Secondary batteries, methods for preparing secondary batteries, and electrical devices using secondary batteries.

Abstract

This application discloses a secondary battery, a method for preparing the secondary battery, and an electrical device thereof. The secondary battery includes a positive electrode sheet, which includes a current collector, an active material layer located on at least one surface of the current collector, and edge coatings located on both sides of the active material layer. The active material layer includes a positive active material and a first binder. The edge coatings include an inorganic ceramic filler and a second binder. The absolute value of the difference in solubility parameters between the first binder and the second binder is greater than or equal to 0.1 MPa. 1 / 2 And less than or equal to 1.5 MPa 1 / 2 This application utilizes this type of positive electrode sheet to solve the problem of virtual edges in the coating process of the active material layer and edge coating of the positive electrode sheet, thereby improving the stability and cycle life of the battery.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a secondary battery, a method for preparing the secondary battery, and an electrical device. Background Technology

[0002] During the coating process of the positive electrode sheet of a secondary battery, a "virtual edge" phenomenon can easily occur between the active material layer and the edge coating layer of the positive electrode sheet. This can lead to a significant decrease in battery stability and cycle life. Summary of the Invention

[0003] In view of the above problems, this application provides a secondary battery, a method for preparing a secondary battery, and an electrical device to solve the problem of virtual edges in the coating process of the active material layer and the edge coating of the positive electrode sheet, thereby improving the stability and cycle life of the battery.

[0004] In a first aspect, this application provides a secondary battery, including a positive electrode sheet. The positive electrode sheet includes a current collector, an active material layer located on at least one surface of the current collector, and edge coatings located on both sides of the active material layer. The active material layer includes a positive active material and a first binder. The edge coatings include an inorganic ceramic filler and a second binder. The absolute value of the difference in solubility parameters between the first binder and the second binder at 25°C is greater than or equal to 0.1 MPa. 1 / 2 And less than or equal to 1.5 MPa 1 / 2 .

[0005] When the difference in solubility parameters between the first and second adhesives at 25°C is small (absolute value greater than or equal to 0.1 MPa) 1 / 2 And less than or equal to 1.5 MPa 1 / 2 When the polarity is similar and the intermolecular forces are similar, the active material layer slurry and the edge coating slurry can be better compatible during the coating process, thereby reducing the uneven coating caused by the difference in interfacial tension between the active material layer slurry and the edge coating slurry. This not only improves the coating quality, but also significantly reduces the occurrence of false edges, thereby improving the stability and cycle life of the battery.

[0006] In some embodiments, the solubility parameter of the second adhesive at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2 the following.

[0007] The solubility parameter reflects the polarity of the binder; the solubility parameter of the second binder at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2The following indicates that the second binder has weak polarity. The weak polarity of the binder and the inorganic ceramic filler have a small polarity difference, allowing the second binder to better wet and bond with the inorganic ceramic filler, achieving uniform dispersion of the inorganic ceramic filler. Simultaneously, it reduces side reactions between the second binder and the active material or electrolyte, improving the chemical stability of the binder. This characteristic enables the binder to form a uniform and stable coating during the coating process, enhancing the structural stability of the electrode and thus improving battery stability and cycle life.

[0008] In some embodiments, the second binder includes a first polymer and a second polymer, wherein the weight-average molecular weight of the first polymer is 100 kDa to 600 kDa and the weight-average molecular weight of the second polymer is 10 kDa to 300 kDa.

[0009] When the weight-average molecular weight of the first polymer and the weight-average molecular weight of the second polymer are within the above-mentioned range, the probability of gelation of the edge coating slurry can be reduced, the viscosity rebound phenomenon can be weakened, and the processing difficulty can be reduced. At the same time, the suspension properties of the first polymer and the second polymer can be enhanced, so that the first polymer and the second polymer are more evenly dispersed in the edge coating slurry. This is conducive to the contact between the first group and the second group and the group on the surface of the inorganic ceramic filler in the edge coating slurry, which can promote the full play of the van der Waals forces between the groups, thereby improving the bonding force between the components of the edge coating slurry and thus improving the adhesion performance of the edge coating slurry.

[0010] In some embodiments, the second binder comprises a first polymer and a second polymer, the first polymer comprising a first group and the second polymer comprising a second group, wherein the total molar fraction of the first group and the second group is 0% to 50% based on the total molar amount of the second binder, wherein the first group and the second group each independently comprise at least one of a benzene ring, a cyano group, a maleic anhydride, a carboxyl group, or an amide group.

[0011] The total molar fraction of the first and second groups is within the above range. The first and second groups are polar groups, which can improve the cohesive properties between polymers and reduce powder shedding. At the same time, they can improve the interaction force between the polymer positive current collector, thereby improving the adhesion performance of the edge coating. In addition, these polar groups can form van der Waals forces with inorganic ceramic fillers, which can better wet and combine with inorganic ceramic fillers, thereby promoting the dispersion stability and uniformity of inorganic particles and realizing the insulation performance of the edge coating.

[0012] In some embodiments, the second binder comprises a first polymer and a second polymer, the first polymer comprising a first group, the molar fraction of the first group being 0% to 50% based on the total molar amount of the first polymer; the second polymer comprising a second group, the molar fraction of the second group being 2% to 40% based on the total molar amount of the second polymer; the weight-average molecular weight of the first polymer being 100 kDa to 600 kDa, and the weight-average molecular weight of the second polymer being 10 kDa to 300 kDa; wherein the first group and the second group each independently comprise at least one selected from benzene ring, cyano group, maleic anhydride, carboxyl group, or amide group.

[0013] By rationally designing the composition and structural characteristics of the second binder, the processing and bonding properties of the edge coating slurry were optimized. The second binder comprises a first polymer and a second polymer, each possessing specific functional groups, their molar fractions, and weight-average molecular weights. The molar fractions of the first and second functional groups are within the aforementioned range. Both the first and second functional groups are polar groups, which can improve the cohesive properties between polymers and reduce powder shedding; simultaneously, they can enhance the interaction force between the polymer's positive electrode current collector, thereby improving the bonding performance of the edge coating. Furthermore, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. When the weight-average molecular weights of the first and second polymers are within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first and second polymers can be enhanced, resulting in more uniform dispersion of the first and second polymers in the edge coating slurry. This facilitates contact between the first and second functional groups and the functional groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between functional groups, thereby improving the bonding force between the components of the edge coating slurry and enhancing its adhesion performance. Through the rational design of molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, significantly enhancing battery stability and cycle life.

[0014] In some embodiments, based on the total molar amount of the first polymer, the molar fraction of the first group is 0% to 20%; the weight-average molecular weight of the first polymer is 100 kDa to 500 kDa; and the weight-average molecular weight of the second polymer is 10 kDa to 250 kDa.

[0015] The molar fraction of the first functional group is within the above-mentioned range. This first functional group is a polar group, which can improve the cohesive properties between polymers and reduce powder shedding. Simultaneously, it can increase the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion of the edge coating. Furthermore, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. The weight-average molecular weight of the first and second polymers is within the above-mentioned range, which can reduce the probability of gelation in the edge coating slurry, reduce viscosity rebound, and thus reduce processing difficulty. It can also enhance the suspension properties of the first and second polymers, making them more uniformly dispersed in the edge coating slurry. This facilitates contact between the first and second functional groups and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between the groups, thereby improving the bonding force between the components of the edge coating slurry and thus enhancing its adhesion. Through the rational design of molecular weight and molar fraction, the coating uniformity and adhesion of the edge coating can be effectively improved, thereby significantly improving battery stability and cycle life.

[0016] In some embodiments, the first polymer comprises at least one of a first hydrogenated polymer containing styrene units and / or acrylonitrile units, a polyolefin polymer, and an acrylic-ethylene polymer; and / or the second polymer comprises at least one of a second hydrogenated polymer containing styrene units and / or acrylonitrile units, a second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, and a copolymer of polypropylene or polyethylene with maleic anhydride.

[0017] By selecting at least one of the following as the first polymer: a first hydrogenated polymer containing styrene and / or acrylonitrile units, a polyolefin polymer, or an acrylic-ethylene polymer, and at least one of the following as the second polymer: a second hydrogenated polymer containing styrene and / or acrylonitrile units, a second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, or a copolymer of polypropylene or polyethylene with maleic anhydride, the polarity and adhesion properties of the second binder can be effectively optimized. Specifically, the use of hydrogenated polymers can reduce the unsaturation of the material, increase the number of saturated bonds, and thus improve the chemical stability and durability of the polymer. Introducing polar units or groups such as styrene, acrylonitrile, acrylic acid, maleic anhydride, and acrylamide can improve the cohesive properties between polymers, reduce powder shedding, and increase the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion properties of the edge coating. Simultaneously, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating.

[0018] In some embodiments, the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer and the second hydrogenated polymer is 10% to 40%, and the degree of hydrogenation of both the first hydrogenated polymer and the second hydrogenated polymer is ≥80% and <100%.

[0019] By limiting the molar fraction of styrene and / or acrylonitrile units in the first and second hydrogenated polymers to 10%–40%, and considering that styrene and acrylonitrile units are polar units, this improves the cohesiveness between polymers, reduces powder shedding, and enhances the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with it, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, limiting the degree of hydrogenation reduces the unsaturation of the material, increasing the number of saturated bonds, thereby improving the chemical stability and durability of the polymer. Through the rational design of the molar fraction of polar units and the degree of hydrogenation, the coating uniformity and adhesion of the edge coating can be further improved, significantly enhancing battery stability and cycle life.

[0020] In some embodiments, the degree of hydrogenation of both the first hydrogenated polymer and the second hydrogenated polymer is ≥89% and <100%.

[0021] By limiting the degree of hydrogenation within the above range, the unsaturation of the material can be reduced, the number of saturated bonds increases, thereby improving the chemical stability and durability of the polymer, and enhancing the stability and cycle life of the battery.

[0022] In some embodiments, the mass ratio of the first polymer to the second polymer is (2%~10%):(5%~18%).

[0023] By limiting the mass ratio of the first polymer to the second polymer to (2%~10%):(5%~18%), the adhesive performance of the binder can be optimized while ensuring the viscosity of the edge coating slurry. Within this range, the ratio of the first polymer to the second polymer ensures that the slurry has sufficient viscosity to support the uniform distribution of the active material, without affecting the uniformity of the coating due to excessive viscosity. Simultaneously, this ratio effectively balances the cohesive and adhesive forces of the binder, thereby further improving the bonding strength and density of the edge coating and reducing the occurrence of false edges. Furthermore, this ratio optimizes the processing performance of the binder, thereby improving the stability and efficiency of the coating process.

[0024] In some embodiments, the first hydrogenated polymer and the second hydrogenated polymer each independently include at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers.

[0025] By selecting at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers as the first and second polymers, the cohesive properties between the polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, the use of hydrogenated polymers can reduce the unsaturation of the material, increasing the number of saturated bonds, thereby improving the chemical stability and durability of the polymer, ultimately significantly improving battery stability and cycle life.

[0026] In some embodiments, hydrogenated polystyrene polymers include at least one of hydrogenated polystyrene-butadiene, hydrogenated polystyrene-isoprene, hydrogenated polystyrene-butadiene-isoprene, hydrogenated polystyrene-butadiene-styrene, hydrogenated polystyrene-isoprene-styrene, and hydrogenated polystyrene-butadiene-isoprene-styrene; hydrogenated polyacrylonitrile polymers include at least one of hydrogenated polyacrylonitrile-butadiene-isoprene, hydrogenated polyacrylonitrile-isoprene, and hydrogenated polyacrylonitrile-butadiene. Hydrogenated polystyrene-acrylonitrile polymers include at least one of hydrogenated polystyrene-acrylonitrile-butadiene, hydrogenated polystyrene-acrylonitrile-isoprene, and hydrogenated polystyrene-acrylonitrile-butadiene-isoprene.

[0027] By selecting at least one of the aforementioned hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers, the cohesive properties between polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, using hydrogenated polymers can reduce the unsaturation degree of the material, increase the number of saturated bonds, improve the chemical stability and durability of the polymer, and ultimately significantly improve battery stability and cycle life.

[0028] In some embodiments, the polyolefin polymer includes at least one of binary or ternary ethylene propylene rubber, polyisobutylene, cyclic polyolefins and their copolymers.

[0029] By selecting at least one of binary or ternary ethylene propylene diene monomer (EPDM), polyisobutylene, cyclic polyolefins, and their copolymers as the polyolefin polymer, the higher molecular weight can increase the viscosity of the solution, thereby improving the stability of the slurry. Simultaneously, it can enhance the interaction force between the polymer and the positive electrode current collector, thus improving the adhesion performance of the edge coating. Furthermore, using polyolefin polymers can reduce the unsaturation of the material, increase the number of saturated bonds, and improve the chemical stability and durability of the polymer, ultimately significantly improving battery stability and cycle life.

[0030] In some embodiments, the weight-average molecular weight of the first hydrogenated polymer is 100 kDa to 600 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer is 10% to 40%; and / or the weight-average molecular weight of the polyolefin polymer is 100 kDa to 600 kDa; and / or the weight-average molecular weight of the acrylic-ethylene polymer is 100 kDa to 300 kDa, and the molar fraction of acrylic units in the acrylic-ethylene polymer is 5% to 20%.

[0031] By limiting the weight-average molecular weight of the first hydrogenated polymer to 100 kDa to 600 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer be 10% to 40%; limiting the weight-average molecular weight of the polyolefin polymer to 100 kDa to 600 kDa; and limiting the weight-average molecular weight of the acrylic-ethylene polymer to 100 kDa to 300 kDa, and requiring that the molar fraction of acrylic units in the acrylic-ethylene polymer be 5% to 20%, the performance of the binder can be further optimized. Styrene and acrylonitrile units are polar units. By limiting the molar fraction of styrene and / or acrylonitrile units within the above ranges, the cohesive properties between polymers can be improved, reducing powder shedding; simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby improving the adhesion performance of the edge coating; furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thereby promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. By limiting the weight-average molecular weights of the first hydrogenated polymer, the polyolefin polymer, and the acrylic-ethylene polymer to within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first polymer can be enhanced, resulting in more uniform dispersion of the first polymer in the edge coating slurry. This facilitates contact between the first polymer and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between the groups, thereby improving the bonding force between the components of the edge coating slurry and enhancing its adhesion performance. Through the rational design of molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, significantly enhancing battery stability and cycle life.

[0032] In some embodiments, the weight-average molecular weight of the second hydrogenated polymer is 10 kDa to 100 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer is 10% to 40%; and / or the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified based on maleic anhydride, acrylic acid, or acrylamide is 100 kDa to 300 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer containing styrene units modified based on maleic anhydride, acrylic acid, or acrylamide is 10% to 40%, and the molar fraction of maleic anhydride, acrylic acid, or acrylamide is 2% to 10%; and / or the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride is 50 kDa to 200 kDa, and the molar fraction of maleic anhydride in the copolymer of polypropylene or polyethylene with maleic anhydride is 2% to 10%.

[0033] By limiting the weight-average molecular weight of the second hydrogenated polymer to 10 kDa to 100 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer be 10% to 40%; limiting the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide to 100 kDa to 300 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the modified polymer be 10% to 40%, and the molar fraction of maleic anhydride, acrylic acid, or acrylamide be 2% to 10%; and limiting the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride to 50 kDa to 200 kDa, and requiring that the molar fraction of maleic anhydride in the copolymer be 2% to 10%, the performance of the binder can be further optimized. By limiting the molar fraction of styrene and / or acrylonitrile units within the aforementioned range, the cohesive properties between polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer positive electrode current collectors can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with it, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. The introduction of acrylic acid, maleic anhydride, and acrylamide further enhances the cohesive and adhesive properties. By ensuring the weight-average molecular weight of the aforementioned polymers is within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first polymer can be enhanced, resulting in more uniform dispersion of the first polymer in the edge coating slurry. This facilitates contact between the first polymer and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between groups, thereby improving the bonding force between the components of the edge coating slurry and ultimately enhancing its adhesion. By rationally designing the molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, thereby significantly enhancing battery stability and cycle life.

