Novel composite current collector and preparation method thereof

Abstract

The invention discloses a novel composite current collector and a preparation method thereof. The novel composite current collector comprises a polymer layer, a connecting layer and a metal conductive layer, the number of the macromolecule layers is two, and the two macromolecule layers are connected in a bonding mode through the connecting layer. The metal conductive layer is arranged on the end faces of the two macromolecule layers, and the metal conductive layer deviates from the connecting layer. The two polymer layers are respectively prepared by depositing the metal conductive layers on the single surfaces, so that the film coating times of the polymer layers in a high-temperature environment are reduced under the condition that the thickness of the deposited metal conductive layers is required to be consistent, and the problem of thermal damage caused by multiple times of heating in the film forming process of the polymer layers is relieved; the composite current collector is provided with two polymer layers, so that when a vehicle has an accident and the battery is damaged, the short-circuit risk of the battery is greatly reduced, and the safety of the composite current collector applied to a battery end is further improved.

Description

Technical Field

[0001] The present invention relates to the field of composite current collectors, and particularly to a novel composite current collector and a preparation method thereof. Background Art

[0002] Under the current technical conditions, the composite current collectors produced generally have a "sandwich" structure. The inner layer is generally a polymer macromolecule layer (such as PET, PP or PI), and the outer layers on both sides are generally metal conductive layers (Cu or Al). Currently, the industrially mass-produced composite current collectors are divided into composite aluminum foils and composite copper foils. Among them, when manufacturing composite copper foils, PP (polypropylene) with a thickness of 4.5 or 6 μm is used as the base material, and a Cu conductive layer with a certain thickness is deposited on both sides of the PP by the "magnetron sputtering method", while composite aluminum foils generally use the "evaporation method" to deposit a certain thickness of Al conductive layer on both sides of PET (polyethylene terephthalate) with a thickness of 6 μm. Due to the relatively thin metal conductive layer on the surface and the relatively light inner polymer layer of the composite current collector, it can better reduce the weight of the current collector itself, thereby increasing the energy density of the lithium-ion battery to a certain extent. At the same time, the relatively light metal layer on its surface is more likely to break when the lithium-ion battery undergoes thermal runaway than the conventional pure metal current collector, thereby blocking the connection between the active material and the current collector and preventing the continuous deterioration of the thermal runaway of the lithium-ion battery.

[0003] The conventional method for preparing composite current collectors is to deposit metal conductive layers on both sides of a single polymer macromolecule layer by the vacuum evaporation method or the magnetron sputtering method. During the manufacturing process of composite current collectors by the magnetron sputtering method and the vacuum evaporation method, the polymer macromolecule layer will pass through the high-temperature target and evaporation source repeatedly. Therefore, no matter which method is used, the polymer macromolecule layer will cause serious thermal damage when passing through the high-temperature evaporation area multiple times. When the metal conductive layer is relatively thick, the traveling speed of the polymer macromolecule layer is slow and the temperature of the evaporation source is high, and the thermal damage caused is particularly obvious, having certain defects. Summary of the Invention

[0004] The purpose of the present invention is to provide a novel composite current collector and a preparation method thereof to improve the production quality of the current collector and further improve the safety of the current collector during use.

[0005] To solve the above technical problems, the present invention provides a novel composite current collector, including a polymer macromolecule layer, a connection layer, and a metal conductive layer;

[0006] There are two layers of the polymer macromolecule layer, and the two layers of the polymer macromolecule layer are adhesively connected through the connection layer;

[0007] The metal conductive layer is arranged on the end faces of the two layers of the polymer macromolecule layer, and the metal conductive layer faces away from the connection layer.

[0008] Further, the polymer layer is at least one of polytetrafluoroethylene film, polyester film, polyethylene terephthalate, polyimide, and polypropylene plastic.

[0009] Further, the thickness of the polymer layer is 0.5 μm - 10 μm.

[0010] Further, the connecting layer is made of at least one of epoxy resin, modified polyolefin resin, ethylene - acrylic acid copolymer, silicone resin, polyacrylate, polyurethane, unsaturated polyester, phenolic resin, polyacrylic acid resin, and ethylene - vinyl acetate copolymer.

