Composite current collector and preparation method thereof, lithium metal battery and electric equipment

Abstract

The invention provides a composite current collector and a preparation method thereof, a lithium metal battery and electric equipment, the composite current collector comprises a base film and a metal layer arranged on at least one side of the base film, the metal layer comprises a copper layer and an alloy layer, and the copper layer is located between the base film and the alloy layer; the alloy layer is formed in a Joule heating mode. The composite current collector provided by the invention has improved structural stability.

Description

Technical Field

[0001] This application relates to the field of current collector technology, and in particular to a composite current collector and its preparation method, lithium metal batteries, and electrical devices. Background Technology

[0002] Currently, the graphite anodes commonly used in commercial lithium-ion batteries (LIBs) have reached near their theoretical specific capacity, failing to meet the requirements of high-energy-density batteries. In contrast, lithium metal battery (LMB) anodes possess extremely high theoretical specific capacity, significantly improving battery energy density. The anode of a lithium metal battery consists of a current collector and lithium metal deposited on the current collector. Due to the large volume expansion of lithium metal battery electrodes and the high susceptibility to lithium dendrite growth, an alloy layer is typically applied to the surface of the current collector to improve local current density, enhance lithium deposition uniformity, and thus mitigate lithium dendrite growth. Among current collectors, compared to traditional pure copper foil current collectors, composite current collectors with a metal / polymer / metal sandwich structure (such as Cu / PET / Cu) offer advantages such as lightweight (e.g., weight reduction of 40%), resistance to dendrite penetration, and high safety, making them a better fit for lithium metal batteries.

[0003] However, if composite current collectors are used in lithium metal batteries, the alloy layer on the surface of the composite current collector usually needs to be prepared by high-temperature calcination. At this time, the polymer material in the middle of the composite current collector is prone to shrinkage and deformation, or even carbonization, when subjected to excessively high temperatures, causing the composite current collector structure to "collapse". Therefore, the current process of preparing an alloy layer on the surface of the current collector by high-temperature calcination is not suitable for composite current collectors. Summary of the Invention

[0004] Based on this, this application provides a composite current collector and its preparation method, a lithium metal battery, and an electrical device, aiming to improve the structural "collapse" of the surface of the composite current collector during the preparation of the alloy layer.

[0005] A first aspect of this application provides a composite current collector, comprising a base film and a metal layer disposed on at least one side of the base film, the metal layer comprising a copper layer and an alloy layer, the copper layer being located between the base film and the alloy layer; the alloy layer being formed by Joule heating.

[0006] In some embodiments of this application, one or more of the following conditions are met:

[0007] (1) The alloy layer is made of Cu-M alloy, and the M element includes one or more of Zn, Ag, Mg and Sn;

[0008] Optionally, the mass percentage of element M in the alloy layer is 48% to 83%;

[0009] (2) The thickness of the base film is 2μm~8μm;

[0010] (3) The thickness of the copper layer is 0.5μm~1.5μm;

[0011] (4) The thickness of the alloy layer is 0.1μm~0.3μm.

[0012] In some embodiments of this application, the copper layer includes a first copper layer and a second copper layer stacked together, wherein the first copper layer is relatively close to the base film and the second copper layer is relatively far from the base film;

[0013] Optionally, the bulk density of the second copper layer is greater than the bulk density of the first copper layer;

[0014] Further optionally, the ratio of the bulk density of the first copper layer to the bulk density of the second copper layer is 1:(1.1~1.3);

[0015] Optionally, the thickness of the second copper layer is 0.05 μm to 0.1 μm;

[0016] Optionally, the thickness of the first copper layer is 0.45 μm to 1.4 μm;

[0017] Optionally, the copper layer further includes a copper seed layer disposed between the base film and the first copper layer.

[0018] In some embodiments of this application, the composite current collector further includes an auxiliary layer disposed between the base film and the copper layer, the auxiliary layer including an insulating layer and / or a buffer layer;

[0019] Optionally, the thickness of the insulating layer is 0.01 μm to 0.1 μm;

[0020] Optionally, the insulating layer may be made of silicon nitride ceramic.

[0021] Optionally, the thickness of the buffer layer is 0.2 μm to 2 μm;

[0022] Optionally, the material of the buffer layer includes polyimide-silicon nanocomposite material and / or silicone rubber.

[0023] A second aspect of this application provides a method for preparing a composite current collector, comprising:

[0024] A metal layer to be alloyed is prepared on at least one side of a composite current collector semi-finished product, wherein the composite current collector semi-finished product includes a base film and a copper layer disposed on at least one side of the base film, and the metal layer to be alloyed is adjacent to the copper layer.

[0025] The metal layer to be alloyed is alloyed by Joule heating to form an alloy layer and prepare a composite current collector.

[0026] In some embodiments of this application, the alloying treatment includes a first alloying treatment and a second alloying treatment, wherein the first alloying treatment is performed by a first pulse Joule heating and the second alloying treatment is performed by a second pulse Joule heating.

[0027] Optionally, the current density of the first pulse Joule heating is 30 A / cm². 2 ~40A / cm 2 The temperature is 470℃~490℃, the single pulse time is 2s~6s, and the pulse interval time is 0.1s~0.3s;

[0028] Optionally, the pulse current density of the second pulse Joule heating is 350 A / cm². 2 ~450A / cm 2 The peak temperature is 700℃~1000℃, the single pulse time is 50ms~60ms, and the pulse interval time is 0.1s~0.3s.

[0029] In some embodiments of this application, the metal layer to be alloyed includes a copper layer to be alloyed and a metal M layer to be alloyed, wherein the copper layer to be alloyed is located between the copper layer and the metal M layer to be alloyed, and the M element includes one or more of Zn, Ag, Mg and Sn;

[0030] Optionally, the copper layer to be alloyed is formed by chemical plating or electroplating.