[0034] In some embodiments, the edge coating further includes a light absorber, which includes titanium dioxide, carbon black, and graphite, and the mass fraction of the light absorber in the edge coating is 0.1% to 1.0%.

[0035] By adding a light absorber to the edge coating and limiting the mass fraction of the light absorber to 0.1%~1.0%, the reflection on the surface of the edge coating can be effectively reduced, thereby improving the absorption capacity of the edge coating. This can further optimize the process window of laser die-cutting and improve the processing performance of the edge coating.

[0036] In some embodiments, the mass ratio of the second binder to the inorganic ceramic filler in the edge coating is (15%~20%):(80%~85%).

[0037] By limiting the ratio of inorganic ceramic filler to the second binder in the edge coating to a certain range, it is possible to ensure that the edge coating has sufficient mechanical strength and chemical stability, as well as its adhesion and insulation properties.

[0038] In some embodiments, the inorganic ceramic filler includes boehmite, alumina, silicon nitride, and aluminum nitride. The addition of inorganic ceramic filler can further improve the mechanical strength and insulation properties of the edge coating, thereby further enhancing the stability and cycle life of the battery.

[0039] In some embodiments, the secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, and solid-state batteries.

[0040] Secondly, this application provides a method for preparing a secondary battery, the secondary battery including a positive electrode sheet, the method for preparing the positive electrode sheet including:

[0041] An active material layer slurry is provided, comprising a first solvent and a first binder and a positive electrode active material dispersed in the first solvent;

[0042] A side coating slurry is provided, the side coating slurry comprising a second solvent and a second binder and an inorganic ceramic filler dispersed in the second solvent;

[0043] An active material layer slurry and a side coating slurry are coated onto a current collector and dried to obtain a positive electrode sheet. The positive electrode sheet includes a current collector, an active material layer located on at least one surface of the current collector, and side coatings located on both sides of the active material layer. The active material layer includes a positive active material and a first binder. The side coatings include an inorganic ceramic filler and a second binder. The absolute value of the difference in solubility parameters between the first binder and the second binder at 25°C is greater than or equal to 0.1 MPa. 1 / 2 And less than or equal to 1.5 MPa 1 / 2 .

[0044] When the difference in solubility parameters between the first and second adhesives at 25°C is small (absolute value greater than or equal to 0.1 MPa) 1 / 2 And less than or equal to 1.5 MPa 1 / 2 When the polarity is similar and the intermolecular forces are similar, the active material layer slurry and the edge coating slurry can be better compatible during the coating process, thereby reducing the uneven coating caused by the difference in interfacial tension between the active material layer slurry and the edge coating slurry. This not only improves the coating quality, but also significantly reduces the occurrence of false edges, and improves battery stability and cycle life.

[0045] In some embodiments, the solubility parameter of the second adhesive at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2 the following.

[0046] The solubility parameter reflects the polarity of the binder; the solubility parameter of the second binder at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2 The following indicates that the second binder possesses weak polarity. The small polarity difference between the weakly polar binder and the inorganic ceramic filler allows for better wetting and bonding with the inorganic ceramic filler, achieving uniform dispersion of the filler. Simultaneously, it reduces side reactions between the second binder and the active material or electrolyte, improving the binder's chemical stability. This characteristic enables the binder to form a uniform and stable coating during the coating process, enhancing the structural stability of the electrode and thus improving battery stability and cycle life.

[0047] Based on the principle of similar compatibility, binders and solvents with similar polarities exhibit better compatibility, thereby reducing interfacial tension differences in the slurry during coating. This allows the slurry to spread uniformly, significantly reducing the occurrence of false edges and improving coating quality and battery consistency. Simultaneously, the reactivity between the low-polarity solvent used to dissolve the low-polarity binder and the active material or electrolyte is significantly reduced, decreasing the likelihood of decomposition of the electrode active material or solid electrolyte, thus enhancing battery stability and cycle life.

[0048] In some embodiments, the absolute value of the difference in solubility parameters between the first binder and the first solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 And / or, the absolute value of the difference in solubility parameters between the second adhesive and the second solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 And / or, the absolute value of the difference in solubility parameters between the first solvent and the second solvent at 25°C is less than or equal to 1.5 MPa. 1 / 2 .

[0049] The absolute value of the difference in solubility parameters between the first binder and the first solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 The first binder and the first solvent have similar polarities and intermolecular forces, allowing for better compatibility. This results in more uniform dispersion of the first binder in the first solvent, improving coating quality and enabling the first binder to form a uniform and stable coating film during coating. This enhances the structural stability of the electrode, thereby improving battery stability and cycle life. The absolute value of the solubility parameter difference between the second binder and the second solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2The second binder and the second solvent have similar polarities and intermolecular forces, allowing for better compatibility. This results in more uniform dispersion of the second binder in the second solvent, improving coating quality and enabling the second binder to form a uniform and stable coating film during the coating process. This enhances the structural stability of the electrode, thereby improving battery stability and cycle life. The absolute value of the difference in solubility parameters between the first and second solvents at 25°C is less than or equal to 1.5 MPa. 1 / 2 The first and second solvents have similar polarities and intermolecular forces, making them easier to mix uniformly. This avoids uneven coating caused by differences in interfacial tension during the coating process. This not only improves coating quality but also significantly reduces the occurrence of false edges, enhancing battery consistency and stability.

[0050] In some embodiments, the second binder comprises a first polymer and a second polymer; the first polymer comprises a first group, the molar fraction of which is 0% to 50% based on the total molar amount of the first polymer; the second polymer comprises a second group, the molar fraction of which is 2% to 40% based on the total molar amount of the second polymer; the weight-average molecular weight of the first polymer is 100 kDa to 600 kDa, and the weight-average molecular weight of the second polymer is 10 kDa to 300 kDa; wherein the first group and the second group each independently comprise at least one of a benzene ring, a cyano group, maleic anhydride, a carboxyl group, or an amide group; the step of dissolving the second binder in a second solvent to obtain a first solution comprises: mixing the first polymer and the second polymer and then dissolving them in the second solvent to obtain the first solution.

[0051] By rationally designing the composition and structural characteristics of the second binder, the processing and bonding properties of the edge coating slurry were optimized. The second binder comprises a first polymer and a second polymer, each possessing specific functional groups, their molar fractions, and weight-average molecular weights. The molar fractions of the first and second functional groups are within the aforementioned range. Both the first and second functional groups are polar groups, which can improve the cohesive properties between polymers and reduce powder shedding; simultaneously, they can enhance the interaction force between the polymer's positive electrode current collector, thereby improving the bonding performance of the edge coating. Furthermore, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. When the weight-average molecular weights of the first and second polymers are within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first and second polymers can be enhanced, resulting in more uniform dispersion of the first and second polymers in the edge coating slurry. This facilitates contact between the first and second functional groups and the functional groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between functional groups, thereby improving the bonding force between the components of the edge coating slurry and enhancing its adhesion performance. Through the rational design of molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, significantly enhancing battery stability and cycle life.

[0052] In some embodiments, the first polymer comprises at least one of a first hydrogenated polymer containing styrene units and / or acrylonitrile units, a polyolefin polymer, and an acrylic-ethylene polymer; and / or the second polymer comprises at least one of a second hydrogenated polymer containing styrene units and / or acrylonitrile units, a second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, and a copolymer of polypropylene or polyethylene with maleic anhydride.

[0053] By selecting at least one of the following as the first polymer: a first hydrogenated polymer containing styrene and / or acrylonitrile units, a polyolefin polymer, or an acrylic-ethylene polymer, and at least one of the following as the second polymer: a second hydrogenated polymer containing styrene and / or acrylonitrile units, a second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, or a copolymer of polypropylene or polyethylene with maleic anhydride, the polarity and adhesion properties of the second binder can be effectively optimized. Specifically, the use of hydrogenated polymers can reduce the unsaturation of the material, increase the number of saturated bonds, and thus improve the chemical stability and durability of the polymer. Introducing polar units or groups such as styrene, acrylonitrile, acrylic acid, maleic anhydride, and acrylamide can improve the cohesive properties between polymers, reduce powder shedding, and increase the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion properties of the edge coating. Simultaneously, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating.

[0054] In some embodiments, the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer and the second hydrogenated polymer is 10% to 40%, and the degree of hydrogenation of both the first hydrogenated polymer and the second hydrogenated polymer is ≥80% and less than 100%.

[0055] By limiting the molar fraction of styrene and / or acrylonitrile units in the first and second polymers to 10%–40%, and recognizing that styrene and acrylonitrile units are polar units, this improves the cohesiveness between polymers, reduces powder shedding, and enhances the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with it, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, limiting the degree of hydrogenation reduces the unsaturation of the material, increasing the number of saturated bonds, thereby improving the chemical stability and durability of the polymer. Through the rational design of the molar fraction of polar units and the degree of hydrogenation, the coating uniformity and adhesion of the edge coating can be further improved, significantly enhancing the battery's stability and cycle life.

[0056] In some embodiments, the mass ratio of the first polymer to the second polymer is (2%~10%):(5%~18%), and the mass ratio of the second binder to the inorganic ceramic filler is (15%~20%):(80%~85%).

[0057] By limiting the mass ratio of the first polymer to the second polymer to (2%~10%):(5%~18%), the adhesive performance of the binder can be optimized while ensuring the viscosity of the edge coating slurry. Within this range, the ratio of the first polymer to the second polymer ensures sufficient viscosity to support the uniform distribution of the active material without affecting the uniformity of the coating due to excessive viscosity. Simultaneously, this ratio effectively balances the cohesive and adhesive forces of the binder, thereby further improving the bonding strength and density of the edge coating and reducing the occurrence of false edges. Furthermore, this ratio optimizes the processing performance of the binder, thereby improving the stability and efficiency of the coating process. By limiting the ratio of inorganic ceramic filler to the second binder in the edge coating to the above range, sufficient mechanical strength and chemical stability of the edge coating can be ensured, as well as its adhesive and insulating properties.

[0058] In some embodiments, the first hydrogenated polymer and the second hydrogenated polymer each independently include at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers.

[0059] By selecting at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers as the first and second polymers, the cohesive properties between the polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, the use of hydrogenated polymers can reduce the unsaturation of the material, increasing the number of saturated bonds, thereby improving the chemical stability and durability of the polymer, ultimately significantly improving battery stability and cycle life.

[0060] In some embodiments, hydrogenated polystyrene polymers include at least one of hydrogenated polystyrene-butadiene, hydrogenated polystyrene-isoprene, hydrogenated polystyrene-butadiene-isoprene, hydrogenated polystyrene-butadiene-styrene, hydrogenated polystyrene-isoprene-styrene, and hydrogenated polystyrene-butadiene-isoprene-styrene; hydrogenated polyacrylonitrile polymers include at least one of hydrogenated polyacrylonitrile-butadiene-isoprene, hydrogenated polyacrylonitrile-isoprene, and hydrogenated polyacrylonitrile-butadiene; and hydrogenated polystyrene-acrylonitrile polymers include at least one of hydrogenated polystyrene-acrylonitrile-butadiene, hydrogenated polystyrene-acrylonitrile-isoprene, and hydrogenated polystyrene-acrylonitrile-butadiene-isoprene.

[0061] By selecting at least one of the aforementioned hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers, the cohesive properties between polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, using hydrogenated polymers can reduce the unsaturation degree of the material, increase the number of saturated bonds, improve the chemical stability and durability of the polymer, and ultimately significantly improve battery stability and cycle life.

[0062] In some embodiments, the polyolefin polymer includes at least one of binary or ternary ethylene propylene rubber, polyisobutylene, cyclic polyolefins and their copolymers.

[0063] By selecting at least one of binary or ternary ethylene propylene diene monomer (EPDM), polyisobutylene, cyclic polyolefins, and their copolymers as the polyolefin polymer, the ultra-high molecular weight can increase the viscosity of the solution, thereby improving the stability of the slurry. Simultaneously, it can enhance the interaction force between the polymer and the positive electrode current collector, thus improving the adhesion performance of the edge coating. Furthermore, using polyolefin polymers can reduce the unsaturation of the material, increase the number of saturated bonds, and improve the chemical stability and durability of the polymer, ultimately significantly improving battery stability and cycle life.

[0064] In some embodiments, the first hydrogenated polymer has a weight-average molecular weight of 100 kDa to 600 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer is 10% to 40%; and / or the polyolefin polymer has a weight-average molecular weight of 100 kDa to 600 kDa; and / or the acrylic-ethylene polymer has a weight-average molecular weight of 100 kDa to 300 kDa, and the molar fraction of acrylic units in the acrylic-ethylene polymer is 5% to 20%.

[0065] By limiting the weight-average molecular weight of the first hydrogenated polymer to 100 kDa to 600 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer be 10% to 40%; limiting the weight-average molecular weight of the polyolefin polymer to 100 kDa to 600 kDa; and limiting the weight-average molecular weight of the acrylic-ethylene polymer to 100 kDa to 300 kDa, and requiring that the molar fraction of acrylic units in the acrylic-ethylene polymer be 5% to 20%, the performance of the binder can be further optimized. Styrene and acrylonitrile units are polar units. By limiting the molar fraction of styrene and / or acrylonitrile units within the above ranges, the cohesive properties between polymers can be improved, reducing powder shedding; simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby improving the adhesion performance of the edge coating; furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thereby promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. By limiting the weight-average molecular weights of the first hydrogenated polymer, the polyolefin polymer, and the acrylic-ethylene polymer to within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first polymer can be enhanced, resulting in more uniform dispersion of the first polymer in the edge coating slurry. This facilitates contact between the first polymer and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between the groups, thereby improving the bonding force between the components of the edge coating slurry and enhancing its adhesion performance. Through the rational design of molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, significantly enhancing battery stability and cycle life.

[0066] In some embodiments, the second hydrogenated polymer has a weight-average molecular weight of 10 kDa to 100 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer is 10% to 40%; and / or the second hydrogenated polymer containing styrene units modified based on maleic anhydride, acrylic acid, or acrylamide has a weight-average molecular weight of 100 kDa to 300 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer containing styrene units modified based on maleic anhydride, acrylic acid, or acrylamide is 10% to 40%, and the molar fraction of maleic anhydride, acrylic acid, or acrylamide is 2% to 10%; and / or the copolymer of polypropylene or polyethylene with maleic anhydride has a weight-average molecular weight of 50 kDa to 200 kDa, and the molar fraction of maleic anhydride in the copolymer of polypropylene or polyethylene with maleic anhydride is 2% to 10%.

[0067] By limiting the weight-average molecular weight of the second hydrogenated polymer to 10 kDa to 100 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer be 10% to 40%; limiting the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide to 100 kDa to 300 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the modified polymer be 10% to 40%, and the molar fraction of maleic anhydride, acrylic acid, or acrylamide be 2% to 10%; and limiting the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride to 50 kDa to 200 kDa, and requiring that the molar fraction of maleic anhydride in the copolymer be 2% to 10%, the performance of the binder can be further optimized. By limiting the molar fraction of styrene and / or acrylonitrile units within the aforementioned range, the cohesive properties between polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer positive electrode current collectors can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with it, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. The introduction of acrylic acid, maleic anhydride, and acrylamide further enhances the cohesive and adhesive properties. By ensuring the weight-average molecular weight of the aforementioned polymers is within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first polymer can be enhanced, resulting in more uniform dispersion of the first polymer in the edge coating slurry. This facilitates contact between the first polymer and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between groups, thereby improving the bonding force between the components of the edge coating slurry and ultimately enhancing its adhesion. By rationally designing the molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, thereby significantly enhancing battery stability and cycle life.

