Polypropylene film and preparation method therefor, composite current collector, electrode sheet, and use thereof

Abstract

The present application relates to a polypropylene film and a preparation method therefor, a composite current collector, an electrode sheet, and the use thereof, and belongs to the technical field of batteries. The preparation method for the polypropylene film comprises the following steps: performing a melt extrusion treatment, a casting treatment, a bidirectional stretching treatment and a heat treatment on raw materials in sequence, so as to obtain a polypropylene film intermediate, wherein the raw materials comprise 99-99.95% of a polypropylene and 0.05-1% of an additive in percentages by mass, the additive comprising a polyacrylic acid-metal ion complex; and performing a corona treatment on the polypropylene film intermediate, so as to obtain a polypropylene film. The polypropylene film prepared by means of the preparation method of the present application improves the storage stability of the surface adhesion performance of the polypropylene film, and realizes the stable preparation of a composite current collector with the polypropylene film as a base film.

Description

Polypropylene film and preparation method thereof, composite current collector, electrode plate and application thereof

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202311552346.8, filed on November 21, 2023, entitled “Polypropylene film, preparation method thereof, composite current collector, electrode plate and application”, the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a polypropylene film and a preparation method thereof, a composite current collector, an electrode plate, and applications thereof. Background Art

[0004] Currently, composite current collectors based on polypropylene films are gaining widespread attention and application in the new energy industry. Compared to traditional current collectors, these composite current collectors offer advantages such as low cost, lightweight, and excellent internal insulation. These advantages enable their use in batteries to reduce costs while increasing energy density and safety.

[0005] However, in the process of preparing composite current collectors using traditional polypropylene film as the base film, the surface tension of the polypropylene film is low due to the weak polarity of the polypropylene film itself. The affinity between the low surface tension polypropylene film and the high surface tension metal layer is poor, resulting in low adhesion between the interface of the two and weak bonding.

[0006] To address the problem of weak bonding between traditional polypropylene film and surface metal layer, the method of corona treatment on the surface of polypropylene film can be used to improve the adhesion between the polypropylene film and the surface metal layer. However, the surface tension of the polypropylene film after corona treatment is unstable. After storage for a period of time, the surface tension will decrease and finally approach the surface tension of the polypropylene film before treatment, causing the adhesion performance of the polypropylene film to deteriorate. That is, there is a problem of unstable storage of the surface adhesion performance of the polypropylene film, which limits the application of polypropylene film in composite current collectors. Summary of the Invention

[0007] Based on this, the present application provides a polypropylene film, a preparation method thereof, a composite current collector, an electrode plate, and applications thereof. Compared to conventional corona-treated polypropylene films, the polypropylene film prepared by the present application's preparation method exhibits higher surface adhesion and storage stability, enabling the stable preparation of composite current collectors using this polypropylene film as a base film.

[0008] In a first aspect of the present application, a method for preparing a polypropylene film is provided, comprising the following steps:

[0009] The raw materials are sequentially subjected to melt extrusion, sheet casting, biaxial stretching, and heat treatment to obtain a polypropylene film intermediate; the raw materials comprise, by mass percentage, 99% to 99.95% polypropylene and 0.05% to 1% additives, wherein the additives comprise one or more polyacrylic acid-metal ion complexes;

[0010] The polypropylene film intermediate is subjected to corona treatment to obtain the polypropylene film.

[0011] In some embodiments, the additive further comprises a polymer salt, and the mass ratio of the polyacrylic acid-metal ion complex to the polymer salt is (0.1-5):1.

[0012] In some embodiments, the crystallinity y of the polypropylene film and the mass ratio x of the polyacrylic acid-metal ion complex and the polymer salt satisfy the following conditions: 0.82x 3 -10.4x 2 +32x+36.9≤y≤80%.

[0013] In some embodiments, the polyacrylic acid-metal ion complex includes one or more of a polyacrylic acid-nickel ion complex, a polyacrylic acid-cobalt ion complex, a polyacrylic acid-zinc ion complex, a polyacrylic acid-iron ion complex, and a polyacrylic acid-copper ion complex.

[0014] In some embodiments, the polymer salt comprises one or more of polyacrylate and poly(ethylene-co-acrylic acid) zinc salt. Alternatively, the polyacrylate comprises one or more of sodium polyacrylate, potassium polyacrylate and ammonium polyacrylate.

[0015] In some embodiments, the polymer salt includes one or more of polyacrylate and poly(ethylene-co-acrylic acid) zinc salt, and the polyacrylate includes one or more of sodium polyacrylate, potassium polyacrylate, and ammonium polyacrylate.

[0016] In some embodiments, the polypropylene film has a crystallinity of ≥40%.

[0017] In some embodiments, the polypropylene film has a crystallinity of 40% to 80%.

[0018] In some embodiments, the polypropylene has a melt index of 3 g / 10 min to 3.9 g / 10 min at 230° C. and a load of 2.16 kg.

[0019] In some embodiments, the polypropylene has an isotacticity of ≥ 95%.

[0020] In some embodiments, the biaxial stretching process includes a longitudinal stretching process and a transverse stretching process performed sequentially.

[0021] In some embodiments, the process conditions of the longitudinal stretching treatment include: a stretching temperature of 140° C.-150° C., and a longitudinal stretching ratio of 7:1-11:1.

[0022] In some embodiments, the process conditions of the transverse stretching treatment include: a stretching temperature of 150° C.-160° C., and a stretching ratio of 3:1-5:1.

[0023] In some embodiments, the process conditions of the heat treatment include: a heat treatment temperature of 110° C.-125° C., and a heat treatment time of ≥5 s.

[0024] In some embodiments, the process conditions of the corona treatment include: a corona power of 50 kW to 100 kW, and a line speed of 50 m / min to 300 m / min.

[0025] In some embodiments, before corona treatment of the polypropylene film intermediate, the method further comprises: preheating the polypropylene film intermediate. Optionally, the preheating process conditions include: a preheating temperature of 25°C to 55°C.

[0026] In some embodiments, before corona treatment of the polypropylene film intermediate, the method further comprises: preheating the polypropylene film intermediate, and the process conditions of the preheating treatment include: a preheating temperature of 25° C.-55° C.

[0027] In some embodiments, the polypropylene film has a thickness of 1 μm to 20 μm.

