Sodium tantalate coated sodium ion layered metal oxide positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of sodium ion battery positive electrode materials, in particular to a sodium tantalate coated sodium ion layered metal oxide positive electrode material and a preparation method thereof. The method comprises the following steps: dissolving anhydrous tantalum pentachloride in absolute ethyl alcohol, and stirring to form a tantalum precursor solution; dissolving citric acid in deionized water, and stirring to form a chelating agent aqueous solution; adding the chelating agent aqueous solution into the tantalum precursor solution to obtain a first mixed solution; dissolving sodium acetate trihydrate and manganese acetate tetrahydrate in deionized water, and stirring to form a metal salt precursor solution; heating a second mixed solution composed of the first mixed solution and the metal salt precursor solution to generate sol; performing vacuum drying treatment, low-temperature carbonization treatment and grinding treatment on the gel generated based on the sol to generate carbonized powder; and tabletting the carbonized powder, carrying out high-temperature calcination in an oxygen atmosphere, cooling, and grinding to obtain the sodium tantalate-coated sodium ion layered metal oxide positive electrode material.

Description

Technical Field

[0001] The present application relates to the technical field of cathode materials for sodium-ion batteries, and particularly to a sodium tantalate-coated sodium-ion layered metal oxide cathode material and a preparation method thereof. Background Art

[0002] With the rapid development of the new energy industry, lithium-ion batteries have become one of the core technologies for energy storage devices due to their advantages such as high energy density, long cycle life, and environmental friendliness. Layered metal oxide cathode materials are an important type of cathode material in lithium batteries, with high theoretical specific capacity and good electrical conductivity. However, in practical applications, they still face problems such as insufficient cycle stability, complex interfacial reactions, and electrochemical performance degradation at high voltages. To overcome these problems, researchers have introduced various modification strategies, such as element doping, surface coating, and lattice structure optimization. Among them, the surface coating technology has received extensive attention.

[0003] Sodium tantalate (NaTaO3), as a typical perovskite-type oxide material, has good chemical stability and thermal stability, and can maintain excellent electrochemical performance in a high-voltage environment. It is expected to be used as a coating layer for layered metal oxide cathode materials to improve the cycle life and rate performance of the materials. However, existing sodium tantalate coating methods still have limitations in terms of uniformity, coating thickness control, and the bonding between the coating layer and the matrix material, which restricts the performance optimization and industrial application promotion of the materials. Summary of the Invention

[0004] The sodium tantalate-coated sodium-ion layered metal oxide cathode material and the preparation method provided by the embodiments of the present invention at least solve the problems in the related art that the existing sodium tantalate coating methods have poor uniformity, coating thickness control, and bonding between the coating layer and the matrix material.

[0005] According to the first aspect of the embodiments of the present invention, a preparation method of a sodium tantalate-coated sodium-ion layered metal oxide cathode material is provided, and the method includes:

[0006] Dissolve anhydrous tantalum pentachloride in absolute ethanol and stir to form a tantalum precursor solution;

[0007] Dissolve citric acid in deionized water and stir to form a chelating agent aqueous solution;

[0008] Dropwise add the chelating agent aqueous solution to the tantalum precursor solution and stir to chelate the tantalum ions in the tantalum precursor solution with citric acid to obtain a first mixed solution;

[0009] Dissolve sodium acetate trihydrate and manganese acetate tetrahydrate in deionized water and stir to form a metal salt precursor solution;

[0010] Heat the second mixed solution composed of the first mixed solution and the metal salt precursor solution under preset heating conditions to generate a sol;

[0011] Perform vacuum drying treatment, low-temperature carbonization treatment and grinding treatment on the gel generated based on the sol to generate carbonized powder. The gel is obtained by evaporating the sol to dryness;

[0012] Press the carbonized powder into tablets, calcine at 950 °C for 12 hours in an oxygen atmosphere, and grind after cooling to obtain a sodium tantalate-coated sodium-ion layered metal oxide cathode material.

[0013] Optionally, the amount of anhydrous tantalum pentachloride used is 0.08 mmol, and the volume of absolute ethanol is 15 ml;

[0014] When dissolving anhydrous tantalum pentachloride in absolute ethanol and stirring to form a tantalum precursor solution, the stirring time is 0.5 hours and the stirring speed is 300 r / min.

[0015] Optionally, the amount of citric acid used is 20.967 mmol, and the volume of deionized water is 15 ml;

[0016] When dissolving citric acid in deionized water and stirring to form a chelating agent aqueous solution, the stirring time is 0.5 hours and the stirring speed is 300 r / min.

[0017] Optionally, the amount of sodium acetate trihydrate used is 6.2625 mmol, the amount of manganese acetate tetrahydrate used is 10 mmol, and the volume of deionized water is 30 ml;

[0018] When adding the chelating agent aqueous solution dropwise to the tantalum precursor solution and stirring to chelate the tantalum ions in the tantalum precursor solution with citric acid to obtain a first mixed solution, the stirring time is 0.5 hours and the stirring speed is 300 r / min.