[0068] In some embodiments, the edge coating also includes a light absorber, including titanium dioxide, carbon black and graphite, and the mass fraction of the light absorber in the edge coating is 0.1% to 1.0%.

[0069] By adding a light absorber to the edge coating and limiting the mass fraction of the light absorber to 0.1%~1.0%, the reflection on the surface of the edge coating can be effectively reduced, thereby improving the absorption capacity of the edge coating. This can further optimize the process window of laser die-cutting and improve the processing performance of the edge coating.

[0070] Thirdly, this application provides an electrical device that includes a secondary battery as described in the above embodiments or a secondary battery prepared by the method described in the above embodiments. The secondary battery is used to provide electrical energy, and the electrical device has at least the same advantages as the secondary battery.

[0071] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0072] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0073] Figure 1 It is the positive electrode of the secondary battery in Example 1;

[0074] Figure 2 It is the positive electrode of the secondary battery in Comparative Example 1;

[0075] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0076] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0077] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application;

[0078] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0079] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown;

[0080] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0081] Explanation of reference numerals in the attached figures:

[0082] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0083] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0084] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0085] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0086] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0087] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0088] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0089] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0090] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0091] During the manufacturing process of the positive electrode sheet of the secondary battery 5, the edges of the positive electrode sheet need to be cut, inevitably resulting in defects such as "white leakage" at the current collector edge, burrs, and fused nodules. These defects can easily lead to short circuits between the positive and negative electrodes or micro-current self-discharge, posing a threat to battery safety. To improve safety, it has become a trend to apply an edge coating to both sides of the active material layer of the positive electrode sheet to reduce burrs and the probability of contact between the positive and negative electrodes during separator shrinkage.

[0092] However, in traditional coating processes, due to the significant polarity difference between the edge coating binder and the active material layer binder, and based on the principle of similar compatibility, the solvents used to dissolve the edge coating binder and the active material layer binder also exhibit a significant polarity difference. This leads to a substantial difference in interfacial tension between the edge coating slurry and the active material layer slurry, making it difficult for the slurry to spread evenly and ultimately resulting in a false edge. This false edge problem not only increases production costs and reduces manufacturing efficiency, but the burrs generated in the uncoated areas directly affect the battery's stability and also reduce the bond strength between the active material and the current collector. The combined effect of these problems will ultimately have a significant impact on the stability and cycle life of the secondary battery 5.

[0093] In addition, commonly used binders, such as PVDF, are usually highly polar polymers that require highly polar solvents (e.g., NMP). These highly polar polymers or solvents can react with the active materials or the electrolyte, causing the active materials or electrolyte to fail, which further exacerbates the deterioration of the stability and cycle life of the secondary battery.

[0094] The inventors noted that by controlling the difference in solubility parameters between the edge coating adhesive and the active material layer adhesive (absolute value greater than or equal to 0.1 MPa), the problem can be solved. 1 / 2 And less than or equal to 1.5 MPa 1 / 2 This makes the polarities of the two similar. According to the principle of similarity compatibility, the solvent polarities of the adhesive used to dissolve the edge coating and the adhesive used to dissolve the active material layer will also be similar, which can achieve uniform spreading of the slurry and solve the problem of false edges.

[0095] Furthermore, by limiting the solubility parameters of the edge coating binder to a range that results in low polarity, the solvent used to dissolve the edge coating binder also exhibits low polarity, based on the principle of like dissolves like. Compared to conventionally used high-polarity binders (e.g., PVDF) and high-polarity solvents (e.g., NMP), the reactivity between low-polarity binders or solvents and the active materials or electrolytes is significantly reduced, decreasing the likelihood of decomposition of the electrode active materials or electrolytes, thereby improving battery stability and cycle life.

[0096] The secondary battery 5 disclosed in this application can be used, but is not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system for such an electrical device can be constructed using the secondary battery 5 disclosed in this application, which helps to improve battery stability and cycle life.

[0097] This application provides a secondary battery 5, a method for preparing the secondary battery 5, and an electrical device. The electrical device can be, but is not limited to, a mobile phone, tablet, laptop, electric toy, power tool, electric vehicle, electric car, ship, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0098] According to some embodiments of this application, this application provides a secondary battery 5, including a positive electrode sheet. The positive electrode sheet includes a current collector, an active material layer located on at least one surface of the current collector, and edge coatings located on both sides of the active material layer. The active material layer includes a first binder, and the edge coatings include an inorganic ceramic filler and a second binder. The absolute value of the difference in solubility parameters between the first binder and the second binder at 25°C is less than or equal to 1.5 MPa. 1 / 2 .

[0099] The square root of the cohesive energy density is defined as the solubility parameter, which describes the sum of intermolecular forces that need to be overcome to dissolve the polymer.

[0100] When the difference in solubility parameters between the first and second adhesives at 25°C is small (absolute value greater than or equal to 0.1 MPa) 1 / 2And less than or equal to 1.5 MPa 1 / 2 When the polarity is similar and the intermolecular forces are similar, the active material layer slurry and the edge coating slurry can be better compatible during the coating process, thereby reducing the uneven coating caused by the difference in interfacial tension between the active material layer slurry and the edge coating slurry. This not only improves the coating quality, but also significantly reduces the occurrence of false edges, and improves battery stability and cycle life.

[0101] Furthermore, this compatibility extends beyond the binders themselves to the solvents used. Solvents with similar polarities mix more easily and uniformly, thus preventing uneven coating caused by differences in solvent interfacial tension during the coating process. This not only improves coating quality but also significantly reduces the occurrence of false edges, enhancing battery consistency and stability.

[0102] As a non-limiting example, the absolute value of the difference in solubility parameters between the first and second adhesives at 25°C includes, but is not limited to, 0.1 MPa. 1 / 2 0.2 MPa 1 / 2 0.3 MPa 1 / 2 0.4 MPa 1 / 2 0.5 MPa 1 / 2 0.6 MPa 1 / 2 0.7MPa 1 / 2 0.8 MPa 1 / 2 0.9 MPa 1 / 2 1.0 MPa 1 / 2 1.1 MPa 1 / 2 1.2 MPa 1 / 2 1.3 MPa 1 / 2 1.4 MPa 1 / 2 1.5MPa 1 / 2 Or the range between any two of the aforementioned.

[0103] Test methods or methods for obtaining the solubility parameters of the first and second adhesives:

[0104] The solubility parameters in this application were calculated using the Hildebrand formula, and the parameters in the formula can be obtained by looking up a table. The Hildebrand formula is as follows: ΔH M =φ1φ2[ε1 1 / 2 -ε2 1 / 2 ] 2 V M Among them, ΔH M φ1 is the heat of mixing of the first and second binders; φ2 is the volume fraction of the first binder; ε1 is the cohesive energy density of the first binder; ε2 is the cohesive energy density of the second binder; VM This represents the total volume after mixing the first and second binders. The square root of the cohesive energy density is defined as the solubility parameter δ, i.e., the solubility parameter δ1 of the first binder = ε1. 1 / 2 The solubility parameter of the second binder is δ2=ε2 1 / 2 When δ1 and δ2 are close to or equal, the Gibbs free energy (ΔG) m =ΔH M -TΔS M A value less than 0 indicates good compatibility between the first and second adhesives. T is the thermodynamic temperature (absolute temperature), and ΔS is the temperature at which the first adhesive and the second adhesive are compatible. M This is the molar entropy change.

[0105] According to the formula for calculating cohesive energy density, we can obtain δ = (ΔE / V). 1 / 2 =F / V=ΣF i / V=(ρΣF i / M0). Where ρ is the density of the binder, M0 is the molecular weight of the repeating structural unit, and F is the molar attraction constant of the group (which can be obtained by referring to Chapter 3, Polymer Solutions, Table 3-3 of "Polymer Physics", 5th Edition, edited by Hua Youqing and Jin Riguang).

[0106] The purification method for the first binder can be achieved by disassembling the secondary battery 5, removing the positive electrode sheet, scraping off the positive active layer of the positive electrode sheet, and using solvents such as pseudotrimethylbenzene, white oil, octyl butyrate, etc., for washing, separation, and drying to obtain the first binder in the positive active layer.

[0107] For the purification method of the second binder, the edge coating of the above positive electrode sheet can be scraped off, and the second binder in the positive electrode active layer can be obtained by washing, separating and drying using solvents such as pseudotrimethylbenzene, white oil, octyl butyrate, etc.

[0108] Optionally, according to some embodiments of this application, the solubility parameter of the second adhesive at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2 the following.

[0109] The solubility parameter reflects the polarity of the binder; the solubility parameter of the second binder at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2The following indicates that the second binder possesses weak polarity. The small polarity difference between the weakly polar binder and the inorganic ceramic filler allows for better wetting and bonding with the inorganic ceramic filler, achieving uniform dispersion of the filler. Simultaneously, it reduces side reactions between the second binder and the active material or electrolyte, improving the binder's chemical stability. This characteristic enables the binder to form a uniform and stable coating during the coating process, enhancing the structural stability of the electrode and thus improving battery stability and cycle life.

[0110] Based on the principle of similar compatibility, binders and solvents with similar polarities exhibit better compatibility, thereby reducing interfacial tension differences in the slurry during coating. This allows the slurry to spread uniformly, significantly reducing the occurrence of false edges and improving coating quality and battery consistency. Simultaneously, the reactivity between the low-polarity solvent used to dissolve the low-polarity binder and the active material or electrolyte is significantly reduced, decreasing the likelihood of decomposition of the electrode active material or solid electrolyte, thus enhancing battery stability and cycle life.

[0111] As a non-limiting example, the solubility parameters of the second adhesive at 25°C include, but are not limited to, 14 MPa. 1 / 2 14.5 MPa 1 / 2 14.8 MPa 1 / 2 15.2 MPa 1 / 2 15.4 MPa 1 / 2 15.9 MPa 1 / 2 16.2 MPa 1 / 2 16.3 MPa 1 / 2 16.4 MPa 1 / 2 16.6 MPa 1 / 2 16.8 MPa 1 / 2 17.1 MPa 1 / 2 17.5 MPa 1 / 2 18.0 MPa 1 / 2 18.2 MPa 1 / 2 18.5 MPa 1 / 2 19.2 MPa 1 / 2 19.5 MPa 1 / 2 20.0MPa 1 / 2 Or the range between any two of the aforementioned.

[0112] According to some embodiments of this application, optionally, the second adhesive includes a first polymer and a second polymer, wherein the weight-average molecular weight of the first polymer is 100kDa to 600kDa, and the weight-average molecular weight of the second polymer is 10kDa to 300kDa.

[0113] Weight-average molecular weight is the statistical average molecular weight based on mass, obtained by averaging over a unit weight.

[0114] When the weight-average molecular weight of the first polymer and the weight-average molecular weight of the second polymer are within the above-mentioned range, the probability of gelation of the edge coating slurry can be reduced, the viscosity rebound phenomenon can be weakened, and the processing difficulty can be reduced. At the same time, the suspension properties of the first polymer and the second polymer can be enhanced, so that the first polymer and the second polymer are more evenly dispersed in the edge coating slurry. This is conducive to the contact between the first group and the second group and the group on the surface of the inorganic ceramic filler in the edge coating slurry, which can promote the full play of the van der Waals forces between the groups, thereby improving the bonding force between the components of the edge coating slurry and thus improving the adhesion performance of the edge coating slurry.

[0115] As a non-limiting example, the weight-average molecular weight of the first polymer includes, but is not limited to, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 600 kDa, or a range between the two aforementioned, and the weight-average molecular weight of the second polymer includes, but is not limited to, 10 kDa, 50 kDa, 80 kDa, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, or a range between the two aforementioned.

[0116] Test method for weight-average molecular weight of the first and second polymers: Dissolve the purified second binder (for purification method, please refer to the test method for solubility parameters above) in tetrahydrofuran, dichloromethane, toluene or ethyl acetate, and measure the molecular weight of the two polymers by gel permeation chromatography.

[0117] According to some embodiments of this application, optionally, the second adhesive includes a first polymer and a second polymer, the first polymer includes a first group, the second polymer includes a second group, and the total molar fraction of the first group and the second group is 0% to 50% based on the total molar amount of the second adhesive, wherein the first group and the second group each independently include at least one of benzene ring, cyano, maleic anhydride, carboxyl or amide.

[0118] The total molar fraction of the first and second groups is within the above range. The first and second groups are polar groups, which can improve the cohesive properties between polymers and reduce powder shedding. At the same time, they can improve the interaction force between the polymer positive current collector, thereby improving the adhesion performance of the edge coating. In addition, these polar groups can form van der Waals forces with inorganic ceramic fillers, which can better wet and combine with inorganic ceramic fillers, thereby promoting the dispersion stability and uniformity of inorganic particles and realizing the insulation performance of the edge coating.

[0119] As a non-limiting example, the total molar fraction of the first and second groups includes, but is not limited to, 0%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, or any range between the two foregoing.

[0120] The method for determining the total molar fraction of the first and second groups based on the total molar amount of the second binder is as follows: The purified second binder (see the solubility parameter test method above for purification methods) is dissolved in deuterated chloroform and subjected to 1H NMR (hydrogen nuclear magnetic resonance) analysis. The characteristic peaks of the benzene ring appear as sharp peaks at 6.2 ppm–6.8 ppm and / or 7.0 ppm–7.2 ppm; the characteristic peak of the methylene group attached to the cyano group appears at 3.0 ppm–3.5 ppm; the characteristic peaks of the two methylene groups attached to maleic anhydride appear at 2.5 ppm–3.2 ppm; the characteristic peak of the carboxyl group appears at 10 ppm–13 ppm; and the characteristic peak of the amide group appears as a broad peak at 6.0 ppm–7.5 ppm. The total molar fraction of the first and second groups can be calculated by the ratio of the integral areas of each peak.

[0121] According to some embodiments of this application, optionally, the second binder includes a first polymer and a second polymer, the first polymer including a first group, the molar fraction of the first group being 0% to 50% based on the total molar amount of the first polymer; the second polymer including a second group, the molar fraction of the second group being 2% to 40% based on the total molar amount of the second polymer; the weight-average molecular weight of the first polymer being 100 kDa to 600 kDa, and the weight-average molecular weight of the second polymer being 10 kDa to 300 kDa; wherein the first group and the second group each independently include at least one selected from benzene ring, cyano, maleic anhydride, carboxyl or amide.

[0122] By rationally designing the composition and structural characteristics of the second binder, the processing and bonding properties of the edge coating slurry were optimized. The second binder comprises a first polymer and a second polymer, each possessing specific functional groups, their molar fractions, and weight-average molecular weights. The molar fractions of the first and second functional groups are within the aforementioned range. Both the first and second functional groups are polar groups, which can improve the cohesive properties between polymers and reduce powder shedding; simultaneously, they can enhance the interaction force between the polymer's positive electrode current collector, thereby improving the bonding performance of the edge coating. Furthermore, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. When the weight-average molecular weights of the first and second polymers are within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first and second polymers can be enhanced, resulting in more uniform dispersion of the first and second polymers in the edge coating slurry. This facilitates contact between the first and second functional groups and the functional groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between functional groups, thereby improving the bonding force between the components of the edge coating slurry and enhancing its adhesion performance. Through the rational design of molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, significantly enhancing battery stability and cycle life.

[0123] As a non-limiting example, the second adhesive includes a first polymer and a second polymer, the first polymer including a first group, and the molar fraction of the first group based on the total molar amount of the first polymer includes, but is not limited to: 0%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, or any range between the foregoing.

[0124] The second polymer includes a second group, and the molar fraction of the second group based on the total molar amount of the second polymer includes, but is not limited to, 2%, 10%, 20%, 30%, 40%, or any range between the two foregoing.

[0125] The weight-average molecular weight of the first polymer includes, but is not limited to, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 600 kDa, or a range between the two aforementioned. The weight-average molecular weight of the second polymer includes, but is not limited to, 10 kDa, 50 kDa, 80 kDa, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, or a range between the two aforementioned.

