Polymer composite film, composite current collector, method for preparing the same, positive electrode and application thereof

Abstract

This application relates to the field of electrochemical technologies, and specifically relates to a polymer composite film, a composite current collector, a preparation method thereof, a positive electrode and an application thereof. The polymer composite film of this application includes a polymer base layer, and a first modification layer and a second modification layer respectively disposed on the opposite two surface of the polymer base layer; the material of the polymer base layer includes one or more of polyethylene terephthalate, poly(1,4-cyclohexanedimethylene terephthalate) and polyethylene terephthalate-1,4-cyclohexanedimethylene terephthalate; the components of the first modification layer and the second modification layer each independently include: a functionalized polymer material; the functionalized polymer material includes one or more of polyethylene naphthalate, poly(m-phenylene adipamide), liquid crystal polymer, polyformaldehyde, polyphenylene sulfide and polyphenylene ether. The polymer composite film of this application can be effectively disconnected when being damaged by strong external force, and thus can effectively prevent the occurrence of battery thermal runaway.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a polymer composite film, a composite current collector and a preparation method thereof, a positive electrode and applications thereof. Background Art

[0002] At present, power batteries generally take high energy density and high rate as their iterative development goals, but the higher the energy density of lithium-ion batteries, the worse their safety is, and they are more likely to cause thermal runaway, which seriously restricts the further development of power batteries in the field of new energy. Among the types of battery thermal runaway, short circuit between negative electrode material and positive electrode material and internal short circuit between positive electrode current collector and positive electrode material are directly related to positive electrode current collector.

[0003] At present, composite current collectors are expected to gradually replace traditional current collectors due to their advantages of high safety, low cost, and high energy density. The existing positive composite current collectors are mainly composed of polyethylene terephthalate (PET) base film and aluminum metal layer. Among them, the insulation properties of PET itself enable the battery to reduce the risk of short circuit in cases such as thermal runaway. However, the elongation of the positive composite current collector generally exceeds 80%, and its excessively high elongation at break makes it impossible for the positive composite current collector to be disconnected in time when it is damaged by external force, and continues to provide a path for abnormal reactions inside the battery, which is not conducive to controlling battery thermal runaway. Therefore, appropriately reducing the elongation of the positive composite current collector can prevent the occurrence of battery thermal runaway. Summary of the invention

[0004] Based on this, the present application provides a polymer composite film, a composite current collector and a preparation method thereof, a positive electrode and an application thereof. The polymer composite film provided in the present application has a low elongation, and when used as a positive electrode current collector base film, it can effectively prevent the occurrence of thermal runaway of the battery.

[0005] In a first aspect of the present application, a polymer composite film is provided, the polymer composite film comprising a polymer base layer and a first modified layer and a second modified layer respectively disposed on two opposite side surfaces of the polymer base layer;

[0006] The material of the polymer base layer includes one or more of polyethylene terephthalate, polyethylene terephthalate-1,4-cyclohexanedimethanol and polyethylene terephthalate-1,4-cyclohexanedimethanol;

[0007] The components of the first modified layer and the second modified layer each independently include: a functionalized polymer material;

[0008] The functionalized polymer material includes one or more of polyethylene naphthalate, poly(m-phenylene adipamide), liquid crystal polymer, polyoxymethylene, polyphenylene sulfide and polyphenylene ether.

[0009] In one embodiment, the components of the first modified layer and the second modified layer independently include: a poly(terephthalate) polymer, an anti-blocking agent, and a functionalized polymer material.

[0010] In one embodiment, the raw materials for preparing the first modified layer and the second modified layer independently include: an anti-blocking masterbatch and a modified masterbatch with a mass ratio of (1~5):(95~99);

[0011] The anti-blocking masterbatch includes the poly(terephthalate) polymer and the anti-blocking agent;

[0012] Wherein, in the anti-blocking masterbatch, the mass ratio of the anti-blocking agent to the poly(terephthalate) polymer is (0.1~5):(95~99.9);

[0013] The modified masterbatch includes the poly(terephthalate) polymer and the functionalized polymer material;

[0014] Wherein, in the modified masterbatch, the mass ratio of the functionalized polymer material to the poly(terephthalate) polymer is (20~60):(40~80).

[0015] In one embodiment, the poly(terephthalate) polymer includes one or more of polyethylene terephthalate, poly(1,4-cyclohexanedimethylene terephthalate), and polyethylene terephthalate-1,4-cyclohexanedimethylene terephthalate;

[0016] And / or, the anti-blocking agent includes one or more of silica, glass microspheres, calcium carbonate, and talc;

[0017] In one embodiment, the polymer composite film has one or more of the following characteristics:

[0018] (1) The thickness ratio of the first modified layer to the polymer base layer is (0.6~1.4):(3.2~4.8);

[0019] (2) The thickness ratio of the second modified layer to the polymer base layer is (0.6~1.4):(3.2~4.8).

[0020] In one embodiment, the raw materials for preparing the first modified layer and the second modified layer independently further include: a nucleating agent; the nucleating agent has one or more of the following characteristics:

[0021] (1) The mass ratio of the nucleating agent to the functionalized polymer material is (1~5):(20~60);

[0022] (2) The nucleating agent includes one or more of calcium carbonate, layered double metal hydroxide, boron nitride, zinc oxide, dibenzylidene sorbitol, and aryl dimethylamide.

[0023] In one embodiment, the polymer composite film further includes: a first heat-conducting layer and a second heat-conducting layer;

[0024] Wherein, the first heat-conducting layer is disposed on a surface of the first modified layer facing away from the polymer base layer;

[0025] The second heat-conducting layer is disposed on a surface of the second modified layer facing away from the polymer base layer.

[0026] In a second aspect of the present application, there is provided a composite current collector, which includes the polymer composite film according to any one of the embodiments of the first aspect of the present application, and a metal layer disposed on at least one surface of the polymer composite film.

[0027] In one embodiment, the material of the metal layer includes one or more of aluminum and aluminum alloy;

[0028] And / or, the thickness of the metal layer is 0.8 μm to 1.2 μm.

