An ionic liquid-modified boehmite, its preparation method, and its applications

Abstract

This invention belongs to the field of inorganic non-metallic materials technology, and discloses an ionic liquid-modified boehmite, its preparation method, and its application. The method includes: ultrasonically dispersing dried boehmite powder in anhydrous ethanol, adding a silane coupling agent and reflux reaction, followed by centrifugation, washing, and drying to obtain silane coupling agent-modified boehmite; then dispersing it in deionized water, adding a chitosan-based polyionic liquid, stirring and mixing, followed by high-speed centrifugation and drying to obtain the final product. The chitosan-based polyionic liquid is prepared by dissolving chitosan and betaine hydrochloride in water at room temperature. This invention also involves coating the modified boehmite with a binder onto the surface of a polyolefin-based membrane to obtain a coated separator. The resulting modified boehmite exhibits excellent interfacial compatibility, a strong coating bond, and can effectively control the uniform deposition of lithium ions, improve ionic conductivity and thermal stability, while reducing equipment wear and raw material costs, making it suitable for high-performance lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic materials technology, specifically relating to an ionic liquid-modified boehmite, its preparation method, and its application. Background Technology

[0002] As a core energy storage device in the new energy field, the safety performance, cycle stability, and interface compatibility of lithium-ion batteries are key factors restricting their high-performance and industrial application. The separator, as one of the core components of lithium-ion batteries, plays a crucial role in isolating the positive and negative electrodes, preventing short circuits, and allowing free lithium-ion transport. Its performance directly determines the battery's charge-discharge efficiency, cycle life, and safety threshold. Coated polyolefin separators, by coating functional materials onto the surface of polyolefin-based films such as polypropylene (PP), can effectively improve electrode interface contact, enhance cell flatness, and strengthen the separator's liquid retention capacity and thermal stability, becoming the mainstream development and upgrading direction for lithium-ion battery separators.

[0003] Among existing coated diaphragms, alumina-coated diaphragms have achieved industrial application. However, these diaphragms have significant technical and cost drawbacks: alumina has a high Mohs hardness, which easily causes severe wear on coating equipment during the coating process, increasing maintenance costs and wear rates; at the same time, the raw material cost of high-purity alumina is high, significantly increasing the overall manufacturing cost of the diaphragm and hindering cost reduction through large-scale production. Therefore, developing inorganic coating particles with lower hardness, lower cost, and comparable performance has become a core research direction for replacing alumina and optimizing the performance of coated diaphragms.

[0004] Boehmite (γ-AlOOH), as a precursor to alumina, possesses a low hardness of 3-3.5 on the Mohs scale, effectively preventing equipment wear during coating. Furthermore, its raw material cost is significantly lower than that of high-purity alumina. It can also effectively absorb hydrofluoric acid (HF) produced by electrolyte decomposition in lithium-ion batteries, mitigating the negative impact of electrolyte degradation on battery performance. Therefore, it is a highly promising inorganic particle for coating polyolefin separators. However, direct coating with pure boehmite suffers from poor interfacial compatibility. The hydroxyl content on the boehmite surface weakens its interfacial bonding with the polyolefin-based film and electrolyte, leading to coating peeling and insufficient electrolyte retention. Moreover, pure boehmite coating cannot effectively control lithium-ion transport and deposition, hindering further improvements in battery ionic conductivity and cycle stability. Therefore, surface modification of boehmite is urgently needed to enhance its interfacial performance and functional properties.

[0005] Ionic liquids, due to their wide electrochemical window, high ionic conductivity, and excellent thermal stability, are widely used in battery interface control. Among them, chitosan-based poly(aprotic-proton) ionic liquids, with their multiple anions (carboxylates, chlorides) and cations (protonated amines, quaternary ammonium salts) in their molecular structure, can efficiently control the solvation structure of the electrolyte through synergistic effects, guiding uniform lithium-ion deposition and significantly improving the stability of the battery interface. However, the technology for modifying chitosan-based polyionic liquids by combining them with boehmite is not yet mature. The lack of efficient and controllable boehmite surface modification methods prevents the stable composite formation of ionic liquids and boehmite, hindering the full realization of their synergistic advantages and limiting their application in battery coatings and separators.

