Carbon-coated current collector and preparation method thereof, dry-method electrode and battery

Abstract

The invention discloses a carbon-coated current collector and a preparation method thereof, a dry-method electrode and a battery, and the preparation method comprises the following steps: S1, selecting a binder, a conductive agent and a wetting agent, and preparing carbon-coated slurry; s2, coating a current collector with the carbon coating slurry; s3, drying to obtain a carbon-coated current collector; wherein the binder is a mixture of acrylic acid and an ethylene-acrylic acid copolymer, and the ethylene-acrylic acid copolymer is modified by introducing hydroxyethyl acrylate. By optimizing the formula and the process of the carbon-coated slurry, the bonding force and the stability of the carbon-coated current collector and the active material layer are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a carbon-coated current collector and its preparation method, a dry electrode, and a battery. Background Technology

[0002] With the rapid iteration of lithium-ion battery technology and the continuous growth of market demand, the optimization of battery performance and manufacturing processes has become the focus of the industry. Among these, dry-process electrode carbon-coated current collectors, as an innovative technology in lithium-ion batteries and solid-state batteries, combine the high efficiency of dry-process electrode technology with the conductivity advantages of carbon-coated current collectors, and are considered an important path to improve battery energy density and cycle life. However, this technology currently faces significant bottlenecks: due to the insufficient compatibility of traditional binder systems (such as single acrylic acid) with dry processes, the adhesion strength between the carbon coating layer and the active material is weak. During subsequent electrode pressing or battery assembly, this easily leads to poor bonding of the active material, or even large-area detachment. This not only directly affects the integrity of the electrode structure but also triggers a chain reaction of problems such as increased battery internal resistance and capacity decay, severely restricting the large-scale application of dry-process electrode technology. Therefore, developing a highly adhesive carbon-coated current collector that can both guarantee initial adhesion strength and adapt to stress changes in the dry process has become an urgent need to overcome the industry's technological barriers. Summary of the Invention

[0003] The purpose of this invention is to provide a carbon-coated current collector and its preparation method, a dry electrode, and a battery, thereby improving the adhesion of the active material in the carbon-coated current collector in the dry electrode by optimizing the slurry formulation and process.

[0004] To achieve the above objectives, the technical solution provided by the present invention is as follows: The first aspect of this application provides a method for preparing a carbon-coated current collector, comprising the following steps: S1: Select binders, conductive agents, and wetting agents to prepare carbon coating paste; S2: Apply carbon-coated slurry to the current collector; S3: Drying to obtain a carbon-coated current collector; The adhesive is a mixture of acrylic acid and ethylene-acrylic acid copolymer, wherein the ethylene-acrylic acid copolymer is an ethylene-acrylic acid copolymer modified with hydroxyethyl acrylate.

[0005] To optimize the above technical solution, the specific measures also include: Furthermore, in the adhesive mixture, the mass ratio of acrylic acid to ethylene-acrylic acid copolymer is 1:7~10.

[0006] Furthermore, the binder has a solid content of 10-50% and a viscosity of 200-3000 mPa·s.

[0007] Furthermore, in the carbon coating slurry, the binder accounts for 10-40% of the mass.

[0008] The conductive agent is selected from carbon black, graphite, or a mixture thereof; the wetting agent is selected from at least one of isopropanol, ethoxylated acetylenol, and ethylene glycol butyl ether.

[0009] Preferably, the method for preparing the carbon coating slurry includes the following steps: Dilute part of the adhesive with water, then add part of the conductive agent, mix well, add the wetting agent, and continue to dilute with water. Add the remaining conductive agent, mix well, and then grind to the required slurry particle size; Add the remaining binder, mix well, and then discharge. Furthermore, the remaining conductive agent is added, mixed evenly, and then ground to the required slurry particle size, wherein the slurry particle size refers to: D50 < 3 μm, D90 < 10 μm, D97 < 15 μm.

[0010] A second aspect of this application provides a carbon-coated current collector, prepared using the method described above.

