A solid porous polymer membrane for metal-air battery and its preparation method and application

Abstract

The present invention discloses a metal-air battery solid porous polymer film and its preparation method and application, and belongs to the field of metal-air battery technology. The preparation method provided by the present invention comprises the following steps: a fluoropolymer, polyethylene oxide and polyethyleneimine having a mass ratio of (2.5-2.7): (0.3-0.5): 1 are dissolved in a solvent to form a casting solution, and the casting solution is then applied to the substrate surface, placed in water after drying and stripped, and dried to obtain a metal-air battery solid porous polymer film. The preparation method of the present invention is simple, and the obtained metal-air battery solid porous polymer film satisfies the functions of oxygen permeability, hydrophobicity and adsorption of CO2 simultaneously, and can significantly extend the battery cycle life of the metal-air battery.

Description

Technical Field

[0001] The present invention relates to the technical field of metal-air batteries, and in particular to a solid porous polymer membrane for metal-air batteries, a preparation method thereof, and applications thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Traditional lithium-ion batteries have limited energy density, and their actual energy density is close to the theoretical energy density, which is far from meeting the needs of electric vehicles and energy storage. Metal-oxygen (air) batteries are secondary batteries with the highest known theoretical energy density, and are also known as the ultimate battery. They undergo reversible charge and discharge cycles through the generation and decomposition of metal oxides. The positive active material of metal-air batteries comes from oxygen in the air or pure oxygen provided by oxygen tanks. According to the negative electrode material, they can include lithium-air batteries, sodium-air batteries, zinc-air batteries and aluminum-air batteries. Metal-air batteries are composed of air positive electrodes, electrolytes and metal negative electrodes. Its high energy density, low cost and environmental friendliness make it the most promising next-generation high-energy-density energy storage and power battery.

[0004] Although metal-air batteries offer many advantages, actual battery testing and operation still primarily utilize metal-oxygen batteries, which use oxygen cylinders to supply pure oxygen to the battery. This battery system ignores key issues related to the impact of other components of air on battery performance, such as the corrosion of the lithium anode by moisture in the air, the irreversible products generated by CO2 reactions, and low oxygen concentrations in the air. Furthermore, using oxygen cylinders to supply oxygen to the battery not only increases the battery's operating costs, but also poses safety risks.

[0005] Therefore, it is an urgent problem to provide a metal-air battery protective film that is hydrophobic and can adsorb CO2 while ensuring the oxygen transmission channel, so that the metal-air battery has a longer service life in an air atmosphere. Summary of the Invention

[0006] In view of this, the present invention provides a solid porous polymer membrane for a metal-air battery, and a preparation method and application thereof. The solid porous polymer membrane provided by the present invention simultaneously satisfies the functions of oxygen permeability, hydrophobicity and CO2 adsorption, can stabilize the actual discharge and charge capacity of the metal-air battery, and improve battery performance such as battery cycle life.

[0007] In a first aspect, the present invention provides a method for preparing a solid porous polymer membrane for a metal-air battery, comprising the following steps:

[0008] A fluorine-containing polymer, polyethylene oxide and polyethyleneimine in a mass ratio of (2.5-2.7): (0.3-0.5): 1 are dissolved in a solvent to form a casting solution, which is then coated on the surface of a substrate. After drying, the substrate is placed in water for demolding, and a solid porous polymer membrane for a metal-air battery is obtained by drying.

[0009] Preferably, the fluorine-containing polymer includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) or polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE).

[0010] Preferably, the weight average molecular weight of the fluorine-containing polymer is greater than 300,000, the weight average molecular weight of polyethylene oxide is greater than 800,000, and the weight average molecular weight of polyethyleneimine is 1,700 to 2,000.

[0011] Preferably, the solvent is selected from one or more of acetone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; and the total mass fraction of the fluoropolymer, polyethylene oxide, and polyethyleneimine in the casting solution is 10 to 20 wt%.

[0012] Preferably, the specific steps of the preparation process of the casting solution are as follows: adding fluorine-containing polymer, polyethylene oxide and polyethyleneimine to a solvent, stirring at 40-60° C. for 3-6 hours to prepare the casting solution.

[0013] Preferably, in the step of coating the casting liquid on the substrate surface, the coating thickness is 400 to 600 μm; in the step of placing the film in water for demolding after drying, the drying temperature is 60 to 100° C.; and the time for demolding in water is 2 to 10 minutes.

