Composite nanofiber membrane, modified nanofiber membrane and application thereof

Abstract

The application discloses a composite nanofiber membrane, a modified nanofiber membrane and application thereof, and relates to the technical field of nanofiber membranes.The composite nanofiber membrane comprises a first electrolyte layer, a modified nanofiber membrane and a second electrolyte layer arranged in sequence.The first electrolyte layer comprises iron phthalocyanine, a first polymer and a first electrolyte lithium salt, and the second electrolyte layer comprises a second polymer and a second electrolyte lithium salt.The modified nanofiber membrane comprises modified nanofibers and a three-dimensional porous structure grown in situ on the modified nanofibers.The modified nanofibers contain ferrous iron, and the material of the three-dimensional porous structure contains iron phthalocyanine.The composite nanofiber membrane greatly improves the content of the electrolyte amorphous region, improves the dissociation of the electrolyte lithium salt, promotes the increase of ionic conductivity and ionic transference number, reduces the generation of side reactions, and is beneficial to realizing stable and long-acting interface performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a solid electrolyte for Li-O2 batteries, specifically to a composite nanofiber membrane, a modified nanofiber membrane, and their applications. Background Technology

[0002] Li-O2 batteries have a higher theoretical energy density than lithium-ion batteries. Oxygen, as an environmentally friendly and low-cost active cathode material, can be derived from the air, which can reduce the cost of batteries to some extent, thus meeting the growing demand for large-scale energy storage systems. The main charging and discharging mechanism of Li-O2 batteries is the reversible conversion of Li2O2 into a product (Li-e). - →Li + ,2Li + +O2+2e - →Li2O2), is a redox reaction that combines the oxidation of lithium metal at the anode with the two-electron reduction of oxygen at the porous cathode.

[0003] However, the commercialization of Li-O2 batteries still faces many challenges, which have affected their industrialization to some extent. In particular, Li-O2 batteries still have shortcomings in terms of limited capacity, cycle life, and energy efficiency. The main reasons are as follows: (1) The specific capacity decay and safety hazards caused by the side reactions (such as lithium dendrites and anode loss) of lithium metal anodes during the cycling process of Li-O2 batteries have affected the long-term stable cycling of Li-O2 batteries in various application environments. (2) Redox reaction during charging and discharging (E0=2.96V vs Li / Li) + The voltage difference between the two leads to a decrease in the round-trip efficiency of the Li-O2 battery. This is mainly manifested in the fact that some undecomposed Li2O2 will cause capacity loss and high voltage on the cathode side, which in turn triggers a series of side reactions caused by high voltage, as well as porous cathode blockage and interface problems caused by the remaining Li2O2. (3) Due to the poor rate of catalytic performance during the charge and discharge process, it is difficult for Li-O2 batteries to meet the requirements of high current charge and discharge. The insolubility of Li2O2 leads to its slow formation and decomposition kinetics, making efficient catalysis at the porous cathode side interface crucial.

[0004] In summary, the main challenges facing Li-O2 batteries in practical applications can be attributed to two aspects. On the one hand, the poor conductivity and solubility of the discharge product Li2O2 affect the low reaction kinetics and high thermodynamic losses, which limit the development of high-performance Li-O2 batteries. On the other hand, there are the side reactions between the electrolyte and the electrode, as well as the instability of the interface between them during electrochemical cycling.

[0005] It should be noted that the information disclosed in the background section above is only for understanding the background of this application. Therefore, the background section of this invention may include background information about the problems or environment of this invention, and is not necessarily a description of the prior art. Thus, the content included in the background section does not constitute an admission of the prior art by the applicant. Summary of the Invention

[0006] The purpose of this invention is to overcome one or more shortcomings in the prior art and provide a new composite nanofiber membrane and a modified nanofiber membrane, which have achieved excellent results as solid electrolytes in Li-O2 batteries, at least improving the interface problem between the electrolyte and the electrode.

[0007] The present invention also provides a composite nanofiber membrane and a modified nanofiber membrane as solid electrolytes in Li-O2 batteries.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A composite nanofiber membrane, the composite nanofiber membrane comprising a first electrolyte layer, a modified nanofiber membrane, and a second electrolyte layer disposed sequentially; The first electrolyte layer comprises iron phthalocyanine (FePc), a first polymer, and a first electrolyte lithium salt; the second electrolyte layer comprises a second polymer and a second electrolyte lithium salt. The modified nanofiber membrane comprises modified nanofibers and a three-dimensional porous structure grown in situ on the modified nanofibers. The modified nanofibers contain ferrous iron, and the material of the three-dimensional porous structure comprises ferrocyanine.

[0009] In this invention, "three-dimensional porous structure" refers to a material whose overall structure presents a three-dimensional form and contains a large number of pore structures. These pore structures can be distributed on the surface or in the inner layer, and the pore structures can be connected or not connected.

[0010] In some embodiments of the present invention, the ratio of the thickness of the first electrolyte layer, the thickness of the modified nanofiber membrane, and the thickness of the second electrolyte layer is 0.25-0.45∶1∶0.25-0.45.

[0011] In some embodiments of the present invention, the ferrous iron in the modified nanofibers exists in the form of ferrous halide.

[0012] According to some preferred and specific aspects of the invention, the ferrous halide accounts for 4.5%-7.5% of the modified nanofibers by mass percentage.

[0013] Furthermore, in the modified nanofibers, the ferrous halide accounts for 5.5%-7.0% by mass percentage.

[0014] According to some specific aspects of the present invention, the ferrous halide in the modified nanofibers comprises 4.5%, 4.8%, 5.0%, 5.2%, 5.5%, 5.8%, 6.0%, 6.2%, 6.5%, 6.8%, 7.0%, 7.2%, 7.5%, etc., by mass percentage.

[0015] Furthermore, the ferrous halide is ferrous chloride.

[0016] In some embodiments of the present invention, the modified nanofiber membrane comprises a matrix formed from modified nanofibers and a three-dimensional porous structure grown in situ on the matrix, the three-dimensional porous structure being composed of multiple nanosheets made of iron phthalocyanine.

[0017] In some embodiments of the present invention, the three-dimensional porous structure has characteristic peaks at 2θ angles of 7.1°±0.2°, 9.2°±0.2°, and 11.4°±0.2° in the X-ray diffraction pattern.

[0018] In some embodiments of the present invention, the modified nanofiber membrane is prepared by the following method: Ferrous chloride or its hydrate and polyacrylonitrile are used to prepare a spinning solution, which is then spun to form a film-like matrix. Phthalonil, ferrous chloride, or their hydrates are dispersed in an alcohol solvent to prepare a mixed solution. The matrix is ​​then immersed in the mixed solution, and the reaction is carried out under a protective gas atmosphere and under heating conditions to prepare the modified nanofiber membrane.

[0019] In some embodiments of the present invention, the molar ratio of the phthalonitrile to the ferrous chloride or its hydrate in the mixed solution is 3.8-4.2:1, for example, it can be 3.9-4.1:1.

[0020] According to one specific aspect of the invention, in the mixed solution, the molar ratio of the phthalonitrile to the ferrous chloride or its hydrate is 4:1.

[0021] According to one specific aspect of the present invention, the hydrate of ferrous chloride can be ferrous chloride tetrahydrate.

[0022] In some embodiments of the present invention, the total mass concentration of the phthalonitrile and the ferrous chloride or its hydrate in the mixed solution is 0.8%-2.5% by mass percentage.

[0023] Furthermore, in the mixed solution, the total mass concentration of the phthalonitrile and the ferrous chloride or its hydrate is 0.8%-1.5% by mass percentage.

[0024] According to certain aspects of the present invention, the total mass concentration of the phthalonitrile and the ferrous chloride or its hydrate in the mixed solution, by mass percentage, is 0.8%, 0.9%, 0.95%, 1.0%, 1.05%, 1.10%, 1.15%, 1.20%, 1.25%, 1.30%, 1.35%, 1.40%, 1.45%, 1.50%, 1.55%, 1.60%, 1.65%, 1.70%, 1.75%, 1.80%, 1.85%, 1.90%, 1.95%, 2.0%, 2.1%, etc.

[0025] In some embodiments of the present invention, the alcohol solvent comprises ethanol.

[0026] In some embodiments of the present invention, the reaction is carried out at 165-190°C.

