阅读说明：本技术 一种在聚酰亚胺纳米纤维膜表面包覆勃姆石陶瓷层的方法 (Method for coating surface of polyimide nanofiber membrane with boehmite ceramic layer ) 是由 齐胜利 杨承沅 董南希 田国峰 武德珍 于 2020-04-05 设计创作，主要内容包括：一种在表面包覆勃姆石陶瓷层的聚酰亚胺纳米纤维膜,其制备方法包括,首先通过静电纺丝法制备聚酰胺酸纳米纤维膜并热亚胺化得到聚酰亚胺纳米纤维膜；然后将聚酰亚胺纳米纤维膜先后浸入氢氧化钾溶液和稀醋酸溶液中进行碱解开环和酸化,再将其浸入氨水中进行季铵化,再浸入铝盐溶液中进行原位络合和吸附水解,最终经过热处理得到表面包覆勃姆石陶瓷层的聚酰亚胺纳米纤维膜。本发明所述方法实施过程简单、包覆效率高、过程绿色无污染,有利于扩大生产。(A preparation method of a polyimide nanofiber membrane with a boehmite ceramic layer coated on the surface comprises the following steps of firstly preparing a polyamic acid nanofiber membrane by an electrostatic spinning method and carrying out thermal imidization to obtain the polyimide nanofiber membrane; and then sequentially immersing the polyimide nano-fiber membrane into a potassium hydroxide solution and a dilute acetic acid solution for alkaline hydrolysis ring opening and acidification, immersing the polyimide nano-fiber membrane into ammonia water for quaternization, immersing the polyimide nano-fiber membrane into an aluminum salt solution for in-situ complexing and adsorption hydrolysis, and finally performing heat treatment to obtain the polyimide nano-fiber membrane with the surface coated with the boehmite ceramic layer. The method disclosed by the invention is simple in implementation process, high in coating efficiency, green and pollution-free in process and beneficial to expanded production.)

1. The polyimide nanofiber membrane coated with the boehmite ceramic layer on the surface is characterized in that the diameter of polyimide nanofibers is 10-650nm, and the surface of the nanofibers is coated with the boehmite ceramic layer with the thickness of 5-150 nm.

2. The polyimide nanofiber membrane of claim 1, wherein the diameter of the polyimide nanofibers is 15-600nm, and the surface of the nanofibers is coated with a boehmite ceramic layer having a thickness of 10-140 nm.

3. A preparation method of a polyimide nanofiber membrane with a boehmite ceramic layer coated on the surface is characterized by comprising the following steps:

a, preparing 0.05-1.5mol/L aluminum salt aqueous solution;

preparing a polyamic acid nano fiber membrane from a polyamic acid solution with the solid content of 8-12% by adopting an electrostatic spinning method, and carrying out heat treatment to obtain the polyimide nano fiber membrane;

c: b, treating the polyimide nano-fiber membrane prepared in the step B in 0.2-6mol/L alkali solution to obtain a polyimide nano-fiber membrane with an alkaline hydrolysis ring on the surface;

d: placing the polyimide nano fiber membrane obtained by the treatment in the step C in an acid solution with the mass fraction of 0.3-25% for acidification to obtain the polyimide nano fiber membrane with the surface containing carboxyl active functional groups;

e, soaking the polyimide nanofiber membrane with the surface containing the carboxyl active functional groups obtained by the step D in 0.005-0.6mol/L diluted ammonia water solution for treatment to obtain the polyimide nanofiber membrane with the surface quaternized;

f: b, placing the polyimide nanofiber membrane with the surface quaternized, which is obtained through the treatment in the step E, in the aluminum salt aqueous solution prepared in the step A for soaking;

and G, carrying out heat treatment on the nanofiber membrane obtained in the step F to obtain the polyimide nanofiber membrane with the surface coated with the boehmite ceramic layer.

4. The method according to claim 3, wherein the aluminum salt in the step A is one or more of anhydrous aluminum chloride, aluminum nitrate and aluminum sulfate, and the concentration of the aluminum salt aqueous solution is 0.1-1 mol/L.

