Modified gel electrolyte and preparation method thereof, and lithium battery

Abstract

This application belongs to the field of lithium battery technology, and particularly relates to modified gel electrolytes and their preparation methods, and lithium batteries. The method includes: heating and reacting a first COF monomer, a second COF monomer, a first solvent, and a catalyst, washing, and vacuum drying to obtain COF powder; dissolving lithium salt and polyethylene glycol in acetonitrile, then adding COF powder and modified diatomaceous earth powder and dispersing, heating for mixing reaction to obtain a bottom slurry; dissolving lithium salt and polyethylene glycol in acetonitrile, then adding Al(OH)3-ammonium formate and barium titanate, heating for mixing reaction to obtain an upper slurry; using a two-in-one slit extrusion molding, hot air drying, and then nitrogen segmented drying to obtain a modified gel electrolyte. The bottom slurry forms a COF skeleton gel layer, and the upper slurry forms a high dielectric constant gel barrier layer above the bottom layer; this method increases the specific surface area, improves the lithium ion transport efficiency, and improves the structural strength; it also inhibits lithium dendrite growth and avoids electron tunneling.

Description

Technical Field

[0001] This application belongs to the field of lithium battery technology, and particularly relates to modified gel electrolytes and their preparation methods, and lithium batteries. Background Technology

[0002] Currently, the solid electrolytes used in lithium-ion batteries are inorganic ceramic electrolytes or polymer electrolytes. Inorganic ceramic electrolytes have poor interfacial contact, while polymer electrolytes have low ionic conductivity and insufficient mechanical properties, which cannot meet the requirements of electric vehicles and storage systems.

[0003] Existing solid electrolyte technologies cannot simultaneously achieve low interfacial impedance, high ionic conductivity, and high mechanical strength. They also suffer from high cost, intermittent synthesis, and large sintering shrinkage. Summary of the Invention

[0004] This application provides a modified gel electrolyte and its preparation method, as well as a lithium battery, aiming to solve to some extent the problems of solid electrolytes, which cannot simultaneously possess low interfacial impedance, high ionic conductivity, and high mechanical strength, and are also characterized by high cost, intermittent synthesis, and large sintering shrinkage.

[0005] In a first aspect, this application provides a method for preparing a modified gel electrolyte, comprising: S1, the first COF monomer, the second COF monomer, the first solvent, and the catalyst are heated and reacted at a first preset temperature, washed, and vacuum dried to obtain COF powder, wherein the first COF monomer and the second COF monomer undergo a condensation reaction. S2, dissolve lithium salt and polyethylene glycol in acetonitrile, then add COF powder and modified diatom shell powder and disperse, heat to a preset temperature and stir for a preset time to carry out the mixing reaction, and obtain the bottom slurry; S3, dissolve lithium salt and polyethylene glycol in acetonitrile, then add ammonium Al(OH)3-formate and barium titanate, heat to a preset temperature and stir for a preset time to carry out the mixing reaction, and obtain the upper slurry; S4, the bottom layer slurry and the top layer slurry are extruded into a two-in-one slit extrusion, dried with hot air, and then dried in stages with nitrogen to obtain the modified gel electrolyte; The modified gel electrolyte comprises a two-layer structure: the bottom slurry forms a COF backbone gel layer, and the upper slurry forms a high dielectric constant gel barrier layer above the bottom layer.

[0006] In one embodiment, the preparation steps of the modified diatom shell powder include: Spread the diatomaceous earth powder evenly in the sample boat with a thickness of ≤2mm, and evacuate to a vacuum degree of ≤1Pa; Inert gas or nitrogen is introduced and purged for 8 to 12 minutes at a volumetric flow rate of 80 to 120 sccm. The vacuum is adjusted to 5 Pa. A mixture of oxygen and inert gas is introduced at a total volumetric flow rate of 45 to 55 sccm. The sample boat is heated to 100°C and rotated at 20 rpm for 10 to 20 minutes. After cooling, it is quickly transferred to a tube furnace, hydrogen is introduced, and the temperature is increased to 280°C to 320°C at a rate of 3°C. The temperature is held for 1.5 to 2.5 hours to obtain modified diatomaceous earth powder.