[0031] Optionally, the metal M layer to be alloyed is formed by vapor deposition;

[0032] Optionally, the thickness of the copper layer to be alloyed is 0.06 μm to 0.25 μm;

[0033] Optionally, the thickness of the metal M layer to be alloyed is 0.05 μm to 0.12 μm;

[0034] Optionally, prior to the alloying process, the method further includes forming micropores on the surface of the copper layer to be alloyed;

[0035] Further optionally, the pore size of the micropores is 5μm~50μm;

[0036] Further optionally, the interval between two adjacent micropores is 1 mm to 5 mm.

[0037] In some embodiments of this application, a preparation step of the composite current collector semi-finished product is also included:

[0038] The copper layer is prepared on at least one side of the base film, wherein the copper layer comprises a first copper layer and a second copper layer stacked thereon, the first copper layer being relatively close to the base film and the second copper layer being relatively far away from the base film;

[0039] Optionally, the volume density ratio of the first copper layer, the second copper layer, and the copper layer to be alloyed is 1:(1.1~1.3):(0.7~0.9).

[0040] Optionally, the first copper layer is formed by electroplating;

[0041] Further optionally, the electroplating current of the first copper layer is greater than the electroplating current of the copper layer to be alloyed;

[0042] Optionally, the second copper layer is formed by magnetron sputtering;

[0043] Optionally, the copper layer further includes a copper seed layer disposed between the base film and the first copper layer;

[0044] Alternatively, the copper seed layer may be prepared by magnetron sputtering.

[0045] In some embodiments of this application, the Joule heating is performed using a Joule heating device, which includes two conductive rollers arranged opposite each other. The composite current collector semi-finished product containing the metal layer to be alloyed contacts the two conductive rollers and moves continuously between the two conductive rollers.

[0046] A third aspect of this application provides a lithium metal battery, including the composite current collector described in the first aspect of this application or a composite current collector prepared by the preparation method described in the second aspect of this application.

[0047] A fourth aspect of this application provides an electrical device including the lithium metal battery described in the third aspect of this application.

[0048] The electrical equipment of this application includes the lithium metal battery provided in this application, and therefore has at least the same advantages as the lithium metal battery.

[0049] In the composite current collector provided in this application, the alloy layer is formed by Joule heating. Joule heating can rapidly generate a large amount of heat, achieving efficient alloying of the composite current collector. Simultaneously, since the heating time of Joule heating is typically short, and the Joule heating effect occurs on the metal layer while almost no thermal effect occurs on the base film (the base film is insulating, and current cannot pass through it during Joule heating, therefore the base film does not experience the Joule heating effect), damage to the base film, deformation, wrinkling, and carbonization can be reduced, thus helping to improve the structural "collapse" of the composite current collector. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of a composite current collector according to one embodiment of this application.

[0051] Reference numerals: 1 base film; 2 auxiliary layer; 3 copper layer; 4 alloy layer; 21 buffer layer; 22 insulating layer; 31 copper seed layer; 32 first copper layer; 33 second copper layer. Detailed Implementation

[0052] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0053] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It should be noted that, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items, "above," "below," includes the stated number, and "one or more" with "multiple" means two or more.

[0055] In this document, when referring to numerical intervals (i.e., numerical ranges), unless otherwise specified, the distribution of selectable values ​​within a numerical interval is considered continuous, and includes the two endpoints (i.e., the minimum and maximum values) of the numerical interval, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, and other numerical interval types.

[0056] In this document, for methods involving multiple steps, unless otherwise explicitly stated herein, there is no strict order constraint on the execution of these steps; they may be executed in any order other than those described. Moreover, any step may include multiple sub-steps or multiple stages, which are not necessarily completed at the same time, but may be executed at different times, and their execution order is not necessarily sequential, but may be executed in turn, alternately, or simultaneously with other steps or parts of the sub-steps or stages of other steps.

[0057] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0058] In a first aspect, this application provides a composite current collector, comprising a base film and a metal layer disposed on at least one side of the base film, the metal layer comprising a copper layer and an alloy layer, the copper layer being located between the base film and the alloy layer; the alloy layer being formed by Joule heating.

[0059] In the composite current collector provided in this application, the alloy layer is formed by Joule heating. Joule heating can rapidly generate a large amount of heat, achieving efficient alloying of the composite current collector. Simultaneously, since the heating time of Joule heating is typically short, and the Joule heating effect occurs on the metal layer while almost no thermal effect occurs on the base film (the base film is insulating, and current cannot pass through it during Joule heating, therefore the base film does not experience the Joule heating effect), damage to the base film, deformation, wrinkling, and carbonization can be reduced, thus helping to improve the structural "collapse" of the composite current collector.

[0060] In some embodiments, the alloy layer is made of a Cu-M alloy, where M is one or more of Zn, Ag, Mg, and Sn. Using these metal elements as M ensures good wettability and conductivity of the alloy layer with lithium, and that the alloying with copper retains the good ductility of copper.

[0061] In some embodiments, the mass percentage of element M in the alloy layer is 48% to 83%. For example, the mass percentage of element M in the alloy layer can be 48%, 59%, 61%, 72%, 83%, or within any range of these values. This results in a high degree of alloying in the alloy layer, which, when used in lithium metal batteries, can effectively improve the local current density of the negative electrode, enhance the uniformity of lithium deposition, and thus mitigate the problem of lithium dendrite growth.

[0062] In some embodiments, the thickness of the base film is 2 μm to 8 μm. For example, the thickness of the base film can be 2 μm, 4 μm, 6 μm, 8 μm, or within any range of the above values.

[0063] In some embodiments, the thickness of the copper layer is 0.5 μm to 1.5 μm. For example, the thickness of the copper layer can be 0.5 μm, 0.8 μm, 1.1 μm, 1.3 μm, 1.5 μm, or within any range of these values. This setting helps to reduce thermal damage to the base film caused by an excessively thick copper layer during the fabrication process.

