Modified diaphragm as well as preparation method and application thereof

Abstract

The invention discloses a modified diaphragm as well as a preparation method and application thereof, and relates to the technical field of electrochemical energy storage, the modified diaphragm comprises a base membrane and a modified inorganic coating arranged on at least one side of the base membrane, the modified inorganic coating comprises an inorganic material and a modifier, the modifier comprises a polyphenol compound, and the polyphenol compound is a phenolic compound. The polyphenol compound comprises an aromatic group and a hydrophilic group, and the hydrophilic group comprises at least one of hydroxyl, carboxyl and carbonyl. The modified inorganic coating in the modified diaphragm provided by the invention adopts the inorganic material and the modifier, the modifier polyphenol compound has good dispersity and excellent adhesiveness, and the modified diaphragm obtained by combining the inorganic material has good thermal stability, mechanical strength, ionic conductivity and electrolyte wettability; under the condition of high current density, the cycling stability of the battery can be remarkably improved, the growth of lithium dendrites is effectively inhibited, the overall safety of the lithium battery is improved, and the service life of the lithium battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a modified diaphragm, a preparation method thereof, and applications thereof. Background Art

[0002] Secondary battery technology has played a vital role in driving the development of high-energy and power-density devices, and is widely used in electric vehicles, hybrid vehicles, and grid energy storage systems. However, secondary batteries face serious safety challenges, especially under extreme conditions such as high temperatures and high-rate charge and discharge.

[0003] Secondary batteries generally consist of three main functional components: electrodes, separators, and electrolytes. The separator's primary function is to prevent electrical contact between the positive and negative electrodes and ensure ion transport. Traditional commercial polyolefin separators (such as polyethylene (PE) and polypropylene (PP)) have low melting points, poor thermal stability, and are prone to thermal shrinkage (greater than 65°C). They also have low mechanical strength, making it easy for lithium dendrites to pierce the separator. These factors can cause internal short circuits in the battery, leading to safety accidents. Summary of the Invention

[0004] The main purpose of the present invention is to provide a modified diaphragm and its preparation method and application, aiming to solve the deficiencies of existing modified diaphragms in thermal stability, mechanical strength and electrolyte affinity, thereby improving the rate performance, long-term cycle stability, safety and service life of secondary batteries.

[0005] To achieve the above-mentioned objectives, the present invention proposes a modified diaphragm, which includes a base membrane and a modified inorganic coating provided on at least one side of the base membrane, wherein the modified inorganic coating includes an inorganic material and a modifier, wherein the modifier includes a polyphenol compound, wherein the polyphenol compound includes an aromatic group and a hydrophilic group, and wherein the hydrophilic group includes at least one of a hydroxyl group, a carboxyl group and a carbonyl group.

[0006] In one embodiment, the polyphenol compound includes at least one of tannic acid, catechin, proanthocyanidin, epigallocatechin gallate, and quercetin.

[0007] In one embodiment, the inorganic material includes at least one of SiO2, Al2O3, boehmite, Mg(OH)2, zeolite, ZrO2, TiO2 and BN.

[0008] The present invention also provides a method for preparing the modified diaphragm as described above, comprising the following steps: Mixing an inorganic material, a modifier, and a solvent to obtain a mixed solution, mixing the mixed solution with grinding beads, and ball milling to obtain a modified inorganic material; mixing the modified inorganic material with an aqueous solvent to obtain a modified inorganic slurry; The modified inorganic slurry is applied to at least one surface of a base film and dried to prepare a modified inorganic coating on at least one surface of the base film to obtain a modified diaphragm.

[0009] In one embodiment, the mass ratio of the inorganic material to the modifier is (3-20):1; and / or, The solvent includes at least one of water, methanol and ethanol.

[0010] In one embodiment, the particle size of the grinding beads is 0.8 mm to 5 mm; and / or, The ratio of the mass of the grinding beads to the sum of the mass of the inorganic material and the modifier is (30-300):1; and / or, The ball milling time is 3h~48h; and / or, The particle size of the modified inorganic material is 0.5 μm to 1.5 μm.

[0011] In one embodiment, the mass ratio of the modified inorganic material to the aqueous solvent is (4-10):40; and / or, The aqueous solvent includes at least one of water, methanol, ethanol, acetonitrile, dimethyl sulfoxide and dimethylformamide; and / or, The step of "mixing the modified inorganic material with an aqueous solvent to obtain a modified inorganic slurry" includes: mixing the modified inorganic material with the aqueous solvent by ultrasonic stirring for 10 nanometers to 30 minutes to obtain a modified inorganic slurry.

[0012] In one embodiment, the drying time is 10 h to 14 h; and / or, The drying temperature is 25°C to 60°C; and / or, The thickness of the modified inorganic coating is 1 μm to 8 μm.

[0013] The present invention also provides an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet, and a separator arranged between the positive electrode sheet and the negative electrode sheet. The separator is the modified separator mentioned above or is prepared by the preparation method of the modified separator mentioned above.

[0014] The present invention also provides a lithium-ion battery, which includes the electrode assembly described above.

[0015] In the technical solution of the present invention, the use of the above-mentioned polyphenol compound as a modifier has good dispersibility and excellent adhesion. The hydrophilic groups in the above-mentioned polyphenol compound can form hydrogen bonds or coordination bonds with the inorganic particles or the base membrane surface, enhancing interfacial bonding. The aromatic ring structure has a certain π-π stacking ability, which helps to adhere to the base membrane surface. In addition, the polyphenol compound can coat the surface of the inorganic particles, reduce the surface energy between the particles, and prevent agglomeration. Therefore, the modifier can not only uniformly coat the inorganic particles in the solution, reduce the specific surface energy, and prevent the inorganic particles from agglomerating, but also enhance the bonding force between the inorganic particles and the base membrane, thereby achieving good dispersibility and excellent adhesion, thereby improving the uniformity of the inorganic particles on the base membrane surface and the bonding force between the inorganic particles and the base membrane. Therefore, the modified separator obtained by modifying the inorganic material with the polyphenol compound has good thermal stability, mechanical strength, ionic conductivity and electrolyte wettability, can significantly improve the cycle stability of the battery under high current density conditions, and effectively inhibit the growth of dendrites, thereby improving the overall safety and service life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0017] Figure 1 This is a comparison diagram of the modified diaphragm prepared in Example 1 of the present invention and the polyethylene-based film; Figure 2 This is a bending test diagram of the modified diaphragm prepared in Example 1 of the present invention; Figure 3 1 is a side view of the droplets obtained after the electrolyte is added dropwise to the modified separator prepared in Example 1 and the polyethylene separator of Comparative Example 1; Figure 4 The top view of the wetting distribution is obtained after the same amount of electrolyte is added dropwise to the modified separator prepared in Example 1 and the polyethylene separator of Comparative Example 1; Figure 5 Graph showing thermal stability test results of the modified diaphragm prepared in Example 1 and the polyethylene diaphragm of Comparative Example 1; Figure 6 The charge and discharge test curves of the Li / separator / Graphite battery prepared with the modified separator in Example 1 of the present invention and the polyethylene separator in Comparative Example 1 at different current densities are shown; Figure 7The cycle performance test of the Li / separator / Graphite battery prepared with the modified separator in Example 1 of the present invention and the polyethylene separator in Comparative Example 1; Figure 8 This is a cycle performance test of the Li / separator / Li battery prepared using the modified separator in Example 1 of the present invention and the polyethylene separator in Comparative Example 1.

