Synthesis method of spiny MgF2 (at) ZnO heterojunction nanofiber for lithium metal solid electrolyte

Abstract

The invention relates to a synthesis method of spiny MgF2 (at) ZnO heterojunction nanofibers for a lithium metal solid electrolyte, and belongs to the technical field of all-solid-state lithium batteries. The preparation method comprises the following steps: (1) preparation of a MgF2 nanofiber precursor: obtaining primary MgF2 nanofibers by adopting an electrostatic melting and blowing process; (2) preparation of MgF2 nanofibers: calcining the precursor nanofibers through a temperature programming method to obtain MgF2 inorganic nanofibers; (3) preparation of spiny MgF2 (at) ZnO heterojunction nanofibers: growing regular array ZnO nanowires on the MgF2 nanofibers through a hydrothermal reaction; and (3) preparation of the composite solid electrolyte: introducing the MgF2 (at) ZnO heterojunction nanofiber into a PEO-LiTFSI solution, pouring on a polyfluortetraethylene plate, and drying and hot-pressing for a certain time to obtain a solid electrolyte diaphragm which can be applied to an all-solid-state lithium metal battery.

Description

Technical Field

[0001] The invention relates to a method for synthesizing thorny MgF2@ZnO heterojunction nanofibers for lithium metal solid electrolytes, belonging to the technical field of lithium metal solid electrolytes. Background Art

[0002] In today's society, energy conservation and carbon reduction are necessary to achieve global green and healthy development. With the rapid development of new energy sources, metallic lithium, which is considered to be the most ideal "battery metal", is hailed as the "white of the future", and global lithium resources are abundant. Liquid lithium-ion batteries face serious interfacial reactions, which lead to the formation of lithium dendrites, resulting in capacity loss and safety hazards due to leakage of liquid electrolytes. Although a variety of methods have been proposed to solve these problems, such as lithium negative electrode modification, positive electrode interface engineering and the application of solid electrolytes, the application and modification of solid electrolytes is still one of the most advanced methods. Among various electrolytes, polyethylene oxide (PEO)-based polymer electrolytes generally have excellent chain flexibility and abundant Li + donor sites, making them one of the most promising polymer electrolyte matrices. However, they still suffer from insufficient ionic conductivity compared to liquid organic electrolytes at room temperature. Among the various enhancers of solid electrolytes, the combination of inorganic nanofillers with PEO-based solid composite electrolytes (CSEs) is the most prominent, which can not only improve ionic conductivity but also establish a stable interface and enhance electrochemical stability. Understanding the interfacial chemical interactions between inorganic fillers and polymer matrices is crucial to regulating ion transport behavior within the composite system under multi-scale lithium coupling environment. One-dimensional (1D) inorganic fillers have unique advantages in promoting lithium ion transport. However, although 1D nanofibers provide a continuous path, more attention must be paid to the design of high interfacial surface area to produce rich organic-inorganic interface regions.

[0003] To further address the challenge of insufficient lithium ion transport flux, incorporating high-performance dielectric ceramic materials into polymer-based electrolytes can provide a promising solution for enhancing lithium ion conductivity. In theory, polarized dielectric materials experience slight displacement and orientation of internal bound charges and dipoles under the influence of an external electric field, resulting in charge accumulation at the material interface and the formation of an induced dipole moment. Introducing dielectric materials with substantial dipole moments into electrolytes can guide Li along the polymer chains. + , thereby generating Li + In addition, these dielectric materials can act as Lewis acids, anchoring anions and effectively promoting the dissociation of lithium salts. For example, ID dielectric ceramic Bi4Ti3O 12 The introduction of nanofibers into PEO-based solid electrolytes can effectively accelerate the +The rapid transfer at the interface reduces the Li + For another example, the parallel structure of BaTiO3-Li 0.33 La 0.56 TiO3 nanowires were introduced into polyvinylidene fluoride matrix for polymer composite solid electrolyte. The polarized dielectric BaTiO3 significantly promoted the dissociation of lithium salts, resulting in mobile Li + Greater availability. Meanwhile, BaTiO3-Li 0.33 La 0.56 TiO3 effectively suppresses the formation of space charge layer in PVDF. Notably, ZnO, a high dielectric material with a wide bandgap, can be hydrothermally grown into nanorods along the c-axis direction, providing a large specific surface area and improved polarization properties. The hydrothermal growth of ZnO can enhance the piezoelectric properties. However, as a polar molecule, ZnO exhibits strong intermolecular attraction, which makes it easy to agglomerate, thereby compromising its dispersibility and compatibility in the polymer matrix. In this context, the growth of ZnO nanofibers (ZO NFs) on organic fiber membranes has been considered as one of the most promising strategies to enhance dispersion. However, to date, there have been no reports on uniformly loading ZO NFs onto inorganic ceramic nanofibers for use in solid-state electrolytes. Summary of the Invention

