Composite current collector, its manufacturing method and its application in lithium-ion batteries

Abstract

The present invention relates to the technical field of current collectors, and more particularly to a current collector, its manufacturing method, and its application in lithium-ion batteries. The current collector includes an upper metal layer, a lower metal layer, and a polymer layer disposed between the upper and lower metal layers, wherein the areal densities of the upper and lower metal layers are independently 0.5 to 30 g / m. 2 The size of the metal crystal grains contained in the upper metal layer and the lower metal layer is 50 nm to 5 μm, the sheet resistance of the current collector is 5 to 5000 mΩ / □, and the resistivity is 1 to 5 μΩ cm. The upper metal layer and the lower metal layer of the current collector according to the present invention are characterized by low residual stress and low defects, are lightweight and ultrathin, and have high conductivity, making them well suited for electrochemical devices.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is based on and claims priority from a Chinese application having CN application number 202211665009.5 and filing date December 23, 2022, and a Chinese application having CN application number 202211665082.2 and filing date December 23, 2022, the disclosures of which are hereby incorporated in their entirety into this application.

[0002] The present invention relates to the technical field of current collectors, and in particular to a composite current collector and its manufacturing method and its application in lithium ion batteries. [Background technology]

[0003] Current collectors are one of the important components of lithium-ion batteries, and their role is to support the active materials and collect and conduct electrons. An ideal current collector for lithium-ion batteries should have (1) high electrical conductivity, (2) good chemical and electrochemical stability, (3) high mechanical strength, (4) good compatibility and bonding strength with the electrode active materials, (5) low cost and availability, and (6) light weight.

[0004] Conventional current collectors generally use aluminum foil as the positive electrode current collector and copper foil as the negative electrode current collector. However, copper foil and aluminum foil have difficulty meeting the increasingly high performance requirements for lithium-ion battery current collectors. To improve the performance of current collectors, people have researched and developed composite current collectors. Composite current collectors are generally fabricated by depositing metallic copper or metallic aluminum on a polymer layer as a substrate.

[0005] Current collectors are one of the important components of lithium-ion batteries, and they can not only support the active material but also collect and output electrons generated by the electrode active material. The future development trends of lithium-ion batteries are toward lighter weight, lower cost, and higher energy density, so current collectors must have the properties of ultra-high purity, high conductivity, high strength, high flexibility, and ultra-thinness.

[0006] Due to limitations in manufacturing technology, it is difficult to further reduce the thickness of copper foil and aluminum foil, and they cannot meet people's performance demands for current collectors.

[0007] The performance of copper or aluminum foil current collectors can be optimized by depositing conductive metals, such as Cu or Al, on a polymer layer (e.g., PET). However, conductive metal layers deposited on polymer layers generally have small crystal grains, relatively many grain boundaries, many lattice defects (vacancies, dislocations, etc.), and defects that are subject to large thermal and growth stresses. Therefore, the conductivity of the current collectors needs to be further improved. Summary of the Invention [Problem to be solved by the invention]

[0008] The objective of the present invention is to provide a composite current collector and its manufacturing method and its application in lithium ion batteries, so as to solve the problem of limited conductivity of the composite current collectors existing in the prior art. [Means for solving the problem]

[0009] In order to achieve the above object, a first aspect of the present invention provides a composite current collector including an upper metal layer, a lower metal layer, and a polymer layer located between the upper metal layer and the lower metal layer, wherein the areal densities of the upper metal layer and the lower metal layer are each independently 0.5 to 30 g / m 2 The size of the metal crystal grains contained in each of the upper metal layer and the lower metal layer is 50 nm to 5 μm, the sheet resistance of the current collector is 5 to 5000 mΩ / □, and the resistivity is 1 to 5 μΩ·cm.

[0010] A second aspect of the present invention provides a method for manufacturing a composite current collector, the method comprising: (1) using a conductive metal source as a deposition raw material, depositing an upper conductive metal thin film on the upper surface of a polymer layer and depositing a lower conductive metal thin film on the lower surface of the polymer layer to obtain a current collector intermediate; (2) subjecting the current collector intermediate to a vacuum heat treatment to modify the upper conductive metal thin film and the lower conductive metal thin film, thereby obtaining a composite current collector including an upper metal layer, a polymer layer, and a lower metal layer, in that order.

[0011] According to the above technical solution, the beneficial technical effects obtained by the present invention are as follows: 1) The composite current collector according to the present invention has upper and lower metal layers characterized by low residual stress and low defects, making the current collector not only light and ultrathin, but also highly conductive, and more suitable for electrochemical devices; 2) The method for manufacturing a composite current collector according to the present invention utilizes vacuum heat treatment to alleviate lattice defects in a metal thin film, release residual stress, induce grain growth, and reduce the scattering effect of grain boundaries on free electrons, thereby significantly improving the conductivity of the composite current collector. 3) The composite current collector according to the present invention has the advantages of high conductivity, high strength, high flexibility, and light and ultra-thin, and a lithium ion battery manufactured using the composite current collector according to the present invention has the characteristics of light weight, low cost, and high energy density. 4) The method for producing the composite current collector according to the present invention is simple and suitable for widespread use. [Brief explanation of the drawings]

[0012] The drawings in the specification that form a part of this invention are used to provide a further understanding of the invention, and the exemplary embodiments of the invention and the description thereof are used to interpret the invention and do not constitute undue limitations on the invention. [Figure 1] 1 is a structural schematic diagram of a current collector according to the present invention. [Figure 2]FIG. 2 is a cross-sectional TEM image of the aluminum composite current collector obtained in Example 2. [Figure 3] FIG. 10 is a cross-sectional TEM image of the aluminum composite current collector of Example 4 before heat treatment. [Figure 4] FIG. 10 is a cross-sectional TEM image of the aluminum composite current collector of Example 4 (after heat treatment). [Figure 5] FIG. 10 is a cross-sectional TEM image of the copper composite current collector obtained in Example 9. [Figure 6] FIG. 11 is a cross-sectional TEM image of the copper composite current collector obtained in Example 13. [Figure 7] 1 is a structural schematic diagram of a composite current collector in one preferred embodiment of the present invention. [Figure 8] FIG. 2 is a structural schematic diagram of a composite current collector in another preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The endpoints of any ranges and any value disclosed herein should not be construed as limiting the range or value to that exact range or value, but rather as including values ​​close to those ranges or values. Numerical ranges between the endpoints of each range, between the endpoints of each range and any single point value, and between any single point value can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0014] Although the names of some layers in the composite current collector of the present invention are different from the reference numerals in the drawings, the meanings shown are the same. Specifically, the substrate 20 essentially corresponds to the polymer layer 1, the upper conductive layer 31 essentially corresponds to the upper metal layer 2, and the lower conductive layer 32 essentially corresponds to the lower metal layer 3.

[0015] A first aspect of the present invention provides a composite current collector, as shown in FIG. 1 , comprising an upper metal layer 2, a lower metal layer 3, and a polymer layer 1 located between the upper metal layer 2 and the lower metal layer 3, wherein the areal densities of the upper metal layer 2 and the lower metal layer 3 are each independently 0.5 to 30 g / m 2The size of the metal crystal grains contained in each of the upper metal layer and the lower metal layer is 50 nm to 5 μm, the sheet resistance of the current collector is 5 to 5000 mΩ / □, and the resistivity is 1 to 5 μΩ·cm.

[0016] In the present invention, the areal density of the upper metal layer 2 and the lower metal layer 3 is independently 0.5 to 30 g / m 2 For example, 0.5 g / m 2 , 1g / m 2 , 3g / m 2 , 5g / m 2 , 8g / m 2 , 10g / m 2 , 15g / m 2 , 20g / m 2 , 25g / m 2 , 30g / m 2 , and any value in the range consisting of any two numbers.

[0017] When both the upper metal layer and the lower metal layer are made of aluminum, the areal density of the upper metal layer and the lower metal layer is preferably 4 to 20 g / m 2 and more preferably 7 to 18 g / m 2 is.

[0018] When both the upper metal layer and the lower metal layer are made of copper, the areal density of the upper metal layer and the lower metal layer is preferably 4 to 30 g / m 2 and more preferably 7 to 28 g / m 2 is.

[0019] In the present invention, the size of the metal crystal grains contained in the upper metal layer and the lower metal layer is 50 nm to 5 μm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, and any value within a range consisting of any two numbers, and preferably 300 nm to 3 μm.

