.5%-3% of that of PP are mixed, co-melted, extruded and stretched to form a film, the PP film is prepared, and then a prefabricated film is obtained after surface modification treatment; (2) spin-coating a transition layer on the surface of the prefabricated film by using a transition liquid, then drying, and etching the transition layer by using Ar ions to obtain a PP film containing a seed layer; the transition liquid is an acrylic emulsion containing a metal complex; and (3) plating a metal layer on the surface of the seed layer of the PP film containing the seed layer through magnetron sputtering, and then performing heat treatment to obtain the high-strength PP film for the composite current collector. The scheme belongs to the field of polymer films, and the high-strength PP film for the composite current collector, which is few in wrinkles, high in strength and good in electrical property, can be obtained.

Description

Technical Field

[0001] The present invention relates to the field of polymer films, and specifically relates to a high-strength PP film for composite current collectors and a preparation method thereof. Background Art

[0002] Due to the large difference in the thermal expansion change laws between PP films and metals such as copper and aluminum, the metal atoms magnetron sputtered onto the PP film have a relatively high temperature, which causes the PP film to easily shrink and wrinkle. The conventional technical solution is to first deposit or sputter a seed layer to reduce the thermal expansion difference between the PP film and metals such as copper and aluminum, and then further deposit the target metal on the seed layer. However, the process of sputtering the seed layer will also cause local heating. Although such a process is effective, the process is complex and the process stability is lacking, and the wrinkle problem may also occur.

[0003] CN 118553919 A discloses a high-adhesion composite copper foil current collector and its preparation method and application, belonging to the technical field of lithium-ion batteries. The method of the present invention includes: performing plasma treatment on a polypropylene (PP) film to enhance the polarity of the PP, magnetron sputtering a strongly reactive metal titanium on the surface of the treated PP as an adhesion layer metal, and then sputtering a seed copper layer thereon; then placing it in an acidic copper plating solution for electroplating copper to obtain a high-adhesion composite copper foil current collector. Summary of the Invention

[0004] In order to solve the above problems, the present invention proposes a high-strength PP film for composite current collectors and a preparation method thereof. By preparing a special transition layer, the compatibility between the metal coating and the PP film is improved, thereby improving the mechanical properties and electrical properties, and solving the problem of wrinkling of the PP film after metal coating.

[0005] To achieve the above object, the technical solution of the present invention is as follows: A preparation method of a high-strength PP film for composite current collectors is obtained by the following method: Step (1): Mix and melt PP resin particles with 0.5%-3% by weight of functional filler of PP, extrude, and stretch into a film to obtain a PP film, and then obtain a prefabricated film after surface modification treatment; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with a transition liquid, then dry it, and etch the transition layer with Ar ions to obtain a PP film containing a seed layer; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): Deposit a metal layer on the surface of the seed layer of the PP film containing the seed layer by magnetron sputtering, and then perform heat treatment to obtain a high-strength PP film for composite current collectors.

[0006] In this solution, when preparing the PP film, the PP resin and the functional filler are melt-blended in a twin-screw extruder. After extruding a thick sheet, it is rapidly shaped by a quenching roll to form an amorphous base film. Subsequently, it enters a biaxial stretching system to form a biaxially oriented high-strength film, and finally, the internal stress is eliminated through heat setting.

[0007] This solution selects the spin-coating method to obtain the transition layer. Subsequently, through Ar ion bombardment, the metal complexes in the transition layer obtain electrons and are reduced to metal particles, and some organic substances are transformed into carbon black particles. This process has the following advantages: 1. Protect the prefabricated film, that is, the PP film layer, to prevent it from overheating and shrinking during subsequent magnetron sputtering deposition of metal; 2. Generate metal and metal oxide particles, making the subsequent magnetron sputtering deposition of metal have better adsorption; 3. The generated carbon black particles have better heat absorption; 4. In the final product, it is divided into a PP film layer, a transition layer containing carbon black, metal particles and organic substances, and a metal layer, making the resistance change more continuous, which can improve the overall life of the device (in the traditional uniform resistance current collector during charge and discharge, due to the current preferentially flowing through the low-resistance path, the utilization of the electrode active material is uneven, accelerating local aging or dendrite growth), and can prevent the diffusion of metal atoms to the PP film during the subsequent heat treatment process.

[0008] Preferably, in step (1), the melt index of the PP resin particles is 2 g / 10 min - 4 g / 10 min; preferably, the crystallinity of the prefabricated film > 60%.

[0009] Preferably, in step (1), the functional filler is one or more of nano-silica, carbon nanotubes, graphene, and nano-titanium dioxide.

