Cathode current collector carbon-coated foil and preparation method thereof

Abstract

The invention discloses a positive electrode current collector carbon-coated foil and a preparation method thereof, the carbon-coated foil comprises a matrix foil and a coating coated on the surface of the matrix foil, a conductive agent of the coating is a single-walled carbon nanotube, the length of the single-walled carbon nanotube is 10-15nm, and the diameter of the single-walled carbon nanotube is not more than 2nm. The coating used by the coating comprises 6-14% of solid single-walled carbon tube, 6-10% of glue solution and the balance of deionized water. Wherein the glue solution is composed of calcium hydroxide, deionized water and gelatinous polyacrylic acid. The coating does not agglomerate, the surface of the current collector is not uniform during processing, a conductive medium between active substance particles is enhanced, the conductivity of the carbon-coated foil is greatly improved, the capacity of the lithium ion battery is effectively improved, and the cycle life of the lithium ion battery is effectively prolonged.

Description

Technical Field

[0001] The invention relates to a positive electrode current collector carbon-coated foil and a preparation method thereof, belonging to the technical field of positive electrode current collector processing for lithium ion batteries. Background Art

[0002] With the rapid development of new energy vehicles and smart electronic application products, the requirements for secondary lithium-ion batteries are getting higher and higher, and the market needs advanced materials. It is predicted that in the next few years, about 88% of the global demand for lithium-ion batteries will come from new energy vehicles (EVs). New energy vehicle manufacturers are seeking solutions to significantly increase the energy density of batteries, battery charge and discharge life, and reduce costs. Therefore, the industrialization and application of new materials is particularly critical; and as the most important battery material, carbon materials have attracted widespread attention from lithium-ion battery manufacturers and the new energy industry due to their excellent performance. Among them, the new generation of carbon nanoconductive materials represented by single-walled carbon nanotubes has also been accelerating the industrialization process in recent years, becoming one of the indispensable materials in the battery industry.

[0003] The internal components of lithium-ion batteries mainly include positive and negative electrodes, separators, and electrolytes. The positive electrode is mainly responsible for providing the active substances in the lithium-ion battery. During oxidation and reduction, it provides the number of intercalated and deintercalated ions. The activity of the intercalated and deintercalated ions is related to factors such as the capacity, cycle life, and energy density of the lithium-ion battery. The activity of the intercalated and deintercalated ions depends on the conductivity of the positive electrode current collector carrier, and the key to the conductivity of the positive electrode current collector carrier lies in the carbon-coated foil.

[0004] The existing carbon-coated foils are all coated with SP carbon black, which has a small particle size, a large specific surface area, and a round shape. When the carbon coating is prepared, it is easy to form agglomerations and form larger soft particles, resulting in an uneven surface after processing, making it difficult to achieve uniform conductivity. After being attached to the positive electrode current collector, the dot-like shape can only fill the gaps between the active material particles and the particles of the electrode, providing a passive conductive ability with limited conductivity.

[0005] In order to enhance the conductivity of the positive electrode current collector, the single-walled carbon tube carbon-coated foil processing technology used as the positive electrode current collector has stronger conductivity and adhesion than the traditional SP (Super P) carbon-coated foil. Summary of the invention

[0006] The purpose of the present invention is to solve the problems in the prior art and provide a positive electrode current collector carbon-coated foil with uniform surface coating and good conductivity, so as to improve the conductivity of the positive electrode current collector and increase the cycle life of lithium-ion batteries.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned carbon-coated foil.

[0008] The objective of the present invention is achieved through the following technical solutions:

[0009] A positive electrode current collector carbon-coated foil comprises a base foil and a coating coated on the surface of the base foil, characterized in that the conductive agent of the coating is a single-walled carbon nanotube, the length of the single-walled carbon nanotube is 10-15nm, and the diameter does not exceed 2nm.

[0010] The coating used in the coating of the present invention includes the following components in percentage by weight:

[0011] Solid single-walled carbon tube 6~14%

[0012] Glue 6~10%

[0013] Deionized water was added to 100%.

[0014] The glue solution is composed of the following components in mass percentage:

[0015] Calcium hydroxide 1~3%

[0016] Deionized water 15-20%

[0017] The gel-like polyacrylic acid was added to 100%.

[0018] The preferred solid content of the gel-like polyacrylic acid is 6%.

[0019] Preferably, the coating solid content is controlled to be 12-15% and the viscosity is 600-1000 mPas.

[0020] The preferred coating thickness is 1-1.2 μm, and the substrate foil is a smooth aluminum foil with a thickness of 12-14 μm. If the coating is less than 1 μm, it is difficult for the primer to be evenly coated on the smooth aluminum foil, and the current process equipment cannot meet this requirement; if the coating is too thick, the contact resistance between the particles will be introduced, which will weaken the conductivity of the electrons; if the carbon coating is too thick, it will affect the EIS impedance value of the battery and reduce the battery performance; and if the carbon coating is too thick, a denser film will be formed in the electrode sheet, which can increase the electrical contact between the active material and the current collector and improve the structural stability of the electrode, but it will also reduce the cycle life of the battery due to stress concentration and cracking, and increase the production cost.

