Functional coating, separator and secondary battery

Abstract

This application belongs to the field of new energy battery technology, specifically relating to a functional coating, a separator, and a secondary battery. The functional coating provided in this application includes a functional material, which comprises a carboxylate with the chemical formula (RCOO). x (OH) y M is a metal ion with a valence of 1-3, x is 1, 2, or 3, y is 0 or 1, and R is an aliphatic hydrocarbon group with 9-20 carbon atoms; the mass content of M is denoted as m% based on the mass of the functional coating, satisfying: 1≤m≤30. The functional coating provided in this application enables the battery to reduce micro-short circuits and has better fast charging performance, thermal safety, and cycle performance.

Description

Technical Field

[0001] This application belongs to the field of new energy battery technology, specifically relating to a functional coating, a separator, and a secondary battery. Background Technology

[0002] With the continuous iteration of industrial technology, the market has placed higher demands on the fast charging capability and safety and reliability of rechargeable batteries under high-temperature environments. As an important component of rechargeable batteries, the separator, currently widely used polyolefin separators, exhibits poor electrolyte wetting performance due to its hydrophobic properties and low ion affinity. This directly affects ion migration and limits the battery's fast charging capability. At the same time, during long-term cycling, uneven electrolyte wetting and slow ion migration will exacerbate the polarization of the electrode interface. Especially under fast charging or high-rate conditions, it is easy to trigger side reactions such as uneven local current distribution and metal deposition. These side reactions not only consume active lithium and electrolyte, but also continuously generate acidic substances (such as HF) and active free radicals, further aggravating the dissolution of transition metals, crystal structure destruction, and chain oxidation decomposition of electrolyte, increasing the occurrence of micro-short circuits. More importantly, most of the above-mentioned side reactions are exothermic processes. Under high-temperature environments, they are easily further aggravated, forming a vicious cycle and greatly increasing the risk of thermal runaway of the battery. All of these factors mean that existing rechargeable batteries cannot simultaneously achieve good fast charging performance and thermal safety. Summary of the Invention

[0003] Therefore, the technical problem to be solved by this application is to overcome the defects of existing secondary batteries that cannot achieve both good fast charging performance and thermal safety, and are prone to micro short circuits, thereby providing a functional coating, separator and secondary battery.

[0004] Therefore, this application provides the following technical solution.

[0005] According to embodiments of this application, in a first aspect, a functional coating is provided, comprising a functional material, said functional material comprising a carboxylate having the chemical formula (RCOO). x (OH) y M is a metal ion with a valence of 1-3, x is 1, 2 or 3, y is 0 or 1, and R is an aliphatic hydrocarbon group with 9-20 carbon atoms. Based on the mass of the functional coating, the mass content of M is denoted as m%, satisfying: 1≤m≤30.

[0006] According to an embodiment of this application, in a second aspect, a diaphragm is also provided, the diaphragm comprising a substrate layer, the substrate layer comprising a base film and a functional coating disposed on at least one side surface of the base film in the thickness direction, the functional coating being the functional coating described in the first aspect.

[0007] According to an embodiment of this application, in a third aspect, a positive electrode sheet is also provided, wherein the functional coating is located on the surface of at least one side of the positive electrode sheet.

[0008] According to an embodiment of this application, in a fourth aspect, a negative electrode sheet is also provided, wherein the functional coating is located on the surface of at least one side of the negative electrode sheet.

[0009] According to an embodiment of this application, in a fifth aspect, a secondary battery is also provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode, the negative electrode, and the separator comprises the functional coating described in the first aspect.

[0010] The technical solution of this application has the following advantages: The functional coating provided in this application includes a functional material, wherein the functional material comprises a carboxylate with the chemical formula (RCOO). x (OH) y M is a metal ion with a valence of 1-3, x is 1, 2, or 3, y is 0 or 1, and R is an aliphatic hydrocarbon group with 9-20 carbon atoms; the mass content of M is denoted as m%, based on the mass of the functional coating, satisfying: 1 ≤ m ≤ 30. The functional coating provided in this application contains specific functional materials, and the carboxylate group (COO) in the functional materials... - Both ions and metal ions possess strong polarity, enabling them to generate strong dipole-dipole interactions or coordination with polar solvents in the electrolyte. This gives the functional coating a strong affinity for polar solvents in the electrolyte, effectively reducing the resistance encountered during electrolyte wetting of the substrate (such as the base film of the separator, the active layers of the positive and negative electrodes). This improves the wetting uniformity and speed, and enhances ion migration rate, thereby improving not only the fast-charging performance of the battery but also reducing polarization. This further suppresses adverse phenomena such as transition metal dissolution, crystal structure destruction, and chain oxidation decomposition of the electrolyte, reducing micro-short circuits and improving the battery's thermal safety and cycle performance. Simultaneously, the 9-... The 20-carbon aliphatic hydrocarbon group can effectively regulate the melting point of the carboxylate to be close to the internal temperature threshold of the battery. When the internal temperature of the battery rises and approaches the melting point, the carboxylate melts and generates microbubbles under the gas generation of the electrolyte. A uniformly distributed microbubble expansion layer is formed on the substrate surface. On the one hand, it can increase the physical distance between the separator and the electrode, thereby providing a buffer space for the thermal expansion of the electrode and reducing the space for the separator to be squeezed. On the other hand, the microbubble expansion layer is a dense and ion-insulating physical barrier that can effectively block the ion and charge transport between the positive and negative electrodes, isolate the continuous occurrence of side reactions, further reduce the continuous increase of heat, reduce the risk of thermal runaway, and improve the thermal safety of the battery.

[0011] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0013] Figure 1 This application provides a type of diaphragm; Figure 2 This is a positive electrode sheet provided in this application; Figure 3 This is a negative electrode sheet provided in this application; Figure 4 This is the infrared spectrum of the functional coating of Embodiment 1 of this application; Figure 5 This is the X-ray diffraction pattern of the functional coating of Embodiment 1 of this application; Explanation of reference numerals in the attached figures: 1. Separator; 11. Substrate layer; 12. Adhesive layer; 111. Base film; 3. Functional coating; 2. Positive electrode sheet; 21. Positive current collector; 22. Positive active layer; 4. Negative electrode sheet; 41. Negative current collector; 42. Negative active layer. Detailed Implementation

[0014] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0015] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0016] To address the issues of poor electrolyte wettability and lack of active safety protection under thermal abuse conditions in existing separators, electrodes, and separator-electrode interfaces, which result in batteries failing to balance fast charging performance and thermal safety and being prone to micro-short circuits, according to embodiments of this application, in a first aspect, a functional coating is provided, comprising a functional material, wherein the functional material comprises a carboxylate, and the chemical formula of the carboxylate is (RCOO). x(OH) y M is a metal ion with a valence of 1-3, x is 1, 2 or 3, y is 0 or 1, and R is an aliphatic hydrocarbon group with 9-20 carbon atoms. Based on the mass of the functional coating, the mass content of M is denoted as m%; satisfying: 1≤m≤30.

