A sodium-ion battery cell inner insulation tape and a preparation method thereof

Abstract

The application discloses a sodium ion battery cell internal insulation adhesive tape and a preparation method thereof, and belongs to the technical field of battery materials and functional adhesive tapes. The sodium ion battery cell internal insulation adhesive tape comprises a substrate layer and a functional adhesive layer arranged on one side surface of the substrate layer. The substrate layer is a low-polarity or electrolyte-resistant low-swelling polymer film, and the thickness of the substrate layer is 10-50 micrometers. The functional adhesive layer comprises a rubber adhesive layer and a modified PMMA adhesive layer. The insulation adhesive tape provided by the application can still maintain a low swelling rate, a high peeling strength retention rate and a high insulation resistance after being soaked in a sodium ion battery electrolyte, and is suitable for internal insulation protection of a sodium ion battery cell.

Description

Technical Field

[0001] This invention belongs to the field of battery materials and functional tapes, and particularly relates to an insulating tape for sodium-ion battery cells and its preparation method. Background Technology

[0002] Sodium-ion batteries possess advantages such as abundant sodium resources, low raw material costs, good low-temperature performance, and suitability for large-scale energy storage applications, making them one of the important technological directions in the field of large-scale energy storage. In sodium-ion battery cells, the internal insulating tape is a key material ensuring the safe operation of the cell. It is typically used at the edges of the electrode sheets, the tab area, the winding end area, the edge area of ​​the stacked sheets, and other areas requiring insulation to isolate live components such as the electrode sheets and tabs, reducing the risk of internal short circuits within the cell.

[0003] However, the electrolytes used in sodium-ion batteries typically contain ether or ester solvent systems. The insulating tape inside the cell needs to simultaneously meet requirements such as electrolyte resistance, low swelling, high adhesion, and high insulation reliability during long-term immersion, high-temperature storage, and cyclic use. Existing insulating tapes for sodium-ion battery applications still have the following shortcomings.

[0004] One existing technology is an insulating tape composed of a conventional PET substrate and an acrylic adhesive layer. This type of tape typically uses a PET polyester film as the substrate, with a single acrylic pressure-sensitive adhesive layer coated on its surface. It offers advantages such as good substrate rigidity, good dimensional stability at room temperature, readily available raw materials, low cost, and compatibility with conventional coating processes. However, this type of tape has significant drawbacks in the sodium-ion battery electrolyte environment: the PET substrate has high polarity, and prolonged contact with ether- or ester-based sodium-ion battery electrolytes can easily cause swelling and deformation, leading to a decrease in the stability of the insulation layer structure; simultaneously, the traditional acrylic adhesive layer is prone to liquid absorption and swelling in the electrolyte, resulting in a significant decrease in adhesion after immersion, easily causing adhesive layer peeling, edge lifting, or detachment, thereby increasing the risk of internal short circuits within the battery cell. This approach struggles to simultaneously meet the requirements of long-term insulation reliability and battery cell cycle life.

[0005] Existing technology two involves insulating tapes made with highly swelling-resistant modified fluorine adhesives or special acrylate adhesives. This type of solution typically improves the electrolyte resistance of the adhesive layer by using a fluorine-modified substrate, highly solvent-resistant acrylate adhesives, or other special swelling-resistant adhesives, offering advantages such as minimal volume change after electrolyte immersion and good insulation stability. However, these swelling-resistant adhesives generally suffer from insufficient initial tack, leading to adhesion misalignment, warping, or edge curling during processes such as cell winding, lamination, and tab attachment, affecting production yield. Some special adhesives also require higher temperatures or longer curing times, making them difficult to directly integrate with existing cell production lines. Furthermore, these adhesives are costly, have insufficient adhesion to metal foils such as copper and aluminum foils, and may still experience interfacial delamination after prolonged immersion.

[0006] Existing technology three involves insulating tapes with a low-polarity or low-swelling substrate combined with a common rubber adhesive layer or an unmodified PMMA adhesive layer. Compared to PET / acrylate tapes, this type of solution improves the electrolyte resistance of the substrate, and the rubber adhesive layer can also provide a certain initial tack. However, because the PMMA has not undergone functional grafting modification such as carboxyl, hydroxyl, or epoxy groups, the interfacial bonding between it and the rubber adhesive layer and the corona-treated substrate is insufficient, making it prone to interlayer delamination after long-term immersion. Furthermore, if the rubber adhesive layer does not form a reasonable system of tackifiers, antioxidants, and crosslinking agents, its initial tack, holding power, cohesive strength, and electrolyte swelling resistance cannot simultaneously meet the requirements for use within the battery cell. This type of single or simple composite structure struggles to achieve a balance between initial tack, holding power, swelling resistance, and insulation reliability.

[0007] Therefore, there is an urgent need to develop an insulating tape suitable for use inside sodium-ion battery cells, which can simultaneously possess low swelling rate, high peel strength retention rate, good insulation performance, and processing performance compatible with existing coating, slitting, winding, and stacking processes under long-term immersion in sodium-ion battery electrolyte and high-temperature operating environments, thereby improving the safety and cycle reliability of sodium-ion battery cells. Summary of the Invention

[0008] This invention aims to solve the problems of swelling, adhesion attenuation, interface debonding, and decreased insulation performance of existing insulating tapes inside sodium-ion battery cells in sodium-ion battery electrolytes, and provides an insulating tape for sodium-ion battery cells and its preparation method.

[0009] To achieve the objectives of this invention, an insulating tape for a sodium-ion battery cell is provided, comprising a substrate layer and a functional adhesive layer disposed on one side of the substrate layer; the substrate layer is a low-polarity or electrolyte-resistant, low-swelling polymer film, and the thickness of the substrate layer is 10 μm to 50 μm; the functional adhesive layer comprises a rubber adhesive layer and a modified PMMA adhesive layer, the rubber adhesive layer comprising a rubber matrix, a tackifying resin, an antioxidant, and an isocyanate crosslinking agent, and the modified PMMA adhesive layer comprising grafted modified polymethyl methacrylate, wherein the grafted modified polymethyl methacrylate contains at least one grafted functional group selected from carboxyl, hydroxyl, and epoxy groups; the total dry film thickness of the functional adhesive layer is 5 μm to 20 μm.

[0010] The substrate layer is one of polypropylene film, biaxially oriented polypropylene film, polyimide film, polyethylene film, polyester film, and polyethylene naphthalate film; the thickness of the substrate layer is 20μm to 30μm; the surface of the substrate layer to be coated is subjected to single-sided atmospheric pressure corona treatment or atmospheric pressure plasma surface treatment.