[0010] Preferably, in step (1), the surface modification treatment is corona treatment or plasma etching treatment.

[0011] To enhance the bonding force with the transition layer, the prefabricated film needs to be subjected to corona treatment or argon-oxygen plasma etching to form a nano-scale rough surface.

[0012] Preferably, the preparation method of the transition liquid in step (2) includes the following steps by weight: Step (2-1): Dissolve 1 part - 2 parts of sodium dodecyl sulfate and 0.5 part - 1 part of alkylphenol polyoxyethylene ether in 100 parts of water, add 50 parts - 100 parts of acrylic monomers, and perform high-speed shear emulsification to obtain a pre-emulsion. Subsequently, add 5 parts - 20 parts of metal complexes and stir evenly to obtain a metal complex composite pre-emulsion; Step (2-2): Take 20 portions of the metal complex composite pre-emulsion, add 0.3 to 0.5 portions of the initiator, adjust the pH under the condition of 70°C - 80°C, react for 15 - 20 minutes, and obtain the seed emulsion. Subsequently, take another 150 - 180 portions of the metal complex composite pre-emulsion and 0.5 - 1.0 portions of the initiator, slowly add them to the seed emulsion, raise the temperature to 80°C - 90°C after adding, and react for 30 - 60 minutes to obtain the metal complex-acrylic acid composite emulsion, that is, the transition liquid.

[0013] Preferably, the acrylic monomer in step (2-1) is one or more of methyl methacrylate, butyl acrylate, acrylic acid, ethyl acrylate, and isooctyl acrylate.

[0014] Preferably, the metal complex in step (2-1) is one or more of copper citrate, aluminum citrate, copper tartrate, and aluminum tartrate.

[0015] In step (2-2), the pH of the system is adjusted by the type of complex using citric acid and ammonia water, where the pH of the copper complex is 6.0 - 7.0 and the pH of the copper complex is 4.5 - 5.5.

[0016] Preferably, the initiator in step (2-2) is ammonium persulfate.

[0017] Preferably, in step (3), the heat treatment process is: under argon gas condition, keep warm at 90°C - 110°C for 30 - 60 minutes, and then cool to room temperature at a rate of 10°C / min - 20°C / min.

[0018] Preferably, in step (2), the process of etching the transition layer with Ar ions is: 50°C - 100°C, 10 sccm - 20 sccm, radio frequency power 300W - 500W, vacuum degree 0 Pa - 3 Pa, and etch for 60 - 90 minutes.

[0019] Adjust the process of etching the transition layer with Ar ions according to different metal complexes, where the temperature refers to the temperature of the PP film and the transition layer, 10 sccm - 20 sccm refers to the Ar ion flow rate, and the vacuum degree refers to the air pressure during the etching process. From a kinetic perspective, compared with copper, the bond energy of the organic ligand of aluminum is weaker, so lower conditions are required, and the specific parameters need to be adjusted according to the type of metal complex. Since this process is only to prepare the PP film with a seed layer, it is not necessary to require complete reduction to metallic elements, and metal oxides and carbon elements can exist.

[0020] This solution also proposes a high-strength PP film for a composite current collector prepared by the above preparation method.

[0021] Compared with the existing technology, this solution has the following advantages: This scheme uses a metal complex-acrylic composite emulsion as a transition layer, which has good affinity with the PP film. After the metal complex-acrylic composite emulsion is dried, ionized Ar ion etching is used to cause a reduction reaction of the metal complex to precipitate metal and metal oxide particles, while partially oxidizing the organic matter to protect the PP film substrate, and part of the organic matter precipitates carbon. The presence of the transition layer reduces the resistance mutation between the metal layer and the PP film, which can improve the anti-puncture performance.

[0022] The preparation process of this solution is simple, the process flow is highly compatible with the production line, and a high-strength PP film composite material can be obtained. DETAILED DESCRIPTION

[0023] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The PP films of Examples 1-4 and Comparative Examples 1-8 of the present scheme are obtained by the following process method: when preparing the PP film, the PP resin and the functional filler are melt-blended in a twin-screw extruder, extruded into a 1.5 mm thick sheet through a T-die, and then quickly shaped with a 20°C rapid cooling roller to form an amorphous base film; then entering the biaxial stretching system, preheated at 140°C in the longitudinal direction and stretched at a rate of 4 times, and then expanded by 9 times at 160°C in a transverse tenter to form a biaxially oriented high-strength film, and finally heat-shaped at 175°C to eliminate internal stress.

