Composite current collector, preparation method therefor and use thereof

Abstract

A composite current collector, a preparation method therefor and a use thereof. The composite current collector comprises a base film and a metal layer on at least one side surface of the base film. A protective layer is further provided on the surface of the metal layer. The metal layer comprises copper or a copper alloy. The protective layer comprises a complex formed by a polythiophene compound, a polyanion compound and metal ions, wherein the metal ions comprise Fe3+, Fe2+ and Cu2+, and the polyanion compound comprises sulfonate. According to the composite current collector, by means of the protective layer provided on the surface of the metal layer, the problem of the metal layer being oxidized due to contact with oxygen can be effectively solved, the conductivity of the composite current collector will not be affected, and the overall stability of the composite current collector can also be improved.

Description

A composite current collector and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of battery current collectors and relates to a composite current collector and a preparation method and application thereof. Background Art

[0002] Currently, composite copper current collectors based on polymer films are gaining widespread attention and application in the new energy sector. These are typically prepared using physical vapor deposition (PVD) to deposit a copper metal layer onto a polymer film (such as polyester or polyolefin), resulting in a highly conductive composite copper current collector.

[0003] Compared to traditional copper current collectors (copper foil), composite copper current collectors based on polymer films have the characteristics of low cost, light weight, and good internal insulation. These characteristics enable composite copper current collectors to reduce battery costs, improve battery energy density, and improve safety when used in batteries. For example, CN 111048788A discloses a current collector, its preparation method, and application. The current collector includes a functional film layer and a metal layer disposed on the upper and lower surfaces of the functional film layer. The functional film layer includes a flame retardant and a polymer. The metal layers on its upper and lower surfaces are supported by a polymer functional base film layer. The addition of the flame retardant to the polymer functional base film layer not only effectively reduces the ignition point, but also allows the flame retardant to be released from the current collector into the electrolyte at high temperatures, thereby improving the safety performance of the battery.

[0004] However, since the metal layer of the composite copper current collector is made of copper, copper metal has a strong reducibility and is easily oxidized, resulting in poor electrical conductivity and affecting its use. Therefore, a protective layer is generally provided on the surface of the composite copper current collector to protect the metal material from oxidation. For example, CN 115850863A discloses a polypropylene film, a preparation method thereof, a composite current collector, and its application. The composite current collector includes a substrate and a metal layer, wherein the metal layer is located on at least one surface of the substrate, and the surface of the metal layer further includes a protective layer. The material of the protective layer includes one or more of copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, nickel-chromium alloy, graphite, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, and graphene. The provision of the protective layer includes the metal layer of the current collector, but the provision of the protective layer can affect the conductivity of the current collector.

[0005] Currently, existing technologies typically utilize hexavalent chromium treatment, whereby a layer of copper-chromium oxide is generated in situ on the surface of the copper layer of the composite copper current collector to protect it from oxidation. However, this method presents the following challenges: ① The hexavalent chromium used in the preparation process is highly hazardous and can pose a threat to human health, and the wastewater generated during the process can pollute water bodies and cause a series of environmental problems; ② The protective layer is made of metal oxide, which has poor conductivity. Improper control of the protective layer's thickness can affect the conductivity of the composite copper current collector, compromising its performance.

[0006] Based on the above research, there is a need to provide a composite current collector in which the metal layer is effectively protected from oxidation and does not affect the conductivity of the current collector. Summary of the Invention

[0007] The purpose of the present invention is to provide a composite current collector and its preparation method and application. The composite current collector can effectively solve the problem of oxidation of the metal layer due to contact with oxygen through the protective layer provided on the surface of the metal layer, and will not affect the conductivity of the composite current collector. At the same time, it can also improve the overall stability of the composite current collector.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a composite current collector, comprising a base film and a metal layer on at least one surface of the base film, wherein a protective layer is further provided on the surface of the metal layer;

[0010] The metal layer comprises copper or a copper alloy;

[0011] The protective layer includes a complex formed by a polythiophene compound, a polyanion compound and a metal ion, wherein the metal ion includes Fe 3+ 、Fe 2+ and Cu 2+ , the polyanion compound includes sulfonate.

