Polymer-based film for composite current collector, composite current collector, and preparation method and application thereof

Abstract

The present application relates to polymer base film for composite current collector, composite current collector and preparation method and application, belong to current collector technical field. The material of polymer base film is n-type conductive polymer, the repeating unit of n-type conductive polymer structure is shown in formula (1): R is same or different, each independently selected from hydrogen, halogen, nitro, cyano, C1-C10 halogen-substituted alkyl, C2-C10 alkenyl, C2-C10 alkynyl and silicon-protected vinyl. The n-type conductive polymer has high conductivity, so it does not need to increase the conductive layer or add conductive agent, and can be used as a kind of minimalist high-performance composite current collector base film material;And can avoid the swelling problem of composite current collector while meeting the adhesion requirement of plating layer.

Description

Technical Field

[0001] This invention relates to the field of current collector technology, specifically to polymer-based films for composite current collectors, composite current collectors, their preparation methods, and applications. Background Technology

[0002] The composite current collector consists of a base film layer and metal layers on both sides of the base film. The metal layers are made of metals such as copper and aluminum, and their thickness is generally required to be around 1 μm. The composite current collector is prepared by forming metal layers on both sides of the base film through vacuum evaporation or magnetron sputtering + electroplating processes, and is suitable for lithium battery current collectors.

[0003] However, since the base film layer is mostly made of polymer materials such as polyethylene terephthalate (PET), which are almost all insulators with extremely poor conductivity, the current collector resistance increases dramatically, affecting the battery's internal resistance and power performance. To solve the aforementioned problems caused by the poor conductivity of polymer base films such as PET, the following two methods are currently mainly used: one is to add inorganic or organic polymer conductive agents to the substrate; the other is to add a conductive layer on the substrate. However, both methods significantly increase the number of steps and difficulty in the preparation of composite current collectors, increase preparation costs, and reduce production efficiency, which is not conducive to large-scale mass production and application in battery cells.

[0004] Besides internal resistance issues, PET and other oxygen-containing group-based film materials contain a large number of ester groups, making them prone to swelling. When the electrolyte in the battery comes into contact with PET or other oxygen-containing group-based film materials, the ester groups in the PET and other oxygen-containing group-based film materials meet and dissolve in the ester groups in the electrolyte. This leads to swelling of the base film layer during long-term battery use, disrupting the chemical bonds between the metal layer and the base film layer. Consequently, the peel force between the metal layer and the base film layer of the composite current collector continuously weakens, making it easy for the metal layer to detach from the base film layer. This, in turn, affects the positive and negative electrode interfaces inside the battery, resulting in poor battery electrical performance and also impacting battery safety. Furthermore, the dissolution of polymer materials into the electrolyte increases the electrolyte viscosity, increasing ion transport resistance and leading to an increase in the battery's internal resistance over time. While using polypropylene (PP) as the base film can alleviate the swelling problem to some extent, the PP material has almost no oxygen-containing groups or other non-CH groups in its molecular structure, which makes it prone to insufficient adhesion to the metal layer. This leads to problems such as metal coating peeling on both sides of the base film, metal coating wrinkles during coating stretching, and active material being peeled off by the separator after being stacked with lithium battery active material. These issues result in a significant decrease in battery yield and are therefore not conducive to large-scale industrial application. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the following: the existing PET base film has extremely poor conductivity; the method of adding conductive agent or increasing conductive layer has high cost and reduced production efficiency; the PET base film has swelling problem, resulting in poor battery cycle performance; and although PP base film can alleviate swelling, it has the problem of insufficient bonding force with metal layer. Thus, a polymer base film for composite current collector, composite current collector, preparation method and application are provided.

[0006] The technical solution of the present invention:

[0007] A polymer-based membrane for composite current collectors, characterized in that the polymer-based membrane is made of an n-type conductive polymer, and the repeating unit of the n-type conductive polymer structure is shown in formula (1);

[0008]

[0009] Wherein, R may be the same or different, and each is independently selected from hydrogen, halogen, nitro, cyano, C1-C10 halogen-substituted alkyl, C2-C10 alkenyl, C2-C10 alkynyl and silicon-protected vinyl.

