Fluorine-free insulating paste, positive electrode sheet, secondary battery, battery module, battery pack, and electric device

Abstract

The application provides a fluorine-free insulating paste, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device, and the fluorine-free insulating paste comprises a first resin, a second resin, an inorganic filler and an organic solvent, wherein the first resin is selected from a resin with a glass transition temperature of 80 DEG C or above and a liquid absorption rate of 15% or less in a standard electrolyte, and the second resin is selected from a resin with a glass transition temperature of-5 DEG C or less. The application can simultaneously improve the coating speed of the insulating paste, the processing performance of the positive electrode sheet and the safety performance of the secondary battery.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a fluorine-free insulating slurry, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the increasing application and promotion of rechargeable batteries, their safety has received growing attention. If the safety of a rechargeable battery cannot be guaranteed, it becomes unusable. Therefore, how to enhance the safety performance of rechargeable batteries is a pressing technical problem that needs to be solved. Summary of the Invention

[0003] The purpose of this application is to provide a fluorine-free insulating slurry, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electrical device, aiming to simultaneously improve the coating speed of the insulating slurry, the processing performance of the positive electrode sheet, and the safety performance of the secondary battery.

[0004] The first aspect of this application provides a fluorine-free insulating paste, comprising a first resin, a second resin, an inorganic filler, and an organic solvent, wherein the first resin is selected from resins with a glass transition temperature above 80°C and a liquid absorption rate in a standard electrolyte below 15%, and the second resin is selected from resins with a glass transition temperature below -5°C.

[0005] The fluorine-free insulating slurry solution of this application can effectively suppress or even prevent the formation of fusion zones, thus fundamentally solving the problem restricting the improvement of coating speed. The fluorine-free insulating slurry solution of this application also ensures that the secondary battery has high energy density. The insulating coating prepared by the fluorine-free insulating slurry of this application simultaneously possesses high mechanical strength, high heat resistance, high insulation, high adhesion, high toughness, and excellent electrolyte resistance. Even when the negative electrode active material layer punctures the separator due to foreign objects, burrs, etc., and comes into contact with the positive electrode sheet, the negative electrode active material layer and the positive electrode current collector will not directly contact each other, ensuring high safety performance of the secondary battery. Furthermore, the fluorine-free insulating slurry of this application ensures that the positive electrode sheet prepared therefrom has good processing performance, low breakage rate, and high yield.

[0006] In any embodiment of this application, based on the total mass of the fluorine-free insulating slurry, the mass percentage w1 of the first resin is 1% to 5%, the mass percentage w2 of the second resin is 2% to 10%, the mass percentage w3 of the inorganic filler is 15% to 30%, and the mass percentage w4 of the organic solvent is 55% to 82%. By reasonably adjusting the mass percentages of the first resin, the second resin, the inorganic filler, and the organic solvent, the coating speed can be significantly improved while effectively suppressing the formation of the fusion zone. Simultaneously, the resulting positive electrode sheet exhibits excellent processing performance, with a lower breakage rate and a higher yield of high-quality products. Furthermore, the resulting insulating coating possesses high mechanical strength, high heat resistance, high insulation, high adhesion, high toughness, and excellent electrolyte resistance. Secondary batteries using this insulating coating exhibit both good electrochemical performance and higher safety performance.

[0007] In any embodiment of this application, w1 / w2 is 0.1 to 1.5. Optionally, w1 / w2 is 0.2 to 1.0. When w1 / w2 is within a suitable range, the toughening effect of the second resin on the first resin and the reinforcing effect of the first resin on the second resin can be fully utilized, so that the insulating coating simultaneously has high adhesion, high toughness and excellent electrolyte resistance, the positive electrode sheet has a lower breakage rate and a higher yield of high-quality products, and the secondary battery has higher safety performance.

[0008] In any embodiment of this application, (w1+w2) / w3 is 0.1 to 0.9. Optionally, (w1+w2) / w3 is 0.2 to 0.7. When (w1+w2) / w3 is within a suitable range, the insulating coating simultaneously possesses high mechanical strength, high heat resistance, high insulation, and high adhesion. Even if the negative electrode active material layer punctures the separator due to foreign objects, burrs, or other reasons and comes into contact with the positive electrode sheet, the negative electrode active material layer and the positive electrode current collector will not come into direct contact, thereby ensuring that the secondary battery has higher safety performance.

[0009] In any embodiment of this application, the viscosity of the fluorine-free insulating slurry at 25°C is 1000 cps to 20000 cps. Optionally, the viscosity of the fluorine-free insulating slurry at 25°C is 2000 cps to 8000 cps.

[0010] In any embodiment of this application, the glass transition temperature of the first resin is 80°C to 350°C.

[0011] In any embodiment of this application, the glass transition temperature of the second resin is -60°C to -5°C.

[0012] In any embodiment of this application, the number average molecular weight of the first resin is 10,000 to 500,000.

[0013] In any embodiment of this application, the number average molecular weight of the second resin is 10,000 to 1,000,000.

[0014] In any embodiment of this application, the first resin is selected from at least one of polyimide resin, polyamide-imide resin, polyamic acid resin, polyacrylamide resin, polyacrylonitrile resin, acrylate resin, acrylamide-acrylonitrile copolymer resin, and acrylamide-acrylonitrile-acrylate copolymer resin.

[0015] In any embodiment of this application, the second resin is selected from at least one of hydrogenated nitrile rubber, hydrogenated natural rubber, acrylate resins, hydrogenated styrene-butadiene-styrene copolymer resins, hydrogenated styrene-isoprene-styrene copolymer resins, hydrogenated styrene-ethylene-butene-styrene copolymer resins, hydrogenated styrene-ethylene-propylene-styrene copolymer resins, hydrogenated styrene-ethylene-butadiene-styrene copolymer resins, vinyl acetate-ethylene copolymer resins, vinyl acetate-acrylate copolymer resins, acrylate-ethylene copolymer resins, and vinyl acetate-ethylene-acrylate copolymer resins.

[0016] Combining the first resin and the second resin allows for full utilization of the excellent electrolyte resistance of the first resin and the flexibility of the second resin, as well as the toughening effect of the second resin on the first resin and the reinforcing effect of the first resin on the second resin. Under their synergistic effect, the insulating coating simultaneously possesses high insulation, high adhesion, and excellent electrolyte resistance, resulting in a lower breakage rate and a higher yield of high-quality products for the positive electrode sheet.

[0017] In any embodiment of this application, the inorganic filler includes at least one of inorganic insulating oxides, inorganic insulating nitrides, inorganic insulating carbides, silicates, aluminosilicates, carbonates, and molecular sieves.

[0018] In any embodiment of this application, the inorganic insulating oxide includes at least one of aluminum oxide, boehmite, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide, and spinel.

[0019] In any embodiment of this application, the inorganic insulating nitride includes at least one of boron nitride, silicon nitride, aluminum nitride, and titanium nitride.

[0020] In any embodiment of this application, the inorganic insulating carbide includes at least one of boron carbide, silicon carbide, and zirconium carbide.

[0021] In any embodiment of this application, the silicate includes at least one of mica powder, fluorophlogopite powder, talc powder, hydrotalcite, hydrotalcite-like material, mullite, and montmorillonite.

[0022] Optionally, the silicate includes at least one of mica powder, fluorophlogopite powder, talc powder, hydrotalcite, and hydrotalcite-like materials. These materials have a two-dimensional (or near-two-dimensional) structure, so when used as an inorganic filler, the diffusion path of the liquid solution (i.e., the resin solution) to the positive electrode slurry coating area becomes longer and the diffusion resistance becomes greater. At this time, the migration speed of the fluorine-free insulating slurry to the positive electrode slurry coating area slows down, thereby further reducing the blur width of the fusion zone, or even preventing the formation of a fusion zone.

[0023] In any embodiment of this application, the aluminosilicate includes at least one of mullite and orthoclase.

[0024] In any embodiment of this application, the carbonate includes at least one of calcium carbonate, magnesium carbonate, calcite, magnesite, dolomite, siderite, rhodochrosite, zirconia, cerussite, strontium carbonate, and barium carbonate.

[0025] In any embodiment of this application, the molecular sieve includes at least one of X-type, Y-type, MFI-type, MOR-type, MWW-type, SAPO-type, FER-type, and PLS-n-type molecular sieves.

[0026] Optionally, the molecular sieve includes at least one of MWW-type, SAPO-type, FER-type, and PLS-n-type molecular sieves. These materials have a two-dimensional (or near-two-dimensional) structure, so when used as an inorganic filler, the diffusion path of the liquid solution (i.e., the resin solution) to the positive electrode slurry coating area becomes longer and the diffusion resistance becomes greater. At this time, the migration speed of the fluorine-free insulating slurry to the positive electrode slurry coating area slows down, thereby further reducing the fuzzy width of the fusion zone, or even preventing the formation of a fusion zone.

[0027] In any embodiment of this application, the volume average particle size Dv50 of the inorganic filler is 0.5 μm to 10 μm. Optionally, the volume average particle size Dv50 of the inorganic filler is 0.5 μm to 5 μm.

[0028] In any embodiment of this application, the organic solvent includes at least one of N-methylpyrrolidone, triethyl phosphate, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and diethylene glycol.

[0029] A second aspect of this application provides a positive electrode sheet, comprising a positive current collector, a positive active material layer, and a fluorine-free insulating coating, wherein the positive active material layer is located on at least a portion of the surface of the positive current collector, the fluorine-free insulating coating is located on the surface of the positive current collector and is in contact with the edge of the positive active material layer, and the fluorine-free insulating coating is a layer formed by drying the fluorine-free insulating slurry described in the first aspect of this application.

[0030] In any embodiment of this application, the fluorine-free insulating coating is located on both sides of the positive electrode active material layer along its length.