[0017] This application research found that by setting a special functional coating containing functional materials in the battery, the above-mentioned problems can be effectively improved. This is because: the functional materials provided in this application contain carboxylate (COO) groups. - Both metal ions and functional coatings possess strong polarity, enabling them to generate intense dipole-dipole interactions or coordination with polar solvents in the electrolyte. This gives the functional coating a strong affinity for polar solvents in the electrolyte. Applying functional coatings to substrates (such as the base film of the separator, or the active layers of the positive and negative electrodes) effectively improves the uniformity and speed of electrolyte wetting, increases ion migration rate, enhances the battery's fast-charging performance, reduces electrode interface polarization, and mitigates side reactions. This further suppresses adverse phenomena such as transition metal dissolution, crystal structure destruction, and chain oxidation decomposition of the electrolyte, reducing micro-short circuits and contributing to battery thermal safety and cycle performance. Simultaneously, the 9-20 carbon atom aliphatic hydrocarbon groups in the functional materials effectively regulate the melting point of the carboxylate to be close to the battery's internal temperature. When the internal temperature of the battery rises and approaches the melting point, the carboxylate melts and generates microbubbles under the gas generation of the electrolyte. This forms a uniformly distributed microbubble expansion layer on the substrate surface. On the one hand, taking the functional coating located between the separator base film and the electrode active layer as an example, this microbubble expansion layer can increase the physical distance between the separator base film and the electrode active layer, thereby providing a buffer space for the thermal expansion of the electrode, reducing the space for the separator to be squeezed, and reducing micro-short circuits. On the other hand, the microbubble expansion layer is also a dense and ion-insulating physical barrier, which can effectively block the ion and charge transport between the positive and negative electrodes, thereby effectively interrupting the electrochemical reaction and chain reaction under high temperature environment, isolating the continuous occurrence of side reactions, further reducing the continuous increase of heat, reducing the risk of thermal runaway, and effectively improving the thermal safety of the battery.

[0018] Furthermore, by controlling the mass content m% of M in the functional coating to satisfy 1≤m≤30, the electrolyte affinity of the functional coating and the effect of forming a microbubble expansion layer can be effectively regulated. The higher the mass content of M, the greater the density of polar centers (metal ions and their coordinated carboxylate groups) per unit mass of coating, and the faster the electrolyte wetting rate. When the aforementioned range is met, there are sufficient polar centers per unit mass of coating to ensure the electrolyte wettability of the functional coating. On the basis of improving the fast charging performance of the battery, the polarization of the electrode interface is reduced, the occurrence of side reactions is alleviated, and the adverse phenomena of transition metal dissolution, crystal structure destruction and chain oxidation decomposition of electrolyte in active materials are further suppressed, reducing micro-short circuits and benefiting the thermal safety and cycle performance of the battery. It can also make the functional coating melt to form a uniform and continuous microbubble expansion layer, effectively blocking ion transport and effectively improving the thermal safety of the battery. Furthermore, it can avoid the excessive adsorption of electrolyte solvent by the coating due to excessive polarity, which would affect the desolvation process of ions at the interface between the separator and the electrode. At the same time, excessive metal content may reduce the mechanical flexibility of the coating, causing functional particles to fall off and reducing the stability of the coating structure, which is not conducive to improving the cycle performance of the battery. It can also avoid excessive inorganic components in the coating, which may significantly increase the melting point, preventing the battery from melting in time before thermal runaway, which is not conducive to improving the thermal safety of the battery.

[0019] For example, the mass content m% of M in the carboxylate can be obtained by conventional testing methods in the art, such as thermogravimetric analysis (TGA) or energy-dispersive X-ray spectroscopy (EDS). For example, the mass content m% of M can be 1%, 1.28%, 1.5%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, etc., or a value within any two of the above ranges.

[0020] In some embodiments, R is at least one selected from heptadecanyl, octadecyl, heptadecanyl monoalkenyl, heptadecanyl polyalkenyl, octadecyl monoalkenyl, and octadecyl polyalkenyl.

[0021] It is understandable that heptadecenyl refers to a straight-chain or branched unsaturated aliphatic hydrocarbon group with 17 carbon atoms and containing two or more carbon-carbon double bonds, including its geometric isomers and stereoisomers. Octadecenyl refers to a straight-chain or branched unsaturated aliphatic hydrocarbon group with 18 carbon atoms and containing two or more carbon-carbon double bonds, including its geometric isomers and stereoisomers.

[0022] In some implementations, 2 ≤ m ≤ 30.

[0023] In some embodiments, M includes at least one of lithium ions, sodium ions, potassium ions, calcium ions, magnesium ions, barium ions, and aluminum ions.

[0024] In some embodiments, the mass content of the functional material is denoted as s1% based on the mass of the functional coating; satisfying 35≤s1≤99. In this case, the functional coating may contain other auxiliary materials commonly used in the art (such as adhesives). In this case, the adhesive and functional material enable the functional coating to have good adhesion, heat resistance and electrolyte wettability.

[0025] For example, the mass content s1% of the functional material can be 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, etc., or a value within the range of any two of the above values.

[0026] In some embodiments, the mass content of the carboxylate is denoted as s11%, based on the mass of the functional coating; satisfying 35≤s11≤99%.

[0027] For example, the mass content s11% of the carboxylate can be obtained by conventional testing methods in the art, such as thermogravimetric analysis (TGA) or energy-dispersive X-ray spectroscopy (EDS). For example, the mass content s11% of the carboxylate can be 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, etc., or a value within any two of the above ranges.

[0028] In some embodiments, the functional material further includes a first filler, the mass content of which is denoted as s12% based on the mass of the functional coating; satisfying 0 < s12 ≤ 64; further, the first filler includes boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, uracil, cytosine, guanine, 2-mercaptobenzimidazole, 2-mercaptobenzimidazole derivatives, N,N'-di(β-naphthyl)-p-phenylenediamine, 4-amino-2,6-dihydroxybenzimidazole, etc. At least one of the following: pyrimidine, 4-amino-2-carbonylpyrimidine, 5,6-amino-5-methyluracil, 5-fluorouracil, 5-cyanouracil, uracil, 2,4-dihydroxy-5-fluoropyrimidine, 2-amino-4,6-dimethyl-5-pyrimidinecarboxylate, 4-amino-2,6-dihydroxypyrimidine, dimethyl aminocarbonate pyrimidine carboxylic acid, 8-mercaptopurine, 6-aminopurine, guanine, hypoxanthine, 2,4-dimercaptopurine, phenolic resin, melamine resin, and cellulose.

[0029] In the invention, the 2-mercaptobenzimidazole derivative includes at least one of 2-mercapto-5-methylbenzimidazole, 2-mercapto-5-methoxybenzimidazole, 2-mercapto-5-ethoxybenzimidazole, 2-mercapto-5-hydroxybenzimidazole, 2-mercapto-5-aminobenzimidazole, 2-mercapto-5-chlorobenzimidazole, 2-mercapto-5-sulfonic acid benzimidazole, 2-mercapto-5-carboxybenzimidazole, 2-mercapto-5-nitrobenzimidazole, 2-mercapto-5-benzimidazole carboxylic acid, 2-mercaptobenzimidazole calcium salt, 2-mercaptobenzimidazole magnesium salt, and 2-mercaptobenzimidazole aluminum salt.

[0030] When the first filler is an organic material, its surface energy is similar to that of the carboxylate, and the two have good interfacial compatibility and good electrolyte affinity. These factors can promote the uniform mixing of the first filler and the carboxylate, improve the consistency of the functional coating, and thus improve the consistency between the functional coating and the substrate. This not only improves the cycle performance of the battery but also reduces the stress unevenness inside the functional coating and / or the substrate at high temperatures, thereby improving the thermal safety of the battery. When the first filler is an organic or inorganic material, the heat resistance of the coating can be further improved, thus enhancing the thermal safety of the battery.

[0031] For example, the mass content s12% of the first filler can be obtained by conventional testing methods in the art, such as thermogravimetric analysis (TGA) or energy-dispersive X-ray spectroscopy (EDS). For example, the mass content s12% of the first filler can be 0.1%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 64%, etc., or a value within the range of any two of the above values.

[0032] In some embodiments, the functional coating further includes an adhesive, the mass content of which is denoted as s2% based on the mass of the functional coating; satisfying 1 ≤ s2 ≤ 65, and further, 1 ≤ s2 ≤ 10. For example, the mass content s2% of the adhesive can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc., or a value within the range of any two of the above values.

