Seven-element high-entropy layered metal oxide sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of chemical engineering, and relates to a seven-element high-entropy layered metal oxide sodium ion battery positive electrode material and a preparation method thereof. The method comprises the following steps: dissolving titanyl acetylacetonate in an organic solvent, and carrying out ultrasonic treatment and stirring to obtain a titanium precursor organic solution; dissolving citric acid in water, and stirring to form a chelating agent aqueous solution; the method comprises the following steps: dissolving a sodium source, a nickel source, a manganese source, a copper source, a calcium source, a tin source and an iron source in water, and stirring to form a mixed metal salt precursor aqueous solution; adding a chelating agent aqueous solution into the titanium precursor organic solution, and stirring to chelate titanyl acetylacetonate and citric acid to obtain a mixed solution; adding the mixed solution into a mixed metal salt precursor aqueous solution, and heating under a preset heating condition to form sol; evaporating the sol to dryness to form gel, and performing vacuum drying and low-temperature carbonization treatment to generate a carbonized precursor; and tabletting the carbonized precursor, carrying out high-temperature calcination in an oxygen atmosphere, and carrying out grinding treatment to obtain the battery positive electrode material.

Description

Technical Field

[0001] This application belongs to the field of chemical engineering technology, and particularly relates to a heptavalent high-entropy layered metal oxide cathode material for sodium-ion batteries and a preparation method thereof. Background Art

[0002] With the continuous growth of global energy demand and the rapid development of renewable energy technologies, electrochemical energy storage devices play an increasingly important role in the modern energy system. Sodium-ion batteries are gradually becoming an important alternative to lithium-ion batteries due to their advantages such as abundant sodium resources, low cost, and environmental friendliness. Their performance depends to a large extent on the chemical properties and structural stability of the cathode material. In recent years, high-entropy materials, composed of multiple metals or other elements, have achieved uniform distribution of multiple metal ions in the lattice through the high-entropy effect, thus exhibiting excellent structural stability, corrosion resistance, and outstanding electrochemical performance, becoming a research hotspot in the field of energy storage. In particular, layered transition metal oxides have always been regarded as ideal candidates for sodium-ion battery cathode materials due to their unique layered structure and good reversible sodium storage capacity.

[0003] However, there are still many technical challenges in the preparation and performance optimization of multi-component high-entropy cathode materials. When preparing layered cathode materials by the traditional solid-phase synthesis method, due to the large differences in the diffusion rates and reaction activities of different metal elements, the chemical composition distribution is often uneven, which directly affects the overall performance of the high-entropy materials. At the same time, the cathode of sodium-ion batteries is prone to lattice oxygen release and structural collapse during charge and discharge processes, resulting in shortened cycle life and decreased capacity retention rate, while the existing materials are insufficient in terms of anti-structure degradation. In addition, the complex elemental composition of high-entropy layered cathode materials may cause blockage of ion diffusion paths, thereby affecting the sodium ion migration rate and electrochemical reaction kinetics. The traditional solid-phase method and sol-gel method usually require high-temperature calcination, which not only brings high energy consumption problems, but also has limited control ability over the microstructure of the materials, making it difficult to achieve uniform distribution of each metal element. Although the high-entropy effect can improve the stability of the materials to a certain extent, local structural defects or side reactions are often introduced during actual preparation, resulting in low initial efficiency and limited cycle stability. At the same time, the current preparation process has strict requirements for process parameters such as reaction temperature and atmosphere, making it difficult to achieve low-cost and large-scale production, thus restricting the industrial application of high-entropy materials in the field of sodium-ion batteries.

[0004] Therefore, the existing technologies have multiple defects such as uneven element distribution, unstable lattice structure, restricted ion transport, high temperature and high energy consumption, and difficulty in achieving low-cost large-scale production when preparing sodium-ion battery cathode materials. Summary of the Invention

[0005] A preparation method of a positive electrode material for a sodium-ion battery using a heptavalent high-entropy layered metal oxide provided by an embodiment of the present invention at least solves the problems of uneven element distribution, unstable lattice structure, limited ion transport, high temperature and high energy consumption, and difficulty in achieving low-cost large-scale production in the preparation of positive electrode materials for sodium-ion batteries in related technologies.

