Copper material with self-assembled nano film layer on surface, preparation method of copper material, negative current collector, negative pole piece and battery monomer

Abstract

The invention discloses a copper material with a self-assembled nano film layer on the surface, a preparation method of the copper material, a negative current collector, a negative pole piece and a battery monomer. The copper material comprises a copper material base body and a film layer arranged on at least part of the surface of the copper material base body; the film layer comprises a coordination structure Cu (BF4-) 42 + and thiophene connected with the coordination structure Cu (BF4-) 42 + through an intermolecular force, and the thiophene comprises one or more of a thiophene compound and a thiophene polymer; the thickness of the film layer ranges from 20 nm to 100 nm. According to the embodiment of the invention, the conductivity of the copper material can be improved, and meanwhile, the corrosion resistance and the high-temperature oxidation resistance of the copper material are improved.

Description

Technical Field

[0001] The present application relates to a copper material with a self-assembled nanometer film layer on its surface, a preparation method thereof, a negative electrode current collector, a negative electrode plate and a battery cell monomer. Background Art

[0002] In the related art, when performing anti-corrosion treatment on the copper surface to block the oxidation of the copper substrate by corrosion media such as oxygen and moisture, coating technologies are usually adopted, for example, using rust-proof paint, varnish, resin or wax agent to coat on the copper surface to form a physical isolation layer.

[0003] The thickness of the film layer formed on the copper surface by the coating technology is in the micron level or even higher, which will reduce the electrical conductivity of the copper. Summary of the Invention

[0004] Embodiments of the present application provide a copper material with a self-assembled nanometer film layer on its surface, a preparation method thereof, a negative electrode current collector, a negative electrode plate and a battery cell monomer, which can improve the electrical conductivity of the copper material, and at the same time improve the corrosion resistance and high-temperature oxidation resistance of the copper material.

[0005] In a first aspect, embodiments of the present application provide a copper material with a self-assembled nanometer film layer on its surface. The copper material includes a copper material substrate and a film layer provided on at least a part of the surface of the copper material substrate; the film layer includes a coordination structure Cu(BF4 - )4 2+ and thiophene connected to the coordination structure Cu(BF4 - )4 2+ through intermolecular forces. The thiophene includes one or more of thiophene compounds and thiophene polymers; the thickness of the film layer is 20-100 nm.

[0006] The film layer provided by the embodiments of the present application has thiophene, which can improve the electrical conductivity and antioxidant property of the film layer; while BF4 - can form a coordination structure with Cu 2+ on the one hand, and can be connected to thiophene through intermolecular forces on the other hand, so as to form a conductive network of Cu 2+ -BF4 - -thiophene, further improving the electrical conductivity of the film layer; at the same time, the thickness of the film layer is in the nanometer level, which has a lower resistance compared with the micron level in the related art, and can reduce the influence of the film layer on the electrical conductivity of the copper material, thereby better improving the electrical conductivity of the copper material. Thus, the electrical conductivity of the copper material can be improved, and at the same time, the corrosion resistance and high-temperature oxidation resistance of the copper material can also be improved.

[0007] In some embodiments, the molecular weight ratio of the coordination structure Cu(BF4 - )4 2+ to thiophene is 1:(0.8-1.2).

[0008] In some embodiments, the thiophene compound includes one or more of 3-thiophenemethanol, 3,4-ethylenedioxythiophene, and 3-hexylthiophene, and the thiophene polymer includes one or more of 3-thiophenemethanol polymer, 3,4-ethylenedioxythiophene polymer, and 3-hexylthiophene polymer.

[0009] In some embodiments, the coordination structure Cu(BF4 - )4 2+ is obtained by coordinating a copper ion with an ionic liquid containing tetrafluoroborate.

[0010] In some embodiments, at 20 °C, the resistivity of the copper material is 2.05 - 2.80 μΩ•cm.

[0011] In a second aspect, an embodiment of the present application provides a method for preparing a copper material with a self-assembled nanomembrane layer on its surface, including the following steps: providing a copper material substrate, providing a film-forming solution, the film-forming solution including an ionic liquid containing tetrafluoroborate, thiophene, and an acid; placing the film-forming solution on the surface of the copper material substrate for heat treatment to obtain a copper material with a self-assembled nanomembrane layer on its surface having a film layer, the film layer including the coordination structure Cu(BF4 - )4 2+ and thiophene connected by intermolecular forces to the coordination structure Cu(BF4 - )4 2+ wherein the thiophene includes one or more of a thiophene compound and a thiophene polymer, and the thickness of the film layer is 20 - 100 nm.

[0012] In some embodiments, the ionic liquid containing tetrafluoroborate includes one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butylimidazolium tetrafluoroborate, and 1-methyl-3-butylimidazolium tetrafluoroborate, the thiophene includes one or more of 3-thiophenemethanol, 3,4-ethylenedioxythiophene, and 3-hexylthiophene, and the acid includes one or more of concentrated sulfuric acid and concentrated nitric acid.

[0013] In some embodiments, the mass ratio of the ionic liquid containing tetrafluoroborate to thiophene is 1:(0.03 - 0.04); based on the film-forming solution, the molar concentration of the acid is 0.001 - 0.002 M.

[0014] In some embodiments, during the heat treatment of placing the film-forming solution on the surface of the copper material substrate, the temperature of the heat treatment is 60 - 100 °C, and the time is 20 - 50 min.