[0033] In some embodiments, the adhesive comprises one or more selected from polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, acrylate polymers, fluoropolymers, styrene-acrylic latex, polyacrylonitrile, polyvinyl acetate, acrylic polymers, and polyurethane. The first polymer comprises an acrylate adhesive, including polymethyl methacrylate, ethylhexyl acrylate, butyl acrylate, acrylate-acrylonitrile copolymer, acrylate-acrylonitrile-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, and methyl acrylate. acrylic acid N,N Dimethacrylamide copolymer, ethyl acrylate acrylic acid 2 (Diethylamino)ethyl acrylate copolymer, ethyl acrylate acrylic acid N,N Diethylacrylamide copolymer, ethyl acrylate acrylic acid 2 At least one of (diethylamino)ethyl acrylate; the content of ester-containing monomers in the first polymer is 50%-100%. The polymerizing monomers of the first polymer include one or more of methyl methacrylate, butyl acrylate, n-propyl acrylate, octyl acrylate, ethyl methacrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate.

[0034] In some embodiments, the functional coating includes a carboxylate and an adhesive. The carboxylate content is 35%-90% by mass, and the adhesive content is 10%-65% by mass, based on the mass of the functional coating. In this case, the functional coating contains more adhesive, which can further improve the adhesion of the functional coating and enhance the interfacial performance between the diaphragm and the electrode.

[0035] In some embodiments, the functional coating comprises a carboxylate, a first filler, and an adhesive, wherein the carboxylate has a mass content of 35%-90%, the first filler has a mass content of 1%-64%, and the adhesive has a mass content of 1%-9%, based on the mass of the functional coating.

[0036] In some embodiments, the functional coating comprises a carboxylate and an adhesive. The carboxylate content is 90%-99% by mass, and the adhesive content is 1%-10% by mass, based on the mass of the functional coating. Although the adhesion of the functional coating is somewhat weakened, the proportion of functional material is relatively large, making it more similar to a ceramic coating. This further improves the electrolyte wettability and the effect of forming a microbubble expansion layer, thereby improving the fast charging performance, cycle performance, and thermal safety of the battery.

[0037] Furthermore, in some embodiments, the thickness of the functional coating is denoted as h1 μm, satisfying 0.2≤h1≤5. In this way, while ensuring the improvement effect of the functional coating, the ion diffusion path is shortened and the ion migration rate is increased, which is beneficial to the fast charging performance and cycle performance of the battery.

[0038] For example, the thickness h1 of the functional coating can be obtained by testing methods conventional in the art, such as by scanning electron microscopy (SEM). For example, the thickness h1 (in μm) of the functional coating can be 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc., or a value within the range of any two of the above values.

[0039] In some embodiments, the melting point Tm of the carboxylate is 100℃-160℃; this indicates that the carboxylate has a melting point that matches the thermal runaway temperature of the battery. When the internal temperature of the battery rises abnormally and reaches near the melting point, the carboxylate will melt and change from a solid to a liquid state. When the temperature rises further, the carboxylate will generate microbubbles under the gas generation of the electrolyte, forming a uniformly distributed microbubble expansion layer, thereby providing a buffer space for the thermal expansion of the electrode and reducing the occurrence of side reactions, thereby reducing micro-short circuits and improving the cycle performance and thermal safety of the battery.

[0040] For example, the melting point Tm of the carboxylate can be obtained by conventional testing methods in the art, such as by differential scanning calorimetry (DSC). For example, the melting point Tm (in °C) of the carboxylate can be 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, etc., or a value within a range of any two of the above values.

[0041] In some embodiments, the thermal decomposition temperature Td of the carboxylate is 200℃-250℃; this indicates that the carboxylate has a high thermal decomposition temperature. Within its melting point temperature range, the structure remains stable and no significant thermal decomposition reaction occurs. This avoids the generation of additional gases or side reactions due to the thermal decomposition of the carboxylate, prevents further heat generation, and inhibits secondary deterioration of the battery's thermal state, which is beneficial to the battery's thermal safety.

[0042] For example, the thermal decomposition temperature Td of the carboxylate can be obtained by conventional testing methods in the art, such as by thermogravimetric analysis (TGA). For example, the thermal decomposition temperature Td (in °C) of the carboxylate can be 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, etc., or a value within a range of any two of the above values.

[0043] In some embodiments, the carboxylate has a polycrystalline structure with a grain size of 0.6 nm-0.9 nm. This grain has a large specific surface area and numerous surface active sites, enabling it to adsorb dissolved transition metal ions and acid byproducts, thereby reducing side reactions, minimizing micro-short circuits, and improving the battery's cycle performance and thermal safety. Simultaneously, the carboxylate exhibits good electrolyte resistance at room temperature, preventing decarboxylation reactions and ensuring the electrolyte wettability of the functional coating. Furthermore, it can form a microbubble expansion layer under high-temperature runaway conditions, enhancing the battery's thermal safety.

[0044] It is understood that the carboxylate is a polycrystalline structure composed of several single-crystal grains. The grain size refers to the grain size of the single-crystal grains separated by independent grain boundaries. Exemplarily, the grain size of the single-crystal grains can be obtained by conventional testing methods in the art, such as observation using an X-ray diffractometer and calculation using the Scherrer formula, or direct observation using a transmission electron microscope. Exemplarily, the grain size (in nm) in the polycrystalline structure can be 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, 0.82, 0.85, 0.88, 0.9, or a value within any two of the above ranges.

[0045] In some embodiments, the infrared spectrum of the functional coating shows a wavenumber of 3400 cm⁻¹. -1 -3750cm -1 An absorption peak is present. This absorption peak is attributed to the OH stretching vibration peak in the carboxyl group. The appearance of the absorption peak indicates the presence of carboxyl ions in the carboxylate. Carboxyl ions can enhance the polarity of the carboxylate, improve the wettability of the electrolyte, ensure the fast charging performance and cycle performance of the battery, and reduce micro-short circuits.

[0046] In some embodiments, the infrared spectrum of the functional coating shows a wavenumber of 2895 cm⁻¹. -1 -2945cm -1 and 2825cm -1 -2875cm -1The infrared spectrum contains absorption peaks. These absorption peaks correspond to the antisymmetric stretching vibration peak and the symmetric stretching vibration peak of the methylene group in the carboxylate, respectively. When the above absorption peaks are present in the infrared spectrum, it indicates that there is a methylene group in the carboxylate. This structure can regulate the melting point of the carboxylate and ensure the thermal safety of the battery.

[0047] For example, the infrared spectrum of the carboxylate can be obtained by conventional testing methods in the art, such as by an infrared spectrometer.

[0048] In some embodiments, the X-ray diffraction pattern of the carboxylate shows diffraction peaks at any position within the ranges of 10º-15º, 15º-25º, and 30º-35º. This indicates that the carboxylate is a crystalline substance with a narrower temperature range compared to amorphous substances. Therefore, it can more accurately trigger the thermal safety function of the functional coating at high temperatures, preventing the functional coating from melting indiscriminately and causing battery failure. Simultaneously, the carboxylate also exhibits good electrolyte resistance at room temperature, ensuring good electrolyte wettability of the functional coating. For example, the X-ray diffraction pattern of the carboxylate may show values ​​at 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 30°, 31°, 32°, 33°, 34°, and 35°, or values ​​within any two of the aforementioned ranges.

[0049] In some embodiments, the carboxylate includes at least one of calcium stearate, magnesium stearate, aluminum monostearate, aluminum distearate, aluminum tripearate, potassium stearate, sodium stearate, barium stearate, lithium stearate, sodium oleate, magnesium oleate, calcium oleate, aluminum trioleate, potassium oleate, barium oleate, and lithium oleate.

[0050] In some embodiments, at 25°C, the solubility of the carboxylate in a polar solvent is less than 1%, and the polar solvent includes at least one of N-methylpyrrolidone, N,N-dimethylacetamide, and acetone. In this way, the functional coating has good stability, ensuring that the improvement effect of the functional coating is stably exerted.

[0051] In some embodiments, the particle size of the carboxylate satisfies at least one of the following conditions: (1) 0.1μm≤Dv10≤0.8μm; preferably 0.2μm≤Dv10≤0.3μm; (2) 0.3μm≤Dv50≤3μm; preferably 0.3μm≤Dv50≤1μm; (3) 0.6μm≤Dv90≤5μm; preferably 0.6μm≤Dv90≤2.5μm; (4) The particle size distribution Span value is less than or equal to 8.