[0012] The present invention prevents the metal layer from being chemically corroded or physically damaged by arranging a protective layer on the surface of the metal layer. The dense structure of the complex formed by the polymer and the metal ions in the protective layer can effectively hinder the contact between the metal and oxygen, thereby preventing the metal layer from being oxidized. The polythiophene compound in the complex can provide good electrical conductivity, and does not affect the conductivity of the composite current collector while protecting the metal layer. When the polyanion compound and the polythiophene compound exist at the same time, the solubility of the polythiophene compound in water can be improved. The polyanion compound and the polythiophene rely on the charge interaction to improve the density of the protective layer. At the same time, Fe 3+It can undergo complexation reaction with O, S, and sulfonate in polythiophene compounds and polyanion compounds, thereby further improving the stability of the protective layer.

[0013] The metal ion of the present invention is Fe 3+ 、Fe 2+ and Cu 2+ , among which Fe 2+ and Cu 2+ It is obtained by the in-situ reaction of trivalent iron ions with copper in the metal layer. 3+ and its reaction product Fe 2+ 、Cu 2+ It can react with O, S in polythiophene compounds and sulfonate in polyanion compounds to further improve the stability of the protective layer; and because trivalent iron can in situ etch the surface of the copper metal layer, it improves the roughness of the composite current collector surface, thereby improving the bonding effect between the protective layer and the current collector and improving the overall stability; the Fe in the complex 2+ It has good reducing properties and can eliminate oxidizing substances that enter the copper, thereby further enhancing the protection of the copper layer.

[0014] Preferably, the polyanion compound includes any one of polystyrene sulfonic acid, polystyrene sulfonate, poly(4-styrene sulfonic acid-co-maleic acid) salt or polynaphthalene formaldehyde sulfonate or a combination of at least two thereof.

[0015] Preferably, the polystyrene sulfonate comprises sodium polystyrene sulfonate and / or ammonium polystyrene sulfonate, the poly(4-styrene sulfonic acid-co-maleic acid) salt comprises sodium poly(4-styrene sulfonic acid-co-maleic acid), and the polynaphthalene formaldehyde sulfonate comprises sodium polynaphthalene formaldehyde sulfonate.

[0016] Preferably, the thickness of the protective layer does not exceed 10% of the thickness of the metal layer, for example, it can be 10%, 8%, 6%, 4%, 2% or 1%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] If the protective layer of the present invention is too thin, the effect is not obvious; if the protective layer is too thick, it affects the improvement of the energy density of the composite current collector battery.

[0018] Preferably, the thickness of the metal layer is 500-2000 nm, for example, it can be 500 nm, 700 nm, 900 nm, 1100 nm, 1300 nm, 1500 nm, 1700 nm, 1900 nm or 2000 nm, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 700-1200 nm.

[0019] If the metal layer of the present invention is too thin, the conductivity will be poor; if it is too thick, the prepared composite current collector will be too thick and heavy, which is not conducive to improving the energy density of the battery.

[0020] Preferably, the thickness of the protective layer is 30-100 nm, for example, 30 nm, 50 nm, 70 nm, 90 nm or 100 nm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the polythiophene compound includes any one of poly (3,4-ethylenedioxythiophene), poly (thiophene-3-(2-(2-methoxyethoxy), poly (3,4-propylenedioxythiophene), poly (3,4-dimethoxythiophene), poly (3-cyclohexyl-4-methylthiophene-2,5-diyl), 3-hexyl substituted polythiophene, 3-octyl substituted polythiophene or poly (2-vinylthiophene) or a combination of at least two thereof.

[0022] Preferably, the base film comprises any one of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene or polyimide, or a combination of at least two thereof.

[0023] Preferably, the thickness of the base film is 1-10 μm, for example, 1 μm, 3 μm, 5 μm, 7 μm, 9 μm or 10 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In order to take into account both the difficulty of the preparation process and the cost, the thickness of the polymer film is preferably 1.0-10 μm.

[0025] In a second aspect, the present invention provides a method for preparing the composite current collector according to the first aspect, the preparation method comprising the following steps:

[0026] A metal layer is prepared on at least one side of the base film to obtain an intermediate, and the intermediate is immersed in a protective layer slurry, or the protective layer slurry is coated on the surface of the intermediate, and then subjected to post-processing to obtain the composite current collector;

[0027] The protective layer slurry is obtained by mixing a polythiophene compound, a polyanion compound, an iron salt and a solvent.