[0064] In some embodiments, the thickness of the alloy layer is 0.1 μm to 0.3 μm. For example, the thickness of the alloy layer can be 0.1 μm, 0.2 μm, 0.3 μm, or within any range of the above values.

[0065] In some embodiments, the copper layer includes a first copper layer and a second copper layer stacked together, the first copper layer being relatively close to the base film and the second copper layer being relatively far from the base film.

[0066] The first copper layer serves as the current-collecting layer of the composite current collector, acting as the main structure for current transmission in lithium metal batteries. The second copper layer acts as a barrier layer to prevent the M-metal material from seeping into the first copper layer, thereby minimizing the need for the entire copper layer of the composite current collector to be alloyed, and improving the conductivity and ductility of the composite current collector.

[0067] In some embodiments, the bulk density of the second copper layer is greater than that of the first copper layer. This configuration results in a higher density for the second copper layer compared to the first, allowing it to act as a barrier layer preventing the M-metal material from seeping into the first copper layer. This avoids the entire copper layer of the composite current collector becoming alloyed, improving the conductivity and ductility of the composite current collector.

[0068] In some embodiments, the volume density ratio of the first copper layer to the second copper layer is 1:(1.1~1.3). For example, the volume density ratio of the first copper layer to the second copper layer can be 1:1.1, 1:1.2, 1:1.3, or within any range of the above values. This setting is beneficial for further improving the conductivity and ductility of the composite current collector.

[0069] In some embodiments, the thickness of the second copper layer is 0.05 μm to 0.1 μm. For example, the thickness of the second copper layer can be 0.05 μm, 0.08 μm, 0.1 μm, or within any range of these values. This configuration helps the second copper layer to effectively block the penetration of metal M into the first copper layer.

[0070] In some embodiments, the thickness of the first copper layer is 0.45 μm to 1.4 μm. For example, the thickness of the first copper layer can be 0.45 μm, 0.8 μm, 1.2 μm, 1.4 μm, or within any range of these values. This configuration is beneficial for enhancing the conductivity of the composite current collector.

[0071] In some embodiments, the copper layer further includes a copper seed layer disposed between the base film and the first copper layer.

[0072] In some embodiments, the composite current collector further includes an auxiliary layer disposed between the base film and the copper layer, the auxiliary layer comprising an insulating layer and / or a buffer layer. The buffer layer can absorb thermal stress during Joule heating, effectively reducing splitting between layers of the composite current collector; the insulating layer helps reduce thermal damage to the base film caused by Joule heating.

[0073] It should be noted that when an insulating layer and a buffer layer are simultaneously set between the base film and the copper layer, the insulating layer and the buffer layer are stacked, and their relative positions can be interchanged.

[0074] In some embodiments, a buffer layer may be disposed on at least one side of the base film, which may be formed together with the base film through multilayer co-extrusion during the preparation of the base film, or may be disposed on the formed base film by coating; the insulating layer may be deposited on the buffer layer by magnetron sputtering.

[0075] In some embodiments, the thickness of the insulating layer is 0.01 μm to 0.1 μm. For example, the thickness of the insulating layer can be 0.01 μm, 0.04 μm, 0.08 μm, 0.1 μm, or within any range of the above values. This setting helps to further reduce Joule heating thermal damage to the base film.

[0076] In some embodiments, the insulating layer is made of silicon nitride ceramic.

[0077] In some embodiments, the thickness of the buffer layer is 0.2 μm to 2 μm. For example, the material of the buffer layer can be 0.2 μm, 0.7 μm, 1.3 μm, 1.7 μm, 2 μm, or within any range of these values. This configuration facilitates better absorption of thermal stress during Joule heating and effectively reduces splitting between the composite current collector layers.

[0078] In some embodiments, the material of the buffer layer includes polyimide-silicon nanocomposite material and / or silicone rubber.

[0079] In some embodiments, the base film material includes polyamide (PA), polyterephthalate, polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PPE), polyvinyl chloride (PVC), aramid, acrylonitrile-butadiene-styrene copolymer (ABS), polybutylene terephthalate (PET), poly(p-phenylene terephthalamide) (PPTA), polypropylene (PPE), polyoxymethylene (POM), epoxy resin, phenolic resin, polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), silicone rubber, polycarbonate (PC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, starch, protein, derivatives of the above materials, crosslinks of at least one of the above materials, and copolymers of at least one of the above materials.

[0080] Secondly, this application provides a method for preparing a composite current collector, which can be used to prepare the composite current collector of the first aspect of this application, and may include the following steps:

[0081] S1. Prepare a metal layer to be alloyed on at least one side of the composite current collector semi-finished product, wherein the composite current collector semi-finished product includes a base film and a copper layer disposed on at least one side of the base film, and the metal layer to be alloyed is adjacent to the copper layer.

[0082] S2. Alloying the metal layer to be alloyed by Joule heating to form an alloy layer and prepare a composite current collector.

[0083] The preparation method provided in this application alloys the metal layer to be alloyed through Joule heating. Joule heating can rapidly generate a large amount of heat, achieving efficient alloying of the composite current collector. Simultaneously, since the heating time of Joule heating is typically short, alloying can be formed in a short time. Furthermore, the Joule heating effect occurs on the metal layer to be alloyed, with almost no thermal effect on the base film (the base film is insulating, and current cannot pass through it during Joule heating, therefore the base film does not experience a Joule heating effect). This reduces thermal damage to the base film, minimizing deformation, wrinkling, and carbonization, thus helping to improve the structural "collapse" of the composite current collector.

[0084] In some embodiments, the alloying treatment includes a first alloying treatment and a second alloying treatment, wherein the first alloying treatment is performed by a first pulse Joule heating and the second alloying treatment is performed by a second pulse Joule heating.