[0025] Example 1 A method for preparing a high-strength PP film for a composite current collector is prepared by the following method: Step (1): PP resin particles are mixed and melted with 1% nano-silicon dioxide, 1% carbon nanotubes and 1% nano-titanium dioxide by weight of PP, extruded, stretched into a film, and a PP film is obtained, which is then subjected to oxygen-argon plasma etching and surface modification to obtain a prefabricated film; the melt index of the PP resin particles is 3g / 10min; the prefabricated film has a crystallinity of 65%; the oxygen-argon plasma composition is an oxygen plasma:argon mass ratio of 1:99, a flow rate of 15sccm at 40°C, a radio frequency power of 150W, a vacuum degree of 2Pa, and an etching time of 10min; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with a transition liquid, then dry it at 60°C, and etch the transition layer with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is: 80°C, 20 sccm, radio frequency power 400 W, vacuum degree 2 Pa, etching for 70 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): Deposit a metal layer on the surface of the seed layer of the PP film containing the seed layer by magnetron sputtering with aluminum as the target, and then perform heat treatment to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon conditions, keep warm at 100°C for 50 min, and then cool to room temperature at a rate of 15°C / min; The preparation method of the transition liquid in step (2) includes the following steps by weight: Step (2-1): Stir and dissolve 1 part of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether in 100 parts of water, add 75 parts of acrylic monomers, and perform high-speed shear emulsification to obtain a pre-emulsion liquid, and then add 15 parts of aluminum citrate, and stir evenly to obtain a metal complex composite pre-emulsion liquid; the acrylic monomers are methyl methacrylate, butyl acrylate and ethyl acrylate with a mass ratio of 1:1:1; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion liquid, add 0.4 part of ammonium persulfate, adjust the pH to 5 at 75°C, react for 20 min to obtain a seed emulsion, and then take another 180 parts of the metal complex composite pre-emulsion liquid and 0.8 part of ammonium persulfate, slowly add them to the seed emulsion, and after the addition is completed, raise the temperature to 85°C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0026] Example 2 A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt the PP resin particles with 0.5% of nano-silica, 1.5% of carbon nanotubes and 0.5% of graphene by weight of PP, extrude and stretch them into a film to obtain a PP film, and then perform surface modification treatment by plasma etching to obtain a prefabricated film; the melt index of the PP resin particles is 4 g / 10 min; the crystallinity of the prefabricated film is 63%; the oxygen-argon plasma composition is the mass ratio of oxygen plasma: argon 1:99, 40°C, the flow rate is 15 sccm, the radio frequency power is 150 W, and the etching time is 10 min; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with a transition liquid, then dry it at 60°C, and etch the transition layer with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is: 60°C, 15 sccm, radio frequency power 300 W, vacuum degree 3 Pa, etching for 60 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): By magnetron sputtering with aluminum as the target, a metal layer is deposited on the surface of the seed layer of the PP film containing the seed layer, and then heat treatment is carried out to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon gas conditions, keep warm at 90 °C for 60 min, and then cool to room temperature at a rate of 20 °C / min; The preparation method of the transition liquid in Step (2) includes the following steps by weight: Step (2-1): Dissolve 2 parts of sodium dodecyl sulfate and 0.5 part of alkylphenol polyoxyethylene ether in 100 parts of water by stirring, add 100 parts of acrylic monomers, and carry out high-speed shear emulsification to obtain a pre-emulsion liquid. Then add 20 parts of aluminum tartrate and stir evenly to obtain a metal complex composite pre-emulsion liquid; the acrylic monomers are one or more of acrylic acid and ethyl acrylate in a ratio of 1:1; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion liquid, add 0.5 part of ammonium persulfate, adjust the pH to 5 at 80 °C, react for 20 min to obtain a seed emulsion. Then take another 170 parts of the metal complex composite pre-emulsion liquid and 0.6 part of ammonium persulfate, slowly add them to the seed emulsion, and after adding, raise the temperature to 90 °C and react for 30 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0027] Example 3 A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt the PP resin particles with 2.5% by weight of nano-silica of PP, extrude and stretch into a film to obtain a PP film, and then carry out surface modification treatment by corona treatment to obtain a prefabricated film; the melt index of the PP resin particles is 2 g / 10 