Carbon-coated current collector with controllable coating structure and preparation method therefor, and secondary battery

Abstract

A preparation method for a carbon-coated current collector with a controllable coating structure. The method comprises: using laser to ablate a carbon coating of a carbon-coated current collector, so as to obtain a carbon-coated current collector having a controllable structure. In the method, the laser is used to perform ablation treatment on the carbon coating, such that the nano-scale treatment of the coating can be realized, and the thickness and areal density of the carbon coating can also be reduced, thereby realizing the thinning treatment and structural design of the carbon coating; and the universality of a plate roller can be realized, and the range of application is wide. The present application further relates to a carbon-coated current collector with a controllable coating structure, and a secondary battery.

Description

Carbon-coated current collector with controllable coating structure, preparation method thereof, and secondary battery Technical Field

[0001] The present application belongs to the field of battery technology and relates to a carbon-coated current collector with a controllable coating structure, a preparation method thereof, and a secondary battery. Background Art

[0002] In the traditional lithium battery electrode manufacturing process, the active material slurry is directly coated on the surface of the base foil current collector. After drying, the active material is fixed on the surface of the base foil current collector by a binder, and then the positive and negative electrodes are prepared. However, conventional base foils have the following problems: ① The contact area between the conventional base foil metal current collector and the active material particles is limited, and the interface resistance is large; ② The bonding strength of the binder is limited. During the continuous charge and discharge process, it is easy for the active material and the current collector to expand and separate, resulting in a further increase in the internal resistance of the battery, which affects the cycle life and safety performance of the battery; ③ Due to the processing technology problems of the conventional base foil metal current collector, the surface roughness of the foil, especially the aluminum foil current collector, is limited. The residual oil of the additive added during the rolling process leads to a large interfacial tension, making it difficult to wet the electrode material coating, and there are problems of missing coating and uneven coating. The processing is difficult and affects the electrical performance of the battery.

[0003] To address these issues, carbon-coated current collectors were developed. Carbon-coated current collectors are made by evenly coating a conductive carbon-coated slurry onto the surface of a base foil, which is then dried and rolled up to form the carbon-coated current collector. This is then coated with electrode materials to form positive and negative electrodes. The existing carbon-coated current collector process is essentially: homogenization (preparation of a conductive slurry) – coating the base foil and unwinding – corona treatment (or preheating the oven) – infeed mechanism – positive coating mechanism – first-layer oven – reverse coating mechanism – second-layer oven – outfeed mechanism – winding – slitting (rewinding) – packaging.

[0004] At present, carbon coating mainly adopts gravure coating technology to apply conductive agent slurry to the surface of base foil and then dry and solidify it. However, the existing carbon coating technology still has the following shortcomings: ① The current coating level of carbon-coated current collector can only reach a thickness of 0.5μm and a gram weight of 0.2g / m 2, if a more precise coating structure is required, it is difficult to achieve it using gravure coating technology; ② With the technological pursuit of thinner coating thickness and surface density without reducing conductivity, if the coating is to be thinned, the existing gravure coating technology will result in coating omissions, and the production difficulty and processing precision are insufficient; ③ Gravure coating technology uses laser or electro-engraving processing to prepare gravure rollers. To achieve thinner coatings, the number of engraving lines will increase, and the depth of the engraved cells will be shallower. Higher line counts and shallower cells will lead to a shorter roller life and increased production costs; ④ As the coating thickness decreases in gravure coating, its microscopic coating structure will be affected by the mesh wall, resulting in uneven coating, reducing the contact uniformity with the battery electrode and reducing the conductive coating ability; ⑤ The coating structure of gravure coating technology is mainly controlled by the gravure roller cell structure and the self-leveling effect of the slurry during the processing process. The control ability is poor and further refined processing cannot be achieved; ⑥ Due to inconsistent customer needs and diversified product types, the coating width size of gravure coating technology requires the roller to be opened according to different product size requirements, and the roller cannot be universal.

[0005] Therefore, there is an urgent need to provide a method to improve the processing accuracy and uniformity of the carbon coating, avoid the occurrence of coating leaks, and not be limited by the coating components themselves such as the gravure roller, and have a wide range of applications.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] This application provides a carbon-coated current collector with a controllable coating structure, a preparation method thereof, and a secondary battery. This application utilizes laser ablation of the carbon coating, enabling nanoscale processing of the coating, improving the processing precision and uniformity of the carbon coating, and effectively reducing the thickness and surface density of the carbon coating, enabling thinning and structural design of the carbon coating. Furthermore, the laser can completely ablate and remove the coating at the corresponding location as required, achieving universal use of the plate roller without changing the plate roller structure and size, preventing coating leaks, and enabling a wide range of applications.

