Functional diaphragm as well as preparation method and application thereof

Abstract

The invention relates to a functional diaphragm as well as a preparation method and application thereof, and belongs to the technical field of sodium ion batteries. The functional diaphragm comprises a base membrane and a functional layer arranged on at least one surface of the base membrane, the functional layer comprises a polymer, a functional filler, graphene oxide and an inorganic filler; the polymer is obtained by in-situ polymerization of an ester monomer, a cross-linking agent and an initiator; the functional filler comprises sodium salt, a plasticizer and an additive; the additive is selected from ester compounds and / or nitrile compounds. When the functional diaphragm is used for a Prussian blue analogue battery, the cycle performance of a Prussian blue analogue positive electrode material is remarkably improved, and relatively good rate capability is shown.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a functionalized diaphragm and a preparation method and application thereof. Background Art

[0002] At present, the research on positive electrode materials of sodium ion batteries mainly focuses on three types: layered transition metal oxides, Prussian blue analogs and polyanion compounds. Among them, Prussian blue analogs have three-dimensional, fast sodium ion deintercalation channels and high working voltage (>3.4V), excellent rate performance and cycle stability, and are usually prepared by co-precipitation process, do not require high-temperature sintering, and have relatively low manufacturing costs, which are suitable for large-scale production. Therefore, considering the electrochemical performance and manufacturing cost, if you want to achieve a low-cost, long-life sodium ion battery system, Prussian blue material is the only choice.

[0003] In battery research, inhibition strategies for Prussian blue-based materials to inhibit the dissolution of transition metal ions have been proposed to stabilize cycle life. Inhibition strategies can include four key aspects: electrolyte engineering, transition metal doping / substitution, defect minimization, and composite materials. Electrolyte engineering protects the cathode from dissolution by reducing the impact of active water on the cathode. Transition metal doping or substitution can change the chemical composition and morphological structure of Prussian blue analogs, adjust their lattice parameters and redox properties, and thus improve their structural stability. Defect minimization is to minimize the defects generated during the synthesis process after designing appropriate chemical composition and morphological structure, and improve the structural stability of the material. The synthesis of composite materials stabilizes the crystal structure and surface morphology. The above four inhibition strategies have their own advantages and disadvantages, but all need to start from the design of active materials and electrolyte materials, and gradually improve through feedback from preparation and application, and the research cycle is very long.

[0004] In the application process of Prussian blue analogues, the most important component in the battery, the diaphragm, is usually ignored in order to solve the many problems caused by the dissolution of transition metal ions. The development direction of existing diaphragms is mostly focused on solving the problems of thermal stability and wettability of batteries, and there is not much research on inhibiting the dissolution of transition metals. How to modify the diaphragm to make it suitable for batteries with Prussian blue analogues as active materials needs to be studied. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a functionalized diaphragm and a preparation method and application thereof. When the functionalized diaphragm is used in a Prussian blue analog battery, the cycle performance of the Prussian blue analog positive electrode material is significantly improved and good rate performance is exhibited.

[0006] The first object of the present invention is to provide a functionalized membrane, comprising a base membrane and a functional layer disposed on at least one side of the base membrane;

[0007] The functional layer comprises a polymer, a functional filler, graphene oxide and an inorganic filler;

[0008] The polymer is obtained by in-situ polymerization of an ester monomer, a crosslinking agent and an initiator;

[0009] The functional filler comprises sodium salt, plasticizer and additives; the additives are selected from ester compounds and / or nitrile compounds.

[0010] In one embodiment of the present invention, the ester monomer is selected from one or more of methyl methacrylate, trifluoroethyl methacrylate, polyethylene glycol diacrylate, polyethylene glycol methyl ether methacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate and ethoxylated pentaerythritol tetraacrylate;

[0011] and / or, the cross-linking agent is selected from one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, ethoxylated pentaerythritol tetraacrylate, pentaerythritol tetraacrylate and 1,6-hexanediol dimethacrylate;

[0012] And / or, the initiator is selected from one or more of benzoyl peroxide, azobisisobutyronitrile, dimethyl azobisisobutyrate, azobisisoheptanenitrile, acetyl peroxide, ammonium persulfate, methyl ethyl ketone peroxide and cyclohexanone peroxide.