[0015] In a third aspect, an embodiment of the present application provides a negative electrode current collector, including a copper material substrate and a film layer provided on at least a part of the surface of the copper material substrate; the film layer includes the coordination structure Cu(BF4 - )4 2+and the coordination structure Cu(BF4 - )4 2+ Thiophene connected by intermolecular forces, and the thiophene includes one or more of thiophene compounds and thiophene polymers; the thickness of the film layer is 20-100 nm.

[0016] In a fourth aspect, an embodiment of the present application provides a negative electrode tab, including the negative electrode current collector of the third aspect and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material.

[0017] In a fifth aspect, an embodiment of the present application provides a battery cell, including the negative electrode tab of the fourth aspect.

[0018] Beneficial effects The film layer provided by the embodiment of the present application has thiophene, which can improve the conductivity and antioxidant properties of the film layer; while BF4 - On the one hand, it can form a coordination structure with Cu 2+ On the other hand, it can be connected to thiophene through intermolecular forces, thereby forming a Cu 2+ -BF4 - -thiophene conductive network, further improving the conductivity of the film layer; at the same time, the thickness of the film layer is nanoscale, which has lower resistance compared with the micron scale in the related art, and can reduce the influence of the film layer on the conductivity of copper materials, thereby better improving the conductivity of copper materials. Thus, it can improve the conductivity of copper materials, and at the same time improve the corrosion resistance and high-temperature antioxidant properties of copper materials. Description of the drawings

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0020] Figure 1 Shows the scanning electron microscope images of the copper material in Embodiment 1 of the present application and the copper material matrix in Comparative Example 1. Among them, a is the SEM image of the surface of the copper material matrix in Comparative Example 1, b is the SEM image of the surface of the copper material in Embodiment 1, and c is the SEM image of the cross-section of the copper material in Embodiment 1.

[0021] Figure 2 Shows the resistivity test results of the copper material in Embodiment 1 of the present application and the copper material matrix in Comparative Example 1 using the four-probe method.

[0022] Figure 3 Shows the residence experiment of the hydrogen peroxide solution of the present application on the surface of the film layer; there are three groups in total, and for each group, the left side is the position where hydrogen peroxide is dropped, and the right side is the photo after wiping after staying for 10 min, 20 min, and 30 min.

[0023] Figure 4 The figure shows the relationship between voltage and current of copper materials after being treated at different heating temperatures in Comparative Example 1 and Example 1 of the present application.

[0024] Figure 5 The figure shows the cycling performance diagrams of lithium-ion batteries and half-cells prepared from the copper materials of Example 1 and the comparative example of the present application. Among them, a is the relationship diagram between voltage and specific capacity of the lithium-ion battery at a current rate of 2C, and b is the relationship diagram between voltage and specific capacity of the half-cell at a current rate of 0.2C.

[0025] Figure 6 It is the XPS characterization of the copper material with a film layer in Example 1. a is the full spectrum, and b, c, and d are the fine spectra of Cu, S, and F respectively.

[0026] Figure 7 They are the infrared spectra of each component of the film-forming solution and the infrared spectra of the film-forming solution after different reaction times. BMIM refers to the infrared spectrum of the ionic liquid, TM refers to the infrared spectrum of 3-thiophene methanol, Film-formation liquid 0min refers to the infrared spectrum of the film-forming solution before the start of the reaction, Film-formation liquid 30 min refers to the infrared spectrum of the film-forming solution after the reaction ends, and BMIM@TM surface 30 min refers to the infrared spectrum of the surface of the copper material with a film layer obtained in Example 1.

[0027] In the drawings, the drawings are not necessarily drawn to actual scale. Detailed implementation manners

[0028] In order to be able to more clearly understand the above-mentioned objects, features, and advantages of the present application, the solutions of the present application will be further described below. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0029] Many specific details are set forth in the following description in order to fully understand the present application, but the present application can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present application, rather than all the embodiments.

[0030] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0032] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0033] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0034] In this application, the terms "a plurality of" and "a variety of" mean two or more than two.

[0035] Unless otherwise stated, the test temperature of each parameter mentioned in this application is 25°C.

[0036] In the embodiments of the present application, the battery cell can independently perform the functions of charging and discharging. The battery cell can be in the shape of a cylinder, a cuboid, or other shapes, and the embodiments of the present application do not limit this.

[0037] In the embodiments of the present application, the battery cell can be a secondary battery, which refers to a battery cell that can activate the active material through charging and continue to be used after discharging.

[0038] The battery cell provided in the embodiments of the present application includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator, and the separator is disposed between the negative electrode and the positive electrode. During the charging and discharging process of the battery cell, active ions (such as lithium ions) are embedded and extracted back and forth between the positive electrode and the negative electrode. The separator is disposed between the positive electrode and the negative electrode, which can prevent the short circuit between the positive and negative electrodes and allow the active ions to pass through at the same time. The electrode assembly can be a wound structure or a laminated structure, and the embodiments of the present application do not limit this.

[0039] The battery cell further includes an outer package for encapsulating the electrode assembly and the electrolyte. The outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of an aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0040] The battery cell provided in the embodiments of the present application can be a lithium-ion battery cell, a sodium-ion battery cell, a sodium-lithium-ion battery cell, a lithium-metal battery cell, a sodium-metal battery cell, a lithium-sulfur battery cell, a magnesium-ion battery cell, a nickel-metal hydride battery cell, a nickel-cadmium battery cell, a lead-acid battery cell, etc., and the embodiments of the present application do not limit this.