[0011] The functional adhesive layer is a double-layer adhesive structure or a multi-layer adhesive structure. When the functional adhesive layer is a double-layer adhesive structure, the inner insulating tape has a structure of substrate layer-rubber adhesive layer-modified PMMA adhesive layer. When the functional adhesive layer is a multi-layer adhesive structure, the inner insulating tape has a structure of substrate layer-rubber adhesive layer-modified PMMA adhesive layer-rubber adhesive layer. The total dry film thickness of the functional adhesive layer is 8μm to 15μm, the dry film thickness of the rubber adhesive layer is 5μm to 10μm, and the dry film thickness of the modified PMMA adhesive layer is 2μm to 5μm.

[0012] The rubber matrix is ​​one of butyl rubber, natural rubber, or styrene-butadiene rubber; the tackifying resin is one of terpene resin, C5 petroleum resin, or C9 petroleum resin; the antioxidant is one of antioxidant 264, antioxidant RD, or antioxidant 4010NA; the isocyanate crosslinking agent is one of toluene diisocyanate trimer, diphenylmethane diisocyanate adduct, or isocyanate trimer; and the solvent is one of toluene / ethyl acetate (1:1), butanone, or butyl acetate.

[0013] The rubber matrix is ​​in the amount of 100 parts by weight, the amount of the tackifying resin is 20-40 parts by weight, the amount of the antioxidant is 1-3 parts by weight, and the amount of the isocyanate crosslinking agent is 2-5 parts by weight; the solvent is only used to adjust the viscosity and does not participate in the reaction, and the solid content is 25%-35%.

[0014] The modified PMMA adhesive layer comprises grafted modified PMMA, a curing agent, a leveling agent, and an organic solvent; based on 100 parts by weight of grafted modified PMMA, the amount of the curing agent is 4-5 parts by weight, the amount of the leveling agent is 0.3-0.8 parts by weight, and the organic solvent is used to adjust the solid content of the modified PMMA adhesive to 20%-30%; the leveling agent is a non-silicone acrylate leveling agent; the grafted modified PMMA is carboxyl-modified PMMA, hydroxyl-modified PMMA, or epoxy-modified PMMA, with a grafting rate of 3%-8% for carboxyl-modified PMMA, 2%-7% for hydroxyl-modified PMMA, and 2%-6% for epoxy-modified PMMA.

[0015] A method for preparing insulating tape inside a sodium-ion battery cell includes the following steps: S1. Perform single-sided atmospheric pressure corona treatment or atmospheric pressure plasma surface treatment on the surface of the substrate layer to be coated. S2. Mix the rubber matrix, tackifying resin, antioxidant, isocyanate crosslinking agent and organic solvent to obtain a rubber adhesive; S3. The rubber adhesive is applied to the surface of the treated substrate layer and dried to form a rubber adhesive layer. S4. Mix the grafted modified PMMA, curing agent, leveling agent and organic solvent to obtain the modified PMMA adhesive; S5. The modified PMMA adhesive is applied to the surface of the rubber adhesive layer, and after drying and curing, a modified PMMA adhesive layer is formed to obtain the insulating tape inside the sodium-ion battery cell.

[0016] The single-sided atmospheric pressure corona treatment is performed using a wide-width corona treatment machine, with the output power adjusted according to the width of the circuit from 3.0 kW / m to 5.0 kW / m, the processing speed from 30 m / min to 60 m / min, and the electrode gap from 1.5 mm to 2.0 mm. The solid content of the rubber adhesive is 25% to 35%, the wet film coating thickness is 15 μm to 30 μm, preferably 20 μm, and it is dried at 80°C for 2 min. The solid content of the modified PMMA adhesive is 20% to 30%, the wet film coating thickness is 10 μm to 20 μm, preferably 15 μm, and it is dried at 100°C for 3 min and cured at 120°C for 2 min.

[0017] The grafted modified PMMA is prepared according to the following method: PMMA resin is dissolved in an organic solvent to prepare a PMMA solution; an initiator is added to the PMMA solution, and a modified monomer is added dropwise at 65℃~90℃ to carry out a solution free radical grafting reaction to obtain a grafted modified PMMA solution; a curing agent and a leveling agent are added to the grafted modified PMMA solution to obtain a modified PMMA adhesive; wherein, the modified monomer is one of methacrylic acid, acrylic acid, maleic anhydride, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, glycidyl methacrylate, or glycidyl acrylate.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: First, this invention uses a low-polarity or electrolyte-resistant, low-swelling polymer film as the substrate layer, and sets a rubber adhesive layer and a modified PMMA adhesive layer on the surface of the substrate layer. Through the synergistic effect between the substrate layer, the rubber adhesive layer, and the modified PMMA adhesive layer, the liquid absorption swelling and dimensional changes of the insulating tape in the sodium-ion battery electrolyte can be reduced. In particular, the modified PMMA adhesive layer can regulate electrolyte penetration and adhesive layer swelling, so that the insulating tape maintains a low swelling rate after being immersed in sodium-ion battery electrolyte at 60°C for 7 days, avoiding insulation structure failure due to substrate deformation, adhesive layer swelling, or interlayer peeling.

[0019] Secondly, the rubber adhesive layer in this invention uses butyl rubber, natural rubber, or styrene-butadiene rubber as the bonding body, and is formulated with tackifying resin, antioxidant, and isocyanate crosslinking agent. The tackifying resin improves the initial tack and peel strength of the adhesive layer to materials such as BOPP, PI, copper foil, and aluminum foil; the antioxidant inhibits the aging degradation of the adhesive layer under high temperature and electrolyte conditions; and the isocyanate crosslinking agent improves the cohesive strength and resistance to electrolyte swelling of the adhesive layer. Therefore, the insulating tape of this invention can maintain a high 180° peel strength retention rate of copper foil or aluminum foil after immersion in electrolyte, effectively reducing the risk of edge curling, detachment, or peeling failure of the tape inside the battery cell.

[0020] Third, this invention uses carboxyl-modified PMMA, hydroxyl-modified PMMA, or epoxy-modified PMMA as the functional adhesive layer material. By introducing functional groups such as carboxyl, hydroxyl, or epoxy groups into the PMMA molecular chain, the interfacial bonding strength between the PMMA adhesive layer and the rubber adhesive layer, as well as the surface of the substrate after corona treatment, can be improved. Among them, carboxyl-modified PMMA can balance interfacial bonding strength, electrolyte resistance, and cost, making it a suitable general preferred solution; hydroxyl-modified PMMA can improve the toughness and bending resistance of the adhesive layer, making it suitable for wound battery cells; epoxy-modified PMMA can improve the crosslinking stability and swelling resistance of the adhesive layer, making it suitable for high-temperature energy storage sodium-ion battery applications.