[0052] By adjusting the particle size of the carboxylates to achieve a suitable particle size distribution, the electrolyte can quickly and uniformly wet the functional coating and substrate, improve the liquid retention capacity of the functional coating and substrate, and reduce micro-short circuits, which is beneficial to the fast charging performance and cycle performance of the battery.

[0053] It is understood that in this application, the particle size distribution Span value is calculated by (Dv90-Dv10) / Dv50; Dv10 is the particle size corresponding to a cumulative volume distribution percentage of 10%; Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50%, which is also the median particle size; Dv90 is the particle size corresponding to a cumulative volume distribution percentage of 90%. Particle sizes Dv10, Dv50, and Dv90 can be obtained by arbitrarily selecting 100μm×100μm in the SEM image of the functional layer surface and combining it with image analysis software (e.g., ImageJ, vavoMeasurer, Matlab, etc.); or, particle sizes Dv10, Dv50, and Dv90 can also be obtained by testing with a laser particle size analyzer. For example, Dv10 (unit μm) can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc., or a value within the range of any two of the above values. For example, Dv50 (unit μm) can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, etc., or a value within the range of any two of the above values. For example, Dv90 (unit μm) can be 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 3, 3.5, 4, 4.5, 5, etc., or a value within the range of any two of the above values. For example, the particle size distribution Span value can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, etc., or a value within the range of any two of the above values.

[0054] According to an embodiment of this application, in a second aspect, a diaphragm is also provided, the diaphragm comprising a substrate layer, the substrate layer comprising a base film and a functional coating disposed on at least one side surface of the base film in the thickness direction, the functional coating being the functional coating described in the first aspect.

[0055] It is understood that the separator provided in this application, having the functional coating described in the first aspect, can effectively improve the electrolyte wetting uniformity and wetting speed of the separator, and improve the interface performance between the separator and the electrode. Furthermore, when the battery experiences thermal runaway, it can form a microbubble expansion layer, which can effectively block the ion and charge transport between the positive and negative electrodes, thereby effectively interrupting the electrochemical reaction and chain reaction under high temperature conditions, isolating the continuous occurrence of side reactions, further reducing the continuous increase of heat, and reducing the risk of thermal runaway. As a result, the battery containing this separator has better fast charging performance, cycle performance, and thermal safety.

[0056] Furthermore, in some embodiments, the diaphragm further includes an adhesive layer located on at least one side surface of the substrate layer in the thickness direction, the adhesive layer comprising a first polymer.

[0057] like Figure 1 As shown, the diaphragm 1 includes a substrate layer 11 and an adhesive layer 12, with the adhesive layer 12 located on both sides of the substrate layer 11. The substrate layer 11 includes a base film 111 and a functional coating 3, with the functional coating 3 located on one side of the base film 111. It should be noted that... Figure 1 The example shown only illustrates the case where the functional coating 3 is located on one side of the base film 111. The functional coating 3 can also be located on both sides of the base film 111.

[0058] When the functional coating is located on the surface of the base film, it can improve the wetting speed and uniformity of the electrolyte on the separator, and can also effectively block electrochemical reactions and chain reactions under high temperature runaway environment, reduce heat generation, thereby improving the battery's fast charging performance, cycle performance and thermal safety; further setting an adhesive layer can shorten the distance between the positive and negative electrodes and the separator, shorten the ion transport path, and further improve the battery's fast charging performance and cycle performance.

[0059] In some embodiments, the coating layer has a porous structure formed from the first polymer. The porous structure significantly enhances the electrolyte wettability of the separator and constructs through-hole ion transport channels, thereby reducing interfacial impedance, increasing the wetting rate, reducing micro-short circuits, and improving the battery's fast-charging and cycle performance. Further, in some embodiments, the first polymer is selected from poly(p-phenylene terephthalamide), poly(m-phenylene isophthalamide), polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, ethylene fluoride-hexafluoropropylene copolymer, ethylene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0060] Furthermore, in some embodiments, the adhesive layer includes a first polymer and a second filler, the adhesive layer having a porous structure formed by the first polymer, wherein the mass content of the first polymer is 30%-80% and the mass content of the second filler is 20%-70% based on the mass of the adhesive layer.

[0061] Furthermore, in some embodiments, the coating layer further includes a second filler dispersed in the porous structure. The second filler includes at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate. Based on the mass of the coating layer, the mass content of the second filler is 20%-70%. The second filler has strong polarity, which can improve the electrolyte wettability of the coating layer, thereby better exerting the improvement effect of the functional coating. At the same time, the second filler can also reduce the surface static electricity of the separator, prevent the separator from wrinkling, being broken by static electricity and causing micro-short circuits, or igniting the electrolyte and further causing thermal runaway, thereby ensuring the thermal safety and cycle performance of the battery.

[0062] For example, the mass content of the second filler can be determined by conventional testing methods in the art, such as separating the adhesive layer and the functional coating and measuring it using energy-dispersive X-ray spectroscopy (EDS). For example, the mass content of the second filler can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 70%, etc., or a value within any two of the above values. For example, the mass content of the first polymer can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., or a value within any two of the above values.

[0063] In some embodiments, the first polymer is in particulate form, and the average particle size d1 of the first polymer is 0.55 μm-0.95 μm. Further, in some embodiments, the first polymer is selected from polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, acrylate-acrylonitrile-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, and methyl acrylate. acrylic acid N,N Dimethacrylamide copolymer, ethyl acrylate acrylic acid 2 (Diethylamino)ethyl acrylate copolymer, ethyl acrylate acrylic acid N,N Diethylacrylamide copolymer, ethyl acrylate acrylic acid 2 At least one of (diethylamino)acrylate.

[0064] Furthermore, in some embodiments, the coating layer further includes second polymer particles, which comprise second primary particles and / or second secondary particles formed by the agglomeration of the second primary particles. The average particle size d2 of the second primary particles is 0.15 μm-0.25 μm, and the average particle size d3 of the second secondary particles is 3.5 μm-18 μm. In some embodiments, the second polymer is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, ethylene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0065] By combining the first and second polymer particles, the bonding strength between the separator and the electrode can be significantly enhanced, thereby reducing relative displacement during cycling, reducing wrinkles, and thus reducing micro-short circuits. At the same time, the coating layer formed by polymers of different particle sizes will have a large number of micro-gaps, which can not only retain more electrolyte, but also form through ion transport channels, thus enhancing the electrolyte wettability of the separator, increasing the ion transport rate, and reducing the interfacial impedance. The excellent wettability of the electrolyte fully wets the cavity in the separator, which is beneficial to the battery's fast charging performance, cycle performance and thermal safety, and reduces micro-short circuits.

[0066] For example, the average particle size d1 of the first polymer, the average particle size d2 of the second primary particles, and the average particle size d3 of the second secondary particles are measured by the following method. Taking the average particle size d1 of the first polymer as an example, specifically: in the SEM image of the adhesive layer surface, arbitrarily select 100μm×100m, identify and randomly select 100 first polymer particles, and draw the rectangle or square with the smallest area that completely surrounds one first polymer particle, that is, draw the rectangle or square tangent to the four sides of the edge of the first polymer particle. The length of the long side of the rectangle or any side of the square is the particle size of the first polymer particle. If there are not enough particles in a single image, multiple images can be taken until the observed first polymer particles accumulate to 100. Calculate the arithmetic mean of the particle sizes of the 100 first polymer particles, which is the average particle size d1 of the first polymer particles. For example, the average particle size d1 (in μm) of the first polymer can be 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a value within any two of the above values. For example, the average particle size d2 (in μm) of the second primary particles can be 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, or a value within any two of the above values. For example, the average particle size d3 (in μm) of the second secondary particles can be 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or a value within any two of the above values.