[0019] Optionally, the preset heating conditions are an 80 °C oil bath and a stirring speed of 300 r / min.

[0020] Optionally, the conditions for the vacuum drying treatment are drying at 100 °C for 12 hours, and the conditions for the low-temperature carbonization treatment are calcining at 500 °C for 6 hours with a heating rate of 5 °C / min.

[0021] Optionally, the oxygen atmosphere flow rate for the high-temperature calcination is 20 mL / min, the heating rate is 5 °C / min, and the cooling rate is 2 °C / min.

[0022] According to the second aspect of the embodiments of the present invention, a sodium tantalate-coated sodium-ion layered metal oxide cathode material is provided. The chemical formula of the sodium-ion layered metal oxide cathode material is NaTaO3@Na 0.44 MnO2, which has a layered structure. The sodium tantalate coating layer is uniformly distributed on the surface of the matrix material, and the thickness of the coating layer is 5-50 nm.

[0023] Optionally, the sodium-ion layered metal oxide cathode material has a capacity retention rate ≥ 83.44% after 100 cycles at a rate of 1C in the voltage range of 2.0-4.3V.

[0024] Advantages of the embodiments of the present invention:

[0025] The sodium-ion layered metal oxide cathode material prepared by the preparation method of the sodium tantalate-coated sodium-ion layered metal oxide cathode material provided by the embodiments of the present invention has significantly improved performance through the introduction of the sodium tantalate coating layer. Specifically, the perovskite-type layered oxide structure of sodium tantalate endows it with excellent chemical stability and conductivity, which can effectively protect the electrode material in high-voltage and high-temperature environments, extend the service life of the battery and improve safety. At the same time, the good compatibility between sodium tantalate and the sodium-ion layered metal oxide avoids the compatibility problems of traditional coating materials, enhances the interfacial bonding between the coating layer and the matrix material, and reduces the phenomenon of coating layer shedding during cycling. The improved surface structure design improves the surface protection and electrochemical stability of the material by controlling the thickness and uniformity of the sodium tantalate coating layer, slows down the occurrence of side reactions, and reduces the volume change and stress-induced degradation of the material. In addition, the preparation process of the embodiments of the present invention is more simple, optimizes the traditional coating process, ensures the uniformity and stability of the sodium tantalate coating layer, reduces the production cost, and is easy to be applied in large-scale industrialization.

[0026] Details of one or more embodiments of the present invention are set forth in the following drawings and description, so that other features, objects, and advantages of the present invention will become more clearly understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other embodiments according to these drawings without creative efforts.

[0028] Figure 1 It is a flowchart of a preparation method of a sodium tantalate-coated sodium-ion layered metal oxide cathode material provided by an embodiment of the present invention.

[0029] Figure 2 Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 MnO2 layered oxide cathode material provided by an embodiment of the present invention.

[0030] Figure 3a Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 Superimposed EDS element distribution map of the MnO2 layered oxide cathode material provided by an embodiment of the present invention.

[0031] Figure 3b Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 Scanning electron microscope morphology image of the MnO2 layered oxide cathode material provided by an embodiment of the present invention.

[0032] Figure 3c Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 Ta element distribution map of the MnO2 layered oxide cathode material provided by an embodiment of the present invention.

[0033] Figure 3d Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 O element distribution map of the MnO2 layered oxide cathode material provided by an embodiment of the present invention.

[0034] Figure 3e Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 Mn element distribution map of the MnO2 layered oxide cathode material provided by an embodiment of the present invention.

[0035] Figure 3f Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 Na element distribution map of the MnO2 layered oxide cathode material provided by an embodiment of the present invention.

[0036] Figure 4 Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 Schematic EDS energy spectrum diagram of the MnO2 layered oxide cathode material provided by an embodiment of the present invention.

[0037] Figure 5 Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 Schematic diagram of the cyclic stability test results of the MnO2 layered oxide cathode material at a 1C rate. Detailed implementation manners

[0038] The embodiments of the present embodiment will be described in more detail below with reference to the accompanying drawings. Although some embodiments of the present embodiment are shown in the drawings, it should be understood that the present embodiment can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to more thoroughly and completely understand the present embodiment. It should be understood that the drawings and embodiments of the present embodiment are only for exemplary purposes and are not used to limit the protection scope of the present embodiment.

[0039] Figure 1 The flowchart of a preparation method of a sodium tantalate-coated sodium-ion layered metal oxide cathode material provided by an embodiment of the present invention is shown. As Figure 1 shown, the method includes the following steps:

[0040] Step S101: Dissolve anhydrous tantalum pentachloride in anhydrous ethanol and stir to form a tantalum precursor solution.

[0041] Step S102: Dissolve citric acid in deionized water and stir to form a chelating agent aqueous solution.

[0042] Step S103: Dropwise add the chelating agent aqueous solution into the tantalum precursor solution and stir to chelate the tantalum ions in the tantalum precursor solution with citric acid to obtain a first mixed solution.