[0011] Further, the thickness of the connecting layer is not greater than 10% of the thickness of the polymer layer.

[0012] Further, the present invention also discloses a method for preparing a novel composite current collector, which is used to prepare the above - mentioned novel composite current collector, and includes:

[0013] Select two polymer layers that meet the material requirements, and perform single - sided coating on these two polymer layers to obtain metal conductive layers;

[0014] Coat an adhesive on the two single - sided coated polymer layers, and dry the adhesive;

[0015] Press and bond the two polymer layers that are respectively coated with the adhesive on one side to form a connecting layer, and obtain a bonded film material;

[0016] Wind up the bonded film material after pressing and bonding to obtain a composite current collector with metal conductive layers on both sides.

[0017] Further, the two polymer layers have the same material, and the single - sided coating of the two polymer layers adopts one of vacuum evaporation coating method or magnetron sputtering method.

[0018] Further, additives are added to the adhesive before the adhesive coating, and the additives at least include a dispersant, a thickener, or a cross - linker.

[0019] Further, the adhesive is dried in a vacuum environment, and the drying temperature is controlled within the range of 50°C - 150°C.

[0020] Further, the polymer layer coated with the adhesive on one side is pressed and bonded through a roller press, and the pressing pressure of the roller press is 3 kg - 50 kg.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] The two polymer layers of the present invention are respectively prepared by single-sided deposition of a metal conductive layer. When the thickness of the deposited metal conductive layer is required to be the same, the coating times of the polymer layer in a high-temperature environment are reduced, and the thermal damage problem caused by multiple heatings of the polymer layer during the film-forming process is alleviated. Moreover, the composite current collector of the present invention has two polymer layers, which greatly reduces the risk of battery short circuit when the battery is damaged in a vehicle accident, and further improves the safety applied to the battery end. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of the overall structure of the novel composite current collector of the present invention;

[0024] Figure 2 is a schematic flow chart of the preparation method of the novel composite current collector of the present invention;

[0025] Figure 3 is a schematic diagram of the overall structure of the production equipment of the novel composite current collector of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The novel composite current collector and its preparation method of the present invention will be described in more detail below with reference to the schematic diagrams, in which the preferred embodiments of the present invention are shown. It should be understood that those skilled in the art can modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as a broad guidance for those skilled in the art and not as a limitation on the present invention.

[0027] In the following paragraphs, the present invention will be described more specifically by way of example with reference to the drawings. The advantages and features of the present invention will be clearer according to the following description and the claims. It should be noted that the drawings are all in a very simplified form and use non-precise scales, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0028] As Figure 1 shown, an embodiment of the present invention provides a novel composite current collector and its preparation method, including a polymer layer 1, a connection layer 3, and a metal conductive layer 2.

[0029] Specifically, two polymer layers 1 are provided, and the two polymer layers 1 are adhesively connected through the connection layer 3.

[0030] The metal conductive layer 2 is disposed on the end faces of the two polymer layers 1, and the metal conductive layer 2 faces away from the connection layer 3.

[0031] In this embodiment, the composite current collector is formed by separately depositing a metal conductive layer 2 on one side of two polymer layers 1 and then laminating and bonding them. When the thickness of the deposited metal conductive layer 2 is required to be consistent, the number of coating times of the polymer layer 1 in a high-temperature environment is reduced. In this method, the number of times the polymer layer 1 passes through the high-temperature deposition area is only half of that of the traditional preparation method, reducing the thermal damage problem caused by the polymer layer 1 being heated multiple times during the film-forming process. Moreover, the composite current collector prepared by the present invention has two polymer layers 1, which greatly reduces the risk of battery short circuit when the battery is damaged in a vehicle accident, further improving the safety when applied to the battery end.

[0032] In a specific embodiment, the polymer layer 1 is at least one of polytetrafluoroethylene film, polyester film, polyethylene terephthalate, polyimide, and polypropylene plastic. The thickness of the polymer layer 1 is 0.5 μm - 10 μm.