[0010] R may be the same or different, and each is independently selected from hydrogen, halogen, nitro, cyano, C1-C5 halogen-substituted alkyl, C2-C5 alkenyl, C2-C5 alkynyl and silicon-protected vinyl; preferably, R may be the same or different, and each is independently selected from hydrogen, halogen, nitro and cyano; more preferably, R is selected from hydrogen.

[0011] The structure of the n-type conductive polymer is shown in formula (2);

[0012]

[0013] Where n is selected from an integer from 1 to 1,000,000, preferably an integer from 1 to 10,000, and more preferably an integer from 1 to 1,000.

[0014] A composite current collector includes a polymer base film layer formed from a polymer base film of the composite current collector and metal layers located on both sides of the polymer base film layer.

[0015] The thickness of the metal layer on each side is 0.3 μm-1.0 μm, preferably 0.5 μm;

[0016] The metal layer is made of any one of copper, aluminum, or tin; preferably copper or aluminum.

[0017] The composite current collector is a composite positive current collector, the metal layer is made of aluminum, and the thickness of the polymer base film layer is 2.7-12μm, preferably 6μm; the thickness of the composite positive current collector is 3.7μm-14μm, preferably 6-8μm.

[0018] The composite current collector is a composite negative electrode current collector, the metal layer is made of copper, and the thickness of the polymer base film layer is 2.7-12μm, preferably 4μm; the thickness of the composite negative electrode current collector is 3.7μm-14μm, preferably 5-7μm.

[0019] A method for preparing a composite current collector, comprising depositing a metal layer on both sides of a polymer base film using vacuum evaporation, includes the following steps: loading a metal target and the polymer base film to be deposited into a vacuum evaporation apparatus, and evacuating the vacuum evaporation apparatus to a vacuum level less than 1×10⁻⁶. -2 Pa; The vacuum evaporation equipment is heated to the evaporation temperature of the metal target, and the metal layer is deposited on both sides of the polymer base film to obtain the composite current collector;

[0020] The composite current collector is a composite positive current collector, and the metal target is an aluminum target; the transport speed of the polymer base film is 50-150 m / min, preferably 100 m / min;

[0021] Alternatively, the composite current collector is a composite negative electrode current collector, the metal target is a copper target, and the metal layer is a copper layer; the transport speed of the polymer base film is 30-120 m / min, preferably 90 m / min.

[0022] The purity of the metal target is 99.9%; and / or the evaporation temperature of the metal target is 600-1600℃, preferably 1100℃.

[0023] An electrode, comprising an electrode material and the composite current collector described herein or the composite current collector obtained by the preparation method described herein;

[0024] Preferably, the electrode material is a positive electrode material, and the composite current collector is a composite positive electrode current collector with a compaction strength of 3.0-3.8 g / cm³. 3 The preferred value is 3.65 g / cm³. 3 .

[0025] Preferably, the electrode material is a negative electrode material, and the composite current collector is a composite negative electrode current collector with a compaction strength of 1.5-1.8 g / cm³. 3 The preferred value is 1.65 g / cm³. 3 .

[0026] The application of the aforementioned electrode in the preparation of lithium-ion batteries.

[0027] The technical solution of this invention has the following advantages:

[0028] 1. A polymer-based membrane for composite current collectors according to the present invention uses an n-type high-conductivity polymer-based membrane material, wherein the n-type high-conductivity polymer is benzodifurandione and its derivatives, and the repeating unit of its structure has the formula (1). The large and rigid conjugated framework of n-type high-conductivity polymers such as poly(benzodifurandione) shown in formula (1) allows for easy delocalization of (bi)polarons and intrachain charge carriers, resulting in high conductivity and thermal conductivity. Therefore, when used in the process of preparing composite current collectors, there is no need to add an additional conductive layer on the base film or add a conductive agent to the base film material. It can be used as a very simple and high-performance composite current collector base film material. At the same time, since n-type high-conductivity polymers such as poly(benzodifurandione) contain ketone groups on the cyclic lactone, they have low compatibility with conventional carbonate electrolytes. This can effectively avoid the swelling problem of the composite current collector prepared from the base film during long-term lithium battery cycling, ensuring that the cycle can reach the target value of lithium battery design. Moreover, n-type high-conductivity polymers such as poly(benzodifurandione) also have a certain number of oxygen-containing groups. Under high-energy conditions, they can combine well with metal atoms such as Cu / Al sputtered on the base film to form a metal oxide seed transition layer, thereby improving the adhesion between the base film and the metal coating / metal layer and meeting the coating adhesion requirements.