[0009] In a first aspect, the present application provides a method for preparing a carbon-coated current collector with a controllable coating structure, the preparation method comprising:

[0010] The carbon coating of the carbon-coated current collector is ablated by laser to obtain the carbon-coated current collector with controllable structure.

[0011] It should be noted that the carbon-coated current collector comprises a base foil and a carbon coating applied to at least one surface of the base foil. The "at least one surface" may be, for example, one or both surfaces. This application does not limit the type of base foil; for example, it may be aluminum foil.

[0012] This application provides a method for preparing a carbon-coated current collector with a controllable coating structure, which has the following advantages:

[0013] (1) Laser ablation of the carbon coating can achieve nanoscale processing of the coating, improve the processing accuracy and uniformity of the carbon coating, and effectively reduce the thickness and surface density of the carbon coating, thereby achieving thinning and structural design of the carbon coating, thereby improving the energy density and cycle life of the battery;

[0014] (2) The carbon coating structure can be designed according to the requirements, which can increase the contact area between the carbon coating and the electrode active material, improve the adhesion between the active material and the current collector, and reduce the manufacturing cost of the electrode;

[0015] (3) The laser can completely ablate and peel off the coating at the corresponding position according to the needs, so that the plate roller can be universal without changing the structure and size of the plate roller, and there will be no missing coating, which has a wide range of uses;

[0016] (4) The carbon coating after laser ablation can protect the current collector from being corroded by the electrolyte;

[0017] (5) The carbon-coated current collector after laser ablation can reduce the internal resistance of the battery and significantly reduce the dynamic internal resistance increase during the cycle process;

[0018] (6) Laser ablation technology can improve the consistency of carbon-coated current collectors and increase the cycle life of batteries; and

[0019] (7) The carbon-coated current collector after laser ablation can inhibit battery polarization, reduce thermal effects, and improve rate performance.

[0020] Preferably, the method for preparing the carbon-coated current collector comprises: roughening the surface of a base foil using a laser, then coating a carbon-containing slurry on the treated surface of the base foil, and baking to obtain the carbon-coated current collector.

[0021] The mainstream existing coating technology uses corona treatment and other methods to treat the residual oil on the current collector (such as aluminum foil). The corona treatment process will produce a large amount of ozone, and a certain concentration of ozone has certain hazards to humans and the environment.

[0022] The present application preferably uses laser to roughen the surface of the base foil. During this process, the oil on the surface of the base foil is also processed without generating harmful components such as ozone.

[0023] Preferably, the carbon coating comprises carbon and a polymer binder.

[0024] In this application, the mechanism of laser ablation of carbon coating (including carbon and polymer binder) is as follows: when the laser scans the carbon coating, the carbon itself does not change, a portion of the polymer binder in the coating is directly vaporized, a portion of the binder melts, and the carbon at the vaporized binder moves toward the base foil and recombines with the melted binder to adhere to the surface of the foil; at the same time, when the laser scans the carbon coating, in addition to the binder absorbing energy, the carbon also absorbs energy, which makes the laser energy gradually smaller along the direction close to the foil surface; combining the above two factors, when the laser scans the carbon coating, a groove with a wide top and a narrow bottom will be formed in the thickness direction of the carbon coating, so as to achieve the purpose of thinning the carbon coating and controlling the structure of the carbon coating. This is conducive to close contact between the carbon-coated current collector and the electrode active material.

[0025] Preferably, the carbon particle size D50 is 30-500 nm.

[0026] In this application, the full size range of 30-500nm is included. The relatively concentrated size distribution of carbon particles is not conducive to dense arrangement, making laser ablation and structural control inconvenient. It is easy to form parameter stacking gaps, which leads to large-scale detachment during ablation. This is due to the principle of close-packed particle stacking. The more dispersed the particle size, the denser the close packing. When particles of a single particle size are stacked, gaps will form between the particles, forming holes during ablation, leading to collapse.

[0027] Preferably, the carbon includes at least one of conductive carbon black, carbon nanotubes, graphene and carbon nanofibers.

[0028] Preferably, the polymer binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol and polyacrylic acid.

[0029] Preferably, based on the total mass of the carbon coating being 100%, the mass fraction of the polymer binder is 4-80%, for example, 4%, 8%, 15%, 30%, 45%, 50% or 70%.