[0033] In addition, the connecting layer 3 is at least one of epoxy resin, modified polyolefin resin, ethylene-acrylic acid copolymer, silicone resin, polyacrylate, polyurethane, unsaturated polyester, phenolic resin, polyacrylic acid resin, and ethylene-vinyl acetate copolymer. The thickness of the connecting layer 3 is not greater than 10% of the thickness of the polymer layer 1.

[0034] Example 2:

[0035] As Figure 2 shown, the present invention discloses a method for preparing a novel composite current collector for preparing the novel composite current collector in Example 1, including:

[0036] S100. Select two polymer layers 1 that meet the material requirements, and perform single-sided coating on these two polymer layers 1 to obtain the metal conductive layer 2.

[0037] Specifically, the two polymer layers 1 are made of the same material, and single-sided coating of the two polymer layers 1 is performed using one of vacuum evaporation or magnetron sputtering. Among them:

[0038] Vacuum evaporation is a method of heating a metal or other material to a molten state under vacuum conditions and depositing it on the surface of the workpiece to form a coating. This method has the advantages of strong coating adhesion, high hardness, strong wear resistance, and good corrosion resistance, and is widely used in products such as plastics, metals, and ceramics. The basic principle of vacuum evaporation is to place the evaporation source and the substrate in a vacuum container, and evaporate the film-forming material by means of resistance heating, ion beam, etc., and the particles fly to the surface of the substrate and condense into a film. The process flow usually includes steps such as pre-coating preparation, vacuum pumping, ion bombardment, baking, preheating, and evaporation.

[0039] The magnetron sputtering method is a physical vapor deposition (PVD) technique, which has the advantages of simple equipment, easy control, large coating area, strong adhesion, etc. Its core principle is to introduce a magnetic field on the surface of the target cathode and use the constraint of the magnetic field on charged particles to increase the plasma density, thereby increasing the sputtering rate. The working principle of the magnetron sputtering method is as follows: an appropriate amount of argon gas is filled under high vacuum conditions, and a DC voltage of several hundred kilovolts is applied between the cathode (usually a cylindrical or planar target) and the anode (the wall of the coating chamber) to generate a magnetron-type abnormal glow discharge, causing the argon gas to ionize. During the process of electrons flying towards the substrate under the action of the electric field, they collide with argon atoms, causing them to ionize and produce Ar+ ions and new electrons. The new electrons fly towards the substrate, and the Ar ions are accelerated by the electric field to bombard the cathode target, causing the target material to sputter. The neutral target atoms or molecules in the sputtered particles are deposited on the substrate to form a thin film, and the generated secondary electrons are affected by the electric field and magnetic field, and drift in the direction indicated by E (electric field) × B (magnetic field), which is simply called E×B drift, and its movement trajectory is approximately a cycloid.

[0040] Particularly, compared with the traditional composite current collector preparation process, this method reduces the coating times of the polymer layer 1 in a high-temperature environment while ensuring the same thickness of the metal conductive layer 2 on the polymer layer 1. The coating times of the polymer layer 1 passing through the high-temperature evaporation zone in this method are only half of the traditional coating times, thereby reducing the thermal damage problem caused by the polymer layer 1 being heated multiple times during the film-forming process, and thus improving the production quality of the composite current collector.

[0041] S200. Coat the binder on the two single-sided coated polymer layers 1 and dry the binder.

[0042] Specifically, the binder is coated on the side of the polymer layer 1 facing away from the metal conductive layer 2. In order to ensure the efficient combination between the binder and the polymer layer 1, additives should be added before the binder is coated. Among them, the additives should at least include dispersants, thickeners or cross-linking agents.

[0043] After the binder coating work is completed, use an oven to dry the coated connection layer 3. Further, it is required that the heating method of the oven mechanism is generally infrared baking or ultraviolet curing, and the baking temperature is generally controlled at 50 - 150 °C. Further, because the polymer film with the connection layer 3 has been coated and there is a metal conductive layer 2 on the surface, in order to protect the metal conductive layer 2 from oxidation in the atmosphere, it is generally required that the oven is in a vacuum environment. Further, it is required that the baking temperature of the oven mechanism has reached the curing temperature before the connection layer 3 on the surface of the polymer layer 1 enters the baking area for curing. Among them, the thickness of the connection layer 3 formed after the binder is dried is not greater than 10% of the thickness of the polymer layer 1.

