Nanometer fibrous lithium ion sieve adsorption film as well as preparation method and application thereof

Abstract

The invention provides a nanofiber-shaped lithium ion sieve adsorption film as well as a preparation method and application thereof, and belongs to the technical field of nanofiber materials. The general chemical formula of the nanofiber lithium ion sieve adsorption film is Hx 'Mny' Oz 'or Ha' Mnb 'Oc', x ', y', z ', a', b 'and c' represent relative atom numbers, x ': y': z '= 1: 0.5-2: 1.5-4, and a': b ': c' = 1: 0.5-1.25: 1.5-3. The nanofiber lithium ion sieve adsorption membrane provided by the invention is not supported by a polymer blend, has the lithium ion sieve content of 100%, has the characteristics of high lithium ion sieve content, large specific surface area, full opening of adsorption sites, light weight, softness and the like, and can ensure that the material has high adsorption rate and adsorption capacity equivalent to those in a powder state; therefore, the special effect application in the field of lithium extraction from salt lakes and seawater is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiber materials, and in particular to a nanofiber-shaped lithium ion sieve adsorption membrane and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid development of new energy vehicles and energy storage technology, the application of lithium in new energy materials and other related fields has received great attention, resulting in a rapid increase in lithium salt consumption. Faced with the current situation of surging demand for lithium, it is particularly important to quickly develop low-cost, high-efficiency and environmentally friendly lithium extraction technology.

[0003] Lithium ion sieve has become a hot topic in the current research of lithium adsorbents extracted from salt lake brine due to its high selective adsorption capacity for lithium ions. However, the lithium ion sieves prepared at this stage are mostly ultrafine powders (particle size is about 1 to 10 μm), which are very easy to cause loss during use and transfer, and have problems such as high dissolution rate and poor permeability. Therefore, constructing lithium ion sieve materials with macroscopic continuity is the key to solving the above problems. However, the current technology mainly prepares lithium ion sieve powder by high-temperature solid phase method, hydrothermal method, sol-gel method, etc., and then blends the micron-level lithium ion sieve powder with organic polymer, and prepares lithium ion sieve adsorption materials with macroscopic continuity by sol-gel method, electrospinning method, granulation, foaming, coating and other methods. Due to the presence of organic polymers, the above materials generally have problems such as low lithium ion sieve loading and closed active sites; in addition, the compatibility problem between lithium ion sieve and organic polymer also seriously affects the dispersion of lithium ion sieve in polymer, making lithium ion sieve prone to agglomeration or uneven distribution, resulting in the lithium adsorption performance of the material cannot meet the actual application requirements. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a nanofibrous lithium ion sieve adsorption membrane and its preparation method and application. The method provided by the present invention can ensure that the finally prepared nanofibrous membrane has no support from the blended polymer, and the lithium ion sieve content reaches 100%, ensuring that the material has a high adsorption rate and adsorption capacity equivalent to its powder state, so as to achieve its special application in the field of lithium extraction from salt lakes and seawater.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is a nanofiber lithium ion sieve adsorption membrane, the chemical formula of which is H x’ Mn y’ O z’ or H a’ Mn b’ O c’, wherein x', y', z', a', b' and c' represent the relative number of atoms, x':y':z'=1:0.5~2:1.5~4, a':b':c'=1:0.5~1.25:1.5~3.

[0007] The second technical solution of the present invention is a method for preparing the above-mentioned nanofibrous lithium ion sieve adsorption membrane, comprising the following steps:

[0008] After dissolving the metal salt, the reactant small molecule and the blended polymer in a solvent, an electrospinning solution is obtained, and then the electrospinning solution is subjected to electrospinning to prepare a nanofiber membrane precursor; the metal salt is a manganese salt or a titanium salt;

[0009] In-situ synthesizing the nanofiber membrane precursor to obtain a metal salt / blended polymer composite nanofiber membrane;

[0010] In situ synthesizing the metal oxide / blended polymer composite nanofiber membrane by a hydrothermal method in a lithium salt aqueous solution;

[0011] The metal oxide / blended polymer composite nanofiber membrane is subjected to high-temperature calcination and acid washing in sequence to obtain the nanofiber-shaped lithium ion sieve adsorption membrane.

