Composite current collector, battery electrode, battery, preparation method and application

Abstract

The invention discloses a composite current collector, a battery electrode, a battery, a preparation method and application. The provided composite current collector comprises a base film and a copper layer arranged on at least one side of the base film, and the whole surface layer of the copper layer contains a copper nitride layer. According to the provided composite current collector, a compact and continuous copper nitride layer is formed on the surface layer of the copper layer, and the metal copper layer on the inner layer is protected from reacting with oxygen in air, so that the oxidation resistance of the copper foil is remarkably enhanced; the hardness of copper nitride is about 800 HV to 1200 HV and is far higher than 40 HV to 50 HV of pure copper. The copper nitride is attached to the surface of the pure copper, contact fatigue between copper can be improved, the defect of copper foil pitting corrosion caused by mutual contact abrasion between film layers can be greatly reduced, the reliability of the composite current collector in practical application is improved, the service life of the composite current collector in practical application is prolonged, and the conductivity of the copper layers is not damaged.

Description

Technical Field

[0001] The present application belongs to the technical field of battery materials and relates to a composite current collector, a battery electrode, a battery, a preparation method and an application. Background Art

[0002] A composite current collector is a functional film made of multiple layers of materials. It usually adopts a "metal-polymer material-metal" structure, with polymer material as the middle layer and metal layers (such as copper and aluminum) plated on both sides. It is mainly used to replace traditional metal foil (such as copper foil and aluminum foil) as positive and negative electrode current collectors.

[0003] The composite current collector is prepared by evaporation, which can be completed in a single evaporation process in a vacuum chamber, reducing equipment investment and improving product yield. However, how to perform antioxidant treatment on the evaporated composite current collector becomes a problem that must be solved. In order to effectively solve the oxidation problem of the evaporated composite current collector, the evaporated composite current collector is usually subjected to secondary treatment, including rolling it up with a roller and performing antioxidant surface treatment with antioxidant agents in an antioxidant tank; or using a magnetron winding device to perform PVD metal nickel plating. However, the current antioxidant surface treatment method for the composite current collector is not conducive to the preparation of the antioxidant layer and the effect is poor. Summary of the Invention

[0004] Based on this, it is necessary to provide a composite current collector, a battery electrode, a battery, a preparation method and an application to improve the oxidation resistance of the composite current collector prepared by evaporation.

[0005] In some embodiments, a composite current collector is provided, comprising a base film and a copper layer disposed on at least one side of the base film, wherein the entire surface of the copper layer comprises a copper nitride layer.

[0006] In some embodiments, in the provided composite current collector, a solid solution layer is further included between the copper layer and the copper nitride layer, and the solid solution layer contains a Cu(N) solid solution.

[0007] In some embodiments, the provided composite current collector satisfies one or more of the following conditions:

[0008] (1) The material of the base film includes one or more of polypropylene, polyethylene terephthalate and polyimide;

[0009] (2) The thickness of the copper layer is 1 μm to 3 μm;

[0010] (3) The thickness of the copper nitride layer is 8 nm to 12 nm;

[0011] (4) The thickness of the solid solution layer is 15 nm to 25 nm; and

[0012] (5) The surface of the copper layer has a concave structure, and the depth of the concave structure is 5nm~10nm.

[0013] In some embodiments, a method for preparing a composite current collector is provided, comprising the following steps:

[0014] Providing a base film, and depositing a copper layer on at least one side of the base film by vacuum evaporation;

[0015] Providing a first nitrogen source, bringing the first nitrogen source into contact with the copper layer, performing a first nitriding process, forming a copper nitride layer on the entire surface of the copper layer, and preparing the composite current collector;

[0016] The first nitrogen source contains active nitrogen ions with high nitrogen potential and / or nitrogen atoms with high nitrogen potential.

[0017] In some embodiments, the method for preparing a composite current collector further includes, after the first nitriding is completed, contacting the composite current collector with a second nitrogen source to perform a second nitriding, so that a solid solution layer is formed between the copper layer and the copper nitride layer, wherein the solid solution layer contains a Cu(N) solid solution;

[0018] The second nitrogen source contains active nitrogen ions with low nitrogen potential and / or nitrogen atoms with low nitrogen potential.

[0019] In some embodiments, in the preparation method of the provided composite current collector, the preparation method of the first nitrogen source includes: controlling the flow rate of the first nitrogen gas to 1000 sccm to 3000 sccm, ionizing the first nitrogen gas under the conditions of an ion source voltage of 1000 V to 3000 V, a duty cycle of 15% to 30%, and a current of 0.5 A to 3 A to prepare the first nitrogen source.

[0020] In some embodiments, in the preparation method of the provided composite current collector, the preparation method of the second nitrogen source includes: controlling the flow rate of the second nitrogen gas to 400 sccm to 600 sccm, ionizing the second nitrogen gas under the conditions of an ion source voltage of 650 V to 800 V, a duty cycle of 50% to 80%, and a current of 0.5 A to 3 A to prepare the second nitrogen source.

[0021] In some embodiments, the provided method for preparing a composite current collector satisfies one or more of the following conditions:

[0022] (1) During the vacuum evaporation process, the base film is placed on a main roller for vacuum evaporation, and the temperature of the main roller is -30°C to 30°C;

[0023] (2) During the first nitriding process, the pretreated composite current collector is placed on a first cooling conductive roller for the first nitriding process, wherein the temperature of the first cooling conductive roller is -30°C to 30°C; and

[0024] (3) During the second nitriding process, the composite current collector is placed on a second cooling conductive roller for the second nitriding process. The ambient temperature of the second nitriding process is 110°C to 130°C, and the temperature of the second cooling conductive roller is -30°C to 30°C.

[0025] In some embodiments, the method for preparing the composite current collector further comprises the following steps: after depositing a copper layer on at least one side of the base film by vacuum evaporation, pre-treating the copper layer to form a concave structure on the surface of the copper layer;

[0026] Optionally, the copper layer is pretreated by physical sputtering;

[0027] Optionally, argon ions are used for the physical sputtering, and the method for preparing the argon ions includes: controlling the argon gas flow rate to 25 sccm to 50 sccm, ionizing the argon gas under the conditions of an ion source voltage of 400V to 1000V, a duty cycle of 20% to 50%, and a current of 0.5A to 3A to prepare the argon ions.

[0028] In some embodiments, there is provided an application of the composite current collector or the composite current collector prepared by the preparation method in preparing a battery electrode.

