Battery diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a battery diaphragm, a preparation method thereof and a lithium ion battery. The invention provides a battery diaphragm. The battery diaphragm comprises a base membrane and an antioxidant heat-resistant coating arranged on the surface of one side of the base membrane, the antioxidant heat-resistant coating comprises a modified porous material and a heat-resistant inorganic material; the modified porous material comprises a porous base material and a light stabilizer loaded on the porous base material. According to the battery diaphragm disclosed by the invention, the light stabilizer is loaded on the porous base material and is matched with the heat-resistant inorganic material to form a coating on the surface of the base membrane, so that the interface stability under high pressure is realized, and the energy density and the cycle performance of a lithium ion battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a battery separator, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries possess unique advantages such as high specific energy, high operating voltage, long cycle life, no pollution, and high safety performance, and have been widely used in various fields such as portable electronic devices, electric vehicles, and energy storage systems. To further improve the energy density of lithium-ion batteries, the development and application of high-voltage cathode materials are considered a key technological path to overcome existing energy bottlenecks. Future development trends will continue to focus on developing cathode materials with higher specific capacity and higher operating voltage platforms. However, in the process of realizing the commercial application of high-voltage systems, the stability of the cathode / electrolyte interface under high voltage, especially the chemical degradation of the electrolyte under high potential conditions, has become a core challenge that urgently needs to be addressed.

[0003] Especially for layered oxide cathode materials, under high-voltage conditions, the surface of the cathode material easily releases active oxygen (such as singlet oxygen) and various free radicals (such as ·CH3, ·OCH3, ·OCOOCH3, and H2C=CH-O·, etc.). These highly active substances continuously attack the electrolyte components, initiating and accelerating the decomposition of the electrolyte. This process not only leads to electrolyte loss but also causes rapid capacity decay and shortened cycle life.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a battery separator that solves the problem of interface stability under high voltage.

[0006] The second objective of this invention is to provide a method for preparing a battery separator.

[0007] A third objective of this invention is to provide a lithium-ion battery.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a battery separator, including a base film and an anti-oxidation and heat-resistant coating disposed on one side surface of the base film; The antioxidant and heat-resistant coating comprises a modified porous material and a heat-resistant inorganic material; the modified porous material comprises a porous substrate and a light stabilizer loaded on the porous substrate.

[0009] Furthermore, it includes at least one of the following features (1) to (3); (1) In the modified porous material, the mass ratio of the porous substrate to the light stabilizer is 4:(1~3). (2) The particle size D50 of the modified porous material is 1.5~5μm; (3) The specific surface area of ​​the modified porous material is 20~55m². 2 / g.

[0010] Furthermore, it includes at least one of the following features (1) to (4); (1) The porous substrate includes at least one of porous alumina, porous silica, metal-organic framework materials, covalent organic framework materials and zeolite; (2) The particle size D50 of the porous substrate is 1.5~5μm; (3) The average pore size of the porous substrate is 5~25nm; (4) The specific surface area of ​​the porous substrate is 200~350m². 2 / g.

[0011] Furthermore, the light stabilizer includes at least one of UV-3346, UV-3853, TH-944, Tinuvin 770, Tinuvin 144, and Sanduvor VSU; And / or, the molecular weight of the light stabilizer is 1000~3000.

[0012] Furthermore, the preparation method of the modified porous material includes: dissolving a light stabilizer in an organic solvent to obtain a mixed solution; mixing the porous substrate and the mixed solution, and then sequentially drying, grinding and sieving to obtain the modified porous material.

[0013] Preferably, the solid content of the mixed solution is 5% to 10%.

[0014] Furthermore, the heat-resistant inorganic material includes at least one of alumina, silicon oxide, silicon carbide, silicon nitride, magnesium silicate, magnesium hydroxide, barium carbonate, and boehmite; And / or, the particle size D50 of the heat-resistant inorganic material is 0.4~1μm.

[0015] Furthermore, the ratio of the particle size of the heat-resistant inorganic material to the particle size of the modified porous material is 1:(2.4~4). And / or, the mass ratio of the heat-resistant inorganic material to the modified porous material is 1:(3~10).

[0016] Furthermore, it includes at least one of the following features (1) to (4); (1) The antioxidant and heat-resistant coating further includes at least one of a binder, a dispersant, and a wetting agent; (2) The moisture content of the antioxidant and heat-resistant coating is 2000~10000ppm; (3) The thickness of the antioxidant and heat-resistant coating is 2~7μm; (4) The base membrane includes at least one of polyethylene microporous membrane, polypropylene microporous membrane and polyolefin multilayer composite microporous membrane.

[0017] The present invention also provides a method for preparing the battery separator as described above, comprising the following steps: A slurry containing modified porous materials and heat-resistant inorganic materials is coated onto one side surface of the base membrane, and after drying, the battery separator is obtained.

[0018] The present invention also provides a lithium-ion battery, comprising: a positive electrode, a battery separator as described above, and a negative electrode; wherein the antioxidant and heat-resistant coatings of the positive electrode and the battery separator are adjacent.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The battery separator of this invention utilizes a porous substrate loaded with a light stabilizer, which is then combined with a heat-resistant inorganic material to form a coating on the base film surface. This achieves interfacial stability under high pressure, thereby improving the energy density and cycle performance of lithium-ion batteries. Specifically, by loading a porous substrate with a light stabilizer and introducing it into the coating of the battery separator, the light stabilizer adsorbs singlet oxygen and free radicals, releasing them onto the surface of the positive electrode active material during the high-temperature formation process to form an ultra-thin, uniform, and effective positive electrode solid electrolyte interface (CEI) layer. This slows down the continuous degradation of the electrolyte and absorbs and removes singlet oxygen and free radicals. The adsorption effect of the porous substrate can also adsorb byproducts (HF, transition metal ions, singlet oxygen, and free radicals) generated during battery cycling, achieving excellent battery performance. At the same time, the loading of the light stabilizer solves the problem of high moisture content when using porous substrates in battery separators. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the lithium-ion battery according to Embodiment 1 of the present invention.

