Composite current collector, preparation method thereof, electrode plate containing composite current collector, and secondary battery

Abstract

The invention discloses a composite current collector, a preparation method thereof, an electrode plate containing the composite current collector, and a secondary battery. The composite current collector sequentially comprises a first conducting layer, a first bonding layer, an insulating layer, a second bonding layer and a second conducting layer, and the first conducting layer and the second conducting layer are both copper layers; binders of the first bonding layer and the second bonding layer are respectively and independently selected from any one of epoxy resin, polyolefin, polyester and polyurethane. The composite current collector prepared by the invention has good structural stability, has low requirements on an insulating layer, is high in safety when being applied to a battery, and is beneficial to improving the energy density of the battery.

Description

Technical Field

[0001] The present invention relates to a composite current collector, a preparation method thereof, an electrode sheet containing the same, and a secondary battery. Background Art

[0002] The current collector is one of the indispensable electrode materials for lithium-ion batteries, and has important functions of carrying active substances (load-bearing property) and collecting microcurrents (conductivity). Thinning and functionalization are the main development directions of the current collector. However, the further thinning of the current collector leads to a reduction in strength, making it difficult to be applied in batches. Although functionalized current collectors such as carbon-coated, LFP, and ceramic can improve adhesion, internal resistance, safety performance, etc., there are still some negative effects, such as higher process control requirements, increased costs, or reduced energy density. The composite current collector integrates the characteristics of being thin and light and having high safety, and has been widely studied in recent years.

[0003] The current collectors widely used in the prior art are mainly copper foil current collectors and aluminum foil current collectors. The preparation methods of composite copper foil current collectors include a one-step method and a two-step method. The one-step method is to select a ready-made biaxially oriented polypropylene film (BOPP) or biaxially oriented polyester film (BOPET) substrate, and through electroless plating connected with electroplating, copper foils with a thickness of 1 μm are gradually formed on both sides of the substrate; the two-step method is to select a ready-made BOPP or BOPET substrate, and after magnetron sputtering and then electroplating to thicken, copper foils with a thickness of 1 μm are formed on both sides of the substrate. The preparation methods of the prior art can only select ultra-thin BOPP or BOPET substrates, and copper foil layers are formed on both sides of the substrate through different processes to form a composite current collector with a "metal-PP / PET-metal" structure similar to a "sandwich". The thickness uniformity and mechanical and physical properties of the core layer material have a great influence on the mechanical properties of the final composite current collector.

[0004] BOPP and BOPET substrates are currently the few optional materials that can meet the requirements in this regard. However, the bonding force between the metal layer and the BOPP or BOPET substrate is insufficient, and the copper layer is likely to fall off during use; moreover, the thickness of the BOPP or BOPET substrate has limitations. The thickness of the core layer substrate used in the current process is above 4 μm, and there are many suppliers. However, below 4 μm, due to high costs and high performance requirements, the selectivity is still small; the electrochemical performance and acid and alkali corrosion resistance of the BOPET substrate need to be improved, while the high temperature resistance of the BOPP substrate needs to be enhanced. In addition, the preparation methods of the prior art have relatively strict requirements for conditions, requiring a vacuum environment, and the product needs to be repeatedly coated, plated, wound, transported and stretched, and dried at high temperature in an acidic or alkaline environment, resulting in low production efficiency (speed), yield (trimming), and good rate. Summary of the Invention

[0005] The present invention mainly aims to overcome the defects in the prior art that the metal layer peels off due to insufficient bonding force between the metal layer and the polymer substrate, and the requirements for the properties of the polymer substrate are harsh, and provides a composite current collector, a preparation method thereof, an electrode sheet containing the same, and a secondary battery. The composite current collector prepared by the present invention has good structural stability, low requirements for the insulating layer, high safety when applied to a battery, and is beneficial to improving the energy density of the battery.

[0006] The present invention solves the above technical problems through the following technical solutions.

[0007] The present invention provides a composite current collector, which sequentially includes a first conductive layer, a first adhesive layer, an insulating layer, a second adhesive layer, and a second conductive layer, wherein both the first conductive layer and the second conductive layer are copper layers; the adhesives of the first adhesive layer and the second adhesive layer are independently selected from any one of epoxy resin, polyolefin, polyester, and polyurethane.

[0008] In the present invention, the thickness of the composite current collector can be 4.4 - 10 μm, for example, 8 μm.