[0029] In a third aspect of the present application, there is provided a method for preparing the composite current collector according to the second aspect of the present application, including the following steps:

[0030] Vacuum-evaporating the material of the metal layer on at least one surface of the polymer composite film to prepare the composite current collector;

[0031] Wherein, the process parameters of the vacuum evaporation have one or more of the following characteristics:

[0032] (1) The wire feeding speed of the material of the metal layer is 400 mm / min to 500 mm / min;

[0033] (2) The evaporation rate of the vacuum evaporation is 10 m / min to 20 m / min;

[0034] (3) The evaporation power of the vacuum evaporation is 7 kW to 12 kW;

[0035] (4) The main roller temperature of the vacuum evaporation is -20 °C to 0 °C;

[0036] (5) The winding tension and the unwinding tension of the vacuum evaporation are each independently 100 N to 300 N;

[0037] (6) The distance between the heat source of the vacuum evaporation and the polymer composite film is 250 mm to 350 mm.

[0038] In the fourth aspect of the present application, a positive electrode is provided, including the composite current collector described in the second aspect.

[0039] In the fifth aspect of the present application, a battery is provided, including the positive electrode described in the fourth aspect.

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

[0041] The polymer composite film provided by the present application has at least the following beneficial effects:

[0042] The polymer composite film provided by the present application includes a first modified layer and a second modified layer respectively disposed on opposite surfaces of the polymer base layer. The components of the first modified layer and the second modified layer include specific types of functionalized polymer materials. Among them, under the mutual cooperation of the specific types of functionalized polymer materials and the polymer base layer of the specific material, the first modified layer and the second modified layer can form a film layer on the surface of the polymer base layer with a lower elongation at break and a higher tensile strength. Further, the lower elongation at break of the first modified layer and the second modified layer enables the polymer composite film of the present application to be more easily broken when used as the base film of the battery current collector under the external force of battery collision or breakdown, etc., and then can timely cut off the abnormal current path inside the battery, making the battery form multiple open circuits, thereby effectively avoiding battery thermal runaway caused by continuous power supply and significantly improving the safety performance of the battery. Description of the Drawings

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0044] Figure 1 It is a schematic structural diagram of a polymer composite film provided by an example of the present application;

[0045] Figure 2 It is a schematic structural diagram of a polymer composite film provided by another example of the present application;

[0046] Figure 3 It is a schematic structural diagram of a positive electrode current collector provided by an example of the present application;

[0047] Figure 4 It is a schematic structural diagram of a positive electrode current collector provided by another example of the present application.

[0048] In the figure, 10-polymer composite film; 110-polymer base layer; 120-first modified layer; 130-second modified layer; 140-first heat conductive layer; 150-second heat conductive layer; 160-first metal layer; 170-second metal layer. DETAILED DESCRIPTION

[0049] The following is a further complete and clear description of the polymer composite film, composite current collector and preparation method thereof, positive electrode and application of the present application in conjunction with specific examples. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0050] At present, power batteries generally take high energy density and high rate as their iterative development goals, which simultaneously brings about the urgent need for high safety of power batteries under high energy density. This application found that the positive electrode sheet is at a higher potential during the battery charging and discharging process and participates in complex redox reactions. Its chemical stability is crucial to the thermal stability of the battery; high energy density positive electrode materials are often more active and more prone to thermal runaway, and the specific capacity and structural stability of the positive electrode material directly affect the energy density and cycle performance of the battery. Once the positive electrode material has problems such as structural collapse, it will not only lead to a decline in battery performance, but may also cause serious safety accidents such as internal short circuits; in addition, the interface reaction between the positive electrode material and the electrolyte may also produce gas, heat, etc., further threatening the safety of the battery. Therefore, compared with other battery components such as negative electrodes, positive electrodes have a greater impact on the safety of power batteries.

[0051] The positive electrode current collector is an important component of the positive electrode sheet. At present, the positive electrode current collector aluminum foil mainly adopts a sandwich structure of "metal-polymer material-metal", with PET polymer material as the middle layer, and aluminum or copper metal deposited on the upper and lower layers to form a metal conductive layer. The elongation of pure aluminum material is 10% to 30%, and the elongation of PET material is generally more than 80%. The overall elongation at break of the composite current collector aluminum foil is mainly determined by the PET film material. The excessive elongation at break makes it impossible for the composite aluminum foil to be disconnected immediately when it is damaged by external force, which is not conducive to controlling battery thermal runaway. Therefore, reducing the elongation of the composite current collector can prevent the occurrence of battery thermal runaway.

[0052] Based on this, the first aspect of this application, refer to Figure 1 , a polymer composite film 10 is provided, wherein the polymer composite film 10 includes a polymer base layer 110 and a first modified layer 120 and a second modified layer 130 respectively disposed on opposite side surfaces of the polymer base layer 110 .

[0053] The material of the polymer base layer 110 includes one or more of polyethylene terephthalate, poly(1,4-cyclohexanedimethylene terephthalate), and polyethylene terephthalate-1,4-cyclohexanedimethylene terephthalate).

[0054] The components of the first modified layer and the second modified layer each independently include: a functionalized polymer material.

[0055] The functionalized polymer material includes one or more of polyethylene naphthalate, poly(m-phenylene adipamide), liquid crystal polymer, polyoxymethylene, polyphenylene sulfide, and polyphenylene ether.

[0056] Liquid crystal polymer LCP is a high molecular material composed of liquid crystal molecules and a polymer matrix. Its structure mainly consists of two parts: a liquid crystal unit with a rigid rod-like structure and a polymer backbone with a flexible chain-like structure. The rigid rod-like LCP has the characteristic of spontaneous orientation, and since LCP is a straight-chain polymer with a tightly packed structure between chains, it exhibits high strength, high modulus, outstanding heat resistance, and excellent dimensional stability.