[0013] In one embodiment of the present invention, the sodium salt is selected from one or more of sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate and sodium difluorooxalatoborate;

[0014] And / or, the plasticizer is selected from one or more of ethylene carbonate, vinylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,3-dioxane, trimethyl phosphate, triethyl phosphate, succinonitrile and adiponitrile;

[0015] And / or, the ester compound is selected from one or more of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)phosphate, diphenyl phosphite, vinyl sulfate and 1,3-propane sultone succinic anhydride;

[0016] And / or, the nitrile compound is selected from ethoxypentafluorocyclotriphosphazene and / or hexafluorocyclotriphosphazene.

[0017] In one embodiment of the present invention, the additive participates in the formation of the SEI film, thereby changing its chemical composition and structure, making it more stable.

[0018] In one embodiment of the present invention, the inorganic filler is selected from one or more of sodium aluminate, nano-β-aluminum oxide, metal organic framework materials and sodium super ion conductors.

[0019] In one embodiment of the present invention, the weight fraction of the polymer in the functional layer is 70%-85%, the weight fraction of the functional filler is 1%-20%, the weight fraction of graphene oxide is 1%-10%, and the weight fraction of the inorganic filler is 0.1%-5%;

[0020] The mass ratio of the ester monomer, the crosslinking agent and the initiator is (90-99):(5-10):(1-5);

[0021] The mass ratio of the sodium salt, the plasticizer and the additive is (30-50):(20-50):(20-50).

[0022] In one embodiment of the present invention, the base film has a thickness of 8 μm-40 μm and a porosity of 30%-80%;

[0023] And / or, the thickness of the functional layer is 1 μm-20 μm.

[0024] In one embodiment of the present invention, the base film is selected from one or more of polyethylene film (PE), polypropylene film (PP), polyethylene terephthalate film (PET), polyimide film (PI), polydimethylsiloxane film (PDMS), polyamide film (PA), non-woven fabric and glass fiber film.

[0025] The second object of the present invention is to provide a method for preparing the functionalized membrane, comprising the following steps:

[0026] S1. Stirring the sodium salt, plasticizer and additives until clear and transparent to obtain a functional filler solution;

[0027] S2, adding ester monomer, crosslinking agent, initiator, graphene oxide and inorganic filler to the functional filler solution described in S1, stirring until clear and transparent, to obtain a functional modified solution;

[0028] S3, placing the functional modification solution described in S2 on at least one side of the base film, performing a polymerization reaction at 40° C.-100° C. to form a functional layer, thereby obtaining the functionalized diaphragm.

[0029] In one embodiment of the present invention, in S3, the graphene oxide is added in the form of a solution, and the solvent of the graphene oxide solution is selected from one or more of methanol, ethanol, isopropanol, ethyl acetate, N-methylpyrrolidone, dimethyl sulfoxide and N,N-dimethylformamide; the concentration of graphene oxide is 5 mg / mL-50 mg / mL.

[0030] In one embodiment of the present invention, in S3, the setting method is selected from one or more of blade coating, roller coating, spray coating, spin coating, dipping, filter pressing, suction filtration, casting and hot pressing.

[0031] The third object of the present invention is to provide a sodium ion battery, wherein the positive electrode material of the sodium ion battery comprises a Lushi blue analogue; and the diaphragm is the functionalized diaphragm.

[0032] The technical solution of the present invention has the following advantages over the prior art:

[0033] (1) The combined effect of graphene oxide and inorganic filler in the functionalized diaphragm of the present invention inhibits the dissolution and migration of transition metal ions in the Prussian blue analog positive electrode material, thereby stabilizing the material structure. This is because graphene oxide has a large number of oxygen-containing functional groups, which can produce d-π conjugated interactions with transition metal ions in the Prussian blue positive electrode, forming chemical constraints, thereby inhibiting the dissolution and migration of transition metal ions; the inorganic filler has an adjustable porous structure, which can form good interface compatibility with the electrode material and reduce the interface impedance. At the same time, the open metal sites of the inorganic filler can promote the dissociation of lithium salts and fix anions through Lewis acid-base interactions, thereby obtaining a higher sodium ion mobility and a high transfer number, thereby constructing a highly compatible electrode / electrolyte interphase layer and an organic / inorganic composite sodium ion conduction path, thereby improving the rate performance of the material.

