Double-layer coating method for positive electrode and negative electrode of thick electrode

Abstract

The invention provides a double-layer coating method for a positive electrode and a negative electrode of a thick electrode. According to the thick electrode positive and negative electrode double-layer coating method, a high-compaction compact layer, an upper layer and camphor nano-particles are arranged, the baking temperature and the adding amount and particle size of the camphor nano-particles are regulated and controlled, the double-layer structure design achieves functional complementation, and the bottom layer guarantees the mechanical strength and energy density of the electrode; the upper layer depends on camphor nano-particle pore forming to improve the ion transmission efficiency; meanwhile, by means of accurate regulation and control of the baking temperature, the particle adding amount and the particle size, pore channel structure customization is achieved, differential performance requirements are met, secondly, coating equipment, drying equipment and the like adopted by the process are conventional equipment for lithium battery production, large-scale production line transformation is not needed, the steps are simple, the operation difficulty is low, an existing industrial production system can be rapidly adapted, and the production cost is low. And batch manufacturing is realized.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrode manufacturing technology, and more specifically, to a method for double-layer coating of thick electrode positive and negative electrodes. Background Technology

[0002] Driven by the rapid development of electric vehicles, energy storage systems, and other fields, the market has placed higher demands on the energy density of lithium-ion batteries. Thick electrode technology, due to its ability to significantly increase the loading of active materials in the electrode, has become one of the key research directions for improving the energy density of lithium-ion batteries.

[0003] However, thick electrodes have the following problems when used: Traditional thick electrodes face several technical bottlenecks in practical applications: First, the excessive density of the internal structure of thick electrodes makes it difficult for the electrolyte to fully wet the electrode interior, extending the ion transport path and increasing the battery's internal resistance. Second, these problems directly affect the battery's rate performance, causing rapid capacity decay under high-rate charge-discharge scenarios and shortening the battery's cycle life. To improve the performance defects of traditional thick electrodes, existing technologies mainly employ the addition of pore-forming agents or adjustments to the slurry formulation. However, adding pore-forming agents can easily lead to uneven pore distribution within the electrode, and some pore-forming agents are difficult to completely remove, with residual substances negatively impacting the battery's electrochemical performance. While adjusting the slurry formulation can optimize the electrode structure to some extent, it is difficult to balance the electrode's structural stability and ion transport efficiency, failing to fundamentally solve the core technical problems of thick electrodes.

[0004] This invention can ensure that the thick electrode has a high solid density to improve the energy density, and can also construct an ordered pore structure to optimize electrolyte wettability and ion transport efficiency. Summary of the Invention

[0005] The present invention aims to solve the technical problems mentioned in the background art and provide a method for thick electrode positive and negative double-layer coating.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for double-layer coating of thick electrode positive and negative electrodes, comprising the following steps: Step 1: Select an active material with orderly particle arrangement, mix it with a conductive agent and a binder in a preset ratio, and prepare a uniform slurry by high-speed stirring and grinding; use a precision coating device to uniformly coat the slurry onto the surface of the current collector, and after preliminary drying, form a high-pressure compacted dense layer, which can guarantee the mechanical strength and energy density of the electrode. Step 2: During the preparation of the slurry, which is the same system as the bottom layer, add camphor nanoparticles at 0.5%-1% of the total mass of the slurry, wherein the particle size of the camphor nanoparticles is controlled at 50-200nm; by mechanical stirring, ensure that the camphor nanoparticles are uniformly dispersed in the slurry and avoid particle agglomeration. Step 3: Using the same precision coating equipment as the base coat, uniformly coat the slurry containing camphor nanoparticles onto the surface of the prepared high-pressure compacted layer, and control the coating thickness to keep the thickness ratio of the base layer to the top layer at 1:1-1:2. Step 4: Place the double-coated electrode in a drying device, control the baking temperature, and adjust the baking time according to the electrode thickness; utilize the sublimation properties of camphor to make the camphor nanoparticles in the upper layer of the electrode completely sublimate and volatilize, forming an ordered and interconnected micron-sized pore structure in the upper layer of the electrode. This pore structure can significantly improve the wettability of the electrolyte and the ion transport efficiency. Step 5: After the above steps, a double-layer coated thick electrode with a total thickness of more than 200 μm is obtained. This electrode has both high compaction density and excellent ion transport performance.