[0126] According to some embodiments of this application, optionally, based on the total molar amount of the first polymer, the molar fraction of the first group is 0% to 20%; the weight-average molecular weight of the first polymer is 100 kDa to 500 kDa. The weight-average molecular weight of the second polymer is 10 kDa to 250 kDa.

[0127] The molar fraction of the first functional group is within the above-mentioned range. This first functional group is a polar group, which can improve the cohesive properties between polymers and reduce powder shedding. Simultaneously, it can increase the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion of the edge coating. Furthermore, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. The weight-average molecular weight of the first and second polymers is within the above-mentioned range, which can reduce the probability of gelation in the edge coating slurry, reduce viscosity rebound, and thus reduce processing difficulty. It can also enhance the suspension properties of the first and second polymers, making them more uniformly dispersed in the edge coating slurry. This facilitates contact between the first and second functional groups and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between the groups, thereby improving the bonding force between the components of the edge coating slurry and thus enhancing its adhesion. Through the rational design of molecular weight and molar fraction, the coating uniformity and adhesion of the edge coating can be effectively improved, thereby significantly improving battery stability and cycle life.

[0128] As a non-limiting example, based on the total molar amount of the first polymer, the molar fraction of the first group includes, but is not limited to: 0%, 10%, 15%, 20%, or any range between the foregoing.

[0129] The weight-average molecular weight of the first polymer includes, but is not limited to, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, or a range between the two aforementioned.

[0130] The weight-average molecular weight of the second polymer includes, but is not limited to, 10 kDa, 50 kDa, 100 kDa, 150 kDa, 200 kDa, 250 kDa, or a range between the two.

[0131] According to some embodiments of this application, optionally, the first polymer includes at least one of a first hydrogenated polymer containing styrene units and / or acrylonitrile units, a polyolefin polymer, and an ethylene acrylic acid polymer (EAA); and / or the second polymer includes at least one of a second hydrogenated polymer containing styrene units and / or acrylonitrile units, a second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, and a copolymer of polypropylene or polyethylene with maleic anhydride.

[0132] By selecting at least one of the following as the first polymer: a first hydrogenated polymer containing styrene and / or acrylonitrile units, a polyolefin polymer, or an acrylic-ethylene polymer, and at least one of the following as the second polymer: a second hydrogenated polymer containing styrene and / or acrylonitrile units, a second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, or a copolymer of polypropylene or polyethylene with maleic anhydride, the polarity and adhesion properties of the second binder can be effectively optimized. Specifically, the use of hydrogenated polymers can reduce the unsaturation of the material, increase the number of saturated bonds, and thus improve the chemical stability and durability of the polymer. Introducing polar units or groups such as styrene, acrylonitrile, acrylic acid, maleic anhydride, and acrylamide can improve the cohesive properties between polymers, reduce powder shedding, and increase the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion properties of the edge coating. Simultaneously, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating.

[0133] According to some embodiments of this application, optionally, the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer and the second hydrogenated polymer is 10% to 40%, and the degree of hydrogenation of the first hydrogenated polymer and the second hydrogenated polymer is ≥80% and <100%.

[0134] By limiting the molar fraction of styrene and / or acrylonitrile units in the first and second polymers to 10%–40%, and recognizing that styrene and acrylonitrile units are polar units, this improves the cohesiveness between polymers, reduces powder shedding, and enhances the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with it, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, limiting the degree of hydrogenation reduces the unsaturation of the material, increasing the number of saturated bonds, thereby improving the chemical stability and durability of the polymer. Through the rational design of the molar fraction of polar units and the degree of hydrogenation, the coating uniformity and adhesion of the edge coating can be further improved, significantly enhancing the battery's stability and cycle life.

[0135] As a non-limiting example, the molar fraction of styrene units and / or acrylonitrile units in the first polymer and the second polymer includes, but is not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any range between the foregoing.

[0136] Degree of hydrogenation refers to the hydrogenation rate of a carbon-carbon double bond: (double bond content before hydrogenation - double bond content after hydrogenation) / double bond content before hydrogenation. The degree of hydrogenation reflects the proportion of the double bond saturated with hydrogen atoms; a higher value indicates more complete hydrogenation.

[0137] As a non-limiting example, the degree of hydrogenation of the first hydrogenated polymer includes, but is not limited to: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range between the foregoing.

[0138] As a non-limiting example, the degree of hydrogenation of the second hydrogenated polymer includes, but is not limited to: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range between the foregoing.

[0139] In some embodiments, the degree of hydrogenation of both the first hydrogenated polymer and the second hydrogenated polymer is ≥89% and <100%.

[0140] By limiting the degree of hydrogenation within the above range, the unsaturation of the material can be reduced, the number of saturated bonds increases, thereby improving the chemical stability and durability of the polymer, and enhancing the stability and cycle life of the battery.

[0141] As a non-limiting example, the degree of hydrogenation of the first hydrogenated polymer includes, but is not limited to, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range between the foregoing.

[0142] As a non-limiting example, the degree of hydrogenation of the second hydrogenated polymer includes, but is not limited to: 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range between the foregoing.

[0143] In some embodiments, the mass ratio of the first polymer to the second polymer is (2%~10%):(5%~18%).

[0144] By limiting the mass ratio of the first polymer to the second polymer to (2%~10%):(5%~18%), the adhesive performance of the binder can be optimized while ensuring the viscosity of the edge coating slurry. Within this range, the ratio of the first polymer to the second polymer ensures that the slurry has sufficient viscosity to support the uniform distribution of the active material, without affecting the uniformity of the coating due to excessive viscosity. Simultaneously, this ratio effectively balances the cohesive and adhesive forces of the binder, thereby further improving the bonding strength and density of the edge coating and reducing the occurrence of false edges. Furthermore, this ratio optimizes the processing performance of the binder, thereby improving the stability and efficiency of the coating process.

[0145] As a non-limiting example, the mass ratio of the first polymer to the second polymer includes, but is not limited to: 2%:18%, 2%:10%, 2%:5%, 10%:18%, 10%:11%, 10%:5%, or any range between the two for the foregoing.

[0146] According to some embodiments of this application, optionally, the first hydrogenated polymer and the second hydrogenated polymer each independently include at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers.

[0147] By selecting at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers as the first and second polymers, the cohesive properties between the polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, the use of hydrogenated polymers can reduce the unsaturation of the material, increasing the number of saturated bonds, thereby improving the chemical stability and durability of the polymer, ultimately significantly improving battery stability and cycle life.

[0148] According to some embodiments of this application, optionally, the hydrogenated polystyrene polymers include at least one of hydrogenated polystyrene-butadiene (SEB), hydrogenated polystyrene-isoprene (SEP), hydrogenated polystyrene-butadiene-isoprene (SEEP), hydrogenated polystyrene-butadiene-styrene (SEBS), hydrogenated polystyrene-isoprene-styrene (SEPS), and hydrogenated polystyrene-butadiene-isoprene-styrene (SEEPS); the hydrogenated polyacrylonitrile polymers include at least one of hydrogenated polyacrylonitrile-butadiene-isoprene, hydrogenated polyacrylonitrile-isoprene, and hydrogenated polyacrylonitrile-butadiene (HNBR); and the hydrogenated polystyrene-acrylonitrile polymers include at least one of hydrogenated polystyrene-acrylonitrile-butadiene, hydrogenated polystyrene-acrylonitrile-isoprene, and hydrogenated polystyrene-acrylonitrile-butadiene-isoprene.

[0149] By selecting at least one of the aforementioned hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers, the cohesive properties between polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, using hydrogenated polymers can reduce the unsaturation degree of the material, increase the number of saturated bonds, improve the chemical stability and durability of the polymer, and ultimately significantly improve battery stability and cycle life.

[0150] According to some embodiments of this application, optionally, the polyolefin polymer includes at least one of binary or ternary ethylene propylene diene monomer (EPDM), polyisobutylene (PIB), cyclic polyolefin (COC / COP), and copolymers thereof.

[0151] By selecting at least one of binary or ternary ethylene propylene diene monomer (EPDM), polyisobutylene, cyclic polyolefins, and their copolymers as the polyolefin polymer, the ultra-high molecular weight can increase the viscosity of the solution, thereby improving the stability of the slurry. Simultaneously, it can enhance the interaction force between the polymer and the positive electrode current collector, thus improving the adhesion performance of the edge coating. Furthermore, using polyolefin polymers can reduce the unsaturation of the material, increase the number of saturated bonds, and improve the chemical stability and durability of the polymer, ultimately significantly improving battery stability and cycle life.

[0152] In the technical solution of this application, the polyolefin polymer includes at least one of binary or ternary ethylene propylene diene monomer (EPDM) rubber, polyisobutylene, cyclic polyolefins, and copolymers of one or more of binary or ternary EPDM rubber, polyisobutylene, and cyclic polyolefins.

[0153] According to some embodiments of this application, optionally, the weight-average molecular weight of the first hydrogenated polymer is 100kDa to 600kDa, and the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer is 10% to 40%; and / or the weight-average molecular weight of the polyolefin polymer is 100kDa to 600kDa; and / or the weight-average molecular weight of the acrylic-ethylene polymer is 100kDa to 300kDa, and the molar fraction of acrylic units in the acrylic-ethylene polymer is 5% to 20%.

[0154] By limiting the weight-average molecular weight of the first hydrogenated polymer to 100 kDa to 600 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer be 10% to 40%; limiting the weight-average molecular weight of the polyolefin polymer to 100 kDa to 600 kDa; and limiting the weight-average molecular weight of the acrylic-ethylene polymer to 100 kDa to 300 kDa, and requiring that the molar fraction of acrylic units in the acrylic-ethylene polymer be 5% to 20%, the performance of the binder can be further optimized. Styrene and acrylonitrile units are polar units. By limiting the molar fraction of styrene and / or acrylonitrile units within the above ranges, the cohesive properties between polymers can be improved, reducing powder shedding; simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby improving the adhesion performance of the edge coating; furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thereby promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. By limiting the weight-average molecular weights of the first hydrogenated polymer, the polyolefin polymer, and the acrylic-ethylene polymer to within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first polymer can be enhanced, resulting in more uniform dispersion of the first polymer in the edge coating slurry. This facilitates contact between the first polymer and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between the groups, thereby improving the bonding force between the components of the edge coating slurry and enhancing its adhesion performance. Through the rational design of molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, significantly enhancing battery stability and cycle life.

[0155] As a non-limiting example, the weight-average molecular weight of the first hydrogenated polymer includes, but is not limited to, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 600 kDa, or any range between the two for the foregoing.

[0156] As a non-limiting example, in the first hydrogenated polymer, the molar fraction of styrene units and / or acrylonitrile units includes, but is not limited to: 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any range between the foregoing.

[0157] As a non-limiting example, the weight-average molecular weight of polyolefin polymers includes, but is not limited to: 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 600 kDa, or any range between the two for the foregoing.

[0158] As a non-limiting example, the weight-average molecular weight of the acrylate-ethylene polymer includes, but is not limited to, 100 kDa, 120 kDa, 180 kDa, 250 kDa, 290 kDa, 300 kDa, or any range between the two for the foregoing.

[0159] As a non-limiting example, in acrylic-ethylene polymers, the molar fraction of acrylic units includes, but is not limited to, 5%, 8%, 12%, 13%, 14%, 15%, 16%, 18%, 20%, or any range between the foregoing.

[0160] According to some embodiments of this application, optionally, the weight-average molecular weight of the second hydrogenated polymer is 10 kDa to 100 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer is 10% to 40%; and / or the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified based on maleic anhydride, acrylic acid, or acrylamide is 100 kDa to 300 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer containing styrene units modified based on maleic anhydride, acrylic acid, or acrylamide is 10% to 40%, and the molar fraction of maleic anhydride, acrylic acid, or acrylamide is 2% to 10%; and / or the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride is 50 kDa to 200 kDa, and the molar fraction of maleic anhydride in the copolymer of polypropylene or polyethylene with maleic anhydride is 2% to 10%.

[0161] By limiting the weight-average molecular weight of the second hydrogenated polymer to 10 kDa to 100 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer be 10% to 40%; limiting the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide to 100 kDa to 300 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the modified polymer be 10% to 40%, and the molar fraction of maleic anhydride, acrylic acid, or acrylamide be 2% to 10%; and limiting the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride to 50 kDa to 200 kDa, and requiring that the molar fraction of maleic anhydride in the copolymer be 2% to 10%, the performance of the binder can be further optimized. By limiting the molar fraction of styrene and / or acrylonitrile units within the aforementioned range, the cohesive properties between polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer positive electrode current collectors can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with it, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. The introduction of acrylic acid, maleic anhydride, and acrylamide further enhances the cohesive and adhesive properties. By ensuring the weight-average molecular weight of the aforementioned polymers is within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first polymer can be enhanced, resulting in more uniform dispersion of the first polymer in the edge coating slurry. This facilitates contact between the first polymer and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between groups, thereby improving the bonding force between the components of the edge coating slurry and ultimately enhancing its adhesion. By rationally designing the molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, thereby significantly enhancing battery stability and cycle life.

[0162] As a non-limiting example, the weight-average molecular weight of the second hydrogenated polymer includes, but is not limited to, 10 kDa, 20 kDa, 30 kDa, 50 kDa, 55 kDa, 60 kDa, 70 kDa, 80 kDa, 90 kDa, 100 kDa, or any two of the foregoing; as a non-limiting example, the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer includes, but is not limited to, 10%, 20%, 30%, 40%, or any two of the foregoing.

[0163] As a non-limiting example, the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide includes, but is not limited to, 100 kDa, 120 kDa, 130 kDa, 150 kDa, 200 kDa, 260 kDa, 270 kDa, 280 kDa, 290 kDa, 300 kDa, or any two of the foregoing; in the second hydrogenated polymer containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide, the molar fraction of styrene units and / or acrylonitrile units includes, but is not limited to, 10%, 14%, 15%, 18%, 20%, 24%, 26%, 30%, 31%, 32%, 33%, 35%, 40%, or any two of the foregoing; and the molar fraction of maleic anhydride, acrylic acid, or acrylamide includes, but is not limited to, 2%, 4%, 5%, 7%, 8%, 9%, 10%, or any two of the foregoing.

[0164] As a non-limiting example, the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride includes, but is not limited to, 50 kDa, 80 kDa, 100 kDa, 120 kDa, 150 kDa, 160 kDa, 180 kDa, 200 kDa or any two of the foregoing, and the molar fraction of maleic anhydride in the copolymer of polypropylene or polyethylene with maleic anhydride includes, but is not limited to, 2%, 4%, 5%, 7%, 8%, 9%, 10% or any two of the foregoing.

[0165] The second hydrogenated polymer containing styrene units, modified with maleic anhydride, acrylic acid, or acrylamide, may include at least one of the following: maleic anhydride-modified hydrogenated polystyrene-isoprene-styrene (SEBS-maleic anhydride); acrylamide-modified hydrogenated polystyrene-butadiene-isoprene-styrene (SEEPS-acrylamide); acrylic acid-modified hydrogenated polystyrene-isoprene-styrene (SEPS-acrylic acid); and maleic anhydride-modified hydrogenated polystyrene-isoprene (SEP-maleic anhydride). The copolymer of polypropylene or polyethylene with maleic anhydride may include at least one of the following: a copolymer of polypropylene with maleic anhydride (PP-maleic anhydride) or a copolymer of polyethylene with maleic anhydride (PE-maleic anhydride).

[0166] According to some embodiments of this application, optionally, the edge coating also includes a light absorber, including titanium dioxide, carbon black and graphite, and the mass fraction of the light absorber in the edge coating is 0.1% to 1.0%.

[0167] By adding a light absorber to the edge coating and limiting the mass fraction of the light absorber to 0.1%~1.0%, the reflection on the surface of the edge coating can be effectively reduced, thereby improving the absorption capacity of the edge coating. This can further optimize the process window of laser die-cutting and improve the processing performance of the edge coating.