5. A method according to claim 3, wherein the heat treatment conditions in steps B and G are: the temperature is 290-350 ℃, preferably 300-330 ℃, and the temperature is kept for 1-5h, preferably 1.5-3.5 h.

6. A method according to claim 3, wherein the treatment time of the nanofibrous membrane in alkali in step C is 20s-6min, preferably 30s-5 min.

7. The method according to claim 3, wherein the acidification time of the nanofiber membrane in the acid solution in step D is 0.5-5 h.

8. The method according to claim 3, wherein the nanofiber membrane is treated in the ammonia water for 0.5-4h in the step E.

9. The method according to claim 3, wherein the soaking time of the nanofiber membrane in the aluminum salt aqueous solution in the step F is 20min-5h, and the aluminum ions in the solution are subjected to adsorption complexation and in-situ hydrolysis deposition on the surfaces of the nanofibers through soaking.

10. The method of claim 3, wherein the heat treatment of step G is carried out under the following conditions: the temperature is 290-350 ℃, preferably 300-330 ℃, and the temperature is kept for 1-5h, preferably 1.5-3.5 h.

Technical Field

The invention belongs to the technical field of polyimide fiber membranes, and particularly relates to a method for coating a boehmite ceramic layer on the surface of a polyimide nanofiber membrane.

Background

With the increasing development speed of modern society, the global energy demand is increasing. The enormous environmental pressure brought by the conventional fossil energy and the severe situation brought by the continuous consumption thereof have become non-negligible social problems, and the development of new energy has been urgently needed. Lithium batteries are one of the most potential energy storage devices today due to their high energy density and low pollution characteristics. However, with the continuous popularization of lithium batteries, the phenomena of spontaneous combustion and explosion of batteries which happen from time to time have become the focus of social attention. The safety of the battery is an important factor which restricts the development of the lithium battery at present.

The lithium battery consists of four parts, namely an anode, a cathode, a diaphragm and electrolyte. The diaphragm plays a role in preventing direct contact between the anode and the cathode and providing an ion transmission channel. Modification of battery separators is one of the important means for improving battery safety. At present, a great deal of research on the modification of the diaphragm is carried out by starting from a preparation method and a diaphragm material. Electrospinning, also known as electrospinning, is a simple and efficient process for producing nanofibers, and has received much attention. The electrospun nanofiber membrane has the advantages of high porosity and uniform and adjustable pore diameter, so that the electrospun nanofiber membrane has great potential as a lithium ion battery diaphragm. At present, a great deal of research on preparing modified lithium battery diaphragms by an electrostatic spinning method is available. The Polyimide (PI) has the excellent characteristics of high temperature resistance, low temperature resistance, high strength and high modulus, high creep resistance, high dimensional stability and the like. The battery diaphragm is prepared by using the PI material or modified, so that the thermal stability of the diaphragm can be further improved, and the safe operation of the battery is ensured. PI/PVDF-HFP/PI nanofiber membranes prepared as patent CN 201711097549.7. In addition, in the modification of battery separator, the application of inorganic particle slurry is one of the most common modification methods, for example, patent CN106299204A reports that an alumina coating with a thickness of 1-4 μm is applied on the surface of a base film to prepare a high-safety lithium battery separator. However, the composite separator modified by the coating method still has a great room for improvement in ion conductivity, thermal stability and the like: coating slurry may cause the blockage of micropores of the diaphragm, and the uniformity of the diaphragm is reduced; coating the slurry increases the thickness and mass of the separator, resulting in a decrease in the energy density of the battery; the coating slurry only covers the surface layer of the base film, and the improvement on the ionic conductivity and the thermal stability is limited. In order to improve the defects, the invention provides a method for modifying functional groups on the surface of the polyimide nano-fiber so as to hydrolyze boehmite precursors on the surface of the fiber in situ, so that the uniform coating of the boehmite ceramic on the polyimide nano-fiber is realized. The method adopted by the invention is simple, the coating effect is good, the functional layer is thin, and the functional layer is not easy to fall off.

Disclosure of Invention

Aiming at the defects of a method for loading an inorganic material on the surface of a diaphragm by a coating method, the invention provides a method for coating a boehmite ceramic layer on the surface of a polyimide nano-fiber membrane, and the method has the advantages of simple process, high coating efficiency and good application prospect.

