Lithium battery composite diaphragm and preparation method thereof, lithium battery

Abstract

The application belongs to the technical field of lithium batteries, and particularly relates to a lithium battery composite diaphragm, a preparation method thereof and a lithium battery. The composite diaphragm is used for a lithium battery, and comprises a base film and a ceramic coating layer covering the surface of the base film. The ceramic coating layer is a porous three-dimensional network structure, and comprises an imidazole group-containing aqueous binder, inorganic nano ceramic particles, a wetting agent and a solvent. The raw material of the imidazole group-containing aqueous binder comprises vinyl imidazole and a polymer monomer. The imidazole group-containing aqueous binder is used for simultaneously adsorbing HF and Mn 2+ The composite diaphragm of the application has a small thermal shrinkage rate. The constructed imidazole group-containing stable high-molecular binder three-dimensional porous network improves the diaphragm structure and interface performance, realizes the dual synergistic removal function of HF and Mn 2+ , and significantly enhances the cycle life and safety stability of the lithium ion battery, thereby providing strong support for a new generation of high-performance energy storage systems.

Description

Technical Field

[0001] This application belongs to the field of lithium battery technology, and particularly relates to a lithium battery composite separator and its preparation method, and a lithium battery. Background Technology

[0002] Lithium-ion batteries (LIBs) are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and low self-discharge rate. However, with the increasing demands on battery operating environments and performance, the long-term stability and safety of lithium-ion batteries are becoming increasingly prominent, especially when operating at high voltages, where the cycle life and capacity retention are severely affected.

[0003] Currently, fluorides in electrolytes (such as LiPF6) undergo hydrolysis in the presence of trace amounts of moisture, generating hydrogen fluoride (HF). This reaction triggers a series of side reactions, leading to a decline in battery performance. HF formation is one of the main factors causing performance degradation in lithium-ion batteries. HF not only corrodes the solid electrolyte interface (SEI) and electrode materials, compromising battery stability, but also promotes the dissolution of metal ions. Especially in batteries using LiMn2O4 as the positive electrode material, the presence of HF accelerates the dissolution and migration of manganese ions. With the deposition of manganese ions at the negative electrode, the SEI film undergoes malignant growth, which in turn consumes lithium ions and leads to battery capacity decay. It may even cause internal short circuits, seriously threatening battery safety.

[0004] Existing technologies employ cathode material coating to form a physical barrier against HF, electrolyte additives to suppress HF generation, and single-function membranes to capture HF or metal ions individually. However, the cathode material coating process is complex and introduces additional interfacial impedance, electrolyte additives can trigger other side reactions and reduce electrolyte performance, and single-function membranes can only prevent HF migration or metal ion migration individually.

[0005] Existing technologies cannot simultaneously suppress the generation of HF in the electrolyte and prevent the dissolution and migration of conductive metal ions in the cathode material. Summary of the Invention

[0006] This application provides a lithium battery composite separator and its preparation method, as well as a lithium battery, aiming to solve to some extent the problem of not being able to simultaneously suppress the generation of HF in the electrolyte and prevent the dissolution and migration of metal conductive ions in the positive electrode material.

[0007] In a first aspect, this application provides a lithium battery composite separator. The composite separator is used in lithium batteries and includes a base film and a ceramic coating layer covering the surface of the base film. The ceramic coating layer has a porous three-dimensional network structure and includes an aqueous binder containing imidazole groups, inorganic nano-ceramic particles, a wetting agent, and a solvent. The aqueous binder containing imidazole groups is used to simultaneously adsorb HF and Mn. 2+ The raw materials for water-based adhesives include vinylimidazole and polymer monomers.

[0008] In one embodiment, the polymer monomer includes at least one selected from acrylamide, N,N-dimethylacrylamide, tetrahydrofuran acrylate, butyl acrylate, ethyl acrylate, methacrylic acid, and acrylic acid.

[0009] In one embodiment, the inorganic nanoceramic particles include at least one of boehmite, alumina, zinc oxide, titanium dioxide, silicon dioxide, and zirconium oxide.

[0010] In one embodiment, the base film comprises any one or a combination of polyethylene, polypropylene, polyethylene-polypropylene composite, polyvinylidene fluoride, polyester, polysulfone, polyethersulfone, and polyimide.

[0011] In one embodiment, the solvent includes at least one of water, ethanol, isopropanol, and N-methylpyrrolidone;

[0012] The wetting agent is any one or a combination of nonionic surfactants, polyvinylpyrrolidone, sodium stearate, and phosphatidylcholine. The nonionic surfactants include polyoxyethylene ether nonionic surfactants, polyethylene oxide nonionic surfactants, or polyoxyethylene sorbitan fatty acid ester nonionic surfactants.

[0013] In one embodiment, the thickness of the base film is 5 micrometers to 50 micrometers;

[0014] The thickness of the ceramic coating is 1 micrometer to 10 micrometers.

[0015] Secondly, this application provides a method for preparing a lithium battery composite separator, used to prepare a lithium battery composite separator as described in any one of the first aspects, comprising:

[0016] A waterborne adhesive containing imidazole groups was synthesized by solution polymerization using vinylimidazole and polymer monomers as raw materials.

[0017] Inorganic nano-ceramic particles are dispersed in a solvent, and then the aqueous binder and wetting agent are added and stirred to obtain a ceramic coating slurry.

[0018] A ceramic coating slurry is uniformly coated onto at least one surface on both sides of a polyolefin-based film, and then baked and dried at a set temperature to obtain a film capable of simultaneously adsorbing HF and Mn. 2+ Ceramic composite separator for lithium-ion batteries.