[0034] (2) The functionalized diaphragm described in the present invention, on the one hand, achieves the purpose of inhibiting the migration and dissolution of transition metal ions of the Prussian blue analog positive electrode material through the base film and the functional layer with chemical restriction effect and rapid sodium ion conductivity; on the other hand, it utilizes the highly compatible electrode / electrolyte interphase layer and the organic / inorganic composite sodium ion conduction path to accelerate the transmission of sodium ions; improve the structural stability and electrochemical performance of the Prussian blue analog positive electrode material; reduce the voltage decay during the cycle process, and significantly improve the cycle life.

[0035] (3) The functionalized diaphragm described in the present invention has the functions of absorbing electrolyte, inhibiting the dissolution of transition metal ions, and isolating the positive and negative electrodes. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0037] In the present invention, unless otherwise explained, technical and scientific terms used in the present invention have the same meanings as commonly understood by those skilled in the art to which the present invention belongs.

[0038] In the present invention, unless otherwise stated, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0039] In the present invention, unless otherwise stated, the experimental methods used in the embodiments of the present invention are conventional methods unless otherwise stated, and the materials, reagents, etc. used are all commercially available unless otherwise stated.

[0040] In the present invention, unless otherwise specified, the Ti-MOF used in the examples of the present invention is purchased from Sigma-Aldrich, and the model is Ti-MOF-79.

[0041] In the present invention, unless otherwise specified, the graphene oxide solution used in the embodiments of the present invention is prepared by dissolving 35 mg of graphene oxide in ethanol to obtain a graphene oxide solution with a concentration of 25 mg / mL.

[0042] Example 1

[0043] The functionalized diaphragm and the preparation method thereof of this embodiment specifically include the following steps:

[0044] S1. Mix 50 mg of sodium perchlorate, 45 mg of propylene carbonate and 45 mg of fluoroethylene carbonate, and stir at room temperature until clear and transparent to obtain a functional filler solution;

[0045] S2, 475 mg of polyethylene glycol methyl diacrylate, 25 mg of pentaerythritol tetraacrylate, 5 mg of Ti-MOF (2% of the total content), graphene oxide solution (50 mg of graphene oxide, 5% of the total content) and 5 mg of azobisisobutyronitrile were mixed and added to the functional filler solution, and stirred until clear and transparent to obtain a functional modified solution;

[0046] S3. Pour the functional modified solution onto a polypropylene film with a thickness of 10 μm and a porosity of 50%, and use a four-sided film-making device to quickly and evenly scrape it. After scraping, place it in an oven at 70°C and heat it for 3 hours to allow the functional modified solution to undergo polymerization reaction to form a functional layer with a thickness of 10 μm, thereby obtaining a functionalized diaphragm with a specific three-dimensional network structure.

[0047] Example 2

[0048] The functionalized diaphragm and the preparation method thereof of this embodiment specifically include the following steps:

[0049] S1. Mix 50 mg of sodium perchlorate, 45 mg of propylene carbonate and 45 mg of fluoroethylene carbonate, and stir at room temperature until clear and transparent to obtain a functional filler solution;

[0050] S2, 475 mg of polyethylene glycol methyl diacrylate, 25 mg of pentaerythritol tetraacrylate, 5 mg of Ti-MOF (2% of the total content), graphene oxide solution (50 mg of graphene oxide, 5% of the total content) and 5 mg of azobisisobutyronitrile were mixed and added to the functional filler solution, and stirred until clear and transparent to obtain a functional modified solution;

[0051] S3. Pour the functional modified solution onto a polypropylene film with a thickness of 10 μm and a porosity of 50%, and use a four-sided film-making device to quickly and evenly scrape it. After scraping, place it in an oven at 70°C and heat it for 3 hours to allow the functional modified solution to undergo polymerization reaction to form a functional layer with a thickness of 5 μm, thereby obtaining a functionalized diaphragm with a specific three-dimensional network structure.

