Cationic covalent organic framework nanofiber membrane and its preparation method and application

Abstract

The present invention belongs to the technical field of lithium battery separators, and relates to a cationic covalent organic framework nanofiber separator, its preparation method, and application. The preparation method comprises the following steps: first, preparing a covalent organic framework powder with a triple-bond side chain through a Schiff base reaction, then preparing a cationic covalent organic framework (ICOFs) through a click reaction, and finally blending the ICOFs with polyacrylonitrile, and preparing an ICOFs-loaded nanofiber separator through an electrospinning method. The ICOFs nanofiber separator prepared by the present invention has high porosity, can effectively inhibit the transmission of anions, promote the dissociation of lithium salts, and improve ionic conductivity and lithium ion selectivity. In addition, the quasi-solid-state lithium battery based on the ICOFs nanofiber separator has excellent rate performance and safety performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and in particular to a cationic covalent organic framework nanofiber separator and its preparation method and application. Background Art

[0002] Balancing high energy density with adequate safety is a key focus for the current generation of batteries. Lithium metal anodes offer advantages such as high theoretical specific capacity, low redox potential (-3.040 V vs. standard hydrogen electrode), and low density (0.59 g cm⁻³), promising high energy density. However, safety concerns remain due to the reactive nature of lithium metal, which can easily generate byproducts during charge and discharge, forming lithium dendrites that can penetrate the separator and pose a risk. The development of high-performance solid electrolytes has become the most effective approach to improving the safety of lithium metal batteries. Quasi-solid-state electrolytes, a type of solid electrolyte, offer superior safety performance. However, compared to liquid electrolytes, their lithium ion mobility is significantly reduced, hindering the ability to achieve high-capacity, fast-charging batteries. As the most important safety valve and ion transport layer in a battery, the separator plays a critical role in ion and mass transfer. Current commercial polyolefin separators, due to their low porosity, often exhibit low ionic conductivity and lithium ion transference number, making it difficult to achieve high lithium ion mobility and uniform lithium deposition in quasi-solid-state electrolyte systems.

[0003] In recent years, covalent organic frameworks (COFs) have attracted considerable attention for their potential as functional modifications in separators due to their high-temperature resistance, lightweight, uniform pore size, and high porosity. Currently developed methods include coating and phase separation. Although separators prepared by these methods exhibit high specific capacities at low current densities, their capacity severely decays at high current densities, making it difficult to achieve safe and efficient operation of quasi-solid-state electrolyte lithium metal batteries at high current densities. Therefore, the design of novel COFs and the processing of separators that simultaneously impart high lithium-ion conductivity and a high lithium-ion transference number, thereby enabling safe, efficient, and fast charging, is of great significance to the development of quasi-solid-state lithium metal batteries.

[0004] Summary of the Invention: The technical problem addressed by this invention is that conventional polyolefin separators are unable to address the problems of hindered lithium ion migration and low lithium ion transference numbers in quasi-solid-state electrolytes, resulting in low lithium battery capacity at high coulomb levels and poor cycling temperature stability. This invention prepares a cationic covalent organic framework (COF) as a functional particle and, through electrospinning, produces a COF nanofiber separator that can anchor anions and facilitate lithium ion migration.

[0005] The first aspect of the present invention provides a method for preparing a cationic covalent organic framework nanofiber membrane, characterized in that it comprises the following steps:

[0006] Step 1: Prepare a covalent organic framework (COFs-[C≡HC]) with a triple bond through a Schiff base reaction, and then modify the azide cation to the covalent organic framework through a click reaction to prepare a new cationic covalent organic framework (ICOFs).

[0007] Step 2: Add a certain amount of ICOFs to the N,N-dimethylformamide (DMF) solution of polyacrylonitrile (PAN), mix and stir evenly to obtain a spinning solution.

[0008] Step 3: Prepare cationic covalent organic framework nanofiber membrane by electrospinning and hot pressing process.

[0009] Further: The specific steps of the Schiff base reaction in step 1 are to disperse the monomer 1,3,5-tris(4-aminophenyl)benzene (112.4 mg, 0.32 mmol) and 2,5-bis(2-propyn-1-yloxy)-1,4-benzenedicarboxaldehyde (116.4 mg, 0.48 mmol) in o-dichlorobenzene / n-butanol (6 mL, volume ratio 1 / 1), ultrasonically treat for 10 minutes, and add acetic acid aqueous solution (0.8 mL, 12 M). The solution mixture is poured into a 20 mL Teflon-lined stainless steel autoclave and heated at 120 ° C for 72 hours. The solid is filtered out, washed with tetrahydrofuran and n-hexane, and then vacuum dried at 60 ° C for 12 hours to obtain COFs-[C≡HC].