[0011] A third aspect of this application provides a dry electrode comprising the aforementioned carbon-coated current collector.

[0012] A fourth aspect of this application provides a battery comprising the aforementioned dry electrode.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention develops a method for preparing a highly adhesive carbon-coated current collector for dry electrode processes. By optimizing the slurry formulation and process, the adhesion and stability between the carbon-coated current collector and the active material layer are significantly improved. In terms of formulation, an innovative mixed system of acrylic acid and modified ethylene-acrylic acid copolymer (modified EAA) is adopted. Acrylic acid provides strong polar groups, ensuring the initial adhesion of the aluminum foil current collector; while the modified ethylene-acrylic acid copolymer, by introducing hydroxyethyl acrylate (HEA) grafted hydroxyl groups, retains the thermal adhesion of the carboxylic acid groups and adds hydrogen and ionic bonding interactions with the metal layer. Simultaneously, its flexible segments enhance the flexibility and crack resistance of the coating. After mixing, while ensuring initial adhesion strength, it effectively buffers the volume expansion stress during electrode charging and discharging, reducing the shedding of the active material layer.

[0014] The mass ratio of acrylic acid to modified ethylene-acrylic acid copolymer is controlled within a certain range to avoid both excessive acrylic acid content leading to increased coating brittleness and excessive modified ethylene-acrylic acid copolymer content weakening interfacial bonding, thereby ensuring the cycle life of the battery. Detailed Implementation

[0015] The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the subject matter of the present invention to the following embodiments. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0016] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the reagents, methods and equipment used are conventional reagents, methods and equipment in this technical field.

[0017] This invention provides a method for preparing a carbon-coated current collector, comprising the following steps: S1: Select binders, conductive agents, and wetting agents to prepare carbon coating paste; S2: Apply carbon-coated slurry to the current collector; S3: Drying to obtain a carbon-coated current collector; The adhesive is a mixture of acrylic acid and ethylene-acrylic acid copolymer, wherein the ethylene-acrylic acid copolymer is an ethylene-acrylic acid copolymer modified with hydroxyethyl acrylate.

[0018] This application develops a method for preparing a highly adhesive carbon-coated current collector specifically for dry electrode processes. This method effectively improves the adhesion and stability between the carbon-coated aluminum foil and the active material layer of the dry electrode by optimizing the slurry formulation and preparation process of the carbon coating layer.

[0019] In terms of slurry formulation, compared to the traditional approach of using acrylic acid (AA) alone as a binder, this invention innovatively employs a modified ethylene-acrylic acid copolymer (modified EAA) as the main component of the binder. Acrylic acid provides strong polar groups, enhancing adhesion to the current collector, while the ethylene-acrylic acid copolymer improves the flexibility and crack resistance of the coating through flexible segments. The combination of the two ensures initial bond strength while mitigating volume expansion stress during electrode charging and discharging, reducing the shedding of the active material layer.

[0020] The modified ethylene-acrylic acid copolymer (modified EAA) retains the excellent thermal adhesion of the original carboxylic acid group by grafting hydroxyl groups onto its molecular chain through the introduction of hydroxyethyl acrylate (HEA). Simultaneously, the newly added hydroxyl groups further enhance its interaction with the current collector metal layer. Its mechanism of action mainly lies in: Polar carboxylic acid groups and hydroxyl groups can form hydrogen bonds with oxides on the surface of current collector metal layers such as aluminum foil. Carboxylic acid groups may also undergo ionization reactions to form ionic bonds with aluminum ions, thereby significantly enhancing interfacial bonding. In addition, these polar groups also disrupt the regular arrangement of polymer molecular chains, reduce the crystallinity of the material, make it more flexible in the molten state, easier to adhere to the substrate, and optimize the bonding effect.

[0021] In some embodiments, the mass ratio of acrylic acid to ethylene-acrylic acid copolymer in the adhesive mixture is 1:7 to 10.

