Preparation method of sodium electric positive electrode material

Abstract

The application discloses a preparation method of a sodium battery positive electrode material, and comprises the following steps: S1, respectively configuring a sol suspension and an ammonium salt alcohol solution, wherein the sol suspension is configured by adding an isopropyl alcohol salt in a polyethylene glycol aqueous solution and uniformly mixing; the ammonium salt alcohol solution is configured by adding an ammonium salt in an alcohol solution; S2, adding a pre-sodium battery positive electrode material in the ammonium salt alcohol solution obtained in S1, uniformly mixing to obtain a mixed solution, and transferring the sol suspension obtained in S1 into the mixed solution after uniform mixing; and S3, filtering, drying and sintering the product obtained in S2 to obtain the sodium battery positive electrode material. The preparation method is simple and easy to operate, can reduce the release of sodium ions in the preparation process of the sodium battery positive electrode material, can reduce the residual alkali on the surface of the finally obtained sodium battery positive electrode material, and forms a coating layer on the surface of the finally obtained sodium battery positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of materials, and more specifically to a method for preparing a sodium-ion cathode material. Background Technology

[0002] Technology changes lives. The diversification of electronic product applications has transformed our lifestyles, making our lives more convenient. While lithium-ion batteries are commonly used in current electronic products, research on sodium-ion batteries is also increasing with advancements in battery technology. Firstly, sodium is abundant; it is one of the most abundant metallic elements on Earth, with an abundance of 2.64% in the Earth's crust, 440 times that of lithium. Sodium resources are widely distributed and easy to refine, eliminating concerns about supply shortages or price fluctuations. Secondly, sodium-ion batteries are inexpensive. The positive electrode material does not require the relatively expensive metals lithium, nickel, and cobalt, and the negative electrode can use cheaper aluminum foil (lithium batteries use copper foil). The material cost of sodium-ion batteries is 30%-40% lower than that of lithium-ion batteries.

[0003] In the existing technology, during the preparation of sodium-ion battery cathode materials, or in the final production of sodium-ion battery cathode materials, researchers have found that due to the high residual alkali content on the surface of sodium-ion battery materials, sodium-ion battery materials have strong water absorption. The Na on the surface of sodium-ion battery materials easily reacts with water to generate sodium hydroxide, which causes sodium ions to be further released from the sodium-ion battery cathode material, ultimately leading to the deterioration of the electrochemical performance of the sodium-ion battery cathode material and directly affecting the significant degradation of the battery's electrical performance. Summary of the Invention

[0004] This invention addresses the problems in the prior art by disclosing a method for preparing sodium-ion battery cathode materials. The sodium-ion battery cathode materials prepared by this invention exhibit less residual alkali, and the process of preparing the sodium-ion battery cathode materials reduces the release of Na ions from the surface of the sodium-ion battery materials. Finally, a coating layer is formed on the surface of the sodium-ion battery cathode materials, further improving the stability of the sodium-ion battery cathode materials in air. Using the sodium-ion battery cathode materials obtained by this invention in batteries is beneficial to improving the electrical performance of the batteries, especially the battery discharge specific capacity.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a method for preparing a sodium-ion battery cathode material, the method comprising:

[0007] S1: Prepare a sol suspension and an ammonium salt alcohol solution respectively. The sol suspension is prepared by adding isopropoxide to a polyethylene glycol aqueous solution and mixing thoroughly. The ammonium salt alcohol solution is prepared by adding ammonium salt to an alcohol solution.

[0008] S2: Add the pre-sodium electrode material to the ammonium salt alcohol solution obtained in S1, mix evenly to obtain a mixed solution, and transfer the sol suspension obtained in S1 to the evenly mixed solution.

[0009] S3: The product obtained in S2 is filtered, dried, and sintered to obtain the sodium-ion cathode material of the present invention.