The polyimide nanofiber membrane coated with the boehmite ceramic layer on the surface is characterized in that the diameter of polyimide nanofibers is 10-650nm, and the surface of the nanofibers is coated with the boehmite ceramic layer with the thickness of 5-150 nm.

Furthermore, the diameter of the polyimide nano-fiber is 15-600nm, and the surface of the nano-fiber is coated with a boehmite ceramic layer with the thickness of 10-140 nm.

Further, the contact angle of the polyimide nanofiber membrane coaxially coated with boehmite is 3-20 °, preferably 4-19 °;

further, the polyimide nanofiber membrane coaxially coated with boehmite has a porosity of 61-88%, preferably 63-86%;

further, the thermal deformation temperature of the polyimide nanofiber membrane coaxially coated with boehmite under 0.02N is 275-319 ℃, preferably 278-319 ℃.

A method for coating a boehmite ceramic layer on the surface of a polyimide nanofiber membrane is characterized by comprising the following steps:

a, preparing 0.05-1.5mol/L aluminum salt aqueous solution;

preparing a polyamic acid nano fiber membrane from a polyamic acid solution with the solid content of 8-12% by adopting an electrostatic spinning method, and carrying out heat treatment to obtain the polyimide nano fiber membrane;

c: b, treating the polyimide nano-fiber membrane prepared in the step B in 0.2-6mol/L alkali solution to obtain a polyimide nano-fiber membrane with an alkaline hydrolysis ring on the surface;

d: placing the polyimide nano fiber membrane obtained by the treatment in the step C in an acid solution with the mass fraction of 0.3-25% for acidification to obtain the polyimide nano fiber membrane with the surface containing carboxyl active functional groups;

e, soaking the polyimide nanofiber membrane with the surface containing the carboxyl active functional groups obtained by the step D in 0.005-0.6mol/L diluted ammonia water solution for treatment to obtain the polyimide nanofiber membrane with the surface quaternized;

f: b, placing the polyimide nanofiber membrane with the surface quaternized, which is obtained through the treatment in the step E, in the aluminum salt aqueous solution prepared in the step A for soaking;

and G, carrying out heat treatment on the nanofiber membrane obtained in the step F to obtain the polyimide nanofiber membrane with the surface coated with the boehmite ceramic layer.

The aluminum salt in the step A is one or more of anhydrous aluminum chloride, aluminum nitrate and aluminum sulfate, and the concentration of the aluminum salt aqueous solution is preferably 0.1-1 mol/L.

The polyamic acid in the step B is prepared by solution condensation polymerization of any one of dicarboxylic anhydride and diamine, wherein the dicarboxylic anhydride and diamine are preferably pyromellitic dianhydride/4, 4 '-diaminodiphenyl ether (PMDA/ODA), 3', 4,4 '-benzophenone tetracarboxylic dianhydride/4, 4' -diaminodiphenyl ether (BTDA/ODA), hexafluoro dianhydride/4, 4 '-diaminodiphenyl ether (6FDA/ODA), 3', 4,4 '-biphenyl tetracarboxylic acid/4, 4' -diaminodiphenyl ether (BPDA/ODA), 4,4 '-biphenyl ether dianhydride/4, 4' -diaminodiphenyl ether (ODPA/ODA). The conditions of the heat treatment are as follows: the temperature is 290-350 ℃, preferably 300-330 ℃, and the temperature is kept for 1-5h, preferably 1.5-3.5h

The alkali in the step C is one or more of sodium hydroxide and potassium hydroxide, the concentration of the alkali is preferably 0.5-5mol/L, and the treatment time of the nanofiber membrane in the alkali is 20s-6min, preferably 30s-5 min. Further, after the alkali treatment, deionized water is used for washing until the solution is neutral. The mass ratio of the alkali solution to the polyimide nanofiber membrane prepared in the step B is more than 10: 1, preferably 20: 1-10⁵：1。