[0168] As a non-limiting example, the mass fraction of the light absorber in the edge coating includes, but is not limited to: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any range between the foregoing.

[0169] According to some embodiments of this application, optionally, the mass ratio of the second binder to the inorganic ceramic filler in the edge coating is (15%~20%):(80%~85%).

[0170] As a non-limiting example, the mass ratio of the second binder to the inorganic ceramic filler in the edge coating includes, but is not limited to: 15%:80%, 15%:85%, 20%:80%, 20%:85%, or any range between the two for the foregoing.

[0171] The test method for the mass ratio of the second binder to the inorganic ceramic filler in the edge coating is as follows:

[0172] After scraping off the edge coating, dissolve, stir, and filter. Wash the residue several times, retaining the filtrate. The dried residue becomes the inorganic ceramic packing. The dried filtrate becomes the second binder. Weigh the second binder and the inorganic ceramic packing separately to obtain the mass ratio of the second binder to the inorganic ceramic packing.

[0173] By limiting the ratio of inorganic ceramic filler to the second binder in the edge coating to a certain range, it is possible to ensure that the edge coating has sufficient mechanical strength and chemical stability, as well as its adhesion and insulation properties.

[0174] According to some embodiments of this application, the inorganic ceramic filler may optionally include boehmite, alumina, silicon nitride, and aluminum nitride.

[0175] The addition of inorganic ceramic fillers can further improve the mechanical strength and insulation properties of the edge coating, thereby enhancing the stability and cycle life of the battery.

[0176] According to some embodiments of this application, optionally, the secondary battery 5 includes at least one of a lithium-ion battery, a sodium-ion battery, and a solid-state battery. The solid-state battery includes lithium-ion solid-state batteries, lithium metal solid-state batteries, or sodium-ion solid-state batteries, etc.

[0177] This application also provides a method for preparing a secondary battery 5, the secondary battery 5 including a positive electrode sheet, the method for preparing the positive electrode sheet including:

[0178] An active material layer slurry is provided, the active material layer slurry comprising a first solvent and a first binder and a positive electrode active material dispersed in the first solvent;

[0179] A side coating slurry is provided, the side coating slurry comprising a second solvent and a second binder and an inorganic ceramic filler dispersed in the second solvent;

[0180] An active material layer slurry and a side coating slurry are coated onto a current collector and dried to obtain a positive electrode sheet. The positive electrode sheet includes a current collector, an active material layer located on at least one surface of the current collector, and side coatings located on both sides of the active material layer. The active material layer includes a positive active material and a first binder. The side coatings include an inorganic ceramic filler and a second binder. The absolute value of the difference in solubility parameters between the first binder and the second binder at 25°C is greater than or equal to 0.1 MPa. 1 / 2 And less than or equal to 1.5 MPa 1 / 2 .

[0181] When the difference in solubility parameters between the first and second adhesives at 25°C is small (absolute value greater than or equal to 0.1 MPa) 1 / 2 And less than or equal to 1.5 MPa 1 / 2 When the polarity is similar and the intermolecular forces are similar, the active material layer slurry and the edge coating slurry can be better compatible during the coating process, thereby reducing the uneven coating caused by the difference in interfacial tension between the active material layer slurry and the edge coating slurry. This not only improves the coating quality, but also significantly reduces the occurrence of false edges, and improves battery stability and cycle life.

[0182] As a non-limiting example, the absolute value of the difference in solubility parameters between the first and second adhesives at 25°C includes, but is not limited to, 0.1 MPa. 1 / 2 0.2 MPa 1 / 2 0.3 MPa 1 / 2 0.4 MPa 1 / 2 0.5 MPa 1 / 2 0.6 MPa 1 / 2 0.7MPa 1 / 2 0.8 MPa 1 / 2 0.9 MPa 1 / 2 1.0 MPa 1 / 2 1.1 MPa 1 / 2 1.2 MPa 1 / 2 1.3 MPa 1 / 2 1.4 MPa 1 / 2 1.5MPa 1 / 2 Or the range between any two of the aforementioned.

[0183] Methods for testing or obtaining solubility parameters:

[0184] The solubility parameters of the first binder, the first solvent, the second binder, and the second solvent can be calculated using the Hildebrand formula. The parameters in the formula can be obtained by looking up a table. For details, please refer to the test method or acquisition method of the solubility parameters of the first binder and the second binder mentioned above.

[0185] Optionally, according to some embodiments of this application, the solubility parameter of the second adhesive at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2 the following.

[0186] The solubility parameter reflects the polarity of the binder; the solubility parameter of the second binder at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2 The following indicates that the second binder possesses weak polarity. The small polarity difference between the weakly polar binder and the inorganic ceramic filler allows for better wetting and bonding with the inorganic ceramic filler, achieving uniform dispersion of the filler. Simultaneously, it reduces side reactions between the second binder and the active material or electrolyte, improving the binder's chemical stability. This characteristic enables the binder to form a uniform and stable coating during the coating process, enhancing the structural stability of the electrode and thus improving battery stability and cycle life.

[0187] Based on the principle of similar compatibility, binders and solvents with similar polarities exhibit better compatibility, thereby reducing interfacial tension differences in the slurry during coating. This allows the slurry to spread uniformly, significantly reducing the occurrence of false edges and improving coating quality and battery consistency. Simultaneously, the reactivity between the low-polarity solvent used to dissolve the low-polarity binder and the active material or electrolyte is significantly reduced, decreasing the likelihood of decomposition of the electrode active material or solid electrolyte, thus enhancing battery stability and cycle life.

[0188] As a non-limiting example, the solubility parameters of the second adhesive at 25°C include, but are not limited to, 14 MPa. 1 / 2 14.5 MPa 1 / 2 14.8 MPa 1 / 2 15.2 MPa 1 / 2 15.4 MPa 1 / 2 15.9 MPa 1 / 2 16.2 MPa 1 / 2 16.3 MPa 1 / 2 16.4 MPa 1 / 2 16.6 MPa 1 / 2 16.8 MPa 1 / 2 17.1 MPa 1 / 2 17.5 MPa1 / 2 18.0 MPa 1 / 2 18.2 MPa 1 / 2 18.5 MPa 1 / 2 19.2 MPa 1 / 2 19.5 MPa 1 / 2 20.0MPa 1 / 2 Or the range between any two of the aforementioned.

[0189] According to some embodiments of this application, optionally, the absolute value of the difference in solubility parameters between the first adhesive and the first solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 And / or, the absolute value of the difference in solubility parameters between the second adhesive and the second solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 And / or, the absolute value of the difference in solubility parameters between the first solvent and the second solvent at 25°C is less than or equal to 1.5 MPa. 1 / 2 .

[0190] The absolute value of the difference in solubility parameters between the first binder and the first solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 The first binder and the first solvent have similar polarities and intermolecular forces, allowing for better compatibility. This results in more uniform dispersion of the first binder in the first solvent, improving coating quality and enabling the first binder to form a uniform and stable coating film during coating. This enhances the structural stability of the electrode, thereby improving battery stability and cycle life. The absolute value of the solubility parameter difference between the second binder and the second solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 The second binder and the second solvent have similar polarities and intermolecular forces, allowing for better compatibility. This results in more uniform dispersion of the second binder in the second solvent, improving coating quality and enabling the second binder to form a uniform and stable coating film during the coating process. This enhances the structural stability of the electrode, thereby improving battery stability and cycle life. The absolute value of the difference in solubility parameters between the first and second solvents at 25°C is less than or equal to 1.5 MPa. 1 / 2 The first and second solvents have similar polarities and intermolecular forces, making them easier to mix uniformly. This avoids uneven coating caused by differences in interfacial tension during the coating process. This not only improves coating quality but also significantly reduces the occurrence of false edges, enhancing battery consistency and stability.

[0191] As a non-limiting example, the absolute value of the difference in solubility parameters between the first adhesive and the first solvent at 25°C includes, but is not limited to, 0.1 MPa. 1 / 2 0.2 MPa 1 / 2 0.3 MPa1 / 2 0.4 MPa 1 / 2 0.5 MPa 1 / 2 0.6 MPa 1 / 2 0.7MPa 1 / 2 0.8 MPa 1 / 2 0.9 MPa 1 / 2 1.0 MPa 1 / 2 1.1 MPa 1 / 2 1.2 MPa 1 / 2 1.3 MPa 1 / 2 1.4 MPa 1 / 2 1.5MPa 1 / 2 2.0 MPa 1 / 2 2.5 MPa 1 / 2 Or the range between any two of the aforementioned.

[0192] As a non-limiting example, the absolute value of the difference in solubility parameters between the second adhesive and the second solvent at 25°C includes, but is not limited to, 0.1 MPa. 1 / 2 0.2 MPa 1 / 2 0.3 MPa 1 / 2 0.4 MPa 1 / 2 0.5 MPa 1 / 2 0.6 MPa 1 / 2 0.7MPa 1 / 2 0.8 MPa 1 / 2 0.9 MPa 1 / 2 1.0 MPa 1 / 2 1.1 MPa 1 / 2 1.2 MPa 1 / 2 1.3 MPa 1 / 2 1.4 MPa 1 / 2 1.5MPa 1 / 2 2.0 MPa 1 / 2 2.5 MPa 1 / 2 Or the range between any two of the aforementioned.

[0193] As a non-limiting example, the absolute value of the difference in solubility parameters between the first solvent and the second solvent at 25°C includes, but is not limited to, 0.1 MPa. 1 / 2 0.2 MPa 1 / 2 0.3 MPa 1 / 2 0.4 MPa 1 / 2 0.5 MPa 1 / 2 0.6 MPa 1 / 2 0.7 MPa 1 / 2 0.8 MPa 1 / 20.9 MPa 1 / 2 1.0 MPa 1 / 2 1.1 MPa 1 / 2 1.2 MPa 1 / 2 1.3 MPa 1 / 2 1.4 MPa 1 / 2 1.5MPa 1 / 2 Or the range between any two of the aforementioned.

[0194] According to some embodiments of this application, optionally, the second binder includes a first polymer and a second polymer; the first polymer includes a first group, and the molar fraction of the first group is 0% to 50% based on the total molar amount of the first polymer; the second polymer includes a second group, and the molar fraction of the second group is 2% to 40% based on the total molar amount of the second polymer; the weight-average molecular weight of the first polymer is 100 kDa to 600 kDa, and the weight-average molecular weight of the second polymer is 10 kDa to 300 kDa; wherein the first group and the second group each independently include at least one of a benzene ring, a cyano group, a maleic anhydride, a carboxyl group, or an amide group; the step of dissolving the second binder in a second solvent to obtain a first solution includes: mixing the first polymer and the second polymer and then dissolving them in the second solvent to obtain the first solution.

[0195] By rationally designing the composition and structural characteristics of the second binder, the processing and bonding properties of the edge coating slurry were optimized. The second binder comprises a first polymer and a second polymer, each possessing specific functional groups, their molar fractions, and weight-average molecular weights. The molar fractions of the first and second functional groups are within the aforementioned range. Both the first and second functional groups are polar groups, which can improve the cohesive properties between polymers and reduce powder shedding; simultaneously, they can enhance the interaction force between the polymer's positive electrode current collector, thereby improving the bonding performance of the edge coating. Furthermore, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. When the weight-average molecular weights of the first and second polymers are within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first and second polymers can be enhanced, resulting in more uniform dispersion of the first and second polymers in the edge coating slurry. This facilitates contact between the first and second functional groups and the functional groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between functional groups, thereby improving the bonding force between the components of the edge coating slurry and enhancing its adhesion performance. Through the rational design of molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, significantly enhancing battery stability and cycle life.

[0196] Based on the total molar amount of the first polymer, the molar fraction of the first group includes, but is not limited to: 0%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, or any range between the two for the foregoing.

[0197] Based on the total molar amount of the second polymer, the molar fraction of the second group includes, but is not limited to, 2%, 10%, 20%, 30%, 40%, or any range between the two mentioned above.

[0198] The weight-average molecular weight of the first polymer includes, but is not limited to, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 600 kDa, or a range between the two aforementioned. The weight-average molecular weight of the second polymer includes, but is not limited to, 10 kDa, 50 kDa, 80 kDa, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, or a range between the two aforementioned.

[0199] Methods for testing the mole fraction of the first and second functional groups:

[0200] The first polymer was dissolved in deuterated chloroform and subjected to 1H NMR analysis. The characteristic peaks of the benzene ring appeared as sharp peaks at 6.2 ppm–6.8 ppm and / or 7.0 ppm–7.2 ppm; the characteristic peak of the methylene group attached to the cyano group appeared at 3.0 ppm–3.5 ppm; the characteristic peaks of the two methylene groups attached to maleic anhydride appeared at 2.5 ppm–3.2 ppm; the characteristic peak of the carboxyl group appeared at 10 ppm–13 ppm; and the characteristic peak of the amide group appeared as a broad peak at 6.0 ppm–7.5 ppm. The mole fraction of the corresponding first functional group could be calculated by the ratio of the integrated areas of each peak. Similarly, the mole fraction of the second functional group could be obtained by dissolving the second polymer in deuterated chloroform and performing 1H NMR analysis.

[0201] Methods for testing the weight-average molecular weight of the first and second polymers:

[0202] The first polymer was dissolved in tetrahydrofuran, dichloromethane, toluene, or ethyl acetate, and its molecular weight was determined by gel permeation chromatography. Similarly, the second polymer was dissolved in tetrahydrofuran, dichloromethane, toluene, or ethyl acetate, and its molecular weight was determined by gel permeation chromatography.

[0203] According to some embodiments of this application, optionally, the first polymer includes at least one of a first hydrogenated polymer containing styrene units and / or acrylonitrile units, a polyolefin polymer, and an acrylic-ethylene polymer; and / or the second polymer includes at least one of a second hydrogenated polymer containing styrene units and / or acrylonitrile units, a second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, and a copolymer of polypropylene or polyethylene with maleic anhydride.

[0204] By selecting at least one of the following as the first polymer: a first hydrogenated polymer containing styrene and / or acrylonitrile units, a polyolefin polymer, or an acrylic-ethylene polymer, and at least one of the following as the second polymer: a second hydrogenated polymer containing styrene and / or acrylonitrile units, a second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, or a copolymer of polypropylene or polyethylene with maleic anhydride, the polarity and adhesion properties of the second binder can be effectively optimized. Specifically, the use of hydrogenated polymers can reduce the unsaturation of the material, increase the number of saturated bonds, and thus improve the chemical stability and durability of the polymer. Introducing polar units or groups such as styrene, acrylonitrile, acrylic acid, maleic anhydride, and acrylamide can improve the cohesive properties between polymers, reduce powder shedding, and increase the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion properties of the edge coating. Simultaneously, these polar groups can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating.

[0205] According to some embodiments of this application, optionally, the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer and the second hydrogenated polymer is 10% to 40%, and the degree of hydrogenation of the first hydrogenated polymer and the second hydrogenated polymer is ≥80% and <100%.

[0206] By limiting the molar fraction of styrene and / or acrylonitrile units in the first and second polymers to 10%–40%, and recognizing that styrene and acrylonitrile units are polar units, this improves the cohesiveness between polymers, reduces powder shedding, and enhances the interaction force between the polymer and the positive electrode current collector, thereby improving the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with it, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, limiting the degree of hydrogenation reduces the unsaturation of the material, increasing the number of saturated bonds, thereby improving the chemical stability and durability of the polymer. Through the rational design of the molar fraction of polar units and the degree of hydrogenation, the coating uniformity and adhesion of the edge coating can be further improved, significantly enhancing the battery's stability and cycle life.

[0207] As a non-limiting example, the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer and the second hydrogenated polymer includes, but is not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any range between the foregoing.

