Composite current collector

Abstract

The invention provides a composite current collector which comprises a supporting layer, coatings containing metal elements and oxygen elements are respectively formed in the thickness direction of the supporting layer, the metal elements enable the composite current collector to achieve a current converging function, and the oxygen elements enable the corrosion resistance of the composite current collector to be improved. The cost of the composite current collector is reduced, and the safety performance of the composite current collector is improved. Meanwhile, the content ratio of the oxygen element is gradually reduced from the side, close to the supporting layer, of the coating to the side, away from the supporting layer, of the coating in the thickness direction of the coating, so that the composite current collector can be prevented from being corroded by the outside.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a composite current collector. Background Art

[0002] In the prior art, the composite current collector is generally a composite copper current collector and a composite aluminum current collector. The composite copper current collector is used for the negative electrode of the battery, and the composite aluminum current collector is used for the positive electrode of the battery.

[0003] However, the existing composite current collectors still need to be improved in terms of antioxidant performance and safety performance. Summary of the Invention

[0004] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a composite current collector, aiming to improve the problems of antioxidant performance and safety performance of the composite current collector in the prior art.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a composite current collector, including a support layer and coatings on two sides of the support layer in the thickness direction. The coatings contain metal elements and oxygen elements, and the content ratio of the oxygen elements decreases along the thickness direction of the coatings from the side of the coatings close to the support layer to the side of the coatings far from the support layer.

[0006] Through the above solution, due to the presence of oxygen elements, whether during the storage and transportation of the current collector or when it is in the electrolyte, the composite current collector of the present invention can resist external erosion and prevent the increase of the surface sheet resistance of the composite current collector. Due to the presence of oxygen elements on the outermost side of the support layer, the current passing through the surface of the composite current collector can be restricted, thereby reducing the generation of heat on the surface of the composite current collector. At the same time, the content ratio of the oxygen elements decreases along the thickness direction of the coatings from the side of the coatings close to the support layer to the side of the coatings far from the support layer. While maintaining the conductivity of the composite current collector, it can prevent chemical substances in the electrolyte from penetrating into the interior of the composite current collector and damaging the support layer.

[0007] In one embodiment, in the coatings, the content of the oxygen elements is less than the content of the metal elements, and the content of the oxygen elements on the side of the coatings close to the support layer is greater than the content of the metal elements.

[0008] Through the above solution, since the content of the oxygen elements is less than the content of the metal elements, the composite current collector of the present application can maintain a predetermined conductivity and also prevent external corrosion. And the content of the oxygen elements on the side close to the support layer being greater than the content of the metal elements can improve the safety performance of the battery.

[0009] In one embodiment, in the coating, the content of carbon element is less than that of the metal element, and the content of carbon element is greater than that of the oxygen element. In a layer close to the support layer, the content of carbon element is less than that of the oxygen element and the metal element.

[0010] Through the above solution, since the content of carbon element is less than that of the metal element, on the one hand, the weight of the composite current collector can be reduced, the problem of the decrease in resistivity caused by the oxygen element can be neutralized, and the corrosion resistance of the composite current collector can be improved. On the other hand, the cost of the composite current collector can be reduced, and the generation of holes on the surface of the composite current collector can be reduced.

[0011] In one embodiment, on the side of the coating far from the support layer, the content of carbon element is greater than that of the oxygen element and less than that of the metal element.

[0012] Through the above solution, since the content of carbon element is greater than that of the oxygen element, the conductivity of the composite current collector can be further improved. At the same time, since the content of carbon element is less than that of the metal element, the cost of the composite current collector can be reduced, which is beneficial to replacing the existing pure metal composite current collector.

[0013] In the coating, on the side far from the support layer, the content of oxygen element on the side of the coating far from the support layer is less than that of the metal element.

[0014] Through the above solution, since the content of oxygen element on the side of the coating far from the support layer is less than that of the metal element, the conductivity of the side of the coating far from the support layer is better while the corrosion from the outside can be reduced.

[0015] In one embodiment, in the coating on the side close to the support layer, the content of oxygen element is greater than the sum of the content of carbon element and the content of metal element. In the coating on the layer far from the support layer, the content of metal element is greater than the sum of the content of oxygen element and the content of carbon element.