[0004] In view of the problems existing in the above background technology, the purpose of the present invention is to propose a method for preparing MgF2@ZnO heterojunction nanofibers (MF@ZO HNFs) based on electrostatic melt blowing and in-situ growth process. This fiber introduces a PEO-based electrolyte to promote lithium salt dissociation and accelerate lithium ion transport. The built-in electric field generated at the MF@ZO HNFs heterojunction enhances the dissociation of lithium salts due to band bending. In addition, the unique interconnected thorn-like 3D structure formed between the composite nanofibers increases the Li + transmission path, and the internal electric field generated by the spontaneously polarized ZnO fiber further accelerates the Li + Transfer rate.

[0005] In order to achieve the above object, the present invention provides a method for synthesizing spiny MgF2@ZnO heterojunction nanofibers for lithium metal solid electrolyte, which is characterized by comprising the following steps:

[0006] (1) Preparation of MgF2 precursor spinning solution: Polyvinyl pyrrolidone, N,N-dimethylformamide (DMF), magnesium acetate and PVDF are mixed uniformly in a certain proportion to prepare a spinning solution;

[0007] (2) Non-woven process of MgF2 precursor nanofiber mat: the spinning solution prepared in step (1) is prepared into a precursor nanofiber mat through an electrostatic dissolution blowing device;

[0008] (3) Pretreatment of the MgF2 precursor fiber mat: heating the precursor fiber mat prepared in step (2) to 200-260°C in an air atmosphere at 2°C per minute and keeping the temperature for 1 hour to obtain a MgF2 pre-oxidized precursor nanofiber mat;

[0009] (4) Preparation of MgF2 nanofibers: The pre-oxidized precursor nanofiber felt prepared in step (3) is heated to 550-700°C at 2-3°C per minute in an argon or nitrogen atmosphere and kept at this temperature for 2 hours before being cooled naturally to form MgF2 fibers.

[0010] (5) Preparation of ZnO seed solution: Isopropyl alcohol, zinc acetate (Zn(NO3)2), and triethylamine were mixed in a certain proportion. The magnesium fluoride prepared in step (4) was immersed in the cooled ZnO seed solution for 8 hours, then removed, rinsed with ethanol, dried, and then cured at 200°C for 1 hour.

[0011] (6) ZnO nanofiber growth step: Zn(NO3)2 and hexamethylenetetramine (HMTA) were dissolved in deionized water at a specific ratio, mixed, and then a certain amount of ammonia (NH3·H2O) was added to prepare a growth solution. The magnesium fluoride fibers with ZnO seeds from step (5) were dispersed in the growth solution and kept at 95°C for a specific time to obtain MgF2@ZnO heterojunction nanofibers.

[0012] (7) Preparation of composite solid electrolyte membrane: a certain amount of PEO and LiTFSI were dissolved in acetonitrile solution, and then the fiber of step (6) was added to the solution and cast on a polytetrafluoroethylene plate. After a certain period of drying and hot pressing, a solid electrolyte membrane was obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the preparation process of MF@ZO HNFs;

[0014] Figure 2 (a) SEM image of MF@ZO HNFs with a molar ratio of Zn(NO3)2 to HMTA of 1:1;

[0015] Figure 2(b) SEM image of MF@ZO HNFs with a molar ratio of Zn(NO3)2 to HMTA of 2:1;

[0016] Figure 2(c) SEM image of MF@ZO HNFs with a molar ratio of Zn(NO3)2 to HMTA of 3:1;

[0017] Figure 3HR-TEM images, EDS mapping, and SAED images of (ac) MF NFs and (dj) MF@ZO HNFs.