[0021] Fourth, by controlling the thickness ratio of the rubber adhesive layer and the modified PMMA adhesive layer, the present invention enables the rubber adhesive layer to provide sufficient initial tack, holding power and metal foil adhesion, while the modified PMMA adhesive layer provides electrolyte resistance, low swelling and interface strengthening, thereby achieving a balance between adhesive performance, swelling resistance, insulation reliability and internal space occupation of the battery cell.

[0022] Fifth, the insulating tape of the present invention can be prepared using existing industrial coating equipment, such as comma knife coating, micro-gravure coating or slot coating, and is compatible with existing battery cell winding, stacking, slitting and attaching processes. It does not require large-scale modification of existing battery cell production lines and has good adaptability to large-scale production.

[0023] Sixth, the insulating tape of the present invention has synergistic advantages in terms of low swelling, high adhesion retention rate and high insulation resistance, which can improve the long-term integrity of the internal insulation layer of sodium-ion battery cells, reduce the risk of internal short circuit caused by tape swelling, debonding, edge lifting or insulation attenuation, thereby improving the safety performance and cycle reliability of sodium-ion batteries. Detailed Implementation

[0024] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In some embodiments, the present invention provides an insulating tape for a sodium-ion battery cell, comprising a substrate layer and a functional adhesive layer disposed on one side surface of the substrate layer; the substrate layer is a low-polarity or electrolyte-resistant, low-swelling polymer film, and the thickness of the substrate layer is 10 μm to 50 μm; the rubber matrix serves as the adhesive host, providing initial tack, holding power, and basic adhesive performance, and forming a good interfacial bond with the low-polarity or electrolyte-resistant, low-swelling substrate layer. The rubber matrix can be one of butyl rubber, natural rubber, or styrene-butadiene rubber, preferably using a single rubber system to reduce the impact of compatibility differences between different rubber components on the uniformity of the adhesive layer, coating stability, and electrolyte resistance.

[0026] The functional adhesive layer comprises a rubber adhesive layer and a modified PMMA adhesive layer. The rubber adhesive layer comprises a rubber matrix, a tackifying resin, an antioxidant, and an isocyanate crosslinking agent. The modified PMMA adhesive layer comprises graft-modified polymethyl methacrylate, which contains at least one grafted functional group selected from carboxyl, hydroxyl, and epoxy groups. The total dry film thickness of the functional adhesive layer is 5 μm to 20 μm, preferably 8 μm to 15 μm. The dry film thickness of the rubber adhesive layer is 5 μm to 10 μm, and the dry film thickness of the modified PMMA adhesive layer is 2 μm to 5 μm.

[0027] In a preferred embodiment, the dry film thickness of the rubber adhesive layer is approximately 7.5 μm, the dry film thickness of the modified PMMA adhesive layer is approximately 3.5 μm, and the total dry film thickness of the functional adhesive layers is approximately 11 μm. This thickness combination enables the rubber adhesive layer to provide sufficient adhesive performance, while the modified PMMA adhesive layer provides electrolyte resistance, low swelling, and interfacial reinforcement.

[0028] In another preferred embodiment, the rubber adhesive has a wet film thickness of 20 μm and a solid content of 30%, and after drying at 80°C for 2 min, it forms a rubber adhesive layer with a theoretical dry film thickness of 6 μm; the modified PMMA adhesive has a wet film thickness of 15 μm and a solid content of 25%, and after drying at 100°C for 3 min to remove the solvent and curing at 120°C for 2 min, it forms a modified PMMA adhesive layer with a theoretical dry film thickness of 3.75 μm; the total theoretical dry film thickness of the functional adhesive layer is 9.75 μm.

[0029] In some embodiments, the substrate layer is one of polypropylene film, biaxially oriented polypropylene film, polyimide film, polyethylene film, polyester film, and polyethylene naphthalate film; the thickness of the substrate layer is 20 μm to 30 μm; the surface of the substrate layer to be coated is subjected to single-sided atmospheric pressure corona treatment or atmospheric pressure plasma surface treatment, and the surface tension is stably reached above 42 mN / m.

[0030] In some embodiments, the functional adhesive layer is a double-layer adhesive structure or a multi-layer adhesive structure. When the functional adhesive layer is a double-layer adhesive structure, the inner insulating tape has a structure of substrate layer-rubber adhesive layer-modified PMMA adhesive layer. When the functional adhesive layer is a multi-layer adhesive structure, the inner insulating tape has a structure of substrate layer-rubber adhesive layer-modified PMMA adhesive layer-rubber adhesive layer. The total dry film thickness of the functional adhesive layer is 8 μm to 15 μm, the dry film thickness of the rubber adhesive layer is 5 μm to 10 μm, and the dry film thickness of the modified PMMA adhesive layer is 2 μm to 5 μm. Preferably, the total dry film thickness of the functional adhesive layer is approximately 11 μm, the dry film thickness of the rubber adhesive layer is approximately 7.5 μm, and the dry film thickness of the modified PMMA adhesive layer is approximately 3.5 μm.

[0031] In some embodiments, the rubber matrix is ​​one of butyl rubber, natural rubber, or styrene-butadiene rubber, preferably a single rubber system, to reduce the impact of compatibility differences between different rubber components on the uniformity of the adhesive layer, coating stability, and electrolyte resistance. The tackifying resin is one of terpene resin, C5 petroleum resin, or C9 petroleum resin. The tackifier is used to improve the adhesion of the rubber adhesive layer to the substrate layer and the copper foil or aluminum foil of the battery cell. When the amount of tackifier is too low, the adhesion of the adhesive layer to the copper foil or aluminum foil is insufficient; when the amount of tackifier is too high, the hardness of the adhesive layer increases, the flexibility decreases, and it is easy to lead to a decrease in initial tack and poor adhesion adaptability. The antioxidant is one of antioxidant 264, antioxidant RD, or antioxidant 4010NA. The antioxidant 264 is chemically named 2,6-di-tert-butyl-p-cresol, also known as BHT. The antioxidant 264 is preferably an industrial-grade single pure product with a purity of not less than 99%. Antioxidant 264 can inhibit the oxidative aging of the rubber adhesive layer under heat, oxygen, and electrolyte environments, maintaining adhesive stability. The isocyanate crosslinking agent is one of toluene diisocyanate trimer, diphenylmethane diisocyanate adduct, or isocyanate trimer. Preferably, the isocyanate crosslinking agent is toluene diisocyanate trimer, which has good compatibility with butyl rubber systems and terpene resins, moderate curing activity, and can improve the cohesive strength, electrolyte immersion resistance, and anti-swelling properties of the rubber adhesive layer. The solvent is one of toluene / ethyl acetate (1:1), butanone, or butyl acetate. Preferably, the organic solvent is a mixed solvent composed of toluene and ethyl acetate in a volume ratio of 1:1. The solid content of the rubber adhesive is controlled at 25%–35%, preferably 30%.

