High-voltage-resistant quick-charge composite binder, positive pole piece and battery containing binder

Abstract

The invention belongs to the technical field of sodium ion battery binders, and discloses a high-voltage-resistant quick-charge composite binder, a positive pole piece and a battery containing the binder. The composite binder provided by the invention comprises a nitrile group-containing polymer and hydroxyethyl cellulose. CN in the nitrile-containing polymer endows strong high pressure resistance, and polar groups in hydroxyethyl cellulose and CN in the nitrile-containing polymer form a hydrogen bond cross-linked network, so that a strong and stable bonding system of the electrode is ensured. Hydroxyl of hydroxyethyl cellulose has higher chemical activity and can be preferentially coordinated with Na < + >, so that the ion desolvation process is accelerated, and the dynamic performance of the positive electrode is improved. By controlling the addition amount of the two components, the composite binder with rapid ion conduction and high voltage resistance can be obtained, and the composite binder is suitable for the positive electrode of a sodium ion battery. The binder prepared by the invention does not contain fluorine element, and the sodium ion battery prepared from the binder meets the environmental protection requirements of European Union; and the method is adaptive to the current battery production process, and is suitable for large-scale amplification and application.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion battery binders, and particularly to a binder. Background Art

[0002] Sodium-ion batteries have advantages such as low cost, high safety, and relatively high energy density, making them highly potential candidates for large-scale energy storage. As the core component of the battery, the battery electrode plays a decisive role in the performance of the battery. The battery electrode mainly consists of four parts: active material, binder, conductive agent, and current collector. Among them, the binder has a small dosage in electrode preparation, but plays an important role in the performance of the battery. The main function of the binder is to adhere the active electrode material and the conductive agent to the current collector, so that they are in close contact with each other to reduce the electrode resistance, maintain good mechanical properties and electrode integrity. The binder does not damage the inherent structure of the active particles and does not require highly precise operations. In addition, it has good controllability and low-cost characteristics, which is beneficial to large-scale production.

[0003] Currently, the commonly used binders in electrodes include PVDF, PI, PAA, CMC, etc. Among them, PVDF has good chemical stability and good adhesion effect. However, it has certain insulating properties and low ionic conductivity, which will lead to an additional barrier to Na + migration at the interface and further lead to a decrease in the charge conduction kinetics; PI has excellent high-temperature resistance, but its mechanical properties are too high, resulting in greater brittleness of the electrode sheet; PAA has good flexibility and strong high-pressure resistance, but its mechanical properties are poor; CMC has good dispersibility, but its mechanical properties are relatively high and its brittleness is large, and it needs to be used in combination with other polymers. There are still several bottlenecks in the existing binder technology. The preparation process is complex (CN115064697A), and the interfacial strengthening effect of the functional groups in the binder molecule in the electrode system is limited (CN112909252A), which cannot meet the requirements of fast-charging cathodes. Therefore, it is necessary to design a binder with high-voltage resistance and fast charging that can improve the electrochemical performance of the device to address the problems of slow ionic conductivity, poor high-pressure resistance, poor dispersibility, easy swelling, and complex preparation process of commonly used binders. Summary of the Invention

[0004] In view of the above technical problems, the present invention provides a high-voltage resistant and fast-charging composite binder, a positive electrode sheet, and a sodium-ion battery including the binder.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] A high-voltage resistant and fast-charging composite binder, comprising a nitrile group-containing polymer and hydroxyethyl cellulose; wherein, the structural formula of the nitrile group-containing polymer is shown in formula (Ⅰ):

[0007]

[0008] Among them, R in formula (I) is one of -(C2H3), -(C3H5), -(C 12 H7O2), and n is 600 - 25000.

[0009] In the above composite binder, -CN in the nitrile-based polymer has a relatively high electronegativity, which improves the high-voltage resistance characteristics of the composite binder, and has a relatively high highest occupied molecular orbital, participating in the formation of an inorganic CEI rich in Na3N. The hydroxyl groups of hydroxyethyl cellulose have higher chemical activity and preferentially adsorb Na + and have a competitive coordination effect with solvent molecules at the interface, reducing the coordination of Na + with the solvent. In addition, hydroxyethyl cellulose is connected to the cellulose backbone through an ethyl chain, and the lone pair electrons on the oxygen atoms thereon can enhance the electron cloud density of adjacent hydroxyl groups through inductive effect and hyperconjugation effect, making the hydroxyl groups thereon more nucleophilic and more likely to combine with Na + . Therefore, hydroxyethyl cellulose is more likely to adsorb Na + and weaken its coordination with solvent molecules, accelerating the + desolvation process and improving the electrode kinetic performance.