[0020] In the present invention, the sheet resistance of the current collector is 5 to 5000 mΩ / □, for example, 5 mΩ / □, 10 mΩ / □, 50 mΩ / □, 100 mΩ / □, 150 mΩ / □, 200 mΩ / □, 300 mΩ / □, 400 mΩ / □, 500 mΩ / □, 600 mΩ / □, 700 mΩ / □, 800 mΩ / □, 900 mΩ / □, 1000 mΩ / □, 1500 mΩ / □, 2000 mΩ / □, 2500 mΩ / □, 3000 mΩ / □, 3500 mΩ / □, 4000 mΩ / □, 4500 mΩ / □, 5000 mΩ / □, and any value within a range consisting of any two numbers, preferably 10 to 1000 mΩ / □.

[0021] In the present invention, the resistivity is 1 to 5 μΩ·cm, for example, 1 μΩ·cm, 1.5 μΩ·cm, 2 μΩ·cm, 2.5 μΩ·cm, 3 μΩ·cm, 3.5 μΩ·cm, 4 μΩ·cm, 4.5 μΩ·cm, 5 μΩ·cm, and any value within a range consisting of any two values.

[0022] Compared with the composite current collector of the prior art, the current collector of the present invention can improve the conductivity by 8% or more and reduce the resistivity by 8% or more. For example, when the material of the metal layer is copper, the resistivity of the current collector of the present invention can be reduced by 30%, and when the material of the metal layer is aluminum, the resistivity of the current collector of the present invention can be reduced by 10%.

[0023] The sheet resistance and resistivity of the current collector of the present invention are significantly superior to those of conventional current collectors. Here, in the present invention, the grain size was measured using a transmission electron microscope (TEM), and the sheet resistance and conductivity tests were performed in accordance with the People's Republic of China National Standard GB / T1552-1995 (Measurement of Resistivity of Silicon and Germanium Single Crystals - In-Line Four-Probe Method). In the present invention, the grain size refers to the size of the metal particles in the upper metal layer 2 and the lower metal layer 3.

[0024] In one preferred embodiment, the material of the polymer layer is selected from one or more of polyethylene (PE), biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyparaphenylene terephthalamide (PPTA), polyimide (PI), polycarbonate (PC), polyether ether ketone (PEEK), polyoxymethylene (POM), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polyvinyl chloride (PVC), polyamide (PA), and polytetrafluoroethylene (PTFE), and preferably, the polymer layer is selected from one of polyethylene terephthalate film, biaxially oriented polypropylene film, and polyimide film with a heat resistance grade of ≧400°C.

[0025] In one preferred embodiment, the polymer layer is selected from one of polyethylene terephthalate film, biaxially oriented polypropylene film, and polyimide film with a heat resistance grade of ≧400° C. Here, all polyethylene terephthalate films and biaxially oriented polypropylene films that can be obtained by those skilled in the art from conventional techniques can be used in the present invention.

[0026] In one preferred embodiment, the thickness of the polymer layer is 0.001 to 0.5 mm, for example, 0.001 mm, 0.005 mm, 0.01 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or any value between the aforementioned values, preferably 0.003 to 0.25 mm.

[0027] In one preferred embodiment, the material of the upper metal layer and the lower metal layer is copper or aluminum.

[0028] In one preferred embodiment, the bonding strength between the upper metal layer and the polymer layer and between the lower metal layer and the polymer layer is 0.5 to 20 N / 15 mm.

[0029] In the present invention, the bonding strength was tested using the national standard of the People's Republic of China GB / T 2792-2014 (test method for peel strength of adhesive tape).

[0030] In one preferred embodiment, the material of the upper metal layer 2 and the lower metal layer 3 is copper or aluminum. In the present invention, when the material of the upper metal layer 2 and the lower metal layer 3 is aluminum, it is a positive electrode current collector, and when the material of the upper metal layer 2 and the lower metal layer 3 is copper, it is a negative electrode current collector.

[0031] In one preferred embodiment, the polymer layer 1 is selected from one of polyethylene terephthalate film, biaxially oriented polypropylene film, and polyimide film with a heat resistance of ≥ 400°C. The biaxially oriented polypropylene film (BOPP) described in the present invention is produced by co-extruding polypropylene particles to form a sheet, which is then stretched in two directions (machine direction and cross direction). Any polyethylene terephthalate film or biaxially oriented polypropylene film available to those skilled in the art from conventional techniques can be used in the present invention.

[0032] In one preferred embodiment, the thickness of the upper metal layer 2 and the lower metal layer 3 is independently 100 to 1500 nm, and may be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, 1200 nm, 1500 nm, or any value between the aforementioned values, and is preferably 100 to 1000 nm.

[0033] In one preferred embodiment, the thickness of the polymer layer 1 is 0.001 to 0.5 mm, for example, 0.001 mm, 0.005 mm, 0.01 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or any value between the aforementioned values, preferably 0.003 to 0.25 mm.

[0034] In one preferred embodiment, the composite current collector further includes an adhesive layer, wherein the adhesive layer is attached to two surfaces of the polymer layer, the upper metal layer and the lower metal layer are respectively located on the adhesive layer and spaced apart from the polymer layer, and the adhesive layer is obtained by curing an adhesive comprising a primary adhesive, an auxiliary adhesive, and a solvent, wherein the primary adhesive is selected from one or more of maleic acid, methylene succinic acid, ethylene succinic acid, methylene adipic acid, guanidinoacetic acid, thioglycolic acid, acrylic acid, methacrylic acid, acrylamide, and glyoxal, and the auxiliary adhesive is selected from one or more of styrene, polystyrene, polyurethane, isocyanate, ethyl acrylate, styrene-butadiene rubber, phenolic resin, urea-formaldehyde resin, epoxy resin, and methyl acrylate.

[0035] Here, in the present invention, depending on the needs of transportation and storage, the main adhesive, auxiliary adhesive, and solvent may be packaged separately, mixed at the time of use, or directly mixed and then packaged.

[0036] Here, in the present invention, the main adhesive and the auxiliary adhesive undergo an in-situ polymerization reaction, and the resulting polymerization product tightly bonds the substrate and the conductive layer, not only improving the bonding strength between the substrate and the conductive layer but also improving the mechanical performance of the substrate and further improving the mechanical performance of the composite current collector.

[0037] Through the above technical solution, the present invention achieves the following beneficial technical effects: 1) The adhesive of the present invention can be used to manufacture a composite current collector, significantly improving the mechanical performance of the composite current collector and increasing the bonding strength between the composite current collector substrate and the conductive layer or underlayer; 2) The composite current collector according to the present invention has a large bonding strength between layers, high mechanical strength, high safety, and a long service life. 3) The method for producing the composite current collector according to the present invention is simple in operation and suitable for widespread industrial application.

[0038] In one preferred embodiment, the primary adhesive is selected from one or two of methylene succinic acid, glyoxal, thioglycolic acid, maleic acid, and guanidinoacetic acid, preferably any two of methylene succinic acid, glyoxal, thioglycolic acid, maleic acid, and guanidinoacetic acid, more preferably methylene succinic acid and any one of glyoxal, thioglycolic acid, maleic acid, and guanidinoacetic acid, and even more preferably methylene succinic acid and glyoxal, wherein the mass ratio of methylene succinic acid to glyoxal is 1:0.5-1.5, preferably 1:0.8-1.2.

[0039] In one preferred embodiment, the mass content of the main adhesive is 1 to 20% based on the total mass of the adhesive.

[0040] Here, in the present invention, the mass content of the main adhesive may be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any value within a range consisting of any two of these values. Preferably, the mass content of the main adhesive is 1 to 10%, more preferably 1 to 4%, based on the total mass of the adhesive.

[0041] In one preferred embodiment, the mass of the auxiliary adhesive is 0.5 to 15% of the mass of the main adhesive.

[0042] Here, in the present invention, the mass of the auxiliary adhesive is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, 15% of the mass of the main adhesive, or any value within a range consisting of any two of these values. Preferably, the mass of the auxiliary adhesive is 0.5 to 6% of the mass of the main adhesive, and more preferably 1 to 3%.

[0043] In one preferred embodiment, the mass content of the auxiliary adhesive is 0.01 to 0.4%, preferably 0.03 to 0.1%.

[0044] In one preferred embodiment, the auxiliary adhesive is selected from one or more of epoxy resin, styrene, isocyanate, and methyl acrylate, and is preferably epoxy resin and / or styrene, wherein the epoxy resin is preferably a liquid epoxy resin.