[0018] Figure 4(a) shows the cross-sectional SEM image of the MF@ZO HNFs composite electrolyte;

[0019] Figure 4(b) is the top view SEM image of the MF@ZO HNFs composite electrolyte;

[0020] Figure 5 is the lithium ion transference number of MF@ZOHNFs composite electrolyte at 50 °C;

[0021] Figure 6 The Li||Li pair battery composed of MF@ZO HNFs composite electrolyte has a performance of 0.3 mA cm at 50 °C. -2 and 0.15mAhcm -2 Voltage distribution during constant current plating / stripping cycles. DETAILED DESCRIPTION

[0022] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1

[0024] (1) Pour 16 mL of DMF into a beaker, then pour 1 g of magnesium acetate and 1 g of PVDF into the beaker in turn, stir in a water bath until completely dissolved, then add 1.6 g of polyvinyl pyrrolidone (PVP) and stir for 6 h. Pour the above spinning solution precursor into an electrostatic blowing device and perform electrostatic blowing at a voltage of 40 kV and an air pressure of 0.05 MPa. Place the nascent fiber in a ceramic crucible and place it in a muffle furnace at 2 ° C min -1 The heating rate was raised from room temperature to 260 °C and the as-spun fibers were pre-oxidized at a constant temperature for 1 h to maintain the fiber morphology. After pre-oxidation, the fibers were heated at a rate of 3 °C min -1 The temperature was raised to 650℃ at a constant temperature for 2 hours and then naturally cooled to form magnesium fluoride fibers.

[0025] (2) Dissolve 0.55 g (2.5 mmol) of zinc acetate (Zn(NO3)2) in 25.0 mL of isopropanol to prepare a 100 mM zinc acetate solution. Then, vigorously stir at 85°C for 15 min, and add 350 μL (2.5 mmol) of triethylamine dropwise to the stirred solution. A transparent solution is obtained, which is stirred at 85°C for another 10 min. The pH value of the seed solution is 7.01 (pH meter). Immerse 0.1 g of the fiber from step (1) in the cooled ZnO seed solution for 8 h, then remove it, rinse it with ethanol, dry it, and then cure it at 200°C for 1 h.

[0026] (3) Dissolve 0.595 g of Zn(NO₃)₂ and 0.28 g of HMTA in 19 mL of deionized water, stir at room temperature for 12 h, and then mix in a beaker. Add 2 mL of NH₃·H₂O. Submerge 0.1 g of the fiber from step (2) in the beaker, which is then placed in a 95°C oven for 10 h.

[0027] (4) 1.84 g of PEO and 1 g of LiTFSI were weighed and dissolved in 12.8 g of acetonitrile. 0.316 g of MF@ZO HNFs obtained in step (3) was then dispersed in the solution. The solution was stirred on a magnetic stirrer until uniformly mixed and then poured into the separation grooves of a polytetrafluoroethylene plate. The entire groove was then placed in a vacuum oven and heated at 60°C until the solvent was completely removed.

[0028] Example 2

[0029] (1) Pour 16 mL of DMF into a beaker, then pour 1 g of magnesium acetate and 1 g of PVDF into the beaker in turn, stir in a water bath until completely dissolved, then add 1.6 g of polyvinyl pyrrolidone (PVP) and stir for 6 h. Pour the above spinning solution precursor into an electrostatic blowing device and perform electrostatic blowing at a voltage of 40 kV and an air pressure of 0.05 MPa. Place the nascent fiber in a ceramic crucible and place it in a muffle furnace at 2 ° C min -1 The heating rate was raised from room temperature to 260 °C and the as-spun fibers were pre-oxidized at a constant temperature for 1 h to maintain the fiber morphology. After pre-oxidation, the fibers were heated at a rate of 3 °C min -1 The temperature was raised to 650℃ at a constant temperature for 2 hours and then naturally cooled to form magnesium fluoride fibers.

[0030] (2) Dissolve 0.55 g (2.5 mmol) of zinc acetate (Zn(NO3)2) in 25.0 mL of isopropanol to prepare a 100 mM zinc acetate solution. Then, vigorously stir at 85°C for 15 min, and add 350 μL (2.5 mmol) of triethylamine dropwise to the stirred solution. A transparent solution is obtained, which is stirred at 85°C for another 10 min. The pH value of the seed solution is 7.01 (pH meter). Immerse 0.1 g of the fiber from step (1) in the cooled ZnO seed solution for 8 h, then remove it, rinse it with ethanol, dry it, and then cure it at 200°C for 1 h.

