CN113073426A

CN113073426A - Porous multi-hollow flexible composite nanofiber membrane material and preparation method thereof

Info

Publication number: CN113073426A
Application number: CN202110207974.7A
Authority: CN
Inventors: 张晶晶; 李光; 苏正康; 彭威; 金俊弘; 杨胜林
Original assignee: Donghua University
Current assignee: Donghua University
Priority date: 2021-02-25
Filing date: 2021-02-25
Publication date: 2021-07-06
Anticipated expiration: 2041-02-25
Also published as: CN113073426B

Abstract

The invention relates to a porous multi-hollow flexible composite nanofiber membrane material and a preparation method thereof, wherein the method comprises the steps of preparing the porous multi-hollow flexible composite nanofiber membrane through coaxial electrostatic spinning; the outer layer solution of the coaxial electrostatic spinning consists of a sacrificial high molecular polymer, a retention high molecular polymer and a solvent A; the inner layer solution of the coaxial electrostatic spinning consists of a sacrificial high molecular polymer, a material which can generate a substance with semiconductor characteristics and low surface energy in the spinning process and a solvent B; then removing the sacrificial high molecular polymer in the porous multi-hollow flexible composite nanofiber membrane to obtain a membrane material formed by stacking porous multi-hollow nanofibers, wherein the porous multi-hollow nanofibers are provided with a plurality of hollow pipelines and a three-dimensional through hole micro-nano structure from the surface to the hollow; the membrane material of the invention has better flexibility and mechanical strength, and solves the problems of easy brittleness, low mechanical strength and the like of porous composite fiber materials and single hollow fiber materials.

Description

Porous multi-hollow flexible composite nanofiber membrane material and preparation method thereof

Technical Field

The invention belongs to the technical field of nanofiber membrane materials, and relates to a porous multi-hollow flexible composite nanofiber membrane material and a preparation method thereof.

Background

In recent years, nanofiber membrane materials are widely used in the fields of new energy, sensing, filtering, seawater desalination, aerospace and the like due to large specific surface area, high porosity and three-dimensional network structures. Chinese patent CN101445963A discloses a method for preparing superfine polymer fiber by wet electrostatic spinning technology, the fiber diameter can be controlled in nanometer to micron level. Designing synthetic porous fibers can increase the specific surface area of the fibers. Chinese patent CN103225135A is to prepare a porous carbon fiber by spinning a spinning solution composed of pore-forming agent calcium carbonate, high molecular polymer and solvent, then carbonizing and pickling. The specific surface area of the fiber can be further improved by designing the hollow cavity in the fiber, and the fiber has higher heat transfer and mass transfer coefficients due to the axial tubular hollow cavity structure of the fiber, so that the fiber has higher application prospect. However, the single hollow fiber membrane is often broken due to the low mechanical strength of the single hollow structure during use, so that the service life of the membrane is reduced. Therefore, it is of great significance to develop a porous multi-hollow flexible composite nanofiber membrane having high mechanical strength, high porosity, large specific surface area and a hierarchical pore structure.

The porous multi-hollow flexible composite nanofiber membrane has high application potential in the field of new energy. The lithium metal negative electrode has extremely high theoretical specific capacity (38)60mAhg^-1) Lower redox potential (-3.04V vs standard hydrogen electrode) and lower weight density (0.534g cm)^-1) And have been extensively studied. However, its practical application is severely limited by problems of volume expansion, solid electrolyte interface film (SEI film) cracking and lithium dendrite growth during cycling, and consequent reduction in coulombic efficiency, electrode pulverization and even battery short-circuiting. Constructing a lithium metal composite electrode by designing a functional three-dimensional host structure is an effective method for stabilizing a lithium metal negative electrode. The porous multi-hollow flexible composite nanofiber membrane is considered as a three-dimensional host material with great prospect due to excellent chemical and electrochemical stability, high mechanical strength and adjustable nanostructure. On one hand, the special porous multi-hollow pipeline increases nucleation centers during the reduction reaction of lithium ions and reduces the local current density of the electrode; on the other hand, a continuous channel is provided for ion transfer, and ion flow is homogenized; while the multiple internal hollow spaces limit the expansion of lithium; and the high pore volume can also provide enough space for electrolyte permeation, thereby improving the coulombic efficiency, the cycle performance and the safety of the lithium metal cathode.

From the metal deposition mechanism, the deposition of lithium is closely related to the matrix. The properties of the matrix directly influence the deposition state of lithium ions. The growth of lithium dendrites cannot be completely inhibited only by depending on different pore structures of the nanofiber material, and metal oxides such as titanium dioxide, tin oxide or zinc oxide are taken as suitable lithium-philic nucleation sites, so that the over potential of lithium nucleation can be effectively reduced, and the formation of dendrites is avoided. Therefore, the lithium-philic metal oxide is compounded with the three-dimensional nanofiber, so that the lithium-philic metal oxide has important application value. As described in the prior art, chinese patent CN101250811 discloses a method for preparing a titanium dioxide coating on the surface of carbon fiber. The patent uses titanium dioxide precursor solution to impregnate carbon fiber, and forms a titanium dioxide coating through subsequent volatilization and sintering. The titanium dioxide coating prepared by the method has poor adhesion with a carbon fiber substrate, so that the long-term service performance is reduced. Chinese patent CN104452268A discloses a method for preparing a fiber composite material loaded with titanium dioxide nanoparticles, but the method has a small titanium dioxide loading (4.5%). Chinese patent CN109346690A prepares carbon fiber in advance, and attaches zinc oxide on the surface of the carbon fiber through hydrothermal reaction to be used as the lithium ion battery cathode material, but the adhesion of the zinc oxide and the carbon fiber is poor. Chinese patent CN104436863A discloses a nano-copper-zinc oxide PTFE fiber air filter material, wherein the material has a small zinc oxide loading amount, and the weight ratio of the nano-copper-zinc oxide PTFE fiber air filter material to a membrane material is 0.0003: 1.7005.

Therefore, in the prior art, the metal oxide nanoparticles are directly mixed with the fiber material, and the problems of uneven dispersion of the nanoparticles, low loading capacity, poor adhesion with the fiber or brittleness of the fiber still exist.