[0022] Acrylic acid has strong polar groups, which are mainly responsible for providing a strong initial adhesion between the acrylic foil current collector and the coating. The dominant material modified with hydroxyethyl acrylate (HEA) imparts excellent flexibility and crack resistance to the coating through the flexible segments in its molecular chain. This combination allows the coating to not only adhere firmly to the current collector, but also effectively buffer the stress caused by the volume change of the active material during the charging and discharging process, thereby significantly reducing the shedding of the active material layer and improving the cycle life of the battery.

[0023] When the proportion of acrylic acid is too high, there are too many rigid components in the mixture, which may result in higher initial bond strength, but will reduce the flexibility of the coating. During battery cycling, the brittle coating is difficult to release stress effectively and is more prone to cracking, leading to the shedding of active materials.

[0024] Conversely, if the proportion of modified EAA is too high, it will lead to insufficient overall polarity of the binder, weakening the interfacial bonding force between the active material coating and the aluminum foil substrate, which may result in substandard adhesion and also fail to guarantee the long-term stability of the electrode structure.

[0025] Therefore, by controlling the mass ratio of acrylic acid to modified EAA within a certain range, the carbon-coated current collector can simultaneously possess excellent adhesion, flexibility, and long-term cycling stability when used in dry electrodes.

[0026] Examples of methods for modifying ethylene-acrylic acid copolymers by introducing hydroxyethyl acrylate are as follows: 1) Add the ethylene-acrylic acid copolymer (EAA) emulsion to the reactor, dilute with deionized water to a solid content of 30%; add emulsifier, stir at 60°C for 30 minutes; purge with nitrogen to remove oxygen for 20 minutes at a flow rate of 1 L / min; 2) Raise the temperature to 60℃ and start adding a mixed aqueous solution of hydroxyethyl acrylate (HEA) and ammonium persulfate (APS) dropwise, while simultaneously adding an aqueous solution of ascorbic acid (Vc). React at 65℃ for 2 hours. 3) Cool it to 30℃ and adjust the pH to 7.5 with ammonia.

[0027] The molar ratio of APS to Vc is 1:0.5; EAA accounts for 62% of the total mass of the system, HEA accounts for 6% of the total mass of the system, APS accounts for 0.12% of the total mass of the system, Vc accounts for 0.06% of the total mass of the system, emulsifier accounts for 0.6% of the total mass of the system, and the remainder is deionized water.

[0028] In some embodiments, the binder has a solid content of 10-50% and a viscosity of 200-3000 mPa·s.

[0029] In carbon coating slurry, the binder accounts for 10-40% of the mass.

[0030] In some embodiments, the conductive agent is selected from carbon black, graphite, or a mixture thereof; the wetting agent is selected from at least one of isopropanol, ethoxylated acetylenol, and ethylene glycol butyl ether.

[0031] In some embodiments, the method for preparing the carbon coating paste includes the following steps: Dilute about half of the adhesive with water, then add about one-third of the conductive agent, mix well, add the wetting agent, and continue to dilute with water. Add the remaining conductive agent, mix well, and then grind to the required slurry particle size; Add the remaining binder, mix well, and then discharge. The binder of this invention is added in two stages. First, deionized water is mixed with the binder and stirred at low speed. This is the first addition of the binder. After the conductive agent has been added to the slurry, it is dispersed and ground at high speed, and then the binder is added again and stirred at low speed. This stepwise addition helps to ensure that the binder is evenly dispersed in the slurry, thereby obtaining better coating effect and electrode performance.

[0032] This invention effectively solves the problem of active materials failing to adhere or falling off during the coating process of dry electrodes by optimizing the adhesive formulation and preparation process, and significantly improves the hot-press peel strength.

[0033] In some embodiments, the slurry particle size refers to: D50 < 3 μm, D90 < 10 μm, D97 < 15 μm.

[0034] The present invention also provides a carbon-coated current collector, which is prepared by the above method.