[0045] In the process of manufacturing a composite current collector, before depositing other layers on a polymer thin film (substrate) using magnetron or vapor deposition, the adhesive of the present invention may be first applied to the polymer layer, and the adhesive may be cured on the polymer layer to form an adhesive layer. This adhesive layer not only improves the connection strength between the polymer layer and the deposited layer, but also reduces the impact of metal particles on the polymer layer during the magnetron and vapor deposition processes, significantly improving the mechanical performance of the composite current collector and the stability and safety of lithium-ion batteries.

[0046] Here, the present invention does not particularly limit the molecular weight of the epoxy resin, polystyrene, polyurethane, styrene-butadiene rubber, phenolic resin, and urea-formaldehyde resin, and those skilled in the art can select them according to actual needs.

[0047] In one preferred embodiment, the solvent is absolute ethanol and / or water, preferably absolute ethanol.

[0048] In one preferred embodiment, the adhesive layer comprises an upper adhesive layer and a lower adhesive layer, wherein the upper adhesive layer is located on the upper surface of the substrate and the lower adhesive layer is located on the lower surface of the substrate.

[0049] In one preferred embodiment, the upper adhesive layer and the lower adhesive layer are each obtained by independently curing an adhesive containing a main adhesive, an auxiliary adhesive, and a solvent.

[0050] In one preferred embodiment, the upper adhesive layer and the lower adhesive layer are made of the same material and have the same thickness. Here, in the present invention, the upper adhesive layer and the lower adhesive layer may be made of the same material and have different thicknesses, and are preferably made of the same material and have the same thickness.

[0051] In one preferred embodiment, the conductive layer is made of copper or aluminum, and when the conductive layer is made of copper, the composite current collector is a negative electrode current collector, and when the conductive layer is made of aluminum, the composite current collector is a positive electrode current collector.

[0052] In one preferred embodiment, the conductive layer includes an upper conductive layer and a lower conductive layer, wherein the upper conductive layer is located on the upper adhesive layer and the lower conductive layer is located on the lower adhesive layer.

[0053] In one preferred embodiment, the upper conductive layer and the lower conductive layer are made of the same material and have the same thickness. Here, in the present invention, the upper conductive layer and the lower conductive layer are made of the same material and may have the same or different thicknesses, preferably the same.

[0054] In one preferred embodiment, the composite current collector further comprises an underlayer, wherein the underlayer is located between the adhesive layer and the conductive layer.

[0055] In one preferred embodiment, the underlayer includes upper and lower underlayers and a lower underlayer, wherein the upper and lower underlayers are located between the upper adhesive layer and the upper conductive layer, and the lower underlayer is located between the lower adhesive layer and the lower conductive layer.

[0056] In one preferred embodiment, the materials of the upper and lower underlayers and the lower underlayer are each independently selected from one or more of nickel, nickel-chromium alloys, and aluminum oxides, and are preferably nickel-chromium alloys, wherein the mass ratio of nickel to chromium in the nickel-chromium alloy is 2 to 5:1.

[0057] In one preferred embodiment, the upper and lower underlayers and the lower underlayer are made of the same material and have the same thickness. Here, in the present invention, the upper and lower underlayers and the lower underlayer may be made of the same material and have different thicknesses, and are preferably made of the same material and thickness.

[0058] In one preferred embodiment, the thickness of the substrate is 2 to 12 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, and any value between two points, preferably 5 to 6 μm.

[0059] In one preferred embodiment, the thickness of the upper adhesive layer and the lower adhesive layer is independently 0.2 to 1 μm, for example, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, or any value between the two points, preferably 0.2 to 0.4 μm.

[0060] In one preferred embodiment, the thickness of the upper conductive layer and the lower conductive layer is independently 0.1 to 1.5 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or any value between the two points, preferably 0.8 to 1.2 μm.

[0061] In one preferred embodiment, the thicknesses of the upper and lower underlayers and the lower underlayer are each independently 0.01 to 0.1 μm, for example, 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, and any value between the two points, preferably 0.01 to 0.04 μm.

[0062] In one preferred embodiment, the bonding strength between the conductive layer and the substrate, or between the underlayer and the substrate, is 0.5 to 20 N / 15 mm, preferably 5 to 10 N / 15 mm, and more preferably 6 to 7.5 N / 15 mm, where the bonding strength is tested in accordance with the National Standard of the People's Republic of China GB / T2792-2014.

[0063] In one preferred embodiment, the composite current collector has a tensile strength of 150 to 400 MPa. When the composite current collector is a negative electrode current collector, the tensile strength of the composite current collector is 200 to 400 MPa, and when the composite current collector is a positive electrode current collector, the tensile strength of the composite current collector is 150 to 400 MPa. The tensile strength was measured in accordance with the National Standard of the People's Republic of China HG / T 2580-2008.

[0064] Here, the tensile strength of the substrate itself is 150-400 MPa, and when an undercoat layer and / or a conductive layer is vapor-deposited on the substrate, the surface of the polymer thin film is easily impacted by metal particles during the magnetron or vapor deposition process, causing a decrease in the tensile strength of the polymer thin film of 50-100 MPa. Through research, the inventors have discovered that the adhesive of the present invention can repair mechanical damage to the substrate, restoring the mechanical performance of the substrate to its original level, or even exceeding it, significantly improving the mechanical performance of the composite current collector, and extending the service life of the composite current collector, thereby broadening the range of applications of the composite current collector.

[0065] In one preferred embodiment, the composite current collector has a longitudinal tensile strength MD of 210 to 240 MPa, preferably 220 to 228 MPa, and a transverse tensile strength TD of 195 to 220 MPa, preferably 202 to 212 MPa.

[0066] A second aspect of the present invention provides a method for manufacturing a composite current collector, said method comprising: (1) using a conductive metal source as a deposition raw material, depositing an upper conductive metal thin film on the upper surface of a polymer layer and depositing a lower conductive metal thin film on the lower surface of the polymer layer to obtain a current collector intermediate; (2) subjecting the current collector intermediate to a vacuum heat treatment to modify the upper conductive metal thin film and the lower conductive metal thin film, thereby obtaining a composite current collector including an upper metal layer, a polymer layer, and a lower metal layer, in that order.

[0067] In the present invention, the conductive metal source is a conductive metal material, including a single metal, an alloy, a composite metal, etc. In the present invention, the conductive metal source is a deposition source. The deposition source refers to a conductive metal material that is vaporized by heating and deposition in a vacuum deposition chamber. The substrate refers to a film material that has been previously deposited, such as a polymer layer.

[0068] Here, in the present invention, the vacuum heat treatment described in step (2) can, on the one hand, induce changes in the metal crystal structure, transforming it from a fibrous structure to a pyramidal structure, a columnar crystal structure, and then to an equiaxed crystal structure, causing some of the fine grain boundaries to disappear; on the other hand, it can induce the growth of fine crystal grains, relieve lattice defects, release residual stress, and give the upper metal layer and lower metal layer the characteristics of low residual stress and low defects.

[0069] The present invention provides appropriate energy to particles in a conductive metal thin film by vacuum heat treatment, for example, by increasing the heat treatment temperature or applying a bias voltage, which can induce changes in the metal crystal structure. In contrast to vacuum heat treatment, recovery at low temperatures relieves stress, induces the tendency for fine crystal grains to grow, and can alleviate lattice defects. Recrystallization and crystal grain growth occur in the temperature range of 270 to 600°C for copper or aluminum.

[0070] Vacuum heat treatment can improve the conductivity, bonding strength, and areal density of the material. That is, heat treatment reduces defects in the metal thin film, increases the thermal diffusion movement between atoms, and makes the metal thin film denser. The resulting material performance is reduced sheet resistance, reduced resistivity, improved bonding strength, and increased areal density.

[0071] The heat treatment of the present invention can grow the crystal grain size from tens of nanometers before heat treatment to hundreds of nanometers, for example, to 300-500 nm, improve resistivity by 2-10%, and reduce sheet resistance by 3-5 mΩ / sq. For example, when detected at the same position, it was found that the crystal grain size before heat treatment was 30 nm and the crystal grain size after heat treatment was 300 nm, the sheet resistance before heat treatment was 38 mΩ / sq, the resistivity was 3.75 μΩ·cm, and the sheet resistance after heat treatment was 30.85 mΩ / sq, the resistivity was 3.03 μΩ·cm. As can be seen from the above, heat treatment brings about very significant improvements.

[0072] In one preferred embodiment, the polymer thin film is selected from one of polyethylene terephthalate film, biaxially oriented polypropylene film, and polyimide film with a heat resistance grade of ≧400° C. Here, all polyethylene terephthalate films and biaxially oriented polypropylene films that can be obtained by those skilled in the art from conventional techniques can be used in the present invention.