[0010] Furthermore: in the step 1, the azide cation is 2-azido-1,3-dimethylimidazolium hexafluorophosphate.

[0011] Further: The specific steps of the click reaction in step 1 are as follows: COFs-[C≡HC] (60 mg), cuprous iodide (6 mg), N,N-diisopropylethylamine (0.2 ml), and 2-azido-1,3-dimethylimidazolium hexafluorophosphate (308 mg) were added to tetrahydrofuran / acetonitrile (0.8 ml / 7.2 ml) under argon atmosphere, stirred at room temperature for 24 hours, and the precipitate was filtered and washed with acetone, acetonitrile, and tetrahydrofuran. The precipitate was vacuum dried at 60°C for 12 hours to obtain ICOFs powder.

[0012] Furthermore: in the step 2, the mass of ICOFs accounts for 10% to 30% of the total mass of ICOFs and PAN, and the concentration of PAN in the DMF solution is 10% to 15%.

[0013] Furthermore, the spinning parameters of the electrospinning method in step 3 are that the spinning rate is set to 0.8-2 mL h -1, the operating voltage is 10-20 kV, the distance between the needle and the collector is 8-15 cm, the temperature is 20-30 ° C, and the humidity is 30-60 ° C.

[0014] Furthermore: the parameters of the hot pressing process in step three are a pressure of 1 to 5N and a temperature of 30 to 100°C.

[0015] The second aspect of the present invention provides an application of a cationic covalent organic framework nanofiber membrane in a quasi-solid-state lithium battery.

[0016] Further: The electrolyte used to prepare the quasi-solid-state electrolyte is a 1M LiPF6 diethyl carbonate / ethylene carbonate (volume ratio = 1 / 1) solution, and the method is to add 5% N,N-dimethylacrylamide, 0.2% polyethylene glycol diacrylate and 0.2% azobisisobutyronitrile to the electrolyte to prepare a polymerization precursor solution.

[0017] Further: using the above-mentioned diaphragm, polymerization precursor, positive electrode material, and negative electrode material, the specific steps are to drop the polymerization precursor into the cationic covalent organic framework nanofiber diaphragm, assemble a button battery, and then carry out an in-situ polymerization reaction at 60°C to obtain the quasi-solid-state lithium battery.

[0018] The present invention has the following advantages:

[0019] (1) The cationic covalent organic framework particles prepared by the present invention have good dispersibility and uniformity in the fiber membrane.

[0020] (2) The cationic covalent organic framework nanofiber membrane prepared by the present invention can effectively inhibit anion transmission, promote lithium salt dissociation, and increase the lithium ion migration number.

[0021] (3) The solid-state lithium battery provided by the present invention has high specific capacity and cycle stability at high current density.

[0022] (4) The preparation process of the present invention is simple, the equipment and machinery are mature, and production can be expanded. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanning electron microscope image of Example 1 of the present invention.

[0024] Figure 2 Graphs showing ionic conductivity and lithium ion transference number for Examples 1-3.

[0025] Figure 3 It is a rate diagram of the quasi-solid-state lithium battery prepared based on the diaphragms of Example 1, Comparative Example 1 and Comparative Example 2 in the application examples.

[0026] Figure 4It is a long cycle diagram of the quasi-solid-state lithium battery prepared based on the diaphragms of Example 1, Comparative Example 1 and Comparative Example 2 in the application example. DETAILED DESCRIPTION

[0027] In order to make the results of the present invention more convincing, the technical solutions provided by the present invention are described in detail with reference to the embodiments. The following preferred examples are only for illustrating the present invention, but do not limit the scope of protection of the present invention.

[0028] All reagents and instruments used in this example are commercially available.

