An easy-peel, high-temperature resistant protective film that can be used to prevent the single-sided electrode of a battery from curling.

Abstract

This invention provides an easily peelable, high-temperature resistant protective film for preventing curling of single-sided battery electrodes. The protective film comprises an acrylate adhesive layer and a base film layer sequentially laminated together. The thickness of the acrylate adhesive layer is 20–40 μm, and the thickness of the base film layer is 30–80 μm. The acrylate adhesive layer is obtained by thermosetting a second acrylate adhesive. The raw materials of the second acrylate adhesive include a first acrylate adhesive, and the raw materials of the first acrylate adhesive include functional monomers. The functional monomers include at least one of fluorocarbon monomers, hydroxyl monomers, carboxyl monomers, and amide monomers. The protective film of this invention possesses excellent properties such as high-temperature resistance and easy peeling, effectively improving the curling situation of single-sided electrodes.

Description

Technical Field

[0001] This invention belongs to the field of battery single-sided electrode protective film technology, specifically relating to an easy-to-peel, high-temperature resistant protective film that can be used to prevent battery single-sided electrode from curling. Background Technology

[0002] Battery electrode materials consist of two main parts: a slurry and a current collector. The slurry primarily comprises active materials, conductive agents, adhesives, and solvents. Current collectors are mainly classified into metallic copper foil and metallic aluminum foil substrates. To reduce the thickness of the aluminum or copper foil substrate and improve the volumetric and gravimetric energy densities of batteries, the structure of battery electrode materials currently used in the market is typically designed with a single-sided coating. The thickness of the metallic aluminum and copper foil substrates used for the positive and negative electrodes is less than 25 μm. However, as the thickness of the aluminum and copper foil substrates decreases, the active material in the electrode slurry, due to its ductility, is prone to curling and burr formation at the edges during the rolling process of single-sided coated electrodes. This is detrimental to die-cutting and stacking processes, significantly reducing production efficiency. Therefore, a protective film needs to be applied during the manufacturing process of single-sided electrodes to improve the problems of edge curling and burr formation.

[0003] Due to the specific limitations of the aforementioned application areas, higher requirements are placed on methods for preventing the curling of single-sided battery electrodes. In existing technology, patent document CN107134561A, entitled "Battery Electrode and Method for Preventing Battery Electrode Curling," mentions setting a polymer material layer on the inactive material surface of the single-sided electrode to enhance its strength and toughness, thereby offsetting or partially offsetting the stress caused by the active material after rolling, thus solving the problem of electrode curling caused by single-sided electrode rolling. However, the polymer material layer uses polyolefins, polyesters, or polyimides, which are expensive. Furthermore, this method involves complex electrode attachment processes, and problems such as the inability to peel off the polymer layer after coating the metal current collector, and the occupation of electrode thickness space, reduce the battery's volumetric energy density and gravimetric energy density. Therefore, it leads to increased production costs and reduced usable battery space, which is detrimental to large-scale production. The patent document CN109326796A, entitled "A Battery Electrode and a Method for Preventing Rolling," mentions that an enhanced hot melt adhesive is applied to the inactive material surface of the current collector. After curing, the adhesive has a certain strength, thereby preventing rolling caused by stress release of the electrode. However, this polymer material is expensive and has limited temperature resistance. After coating the metal current collector with the polymer layer, it passes through a high-temperature oven. When the coating roller temperature rises to 110°C, the hot melt adhesive is prone to creep, leading to sticking to the roller. This can also cause problems such as the inability to peel off the polymer layer after coating the metal current collector and the occupation of electrode thickness space, resulting in increased production costs and reduced usable battery space, which is not conducive to large-scale production.

[0004] Existing protective films are attached to aluminum or copper foil metal substrates. As the attachment time increases, the wetting performance becomes unstable, making them difficult to peel off. When peeling, the other side of the battery electrode tends to curl up. In addition, the temperature resistance is generally poor, and after high-temperature curing of over-coating, creep will occur. After rolling the attached single-sided battery electrode, it is easy to stretch, resulting in problems such as displacement, edge overflow, and residual adhesive after peeling. Summary of the Invention

[0005] In order to address the problems and shortcomings of the existing technology, the present invention provides an easy-to-peel high-temperature resistant protective film that can be used to prevent single-sided electrode sheets from curling, thereby improving the problem of easy curling of electrode sheets during the rolling process.

[0006] This invention provides an easy-to-peel, high-temperature resistant protective film for preventing the curling of single-sided electrode sheets in batteries. The protective film comprises an acrylate adhesive layer and a base film layer sequentially laminated together. The thickness of the acrylate adhesive layer is 20–40 μm, and the thickness of the base film layer is 30–80 μm. The acrylate adhesive layer is obtained by thermosetting a second acrylate adhesive. The raw materials of the second acrylate adhesive include a first acrylate adhesive, and the raw materials of the first acrylate adhesive include functional monomers. The functional monomers include at least one of fluorocarbon monomers, hydroxyl monomers, carboxyl monomers, and amide monomers.

[0007] Existing technologies rarely involve using acrylic tape as a protective film for single-sided electrodes to improve the curling of single-sided electrodes. Generally speaking, acrylic tape has high adhesion, is easy to peel off and leaves adhesive residue, and after peeling, it tends to adhere to the active material layer of adjacent electrodes, causing problems such as back adhesion and falling off of active material.