[0028] In a second aspect of the present application, a polypropylene film is provided. The raw materials of the polypropylene film include, by mass percentage, 99%-99.95% polypropylene and 0.05%-1% additives, and the additives include one or more polyacrylic acid-metal ion complexes.

[0029] In some embodiments, the additive further comprises a polymer salt, and the mass ratio of the polyacrylic acid-metal ion complex to the polymer salt is (0.1-5):1.

[0030] In some embodiments, the crystallinity y of the polypropylene film and the mass ratio x of the polyacrylic acid-metal ion complex and the polymer salt satisfy the following conditions: 0.82x 3 -10.4x 2 +32x+36.9≤y≤80%.

[0031] The third aspect of the present application provides a composite current collector, comprising a polypropylene film and a metal layer, wherein the metal layer is arranged on at least one surface of the polypropylene film, and the polypropylene film is prepared by the preparation method described in the first aspect of the present application and at least one of the polypropylene films described in the second aspect of the present application.

[0032] In some embodiments, the composite current collector further includes a protective layer, and the protective layer is disposed on a side of the metal layer away from the polypropylene film.

[0033] In some embodiments, the thickness H1 of the protective layer and the thickness H2 of the metal layer satisfy the following condition: H1 / H2≤10%.

[0034] In some embodiments, the protective layer has a thickness of 10 nm to 150 nm.

[0035] In some embodiments, the material of the protective layer includes one or more of nickel, chromium, nickel-based alloys, copper-based alloys, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers and graphene.

[0036] In some embodiments, the thickness of the metal layer is 500 nm-2000 nm.

[0037] In some embodiments, the material of the metal layer includes one or more of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium and silver.

[0038] The fourth aspect of the present application provides an electrode plate comprising the composite current collector described in the third aspect of the present application.

[0039] The fifth aspect of the present application provides a battery comprising the electrode plate described in the fourth aspect of the present application.

[0040] In a sixth aspect of the present application, an electrical device is provided, comprising the battery described in the fifth aspect of the present application.

[0041] Compared with traditional technologies, the above-mentioned polypropylene film and its preparation method, composite current collector, electrode plate and application have at least the following advantages:

[0042] In the above-mentioned polypropylene film, by controlling the content of the additive containing polyacrylic acid-metal ion complex in the raw material within a reasonable range, the crystallization of polypropylene can be promoted, so that the crystallinity of the polypropylene film is within a certain range, thereby improving the storage stability of the surface adhesion performance of the polypropylene film and realizing the stable preparation of the composite current collector with the polypropylene film as the base film. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without any creative work.

[0044] FIG1 is a cross-sectional view of the composite current collector prepared in Example 1 of the present application.

[0045] In the picture:

[0046] 1-composite current collector; 11-polypropylene film; 12-metal layer; 13-protective layer. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0048] In the description of this application, unless otherwise defined, technical terms and professional words not explicitly stated have the same meaning as commonly understood by those skilled in the art and are common knowledge to those skilled in the art. Methods not explicitly stated are conventional methods known to those skilled in the art. The term "multiple" in this application means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0049] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0050] In a first aspect of the present application, a method for preparing a polypropylene film is provided, comprising the following steps:

[0051] The raw materials are sequentially subjected to melt extrusion, sheet casting, biaxial stretching, and heat treatment to obtain a polypropylene film intermediate; the raw materials comprise, by mass percentage, 99% to 99.95% polypropylene and 0.05% to 1% additives, wherein the additives comprise one or more polyacrylic acid-metal ion complexes;

[0052] The polypropylene film intermediate is subjected to corona treatment to obtain a polypropylene film.

[0053] In the above preparation method, by controlling the content of the additive containing polyacrylic acid-metal ion complex in the raw material within a reasonable range, the crystallization of polypropylene can be promoted, so that the crystallinity of the polypropylene film is within a certain range, thereby improving the storage stability of the surface adhesion performance of the polypropylene film, and realizing the stable preparation of the composite current collector with the polypropylene film as the base film. When the content of the additive in the polypropylene film is too high, the improvement of the crystallinity of the polypropylene film is limited and the film forming property is affected. In addition, the preparation method of the above polypropylene film is simple and easy, low in cost, high in processing efficiency, and easy to scale up. It can be understood that the raw materials of the polypropylene film may include: 99% polypropylene and 1% additives; or 99.2% polypropylene and 0.8% additives; or 99.4% polypropylene and 0.6% additives; or 99.6% polypropylene and 0.4% additives; or 99.8% polypropylene and 0.2% additives; or 99.95% polypropylene and 0.05% additives, etc.

[0054] In addition, the reason why the surface adhesion performance of traditional corona-treated polypropylene films decays during storage is that the polypropylene polymer after the surface corona treatment migrates to the interior of the polypropylene film due to its own movement during storage, thereby reducing the surface tension of the polypropylene film and causing the surface adhesion performance to decay. The polypropylene film prepared by the above preparation method, due to the addition of polyacrylic acid-metal ion complex, makes the crystallinity of the polypropylene film within a certain range, restricts the migration of the polypropylene polymer after the surface corona treatment to the interior of the polypropylene film, thereby improving the stability of the surface adhesion performance of the polypropylene film during storage. Therefore, compared with the traditional corona-treated polypropylene film, the surface adhesion performance of the polypropylene film prepared by the above preparation method is higher in storage stability, realizing the stable preparation of the composite current collector with the polypropylene film as the base film.

[0055] In the present application, the polyacrylic acid-metal ion complex refers to a complex formed by polyacrylic acid and metal ions, which is different from polyacrylate.

[0056] First, in polyacrylic acid-metal ion complexes, metal ions react with the carboxyl groups of polyacrylic acid to form a complex with a repeating unit structure of ligand-metal ion. In polyacrylic acid salts, the hydrogen atoms in the carboxyl groups of polyacrylic acid are replaced by metal ions, forming a salt structure.

[0057] Secondly, polyacrylates promote polypropylene crystallization primarily through the nucleation effect of polyacrylates, while polyacrylic acid-metal ion complexes promote polypropylene crystallization through the electron delocalization conjugated structure formed by polyacrylic acid and metal ions, as well as their more regular arrangement structure. Polyacrylic acid-metal ion complexes and polyacrylates have different mechanisms for promoting polypropylene crystallization, resulting in different crystallization behaviors and effects.