[0027] In some embodiments of the invention, the reaction is carried out in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).

[0028] In some embodiments of the present invention, the added mass of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) accounts for 10%-60% of the added mass of phthalonitrile, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc.

[0029] In some embodiments of the present invention, the spinning solution is prepared by dispersing ferrous chloride or its hydrate and polyacrylonitrile in an organic solvent. Further, the organic solvent may be N,N-dimethylformamide.

[0030] According to some specific aspects of the invention, the mass concentration of the spinning solution is 10%-15%.

[0031] In some embodiments of the present invention, the spinning can be performed using an electrospinning method. Further, the process parameters of the electrospinning method include: a voltage of 20-30 kV, an extrusion speed of 0.1-0.5 mL / min, and a roller rotation speed of 10-100 r / min.

[0032] According to some specific aspects of the present invention, the spinning process of the electrospinning method is carried out at room temperature.

[0033] According to some specific aspects of the present invention, the thickness of the film-like substrate can be set as needed, for example, it can be 30-40 μm, etc.

[0034] In some embodiments of the present invention, the reaction is carried out in a hydrothermal reactor.

[0035] In some embodiments of the present invention, after the reaction is completed, the resulting intermediate film layer is washed and dried. Further, the washing can be performed using ethanol and water respectively, and the drying can be carried out at 40-60°C.

[0036] In some embodiments of the present invention, in the first electrolyte layer, based on the total mass of the iron phthalocyanine, the first polymer and the first electrolyte lithium salt as 100%, the iron phthalocyanine accounts for 0.5%-1.5%, the first polymer accounts for 62%-66%, and the first electrolyte lithium salt accounts for 33%-37%.

[0037] Furthermore, in the first electrolyte layer, based on the total mass of the iron phthalocyanine, the first polymer, and the first electrolyte lithium salt as 100%, the iron phthalocyanine accounts for 0.5%-1.5%, the first polymer accounts for 63.8%-64.5%, and the first electrolyte lithium salt accounts for 34.7%-35%.

[0038] In some embodiments of the present invention, in the second electrolyte layer, the second polymer accounts for 63%-67% and the second electrolyte lithium salt accounts for 33%-37% based on the total mass of the second polymer and the second electrolyte lithium salt being 100%.

[0039] Furthermore, in the second electrolyte layer, based on the total mass of the second polymer and the second electrolyte lithium salt being 100%, the second polymer accounts for 64.8% and the second electrolyte lithium salt accounts for 35.2%.

[0040] In some embodiments of the present invention, both the first polymer and the second polymer are polyethylene oxide (PEO).

[0041] In some embodiments of the present invention, both the first electrolyte lithium salt and the second electrolyte lithium salt are lithium bis(trifluoromethanesulfonylimide) (LiTFSI).

[0042] In some embodiments of the present invention, the composite nanofiber membrane is prepared by the following method: An electrolyte mixture slurry containing iron phthalocyanine, a first polymer, and a first electrolyte lithium salt is applied to a first side of the modified nanofiber membrane to form a first electrolyte layer; an electrolyte mixture slurry containing a second polymer and a second electrolyte lithium salt is applied to a second side of the modified nanofiber membrane to form a second electrolyte layer; the first side and the second side are disposed opposite to each other.

[0043] Furthermore, the coating method may include, but is not limited to, spraying, scraping, etc.

[0044] Furthermore, after coating, a drying process can be performed to remove the solvent.

[0045] Another technical solution provided by the present invention: a method for preparing a composite nanofiber membrane, the preparation method comprising: (1) Preparation of modified nanofiber membranes: Ferrous halide or its hydrate and polyacrylonitrile are dispersed in an organic solvent to prepare a spinning solution, which is then electrospun to obtain a film-like matrix. Phthalonil, ferrous chloride, or their hydrates are dispersed in an alcohol solvent to prepare a mixed solution. The matrix is ​​then immersed in the mixed solution and reacted under a protective gas atmosphere and heating conditions to prepare the modified nanofiber membrane. (2) An electrolyte mixture slurry containing iron phthalocyanine, a first polymer and a first electrolyte lithium salt is applied to the first side of the modified nanofiber membrane to form the first electrolyte layer; an electrolyte mixture slurry containing a second polymer and a second electrolyte lithium salt is applied to the second side of the modified nanofiber membrane to form the second electrolyte layer; the first side and the second side are disposed opposite to each other.

[0046] This invention enables the in-situ growth of FePc on nanofiber membranes, allowing it to self-assemble into a three-dimensional porous structure. This avoids the harmful shuttle effect of conventional FePc and amplifies its catalytic effect. Furthermore, the in-situ growth of the FePc three-dimensional porous structure can be achieved by controlling the concentration of ferrous halide or its hydrate in the spinning solution and the concentration of raw materials in the hydrothermal solution. Due to the coordination structure of FePc, a one-molecular-weight iron ion corresponds to a four-molecular-weight large π bond, forming a two-dimensional metal-organic macromolecule. The iron ions introduced into the spinning solution can serve as an in-situ growth template. The uniformly distributed iron ion sites in the nanofibers provide the possibility for concentrated growth of FePc while better immobilizing it on the nanofiber surface, reducing losses during cycling and facilitating the full utilization of the active material. Furthermore, the carbon defect matrix generated under the high-temperature environment of FePc synthesis can further promote the self-assembly of the three-dimensional porous FePc structure. The ordered growth of FePc exhibits a unique crystalline structure, and the tiny nanosheets in the three-dimensional porous structure can be uniformly dispersed between PEO segments, avoiding FePc aggregation. This invention can also avoid the problem of irreversible degradation of catalytic performance caused by the shuttling of FePc during cycling and the covering of active sites. At the same time, the high loading and high specific surface area of ​​the nanofiber membrane are conducive to the large-scale exposure of active iron sites, which is beneficial for TFSI. - The strong adsorption of anions promoted the Li + The full solvation, combined with the continuous Li provided by the fiber filaments+ The channels significantly improve the ionic conductivity of the composite nanofiber membrane (i.e., the solid electrolyte membrane).

[0047] Another technical solution provided by the present invention is a modified nanofiber membrane, wherein the modified nanofiber membrane comprises modified nanofibers and a three-dimensional porous structure grown in situ on the modified nanofibers, wherein the modified nanofibers contain ferrous iron, and the material of the three-dimensional porous structure comprises ferrocyanine.

[0048] Another technical solution provided by the present invention: a method for preparing a modified nanofiber membrane, the preparation method comprising: Ferrous halide or its hydrate and polyacrylonitrile are dispersed in an organic solvent to prepare a spinning solution, which is then electrospun to obtain a film-like matrix. Phthalonil, ferrous chloride, or their hydrates are dispersed in an alcohol solvent to prepare a mixed solution. The matrix is ​​then immersed in the mixed solution, and the reaction is carried out under a protective gas atmosphere and under heating conditions to prepare the modified nanofiber membrane.

[0049] Another technical solution provided by the present invention is the application of the above-described composite nanofiber membrane or the above-described modified nanofiber membrane in a Li-O2 battery.