[0008] First, the protective film for single-sided electrodes needs to have good high-temperature resistance. Generally speaking, the thinner the base film of the protective film, the higher the thermal shrinkage rate, which affects the protective effect of the protective film on the single-sided electrode. To reduce the thermal shrinkage rate of the base film, the thicker the base film, the better. However, to reduce the cost of the base film, the thinner the base film layer, the better. But the thinner the base film layer, the lower its toughness, tensile strength, and elongation strength. After the protective film is prepared in this way, it is difficult to prevent the curling phenomenon that easily occurs in the electrode during the rolling process. Moreover, the shrinkage rate of the base film layer is high after high-temperature baking, which easily causes deformation and leads to misalignment of the edge of the protective film tape attached to the electrode. Therefore, the thickness of the base film needs to be controlled within a suitable range. Furthermore, the thicker the adhesive layer, the less likely the single-sided electrode with the protective film is to curl. However, an adhesive layer with a thickness greater than 20μm is prone to serious adhesive overflow at the edge during the electrode rolling process. Therefore, in actual production, to prevent adhesive overflow, the base film layer is generally paired with an acrylic adhesive layer of less than 20μm. However, a thin acrylic adhesive layer often lacks sufficient adhesion, which is detrimental to the anti-winding ability of the battery's single-sided electrode. Therefore, it is necessary to control the thickness of the acrylic adhesive layer and the substrate layer within a certain range to maximize the improvement of the winding problem of the battery's single-sided electrode, while simultaneously ensuring a low thermal shrinkage rate of the substrate layer and reducing production costs.

[0009] This solution employs an acrylate adhesive layer with a thickness of 20–40 μm paired with a base film layer of 30–80 μm. This not only ensures the toughness, tensile strength, and elongation of the base film layer, allowing the protective film to largely offset the stress caused by the stretching of the active material after the electrode rolling process, thus maintaining the electrode in a state of mechanical balance and improving electrode curling, but also reduces misalignment between the protective film and the electrode, preventing adhesion to the rollers during the high-temperature curing process after electrode coating. Furthermore, the acrylate adhesive layer in this invention includes functional monomers with special functional groups, which further enhance the overall performance of the acrylate adhesive layer, improve the wettability and peel strength balance between the acrylate adhesive layer and the copper or aluminum foil, and make the adhesion between the acrylate adhesive layer and the copper or aluminum foil more stable over time, achieving easy peeling and improving problems such as adhesion to adjacent electrode active material layers and active material detachment after the protective film is peeled off. Furthermore, the addition of functional monomers further enhances the high-temperature resistance of the acrylate adhesive layer in this invention, making it less prone to overflow during the rolling process even when the acrylate adhesive layer is thicker.

[0010] Preferably, the functional monomers include fluorocarbon monomers. Fluorine atoms possess high electronegativity, small radius, and high oxidizing power, giving fluorocarbon chains extremely high surface activity, thermal stability, and excellent water and stain resistance. Therefore, acrylate adhesive layers prepared with fluorocarbon monomers can quickly achieve a good wetting balance with the surface of copper or aluminum foil substrates, controlling the peel force increase and balancing the wetting properties and peel force of the acrylate adhesive layer, thus giving the acrylate adhesive layer easy-to-peel properties.

[0011] Preferably, the functional monomers also include at least one of hydroxyl monomers, carboxyl monomers, and amide monomers. The functional groups of these functional monomers can enhance the affinity of the acrylate adhesive layer for the substrate and the binding force of its internal molecules. When used in combination with fluorocarbon monomers, the balance between the wetting properties and peel strength of the acrylate adhesive layer can be better controlled, resulting in easier peeling of the protective film after roll pressing.

[0012] Preferably, the functional monomers include fluorocarbon monomers and carboxyl monomers. By using both fluorocarbon monomers and carboxyl monomers, the protective film can simultaneously possess excellent high-temperature performance, prevent adhesive overflow and contamination of the electrode sheets during rolling, and leave no adhesive residue during peeling, making it a highly competitive anti-rolling protective film.

[0013] Preferably, the fluorocarbon monomers include trifluoroethyl methacrylate, the hydroxyl monomers include at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl methacrylate, the carboxyl monomers include methacrylic acid, and the amide monomers include methacrylamide.

[0014] Preferably, the thickness of the acrylate adhesive layer is 20–40 μm, and the thickness of the base film layer is 30–80 μm. A protective film meeting these characteristics can significantly reduce the curling height of the electrode sheet, effectively improving the curling problem of single-sided electrode sheets in the rolling process.

[0015] Preferably, the thickness of the acrylate adhesive layer is 30 μm, and the thickness of the base film layer is 50 μm. A protective film meeting these characteristics can effectively improve the curling problem of single-sided electrode sheets in batteries, reduce the thickness of the acrylate adhesive layer, improve the problem of adhesive overflow, and reduce production costs.

[0016] Preferably, the base film layer includes a PET base film and a POPP base film. PET base film refers to polyethylene terephthalate base film, and POPP refers to biaxially oriented polypropylene base film.

[0017] Preferably, the base film layer is a PET base film.

[0018] Preferably, one side of the base film layer is corona treated, with a corona value ≥ 50 dyne, and the corona-treated side of the base film layer is laminated with the acrylic adhesive layer. Corona treatment of the base film layer can improve the adhesion between the acrylic adhesive layer and the base film layer, enhancing their bonding effect.

[0019] Preferably, the second acrylate adhesive comprises, by weight, the following materials: 90-110 parts of the first acrylate adhesive, 0.1-5 parts of curing agent, 0.1-5 parts of nano-fumed silica, and 20-60 parts of the second organic solvent; the raw materials of the first acrylate adhesive include soft monomers, hard monomers, and functional monomers; the soft monomers include acrylate monomers, and the glass transition temperature of the soft monomers is -70 to -20°C; the glass transition temperature of the hard monomers is 10 to 100°C.