[0006] In summary, the existing technology lacks a modification method that can achieve stable composite of boehmite and chitosan-based polyionic liquid, and a high-performance coated separator based on this modified boehmite has not yet been developed. Therefore, developing a simple and controllable method for preparing ionic liquid-modified boehmite and applying it to polyolefin separator coating to prepare a battery coated separator with low preparation cost, excellent interfacial compatibility, high ionic conductivity, and good safety performance has become an urgent need to solve the current bottleneck of lithium-ion battery separator technology. Summary of the Invention

[0007] To address the problems mentioned in the background art, this invention proposes an ionic liquid-modified boehmite, its preparation method, and its application. The method involves surface modification of boehmite using a silane coupling agent to introduce active functional groups, followed by stable grafting of a chitosan-based polyionic liquid onto the boehmite surface via hydrogen bonding and electrostatic interactions, forming a composite modified layer with synergistic effects of multiple anions and cations. This modified boehmite exhibits good interfacial compatibility with polyolefin-based membranes and electrolytes, strong coating adhesion, and is not easily detached, thus improving the structural stability and liquid retention capacity of the membrane.

[0008] The technical solution adopted by this invention to solve its technical problem is: to provide a method for preparing ionic liquid modified boehmite, comprising the following steps:

[0009] S1. Dry the boehmite powder, then disperse it in anhydrous ethanol and sonicate it to obtain a boehmite dispersion.

[0010] S2. According to the mass of the boehmite powder, add silane coupling agent to the boehmite dispersion and carry out reflux reaction. After the reaction is completed, centrifuge, wash and vacuum dry to obtain silane coupling agent modified boehmite.

[0011] S3. Disperse the modified boehmite obtained in step S2 in deionized water, add chitosan-based polyionic liquid, stir and mix, then perform high-speed centrifugation, and dry the resulting solid product to obtain the ionic liquid modified boehmite.

[0012] Further, in step S1, the particle size of the boehmite powder is 300 nm to 1000 nm.

[0013] Furthermore, in step S1, the drying temperature is between 50°C and 120°C.

[0014] Further, in step S2, the silane coupling agent includes one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or γ-methacryloyloxypropyltrimethoxysilane.

[0015] Further, in step S2, the mass ratio of the boehmite powder to the silane coupling agent is 1:8 to 1:10.

[0016] Furthermore, in step S2, the reflux reaction temperature is 45°C to 60°C, and the reaction time is 6 hours.

[0017] Further, in step S3, the chitosan-based polyionic liquid is prepared by a method including the following steps: dissolving chitosan and betaine hydrochloride in deionized water and stirring until completely dissolved to obtain the chitosan-based polyionic liquid solution.

[0018] Furthermore, when preparing the chitosan-based polyionic liquid, the viscosity of the chitosan is 200 mPa·s to 400 mPa·s; and / or, the concentration of the chitosan in the solution is 0.8 g / L to 6.4 g / L; and / or, the molar ratio of the amino group in the chitosan to the carboxyl group in the betaine hydrochloride is 1:1 to 1:2.

[0019] An ionic liquid-modified boehmite prepared by a preparation method.

[0020] A coated membrane includes a polyolefin-based membrane and a functional coating applied to at least one surface of the polyolefin-based membrane; the functional coating comprises the aforementioned ionic liquid-modified boehmite; the polyolefin-based membrane is a polypropylene membrane.