[0044] S300. Press and bond the two polymer layers 1 coated with the binder on one side respectively to form a connection layer 3, thereby obtaining an adhesive film material.

[0045] Specifically, the two polymer layers 1 coated with the binder on one side respectively are joined by a roller press mechanism for two polymer layers 1 each with the binder on one side. The two polymer layers 1 are conveyed in the same direction under the driving of the roller set of the roller press mechanism, and the distance between them gradually decreases.

[0046] Among them, the two polymer layers 1 coated with the binder on one side respectively have the same transmission speed, and before joining, it is necessary to check the alignment of the end faces of the two polymer layers 1, and the deviation range thereof is not more than 2 mm. The pressing force is 3 kg to 50 kg.

[0047] S400. Wind up the adhesive film material after pressing and bonding to obtain a composite current collector with metal conductive layers 2 on both sides.

[0048] Example 3:

[0049] As Figure 3 shown, the present invention also discloses a production device for a novel composite current collector, which uses the preparation method of the novel composite current collector in Example 2 to produce the novel composite current collector in the example.

[0050] The production device includes a polymer layer base film roll 51, a coating device 52, a connection layer coating device (coating machine) 53, a drying mechanism 54 (oven), a rolling mechanism 55, and a winding mechanism 56 after rolling and combining. It should be noted that the sorting method of all mechanisms in this preparation device is only one sorting scheme, and the specific process flow should be formulated according to the actual situation of the operation site. Similarly, the preparation process shown in this device is not required to be consistent, and can be flexibly adjusted according to the process requirements.

[0051] For example: The connection layer 3 coating mechanism can be placed in the previous process of the coating device 52, that is, coating with glue first and then coating. At this time, the drying mechanism 54 should also be placed after the coating machine and before the coating device 52; Similarly, regarding the explanation of the consistency of the process flow, considering that the preparation components contained in the connection layer 3 used in the process may be different, or the added auxiliary components are different, it may be necessary to stand still for a certain period of time in the atmosphere or vacuum environment to take effect. Therefore, the process flow should also include the standing time required by the process requirements, rather than immediately proceeding to the next process after the end of the previous process. The specific definition of the standing time should be flexibly set with reference to the requirements of relevant technical documents.

[0052] Use the production device of the novel composite current collector to produce a composite current collector, and analyze the performance of the produced composite current collector, as follows:

[0053] (1) The material of the polymer layer 1 is a PET film, and the thickness of the polymer layer 1 is 0.5 - 10 μm. Among them, when the thickness of the polymer layer 1 is 2 - 8 μm, the overall preparation effect is better, and the optimal thickness of the polymer layer 1 is 3 - 6 μm. If the polymer layer 1 is too thin, it is easily scalded during the coating process due to its physical properties. If it is too thick, the overall thickness of the finally prepared composite current collector will be too large, which will have an adverse impact on the energy density and volume energy density of the battery when the battery is prepared. The specific preparation process is as follows:

[0054] S1: When coating one side of the polymer layer 1 with an aluminum metal conductive layer 2, the coating methods include vacuum evaporation coating, magnetron sputtering coating, and chemical coating, and different coating methods can be reused. Among them, vacuum evaporation coating is to evaporate the metal material in a vacuum and deposit it on the surface of the polymer layer 1 to form the aluminum metal conductive layer 2. In this embodiment, the vacuum evaporation coating method is preferably used because the film formation speed of vacuum evaporation coating is fast and the efficiency is high. In the traditional method for preparing a composite current collector, since the metal conductive layer 2 needs to be coated on both sides of a base film, the polymer layer 1 passing through the high-temperature evaporation area multiple times may cause high-temperature scalding, which will be improved because the polymer layer 1 is coated with a metal layer on one side in this embodiment, resulting in a significant reduction in the coating times. In this embodiment, the thickness of the aluminum metal conductive layer 2 is 500 - 2000 nm.