[0058] Finally, compared with polyacrylates, the presence of metal ions in polyacrylic acid-metal ion complexes provides additional crystallization sites, promoting the crystallization of polypropylene. In addition, due to the stronger restriction of chain movement by the complexation effect, the polyacrylic acid-metal ion complex has a better effect in promoting crystallization.

[0059] In some embodiments, the additive further comprises a polymer salt, and the mass ratio of the polyacrylic acid-metal ion complex to the polymer salt is (0.1-5):1. This can further enhance the surface adhesion and storage stability of the polypropylene film. It is understood that the mass ratio of the two includes, but is not limited to, 0.1:1, 1:1, 2:1, 3:1, 4:1, and 5:1.

[0060] In some embodiments, the crystallinity y of the polypropylene film and the mass ratio x of the polyacrylic acid-metal ion complex and the polymer salt satisfy the following conditions: 0.82x 3 -10.4x 2 +32x+36.9≤y≤80%. The crystallinity of the polypropylene film and the mass ratio of the polyacrylic acid-metal ion complex to the polymer salt meet the above conditions, which can further improve the storage stability of the surface adhesion performance of the polypropylene film. Optionally, x=0.1-5.

[0061] In some embodiments, the polyacrylic acid-metal ion complex includes one or more of a polyacrylic acid-nickel ion complex, a polyacrylic acid-cobalt ion complex, a polyacrylic acid-zinc ion complex, a polyacrylic acid-ferric ion complex, and a polyacrylic acid-copper ion complex. The polyacrylic acid-nickel ion complex, the polyacrylic acid-cobalt ion complex, the polyacrylic acid-zinc ion complex, the polyacrylic acid-ferric ion complex, and the polyacrylic acid-copper ion complex have a crystalline structure similar to that of polypropylene, can reduce interfacial surface free energy, are uniformly dispersed in polypropylene, provide sites for polypropylene crystallization, and further improve the storage stability of the surface adhesion performance of the polypropylene film.

[0062] In the present application, the nickel element in the "polyacrylic acid-nickel ion complex" can be +2 valence or +3 valence; the cobalt element in the "polyacrylic acid-cobalt ion complex" can be +2 valence or +3 valence; the zinc element in the "polyacrylic acid-zinc ion complex" can be +2 valence; the iron element in the "polyacrylic acid-iron ion complex" can be +2 valence or +3 valence; the copper element in the "polyacrylic acid-copper ion complex" can be +2 valence.

[0063] In some embodiments, the polymer salt includes one or more of a polyacrylate and a zinc poly(ethylene-co-acrylic acid). Alternatively, the polyacrylate includes one or more of sodium polyacrylate, potassium polyacrylate, and ammonium polyacrylate. Sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, zinc poly(ethylene-co-acrylic acid), and polypropylene have similar crystalline structures, which can reduce interfacial surface free energy, uniformly disperse in polypropylene, provide sites for polypropylene crystallization, and further enhance the storage stability of the surface adhesion properties of the polypropylene film.

[0064] In some embodiments, the polypropylene film has a crystallinity of 40% or greater. If the crystallinity of the polypropylene film is too low, the surface adhesion properties of the polypropylene after corona treatment will degrade too quickly. Therefore, controlling the crystallinity of the polypropylene film to 40% or greater can further improve the storage stability of the surface adhesion properties of the polypropylene film. It is understood that the crystallinity of the polypropylene film includes, but is not limited to, 40%, 45%, 50%, 60%, 65%, 70%, 75%, 80%, and 85%.

[0065] In some embodiments, the polypropylene film has a crystallinity of 40% to 80%. This can further improve the storage stability of the surface adhesion performance of the polypropylene film. Excessively high crystallinity of the polypropylene film is difficult to achieve and is prone to film breakage during the film production process.

[0066] In some embodiments, the melt index of polypropylene at 230°C and a load of 2.16 kg is 3 g / 10 min to 3.9 g / 10 min. This can improve the film forming properties and mechanical properties of the polypropylene film. For example, the melt index of polypropylene at 230°C and a load of 2.16 kg can be 3 g / 10 min, 3.3 g / 10 min, 3.6 g / 10 min, 3.9 g / 10 min, etc.

[0067] In some embodiments, the isotacticity of the polypropylene is ≥95%. This further improves the storage stability of the surface adhesion performance of the polypropylene film. If the isotacticity of the polypropylene is too low, the crystallization performance of the polypropylene is poor, resulting in low crystallinity of the polypropylene film, which may cause unstable surface adhesion performance of the polypropylene film.

[0068] In some embodiments, the biaxial stretching process includes a longitudinal stretching process and a transverse stretching process performed sequentially.

[0069] In some embodiments, the process conditions of the longitudinal stretching treatment include: a stretching temperature of 140° C. to 150° C., and a longitudinal stretching ratio of 7:1 to 11:1.

[0070] In the above preparation method, the longitudinal stretch ratio is controlled to 7:1-11:1, so that the polypropylene polymer is highly oriented, which can further promote the crystallization of polypropylene and improve the tensile strength of the polypropylene film. If the longitudinal stretch ratio is too low, the crystallinity of the polypropylene film will not be significantly improved; if the longitudinal stretch ratio is too high, the film will easily break, affecting the yield rate of the polypropylene film. It is understood that the longitudinal stretching temperature includes but is not limited to: 140°C, 142°C, 144°C, 146°C, 148°C, and 150°C, and the longitudinal stretch ratio includes but is not limited to: 7:1, 8:1, 9:1, 10:1, and 11:1.

[0071] In some optional embodiments, the process conditions of the longitudinal stretching treatment further include: a preheating temperature of 110°C-135°C.

[0072] In some embodiments, the process conditions of the transverse stretching treatment include: a stretching temperature of 150° C. to 160° C., and a stretch ratio of 3:1 to 5:1. It is understood that the transverse stretching temperature includes, but is not limited to, 150° C., 152° C., 154° C., 156° C., 158° C., and 160° C., and the transverse stretch ratio includes, but is not limited to, 3:1, 4:1, and 5:1.

[0073] In some optional embodiments, the process conditions of the transverse stretching treatment further include: a preheating temperature of 120°C-140°C.