[0021] A method for preparing the above-mentioned positive electrode current collector carbon-coated foil is characterized by comprising the following steps:

[0022] a. Prepare glue solution: add calcium hydroxide into deionized water, stir evenly, then add solid polyacrylic acid and stir evenly;

[0023] b. Preparation of carbon coating: Add solid single-walled carbon nanotubes into the glue solution, stir slowly until the single-walled carbon nanotubes are fully soaked by the glue solution, add part of deionized water and stir at high speed for 30 minutes, then add the remaining deionized water and stir at high speed;

[0024] c. Primer: Apply the prepared carbon coating evenly on both sides of the base foil, and leave it in a refrigerated environment for one week after drying.

[0025] Among them, the uniform state of calcium hydroxide after adding deionized water in step a is turbid and has no agglomerated shape.

[0026] The stirring speed of the slow stirring in the present invention is 5 rpm / min, and the dispersion speed is 100 rpm / min. The stirring speed of the high-speed stirring is 20-35 rpm / min, and the dispersion speed is 1000-1600 rpm / min.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] The present invention adopts single-walled carbon tubes as the carbon coating of the positive electrode current collector carbon-coated foil. Since the single-walled carbon tubes are in the shape of nano strips and the tube length is between 10-15nm, no coating agglomeration will be formed, and there will be no uneven surface of the current collector during processing. The strip tube diameters are staggered to form a three-dimensional network structure, which provides a large number of contact sites for the active material of the electrode, enhances the conductive medium between the active material particles, and greatly improves the conductivity of the carbon-coated foil.

[0029] The carbon coating uses carbon tubes with a diameter of less than 2nm. The carbon tubes have a small diameter and almost no deformation. When coated on a smooth aluminum foil, the carbon tubes adhere to the foil surface without generating a gap. The conductivity is stronger than that of multi-walled carbon tubes and layered conductive agents. The coating of the present invention uses a PAA binder, which contains more polar functional groups, thereby improving the structural stability of the coating and enhancing the adhesion between the coating and the foil.

[0030] The positive electrode current collector using the carbon-coated foil of the present invention has good conductivity and effectively improves the capacity and cycle life of the lithium ion battery. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to specific embodiments.

[0032] A positive electrode current collector carbon-coated foil comprises a base foil and a coating applied on the surface thereof, wherein the coating used for the coating comprises the following components in mass percentage:

[0033] Solid single-walled carbon nanotubes 6-14%

[0034] Glue 6-10%

[0035] Deionized water was added to 100%,

[0036] The length of the solid single-walled carbon nanotubes is 10-15 nm, the diameter does not exceed 2 nm, and the glue is composed of the following mass percentage components:

[0037] Calcium hydroxide 1-3%

[0038] Deionized water 15-20%

[0039] The gel-like polyacrylic acid was added to 100%.

[0040] The solid content of the gel-like polyacrylic acid is 6%, the solid content of the coating of the invention is controlled to be 12-15%, the viscosity is 600-1000 mPas, the thickness of the coating is 1-1.2 μm, and the base foil is a smooth aluminum foil with a thickness of 12-14 μm.

[0041] The coating components, foil layers and coating thicknesses of Examples 1-5 are shown in Table 1. The length of the single-walled carbon tubes of Examples 1-5 is 10-15 nm, and the diameter is no more than 2 nm.

[0042] Table 1: The units of each component are mass percentage %

[0043]

[0044] The preparation method of Examples 1-5 is:

[0045] a. Prepare glue solution: add calcium hydroxide into deionized water, stir evenly until the solution is turbid and without agglomeration, then add solid polyacrylic acid and stir evenly;

[0046] b. Preparation of carbon coating: adding solid single-walled carbon nanotubes into the glue solution, stirring slowly until the single-walled carbon nanotubes are fully soaked by the glue solution, adding part of deionized water and stirring at high speed for 30 minutes, and then adding the remaining deionized water and stirring at high speed;

[0047] c. Primer: Use primer equipment to evenly apply the prepared carbon coating on both sides of the base foil. After drying, place it in a refrigerated environment at 5±2℃ for one week.

[0048] The single-walled carbon tubes in Examples 1-5 were replaced with SP carbon black, and Comparative Examples 1-5 were prepared by the same preparation method. The single-walled carbon tubes in Examples 1-5 were replaced with single-walled carbon tubes with a length of 10 to 15 nm and a tube diameter greater than 2 nm, and Comparative Examples 6-10 were prepared by the same preparation method. The carbon-coated current collectors of Examples 1-5 and Comparative Examples 1-10 were tested for relevant properties, and the conductivity and adhesion tests were compared. The test methods are as follows:

[0049] The conductivity test method adopts: DC method: by applying a stable DC voltage at both ends of the sample, measuring the current passing through the sample, and then calculating the resistivity according to Ohm's law, and then obtaining the conductivity. The formula for converting resistivity (ρ) to conductivity (σ) is:

[0050] The adhesion test method is GB / T 9286-2023, using a cross-cut adhesion tester: the device scratches a certain number of small squares (usually 100) on the coating surface, then uses 3M tape (special for adhesion testing) to stick and quickly tear off, and observes the peeling of the squares and the peeling force displayed by the device to evaluate the adhesion of the coating. The greater the peeling force, the better the adhesion.