[0055] S2: The coating position of the connecting layer 3 should be on the non-coated surface of the polymer layer 1, and the coating thickness of the connecting layer 3 is 0.1 - 1 μm. Among them, when the thickness of the connecting layer 3 is 0.1 - 0.8 μm, the preparation effect is better, and the optimal thickness of the connecting layer 3 is 0.2 - 0.5 μm. Generally, it is required that the thickness of the connecting layer 3 does not exceed 10% of the thickness of the polymer layer 1 because the thickness of the connecting layer 3 will affect the thickness of the finally prepared composite current collector, and the composite current collector is applied in the battery. An excessive thickness will cause the thickness of the battery to increase accordingly, which will have an adverse impact on both the energy density and volume energy density of the battery.

[0056] Use a drying mechanism 54 to dry the connecting layer 3. Before drying, preheat the oven to reach the required drying temperature. The drying methods of the oven include hot air baking, infrared baking, and ultraviolet curing, and the baking temperature is controlled between 50 - 150 °C.

[0057] To reduce the oxidation degree of the aluminum metal layer on the surface of the polymer layer 1 in the atmosphere, it is required that the oven works in a vacuum environment.

[0058] S3: Use a roller mechanism to match and bond two polymer layers 1 each with a connecting layer 3.

[0059] Two polymer layers 1 each with a connecting layer 3 run in the same direction under the drive of a roller press mechanism. Before entering the roller press, it is necessary to check whether the fitting degree of the two polymer layers 1 meets the fitting standard. Because if there is a large deviation between the two before fitting, it is necessary to cut off a large area of the curled edge of the composite current collector film after fitting, directly reducing the raw material utilization rate and increasing costs.

[0060] In this embodiment, it is required that the edge deviation of the two polymer layers 1 during fitting be controlled within 1 mm.

[0061] When the polymer layer 1 enters the roller press for fitting, it is required that the roller press apply a certain pressure to the two polymer layers 11. Further, it is required that the pressure range be 3 kg - 50 kg, preferably 5 kg - 20 kg.

[0062] In this embodiment, the pressure applied by the roller press is 8 kg.

[0063] S4: Wind up the two polymer layers 1 after being fitted by the roller press to obtain a composite current collector film roll with metal conductive layers 2 on both sides.

[0064] The composite current collector provided by this solution is formed by coating two polymer layers 1 with single-sided metal conductive layers 2 through a connecting layer 3, drying, and then fitting through a roller press mechanism 55 to form a composite current collector film roll with metal conductive layers 2 on both sides. Each polymer film only needs to be coated on one side. In the traditional preparation method, after the single-sided metal conductive layer 2 is coated on the single polymer layer 1, the polymer layer 1 needs to be turned over to the coating side for coating again. In this solution, the polymer layer 1 only needs to be coated half as many times as the traditional method under the same technical parameter requirements, avoiding the thermal damage caused by the large amount of heat generated by vacuum evaporation coating to the ultra-thin film in a high-temperature environment, effectively ensuring the performance of the composite current collector. At the same time, the two polymer layers 1 and the intermediate coated connecting layer 3 are all insulating materials, further improving the safety of the final application at the battery end.

[0065] (2) In this group, the polymer layer 1 is a 3-μm PET film, and a 1000-nm-thick copper metal conductive layer 2 is evaporated on its surface by vacuum evaporation coating. Here, a one-time film-forming process is selected, and by adjusting the evaporation amount of the coating, a thickness of 1000 nm is coated at one time; after the single-sided coating is completed, a 0.3-μm-thick connecting layer 3 is coated on the non-coated surface of the polymer layer 1, and then baking is carried out, and the baking temperature is set at 60 °C.

[0066] Set the pressure of the roller press group to 10 kg, check that the fitting degree of the two polymers meets the requirements before rolling, and wind up the fitted composite current collector.

[0067] In this embodiment, the surface of the finally produced composite current collector product is flat, without visible defects to the naked eye, without thermal damage, and the two polymer layers 1 are firmly adhered, and the bonding force between the metal conductive layer 2 made of copper material and the polymer layer 1 is excellent.