[0010] The above-described design and method of this invention reduce the release of sodium ions during the preparation of sodium-ion cathode materials. Specifically, the sol formed by mixing polyethylene glycol and isopropoxide, when transferred from S1 to S2, forms a coating layer on the surface of the pre-sodium-ion cathode material. This coating layer confines the release of sodium ions within the pre-sodium-ion cathode material, thereby trapping them within the material. Furthermore, the coating layer enhances the stability of the sodium-ion cathode material in air. Based on this, the pre-sodium-ion cathode material is placed in the ammonium salt alcohol solution prepared in S1. On one hand, the ammonium salt alcohol solution rapidly absorbs heat from the mixed solution, lowering the temperature and slowing the low-temperature release of Na ions from the crystal lattice. This provides conditions and time for the sol to form a uniform coating layer on the surface of the pre-sodium-ion cathode material, balancing the coating rate. On the other hand, the preparation of the ammonium salt alcohol solution in S1 also generates a small amount of H₂. + This material, working in conjunction with the coating layer, neutralizes some residual alkali on the surface of the pre-sodium cathode material. Furthermore, this invention utilizes polyethylene glycol, an alcohol solution, and isopropoxide, which exhibit good compatibility and synergistic effects, forming two mutually compatible solution systems: a sol suspension and an ammonium salt alcohol solution. This facilitates the sequential addition of the two solution systems and the formation of a uniform coating, thereby enhancing the synergy between the substances in the solution and promoting the formation of the coating layer on the surface of the pre-sodium cathode material. Therefore, the sodium cathode material prepared by this invention not only possesses a high specific capacity but also exhibits low residual alkali. Applying this sodium cathode material to batteries can improve the electrical performance of sodium-ion batteries.

[0011] As a further option, those skilled in the art can select different precursor sodium cathode materials or purchase different precursor sodium cathode materials according to their actual needs. The precursor sodium cathode material in this invention refers to the sodium cathode material obtained after preliminary sintering of the sodium cathode material precursor and sodium source, or the final sodium cathode material.

[0012] As a best example in this case, the pre-sodium electrode material is selected as a nickel-iron-manganese pre-sodium electrode material. The nickel-iron-manganese pre-sodium electrode material has a layered structure. Using the method of the present invention to coat it can further reduce the release of Na ions from the layered structure and significantly improve the capacity of the final sodium electrode material.

[0013] As a further embodiment, the weight-average molecular weight of polyethylene glycol in the polyethylene glycol aqueous solution in S1 is 1000-2000.

[0014] As a further embodiment, the mass percentage of polyethylene glycol in the polyethylene glycol aqueous solution in S1 is 2%-4%.

[0015] As a further embodiment, the mass percentage of isopropoxide in the sol suspension is 3%-5%.

[0016] As a further embodiment, the amount of isopropoxide added in S1 is 0.5%-1.5% of the mass of the pre-sodium cathode material; the mass of the sol suspension of S1 transferred in S2 does not exceed 20g and is not less than 5g. Achieving a suitable coating thickness allows for the formation of a better porosity structure. The amount of isopropoxide added affects the pore size in the coating layer. When the amount added is greater than 1.5%, the pore structure becomes more compact, affecting the insertion and extraction of sodium ions. Conversely, when the amount added is less than 0.5%, the pore structure becomes looser, leading to a decrease in the mechanical properties of the coating layer and the inability to restrain the extraction of sodium ions during the coating process.

[0017] As a further refinement, the amount of isopropoxide added in S1 is 0.8%-1.2% of the mass of the pre-sodium cathode material; the mass of the sol suspension of S1 transferred in S2 does not exceed 17g and is not less than 13g. This results in a coating layer and void structure with more suitable pore size.

[0018] As a further embodiment, the isopropoxide includes one or more of aluminum isopropoxide, titanium isopropoxide, magnesium isopropoxide, and zirconium isopropoxide.

[0019] As a further embodiment, the ammonium salt in S1 includes one or more of ammonium nitrate, ammonium chloride, ammonium carbonate, and ammonium sulfate.