[0050] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: Based on the side reactions between the electrolyte and electrodes in Li-O2 batteries and the instability of their interface during electrochemical cycling, the inventors of this invention have innovatively designed a modified nanofiber membrane and a further improved multilayer composite nanofiber membrane. These, as solid electrolytes, can effectively solve the aforementioned problems. Specifically, the modified nanofiber membrane of this invention uses a high specific surface area nanofiber membrane as a three-dimensional framework for in-situ growth of FePc. Unexpectedly, it was discovered that when the nanofibers contain divalent iron, the in-situ grown FePc can exist in a three-dimensional porous structure. The presence of this special structure greatly increases the content of the amorphous region of the electrolyte and improves the dissociation of the lithium salt in the electrolyte, promoting an increase in ionic conductivity and ion transference number, and suppressing reactive oxygen species (such as superoxide radical ions) in the electrolyte during charging and discharging processes. 2- The generation of )) reduces the occurrence of side reactions, improves long-cycle stability, and achieves stable and long-lasting interface performance, which is conducive to the development of high-performance all-solid-state Li-O2 batteries. Attached Figure Description

[0051] Figure 1 SEM images (scale bar 5 μm) of the modified nanofiber membranes obtained in Examples 1-2 and Comparative Examples 1-10 of this invention. Figure 2SEM image (scale bar 20 μm) of the FeCl2-PAN nanofiber membrane prepared in Example 2 of this invention. Figure 3 SEM image (scale bar 20 μm) of the modified nanofiber membrane prepared in Example 2 of this invention. Figure 4 This is a SEM image (scale bar 1 μm) of the three-dimensional porous FePc structure in the modified nanofiber membrane prepared in Example 2 of the present invention at a higher magnification. Figure 5 This is an EDS image of the three-dimensional porous FePc structure in the modified nanofiber membrane prepared in Example 2 of this invention; Figure 6 Nitrogen isotherm adsorption-desorption curves for PAN nanofiber membranes; Figure 7 The nitrogen isotherm adsorption-desorption curve of the modified nanofiber membrane prepared in Example 2 of this invention; Figure 8 SEM image of the cross section of the composite nanofiber membrane prepared in Application Example 1; Figure 9 EDS image of the composite nanofiber membrane prepared in Example 1; Figure 10 The XRD patterns of the composite nanofiber membranes obtained by Comparative Example 1, Comparative Example 2, Example 1, and Example 2 of this invention are shown. Figure 11 The images show the Raman spectra of the composite nanofiber membranes obtained by Comparative Example 1, Comparative Example 2, Example 1, and Example 2 of this invention, as well as the Raman spectra of PEO-LiTFSI. Figure 12 Raman spectra of PEO-LiTFSI and FePc-PEO-LiTFSI / 0.5 FePc-PAN prepared in Application Example 1; Figure 13 The composite nanofiber membranes obtained by Comparative Example 1, Comparative Example 2, Example 1, and Example 2 of this invention, and the DSC curves of PEO-LiTFSI; Figure 14 The composite nanofiber membranes obtained by Comparative Example 1, Comparative Example 2, Example 1, and Example 2 of this invention, and the enthalpy change curves of PEO-LiTFSI are shown. Figure 15 AFM images of PEO-LiTFSI and FePc-PEO-LiTFSI / 0.5 FePc-PAN prepared in Example 1; Figure 16The composite nanofiber membranes obtained by Comparative Example 1, Comparative Example 2, Example 1, and Example 2 of this invention, and the ionic conductivity-temperature relationship graph of PEO-LiTFSI are shown. Figure 17 The current-time polarization curve of PEO-LiTFSI; Figure 18 The current-time polarization curve of the composite nanofiber membrane obtained in Example 1 is shown. Figure 19 The images show the DEMs of the composite nanofiber membrane obtained in Application Example 1 and PEO-LiTFSI. Figure 20 The interfacial impedance diagrams of the composite nanofiber membrane obtained in Application Example 1 and PEO-LiTFSI are shown. Figure 21 The DRT curves of the composite nanofiber membrane obtained in Application Example 1 and PEO-LiTFSI are shown. Figure 22 CCD curves of the composite nanofiber membrane obtained in Application Example 1 and PEO-LiTFSI; Figure 23 In-situ EIS electrochemical impedance spectroscopy of a Li‖Li symmetric cell assembled for PEO-LiTFSI; Figure 24 The in-situ EIS electrochemical impedance spectroscopy of the Li‖Li symmetric battery assembled using the composite nanofiber membrane obtained in Example 1. Figure 25 A Li‖FePc-PEO-LiTFSI / 0.5 FePc-PAN‖Li symmetric cell was constructed at 0.1 mAh·cm⁻¹. -2 Continuous stripping / lithium plating step cycle curves under the specified conditions; Figure 26 Constant current charging diagram of Li‖Li symmetric cells assembled with PEO-LiTFSI and FePc-PEO-LiTFSI / 0.5 FePc-PAN electrolytes; Figure 27 Long-cycle curves of Li‖PEO-LiTFSI‖Li and Li‖FePc-PEO-LiTFSI / 0.5 FePc-PAN‖Li symmetric cells. Detailed Implementation

[0052] The above-mentioned solution will be further described below with reference to specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments; the implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0053] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0054] In the following examples, the experimental materials and reagents used are shown in Table 1 below: Table 1

[0055] Example 1: This example provides a method for preparing a modified nanofiber membrane and the prepared modified nanofiber membrane. Specifically, the preparation method includes: (1) Preparation of FeCl2-PAN nanofiber membrane: Take 8.8 g of N,N-dimethylformamide, then weigh 0.12 g of ferrous chloride tetrahydrate (FeCl2•4H2O), and mix and stir for 5 min to obtain a mixed solution. Weigh 1.2 g of PAN powder and slowly add it to the mixed solution. Stir at room temperature for 2 h to ensure that the PAN powder is uniformly dispersed in the solution. After stirring, the solution is ultrasonically defoamed for 15 min to complete the preparation of the spinning solution. Use a 10 mL disposable medical syringe to draw a portion of the spinning solution and load it into an electrospinning machine for spinning. Set the voltage to 25 kV DC, the pump extrusion speed to 0.3 mL / min, and the roller speed to 60 r / min. Electrospin at room temperature for 2 h to obtain a nanofiber membrane with a thickness of approximately 30 μm. Place it in a 50℃ forced-air drying oven for 12 h to evaporate and remove excess solvent, thus preparing the FeCl2-PAN nanofiber membrane (or membrane-like matrix).

[0056] (2) Preparation of modified nanofiber membranes: 60 mL of ethylene glycol was placed in a 100 mL tetrafluoroethylene liner. 0.3976 g of FeCl2·4H2O and 1.025 g of phthalonitrile (the molar ratio of FeCl2·4H2O to phthalonitrile was approximately 1:4) were weighed out. The phthalonitrile was added to the liner and stirred for 10 min. After the solution became clear, FeCl2·4H2O was slowly added and stirred for 10 min. 0.5 mL of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was added to the mixed solution using a pipette and stirred at room temperature for 1 h to ensure thorough mixing. A 5 cm × 5 cm FeCl2-PAN nanofiber membrane was cut and placed in the solution, ensuring complete immersion. Nitrogen gas was then introduced into the liner for a certain period before quickly sealing and placing the membrane in a hydrothermal reactor. The reactor was then placed in a high-temperature explosion-proof oven at 175 °C for 4 h. After the reaction was completed, the temperature was lowered. Once the temperature of the reactor had dropped to room temperature, the fiber membrane was removed. The obtained fiber membrane was washed three times with ethanol and water, and then dried in a 50°C oven for 12 hours to obtain a hydrothermal FePc-PAN nanofiber membrane (also known as a modified nanofiber membrane or 1 FePc-PAN).

[0057] Example 2: This example provides a method for preparing a modified nanofiber membrane and the prepared modified nanofiber membrane, which is basically the same as in Example 1, except that in step (2), the concentration of the raw materials in the reaction solution is reduced during the preparation of the modified nanofiber membrane. Specifically, 0.1988 g FeCl2·4H2O and 0.5152 g phthalonitrile are used (the molar ratio of FeCl2·4H2O to phthalonitrile is approximately 1:4). The modified nanofiber membrane prepared in this example is also called 0.5 FePc-PAN.

[0058] Comparative Example 1: This example provides a method for preparing a modified nanofiber membrane and the prepared modified nanofiber membrane, which is basically the same as in Example 1, except that in step (2), the concentration of the raw materials in the reaction solution is reduced, specifically using 0.0398 g FeCl2·4H2O and 0.1025 g phthalonitrile (the molar ratio of FeCl2·4H2O to phthalonitrile is approximately 1:4). The modified nanofiber membrane prepared in this example is also called 0.1 FePc-PAN.

[0059] Comparative Example 2: This example provides a method for preparing a modified nanofiber membrane and the prepared modified nanofiber membrane, which is basically the same as in Example 1, except that in step (2), the concentration of the raw materials in the reaction solution is reduced during the preparation of the modified nanofiber membrane. Specifically, 0.1193 g FeCl2·4H2O and 0.3075 g phthalonitrile are used (the molar ratio of FeCl2·4H2O to phthalonitrile is approximately 1:4). The modified nanofiber membrane prepared in this example is also called 0.3 FePc-PAN.