[0007] Further preferred options: In step one, the positive electrode can be lithium iron phosphate or ternary active materials, and the negative electrode can be graphite or silicon-based active materials.

[0008] Further preferred option: In step one, the conductive agent can be carbon black or carbon nanotube materials.

[0009] Further preferred option: In step one, the adhesive can be polyvinylidene fluoride or styrene-butadiene rubber.

[0010] Further preferred option: In step one, the current collector can be made of aluminum foil or copper foil, with aluminum foil being used for the positive electrode and copper foil being used for the negative electrode.

[0011] A further preferred option: In step two, the proportions of active materials, conductive agents, and binders in the slurry are consistent with those in the underlying layer.

[0012] A further preferred option: In step four, the baking temperature is 80°C-120°C, and the baking time is 2-3 hours. Beneficial effects

[0013] 1. By setting up a high-pressure compact layer and an upper layer, the bottom high-pressure compact layer uses an orderly arranged active material, combined with a suitable conductive agent, binder and current collector. After precision coating and drying, it lays a solid mechanical strength foundation for the electrode, while ensuring high compaction density and laying the core support for energy density. The upper layer adds camphor nanoparticles of a specific size as a pore-forming agent. After baking and sublimation, it forms orderly interconnected micron-level pores, which greatly improves electrolyte wettability and ion transport efficiency. The double-layer structure achieves functional complementarity, and finally a thick electrode with a total thickness of more than 200μm is obtained, which takes into account both high energy density and excellent transport performance. 2. By incorporating camphor nanoparticles as a pore-forming agent, its unique sublimation properties are fully utilized during the baking process. It can completely sublimate and volatilize within a process temperature range of 80°C-120°C, leaving no residue throughout the process. This fundamentally avoids problems such as increased interfacial impedance and electrolyte contamination caused by traditional pore-forming agent residues, effectively preventing negative impacts on key electrochemical performances such as battery charge-discharge efficiency and capacity retention. This residue-free characteristic creates a stable internal reaction environment for the battery, significantly improving the structural stability and performance consistency of the battery during long-term cycling. 3. By controlling the baking temperature within the range of 80°C-120°C, the sublimation rate of camphor nanoparticles can be matched, avoiding pore collapse due to excessively high temperatures or incomplete sublimation due to excessively low temperatures; by adjusting the addition amount within the range of 0.5%-1%, the pore distribution density can be flexibly adjusted to meet the requirements of different electrolyte wetting and ion transport efficiency; by controlling the particle size between 50-200nm, the pore size and specifications can be directly determined. The coordinated control of these three factors can precisely control the size, distribution uniformity, and connectivity of the pores, achieving a precise match from pore structure to electrode performance, thereby adapting to the differentiated requirements of battery energy density, rate performance, etc. in different scenarios; 4. In summary, this method of thick electrode double-layer coating for both positive and negative electrodes achieves complementary functions through a double-layer structure design that incorporates a high-pressure compact layer, an upper layer, camphor nanoparticles, and controlled baking temperature, amount, and particle size of camphor nanoparticles. The bottom layer ensures the mechanical strength and energy density of the electrode, while the upper layer utilizes camphor nanoparticles to create pores and improve ion transport efficiency. Furthermore, precise control of baking temperature, particle amount, and particle size allows for customized pore structures to meet diverse performance requirements. Additionally, the coating and drying equipment used in the process are conventional lithium battery production equipment, requiring no large-scale production line modifications. The process is simple, easy to operate, and can be quickly adapted to existing industrial production systems for mass production. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