[0020] As a preferred embodiment, the ammonium salt in S1 includes ammonium nitrate. Ammonium nitrate dissolves quickly and has a more pronounced endothermic reaction time; furthermore, nitrates are easily decomposed during sintering.

[0021] As a further option, the alcohol solution in S1 includes ethanol.

[0022] As a further embodiment, the concentration of the ammonium salt alcohol solution in S1 is 10 g / L-20 g / L; the concentration of the pre-sodium electrode material in the mixed solution in S2 is 80 g / 100 mL-120 g / 100 mL. The ammonium salt alcohol concentration directly affects the coating environment temperature of the pre-sodium electrode material. The coating temperature not only affects the extraction of sodium ions from the crystal lattice but also the uniformity of the coating layer formation and the coating time. The selection of the ammonium salt alcohol concentration needs to balance the coating layer rate and the extraction of sodium ions, so as to reduce the extraction of sodium ions while achieving uniform and rapid coating. When the concentration of ammonium salt alcohol and the concentration of the pre-sodium electrode material are matched, the extraction of sodium ions from the pre-sodium electrode material can be significantly reduced.

[0023] As a further refinement, the concentration of the ammonium salt alcohol solution in S1 is 13 g / L-17 g / L; and the concentration of the pre-sodium cathode material in the mixed solution in S2 is 90 g / 100 mL-110 g / 100 mL. This allows for better coating while reducing the extraction of sodium ions from the crystal lattice at a more suitable temperature.

[0024] As a further embodiment, the ammonium salt alcohol solution obtained in step S1 is placed in a low-temperature constant-temperature water bath. Technicians can adjust the water temperature range of the low-temperature constant-temperature water bath according to actual needs, with the optimal low-temperature range being 2℃-10℃.

[0025] As a further option, the mixing method in S2 is to stir for 2.5 min to 3.5 min to achieve uniform mixing.

[0026] As a further embodiment, the transfer rate in S2 is 1 g / min to 3 g / min. The transfer rate affects the uniformity of the coating.

[0027] As a further embodiment, the transfer rate in S2 is 1.8 g / min - 2.2 g / min.

[0028] As a further option, the optimal method of filtration in S3 is vacuum filtration.

[0029] As a further option, the drying method in S3 is vacuum drying.

[0030] As a further improvement, the vacuum drying temperature is 60℃-100℃; the vacuum drying time is 12h-24h.

[0031] As a further embodiment, the sintering in S3 is carried out at a temperature of 400℃-600℃ for a time of 4h-8h.

[0032] The present invention also provides the application of the sodium-ion cathode material in cathode sheets, batteries or electrochemical devices.

[0033] The features and beneficial effects of this invention are as follows:

[0034] (1) The preparation method of the present invention is simple and easy to operate, which can reduce the release of sodium ions during the preparation of sodium-ion cathode materials, reduce the residual alkali on the surface of the final sodium-ion cathode material, and form a coating layer on the surface of the final sodium-ion cathode material. The preparation method of the present invention yields a high-capacity, structurally stable sodium-ion cathode material.

[0035] (2) The sodium-ion cathode material obtained by this invention can be used in batteries to improve the discharge specific capacity and cycle performance of batteries. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a SEM image of the sodium-ion cathode material in Example 1.

[0038] Figure 2 This is an element distribution diagram for Example 18, in which, Figure 2 a is the sodium-ion cathode material of Example 18. Figure 2 b represents the distribution of element Na in the sodium-ion battery cathode material. Figure 2 c represents the distribution of Mg element in the sodium-ion cathode material. Figure 2 d represents the distribution of Zr element in the sodium-ion battery cathode material. Figure 2 e represents the distribution of Ti element in the sodium-ion cathode material. Figure 2 f represents the distribution of Mn elements in the sodium electrode material. Detailed Implementation

[0039] To facilitate understanding of the preparation method of the sodium-ion cathode material of the present invention, a more comprehensive description of the preparation method of the sodium-ion cathode material of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0040] The method of the present invention is not limited to the preparation of sodium-ion cathode materials in the examples of the present invention. The present invention only provides an example of a method for preparing a pre-sodium-ion cathode material. Those skilled in the art can adjust the preparation method of different pre-sodium-ion cathode materials or purchase different pre-sodium-ion cathode materials according to their actual needs.