[0029] Example 1

[0030] This example provides a method for preparing a cationic covalent organic framework nanofiber membrane, comprising the following steps:

[0031] (1) Monomers 1,3,5-tris(4-aminophenyl)benzene (112.4 mg, 0.32 mmol) and 2,5-bis(2-propyn-1-yloxy)-1,4-benzenedicarboxaldehyde (116.4 mg, 0.48 mmol) were dispersed in o-dichlorobenzene / n-butanol (6 mL, volume ratio 1 / 1), ultrasonically treated for 10 minutes, and then added with aqueous acetic acid (0.8 mL, 12 M). The solution mixture was poured into a 20 mL Teflon-lined stainless steel autoclave and heated at 120°C for 72 hours. The solid was filtered, washed with tetrahydrofuran and n-hexane, and then dried in vacuo at 60°C for 12 hours to obtain COFs-[C≡HC].

[0032] (2) Under an argon atmosphere, COFs-[C≡HC] (60 mg), cuprous iodide (6 mg), N,N-diisopropylethylamine (0.2 ml), and 2-azido-1,3-dimethylimidazolium hexafluorophosphate (308 mg) were added to tetrahydrofuran / acetonitrile (0.8 ml / 7.2 ml) and stirred at room temperature for 24 hours. The precipitate was filtered and washed with acetone, acetonitrile, and tetrahydrofuran. The precipitate was vacuum dried at 60°C for 12 hours to obtain ICOFs powder.

[0033] (3) Prepare a PAN solution with a mass fraction of 15%. Then add ICOFs with a mass fraction of 20% of the total mass of ICOFs and PAN into the PAN solution and stir evenly to form a spinning solution.

[0034] (4) 20% ICOFs / PAN nanofiber membrane was prepared by electrospinning. The spinning parameters of the electrospinning method were set at a spinning rate of 0.8-2 mL h -1 , the operating voltage is 10-20 kV, the distance between the needle and the collector is 8-15 cm, the temperature is 20-30 ° C, and the humidity is 30-60 ° C.

[0035] (5) Finally, the cationic covalent organic framework nanofiber membrane was hot-pressed at 70°C and 2N, and the obtained membrane was recorded as 20% ICOFs / PAN.

[0036] Example 2

[0037] This example provides a method for preparing a cationic covalent organic framework nanofiber membrane, which specifically refers to Example 1, except that the mass fraction of ICOFs in step (3) is changed to 10%, recorded as 10% ICOFs / PAN.

[0038] Example 3

[0039] This example provides a method for preparing a cationic covalent organic framework nanofiber membrane, which is specifically referred to Example 1, except that the mass fraction of ICOFs in step (3) is changed to 30%, recorded as 30% ICOFs / PAN.

[0040] Comparative Example 1

[0041] The commercially available model is Celgard 2400 PP separator.

[0042] Comparative Example 2

[0043] The PAN nanofiber membrane provided in this example is specifically prepared with reference to Example 1, except that ICOFs are not added in step (3).

[0044] from Figure 1 The scanning electron microscopy images show that the ICOFs particles in Example 1 (20% ICOFs / PAN) are uniformly dispersed in the nanofiber membrane, proving that ICOFs have good dispersibility and processability. Figure 3 The ionic conductivity and lithium ion migration number of Examples 1-3 and Comparative Example 2 were tested. When the ICOFs content was 20%, the maximum ionic conductivity was 1.95 mS / cm, and the maximum lithium ion migration number was 0.74, which were significantly higher than 1.24 mS / cm and 0.55 of Comparative Example 2, indicating that the imidazolium cationic groups in ICOFs can effectively fix anions to promote the rapid transport of lithium ions.

[0045] Application Examples

[0046] The present invention provides a method for preparing a quasi-solid-state lithium battery with a cationic covalent organic framework nanofiber separator, comprising the following steps:

[0047] (1) Prepare a polymerization precursor solution by adding 5% N,N-dimethylacrylamide, 0.2% polyethylene glycol diacrylate, and 0.2% azobisisobutyronitrile to a 1M LiPF6 diethyl carbonate / ethylene carbonate (volume ratio = 1 / 1) electrolyte and stirring for 20 minutes.

[0048] (2) The polymerization precursor solution was added dropwise to the separators prepared in Examples 1-3 and Comparative Examples 1-2, and button batteries were assembled. Subsequently, in-situ polymerization was performed at 60° C. for 2 hours to obtain a quasi-solid-state lithium battery, wherein the positive electrode was NCM811 and the negative electrode was lithium metal.