[0006] According to the first aspect of the embodiments of the present invention, a preparation method of a positive electrode material for a sodium-ion battery using a heptavalent high-entropy layered metal oxide is provided. The method includes:

[0007] Dissolve titanium acetylacetonate in an organic solvent, perform ultrasonic treatment and stirring to obtain a titanium precursor organic solution;

[0008] Dissolve citric acid in water and stir to form a chelating agent aqueous solution;

[0009] Dissolve a sodium source, a nickel source, a manganese source, a copper source, a calcium source, a tin source, and an iron source in water and stir to form a mixed metal salt precursor aqueous solution;

[0010] Add the chelating agent aqueous solution to the titanium precursor organic solution and stir to chelate the titanium acetylacetonate with the citric acid to obtain a mixed solution;

[0011] Add the mixed solution to the mixed metal salt precursor aqueous solution and heat under preset heating conditions to form a sol;

[0012] Evaporate the sol to dryness to form a gel, and perform vacuum drying and low-temperature carbonization treatment to generate a carbonized precursor;

[0013] Press the carbonized precursor into tablets, perform high-temperature calcination in an oxygen atmosphere and grinding treatment to obtain a positive electrode material for the battery.

[0014] Optionally, the organic solvent is isopropanol, and the concentration of titanium acetylacetonate is 0.35 mmol / 20 ml;

[0015] When dissolving titanium acetylacetonate in the organic solvent, performing ultrasonic treatment and stirring, the ultrasonic treatment time is 30 minutes, and the stirring time is 20 minutes.

[0016] Optionally, the dosage of citric acid is 5.1683 g / 30 ml of water;

[0017] When dissolving citric acid in water and stirring to form a chelating agent aqueous solution, the stirring speed is 300 rpm, and the stirring time is 15 minutes.

[0018] Optionally, the sodium source is sodium acetate trihydrate, the nickel source is nickel acetate tetrahydrate, the manganese source is manganese acetate tetrahydrate, the copper source is copper acetate monohydrate, the calcium source is calcium acetate monohydrate, the tin source is stannous acetate, and the iron source is iron acetate;

[0019] The molar ratios of the sodium source, the nickel source, the manganese source, the copper source, the calcium source, the tin source and the iron source are 9.3:2.5:5:0.7:0.35:0.23:2.5 in sequence.

[0020] Optionally, the preset heating condition is an oil bath at 70 °C for 12 hours of heat preservation.

[0021] Optionally, the treatment conditions for the low-temperature carbonization treatment are calcination at 450 °C for 6 hours, and the heating rate is 5 °C / min;

[0022] The treatment conditions for the high-temperature calcination are 900 °C, an oxygen flow rate of 20 mL / min, 15 hours of heat preservation, and the heating rate is 5 °C / min.

[0023] According to the second aspect of the embodiments of the present invention, a positive electrode material for a sodium-ion battery of a heptavalent high-entropy layered metal oxide is provided, characterized in that the chemical formula of the positive electrode material of the battery is: Na 0.83 Ni 0.215 Fe 0.215 Mn 0.43 Cu 0.06 Ca 0.03 Sn 0.02 Ti 0.03 O2; wherein, the positive electrode material of the battery has a layered crystal structure, and the nickel element, iron element, manganese element, copper element, calcium element, tin element and titanium element in the layered crystal structure are atomically uniformly distributed in the crystal lattice.

[0024] Optionally, when the positive electrode material of the battery is at a cut-off voltage of 4.3 V, the capacity retention rate is ≥95.6% after 200 cycles at a 1C rate, and the capacity retention rate is ≥81.1% after 1000 cycles at a 5C rate.

[0025] Optionally, the crystal structure of the positive electrode material of the battery is an O3-type layered structure, the space group is R-3m, and the unit cell parameters satisfy:

[0026] Optionally, the particle size distribution of the positive electrode material of the battery is 0.5 μm to 5 μm, and the specific surface area is 2 m 2 / g to 5 m 2 / g.