[0014] Preferably, in the step of drying to obtain the solid porous polymer membrane for metal-air batteries, the drying temperature is 15-35°C.

[0015] In a second aspect, the present invention provides a solid porous polymer membrane for a metal-air battery prepared by the above preparation method.

[0016] In a third aspect, the present invention provides a solid porous polymer membrane for a metal-air battery prepared by the above preparation method or the use of the solid porous polymer membrane for a metal-air battery in a metal-air battery.

[0017] In a fourth aspect, the present invention provides a metal-air battery, comprising a positive electrode shell, a gas separation membrane, a positive electrode, an electrolyte layer, a metal negative electrode, a steel sheet, a spring sheet and a negative electrode shell in contact with each other in sequence; the gas separation membrane is a solid porous polymer membrane for a metal-air battery prepared by the above-mentioned preparation method or the above-mentioned solid porous polymer membrane for a metal-air battery.

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0019] The present invention provides a simple method for preparing a solid-state porous polymer membrane for a metal-air battery. This method can produce a solid-state porous polymer membrane with a suitable pore size and morphology. This membrane ensures oxygen diffusion necessary for the reaction, adsorbs CO₂, and reduces the permeation of "impurity" CO₂ gas. It also exhibits excellent hydrophobic properties, reducing the impact of water vapor on the metal-air battery. Application of the present invention's solid-state porous polymer membrane in a metal-air battery can significantly improve the battery's cycle life in an air environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute undue limitations thereon. It is obvious that one of ordinary skill in the art could derive other drawings based on these drawings without inventive effort.

[0021] Figure 1 This is a surface scanning electron microscope image of the solid porous polymer membrane of Example 1 of the present invention, wherein a) is at a magnification of 1600, and b) is at a magnification of 50,000;

[0022] Figure 2 This is a surface scanning electron microscope image of the solid porous polymer membrane of Comparative Example 1 of the present invention, wherein a) is at a magnification of 1600, and b) is at a magnification of 16000;

[0023] Figure 3 This is a surface scanning electron microscope image of the polymer film of Comparative Example 2 of the present invention;

[0024] Figure 4 These are macroscopic photographs of the casting solutions prepared in Comparative Example 3(a), Example 1(b), and Comparative Example 4(c) of the present invention;

[0025] Figure 5 are macroscopic photographs of the solid porous polymer membranes of Comparative Example 3(a) and Example 1(b) of the present invention;

[0026] Figure 6This is a surface scanning electron microscope image of the solid porous polymer membrane of Comparative Example 5 of the present invention; wherein a, the magnification is 500, b, the magnification is 40000;

[0027] Figure 7 Schematic diagram of the assembly structure of the lithium-air battery in the test example of the present invention;

[0028] Figure 8 This is a graph showing the results of the first cycle deep discharge / charge test of a lithium-air battery assembled in a test example of the present invention;

[0029] Figure 9 This is a graph showing the results of a constant capacity cyclic discharge / charge test of a lithium-air battery assembled in a test example of the present invention;

[0030] Figure 10 This is a schematic diagram of the working principle of the solid porous polymer membrane of Example 1 of the present invention when used as a gas separation membrane. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0032] Metal-air batteries operating in an air environment have low gas pressure and low oxygen concentration. Furthermore, impurity gases in the ambient air (such as H2O and CO2) can generate side reaction products during electrochemical reactions, thereby affecting the reaction. For example, water vapor in the air can corrode the lithium metal anode, generating the side reaction product LiOH·H2O. Water vapor and CO2 in the air can also generate side reaction products LiOH and Li2CO3 on the positive electrode side of the battery. As the battery continues to discharge / charge, "dead lithium" will appear on the metal anode, while other products will adhere to the surface of the positive electrode catalyst and the interior of the positive electrode, blocking the transmission channel of the reaction gas from the positive electrode to the electrolyte, reducing the actual discharge capacity of the battery and shortening the battery's cycle life.

[0033] Therefore, the present invention provides a method for preparing a solid porous polymer membrane for a metal-air battery, comprising the following steps:

[0034] A fluorine-containing polymer, polyethylene oxide and polyethyleneimine in a mass ratio of (2.5-2.7): (0.3-0.5): 1 are dissolved in a solvent to form a casting solution, which is then coated on the surface of a substrate. After drying, the substrate is placed in water for demolding, and a solid porous polymer membrane for a metal-air battery is obtained by drying.