Disclosure of Invention

The technical problem to be solved by the invention is to overcome the defects in the prior art and provide a porous multi-hollow flexible composite nanofiber membrane. The porous multi-hollow flexible composite nanofiber membrane material is an ideal lithium metal carrier and/or protective layer material. The three-dimensional porous hollow structure and the hierarchical structure with the lithium-philic phase are beneficial to the rapid diffusion and uniform deposition of lithium ions and the buffer volume expansion, thereby effectively inhibiting the growth of lithium dendrites and obviously improving the cycle stability, the coulombic efficiency and the safety of the lithium dendrites. The material can also be used in the technical fields of lithium ion batteries, solid lithium ion batteries, lithium sulfur batteries, metal air batteries, solar batteries, optical catalysis, filtration, membrane separation and the like.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the porous multi-hollow flexible composite nanofiber membrane material is formed by stacking porous multi-hollow nanofibers; the porous multi-hollow nanofiber refers to a nanofiber which is provided with a plurality of hollow pipelines and a three-dimensional through hole micro-nano structure from the surface to the hollow.

As a preferred technical scheme:

the porous multi-hollow flexible composite nanofiber membrane material is characterized in that the fibers inside the fiber membrane are stacked layer by layer to form a three-dimensional interpenetrating network and a stacked pore structure.

The porous multi-hollow flexible composite nanofiber membrane material has the advantages that the average diameter of the porous multi-hollow nanofibers is 100-1000 nm, the fiber walls have a porous structure, and the pore diameter is 5-200 nm.

According to the porous multi-hollow flexible composite nanofiber membrane material, the multi-hollow pipelines of the porous multi-hollow nanofibers refer to 2-15 hollow pipelines, and the diameters of the hollow pipelines are 10-150 nm.

In the porous multi-hollow flexible composite nanofiber membrane material, the three-dimensional through hole is a through hole structure which connects the hollow part inside the fiber and the three-dimensional stacked holes between the fibers through the holes on the fiber wall.

The porous multi-hollow flexible composite nanofiber membrane material comprises the porous multi-hollow nanofibers made of a single material or the porous multi-hollow nanofibers made of more than two different materials; the porous hollow nanofibers are made of carbon materials and/or polymer materials.

The porous multi-hollow flexible composite nanofiber membrane material has a young's modulus of 1GPa to 20 GPa.

The invention also provides a preparation method of the porous multi-hollow flexible composite nanofiber membrane material, which is used for preparing the porous multi-hollow flexible composite nanofiber membrane through coaxial electrostatic spinning; the outer layer solution of the coaxial electrostatic spinning consists of a sacrificial high molecular polymer, a retention high molecular polymer and a solvent A; the inner layer solution of the coaxial electrostatic spinning consists of a sacrificial high molecular polymer, a material which can generate a substance with semiconductor characteristics and low surface energy in the spinning process and a solvent B; and then removing the sacrificial high molecular polymer in the porous multi-hollow flexible composite nanofiber membrane to obtain the porous multi-hollow flexible composite nanofiber membrane material.

As a preferred technical scheme:

in the above-mentioned preparation method, the sacrificial polymer and the retention polymer are the sacrificial polymers that can be removed by retaining the retention polymer under a certain treatment condition.

According to the preparation method, in the coaxial electrostatic spinning inner layer solution, the molar ratio of a material capable of generating a substance with semiconductor characteristics and low surface energy to the sacrificial high polymer in the spinning process is 1-5000: 1; the mass ratio of the sacrificial high-molecular polymer to the solvent B is 20-50: 100; in the coaxial electrostatic spinning outer layer solution, the mass ratio of the retention type high molecular polymer to the sacrificial type high molecular polymer to the solvent A is 8-13: 2-7: 100.

In the above preparation method, the sacrificial polymer is at least one of polymethyl methacrylate, polyvinylpyrrolidone, polyethylene oxide, polyethylene glycol and polystyrene.

In the preparation method, the retention type high molecular polymer is more than one of polyacrylonitrile, phenolic resin and cellulose.

In the preparation method, the solvent A or the solvent B is more than one of N, N-dimethylformamide, N-dimethylacetamide, tetrahydrofuran and ethanol.

In the preparation method, more than one material which can generate substances with both semiconductor characteristics and low surface energy is used as a metal source in the spinning process; the metal source is a titanium source, a zinc source and a tin source; the titanium source is tetrabutyl titanate, isopropyl titanate, tetraethyl titanate or titanium tetrachloride; the zinc source is zinc acetate, zinc nitrate or zinc chloride; the tin source is tin acetate, tin tetrachloride, stannous chloride, tin hydroxide, stannous sulfate or stannous oxalate.

The preparation method comprises the following steps: dissolving the sacrificial high molecular polymer in the solvent B at 15-60 ℃, stirring for 2-12 h, then adding a metal source, stirring for 0.5-12 h, and uniformly mixing; the preparation method of the coaxial electrostatic spinning outer layer solution comprises the following steps: dissolving a sacrificial high-molecular polymer and a retention high-molecular polymer in a solvent A at 15-60 ℃, stirring for 2-12 h, and uniformly mixing; the flow rate ratio of the inner layer solution to the outer layer solution of the coaxial electrostatic spinning is 1 (1-5), and the total liquid supply flow rate is 0.3-6 mL/h; the distance between the needle head and the receiving plate is 10-30 cm; the voltage is 1-40 kV; the ambient temperature is 10-50 ℃; the environmental humidity is 20-80%; the receiving device is a metal roller, and the rotating speed of the roller is 20-100 r/min.

The preparation method as described above, wherein the certain treatment condition is carbonization or solvent soaking.

According to the preparation method, in the carbonization process, the pre-oxidation temperature is 200-300 ℃, and the time is 0.5-2.5 h; the temperature of the carbonization treatment is 450-1000 ℃, and the time is 1-5 h.

In the preparation method, in the solvent soaking process, the solvent C is one or more of high-purity water, methanol, ethanol, propanol, butanol, cyclohexanol, chloroform, dichloromethane, propylene glycol, butanediol, glycerol, triethanolamine, acetic acid and carbonate, the soaking time is 1-24 h, and the soaked nanofibers are washed 3-5 times by the solvent C.

The principle of the invention is as follows:

the porous multi-hollow flexible composite nanofiber membrane material prepared by utilizing the coaxial electrostatic spinning technology has the advantages of controllable appearance, structure, mechanical strength, oxide content and the like. During spinning, the metal source is dispersed homogeneously in the spinning solution of high molecular polymer and hydrolyzed slowly into metal oxide grains of relatively small size, such as titania, tin oxide and zinc oxide. Since these metal oxides have low surface energy, they are uniformly diffused in the inner spinning solution. Meanwhile, based on the semiconductor characteristics of the metal oxide nanoparticles, the metal oxide nanoparticles can directionally migrate along the axial direction of the fiber under the action of an electric field, so that the metal oxide nanoparticles are directionally assembled in the polymer fiber. The metal oxide loading with different loading amounts can be realized by regulating the content of the metal source in the spinning solution. Through subsequent carbonization or solvent soaking, in the inner layer solution of electrostatic spinning, the sacrificial high molecular polymer is completely removed, and a multi-hollow structure is left; in the solution of the electrostatic spinning outer layer, the sacrificial high molecular polymer is completely removed, so that a through hole structure which is hollow inside the connection structure is generated. The metal oxide is generated in situ in the fiber and forms a continuous framework along the axial direction of the fiber, so that the metal oxide has better viscosity with the fiber, and the flexibility and the mechanical strength of the fiber are improved.

