A high-strength PP film for composite current collectors and its preparation method

Abstract

The present invention discloses a high-strength PP film for composite current collectors and a preparation method thereof, which are obtained by the following method: Step (1): Mix and melt PP resin particles with 0.5%-3% by weight of functional fillers based on the weight 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. This solution belongs to the field of polymer films and can obtain a high-strength PP film for composite current collectors with few wrinkles, high strength and good electrical properties.

Description

Technical Field

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

[0002] Because the thermal expansion behavior of PP film differs significantly from that of metals like copper and aluminum, the metal atoms magnetron sputtered onto the PP film have a higher temperature, which can easily cause the film to shrink and wrinkle. Conventional technology involves first depositing or sputtering a seed layer to minimize the thermal expansion difference between the PP film and metals like copper and aluminum. The target metal is then deposited on top of the seed layer. However, sputtering the seed layer also causes localized heating. While effective, this process is complex, lacks stability, and can also lead to wrinkling.

[0003] CN 118553919 A discloses a high-adhesion composite copper foil current collector, a preparation method, and an application thereof, belonging to the technical field of lithium-ion batteries. The method comprises: subjecting a polypropylene (PP) film to plasma treatment to enhance the polarity of the PP; magnetron sputtering highly reactive titanium as an adhesion layer metal on the treated PP surface; and then sputtering a seed copper layer thereon; and then placing the PP film 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 a composite current collector 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 and electrical properties, and solving the problem of wrinkles on the PP film after metal coating.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] A method for preparing a high-strength PP film for a composite current collector is prepared by the following method:

[0007] Step (1): PP resin particles are mixed and melted with 0.5%-3% of the functional filler by weight of PP, extruded, and stretched into a film to obtain a PP film, which is then subjected to surface modification treatment to obtain a prefabricated film;

[0008] 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;

[0009] The transition liquid is an acrylic emulsion containing a metal complex;

[0010] 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 the composite current collector.

[0011] 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 the thick sheet, it is quickly shaped by a chill 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 by heat setting.

[0012] 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 part of the organic matter is 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 metals; 2. Generate metal and metal oxide particles, making the subsequent magnetron sputtering deposition of metals 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 matter, and a metal layer, making the resistance change more continuous, which can improve the overall life of the device (in traditional uniform resistance current collectors, during charge and discharge, due to the current preferentially flowing through low-resistance paths, it leads to uneven utilization of electrode active materials, accelerating local aging or dendrite growth), and can prevent the diffusion of metal atoms into the PP film during subsequent heat treatment.

[0013] 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%.

[0014] Preferably, in step (1), the functional filler is one or more of nano-silica, carbon nanotubes, graphene, and nano-titanium dioxide.

[0015] Preferably, in step (1), the surface modification treatment is corona treatment or plasma etching treatment.

[0016] 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.

[0017] Preferably, the preparation method of the transition liquid in step (2) includes the following steps by weight:

[0018] Step (2-1): Stir and 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;

[0019] 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 the addition is completed, and react for 30 - 60 minutes to obtain the metal complex-acrylic composite emulsion, that is, the transition liquid.

[0020] Preferably, the acrylic monomer in step (2-1) is one or more of methyl methacrylate, butyl acrylate, acrylic acid, ethyl acrylate, and isooctyl acrylate.

[0021] Preferably, the metal complex in step (2-1) is one or more of copper citrate, aluminum citrate, copper tartrate, and aluminum tartrate.

[0022] In step (2-2), adjust the pH of the system 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.

[0023] Preferably, the initiator in step (2-2) is ammonium persulfate.

[0024] Preferably, in step (3), the heat treatment process is: under argon gas conditions, 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.

[0025] 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.

[0026] 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 for preparing the PP film with a seed layer, it is not necessary to require complete reduction to metallic elements, and there can be metal oxides and carbon elements, etc.

[0027] This solution also proposes a high-strength PP film for a composite current collector prepared by the above preparation method.

[0028] Compared with existing technologies, this solution has the following advantages:

[0029] This solution 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 dries, ionized Ar ion etching is used to cause the metal complex to undergo a reduction reaction, precipitating metal and metal oxide particles. At the same time, the organic matter is partially oxidized, protecting the PP film substrate, and some 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.

[0030] The preparation process of this solution is simple, the process flow is highly compatible with the production line, and high-strength PP film composite materials can be obtained. DETAILED DESCRIPTION

[0031] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0032] Examples 1-4 and Comparative Examples 1-8 of this scheme all obtain PP films through 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 using a 20°C chill 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 9 times at 160°C in a transverse tenter to form a biaxially oriented high-strength film, and finally heat-set at 175°C to eliminate internal stress.