[0022] Figure Labels 1-Positive electrode sheet; 2-Heat-resistant inorganic material; 3-Modified porous material; 4-Base film; 5-Negative electrode sheet. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0024] In some embodiments of the present invention, a battery separator is provided, including a base film and an anti-oxidation and heat-resistant coating disposed on one side surface of the base film; Antioxidant and heat-resistant coatings include modified porous materials and heat-resistant inorganic materials; modified porous materials include porous substrates and light stabilizers loaded on porous substrates.

[0025] The light stabilizer is loaded onto the porous substrate, filling the pores of the porous substrate and adhering to its surface. This reduces the surface area of ​​the modified porous material. Furthermore, the light stabilizer's water-insoluble properties reduce water diffusion into the porous substrate, thereby lowering the moisture content of the battery separator composed of the modified porous material. This reduces the decomposition of LiPF6 by moisture, thus preventing the accelerated degradation of battery performance due to hydrofluoric acid. This solves the problem of high moisture content in porous substrates used for battery separators.

[0026] By introducing light stabilizers into the coating of the battery separator, and utilizing their adsorption effect on singlet oxygen and free radicals, the light stabilizers dissolve in the electrolyte and migrate to the surface of the cathode material during the high-temperature battery formation process, forming an ultra-thin, uniform, and effective cathode solid electrolyte interface (CEI) layer. This slows down the continuous degradation of electrolyte components and absorbs and removes singlet oxygen and free radicals, thereby adsorbing byproducts (HF, transition metal ions, singlet oxygen, and free radicals) generated during battery cycling. This solves the interfacial stability problem under high voltage and achieves excellent battery performance. However, light stabilizers cannot be completely dissolved in the electrolyte at room temperature and therefore cannot be used as electrolyte additives.

[0027] After releasing the stabilizer, the modified porous material restores its high specific surface area, improves its ionic conductivity, and helps reduce local current density. It can also capture and adsorb trace amounts of HF acid in the electrolyte, protecting the electrode material and slowing down capacity decay.

[0028] Porous materials, characterized by high porosity and low density, result in weak binding force on the base film when used alone as a coating. During thermal shrinkage of the battery separator, the fragile porous material coating structure bears this stress, leading to large-scale peeling, powdering, or penetration of the coating from the base film. Therefore, it is necessary to use it in combination with heat-resistant inorganic materials to improve the thermal shrinkage problem. This invention fills porous materials with light stabilizers and directly mixes them with heat-resistant inorganic materials to form a coating. This aims to alleviate the stress concentration issues that occur when using porous materials alone to form a coating, leading to coating peeling or insufficient thermal shrinkage.

[0029] In some embodiments of the present invention, the mass ratio of the porous substrate to the light stabilizer in the modified porous material is 4:(1 to 3); typically, but not limitingly, for example, the mass ratio of the porous substrate to the light stabilizer in the modified porous material can be 4:1, 4:2, 4:3, and any value between any two of these.

[0030] Increasing the content of light stabilizers can significantly reduce the specific surface area of ​​modified porous materials, thus reducing the moisture content of the battery separator formed by them. Within an appropriate range, the light stabilizer content in modified porous materials is beneficial for improving battery cycle life. This is mainly because the light stabilizer dissolves in the electrolyte, migrates to the surface of the cathode material to form a solid electrolyte interphase (CEI) layer, thereby slowing down the continuous degradation of the electrolyte. While absorbing and removing singlet oxygen and free radicals, it restores the high specific surface area characteristic of the porous substrate, reducing the battery's internal resistance, increasing ionic conductivity, and helping to reduce local current density. However, excessive light stabilizer, resulting in excessive subsequent dissolution in the electrolyte, can easily trigger side reactions, increasing electrolyte viscosity and negatively impacting ionic conductivity, thus affecting battery cycle life. Conversely, insufficient light stabilizer can lead to increased moisture content, which is also detrimental to improving battery cycle life.

[0031] In some embodiments of the present invention, the particle size D50 of the modified porous material is 1.5 to 5 μm; typically, but not limitingly, for example, the particle size D50 of the modified porous material can be 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm and any value between any two thereof; preferably, the particle size D50 of the modified porous material is 1.5 to 2.5 μm.

[0032] The particle size of the modified porous material mainly affects the coating thickness, which in turn indirectly affects the ionic conductivity of the battery separator. Using modified porous materials within the aforementioned particle size range is beneficial for preparing coatings of suitable thickness, thereby improving battery energy density.

[0033] In some embodiments of the present invention, the specific surface area of ​​the modified porous material is 20-55 m². 2 / g; typically, but not limitingly, for example, the specific surface area of ​​the modified porous material can be 20 m². 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g, 50m 2 / g、55m 2 / g and any value between any two of them. The specific surface area of ​​the modified porous material is lower than that of the porous substrate, which can indirectly indicate the loading condition.

[0034] The particle size of the modified porous material was tested using a Malvern 3000 particle size analyzer.

[0035] The specific surface area of ​​the modified porous material was measured by the gas adsorption method (BET method). A linear relationship was established using the adsorption isotherms of nitrogen (or argon) in the range of relative pressure 0.05~0.3, and the specific surface area was calculated.