[0021] A method for preparing a coated membrane includes the following steps: mixing ionic liquid-modified boehmite, a binder, and water to form a slurry; coating the slurry onto at least one side surface of a polyolefin-based membrane, and then drying it to obtain the coated membrane. The binder is polyacrylic acid, and the mass ratio of the ionic liquid-modified boehmite to the binder is 9:1.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) In this invention, a silane coupling agent is used to modify the surface of boehmite, introducing active functional groups. Then, chitosan-based polyionic liquid is stably grafted onto the surface of boehmite through hydrogen bonding and electrostatic interaction, forming a composite modified layer with synergistic effects of multiple anions and cations. This modified boehmite has good interfacial compatibility with polyolefin-based membranes and electrolytes, strong coating adhesion, and is not easy to fall off, thus improving the structural stability and liquid retention capacity of the membrane.

[0024] (2) The polyanions (carboxylate ions, chloride ions) and cations (protonated amines, quaternary ammonium salts) in chitosan-based polyionic liquids can synergistically regulate the solvation structure and deposition behavior of lithium ions, promoting uniform lithium ion transport and deposition. The coating membrane prepared by the modified boehmite of this invention has significantly improved ionic conductivity, which helps to improve the rate performance and cycle life of the battery.

[0025] (3) This invention uses boehmite as the core inorganic material, which has a Mohs hardness of only 3-3.5, far lower than that of alumina (Mohs hardness 9). This results in minimal wear on equipment during the coating process, reducing the maintenance costs of production equipment. At the same time, as a precursor to alumina, boehmite has a much lower raw material cost than high-purity alumina, making it suitable for large-scale production applications.

[0026] (4) The modified boehmite coating membrane maintains good structural integrity under high temperature conditions, effectively absorbs hydrofluoric acid (HF) produced by electrolyte decomposition, slows down electrolyte degradation, inhibits side reactions, and improves the thermal stability and safety performance of the battery.

[0027] (5) The modified boehmite preparation method provided by the present invention has clear steps, mild conditions, wide availability of raw materials, good process repeatability, and is easy to scale up for industrial use. The modified boehmite obtained can be directly used in aqueous coating processes to prepare coated membranes, is compatible with existing coating equipment, and has good industrialization prospects. Attached Figure Description

[0028] Figure 1 Scanning electron microscope image of boehmite modified by ionic liquid;

[0029] Figure 2 EDS spectrum of characteristic peaks of C Ka1,2 in boehmite modified by ionic liquid;

[0030] Figure 3 EDS spectrum of characteristic peaks of N Ka1,2 in boehmite modified by ionic liquid;

[0031] Figure 4 Infrared comparison images of boehmite and ionic liquid-modified boehmite;

[0032] Figure 5A comparison of the ionic conductivity of the original PP membrane, the boehmite-coated membrane, and the ionic liquid-modified boehmite-coated membrane. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1:

[0035] Preparation of ionic liquids:

[0036] Raw material preparation:

[0037] Chitosan (CS): Select chitosan powder with a known degree of deacetylation (e.g., ≥85%).

[0038] Betaine hydrochloride (BHC)

[0039] Preparation of acid solution:

[0040] Precisely weigh betaine hydrochloride (BHC), dissolve it in a measured amount of deionized water, and prepare an acid stock solution of a certain concentration. The amount of betaine hydrochloride (BHC) used is calculated based on the total number of moles of its carboxyl groups (-COOH).

[0041] The ratio of the total molar number of (-COOH) to the molar number of amino (-NH2) in chitosan is controlled to be 1:1.

[0042] Under normal temperature (e.g., 20-30°C) and pressure conditions, the prepared chitosan powder is slowly added to an aqueous solution containing betaine hydrochloride.

[0043] Continue stirring, for example using a magnetic stirrer at 300-600 rpm, until the chitosan is completely dissolved, forming a homogeneous, clear or slightly viscous solution.

[0044] To study or apply its concentration effect, the CPILS additive was formulated into a series of aqueous solutions of different concentrations. Specifically, it was formulated based on a concentration gradient of the CPILS additive (based on the mass of chitosan contained therein) in water, with typical concentration series being: 0 g / L, 0.8 g / L, 1.6 g / L, 3.2 g / L, and 6.4 g / L.