[0019] In one embodiment, the stirring temperature is 20℃~60℃, and the stirring time is 0.5h~4h;

[0020] The mass ratio of vinylimidazole to polymer monomer is (0.5~1.5):(3.5~4.5).

[0021] In one embodiment, the baking temperature is set at 60°C to 120°C; the baking and drying time is 0.5h to 48h.

[0022] Thirdly, this application provides a lithium battery, including a composite separator as described in any one of the first aspects, or a composite separator prepared by any one of the composite separator preparation methods described in any one of the second aspects.

[0023] It is understood that the beneficial effects of the second and third aspects mentioned above can be found in the relevant descriptions in the first aspect above, and will not be repeated here.

[0024] The advantages of this application compared to the prior art are:

[0025] This application describes a composite separator for lithium batteries. The composite separator comprises a base membrane and a ceramic coating layer covering the surface of the base membrane. The ceramic coating layer has a porous three-dimensional network structure and includes an aqueous binder containing imidazole groups, inorganic nano-ceramic particles, a wetting agent, and a solvent. The aqueous binder is made from vinylimidazolium and polymer monomers. The aqueous binder containing imidazole groups is used to simultaneously adsorb HF and Mn. 2+ After heat treatment, the composite separator exhibits a thermal shrinkage rate of less than 5%, ensuring stable structure and performance even at high temperatures, thus guaranteeing battery safety and long-term reliability. Furthermore, the porous network structure formed by inorganic nano-ceramic particles and functionalized aqueous binders significantly improves electrolyte wettability, with a contact angle approaching zero degrees, allowing for rapid and uniform electrolyte penetration and distribution, effectively enhancing lithium-ion transport rates. The high liquid absorption rate of the composite separator significantly improves battery charge / discharge efficiency and power density. The three-dimensional porous network of imidazole-containing stable polymer binders constructed in this application not only improves the separator structure and interfacial performance but also achieves the mixing of HF and Mn. 2+The dual synergistic cleaning function significantly enhances the cycle life and safety stability of lithium-ion batteries, providing strong support for the next generation of high-performance energy storage systems. In addition, the preparation process of the lithium battery composite separator in this application is based on an aqueous system, without the use of organic solvents, which conforms to green manufacturing technology. Moreover, the preparation process is simple and easy to implement, suitable for large-scale production, and has high industrialization potential. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic flowchart of a method for preparing a composite diaphragm according to an embodiment of this application;

[0028] Figure 2 This is a schematic diagram of the surface scanning electron microscope (SEM) of the composite membrane in Example 1;

[0029] Figure 3 This is a schematic diagram of the cross-sectional scanning electron microscope (SEM) of the composite membrane of Example 1;

[0030] Figure 4 This is a comparative schematic diagram of the X-ray photoelectron spectroscopy (XPS) spectra of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0031] Figure 5 This is a comparative schematic diagram showing the thermal stability test results of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0032] Figure 6 This is a comparative schematic diagram showing the electrolyte contact angle test results of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0033] Figure 7 This is a comparative schematic diagram of the Nyquist impedance diagrams of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 in stainless steel / stainless steel (SS / SS) symmetric cells.

[0034] Figure 8 This is a comparative schematic diagram showing the HF content in the electrolytes of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0035] Figure 9 The composite membranes Mn prepared in Example 1, Comparative Example 1, and Comparative Example 2 are 2+A diagram illustrating the comparison of adsorption amounts;

[0036] Figure 10 This is a schematic diagram comparing the discharge capacity of Li|separator|LiMn2O4 batteries (Li metal as the negative electrode and LiMn2O4 as the positive electrode, "|" represents the phase interface) prepared using composite separators of Example 1, Comparative Example 1, and Comparative Example 2, respectively, under 1C current cycling.

[0037] Figure 11 This is a schematic diagram comparing the coulombic efficiency of Li|separator|LiMn2O4 batteries (Li metal as the negative electrode and LiMn2O4 as the positive electrode, "|" represents the phase interface) prepared using composite separators of Example 1, Comparative Example 1, and Comparative Example 2, respectively, under 1C current cycling.

[0038] Figure 12 This is a schematic diagram comparing the discharge capacity of Li|separator|LiMn2O4 batteries (Li metal as the negative electrode and LiMn2O4 as the positive electrode, "|" represents the phase interface) prepared using the composite separators of Example 1, Comparative Example 1, and Comparative Example 2, respectively, under a 0.5C current cycling condition.

[0039] Figure 13 This is a schematic diagram comparing the coulombic efficiency of Li|separator|LiMn2O4 batteries (Li metal as the negative electrode and LiMn2O4 as the positive electrode, "|" represents the phase interface) prepared using the composite separators of Example 1, Comparative Example 1, and Comparative Example 2, respectively, under a 0.5C current cycle. Detailed Implementation

[0040] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0041] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0042] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple.

[0043] The terms "first" and "second" are used only to describe the purpose and to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the provisions of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0044] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0045] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0046] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0047] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0048] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0049] Existing technologies employ methods such as coating the cathode material to form a physical barrier against HF, using electrolyte additives to suppress HF generation, and using single-function separators to individually capture HF or metal ions. Cathode material coating, by coating the cathode material with an HF scavenger to form a physical barrier and prevent HF from directly corroding the cathode, requires complex processes, making large-scale application difficult, and introduces additional interfacial impedance, affecting the overall battery performance. Electrolyte additives involve adding HF scavengers or molecules that inhibit HF formation to the electrolyte. While this can reduce the harmful effects of HF on the battery, it can trigger other side reactions, reducing the ionic conductivity of the electrolyte and battery performance. Furthermore, the Mn content of the cathode material... 2+ After migrating to the negative electrode, HF molecules undergo a reduction reaction and deposit on the negative electrode surface, disrupting the stability of the positive electrode electrolyte interphase (SEI) membrane, catalyzing electrolyte decomposition, and leading to impedance increase and capacity decay. Single-function separators, on the other hand, fix HF-capturing molecules or metal ion-capturing materials onto the separator, but can only prevent the migration of HF or metal ions within the battery.