[0010] The above nitrile-based polymer is one of polyacrylonitrile, polybutenenitrile, and polyarylether nitrile.

[0011] In the above high-voltage fast-charging composite binder, the mass fraction of the nitrile-based polymer in the total mass of hydroxyethyl cellulose and the nitrile-based polymer is 50 - 90%.

[0012] The average molecular weight of the above nitrile-based polymer is 100,000 - 1,000,000, and the average molecular weight of hydroxyethyl cellulose is 10,000 - 200,000. Any value within the range of the average molecular weight of the nitrile-based polymer being 100,000 - 1,000,000 is acceptable. For example, the average molecular weight of the nitrile-based polymer can be 100,000, 180,000, 190,000, 200,000, or 1,000,000, etc.; any value within the range of the average molecular weight of hydroxyethyl cellulose being 10,000 - 200,000 is acceptable.

[0013] The preparation method of the above high-voltage fast-charging composite binder is as follows: Mix the nitrile-based polymer solution and the hydroxyethyl cellulose solution to obtain the high-voltage fast-charging composite binder.

[0014] The mass ratio of the nitrile-based polymer in the above nitrile-based polymer solution to the hydroxyethyl cellulose in the hydroxyethyl cellulose solution is (5 - 9):(5 - 1); the solvent in the nitrile-based polymer solution and the hydroxyethyl cellulose solution is any one of DMF, DMSO, NMP, and DMAc.

[0015] Further, the solvent is any one of DMF, DMSO, NMP, and DMAc.

[0016] A positive electrode sheet includes a binder, a positive electrode material, and a conductive material. Among them, the binder is the high-voltage fast-charging composite binder of the present invention.

[0017] Further, the mass ratio of the above-mentioned positive electrode material, conductive material to the effective components (including nitrile-based polymer and hydroxyethyl cellulose) in the high-voltage fast-charging composite binder is (14 - 18):(1 - 4):(1 - 3).

[0018] Preferably, the mass ratio of the above-mentioned positive electrode material, conductive material to the effective components (including nitrile-based polymer and hydroxyethyl cellulose) in the high-voltage fast-charging composite binder is 7:2:1.

[0019] Further, the above-mentioned positive electrode material is a layered transition metal oxide or a polyanion compound, and the conductive material is any one of acetylene black, Ketjen black, and Super P Li. Among them, the layered transition metal oxide is such as sodium nickel iron manganese oxide; the polyanion compound is such as sodium fluorophosphate vanadate, sodium vanadium phosphate, sodium pyrophosphate iron, sodium ferrous sulfate, etc.

[0020] The preparation method of the above-mentioned positive electrode sheet includes the following steps:

[0021] (1) Prepare a positive electrode slurry: Add the conductive material, positive electrode material, and the high-voltage fast-charging composite binder of the present invention according to the mass ratio, and then add an oily solvent and stir to mix evenly to obtain a positive electrode slurry.

[0022] (2) Prepare a sodium-ion battery positive electrode sheet: Coating the above-mentioned positive electrode slurry on an aluminum foil, drying at 80 - 140 °C for 6 - 12 h, to obtain a sodium-ion battery positive electrode sheet.

[0023] A sodium-ion battery includes the above-mentioned positive electrode sheet, negative electrode sheet, separator, and electrolyte of the present invention. By winding the above-mentioned positive electrode sheet, negative electrode sheet, and separator to form a pole group, and then through processes such as liquid injection, formation, grading, and aging, a sodium-ion battery is prepared.

[0024] Further, the above-mentioned negative electrode sheet is a carbon material electrode sheet (hard carbon), a conversion-type negative electrode material electrode sheet (iron sulfide, selenium sulfide, zinc sulfide), an alloy-type material (tin-based alloy, antimony-based alloy, phosphorus-based alloy, silicon-based alloy), or sodium metal; the separator includes but is not limited to at least one of polyolefin separators, polyester films, glass fiber films, polyimide films (PI), polyamide films (PA), spandex or aramid films, woven films, non-woven films (non-woven fabrics), microporous films, composite films, separator papers, rolled films, or spun films, etc.; the electrolyte includes but is not limited to sodium salts and non-aqueous solvents.

[0025] The high-voltage fast-charging composite binder prepared by the present invention is not only applicable to the sodium-ion battery system, but also has a certain universality and can play a good role in the lithium-ion battery system.