[0036] In some embodiments of the present invention, the porous substrate includes at least one of porous alumina, porous silica, metal-organic framework materials, covalent organic framework materials, and zeolites; preferably, the metal-organic framework materials include at least one of MOF-5, MOF-74, MOF-505, MOF-525, ZIF-8, ZIF-67, HKUST-1, MIL-53, MIL-100, MIL-101, CPL-1, CPL-2, UiO-66, UiO-67, PCN-222, NU-1000, ZJU-7, and CPO-27; the covalent organic framework materials include at least one of TpPa-SO3H, TpPa-SO3Li, COF-1, COF-5, LZU-1, and covalent organic framework materials with a three-dimensional framework structure; the covalent organic framework materials with a three-dimensional framework structure include at least one of CTF, COF-300, CD-COF, and EB-COF.

[0037] In some embodiments of the present invention, the particle size D50 of the porous substrate is 1.5 to 5 μm; typically, but not limitingly, for example, the particle size D50 of the porous substrate can be 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm and any value between any two thereof; preferably, the particle size D50 of the porous substrate is 1.5 to 2.5 μm.

[0038] If the particle size of the porous substrate is too small, it is difficult to load light stabilizers, and the specific surface area decreases less, resulting in high moisture content in the battery separator, which accelerates battery capacity degradation when introduced into the battery. If the particle size of the porous substrate is too large, the coating will be too thick, which is not conducive to improving battery energy density.

[0039] In some embodiments of the present invention, the average pore size of the porous substrate is 5 to 25 nm; typically, but not limitingly, for example, the average pore size of the porous substrate can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, and any value between any two of these.

[0040] The pore size of the porous substrate affects the specific surface area of ​​the modified porous material obtained after loading; moreover, excessively large pore size will lead to low material density, which is not conducive to thermal shrinkage performance, and the coating moisture will increase, affecting the battery cycle performance; excessively small pore size will have the opposite effect on the battery's ionic conductivity and lithium-ion transference number, which will also deteriorate the cycle performance.

[0041] In some embodiments of the present invention, the specific surface area of ​​the porous substrate is 200~350m². 2 / g; typically, but not limitingly, for example, the specific surface area of ​​the porous substrate can be 200m². 2 / g、230m 2 / g、250m 2 / g、270m 2 / g、300m 2 / g、320m 2 / g, 350m 2 / g and any value between any two of them.

[0042] In some embodiments of the present invention, the moisture content of the porous substrate is 20,000 to 100,000 ppm; typically, but not limitingly, for example, the moisture content of the porous substrate can be 20,000 ppm, 40,000 ppm, 60,000 ppm, 80,000 ppm, 100,000 ppm, and any value between any two of these.

[0043] The particle size of the porous substrate was measured using a Malvern 3000 particle size analyzer. The specific surface area and average pore size of the porous substrate were determined using the Biosorption Spectrometry (BET) method. A linear relationship was established using the adsorption isotherms of nitrogen (or argon) in the relative pressure range of 0.05–0.3, the specific surface area was calculated, and the pore size distribution curve was output to obtain the average pore size. The moisture content of the porous substrate was determined using the Karl Fischer method.

[0044] In some embodiments of the present invention, the light stabilizer includes at least one of UV-3346, UV-3853, TH-944, Tinuvin 770, Tinuvin 144 and Sanduvor VSU.

[0045] The aforementioned light stabilizers are insoluble in water but soluble in organic solvents such as DMAC, NMP, and ethanol. They can also dissolve in electrolyte solvents such as carbonates and carboxylic acid esters at 40-60°C, which is beneficial for their release and diffusion from the modified porous material into the electrolyte during the formation of the battery at elevated temperatures.

[0046] In some embodiments of the invention, the molecular weight of the light stabilizer is 1000 to 3000; typically, but not limitingly, for example, the molecular weight of the light stabilizer can be 1000, 1500, 2000, 2500, 3000, and any value between any two of these. A small molecular weight of the light stabilizer facilitates diffusion into the porous substrate.

[0047] In some embodiments of the present invention, the method for preparing the modified porous material includes: dissolving a light stabilizer in an organic solvent to obtain a mixed solution; mixing the porous substrate and the mixed solution, and then sequentially drying, grinding and sieving to obtain the modified porous material.

[0048] The porous substrate is added to an organic solvent containing a light stabilizer for physical adsorption, thereby loading the light stabilizer onto the porous substrate.

[0049] In some embodiments of the present invention, in the preparation method of the modified porous material, the solid content of the mixed solution is 5% to 10%; typically, but not limitingly, for example, the solid content of the mixed solution can be 5%, 6%, 7%, 8%, 9%, 10%, and any value between any two thereof; after the light stabilizer is completely dissolved in the organic solvent, the interaction between the light stabilizer molecular chains is weak and there is no entanglement at a low concentration.

[0050] In some embodiments of the present invention, the method for preparing the modified porous material includes, but is not limited to, at least one of N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and ethanol; mixing the porous substrate and the mixed solution includes vacuum stirring for 20-40 min; drying at a temperature of 70-100°C for 5-12 h; and sieving through a 1000-mesh sieve.

[0051] In some embodiments of the present invention, the heat-resistant inorganic material includes at least one of alumina, silicon oxide, silicon carbide, silicon nitride, magnesium silicate, magnesium hydroxide, barium carbonate, and boehmite.

[0052] In some embodiments of the present invention, the particle size D50 of the heat-resistant inorganic material is 0.4 to 1 μm; typically, but not limitingly, for example, the particle size D50 of the heat-resistant inorganic material can be 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, and any value between any two of these.

