Sodium-ion battery separator, preparation method thereof and sodium-ion battery

Abstract

The application discloses a sodium ion battery diaphragm, a preparation method thereof and a sodium ion battery, and belongs to the technical field of sodium ion batteries. The sodium ion battery diaphragm comprises a glass fiber diaphragm and modified coating applied on one side of the glass fiber diaphragm. The modified coating faces the negative electrode side of the sodium ion battery. The modified coating comprises the following raw materials in mass fractions: 10 parts of chitosan, 0.4-0.6 parts of cellulose nanofiber, 0.02-0.04 parts of a crosslinking agent and 90-150 parts of a solvent. A large number of polar groups in the chitosan can adsorb sodium ions through electrostatic action, reduce the difference in local current density, effectively inhibit the growth of sodium dendrites, cellulose nanofiber as a rigid filler, can form a dense and uniform network structure with chitosan, improve the mechanical strength of the diaphragm, directly hinder the penetration of sodium dendrites, and adjust the pore size of the diaphragm, help the uniform transmission of ions, and improve the cycle stability of the sodium ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a sodium ion battery diaphragm, a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] With the increasing urgency of fully developing and utilizing clean energy, it is particularly important to vigorously develop new energy storage systems. Electrochemical energy storage has unique advantages in different scenarios and responds faster. Lithium ion batteries are a representative of electrochemical energy storage, and have the characteristics of long service life, high energy density and strong environmental adaptability. However, the low abundance and high cost of metal lithium make it the biggest obstacle to sustainable development.

[0003] Sodium ion batteries similar in principle have the advantages of more prominent safety, excellent high-low temperature performance, high fast charging rate and environmental friendliness, and have become a research hotspot. Moreover, metal sodium is widely available and non-toxic, and is more sustainable. As a key part of the internal sodium ion battery, the diaphragm can isolate the positive and negative electrodes of the battery, store electrolyte for the free transmission of sodium ions, and play an important role in the electrochemical performance of the battery, and largely determines the safety of the battery.

[0004] Glass fiber diaphragms are made of a large number of inorganic fibers by non-woven method, have a rich porous network, high porosity and thermal stability, and have excellent wettability for the electrolyte of the sodium ion battery. However, during the long cycle of the sodium ion battery, the uneven distribution of the power density will cause the sodium ions to deposit unevenly on the negative electrode surface, gradually forming needle-shaped or dendritic sodium metal deposits, i.e. sodium dendrites. The mechanical properties of the glass fiber diaphragm are not good, and the anti-dendrite puncture performance is not good. The dendrites can easily pierce the diaphragm and cause short circuits in the battery. Moreover, the existence of tens of microns of large pores on the glass fiber diaphragm, which are not uniform in size, will more easily lead to uneven current density, and in turn induce the growth of sodium dendrites, which is not conducive to the long-term cycle stability of the sodium ion battery. SUMMARY

[0005] The purpose of the present application is to provide a sodium ion battery diaphragm, a preparation method thereof and a sodium ion battery, to solve the problem of poor mechanical properties of glass fiber diaphragms for sodium ion batteries and poor anti-sodium dendrite puncture performance.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] In a first aspect, the present application provides a sodium ion battery diaphragm, which comprises a glass fiber diaphragm and a modified coating coated on one side of the glass fiber diaphragm; the modified coating faces the negative electrode side of the sodium ion battery.

[0008] The modified coating comprises the following raw materials in mass fraction:

[0009] Chitosan 10 parts;

[0010] Cellulose nanofiber 0.4-0.6 parts;

[0011] Crosslinking agent 0.02-0.04 parts;

[0012] Solvent 90-150 parts.

[0013] Preferably, the coating amount of the modified coating is 0.3-0.6 mg / cm 2 .

[0014] Preferably, the fiber length of the cellulose nanofiber is 100-500 nm, and the fiber diameter is 5-10 nm.

[0015] Preferably, the crosslinking agent includes one or more combinations of genipin, tannic acid, and carbodiimide.

[0016] Preferably, the pore size of the glass fiber separator is 1-5 μm, and the thickness is 100-400 μm.

[0017] Preferably, the solvent includes any one of an aqueous acetic acid solution, an aqueous acetic acid solution, an aqueous hydrochloric acid solution, and an aqueous lactic acid solution with a mass fraction of 0.5-2%.