[0031] (3) Dissolve 0.773 g of Zn(NO₃)₂ and 0.182 g of HMTA in 19 mL of deionized water, stir at room temperature for 12 h, and then mix in a beaker. Add 2 mL of NH₃·H₂O. Submerge 0.1 g of the fiber from step (2) in the beaker, which is then placed in a 95°C oven for 10 h.

[0032] (4) 1.84 g of PEO and 1 g of LiTFSI were weighed and dissolved in 12.8 g of acetonitrile. 0.316 g of MF@ZO HNFs obtained in step (3) was then dispersed in the solution. The solution was stirred on a magnetic stirrer until uniformly mixed and then poured into the separation grooves of a polytetrafluoroethylene plate. The entire groove was then placed in a vacuum oven and heated at 60°C until the solvent was completely removed.

[0033] Example 3

[0034] (1) Pour 16 mL of DMF into a beaker, then pour 1 g of magnesium acetate and 1 g of PVDF into the beaker in turn, stir in a water bath until completely dissolved, then add 1.6 g of polyvinyl pyrrolidone (PVP) and stir for 6 h. Pour the above spinning solution precursor into an electrostatic blowing device and perform electrostatic blowing at a voltage of 40 kV and an air pressure of 0.05 MPa. Place the nascent fiber in a ceramic crucible and place it in a muffle furnace at 2 ° C min -1 The heating rate was raised from room temperature to 260 °C and the as-spun fibers were pre-oxidized at a constant temperature for 1 h to maintain the fiber morphology. After pre-oxidation, the fibers were heated at a rate of 3 °C min -1 The temperature was raised to 650℃ at a constant temperature for 2 hours and then naturally cooled to form magnesium fluoride fibers.

[0035] (2) Dissolve 0.55 g (2.5 mmol) of zinc acetate (Zn(NO3)2) in 25.0 mL of isopropanol to prepare a 100 mM zinc acetate solution. Then, vigorously stir at 85°C for 15 min, and add 350 μL (2.5 mmol) of triethylamine dropwise to the stirred solution. A transparent solution is obtained, which is stirred at 85°C for another 10 min. The pH value of the seed solution is 7.01 (pH meter). Immerse 0.1 g of the fiber from step (1) in the cooled ZnO seed solution for 8 h, then remove it, rinse it with ethanol, dry it, and then cure it at 200°C for 1 h.

[0036] (3) Dissolve 0.892 g of Zn(NO₃)₂ and 0.140 g of HMTA in 19 mL of deionized water, stir at room temperature for 12 h, and then mix in a beaker. Add 2 mL of NH₃·H₂O. Submerge 0.1 g of the fiber from step (2) in the beaker, which is then placed in a 95°C oven for 10 h.

[0037] (4) 1.84 g of PEO and 1 g of LiTFSI were weighed and dissolved in 12.8 g of acetonitrile. 0.316 g of MF@ZO HNFs obtained in step (3) was then dispersed in the solution. The solution was stirred on a magnetic stirrer until uniformly mixed and then poured into the separation grooves of a polytetrafluoroethylene plate. The entire groove was then placed in a vacuum oven and heated at 60°C until the solvent was completely removed.

[0038] Performance testing:

[0039] The composite all-solid electrolyte disclosed in this application is characterized by preparing 3D thorn-like MgF2@ZnO heterojunction nanofibers with uniform morphology as filler, and the composite all-solid electrolyte is based on PEO. By utilizing the interconnected thorn-like structure and built-in electric field generated by MF@ZO HNFs, the composite solid electrolyte increases the Li + transmission path, promoting high-speed Li + In addition, the electrolyte was analyzed in terms of various physical and electrochemical properties, and the developed electrolyte performed excellently.

[0040] Figure 1 This is a flow chart for preparing MgF2@ZnO heterojunction nanofibers. Through a hydrothermal reaction, one-dimensional ZnO spiny fibers were grown on the surface of the MgF2 fibers, successfully producing piezoelectric-based MgF2@ZnO heterojunction nanofibers with uniform morphology. The MgF2 fibers were prepared using a one-step electrostatic melt-blowing and high-temperature calcination process.