[0045] A method for preparing ionic liquid-modified boehmite includes the following steps:

[0046] S1: After vacuum drying the boehmite powder at 80℃ for 12h, mix 2g of boehmite powder with 20ml of anhydrous ethanol and ultrasonically disperse for 10min to obtain anhydrous ethanol dispersion of boehmite.

[0047] S2: Weigh 1 / 10 of the mass of boehmite powder γ-aminopropyltriethoxysilane coupling agent, add 2 ml of anhydrous ethanol, and dissolve at 30°C for 35 min to form a solution.

[0048] S3: Add the silane coupling agent KH-550 solution to the boehmite anhydrous ethanol dispersion at a rate of 2-3 drops per second, heat and reflux in an oil bath at 45°C for 6 hours, then centrifuge at high speed, wash 3-4 times with anhydrous ethanol, and dry at 80°C for 24 hours to obtain the product.

[0049] S4: Disperse 1g of treated boehmite in 5ml of deionized water, add 3ml of ionic liquid with a concentration of 3.2g / L, stir for 6h, then centrifuge at high speed and dry at 60℃ for 24h to obtain ionic liquid modified boehmite.

[0050] Example 2:

[0051] A method for preparing ionic liquid-modified boehmite includes the following steps:

[0052] S1: After vacuum drying the boehmite powder at 80℃ for 12h, mix 2g of boehmite powder with 20ml of anhydrous ethanol and ultrasonically disperse for 10min to obtain anhydrous ethanol dispersion of boehmite.

[0053] S2: Weigh γ-aminopropyltriethoxysilane, the silane coupling agent, at 1 / 10 of the mass of boehmite powder, add 2 ml of anhydrous ethanol, and dissolve at 30°C for 35 min to form a solution.

[0054] S3: Add the silane coupling agent KH-550 solution to the boehmite anhydrous ethanol dispersion at a rate of 2-3 drops per second, heat and reflux in an oil bath at 45°C for 6 hours, then centrifuge at high speed, wash 3-4 times with anhydrous ethanol, and dry at 80°C for 24 hours to obtain the product.

[0055] S4: Disperse 1g of treated boehmite in 5ml of deionized water, add 3ml of ionic liquid with a concentration of 3.2g / L, stir for 6h, then centrifuge at high speed and dry at 60℃ for 24h to obtain ionic liquid modified boehmite.

[0056] Example 3:

[0057] A method for preparing ionic liquid-modified boehmite includes the following steps:

[0058] S1: After vacuum drying the boehmite powder at 80℃ for 12h, mix 2g of boehmite powder with 20ml of anhydrous ethanol and ultrasonically disperse for 10min to obtain anhydrous ethanol dispersion of boehmite.

[0059] S2: Weigh γ-aminopropyltriethoxysilane, the silane coupling agent, at 1 / 10 of the mass of boehmite powder, add 2 ml of anhydrous ethanol, and dissolve at 30°C for 35 min to form a solution.

[0060] S3: Add the silane coupling agent KH-550 solution to the boehmite anhydrous ethanol dispersion at a rate of 2-3 drops per second, heat and reflux in an oil bath at 45°C for 6 hours, then centrifuge at high speed, wash 3-4 times with anhydrous ethanol, and dry at 80°C for 24 hours to obtain the product.

[0061] S4: Disperse 1g of treated boehmite in 5ml of deionized water, add 3ml of ionic liquid with a concentration of 3.2g / L, stir for 6h, then centrifuge at high speed and dry at 60℃ for 24h to obtain ionic liquid modified boehmite.

[0062] Comparative Example 1:

[0063] Boehmite was dried under vacuum at 80°C to obtain dried boehmite.