[0067] Furthermore, based on the mass of the coating layer, the mass content of the second polymer particles is 10%-60%.

[0068] For example, the mass content of the second polymer particles may be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a value within the range of any two of the above values.

[0069] In some embodiments, the porosity of the base film is 30-70%, and the average pore size is 30-50 nm.

[0070] In some embodiments, the material of the base film is selected from one or more of polyolefins, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalate), poly(m-phenylene isophthalate), or polymer derivatives thereof.

[0071] According to an embodiment of this application, in a third aspect, a positive electrode sheet is also provided, wherein the functional coating is located on the surface of at least one side of the positive electrode sheet.

[0072] In some embodiments, the positive electrode includes a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector, wherein the functional coating is located on the surface of the positive active layer. It is understood that, due to the functional coating described in the first aspect, the positive electrode can effectively improve the electrolyte wetting uniformity and wetting speed of the positive electrode active layer, and improve the interfacial performance between the positive electrode and the separator; furthermore, in the event of battery thermal runaway, a microbubble expansion layer can be formed, which can effectively block the ion and charge transport between the positive and negative electrodes, thereby effectively interrupting the electrochemical reaction and chain reaction under high-temperature conditions, isolating the continuous occurrence of side reactions, further reducing the continuous increase of heat, and reducing the risk of thermal runaway. Thus, the battery containing this positive electrode has better fast-charging performance, cycle performance, and thermal safety.

[0073] like Figure 2 As shown, the positive electrode 2 includes a positive current collector 21 and a positive active layer 22 located on both sides of the positive current collector 21. The positive active layer includes a positive active material, and the functional coating 3 is located on the surface of the positive active layer 22 away from the positive current collector 21. It should be noted that... Figure 2 This only illustrates the case where the functional coating 3 is located on one side of the positive electrode active layer 22. The functional coating 3 can also be located on both sides of the positive electrode active layer 22 away from the positive electrode current collector.

[0074] In some embodiments, the positive electrode active layer includes a positive electrode active material; the positive electrode active material includes at least one of lithium nickel oxide, lithium titanate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide.

[0075] In some embodiments, the positive electrode active layer further includes a conductive agent, which includes at least one of conductive carbon black, carbon nanotubes, conductive graphite, and graphene.

[0076] In some embodiments, the positive electrode active layer further includes a binder, the binder comprising at least one of polyvinylidene fluoride (PVDF), acrylic-modified PVDF, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0077] According to an embodiment of this application, in a fourth aspect, a negative electrode sheet is also provided, wherein the functional coating is located on the surface of at least one side of the negative electrode sheet.

[0078] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, wherein the functional coating is located on the surface of the negative electrode active layer. It is understood that, due to the functional coating described in the first aspect, the negative electrode sheet can effectively improve the electrolyte wetting uniformity and wetting speed of the negative electrode sheet active layer, and improve the interface performance between the negative electrode sheet and the separator; furthermore, in the event of battery thermal runaway, a microbubble expansion layer can be formed, which can effectively block the ion and charge transport between the positive and negative electrodes, thereby effectively interrupting the electrochemical reaction and chain reaction under high-temperature conditions, isolating the continuous occurrence of side reactions, further reducing the continuous increase of heat, and reducing the risk of thermal runaway. Therefore, the battery containing this negative electrode sheet has better fast-charging performance, cycle performance, and thermal safety.

[0079] like Figure 3 As shown, the negative electrode sheet 4 includes a negative electrode current collector 41 and a negative electrode active layer 42 located on both sides of the negative electrode current collector 41. The negative electrode active layer includes a negative electrode active material, and the functional coating 3 is located on the surface of the negative electrode active layer 42 away from the negative electrode current collector 41. It should be noted that... Figure 3 This only illustrates the case where the functional coating 3 is located on one side of the surface of the negative electrode active layer 42. The functional coating 3 can also be located on both sides of the negative electrode active layer 42, away from the negative electrode current collector.

[0080] In some embodiments, the negative electrode active layer comprises a negative electrode active material; the negative electrode active material comprises silicon-based material and / or carbon-based material.

[0081] In some embodiments, the silicon-based material is selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0082] In some embodiments, the median particle size of the silicon-based material is 5 μm-12 μm.

[0083] In some embodiments, the negative electrode active layer further includes a conductive agent, which includes at least one of conductive carbon black, carbon nanotubes, conductive graphite, and graphene.

[0084] In some embodiments, the negative electrode active layer further includes a binder, the binder including at least one of polyvinylidene fluoride (PVDF), acrylic-modified PVDF, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene, polyacrylonitrile, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0085] According to an embodiment of this application, in a fifth aspect, a secondary battery is also provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode, the negative electrode, and the separator comprises the functional coating described in the first aspect. In some embodiments, the secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is the separator described in the second aspect.

[0086] In some embodiments, the secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the positive electrode described in the third aspect.

[0087] In some embodiments, the secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode described in the fourth aspect.

[0088] Furthermore, in some embodiments, the electrolyte comprises lithium salt and cyclic carbonate, wherein the cyclic carbonate content is 15%-70% by mass, based on the mass of the electrolyte. Cyclic carbonate can better wet the functional coating, thereby improving ion transport rate, reducing micro-short circuits, and benefiting the battery's fast-charging and cycle performance.

[0089] For example, the mass content of the cyclic carbonate can be determined by conventional testing methods in the art, such as GC-MS (gas chromatography-mass spectrometry). For example, the mass content of the cyclic carbonate can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc., or a value within a range of any two of the above values.

[0090] Furthermore, the cyclic carbonates include fluorinated cyclic carbonates and non-fluorinated cyclic carbonates. Based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonates is denoted as a%, and the mass content of the non-fluorinated cyclic carbonates is denoted as b%. When the fluorinated cyclic carbonates satisfy 0.9≤a / b≤7.5, particularly 5≤a≤40, 3.5≤b≤50, and further satisfy 10≤a≤28, the fluorinated cyclic carbonates can improve the stability of silicon-based materials at room temperature, thereby reducing side reactions in the electrolyte caused by silicon-based materials, further improving the stability of the functional coating, ensuring the electrolyte wettability and thermal safety of the functional coating, and thus ensuring the fast-charging performance, cycle performance, and thermal safety of the battery.

[0091] For example, the mass content a% of the fluorinated cyclic carbonate can be obtained by conventional testing methods in the art, such as GC-MS (gas chromatography-mass spectrometry). For example, the mass content b% of the non-fluorinated cyclic carbonate can be obtained by conventional testing methods in the art, such as GC-MS (gas chromatography-mass spectrometry). For example, a / b can be 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, etc., or values ​​within the range of any two of the above values.

[0092] For example, the mass content a% of the fluorinated cyclic carbonate can be 5%, 10%, 15%, 20%, 25%, 28%, 30%, 35%, 40%, or a value within the range of any two of the above values. For example, the mass content b% of the non-fluorinated cyclic carbonate can be 3.5%, 5%, 10%, 15%, 20%, 25%, 28%, 30%, 35%, 40%, 45%, 50%, or a value within the range of any two of the above values.

[0093] In some embodiments, the fluorocyclic carbonate includes at least one of fluoroethylene carbonate and difluoroethylene carbonate.

[0094] In some embodiments, the non-fluorinated cyclic carbonate includes at least one of vinylene carbonate, ethylene carbonate (EC), and propylene carbonate (PC).

[0095] In some embodiments, the lithium salt includes lithium hexafluorophosphate and a second lithium salt, the second lithium salt including at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide; further, based on the mass of the electrolyte, the mass content of the lithium hexafluorophosphate is denoted as e%, and the mass content of the second lithium salt is denoted as d%, satisfying 0.07≤d / e≤0.5. At high temperatures close to the battery temperature threshold, byproducts of lithium hexafluorophosphate can promote electrolyte decomposition and gas generation near the functional coating, and dissolve the functional coating to form a foam-like microbubble expansion layer, thereby blocking electrochemical reactions and chain reactions and improving the battery's thermal safety. However, lithium hexafluorophosphate has an adverse effect on the functional coating at room temperature. Furthermore, adding a second lithium salt with better stability can reduce side reactions generated by the electrolyte and improve the stability of the functional coating at room temperature. However, the second lithium salt will hinder the formation of the microbubble expansion layer of the functional coating at high temperatures. Therefore, adjusting 0.07≤d / e≤0.5 can enable the functional coating to balance room temperature stability and thermal safety, effectively exert the improvement effect of the functional coating, and thus ensure the battery's fast charging performance, cycle performance, and thermal safety.