[0018] By using the above technical solution, a layer of modified coating is coated on the side of the glass fiber separator close to the negative electrode of the battery, and the modified coating is mainly composed of a composite of chitosan and cellulose nanofiber. Since the formation of sodium dendrites in sodium ion batteries is mainly due to uneven distribution of electric field on the electrode surface and uneven distribution of ion nucleation sites, leading to sodium ion deposition to form sodium dendrites. The surface of the separator close to the negative electrode, i.e. the end of the sodium dendrite growth, is coated with a modified coating, and the formed chitosan composite cellulose nanofiber layer can form a dense microstructure, which can directly hinder the penetration of sodium dendrites, and on the other hand, can regulate the pore size structure of the glass fiber separator, making the pore size distribution on the surface of the glass fiber separator more uniform. The uniform pore size can help the uniform transmission of ions in the electrolyte, thereby avoiding uneven current density and inducing sodium dendrite growth, indirectly inhibiting the growth rate of sodium dendrites in sodium ion batteries, thereby improving the long-term cycle stability of sodium ion batteries.

[0019] And chitosan contains a large number of polar groups such as amino and hydroxyl groups, which can adsorb sodium ions through electrostatic interaction, thereby inhibiting the growth of sodium dendrite tips caused by local concentration gradient, thereby significantly delaying dendrite nucleation, and the introduction of cellulose nanofiber can form a three-dimensional network on the surface of the glass fiber separator, which can prolong the diffusion path of sodium ions and uniform ion distribution, thereby inhibiting the growth of sodium dendrites.

[0020] Moreover, the cellulose nanofiber in the modified coating can act as a rigid filler, and between the chitosan matrix, through the action of a crosslinking agent, form an interpenetrating network structure, greatly improve the mechanical strength of the glass fiber separator, and the cellulose nanofiber is uniformly dispersed on the surface of the glass fiber separator, and the aspect ratio characteristics further enhance the stress transfer ability of the glass fiber separator, improve the tensile properties of the glass fiber separator. The modified coating and the glass fiber separator can also interact through hydrogen bonding or electrostatic interaction, increase the interfacial bonding between the two, so that the modified coating is not easy to fall off from the surface of the glass fiber separator, also inhibits crack propagation, improves the mechanical strength of the glass fiber separator and the anti-sodium dendrite puncture performance.

[0021] At the same time, the hydrophilicity of chitosan and the porous structure of cellulose nanofiber also do not affect the wettability of the glass fiber separator, but will improve the wettability and liquid retention of the separator to some extent, thereby reducing the interface impedance and improving the cycle performance of the sodium ion battery.

[0022] Preferably, the chitosan is modified by sodium tripolyphosphate; the mass ratio of the chitosan and sodium tripolyphosphate is 1:(0.2-0.3).

[0023] By adopting the above technical scheme, the sodium tripolyphosphate contains negatively charged phosphate groups, and when the chitosan is modified by sodium tripolyphosphate, ionic crosslinking agents are formed between the phosphate groups and the amino groups and hydroxyl groups in the chitosan, which not only enhances the mechanical strength of the chitosan, thereby indirectly improving the mechanical strength of the glass fiber separator, but also introduces a large number of negatively charged phosphate ions into the modified coating, which can enhance the adsorption capacity of the glass fiber separator for sodium ions, stabilize the adsorption of sodium ions on the surface of the separator, thereby reducing the interface impedance and improving the sodium affinity of the modified coating.

[0024] When the modified coating is coated on the surface of the glass fiber separator, the sodium affinity of the surface of the separator near the negative electrode end is also enhanced accordingly, and the improvement of the sodium affinity can reduce the nucleation barrier of sodium ions, inhibit the growth of sodium dendrites, and the uniform adsorption of sodium ions on the sodium-affine surface can eliminate the accumulation of local charges. When the charges on the surface of the separator are uniformly distributed, the growth of sodium dendrites can be greatly inhibited, and the short circuit problem caused by the puncture of sodium dendrites can be avoided.

[0025] After the modification treatment by sodium tripolyphosphate, a more compact network structure can be formed, which can reduce the difference in local current density, guide the transmission of sodium ions along a uniform path, avoid the formation of ion concentration gradient on the surface of the glass fiber separator, and effectively inhibit the nucleation of sodium dendrites. While improving the mechanical strength of the glass fiber separator, the addition of sodium tripolyphosphate can improve the liquid retention of the material and maintain the wettability of the electrolyte.