[0032] In some embodiments, the rubber matrix is ​​100 parts by weight, the amount of the tackifying resin is 20-40 parts by weight, preferably 30 parts by weight; the amount of the antioxidant is 1-3 parts by weight, preferably 2 parts by weight; the amount of the isocyanate crosslinking agent is 2-5 parts by weight; the solvent only adjusts the viscosity and does not participate in the reaction, and the solid content is 25%-35%.

[0033] In one specific embodiment, the rubber adhesive layer comprises 100 parts by weight of butyl rubber, 30 parts by weight of terpene resin, 2 parts by weight of antioxidant 264, and 3 parts by weight of toluene diisocyanate trimer; the antioxidant 264 is 2,6-di-tert-butyl-p-cresol with a purity of not less than 99%; the rubber adhesive layer is formed by coating and drying a rubber adhesive with a solid content of 30%, and the solvent of the rubber adhesive is a mixed solvent composed of toluene and ethyl acetate in a volume ratio of 1:1.

[0034] In some embodiments, the modified PMMA adhesive layer comprises grafted modified PMMA, a curing agent, a leveling agent, and an organic solvent; based on 100 parts by weight of grafted modified PMMA, the amount of the curing agent is 4-5 parts by weight, the amount of the leveling agent is 0.3-0.8 parts by weight, and the organic solvent is used to adjust the solid content of the modified PMMA adhesive to 20%-30%; the leveling agent is a non-silicone acrylate leveling agent; the grafted modified PMMA is carboxyl-modified PMMA, hydroxyl-modified PMMA, or epoxy-modified PMMA. By introducing functional groups such as carboxyl, hydroxyl, or epoxy groups into the PMMA molecular chain, the PMMA adhesive layer maintains the good film-forming properties, electrolyte resistance, and dimensional stability of PMMA itself, while also improving its interfacial bonding force with the rubber adhesive layer and the corona-treated substrate layer; The grafting rate of carboxyl-modified PMMA is 3%–8%. The grafting rate can be theoretically interpreted as the percentage of the mass of the modified PMMA relative to the mass of the PMMA resin used, or it can be understood as the amount of functional groups introduced, calculated through infrared spectroscopy, nuclear magnetic resonance, acid value, hydroxyl value, or epoxy value testing. By controlling the grafting rate, a balance can be achieved between interfacial bonding strength and electrolyte swelling rate. Furthermore, the carboxyl-modified monomer is methacrylic acid, acrylic acid, or maleic anhydride, wherein maleic anhydride can form a carboxyl structure after hydrolysis; the grafting rate of hydroxyl-modified PMMA is 2%–7%, preferably 4%–6%, and more preferably 5%. The carboxyl groups introduced into the carboxyl-modified PMMA can form hydrogen bonds or chemical bonds with the polar components in the rubber adhesive layer, the isocyanate crosslinking system, and the surface of the substrate after corona treatment, thereby improving the interfacial bonding force; specifically, the carboxyl-modified PMMA can be prepared by the following method: dissolving PMMA resin in methyl ethyl ketone to prepare a PMMA solution with a solid content of 25%; heating the PMMA solution to 75°C–85°C, adding the initiator benzoyl peroxide, wherein the amount of benzoyl peroxide is 0.5%–1.0% of the mass of PMMA; then slowly adding the carboxyl-modified monomer, and reacting at a constant temperature of 75°C–85°C for 4h–6h; after the reaction is completed, cooling to below 30°C, adding a polymerization inhibitor to terminate the reaction, and obtaining the carboxyl-modified PMMA solution.

[0035] Furthermore, the hydroxyl-modified PMMA is obtained by solution free radical grafting reaction of PMMA and hydroxyl-modified monomers. The hydroxyl-modified monomers are hydroxyethyl methacrylate, hydroxypropyl methacrylate, or hydroxyethyl acrylate; the grafting rate of epoxy-modified PMMA is 2% to 6%, preferably 3% to 5%. The hydroxyl groups introduced into the hydroxyl-modified PMMA can improve the hydrogen bonding between the PMMA adhesive layer and the rubber adhesive layer, improve the flexibility of the adhesive layer, and reduce the interfacial stress of the adhesive layer during winding and bending, making the insulating tape more suitable for wound sodium-ion battery cells; Specifically, hydroxyl-modified PMMA can be prepared as follows: PMMA resin is dissolved in a mixed solvent of butanone and butyl acetate to prepare a PMMA solution with a solid content of 25%; the PMMA solution is heated to 65℃~80℃, and the initiator azobisisobutyronitrile is added, wherein the amount of azobisisobutyronitrile is 0.6%~1.2% of the mass of PMMA; then the hydroxyl-modified monomer is added dropwise, and the reaction is carried out at a constant temperature of 65℃~80℃ for 5h~7h; after the reaction is completed, the temperature is lowered and the reaction is terminated to obtain the hydroxyl-modified PMMA solution.

[0036] Furthermore, the epoxy-modified PMMA is obtained by solution free radical grafting reaction of PMMA and epoxy-modified monomers. The epoxy-modified monomer is glycidyl methacrylate or glycidyl acrylate, and the grafting rate of the epoxy-modified PMMA is 2% to 6%, preferably 3% to 5%. The epoxy groups introduced into the epoxy-modified PMMA are reactive and can react with carboxyl groups, hydroxyl groups, or other groups containing active hydrogen in the adhesive layer system during the curing process, and together with the isocyanate crosslinking system, form a stable crosslinking network, which is suitable for insulation protection in high-temperature energy storage sodium-ion battery cells.

[0037] Specifically, epoxy-modified PMMA can be prepared as follows: PMMA resin is dissolved in methyl ethyl ketone to prepare a PMMA solution with a solid content of 25%; the PMMA solution is heated to 75℃~90℃, and benzoyl peroxide initiator is added, wherein the amount of benzoyl peroxide is 0.5%~1.0% of the mass of PMMA; then epoxy-modified monomer is added dropwise, and the reaction is carried out at a constant temperature of 75℃~90℃ for 3h~5h; after the reaction is completed, the temperature is lowered and the reaction is terminated to obtain an epoxy-modified PMMA solution.

[0038] In one specific embodiment, the modified PMMA adhesive layer comprises 100 parts by weight of grafted modified polymethyl methacrylate, 4-5 parts by weight of curing agent, 0.5 parts by weight of leveling agent, and methyl ethyl ketone solvent, and the solid content of the modified PMMA adhesive layer is 25%; when the grafted modified polymethyl methacrylate is carboxyl-modified PMMA, the curing agent is an epoxy curing agent; when the grafted modified polymethyl methacrylate is hydroxyl-modified PMMA, the curing agent is an isocyanate curing agent; when the grafted modified polymethyl methacrylate is epoxy-modified PMMA, the curing agent is a carboxyl curing agent; and the leveling agent is a non-silicone acrylate leveling agent.