[0030] Preferably, the carbon coating has a thickness of 0.5-2 μm, for example, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm or 1.8 μm.

[0031] Preferably, the single-surface density of the carbon coating is 0.3-0.4 g / m 2 , for example, it can be 0.3g / m 2 , 0.32g / m 2 , 0.34g / m 2 , 0.35g / m 2 , 0.38g / m 2 or 0.4g / m 2 wait.

[0032] Preferably, the laser comprises a picosecond laser.

[0033] Preferably, the power of the picosecond laser is 300-450W, for example, 300W, 320W, 350W, 380W, 400W, 420W or 450W, etc., preferably 380W.

[0034] In this application, if the power of the picosecond laser is too low, the ablation ability is insufficient, and the coating structure cannot be accurately controlled and the thickness cannot be reduced by ablation; if the power of the picosecond laser is too high, the ablation ability cannot be controlled, which can easily cause excessive ablation of the coating, damage the foil, and form pinholes.

[0035] Preferably, the wavelength of the picosecond laser is 800-1200 nm, for example, 800 nm, 900 nm, 1000 nm, 1100 nm or 1200 nm.

[0036] Preferably, the pulse frequency of the picosecond laser is 100-150 MHz, for example, 100 MHz, 110 MHz, 120 MHz, 130 MHz, 140 MHz or 150 MHz, etc., preferably 120 MHz.

[0037] Preferably, the laser scanning speed of the picosecond laser is 200-400 mm / s, for example, it can be 200 mm / s, 220 mm / s, 250 mm / s, 280 mm / s, 300 mm / s, 350 mm / s or 380 mm / s, etc., preferably 320 mm / s.

[0038] In a preferred embodiment of the present application, the method for preparing the carbon-coated current collector with controllable coating structure specifically comprises the following steps:

[0039] A1. Unwinding;

[0040] A2. Laser surface treatment: The surface of the base foil is roughened by laser, and then the thickness of the treated base foil is measured by a thickness measuring laser device; the measured base foil thickness data is transmitted to the CNC host system;

[0041] A3. Front coating: Coating the carbon-containing slurry on the front side of the treated base foil;

[0042] A4. Front coating baking: bake the current collector that has been coated on the front side;

[0043] A5. Laser ablation thinning / structural design (front coating): The CNC host system performs a closed-loop thinning process based on thickness measurement feedback data. Based on the CNC programming structural design, the laser is controlled to perform thinning and / or structural design on the baked front coating of the current collector.

[0044] A6. Back coating: Coating the carbon slurry on the back side of the current collector that has been coated on the front side;

[0045] A7. Back-coated surface baking: bake the current collector that has been back-coated;

[0046] A8. Laser ablation thinning / structural design (reverse coating): The CNC host system performs a closed-loop thinning process based on thickness measurement feedback data and controls the laser to perform thinning and / or structural design on the reverse side of the baked current collector coating according to CNC programming structural design; and

[0047] A9. Roll up.

[0048] Optionally, the present application provides the device components required for the above preferred embodiments, as shown below:

[0049] Unwinding: It includes a frame and a three-phase brake reduction motor, an air shaft, a coating substrate, a roller, a tension detection device, an unwinding correction device and a control circuit arranged on the frame;

[0050] Thickness measurement laser module: including laser thickness measurement electric eye probe, laser ablation processing device, data acquisition encoder, control circuit and data acquisition circuit;

[0051] CNC host system: The program instructions input into the control part by the dedicated control computer are recorded on the information carrier and received by the program reading device, or directly input manually through the keyboard of the control part. It can realize the input decoding analysis of data, the establishment of the coating structure design model or the issuance of coating thinning depth control instructions;

[0052] Front coating: including material box, feeding system, rubber pressure roller, gravure roller, high-precision servo motor, scraper device and pressure sensor;

[0053] Front coating baking: including heating package, fresh air control system, exhaust air control system, return air control system, waste heat recovery system, transmission roller, oven cavity and temperature and wind frequency control circuit;

[0054] Front laser ablation device module: including data transmission circuit, picosecond laser ablation device, drive motor, multi-track motion module, heat dissipation system and carbon powder negative pressure adsorption device;

[0055] Rear coating: same as front coating;

[0056] Back coating baking: the same as the front coating baking;

[0057] Rear laser ablation device module: the same as the front laser ablation device module;

[0058] Winding: It includes a frame and a three-phase brake reduction motor, an air shaft, a coating substrate, a roller, a tension detection device, a winding roll correction micro-swing device and a control circuit arranged on the frame.