[0073] In one preferred embodiment, the thickness of the polymer thin film is 0.001 to 0.5 mm, for example, 0.001 mm, 0.005 mm, 0.01 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or any value between the aforementioned values, preferably 0.003 to 0.25 mm.

[0074] In one preferred embodiment, the thickness of the upper conductive metal thin film is 100 to 1500 nm, preferably 100 to 1000 nm, and the thickness of the lower conductive metal thin film is 100 to 1500 nm, preferably 100 to 1000 nm.

[0075] In one preferred embodiment, the conductive metal source is selected from aluminum wire with a purity of 3N or higher or copper wire with a purity of 3N or higher, where 3N refers to a purity of 99.9 wt% or higher. Aluminum wire with a purity of 3N or higher refers to aluminum wire with a purity of 99.9% or higher, and copper wire with a purity of 3N or higher refers to copper wire with a purity of 99.9 wt% or higher.

[0076] In one preferred embodiment, the deposition method in step (1) is selected from the group consisting of vacuum deposition coating, vacuum sputtering coating, vacuum ion deposition coating, and vacuum chemical vapor deposition coating, and is preferably vacuum deposition coating. In step (1) of the present invention, the deposition of the upper conductive metal thin film and the lower conductive metal thin film on the upper and lower surfaces of the polymer layer is performed independently using the above-mentioned method.

[0077] In one preferred embodiment, the vacuum deposition coating operation includes turning on a deposition source current, heating a conductive metal source, and depositing and forming an upper conductive metal thin film and a lower conductive metal thin film on the surface of the polymer thin film.

[0078] In one preferred embodiment, the operating conditions for the vacuum deposition coating are: The vacuum level is higher than 10-3 Pa; the chill roll temperature is -25°C to 35°C, for example, -25°C, -15°C, -5°C, 0°C, 10°C, 20°C, 25°C, 30°C, 35°C, or any value between the aforementioned values; the ES distance is ≥ 50 mm, for example, 50 mm, 55 mm, 60 mm, 70 mm, 80 mm, 100 mm, 120 mm, or any value between the aforementioned values, preferably 50 to 500 mm; and the deposition temperature is ≥ 800°C, for example, 800°C, 850°C, 900°C, 1000°C, 1100°C, 1200°C, 1500°C, or any value between the aforementioned values, preferably 800 to 2000°C.

[0079] The description of the degree of vacuum is as follows: It is the degree of gas dilution in a vacuum state, and the smaller the value, the more dilution of gas and the higher the degree of vacuum.

[0080] In the present invention, the ES distance refers to the distance between the deposition source and the substrate.

[0081] The deposition source refers to a conductive metal material that is vaporized by heating in a vacuum deposition chamber, and the substrate refers to a pre-deposited film material, such as a polymer thin film.

[0082] In one preferred embodiment, the operating conditions of the vacuum heat treatment described in step (2) include: a vacuum degree higher than 133 Pa, for example, 10 Pa, 10 Pa, or 10 Pa; a vacuum heat treatment temperature of 60 to 600°C, for example, 60°C, 80°C, 100°C, 150°C, 200°C, 300°C, 400°C, 500°C, 600°C, or any value between the aforementioned values, preferably 60 to 500°C; and a vacuum heat treatment time of 3 to 30 min, for example, 3 min, 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min, or any value between the aforementioned values, preferably 5 to 20 min.

[0083] In one preferred embodiment, cooling is performed after the vacuum heat treatment described in step (2), and the cooling is preferably air-cooling or rapid cooling. In the present invention, after the vacuum heat treatment described in step (2), the current collector intermediate is subjected to a cooling operation, and the cooling method can be selected from air-cooling and rapid cooling.

[0084] Air cooling is natural cooling in air. Rapid cooling can be achieved by directly blowing compressed air or liquid nitrogen onto the material, and the cooling rate is faster than that of air cooling. Rapid cooling can maintain the crystalline state at the heat treatment temperature.

[0085] In one preferred embodiment, when the upper conductive metal thin film and the lower conductive metal thin film in the current collector intermediate are each independently an aluminum film, the operating conditions for the vacuum heat treatment include a vacuum degree higher than 133 Pa, for example 10 Pa, 10 Pa, or 10 Pa; a vacuum heat treatment temperature of 60 to 400°C, for example 60°C, 80°C, 100°C, 200°C, 300°C, or 400°C, or any value between the aforementioned values; and a vacuum heat treatment time of 3 to 30 minutes, for example 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes, or any value between the aforementioned values, preferably 5 to 20 minutes.

[0086] In one preferred embodiment, when the upper conductive metal thin film and the lower conductive metal thin film are each independently a copper film, the operating conditions of the vacuum heat treatment include: a vacuum degree higher than 133 Pa, for example 10 Pa, 10 Pa, 10 Pa, or 10 Pa; a vacuum heat treatment temperature of 100 to 600°C, for example 100°C, 120°C, 140°C, 200°C, 300°C, 400°C, 500°C, 600°C, or any value between the aforementioned values, preferably 100 to 500°C; and a vacuum heat treatment time of 3 to 30 min, for example 3 min, 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min, or any value between the aforementioned values, preferably 5 to 20 min.

[0087] In the present invention, since the melting points of copper and aluminum are different, the recrystallization temperatures are also different, and the heat treatment temperature must be determined based on the recrystallization temperatures of both.

[0088] In the present invention, the upper conductive metal layer deposited on the upper surface of the polymer thin film and the lower conductive metal layer deposited on the lower surface of the polymer thin film undergo vacuum heat treatment to alleviate lattice defects in the conductive metal thin film, release residual stress generated during the conductive metal deposition process, induce the growth of crystal grains in the conductive metal, reduce the scattering effect of grain boundaries on free electrons, and effectively improve the conductive performance of the current collector.

[0089] In one preferred embodiment, the method for producing a composite current collector further comprises applying the aforementioned adhesive of the present invention to a substrate, and then depositing an underlayer and / or a conductive layer.

[0090] In the present invention, after the adhesive is applied to the substrate, the solvent gradually evaporates under the application conditions, and the main adhesive and auxiliary adhesive undergo an in-situ polymerization reaction to form a single adhesive layer on the substrate. To further ensure the application effect, a drying treatment may be performed after application is completed.

[0091] In one preferred embodiment, the method of manufacture comprises: (1) applying the adhesive according to the first aspect of the present invention to the upper and lower surfaces of a substrate to obtain a first intermediate body having a structure of upper adhesive layer-substrate-lower adhesive layer; (2) producing an upper conductive layer on the upper adhesive layer and a lower conductive layer on the lower adhesive layer to obtain a composite current collector having a structure of upper conductive layer-upper adhesive layer-substrate-lower adhesive layer-lower conductive layer.

[0092] Here, in the present invention, the structure of upper adhesive layer-substrate-lower adhesive layer means that the first intermediate contains an upper adhesive layer, a substrate, and a lower adhesive layer in this order. The structure of upper conductive layer-upper adhesive layer-substrate-lower adhesive layer-lower conductive layer means that the composite current collector contains an upper conductive layer 31, an upper adhesive layer 21, a substrate 20, a lower adhesive layer 22, and a lower conductive layer 32 in this order, as specifically shown in FIG. 7.

[0093] In one preferred embodiment, the method of manufacture comprises: (1) applying the adhesive according to the first aspect of the present invention to the upper and lower surfaces of a substrate to obtain a first intermediate body having a structure of upper adhesive layer-substrate-lower adhesive layer; (2) manufacturing upper and lower base layers on the upper adhesive layer, and manufacturing a lower base layer on the lower adhesive layer to obtain a second intermediate body having a structure of upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer; (3) Producing an upper conductive layer on the upper and lower base layers, and producing a lower conductive layer on the lower base layer, to obtain a composite current collector having a structure of upper conductive layer-upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer-lower conductive layer.

[0094] Here, in the present invention, the structure of upper adhesive layer-substrate-lower adhesive layer means that the first intermediate contains, in order, an upper adhesive layer, a substrate, and a lower adhesive layer. The structure of upper and lower ground layers-upper adhesive layer-substrate-lower adhesive layer-lower ground layer means that the second intermediate contains, in order, upper and lower ground layers, an upper adhesive layer, a substrate, a lower adhesive layer, and a lower ground layer. The structure of upper conductive layer-upper and lower ground layers-upper adhesive layer-substrate-lower adhesive layer-lower ground layer-lower conductive layer means that the composite current collector contains, in order, an upper conductive layer 31, upper and lower ground layers 41, an upper adhesive layer 21, a substrate 20, a lower adhesive layer 22, a lower ground layer 42, and a lower conductive layer 32, as specifically shown in FIG. 8.