[0031] In any embodiment of this application, the thickness of the fluorine-free insulating coating is 5 μm to 100 μm.

[0032] In any embodiment of this application, the width of the fluorine-free insulating coating is 0.1 mm to 15 mm.

[0033] A third aspect of this application provides a secondary battery, which includes the positive electrode sheet of the second aspect of this application.

[0034] The fourth aspect of this application provides a battery module that includes the secondary battery of the third aspect of this application.

[0035] The fifth aspect of this application provides a battery pack, which includes one of the secondary battery of the third aspect of this application and the battery module of the fourth aspect.

[0036] The sixth aspect of this application provides an electrical device that includes at least one of the secondary battery of the third aspect of this application, the battery module of the fourth aspect, and the battery pack of the fifth aspect.

[0037] [Beneficial Effects]

[0038] The fluorine-free insulating slurry of this application can effectively suppress the formation of the fusion zone in the positive electrode sheet, or even prevent the formation of the fusion zone altogether, thus fundamentally solving the problem restricting the improvement of coating speed. The fluorine-free insulating slurry of this application also ensures that the secondary battery has high energy density. The insulating coating prepared from the fluorine-free insulating slurry of this application simultaneously possesses high mechanical strength, high heat resistance, high insulation, high adhesion, high toughness, and excellent electrolyte resistance. Even when the negative electrode active material layer punctures the separator due to foreign objects, burrs, etc., and comes into contact with the positive electrode sheet, the negative electrode active material layer and the positive electrode current collector will not come into direct contact, ensuring high safety performance of the secondary battery. Furthermore, the fluorine-free insulating slurry of this application ensures that the positive electrode sheet prepared therefrom has good processing performance, with a low breakage rate and a high yield of high-quality products.

[0039] The battery module, battery pack, and power device of this application include the secondary battery provided in this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of one embodiment of the positive electrode sheet of this application.

[0042] Figure 2 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0043] Figure 3 yes Figure 2 An exploded view of an implementation method for a secondary battery.

[0044] Figure 4 This is a schematic diagram of one embodiment of the battery module of this application.

[0045] Figure 5 This is a schematic diagram of one embodiment of the battery pack of this application.

[0046] Figure 6 yes Figure 5 An exploded view of an embodiment of the battery pack shown.

[0047] Figure 7 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0048] Figure 8 This is a comparison chart showing the results of high-speed coating of the fluorine-free insulating slurry prepared in Example 1 and Comparative Example 1.

[0049] The accompanying drawings are not necessarily drawn to scale. Detailed Implementation

[0050] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the fluorine-free insulating slurry, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0051] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0053] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0054] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0055] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0056] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0057] Unless otherwise specified, in this application, the term "acrylate" refers to a monomer, which is a general term for esters of acrylic acid and its derivatives and homologues, which can self-polymerize or copolymerize with other monomers.

[0058] Unless otherwise specified, in this application, the term "acrylate resin" refers to a general term for a series of polymers made by self-polymerization or copolymerization of acrylic acid and its derivatives, as well as their homologues, with these as the main component and other monomers. Acrylic resins with different properties can be obtained depending on the formulation and production process. In this application, acrylate resins that can be used as the first resin must at least meet the following requirements: a glass transition temperature above 80°C and a liquid absorption rate in a standard electrolyte below 15%. Acrylic resins that can be used as the second resin must at least meet the following requirement: a glass transition temperature below -5°C.

[0059] Unless otherwise specified, in this application, the term "copolymer" means any one of random copolymer, alternating copolymer, block copolymer, and graft copolymer.

[0060] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The positive electrode includes a positive current collector and a layer of positive active material, which is coated on the surface of the current collector and contains positive active material. The negative electrode includes a negative current collector and a layer of negative active material, which is coated on the surface of the current collector and contains negative active material. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, conducts the active ions.

[0061] Safety issues are a major factor restricting the application and promotion of secondary batteries. Among them, internal short circuits are the main cause of safety problems and even battery failure. The main forms of internal short circuits in secondary batteries include the following four types: (1) short circuit between the negative electrode current collector and the positive electrode current collector; (2) short circuit between the negative electrode active material layer and the positive electrode active material layer; (3) short circuit between the negative electrode active material layer and the positive electrode current collector; (4) short circuit between the positive electrode active material layer and the negative electrode current collector. Most studies believe that the short circuit between the negative electrode active material layer and the positive electrode current collector is the most dangerous, mainly because the negative electrode active material layer is a good conductor of electrons. Therefore, the impedance at the short circuit point is small. After the short circuit, the voltage will drop sharply and the temperature at the circuit point will rise sharply, which may eventually cause combustion or even explosion.

[0062] To improve the safety performance of secondary batteries, a common strategy is to insulate the area of ​​the positive electrode current collector surface adjacent to the positive electrode active material layer, for example, by coating an insulating layer. Existing insulating slurries are divided into two main categories: oil-based and water-based. Because oil-based solvents, such as N-methylpyrrolidone (NMP), are widely used in current positive electrode slurries, there are compatibility issues between oil-based positive electrode slurries and water-based insulating slurries (such as traditional alumina insulating slurries). During coating, when the oil-based positive electrode slurry encounters the water-based insulating slurry, the N-methylpyrrolidone in the oil-based slurry is rapidly absorbed by the water in the water-based insulating slurry. This causes the binder and positive electrode active material powders, which were originally dissolved or dispersed in the N-methylpyrrolidone, to quickly clump together. This results in rapid bulging of the fusion zone between the oil-based and water-based insulating slurries, making the positive electrode sheet brittle, and even causing tape breakage during positive electrode sheet winding, thus preventing the coating process from continuing. Therefore, the widely used insulating grout is mainly oil-based insulating grout.

[0063] During their research, the inventors noticed that in the positive electrode drying process, existing oil-based insulating slurry migrates towards the positive electrode slurry coating area. This results in a fusion zone (commonly known as a "virtual edge," or migration width of insulating coating to positive active material layer) forming at the boundary between the positive active material layer and the insulating coating after drying. The blurred width of this fusion zone is actually the distance the insulating slurry migrates towards the positive electrode slurry coating area, or the width of the area of ​​the positive active material layer covered by the insulating coating. The presence of this fusion zone leads to difficulties in positioning the CCD (Charge Coupled Device) visual inspection equipment during laser die-cutting, inaccurate die-cutting dimensions of the positive electrode, and even endangers the overhang of the secondary battery, posing a serious safety hazard. Furthermore, since the fusion zone is essentially a region formed by the fusion of insulating coating components and positive active material layer components, or a region where the positive active material layer is covered by the insulating coating, the ion conductivity of the fusion zone is usually poor, thus blocking / impeding the extraction and insertion of some active ions. Therefore, the presence of the fusion zone also reduces the energy density of the secondary battery, and the wider the fusion zone, the more significant the decrease in energy density.

[0064] The inventors unexpectedly discovered through extensive research that the main reason existing oil-based insulating slurries easily migrate to the positive electrode coating area is the widespread use of fluoropolymers in these slurries. Fluorine has the highest electronegativity and strong electron-withdrawing properties, resulting in high CF bond energy. Consequently, fluoropolymers have high surface activity and low surface tension, leading to a lower surface tension in the insulating slurry, significantly lower than that of the positive electrode slurry. Therefore, during the drying process of the positive electrode sheet, existing oil-based insulating slurries easily migrate to the positive electrode coating area, and after drying, a wide fusion zone is formed between the positive electrode active material layer and the insulating coating. Furthermore, the faster the coating speed, the wider the fusion zone; even at high-speed coating, such as coating speeds >30 m / min, the blurred width of the fusion zone may exceed 3 mm. This is mainly because faster coating speeds correspond to higher drying temperatures. At higher temperatures, the insulating slurry has better fluidity and lower surface tension, making it easier to migrate to the positive electrode coating area.

[0065] Based on this, the inventors, through in-depth research, proposed a technical solution for a fluorine-free insulating slurry.

[0066] Fluorine-free insulating paste

[0067] The first aspect of this application provides a fluorine-free insulating paste, comprising a first resin, a second resin, an inorganic filler, and an organic solvent, wherein the first resin is selected from resins with a glass transition temperature (Tg) above 80°C and a liquid absorption rate in a standard electrolyte below 15%, and the second resin is selected from resins with a glass transition temperature below -5°C.

[0068] In this application, the term "standard electrolyte" refers to an electrolyte with a LiPF6 concentration of 1 mol / L formed by a mixed solvent of lithium hexafluorophosphate (LiPF6) and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1.

[0069] In this application, the term "liquid absorption rate in standard electrolyte" refers to the result calculated using the formula liquid absorption rate = (m2-m1) / m1 × 100% after immersing a certain mass of resin sample in the standard electrolyte for 168 hours, where m1 represents the mass of the resin sample before immersion and m2 represents the mass of the resin sample after immersion. The liquid absorption rate test can be referenced in QB / T2303.11-2008 "Battery Pulp Paper - Part 11: Determination of Liquid Absorption Rate". An exemplary test method includes the following steps: at 25°C and standard atmospheric pressure, a resin sample with dimensions of 20mm × 10mm × 1mm (length × width × thickness) is immersed in the aforementioned standard electrolyte for 168 hours. After removal, the sample surface is wiped clean with lint-free paper, and then quickly weighed. The liquid absorption rate of the resin sample in the standard electrolyte is calculated using the formula liquid absorption rate = (m2-m1) / m1 × 100%.