[0018] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0021] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" or "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0022] Secondary batteries generally consist of three main functional components: electrodes, separators, and electrolytes. The separator's primary function is to prevent electrical contact between the positive and negative electrodes and ensure ion transport. Traditional commercial polyolefin separators (such as polyethylene (PE) and polypropylene (PP)) have low melting points, poor thermal stability, and are prone to thermal shrinkage (greater than 65°C). They also have low mechanical strength, making it easy for lithium dendrites to pierce the separator. These factors can cause internal short circuits in the battery, leading to safety accidents.

[0023] The thermal stability of traditional polyolefin separators can be improved by coating them with inorganic solid particles. However, these inorganically modified separators present numerous challenges in practical applications, including the high specific surface energy of the inorganic powder, easy agglomeration, and poor coating uniformity. The inorganically modified inorganic coating exhibits weak bonding to the base membrane, and the inorganic solid particles exhibit poor adhesion, resulting in the modified inorganic coating being susceptible to powdering and shedding. Applying an organically modified inorganic coating, such as polyvinylidene fluoride (PVDF), to the surface of the inorganically modified inorganic coating can improve adhesion to a certain extent, but this can lead to increased internal resistance and the risk of pore clogging, resulting in a cumbersome process and increased production costs. Excessive amounts of additives (dispersants, thickeners, binders, solvents, wetting agents, etc.) in the inorganic solid slurry can lead to dissolution and migration in the electrolyte over time, resulting in side reactions and impacting the battery's cycle life.

[0024] In view of this, the present invention proposes a modified diaphragm, which includes a base membrane and a modified inorganic coating provided on at least one side of the base membrane, wherein the modified inorganic coating includes an inorganic material and a modifier, wherein the modifier includes a polyphenol compound, wherein the polyphenol compound includes an aromatic group and a hydrophilic group, and wherein the hydrophilic group includes at least one of a hydroxyl group, a carboxyl group and a carbonyl group.

[0025] In the technical solution of the present invention, the use of the above-mentioned polyphenol compound as a modifier has good dispersibility and excellent adhesion. The hydrophilic groups in the above-mentioned polyphenol compound can form hydrogen bonds or coordination bonds with the inorganic particles or the base membrane surface, enhancing interfacial bonding. The aromatic ring structure has a certain π-π stacking ability, which helps to adhere to the base membrane surface. In addition, the polyphenol compound can coat the surface of the inorganic particles, reduce the surface energy between the particles, and prevent agglomeration. Therefore, the modifier can not only uniformly coat the inorganic particles in the solution, reduce the specific surface energy, and prevent the inorganic particles from agglomerating, but also enhance the bonding force between the inorganic particles and the base membrane, thereby achieving good dispersibility and excellent adhesion, thereby improving the uniformity of the inorganic particles on the base membrane surface and the bonding force between the inorganic particles and the base membrane. Therefore, the modified separator obtained by modifying the inorganic material with the polyphenol compound has good thermal stability, mechanical strength, ionic conductivity and electrolyte wettability, can significantly improve the cycle stability of the battery under high current density conditions, and effectively inhibit the growth of dendrites, thereby improving the overall safety and service life of the battery.

[0026] It should be noted that the modified inorganic coating in the present application can be composed of a modifier and an inorganic material, and can have the above-mentioned good effects without adding other additives (such as adhesives / thickeners), thereby solving the problem that a large amount of additives (such as dispersants, thickeners, binders, solvents, wetting agents, etc.) added to the slurry during inorganic material coating will cause the material to dissolve and migrate in the electrolyte for a long time, resulting in side reactions and affecting the cycle life of the battery.

[0027] In addition, compared with the solution of applying a layer of organic modified inorganic coating such as polyvinylidene fluoride (PVDF) on the surface of the inorganic modified inorganic coating, the technical solution of the present application can not only reduce the risk of increased internal resistance and pore clogging, but also has a simpler process and lower production costs.

[0028] Therefore, the technical solution of the present invention breaks through the problem that traditional organic material systems rely on organic binders (such as PVDF), avoids the adverse effects of binders such as increased internal resistance, electrolyte side reactions, and pore clogging, and realizes a modification solution that does not require the addition of binders / thickeners.

[0029] It is understood that the base film may be a polyolefin separator, which can be purchased such as polyethylene PE and polypropylene PP.

[0030] The polyphenol compound can be a synthetic polyphenol compound or a natural polyphenol compound. In some embodiments, the polyphenol compound includes a natural polyphenol compound, and the natural polyphenol compound includes at least one of tannic acid, catechin, proanthocyanidin, epigallocatechin gallate, and quercetin. Natural polyphenol compounds derived from plants are rich in hydrophilic groups. Compared with other modifiers, they have the advantages of being natural and environmentally friendly, non-toxic, low-cost, and having strong adhesion. They not only promote the uniform dispersion of inorganic solid particles, but also enhance the bonding between the inorganic solid particles and the basement membrane.

[0031] In some embodiments, the inorganic material includes at least one of SiO2, Al2O3, boehmite, Mg(OH)2, zeolite, ZrO2, TiO2, and BN. The use of the above inorganic materials can effectively improve the thermal stability of the polyolefin-based film.