[0095] The present invention does not particularly limit the specific manufacturing conditions for the composite current collector, and the manufacturing can be carried out according to conventional procedures in this field. The underlayer and the conductive layer can be manufactured by vapor deposition, sputtering, and in-situ reaction.

[0096] A third aspect of the present invention provides the application of the current collector according to the first aspect of the present invention or the current collector produced using the method according to the second aspect of the present invention in a lithium ion battery.

[0097] The current collector according to the present invention is characterized by high conductivity, high strength, high flexibility, light weight and extremely thin.

[0098] Polymer materials are lighter and more affordable than metal foils. For the same area and thickness, the current collector of the present invention has a mass that is 59.04% lighter than that of copper foil, thereby reducing the battery weight. The reduced weight of the composite current collector leads to a 5-10% increase in battery energy density.

[0099] Furthermore, the cost of polymers is lower than that of copper-aluminum foils, and the current collectors manufactured by the method of the present invention have improved conductivity compared to conventional current collectors. After the conductivity is improved, the thickness of the metal layer can be further reduced (<1000 nm), further reducing the amount of copper and aluminum used and reducing costs.

[0100] When a battery is manufactured using the current collector produced by the present invention, the safety of the battery is improved compared to batteries manufactured using conventional copper-aluminum foil current collectors. When the battery is short-circuited, the conductive layer is subjected to force at the short-circuit point and cracks and peels off, or is instantaneously melted by the action of the large short-circuit current, thereby breaking the short-circuit current circuit within milliseconds. The polymer layer is subjected to heat at the short-circuit surface and melts, forming a current collector structure that collapses locally, breaking the short-circuit current circuit before thermal runaway occurs, thereby improving battery safety.

[0101] Therefore, a lithium ion battery manufactured using the current collector according to the present invention is characterized by light weight, low cost, and high energy density.

[0102] In order to further understand the present invention, the following clearly and completely describes the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any creative efforts are all within the protection scope of the present invention.

[0103] Unless otherwise stated, all reagents relating to the examples of the present invention are commercially available products and can be purchased through commercial channels.

[0104] In the following examples and comparative examples, Thickness: China National Standard GB / T 11378-2005 (Metallic Coating Layer Thickness Measurement by Contour Meter Method). Areal density: China national standard GB / T 22638.10-2016 (Aluminum foil test method Part 10: Determination of coating areal density). Sheet resistance / resistivity: US ASTM F390 (Standard Test Method for Measuring Sheet Resistance of Thin Metallic Films by the Collinear Four-Probe Method). Bond strength: China national standard GB / T 2792-2014 (test method for peel strength of adhesive tape).

[0105] <Example of a composite current collector that does not include an adhesive layer> Example 1 The thickness of the substrate PET was 6 μm, the evaporation source metal was Al, the Al purity was ≥ 3N, the vacuum degree was 10-4 Pa, the evaporation rate was 5 A / s, and deposition was performed in one go to form 100 nm Al metal layers on the top and bottom surfaces of the substrate PET, respectively. After film formation, the Al composite current collector was subjected to vacuum heat treatment at a vacuum degree of 10-3 Pa, a temperature of 80°C, and a time of 5 minutes.

[0106] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0107] <Example 2> The thickness of the substrate PET was 6 μm, the evaporation source metal was Al, the Al purity was ≥ 3N, the vacuum degree was 10-4 Pa, the evaporation rate was 5 A / s, and deposition was performed in one go to form 1000 nm Al metal layers on the top and bottom surfaces of the substrate PET, respectively. After film formation, the Al composite current collector was subjected to vacuum heat treatment at a vacuum degree of 10-3 Pa, a temperature of 80°C, and a time of 5 minutes.

[0108] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0109] FIG. 2 is a cross-sectional TEM image of the aluminum composite current collector obtained in Example 2. As can be seen from FIG. 2, the crystal grain size is 100 to 300 nm, a large number of line defects exist within the crystal grains, and the conductivity is higher than that of bulk metal Al.

[0110] Example 3 The PET substrate was 6 μm thick, and the evaporation source metal was Al, with an Al purity of ≥ 3N. The vacuum was 10-4 Pa, the evaporation rate was 5 A / s, and deposition was performed in a single step to form 1000 nm Al metal layers on the top and bottom surfaces of the PET substrate. After film formation, the Al composite current collector was subjected to vacuum heat treatment at a vacuum of 10-3 Pa, a temperature of 120°C, and a time of 5 minutes.

[0111] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0112] Example 4 The thickness of the substrate PET was 6 μm, the evaporation source metal was Al, the Al purity was ≥ 3N, the vacuum degree was 10-4 Pa, the evaporation rate was 5 A / s, and deposition was performed in one go to form 1000 nm thick Al metal layers on the top and bottom surfaces of the substrate PET, respectively. After film formation, the Al composite current collector was subjected to vacuum heat treatment at a vacuum degree of 10-3 Pa, a temperature of 180°C, and a time of 5 minutes.

[0113] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0114] 3 and 4 are TEM images of the aluminum composite current collector of Example 4 before and after heat treatment, respectively, showing the cross-sectional structures of the resulting aluminum composite current collector before and after heat treatment. As can be seen from FIGS. 3 and 4, the size of the crystal grains before heat treatment is in the range of 30 to 100 nm, and after heat treatment, the size of the crystal grains is in the range of 300 to 500 nm, and the crystal grains grow, the arrangement of the crystal grains becomes more uniform, defects are reduced, and conductivity is improved.

[0115] <Comparative Example 1> An aluminum composite current collector was produced according to the method of Example 1, with the only difference being that the vacuum heat treatment was not performed on the Al composite current collector after film formation.

[0116] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0117] <Comparative Example 2> An aluminum composite current collector was produced according to the method of Example 2, with the only difference being that the vacuum heat treatment was not performed on the Al composite current collector after film formation.

[0118] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0119] <Example 5> The substrate PI was 7.5 μm thick, and the evaporation source metal was Al, with an Al purity of 3N or higher, at a vacuum level of 10 Pa and a deposition rate of 5 A / s. Deposition was performed in a single step to form 100 nm Al metal layers on the top and bottom surfaces of the substrate PI. After film formation, the Al composite current collector was subjected to vacuum heat treatment at a vacuum level of 10 Pa, a temperature of 150°C, and a time of 5 minutes.

[0120] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0121] Example 6 The substrate PI was 7.5 μm thick, and the evaporation source metal was Al, with an Al purity of 3N or higher, under a vacuum of 10 Pa and a deposition rate of 5 A / s. Deposition was performed in a single step to form 1000 nm thick Al metal layers on the top and bottom surfaces of the substrate PI. The Al composite current collector after film formation was subjected to vacuum heat treatment at a vacuum of 10 Pa, a temperature of 150°C, and a time of 5 minutes.

[0122] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0123] Example 7 The substrate PI was 7.5 μm thick, and the evaporation source metal was Al, with an Al purity of 3N or higher, at a vacuum level of 10 Pa and a deposition rate of 5 A / s. Deposition was performed in a single step to form 1000 nm thick Al metal layers on the top and bottom surfaces of the substrate PI. After film formation, the Al composite current collector was subjected to vacuum heat treatment at a vacuum level of 10 Pa, a temperature of 300°C, and a time of 5 minutes.

[0124] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0125] <Comparative Example 3> An aluminum composite current collector was produced according to the method of Example 5, with the only difference being that the vacuum heat treatment was not performed on the Al composite current collector after film formation.

[0126] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1.

[0127] <Comparative Example 4> An aluminum composite current collector was produced according to the method of Example 6, with the only difference being that the vacuum heat treatment was not performed on the Al composite current collector after film formation.

[0128] The bond strength, surface density, sheet resistance, and resistivity of the aluminum composite current collector determined by the detection are shown in Table 1. [Table 1]

[0129] As can be seen from the data in Table 1, in Example 1, compared to Comparative Example 1, the vacuum heat treatment reduced the sheet resistance and resistivity of the material structure, improved the bonding strength, and increased the areal density of the material. Similarly, in Example 2, compared to Comparative Example 2, in Example 5, compared to Comparative Example 3, and in Example 6, compared to Comparative Example 4, the vacuum heat treatment also improved the conductivity, bonding strength, and areal density of the material.

[0130] Example 8 The PET substrate had a thickness of 6 μm, and the deposition source metal was Cu with a Cu purity of 3N or higher. The vacuum was 10-4 Pa and the deposition rate was 5 A / s. Deposition was performed in a single step to form 100 nm Cu metal layers on the top and bottom surfaces of the PET substrate. The Cu composite current collector after film formation was subjected to vacuum heat treatment at a vacuum of 10-3 Pa, a temperature of 100°C, and a time of 5 minutes.