[0074] In some embodiments, the process conditions of the heat treatment include: a heat treatment temperature of 110°C-125°C, and a heat treatment time ≥5s. Controlling the heat treatment temperature and heat treatment time within the above range can further improve the storage stability of the surface adhesion performance of the polypropylene film. Rapid crystallization of polypropylene can be achieved within the above heat treatment temperature range. If the heat treatment temperature is too high, the polypropylene polymer will be deoriented and the crystallinity of the polypropylene film will be reduced. It can be understood that the heat treatment temperature includes but is not limited to: 110°C, 115°C, 120°C, 125°C; the heat treatment time includes but is not limited to: 1s, 3s, 5s, 8s, 10s, 12s, 15s. Taking into account production efficiency, the heat treatment time can be selected as 1s-10s.

[0075] In some embodiments, the process conditions of the corona treatment include: a corona power of 50 kW to 100 kW and a line speed of 50 m / min to 300 m / min. It is understood that the corona power includes but is not limited to: 50 kW, 60 kW, 70 kW, 80 kW, 90 kW, 100 kW; the line speed includes but is not limited to: 50 m / min, 100 m / min, 150 m / min, 200 m / min, 250 m / min, 300 m / min.

[0076] In some embodiments, the method further includes preheating the polypropylene film intermediate before corona treatment. Optionally, the preheating temperature includes a preheating temperature of 25°C to 55°C. Preheating temperatures include, but are not limited to, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, and 55°C.

[0077] In some embodiments, before corona treatment of the polypropylene film intermediate, the method further includes preheating the polypropylene film intermediate, and the process conditions of the preheating treatment include a preheating temperature of 25° C. to 55° C. It is understood that the preheating temperature includes but is not limited to 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., and 55° C.

[0078] In some embodiments, the polypropylene film has a thickness of 1 μm to 20 μm. Taking into account the application requirements of the composite current collector, while also considering the difficulty and cost of the preparation process, the thickness of the polypropylene film is 1 μm to 20 μm. It is understood that the thickness of the polypropylene film includes, but is not limited to, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, and 20 μm.

[0079] In a second aspect of the present application, a polypropylene film is provided. The raw materials of the polypropylene film include, by mass percentage, 99%-99.95% polypropylene and 0.05%-1% additives, wherein the additives include a polyacrylic acid-metal ion complex.

[0080] In the above-mentioned polypropylene film, by controlling the content of the additive containing polyacrylic acid-metal ion complex in the raw material within a reasonable range, the crystallization of polypropylene can be promoted, so that the crystallinity of the polypropylene film is within a certain range, thereby improving the storage stability of the surface adhesion performance of the polypropylene film and realizing the stable preparation of the composite current collector with the polypropylene film as the base film.

[0081] In some embodiments, the additive further comprises a polymer salt, and the mass ratio of the polyacrylic acid-metal ion complex to the polymer salt is (0.1-5):1. This can further enhance the surface adhesion and storage stability of the polypropylene film. It is understood that the mass ratio of the two includes, but is not limited to, 0.1:1, 1:1, 2:1, 3:1, 4:1, and 5:1.

[0082] In some embodiments, the crystallinity y of the polypropylene film and the mass ratio x of the polyacrylic acid-metal ion complex and the polymer salt satisfy the following conditions: 0.82x 3 -10.4x 2+32x+36.9≤y≤80%. The crystallinity of the polypropylene film and the mass ratio of the polyacrylic acid-metal ion complex to the polymer salt meet the above conditions, which can further improve the storage stability of the surface adhesion performance of the polypropylene film. Optionally, x=0.1-5.

[0083] In some embodiments, the polypropylene film is prepared by the preparation method described in the first aspect of the present application.

[0084] The third aspect of the present application provides a composite current collector, comprising a polypropylene film and a metal layer, wherein the metal layer is arranged on at least one surface of the polypropylene film, and the polypropylene film is prepared by the preparation method described in the first aspect of the present application and at least one of the polypropylene films described in the second aspect of the present application.

[0085] Illustratively, in the above embodiment, the metal layer may be located on one surface of the polypropylene film along the thickness direction; or the metal layer may be located on both surfaces of the polypropylene film along the thickness direction; the material of the metal layers located on the two surfaces of the polypropylene film is the same; and the provided metal layer is used for conduction.

[0086] In some embodiments, the composite current collector further includes a protective layer disposed on a side of the metal layer away from the polypropylene film. The protective layer can protect the metal layer from chemical corrosion or physical damage. Furthermore, when multiple protective layers are disposed in the composite current collector, the materials of the multiple protective layers can be the same or different, and the thicknesses can be the same or different.

[0087] In some embodiments, the thickness H1 of the protective layer and the thickness H2 of the metal layer satisfy the following condition: H1 / H2≤10%.

[0088] In some embodiments, the thickness of the protective layer is 10 nm to 150 nm. It is understood that the thickness of the protective layer includes but is not limited to: 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, 120 nm, and 150 nm.

[0089] In some optional embodiments, the thickness of the protective layer is 20 nm-100 nm.

[0090] In some embodiments, the material of the protective layer includes one or more of nickel, chromium, nickel-based alloys, copper-based alloys, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, and graphene. Optionally, the carbon black includes one or more of acetylene black and Ketjen black.

[0091] In some embodiments, the protective layer is prepared by one or more methods selected from physical vapor deposition, chemical vapor deposition, in-situ forming, and coating. The vapor deposition method may be one or more of vacuum evaporation and magnetron sputtering; the chemical vapor deposition method may be one or more of atmospheric pressure chemical vapor deposition and plasma-enhanced chemical vapor deposition; the in-situ forming method may be a method for in-situ forming a metal oxide passivation layer on the surface of the metal layer; and the coating method may be one or more of die coating, blade coating, and extrusion coating.

[0092] In some embodiments, the thickness of the metal layer is 500 nm to 2000 nm. Considering the conductivity of the metal layer, the thickness of the metal layer can be set within the above range. It is understood that the thickness of the metal layer includes, but is not limited to, 500 nm, 700 nm, 1000 nm, 1200 nm, 1500 nm, 1700 nm, and 2000 nm.

[0093] In some optional embodiments, the thickness of the metal layer is 700 nm-1200 nm.

[0094] In some embodiments, the material of the metal layer includes one or more of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, and silver.

[0095] In some embodiments, the metal layer can be prepared by one or more of physical vapor deposition, electroplating, and chemical plating. Physical vapor deposition can include one or more of resistance heating vacuum evaporation, electron beam heating vacuum evaporation, laser heating vacuum evaporation, and magnetron sputtering.

[0096] The fourth aspect of the present application provides an electrode plate comprising the composite current collector described in the third aspect of the present application.