min; the crystallinity of the prefabricated film is 63%; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with the transition liquid, then dry it, and etch the transition layer with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is: 100 °C, 20 sccm, radio frequency power 500 W, vacuum degree 2 Pa, etch for 80 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): By magnetron sputtering with aluminum as the target, a metal layer is deposited on the surface of the seed layer of the PP film containing the seed layer, and then heat treatment is carried out to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon gas conditions, keep warm at 110 °C for 30 min, and then cool to room temperature at a rate of 10 °C / min; The preparation method of the transition liquid in Step (2) includes the following steps by weight: Step (2-1): Dissolve 1.5 parts of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether by stirring in 100 parts of water. Add 50 parts of acrylic monomers, and perform high-speed shear emulsification to obtain a pre-emulsion. Subsequently, add 13 parts of aluminum citrate, and stir evenly to obtain a metal complex composite pre-emulsion; the acrylic monomers are ethyl acrylate and isooctyl acrylate in a ratio of 1:1. Step (2-2): Take 20 parts of the metal complex composite pre-emulsion, add 0.4 part of ammonium persulfate, adjust the pH to 6.5 at 75 °C, and react for 20 min to obtain a seed emulsion. Subsequently, take another 170 parts of the metal complex composite pre-emulsion and 0.8 part of ammonium persulfate, and slowly add them to the seed emulsion. After the addition is completed, raise the temperature to 85 °C and react for 40 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0028] Example 4 A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt PP resin particles with 1% by weight of nano-silica and 1% by weight of nano-titanium dioxide, extrude, and stretch into a film to obtain a PP film. Subsequently, perform surface modification treatment by plasma etching to obtain a prefabricated film; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is the mass ratio of oxygen plasma to argon of 1:99, 40 °C, the flow rate is 15 sccm, the radio frequency power is 150 W, and the etching time is 10 min. Step (2): Spin-coat a transition layer on the surface of the prefabricated film with the transition liquid, and then dry it. Etch the transition layer with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is: 100 °C, 15 sccm, radio frequency power 400 W, vacuum degree 3 Pa, etching for 70 min. The transition liquid is an acrylic emulsion containing a metal complex. Step (3): Deposit a metal layer on the surface of the seed layer of the PP film containing the seed layer by magnetron sputtering with aluminum as the target, and then perform heat treatment to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon gas conditions, keep warm at 100 °C for 40 min, and then cool to room temperature at a rate of 20 °C / min. The preparation method of the transition liquid in Step (2) includes the following steps by weight: Step (2-1): Dissolve 2 parts of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether by stirring in 100 parts of water. Add 60 parts of acrylic monomers, and perform high-speed shear emulsification to obtain a pre-emulsion. Subsequently, add 16 parts of copper citrate, and stir evenly to obtain a metal complex composite pre-emulsion; the acrylic monomers are one or more of methyl methacrylate, butyl acrylate, acrylic acid, ethyl acrylate, and isooctyl acrylate. Step (2-2): Take 20 portions of the metal complex composite pre-emulsion, add 0.3 to 0.5 portions of ammonium persulfate, adjust the pH to 6.5 under the condition of 70°C - 80°C, react for 15 min, and obtain a seed emulsion. Subsequently, take another 160 portions of the metal complex composite pre-emulsion and 0.7 portions of ammonium persulfate, slowly add them to the seed emulsion, and after the addition, raise the temperature to 86°C and react for 50 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0029] Comparative Example 1 The difference from Example 1 is that there is no transition layer, specifically: A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt blend PP resin particles with 1% by weight of PP of nano-silica, 1% of carbon nanotubes, and 1% of nano-titanium dioxide, extrude and stretch into a film to obtain a PP film, and then perform oxygen-argon plasma etching treatment and surface modification treatment to obtain a prefabricated film; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is the mass ratio of oxygen plasma: argon of 1:99, the flow rate at 40°C is 15 sccm, the radio frequency power is 150 W, the vacuum degree is 2 Pa, and the etching time is 10 min; Step (2): Deposit a metal layer on the surface of the prefabricated film by magnetron sputtering with aluminum as the target, and then perform heat treatment to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon gas conditions, keep warm at 100°C for 50 min, and then cool to room temperature at a rate of 15°C / min.