[0052] Comparative Example 1

[0053] The method is basically the same as Example 1, except that graphene oxide is not added, and specifically comprises the following steps:

[0054] S1. Mix 50 mg of sodium perchlorate, 45 mg of propylene carbonate and 45 mg of fluoroethylene carbonate, and stir at room temperature until clear and transparent to obtain a functional filler solution;

[0055] S2, adding 475 mg of polyethylene glycol methyl diacrylate, 25 mg of pentaerythritol tetraacrylate, 5 mg of Ti-MOF and 5 mg of azobisisobutyronitrile to the functional filler solution, and stirring until clear and transparent to obtain a functional modified solution;

[0056] S3. Pour the functional modified solution onto a polypropylene film with a thickness of 10 μm and a porosity of 50%, and use a four-sided film former to quickly and evenly scrape it. After scraping, place it in an oven at 70°C and heat it for 3 hours to allow the functional modified solution to undergo polymerization reaction to form a functional layer with a thickness of 10 μm, thereby obtaining a diaphragm.

[0057] Comparative Example 2

[0058] The method is basically the same as Example 1, except that Ti-MOF is not added, and specifically comprises the following steps:

[0059] S1. Mix 50 mg of sodium perchlorate, 45 mg of propylene carbonate and 45 mg of fluoroethylene carbonate, and stir at room temperature until clear and transparent to obtain a functional filler solution;

[0060] S2, adding 475 mg of polyethylene glycol methyl diacrylate, 25 mg of pentaerythritol tetraacrylate, graphene oxide solution (50 mg of graphene oxide) and 5 mg of azobisisobutyronitrile to the functional filler solution, stirring until clear and transparent to obtain a functional modified solution;

[0061] S3. Pour the functional modified solution onto a polypropylene film with a thickness of 10 μm and a porosity of 50%, and use a four-sided film former to quickly and evenly scrape it. After scraping, place it in an oven at 70°C and heat it for 3 hours to allow the functional modified solution to undergo polymerization reaction to form a functional layer with a thickness of 10 μm, thereby obtaining a diaphragm.

[0062] Comparative Example 3

[0063] A polypropylene film with a thickness of 10 μm and a porosity of 50% was placed in an oven at 70° C. and heated for 3 h to obtain a separator.

[0064] Test Example 1: Battery production and performance testing based on the separators of Examples 1-2 and Comparative Examples 1-3

[0065] Assembly of sodium-ion battery: A slurry containing 80% of the Prussian analogue cathode material Na2MnFe(CN)6, 10% superP and 10% polyvinylidene fluoride was coated on aluminum foil and dried at 100°C for 10 h. The electrode film was then punched into a cathode sheet with a diameter of 14 mm, in which the mass loading of the active material was about 2.5 mg / cm 2 ; Sodium hexafluorophosphate is dissolved in ethylene carbonate to prepare an electrolyte with a concentration of 1 mol / L; In a glove box filled with argon, the positive electrode sheet, diaphragm, sodium metal sheet, diaphragm and electrolyte are assembled into a sodium ion battery.

[0066] Activation of sodium ion batteries: The assembled batteries were placed in a 45°C constant temperature box and activated using a Blue Electric charge and discharge instrument. The activation voltage range was 2V-4V, and the charge and discharge rate was 0.1C. The charge and discharge were performed for 3 weeks.

[0067] Battery cycle stability test: The activated battery is subjected to 2C, 10,000-cycle cycle stability test, with the charge and discharge voltage range of 2V-4V. During the test, the instrument automatically records the charge and discharge data and related curves; the discharge medium voltage after 500 cycles is recorded and subtracted from the discharge medium voltage of the first cycle to obtain the change value of the discharge medium voltage;

[0068] Battery rate performance test: The activated battery is subjected to constant current charge and discharge tests at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C. The charge and discharge voltage range is 2V-4V. During the test, the instrument automatically records the charge and discharge data and related curves.