[0064] Tests were conducted on Examples 1-3, Example 1, and the original PP diaphragm. The test methods are as follows:

[0065] Weigh 1.5g of dried boehmite powder into a beaker and add 10ml of water. Stir at room temperature for 6 hours to form a white suspension. Add binder to the above solution at a weight ratio of powder to polyacrylic acid of 9:1, and continue stirring for 3 hours to obtain a mixed slurry. Apply the slurry to one side of a PP separator using a coating machine, and vacuum dry at 60℃ for 12 hours to obtain the coated separator. Assemble a steel sheet|separator|steel sheet battery for testing, and calculate the ionic conductivity of the separator.

[0066] Ionic conductivity:

[0067] Assemble the steel sheet | separator | steel sheet battery and test it. ε=L / (A·R) where L is the separator thickness, A is the area of ​​the stainless steel used, and R is the x-coordinate of the intersection point with the X-axis in the Nyquist plot.

[0068] The present invention will now be described in further detail with reference to the accompanying drawings:

[0069] See Figure 1 , Figure 2 and Figure 3The images show scanning electron microscope (SEM) and EDS images of boehmite modified with ionic liquid. The molecular formula of boehmite is γ-AlOOH, which does not contain nitrogen, indicating that the chitosan-based ionic liquid is fully incorporated into the boehmite.

[0070] See Figure 4 1625 cm -1 A new, strong absorption peak appeared at this point. This is a typical characteristic peak of the amide I band (C=O stretching vibration) in chitosan-based polymers. Untreated boehmite showed no absorption peak at this location. This directly proves that the polymer was successfully incorporated into the material, within the OH / NH stretching vibration region (approximately 3000-3300 cm⁻¹). -1 Comparing the two spectral lines, the peaks of the composite material (3262, 3082 cm⁻¹) -1 Compared to the peaks of pure boehmite (3275, 3090 cm), -1 A redshift (shift to lower wavenumbers) occurred. This is because the hydroxyl groups (-OH) on the boehmite surface react with the hydroxyl groups (-OH) and protonated amino groups (-NH3) on CPCIPILs-B. + New hydrogen bonds are formed. The formation of hydrogen bonds weakens the OH bond, lowering its vibrational frequency, which is classic evidence of a strong interaction between the two.

[0071] See Figure 5 The figure shows a comparison of the ionic conductivity test results of the original PP separator, the unmodified boehmite-coated separator (Comparative Example 1), and the ionic liquid-modified boehmite-coated separators prepared in Examples 1-3 of this invention. The test used a steel sheet|separator|steel sheet blocking battery structure. The bulk resistance (R) of the separator was measured by electrochemical impedance spectroscopy (EIS), and the ionic conductivity was calculated using the formula σ = L / (A·R) based on the separator thickness (L) and the stainless steel electrode area (A).

[0072] from Figure 5 As can be seen, the original PP membrane has low ionic conductivity. After coating with unmodified boehmite (Comparative Example 1), the ionic conductivity is improved to some extent, but the improvement is limited. However, the ionic conductivity of the boehmite-coated membranes modified with ionic liquids prepared in Examples 1-3 of this invention is significantly higher than that of Comparative Example 1 and the original PP membrane. Specifically, with the increase of ionic liquid dosage (Examples 1 to 3), the ionic conductivity shows a trend of first increasing and then stabilizing, indicating that appropriate chitosan-based polyionic liquid composite modification can effectively optimize the ion transport channels of the membrane and improve the migration ability of lithium ions.

[0073] The results fully demonstrate that by grafting chitosan-based polyionic liquid onto the surface of boehmite, the present invention effectively regulates the solvation structure and ion conduction behavior of the membrane / electrolyte interface through the synergistic effect of its multiple anions and cations, thereby significantly improving the ionic conductivity of the coated membrane and providing a strong guarantee for improving the rate performance and cycle stability of lithium-ion batteries.