[0060] Comparative Example 3: This example provides a method for preparing a modified nanofiber membrane and the modified nanofiber membrane prepared therefrom, which is basically the same as in Example 1. The only difference is that in the preparation process of FeCl2-PAN nanofiber membrane in step (1), the concentration of ferrous chloride tetrahydrate in the spinning solution is reduced. Specifically, the amount of ferrous chloride tetrahydrate (FeCl2·4H2O) is 0.06g.

[0061] Comparative Example 4: This example provides a method for preparing a modified nanofiber membrane and the modified nanofiber membrane prepared therefrom, which is basically the same as in Example 1. The only difference is that in the preparation of the FeCl2-PAN nanofiber membrane in step (1), the concentration of ferrous chloride tetrahydrate in the spinning solution is reduced, specifically using 0.06 g of ferrous chloride tetrahydrate (FeCl2·4H2O); in the preparation of the modified nanofiber membrane in step (2), the concentration of the raw materials in the reaction solution is reduced, specifically using 0.0398 g of FeCl2·4H2O and 0.1025 g of phthalonitrile (the molar ratio of FeCl2·4H2O to phthalonitrile is about 1:4).

[0062] Comparative Example 5: This example provides a method for preparing a modified nanofiber membrane and the modified nanofiber membrane prepared therefrom, which is basically the same as in Example 1. The only difference is that in the preparation of the FeCl2-PAN nanofiber membrane in step (1), the concentration of ferrous chloride tetrahydrate in the spinning solution is reduced, specifically using 0.06 g of ferrous chloride tetrahydrate (FeCl2·4H2O); in the preparation of the modified nanofiber membrane in step (2), the concentration of the raw materials in the reaction solution is reduced, specifically using 0.1193 g of FeCl2·4H2O and 0.3075 g of phthalonitrile (the molar ratio of FeCl2·4H2O to phthalonitrile is about 1:4).

[0063] Comparative Example 6: This example provides a method for preparing a modified nanofiber membrane and the modified nanofiber membrane prepared therefrom, which is basically the same as in Example 1. The only difference is that in the preparation of the FeCl2-PAN nanofiber membrane in step (1), the concentration of ferrous chloride tetrahydrate in the spinning solution is reduced, specifically using 0.06 g of ferrous chloride tetrahydrate (FeCl2·4H2O); in the preparation of the modified nanofiber membrane in step (2), the concentration of the raw materials in the reaction solution is reduced, specifically using 0.1988 g of FeCl2·4H2O and 0.5152 g of phthalonitrile (the molar ratio of FeCl2·4H2O to phthalonitrile is about 1:4).

[0064] Comparative Example 7: This example provides a method for preparing a modified nanofiber membrane and the modified nanofiber membrane prepared therefrom, which is basically the same as in Example 1. The only difference is that in the preparation of the FeCl2-PAN nanofiber membrane in step (1), the concentration of ferrous chloride tetrahydrate in the spinning solution is increased, specifically using 0.18 g of ferrous chloride tetrahydrate (FeCl2·4H2O); in the preparation of the modified nanofiber membrane in step (2), the concentration of the raw materials in the reaction solution is reduced, specifically using 0.0398 g of FeCl2·4H2O and 0.1025 g of phthalonitrile (the molar ratio of FeCl2·4H2O to phthalonitrile is about 1:4).

[0065] Comparative Example 8: This example provides a method for preparing a modified nanofiber membrane and the modified nanofiber membrane prepared therefrom, which is basically the same as in Example 1. The only difference is that in the preparation of the FeCl2-PAN nanofiber membrane in step (1), the concentration of ferrous chloride tetrahydrate in the spinning solution is increased, specifically using 0.18 g of ferrous chloride tetrahydrate (FeCl2·4H2O); in the preparation of the modified nanofiber membrane in step (2), the concentration of the raw materials in the reaction solution is reduced, specifically using 0.1193 g of FeCl2·4H2O and 0.3075 g of phthalonitrile (the molar ratio of FeCl2·4H2O to phthalonitrile is about 1:4).

[0066] Comparative Example 9: This example provides a method for preparing a modified nanofiber membrane and the modified nanofiber membrane prepared therefrom, which is basically the same as in Example 1. The only difference is that in the preparation process of FeCl2-PAN nanofiber membrane in step (1), the concentration of ferrous chloride tetrahydrate in the spinning solution is increased, specifically using 0.18 g of ferrous chloride tetrahydrate (FeCl2·4H2O); in the preparation process of modified nanofiber membrane in step (2), the concentration of raw materials in the reaction solution is reduced, specifically using 0.1988 g of FeCl2•4H2O and 0.5152 g of phthalonitrile (the molar ratio of FeCl2•4H2O to phthalonitrile is about 1:4).

[0067] Example 10: This example provides a method for preparing a modified nanofiber membrane and the modified nanofiber membrane prepared therefrom, which is basically the same as in Example 1. The only difference is that in the preparation process of FeCl2-PAN nanofiber membrane in step (1), the concentration of ferrous chloride tetrahydrate in the spinning solution is increased. Specifically, the amount of ferrous chloride tetrahydrate (FeCl2·4H2O) is 0.18g.

[0068] Performance Test 1: (1) The modified nanofiber membranes obtained in Examples 1-2 and Comparative Examples 1-10 of the present invention were tested. Specifically, the growth of FePc on the nanofiber membranes was observed by scanning electron microscopy (SEM). The results are shown in [reference]. Figure 1 As shown.

[0069] Depend on Figure 1It is evident that only the embodiments of this invention show the in-situ growth of three-dimensional porous FePc structures (see illustration, resembling flowers, which can be referred to as flower-shaped FePc) on nanofibers or their membranes. In particular, the three-dimensional porous FePc structures in Example 2 exhibit a greater number and more uniformity, along with a more pronounced morphology. Analysis suggests that under suitable conditions, each flower-shaped structure is composed of tightly packed small-diameter nanosheets. This is attributed to the presence of iron ions in the fiber membrane altering the FePc synthesis process, inducing the self-assembly of tiny nanosheets to generate novel flower-shaped radial structures. In contrast, comparative examples 1-10, limited by the concentrations of ferrous chloride tetrahydrate in the spinning solution and the raw material concentrations in the reaction solution, did not generate three-dimensional porous FePc structures. When the concentration of ferrous chloride tetrahydrate in the spinning solution is low (the ratio of ferrous chloride tetrahydrate to PAN is approximately 0.05), nanorod-like structures gradually form on the fiber membrane as the concentration of the raw materials in the reaction solution increases. However, when the ratio of ferrous chloride tetrahydrate to PAN is approximately 0.1, and the concentration of the raw materials in the reaction solution is insufficient, only a small number of irregular morphologies appear. When the ratio of ferrous chloride tetrahydrate to PAN is approximately 0.15, irregular lumps appear on the nanofibers or their membranes. Analysis suggests that this is due to the disordered stacking of FePc caused by the forces between the highly dense iron ion growth sites, resulting in macroscopically chaotic growth.

[0070] The unique three-dimensional porous structure of FePc in this invention can expose more catalytic sites, increase the accessible surface area, and improve catalytic and other effects.

[0071] (2) Figure 2 The image shown is a SEM image of the FeCl2-PAN nanofiber membrane (or membrane substrate) prepared in step (1) of Example 2. It can be seen that before the hydrothermal reaction for in-situ growth, the fibers are smooth, dense, and uniformly arranged in all directions. Figure 3 The image shown is a SEM image of the modified nanofiber membrane prepared in step (2) of Example 2. It can be seen that after the in-situ growth reaction, FePc with a three-dimensional porous structure grows uniformly on the surface of the fiber membrane, is densely distributed, and has a radial size of about 3~5 μm.

[0072] Figure 4 This is an electron microscope image of FePc with a three-dimensional porous structure at a higher magnification. Figure 5The EDS elemental scan of the three-dimensional porous FePc structure clearly shows that it is assembled from multiple stacked sheet-like structures, with C and Fe elements dominating and a significant N element distribution. The high C content characterizes the organic ligands and fibrous membrane matrix of FePc. In contrast, the Fe content in the three-dimensional porous structure is much higher than that in the fibrous membrane, demonstrating that the high specific surface area structure design effectively exposes active sites, facilitating the full utilization of FePc. The uniform N element distribution also corresponds to the phthalocyanine N4 structure in the FePc product and the elemental distribution of nitrile groups (-CN) in the polyacrylonitrile fibers.