[0069] Table 1 shows the relevant performance parameters finally measured:

[0070] Table 1

[0071]

[0072] As can be seen from Table 1, the cycle stability of the sodium ion batteries of the embodiments has been improved. The capacity retention rate of the sodium ion battery of the embodiment after 10,000 cycles is much higher than that of the comparative example, and the decrease in the discharge medium voltage after 500 cycles is much lower than that of the comparative example. This is because the combined effect of graphene oxide and inorganic fillers in the functionalized diaphragm inhibits the dissolution and migration of transition metal ions in the Prussian positive electrode, stabilizes the material structure, and has a high reaction potential, so the capacity retention rate and discharge medium voltage can be maintained.

[0073] By comparing Examples 1-2, it can be seen that the stability of the discharge medium voltage of the sodium ion battery of Example 1 remains the best. Compared with the functionalized diaphragm of the thin functional layer in Example 2, the effect of inhibiting the dissolution and migration of transition metal ions is better, which further verifies the role of the functional layer in stabilizing the discharge medium voltage of the Prussian blue analogue positive electrode material.

[0074] Comparison of Example 1 and Comparative Example 1 shows that the performance of Comparative Example 1 is reduced because graphene oxide is not added. This is because graphene oxide has more oxygen-containing functional groups, which can produce d-π conjugated interactions with transition metal ions in the Prussian blue positive electrode to form chemical constraints, thereby inhibiting the dissolution and migration of transition metal ions.

[0075] Comparison of Example 1 and Comparative Example 2 shows that the performance of Comparative Example 2 is reduced without adding Ti-MOF. This is because the inorganic filler Ti-MOF has adjustable porosity and can form good interface compatibility with the electrode material, reducing the interface impedance. At the same time, the open metal sites of Ti-MOF can promote the dissociation of lithium salts and fix anions through Lewis acid-base interactions, thereby obtaining a higher sodium ion mobility and a high transfer number, thus constructing a highly compatible electrode / electrolyte interphase layer and an organic / inorganic composite sodium ion conduction path, thereby improving the rate performance of the material.

[0076] Comparing Example 1 and Comparative Example 3, it can be seen that in Comparative Example 3, no functional layer is provided, the rate performance of the battery is not improved, and its capacity retention rate drops sharply.

[0077] Test Example 2

[0078] Based on Example 1 and Test Example 1, the effects of the thickness of the functional layer, the type and amount of the inorganic filler, and the amount of graphene oxide on the performance of the sodium ion battery were explored. Table 2 shows the relevant variables and performance parameters:

[0079] Table 2

[0080]

[0081] As can be seen from Table 2, sodium ion batteries with excellent performance can be obtained by using the inorganic fillers of the present application. As the amount of inorganic filler increases, the rate performance of the sodium ion battery does not change much, but the capacity retention rate and the discharge voltage drop decrease and increase to varying degrees respectively. This is because as the proportion of inorganic filler increases, the polymerization strength of the functional layer decreases, various microcracks are easily generated, and ion transmission is concentrated around the microcracks, thereby hindering the functional layer from playing a role. As the amount of graphene oxide increases, the rate performance remains basically unchanged, but the capacity retention rate increases. However, when the content of graphene oxide is too high (greater than 20%), it will cause micro-short circuits when applied to the diaphragm. As the thickness of the functional layer increases, its rate performance gradually decreases. This is because the increase in the thickness of the functional layer increases the distance of ion transmission, thereby increasing the migration resistance of sodium ions in the diaphragm, which in turn affects the rapid charge and discharge capability of the battery. Therefore, when the functional layer is less than 1μm, the functional material content is small and it has no substantial effect, and the capacity retention rate drops sharply; when the functional layer is greater than 20μm, the coating layer is too thick and the diaphragm will peel off during the battery cycle, thus affecting the cycle performance.

[0082] In summary, under the action of the functionalized diaphragm, the capacity retention rate of the Prussian blue analog positive electrode material after 10,000 cycles is above 96%, and the capacity utilization rate reaches above 80% at a high rate of 5C charge and discharge. In addition, the functionalized diaphragm has a simple preparation process and abundant raw material resources, which can effectively improve the stability of the Prussian blue analog positive electrode material, extend the cycle life of the Prussian blue analog positive electrode material in sodium ion batteries, and significantly improve the practical application value of sodium ion batteries using Prussian blue analog positive electrodes.