[0131] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0132] Example 9 The PET substrate had a thickness of 6 μm, and the evaporation source metal was Cu with a Cu purity of 3N or higher. The vacuum level was 10-4 Pa, and the evaporation rate was 5 A / s. Deposition was performed in a single step to form 1000 nm Cu metal layers on the top and bottom surfaces of the PET substrate. The Cu composite current collector after film formation was subjected to vacuum heat treatment at a vacuum level of 10-3 Pa, a temperature of 100°C, and a time of 5 minutes.

[0133] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0134] FIG. 5 is a cross-sectional TEM image of the copper composite current collector obtained in Example 9. As can be seen from FIG. 5, the size of the copper metal crystal grains is 100 to 400 nm, the crystal grain boundaries are clear, the orientation inside the crystal grains is almost uniform, and the conductivity is high.

[0135] Example 10 The PET substrate had a thickness of 6 μm, and the evaporation source metal was Cu with a Cu purity of 3N or higher. The vacuum level was 10-4 Pa, and the evaporation rate was 5 A / s. Deposition was performed in a single step to form 1000 nm Cu metal layers on the top and bottom surfaces of the PET substrate. The Cu composite current collector after film formation was subjected to vacuum heat treatment at a vacuum level of 10-3 Pa, a temperature of 150°C, and a time of 5 minutes.

[0136] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0137] Example 11 The PET substrate had a thickness of 6 μm, and the evaporation source metal was Cu with a Cu purity of 3N or higher. The vacuum degree was 10-4 Pa, and the evaporation rate was 5 A / s. Deposition was performed in a single step to form 1000 nm Cu metal layers on the top and bottom surfaces of the PET substrate. The Cu composite current collector after film formation was subjected to vacuum heat treatment at a vacuum degree of 10-3 Pa, a temperature of 180°C, and a time of 5 minutes.

[0138] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0139] <Comparative Example 5> A copper composite current collector was produced according to the method of Example 8, with the only difference being that the vacuum heat treatment was not performed on the Cu composite current collector after film formation.

[0140] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0141] <Comparative Example 6> A copper composite current collector was produced according to the method of Example 9, with the only difference being that the vacuum heat treatment was not performed on the Cu composite current collector after film formation.

[0142] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0143] Example 12 The PI substrate was 7.5 μm thick, and the evaporation source metal was Cu with a Cu purity of 3N or higher, under a vacuum of 10 Pa and a deposition rate of 5 A / s. A 100 nm Cu metal layer was formed on each of the top and bottom surfaces of the PI substrate in a single deposition run. The Cu composite current collector after film formation was subjected to vacuum heat treatment at a vacuum of 10 Pa, a temperature of 100°C, and a time of 5 minutes.

[0144] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0145] Example 13 The PI substrate was 7.5 μm thick, and the evaporation source metal was Cu with a Cu purity of 3N or higher, under a vacuum of 10 Pa and a deposition rate of 5 A / s. Deposition was performed in a single step to form 800 nm Cu metal layers on the top and bottom surfaces of the PI substrate. The Cu composite current collector after film formation was subjected to vacuum heat treatment at a vacuum of 10 Pa, a temperature of 100°C, and a time of 5 minutes.

[0146] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0147] FIG. 6 is a cross-sectional TEM image of the copper composite current collector obtained in Example 13. As can be seen from FIG. 6, after the vacuum heat treatment, the copper metal crystal grain size was 239.8 nm, the resistivity was 1.74 μΩ cm, and the conductivity was close to that of bulk Cu.

[0148] Example 14 The PI substrate was 7.5 μm thick, and the evaporation source metal was Cu with a Cu purity of 3N or higher. The vacuum level was 10 Pa, the evaporation rate was 5 A / s, and deposition was performed in a single step to form 800 nm Cu metal layers on the top and bottom surfaces of the PI substrate. After film formation, the Cu composite current collector was subjected to vacuum heat treatment at a vacuum level of 10 Pa, a temperature of 200°C, and a time of 5 minutes.

[0149] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0150] Example 15 The PI substrate was 7.5 μm thick, and the evaporation source metal was Cu with a Cu purity of 3N or higher, under a vacuum of 10 Pa and a deposition rate of 5 A / s. Deposition was performed in a single step to form 800 nm Cu metal layers on the top and bottom surfaces of the PI substrate. The Cu composite current collector after film formation was subjected to vacuum heat treatment at a vacuum of 10 Pa, a temperature of 400°C, and a time of 5 minutes.

[0151] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0152] <Comparative Example 7> An aluminum composite current collector was produced according to the method of Example 12, with the only difference being that the vacuum heat treatment was not performed on the Cu composite current collector after film formation.

[0153] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2.

[0154] <Comparative Example 8> An aluminum composite current collector was produced according to the method of Example 13, with the only difference being that the vacuum heat treatment was not performed on the Cu composite current collector after film formation.

[0155] The bond strength, surface density, sheet resistance, and resistivity of the copper composite current collector determined by the detection are shown in Table 2. [Table 2]

[0156] As can be seen from the data in Table 2, comparing Example 8 with Comparative Example 5, the heat treatment reduced the sheet resistance and resistivity of the material structure, improved the bond strength, and increased the areal density of the material; similarly, comparing Example 9 with Comparative Example 6, comparing Example 12 with Comparative Example 7, and comparing Example 13 with Comparative Example 8, the heat treatment also improved the conductivity, bond strength, and areal density of the material.

[0157] As can be seen from the data in Tables 1 and 2, the upper conductive metal layer deposited on the upper surface of the polymer thin film and the lower conductive metal layer deposited on the lower surface of the polymer thin film undergo vacuum heat treatment to alleviate lattice defects in the conductive metal thin film, release residual stress generated during the conductive metal deposition process, induce grain growth in the conductive metal, reduce the scattering effect of grain boundaries on free electrons, and effectively improve the conductive performance of the current collector.

[0158] <Example of a composite current collector including an adhesive layer> Here, the liquid epoxy resin was purchased from Henan Shuizhihuan Industrial Co., Ltd., and the product number is NPEL128.

[0159] Example 1 (1) Using a microgravure coater, an adhesive is applied to the upper and lower surfaces of a polyethylene terephthalate film having a thickness of 6 μm under the conditions of a running speed of 0.5 m / min, a take-up tension of 16 N, an unwinding tension of 14 N, and an oven temperature of 80° C., to obtain a first intermediate having a structure of an upper adhesive layer-substrate-lower adhesive layer; Here, the adhesive is a mixture of methylene succinic acid, glyoxal, epoxy resin and anhydrous ethanol, containing 1.5 wt% methylene succinic acid, 1.5 wt% glyoxal and 0.03 wt% epoxy resin, and the upper adhesive layer and the lower adhesive layer are the same and both have a thickness of 0.2 μm. (2) depositing one nickel-chromium alloy layer on each of the upper and lower surfaces of the first intermediate body to obtain a second intermediate body having a structure of upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer, wherein the upper and lower base layers and the lower base layer are the same and have a thickness of 0.01 μm, and the mass ratio of nickel to chromium in the nickel-chromium alloy is 3:1; (3) A copper layer was vapor-deposited on each of the upper and lower surfaces of the second intermediate to obtain a composite current collector having a structure of upper conductive layer-upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer-lower conductive layer, where the upper conductive layer and the lower conductive layer were the same and each had a thickness of 1 μm.

[0160] <Example 2> (1) Using a microgravure coater, an adhesive is applied to the upper and lower surfaces of a polyethylene terephthalate film having a thickness of 6 μm under the conditions of a running speed of 0.5 m / min, a take-up tension of 16 N, an unwinding tension of 14 N, and an oven temperature of 80° C., to obtain a first intermediate having a structure of an upper adhesive layer-substrate-lower adhesive layer; Here, the adhesive is a mixture of methylene succinic acid, thioglycolic acid, styrene and anhydrous ethanol, containing 2 wt% methylene succinic acid, 2 wt% thioglycolic acid and 0.08 wt% styrene, the upper adhesive layer and the lower adhesive layer are the same and both have a thickness of 0.3 μm, (2) depositing one nickel-chromium alloy layer on each of the upper and lower surfaces of the first intermediate body to obtain a second intermediate body having a structure of upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer, wherein the upper and lower base layers and the lower base layer are the same and have a thickness of 0.02 μm, and the mass ratio of nickel to chromium in the nickel-chromium alloy is 3:1; (3) A layer of copper was vapor-deposited onto each of the upper and lower surfaces of the second intermediate body to obtain a composite current collector having a structure of upper conductive layer-upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer-lower conductive layer, where the upper conductive layer and the lower conductive layer were the same and each had a thickness of 1 μm.