[0035] The present invention also provides a dry electrode comprising the above-described carbon-coated current collector.

[0036] The present invention also provides a battery comprising the above-described dry electrode.

[0037] The technical solution of the present invention will be further described in detail below with reference to specific embodiments: Example 1: Mix deionized water with half of the binder and stir at a low speed of 25 rpm / min for 30 min in a 200L twin-star mixing tank. Add one-third of the conductive agent and disperse at high speed of 2200 rpm / min for 30 min in a 200L double-star stirring tank; Add wetting agent and water, and stir at low speed of 20 rpm / min for 20 min in a 200L double star mixing tank; Add the remaining conductive agent and disperse at high speed of 2400 rpm / min for 60 min in a 200 L double-star stirred tank; The slurry was ground 6 times with a grinder to ensure that the slurry particle size D50 < 3 μm, D90 < 10 μm, and D97 < 15 μm. Add the other half of the binder, and stir at a low speed of 15 rpm / min for 30 minutes in a 200L twin-star mixing tank before discharging. Carbon-coated aluminum foil is produced by uniformly coating the slurry onto aluminum foil using a gravure coating machine and then drying it. The surface density of the coating is 0.8 g / m³. 2 The coating thickness on one side is 0.5μm.

[0038] The binder accounts for 25% of the total slurry mass, and the mass ratio of binder to conductive agent is 1:1. In the adhesive, the mass ratio of acrylic acid to modified ethylene acrylic acid copolymer (modified EAA) is 1:8.5, and the solid content of the adhesive is 20%; carbon black is used as the conductive agent, and isopropanol is used as the wetting agent.

[0039] Example 2: The scheme in this embodiment is basically the same as that in embodiment 1, except that the mass ratio of acrylic acid to modified ethylene acrylic acid copolymer (modified EAA) in the adhesive is 1:7.

[0040] Example 3: The scheme in this embodiment is basically the same as that in Example 1, except that the mass ratio of acrylic acid to modified ethylene acrylic acid copolymer (modified EAA) in the adhesive is 1:10.

[0041] Example 4: The scheme in this embodiment is basically the same as that in embodiment 1, except that the mass ratio of acrylic acid to modified ethylene acrylic acid copolymer (modified EAA) in the adhesive is 1:5.

[0042] Example 5: The scheme in this embodiment is basically the same as that in embodiment 1, except that the mass ratio of acrylic acid to modified ethylene acrylic acid copolymer (modified EAA) in the adhesive is 1:15.

[0043] Example 6: In this comparative example, all the adhesive is added at the very beginning of the step: Mix deionized water with all the binder and stir at a low speed of 25 rpm / min for 30 min in a 200L double star mixing tank. Add one-third of the conductive agent and disperse at high speed of 2200 rpm / min for 30 min in a 200L double-star stirring tank; Add wetting agent and water, and stir at low speed of 20 rpm / min for 20 min in a 200L double star mixing tank; Add the remaining conductive agent and disperse at high speed of 2400 rpm / min for 60 min in a 200 L double-star stirred tank; The slurry was ground 6 times with a grinder to ensure that the slurry particle size D50 < 3 μm, D90 < 10 μm, and D97 < 15 μm. After stirring at a low speed of 15 rpm / min for 30 minutes in a 200L twin-star mixing tank, the material is discharged. Carbon-coated aluminum foil is produced by uniformly coating the slurry onto aluminum foil using a gravure coating machine and then drying it. The surface density of the coating is 0.8 g / m³. 2 The coating thickness on one side is 0.5 μm, and the rest is the same as in Example 1.

[0044] Comparative Example 1: The adhesive used in this comparative example is entirely acrylic acid, without modified ethylene-acrylic acid copolymer (modified EAA), and otherwise identical to that in Example 1.

[0045] Comparative Example 2: The scheme of this comparative example is basically the same as that of Example 1, except that the mass ratio of acrylic acid to modified ethylene acrylic acid copolymer (modified EAA) in the adhesive is 1:2.

