High-capacity lithium battery steel shell structure with local insulating coating and preparation method of high-capacity lithium battery steel shell structure

Abstract

The invention discloses a high-capacity lithium battery steel shell structure with a local insulating coating and a preparation method of the high-capacity lithium battery steel shell structure. The preparation method comprises the following steps: (1) preparing aqueous composite slurry; (2) performing mask positioning; (3) performing local spraying; water-based composite slurry with a unique ratio is sprayed on the inner surface of the steel shell body through a spraying process and is cured to form an insulating coating, the corrosion path of the steel shell body and electrolyte is blocked, the risk of short circuit is reduced, meanwhile, the adhesive force of the insulating coating on the inner surface of the steel shell body is high, the insulating coating is not prone to peeling off when soaked in the electrolyte, and the service life of the steel shell is prolonged. And the safety performance of the high-capacity lithium battery is greatly improved. The mask positioning and local spraying modes are adopted, secondary machining of a welding area is not needed, the preparation technology is more efficient, and meanwhile the quality of the high-capacity lithium battery steel shell structure is greatly improved; therefore, the steel shell structure of the high-capacity lithium battery is applicable to the fields with strict requirements on corrosion resistance and safety, such as high-energy-density power batteries, energy storage batteries and the like.

Description

Technical Field

[0001] This invention relates to the development technology of high-capacity lithium battery steel shell structure, belonging to the field of lithium-ion battery manufacturing technology, specifically to a high-capacity lithium battery steel shell structure with a local insulating coating and its preparation method. Background Technology

[0002] A battery steel casing refers to the metal outer shell of a battery, typically made of nickel-plated steel. It primarily serves as physical protection, a seal, and a current pathway, making it a key component in the battery structure. Taking lithium-ion batteries as an example, existing lithium-ion battery steel casings refer to lithium-ion battery structures using steel as the outer shell, commonly found in cylindrical or prismatic batteries. For example, the common 21700 model lithium battery (also known as a high-capacity lithium battery) has a cylindrical steel casing with a diameter of approximately 21mm and a height of approximately 70mm, primarily used for encapsulating 21700 model lithium-ion batteries.

[0003] Traditional 21700 lithium battery steel casings are prone to electrochemical corrosion when the inner wall is in direct contact with the electrolyte, leading to casing perforation or electrolyte contamination. In existing technologies, some battery casing manufacturers have attempted to address this issue by applying an insulating coating (such as epoxy resin, polyurethane resin, or acrylic resin) to the entire inner wall of the casing using a high-temperature curing method (i.e., thermosetting, typically at 120℃ to 150℃). While this design addresses the electrochemical corrosion problem to some extent, the performance and coating process of existing conventional insulating coatings are not ideal, resulting in the following drawbacks: insufficient adhesion of conventional insulating coatings to the inner wall of the casing; easy peeling of conventional insulating coatings under electrolyte immersion, leading to leakage risks; poor weldability of the insulating coating after thermosetting, requiring additional removal when the insulating layer covers the bottom welding area, increasing process complexity; and the use of a high-temperature curing method (i.e., thermosetting) to coat the entire inner wall of the casing with an insulating coating, which may affect the mechanical properties of the battery steel casing itself, significantly reducing its temperature resistance. Summary of the Invention

[0004] This invention provides a high-capacity lithium battery steel shell structure with a local insulating coating and its preparation method. The purpose is to overcome the technical problems of existing conventional insulating coatings, such as unsatisfactory performance and coating process, insufficient adhesion, poor welding compatibility, and reduced temperature resistance of the battery steel shell.

[0005] A high-capacity lithium battery steel shell structure with a partial insulating coating includes a steel shell body and an insulating coating covering its inner surface. The insulating coating includes a first insulating coating covering the inner sidewall of the steel shell body and a second insulating coating seamlessly connected to the bottom edge of the first insulating coating and covering the bottom surface of the inner surface of the steel shell body. The second insulating coating has a ring structure, and the central region of the ring structure forms a welded area without an insulating coating. The second insulating coating and the first insulating coating are integrally sprayed by a spraying process, and the thickness of the second insulating coating and the first insulating coating is controlled at 10-20 μm. The welded area is circular, and its diameter is controlled at 8-10 mm.

[0006] Furthermore, the insulating coating is formed by spraying an aqueous composite slurry composed of acrylic resin, nano-alumina, silane coupling agent and deionized water onto the inner surface of the steel shell body through a spraying process and then curing it.