[0027] The beneficial effects of the embodiments of the present invention:

[0028] An embodiment of the present invention provides a method for preparing a cathode material for a sodium-ion battery based on a heptametal high-entropy layered metal oxide. By adopting a high-entropy spin-gate modulation strategy, the defects existing in the prior art, such as uneven chemical component distribution, unstable lattice structure, limited ion transport, and high temperature and high energy consumption, are effectively solved, and the overall performance of the cathode material for a sodium-ion battery is fundamentally improved. The cathode material for a battery prepared based on the above method has a stable TM 3d-O 2p hybridized spin-down bandgap and a narrow oxidized oxygen spin-up split bandgap, so as to act as an efficient spin gate during the deep charge and discharge process and promote the reversible redox reaction of active metals and oxygen. Cu 2+ and Sn 2+ are introduced to effectively stabilize the spin-down electrons and enhance the covalent bond interaction between TM and O, while Ti 3+ and Ca 2+ respectively improve the working voltage and mechanical strength of the material, thereby reducing the risk of lattice distortion under high-voltage operation. In addition, the cooperative spin-gate effect further enhances the local electron interaction between adjacent TMO6 units, effectively eliminates the two-phase grain boundary, and inhibits the overoxidation of Ni 3+ , thereby ensuring the structural integrity and efficient Na + transport during the long-term cycling process of the cathode material. The results show that at a high cut-off voltage of 4.3 V, the capacity retention rate of the SG-HEO cathode reaches 95.6% after 200 cycles at a 1C rate and 81.1% after 1000 cycles at a 5C rate, showing excellent cycle stability and rate performance far exceeding those of traditional materials; meanwhile, in a full-cell sodium-ion system, the cathode material also achieves an energy density as high as 370.7 Wh / kg. Therefore, the cathode material prepared by the preparation method provided by the embodiment of the present invention not only significantly improves the electrochemical performance of the material through the uniform distribution of multi-metals at the molecular level and spin-gate regulation, but also provides an effective solution for the low-cost large-scale production of cathode materials for sodium-ion batteries by reducing the process temperature and energy consumption, thereby having significant technical effects in improving the energy density, cycle life, and overall performance in high-voltage applications.

[0029] Details of one or more embodiments of the present invention are set forth in the following drawings and description to make other features, objects, and advantages of the present invention more concise and understandable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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 based on these drawings without creative efforts.

[0031] Figure 1 Flow chart of a preparation method for a positive electrode material of a sodium-ion battery based on a heptavalent high-entropy layered metal oxide provided by an embodiment of the present invention.

[0032] Figure 2a XRD schematic diagram of SG-HEO provided by an embodiment of the present invention.

[0033] Figure 2b XRD schematic diagram of the NFM sample provided by an embodiment of the present invention.

[0034] Figure 2c Schematic diagram of a transmission electron microscope image of the SG-HEO positive electrode material provided by an embodiment of the present invention

[0035] Figure 2d Schematic diagram of a high-resolution transmission electron microscope image of the SG-HEO positive electrode material provided by an embodiment of the present invention.

[0036] Figure 2e Schematic diagram of a high-angle annular dark-field scanning transmission electron microscope image of the

[001] zone axis provided by an embodiment of the present invention.

[0037] Figure 2f Schematic diagram of a selected area electron diffraction image of the

[001] zone axis provided by an embodiment of the present invention.

[0038] Figure 2g Schematic diagram of a high-angle annular dark-field scanning transmission electron microscope image of the

[010] zone axis provided by an embodiment of the present invention.

[0039] Figure 2h Schematic diagram of a transmission electron microscope and corresponding energy spectrum element mapping of the SG-HEO positive electrode material provided by an embodiment of the present invention.

[0040] Figure 3a Schematic diagram of the galvanostatic charge-discharge curves of the SG-HEO and NFM cathode materials provided by an embodiment of the present invention.

[0041] Figure 3b Schematic diagram of the differential specific capacity curves of the SG-HEO and NFM cathodes within three cycles provided by an embodiment of the present invention.

[0042] Figure 3c Schematic diagram of the specific capacities of the SG-HEO and NFM cathodes at different rates provided by an embodiment of the present invention.

[0043] Figure 3d Schematic diagram of the long-term cycling performance of the SG-HEO and NFM cathodes at a 1C rate provided by an embodiment of the present invention.