[0012] A third technical solution of the present invention is an application of the above-mentioned nanofibrous lithium ion sieve adsorption membrane in the selective extraction of lithium from salt lakes and seawater with a high magnesium-to-lithium ratio.

[0013] A fourth technical solution of the present invention is a method for selectively extracting lithium from a salt lake with a high magnesium-to-lithium ratio, using the above-mentioned nanofibrous lithium ion sieve adsorption membrane to adsorb lithium in a salt lake with a high magnesium-to-lithium ratio.

[0014] The present invention discloses the following technical effects

[0015] The nanofibrous lithium ion sieve adsorption membrane provided by the present invention has no blended polymer support, and the lithium ion sieve content reaches 100%. It has the characteristics of high lithium ion sieve content, large specific surface area, fully open adsorption sites, light weight, softness, etc., which can ensure that the material has a high adsorption rate and adsorption capacity equivalent to its powder state, so as to achieve its special application in the field of lithium extraction from salt lakes and seawater.

[0016] The preparation method provided by the present invention can ensure that the content of lithium ion sieve in the final prepared nanofiber membrane reaches 100%, which gives the material macroscopic continuity, lightness and flexibility on the basis of retaining the high specific surface area and adsorption sites of the lithium ion sieve itself. At the same time, the micrometer pores constructed by the intertwining of the nanofiber-like lithium ion sieve can effectively reduce the mass transfer resistance of the water flow. The lithium ion sieve uniformly grown in the form of nanofibers can provide a high specific surface area and a large number of adsorption sites, achieving the requirements of high throughput, high adsorption rate, high adsorption capacity, and excellent adsorption cyclicity that need to be met in the lithium extraction technology of salt lakes and seawater. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 The nanofibrous H obtained in Example 1 1.6 Mn 1.6 Nitrogen adsorption diagram and specific surface area of ​​O4 adsorption film;

[0019] Figure 2 The nanofibrous H obtained in Example 1 1.6 Mn 1.6 Lithium ion adsorption isotherm of O4 adsorption film;

[0020] Figure 3 The nanofibrous H obtained in Example 1 1.6 Mn 1.6 SEM image of O4 adsorption film;

[0021] Figure 4 The nanofibrous H obtained in Example 1 1.6 Mn 1.6 Optical photograph of O4 adsorption film. DETAILED DESCRIPTION

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0024] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0025] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] The present invention provides a nanofiber lithium ion sieve adsorption membrane, the general chemical formula of which is H x’ Mn y’ O z’ or H a’ Mn b’ O c’ , wherein x', y', z', a', b' and c' represent the relative number of atoms, x':y':z'=1:0.5~2:1.5~4, a':b':c'=1:0.5~1.25:1.5~3.

[0028] The present invention also provides a method for preparing the nanofibrous lithium ion sieve adsorption membrane, comprising the following steps:

[0029] After dissolving the metal salt, the reactant small molecule and the blended polymer in a solvent, an electrospinning solution is obtained, and then the electrospinning solution is subjected to electrospinning to prepare a nanofiber membrane precursor; the metal salt is a manganese salt or a titanium salt;

[0030] In-situ synthesizing the nanofiber membrane precursor to obtain a metal salt / blended polymer composite nanofiber membrane;

[0031] In situ synthesizing the metal oxide / blended polymer composite nanofiber membrane by a hydrothermal method in a lithium salt aqueous solution;

[0032] The metal oxide / blended polymer composite nanofiber membrane is subjected to high-temperature calcination and acid washing in sequence to obtain the nanofiber-shaped lithium ion sieve adsorption membrane.