[0096] For example, the mass content e% of the lithium hexafluorophosphate can be obtained by conventional testing methods in the art, such as GC-MS (gas chromatography-mass spectrometry). For example, the mass content d% of the second lithium salt can be obtained by conventional testing methods in the art, such as GC-MS (gas chromatography-mass spectrometry). For example, d / e can be 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc., or a value within the range of any two of the above values.

[0097] In some implementations, 1 ≤ d ≤ 15.

[0098] In some implementations, 7 ≤ e ≤ 25.

[0099] In some embodiments, the charging cutoff voltage of the secondary battery is greater than or equal to 4.5V.

[0100] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Where specific experimental steps or conditions are not specified in the embodiments and comparative examples, they can be performed according to the conventional experimental steps or conditions described in the literature in the art. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products. In all embodiments and comparative examples of this application, the unit % represents mass percentage.

[0101] Example 1 This embodiment provides a method for preparing a battery, including the following steps: (1) Preparation of positive electrode Lithium cobalt oxide, polyvinylidene fluoride (PVDF 500) binder, and conductive agent (Super P and carbon nanotubes in a mass ratio of 2:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 98:1:1. The mixture was continuously stirred under the action of a stirrer to form a homogeneous and fluid positive electrode slurry. Subsequently, the positive electrode slurry was coated onto an aluminum foil with a thickness of 10 μm and dried in a vacuum oven at 120 °C for 6 h. After that, it was rolled and slit to obtain the positive electrode sheet.

[0102] (2) Preparation of negative electrode sheet Graphite, silicon carbide material (Dv50=7μm), conductive agent (carbon black and carbon nanotubes in a mass ratio of 1:1), sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber were mixed in a deionized water solvent at a weight ratio of 90:8:1:0.5:0.5 and continuously stirred under the action of a stirrer to form a homogeneous and fluid negative electrode slurry. Subsequently, the slurry was coated on the surface of a 10μm thick current collector copper foil and dried in a vacuum oven at 120℃ for 6 hours. Then, after rolling, slitting, and wire bonding, the negative electrode sheet was obtained.

[0103] (3) Electrolyte preparation In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate were mixed uniformly. Then, based on the electrolyte mass, 16wt% LiPF6, 5wt% lithium bis(trifluoromethanesulfonyl)imide, 3wt% 1,3,6-hexanetrionitrile, and 20wt% fluoroethylene carbonate were slowly added. After thorough stirring, the desired lithium-ion battery electrolyte was obtained. Based on the electrolyte mass, the ethylene carbonate content was 7.5%, the propylene carbonate content was 7.5%, the propyl propionate to ethyl propionate mass ratio was 1:1, and the remainder of the electrolyte consisted of propyl propionate and ethyl propionate.

[0104] (4) Preparation of the diaphragm 95 parts of aluminum tristearate (parameters detailed in Table 1) and 5 parts of polymethyl methacrylate were mixed in water and stirred thoroughly to obtain a mixed slurry with a solid content of 25%. The mixed slurry was coated onto one side of a polyethylene film using a gravure roller and dried in an oven at 60°C to form a functional coating with a thickness h1 of 2 μm, thus obtaining the substrate layer. Vinylidene fluoride-hexafluoropropylene copolymer and boehmite were dissolved in N,N-dimethylacetamide (DMAC) and stirred thoroughly until the vinylidene fluoride-hexafluoropropylene copolymer was dissolved to obtain a solution with a solid content of 10%. This solution was coated onto both sides of the substrate layer using a gravure roller, then extracted in a water bath and dried at 60°C. The thickness of the coating layer on one side was 1 μm, thus obtaining the diaphragm. The coating layer has a porous structure formed by vinylidene fluoride-hexafluoropropylene copolymer. Based on the mass of the coating layer, the mass content of vinylidene fluoride-hexafluoropropylene copolymer is 60%, and the mass content of boehmite is 40%.

[0105] The infrared spectrum of the functional coating in this embodiment is shown below. Figure 4 X-ray diffraction pattern can be found Figure 5 Transmission electron microscopy revealed that the grain size of the single crystals in aluminum tristearate was 0.6 nm to 0.9 nm.

[0106] (5) Preparation of lithium-ion batteries The above-prepared positive electrode, separator, and negative electrode are wound together to form a bare cell, with the functional coating facing the positive electrode. The bare cell is then placed in an aluminum-plastic film, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, room temperature standing, and high temperature formation, the desired lithium-ion battery is obtained.

[0107] The preparation methods of Examples 2-18 are basically the same as those of Example 1, with differences shown in Tables 1-3. " / " indicates that the item does not exist. In Tables 1-3, m% is the mass content of M in the functional coating, s1% is the mass content of the functional material in the functional coating, and the Span value of the carboxylate particle size distribution is (Dv90-Dv10) / Dv50; s11% is the mass content of the carboxylate in the functional material, s12% is the mass content of the first filler in the functional material, s2% is the mass content of the adhesive in the functional coating, h1 μm is the thickness of the functional coating, a% is the mass content of the fluorinated cyclic carbonate, b% is the mass content of the non-fluorinated cyclic carbonate, e% is the mass content of lithium hexafluorophosphate, d% is the mass content of the second lithium salt, EC is ethylene carbonate, PC is propylene carbonate, and VC is vinylene carbonate. (C) of Example 1 17 H 25 The melting point of COO)3Al is 115℃, and the C in Example 2 18 H 37 The melting point of COOK is 170°C, and the C in Example 3... 17 H 33 COONa has a melting point of 270°C, and the (C) in Example 4 17 H 35 The melting point of COO)2Ca is 148℃.

[0108] Example 19 This embodiment provides a method for preparing a battery. Compared with Embodiment 1, the difference lies in step (4). Step (4) in this embodiment includes: 95 parts of aluminum tristearate (parameters detailed in Table 1) and 5 parts of polymethyl methacrylate were mixed in water and stirred thoroughly to obtain a mixed slurry with a solid content of 25%. The mixed slurry was coated onto one side of the base film using a gravure roller and dried in an oven at 60°C to form a functional coating with a thickness h1 of 2 μm, thus obtaining the substrate layer. Polymethyl methacrylate (particulate first polymer) and polyvinylidene fluoride (second polymer particles) were dispersed in a solvent water and stirred thoroughly to obtain a solution with a solid content of 10%. This solution was coated onto both sides of the substrate layer using a gravure roller and dried at 60°C to obtain a diaphragm. The average particle size d1 of the first polymer was 0.7 μm. The second polymer particles included primary particles and secondary particles formed by the agglomeration of primary particles. The average particle size d2 of the primary particles was 0.2 μm, and the average particle size d3 of the secondary particles was 10 μm. Based on the mass of the coating layer, the mass content of the second polymer particles was 30%.

[0109] Example 20 This embodiment provides a method for preparing a battery, which differs from Embodiment 19 in that: The first polymer in granular form is composed of acrylate-acrylonitrile copolymer, and the average particle size d1 of the first polymer is 0.55 μm. The second polymer particles are composed of vinylidene fluoride-hexafluoropropylene copolymer, and the average particle size d2 of the primary particles of the second polymer particles is 0.25 μm, and the average particle size d3 of the secondary particles is 18 μm. Based on the mass of the coating layer, the mass content of the second polymer particles is 60%.