[0051] The carbon-coated current collectors of Examples 1-5 and Comparative Examples 1-10 were made into lithium batteries with the same rated capacity according to the same parameters. The maximum capacity of the finished lithium battery shall not be higher than the rated capacity by 5%, and the minimum capacity shall not be lower than the designed rated capacity. The lithium battery AC internal resistance and cycle test were carried out. The test method is as follows:

[0052] Lithium battery AC internal resistance test method: Use a lithium battery AC internal resistance tester, connect the positive and negative test terminals of the device to the positive and negative polarity terminals of the lithium battery, and read the AC internal resistance value of the single lithium battery through the device display.

[0053] The lithium battery cycle test method is carried out according to the lithium battery cycle test standard in GB / T 31484-2015: using 5V60A test equipment, at room temperature, with the lithium battery design rated capacity as the reference current, the charging voltage value is set at the upper limit of the lithium battery design maximum voltage, and the discharge voltage value is set at the lower limit of the lithium battery design discharge minimum voltage, and 1C / 1C current charging and discharging are performed, and the first discharge full capacity is used as the initial capacity. When the discharge capacity is less than 80% of the initial discharge capacity at a certain cycle, the cycle test is stopped to determine the life of the lithium battery. The test results of Examples 1-5 and Comparative Examples 1-10 are shown in Tables 2 and 3.

[0054] Table 2: Performance test results of carbon-coated foils of Examples 1-5 and corresponding lithium battery performance tests

[0055]

[0056] Table 3: Comparative Examples 1-10 carbon-coated foil performance test results and corresponding lithium battery performance test, wherein Comparative Examples 6-10 show the diameter of the single-walled carbon tube.

[0057]

[0058]

[0059] It can be seen from the test results of the embodiments and comparative examples that various properties of embodiments 1-5 of the present invention are better than those of the current collectors of the comparative examples, while in comparative examples 6-10, the larger the diameter of the single-walled carbon tubes, the easier it is for the single-walled carbon tube walls to break during the charge and discharge cycle, and the number of cycles is significantly reduced.

Claims

1. A positive electrode current collector coated carbon foil, comprising a base foil and a coating applied on the surface of the base foil, characterized in that: The conductive agent of the coating is a single-walled carbon nanotube, the length of the single-walled carbon nanotube is 10-15nm, and the diameter does not exceed 2nm.

2. The positive electrode current collector coated carbon foil according to claim 1, characterized in that The coating used in the coating comprises the following components in percentage by weight: Solid single-walled carbon tube 6~14% Glue 6~10% Deionized water was added to 100%.

3. A positive electrode current collector coated carbon foil according to claim 2, characterized in that The glue solution is composed of the following components in percentage by weight: Calcium hydroxide 1~3% Deionized water 15-20% The gel-like polyacrylic acid was added to 100%.

4. The positive electrode current collector coated carbon foil according to claim 3, characterized in that The solid content of the gel-like polyacrylic acid is 6%.

5. The positive electrode current collector coated carbon foil according to claim 3, characterized in that The coating solid content of the coating is controlled to be 12-15%, and the viscosity is 600-1000 mPas.

6. The positive electrode current collector coated carbon foil according to claim 3, characterized in that The coating has a thickness of 1 to 1.2 μm.

7. The positive electrode current collector coated carbon foil according to claim 1, characterized in that The base foil is a smooth aluminum foil with a thickness of 12 to 14 μm.

8. A method for preparing the positive electrode current collector coated carbon foil according to any one of claims 3 to 7, characterized in that The following steps are involved: a. Prepare glue solution: add calcium hydroxide into deionized water, stir evenly, then add solid polyacrylic acid and stir evenly; b. Preparation of carbon coating: adding solid single-walled carbon nanotubes into the glue solution, stirring slowly until the single-walled carbon nanotubes are fully soaked by the glue solution, adding part of deionized water and stirring at high speed for 30 minutes, and then adding the remaining amount of deionized water and stirring at high speed; c. Primer: Apply the prepared carbon coating evenly on both sides of the base foil, dry it, and place it in a refrigerated environment for one week.

9. The method for preparing a positive electrode current collector coated with carbon foil according to claim 8, characterized in that The uniform state of calcium hydroxide after adding deionized water in step a is turbid without agglomeration.

10. The method for preparing a positive electrode current collector coated with carbon foil according to claim 8, characterized in that The slow stirring has a stirring speed of 5 rpm / min and a dispersion speed of 100 rpm / min, and the high-speed stirring has a stirring speed of 20-35 rpm / min and a dispersion speed of 1000-1600 rpm / min.

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