[0032] It should be noted that the above conditions can be met one or all of them. When all of them are met, the modified inorganic coating of the present invention can significantly improve the affinity and wettability of the electrolyte, have high ionic conductivity, and can improve the rate performance and long-term cycle stability of the battery. Compared with traditional commercial separators, the modified separator of the present invention has excellent thermal stability, thermal conductivity, and mechanical strength, reduces the separator's thermal shrinkage under high battery temperatures or high charge and discharge currents, and can inhibit the growth of lithium dendrites in the battery's metal anode to a certain extent, thereby improving the safety and service life of the battery.

[0033] The present invention further provides a method for preparing the modified diaphragm as described above, comprising the following steps: Mixing an inorganic material, a modifier, and a solvent to obtain a mixed solution, mixing the mixed solution with grinding beads, and ball milling to obtain a modified inorganic material; mixing the modified inorganic material with an aqueous solvent to obtain a modified inorganic slurry; The modified inorganic slurry is applied to at least one surface of the base film and dried to prepare a modified inorganic coating on at least one surface of the base film to obtain a modified diaphragm.

[0034] In the technical solution of this invention, the continuous shearing and collision effects of the liquid phase environment and ball milling promote in-situ adsorption and coating of the modifier on the surface of the inorganic material particles, forming a stable particle dispersion system. This not only improves the uniformity, stability, and dispersibility of the particles, but also enhances the coating quality of the inorganic solid particles on the base film. It significantly reduces the problems of particle agglomeration, sedimentation, and modified inorganic coating defects in traditional slurries, providing a high-quality precursor for subsequent film formation.

[0035] It is understood that the hydrophilic groups on the surface of the modifier-coated inorganic material particles (modified inorganic material) enable good dispersibility in aqueous solvents, making the resulting modified inorganic slurry more uniform and stable. Furthermore, the aqueous solvent leaves no residue after drying, eliminating the need for complex recycling processes and reducing energy consumption and costs.

[0036] Furthermore, in the step of mixing the inorganic material, modifier, and solvent, the mass ratio of the inorganic material to the modifier is (3-20):1. Specifically, the mass ratio of the inorganic material to the modifier can be 3:1, 5:1, 10:1, 15:1, 20:1, etc. While the modifier can improve dispersibility and compatibility, a significantly higher ratio may coat the particle surface, forming a dense organic layer that hinders ion migration. Polyphenols themselves do not have ion conductivity, and excessive accumulation of them dilutes the ion-conducting contribution of the inorganic phase. The organic layer may absorb moisture and expand, causing localized occlusion or distortion of the pore structure. Surface energy differences may lead to non-uniform film formation, forming "high-resistance regions." A mass ratio of the inorganic material to the modifier within this range allows for better coating of the inorganic particle surface, reducing the interparticle surface energy and preventing agglomeration, thereby resulting in a modified separator with lower internal resistance. In some embodiments, the mass ratio of the inorganic material to the modifier is (5~15):1. Within this range, the coating slurry has better dispersibility and stronger particle binding, and the resulting diaphragm exhibits better performance in terms of internal resistance, mechanical strength, thermal stability, wettability, conductivity and cycle life.

[0037] The solvent includes at least one of water, methanol, and ethanol. The solvent has good solubility and dispersion properties, is beneficial for subsequent wet ball milling, and can be removed during the subsequent drying process. For example, in one embodiment, a 50% ethanol-water solution can be used as the solvent.

[0038] It is understandable that in the steps of mixing the inorganic material, the modifier and the solvent to obtain a mixed solution, mixing the mixed solution with grinding beads and ball milling to obtain the modified inorganic material, the modifier and the solvent can be mixed first, and then the inorganic material can be added for ball milling.

[0039] Furthermore, in the step of mixing the mixed liquid with grinding beads and ball milling to obtain a modified inorganic material, the particle size of the modified inorganic material obtained is 0.5μm~1.5μm. Specifically, the particle size of the modified inorganic material is 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm or in a range consisting of any two of the above values. The modified inorganic material particles within the above range have a moderate specific surface area, a small tendency to agglomerate, and can be stably dispersed in the slurry, which is conducive to forming a continuous, uniform, and dense modified inorganic coating structure, thereby improving the overall consistency of the modified diaphragm. The particles in this particle size range act synergistically with the environmentally friendly modifier (natural polyphenol compound), can effectively form hydrogen bonds or interfacial polarity with the surface of the base membrane, improve adhesion, reduce powdering and shedding, and enhance the structural stability of the diaphragm. Controlling the particle size below micrometers creates moderate porosity, facilitating rapid electrolyte penetration and storage, improving the separator's electrolyte absorption rate, and enhancing the permeability of ion channels, thereby improving ionic conductivity and rate performance. The inorganic ceramic-modified inorganic coating formed within this particle size range has a dense structure and high mechanical strength, effectively blocking the growth path of lithium dendrites under high-rate or long-cycle conditions, thereby enhancing the battery's thermal stability and safety.

[0040] The particle size of the modified inorganic material can be controlled within the above range by controlling the particle size of the grinding beads and / or the time of ball milling.

[0041] In some embodiments, the grinding beads have a particle size of 0.8 mm to 5 mm. Specifically, the grinding beads can have a particle size of 0.8 mm, 1.5 mm, 2.5 mm, 3.5 mm, 4.5 mm, 5 mm, etc. Grinding beads within the above particle size range can achieve better grinding effects.

[0042] In some embodiments, the ball milling time is 3 h to 48 h. Specifically, the ball milling time can be 3 h, 8 h, 15 h, 24 h, 32 h, 48 h, etc. The ball milling time within the above range can achieve better grinding effect.

[0043] Furthermore, in some embodiments, the ratio of the mass of the grinding beads to the sum of the mass of the inorganic material and the modifier is (30-300):1. Specifically, the ratio of the mass of the grinding beads to the sum of the mass of the inorganic material and the modifier can be 30:1, 50:1, 80:1, 150:1, 200:1, 250:1, 300:1, etc. The ratio of the mass of the grinding beads to the sum of the mass of the inorganic material and the modifier within the above range can promote in-situ adsorption and coating of the modifier on the surface of the inorganic material particles, thereby forming a stable particle dispersion system.