[0020] Soft monomers have a lower glass transition temperature, providing better toughness, adhesion, wettability, and high initial tack. Hard monomers have a higher glass transition temperature, which can improve the cohesiveness of the adhesive layer, making it easier to peel off and less prone to residue. Nano-fumed silica surface aggregates are aggregates containing multiple silanol groups, which readily form a uniform three-dimensional network structure in acrylate systems, enhancing the rigidity and hardness of the acrylate protective film. The three-dimensional network structure is also less prone to collapse at high temperatures, thus improving the high-temperature resistance of the protective film. Furthermore, because the nano-fumed silica is uniformly dispersed in the network structure, it effectively reduces adhesive overflow, ensuring that the protective film tape applied to the electrode sheet leaves no adhesive residue after baking at high temperatures and peeling off at room temperature. It also effectively prevents adhesive overflow during the electrode sheet application rolling process. Thus, even when the adhesive layer exceeds 20μm, there is no adhesive overflow problem, making it feasible for adhesive layers thicker than 20μm. In addition, adding a specific proportion of nano-sized fumed silica can interact with a specific proportion of curing agent to further enhance the overall performance of the acrylate adhesive layer.

[0021] Preferably, the curing agent is hexamethylene diisocyanate.

[0022] Preferably, the nano-fumed silica is surface-modified with a silane coupling agent selected from at least one of trimethylsiloxane, propyltriethoxysilane isocyanate, vinyltrimethoxysilane, and 3,4-epoxycyclohexylethyltrimethoxysilane.

[0023] Preferably, the silane coupling agent is 3,4-epoxycyclohexylethyltrimethoxysilane.

[0024] Preferably, the second organic solvent includes at least one selected from ethyl acetate, toluene, butyl acetate, and cyclohexane.

[0025] Preferably, the soft monomer includes at least one of ethyl acrylate, isooctyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; the hard monomer includes at least one of methyl methacrylate, methyl acrylate, acrylonitrile, styrene, vinyl acetate, and acrylamide.

[0026] Preferably, the first acrylate adhesive comprises the following raw materials in parts by weight: 40-50 parts soft monomer, 10-20 parts hard monomer, 1-2 parts functional monomer, 0.2-0.8 parts initiator, and 30-50 parts first organic solvent.

[0027] Preferably, the first organic solvent includes at least one selected from ethyl acetate, toluene, butyl acetate, and cyclohexane.

[0028] Preferably, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and tert-butyl peroxide.

[0029] Preferably, the method for preparing the above-mentioned first acrylate adhesive includes the following steps: S1. Mixing the functional monomer with 3-5 parts of a first organic solvent to form a first mixture; S2. Mixing the soft monomer and hard monomer with 21-35 parts of the first organic solvent to form a second mixture; S3. Under nitrogen protection, heating the second mixture to 78-80°C with stirring, then adding the first mixture, and continuing the reaction at this temperature for 1.5-3 hours to obtain an acrylate prepolymer; S4. Mixing the initiator and the remaining first organic solvent to form a third mixture, adding the third mixture to the acrylate prepolymer, adjusting the temperature of the reaction system to 75-77°C, and maintaining the reaction at this temperature for 3-5 hours to obtain the first acrylate adhesive. Using the above preparation method, the polymerization rate of the polymerizable monomers can be better controlled, avoiding rapid polymerization, resulting in a reaction product with a more uniform degree of polymerization and a more suitable molecular weight, so that the adhesive layer obtained after curing has a more suitable peel force, achieving a more easily peelable effect.

[0030] Preferably, in step S3, the first mixture is added to the second mixture by dripping for 15 to 60 minutes.

[0031] Preferably, in S4, the third mixture is added to the acrylate prepolymer by dripping for 15 to 60 minutes.

[0032] In steps S3 and S4 above, the dropwise addition method can control the polymerization rate, better avoid burst polymerization, achieve controllable reaction, and result in reaction products with appropriate molecular weight and narrower molecular weight distribution, thereby improving the quality of the reaction products.

[0033] Preferably, the method for preparing the second acrylate adhesive includes the following steps: Step 1, mixing nano-fumed silica with 2-6 parts of a second organic solvent to form a nano-fumed silica solution; Step 2, mixing the first acrylate adhesive with the remaining second organic solvent, then adding the nano-fumed silica solution and mixing until homogeneous, and then adding a curing agent to obtain the second acrylate adhesive. In the above method for preparing the second acrylate adhesive, the nano-fumed silica is first thoroughly mixed with a portion of the organic solvent, so that it is less likely to agglomerate when mixed with the first acrylate adhesive, thereby improving the dispersion of the nano-fumed silica in the acrylate adhesive system. This allows it to form a good three-dimensional network structure with the acrylate adhesive system, fully contacting the curing agent and working together to enhance the overall performance of the acrylate adhesive layer. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0035] Example 1

[0036] Preparation of the first acrylate adhesive:

[0037] Weigh each component according to the formulation of the first acrylic adhesive in Table 1, and then prepare the first acrylic adhesive of this embodiment according to the following steps:

[0038] S1. Mix the functional monomer with 4 parts of ethyl acetate to form a first mixture;

[0039] S2. Mix the soft monomer, hard monomer and 28 parts of ethyl acetate to form a second mixture;

[0040] S3. Under nitrogen protection, the second mixture is heated to 78-79°C while being stirred. Then, the first mixture is added dropwise over a period of 30 minutes. After the addition is complete, the reaction is continued at this temperature for 2 hours to obtain the acrylate prepolymer.