[0033] The present invention first dissolves metal salt, reactant small molecules and blended polymer in a solvent to obtain an electrospinning solution with specific viscosity and conductivity, and then uses the electrospinning technology to prepare a nanofiber membrane precursor from the electrospinning solution.

[0034] In some embodiments, the manganese salt is at least one of potassium permanganate, manganese carbonate, manganese nitrate, MnO2, Mn2O3, γ-MnOOH, manganese acetate, manganese chloride and manganese sulfate;

[0035] The titanium salt is at least one of TiO2, metatitanic acid, tetrabutyl titanate and anhydrous titanium sulfate;

[0036] The reactant small molecule is at least one of ethylene glycol, sodium dodecyl sulfate, hydrazine hydrate, sucrose, potassium persulfate, sodium persulfate, sodium fluoride and urea;

[0037] The blended polymer is at least one of polyacrylonitrile, polyethylene glycol, polyacrylamide, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, hydroxymethyl cellulose, nylon 6, ethylene-vinyl alcohol copolymer, polymethyl methacrylate and polyvinylidene fluoride;

[0038] The solvent is mesitylene, methanol, chloroform, benzyl alcohol, ethanol, n-butanol, chloroform, dichloromethane, tetrahydrofuran, 1,4-dioxane, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetone or formic acid.

[0039] In some embodiments, the mass ratio of the metal salt, the reactant small molecule, the blended polymer and the solvent is 0.5-3.0:0-10:4-12:100.

[0040] In the present invention, when the amounts of metal salt, reactant small molecules, blended polymer and solvent are not within the above ranges, the following situations will occur: (1) the spinning solution cannot form nanofibers with uniform diameters through an electrospinning method; (2) the amount of metal salt synthesized in the subsequent metal salt / blend polymer composite nanofiber membrane is insufficient, and it is difficult to maintain the original nanofiber morphology after the subsequent calcination and removal of the blended polymer.

[0041] In some embodiments, the electrospinning process parameters are: voltage 15-30 kV, liquid supply rate 0.2-5.0 mL / min, receiving distance 10-40 cm, drum speed 30-80 r / min, spinning temperature 20-28° C., and humidity 20-80%.

[0042] In the present invention, if the electrospinning parameters are not within the above range, the spinning solution will not be able to break through the surface tension of the spinning solution under the action of charging, and will not be able to form a Taylor cone and continuously spray out into filaments, making it impossible for the material to form a nanofiber morphology with uniform diameter, resulting in low lithium adsorption and poor mechanical properties of the material.

[0043] In some embodiments, the material for receiving the fiber membrane in the electrospinning is oil-absorbing paper, tin foil, aluminum foil or non-woven fabric.

[0044] After obtaining the nanofiber membrane precursor, the present invention performs in-situ synthesis on the nanofiber membrane precursor to obtain a metal salt / blended polymer composite nanofiber membrane.

[0045] In some embodiments, the nanofiber membrane precursor is subjected to in-situ synthesis at a temperature of 25-150° C. and a time of 1-24 h.

[0046] After obtaining the metal salt / blended polymer composite nanofiber membrane, the present invention uses the metal salt / blended polymer composite nanofiber membrane to in situ synthesize a metal oxide / blended polymer composite nanofiber membrane in a lithium salt aqueous solution by a hydrothermal method. Wherein, when the metal oxide in the metal oxide / blended polymer composite nanofiber membrane is lithium manganese oxide, the chemical formula of the lithium manganese oxide is Li x Mn y O z , where x, y, z represent the relative number of atoms, x:y:z=1:0.5~2:1.5~4;

[0047] When the metal oxide in the metal oxide / blended polymer composite nanofiber membrane is lithium titanium oxide, the general chemical formula of the lithium titanium oxide is Li a Ti b O c , where a, b, c represent the relative number of atoms, a:b:c=1:0.5~1.25:1.5~3.