The acid in the step D is one or more of acetic acid, sulfuric acid, nitric acid and hydrochloric acid, the mass fraction of the acid is preferably 0.5-20%, and the acidification time of the nanofiber membrane in the acid solution is 0.5-5h, preferably 1-4 h. Further, after acidification, washing with deionized water to neutrality. And D, the mass of the acid solution and the polyimide nanofiber membrane obtained by the treatment in the step C is more than 10: 1, preferably 20: 1-10⁴：1。

The concentration of the dilute ammonia water in the step E is preferably 0.01-0.5mol/L, and the treatment time of the nanofiber membrane in the ammonia water is 0.5-4h, preferably 1-3 h. Carrying out treatment on dilute ammonia water to enable carboxyl on the surface of the nanofiber to be quaternized; further, preferably, the treated product is ultrasonically cleaned by deionized water for 10-60min, preferably 20-50 min. And D, the mass ratio of the dilute ammonia solution to the polyimide nanofiber membrane with the surface containing the carboxyl active functional groups obtained by the treatment in the step D to the dilute ammonia solution is more than 10: 1, preferably 20: 1-10⁵：1。

And F, soaking the nanofiber membrane in the aluminum salt aqueous solution for 20min-5h, preferably 30min-4 h. Soaking to make the aluminium ion in the solution produce adsorption complexation and in-situ hydrolysis deposition on the surface of the nano-fiber. Further, preferably, deionized water is ultrasonically cleaned for 10-60min, preferably 20-50min after soaking. The mass ratio of the aluminum salt aqueous solution to the polyimide nanofiber membrane with the surface quaternized to the aluminum salt aqueous solution is more than 10: 1, preferably 20: 1-10⁵：1。

Wherein, the heat treatment conditions in the step G are as follows: the temperature is 290-350 ℃, preferably 300-330 ℃, and the temperature is kept for 1-5h, preferably 1.5-3.5 h.

Compared with the prior art, the invention has the following excellent effects:

1. the adsorption complexation and hydrolysis deposition of the boehmite precursor are completed in one-step operation, so that the uniformity of the diaphragm is favorably kept, the operation is simpler and more convenient, the solutions used in the soaking treatment process are aqueous solutions, organic solvents are not used, the environment is not polluted, and the expanded production is favorably realized.

2. The polyimide nano-fiber film with the surface coated with the boehmite ceramic layer prepared by the invention can realize the coaxial coating of the boehmite ceramic layer on the surface of the polyimide nano-fiber,

has high electrolyte wettability and thermal stability.

3. Compared with the coating modification method, the composite diaphragm prepared by the invention has the advantages that the inorganic layer is uniformly coated on the surface of the fiber, the thickness of the inorganic layer is thinner, the quality and the thickness of the diaphragm are greatly reduced, and the energy density of the battery is favorably improved.

Drawings

Fig. 1 is a scanning electron microscope image of a polyimide nanofiber membrane surface-coated with a boehmite ceramic layer prepared according to example 1, with a magnification of 5000 times.

Fig. 2 is a scanning electron microscope image of a polyimide nanofiber membrane with a boehmite ceramic layer coated on the surface thereof prepared according to example 2, with a magnification of 5000 times.

Fig. 3 is a scanning electron micrograph of a polyimide nanofiber membrane with a surface-coated boehmite ceramic layer prepared according to example 3, magnified 5000 times.

Fig. 4 is a scanning electron microscope image, 5000 times magnified, of the polyimide nanofiber film surface-coated with a boehmite ceramic layer prepared according to example 4.

Fig. 5 is a scanning electron micrograph of a polyimide nanofiber membrane with a surface-coated boehmite ceramic layer prepared according to example 5, at 5000 times magnification.