[0009] In the present invention, the thickness of the first conductive layer can be 1 - 2 μm, for example, 1.5 μm.

[0010] In the present invention, the thickness of the second conductive layer can be 1 - 2 μm, for example, 1.5 μm.

[0011] In the present invention, the first conductive layer and the second conductive layer have the same thickness.

[0012] In the present invention, the thickness of the first adhesive layer is preferably 0.2 μm - 1 μm, for example, 0.5 μm.

[0013] In the present invention, the thickness of the second adhesive layer is preferably 0.2 μm - 1 μm, for example, 0.5 μm.

[0014] In the present invention, the first adhesive layer and the second adhesive layer have the same thickness.

[0015] In the present invention, the thickness ratio of the first conductive layer to the first adhesive layer can be (2 - 5):1, for example, 3:1.

[0016] In the present invention, the thickness ratio of the first conductive layer to the insulating layer can be 1:(0.5 - 4), for example, 1:2.

[0017] In the present invention, the total thickness of the first adhesive layer, the second adhesive layer, and the insulating layer can be 3 μm - 6 μm, for example, 5 μm.

[0018] In the present invention, the thickness of the insulating layer can be 2 μm - 5 μm, such as 4 μm or 4.5 μm; the thickness tolerance is within the range of ±5%.

[0019] In the present invention, the material of the insulating layer can be a conventional polymer film in the art, preferably a BOPET film or a BOPP film.

[0020] The present invention provides a method for preparing a composite current collector, which successively includes a first conductive layer, a first adhesive layer, an insulating layer, a second adhesive layer and a second conductive layer. The method for preparing the composite current collector includes the following steps:

[0021] S1. Transfer the first conductive layer onto a first carrier film to obtain a first composite layer, and the first conductive layer is obtained by electroplating on a cathode device with an electroplating solution;

[0022] Transfer the second conductive layer onto a second carrier film to obtain a second composite layer, and the second conductive layer is obtained by electroplating on a cathode device with an electroplating solution;

[0023] The electroplating solution contains copper ions, hydrogen ions, chloride ions and additives, and the additives include at least one of polyethylene glycol, sulfonate or polyether thiol;

[0024] S2. Composite the first conductive layer in the first composite layer and the second conductive layer in the second composite layer on two opposite surfaces of the insulating layer through the first adhesive layer and the second adhesive layer respectively. After peeling off the first carrier film and the second carrier film, the remaining part is the composite current collector; the adhesives of the first adhesive layer and the second adhesive layer are independently selected from any one of epoxy, polyolefin, polyester and polyurethane.

[0025] In S1, the sulfonate is preferably one or more of sodium sulfonate, calcium sulfonate, magnesium sulfonate and barium sulfonate.

[0026] In S1, the cathode device can be a cathode roller; the surface roughness of the cathode roller is preferably less than 0.1 μm. The surface roughness refers to the unevenness of the smaller spacing and tiny peaks and valleys on the surface of the cathode roller. The cathode roller has super smoothness.

[0027] Among them, the material of the cathode roller is titanium metal.

[0028] Among them, the diameter of the cathode roller is preferably 400 - 1000 mm, such as 500 mm.

[0029] Among them, the width of the roller surface of the cathode roller is preferably 300 - 800 mm, such as 500 mm.

[0030] In S1, the temperature of the electroplating solution can be 45 - 60 °C, such as 52 °C.

[0031] In S1, the current density during electroplating can be conventional in the art, preferably 27 A / cm 2 -73 A / cm 2 , for example, 50 A / cm 2 .

[0032] In S1, the linear velocity of the cathode device can be conventional in the art, preferably 1-5 m / min, for example, 3 m / min.

[0033] In S1, using the electrochemical principle, the electroplating solution generates an ultrathin copper foil with high density and uniformity and high tensile strength and high elongation rate on the surface of the cathode device under the action of an electric field.

[0034] In S1, the source of copper ions can be a copper-containing compound soluble in water at 45-60 °C, preferably copper sulfate.

[0035] In S1, the source of hydrogen ions can be an acidic substance, preferably an acid, for example, sulfuric acid.

[0036] In S1, the source of chloride ions can be a soluble chlorine-containing compound, preferably hydrochloric acid.

[0037] In S1, based on the electroplating solution, the concentration of copper ions in the electroplating solution can be 60-150 g / L, for example, 60 g / L, 100 g / L or 150 g / L.