[0041] The technical solutions described in the embodiments of the present application are applicable to various electrical devices using battery cells and battery devices, such as but not limited to mobile devices (such as mobile phones, tablet computers, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains (subways, trains, bullet trains, high-speed rails, etc.), ships, satellites, energy storage systems, etc. The battery cell and the battery device are used to store or provide electrical energy.

[0042] In view of the problems in the background art, the present application provides a copper material with a self-assembled nanometer film layer on its surface, a preparation method thereof, a negative electrode current collector, a negative electrode plate, and a battery cell, which can improve the electrical conductivity of the copper material and at the same time improve the stability of the copper material.

[0043] Copper material with a self-assembled nanometer film layer on its surface A copper material with a self-assembled nanometer film layer on its surface, the copper material comprising a copper material substrate and a film layer provided on at least a part of the surface of the copper material substrate; the film layer comprises a coordination structure Cu(BF4 - )4 2+ and thiophene connected by intermolecular forces to the coordination structure Cu(BF4 - )4 2+ , the thiophene comprising one or more of a thiophene compound and a thiophene polymer; the thickness of the film layer is 20-100 nm.

[0044] The coordination structure (Coordination Structure) refers to the spatial arrangement formed by the combination of a central atom / ion and ligands (Ligands) arranged around it through a coordination bond (Coordinate Bond). In the Cu(BF4 - )4 2+ provided by the embodiment of the present application, Cu 2+ is the central ion and BF4 - is the ligand. It can be measured by XPS and FTIR.

[0045] The intermolecular force refers to the mutual force existing between neutral molecules or charged molecules (ions), and its strength is much smaller than that of chemical bonds (such as covalent bonds and ionic bonds), including van der Waals forces, hydrogen bonds, ion-dipole interactions, hydrophobic interactions, π-π stacking interactions, and cation-π interactions, etc. The type of intermolecular force in the embodiment of the present application is related to the structure of thiophene. For example, when thiophene is 3-thiophene methanol, the intermolecular force is the hydrogen bond OH-F - formed by the hydroxyl group and F - .

[0046] The thiophene polymer can be a thiophene oligomer, that is, a polymer containing 2-10 thiophene rings.

[0047] The film layer provided by the embodiment of the present application has thiophene, which can improve the conductivity and antioxidant properties of the film layer; while BF4 - on the one hand can form a coordination structure with Cu 2+ , and on the other hand can be connected to thiophene through intermolecular forces, thereby forming a conductive network of Cu 2+ -BF4 - -thiophene, further improving the conductivity of the film layer; at the same time, the thickness of the film layer is nanoscale, which has a lower resistance compared with the micron scale in the related art, and can reduce the influence of the film layer on the conductivity of the copper material, thereby better improving the conductivity of the copper material. Thus, the conductivity of the copper material can be improved, and at the same time, the corrosion resistance and high-temperature antioxidant properties of the copper material can also be improved.

[0048] Optionally, the thickness of the film layer is independently selected from any value among 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm or a range value between any two of them.

[0049] In some embodiments, the mass ratio of the coordination structure Cu(BF 4- )4 2+ to thiophene is 1:(0.8~1.2).

[0050] The coordination structure Cu(BF 4- )4 2+ with a suitable mass ratio to thiophene can form a more complete conductive network to improve the conductivity of copper, and can contain more thiophene to better improve the conductivity and stability of copper.

[0051] Optionally, the mass ratio of the coordination structure Cu(BF 4- )4 2+ to thiophene is independently selected from any value among 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2 or a range value between any two of them.

[0052] In some embodiments, the thiophene compound includes one or more of 3-thiophenemethanol, 3,4-ethylenedioxythiophene and 3-hexylthiophene, and the thiophene polymer includes one or more of 3-thiophenemethanol polymer, 3,4-ethylenedioxythiophene polymer and 3-hexylthiophene polymer.

[0053] The thiophene compound and thiophene polymer with a suitable range have a conjugated π-electron system and a π-π stacking effect. Among them, the conjugated π-electron system enables electrons to move freely along the polymer backbone, providing a basis for conductivity; the π-π stacking effect can promote intermolecular electron transition and further enhance conductivity.

[0054] In the thiophene compound and thiophene polymer with a suitable range, the lone pair electrons of sulfur atoms can better participate in the conjugated system, enhancing the overall stability of the molecule; while the conjugated π-electron system can quickly delocalize the charges generated by oxidation, reducing the possibility of local over-oxidation.

[0055] In some embodiments, the coordination structure Cu(BF4 - )4 2+ is obtained by coordinating copper ions with an ionic liquid containing tetrafluoroborate.

[0056] The ionic liquid in the embodiments of the present application serves as both a solvent and a solute. Driven by thermodynamics at 65°C, the excessive tetrafluoroborate coordinates with divalent copper ions; in addition, there is no water in the system, which can reduce the coordination of water with strong coordination ability to divalent copper ions.

[0057] Thus, tetrafluoroborate can coordinate with copper ions, providing a driving force for self-assembled film formation to form a coordination structure Cu(BF4 - )4 2+ .

