Composite current collector and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a composite current collector and a preparation method therefor and the use thereof. The composite current collector comprises a substrate layer, a transition layer, an electrically conductive layer, a columnar porous array layer, a metal replenishment layer, and a surface coating layer, which are sequentially stacked, wherein the columnar porous array layer is formed by means of a metal column array; and the material of the metal replenishment layer is selected from a lithium alloy, a sodium alloy, or a potassium alloy. In the composite current collector in the present invention, by means of providing the metal replenishment layer used for replenishing metal loss in a metal-ion battery cycle process, and due to the metal replenishment layer being present in the form of a metal alloy, metal oxidation can be avoided, and a metal preservation time can be prolonged, thereby achieving metal replenishment for the full life cycle of a metal-ion battery; and by means of providing the columnar porous array layer, a buffer space can be provided for thermal expansion in a metal-ion cycle process, thereby improving the first cycle coulombic efficiency and capacity retention of the battery, and prolonging the service life of the metal-ion battery.

Description

Composite current collector and its preparation method and application Technical Field

[0001] The present invention belongs to the field of lithium ion batteries, and in particular relates to a composite current collector and a preparation method and application thereof. Background Art

[0002] Traditional lithium-ion batteries, with their advantages of high energy density, long life, and lack of memory effect, have been widely used in mobile phones, laptops, electric vehicles, and other fields. With the development of lithium-ion power battery technology, the market penetration of new energy vehicles has rapidly increased, and this has also led to higher demands for the energy density of power batteries. However, due to the limitations of key lithium-ion battery materials, increasing energy density solely through cell and battery system design has currently reached its theoretical limit, becoming a major bottleneck restricting the future development of the new energy vehicle industry. Developing lightweight current collectors and increasing the proportion of active materials are feasible solutions to improve energy density. Composite current collectors, due to their high mechanical strength and electrical conductivity, have become a research hotspot. Composite current collectors are typically composed of conductive materials and polymer materials, such as PET films coated with graphene slurry or metallized polymer films. Metallized polymer films can be deposited on polymer films (such as PET and PI) using magnetron sputtering or thermal evaporation processes to form ultrathin metal films. They offer lightweight, high strength, and high electrical conductivity. Furthermore, due to the excellent insulating properties of the polymer films, thermal runaway can be effectively suppressed during the needle puncture process. However, due to the smooth surface of conventional composite current collectors and their poor bonding with active materials, the active materials are prone to peeling off during production and battery operation. Furthermore, many lithium-ion batteries currently suffer from low first-cycle coulombic efficiency, where the active lithium in the battery is irreversibly consumed during the formation of the SEI film (solid electrolyte interface), resulting in low battery capacity and short cycle life.

[0003] Summary of the Invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, one of the objectives of the present invention is to provide a composite current collector.

[0005] A second object of the present invention is to provide a method for preparing a composite current collector.

[0006] A third object of the present invention is to provide a metal ion battery.

[0007] A fourth object of the present invention is to provide an application of a composite current collector in a battery.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] The first aspect of the present invention provides a composite current collector, comprising a base layer, a transition layer, a conductive layer, a columnar porous array layer, a metal supplement layer and a surface coating layer stacked in sequence; the columnar porous array layer is composed of a metal column array; the material of the metal supplement layer is selected from lithium alloy, sodium alloy or potassium alloy.

[0010] Preferably, the columnar porous array layer has a columnar porous structure. The columnar porous array layer of the present invention provides space for the metal replenishment layer and a buffer for volume changes during the metal replenishment layer's formation and metal replenishment processes, thereby improving the structural stability of the metal replenishment layer and enabling metal replenishment throughout the metal ion battery's lifecycle.

[0011] Preferably, the metal supplement layer is a lithium-containing alloy layer, a sodium-containing alloy layer, or a potassium-containing alloy layer formed by an alloying reaction between lithium, sodium, or potassium metal and the metal in the columnar porous array layer. When the composite current collector is used in a lithium-ion battery, the metal supplement layer is made of a lithium alloy; when the composite current collector is used in a sodium-ion battery, the metal supplement layer is made of a sodium alloy; and when the composite current collector is used in a potassium-ion battery, the metal supplement layer is made of a potassium alloy.

[0012] Preferably, the material of the transition layer is an oxide of the conductive metal used in the conductive layer. The introduction of the transition layer increases the bonding strength between the base layer and the metal conductive layer.

[0013] Preferably, the material of the base layer is at least one of a conductive polymer and a light polymer film material. The material of the base layer in the present invention is a high-strength light polymer material, which can make the prepared composite current collector lightweight.

[0014] Preferably, the conductive polymer is selected from at least one of polypyrrole, polyacetylene, polyphenylene, polyacene, polythiophene, pyrolyzed polyacrylonitrile, and pyrolyzed polyvinyl alcohol.

[0015] Preferably, the lightweight polymer film material is selected from at least one of polyethylene terephthalate, polyethylene, polyvinyl chloride, polyvinyl alcohol, polypropylene, and polyacrylate.

[0016] Preferably, the surface coating layer comprises a metal alloy layer located on the metal supplementary layer and a nanocrystalline graphite material located on the surface of the metal alloy layer.

[0017] Preferably, the nanocrystalline graphite material is island-shaped nanocrystalline graphite islands.