[0038] In S1, based on the electroplating solution, the concentration of hydrogen ions in the electroplating solution can be 60-150 g / L, for example, 60 g / L, 100 g / L or 150 g / L.

[0039] In S1, based on the electroplating solution, the concentration of chloride ions in the electroplating solution can be 10-50 ppm, for example, 10 ppm, 30 ppm or 50 ppm.

[0040] In S1, based on the electroplating solution, the concentration of the additive can be 1-50 ppm, for example, 10 ppm, 30 ppm or 50 ppm.

[0041] In S1, the formulation of the electroplating solution can be: copper ions with a concentration of 60-150 g / L, chloride ions with a concentration of 10-50 ppm, hydrogen ions with a concentration of 60-150 g / L, and an additive with a concentration of 1-50 ppm.

[0042] In some specific embodiments, the formulation of the electroplating solution is: copper ions with a concentration of 100 g / L, chloride ions with a concentration of 30 ppm, hydrogen ions with a concentration of 100 g / L, and PEG-600 with a concentration of 30 ppm.

[0043] In some specific embodiments, the formulation of the electroplating solution is as follows: copper ions with a concentration of 60 g / L, chloride ions with a concentration of 10 ppm, hydrogen ions with a concentration of 60 g / L, and PEG-600 with a concentration of 10 ppm.

[0044] In some specific embodiments, the formulation of the electroplating solution is as follows: copper ions with a concentration of 150 g / L, chloride ions with a concentration of 50 ppm, hydrogen ions with a concentration of 140 g / L, and PEG-600 with a concentration of 50 ppm.

[0045] In some specific embodiments, the formulation of the electroplating solution is as follows: copper ions with a concentration of 100 g / L, chloride ions with a concentration of 30 ppm, hydrogen ions with a concentration of 100 g / L, and polyether thiol with a concentration of 30 ppm.

[0046] In S1, the first carrier film and the second carrier film can be conventional polymer films in the art, preferably BOPET films; the thickness of the BOPET film is preferably 25 μm.

[0047] In S1, the first carrier film and the second carrier film preferably further include a release layer. During the transfer process, the release layer is in direct contact with the first conductive layer or the second conductive layer; the preparation method of the release layer can be conventional in the art, preferably obtained by coating a release agent on a polymer film. The polymer film is any one of PET films, PP films, BOPET films, and BOPP films, and the thickness of the polymer film is preferably 25 μm; the release agent is preferably alkylated polyethyleneimine or polyethyleneimine. Among them, there is no component migration of the release agent.

[0048] Among them, the coating method is preferably any one of slit coating, knife coating, microgravure coating, and roll transfer printing.

[0049] Among them, the surface peel force of the release layer is preferably 10 gf - 20 gf. The surface peel force refers to the force when the intermolecular adsorption and adhesion forces are destroyed under the action of an external force on the surface of the release layer, resulting in the peeling of the surface of the release layer; it is measured by GB 8808-1988 "Test Method for Peel Strength of Soft Composite Plastic Materials".

[0050] In S1, the first composite layer and the second composite layer are also subjected to cleaning, anti-oxidation treatment, and passivation treatment by a post-treatment machine. The carrier film can be recycled multiple times.

[0051] In S1, during the transfer process, the film running speed of the first carrier film and the second carrier film can be 1 - 5 m / min, for example, 3 m / min. The film running speed refers to the length of the copper foil (film) generated per minute. During the transfer process, pressure is applied to the conductive layer through a pressure roller to peel it off from the cathode device and compound it with the carrier film.

[0052] In some specific embodiments, during the compounding process, the first composite layer and the second composite layer are compounded with the insulating layer simultaneously.

[0053] In S2, during the compounding process, pressure can be applied to the first composite layer and the second composite layer through a laminator, so that the first conductive layer and the second conductive layer are respectively compounded on two opposite surfaces of the insulating layer through the first adhesive layer and the second adhesive layer.

[0054] Among them, the pressure is preferably 0.3 MPa - 0.6 MPa, for example, 0.5 MPa.

[0055] In S2, after the compounding, preferably, a curing step is further included. The curing is to place it in an oven and process it at 120 - 180 °C for 10 - 60 s, for example, process it at 150 °C for 30 s.

[0056] In S2, the material of the insulating layer can be a conventional polymer film in the art, preferably a BOPET film or a BOPP film.

[0057] In S2, the thickness of the insulating layer is preferably 2 μm - 5 μm; the thickness tolerance is within the range of ±5%, for example, 4 or 4.5 μm.