[0058] In some embodiments, at 20 °C, the resistivity of the copper material is 2.05-2.80 μΩ•cm. For example, it can be 2.05 μΩ•cm, 2.06 μΩ•cm, 2.07 μΩ•cm, 2.08 μΩ•cm, 2.09 μΩ•cm, 2.10 μΩ•cm, 2.11 μΩ•cm, 2.12 μΩ•cm, 2.13 μΩ•cm, 2.14 μΩ•cm, 2.15 μΩ•cm, 2.16 μΩ•cm, 2.17 μΩ•cm, 2.18 μΩ•cm, 2.19 μΩ•cm, 2.20 μΩ•cm, 2.30 μΩ•cm, 2.40 μΩ•cm, 2.50 μΩ•cm, 2.60 μΩ•cm, 2.70 μΩ•cm, 2.80 μΩ•cm, or a range composed of any of the above values. Compared with the bare copper under the same pretreatment and test conditions, the resistivity of the copper material with a film layer on its surface only increases by 2.0% - 9.5%.

[0059] Preparation method of copper material with self-assembled nanometer film layer on the surface A preparation method of a copper material with a self-assembled nanometer film layer on the surface includes the following steps: providing a copper material substrate, providing a film-forming solution, the film-forming solution including an ionic liquid containing tetrafluoroborate, thiophene, and an acid; heating the film-forming solution on the surface of the copper material substrate to obtain a copper material with a self-assembled nanometer film layer on the surface having a film layer, the film layer including a coordination structure Cu(BF4 - )4 2+ and thiophene connected by intermolecular forces to the coordination structure Cu(BF4 - )4 2+ The thiophene includes one or more of thiophene compounds and thiophene polymers, and the thickness of the film layer is 20 - 100 nm.

[0060] The film-forming solution provided in the embodiments of the present application contains an acid, which can etch the surface of the copper material substrate to obtain copper ions (Cu 2+ ) with higher activity than copper atoms. The reaction process is Cu + 2H + →Cu 2+ + H2. And these copper ions attached to the surface of the copper material substrate will undergo a coordination reaction with the anionic group tetrafluoroborate (BF4 - ) in the ionic liquid to form Cu(BF4 - )4 2+This coordination process provides a strong driving force for the formation of a film layer on the surface of the copper substrate. In addition, the acid in the film-forming solution can oxidize thiophene to form free radicals and oligomers. These free radicals and oligomers can form intermolecular forces through the functional groups they carry and the F in the highly electronegative tetrafluoroborate - to form intermolecular forces, thereby providing another driving force for the formation of a film layer on the surface of the copper substrate. Therefore, the film-forming solution self-assembles into a nanoscale film layer under the drive of coordination and intermolecular forces.

[0061] The ionic liquid contained in the film-forming solution serves as both a solvent and a solute. Therefore, the film-forming solution can be free of water, which can reduce the coordination of water with strong coordination ability and divalent copper ions. As a result, an excessive amount of tetrafluoroborate coordinates with divalent copper ions under the thermodynamic drive at 65°C. The cations and anions of the ionic liquid can remain in the film layer, thereby enhancing the conductivity of the film layer under the action of an external electric field.

[0062] In addition, tetrafluoroborate can form connections with copper ions through coordination and also form connections with thiophene through intermolecular forces, thereby forming a Cu 2+ -BF4 - -thiophene conductive network.

[0063] When providing the copper substrate, the surface of the copper substrate can also be pretreated to remove the oil stain and passivation layer on the surface of the copper substrate, facilitating subsequent film formation. In some other embodiments, providing the copper substrate includes the following steps: mixing water and nitric acid in a volume ratio of 1:1, then placing the copper substrate in the mixed solution for pickling, and obtaining the pretreated copper substrate after washing and drying.

[0064] In some embodiments, the ionic liquid containing tetrafluoroborate includes one or more of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate ([EMI]BF4), 1-butylimidazolium tetrafluoroborate ([HC4im]BF4), and 1-methyl-3-butylimidazolium tetrafluoroborate ([BMI]BF4), thiophene includes one or more of 3-thiophenemethanol, 3,4-ethylenedioxythiophene, and 3-hexylthiophene, and the acid includes one or more of concentrated sulfuric acid and concentrated nitric acid.

[0065] In some embodiments, the mass ratio of the ionic liquid containing tetrafluoroborate to thiophene is 1:(0.03 - 0.04); based on the film-forming solution, the molar concentration of the acid is 0.001 - 0.002M.

[0066] The film-forming solution with a suitable component ratio can better achieve self-assembled film formation and reach the preset thickness of the film layer. At the same time, it can also better improve the conductivity and stability of the copper material.

[0067] In some embodiments, the film-forming solution is placed on the surface of the copper substrate for heat treatment. The temperature of the heat treatment is 60~100°C, and the time is 20~50 min.

[0068] Optionally, the temperature of the heat treatment is independently selected from any value of 60°C, 70°C, 80°C, 90°C, 100°C or the range value between any two of them.

[0069] Optionally, the time of the heat treatment is independently selected from any value of 20 min, 30 min, 40 min, 50 min or the range value between any two of them.

[0070] Negative electrode plate In some embodiments, the negative electrode plate may include a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0071] The negative electrode active material can be a material known in the art that can be used in battery monomers. As an example, the negative electrode active material may include, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include, but are not limited to, one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. The tin-based materials may include, but are not limited to, one or more of elemental tin, tin oxides, and tin alloy materials.

[0072] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0073] In some embodiments, the negative electrode film layer may further include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0074] In some embodiments, the negative electrode film layer may further include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0075] In some embodiments, the negative electrode current collector includes a copper substrate and a film layer provided on at least a part of the surface of the copper substrate; the film layer includes a coordination structure Cu(BF4 - )4 2+ and thiophene connected to the coordination structure Cu(BF4 - )4 2+ by intermolecular forces, and the thiophene includes one or more of thiophene compounds and thiophene polymers; the thickness of the film layer is 20~100 nm.