[0050] To partially address the aforementioned technical problems, the first aspect of this application provides a lithium battery composite separator. The composite separator is used in lithium batteries and includes a base film and a ceramic coating layer covering the surface of the base film. The ceramic coating layer has a porous three-dimensional network structure and includes an aqueous binder containing imidazole groups, inorganic nano-ceramic particles, a wetting agent, and a solvent. The aqueous binder containing imidazole groups is used to simultaneously adsorb HF and Mn. 2+ The raw materials for water-based adhesives include vinylimidazole and polymer monomers.

[0051] This embodiment provides a lithium battery composite separator, which has the following advantages compared with the prior art:

[0052] 1. Significantly improved battery cycle life:

[0053] Vinyl imidazole copolymerizes with polymer monomers to form an imidazole-containing aqueous binder. Vinyl imidazole provides a large number of imidazole ring functional groups. The aqueous binder can adsorb HF (hydrofluoric acid). Because the nitrogen atom (N) at the third position of the imidazole ring has a lone pair of electrons, it acts as a Lewis base and reacts with HF molecules (H+) as a Lewis acid. + The aqueous binder can bind to empty orbitals to form hydrogen bonds, or directly accept protons, effectively capturing and fixing HF through acid-base interactions; at the same time, the aqueous binder can also adsorb Mn. 2+ (Manganese ion), the imidazole ring acts as a chelating ligand, and the two nitrogen atoms in the imidazole ring react with Mn. 2+Once the transition metal ions form stable coordination bonds, they are firmly locked onto the membrane surface, preventing them from moving freely in the electrolyte. This effectively removes HF and Mn. 2+ This reduces corrosion and damage to the positive and negative electrode materials, slows down the loss of active lithium and reduces impedance, thereby resulting in higher battery capacity retention, a significant increase in the number of cycles, and thus improved battery cycle life.

[0054] 2. Enhanced high-temperature performance and safety:

[0055] Traditional pure polymer-based membranes (such as PE / PP) soften, shrink, or even melt at high temperatures, failing to resist dendrite penetration and lacking the ability to purify harmful impurities in the electrolyte. In contrast, the inorganic nano-ceramic particles in the composite separator of this application provide extremely high hardness and strength. The binder polymerizes to form a stable polymer chain structure that firmly bonds the hard ceramic particles together and effectively disperses stress, avoiding the brittleness problem of high-proportion ceramic coating slurry layers. This results in higher puncture resistance of the composite separator, constructing a robust porous three-dimensional network structure that forms a strong heat-resistant skeleton. When the internal base membrane shrinks due to heat, the high-temperature resistance of the ceramic material greatly reduces the thermal shrinkage of the separator, allowing the outer ceramic coating slurry layer to maintain the separator's shape and integrity. The overall shrinkage rate of the composite separator is low, and the hard ceramic layer effectively resists lithium dendrite penetration, preventing physical contact between the positive and negative electrodes of the battery, improving battery safety, enhancing thermal stability, and thus greatly reducing the risk of short circuits, fires, and explosions. It also improves the mechanical strength of the composite separator.

[0056] In addition, removing HF from the electrolyte also indirectly improves safety, because the corrosion of battery materials by HF is an exothermic reaction, which will exacerbate the risk of thermal runaway.

[0057] 3. Improved rate capability:

[0058] The addition of wetting agents directly improves the spreadability of the slurry and the affinity of the coated separator for the electrolyte. Inorganic nano-ceramic particles, with their high surface energy and abundant porous structure, provide ample storage and channel space for the electrolyte. After curing, the aqueous binder and ceramic particles form a three-dimensional network structure, which firmly fixes the ceramic particles without completely blocking the electrolyte channels. This gives the ceramic surface hydrophilicity, allowing the electrolyte to wet the composite separator more quickly and uniformly, significantly improving the contact angle wetting performance between the separator and the electrolyte. Consequently, the composite separator can absorb the electrolyte more quickly and fully, and has a strong electrolyte retention capacity. This also reduces the resistance to ion migration, thereby lowering the battery's internal resistance and improving ionic conductivity, resulting in better rate performance (fast charging and discharging) and cycle performance.

[0059] 4. Improved interface stability:

[0060] The organic portion of the aqueous binder exhibits good compatibility with the polymer-based film and electrode binders (which are typically acrylic-based). Meanwhile, the imidazole ring functional group can bind with the inorganic nano-ceramic particles and the surface of the electrode active material, forming a low-resistance transition layer. This results in better interfacial contact between the composite separator and the electrode, more uniform lithium-ion transport at the interface, reduced interfacial impedance, and improved long-term stable cycle performance of the lithium battery. Simultaneously, the clean electrolyte environment without HF facilitates the formation of a more stable and robust SEI film on the negative electrode surface, reducing the occurrence of side reactions.