[0007] In one embodiment, the first COF monomer is p-phenylenediamine, the second COF monomer is trialdehyde-resorcinol, the first solvent is a solvent mixture of mesitylene and dioxane, and the catalyst is acetic acid.

[0008] In one embodiment, the lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate.

[0009] In one embodiment, the ratio of the first COF monomer, the second COF monomer, the first solvent, and the catalyst in step S1 is 0.5 mmol:0.33 mmol:10 mL:1.2 mmol; the first preset temperature is 110°C to 130°C, and the heating reaction time is 20 h to 30 h.

[0010] In one embodiment, the mass ratio of lithium salt, polyethylene glycol (PEG), acetonitrile, COF powder, and modified diatomaceous earth powder in step S2 is 15%:35%:35%:10%:5%; In step S3, the mass ratio of lithium salt, polyethylene glycol, acetonitrile, ammonium Al(OH)3-formate, and barium titanate is 15%:37%:30%:3%:15%.

[0011] In one embodiment, the second preset temperature is 60°C to 80°C, and the preset duration is 1 hour to 3 hours.

[0012] In one embodiment, the height of the first slit corresponding to the bottom layer in the two-in-one slit is 150 micrometers, and the height of the second slit corresponding to the bottom layer is 20 micrometers.

[0013] In one embodiment, the extrusion belt speed is 0.2 m / min.

[0014] In one embodiment, the hot air drying temperature is 75°C to 85°C, and the hot air drying time is 10 minutes to 15 minutes.

[0015] In one embodiment, nitrogen drying is performed in stages: first, drying at 100°C for 20 minutes, then heating to 130°C for 30 minutes, and then heating to 160°C for 1 to 1.5 hours.

[0016] Secondly, this application provides a modified gel electrolyte, which is prepared using the method for preparing a modified gel electrolyte as described in any one of the first aspects.

[0017] Thirdly, this application provides a lithium battery in which the electrolyte is a modified gel electrolyte obtained by modifying the gel electrolyte as described in any one of the first aspects, or a modified gel electrolyte as described in the second aspect.

[0018] 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.

[0019] The advantages of this application compared to the prior art are: The method for preparing the modified gel electrolyte provided in this application includes the following steps: S1, heating and reacting a first COF monomer, a second COF monomer, a first solvent, and a catalyst at a first preset temperature, washing, and vacuum drying to obtain COF powder, wherein the first COF monomer and the second COF monomer undergo a condensation reaction; S2, dissolving lithium salt and polyethylene glycol in acetonitrile, then adding COF powder and modified diatomaceous earth powder and dispersing, heating to a preset temperature and stirring for a preset time to mix and react, obtaining a bottom slurry; S3, dissolving lithium salt and polyethylene glycol in acetonitrile, then adding Al(OH)3-ammonium formate and barium titanate, and heating... The mixture is stirred at a preset temperature for a preset time to obtain an upper slurry; S4, the bottom and upper slurries are shaped by two-in-one slit extrusion, dried with hot air, and then dried in stages with nitrogen to obtain a modified gel electrolyte; the modified gel electrolyte includes a two-layer structure, with the bottom slurry forming a COF backbone gel layer and the upper slurry forming a high dielectric constant gel barrier layer above the bottom layer; compared with the prior art, the first and second COF monomers in the COF backbone gel layer undergo a condensation reaction to form a β-ketoenamine-linked COF backbone network, providing a porous framework, increasing the specific surface area, and improving lithium ion transfer. Efficiency is improved by polyethylene glycol (PEG) filling the pores, which enhances ionic conductivity. Lithium salt dissociation provides charge carriers, while modified diatomaceous earth powder provides micron-sized reservoir pores and improves structural strength. In the high-dielectric-constant gel barrier layer, barium titanate and Al(OH)3 act as fillers, increasing the dielectric constant (ε is approximately 15-25). Ammonium formate decomposes to generate gas, forming micropores and regulating pH, collectively creating a high-dielectric-constant environment that homogenizes the electric field, inhibits lithium dendrite growth, and prevents electron tunneling. The COF framework gel layer and the high-dielectric-constant gel barrier layer work synergistically, with continuous interfacial miscibility, reducing the risk of delamination. This process improves the electrochemical window (greater than 4.7V). The ordered pores of the bottom COF framework gel layer, in synergy with polyethylene glycol, promote rapid lithium-ion transport and improve ion conductivity. The COF network and diatom shell framework enhance mechanical strength, while polyethylene glycol provides flexibility, forming a self-supporting gel film that further improves mechanical stability. The upper high-dielectric-constant gel barrier layer improves the uniformity of the interfacial electric field, reduces local charge accumulation, delays dendrite formation, enhances interfacial stability, provides a safety barrier, and enables functional gradient design. The layered two-in-one co-extrusion molding process is suitable for continuous production. Attached Figure Description