[0058] In S2, the preparation method of the first adhesive layer and the second adhesive layer preferably includes the following steps: coating the adhesive on two opposite surfaces of the insulating layer respectively, and obtaining it after curing. The coating method is preferably any one of slit coating, knife coating, microgravure coating, and roll transfer printing.

[0059] The electrochemical performance of the adhesive is stable, resistant to electrolyte corrosion, and has a strong bonding force with metal materials.

[0060] Among them, the curing temperature is preferably 80 °C - 120 °C, for example, 100 °C.

[0061] Among them, the curing time is preferably 10 - 60 s, for example, 30 s.

[0062] In S2, the epoxy resin can be at least one of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, alicyclic epoxy resin, and epoxy olefin epoxy resin; for example, glycidyl ether epoxy resin.

[0063] In S2, the polyurethane is at least one of an anionic polyurethane, a cationic polyurethane, and a nonionic polyurethane; for example, a nonionic polyurethane.

[0064] In S2, the polyolefin is preferably at least one of polyethylene and polypropylene.

[0065] In S2, the polyester is preferably one or more of polyethylene glycol ester, polyethylene terephthalate, polybutylene terephthalate, polyhydroxybutyrate / pentanoate, polylactide (polylactic acid), and polycaprolactone (PCL).

[0066] In S2, the total thickness of the first adhesive layer, the second adhesive layer, and the insulating layer can be 3 μm - 6 μm.

[0067] The present invention provides a composite current collector prepared by the preparation method of the composite current collector as described above.

[0068] The present invention provides an electrode sheet, which includes the composite current collector as described above and an electrode material layer, and the electrode material layer is disposed on at least one outer surface of the composite current collector.

[0069] In the present invention, the electrode sheet can be a positive electrode sheet or a negative electrode sheet.

[0070] In the present invention, the electrode material layer may include an active material, and according to needs, a binder and a conductive agent may be further added.

[0071] Among them, the active material can be a positive electrode active material or a negative electrode active material.

[0072] The positive electrode active material can be a positive electrode active material conventionally used in the positive electrode of a lithium-ion battery in the art, and the positive electrode active material may include, but is not limited to, one or more of lithium iron phosphate, lithium manganese iron phosphate, ternary positive electrode materials, and lithium-rich manganese-based materials.

[0073] The negative electrode active material may be a compound capable of reversibly inserting and extracting lithium. Specific examples of the negative electrode active material include, but are not limited to: carbon materials such as crystalline carbon (natural graphite, artificial graphite, etc.), amorphous carbon, carbon-coated graphite, and resin-coated graphite; or oxide materials such as indium oxide, silicon oxide, tin oxide, lithium titanate, zinc oxide, and lithium oxide. It may also be lithium metal or a metal material capable of forming an alloy with lithium. Among them, the metal material capable of forming an alloy with lithium is, for example, Cu, Sn, Si, Co, Mn, Fe, Sb, and Ag. A binary or ternary alloy containing these metals and lithium may also be used as the negative electrode active material. These negative electrode active materials may be used alone or in combination of two or more. From the perspective of high energy density, carbon materials such as graphite may also be used in combination with Si-based materials such as Si, Si alloy, and Si oxide.

[0074] Among them, the binder may be a component that helps the binding between the active material and the conductive agent and helps the binding between the active material and the current collector. It can generally be selected from polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0075] Among them, the conductive agent may be a reagent for ensuring good charge and discharge performance of the electrode. It can be arbitrarily selected from graphite-based materials such as natural graphite and artificial graphite, carbon black-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride powder, aluminum powder, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium dioxide or polyphenylene derivatives.

[0076] The present invention provides a secondary battery, which includes the electrode sheet, separator, and electrolyte as described above.

[0077] In the present invention, the separator may be a conventional polymer film in the art, such as a polypropylene separator or a polyethylene separator. In the present invention, the electrolyte may be a conventional electrolyte for batteries in the art, generally including a non-aqueous solvent, a lithium salt, and an additive.

[0078] Among them, the non-aqueous solvent can be a conventional non-aqueous solvent in the art, preferably an ester solvent, and more preferably a carbonate solvent. The carbonate solvent can be selected from one or more of ethylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene sulfite (EC), propylene sulfite (PC), and butylene sulfite (BC).

[0079] Among them, the additive can be selected from one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene vinylene carbonate (VEC), divinyl sulfate (DTD), vinyl sulfite, 1,3-propane sultone (PS), allyl sulfonic acid lactone, and 1,4-butane sultone.