[0041] Preparation method of pre-sodium electrode material: A 111 nickel-iron-manganese precursor with a particle size D50 of 10±1 μm and sodium carbonate with a particle size D50 of 6±1 μm are mixed at a ratio of 1:1.03 and sintered at 850℃-900℃ for 10-15 hours to produce a 111 polycrystalline material. After crushing by a jaw crusher, roller mill, and mechanical mill, an O3-type pre-sodium electrode material with a D50 of approximately 10±1 μm is synthesized.

[0042] Example 1: Polyethylene glycol (PEG) (molecular weight 1000-2000) was added to pure water to prepare a 3% PEG aqueous solution S1. Isopropoxide was added, with the isopropoxide content being 1% of the mass of the sodium electrode material. The mixture was stirred thoroughly to form a good sol suspension S2. The mass percentage of isopropoxide in the sol suspension was 4%. The isopropoxide was selected as aluminum isopropoxide.

[0043] Preparation of ammonium nitrate alcohol solution: Prepare an ammonium salt alcohol solution of a certain concentration using ethanol, wherein the ammonium salt is ammonium nitrate, and the concentration of the ammonium salt alcohol solution is 15 g / L. Place it in a low-temperature (5℃) constant temperature water bath. Add 100 g of pre-sodium electrode material to 100 mL of ammonium salt alcohol solution, stir for 3 min, and then label the mixture as S3. Continue stirring while adding S2 to S3 at a rate of 2 g / min, with a transfer amount of 15 g.

[0044] The material was filtered, vacuum dried, and then sintered in a muffle furnace at a low temperature of 400℃-600℃. This yielded the target sodium-ion cathode material with an Al-ion-coated layer covering the pre-constituted sodium-ion cathode material.

[0045] Example 2: In Example 2, the content of isopropoxide added is 0.5% of the mass of sodium electrode material, and other parameters are the same as in Example 1.

[0046] Example 3: In Example 3, the content of isopropoxide was 1.5% of the mass of the sodium electrode material, and the other parameters were the same as in Example 1.

[0047] Example 4: In Example 4, the concentration of the ammonium salt alcohol solution was 10 g / L, and the other parameters were the same as in Example 1.

[0048] Example 5: In Example 5, the concentration of the ammonium salt alcohol solution was 20 g / L, and the other parameters were the same as in Example 1.

[0049] Example 6: In Example 6, 80g of pre-sodium electrode material was added to 100mL of ammonium salt alcohol solution, and other parameters were the same as in Example 1.

[0050] Example 7: In Example 7, 120g of pre-sodium electrode material was added to 100mL of ammonium salt alcohol solution, and other parameters were the same as in Example 1.

[0051] Example 8: In Example 8, S2 was added to S3 at a rate of 1 g / min, and other parameters were the same as in Example 1.

[0052] Example 9: In Example 9, S2 was added to S3 at a rate of 3g / min, and other parameters were the same as in Example 1.

[0053] Example 10: Example 10 uses a transfer amount of 10g, and other parameters are the same as in Example 1.

[0054] Example 11: Example 11 uses a transfer amount of 20g, and other parameters are the same as in Example 1.

[0055] Example 12: The ammonium salt used in Example 12 is ammonium chloride, and other parameters are the same as in Example 1.

[0056] Example 13: The ammonium salt used in Example 13 is ammonium carbonate, and other parameters are the same as in Example 1.