[0041] S4. Mix the initiator and the remaining ethyl acetate to form a third mixture. Add the third mixture dropwise to the acrylate prepolymer over a period of 30 minutes. After the addition is complete, adjust the temperature of the reaction system to 75-76°C and maintain the temperature for 4 hours. After the reaction is complete, cool the temperature to below 45°C and remove the nitrogen gas to obtain the first acrylate adhesive.

[0042] Table 1 Formulation for the preparation of the first acrylate adhesive in Example 1

[0043]

[0044] Example 2

[0045] Preparation of the first acrylate adhesive:

[0046] The difference between this embodiment and Embodiment 1 is that the quality of the functional unit used is different, but the rest is the same as in Embodiment 1.

[0047] Weigh each component according to the formulation of the first acrylate adhesive in Table 2, and then prepare the first acrylate adhesive of this embodiment according to the method in Example 1.

[0048] Table 2 Formulation for the preparation of the first acrylate adhesive in Example 2

[0049]

[0050]

[0051] Example 3

[0052] Preparation of the first acrylate adhesive:

[0053] The difference between this embodiment and Embodiment 1 is that the functional monomer used is different. The functional monomer used in this embodiment is methacrylic acid, while the rest is the same as in Embodiment 1.

[0054] The first acrylate adhesive of this embodiment was prepared according to the method in Example 1.

[0055] Example 4

[0056] Preparation of the first acrylate adhesive:

[0057] The difference between this embodiment and Embodiment 1 is that the functional monomer used is different. The functional monomer used in this embodiment is hydroxyethyl methacrylate, while the rest is the same as in Embodiment 1.

[0058] The first acrylate adhesive of this embodiment was prepared according to the method in Example 1.

[0059] Example 5

[0060] Preparation of the first acrylate adhesive:

[0061] The difference between this embodiment and Embodiment 1 is that the functional monomer used is different. The functional monomer used in this embodiment is acrylamide, while the rest is the same as in Embodiment 1.

[0062] The first acrylate adhesive of this embodiment was prepared according to the method in Example 1.

[0063] Example 6

[0064] Preparation of the first acrylate adhesive:

[0065] The difference between this embodiment and Embodiment 1 is that the functional monomers used are different. The functional monomers used in this embodiment are methacrylic acid and trifluoroethyl methacrylate, and the mass of methacrylic acid and trifluoroethyl methacrylate is 1 kg and 1 kg respectively. The rest is the same as in Embodiment 1.

[0066] The first acrylate adhesive of this embodiment was prepared according to the method in Example 1.

[0067] Example 7

[0068] Preparation of the first acrylate adhesive:

[0069] The difference between this embodiment and Embodiment 1 is that the functional monomers used are different. The functional monomers used in this embodiment are hydroxyethyl methacrylate and trifluoroethyl methacrylate, and the mass of methacrylic acid and trifluoroethyl methacrylate is 1 kg and 1 kg respectively. The rest is the same as in Embodiment 1.

[0070] The first acrylate adhesive of this embodiment was prepared according to the method in Example 1.

[0071] Example 8

[0072] Preparation of the first acrylate adhesive:

[0073] The difference between this embodiment and Example 1 is that the functional monomers used are different. The functional monomers used in this embodiment are acrylamide and trifluoroethyl methacrylate, and the mass of methacrylic acid and trifluoroethyl methacrylate is 1 kg and 1 kg respectively. The rest is the same as in Example 1.

[0074] The first acrylate adhesive of this embodiment was prepared according to the method in Example 1.

[0075] Comparative Example 1

[0076] Preparation of the first acrylate adhesive:

[0077] The difference between this comparative example and Example 1 is that a functional monomer is not used; otherwise, the steps are the same as in Example 1. The specific steps are as follows:

[0078] S1. Mix the soft monomer, hard monomer and 30 parts of ethyl acetate to form a first mixture;

[0079] S2. Under nitrogen protection, the first mixture is heated to 78-79°C with stirring, and the reaction is maintained at this temperature for 2 hours to obtain the acrylate prepolymer;

[0080] S3. Mix the initiator and the remaining ethyl acetate to form a second mixture. Add the second mixture dropwise to the acrylate prepolymer over a period of 30 minutes. After the addition is complete, adjust the temperature of the reaction system to 75-76°C and keep it at that temperature for 4 hours. After the reaction is complete, cool the temperature to below 45°C and remove the nitrogen gas to obtain the first acrylate adhesive.

[0081] Example 9

[0082] (1) Preparation of the second acrylate adhesive:

[0083] Weigh each component according to the formula of the second acrylate adhesive in Table 3, and then prepare the second acrylate adhesive of this embodiment according to the following steps:

[0084] Step 1: Mix nano-fumed silica and 4 parts of ethyl acetate to form a nano-fumed silica solution. The stirring speed during mixing is 500 r / min and the mixing time is 10 min.

[0085] Step 2: Mix the first acrylate adhesive prepared in Example 1 with the remaining ethyl acetate. After mixing evenly, add hexamethylene diisocyanate and continue mixing. After mixing evenly, filter through a 400-mesh filter to obtain the second acrylate adhesive. When mixing the first acrylate adhesive with the remaining ethyl acetate, the stirring speed is 500 r / min and the mixing time is 20 min. When mixing after adding hexamethylene diisocyanate, the stirring speed is 500 r / min and the mixing time is 20 min.