[0016] Through the above solution, since the content of oxygen element in the coating on the side close to the support layer is greater than the sum of the content of carbon element and the content of metal element, the conductivity of the part of the coating close to the support layer is lower. When a sharp object from the outside pierces the composite current collector, the coating on the side close to the support layer will enter the other side of the support layer along with the sharp object, thereby preventing the coating on one side of the support layer from contacting the coating on the other side and reducing the occurrence of risks. And the content of metal element on the side far from the support layer is greater than the sum of the content of oxygen element and the content of carbon element, which can enable the composite current collector to maintain a predetermined conductivity.

[0017] Second aspect, the present application provides a method for preparing a composite current collector, including the following steps: S1. Under vacuum conditions, introduce oxygen with a flow rate of N sccm onto the support layer, and simultaneously form a first layer on the support layer; S2. Introduce oxygen with a flow rate of M sccm onto the support layer, and simultaneously form a second layer on the first layer, where N is greater than M; Through the above method, a coating containing metal elements and oxygen elements can be formed on the support layer, and the content ratio of the oxygen elements decreases along the thickness direction of the coating from the side of the coating close to the support layer to the side of the coating far from the support layer.

[0018] In one embodiment, in steps S1 and S2, while forming metal elements on the support layer, carbon elements are formed on the support layer.

[0019] Through the above method, a coating containing carbon elements, metal elements, and oxygen elements can be formed on the support layer.

[0020] In one embodiment, the content of carbon formed on the support layer in step S1 is less than the content of carbon formed on the support layer in step S2.

[0021] Through the above method, a coating with a decreasing carbon element content can be formed on the support layer along the thickness direction of the coating.

[0022] Compared with the prior art, a composite current collector provided by the present invention includes a support layer. In the thickness direction of the support layer, a coating containing metal elements and oxygen elements is respectively formed. The metal elements enable the composite current collector to achieve the function of converging current, while the oxygen elements improve the corrosion resistance of the composite current collector, reduce the cost of the composite current collector, and also improve the safety performance of the composite current collector of the present invention. At the same time, the content ratio of the oxygen elements decreases along the thickness direction of the coating from the side of the coating close to the support layer to the side of the coating far from the support layer, which can prevent the outside from eroding the composite current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] 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 for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings. In the drawings: Figure 1 It is the first structural schematic diagram of the composite current collector in the embodiment of the present invention; Figure 2 This is the second structural schematic diagram of the composite current collector in the embodiment of the present invention; Figure 3 This is the third structural schematic diagram of the composite current collector in the embodiment of the present invention; Figure 4 This is the fourth structural schematic diagram of the composite current collector in the embodiment of the present invention; Figure 5 This is the fifth structural schematic diagram of the composite current collector in the embodiment of the present invention; Figure 6 This is the schematic diagram of the preparation process of the composite current collector in the embodiment of the present invention.

[0024] In the figure: 1. Support layer, 2. First surface, 3. Second surface, 4. Coating, 5. First layer, 6. Second layer, 7. First side, 8. Second side, 9. Third side, 10. First coating, 11. Second coating, 12. Third coating. Detailed implementation manners

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by the embodiments of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, the connection can be for a fixing function or for a circuit connection function.

[0027] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0028] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, "a plurality of" means two or more unless otherwise specifically defined. Additionally, the technical solutions between various embodiments can be combined with each other, but it must be based on the fact that those skilled in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0029] The present invention provides a composite current collector. As Figure 1 and Figure 2 shown, the composite current collector includes a support layer 1. When viewed from the thickness direction of the support layer, the support layer 1 has a first surface 2 and a second surface 3. On the first surface 2 and the second surface 3, coating layers 4 are provided, thereby forming a composite current collector having a sandwich structure. In this embodiment, the coating layer contains metal elements and oxygen elements. The metal elements are used to endow the coating layer with a current collecting function and can also improve the mechanical strength of the composite current collector, while the oxygen elements enable the composite current collector to have a function of resisting external corrosion. Moreover, the use of oxygen elements can reduce the use of metal elements and the cost of the composite current collector. In the coating layers 4 on the first surface 2 and the second surface 3 on both sides in the thickness direction of the support layer, the proportion of the content of oxygen elements decreases along the thickness direction of the coating layer from the side of the coating layer 4 close to the support layer 1 to the side of the coating layer 4 far from the support layer 1. This can greatly improve the safety performance and service life of the composite current collector. In terms of safety performance, this is because the high content of oxygen elements in the coating layer 4 on the side close to the support layer 1 can reduce the conductivity here. In this way, when a sharp object from the outside pierces the composite current collector, the coating layer 4 on the side close to the support layer 1 can enter the other side of the support layer 1 along with the sharp object. Since the content of oxygen elements in the coating layer 4 on the side close to the support layer 1 is high, the coating layer 4 on the side close to the support layer 1 has poor conductivity or is non-conductive. Even if the coating layer 4 on the side close to the support layer 1 pierces the separator and contacts another electrode, there will be no short-circuit risk. In terms of service life, due to the presence of oxygen elements, it can prevent the corrosion of external air or electrolyte, thereby improving the service life of the composite current collector.