[0029] 2. Poly(benzodifuran dione) (PBFDO) is a material with an electrical conductivity of 2000 S / cm. -1 The highly conductive polymer molecules are 10 times more conductive than the conventional n-type polymers shown in the non-structure (1), which can alleviate the problem of increased current collector internal resistance caused by polymer base film, reduce the internal resistance of electrode and battery, and reduce the heat generated by battery cell.

[0030] 3. Using n-type high-conductivity polymers such as poly(benzodifurandione) as the current collector base film can reduce the thickness of the composite current collector metal plating / metal layer while ensuring that the resistivity remains basically unchanged. It can be reduced from the conventional 0.6-1.2um (preferably 0.8um) to 0.3-1.0um (preferably 0.5um), saving plating time and material costs and improving product competitiveness.

[0031] 4. Using n-type high-conductivity polymer base film materials such as poly(benzodifurandione) improves thermal conductivity, resulting in an increase in heat resistance temperature of the base film during evaporation or electromagnetic sputtering, which can further accelerate the coating transfer speed of the base film. The transfer speed of the aluminum-plated polymer base film (composite positive electrode current collector) is 50-150 m / min, preferably 100 m / min; the transfer speed of the copper-plated polymer base film (composite negative electrode current collector) is 30-120 m / min, preferably 90 m / min.

[0032] 5. Due to the improved adhesion between the n-type high-conductivity polymer base film material (such as poly(benzodifurandione)) and the metal coating / metal layer, both the positive and negative electrodes can be coated using vapor deposition. Furthermore, the metal coating and substrate are not easily peeled off under high pressure. After the aluminized polymer base film (composite positive electrode current collector) is made into an electrode sheet, the compaction of the composite positive electrode current collector remains at 3.0-3.8 g / cm³. 3 The preferred value is 3.65 g / cm³. 3 It is greater than the usual 3.4 g / cm³. 3 This improves cell quality and volumetric energy density, and increases the upper limit of foil compaction.

[0033] 6. A composite current collector using n-type high conductivity polymers such as poly(benzodifurandione) as the base film is used to obtain battery electrodes. When entering the welding process, there is no need to add welding transfer pieces. The electrodes can be directly connected to the ultrasonic welding connection pieces, reducing welding process materials, reducing the number of electrode connection pieces, reducing the volume of the electrode tabs in the cell casing, and increasing the volumetric energy density of the cell.

[0034] 7. The composite current collector, which uses n-type high conductivity polymers such as poly(benzodifurandione) as the base film, can help the composite current collector to be quickly introduced into the battery cell and successfully pass safety performance verifications such as 5mm steel needle puncture, 150-degree hot box and thermal spread, which greatly expands the application range of batteries and promotes the development of the new energy industry. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 The capacity retention curves of the batteries in Example 1 and Comparative Example 1 after 40 cycles are shown.

[0037] Figure 2 The graphs show the EIS internal resistance test curves of the composite positive current collector in Example 1 and Comparative Example 1. Detailed Implementation

[0038] Example 1

[0039] A composite positive current collector is a composite foil material comprising a conductive polymer base film layer and metal layers located on both sides of the conductive polymer base film layer; the conductive polymer base film layer is made of poly(benzodifuran dione) (PBFDO), and its structural formula is shown in formula (2), where n is 500. The thickness of the base film layer is 6 μm. The metal layers are made of aluminum, and the thickness of each aluminum layer is 0.5 μm.