[0059] In a second aspect, the present application provides a carbon-coated current collector with a controllable coating structure, wherein the carbon-coated current collector with a controllable coating structure is prepared by the preparation method described in the first aspect.

[0060] In the present application, the carbon coating structure of the carbon-coated current collector may be, for example, equidistantly arranged tetrahedrons, equidistantly arranged hexahedrons, equidistantly arranged octahedrons, or closely arranged horizontal and vertical lines.

[0061] In a third aspect, the present application provides a secondary battery, wherein the electrode of the secondary battery includes the carbon-coated current collector with controllable coating structure as described in the second aspect.

[0062] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to limited space and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0063] Compared with the related art, the beneficial effects of this application are:

[0064] This application provides a method for preparing a carbon-coated current collector with a controllable coating structure, which has the following advantages:

[0065] (1) Laser ablation of the carbon coating can achieve nanoscale processing of the coating, improve the processing accuracy and uniformity of the carbon coating, and effectively reduce the thickness and surface density of the carbon coating, thereby achieving thinning and structural design of the carbon coating, thereby improving the energy density and cycle life of the battery;

[0066] (2) The carbon coating structure can be designed according to the requirements, which can increase the contact area between the carbon coating and the electrode active material, improve the adhesion between the active material and the current collector, and reduce the manufacturing cost of the electrode;

[0067] (3) The laser can completely ablate and peel off the coating at the corresponding position according to the needs, so that the plate roller can be universal without changing the structure and size of the plate roller, and there will be no missing coating, which has a wide range of uses;

[0068] (4) The carbon coating after laser ablation can protect the current collector from being corroded by the electrolyte;

[0069] (5) The carbon-coated current collector after laser ablation can reduce the internal resistance of the battery and significantly reduce the dynamic internal resistance increase during the cycle process;

[0070] (6) Laser ablation technology can improve the consistency of carbon-coated current collectors and increase the cycle life of batteries; and

[0071] (7) The carbon-coated current collector after laser ablation can inhibit battery polarization, reduce thermal effects, and improve rate performance.

[0072] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] FIG1 is a schematic flow chart of a method for preparing a carbon-coated current collector according to a specific embodiment of the present application.

[0074] FIG2 is a microscopic diagram of the carbon-coated current collector after ablation and thinning provided in Example 1 of the present application.

[0075] FIG3 is a microstructure diagram of the carbon-coated current collector provided in Comparative Example 1 of the present application.

[0076] FIG4 is a schematic top view of a carbon coating with a tetrahedral structure provided in Example 6 of the present application.

[0077] FIG5 is a schematic cross-sectional view of the carbon-coated current collector after ablation provided in Example 6 of the present application.

[0078] FIG6 is a schematic top view of the carbon coating of the carbon-coated current collector provided in Comparative Example 3 of the present application.

[0079] FIG7 is a schematic cross-sectional view of the carbon-coated current collector provided in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0080] The technical solution of this application is further explained below through specific implementation methods.

[0081] In one embodiment, the present application provides a method for preparing a carbon-coated current collector with a controllable coating structure, the process of which is shown in FIG1 and specifically includes the following steps:

[0082] A1. Unwinding;

[0083] A2. Laser surface treatment: The surface of the base foil is roughened by laser, and then the thickness of the treated base foil is measured by a thickness measuring laser device; the measured base foil thickness data is transmitted to the CNC host system;

[0084] A3. Front coating: Coating the carbon-containing slurry on the front side of the treated base foil;

[0085] A4. Front coating baking: bake the current collector that has been coated on the front side;

[0086] A5. Laser ablation thinning / structural design (front coating): The CNC host system performs a closed-loop thinning process based on thickness measurement feedback data. Based on the CNC programming structural design, the laser is controlled to perform thinning and / or structural design on the baked front coating of the current collector.

[0087] A6. Back coating: Coating the carbon slurry on the back side of the current collector that has been coated on the front side;

[0088] A7. Back-coated surface baking: bake the current collector that has been back-coated;

[0089] A8. Laser ablation thinning / structural design (reverse coating): The CNC host system performs a closed-loop thinning process based on thickness measurement feedback data and controls the laser to perform thinning and / or structural design on the reverse side of the baked current collector coating according to CNC programming structural design; and

[0090] A9. Roll up.