[0053] The particle size of heat-resistant inorganic materials affects the density of the coating and has an impact on the thermal shrinkage and peel strength properties of the battery separator and its coating. Using heat-resistant inorganic materials within the above-mentioned particle size range is beneficial to improving the thermal shrinkage and peel strength properties of the battery separator.

[0054] In some embodiments of the present invention, the ratio of the particle size of the heat-resistant inorganic material to the particle size of the modified porous material is 1:(2.4~4); typically, but not limitingly, for example, the ratio of the particle size of the heat-resistant inorganic material to the particle size of the modified porous material can be 1:2.4, 1:3, 1:3.5, 1:4, and any value between any two of these.

[0055] By forming a coating skeleton with large-particle-size modified porous materials and filling it with small-particle-size heat-resistant inorganic materials, a dense coating is formed. The pores become smaller and smoother, which significantly reduces the stress concentration effect and thus improves the structural integrity, flexibility and adhesion of the coating to the substrate.

[0056] In some embodiments of the present invention, the mass ratio of the heat-resistant inorganic material to the modified porous material is 1:(3~10); typically, but not limitingly, for example, the mass ratio of the heat-resistant inorganic material to the modified porous material can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 and any value between any two of them.

[0057] Within the above-mentioned mass ratio range, modified porous materials and heat-resistant inorganic materials with two different particle sizes are mixed to form a mechanical interlock inside the coating, increasing the peel strength. However, the high proportion of modified porous materials in the coating leads to poor thermal shrinkage performance, mainly because the porous substrate itself has low density and weak binding effect on the battery separator.

[0058] In some embodiments of the present invention, the antioxidant and heat-resistant coating further includes at least one of a binder, a dispersant, and a wetting agent.

[0059] In some embodiments of the present invention, the mass of the binder accounts for 0.1% to 10% of the total mass of the modified porous heat-resistant inorganic material, binder, dispersant, and wetting agent; the mass of the dispersant accounts for 0.1% to 10% of the total mass of the modified porous heat-resistant inorganic material, binder, dispersant, and wetting agent; and the mass of the wetting agent accounts for 0.5% to 15% of the total mass of the modified porous heat-resistant inorganic material, binder, dispersant, and wetting agent.

[0060] In some embodiments of the present invention, the binder includes at least one of polyacrylic acid, styrene-acrylic emulsion, polyamic acid salt, polyacrylamide, and styrene-butadiene emulsion.

[0061] In some embodiments of the present invention, the dispersant includes at least one of sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, and sodium polycarboxylate.

[0062] In some embodiments of the present invention, the wetting agent includes at least one of organosilicon wetting agents, polyvinyl alcohol wetting agents, and ethoxylated alcohol wetting agents.

[0063] In some embodiments of the present invention, the moisture content of the antioxidant and heat-resistant coating is 2000~10000 ppm; typically, but not limitingly, for example, the moisture content of the antioxidant and heat-resistant coating can be 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, and any value between any two of these. The moisture content of the antioxidant and heat-resistant coating is determined by Karl Fischer method.

[0064] In some embodiments of the present invention, the thickness of the antioxidant and heat-resistant coating is 2 to 7 μm; typically, but not limitingly, for example, the thickness of the antioxidant and heat-resistant coating can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm and any value between any two thereof; preferably, the thickness of the antioxidant and heat-resistant coating is 2 to 3 μm; while ensuring the heat resistance of the coating, the migration path of the light stabilizer is reduced.

[0065] In some embodiments of the present invention, the base membrane includes at least one of polyethylene microporous membrane, polypropylene microporous membrane and polyolefin multilayer composite microporous membrane; preferably, the thickness of the base membrane is 5~16μm.

[0066] In some embodiments of the present invention, a method for preparing the above-mentioned battery separator is also provided, comprising the following steps: A slurry containing modified porous materials and heat-resistant inorganic materials is coated onto one side of the base membrane. After drying, a battery separator is obtained.

[0067] In some embodiments of the present invention, the slurry further includes a binder, a dispersant, a wetting agent, and water.

[0068] In some embodiments of the present invention, the solid content of the slurry is 30% to 40%.

[0069] In some embodiments of the present invention, the drying temperature is 55~80°C and the drying time is 2~10s.

[0070] In some embodiments of the present invention, a lithium-ion battery is also provided, comprising: a positive electrode, the battery separator described above, and a negative electrode; the anti-oxidation and heat-resistant coatings of the positive electrode and the battery separator are adjacent.

[0071] By placing the antioxidant and heat-resistant coating in the battery separator towards the positive electrode, the antioxidant and heat-resistant coating can be directly attached to the positive electrode sheet. The modified porous material can directly contact the positive electrode active material, which is beneficial to improving cycle performance. This is mainly because the light stabilizer can be transferred to the positive electrode faster and in greater quantities after dissolving, reducing the loss at the negative electrode.

[0072] See Figure 1 In some embodiments of the present invention, a lithium-ion battery includes: a positive electrode 1, a battery separator, and a negative electrode 5; the battery separator includes a base film 4 and an anti-oxidation and heat-resistant coating, the positive electrode 1 and the anti-oxidation and heat-resistant coating are adjacent, and the anti-oxidation and heat-resistant coating includes a modified porous material 3 and a heat-resistant inorganic material 2.

[0073] In some embodiments of the present invention, the positive electrode active material of the positive electrode sheet includes, but is not limited to, NCM811, and the negative electrode active material of the negative electrode sheet includes, but is not limited to, graphite.