[0086] Table 3 Formulation for the preparation of the second acrylate adhesive in Example 9

[0087] Components Mass (kg) Example 1: First Acrylic Adhesive 100 Hexamethylene diisocyanate 0.4 Nano-fumed silica 0.2 Ethyl acetate 40 Total mass 140.6

[0088] (2) Preparation of protective film:

[0089] The second acrylate adhesive is coated onto the corona-exposed surface of a 50μm PET base film using a micro-grooved roller or doctor blade roller coating method. The coating thickness is controlled at 27–33μm, the coating speed at 20–60m / min, and the coating temperature at 70℃–110℃. After high-temperature curing, the second acrylate adhesive forms an acrylate adhesive layer on the base film. The product is then wound up using a direct coating and winding process, and further cured at 50–60℃ for 24–72 hours to obtain a protective film.

[0090] Example 10

[0091] (1) Preparation of the second acrylate adhesive:

[0092] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the first acrylate adhesive used is the first acrylate adhesive prepared in Example 2, while the rest is the same as in Example 9.

[0093] (2) Preparation of protective film:

[0094] The preparation of the protective film in this embodiment is the same as in Example 9.

[0095] Example 11

[0096] (1) Preparation of the second acrylate adhesive:

[0097] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the first acrylate adhesive used is the first acrylate adhesive prepared in Example 3, while the rest is the same as in Example 9.

[0098] (2) Preparation of protective film:

[0099] The preparation of the protective film in this embodiment is the same as in Example 9.

[0100] Example 12

[0101] (1) Preparation of the second acrylate adhesive:

[0102] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the first acrylate adhesive used is the first acrylate adhesive prepared in Example 4, while the rest is the same as in Example 9.

[0103] (2) Preparation of protective film:

[0104] The preparation of the protective film in this embodiment is the same as in Example 9.

[0105] Example 13

[0106] (1) Preparation of the second acrylate adhesive:

[0107] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the first acrylate adhesive used is the first acrylate adhesive prepared in Example 5, while the rest is the same as in Example 9.

[0108] (2) Preparation of protective film:

[0109] The preparation of the protective film in this embodiment is the same as in Example 9.

[0110] Example 14

[0111] (1) Preparation of the second acrylate adhesive:

[0112] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the first acrylate adhesive used is the first acrylate adhesive prepared in Example 6, while the rest is the same as in Example 9.

[0113] (2) Preparation of protective film:

[0114] The preparation of the protective film in this embodiment is the same as in Example 9.

[0115] Example 15

[0116] (1) Preparation of the second acrylate adhesive:

[0117] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the first acrylate adhesive used is the first acrylate adhesive prepared in Example 7, while the rest is the same as in Example 9.

[0118] (2) Preparation of protective film:

[0119] The preparation of the protective film in this embodiment is the same as in Example 9.

[0120] Example 16

[0121] (1) Preparation of the second acrylate adhesive:

[0122] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the first acrylate adhesive used is the first acrylate adhesive prepared in Example 7, while the rest is the same as in Example 9.

[0123] (2) Preparation of protective film:

[0124] The preparation of the protective film in this embodiment is the same as in Example 9.

[0125] Example 17

[0126] (1) Preparation of the second acrylate adhesive:

[0127] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that nano-fumed silica is not added; otherwise, it is the same as in Example 9. The specific steps are as follows:

[0128] The first acrylate adhesive prepared in Example 1 was mixed with ethyl acetate, and then hexamethylene diisocyanate was added to the resulting mixture. The mixture was continued to be mixed until homogeneous, and then filtered through a 400-mesh filter to obtain the second acrylate adhesive. The mixing speed of the first acrylate adhesive with ethyl acetate was 500 r / min and the mixing time was 20 min. The mixing speed of the first acrylate adhesive with ethyl acetate was 500 r / min and the mixing time was 20 min.

[0129] (2) Preparation of protective film:

[0130] The preparation of the protective film in this embodiment is the same as in Example 9.

[0131] Example 18

[0132] (1) Preparation of the second acrylate adhesive:

[0133] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 10 in that nano-fumed silica is not added; otherwise, it is the same as in Example 10. The specific steps are as follows:

[0134] The first acrylate adhesive prepared in Example 1 was mixed with ethyl acetate, and then hexamethylene diisocyanate was added to the resulting mixture. The mixture was continued to be mixed until homogeneous, and then filtered through a 400-mesh filter to obtain the second acrylate adhesive. The mixing speed of the first acrylate adhesive with ethyl acetate was 500 r / min and the mixing time was 20 min. The mixing speed of the first acrylate adhesive with ethyl acetate was 500 r / min and the mixing time was 20 min.

[0135] (2) Preparation of protective film:

[0136] The preparation of the protective film in this embodiment is the same as in Example 10.

[0137] Example 19

[0138] (1) Preparation of the second acrylate adhesive:

[0139] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the nano-fumed silica used is surface-modified with the silane coupling agent trimethylsiloxane, while the rest is the same as in Example 9.

[0140] The specific operation for surface modification of nano-fumed silica is as follows: Silane coupling agent and anhydrous ethanol are mixed to achieve a silane coupling agent concentration of 2%. Glacial acetic acid (AcOH) is added to adjust the pH to 5.5, and the mixture is ultrasonically dispersed for 10 minutes and stirred for later use. 100g of n-butanol is weighed and added to a beaker, followed by 5g of fumed silica. The mixture is stirred until the fumed silica is completely impregnated, and then ultrasonically dispersed for 15 minutes to prepare a fumed silica dispersion. The fumed silica dispersion is added to a round-bottom flask, placed in an oil bath, and heated with stirring. After the temperature reaches 70℃ and stabilizes at this temperature, the prepared silane coupling agent solution is slowly added dropwise (the mass ratio of fumed silica to silane coupling agent is 1:0.03), and the reaction is maintained at 70℃ for 60 minutes. After the reaction is complete, the mixture is centrifuged and washed, with anhydrous ethanol used to wash three times to remove unloaded silane coupling agent. The mixture is then dried in an oven at 70℃, ground, and sealed for later use.