[0033] Example 1

[0034] A method for preparing a high-strength PP film for a composite current collector is prepared by the following method:

[0035] 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 and stretched into a film to obtain a PP film, 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 3 g / 10 min; 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 15 sccm at 40°C, a radio frequency power of 150 W, a vacuum degree of 2 Pa, and an etching time of 10 min;

[0036] 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;

[0037] The transition liquid is an acrylic emulsion containing a metal complex;

[0038] 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;

[0039] The preparation method of the transition liquid in step (2) includes the following steps by weight:

[0040] 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, and 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;

[0041] 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, and 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 the addition, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0042] Example 2

[0043] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0044] Step (1): Mix and melt 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 an oxygen plasma:argon mass ratio of 1:99, 40 °C, a flow rate of 15 sccm, a radio frequency power of 150 W, and an etching time of 10 min;

[0045] 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 as follows: 60°C, 15 sccm, radio frequency power 300 W, vacuum degree 3 Pa, etching for 60 min;

[0046] The transition liquid is an acrylic emulsion containing a metal complex;

[0047] 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 as follows: Under argon conditions, keep warm at 90°C for 60 min, and then cool to room temperature at a rate of 20°C / min;

[0048] The preparation method of the transition liquid in Step (2) includes the following steps by weight:

[0049] Step (2-1): Stir and dissolve 2 parts of sodium dodecyl sulfate and 0.5 part of alkylphenol polyoxyethylene ether in 100 parts of water, add 100 parts of acrylic monomers, and perform 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;

[0050] 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.

[0051] Example 3

[0052] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0053] Step (1): Mix and melt PP resin particles with 2.5% by weight of nano-silica based on the weight of PP, extrude, and stretch into a film to obtain a PP film. Then, after corona treatment for surface modification, a prefabricated film is obtained; The melt index of the PP resin particles is 2 g / 10 min; The crystallinity of the prefabricated film is 63%;

[0054] 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 with a seed layer; The process of etching the transition layer with Ar ions is as follows: 100°C, 20 sccm, radio frequency power 500 W, vacuum degree 2 Pa, etching for 80 min;

[0055] The transition liquid is an acrylic emulsion containing a metal complex;

[0056] 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 110 °C for 30 min, and then cool to room temperature at a rate of 10 °C / min;

[0057] The preparation method of the transition liquid in step (2) includes the following steps by weight:

[0058] Step (2-1): Dissolve 1.5 parts of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether in 100 parts of water by stirring, add 50 parts of acrylic monomers, and carry out high-speed shear emulsification to obtain a pre-emulsion. Then 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;

[0059] 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, react for 20 min to obtain a seed emulsion. Then take another 170 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 40 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0060] Example 4

[0061] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0062] Step (1): Mix and melt PP resin particles with 1% of nano-silica 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 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: 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;

[0063] 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, 15 sccm, radio frequency power 400 W, vacuum degree 3 Pa, etching for 70 min;

[0064] The transition liquid is an acrylic emulsion containing a metal complex;

[0065] 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 40 min, and then cool to room temperature at a rate of 20 °C / min;

[0066] The preparation method of the transition liquid in step (2) includes the following steps by weight:

[0067] 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 carry out high-speed shear emulsification to obtain a pre-emulsion. Then 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;

[0068] Step (2-2): Take 20 parts of the metal complex composite pre-emulsion, add 0.3 part - 0.5 part of ammonium persulfate, adjust the pH to 6.5 under the condition of 70 °C - 80 °C, react for 15 min to obtain a seed emulsion. Then take another 160 parts of the metal complex composite pre-emulsion and 0.7 part 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.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that there is no transition layer, specifically:

[0071] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0072] Step (1): Mix and melt the PP resin particles with 1% of nano-silica, 1% of carbon nanotubes, and 1% of nano-titanium dioxide based on the weight of the PP, extrude and stretch into a film to obtain a PP film, and then carry out oxygen-argon plasma etching treatment for surface modification 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;

[0073] 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 the composite current collector; the heat treatment process is as follows: under argon atmosphere, keep at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min.