[0029] In some embodiments, a battery pole piece is provided, wherein the battery pole piece contains the composite current collector or the composite current collector prepared by the preparation method.

[0030] In some embodiments, a battery is provided, comprising the battery electrode sheet.

[0031] The provided composite current collector forms a dense and continuous copper nitride layer on the surface of the copper layer, protecting the inner metallic copper layer from reacting with oxygen in the air, thereby significantly enhancing the copper foil's antioxidant capacity. The hardness of copper nitride is approximately 800HV to 1200HV, far higher than the 40HV to 50HV of pure copper. During the winding process, copper nitride adheres to the pure copper surface, which can improve contact fatigue between copper and copper. The defects of copper foil pitting caused by mutual contact wear between film layers can be significantly reduced, thereby improving the reliability and service life of the composite current collector in practical applications without compromising the conductivity of the copper layer. By introducing nitriding treatment technology during the vacuum evaporation process of the composite copper foil, the surface of the composite copper foil is nitrided after the evaporation copper foil is prepared using the vacuum environment of the evaporation equipment. This eliminates the need to remove the composite copper foil from the vacuum equipment, avoids product oxidation during transportation, reduces losses, and improves efficiency. DETAILED DESCRIPTION

[0032] To facilitate understanding of the present invention, the present invention will be described more fully below. However, the present invention 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 invention more thorough and comprehensive.

[0033] It should be noted that when an element is referred to as being “fixed to” another element, it may be directly on the other element or there may be an intermediate element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or there may be an intermediate element.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0035] the term

[0036] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0037] The terms "and / or", "or / and", and "and / or" used in this application include any one of two or more related listed items, and also include any and all combinations of the related listed items, and the said any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that in this application, the technical solution undoubtedly includes technical solutions that are all connected by "logical and", and undoubtedly includes technical solutions that are all connected by "logical or". For example, "A and / or B" includes three parallel solutions: A, B and "a combination of A and B".

[0038] In this application, "plurality", "multiple", "multiple times", "multiples", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0039] The terms "combination thereof", "any combination thereof", "any combination thereof" and the like used in this application include all suitable combinations of any two or more of the listed items.

[0040] In this application, the "suitable" mentioned in "suitable combination", "suitable method", "any suitable method", etc. is based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0041] In this application, "preferred", "better", "more preferred" and "suitable" are only used to describe implementation methods or examples with better effects. It should be understood that they do not constitute a limitation on the scope of protection of this application.

[0042] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0043] In this application, the terms "optionally," "optional," and "optional" mean optional or dispensable, i.e., they refer to either option being selected from two parallel options: "with" or "without." If a technical solution contains multiple "optional" clauses, each "optional" clause is independent unless otherwise specified and there are no contradictions or constraints.

[0044] In the present invention, in the "first aspect," "second aspect," "third aspect," "fourth aspect," etc., the terms "first," "second," "third," "fourth," etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the technical features indicated. Furthermore, "first," "second," "third," "fourth," etc. serve only as non-exhaustive enumeration and description and should be understood not to constitute a closed-ended limitation on quantity.

[0045] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0046] In this application, when referring to a numerical interval (i.e., a numerical range), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval and includes the two numerical endpoints of the numerical range (i.e., the minimum and maximum values), as well as each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval refers only to integers within the numerical interval, it includes the two endpoint integers of the numerical range, as well as each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges included therein.

[0047] Unless otherwise specified, the temperature parameters in this application allow for both constant temperature treatment and temperature fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for temperature fluctuations within the accuracy range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

[0048] In this application, % (w / w) and wt% both refer to weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage.

[0049] The "room temperature" in this application generally refers to 5°C to 30°C, preferably 25±5°C.

[0050] Before the current vapor-deposited composite current collector undergoes antioxidant treatment, it is necessary to remove the composite current collector from the vacuum chamber and then pass it through an antioxidant tank or use a magnetic control device to perform antioxidant treatment on its surface. During the transportation process, the metallic copper layer will chemically react with oxygen in the air to generate copper oxide, which is not conducive to the preparation of the antioxidant layer. In addition, oxidation may cause the conductivity of the copper foil to decrease, increase resistance, trigger side reactions inside the battery, reduce the performance and cycle life of the battery, and also pose a potential threat to the safety and stability of the battery.

[0051] In some embodiments, a composite current collector is provided, comprising a base film and a copper layer disposed on at least one side of the base film, wherein the entire surface of the copper layer comprises a copper nitride layer.

[0052] In some embodiments, in the provided composite current collector, a solid solution layer is further included between the copper layer and the copper nitride layer, and the solid solution layer contains a Cu(N) solid solution.

[0053] In some embodiments, in the provided composite current collector, the material of the base film includes one or more of polypropylene, polyethylene terephthalate, and polyimide.

[0054] In some embodiments, in the provided composite current collector, the copper layer has a thickness of 1 μm to 3 μm.

[0055] In some embodiments, in the provided composite current collector, the thickness of the copper nitride layer is 8 nm to 12 nm.

[0056] The copper nitride layer thickness within this range is beneficial to improving the performance of the composite current collector. If the copper nitride layer thickness is too small, its oxidation resistance and corrosion resistance are poor, and if the thickness is too large, the sheet resistance will increase.

[0057] In some embodiments, in the provided composite current collector, the thickness of the solid solution layer is 15 nm to 25 nm.

[0058] The thickness of the solid solution layer within this range is beneficial to improving the performance of the composite current collector. If the thickness is too small, it will not be conducive to preventing the copper nitride layer from cracking, and if the thickness is too large, the square resistance will increase.

[0059] In some embodiments, in the provided composite current collector, the surface of the copper layer has a recessed structure, and the depth of the recessed structure is 5 nm to 10 nm.

[0060] In some embodiments, a method for preparing a composite current collector is provided, comprising the following steps:

[0061] Providing a base film, and depositing a copper layer on at least one side of the base film by vacuum evaporation;

[0062] Providing a first nitrogen source, bringing the first nitrogen source into contact with the copper layer, performing a first nitriding process, forming a copper nitride layer on the entire surface of the copper layer, and preparing the composite current collector;

[0063] The first nitrogen source contains active nitrogen ions with high nitrogen potential and / or nitrogen atoms with high nitrogen potential.

[0064] The composite current collector is placed in a vacuum evaporation winding coating device, and nitrogen is ionized into nitrogen ions through a high-voltage ion source. Nitrogen ions react with copper on the surface of the composite copper foil to form copper nitride, forming a dense and continuous copper nitride layer. This protects the inner metal copper layer from reacting with oxygen in the air, providing a reliable protective barrier for the composite current collector.