[0028] Preferably, the iron salt comprises a ferric iron salt.

[0029] The present invention first prepares a metal layer on the surface of the base film, and then directly sets a protective layer on the surface of the metal layer by dipping or direct coating. The protective layer slurry only needs to use polythiophene compounds, polyanion compounds, trivalent iron salts and solvents.

[0030] In the present invention, when preparing the protective layer slurry, in order to completely dissolve the raw materials, the polythiophene compound, the polyanion compound, the iron salt and the solvent are mixed under stirring and heating conditions.

[0031] Preferably, the immersion time is 10-60s, for example, 10s, 20s, 30s, 40s, 50s or 60s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] If the immersion treatment time of the present invention is too short, the treatment effect is not obvious; if the time is too long, the treatment effect cannot be further improved, and in the case of high Fe 3+ The copper layer is severely damaged at low concentrations.

[0033] Preferably, the ferric salt includes any one of ferric chloride, ferric nitrate or ferric sulfate, or a combination of at least two thereof.

[0034] Preferably, the solvent comprises water.

[0035] Preferably, in the protective layer slurry, the mass concentrations of the polythiophene compound and the polyanion compound are independently 0.1-2wt%, for example, 0.1wt%, 0.5wt%, 1wt%, 1.5wt% or 2wt%, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In the protective layer slurry of the present invention, when the concentration of the polythiophene compound and / or the polyanion compound is too low, the prepared protective layer will be too thin, resulting in poor protective effect. When the concentration is too high, the viscosity of the protective layer slurry increases, resulting in poor dipping uniformity, and the prepared protective layer is too thick. An excessively thick protective layer cannot further enhance the protective effect, and affects the conductivity of the composite current collector, and increases the surface density of the composite current collector, resulting in a decrease in the energy density of the battery based on the composite current collector.

[0037] Preferably, in the protective layer slurry, Fe 3+ The concentration is 0.01-0.5 mol / L, for example, it can be 0.01 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] In the protective layer slurry of the present invention, if the concentration of trivalent iron ions is too low, the effect is not obvious. If the concentration is too high, the copper layer of the composite current collector is severely corroded, affecting the conductivity of the composite current collector.

[0039] Preferably, the method for preparing the metal layer includes any one of physical vapor deposition, chemical vapor deposition, electroplating or chemical plating.

[0040] Preferably, the post-processing comprises extrusion and drying performed in sequence.

[0041] Preferably, the drying temperature is 50-90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C, and the drying time is 1-5 min, for example, 1 min, 2 min, 3 min, 4 min or 5 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0043] A metal layer is prepared on at least one surface of the base film by physical vapor deposition, chemical vapor deposition, electroplating or chemical plating, or a combination of at least two methods to obtain an intermediate, and the intermediate is immersed in a protective layer slurry for 10-60 seconds, and then extruded and dried to obtain the composite current collector;

[0044] The protective layer slurry is obtained by mixing a polythiophene compound, a polyanion compound, a trivalent iron salt and a solvent, wherein the mass concentrations of the polythiophene compound and the polyanion compound in the protective layer slurry are independently 0.1-2 wt %, Fe 3+ The concentration is 0.01-0.5mol / L.

[0045] In a second aspect, the present invention provides a pole piece, which includes the composite current collector as described in the first aspect.

[0046] In a third aspect, the present invention provides a battery, comprising the electrode as described in the first aspect.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The present invention prevents the metal layer from being chemically corroded or physically damaged by providing a protective layer on the surface of the metal layer. The dense structure of the complex formed by the polymer and metal ions in the protective layer can effectively hinder the contact between the metal and oxygen, which not only prevents the metal layer from being oxidized, but also does not affect the conductivity of the composite current collector and can improve the density of the protective layer. At the same time, Fe 3+ It can undergo complexation reaction with O, S, and sulfonate in polythiophene compounds and polyanion compounds, thereby further improving the stability of the protective layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG1 is a schematic structural diagram of the composite current collector according to Example 1 of the present invention;