[0030] Comparative Example 2 The difference from Example 1 is that the process of Ar ion etching the transition layer in step (2) is different, specifically: A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt blend PP resin particles with 1% by weight of PP of nano-silica, 1% of carbon nanotubes, and 1% of nano-titanium dioxide, extrude and stretch into a film to obtain a PP film, and then perform oxygen-argon plasma etching treatment and surface modification treatment to obtain a prefabricated film; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is the mass ratio of oxygen plasma: argon of 1:99, the flow rate at 40°C is 15 sccm, the radio frequency power is 150 W, the vacuum degree is 2 Pa, and the etching time is 10 min; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with a transition liquid, then dry it at 60 °C, and etch the transition layer with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is as follows: 30 °C, 20 sccm, radio frequency power 500 W, vacuum degree 2 Pa, etching for 70 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): Deposit a metal layer on the surface of the seed layer of the PP film containing the seed layer by magnetron sputtering with aluminum as the target, and then perform heat treatment to obtain a high-strength PP film for a composite current collector; the heat treatment process is as follows: under argon conditions, keep warm at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min; The preparation method of the transition liquid in step (2) includes the following steps by weight: Step (2-1): Stir and dissolve 1 part of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether in 100 parts of water, add 75 parts of acrylic monomers, and perform high-speed shear emulsification to obtain a pre-emulsion. Then add 15 parts of aluminum citrate, and stir evenly to obtain a metal complex composite pre-emulsion; the acrylic monomers are methyl methacrylate, butyl acrylate, and ethyl acrylate with a mass ratio of 1:1:1; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion, add 0.4 part of ammonium persulfate, adjust the pH to 5 at 75 °C, react for 20 min to obtain a seed emulsion. Then take another 180 parts of the metal complex composite pre-emulsion and 0.8 part of ammonium persulfate, slowly add them to the seed emulsion, and after adding, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0031] Comparative Example 3 The difference from Example 1 is that in step (2-1), the concentration of the metal complex is too low, specifically: A method for preparing a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt PP resin particles with 1% by weight of nano-silica, 1% of carbon nanotubes, and 1% of nano-titanium dioxide, extrude and stretch them into a film to obtain a PP film. Then perform surface modification treatment by oxygen-argon plasma etching; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is an oxygen plasma:argon mass ratio of 1:99, the flow rate at 40 °C is 15 sccm, the radio frequency power is 150 W, the vacuum degree is 2 Pa, and the etching time is 10 min; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with a transition liquid, then dry it at 60 °C, and etch the transition layer with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is: 80 °C, 20 sccm, radio frequency power 400 W, vacuum degree 2 Pa, etching for 70 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): Deposit a metal layer on the surface of the seed layer of the PP film containing the seed layer by magnetron sputtering with aluminum as the target, and then perform heat treatment to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon conditions, keep warm at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min; The preparation method of the transition liquid in step (2) includes the following steps by weight: Step (2-1): Stir and dissolve 1 part of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether in 100 parts of water, add 75 parts of acrylic monomers, and perform high-speed shear emulsification to obtain a pre-emulsion. Then add 3 parts of aluminum citrate, and stir evenly to obtain a metal complex composite pre-emulsion; the acrylic monomers are methyl methacrylate, butyl acrylate, and ethyl acrylate with a mass ratio of 1:1:1; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion, add 0.4 part of ammonium persulfate, adjust the pH to 5 at 75 °C, react for 20 min to obtain a seed emulsion. Then take another 180 parts of the metal complex composite pre-emulsion and 0.8 part of ammonium persulfate, slowly add them to the seed emulsion, and after adding, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0032] Comparative Example 4 The difference from Example 1 is that in step (2), the process of etching the transition layer with Ar ions is different; A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt PP resin particles with 1% by weight of nano-silica, 1% of carbon nanotubes, and 1% of nano-titanium dioxide of PP, extrude and stretch them into a film to obtain a PP film, and then perform oxygen-argon plasma etching treatment and surface modification treatment to obtain a prefabricated film; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is the mass ratio of oxygen plasma: argon 1:99, the flow rate at 40 °C is 15 sccm, the radio frequency power is 150 W, the vacuum degree is 2 Pa, and the etching time is 10 min; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with a transition liquid, then dry it at 60 °C, and etch the transition layer with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is as follows: 80 °C, 20 sccm, radio frequency power 250 W, vacuum degree 2 Pa, etching for 70 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): Deposit a metal layer on the surface of the seed layer of the PP film containing the seed layer by magnetron sputtering with aluminum as the target, and then perform heat treatment to obtain a high-strength PP film for a composite current collector; the heat treatment process is as follows: under argon conditions, keep warm at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min; The preparation method of the transition liquid in step (2) includes the following steps by weight: Step (2-1): Stir and dissolve 1 part of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether in 100 parts of water, add 75 parts of acrylic monomers, and perform high-speed shear emulsification to obtain a pre-emulsion. Then add 15 parts of aluminum citrate and stir evenly to obtain a metal complex composite pre-emulsion; the acrylic monomers are methyl methacrylate, butyl acrylate, and ethyl acrylate with a mass ratio of 1:1:1; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion, add 0.4 part of ammonium persulfate, adjust the pH to 5 at 75 °C, react for 20 min to obtain a seed emulsion. Then take another 180 parts of the metal complex composite pre-emulsion and 0.8 part of ammonium persulfate, slowly add them to the seed emulsion, and after adding, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0033] Comparative Example 5 The difference from Example 1 is that in step (2-2), the seed emulsion is used as the transition liquid, specifically: A method for preparing a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt PP resin particles with 1% by weight of nano-silica, 1% of carbon nanotubes, and 1% of nano-titanium dioxide of PP, extrude, and stretch into a film to obtain a PP film. Then perform oxygen-argon plasma etching treatment and surface modification treatment to obtain a prefabricated film; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is an oxygen plasma:argon mass ratio of 1:99, the flow rate at 40 °C is 15 sccm, the radio frequency power is 150 W, the vacuum degree is 2 Pa, and the etching time is 10 min; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with a transition liquid, then dry it at 60°C, and etch the transition layer with Ar ions to obtain a PP film with a seed layer; the process of etching the transition layer with Ar ions is: 80°C, 20 sccm, radio frequency power 400 W, vacuum degree 2 Pa, etching for 70 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): Deposit a metal layer on the surface of the seed layer of the PP film with a seed layer by magnetron sputtering using aluminum as the target, and then perform heat treatment to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon gas conditions, keep warm at 100°C for 50 min, and then cool to room temperature at a rate of 15°C / min; The preparation method of the transition liquid in Step (2) includes the following steps by weight: Step (2-1): Stir and dissolve 1 part of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether in 100 parts of water, add 75 parts of acrylic monomers, and perform high-speed shear emulsification to obtain a pre-emulsion liquid, and then add 15 parts of copper citrate, and stir evenly to obtain a metal complex composite pre-emulsion liquid; the acrylic monomers are methyl methacrylate, butyl acrylate and ethyl acrylate with a mass ratio of 1:1:1; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion liquid, add 0.4 part of ammonium persulfate, adjust the pH to 5 at 75°C, and react for 20 min to obtain a seed emulsion, that is, the transition liquid.