[0085] The first pulse Joule heating in the first alloying process enables low-temperature thermal diffusion of the metal in the metal layer to be alloyed at a relatively low temperature for a longer period of time. The second pulse Joule heating in the second alloying process, with its instantaneous Joule heating effect, allows the metal in the metal layer to form an alloy. Dividing the alloying process into two stages reduces the peak high temperature of the Joule heating and the time of high-temperature treatment, thereby reducing thermal damage to the base film.

[0086] It is understood that the "first pulse Joule heating" and "second pulse Joule heating" mentioned in this application both refer to the use of pulsed current during Joule heating.

[0087] In some embodiments, the current density of the first pulse Joule heating is 30 A / cm². 2 ~40A / cm 2 The temperature is set at 470℃~490℃, the single pulse duration is 2s~6s, and the pulse interval is 0.1s~0.3s. This configuration allows the metal in the metal layer to be alloyed to achieve low-temperature thermal diffusion at a lower temperature and for a longer time, reducing thermal damage to the base film. Simultaneously, the penetration depth of metal M in the metal layer to be alloyed can be controlled within the copper layer to be alloyed, minimizing further diffusion into the copper layer.

[0088] In some embodiments, the pulse current density of the second pulse Joule heating is 350 A / cm². 2 ~450A / cm 2 The peak temperature is 700℃~1000℃, the single pulse time is 40ms~60ms, and the pulse interval time is 0.1s~0.3s.

[0089] This configuration allows for more complete alloying between the copper layer to be alloyed and the metal M layer to be alloyed, and controls the content of metal M infiltrated into the second copper layer to be less than 15 at%, and the content of metal M infiltrated into the first copper layer to be less than 5 at%. It also helps to reduce the high-temperature processing time, thereby reducing thermal damage to the base film. Simultaneously, because the second pulse Joule heating presents a pulsed current with a higher heating temperature, shorter interval, and higher pulse frequency, the alloy layer thickness and alloying degree on the etched composite current collector surface are more uniform.

[0090] As a non-limiting example, the first alloying process is as follows: Equipment: Joule heating of conductive rollers (roller diameter 200mm), specific process parameters: current density 35A / cm² 2 The temperature is 470℃~490℃, the single pulse time is 4s, and the pulse interval time is 0.1s~0.3s.

[0091] As a non-limiting example, the second alloying process is as follows: Joule heating of the conductive roller (roller diameter 200mm), with specific process parameters of: pulse current density 400A / cm². 2 The peak temperature is 700℃~1000℃, the single pulse time is 50ms, and the pulse interval time is 0.1s~0.3s.

[0092] In some embodiments, the metal layer to be alloyed includes a copper layer to be alloyed and a metal M layer to be alloyed, wherein the copper layer to be alloyed is located between the copper layer and the metal M layer to be alloyed, and the M element includes one or more of Zn, Ag, Mg and Sn.

[0093] In some embodiments, the thickness of the copper layer to be alloyed is 0.06 μm to 0.25 μm. For example, the thickness of the copper layer to be alloyed can be 0.06 μm, 0.09 μm, 0.13 μm, 0.18 μm, 0.21 μm, 0.25 μm, or within any range of the above values.

[0094] In some embodiments, the thickness of the metal layer to be alloyed, M, is 0.05 μm to 0.12 μm. For example, the thickness of the metal layer to be alloyed, M, can be 0.05 μm, 0.09 μm, 0.12 μm, or within any of the above values.

[0095] In some embodiments, the copper layer to be alloyed is formed by chemical plating or electroplating.

[0096] As a non-limiting example, the copper layer to be alloyed can be prepared by the following method:

[0097] Method (1) Preparation of the copper layer to be alloyed by electroplating: The electroplating solution is a mixture of copper sulfate and auxiliary solvents, including hydrochloric acid, sulfuric acid, brightener, and carrier agent; the solution temperature is 20℃~50℃; the product to be electroplated is immersed in the solution for electroplating, and then removed from the solution for baking at a temperature of 140℃~160℃ for 20s~300s. Multi-stage electroplating is used, with each stage having a current of 100A~200A and a linear velocity of 3m / min~20m / min. By reducing the electroplating current, the density of the copper layer to be alloyed can be reduced.

[0098] Method (2): Preparation of the copper layer to be alloyed by chemical plating: The plating solution consists of copper sulfate, complexing agent EDTA-2Na, formaldehyde, polyethylene glycol, thiourea, and sodium hydroxide. The temperature is 30℃~60℃, and the linear velocity is 1m / min~5m / min. The density of the copper layer prepared by chemical plating is lower than that of electroplated copper.

[0099] In some embodiments, the metal M layer to be alloyed is formed by vapor deposition. Vapor deposition allows the metal M to be alloyed to be deposited on the copper layer to be alloyed, and allows the alloying metal M particles to penetrate into the copper layer.

[0100] As a non-limiting example, the metal M layer to be alloyed can be prepared by the following method: deposition by evaporation boat: the main drum temperature is set to -15℃ to 15℃; after the evaporation begins, the evaporation power is 3KW to 5KW and the linear speed is 15m / min to 25m / min.

[0101] In some embodiments, prior to the alloying process, micropores are formed on the surface of the copper layer to be alloyed. This allows the metal M in the metal M layer to further penetrate into the copper layer, achieving better alloying.

[0102] In some embodiments, the pore size of the micropores is 5 μm to 50 μm. For example, the pore size of the micropores can be 5 μm, 8 μm, 13 μm, 24 μm, 35 μm, 46 μm, 50 μm, or within any range of these values. This configuration facilitates further penetration of metal M into the copper layer to be alloyed, resulting in better alloying.

[0103] In some embodiments, the spacing between two adjacent micropores is 1 mm to 5 mm. For example, the spacing between any two micropores can be 1 mm, 3 mm, 5 mm, or any value within the range above. This arrangement facilitates further penetration of the metal M into the copper layer to be alloyed, resulting in better alloying.

[0104] It is understood that the "interval between two adjacent micropores" mentioned in this application refers to the distance between the centers of any two adjacent micropores.