[0110] Example 21 This embodiment provides a method for preparing a battery, which differs from Embodiment 19 in that: The first polymer in granular form is composed of styrene-acrylate monomers-acrylonitrile, and the average particle size d1 of the first polymer is 0.95 μm. The second polymer particles are composed of polyvinylidene fluoride, and the average particle size d2 of the primary particles of the second polymer particles is 0.15 μm, and the average particle size d3 of the secondary particles is 3.5 μm. Based on the mass of the coating layer, the mass content of the second polymer particles is 20%.

[0111] The preparation methods of Examples 22-28 are basically the same as those of Example 1, with the differences shown in Tables 1-3. " / " indicates that the item does not exist.

[0112] Example 29 This embodiment provides a method for preparing a battery. Compared with Embodiment 1, the difference lies in the fact that steps (1) and (4) are different. Step (1) of this embodiment is as follows: Lithium cobalt oxide, polyvinylidene fluoride (PVDF 500) binder, and conductive agent (Super P and carbon nanotubes in a 2:1 mass ratio) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 98:1:1 and continuously stirred under a stirrer to form a homogeneous, flowing positive electrode slurry. The positive electrode slurry was then coated onto a 10 μm thick aluminum foil and dried in a 120°C vacuum oven for 6 hours to obtain the positive electrode active layer. 95 parts of aluminum tristearate and 5 parts of polymethacrylic acid were mixed in water and stirred thoroughly to obtain a mixed slurry with a solid content of 25%. This mixed slurry was coated onto one side of the positive electrode active layer using a gravure roller and dried in a 60°C oven to form a functional coating with a thickness h1 of 2 μm. The coating was then rolled and slit to obtain the positive electrode sheet.

[0113] In step (4) of this embodiment: the total mass of aluminum tristearate and polymethacrylic acid in Example 1 is replaced with the same mass of alumina particles.

[0114] Example 30 This embodiment provides a method for preparing a battery. Compared with Embodiment 1, the difference lies in the fact that steps (1) and (4) are different. Step (1) of this embodiment is as follows: Graphite, silicon carbide material (Dv50=7μm), conductive agent (carbon black and carbon nanotubes in a mass ratio of 1:1), sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber were mixed in a deionized water solvent at a weight ratio of 90:8:1:0.5:0.5 and continuously stirred under the action of a stirrer to form a homogeneous and fluid negative electrode slurry. The slurry was then coated onto the surface of a 10μm thick current collector copper foil and dried in a vacuum oven at 120℃ for 6 hours to obtain the negative electrode active layer. 95 parts of aluminum tristearate and 5 parts of polymethyl methacrylate were mixed in water and stirred thoroughly to obtain a mixed slurry with a solid content of 25%. This mixed slurry was coated onto one side of the negative electrode active layer using a gravure roller and dried in a 60℃ oven to form a functional coating with a thickness h1 of 2μm. The coating was then rolled, slit, and wire-cast to obtain the negative electrode sheet.

[0115] In step (4) of this embodiment: the total mass of aluminum tristearate and polymethacrylic acid in Example 1 is replaced with the same mass of alumina particles.

[0116] Example 31 This embodiment provides a method for preparing a battery. Compared with embodiment 1, the difference is that in step (5), the functional coating is oriented towards the negative electrode.

[0117] The preparation methods of Examples 32-33 are basically the same as those of Example 1, with the differences shown in Tables 1-3. " / " indicates that the item does not exist.

[0118] Example 34 This embodiment provides a method for preparing a battery. Compared with Embodiment 1, the difference lies in step (4). Step (4) in this embodiment includes: 92 parts of aluminum monostearate (parameters detailed in Table 1), 5 parts of melamine thiocyanate, and 3 parts of polybutyl acrylate were mixed in water and stirred thoroughly to obtain a mixed slurry with a solid content of 25%. The mixed slurry was coated onto one side of the base film using a gravure roller and dried in a 60°C oven to form a functional coating with a thickness h1 of 1.5 μm, thus obtaining the substrate layer. Ethylhexyl polyacrylate (particulate first polymer) and vinylidene fluoride-hexafluoropropylene copolymer (second polymer particles) were dispersed in solvent water and stirred thoroughly to obtain a solution with a solid content of 10%. This solution was coated onto both sides of the substrate layer using a gravure roller and dried at 60°C to obtain a diaphragm. The average particle size d1 of the first polymer was 0.75 μm. The second polymer particles included primary particles and secondary particles formed by the agglomeration of primary particles. The average particle size d2 of the primary particles was 0.18 μm, and the average particle size d3 of the secondary particles was 8 μm. Based on the mass of the coating layer, the mass content of the second polymer particles was 35%.

[0119] Comparative Example 1 This comparative example provides a method for preparing a battery. The difference from Example 1 is that step (4) is different. In step (4), aluminum oxide is used instead of aluminum tristearate in Example 1.

[0120] Comparative Example 2 This comparative example provides a method for preparing a battery. The difference between this method and Example 1 is that step (4) is different. In step (4), stearic acid is used instead of aluminum tristearate in Example 1.

[0121] Comparative Example 3 This comparative example provides a method for preparing a battery. The difference between this method and Example 1 is that step (4) is different. In step (4), sodium hexanoate (CAS: 10051-44-2) is used instead of aluminum tristearate in Example 1.

[0122] Comparative Example 4 This comparative example provides a method for preparing a battery. Compared with Example 1, the difference is that step (4) is different. In step (4), 25 parts of aluminum tristearate and 70 parts of melamine cyanurate are used instead of aluminum tristearate in Example 1, and the mass content m% of M in the functional coating is 0.79%.

[0123] Table 1. Variables in the Examples and Comparative Examples 1

[0124] Table 2 Variables for Example and Comparative Example 2

[0125] Table 3 Variable 3 of the Example

[0126] Test case 1. Fast charging performance test: Under the environment of 25℃±2℃, the battery is discharged to 3V at a constant current of 0.2C and recorded as the initial discharge capacity Q0. After standing for 10 minutes, it is fully charged at 0.7C (100% SOC) with a cutoff current of 0.025C and left to stand for 10 minutes. Then, it is discharged to 3V at a 1C rate and left to stand for 10 minutes. The discharge capacity at this time is recorded as Q1. The rate discharge capacity retention rate = (Q1 / Q0)×100%.

[0127] 2. Cyclic Performance Test: Under conditions of 25℃±2℃, the battery was charged at 0.7C constant current and constant voltage to 4.53V, cut off at 0.05C, and then discharged at 0.2C constant current to 3.0V. The initial discharge capacity was recorded as C0. After resting for 10 minutes, the cycling pattern was: 3C constant current and constant voltage charging to 4.25V, cut off at 2C, then 2C constant current and constant voltage charging to 4.48V, cut off at 1.5C, then 1.5C constant current and constant voltage charging to 4.53V, cut off at 0.18C, resting for 5 minutes, and then discharging at 0.7C to 3.0V. After 800 cycles, the battery was charged at 0.7C constant current and constant voltage to 4.53V, cut off at 0.05C, and then discharged at 0.2C constant current to 3.0V. The initial discharge capacity was recorded as C1.

[0128] Capacity retention rate: C = (C1 / C0) × 100%, 3. Furnace temperature test: The lithium-ion batteries are heated in a convection air chamber at an initial temperature of (25±5)℃, with a temperature change rate of (5±2)℃ / min. The temperature is raised to a certain temperature A and held for 60 minutes before the test ends. The battery status is recorded. 20 battery samples are tested for each example and comparative example. If none of the 20 battery samples explode and / or catch fire, it is considered a "pass". The temperature of the air chamber is adjusted to A+2℃ and held for 60 minutes before the test ends. The temperature is continued to rise until at least one of the 20 battery samples explodes and / or catches fire. The pass rate is then calculated as: Furnace temperature pass rate = number of samples that did not explode and / or catch fire / 20 samples.