[0030] In this embodiment, as Figure 3As shown, the coating further includes carbon element, and the carbon element increases from the side close to the support layer 1 to the side away from the support layer 1 along the thickness direction of the coating. In this embodiment, for convenience of description, the side of the coating close to the support layer is called the first layer 5, and the side of the coating away from the support layer is called the second layer 6. Preferably, in the first layer 5, the mass ratio of the carbon element in the coating is 0%-5%, the mass ratio of the metal element in the coating is 90%-99%, and the mass ratio of the oxygen element in the coating is 0-15%. In the second layer 6, the mass ratio of the carbon element in the coating is 1%-10%, the mass ratio of the metal element in the coating is 80%-98%, and the mass ratio of the oxygen element in the coating is 1-10%. By regulating the contents of the oxygen element, the carbon element and the metal element in the first layer 5 and the second layer 6, not only can the foregoing effects be obtained, but also the heat conduction performance of the composite current collector can be improved. In terms of improving the heat conduction performance of the composite current collector, since the carbon element content in the first layer 5 is between 0% and 5%, and the metal element content is between 90% and 99%, a carbon / metal composite material can be formed between the carbon element and the metal element in the first layer 5. In the carbon / metal composite material, heat is transferred from the atoms of the metal element to the photons of the carbon element and then transferred out to the second layer 6. In the second layer 6, the heat transferred to the second layer 6 and the heat transferred by the metal element in the second layer 6 can be transferred out by the carbon element in the second layer 6, greatly improving the heat conduction performance of the composite current collector of the present invention. Preferably, the carbon element and the metal element in the first layer 5 are mutually embedded with the carbon element and the metal element in the second layer 6. In this way, the carbon element in the second layer 6 and the metal element in the first layer 5 mutually form a carbon / metal composite material, and the metal element in the second layer 6 and the carbon element in the first layer 5 mutually form a carbon / metal composite material, which can greatly improve the heat conduction performance of the composite current collector of the present invention and also prevent the first layer 5 and the second layer 6 from separating from each other.

[0031] Further, the thickness of the support layer 1 of the composite current collector provided by the present invention can be 3um-12um, and the thickness of the coating can be 100nm-1200nm. In this embodiment, as Figure 4As shown, the content of oxygen element in the coating is less than that of the metal element, while the content of oxygen element on the side of the coating close to the support layer is greater than that of the metal element. For the convenience of description, in this embodiment, the side of the coating close to the support layer 1 is referred to as the first side 7. A second side 8 is formed on the side of the first side 7 away from the support layer 1, and a third side 9 is formed on the side of the second side 8 away from the first side 7. In the first side 7, the content of the metal element is preferably 40%-60%, the content of the oxygen element is preferably 40%-50%, and the content of the carbon element is preferably 0%-1%. Through the above scheme, a composite current collector with a surface coating that is not easily peeled off can be obtained, and at the same time, it can also prevent external electrolytes from penetrating into the interior of the support layer 1, resulting in a shortened lifespan of the support layer 1. The coating is not easily peeled off from the composite current collector because the oxygen element will form sufficient hydroxyl groups with the hydrogen element on the surface of the support layer, thereby improving the bonding force between the coating and the support layer 1. In the second side 8, the content of the metal element is preferably 50%-90%, the content of the oxygen element is preferably 5%-10%, and the content of the carbon element is 2%-4%. Through the above content ratio of oxygen element, metal element, and carbon element, the second side 8 can be more closely combined with the first side 7 and have a higher bonding force. This is because the oxygen element in the first side 7 is greater than that in the second side 8, so on the one hand, the oxygen element in the first side 7 connects the first side 7 to the support layer 1, and on the other hand, the metal element in the first side 7 can form a carbon / metal composite material with the carbon element in the second side 8. At the same time, the metal element and the carbon element in the second side 8 also form a carbon / metal composite material. That is to say, the elements in the first side 7 and the second side 8 are interconnected and mutually strengthened, thereby improving the bonding force between the second side 8 and the first side 7 and the bonding force between the first side 7 and the support layer 1. At the same time, due to this relationship between the elements in the first side 7 and the second side 8, the elements in the first side 7 and the second side 8 mutually form a protective network, thereby strengthening the corrosion resistance to the outside. In the third side 9, the content of the metal element is 90%-95%, the content of the oxygen element is 1%-10%, and the content of the carbon element is 0%-5%. Through the above ratio, it can not only achieve a coordinated interaction with the elements in the first side 7 and the second side 8, but also improve the resistance of the composite current collector to damage by external sharp objects, thereby improving the safety performance of the battery using the composite current collector of the present invention.