[0048] In some embodiments, the metal salt / blended polymer composite nanofiber membrane is in situ synthesized into a metal oxide / blended polymer composite nanofiber membrane by a hydrothermal method in a lithium salt aqueous solution, wherein the lithium salt aqueous solution is a lithium hydroxide aqueous solution, a lithium nitrate aqueous solution, a lithium carbonate aqueous solution or a lithium sulfate aqueous solution, and the concentration of the lithium salt aqueous solution is 0.1 to 4.0 mol / L; the reaction temperature of the hydrothermal method is 25-150°C, and the time is 1-24h.

[0049] In some embodiments, the concentration of the lithium salt aqueous solution is 2.0-4.0 mol / L; the reaction temperature of the hydrothermal method is 100-150° C., and the reaction time is 20-24 h.

[0050] In the present invention, if the reaction temperature and time of the hydrothermal method are lower than the above parameter ranges, the target metal oxide / blend polymer composite nanofiber membrane cannot be synthesized.

[0051] In some embodiments, after the hydrothermal reaction is completed, the steps of water washing and drying are further included; the drying temperature is 80° C. and the drying time is 6-24 hours.

[0052] A metal oxide / blended polymer composite nanofiber membrane is obtained. The metal oxide / blended polymer composite nanofiber membrane is subjected to high-temperature calcination and acid washing in sequence to obtain the nanofiber-shaped lithium ion sieve adsorption membrane.

[0053] In some embodiments, the high temperature calcination temperature is 200-750° C., and the time is 1-8 hours.

[0054] The present invention uses high-temperature calcination to crystallize the metal oxide (lithium manganese or lithium titanium oxide), and removes the blended polymer by high-temperature melting. When the calcination temperature and time are lower than the above range, the metal oxide (lithium manganese or lithium titanium oxide) will have low crystallinity and incomplete removal of the blended polymer; when the calcination temperature is higher than the above range, the blended polymer will be easily melted and removed too quickly, causing the nanofiber structure to collapse; both of the above situations will have an adverse effect on the lithium adsorption performance and mechanical properties of the final material.

[0055] In some embodiments, the acid solution used in the pickling is nitric acid, hydrochloric acid or sulfuric acid; the concentration of the acid solution is 0.1-2.0 mol / L; the temperature of the pickling is 25-80° C., and the pickling time is 1-24 h.

[0056] In some embodiments, after the acid washing is completed, the process further comprises the steps of washing the product obtained by the acid washing with water and drying the product; the drying temperature is 80° C. and the drying time is 6-24 hours.

[0057] The present invention also provides the use of the nanofiber lithium ion sieve adsorption membrane in selectively extracting lithium from salt lakes and seawater with a high magnesium-to-lithium ratio.

[0058] The present invention also provides a method for selectively extracting lithium from a salt lake with a high magnesium-to-lithium ratio, using the nanofiber-shaped lithium ion sieve adsorption membrane to adsorb lithium in the salt lake with a high magnesium-to-lithium ratio.

[0059] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0060] The raw materials and reagents used in the examples can be obtained through commercial sources.

[0061] Example 1

[0062] This embodiment provides a nanofibrous lithium ion sieve adsorption membrane (H 1.6 Mn 1.6 O4 adsorption film).

[0063] The preparation steps are as follows:

[0064] S1: Potassium permanganate (0.18 g), ethylene glycol (0.9 mL) and polyacrylonitrile (MW = 150,000, 0.8 g) were mixed and dissolved in 10 mL N, N-dimethylformamide to obtain an electrospinning solution with a viscosity of 4.5 Pa·s and a conductivity of 3072 μS / mm; then, a potassium permanganate / ethylene glycol / polyacrylonitrile ternary system nanofiber membrane was obtained by electrospinning technology, and the specific electrospinning parameters were: voltage 22.5 kV, liquid supply rate 1.0 mL / min, receiving distance 15 cm, drum speed 30 r / min, the material receiving the fiber membrane was oil-absorbing paper, the spinning temperature was 25 ° C, and the humidity was 55%. Then, the potassium permanganate / ethylene glycol / polyacrylonitrile ternary system nanofiber membrane obtained above was placed in a 120 ° C forced air oven for 10 hours to obtain a γ-MnOOH / polyacrylonitrile composite nanofiber membrane.