[0018] Preferably, the preparation method of the nanocrystalline graphite material is: magnetron sputtering is performed on a metal alloy layer using a magnetron sputtering method, using a carbon target as a target material, and depositing for 20 to 40 minutes when the gas flow rate of carbon tetrafluoride is 200 to 400 sccm, the deposition power of the carbon target is 1000 to 2000 W, and the bias voltage is 40 to 60 V to obtain the nanocrystalline graphite material.

[0019] Preferably, the thickness of the nanocrystalline graphite material is 300-500 nm; further preferably, the thickness of the nanocrystalline graphite material is 300-450 nm; even further preferably, the thickness of the nanocrystalline graphite material is 350-400 nm.

[0020] The surface coating in the present invention effectively isolates water and oxygen, improving the environmental stability of the metal supplement layer and preventing the active metal in the metal supplement layer from reacting with water and oxygen. Furthermore, the affinity between the abundant polar functional groups on the surface of the nanocrystalline graphite material and the negative electrode material, as well as the large contact area between the island structure and the negative electrode material, significantly improves the bonding strength and compatibility between the composite current collector and the negative electrode material. To enhance the bonding strength between the composite current collector and the negative electrode material, the present invention provides a surface coating. The special material and structure of the surface coating achieve a strong bonding between the composite current collector and the negative electrode material. The present invention does not use a binder, which does not affect battery performance. Furthermore, the absence of an amorphous carbon layer eliminates the problem of high interfacial impedance caused by the poor conductivity of the amorphous carbon layer.

[0021] Preferably, the material of the metal alloy layer includes copper-aluminum alloy.

[0022] Preferably, the thickness of the metal alloy layer is 10 to 30 nm; further preferably, the thickness of the metal alloy layer is 12 to 24 nm; even further preferably, the thickness of the metal alloy layer is 12 to 15 nm.

[0023] Preferably, the thickness of the transition layer is 50 to 250 nm; more preferably, the thickness of the transition layer is 150 to 200 nm; and even more preferably, the thickness of the transition layer is 150 to 180 nm. The function of the transition layer is to improve the compatibility and bonding strength between the base layer and the conductive layer.

[0024] Preferably, the thickness of the conductive layer is 100 to 500 nm; preferably, the thickness of the conductive layer is 300 to 500 nm; further preferably, the thickness of the conductive layer is 300 to 400 nm.

[0025] Preferably, the columnar porous array layer has a thickness of 2 to 5 μm; more preferably, the columnar porous array layer has a thickness of 2 to 3 μm. The columnar porous array layer has a porous structure formed by an array of porous metal columns.

[0026] Preferably, the thickness of the surface coating layer is 310 to 530 nm.

[0027] Preferably, the base layer has a thickness of 1 to 10 μm.

[0028] Preferably, the thickness of the metal supplementary layer is 1-5 μm.

[0029] Preferably, the material of the metal column is selected from at least one of aluminum, tin, magnesium, iron, zinc, silver, and antimony.

[0030] Preferably, the diameter of the metal column is 100-200 nm; further preferably, the diameter of the metal column is 125-175 nm.

[0031] Preferably, the surface of the metal column has a porous structure.

[0032] Preferably, the conductive layer is made of copper.

[0033] Preferably, the material of the transition layer is copper oxide.

[0034] The second aspect of the present invention provides a method for preparing the composite current collector provided in the first aspect of the present invention, comprising the following steps:

[0035] S1: depositing a transition layer, a conductive layer, and a metal layer on the base layer in sequence;

[0036] S2: using a metallographic etchant to etch the metal layer in step S1 to obtain a columnar porous array layer;

[0037] S3: forming a metal supplementary layer on the surface of the columnar porous array layer;

[0038] S4: forming a surface coating layer on the metal supplementary layer to obtain the composite current collector.

[0039] Preferably, in step S1, a magnetron sputtering method is used to deposit a transition layer, a conductive layer, and a metal layer on the substrate.

[0040] Preferably, the gas flow rate of the magnetron sputtering method in step S1 is 200-400 sccm, the deposition power is 1000-2000 W, and the bias voltage is 10-100 V.

[0041] Preferably, step S1 includes the following steps:

[0042] S11: Deposition of transition layer: Depositing a transition layer on the surface of the cleaned substrate layer by magnetron sputtering. First, the working gas is set to a mixture of argon and oxygen, with a total gas flow rate of 200-400 sccm and an argon to oxygen ratio of (4-2):1. A metal target with a purity of more than 99.99% is selected, the deposition power is 1000-2000 W, the bias voltage is set at 40-60 V, and the deposition time is 3-5 minutes. During the deposition process, the oxygen flow rate is gradually reduced until it reaches 0.

[0043] S12: Conductive layer deposition: Depositing a conductive layer on the transition layer, the working gas is argon, the gas flow rate is 200-400 sccm, the deposition power is 1000-2000 W, the bias voltage is set at 10-30 V, and the deposition time is 5-15 min;

[0044] S13: Metal layer deposition: A metal layer is deposited on the surface of the conductive layer by magnetron sputtering. The working gas is argon, the gas flow rate is 200-400sccm, a metal target with a purity of more than 99.99% is selected, the deposition power is 1500-3000W, the bias voltage is set at 25-100V, and the deposition time is 2-4 hours. The deposited metal is a densely arranged columnar crystal structure with a thickness of about 2-5μm.

[0045] Preferably, step S2 comprises etching the metal layer from step S1 using a sodium hydroxide solution having a mass percentage of 0.04-0.06% for 5-10 minutes to form a columnar porous structure. The metal layer has a columnar crystal structure, and selective etching of the metal layer using a metallographic etchant preferentially etches the grain boundaries, thereby forming a columnar porous array layer.