[0070] The inventors unexpectedly discovered that the main reason why existing oil-based insulating slurries easily migrate to the positive electrode coating area is the widespread use of fluoropolymers in these slurries, resulting in a wide fusion zone. The fluorine-free insulating slurry of this application, due to the absence of fluoropolymers, exhibits higher surface tension, thus fundamentally solving the problem of wide fusion zones during insulating slurry coating and avoiding safety issues in secondary batteries. Furthermore, even at high-speed coating, such as coating speeds above 30 m / min, or even above 60 m / min or 70 m / min, the fluorine-free insulating slurry of this application does not form a wide fusion zone, or even any fusion zone at all. Therefore, the technical solution of this application fundamentally solves the problem restricting the improvement of coating speed, thus significantly improving the production efficiency of secondary batteries while avoiding safety issues caused by secondary batteries.

[0071] The fluorine-free insulating slurry provided in this application, comprising a first resin with a glass transition temperature above 80°C and a liquid absorption rate in a standard electrolyte below 15% and a second resin with a glass transition temperature below -5°C, has the following specific beneficial effects:

[0072] Firstly, the positive electrode insulating slurry of this application can significantly reduce the blurring width of the fusion zone of the positive electrode sheet. Because the entire positive electrode insulating slurry system is fluorine-free, it can significantly reduce the surface tension of the positive electrode insulating slurry, narrowing the difference between its surface tension and that of the positive electrode slurry. This greatly increases the coating speed while effectively suppressing the formation of a wider fusion zone, thereby significantly improving the safety performance and energy density of the secondary battery. The technical solution of this application achieves a blurring width of the fusion zone of <1mm, ≤0.5mm, or even ≤0.2mm at coating speeds above 70m / min, significantly better than the industry average (when coating speeds are between 30m / min and 45m / min, the blurring width of the fusion zone is >1mm, or even greater than 2mm).

[0073] Secondly, the insulating coating formed by the positive electrode insulating slurry of this application has good electrolyte resistance properties, thus exhibiting good adhesion properties. The first resin has an absorption rate of less than 15% in the standard electrolyte, demonstrating excellent electrolyte resistance properties. This results in the insulating coating having good electrolyte resistance, effectively preventing the insulating coating from detaching from the positive electrode current collector due to immersion in the electrolyte, and ensuring high safety performance of the secondary battery.

[0074] Thirdly, the insulating coating formed by the positive electrode insulating slurry of this application has good flexibility. Because the first resin has excellent electrolyte resistance, its glass transition temperature is usually high (at room temperature, the first resin is often in a glassy state), resulting in poor flexibility of its molecular chains. This leads to high brittleness in the insulating coating prepared when the first resin is used alone, making it prone to breakage during positive electrode sheet winding. However, the second resin in the positive electrode insulating slurry of this application has a glass transition temperature below -5℃ (at room temperature, the second resin is often in a highly elastic state), thus exhibiting better molecular chain flexibility. Therefore, the second resin can avoid the problem of easy breakage during positive electrode sheet winding caused by the high glass transition temperature of the first resin, ensuring good processing performance of the positive electrode sheet.

[0075] Fourth, the positive electrode insulating slurry of this application also includes inorganic fillers, which can increase the mechanical strength and heat resistance of the insulating coating, effectively prevent the negative electrode active material layer and the positive electrode current collector from directly contacting each other. Even if the negative electrode active material layer punctures the separator and comes into contact with the positive electrode sheet due to foreign objects, burrs or other reasons, the negative electrode active material layer and the positive electrode current collector will not come into direct contact, ensuring that the secondary battery has high safety performance.

[0076] Therefore, the fluorine-free insulating slurry solution of this application can effectively suppress the formation of fusion zones or even prevent the formation of fusion zones, thereby fundamentally solving the problem restricting the improvement of coating speed. The fluorine-free insulating slurry solution of this application can also ensure that the secondary battery has high energy density. The insulating coating prepared by the fluorine-free insulating slurry of this application can simultaneously possess high mechanical strength, high heat resistance, high insulation, high adhesion, high toughness, and excellent electrolyte resistance. Even when the negative electrode active material layer punctures the separator due to foreign objects, burrs, etc., and comes into contact with the positive electrode sheet, the negative electrode active material layer and the positive electrode current collector will not come into direct contact, ensuring that the secondary battery has high safety performance. Furthermore, the fluorine-free insulating slurry of this application can ensure that the positive electrode sheet prepared therefrom has good processing performance, low breakage rate, and high yield.

[0077] In some embodiments, the mass percentage w1 of the first resin, based on the total mass of the fluorine-free insulating paste, can be a range consisting of any value greater than 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or higher. Optionally, the mass percentage w1 of the first resin can be 1%–5%, 1.5%–5%, 2%–5%, 2.5%–5%, 3%–5%, 3.5%–5%, 4%–5%, 1%–4%, 1.5%–4%, 2%–4%, 2.5%–4%, 3%–4%, 3.5%–4%, 1%–3%, 1.5%–3%, 2%–3%, 2.5%–3%, 1%–2%, or 1.5%–2%.

[0078] When the mass percentage of the first resin is high, the insulating coating becomes more brittle and less tough, increasing the breakage rate during positive electrode winding. When the mass percentage of the first resin is low, the insulating coating has poor electrolyte resistance, making it prone to detaching from the positive electrode current collector during long-term storage and use, thus degrading the safety performance of the secondary battery. Therefore, when the mass percentage of the first resin is within a suitable range, the insulating coating simultaneously possesses high adhesion, high toughness, and excellent electrolyte resistance, ensuring high safety performance of the secondary battery during long-term storage and use, while also resulting in a lower breakage rate and a higher yield of high-quality positive electrode sheets.

[0079] In some embodiments, based on the total mass of the fluorine-free insulating paste, the mass percentage w2 of the second resin can be a range consisting of any value of 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or higher. Optionally, the mass percentage w2 of the second resin is 2%–10%, 3%–10%, 4%–10%, 5%–10%, 6%–10%, 7%–10%, 8%–10%, 9%–10%, 2%–9%, ​​3%–9%, ​​4%–9%, ​​5%–9%, ​​6%–9%, ​​7%–9%, ​​8%–9%, ​​2%–8%, 3%–8%, 4%–8%, 5%–8%, 6%–8%, 7%–8%, 2%–7%, 3%–7%, 4%–7%, 5%–7%, 6%–7%, 2%–6%, 3%–6%, 4%–6%, 5%–6%, 2%–5%, 3%–5%, or 4%–5%.

[0080] When the mass percentage of the second resin is high, the liquid absorption rate of the insulating coating is high, resulting in poor electrolyte wettability of the positive and negative electrode sheets, thus deteriorating the electrochemical performance of the secondary battery. Simultaneously, the insulating coating also has poor electrolyte resistance, making it prone to detaching from the positive current collector during long-term storage and use, thus compromising the safety performance of the secondary battery during this period. Conversely, when the mass percentage of the second resin is low, the insulating coating is more brittle, increasing the breakage rate of the positive electrode sheet during winding. Therefore, when the mass percentage of the second resin is within a suitable range, the insulating coating simultaneously possesses high adhesion, high toughness, and excellent electrolyte resistance, ensuring high safety performance of the secondary battery during long-term storage and use, while also exhibiting a lower breakage rate and a higher yield of high-quality positive electrode sheets.

[0081] In some embodiments, the mass percentage w3 of the inorganic filler, based on the total mass of the fluorine-free insulating paste, can be a range consisting of any value comprising 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, 30%, or more. Optionally, the mass percentage w3 of the inorganic filler is 15%–30%, 17.5%–30%, 20%–30%, 22.5%–30%, 25%–30%, 27.5%–30%, 15%–25%, 17.5%–25%, 20%–25%, 22.5%–25%, 15%–20%, or 17.5%–20%.

[0082] When the inorganic filler content is high, the adhesion of the insulating coating deteriorates, making it prone to detaching from the positive electrode current collector during long-term storage and use, thus compromising the battery's safety. Conversely, when the inorganic filler content is low, the insulating coating exhibits poor mechanical strength, heat resistance, and insulation, failing to effectively prevent direct contact between the negative electrode active material layer and the positive electrode current collector, increasing the risk of internal short circuits. Therefore, when the inorganic filler content is within a suitable range, the insulating coating simultaneously possesses high mechanical strength, high heat resistance, high insulation, high adhesion, high toughness, and excellent electrolyte resistance. Even if the negative electrode active material layer punctures the separator due to foreign objects or burrs and comes into contact with the positive electrode, direct contact between the negative electrode active material layer and the positive electrode current collector will not occur, ensuring higher safety performance of the secondary battery.

[0083] In some embodiments, the mass percentage w4 of the organic solvent, based on the total mass of the fluorine-free insulating paste, can be a range consisting of any value comprising 55%, 60%, 65%, 70%, 75%, 80%, 82%, or higher. Optionally, the mass percentage w4 of the organic solvent is 55%–82%, 60%–82%, 65%–82%, 70%–82%, 75%–82%, 55%–80%, 60%–80%, 65%–80%, 70%–80%, 75%–80%, 55%–75%, 60%–75%, 65%–75%, 70%–75%, 55%–70%, 60%–70%, 65%–70%, 55%–65%, 60%–65%, or 55%–60%.

[0084] In some embodiments, based on the total mass of the fluorine-free insulating slurry, the mass percentage w1 of the first resin is 1%–5%, the mass percentage w2 of the second resin is 2%–10%, the mass percentage w3 of the inorganic filler is 15%–30%, and the mass percentage w4 of the organic solvent is 55%–82%. By rationally adjusting the mass percentages of the first resin, the second resin, the inorganic filler, and the organic solvent, the coating speed can be significantly increased while effectively suppressing the formation of fusion zones. Simultaneously, the resulting positive electrode sheet exhibits excellent processing performance, with a lower breakage rate and a higher yield of high-quality products. Furthermore, the resulting insulating coating possesses high mechanical strength, high heat resistance, high insulation, high adhesion, high toughness, and excellent electrolyte resistance. Secondary batteries using this insulating coating exhibit both good electrochemical performance and higher safety performance.