[0044] It should be noted that the slurry after ball milling can be centrifuged, filtered, and dried to obtain a powdered modified inorganic material.

[0045] The above conditions can be set one by one or simultaneously. This application does not impose any restrictions. It is sufficient as long as the particle size of the modified inorganic material is controlled within the range of 0.5 μm to 1.5 μm.

[0046] Furthermore, in some embodiments, the above conditions can be set simultaneously, that is, the inorganic material solid particles and the modifier natural polyphenol compound can be co-dispersed in a mixed solvent system of water and ethanol, and grinding beads with a diameter of 0.8mm to 5mm can be added. By controlling the ball-to-powder ratio to (30-300):1 and the sanding time to 3h to 48h, the particle size can be precisely controlled between 0.5μm and 1.5μm. At the same time, the liquid phase environment and continuous shear collision effects promote the in-situ adsorption and coating of the modifier on the particle surface, forming a stable particle dispersion system. This greatly improves the uniformity, stability, and dispersibility of the particles, significantly improves the coating quality of the inorganic solid particles on the base film, avoids the problems of particle agglomeration, sedimentation, and modified inorganic coating defects in traditional slurries, and provides a high-quality precursor for subsequent film formation.

[0047] Furthermore, the mass ratio of the modified inorganic material to the aqueous solvent is 1:(4-10); the mass ratio of the modified inorganic material to the aqueous solvent is 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc. Within the above ranges, the modified inorganic slurry has good fluidity and stability, the modified coating after application is uniform and dense, has good adhesion and thermal stability, and significantly enhances electrolyte wettability and ionic conductivity. In some embodiments, the mass ratio of the modified inorganic material to the aqueous solvent is 1:(5-6). The modified diaphragm prepared within this range has better performance in terms of electrolyte absorption rate, ionic conductivity, thermal stability, and mechanical properties, and is suitable for harsh electrochemical environments such as high-rate cycling.

[0048] Furthermore, in the step of mixing the modified inorganic material with an aqueous solvent to obtain a modified inorganic slurry, the aqueous solvent includes at least one of methanol, ethanol, acetonitrile, dimethyl sulfoxide and dimethylformamide; it should be noted that the aqueous solvent is a solvent in which the mass proportion of water is greater than 50%, and the aqueous solvent is based on water or a solvent system that can be well mixed with water, such as a mixture of water and polar solvents such as methanol, ethanol, acetonitrile, dimethyl sulfoxide and dimethylformamide.

[0049] Furthermore, the step of "mixing the modified inorganic material with an aqueous solvent to obtain a modified inorganic slurry" includes: ultrasonically stirring the modified inorganic material and the aqueous solvent for 10 nanometers to 30 minutes to obtain the modified inorganic slurry. Ultrasonic stirring for 10 nanometers to 30 minutes can better disperse the particles and improve mixing efficiency.

[0050] Furthermore, the thickness of the modified inorganic coating is 1 μm to 8 μm. When the thickness of the modified inorganic coating is 1 μm to 8 μm, particles with a particle size of 0.5 μm to 1.5 μm have good fluidity and film-forming properties, making it easier to achieve a stable and controllable industrial preparation process through a doctor blade coating process. In some embodiments, the thickness of the modified inorganic coating is 1 μm to 2 μm. Within this range, the resulting diaphragm exhibits better performance in terms of internal resistance, mechanical strength, thermal stability, wettability, conductivity, and cycle life.

[0051] It is understood that the modified inorganic slurry can be coated on the surface of the battery base membrane by a doctor blade coating method, and the thickness of the modified inorganic coating can be controlled by adjusting the height of the doctor blade. After drying, the modified separator can be obtained.

[0052] Furthermore, the drying time is 10h~14h; the drying temperature is 25℃~60℃; specifically, the drying time can be 10h, 11h, 12h, 13h, 14h, etc., and the drying temperature can be 25℃, 30℃, 40℃, 45℃, 50℃, 60℃, etc. The drying temperature and time within the above range can enable the obtained modified diaphragm to have a better electrolyte absorption rate.

[0053] The modified diaphragm developed in this application has the following effects in practical applications: (1) The thermal stability of the modified diaphragm is significantly enhanced. The modified diaphragm has no obvious shrinkage at 120°C, which is much better than commercial PE diaphragm. (2) The modified diaphragm has improved wettability to the electrolyte and ionic conductivity, the contact angle is reduced from 54° to 16°, and the ionic conductivity is increased to 0.70 mS / cm; (3) The mechanical properties of the modified diaphragm are better, with tensile strength and puncture strength increased by more than 20%; (4) Better cycle stability. The capacity retention rate at high rate (5C) is much higher than that of traditional separators, and the cycle life of lithium symmetric batteries is increased to more than 1000 cycles. (5) It has the beneficial effects of being green, environmentally friendly, low-cost and scalable.

[0054] Therefore, the present invention uses the synergistic modification of natural and environmentally friendly polyphenol modifiers and inorganic solid particles as the core material, and uses wet sand grinding to achieve particle dispersion and particle size control as the core process, thereby preparing a high-safety modified diaphragm with high thermal stability, high mechanical strength, high electrical conductivity, low internal resistance, and green environmental protection.

[0055] The present invention also proposes an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, the separator includes a base film and a modified inorganic coating provided on at least one side of the base film, the modified inorganic coating includes an inorganic material and a modifier, the modifier includes a polyphenol compound, the polyphenol compound includes an aromatic group and a hydrophilic group, and the hydrophilic group includes at least one of a hydroxyl group, a carboxyl group and a carbonyl group.

[0056] The present invention also provides a lithium-ion battery comprising the electrode assembly described above. The modified separator can be directly used in lithium-ion battery systems, exhibiting improved safety and performance, particularly under high-temperature and high-current conditions, preventing battery short circuits and inhibiting the growth of lithium dendrites.