[0026] Preferably, the sodium tripolyphosphate modified chitosan is prepared according to the following method:

[0027] Pre-treatment of chitosan: chitosan is dissolved in a weak acid solution, an oxidizing agent is added, and the mixture is stirred at 50-55℃ for 4-5h to obtain a pre-treated chitosan solution;

[0028] Sodium tripolyphosphate modified chitosan: sodium tripolyphosphate solution is added dropwise to the pre-treated chitosan solution, and the reaction is stirred at 40-50℃ for 30-60min. Finally, centrifugation, washing and freeze-drying are performed to obtain the product.

[0029] Preferably, the weak acid solution includes any one of acetic acid solution and acetic acid solution with a mass fraction of 1-5%.

[0030] Preferably, the oxidizing agent includes one or a combination of hydrogen peroxide, hydrogen peroxide and sodium hypochlorite.

[0031] By using the above technical solution, the chitosan is first pre-treated by an oxidizing agent. The chitosan after oxidation treatment can increase the number of polar groups in the chitosan, introduce more active sites, and destroy the crystal structure of the chitosan, thereby improving the flexibility of the chitosan molecular chain, which is conducive to further reaction and crosslinking with sodium tripolyphosphate.

[0032] Then, sodium tripolyphosphate solution is added dropwise. The protonated amino groups in the chitosan can form ionic bonds with the phosphate ions in the sodium tripolyphosphate, thereby forming a stable modified compound. The hydrogen bonds formed between the two can also help to further stabilize the crosslinked structure, convert the linear structure of the chitosan into a three-dimensional network, and improve the mechanical strength of the chitosan, thereby indirectly improving the effect of the modified coating on improving the mechanical properties of the glass fiber separator. The modified layer formed on the surface of the glass fiber separator by the modified coating can guide the uniform deposition of sodium ions, reduce the local current density difference, and inhibit the growth of sodium dendrites.

[0033] After the sodium tripolyphosphate modification treatment, the binding sites between the chitosan and the cellulose nanofiber are also increased. Through electrostatic attraction and hydrogen bonding between the two, the interfacial bonding force is improved, the interfacial stress transfer effect is further enhanced, thereby improving the mechanical strength of the separator, and a more uniform ion transport channel can also be formed.

[0034] In a second aspect, the present application provides a preparation method of a sodium ion battery separator, comprising the following process steps:

[0035] S1. Chitosan is added to a solvent, stirred and mixed for 4-6h, then cellulose nanofiber is added, stirred and dispersed for 20-40min, and a crosslinking agent is added, and the stirring is continued for 30-60min to obtain a modified coating;

[0036] S2. The modified coating is applied to one side of the glass fiber separator, and after drying at 40-50℃ for 2-3h, a sodium ion battery separator is obtained.

[0037] Preferably, the technical effects of the present application can also be achieved without modifying the chitosan with sodium tripolyphosphate.

[0038] By using the above technical solution, the chitosan, cellulose nanofiber and crosslinking agent are mixed in an acidic solution to form a homogeneous dispersion system, and the obtained modified coating is applied to one side of the glass fiber separator. After the solvent evaporates, the chitosan segments and cellulose nanofiber gradually condense through hydrogen bonding and the action of the crosslinking agent to form a dense and stable porous structure. The cellulose nanofiber, as a rigid nanofiller, is embedded in the chitosan matrix to form an interpenetrating network through physical entanglement, further improving the mechanical strength.

[0039] When applied to the surface of the glass fiber separator, the modified coating can also form a firm interface layer by using hydrogen bonding and van der Waals forces between the polar groups contained in the modified coating and the polar groups on the surface of the glass fiber separator, thereby improving the adhesion between the modified coating and the glass fiber separator and enhancing the interfacial stress transfer effect.

[0040] By applying the modified coating to the surface of the glass fiber separator near the negative electrode side, the mechanical properties of the separator can be significantly improved, directly manifested as an increase in the tensile strength of the separator and an effective resistance to mechanical penetration of sodium dendrites. The aspect ratio of the cellulose nanofiber can also disperse local stress through stress transfer, avoiding local fracture.

[0041] At the same time, the pore structure of the separator surface can also be controlled to help form a uniform physical barrier on the surface of the separator, which is conducive to the uniform transmission of sodium ions and reduces local polarization. At the same time, the excellent wettability and liquid retention of the glass fiber separator can also be maintained, reducing the interfacial impedance.

[0042] In a third aspect, the present application provides a sodium ion battery, wherein the separator thereof is the sodium ion battery separator obtained as described above.