[0085] In some embodiments, the mass ratio of the first resin to the second resin is 0.1 to 1.5, i.e., w1 / w2 is 0.1 to 1.5. Optionally, w1 / w2 is 0.2 to 1.0. By adjusting the mass ratio of the first resin to the second resin within a suitable range, the toughening effect of the second resin on the first resin and the reinforcing effect of the first resin on the second resin can be fully utilized. As a result, the insulating coating simultaneously possesses high adhesion, high toughness, and excellent electrolyte resistance; the positive electrode sheet exhibits a lower breakage rate and a higher yield of high-quality products; and the secondary battery demonstrates higher safety performance.

[0086] In some embodiments, the ratio of the total mass of the first resin and the second resin to the mass of the inorganic filler is 0.1 to 0.9, i.e., (w1+w2) / w3 is 0.1 to 0.9. Optionally, (w1+w2) / w3 is 0.2 to 0.7. By adjusting the ratio of the total mass of the first resin and the second resin to the mass of the inorganic filler within a suitable range, the insulating coating simultaneously possesses high mechanical strength, high heat resistance, high insulation, and high adhesion. Even when the negative electrode active material layer punctures the separator and comes into contact with the positive electrode sheet due to foreign objects, burrs, etc., the negative electrode active material layer and the positive electrode current collector will not come into direct contact, ensuring that the secondary battery has higher safety performance.

[0087] In some embodiments, w1 / w2 is 0.1–1.5, and (w1+w2) / w3 is 0.1–0.9. In this case, the insulating coating simultaneously possesses high mechanical strength, high heat resistance, high insulation, high adhesion, high toughness, and excellent electrolyte resistance. Even when the negative electrode active material layer punctures the separator due to foreign objects, burrs, etc., and comes into contact with the positive electrode sheet, the negative electrode active material layer and the positive electrode current collector will not directly contact each other, ensuring higher safety performance of the secondary battery. Simultaneously, the positive electrode sheet can have a lower breakage rate and a higher yield of high-quality products. Further, w1 / w2 is 0.2–1.0, and (w1+w2) / w3 is 0.2–0.7.

[0088] The viscosity of the fluorine-free insulating slurry primarily affects its coating performance. Excessive viscosity prevents the slurry from being coated onto the surface of the positive current collector; conversely, excessively low viscosity leads to high fluidity and a wider fusion zone. In some embodiments, the viscosity of the fluorine-free insulating slurry at 25°C is 1000 cps to 20000 cps. For example, the viscosity of the fluorine-free insulating paste at 25°C is a range consisting of 1000 cps, 2000 cps, 3000 cps, 4000 cps, 5000 cps, 6000 cps, 7000 cps, 8000 cps, 9000 cps, 10000 cps, 11000 cps, 12000 cps, 13000 cps, 14000 cps, 15000 cps, 16000 cps, 17000 cps, 18000 cps, 19000 cps, 20000 cps, or any of the above values. Optionally, the viscosity of the fluorine-free insulating slurry at 25°C is 2000cps~20000cps, 4000cps~20000cps, 6000cps~20000cps, 8000cps~20000cps, 10000cps~20000cps, 12000cps~20000cps, 14000cps~20000cps, 16000cps~20000cps, 18000cps~20000cps, 1000cps~15000cps, 2000cps~15000cps, 4000cps~15000cps, 6000cps~15000cps, 8000cps~15000cps, 10000cps~ 15000cps, 12000cps~15000cps, 1000cps~10000cps, 2000cps~10000cps, 4000cps ~10000cps, 6000cps~10000cps, 8000cps~10000cps, 1000cps~8000cps, 2000cps~ 8000cps, 3000cps~8000cps, 4000cps~8000cps, 5000cps~8000cps, 6000cps~8000 cps, 1000cps~5000cps, 2000cps~5000cps, 3000cps~5000cps, or 4000cps~5000cps.

[0089] In some embodiments, the glass transition temperature of the first resin is above 80°C, for example above 100°C, above 120°C, above 150°C, or above 180°C. The glass transition temperature of the first resin should also not be too high; in some embodiments, the glass transition temperature of the first resin is further satisfied to be below 400°C, for example below 350°C, below 300°C, below 250°C, below 200°C, or below 150°C. Optionally, the glass transition temperature of the first resin is 80℃~350℃, 80℃~300℃, 80℃~250℃, 80℃~200℃, 80℃~150℃, 100℃~350℃, 100℃~300℃, 100℃~250℃, 100℃~200℃, 100℃~150℃, 120℃~350℃, 120℃~300℃, 120℃~250℃, 120℃~200℃, 120℃~150℃, 150℃~350℃, 150℃~300℃, 150℃~250℃, 150℃~200℃, 180℃~350℃, 180℃~300℃, 180℃~250℃, or 180℃~200℃.

[0090] In some embodiments, the glass transition temperature of the second resin is below -5°C, for example below -10°C, -15°C, -20°C, -25°C, -30°C, or -35°C. The glass transition temperature of the second resin should also not be too low. In some embodiments, the glass transition temperature of the second resin is further satisfied to be above -80°C, for example above -70°C, -60°C, -50°C, -40°C, or -30°C. Optionally, the glass transition temperature of the second resin is -60℃ to -5℃, -55℃ to -5℃, -50℃ to -5℃, -45℃ to -5℃, -40℃ to -5℃, -35℃ to -5℃, -60℃ to -10℃, -55℃ to -10℃, -50℃ to -10℃, -45℃ to -10℃, -40℃ to -10℃, -35℃ to -10℃, -60℃ to -15℃, -55℃ to -15℃, -50℃ to -15℃, -45℃ to -15℃, -40℃ to -15℃, or -35℃ to -15℃.

[0091] In some embodiments, the first resin has an absorption rate of less than 15% in a standard electrolyte, for example, less than 14%, less than 13%, less than 12%, less than 11%, less than 10%, less than 9%, less than 8%, less than 7%, less than 6%, less than 5%, less than 4%, or even less than 3%.

[0092] In this application, the second resin is a resin with a glass transition temperature below -5°C. At room temperature, the second resin is often in a highly elastic state with good molecular chain flexibility. Therefore, its liquid absorption rate in the standard electrolyte is usually high, for example, above 50%, 60%, 70%, 80%, 100%, or 200%. The liquid absorption rate of the second resin in the standard electrolyte should not be too high, usually below 1000%, and further below 800%, 600%, 500%, 400%, or 300%. Optionally, the absorption rate of the second resin in the standard electrolyte is 50%–1000%, 80%–1000%, 100%–1000%, 50%–500%, 80%–500%, 100%–500%, 50%–400%, 80%–400%, 100%–400%, 50%–300%, 80%–300%, 100%–300%, 50%–200%, 80%–200%, or 100%–200%.

[0093] In some embodiments, the number average molecular weight of the first resin is 10,000 to 500,000. Optionally, the number average molecular weight of the first resin is 20,000 to 500,000, 50,000 to 500,000, 100,000 to 500,000, 150,000 to 500,000, 200,000 to 500,000, 250,000 to 500,000, 300,000 to 500,000, 350,000 to 500,000, 400,000 to 500,000, 450,000 to 500,000, 10,000 to 400,000, 20,000 to 400,000, 50,000 to 400000, 100000~400000, 150000~400000, 200000~400000, 250000~400000, 300000~400000, 350000~400000, 10000~300000, 20000~300000, 50000~300000, 100000~300000, 150000~300000, 200000~300000, or 250000~300000.

[0094] In some embodiments, the number average molecular weight of the second resin is 10,000 to 1,000,000. Optionally, the number average molecular weight of the second resin is 10,000 to 1,000,000, 20,000 to 1,000,000, 50,000 to 1,000,000, 100,000 to 1,000,000, 200,000 to 1,000,000, 300,000 to 1,000,000, 400,000 to 1,000,000, 500,000 to 1,000,000, 600,000 to 1,000,000, 700,000 to 1,000,000, 800,000 to 1,000,000, 10,000 to 800,000, 20,000 to 800,000, 50,000 to 800,000, 100,000 to 800000, 200000~800000, 300000~800000, 400000~800000, 500000~800000, 600000~800000, 10000~500000, 20000~500000, 50000~500000, 100000~500000, 200000~500000, 300000~500000, 400000~500000, 10000~200000, 20000~200000, 50000~200000, or 100000~200000.

[0095] In some embodiments, the first resin is selected from at least one of the following: polyimide resin, polyamide-imide resin, polyamic acid resin, polyacrylamide resin, polyacrylonitrile resin, acrylate resin, acrylamide-acrylonitrile copolymer resin, and acrylamide-acrylonitrile-acrylate copolymer resin, which have a glass transition temperature above 80°C and a liquid absorption rate in a standard electrolyte of less than 15%. In the acrylamide-acrylonitrile-acrylate copolymer resin, the type of acrylate monomer is not specifically limited, as long as the glass transition temperature of the acrylamide-acrylonitrile-acrylate copolymer resin is above 80°C and the liquid absorption rate in a standard electrolyte is less than 15%.

[0096] In some embodiments, the first resin is selected from at least one of the following: polyimide resin, polyamide-imide resin, polyamic acid resin, polyacrylamide resin, polyacrylonitrile resin, acrylate resin, acrylamide-acrylonitrile copolymer resin, and acrylamide-acrylonitrile-acrylate copolymer resin, which have a glass transition temperature above 80°C, a liquid absorption rate in a standard electrolyte below 15%, and a number average molecular weight of 10,000 to 500,000. In the acrylamide-acrylonitrile-acrylate copolymer resin, the type of acrylate monomer is not specifically limited, as long as the glass transition temperature of the acrylamide-acrylonitrile-acrylate copolymer resin is above 80°C, the liquid absorption rate in a standard electrolyte is below 15%, and the number average molecular weight is 10,000 to 500,000.