[0046] Preferably, the step S3 adopts a metal sheet hot pressing method, an electrochemical method or a vapor deposition method.

[0047] Preferably, the metal sheet hot pressing method is to hot press the metal sheet and the columnar porous structure under the protection of inert gas, with the hot pressing temperature being 60-120° C. and the pressure being 3-5 MPa.

[0048] Preferably, the step S4 is: first forming a metal alloy layer on the metal supplementary layer by a magnetron sputtering method, and then forming a nanocrystalline graphite material on the metal alloy layer.

[0049] Preferably, step S4 is: step S4 specifically comprises: first performing magnetron sputtering on the metal supplementary layer by a magnetron sputtering method, using metal target A and metal target B as target materials, and depositing for 5 to 15 minutes when the argon flow rate is 200 to 400 sccm, the deposition power of metal target A is 500 to 1000 W, the deposition power of metal target B is 50 to 300 W, and the bias voltage is 40 to 60 V to obtain a metal alloy layer; then, performing magnetron sputtering on the metal alloy layer by a magnetron sputtering method, using a carbon target as the target material, and depositing for 20 to 40 minutes when the gas flow rate of carbon tetrafluoride is 200 to 400 sccm, the deposition power of the carbon target is 1000 to 2000 W, and the bias voltage is 40 to 60 V to obtain a nanocrystalline graphite material. In this step, nanocrystalline graphite nucleates and grows within the amorphous carbon layer under the catalysis of the metal alloy layer. Simultaneously, the amorphous carbon is preferentially etched by the fluorine plasma, leaving dispersed islands of nanocrystalline graphite material, or nanocrystalline graphite islands, within the metal alloy layer. This nanocrystalline graphite material does not contain an amorphous carbon layer, eliminating the problem of high interfacial impedance caused by the poor conductivity of the amorphous carbon layer. When the metal alloy layer is a copper-aluminum composite material, metal target A is copper and metal target B is aluminum.

[0050] Preferably, the preparation method further comprises the step of physically or chemically cleaning the substrate layer before step S1.

[0051] Preferably, the preparation method further includes the step of cleaning the base layer using at least one of alcohol washing, alkali washing, acid washing, and water washing before step S1, and then performing glow discharge cleaning; further preferably, the preparation method further includes the step of sequentially performing alcohol washing, alkali washing, water washing, acid washing, and water washing on the base layer, and then performing glow discharge cleaning.

[0052] Preferably, in the glow discharge cleaning step, the gas flow rate is 200-400 sccm.

[0053] Preferably, in the glow discharge cleaning step, the cleaning voltage is 400-600V.

[0054] Preferably, in the glow discharge cleaning step, the cleaning time is 10-20 minutes.

[0055] Preferably, the preparation method also includes a method of pre-treating the substrate before step S1, using alcohol and deionized water to perform ultrasonic degreasing on the surface of the substrate material, and then performing alkaline washing, usually using 5% sodium hydroxide solution for washing at 50-60°C for 0.5-1 minute, and after washing again with water, using 20% ​​nitric acid for washing at room temperature for 0.5-1 minute to remove the alkaline washing residue, and then drying at 80°C; then performing glow discharge cleaning, with a gas flow rate of 200-400sccm, a cleaning voltage of 400-600V, and a cleaning time of 10-20 minutes.

[0056] The third aspect of the present invention provides a metal ion battery, comprising a positive electrode material, a negative electrode material and a positive electrode current collector, and also comprising a negative electrode current collector, wherein the negative electrode current collector is the composite current collector provided by the first aspect of the present invention.

[0057] Preferably, the metal ion battery is selected from lithium ion batteries, sodium ion batteries, and potassium ion batteries.

[0058] The fourth aspect of the present invention provides use of the composite current collector provided by the first aspect of the present invention in a battery.

[0059] The beneficial effects of the present invention are as follows: the composite current collector of the present invention replenishes the metal loss during the cycle of the metal ion battery by setting a metal replenishment layer, and the metal replenishment layer exists in the form of a metal alloy, which can avoid metal oxidation and extend the metal storage time, thereby achieving the replenishment of metal for the entire life cycle of the metal ion battery, and by setting a columnar porous array layer, a buffer space can be provided for the thermal expansion during the metal ion cycle, thereby achieving the improvement of the battery's first cycle coulombic efficiency and capacity retention rate, and extending the service life of the metal ion battery.

[0060] In addition, the composite current collector of the present invention can reduce the thickness and mass of the current collector while ensuring that the basic functions of the current collector are not affected, thereby achieving lightweighting, and can increase the interfacial bonding strength between the current collector and the active material to prevent the active material from falling off.

[0061] The preparation method of the present invention is simple and easy to operate, green and pollution-free, and has a stable process, and can be applied to industrial batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] FIG1 is a schematic structural diagram of a composite current collector in an embodiment of the present invention.

[0063] FIG2 is a SEM image of the columnar porous array layer in Example 1 of the present invention.

[0064] Reference numerals: base layer 1 ; transition layer 2 ; conductive layer 3 ; columnar porous array layer 4 ; lithium replenishing layer 5 ; surface coating layer 6 . DETAILED DESCRIPTION

[0065] The specific implementation of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are any processes that are not particularly described in detail below, they can be implemented or understood by those skilled in the art with reference to the prior art. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be purchased commercially.