[0065] By introducing nitriding treatment technology into the process of vacuum evaporation of composite copper foil, the surface of the composite copper foil is nitrided after the preparation of the evaporation copper foil is completed by utilizing the vacuum environment of the evaporation equipment. There is no need to remove the composite copper foil from the vacuum equipment, thus avoiding product oxidation during transportation, reducing losses and improving efficiency.

[0066] In some embodiments, the vacuum evaporation winding coating equipment, in addition to the normal vacuum system, winding system, evaporation system, gas delivery system, and pressure detection system, should also add multiple chambers including a cooling conductive roller and an ion source to the roller system before the winding shaft, which are a pretreatment chamber, a high nitrogen chamber, and a low nitrogen chamber.

[0067] Nitriding principle: The chamber wall of the chamber is used as the anode, and the composite copper foil on the cooling conductive roller is used as the cathode. Voltage is applied between the cathode and cathode through an ion source. Nitrogen (N2) will be ionized under the action of the high-voltage ion source, and high-energy nitrogen ions will bombard the surface of the composite copper foil under the acceleration of the electric field.

[0068] The reason why this newly formed copper nitride layer effectively prevents further oxidation of the copper foil is mainly based on the following reasons. Structurally, the copper nitride layer has a tightly ordered crystal structure and strong interatomic bonding. This structural characteristic makes it difficult for oxygen molecules to penetrate the copper nitride layer and reach the surface of the copper foil substrate. From a chemical property perspective, the copper nitrogen compounds in the copper nitride layer are relatively stable and their chemical activity is far lower than that of metallic copper. When oxygen comes into contact with the copper nitride layer, it is difficult to chemically react with the elements therein, thus providing a reliable protective barrier for the copper foil.

[0069] In some embodiments, in the preparation method of the provided composite current collector, the preparation method of the first nitrogen source includes: controlling the flow rate of the first nitrogen gas to 1000 sccm to 3000 sccm, ionizing the first nitrogen gas under the conditions of an ion source voltage of 1000 V to 3000 V, a duty cycle of 15% to 30%, and a current of 0.5 A to 3 A to prepare the first nitrogen source.

[0070] The copper foil is wound into a high nitrogen chamber containing a cooling conductive roller and an ion source system. The ion source voltage is 1000V to 3000V, the duty cycle is 15% to 30%, the current is 0.5A to 3A, and the nitrogen flow rate is precisely controlled by a gas flow meter. The nitrogen flow rate is generally between 1000sccm and 3000sccm to ensure the formation of a stable and appropriate nitrogen atmosphere in the ion source. At high nitrogen potential, a large number of active nitrogen ions and nitrogen atoms are provided to directly react with the copper surface to form a copper nitride layer. In addition, in the voltage range of 1000 to 3000V, the higher the voltage, the faster the ionization rate of nitrogen, the more active nitrogen ions and nitrogen atoms are produced, and the greater the diffusion coefficient of active nitrogen ions and nitrogen atoms in the copper foil, which significantly increases the nitriding rate.

[0071] The nitrogen flow rate in the high nitrogen chamber directly affects the concentration of nitrogen ions and the generation rate of active nitrogen ions. When the nitrogen flow rate is too low, the number of active nitrogen ions generated by ion source ionization is limited, and the concentration of nitrogen ions deposited and attached to the composite copper foil is insufficient, which will lead to a slow nitriding rate and difficulty in forming a copper nitride layer of sufficient thickness and quality. On the contrary, if the nitrogen flow rate is too large, although it can increase the generation rate of ionized nitrogen atoms, it may cause nitrogen waste; at the same time, excess nitrogen will affect the movement path of nitrogen ions, reduce the energy and number of nitrogen ions bombarding the copper foil, and weaken the nitriding rate of the ion source; at the same time, too high a nitrogen atmosphere concentration may cause the copper nitride layer to grow too fast, resulting in a loose structure and reduced quality. Therefore, controlling the nitrogen flow rate within the range of 800 to 3000 sccm can achieve better cost-effectiveness while ensuring the nitriding effect.

[0072] The duty cycle refers to the proportion of the ion source switching time. In a pulse cycle, the percentage of time the signal is in the "on" state in the entire cycle. The larger the duty cycle, the longer the ion source is on, the more ionized charge is, and an oscillating electric field is generated. The ion motion trajectory changes from linear acceleration to spiral oscillation, increasing the collision between ions and gas, resulting in a decrease in ion energy, and a long time of bombarding the substrate, which will cause continuous heating of the surface; the lower the duty cycle, the shorter the ion bombardment time, the larger the cooling cycle, and the lower the substrate temperature rise. Moreover, ions are only generated and accelerated during the pulse on time. The ion beam quickly passes through the vacuum area with very few collisions, and can retain a higher energy to bombard the surface. Therefore, in the first nitrogen source, a lower duty cycle is used. On the one hand, the heat input is reduced and the cooling time is longer, which will not cause rapid heating of the substrate and thermal damage to the base film. On the other hand, the nitrogen ions are accelerated and collided less in the electric field, and the ion energy is high. Direct injection of high-energy N ions into the copper lattice is conducive to the rapid formation of dense copper nitride.

[0073] In the process of preparing the first nitrogen source, in order to quickly generate copper nitride, in addition to controlling the high nitrogen flow and high voltage to ensure the provision of a large number of active nitrogen ions and nitrogen atoms, as well as high-energy ions, to accelerate the forced bonding of nitrogen ions with copper atoms to generate copper nitride, the duty cycle is also reduced. On the one hand, the heat input is reduced and the cooling time is longer, which will not cause the substrate to heat up rapidly and cause thermal damage to the base film. On the other hand, the nitrogen ions are accelerated and collided less in the electric field, and the ion energy is high. The direct injection of high-energy N ions into the copper lattice is conducive to the rapid generation of dense copper nitride. If the duty cycle is high, the longer the ion source is turned on, the more ionized charges are generated, an oscillating electric field will be generated, and the ion motion trajectory will change from linear acceleration to spiral oscillation. The increase in collisions between ions and gas will lead to a decrease in ion energy, which is not conducive to forced bonding with copper atoms to generate copper nitride. In addition, the long time of bombarding the substrate will cause continuous heating of the surface, which will cause thermal damage to the base film.