[0057] The polymer composite film provided in this application can be used as the base film of a composite current collector, which can effectively reduce the elongation rate of the PET material, so it can effectively prevent the occurrence of battery thermal runaway. Specifically, the polymer composite film provided in this application includes a first modified layer and a second modified layer respectively disposed on the opposite two surfaces of the polymer base layer. The components of the first modified layer and the second modified layer include specific types of functionalized polymer materials. Among them, with the mutual cooperation of the specific types of functionalized polymer materials and the polymer base layer of specific materials, the first modified layer and the second modified layer can form a film layer with a lower elongation at break and a higher tensile strength on the surface of the polymer base layer. In addition, the inventors found that by disposing the first modified layer and the second modified layer on the opposite two surfaces of the polymer base layer, on the one hand, the film-forming property of the polymer composite film can be retained to prevent the composite film from breaking due to excessive rigidity during the film drawing process. On the other hand, the modified layer cannot achieve a high degree of crystallinity during the film drawing stage. Setting the modified layer on the surface of the polymer base layer is beneficial to further crystallization during the heat treatment stage of vapor deposition for preparing the composite current collector subsequently, thereby reducing the elongation rate. Moreover, the modified layer disposed on the surface layer of the polymer base layer can significantly improve the temperature resistance of the composite film. Under higher heat treatment conditions, a high degree of crystallinity can be ensured, and thermal shrinkage and deformation of the composite film can be prevented. Further, the lower elongation at break of the first modified layer and the second modified layer enables the polymer composite film of this application to be more easily broken when used as the base film of a battery current collector under external force, thereby timely cutting off the abnormal current path inside the battery and effectively avoiding battery thermal runaway caused by continuous power supply, significantly improving the safety performance of the battery.

[0058] In addition, the addition of the first modified layer and the second modified layer can also enhance the bonding force with the metal layer, and the polymer composite film of the present application can reduce its thermal shrinkage performance, which is beneficial to the process of vapor deposition coating to prepare the metal layer.

[0059] Preferably, the functionalized polymer material includes one or more of polyethylene naphthalate, poly(m-phenylene adipamide), and polyphenylene sulfide. The structure of polyethylene naphthalate (PEN) is similar to that of PET, in which the more rigid naphthalene ring replaces the benzene ring in PET. Due to the more stable resonance structure of the naphthalene ring than the benzene ring, the molecular chain of PEN has greater rigidity, and its glass transition temperature, crystallization temperature, and melting point are all higher than those of PET. In addition, the tensile strength of PEN is 35% higher than that of PET, and the flexural modulus is about 50% higher. It has small molding thermal shrinkage and good dimensional stability.

[0060] More preferably, the functionalized polymer material includes one or more of poly(m-phenylene adipamide) and polyphenylene sulfide.

[0061] Poly(m-phenylene adipamide) (MXD6) is a semi-crystalline semi-aromatic polyamide. There are rigid m-phenylene groups on the main chain of MXD6, and the amide groups in the molecular chain can form intermolecular hydrogen bonds. It has the advantages of high dimensional stability, low moisture absorption rate, strong rigidity, wide use temperature range, and small thermal expansion coefficient. The presence of the benzene ring structure makes the toughness of MXD6 poor, and the notch impact strength is only about 20 J / m. It is a hard and brittle material.

[0062] In one example, the components of the first modified layer and the second modified layer each independently include: a polyterephthalate polymer, an anti-blocking agent, and a functionalized polymer material.

[0063] Furthermore, the preparation raw materials of the first modified layer and the second modified layer each independently include: an anti-blocking masterbatch and a modified masterbatch with a mass ratio of (1~5):(95~99).

[0064] Among them, in the anti-blocking masterbatch, the mass ratio of the anti-blocking agent to the polyterephthalate polymer is (0.1~5):(95~99.9).

[0065] Among them, in the modified masterbatch, the mass ratio of the functionalized polymer material to the polyterephthalate polymer is (20~60):(40~80).

[0066] In the preparation raw materials of the present application, an anti-blocking masterbatch including an anti-blocking agent and a polyterephthalate polymer and a modified masterbatch including a functionalized polymer material and a polyterephthalate polymer are selected. Among them, the anti-blocking masterbatch can ensure the anti-blocking effect between the polymer base layer and the modified layer, and can also ensure sufficient rigidity of the modified layer to enhance the modification effect. The modified material helps to improve the brittleness of the modified layer, thereby reducing the elongation at break of the modified layer. It can be understood that in the present application, the mass ratio of the anti-blocking masterbatch to the modified masterbatch includes but is not limited to 1:99, 1.5:98.5, 2:98, 2.5:97.5, 3:97, 3.5:96.5, 4:96, 4.5:95.5 or 5:95, or within the range formed by any two of the above point values as the end point values. If the content of the anti-blocking masterbatch is less, it will cause the composite films to adhere to each other during winding and unwinding. If the content of the anti-blocking masterbatch is more, it will cause the composite film to be easily broken during film drawing, affecting the yield.

[0067] Further, in the anti-blocking masterbatch, the mass ratio of the anti-blocking agent to the polyterephthalate polymer is (0.1~5):(95~99.9). The anti-blocking effect between the modified layers can be ensured within this range of the anti-blocking agent content. Further, the mass ratio of the anti-blocking agent to the polyterephthalate polymer includes but is not limited to 0.1:99.9, 0.5:99.5, 1:99, 2:98, 3:97, 4:96 or 5:95, or within the range formed by any two of the above point values as the end point values.

[0068] Preferably, in the anti-blocking masterbatch, the mass ratio of the anti-blocking agent to the polyterephthalate polymer is (3~5):(95~97).

[0069] Further, in the modified masterbatch, the mass ratio of the functionalized polymer material to the polyterephthalate polymer is (20~60):(40~80). The modification effect can be ensured within this range of the mass percentage of the functionalized polymer material. If the addition amount of the functionalized polymer material is slightly less, it is likely that the decrease in the elongation at break of the modified layer is not obvious; if the addition amount of the functionalized polymer material is slightly more, it will increase the risk of film breakage of the polymer composite film. For example, the mass ratio of the functionalized polymer material to the polyterephthalate polymer includes but is not limited to 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, or 60:40, or within the range formed by any two of the above point values as the end point values. Further, the mass ratio of the functionalized polymer material to the polyterephthalate polymer is (50~60):(40~50).

[0070] In one example, the poly(terephthalate) polymer includes one or more of polyethylene terephthalate, poly(1,4-cyclohexanedimethylene terephthalate), and polyethylene terephthalate-1,4-cyclohexanedimethylene terephthalate).

[0071] Preferably, the poly(terephthalate) polymer includes polyethylene terephthalate.