[0050] Among them, 1-base film, 2-copper layer, 3-protective layer. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0052] Example 1

[0053] This embodiment provides a composite current collector, the structure of which is shown in FIG1 , comprising a base film 1 and copper layers 2 on both sides of the base film 1, a protective layer 3 further provided on the surface of the copper layer 2, and the protective layer 3 comprising a complex formed by poly (3,4-ethylenedioxythiophene), polystyrene sulfonic acid and metal ions, wherein the metal ions include Fe 3+ 、Fe 2+ and Cu 2+ ;

[0054] The copper layer 2 has a thickness of 1000 nm, the base film 1 includes PET (polyethylene terephthalate), and the base film 1 has a thickness of 4.5 μm;

[0055] The preparation method of the composite current collector comprises the following steps:

[0056] (1) The biaxially oriented PET film was placed in a vacuum magnetron sputtering machine, and copper metal was deposited on each film surface in turn. The deposition conditions were: the target material was a metallic copper target (purity of 99.99%), the target power supply was a DC power supply, and the power density was 80W / cm 2 The vacuum degree of the vacuum chamber is 0.09 Pa, the gas source is argon, the argon flow rate is 80 mL / min, and the deposition time is 70 s. A copper layer 2 with a thickness of 1000 nm is prepared on the PET surface, that is, a PET-Cu composite film is obtained;

[0057] (2) Poly (3,4-ethylenedioxythiophene) (CAS No.: 126213-50-1), sodium polystyrene sulfonate (CAS No.: 25704-18-1) and ferric chloride (CAS No.: 7705-08-0) were placed in pure water, heated to 60°C and stirred at 1000 rpm until completely dissolved to obtain a protective layer 3 slurry, wherein the mass concentrations of the polythiophene compound and sodium polystyrene sulfonate were 0.1 wt %, FeCl2, and FeCl3, respectively. 3+ The concentration is 0.01 mol / L;

[0058] The PET-Cu composite film was placed in the protective layer 3 slurry and dipped for 10 seconds. The excess protective layer 3 slurry was then removed by extrusion, and then dried at 80° C. for 2 minutes to obtain the composite current collector.

[0059] Example 2

[0060] This embodiment provides a composite current collector. The composite current collector is the same as Example 1 except that in its preparation method, the mass concentrations of poly (3,4-ethylenedioxythiophene) and sodium polystyrene sulfonate in the protective layer slurry are independently 1 wt %, so that the adaptability of the composite current collector is changed.

[0061] Example 3

[0062] This embodiment provides a composite current collector. The composite current collector is the same as Example 1 except that in its preparation method, the mass concentrations of poly (3,4-ethylenedioxythiophene) and sodium polystyrene sulfonate in the protective layer slurry are independently 2 wt % to adapt the composite current collector.

[0063] Example 4

[0064] This embodiment provides a composite current collector, wherein in addition to the preparation method thereof, the protective layer slurry contains Fe 3+ The concentration of 0.1 mol / L is the same as that of Example 1 except that the adaptability of the composite current collector is changed.

[0065] Example 5

[0066] This embodiment provides a composite current collector, wherein in addition to the preparation method thereof, the protective layer slurry contains Fe 3+ The concentration of 0.5 mol / L is the same as that of Example 1 except that the adaptability of the composite current collector is changed.

[0067] Example 6

[0068] This embodiment provides a composite current collector. The composite current collector is the same as that in embodiment 1 except that in its preparation method, the dipping time is 30 seconds to adapt the composite current collector.

[0069] Example 7

[0070] This embodiment provides a composite current collector. The composite current collector is the same as that in embodiment 1 except that in its preparation method, the dipping time is 60 seconds to adapt the composite current collector.

[0071] Example 8

[0072] This embodiment provides a composite current collector. In addition to the preparation method of the composite current collector, in the protective layer slurry, the mass concentrations of poly (3,4-ethylenedioxythiophene) and sodium polystyrene sulfonate are both 1 wt %, Fe 3+ The ion concentration was 0.1 mol / L, and the dipping time was 30 s to adapt the composite current collector. Others were the same as in Example 1.