[0074] In some embodiments, the vacuum evaporation process includes: after the base film is normally passed through the film, the chamber is closed, the vacuum system is started, and the air in the device is extracted to make the vacuum degree in the device reach 10 -3 ~10 -2 Pa range.

[0075] In some embodiments, the winding system is started (at a speed of 8-12 m / min), the evaporation system is activated, and evaporation begins. The base film is unwound by a reel, pulled by guide rollers and flattening rollers, and then passes through a first cooling drum to vacuum-deposit a first copper layer on surface A of the base film. The base film is then flipped over by a guide roller, and then passed through a second cooling drum to vacuum-deposit a second copper layer on surface B of the base film. After a one-step deposition of 1 μm of pure copper on both sides of the polymer layer, a composite copper foil is produced.

[0076] In some embodiments, the method for preparing a composite current collector further includes, after the first nitriding is completed, contacting the composite current collector with a second nitrogen source to perform a second nitriding, so that a solid solution layer is formed between the copper layer and the copper nitride layer, wherein the solid solution layer contains a Cu(N) solid solution;

[0077] The second nitrogen source contains active nitrogen ions with low nitrogen potential and / or nitrogen atoms with low nitrogen potential.

[0078] In the high-nitrogen chamber, nitrogen ions, driven by their kinetic energy, directly break through the reaction energy barrier and forcibly bond with copper atoms to form copper nitride. In the low-nitrogen chamber, the chamber environment is heated to 120°C by a heat source, and the nitrogen ion bombardment causes local heating, causing the surface of the copper nitride layer to undergo micro-decomposition and release nitrogen atoms. Nitrogen ions bombard the surface of the copper nitride layer, where they gain electrons and are reduced to active nitrogen atoms. These, along with the nitrogen atoms released by the micro-decomposition of the copper nitride layer, are adsorbed on the surface of the copper nitride layer to form an adsorption layer (nitrogen atom film). This layer not only provides nitrogen atoms for deep diffusion, but also protects the main structure of the copper nitride from decomposition and blocks the escape of nitrogen atoms. Due to the high nitrogen concentration in the surface adsorption layer and the extremely low nitrogen concentration within the copper matrix, nitrogen atoms continue to diffuse into the copper layer under the triple effects of the concentration potential difference, the surface adsorption layer blockade, and the thrust of the ion bombardment. The diffusion pathways are mainly along grain boundaries and dislocations, and nitrogen atoms enter the octahedral interstitial positions of the copper lattice, forming a Cu(N) solid solution layer.

[0079] In some embodiments, the preparation method of the second nitrogen source in the provided composite current collector preparation method includes: controlling the flow rate of the second nitrogen gas to 400-600 sccm, ionizing the second nitrogen gas under the conditions of an ion source voltage of 650-800 V, a duty cycle of 50-80%, and a current of 0.5-3 A to prepare the second nitrogen source.

[0080] In the process of preparing the second nitrogen source, a low-concentration nitrogen environment is required. If the nitrogen concentration is too high, a large number of nitrogen molecules will block the key adsorption sites, causing the occupied active sites to form molecular-level "roadblocks", directly blocking the entrance of the atomic diffusion channel. The diffusion path is blocked, which is not conducive to the diffusion of nitrogen atoms inward.

[0081] In the process of preparing the second nitrogen source, the surface is bombarded for a long time with low energy ions at a high duty cycle and low ion source voltage, so that the surface temperature rises, and the surface of the copper nitride layer is micro-decomposed to release nitrogen atoms. When the nitrogen ions bombard the surface of the copper nitride layer, the nitrogen ions obtain electrons on the surface of the composite copper foil and are reduced to active nitrogen atoms. Together with the nitrogen atoms released by the micro-decomposition on the surface of the copper nitride layer, they are adsorbed on the surface of the copper nitride layer to form an adsorption layer (nitrogen atom film), which not only provides nitrogen atoms for deep diffusion, but also protects the main structure of the copper nitride from decomposition and blocks the escape of nitrogen atoms. The nitrogen concentration in the adsorption layer is high, while the nitrogen concentration inside the copper matrix is ​​extremely low. Under the triple effects of concentration potential difference, surface adsorption layer blockade and ion bombardment thrust, nitrogen atoms continue to diffuse into the copper layer. The diffusion path is mainly through grain boundaries and dislocations. Nitrogen atoms enter the octahedral gap positions of the copper lattice, promoting the surface lattice vibration excitation diffusion, causing the concentration gradient diffusion from the high-nitrogen surface layer to the low-nitrogen copper matrix, activating nitrogen atoms to diffuse into the copper lattice, and promoting the formation of a Cu(N) solid solution layer. Moreover, through the low ion voltage setting, the nitrogen ion energy is low, which can prevent copper nitride from being destroyed by high-energy ions.

[0082] The composite copper foil treated in the high nitrogen chamber generates a copper nitride layer on the surface of the metal layer. Due to the high brittleness of the copper nitride layer, the nitride layer may be prone to cracking when it is rolled up or subjected to stress. Therefore, the composite copper foil treated in the high nitrogen chamber is transferred to the low nitrogen chamber through a roller system. In the low nitrogen chamber, the ion source voltage is 650-800V, the duty cycle is 40-50%, the current is 0.5-1A, and the nitrogen flow rate is controlled at 500-800sccm. In the low nitrogen chamber, a diffusion transition layer can be formed in the copper layer by reducing the nitrogen concentration and ion energy. , which is conducive to achieving a balance between the hardness and toughness of the nitride layer. The ductility of the diffusion transition layer formed by the solid solution is significantly better than that of the brittle compound layer, and it can absorb the strain energy during winding or bending, thereby alleviating the interface stress between the hard and brittle surface copper nitride and the substrate. The polymer layer of the composite copper current collector has a synergistic effect and can absorb most of the deformation stress during the winding process, avoiding the nitride layer from directly bearing stress and preventing the nitride layer from cracking. The diffusion transition layer and the nitride layer can also form a synergistic effect to inhibit the oxidation reaction of copper, further ensuring the corrosion resistance and oxidation resistance.

[0083] In some embodiments, in the method for preparing the composite current collector, during the vacuum evaporation process, the base film is placed on a main roller for vacuum evaporation, and the temperature of the main roller is -30 to 30°C.

[0084] In some embodiments, in the method for preparing the composite current collector provided, during the first nitriding process, the pretreated composite current collector is placed on a first cooling conductive roller for the first nitriding, and the temperature of the first cooling conductive roller is -30 to 30°C.