[0044] Figure 3eSchematic diagram of the long cycle performance of the SG-HEO and NFM cathodes provided by the embodiments of the present invention at a 10C rate.

[0045] Figure 3f Schematic diagram for comparing the electrochemical performance of O3-type high-entropy layered oxide cathodes at different upper voltage limits provided by the embodiments of the present invention.

[0046] Figure 3g Schematic diagram of the electrochemical impedance spectroscopy (EIS) of the SG-HEO and NFM cathodes before and after cycling provided by the embodiments of the present invention.

[0047] Figure 3h Calculated logDNa of the SG-HEO and NFM cathodes provided by the embodiments of the present invention during the initial and secondary charge-discharge processes + Schematic diagram.

[0048] Figure 4a Schematic diagram of the in-situ XRD pattern and the a-axis and c-axis parameters of the dominant phase during the first charge-discharge process of the SG-HEO positive electrode material provided by the embodiments of the present invention.

[0049] Figure 4b Schematic diagram of the coexisting phases and the two-phase coexistence path during the transformation from the P3 phase to the OP2 phase under high sodiation removal conditions provided by the embodiments of the present invention.

[0050] Figure 4c Schematic diagram of HAADF-STEM of the SG-HEO positive electrode material after 100 cycles provided by the embodiments of the present invention.

[0051] Figure 4d Schematic diagram of HAADF-STEM of the NFM positive electrode material after 100 cycles.

[0052] Figure 5a Schematic diagram of a SG-HEO / / HC battery provided by the embodiments of the present invention.

[0053] Figure 5b Schematic diagram for comparing the capacities of the SG-HEO cathode and the hard carbon anode of the SG-HEO / / HC battery provided by the embodiments of the present invention under 0.1C conditions.

[0054] Figure 5c Schematic diagram of the constant current charge-discharge curve of the SG-HEO / / HC battery system provided by the embodiments of the present invention under 0.1C conditions.

[0055] Figure 5d Schematic diagram of the rate performance test curve of the SG-HEO / / HC battery provided by the embodiments of the present invention. Detailed implementation manners

[0056] 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.

[0057] Figure 1 The flowchart of a preparation method for a cathode material of a sodium-ion battery based on a seven-element high-entropy layered metal oxide provided by an embodiment of the present invention is as follows. As Figure 1 shown, the method includes the following steps:

[0058] Step S101, dissolve titanium acetylacetonate in an organic solvent, perform ultrasonic treatment and stirring to obtain a titanium precursor organic solution.

[0059] Step S102, dissolve citric acid in water and stir to form a chelating agent aqueous solution.

[0060] Step S103, dissolve a sodium source, a nickel source, a manganese source, a copper source, a calcium source, a tin source, and an iron source in water and stir to form a mixed metal salt precursor aqueous solution.

[0061] Step S104, add the chelating agent aqueous solution to the titanium precursor organic solution and stir to chelate titanium acetylacetonate with citric acid to obtain a mixed solution.

[0062] Step S105, add the mixed solution to the mixed metal salt precursor aqueous solution and heat it under preset heating conditions to form a sol.

[0063] Step S106, evaporate the sol to dryness to form a gel, and perform vacuum drying and low-temperature carbonization treatment to generate a carbonized precursor.

[0064] Step S107, press the carbonized precursor into tablets, perform high-temperature calcination and grinding treatment in an oxygen atmosphere to obtain the cathode material of the battery.

[0065] First, dissolve titanium acetylacetonate in an organic solvent, perform ultrasonic treatment and stirring to obtain a titanium precursor organic solution. By preparing a uniformly dispersed titanium precursor organic solution, a basis is provided for the subsequent chelation reaction.

[0066] In this embodiment, titanium acetylacetonate is used as the titanium source precursor. Its chemical structure contains titanium-oxygen bonds, which can form titanium oxides in subsequent reactions. Since titanium acetylacetonate has good solubility in organic solvents and can form a uniform solution, titanium acetylacetonate can be dissolved in an organic solvent in this embodiment. In this embodiment, the organic solvent can be isopropanol or the like.