[0043] Step S104: Dissolve sodium acetate trihydrate and manganese acetate tetrahydrate in deionized water and stir to form a metal salt precursor solution.

[0044] Step S105: Heat the second mixed solution composed of the first mixed solution and the metal salt precursor solution under preset heating conditions to generate a sol.

[0045] Step S106: Perform vacuum drying treatment, low-temperature carbonization treatment and grinding treatment on the gel generated based on the sol to generate a carbonized powder. The gel is obtained by evaporating the sol to dryness.

[0046] Step S107: Press the carbonized powder into tablets, calcine at 950 °C for 12 hours in an oxygen atmosphere, and grind after cooling to obtain a sodium tantalate-coated sodium-ion layered metal oxide cathode material.

[0047] First, dissolve anhydrous tantalum pentachloride in anhydrous ethanol and stir to form a tantalum precursor solution. In this embodiment, anhydrous ethanol is used as a solvent to fully dissolve anhydrous tantalum pentachloride to form a homogeneous dispersion system of tantalum ions, constituting the tantalum precursor solution. This tantalum precursor solution can provide a source of tantalum ions for the subsequent formation of the sodium tantalate coating layer.

[0048] In this embodiment, the amount of tantalum pentachloride anhydrous can be 0.08 mmol, and the volume of absolute ethanol can be 15 ml. Further, when dissolving tantalum pentachloride anhydrous in absolute ethanol and stirring to form a tantalum precursor solution, the stirring time can be 0.5 hours and the stirring speed can be 300 r / min.

[0049] The precise quantification of the used tantalum pentachloride anhydrous (0.08 mmol) and the volume of absolute ethanol (15 mL) are used to ensure the accurate metering of the reaction raw materials and to ensure the uniformity of subsequent reactions. At the same time, the above-mentioned stirring time and stirring speed can ensure the full dissolution and uniform dispersion of tantalum pentachloride anhydrous in absolute ethanol, forming a high-quality tantalum precursor solution. Precise quantification and a uniform solution can make the subsequent chelation and coating reactions more stable, improving the uniformity and performance consistency of the final product.

[0050] Then, citric acid is dissolved in deionized water and stirred to form an aqueous solution of the chelating agent. In this embodiment, after citric acid is dissolved in water, a stable aqueous solution of the chelating agent is formed, whose function is to chelate with tantalum ions, prevent the uneven precipitation of tantalum ions in the solution, and at the same time contribute to controlling the formation of the subsequent coating layer.

[0051] In this embodiment, the amount of citric acid can be 20.967 mmol, and the volume of deionized water can be 15 ml. Further, when dissolving citric acid in deionized water and stirring to form an aqueous solution of the chelating agent, the stirring time can be 0.5 hours and the stirring speed can be 300 r / min.

[0052] By specifying the specific amount of citric acid (20.967 mmol) and the volume of deionized water used for dissolution (15 mL), it can be ensured that the concentration of citric acid in the resulting aqueous solution of the chelating agent reaches the expected requirements. At the same time, the stirring time and rotation speed (0.5 hours, 300 r / min) are also specified, which can ensure that citric acid can be completely dissolved in water to form a homogeneous and stable aqueous solution of the chelating agent. This step is crucial for the subsequent chelation reaction between tantalum ions and citric acid. Only when the aqueous solution of the chelating agent is sufficient and homogeneous can an effective chelation reaction be achieved when adding the tantalum precursor solution, ensuring the quality and uniformity of the first mixed solution.

[0053] After obtaining the aqueous solution of the chelating agent and the tantalum precursor solution, the aqueous solution of the chelating agent can be added dropwise to the tantalum precursor solution and stirred to chelate the tantalum ions in the tantalum precursor solution to obtain a first mixed solution. In this embodiment, by adding dropwise and continuously stirring, the tantalum ions and citric acid are brought into full contact to undergo a chelation reaction, forming a homogeneous first mixed solution. Further, this step is a key step to ensure the uniform distribution of tantalum elements in subsequent reactions.

[0054] Subsequently, sodium acetate trihydrate and manganese acetate tetrahydrate need to be dissolved in deionized water and stirred to form a metal salt precursor solution. In this embodiment, after the two metal salts are dissolved, a uniform precursor solution is formed, providing sodium and manganese ions as the components of the matrix of the sodium-based layered metal oxide cathode material.

[0055] In this embodiment, the amount of sodium acetate trihydrate can be 6.2625 mmol, the amount of manganese acetate tetrahydrate can be 10 mmol, and the volume of deionized water can be 30 ml. Further, the chelating agent aqueous solution is added dropwise to the tantalum precursor solution, and the tantalum ions in the tantalum precursor solution are chelated with citric acid by stirring. When the first mixed solution is obtained, the stirring time can be 0.5 hours and the stirring speed can be 300 r / min.