[0046] The results of the experiments conducted on each embodiment and comparative example are shown in Table 1: Table 1

[0047] Examples 1-5 all showed uniform coating without peeling, while Example 6 and Comparative Examples 1 and 2 showed local peeling.

[0048] The pure acrylic system in Comparative Example 1 lacks flexible segments, which easily leads to stress concentration and peeling during the coating process; Comparative Example 2 also shows local peeling because the proportion of modified EAA is too low and it cannot effectively buffer the hot-pressing stress.

[0049] In this invention, the stepwise addition of the binder also plays a key role in ensuring uniform dispersion. The first addition of the binder, with low-speed stirring, allows the binder and deionized water to form a uniform dispersion system, providing a stable interface for the subsequent mixing of the conductive agent. The second addition of the binder avoids agglomeration caused by high-speed dispersion, ensuring that the binder is evenly distributed in the slurry.

[0050] The synergy between the formulation and the process can affect the hot-pressing peel strength. When the ratio of AA to modified EAA was gradually adjusted from 1:15 (Example 5) to 1:5 (Example 4), 1:7 (Example 2), 1:8.5 (Example 1), and 1:10 (Example 3), the hot-pressing peel strength showed a trend of first increasing and then decreasing. Example 1 (1:8.5) reached a peak of 21.72 N / m; the low proportion of modified EAA resulted in insufficient flexible segments, which could not effectively buffer the hot-pressing stress, leading to low strength; the high proportion of modified EAA reduced the proportion of polar groups, weakened the interfacial bonding force, and decreased the strength. The optimal ratio was Example 1, where the strong polar groups of AA and the flexible segments of modified EAA formed a synergistic effect, achieving both high initial bonding force and stress release capability, while also ensuring good coating uniformity.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a carbon-coated current collector, characterized in that, Includes the following steps: S1: Select binders, conductive agents, and wetting agents to prepare carbon coating paste; S2: Apply carbon-coated slurry to the current collector; S3: Drying to obtain a carbon-coated current collector; The adhesive is a mixture of acrylic acid and ethylene-acrylic acid copolymer, wherein the ethylene-acrylic acid copolymer is an ethylene-acrylic acid copolymer modified with hydroxyethyl acrylate.

2. The method for preparing the carbon-coated current collector according to claim 1, characterized in that: In the adhesive mixture, the mass ratio of acrylic acid to ethylene-acrylic acid copolymer is 1:7~10.

3. The method for preparing the carbon-coated current collector according to claim 1, characterized in that: The binder has a solid content of 10-50% and a viscosity of 200-3000 mPa·s.

4. The method for preparing the carbon-coated current collector according to claim 1, characterized in that: In carbon coating slurry, the binder accounts for 10-40% of the mass.

5. The method for preparing the carbon-coated current collector according to claim 1, characterized in that: The conductive agent is selected from carbon black, graphite, or a mixture thereof; the wetting agent is selected from at least one of isopropanol, ethoxylated acetylenol, and ethylene glycol butyl ether.

6. The method for preparing the carbon-coated current collector according to claim 1, characterized in that: The preparation method of the carbon coating slurry includes the following steps: Dilute part of the adhesive with water, then add part of the conductive agent, mix well, add the wetting agent, and continue to dilute with water. Add the remaining conductive agent, mix well, and then grind to the required slurry particle size; Add the remaining binder, mix well, and then discharge.

7. The method for preparing the carbon-coated current collector according to claim 1, characterized in that: The remaining conductive agent is added, mixed evenly, and then ground to the required slurry particle size, wherein the slurry particle size refers to: D50 < 3 μm, D90 < 10 μm, D97 < 15 μm.

8. A carbon-coated current collector, characterized in that: Prepared using the method described in any one of claims 1 to 7.

9. A dry electrode, characterized in that: It includes the carbon-coated current collector as described in claim 8.

10. A battery, characterized in that: It includes the dry electrode as described in claim 9.

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