[0085] The process of nitrogen ion bombardment of the base film will cause the temperature of the composite copper foil to rise, which may cause the grain growth of the copper foil and the decrease of the mechanical properties of the material. Excessive temperature will also cause thermal damage to the polymer layer of the composite copper foil. Under the action of high-temperature heat transfer, the rate and depth of nitriding can be accelerated. The growth of the copper nitride layer may be too rapid, resulting in a thicker copper nitride layer, affecting the conductive properties of the composite copper foil. Therefore, a cooling function is added to the conductive roller facing the ion source. The cooling temperature range of the cooling conductive roller is between -30 and 30°C. The cooling function of the conductive roller is beneficial to reduce the thermal damage to the polymer layer on the one hand, and on the other hand, it is beneficial to suppress the heat transfer of the composite copper foil, preventing the acceleration of the penetration depth of nitrogen atoms under the transfer of temperature, resulting in a thicker nitride layer. During the entire nitriding process, the gas flow rate and the ion source voltage and current are continuously monitored to ensure that they are always kept within the set parameter range.

[0086] In some embodiments, in the preparation method of the provided composite current collector, during the second nitriding process, the composite current collector is placed on a second cooling conductive roller for the second nitriding, the ambient temperature of the second nitriding is 110°C~130°C, and the temperature of the second cooling conductive roller is -30~30°C.

[0087] By increasing the ambient temperature of the second nitriding process and bombarding the surface with low-energy ions for a long time, the surface temperature is increased, which promotes the micro-decomposition of the surface of the copper nitride layer to release nitrogen atoms, which is beneficial to the formation of an adsorption layer (nitrogen atom film) on the surface of the copper nitride layer. It not only provides nitrogen atoms for deep diffusion, but also protects the main structure of the copper nitride from decomposition, while blocking the escape of nitrogen atoms. Under the triple effects of concentration potential difference, surface adsorption layer blockade and ion bombardment thrust, it is beneficial for nitrogen atoms to continue to diffuse into the copper layer and form a solid solution. The surface temperature of the composite current collector can be controlled by infrared heating and other methods.

[0088] In some embodiments, the preparation method of the provided composite current collector further includes the following steps: after depositing a copper layer on at least one side of the base film by vacuum evaporation, the copper layer is pretreated to form a recessed structure on the surface of the copper layer.

[0089] By pre-treating the copper layer before nitriding, such as by bombarding it with argon ions, a recessed structure is formed on the surface of the copper layer. This promotes the nitriding reaction in the high-nitrogen chamber, forming a copper nitride layer. Controlling the depth of the recessed structure can also control the thickness of the nitride layer to a certain extent, preventing the copper nitride layer from being too thick and affecting conductivity.

[0090] Pretreatment forms a concave structure, the surface area of ​​the copper layer increases, and the surface lattice defects (vacancies, dislocations) reduce the activation energy of nitrogen atom migration, which is conducive to the forced bonding of nitrogen ions and copper atoms to form copper nitride, thereby accelerating the formation of copper nitride. High-energy nitrogen ions need to destroy the copper lattice before forming copper nitride. After pretreatment, the grain size on the surface of the copper layer becomes smaller, and the manufacturing defects and texture significantly reduce the energy barrier of the subsequent nitridation reaction, further accelerating the formation of copper nitride.

[0091] In some embodiments, in the provided method for preparing the composite current collector, physical sputtering is used to pretreat the copper layer.

[0092] In some embodiments, in the preparation method of the provided composite current collector, argon ions are used for the physical sputtering, and the preparation method of the argon ions includes: controlling the argon gas flow rate to 25sccm~50sccm, ionizing the argon gas under the conditions of an ion source voltage of 400V~1000V, a duty cycle of 20%~50%, and a current of 0.5A~3A to prepare the argon ions.

[0093] The copper foil is wound and transported to a pretreatment chamber where nitriding recesses are formed in the metal layer. The ion source voltage is 400V to 1000V, with a duty cycle of 20% to 50%. The argon gas flow rate is controlled at 25sccm to 50sccm to ensure plasma stability. Argon ions gain kinetic energy under the high-voltage electric field. When they bombard the copper surface, they physically sputter, removing surface atoms. This increases the density of lattice dislocations and vacancies on the copper surface, forming nanoscale nitriding recesses with a depth of 5nm to 10nm. During the subsequent nitriding process, surface lattice defects (vacancies and dislocations) reduce the activation energy for nitrogen atom migration, accelerating penetration and facilitating faster formation of the nitride layer. Controlling the depth of the recesses also controls the thickness of the nitride layer to a certain extent.

[0094] In some embodiments, after the evaporation and nitriding processes are completed, the film forming system and the winding system are stopped, all gas valves are closed, the diffusion pump is turned off, the equipment is turned on and the temperature is returned to room temperature, the chamber is inflated and opened, and the copper foil is taken out.

[0095] Because both the copper evaporation process and the nitriding process are performed in the vacuum evaporation roll-to-roll coating equipment, there is no secondary processing process and the yield is achieved in one pass. Furthermore, there is no need for new equipment and no significant increase in equipment costs, which demonstrates the significant advantages of cost reduction, efficiency improvement and optimization.

[0096] In some embodiments, a composite current collector or a composite current collector prepared by the preparation method is provided for use in preparing battery pole pieces.

[0097] In some embodiments, a battery pole piece is provided, which contains a composite current collector or a composite current collector prepared by the aforementioned preparation method.

[0098] In some embodiments, a battery is provided, comprising a battery electrode.

[0099] The following are specific examples. They are intended to further explain this application in detail to help those skilled in the art and researchers further understand it. The relevant technical conditions, etc., do not constitute any limitation on this application. Any modifications made within the scope of the claims of this application are within the scope of protection of the claims of this application.

[0100] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods. Experimental methods without specific conditions specified in the examples were carried out according to conventional conditions, such as those described in literature or books or methods recommended by manufacturers.

[0101] Example 1

[0102] The preparation method of the composite current collector comprises the following steps:

[0103] (1) A metal layer (copper layer, 1 μm thick) was prepared on the surface of a base film (polypropylene, 5 μm thick) by vacuum evaporation at a line speed of 10 m / min;

[0104] (2) In a high nitrogen chamber, a first nitriding treatment is performed on the surface of the composite copper current collector, a first nitrogen source is brought into contact with the composite current collector, and the pretreated composite copper current collector is subjected to plasma bombardment treatment, the flow rate of the first nitrogen gas is controlled to be 2000 sccm, the ion source voltage is 1800 V, the duty cycle is 20%, and the current is 1 A. After the plasma bombardment treatment is performed, a copper nitride layer is prepared on the surface of the composite copper current collector;

[0105] (3) After the first nitriding treatment is completed, a composite current collector is prepared.