[0020] 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.

[0021] Figure 1 This is a schematic flowchart of a method for preparing a modified gel electrolyte according to an embodiment of this application; Figure 2 This is an electron microscope schematic diagram of the modified gel electrolyte of Example 1 of this application. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The terms "first" and "second" are used for descriptive purposes only, 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 embodiments 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, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0026] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0027] 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 embodiments of this application.

[0028] The weights of the relevant components mentioned in this application specification 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 this application specification is within the scope of disclosure in this application specification. Specifically, the mass mentioned in this application specification can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0029] 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.

[0030] 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.

[0031] Existing solid electrolyte technologies cannot simultaneously achieve low interfacial impedance, high ionic conductivity, and high mechanical strength. They also suffer from high cost, intermittent synthesis, and large sintering shrinkage.

[0032] To address the aforementioned problems to some extent, firstly, such as Figure 1 As shown, this application provides a method for preparing modified gel electrolytes, including: S1, the first COF monomer, the second COF monomer, the first solvent, and the catalyst are heated and reacted at a first preset temperature, washed, and vacuum dried to obtain COF powder, wherein the first COF monomer and the second COF monomer undergo a condensation reaction. S2, dissolve lithium salt and polyethylene glycol in acetonitrile, then add COF powder and modified diatom shell powder and disperse, heat to a preset temperature and stir for a preset time to carry out the mixing reaction, and obtain the bottom slurry; S3, dissolve lithium salt and polyethylene glycol in acetonitrile, then add ammonium Al(OH)3-formate and barium titanate, heat to a preset temperature and stir for a preset time to carry out the mixing reaction, and obtain the upper slurry; S4, the bottom layer slurry and the top layer slurry are extruded into a two-in-one slit extrusion, dried with hot air, and then dried in stages with nitrogen to obtain the modified gel electrolyte; The modified gel electrolyte comprises a two-layer structure: the bottom slurry forms a COF backbone gel layer, and the upper slurry forms a high dielectric constant gel barrier layer above the bottom layer.