Advantageous effects

(1) The porous multi-hollow flexible composite nanofiber membrane material disclosed by the invention has better flexibility and mechanical strength, and solves the problems that a porous composite fiber material and a single hollow fiber material are fragile and low in mechanical strength and the like;

(2) the porous multi-hollow flexible composite nanofiber membrane material not only ensures a larger specific surface area, but also has rich multi-stage pore structures, so that the material has a wide practical application value;

(3) the porous multi-hollow flexible composite nanofiber membrane material is an ideal lithium metal carrier and/or protective layer material. Because the metal oxides of titanium dioxide, tin oxide and zinc oxide have better lithium affinity, a hierarchical structure with unique lithium affinity nucleation sites can be constructed in the composite nanofiber by utilizing rich hierarchical pore structures, and uniform nucleation and deposition of lithium metal are facilitated; moreover, the flexibility and the mechanical strength of the porous multi-hollow flexible composite nanofiber membrane material inhibit the growth of lithium dendrites and potential safety hazards caused by the growth of the lithium dendrites; therefore, the porous multi-hollow composite nanofiber membrane prepared by the method can effectively improve the cycle stability, coulombic efficiency and safety of the lithium metal battery;

(4) the porous multi-hollow flexible composite nanofiber membrane material is a very potential lithium ion battery cathode material. The smaller metal oxide nanoparticles shorten the transmission path of lithium ions, and are beneficial to the rapid de-intercalation of the lithium ions; the one-dimensional multi-hollow fiber substrate and the abundant pore structure are also beneficial to the infiltration of electrolyte, the diffusion of lithium ions and the volume expansion of the buffer material in the charge and discharge processes;

(5) the porous multi-hollow flexible composite nanofiber membrane material can be used in the technical fields of membrane separation and the like, such as wastewater treatment; compared with a single hollow fiber ultrafiltration membrane, the single hollow fiber ultrafiltration membrane has the advantages that the phenomenon of filament breakage caused by low strength of the single hollow membrane is easily caused under the impact of multiple water flow turbulence and water pressure, the high-strength multi-hollow fiber membrane disclosed by the invention can prolong the service life of the membrane, and meanwhile, the abundant and uniform pore structure can ensure that water flow is uniformly distributed without dead angles, and the pollution resistance is good;

(6) the preparation method of the porous multi-hollow flexible composite nanofiber membrane material has the advantages that the used electrostatic spinning technical equipment is simple, the cost is low, and more spinnable raw materials are available;

(7) according to the preparation method of the porous multi-hollow flexible composite nanofiber membrane material, the carbonization temperature and the carbonization time for preparing the porous multi-hollow flexible carbon composite nanofiber membrane material are low; the porous multi-hollow flexible polymer composite nanofiber membrane material is prepared by soaking and removing the sacrificial high molecular polymer by utilizing the characteristic that the sacrificial high molecular polymer is dissolved in some solvents, and the process is simple;

(8) according to the preparation method of the porous multi-hollow flexible composite nanofiber membrane material, the content of the metal oxide in the porous multi-hollow flexible composite nanofiber membrane material is controllable, the dispersion is easy, and the large-scale production potential is high.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) image of a porous multi-hollow flexible composite nanofiber prepared in examples 1-7;

FIG. 2 is a Transmission Electron Microscope (TEM) image of the porous multi-hollow flexible composite nanofiber prepared in examples 1-6;

FIG. 3 is a high power transmission electron micrograph (HRTEM) of the porous multi-hollow flexible composite nanofiber prepared in example 7;

FIG. 4 is a thermogravimetric plot (TGA) of the porous multi-hollow flexible composite nanofiber prepared in example 6;

FIG. 5 is a thermogravimetric plot (TGA) of the porous multi-hollow flexible composite nanofiber prepared in example 7;

fig. 6 is a nitrogen adsorption and desorption curve (left) and a pore size distribution curve (right) of the porous multi-hollow flexible composite nanofiber prepared in example 6;

FIG. 7 is a first lithium deposition curve of a porous multi-hollow flexible composite nanofiber prepared in example 6;

fig. 8 is a cycle performance diagram of a symmetric battery assembled by the porous multi-hollow flexible composite nanofiber prepared in example 6 and loaded with lithium metal.

Detailed Description

The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

A preparation method of a porous multi-hollow flexible composite nanofiber membrane material comprises the following specific steps:

(1) preparing an outer layer solution of coaxial electrostatic spinning and an inner layer solution of coaxial electrostatic spinning;

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and polyacrylonitrile in N, N-dimethylformamide at 42 ℃, stirring for 6 hours, and uniformly mixing; wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate to N, N-dimethylformamide is 8:2: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylformamide at 36 ℃, stirring for 5 hours, then adding tetrabutyl titanate, stirring for 0.5 hour, and uniformly mixing; the molar ratio of tetrabutyl titanate to polymethyl methacrylate is 48: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylformamide is 20: 100;

(2) pouring the outer layer solution of the coaxial electrostatic spinning and the inner layer solution of the coaxial electrostatic spinning into a disposable syringe with the capacity of 10mL, placing the disposable syringe in a propulsion pump, and carrying out coaxial electrostatic spinning to prepare a porous multi-hollow flexible composite nanofiber membrane;

wherein in the electrostatic spinning process, the flow rate ratio of the inner layer solution to the outer layer solution in coaxial electrostatic spinning is 1:1, and the total liquid supply flow rate is 6 mL/h; the distance between the needle head and the receiving plate is 30 cm; the voltage is 40 kV; the ambient temperature is 50 ℃; the environmental humidity is 20%; the receiving device is a metal roller, and the rotating speed of the roller is 100 r/min.