[0007] Furthermore, the water-based composite slurry is prepared according to the following components in parts by weight: 40-60 parts acrylic resin, 20-30 parts nano alumina, 4-6 parts silane coupling agent, and a small amount of deionized water.

[0008] Furthermore, the water-based composite slurry is prepared from the raw materials of the components in parts by weight, and it also includes 1-3 parts of zinc phosphate.

[0009] A method for preparing a high-capacity lithium battery steel shell structure with a localized insulating coating includes the following steps: 1) Preparation of an aqueous composite slurry: Raw materials are prepared according to the following components by weight: 40-60 parts acrylic resin, 20-30 parts nano-alumina, 4-6 parts silane coupling agent, and 10-15 parts deionized water; 2) Mask positioning: A mask with a diameter of 8-10 mm is adsorbed and fixed in the central area of ​​the bottom surface of the steel shell body using a vacuum adsorption fixture. This central area is the welding area, and the positioning accuracy of the mask is controlled within ± 0.1mm; 3) Local spraying: The inner surface of the steel shell is sprayed with a water-based composite slurry. After spraying, the inner surface is cured by hot air curing to ensure that a stable and firm insulating coating is formed on the inner surface of the steel shell. The thickness of the insulating coating is controlled at 10-20μm, and the thickness deviation is controlled at ±2μm. Finally, the mask on the inner bottom surface of the steel shell is removed to expose the welding area on the inner bottom surface, thus obtaining a high-capacity lithium battery steel shell structure.

[0010] Furthermore, it also includes the following steps: 4) Testing and verification: The high-capacity lithium battery steel shell structure is subjected to leakage current, welding resistance and salt spray treatment in sequence. All tests are passed to obtain a qualified high-capacity lithium battery steel shell structure. The leakage current test value of the qualified high-capacity lithium battery steel shell structure is ≤0.8μA, the contact resistance of the welding area is ≤0.1mΩ and there is no corrosion expansion of the insulation coating.

[0011] As described above, compared with the prior art, the advantages of this invention are as follows: The high-capacity lithium battery steel shell structure and its preparation method are ideally designed. A uniquely proportioned water-based composite slurry is sprayed onto the inner surface of the steel shell body using a spraying process, and after curing, an insulating coating (i.e., a dense insulating layer) is formed. This blocks the corrosion path between the steel shell body and the electrolyte, reducing the risk of short circuits (i.e., leakage). Simultaneously, the insulating coating has strong adhesion to the inner surface of the steel shell body and is not easily peeled off under electrolyte immersion, greatly improving the safety performance of the high-capacity lithium battery. This preparation method uses mask positioning and local spraying, eliminating the need for secondary processing of the welding area, simplifying the process complexity, and making the preparation process more efficient. At the same time, it significantly improves the insulation performance and welding area strength of the high-capacity lithium battery steel shell structure, greatly enhancing the quality of the high-capacity lithium battery steel shell structure. This makes the high-capacity lithium battery steel shell structure suitable for use in high-energy-density power batteries, energy storage batteries, and other fields with stringent requirements for corrosion resistance and safety. This water-based composite slurry has low volatile organic compound content, no VOC emissions, complies with RoHS standards, and meets environmental protection requirements. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the high-capacity lithium battery in this invention.

[0013] Figure 2 This is a partial cross-sectional view of the steel shell body in this invention.

[0014] Figure 3 This is a schematic diagram of the steel shell body in this invention from a top view. Detailed Implementation

[0015] Example 1 Reference manual attached Figure 1 , Figure 2 and Figure 3A high-capacity lithium battery steel shell structure with a partial insulating coating includes a steel shell body 1 and an insulating coating covering its inner surface. The insulating coating includes a first insulating coating 2 covering the inner wall of the steel shell body 1 and a second insulating coating 3 seamlessly connected to the bottom edge of the first insulating coating 2 and covering the bottom surface of the inner wall of the steel shell body. The second insulating coating 3 has a ring-shaped structure, and a welded area 4 without an insulating coating is formed in the central region of the ring-shaped structure. The welded area 4 is circular, and its diameter is controlled between 8-10 mm (optimal diameter is 9 mm). The second insulating coating 3 and the first insulating coating 2 are integrally sprayed using a spraying process (such as high-pressure airless spraying equipment, such as an inner wall spraying machine, which is an industrial spraying tool that pressurizes the slurry to a pressure of 0.3-0.5 MPa using a high-pressure pump, and then atomizes it through a nozzle to form a dense coating (i.e., the insulating coating)). The thickness of the second insulating coating 3 and the first insulating coating 2 is controlled between 10-20 μm (optimal thickness is 15 μm). The volume resistivity of the insulating coating is required to be ≥10¹² Ω·cm, and the leakage current is required to be ≤1μA (1000V DC). The inner wall spraying machine is a common industrial spraying tool, therefore, its internal structure and working principle will not be described in detail again.