[0080] In the present invention, when the electrode sheet is a positive electrode sheet, the preparation method of the secondary battery can be winding the positive electrode sheet, the negative electrode sheet, and the separator to obtain an electrode core, and then performing packaging with a packaging shell and injecting the electrolyte; or it can be sequentially stacking the negative electrode sheet, the separator, the positive electrode sheet, and the separator in this order to obtain an electrode core, and then performing packaging with a packaging shell and injecting the electrolyte.

[0081] On the basis of conforming to the common knowledge in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain various preferred examples of the present invention.

[0082] The reagents and raw materials used in the present invention are all commercially available.

[0083] The positive progress effect of the present invention is as follows:

[0084] The composite current collector provided by the present invention makes up for the deficiencies in the electrochemical performance of the insulating layer in the prior art through a specific binder, reduces the requirements for the performance of the insulating layer material, effectively improves the situation of metal peeling caused by insufficient bonding force during use, has good structural stability, toughness, and ductility, and can improve the energy density of the battery and has good safety during application. Further, it also brings better electrolyte resistance performance, which is beneficial to improving the service life of the battery.

[0085] The preparation method of the present invention can generate a conductive layer at one time, the production process is continuous, the number of processes is small, the electroplating process and equipment are simplified, the yield and the good product rate of the product can be greatly improved, the quality consistency and stability of the product are improved, the compactness and uniformity of the prepared conductive layer are good, the bonding force with the insulating layer is strong, and the battery has good cycle performance and good electrolyte resistance when applied to the battery. And the carrier film can be reused multiple times, and the production cost is relatively low. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 Schematic flow chart of the preparation method of the present invention.

[0087] Figure 2 Schematic structural diagram of the composite current collector prepared by the present invention. (1, first conductive layer; 2, first adhesive layer; 3, insulating layer; 4, second adhesive layer; 5, second conductive layer) Specific embodiments

[0088] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0089] Example 1

[0090] (1) A 25-μm-thick general-purpose BOPET protective film was selected, and polyethyleneimine was coated on its surface to obtain a carrier film;

[0091] (2) A titanium roller with a surface roughness less than 0.1 μm was used as the cathode roller for electroplating to prepare a 1.5-μm-thick conductive layer; the electroplating solution formula was: copper sulfate with a concentration of 100 g / L, hydrochloric acid with a concentration of 30 ppm, sulfuric acid with a concentration of 50 g / L, and PEG-600 with a concentration of 30 ppm; the temperature of the electroplating solution was 50 °C; the electroplating parameters were set as: current density of 52 A / cm 2 ; linear velocity of 3 m / min; diameter of the titanium roller of 500 mm, and roller surface width of 500 mm;

[0092] (3) Pressure was applied to the conductive layer through a pressure roller to peel it off from the cathode roller and compound it with the carrier film, and the running speed of the carrier film was 3 m / min;

[0093] (4) A BOPET film with a thickness of 4 μm (thickness tolerance within ±5%) was selected as the insulating layer, and glycidyl ether epoxy resin was coated on both sides of the film by coating, and cured at a temperature of 100 °C for 30 s to form a 0.5-μm-thick first adhesive layer and second adhesive layer;

[0094] (5) On a laminating machine, the conductive layers on two carrier films were simultaneously compounded with the insulating layer through the first adhesive layer and the second adhesive layer respectively. The pressure of the laminating machine was 0.5 MPa, and then it was put into an oven and treated at 150 °C for 30 s for curing and shaping. After peeling off the carrier film, the edges were trimmed to obtain the composite current collector.

[0095] Example 2

[0096] The difference from Example 1 is only that the glycidyl ether epoxy resin in step (4) is replaced by polybutylene terephthalate.

[0097] Example 3

[0098] The difference from Example 1 is only that the glycidyl ether epoxy resin in step (4) is replaced by a non-ionic polyurethane.

[0099] Example 4

[0100] The difference from Example 1 is only that in the electroplating solution of step (2), the concentration of copper sulfate is 60 g / L, the concentration of hydrochloric acid is 10 ppm, the concentration of sulfuric acid is 30 g / L, and the concentration of polyethylene glycol is 10 ppm.

[0101] Example 5

[0102] The difference from Example 1 is only that in the electroplating solution of step (2), the concentration of copper sulfate is 150 g / L, the concentration of hydrochloric acid is 50 ppm, the concentration of sulfuric acid is 70 g / L, and the concentration of polyethylene glycol is 50 ppm.