(3) Removing polymethyl methacrylate in the porous multi-hollow flexible composite nanofiber membrane through a carbonization process to obtain a porous multi-hollow flexible composite nanofiber membrane material; wherein the pre-oxidation temperature is 280 ℃ and the time is 0.5 h; the temperature of the carbonization treatment is 700 ℃ and the time is 2 h.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 2GPa, the porous multi-hollow nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers (a scanning electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 1(a), and a transmission electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 2 (a)), and a three-dimensional interpenetrating network and a stacking pore structure are formed; wherein the porous hollow nanofibers are made of carbon materials, the average diameter is 580nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 2

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and polyacrylonitrile in N, N-dimethylformamide at 25 ℃, stirring for 12h, and uniformly mixing; wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate to N, N-dimethylformamide is 11:5: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylformamide at 25 ℃, stirring for 12 hours, then adding tetrabutyl titanate, stirring for 2 hours, and uniformly mixing; the molar ratio of tetrabutyl titanate to polymethyl methacrylate is 95: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylformamide is 28: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 3:5, and the total liquid supply flow rate is 0.8 mL/h; the distance between the needle head and the receiving plate is 15 cm; the voltage is 21 kV; the ambient temperature is 20 ℃; the environmental humidity is 30%; the receiving device is a metal roller, and the rotating speed of the roller is 50 r/min.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 3GPa, the porous multi-hollow nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers (a scanning electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 1(b), and a transmission electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 2 (b)), and a three-dimensional interpenetrating network and a stacking pore structure are formed; wherein the porous hollow nanofibers are made of carbon materials, the average diameter is 470nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 3

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and polyacrylonitrile in N, N-dimethylformamide at 15 ℃, stirring for 12h, and uniformly mixing; wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate to N, N-dimethylformamide is 9:3: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylformamide at 52 ℃, stirring for 3 hours, then adding tetrabutyl titanate, stirring for 1 hour, and uniformly mixing; the molar ratio of tetrabutyl titanate to polymethyl methacrylate is 191: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylformamide is 22: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the inner layer solution to the outer layer solution in coaxial electrostatic spinning is 1:3, and the total liquid supply flow rate is 4 mL/h; the distance between the needle head and the receiving plate is 17 cm; the voltage is 15 kV; the ambient temperature is 44 ℃; the ambient humidity is 23%; the receiving device is a metal roller, and the rotating speed of the roller is 36 r/min.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 5GPa, the porous multi-hollow nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers (a scanning electron microscope image of the porous multi-hollow flexible composite nanofiber membrane material is shown in figure 1(c), and a transmission electron microscope image of the porous multi-hollow flexible composite nanofiber membrane material is shown in figure 2 (c)), and a three-dimensional interpenetrating network and a stacking pore structure are formed; wherein the porous hollow nanofibers are made of carbon materials, the average diameter is 420nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 4

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and polyacrylonitrile in N, N-dimethylformamide at 26 ℃, stirring for 10 hours, and uniformly mixing; wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate to N, N-dimethylformamide is 10:4: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylformamide at 15 ℃, stirring for 12 hours, then adding tetrabutyl titanate, stirring for 4 hours, and uniformly mixing; the molar ratio of tetrabutyl titanate to polymethyl methacrylate is 477: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylformamide is 27: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:4, and the total liquid supply flow rate is 2.5 mL/h; the distance between the needle head and the receiving plate is 10 cm; the voltage is 1 kV; the ambient temperature is 31 ℃; the ambient humidity is 27%; the receiving device is a metal roller, and the rotating speed of the roller is 20 r/min.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 6.5GPa, the porous multi-hollow nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers (a scanning electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 1(d), and a transmission electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 2 (d)), and a three-dimensional interpenetrating network and a stacked pore structure are formed; wherein the porous hollow nanofibers are made of carbon materials, the average diameter of the porous hollow nanofibers is 370nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 5

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and polyacrylonitrile in N, N-dimethylformamide at 31 ℃, stirring for 8 hours, and uniformly mixing; wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate to N, N-dimethylformamide is 11:5: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylformamide at 22 ℃, stirring for 9 hours, then adding tetrabutyl titanate, stirring for 12 hours, and uniformly mixing; the molar ratio of tetrabutyl titanate to polymethyl methacrylate is 955: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylformamide is 28: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:5, and the total liquid supply flow rate is 0.8 mL/h; the distance between the needle head and the receiving plate is 22 cm; the voltage is 35 kV; the ambient temperature is 20 ℃; the environmental humidity is 30%; the receiving device is a metal roller, and the rotating speed of the roller is 80 r/min.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 8GPa, the porous multi-hollow nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers (a scanning electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 1(e), and a transmission electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 2 (e)), and a three-dimensional interpenetrating network and a stacking pore structure are formed; wherein the porous multi-hollow nano-fiber is made of a carbon material, the average diameter is 340nm, and the fiber wall has a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 6

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and polyacrylonitrile in N, N-dimethylformamide at 55 ℃, stirring for 3h, and uniformly mixing; wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate to N, N-dimethylformamide is 12:6: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylformamide at 28 ℃, stirring for 7 hours, then adding tetrabutyl titanate, stirring for 7 hours, and uniformly mixing; the molar ratio of tetrabutyl titanate to polymethyl methacrylate is 1910: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylformamide is 38: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:4, and the total liquid supply flow rate is 0.5 mL/h; the distance between the needle head and the receiving plate is 27 cm; the voltage is 28 kV; the ambient temperature is 16 ℃; ambient humidity 66%; the receiving device is a metal roller, and the rotating speed of the roller is 60 r/min.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 11GPa, the porous multi-hollow nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers (a scanning electron microscope image of the porous multi-hollow flexible composite nanofiber membrane material is shown in figures 1(f) and (g), and a transmission electron microscope image of the porous multi-hollow nanofiber membrane material is shown in figure 2 (f)), and a three-dimensional interpenetrating network and a stacked pore structure are formed; wherein the porous multi-hollow nano-fiber is made of a carbon material, the average diameter is 280nm, and the fiber wall has a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part in the fiber and the three-dimensional stacking hole between the fibers through the holes on the fiber wall; thermogravimetric test is carried out on the prepared porous multi-hollow flexible composite nanofiber membrane material, and as can be seen from fig. 4, the content of titanium dioxide in the porous multi-hollow flexible composite nanofiber is 38.3%. Carrying out nitrogen adsorption and desorption experiments on the prepared porous multi-hollow flexible composite nanofiber; the porous multi-hollow titanium dioxide-carbon composite nano-fiber in the figure 6 has larger specific surface area (75.2 m)²A/g) and a hierarchical pore structure with sizes of 2, 4 and 26 nm;