[0141] (2) Preparation of protective film:

[0142] The preparation of the protective film in this embodiment is the same as in Example 9.

[0143] Example 20

[0144] (1) Preparation of the second acrylate adhesive:

[0145] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the nano-fumed silica used is surface-modified with the silane coupling agent isocyanate propyltriethoxysilane, while the rest is the same as in Example 9.

[0146] The specific operation for surface modification of nano-fumed silica is as follows: Silane coupling agent and anhydrous ethanol are mixed to achieve a silane coupling agent concentration of 2%. Glacial acetic acid (AcOH) is added to adjust the pH to 5.5, and the mixture is ultrasonically dispersed for 10 minutes and stirred for later use. 100g of n-butanol is weighed and added to a beaker, followed by 5g of fumed silica. The mixture is stirred until the fumed silica is completely impregnated, and then ultrasonically dispersed for 15 minutes to prepare a fumed silica dispersion. The fumed silica dispersion is added to a round-bottom flask, placed in an oil bath, and heated with stirring. After the temperature reaches 70℃ and stabilizes at this temperature, the prepared silane coupling agent solution is slowly added dropwise (the mass ratio of fumed silica to silane coupling agent is 1:0.03), and the reaction is maintained at 70℃ for 60 minutes. After the reaction is complete, the mixture is centrifuged and washed, with anhydrous ethanol used to wash three times to remove unloaded silane coupling agent. The mixture is then dried in an oven at 70℃, ground, and sealed for later use.

[0147] (2) Preparation of protective film:

[0148] The preparation of the protective film in this embodiment is the same as in Example 9.

[0149] Example 21

[0150] (1) Preparation of the second acrylate adhesive:

[0151] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the nano-fumed silica used is surface-modified with the silane coupling agent vinyltrimethoxysilane, while the rest is the same as in Example 9.

[0152] The specific operation for surface modification of nano-fumed silica is as follows: Silane coupling agent and anhydrous ethanol are mixed to achieve a silane coupling agent concentration of 2%. Glacial acetic acid (AcOH) is added to adjust the pH to 5.5, and the mixture is ultrasonically dispersed for 10 minutes and stirred for later use. 100g of n-butanol is weighed and added to a beaker, followed by 5g of fumed silica. The mixture is stirred until the fumed silica is completely impregnated, and then ultrasonically dispersed for 15 minutes to prepare a fumed silica dispersion. The fumed silica dispersion is added to a round-bottom flask, placed in an oil bath, and heated with stirring. After the temperature reaches 70℃ and stabilizes at this temperature, the prepared silane coupling agent solution is slowly added dropwise (the mass ratio of fumed silica to silane coupling agent is 1:0.03), and the reaction is maintained at 70℃ for 60 minutes. After the reaction is complete, the mixture is centrifuged and washed, with anhydrous ethanol used to wash three times to remove unloaded silane coupling agent. The mixture is then dried in an oven at 70℃, ground, and sealed for later use.

[0153] (2) Preparation of protective film:

[0154] The preparation of the protective film in this embodiment is the same as in Example 9.

[0155] Example 22

[0156] (1) Preparation of the second acrylate adhesive:

[0157] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the nano-fumed silica used is surface-modified with the silane coupling agent 3,4-epoxycyclohexylethyltrimethoxysilane, while the rest is the same as in Example 9.

[0158] The specific operation for surface modification of nano-fumed silica is as follows: Silane coupling agent and anhydrous ethanol are mixed to achieve a silane coupling agent concentration of 2%. Glacial acetic acid (AcOH) is added to adjust the pH to 5.5, and the mixture is ultrasonically dispersed for 10 minutes and stirred for later use. 100g of n-butanol is weighed and added to a beaker, followed by 5g of fumed silica. The mixture is stirred until the fumed silica is completely impregnated, and then ultrasonically dispersed for 15 minutes to prepare a fumed silica dispersion. The fumed silica dispersion is added to a round-bottom flask, placed in an oil bath, and heated with stirring. After the temperature reaches 70℃ and stabilizes at this temperature, the prepared silane coupling agent solution is slowly added dropwise (the mass ratio of fumed silica to silane coupling agent is 1:0.03), and the reaction is maintained at 70℃ for 60 minutes. After the reaction is complete, the mixture is centrifuged and washed, with anhydrous ethanol used to wash three times to remove unloaded silane coupling agent. The mixture is then dried in an oven at 70℃, ground, and sealed for later use.

[0159] (2) Preparation of protective film:

[0160] The preparation of the protective film in this embodiment is the same as in Example 9.

[0161] Comparative Example 2

[0162] (1) Preparation of the second acrylate adhesive:

[0163] The preparation of the second acrylate adhesive in this embodiment differs from that in Example 9 in that the first acrylate adhesive used is the first acrylate adhesive prepared in Comparative Example 1, while the rest is the same as in Example 9.

[0164] (2) Preparation of protective film:

[0165] The preparation of the protective film in this embodiment is the same as in Example 9.

[0166] Test Example 1

[0167] 1. Experimental Construction Method

[0168] The protective films in Examples 9-22 and Comparative Example 2 were tested for steel plate peel force, electrode peel force, high temperature resistance, and adhesive overflow performance. The specific test methods are as follows:

[0169] (1) Peel strength of steel plate: Cut a protective film sample with a width of 25mm and a length of 300mm. Use a 2kg rubber roller to roll the protective film back and forth 3 times at a speed of 10mm / s. After standing for 20min under the conditions of temperature of 23±2℃ and humidity of 60±10%, use a peel strength tester to pull it open at a speed of 300mm / min and take a displacement of 20-80mm. Repeat the test on three protective film samples and take the average value.