[0103] Example 6

[0104] The difference from Example 1 is only that the additive in the electroplating solution of step (2) is polyether thiol.

[0105] Example 7

[0106] Positive electrode sheet

[0107] Mix the positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride, and the conductive agent small particle conductive carbon black (hereinafter referred to as Super P) in a weight ratio of 98:1:1, add N-methylpyrrolidone (NMP), and stir in a vacuum blender until the system becomes homogeneous and transparent to obtain a positive electrode paste; uniformly coat the positive electrode paste on both sides of the aluminum foil, dry it at room temperature and then transfer it to an oven for drying, and then obtain the positive electrode sheet through cold pressing and slitting.

[0108] Negative electrode sheet

[0109] Weigh the corresponding substances according to 96% graphite of the negative electrode active material, 1% negative electrode conductive agent SP, 2% negative electrode binder PAA+SBR, and 1% negative electrode dispersant CMC-Na, stir them evenly in a blender, and then add N-methylpyrrolidone according to a solid content of 58%, stir and mix evenly to prepare a negative electrode paste; then uniformly coat the negative electrode paste on both sides of the composite current collector prepared in Example 1, dry it at room temperature and then transfer it to an oven for drying, and then obtain the negative electrode sheet through cold pressing and slitting.

[0110] Electrolyte

[0111] In an argon atmosphere glove box with a water content of < 10 ppm, battery-grade ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl acetate (EA) are mixed in a mass ratio of 1:1:2:6 to form an organic solvent. A fully dried lithium salt (LiPF6) is dissolved in the above organic solvent, and after mixing evenly, an electrolyte solution is obtained, where the concentration of LiPF6 is 1 mol / L.

[0112] Separator

[0113] A 12-μm-thick polypropylene separator is selected.

[0114] The positive electrode sheet, negative electrode sheet, and separator prepared above are wound to obtain an electrode core, which is then packaged in a packaging case and filled with the electrolyte solution to obtain a secondary battery.

[0115] Comparative Example 1

[0116] Compared with Example 1, the difference is that the electroplating solution does not contain additives.

[0117] Comparative Example 2

[0118] Compared with Example 1, the difference is that the first carrier film and the second carrier film are aluminum foils, and a conductive layer is directly electroplated on the aluminum foils.

[0119] Effect Example

[0120] 1. According to the GB / T 3923.1-1997 standard, the composite current collectors prepared in Examples 1-6 and Comparative Examples 1-2 are cut into small strips 1 cm wide and tested with a tensile machine.

[0121] Figure 1 It is a process schematic diagram of the preparation method of the present invention. Figure 2 It is a structural schematic diagram of the composite current collector prepared by the present invention. According to the results of the above tests, the bonding force between the conductive layer and the insulating layer of the composite current collector prepared by the present invention is ≥ 4 N / cm, preferably 6 or 7 N / cm. The bonding force between the conductive layer and the insulating layer of the composite current collector prepared in Comparative Examples 1-2 is < 3 N / cm.

[0122]

[0123] 2. Density reduction rate

[0124] Control example: A single-layer copper foil with a thickness of 8 μm is used as the current collector.

[0125] Based on the density of the current collector in the control example, the density reduction rates of other examples are calculated. The density of copper is calculated according to 8.9 g / cm 3 Calculated, the density of the BOPET film is calculated according to 1.39 g / cm3 Calculation: The density of the adhesive layer is calculated as 1.3 g / cm 3 Calculation. Taking Example 1 as an example:

[0126] Density reduction rate = (Density of the copper foil current collector in Comparative Example 3 - Density of the composite current collector in Example 1) / Density of the copper foil current collector in Comparative Example 3 × 100%

[0127] Specifically: [8.9 - (1.5 * 8.9 * 2 + 0.5 * 1.3 * 2 + 3 + 1.39 * 4) / 8] / 8.9 * 100% = 54%

[0128] It can be seen that the density of the composite current collector of the present invention is much smaller than that of the control example, indicating that for current collectors of the same mass, the composite current collector of the present invention has a larger volume and more charge storage units. When applied to secondary batteries, it is beneficial to improve the energy density of the battery and has good safety. At the same time, due to the good electrolyte resistance performance of the composite current collector of the present invention, the service life of the battery can be extended.