[0032] Further, in the composite current collector provided by the present invention, in the coating, the content of carbon element is less than that of metal element, and the content of carbon element is greater than that of oxygen element. In the layer close to the support layer, the content of carbon element is less than the sum of the content of oxygen element and the content of metal element. In the present application, the metal element may be elements such as copper, aluminum, nickel, chromium, etc. Since the content of carbon element is less than that of metal element, on the one hand, the weight of the composite current collector can be reduced, the problem of the decrease in resistivity caused by oxygen element can be neutralized, and the corrosion resistance of the composite current collector can be improved. On the other hand, the cost of the composite current collector can be reduced, and the generation of holes on the surface of the composite current collector can be reduced.

[0033] Further, in the composite current collector of the present invention, the content of oxygen element in the coating on the side close to the support layer is greater than the sum of the content of carbon element and the content of metal element. In the coating of the layer far from the support layer, the content of metal element is greater than the sum of the content of oxygen element and the content of carbon element. In this embodiment, as Figure 5 shown, for the convenience of description, the coating can be divided into a first coating 10, a second coating 11 and a third coating 12. The first coating 10 is located on two surfaces of the support layer 1 along the thickness direction, and the second coating 11 is located on the surface of the first coating 10 far from the support layer 1, and the third coating 12 is located on the surface of the second coating 11 far from the first coating 10. Preferably, in the first coating 10, the content of oxygen element can be 50%-80%, the content of metal element can be 10%-60%, and the content of carbon element can be 0%-20%. Through the mutual cooperation of the above oxygen element, metal element and carbon element, the conductivity of the part of the coating close to the support layer 1 is lower. When a sharp object in the outside world pierces the composite current collector, the coating on the side close to the support layer 1 will enter the other side of the support layer 1 along with the sharp object, thereby preventing the coating on one side of the support layer from contacting the coating on the other side and reducing the occurrence of risks. And the content of metal element on the side far from the support layer is greater than the sum of the content of oxygen element and the content of carbon element, which can make the composite current collector maintain a predetermined conductivity. On the other hand, due to the hydroxyl group formed between the oxygen element and the support layer 1, and the composite material structure formed between carbon and metal, the bonding force between the first coating 10 of the composite current collector of the present invention and the support layer 1 is greater.

[0034] On the other hand, the present invention also provides a preparation method of the above composite current collector, such as Figure 6As shown, it includes step S1. The step S1 includes introducing oxygen with a flow rate of N sccm onto the support layer under vacuum conditions, and at the same time forming a metal element on the support layer. Specifically, first, unwind the support layer into the vacuum chamber. In this application, the support layer can be one of polyethylene terephthalate, polyamide, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate glycol, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl formal, polyvinyl butyral, polyurethane, polycarbamate, polyacrylonitrile, polyvinyl acetate, polyformaldehyde, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, polycarbonate, polysulfone, polyethersulfone, and polyphenylene ether. After unwinding the support layer into the vacuum chamber, evacuate the vacuum chamber to less than 1×10-2 Pa, introduce oxygen with a flow rate of 3000 sccm - 4000 sccm near the support layer, and then start magnetron sputtering to sputter the metal element on the target onto the support layer, thereby forming a coating. At this time, the coating containing the metal element sputtered onto the support layer is a coating containing metal elements and oxygen elements, and the obtained coating can be called the first layer.