[0057] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0058] Example 1 A modified diaphragm is provided, which is prepared by the following method: 1g of modifier (tannic acid) powder was dissolved in a mixed solvent (water:ethanol = 50 vol%:50 vol%), and 9g of hexagonal boron nitride powder was added. The mixture was sand-milled at 400 rpm for 5 hours (using 1mm bead size). After centrifugation, filtration, and drying, a modified boron nitride (fBN) powder with a particle size of 1μm was obtained. 6g of the modified boron nitride powder was added to 40mL of N,N-dimethylformamide (DMF) solvent and ultrasonically stirred for 10 minutes to obtain a uniformly and stably dispersed fBN modified slurry. This fBN modified slurry was then coated onto a polyethylene (PE) separator, and the coating thickness was controlled using a doctor blade. After vacuum drying at 40°C, a modified separator with a coating thickness of approximately 2μm was obtained.

[0059] Example 2 A modified diaphragm is provided, which is prepared by the following method: 1g of modifier (tannic acid) powder was dissolved in a mixed solvent (water:ethanol = 50 vol%:50 vol%), and 9g of hexagonal boron nitride powder was added. The mixture was sand-milled at 400 rpm for 5 hours (using a 1mm bead size). After centrifugation, filtration, and drying, a modified boron nitride (fBN) powder with a particle size of 1μm was obtained. 4g of the modified boron nitride powder was added to 40mL of N,N-dimethylformamide (DMF) solvent and ultrasonically stirred for 10 minutes to obtain a uniformly and stably dispersed fBN modified slurry. This fBN modified slurry was then coated onto a polyethylene (PE) substrate, and the coating thickness was controlled using a doctor blade. After vacuum drying at 40°C, a modified separator with a coating thickness of approximately 2μm was obtained.

[0060] Example 3 A modified diaphragm is provided, which is prepared by the following method: 1g of the modifier (tannic acid) powder was dissolved in a mixed solvent (water:ethanol = 50 vol%:50 vol%), and 9g of hexagonal boron nitride powder was added. The mixture was then sand-milled at 400 rpm for 5 hours (using a 1mm bead size). After centrifugation, filtration, and drying, a modified boron nitride (fBN) powder with a particle size of 1μm was obtained. 8g of the modified boron nitride powder was then added to 40mL of N,N-dimethylformamide (DMF) solvent and ultrasonically stirred for 10 minutes to obtain a uniformly and stably dispersed fBN-modified slurry. This fBN-modified slurry was then coated onto a polyethylene (PE) separator, and the coating thickness was controlled using a doctor blade. After vacuum drying at 40°C, a modified separator with a coating thickness of approximately 2μm was obtained.

[0061] Examples 4 to 11 were prepared using similar steps to Example 1. The differences are shown in Table 1.

[0062] The difference between Example 4 and Example 1 is that the average particle size of the modified inorganic material is different, and the thickness of the prepared modified inorganic coating is different. The specific parameters are shown in Table 1.

[0063] The preparation method of the modified diaphragm provided in Example 4 is: 1g of modifier (tannic acid) powder was dissolved in a mixed solvent (water:ethanol = 50 vol%:50 vol%), and 9g of hexagonal boron nitride powder was added. The mixture was then sand-milled at 600 rpm for 10 hours (using 1mm bead size). After centrifugation, filtration, and drying, a modified boron nitride (fBN) powder with a particle size of 0.7μm was obtained. 6g of the modified boron nitride powder was then added to 40mL of N,N-dimethylformamide (DMF) solvent and ultrasonically stirred for 10 minutes to obtain a uniformly and stably dispersed fBN modified slurry. This fBN modified slurry was then coated onto a polyethylene (PE) separator, and the coating thickness was controlled using a doctor blade. After vacuum drying at 40°C, a modified separator with a coating thickness of approximately 1μm was obtained.

[0064] The difference between Examples 5 and 6 and Example 1 is that the average particle size of the modified inorganic material is different. The specific parameters are shown in Table 1.

[0065] The preparation method of the modified diaphragm provided in Example 5 is: 1g of the modifier (tannic acid) powder was dissolved in a mixed solvent (water:ethanol = 50 vol%:50 vol%), and 9g of hexagonal boron nitride powder was added. The mixture was then sand-milled at 300 rpm for 3 hours (using a 2mm bead size). After centrifugation, filtration, and drying, a modified boron nitride (fBN) powder with a particle size of 1.5μm was obtained. 6g of the modified boron nitride powder was then added to 40mL of N,N-dimethylformamide (DMF) solvent and ultrasonically stirred for 10 minutes to obtain a uniformly and stably dispersed fBN-modified slurry. This fBN-modified slurry was then coated onto a polyethylene (PE) separator, and the coating thickness was controlled using a doctor blade. After vacuum drying at 40°C, a modified separator with a coating thickness of approximately 2μm was obtained.

[0066] The preparation method of the modified diaphragm provided in Example 6 is: 1g of modifier (tannic acid) powder was dissolved in a mixed solvent (water:ethanol = 50 vol%:50 vol%), and 9g of hexagonal boron nitride powder was added. The mixture was then sand-milled at 650 rpm for 12 hours (using 1mm bead size). After centrifugation, filtration, and drying, a modified boron nitride (fBN) powder with a particle size of 0.5μm was obtained. 6g of modified boron nitride powder was then added to 40mL of N,N-dimethylformamide (DMF) solvent and ultrasonically stirred for 10 minutes to obtain a uniformly and stably dispersed fBN modified slurry. This fBN modified slurry was then coated onto a polyethylene (PE) separator, and the coating thickness was controlled using a doctor blade. After vacuum drying at 40°C, a modified separator with a coating thickness of approximately 1μm was obtained.

[0067] The difference between Example 7 and Example 1 is that the modifiers are different and the thickness of the modified inorganic coating obtained is different. The specific parameters are shown in Table 1.

[0068] The preparation method of the modified diaphragm provided in Example 7 is: 1g of the modifier (catechin) powder was dissolved in a mixed solvent (water:ethanol = 50 vol%:50 vol%). 9g of hexagonal boron nitride powder was added and the mixture was sand-milled at 350 rpm for 4 hours (using a 1.5mm bead size). After centrifugation, filtration, and drying, a modified boron nitride (fBN) powder with a particle size of 1.2μm was obtained. 6g of the modified boron nitride powder was added to 40mL of N,N-dimethylformamide (DMF) solvent and ultrasonically stirred for 10 minutes to obtain a uniformly and stably dispersed fBN modified slurry. This fBN modified slurry was then coated onto a polyethylene (PE) separator, with the coating thickness controlled by a doctor blade. After vacuum drying at 40°C, a modified separator with a coating thickness of approximately 2μm was obtained.