[0097] The above-mentioned electrode plates can be prepared, for example, by mixing positive electrode active material / negative electrode active material, conductive agent, binder and solvent to form an electrode slurry. For example, the method for preparing electrode plates well known to those skilled in the art can be used to coat the electrode slurry on at least one surface of the composite current collector described in the third aspect of the present application to obtain the above-mentioned electrode plates. The positive electrode active materials include but are not limited to: one or more of ternary positive electrode materials (such as nickel-cobalt-manganese ternary positive electrode materials, nickel-cobalt-aluminum ternary positive electrode materials), lithium cobaltate, lithium manganate and lithium iron phosphate; the negative electrode active materials include but are not limited to: one or more of graphite, hard carbon, soft carbon, silicon-based materials and lithium titanate. Depending on the active material, the electrode plates can be divided into positive electrode plates and negative electrode plates. The present application has no particular restrictions on the preparation method of the electrode plates, and the preparation method used can produce the above-mentioned electrode plates.

[0098] The fifth aspect of the present application provides a battery comprising the electrode plate described in the fourth aspect of the present application. The above-mentioned battery comprises a secondary battery, and the secondary battery comprises one or more of a lithium-ion battery and a sodium-ion battery. The above-mentioned battery may, for example, comprise a positive electrode plate, a negative electrode plate, an electrolyte and a diaphragm. The diaphragm is arranged between the positive electrode plate and the negative electrode plate, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The electrolyte plays the role of conducting ions between the positive electrode plate and the negative electrode plate. During the charge and discharge process of the battery, lithium ions or sodium ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The positive electrode plate and / or the negative electrode plate may adopt the electrode plate described in the fourth aspect of the present application.

[0099] A sixth aspect of the present application provides an electrical device comprising the battery described in the fifth aspect of the present application. The battery can be used as a power source or energy storage unit in the electrical device, including but not limited to electric vehicles, smart home appliances, computers, tablets, mobile phones, digital cameras, power tools, etc.

[0100] The present application is further described in detail below with reference to specific examples and comparative examples. For experimental parameters not specified in the following specific examples, reference should be made to the guidance provided in the present application documents. Reference may also be made to experimental manuals in the art or other experimental methods known in the art, or to the experimental conditions recommended by the manufacturer. It is understood that the instruments and raw materials used in the following examples are relatively specific and may not be limited thereto in other specific examples.

[0101] Example 1

[0102] (1) Preparation of polypropylene film

[0103] (1.1) The raw materials of the polypropylene film are polypropylene (manufacturer: Borealis, model: HC312BF) and additives. The additives are sodium polyacrylate (manufacturer: Sigma-Aldrich, CAS No.: 9003-04-7) and a polyacrylic acid-zinc ion complex. The weight ratio of the polyacrylic acid-zinc ion complex to the sodium polyacrylate is 1:10. The melt index of the polypropylene at 230°C and a load of 2.16 kg is 3.2 g / 10 min (230°C / 2.16 kg), and the isotacticity is 96%.

[0104] The preparation method of the polyacrylic acid-zinc ion complex is as follows: 50g of polyacrylic acid (Mw: 80000, manufacturer: Sigma-Aldrich, number: 435325) and 100g of zinc chloride (mass ratio of the two is 1:2) are added to 850g of pure water, stirred at 500rpm for 24h, and then filtered to remove water from the solution. After filtration, the reaction product is repeatedly washed with pure water to remove excess zinc chloride (ZnCl2). After washing, the reaction product is placed in an 80°C oven to dry to obtain the polyacrylic acid-zinc ion complex.

[0105] (1.2) Melt Extrusion: The above raw materials were added to the corresponding twin-screw extruder. The mass percentages of polypropylene and additives in the raw materials were 99.95% and 0.05%, respectively. The raw materials were melted at 250°C, and then filtered through a filter (10 μm filter mesh). The melt was extruded through a die head at a die head temperature of 260°C.

[0106] (1.3) Casting: The molten polypropylene material extruded from the die is cast onto the casting roller and formed by the casting roller and water cooling treatment. The cooling temperature is 30°C.

[0107] (1.4) Biaxial stretching: ① Longitudinal stretching: preheating temperature is 120℃, stretching temperature is 145℃, longitudinal stretch ratio is 7:1, and then cool to room temperature. ② Transverse stretching: preheating temperature is 140℃, stretching temperature is 150℃, and stretch ratio is 3:1.

[0108] (1.5) Heat treatment: The heat treatment temperature is 110°C and the treatment time is 5s.

[0109] (1.6) Winding: The heat-treated film is air-cooled in the platform area and then enters the winding system through the traction system for film winding. The winding tension is 30N / m, and a polypropylene film intermediate with a thickness of 4.5μm is prepared.

[0110] (1.7) Corona: Before corona treatment, the prepared polypropylene film intermediate was preheated at 25°C and then entered the corona system. The corona power was set to 50 kW and the processing line speed was 50 m / min. The thickness of the prepared polypropylene film was 4.5 μm.

[0111] (2) Preparation of composite current collector

[0112] (2.1) Preparation of a metal layer: The polypropylene film prepared in step (1.7) was allowed to stand for one month and then placed in a magnetron sputtering chamber. Using 99.99% pure copper metal as a target and argon gas as a gas source, a copper metal layer 80 nm thick was deposited on both sides of the polypropylene film prepared in step (1.7) along the thickness direction by magnetron sputtering in the magnetron sputtering chamber to obtain a composite film.

[0113] Then, the prepared composite film was used as a substrate for electroplating to thicken the conductive copper layer. The electroplating process was divided into the following three steps: ① Electroplating to thicken the metal layer: the electroplating solution was 120 g / L copper sulfate, 100 g / L sulfuric acid, 50 mg / L chloride ion, 1.2 mg / L sodium 3-mercapto-1-propane sulfonate, 0.5 mg / L 2-mercaptopyridine, and 180 mg / L polyethylene glycol 10000. The electroplating solution temperature was 25°C, and the average cathode current density was 2 A / dm 2 , electroplating treatment for 5 minutes.

[0114] (2.2) Preparation of a Protective Layer: After electroplating, the plated film was rinsed in a clean water tank. A surface protective layer was then prepared in a tank containing a 5g / L potassium dichromate aqueous solution at 25°C for 25 seconds. The film was then rinsed again in a clean water tank. The washed film was then dried in an oven at 65°C to obtain a composite current collector with a total thickness of 1.2 μm for the copper metal layer and protective layer.