[0208] As a non-limiting example, the degree of hydrogenation of the first hydrogenated polymer includes, but is not limited to: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range between the foregoing.

[0209] As a non-limiting example, the degree of hydrogenation of the second hydrogenated polymer includes, but is not limited to: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range between the foregoing.

[0210] Test methods for the molar fraction of styrene units and / or acrylonitrile units in the first and second hydrogenated polymers:

[0211] The first hydrogenated polymer was dissolved in deuterated chloroform and subjected to 1H NMR analysis. The characteristic peaks of the benzene ring appeared at 6.2 ppm–6.8 ppm and / or 7.0 ppm–7.2 ppm, while the characteristic peak of the methylene group linked to the cyano group appeared at 3.0 ppm–3.5 ppm. The molar fractions of styrene and acrylonitrile could be calculated by the ratio of the integrated areas of each peak, thus yielding the molar fractions of styrene and / or acrylonitrile units in the first hydrogenated polymer. Similarly, the molar fractions of styrene and / or acrylonitrile units in the second hydrogenated polymer could be obtained by dissolving the second hydrogenated polymer in deuterated chloroform and performing 1H NMR analysis.

[0212] Test methods for the degree of hydrogenation of the first and second hydrogenated polymers:

[0213] The degree of unsaturation of hydrogenated polymers is tested using the iodine value method. This involves an addition reaction between the unsaturated bonds in the first hydrogenated polymer and the Widmanstätten reagent (iodine chloride dissolved in acetic acid). The double bond content per 100g of the first hydrogenated polymer is calculated based on the amount of iodine consumed. The degree of hydrogenation of the first hydrogenated polymer is then calculated using the formula: (Double bond content before hydrogenation - Double bond content after hydrogenation) / Double bond content before hydrogenation. The double bond content before hydrogenation can be calculated based on the repeating unit structure of the original polymer. For example, in hydrogenated polystyrene-butadiene, the original polymer is a styrene-butadiene copolymer (the molar ratio of styrene to butadiene is m:n). Styrene units have no double bonds, while butadiene units each contain one double bond. First, the butadiene molar fraction f(butadiene) = n / (m+n) is calculated. Then, combining this with the molecular weight of the repeating units of the copolymer (M = (m×10⁴ + n×5⁴) / (m+n), where 10⁴ and 5⁴ are the molecular weights of styrene and butadiene, respectively), the double bond content before hydrogenation is calculated as f(butadiene) × 100 / M. Similarly, the degree of hydrogenation of the second hydrogenated polymer can be obtained by reacting the unsaturated bonds in the second hydrogenated polymer with the Widmanstätten reagent (iodine chloride dissolved in acetic acid).

[0214] According to some embodiments of this application, optionally, the mass ratio of the first polymer to the second polymer is (2%~10%):(5%~18%), and / or, the mass ratio of the second binder to the inorganic ceramic filler is (15%~20%):(80%~85%).

[0215] By limiting the mass ratio of the first polymer to the second polymer to (2%~10%):(5%~18%), the adhesive performance of the binder can be optimized while ensuring the viscosity of the edge coating slurry. Within this range, the ratio of the first polymer to the second polymer ensures sufficient viscosity to support the uniform distribution of the active material without affecting the uniformity of the coating due to excessive viscosity. Simultaneously, this ratio effectively balances the cohesive and adhesive forces of the binder, thereby further improving the bonding strength and density of the edge coating and reducing the occurrence of false edges. Furthermore, this ratio optimizes the processing performance of the binder, thereby improving the stability and efficiency of the coating process. By limiting the ratio of inorganic ceramic filler to the second binder in the edge coating to the above range, sufficient mechanical strength and chemical stability of the edge coating can be ensured, as well as its adhesive and insulating properties.

[0216] As a non-limiting example, the mass ratio of the first polymer to the second polymer includes, but is not limited to, 2%:18%, 2%:10%, 2%:5%, 10%:18%, 10%:11%, 10%:5%, or any two of the foregoing; and the mass ratio of the second binder to the inorganic ceramic filler in the edge coating includes, but is not limited to, 15%:80%, 15%:85%, 20%:80%, 20%:85%, or any two of the foregoing.

[0217] The mass ratio of the first polymer to the second polymer and the mass ratio of the second binder to the inorganic ceramic filler can be obtained by weighing before preparing the edge coating slurry.

[0218] According to some embodiments of this application, optionally, the first hydrogenated polymer and the second hydrogenated polymer each independently include at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers.

[0219] By selecting at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers as the first and second polymers, the cohesive properties between the polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, the use of hydrogenated polymers can reduce the unsaturation of the material, increasing the number of saturated bonds, thereby improving the chemical stability and durability of the polymer, ultimately significantly improving battery stability and cycle life.

[0220] According to some embodiments of this application, optionally, the hydrogenated polystyrene polymers include at least one of hydrogenated polystyrene-butadiene (SEB), hydrogenated polystyrene-isoprene (SEP), hydrogenated polystyrene-butadiene-isoprene (SEEP), hydrogenated polystyrene-butadiene-styrene (SEBS), hydrogenated polystyrene-isoprene-styrene (SEPS), and hydrogenated polystyrene-butadiene-isoprene-styrene (SEEPS); the hydrogenated polyacrylonitrile polymers include at least one of hydrogenated polyacrylonitrile-butadiene-isoprene, hydrogenated polyacrylonitrile-isoprene, and hydrogenated polyacrylonitrile-butadiene (HNBR); and the hydrogenated polystyrene-acrylonitrile polymers include at least one of hydrogenated polystyrene-acrylonitrile-butadiene, hydrogenated polystyrene-acrylonitrile-isoprene, and hydrogenated polystyrene-acrylonitrile-butadiene-isoprene.

[0221] By selecting at least one of the aforementioned hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers, the cohesive properties between polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. In addition, using hydrogenated polymers can reduce the unsaturation degree of the material, increase the number of saturated bonds, improve the chemical stability and durability of the polymer, and ultimately significantly improve battery stability and cycle life.

[0222] According to some embodiments of this application, optionally, the polyolefin polymer includes at least one of binary or ternary ethylene propylene diene monomer (EPDM), polyisobutylene (PIB), cyclic polyolefin (COC / COP), and copolymers thereof.

[0223] By selecting at least one of binary or ternary ethylene propylene diene monomer (EPDM), polyisobutylene, cyclic polyolefins, and their copolymers as the polyolefin polymer, the ultra-high molecular weight can increase the viscosity of the solution, thereby improving the stability of the slurry. Simultaneously, it can enhance the interaction force between the polymer and the positive electrode current collector, thus improving the adhesion performance of the edge coating. Furthermore, using polyolefin polymers can reduce the unsaturation of the material, increase the number of saturated bonds, and improve the chemical stability and durability of the polymer, ultimately significantly improving battery stability and cycle life.

[0224] In the technical solution of this application, the polyolefin polymer includes at least one of binary or ternary ethylene propylene diene monomer (EPDM) rubber, polyisobutylene, cyclic polyolefins, and copolymers of one or more of binary or ternary EPDM rubber, polyisobutylene, and cyclic polyolefins.

[0225] According to some embodiments of this application, optionally, the weight-average molecular weight of the first hydrogenated polymer is 100kDa to 600kDa, and the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer is 10% to 40%; and / or the weight-average molecular weight of the polyolefin polymer is 100kDa to 600kDa; and / or the weight-average molecular weight of the acrylic-ethylene polymer is 100kDa to 300kDa, and the molar fraction of acrylic units in the acrylic-ethylene polymer is 5% to 20%.

[0226] By limiting the weight-average molecular weight of the first hydrogenated polymer to 100 kDa to 600 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer be 10% to 40%; limiting the weight-average molecular weight of the polyolefin polymer to 100 kDa to 600 kDa; and limiting the weight-average molecular weight of the acrylic-ethylene polymer to 100 kDa to 300 kDa, and requiring that the molar fraction of acrylic units in the acrylic-ethylene polymer be 5% to 20%, the performance of the binder can be further optimized. Styrene and acrylonitrile units are polar units. By limiting the molar fraction of styrene and / or acrylonitrile units within the above ranges, the cohesive properties between polymers can be improved, reducing powder shedding; simultaneously, the interaction force between the polymer and the positive electrode current collector can be increased, thereby improving the adhesion performance of the edge coating; furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with the inorganic ceramic filler, thereby promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. By limiting the weight-average molecular weights of the first hydrogenated polymer, the polyolefin polymer, and the acrylic-ethylene polymer to within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first polymer can be enhanced, resulting in more uniform dispersion of the first polymer in the edge coating slurry. This facilitates contact between the first polymer and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between the groups, thereby improving the bonding force between the components of the edge coating slurry and enhancing its adhesion performance. Through the rational design of molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, significantly enhancing battery stability and cycle life.

[0227] As a non-limiting example, the weight-average molecular weight of the first hydrogenated polymer includes, but is not limited to, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 600 kDa, or any range between the two for the foregoing.

[0228] As a non-limiting example, in the first hydrogenated polymer, the molar fraction of styrene units and / or acrylonitrile units includes, but is not limited to: 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any range between the foregoing.

[0229] As a non-limiting example, the weight-average molecular weight of polyolefin polymers includes, but is not limited to: 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 350 kDa, 400 kDa, 450 kDa, 500 kDa, 600 kDa, or any range between the two for the foregoing.

[0230] As a non-limiting example, the weight-average molecular weight of the acrylate-ethylene polymer includes, but is not limited to, 100 kDa, 120 kDa, 180 kDa, 250 kDa, 290 kDa, 300 kDa, or any range between the two for the foregoing.

[0231] As a non-limiting example, in acrylic-ethylene polymers, the molar fraction of acrylic units includes, but is not limited to, 5%, 8%, 12%, 13%, 14%, 15%, 16%, 18%, 20%, or any range between the foregoing.

[0232] Methods for determining the weight-average molecular weight of first hydrogenated polymers, polyolefin polymers, and acrylate-ethylene polymers:

[0233] The first hydrogenated polymer was dissolved in tetrahydrofuran, dichloromethane, toluene, or ethyl acetate, and its molecular weight was determined by gel permeation chromatography. Similarly, the molecular weight of the polyolefin polymer or the ethylene acrylic acid polymer was determined by gel permeation chromatography after dissolving it in tetrahydrofuran, dichloromethane, toluene, or ethyl acetate.

[0234] Test method for the molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer:

[0235] The first hydrogenated polymer was dissolved in deuterated chloroform and subjected to 1H NMR analysis. The characteristic peaks of the benzene ring appeared at 6.2 ppm–6.8 ppm and / or 7.0 ppm–7.2 ppm, while the characteristic peak of the methylene group linked to the cyano group appeared at 3.0 ppm–3.5 ppm. The molar fractions of styrene and acrylonitrile could be calculated by the ratio of the integrated areas of each peak, thus yielding the molar fractions of styrene and / or acrylonitrile units in the first hydrogenated polymer.

[0236] Methods for testing the molar fraction of acrylic acid units in acrylic acid-ethylene polymers:

[0237] The acrylic-ethylene polymer was dissolved in deuterated chloroform and subjected to 1H NMR analysis. The characteristic peak of the carboxyl group appeared in the range of 10 ppm to 13 ppm. The molar fraction of acrylic units could be calculated by integrating the area.

[0238] According to some embodiments of this application, optionally, the weight-average molecular weight of the second hydrogenated polymer is 10 kDa to 100 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer is 10% to 40%; and / or the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified based on maleic anhydride, acrylic acid, or acrylamide is 100 kDa to 300 kDa, and the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer containing styrene units modified based on maleic anhydride, acrylic acid, or acrylamide is 10% to 40%, and the molar fraction of maleic anhydride, acrylic acid, or acrylamide is 2% to 10%; and / or the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride is 50 kDa to 200 kDa, and the molar fraction of maleic anhydride in the copolymer of polypropylene or polyethylene with maleic anhydride is 2% to 10%.

[0239] By limiting the weight-average molecular weight of the second hydrogenated polymer to 10 kDa to 100 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer be 10% to 40%; limiting the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide to 100 kDa to 300 kDa, and requiring that the molar fraction of styrene units and / or acrylonitrile units in the modified polymer be 10% to 40%, and the molar fraction of maleic anhydride, acrylic acid, or acrylamide be 2% to 10%; and limiting the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride to 50 kDa to 200 kDa, and requiring that the molar fraction of maleic anhydride in the copolymer be 2% to 10%, the performance of the binder can be further optimized. By limiting the molar fraction of styrene and / or acrylonitrile units within the aforementioned range, the cohesive properties between polymers can be improved, reducing powder shedding. Simultaneously, the interaction force between the polymer positive electrode current collectors can be increased, thereby enhancing the adhesion of the edge coating. Furthermore, these polar units can form van der Waals forces with the inorganic ceramic filler, enabling better wetting and bonding with it, thus promoting the dispersion stability and uniformity of inorganic particles and achieving the insulating properties of the edge coating. The introduction of acrylic acid, maleic anhydride, and acrylamide further enhances the cohesive and adhesive properties. By ensuring the weight-average molecular weight of the aforementioned polymers is within the aforementioned range, the probability of gelation in the edge coating slurry can be reduced, viscosity rebound can be weakened, and processing difficulty can be decreased. Simultaneously, the suspension properties of the first polymer can be enhanced, resulting in more uniform dispersion of the first polymer in the edge coating slurry. This facilitates contact between the first polymer and the groups on the surface of the inorganic ceramic filler in the edge coating slurry, promoting the full utilization of van der Waals forces between groups, thereby improving the bonding force between the components of the edge coating slurry and ultimately enhancing its adhesion. By rationally designing the molecular weight and mole fraction, the coating uniformity and adhesion performance of the edge coating can be effectively improved, thereby significantly enhancing battery stability and cycle life.

[0240] As a non-limiting example, the weight-average molecular weight of the second hydrogenated polymer includes, but is not limited to, 10 kDa, 20 kDa, 30 kDa, 50 kDa, 55 kDa, 60 kDa, 70 kDa, 80 kDa, 90 kDa, 100 kDa, or any two of the foregoing; as a non-limiting example, the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer includes, but is not limited to, 10%, 20%, 30%, 40%, or any two of the foregoing.

[0241] As a non-limiting example, the weight-average molecular weight of the second hydrogenated polymer containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide includes, but is not limited to, 100 kDa, 120 kDa, 130 kDa, 150 kDa, 200 kDa, 260 kDa, 270 kDa, 280 kDa, 290 kDa, 300 kDa, or any two of the foregoing; in the second hydrogenated polymer containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide, the molar fraction of styrene units and / or acrylonitrile units includes, but is not limited to, 10%, 14%, 15%, 18%, 20%, 24%, 26%, 30%, 31%, 32%, 33%, 35%, 40%, or any two of the foregoing; and the molar fraction of maleic anhydride, acrylic acid, or acrylamide includes, but is not limited to, 2%, 4%, 5%, 7%, 8%, 9%, 10%, or any two of the foregoing.

[0242] As a non-limiting example, the weight-average molecular weight of the copolymer of polypropylene or polyethylene with maleic anhydride includes, but is not limited to, 50 kDa, 80 kDa, 100 kDa, 120 kDa, 150 kDa, 160 kDa, 180 kDa, 200 kDa or any two of the foregoing, and the molar fraction of maleic anhydride in the copolymer of polypropylene or polyethylene with maleic anhydride includes, but is not limited to, 2%, 4%, 5%, 7%, 8%, 9%, 10% or any two of the foregoing.

[0243] The second hydrogenated polymer containing styrene units, modified with maleic anhydride, acrylic acid, or acrylamide, may include at least one of the following: maleic anhydride-modified hydrogenated polystyrene-isoprene-styrene (SEBS-maleic anhydride); acrylamide-modified hydrogenated polystyrene-butadiene-isoprene-styrene (SEEPS-acrylamide); acrylic acid-modified hydrogenated polystyrene-isoprene-styrene (SEPS-acrylic acid); and maleic anhydride-modified hydrogenated polystyrene-isoprene (SEP-maleic anhydride). The copolymer of polypropylene or polyethylene with maleic anhydride may include at least one of the following: a copolymer of polypropylene with maleic anhydride (PP-maleic anhydride) or a copolymer of polyethylene with maleic anhydride (PE-maleic anhydride).