[0066] 1 , in some embodiments of the present invention, the structure of the composite current collector includes a base layer 1, a transition layer 2, a conductive layer 3, a columnar porous array layer 4, a metal supplementary layer, and a surface coating layer 6 stacked in sequence.

[0067] In some embodiments of the present invention, the material of the base layer 1 is a high-strength lightweight polymer material. In some preferred embodiments of the present invention, the material of the base layer 1 can be selected from at least one of polypyrrole, polyacetylene, iodine-doped polyacetylene, polythiophene, polyaniline, polyphenylene, polyphenylene, pyrolyzed polyacrylonitrile, pyrolyzed polyvinyl alcohol, polyimide, polyethylene, polyvinyl chloride, polypropylene, polyacrylate, and polyethylene terephthalate.

[0068] In some embodiments of the present invention, transition layer 2 is made of copper oxide. Its primary function is to enhance the bonding strength between the polymer material in base layer 1 and the copper. In some embodiments of the present invention, transition layer 2 has a thickness of 50 to 250 nm; in some preferred embodiments, transition layer 2 has a thickness of 150 to 200 nm.

[0069] In some embodiments of the present invention, the conductive layer 3 is a metallic copper layer, and the conductive layer 3 is a functional layer for achieving electron transport. In some embodiments of the present invention, the conductive layer 3 has a thickness of 100 to 500 nm; in some preferred embodiments of the present invention, the conductive layer 3 has a thickness of 300 to 500 nm.

[0070] In some embodiments of the present invention, the columnar porous array layer 4 is an active metal layer having a columnar porous structure. In some preferred embodiments of the present invention, the material of the active metal layer is selected from at least one of aluminum, tin, magnesium, iron, zinc, silver, and antimony. The material of the active metal layer is not limited to the metal materials listed above. Any material that can form an alloy with lithium can be used as the material of the active metal layer in the present invention. The columnar porous array layer 4 provides a storage space for the lithium replenishment layer 5 on the one hand, and a buffer space for the volume change of the lithium replenishment layer 5 during its formation and participation in the lithium replenishment process on the other hand. In some preferred embodiments of the present invention, the columnar porous array layer 4 is an aluminum layer having a columnar porous structure, and the diameter of the aluminum column is 100 to 200 nm; in some more preferred embodiments of the present invention, the diameter of the aluminum column is 125 to 175 nm.

[0071] In some embodiments of the present invention, the metal replenishment layer is a lithium replenishment layer 5. The material of the lithium replenishment layer 5 is a lithium-containing alloy generated by an alloying reaction between metallic lithium and the active metal in the columnar porous array layer 4. During the operation of the battery, it can serve as a lithium source to achieve lithium replenishment throughout the battery life cycle. In some embodiments of the present invention, the lithium replenishment layer can be prepared by hot pressing of lithium foil, electrochemical lithiation, or evaporation. When the material of the metal replenishment layer is a lithium-containing alloy, it can be used to replenish the lithium consumed by the lithium-ion battery during the cycle, and can also provide a buffer space for the lithium-ion battery to expand during the cycle.

[0072] In some embodiments of the present invention, the metal replenishment layer is a sodium replenishment layer. The material of the sodium replenishment layer is a sodium-containing alloy formed by an alloying reaction between metallic sodium and an active metal in the columnar porous array layer 4, such as tin. This alloy can serve as a sodium source to replenish sodium throughout the battery's lifecycle during operation. When the metal replenishment layer is made of a sodium-containing alloy, it can be used to replenish sodium consumed during the sodium-ion battery's cycling process and also provide a buffer for expansion during cycling.

[0073] In some embodiments of the present invention, the metal replenishment layer is a potassium replenishment layer. The material of the potassium replenishment layer is a potassium-containing alloy formed by an alloying reaction between metallic potassium and an active metal in the columnar porous array layer 4, such as tin. This alloy can serve as a potassium source to replenish potassium throughout the battery's lifecycle during operation. When the metal replenishment layer is made of a potassium-containing alloy, it can be used to replenish potassium consumed during the cycling of the potassium-ion battery and also provide a buffer space for expansion during the cycling of the potassium-ion battery.

[0074] In some embodiments of the present invention, the surface coating layer 6 has a double-layer structure, with a bottom layer being a copper-aluminum composite layer and a surface layer comprising dispersed nanocrystalline graphite islands. The nanocrystalline graphite islands are island-like crystals of submicron-sized graphite dispersed on the surface of the copper-aluminum composite layer. The surface coating layer 6 not only blocks water and oxygen from the air, improving the environmental stability of the lithium replenishment layer 5, but also enhances molecular bonding with the negative electrode material through the abundant polar functional groups on the carbon surface of the nanocrystalline graphite. The island-like structure increases the contact area between the current collector and the negative electrode material, achieving a high bonding strength between the current collector and the negative electrode material. In some preferred embodiments of the present invention, the thickness of the copper-aluminum composite layer is 10 to 30 nm; in some more preferred embodiments, the thickness of the copper-aluminum composite layer is 12 to 24 nm. In some preferred embodiments of the present invention, the thickness of the nanocrystalline graphite islands is 300 to 500 nm; in some more preferred embodiments, the thickness of the nanocrystalline graphite islands is 300 to 450 nm.