[0061] In summary, the lithium battery prepared using the composite separator of this application exhibits excellent cycle stability and charge / discharge rate performance. Therefore, the composite separator of this application combines the advantages of good heat resistance, low moisture content, high electrolyte wettability, high adhesion, excellent electrochemical performance, structural stability, ease of preparation, and environmental friendliness. Furthermore, since manganese dissolution is one of the main causes of battery degradation in manganese-rich cathodes (such as low-nickel, high-manganese ternary materials), this application addresses this issue by capturing dissolved Mn. 2+ The use of manganese ions (as a cathode) avoids dissolving into the electrolyte, thus improving the electrochemical performance of high-manganese cathode battery systems, such as LiMn2O4 / Li half-cells (Li metal as the anode and LiMn2O4 as the cathode) and LiMn2O4 / Gr full-cells (Gr metal as the anode and LiMn2O4 as the cathode). Furthermore, the preparation method in this application uses an aqueous binder and water as a solvent, avoiding the environmental, health, and recycling cost problems associated with the use of toxic organic solvents (such as NMP) in traditional oil-based systems. The preparation process is highly compatible with existing coating equipment, easily enabling large-scale production, achieving both environmental friendliness and process friendliness.

[0062] In one embodiment, the polymer monomer includes at least one selected from acrylamide, N,N-dimethylacrylamide, tetrahydrofuran acrylate, butyl acrylate, ethyl acrylate, methacrylic acid, and acrylic acid. In this embodiment, tetrahydrofuran acrylate significantly improves the hydrophobicity, water resistance, and adhesion of the waterborne adhesive; butyl acrylate and / or ethyl acrylate also improve the flexibility, film-forming properties, and adhesion of the composite membrane; methacrylic acid and / or acrylic acid provide carboxyl groups (-COOH), which improve the stability of the waterborne adhesive through steric hindrance and electrostatic repulsion, and enhance the adhesion to the base membrane and including inorganic nano-ceramic particles.

[0063] In one embodiment, the inorganic nanoceramic particles include at least one of boehmite, alumina, zinc oxide, titanium dioxide, silicon dioxide, and zirconium oxide.

[0064] In one embodiment, the base film comprises any one or a combination of polyethylene, polypropylene, polyethylene-polypropylene composite, polyvinylidene fluoride, polyester, polysulfone, polyethersulfone, and polyimide.

[0065] In one embodiment, the solvent includes at least one of water, ethanol, isopropanol, and N-methylpyrrolidone; the wetting agent is any one or a combination of nonionic surfactant, polyvinylpyrrolidone, sodium stearate, and phosphatidylcholine, and the nonionic surfactant includes polyoxyethylene ether nonionic surfactant (e.g., Emulgen), polyethylene oxide nonionic surfactant (e.g., Triton X-100), or polyoxyethylene sorbitan fatty acid ester nonionic surfactant (e.g., Tween).

[0066] In one embodiment, the thickness of the base film is 5 micrometers to 50 micrometers, and the thickness of the ceramic coating layer is 1 micrometer to 10 micrometers. The ceramic coating slurry layer within this thickness range can serve as a physical barrier between the positive and negative electrodes inside the battery to prevent direct contact between the electrodes and cause a short circuit, and also provides a shorter migration channel for lithium ions.

[0067] Secondly, such as Figure 1 As shown, this application provides a method for preparing a lithium battery composite separator, used to prepare a lithium battery composite separator as described in any one of the first aspects, comprising:

[0068] S1 is an aqueous binder containing imidazole groups synthesized by solution polymerization using vinylimidazole and polymer monomers as raw materials.

[0069] S2, Inorganic nano-ceramic particles are dispersed in a solvent, then an aqueous binder and a wetting agent are added and stirred to obtain a ceramic coating slurry.

[0070] S3, a ceramic coating slurry is uniformly coated onto at least one surface on both sides of a polyolefin-based film, and then baked and dried at a set temperature to obtain a film capable of simultaneously adsorbing HF and Mn. 2+ Ceramic composite separator for lithium-ion batteries.

[0071] In this embodiment, compared with the prior art, the lithium battery composite separator prepared by this method ingeniously integrates physical protection (thermal stability and mechanical strength of the ceramic layer) with chemical protection (chemical adsorption of harmful substances by the imidazole binder), thus creating a "smart" functional separator. It is not merely a physical isolation layer, but also a purifier of the electrochemical microenvironment, simultaneously curbing the two key factors (HF and Mn) that lead to battery performance degradation at the source. 2+ This comprehensively improves the cycle life, safety, and overall performance of lithium batteries.

[0072] In one embodiment, the stirring temperature is 20°C to 60°C, and the stirring time is 0.5 h to 4 h; the mass ratio of vinylimidazole to polymer monomer is (0.5 to 1.5):(3.5 to 4.5). This mass ratio within the range of this embodiment avoids insufficient adhesion of the water-based adhesive due to excessive imidazole, or simultaneous adsorption of HF and Mn due to excessive polymer monomer. 2+ Their abilities have declined.

[0073] In one embodiment, the mass ratio of the aqueous binder to the inorganic nano-ceramic particles is (10~12):(0.5~1.5).

[0074] In one embodiment, the baking temperature is set at 60°C to 120°C; the baking drying time is 0.5h to 48h; baking can remove moisture and also allow the core-shell structure binder to form a film and solidify, allowing the long chains in the styrene-acrylic emulsion particles to fuse and form a continuous phase, thereby allowing the silica sol to better cover the surface of the styrene-acrylic emulsion particles, and also improving the adhesion between inorganic nano-ceramic particles.

[0075] The technical solution of this application will be illustrated below through specific embodiments and comparative examples.