[0074] Example 1 The method for preparing the battery separator provided in this embodiment includes the following steps: S1. Dissolve 5g of light stabilizer (UV-3346, molecular weight 1645) in 20g of N,N-dimethylacetamide (DMAC). After complete dissolution, add 20g of porous alumina (particle size D50 1.5μm, average pore size 12nm, specific surface area 298.6m²). 2 / g, then vacuum stirred for 30min to ensure complete dispersion, dried at 80℃ for 8h, ground into powder and sieved through a 1000-mesh sieve to obtain modified porous alumina (particle size D50 of 1.5μm, specific surface area of ​​54.3m²). 2 / g); S2. Mix 23.95 parts of alumina (particle size D50 of 0.4 μm), 71.85 parts of modified porous alumina, 4 parts of binder (styrene-butadiene emulsion), 0.1 parts of dispersant (sodium acrylate dispersant), 0.1 parts of wetting agent (organosilicon wetting agent) and water to obtain a slurry with a solid content of 35%. Coat the slurry onto one side surface of a polyethylene microporous membrane with a thickness of 9 μm, and then dry it at 60°C for 4 s to form an antioxidant and heat-resistant coating with a thickness of 2 μm, thus obtaining the battery separator.

[0075] The method for preparing a lithium-ion battery provided in this embodiment includes the following steps: The negative electrode, positive electrode, and the aforementioned battery separator are combined with a liquid electrolyte to assemble a lithium-ion battery. The anti-oxidation and heat-resistant coating in the battery separator faces the positive electrode; the positive active material of the positive electrode is NCM811, and the negative active material of the negative electrode is graphite.

[0076] Example 2 The battery separator preparation method provided in this embodiment is the same as that in embodiment 1. The only difference in step S2 is that the mass fraction of alumina is 8.71 parts and the mass fraction of modified porous alumina is 87.09 parts.

[0077] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0078] Example 3 The battery separator preparation method provided in this embodiment is the same as that in Embodiment 1, except that in step S2, the mass fraction of alumina is 15.97 parts and the mass fraction of modified porous alumina is 79.83 parts.

[0079] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0080] Example 4 The battery separator preparation method provided in this embodiment is the same as in Embodiment 3, except that in step S1, 10g of light stabilizer is dissolved in 40g of N,N-dimethylacetamide (DMAC). After complete dissolution, 20g of porous alumina is added, resulting in modified porous alumina with a particle size D50 of 1.5μm and a specific surface area of ​​37.6m². 2 / g.

[0081] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0082] Example 5 The battery separator preparation method provided in this embodiment is the same as in Embodiment 3, except that in step S1, 15g of light stabilizer is dissolved in 60g of N,N-dimethylacetamide (DMAC). After complete dissolution, 20g of porous alumina is added, resulting in modified porous alumina with a particle size D50 of 1.5μm and a specific surface area of ​​21.8m². 2 / g.

[0083] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0084] Example 6 The method for preparing the battery separator provided in this embodiment is the same as in Embodiment 4, except that the particle size D50 of alumina is 1 μm in step S2.

[0085] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0086] Example 7 The battery separator preparation method provided in this embodiment is the same as that in Embodiment 4, except that in step S1, the porous alumina has a particle size D50 of 3 μm, an average pore size of 12 nm, and a specific surface area of ​​233.7 m². 2 / g, the resulting modified porous alumina had a particle size D50 of 3μm and a specific surface area of ​​48.3m². 2 / g; In step S2, the thickness of the antioxidant and heat-resistant coating is 5μm.

[0087] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0088] Example 8 The battery separator preparation method provided in this embodiment is the same as that in Embodiment 4, except that in step S1, the porous alumina has a particle size D50 of 2.5 μm, an average pore size of 12 nm, and a specific surface area of ​​268.1 m². 2 / g, the resulting modified porous alumina had a particle size D50 of 2.5μm and a specific surface area of ​​35.2m². 2 / g; In step S2, the thickness of the antioxidant and heat-resistant coating is 3μm.

[0089] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0090] Example 9 The battery separator preparation method provided in this embodiment is the same as in Embodiment 4, except that in step S1, the porous alumina has a particle size D50 of 5 μm, an average pore size of 12 nm, and a specific surface area of ​​207.4 m². 2 / g, the resulting modified porous alumina had a particle size D50 of 5μm and a specific surface area of ​​27.6m². 2 / g; In step S2, the particle size D50 of alumina is 0.4μm, and the thickness of the anti-oxidation and heat-resistant coating is 7μm.

[0091] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0092] Example 10 The battery separator preparation method provided in this embodiment is the same as in Embodiment 4, except that in step S1, the porous alumina has a particle size D50 of 1.5 μm, an average pore size of 25 nm, and a specific surface area of ​​273.4 m². 2 / g, the resulting modified porous alumina had a particle size D50 of 1.5μm and a specific surface area of ​​35.4m². 2 / g.

[0093] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0094] Example 11 The battery separator preparation method provided in this embodiment is the same as in Embodiment 4, except that in step S1, the porous alumina has a particle size D50 of 1.5 μm, an average pore size of 5 nm, and a specific surface area of ​​342.7 m². 2 / g, the resulting modified porous alumina had a particle size D50 of 1.5μm and a specific surface area of ​​39.7m². 2 / g.

[0095] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0096] Example 12 The battery separator preparation method provided in this embodiment is the same as in Embodiment 4, except that in step S1, porous alumina is replaced with MOF-5. MOF-5 has a particle size D50 of 1.8 μm, an average pore size of 17 nm, and a specific surface area of ​​278.4 m². 2 / g, the obtained modified MOF-5 has a particle size D50 of 1.8μm and a specific surface area of ​​40.7m². 2 / g.