[0057] Example 14: The ammonium salt used in Example 14 is ammonium sulfate, and other parameters are the same as in Example 1.

[0058] Example 15: The isopropoxide salt in Example 15 is titanium isopropoxide, and other parameters are the same as in Example 1.

[0059] Example 16: The isopropoxide salt in Example 16 is magnesium isopropoxide, and other parameters are the same as in Example 1.

[0060] Example 17: The isopropoxide salt in Example 17 is zirconium isopropoxide, and other parameters are the same as in Example 1.

[0061] Example 18: In Example 18, the isopropoxide salts selected are titanium isopropoxide, magnesium isopropoxide, and zirconium isopropoxide, wherein the molar mass ratio of titanium isopropoxide, magnesium isopropoxide, and zirconium isopropoxide is 1:1:1, and other parameters are the same as in Example 1.

[0062] Comparative Example 1: Sodium-ion cathode material achieved by coating in the prior art. The asphalt and pre-concentrated sodium-ion cathode material were directly mixed in a high-speed mixer, with 20g of asphalt and 100g of pre-concentrated sodium-ion cathode material; the mixture was then sintered at a low temperature of 400℃-600℃ in a muffle furnace.

[0063] Comparative Example 2: Comparative Example 2 uses aluminum isopropoxide, with the aluminum isopropoxide content being 0.25% of the mass of the sodium-ion cathode material. Other parameters are the same as in Example 1.

[0064] Comparative Example 3: Comparative Example 3 uses aluminum isopropoxide, with the aluminum isopropoxide content being 1.75% of the mass of the sodium-ion cathode material. Other parameters are the same as in Example 1.

[0065] Comparative Example 4: The concentration of the ammonium salt alcohol solution used in Comparative Example 4 was 5 g / L, and the other parameters were the same as in Example 1.

[0066] Comparative Example 5: The concentration of the ammonium salt alcohol solution used in Comparative Example 5 was 25 g / L, and the other parameters were the same as in Example 1.

[0067] Comparative Example 6: In Comparative Example 6, S2 was added to S3 at a rate of 0.5 g / min, and other parameters were the same as in Example 1.

[0068] Comparative Example 7: In Comparative Example 7, S2 was added to S3 at a transfer rate of 3.5 g / min, and other parameters were the same as in Example 1.

[0069] Comparative Example 8: The transfer amount used in Comparative Example 8 was 5g, and other parameters were the same as in Example 1.

[0070] Comparative Example 9: The transfer amount used in Comparative Example 9 was 25g, and other parameters were the same as in Example 1.

[0071] We will also obtain sodium-ion cathode materials for use in coin cells, wherein the preparation method of the coin cells includes:

[0072] The sodium-ion battery cathode material, conductive agent Super P (conductive carbon black), and binder PVDF (polyvinylidene fluoride) of this invention are prepared into a cathode material slurry using a degassing machine at a mass ratio of 90:5:5. After adjusting the solid content of the slurry to 39% using N-methylpyrrolidone (NMP), the adjusted slurry is coated onto aluminum foil using an automatic coating machine, dried in a vacuum drying oven at 120°C, rolled by a roller press, and punched by a slicing machine. Then, button-type 2032 batteries are assembled in a glove box. The electrolyte is 1.2 mol / L NaPF6 (sodium hexafluorophosphate), wherein the solvent is EC (ethylene carbonate):PC (propylene carbonate):EMC (ethyl methyl carbonate) = 1:1:1 (volume ratio), with an additional 2 wt% FEC (fluoroethylene carbonate). The separator is a glass fiber separator, and a sodium metal sheet is used as the counter electrode.

[0073] We also obtained coin cell half-cells for testing:

[0074] (1) Specific capacity test: The initial charge specific capacity and discharge specific capacity at 0.1C were tested using the Xinwei test cabinet at 2.5-4.1V.

[0075] (2) Cyclic performance test: Capacity retention rate of 50 cycles at 1C rate under 2.5V-4.1V.