[0056] In this embodiment, the amounts of the two metal salts used to prepare the metal salt precursor solution and the volume of deionized water used are clearly specified. This precise measurement helps to ensure that the ratio of sodium and manganese in the matrix material meets the design requirements. In addition, the operation process of adding the chelating agent aqueous solution dropwise to the tantalum precursor solution is further clarified, and the stirring conditions (0.5 hours, 300 r / min) are specified to ensure that the tantalum ions are fully chelated with citric acid to form a uniform first mixed solution. The above fine operation control makes the components disperse evenly in the solution, providing a uniform reaction basis for the subsequent generation of the sol and the entire preparation process, thereby improving the structural uniformity and electrochemical performance of the final product.

[0057] After the first mixed solution and the metal salt precursor solution are prepared, the first mixed solution and the metal salt precursor solution can be mixed to obtain a second mixed solution, and then the second mixed solution is heated under a preset heating condition to generate a sol. In this embodiment, under the preset heating condition, the two precursor solutions are mixed and heated to generate a sol. The sol is a colloidal solution composed of suspended fine particles, providing a basis for subsequent gelation and uniform dispersion of the final material.

[0058] In practical applications, the preset heating condition can include an 80°C oil bath with a stirring speed of 300 r / min.

[0059] Subsequently, the gel formed based on the sol can be subjected to vacuum drying treatment, low-temperature carbonization treatment, and grinding treatment to generate carbonized powder. The gel is obtained by evaporating the sol to dryness. In this embodiment, through the evaporation-drying treatment of the sol, the solid precursor components in the gel can aggregate together. In addition, the above-mentioned vacuum drying treatment can further remove the residual solvent to ensure uniform drying of the gel; the low-temperature carbonization treatment is carried out by calcining at a relatively low temperature (such as 500 °C) to remove the organic residue and convert part of the precursor into an oxide form; the grinding treatment is to grind the dried product into powder to obtain a uniform carbonized powder, providing a good reaction interface for subsequent high-temperature calcination.

[0060] In this embodiment, the conditions for the vacuum drying treatment are drying at 100 °C for 12 hours, and the conditions for the low-temperature carbonization treatment are calcining at 500 °C for 6 hours with a heating rate of 5 °C / min.

[0061] When performing the vacuum drying treatment, it is specified to dry at 100 °C for 12 hours, and the vacuum environment is used to remove the residual solvent in the gel, preventing local overheating or uneven reaction caused by the residual solvent during the high-temperature calcination process.

[0062] When performing the low-temperature carbonization treatment, calcine at 500 °C for 6 hours with a heating rate controlled at 5 °C / min. This process helps to convert the organic matter in the partially carbonized gel into carbides and simultaneously pre-forms a partial oxide structure, laying a foundation for subsequent high-temperature treatment.

[0063] The above steps ensure the full drying of the gel and also stabilize the precursor structure of the material through low-temperature pre-calcination, reducing the structural stress and defects during high-temperature calcination, which helps to obtain a more uniform final product.

[0064] Finally, the carbonized powder is pressed into tablets and calcined at 950 °C for 12 hours in an oxygen atmosphere, and after cooling, it is ground to obtain a sodium tantalate-coated sodium-ion layered metal oxide cathode material. In this embodiment, by pressing the carbonized powder into tablets and calcining at high temperature for 12 hours in an oxygen atmosphere, metal ions such as tantalum, sodium, and manganese are fully reacted and oxidized to form a sodium-ion layered metal oxide with an expected layered structure, and at the same time, a uniformly distributed sodium tantalate coating layer is formed on the surface of the matrix. After calcination and cooling and grinding, the final product, namely the sodium tantalate-coated sodium-ion layered metal oxide cathode material, can be obtained.

[0065] In this embodiment, the oxygen atmosphere flow rate during high-temperature calcination is 20 mL / min, the heating rate is 5 °C / min, and the cooling rate is 2 °C / min.

[0066] During the high-temperature calcination stage, the oxygen flow rate is set at 20 mL / min, which can ensure sufficient oxygen supply during the calcination process, facilitating the full oxidation of various metal ions and thus forming a stable oxide phase. A heating rate of 5 °C / min can ensure a uniform temperature rise and avoid thermal stress caused by too rapid temperature changes; a cooling rate of 2 °C / min helps to gradually cool down after the calcination is completed, preventing structural defects caused by thermal shock.

[0067] The above parameters can ensure that all components of the material react uniformly and crystallize fully during the high-temperature calcination process, forming an ideal layered structure and a dense sodium tantalate coating layer, thereby improving the cycle stability and rate performance of the cathode material.

[0068] An embodiment of the present invention also provides a sodium tantalate-coated sodium-ion layered metal oxide cathode material, wherein the chemical formula of the sodium-ion layered metal oxide cathode material is NaTaO3@Na 0.44 MnO2, which has a layered structure. The sodium tantalate coating layer is uniformly distributed on the surface of the matrix material, and the coating layer thickness is 5 - 50 nm. Further, the sodium-ion layered metal oxide cathode material has a capacity retention rate ≥ 83.44% after 100 cycles at a rate of 1C within the voltage range of 2.0 - 4.3 V.