[0039] In some embodiments, the present invention also provides a method for preparing insulating tape inside a sodium-ion battery cell, comprising the following steps: S1. Perform single-sided atmospheric pressure corona treatment or atmospheric pressure plasma surface treatment on the surface of the substrate layer to be coated. S2. Mix the rubber matrix, tackifying resin, antioxidant, isocyanate crosslinking agent and organic solvent to obtain a rubber adhesive; S3. The rubber adhesive is applied to the surface of the treated substrate layer and dried to form a rubber adhesive layer. S4. Mix the grafted modified PMMA, curing agent, leveling agent and organic solvent to obtain the modified PMMA adhesive; S5. The modified PMMA adhesive is applied to the surface of the rubber adhesive layer, and after drying and curing, a modified PMMA adhesive layer is formed to obtain the insulating tape inside the sodium-ion battery cell.

[0040] In some embodiments, the single-sided atmospheric pressure corona treatment is performed using a wide-width corona treatment machine, with the output power adjusted according to the width of the circuit to 3.0 kW / m to 5.0 kW / m, the processing speed to 30 m / min to 60 m / min, and the electrode gap to 1.5 mm to 2.0 mm; the solid content of the rubber adhesive is 25% to 35%, and the wet film coating thickness is 15 μm to 30 μm. Preferably, the rubber adhesive is coated using a comma knife or microgravure coating process, and the wet film coating thickness is... The film coating thickness is 20 μm and the solid content is 30%. After drying at 80°C for 2 min, a rubber adhesive layer with a theoretical dry film thickness of 6 μm is formed. The modified PMMA adhesive has a solid content of 20% to 30% and a wet film coating thickness of 10 μm to 20 μm. Preferably, the wet film coating thickness is 15 μm and the solid content is 25%. After drying at 100°C for 3 min and curing at 120°C for 2 min, a modified PMMA adhesive layer with a thickness of 3.75 μm is formed.

[0041] In some embodiments, the grafted modified PMMA is prepared by the following method: dissolving PMMA resin in an organic solvent to prepare a PMMA solution; adding an initiator to the PMMA solution and dropwise adding a modified monomer at 65°C to 90°C to carry out a solution free radical grafting reaction to obtain a grafted modified PMMA solution; adding a curing agent and a leveling agent to the grafted modified PMMA solution to obtain a modified PMMA adhesive; wherein the modified monomer is one of methacrylic acid, acrylic acid, maleic anhydride, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, glycidyl methacrylate, or glycidyl acrylate.

[0042] Furthermore, the preparation of carboxyl-modified PMMA includes: dissolving PMMA resin in methyl ethyl ketone to form a solution with a solid content of 25%, adding benzoyl peroxide and adding carboxyl-modified monomers dropwise at 75℃~85℃, and terminating the reaction after reacting at a constant temperature for 4h~6h; the preparation of hydroxyl-modified PMMA includes: dissolving PMMA resin in a methyl ethyl ketone / butyl acetate mixed solvent to form a solution with a solid content of 25%, adding azobisisobutyronitrile and adding hydroxyl-modified monomers dropwise at 65℃~80℃, and terminating the reaction after reacting at a constant temperature for 5h~7h; the preparation of epoxy-modified PMMA includes: dissolving PMMA resin in methyl ethyl ketone to form a solution with a solid content of 25%, adding benzoyl peroxide and adding epoxy-modified monomers dropwise at 75℃~90℃, and terminating the reaction after reacting at a constant temperature for 3h~5h.

[0043] The testing method is as follows: the swelling rate can be evaluated by the change in sample thickness, mass, or size before and after immersion. In this embodiment of the invention, the swelling rate is preferably calculated based on the change in tape thickness before and after immersion, and the calculation formula is: swelling rate = (thickness after immersion - thickness before immersion) / thickness before immersion × 100%.

[0044] The peel strength retention rate is calculated using the following formula: Peel strength retention rate = (180° peel strength of copper foil after immersion) / (180° peel strength of initial copper foil) × 100%. For the 180° peel strength test, refer to GB / T 2792-2014 or ASTM D3330 for further refinement of sample width, bonding pressure, pressure rollers, settling time, peel rate, and test temperature and humidity. For insulation resistance, refer to ASTM D257, IEC 62631-3-1, or IEC 62631-3-2 for further refinement of test voltage, electrode structure, pressure application time, and environmental conditions. Unless otherwise specified, the electrolyte immersion conditions are: 1 mol / L NaPF6 / EC:DMC = 1:1, immersion at 60°C for 7 days.

[0045] Example 1: This embodiment provides an insulating tape for a sodium-ion battery cell, the insulating tape comprising a BOPP substrate layer, a rubber adhesive layer, and a carboxyl-modified PMMA adhesive layer.

[0046] The substrate layer is a 25μm thick biaxially oriented polypropylene film, i.e., BOPP film. Before coating, the surface of the BOPP film to be coated is subjected to single-sided atmospheric pressure corona treatment using a wide-width corona treatment machine. After treatment, the surface tension of the treated BOPP film reaches 42mN / m using a dyne pen test.

[0047] The formulation of the rubber adhesive layer is as follows: Based on 100 parts by weight of butyl rubber, add 30 parts by weight of terpene resin, 2 parts by weight of antioxidant 264, 3 parts by weight of isocyanate crosslinking agent, and a mixed solvent composed of toluene and ethyl acetate in a volume ratio of 1:1. Adjust the solid content of the system to 30%, and after stirring and dispersing evenly, obtain the rubber adhesive. Among them, antioxidant 264 is 2,6-di-tert-butyl-p-cresol, and the isocyanate crosslinking agent is preferably toluene diisocyanate trimer.

[0048] The formulation of the carboxyl-modified PMMA adhesive layer is as follows: Based on 100 parts by weight of carboxyl-modified PMMA, add 5 parts by weight of epoxy crosslinking agent or modified alicyclic amine epoxy curing agent, 0.5 parts by weight of non-silicone acrylate leveling agent, and methyl ethyl ketone solvent. Adjust the solid content of the system to 25%, and stir evenly to obtain the carboxyl-modified PMMA adhesive. The carboxyl grafting rate of the carboxyl-modified PMMA is 5%.