[0033] In this embodiment, the condensation reaction of the first and second COF monomers forms a β-keto-enamine linked COF (covalent organic framework) backbone network, providing a porous framework and improving lithium-ion transport efficiency. The keto-enol tautomerism provides hydrogen bonding sites, enhancing the interfacial bonding with polyethylene glycol (PEG). PEG fills the pores, improving ionic conductivity and providing the flexibility required for the gel state, preventing brittleness. Lithium ions after lithium salt dissociation provide charge carriers. The first solvent provides a suitable polar environment, promoting the forward shift of the imine condensation reaction equilibrium, thereby obtaining a highly crystalline COF. The catalyst catalyzes the formation of imine bonds under weakly acidic conditions, increasing the reaction rate. COF powder can form a through-type nanoscale ion transport network, which improves lithium-ion conductivity. The micron-sized pores of modified diatom shell powder can act as ion buffers, increasing the electrolyte retention capacity. The surface functional groups of diatom shell powder can chemically bond with polyethylene glycol (PEG), improving structural stability. The irregular morphology of diatom shell powder pins polymer chains, inhibiting PEG crystallization and improving the low-temperature performance of the electrolyte.Barium titanate possesses a high dielectric constant (>1000), which improves the uniformity of the interfacial electric field, reduces local current density, and inhibits lithium dendrite growth. Simultaneously, the nanoparticles (D50 of 50 nm) exhibit good dispersion and do not increase film thickness. In Al(OH)3-ammonium formate, the thermal decomposition of ammonium formate produces NH3 and CO2, forming uniform micropores (approximately 0.5 μm to 2 μm), reducing the ion transport impedance of the upper layer. The alkaline NH3 neutralizes trace amounts of acid in the system, regulating pH and protecting lithium salt and PEG. Al(OH)3, with a dielectric constant of 8-10, synergistically enhances dielectric properties with barium titanate. Furthermore, partial dehydration to AlO(OH) further improves dielectric and mechanical strength. Al(OH)3 and barium titanate, acting as fillers, enhance the dielectric constant, jointly forming a high-dielectric environment, creating a uniform electric field, inhibiting lithium dendrite growth, and preventing electron tunneling. A two-in-one slit extrusion process creates two layers of modified gel electrolyte, corresponding to the underlying COF framework. The adhesive layer and the upper high-dielectric-constant gel barrier layer are extruded simultaneously. Component interdiffusion at the interface creates a gradient transition, avoiding delamination. Hot air drying and nitrogen-stage drying remove acetonitrile solvent and improve COF crystallinity. The COF framework gel layer and the high-dielectric-constant gel barrier layer work synergistically. The ordered pores of the bottom COF framework gel layer, in conjunction with polyethylene glycol, promote rapid lithium-ion transport, increasing ionic conductivity. The COF network enhances mechanical strength, while polyethylene glycol provides flexibility, forming a self-supporting gel film and thus improving mechanical stability. The uniform electric field of the upper high-dielectric-constant gel barrier layer reduces local charge accumulation, delays dendrite formation, and enhances interface stability. The polyethylene glycol gel improves contact with the electrode interface, reduces interfacial impedance, and achieves functional gradient design. The layered, two-in-one co-extrusion molding process eliminates the need for two drying and two coating steps, making it suitable for continuous production and improving efficiency.

[0034] In one embodiment, the preparation steps of modified diatom shell powder include: uniformly spreading diatom shell powder in a sample boat with a thickness ≤2mm, and evacuating to a vacuum degree ≤1Pa; introducing inert gas or nitrogen and purging for 8 to 12 minutes at a volume flow rate of 80sccm to 120sccm, adjusting the vacuum degree to 5Pa, introducing a mixture of oxygen and inert gas with a total volume flow rate of 45sccm to 55sccm, heating the sample boat to 100°C, rotating it at a speed of 20rpm for 10 to 20 minutes, cooling it, and then quickly transferring it to a tube furnace, introducing hydrogen, and heating it to 280°C to 320°C at a heating rate of 3°C, and holding it at that temperature for 1.5 to 2.5 hours to obtain modified diatom shell powder.

[0035] In this embodiment, the thin layer allows for uniform processing in the atmosphere, while the high vacuum removes moisture and air adsorbed within the pores of the diatomaceous earth powder, preventing high-temperature oxidation. Purging replaces residual air, establishing a stable low-pressure environment of 5 Pa, providing a controllable environment for mixed gas processing. Heating and rotating the mixed gas at low temperatures introduces oxygen-containing functional groups such as hydroxyl and carbonyl groups, enhancing hydrogen bonding with polyethylene glycol (PEG / COF). Rotation also prevents powder agglomeration, achieving uniform surface activation without damaging the natural porous structure of the diatomaceous earth. After transfer, hydrogen sintering removes hydroxyl groups from the diatomaceous earth surface, forming a siloxane network, improving hydrophobicity and chemical stability. It also eliminates residual organic matter, preventing carbonized impurities, and reduces surface dangling bonds, generating electronic defect sites and improving dielectric response. Because the temperature is far below the SiO2 phase transition point, the micron-sized pores are completely preserved.

[0036] In one embodiment, the first COF monomer is p-phenylenediamine, and the second COF monomer is trialdehyde phloroglucinol; p-phenylenediamine and trialdehyde phloroglucinol generate a β-ketoenamine-linked COF network through an imine condensation reaction; the first solvent is a solvent mixture of mesitylene and dioxane, and the catalyst is an aqueous solution of acetic acid, with a volume ratio of mesitylene to dioxane of 1:1. The weak acidity of acetic acid allows the catalytic reaction to proceed gently, avoiding the use of strong acids that could damage the monomer structure.