[0076] The negative electrode film layer is usually formed by coating a negative electrode slurry on the negative electrode current collector and then drying and cold pressing. The negative electrode slurry is usually formed by dispersing a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and other optional additives in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0077] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet further includes a conductive bottom layer (such as composed of a conductive agent and a binder) provided on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer.

[0078] In some embodiments, the negative electrode sheet can use a foam metal. The foam metal can be foam copper, and a film layer is provided on at least a part of the surface of the foam copper; the film layer includes a coordination structure Cu(BF4 - )4 2+ and thiophene connected to the coordination structure Cu(BF4 - )4 2+ by intermolecular forces, and the thiophene includes one or more of thiophene compounds and thiophene polymers; the thickness of the film layer is 20~100 nm. When the foam metal is used as the negative electrode sheet, the negative electrode active material may not be provided on the surface of the foam metal, or of course, the negative electrode active material may also be provided.

[0079] Positive electrode sheet In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0080] In some embodiments, the positive electrode active material includes a material capable of deintercalating and intercalating lithium.

[0081] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, metal chalcogenides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium titanium oxide, and their respective modified compounds. The lithium transition metal oxides may include, but are not limited to, a layered structure and a spinel structure. Examples of lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0082] The modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0083] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, fluorinated acrylate resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0085] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0086] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0087] Electrolyte This application does not specifically limit the type of the electrolyte, which can be selected according to requirements. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte solution).

[0088] In some embodiments, the electrolyte uses an electrolyte solution, and the electrolyte solution includes an electrolyte salt and a solvent.

[0089] Taking a lithium battery monomer as an example, the electrolyte salt can include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0090] The type of the solvent is not specifically limited and can be selected according to actual requirements. In some embodiments, by way of example, the solvent can include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), diethyl sulfone (ESE), ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ether.

[0091] In some embodiments, the electrolyte may further optionally include additives. For example, the additives may include negative electrode film-forming additives, or may include positive electrode film-forming additives, or may also include additives that can improve certain properties of the battery cell, such as additives for improving the overcharge performance of the battery cell, additives for improving the high-temperature performance of the battery cell, additives for improving the low-temperature power performance of the battery cell, and the like.

[0092] Separator In battery cells using an electrolyte and some battery cells using a solid electrolyte, a separator is further included. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing metal ions to pass through. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0093] In some embodiments, the separator includes a porous base film and a coating located on at least one side of the porous base film.

[0094] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0095] In some embodiments, the coating includes a heat-resistant layer and an adhesive layer. The heat-resistant layer is disposed between the base film and the adhesive layer. The heat-resistant layer includes heat-resistant particles, and the adhesive layer includes organic particles.

[0096] In some embodiments, the heat-resistant particles include one or more of inorganic particles or organic particles.

[0097] In some embodiments, the coating includes a binder, and the binder may include, but is not limited to, one or more of polyacrylate binders, nitrile rubber binders, polyacrylic acid, polymethacrylic acid, sodium polyacrylate, polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0098] In some embodiments, the coating may further include a dispersant, for example, may include, but is not limited to, one or more of dispersants such as alkylphenol polyoxyethylene ether, polyacrylic acid-based dispersants, and cellulose-based dispersants. As an example, the dispersant may include, but is not limited to, one or more of sodium carboxymethyl cellulose, sodium polyacrylate, and ammonium polyacrylate.

[0099] Examples The following examples more specifically describe the content disclosed in the present application. These examples are only for illustrative purposes, as various modifications and variations within the scope of the present application disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0100] Example 1 Pretreatment of copper substrate The commercial copper material was placed in an acid cleaning solution prepared by mixing water and nitric acid in a volume ratio of 1:1 for pretreatment, and the copper substrate was obtained after washing and drying.

[0101] Surface modification of copper substrate Ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, 3-thiophene methanol, and concentrated sulfuric acid were mixed into a film-forming solution and placed on the surface of the copper substrate. It was heated at 65 °C in a water bath for 30 min, and then the surface of the copper was rinsed with deionized water and dried to obtain copper with a 54 nm film layer. The mass ratio of 1-butyl-3-methylimidazolium tetrafluoroborate to 3-thiophene methanol was 1:0.03, and the molar concentration of concentrated sulfuric acid was 0.001 M.

[0102] Performance testing Test of resistivity: At 25 °C, the four-probe method was used to test the resistivity.

[0103] Examples 2 - 4 The pretreatment and performance testing of the copper substrate were the same as those in Example 1, except that the preparation method of the copper material was different, that is, the types of ionic liquid, thiophene, or acid were different. See Table 1 for details.

[0104] Examples 5 - 6 The pretreatment and performance testing of the copper substrate were the same as those in Example 1, except that the preparation method of the copper material was different, that is, the ratios of ionic liquid, thiophene, and acid were different. See Table 1 for details.

[0105] Comparative Example 1 The pretreatment and performance testing of the copper substrate were the same as those in Example 1, except that the surface film-forming modification of the copper substrate was not carried out. See Table 1 for details.

[0106] Comparative Example 2 The pretreatment and performance testing of the copper substrate were the same as those in Example 1, except that the surface modification of the copper substrate was different, that is, the ionic liquid was replaced with non-ionic liquid aryl diazonium tetrafluoroborate. See Table 1 for details.