[0026] The beneficial effects of the present invention are as follows:

[0027] (1) The composite binder provided by the present invention includes a first component (containing a nitrile-based polymer) and a second component (hydroxyethyl cellulose polymer). Through physical blending, hydrogen bonding occurs between the polar functional groups contained in the two components of the composite binder, forming a hydrogen-bonded crosslinked polymer. This unique network structure helps to disperse the electrode material and improve the uniformity of the slurry. In addition, this binder can have an electrostatic interaction with the positive electrode material, stabilize the positive electrode material, inhibit electrode cracking, and inhibit the generation of intergranular and intragranular cracks, effectively improving the electrochemical performance of the positive electrode. Moreover, the -CN in the first component nitrile-based polymer has a high electronegativity, which improves the high-voltage resistance characteristics of the composite binder, and has a relatively high highest occupied molecular orbital, participating in the formation of an inorganic CEI rich in NaN3. The hydroxyl group of hydroxyethyl cellulose has higher chemical activity and preferentially adsorbs Na + and has a competitive coordination effect with the solvent molecules at the interface, reducing the coordination of Na + with the solvent. As a result, Na + is more easily desolvated, enhancing the transfer kinetics of Na + between the electrode-electrolyte interface and improving the kinetic performance of the positive electrode.

[0028] (2) Due to the binder covering the surface of the electrode in the sodium-ion battery provided by the present invention, the surface of the positive electrode material is effectively passivated, inhibiting the continuous decomposition of the electrolyte, forming a thin and uniform CEI film, and improving the interfacial stability of the positive electrode. In addition, PAN acts as a sacrificial component and participates in the formation of a dense and tough CEI rich in Na3N, NaCl, and NaF, further inhibiting the side reaction between the electrode and the electrolyte, stabilizing the interface, and improving the kinetic performance of the sodium iron sulfate positive electrode.

[0029] (3) The composite binder prepared by the present invention enables the positive electrode to achieve fast-charging performance and high reversible capacity. Specifically, the fast-charging performance of batteries with different binders was tested at a higher current density of 10C. The battery assembled at a current density of 10C completed one week of charge and discharge in 12 minutes, and the first-week discharge capacity was 91.5 mAh g -1 , and there was still a reversible capacity of 69.79 mAh g -1 after 4500 cycles. In contrast, the NFS-PVDF electrode only provided a discharge capacity of 54.67 mAh g -1 after 4500 cycles. Description of the Drawings

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0031] Figure 1 Infrared spectrum diagram of the high-voltage fast-charging composite binder prepared in Example 1 of the present invention.

[0032] Figure 2 Comparison chart of the first-cycle charge and discharge performance of the sodium-ion half-cell assembled with the sodium iron sulfate positive electrode sheets prepared in Example 1 and Comparative Example 1.

[0033] Figure 3 Comparison chart of the rate performance of the sodium-ion half-cell assembled with the sodium iron sulfate positive electrode sheets prepared in Example 1 and Comparative Example 1.

[0034] Figure 4 Charge and discharge curves of the sodium-ion half-cell assembled with the sodium iron sulfate positive electrode sheets prepared in Example 1 and Comparative Example 1 at 10C for the first cycle and 4500 cycles.

[0035] Figure 5 Transmission electron microscope image of the sodium-ion half-cell assembled with the sodium iron sulfate positive electrode sheets prepared in Example 1 and Comparative Example 1 after three cycles. Detailed implementation manners

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0037] The weights of the relevant components mentioned in the embodiments of the present invention not only can refer to the specific contents of each component, but also can represent the proportional relationship of the weights between each component. Therefore, as long as the contents of the relevant components in the embodiments of the present invention are enlarged or reduced in proportion, they are within the scope disclosed in the embodiments of the present invention. Specifically, the weights described in the embodiments of the present invention can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0038] In the examples and comparative examples of the present invention, the molecular weight of polyvinylidene fluoride (PVDF) used is 500,000, the molecular weight of polyacrylonitrile (PAN) is 200,000, the molecular weight of hydroxyethyl cellulose (HEC) is 10,000, the molecular weight of polybutenenitrile is 180,000, and the molecular weight of polyarylether nitrile is 190,000. Except for PAN which was purchased from the Macklin official website, the rest of the materials were purchased from the Aladdin official website.