[0041] Figure 2(a) shows the SEM image of MgF2@ZnO heterojunction nanofibers. The electron microscope images of MF@ZO HNFs show that the ZnO nanorods prepared by heat treatment and hydrothermal growth have a uniform structure and grow radially along the nanofibers. By comparing these images, it can be seen that when the concentration of Zn(NO3)2 is too low (the molar ratio of Zn(NO3)2·6H2O to HMTA is 1:1), the system does not reach supersaturation, which seriously affects the length and distribution density of the resulting ZnO crystals ( Figure 2a ). In addition, HMTA, as a chelating agent, preferentially adsorbs or attaches to the non-polar surface of ZnO, exposing its polar surface to ionic substances in the solution. Therefore, the higher the HMTA concentration, the axial growth of ZnO nanorods is inhibited to a certain extent, while the radial growth is inhibited to a certain extent. Figure 2b As shown, with the growth solution Zn 2+ With the increase of the concentration (ratio of 2:1), the uniformity and distribution density of ZnO nanorods can be greatly improved. However, at a higher growth solution concentration (3:1), the axial growth rate of ZnO nanorods decreases, resulting in a decrease in the length of the nanorods and an increase in the diameter, which leads to a serious decrease in the aspect ratio ( Figure 2c).

[0042] Figure 3 TEM and HR-TEM images of MF NFs, ZO NFs, and MF@ZO HNFs are further shown, which can clearly demonstrate the morphology and structure of the synthesized materials. Figure 3 a depicts the synthesized MF NFs, which exhibit a one-dimensional elongated fiber morphology with a diameter of approximately 380 nm. From the HR-TEM image ( Figure 3 b) It can be observed that the spacing of the lattice fringes is 0.2547 nm, which is consistent with the standard value of the MF (101) plane. Elemental mapping shows that MF is uniformly distributed in the one-dimensional nanofibers, indicating that the purity of MF NFs is high ( Figure 3 c). In addition, the electron diffraction patterns from selected areas also showed that the MFNFs had good crystallinity with well-defined individual particles. Figure 3 As shown in Figure d, the microstructure of ZO NFs shows excellent morphology with clear ultrafine fiber features and relatively uniform size of about 30 nm. These prepared ultrafine fibers are evenly distributed on the surface of MF NFs and are vertically oriented, thus forming a structure with a high specific surface area. The irregular 1D morphology formed can effectively enhance the interaction with the PEO / LiTFSI matrix and provide obvious tight bonding. In addition, the thorn-like structure can also introduce a large number of heterojunction interfaces, promote the dissociation of lithium salts, and improve the transport of lithium ions. The HR-TEM images of the tested MF@ZO HNFs are shown in Figure d. Figure 3 f, indicating that a typical heterojunction structure can be formed at the interface. The formed interface is obvious, and lattice fringes are observed at 0.3268nm and 0.2817nm, corresponding to the (110) crystal plane of MF NFs and the (100) crystal plane of ZO NFs, respectively. These observations further confirm the successful integration of MF and ZO NFs, highlighting that MF@ZOHNFs can be effectively constructed by rationally combining ID MF NFs with 1D piezoelectric ceramic ZO NFs. This result is further supported by high-resolution elemental mapping, with clear distribution patterns of elements (Mg, F, O and Zn) corresponding to nanoscale structural features ( Figure 3 gj). These experimental and theoretical results together confirm the successful synthesis of the prepared MF@ZO high-throughput nanofibers.

[0043] Figure 4 shows the SEM image of the MF@ZO HNFs composite electrolyte. By adding MF@ZO HNFs to the PEO / LiTFSI-based electrolyte, a solid electrolyte with an average thickness of 90 μm can be prepared ( Figure 4a ). The SEM image of the electrolyte shows some fibers, and the fibers are evenly distributed ( Figure 4b ).

[0044] Figure 5 is the lithium ion transfer number of the MF@ZO HNFs composite electrolyte. This demonstrates the role of MF@ZO HNFs in promoting lithium ion transport and lithium salt dissociation. The lithium ion transfer number of the MF@ZO HNFs composite electrolyte is 0.498. This phenomenon is primarily due to the fact that inorganic MF@ZO HNFs, as ceramic fillers, act like plasticizers, enhancing the ability of PEO to transport lithium ions. Furthermore, the long-range organic-inorganic interface channels constructed by the one-dimensional heterojunction nanofibers and the interfacial electric field that promotes lithium ions are also crucial.