[0107] Comparative Example 3 The pretreatment and performance testing of the copper substrate were the same as those in Example 1, except that the surface modification of the copper substrate was different, that is, the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate was replaced with the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. See Table 1 for details.

[0108] Table 1 Experimental parameters and properties in Examples 1-6 and Comparative Examples 1-3

[0109] As can be seen from Table 1, the ionic liquids in Examples 1-6 served as both solvents and solutes, mixing the film-forming components into a film-forming solution, so that the film-forming components could better contact and react to self-assemble into a nanometer film layer with a Cu 2+ -BF4 - -thiophene conductive network. Although Comparative Example 2 contained Cu 2+ , BF4 - and thiophene, the aryldiazonium tetrafluoroborate was a non-ionic liquid and could only serve as a solute and not as a solvent. Therefore, a film-forming solution could not be formed in Comparative Example 2, and thus no film could be formed. Although the ionic liquid in Comparative Example 3 could serve as a solvent to make the film-forming components form a solution, the anion of its ionic liquid was hexafluorophosphate and could not coordinate, so a film layer could not be formed.

[0110] Figure 1 Figs. are the scanning electron microscope images of the copper materials in Example 1 and the copper substrate in Comparative Example 1. Among them, a is the SEM image of the surface of the copper substrate in Comparative Example 1, b is the SEM image of the surface of the copper material in Example 1, and c is the SEM image of the cross-section of the copper material in Example 1. As Figure 1 can be seen, the film layer disclosed in the examples of the present application is nanoscale; as Figure 1 shown by c in

[0111] Figure 2 The results of resistivity testing of the copper materials in Example 1 and the copper substrate in Comparative Example 1 by the four-probe method are disclosed. The resistivity of the copper substrate in Comparative Example 1 was 2.01 μΩ•cm, and the resistivity of the copper material in Example 1 was 2.18 μΩ•cm, with only an increase of about 8% in its resistivity. This low-resistance performance was due to the self-assembled film layer modification on the surface of the copper substrate in the examples of the present application.

[0112] The antioxidant property of the copper material with a film layer in Example 1 was tested: A strong oxidant hydrogen peroxide solution was dropped on the surfaces of multiple copper material film layers, and after standing for 10 min, 20 min, and 30 min respectively, the hydrogen peroxide solution was wiped off, and it was observed whether oxidation marks appeared on the copper material film layer. See Figure 3 .

[0113] AsFigure 3 When the shown strong oxidant hydrogen peroxide solution is dropped on the surface of the copper material, whether it is for 10 minutes, 20 minutes, or 30 minutes, there are almost no oxidation traces on the film surface of the copper material after wiping. This is because 3-thiophenemethanol in the surface film has antioxidant properties and can be preferentially oxidized in place of the copper material when contacting oxidizing substances.

[0114] The high-temperature stability of the copper material with the film layer in Example 1 and the copper material substrate in Comparative Example 1 was tested: Multiple copper materials were placed in a muffle furnace, heated at different temperatures for 10 minutes and then taken out. Then, the longitudinal voltage (U) and current (I) were measured, and the resistance could be calculated according to R = U / I. The stability of the copper material was evaluated by comparing the change rate of the resistance at different temperatures. See Table 2 and Figure 4 .

[0115] Table 2 Resistance of copper materials in Comparative Example 1 and Example 1 at different temperatures

[0116] Figure 4 In it, BC (abbreviation for Bare copper) represents Comparative Example 1, BT (abbreviation for BMIM@TM) represents Example 1, and the numbers after BC / BT represent the heating temperature. By comparing the resistance (0.23 Ω) of the copper material substrate in Comparative Example 1 at room temperature (20 °C), the resistance increase rate of the modified copper material in Example 1 compared to Comparative Example 1 can be obtained. For example, at 300 °C, the resistance of the copper material substrate in the comparative example is 0.64 Ω, then the resistance increase rate of the copper material in Example 1 is (0.64 / 0.23 - 1) × 100%, that is, 178.3%. And the resistance of the product at 300 °C is 0.40 Ω, and the increase rate is 73.9%. When the copper material substrate of Comparative Example 1 and the copper material of Example 1 are both tested at 400 °C, the resistance of the copper material substrate of Comparative Example 1 increases directly from 9.23 Ω to 3913.1% of the resistance of the copper material substrate of Comparative Example 1 at room temperature. And the resistance of the copper material in Example 1 at 400 °C is almost the same as that at 300 °C. Therefore, the copper material with film layer modification provided in the embodiments of the present application has strong stability at high temperatures and can maintain the electrical conductivity of the copper material to a large extent.

[0117] Preparation of lithium-ion battery The copper material in Example 1 and the copper material substrate in Comparative Example 1 were used as the negative current collector, and a lithium-ion battery was prepared according to the following method: Preparation of the positive electrode sheet Lithium iron phosphate, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were thoroughly stirred and mixed in a mass ratio of 90:5:5 in an appropriate amount of solvent NMP to form a uniform positive electrode slurry; the positive electrode slurry was uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode plate was obtained.

[0118] Preparation of negative electrode plate Graphite, conductive agent (Super P), and binder styrene-butadiene rubber (SBR) were fully stirred in a mass ratio of 90:5:5 in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry, and then the negative electrode slurry was coated on the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode plate was made.