[0074] Comparative Example 2

[0075] The difference from Example 1 lies in that the process of Ar ion etching the transition layer in Step (2) is different, specifically:

[0076] A method for preparing a high-strength PP film for a composite current collector is obtained by the following method:

[0077] Step (1): Mix and melt PP resin particles with 1% by weight of nano-silica, carbon nanotubes, and 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 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;

[0078] 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;

[0079] The transition liquid is an acrylic emulsion containing a metal complex;

[0080] 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 the composite current collector; the heat treatment process is as follows: under argon atmosphere, keep at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min;

[0081] The preparation method of the transition liquid in Step (2) includes the following steps by weight:

[0082] 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, and 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;

[0083] 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, and react for 20 min to obtain a seed emulsion. Subsequently, 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 the addition, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that in step (2-1), the concentration of the metal complex is too low, specifically:

[0086] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0087] 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 based on the weight of PP, extrude, and stretch into a film to obtain a PP film. Subsequently, perform oxygen-argon plasma etching treatment, and after surface modification treatment, 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 composition of the oxygen-argon plasma 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;

[0088] Step (2): Spin-coat a transition layer on the surface of the prefabricated film with the transition liquid, and then dry it at 60 °C. 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, and etching for 70 min;

[0089] The transition liquid is an acrylic emulsion containing a metal complex;

[0090] 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 50 min, and then cool to room temperature at a rate of 15 °C / min;

[0091] The preparation method of the transition liquid in step (2) includes the following steps by weight:

[0092] 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 perform high-speed shear emulsification to obtain a pre-emulsion. Subsequently, 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.

[0093] 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, and react for 20 min to obtain a seed emulsion. Subsequently, 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 the addition is complete, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0094] Comparative Example 4

[0095] The difference from Example 1 is that in step (2), the process of etching the transition layer with Ar ions is different.

[0096] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0097] Step (1): Mix and melt PP resin particles with 1% of nano-silica, 1% of carbon nanotubes, and 1% of nano-titanium dioxide based on the weight of PP, extrude, and stretch into a film to obtain a PP film. Subsequently, perform surface modification treatment by oxygen-argon 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 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.

[0098] 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 250 W, vacuum degree 2 Pa, etching for 70 min.

[0099] The transition liquid is an acrylic emulsion containing a metal complex.

[0100] 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 50 min, and then cool to room temperature at a rate of 15 °C / min.

[0101] The preparation method of the transition liquid in step (2) includes the following steps by weight:

[0102] 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 perform high-speed shear emulsification to obtain a pre-emulsion. Subsequently, 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.

[0103] 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. Subsequently, 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 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.

[0104] Comparative Example 5

[0105] The difference from Example 1 is that the seed emulsion in step (2-2) is used as the transition liquid, specifically:

[0106] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0107] 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. Subsequently, perform surface modification treatment by oxygen-argon 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 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.

[0108] Step (2): Spin-coat a transition layer on the surface of the prefabricated film with the transition liquid, and then dry it at 60 °C. 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.

[0109] The transition liquid is an acrylic emulsion containing a metal complex.

[0110] Step (3): By magnetron sputtering with aluminum as the target, deposit a metal layer on the surface of the seed layer of the PP film containing the seed layer, and then perform heat treatment 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;

[0111] The preparation method of the transition liquid in step (2) includes the following steps by weight:

[0112] 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 copper 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;

[0113] 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, and react for 20 min to obtain a seed emulsion, that is, the transition liquid.

[0114] Comparative Example 6

[0115] The difference from Example 1 is that in step (2), the process of etching the transition layer with Ar ions is different;

[0116] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0117] 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. Then perform surface modification treatment by oxygen-argon 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 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;

[0118] 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: 120 °C, 20 sccm, radio frequency power 500 W, vacuum degree 2 Pa, etching for 70 min;

[0119] The transition liquid is an acrylic emulsion containing a metal complex;

[0120] 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;

[0121] The preparation method of the transition liquid in step (2) includes the following steps by weight:

[0122] Step (2-1): Dissolve 1 part of sodium dodecyl sulfate and 1 part of alkylphenol polyoxyethylene ether in 100 parts of water by stirring, 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;

[0123] 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, heat up to 85 °C after adding, and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0124] Comparative Example 7

[0125] It is different from Example 1 in that in step (2), the process of etching the transition layer with Ar ions is different;

[0126] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0127] 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 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;

[0128] 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;

[0129] The transition liquid is an acrylic emulsion containing a metal complex;

[0130] 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 conditions, keep warm at 100 °C for 50 min, and then cool to room temperature at a rate of 15 °C / min;

[0131] The preparation method of the transition liquid in step (2) includes the following steps by weight:

[0132] 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 liquid. 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;

[0133] 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. 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, raise the temperature to 85 °C and react for 45 min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid.