[0129] The above-described embodiments are only preferred embodiments of the present invention, which are convenient for those skilled in the art to understand and use the present invention. Obviously, any person skilled in the art can make minor modifications or changes to this embodiment without creative labor and apply it to other embodiments. Therefore, the present invention is not limited to the above embodiments, and any equivalent changes, simple modifications, and decorations made within the scope of the present invention still fall within the scope covered by the present invention.

Claims

1. A composite current collector, characterized in that, It sequentially includes a first conductive layer, a first adhesive layer, an insulating layer, a second adhesive layer and a second conductive layer. Among them, both the first conductive layer and the second conductive layer are copper layers; the adhesives of the first adhesive layer and the second adhesive layer are independently selected from any one of epoxy resin, polyolefin, polyester and polyurethane.

2. The composite current collector according to claim 1, wherein, The thickness of the composite current collector is 4.4 - 10 μm, such as 8 μm; and / or, the thickness of the first conductive layer is 1 - 2 μm, such as 1.5 μm; and / or, the thickness of the second conductive layer is 1 - 2 μm, such as 1.5 μm; and / or, the thicknesses of the first conductive layer and the second conductive layer are the same; and / or, the thickness of the first adhesive layer is 0.2 μm - 1 μm, such as 0.5 μm; and / or, the thickness of the second adhesive layer is 0.2 μm - 1 μm, such as 0.5 μm; and / or, the thicknesses of the first adhesive layer and the second adhesive layer are the same; and / or, the thickness ratio of the first conductive layer to the first adhesive layer is (2 - 5):1, such as 3:1; and / or, the thickness ratio of the first conductive layer to the insulating layer is 1:(0.5 - 4), such as 1:2; and / or, the total thickness of the first adhesive layer, the second adhesive layer and the insulating layer is 3 μm - 6 μm, such as 5 μm; and / or, the thickness of the insulating layer is 2 μm - 5 μm, such as 4 μm or 4.5 μm; where the thickness tolerance is within ±5%; and / or, the material of the insulating layer is BOPET film or BOPP film.

3. A preparation method of a composite current collector, characterized in that, The composite current collector sequentially includes a first conductive layer, a first adhesive layer, an insulating layer, a second adhesive layer and a second conductive layer. The preparation method of the composite current collector includes the following steps: S1. Transfer the first conductive layer onto a first carrier film to obtain a first composite layer. The first conductive layer is obtained by electroplating on a cathode device with an electroplating solution; Transfer the second conductive layer onto a second carrier film to obtain a second composite layer. The second conductive layer is obtained by electroplating on a cathode device with an electroplating solution; The electroplating solution contains copper ions, hydrogen ions, chloride ions and additives. The additives include at least one of polyethylene glycol, sulfonate or polyether thiol; S2. Composite the first conductive layer in the first composite layer and the second conductive layer in the second composite layer on two opposite surfaces of the insulating layer through the first adhesive layer and the second adhesive layer respectively. After peeling off the first carrier film and the second carrier film, the remaining part is the composite current collector; the adhesives of the first adhesive layer and the second adhesive layer are independently selected from any one of epoxy resin, polyolefin, polyester and polyurethane.

4. The preparation method of the composite current collector according to claim 3, wherein, The cathode device is a cathode roller; the surface roughness of the cathode roller is preferably less than 0.1 μm; the material of the cathode roller is preferably titanium metal; the diameter of the cathode roller is preferably 400 - 1000 mm, such as 500 mm; the width of the roller surface of the cathode roller is preferably 300 - 800 mm, such as 500 mm; and / or, the temperature of the electroplating solution is 45 - 60 °C, such as 52 °C; and / or, the current density during electroplating is 27 A / cm 2 -73 A / cm 2 , such as 50 A / cm 2 ; And / or, the linear velocity of the cathode device is 1 - 5 m / min, such as 3 m / min.