[0037] In one embodiment, the lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium hexafluorophosphate, and the lithium salt is used to provide lithium ions, thereby improving ionic conductivity.

[0038] In one embodiment, the ratio of the first COF monomer, the second COF monomer, the first solvent, and the catalyst in step S1 is 0.5 mmol: 0.33 mmol: 10 mL: 1.2 mmol; the first preset temperature is 110℃~130℃, and the heating reaction time is 20h~30h, which is used to increase the system temperature of the condensation reaction, accelerate the reaction, promote the growth of COF grains, improve the formation of ordered COF in the framework layer, and thus increase the specific surface area of ​​the COF framework.

[0039] In one embodiment, the mass ratio of lithium salt, polyethylene glycol, acetonitrile, COF powder, and modified diatomaceous earth powder in step S2 is 15%:35%:35%:10%:5%; the mass ratio in this embodiment makes the conductive network more continuous.

[0040] In one embodiment, the mass ratio of lithium salt, polyethylene glycol, acetonitrile, ammonium Al(OH)3-formate, and barium titanate in step S3 is 15%:37%:30%:3%:15%. The mass ratio in this embodiment ensures chain movement capability, is suitable for coating, and also takes into account dielectric properties and film-forming properties.

[0041] In one embodiment, the second preset temperature is 60℃~80℃ and the preset duration is 1h~3h. In this embodiment, the stirring at the second preset temperature and the preset duration in step S2 can promote the movement of PEG chain segments, fully wet the filler surface, accelerate the formation of hydrogen bonds, make the slurry uniform and stable, and also shorten the stirring time to avoid damage to the COF structure. In step S3, aluminum hydroxide and barium titanate can be uniformly dispersed, while ammonium formate is partially dissolved and the microenvironment pH is adjusted to prevent hydrolysis of the barium titanate surface.

[0042] In one embodiment, the height of the first slit corresponding to the COF framework gel layer in the two-in-one slit is 150 micrometers, and the height of the second slit corresponding to the high dielectric constant gel barrier layer is 20 micrometers. The first slit height is equal to the thickness of the COF framework gel layer, and the second slit height is equal to the thickness of the high dielectric constant gel barrier layer. The thickness of the COF framework gel layer is greater than that of the high dielectric constant gel barrier layer, thus providing structural support, sufficient mechanical strength, and more ion conduction paths. It also acts as a buffer layer during electrode volume changes during charging and discharging, and the dense / microporous structure can prevent dendrite penetration. The thin layer thickness of the high dielectric constant gel barrier layer reduces ion transport distance and lowers polarization resistance. It should be noted that the error range of the first slit height is 10 micrometers, i.e., the first slit height is 140 micrometers to 160 micrometers, and the COF framework gel layer after drying is approximately 60 micrometers to 70 micrometers. The error range of the second slit height is 2 micrometers, i.e., the second slit height is 18 micrometers to 22 micrometers, and the high dielectric constant gel barrier layer after drying is approximately 8 micrometers to 10 micrometers.

[0043] In one embodiment, the extrusion belt speed is 0.2 m / min to ensure extrusion stability and avoid thickness fluctuations.

[0044] In one embodiment, the hot air drying temperature is 75°C to 85°C, and the hot air drying time is 10 minutes to 15 minutes. The temperature in this embodiment allows polyethylene glycol to melt and penetrate into the COF backbone to form an interpenetrating network, removes acetonitrile solvent, and also avoids the decomposition of ammonium formate.

[0045] In one embodiment, nitrogen-stage drying is performed as follows: first, drying at 100°C for 20 minutes, then increasing the temperature to 130°C for 30 minutes, and then increasing the temperature to 160°C for 1-1.5 hours. The first step removes residual acetonitrile, softens the polyethylene glycol (PEG) segments, and allows the two layers to diffuse into each other, improving the interfacial bonding strength and anchoring barium titanate and aluminum hydroxide. The third step completely decomposes ammonium formate, forming interconnected micropores in the upper COF backbone gel layer, reducing ion impedance and preventing blockage. At the same time, partial dehydration of aluminum hydroxide improves the dielectric constant and mechanical strength. The nitrogen-stage drying and hot air drying form a two-stage drying process, which improves the crystallinity of COF, makes the ion channels more ordered, improves the ion conductivity, and forms a dense barrier layer and a stable COF backbone layer.