[0043] The beneficial effects of the present application are as follows:

[0044] 1. The sodium ion battery separator of the present application uses a glass fiber separator as the base material, and a modified coating is applied to one end of the glass fiber separator near the negative electrode. The chitosan in the modified coating contains a large number of polar groups, which can adsorb sodium ions through electrostatic attraction, reduce the difference in local current density, and effectively inhibit the growth of sodium dendrites. The cellulose nanofiber, as a rigid filler, is combined with chitosan to form a dense and uniform network structure, improving the mechanical strength of the separator and directly hindering the penetration of sodium dendrites. The pore size of the separator can be adjusted to help the uniform transmission of ions and reduce the growth of sodium dendrites, thereby improving the cycle stability of the sodium ion battery.

[0045] 2、The sodium ion battery diaphragm surface coating of the application is coated with a modified coating, and the chitosan can be modified by sodium tripolyphosphate. The introduction of sodium tripolyphosphate can significantly improve the sodium affinity of the modified coating, thereby reducing the interface impedance, eliminating the accumulation of local charges, inhibiting the growth of sodium dendrites, and avoiding the short circuit problem caused by the penetration of sodium dendrites. Meanwhile, the mechanical strength of the modified coating can be further improved, the uniformity of ion transmission can be improved, and the puncture resistance can be improved. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0047] Preparation Example

[0048] Preparation Example 1, a sodium tripolyphosphate modified chitosan, is prepared according to the following method:

[0049] Pretreatment of chitosan: 10g of chitosan is dissolved in 500mL of 3% acetic acid solution, 5mL of hydrogen peroxide is added, and the mixture is stirred at 55℃ for 4h to obtain a pretreated chitosan solution;

[0050] Sodium tripolyphosphate modified chitosan: 10% sodium tripolyphosphate solution (2g of sodium tripolyphosphate is added) is added dropwise to the pretreated chitosan solution, and the mixture is stirred at 50℃ for 40min. Finally, centrifugation, washing and freeze-drying are performed to obtain the product.

[0051] Preparation Example 2, a sodium tripolyphosphate modified chitosan, is different from Preparation Example 1 only in that the amount of sodium tripolyphosphate added is 3g.

[0052] Preparation Example 3, a sodium tripolyphosphate modified chitosan, is different from Preparation Example 1 only in that the amount of sodium tripolyphosphate added is 1g.

[0053] Preparation Example 4, a sodium tripolyphosphate modified chitosan, is different from Preparation Example 1 only in that the amount of sodium tripolyphosphate added is 4g.

[0054] Embodiment

[0055] Embodiment 1, a sodium ion battery diaphragm, is prepared according to the following steps:

[0056] S1. 10 g of chitosan was added to 120 g of 1% acetic acid solution, stirred and mixed for 4 h, then 0.5 g of cellulose nanofiber (average length of 300 nm, average diameter of 6 nm) was added, stirred and dispersed for 30 min, 0.02 g of genipin was added, and stirring was continued for 60 min to obtain a modified coating;

[0057] S2. The modified coating was coated on one side of a glass fiber separator (average pore size of 2.8 μm, average thickness of 260 μm), and the coating amount was 0.5 mg / cm 2 After drying at 40℃ for 3 h, a sodium ion battery separator was obtained.

[0058] Example 2 and Example 3, a sodium ion battery separator, the difference from Preparation Example 1 is only that the raw material ratio of the modified coating is adjusted, as shown in Table 1:

[0059] Table 1 Raw material ratio of modified coating of Example 1-Example 3

[0060] Example 1 Example 2 Example 3 Chitosan / g 10 10 10 Cellulose nanofiber / g 0.5 0.4 0.6 Genipin / g 0.02 0.02 0.03 Acetic acid solution / g 120 90 150

[0061] The coating amount of the modified coating on the surface of the glass fiber separator in Example 2 is 0.6 mg / cm 2 ; the coating amount of the modified coating on the surface of the glass fiber separator in Example 3 is 0.3 mg / cm 2 .

[0062] Example 4, a sodium ion battery separator, the difference from Example 1 is only that the chitosan is replaced by an equal amount of sodium tripolyphosphate modified chitosan prepared in Preparation Example 1.

[0063] Example 5, a sodium ion battery separator, the difference from Example 1 is only that the chitosan is replaced by an equal amount of sodium tripolyphosphate modified chitosan prepared in Preparation Example 2.