[0072] Preferably, the material of the polymer base layer includes polyethylene terephthalate.

[0073] In one example, the anti-adhesion agent includes one or more of silica, glass microspheres, calcium carbonate, and talcum powder.

[0074] In one example, the thickness of the polymer base layer is 3 μm to 15 μm. When the thickness of the polymer base layer is within a reasonable range, an appropriate thickness can provide ideal mechanical strength and flexibility, making the composite current collector less likely to crack, wrinkle, etc. during battery production and use, enhancing the structural stability; furthermore, an appropriate thickness is conducive to controlling the weight and cost of the entire composite current collector, achieving lightweight design and reducing material costs while meeting performance requirements; in addition, precisely defining the thickness can also optimize the internal space layout of the battery, improve the energy density of the battery, and thus enhance the overall performance of the battery.

[0075] In one example, the thickness ratio of the first modified layer to the polymer base layer is (0.6~1.4):(3.2~4.8). Defining the thickness ratio of the first modified layer to the polymer base layer plays an important role in ensuring the modification effect of the modified layer on the polymer base layer and does not affect the film-forming stability of the polymer composite film. Exemplarily, the thickness ratio of the first modified layer to the polymer base layer includes, but is not limited to, 0.6:4.8, 0.8:4.4, 1:4, 1.2:3.6, or 1.4:3.2, or within the range formed by any two of the above point values as end point values.

[0076] In one example, the thickness ratio of the second modified layer to the polymer base layer is (0.6~1.4):(3.2~4.8). Further, the thickness ratio of the second modified layer to the polymer base layer includes, but is not limited to, 0.6:4.8, 0.8:4.4, 1:4, 1.2:3.6, or 1.4:3.2, or within the range formed by any two of the above point values as end point values.

[0077] In one example, the raw materials for preparing the first modified layer and the second modified layer each independently further include: a nucleating agent. Adding a nucleating agent to the raw materials for the first modified layer and the second modified layer can significantly accelerate the crystallization rate during the preparation of the polymer composite film, so as to improve the crystallinity and mechanical properties of the polymer composite film and reduce its elongation rate.

[0078] In one example, the mass ratio of the nucleating agent to the functionalized polymer material is (1 to 5):(20 to 60). A suitable mass ratio can enable the nucleating agent to better play the role of heterogeneous nucleation, provide more crystal nuclei for the crystallization of the functionalized polymer material, accelerate the crystallization speed, make the crystal structure more regular, fine and uniform, thereby improving the crystallinity and reducing the elongation at break of the modified layer. Exemplarily, the mass ratio of the nucleating agent to the functionalized polymer material includes but is not limited to 1:20, 2:30, 4:50, 5:50, 5:52, 5:56, 5:57, 5:58 or 5:60, or within the range formed by any two of the above point values as the end point values.

[0079] In one example, the nucleating agent includes one or more of calcium carbonate, layered double metal salt hydroxide, boron nitride, zinc oxide, dibenzylidene sorbitol and aryl dimethylamide.

[0080] In one example, the polymer base layer does not include a nucleating agent.

[0081] It is found in this application that when a relatively excessive amount of nucleating agent is added to the first modified layer and the second modified layer and no nucleating agent is added to the polymer base layer, it is more conducive to the preparation of the polymer composite film and the composite current collector. Specifically, in the process of preparing the polymer composite film, since the raw materials for preparing the first modified layer, the polymer base film and the second modified layer form a micro-melt blend with a specific layered structure after melt blending, and the step of stretching the micro-melt blend, the stretching treatment at this time can provide power for the excessive nucleating agent in the first modified layer and the second modified layer to come into contact with the polymer base film and for the diffusion and migration of the excessive nucleating agent into the polymer base film, so that the unreacted nucleating agent in the first modified layer and the second modified layer enters the polymer base layer. Since the nucleating agent in the modified layer enters the polymer base layer in the second half of the film stretching process, the time for maintaining a high temperature is short at this time, and the nucleating agent and the polymer base layer will not react completely. During the vacuum evaporation process, a relatively high temperature and a long time will be maintained, and the nucleating agent entering the polymer base layer will further crystallize with the polymer base layer during the evaporation process, thereby appropriately reducing the elongation of the polymer base layer. In addition, the reason for not directly adding the excessive nucleating agent to the polymer base layer is that: the reaction rate between the polymer base layer and the nucleating agent is faster than that between the modified layer and the nucleating agent. Directly adding the nucleating agent to the polymer base layer will cause all the nucleating agent in the polymer base layer to react during the film stretching process, resulting in too high a crystallinity of the composite film, which will cause the polymer composite film to be easily broken during the stretching treatment in the preparation process, and further lead to a decrease in the preparation yield of the polymer composite film. At the same time, when the polymer composite film is used as the base film in the evaporation process of the composite current collector metal layer, it also has the disadvantage of being difficult to withstand the thermal stress or mechanical stress of the evaporation, and thus is prone to film breakage.

[0082] Referring to Figure 2 , in one example, the polymer composite film further includes: a first heat-conducting layer 140 and a second heat-conducting layer 150.

[0083] Wherein, the first heat-conducting layer 140 is disposed on the surface of the first modified layer 120 facing away from the polymer base layer 110.

[0084] The second heat-conducting layer 150 is disposed on the surface of the second modified layer 130 facing away from the polymer base layer 110.

[0085] In one example, the first heat-conducting layer and the second heat-conducting layer are provided by spraying or magnetron sputtering. The materials of the first heat-conducting layer and the second heat-conducting layer are independently selected from one or more of metallic materials, carbon-based materials, and non-metallic carbides. Exemplarily, the metallic materials of the first heat-conducting layer and the second heat-conducting layer include, but are not limited to, copper, aluminum, or silver. The carbon-based materials of the first heat-conducting layer and the second heat-conducting layer include, but are not limited to, graphene or carbon nanotubes. The non-metallic carbide materials of the first heat-conducting layer and the second heat-conducting layer include, but are not limited to, silicon carbide or boron carbide.

[0086] Preferably, by providing the first heat-conducting layer and the second heat-conducting layer, heat can be rapidly transferred to the polymer substrate during the preparation of the metal layer, enabling the nucleating agent to cause crystallization of the polymer substrate by means of this heat.