[0105] In some embodiments, micropores can be formed on the surface of the copper layer to be alloyed by laser drilling. Laser drilling can be controlled to form micropores only on the copper layer to be alloyed without affecting the copper layer itself.

[0106] In some embodiments, the method further includes a preparation step for the composite current collector semi-finished product:

[0107] The copper layer is prepared on at least one side of the base film, wherein the copper layer comprises a first copper layer and a second copper layer stacked thereon, the first copper layer being relatively close to the base film and the second copper layer being relatively far away from the base film.

[0108] In some embodiments, the volume density ratio of the first copper layer, the second copper layer, and the copper layer to be alloyed is 1:(1.1~1.3):(0.7~0.9). For example, this volume density ratio can be 1:1.1:0.9, 1:1.3:0.7, 1:1.1:0.7, 1:1.2:0.8, 1:1.3:0.9, 1:1.1:0.9, 1:1.3:0.7, or within any range of the above values.

[0109] This indicates that the density of the copper layer to be alloyed is lower than that of the second and first copper layers, which is beneficial for the metal M in the metal M layer to be alloyed to be at least partially embedded in the copper layer to be alloyed during the vapor deposition process, and for the copper layer to be alloyed and the metal M to be alloyed to be more efficient and complete alloying to be achieved when heated by Joule.

[0110] In some embodiments, the first copper layer is formed by electroplating.

[0111] As a non-limiting example, the first copper layer can be prepared by the following method:

[0112] The first copper layer is prepared by electroplating. The electroplating solution is a mixture of copper sulfate and auxiliary solvents, including hydrochloric acid, sulfuric acid, brightener, and carrier agent. The solution temperature is 20℃~50℃. The product to be electroplated is immersed in the solution for electroplating, and then removed from the solution for baking. The baking temperature is 100℃~160℃, and the baking time is 20s~300s. Multi-stage electroplating is performed, with each stage using a current of 200A~800A and a linear velocity of 3m / min~20m / min.

[0113] In some embodiments, the plating current of the first copper layer is greater than the plating current of the copper layer to be alloyed.

[0114] In some embodiments, the second copper layer is formed by magnetron sputtering.

[0115] As a non-limiting example, the second copper layer can be prepared by the following method:

[0116] The coating was prepared by magnetron sputtering, using 4 to 10 copper targets (purity: 99.99%) as the target material, with a target power of 10kW to 30kW, an argon flow rate of 100sccm to 200sccm, a coating vacuum of 0.1Pa to 0.5Pa, a linear velocity of 10m / min, and a main roller temperature of 20℃ to -20℃ during the coating process.

[0117] In some embodiments, the copper layer further includes a copper seed layer disposed between the base film and the first copper layer. The purpose of the copper seed layer is to make the semi-finished product containing the base film conductive, so as to facilitate subsequent electroplating.

[0118] In some embodiments, the copper seed layer is formed by magnetron sputtering.

[0119] As a non-limiting example, the copper seed layer can be prepared by the following method:

[0120] The coating was prepared by magnetron sputtering, using 4 to 10 copper targets (purity: 99.99%) as the target material, with a target power of 3 kW to 20 kW, an argon flow rate of 100 sccm to 200 sccm, a coating vacuum of 0.1 Pa to 0.5 Pa, a linear velocity of 10 m / min, and a main roller temperature of 20℃ to -20℃ during the coating process.

[0121] In some embodiments, the preparation method further includes a step of preparing an auxiliary layer, wherein the auxiliary layer includes an insulating layer and / or a buffer layer.

[0122] For example, the preparation steps of the insulating layer are as follows: it is prepared by magnetron sputtering, using 2 to 4 silicon nitride targets, with a target power of 3kW to 20kW, an argon flow rate of 100sccm to 200sccm, a coating vacuum of 0.1Pa to 0.5Pa, a linear speed of 10m / min, and a main roller temperature of 20℃ to -20℃ during the coating process.

[0123] For example, the preparation steps of the buffer layer are as follows: polyimide (PI) and silicon dioxide (e.g., mass ratio of PI:SiO2=8:2) are melted and coated on the surface of the base film, and then dried.

[0124] In some embodiments, the Joule heating is performed using a Joule heating device, which includes two conductive rollers arranged opposite each other. The composite current collector semi-finished product containing the metal layer to be alloyed is in contact with the two conductive rollers and moves continuously between the two conductive rollers.

[0125] In the Joule heating device described above, two conductive rollers contact the surface of the composite current collector semi-finished product. The copper layer and the M layer of the metal to be alloyed, located between the two conductive rollers, form a conductive circuit with the conductive rollers. Joule heating is achieved by utilizing the Joule heating effect that occurs during the flow of current through the copper layer and the M layer. This Joule heating device can achieve continuous heating of the coil material through the conductive rollers, enabling continuous production.

[0126] In some embodiments, the Joule heating device further includes a cooling roller disposed on the side of the composite current collector opposite to the conductive roller, which further reduces thermal damage to the base film. Optionally, the temperature of the cooling roller is -20°C to 20°C.

[0127] Thirdly, this application provides a lithium metal battery, including the composite current collector described in the first aspect of this application or the composite current collector prepared by the preparation method described in the second aspect of this application.

[0128] Fourthly, this application provides an electrical device including the lithium metal battery described in the third aspect of this application.

[0129] The following are specific embodiments, which describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0130] Example 1

[0131] Step 1: Prepare a buffer layer on two opposing surfaces of the PET base film: Melt polyimide (PI) and silica (mass ratio of PI:SiO2=8:2) and coat it on the surface of the base film, then dry it to form a buffer layer (thickness of 0.5μm).

[0132] Step 2: Prepare an insulating layer on the buffer layer on each side: Prepared by magnetron sputtering using 4 silicon nitride targets with a target power of 15kW, an argon flow rate of 150sccm, a coating vacuum of 0.3Pa, a linear speed of 10m / min, and a main roller temperature of 20℃~-20℃ during the coating process to form an insulating layer (thickness of 0.05μm).