[0045] Figure 6 The Li||Li pair battery composed of MF@ZO HNFs composite electrolyte was tested at 0.3 mA cm -2 and 0.15 mAh cm -2 Voltage distribution during constant current plating / stripping cycles. Li||Li pair battery composed of MF@ZO HNFs composite electrolyte at 0.3 mA cm -2 and 0.15 mAh cm -2 The composite electrolyte was tested for over 1270 hours at a high capacity. This test demonstrates the excellent ability of the composite electrolyte to suppress lithium dendrites and maintain the stability of the lithium metal / electrolyte interface over long cycling periods.

[0046] Example 2 is the best example of this application. Examples 1 and 3 also show the same performance characteristics after the above performance tests. Therefore, in summary, the ionic conductivity of the composite electrolyte prepared by MF@ZO HNFs grown in the ZnO growth solution (with a molar ratio of Zn(NO3)2·6H2O to HMTA of 2:1) is the highest (5.0×10 -4 S cm -1 , 50℃), which can suppress the generation of lithium dendrites. The built-in electric field generated at the MF@ZO HNFs heterojunction enhances the dissociation of lithium salts due to band bending. In addition, the unique interconnected thorn-like 3D structure formed between the composite nanofibers increases the Li + transmission path, and the internal electric field generated by the spontaneously polarized ZnO fiber further accelerates the Li + Transfer rate.

Claims

1. A method for synthesizing spiny MgF2@ZnO heterojunction nanofibers for lithium metal solid electrolytes, characterized by comprising the following steps: (1) Preparation of MgF2 precursor spinning solution: Polyvinyl pyrrolidone, N,N-dimethylformamide (DMF), magnesium acetate and PVDF are mixed uniformly in a certain proportion to prepare a spinning solution; (2) Non-woven process of MgF2 precursor nanofiber mat: the spinning solution prepared in step (1) is prepared into a precursor nanofiber mat through an electrostatic dissolution blowing device; (3) Pretreatment of the MgF2 precursor fiber mat: heating the precursor fiber mat prepared in step (2) to 200-260°C in an air atmosphere at 2°C per minute and keeping the temperature for 1 hour to obtain a MgF2 pre-oxidized precursor nanofiber mat; (4) Preparation of MgF2 nanofibers: The pre-oxidized precursor nanofiber felt prepared in step (3) is heated to 550-700°C at 1.5-3°C per minute in an argon or nitrogen atmosphere and kept at this temperature for 2 hours before being cooled naturally to form MgF2 fibers. (5) Preparation of ZnO seed solution: Isopropyl alcohol, zinc acetate (Zn(NO3)2), and triethylamine were mixed in a certain proportion. The MgF2 prepared in step (4) was immersed in the cooled ZnO seed solution for 8 hours, then removed, rinsed with ethanol, dried, and then cured at 200°C for 1 hour. (6) ZnO nanofiber growth step: Zn(NO3)2 and hexamethylenetetramine (HMTA) were dissolved in deionized water at a specific ratio, mixed, and then a certain amount of ammonia (NH3·H2O) was added to prepare a growth solution. The magnesium fluoride fibers with ZnO seeds from step (5) were dispersed in the growth solution and kept at 95°C for a specific time to obtain MgF2@ZnO heterojunction nanofibers. (7) Preparation of composite solid electrolyte membrane: a certain amount of PEO and LiTFSI were dissolved in acetonitrile solution, and then the fiber of step (6) was added to the solution and cast on a polytetrafluoroethylene plate. After a certain period of drying and hot pressing, a solid electrolyte membrane was obtained.

2. The spinning solution preparation according to claim 1, characterized in that: The mass fraction of the magnesium acetate in the spinning solution is 3.2wt% to 8wt%.

3. The preparation of MgF2 nanofibers according to claim 1, characterized in that: The MgF2 nanofibers are prepared by heating the temperature to 550-700°C at a rate of 1.5-3°C per minute and keeping the temperature for 2 hours.

4. The preparation of MgF2@ZnO heterojunction nanofibers according to claim 1, characterized in that: The ratios of Zn(NO3)2 and hexamethylenetetramine (HMTA) in the ZnO growth solution are 1:1, 2:1, and 3:1.

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