A functionalized membrane, its preparation method and application

Abstract

This invention relates to a functionalized separator, its preparation method, and its application, belonging to the field of sodium-ion battery technology. The functionalized separator of this invention includes a base film and a functional layer disposed on at least one side of the base film; the functional layer includes a polymer, functional fillers, graphene oxide, and inorganic fillers; the polymer is obtained by in-situ polymerization of ester monomers, crosslinking agents, and initiators; the functional fillers include sodium salts, plasticizers, and additives; the additives are selected from ester compounds and / or nitrile compounds. When used in Prussian blue analog batteries, this functionalized separator significantly improves the cycle performance of the Prussian blue analog cathode material and exhibits good rate performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a functionalized separator, its preparation method and application. Background Technology

[0002] Current research on cathode materials for sodium-ion batteries mainly focuses on three types: layered transition metal oxides, Prussian blue analogs, and polyanionic compounds. Among them, Prussian blue analogs possess three-dimensional, rapid sodium-ion insertion / extraction channels and high operating voltage (>3.4V), excellent rate performance and cycle stability, and are typically prepared using a co-precipitation process, eliminating the need for high-temperature sintering, resulting in relatively low manufacturing costs and suitability for large-scale production. Therefore, considering both electrochemical performance and manufacturing cost, Prussian blue material is undoubtedly the best choice for achieving a low-cost, long-life sodium-ion battery system.

[0003] In battery research, strategies to suppress the dissolution of transition metal ions in Prussian blue analogues have been proposed to stabilize cycle life. These 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 influence of active water on it. Transition metal doping or substitution can alter the chemical composition and morphology of Prussian blue analogues, adjusting their lattice parameters and redox properties to improve structural stability. Defect minimization, after designing suitable chemical composition and morphology, minimizes defects generated during synthesis to enhance material structural stability. Composite material synthesis stabilizes the crystal structure and surface morphology. Each of these four suppression strategies has its advantages and disadvantages, but all require starting from the design of active and electrolyte materials, and gradual improvement through feedback from preparation and application, resulting in a long research cycle.

[0004] In the application of Prussian blue analogues, the most important component in the battery—the separator—is often overlooked in addressing the numerous problems caused by the dissolution of transition metal ions. The development of existing separators has mostly focused on solving the problems of battery thermal stability and wettability, with little research on inhibiting the dissolution of transition metals. How to modify the separator to be suitable for batteries using Prussian blue analogues as active materials remains to be studied. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a functionalized separator, its preparation method, and its application. When used in Prussian blue analog batteries, this functionalized separator significantly improves the cycle performance of the Prussian blue analog cathode material and exhibits better rate performance.

[0006] The first objective of this 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 includes polymers, functional fillers, graphene oxide, and inorganic fillers;

[0008] The polymer is obtained by in-situ polymerization of ester monomers, crosslinking agents, and initiators;

[0009] The functional filler includes sodium salts, plasticizers, 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 crosslinking 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 difluorooxalate borate.

[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-dioxane, 1,3-dioxane, trimethyl phosphate, triethyl phosphate, succinate, and adiponitrile;

[0015] And / or, the ester compound is selected from one or more of vinylene carbonate, fluorovinyl carbonate, tris(trimethylsilane) phosphate, diphenyl phosphite, vinyl sulfate, and 1,3-propanesulfonate lactone 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 altering its chemical composition and structure and 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-alumina, metal-organic framework materials and sodium superionic conductors.

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

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

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

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

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

[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), nonwoven fabric and glass fiber film.

[0025] A second objective of this invention is to provide a method for preparing the aforementioned functionalized membrane, comprising the following steps:

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

[0027] S2. Add ester monomers, crosslinking agents, initiators, graphene oxide, and inorganic fillers to the functional filler solution described in S1 and stir until clear and transparent to obtain a functional modified solution.

[0028] S3. The functional modification solution described in S2 is placed on at least one side of the base membrane, and a polymerization reaction is carried out at 40℃-100℃ to form a functional layer, thereby obtaining the functionalized membrane.

[0029] In one embodiment of the present invention, in S3, the graphene oxide is added in the form of a solution, wherein 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; and the concentration of graphene oxide is 5 mg / mL to 50 mg / mL.