[0049] In the preparation process, a rubber adhesive was first coated onto the surface of a corona-treated BOPP film, with a wet film thickness controlled at 20 μm. It was then dried at 80°C for 2 minutes to allow solvent evaporation and form a rubber adhesive layer. Based on the solid content, the theoretical dry film thickness of the rubber adhesive layer was 6 μm. Next, a carboxyl-modified PMMA adhesive was coated onto the surface of the rubber adhesive layer, with a wet film thickness controlled at 15 μm. This was then dried at 100°C for 3 minutes to remove the solvent, followed by curing at 120°C for 2 minutes to complete the cross-linking and curing of the carboxyl-modified PMMA adhesive layer. Based on the solid content, the theoretical dry film thickness of the carboxyl-modified PMMA adhesive layer was 3.75 μm. The resulting functional adhesive layer has a theoretical total dry film thickness of 9.75 μm.

[0050] The obtained insulating tape was immersed in a sodium-ion battery electrolyte of 1 mol / L NaPF6 / EC:DMC=1:1 for 7 days at 60°C. Test results showed that the swelling rate of the insulating tape was 3.2%; the initial 180° peel strength of the copper foil was 12.5 N / cm, which decreased to 10.8 N / cm after immersion, with a peel strength retention rate of 86.4%; the initial insulation resistance was ≥10^12 Ω, and remained ≥10^11 Ω after immersion, meeting the internal insulation protection requirements of the sodium-ion battery cell.

[0051] Example 2: This embodiment is basically the same as Embodiment 1, except that the rubber adhesive includes 100 parts by weight of natural rubber, 25 parts by weight of terpene resin, 1.5 parts by weight of antioxidant 264, and 2.5 parts by weight of isocyanate crosslinking agent. The solid content of the system is adjusted to 30% using a mixed solvent of toluene and ethyl acetate. This embodiment illustrates that when natural rubber is used as a single rubber matrix, a rubber adhesive layer suitable for insulating tape inside sodium-ion battery cells can be formed within the proportion range of tackifier, antioxidant, and crosslinking agent defined in this invention.

[0052] Example 3: This embodiment is basically the same as Embodiment 1, except that the rubber adhesive includes 100 parts by weight of styrene-butadiene rubber, 35 parts by weight of C5 petroleum resin, 2 parts by weight of antioxidant RD, and 4 parts by weight of isocyanate crosslinking agent. The solid content of the system is adjusted to 30% using a mixed solvent of toluene and ethyl acetate. This embodiment illustrates that when styrene-butadiene rubber is combined with C5 petroleum resin, it can improve the adhesion of the adhesive layer to copper and aluminum foils, and improve the cohesive strength and resistance to electrolyte swelling of the adhesive layer through isocyanate crosslinking agents.

[0053] Example 4: This embodiment is basically the same as Example 1, except that the modified PMMA adhesive layer is a hydroxyl-modified PMMA adhesive layer. The hydroxyl-modified PMMA is prepared by solution free radical grafting reaction of PMMA and hydroxyethyl methacrylate, with a grafting rate of 4%. The formulation of the hydroxyl-modified PMMA adhesive layer includes 100 parts by weight of hydroxyl-modified PMMA, 4 parts by weight of isocyanate curing agent, 0.5 parts by weight of leveling agent, and methyl ethyl ketone (MEK), which is used to adjust the solid content of the system to 25%.

[0054] The obtained insulating tape was immersed in a 1 mol / L NaPF6 / EC:DMC = 1:1 sodium-ion battery electrolyte at 60°C for 7 days. Test results showed that the insulating tape had a swelling rate of 3.5%, a copper foil peel strength retention rate of 85.8%, and an insulation resistance ≥10^11 Ω. After 1000 bending tests, the adhesive layer showed no cracking. This example demonstrates that the hydroxyl-modified PMMA adhesive layer can improve the toughness and bending resistance of the adhesive layer, making it suitable for internal insulation protection in wound sodium-ion battery cells.

[0055] Example 5: This embodiment is basically the same as Example 1, except that the modified PMMA adhesive layer is an epoxy-modified PMMA adhesive layer. The epoxy-modified PMMA is prepared by a solution free radical grafting reaction of PMMA and glycidyl methacrylate, with a grafting rate of 4%. The formulation of the epoxy-modified PMMA adhesive layer includes 100 parts by weight of epoxy-modified PMMA, 5 parts by weight of carboxyl curing agent, 0.5 parts by weight of leveling agent, and methyl ethyl ketone (MEK), which is used to adjust the solid content of the system to 25%.

[0056] The obtained insulating tape was immersed in a 1 mol / L NaPF6 / EC:DMC=1:1 sodium-ion battery electrolyte at 60°C for 7 days. Test results showed that the insulating tape had a swelling rate of 2.8%, a copper foil peel strength retention rate of 87.2%, and an insulation resistance ≥10^11 Ω. This example demonstrates that the epoxy-modified PMMA adhesive layer can further improve the crosslinking stability and electrolyte resistance of the adhesive layer, making it suitable for internal insulation protection in high-temperature energy storage sodium-ion battery cells.

[0057] Example 6: This embodiment is basically the same as Embodiment 1, except that the substrate layer uses a PI film with a thickness of 25 μm. The formulation and process of the rubber adhesive layer and the carboxyl-modified PMMA adhesive layer are the same as in Embodiment 1. This embodiment is used to illustrate that the structure of the rubber adhesive layer and the modified PMMA adhesive layer of the present invention is not only applicable to BOPP substrates, but also applicable to heat-resistant, electrolyte-resistant, and low-swelling polymer films such as PI.

[0058] Example 7: This embodiment is essentially the same as Embodiment 1, except that the total dry film thickness of the functional adhesive layer is controlled to be approximately 11 μm, of which the dry film thickness of the rubber adhesive layer is approximately 7.5 μm and the dry film thickness of the carboxyl-modified PMMA adhesive layer is approximately 3.5 μm. This thickness combination allows the rubber adhesive layer to provide sufficient adhesive performance, while the carboxyl-modified PMMA adhesive layer provides electrolyte resistance, low swelling, and interface reinforcement, thereby achieving a balance between adhesive strength, swelling resistance, insulation reliability, and internal space occupancy of the battery cell.

[0059] Example 8: This embodiment is basically the same as Embodiment 1, except that the adhesive layer structure is "BOPP substrate layer - rubber adhesive layer - modified PMMA adhesive layer - rubber adhesive layer", wherein the total dry film thickness of the two rubber adhesive layers is 5μm to 10μm, preferably 7.5μm; the dry film thickness of the modified PMMA adhesive layer is 2μm to 5μm, preferably 3.5μm; and the total dry film thickness of the functional adhesive layer is preferably 11μm. In this multilayer structure, the rubber adhesive layer near the substrate layer is used to improve the interfacial adhesion of the substrate layer, the modified PMMA adhesive layer is used to reduce electrolyte swelling and enhance interfacial stability, and the outer rubber adhesive layer is used to improve the adhesion reliability of the tape to the copper foil, aluminum foil, or the internal bonding parts of the battery cell.