[0119] Electrolyte Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in equal volumes to obtain an organic solvent, and then LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0120] Assembly The above positive electrode plate, separator membrane, and negative electrode plate were stacked in sequence, then wound together, and then hot pressed to make the separator membrane play a role of isolation between the positive electrode plate and the negative electrode plate, and the prepared electrolyte was added to complete the preparation of the lithium-ion battery.

[0121] Preparation of half cell The copper materials in Example 1 and the copper material substrate in Comparative Example 1 were used as the negative electrode current collector, and a lithium-ion battery was prepared according to the following method: Preparation of negative electrode plate Graphite, conductive agent (Super P), and binder styrene-butadiene rubber (SBR) were fully stirred in a mass ratio of 90:5:5 in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry, and then the negative electrode slurry was coated on the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode plate was made.

[0122] Assembly A lithium sheet was used as the counter electrode, and the negative electrode plate in Example 1 and Comparative Example 1 was used to make a half cell.

[0123] Cycling performance test Half-cell, lithium-ion battery: At 45 °C, the battery is charged at a constant current of 2C to 4.3V, and then charged at a constant voltage until the current reaches 0.05C. At this time, the battery is fully charged, and the charging capacity at this time is recorded as the charging capacity of the first cycle; after the battery is left standing for 5 minutes, it is discharged at a constant current of 2C to 2.8V. This is a cycle of charge and discharge process, and the discharge capacity at this time is recorded as the discharge capacity of the first cycle. The battery is tested for cyclic charge and discharge according to the above method, and the discharge capacity after each cycle is recorded. The specific capacity of the battery after 100 cycles at 45 °C = discharge capacity after 100 cycles / mass of lithium iron phosphate × 100%.

[0124] The cyclic performance results are shown in Figure 5 , Figure 5 In which, a is the relationship diagram of voltage and specific capacity obtained during the large current charge and discharge test of the lithium-ion battery at a 2C rate. It can be seen from the figure that compared with the lithium-ion battery prepared with the copper substrate of Comparative Example 1, the lithium-ion battery prepared with the copper material of Example 1 shows the lowest polarization potential (0.3V) in the first charge and discharge test. It is generally considered that the smaller the charge and discharge voltage difference, the better the control of the internal polarization effect of the battery, the smaller the internal resistance, which can effectively reduce the possibility of overcharge and over-discharge, so that the battery can be applied to high-power scenarios. The copper material with a film layer in the embodiment of the present application can not only conduct electricity normally, but also enhance its polarization stability in the lithium-ion battery at higher voltages and large currents due to its strong antioxidant property.

[0125] Figure 5 In which, b is the charge and discharge performance test of the half-cell at a small rate of 0.2C. The half-cell of Example 1 has a higher specific capacity at a rate of 0.2C, and when the specific capacity is within 400 mAh g -1 , it has a more stable charge and discharge curve and a closer charge and discharge voltage difference. Therefore, compared with the half-cell of Comparative Example 1, the copper material of the embodiment of the present application used as the negative current collector in the half-cell also has strong stability.

[0126] Figure 6XPS characterization of the copper material with a film layer in Example 1. a is the full spectrum, and b, c, and d are the fine spectra of Cu, S, and F respectively. Among them, from a, it can be seen that the characteristic elements (F, S) of both the ionic liquid and 3-thiophenemethanol appear on the surface of the sample, indicating that both the ionic liquid and 3-thiophenemethanol participate in the film-forming reaction. In b, the state of copper on the surface in the fine spectrum of Cu is identified as copper atoms and divalent copper ions. The strong satellite peaks in this fine spectrum prove the existence of copper ions. The reason for the presence of copper atoms on the sample surface is that the relatively thin film layer enables the XPS test to detect the copper substrate. To a certain extent, this also indicates that the state of copper in contact with the substrate in the film layer may be a layer of fresh copper atoms. The divalent copper ions come from the etching of sulfuric acid in the solution environment but do not exist in the film layer in the form of simple CuSO4. Because, in c, the fine spectrum of S can only be divided into peaks of S-C bonds derived from 3-thiophenemethanol, and there are no peaks that can be divided to represent SO4 2- at high binding energy. Further, the fine spectrum of the F element in the figure can be divided into three peaks with a half-peak width of 1.9 each. The substances represented by these three peaks can be regarded as BF 4- forming hydrogen bonds with the hydrogen on the hydroxyl group in order of increasing binding energy; BF 4- that does not participate in any reaction; and BF 2+ coordinated with Cu 4- .