[0015] In this embodiment of the invention, a method for double-layer coating of thick electrodes (positive and negative) includes the following steps: Step 1: Select an active material with orderly particle arrangement, mix it with a conductive agent and a binder in a preset ratio, and prepare a uniform slurry by high-speed stirring and grinding; use a precision coating device to uniformly coat the slurry onto the surface of the current collector, and after preliminary drying, form a high-pressure compacted dense layer, which can guarantee the mechanical strength and energy density of the electrode. Step 2: During the preparation of the slurry, which is the same system as the bottom layer, add camphor nanoparticles at 0.5%-1% of the total mass of the slurry, wherein the particle size of the camphor nanoparticles is controlled at 50-200nm; by mechanical stirring, ensure that the camphor nanoparticles are uniformly dispersed in the slurry and avoid particle agglomeration. Step 3: Using the same precision coating equipment as the base coat, uniformly coat the slurry containing camphor nanoparticles onto the surface of the prepared high-pressure compacted layer, and control the coating thickness to keep the thickness ratio of the base layer to the top layer at 1:1-1:2. Step 4: Place the double-coated electrode in a drying device, control the baking temperature, and adjust the baking time according to the electrode thickness; utilize the sublimation properties of camphor to make the camphor nanoparticles in the upper layer of the electrode completely sublimate and volatilize, forming an ordered and interconnected micron-sized pore structure in the upper layer of the electrode. This pore structure can significantly improve the wettability of the electrolyte and the ion transport efficiency. Step 5: After the above steps, a double-layer coated thick electrode with a total thickness of more than 200 μm is obtained. This electrode has both high compaction density and excellent ion transport performance. In step one, the positive electrode can be lithium iron phosphate or ternary active materials, and the negative electrode can be graphite or silicon-based active materials; in step one, the conductive agent can be carbon black or carbon nanotube materials; in step one, the binder can be polyvinylidene fluoride or styrene-butadiene rubber materials; in step one, the current collector can be aluminum foil or copper foil materials, with aluminum foil used for the positive electrode and copper foil used for the negative electrode; in step two, the proportions of active materials, conductive agents, and binders in the slurry are the same as those in the bottom layer; in step four, the baking temperature is 80°C-120°C, and the baking time is 2-3 hours. The preparation of the thick electrode positive double-layer coating is carried out according to the above steps, and the specific steps are as follows: Step 1: Select an active material with an orderly particle arrangement according to a certain mass ratio. The active material is lithium iron phosphate, the conductive agent is carbon black, and the binder is polyvinylidene fluoride. Add N-methylpyrrolidone solvent, stir at high speed for 1 hour, and grind to make a uniform slurry. Step 2: The above slurry is coated onto the surface of the current collector. The current collector material is aluminum foil. After drying, a high-pressure compacted layer with a thickness of 100μm is formed, which is the bottom layer. Step 3: Add camphor nanoparticles with a particle size of 100nm to the slurry with the same formula as the bottom layer at 0.5% of the total mass of the slurry. Disperse the slurry with ultrasound and stir at high speed to make a uniform slurry. Step 4: Continue to coat the bottom layer with a slurry containing camphor nanoparticles, controlling the coating thickness to be 100μm, so that the thickness ratio of the bottom layer to the top layer is 1:1. Step 5: Place the double-coated electrode in a hot air circulating drying oven, set the baking temperature to 100°C and the baking time to 2 hours; after the camphor nanoparticles have completely sublimated and volatilized, roll and cut the electrode to obtain a positive electrode with a total thickness of 200μm.

[0016] The preparation of the thick electrode negative electrode double-layer coating is carried out according to the above steps. The specific steps are as follows: Step 1: Select an active material with an orderly particle arrangement according to a certain mass ratio. The active material is natural graphite, the conductive agent is carbon nanotubes, and the binder is styrene-butadiene rubber and sodium carboxymethyl cellulose in a mass ratio of 1:1. Mix them, add deionized water, stir at high speed for 1.5 hours, and grind to make a uniform slurry. Step 2: The above slurry is coated onto the surface of the current collector using a micro-gravure coating machine. The current collector is made of copper foil material. After drying, a high-pressure compacted dense layer with a thickness of 80μm is formed, which is the bottom layer. Step 3: In the same slurry as the bottom layer, add camphor nanoparticles with a particle size of 150nm at 0.5% of the total mass of the slurry. After ultrasonic dispersion and high-speed stirring, a uniform slurry is prepared. Step 4: Coat the bottom layer with a slurry containing camphor nanoparticles, controlling the coating thickness to be 120μm, so that the thickness ratio of the bottom layer to the top layer is 1:1.5; Step 5: Place the double-coated electrode in a vacuum drying oven, set the baking temperature to 90°C and the baking time to 2.5h; after the camphor nanoparticles have completely sublimated and volatilized, roll and slit the electrode to obtain a negative electrode with a total thickness of 200μm.