[0065] S2: The γ-MnOOH / polyacrylonitrile composite nanofiber membrane (0.1 g) obtained in S1 was placed in 40 mL of lithium hydroxide aqueous solution (2.0 mol / L), and reacted at 120 ° C for 24 h by a hydrothermal method. The fiber membrane after the reaction was washed with water and dried in a vacuum oven at 80 ° C for 12 h to obtain Li 1.6 Mn 1.6 O4 / polyacrylonitrile composite nanofiber membrane.

[0066] S3: Li obtained in S2 1.6 Mn 1.6The O4 / polyacrylonitrile composite nanofiber membrane (0.1 g) was placed in a muffle furnace and calcined at 400 °C in air for 4 h to make Li 1.6 Mn 1.6 O4 crystallization, and high temperature melting to remove polyacrylonitrile, thereby obtaining Li 1.6 Mn 1.6 O4 nanofiber membrane.

[0067] S4: Li obtained in S3 1.6 Mn 1.6 The O4 nanofiber membrane was immersed in a hydrochloric acid solution (0.5 mol / L) at room temperature for 24 h, then washed with deionized water and methanol in sequence, and dried in an oven at 80 °C for 12 h to obtain a nanofiber-shaped H 1.6 Mn 1.6 O4 adsorption film.

[0068] The obtained nanofibrous H 1.6 Mn 1.6 The specific surface area of ​​the O4 adsorption film was 21.74 g / m 2 ( Figure 1 ), the lithium ion adsorption capacity is 46.11 mg / g ( Figure 2 ). Figure 3 The nanofiber-shaped H 1.6 Mn 1.6 Scanning electron microscopy (SEM) images of O4 adsorption films show that the fiber surface presents a uniformly distributed rough structure; Figure 4 The optical image shows the nanofiber-shaped H 1.6 Mn 1.6 The O4 adsorption film is macroscopically continuous and flexible.

[0069] Example 2

[0070] This embodiment provides a nanofibrous lithium ion sieve adsorption membrane (HMn2O4 adsorption membrane).

[0071] The preparation steps are as follows:

[0072] S1: Potassium permanganate (0.25g), sucrose (1.2g) and polyethylene glycol (MW = 1,000,000, 1.0g) were mixed and dissolved in 10mL of ethanol to obtain an electrospinning solution with a viscosity of 4.0Pa·s and a conductivity of 3500μS / mm; then, a potassium permanganate / sucrose / polyethylene glycol ternary system nanofiber membrane was obtained by electrospinning technology, and the specific electrospinning parameters were: voltage 20kV, liquid supply rate 1.0mL / min, receiving distance 20cm, drum speed 60r / min, the material of the receiving fiber membrane was oil-absorbing paper, the spinning temperature was 25°C, and the humidity was 55%. Then, the potassium permanganate / sucrose / polyethylene glycol ternary system nanofiber membrane obtained above was placed in a 120°C forced air oven for 12h to obtain a γ-MnOOH / polyethylene glycol composite nanofiber membrane.

[0073] S2: The γ-MnOOH / polyethylene glycol composite nanofiber membrane (0.1 g) obtained in S1 was placed in 40 mL of lithium hydroxide aqueous solution (4.0 mol / L), and reacted at 120°C for 24 h by a hydrothermal method. The fiber membrane after the reaction was washed with water and dried in a vacuum oven at 80°C for 12 h to obtain a LiMn2O4 / polyethylene glycol composite nanofiber membrane.