[0035] The present invention uses fluoropolymer as the main matrix material, which plays a supporting and hydrophobic role, blocking water vapor from entering the interior of the metal-air battery. The introduction of polyethylene oxide can make the solid porous polymer membrane have a good pore structure, thereby ensuring the smooth penetration of oxygen; if the addition amount of polyethylene oxide is too low, it will cause the membrane surface to be dense, which is difficult to apply in actual metal-air batteries; if the addition amount of polyethylene oxide is too high, it will not only have an adverse effect on the pore structure, but also cause the hydrophobicity of the solid porous polymer membrane to decrease. The introduction of polyethyleneimine can improve the adsorption of CO2 by the solid porous polymer membrane and reduce its impact on the reaction. The appropriate component mass ratio ensures that the solid porous polymer membrane has multiple functions of oxygen permeability, hydrophobicity and CO2 adsorption, thereby stabilizing the actual discharge and charge capacity of the metal-air battery and improving battery performance such as battery cycle life.

[0036] In the present invention, the fluoropolymer includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), or polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE). In one or more embodiments of the present invention, the fluoropolymer is selected from polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0037] In the present invention, the weight average molecular weight of the fluoropolymer is greater than 300,000, the weight average molecular weight of polyethylene oxide is greater than 800,000, and the weight average molecular weight of polyethyleneimine is 1700 to 2000. Suitable molecular weights can ensure good film-forming properties and high mechanical strength of the resulting film.

[0038] In the present invention, the solvent is selected from one or more of acetone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0039] In the present invention, the total mass fraction of the fluoropolymer, polyethylene oxide, and polyethyleneimine in the casting solution is 10-20 wt%, more preferably 12-18 wt%. The appropriate mass fraction can ensure that the casting solution has a suitable viscosity, which is beneficial for subsequent coating and film forming processes.

[0040] In the present invention, the specific steps of preparing the casting solution are as follows: adding a fluoropolymer, polyethylene oxide, and polyethyleneimine to a solvent and stirring at 40-60°C for 3-6 hours to prepare the casting solution. The present inventors found that it is difficult to prepare a uniform, transparent casting solution by stirring at room temperature, while stirring for too long or at too high a temperature can cause gelation, making the solution unusable for subsequent experiments.

[0041] In the step of applying the casting solution to the substrate surface, the coating thickness is 400 to 600 μm, ensuring that the thickness of the resulting solid porous polymer membrane for metal-air batteries is 80 to 300 μm. The appropriate thickness balances the membrane's oxygen permeability, hydrophobicity, and CO adsorption properties. Too thin a thickness can lead to insufficient impurity gas adsorption and barrier properties, while too thick a thickness can result in poor oxygen permeability, affecting electrochemical reaction efficiency.

[0042] In the present invention, in the step of coating the casting liquid on the surface of the substrate, the coating is selected from any one of casting, scraping, spraying, sprinkling or dripping, and the present invention does not impose any special restrictions on this; the material of the substrate can be a glass plate, a polytetrafluoroethylene mold, a metal plate, etc., and the present invention does not impose any special restrictions on this.

[0043] In the step of removing the film from the film after drying in water, the drying temperature is 60-100° C. The present invention does not impose any particular limitation on the drying time as long as the solvent can be completely removed. The drying process is preferably vacuum drying.

[0044] The demolding time in water is 2 to 10 minutes. This operation is to separate the dried film from the substrate and to release some of the polyethylene oxide from the film to form pores. The demolding time should not be too long, otherwise it will lead to the loss of polyethyleneimine.

[0045] In the step of drying to obtain the solid porous polymer membrane for metal-air batteries of the present invention, the drying temperature is 15 to 35° C., and the drying is preferably carried out in a natural drying manner to avoid curling and wrinkling of the wet membrane.

[0046] The present invention provides a solid porous polymer membrane for a metal-air battery prepared by the above preparation method, which has evenly distributed pores on its surface with a pore size of 100 to 500 nm.

[0047] The present invention also provides application of the solid porous polymer membrane for metal-air batteries in metal-air batteries.