[0034] Comparative Example 6 The difference from Example 1 is that in Step (2), the process of etching the transition layer with Ar ions is different; A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt PP resin particles with 1% by weight of PP of nano-silica, 1% of carbon nanotubes and 1% of nano-titanium dioxide, extrude and stretch into a film to obtain a PP film, and then perform surface modification treatment by oxygen-argon plasma etching; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is the mass ratio of oxygen plasma: argon 1:99, the flow rate at 40°C is 15 sccm, the radio frequency power is 150 W, the vacuum degree is 2 Pa, and the etching time is 10 min; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with a transition liquid, then dry it at 60°C, and etch the transition layer with Ar ions to obtain a PP film with a seed layer; the process of etching the transition layer with Ar ions is: 120°C, 20 sccm, radio frequency power 500 W, vacuum degree 2 Pa, etching for 70 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): By magnetron sputtering with aluminum as the target, a metal layer is deposited on the surface of the seed layer of the PP film containing the seed layer, and then heat treatment is carried out to obtain a high-strength PP film for the composite current collector; the heat treatment process is: under argon gas conditions, keep warm at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min; The preparation method of the transition liquid in step (2) includes the following steps by weight: Step (2-1): Dissolve 1 part of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether by stirring in 100 parts of water, add 75 parts of acrylic monomers, and carry out high-speed shear emulsification to obtain a pre-emulsion. Then add 15 parts of aluminum citrate and stir evenly to obtain a metal complex composite pre-emulsion; the acrylic monomers are methyl methacrylate, butyl acrylate, and ethyl acrylate with a mass ratio of 1:1:1; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion, add 0.4 part of ammonium persulfate, adjust the pH to 5 at 75 °C, react for 20 min to obtain a seed emulsion. Then take another 180 parts of the metal complex composite pre-emulsion and 0.8 part of ammonium persulfate, and slowly add them to the seed emulsion. After adding, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0035] Comparative Example 7 The difference from Example 1 is that in step (2), the process of etching the transition layer with Ar ions is different; A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt PP resin particles with 1% by weight of PP of nano-silica, 1% of carbon nanotubes, and 1% of nano-titanium dioxide, extrude, and stretch into a film to obtain a PP film. Then, after oxygen-argon plasma etching treatment and surface modification treatment, a prefabricated film is obtained; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is an oxygen plasma:argon mass ratio of 1:99, the flow rate at 40 °C is 15 sccm, the radio frequency power is 150 W, the vacuum degree is 2 Pa, and the etching time is 10 min; Step (2): Spin-coat a transition layer on the surface of the prefabricated film with the transition liquid, then dry it at 60 °C, and etch the transition layer with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is: 80 °C, 20 sccm, radio frequency power 600 W, vacuum degree 2 Pa, etching for 70 min; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): By magnetron sputtering with aluminum as the target, a metal layer is deposited on the surface of the seed layer of the PP film containing the seed layer, and then heat treatment is carried out to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon gas conditions, keep warm at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min; The preparation method of the transition liquid in step (2) includes the following steps by weight: Step (2-1): Dissolve 1 part of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether by stirring in 100 parts of water, add 75 parts of acrylic monomers, and carry out high-speed shear emulsification to obtain a pre-emulsion. Then add 15 parts of aluminum citrate and stir evenly to obtain a metal complex composite pre-emulsion; the acrylic monomers are methyl methacrylate, butyl acrylate and ethyl acrylate with a mass ratio of 1:1:1; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion, add 0.4 part of ammonium persulfate, adjust the pH to 5 at 75 °C, react for 20 min to obtain a seed emulsion. Then take another 180 parts of the metal complex composite pre-emulsion and 0.8 part of ammonium persulfate, and slowly add them to the seed emulsion. After adding, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0036] Comparative Example 8 It is different from Example 1 in that a traditional metal transition layer is selected: A preparation method of a high-strength PP film for a composite current collector is obtained by the following method: Step (1): Mix and melt PP resin particles with 1% of nano-silica, 1% of carbon nanotubes and 1% of nano-titanium dioxide by weight of PP, extrude and stretch into a film to obtain a PP film, and then carry out oxygen-argon plasma etching treatment to perform surface modification treatment to obtain a prefabricated film; the melt index of the PP resin particles is 3 g / 10 min; the crystallinity of the prefabricated film is 65%; the oxygen-argon plasma composition is the mass ratio of oxygen plasma: argon of 1:99, the flow rate at 40 °C is 15 sccm, the radio frequency power is 150 W, the vacuum degree is 2 Pa, and the etching time is 10 min; Step (2): By magnetron sputtering with titanium as the target, a transition metal layer is deposited on the surface of the prefabricated film, and then the transition layer is etched with Ar ions to obtain a PP film containing a seed layer; the process of etching the transition layer with Ar ions is: 80 °C, 20 sccm, radio frequency power 400 W, vacuum degree 2 Pa, etching for 70 min; Step (3): By magnetron sputtering with aluminum as the target, a metal layer is deposited on the surface of the seed layer of the PP film containing the seed layer, and then heat treatment is carried out to obtain a high-strength PP film for a composite current collector; the heat treatment process is: under argon gas conditions, keep warm at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min.