[0087] In one example, the thicknesses of the first heat-conducting layer and the second heat-conducting layer are independently selected from 30 nm to 70 nm. Exemplarily, the thicknesses of the first heat-conducting layer and the second heat-conducting layer include, but are not limited to, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, or 70 nm, or any range formed by any two of the above point values as endpoint values.

[0088] The present application also provides a method for preparing a polymer composite film, comprising the following steps:

[0089] The first modified layer, the polymer base film, the second modified layer, and the preparation raw materials are independently mixed, melt-extruded, and sliced to separately obtain a first mixture, a second mixture, and a third mixture;

[0090] The first mixture, the second mixture, and the third mixture are melt-blended and extruded to prepare a blend;

[0091] The blend is subjected to a stretching treatment to prepare a polymer composite film.

[0092] Wherein, the polymer composite film includes a polymer substrate and a first modified layer and a second modified layer respectively disposed on opposite surfaces of the polymer substrate.

[0093] In a second aspect of the present application, a composite current collector is provided, which includes the polymer composite film according to any example of the first aspect of the present application, and a metal layer disposed on at least one surface of the polymer composite film.

[0094] The present application finds that reducing the elongation at break of the positive current collector rather than the negative current collector has a positive effect on preventing thermal runaway. Based on this, in one example, the material of the metal layer includes one or more of aluminum and aluminum alloys.

[0095] In one example, the metal layer includes a first metal layer and a second metal layer.

[0096] Refer to Figure 3 , in one example, the positive current collector includes a first metal layer 160, a first modified layer 120, a polymer base layer 110, a second modified layer 130, and a second metal layer 170 which are stacked.

[0097] Refer to Figure 4 , in one example, the positive current collector includes a first metal layer 160, a first heat-conducting layer 140, a first modified layer 120, a polymer base layer 110, a second modified layer 130, a second heat-conducting layer 150, and a second metal layer 170 which are stacked.

[0098] In one example, the thickness of the metal layer is 0.8 μm to 1.2 μm. This thickness range can ensure that the metal layer has good electrical conductivity, can effectively reduce the internal resistance of the battery, improve the charge and discharge efficiency and performance stability of the battery; it can provide sufficient mechanical strength, so that the composite current collector is not prone to problems such as cracking and deformation during battery production and use, enhancing the reliability of the overall structure. In addition, the metal layer within this thickness range has good compatibility with the polymer composite film, which can effectively ensure that the composite current collector has a low elongation at break. Exemplarily, the thickness of the metal layer includes but is not limited to 0.8 μm, 0.9 μm, 1 μm, 1.1 μm or 1.2 μm, or within the range formed by any two of the above point values as endpoint values.

[0099] In the third aspect of the present application, a method for preparing the composite current collector described in the second aspect of the present application is provided, including the following steps:

[0100] Vacuum deposit the material of the metal layer on at least one surface of the polymer composite film to prepare the composite current collector.

[0101] In one example, the material of the metal layer is aluminum. Exemplarily, the diameter of the aluminum is 1 mm to 3 mm.

[0102] Exemplarily, the equipment for vacuum deposition includes but is not limited to an evaporation boat. More exemplarily, the equipment for vacuum deposition is 72 groups of evaporation boats.

[0103] In one example, the process parameters of the vacuum evaporation include: the wire feeding speed of the material of the metal layer is 400 mm / min to 500 mm / min. Exemplarily, the wire feeding speed of the material of the metal layer includes, but is not limited to, 400 mm / min, 410 mm / min, 420 mm / min, 430 mm / min, 440 mm / min, 450 mm / min, 460 mm / min, 470 mm / min, 480 mm / min, 490 mm / min or 500 mm / min, or any range formed by any two of the above point values as the end point values.

[0104] In one example, the evaporation rate of the vacuum evaporation is 10 m / min to 20 m / min. The evaporation rate within the above range can ensure the production efficiency while ensuring the yield of the evaporated product and avoiding excessive production costs. Exemplarily, the evaporation rate includes, but is not limited to, 10 m / min, 12 m / min, 15 m / min, 18 m / min or 20 m / min, or any range formed by any two of the above point values as the end point values.

[0105] In one example, the evaporation power of the vacuum evaporation is 7 kW to 12 kW. The evaporation power of the vacuum evaporation is generally about 5 kW. The evaporation power of this application within the above range can ensure sufficient heat treatment effect. If the evaporation power is too large, it will cause excessive thermal damage to the polymer composite film and its tensile strength will be significantly reduced. If the evaporation power is too small, the crystallinity of the polymer composite film will be insufficient, resulting in an insignificant decrease in its elongation. Exemplarily, the evaporation power of the vacuum evaporation includes, but is not limited to, 7 kW, 7.5 kW, 8 kW, 8.5 kW, 9 kW, 9.5 kW, 10 kW, 10.5 kW, 11 kW, 11.5 kW or 12 kW, or any range formed by any two of the above point values.

[0106] In one example, the temperature of the main roller of the vacuum evaporation is -20°C to 0°C. The temperature of the evaporation main roller within the above range synergizes with the evaporation power, which can ensure sufficient heat treatment effect to prevent the disadvantage of high elongation of the polymer composite film caused by insufficient heat treatment effect and insufficient crystallinity. At the same time, it can also prevent the disadvantage of excessive thermal damage and reduced tensile strength caused by the inability to dissipate heat in time due to too high temperature of the evaporation main roller. Exemplarily, the temperature of the main roller of the vacuum evaporation includes, but is not limited to, -20°C, -18°C, -16°C, -14°C, -12°C, -10°C, -8°C, -6°C, -4°C, -2°C or 0°C, or any range formed by any two of the above point values.

[0107] In one example, the winding tension and unwinding tension of the vacuum evaporation coating are each independently 100 N to 300 N. When the winding and unwinding tensions are within the above range, it can not only accelerate the optimization of the heat treatment effect but also ensure good winding effect and appearance quality. For example, the winding tension and unwinding tension of the vacuum evaporation coating each independently include, but are not limited to, 100 N, 110 N, 120 N, 150 N, 180 N, 200 N, 220 N, 250 N, 270 N, 280 N or 300 N, or within the range formed by any two of the above point values as the end point values.