[0048] The present invention also provides a metal-air battery, comprising a positive electrode shell, a gas separation membrane, a positive electrode, an electrolyte layer, a metal negative electrode, a steel sheet, a spring sheet and a negative electrode shell in contact with each other in sequence; the gas separation membrane is the solid porous polymer membrane for the metal-air battery mentioned above.

[0049] In the present invention, the positive electrode shell, in addition to serving as a support and conductive material, has its surface covered with uniformly sized and evenly distributed small holes, providing a channel for air transmission. The steel sheet, spring sheet, and negative electrode shell serve as support and conductive material.

[0050] The present invention does not impose any special restrictions on the materials of the positive electrode, electrolyte layer, and metal negative electrode, and materials commonly used in the field can be used. Preferably, the positive electrode includes a conductive support material and a catalyst layer, and the conductive support material includes but is not limited to hydrophilic and hydrophobic carbon paper, nickel foam, etc.; the catalyst material of the catalyst layer is two or more of acetylene black, carbon nanotubes, manganese dioxide (MnO2), or ruthenium dioxide (RuO2), and the catalyst material loading is 0.1 to 0.5 mg / cm 2 .

[0051] The electrolyte layer, located between the positive electrode and the metal negative electrode, consists of a glass fiber membrane soaked with an organic electrolyte of varying concentrations. It can also be a solid electrolyte. The glass fiber membrane is a fiber separator with a certain liquid absorption rate. The organic electrolyte is composed of a metal salt and an organic solvent. The metal salt is determined by the metal negative electrode. For example, when the negative electrode is lithium metal, the metal salt is a lithium salt (including one or more of LiClO4, LiPF6, LiAsF6, LiTFSI, etc.). The organic solvent includes one or more of dimethyl sulfoxide, ether solvents, carbonate solvents, amide solvents, and acetonitrile solvents. The thickness of the electrolyte layer is 0.3 to 1 mm.

[0052] The metal negative electrode includes but is not limited to a lithium negative electrode, a magnesium negative electrode or a sodium negative electrode; the metal-air battery includes but is not limited to an all-solid-state metal-air battery, an organic electrolyte metal-air battery, a dual electrolyte metal-air battery, etc.

[0053] The technical solution of the present invention will be further described below in conjunction with specific examples. The present invention has no particular restrictions on the source of the reagents used, and commercially available products well known to those skilled in the art can be used. In the following examples, the weight-average molecular weight of PVDF-HFP is 400,000, the weight-average molecular weight of PEO is 1,000,000, and the molecular weight of PEI is 1,800.

[0054] Example 1

[0055] This embodiment provides a method for preparing a solid porous polymer membrane.

[0056] (1) Weigh 2.5 g of PVDF-HFP and 0.5 g of PEO, put them into a small beaker, drop 24 g of solvent (6 g of acetone, 18 g of DMF), put in a rotor, place it on a stirrer and stir at 400 r / min for 30 min, then add 1 g of PEI to the resulting slurry, then heat to 50 ° C and stir at a stirring speed of 400 r / min. After stirring for 5 h, the casting solution is obtained.

[0057] (2) The casting solution obtained in step (1) was coated on a transparent glass sheet (10 cm×10 cm×5.5 mm) using an infrared flatbed coating machine, with a coating height of 0.5 mm.

[0058] (3) Place the glass sheet coated with the casting solution in step (2) in a vacuum drying oven, set the temperature to 70° C., and dry for 10 hours to obtain a dry film.

[0059] (4) Immerse the glass sheet with the dry film in step (3) in deionized water for film removal. After about 5 minutes, separate the film from the glass sheet. After taking it out, use filter paper to absorb the water on the surface of the film, and then dry it naturally to obtain a solid porous polymer film.

[0060] The average thickness of the solid porous polymer membrane prepared in this example was measured to be 100 μm, and the water contact angle was 94°, showing hydrophobic properties. It was cut into 15 mm diameter discs using a hydraulic slicer and placed in a glove box for later use. Figure 1 As shown, it can be seen that the solid porous polymer membrane prepared in this embodiment has a circular pore morphology, which is evenly distributed on the surface of the gas separation membrane, and the pore size is about 200-400 nm.