[0049] The quasi-solid-state lithium battery based on the separators of Example 1 (20% ICOFs / PAN), Comparative Example 1 (PP), and Comparative Example 2 (PAN) was subjected to rate and cycle tests. Figure 3 The specific capacities of Example 1 at 0.5C, 1C, 2C, 3C, and 5C are 175.2 mAh g -1 、161.3mAh g -1 、149.1mAh g -1 、143.0mAh g -1 and 131.8mAh g -1 , which is significantly higher than the 160.6 mAh g in Comparative Example 1. -1 、148.5mAh g -1 、136.3mAh g -1 、127.6mAh g -1 and 113.5mAh g -1 and 170.2 mAh g of Comparative Example 2 -1 、160.4mAh g -1 , 148.4mAh g -1 、138.5mAh g -1 , 121.7mAh g -1 .like Figure 4 After 300 cycles at a high current density of 5C, the capacity retention rates of Example 1, Comparative Example 1, and Comparative Example 2 were 83.2%, 18.8%, and 34.3%, respectively. This demonstrates that the cationic covalent organic framework nanofiber separator prepared by the present invention has excellent performance and great prospects for application in quasi-solid-state lithium batteries.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the scope of protection of the present invention. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a cationic covalent organic framework nanofiber membrane, characterized in that: The steps include: Step 1: Prepare a covalent organic framework COFs-[C≡HC] with a triple bond by Schiff base reaction. The specific steps are to disperse the monomers 1,3,5-tris(4-aminophenyl)benzene and 2,5-bis(2-propyn-1-yloxy)-1,4-benzenedicarboxaldehyde into o-dichlorobenzene / n-butanol, use acetic acid aqueous solution as a catalyst, and react at 120°C for 48-72 hours; then wash with tetrahydrofuran and n-hexane, filter, and vacuum dry to obtain COFs-[C ≡HC]; then, the azide cation is modified onto the covalent organic framework through a click reaction to prepare the cationic covalent organic framework ICOFs. The specific steps are as follows: under an argon atmosphere, COFs-[C≡HC], cuprous iodide, N,N-diisopropylethylamine and 2-azido-1,3-dimethylimidazolium hexafluorophosphate are dispersed in tetrahydrofuran / acetonitrile, stirred at room temperature for 24 hours, washed with acetone, acetonitrile and tetrahydrofuran, filtered, and dried in vacuo to obtain ICOFs; Step 2: adding a certain amount of ICOFs to the N,N-dimethylformamide (DMF) solution of polyacrylonitrile (PAN) and mixing and stirring to obtain a spinning solution; Step 3: Prepare cationic covalent organic framework nanofiber membrane by electrospinning and hot pressing process.

2. The method for preparing a cationic covalent organic framework nanofiber membrane according to claim 1, characterized in that: In the step 2, the mass of ICOFs accounts for 10% to 30% of the total mass of ICOFs and PAN, and the concentration of PAN in the DMF solution is 10% to 15%.

3. The method for preparing a cationic covalent organic framework nanofiber membrane according to claim 1, characterized in that: The spinning parameters of the electrospinning method in step 3 are a spinning rate of 0.8-2 mL·h -1 , the operating voltage is 10~20kV, the distance between the needle and the collector is 8~15cm, the temperature is 20~30°C, and the humidity is 30~60°.

4. The method for preparing a cationic covalent organic framework nanofiber membrane according to claim 1, characterized in that: The parameters of the hot pressing process in step 3 are a pressure of 1-5N and a temperature of 30-100°C.

5. Use of a cationic covalent organic framework nanofiber separator obtained by the preparation method according to any one of claims 1 to 4 in a quasi-solid-state lithium battery.

6. The use according to claim 5, characterized in that The preparation method of the quasi-solid electrolyte is to add N,N-dimethylacrylamide, polyethylene glycol diacrylate, and azobisisobutyronitrile to the electrolyte and polymerize them at 60°C for 2 to 4 hours; the electrolyte used to prepare the quasi-solid electrolyte is 1M LiPF6 diethyl carbonate / ethylene carbonate solution.

7. The use according to claim 6, characterized in that The volume ratio of diethyl carbonate to ethylene carbonate is 1:

1.

8. The use according to claim 5, characterized in that The positive electrode materials used in quasi-solid-state lithium batteries include any one of lithium iron phosphate or nickel-cobalt-manganese ternary material electrodes, and the negative electrode materials include any one of metallic lithium, graphite, and silicon-carbon negative electrodes.

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