[0115] A cross-sectional view of the composite current collector prepared in Example 1 is shown in FIG1 . The composite current collector 1 comprises a polypropylene film 11 and a metal layer 12 and a protective layer 13 sequentially disposed on both sides of the polypropylene film 11 in the thickness direction and away from the polypropylene film 11 . The metal layer 12 is a copper metal layer.

[0116] Example 2

[0117] The method is basically the same as Example 1, except that the mass percentages of polypropylene and additives in the raw material are 99.5% and 0.5% respectively.

[0118] Example 3

[0119] The method is basically the same as Example 1, except that the mass percentages of polypropylene and additives in the raw materials are 99% and 1% respectively.

[0120] Example 4

[0121] The method is basically the same as Example 1, except that the sodium polyacrylate in the additive is replaced by potassium polyacrylate (manufacturer: Sigma-Aldrich, CAS No.: 25608-12-2).

[0122] Example 5

[0123] The method is basically the same as Example 1, except that the sodium polyacrylate in the additive is replaced by poly(ethylene-co-acrylic acid) zinc salt (manufacturer: Shanghai Guchen Biotechnology Co., Ltd., CAS No.: 28208-80-2).

[0124] Example 6

[0125] The reaction mixture is substantially the same as in Example 2, except that the additive in the raw material is replaced by a polyacrylic acid-nickel ion complex. The preparation method of the polyacrylic acid-nickel ion complex is as follows: 60 g of polyacrylic acid (Mw: 80,000, manufacturer: Sigma-Aldrich, number: 435325) and 180 g of nickel chloride (the mass ratio of the two is 1: 3) are added to 760 g of pure water, stirred at 500 rpm for 24 h, and then filtered to remove water from the solution. After filtration, the reaction product is repeatedly washed with pure water to remove excess nickel chloride (NiCl2). After cleaning, the reaction product is placed in an 80 ° C oven and dried to obtain a polyacrylic acid-nickel ion complex.

[0126] Example 7

[0127] The reaction mixture was substantially the same as in Example 2, except that the additive in the raw material was replaced with a polyacrylic acid-cobalt ion complex. The preparation method of the polyacrylic acid-cobalt ion complex was as follows: 50 g of polyacrylic acid (Mw: 80,000, manufacturer: Sigma-Aldrich, number: 435325) and 125 g of cobalt chloride (the mass ratio of the two was 1: 2.5) were added to 825 g of pure water, stirred at 500 rpm for 24 h, and then filtered to remove water from the solution. After filtration, the reaction product was repeatedly washed with pure water to remove excess cobalt chloride (CoCl2). After washing, the reaction product was placed in an oven at 80 ° C. and dried to obtain a polyacrylic acid-cobalt ion complex.

[0128] Example 8

[0129] The method is basically the same as Example 2, except that the additive in the raw material is replaced by a polyacrylic acid-zinc ion complex. The preparation method of the polyacrylic acid-zinc ion complex is as follows: 50 g of polyacrylic acid (Mw: 80000, manufacturer: Sigma-Aldrich, number: 435325) and 100 g of zinc chloride (the mass ratio of the two is 1: 2) are added to 850 g of pure water, stirred at 500 rpm for 24 h, and then filtered to remove water from the solution. After filtration, the reaction product is repeatedly washed with pure water to remove excess zinc chloride (ZnCl2). After washing, the reaction product is placed in an 80°C oven and dried to obtain a polyacrylic acid-zinc ion complex.

[0130] Example 9

[0131] Substantially the same as Example 2, except that the additive in the raw material is replaced by a polyacrylic acid-iron ion complex. The preparation method of the polyacrylic acid-iron ion complex is as follows: 50 g of polyacrylic acid (Mw: 80000, manufacturer: Sigma-Aldrich, number: 435325) and 150 g of ferric chloride (the mass ratio of the two is 1: 3) are taken, added to 800 g of pure water, stirred at 500 rpm for 24 h, and then filtered to remove the water in the solution. After filtration, the reaction product is repeatedly washed with pure water to remove excess ferric chloride (FeCl3). After cleaning, the reaction product is placed in an 80 ° C oven and dried to obtain a polyacrylic acid-iron ion complex.

[0132] Example 10

[0133] The invention is basically the same as Example 2, except that the additive in the raw material is replaced by a polyacrylic acid-copper ion complex, and the preparation method of the polyacrylic acid-copper ion complex is as follows: 50g of polyacrylic acid (Mw: 80000, manufacturer: Sigma-Aldrich, number: 435325) and 100g of copper sulfate (the mass ratio of the two is 1: 2) are taken, added to 850g of pure water, stirred at 500rpm for 24h, and then filtered to remove the water in the solution. After filtration, the reaction product is repeatedly washed with pure water to remove excess copper sulfate. After cleaning, the reaction product is placed in an 80°C oven and dried to obtain a polyacrylic acid-copper ion complex.

[0134] Example 11

[0135] The process is basically the same as Example 1, except that the isotacticity of the polypropylene in the raw material is 98%.

[0136] Example 12

[0137] The process is basically the same as Example 1, except that the isotacticity of the polypropylene in the raw material is 93%.

[0138] Example 13

[0139] Basically the same as Example 1, except that the longitudinal stretching ratio is 9:1.

[0140] Example 14

[0141] It is basically the same as Example 1, except that the longitudinal stretching ratio is 11:1.

[0142] Example 15

[0143] Basically the same as Example 1, except that the longitudinal stretching ratio is 6:1.

[0144] Example 16

[0145] Basically the same as Example 1, except that the longitudinal stretching ratio is 12:1.

[0146] Example 17

[0147] Basically the same as Example 1, except that the heat treatment temperature is 118°C.

[0148] Example 18

[0149] Basically the same as Example 1, except that the heat treatment temperature is 125°C.

[0150] Example 19

[0151] Basically the same as Example 1, except that the heat treatment temperature is 100°C.

[0152] Example 20

[0153] Basically the same as Example 1, except that the heat treatment temperature is 130°C.

[0154] Example 21

[0155] The process is basically the same as Example 1, except that the heat treatment time is 10s.

[0156] Example 22

[0157] Basically the same as Example 1, except that the heat treatment time is 15s.

[0158] Example 23

[0159] It is basically the same as Example 1, except that the heat treatment time is 2s.

[0160] Example 24

[0161] The method is basically the same as Example 1, except that the preheating temperature before corona treatment is 40°C.