[0069] Next, in combination with specific embodiments, a preparation method of a sodium tantalate-coated sodium-ion layered metal oxide cathode material (chemical formula: NaTaO3@Na 0.44 MnO2) will be described in detail.

[0070] 1. Preparation of tantalum precursor solution

[0071] 1.1. Weigh 0.08 mmol of anhydrous tantalum pentachloride and add it to 15 mL of anhydrous ethanol. Since anhydrous tantalum pentachloride is insoluble in water, anhydrous ethanol is selected as the solvent.

[0072] 1.2. Place the mixture on a magnetic stirrer and stir at a speed of 300 r / min for 0.5 hours until the anhydrous tantalum pentachloride is fully dissolved to form a homogeneous tantalum precursor solution.

[0073] 2. Preparation of chelating agent aqueous solution

[0074] 2.1. Weigh 20.967 mmol of citric acid and add it to 15 mL of deionized water.

[0075] 2.2. Under the stirring condition of 300 r / min, continuously stir for 0.5 hours to completely dissolve the citric acid and form a homogeneous chelating agent aqueous solution.

[0076] 3. Preliminary chelation of tantalum ions and citric acid

[0077] 3.1. Slowly add the aqueous citric acid solution prepared in Step 2 drop by drop into the tantalum precursor solution obtained in Step 1 at the slowest possible rate using a dropper.

[0078] 3.2. During the addition process, maintain stirring at 300 r / min and continue stirring for 0.5 hours after the addition is complete to ensure that the tantalum ions and citric acid fully chelate to form a homogeneous first mixed solution.

[0079] 4. Preparation of the metal salt precursor solution

[0080] 4.1. Weigh 6.2625 mmol of sodium acetate trihydrate and 10 mmol of manganese acetate tetrahydrate separately.

[0081] 4.2. Add the above two metal salts simultaneously to 30 mL of deionized water, place it on a magnetic stirrer and stir at a speed of 300 r / min for 0.5 hours until the metal salts are completely dissolved to form a homogeneous metal salt precursor solution.

[0082] 5. Preparation of the second mixed solution and formation of the sol

[0083] 5.1. Slowly add the first mixed solution obtained in Step 3 to the metal salt precursor solution prepared in Step 4.

[0084] 5.2. Continue stirring at 300 r / min to ensure that all components are fully mixed uniformly to obtain a homogeneous second mixed solution.

[0085] 5.3. Place the second mixed solution in an oil bath, heat it to 80 °C, and continuously stir at 300 r / min at 80 °C to gradually form a sol, and a condensation reaction occurs during the heating process while partially evaporating the solvent to obtain a preliminary gel.

[0086] 6. Drying, low-temperature carbonization and grinding of the gel

[0087] 6.1. Transfer the gel obtained in Step 5 to a vacuum drying oven and dry it at 100 °C for 12 hours to ensure complete removal of the residual solvent.

[0088] 6.2. Perform low-temperature carbonization treatment on the dried gel: Place the gel in the furnace, heat it to 500 °C at a heating rate of 5 °C / min, and keep calcining at 500 °C for 6 hours to complete the low-temperature carbonization treatment.

[0089] 6.3. After the calcination is completed, take out the product and grind it thoroughly into a homogeneous carbonized powder.

[0090] 7. Medium-temperature calcination and flake preparation

[0091] 7.1. Place the carbonized powder obtained in Step 6 into a muffle furnace for medium-temperature calcination. Set the calcination temperature at 500 °C, with a heating rate of 5 °C / min and a cooling rate of 5 °C / min, and maintain the calcination for 6 hours, aiming to further remove organic residues and promote the precursor reaction.

[0092] 7.2. After the sample cools naturally, grind the calcined product into powder and press it into flakes under a pressure of 12 MPa to provide a reaction interface with good contact for subsequent high-temperature treatment.

[0093] 8. High-temperature Calcination and Final Product Preparation

[0094] 8.1. Place the product pressed into flakes in Step 7 into a tubular furnace and conduct high-temperature calcination in an oxygen atmosphere.

[0095] 8.2. Operate according to the following steps:

[0096] 8.2.1. Raise the temperature to 950 °C at a rate of 5 °C / min;

[0097] 8.2.2. Maintain the calcination at 950 °C for 12 hours to allow the metal ions to fully melt and undergo oxidation reactions, thereby forming a cathode material with a layered structure;

[0098] 8.2.3. Set the cooling rate at 2 °C / min to gradually cool the sample and prevent structural defects caused by thermal stress.

[0099] 8.3. After the high-temperature calcination is completed, take out the product and grind it into fine powder to obtain the sodium tantalate-coated sodium-ion layered metal oxide cathode material.

[0100] Based on the above method, the finally obtained cathode material is named NaTaO3@Na 0.44 MnO2, where the sodium tantalate coating layer is uniformly distributed on the surface of the Na 0.44 MnO2 matrix.