[0170] (2) Electrode peel force: Cut protective film samples with a width of 25 mm and a length of 300 mm and attach them to the electrode. After baking at 120℃ for 2 hours, place them at 23±2℃ for 4 hours. Then, use a peel force tester to pull them apart at a speed of 300 mm / min and take a displacement of 20-80 mm. Repeat the test on three protective film samples and take the average value.

[0171] (3) High temperature resistance (120℃×2h): Cut a protective film sample with a width of 50mm and a length of 100mm and attach it to the non-active material side of the battery electrode. After baking at 120℃ for 2h, place it at 23±2℃ for 4h and then remove the protective film sample to observe the residual adhesive.

[0172] (4) Degree of adhesive overflow: Cut a protective film sample with a width of 50 mm and a length of 100 mm, attach it to the battery electrode, bake it at a high temperature of 120℃ for 2 hours, and then place it at 23±2℃ for 4 hours. Observe the degree of adhesive overflow at the edge using a microscope at 50x magnification.

[0173] 2. Experimental Results

[0174] The results of tests on the protective films of Examples 9-22 and Comparative Example 2 regarding steel plate peel force, electrode peel force, high temperature resistance, and adhesive overflow performance are shown in Table 4.

[0175] Table 4 shows the test results of the protective film in Examples 9-22 and Comparative Example 2 for steel plate peel force, electrode peel force, high temperature resistance, and adhesive overflow performance.

[0176]

[0177]

[0178] In Examples 9-22 and Comparative Example 2, the base film layer thickness was 50 μm, and the acrylate adhesive layer thickness was approximately 30 μm. As shown in Table 4 above, the first acrylate adhesives in Examples 9-22 all contained functional monomers, resulting in protective films with lower peel strength and easier peeling. In contrast, the first acrylate adhesive in Comparative Example 2 did not contain functional monomers, resulting in protective films with higher peel strength and less ease of peeling. Comparing Examples 9-13, the functional monomers used in Examples 9 and 10 were fluorocarbon monomers, resulting in protective films with even lower peel strength, easier peeling, and no adhesive residue or overflow. Protective films using other functional monomers, such as carboxyl monomers, hydroxyl monomers, and amide monomers, showed slight adhesive residue or slight overflow. Furthermore, comparing Examples 1 and 14-16, Examples 14-16 used two functional monomers in combination, resulting in lower peel strength of the protective film, with only slight residue appearing in a few cases. However, Example 14 used carboxyl and fluorocarbon monomers, which had even lower peel strength and were easier to peel than Examples 1 and 15-16, indicating that the overall performance of the protective film was better when carboxyl and fluorocarbon monomers were used together. Comparing Examples 9 and 17, and Examples 10 and 18, Examples 17 and 18 did not contain nano-sized fumed silica, resulting in more severe residue and overflow in the protective film. The difference lies in the fact that nano-sized fumed silica can synergistically interact with the functional monomers to improve the stability of the internal network structure of the acrylate adhesive layer. Therefore, even a thicker acrylate adhesive layer can have good high-temperature resistance, and significant residue or overflow is less likely to occur under high-temperature or rolling conditions.It is worth noting that, under the combined action of fluorocarbon monomers, carboxyl monomers, and nano-sized fumed silica, the acrylate adhesive layer exhibits better structural stability, superior high-temperature resistance, easy peeling, and anti-rolling properties, without leaving residue or overflowing adhesive. The main reason for this technical effect is that the acrylate adhesive layer prepared with the participation of fluorocarbon monomers can quickly achieve a good wetting balance with the surface of the copper and aluminum foil substrates, controlling the peel force escalation and balancing the wetting performance and peel force of the acrylate adhesive layer, thus giving it easy peeling properties. Furthermore, the functional monomers, including one of hydroxyl, carboxyl, or amide monomers, can enhance the affinity of the acrylate adhesive layer for the substrate and the binding force of its internal molecules, thereby improving the adhesion of the acrylate adhesive layer. Furthermore, the functional monomers, including nano-sized fumed silica, enhance the affinity of the acrylate adhesive layer for the substrate and the binding force of its internal molecules, thereby improving the adhesion of the acrylate adhesive layer. The nano-fumed silica surface aggregates, containing multiple silanol groups, readily form a uniform three-dimensional network structure in the acrylate system, enhancing the rigidity and hardness of the acrylate protective film. This three-dimensional network structure is also less prone to collapse at high temperatures, thus improving the high-temperature resistance of the protective film. Moreover, because the nano-fumed silica is uniformly dispersed within the network structure, it effectively reduces adhesive overflow, ensuring that after the protective film tape is baked at high temperatures and then peeled off at room temperature, there is no adhesive residue on the electrode surface. It also effectively prevents adhesive overflow during the electrode application rolling process. Therefore, the combination of these three functional monomers gives the protective film excellent comprehensive properties, including high adhesion, low adhesive overflow, easy peeling, and high-temperature non-deformation, making it particularly suitable as a protective film for preventing curling of single-sided electrodes.