[0040]

[0041] The above-mentioned method for preparing a composite positive current collector employs a vacuum evaporation method to deposit a metal layer, comprising the following steps: loading a 6μm base film and a 99.9% pure metal target into a vacuum evaporation apparatus, and evacuating the vacuum evaporation apparatus to a vacuum level less than 1×10⁻⁶. -2 Pa; The vacuum evaporation equipment is heated to 1100℃ to evaporate the aluminum target material, maintaining the transport speed of the base film at 100m / min. A 0.5μm thick aluminum layer is deposited on both sides of the base film layer to obtain a 7μm thick composite aluminum current collector / composite positive electrode current collector / composite foil. After the aluminum-plated composite current collector is prepared, it undergoes surface oxide treatment for inert protection, followed by slitting, winding, and vacuum packaging.

[0042] Battery manufacturing process: The composite foil obtained above is used as the positive electrode current collector for slurry coating of a soft-pack battery. The slurry coating is carried out according to the mass ratio of active material (NCM811): conductive agent SP (conductive carbon black): binder PVDF (polyvinylidene fluoride) = 96.8:1.2:2. After drying, the corresponding positive electrode sheet coated with the active material is obtained. The positive electrode sheet is compacted. Due to the strong adhesion of the coating, the compaction is maintained at 3.65 g / cm³. 3 After the positive electrode sheet is cut and stacked, the composite positive current collector tab is directly welded to the connecting piece. Then, processes such as liquid injection, encapsulation, and pre-charge formation are carried out to obtain a soft-pack battery.

[0043] Example 2

[0044] A composite negative electrode current collector is a composite foil material comprising a conductive polymer base film layer and metal layers located on both sides of the conductive polymer base film layer; the conductive polymer base film layer is made of poly(benzodifuran dione) (PBFDO), and its structural formula is shown in formula (2), where n is 500. The thickness of the base film layer is 4 μm. The metal layers are made of copper, and the thickness of the copper layer on each side is 0.5 μm.

[0045]

[0046] The above-mentioned method for preparing a composite negative electrode current collector employs a vacuum evaporation method to deposit a metal layer, comprising the following steps: loading a 4μm base film and a 99.9% pure metal target into a vacuum evaporation apparatus, and evacuating the vacuum evaporation apparatus until the vacuum degree inside the apparatus is less than 1×10⁻⁶. -2 Pa; The vacuum evaporation equipment is heated to 1100℃ to evaporate the copper target material, maintaining the transport speed of the base film at 90m / min. A 0.5μm thick copper layer is deposited on both sides of the base film layer to obtain a 5μm thick composite copper current collector / composite negative electrode current collector / composite foil. After the composite copper current collector is prepared, it undergoes surface oxide treatment for inert protection, followed by slitting, winding, and vacuum packaging.

[0047] Battery fabrication process: The composite foil obtained above is used as the positive electrode current collector for slurry coating of a soft-pack battery. The slurry coating ratio is as follows: active material (graphite): conductive agent SP (conductive carbon black): binder SBR (styrene-butadiene rubber): binder CMC (sodium carboxymethyl cellulose) = 97.3:1.2:0.5:1.0. After drying, the corresponding active material coating is obtained as the negative electrode sheet. The negative electrode sheet is compacted, and due to the strong adhesion of the coating, the compaction is maintained at 1.65 g / cm³. 3 After the negative electrode sheet is cut and stacked, the composite foil tabs are directly welded to the connecting piece. Then, processes such as liquid injection, encapsulation, and pre-charge formation are carried out to obtain the soft-pack battery.

[0048] Example 3

[0049] A composite positive current collector is a composite foil material comprising a conductive polymer base film layer and metal layers located on both sides of the conductive polymer base film layer; the conductive polymer base film layer is made of poly(dinitrobenzodifuran dione), and its structural formula is shown in formula (4), where n is 500. The thickness of the base film layer is 2.7 μm. The metal layers are made of aluminum, and the thickness of each aluminum layer is 1.0 μm.