[0076] Example 1

[0077] A method for preparing a lithium battery composite separator includes:

[0078] S1 is a water-based adhesive containing imidazole groups synthesized by solution polymerization using vinylimidazole and polymer monomers as raw materials. The polymer monomers include acrylamide and tetrahydrofuran acrylate.

[0079] Specifically, add 5g of acrylamide, 3g of tetrahydrofuran acrylate and 0.04g of 2,2-azobisisobutylamidine dihydrochloride (also known as V50) to 40mL of deionized water, and stir until completely dissolved to obtain a polymer monomer solution.

[0080] Take another 50 mL of deionized water, add 2 g of N-vinylimidazolium and 0.04 g of 2,2-azobisisobutylamidine dihydrochloride, purge with nitrogen and stir at 200 rpm for 30 minutes, then heat to 65 °C; after the temperature reaches 65 °C, slowly add the pre-dissolved polymer monomer solution dropwise to the reaction system of this step over 3 hours; after the addition is complete, continue stirring under nitrogen protection for 4 hours to finally obtain a functional binder containing imidazolium groups, labeled as PMI.

[0081] S2, Inorganic nano-ceramic particles are dispersed in a solvent, then an aqueous binder and a wetting agent are added and stirred to obtain a ceramic coating slurry.

[0082] Specifically, 30g of boehmite (AlOOH) was weighed and added to 50mL of deionized water. The mixture was stirred and dispersed at 500 rpm for 1 hour to obtain a uniform dispersion of ceramic particles.

[0083] Subsequently, 2.0 g of water-based binder PMI was added to the ceramic particle dispersion system, and the mixture was stirred for 30 minutes at 40°C and 500 rpm. Then, 0.05 g of wetting agent (Emulgen A-90) was added, and the mixture was stirred for another hour at 40°C and 500 rpm to obtain the ceramic coating slurry.

[0084] S3, a ceramic coating slurry is uniformly coated onto at least one surface on both sides of a polyolefin-based film, and then baked and dried at a set temperature to obtain a film capable of simultaneously adsorbing HF and Mn. 2+ Ceramic composite separator for lithium-ion batteries.

[0085] Specifically, an automated coating machine was used to coat a ceramic slurry onto one surface of a 9-micron-thick polyethylene (PE) base film, which was then dried in a vacuum drying oven at 80°C for 0.5 hours. The thickness of the ceramic coating was controlled to be approximately 2 microns, resulting in a lithium-ion battery coupling ceramic composite separator, named PE@PMI / AlOOH. The scanning electron microscopy and X-ray energy dispersive spectroscopy characterization of the composite separator are as follows: Figure 2 , Figure 3 As shown, Figure 2 This is a schematic diagram of the surface scanning electron microscope (SEM) of the composite membrane in Example 1. Figure 3 This is a schematic diagram of a cross-sectional scanning electron microscope (SEM) image of the composite diaphragm in Example 1. Figure 2 , Figure 3 The data shows that the ceramic particles are evenly distributed and the binder is fully covered, indicating that the composite structure is fully formed.

[0086] Example 2: Modification of Monomer Type in Imidazole-Containing Functional Binder and Preparation and Performance Testing of its Composite Membrane. Based on Example 1, this example optimizes the synthesis formulation of the water-based binder by replacing acrylamide with N,N-dimethylacrylamide (DMAA) to enhance the flexibility and film-forming properties of the resulting polymer skeleton, further improving the mechanical stability and interfacial bonding ability of the membrane. The remaining steps are basically the same as in Example 1.

[0087] The specific operation of step S1 is as follows: In 40 mL of deionized water, add 3 g DMAA, 2 g acrylamide, 3 g tetrahydrofuran acrylate and 0.04 g 2,2-azobisisobutylamidine dihydrochloride (V50), and stir until completely dissolved to obtain a polymer monomer solution for later use; Take another 50 mL of deionized water, add 2 g N-vinylimidazolium and 0.04 g V50, purge with nitrogen gas and stir at 200 rpm for 30 min, raise the temperature to 65 °C, and slowly add the above polymer monomer solution to the reaction system of this step over a period of 3 h. After the addition is complete, continue stirring under nitrogen protection for 4 hours. After the reaction is complete, a functional binder containing imidazole groups is obtained, labeled as PMI-2.

[0088] The obtained PMI-2 was used to prepare a ceramic slurry by compounding with boehmite, and a lithium battery coupling ceramic composite membrane was prepared according to the process of steps S2 and S3 in Example 1, named PE@PMI-2 / AlOOH.

[0089] To verify the effectiveness of this modification scheme, the composite membrane of Example 2 was tested for thermal stability, electrolyte wettability, and HF / Mn ratio. 2+ Adsorption performance test. The results showed that the composite membrane of Example 2 had a thermal shrinkage rate of less than 5% after heat treatment at 150℃ for 30 min, which was comparable to the results of Example 1; the contact angle with the electrolyte was zero degrees, showing good wettability; HF and Mn 2+ The adsorption capacity of both membranes was significantly enhanced compared to the composite membrane in Comparative Example 2, with the residual HF content decreasing by approximately 30% and the Mn content decreasing by approximately 30%. 2+ The removal rate increased by about 20%, indicating that the adjustment of the adhesive structure can still effectively maintain or even enhance its functional performance.

[0090] Furthermore, electrochemical impedance spectroscopy (EIS) tests showed that the ionic conductivity of the composite membrane in Example 2 was comparable to that in Example 1, at 10... -3 S·cm -1 The membrane is suitable for lithium-ion battery systems. The assembled LiMn2O4 / Li half-cell (Li metal as the negative electrode and LiMn2O4 as the positive electrode) retains more than 80% of its capacity after 300 cycles at 1C, indicating that the fabricated separator has good stability and promising practical application prospects.