[0074] S3: The LiMn2O4 / polyethylene glycol composite nanofiber membrane (0.1 g) obtained in S2 is placed in a muffle furnace and calcined at 600°C in air for 5 h to crystallize LiMn2O4 and remove the polyethylene glycol by high-temperature melting, thereby obtaining a LiMn2O4 nanofiber membrane.

[0075] S4: The LiMn2O4 nanofiber membrane obtained in S3 was immersed in a hydrochloric acid solution (0.5 mol / L) at room temperature for 24 h, then washed with deionized water and methanol in turn, and dried in an oven at 80°C for 12 h to obtain a nanofibrous HMn2O4 adsorption membrane.

[0076] The specific surface area of ​​the obtained nanofibrous HMn2O4 adsorption film was measured to be 25.66 g / m 2 , the lithium ion adsorption capacity is 36.80 mg / g.

[0077] Example 3

[0078] This embodiment provides a nanofibrous lithium ion sieve adsorption membrane (H2TiO3 adsorption membrane).

[0079] The preparation steps are as follows:

[0080] S1: Anhydrous titanium sulfate (0.15g), sodium fluoride (0.02g), urea (0.9mL) and polyacrylonitrile (MW=150,000, 0.8g) were mixed and dissolved in 10mL N,N-dimethylformamide to obtain an electrospinning solution with a viscosity of 6.0Pa·s and a conductivity of 8500μS / mm; then an anhydrous titanium sulfate / sodium fluoride / urea / polyacrylonitrile quaternary system nanofiber membrane was obtained by electrospinning technology, and the specific electrospinning parameters were: voltage 25kV, liquid supply rate 0.5mL / min, receiving distance 15cm, drum speed 30r / min, the material of the receiving fiber membrane was oil-absorbing paper, spinning temperature was 25℃, and humidity was 55%. Then, the above-obtained anhydrous titanium sulfate / sodium fluoride / urea / polyacrylonitrile quaternary system nanofiber membrane was placed in a 150℃ forced air oven for 8h to obtain a TiO2 / polyacrylonitrile composite nanofiber membrane.

[0081] S2: The TiO2 / polyacrylonitrile composite nanofiber membrane (0.1 g) obtained in S1 was placed in 40 mL of lithium hydroxide aqueous solution (2.0 mol / L), and reacted at 150°C for 20 h by a hydrothermal method. The fiber membrane after the reaction was washed with water and dried in a vacuum oven at 80°C for 12 h to obtain a Li2TiO3 / polyacrylonitrile composite nanofiber membrane.

[0082] S3: The Li2TiO3 / polyacrylonitrile composite nanofiber membrane (0.1 g) obtained in S2 was placed in a muffle furnace and calcined at 750°C in air for 5 h to crystallize Li2TiO3 and remove polyacrylonitrile by high-temperature melting, thereby obtaining a Li2TiO3 nanofiber membrane.

[0083] S4: The Li2TiO3 nanofiber membrane obtained in S3 was immersed in a hydrochloric acid solution (0.5 mol / L) at room temperature for 24 h, then washed with deionized water and methanol in turn, and dried in an oven at 80°C for 12 h to obtain a nanofibrous H2TiO3 adsorption membrane.

[0084] The specific surface area of ​​the obtained nanofibrous H2TiO3 adsorption film was measured to be 35.44 g / m 2 , the lithium ion adsorption capacity is 66.80 mg / g.

[0085] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A nanofibrous lithium ion sieve adsorption membrane, characterized in that: The chemical formula is H x’ Mn y’ O z’ or H a’ Mn b’ O c’ , wherein x', y', z', a', b' and c' represent the relative number of atoms, x':y':z'=1:0.5~2:1.5~4, a':b':c'=1:0.5~1.25:1.5~3.