[0073] Example 9

[0074] This embodiment provides a composite current collector. The composite current collector is the same as Example 8 except that in its preparation method, the mass of the poly 3,4-ethylenedioxythiophene is replaced with poly (thiophene-3-(2-(2-methoxyethoxy)) (CAS No.: 1003582-37-3) to adapt the composite current collector.

[0075] Example 10

[0076] This embodiment provides a composite current collector. The composite current collector is the same as Example 8 except that in its preparation method, the mass of the poly 3,4-ethylenedioxythiophene is replaced with poly (3-cyclohexyl-4-methylthiophene-2,5-diyl) (CAS No.: 110134-47-9) to change the adaptability of the composite current collector.

[0077] Example 11

[0078] This embodiment provides a composite current collector. The composite current collector is the same as Example 8 except that in its preparation method, the mass of the poly (3,4-ethylenedioxythiophene) is replaced with poly (2-vinylthiophene) (CAS No.: 25988-40-3) to change the adaptability of the composite current collector.

[0079] Example 12

[0080] This embodiment provides a composite current collector. The composite current collector is the same as Example 1 except that in the preparation method, the mass concentrations of the polythiophene compound and sodium polystyrene sulfonate in the protective layer slurry are independently 0.05wt% to adapt the composite current collector.

[0081] Example 13

[0082] This embodiment provides a composite current collector. The composite current collector is the same as Example 1 except that in its preparation method, the mass concentrations of the polythiophene compound and sodium polystyrene sulfonate in the protective layer slurry are independently 2.5wt% to adapt the composite current collector.

[0083] Example 14

[0084] This embodiment provides a composite current collector, wherein in addition to the preparation method thereof, the protective layer slurry contains Fe 3+ The concentration of 0.005 mol / L is the same as that of Example 1 except that the adaptability of the composite current collector is changed.

[0085] Example 15

[0086] This embodiment provides a composite current collector, wherein in addition to the preparation method thereof, the protective layer slurry contains Fe 3+ The concentration of 0.55 mol / L is the same as that of Example 1 except that the adaptability of the composite current collector is changed.

[0087] Example 16

[0088] This embodiment provides a composite current collector. The composite current collector is the same as that in embodiment 1 except that in its preparation method, the dipping time is 5 seconds to adapt the composite current collector.

[0089] Example 17

[0090] This embodiment provides a composite current collector. The composite current collector is the same as that in Example 8 except that in its preparation method, the dipping time is 70 seconds to adapt the composite current collector.

[0091] Comparative Example 1

[0092] This comparative example provides a composite current collector, which is the same as Example 1 except that the composite current collector is not provided with a protective layer;

[0093] The preparation method of the composite current collector is the same as that of Example 1 except that step (2) is not performed.

[0094] Comparative Example 2

[0095] This comparative example provides a composite current collector, which is the same as Example 1 except that in its preparation method, ferric chloride is not added to the protective layer slurry to change the adaptability of the composite current collector.

[0096] Comparative Example 3

[0097] This comparative example provides a composite current collector, which is the same as Example 1 except that in its preparation method, ferric chloride is replaced by ferrous chloride in equal moles to change the adaptability of the composite current collector.

[0098] Comparative Example 4

[0099] This comparative example provides a composite current collector, which is the same as Example 1 except that step (2) in its preparation method is different from that in Example 1;

[0100] The specific step (2) of this comparative example is: the composite membrane prepared in step (1) is washed in a clean water tank, then placed in a 1.5g / L chromic anhydride aqueous solution (25°C) for 20s, and finally washed again in a clean water tank. After washing, it is dried in an oven at a temperature of 65°C to obtain a composite current collector.

[0101] The composite current collectors obtained in the above examples and comparative examples were subjected to electrical performance, antioxidant properties, stability of the protective layer, and performance tests during the battery charge and discharge cycle to verify that the protective layer prepared by the present invention improves the antioxidant properties and stability of the composite copper current collector during battery application without affecting the composite copper current collector. In addition, the thickness of the protective layer of the composite current collector was characterized to indicate the presence of the protective layer. The specific testing method is as follows:

[0102] ① Conductive performance: characterized by square resistance. Specifically, the prepared flat composite current collector sample was placed on a sample table, and the square resistance of the sample was tested using a four-probe square resistance meter.