[0108] In one example, the distance between the evaporation boat and the polymer composite film in the vacuum evaporation coating is 250 mm to 350 mm. When the distance between the evaporation boat and the polymer composite film is within the above range, it can not only ensure the heat treatment effect but also prevent excessive thermal damage to the polymer composite film. For example, the distance between the evaporation boat and the polymer composite film in the vacuum evaporation coating includes, but is not limited to, 250 mm, 270 mm, 290 mm, 310 mm, 330 mm or 350 mm, or within the range formed by any two of the above point values as the end point values.

[0109] In the fourth aspect of the present application, a positive electrode is provided, including the composite current collector described in the second aspect of the present application.

[0110] In the fifth aspect of the present application, a battery is provided, including the positive electrode described in the fourth aspect.

[0111] In the sixth aspect of the present application, an electrical device is provided, including the battery described in the fifth aspect.

[0112] The following further specific embodiments are used to illustrate the present application in detail. Similarly, it should be understood that the following embodiments are only used to further illustrate the present application and cannot be construed as limiting the protection scope of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application all fall within the protection scope of the present application. The specific process parameters and the like in the following embodiments are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description in this article, rather than necessarily being limited to the specific values in the following embodiments.

[0113] Example 1

[0114] Example 1 of the present application provides a polymer composite film, a composite current collector and a preparation method thereof.

[0115] Polymer composite film: The polymer composite film includes a polymer base layer and a first modified layer and a second modified layer respectively disposed on the surfaces of the polymer base layer on opposite sides; wherein the material of the polymer base layer is a PET layer with a thickness of 6 μm; the thickness ratio of the first modified layer to the polymer base layer is 1.4:3.2, and the thickness ratio of the second modified layer to the polymer base layer is 1.4:3.2. wherein the raw materials for preparing the first modified layer and the second modified layer both include: an anti-adhesive masterbatch and a modified masterbatch in a ratio of 5:95. the components of the anti-adhesive masterbatch include 1% silicon dioxide and 99% PET material. the components of the modified masterbatch include 60% polyethylene naphthalate and 40% PET material.

[0116] A composite current collector and a preparation method thereof: using 72 groups of evaporation boats and aluminum wires with a diameter of 2 mm, the aluminum wires are vacuum evaporated onto the surfaces of both sides of a polymer composite film to prepare a first metal layer and a second metal layer respectively, the first metal layer is arranged on the surface of the first modified layer on the side away from the polymer base layer, the second metal layer is arranged on the surface of the second modified layer on the side away from the polymer base layer, and the thickness of the first metal layer and the second metal layer is 1 μm; a composite current collector is obtained.

[0117] Among them, the process parameters of vacuum evaporation include: aluminum wire feeding speed 450mm / min, evaporation rate 15m / min, evaporation power 8kW, evaporation main roller temperature -10℃, evaporation winding and unwinding tension 200N, and the distance between the vacuum evaporation evaporation boat and the polymer composite film is 300mm.

[0118] Example 2

[0119] The polymer composite membrane of Example 2 of the present application is basically the same as Example 1, with the main difference being that the raw materials for preparing the first modified layer and the second modified layer of the polymer composite membrane of Example 2 further include a nucleating agent.

[0120] The polymer composite film of Example 2 includes a polymer base layer and a first modified layer and a second modified layer respectively arranged on the surfaces of the opposite sides of the polymer base layer; wherein the material of the polymer base layer is a PET layer with a thickness of 6 μm; the thickness ratio of the first modified layer to the polymer base layer is 1.4:3.2, and the thickness ratio of the second modified layer to the polymer base layer is 1.4:3.2. wherein the raw materials for preparing the first modified layer and the second modified layer both include: an anti-adhesive masterbatch, a modified masterbatch and a nucleating agent in a ratio of 5:95:5. the components of the anti-adhesive masterbatch include 1% silicon dioxide and 99% PET material. the components of the modified masterbatch include 60% polyethylene naphthalate and 40% PET material. the type of the nucleating agent is calcium carbonate.

[0121] Composite current collector and preparation method thereof: same as in Example 1.

[0122] Example 3

[0123] The polymer composite film of Example 3 of the present application is basically the same as that of Example 2, with the main difference being that the polymer composite film of Example 3 further includes a first heat-conducting layer and a second heat-conducting layer.

[0124] The polymer composite film of Example 3 includes a first heat-conducting layer (silicon carbide), a first modified layer, a polymer base layer, a second modified layer and a second heat-conducting layer (silicon carbide) stacked in layers. Among them, the material of the polymer base layer is a PET layer with a thickness of 6μm; the thickness of the first heat-conducting layer and the second heat-conducting layer is 50nm, the thickness ratio of the first modified layer to the polymer base layer is 1.4:3.2, and the thickness ratio of the second modified layer to the polymer base layer is 1.4:3.2. Among them, the raw materials for preparing the first modified layer and the second modified layer both include: an anti-adhesive masterbatch, a modified masterbatch and a nucleating agent in a ratio of 5:95:5. The components of the anti-adhesive masterbatch include 1% silicon dioxide and 99% PET material. The components of the modified masterbatch include 60% polyethylene naphthalate and 40% PET material. The type of nucleating agent is calcium carbonate.

[0125] Composite current collector and preparation method thereof

[0126] Using 72 groups of evaporation boats and aluminum wires with a diameter of 2 mm, the aluminum wires were vacuum evaporated onto the two side surfaces of the polymer composite film to prepare the first metal layer and the second metal layer respectively. The first metal layer was arranged on the side of the first thermal conductive layer away from the first modified layer, and the second metal layer was arranged on the side of the second thermal conductive layer away from the second modified layer. The thickness of the first metal layer and the second metal layer was 1 μm. A composite current collector was obtained.

[0127] Among them, the process parameters of vacuum evaporation include: aluminum wire feeding speed 450mm / min, evaporation rate 15m / min, evaporation power 8kW, evaporation main roller temperature -10℃, evaporation winding and unwinding tension 200N, and the distance between the vacuum evaporation evaporation boat and the polymer composite film is 300mm.

[0128] Example 4

[0129] Polymer composite film: Same as Example 3, the main difference is that the modified masterbatch of Example 4 includes 60% poly(m-phenylene adipamide) and 40% PET material.