[0069] The difference between Examples 8 to 11 and Example 1 is that the mass ratios of the inorganic material and the modifier are different. The specific parameters are shown in Table 1.

[0070] The polyethylene (PE) separators in Examples 1 to 11 were all purchased from BAK Battery Co., Ltd.

[0071] Table 1 Preparation parameters of modified membranes of Examples 1 to 11

[0072] Comparative Example 1 A polyethylene separator was provided and purchased from BAK Battery Co., Ltd.

[0073] Comparative Example 2 A modified diaphragm is provided, which is prepared by the following method: 6 g of boron nitride powder was mixed with 0.5 g of PVDF binder and 40 g of NMP solvent, 0.5 g of dispersant was added, and shear dispersion was performed at 1000 rpm for 1 h to obtain a slurry; The slurry was coated on the surface of a polyethylene separator (purchased from BAK Battery Co., Ltd.), the coating thickness was controlled by a scraper, and after vacuum drying at 60°C, a composite separator with a coating thickness of about 2 μm was obtained.

[0074] Comparative Example 3 A modified diaphragm is provided, which is prepared by the following method: 1g of modifier (tannic acid) powder was dissolved in a mixed solvent (water:ethanol = 50 vol%:50 vol%), and 9g of hexagonal boron nitride powder was added. The mixture was sheared and dispersed at 500 rpm for 5 hours. After centrifugation, filtration, and drying, a modified boron nitride (fBN) powder with a particle size of 1.6μm was obtained. 6g of modified boron nitride powder was added to 40mL of N,N-dimethylformamide (DMF) solvent and ultrasonically stirred for 10 minutes to obtain a uniformly and stably dispersed fBN modified slurry. This fBN modified slurry was then coated onto a polyethylene (PE) separator (purchased from BAK Battery Co., Ltd.) with a doctor blade to control the coating thickness. After vacuum drying at 40°C, a modified separator with a coating thickness of approximately 2μm was obtained.

[0075] Diaphragm performance test (1) Bending test The modified diaphragm prepared in Example 1 was subjected to the following Figure 2 From the bending shown, it can be seen that the modified diaphragm prepared in Example 1 still maintains the good flexibility of the PE base film and can be bent arbitrarily without obvious damage. The modified coating is not easy to peel off or crack.

[0076] (2) Electrolyte affinity and wettability test Preparation of electrolyte: LiPF6 was dissolved in a mixed solvent of EC and DEC in a volume ratio of 1:1 to obtain an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L.

[0077] The modified diaphragm prepared in Example 1 and the polyethylene diaphragm of Comparative Example 1 were cut into discs of the same size (17 mm in diameter) by a punching machine for contact angle testing. The states of the electrolyte droplet on the diaphragm surface at the moment and 5 s later were recorded, as shown in FIG. Figure 3 shown. Figure 3 1 and 2 are side views of droplets obtained after the electrolyte is added dropwise to the modified diaphragm prepared in Example 1 and the polyethylene diaphragm of Comparative Example 1, respectively. Figure 3 (a) is a side view of the droplet at 0s when the above electrolyte solution is added to the surface of the polyethylene separator of Comparative Example 1; Figure 3 (b) is a side view of the droplet 5 seconds after the above electrolyte was added to the surface of the polyethylene separator of Comparative Example 1; Figure 3 (c) is a side view of the droplet at the instant 0s after the above electrolyte solution is added to the surface of the modified diaphragm of Example 1; Figure 3 (d) is a side view of the electrolyte droplet added to the modified diaphragm surface of Example 1 5s later. Figure 3It can be seen that at the moment the electrolyte contacts the separator, the contact angles of the polyethylene separator of Comparative Example 1 and the modified separator of Example 1 are 54° and 16°, respectively. After 5 seconds, the contact angle of the polyethylene separator decreases slightly to 49°, while the electrolyte droplet on the modified separator of Example 1 has completely spread out. This indicates that the modified separator of Example 1 exhibits better affinity with the electrolyte than Comparative Example 1.

[0078] Figure 4 The top view of the wetting distribution is obtained after the same amount of electrolyte is added dropwise to the modified separator prepared in Example 1 and the polyethylene separator of Comparative Example 1; Figure 4 (e) is a top view of the wetting distribution of the polyethylene separator before the above electrolyte is added dropwise to the polyethylene separator of Comparative Example 1; Figure 4 (f) is a top view of the wetting distribution diagram after the above electrolyte solution is added dropwise to the surface of the polyethylene separator of Comparative Example 1 for 5 minutes; Figure 4 (g) is a top view of the wetting distribution of the polyethylene separator before the above electrolyte is added dropwise to the modified separator of Example 1; Figure 4 (h) is a top view of the wetting distribution diagram after the above electrolyte solution is added to the surface of the modified diaphragm of Example 1 for 5 minutes; Figure 4 It can be seen that 5 minutes after the electrolyte was added, the electrolyte on the PE membrane still appeared as large droplets, showing only a small area of wetting. In contrast, the electrolyte on the surface of the modified membrane in Example 1 has already penetrated and diffused over a large area and is completely absorbed by the modified membrane, showing excellent electrolyte wettability. This is because the polar hydroxyl groups of the modified inorganic coating improve its compatibility with polar electrolytes, thereby showing better wetting properties and thus having higher ionic conductivity.

[0079] (3) Thermal stability test The modified diaphragm prepared in Example 1 and the polyethylene diaphragm of Comparative Example 1 were cut into multiple discs of the same size (diameter 17 mm) by a punching machine, and were placed at 60°C, 80°C, 100°C, 120°C, and 130°C for 5 minutes, respectively, and their deformation was observed to obtain Figure 5 . Figure 5 This is a graph showing the thermal stability test results of the modified diaphragm prepared in Example 1 and the polyethylene diaphragm of Comparative Example 1.