[0097] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0098] Example 13 The battery separator preparation method provided in this embodiment is the same as in Embodiment 4, except that in step S1, porous alumina is replaced with COF-5. COF-5 has a particle size D50 of 2 μm, an average pore size of 16 nm, and a specific surface area of ​​312.4 m². 2 / g, the obtained modified COF-5 had a particle size D50 of 2μm and a specific surface area of ​​41.8m². 2 / g.

[0099] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0100] Example 14 The battery separator preparation method provided in this embodiment is the same as in Example 4, except that in step S1, the light stabilizer is Tinuvin 770 (molecular weight 2400), and the resulting modified porous alumina has a particle size D50 of 1.5 μm and a specific surface area of ​​40.1 m². 2 / g.

[0101] The method for preparing the lithium-ion battery provided in this embodiment is the same as in Embodiment 1.

[0102] Comparative Example 1 The battery separator provided in this comparative example is prepared using the same method as in Example 4, except that in step S1, the porous alumina has a particle size D50 of 1 μm, an average pore size of 12 nm, and a specific surface area of ​​354.1 m². 2 / g, the resulting modified porous alumina had a particle size D50 of 1μm and a specific surface area of ​​154.1m². 2 / g.

[0103] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0104] Comparative Example 2 The preparation method of the battery separator provided in this comparative example is the same as that in Example 4, except that in step S1, the mass fraction of alumina is 50 parts and the mass fraction of modified porous alumina is 50 parts.

[0105] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0106] Comparative Example 3 The preparation method of the battery separator provided in this comparative example is the same as that in Example 4, except that in step S2, the mass fraction of alumina is 4.56 parts and the mass fraction of modified porous alumina is 91.24 parts.

[0107] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0108] Comparative Example 4 The preparation method of the battery separator provided in this comparative example is the same as in Example 3, except that in step S1, 20g of light stabilizer (UV-3346) is dissolved in 80g of N,N-dimethylacetamide (DMAC). After complete dissolution, 20g of porous alumina is added, resulting in modified porous alumina with a particle size D50 of 1.5μm and a specific surface area of ​​21.4m². 2 / g.

[0109] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0110] Comparative Example 5 The preparation method of the battery separator provided in this comparative example is the same as in Example 3, except that in step S1, 2g of light stabilizer (UV-3346) is dissolved in 8g of N,N-dimethylacetamide (DMAC). After complete dissolution, 20g of porous alumina is added, resulting in modified porous alumina with a particle size D50 of 1.5μm and a specific surface area of ​​178.6m². 2 / g.

[0111] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0112] Comparative Example 6 The method for preparing the battery separator provided in this comparative example is described in Example 4.

[0113] The method for preparing the lithium-ion battery provided in this comparative example is the same as in Example 1, except that the anti-oxidation and heat-resistant coating in the battery separator is adjacent to the negative electrode sheet.

[0114] Comparative Example 7 The battery separator provided in this comparative example is prepared using the same method as in Example 4, except that in step S1, the porous alumina has a particle size D50 of 1.5 μm, an average pore size of 50 nm, and a specific surface area of ​​154.6 m². 2 / g, the resulting modified porous alumina had a particle size D50 of 1.5μm and a specific surface area of ​​18.4m². 2 / g.

[0115] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0116] Comparative Example 8 The battery separator provided in this comparative example is prepared using the same method as in Example 4, except that in step S1, the porous alumina has a particle size D50 of 1.5 μm, an average pore size of 2 nm, and a specific surface area of ​​364.9 m². 2 The modified porous alumina obtained was 1.5 μm in size (D50) and 86.2 m² / g. 2 / g.

[0117] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0118] Comparative Example 9 The preparation method of the battery separator provided in this comparative example is the same as that in Example 4, except that 23.95 parts of alumina (particle size D50 of 0.4 μm), 47.9 parts of porous alumina, 23.95 parts of light stabilizer (UV-3346), 4 parts of binder (styrene-butadiene emulsion), 0.1 parts of dispersant (sodium acrylate dispersant), 0.1 parts of wetting agent (organosilicon wetting agent) and water are mixed to obtain a slurry with a solid content of 35%.

[0119] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0120] Comparative Example 10 The preparation method of the battery separator provided in this comparative example is the same as that in Example 4, except that in step S2, 98.5 parts of alumina (particle size D50 of 0.4 μm), 4 parts of binder (styrene-butadiene emulsion), 0.1 parts of dispersant (sodium acrylate dispersant), 0.1 parts of wetting agent (organosilicon wetting agent) and water are mixed to obtain slurry A with a solid content of 35%; 98.5 parts of modified porous alumina, 4 parts of binder (styrene-butadiene emulsion), 0.1 parts of dispersant (sodium acrylate dispersant), 0.1 parts of wetting agent (organosilicon wetting agent) and water are mixed to obtain slurry B with a solid content of 35%; slurry A is coated on one side surface of a polyethylene microporous membrane with a thickness of 9 μm, and then dried at 60°C for 5 s to form a heat-resistant coating with a thickness of 0.5 μm; then slurry B is coated on the heat-resistant coating surface and dried at 60°C for 5 s to form an antioxidant coating with a thickness of 3.5 μm, thus obtaining the battery separator.

[0121] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0122] Comparative Example 11 The method for preparing the battery separator provided in this comparative example is the same as that in Comparative Example 10, except that in step S2, the positions of the coatings formed by slurry A and slurry B are interchanged.

[0123] The method for preparing the lithium-ion battery provided in this comparative example is as described in Example 1.

[0124] Test case The parameters in the preparation methods of the battery separators of Examples 1-14 and Comparative Examples 1-11 are shown in Table 1.

[0125] Average particle size D50 test method: obtained by Malvern 3000 particle size analyzer.