[0046] The technical solution of this application will be illustrated below through specific embodiments and comparative examples.

[0047] Preparation Example 1 The preparation steps of modified diatom shell powder include: uniformly spreading diatom shell powder in a sample boat with a thickness of 2 mm, and evacuating to a vacuum degree of 1 Pa; introducing inert gas or nitrogen and purging with a volume flow rate of 80 sccm~120 sccm for 8 to 12 minutes, adjusting the vacuum degree to 5 Pa, introducing a mixed gas of oxygen and inert gas with a total volume flow rate of 45 sccm~55 sccm, heating the sample boat to 100℃, rotating it at a speed of 20 rpm for 10 to 20 minutes, cooling it, and then quickly transferring it to a tube furnace, introducing hydrogen, and heating it to 280℃~320℃ at a heating rate of 3℃, and holding it at that temperature for 1.5 to 2.5 hours to obtain modified diatom shell powder.

[0048] Example 1 The preparation method of modified gel electrolyte includes: S1, add 0.5 mmol of p-phenylenediamine, 0.33 mmol of trialdehyde resorcinol, 10 mL of a solvent mixture of mesitylene and dioxane (volume ratio 1:1), and 1.2 mmol of acetic acid, and heat to the first preset temperature of 120°C for 24 h to carry out the condensation reaction.

[0049] S2, 2.87g LiTFSI lithium salt and 6.685g polyethylene glycol are dissolved in 6.685g acetonitrile, then 1.91g COF powder and 0.955g modified diatom shell powder are added and ultrasonically dispersed. The mixture is heated to a second preset temperature of 70℃ and stirred for a preset time of 2h to carry out the mixing reaction, and the bottom slurry is obtained.

[0050] S3, dissolve 2.87g LiTFSI lithium salt and 7.1g polyethylene glycol in 5.73g acetonitrile, then add 0.573g Al(OH)3-ammonium formate and 2.87g barium titanate, heat to the second preset temperature of 70℃ and stir for a preset time of 2h to carry out the mixing reaction, and obtain the upper slurry.

[0051] S4. Using a two-in-one slit extruder, the bottom and top slurries are extruded into a molded solution. The height of the dual-cavity slit head is adjusted, with the upper slit height being 20 micrometers and the lower slit height being 150 micrometers. The conveyor speed is 0.2 m / min. The solution is then extruded and molded, and dried in a hot air drying oven at 80°C for 10 min. Then, it is dried in stages under nitrogen, first at 100°C for 20 min, then at 130°C for 30 min, and finally at 160°C for 1 h to 1.5 h to obtain the modified gel electrolyte. The modified gel electrolyte consists of two layers: the bottom slurry forms a COF backbone gel layer, and the top slurry forms a high dielectric constant gel barrier layer above the bottom layer. Figure 2 This is an electron microscope schematic diagram of the modified gel electrolyte of Example 1.

[0052] Example 2: The difference from Example 1 is that the lithium salt is replaced with lithium bis(fluorosulfonyl)imide (LiFSI).

[0053] Example 3: The difference from Example 1 is that the lithium salt is replaced with lithium hexafluorophosphate (LiPF6).

[0054] The difference between Comparative Example 1 and Example 1 is that the stirring time in S2 and S3 is preset to 30 minutes.

[0055] Comparative Example 2 differs from Example 1 in that the belt speed in S4 is 0.5 m / min.

[0056] Comparative Example 3 differs from Example 1 in that, in S4, the hot air drying oven was used to dry the product at 100°C for 5 minutes.

[0057] Comparative Example 4 differs from Example 2 in that the stirring time in S2 and S3 is preset to 30 minutes.

[0058] Comparative Example 5 differs from Example 2 in that the belt speed in S4 is 0.5 m / min.

[0059] Comparative Example 6 differs from Example 2 in that, in S4, the hot air drying oven was used to dry the product at 100°C for 5 minutes.

[0060] The difference between Comparative Example 7 and Example 3 is that the stirring time in S2 and S3 is preset to 30 minutes.

[0061] Comparative Example 8 differs from Example 3 in that the belt speed in S4 is 0.5 m / min.