[0074] Based on the above embodiments, comparative examples, and corresponding characterization test results, we can conclude that:

[0075] This invention successfully developed a method for preparing ionic liquid-modified boehmite, and applied it to the surface of a polypropylene membrane through a coating process to form a functional coating. The preparation method has a clear process route and mild, controllable conditions. It utilizes a silane coupling agent to activate the surface of boehmite, thereby introducing a chitosan-based polyionic liquid (obtained by reacting chitosan with betaine hydrochloride), achieving an effective composite of organic and inorganic materials.

[0076] The characterization results show that scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) confirmed that the chitosan-based ionic liquid was successfully composited on the boehmite surface; the shift of the characteristic peak of amide I band and the hydroxyl peak in the Fourier transform infrared (FTIR) further proved that there are strong interactions such as hydrogen bonding between the two, forming a stable composite structure.

[0077] In terms of performance testing, the modified boehmite was compounded with a polyacrylic acid binder to form a slurry, which was then coated onto a PP separator before assembling a battery for ionic conductivity testing. The results showed that, compared to the original PP separator and the unmodified boehmite-coated separator, the coated separator prepared using the modified boehmite of this invention exhibited higher ionic conductivity, indicating that the modified material can effectively improve the ion transport performance of the separator, thus contributing to improved rate performance and cycle stability of the battery.

[0078] In summary, the ionic liquid-modified boehmite provided by this invention combines low hardness, low cost, good interfacial compatibility, and ion control capability, and has significant application potential and industrialization value in the field of lithium-ion battery coating membranes.

[0079] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ionic liquid-modified boehmite, characterized in that, Includes the following steps: S1. Dry the boehmite powder, then disperse it in anhydrous ethanol and sonicate it to obtain a boehmite dispersion. S2. According to the mass of the boehmite powder, add silane coupling agent to the boehmite dispersion and carry out reflux reaction. After the reaction is completed, centrifuge, wash and vacuum dry to obtain silane coupling agent modified boehmite. S3. Disperse the modified boehmite obtained in step S2 in deionized water, add chitosan-based polyionic liquid, stir and mix, then perform high-speed centrifugation, and dry the resulting solid product to obtain the ionic liquid modified boehmite.

2. The method for preparing ionic liquid-modified boehmite according to claim 1, characterized in that, In step S1, the particle size of the boehmite powder is 300 nm to 1000 nm.

3. The method for preparing ionic liquid-modified boehmite according to claim 1, characterized in that, In step S1, the drying temperature is between 50°C and 120°C.

4. The method for preparing ionic liquid-modified boehmite according to claim 1, characterized in that, In step S2, the silane coupling agent includes one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or γ-methacryloyloxypropyltrimethoxysilane.

5. A method for preparing ionic liquid-modified boehmite according to claim 1 or 4, characterized in that, In step S2, the mass ratio of the boehmite powder to the silane coupling agent is 1:8 to 1:

10.

6. The method for preparing ionic liquid-modified boehmite according to claim 1, characterized in that, In step S2, the reflux reaction temperature is 45°C to 60°C, and the reaction time is 6 hours.

7. The method for preparing ionic liquid-modified boehmite according to claim 1, characterized in that, In step S3, the preparation of the chitosan-based polyionic liquid includes: dissolving chitosan and betaine hydrochloride in deionized water and stirring until completely dissolved to obtain the chitosan-based polyionic liquid solution.

8. The method for preparing ionic liquid-modified boehmite according to claim 7, characterized in that, When preparing the chitosan-based polyionic liquid, the viscosity of the chitosan is 200 mPa·s to 400 mPa·s; and / or, the concentration of the chitosan in the solution is 0.8 g / L to 6.4 g / L; and / or, the molar ratio of the amino groups in the chitosan to the carboxyl groups in the betaine hydrochloride is 1:1 to 1:

2.

9. An ionic liquid-modified boehmite prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the ionic liquid modified boehmite as described in claim 9 in the preparation of coated membranes.

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