[0127] Figure 7 are the infrared spectra of each component of the film-forming solution and the infrared spectra of the film-forming solution at different reaction times. BMIM refers to the infrared spectrum of the ionic liquid, TM refers to the infrared spectrum of 3-thiophenemethanol, Film-formation liquid 0min refers to the infrared spectrum of the film-forming solution before the start of the reaction, Film-formation liquid 30 min refers to the infrared spectrum of the film-forming solution after the reaction ends, and BMIM@TM surface 30 min refers to the infrared spectrum of the surface of the copper material with a film layer obtained in Example 1. The infrared curve of the BMIM ionic liquid shows that the stretching vibration peaks of C-H and C=N on its imidazole ring appear at 3100 - 3200 cm -1 and 1500 - 1600 cm -1 respectively; the stretching vibration peak of C-H on its alkyl chain appears at 2850 - 3000 cm -1 ; the stretching vibration peak of B-F in the anion group, tetrafluoroborate ion, appears at 1050 - 1100 cm -1 . TM 3-thiophenemethanol shows that the stretching vibration peak of O-H appears at 3200 - 3600 cm -1 ; the stretching vibration peak of C-H on the thiophene ring appears at 3050 - 3100 cm-1 The position is different from that of the C-H peak in the ionic liquid; in addition, its C-S stretching vibration peak appears at 600 - 700 cm -1 at this position. The infrared curve of the film-forming liquid before the start of the reaction of Film-formation liquid 0 min and the infrared curve of the film-forming liquid after the reaction of Film-formation liquid 30 min are relatively similar to the infrared curve of the BMIM ionic liquid because the amount of the ionic liquid used as the solvent is much larger than that of 3-thiophene methanol. However, for the infrared spectrum of the surface of the copper material with a film layer obtained in Example 1 of BMIM@TM surface 30 min, the C-H stretching vibration and C-S stretching vibration on the thiophene ring can be detected. This indicates that TM can participate in the film-forming reaction. In the infrared curve of BMIM@TM surface 30 min, the C-H stretching vibration on the imidazole ring disappears, and the C=N stretching vibration is also almost absent. These phenomena further confirm that almost no part of the imidazolium cation in the ionic liquid participates in the film-forming reaction. Additionally, it is also worth noting that the B-F stretching vibration peak in the solid infrared of BMIM@TM undergoes a blue shift. This may be due to hydrogen bonding or electrostatic interaction, resulting in an increase in the vibration frequency of B-F. To sum up, in the film-forming reaction, the coordination of tetrafluoroborate with copper ions and the hydrogen bonding with hydroxyl groups are both indispensable.

[0128] As described above, the above is only the specific implementation manner of the present application. Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described systems, modules, and units can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein. It should be understood that the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present application.

Claims

1. A copper material with a self-assembled nanometer film layer on its surface, characterized in that, The copper material includes a copper material substrate and a film layer provided on at least a part of the surface of the copper material substrate; The film layer includes a coordination structure Cu(BF4 - )4 2+ and thiophene connected to the coordination structure Cu(BF4 - )4 2+ by intermolecular forces, and the thiophene includes one or more of a thiophene compound and a thiophene polymer; The thickness of the film layer is 20 to 100 nm.

2. The copper material with a self-assembled nanometer film layer on its surface according to claim 1, characterized in that, The coordination structure Cu(BF4 - )4 2+ has a molecular weight ratio to the thiophene of 1:(0.8 - 1.2).

3. The copper material with a self-assembled nanometer film layer on its surface according to claim 1, characterized in that, The thiophene compound includes one or more of 3-thiophene methanol, 3,4-ethylenedioxythiophene, and 3-hexylthiophene, The thiophene polymer includes one or more of 3-thiophene methanol polymer, 3,4-ethylenedioxythiophene polymer, and 3-hexylthiophene polymer.

4. The copper material with a self-assembled nanometer film layer on its surface according to claim 1, characterized in that, The coordination structure Cu(BF4 - )4 2+ is obtained by coordinating copper ions with an ionic liquid containing tetrafluoroborate ions.

5. The copper material with a self-assembled nanometer film layer on its surface according to any one of claims 1-4, characterized in that, At 20 °C, the resistivity of the copper material is 2.05 to 2.80 μΩ•cm.

6. A preparation method of a copper material with a self-assembled nanometer film layer on its surface, characterized in that, It includes the following steps: Provide a copper material substrate, Provide a film-forming solution, the film-forming solution includes an ionic liquid containing tetrafluoroborate, thiophene, and an acid; Place the film-forming solution on the surface of the copper substrate and perform heat treatment to obtain a copper material with a self-assembled nanometer film layer on the surface having a film layer, the film layer including a coordination structure Cu(BF4 - )4 2+ and thiophene connected by intermolecular forces to the coordination structure Cu(BF4 - )4 2+ The thiophene includes one or more of thiophene compounds and thiophene polymers, and the thickness of the film layer is 20-100 nm.

7. The preparation method according to claim 6, characterized in that, The ionic liquid containing tetrafluoroborate includes one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butylimidazolium tetrafluoroborate, and 1-methyl-3-butylimidazolium tetrafluoroborate, The thiophene includes one or more of 3-thiophene methanol, 3,4-ethylenedioxythiophene, and 3-hexylthiophene, The acid includes one or more of concentrated sulfuric acid and concentrated nitric acid.

8. The preparation method according to claim 6, characterized in that, The mass ratio of the ionic liquid containing tetrafluoroborate to the thiophene is 1:(0.03 to 0.04); Based on the film-forming solution, the molar concentration of the acid is 0.001 to 0.002 M.

9. The preparation method according to claim 6, characterized in that, Place the film-forming solution on the surface of the copper material substrate for heat treatment, the temperature of the heat treatment is 60 to 100 °C, and the time is 20 to 50 min.

10. A negative electrode current collector, characterized in that, It includes a copper material substrate and a film layer provided on at least a part of the surface of the copper material substrate; The film layer includes a coordination structure Cu(BF4 - )4 2+ and thiophene connected to the coordination structure Cu(BF4 - )4 2+ by intermolecular forces, and the thiophene includes one or more of a thiophene compound and a thiophene polymer; The thickness of the film layer is 20 to 100 nm.

11. A negative electrode plate, characterized in that, It includes the negative electrode current collector described in claim 10 and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material.

12. A battery cell, characterized in that, It includes the negative electrode plate described in claim 11.

Images