FIG. 6 is a scanning electron micrograph of a cross-section of a polyimide nanofiber membrane with a surface coated with a boehmite ceramic layer prepared according to example 5, magnified 50000 times.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be noted that: the following examples are only for illustrating the present invention and are not intended to limit the technical solutions described in the present invention. Thus, while the present invention has been described in detail with reference to the following examples, it will be understood by those skilled in the art that the present invention may be modified and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Example 1

(1) Weighing 4.17g of anhydrous aluminum chloride, slowly adding the anhydrous aluminum chloride into 80ml of deionized water, and completely dissolving the anhydrous aluminum chloride to prepare 0.4mol/L anhydrous aluminum chloride solution; (2) weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.84g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA in batches under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2h for homogenization, finally filling the polyamic acid solution into a 20ml syringe, and preparing the polyamic acid nanofiber membrane by using an electrostatic spinning technology, wherein the specific parameters in the electrostatic spinning process are spinning voltage: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 400 rpm; receiving distance: 20 cm. Firstly, placing the prepared polyamic acid nanofiber membrane in a super clean bench, standing for 12h, then placing the polyamic acid nanofiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2h to prepare the polyimide nanofiber membrane; (3) weighing 8.98g of potassium hydroxide, dissolving the potassium hydroxide in deionized water to prepare a 2mol/L potassium hydroxide solution, and weighing acetic acid to prepare an acetic acid solution with the mass fraction of 5%; (4) soaking the polyimide nano-fiber membrane in a potassium hydroxide solution for 2min, taking out, ultrasonically cleaning for 5min, soaking in acetic acid for 2h, taking out, ultrasonically cleaning for 30min, and obtaining the polyimide nano-fiber membrane with the surface containing carboxyl active functional groups; (5) preparing 0.04mol/L dilute ammonia solution from 1ml of ammonia water, soaking the polyimide nanofiber membrane with the surface containing the carboxyl active functional groups, which is obtained by the treatment in the step (4), in the dilute ammonia water for 1 hour, taking out and ultrasonically cleaning for 30min to obtain the polyimide nanofiber membrane with the quaternized surface; (6) soaking the polyimide nanofiber membrane with the surface quaternized, which is obtained by the treatment in the step (5), in an anhydrous aluminum chloride solution for 1h, taking out, and ultrasonically cleaning for 30 min; (7) and (3) placing the nanofiber membrane obtained by the treatment in the step (6) in a 300 ℃ oven for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with the boehmite ceramic layer, wherein the diameter of the nanofiber is 420nm, the thickness of the boehmite coating layer of the nanofiber is 54nm, the tensile strength is 8.2Mpa, the contact angle of the electrolyte is 5.9 degrees, the thermal deformation temperature is 280 ℃ at 0.02N, and the porosity is 73.5 percent. The morphology of the obtained fiber membrane is shown in figure 1.

Example 2

(1) Weighing 4.17g of anhydrous aluminum chloride, slowly adding the anhydrous aluminum chloride into 80ml of deionized water, and completely dissolving the anhydrous aluminum chloride to prepare 0.4mol/L anhydrous aluminum chloride solution; (2) weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.84g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA in batches under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2h for homogenization, finally filling the polyamic acid solution into a 20ml syringe, and preparing the polyamic acid nanofiber membrane by using an electrostatic spinning technology, wherein the specific parameters in the electrostatic spinning process are spinning voltage: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 400 rpm; receiving distance: 20 cm. Firstly, placing the prepared polyamic acid nanofiber membrane in a super clean bench, standing for 12h, then placing the polyamic acid nanofiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2h to prepare the polyimide nanofiber membrane; (3) weighing 8.98g of potassium hydroxide, dissolving the potassium hydroxide in 80ml of deionized water to prepare a 2mol/L potassium hydroxide solution, and weighing acetic acid to prepare an acetic acid solution with the mass fraction of 5%; (4) soaking the polyimide nano-fiber membrane in a potassium hydroxide solution for 2min, taking out, ultrasonically cleaning for 5min, soaking in acetic acid for 1h, taking out, ultrasonically cleaning for 30min, and obtaining the polyimide nano-fiber membrane with the surface containing carboxyl active functional groups; (5) preparing 0.04mol/L dilute ammonia solution from 1ml of ammonia water, soaking the polyimide nanofiber membrane with the surface containing the carboxyl active functional groups, which is obtained by the treatment in the step (4), in the dilute ammonia water for 1 hour, taking out and ultrasonically cleaning for 30min to obtain the polyimide nanofiber membrane with the quaternized surface; (6) soaking the polyimide nanofiber membrane with the surface quaternized, which is obtained by the treatment in the step (5), in an anhydrous aluminum chloride solution for 1h, taking out, and ultrasonically cleaning for 30 min; (7) and (3) placing the nanofiber membrane obtained by the treatment in the step (6) in an oven at 300 ℃ for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with the boehmite ceramic layer, wherein the diameter of the nanofiber is 350nm, the thickness of the boehmite coating layer of the nanofiber is 48nm, the tensile strength is 12.3Mpa, the contact angle of the electrolyte is 6.5 degrees, the thermal deformation temperature is 291 ℃ at 0.02N, and the porosity is 75.7 percent. The morphology of the obtained fiber membrane is shown in figure 2.