[0244] Methods for determining the weight-average molecular weight of second hydrogenated polymers, second hydrogenated polymers containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide, and copolymers of polypropylene or polyethylene with maleic anhydride:

[0245] The second hydrogenated polymer was dissolved in tetrahydrofuran, dichloromethane, toluene, or ethyl acetate, and its weight-average molecular weight was determined by gel permeation chromatography. Similarly, the weight-average molecular weight of the second hydrogenated polymer containing styrene units, modified with maleic anhydride, acrylic acid, or acrylamide, or the copolymer of polypropylene or polyethylene with maleic anhydride, was determined by gel permeation chromatography in tetrahydrofuran, dichloromethane, toluene, or ethyl acetate.

[0246] Test method for the molar fraction of styrene units and / or acrylonitrile units in the second hydrogenated polymer:

[0247] The second hydrogenated polymer was dissolved in deuterated chloroform and subjected to 1H NMR analysis. The characteristic peaks of the benzene ring appeared at 6.2 ppm–6.8 ppm and / or 7.0 ppm–7.2 ppm, while the characteristic peak of the methylene group linked to the cyano group appeared at 3.0 ppm–3.5 ppm. The molar fractions of styrene and acrylonitrile could be calculated by the ratio of the integrated areas of each peak, thus yielding the molar fractions of styrene and / or acrylonitrile units in the second hydrogenated polymer.

[0248] Test method for the molar fraction of styrene units, maleic anhydride, acrylic acid, or acrylamide in second hydrogenated polymers containing styrene units modified with maleic anhydride, acrylic acid, or acrylamide:

[0249] A second hydrogenated polymer containing styrene units, modified with maleic anhydride, acrylic acid, or acrylamide, was dissolved in deuterated chloroform and subjected to 1H NMR analysis. The characteristic peaks of the benzene ring appeared as sharp peaks at 6.2 ppm–6.8 ppm and / or 7.0 ppm–7.2 ppm; the characteristic peaks of the two methylene groups linked to maleic anhydride appeared at 2.5 ppm–3.2 ppm; the characteristic peak of the carboxyl group appeared at 10 ppm–13 ppm; and the characteristic peak of the amide group appeared as broad peaks at 6.0 ppm–7.5 ppm. The molar fractions of styrene units, maleic anhydride, acrylic acid, or acrylamide could be calculated by the ratio of the integrated areas of each peak.

[0250] Test method for the mole fraction of maleic anhydride in copolymers of polypropylene or polyethylene and maleic anhydride:

[0251] A copolymer of polypropylene or polyethylene and maleic anhydride was dissolved in deuterated chloroform and subjected to 1H NMR analysis. The two methylene characteristic peaks linked to maleic anhydride appeared in the range of 2.5 ppm to 3.2 ppm. The mole fraction of maleic anhydride could be calculated from the integrated area.

[0252] According to some embodiments of this application, optionally, the edge coating also includes a light absorber, including titanium dioxide, carbon black and graphite, and the mass fraction of the light absorber in the edge coating is 0.1% to 1.0%.

[0253] By adding a light absorber to the edge coating and limiting the mass fraction of the light absorber to 0.1%~1.0%, the reflection on the surface of the edge coating can be effectively reduced, thereby improving the absorption capacity of the edge coating. This can further optimize the process window of laser die-cutting and improve the processing performance of the edge coating.

[0254] As a non-limiting example, the mass fraction of the light absorber in the edge coating includes, but is not limited to: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any range between the foregoing.

[0255] In addition, the secondary battery 5, battery module 4, battery pack 1 and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0256] In one embodiment of this application, a secondary battery 5 is provided.

[0257] Typically, a secondary battery 5 includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0258] [Positive electrode plate]

[0259] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0260] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0261] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0262] In some embodiments, when the secondary battery 5 is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0263] In some embodiments, when the secondary battery 5 is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, in the sodium transition metal oxide, the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, and Ce. Examples of sodium transition metal oxides include Na... x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1. Examples of polyanionic compounds may include, but are not limited to, compounds containing sodium ions, transition metal ions, and tetrahedral (YO4). n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state. Examples of polyanionic compounds may include, but are not limited to, compounds with sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- Valence state: The halogen can be at least one of F, Cl, and Br. Examples of polyanionic compounds include, but are not limited to, compounds with sodium ions, tetrahedral (YO4) valence. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- Valence state: Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ Valence state: The halogen can be at least one of F, Cl, and Br. Examples of polyanionic compounds include, but are not limited to, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni), and Na3(VO4). y )2(PO4)2F 3-2yAt least one of (0≤y≤1). Examples of Prussian blue compounds may include, but are not limited to, compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds containing Prussian blue. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include, but are not limited to, Na. a Me b Me ’ c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0264] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyisobutylene, hydrogenated styrene-butadiene rubber, hydrogenated nitrile rubber, maleic anhydride-grafted modified hydrogenated styrene-butadiene rubber, hydrogenated styrene-butadiene-styrene polymer, and hydrogenated styrene-isoprene-styrene polymer.

[0265] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0266] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., pseudotrimethylbenzene) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0267] In some embodiments, when the secondary battery 5 is a solid-state battery, the positive electrode active material may be a positive electrode active material known in the art for solid-state batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0268] In some embodiments, the positive electrode film further includes a solid electrolyte, which includes one or more of halide electrolytes, sulfide electrolytes, and oxide electrolytes, such as Li3YCl6 (lithium yttrium chloride), Li3YBr6 (lithium yttrium bromide), Li2ZrCl6 (lithium zirconium chloride), Li6PS5Cl (lithium phosphine sulfide), and Li... 10 GeP2S 12 (Germ, Phosphorus, Sulfur, Lithium), Li7P3S 11 (Lithium phosphate, sulfur, and phosphorus), Li7La3Zr2O 12 (Lanium zirconium lithium oxide, LLZO), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (aluminum titanium phosphate lithium oxide, LATP), Li 1.5 Al 0.5 Ge 1.5 (PO4)3 (aluminum germanium phosphorus lithium oxide, LAGP), etc.

[0269] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyisobutylene, hydrogenated styrene-butadiene rubber, hydrogenated nitrile rubber, maleic anhydride-grafted modified hydrogenated styrene-butadiene rubber, hydrogenated styrene-butadiene-styrene polymer, and hydrogenated styrene-isoprene-styrene polymer.

[0270] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0271] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, solid electrolyte conductive agent, binder and any other components, in a solvent (e.g., pseudotrimethylbenzene) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0272] [Negative electrode plate]

[0273] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0274] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0275] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0276] In some embodiments, when the secondary battery 5 is a sodium-ion battery or a lithium-ion battery, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0277] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0278] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0279] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0280] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0281] In some embodiments, when the secondary battery 5 is a solid-state battery, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0282] In some embodiments, the negative electrode film further includes a solid electrolyte, which includes one or more of halide electrolytes, sulfide electrolytes, and oxide electrolytes, such as Li3YCl6 (lithium yttrium chloride), Li3YBr6 (lithium yttrium bromide), Li2ZrCl6 (lithium zirconium chloride), Li6PS5Cl (lithium phosphine sulfide), and Li... 10 GeP2S 12 (Germ, Phosphorus, Sulfur, Lithium), Li7P3S 11 (Lithium phosphate, sulfur, and phosphorus), Li7La3Zr2O 12 (Lanium zirconium lithium oxide, LLZO), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (aluminum titanium phosphate lithium oxide, LATP), Li 1.5 Al0.5 Ge 1.5 (PO4)3 (aluminum germanium phosphorus lithium oxide, LAGP), etc.

[0283] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may include at least one of polyisobutylene, hydrogenated styrene-butadiene rubber, hydrogenated nitrile rubber, maleic anhydride-grafted modified hydrogenated styrene-butadiene rubber, hydrogenated styrene-butadiene-styrene polymer, and hydrogenated styrene-isoprene-styrene polymer.

[0284] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0285] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0286] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as negative electrode active material, solid electrolyte, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0287] [Electrolytes]

[0288] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0289] In some embodiments, when the secondary battery 5 is a lithium-ion battery, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0290] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0291] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0292] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0293] In some embodiments, when the secondary battery 5 is a sodium-ion battery, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. In some embodiments, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0294] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, tetrahydrofuran, sulfolane, ethylene glycol dimethyl ether, and dimethoxyethane.

[0295] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0296] In some embodiments, when the secondary battery 5 is a solid-state battery, the electrolyte is a solid-state electrolyte membrane. The solid-state electrolyte membrane includes a solid electrolyte and a binder. The solid electrolyte includes one or more of halide electrolytes, sulfide electrolytes, and oxide electrolytes, such as Li3YCl6 (lithium yttrium chloride), Li3YBr6 (lithium yttrium bromide), Li2ZrCl6 (lithium zirconium chloride), Li6PS5Cl (lithium phosphine sulfide), and Li... 10 GeP2S 12 (Germ, Phosphorus, Sulfur, Lithium), Li7P3S 11 (Lithium phosphate, sulfur, and phosphorus), Li7La3Zr2O 12 (Lanium zirconium lithium oxide, LLZO), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (aluminum titanium phosphate lithium oxide, LATP), Li 1.5 Al 0.5 Ge1.5 (PO4)3 (aluminum germanium phosphorus lithium oxide, LAGP), etc. Adhesives include one or more of the following: styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber (HSBR), hydrogenated styrene-ethylene-butene-benzene copolymer (SEBS), nitrile rubber (NBR), and hydrogenated nitrile rubber (HNBR).

[0297] [Isolation membrane]

[0298] In some embodiments, when the secondary battery 5 is a lithium-ion battery or a sodium-ion battery, the secondary battery 5 also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0299] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0300] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into electrode assembly 52 by a winding process or a stacking process.

[0301] In some embodiments, the secondary battery 5 may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly 52 and the electrolyte described above.

[0302] In some embodiments, the outer packaging of the secondary battery 5 can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery 5 can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0303] This application does not impose any particular limitation on the shape of the secondary battery 5; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0304] In some implementations, refer to Figure 4The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0305] In some embodiments, the secondary battery 5 can be assembled into a battery module 4, and the number of secondary batteries 5 contained in the battery module 4 can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module 4.

[0306] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0307] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0308] In some embodiments, the battery module 4 can also be assembled into a battery pack 1. The battery pack 1 may contain one or more battery modules 4, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack 1.

[0309] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0310] In addition, this application also provides an electrical device, which includes at least one of the secondary battery 5, battery module 4, or battery pack 1 provided in this application. The secondary battery 5, battery module 4, or battery pack 1 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0311] As the electrical device, a secondary battery 5, a battery module 4, or a battery pack 1 can be selected according to its usage requirements.

[0312] Figure 8 This is an example of an electrical device. The device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery 5, a battery pack 1 or a battery module 4 can be used.

[0313] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0314] Example

[0315] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0316] Example 1

[0317] (1) Preparation of positive electrode sheet:

[0318] (1a) Obtain the positive current collector aluminum foil with a thickness of 13 μm.

[0319] (1b) Preparation of active material slurry: Sodium iron phosphate, conductive agent SuperP, and hydrogenated styrene-butadiene rubber (SBR) were mixed in a weight ratio of 95.5:2:2.5. Tris(II)-methylbenzene was added as a solvent, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 60 wt%. The positive electrode slurry was then mixed at a concentration of 300 mg / 1540.25 mm. 2 The amount of material used is evenly coated onto an aluminum foil current collector to obtain a positive electrode film layer. After drying and cold pressing, a positive electrode sheet is obtained, with a compaction density of 1.9 g / cm³.3 .

[0320] (1c) Preparation of edge coating slurry: The first polymer, hydrogenated polystyrene-butadiene-isoprene-styrene (SEEPS), and the second polymer, a copolymer of polypropylene and maleic anhydride (PP-maleic anhydride), are mixed and the solvent oil, pseudotrimethylbenzene, is added to obtain a solution with a mass fraction of 7%. Then, the inorganic ceramic filler, boehmite, is added and mixed to obtain the edge coating slurry. The mass ratio of the first polymer, the second polymer and the inorganic ceramic filler is 5:10:85, and the solid content of the edge coating slurry is 30wt%.

[0321] (1d) The active material layer slurry and the edge coating slurry are simultaneously and uniformly coated on the positive current collector aluminum foil, and then dried, cold pressed and cut to obtain the positive electrode sheet.

[0322] (2) Preparation of negative electrode sheet:

[0323] (2a) Obtain a copper foil for the negative electrode current collector with a thickness of 6 μm.

[0324] (2b) Hard carbon, conductive carbon black, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) thickener were mixed evenly in a weight percentage ratio of 95:1.0:2.0:2.0, and deionized water was added. After stirring and dispersing, a negative electrode slurry was obtained. The negative electrode slurry was then mixed at 211 mg / 1540 mm. 2 The negative electrode sheet is obtained by coating the copper foil substrate, drying, cold pressing, slitting, and sheet forming.

[0325] (3) Preparation of the separating membrane:

[0326] A porous polyethylene (PE) polymer film with a thickness of 12 μm was used as the separator.

[0327] (4) Preparation of electrolyte:

[0328] The fully dried sodium salt NaPF6 was dissolved in diethylene glycol dimethyl ether to prepare an electrolyte with a NaPF6 concentration of 1 mol / L.

[0329] (5) Assembly:

[0330] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound to obtain a bare cell. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing.

[0331] After the above steps (1) to (5), a sodium-ion battery is obtained.

[0332] Example 2

[0333] Example 2 is similar to Example 1 in the steps of preparing sodium-ion batteries. The difference is that in step (1c), after obtaining a solution with a mass fraction of 7%, inorganic ceramic filler boehmite and light absorber titanium dioxide are added and mixed to obtain a side coating slurry. The mass ratio of the first polymer, the second polymer, the inorganic ceramic filler and the light absorber is 3:12:84:1, and the solid content of the side coating slurry is 30wt%.

[0334] The remaining steps are the same as in Example 1.

[0335] Examples 3-10 are similar to Example 2; for differences, please refer to Tables 1-2.

[0336] Comparative Example 1 is similar to Example 2; for the differences, please refer to Tables 1-2.

[0337] Observe the positive electrode plates of Example 1 and Comparative Example 1, such as Figures 1-2 As shown, Figure 1 It is the positive electrode of the secondary battery in Example 1. Figure 2 This is the positive electrode of the secondary battery in Comparative Example 1. Figure 1 , Figure 2 The darker area on the right is the positive electrode active material layer, and the lighter area on the left is the edge coating layer. From Figures 1-2 It can be seen that there is no false edge between the active material layer and the edge coating layer of the positive electrode sheet in Example 1, while there is a clear false edge between the active material layer and the edge coating layer of the positive electrode sheet in Comparative Example 1. This indicates that the positive electrode sheet provided in this application achieves this effect by controlling the absolute value of the difference in solubility parameters between the first binder and the second binder at 25°C to be less than or equal to 1.5 MPa. 1 / 2 This can solve the problem of virtual edges in the coating process of the active material layer and edge coating of the positive electrode sheet.

[0338] The testing methods involved in this invention are as follows:

[0339] (1) Edge coating adhesion and cohesion test:

[0340] Instrument: Instron 3365 tensile testing machine.

[0341] Method: The cohesive and adhesive strength of the edge coating were tested using a universal testing machine with a 90° peel method.

[0342] Detailed steps for peel strength (adhesion): Fix the edge coating to the stainless steel sheet with double-sided tape, fix one end of the electrode with a clamp, and test the adhesion by peeling at 90°.