[0016] Reference manual attached Figure 1 , Figure 2 and Figure 3 A water-based composite slurry composed of acrylic resin, nano-alumina, silane coupling agent, and deionized water is used to form the insulating coating (i.e., dense insulating layer) after being sprayed onto the inner surface of the steel shell body 1 and cured. The water-based composite slurry is prepared according to the following parts by weight: 55 parts acrylic resin, 25 parts nano-alumina, 5 parts silane coupling agent, and a small amount of deionized water (e.g., 12 parts by weight). The acrylic resin serves as the matrix material, providing adhesion and film-forming properties. The nano-alumina, as a reinforcing filler, enhances the material's hardness, wear resistance, and thermal stability. The silane coupling agent improves the interfacial bonding between the nano-alumina and the acrylic resin, thereby enhancing the overall performance of the composite material. Specifically, the silane coupling agent is an epoxy-based silane coupling agent (such as 3-(2,3-epoxypropoxy)propyltrimethoxysilane). The selection of epoxy-based silane coupling agents allows them to react with the hydroxyl groups on the surface of the nano-alumina and chemically bond with the resin matrix, significantly improving interfacial strength. Deionized water may be used as a solvent or dispersion medium in this formulation.

[0017] In addition, the water-based composite slurry is prepared according to the following component parts by weight, including 1-3 parts of zinc phosphate (preferably 2 parts by weight). The water-based composite slurry adds zinc phosphate as a corrosion inhibitor to suppress localized corrosion of the steel shell body 1 and enhance the corrosion resistance of the inner surface of the steel shell body 1.

[0018] Reference manual attached Figure 1 , Figure 2 and Figure 3 A method for preparing a high-capacity lithium battery steel shell structure with a local insulating coating includes the following steps: 1) Preparation of an aqueous composite slurry: raw materials are prepared according to the following components by weight: 55 parts acrylic resin, 25 parts nano-alumina, 5 parts silane coupling agent, and 12 parts deionized water; then, the nano-alumina and silane coupling agent are placed in a high-speed disperser for dispersion and mixing to ensure uniform particle dispersion. The speed of the high-speed disperser is controlled at 1200-1500 r / min, and the dispersion time is controlled at 28-35 minutes; then, acrylic resin and deionized water are added, and dispersion continues until the viscosity of the slurry system stabilizes to obtain the aqueous composite slurry; the viscosity of the aqueous composite slurry is controlled at 2500-3000 mPa·s. Using a uniquely formulated water-based composite slurry as the insulating coating material, the corrosion path between the steel shell and the electrolyte is blocked, reducing the risk of short circuits (i.e., leakage). Simultaneously, the resulting insulating coating exhibits strong adhesion to the inner surface of the steel shell and is not easily peeled off even when immersed in the electrolyte, significantly improving the safety performance of high-capacity lithium batteries. This water-based composite slurry itself has low volatile organic compound content, no VOC emissions, and complies with RoHS standards.

[0019] In addition, the pH of this water-based composite slurry can be adjusted to 7.5-8.3, and a defoamer can be added for static defoaming treatment. Then, it is filtered through a 200-mesh filter to remove impurities, further improving the uniformity of the water-based composite slurry. The amount of defoamer added is controlled at 0.1%-0.2% of the total weight of the slurry; the defoamer is a polysiloxane-based defoamer, whose core component is a polysiloxane compound, which can effectively reduce the surface tension of the slurry and quickly eliminate foam.

[0020] 2) Steel Shell Pretreatment: The inner surface of the steel shell body undergoes roughening, alkaline washing, and phosphoric acid passivation treatment to achieve an inner surface roughness Ra of 0.8-1.2 μm. Specifically, firstly, laser roughening treatment: a high-energy pulsed laser is used to irradiate the inner surface of the steel shell body, forming a micron-level rough structure on its inner surface, achieving an inner surface roughness Ra value of 0.8-1.2 μm; secondly, alkaline washing treatment: a 5% sodium hydroxide solution is used to perform alkaline washing treatment on the steel shell body at a temperature of 60°C to remove oil, rust, and impurities, ensuring surface cleanliness; finally, phosphoric acid passivation treatment: the steel shell body is immersed in a phosphate solution (such as a 5%-15% phosphoric acid solution) and reacted at room temperature to medium temperature (50-75°C) for 3-10 minutes to form a dense phosphate film. This dense phosphate film enhances the bonding force with the water-based composite slurry and provides a basis for the precise positioning of the subsequent mask.