[0134] Comparative Example 8

[0135] The difference from Example 1 is that a traditional metal transition layer is selected:

[0136] A preparation method of a high-strength PP film for a composite current collector is obtained by the following method:

[0137] Step (1): Mix and melt blend 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 for surface modification 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;

[0138] Step (2): Using titanium as a target, magnetron sputtering is used to deposit a transition metal layer 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 for etching the transition layer with Ar ions is: 80°C, 20 sccm, RF power 400W, vacuum degree 2Pa, and etching for 70 min;

[0139] Step (3): A metal layer is plated on the surface of the seed layer of the PP film containing the seed layer by magnetron sputtering with aluminum as the target material, followed by heat treatment to obtain a high-strength PP film for the composite current collector; the heat treatment process is: under argon conditions, keep warm at 100°C for 50 minutes, and then cool to room temperature at a rate of 15°C / min.

[0140] Performance tests were performed on Examples 1-4 and Comparative Examples 1-8.

[0141] Tensile strength: according to ASTM D638, required to be ≥50 MPa;

[0142] Elongation at break: According to ASTM D638, the requirement is 5%-20%;

[0143] Puncture strength: according to ASTM D4833, requirement ≥200 N / mm;

[0144] Surface resistance: IEC 60093 is carried out according to the four-probe method, and the requirement is ≤5Ω / sq;

[0145] Coating adhesion: According to ASTM D3359, the requirement is ≥4B;

[0146] 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 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.

[0147] The performance test results are shown in Table 1.

[0148] Table 1

[0149]

[0150] 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.

[0151] Compared with Example 1, the comparative example has poor performance and has the following differences:

[0152] 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 resulting in 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, further leading to the decline of conductivity and bonding force, and the PP film is pulled to form grid deformation 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, due to too high substrate temperature in the etching process of step (2), the PP film is thermally degraded and deformed, resulting in the decline of mechanical properties and many wrinkles; in Comparative Example 7, due to too high etching power in the etching process of step (2), the energy is too high 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 preparation method of a high-strength PP film for a composite current collector, characterized in that It includes the following steps: Step (1): Mix and melt PP resin particles with 0.5%-3% by weight of functional filler based on the weight of PP, extrude and stretch into a film to obtain a PP film, and then obtain a prefabricated film through 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; The process of etching the transition layer with Ar ions is: 50℃-100℃, 10sccm-20sccm, radio frequency power 300W-500W, vacuum degree 0Pa-3Pa, etching for 60min-90min; The preparation method of the transition liquid includes the following steps by weight: Step (2-1): Stir and 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, and then add 5 parts-20 parts of metal complex, and stir 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 part-0.5 part of initiator, adjust the pH under the condition of 70℃-80℃, react for 15min-20min to obtain a seed emulsion, and then take another 150 parts-180 parts of the metal complex composite pre-emulsion and 0.5 part-1.0 part of initiator, slowly add them to the seed emulsion, and after the addition, raise the temperature to 80℃-90℃ and react for 30min-60min to obtain a metal complex-acrylic composite emulsion, that is, the transition liquid; 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 a composite current collector.

2. The preparation method of the high-strength PP film for composite current collectors 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 crystallinity of the prefabricated film is >60%.

3. The preparation method of the 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-silica, carbon nanotubes, graphene, and nano-titanium dioxide.

4. The preparation method of the 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 preparation method of the high-strength PP film for a composite current collector according to claim 1, characterized in that, The acrylic monomers in step (2-1) are one or more of methyl methacrylate, butyl acrylate, acrylic acid, ethyl acrylate, and isooctyl acrylate.

6. The preparation method of the high-strength PP film for composite current collectors according to claim 1, characterized in that, The metal complexes in step (2-1) are one or more of copper citrate, aluminum citrate, copper tartrate, and aluminum tartrate.

7. The preparation method of the high-strength PP film for composite current collectors according to claim 1, wherein, The initiator in step (2-2) is ammonium persulfate.

8. The preparation method of the high-strength PP film for composite current collectors according to claim 1, characterized in that, In step (3), the process of the heat treatment is: under argon condition, keep warm at 90℃-110℃ for 30min-60min, and then cool to room temperature at a rate of 10℃ / min-20℃ / min.

9. A high-strength PP film for a composite current collector prepared by the preparation method of a high-strength PP film for a composite current collector according to any one of the above claims 1-8.

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