[0067] In the process of dissolving titanium acetylacetonate in an organic solvent, the cavitation effect of ultrasonic waves can be utilized to fully disperse titanium acetylacetonate in the organic solvent, accelerate the dissolution process, and ensure the uniformity of the solution. At the same time, mechanical stirring can be further used to promote the mixing of titanium acetylacetonate and the organic solvent, ensuring the uniformity and stability of the solution. In this embodiment, when dissolving titanium acetylacetonate in an organic solvent and performing ultrasonic treatment and stirring, the ultrasonic treatment time can be 30 minutes, and the stirring time can be 20 minutes.

[0068] In practical applications, when isopropanol is used as the organic solvent, the concentration of titanium acetylacetonate can be 0.35 mmol / 20 ml.

[0069] Then, citric acid can be dissolved in water and stirred to form an aqueous solution of the chelating agent. By preparing the aqueous solution of the citric acid chelating agent, necessary reagents for subsequent chelation reactions can be provided.

[0070] In this embodiment, citric acid, as a chelating agent, can form stable chelates with metal ions, preventing the precipitation or agglomeration of metal ions in subsequent reactions. Citric acid has good solubility in water, and by using water as the solvent, a uniform aqueous solution can be formed.

[0071] In the process of dissolving citric acid in water, mechanical stirring can be used to fully dissolve citric acid in water to form a uniform aqueous solution of the chelating agent.

[0072] In practical applications, the dosage of citric acid can be 5.1683 g / 30 ml of water. Further, when dissolving citric acid in water and stirring to form an aqueous solution of the chelating agent, the stirring speed can be 300 rpm, and the stirring time can be 15 minutes.

[0073] Subsequently, the sodium source, nickel source, manganese source, copper source, calcium source, tin source, and iron source can be dissolved in water and stirred to form an aqueous solution of the mixed metal salt precursor. By preparing the aqueous solution of the precursor containing multiple metal ions, a necessary metal ion source for subsequent sol-gel reactions can be provided.

[0074] In this embodiment, the sodium source, nickel source, manganese source, copper source, calcium source, tin source, and iron source can respectively provide sodium, nickel, manganese, copper, calcium, tin, and iron elements, and these elements play key roles in the final cathode material. Using water as the solvent, the metal salts can dissolve in water to form a uniform aqueous solution.

[0075] In the process of dissolving the sodium source, nickel source, manganese source, copper source, calcium source, tin source, and iron source in water, mechanical stirring can be used to fully dissolve various metal salts in water to form a uniform aqueous solution of the mixed metal salt precursor. Specifically, at room temperature, the stirring speed can be 300 rpm.

[0076] In practical applications, the sodium source can be sodium acetate trihydrate, the nickel source can be nickel acetate tetrahydrate, the manganese source can be manganese acetate tetrahydrate, the copper source can be copper acetate monohydrate, the calcium source can be calcium acetate monohydrate, the tin source can be stannous acetate, and the iron source can be iron acetate. Among them, the molar ratios of the sodium source, nickel source, manganese source, copper source, calcium source, tin source, and iron source can be 9.3:2.5:5:0.7:0.35:0.23:2.5 in sequence. Further, sodium acetate trihydrate, nickel acetate tetrahydrate, manganese acetate tetrahydrate, copper acetate monohydrate, calcium acetate monohydrate, stannous acetate, and iron acetate can be put into 50 ml of water according to the above molar ratios to obtain an aqueous solution of a mixed metal salt precursor.

[0077] After obtaining the aqueous solution of the chelating agent, the organic solution of the titanium precursor, and the aqueous solution of the mixed metal salt precursor, the aqueous solution of the chelating agent can be first added to the organic solution of the titanium precursor to obtain a mixed solution, and then the mixed solution can be added to the aqueous solution of the mixed metal salt precursor to obtain a sol.

[0078] Specifically, first, the aqueous solution of the chelating agent can be added to the organic solution of the titanium precursor and stirred to chelate titanium acetylacetonate with citric acid to obtain a mixed solution. By preparing a uniform mixed solution, a basis can be provided for the subsequent sol-gel reaction.