[0097] In some embodiments, the second resin is selected from at least one of the following: hydrogenated nitrile rubber, hydrogenated natural rubber, acrylate resins, hydrogenated styrene-butadiene-styrene copolymer resin, hydrogenated styrene-isoprene-styrene copolymer resin, hydrogenated styrene-ethylene-butene-styrene copolymer resin, hydrogenated styrene-ethylene-propylene-styrene copolymer resin, hydrogenated styrene-ethylene-butadiene-styrene copolymer resin, vinyl acetate-ethylene copolymer resin, vinyl acetate-acrylate copolymer resin, acrylate-ethylene copolymer resin, and vinyl acetate-ethylene-acrylate copolymer resin. Optionally, the acrylate resin is selected from at least one of the following: polypropyl acrylate resin, polyisopropyl acrylate resin, polybutyl acrylate resin, polyisobutyl acrylate resin, polypentyl acrylate resin, polyhexyl acrylate resin, 2-ethylhexyl acrylate resin, polylauryl acrylate resin, polyhydroxypropyl acrylate resin, polyhexyl methacrylate, polyoctyl methacrylate, and polylauryl methacrylate resin. In vinyl acetate-acrylate copolymer resins, acrylate-ethylene copolymer resins, and vinyl acetate-ethylene-acrylate copolymer resins, the type of acrylate monomer is not specifically limited, as long as the glass transition temperature of the vinyl acetate-acrylate copolymer resin, the acrylate-ethylene copolymer resin, and the vinyl acetate-ethylene-acrylate copolymer resin is below -5°C. Optionally, the acrylate monomer is selected from at least one of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, and lauryl methacrylate.

[0098] In some embodiments, the second resin is selected from at least one of the following: hydrogenated nitrile rubber, hydrogenated natural rubber, acrylate resins, hydrogenated styrene-butadiene-styrene copolymer resins, hydrogenated styrene-isoprene-styrene copolymer resins, hydrogenated styrene-ethylene-butene-styrene copolymer resins, hydrogenated styrene-ethylene-propylene-styrene copolymer resins, hydrogenated styrene-ethylene-butadiene-styrene copolymer resins, vinyl acetate-ethylene copolymer resins, vinyl acetate-acrylate copolymer resins, acrylate-ethylene copolymer resins, and vinyl acetate-ethylene-acrylate copolymer resins, which have a glass transition temperature of -60°C to -5°C and a number average molecular weight of 10,000 to 1,000,000. Optionally, the acrylate resin is selected from at least one of the following: polypropyl acrylate resin, polyisopropyl acrylate resin, polybutyl acrylate resin, polyisobutyl acrylate resin, polypentyl acrylate resin, polyhexyl acrylate resin, 2-ethylhexyl acrylate resin, polylauryl acrylate resin, polyhydroxypropyl acrylate resin, polyhexyl methacrylate, polyoctyl methacrylate, and polylauryl methacrylate resin. In the vinyl acetate-acrylate copolymer resin, acrylate-ethylene copolymer resin, and vinyl acetate-ethylene-acrylate copolymer resin, the type of acrylate monomer is not specifically limited, as long as the glass transition temperature of the vinyl acetate-acrylate copolymer resin, the acrylate-ethylene copolymer resin, and the vinyl acetate-ethylene-acrylate copolymer resin is -60℃ to -5℃, and the number average molecular weight is 10,000 to 1,000,000. Optionally, the acrylate monomer is selected from at least one of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, and lauryl methacrylate.

[0099] Combining the first and second resins allows for full utilization of the excellent electrolyte resistance of the first resin and the flexibility of the second resin, as well as the toughening effect of the second resin on the first resin and the reinforcing effect of the first resin on the second resin. Through their synergistic effect, the insulating coating simultaneously possesses high insulation, high adhesion, and excellent electrolyte resistance, resulting in a lower breakage rate and a higher yield of high-quality products for the positive electrode. Furthermore, selecting appropriate combinations of the first and second resins does not affect the electrolyte wettability of the positive and negative electrode sheets, thus enabling the secondary battery to achieve both good electrochemical performance and enhanced safety.

[0100] This application does not impose any particular limitation on the type of inorganic filler, and materials with insulating, thermally stable, and electrochemically stable properties known in the art can be used. In some embodiments, the inorganic filler includes, but is not limited to, at least one of inorganic insulating oxides, inorganic insulating nitrides, inorganic insulating carbides, silicates, aluminosilicates, carbonates, and molecular sieves.

[0101] As an example, the inorganic insulating oxide includes, but is not limited to, at least one of alumina, boehmite, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide, and spinel. As an example, the inorganic insulating nitride is selected from at least one of boron nitride, silicon nitride, aluminum nitride, and titanium nitride. As an example, the inorganic insulating carbide includes, but is not limited to, at least one of boron carbide, silicon carbide, and zirconium carbide. As an example, the silicate includes, but is not limited to, at least one of mica powder, fluorophlogopite powder, talc powder, hydrotalcite, hydrotalcite-like minerals, mullite, and montmorillonite. As an example, the aluminosilicate includes, but is not limited to, at least one of mullite and orthoclase. As an example, the carbonate includes, but is not limited to, at least one of calcium carbonate, magnesium carbonate, calcite, magnesite, dolomite, siderite, rhodochrosite, zirconia, cerussite, strontium carbonate, and barium carbonate. Optionally, the molecular sieve includes, but is not limited to, at least one of the following molecular sieves: X-type, Y-type, MFI-type, MOR-type, MWW-type, SAPO-type, FER-type, and PLS-n-type.

[0102] In some embodiments, the inorganic filler has a two-dimensional or near-two-dimensional structure, such as a layered, sheet-like, or plate-like structure. When the inorganic filler has a two-dimensional (or near-two-dimensional) structure, the path of diffusion of the liquid solution (i.e., the resin solution) to the positive electrode slurry coating area becomes longer and the diffusion resistance becomes greater. At this time, the migration speed of the fluorine-free insulating slurry to the positive electrode slurry coating area slows down, thereby further reducing the blur width of the fusion zone, or even preventing the formation of a fusion zone.

[0103] Optionally, the two-dimensional (or near-two-dimensional) inorganic filler includes, but is not limited to, at least one of two-dimensional inorganic layered silicates and two-dimensional inorganic molecular sieves. The crystal structure of the inorganic layered silicate is formed by parallel stacking of structural unit layers (or crystal layers). Each structural unit layer comprises two parts: sheets and interlayer material. The sheets are typically composed of silicon-oxygen tetrahedral sheets and metal cations (e.g., Mg). 2+ Fe 2+ Al 3+The inorganic molecular sieve is composed of silicon-oxygen tetrahedra in a 1:1 or 2:1 ratio. The spaces between the layers are interlayers, which can be empty or filled with water molecules, cations, anions, etc. The inorganic molecular sieve is a crystalline aluminosilicate whose spatial network structure is composed of alternating silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. The two-dimensional inorganic layered silicate refers to an inorganic layered silicate with a two-dimensional or near-two-dimensional structure, such as layered, sheet-like, or plate-like structures.

[0104] Two-dimensional inorganic layered silicates and two-dimensional inorganic molecular sieves have strong adsorption capacity and can bind with the first and second resins in fluorine-free insulating slurries through van der Waals forces, thereby further reducing the migration speed of fluorine-free insulating slurries and the fuzzy width of the fusion zone.

[0105] Two-dimensional inorganic layered silicates and two-dimensional inorganic molecular sieves both possess advantages such as good thermal stability and low cost. They also exhibit graphite-like layered structures, and the van der Waals forces between the layers are much smaller than the ionic forces within the layers, allowing for interlayer sliding under compression. Therefore, insulating coatings using these inorganic fillers exhibit superior heat resistance and insulation properties, further enhancing the safety performance of secondary batteries. Furthermore, two-dimensional inorganic layered silicates and two-dimensional inorganic molecular sieves also possess good toughness, resulting in positive electrode sheets prepared from them exhibiting excellent processing performance.

[0106] When the inorganic filler has a two-dimensional (or near-two-dimensional) structure, its morphology is layered, sheet-like, or plate-like, and it typically has a high diameter-thickness ratio. When the diameter-thickness ratio of the inorganic filler is small, its effect on reducing the migration speed of the fluorine-free insulating slurry is weaker, resulting in a slight increase in the fuzzy width of the fusion zone. In some embodiments, the diameter-thickness ratio of the inorganic filler can be ≥30:1, ≥40:1, ≥50:1, ≥60:1, ≥70:1, ≥80:1, ≥90:1, ≥100:1, ≥110:1, ≥120:1, ≥130:1, ≥140:1, or ≥150:1. The larger the diameter-thickness ratio of the inorganic filler, the more significant its effect on reducing the migration speed of the fluorine-free insulating slurry; however, this increases the manufacturing cost of the inorganic filler. In some embodiments, optionally, when the inorganic filler has a two-dimensional (or near-two-dimensional) structure, the diameter-to-thickness ratio of the inorganic filler is 50:1 to 150:1, 50:1 to 140:1, 50:1 to 130:1, 50:1 to 120:1, 50:1 to 110:1, 50:1 to 100:1, 50:1 to 90:1, or 50:1 to 80:1.

[0107] As an example, the two-dimensional inorganic layered silicate includes, but is not limited to, at least one of mica powder, fluorophlogopite powder, talc powder, hydrotalcite, and hydrotalcite-like materials. As an example, the two-dimensional inorganic molecular sieve includes, but is not limited to, at least one of MWW-type, SAPO-type, FER-type, and PLS-n-type molecular sieves. Further, the two-dimensional inorganic molecular sieve includes at least one of MCM-22, MCM-49, MCM-56, SAPO-34, SAPO-18, and Al-PLS-3.