[0080] Depend on Figure 5It can be seen that the modified diaphragm of Example 1 has excellent thermal stability at temperatures up to 120°C, without any shrinkage deformation, and finally maintains its original state. The PE diaphragm of Comparative Example 1 begins to curl at the edges from 80°C, and the thermal shrinkage deformation becomes more obvious as the temperature rises. At a temperature of 120°C, the PE diaphragm is completely deformed and shrunk and begins to melt, while the modified diaphragm of Example 1 still maintains dimensional stability. When the temperature rises to 130°C, the edges of the modified diaphragm begin to shrink, while the PE diaphragm is almost completely melted, and the area shrinks to one twelfth of the original size. The excellent thermal stability of the modified diaphragm of Example 1 is due to the high temperature resistance and high thermal conductivity of the inorganic solid material itself, which resists the melting shrinkage of the PE base film at high temperatures.

[0081] The following tests were performed on the separators of Examples 1 to 11 and Comparative Examples 1 to 3, and the test results are recorded in Table 2.

[0082] (4) Mechanical properties The separators from Examples 1 to 11 and Comparative Examples 1 to 3 were each prepared into rectangular separator samples measuring 3 mm × 10 mm. Tensile strength tests were performed on a Zwick Roell Z010 AllroundLine universal testing machine, and puncture strength tests were performed on a lithium battery separator puncture strength tester. The test data are recorded in Table 2.

[0083] (5) Thermal diffusivity The thermal diffusivity of the membrane was measured by a laser thermal conductivity meter (Netzsch, LFA467). The test data are recorded in Table 2.

[0084] (6) Electrolyte absorption rate In the electrolyte absorption test, the separators were immersed in electrolyte for 2 hours, wiped with filter paper to remove excess electrolyte, and then each separator was weighed. The electrolyte absorption was calculated using the following formula:

[0085] Among them, w0 and w1 are the weight of the dry diaphragm and the weight after absorbing the electrolyte, respectively.

[0086] The following tests were performed on the separators of Example 1 and Comparative Examples 2 and 3, and the test results are recorded in Table 3.

[0087] Impedance and ionic conductivity tests: The ionic conductivity of the diaphragm was calculated using the electrochemical impedance spectroscopy (EIS) measurement method using a Chenhua CHI760E electrochemical workstation. The test method was to form a button cell with two parallel stainless steel disc electrodes, with a diaphragm soaked in the same volume of electrolyte (1.0 M LiPF, EC / DEC (1 / 1 v / v)) sandwiched in the middle. After overnight aging, the diaphragm was assembled into a button cell in a glove box filled with argon atmosphere. The assembled pair of steel cells was clamped on the electrode clamp of the electrochemical workstation, and an AC amplitude of 10 mV was applied in the frequency range of 0.1 Hz to 1 MHz. The Nyquist curve was obtained, and the electrolyte impedance value R corresponding to the intercept in the high-frequency region was measured. The ionic conductivity (σ) was calculated by the following formula:

[0088] Where t is the thickness of the diaphragm, R is the resistance measured by EIS, and A is the area of the stainless steel disk electrode.

[0089] Table 2 Performance data of the diaphragms obtained in Examples 1 to 11 and Comparative Examples 1 to 3

[0090] It can be seen from Table 2 that, compared with the polyethylene diaphragm of Comparative Example 1, the modified diaphragm provided by the present invention has higher tensile strength, puncture strength, thermal diffusion coefficient and electrolyte absorption rate.

[0091] Compared with the polyethylene diaphragm modified by adhesive and boron nitride powder in Comparative Example 2, the modified diaphragm provided by the present invention has higher tensile strength, puncture strength, thermal diffusion coefficient and electrolyte absorption rate.

[0092] Compared with the modified polyethylene diaphragm prepared by shear-dispersed particles in Comparative Example 3, the modified diaphragm provided by the present invention has higher tensile strength, puncture strength, thermal diffusion coefficient and electrolyte absorption rate.

[0093] Table 3 Performance data of the diaphragms obtained in Example 1 and Comparative Examples 2 and 3

[0094] As can be seen from Table 2, the impedance of the polyethylene diaphragm modified with adhesive and boron nitride powder in Comparative Example 2 is 2.4Ω, which is greater than the impedance of the modified polyethylene diaphragm in Example 1, indicating that the technical solution of the present invention can reduce the internal resistance.

[0095] Comparative Example 3, in which shear dispersion was used instead of sand milling, resulted in uneven particle distribution and severe agglomeration, resulting in irregular or non-interpenetrating pore structures in the coating. Large particles exhibited weak bonding, prone to cracks and localized shedding, and the formation of "high resistance points." The coating structure was loose, resulting in high interfacial contact resistance. While the electrolyte absorption rate was acceptable (175%), the proportion of "ineffective channels" in the internal structure was high. Therefore, the present invention utilizes sand milling to achieve uniform particle size in the modified inorganic material, resulting in a modified separator with good overall performance and lower impedance.

[0096] In order to verify the performance of the modified battery separator of the present invention, Example 1 of the present invention and the unmodified PE separator were assembled into batteries, and the electrochemical performance was tested. The specific test method is as follows: Battery preparation (1) Li / separator / Graphite battery (half-cell) Commercial graphite negative electrode material, conductive carbon black and binder (PVDF mass fraction of 7 wt%) were mixed in a mass ratio of 8:1:1, and then an appropriate amount of NMP solvent was added to adjust the viscosity of the slurry to a semi-fluid state, and then stirred for 8 hours to obtain a uniform electrode slurry. The slurry was evenly coated on a copper foil and placed in a vacuum oven at 60 ° C for 12 hours. The dried electrode was cut into electrode sheets with a diameter of 13 mm by a punching machine, and then the battery was assembled in a glove box filled with argon atmosphere. When assembling the button half-cell, 1.0 M LiPF6 was selected as the electrolyte (the volume ratio of ethylene carbonate EC and dimethyl carbonate DEC was 1:1 vol%), the PE diaphragm in comparative example 1 and the modified diaphragm in example 1 were used as the diaphragm, the metal lithium sheet was used as the counter electrode, and the electrode sheet was used as the working electrode to obtain a CR2032 button half-cell. The assembled button half-cell was subjected to charge and discharge tests and cycle performance tests at different current densities using the Xinwei battery testing system, and the results are shown in FIG. Figure 6 、 Figure 7 .

[0097] (2) Li / separator / Li battery (lithium symmetrical battery) The positive and negative electrodes of the lithium-ion battery are both Li sheets, and the positive electrode, negative electrode and the PE separator in comparative example 1 / the modified separator in embodiment 1 are assembled into a Li / Li battery, and a cycle test is performed. The results are as follows. Figure 8 shown.