[0017] In the preparation of both electrodes, camphor nanoparticles were selected as a pore-forming agent when preparing the upper electrode. Utilizing the sublimation properties of camphor, the camphor nanoparticles in the upper electrode layer completely sublimated and volatilized, forming ordered and interconnected micron-sized channels. This channel structure significantly improves electrolyte wettability and ion transport efficiency. Furthermore, it completely sublimates and volatilizes during baking, leaving no residue, thus avoiding the negative impact of traditional pore-forming agent residues on battery electrochemical performance and ensuring long-term cycle stability. During baking, the baking temperature can be controlled within the range of 80°C-120°C, and the amount of camphor nanoparticles added can be controlled between 0.5% and 1%. Within a certain range and with a particle size between 50-200 nm, the size, distribution density, and connectivity of the upper layer pores of the electrode can be precisely controlled to meet the electrode preparation requirements of different performance needs. By utilizing the upper and lower layers to form a double-layer electrode, the double-layer structure design can achieve functional complementarity. The high-compact and dense lower layer ensures the compaction density and mechanical strength of the electrode, while the ordered pore structure of the upper layer optimizes electrolyte wettability and ion transport efficiency. Furthermore, the coating, drying, and other equipment used in this invention are all conventional equipment in the field of lithium-ion battery production, requiring no large-scale modification of the production line. The process steps are simple, the operation is easy, and it is convenient to achieve industrial mass production, thus having high industrial application value.

[0018] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for double-layer coating of thick electrodes (positive and negative), characterized in that: Includes the following steps: Step 1: Select an active material with orderly particle arrangement, mix it with a conductive agent and a binder in a preset ratio, and prepare a uniform slurry by high-speed stirring and grinding; use a precision coating device to uniformly coat the slurry onto the surface of the current collector, and after preliminary drying, form a high-pressure compacted dense layer, which ensures the mechanical strength and energy density of the electrode. Step 2: During the preparation of the slurry, which is the same system as the bottom layer, add camphor nanoparticles at 0.5%-1% of the total mass of the slurry, wherein the particle size of the camphor nanoparticles is controlled at 50-200nm; by mechanical stirring, ensure that the camphor nanoparticles are uniformly dispersed in the slurry and avoid particle agglomeration. Step 3: Using the same precision coating equipment as the base coat, uniformly coat the slurry containing camphor nanoparticles onto the surface of the prepared high-pressure compacted layer, and control the coating thickness to keep the thickness ratio of the base layer to the top layer at 1:1-1:

2. Step 4: Place the double-coated electrode in a drying device, control the baking temperature, and adjust the baking time according to the electrode thickness; utilize the sublimation properties of camphor to make the camphor nanoparticles in the upper layer of the electrode completely sublimate and volatilize, forming an ordered and interconnected micron-sized pore structure in the upper layer of the electrode. This pore structure significantly improves the wettability of the electrolyte and the ion transport efficiency. Step 5: After the above steps, a double-layer coated thick electrode with a total thickness of more than 200 μm is obtained. This electrode has both high compaction density and excellent ion transport performance.

2. The method for double-layer coating of thick electrode positive and negative electrodes according to claim 1, characterized in that: In step one, the positive electrode is selected from lithium iron phosphate and ternary active materials, and the negative electrode is selected from graphite and silicon-based active materials.

3. The method for double-layer coating of thick electrode positive and negative electrodes according to claim 1, characterized in that: In step one, carbon black and carbon nanotube materials are selected as conductive agents.

4. The method for double-layer coating of thick electrode positive and negative electrodes according to claim 1, characterized in that: In step one, the adhesive used is polyvinylidene fluoride and styrene-butadiene rubber.

5. The method for double-layer coating of thick electrode positive and negative electrodes according to claim 1, characterized in that: In step one, the current collector is made of aluminum foil or copper foil, with aluminum foil used for the positive electrode and copper foil used for the negative electrode.

6. The method for double-layer coating of thick electrode positive and negative electrodes according to claim 1, characterized in that: In step two, the proportions of active materials, conductive agents, and binders in the slurry are consistent with those in the underlying layer.

7. The method for double-layer coating of thick electrode positive and negative electrodes according to claim 1, characterized in that: In step four, the baking temperature is 80°C-120°C, and the baking time is 2-3 hours.