[0129] 4. Micro-short circuit test: At 25±5℃, discharge the battery to 3V at 0.2C, let it stand for 10 minutes, then charge it to 100% SOC at 0.7C with a cutoff current of 0.05C. After standing for 10 minutes, measure the voltage and record it as the initial voltage V0. Then store it at 25±2℃ for 90 days, measuring the voltage every 5 days. After storage, measure the final voltage as V1. The voltage drop ΔV = V0 - V1.

[0130] The specific test results are shown in Table 4.

[0131] Table 4 Test results of the examples and comparative examples

[0132] As can be seen from Tables 1-4, the functional materials of the functional coatings provided in this application contain carboxylate (COO) groups. - Both carbon and metal ions have strong polarity, which can generate strong dipole-dipole interactions or coordination with polar solvents in the electrolyte, thereby improving the wettability and wettability rate of the electrolyte. The aliphatic hydrocarbon groups with 9-20 carbon atoms can effectively regulate the melting point of carboxylate to be close to the internal temperature threshold of the battery. When the battery is at risk of thermal runaway, the carboxylate will melt and generate microbubbles under the gas generation of the electrolyte. A uniformly distributed, dense and ionically insulating microbubble expansion layer is formed on the substrate surface. While effectively reducing micro-short circuits, the fast charging performance, thermal safety and cycle performance of the battery are improved to varying degrees.

[0133] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A functional coating comprising a functional material, characterized in that, The functional material includes a carboxylate, the chemical formula of which is (RCOO). x (OH) y M is a metal ion with a valence of 1-3, x is 1, 2 or 3, y is 0 or 1, and R is an aliphatic hydrocarbon group with 9-20 carbon atoms. Based on the mass of the functional coating, the mass content of M is denoted as m%; satisfying: 1≤m≤30。 2. The functional coating according to claim 1, characterized in that, The carboxylate salt satisfies at least one of the following conditions: (1) Melting point Tm is 100℃-160℃; (2) The thermal decomposition temperature Td is 200℃-250℃; (3) It has a polycrystalline structure, wherein the grain size in the polycrystalline structure is 0.6 nm-0.9 nm; (4) In the X-ray diffraction pattern, there are diffraction peaks at any position among 10º-15º, 15º-25º, and 30º-35º; (5) R is at least one of heptadecanyl, octadecyl, heptadecanyl monoalkenyl, heptadecanyl polyalkenyl, octadecyl monoalkenyl, and octadecyl polyalkenyl; (6) M includes at least one of lithium ion, sodium ion, potassium ion, calcium ion, magnesium ion, barium ion, and aluminum ion.

3. The functional coating according to claim 1 or 2, characterized in that, In the infrared spectrum of the functional coating, at a wavenumber of 3400 cm⁻¹ -1 -3750cm -1 2895cm -1 -2945cm -1 2825cm -1 -2875cm -1 At least one of them has an absorption peak; And / or, based on the mass of the functional coating, the mass content of the functional material is denoted as s1%; satisfying 35≤s1≤99, preferably 90≤s1≤99; And / or, the thickness of the functional coating is denoted as h1 μm, satisfying 0.2≤h1≤5.

4. The functional coating according to claim 1 or 2, characterized in that, The carboxylates include at least one of calcium stearate, magnesium stearate, aluminum monostearate, aluminum distearate, aluminum tripearate, potassium stearate, sodium stearate, barium stearate, lithium stearate, sodium oleate, magnesium oleate, calcium oleate, aluminum trioleate, potassium oleate, barium oleate, and lithium oleate. And / or, at 25°C, the solubility of the carboxylate in a polar solvent is less than 1%, the polar solvent including at least one of N-methylpyrrolidone, N,N-dimethylacetamide, and acetone; And / or, the particle size of the carboxylate satisfies at least one of the following conditions: (1) 0.1μm≤Dv10≤0.8μm; preferably 0.2μm≤Dv10≤0.3μm; (2) 0.3μm≤Dv50≤3μm; preferably 0.3μm≤Dv50≤1μm; (3) 0.6μm≤Dv90≤5μm; preferably 0.6μm≤Dv90≤2.5μm; (4) The particle size distribution Span value is less than or equal to 8.

5. The functional coating according to claim 1, 2, or 3, characterized in that, The functional material further includes a first filler, the mass content of which is denoted as s12% based on the mass of the functional coating; satisfying 0 < s12 ≤ 64%; preferably, the first filler includes boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, uracil, cytosine, guanine, 2-mercaptobenzimidazole, 2-mercaptobenzimidazole derivative, N,N'-di(β-naphthyl)-p-phenylenediamine, and 4-amino-2,6-dihydroxybenzimidazole. At least one of the following: pyrimidine, 4-amino-2-carbonylpyrimidine, 5,6-amino-5-methyluracil, 5-fluorouracil, 5-cyanouracil, uracil, 2,4-dihydroxy-5-fluoropyrimidine, 2-amino-4,6-dimethyl-5-pyrimidinecarboxylate, 4-amino-2,6-dihydroxypyrimidine, dimethyl aminocarbonate pyrimidine carboxylic acid, 8-mercaptopurine, 6-aminopurine, guanine, hypoxanthine, 2,4-dimercaptopurine, phenolic resin, melamine resin, and cellulose; And / or, the functional coating further includes an adhesive, the mass content of which is denoted as s2% based on the mass of the functional coating; satisfying 1≤s2≤65, preferably 1≤s2≤10.

6. A diaphragm, characterized in that, The diaphragm includes a substrate layer, the substrate layer includes a base film and a functional coating disposed on at least one side surface in the thickness direction of the base film, the functional coating being the functional coating of any one of claims 1-5; Preferably, the diaphragm further includes an adhesive layer located on at least one side surface of the substrate layer in the thickness direction, the adhesive layer comprising a first polymer.

7. The diaphragm according to claim 6, characterized in that, The adhesive layer has a porous structure formed from the first polymer; Preferably, the coating layer further includes a second filler, which is dispersed in the porous structure. The second filler includes at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate. More preferably, based on the mass of the adhesive layer, the mass content of the second filler is 20%-70%.

8. The diaphragm according to claim 6 or 7, characterized in that, The first polymer is in particulate form, and the average particle size d1 of the first polymer is 0.55 μm-0.95 μm; Preferably, the coating layer further includes second polymer particles, which include second primary particles and / or second secondary particles formed by agglomeration of the second primary particles, wherein the average particle size d2 of the second primary particles is 0.15μm-0.25μm, and the average particle size d3 of the second secondary particles is 3.5μm-18μm. More preferably, based on the mass of the adhesive layer, the mass content of the second polymer particles is 10%-60%.

9. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, At least one of the positive electrode, negative electrode and separator comprises the functional coating of any one of claims 1-5; or, the separator is the separator of any one of claims 6-8; Preferably, the electrolyte comprises lithium salt and cyclic carbonate, and the cyclic carbonate content is 15%-70% by mass, based on the mass of the electrolyte. More preferably, the cyclic carbonate includes fluorinated cyclic carbonate and non-fluorinated cyclic carbonate. Based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is denoted as a%, and the mass content of the non-fluorinated cyclic carbonate is denoted as b%, satisfying 0.9≤a / b≤7.

5.

10. The secondary battery according to claim 9, characterized in that, 5 ≤ a ≤ 40; preferably, 10 ≤ a ≤ 28; And / or, 3.5 ≤ b ≤ 50; And / or, the fluorocyclic carbonate includes at least one of fluoroethylene carbonate and difluoroethylene carbonate; And / or, the non-fluorinated cyclic carbonate includes at least one of vinylene carbonate, ethylene carbonate, and propylene carbonate; And / or, the lithium salt includes lithium hexafluorophosphate and a second lithium salt, the second lithium salt including at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide; preferably, based on the mass of the electrolyte, the mass content of the lithium hexafluorophosphate is denoted as e%, the mass content of the second lithium salt is denoted as d%, satisfying 0.07≤d / e≤0.5; And / or, the charging cut-off voltage of the secondary battery is greater than or equal to 4.5V.

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