[0130] Composite current collector and preparation method thereof: same as Example 3.

[0131] Example 5

[0132] Polymer composite film: Same as Example 3, the main difference is that the modified masterbatch of Example 5 includes 60% polyphenylene sulfide and 40% PET material.

[0133] Composite current collector and its preparation method: same as Example 3.

[0134] Example 6

[0135] Polymer composite film: same as Example 3, the main difference is that the components of the modified masterbatch in Example 6 include 40% polyethylene naphthalate and 60% PET material.

[0136] Composite current collector and its preparation method: same as Example 3.

[0137] Example 7

[0138] Polymer composite film: same as Example 3, the main difference is that the components of the modified masterbatch in Example 7 include 20% polyethylene naphthalate and 80% PET material.

[0139] Composite current collector and its preparation method: same as Example 3.

[0140] Example 8

[0141] Polymer composite film: same as Example 3, the main difference is that the components of the anti - adhesion masterbatch in Example 8 include 3% silica and 97% PET material.

[0142] Composite current collector and its preparation method: same as Example 3.

[0143] Example 9

[0144] Polymer composite film: same as Example 3, the main difference is that the components of the anti - adhesion masterbatch in Example 9 include 5% silica and 95% PET material.

[0145] Composite current collector and its preparation method: same as Example 3.

[0146] Comparative Example 1

[0147] Polymer substrate: The material of the polymer substrate is a PET layer with a thickness of 6 μm.

[0148] Composite current collector and its preparation method: 72 evaporation boats and aluminum wires with a diameter of 2 mm are used. The aluminum wires are vacuum - evaporated on both side surfaces of the polymer substrate to prepare the first metal layer and the second metal layer respectively, and the thickness of the first metal layer and the second metal layer is 1 μm; thus, a composite current collector is obtained.

[0149] Among them, the process parameters of the vacuum evaporation include: the wire feeding speed of the aluminum wire is 450 mm / min, the evaporation rate is 15 m / min, the evaporation power is 8 kW, the temperature of the evaporation main roller is - 10 °C, the tension of the winding and unwinding during evaporation is 200 N, and the distance between the evaporation boat of the vacuum evaporation and the polymer composite film is 300 mm.

[0150] Performance test:

[0151] Mechanical property test of composite current collector

[0152] Tensile strength and elongation at break of the composite current collectors prepared in Examples 1-9 and Comparative Example 1 were tested. The composite current collector to be tested was cut into test strips by a strip cutting machine. For each group of samples in the examples, 10 test specimens were cut, with a width of 15 mm and a length of 150 mm. The tensile rate was 100 mm / min, the distance between the tensile chucks was 100 mm. The tensile strength and elongation at break data in the MD direction were tested and averaged. The test data are shown in Table 1.

[0153] Table 1

[0154]

[0155] Battery collision safety performance test

[0156] The ternary active material NCM811, conductive carbon black, and binder PVDF were fully stirred and mixed evenly in NMP at a weight ratio of 93:2:5 to obtain a positive electrode paste. The positive electrode paste was coated on the current collector samples of the examples or comparative examples, dried, rolled, and then die-cut to obtain positive electrode plates.

[0157] The negative active material artificial graphite, binder SBR, dispersant CMC, and conductive carbon black were fully stirred and mixed evenly in water at a weight ratio of 95.5:2.3:1.5:0.7 to obtain a negative electrode paste. The negative electrode paste was coated on a copper foil, dried, rolled, and then die-cut to obtain negative electrode plates.

[0158] The above positive electrode plates, separator (PE film), and negative electrode plates were stacked in sequence, wound to obtain an electrode core, placed in a battery case, and electrolyte (lithium salt LiPF6, concentration 1 mol / L, carbonate solvent) was added. After encapsulation, battery samples were obtained.

[0159] The battery samples obtained from the composite current collectors prepared in Examples 1-9 and Comparative Example 1 were respectively subjected to collision safety performance tests.

[0160] (1) Battery pretreatment

[0161] The encapsulated battery samples were charged to the rated capacity (SOC = 100%) and left standing for more than 4 hours to eliminate the polarization effect. Temperature measurement holes were reserved during battery production, and a micro-thermocouple was placed for temperature measurement.

[0162] (2) Battery fixation

[0163] Fix the battery sample on the test bench, use three-point clamping, and install a metal pendulum on the test bench to ensure that the battery axis is completely perpendicular to the movement trajectory of the pendulum. Mark the impact center point on the front of the battery.

[0164] (3)Collision test

[0165] Release the pendulum to impact the center point of the front of the battery three times in free fall motion, and record the temperature value inside the battery sample 10 minutes after the impact. The test data is shown in Table 2.

[0166] Table 2

[0167]

[0168] As can be seen from Table 1, the tensile strength of the composite current collector prepared in the embodiment of the present application is higher than that of Comparative Example 1, which indicates that the composite current collector of the embodiment of the present application has good ability to resist tensile failure. At the same time, the elongation at break of the composite current collector prepared in the embodiment of the present application is lower than that of Comparative Example 1, which shows that during the stretching process of the composite current collector, the amount of deformation experienced from the beginning of force application to fracture is smaller, and the extensibility of the composite current collector is poor. This enables the composite current collector of the embodiment of the present application to be assembled into a battery, so that when the battery is subjected to external forces such as battery breakdown and battery collision, it can break more easily, thereby timely cutting off the abnormal path inside the battery, opening the circuit of the battery cell, and inhibiting the increase in the temperature of the battery cell.

[0169] Example 1 and Example 2 are basically the same, and the main difference is that a nucleating agent is further added in Example 2. From the test results of Table 1 and Table 2, the tensile strength of the composite current collector in Example 2 is relatively high, indicating that the composite current collector in Example 2 has excellent performance in resisting tensile failure; and the elongation at break of the composite current collector in Example 2 is relatively low, indicating that the material will reach the failure limit under relatively small deformation. Further, as can be seen from Table 2, the temperature of the battery cell in Example 2 is lower, which shows that when the composite current collector in Example 2 is subjected to external force damage such as collision, there are more open circuits inside the battery cell, so that its battery cell temperature is lower, and the safety performance of the battery cell in Example 2 is more excellent.