[0035] In the present invention, the preparation method of the composite current collector further includes step S2. The step S2 is: introducing oxygen with a flow rate of M sccm onto the support layer, and at the same time forming a second layer on the first layer by means of magnetron sputtering, where N is greater than M; specifically, M can be 1000 sccm - 2000 sccm. In this way, a second layer with an oxygen content greater than that of the first layer can be formed on the support layer. In this application, the thickness of the first layer can be 10 nm - 60 nm, and the thickness of the second layer is 100 nm - 1000 nm. In this embodiment, if it is necessary to make the second layer contain carbon elements, a carbon target can be used. For example, the metal target and the carbon target can be arranged around the cooling roller in sequence, and then sputtering simultaneously can form a second layer containing carbon elements on the first layer. Similarly, if it is necessary to form carbon elements in the first layer, a carbon target can also be set near the target of the metal element when forming the first layer. By the above method, a carbon / metal composite material can be formed, which can not only improve the thermal conductivity of the composite current collector shown, but also improve the electrical conductivity of the composite current collector shown.

[0036] In summary, a composite current collector provided by the present invention includes a support layer. In the thickness direction of the support layer, a coating containing metal elements and oxygen elements is respectively formed. The metal elements enable the composite current collector to achieve the function of converging current, while the oxygen elements improve the corrosion resistance of the composite current collector, reduce the cost of the composite current collector, and also improve the safety performance of the composite current collector of the present invention. At the same time, the content ratio of the oxygen elements decreases along the thickness direction of the coating from the side of the coating close to the support layer to the side of the coating far from the support layer, which can enable the composite current collector of the present invention to block the erosion of the outside world on the composite current collector.

[0037] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those skilled in the art to which the present invention pertains, without departing from the concept of the present invention, several equivalent substitutions or obvious variations can be made, and as long as the performance or use is the same, they should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A composite current collector, characterized in that, It includes a support layer and coatings on two sides in the thickness direction of the support layer. The coatings contain metal elements and oxygen elements, and the content ratio of the oxygen elements decreases along the thickness direction of the coatings from the side of the coatings close to the support layer to the side of the coatings far from the support layer.

2. The composite current collector according to claim 1, wherein The coatings further include carbon elements, and the content of the carbon elements increases along the thickness direction of the coatings from the side close to the support layer to the side far from the support layer.

3. The composite current collector according to claim 1, characterized in that, In the coatings, the content of the oxygen elements is less than that of the metal elements, and the content of the oxygen elements on the side of the coatings close to the support layer is greater than that of the metal elements.

4. The composite current collector according to claim 2, wherein In the coatings, the content of the carbon elements is less than that of the metal elements, and the content of the carbon elements is greater than that of the oxygen elements. On the layer close to the support layer, the content of the carbon elements is less than the sum of the content of the oxygen elements and the content of the metal elements.

5. The composite current collector according to claim 4, wherein In the coatings, on the side far from the support layer, the content of the carbon elements is greater than that of the oxygen elements and less than that of the metal elements.

6. The composite current collector according to claim 3, wherein In the coatings, on the side far from the support layer, the content of the oxygen elements is less than that of the metal elements.

7. The composite current collector according to any one of claims 1-6, characterized in that, The content of the oxygen elements in the coatings on the side close to the support layer is greater than the sum of the content of the carbon elements and the content of the metal elements. In the coatings on the layer far from the support layer, the content of the metal elements is greater than the sum of the content of the oxygen elements and the content of the carbon elements.

8. The preparation method of the current collector according to any one of claims 1-7, characterized in that It includes the following steps: S1. Under vacuum conditions, introduce oxygen with a flow rate of N sccm onto the support layer, and at the same time form metal elements on the support layer. S2. Introduce oxygen with a flow rate of M sccm onto the support layer, and at the same time form metal elements on the support layer, where N is greater than M.

9. The method for preparing a current collector according to claim 7, wherein, In the steps S1 and S2, when forming metal elements on the support layer, carbon elements are formed on the support layer at the same time.

10. The method for preparing a current collector according to claim 8, characterized in that, The content of the carbon elements formed on the support layer in step S1 is less than the content of the carbon elements formed on the support layer in step S2.

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