[0108] In some embodiments, when the fluorine-free insulating slurry includes at least one of mica powder and talc powder, some transition metal impurities in the mica powder and talc powder can be removed beforehand by acid washing and water washing processes. These transition metal impurities may hinder the electrochemical performance of the secondary battery, such as increasing the self-discharge of the secondary battery. This application does not have a particular limitation on the number of acid washing and water washing cycles, which can be selected according to actual needs. A weak acid aqueous solution, such as boric acid aqueous solution, is preferably used for acid washing. Of course, a dilute solution of a strong acid, such as an aqueous solution of nitric acid, sulfuric acid, or hydrochloric acid with a mass fraction of about 1%, can also be selected.

[0109] In some embodiments, the volume average particle size Dv50 of the inorganic filler is 0.5 μm to 10 μm. For example, the volume average particle size Dv50 of the inorganic filler is a range consisting of 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any of the above values. Optionally, the volume average particle size of the inorganic filler is 0.5μm~9μm, 0.5μm~8μm, 0.5μm~7μm, 0.5μm~6μm, 0.5μm~5μm, 0.5μm~4μm, 0.5μm~3μm, 1μm~10μm, 1μm~9μm, 1μm~8μm, 1μm~7μm, 1μm~6μm, 1μm~5μm, 1μm~4μm, or 1μm~3μm.

[0110] This application does not impose any particular limitation on the type of organic solvent used; compounds known in the art that can dissolve the first resin and the second resin may be used. In some embodiments, the organic solvent includes, but is not limited to, at least one of N-methylpyrrolidone (NMP), triethyl phosphate, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and diethylene glycol.

[0111] In some embodiments, the fluorine-free insulating grout comprises a first resin, a second resin, an inorganic filler, and an organic solvent; based on the total mass of the fluorine-free insulating grout, the mass percentage w1 of the first resin is 1% to 5%, the mass percentage w2 of the second resin is 2% to 10%, the mass percentage w3 of the inorganic filler is 15% to 30%, and the mass percentage w4 of the organic solvent is 55% to 82%; the first resin is selected from at least one of polyimide resin, polyamide-imide resin, polyamic acid resin, polyacrylamide resin, polyacrylonitrile resin, acrylate resin, acrylamide-acrylonitrile copolymer resin, and acrylamide-acrylonitrile-acrylate copolymer resin, which have a glass transition temperature above 80°C and a liquid absorption rate in a standard electrolyte below 15%; the second resin is selected from a resin with a glass transition temperature above 80°C and a liquid absorption rate below 15%. The resin is selected from at least one of the following: hydrogenated nitrile rubber, hydrogenated natural rubber, acrylate resins, hydrogenated styrene-butadiene-styrene copolymer resin, hydrogenated styrene-isoprene-styrene copolymer resin, hydrogenated styrene-ethylene-butene-styrene copolymer resin, hydrogenated styrene-ethylene-propylene-styrene copolymer resin, hydrogenated styrene-ethylene-butadiene-styrene copolymer resin, vinyl acetate-ethylene copolymer resin, vinyl acetate-acrylate copolymer resin, acrylate-ethylene copolymer resin, and vinyl acetate-ethylene-acrylate copolymer resin, with the inorganic filler comprising at least one of the following: inorganic insulating oxides, inorganic insulating nitrides, inorganic insulating carbides, silicates, aluminosilicates, carbonates, and molecular sieves. Optionally, the inorganic filler comprises at least one of the following: two-dimensional inorganic layered silicates and two-dimensional inorganic molecular sieves.

[0112] In some embodiments, the fluorine-free insulating grout comprises a first resin, a second resin, an inorganic filler, and an organic solvent; based on the total mass of the fluorine-free insulating grout, the mass percentage w1 of the first resin is 1% to 5%, the mass percentage w2 of the second resin is 2% to 10%, the mass percentage w3 of the inorganic filler is 15% to 30%, and the mass percentage w4 of the organic solvent is 55% to 82%; w1 / w2 is 0.1 to 1.5, optionally 0.2 to 1.0; (w1+w2) / w3 is 0.1 to 0.9, optionally 0.2 to 0.7; the first resin is selected from polyimide resins, polyamide-imide resins, polyamic acid resins, polyacrylamide resins, polyacrylonitrile resins, acrylate resins, acrylamide-acrylonitrile copolymer resins, and acrylamide-acrylonitrile-acrylate resins with a glass transition temperature above 80°C, a liquid absorption rate in standard electrolyte below 15%, and a number average molecular weight of 10,000 to 500,000. The second resin is selected from at least one of the following: hydrogenated nitrile rubber, hydrogenated natural rubber, acrylate resins, hydrogenated styrene-butadiene-styrene copolymer resins, hydrogenated styrene-isoprene-styrene copolymer resins, hydrogenated styrene-ethylene-butene-styrene copolymer resins, hydrogenated styrene-ethylene-propylene-styrene copolymer resins, hydrogenated styrene-ethylene-butadiene-styrene copolymer resins, vinyl acetate-ethylene copolymer resins, vinyl acetate-acrylate copolymer resins, and vinyl acetate-ethylene-acrylate copolymer resins; the inorganic filler includes at least one of the following: inorganic insulating oxides, inorganic insulating nitrides, inorganic insulating carbides, silicates, aluminosilicates, carbonates, and molecular sieves; optionally, the inorganic filler includes at least one of two-dimensional inorganic layered silicates and two-dimensional inorganic molecular sieves.

[0113] In this application, the fluorine-free insulating slurry can be prepared according to methods known in the art. For example, a first resin, a second resin, an inorganic filler, and an organic solvent can be mixed evenly to obtain the fluorine-free insulating slurry. There are no particular restrictions on the order of addition of the materials. For example, the inorganic filler can be added to the organic solvent and mixed evenly first, and then the first and second resins can be added to obtain the fluorine-free insulating slurry; or, the first and second resins can be added to the organic solvent first, and then the inorganic filler can be added to obtain the fluorine-free insulating slurry. The first and second resins can be added simultaneously or separately; the organic solvent can be added all at once or in batches.

[0114] In some embodiments, the fluorine-free insulating slurry can be prepared according to the following steps: S101, dispersing an organic solvent and an inorganic filler evenly to obtain a slurry; S102, adding a first resin and a second resin to the obtained slurry in a dispersed state, dispersing evenly, and then filtering with a 100-200 mesh filter to obtain the fluorine-free insulating slurry. In S101, the dispersion linear velocity is 20 m / s to 100 m / s, and the dispersion time is 15 min to 120 min. In S102, the dispersion linear velocity is 20 m / s to 100 m / s, and the dispersion time is 120 min to 480 min. In other embodiments, the fluorine-free insulating slurry can be prepared according to the following steps: S201, dispersing an organic solvent, a first resin, and a second resin evenly to obtain a slurry; S202, adding an inorganic filler to the obtained slurry in a dispersed state, dispersing evenly, and then filtering with a 100-200 mesh filter to obtain the fluorine-free insulating slurry. In S201, the dispersion linear velocity is 20 m / s to 100 m / s, and the dispersion time is 15 min to 120 min. In S202, the dispersion linear velocity is 20 m / s to 100 m / s, and the dispersion time is 120 min to 480 min.

[0115] In this application, the glass transition temperature of the resin has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined with reference to GB / T 29611-2013 "Determination of Glass Transition Temperature of Raw Rubber - Differential Scanning Calorimetry (DSC)", and the test can be performed using a Mettler-Toledo DSC-3 differential scanning calorimeter.

[0116] In this application, the number-average molecular weight of the resin has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined by gel permeation chromatography (GPC) using an Agilent 1290 Infinity II GPC system.

[0117] In this application, the viscosity of the slurry has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be measured with reference to GB / T 2794-2013 "Determination of Viscosity of Adhesives - Single Cylinder Rotation Viscometer Method".

[0118] In this application, the volume average particle size Dv50 of the inorganic filler has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0119] In this application, the aspect ratio of the material has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be measured with reference to JC / T 2063-2011 "Method for Determination of Aspect Ratio of Mica Powder".

[0120] Positive electrode sheet

[0121] A second aspect of this application provides a positive electrode sheet, comprising a positive current collector, a positive active material layer, and a fluorine-free insulating coating, wherein the positive active material layer is located on at least a portion of the surface of the positive current collector, the fluorine-free insulating coating is located on the surface of the positive current collector and is in contact with the edge of the positive active material layer, and the fluorine-free insulating coating is a layer formed by drying the fluorine-free insulating slurry according to any embodiment of the first aspect of this application.

[0122] The positive electrode sheet of this application can reduce the probability of direct contact between the negative electrode active material layer and the positive electrode current collector, ensuring high safety performance of the secondary battery. The positive electrode sheet of this application also has good processing performance and is not easily broken during winding.

[0123] In some embodiments, the fluorine-free insulating coating is located on one or both sides of the positive electrode active material layer along its length. Optionally, the fluorine-free insulating coating is located on both sides of the positive electrode active material layer along its length. Figure 1 This is a schematic diagram of one embodiment of the positive electrode sheet of this application. Figure 1 As shown, the positive electrode sheet includes a positive current collector 101, a positive active material layer 102, and a fluorine-free insulating coating 103. The fluorine-free insulating coating 103 is located on both sides of the positive active material layer 102 along the length direction L, but this application is not limited thereto.

[0124] This application does not impose any particular limitation on the thickness of the fluorine-free insulating coating, which can be adjusted according to actual needs. In some embodiments, the thickness of the fluorine-free insulating coating is 5 μm to 100 μm.