[0075] Example 1

[0076] Referring to the schematic diagram in Figure 1 , the composite current collector in this example comprises a sequentially stacked base layer 1, a transition layer 2, a conductive layer 3, a columnar porous array layer 4, a lithium replenishing layer 5, and a surface coating layer 6. Base layer 1 is made of an iodine-doped polyacetylene film and has a thickness of 5 μm. Transition layer 2 is made of copper oxide and has a thickness of 150 nm. Conductive layer 3 is made of metallic copper and has a thickness of 300 nm. Columnar porous array layer 4 is an aluminum layer with a columnar porous structure. A SEM image of columnar porous array layer 4 is shown in Figure 2 . The columnar porous array layer 4 is 4 μm thick, with aluminum columns having a diameter of 150 nm and gaps between columns of 80 nm. Lithium replenishing layer 5 is made of a lithium-aluminum alloy and has a thickness of 1 μm. The copper-aluminum composite layer in surface coating layer 6 is 12 nm thick, and the nanocrystalline graphite islands are 360 ​​nm thick.

[0077] The composite current collector in this example is prepared by the following preparation method, which specifically includes the following steps:

[0078] (1) Substrate pretreatment: Take iodine-doped polyacetylene film as the substrate material, first use anhydrous ethanol and deionized water to ultrasonically clean its surface to remove surface oil, then use 5% sodium hydroxide solution to clean its surface for about 30 seconds, use deionized water to clean it, and then use 20% nitric acid to clean it for 30 seconds to remove residues, then use deionized water and anhydrous ethanol to clean it several times, dry it, and then perform glow cleaning. First, pump the air pressure to 5×10 -3Pa, then introduce argon gas with a gas flow rate of 300 sccm. At this time, the gas pressure is approximately between 0.5-0.6 Pa. Then set the cleaning voltage to 500 V and start glow cleaning. The cleaning time is 15 minutes.

[0079] (2) Deposition of transition layer 2: After the above-mentioned glow cleaning treatment, the working gas was changed to a mixture of argon and oxygen, where the argon flow rate was 225 sccm and the oxygen flow rate was 75 sccm. The bias voltage was then set to 50 V, the deposition power of the copper target was set to 1500 W, and the deposition time was set to 5 minutes. During the deposition process, the oxygen flow rate was gradually reduced to 0.

[0080] (3) Based on step 2, the working gas was changed to argon with a gas flow rate of 300 sccm, and the metal copper deposition was continued for 10 minutes.

[0081] (4) Metal layer deposition: Based on the copper layer deposited above, the copper target was turned off and the aluminum target was turned on. Other operating parameters remained unchanged. The deposition power of the aluminum target was set to 2500 W and the deposition time was set to 3 hours.

[0082] (5) Preparation of columnar porous array layer 4: After step (4), the metal aluminum layer on the surface of the sample is corroded using a 0.05% sodium hydroxide solution for about 450 seconds, then cleaned with deionized water and anhydrous ethanol, and then dried.

[0083] (6) Preparation of lithium replenishment layer 5: In an inert gas atmosphere, a metal lithium foil is coated on the surface of the composite current collector prepared above and subjected to hot pressing treatment, wherein the temperature is set to 80°C and the pressure is set to 3 MPa. Under the action of hot pressing, the metal lithium foil and the aluminum of the columnar porous array layer 4 undergo an alloying reaction to form a lithium-aluminum alloy.

[0084] (7) Preparation of surface coating layer 6: Set the working gas to argon with a gas flow rate of 300 sccm, select a copper target and an aluminum target with a purity of more than 99.99%, the deposition power of the copper target is 800 W, the deposition power of the aluminum target is 200 W, the bias voltage is set to 50 V, and the deposition time is 10 minutes. Then, replace the working gas with carbon tetrafluoride with a gas flow rate of 300 sccm, select a carbon target with a purity of more than 99.99%, the deposition power is 1500 W, the bias voltage is set to 50 V, and the deposition time is 25 minutes to obtain the composite current collector.

[0085] Comparative Example 1

[0086] The structure of the composite current collector in this example includes a stacked base layer 1 and a conductive layer 3, wherein the base layer 1 is made of iodine-doped polyacetylene film; the conductive layer 3 is made of metallic copper, and the thickness of the conductive layer 3 is 300 nm.

[0087] The composite current collector in this example is prepared by the following preparation method, which specifically includes the following steps:

[0088] (1) Substrate pretreatment: The substrate material is treated using the same substrate pretreatment method as step (1) in Example 1.

[0089] (2) Preparation of conductive layer 3: After the treatment in step (1), the working gas was changed to argon with a gas flow rate of 300 sccm, the bias voltage was set to 50 V, the deposition power of the copper target was set to 1500 W, and the deposition time was set to 10 minutes to perform metal copper deposition to obtain the composite current collector in this example.

[0090] The composite current collectors in Example 1 and Comparative Example 1 were tested for membrane-substrate bonding strength, current collector-negative electrode material bonding strength, battery initial coulombic efficiency, and battery cycle life. The membrane-substrate bonding strength was evaluated by a cyclic bending method with a bending radius of 3 mm and 50,000 bending times. The membrane-substrate bonding strength was evaluated by the mass loss after 50,000 bending times. The bonding strength between the current collector and the negative electrode material was tested by a 100-grid method. In the 100-grid method test results, level 0 indicates that the edge of the incision is completely smooth and there is no peeling at the edge of the grid; level 1 indicates that there is small peeling at the intersection of the incision, and the actual damage in the grid area does not exceed 5%; level 2 indicates that the edge and / or intersection of the incision is peeled off, and its area is greater than 5% but less than 15%; level 3 indicates that there is large peeling along the edge of the incision / or some squares are partially or completely peeled off, and its area is greater than 35% but not more than 65% of the grid area. The first coulombic efficiency and cycle life of the battery were characterized by using 18650 cylindrical battery performance tests, wherein the negative electrode material was graphite, the positive electrode material was lithium iron phosphate, the negative electrode current collectors were the composite current collectors in Example 1 and Comparative Example 1, respectively, and the positive electrode current collector was a conventional aluminum foil current collector. The battery capacity was 1.7 Ah, and the charge and discharge rate was 1 C. The test results obtained by the above test method are shown in Table 1.