[0133] Step 3: Prepare a copper seed layer on the insulating layer on each side: Prepared by magnetron sputtering using 8 copper targets (purity: 99.99%), target power of 15kW, argon flow rate of 150sccm, coating vacuum of 0.3Pa, linear speed of 10m / min, and the temperature of the main roller during the coating process is 20℃~-20℃, forming a copper seed layer (thickness of 30nm).

[0134] Step 4: Prepare the first copper layer on each side of the copper seed layer: The first copper layer is prepared by electroplating. The electroplating solution is a mixture of copper sulfate (concentration 130 g / L) and auxiliary solvents. The auxiliary solvents include hydrochloric acid (chloride ion mass percentage 50 ppm), sulfuric acid (concentration 90 g / L), brightener sodium polydisulfide dipropane sulfonate (concentration 0.3 ml / L), and carrier agent polyethylene glycol (concentration 3 ml / L). The solution temperature is 40℃. The product to be electroplated is immersed in the solution for electroplating, and then removed from the solution for baking at 130℃ for 100 seconds. Through 8-stage electroplating, each stage has a current of 500 A and a linear velocity of 10 m / min, forming the first copper layer (thickness 0.92 μm, bulk density 8.9 g / cm³). 3 ).

[0135] Step 5: Prepare a second copper layer on the first copper layer on each side: This is done by magnetron sputtering using six copper targets (purity: 99.99%), a target power of 20 kW, an argon flow rate of 150 sccm, a deposition vacuum of 0.3 Pa, a linear velocity of 10 m / min, and a main roller temperature of 20℃ to -20℃ during the deposition process. This forms a second copper layer (thickness 0.08 μm, bulk density 10.68 g / cm³). 3 ).

[0136] Step Six: Prepare the copper layer to be alloyed on the second copper layer on each side: Prepare the copper layer to be alloyed by electroplating. The electroplating solution is a mixture of copper sulfate (concentration 130 g / L) and auxiliary solvents. The auxiliary solvents include hydrochloric acid (chloride ion mass percentage 50 ppm), sulfuric acid (concentration 90 g / L), brightener sodium polydisulfide dipropane sulfonate (concentration 0.3 ml / L), and carrier agent polyethylene glycol (concentration 3 ml / L). The solution temperature is 40℃. Electroplat the product to be electroplated in the solution, and then bake it after removing it from the solution at a baking temperature of 150℃ for 200 s. Through 8-stage electroplating, with a current of 150 A and a linear velocity of 15 m / min per stage, a copper layer to be alloyed (thickness 0.15 μm, bulk density 7.12 g / cm³) is formed.

[0137] Step 7: Micropores are formed on the copper layer to be alloyed by laser drilling. The diameter of the micropores is 25μm and the spacing between two adjacent micropores is 3mm.

[0138] Step 8: Prepare the zinc layer to be alloyed on the copper layers on both sides: Deposit the zinc layer to be alloyed by evaporation boat deposition. Set the main drum temperature to MR1 of 15℃; after the deposition begins, set the evaporation power to 5 kW and the linear velocity to 20 m / min to deposit the zinc layer to be alloyed (thickness of 0.1 μm).

[0139] Step 9: Perform the first alloying treatment on each side of the composite current collector: Equipment: Joule heating of conductive roller (roller diameter 200 mm), specific process parameters are: current density 35 A / cm², temperature 480℃, single pulse time is 4s, pulse interval time is 0.2s.

[0140] Step 10: Perform a second alloying treatment on each side of the composite current collector: Equipment: Joule heating of conductive roller (roller diameter 200 mm), specific process parameters are: pulse current density 400 A / cm², peak temperature 800℃, single pulse time 50ms, pulse interval 0.3 s, forming an alloy layer with a thickness of 0.2μm.

[0141] Example 2

[0142] Similar to the preparation method in Example 1, the main difference is that the electroplating current in step four is adjusted to 800A so that the volume density ratio of the first copper layer to the second copper layer is 1:1.1.

[0143] Example 3

[0144] Similar to the preparation method in Example 1, the main difference is that the electroplating current in step four is adjusted to 200A so that the volume density ratio of the first copper layer to the second copper layer is 1:1.3.

[0145] Example 4

[0146] Similar to the preparation method in Example 1, the main difference is that the electroplating current in step four is adjusted to 1100A so that the volume density ratio of the first copper layer to the second copper layer is 1:1.

[0147] Example 5

[0148] Similar to the preparation method in Example 1, the main difference is that the preparation parameters for preparing the copper layer to be alloyed in step six are the same as in step four.

[0149] Example 6

[0150] The preparation method is similar to that in Example 1, except that step five, i.e. the second copper layer, is omitted.

[0151] Example 7

[0152] The preparation method is similar to that in Example 1, except that step seven is omitted.

[0153] Example 8

[0154] The preparation method is similar to that in Example 1, except that step nine is omitted.

[0155] Comparative Example 1

[0156] The preparation method is similar to that in Example 1, the main difference being that the alloy layer is prepared using a traditional high-temperature calcination method, as detailed below:

[0157] The unalloyed composite current collector sheet was transferred to a tube furnace, and an alloy layer was prepared under the conditions of heating rate of 2℃ / min, calcination temperature of 580℃, and holding time of 5min.

[0158] The composite current collectors prepared in Examples 1-8 and Comparative Example 1 were subjected to relevant performance tests, and the test results are shown in Table 1 below.