the porous multi-hollow flexible composite nanofiber membrane material prepared in example 6 was subjected to a lithium deposition experiment, and the test method was: cutting porous multi-hollow flexible composite nano-fiber membrane material into circular sheets with the diameter of 12mmCR2025 coin cells were assembled in an argon-filled glove box (mikelonavirilial) using an electrolyte of 1M LiTFSI in dimethyl ether (DME) and 1, 3-Dioxolane (DOL) (volume ratio 1:1), a separator of PE membrane (Celgard 2400), and a counter electrode of lithium metal. Meanwhile, a symmetrical battery was assembled with metallic lithium as a working electrode and a counter electrode as a comparative sample. Constant current discharge tests were performed at 25 ℃ on a LAND cell test system (CT 2007A, Wuhan Lantian Corp.) to evaluate lithium nucleation overpotential. For the discharge (lithium deposition) process, the current density was 1mA/cm²The discharge time was 5 h. Fig. 7 is a first lithium deposition curve of the porous multi-hollow flexible composite nanofiber membrane material and lithium metal prepared in example 6. As can be seen from fig. 7, the lithium nucleation overpotential of the porous multi-hollow flexible composite nanofiber membrane material is significantly reduced to 50.2mV relative to metallic lithium.

After the porous multi-hollow flexible composite nanofiber membrane material prepared in example 6 is loaded with lithium metal, the porous multi-hollow flexible composite nanofiber membrane material and the lithium metal are assembled into a symmetric battery, and then the cycle performance of the symmetric battery is tested, wherein the test method comprises the following steps: the porous multi-hollow flexible composite nanofiber membrane material was cut into disks with a diameter of 12mm, CR2025 coin cells were assembled in an argon filled glove box (michananovial) using an electrolyte of 1M LiTFSI containing dimethyl ether (DME) and 1, 3-Dioxolane (DOL) (volume ratio 1:1), the separator was a PE membrane (Celgard 2400), and the counter electrode was lithium metal. Meanwhile, a symmetrical battery was assembled with metallic lithium as a working electrode and a counter electrode as a comparative sample. The test was performed on a LAND cell test system (CT 2007A, Wuhan Lantian, Inc.) at 25 ℃. First, at 1mA/cm²Is discharged for 5h at a current density of 1mA/cm²The charge and discharge were carried out at the current density of (1) for 1 hour. Fig. 8 is a cycle performance diagram of a symmetric battery assembled by the porous multi-hollow flexible composite nanofiber membrane material prepared in example 6 and loaded with lithium metal. As can be seen from fig. 8, compared with lithium metal, the cycle stability of the porous multi-hollow flexible composite nanofiber membrane material is significantly improved, and the material can stably cycle for 900 hours after lithium is loaded.

In conclusion, the porous multi-hollow flexible composite nanofiber is an ideal lithium metal carrier, and compared with metal lithium, the lithium nucleation overpotential of the porous multi-hollow flexible composite nanofiber is obviously reduced, so that the metal lithium can be rapidly and uniformly deposited. The symmetrical battery assembled after lithium loading has better charge-discharge cycling stability, and the charge-discharge overpotential is not obviously increased after 900 hours of cycling.

Example 7

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and polyacrylonitrile in N, N-dimethylformamide at 60 ℃, stirring for 2h, and uniformly mixing; wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate to N, N-dimethylformamide is 13:7: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylformamide at 60 ℃, stirring for 2 hours, then adding tetrabutyl titanate, stirring for 6 hours, and uniformly mixing; the molar ratio of tetrabutyl titanate to polymethyl methacrylate is 2592: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylformamide is 50: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:3, and the total liquid supply flow rate is 0.3 mL/h; the distance between the needle head and the receiving plate is 25 cm; the voltage is 18 kV; the ambient temperature is 10 ℃; the environmental humidity is 80%; the receiving device is a metal roller, and the rotating speed of the roller is 45 r/min.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 12GPa, the porous multi-hollow nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers (a scanning electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 1(h), and a high-power transmission electron microscope image of the porous multi-hollow flexible composite nanofiber membrane is shown in figure 3), and a three-dimensional interpenetrating network and a stacking pore structure are formed; as can be seen from fig. 3, the lattice of titanium dioxide nanoparticles (shown in the circle in the figure) is visible inside the fiber, and the high loading of titanium dioxide nanoparticles is uniformly dispersed; wherein the porous multi-hollow nano-fiber is made of a carbon material, the average diameter is 210nm, and the fiber wall has a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part in the fiber and the three-dimensional stacking hole between the fibers through the holes on the fiber wall; thermogravimetric test is carried out on the prepared porous multi-hollow flexible composite nanofiber membrane material, and as can be seen from fig. 5, the content of titanium dioxide in the porous multi-hollow flexible composite nanofiber in fig. 5 is 47.2%.

Example 8

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and polyacrylonitrile in N, N-dimethylformamide at 15 ℃, stirring for 12h, and uniformly mixing; wherein the mass ratio of polyacrylonitrile to polymethyl methacrylate to N, N-dimethylformamide is 8:2: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylformamide at 15 ℃, stirring for 12h, then adding isopropyl titanate, stirring for 0.5h, and uniformly mixing; the molar ratio of isopropyl titanate to polymethyl methacrylate is 1: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylformamide is 20: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the inner layer solution to the outer layer solution in coaxial electrostatic spinning is 1:1, and the total liquid supply flow rate is 6 mL/h; the distance between the needle head and the receiving plate is 30 cm; the voltage is 40 kV; the ambient temperature is 50 ℃; the environmental humidity is 20%; the receiving device is a metal roller, and the rotating speed of the roller is 20 r/min.

(3) Removing polymethyl methacrylate in the porous multi-hollow flexible composite nanofiber membrane through a carbonization process to obtain a porous multi-hollow flexible composite nanofiber membrane material; in the carbonization process, the pre-oxidation temperature is 200 ℃ and the time is 2.5 h; the temperature of the carbonization treatment is 450 ℃ and the time is 5 h.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 1GPa, the porous multi-hollow flexible composite nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers, and a three-dimensional interpenetrating network and a stacked pore structure are formed; wherein the porous hollow nanofibers are made of carbon materials, the average diameter of the porous hollow nanofibers is 700nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 9

preparation of outer layer solution for coaxial electrospinning: dissolving polyvinylpyrrolidone and phenolic resin in ethanol at 23 ℃, stirring for 11h, and mixing uniformly; wherein the mass ratio of the phenolic resin to the polyvinylpyrrolidone to the ethanol is 9:3: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polyethylene glycol in ethanol at 23 ℃, stirring for 10h, then adding tetraethyl titanate, stirring for 1h, and mixing uniformly; the molar ratio of tetraethyl titanate to polyethylene glycol is 500: 1; the mass ratio of the polyethylene glycol to the ethanol is 22: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:5, and the total liquid supply flow rate is 4 mL/h; the distance between the needle head and the receiving plate is 17 cm; the voltage is 15 kV; the ambient temperature is 44 ℃; the ambient humidity is 23%; the receiving device is a metal roller, and the rotating speed of the roller is 37 r/min.