[0021] 3) Mask positioning: A mask with a diameter of 8-10 mm is adsorbed and fixed in the center area of ​​the bottom surface of the steel shell body (i.e., the welding area) using a vacuum adsorption fixture. The positioning accuracy of the mask is controlled within ±0.1 mm; the mask is a high-temperature resistant polyimide mask, and its optimal diameter is 9 mm. The high-temperature resistant polyimide mask is a circular mask made of polyimide (PI) material.

[0022] 4) Local spraying: The inner surface of the steel shell is sprayed with a water-based composite slurry. After spraying, the inner surface is cured using a stepped hot air curing method to ensure that a stable and firm insulating coating (i.e., a dense insulating layer) is formed on the inner surface of the steel shell. The thickness of the insulating coating is controlled at 10-20μm (the optimal thickness is 15μm), and the thickness deviation is controlled within ±2μm. Specifically, firstly, using high-pressure airless spraying equipment (such as an internal wall spraying machine), the coating (i.e., water-based composite slurry) is pressurized to about 0.3-0.5 MPa by a high-pressure pump and atomized through nozzles to spray the inner surface of the steel shell body rotating at 200-300 rpm. Secondly, after the spraying is completed, the inner surface of the steel shell body is cured using a stepped hot air curing method, with the curing time controlled at 30 minutes. This stepped hot air curing method is as follows: first, 70℃ hot air is used for curing for 10 minutes, and then the temperature is increased to 90℃ for another 20 minutes of curing. Finally, the mask on the inner bottom surface of the steel shell body is removed to expose the welding area on its inner bottom surface, thereby ensuring good conductivity and connection reliability of the welding area, resulting in a high-capacity lithium battery steel shell structure. This preparation method uses mask positioning and local spraying, eliminating the need for secondary processing of the welding area. This simplifies the process and makes the preparation process more efficient. At the same time, it significantly improves the insulation performance and welding area strength of the high-capacity lithium battery steel shell structure, greatly enhancing the quality of the high-capacity lithium battery steel shell structure. This makes the high-capacity lithium battery steel shell structure suitable for use in fields with stringent requirements for corrosion resistance and safety, such as high-energy-density power batteries and energy storage batteries.

[0023] 5) Test verification: The steel shell structure of the high-capacity lithium battery is successively subjected to leakage current, welding resistance, and salt spray treatments for testing operations. All the testing operations are passed, and a qualified steel shell structure of the high-capacity lithium battery is obtained. The leakage current test value of the qualified steel shell structure of the high-capacity lithium battery is ≤0.8 μA, the contact resistance of the welding area is ≤0.1 mΩ, and there is no corrosion expansion phenomenon in the insulating coating. The steel shell structure of the high-capacity lithium battery is the steel shell structure of the 21700 lithium battery, which is the core component of the 21700-type lithium battery. The leakage current treatment: Apply a 1000V DC voltage on the surface of the insulating coating inside the steel shell body for 60 seconds. It is required that the leakage current ≤1 μA is considered qualified. The temperature of the test environment is controlled at 24°C - 26°C, and the humidity is controlled at 48% - 52%. The leakage current test value of the steel shell structure product of the high-capacity lithium battery is ≤0.8 μA. The welding resistance treatment: Test the welding area 4 on the inner bottom surface of the steel shell body 1 with a laser welding shear force of ≥50 N. There is no peeling at the edge of the second insulating coating 3, and the mechanical properties are strong; then use a micro-resistance tester to measure the welding area 4, and the contact resistance of the welding area 4 is ≤0.1 mΩ, and the electrical properties are good. The salt spray treatment: After placing the steel shell body 1 in a 5% NaCl salt spray environment for 96 hours of testing, there is no corrosion expansion phenomenon in the insulating coating (i.e., the first insulating coating 2 and the second insulating coating 3).