[0125] This application does not impose any particular limitation on the width of the fluorine-free insulating coating, which can be adjusted according to actual needs. In some embodiments, the width of the fluorine-free insulating coating is 0.1 mm to 15 mm.

[0126] In some embodiments, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0127] In some embodiments, the positive current collector has two surfaces opposite each other in its thickness direction, and the fluorine-free insulating coating is disposed on either or both of the two opposite surfaces of the positive current collector.

[0128] The positive electrode active material layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. In this application, the modified compounds of the above-mentioned positive electrode active materials may be used for doping modification or surface coating modification of the positive electrode active materials.

[0129] In one embodiment, the positive electrode active material comprises at least one of a lithium phosphate with an olivine structure and a modified compound thereof.

[0130] In some embodiments, the positive electrode active material layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode conductive agent is ≤5%.

[0131] In some embodiments, the positive electrode active material layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is ≤5% based on the total mass of the positive electrode active material layer.

[0132] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be selected from at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0133] The positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0134] The method for preparing the positive electrode sheet of this application is well known. In some embodiments, the positive electrode slurry and the fluorine-free insulating slurry described in any embodiment of the first aspect of this application can be coated on the positive electrode current collector, and then dried and cold-pressed.

[0135] Secondary batteries

[0136] A third aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the secondary battery, active ions are inserted and extracted back and forth between the positive electrode and the negative electrode, and the electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode.

[0137] [Positive electrode plate]

[0138] The positive electrode used in the secondary battery of this application is the positive electrode described in any embodiment of the second aspect of the embodiments of this application.

[0139] [Negative electrode plate]

[0140] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector and comprising a negative active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative active material layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0141] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0142] In some embodiments, the negative electrode active material layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total mass of the negative electrode active material layer, the mass percentage of the negative electrode conductive agent is ≤5%.

[0143] In some embodiments, the negative electrode active material layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5% based on the total mass of the negative electrode active material layer.

[0144] In some embodiments, the negative electrode active material layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is ≤2% based on the total mass of the negative electrode active material layer.

[0145] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material may be selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0146] The negative electrode active material layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0147] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode active material layer.

[0148] [Electrolytes]

[0149] This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0150] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0151] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0152] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0153] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0154] [Isolation membrane]

[0155] Secondary batteries using electrolytes, as well as some secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. 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.

[0156] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0157] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0158] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0159] In some embodiments, the outer packaging of the secondary battery 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 can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0160] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 2 This is an example of a square-structured secondary battery 5.

[0161] In some embodiments, such as Figure 3 As shown, the 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 is used to cover the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in 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 adjusted according to requirements.

[0162] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0163] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0164] Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 As shown, 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.

[0165] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0166] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0167] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6 As shown, 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. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0168] Electrical appliances

[0169] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, 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.

[0170] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0171] Figure 7 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0172] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0173] Example

[0174] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0175] Example 1

[0176] Preparation of fluorine-free insulating paste

[0177] A first resin, acrylamide-acrylonitrile copolymer, with a number-average molecular weight of 300,000, a Tg of 120℃, and a liquid absorption rate of 5% in standard electrolyte, and a second resin, polybutyl acrylate, with a number-average molecular weight of 250,000 and a Tg of -55℃, were sequentially added to an organic solvent, NMP, under stirring. The dispersion linear velocity was 22 m / s, and the dispersion time was 60 min. Then, boehmite with a volume average particle size (Dv50) of 2 μm was added under dispersion conditions, with a dispersion linear velocity of 20 m / s and a dispersion time of 180 min. The mixture was filtered through a 150-mesh filter to obtain a fluorine-free insulating slurry. Based on the total mass of the fluorine-free insulating slurry, the mass percentage of the first resin, w1, was 1.25%, the mass percentage of the second resin, w2, was 3.75%, the mass percentage of the inorganic filler, w3, was 20%, and the mass percentage of the organic solvent, w4, was 75%.

[0178] Preparation of positive electrode sheet

[0179] Lithium iron phosphate (LiFePO4), carbon black (SuperP), and polyvinylidene fluoride (PVDF) binder were thoroughly mixed in an appropriate amount of NMP solvent at a mass ratio of 97:1:2 to form a uniform positive electrode slurry. The positive electrode slurry and the aforementioned fluorine-free insulating slurry were then... Figure 1 The positive electrode slurry was uniformly coated onto the surface of the positive current collector aluminum foil at the same coating speed, as shown. After drying (until the NMP content in the positive electrode sheet is <0.3%) and cold pressing, the positive electrode sheet was obtained. The coating weight of the positive electrode slurry was 360 mg / 1540.25 mm. 2 The coating width of the fluorine-free insulating slurry is 10 mm, and the coating speed is 70 m / min.

[0180] Preparation of negative electrode sheet

[0181] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (SuperP) are mixed thoroughly in an appropriate amount of deionized water at a mass ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0182] Preparation of electrolyte

[0183] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0184] Preparation of the separating membrane

[0185] Porous polyethylene film is used as the separator.

[0186] Preparation of secondary batteries

[0187] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0188] Examples 2-18 and Comparative Examples 1-4

[0189] The preparation method of the secondary battery is similar to that of Example 1, except that the composition of the fluorine-free insulating slurry is different. Specific parameters are detailed in Table 1. The first and second resins used in each example and comparative example are abbreviated as follows: Acrylamide-acrylonitrile copolymer, A1, purchased from Zeon Corporation, Japan; Polyimide, A2, purchased from Wuhan Yimaide New Material Technology Co., Ltd.; Polyamic acid, A3, purchased from Wuhan Yimaide New Material Technology Co., Ltd.; Polyvinylidene fluoride, grade [not specified]. HSV 900, A4, purchased from Arkema; ​​polybutyl acrylate, B1; vinyl acetate-ethylene copolymer, B2; hydrogenated nitrile butadiene rubber, B3; hydrogenated natural rubber, B4; hydrogenated styrene-ethylene-butadiene-styrene copolymer, B5; polybutyl methacrylate, B6.

[0190] Test section

[0191] (1) Liquid absorption rate test

[0192] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare a standard electrolyte with a LiPF6 concentration of 1 mol / L.

[0193] At 25℃ and standard atmospheric pressure, a first resin sample with dimensions of 20mm × 10mm × 1mm (length × width × thickness) was immersed in the aforementioned standard electrolyte for 168 hours. After removal, the sample surface was wiped clean with lint-free paper, and then quickly weighed. The liquid absorption rate of the first resin sample in the standard electrolyte was calculated using the formula: Liquid Absorption Rate = (m2 - m1) / m1 × 100%. Here, m1 represents the mass of the first resin sample before immersion, and m2 represents the mass of the first resin sample after immersion.

[0194] (2) Viscosity test of fluorine-free insulating paste

[0195] The viscosity of the obtained fluorine-free insulating slurry was determined according to GB / T 2794-2013 "Determination of Viscosity of Adhesives - Single-Cylinder Rotational Viscometer Method". The test temperature was 25℃, and the test instrument was a Brookfield DVS+ rotational viscometer from Brookfield Instruments, Inc., USA.

[0196] (3) Surface tension test of fluorine-free insulating paste

[0197] The surface tension of the obtained fluorine-free insulating paste at 25°C was measured using a DCAT9T surface tension tester from Dataphysics, Germany.

[0198] (4) Analysis of high-speed coating results of fluorine-free insulating paste

[0199] The fuzzy width (i.e., maximum width) of the fusion region on the positive electrode sheets corresponding to each embodiment and comparative example was measured using a CCD vision inspection device. Specifically, the coating speed of the positive electrode slurry and the fluorine-free insulating slurry in Comparative Example 1 was 36 m / min; the coating speed of the positive electrode slurry and the fluorine-free insulating slurry in Comparative Example 2 was 40 m / min; and the coating speed of the positive electrode slurry and the fluorine-free insulating slurry in Examples 1-18 and Comparative Examples 3-4 was 70 m / min.

[0200] (5) Electrolyte resistance test of fluorine-free insulating coating

[0201] The positive electrode sheets corresponding to each embodiment and comparative example were immersed in the above-mentioned standard electrolyte at room temperature for 168 hours. Afterwards, the standard electrolyte was removed in a glove box, and the fluorine-free insulating coating was repeatedly wiped with cotton swabs until it fell off. The more times the cotton swabs were used to wipe, the better the electrolyte resistance of the fluorine-free insulating coating.

[0202] (6) Adhesion test of fluorine-free insulating coating

[0203] The secondary batteries prepared in each embodiment and comparative example were charged at 60°C with a constant current of 1C to 3.65V, and then charged at 3.65V with a constant voltage until the current ≤0.05mA. After standing for 5 minutes, they were discharged at a constant current of 1C to 2.50V, which constitutes one charge-discharge cycle. After the secondary batteries were subjected to 500 charge-discharge cycles according to the above method, they were disassembled to observe whether the fluorine-free insulating coating had peeled off.

[0204] (7) Processing performance test of positive electrode sheet

[0205] The processing performance of positive electrode sheets is characterized by the breakage rate of the winding. A lower breakage rate indicates better processing performance. The breakage rate refers to the number of breaks per roll of positive electrode sheet. The processing performance of positive electrode sheets is categorized into three levels: excellent (average breakage rate less than 0.24 times / roll), medium (average breakage rate not less than 0.24 times / roll and not exceeding 0.4 times / roll), and poor (average breakage rate exceeding 0.4 times / roll).

[0206] Table 2 shows the performance test results of Examples 1-18 and Comparative Examples 1-4.