[0030] In one embodiment of the present invention, in S3, the setting method is selected from one or more of the following: scraping, roller coating, spraying, spin coating, dipping, pressure filtration, vacuum filtration, casting, and hot pressing.

[0031] A third objective of this invention is to provide a sodium-ion battery, wherein the positive electrode material of the sodium-ion battery includes a Russo blue analogue; and the separator is the aforementioned functionalized separator.

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

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

[0034] (2) The functionalized membrane described in this invention, on the one hand, achieves the purpose of inhibiting the migration and dissolution of transition metal ions in Prussian blue analog cathode materials through the base membrane and the functional layer with chemical restriction and rapid sodium ion conduction; on the other hand, it accelerates the transport of sodium ions by utilizing the highly compatible electrode / electrolyte interphase layer and organic / inorganic composite sodium ion conduction pathway; improves the structural stability and electrochemical performance of Prussian blue analog cathode materials; reduces voltage decay during cycling, and significantly improves cycle life.

[0035] (3) The functionalized membrane described in this invention has functions such as adsorbing electrolyte, inhibiting the dissolution of transition metal ions, and isolating the positive and negative electrodes. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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 this invention, unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

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

[0039] In this invention, unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

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

[0041] In this invention, unless otherwise stated, the graphene oxide solution used in the embodiments of this invention is obtained 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 its preparation method in this embodiment specifically include the following steps:

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

[0045] S2. Mix 475 mg of polyethylene glycol diacrylate, 25 mg of pentaerythritol tetraacrylate, 5 mg of Ti-MOF (2% of total content), graphene oxide solution (50 mg of graphene oxide, 5% of total content) and 5 mg of azobisisobutyronitrile and add them to the functional filler solution. Stir until clear and transparent to obtain the functional modified solution.

[0046] S3. Pour the functional modification solution onto a polypropylene membrane with a thickness of 10 μm and a porosity of 50%, and use a four-sided film maker to quickly and uniformly coat it. After coating, place it in an oven at 70°C and heat for 3 hours to allow the functional modification solution to undergo a polymerization reaction to form a functional layer with a thickness of 10 μm, thus obtaining a functionalized membrane with a specific three-dimensional network structure.

[0047] Example 2

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

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

[0050] S2. Mix 475 mg of polyethylene glycol diacrylate, 25 mg of pentaerythritol tetraacrylate, 5 mg of Ti-MOF (2% of total content), graphene oxide solution (50 mg of graphene oxide, 5% of total content) and 5 mg of azobisisobutyronitrile and add them to the functional filler solution. Stir until clear and transparent to obtain the functional modified solution.

[0051] S3. Pour the functional modification solution onto a polypropylene membrane with a thickness of 10 μm and a porosity of 50%, and use a four-sided film maker to quickly and uniformly coat it. After coating, place it in an oven at 70°C and heat for 3 hours to allow the functional modification solution to undergo a polymerization reaction to form a functional layer with a thickness of 5 μm, thus obtaining a functionalized membrane with a specific three-dimensional network structure.

[0052] Comparative Example 1

[0053] The process is basically the same as in Example 1, except that graphene oxide is not added. Specifically, it includes the following steps:

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

[0055] S2. Mix 475 mg of polyethylene glycol diacrylate, 25 mg of pentaerythritol tetraacrylate, 5 mg of Ti-MOF and 5 mg of azobisisobutyronitrile and add them to the functional filler solution. Stir until clear and transparent to obtain the functional modified solution.

[0056] S3. Pour the functional modification solution onto a polypropylene membrane with a thickness of 10 μm and a porosity of 50%, and use a four-sided film forming device to quickly and uniformly coat it. After coating, place it in an oven at 70°C and heat for 3 hours to allow the functional modification solution to undergo a polymerization reaction to form a functional layer with a thickness of 10 μm, thus obtaining a separator.

[0057] Comparative Example 2

[0058] The process is basically the same as in Example 1, except that Ti-MOF is not added. Specifically, it includes the following steps:

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

[0060] S2. Mix 475 mg of polyethylene glycol diacrylate, 25 mg of pentaerythritol tetraacrylate, graphene oxide solution (50 mg of graphene oxide) and 5 mg of azobisisobutyronitrile and add them to the functional filler solution. Stir until clear and transparent to obtain the functional modified solution.