Example 3

(1) Weighing 4.17g of anhydrous aluminum chloride, slowly adding the anhydrous aluminum chloride into 80ml of deionized water, and completely dissolving the anhydrous aluminum chloride to prepare 0.4mol/L anhydrous aluminum chloride solution; (2) weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.84g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA in batches under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2h for homogenization, finally filling the polyamic acid solution into a 20ml syringe, and preparing the polyamic acid nanofiber membrane by using an electrostatic spinning technology, wherein the specific parameters in the electrostatic spinning process are spinning voltage: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 400 rpm; receiving distance: 20 cm. Firstly, placing the prepared polyamic acid nanofiber membrane in a super clean bench, standing for 12h, then placing the polyamic acid nanofiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2h to prepare the polyimide nanofiber membrane; (3) weighing 8.98g of potassium hydroxide, dissolving the potassium hydroxide in 80ml of deionized water to prepare a 2mol/L potassium hydroxide solution, and weighing acetic acid to prepare an acetic acid solution with the mass fraction of 5%; (4) soaking the polyimide nano-fiber membrane in a potassium hydroxide solution for 1min, taking out, ultrasonically cleaning for 5min, soaking in acetic acid for 1h, taking out, ultrasonically cleaning for 30min, and obtaining the polyimide nano-fiber membrane with the surface containing carboxyl active functional groups; (5) 1ml of ammonia water is taken to prepare 0.04mol/L dilute ammonia water solution; soaking the polyimide nanofiber membrane with the surface containing the carboxyl active functional groups, which is obtained by the treatment in the step (4), in dilute ammonia water for 1h, taking out and ultrasonically cleaning for 30min to obtain the polyimide nanofiber membrane with the surface quaternized; (6) soaking the polyimide nanofiber membrane with the surface quaternized, which is obtained by the treatment in the step (5), in an anhydrous aluminum chloride solution for 1h, taking out, and ultrasonically cleaning for 30 min; (7) and (3) placing the nanofiber membrane obtained by the treatment in the step (6) in a 300 ℃ drying oven for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with the boehmite ceramic layer, wherein the diameter of the nanofiber is 345nm, the thickness of the boehmite coating layer of the nanofiber is 42nm, the tensile strength is 18.3Mpa, the contact angle of the electrolyte is 7.1 degrees, the thermal deformation temperature is 295 ℃ at 0.02N, and the porosity is 75.4 percent. The morphology of the obtained fiber membrane is shown in figure 3.