[0064] Example 6, a sodium ion battery separator, the difference from Example 1 is only that the chitosan is replaced by an equal amount of sodium tripolyphosphate modified chitosan prepared in Preparation Example 3.

[0065] Example 7, a sodium ion battery separator, the difference from Example 1 is only that the chitosan is replaced by an equal amount of sodium tripolyphosphate modified chitosan prepared in Preparation Example 8.

[0066] Example 8, a sodium ion battery separator, the difference from Example 1 is only that the coating amount of the modified coating on the surface of the glass fiber separator is 0.8 mg / cm 2 .

[0067] Comparative Example

[0068] Comparative Example 1, a sodium ion battery separator, differs from Example 1 only in that the amount of cellulose nanofiber added in the modified coating is 0.2 g.

[0069] Comparative Example 2, a sodium ion battery separator, differs from Example 1 only in that the amount of cellulose nanofiber added in the modified coating is 0.8 g.

[0070] Comparative Example 3, a sodium ion battery separator, differs from Example 1 only in that no cellulose nanofiber is added in the modified coating.

[0071] Performance detection test

[0072] 1. Mechanical property test: The tensile strength of the sodium ion battery separators obtained in the examples and comparative examples was tested according to the method for testing tensile strength described in GB / T 36363-2018 "Polyolefin separator for lithium ion battery", and a glass fiber separator (average pore size 2.8 μm, average thickness 260 μm) without coating treatment was set as control group 1.

[0073] The test results are shown in Table 2.

[0074] 2. Long-term cycle stability test:

[0075] Sample preparation: hard carbon, sodium polyacrylate, and carbon black were mixed uniformly in deionized water at a mass ratio of 93:4:3 to obtain a negative electrode slurry, and then the negative electrode slurry was coated on an aluminum foil, and after baking and rolling, a negative electrode sheet was obtained; sodium iron phosphate, polyvinylidene fluoride, and carbon black were mixed uniformly in an appropriate amount of NMP at a mass ratio of 92:4:4 to obtain a positive electrode slurry; then the positive electrode slurry was coated on an aluminum foil, and after baking and rolling, a positive electrode sheet was obtained.

[0076] The obtained negative electrode sheet, positive electrode sheet, and sodium ion battery separator obtained in the examples and comparative examples were assembled into sodium ion batteries, wherein the side coated with the modified coating was close to the negative electrode sheet of the sodium ion battery, and the electrolyte of the sodium ion battery was NaPF6 and propylene carbonate at a mass ratio of 2:1.

[0077] And the sodium ion battery prepared by the glass fiber separator without coating was set as control group 1; the side of the sodium ion battery separator obtained in Example 1 coated with the modified coating faced the positive electrode sheet, and the assembled sodium ion battery was set as control group 2.

[0078] Test test: The sample batteries of the examples, comparative examples, and control groups 1 and 2 were subjected to cycle performance test, and were subjected to long cycle at 25℃ and 3C rate, and the cycle voltage was 0.3-1.9V. The capacity retention rate of the sample battery after 500 cycles was tested, wherein the capacity retention rate was calculated according to the following method:

[0079]

[0080] The test results are shown in Table 3.

[0081] Table 2 Tensile strength test results

[0082]

[0083] Table 3 Cycle stability test results

[0084]

[0085] According to Table 2 and Table 3, combined with Example 1 and Example 4, it can be seen that the capacity retention rate and tensile strength of Example 4 are both increased compared with Example 1, and the reason is that in the modified coating in Example 4, the cross-linking density of chitosan is improved after the modification treatment of sodium tripolyphosphate, thereby improving the mechanical properties, and the sodium affinity of the modified coating is improved, the interfacial impedance is reduced, the accumulation of local charges is eliminated, the growth of sodium dendrites is inhibited, so that the battery performance can be kept stable during long-term cycling.

[0086] Combined with Example 4, Example 6 and Example 7, it can be seen that the performance of Example 6 and Example 7 is decreased compared with Example 4, and the reason is that the addition amount of sodium tripolyphosphate is reduced in Example 6, and the modification effect of chitosan is decreased; the addition amount of sodium tripolyphosphate is increased in Example 7, which leads to that the cross-linking density of the modified chitosan and cellulose nanofiber is increased when they are compounded, and the pores are partially blocked, which is not conducive to ion transmission, and will affect the battery performance.