[0101] The above embodiments have described in detail the specific operating conditions and parameters of each step from raw material preparation, chelation reaction, sol-gel method, drying and carbonization treatment to medium-temperature and high-temperature calcination. All parameters (such as raw material dosage, stirring time, temperature, heating and cooling rates, calcination time, etc.) are the preferred implementation modes of this embodiment. Those skilled in the art can make appropriate adjustments to the conditions of each step without departing from the spirit and technical solutions of the present invention.

[0102] The sodium tantalate-coated sodium-ion layered metal oxide cathode material obtained in this specific embodiment has a uniform structure, and the interface between the sodium tantalate coating layer and the matrix material is tightly combined, significantly improving the stability of the material under high rate and long cycle conditions, meeting the technical effects required in the claims of the present invention.

[0103] Figure 2 Powder X-ray diffraction pattern of the NaTaO3@Na 0.44 MnO2 layered oxide cathode material provided by the embodiment of the present invention.

[0104] As Figure 2 shown, by comparing with the standard PDF card, it is confirmed that both P2-type layered Na 0.44 MnO2 and NaTaO3 phases exist in the sample. Among them:

[0105] The PDF card corresponding to P2-type Na 0.44 MnO2 is No. 97-24-6579, and its space group is P63 / mmc, which is a typical P2-type layered structure.

[0106] The PDF card corresponding to NaTaO3 is No. 04-002-5064, and its characteristic diffraction peaks are also marked in the figure.

[0107] From Figure 2 it can be seen that the overall crystallinity of the sample is relatively high, the main diffraction peaks are sharp, and the background interference is low, indicating that the synthesized material is pure and the crystallization is complete, and there is basically no obvious impurity phase.

[0108] The diffraction peaks of P2-type Na 0.44 MnO2 usually show obvious layered structure characteristic peaks at low angles (such as 10° - 15°), and other peaks with higher intensities are distributed in the 2θ regions of 20° - 40° and higher. Compared with the PDF card 97-24-6579, Figure 2 the main diffraction peaks in it match well with the positions and relative intensities of the standard card, indicating that a P2-type layered structure is indeed formed in the sample.

[0109] The space group of the P2-type layered structure is P63 / mmc, and the interlayer Na ions can be reversibly deintercalated and intercalated during charge and discharge. The XRD results show that there is no obvious distortion or impurity phase in this structure, proving that the synthesis process keeps the manganese-oxygen framework in a good layered arrangement, laying a foundation for the subsequent electrochemical performance.

[0110] Again, as Figure 2 shown, the peak shapes of each diffraction peak are sharp and the full width at half maximum is relatively narrow, indicating that the grain size is relatively large or the crystal order is relatively high; there is no obvious diffraction peak splitting or offset, which also shows that the lattice structure of the material is relatively complete and uniform.

[0111] By comparing with the PDF card 04-002-5064, some characteristic peaks of NaTaO3 can be identified in the higher angle region. Since the proportion of NaTaO3 in the whole material system is relatively small and it often exists in the form of a coating layer or surface modification, its diffraction peak intensity is usually weaker than that of the main phase Na0.44 The diffraction peaks of MnO2 can still be identified by comparing with the standard cards.

[0112] Although the morphology or thickness of the coating layer cannot be directly observed from the XRD pattern, the diffraction peaks corresponding to NaTaO3 appear in the sample, indicating that the tantalum source has been successfully converted into NaTaO3 on the surface or interface of the material. Combining the synthesis process and subsequent characterizations (such as TEM, SEM, etc.), it can be further confirmed that the NaTaO3 uniformly forms a nanoscale thin layer on the material surface, thus playing a role in surface modification and stabilization.

[0113] NaTaO3@Na in this example 0.44 The preparation of the NaTaO3@NaMnO2 layered oxide cathode material adopted a route combining the sol-gel method and stepwise calcination (first low-temperature carbonization and then high-temperature calcination).

[0114] The organic components were removed and the oxide skeleton was pre-formed in the low-temperature carbonization stage;

[0115] In the high-temperature calcination stage (950 °C, 12 hours), Na, Mn, Ta and other ions underwent sufficient solid-phase reaction and crystallization to obtain the P2-type NaMnO2 matrix and the surface NaTaO3 coating layer. 0.44 MnO2 matrix and surface NaTaO3 coating layer.

[0116] There are no obvious impurity peaks or by-product peaks in the XRD pattern, indicating that the temperature and holding time of this stepwise calcination are appropriate, enabling the coating layer and the main phase to form simultaneously without interference, and finally obtaining a pure NaTaO3@NaMnO2 composite structure. 0.44 MnO2 composite structure.