[0091] This embodiment illustrates that even with changes in the polymer monomer composition, the synthesized waterborne binder containing imidazole groups can still construct a stable network structure after being combined with ceramic particles, and achieve the desired interaction between HF and Mn. 2+ The dual adsorption function demonstrates that the technical solution of this invention has strong universality and controllability.

[0092] Example 3: Preparation of composite membranes using PP-based membranes and verification of their performance

[0093] To verify the applicability of the technical solution of the present invention to different polyolefin-based films, this embodiment uses a polypropylene (PP)-based film instead of the polyethylene (PE)-based film in Example 1 to prepare a film containing HF and Mn. 2+ A ceramic composite membrane with dual adsorption function.

[0094] The specific steps for S3 are as follows:

[0095] A 10-micron thick biaxially oriented polypropylene (PP) film was selected as the substrate. The functional binder PMI was synthesized according to the method described in Example 1, and a ceramic coating slurry (boehmite being inorganic ceramic particles containing PMI and a wetting agent) was prepared. The ceramic slurry was uniformly coated onto one side of the PP film using an automatic coating machine, controlling the ceramic layer thickness to approximately 2 microns. Subsequently, it was dried in a vacuum drying oven at 80°C for 30 minutes to obtain a composite ceramic membrane, named PP@PMI / AlOOH.

[0096] The composite membrane of Example 3 was compared with the composite membrane of Example 1 to evaluate its thermal stability, electrolyte wettability, and the reaction of HF and Mn. 2+ Adsorption capacity.

[0097] The test results show that:

[0098] After heat treatment at 150°C for 30 min, the thermal shrinkage rate of the composite membrane in Example 3 was controlled within about 5%, which was significantly better than that of the untreated PP membrane (thermal shrinkage rate >20%), indicating that the ceramic-binder network structure has a significant enhancing effect on thermal stability.

[0099] The electrolyte contact angle is zero degrees, indicating that the membrane surface has good wettability.

[0100] HF and Mn 2+ The adsorption capacity is basically the same as that of Example 1, and the residual HF content is reduced by more than 30% compared with the comparative example, Mn 2+ The concentration decreased by more than 20%, proving that the imidazole groups in the adhesive still have good functional performance on the PP base film.

[0101] Electrochemical impedance spectroscopy (EIS) measurements showed that its ionic conductivity was 1.2 × 10⁻⁶. -3 S·cm -1 It has good electrolyte permeability.

[0102] The assembled LiMn2O4 / Li half-cell (Li metal as the negative electrode and LiMn2O4 as the positive electrode) retained 83% of its capacity after 300 cycles at a current density of 1 C, indicating that the membrane structure is stable and has excellent performance.

[0103] This embodiment demonstrates that even when the PP base membrane is replaced with one of different polarities and thermal properties, the ceramic composite membrane prepared using the technical solution of this invention can still achieve high thermal stability, electrolyte affinity, and resistance to HF and Mn. 2+ The synergistic adsorption performance further verifies that the network structure constructed by the imidazole functional binder has good substrate adaptability and industrial promotion value.

[0104] Comparative Example 1

[0105] The difference from Example 1 is that the base membrane is made of polyethylene (PE) to prepare a composite membrane, which is labeled as base membrane PE (or PE base membrane).

[0106] Comparative Example 2

[0107] The difference from Example 1 is that the base membrane is made of polyethylene (PE), and step S1 uses only an aqueous binder without imidazole groups of polymer monomers to prepare the composite membrane. The polymer monomers include acrylamide and tetrahydrofuran acrylate, labeled as PE@P(AM-THFA) / AlOOH.

[0108] Performance / Data Testing:

[0109] 1. Comparison of X-ray photoelectron spectroscopy (XPS) spectra;

[0110] The composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 were compared using X-ray photoelectron spectroscopy (XPS) spectra. Figure 4 As shown, Figure 4 This is a schematic diagram comparing the X-ray photoelectron spectroscopy (XPS) spectra of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0111] 2. Comparison of thermal stability;

[0112] The composite diaphragm prepared in Example 1, the composite base membrane prepared in Comparative Example 1, and the composite diaphragm prepared in Comparative Example 2 were subjected to comparative thermal stability tests. The three types of diaphragms were cut into squares of 2×2 cm and baked in ovens at room temperature of 25°C and 150°C for 30 minutes to test the thermal stability of the diaphragms, i.e., to test the thermal shrinkage performance of the diaphragms.

[0113] The results of the thermal stability comparison are as follows Figure 5 As shown, Figure 5 This diagram illustrates a comparison of the thermal stability test results of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2. It shows that the composite membrane of Example 1 exhibits high thermal stability; after heat treatment at 150°C for 30 minutes, the membrane still maintains a thermal shrinkage rate of less than 5%, significantly superior to the composite membrane of Comparative Example 1 and the imidazole-free composite membrane of Comparative Example 2.

[0114] 3. Comparison of electrolyte contact angle and ionic conductivity;

[0115] The composite membrane prepared in Example 1, the composite base membrane prepared in Comparative Example 1, and the composite membrane prepared in Comparative Example 2 were subjected to electrolyte contact angle comparison tests. The electrolyte contact angle of the three membranes was measured to characterize the electrolyte wettability of the membranes. The electrolyte included 1 mol / L lithium hexafluorophosphate (LiPF6) as the lithium salt, and the solvent was a 1:1 volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 were cut into 2×2 cm squares and immersed in the electrolyte for 30 min. After that, the membranes were removed and the electrolyte on the surface was wiped with filter paper. The mass of the membranes before and after immersion in the electrolyte was measured. The mass of the membrane before immersion was W. dry The mass of the diaphragm after soaking is W. wet The absorption rate of the diaphragm electrolyte (i.e., the liquid absorption rate) is obtained using the liquid absorption rate calculation formula: EU = ((W wet -W dry ) / W dry )×100%, the comparison results are as follows Figure 6 As shown.