[0091] Table 1. Composite current collector performance test results in Example 1 and Comparative Example 1

[0092] It can be seen from Table 1 that compared with the composite current collector in Comparative Example 1, the composite current collector in Example 1 of the present invention has significant improvements in membrane-substrate bonding strength, current collector and negative electrode material bonding strength, battery first coulombic efficiency and battery cycle life.

[0093] Example 2-10

[0094] The difference between the composite current collector in Example 2-10 and the composite current collector in Example 1 is that the base material of the composite current collector in Example 2-10 is different. The base material of the composite current collector in Example 2-10 adopts the base material corresponding to Table 2.

[0095] The membrane-substrate bonding strength of the composite current collectors in Examples 1 to 10 was tested, and the conductivity of the composite current collectors was tested using a DC four-probe method. The specific test results are shown in Table 2 below:

[0096] Table 2. Test results of membrane-substrate bonding strength and electrical conductivity of composite current collectors in Examples 2-10

[0097] As shown in Table 2, the composite current collectors in Examples 1 to 10 can obtain excellent membrane-substrate bonding strength using different substrate materials. The mass loss rate after 50,000 bends is 1.2 to 2.8%. In addition, Examples 1 to 5 and Examples 9 to 10 all have excellent electrical conductivity, with the electrical conductivity reaching 41.2×10 4 S / cm.

[0098] Examples 11-14

[0099] The difference between the composite current collectors in Examples 11-14 and the composite current collector in Example 1 is that the thickness of the transition layer 2 of the composite current collectors in Examples 11-14 is different. The thickness of the transition layer 2 of the composite current collectors in Examples 11-14 is shown in Table 3.

[0100] The membrane-substrate bonding strength of the composite current collectors in Examples 11-14 was tested. The specific test results are shown in Table 3 below:

[0101] Table 3. Test results of transition layer 2 thickness and membrane-substrate bonding strength of composite current collectors in Example 1 and Examples 11-14

[0102] It can be seen from Table 3 that when the thickness of the transition layer 2 is in the range of 50 to 250 nm, the mass loss rate of the composite current collector after 50,000 bends is between 1.2% and 18%, and it still has good membrane-substrate bonding strength. If the thickness of the transition layer 2 is less than 50 nm, as the thickness of the transition layer 2 decreases, the mass loss rate of the composite current collector after 50,000 bends gradually increases; if the thickness of the transition layer 2 exceeds 250 nm, as the thickness of the transition layer 2 increases, the mass loss rate of the composite current collector after 50,000 bends also gradually increases. It can be seen that there is a preferred range for the thickness of the transition layer 2 in the composite current collector in the present invention. When the thickness of the transition layer 2 is about 150 nm, the membrane-substrate bonding strength of the composite current collector is better than that of the composite current collector with other thicknesses of transition layer 2.

[0103] Examples 15-18

[0104] The difference between the composite current collectors in Examples 15-18 and the composite current collector in Example 1 is that the thickness of the conductive layer 3 of the composite current collectors in Examples 15-18 is different. The thickness of the conductive layer 3 of the composite current collectors in Examples 15-18 is shown in Table 4. Then, the battery internal resistance of the composite current collectors in Examples 1 and 15-18 was tested respectively, and the specific test results are shown in Table 4.

[0105] Table 4. Thickness of the conductive layer 3 of the composite current collector and the battery internal resistance test results in Example 1 and Examples 15-18

[0106] It can be seen from Table 4 that when the thickness of the conductive layer 3 is between 100 nm and 500 nm, the internal resistance of the battery is between 40 mΩ and 94 mΩ, which meets the use requirements. As the thickness of the conductive layer 3 increases, the internal resistance of the battery gradually decreases.

[0107] Examples 19-28

[0108] The difference between the composite current collectors in Examples 19-28 and the composite current collector in Example 1 is that the metal materials used in the columnar porous array layer 4 of the composite current collectors in Examples 19-28 are different. The specific types and weights of the selected metal materials are shown in Table 5.

[0109] Table 5. Types and qualities of metal materials used in the columnar porous array layer 4 of the composite current collector in Examples 19-28

[0110] As can be seen from Table 5, the material of the columnar porous array layer 4 in the composite current collector of the present invention can be selected from at least one material of aluminum, tin, magnesium, iron, zinc, and silver.