[0091] Example 1

[0092] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0093] (1) A 1000W laser is used to roughen the surface of an aluminum foil, and a carbon-containing slurry is coated on the surface of the aluminum foil. After baking, a carbon-coated current collector is obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coating parameters on both sides are the same, wherein the carbon coating contains carbon and polyvinylidene fluoride (polymer binder), the carbon particle size D50 is 50nm, and the mass fraction of polyvinylidene fluoride is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0094] (2) The carbon coatings on both sides were ablated and thinned using a picosecond laser. The power of the picosecond laser was 420 W, the wavelength was 800-1200 nm, the pulse frequency was 120 MHz, and the laser scanning speed was 320 mm / s. The microstructure of the carbon-coated current collector after thinning is shown in Figure 2.

[0095] Example 2

[0096] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0097] (1) A 1000W laser is used to roughen the surface of an aluminum foil, and a carbon-containing slurry is coated on the surface of the aluminum foil. After baking, a carbon-coated current collector is obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coating parameters on both sides are the same, wherein the carbon coating contains carbon and polyvinylidene fluoride (polymer binder), the carbon particle size D50 is 50nm, and the mass fraction of polyvinylidene fluoride is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0098] (2) The carbon coatings on both sides are ablated and thinned by using a picosecond laser, wherein the power of the picosecond laser is 400 W, the wavelength of the picosecond laser is 800-1200 nm, the pulse frequency of the picosecond laser is 120 MHz, and the laser scanning speed of the picosecond laser is 320 mm / s.

[0099] Example 3

[0100] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0101] (1) A 1000W laser is used to roughen the surface of an aluminum foil, and a carbon-containing slurry is coated on the surface of the aluminum foil. After baking, a carbon-coated current collector is obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coating parameters on both sides are the same, wherein the carbon coating contains carbon and polyvinylidene fluoride (polymer binder), the carbon particle size D50 is 50nm, and the mass fraction of polyvinylidene fluoride is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0102] (2) The carbon coatings on both sides are ablated and thinned by using a picosecond laser, wherein the power of the picosecond laser is 380 W, the wavelength of the picosecond laser is 800-1200 nm, the pulse frequency of the picosecond laser is 120 MHz, and the laser scanning speed of the picosecond laser is 320 mm / s.

[0103] Example 4

[0104] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0105] (1) A 1000W laser is used to roughen the surface of an aluminum foil, and a carbon-containing slurry is coated on the surface of the aluminum foil. After baking, a carbon-coated current collector is obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coating parameters on both sides are the same, wherein the carbon coating contains carbon and polyvinylidene fluoride (polymer binder), the carbon particle size D50 is 50nm, and the mass fraction of polyvinylidene fluoride is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0106] (2) The carbon coatings on both sides are ablated and thinned by a picosecond laser, wherein the power of the picosecond laser is 360 W, the wavelength of the picosecond laser is 800-1200 nm, the pulse frequency of the picosecond laser is 120 MHz, and the laser scanning speed of the picosecond laser is 320 mm / s.

[0107] Example 5

[0108] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0109] (1) A 1000W laser is used to roughen the surface of an aluminum foil, and a carbon-containing slurry is coated on the surface of the aluminum foil. After baking, a carbon-coated current collector is obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coating parameters on both sides are the same, wherein the carbon coating contains carbon and polyvinylidene fluoride (polymer binder), the carbon particle size D50 is 50nm, and the mass fraction of polyvinylidene fluoride is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0110] (2) The carbon coatings on both sides are ablated and thinned by using a picosecond laser, wherein the power of the picosecond laser is 340 W, the wavelength of the picosecond laser is 800-1200 nm, the pulse frequency of the picosecond laser is 120 MHz, and the laser scanning speed of the picosecond laser is 320 mm / s.

[0111] Comparative Example 1

[0112] This comparative example provides a carbon-coated current collector, which is exactly the same as that in Example 1.

[0113] The microstructure of the carbon-coated current collector of Comparative Example 1 is shown in FIG3 . Compared with the microstructure of the carbon-coated current collector after thinning of Example 1 ( FIG2 ), it can be seen that the method of the present application can make the coating uniform and regular, while the carbon coating without ablation treatment has poor uniformity.

[0114] Comparative Example 2

[0115] This comparative example provides a current collector, namely aluminum foil, which is exactly the same as the aluminum foil provided in Example 1.