[0050]

[0051] The above-mentioned method for preparing a composite positive current collector employs a vacuum evaporation method to deposit a metal layer, comprising the following steps: loading a 2.7 μm base film and a 99.9% pure metal target into a vacuum evaporation apparatus, and evacuating the apparatus until the vacuum level is less than 1 × 10⁻⁶. -2Pa; The vacuum evaporation equipment is heated to 1100℃ to evaporate the aluminum target material, maintaining the transport speed of the base film at 50m / min. A 1.0μm thick aluminum layer is deposited on both sides of the base film layer to obtain a 4.7μm thick composite aluminum current collector / composite positive electrode current collector. After the composite aluminum current collector is prepared, it undergoes surface oxide treatment for inert protection, followed by slitting, winding, and vacuum packaging.

[0052] Battery manufacturing process: The composite foil obtained above is used as the positive electrode current collector for slurry coating of a soft-pack battery. The coating ratio is: active material (NCM811): conductive agent SP (conductive carbon black): binder PVDF (polyvinylidene fluoride) = 96.8:1.2:2 by mass. After drying, the corresponding positive electrode sheet with the active material coating is obtained. The positive electrode sheet is then compacted. Due to the strong adhesion of the coating, the compaction is maintained at 3.65 g / cm³. 3 After the positive electrode sheet is slit and stacked, the composite foil tabs are directly welded to the connecting piece, followed by processes such as liquid injection, encapsulation, and pre-charge formation to obtain a soft-pack battery.

[0053] Example 4

[0054] A composite positive current collector is a composite foil material comprising a conductive polymer base film layer and metal layers located on both sides of the conductive polymer base film layer; the conductive polymer base film layer is made of poly(benzodifuran dione), and its structural formula is shown in formula (2), where n is 500. The thickness of the base film layer is 12 μm. The metal layers are made of aluminum, and the thickness of each aluminum layer is 0.3 μm.

[0055]

[0056] The above-mentioned method for preparing a composite positive current collector employs a vacuum evaporation method to deposit a metal layer, comprising the following steps: loading a 12μm base film and a 99.9% pure metal target into a vacuum evaporation apparatus, and evacuating the vacuum evaporation apparatus until the vacuum degree inside the apparatus is less than 1×10⁻⁶. -2 Pa; The vacuum evaporation equipment is heated to 1100℃ to evaporate the aluminum target material, maintaining the transport speed of the base film at 150m / min. A 0.3µm thick aluminum layer is deposited on both sides of the base film layer to obtain a 12.6µm thick composite aluminum current collector / composite positive electrode current collector. After the composite aluminum current collector is prepared, it undergoes surface oxide treatment for inert protection, followed by slitting, winding, and vacuum packaging.

[0057] Battery manufacturing process: The composite foil obtained above is used as the positive electrode current collector for slurry coating of a soft-pack battery. The coating ratio is: active material (NCM811): conductive agent SP (conductive carbon black): binder PVDF (polyvinylidene fluoride) = 96.8:1.2:2 by mass. After drying, the corresponding positive electrode sheet with the active material coating is obtained. The positive electrode sheet is then compacted. Due to the strong adhesion of the coating, the compaction is maintained at 3.65 g / cm³. 3 After the positive electrode sheet is slit and stacked, the composite foil tabs are directly welded to the connecting piece, followed by processes such as liquid injection, encapsulation, and pre-charge formation to obtain a soft-pack battery.

[0058] Comparative Example 1

[0059] A composite positive current collector is a composite foil material comprising a PET base film layer and metal layers located on both sides of the base film layer; the thickness of the base film layer is 6 μm. The metal layers are made of aluminum, and the thickness of each aluminum layer is 0.8 μm.