[0111] Examples 29-32

[0112] The difference between the composite current collectors in Examples 29-32 and the composite current collector in Example 1 is that the diameters of the aluminum columns of the columnar porous array layer 4 of the composite current collectors in Examples 29-32 are different. The specific diameters of the aluminum columns of the columnar porous array layer 4 are shown in Table 6. The bonding strengths between the composite current collectors in Examples 1 and 29-32 and the negative electrode materials were tested, and the specific test results are shown in Table 6:

[0113] Table 6. Test results of bonding strength between composite current collector and negative electrode material with different aluminum column diameters

[0114] Table 6 shows that when the diameter of the aluminum pillars in the columnar porous array layer 4 is between 100 and 200 nm, the bonding strength between the composite current collector and the negative electrode material is between levels 0 and 3, meeting the requirements. As the diameter of the aluminum pillars gradually increases from 100 to 200 nm, the bonding strength between the composite current collector and the negative electrode material first increases and then decreases. When the diameter of the aluminum pillars is around 150 nm, the bonding strength between the composite current collector and the negative electrode material is even better.

[0115] Examples 33-34

[0116] The difference between the composite current collectors in Examples 33-34 and the composite current collectors in Example 1 is that the preparation methods of the lithium replenishing layer 5 of the composite current collectors in Examples 33-34 are different. In Example 33, the composite current collectors are assembled with lithium into a lithium half-cell by an electrochemical lithiation method. 2 The lithium-aluminum alloy is discharged to 0V at a current density of 1000 nm to obtain a lithium-aluminum alloy as the lithium replenishing layer 5. In Example 34, a layer of lithium is evaporated on the surface of the composite current collector at a temperature of 350° C. The lithium layer reacts with the aluminum of the columnar porous array layer 4 to obtain a lithium-aluminum alloy as the lithium replenishing layer 5. Then, the first coulombic efficiency and cycle life of 18650 cylindrical batteries (the battery structure is the same as the test part of Example 1 of the present invention) using the composite current collectors of Example 1 and Examples 33-34 as the battery negative electrode current collector are tested respectively. The test results are shown in Table 7:

[0117] Table 7. Battery performance test results using the composite current collectors in Example 1 and Examples 33-34

[0118] As can be seen from Table 7, the lithium replenishment layer 5 prepared by the metal lithium foil hot pressing method, the electrochemical lithiation method and the evaporation method can be applied to the current collector structure of the present invention to achieve a good lithium replenishment effect, and the current collector of the present invention can achieve an initial coulombic efficiency of the battery of 92-96%, and the capacity retention rate of the battery is 80% when the battery is cycled for 8000-15000-120000 cycles, which has excellent initial coulombic efficiency and battery cycle life.

[0119] Examples 35-38

[0120] The difference between the composite current collectors in Examples 35-38 and the composite current collector in Example 1 is that the thickness of the copper-aluminum composite layer in the surface coating layer 6 of the composite current collectors in Examples 35-38 is different, and the specific thickness is shown in Table 8. After being placed in air for one week, they were assembled into 18650 cylindrical batteries (the battery structure was the same as the test part in Example 1), and then the first coulombic efficiency and cycle life of the batteries were tested respectively. The test results are shown in Table 8:

[0121] Table 8. Battery performance test results using the composite current collectors in Example 1 and Examples 35-38

[0122] It can be seen from Table 8 that the composite current collector prepared when the thickness of the copper-aluminum composite layer is in the range of 10 to 30 nm can achieve a good lithium replenishment effect when used in the battery, and the battery's first coulombic efficiency reaches 90 to 95%, and the battery's capacity retention rate is 80% when the cycle is 5000 to 18000, with excellent battery first coulombic efficiency and battery cycle life. In addition, when the thickness of the copper-aluminum composite layer is in the range of 12 to 24 nm, the battery's first coulombic efficiency is 92 to 95%, and the capacity retention rate is 80% when the cycle is 12000 to 18000, and the battery performance is better.

[0123] Examples 39-42

[0124] The difference between the composite current collectors in Examples 39-42 and the composite current collectors in Example 1 is that the thickness of the nanocrystalline graphite islands in the composite current collectors in Examples 39-42 is different, and the specific thicknesses are shown in Table 9. The bonding strength between the composite current collectors and the negative electrode material is then tested, and the test results are shown in Table 9.

[0125] Table 9. Test results of the bonding strength between the composite current collector and the negative electrode material in Examples 39-42

[0126] It can be seen from Table 9 that when the thickness of the nanocrystalline graphite island is 300-500 nm, the bonding strength between the composite current collector and the negative electrode material is level 0-2, which meets the use requirements of the current collector, and when the thickness of the nanocrystalline graphite island is 300-450 nm, the bonding strength is level 0-1, which is better.

[0127] The testing methods used in Examples 2 to 42 of the present invention are the same as the corresponding testing methods in Example 1.

[0128] In summary, the composite current collector of the present invention is used to replenish the metal loss during the metal ion battery cycle by setting a metal supplement layer, and the metal supplement layer exists in the form of a metal alloy, which can avoid metal oxidation and prolong the metal storage time, thereby achieving the replenishment of metal for the entire life cycle of the metal ion battery. By setting a columnar porous array layer, a buffer space can be provided for the thermal expansion of the metal ion cycle, thereby improving the battery's first cycle coulombic efficiency and capacity retention rate, and extending the service life of the metal ion battery. In addition, the composite current collector of the present invention can reduce the thickness and mass of the current collector while ensuring that the basic functions of the current collector are not affected, achieving lightweight, and can increase the interface bonding strength between the current collector and the active material to prevent the active material from falling off.

[0129] While the embodiments of the present invention have been described in detail above, the present invention is not limited to these embodiments. Various modifications are possible within the scope of knowledge possessed by persons of ordinary skill in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another, unless there is a conflict.