[0106] Example 2

[0107] Example 2 is basically the same as Example 1, with the main difference being that physical sputtering is performed before the first nitriding treatment, and the ions used for plasma bombardment treatment of the composite copper current collector surface are argon ions. The argon gas flow rate is controlled to be 35 sccm, the ion source voltage is 800 V, the duty cycle is 35%, and after plasma bombardment treatment under current conditions of 1 A, a recessed structure is formed on the surface of the copper layer.

[0108] Example 3

[0109] Example 3 is basically the same as Example 2, except that after the first nitriding treatment, a second nitriding treatment is performed on the surface of the composite copper current collector in a low nitrogen chamber. The preparation method of the composite current collector is as follows:

[0110] (1) A metal layer (copper layer, 1 μm thick) was prepared on the surface of a base film (polypropylene, 5 μm thick) by vacuum evaporation at a line speed of 10 m / min;

[0111] (2) The surface of the composite copper current collector was pretreated by physical sputtering. The ions used for plasma bombardment treatment on the surface of the composite copper current collector were argon ions. The argon gas flow rate was controlled to be 35 sccm, the ion source voltage was 800 V, the duty cycle was 35%, and the current was 1 A. After plasma bombardment treatment, a concave structure was formed on the surface of the copper layer.

[0112] (3) After the pretreatment is completed, the surface of the composite copper current collector is subjected to a first nitriding treatment in a high nitrogen chamber, a first nitrogen source is brought into contact with the pretreated composite current collector, and the pretreated composite copper current collector is subjected to a plasma bombardment treatment, the flow rate of the first nitrogen gas is controlled to be 2000 sccm, the ion source voltage is 1800 V, the duty cycle is 20%, and the current is 1 A. After the plasma bombardment treatment is performed, a copper nitride layer is prepared on the surface of the composite copper current collector;

[0113] (4) In a low nitrogen chamber, a second nitriding treatment is performed on the surface of the composite copper current collector, a second nitrogen source is brought into contact with the composite copper current collector after the copper nitride layer is prepared, and a plasma bombardment treatment is performed on the composite copper current collector after the copper nitride layer is prepared, and the plasma bombardment treatment is performed under the conditions of controlling the flow rate of the second nitrogen gas to 500 sccm, the ion source voltage to 700 V, the duty cycle to 60%, and the current to 1 A, and then a solid solution layer is prepared between the copper layer and the copper nitride layer;

[0114] (5) After the second nitriding treatment is completed, a composite copper current collector is prepared.

[0115] Example 4-1

[0116] Example 4-1 is basically the same as Example 3, the main difference being that the voltage parameters of the first nitriding treatment in Example 4-1 are different. Step (3) of Example 4-1 is specifically as follows:

[0117] (3) After the pretreatment, the surface of the composite copper current collector is subjected to a first nitriding treatment in a high nitrogen chamber, the first nitrogen source is brought into contact with the pretreated composite current collector, and the pretreated composite copper current collector is subjected to a plasma bombardment treatment. The flow rate of the first nitrogen gas is controlled to be 2000 sccm, the ion source voltage is 800 V, the duty cycle is 20%, and the current is 1 A. After the plasma bombardment treatment is performed, a copper nitride layer is prepared on the surface of the composite copper current collector.

[0118] Example 4-2

[0119] Example 4-2 is basically the same as Example 3, the main difference being that the voltage parameters of the second nitriding treatment in Example 4-2 are different. Step (4) of Example 4-2 is specifically as follows:

[0120] (4) In a low nitrogen chamber, a second nitriding treatment is performed on the surface of the composite copper current collector, a second nitrogen source is brought into contact with the composite copper current collector after the copper nitride layer is prepared, and a plasma bombardment treatment is performed on the composite copper current collector after the copper nitride layer is prepared. The flow rate of the second nitrogen is controlled to be 500 sccm, the ion source voltage is 1000 V, the duty cycle is 60%, and the current is 1 A. After the plasma bombardment treatment is performed, a solid solution layer is prepared between the copper layer and the copper nitride layer.

[0121] Example 5-1

[0122] Example 5-1 is basically the same as Example 3, the main difference being that the duty cycle parameters of the first nitriding treatment in Example 5-1 are different. Step (3) of Example 5-1 is specifically as follows:

[0123] (3) After the pretreatment, the surface of the composite copper current collector is subjected to a first nitriding treatment in a high nitrogen chamber, the first nitrogen source is brought into contact with the pretreated composite current collector, and the pretreated composite copper current collector is subjected to a plasma bombardment treatment. The flow rate of the first nitrogen gas is controlled to be 2000 sccm, the ion source voltage is 1800 V, the duty cycle is 40%, and the current is 1 A. After the plasma bombardment treatment is performed, a copper nitride layer is prepared on the surface of the composite copper current collector.

[0124] Example 5-2

[0125] Example 5-2 is basically the same as Example 3, the main difference being that the duty cycle parameters of the second nitriding treatment in Example 5-2 are different. Step (4) of Example 5-2 is specifically as follows:

[0126] (4) In a low nitrogen chamber, a second nitriding treatment is performed on the surface of the composite copper current collector, a second nitrogen source is brought into contact with the composite copper current collector after the copper nitride layer is prepared, and a plasma bombardment treatment is performed on the composite copper current collector after the copper nitride layer is prepared. The flow rate of the second nitrogen is controlled to be 500 sccm, the ion source voltage is 700 V, the duty cycle is 40%, and the current is 1 A. After the plasma bombardment treatment is performed, a solid solution layer is prepared between the copper layer and the copper nitride layer.

[0127] Example 6-1

[0128] Example 6-1 is basically the same as Example 3, the main difference being that the nitrogen flow rate parameters of the first nitriding treatment in Example 6-1 are different. Step (3) of Example 6-1 is specifically as follows:

[0129] (3) After the pretreatment, the surface of the composite copper current collector is subjected to a first nitriding treatment in a high nitrogen chamber, the first nitrogen source is brought into contact with the pretreated composite current collector, and the pretreated composite copper current collector is subjected to a plasma bombardment treatment. The flow rate of the first nitrogen gas is controlled to be 800 sccm, the ion source voltage is 1800 V, the duty cycle is 20%, and the current is 1 A. After the plasma bombardment treatment is performed, a copper nitride layer is prepared on the surface of the composite copper current collector.