(3) Removing polyvinylpyrrolidone and polyethylene glycol in the porous multi-hollow flexible composite nanofiber membrane by a carbonization process to obtain a porous multi-hollow flexible composite nanofiber membrane material; wherein in the carbonization process, the pre-oxidation temperature is 300 ℃ and the time is 0.5 h; the temperature of the carbonization treatment is 1000 ℃ and the time is 1 h.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 6.6GPa, the material is formed by stacking porous multi-hollow nanofiber layers, and a three-dimensional interpenetrating network and a stacking pore structure are formed; wherein the porous hollow nanofibers are made of carbon materials, the average diameter of the porous hollow nanofibers is 380nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 10

preparation of outer layer solution for coaxial electrospinning: dissolving polystyrene and cellulose in tetrahydrofuran at 29 ℃, stirring for 9 hours, and uniformly mixing; wherein the mass ratio of the cellulose to the polystyrene to the tetrahydrofuran is 10:4: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polystyrene in tetrahydrofuran at 29 ℃, stirring for 8 hours, then adding titanium tetrachloride, stirring for 2 hours, and uniformly mixing; the molar ratio of titanium tetrachloride to polystyrene is 1000: 1; the mass ratio of the polystyrene to the tetrahydrofuran is 27: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:2, and the total liquid supply flow rate is 2.5 mL/h; the distance between the needle head and the receiving plate is 10 cm; the voltage is 1 kV; the ambient temperature is 31 ℃; the ambient humidity is 27%; the receiving device is a metal roller, and the rotating speed of the roller is 41 r/min.

(3) Removing polystyrene in the porous multi-hollow flexible composite nanofiber membrane through a carbonization process to obtain a porous multi-hollow flexible composite nanofiber membrane material;

wherein in the carbonization process, the pre-oxidation temperature is 250 ℃ and the time is 1.5 h; the temperature of the carbonization treatment is 670 ℃ and the time is 3 h.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 8.2GPa, the membrane material is formed by stacking porous multi-hollow nanofiber layers, and a three-dimensional interpenetrating network and a stacking pore structure are formed; wherein the porous multi-hollow nano-fiber is made of a carbon material, the average diameter is 340nm, and the fiber wall has a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 11

preparation of outer layer solution for coaxial electrospinning: dissolving polyvinylpyrrolidone and polyacrylonitrile in N, N-dimethylformamide at 36 deg.C, stirring for 8 hr, and mixing; wherein the mass ratio of polyacrylonitrile, polyvinylpyrrolidone and N, N-dimethylformamide is 11:5: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polyvinylpyrrolidone in N, N-dimethylformamide at 36 deg.C, stirring for 7 hr, adding zinc acetate, stirring for 4 hr, and mixing; the molar ratio of zinc acetate to polyvinylpyrrolidone is 2200: 1; the mass ratio of the polyvinylpyrrolidone to the N, N-dimethylformamide is 28: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:3, and the total liquid supply flow rate is 0.8 mL/h; the distance between the needle head and the receiving plate is 22 cm; the voltage is 35 kV; the ambient temperature is 20 ℃; the environmental humidity is 30%; the receiving device is a metal roller, and the rotating speed of the roller is 55 r/min.

(3) Removing polyvinylpyrrolidone in the porous multi-hollow flexible composite nanofiber membrane by a solvent soaking process to obtain a porous multi-hollow flexible composite nanofiber membrane material;

in the solvent soaking process, the solvent is high-purity water, the soaking time is 1h, and the soaked nano fibers are washed for 5 times by the solvent.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 11.7GPa, the material is formed by stacking porous multi-hollow nanofiber layers, and a three-dimensional interpenetrating network and a stacking pore structure are formed; wherein the porous hollow nanofibers are made of polymer materials, the average diameter is 260nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-150 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 12

preparation of outer layer solution for coaxial electrospinning: dissolving polymethyl methacrylate and phenolic resin in N, N-dimethylacetamide at 44 ℃, stirring for 5h, and mixing uniformly; wherein the mass ratio of the phenolic resin to the polymethyl methacrylate to the N, N-dimethylacetamide is 12:6: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polymethyl methacrylate in N, N-dimethylacetamide at 44 ℃, stirring for 5 hours, then adding zinc nitrate, stirring for 6 hours, and uniformly mixing; the molar ratio of zinc nitrate to polymethyl methacrylate is 3000: 1; the mass ratio of the polymethyl methacrylate to the N, N-dimethylacetamide is 38: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:4, and the total liquid supply flow rate is 0.5 mL/h; the distance between the needle head and the receiving plate is 27 cm; the voltage is 28 kV; the ambient temperature is 16 ℃; ambient humidity 66%; the receiving device is a metal roller, and the rotating speed of the roller is 63 r/min.

(3) Removing polymethyl methacrylate in the porous multi-hollow flexible composite nanofiber membrane by a solvent soaking process to obtain a porous multi-hollow flexible composite nanofiber membrane material;

in the solvent soaking process, the solvent is carbonic ester, the soaking time is 24 hours, and the soaked nano-fibers are washed for 3 times by the solvent.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 14GPa, the porous multi-hollow flexible composite nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers, and a three-dimensional interpenetrating network and a stacked pore structure are formed; wherein the porous hollow nanofibers are made of polymer materials, the average diameter of the porous hollow nanofibers is 180nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-110 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 13

preparation of outer layer solution for coaxial electrospinning: dissolving polyoxyethylene and cellulose in tetrahydrofuran at 50 ℃, stirring for 4h, and uniformly mixing; wherein the mass ratio of the cellulose to the polyoxyethylene to the tetrahydrofuran is 13:7: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polyoxyethylene in tetrahydrofuran at 50 ℃, stirring for 4 hours, then adding zinc chloride, stirring for 8 hours, and uniformly mixing; the molar ratio of zinc chloride to polyethylene oxide is 3500: 1; the mass ratio of polyoxyethylene to tetrahydrofuran is 50: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution at the inner layer and the solution at the outer layer of the coaxial electrostatic spinning is 1:2, and the total liquid supply flow rate is 0.3 mL/h; the distance between the needle head and the receiving plate is 25 cm; the voltage is 18 kV; the ambient temperature is 10 ℃; the environmental humidity is 80%; the receiving device is a metal roller, and the rotating speed of the roller is 75 r/min.