[0061] S3. Pour the functional modification solution onto a polypropylene membrane with a thickness of 10 μm and a porosity of 50%, and use a four-sided film forming device to quickly and uniformly coat it. After coating, place it in an oven at 70°C and heat for 3 hours to allow the functional modification solution to undergo a polymerization reaction to form a functional layer with a thickness of 10 μm, thus obtaining a separator.

[0062] Comparative Example 3

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

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

[0065] Assembly of sodium-ion batteries: A slurry containing 80% Prussian analog cathode material Na2MnFe(CN)6, 10% superP, and 10% polyvinylidene fluoride was coated onto aluminum foil. After drying at 100°C for 10 hours, the electrode film was perforated to form a cathode sheet with a diameter of 14 mm, wherein the mass loading of the active material was approximately 2.5 mg / cm³. 2 Sodium hexafluorophosphate was 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, separator, sodium metal sheet, separator and electrolyte were assembled into a sodium-ion battery.

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

[0067] Battery cycle stability test: The activated battery is subjected to 2C, 10,000-cycle cycle stability test, with a 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 voltage after 500 cycles is recorded and subtracted from the discharge voltage of the first cycle to obtain the change in discharge voltage.

[0068] Battery rate performance test: The activated battery was 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 was 2V-4V. During the test, the instrument automatically recorded the charge and discharge data and related curves.

[0069] Table 1 shows the final measured performance parameters:

[0070] Table 1

[0071]

[0072] As shown in Table 1, the cycle stability of the sodium-ion batteries in the examples was improved. The capacity retention of the sodium-ion batteries in the examples after 10,000 cycles was significantly higher than that of the comparative examples, and the decrease in discharge voltage after 500 cycles was significantly smaller than that of the comparative examples. This is because the combined effect of graphene oxide and inorganic fillers in the functionalized separator inhibited the dissolution and migration of transition metal ions in the Prussian cathode, stabilizing the material structure and resulting in a higher reaction potential, thus maintaining the capacity retention and discharge voltage.

[0073] Comparing Examples 1 and 2, it can be seen that the sodium-ion battery in Example 1 maintains the best stability of discharge voltage. Compared with the functionalized separator with thin functional layer in Example 2, it has a better effect on inhibiting the dissolution and migration of transition metal ions, further verifying the role of the functional layer in stabilizing the discharge voltage of the Prussian blue analog cathode material.

[0074] Comparing Example 1 and Comparative Example 1, it can be seen that the performance of Comparative Example 1 is reduced because graphene oxide was not added. This is because graphene oxide has more oxygen-containing functional groups, which can generate d-π conjugated interactions with transition metal ions in the Prussian blue cathode, forming chemical constraints and thus inhibiting the dissolution and migration of transition metal ions.

[0075] Comparing Example 1 and Comparative Example 2, it can be seen that the performance of Comparative Example 2, which did not include Ti-MOF, decreased. This is because the inorganic filler Ti-MOF has tunable porosity, which allows it to form good interfacial compatibility with the electrode material, reducing interfacial impedance. At the same time, the open metal sites of Ti-MOF can promote the dissociation of lithium salt and fixation of anions through Lewis acid-base interactions, thereby obtaining higher sodium ion mobility and high transfer number. Therefore, a highly compatible electrode / electrolyte interphase layer and an organic / inorganic composite sodium ion conduction pathway are constructed, improving the rate performance of the material.

[0076] Comparing Example 1 and Comparative Example 3, it can be seen that Comparative Example 3 does not have a functional layer, so 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 functional layer thickness, type and amount of inorganic filler, and amount of graphene oxide on the performance of sodium-ion batteries were investigated. Table 2 shows the relevant variables and performance parameters:

[0079] Table 2

[0080]