[0039] Example 1

[0040] The preparation method of the high-voltage fast-charging composite binder in this example is as follows:

[0041] Place 0.4 g of polyacrylonitrile in a sample bottle and add 3.6 g of DMF solvent to obtain a polyacrylonitrile solution. Similarly, place 0.4 g of hydroxyethyl cellulose in a sample bottle and add 3.6 g of DMSO solvent to obtain a hydroxyethyl cellulose solution. Stir the two evenly on a magnetic stirrer for 4 h, and mix the above two solutions evenly according to a mass ratio of 9:1 to obtain the high-voltage fast-charging composite binder.

[0042] Figure 1 This is the infrared spectrum of the high-voltage fast-charging composite binder prepared in Example 1 of the present invention. It can be seen that the characteristic peaks at 2924, 2239, and 1446 cm -1 belong to the stretching vibration of methylene -CH, the stretching vibration of cyano -CN, and the in-plane bending vibration of -CH respectively. It can be determined that there are various polar functional groups in this oily binder, which can better adhere to sodium ferrous sulfate, improve its dispersion degree, contribute to the smoothness of the electrode sheet, and enhance the bonding effect on the electrode. And after adding HEC, the peak at 2239 cm -1 shifts to 2231 cm -1 , indicating the formation of hydrogen bonds.

[0043] Example 2

[0044] The preparation method of the high-voltage fast-charging composite binder in this example is as follows:

[0045] Place 0.4 g of polyacrylonitrile in a sample bottle and add 3.6 g of DMF solvent to obtain a polyacrylonitrile solution. Similarly, place 0.4 g of hydroxyethyl cellulose in a sample bottle and add 3.6 g of DMSO solvent to obtain a hydroxyethyl cellulose solution. Stir the two evenly on a magnetic stirrer for 2 h, and mix the above two solutions evenly according to a mass ratio of 7:3 to obtain the high-voltage fast-charging composite binder.

[0046] Example 3

[0047] The preparation method of the high-voltage fast-charging composite binder in this example is as follows:

[0048] Place 0.4 g of polyacrylonitrile in a sample bottle, and add 3.6 g of DMF solvent to obtain a polyacrylonitrile solution. Similarly, place 0.4 g of hydroxyethyl cellulose in a sample bottle, and add 3.6 g of DMSO solvent to obtain a hydroxyethyl cellulose solution. Stir the two evenly on a magnetic stirrer for 8 h, and mix the above two solutions evenly according to a mass ratio of 4:1 to obtain a high-voltage fast-charging resistant composite binder.

[0049] Example 4

[0050] The preparation method of the high-voltage fast-charging resistant composite binder in this example is as follows:

[0051] Place 0.4 g of polyacrylonitrile in a sample bottle, and add 3.6 g of DMF solvent to obtain a polyacrylonitrile solution. Similarly, place 0.4 g of hydroxyethyl cellulose in a sample bottle, and add 3.6 g of DMSO solvent to obtain a hydroxyethyl cellulose solution. Stir the two evenly on a magnetic stirrer for 8 h, and mix the above two solutions according to a mass ratio of 6:4 to obtain a high-voltage fast-charging resistant composite binder.

[0052] Example 5

[0053] The preparation method of the high-voltage fast-charging resistant composite binder in this example is as follows:

[0054] Place 0.4 g of polyacrylonitrile in a sample bottle, and add 3.6 g of DMF solvent to obtain a polyacrylonitrile solution. Similarly, place 0.4 g of hydroxyethyl cellulose in a sample bottle, and add 3.6 g of DMSO solvent to obtain a hydroxyethyl cellulose solution. Stir the two evenly on a magnetic stirrer for 8 h, and mix the above two solutions evenly according to a mass ratio of 5:5 to obtain a high-voltage fast-charging resistant composite binder.

[0055] Example 6

[0056] Place 0.4 g of polybutenenitrile (molecular weight of 180,000) in a sample bottle, and add 2.8 g of DMF solvent to obtain a polyacrylonitrile solution. Similarly, place 0.4 g of hydroxyethyl cellulose in a sample bottle, and add 2.8 g of DMSO solvent to obtain a hydroxyethyl cellulose solution. Stir the two evenly on a magnetic stirrer for 4 h, and mix the above two solutions evenly according to a mass ratio of 9:1 to obtain a high-voltage fast-charging resistant composite binder.

[0057] Example 7

[0058] Place 0.4 g of polyarylether nitrile (molecular weight 190,000) in a sample bottle, and add 2.8 g of DMF solvent to obtain a polyacrylonitrile solution. Similarly, place 0.4 g of hydroxyethyl cellulose in a sample bottle, add 2.8 g of DMSO solvent to obtain a hydroxyethyl cellulose solution. Stir the two solutions evenly on a magnetic stirrer for 4 h, and mix the above two solutions evenly according to a mass ratio of 9:1 to obtain a high-pressure-resistant and fast-charging composite binder.