(3) Removing polyoxyethylene in the porous multi-hollow flexible composite nanofiber membrane by a solvent soaking process to obtain a porous multi-hollow flexible composite nanofiber membrane material;

in the solvent soaking process, the solvent is high-purity water, the soaking time is 15 hours, and the soaked nano fibers are washed for 5 times by the solvent.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 16GPa, the porous multi-hollow flexible composite nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers, and a three-dimensional interpenetrating network and a stacked pore structure are formed; wherein the porous hollow nanofibers are made of polymer materials, the average diameter is 150nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-80 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 14

preparation of outer layer solution for coaxial electrospinning: dissolving polyethylene glycol and cellulose in N, N-dimethylformamide at 53 ℃, stirring for 3h, and mixing uniformly; wherein the mass ratio of the cellulose to the polyethylene glycol to the N, N-dimethylformamide is 9:3: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving polyethylene glycol in N, N-dimethylformamide at 53 deg.C, stirring for 3 hr, adding tin acetate, stirring for 12 hr, and mixing; the molar ratio of the tin acetate to the polyethylene glycol is 4000: 1; the mass ratio of the polyethylene glycol to the N, N-dimethylformamide is 22: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the inner layer solution to the outer layer solution in coaxial electrostatic spinning is 1:4, and the total liquid supply flow rate is 4 mL/h; the distance between the needle head and the receiving plate is 17 cm; the voltage is 15 kV; the ambient temperature is 44 ℃; the ambient humidity is 23%; the receiving device is a metal roller, and the rotating speed of the roller is 89 r/min.

(3) Removing polyethylene glycol in the porous multi-hollow flexible composite nanofiber membrane by a solvent soaking process to obtain a porous multi-hollow flexible composite nanofiber membrane material;

in the solvent soaking process, the solvent is ethanol, the soaking time is 10 hours, and the soaked nano-fibers are washed by the solvent for 4 times.

The prepared porous multi-hollow flexible composite nanofiber membrane material has the Young modulus of 18GPa, is formed by stacking porous multi-hollow nanofiber layers, and forms a three-dimensional interpenetrating network and a stacked pore structure; wherein the porous hollow nanofibers are made of polymer materials, the average diameter is 130nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-60 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 15

preparation of outer layer solution for coaxial electrospinning: dissolving a mixture of polymethyl methacrylate and polyvinylpyrrolidone in a mass ratio of 1:1 and a mixture of polyacrylonitrile and cellulose in a mass ratio of 1:1 in a mixture of tetrahydrofuran and N, N-dimethylformamide in a mass ratio of 1:1 at 60 ℃, stirring for 2 hours, and uniformly mixing; wherein the mass ratio of the mixture of polyacrylonitrile and cellulose, the mixture of polymethyl methacrylate and polyvinylpyrrolidone to the mixture of tetrahydrofuran and N, N-dimethylformamide is 10:4: 100;

preparing a coaxial electrostatic spinning inner layer solution: dissolving a mixture of polymethyl methacrylate and polyvinylpyrrolidone in a mass ratio of 1:1 in a mixture of tetrahydrofuran and N, N-dimethylformamide in a mass ratio of 1:1 at the temperature of 60 ℃, stirring for 2 hours, then adding stannic chloride, stirring for 11 hours, and uniformly mixing; the molar ratio of tin tetrachloride to the mixture of polymethyl methacrylate and polyvinylpyrrolidone is 5000: 1; the mass ratio of the mixture of polymethyl methacrylate and polyvinylpyrrolidone to the mixture of tetrahydrofuran and N, N-dimethylformamide is 27: 100;

wherein in the electrostatic spinning process, the flow rate ratio of the solution on the inner layer and the solution on the outer layer of the coaxial electrostatic spinning is 1:1, and the total liquid supply flow rate is 2.5 mL/h; the distance between the needle head and the receiving plate is 10 cm; the voltage is 1 kV; the ambient temperature is 31 ℃; the ambient humidity is 27%; the receiving device is a metal roller, and the rotating speed of the roller is 100 r/min.

(3) Removing polymethyl methacrylate and polyvinylpyrrolidone in the porous multi-hollow flexible composite nanofiber membrane by a solvent soaking process to obtain a porous multi-hollow flexible composite nanofiber membrane material;

in the solvent soaking process, the solvent is a mixture of high-purity water and carbonic ester with the mass ratio of 1:1, the soaking time is 24 hours, and the soaked nano fibers are washed for 3 times by the solvent.

The Young modulus of the prepared porous multi-hollow flexible composite nanofiber membrane material is 20GPa, the porous multi-hollow flexible composite nanofiber membrane material is formed by stacking porous multi-hollow nanofiber layers, and a three-dimensional interpenetrating network and a stacked pore structure are formed; wherein the porous hollow nanofibers are made of polymer materials, the average diameter is 100nm, and the fiber walls have a porous structure with the pore diameter of 5-200 nm; the porous multi-hollow nanofiber comprises 2-15 hollow pipelines with the diameter of 10-30 nm and a plurality of three-dimensional through hole micro-nano structures from the surface to the hollow part; the three-dimensional through hole is a through hole structure which is connected with the hollow part of the fiber and the three-dimensional stacking holes among the fibers through the holes on the fiber wall.

Example 16

The specific steps of the preparation method of the porous multi-hollow flexible composite nanofiber membrane material are basically the same as those of the embodiment 1, the difference is only that the adopted metal source is different, and stannous chloride is adopted, and the performance index of the prepared porous multi-hollow flexible composite nanofiber membrane material is shown in the following table 1.

Example 17

The specific steps of the preparation method of the porous multi-hollow flexible composite nanofiber membrane material are basically the same as those of the embodiment 2, the difference is only that the adopted metal source is different, and tin hydroxide is adopted, and the performance indexes of the prepared porous multi-hollow flexible composite nanofiber membrane material are shown in the following table 1.

Example 18

The specific steps of the preparation method of the porous multi-hollow flexible composite nanofiber membrane material are basically the same as those of the embodiment 3, the difference is only that the adopted metal source is different, and stannous sulfate is adopted, and the performance indexes of the prepared porous multi-hollow flexible composite nanofiber membrane material are shown in the following table 1.

Example 19

The specific steps of the preparation method of the porous multi-hollow flexible composite nanofiber membrane material are basically the same as those of the embodiment 4, the difference is only that the adopted metal source is different, and stannous oxalate is adopted, and the performance indexes of the prepared porous multi-hollow flexible composite nanofiber membrane material are shown in the following table 1.