[0076] (3) Surface pH test: 2g of sodium-ion battery positive electrode material was placed in 40g of pure water, stirred for 15min, and then tested with a pH meter.

[0077] (4) Surface C% test method: The C% content of the material is tested by a carbon-sulfur analyzer, and the Na2CO3 content on the surface of the sodium electrode material can be deduced.

[0078] (5) The test results in this invention are all average values ​​obtained from three sets of parallel data.

[0079] Validation Result Analysis

[0080] Table 1 Test results of embodiments and comparative examples of the present invention

[0081]

[0082]

[0083] We have successfully obtained a sodium-ion battery cathode material with a coating layer using the preparation method of this invention. The sodium-ion battery cathode material obtained by this invention exhibits high capacity and high stability in air, such as... Figure 1 As shown in Table 1, through the experimental data of Examples 1-18 and Comparative Examples 1-9 in Table 1, we can find that the sodium-ion cathode material obtained in Examples 1-18 of this invention, when used in batteries, results in batteries with higher electrical performance. We believe this is because the preparation method of this invention is particularly suitable for preparing sodium-ion cathode materials. In the method of this invention, by preparing an ammonium salt alcohol solution, the pre-sodium-ion cathode material is placed in the ammonium salt alcohol solution. The prepared ammonium salt alcohol solution can quickly absorb heat from the solution, lowering the solution temperature, thereby slowing down the low-temperature release of Na ions from the lattice of the pre-sodium-ion cathode material, thus providing environmental conditions and time for sol coating; on the other hand, the ammonium salt alcohol solution can also generate a small amount of H2O. +This reduces residual alkali on the surface of the pre-sodium battery cathode material and further improves the stability of the final sodium battery cathode material. We can observe that the alkalinity of the sodium battery cathode materials obtained in Examples 1-18 and the residual alkali (Na2CO3) on the surface of the sodium battery cathode material are lower than those in Comparative Examples 1-9. Based on this, to coordinate with the ammonium salt alcohol solution, we further selected materials containing polyethylene glycol and isopropoxide salts that can cooperate with it to obtain a sol. The materials have good compatibility and synergistic effects, forming two mutually compatible solution systems: a sol suspension and an ammonium salt alcohol solution. This facilitates the sequential addition of the two solution systems and the formation of a uniform coating, thereby improving the coordination between substances in the solution and promoting the formation of the coating layer on the surface of the pre-sodium battery cathode material. We can see from this... Figure 2 a- Figure 2 As seen in Figure f, the coating layer in Example 18 uniformly coats the surface of the pre-sodium electrode material. When the sol obtained in S1 is transferred to S2, a coating layer can be formed on the surface of the pre-sodium electrode material. This coating layer can restrict the extraction of sodium ions from the pre-sodium electrode material, trapping them within the material. Furthermore, the coating layer can improve the stability and structural stability of the sodium electrode material in air. In addition, the isopropoxide in this invention can increase the ionic conductivity of the coating layer, thereby facilitating the insertion / extraction of the sodium electrode material. Therefore, the sodium electrode material prepared by this invention not only possesses high specific capacity and cycle performance, but its application in batteries can also improve the electrical performance of sodium-ion batteries.

[0084] Building upon this, we further investigated how the method of this invention improves the electrical properties and stability of the final sodium-ion cathode material. As shown in Table 1, we further designed examples and comparative cases for further study.