Claims

1. A composite current collector, characterized in that: It includes a base layer, a transition layer, a conductive layer, a columnar porous array layer, a metal supplement layer and a surface coating layer which are stacked in sequence; the columnar porous array layer is formed by a metal column array; the material of the metal supplement layer is selected from lithium alloy, sodium alloy or potassium alloy.

2. The composite current collector according to claim 1, characterized in that: The material of the transition layer is an oxide of the conductive metal used in the conductive layer; and / or the material of the base layer is at least one of a conductive polymer and a light polymer film material.

3. The composite current collector according to claim 2, characterized in that: The conductive polymer is selected from at least one of polypyrrole, polyacetylene, polyphenylene, polyacene, polythiophene, pyrolyzed polyacrylonitrile, and pyrolyzed polyvinyl alcohol; and / or the lightweight polymer film material is selected from at least one of polyethylene terephthalate, polyethylene, polyvinyl chloride, polyvinyl alcohol, polypropylene, and polyacrylate.

4. The composite current collector according to claim 1, characterized in that: The surface coating layer comprises a metal alloy layer located on the metal supplementary layer and a nanocrystalline graphite material located on the surface of the metal alloy layer.

5. The composite current collector according to claim 4, characterized in that: The nanocrystalline graphite material is island-shaped nanocrystalline graphite islands; and / or the thickness of the nanocrystalline graphite material is 300-500 nm.

6. The composite current collector according to claim 4, characterized in that: The material of the metal alloy layer includes copper-aluminum alloy; and / or the thickness of the metal alloy layer is 10-30 nm.

7. The composite current collector according to claim 1, characterized in that: The thickness of the transition layer is 50 to 250 nm; and / or the thickness of the conductive layer is 100 to 500 nm; and / or the thickness of the columnar porous array layer is 2 to 5 μm; and / or the thickness of the surface coating layer is 310 to 530 nm.

8. The composite current collector according to claim 1, characterized in that: The material of the metal column is selected from at least one of aluminum, tin, magnesium, iron, zinc, silver and antimony; and / or the diameter of the metal column is 100-200 nm.

9. The composite current collector according to claim 1 or 8, characterized in that: The surface of the metal column has a porous structure.

10. The composite current collector according to claim 1, characterized in that: The material of the conductive layer is copper, and the material of the transition layer is copper oxide.

11. The method for preparing the composite current collector according to any one of claims 1 to 10, characterized in that: The following steps are involved: S1: depositing a transition layer, a conductive layer, and a metal layer on the base layer in sequence; S2: using a metallographic etching agent to corrode the metal layer in step S1 to obtain a columnar porous array layer; S3: forming a metal supplementary layer on the surface of the columnar porous array layer; S4: forming a surface coating layer on the metal supplementary layer to obtain the composite current collector.

12. The method for preparing a composite current collector according to claim 11, characterized in that: The step S1 uses a magnetron sputtering method to deposit a transition layer, a conductive layer, and a metal layer on the substrate; preferably, the gas flow rate of the magnetron sputtering method in the step S1 is 200-400sccm, the deposition power is 1000-2000W, and the bias voltage is 10-100V.

13. The method for preparing a composite current collector according to claim 11, characterized in that: The step S2 is to use a sodium hydroxide solution with a mass percentage of 0.04-0.06% to corrode the metal layer in step S1 for 5-10 minutes to form a columnar porous structure.

14. The method for preparing a composite current collector according to claim 11, characterized in that: The step S3 adopts metal sheet hot pressing method, electrochemical method or evaporation method; preferably, the metal sheet hot pressing method is to hot press the metal sheet and the columnar porous structure under the protection of inert gas, the hot pressing temperature is 60-120°C, and the pressure is 3-5MPa.

15. The method for preparing a composite current collector according to claim 11, characterized in that: The step S4 is: firstly forming a metal alloy layer on the metal supplementary layer by a magnetron sputtering method, and then forming a nanocrystalline graphite material on the metal alloy layer.

16. The method for preparing a composite current collector according to claim 11 or 15, characterized in that: The step S4 is specifically as follows: magnetron sputtering is first performed on the metal supplementary layer by a magnetron sputtering method, with metal target A and metal target B as target materials, and the metal alloy layer is obtained by depositing for 5 to 15 minutes at an argon flow rate of 200 to 400 sccm, a deposition power of metal target A of 500 to 1000 W, a deposition power of metal target B of 50 to 300 W, and a bias voltage of 40 to 60 V, and then magnetron sputtering is performed on the metal alloy layer by a magnetron sputtering method, with a carbon target as the target material, and the carbon tetrafluoride gas flow rate is 200 to 400 sccm, the deposition power of the carbon target is 1000 to 2000 W, and the bias voltage is 40 to 60 V. Deposition is performed for 20 to 40 minutes to obtain a nanocrystalline graphite material.

17. The method for preparing a composite current collector according to claim 11, characterized in that: The preparation method further comprises the steps of cleaning the base layer by using at least one of alcohol washing, alkali washing, acid washing and water washing before step S1, and then performing glow discharge cleaning.

18. A metal ion battery comprising a positive electrode material, a negative electrode material and a positive electrode current collector, characterized in that: The invention also comprises a negative electrode current collector, wherein the negative electrode current collector is the composite current collector according to any one of claims 1 to 10.

19. The metal ion battery according to claim 18, characterized in that: The metal ion battery is selected from lithium ion batteries, sodium ion batteries, and potassium ion batteries.

20. Use of the composite current collector according to any one of claims 1 to 10 in a battery.

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