[0061] Example 2

[0062] The difference between this embodiment and embodiment 1 is that, in this embodiment, PVDF-HFP is 2.7 g, PEO is 0.3 g, PEI is 1 g, and the solvent is 20 g.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that PEI is not added in this comparative example. The surface scanning electron microscope image of the solid porous polymer membrane prepared in this comparative example is as follows: Figure 2 As shown, the pore size is about 400 to 600 nm and is evenly distributed on the membrane surface.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that PEO is not added in this comparative example. The surface scanning electron microscope image of the polymer film prepared in this comparative example is as follows: Figure 3 As shown, it can be seen that when no PEO is added, the membrane surface is dense and no obvious pores are observed.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, stirring is performed at room temperature without heating. Figure 4As shown in a, it can be seen that the compatibility between PEO and the solvent is very poor, and there is undissolved polymer solid. The macroscopic photo of the solid porous polymer film obtained in this comparative example is shown in FIG. Figure 5 As shown in a, it can be seen that the uniformity of the prepared solid porous polymer film is very poor. The macroscopic photo of the solid porous polymer film of Example 1 is shown in FIG. Figure 5 As shown in b, it exhibits good uniformity.

[0069] Comparative Example 4

[0070] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, the heating temperature is 50°C, the stirring speed is 400r / min, and the stirring is 8h. Figure 4 As shown in c, the casting solution prepared in Example 1 is as Figure 4 As shown in b, it can be seen that the heating and stirring time of this comparative example is too long, and the casting liquid undergoes gelation, while Example 1 obtains a uniform casting liquid.

[0071] Comparative Example 5

[0072] Compared with Example 1, the difference between this comparative example and Example 1 is that the amount of PVDF-HFP is 2.4 g, the amount of PEO is 0.6 g, and the amount of PEI is 1 g.

[0073] The water contact angle of the solid porous polymer membrane prepared in this comparative example is 86.2°, indicating that the membrane is hydrophilic; the scanning electron microscope image thereof is shown in FIG. Figure 6 As shown, it can be seen that the pores on the surface of the solid porous polymer membrane prepared in this comparative example are unevenly distributed and the pore sizes are uneven, and the number of pores is very small. It can be seen that an increase in the amount of PEO does not lead to an increase in pores, but will have an adverse effect on the pore structure of the membrane.

[0074] Test example

[0075] 1. Gas permeability test

[0076] The gas permeability test was performed on the solid porous polymer membrane of Example 1 and the solid porous polymer membrane of Comparative Example 1, as shown in Table 1.

[0077] Table 1 Gas permeability test results

[0078] serial number <![CDATA[O2 Permeability (cm 3 / (m 2 ·d·Pa))]]> <![CDATA[CO2 permeability (cm 3 / (m 2 ·d·Pa))]]> Example 1 <![CDATA[2.699×10 -4 ]]> <![CDATA[1.579×10 -3 ]]> Comparative Example 1 <![CDATA[2.887×10 -4 ]]> <![CDATA[1.695×10 -3 ]]>

[0079] As can be seen from Table 1, after the addition of PEI, the O2 permeability and CO2 permeability of the solid porous polymer membrane of Example 1 are both reduced compared with those of Comparative Example 1. This is mainly because the pore size of the membrane of Example 1 is smaller than that of the membrane of Comparative Example 1.

[0080] 2. Assembly and electrochemical performance testing of lithium-air batteries:

[0081] The solid porous polymer membrane of Example 1 and the solid porous polymer membrane of Comparative Example 1 were respectively assembled into lithium-air batteries as gas separation membranes (GSM). The battery assembly structure diagram is shown in FIG. Figure 7 As shown, the gas separation membrane is arranged between the cathode shell and the air cathode. The air cathode is a CNT / RuO2 composite cathode, the electrolyte is 1M TEGDME-LiTFSI, and the metal anode is a lithium sheet.

[0082] Assembly method: First, place a spring washer and steel sheet in the negative electrode shell, and place the lithium sheet on top of the steel sheet. Next, place the glass fiber membrane on the lithium sheet and drip 80uL of 1M TEGDME-LiTFSI organic electrolyte, ensuring that the electrolyte evenly soaks the glass fiber membrane. Next, place the air positive electrode (CNT / RuO2 composite positive electrode) on the surface of the glass fiber membrane, and place the gas separation membrane on the surface of the positive electrode, keeping them concentric. Finally, cover the above components with the positive electrode shell, and press the battery with a hydraulic press at 500psi.