Example 20

The specific steps of the preparation method of the porous multi-hollow flexible composite nanofiber membrane material are basically the same as those of the embodiment 5, the difference is only that the adopted metal source is different, the metal source is a mixture of stannous chloride and tetraethyl titanate with the mass ratio of 1:1, and the performance index of the prepared porous multi-hollow flexible composite nanofiber membrane material is shown in the following table 1.

TABLE 1

Example number

Unit of

Example 16

Example 17

Example 18

Example 19

Example 20

Young's modulus

GPa

1.8

2.7

5.2

6.3

8.2

Average diameter

nm

600

500

410

380

340

Pore diameter

nm

5～200

Number of hollow pipes

An

2～15

Diameter of hollow pipe

nm

10～150

Claims

1. Porous many cavity flexible composite nanofiber membrane material, characterized by: the porous multi-hollow flexible composite nanofiber membrane material is formed by stacking porous multi-hollow nanofibers; the porous multi-hollow nanofiber refers to a nanofiber which is provided with a plurality of hollow pipelines and a three-dimensional through hole micro-nano structure from the surface to the hollow.

2. The porous multi-hollow flexible composite nanofiber membrane material as claimed in claim 1, wherein the stacking means that the fiber layers inside the fiber membrane are stacked layer by layer to form a three-dimensional interpenetrating network and a stacked pore structure.

3. The porous multi-hollow flexible composite nanofiber membrane material as claimed in claim 1, wherein the average diameter of the porous multi-hollow nanofibers is 100-1000 nm, the fiber wall has a porous structure, and the pore diameter is 5-200 nm.

4. The porous multi-hollow flexible composite nanofiber membrane material as claimed in claim 1, wherein the number of hollow channels of the porous multi-hollow nanofiber is 2-15 hollow channels, and the diameter of the hollow channels is 10-150 nm.

5. The porous multi-hollow flexible composite nanofiber membrane material as claimed in claim 3, wherein the three-dimensional through via is a through via structure connecting hollow inside the fiber and three-dimensional stacked holes between fibers through holes on the fiber wall.

6. The porous multi-hollow flexible composite nanofiber membrane material according to claim 1, wherein the porous multi-hollow flexible composite nanofiber membrane material comprises the porous multi-hollow nanofibers of a single material or the porous multi-hollow nanofibers of two or more different materials; the porous hollow nanofibers are made of carbon materials and/or polymer materials.

7. The porous multi-hollow flexible composite nanofiber membrane material as claimed in claim 1, wherein the young's modulus of the porous multi-hollow flexible composite nanofiber membrane material is 1GPa to 20 GPa.

8. The preparation method of the porous multi-hollow flexible composite nanofiber membrane material is characterized by comprising the following steps of: preparing a porous multi-hollow flexible composite nanofiber membrane through coaxial electrostatic spinning; the outer layer solution of the coaxial electrostatic spinning consists of a sacrificial high molecular polymer, a retention high molecular polymer and a solvent A; the inner layer solution of the coaxial electrostatic spinning consists of a sacrificial high molecular polymer, a material which can generate a substance with semiconductor characteristics and low surface energy in the spinning process and a solvent B; and then removing the sacrificial high molecular polymer in the porous multi-hollow flexible composite nanofiber membrane to obtain the porous multi-hollow flexible composite nanofiber membrane material.

9. The method according to claim 8, wherein the sacrificial polymer and the retentive polymer are the sacrificial polymer that can be removed while retaining the retentive polymer under a certain treatment condition.

10. The preparation method according to claim 8, wherein in the coaxial electrospinning inner layer solution, the molar ratio of a material capable of generating a substance with both semiconductor characteristics and low surface energy to the sacrificial high polymer in the spinning process is 1-5000: 1; the mass ratio of the sacrificial high-molecular polymer to the solvent B is 20-50: 100; in the coaxial electrostatic spinning outer layer solution, the mass ratio of the retention type high molecular polymer to the sacrificial type high molecular polymer to the solvent A is 8-13: 2-7: 100.

11. The method according to claim 8, wherein the sacrificial polymer is one or more of polymethyl methacrylate, polyvinylpyrrolidone, polyethylene oxide, polyethylene glycol, and polystyrene.

12. The method according to claim 8, wherein the retention type high molecular polymer is one or more of polyacrylonitrile, a phenol resin, and cellulose.

13. The method according to claim 8, wherein the solvent A or the solvent B is one or more selected from the group consisting of N, N-dimethylformamide, N-dimethylacetamide, tetrahydrofuran, and ethanol.

14. The method according to claim 8, wherein the material capable of generating a substance having both semiconductor characteristics and low surface energy in the spinning process is one or more of a metal source; the metal source is a titanium source, a zinc source or a tin source; the titanium source is tetrabutyl titanate, isopropyl titanate, tetraethyl titanate or titanium tetrachloride; the zinc source is zinc acetate, zinc nitrate or zinc chloride; the tin source is tin acetate, tin tetrachloride, stannous chloride, tin hydroxide, stannous sulfate or stannous oxalate.

15. The preparation method of claim 8, wherein the coaxial electrospinning inner layer solution is prepared by: dissolving the sacrificial high molecular polymer in the solvent B at 15-60 ℃, stirring for 2-12 h, then adding a metal source, stirring for 0.5-12 h, and uniformly mixing; the preparation method of the coaxial electrostatic spinning outer layer solution comprises the following steps: dissolving a sacrificial high-molecular polymer and a retention high-molecular polymer in a solvent A at 15-60 ℃, stirring for 2-12 h, and uniformly mixing; the flow rate ratio of the inner layer solution to the outer layer solution of the coaxial electrostatic spinning is 1 (1-5), and the total liquid supply flow rate is 0.3-6 mL/h; the distance between the needle head and the receiving plate is 10-30 cm; the voltage is 1-40 kV; the ambient temperature is 10-50 ℃; the environmental humidity is 20-80%; the receiving device is a metal roller, and the rotating speed of the roller is 20-100 r/min.

16. The method of claim 9, wherein the certain processing conditions are carbonization or solvent soaking.

17. The preparation method according to claim 16, wherein in the carbonization process, the pre-oxidation temperature is 200-300 ℃ and the time is 0.5-2.5 h; the temperature of the carbonization treatment is 450-1000 ℃, and the time is 1-5 h.

18. The preparation method according to claim 16, wherein in the solvent soaking process, the solvent C is one or more of high-purity water, methanol, ethanol, propanol, butanol, cyclohexanol, chloroform, dichloromethane, propylene glycol, butylene glycol, glycerol, triethanolamine, acetic acid, and carbonate, the soaking time is 1-24 hours, and the soaked nanofibers are washed 3-5 times with the solvent C.