[0117] By comparing the XRD pattern with the standard PDF card, it can be seen that the main phase of the NaTaO3@NaMnO2 layered oxide cathode material is P2-type NaMnO2, and the diffraction peaks are consistent with PDF No. 97-24-6579, indicating that the material has a typical P2 layered structure and high crystallinity; the characteristic peaks of NaTaO3 in the sample match PDF No. 04-002-5064, indicating that the tantalum source was successfully introduced during the synthesis process and a NaTaO3 coating layer was formed on the material surface; no other impurity phases or obvious diffraction peak shifts appear, indicating that the synthesis process of this composite material is reasonable and the ratio is accurate, and finally a pure NaTaO3@NaMnO2 layered cathode material is obtained. 0.44 MnO2, the diffraction peaks are consistent with PDF No. 97-24-6579, indicating that the material has a typical P2 layered structure and high crystallinity; the characteristic peaks of NaTaO3 in the sample match PDF No. 04-002-5064, indicating that the tantalum source was successfully introduced during the synthesis process and a NaTaO3 coating layer was formed on the material surface; no other impurity phases or obvious diffraction peak shifts appear, indicating that the synthesis process of this composite material is reasonable and the ratio is accurate, and finally a pure NaTaO3@NaMnO2 layered cathode material is obtained. 0.44 MnO2, the diffraction peaks are consistent with PDF No. 97-24-6579, indicating that the material has a typical P2 layered structure and high crystallinity; the characteristic peaks of NaTaO3 in the sample match PDF No. 04-002-5064, indicating that the tantalum source was successfully introduced during the synthesis process and a NaTaO3 coating layer was formed on the material surface; no other impurity phases or obvious diffraction peak shifts appear, indicating that the synthesis process of this composite material is reasonable and the ratio is accurate, and finally a pure NaTaO3@NaMnO2 layered cathode material is obtained. 0.44 MnO2 layered cathode material.

[0118] Therefore, the XRD results confirm the successful preparation of the NaTaO3@NaMnO2 material from the aspects of structure and phase composition, and also provide a structural basis for its subsequent performance in electrochemical properties (cycle stability, rate performance, etc.). 0.44 MnO2 material, and also provide a structural basis for its subsequent performance in electrochemical properties (cycle stability, rate performance, etc.).

[0119] Figure 3a NaTaO3@Na provided by the embodiment of the present invention 0.44 EDS elemental distribution overlay map of the NaTaO3@NaMnO2 layered oxide cathode material Figure 3b NaTaO3@Na provided by the embodiment of the present invention 0.44 Scanning electron microscope morphology map of the NaTaO3@NaMnO2 layered oxide cathode material Figure 3c NaTaO3@Na provided by the embodiment of the present invention 0.44 Ta elemental distribution map of the NaTaO3@NaMnO2 layered oxide cathode material Figure 3d NaTaO3@Na provided by the embodiment of the present invention 0.44 O elemental distribution map of the NaTaO3@NaMnO2 layered oxide cathode material Figure 3e NaTaO3@Na provided by the embodiment of the present invention 0.44 Mn elemental distribution map of the NaTaO3@NaMnO2 layered oxide cathode material Figure 3f NaTaO3@Na provided by the embodiment of the present invention 0.44 Na elemental distribution map of the NaTaO3@NaMnO2 layered oxide cathode material

[0120] As Figures 3a to 3f shown, it shows the scanning electron microscope (SEM) morphology and energy spectrum (EDS) elemental distribution of the NaTaO3@NaMnO2 layered oxide cathode material. The SEM morphology map clearly shows the microstructure of the material, while the EDS elemental distribution map reveals the uniform distribution of Na, Mn, and O elements in the whole layered oxide particles, indicating that the Na 0.44 MnO2 main phase is well formed and uniform. It should be noted that the distribution of Ta element is different from that of Na, Mn, and O. The Ta signal is mainly concentrated on the outer layer of the particles, and almost undetectable inside the particles, which indicates that Ta mainly exists on the surface of the material rather than entering the main layered structure, thus proving the structure of NaTaO3 coated on Na 0.44 MnO2 0.44

[0121] Figure 4 NaTaO3@Na provided by the embodiment of the present invention 0.44 EDS energy spectrum schematic diagram of the NaTaO3@NaMnO2 layered oxide cathode material

[0122] As Figure 4 ​As shown, the peaks of Na, Mn, and O in the spectrogram are relatively prominent, indicating that these elements are the main components of the material. At the same time, the peak of Ta can also be clearly detected, but it is relatively weak, further confirming the existence of the NaTaO3 coating layer. That is to say, the NaTaO3 coating layer is not only successfully formed, but also mainly located on the particle surface and does not dope into the Na 0.44 MnO2 main structure. The existence of this coating layer helps to improve the stability of the material, reduce the dissolution of Mn, and can optimize the electrochemical performance, laying a foundation for subsequent electrochemical tests.

[0123] Figure 5 This is the NaTaO3@Na provided by the embodiment of the present invention 0.44 Schematic diagram of the cyclic stability test results of the layered oxide cathode material at a rate of 1C.