[0087] Combined with Example 1 and Example 8, it can be seen that the performance of Example 8 is decreased compared with Example 1, and the reason is that the coating amount of the modified coating on the surface of the glass fiber separator in the example 8 is increased, which is not conducive to the regulation of the pore uniformity of the separator surface, and the pores are blocked by the coating, which is not conducive to ion transmission.

[0088] Compared with Example 1, the performance of Comparative Examples 1-3 is obviously decreased, which is because the amount of cellulose nanofiber in the modified coating is changed in Comparative Examples 1-3. In Comparative Example 1, the content of cellulose nanofiber is reduced, and the content of rigid filler is also reduced, which reduces the improvement effect on the mechanical strength of the separator and the ability to resist stress and strain, and also reduces the puncture resistance. In Comparative Example 3, no cellulose nanofiber is added, and the performance is more obviously decreased. In Comparative Example 2, the content of cellulose nanofiber is increased, and the excess cellulose nanofiber will agglomerate due to its own polarity in the coating, which will block the pores on the surface of the separator, affect ion transmission, and also introduce stress concentration points, which is not conducive to the improvement of the mechanical strength.

[0089] Compared with Example 1, the performance of Comparative Example 1 is obviously decreased, which shows that the modified coating coated on one side of the glass fiber separator in Example 1 can significantly improve the mechanical strength and puncture resistance of the separator, thereby enhancing the long-term cycle stability of the sodium ion battery.

[0090] Compared with Example 1, the capacity retention rate of Comparative Example 2 is decreased, which is because the modified coating in Comparative Example 2 is close to the positive electrode sheet, and sodium dendrites are more likely to nucleate and grow on the negative electrode sheet, which cannot effectively protect the separator.

[0091] It should be noted that the relational terms such as first and second, and the like, are used merely to distinguish one entity or action from another, without necessarily requiring or implying that there is any such actual relationship or order between them. In addition, the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or equipment including a series of elements includes not only those elements, but also other elements not explicitly listed, or inherent to such a process, method, article, or equipment.

[0092] Although the embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A sodium-ion battery separator, characterized in that, The sodium ion battery separator comprises a glass fiber separator and a modified coating coated on one side of the glass fiber separator; the modified coating faces the negative electrode side of the sodium ion battery; The modified coating comprises the following raw materials in mass fraction: Chitosan 10 parts; Cellulose nanofiber 0.4-0.6 parts; Crosslinking agent 0.02-0.04 parts; Solvent 90-150 parts; The chitosan is modified by sodium tripolyphosphate; the mass ratio of the chitosan to the sodium tripolyphosphate is 1:(0.2-0.3); The cellulose nanofiber has a fiber length of 100-500 nm and a fiber diameter of 5-10 nm.

2. The sodium-ion battery separator of claim 1, wherein, The modified coating is applied in an amount of 0.3 to 0.6 mg / cm 2 .

3. The sodium-ion battery separator of claim 1, wherein, The sodium tripolyphosphate modified chitosan is prepared by the following method: Pretreatment of chitosan: dissolve the chitosan in a weak acid solution, add an oxidizing agent, and stir and mix at 50-55°C for 4-5 h to obtain a pretreated chitosan solution; Sodium tripolyphosphate modified chitosan: drop sodium tripolyphosphate solution into the pretreated chitosan solution, stir and react at 40-50°C for 30-60 min, and then centrifuge, wash, and freeze-dry to obtain the sodium tripolyphosphate modified chitosan.

4. The sodium-ion battery separator of claim 3, wherein, The oxidizing agent comprises one or more of a combination of hydrogen peroxide, hydrogen peroxide, and sodium hypochlorite.

5. The sodium-ion battery separator of claim 1, wherein, The crosslinking agent comprises one or more of a combination of genipin, tannic acid, and carbodiimide.

6. The sodium-ion battery separator of claim 1, wherein, The glass fiber separator has a pore size of 1-5 μm and a thickness of 100-400 μm.

7. The method of producing a sodium-ion battery separator according to any one of claims 1 to 6, characterized in that, The process comprises the following steps: S1. Add chitosan to a solvent, stir and mix for 4-6 h, then add cellulose nanofiber, stir and disperse for 20-40 min, add a crosslinking agent, and continue to stir for 30-60 min to obtain a modified coating; S2. Coat the modified coating on one side of the glass fiber separator, dry at 40-50°C for 2-3 h, and obtain a sodium ion battery separator.

8. A sodium-ion battery, characterized in that, The sodium ion battery uses the sodium ion battery separator of any one of claims 1-6.

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