[0083] The assembled lithium-air battery was subjected to the first cycle deep discharge / charge test, and the test results are as follows Figure 8 As shown. It can be seen from the figure: when the battery is directly exposed to the ambient air, the maximum discharge capacity of the battery is 10.49mAh, and the discharge voltage platform is stable at about 2.6V; the maximum charge capacity of the battery is 6.06mAh, and the charge voltage platform is stable at about 4.0V. When the battery is equipped with the gas separation membrane of Comparative Example 1, the maximum discharge capacity of the battery in the first cycle is 6.64mAh, and the discharge voltage platform is still stable at about 2.6V; the maximum charge capacity of the battery is 6.56mAh. When the battery is equipped with the gas separation membrane of Example 1, the maximum discharge capacity of the battery in the first cycle is 6.09mAh, and the discharge voltage platform is stable at about 2.6V; the maximum charge capacity of the battery is 5.82mAh. Although the discharge capacity of the battery assembled with the gas separation membranes of Example 1 and Comparative Example 1 is reduced, the effective charge capacity is not reduced.

[0084] The assembled lithium-air battery was subjected to constant capacity cycle discharge / charge test, and the test results are as follows Figure 9 As shown. Figure 9 As can be seen from the graph, the battery equipped with the gas separation membrane of Comparative Example 1 continuously discharges / charges for 400 hours, while the battery equipped with the gas separation membrane of Example 1 continuously discharges / charges for 780 hours. The lithium-air battery without the gas separation membrane only discharges / charges for 270 hours. This shows that the gas separation membrane provided by Example 1 of the present invention can effectively protect the battery and significantly extend its life. Its working principle is as follows: Figure 10As shown, the gas separation membrane is placed on the outside of the air positive electrode. Due to its good surface hydrophobicity, water vapor in the air slides away on the membrane surface and cannot penetrate into the gas separation membrane. At the same time, since the membrane itself has good gas permeability, its surface pores provide a transmission channel for the gas required for the reaction, and filter part of CO2 under the effect of porosity and adsorb part of CO2 under the effect of PEI.

[0085] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a solid porous polymer membrane for a metal-air battery, characterized in that: The steps include: A fluorine-containing polymer, polyethylene oxide, and polyethyleneimine in a mass ratio of (2.5-2.7): (0.3-0.5): 1 are dissolved in a solvent to form a casting solution. The casting solution is then coated on the surface of a substrate, dried, and then placed in water for demolding. After drying, a solid porous polymer membrane for a metal-air battery is obtained.

2. The preparation method according to claim 1, wherein The fluorine-containing polymer includes one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), or polyvinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE).

3. The preparation method according to claim 1, wherein The weight average molecular weight of the fluorine-containing polymer is greater than 300,000, the weight average molecular weight of polyethylene oxide is greater than 800,000, and the weight average molecular weight of polyethyleneimine is 1,700-2,000.

4. The preparation method according to claim 1, wherein The solvent is selected from one or more of acetone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; and in the casting solution, the total mass fraction of the fluorine-containing polymer, polyethylene oxide, and polyethyleneimine is 10-20 wt%.

5. The preparation method according to claim 1, wherein The specific steps of the preparation process of the casting solution are as follows: adding a fluorine-containing polymer, polyethylene oxide and polyethyleneimine to a solvent, stirring at 40-60° C. for 3-6 hours to prepare the casting solution.

6. The preparation method according to claim 1, wherein In the step of coating the casting solution on the substrate surface, the coating thickness is 400-600 μm; in the step of placing the film in water for demolding after drying, the drying temperature is 60-100° C.; and the time for placing the film in water for demolding is 2-10 minutes.

7. The preparation method according to claim 1, wherein In the step of drying to obtain the solid porous polymer membrane for metal-air batteries, the drying temperature is 15-35°C.

8. A solid porous polymer membrane for a metal-air battery prepared by the preparation method according to any one of claims 1 to 7. 9 . Use of the solid porous polymer membrane for metal-air batteries according to claim 8 in metal-air batteries.

10. A metal-air battery, characterized in that: It comprises a positive electrode shell, a gas separation membrane, a positive electrode, an electrolyte layer, a metal negative electrode, a steel sheet, a spring sheet and a negative electrode shell that are in contact with each other in sequence; the gas separation membrane is the solid porous polymer membrane for the metal-air battery according to claim 8.

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