[0162] Example 25

[0163] The method is basically the same as Example 1, except that the preheating temperature before corona treatment is 55°C.

[0164] Example 26

[0165] The method is basically the same as Example 1, except that the power of the corona treatment is 80 kW.

[0166] Example 27

[0167] The method is basically the same as Example 1, except that the power of the corona treatment is 100 kW.

[0168] Example 28

[0169] The method is basically the same as Example 1, except that: in step (2.1), the metal layer is an aluminum metal layer;

[0170] Specifically:

[0171] The polypropylene film prepared in step (1.7) was placed in a magnetron sputtering chamber after being left for one month. Aluminum metal with a purity of 99.99% was used as a target material and argon gas was used as a gas source. A 1200 nm thick aluminum metal layer was plated on both sides of the polypropylene film prepared in step (1.7) along the thickness direction by magnetron sputtering in the magnetron sputtering chamber to obtain a composite aluminum current collector.

[0172] Example 29

[0173] The method is basically the same as Example 1, except that the mass ratio of the polyacrylic acid-zinc ion complex to sodium polyacrylate in the additive is 2:1.

[0174] Example 30

[0175] The method is basically the same as Example 1, except that the mass ratio of the polyacrylic acid-zinc ion complex to sodium polyacrylate in the additive is 5:1.

[0176] Comparative Example 1

[0177] The method is basically the same as Example 1, except that the contents of polypropylene and additives in the raw materials are 99.98% and 0.02% respectively.

[0178] Comparative Example 2

[0179] The method is basically the same as Example 1, except that the contents of polypropylene and additives in the raw materials are 98.8% and 1.2% respectively.

[0180] Comparative Example 3

[0181] It is basically the same as Example 28, except that the contents of polypropylene and additives in the raw materials are 99.98% and 0.02% respectively.

[0182] Comparative Example 4

[0183] It is basically the same as Example 28, except that the contents of polypropylene and additives in the raw materials are 98.8% and 1.2% respectively.

[0184] Comparative Example 5

[0185] The method is basically the same as Example 1, except that the raw material contains only polypropylene and no additives.

[0186] Performance Testing

[0187] (1) Crystallinity: The crystallinity was tested using a differential scanning calorimeter (DSC) method. Specifically, according to the DSC instrument requirements, an appropriate amount of the polypropylene film prepared in the present application was taken and tested under the following conditions: first, the temperature was raised from 30°C to 200°C at a rate of 10°C / min, then kept at 200°C for 3 minutes, and finally, the temperature was lowered from 200°C to 30°C at a rate of 10°C / min. The DSC curve test was performed, and the melting enthalpy (ΔH f ), and the crystallinity was calculated according to the following formula.

[0188] Xc=△H f / △H f c ×100%

[0189] Among them, Xc is the crystallinity, △H f c It is the melting enthalpy of PP in the fully crystalline state (taken as 209 J / g).

[0190] (2) Surface Tension: The initial surface tension and surface tension after one month of storage of the polypropylene films prepared in the above examples and comparative examples were measured in accordance with GB / T 14216-2008. The rate of change in surface tension of the polypropylene film before and after storage = (initial surface tension of the polypropylene film prepared in step (1.7) - surface tension of the polypropylene film prepared in step (1.7) after one month of storage) / initial surface tension of the polypropylene film prepared in step (1.7) × 100%.

[0191] (3) Tensile strength of polypropylene film: Samples were taken longitudinally from the prepared polypropylene film roll, and the tensile strength of the film was tested according to the national standard GB / T 1040.3-2006.

[0192] (4) Adhesion between the polypropylene film and the metal layer in the composite current collector: A layer of Permacel P-94 double-sided tape was adhered to a 1 mm thick aluminum foil, the composite current collector was adhered on top of the double-sided tape, and a layer of ethylene acrylic acid copolymer film (DuPont Nurcel0903, thickness of 50 μm) was covered on the composite current collector. 5 N / m 2 The sample was hot-pressed at 120°C for 10 seconds, cooled to room temperature, and cut into 150mm x 15mm strips. Finally, the ethylene acrylic acid copolymer film strip was fixed to the upper fixture of the tensile testing machine, and the remaining film strip was fixed to the lower fixture. After the two were fixed, the metal layer was peeled off from the polypropylene film at an angle of 180° and a speed of 100mm / min to test the peel force, that is, the adhesion between the polypropylene film and the metal layer.

[0193] (5) Defective rate caused by film breakage: The defective rate is the percentage of the length of the polypropylene film caused by film breakage to the total length of the prepared polypropylene film.

[0194] Table 1 Performance test results

[0195] From the data in Table 1, we can see that

[0196] ① It can be seen from Examples 1-10, Comparative Examples 1-2 and Comparative Example 5 that adding a certain amount of polyacrylate and polyacrylic acid-metal ion complex or only adding a certain amount of polyacrylic acid-metal ion complex during the preparation of the polypropylene film and controlling the crystallinity of the polypropylene film within a certain range can reduce the rate of change of the surface tension of the polypropylene film during the placement process, and improve the adhesion between the metal layer and the base film of the composite current collector prepared with the placed polypropylene film as the base film.

[0197] ② Comparing Examples 1-3, 1-2, and 5, and comparing Example 28 with Comparative Examples 3-5, it can be seen that controlling the content of the additive in the raw material to 0.05%-1% can reduce the rate of change of the surface tension of the polypropylene film before and after placement, thereby improving the storage stability of the surface adhesion performance of the polypropylene film, and improving the bonding force between the polypropylene film and the metal layer (e.g., copper metal layer or aluminum metal layer). In addition, by increasing the content of the additive, the change in the surface tension of the polypropylene film during placement first decreases and then increases, the tensile strength first increases and then decreases, and the bonding force between the metal layer and the base film of the composite current collector prepared with the placed polypropylene film as the base film first increases and then decreases.

[0198] ③ From Examples 1 and 13-16, it can be seen that: the longitudinal stretching ratio of the polypropylene film is within a certain range, the rate of change of the surface tension of the polypropylene film during the placement process is low, the tensile strength is high, and the metal layer of the composite current collector prepared with the placed polypropylene film as the base film has a high bonding force with the base film.