[0103] ② Antioxidant performance: The change in square resistance before and after baking is used for indirect characterization. Specifically, the prepared flat composite current collector sample and the composite current collector sample baked at 150°C for 30 minutes are placed on the sample table, and the square resistance of the samples is tested using a four-probe square resistance meter. The change in square resistance before and after baking is compared. The smaller the change, the better the antioxidant performance.

[0104] ③Stability of the protective layer: 3M with a width of 20mm TM Scotch TM 600 transparent film tape was adhered to the composite copper current collector prepared above and squeezed twice with a roller. Then the tape was torn off at an angle of 45 degrees, the area where the tape was torn off was marked, and the tape was placed in an oven at 150°C and baked for 30 minutes. After baking, the square resistance of the marked area was tested; if the square resistance changed significantly, it meant that the protective layer was peeled off from the surface of the composite copper current collector, that is, the stability of the composite copper current collector based on the protective layer was poor.

[0105] ④ Performance of composite current collector during battery cycle charge and discharge: characterized by 1C charge and discharge rate and battery capacity retention after 1000 cycles. Specifically, for composite copper current collector: Li-ion battery assembly: For the positive electrode, the positive electrode current collector uses traditional aluminum foil (thickness of 12 microns), and the positive electrode material uses LiNi 0.6 Mn 0.2 Co 0.2O2 (NCM622); for the negative electrode: the negative electrode current collector uses the composite current collector prepared by the present invention, and the negative electrode material uses artificial graphite; for the separator, an alumina ceramic-coated polyethylene separator (thickness 25 microns) is used; for the electrolyte, 1 mol·L -1 A LiPF6 carbonate solution, containing propylene carbonate, ethylene carbonate, and ethyl methyl carbonate in a 1:1:1 mass ratio, was used to assemble a lithium-ion battery. The assembled battery was cycled 1000 times at a 1C charge / discharge rate, and the capacity retention after each cycle was recorded to characterize the composite current collector's stability during battery application.

[0106] ⑤ Test of the adhesion between the electrode material and the composite current collector in the electrode piece: a layer of Permacel P-94 double-sided tape was adhered to a 1 mm thick aluminum foil, a negative electrode piece based on the composite current collector was adhered on the double-sided tape, and a layer of ethylene acrylic acid copolymer film (DuPont Nurcel0903, thickness of 50 μm) was covered on the negative electrode piece, and then 5 N / m 2 The film was hot-pressed at 120°C for 10 seconds, cooled to room temperature, and cut into 150mm x 15mm strips. The ethylene acrylic acid copolymer film strip was fixed to the upper fixture of the tensile testing machine, while the remaining film strip was fixed to the lower fixture. After the two strips were fixed, they were peeled off at an angle of 180° and a speed of 100mm / min to test the peel force, i.e., the adhesion between the composite current collector and the negative electrode material in the negative electrode sheet.

[0107] ⑥ Characterization of the thickness of the protective layer of the composite copper current collector: The prepared composite current collector is prepared according to the sample preparation requirements of the focused ion beam field emission microscope (FIB-SEM), and then the sample is placed in the FIB-SEM. The sample is cut by the ion beam to prepare a cross-sectional sample. After the cross-sectional sample is prepared, the cross-section is observed using the field emission microscope lens, magnified 50,000 times, and after adjustment, the thickness of the protective layer in the cross-sectional morphology photo is measured using the measurement software provided by the electron microscope, thereby obtaining the thickness data of the protective layer.

[0108] The test results are shown in Table 1:

[0109] Table 1

[0110] From Table 1, we can see the following points:

[0111] (1) It can be seen from Examples 1-8 and Comparative Example 1 that compared with the composite current collector without a protective layer, the square resistance of the composite current collector with a protective layer prepared by the present invention does not change before and after baking at 150°C, indicating that the protective layer has good antioxidant properties. Due to the improvement in antioxidant properties, the capacity retention rate of the battery of the composite copper current collector of the present invention is improved, indicating that it has high stability during application. At a charge and discharge rate of 1C and after 1000 cycles, the battery capacity retention rate can reach more than 82%.