[0130] Example 6-2

[0131] Example 6-2 is basically the same as Example 3, the main difference being that the nitrogen flow rate parameters of the second nitriding treatment in Example 6-2 are different. Step (3) of Example 6-1 is specifically as follows:

[0132] (3) In a low nitrogen chamber, a second nitriding treatment is performed on the surface of the composite copper current collector, a second nitrogen source is brought into contact with the composite copper current collector after the copper nitride layer is prepared, and a plasma bombardment treatment is performed on the composite copper current collector after the copper nitride layer is prepared. The flow rate of the second nitrogen is controlled to be 800 sccm, the ion source voltage is 700 V, the duty cycle is 20%, and the current is 1 A. After the plasma bombardment treatment is performed, a solid solution layer is prepared between the copper layer and the copper nitride layer.

[0133] Example 7

[0134] Example 7 is basically the same as Example 3, with the main difference being that during the second nitriding treatment in Example 7, infrared heating is provided and the ambient temperature is controlled to be 120°C.

[0135] Example 8

[0136] Example 8 is basically the same as Example 2, the main difference being that the line speed in Example 8 is different, and the prepared line speed is 6 m / min.

[0137] Comparative Example 1

[0138] A metal layer (copper layer, 1 μm thick) was prepared on the surface of a base film (made of polypropylene, 5 μm thick) by vacuum evaporation to obtain a composite copper current collector. No anti-oxidation layer was set on the surface of the composite copper current collector.

[0139] Performance Testing

[0140] 1. Antioxidant performance test

[0141] The change in square resistance before and after baking was used for indirect characterization. The flat composite current collector samples prepared in the examples and comparative examples were baked at 150°C for 30 minutes and then placed on a sample table. The square resistance of the samples was tested using a four-probe square resistance meter to compare the changes in square resistance before and after baking.

[0142] The composite current collectors prepared in the examples and comparative examples were bent 90° back and forth 50 times using a bending machine. After being bent, they were baked at 150°C for 30 minutes and placed on a sample table. The sheet resistance at the bend was measured using a four-probe sheet resistance meter. The change in sheet resistance before and after the bending treatment was compared. The sheet resistance change rate was calculated as follows: (sheet resistance of one side after bending - sheet resistance of one side before bending) / sheet resistance of one side before bending × 100%.

[0143] 2. Thickness test of copper nitride layer and solid solution layer

[0144] The prepared composite copper current collector was prepared according to the sample preparation requirements of the focused ion beam field emission microscope (FIB-SEM), and then the sample was placed in the FIB-SEM. The sample was cut by the ion beam to prepare a cross-sectional sample. After the cross-sectional sample was prepared, the cross-section was observed using the Zeiss GeminiSEM 300 microscope lens, magnified 50,000 times, and after adjustment, the thickness of the protective layer in the cross-sectional morphology photograph was measured using the measurement software provided by the electron microscope, thereby obtaining the thickness data of the antioxidant layer and the solid solution layer.

[0145] Table 1

[0146]

[0147] It can be seen from the data in Table 1 that compared with Comparative Example 1, Examples 1 to 7 generate an oxide layer in Comparative Example 1, and the excessive square resistance causes the composite current collector to lose its conductive properties. The single-sided square resistance of Examples 1 to 7 is much lower than that of Comparative Example 1, indicating that the copper nitride layer plays an antioxidant role and has excellent antioxidant properties.

[0148] The thickness of the copper nitride layer in Example 2 is higher than that in Example 1, and the single-sided square resistance value in Example 2 is lower than that in Example 1, indicating that the thickness of the copper nitride layer generated by the pretreated composite current collector is in the range of 8 nm to 12 nm. This thickness improves the density of the copper nitride layer, and the antioxidant performance is better than that in Example 1.

[0149] The thickness of the copper nitride layer in Example 8 is higher than that in Example 2. On the contrary, the single-sided square resistance value of Example 8 is higher than that of Example 2, indicating that the thicker the copper nitride layer generated by the pretreated composite current collector, the higher the square resistance, which affects the conductive performance.

[0150] By comparing the results of Example 3 with those of Example 1 and Example 2, it can be seen that the composite current collector of Example 3 has a smaller single-sided square resistance, and after oxidation treatment after bending, the measured square resistance change rate is much lower than that of Example 1 and Example 2, indicating that the solid solution layer has high ductility, which is beneficial to prevent cracking of the copper nitride layer and ensure antioxidant performance.

[0151] By comparing the results of Example 4-1 with Example 3, it can be seen that the single-sided square resistance of the composite current collector of Example 4-1 without using high voltage during the first nitriding treatment is higher than the square resistance of Example 3. At this time, the thickness of the copper nitride layer of Example 4-1 is lower than that of Example 3, indicating that high voltage conditions are more conducive to the generation of a copper nitride layer in the composite current collector in the range of 8nm~12nm. This thickness improves the density of the copper nitride layer, and the antioxidant performance of Example 3 is better than that of Example 4-1.

[0152] By comparing the results of Example 4-2 with Example 3, it can be seen that a low-voltage composite current collector was not used during the second nitriding treatment. At this time, the thickness of the solid solution layer of Example 4-2 is lower than that of Example 3. After bending and oxidation treatment, the square resistance change rate measured in Example 4-2 is much higher than that of Example 3, indicating that low voltage is more conducive to the preparation of the solid solution layer. The solid solution thickness is in the range of 15nm~25nm, which prevents cracking of the copper nitride layer and ensures antioxidant performance.

[0153] By comparing the results of Example 5-1 with Example 3, it can be seen that the single-sided square resistance of the composite current collector prepared in Example 5-1 without using a low duty cycle during the first nitriding treatment is higher than the square resistance of Example 3. At this time, the thickness of the copper nitride layer of Example 5-1 is lower than the thickness of Example 3, indicating that the thickness of the copper nitride layer generated under low duty cycle conditions is in the range of 8nm~12nm, which is more conducive to the composite current collector to generate a copper nitride layer that meets the thickness requirements at the same line speed. This thickness improves the density of the copper nitride layer, and the antioxidant performance of Example 3 is better than that of Example 5-1.