[0207] Figure 8 These are comparison images of the results of high-speed coating of the fluorine-free insulating slurry prepared in Example 1 and Comparative Example 1. Figure 8 As shown, the technical solution of the fluorine-free insulating slurry of this application can effectively reduce the blur width of the fusion zone, fundamentally solving the problem restricting the improvement of coating speed. As can be seen from the test results in Table 2, the fluorine-free insulating slurry prepared in Example 1 has a blur width of only 0.2 mm in the fusion zone at a coating speed of 70 m / min, while the fluorine-containing insulating slurry prepared in Comparative Example 1 has a blur width of 2.2 mm in the fusion zone at a coating speed of 36 m / min.

[0208] The test results in Table 2 also show that the fluorine-free insulating coating prepared from the fluorine-free insulating slurry of this application simultaneously possesses high adhesion, high toughness, and excellent electrolyte resistance, while the positive electrode also exhibits good processing performance. In Comparative Example 2, the fluorine-free insulating slurry only uses the first resin, resulting in a fluorine-free insulating coating with high brittleness, poor processing performance of the positive electrode, and easy breakage during winding. Furthermore, due to the high brittleness of the fluorine-free insulating coating, its internal stress distribution is concentrated, leading to poor adhesion after long-term immersion in electrolyte and easy detachment from the positive electrode current collector. In Comparative Example 3, the fluorine-free insulating slurry only uses the second resin, resulting in a fluorine-free insulating coating with poor electrolyte resistance and adhesion, and the fluorine-free insulating coating easily detaches from the positive electrode current collector after long-term use of the secondary battery. The fluorine-free insulating slurry in Comparative Example 4 uses a combination of the first resin and the second resin. However, the glass transition temperature of the second resin is relatively high, and it is in a glassy state at room temperature, which results in poor processing performance of the positive electrode sheet and easy breakage of the tape during winding. At the same time, the second resin cannot improve the brittleness of the first resin. As a result, the fluorine-free insulating coating prepared is still brittle, with a relatively concentrated internal stress distribution. After long-term immersion in electrolyte, the adhesion deteriorates, and it is easy to fall off from the positive current collector.

[0209] The test results in Table 2 also show that by reasonably adjusting the mass percentages of the first resin, second resin, inorganic filler, and organic solvent in the fluorine-free insulating slurry to meet the following conditions, w1 is 1%–5%, w2 is 2%–10%, w3 is 15%–30%, and w4 is 55%–82%, the positive electrode sheet can have a lower fuzzy width in the fusion zone and excellent processing performance, while the fluorine-free insulating coating can have higher adhesion and better electrolyte resistance. In Example 7, the mass percentage of the first resin in the fluorine-free insulating slurry, w1, is less than 1%, and the adhesion and electrolyte resistance of the fluorine-free insulating coating are slightly poor. In Example 8, the mass percentage of the first resin in the fluorine-free insulating slurry, w1, is greater than 5%, and the fluorine-free insulating coating has high adhesion and excellent electrolyte resistance, but the processing performance of the positive electrode sheet is slightly poor. In Example 9, the mass percentage w2 of the second resin in the fluorine-free insulating slurry is less than 2%. The fluorine-free insulating coating exhibits high adhesion and excellent electrolyte resistance. However, the second resin cannot effectively improve the brittleness of the first resin, resulting in slightly poorer processing performance of the positive electrode sheet. In Example 10, the mass percentage w2 of the second resin in the fluorine-free insulating slurry is greater than 10%. The positive electrode sheet exhibits excellent processing performance, but the adhesion and electrolyte resistance of the fluorine-free insulating coating are slightly poor.

[0210] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

[0211]

[0212]

Claims

1. A positive electrode sheet, comprising: Positive current collector; A positive electrode active material layer is located on at least a portion of the surface of the positive electrode current collector; as well as A fluorine-free insulating coating is located on the surface of the positive electrode current collector and is in contact with the edge of the positive electrode active material layer. The fluorine-free insulating coating comprises a first resin, a second resin, and an inorganic filler, wherein... The first resin is selected from resins with a glass transition temperature above 80°C and a liquid absorption rate in a standard electrolyte below 15%. The second resin is selected from resins with a glass transition temperature below -5°C; the standard electrolyte is a LiPF6 concentration of 1 mol / L formed by a mixed solvent of lithium hexafluorophosphate, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:

1. The liquid absorption rate is the result calculated according to the formula: liquid absorption rate = (m2-m1) / m1×100% after the first resin sample is immersed in the standard electrolyte at 25°C and standard atmospheric pressure for 168 hours, where m1 represents the mass of the first resin sample before immersion and m2 represents the mass of the first resin sample after immersion.

2. The positive electrode sheet according to claim 1, wherein, The glass transition temperature of the first resin is 80℃~350℃; and / or, The glass transition temperature of the second resin is -60℃ to -5℃.

3. The positive electrode sheet according to claim 1, wherein, The number-average molecular weight of the first resin is 10,000 to 500,000; and / or, The number average molecular weight of the second resin is 10,000 to 1,000,000.

4. The positive electrode sheet according to claim 1, wherein, The first resin is selected from at least one of polyimide resin, polyamide-imide resin, polyamic acid resin, polyacrylamide resin, polyacrylonitrile resin, acrylate resin, acrylamide-acrylonitrile copolymer resin, and acrylamide-acrylonitrile-acrylate copolymer resin; and / or, The second resin is selected from at least one of hydrogenated nitrile rubber, hydrogenated natural rubber, acrylate resins, hydrogenated styrene-butadiene-styrene copolymer resins, hydrogenated styrene-isoprene-styrene copolymer resins, hydrogenated styrene-ethylene-butene-styrene copolymer resins, hydrogenated styrene-ethylene-propylene-styrene copolymer resins, hydrogenated styrene-ethylene-butadiene-styrene copolymer resins, vinyl acetate-ethylene copolymer resins, vinyl acetate-acrylate copolymer resins, acrylate-ethylene copolymer resins, and vinyl acetate-ethylene-acrylate copolymer resins.

5. The positive electrode sheet according to claim 1, wherein, The inorganic filler includes at least one of inorganic insulating oxides, inorganic insulating nitrides, inorganic insulating carbides, silicates, aluminosilicates, carbonates, and molecular sieves.

6. The positive electrode sheet according to claim 5, wherein, The inorganic insulating oxide includes at least one selected from aluminum oxide, boehmite, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, calcium oxide, beryllium oxide, and spinel; and / or, The inorganic insulating nitride includes at least one of boron nitride, silicon nitride, aluminum nitride, and titanium nitride; and / or, The inorganic insulating carbide includes at least one of boron carbide, silicon carbide, and zirconium carbide; and / or, The silicate comprises at least one of mica powder, fluorophlogopite powder, talc powder, hydrotalcite, hydrotalcite-like material, mullite, and montmorillonite; and / or, The aluminosilicate includes at least one of mullite and orthoclase; and / or The carbonate includes at least one of calcium carbonate, magnesium carbonate, calcite, magnesite, dolomite, siderite, rhodochrosite, zirconia, cerussite, strontium carbonate, and barium carbonate; and / or, The molecular sieve includes at least one of the following: X-type, Y-type, MFI-type, MOR-type, MWW-type, SAPO-type, FER-type, and PLS-n-type molecular sieves.

7. The positive electrode sheet according to claim 5, wherein, The silicate includes at least one of mica powder, fluorophlogopite powder, talc powder, hydrotalcite, and hydrotalcite-like materials; and / or The molecular sieve includes at least one of the following: MWW type, SAPO type, FER type, and PLS-n type molecular sieves.

8. The positive electrode sheet according to claim 1, wherein, The volume average particle size Dv50 of the inorganic filler is 0.5μm~10μm.

9. The positive electrode sheet according to claim 8, wherein, The volume average particle size Dv50 of the inorganic filler is 0.5μm~5μm.

10. The positive electrode sheet according to claim 1, wherein, The fluorine-free insulating coating is a layer formed by drying a fluorine-free insulating slurry, which includes the first resin, the second resin, the inorganic filler, and an organic solvent.

11. The positive electrode sheet according to claim 10, wherein, The organic solvent includes at least one of N-methylpyrrolidone, triethyl phosphate, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and diethylene glycol.

12. The positive electrode sheet according to claim 10, wherein, Based on the total mass of the fluorine-free insulating slurry, the mass percentage w1 of the first resin is 1% to 5%, the mass percentage w2 of the second resin is 2% to 10%, the mass percentage w3 of the inorganic filler is 15% to 30%, and the mass percentage w4 of the organic solvent is 55% to 82%.

13. The positive electrode sheet according to claim 12, wherein, w1 / w2 is 0.1~1.5; and / or, (w1+w2) / w3 is 0.1~0.

9.

14. The positive electrode sheet according to claim 13, wherein, w1 / w2 is 0.2~1.0; and / or, (w1+w2) / w3 is 0.2~0.

7.

15. The positive electrode sheet according to claim 10, wherein, The viscosity of the fluorine-free insulating slurry at 25°C is 1000 mPa·s to 20000 mPa·s.

16. The positive electrode sheet according to claim 15, wherein, The viscosity of the fluorine-free insulating slurry at 25°C is 2000 mPa·s to 8000 mPa·s.

17. The positive electrode sheet according to any one of claims 1-16, wherein, The fluorine-free insulating coating is located on both sides of the positive electrode active material layer along its length.

18. The positive electrode sheet according to any one of claims 1-16, wherein, The thickness of the fluorine-free insulating coating is 5μm~100μm; and / or, The width of the fluorine-free insulating coating is 0.1mm to 15mm.

19. A secondary battery comprising a positive electrode sheet according to any one of claims 1-18.

20. A battery module comprising the secondary battery according to claim 19.

21. A battery pack comprising a secondary battery according to claim 19 or a battery module according to claim 20.

22. An electrical device comprising at least one of the secondary battery according to claim 19, the battery module according to claim 20, and the battery pack according to claim 21.

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