[0116] Three types of separators were immersed in electrolyte and sandwiched between two stainless steel (SS) electrodes to assemble a blocked battery. Electrochemical impedance spectroscopy was measured using an electrochemical workstation in the frequency range of 100 mHz–100 kHz. The results are compared as follows: Figure 7 As shown. The ionic conductivity (σ) is calculated using the formula σ=d / (R×S), where d is the membrane thickness, R is the membrane internal resistance, S is the effective contact area, and the intersection of the impedance with the x-axis is the membrane internal resistance R. The ionic conductivity of the membrane is then calculated using the formula. For example, the ionic conductivity of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 are 0.35×10⁻⁶, respectively. -3 S·cm -1 0.31×10 -3 S·cm -1 0.34×10 -3 S·cm -1 .

[0117] Figure 6 This is a comparative schematic diagram showing the electrolyte contact angle test results of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2. Figure 7 This is a comparative schematic diagram of the Nyquist impedance diagrams of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 in stainless steel / stainless steel (SS / SS) symmetric cells. Figure 6The composite diaphragm of Example 1 demonstrates good electrolyte wettability and high liquid absorption rate. The porous network structure formed by the ceramic particles and the aqueous binder containing imidazole groups significantly improves the contact angle wettability (contact angle of zero degrees) between the diaphragm and the electrolyte.

[0118] 4. Comparison of HF adsorption capacity

[0119] The composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 were compared in terms of their HF adsorption capacity. The composite membranes from Example 1, Comparative Example 1, and Comparative Example 2 were cut into discs with a diameter of 18 mm, each with a total mass of approximately 20 mg. Each disc was immersed in 2 mL of an aqueous electrolyte containing 1 mol / L lithium hexafluorophosphate (LiPF6) as the lithium salt. The solvent was a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio, with a water content of 500 ppm. The electrolyte was allowed to stand at room temperature for 5 days to generate HF. The resulting electrolyte was quantitatively analyzed for HF using 19F nuclear magnetic resonance (NMR). To avoid HF reaction with glass, the electrolyte was stored in polytetrafluoroethylene (PTFE) tubes and loaded into coaxial NMR tubes. The internal standard was tetrafluorobenzene (C6F6, 1% by mass) dissolved in tetrahydrofuran-d8. By comparing with a standard curve, the HF concentration in the electrolyte is calculated, and the adsorption effect of the membrane on HF is evaluated.

[0120] The results are as follows Figure 8 As shown, Figure 8 This diagram illustrates the comparison of HF content in the electrolytes of the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2. It shows that the higher the HF content in the electrolyte, the weaker the membrane's ability to adsorb HF; conversely, the lower the HF content in the electrolyte, the stronger the membrane's ability to adsorb HF. The diagram shows that the PE@PMI / AlOOH membrane significantly reduced the HF concentration in the electrolyte, indicating that the water-based binder containing imidazole functional groups in the composite membrane of Example 1 can effectively capture HF, thereby inhibiting the generation of free HF.

[0121] 4. Mn 2+ Comparison of adsorption capacity

[0122] The composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to Mn treatment. 2+For comparative tests of adsorption capacity, the composite membranes of Example 1, Comparative Example 1, and Comparative Example 2 were cut into discs with a diameter of 18 mm. Each membrane was weighed to ensure a total mass of approximately 20 mg for each group. 0.0659 g of manganese perchlorate hexahydrate was weighed and dissolved in 20 g of electrolyte. The electrolyte included 1 mol / L lithium hexafluorophosphate (LiPF6) as the lithium salt, and the solvent was a 1:1 volume ratio mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) to prepare a solution containing Mn. 2+ The electrolyte was prepared by placing the diaphragm samples into centrifuge tubes containing 3 mL of the solution and incubating at 25°C for 2 weeks. After incubation, 0.1 g of the supernatant was collected, digested with nitric acid, and then diluted to 50 mL with deionized water. Separately, samples containing Mn that had not been in contact with the diaphragm were also prepared. 2+ The electrolyte was used as a control sample, and Mn was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). 2+ Concentration, calculated by the concentration difference between the sample and the control, for each membrane's Mn content. 2+ Adsorption capacity. Results are as follows: Figure 9 As shown, Figure 9 The composite membranes Mn prepared for Example 1, Comparative Example 1, and Comparative Example 2 2+ A comparative diagram of adsorption capacity; the composite membrane of Example 1 for Mn 2+ The adsorption capacity reached 2.93 mg / g, which is much higher than that of the composite membrane in Comparative Example 1 (0.28 mg / g) and Comparative Example 2 (1.21 mg / g), indicating that the water-based binder containing imidazole functional groups in the composite membrane of Example 1 significantly improved the metal ion complexation ability.