[0154] By comparing the results of Example 5-2 with those of Example 3, it can be seen that Example 5-2 did not use a high-duty-cycle composite current collector during the second nitriding treatment. At this time, the thickness of the solid solution layer of Example 5-2 was lower than that of Example 3. After bending and oxidation treatment, the square resistance change rate measured in Example 5-2 was much higher than that of Example 3, indicating that a low duty cycle is more conducive to the preparation of the solid solution layer. The solid solution thickness is in the range of 15nm~25nm, which prevents cracking of the copper nitride layer and ensures antioxidant performance.

[0155] By comparing the results of Example 6-1 with Example 3, it can be seen that the single-sided square resistance of the composite current collector of Example 6-1, which does not use a high nitrogen flow rate during the first nitriding treatment, is higher than the square resistance of Example 3. At this time, the thickness of the copper nitride layer of Example 6-1 is lower than that of Example 3, indicating that the thickness of the copper nitride layer generated under high nitrogen flow conditions is in the range of 8nm~12nm, which is more conducive to the composite current collector to generate a copper nitride layer that meets the thickness requirements at the same line speed. This thickness improves the density of the copper nitride layer, and the antioxidant performance of Example 3 is better than that of Example 6-1.

[0156] By comparing the results of Example 6-2 with Example 3, it can be seen that Example 6-2 did not use a composite current collector with a low nitrogen flow rate during the second nitriding treatment. At this time, the thickness of the solid solution layer of Example 6-2 was lower than that of Example 3. After bending and oxidation treatment, the square resistance change rate measured in Example 6-2 was much higher than that of Example 3, indicating that a low duty cycle is more conducive to the preparation of the solid solution layer. The solid solution thickness is in the range of 15nm~25nm, which prevents cracking of the copper nitride layer and ensures antioxidant performance.

[0157] Comparing the results of Example 7 with those of Example 3, it can be seen that in Example 7, a heat source is set during the second nitriding treatment to control the ambient temperature during the second nitriding treatment. At this time, the thickness of the solid solution layer of Example 7 is higher than that of Example 3. After bending and oxidation treatment, the square resistance change rate measured in Example 7 is lower than that of Example 3, indicating that the ambient temperature of the second nitriding is conducive to increasing the thickness of the solid solution layer and ensuring the antioxidant performance.

[0158] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0159] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims, and the specification shall serve to interpret the content of the claims.

Claims

1. A composite current collector, characterized in that: The invention comprises a base film and a copper layer arranged on at least one side of the base film, wherein the entire surface of the copper layer contains a copper nitride layer.

2. The composite current collector according to claim 1, characterized in that A solid solution layer is further included between the copper layer and the copper nitride layer, and the solid solution layer contains Cu(N) solid solution.

3. The composite current collector according to claim 2, characterized in that: One or more of the following conditions are met: (1) The material of the base film includes one or more of polypropylene, polyethylene terephthalate and polyimide; (2) The thickness of the copper layer is 1 μm to 3 μm; (3) The thickness of the copper nitride layer is 8 nm to 12 nm; (4) The thickness of the solid solution layer is 15 nm to 25 nm; and (5) The surface of the copper layer has a concave structure, and the depth of the concave structure is 5nm~10nm.

4. A method for preparing a composite current collector, characterized in that: The steps include: Providing a base film, and depositing a copper layer on at least one side of the base film by vacuum evaporation; Providing a first nitrogen source, bringing the first nitrogen source into contact with the copper layer, performing a first nitriding process, forming a copper nitride layer on the entire surface of the copper layer, and preparing the composite current collector; The first nitrogen source contains active nitrogen ions with high nitrogen potential and / or nitrogen atoms with high nitrogen potential.

5. The method for preparing a composite current collector according to claim 4, wherein: The preparation method further includes, after the first nitriding is completed, contacting the composite current collector with a second nitrogen source to perform a second nitriding, so that a solid solution layer is formed between the copper layer and the copper nitride layer, wherein the solid solution layer contains a Cu(N) solid solution; The second nitrogen source contains active nitrogen ions with low nitrogen potential and / or nitrogen atoms with low nitrogen potential.

6. The method for preparing a composite current collector according to claim 4, wherein: The preparation method of the first nitrogen source includes: controlling the flow rate of the first nitrogen gas to 1000 sccm to 3000 sccm, ionizing the first nitrogen gas under the conditions of an ion source voltage of 1000 V to 3000 V, a duty cycle of 15% to 30%, and a current of 0.5 A to 3 A to prepare the first nitrogen source.

7. The method for preparing a composite current collector according to claim 5, wherein: The preparation method of the second nitrogen source includes: controlling the flow rate of the second nitrogen gas to 400 sccm to 600 sccm, ionizing the second nitrogen gas under the conditions of an ion source voltage of 650 V to 800 V, a duty cycle of 50% to 80%, and a current of 0.5 A to 3 A to prepare the second nitrogen source.

8. The method for preparing a composite current collector according to claim 5, wherein: One or more of the following conditions are met: (1) During the vacuum evaporation process, the base film is placed on a main roller for vacuum evaporation, and the temperature of the main roller is -30°C to 30°C; (2) During the first nitriding process, the pretreated composite current collector is placed on a first cooling conductive roller for the first nitriding process, wherein the temperature of the first cooling conductive roller is -30°C to 30°C; and (3) During the second nitriding process, the composite current collector is placed on a second cooling conductive roller for the second nitriding process. The ambient temperature of the second nitriding process is 110°C to 130°C, and the temperature of the second cooling conductive roller is -30°C to 30°C.

9. The method for preparing a composite current collector according to any one of claims 4 to 8, wherein: The method further includes the following steps: after depositing a copper layer on at least one side of the base film by vacuum evaporation, pre-treating the copper layer to form a concave structure on the surface of the copper layer; Optionally, the copper layer is pretreated by physical sputtering; Optionally, argon ions are used for the physical sputtering, and the method for preparing the argon ions includes: controlling the argon gas flow rate to 25 sccm to 50 sccm, ionizing the argon gas under the conditions of an ion source voltage of 400V to 1000V, a duty cycle of 20% to 50%, and a current of 0.5A to 3A to prepare the argon ions.

10. Use of the composite current collector according to any one of claims 1 to 3 or the composite current collector prepared by the preparation method according to any one of claims 4 to 9 in preparing battery pole pieces.

11. A battery pole piece, characterized in that: The battery pole piece contains the composite current collector according to any one of claims 1 to 3 or the composite current collector prepared by the preparation method according to any one of claims 4 to 9.

12. A battery, characterized in that: The battery contains the battery electrode according to claim 11.

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