[0126] Methods for testing specific surface area and average pore size: The BET (Break-Earth Expansion Test) method is used. A linear relationship is established using the adsorption isotherms of nitrogen (or argon) within a relative pressure range of 0.05–0.3. The specific surface area is calculated, and the pore size distribution curve is output to obtain the average pore size. Methods for testing the specific surface area of ​​modified porous materials after immersion in electrolyte: The modified porous material after immersion in electrolyte is placed in an 80℃ oven and baked for 8 hours. After grinding, it is sieved through a 1000-mesh sieve. The specific surface area is calculated using the BET method, which establishes a linear relationship using the adsorption isotherms of nitrogen (or argon) within a relative pressure range of 0.05–0.3.

[0127] Moisture content: The moisture content of the diaphragm was tested using the Karl Fischer method.

[0128] In Table 1, in Examples 1-11, 14 and Comparative Examples 1-11, the porous substrate is porous alumina, and the modified porous material is modified porous alumina; in Example 12, the porous substrate is MOF-5, and the modified porous material is modified MOF-5; in Example 13, the porous substrate is COF-5, and the modified COF-5 is modified porous alumina; the specific surface area of ​​the modified porous material in Comparative Example 9 after immersion in the electrolyte refers to the specific surface area of ​​the porous alumina after immersion in the electrolyte. In Comparative Examples 10 and 11, considering thickness and density, the mass ratio of alumina to modified porous material is calculated using areal density.

[0129] Table 1

[0130] The performance of the battery separators of Examples 1-14 and Comparative Examples 1-11 is shown in Table 2.

[0131] Peel strength test method: The diaphragm is bonded with transparent tape, and a 180° peel strength test is performed using a universal tensile testing machine.

[0132] Shrinkage test method: The diaphragm is cut into fixed size, placed in an oven at 150℃, left to stand for 1 hour, and then taken out to measure the dimensional change rate.

[0133] Ionic conductivity testing method: In an argon-filled glove box, a 2016 button cell was fabricated with a separator. An appropriate amount of electrolyte (EC:EMC:DEC = 3:5:2 (volume ratio), LiPF6, 1 mol / L) was added. The ionic conductivity was measured using an electrochemical workstation. σ = L / (Rb) A), where σ is the ionic conductivity (S cm). 1 L is the thickness of the diaphragm (cm); Rb is the intrinsic resistance of the diaphragm (Ω); A is the effective area (cm²). 2 ).

[0134] Lithium-ion transport number testing method: Assemble a battery and fabricate a Li-symmetric cell using a separator. First, perform electrochemical impedance spectroscopy (EIS) on the battery, and obtain the initial interfacial impedance R0 through equivalent circuit fitting. Then, apply a small constant DC voltage (ΔV, typically 10mV) to the battery and record the current-time curve. As the current gradually decays from a large initial current I0 to a small steady-state current Iss, immediately after the polarization test, perform an AC impedance test again to obtain the steady-state interfacial impedance Rss. Calculate the transport number t. + , .

[0135] Test method for 80% capacity retention cycle count: Assemble single-cell batteries with the following ratios: positive electrode: NCM811:PVDF:SP = 96:2:2; negative electrode: graphite:SP:CMC:SBR = 96:0.7:1.3:2; electrolyte: 1 mol / L LiPF6 solution, solvent:EC:EMC:DEC (3:5:2, volume ratio). Cyclic tests were performed on the two assembled single-cell batteries. Specifically, 0.5C / 1C charge-discharge cycle tests were conducted in a 25℃ constant temperature chamber, with a voltage range of 2.75~4.5V. The batteries were cycled at 25℃ under 1C charge-discharge conditions, and the number of cycles required to maintain 80% capacity retention was measured. Capacity retention = capacity after cycle / capacity before cycle.

[0136] Table 2

[0137] In Examples 1-3, the ratio of modified porous alumina to alumina was adjusted. By mixing two different particle sizes, mechanical interlocking was formed inside the coating, increasing the peel strength. However, the high proportion of modified porous alumina in the coating resulted in poor thermal shrinkage performance, mainly because the porous alumina itself has a low density and a weak binding effect on the diaphragm.

[0138] Comparing Examples 3-5 and Comparative Examples 4-5, adjusting the ratio of light stabilizer to porous alumina significantly reduced the specific surface area of ​​the porous alumina as the light stabilizer content increased; consequently, the moisture content of the resulting separator decreased. Increasing the proportion of modified porous material within an appropriate range increased cycle life, primarily because the light stabilizer dissolved in the electrolyte and migrated to the surface of the cathode material to form a solid electrolyte interface (CEI) layer. This slowed down the continuous degradation of the electrolyte and, while absorbing and removing singlet oxygen and free radicals, restored the high specific surface area characteristic of porous alumina, reducing the battery's internal resistance, improving ionic conductivity, and helping to reduce local current density. However, excessive light stabilizer, leading to excessive subsequent dissolution in the electrolyte, can easily trigger side reactions, increasing electrolyte viscosity and negatively impacting ionic conductivity, thus affecting battery cycle life. Conversely, insufficient light stabilizer can cause increased moisture content, also affecting battery cycle life.

[0139] Compared with Comparative Examples 9-11, Comparative Example 10, where modified porous alumina was placed near the diaphragm side, showed a significant side effect of weak binding force on the diaphragm. Comparative Example 11 exhibited a coating structure opposite to Comparative Example 10; its thermal shrinkage performance was good due to the protection of the heat-resistant layer, but the dense coating formed by the concentration of small-diameter alumina on one side of the diaphragm negatively impacted the permeability and ionic conductivity of the coating film. Comparative Example 9 directly mixed the light stabilizer with other components into the coating; however, because the melting point of the light stabilizer was between 110 and 130°C, its deformation upon heating caused stress within the coating, resulting in insufficient thermal shrinkage performance. However, when introduced into porous alumina, even at the integration temperature, the stress generated on the coating was lower due to the fixation of the alumina framework compared to using it alone.