[0116] test

[0117] The current collectors obtained in Examples 1-5 and Comparative Examples 1-2 were tested, specifically including:

[0118] (1) Thickness test

[0119] The thickness of the carbon coating on one side was tested using a Mahr thickness gauge.

[0120] (2) Single-sided density test

[0121] The samples were weighed using an electronic analytical balance and the single-surface density was calculated by mass / unit area.

[0122] (3) Carbon coating coverage test

[0123] A charge coupled device (CCD) camera was used to take photos to detect the coating coverage.

[0124] (4) Carbon coating surface roughness test

[0125] The surface height difference was scanned using a SEM scanning electron microscope, and the maximum height difference of the coating on both sides was used as the value to characterize the surface roughness.

[0126] The test results are shown in Table 1.

[0127] Table 1

[0128] Example 6

[0129] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0130] (1) A 1000W laser was used to roughen the surface of an aluminum foil, and a carbon-containing slurry was coated on the surface of the aluminum foil. After baking, a carbon-coated current collector was obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coatings on both sides have the same parameters, wherein the carbon coating contains carbon and polyacrylic acid (polymer binder), the carbon particle size D50 is 60nm, and the mass fraction of polyacrylic acid is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0131] (2) The carbon coatings on both sides were ablated and thinned using a picosecond laser. The power of the picosecond laser was 380 W, the wavelength was 800-1200 nm, the pulse frequency was 120 MHz, and the laser scanning speed was 320 mm / s. After ablation, the structure of the carbon coating on each side was a 10 nm equidistant tetrahedron (1 / 2), as shown in Figures 4 and 5.

[0132] Example 7

[0133] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0134] (1) A 1000W laser was used to roughen the surface of an aluminum foil, and a carbon-containing slurry was coated on the surface of the aluminum foil. After baking, a carbon-coated current collector was obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coatings on both sides have the same parameters, wherein the carbon coating contains carbon and polyacrylic acid (polymer binder), the carbon particle size D50 is 60nm, and the mass fraction of polyacrylic acid is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0135] (2) The carbon coatings on both sides were ablated and thinned using a picosecond laser. The power of the picosecond laser was 380 W, the wavelength of the picosecond laser was 800-1200 nm, the pulse frequency of the picosecond laser was 120 MHz, and the laser scanning speed of the picosecond laser was 360 mm / s. After ablation, the structure of the carbon coating on each side was a 10 nm equidistant hexahedron (1 / 2).

[0136] Example 8

[0137] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0138] (1) A 1000W laser was used to roughen the surface of an aluminum foil, and a carbon-containing slurry was coated on the surface of the aluminum foil. After baking, a carbon-coated current collector was obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coatings on both sides have the same parameters, wherein the carbon coating contains carbon and polyacrylic acid (polymer binder), the carbon particle size D50 is 60nm, and the mass fraction of polyacrylic acid is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0139] (2) The carbon coatings on both sides were ablated and thinned using a picosecond laser. The power of the picosecond laser was 380 W, the wavelength of the picosecond laser was 800-1200 nm, the pulse frequency of the picosecond laser was 120 MHz, and the laser scanning speed of the picosecond laser was 400 mm / s. After ablation, the structure of the carbon coating on each side was 10 nm equidistant octahedrons (1 / 2).

[0140] Example 9

[0141] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0142] (1) A 1000W laser was used to roughen the surface of an aluminum foil, and a carbon-containing slurry was coated on the surface of the aluminum foil. After baking, a carbon-coated current collector was obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coatings on both sides have the same parameters, wherein the carbon coating contains carbon and polyacrylic acid (polymer binder), the carbon particle size D50 is 60nm, and the mass fraction of polyacrylic acid is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0143] (2) The carbon coatings on both sides were ablated and thinned using a picosecond laser. The power of the picosecond laser was 420 W, the wavelength was 800-1200 nm, the pulse frequency was 120 MHz, and the laser scanning speed was 320 mm / s. After ablation, the structure of the carbon coating on each side was composed of closely spaced horizontal and vertical lines with a spacing of 15 nm and an ablation depth of 20 nm.

[0144] Example 10

[0145] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0146] (1) A 1000W laser was used to roughen the surface of an aluminum foil, and a carbon-containing slurry was coated on the surface of the aluminum foil. After baking, a carbon-coated current collector was obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coatings on both sides have the same parameters, wherein the carbon coating contains carbon and polyacrylic acid (polymer binder), the carbon particle size D50 is 60nm, and the mass fraction of polyacrylic acid is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0147] (2) The carbon coatings on both sides were ablated and thinned using a picosecond laser. The power of the picosecond laser was 420 W, the wavelength was 800-1200 nm, the pulse frequency was 120 MHz, and the laser scanning speed was 350 mm / s. After ablation, the structure of the carbon coating on each side was closely arranged horizontal and vertical lines with a spacing of 10 nm and an ablation depth of 20 nm.