[0024] Example 2 The implementation mode of this example and Example 1 is basically the same, the difference is that: the water-based composite slurry is prepared from the following raw materials in parts by weight, and it includes 40 parts of acrylic resin, 30 parts of nano-aluminum oxide, 4 parts of silane coupling agent, and a small amount of deionized water (such as 15 parts in parts by weight). The silane coupling agent is an epoxy-based silane coupling agent (such as 3-(2,3-epoxypropoxy)propyltrimethoxysilane).

[0025] In addition, the water-based composite slurry is prepared from the following raw materials in parts by weight, and it also includes 4 - 6 parts (the best is 5 parts in parts by weight) of glycidyl methacrylate. The design of adding glycidyl methacrylate can enhance the intermolecular force of the material, and at the same time form a network structure through thermal curing, greatly improving the solvent resistance and mechanical strength of the insulating coating (i.e., the dense insulating layer), such as significantly improving mechanical properties such as tensile strength and impact resistance.

[0026] Example 3 The implementation mode of this example and Example 1 is basically the same, the difference is that: the water-based composite slurry is prepared from the following raw materials in parts by weight, and it includes 60 parts of acrylic resin, 20 parts of nano-aluminum oxide, 6 parts of silane coupling agent (such as epoxy-based silane coupling agent), and 10 parts of deionized water.

[0027] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A high-capacity lithium battery steel shell structure with a partially insulating coating, characterized in that, The device includes a steel shell body and its inner surface covered with an insulating coating. The insulating coating includes a first insulating coating covering the inner sidewall of the steel shell body and a second insulating coating seamlessly connected to the bottom edge of the first insulating coating and covering the bottom surface of the inner surface of the steel shell body. The second insulating coating has a ring structure, and the central area of ​​the ring structure forms a welded area without an insulating coating. The second insulating coating and the first insulating coating are integrally sprayed by a spraying process, and the thickness of the second insulating coating and the first insulating coating is controlled at 10-20μm. The welded area is circular, and its diameter is controlled at 8-10mm.

2. The high-capacity lithium battery steel shell structure with a partially insulating coating as described in claim 1, characterized in that: An aqueous composite slurry composed of acrylic resin, nano-alumina, silane coupling agent and deionized water is used to form an insulating coating by spraying the aqueous composite slurry onto the inner surface of a steel shell through a spraying process and curing it. A high-capacity lithium battery steel shell structure with a partial insulating coating as described in claim 2, characterized in that: the aqueous composite slurry is prepared from the following components in parts by weight, comprising 40-60 parts of acrylic resin, 20-30 parts of nano-alumina, 4-6 parts of silane coupling agent and a small amount of deionized water.

3. A high-capacity lithium battery steel shell structure with a partially insulating coating as described in claim 3, characterized in that: The water-based composite slurry is prepared from the component raw materials according to the parts by weight, and it also includes 1-3 parts of zinc phosphate.

4. A method for preparing a high-capacity lithium battery steel shell structure with a locally insulating coating, characterized in that, It includes the following steps: 1) Preparation of water-based composite slurry: Prepare raw materials according to the following components by weight: 40-60 parts acrylic resin, 20-30 parts nano-alumina, 4-6 parts silane coupling agent, and 10-15 parts deionized water; 2) Mask positioning: Use a vacuum adsorption fixture to adsorb and fix a mask with a diameter of 8-10 mm onto the central area of ​​the inner bottom surface of the steel shell body. This central area is the welding area. The positioning accuracy of the mask is controlled within ±0.1 mm; 3) Local spraying: Spray the water-based composite slurry onto the inner surface of the steel shell body using a spraying process. After spraying, cure the inner surface with hot air to ensure that a stable and firm insulating coating is formed on the inner surface of the steel shell body. The thickness of the insulating coating is controlled within 10-20 μm, and its thickness deviation is controlled within ±2 μm; Finally, remove the mask from the inner bottom surface of the steel shell body to expose the welding area on the inner bottom surface, thus obtaining a high-capacity lithium battery steel shell structure.

5. The method for preparing a high-capacity lithium battery steel shell structure with a locally insulating coating as described in claim 5, characterized in that: It also includes the following steps: 4) Testing and verification: The high-capacity lithium battery steel shell structure is subjected to leakage current, welding resistance and salt spray treatment in sequence. All tests are passed to obtain a qualified high-capacity lithium battery steel shell structure. The leakage current test value of the qualified high-capacity lithium battery steel shell structure is ≤0.8μA, the contact resistance of the welding area is ≤0.1mΩ and there is no corrosion expansion of the insulation coating.

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