[0085] First, we investigated the relationship between the thickness and structure of the coating layer on the improvement of sodium-ion cathode materials. In this invention, the coating layer serves two purposes: firstly, it binds the extraction of sodium ions from the crystal lattice; secondly, it enhances the stability of the sodium-ion cathode material in air. Therefore, to ensure the precursor sodium-ion cathode material has a suitable coating layer thickness, we first need to achieve an appropriate coating thickness. For example, Examples 1, 10-11 compared the transfer amounts, with Example 1 exhibiting the best electrical performance. We believe that the transfer amount is related to the coating thickness. If the coating layer is too thick, it will affect the insertion / extraction of sodium ions; conversely, if the transfer amount is too small, it will affect whether the sodium-ion cathode material is fully coated, both impacting the coating effect. We can verify our hypothesis through comparisons in Examples 8-9. With a precursor sodium-ion cathode material of suitable thickness, the amount of isopropoxide added in the transfer product directly affects the coating layer structure. Comparing Examples 1-3, we found that Example 1 achieved the best electrical performance. We believe that the gel suspension forms a porous coating layer on the surface of the pre-sodium cathode material. Sodium ions can be inserted and extracted through the interlaced pores in the coating layer. The amount of isopropoxide added affects the pore size of the coating layer. If the amount of isopropoxide added is too small, the coating layer formed on the pre-sodium cathode material will result in a looser pore structure, which cannot prevent sodium ions from being extracted during the coating process. Conversely, if the amount of isopropoxide added is too large, the pore structure will be too dense, both of which will affect the insertion and extraction of sodium ions and the insertion and extraction balance during battery cycling. We can also verify this by comparing Comparative Examples 2 and 3, which show poor cycle performance and discharge specific capacity. Therefore, based on the optimal transfer amount of 13g-17g, we further optimize the amount of isopropoxide added to be 0.8%-1.2% of the pre-sodium cathode material.

[0086] Based on this, we further investigated the relationship between the temperature of the coating environment and the concentration of the pre-coated sodium cathode material. When the concentrations of the pre-coated sodium cathode material and the ammonium salt alcohol are mismatched, on the one hand, the temperature of the mixed solution cannot suppress the release of sodium ions from the pre-coated sodium cathode material. If the concentration of the pre-coated sodium cathode material is too high, the concentration of the ammonium salt alcohol is insufficient to suppress the release of all sodium ions from the pre-coated sodium cathode material, leading to a decrease in the capacity of the final sodium cathode material. On the other hand, it also affects the uniformity and time of the coating layer. Therefore, the selection of the ammonium salt alcohol concentration needs to balance the coating speed and the release of sodium ions, so as to reduce sodium ion release while achieving uniform and rapid coating. We can refer to Examples 1, 4-7. We can observe that, comparing Examples 1 and Examples 4-5, when a suitable concentration of pre-sodium cathode material is matched with a higher concentration of ammonium salt alcohol solution (as in Example 5), although the capacity of the sodium cathode material in Example 5 is higher than that when matched with a lower concentration of ammonium salt alcohol solution (Example 4), the cycle performance of Example 5 is lower than that of Example 4. We believe that the lower concentration of ammonium salt alcohol in Example 4 may have resulted in the coating environment being insufficient to suppress the release of sodium ions from the pre-sodium cathode material. While the coating environment in Example 5 can effectively suppress the release of sodium ions from the pre-sodium cathode material, the coating layer, due to its lower temperature, affects the coating effect, resulting in uneven or insufficient coating. We can also verify this through comparisons of Examples 6-7 and Comparative Examples 4-5. The selection of the concentration of ammonium salt alcohol and the concentration of the pre-sodium cathode material not only affects the uniformity of the coating layer of the final sodium cathode material but also influences the final discharge specific capacity of the sodium cathode material. We further optimized the concentration of ammonium salt alcohol to 13g / L-17g / L and the concentration of the pre-sodium electrode positive material to 90g / 100mL-110g / 100mL.

[0087] We also investigated the effect of the transfer rate of the sol-gel obtained in S1 on the improvement of the sodium-ion cathode material. We compared Examples 1, 8, and 9, and Example 1 showed better electrical performance and air stability. We believe this is because the transfer rate affects the formation of the coating layer. A faster transfer rate may lead to uneven coating, while a slower transfer rate may lead to incomplete coating, both resulting in poor uniformity of the coating layer and ultimately affecting the battery's electrical performance. We can also verify this through comparisons with Comparative Examples 6 and 7, which both showed poor electrical performance and air stability. Therefore, we further optimized the transfer rate to be 1.8 g / min–2.2 g / min.