[0060] Comparative Example 1: This comparative example uses conventional insulating tape, which comprises a 25 μm thick PET substrate and an acrylic adhesive layer. The test conditions are the same as in Example 1, i.e., the conventional insulating tape is immersed in a 1 mol / L NaPF6 / EC:DMC=1:1 sodium-ion battery electrolyte at 60°C for 7 days.

[0061] Test results show that the swelling rate of the conventional insulating tape after immersion is 16.8%; the initial 180° peel strength of the copper foil is 8.2 N / cm, which decreases to 3.5 N / cm after immersion, with a peel strength retention rate of only 42.7%; the insulation resistance decreases to 10^9 Ω after immersion. This indicates that the combination of conventional PET substrate and acrylic adhesive layer is prone to significant swelling, adhesion attenuation, and decreased insulation performance in the sodium-ion battery electrolyte environment, making it difficult to meet the long-term insulation protection requirements inside sodium-ion battery cells.

[0062] Comparative Example 2: This comparative example is essentially the same as Example 1, except that a carboxyl-modified PMMA adhesive layer is not included; only a single-layer rubber adhesive layer is used. The rubber adhesive layer formulation is the same as in Example 1. During preparation, the rubber adhesive is applied only to the surface of a corona-treated BOPP film, with the wet film thickness controlled at 20 μm. After drying at 80°C for 2 minutes, it is then cured at 120°C for 2 minutes to obtain an insulating tape containing only the rubber adhesive layer. Based on the solid content, the theoretical dry film thickness of the rubber adhesive layer is 6 μm.

[0063] The test was conducted under the same electrolyte immersion conditions as in Example 1. The test results showed that the swelling rate of the insulating tape was 9.5%; the initial 180° peel strength of the copper foil was 11.2 N / cm, which decreased to 6.3 N / cm after immersion, with a peel strength retention rate of 56.3%; and the insulation resistance decreased to 10^10 Ω after immersion. This demonstrates that without the carboxyl-modified PMMA adhesive layer, although the rubber adhesive layer can provide a certain initial adhesive force, it lacks the ability to regulate electrolyte penetration and adhesive layer swelling, resulting in significant swelling of the adhesive layer after immersion, a decrease in adhesive strength retention rate, and accompanying attenuation of insulation performance.

[0064] Comparative Example 3: This comparative example is basically the same as Example 1, except that no terpene resin is added to the rubber adhesive layer. Specifically, the formulation of the rubber adhesive layer is: 100 parts by weight of butyl rubber, 2 parts by weight of antioxidant 264, 3 parts by weight of isocyanate crosslinking agent, and a mixed solvent composed of toluene and ethyl acetate in a volume ratio of 1:1, adjusting the solid content of the system to 30%, without adding terpene resin. The formulation and preparation process of the carboxyl-modified PMMA adhesive layer are the same as in Example 1. In the obtained insulating tape, the theoretical dry film thickness of the rubber adhesive layer is 6 μm, the theoretical dry film thickness of the carboxyl-modified PMMA adhesive layer is 3.75 μm, and the theoretical total dry film thickness of the functional adhesive layer is 9.75 μm.

[0065] The test was conducted under the same electrolyte immersion conditions as in Example 1. The test results showed that the swelling rate of the insulating tape was 3.3%; the initial 180° peel strength of the copper foil was only 5.8 N / cm, decreasing to 3.1 N / cm after immersion, with a peel strength retention rate of 53.4%; the insulation resistance remained ≥10^11 Ω. This indicates that although the carboxyl-modified PMMA adhesive layer can still improve swelling and insulation performance to some extent when no terpene resin is added to the rubber adhesive layer, the initial adhesion and holding power of the rubber adhesive layer to the copper foil are significantly insufficient.

[0066] Comparative Example 4: This comparative example is essentially the same as Example 1, except that the carboxyl-modified PMMA is replaced with ordinary unmodified PMMA. Specifically, the rubber adhesive layer formulation is the same as in Example 1. The PMMA adhesive layer formulation is: 100 parts by weight of ordinary unmodified PMMA, 5 parts by weight of epoxy crosslinking agent, 0.5 parts by weight of non-silicone acrylate leveling agent, and methyl ethyl ketone solvent, adjusting the solid content of the system to 25%. The preparation process is the same as in Example 1. In the resulting insulating tape, the theoretical dry film thickness of the rubber adhesive layer is 6 μm, the theoretical dry film thickness of the ordinary PMMA adhesive layer is 3.75 μm, and the theoretical total dry film thickness of the functional adhesive layers is 9.75 μm.

[0067] The test was conducted under the same electrolyte immersion conditions as in Example 1. The test results showed that the swelling rate of the insulating tape was 7.8%; the initial 180° peel strength of the copper foil was 12.3 N / cm, which decreased to 7.5 N / cm after immersion, with a peel strength retention rate of 61.0%; the insulation resistance decreased to 10^10 Ω after immersion. This demonstrates that ordinary unmodified PMMA lacks polar grafting groups such as carboxyl groups, making it difficult to form a stable interfacial bond with the rubber adhesive layer and the corona-treated BOPP substrate. This results in insufficient interfacial stability, increased swelling rate, decreased peel strength retention rate, and decreased insulation performance after electrolyte immersion.

[0068] Comparative Example 5: This comparative example is basically the same as Example 1, except that the BOPP film was not corona treated before the rubber adhesive was applied; the rubber adhesive was applied directly to the surface of the BOPP film. This comparative example illustrates that the BOPP film without corona treatment has a lower surface energy, resulting in insufficient wettability of the rubber adhesive on its surface, which easily leads to a decrease in initial peel strength and interfacial debonding or a reduced peel strength retention rate after immersion in the electrolyte.

[0069] Comparative Example 6: This comparative example is essentially the same as Example 1, except that no isocyanate crosslinking agent is added to the rubber adhesive layer. This comparative example is used to illustrate that crosslinking agents can improve the cohesive strength and electrolyte swelling resistance of the rubber adhesive layer. When crosslinking agents are lacking, the degree of crosslinking of the adhesive layer is insufficient, and the swelling rate and peel strength retention rate after electrolyte immersion are easily deteriorated.

[0070] Comparative Example 7: This comparative example is essentially the same as Example 1, except that no epoxy crosslinking agent or modified alicyclic amine epoxy curing agent is added to the carboxyl-modified PMMA adhesive layer. This comparative example is used to illustrate that the curing agent can further improve the film-forming stability and electrolyte immersion resistance of the modified PMMA adhesive layer, and reduce the risk of interface failure after electrolyte immersion.