[0081] As shown in Table 2, sodium-ion batteries with excellent performance can be obtained using the inorganic fillers described in this application. With increasing amounts of inorganic fillers, the rate performance of the sodium-ion battery does not change significantly, but the capacity retention rate and voltage drop during discharge decrease and increase to varying degrees, respectively. This is because as the proportion of inorganic fillers increases, the polymerization strength of the functional layer decreases, making it prone to generating various microcracks. Ion transport is concentrated around these microcracks, thus hindering the functional layer from functioning effectively. With increasing amounts of graphene oxide, the rate performance remains essentially unchanged, but the capacity retention rate improves. However, when the graphene oxide content is too high (greater than 20%), it can cause micro-short circuits when coated on the separator. With increasing functional layer thickness, the rate performance gradually decreases. This is because increasing the functional layer thickness increases the ion transport distance, thereby increasing the migration resistance of sodium ions in the separator, and consequently affecting the battery's rapid charge and discharge capability. Therefore, when the functional layer is less than 1 μm, it cannot play a substantial role due to the low content of functional materials, and the capacity retention rate drops sharply; when the functional layer is greater than 20 μm, the coating layer is too thick, and the separator will peel off during battery cycling, thus affecting the cycle performance.

[0082] In summary, under the influence of this functionalized separator, the capacity retention rate of the Prussian blue analog cathode material after 10,000 cycles exceeds 96%, and the capacity utilization rate reaches over 80% during high-rate charge-discharge (5C). Furthermore, this functionalized separator has a simple manufacturing process and abundant raw material resources, effectively improving the stability of the Prussian blue analog cathode material, extending its cycle life in sodium-ion batteries, and significantly enhancing the practical application value of sodium-ion batteries using Prussian blue analog cathodes.

[0083] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A sodium-ion battery, characterized in that, The functionalized separator comprises a base film and a functional layer arranged 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 inorganic filler is selected from one or more of sodium metaaluminate, nano-beta-aluminum oxide, metal organic framework material and sodium superionic conductor; 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 polymer is obtained by in-situ polymerization of ester monomers, a crosslinking agent and an initiator; The functional filler comprises a sodium salt, a plasticizer and an additive; the additive is selected from ester compounds and / or nitrile compounds; the mass ratio of the sodium salt, the plasticizer and the additive is (30-50):(20-50):(20-50); The positive electrode material of the sodium ion battery comprises a Prussian blue analogue; The preparation method of the functionalized separator comprises the following steps: S1, stirring the sodium salt, the plasticizer and the additive to be clear and transparent to obtain a functional filler solution; S2, adding ester monomers, a crosslinking agent, an initiator, graphene oxide and an inorganic filler to the functional filler solution of S1 to be clear and transparent to obtain a functional modification solution; S3, arranging the functional modification solution of S2 on at least one side of the base film, and performing a polymerization reaction at 40-100 DEG C to form a functional layer to obtain the functionalized separator.

2. The sodium-ion battery of claim 1, wherein, The ester monomers are 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 crosslinking 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, azobisisoheptyl nitrile, acetyl peroxide, ammonium persulfate, methyl ethyl ketone peroxide and cyclohexanone peroxide.

3. The sodium-ion battery of claim 1, wherein, 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 difluoro(oxalato)borate; 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, butanedinitrile and hexanedinitrile; 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 sulfone acid lactone succinic anhydride; And / or, the nitrile compound is selected from ethoxy pentafluorocyclo-triphosphazene and / or hexafluorocyclo-triphosphazene.

4. The sodium-ion battery of claim 1, wherein, The mass ratio of the ester monomer, crosslinking agent and initiator is (90-99):(5-10):(1-5).

5. The sodium-ion battery of claim 1, wherein, The thickness of the base film is 8-40 μm, and the porosity is 30%-80%. And / or, the thickness of the functional layer is 1-20 μm.

6. The sodium-ion battery of claim 1, wherein, 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.

7. The method of producing a sodium-ion battery according to any one of claims 1 to 6, wherein The preparation of the functionalized separator includes the following steps: S1, stirring the sodium salt, plasticizer and additive to be clear and transparent to obtain a functional filler solution; S2, adding the ester monomer, crosslinking agent, initiator, graphene oxide and inorganic filler to the functional filler solution of S1 to be clear and transparent to obtain a functional modification solution; S3, setting the functional modification solution of S2 on at least one side of the base film, and performing polymerization at 40-100°C to form a functional layer to obtain the functionalized separator.

8. The method of producing a sodium-ion battery according to claim 7, wherein In S3, the setting mode is selected from one or more of doctor blade coating, roller coating, spraying, spin coating, immersion, pressure filtration, suction filtration, casting and hot pressing.

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