[0123] 5. Comparison of battery performance using composite separator assembly;

[0124] The composite separator prepared in Example 1, the composite base membrane prepared in Comparative Example 1, and the composite separator prepared in Comparative Example 2 were respectively assembled into LiMn2O4 / Li coin cells (Li metal as the negative electrode and LiMn2O4 as the positive electrode) for comparative battery performance testing. First, the CR2032 coin cell was activated by undergoing 5 charge-discharge cycles at a current density of 0.2C. Then, it was subjected to 300 continuous charge-discharge cycles at a current density of 1C to test its cycle stability. The charge-discharge voltage range was set to 3.0~4.3V. The results are as follows: Figure 10 , 11 As shown, after 300 charge-discharge cycles, the capacity retention rate of the composite membrane assembled battery of Example 1 reached 98%, which is significantly better than the composite membrane assembled battery of Comparative Example 1 (39%) and the composite membrane assembled battery of Comparative Example 2 (80%). Figure 10 and Figure 11The diagrams show a comparison of the discharge capacity and coulombic efficiency of Li|separator|LiMn2O4 batteries (Li metal as the negative electrode and LiMn2O4 as the positive electrode, "|" represents the phase interface) prepared using the composite separators of Example 1, Comparative Example 1, and Comparative Example 2, respectively, during 1C current cycling.

[0125] In addition, the CR2032 coin cell was activated for 5 cycles at a current density of 0.2C, followed by 200 charge-discharge cycles at a current density of 0.5C to evaluate the impact of the separator on the long-term stability of the battery. The charge-discharge voltage range was 3.0~4.3V. The results are as follows: Figure 12 , 13 As shown, the composite membrane assembled battery of Example 1 has a capacity retention rate of 82%, which is significantly better than the composite membrane assembled battery of Comparative Example 1 (59%) and the composite membrane assembled battery of Comparative Example 2 (61%). Figure 12 and Figure 13 The diagrams show a comparison of the discharge capacity and coulombic efficiency of Li|separator|LiMn2O4 batteries (Li metal as the negative electrode and LiMn2O4 as the positive electrode, "|" represents the phase interface) prepared using the composite separators of Example 1, Comparative Example 1, and Comparative Example 2, respectively, under a 0.5C current cycle.

[0126] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0127] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0128] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A lithium battery composite separator, characterized by, The composite diaphragm is used for lithium battery, and the composite diaphragm comprises a base film and a ceramic coating layer covering the surface of the base film, the ceramic coating layer is a porous three-dimensional network structure, and the ceramic coating layer comprises an imidazole group-containing aqueous binder, inorganic nano ceramic particles, a wetting agent and a solvent, the imidazole group-containing aqueous binder is used for simultaneously adsorbing HF and Mn 2+ , the imidazole ring in the aqueous binder combines with HF molecules to form a hydrogen bond, or directly accepts a proton, thereby effectively capturing and fixing HF through acid-base interaction; meanwhile, the imidazole ring acts as a chelating ligand to form a stable coordination bond with Mn 2+ , the raw materials of the aqueous binder include vinyl imidazole and a polymer monomer; the polymer monomer includes at least one of acrylamide, N,N-dimethyl acrylamide, tetrahydrofurfuryl acrylate, butyl acrylate, ethyl acrylate, methyl methacrylate and acrylic acid. The imidazole group-containing water-based adhesive is synthesized by using a solution polymerization method with a vinyl imidazole and a polymer monomer as raw materials, and the Mn 2+ of the adsorbent reaches 2.93 mg / g.

2. The lithium battery composite separator of claim 1, wherein, The inorganic nano ceramic particles include at least one of boehmite, alumina, zinc oxide, titanium dioxide, silicon dioxide, and zirconium oxide.

3. The lithium battery composite separator of claim 1, wherein, The base film includes any one or combination of polyethylene, polypropylene, polyethylene-polypropylene composite, polyvinylidene fluoride, polyester, polysulfone, polyethersulfone, and polyimide.

4. The lithium battery composite separator of claim 1, wherein, The solvent includes at least one of water, ethanol, isopropyl alcohol, and N-methyl pyrrolidone. The wetting agent is any one or combination of a non-ionic surfactant, polyvinylpyrrolidone, sodium stearate, and phosphatidylcholine, and the non-ionic surfactant includes a polyoxyethylene ether non-ionic surfactant, a polyethylene oxide non-ionic surfactant, or a polyoxyethylene sorbitan fatty acid ester non-ionic surfactant.

5. The lithium battery composite separator of claim 1, wherein, The thickness of the base film is 5-50 microns. The thickness of the ceramic coating layer is 1-10 microns.

6. A method for preparing a lithium battery composite separator, characterized by, A method for preparing the lithium battery composite separator according to any one of claims 1-5, comprising: An aqueous binder containing imidazole groups is synthesized by using vinyl imidazole and polymer monomers as raw materials and by adopting a solution polymerization method; Inorganic nano ceramic particles are dispersed in a solvent, and then the aqueous binder and the wetting agent are added and stirred to obtain a ceramic coating slurry; The ceramic coating slurry is uniformly coated on at least one surface of both sides of the polyolefin-based base film, and baked and dried at a set temperature to obtain a lithium ion battery ceramic composite separator capable of simultaneously adsorbing HF and Mn 2+ .

7. The method for preparing the lithium battery composite separator as described in claim 6, characterized in that, The stirring temperature is 20-60°C, and the stirring time is 0.5-4 hours. The mass ratio of vinyl imidazole to polymer monomers is (0.5-1.5):(3.5-4.5).

8. The method for preparing the lithium battery composite separator as described in claim 7, characterized in that, The setting temperature of baking is 60-120°C, and the baking drying time is 0.5-48 hours.

9. A lithium battery, characterized by The lithium battery composite separator according to any one of claims 1-5, or the lithium battery composite separator prepared by the method according to any one of claims 6-8.

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