[0059] Comparative Example 1

[0060] The binder in this comparative example is PVDF, and the specific preparation method of the binder is as follows:

[0061] Weigh 0.3 g of PVDF, dissolve it in 9.7 g of NMP solvent, and stir to obtain a 3% PVDF binder solution.

[0062] Application Example

[0063] To explore the effects of different conductive materials, different ratios of electrode active materials (sodium ferrous sulfate), conductive materials, and binders on the performance of sodium-ion batteries, the high-pressure-resistant and fast-charging composite binder prepared in Example 1 and the PVDF binder in Comparative Example 1 were used to prepare positive electrode plates 1-8 in the following manner. The specific preparation process is as follows:

[0064] Using the high-pressure-resistant and fast-charging composite binder prepared in Example 1 (or the PVDF binder in Comparative Example 1), DMF solvent (NMP solvent), and sodium ferrous sulfate and conductive materials (Super P Li or acetylene black) to prepare a sodium-ion battery sodium ferrous sulfate electrode plate. The method is as follows: Weigh the electrode active material (sodium ferrous sulfate material), conductive material, and binder according to the mass ratio, mix them evenly, then add the solvent and grind and mix them evenly to make the battery electrode plate slurry; use a scraper to evenly coat the battery electrode plate slurry on the current collector aluminum foil, and dry it in a vacuum drying oven at 120 °C for 12 h to obtain the sodium-ion battery sodium ferrous sulfate positive electrode plate. In Table 1, in the mass ratio of the positive electrode material, conductive material, and binder, the amount of the binder refers to the content of the effective component after removing the solvent in the binder.

[0065] The materials and formulations used for different positive electrode plates are shown in Table 1:

[0066] Table 1

[0067]

[0068]

[0069] The sodium-ion battery sodium iron sulfate positive electrode sheets 1-8 prepared above were assembled into coin-type half-cells respectively, and the method is as follows: The prepared sodium iron sulfate positive electrode sheets were stamped into small round sheets with a diameter of 12 mm, and then in a glove box filled with argon, the positive electrode sheets, separator (glass fiber), electrolyte, sodium sheet, shrapnel and gasket were encapsulated with positive and negative electrode cases to obtain 2025 coin-type half-cells. Among them, the electrolyte is 1M NaClO4 EC / PC 5% FEC prepared.

[0070] The cyclic stability and rate performance of each sodium-ion battery were tested by the constant current method, the potential window was 2-4.5V, the electrode material was sodium iron sulfate material, and the current density was 120 mA / g; the test results are shown in Table 2.

[0071] Table 2 Performance test results of sodium-ion half-cells assembled with different positive electrode sheets

[0072]

[0073] It can be seen from the data in Table 2 that the initial Coulomb efficiency of the sodium-ion batteries assembled with the high-voltage resistant and fast composite binder prepared in Example 1 of the present invention is generally high, and the specific capacity after cycling a certain number of weeks is improved compared with the sodium-ion batteries assembled with the binder prepared in Comparative Example 1, indicating that the oily binder prepared in the present invention can be well applied to the sodium iron sulfate positive electrode of sodium-ion batteries and plays an important role in improving the performance of sodium batteries.

[0074] Figure 2 They are respectively the first-cycle charge-discharge curves of sodium-ion half-cells 1 and 5 assembled with the binders prepared in Example 1 and Comparative Example 1. It can be seen that sodium-ion battery 1 has a better initial Coulomb efficiency. Specifically, the initial Coulomb efficiency (ICE) of sodium-ion battery 1 is 92.8%, which is significantly higher than that of the PVDF electrode (89.74%). This is mainly attributed to the fact that the composite binder can well wrap the active material and conductive carbon, which can reduce the side reaction with the electrolyte during the first charge cycle and further improve the utilization rate and first efficiency of the active material.

[0075] Figure 3 It is a comparative chart of the rate performance of sodium-ion half-cells 1 and 5 assembled with the binders prepared in Example 1 and Comparative Example 1. Example 1 provides reversible capacities of 111.1, 108.8, 105.6, 102.7, 99.8, 94.5, 90.1 and 81.2 mAh g at 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, 5.0C, 10.0C and 20.0C respectively -1 which is much higher than that of the battery using PVDF binder (95.0, 93.08, 89.3, 86.1, 82.2, 73.7, 66.4 and 53.8 mAh g -1) This is because the composite binder improves the Na + interface kinetic behavior, which is beneficial to the surface electrons and Na + transport at high current densities. Therefore, the greater the current density, the greater the capacity gap between the two, which proves that the oily binder prepared by the present invention has the function of rapidly conducting Na + and has a high ionic conductivity.