[0079] In this embodiment, when the aqueous solution of the citric acid chelating agent is slowly added to the organic solution of the titanium precursor, it is necessary to ensure that the two solutions are fully mixed. Specifically, mechanical stirring can be used to make titanium acetylacetonate and citric acid fully contact and undergo a chelation reaction to form a stable mixed solution. In practical applications, the carboxyl group in citric acid can form a chelate with the titanium ion in titanium acetylacetonate, preventing the titanium ion from precipitating or aggregating in the subsequent reaction.

[0080] After obtaining the mixed solution, the mixed solution can be added to the aqueous solution of the mixed metal salt precursor and heated under preset heating conditions to form a sol. By heating, the metal ions in the solution can react fully with the chelating agent to form a uniform sol.

[0081] In this embodiment, when the mixed solution is slowly added to the aqueous solution of the mixed metal salt precursor, it is necessary to ensure that the two solutions are fully mixed.

[0082] The preset heating conditions in this embodiment can be heating in an oil bath, with the temperature controlled at about 70 °C and kept warm for 12 hours. The purpose of heating is to make the metal ions in the solution react fully with the chelating agent to form a uniform sol. Under the heating conditions, the metal ions in the solution and the chelating agent undergo a cross-linking reaction to form a sol with a three-dimensional network structure.

[0083] After obtaining the sol, the sol can be evaporated to dryness to form a gel, followed by vacuum drying and low-temperature carbonization treatment to generate a carbonization precursor. Through evaporation to dryness, vacuum drying, and low-temperature carbonization treatment, a stable carbonization precursor is formed, which provides a basis for subsequent high-temperature calcination.

[0084] During the evaporation to dryness treatment, the sol can be stirred at a temperature of about 80 °C, causing the sol to gradually condense and evaporate to dryness, forming a green gel. The purpose of evaporation to dryness is to remove the solvent in the sol and transform the sol into a gel.

[0085] During the vacuum drying treatment, the gel can be dried at 120 °C for 12 hours under vacuum conditions to further remove the moisture and organic solvents in the gel, forming a dry gel.

[0086] During the low-temperature carbonization treatment, the dry gel can be calcined at 450 °C for 6 hours with a heating rate of 5 °C / min. The purpose of carbonization treatment is to partially decompose the organic components in the gel to form a carbonization precursor, preparing for subsequent high-temperature calcination.

[0087] In practical applications, during the low-temperature carbonization treatment, it can be fully ground and placed in a porcelain boat, then calcined in a muffle furnace. Heat it to 450 degrees at a rate of 5 degrees per minute and keep the calcination process for 6 hours, and then cool it at a rate of 5 degrees per minute for high-temperature carbon removal.

[0088] Finally, the carbonization precursor can be pressed into tablets, calcined at high temperature in an oxygen atmosphere, and ground to obtain the cathode material for the battery.

[0089] In this embodiment, the carbonization precursor is pressed into sheets. The purpose is to make the precursor have a certain shape and density, facilitating subsequent high-temperature calcination. The pressed precursor is calcined in oxygen at 900 °C for 15 hours with a heating rate of 5 °C / min. The purpose of high-temperature calcination is to enable the metal oxides in the precursor to react fully to form a cathode material with a layered structure.

[0090] During the calcination process, introducing oxygen can ensure the full oxidation of metal oxides and form a stable oxide structure. Grinding the calcined bulk material into fine powders aims to endow the material with good electrode performance and electrochemical activity.

[0091] Based on the above method, the chemical formula of the heptavalent high-entropy layered metal oxide sodium-ion battery cathode material is: Na 0.83 Ni 0.215 Fe 0.215 Mn 0.43 Cu 0.06 Ca 0.03 Sn 0.02 Ti 0.03O2. Among them, the positive electrode material of the battery has a layered crystal structure, and the nickel, iron, manganese, copper, calcium, tin and titanium elements in the layered crystal structure are evenly distributed at the atomic level in the lattice.

[0092] Among them, at a cut-off voltage of 4.3V, the capacity retention rate of the battery positive electrode material after 200 cycles at 1C rate is ≥95.6%, and the capacity retention rate after 1000 cycles at 5C rate is ≥81.1%. The crystal structure of the battery positive electrode material is an O3-type layered structure, the space group is R-3m, and the unit cell parameters satisfy: In addition, the particle size distribution of the positive electrode material of the battery is 0.5μm to 5μm, and the specific surface area is 2m 2 / g~5m 2 / g.