[0159] The test conditions or standards for each performance test item are as follows:

[0160] (1) Peel force test

[0161] A vertical tensile testing machine was used to conduct a peel force test on the composite current collector to evaluate the adhesion of the copper foil coating. The peel force test method for the composite current collector is as follows:

[0162] 3M double-sided tape (150mm long, 20mm wide) and a composite current collector sample (160mm long, 30mm wide) were sequentially adhered to a stainless steel plate. A 1kg roller was used to roll the 3M 9080 single-sided tape three times in the same direction at a uniform speed to ensure full adhesion between the composite current collector sample and the 3M double-sided tape on the stainless steel plate. Then, 3M 9080 single-sided tape (60mm long, 20mm wide) was adhered to the surface of the composite current collector. The end of the 3M 9080 single-sided tape was connected 5mm to a strip of white paper (150mm long, 20mm wide) for fixation to the fixture. The stainless steel plate was horizontally fixed to the tensile testing machine fixture. The sample peeling parameters (sample length, width, etc.) were set, and a 180° coating pull-off test was performed at a speed of 500mm / min.

[0163] (2) Density test

[0164] Samples were taken from the semi-finished products after preparing the copper seed layer, the semi-finished products after preparing the first copper layer, the semi-finished products after preparing the second copper layer, and the semi-finished products after preparing the copper layer to be alloyed. Samples of the same size (80 mm in length and 80 mm in width) were taken for weighing. The weight of each copper layer was calculated by the difference in weight. The samples were then placed in FIB-SEM and the thickness of the metal layer in the cross-sectional morphology photograph was measured. The thickness of each copper layer was calculated by the difference in thickness. The bulk density of each copper layer was then calculated as: copper layer weight / (area × thickness).

[0165] (3) Alloy thickness test

[0166] The composite current collector was prepared according to the sample preparation requirements of focused ion beam field emission microscopy (FIB-SEM). The sample was then placed in the FIB-SEM, and the sample was cut using an ion beam to prepare a cross-sectional sample. After the cross-sectional sample was prepared, the cross-section was observed using the field emission microscope lens at 50,000x magnification. After the image was clear, the thickness of the alloy layer in the cross-sectional morphology image was measured using the measurement software built into the electron microscope, thus obtaining the thickness data of the alloy layer.

[0167] (4) Conductivity test

[0168] The sheet resistance was used for characterization. Specifically, the prepared flat composite current collector sample was placed on the sample stage, and the sheet resistance of the sample was tested using a four-probe sheet resistance meter.

[0169] (5) Coulomb efficiency test

[0170] Preparation of positive electrode sheet: Lithium iron phosphate, polyvinylidene fluoride (PVDF) and conductive carbon black (SP) are mixed in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) is added and stirred evenly to obtain positive electrode active slurry. The positive electrode slurry is coated on both sides of aluminum foil to obtain positive electrode homogenized coating. After drying, pressing and cutting, the positive electrode sheet is obtained.

[0171] Preparation of negative electrode sheet: In a glove box filled with argon (O2 and H2O < 0.1 ppm), at a temperature of 250°C, equal amounts of molten lithium were injected into the composite current collectors prepared in Examples 1-8 and Comparative Example 1 to prepare the corresponding negative electrode sheets.

[0172] Electrolyte: Ethyl carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:2:1 to obtain a mixed organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare the electrolyte.

[0173] Diaphragm: Polypropylene diaphragm.

[0174] Assembly: The negative electrode, separator, and positive electrode are wound to obtain the battery cell. The battery cell is then placed in a battery case, dried, injected with electrolyte, and sealed to obtain the assembled battery.

[0175] Battery initial efficiency test method: First, the battery is formed by constant current charging at a rate of 0.1C to 3.4V. This step is the SEI film formation stage, and the battery capacity C1 after formation is recorded. Second, the battery is charged at a rate of 1C to 3.65V, and then charged at a constant voltage of 3.65V until the current is ≤0.05C to fully charge the battery, and the charging capacity C2 is recorded. Finally, the battery is discharged at a rate of 1C to 2.0V to obtain the battery discharge capacity C3. The initial coulombic efficiency is calculated using the formula C3 / (C1+C2).

[0176] Table 1

[0177]

[0178] As shown in Table 1, the alloy layer prepared by high-temperature calcination in Comparative Example 1 resulted in carbonization of the base film layer of the composite current collector and detachment of the metal layer of the composite current collector, causing the composite current collector to lose its reliability and safety performance and fail to meet the usage conditions.

[0179] The batteries in Examples 1-3 and Example 4 all have relatively high initial coulombic efficiency. Furthermore, comparing the results of Examples 1-3 with those of Example 4, it can be seen that when the volume density ratio of the first copper layer to the second copper layer is 1:(1.1-1.3), the density of the second copper layer is higher than that of the first copper layer. This is beneficial for better blocking the penetration of the zinc layer to be alloyed into the first copper layer, better preventing the influence on the conductivity of the composite current collector, and thus achieving higher coulombic efficiency.

[0180] The batteries in Examples 1-3 and Example 4 all have relatively high initial coulombic efficiencies. Furthermore, comparing the results of Examples 1-3 with those of Example 5, it can be seen that the higher the density of the copper layer to be alloyed, the less favorable it is for the zinc particles to be alloyed to penetrate into the third copper layer through vapor deposition. This is also less favorable for generating an alloy layer that meets the thickness requirements, affecting the uniformity of lithium deposition, and resulting in a decrease in the coulombic efficiency of Example 4 compared to Examples 1-3.

[0181] A comparison of the results of Examples 1-3 with that of Example 6 shows that the absence of a dense second copper layer as a barrier layer accelerates the penetration of zinc particles into the first copper layer, resulting in an excessively thick alloy layer, excessive sheet resistance, and an impact on the conductivity of the composite current collector, leading to a relative decrease in coulombic efficiency.

[0182] A comparison of the results of Examples 1-3 with that of Example 7 shows that forming micropores on the surface of the copper layer to be alloyed is beneficial to the preparation of the alloy layer and improves the coulombic efficiency.