[0112] (2) From Examples 1-3 and 12-13, it can be seen that: as the content of polythiophene compounds in the protective layer slurry is increased, the thickness of the prepared protective layer shows an increasing trend, and the square resistance of the prepared composite current collector does not change before and after baking, indicating that the prepared protective layer has good antioxidant properties; compared with the initial square resistance, the square resistance of the composite copper current collector increases after the tape is torn and baked at 150°C for 30 minutes. This is because the Fe 3+ The concentration is relatively low, and the etching of the composite copper current collector surface is not obvious, resulting in a lower surface roughness of the composite copper current collector, which in turn causes slightly poor adhesion between the protective layer and the composite copper current collector; if the content of poly 3,4-ethylenedioxythiophene in the dipping solution is increased, the capacity retention of the battery of the composite copper current collector of the present invention first increases and then decreases. This is because the increase in the content of poly 3,4-ethylenedioxythiophene increases the thickness of the prepared protective layer, thereby improving the antioxidant performance of the protective layer. When its content is too high, the viscosity of the dipping solution increases, the uniformity of the dipping and its adhesion to the substrate deteriorate, thereby reducing the capacity retention rate of the battery.

[0113] (3) From Examples 1, 4, 5 and 14-15, it can be seen that: the Fe content in the protective layer slurry is increased. 3+ The thickness of the prepared protective layer increased slightly, and the square resistance of the prepared composite copper current collector remained unchanged before and after baking. The square resistance after the tape was pasted, torn and baked first decreased and then increased. The corresponding battery capacity first increased and then decreased. This is because as Fe 3+ With the increase of Fe concentration, the etching of the composite copper current collector surface is deepened during the in-situ preparation of the protective layer, resulting in an increase in its surface roughness, promoting the deposition of active substances in the dipping solution on its surface, and improving the adhesion between the dipping coating and the composite copper current collector, thereby promoting performance improvement. 3+ If the concentration is too high, the etching of the composite copper current collector surface is uneven and too severe, which leads to a poor bonding effect between the protective layer and the metal layer, resulting in poor performance.

[0114] (4) From Examples 1, 6, 7 and 16: increasing the dipping time, the thickness of the prepared protective layer first increases and then remains unchanged, the square resistance of the prepared composite copper current collector remains unchanged before and after baking, the square resistance after the tape is pasted, torn and baked first decreases and then remains unchanged, and the capacity of the corresponding battery first increases and then remains unchanged. This is because as the dipping time increases, the deposition amount of the active material in the dipping solution on the membrane surface first increases and then reaches saturation and stability. Further increasing the time has a significant effect on increasing the thickness of the protective layer, and increasing the dipping time further strengthens the Fe 3+ The reaction with the metallic copper layer leads to an improvement in the bonding strength between the protective layer and the metal layer. However, as the dipping process proceeds, the surface layer is occupied by the material in the protective layer, resulting in the termination of the reaction, thereby promoting the square resistance after the tape is pasted, torn and baked to first decrease and then remain unchanged, thereby causing the battery capacity to first increase and then remain unchanged. However, it can be seen from Examples 8 and 17 that dipping for too long will lead to excessive etching of the copper metal layer.

[0115] (5) It can be seen from Examples 8-11 that protective layers based on different types of polythiophene all play a role in promoting the performance improvement of the composite copper current collector.

[0116] (6) It can be seen from Example 1 and Comparative Examples 2-3 that since only trivalent iron ions can etch copper, the complex of the present invention is generated, which not only improves the stability of the protective layer, but also improves the roughness of the surface of the composite current collector, thereby improving the bonding effect between the protective layer and the current collector and improving the overall stability.

[0117] (7) It can be seen from Example 1 and Comparative Example 4 that compared with the protective layer prepared by traditional hexavalent chromium passivation, the bonding force between the protective layer proposed in the present invention and the negative electrode material is stronger. This is because the protective layer material proposed in the present invention is rich in epoxy and sulfonate groups, which can improve the hydrophilicity, thereby improving the coating effect with the aqueous negative electrode slurry, and the protective layer interacts strongly with the hydrophilic additives in the slurry, thereby improving the bonding force between the composite current collector and the negative electrode material; in addition, the cyclic structure of polythiophene in the protective layer forms a conjugated delocalized electronic structure with the benzene ring and vinyl in polystyrene sulfonic acid, which can further form a conjugated effect with the delocalized electronic structure in graphite, thereby further improving the bonding force between the composite current collector and the negative electrode material in the negative electrode sheet.