[0062] Comparative Example 9 differs from Example 3 in that, in S4, the hot air drying oven was used to dry the product at 100°C for 5 minutes.

[0063] Comparative Example 10 differs from Example 1 in that nitrogen in S4 is dried at 200°C for 30 minutes without segmentation.

[0064] Comparative Example 11 differs from Example 1 in that the hot air drying oven in S4 dries the product at 60°C.

[0065] Comparative Example 12 differs from Example 1 in that nitrogen in S4 is dried at 100°C for 30 minutes without segmentation.

[0066] Comparative Example 13 differs from Example 1 in that modified diatomaceous earth powder is not used in S2.

[0067] Comparative Example 14 differs from Example 1 in that it does not have S3, and instead uses a single-slit method to extrude the bottom slurry in S4.

[0068] Performance / Data Testing: Using NCM811 as the positive electrode, lithium metal as the negative electrode, and the modified gel electrolyte prepared in each example and comparative example as the electrolyte, the batteries were assembled into CR2032 coin cells in an argon-protected glove box. The batteries were tested on a Land tester, and the test data are shown in Table 1.

[0069] Table 1. Coulombic efficiency and capacity retention of the batteries in each embodiment and comparative example.

[0070] Because Comparative Examples 1, 4, and 7 shortened the preset stirring time in steps S2 and S3, the bottom and top slurries were not stirred evenly, failing to fully wet the filler surface, reducing the hydrogen bond formation rate, and causing a decrease in the performance of the bilayer structure, thereby reducing coulombic efficiency and capacity retention. Comparative Examples 2, 5, and 8 increased the extrusion belt speed, which could not guarantee extrusion stability, increased thickness fluctuations, and reduced the thickness of the bottom COF skeleton gel layer and the top high-dielectric-constant gel barrier layer, thus reducing the performance of the bilayer structure. Comparative Examples 3, 6, and 9 increased the hot air drying temperature and reduced the hot air drying time. 100℃ exceeded the boiling point of acetonitrile (82℃) by too much, causing rapid evaporation and generating bubbles in the bilayer structure. Simultaneously, too much time prevented the polyethylene glycol from melting completely. The penetration of COF backbone affected the performance of the bilayer structure. Comparative Example 11 reduced the hot air drying temperature to 60℃, which is below the boiling point of acetonitrile (82℃), and thus could not remove the acetonitrile solvent, affecting the performance of the bilayer structure. Comparative Example 10 used nitrogen atmosphere for unsegmented drying at 200℃ for 30 min, which caused polyethylene glycol degradation and weight loss. At the same time, the temperature was too high, exceeding the decomposition temperature of ammonium formate (about 160℃) by a large margin. The excessively rapid decomposition of ammonium formate caused violent gas release, leading to membrane defects and thus reducing the performance of the bilayer structure. Comparative Example 12 used nitrogen atmosphere for unsegmented drying at 100℃ for 30 min. The temperature was too low to reach the decomposition temperature of ammonium formate and could not soften the polyethylene glycol PEG segments, reducing the interfacial bonding strength and thus reducing the performance of the bilayer structure.

[0071] Comparative Example 13, lacking modified diatomaceous earth powder, failed to increase electrolyte retention, nor chemically bond with polyethylene glycol (PEG), thus reducing structural stability. It also failed to inhibit PEG crystallization and improve low-temperature electrolyte performance, consequently lowering coulombic efficiency and capacity retention. Comparative Example 14, omitting S3, employed single-slit extrusion molding in S4. This resulted in the absence of a high-dielectric-constant gel barrier layer, hindering bilayer synergy, electric field homogenization, reduction of localized charge accumulation, and dendrite formation delay. Consequently, it reduced interfacial stability, increased interfacial impedance, and further decreased coulombic efficiency and capacity retention.

[0072] Therefore, the coulombic efficiency and capacity retention of each embodiment are superior to those of the respective comparative embodiments.

[0073] 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.

[0074] 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 mentioned above, and will not be repeated here.

[0075] 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.