[0179] Further analysis of Examples 9 and 19-22 reveals that the protective films in Examples 9 and 19-22 all exhibit low peel strength, are easy to peel, and show no residue or overflow after 2 hours at 120°C. However, when further testing the high-temperature resistance of these protective films over longer periods, the protective film in Example 9 showed a small amount of overflow after 4 hours at 120°C, while the protective films in Examples 19-21 showed a small amount of residue and overflow after 6 hours at 120°C. In contrast, the protective film in Example 22 showed no residue or overflow after 6 hours at 120°C, demonstrating better high-temperature resistance. The reason for this difference may be that the surface modification of the nano-fumed silica with a silane coupling agent further improves the dispersibility of the nano-fumed silica in the adhesive, which is more conducive to enhancing the stability of the three-dimensional network structure formed with the acrylate system. This further improves the high-temperature resistance of the protective film, ensuring that it still has good anti-rolling properties at high temperatures.

[0180] Example 23

[0181] Referring to the preparation method of the protective film in Example 9, protective films with different acrylate adhesive layer thicknesses were prepared by adjusting conditions such as coating thickness and coating speed. In this example, the acrylate adhesive layer thickness and the base film layer were used as variables. The appropriate acrylate adhesive layer thickness and base film layer thickness were explored by measuring the corresponding electrode curling height. Table 5 below shows the specific variable changes and the corresponding electrode curling height.

[0182] In this embodiment, when measuring the height of the electrode curling, the metal current collector of the electrode used is 12μm and the active material thickness is 55-65μm.

[0183] Table 5. Electrode rolling conditions under different acrylate adhesive layer thicknesses and different base film layer thicknesses in Example 23.

[0184]

[0185]

[0186] In actual production, when the curling height is 3–10 mm, the electrode production yield is 85%; when the curling height is <3 mm, the electrode production yield is >99%. During the electrode pressing process, there is no glue overflow and no sticking to the rollers, thus not affecting production. Analysis of the data in Table 5 shows that when the base film thickness is not less than 40 μm, and the acrylate adhesive layer thickness is within the range of 20–40 μm, the resulting protective film can provide good protection for the electrode, and the curling height is <3 mm.

[0187] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A peelable, high-temperature resistant protective film for preventing curling of single-sided electrode sheets in batteries, characterized in that: The protective film comprises an acrylic adhesive layer and a base film layer sequentially laminated together; the thickness of the acrylic adhesive layer is 20–40 μm, and the thickness of the base film layer is 30–80 μm; The acrylate adhesive layer is obtained by heat curing a second acrylate adhesive. According to the weight parts, the second acrylate adhesive comprises the following materials: 90 to 110 parts of the first acrylate adhesive, 0.1 to 5 parts of curing agent, 0.1 to 5 parts of nano-fumed silica, and 20 to 60 parts of the second organic solvent; The raw materials of the first acrylic adhesive include soft monomers, hard monomers, and functional monomers; the soft monomers include acrylic monomers, and the glass transition temperature of the soft monomers is -70 to -20°C; the glass transition temperature of the hard monomers is 10 to 100°C. The functional monomer is trifluoroethyl methacrylate, or the functional monomer includes trifluoroethyl methacrylate and at least one of hydroxy monomers, carboxyl monomers, and amide monomers.

2. The easily peelable, high-temperature resistant protective film for preventing curling of single-sided electrode sheets in batteries as described in claim 1, characterized in that: The hydroxyl monomer includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl methacrylate; the carboxyl monomer includes methacrylic acid; and the amide monomer includes methacrylamide.

3. The easily peelable, high-temperature resistant protective film for preventing curling of single-sided electrode sheets in batteries as described in claim 1, characterized in that, The first acrylate adhesive comprises the following raw materials in parts by weight: 40-50 parts of the soft monomer, 10-20 parts of the hard monomer, 1-2 parts of the functional monomer, 0.2-0.8 parts of initiator, and 30-50 parts of the first organic solvent.

4. The easily peelable, high-temperature resistant protective film for preventing curling of single-sided electrode sheets in batteries as described in claim 1, characterized in that: The soft monomer includes at least one of ethyl acrylate, isooctyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; The hard monomer includes at least one of methyl methacrylate, methyl acrylate, acrylonitrile, styrene, vinyl acetate, and acrylamide.

5. The easily peelable, high-temperature resistant protective film for preventing curling of single-sided electrode sheets in batteries as described in claim 1, characterized in that: The nano-sized fumed silica is surface-modified with a silane coupling agent selected from at least one of trimethylsiloxane, propyltriethoxysilane isocyanate, vinyltrimethoxysilane, and 3,4-epoxycyclohexylethyltrimethoxysilane.

6. The easily peelable, high-temperature resistant protective film for preventing curling of single-sided electrode sheets in batteries as described in claim 3, characterized in that, The method for preparing the first acrylate adhesive includes the following steps: S1. Mix the functional monomer with 3 to 5 parts of the first organic solvent to form a first mixture; S2. Mix the soft monomer, the hard monomer, and 21-35 parts of the first organic solvent to form a second mixture; S3. Under nitrogen protection, the second mixture is heated to 78-80°C while being stirred, and then the first mixture is added to it. The reaction is continued for 1.5-3 hours to obtain the acrylate prepolymer. S4. Mix the initiator and the remaining first organic solvent to form a third mixture, add the third mixture to the acrylate prepolymer, adjust the temperature of the reaction system to 75-77°C, and keep the reaction at this temperature for 3-5 hours to obtain the first acrylate adhesive.

7. The easily peelable, high-temperature resistant protective film for preventing curling of single-sided electrode sheets in batteries as described in claim 1, characterized in that, The method for preparing the second acrylate adhesive includes the following steps: Step 1: Mix the nano-fumed silica with 2 to 6 parts of the second organic solvent to form a nano-fumed silica solution; Step two: Mix the first acrylate adhesive with the remaining second organic solvent, then add the nano-fumed silica solution and mix. After mixing evenly, continue to add the curing agent to obtain the second acrylate adhesive.

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