[0088] We also discovered that the type of ammonium salt affects the properties of the coating layer. Through comparisons of Examples 1 and 12-14, we found that ammonium nitrate was optimal. We believe this is because ammonium nitrate dissolves quickly and has a more pronounced endothermic reaction, and nitrates are also prone to decomposition during sintering. Therefore, we further optimized the ammonium salt to be ammonium nitrate.

[0089] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, The preparation method includes: S1: Prepare a sol suspension and an ammonium salt alcohol solution respectively. The sol suspension is prepared by adding isopropoxide to a polyethylene glycol aqueous solution and mixing thoroughly. The ammonium salt alcohol solution is prepared by adding ammonium salt to an alcohol solution. S2: Add the pre-sodium electrode material to the ammonium salt alcohol solution obtained in S1, mix evenly to obtain a mixed solution, and transfer the sol suspension obtained in S1 to the evenly mixed solution. S3: The product obtained in S2 is filtered, dried, and sintered to obtain sodium-ion cathode material; The weight-average molecular weight of polyethylene glycol in the polyethylene glycol aqueous solution in S1 is 1000-2000; The mass percentage of polyethylene glycol in the polyethylene glycol aqueous solution in S1 is 2%-4%; The mass percentage of isopropoxide in the sol suspension is 3%-5%; The isopropoxide salt is one or more of aluminum isopropoxide, titanium isopropoxide, magnesium isopropoxide, and zirconium isopropoxide; the ammonium salt in S1 is one or more of ammonium nitrate, ammonium chloride, ammonium carbonate, and ammonium sulfate.

2. The preparation method according to claim 1, characterized in that, The amount of isopropoxide added in S1 is 0.5%-1.5% of the mass of the pre-sodium electrode material; the mass of the sol suspension of S1 transferred in S2 is not more than 20g and not less than 5g.

3. The preparation method according to claim 1, characterized in that, The amount of isopropoxide added in S1 is 0.8%-1.2% of the mass of the pre-sodium cathode material; the mass of the sol suspension of S1 transferred in S2 is not more than 17g and not less than 13g.

4. The preparation method according to claim 1, characterized in that, The ammonium salt in S1 is ammonium nitrate.

5. The preparation method according to claim 1, characterized in that, The concentration of the ammonium salt alcohol solution in S1 is 10 g / L-20 g / L; the concentration of the pre-sodium electrode material in the mixed solution in S2 is 80 g / 100 mL-120 g / 100 mL.

6. The preparation method according to claim 1, characterized in that, The concentration of the ammonium salt alcohol solution in S1 is 13g / L-17g / L; the concentration of the pre-sodium electrode material in the mixed solution in S2 is 90g / 100mL-110g / 100mL.

7. The preparation method according to claim 1, characterized in that, The transfer rate in S2 is 1g / min-3g / min.

8. The preparation method according to claim 1, characterized in that, The transfer rate in S2 is 1.8 g / min - 2.2 g / min.

9. The preparation method according to claim 1, characterized in that, The ammonium salt alcohol solution obtained in step S1 is placed in a low-temperature constant temperature water bath; the alcohol solution in step S1 includes ethanol; The drying method in S3 is vacuum drying.

10. The preparation method according to claim 9, characterized in that, The vacuum drying temperature is 60℃-100℃; the vacuum drying time is 12h-24h.

11. The preparation method according to claim 1, characterized in that, The sintering in S3 is carried out at a temperature of 400℃-600℃ for a time of 4h-8h.

12. The method for preparing the sodium-ion cathode material according to any one of claims 1-11 yields the application of the sodium-ion cathode material in cathode sheets, batteries, or electrochemical devices.

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