[0073] (3) See Figure 6 and Figure 7 As shown, Figure 6 The nitrogen isotherm adsorption-desorption curves of the PAN nanofiber membrane are shown. Figure 7 The nitrogen isotherm adsorption-desorption curves for the modified nanofiber membrane prepared in Example 2 are shown. Compared with the PAN nanofiber membrane, the fiber membrane with flower-like FePc grown on its surface exhibits a certain hysteresis loop during nitrogen adsorption-desorption. The appearance of the hysteresis loop often indicates a special pore structure in BET surface area measurements, which is helpful for further analysis of the porous structure of the material. Figure 6 and Figure 7 The adsorption isotherm exhibits typical Type IV characteristics in the high relative pressure region (P / P0 = 0.8-1.0); in the high relative pressure region (P > 0.8), the isotherm rises rapidly. This phenomenon is likely due to the pore-like structure created by the accumulation of the flower-like FePc plates, leading to capillary condensation of nitrogen during adsorption and desorption under the influence of the mesoporous material. The specific surface area of ​​the fiber membrane can be calculated using the nitrogen isotherm adsorption-desorption curve, where the specific surface area of ​​the PAN nanofiber membrane is 9.905 m². 2 / g, the specific surface area of ​​the modified nanofiber membrane (or 0.5 FePc-PAN) prepared in Example 2 is 13.034 m² / g. 2 / g, the specific surface area increased by approximately 32%, thanks to the in-situ growth of FePc on the fiber membrane surface into a three-dimensional flower-like structure composed of numerous nanosheets. These secondary structures provided a significant additional surface area. Furthermore, the staggered stacking of these two-dimensional nanosheets formed a certain number of mesoporous pores, contributing not only to a greater specific surface area but also enriching the active sites, which is beneficial for its full utilization in the PEO matrix.

[0074] Application Example 1: This example provides a method for preparing a composite nanofiber membrane and the prepared composite nanofiber membrane. Specifically, the preparation method includes: Modified nanofiber membranes were prepared using the method described in Example 2; Take a 1% FePc-PEO-LiTFSI electrolyte mixed solution and use a scraper to uniformly disperse the solution on one side of the modified nanofiber membrane prepared by the method in Example 2, so that the solution fully wets the nanofiber membrane. Then, take a PEO-LiTFSI electrolyte solution and scrape it onto the other side of the modified nanofiber membrane in the same way. Then place it in a vacuum oven at 65°C and dry for 8 h to remove the solvent, to obtain a composite nanofiber membrane (or solid electrolyte film, or FePc-PEO-LiTFSI / 0.5 FePc-PAN) with a first electrolyte layer, a modified nanofiber membrane and a second electrolyte layer sequentially disposed. The 1% FePc-PEO-LiTFSI electrolyte mixed solution contains iron phthalocyanine, polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide, and anhydrous acetonitrile. Based on the total mass of iron phthalocyanine (commercially available from Shanghai Aladdin Biochemical Technology Co., Ltd., iron phthalocyanine (II), FePc), polyethylene oxide (PEO), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as 100%, iron phthalocyanine accounts for 1%, polyethylene oxide (PEO) accounts for 64.1%, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) accounts for 34.9%, with a total solute mass concentration of 12.5%. The PEO-LiTFSI electrolyte solution contains polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide, and anhydrous acetonitrile. Based on the total mass of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as 100%, polyethylene oxide (PEO) accounts for 64.8%, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) accounts for 35.2%, and the total mass concentration of solute in the PEO-LiTFSI electrolyte solution is 12.4%.

[0075] In the fabricated composite nanofiber membrane, the thickness of the first electrolyte layer is approximately 10 μm, the thickness of the modified nanofiber membrane is approximately 30 μm, and the thickness of the second electrolyte layer is approximately 10 μm.

[0076] Subsequently, depending on the type of Li-O2 battery prepared, the composite nanofiber membrane (or solid electrolyte membrane) of appropriate size can be cut using a cutting machine and transferred to a glove box under an argon atmosphere for storage for 24 hours before use.

[0077] Application Example 2: This example provides a method for preparing a composite nanofiber membrane and the prepared composite nanofiber membrane, which is basically the same as in Example 1, except that "the modified nanofiber membrane prepared by the method of Example 2" is replaced with "the modified nanofiber membrane prepared by the method of Example 1". The composite nanofiber membrane prepared in this example can also be called FePc-PEO-LiTFSI / 1FePc-PAN.

[0078] Application Comparative Example 1: This example provides a method for preparing a composite nanofiber membrane and the prepared composite nanofiber membrane, which is basically the same as in Example 1, except that "the modified nanofiber membrane prepared by the method of Example 2" is replaced with "the modified nanofiber membrane prepared by the method of Comparative Example 1". The composite nanofiber membrane prepared in this example can also be called FePc-PEO-LiTFSI / 0.1FePc-PAN.

[0079] Application Comparative Example 2: This example provides a method for preparing a composite nanofiber membrane and the prepared composite nanofiber membrane, which is basically the same as in Example 1, except that "the modified nanofiber membrane prepared by the method of Example 2" is replaced with "the modified nanofiber membrane prepared by the method of Comparative Example 2". The composite nanofiber membrane prepared in this example can also be called FePc-PEO-LiTFSI / 0.3FePc-PAN.

[0080] Performance Test 2: (1) See Figure 8 and Figure 9 As shown, Figure 8 This is a cross-sectional morphology image of the composite nanofiber membrane (or solid electrolyte film) prepared in Application Example 1. Figure 9 The EDS spectrum of the composite nanofiber membrane prepared in Example 1 shows that the composite nanofiber membrane has a uniform thickness, which is due to the better permeation of the electrolyte in the fiber membrane. It is relatively thin, only about 50 μm. C, O, and F elements are uniformly distributed throughout the composite nanofiber membrane. The C and O elements are derived from the chain segments of the PEO matrix, indicating that PEO is fully filled in the electrolyte. The F element comes from LiTFSI, and the uniform dispersion of LiTFSI in PEO is beneficial to the Li... + Transport within the electrolyte. Fe exhibits greater dispersion on one side and some aggregation in the middle, characterizing the in-situ growth of FePc on the fiber membrane and the introduction of some FePc into the PEO matrix on one side. Targeted asymmetric FePc design introduces FePc into the cathode-side interface, optimizing the contact between the cathode and electrolyte film while facilitating the charge-discharge reaction of the Li-O2 battery. The in-situ growth of FePc in the fiber membrane increases iron ion catalytic sites while limiting the shuttle effect of FePc in the reaction, ensuring the fusion of the composite electrolyte and the long-term effect of FePc.

[0081] (2) To further verify the synthesis and crystallinity changes of the three-dimensional porous FePc structure (flower-like FePc structure), X-ray diffraction (XRD) tests were performed and compared with the XRD standard card of FePc (No. 14-0926). Figure 10In the composite nanofiber membranes (or solid electrolyte films) prepared by hydrothermal synthesis of FePc under four different reaction solution concentrations (Comparative Example 1, Comparative Example 2, Example 1, and Example 2), characteristic peaks of FePc at 7.1° and 9.2° were observed, corresponding to the (100) and (102) crystal planes. In addition, a unique crystalline peak of flower-like FePc was observed at 11.4°. These microstructures grow along the polar direction and are densely packed in a flower-like appearance. The formation of the sharp peaks also indicates the regularity and high crystallinity of the structure. The growth and stacking of FePc is ordered, which also explains the exposure of high iron content sites. The peak value is the largest in FePc-PEO-LiTFSI / 0.5 FePc-PAN, corresponding to the high content of the synthesized flower-like structure. Due to the high specific surface area of ​​the nanofiber membrane, the mass of ferrous chloride tetrahydrate in the fiber membrane is small. The reaction solution concentration used in Comparative Example 1 is the lowest, and the synthesis of FePc is insufficient. As the solution concentration increases, more flower-like structures grow and more nanosheet structures stack. The higher crystallization peak observed in Application Example 1 indicates that a higher concentration of the reaction solution raw materials is not necessarily better. In fact, higher concentrations are beneficial for FePc synthesis in solution, while the utilization rate of the nanofiber membrane for the raw materials in solution decreases, resulting in smaller in-situ flower-like structures and lower crystallinity. Furthermore, the introduction of the nanofiber membrane for in-situ FePc growth significantly improves the crystallinity of PEO. The characteristic diffraction peaks at 19° and 23° of the PEO electrolyte are almost invisible, indicating a transformation of the PEO crystalline region into the amorphous region. This is attributed to the combined effect of FePc anchoring in the nanofiber membrane and the high specific surface area of ​​the flower-like FePc, resulting in better dispersion and a higher FePc loading compared to PEO.