[0199] ④ From Examples 1 and 17-20, it can be seen that: as the heat treatment temperature is increased, the surface tension of the polypropylene film during the placement process first decreases and then increases, the tensile strength first increases and then decreases, and the adhesion between the metal layer of the composite current collector prepared with the placed polypropylene film as the base film and the base film first increases and then decreases.

[0200] ⑤ From Examples 1 and 21-23, it can be seen that: by increasing the heat treatment time, the rate of change of the surface tension of the polypropylene film during the placement process decreases, the tensile strength increases, and the adhesion between the metal layer of the composite current collector prepared with the placed polypropylene film as the base film and the base film increases.

[0201] ⑥ It can be seen from Examples 1 and 24-27 that: based on Example 1, improving the corona process (for example, improving the preheating temperature before corona treatment, the power of corona treatment, etc.) can further promote the increase in the adhesion between the metal layer of the prepared composite current collector and the base film.

[0202] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0203] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A method for preparing a polypropylene film, comprising the following steps: The raw material is sequentially subjected to melt extrusion treatment, sheet casting treatment, biaxial stretching treatment and heat treatment to obtain a polypropylene film intermediate; the raw material comprises 99%-99.95% polypropylene and 0.05%-1% additives in terms of mass percentage, and the additives comprise polyacrylic acid-metal ion complex; The polypropylene film intermediate is subjected to corona treatment to obtain the polypropylene film.

2. The preparation method according to claim 1, wherein The additive also includes a polymer salt, and the mass ratio of the polyacrylic acid-metal ion complex to the polymer salt is (0.1-5):

1.

3. The preparation method according to claim 2, wherein The crystallinity y of the polypropylene film and the mass ratio x of the polyacrylic acid-metal ion complex and the polymer salt satisfy the following conditions: 0.82x 3 -10.4x 2 +32x+36.9≤y≤80%.

4. The preparation method according to any one of claims 1 to 3, wherein: The polyacrylic acid-metal ion complex includes one or more of a polyacrylic acid-nickel ion complex, a polyacrylic acid-cobalt ion complex, a polyacrylic acid-zinc ion complex, a polyacrylic acid-iron ion complex and a polyacrylic acid-copper ion complex.

5. The preparation method according to any one of claims 2 to 3, wherein: The polymer salt includes one or more of polyacrylate and poly(ethylene-co-acrylic acid) zinc salt, and the polyacrylate includes one or more of sodium polyacrylate, potassium polyacrylate and ammonium polyacrylate.

6. The preparation method according to any one of claims 1 to 5, wherein: The crystallinity of the polypropylene film is ≥40%.

7. The preparation method according to any one of claims 1 to 6, wherein: The crystallinity of the polypropylene film is 40%-80%.

8. The preparation method according to any one of claims 1 to 7, wherein: The polypropylene has one or more of the following characteristics: (1) The melt index of the polypropylene at 230° C. and 2.16 kg load is 3 g / 10 min to 3.9 g / 10 min; (2) The isotacticity of the polypropylene is ≥95%.

9. The preparation method according to any one of claims 1 to 8, wherein: The biaxial stretching process includes a longitudinal stretching process and a transverse stretching process performed sequentially; the biaxial stretching process has one or more of the following characteristics: (1) The process conditions of the longitudinal stretching treatment include: a stretching temperature of 140° C. to 150° C. and a longitudinal stretching ratio of 7:1 to 11:1; (2) The process conditions of the transverse stretching treatment include: a stretching temperature of 150°C-160°C and a stretching ratio of 3:1-5:

1.

10. The preparation method according to any one of claims 1 to 9, wherein: The process conditions of the heat treatment include: the heat treatment temperature is 110° C.-125° C., and the heat treatment time is ≥5s.

11. The preparation method according to any one of claims 1 to 10, wherein: The preparation method meets one or more of the following conditions: (1) The process conditions of the corona treatment include: corona power of 50 kW to 100 kW and line speed of 50 m / min to 300 m / min; (2) Before the polypropylene film intermediate is subjected to corona treatment, the method further comprises: performing a preheating treatment on the polypropylene film intermediate, and the process conditions of the preheating treatment include: a preheating temperature of 25° C.-55° C.

12. The preparation method according to any one of claims 1 to 11, wherein: The thickness of the polypropylene film is 1 μm-20 μm.

13. A polypropylene film, wherein the raw materials of the polypropylene film comprise, by mass percentage, 99%-99.95% polypropylene and 0.05%-1% additives, wherein the additives comprise polyacrylic acid-metal ion complexes.

14. The polypropylene film according to claim 13, wherein The additive also includes a polymer salt, and the mass ratio of the polyacrylic acid-metal ion complex to the polymer salt is (0.1-5):

1.

15. The polypropylene film according to claim 14, wherein The crystallinity y of the polypropylene film and the mass ratio x of the polyacrylic acid-metal ion complex and the polymer salt satisfy the following conditions: 0.82x 3 -10.4x 2 +32x+36.9≤y≤80%.

16. A composite current collector, comprising a polypropylene film and a metal layer, wherein the metal layer is arranged on at least one surface of the polypropylene film, and the polypropylene film is at least one of the polypropylene film prepared by the preparation method according to any one of claims 1 to 12 and the polypropylene film according to any one of claims 13 to 15.

17. The composite current collector according to claim 16, wherein: The invention also comprises a protective layer, wherein the protective layer is arranged on a side of the metal layer away from the polypropylene film.

18. The composite current collector according to claim 17, wherein: The protective layer has one or more of the following features: (1) The thickness H1 of the protective layer and the thickness H2 of the metal layer satisfy the following condition: H1 / H2≤10%; (2) The thickness of the protective layer is 10nm-150nm; (3) The material of the protective layer includes one or more of nickel, chromium, nickel-based alloy, copper-based alloy, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers and graphene.

19. The composite current collector according to any one of claims 16 to 18, wherein: The metal layer meets one or more of the following conditions: (1) The thickness of the metal layer is 500nm-2000nm; (2) The material of the metal layer includes one or more of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium and silver.

20. An electrode plate, comprising at least one of the polypropylene film prepared by the preparation method according to any one of claims 1 to 12, the polypropylene film according to any one of claims 13 to 15, and the composite current collector according to any one of claims 16 to 19.

21. A battery comprising at least one of the composite current collector according to any one of claims 16 to 19 and the electrode plate according to claim 20.

22. An electrical device comprising at least one of the composite current collector according to any one of claims 16 to 19, the electrode sheet according to claim 20, and the battery according to claim 21.

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