[0161] Example 3 (1) Using a microgravure coater, an adhesive is applied to the upper and lower surfaces of a polyethylene terephthalate film having a thickness of 6 μm under the conditions of a running speed of 0.5 m / min, a take-up tension of 16 N, an unwinding tension of 14 N, and an oven temperature of 80° C., to obtain a first intermediate having a structure of an upper adhesive layer-substrate-lower adhesive layer; Here, the adhesive is a mixture of methylene succinic acid, styrene, and anhydrous ethanol, containing 1 wt% methylene succinic acid and 0.03 wt% styrene, and the upper adhesive layer and the lower adhesive layer are the same and each have a thickness of 0.4 μm. (2) depositing one nickel-chromium alloy layer on each of the upper and lower surfaces of the first intermediate body to obtain a second intermediate body having a structure of upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer, where the upper and lower base layers and the lower base layer are the same and have a thickness of 0.04 μm, and the mass ratio of nickel to chromium in the nickel-chromium alloy is 3:1; (3) A layer of copper was vapor-deposited onto each of the upper and lower surfaces of the second intermediate body to obtain a composite current collector having a structure of upper conductive layer-upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer-lower conductive layer, where the upper conductive layer and the lower conductive layer were the same and each had a thickness of 1 μm.

[0162] Example 4 (1) Using a microgravure coater, an adhesive is applied to the upper and lower surfaces of a 4.5 μm thick polyethylene terephthalate film under the conditions of a running speed of 0.5 m / min, a take-up tension of 16 N, an unwinding tension of 14 N, and an oven temperature of 80° C. to obtain a first intermediate having a structure of upper adhesive layer-substrate-lower adhesive layer; Here, the adhesive is a mixture of maleic acid, isocyanate, and anhydrous ethanol, containing 6 wt% maleic acid and 0.36 wt% isocyanate, and the upper adhesive layer and the lower adhesive layer are the same and both have a thickness of 0.6 μm. (2) Vaporizing one layer of nickel on each of the upper and lower surfaces of the first intermediate body to obtain a second intermediate body having a structure of upper and lower base layers - upper adhesive layer - substrate - lower adhesive layer - lower base layer, where the upper and lower base layers and the lower base layer are the same and each have a thickness of 0.05 μm; (3) A layer of copper was vapor-deposited onto each of the upper and lower surfaces of the second intermediate body to obtain a composite current collector having a structure of upper conductive layer-upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer-lower conductive layer, where the upper conductive layer and the lower conductive layer were the same and each had a thickness of 1 μm.

[0163] <Example 5> (1) Using a microgravure coater, an adhesive is applied to the upper and lower surfaces of an 8 μm thick polyethylene terephthalate film under the conditions of a running speed of 0.5 m / min, a take-up tension of 16 N, an unwinding tension of 14 N, and an oven temperature of 80° C. to obtain a first intermediate having a structure of upper adhesive layer-substrate-lower adhesive layer; Here, the adhesive is a mixture of guanidinoacetic acid, methyl acrylate and absolute ethanol, containing 8 wt% guanidinoacetic acid and 0.04 wt% methyl acrylate, and the upper adhesive layer and the lower adhesive layer are the same and both have a thickness of 0.8 μm. (2) depositing a layer of aluminum oxide on each of the upper and lower surfaces of the first intermediate body to obtain a second intermediate body having a structure of upper and lower base layers - upper adhesive layer - substrate - lower adhesive layer - lower base layer, where the upper and lower base layers and the lower base layer are the same and each have a thickness of 0.06 μm; (3) A layer of copper was vapor-deposited onto each of the upper and lower surfaces of the second intermediate body to obtain a composite current collector having a structure of upper conductive layer-upper and lower base layers-upper adhesive layer-substrate-lower adhesive layer-lower base layer-lower conductive layer, where the upper conductive layer and the lower conductive layer were the same and each had a thickness of 1 μm.

[0164] Example 6 This is the same as Example 1, except that the conductive layer is an aluminum layer and the material of the underlayer is an oxide of aluminum.

[0165] <Comparative Example 1> The difference from Example 1 is that the adhesive layer is omitted.

[0166] <Comparative Example 2> JPEG2025540476000004.jpg23170

[0167] <Comparative Example 3> The difference compared to Example 5 is that the adhesive is an acrylic resin curing adhesive, purchased from Shenzhen Kunyang Technology Co., Ltd., with the product name 3M DP810NS.

[0168] <Test Example 1> The mechanical performance of the composite current collectors manufactured in the examples and comparative examples was characterized, and the results are shown in Table 1. The tensile strength of the composite current collectors was tested in accordance with the National Standard of the People's Republic of China HG / T 2580-2008. MD is the tensile strength in the machine direction (MPa), and TD is the tensile strength in the transverse direction (MPa).

[0169] The bonding strength between the underlayer and the substrate was tested in accordance with the National Standard of the People's Republic of China GB / T2792-2014. The bonding strength between the upper and lower underlayers and the substrate, and the bonding strength between the lower underlayer and the substrate were measured separately, and then the average value was taken. [Table 1]

[0170] <Test Example 2> The current collectors manufactured in the examples and comparative examples were assembled into batteries, and the performance parameters of the batteries were tested. The test results are shown in Table 2.

[0171] The battery is assembled as follows.

[0172] LiNi0.5Co0.2Mn0.3O2, adhesive polyvinylidene fluoride, and conductive agent carbon black were mixed in a ratio of 95:3:2 by weight, and 43 parts by weight of N-methyl-2-pyrrolidone was added to 100 parts by weight of the mixture and stirred to obtain a positive electrode slurry. The positive electrode slurry was uniformly applied to both sides of a positive electrode current collector, with the application weight on one side being 205 g / m2, and then dried, roll pressed, die-cut, and punched to obtain a positive electrode plate.

[0173] Graphite particles, styrene butadiene rubber adhesive, sodium carboxymethylcellulose, and carbon black conductive agent were mixed in a ratio of 95:2.5:1.5:1 by weight, and 82 parts by weight of water were added to 100 parts by weight of the mixture and stirred to obtain a negative electrode slurry. The negative electrode slurry was uniformly applied to both sides of a negative electrode current collector, with a coating weight of 100 g / m2 per side, and then dried, roll-pressed, die-cut, and punched to obtain a negative electrode plate.

[0174] In a glove box filled with argon gas, the water content and oxygen gas content of which were both less than 5 ppm, the positive electrode plate, PP / PE / PP separator, and negative electrode plate were wound together into a bare cell, which was then placed in a battery case. An electrolyte (the volume ratio of EC:EMC was 3:7, and LiPF6 was 1 mol / L) was injected, and then sealing and chemical formation processes were carried out to obtain a lithium ion secondary battery (hereinafter referred to as the battery).

[0175] When the composite current collectors produced in Examples 1 to 5 are used as negative electrode current collectors, the positive electrode current collector in the battery is aluminum foil. When the composite current collector produced in Example 6 is used as positive electrode current collector, the positive electrode current collector in the battery is copper foil.

[0176] The charge / discharge voltage range was controlled to 3 to 4.3 V, and the battery was subjected to a charge / discharge test at 0.2 C three times at room temperature. The average values ​​of the three tests were obtained, and the initial discharge capacity, initial charge / discharge efficiency, and energy density of the battery were evaluated.

[0177] The charge / discharge voltage range was controlled to 3 to 4.3 V, and the battery was subjected to three charge / discharge cycles at 0.2 C at a constant temperature of 45°C to obtain the standard capacity. Then, a charge / discharge cycle was performed at 1 C, and the number of cycles when the capacity decreased to 70% was recorded. [Table 2]

[0178] Although the preferred embodiments of the present application have been described in detail above, the present invention is not limited thereto. Within the scope of the technical idea of ​​the present invention, various simple modifications can be made to the technical solution of the present invention, including combining each technical feature in any other suitable manner, and these simple modifications and combinations should also be considered as the contents disclosed in the present invention, and all fall within the protection scope of the present invention. [Explanation of symbols]

[0179] 20 Base material 21 Upper adhesive layer 22 Lower adhesive layer 31 Upper conductive layer 32 Lower conductive layer 41 Upper and lower strata 42 Subsoil layer 1 polymer layer 2 Upper metal layer 3 Lower metal layer

Claims

1. A composite current collector comprising an upper metal layer, a lower metal layer, and a polymer layer located between the upper metal layer and the lower metal layer, wherein the areal density of the upper metal layer and the lower metal layer is independently 0.5 to 30 g / m ２ wherein the size of the metal crystal grains contained in each of the upper metal layer and the lower metal layer is 50 nm to 5 μm, the sheet resistance of the composite current collector is 5 to 5000 mΩ / □, and the resistivity is 1 to 5 μΩ cm.