[0170] A heat-conducting layer is added in Example 3, and its tensile strength is higher and elongation at break is lower than that of Example 2, and the temperature of the battery cell is also lower. This shows that the safety performance of the battery cell in Example 3 is more excellent than that in Example 2.

[0171] Example 3, Example 4, and Example 5 are basically the same, and the main difference lies in the types of functionalized polymer materials. In terms of technical effects, the safety performance of Example 4 with poly(m-phenylene adipamide) as the functionalized polymer material is better than that of Example 5 with polyphenylene sulfide as the functionalized polymer material and Example 3 with polyethylene naphthalate as the functionalized polymer material.

[0172] Example 3, Example 6, and Example 7 are basically the same, and the main difference lies in the contents of the components in the modified masterbatch. In Example 3, when the mass ratio of the functionalized polymer material to the PET material is 60:40, the safety performance of the battery cell is more excellent.

[0173] Example 3, Example 8, and Example 9 are basically the same, and the main difference lies in the contents of the components in the anti-blocking masterbatch. In Example 9, when the mass ratio of the anti-blocking agent to the PET material is 5:95, the safety performance of the battery cell is more excellent.

[0174] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0175] The above-described embodiments only represent several implementation manners of the present application, which are convenient for understanding the technical solutions of the present application specifically and in detail, but should not be construed as a limitation on the protection scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can be made, and these all belong to the protection scope of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning, or limited experiments based on the technical solutions provided in the present application are all within the protection scope of the appended claims of the present application. Therefore, the protection scope of the patent of the present application should be subject to the content of the appended claims, and the description can be used to explain the content of the claims.

Claims

1. A polymer composite film, characterized in that The polymer composite film comprises a polymer base layer and a first modified layer and a second modified layer respectively disposed on two opposite side surfaces of the polymer base layer; The material of the polymer base layer includes one or more of polyethylene terephthalate, polyethylene terephthalate-1,4-cyclohexanedimethanol and polyethylene terephthalate-1,4-cyclohexanedimethanol; The components of the first modified layer and the second modified layer each independently include: a functionalized polymer material; The functionalized polymer material includes one or more of polyethylene naphthalate, poly(m-phenylene adipamide) and polyphenylene sulfide; The raw materials for preparing the first modified layer and the second modified layer independently further include: a nucleating agent; the raw materials for preparing the polymer base layer do not include a nucleating agent; The polymer composite film further comprises: a first heat-conducting layer and a second heat-conducting layer; Wherein, the first heat-conducting layer is arranged on a surface of the first modified layer which is away from the polymer base layer; The second heat-conducting layer is disposed on a surface of the second modified layer that is away from the polymer-based layer.

2. The polymer composite membrane according to claim 1, characterized in that The components of the first modified layer and the second modified layer independently include: a polyterephthalate polymer, an anti-blocking agent and a functionalized polymer material.

3. The polymer composite membrane according to claim 2, characterized in that The raw materials for preparing the first modified layer and the second modified layer independently include: an anti-adhesive masterbatch and a modified masterbatch in a mass ratio of (1-5): (95-99); The anti-blocking masterbatch comprises the polyterephthalate polymer and the anti-blocking agent; Wherein, in the anti-blocking masterbatch, the mass ratio of the anti-blocking agent to the polyterephthalate polymer is (0.1-5): (95-99.9); The modified masterbatch comprises the polyterephthalate polymer and the functionalized polymer material; Among them, in the modified masterbatch, the mass ratio of the functionalized polymer material to the polyester terephthalate polymer is (20~60): (40~80).

4. The polymer composite membrane according to claim 2 or 3, characterized in that: The polyethylene terephthalate polymer includes one or more of polyethylene terephthalate, polyethylene terephthalate-1,4-cyclohexanedimethanol and polyethylene terephthalate-1,4-cyclohexanedimethanol; And / or, the anti-adhesive agent includes one or more of silicon dioxide, glass microspheres, calcium carbonate and talc.

5. The polymer composite film according to any one of claims 1 to 3, characterized in that: The polymer composite film has one or more of the following characteristics: (1) The thickness ratio of the first modified layer to the polymer base layer is (0.6-1.4): (3.2-4.8); (2) The thickness ratio of the second modified layer to the polymer base layer is (0.6-1.4):(3.2-4.8).

6. The polymer composite membrane according to claim 1, characterized in that The raw materials for preparing the first modified layer and the second modified layer independently further include: a nucleating agent; the nucleating agent has one or more of the following characteristics: (1) The mass ratio of the nucleating agent to the functionalized polymer material is (1-5): (20-60); (2) The nucleating agent includes one or more of calcium carbonate, layered double metal hydroxide, boron nitride, zinc oxide, dibenzylidene sorbitol and aryl dicarbonamide.

7. A composite current collector, characterized in that: The composite current collector comprises the polymer composite film according to any one of claims 1 to 6, and a metal layer disposed on at least one surface of the polymer composite film.

8. The composite current collector according to claim 7, characterized in that: The material of the metal layer includes one or more of aluminum and aluminum alloy; And / or, the thickness of the metal layer is 0.8 μm to 1.2 μm.

9. A method for preparing the composite current collector according to claim 7 or 8, characterized in that: The following steps are involved: Vacuum evaporating the material of the metal layer on at least one side surface of the polymer composite film to prepare the composite current collector; The process parameters of the vacuum evaporation have one or more of the following characteristics: (1) The wire feeding speed of the material of the metal layer is 400 mm / min to 500 mm / min; (2) The vacuum evaporation rate is 10 m / min to 20 m / min; (3) The vacuum evaporation power is 7 kW to 12 kW; (4) The temperature of the main roller of the vacuum evaporation is -20°C to 0°C; (5) The rewinding tension and unwinding tension of the vacuum evaporation are independently 100N~300N; (6) The distance between the heat source of the vacuum evaporation and the polymer composite film is 250 mm to 350 mm.

10. A positive electrode, characterized in that: Comprising the composite current collector according to claim 7 or 8.

11. A battery, characterized in that: Comprising the positive electrode as claimed in claim 10.

12. An electrical device, characterized in that: Comprising the battery of claim 11.

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