[0071] Performance test results

[0072] The insulating tape for sodium-ion battery cells described in this invention can be prepared through a continuous process including atmospheric pressure corona treatment, comma-knife coating, microgravure coating, drying and curing, and winding and slitting. This process window is suitable for industrial production. The resulting insulating tape can be applied to the tab area, electrode edge area, cell winding end area, cell stack edge area, and other internal insulation and protection areas of sodium-ion battery cells, demonstrating promising prospects for industrial application.

[0073] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0074] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. An insulating tape for the inner cavity of a sodium-ion battery cell, characterized in that, The device includes a substrate layer and a functional adhesive layer disposed on one side of the substrate layer. The substrate layer is a low-polarity or electrolyte-resistant, low-swelling polymer film with a thickness of 10 μm to 50 μm. The functional adhesive layer includes a rubber adhesive layer and a modified PMMA adhesive layer. The rubber adhesive layer includes a rubber matrix, a tackifying resin, an antioxidant, and an isocyanate crosslinking agent. The modified PMMA adhesive layer includes grafted modified polymethyl methacrylate (PMMA), which contains at least one grafted functional group selected from carboxyl, hydroxyl, and epoxy groups. The total dry film thickness of the functional adhesive layer is 5 μm to 20 μm.

2. The insulating tape inside the sodium-ion battery cell according to claim 1, characterized in that, The substrate layer is one of polypropylene film, biaxially oriented polypropylene film, polyimide film, polyethylene film, polyester film, and polyethylene naphthalate film; the thickness of the substrate layer is 20μm to 30μm; the surface of the substrate layer to be coated is subjected to single-sided atmospheric pressure corona treatment or atmospheric pressure plasma surface treatment.

3. The insulating tape inside the sodium-ion battery cell according to claim 2, characterized in that, The functional adhesive layer is a double-layer adhesive structure or a multi-layer adhesive structure. When the functional adhesive layer is a double-layer adhesive structure, the inner insulating tape has a structure of substrate layer-rubber adhesive layer-modified PMMA adhesive layer. When the functional adhesive layer is a multi-layer adhesive structure, the inner insulating tape has a structure of substrate layer-rubber adhesive layer-modified PMMA adhesive layer-rubber adhesive layer. The total dry film thickness of the functional adhesive layer is 8μm to 15μm, the dry film thickness of the rubber adhesive layer is 5μm to 10μm, and the dry film thickness of the modified PMMA adhesive layer is 2μm to 5μm.

4. The insulating tape inside the sodium-ion battery cell according to claim 3, characterized in that, The rubber matrix is ​​one of butyl rubber, natural rubber, or styrene-butadiene rubber; the tackifying resin is one of terpene resin, C5 petroleum resin, or C9 petroleum resin; the antioxidant is one of antioxidant 264, antioxidant RD, or antioxidant 4010NA; the isocyanate crosslinking agent is one of toluene diisocyanate trimer, diphenylmethane diisocyanate adduct, or isocyanate trimer; and the solvent is one of toluene / ethyl acetate (1:1), butanone, or butyl acetate.

5. The insulating tape inside the sodium-ion battery cell according to claim 4, characterized in that, The rubber matrix is ​​in the amount of 100 parts by weight, the amount of the tackifying resin is 20-40 parts by weight, the amount of the antioxidant is 1-3 parts by weight, and the amount of the isocyanate crosslinking agent is 2-5 parts by weight; the solvent is only used to adjust the viscosity and does not participate in the reaction, and the solid content is 25%-35%.

6. The insulating tape inside the sodium-ion battery cell according to claim 5, characterized in that, The modified PMMA adhesive layer comprises grafted modified PMMA, a curing agent, a leveling agent, and an organic solvent; based on 100 parts by weight of grafted modified PMMA, the amount of the curing agent is 4-5 parts by weight, the amount of the leveling agent is 0.3-0.8 parts by weight, and the organic solvent is used to adjust the solid content of the modified PMMA adhesive to 20%-30%; the leveling agent is a non-silicone acrylate leveling agent; the grafted modified PMMA is carboxyl-modified PMMA, hydroxyl-modified PMMA, or epoxy-modified PMMA, with a grafting rate of 3%-8% for carboxyl-modified PMMA, 2%-7% for hydroxyl-modified PMMA, and 2%-6% for epoxy-modified PMMA.

7. A method for preparing an insulating tape for a sodium-ion battery cell, used to prepare the insulating tape for a sodium-ion battery cell as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Perform single-sided atmospheric pressure corona treatment or atmospheric pressure plasma surface treatment on the surface of the substrate layer to be coated. S2. Mix the rubber matrix, tackifying resin, antioxidant, isocyanate crosslinking agent and organic solvent to obtain a rubber adhesive; S3. The rubber adhesive is applied to the surface of the treated substrate layer and dried to form a rubber adhesive layer. S4. Mix the grafted modified PMMA, curing agent, leveling agent and organic solvent to obtain the modified PMMA adhesive; S5. The modified PMMA adhesive is applied to the surface of the rubber adhesive layer, and after drying and curing, a modified PMMA adhesive layer is formed to obtain the insulating tape inside the sodium-ion battery cell.

8. The method for preparing the insulating tape inside the sodium-ion battery cell according to claim 7, characterized in that, The single-sided atmospheric pressure corona treatment is performed using a wide-width corona treatment machine, with the output power adjusted according to the width of the circuit from 3.0 kW / m to 5.0 kW / m, the processing speed from 30 m / min to 60 m / min, and the electrode gap from 1.5 mm to 2.0 mm. The solid content of the rubber adhesive is 25% to 35%, and the wet film coating thickness is 15 μm to 30 μm. The solid content of the modified PMMA adhesive is 20% to 30%, and the wet film coating thickness is 10 μm to 20 μm.

9. The method for preparing the insulating tape inside the sodium-ion battery cell according to claim 8, characterized in that, The rubber adhesive has a wet film coating thickness of 20 μm and is dried at 80°C for 2 min; the modified PMMA adhesive has a wet film coating thickness of 15 μm and is dried at 100°C for 3 min and cured at 120°C for 2 min.

10. The method for preparing the insulating tape inside the sodium-ion battery cell according to claim 9, characterized in that, The grafted modified PMMA is prepared according to the following method: PMMA resin is dissolved in an organic solvent to prepare a PMMA solution; an initiator is added to the PMMA solution, and a modified monomer is added dropwise at 65℃~90℃ to carry out a solution free radical grafting reaction to obtain a grafted modified PMMA solution; a curing agent and a leveling agent are added to the grafted modified PMMA solution to obtain a modified PMMA adhesive; wherein, the modified monomer is one of methacrylic acid, acrylic acid, maleic anhydride, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, glycidyl methacrylate, or glycidyl acrylate.

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