2. 2. The composite current collector according to claim 1, wherein the material of the polymer layer is selected from one or more of polyethylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene naphthalate, polyparaphenylene terephthalamide, polyimide, polycarbonate, polyether ether ketone, polyoxymethylene, polyphenylene sulfide, polyphenylene oxide, polyvinyl chloride, polyamide, and polytetrafluoroethylene; preferably, the polymer layer is selected from one of polyethylene terephthalate film, biaxially oriented polypropylene film, and polyimide film with a heat resistance grade of ≧400°C.

3. 2. The composite current collector according to claim 1, wherein the material of the upper metal layer and the lower metal layer is copper or aluminum.

4. 4. The composite current collector according to claim 1, wherein the bonding strength between the upper metal layer and the polymer layer and between the lower metal layer and the polymer layer is 0.5 to 20 N / 15 mm.

5. the thickness of the upper metal layer and the thickness of the lower metal layer are each independently 100 to 1500 nm, preferably 100 to 1000 nm; A composite current collector according to any one of claims 1 to 3, characterized in that the thickness of the polymer layer is preferably between 0.001 and 0.5 mm, preferably between 0.003 and 0.25 mm.

6. the composite current collector further comprises an adhesive layer, wherein the adhesive layer is attached to two surfaces of the polymer layer, and the upper metal layer and the lower metal layer are respectively located on the adhesive layer and spaced apart from the polymer layer; 4. The composite current collector according to claim 1, wherein the adhesive layer is obtained by curing an adhesive comprising a primary adhesive, an auxiliary adhesive, and a solvent, wherein the primary adhesive is selected from one or more of maleic acid, methylene succinic acid, ethylene succinic acid, methylene adipic acid, guanidinoacetic acid, thioglycolic acid, acrylic acid, methacrylic acid, acrylamide, and glyoxal, and the auxiliary adhesive is selected from one or more of styrene, polystyrene, polyurethane, isocyanate, ethyl acrylate, styrene-butadiene rubber, phenolic resin, urea-formaldehyde resin, epoxy resin, and methyl acrylate.

7. 7. The composite current collector according to claim 6, wherein, based on the total mass of the adhesive, the mass content of the main adhesive is 1 to 20%, the mass content of the auxiliary adhesive is 0.5 to 15% of the mass of the main adhesive, and the solvent is preferably water, preferably deionized water.

8. The adhesive layer includes an upper adhesive layer and a lower adhesive layer, wherein the upper adhesive layer is located on the upper surface of the polymer layer, and the lower adhesive layer is located on the lower surface of the polymer layer. Preferably, the upper adhesive layer and the lower adhesive layer are obtained by independently curing an adhesive containing a main adhesive, an auxiliary adhesive, and a solvent. Preferably, the upper adhesive layer and the lower adhesive layer are made of the same material and have the same thickness.

7. The composite current collector according to claim 6, wherein the upper metal layer is located on the upper adhesive layer, and the lower metal layer is located on the lower adhesive layer, and preferably the upper metal layer and the lower metal layer are made of the same material and have the same thickness.

9. the composite current collector further includes an underlayer, wherein the underlayer is located between the adhesive layer and the upper metal layer, or the underlayer is located between the adhesive layer and the lower metal layer; Preferably, the material of the underlayer is selected from one or more of nickel, nickel-chromium alloy, and aluminum oxide; Preferably, the adhesive layer includes an upper adhesive layer and a lower adhesive layer, the underlayer includes upper and lower underlayers and a lower underlayer, the upper adhesive layer is located on the upper surface of the polymer layer, the lower adhesive layer is located on the lower surface of the polymer layer, the upper metal layer is located on the upper adhesive layer, the lower metal layer is located on the lower adhesive layer, the upper and lower underlayers are located between the upper adhesive layer and the upper metal layer, and the lower underlayer is located between the lower adhesive layer and the lower metal layer, Preferably, the materials of the upper and lower underlayers and the lower underlayer are each independently selected from one or more of nickel, nickel-chromium alloy, and aluminum oxide; 9. The composite current collector according to claim 8, wherein the upper and lower underlayers and the lower underlayer are preferably made of the same material and have the same thickness.

10. The method comprises: (1) using a conductive metal source as a deposition raw material, depositing an upper conductive metal thin film on the upper surface of a polymer layer and depositing a lower conductive metal thin film on the lower surface of the polymer layer to obtain a current collector intermediate; (2) performing a vacuum heat treatment on the current collector intermediate to modify the upper conductive metal thin film and the lower conductive metal thin film, thereby obtaining a current collector including an upper metal layer, a polymer layer, and a lower metal layer, in that order.

11. 11. The method of claim 10, wherein the conductive metal source is selected from copper wire with a purity of ≥ 3N or aluminum wire with a purity of ≥ 3N.

12. The deposition process in step (1) is selected from one of vacuum deposition coating, vacuum sputtering coating, vacuum ion coating, and vacuum chemical vapor deposition coating, and is preferably vacuum deposition coating; Preferably, the vacuum deposition coating operation includes turning on a deposition source current, heating a conductive metal source, and depositing and forming an upper conductive metal thin film and a lower conductive metal thin film on the surface of the polymer layer; The manufacturing method according to claim 10, wherein the operation conditions of the vacuum deposition coating preferably include: a vacuum degree higher than 10-3 Pa; a chill roll temperature between -25°C and 35°C; an ES distance ≥ 50 mm, preferably 50-500 mm; and a deposition temperature ≥ 800°C, preferably 800-2000°C.

13. The operating conditions of the vacuum heat treatment described in step (2) include: a degree of vacuum higher than 133 Pa; a vacuum heat treatment temperature of 60 to 600°C, preferably 60 to 500°C; and a vacuum heat treatment time of 3 to 30 minutes, preferably 5 to 20 minutes; The method according to claim 10, wherein the vacuum heat treatment in step (2) is preferably followed by cooling, and the cooling is preferably air cooling or rapid cooling.

14. When the upper conductive metal thin film and the lower conductive metal thin film are each independently an aluminum film, the operating conditions of the vacuum heat treatment include a degree of vacuum higher than 133 Pa, a vacuum heat treatment temperature of 60 to 400°C, and a vacuum heat treatment time of 3 to 30 minutes, preferably 5 to 20 minutes; Preferably, when the upper conductive metal thin film and the lower conductive metal thin film are each independently a copper film, the operating conditions of the vacuum heat treatment include a degree of vacuum higher than 133 Pa, a vacuum heat treatment temperature of 100 to 600°C, preferably 100 to 500°C, and a vacuum heat treatment time of 3 to 30 minutes, preferably 5 to 20 minutes.

15. The manufacturing method further comprises applying an adhesive onto the polymer layer and then depositing an underlayer and / or a conductive layer; Preferably, the manufacturing method comprises: (1) applying adhesive to the upper and lower surfaces of a polymer layer to obtain a first intermediate body having a structure of upper adhesive layer-polymer layer-lower adhesive layer; (2) fabricating an upper conductive layer on the upper adhesive layer and a lower conductive layer on the lower adhesive layer to obtain a composite current collector with a structure of upper conductive layer-upper adhesive layer-polymer layer-lower adhesive layer-lower conductive layer; Preferably, the manufacturing method comprises: (1) applying adhesive to the upper and lower surfaces of a polymer layer to obtain a first intermediate body having a structure of upper adhesive layer-polymer layer-lower adhesive layer; (2) manufacturing upper and lower base layers on the upper adhesive layer, and manufacturing a lower base layer on the lower adhesive layer to obtain a second intermediate body having a structure of upper and lower base layers - upper adhesive layer - polymer layer - lower adhesive layer - lower base layer; (3) producing an upper conductive layer on the upper and lower base layers, and a lower conductive layer on the lower base layer, to obtain a composite current collector having a structure of upper conductive layer-upper and lower base layers-upper adhesive layer-polymer layer-lower adhesive layer-lower base layer-lower conductive layer.

16. 16. Application of the composite current collector according to any one of claims 1 to 9 or the composite current collector produced by the production method according to any one of claims 10 to 15 in a lithium ion battery.

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