[0148] Example 11

[0149] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0150] (1) A 1000W laser was used to roughen the surface of an aluminum foil, and a carbon-containing slurry was coated on the surface of the aluminum foil. After baking, a carbon-coated current collector was obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coatings on both sides have the same parameters, wherein the carbon coating contains carbon and polyacrylic acid (polymer binder), the carbon particle size D50 is 60nm, and the mass fraction of polyacrylic acid is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;as well as

[0151] (2) The carbon coatings on both sides were ablated and thinned using a picosecond laser. The power of the picosecond laser was 380 W, the wavelength was 800-1200 nm, the pulse frequency was 120 MHz, and the laser scanning speed was 350 mm / s. After ablation, the structure of the carbon coating on each side was closely spaced horizontal and vertical lines with a spacing of 10 nm and an ablation depth of 10 nm.

[0152] Example 12

[0153] This embodiment provides a method for preparing a carbon-coated current collector with a controllable coating structure, comprising the following steps:

[0154] (1) A 1000W laser was used to roughen the surface of an aluminum foil, and a carbon-containing slurry was coated on the surface of the aluminum foil. After baking, a carbon-coated current collector was obtained, wherein the carbon-coated current collector comprises an aluminum foil and a carbon coating coated on both sides of the aluminum foil. The carbon coatings on both sides have the same parameters, wherein the carbon coating contains carbon and polyacrylic acid (polymer binder), the carbon particle size D50 is 60nm, and the mass fraction of polyacrylic acid is 30% (based on the total mass of the carbon coating as 100%); the thickness of the carbon coating on one side is 0.5μm, and the single-side surface density of the carbon coating is 0.3g / m 2 ;

[0155] (2) The carbon coatings on both sides were ablated and thinned using a picosecond laser. The power of the picosecond laser was 380 W, the wavelength of the picosecond laser was 800-1200 nm, the pulse frequency of the picosecond laser was 120 MHz, and the laser scanning speed was 380 mm / s. After ablation, the structure of the carbon coating on each side was closely arranged horizontal and vertical lines with a spacing of 5 nm and an ablation depth of 10 nm.

[0156] Example 13

[0157] The difference between this embodiment and embodiment 10 is that the power of the picosecond laser is adjusted to 280 W, and the other parameters are exactly the same as those in embodiment 10.

[0158] Example 14

[0159] The difference between this embodiment and embodiment 10 is that the power of the picosecond laser is adjusted to 480 W, and the other parameters are exactly the same as those in embodiment 10.

[0160] Comparative Example 3

[0161] This comparative example provides a carbon-coated current collector, which is exactly the same as that of Example 6.

[0162] The carbon coating structure of the carbon-coated current collector of Comparative Example 3 is shown in Figures 6 and 7. Compared with the carbon coating structure of the carbon-coated current collector of Example 6 (Figures 4 and 5), it can be seen that the method of the present application can control the coating structure and thickness, and can accurately control the coating, while the carbon coating that has not been ablated is irregular.

[0163] Comparative Example 4

[0164] This comparative example provides a current collector, namely aluminum foil, which is exactly the same as the aluminum foil provided in Example 6.

[0165] test

[0166] The current collectors obtained in Examples 6-12 and Comparative Examples 3-4 were tested, specifically including:

[0167] (1) Test of adhesion between current collector and active material layer:

[0168] Refer to GB / T 2792-2014 Test method for peel strength of adhesive tape to test the coating adhesion.

[0169] (2) Interface resistivity test:

[0170] The resistance test was performed using a four-probe square resistance tester HPS2523.

[0171] The test results are shown in Table 2.

[0172] Table 2

[0173] Performance Testing

[0174] The positive electrode slurry was applied to the current collectors provided in Examples 1-14 and Comparative Examples 1-4, respectively, and baked to obtain positive electrode sheets. These sheets were then assembled with a separator and a graphite negative electrode to form lithium-ion batteries. The positive electrode slurry comprised lithium iron phosphate, acetylene black, polyvinylidene fluoride, and N-methylpyrrolidone, and the commercially available LiPF6 electrolyte was used. The assembled lithium-ion batteries were then subjected to performance testing.