[0037] Performance tests were performed on Examples 1-4 and Comparative Examples 1-8.

[0038] Tensile strength: According to ASTM D638, required to be ≥50 MPa; Elongation at break: According to ASTM D638, the requirement is 5%-20%; Puncture strength: according to ASTM D4833, required to be ≥200 N / mm; Surface resistance: IEC 60093 is carried out according to the four-probe method, and the requirement is ≤5Ω / sq; Coating adhesion: According to ASTM D3359, requirement ≥4B; Wrinkle detection: Use a high-resolution camera to capture the image of the film, analyze the image through image processing software, divide the unit table, and record the level from A to E from the least to the most according to the number of wrinkles affecting the table in the view. Level A means no wrinkles, and level E means the affected area is greater than 50%. Level A is required.

[0039] The performance test results are shown in Table 1.

[0040] Table 1

[0041] From the analysis of the results of Examples 1-4 and Comparative Examples 1-8, the present solution can obtain samples with good comprehensive performance. The performance of Examples 1-3 is higher than that of Example 4. This may be because the copper ion complex requires more severe etching conditions to be better reduced. The copper element generated under the current conditions is not much, but this will exceed the tolerance of the PP film.

[0042] Compared with Example 1, the comparative example has poor performance and has the following differences: There is no transition layer in the process of Comparative Example 1, which results in the direct sputtering of metal on the surface of PP, leading to poor interfacial bonding, discontinuous conductive layer, ultimately causing the decline of mechanical and electrical properties, and the interfacial stress concentration causes uneven shrinkage of the base film, resulting in wrinkles; in Comparative Example 2, the temperature of the Ar ion etching transition layer in step (2) is too low, resulting in insufficient activation of the transition layer, poor adhesion of the coating, and increased brittleness of the film; in Comparative Example 3, due to insufficient metal anchor points in the transition layer, the coating is loose and porous, thus leading to the decline of conductivity and bonding force, and the grid deformation is caused by the pulling of the PP film when the coating shrinks, resulting in wrinkles; in Comparative Example 4, due to too low radio frequency power, insufficient surface roughness of the transition layer, and insufficient reduction amount of aluminum, the metal layer is not firmly anchored and the bonding force is weak; in Comparative Example 5, the seed emulsion is used as the transition liquid, which results in an incomplete transition layer and uneven distribution of metal complexes, leading to uneven stress distribution, ultimately resulting in poor adhesion and conductivity of the coating, and many wrinkles; in Comparative Example 6, in the etching process of step (2), the substrate temperature is too high, resulting in thermal degradation and deformation of the PP film, causing the decline of mechanical properties and many wrinkles; in Comparative Example 7, in the etching process of step (2), the etching power is too high, resulting in too high energy when the plasma bombards the transition layer, affecting the structure of the PP film, ultimately resulting in poor adhesion of the coating and many wrinkles; in Comparative Example 8, the metal titanium coating is used as the transition layer, and the mechanical properties can meet the requirements, but the adhesion effect of the coating is poor and there are many wrinkles.