Example 4

(1) Weighing 4.17g of anhydrous aluminum chloride, slowly adding the anhydrous aluminum chloride into 80ml of deionized water, and completely dissolving the anhydrous aluminum chloride to prepare 0.4mol/L anhydrous aluminum chloride solution; (2) weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.84g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA in batches under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2h for homogenization, finally filling the polyamic acid solution into a 20ml syringe, and preparing the polyamic acid nanofiber membrane by using an electrostatic spinning technology, wherein the specific parameters in the electrostatic spinning process are spinning voltage: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 400 rpm; receiving distance: 20 cm. Firstly, placing the prepared polyamic acid nanofiber membrane in a super clean bench, standing for 12h, then placing the polyamic acid nanofiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2h to prepare the polyimide nanofiber membrane; (3) weighing 4.49g of potassium hydroxide, dissolving the potassium hydroxide in 80ml of deionized water to prepare 1mol/L potassium hydroxide solution, and then weighing acetic acid to prepare acetic acid solution with the mass fraction of 5%; (4) soaking the polyimide nano-fiber membrane in a potassium hydroxide solution for 1min, taking out, ultrasonically cleaning for 5min, soaking in acetic acid for 1h, taking out, ultrasonically cleaning for 30min, and obtaining the polyimide nano-fiber membrane with the surface containing carboxyl active functional groups; (5) 1ml of ammonia water is taken to prepare 0.04mol/L dilute ammonia water solution; soaking the polyimide nanofiber membrane with the surface containing the carboxyl active functional groups, which is obtained by the treatment in the step (4), in dilute ammonia water for 1h, taking out and ultrasonically cleaning for 30min to obtain the polyimide nanofiber membrane with the surface quaternized; (6) soaking the polyimide nanofiber membrane with the surface quaternized, obtained in the step (5), in an anhydrous aluminum chloride solution for 1h, taking out, and ultrasonically cleaning for 30 min; (7) and (3) placing the nanofiber membrane obtained by the treatment in the step (6) in a 300 ℃ oven for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with the boehmite ceramic layer, wherein the diameter of the nanofiber is 305nm, the thickness of the boehmite coating layer of the nanofiber is 31nm, the tensile strength is 38.2Mpa, the contact angle of electrolyte is 7.4 degrees, the thermal deformation temperature under 0.02N is 308 ℃, and the porosity is 77.5%. The morphology of the obtained fiber membrane is shown in figure 4.

Example 5

(1) Weighing 3.07g of anhydrous aluminum chloride, slowly adding the anhydrous aluminum chloride into 80ml of deionized water, and completely dissolving the anhydrous aluminum chloride to prepare 0.1mol/L anhydrous aluminum chloride solution; (2) weighing 2.0g of 4,4 '-diphenyl ether dianhydride (ODPA) and 1.29g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, and after completely dissolving ODA in DMF, adding ODPA in batches under the condition of ice-water bath; and after obtaining a polyamic acid solution with moderate viscosity, mechanically stirring for 2h for homogenization, finally filling the polyamic acid solution into a 20ml syringe, and preparing the polyamic acid nanofiber membrane by applying an electrostatic spinning technology, wherein the specific parameters of the electrostatic spinning process are spinning voltage: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 400 rpm; receiving distance: 20 cm. Firstly, placing the prepared polyamic acid nanofiber membrane in a super clean bench, standing for 12h, then placing the polyamic acid nanofiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2h to prepare the polyimide nanofiber membrane; (3) weighing 4.49g of potassium hydroxide, dissolving the potassium hydroxide in deionized water to prepare 1mol/L potassium hydroxide solution, and weighing acetic acid to prepare 5% acetic acid solution by mass fraction; (4) soaking the polyimide nano-fiber membrane in a potassium hydroxide solution for 1min, taking out, ultrasonically cleaning for 5min, soaking in acetic acid for 1h, taking out, ultrasonically cleaning for 30min, and obtaining the polyimide nano-fiber membrane with the surface containing carboxyl active functional groups; (5) preparing 0.04mol/L dilute ammonia solution from 1ml of ammonia water, soaking the polyimide nanofiber membrane with the surface containing the carboxyl active functional groups, which is obtained by the treatment in the step (4), in the dilute ammonia water for 1 hour, taking out and ultrasonically cleaning for 30min to obtain the polyimide nanofiber membrane with the quaternized surface; (6) soaking the polyimide nanofiber membrane with the surface quaternized, which is obtained by the treatment in the step (5), in an anhydrous aluminum chloride solution for 1h, taking out, and ultrasonically cleaning for 30 min; (7) and (3) placing the nanofiber membrane obtained by the treatment in the step (6) in an oven at 300 ℃ for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with the boehmite ceramic layer, wherein the diameter of the nanofiber is 294nm, the thickness of the boehmite coating layer of the nanofiber is 21nm, the tensile strength is 42.4Mpa, the contact angle of the electrolyte is 9.8 degrees, the thermal deformation temperature is 315 ℃ at 0.02N, and the porosity is 80.5 percent. The morphology of the obtained fiber membrane is shown in figure 5; the fibers were embedded with resin and quenched in liquid nitrogen to obtain a fiber profile as shown in FIG. 6.