[0140] Compared with Examples 4, 7-9 and Comparative Example 1, the particle size of the modified porous alumina mainly affects the coating thickness, which in turn indirectly affects the ionic conductivity of the separator. When the particle size is too small, it is difficult to load the light stabilizer, and the specific surface area decreases less, resulting in high moisture content in the separator, which accelerates the capacity degradation of the battery when introduced into it.

[0141] Examples 4 and 6 show that adjusting the particle size of alumina affects the density of the coating, which in turn affects the thermal shrinkage and peel strength properties of the diaphragm and its coating.

[0142] Comparing Example 4 and Comparative Example 6, the coating facing the positive electrode is beneficial to improving cycle performance, mainly because the light stabilizer can be transferred to the positive electrode more quickly and in greater quantities after dissolution, reducing losses at the negative electrode.

[0143] Comparing Examples 4, 10, 11 with Comparative Examples 7 and 8, the pore size of the porous alumina was adjusted. The size of the pore size affects the specific surface area of ​​the material after loading. If the pore size is too large, the material density will be low, which is not conducive to thermal shrinkage performance and the increased moisture in the coating film will affect the battery cycle performance. If the pore size is too small, it will have the opposite effect on the ionic conductivity and lithium ion transference number of the battery, which will also deteriorate the cycle performance.

[0144] Examples 12 and 13 use MOF and COF, two porous materials, instead of porous alumina, which allows for the coating of light stabilizers and yields experimental results similar to those obtained with porous alumina. However, due to the density difference between MOF and COF and porous alumina, thermal shrinkage varies.

[0145] Example 14: Adjusting the type of light stabilizer has little impact on product performance and can still meet design requirements.

[0146] In summary, by introducing light-stabilized modified porous materials into the coating of the battery separator, the light stabilizers, which dissolve in the electrolyte at high temperatures, facilitate migration to the positive electrode surface to participate in the formation of CEI, thus protecting the positive electrode material. Simultaneously, the porous materials provide more pathways for ions within the battery, helping to reduce local current density and adsorb HF, among other advantages.

[0147] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A battery separator, characterized in that, Includes a base film and an antioxidant and heat-resistant coating disposed on one side surface of the base film; The antioxidant and heat-resistant coating comprises a modified porous material and a heat-resistant inorganic material; the modified porous material comprises a porous substrate and a light stabilizer loaded on the porous substrate.

2. The battery separator according to claim 1, characterized in that, Includes at least one of the following features (1) to (3); (1) In the modified porous material, the mass ratio of the porous substrate to the light stabilizer is 4:(1~3). (2) The particle size D50 of the modified porous material is 1.5~5μm; (3) The specific surface area of ​​the modified porous material is 20~55m². 2 / g.

3. The battery separator according to claim 1, characterized in that, Includes at least one of the following features (1) to (4); (1) The porous substrate includes at least one of porous alumina, porous silica, metal-organic framework materials, covalent organic framework materials and zeolite; (2) The particle size D50 of the porous substrate is 1.5~5μm; (3) The average pore size of the porous substrate is 5~25nm; (4) The specific surface area of ​​the porous substrate is 200~350m². 2 / g.

4. The battery separator according to claim 1, characterized in that, The light stabilizer includes at least one of UV-3346, UV-3853, TH-944, Tinuvin 770, Tinuvin 144, and Sanduvor VSU; And / or, the molecular weight of the light stabilizer is 1000~3000.

5. The battery separator according to claim 1, characterized in that, The method for preparing the modified porous material includes: dissolving a light stabilizer in an organic solvent to obtain a mixed solution; mixing the porous substrate and the mixed solution, and then sequentially drying, grinding, and sieving to obtain the modified porous material. Preferably, the solid content of the mixed solution is 5% to 10%.

6. The battery separator according to claim 1, characterized in that, The heat-resistant inorganic material includes at least one of alumina, silicon oxide, silicon carbide, silicon nitride, magnesium silicate, magnesium hydroxide, barium carbonate, and boehmite. And / or, the particle size D50 of the heat-resistant inorganic material is 0.4~1μm.

7. The battery separator according to claim 1, characterized in that, The ratio of the particle size of the heat-resistant inorganic material to the particle size of the modified porous material is 1:(2.4~4). And / or, the mass ratio of the heat-resistant inorganic material to the modified porous material is 1:(3~10).

8. The battery separator according to claim 1, characterized in that, Includes at least one of the following features (1) to (4); (1) The antioxidant and heat-resistant coating further includes at least one of a binder, a dispersant, and a wetting agent; (2) The moisture content of the antioxidant and heat-resistant coating is 2000~10000ppm; (3) The thickness of the antioxidant and heat-resistant coating is 2~7μm; (4) The base membrane includes at least one of polyethylene microporous membrane, polypropylene microporous membrane and polyolefin multilayer composite microporous membrane.

9. The method for preparing the battery separator according to any one of claims 1 to 8, characterized in that, Includes the following steps: A slurry containing modified porous materials and heat-resistant inorganic materials is coated onto one side surface of the base membrane, and after drying, the battery separator is obtained.

10. A lithium-ion battery, characterized in that, include: The positive electrode, the battery separator according to any one of claims 1 to 8, and the negative electrode; the positive electrode and the anti-oxidation and heat-resistant coating of the battery separator are adjacent.

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