[0076] Figure 4 Figure 10 shows the charge-discharge curves of sodium-ion half-cells 2 and 6 assembled with the sodium ferrous sulfate positive electrode sheets prepared in Example 1 and Comparative Example 1 at 10C for the first cycle and 4500 cycles. It can be seen from the figure that after 4500 cycles at 10C, the discharge capacity decreases from 91.5 mAh g -1 to 69.79 mAh g -1 , and the capacity retention rate is 76.27%. In contrast, the NFS-PVDF electrode only provides a discharge capacity of 54.67 mAh g -1 after 4500 cycles, and the capacity retention rate is 59.5%. Therefore, compared with the traditional PVDF binder, the composite binder prepared by the invention enables the positive electrode to achieve fast charging performance and high reversible capacity.

[0077] Figure 5 Figure 11 shows the transmission electron microscope (TEM) images of sodium-ion half-cells 3 and 7 assembled with the binders prepared in Example 1 and Comparative Example 1. From the TEM images of the solid electrolyte interface (CEI) after three weeks of discharge, it can be seen that the CEI formed on the electrode surface induced by the composite binder of the present invention is thinner (13.2 nm) and more uniform, while the CEI of the comparative example is thicker and less uniform. The thinner CEI indicates less electrolyte consumption on the electrode side, and at the same time, the uniform interface helps to improve the sodium ion transport rate, thereby improving its kinetic characteristics and cycle stability. The thicker CEI indicates excessive electrolyte consumption, which is not conducive to the rapid transport of sodium ions, and thus leads to a decrease in the first-cycle Coulomb efficiency and cycle stability of the battery.

[0078] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-voltage resistant and fast-charging composite binder, characterized in that, The high-voltage fast-charging composite binder includes a nitrile-group-containing polymer and hydroxyethyl cellulose; wherein, the structural formula of the nitrile-group-containing polymer is shown in Formula (Ⅰ): ； Among them, R in formula (I) is one of -(C2H3), -(C3H5), -(C 12 H7O2), and n is 600 - 25000.

2. The high-voltage fast-charging composite binder according to claim 1, wherein The nitrile-group-containing polymer is one of polyacrylonitrile, polybutenenitrile, and polyarylether nitrile.

3. The high-voltage resistant and fast-charging composite binder according to claim 2, wherein In the high-voltage fast-charging composite binder, the mass fraction of the nitrile-group-containing polymer in the total mass of hydroxyethyl cellulose and the nitrile-group-containing polymer is 50-90%.

4. The high-pressure fast-charging resistant composite adhesive according to claim 3, characterized in that: The average molecular weight of the nitrile-group-containing polymer is 100,000-1,000,000, and the average molecular weight of hydroxyethyl cellulose is 10,000-200,000.

5. The method for preparing the high-pressure fast-charging resistant composite adhesive according to claim 1, characterized in that: The steps are as follows: Mix the nitrile-group-containing polymer solution and the hydroxyethyl cellulose solution to obtain the high-voltage fast-charging composite binder.

6. The preparation method of the high-voltage resistant and fast-charging composite binder according to claim 5, wherein The mass ratio of the nitrile-group-containing polymer to hydroxyethyl cellulose is (5-9):(5-1); the solvent in the nitrile-group-containing polymer solution and the hydroxyethyl cellulose solution is any one of DMF, DMSO, NMP, and DMAc.

7. A positive electrode sheet, comprising a binder, a positive electrode material and a conductive material, characterized in that: The binder is the high-voltage fast-charging composite binder according to any one of claims 1-4.

8. The positive electrode sheet according to claim 7, wherein, The positive electrode material is a layered transition metal oxide or a polyanion compound, and the conductive material is any one of acetylene black, Ketjen black, and Super P Li.

9. The positive electrode sheet according to claim 8, wherein The layered transition metal oxide is sodium nickel iron manganese oxide; the polyanion compound is any one of sodium fluorophosphate vanadate, sodium vanadium phosphate, sodium pyrophosphate iron, and sodium ferrous sulfate.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode sheet, negative electrode sheet, separator, and electrolyte according to claim 7.

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