[0082] The bonding of the flower-like structures in the composite solid electrolyte was analyzed by Raman spectroscopy (e.g., Figure 11 The solid electrolyte membrane prepared by hydrothermal synthesis of FePc fiber membrane under different reaction solution concentrations (using Comparative Example 1, Comparative Example 2, Example 1, and Example 2) was compared at 1350 cm⁻¹. -1 A new diffraction peak appeared, which is usually the D peak of carbon materials, indicating its defect structure, and at 1580 cm⁻¹ -1The G peak at that location also corresponds to the stretching vibration of graphitic carbon. The higher peak intensity ratio (ID / IG) of carbon points from the more flower-like FePc indicates a greater carbon defect signal; the content of flower-like FePc is directly proportional to the intensity of carbon defects. This may be due to the carbon transformation of the exposed iron sites on the nanofiber membrane substrate. During the FePc synthesis process, defective carbon provides growth sites for the self-assembly of flower-like FePc. The presence of the nanofiber membrane supports the growth of flower-like FePc, both introducing ferrous chloride tetrahydrate as anchoring sites and providing a carbon defect matrix to promote the self-assembly of flower-like FePc. The flower-like FePc is uniformly distributed under the influence of the nanofiber membrane.

[0083] (3) The effect of flower-like FePc on LiTFSI in PEO was further analyzed. Figure 12 The Raman spectra of PEO-LiTFSI and FePc-PEO-LiTFSI / 0.5 FePc-PAN prepared in Example 1 were compared. PEO-LiTFSI showed a higher Raman spectrum at 742 cm⁻¹. -1 Characteristic peaks of LiTFSI were found nearby, while no obvious peaks were observed in FePc-PEO-LiTFSI / 0.5 FePc-PAN. The specific FePc flower morphology increased the Li... + The dissociation and migration of active sites, along with the uniform particle size and flower-like morphology, effectively prevents filler agglomeration, promoting the uniform dispersion of micro-FePc structures between PEO chains. The high specific surface area and high loading of the flower-like FePc, along with the abundant exposed iron sites, strongly enhances the adsorption of anions, thus mitigating the Li+ adsorption. + and TFSI - The interaction between them causes LiTFSI in the composite nanofiber membrane (or solid electrolyte membrane) to almost completely dissociate, and the solvation of LiTFSI allows Li to... + In the electrolyte, it becomes free, and free Li becomes... + Increased Li concentration is beneficial for more Li + Rapid migration during battery cycling.

[0084] (4) The glass transition temperature and enthalpy change (ΔHm) of solid electrolyte films prepared by hydrothermal synthesis of FePc using fiber membranes under different reaction solution raw material concentrations (using Comparative Example 1, Comparative Example 2, Example 1, and Example 2) were tested using DSC. Figure 13As shown, with the increasing abundance of the flower-like structure (the concentration of the reaction solution raw materials continuously increases, in the order of Application Comparative Example 1, Application Comparative Example 2, and Application Example 1), the glass transition temperature of the solid electrolyte film is lower, while the smaller flower-like growth in the reaction solution raw material solution affects the effect of FePc. Among them, the glass transition temperature of FePc-PEO-LiTFSI / 0.5 FePc-PAN is about -41.95℃, which is much lower than that of PEO-LiTFSI (-38.3℃). This also indicates that the microstructures in the flower-like FePc loaded on the PAN nanofiber membrane have sufficient contact with PEO, promoting the chain segment movement of the matrix. Figure 14 These are the endothermic peaks for each test example. The crystalline structure of PEO-LiTFSI reflects a large enthalpy change of 28.496 J / g, indicating that chain segment movement requires greater energy. After doping the fiber film with flower-like FePc, the area of ​​the endothermic peak decreased significantly. However, with the increase of the flower-like FePc content, ΔHm increased slightly. This is due to the enthalpy change caused by the stacking and crystallization of FePc nanosheets; incompletely grown FePc also exhibited additional peaks. Therefore, this strongly suggests that the introduction of the flower-like FePc structure disrupts the crystallinity of PEO, reduces the crystallinity of the PEO matrix, and simultaneously promotes faster chain segment movement, which is beneficial to Li... + Improved transfer dynamics.

[0085] (5) Figure 15 AFM images of PEO-LiTFSI and FePc-PEO-LiTFSI / 0.5 FePc-PAN prepared in Example 1 show that the introduction of flower-like FePc into the fiber membrane still maintains the surface tension of the fiber membrane. Thanks to the flower-like structure of FePc, the plasticity of PEO is further improved, and the polymer electrolyte is better dispersed. FePc-PEO-LiTFSI / 0.5 FePc-PAN has a smaller surface roughness than PEO-LiTFSI, which is beneficial for good interfacial contact on the positive electrode side during battery cycling.

[0086] (6) Figures 16 to 18 This demonstrates the effect of in-situ growth of flower-like FePc on improving the ion transport performance of solid electrolyte films. The ionic conductivity of the composite nanofiber membranes (or solid electrolyte films) obtained from Application Examples 1-2 and Comparative Examples 1-2, as well as the untreated PEO-LiTFSI, was tested at different temperatures. Figure 16As shown, the ionic conductivity increases significantly with the increase of the flower-like FePc content in the composite nanofiber membrane. However, in Application Example 2, the in-situ grown FePc suffered from insufficient growth of the flower-like structure due to competition from the synthesis of other morphologies, such as rod-shaped FePc. The substitution of some flower-like FePc affected the interaction between its multi-metal active sites and PEO segments. Therefore, the FePc-PEO-LiTFSI / 0.5 FePc-PAN solid electrolyte film of Application Example 1 exhibits the best ion transport performance, with an ionic conductivity of 8.36 × 10⁻⁶ at an operating temperature of 60 °C. -4 S·cm -1 This is attributed to the improved multi-site catalysis and ion transport channels of the fibrous membrane through the structural design of FePc. The addition of flower-like FePc and nanofiber membranes modulates the movement of polymer segments and interfacial properties, thus enabling Li... + The rapid transmission provides convenience. To further verify Li + The migration process of Li was investigated, and the polarization potential of the electrolyte and the impedance changes before and after battery polarization were measured. Based on this, the Li... + migration number t Li + The study aimed to verify the effect of adding filler on the electrochemical performance of solid electrolytes. Figures 17-18 The performance of untreated PEO-LiTFSI and FePc-PEO-LiTFSI / 0.5 FePc-PAN composite solid electrolytes at operating temperature (60℃) was compared. + Migration number. t of PEO-LiTFSI electrolyte Li + Only 0.25, Li + Migration is difficult due to the highly crystalline region of PEO. With the introduction of flower-like FePc and nanofiber membranes, the t of the FePc-PEO-LiTFSI / 0.5 FePc-PAN membrane of this invention is improved. Li + The value was increased to approximately 0.54. Analysis suggests that the active center of FePc can interact with EO via hydrogen bonds, which effectively reduces the electron density of O in the ether group, thereby weakening the interaction between PEO and Li. + Coordination between them, weak coordination EO-Li + The formation of Li can endow Li + Greater mobility. Simultaneously, the enhancement of the amorphous region of the PEO electrolyte and the binding of LiTFSI anions by FePc promote a large amount of Li... + The full solvation of Li improved + Concentration, and significantly increased Li under three-dimensional fiber membrane conduction. + The migration of Li is beneficial to improving Li +The conductivity of PEO-based composite solid electrolytes contributes to their efficient application in Li-O2 batteries.