[0175] (1) Cyclic performance test

[0176] 1C / 1C charge and discharge, record the battery capacity retention rate after 500 cycles.

[0177] (2) Rate performance test

[0178] a. Charge the lithium-ion battery at a constant current of 1C to the lithium battery charging termination voltage, then switch to constant voltage charging until the charging current drops to 0.05C, at which point charging stops; and

[0179] b. At room temperature, discharge the lithium battery at a current of 10C until the battery reaches the discharge termination voltage, and record the discharge capacity; calculate the ratio of the above discharge capacity to the discharge capacity at the rated 1C.

[0180] The test results are shown in Table 3.

[0181] Table 3

[0182] analyze:

[0183] Based on the data in Table 1, Examples 1-5 show that using laser ablation to thin the carbon coating can achieve nanoscale processing of the coating, effectively reducing the thickness and surface density of the carbon coating. Furthermore, the thinned carbon coating can still achieve 100% coverage. The thinned carbon coating has a high roughness, which facilitates close contact with the active material layer. Compared with Comparative Example 1, the conventional carbon-coated current collector is thicker and has a higher single-sided surface density, which affects the energy density of the battery. Furthermore, it is impossible to achieve 100% coverage of the carbon coating, only 98%, and the carbon coating roughness is also relatively low. Compared with Comparative Example 2, the surface roughness of the current collector without a carbon coating is lower.

[0184] Based on the data in Table 2, it can be seen from Examples 6-12 that the use of laser to ablate the carbon coating can realize the design of various structures, realize nano-scale processing of the carbon coating, and have high processing precision of the carbon coating; it can increase the contact area between the carbon coating and the electrode active material, and the bonding force between the carbon-coated current collector and the active material layer is high, which reduces the manufacturing cost of the electrode and can reduce the interface internal resistance. It can be seen from Example 10 and Examples 13-14 that if the power of the picosecond laser is too low, the ablation ability is insufficient, and it is impossible to accurately control the structure of the coating and ablate the thickness; if the power of the picosecond laser is too high, the ablation ability is uncontrollable, which can easily cause excessive ablation of the coating, damage the foil, and form pinholes. It can be seen from Example 6 and Comparative Examples 3-4 that the use of conventional carbon-coated current collectors or simple aluminum foils will lead to a decrease in the bonding force between the current collector and the active material layer and an increase in the interface resistivity.

[0185] Based on the data in Table 3, Examples 1-12 show that laser ablation of the carbon coating allows for thinning and a variety of structural designs. When applied to lithium batteries, the batteries exhibit excellent cycle and rate performance. Examples 10 and 13-14 show that excessively low or high picosecond laser power can lead to decreased cycle and rate performance. Examples 1, 6, and Comparative Examples 1-4 show that conventional carbon-coated current collectors or simple aluminum foil exhibit poor cycle and rate performance.

[0186] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A method for preparing a carbon-coated current collector with a controllable coating structure, comprising: The carbon coating of the carbon-coated current collector is ablated by laser to obtain the carbon-coated current collector with controllable structure.

2. The preparation method according to claim 1, wherein The carbon coating comprises carbon and a polymer binder.

3. The preparation method according to claim 2, wherein The particle size D50 of the carbon is 30-500 nm.

4. The preparation method according to claim 2 or 3, wherein The polymer binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol and polyacrylic acid; Preferably, based on the total mass of the carbon coating being 100%, the mass fraction of the polymer binder is 4-80%.

5. The preparation method according to any one of claims 1 to 4, wherein: The thickness of the carbon coating is 0.5-2 μm; Preferably, the single-sided surface density of the carbon coating is 0.3-0.4 g / m 2 .

6. The preparation method according to any one of claims 1 to 5, wherein: The laser includes a picosecond laser.

7. The preparation method according to claim 6, wherein: The power of the picosecond laser is 300-450W; Preferably, the wavelength of the picosecond laser is 800-1200nm; Preferably, the pulse frequency of the picosecond laser is 100-150 MHz.

8. The preparation method according to claim 6 or 7, wherein: The laser scanning speed of the picosecond laser is 200-400 mm / s.

9. A carbon-coated current collector with controllable coating structure, prepared by the preparation method according to any one of claims 1 to 8.

10. A secondary battery, wherein the electrode of the secondary battery comprises the carbon-coated current collector with controllable coating structure as claimed in claim 9.

Images