[0183] A comparison of the results of Examples 1-3 with that of Example 8 shows that the first alloying treatment facilitates low-temperature thermal diffusion of zinc metal at a lower temperature. Then, the second alloying treatment involves instantaneous Joule heating at high temperature to form an alloy between copper and zinc. Dividing the alloying process into two stages reduces the peak temperature of the Joule heating and the duration of the high-temperature treatment, thereby reducing thermal damage to the base film, improving the adhesion between the metal layer and the base film, and ensuring battery performance.

[0184] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0185] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A composite current collector, characterized in that, It includes a base film and a metal layer disposed on at least one side of the base film, the metal layer including a copper layer and an alloy layer, the copper layer being located between the base film and the alloy layer; the alloy layer is formed by Joule heating.

2. The composite current collector according to claim 1, characterized in that, One or more of the following conditions must be met: (1) The alloy layer is made of Cu-M alloy, and the M element includes one or more of Zn, Ag, Mg and Sn; Optionally, the mass percentage of element M in the alloy layer is 48% to 83%; (2) The thickness of the base film is 2μm~8μm; (3) The thickness of the copper layer is 0.5 μm to 1.5 μm; and, (4) The thickness of the alloy layer is 0.1μm~0.3μm.

3. The composite current collector according to claim 1 or 2, characterized in that, The copper layer includes a first copper layer and a second copper layer stacked together, wherein the first copper layer is relatively close to the base film and the second copper layer is relatively far away from the base film.

4. The composite current collector according to claim 3, characterized in that, One or more of the following conditions must be met: (1) The bulk density of the second copper layer is greater than that of the first copper layer; (2) The ratio of the bulk density of the first copper layer to the bulk density of the second copper layer is 1:(1.1~1.3); (3) The thickness of the second copper layer is 0.05 μm to 0.1 μm; (4) The thickness of the first copper layer is 0.45 μm to 1.4 μm; (5) The copper layer further includes a copper seed layer, which is disposed between the base film and the first copper layer.

5. The composite current collector according to claim 1 or 2, characterized in that, The composite current collector also includes an auxiliary layer disposed between the base film and the copper layer, the auxiliary layer including an insulating layer and / or a buffer layer.

6. The composite current collector according to claim 5, characterized in that, One or more of the following conditions must be met: (1) The thickness of the insulating layer is 0.01 μm to 0.1 μm; (2) The material of the insulating layer includes silicon nitride ceramic; (3) The thickness of the buffer layer is 0.2μm~2μm; (4) The material of the buffer layer includes polyimide-silicon nanocomposite material and / or silicone rubber.

7. A method for preparing a composite current collector, characterized in that, include: A metal layer to be alloyed is prepared on at least one side of a composite current collector semi-finished product, wherein the composite current collector semi-finished product includes a base film and a copper layer disposed on at least one side of the base film, and the metal layer to be alloyed is adjacent to the copper layer. The metal layer to be alloyed is alloyed by Joule heating to form an alloy layer and prepare a composite current collector.

8. The preparation method according to claim 7, characterized in that, The alloying process includes a first alloying process and a second alloying process. The first alloying process is performed by a first pulse Joule heating, and the second alloying process is performed by a second pulse Joule heating. The current density of the first pulse Joule heating is 30 A / cm. 2 ~40A / cm 2 The temperature is 470℃~490℃, the single pulse time is 2s~6s, and the pulse interval time is 0.1s~0.3s; The pulse current density of the second pulse Joule heating is 350 A / cm. 2 ~450A / cm 2 The peak temperature is 700℃~1000℃, the single pulse time is 40ms~60ms, and the pulse interval time is 0.1s~0.3s.

9. The preparation method according to claim 7 or 8, characterized in that, The metal layer to be alloyed includes a copper layer to be alloyed and a metal M layer to be alloyed. The copper layer to be alloyed is located between the copper layer and the metal M layer to be alloyed. The M element includes one or more of Zn, Ag, Mg and Sn.

10. The preparation method according to claim 9, characterized in that, One or more of the following conditions must be met: (1) The copper layer to be alloyed is prepared by chemical plating or electroplating; (2) The metal M layer to be alloyed is prepared by vapor deposition; (3) The thickness of the copper layer to be alloyed is 0.06μm~0.25μm; (4) The thickness of the metal M layer to be alloyed is 0.05 μm to 0.12 μm; (5) Before the alloying process, the method further includes: forming micropores on the surface of the copper layer to be alloyed, wherein the pore diameter of the micropores is 5μm~50μm and the interval between two adjacent micropores is 1mm~5mm.

11. The preparation method according to claim 10, characterized in that, It also includes the preparation steps of the composite current collector semi-finished product: The copper layer is prepared on at least one side of the base film, wherein the copper layer comprises a first copper layer and a second copper layer stacked thereon, the first copper layer being relatively close to the base film and the second copper layer being relatively far away from the base film.

12. The preparation method according to claim 11, characterized in that, One or more of the following conditions must be met: (1) The volume density ratio of the first copper layer, the second copper layer, and the copper layer to be alloyed is 1:(1.1~1.3):(0.7~0.9). (2) The first copper layer is formed by electroplating, and the electroplating current of the first copper layer is greater than the electroplating current of the copper layer to be alloyed. (3) The second copper layer is formed by magnetron sputtering; (4) The copper layer further includes a copper seed layer disposed between the base film and the first copper layer, and the copper seed layer is formed by magnetron sputtering.

13. The preparation method according to claim 7 or 8, characterized in that, The Joule heating is performed using a Joule heating device, which includes two conductive rollers arranged opposite each other. The composite current collector semi-finished product containing the metal layer to be alloyed is in contact with the two conductive rollers and moves continuously between the two conductive rollers.

14. A lithium metal battery, characterized in that, The composite current collector includes the composite current collector as described in any one of claims 1 to 6 or the composite current collector prepared by the preparation method described in any one of claims 7 to 13.

15. An electrical appliance, characterized in that, Including the lithium metal battery of claim 14.

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