[0087] (7) For solid electrolyte films, the uniform fusion and electrochemical stability of each component determine the long-term stability of the Li-O2 battery during charge and discharge. To analyze the effect of flower-like FePc on the electrochemical stability of the composite electrolyte, differential electrochemical mass spectrometry (DEMs) was used to characterize the gas changes during battery cycling. Due to the high-voltage phenomenon during charging in Li-O2 batteries, the wide electrochemical window of the solid electrolyte film is particularly important. Under high voltage, the polymer matrix easily reacts with Li2O2 to produce harmful byproducts Li2CO3. The high decomposition voltage of Li2CO3 prevents it from decomposing during the charging process of Li-O2 batteries. As the reaction cycle progresses, it accumulates in the porous cathode, blocking oxygen channels and hindering ion transport. These side reactions result in low lifetime and low efficiency of Li-O2 batteries.

[0088] Assembly of Solid-State Lithium-Oxygen Button Cells: The assembly of solid-state lithium-oxygen button cells was carried out in a glove box filled with an argon atmosphere, using a CR2032 porous positive electrode shell, stainless steel gaskets, springs, and a negative electrode shell. Since oxygen participates in battery cycling as a reactant, the porous positive electrode shell was used to allow oxygen to pass through. Using the CR2032 porous positive electrode shell as a base, a PtRuC catalyst-supported carbon paper positive electrode, an electrolyte film, and a commercially available lithium sheet negative electrode were stacked sequentially. The positive electrode was ensured to completely cover the pores in the positive electrode shell. For the FePc-PEO-LiTFSI / 0.5 FePc-PAN of this invention, the side coated with 1% FePc-PEO-LiTFSI electrolyte was closer to the positive electrode, and the side coated with PEO-LiTFSI electrolyte was closer to the negative electrode, while the positive and negative electrodes did not directly contact each other. Then, stainless steel gaskets, springs, and the negative electrode shell were placed on top sequentially, and after stacking, the cells were pressurized and sealed using a button cell packaging machine. After assembly, the cells were transferred to a sealed lithium-oxygen battery testing device, and excess oxygen was introduced for subsequent testing and characterization. The consumption / release of oxygen and carbon dioxide during five cycles was compared between an unmodified electrolyte (PEO-LiTFSI) and an electrolyte with in-situ flower-like FePc grown on a fiber membrane (FePc-PEO-LiTFSI / 0.5 FePc-PAN). Figure 19 As shown. Both electrolytes exhibit CO2 release during cycling. Corresponding to the later stages of Li-O2 battery charging, as the charging process progresses, under the combined action of the positive electrode PtRuC and the interfacial FePc, the Li2O2 discharge products gradually decompose under the influence of catalyst and voltage. Limited by the electrical insulation properties of Li2O2, the charging voltage gradually increases, and the high voltage and active singlet oxygen ( 1Electrolyte decomposition caused by O2 introduces unavoidable carbon (C) into the Li-O2 battery system. The generation of the byproduct Li2CO3 consumes part of the inherent capacity of Li2O2 and further increases the charging voltage. Voltages above 3.8 V are used for Li2CO3 catalysis, where the main decomposition of the product is the conversion of Li2O2 to Li2CO3, accompanied by the release of CO2. Furthermore, as... Figure 19 As shown, during charging, both solid electrolyte films exhibited high and narrow CO2 peaks, producing different amounts of CO2. Under the same oxygen consumption, compared to the unfilled PEO-LiTFSI solid electrolyte film, the solid electrolyte film with in-situ flower-shaped FePc grown on the fiber film showed less CO2 release. This is due to the byproduct suppression effect brought about by the high and uniform distribution of FePc in the electrolyte. The high redox potential of FePc may facilitate the catalytic activity of byproducts at low potentials for Li2CO3. In addition, the presence of FePc can stabilize superoxide radical ions (O2). - This inhibits electrolyte decomposition, which is beneficial to improving the electrochemical stability of the electrolyte. Furthermore, the FePc-PEO-LiTFSI / 0.5 FePc-PAN electrolyte exhibits lower CO2 release and fewer side reactions during cycling, demonstrating good electrochemical stability.

[0089] In addition, considering the oxygen consumption and generation during cycling, the battery using the FePc-PEO-LiTFSI / 0.5 FePc-PAN of this invention exhibits better reversibility and smoother gas changes during charging and discharging. The use of the FePc-PEO-LiTFSI / 0.5 FePc-PAN composite electrolyte promotes further discharge of the Li-O2 battery. The presence of flower-shaped FePc at the interface provides numerous oxygen-binding active sites, facilitating the growth of discharge products at the electrolyte interface, which is beneficial for improving the capacity and stabilizing cycling of the Li-O2 battery.

[0090] (8) Unlike the addition of FePc to the electrolyte, the in-situ growth of flower-like FePc retains more crystalline micro / nano-sheet structures. To verify the influence of the flower-like structure on the interface and stability of the composite solid electrolyte, Li‖PEO-LiTFSI‖Li and Li‖FePc-PEO-LiTFSI / 0.5 FePc-PAN‖Li symmetric cells were assembled. First, the interfacial impedance of the two electrolytes at 60℃ was tested. Figure 20 And perform relaxation time distribution (DRT) analysis. Figure 21 In comparison, the FePc-PEO-LiTFSI / 0.5 FePc-PAN electrolyte exhibits a lower impedance of only 107 Ω, indicating that the flower-like structure of FePc has a relatively small impact on impedance. Figure 21The decrease in impedance in FePc-PEO-LiTFSI / 0.5 FePc-PAN electrolyte is mainly due to the Li at the interface. + Transport (S2) and Li inside the electrolyte + The peak value of the diffusion resistance (S4) decreased, and the extensive growth of FePc flower-like structures at 60℃ promoted the Li at the interface. + The rapid transfer and the large-scale formation of amorphous regions in the PEO matrix reduce the Li + The peak value of the time required for interface migration shifts towards higher frequencies. Additionally, the relatively low contact resistance (S1) indicates good interfacial adhesion of the electrolyte at 60°C. + The broader peak shape of the diffusion resistance (S4) also indicates that the Li in the electrolyte is affected by the flower-like structure of FePc. + The conduction path changes. Subsequently, the critical current density (CCD) of the solid electrolyte film is measured to evaluate the stability of its lithium stripping / plating process. Figure 22 The FePc-PEO-LiTFSI / 0.5 FePc-PAN electrolyte film exhibited a significant decrease in polarization voltage at a current density of 0.25 mA·cm⁻¹. -2 Its voltage is only 2 / 7 that of PEO-LiTFSI electrolyte, and its critical current density is as high as 8.5 mA·cm⁻¹. -2 It also exhibits a high critical current density and a low polarization voltage, indicating that the anchoring effect of the fiber membrane on the flower-shaped FePc brings about internal electrolyte stability and efficient catalysis.

[0091] Furthermore, impedance changes during long-term cycling better reflect the interfacial stability of the electrolyte film. Based on Li‖PEO-LiTFSI‖Li and Li‖FePc-PEO-LiTFSI / 0.5 FePc-PAN‖Li symmetric cells, charge-discharge cycles were performed, and electrochemical impedance spectroscopy (EIS) was recorded after each cycle. For example... Figure 23 The impedance of the symmetric cell assembled with PEO-LiTFSI electrolyte decreased after the first cycle, which is due to the Li + The initial exchange and high temperature improved the interfacial contact. However, with repeated cycles, the interfacial impedance did not change significantly, and Li... + Transport performance at the electrolyte interface is limited. For example... Figure 24 The impedance of the symmetric cell using FePc-PEO-LiTFSI / 0.5FePc-PAN electrolyte film gradually decreased with increasing cycle number (from approximately 105 Ω to 80 Ω). Uniform and minute FePc particles achieved better deposition at the interface, establishing a well-conducting charge-transfer SEI layer. Simultaneously, due to the fixation effect of the fiber film on the flower-like FePc particles, rapid Li-plating was achieved during lithium stripping / plating by bonding the interfacial FePc particles with the fiber film.+ The transport channel enables rapid transfer of electrolyte from its interior to its surface.