5. The preparation method of the composite current collector according to claim 3, wherein, The sulfonate is one or more of sodium sulfonate, calcium sulfonate, magnesium sulfonate, and barium sulfonate; And / or, the source of the copper ions is a copper-containing compound that is soluble in water at 45 - 60 °C; preferably copper sulfate; And / or, the source of the hydrogen ions is an acid, such as sulfuric acid; And / or, the source of the chloride ions is hydrochloric acid; And / or, based on the electroplating solution, the concentration of copper ions in the electroplating solution is 60 - 150 g / L, such as 60 g / L, 100 g / L, or 150 g / L; And / or, based on the electroplating solution, the concentration of hydrogen ions in the electroplating solution is 60 - 150 g / L, such as 60 g / L, 100 g / L, or 140 g / L; And / or, based on the electroplating solution, the concentration of chloride ions in the electroplating solution is 10 - 50 ppm, such as 10 ppm, 30 ppm, or 50 ppm; And / or, based on the electroplating solution, the concentration of the additive is 1 - 50 ppm, such as 10 ppm, 30 ppm or 50 ppm; And / or, the epoxy resin is at least one of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, alicyclic epoxy resin, and epoxy olefin epoxy resin; such as glycidyl ether epoxy resin; And / or, the polyurethane is at least one of anionic polyurethane, cationic polyurethane, and non-ionic polyurethane; such as non-ionic polyurethane; And / or, the polyolefin is at least one of polyethylene and polypropylene; And / or, the polyester is one or more of polyethylene glycol ester, polyethylene terephthalate, polybutylene terephthalate, polyhydroxybutyrate, polyhydroxyvalerate, polylactide, and polycaprolactone.

6. The preparation method of the composite current collector according to claim 3, wherein, The first carrier film and the second carrier film include a release layer. During the transfer process, the release layer is in direct contact with the first conductive layer or the second conductive layer; the release layer is prepared by coating a release agent on a polymer film, and the polymer film is any one of PET film, PP film, BOPET film, and BOPP film. The thickness of the polymer film is preferably 25 μm; the release agent is preferably alkylated polyethyleneimine or polyethyleneimine; the surface peel force of the release layer is preferably 10 gf - 20 gf; And / or, during the transfer process, the film running speed of the first carrier film and the second carrier film is 1 - 5 m / min, such as 3 m / min; And / or, in S1, the first composite layer and the second composite layer are also subjected to cleaning, anti-oxidation treatment, and passivation treatment by a post-treatment machine; And / or, the materials of the first carrier film and the second carrier film are BOPET films; the thickness of the BOPET film is preferably 25 μm; And / or, the formulation of the electroplating solution is: copper ions with a concentration of 60 - 150 g / L, chloride ions with a concentration of 10 - 50 ppm, hydrogen ions with a concentration of 60 - 150 g / L, and an additive with a concentration of 1 - 50 ppm.

7. The preparation method of the composite current collector according to claim 3, wherein, In S2, during the compounding process, pressure is applied to the first composite layer and the second composite layer by a laminator, so that the first conductive layer and the second conductive layer are respectively compounded on two opposite surfaces of the insulating layer through the first adhesive layer and the second adhesive layer; the pressure is preferably 0.3 MPa - 0.6 MPa, such as 0.5 MPa; And / or, in S2, after the compounding, when peeling between the first carrier film and the second carrier film, there is also a step of curing, which is to place it in an oven and process it at 120 - 180 °C for 10 - 60 s, such as processing it at 150 °C for 30 s; And / or, the preparation method of the first adhesive layer and the second adhesive layer includes the following steps: coating the adhesive on two opposite surfaces of the insulating layer respectively, and obtaining it after curing; the curing temperature is preferably 80 °C - 120 °C, such as 100 °C; the curing time is preferably 10 - 60 s, such as 30 s; And / or, the formula of the electroplating solution is: copper ions with a concentration of 100 g / L, chlorine ions with a concentration of 30 ppm, hydrogen ions with a concentration of 100 g / L, and PEG - 600 with a concentration of 30 ppm; or, copper ions with a concentration of 60 g / L, chlorine ions with a concentration of 10 ppm, hydrogen ions with a concentration of 60 g / L, and PEG - 600 with a concentration of 10 ppm; or copper ions with a concentration of 150 g / L, chlorine ions with a concentration of 50 ppm, hydrogen ions with a concentration of 140 g / L, and PEG - 600 with a concentration of 50 ppm; or copper ions with a concentration of 100 g / L, chlorine ions with a concentration of 30 ppm, hydrogen ions with a concentration of 100 g / L, and polyether thiol with a concentration of 30 ppm.

8. A composite current collector, characterized in that, It is prepared by using the preparation method described in any one of claims 3 - 7.

9. An electrode sheet, characterized in that, It includes the composite current collector and the electrode material layer described in any one of claims 1, 2 or 8, and the electrode material layer is arranged on at least one outer surface of the composite current collector.

10. A secondary battery, characterized in that, It includes the electrode sheet, the separator and the electrolyte described in claim 9.

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