[0343] Detailed steps for film strength (cohesion): Fix the edge coating to the stainless steel sheet with double-sided tape, then apply adhesive to the edge coating. Fix one end of the tape on the upper surface of the electrode with a clamp and test the cohesion by peeling at 90°.

[0344] The greater the peel strength, the greater the film strength (cohesion) of the edge coating or the greater the adhesion to the film substrate (such as aluminum foil).

[0345] (3) Battery cycle life and stability test:

[0346] 1. Capacity retention rate after 500 cycles:

[0347] Test procedure: 45℃, 1C / 1C cycle, voltage range 2.5V~3.65V, capacity retention is measured after 500 cycles.

[0348] Detailed steps: At 45℃, charge the battery under test to 3.65V at a constant current of 1C, then charge it to the cutoff current of 0.05C at a constant voltage of 3.65V, let it rest for 10 minutes, and then discharge it to 2.5V at a constant current of 1C, let it rest for 5 minutes. This is one charge-discharge cycle. Record the discharge capacity at this time as C0.

[0349] Repeat this charge-discharge cycle process for the same battery and record the discharge capacity Cn for the 1st cycle, 2nd cycle, ..., nth cycle, where the number of cycles is 500.

[0350] Record the battery's cycle capacity retention rate after 500 cycles: P500 = C500 / C0 × 100%. The higher the capacity retention rate, the better the battery's cycle life.

[0351] 2. Storage capacity decay rate over 60 days:

[0352] Test procedure: 45℃, 1C / 1C cycle, voltage range 2.5V~3.65V, capacity retention is measured after 60 days of storage.

[0353] Detailed steps: At 45℃, charge the battery under test to 3.65V at a constant current of 1C, then charge it to the cutoff current of 0.05C at a constant voltage of 3.65V, let it rest for 10 minutes, and then discharge it to 2.5V at a constant current of 1C, let it rest for 5 minutes. This is one charge-discharge cycle. Record the discharge capacity at this time as C0.

[0354] After storing the battery for 60 days, repeat the above charge-discharge cycle and record the discharge capacity C60d. The capacity decay rate after 60 days of storage is calculated as (C0 - C60d) / C0 × 100%. The smaller the capacity decay rate, the better the battery stability.

[0355] Table 1 shows the process parameters and performance test data of the secondary batteries prepared in each embodiment and comparative example.

[0356]

[0357] Table 2 shows the composition of the first and second polymers in each embodiment and comparative example.

[0358]

[0359] As shown in Table 1, compared with Comparative Example 1, the capacity retention rate (500 cycles) of the secondary batteries in Examples 1-10 is higher than that in Comparative Example 1, and the storage capacity decay rate (60 days) of the secondary batteries in Examples 1-10 is lower than that in Comparative Example 1. This indicates that the stability and cycle life of the batteries in Examples 1-10 are superior to those in Comparative Example 1. The absolute value of the difference in solubility parameters between the first binder of the positive electrode active material layer and the second binder of the edge coating layer in the secondary batteries of Examples 1-10 is less than or equal to 1.5 MPa. 1 / 2 This indicates that by using the positive electrode sheet provided in this application, the problem of virtual edges in the coating process of the active material layer and the edge coating layer of the positive electrode sheet is solved, thereby improving the stability and cycle life of the battery.

[0360] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, comprising a positive electrode, said positive electrode comprising a current collector, an active material layer located on at least one surface of said current collector, and edge coatings located on both sides of the active material layer, characterized in that, The active material layer includes a positive electrode active material and a first binder, the edge coating layer includes an inorganic ceramic filler and a second binder, and an absolute value of a difference between solubility parameters of the first binder and the second binder at 25°C is greater than or equal to 0.1 MPa 1 / 2 and less than or equal to 1.5 MPa 1 / 2 ; The second adhesive comprises a first polymer and a second polymer, wherein the first polymer comprises at least one of a first hydrogenated polymer containing styrene units and / or acrylonitrile units, a polyolefin polymer, and an acrylic-ethylene polymer; and the second polymer comprises at least one of a second hydrogenated polymer containing styrene units and / or acrylonitrile units, the second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, and a copolymer of polypropylene or polyethylene with maleic anhydride.

2. The secondary battery according to claim 1, characterized in that, The solubility parameter of the second adhesive at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2 the following.

3. The secondary battery according to claim 1, characterized in that, The weight-average molecular weight of the first polymer is 100kDa to 600kDa, and the weight-average molecular weight of the second polymer is 10kDa to 300kDa.

4. The secondary battery according to claim 1, characterized in that, The first polymer includes a first group, the second polymer includes a second group, and the total molar fraction of the first group and the second group is 0% to 50% based on the total molar amount of the second binder, wherein the first group and the second group each independently include at least one of a benzene ring, a cyano group, a maleic anhydride, a carboxyl group, or an amide group.

5. The secondary battery according to claim 3, characterized in that, The first polymer includes a first group, the molar fraction of which is 0% to 50% based on the total molar amount of the first polymer; the second polymer includes a second group, the molar fraction of which is 2% to 40% based on the total molar amount of the second polymer; wherein the first group and the second group each independently include at least one of a benzene ring, a cyano group, a maleic anhydride group, a carboxyl group, or an amide group.

6. The secondary battery according to claim 5, characterized in that, Based on the total molar amount of the first polymer, the molar fraction of the first group is 0% to 20%; the weight-average molecular weight of the first polymer is 100 kDa to 500 kDa; and the weight-average molecular weight of the second polymer is 10 kDa to 250 kDa.

7. The secondary battery according to claim 1, characterized in that, The molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer and the second hydrogenated polymer is 10% to 40%, and the degree of hydrogenation of the first hydrogenated polymer and the second hydrogenated polymer is ≥80% and <100%.

8. The secondary battery according to claim 7, characterized in that, The degree of hydrogenation of both the first hydrogenated polymer and the second hydrogenated polymer is ≥89% and <100%.

9. The secondary battery according to claim 3, characterized in that, The mass ratio of the first polymer to the second polymer is (2%~10%): (5%~18%).

10. The secondary battery according to claim 1, characterized in that, The first hydrogenated polymer and the second hydrogenated polymer each independently include at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers.

11. The secondary battery according to claim 10, characterized in that, The hydrogenated polystyrene polymers include at least one of hydrogenated polystyrene-butadiene, hydrogenated polystyrene-isoprene, hydrogenated polystyrene-butadiene-isoprene, hydrogenated polystyrene-butadiene-styrene, hydrogenated polystyrene-isoprene-styrene, and hydrogenated polystyrene-butadiene-isoprene-styrene. The hydrogenated polyacrylonitrile polymers include at least one of hydrogenated polyacrylonitrile-butadiene-isoprene, hydrogenated polyacrylonitrile-isoprene, and hydrogenated polyacrylonitrile-butadiene. The hydrogenated polystyrene-acrylonitrile polymers include at least one of hydrogenated polystyrene-acrylonitrile-butadiene, hydrogenated polystyrene-acrylonitrile-isoprene, and hydrogenated polystyrene-acrylonitrile-butadiene-isoprene.

12. The secondary battery according to claim 1, characterized in that, The polyolefin polymer includes at least one of binary or ternary ethylene propylene rubber, polyisobutylene, cyclic polyolefins and their copolymers.

13. The secondary battery according to claim 1, characterized in that, The first hydrogenated polymer has a weight-average molecular weight of 100 kDa to 600 kDa, and the molar fraction of the styrene units and / or acrylonitrile units in the first hydrogenated polymer is 10% to 40%; and / or The weight-average molecular weight of the polyolefin polymer is 100 kDa to 600 kDa; and / or The acrylic acid-ethylene polymer has a weight-average molecular weight of 100 kDa to 300 kDa, and the molar fraction of acrylic acid units in the acrylic acid-ethylene polymer is 5% to 20%.

14. The secondary battery according to claim 1, characterized in that, The second hydrogenated polymer has a weight-average molecular weight of 10 kDa to 100 kDa, and the molar fraction of the styrene units and / or acrylonitrile units in the second hydrogenated polymer is 10% to 40%; and / or The weight-average molecular weight of the second hydrogenated polymer containing styrene units, modified with maleic anhydride, acrylic acid, or acrylamide, is 100 kDa to 300 kDa. In the second hydrogenated polymer containing styrene units, modified with maleic anhydride, acrylic acid, or acrylamide, the molar fraction of the styrene units and / or acrylonitrile units is 10% to 40%, and the molar fraction of the maleic anhydride, acrylic acid, or acrylamide is 2% to 10%; and / or The weight-average molecular weight of the copolymer of polypropylene or polyethylene and maleic anhydride is 50 kDa to 200 kDa, and the molar fraction of maleic anhydride in the copolymer of polypropylene or polyethylene and maleic anhydride is 2% to 10%.

15. The secondary battery according to claim 1, characterized in that, The edge coating also includes a light absorber, which includes titanium dioxide, carbon black and graphite, and the mass fraction of the light absorber in the edge coating is 0.1% to 1.0%.

16. The secondary battery according to claim 1, characterized in that, The mass ratio of the second adhesive to the inorganic ceramic filler in the edge coating is (15%~20%):(80%~85%).

17. The secondary battery according to claim 1, characterized in that, The inorganic ceramic filler includes boehmite, alumina, silicon nitride, and aluminum nitride.

18. The secondary battery according to claim 1, characterized in that, The secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, and solid-state batteries.

19. A method for preparing a secondary battery, characterized in that, The secondary battery includes a positive electrode sheet, and the method for preparing the positive electrode sheet includes: An active material layer slurry is provided, the active material layer slurry comprising a first solvent and a first binder and a positive electrode active material dispersed in the first solvent; A side coating slurry is provided, the side coating slurry comprising a second solvent and a second binder and an inorganic ceramic filler dispersed in the second solvent; The active material layer slurry and the edge coating slurry are coated onto a current collector and dried to obtain the positive electrode sheet. The positive electrode sheet includes a current collector, an active material layer located on at least one surface of the current collector, and edge coatings located on both sides of the active material layer. The active material layer includes the positive active material and the first binder, and the edge coatings include the inorganic ceramic filler and the second binder. The absolute value of the difference in solubility parameters between the first binder and the second binder at 25°C is greater than or equal to 0.1 MPa. 1 / 2 And less than or equal to 1.5 MPa 1 / 2 ; The second adhesive comprises a first polymer and a second polymer, wherein the first polymer comprises at least one of a first hydrogenated polymer containing styrene units and / or acrylonitrile units, a polyolefin polymer, and an acrylic-ethylene polymer; and the second polymer comprises at least one of a second hydrogenated polymer containing styrene units and / or acrylonitrile units, the second hydrogenated polymer containing styrene units modified based on maleic anhydride units, acrylic units, or acrylamide units, and a copolymer of polypropylene or polyethylene with maleic anhydride.

20. The method for preparing a secondary battery according to claim 19, characterized in that, The solubility parameter of the second adhesive at 25°C is 14.0 MPa. 1 / 2 Above and 20.0 MPa 1 / 2 the following.

21. The method for preparing a secondary battery according to claim 19, characterized in that, The absolute value of the difference in solubility parameters between the first adhesive and the first solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 And / or, the absolute value of the difference in solubility parameters between the second adhesive and the second solvent at 25°C is less than or equal to 2.5 MPa. 1 / 2 And / or, the absolute value of the difference in solubility parameters between the first solvent and the second solvent at 25°C is less than or equal to 1.5 MPa. 1 / 2 .

22. The method for preparing a secondary battery according to claim 19, characterized in that, The first polymer includes a first group, the molar fraction of which is 0% to 50% based on the total molar amount of the first polymer; the second polymer includes a second group, the molar fraction of which is 2% to 40% based on the total molar amount of the second polymer; the weight-average molecular weight of the first polymer is 100 kDa to 600 kDa, and the weight-average molecular weight of the second polymer is 10 kDa to 300 kDa; wherein the first group and the second group each independently include at least one of a benzene ring, a cyano group, a maleic anhydride group, a carboxyl group, or an amide group.

23. The method for preparing a secondary battery according to claim 19, characterized in that, The molar fraction of styrene units and / or acrylonitrile units in the first hydrogenated polymer and the second hydrogenated polymer is 10% to 40%, and the degree of hydrogenation of both the first hydrogenated polymer and the second hydrogenated polymer is ≥80% and <100%.

24. The method for preparing a secondary battery according to claim 22, characterized in that, The mass ratio of the first polymer to the second polymer is (2%~10%):(5%~18%), and / or the mass ratio of the second binder to the inorganic ceramic filler is (15%~20%):(80%~85%).

25. The method for preparing a secondary battery according to claim 19, characterized in that, The first hydrogenated polymer and the second hydrogenated polymer each independently include at least one of hydrogenated polystyrene polymers, hydrogenated polyacrylonitrile polymers, and hydrogenated polystyrene-acrylonitrile polymers.

26. The method for preparing a secondary battery according to claim 25, characterized in that, The hydrogenated polystyrene polymers include at least one of hydrogenated polystyrene-butadiene, hydrogenated polystyrene-isoprene, hydrogenated polystyrene-butadiene-isoprene, hydrogenated polystyrene-butadiene-styrene, hydrogenated polystyrene-isoprene-styrene, and hydrogenated polystyrene-butadiene-isoprene-styrene. The hydrogenated polyacrylonitrile polymers include at least one of hydrogenated polyacrylonitrile-butadiene-isoprene, hydrogenated polyacrylonitrile-isoprene, and hydrogenated polyacrylonitrile-butadiene. The hydrogenated polystyrene-acrylonitrile polymers include at least one of hydrogenated polystyrene-acrylonitrile-butadiene, hydrogenated polystyrene-acrylonitrile-isoprene, and hydrogenated polystyrene-acrylonitrile-butadiene-isoprene.

27. The method for preparing a secondary battery according to claim 19, characterized in that, The polyolefin polymer includes at least one of binary or ternary ethylene propylene rubber, polyisobutylene, cyclic polyolefins and their copolymers.

28. The method for preparing a secondary battery according to claim 19, characterized in that: The first hydrogenated polymer has a weight-average molecular weight of 100 kDa to 600 kDa, and the molar fraction of the styrene units and / or acrylonitrile units in the first hydrogenated polymer is 10% to 40%; and / or The weight-average molecular weight of the polyolefin polymer is 100 kDa to 600 kDa; and / or The acrylic acid-ethylene polymer has a weight-average molecular weight of 100 kDa to 300 kDa, and the molar fraction of acrylic acid units in the acrylic acid-ethylene polymer is 5% to 20%.

29. The method for preparing a secondary battery according to claim 23, characterized in that: The second hydrogenated polymer has a weight-average molecular weight of 10 kDa to 100 kDa, and the molar fraction of the styrene units and / or acrylonitrile units in the second hydrogenated polymer is 10% to 40%; and / or The weight-average molecular weight of the second hydrogenated polymer containing styrene units, modified with maleic anhydride, acrylic acid, or acrylamide, is 100 kDa to 300 kDa. In the second hydrogenated polymer containing styrene units, modified with maleic anhydride, acrylic acid, or acrylamide, the molar fraction of the styrene units and / or acrylonitrile units is 10% to 40%, and the molar fraction of the maleic anhydride, acrylic acid, or acrylamide is 2% to 10%; and / or The weight-average molecular weight of the copolymer of polypropylene or polyethylene and maleic anhydride is 50 kDa to 200 kDa, and the molar fraction of maleic anhydride in the copolymer of polypropylene or polyethylene and maleic anhydride is 2% to 10%.

30. The method for preparing a secondary battery according to claim 19, characterized in that, The edge coating also includes a light absorber, which includes titanium dioxide, carbon black and graphite, and the mass fraction of the light absorber in the edge coating is 0.1% to 1.0%.

31. An electrical device, characterized in that, This includes secondary batteries prepared by the method of preparing a secondary battery as described in any one of claims 1 to 18 or as described in any one of claims 19 to 30.

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