2. A method for preparing the nanofibrous lithium ion sieve adsorption membrane according to claim 1, characterized in that: The following steps are involved: After dissolving the metal salt, the reactant small molecule and the blended polymer in a solvent, an electrospinning solution is obtained, and then the electrospinning solution is subjected to electrospinning to prepare a nanofiber membrane precursor; the metal salt is a manganese salt or a titanium salt; In-situ synthesizing the nanofiber membrane precursor to obtain a metal salt / blended polymer composite nanofiber membrane; In situ synthesizing the metal oxide / blended polymer composite nanofiber membrane by a hydrothermal method in a lithium salt aqueous solution; The metal oxide / blended polymer composite nanofiber membrane is subjected to high-temperature calcination and acid washing in sequence to obtain the nanofiber-shaped lithium ion sieve adsorption membrane.

3. The method for preparing the nanofibrous lithium ion sieve adsorption membrane according to claim 2, characterized in that: The manganese salt is at least one of potassium permanganate, manganese carbonate, manganese nitrate, MnO2, Mn2O3, γ-MnOOH, manganese acetate, manganese chloride and manganese sulfate; The titanium salt is at least one of TiO2, metatitanic acid, tetrabutyl titanate and anhydrous titanium sulfate; The reactant small molecule is at least one of ethylene glycol, sodium dodecyl sulfate, hydrazine hydrate, sucrose, potassium persulfate, sodium persulfate, sodium fluoride and urea; The blended polymer is at least one of polyacrylonitrile, polyethylene glycol, polyacrylamide, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, hydroxymethyl cellulose, nylon 6, ethylene-vinyl alcohol copolymer, polymethyl methacrylate and polyvinylidene fluoride; The solvent is mesitylene, methanol, chloroform, benzyl alcohol, ethanol, n-butanol, chloroform, dichloromethane, tetrahydrofuran, 1,4-dioxane, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetone or formic acid.

4. The method for preparing the nanofibrous lithium ion sieve adsorption membrane according to claim 2, characterized in that: The process parameters of the electrostatic spinning are: voltage 15-30 kV, liquid supply rate 0.2-5.0 mL / min, receiving distance 10-40 cm, drum speed 30-80 r / min, spinning temperature 20-28° C., and humidity 20-80%.

5. The method for preparing the nanofibrous lithium ion sieve adsorption membrane according to claim 2, characterized in that: The nanofiber membrane precursor is subjected to in-situ synthesis, wherein the temperature of the in-situ synthesis is 25-150° C. and the time is 1-24 hours.

6. The method for preparing the nanofibrous lithium ion sieve adsorption membrane according to claim 2, characterized in that: The lithium salt aqueous solution is a lithium hydroxide aqueous solution, a lithium nitrate aqueous solution, a lithium carbonate aqueous solution or a lithium sulfate aqueous solution, and the concentration of the lithium salt aqueous solution is 0.1-4.0 mol / L; the reaction temperature of the hydrothermal method is 25-150° C., and the reaction time is 1-24 h.

7. The method for preparing the nanofibrous lithium ion sieve adsorption membrane according to claim 2, characterized in that: The high temperature calcination is carried out at a temperature of 200-750° C. and for a time of 1-8 hours.

8. The method for preparing the nanofibrous lithium ion sieve adsorption membrane according to claim 2, characterized in that: The acid solution used in the pickling is nitric acid, hydrochloric acid or sulfuric acid; the concentration of the acid solution is 0.1-2.0 mol / L; the temperature of the pickling is 25-80° C., and the pickling time is 1-24 hours.

9. Use of the nanofibrous lithium ion sieve adsorption membrane according to claim 1 in selectively extracting lithium from salt lakes and seawater with a high magnesium-to-lithium ratio.

10. A method for selectively extracting lithium from a salt lake with a high magnesium-to-lithium ratio, characterized in that: The nanofibrous lithium ion sieve adsorption membrane according to claim 1 is used to adsorb lithium in a salt lake with a high magnesium-lithium ratio.

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