[0083] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A functionalized membrane, characterized in that: It includes a base film and a functional layer disposed on at least one side of the base film; The functional layer comprises a polymer, a functional filler, graphene oxide and an inorganic filler; The polymer is obtained by in-situ polymerization of an ester monomer, a crosslinking agent and an initiator; The functional filler comprises sodium salt, plasticizer and additives; the additives are selected from ester compounds and / or nitrile compounds.

2. The functionalized membrane according to claim 1, characterized in that: The ester monomer is selected from one or more of methyl methacrylate, trifluoroethyl methacrylate, polyethylene glycol diacrylate, polyethylene glycol methyl ether methacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate and ethoxylated pentaerythritol tetraacrylate; and / or, the cross-linking agent is selected from one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, ethoxylated pentaerythritol tetraacrylate, pentaerythritol tetraacrylate and 1,6-hexanediol dimethacrylate; And / or, the initiator is selected from one or more of benzoyl peroxide, azobisisobutyronitrile, dimethyl azobisisobutyrate, azobisisoheptanenitrile, acetyl peroxide, ammonium persulfate, methyl ethyl ketone peroxide and cyclohexanone peroxide.

3. The functionalized membrane according to claim 1, characterized in that: The sodium salt is selected from one or more of sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate and sodium difluorooxalatoborate; And / or, the plasticizer is selected from one or more of ethylene carbonate, vinylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, 1,3-dioxane, trimethyl phosphate, triethyl phosphate, succinonitrile and adiponitrile; And / or, the ester compound is selected from one or more of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)phosphate, diphenyl phosphite, vinyl sulfate and 1,3-propane sultone succinic anhydride; And / or, the nitrile compound is selected from ethoxypentafluorocyclotriphosphazene and / or hexafluorocyclotriphosphazene.

4. The functionalized membrane according to claim 1, characterized in that: The inorganic filler is selected from one or more of sodium aluminate, nano-β-aluminum oxide, metal organic framework materials and sodium super ion conductors.

5. The functionalized membrane according to claim 1, characterized in that: The weight fraction of the polymer in the functional layer is 70%-85%, the weight fraction of the functional filler is 1%-20%, the weight fraction of graphene oxide is 1%-10%, and the weight fraction of the inorganic filler is 0.1%-5%; The mass ratio of the ester monomer, the crosslinking agent and the initiator is (90-99):(5-10):(1-5); The mass ratio of the sodium salt, the plasticizer and the additive is (30-50):(20-50):(20-50).

6. The functionalized membrane according to claim 1, characterized in that: The base film has a thickness of 8 μm-40 μm and a porosity of 30%-80%; And / or, the thickness of the functional layer is 1 μm-20 μm.

7. The functionalized membrane according to claim 1, characterized in that: The base film is selected from one or more of polyethylene film, polypropylene film, polyethylene terephthalate film, polyimide film, polydimethylsiloxane film, polyamide film, non-woven fabric and glass fiber film.

8. The method for preparing a functionalized membrane according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Stirring the sodium salt, plasticizer and additives until clear and transparent to obtain a functional filler solution; S2, adding ester monomer, crosslinking agent, initiator, graphene oxide and inorganic filler to the functional filler solution described in S1, stirring until clear and transparent, to obtain a functional modified solution; S3, placing the functional modification solution described in S2 on at least one side of the base film, performing a polymerization reaction at 40° C.-100° C. to form a functional layer, thereby obtaining the functionalized diaphragm.

9. The method for preparing a functionalized diaphragm according to claim 8, characterized in that: In S3, the setting method is selected from one or more of blade coating, roller coating, spray coating, spin coating, dipping, filter pressing, suction filtration, casting and hot pressing.

10. A sodium ion battery, characterized in that: The positive electrode material of the sodium ion battery includes a Lushi blue analog; and the diaphragm is the functionalized diaphragm according to any one of claims 1 to 7.

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