[0124] As Figure 5 shown, the cyclic stability of the NaTaO3@Na 0.44 MnO2 layered oxide cathode material at a rate of 1C (i.e., 120 mA / g) and in a wide voltage range of 2V to 4.3V. The test results show that the initial capacity of this material is 110.28 mAh / g. After 100 cycles, the capacity remains at 107.55 mAh / g, and the capacity retention rate reaches 83.44%. Compared with Na 0.44 MnO2 matrix, this composite material shows significant advantages in terms of capacity and cycle retention rate, demonstrating the effective improvement of the NaTaO3 coating layer on the electrochemical performance of the cathode material.

[0125] It should be noted that the term "including" and its variants used in the embodiments of the present invention are open-ended, that is, "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The modifications of "one" and "multiple" mentioned in the embodiments of the present invention are illustrative rather than restrictive. Those skilled in the art should understand that unless clearly stated otherwise in the context, it should be understood as "one or more".

[0126] In the method embodiments provided by the embodiments of the present invention, the steps recorded can be executed in different orders and / or executed in parallel. In addition, the method embodiments may include additional steps and / or omit the steps shown. The protection scope of the present invention is not limited in this regard.

[0127] The term "embodiment" in this specification means that the specific features, structures or characteristics described in connection with an embodiment may be included in at least one embodiment of the present invention. The phrase appears in various positions in the specification and does not necessarily mean the same embodiment, nor does it mean independence or alternative to other embodiments that are mutually exclusive. The various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments are cross-referred to. In particular, for device, equipment, and system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and the relevant parts refer to the partial description of the method embodiments.

[0128] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of patent protection. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the appended claims.

Claims

1. A method for preparing a sodium tantalate-coated sodium ion layered metal oxide positive electrode material, characterized in that: The method comprises: dissolving anhydrous tantalum pentachloride in anhydrous ethanol and stirring to form a tantalum precursor solution; Dissolve citric acid in deionized water and stir to form a chelating agent aqueous solution; adding the chelating agent aqueous solution dropwise into the tantalum precursor solution, stirring to allow the tantalum ions in the tantalum precursor solution to chelate with citric acid, to obtain a first mixed solution; Dissolving sodium acetate trihydrate and manganese acetate tetrahydrate in deionized water and stirring to form a metal salt precursor solution; heating the first mixed solution and the second mixed solution consisting of the metal salt precursor solution under a preset heating condition to generate a sol; performing vacuum drying, low-temperature carbonization and grinding on a gel generated based on the sol to generate a carbonized powder, wherein the gel is obtained by evaporating the sol; The carbonized powder is pressed into tablets, calcined at 950° C. for 12 hours in an oxygen atmosphere, and ground after cooling to obtain a sodium ion layered metal oxide positive electrode material coated with sodium tantalate.

2. The method according to claim 1, characterized in that: The amount of anhydrous tantalum pentachloride is 0.08 mmol, and the volume of anhydrous ethanol is 15 ml; When anhydrous tantalum pentachloride is dissolved in anhydrous ethanol and stirred to form a tantalum precursor solution, the stirring time is 0.5 hours and the stirring speed is 300 r / min.

3. The method according to claim 1, characterized in that The amount of citric acid used is 20.967 mmol, and the volume of deionized water is 15 ml; When the citric acid is dissolved in deionized water and stirred to form a chelating agent aqueous solution, the stirring time is 0.5 hours and the stirring speed is 300 r / min.

4. The method according to claim 1, characterized in that: The amount of sodium acetate trihydrate is 6.2625mmol, the amount of manganese acetate tetrahydrate is 10mmol, and the volume of deionized water is 30ml; The chelating agent aqueous solution is added dropwise into the tantalum precursor solution, and stirred to chelate the tantalum ions in the tantalum precursor solution with citric acid to obtain a first mixed solution. The stirring time is 0.5 hours and the stirring speed is 300 r / min.

5. The method according to claim 1, characterized in that The preset heating condition is 80° C. oil bath and the stirring speed is 300 r / min.

6. The method according to claim 1, characterized in that The vacuum drying treatment was carried out under the conditions of 100° C. for 12 hours, and the low-temperature carbonization treatment was carried out under the conditions of 500° C. for 6 hours with a heating rate of 5° C. / min.

7. The method according to claim 1, characterized in that The oxygen atmosphere flow rate of the high temperature calcination is 20 mL / min, the heating rate is 5° C. / min, and the cooling rate is 2° C. / min.

8. A sodium tantalate-coated sodium ion layered metal oxide positive electrode material, characterized in that: The chemical formula of the sodium ion layered metal oxide positive electrode material is NaTaO3@Na 0.44 MnO2 has a layered structure, and the sodium tantalate coating layer is evenly distributed on the surface of the base material, and the coating layer thickness is 5 to 50 nm.

9. The positive electrode material according to claim 8, characterized in that The sodium ion layered metal oxide positive electrode material has a capacity retention rate of ≥83.44% after 100 cycles at 1C rate within a voltage range of 2.0 to 4.3 V.

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