[0068] (3) In this group, the polymer layer 1 selects a 4-μm PP film, and a metal conductive layer 2 made of copper material with a thickness of 1000 nm is evaporated on its surface by magnetron sputtering coating. Here, a multi-film-forming process is selected, and by adjusting the evaporation amount of the coating, a thickness of 1000 nm is achieved in four coatings. After the single-sided evaporation of the copper metal conductive layer 2 is completed, a connecting layer with a thickness of 0.3 μm is coated on its non-coated surface. 3 Subsequently, baking is carried out, and the oven temperature is set at 60 °C.

[0069] Set the pressure of the pressure roller group to 10 kg. Before rolling, check that the adhesion of the two polymer layers meets the requirements, and wind up the adhered composite current collector.

[0070] In this group, the surface of the finally produced composite current collector product is flat, without visible defects to the naked eye, without thermal damage, and the two polymer layers 1 are firmly adhered, and the bonding force between the metal conductive layer 2 made of copper material and the polymer layer 1 is excellent.

[0071] Compared with the prior art, the present invention has at least the following beneficial effects:

[0072] Compared with the traditional preparation method of the composite current collector, the present invention has two ultra-thin polymer layers for single-sided deposition respectively and is formed by preparing a metal conductive layer, reducing the coating times of the polymer layer at high temperature under the condition that the required thickness of the deposited metal conductive layer is consistent. The number of times the polymer layer passes through the high-temperature evaporation area in the present invention is only half of that of the traditional preparation method, alleviating the problem of thermal damage caused by multiple heatings of the polymer layer during the film-forming process. Moreover, the composite current collector prepared by the present invention has two polymer layers. When the battery is damaged in a vehicle accident, the risk of battery short circuit is greatly reduced, further improving the safety applied at the battery end ​ .

[0073] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A novel composite current collector, characterized in that: It includes a polymer layer, a connecting layer and a metal conductive layer; The polymer layer is provided with two layers, and the two polymer layers are bonded and connected by the connecting layer; The metal conductive layer is arranged on the end surfaces of the two polymer layers, and the metal conductive layer is away from the connecting layer.

2. The novel composite current collector according to claim 1, characterized in that: The polymer layer is at least one of polytetrafluoroethylene film, polyester film, polyethylene terephthalate, polyimide and polypropylene plastic.

3. The novel composite current collector according to claim 1, characterized in that: The thickness of the polymer layer is 0.5 μm-10 μm.

4. The novel composite current collector according to claim 1, characterized in that: The connecting layer is made of at least one of epoxy resin, modified polyolefin resin, ethylene-acrylic acid copolymer, silicone resin, polyacrylate, polyurethane, unsaturated polyester, phenolic resin, polyacrylic acid resin and ethylene-vinyl acetate copolymer.

5. The novel composite current collector according to claim 1, characterized in that: The thickness of the connecting layer is not greater than 10% of the thickness of the polymer layer.

6. A method for preparing a novel composite current collector, used for preparing the novel composite current collector as claimed in any one of claims 1 to 5, characterized in that: include: Select two polymer layers that meet the material requirements, and perform single-sided coating on the two polymer layers to obtain metal conductive layers; Applying adhesive to the two single-sided coated polymer layers, and drying the adhesive; The two polymer layers coated with adhesive on one side are pressed and bonded to form a connecting layer to obtain an adhesive film material; The adhesive film material after pressing and bonding is rolled up to obtain a composite current collector with metal conductive layers on both sides.

7. The method for preparing the novel composite current collector according to claim 6, characterized in that: The two polymer layers are made of the same material, and the single-side coating of the two polymer layers is performed by vacuum evaporation or magnetron sputtering.

8. The method for preparing the novel composite current collector according to claim 6, characterized in that: An auxiliary agent is added to the adhesive before coating the adhesive, and the auxiliary agent at least includes a dispersant, a thickener or a cross-linking agent.

9. The method for preparing the novel composite current collector according to claim 6, characterized in that: The adhesive is dried in a vacuum environment, and the drying temperature is controlled within a range of 50°C-150°C.

10. The method for preparing the novel composite current collector according to claim 6, characterized in that: The polymer layer coated with adhesive on one side is pressed and bonded by a roller press, and the pressing pressure of the roller press is 3kg-50kg.

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