[0118] In summary, the present invention provides a composite current collector, a preparation method and an application thereof. The composite current collector can effectively solve the problem of oxidation of the metal layer due to contact with oxygen through a protective layer provided on the surface of the metal layer, and will not affect the conductivity of the composite current collector. At the same time, it can also improve the overall stability of the composite current collector.

[0119] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite current collector, characterized in that: The composite current collector comprises a base film and a metal layer on at least one side of the base film, and a protective layer is further provided on the surface of the metal layer; The metal layer comprises copper or a copper alloy; The protective layer includes a complex formed by a polythiophene compound, a polyanion compound and a metal ion, wherein the metal ion includes Fe 3+ , Fe 2+ and Cu 2+ , the polyanion compound includes sulfonate.

2. The composite current collector according to claim 1, characterized in that: The polyanion compound includes any one of polystyrene sulfonic acid, polystyrene sulfonate, poly(4-styrene sulfonic acid-co-maleic acid) salt or polynaphthaldehyde sulfonate or a combination of at least two thereof.

3. The composite current collector according to claim 1 or 2, characterized in that: The thickness of the protective layer does not exceed 10% of the thickness of the metal layer; The thickness of the metal layer is 500-2000nm; The thickness of the protective layer is 30-100 nm.

4. The composite current collector according to claim 1 or 2, characterized in that: The polythiophene compound includes any one of poly-3,4-ethylenedioxythiophene, poly-thiophene-3-(2-(2-methoxyethoxy), poly-3,4-propylenedioxythiophene, poly-3,4-dimethoxythiophene, poly-(3-cyclohexyl-4-methylthiophene-2,5-diyl), 3-hexyl substituted polythiophene, 3-octyl substituted polythiophene or poly(2-vinylthiophene) or a combination of at least two thereof; The base film comprises any one of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene or polyimide, or a combination of at least two thereof; The base film has a thickness of 1-10 μm.

5. A method for preparing a composite current collector according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: A metal layer is prepared on at least one side of the base film to obtain an intermediate, and the intermediate is immersed in a protective layer slurry, or the protective layer slurry is coated on the surface of the intermediate, and then subjected to post-treatment to obtain the composite current collector; The protective layer slurry is obtained by mixing a polythiophene compound, a polyanion compound, an iron salt and a solvent.

6. The preparation method according to claim 5, characterized in that: The iron salt includes a ferric iron salt; The immersion time is 10-60s; In the protective layer slurry, the mass concentrations of the polythiophene compound and the polyanion compound are independently 0.1-2wt%; In the protective layer slurry, Fe 3+ The concentration is 0.01-0.5mol / L.

7. The preparation method according to claim 5 or 6, characterized in that: The method for preparing the metal layer comprises any one of physical vapor deposition, chemical vapor deposition, electroplating or chemical plating, or a combination of at least two thereof; The post-processing includes extrusion and drying performed in sequence; The drying temperature is 50-90° C. and the drying time is 1-5 min.

8. The preparation method according to claim 5 or 6, characterized in that: The preparation method comprises the following steps: A metal layer is prepared on at least one side of the base film by any one of physical vapor deposition, chemical vapor deposition, electroplating or chemical plating or a combination of at least two methods to obtain an intermediate, and the intermediate is immersed in a protective layer slurry, wherein the immersion time is 10-60s, and then extruded and dried to obtain the composite current collector; The protective layer slurry is obtained by mixing a polythiophene compound, a polyanion compound, a trivalent iron salt and a solvent, wherein the mass concentrations of the polythiophene compound and the polyanion compound in the protective layer slurry are independently 0.1-2wt%, Fe 3+ The concentration is 0.01-0.5mol / L.

9. A pole piece, characterized in that: The pole piece comprises the composite current collector as described in any one of claims 1 to 4.

10. A battery, characterized in that: The battery comprises the pole piece as claimed in claim 9.

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