[0098] Electrochemical testing (1) The Li / separator / Graphite battery (half-cell) prepared from the modified diaphragm in Example 1 and the polyethylene diaphragm in Comparative Example 1 was subjected to charge and discharge tests at different current densities, with the current densities being 0.1C, 0.5C, 1C, 2C, 3C, 5C, and 0.1C, respectively. The results are shown in the figure below: Figure 6 shown by Figure 6 It can be seen that at different current densities, both batteries exhibit relatively stable cycling. As the current density increases, the discharge capacity of the battery gradually decreases. Due to the higher ionic conductivity and electrolyte absorption rate of the modified diaphragm of Example 1, the discharge capacity of the half-cell using the modified diaphragm is higher than that of the PE diaphragm at all current densities. Especially at a high current density of 5 C, the advantage of the modified diaphragm of Example 1 is more obvious, and the capacity is maintained at 59 mAh g -1 , while the capacity of PE separator decays to 33 mAh g -1 This means that the modified separator in Example 1 can withstand high currents by absorbing excess heat and transferring heat through the modified inorganic coating during cycling. However, if ordinary PE film fails to dissipate this excess heat in a timely manner, it will reduce cycling performance and pose a potential risk to the battery, especially by accelerating thermal shrinkage of the separator.

[0099] (2) The Li / separator / Graphite battery (half-cell) prepared from the modified diaphragm in Example 1 and the polyethylene diaphragm in Comparative Example 1 was subjected to a cycling performance test at a current density of 3 C. The results are shown in FIG. Figure 7 As shown in Figure 2 (the two slightly overlapping curves above correspond to the Coulombic efficiency, and the two curves below correspond to the specific capacity), the performance of the modified membrane of Example 2 exceeds that of the commercial PE membrane, showing good stability and maintaining a capacity of 98.6 mAh g after 400 cycles (3 C). -1 The retention rate is 89%, which is better than that of PE diaphragm (66.5 mAh g -1 , 83%).

[0100] (3) The Li / separator / Li battery (lithium symmetrical battery) prepared from the modified diaphragm in Example 1 and the polyethylene diaphragm in Comparative Example 1 was tested at a current density of 5 mA cm -2 , capacity of 1 mAh cm -2 The cycle performance test was carried out under the conditions of Figure 8 As shown. During the lithium symmetric battery cycle, due to the symmetry of the battery, the voltage signal comes from the overpotential difference of lithium dissolution and deposition between the positive and negative electrodes. At a current density of 5 mA cm -2 , capacity of 1 mAh cm -2Under the condition of , the overpotential of Comparative Example 1 at the 100th cycle is 57.3 mV, while the overpotential of Example 1 is only 9.8 mV. The overpotentials of Comparative Example 1 and Example 1 at the 400th cycle are 40.5 and 9.1 mV, respectively. The results show that the lithium nucleation barrier using the PE diaphragm is higher than that using Example 2, which is mainly due to the higher affinity and wettability of the modified diaphragm of Example 2 with the electrolyte. After 512 cycles, the voltage signal of the PE battery suddenly dropped to 0, indicating that lithium dendrites pierced the diaphragm and caused a short circuit. In contrast, the overpotential of the battery of Example 2 remained stable at ~10 mV after 1000 cycles, showing good cycle stability. This is because the modified inorganic coating with excellent mechanical properties and thermal stability is conducive to blocking the growth of lithium dendrites and extending battery life.

[0101] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A modified diaphragm, characterized in that: The modified diaphragm includes a base membrane and a modified inorganic coating provided on at least one side of the base membrane, the modified inorganic coating includes an inorganic material and a modifier, the modifier includes a polyphenol compound, the polyphenol compound includes an aromatic group and a hydrophilic group, and the hydrophilic group includes at least one of a hydroxyl group, a carboxyl group and a carbonyl group.

2. The modified diaphragm according to claim 1, wherein The polyphenol compound includes at least one of tannic acid, catechin, proanthocyanidin, epigallocatechin gallate and quercetin.

3. The modified diaphragm according to claim 1, wherein The inorganic material includes at least one of SiO2, Al2O3, boehmite, Mg(OH)2, zeolite, ZrO2, TiO2 and BN.

4. A method for preparing a modified diaphragm according to any one of claims 1 to 3, characterized in that: The following steps are involved: Mixing an inorganic material, a modifier, and a solvent to obtain a mixed solution, mixing the mixed solution with grinding beads, and ball milling to obtain a modified inorganic material; mixing the modified inorganic material with an aqueous solvent to obtain a modified inorganic slurry; The modified inorganic slurry is applied to at least one surface of a base film and dried to prepare a modified inorganic coating on at least one surface of the base film to obtain a modified diaphragm.

5. The method for preparing the modified diaphragm according to claim 4, wherein: The mass ratio of the inorganic material to the modifier is (3-20):1; and / or, The solvent includes at least one of water, methanol and ethanol.

6. The method for preparing the modified diaphragm according to claim 4, wherein: The particle size of the grinding beads is 0.8 mm to 5 mm; and / or, The ratio of the mass of the grinding beads to the sum of the mass of the inorganic material and the modifier is (30-300):1; and / or, The ball milling time is 3h~48h; and / or, The particle size of the modified inorganic material is 0.5 μm to 1.5 μm.

7. The method for preparing the modified diaphragm according to claim 4, wherein: The mass ratio of the modified inorganic material to the aqueous solvent is (4-10):40; The aqueous solvent includes at least one of water, methanol, ethanol, acetonitrile, dimethyl sulfoxide and dimethylformamide; and / or, The step of "mixing the modified inorganic material with an aqueous solvent to obtain a modified inorganic slurry" includes: mixing the modified inorganic material with the aqueous solvent by ultrasonic stirring for 10 nanometers to 30 minutes to obtain a modified inorganic slurry.

8. The method for preparing the modified diaphragm according to claim 4, wherein: The drying time is 10h~14h; and / or, The drying temperature is 25°C to 60°C; and / or, The thickness of the modified inorganic coating is 1 μm to 8 μm.

9. An electrode assembly, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the separator is a modified separator according to any one of claims 1 to 3 or a separator prepared by the preparation method of the modified separator according to any one of claims 4 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery includes the electrode assembly according to claim 9.

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