[0092] Further testing was conducted on the FePc-PEO-LiTFSI / 0.5 FePc-PAN electrolyte film at different current densities (from 0.1 mA·cm⁻¹). -2 Up to 1.0 mA·cm -2 The current density increases by 0.1 mA·cm² every 10 h. -2 Electrochemical stability at 0.1 mAh·cm⁻¹ -2 surface capacity ( Figure 25 The FePc-PEO-LiTFSI / 0.5 FePc-PAN electrolyte exhibited good lithium stripping / plating reversibility until the current density increased to 0.9 mA·cm⁻¹. -2 It can still cycle stably. The introduction of flower-shaped FePc and the high-strength PAN fiber membrane further enhance the overall dendrite penetration resistance of the composite electrolyte, while the tight interfacial contact enables Li... + Uniform deposition at high current densities. For example... Figure 26 As shown, based on PEO-LiTFSI and FePc-PEO-LiTFSI / 0.5FePc-PAN electrolyte films at 0.1 mA·cm⁻¹ -2 The constant current charging test at the specified current density also verified the above conclusions. Compared to PEO-LiTFSI, which can only be charged for 3 hours, the FePc-PEO-LiTFSI / 0.5 FePc-PAN electrolyte film can be stably charged for up to 74 hours, exhibiting good Li-terministic properties. + Deposition interface.

[0093] To test the availability of solid electrolytes in long-term electrochemical cycling, an areal capacity of 0.1 mAh·cm⁻¹ was used. -2 The current density is 0.1 mA·cm -2 The long-term cycling stability of the Li‖PEO-LiTFSI‖Li symmetric cell was tested under the condition of a current density of 0.1 mA·cm⁻¹. -2 The areal capacity of 0.1 mAh·cm⁻¹ was tested under the following conditions. -2 Surface capacity 0.2 mAh·cm -2 Long-term cycle stability of Li‖FePc-PEO-LiTFSI / 0.5 FePc-PAN‖Li symmetric cells (e.g.) Figure 27The Li‖PEO-LiTFSI‖Li symmetric cell experienced a short circuit after only 125 h of cycling, while the Li‖FePc-PEO-LiTFSI / 0.5FePc-PAN‖Li cell maintained a low potential even after over 1200 or 1400 h of cycling. Furthermore, the symmetric cell using the FePc-PEO-LiTFSI / 0.5FePc-PAN electrolyte exhibited an extremely low polarization voltage (only 30 mV) and a smooth, stable curve. This is attributed to the uniform distribution of in-situ FePc supported by the PAN fiber membrane. The high specific surface area flower-like FePc promoted the formation of a good interface, which is beneficial for Li… + Surface deposition of the flower-like FePc suppresses lithium dendrite growth, achieving long-cycle stability of the battery under low polarization voltage. In summary, the in-situ growth of flower-like FePc on the fiber film not only provides more active sites to improve PEO ion transport capacity while reducing electrolyte side reactions, but also promotes interfacial charge distribution and Li... + The deposition reduces the polarization voltage and improves the long-cycle stability of the composite electrolyte, which is expected to better adapt to the high oxidation environment of Li-O2 batteries.

[0094] In summary, this invention designs a self-assembled three-dimensional porous FePc structure (see figure, flower-like in shape, which can be referred to as flower-shaped FePc) based on in-situ growth of FePc on a fiber membrane. High-strength and heat-resistant PAN is selected as the growth carrier for the flower-shaped FePc, and ferrous halide is introduced to provide growth sites. The defective carbon in the PAN nanofiber membrane at high temperatures promotes the self-assembly of FePc, and the orderly stacking of tiny nanosheets provides a larger specific surface area and exposes a large number of iron active sites. Increased contact between PEO in the electrolyte layer and the flower-shaped FePc promotes the increase of the amorphous region of the electrolyte and the dissociation of LiTFSI, resulting in increased ionic conductivity and ion transference number. The in-situ growth of FePc on the fiber membrane not only loads more active iron metal centers but also prevents harmful FePc shuttle, suppresses the generation of active oxygen in the electrolyte during charge and discharge, reduces side reactions, and improves long-term cycle stability, making it a promising candidate for the development of high-performance all-solid-state Li-O2 batteries.

[0095] As used throughout the specification and claims, the term "comprising" is an open-ended term and should be interpreted as "comprising but not limited to." "Substantially" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect. It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the product or system comprising said element.

[0096] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0097] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A composite nanofiber membrane, characterized in that, The composite nanofiber membrane comprises a first electrolyte layer, a modified nanofiber membrane, and a second electrolyte layer arranged sequentially. The first electrolyte layer comprises iron phthalocyanine, a first polymer, and a first electrolyte lithium salt; the second electrolyte layer comprises a second polymer and a second electrolyte lithium salt. The modified nanofiber membrane comprises modified nanofibers and a three-dimensional porous structure grown in situ on the modified nanofibers. The modified nanofibers contain ferrous iron, and the material of the three-dimensional porous structure comprises ferrocyanine.

2. The composite nanofiber membrane according to claim 1, characterized in that, The ratio of the thickness of the first electrolyte layer, the thickness of the modified nanofiber membrane, and the thickness of the second electrolyte layer is 0.25-0.45:1:0.25-0.

45.

3. The composite nanofiber membrane according to claim 1, characterized in that, In the modified nanofibers, ferrous iron exists in the form of ferrous halide; wherein, by mass percentage, the ferrous halide accounts for 4.5%-7.5% of the modified nanofibers.

4. The composite nanofiber membrane according to claim 3, characterized in that, In the modified nanofibers, the ferrous halide accounts for 5.5%-7.0% by mass percentage; and / or, the ferrous halide is ferrous chloride.

5. The composite nanofiber membrane according to claim 1, characterized in that, The modified nanofiber membrane comprises a matrix formed from modified nanofibers and a three-dimensional porous structure grown in situ on the matrix, wherein the three-dimensional porous structure is composed of multiple nanosheets made of iron phthalocyanine; and / or, in X-ray diffraction patterns, the three-dimensional porous structure has characteristic peaks at 2θ angles of 7.1°±0.2°, 9.2°±0.2°, and 11.4°±0.2°.

6. The composite nanofiber membrane according to claim 1, characterized in that, The modified nanofiber membrane was prepared by the following method: Ferrous chloride or its hydrate and polyacrylonitrile are used to prepare a spinning solution, which is then spun to form a film-like matrix. Phthalonil, ferrous chloride or their hydrates are dispersed in an alcohol solvent to prepare a mixed solution. The matrix is ​​then immersed in the mixed solution and reacted under a protective gas atmosphere and under heating conditions to prepare the modified nanofiber membrane. The total mass concentration of phthalonitrile and ferrous chloride or their hydrates in the mixed solution is 0.8%-2.5% by mass percentage.

7. The composite nanofiber membrane according to claim 6, characterized in that, In the mixed solution, the molar ratio of phthalonitrile to ferrous chloride or its hydrate is 3.8-4.2:1; and / or, by mass percentage, the total mass concentration of phthalonitrile and ferrous chloride or its hydrate in the mixed solution is 0.8%-1.5%; and / or, the alcohol solvent includes ethanol; and / or, the reaction is carried out at 165-190°C; and / or, the reaction is carried out in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene.

8. The composite nanofiber membrane according to claim 1, characterized in that, In the first electrolyte layer, based on the total mass of the iron phthalocyanine, the first polymer, and the first electrolyte lithium salt as 100%, the iron phthalocyanine accounts for 0.5%-1.5%, the first polymer accounts for 62%-66%, and the first electrolyte lithium salt accounts for 33%-37%; and / or, in the second electrolyte layer, based on the total mass of the second polymer and the second electrolyte lithium salt as 100%, the second polymer accounts for 63%-67%, and the second electrolyte lithium salt accounts for 33%-37%; and / or, the first polymer and the second polymer are both polyethylene oxide; and / or, the first electrolyte lithium salt and the second electrolyte lithium salt are both lithium bis(trifluoromethanesulfonylimide); and / or, the composite nanofiber membrane is prepared by the following method: applying an electrolyte mixture slurry containing iron phthalocyanine, the first polymer, and the first electrolyte lithium salt to a first side of the modified nanofiber membrane to form the first electrolyte layer; applying an electrolyte mixture slurry containing a second polymer and a second electrolyte lithium salt to a second side of the modified nanofiber membrane to form the second electrolyte layer; the first side and the second side are disposed opposite to each other.

9. A modified nanofiber membrane, characterized in that, The modified nanofiber membrane comprises modified nanofibers and a three-dimensional porous structure grown in situ on the modified nanofibers. The modified nanofibers contain ferrous iron, and the material of the three-dimensional porous structure comprises ferrocyanine.

10. The application of a composite nanofiber membrane according to any one of claims 1-8, or the modified nanofiber membrane according to claim 9, in a Li-O2 battery.

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