[0076] 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 method for preparing modified gel electrolytes, characterized in that, include: S1, the first COF monomer, the second COF monomer, the first solvent, and the catalyst are heated and reacted at a first preset temperature, washed, and vacuum dried to obtain COF powder, wherein the first COF monomer and the second COF monomer undergo a condensation reaction. S2, dissolve lithium salt and polyethylene glycol in acetonitrile, then add COF powder and modified diatom shell powder and disperse, heat to the second preset temperature and stir for a preset time to carry out the mixing reaction, and obtain the bottom slurry; S3, dissolve lithium salt and polyethylene glycol in acetonitrile, then add ammonium Al(OH)3-formate and barium titanate, heat to the second preset temperature and stir for a preset time to carry out the mixing reaction, and obtain the upper slurry; S4, the bottom slurry and the top slurry are extruded into a two-in-one slit extrusion, dried with hot air, and then dried in stages with nitrogen to obtain the modified gel electrolyte; The modified gel electrolyte comprises a two-layer structure: the bottom slurry forms a COF backbone gel layer, and the upper slurry forms a high dielectric constant gel barrier layer above the bottom layer. The first COF monomer is p-phenylenediamine, the second COF monomer is trialdehyde-resorcinol, the first solvent is a solvent mixture of mesitylene and dioxane, and the catalyst is acetic acid.

2. The method for preparing the modified gel electrolyte as described in claim 1, characterized in that, The preparation steps of modified diatom shell powder include: Spread the diatomaceous earth powder evenly in the sample boat with a thickness of ≤2mm, and evacuate to a vacuum degree of ≤1Pa; Inert gas or nitrogen is introduced and purged for 8 to 12 minutes at a volumetric flow rate of 80 to 120 sccm. The vacuum is adjusted to 5 Pa. A mixture of oxygen and inert gas is introduced at a total volumetric flow rate of 45 to 55 sccm. The sample boat is heated to 100°C and rotated at 20 rpm for 10 to 20 minutes. After cooling, it is quickly transferred to a tube furnace, hydrogen is introduced, and the temperature is increased to 280°C to 320°C at a rate of 3°C. The temperature is held for 1.5 to 2.5 hours to obtain modified diatomaceous earth powder.

3. The method for preparing the modified gel electrolyte as described in claim 1, characterized in that, The lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate.

4. The method for preparing the modified gel electrolyte as described in claim 1, characterized in that, In step S1, the ratio of the first COF monomer, the second COF monomer, the first solvent, and the catalyst is 0.5 mmol:0.33 mmol:10 mL:1.2 mmol; the first preset temperature is 110℃~130℃, and the heating reaction time is 20h~30h.

5. The method for preparing the modified gel electrolyte as described in claim 1, characterized in that, In step S2, the mass ratio of lithium salt, polyethylene glycol, acetonitrile, COF powder, and modified diatomaceous earth powder is 15%:35%:35%:10%:5%. In step S3, the mass ratio of lithium salt, polyethylene glycol, acetonitrile, ammonium Al(OH)3-formate, and barium titanate is 15%:37%:30%:3%:15%. The second preset temperature is 60℃~80℃, and the preset duration is 1h~3h.

6. The method for preparing the modified gel electrolyte as described in claim 1, characterized in that, The height of the first slit corresponding to the COF skeleton gel layer in the two-in-one slit is 150 micrometers, and the height of the second slit corresponding to the high dielectric constant gel barrier layer is 20 micrometers; the extrusion molding conveyor speed is 0.2 m / min.

7. The method for preparing the modified gel electrolyte as described in claim 1, characterized in that, The temperature for hot air drying is 75℃~85℃, and the drying time is 10 minutes~15 minutes.

8. The method for preparing the modified gel electrolyte as described in claim 1, characterized in that, Nitrogen drying in stages is as follows: first, dry at 100℃ for 20 minutes, then raise the temperature to 130℃ for 30 minutes, and then raise the temperature to 160℃ for 1 to 1.5 hours.

9. A modified gel electrolyte, characterized in that, It is prepared by the method described in any one of claims 1 to 8 for the preparation of modified gel electrolyte.

10. A lithium battery, characterized in that, The electrolyte of the lithium battery is a modified gel electrolyte obtained by the preparation method of the modified gel electrolyte as described in any one of claims 1 to 8, or a modified gel electrolyte as described in claim 9.

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