[0060] The above-mentioned method for preparing a composite positive current collector employs a vacuum evaporation method to deposit a metal layer, comprising the following steps: loading a 6μm base film and a 99.9% pure metal target into a vacuum evaporation apparatus, and evacuating the vacuum evaporation apparatus to a vacuum level less than 1×10⁻⁶. -2 Pa; The vacuum evaporation equipment is heated to 1100℃ to evaporate the aluminum target material, maintaining the transport speed of the base film at 50m / min. A 0.8µm thick aluminum layer is deposited on both sides of the base film layer to obtain a 7.6µm thick composite aluminum current collector / composite positive electrode current collector. After the composite aluminum current collector is prepared, it undergoes surface oxide treatment for inert protection, followed by slitting, winding, and vacuum packaging.

[0061] Battery fabrication process: The composite foil obtained above is used as the positive electrode current collector for slurry coating in a soft-pack battery. The mixture is prepared according to a mass ratio of active material (NCM811): conductive agent SP (conductive carbon black): binder PVDF (polyvinylidene fluoride) = 96.8:1.2:2. After drying, the corresponding positive electrode sheet with the active material coating is obtained. The positive electrode sheet is then compacted to a density of 3.4 g / cm³. 3 After the positive electrode sheets are slit and stacked, the composite positive current collector is transferred to the tab and then welded onto the connecting piece during welding. Then, processes such as electrolyte injection, encapsulation, and pre-charge formation are performed to obtain the pouch battery.

[0062] Comparative Example 2

[0063] A composite positive electrode current collector is a composite foil material comprising a PP base film layer and metal layers located on both sides of the base film layer; the thickness of the base film layer is 6 μm. The metal layers are made of aluminum, and the thickness of each aluminum layer is 0.8 μm.

[0064] The above-mentioned method for preparing a composite positive current collector employs a vacuum evaporation method to deposit a metal layer, comprising the following steps: loading a 6μm base film and a 99.9% pure metal target into a vacuum evaporation apparatus, and evacuating the vacuum evaporation apparatus to a vacuum level less than 1×10⁻⁶. -2 Pa; The vacuum evaporation equipment is heated to 1100℃ to evaporate the aluminum target material, maintaining the transport speed of the base film at 50m / min. A 0.8µm thick aluminum layer is deposited on both sides of the base film layer to obtain a 7.6µm thick composite aluminum current collector / composite positive electrode current collector. After the aluminum-plated composite current collector is prepared, a surface oxide layer is applied for inert protection, followed by slitting, winding, and vacuum packaging.

[0065] Battery fabrication process: The composite foil obtained above is used as the positive electrode current collector for slurry coating in a soft-pack battery. The mixture is prepared according to a mass ratio of active material (NCM811): conductive agent SP (conductive carbon black): binder PVDF (polyvinylidene fluoride) = 96.8:1.2:2. After drying, the corresponding positive electrode sheet with the active material coating is obtained. The positive electrode sheet is then compacted to a density of 3.4 g / cm³. 3 After the positive electrode sheets are slit and stacked, the composite positive current collector is transferred to the tab and then welded onto the connecting piece during welding. Then, processes such as electrolyte injection, encapsulation, and pre-charge formation are performed to obtain the pouch battery.

[0066] Test case

[0067] Cyclic performance testing: Cyclic tests were conducted on the pouch batteries obtained in the examples and comparative examples, respectively. The charge / discharge conditions were 0.33C / 1C, and the temperature was 25℃. The capacity retention data during the cycling process were measured, and the results are shown in Table 1 and 2. Figure 1 As shown in Table 1, the corresponding electrode sheets were obtained after the battery cell was cycled and the degree of swelling of the electrode sheets was tested.

[0068] Table 1. Test Data

[0069]

[0070] Note: Electrode swelling degree = (W2-W1) / W1×100%, where W2 is the mass after soaking and W1 is the mass before soaking.

[0071] like Figure 1As shown in Table 1, the current collector cycling performance of the PBFDO-based film and poly(dinitrobenzodifurandione)-based film current collectors in Examples 1-4 is superior to that of the composite current collector with PET-based film in Comparative Example 1 and the composite current collector with PP-based film in Comparative Example 2. This is because PBFDO contains ketone groups on the cyclic lactone, which have low compatibility with conventional carbonate electrolytes. This can effectively avoid the swelling problem of the composite current collector prepared from the base film during long-term lithium battery cycling, ensuring that the cycling can reach the target value of the lithium battery design cycle.