Claims

1. A method for preparing a high-strength PP film for a composite current collector, characterized in that: The following steps are involved: Step (1): PP resin particles are mixed and melted with 0.5% to 3% of the functional filler by weight of PP, extruded, stretched into a film, and a PP film is prepared, and then a prefabricated film is obtained after surface modification treatment; Step (2): spin coating a transition layer on the surface of the prefabricated film with a transition liquid, then drying, and etching the transition layer with Ar ions to obtain a PP film containing a seed layer; The transition liquid is an acrylic emulsion containing a metal complex; Step (3): by magnetron sputtering, a metal layer is plated on the surface of the seed layer of the PP film containing the seed layer, followed by heat treatment to obtain a high-strength PP film for a composite current collector.

2. The method for preparing a high-strength PP film for a composite current collector according to claim 1, characterized in that: In step (1), the melt index of the PP resin particles is 2g / 10min-4g / 10min; preferably, the prefabricated film has a crystallinity of >60%.

3. The method for preparing a high-strength PP film for a composite current collector according to claim 1, characterized in that: In step (1), the functional filler is one or more of nano-silicon dioxide, carbon nanotubes, graphene, and nano-titanium dioxide.

4. The method for preparing a high-strength PP film for a composite current collector according to claim 1, characterized in that: In step (1), the surface modification treatment is corona treatment or plasma etching treatment.

5. The method for preparing a high-strength PP film for a composite current collector according to claim 1, characterized in that: The method for preparing the transition liquid described in step (2) comprises the following steps, measured by weight: Step (2-1): 1-2 parts of sodium dodecyl sulfate and 0.5-1 parts of alkylphenol polyoxyethylene ether are stirred and dissolved in 100 parts of water, 50-100 parts of acrylic monomers are added, and emulsification is performed at high speed shear to obtain a pre-emulsion, and then 5-20 parts of a metal complex are added, and the mixture is stirred evenly to obtain a metal complex composite pre-emulsion; Step (2-2): Take 20 parts of the metal complex composite pre-emulsion, add 0.3 parts to 0.5 parts of the initiator, adjust the pH at 70°C to 80°C, react for 15min to 20min, and obtain a seed emulsion. Then, take another 150 parts to 180 parts of the metal complex composite pre-emulsion and 0.5 parts to 1.0 parts of the initiator, slowly add them to the seed emulsion, raise the temperature to 80°C to 90°C after the addition is completed, and react for 30min to 60min to obtain a metal complex-acrylic acid composite emulsion, i.e., a transition liquid.

6. The method for preparing a high-strength PP film for a composite current collector according to claim 5, characterized in that: The acrylic monomer in step (2-1) is one or more of methyl methacrylate, butyl acrylate, acrylic acid, ethyl acrylate, and isooctyl acrylate.

7. The method for preparing a high-strength PP film for a composite current collector according to claim 5, characterized in that: The metal complex in step (2-1) is one or more of copper citrate, aluminum citrate, copper tartrate, and aluminum tartrate.

8. The method for preparing a high-strength PP film for a composite current collector according to claim 5, characterized in that: The initiator in step (2-2) is ammonium persulfate.

9. The method for preparing a high-strength PP film for a composite current collector according to claim 1, characterized in that: In step (3), the heat treatment process is: under argon conditions, keep warm at 90°C-110°C for 30min-60min, and then cool to room temperature at a rate of 10°C / min-20°C / min; in step (2), the process of etching the transition layer with Ar ions is: 50°C-100°C, 10sccm-20sccm, RF power 300W-500W, vacuum degree 0Pa-3Pa, etching 60min-90min.

10. A high-strength PP film for a composite current collector prepared by the method for preparing a high-strength PP film for a composite current collector according to any one of claims 1 to 9.

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