[0072] EIS (Electrochemical Impedance Spectroscopy) Internal Resistance Test: EIS internal resistance tests were performed on the coin cells obtained in Example 1 and Comparative Example 1, respectively. After the coin cells were formed, on the third cycle, maintaining 50% SOC (state of charge), impedance measurements were immediately performed after cycling at a potential amplitude of 5 mV within a frequency range of 100 kHz to 10 mHz. Figure 2 As shown, the internal resistance test of the PBFDO base film in Example 1 is superior to that of the PET base film in Comparative Example 1.

[0073] Peel strength test: Peel strength tests were performed on the composite positive current collectors / composite foils obtained in Example 1 and Comparative Examples 1 and 2, respectively. The peel strength test method and process were as follows: 1. Cut the composite foil: Cut the composite foil to be tested to a size of 300mm × 30mm using a die. 2. Adhere and fix the composite foil: Take a flat thin steel plate with a size of 400mm × 40mm. First, attach a strip of double-sided tape (its length should be greater than the test length of the composite foil and the same width as the composite foil) to the center of the steel plate, and smooth it out to ensure that the double-sided tape is tightly adhered to the center of the steel plate. Peel off the double-sided tape and attach the lower surface of the metal plating on one side of the composite foil to be tested to the tape. It is necessary to ensure that the composite foil and the tape are completely matched and adhered at the tape-attached part. 3. Installation and Testing: The tensile testing machine has two clamps, upper and lower. Insert the steel plate with the pre-attached composite foil into the lower clamp and fix it vertically, with the adhesive portion of the composite foil at the bottom and the unattached portion at the top. Insert the unattached portion of the composite foil into the upper clamp and fix it, keeping the composite foil vertical, even if the adhesive and unattached portions form a 180° angle. After fixing the test sample, first calibrate and zero it, setting the test width to 23mm, the electrode peeling length to 75mm, and the peeling speed to 150mm / min. Then start the test. The results are shown in Table 2.

[0074] Table 2. Peel force test data

[0075]

[0076] As shown in Table 2, the peel strength of the PBFDO base film of Example 1 is better than that of the PP base film of Comparative Example 2 and close to that of the PET base film of Comparative Example 1, which can meet the coating adhesion requirements.

[0077] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite current collector, characterized in that, The composite current collector is a composite positive current collector, comprising a conductive polymer base film layer and metal layers located on both sides of the conductive polymer base film layer. The structure of the conductive polymer base film material constituting the conductive polymer base film layer is shown in formula (2). （2）； Where n is 500, the thickness of the base film is 12μm; the metal layer is made of aluminum, the thickness of the aluminum layer on each side is 0.3μm, and the metal layer is deposited on both sides of the polymer base film by vacuum evaporation. The process includes the following steps: loading the metal target and the polymer base film to be deposited into a vacuum evaporation equipment, and evacuating the equipment until the vacuum level inside the equipment is less than 1×10⁻⁶. -2 Pa; The vacuum evaporation equipment is heated to the evaporation temperature of the metal target, and the metal layer is deposited on both sides of the polymer base film to obtain the composite current collector; The composite current collector is a composite positive current collector, and the metal target is an aluminum target; the transport speed of the polymer base film is 150 m / min, and the evaporation temperature of the metal target is 1100℃.

2. The composite current collector according to claim 1, characterized in that, The purity of the metal target is 99.9%.

3. A positive electrode sheet, characterized in that, Includes the positive electrode material and the composite current collector as described in claim 1 or 2.

4. The positive electrode sheet according to claim 3, characterized in that, The compaction of the composite positive electrode current collector is maintained at 3.0-3.8 g / cm³. 3 .

5. The positive electrode sheet according to claim 4, characterized in that, The compaction density of the composite positive electrode current collector is 3.65 g / cm³. 3 .

6. The application of the electrode according to any one of claims 3-5 in the preparation of lithium-ion batteries.

Images