[0093] The seven-element high entropy layered metal oxide sodium ion battery positive electrode material and the preparation method thereof provided in the embodiments of the present invention are described in detail below in conjunction with specific embodiments.

[0094] 1. Preparation of titanium precursor organic solution:

[0095] 0.35 mmol of titanium acetylacetonate was added to 20 mL of isopropanol. First, the mixed solution was placed in an ultrasonic cleaning machine for 30 minutes, and then transferred to a magnetic stirring device and stirred at room temperature for 20 minutes to fully dissolve the titanium acetylacetonate to obtain a uniform titanium precursor organic solution.

[0096] 2. Preparation of chelating agent aqueous solution:

[0097] 5168.3 mg of citric acid was weighed and added to 30 mL of deionized water, and stirred at 300 rpm for 15 minutes until the citric acid was completely dissolved to form a uniform chelating agent aqueous solution.

[0098] 3. Preparation of mixed metal salt precursor aqueous solution:

[0099] Weigh the following metal salts and dissolve them in 50 mL of deionized water:

[0100] Sodium acetate trihydrate 9.3 mmol (to compensate for possible sodium loss in the reaction, an additional 5% excess was used), nickel acetate tetrahydrate 2.5 mmol, manganese acetate tetrahydrate 5 mmol, copper acetate monohydrate 0.7 mmol, calcium acetate monohydrate 0.35 mmol, divalent tin acetate 0.23 mmol, and iron acetate 2.5 mmol.

[0101] The mixed solution is placed in an oil bath and stirred at room temperature at a stirring speed of 300-500 rpm to ensure that each metal salt is completely dissolved to obtain a uniform mixed metal salt precursor aqueous solution.

[0102] 4. Chelation reaction of titanium and citric acid:

[0103] Slowly pour the aqueous solution of the chelating agent into the organic solution of the titanium precursor, and continue magnetic stirring for 3 hours to fully chelate citric acid with titanium acetylacetonate. Due to the large dosage of citric acid, it can effectively prevent Ti from forming impurity TiO2, thus ensuring that titanium is uniformly dispersed in a complex state.

[0104] 5. Preparation of sol:

[0105] Pour the mixed solution obtained in step 4 into the aqueous solution of the mixed metal salt precursor, place it in an oil bath pot, and keep it at 70 °C for 12 hours. During this process, each metal ion is fully complexed with citric acid and uniformly mixed, and finally a stable sol is formed.

[0106] 6. Gel formation:

[0107] After the oil bath heating is completed, open the plastic wrap and stir at 80 °C to gradually condense and evaporate the sol until a uniform green gel is formed.

[0108] 7. Drying of the precursor and low-temperature carbonization treatment:

[0109] After taking out the formed green gel, dry it at 120 °C for 12 hours under vacuum conditions to obtain the dried precursor. Subsequently, fully grind the dried precursor, place it in a porcelain boat with a size of 6 cm × 4 cm, and put it into a muffle furnace. Heat it to 450 °C at a heating rate of 5 °C / min, keep it at 450 °C for 6 hours, and then cool it at a rate of 5 °C / min to achieve the purpose of low-temperature carbonization and partial carbon removal.

[0110] 8. High-temperature calcination and oxidation treatment:

[0111] After the powder after low-temperature carbonization is fully ground, press it into tablets under a pressure of 12 MPa. Put the tablets into a tube furnace, pass 20 mL / min of oxygen, heat it to 900 °C at a heating rate of 5 °C / min, and keep it at 900 °C for 15 hours. This process promotes the full diffusion and uniform oxidation of each metal ion at high temperature, and finally forms a seven-element high-entropy metal oxide cathode material with an O3-type layered crystal structure.

[0112] 9. Preparation of the final product:

[0113] After high-temperature calcination, take out the obtained block and fully grind it to obtain a fine powder of the cathode material. The chemical formula of the cathode material prepared by the above method is Na 0.83 Ni 0.215 Fe 0.215 Mn 0.43 Cu 0.06 Ca 0.03 Sn0.02 Ti 0.03 O₂, whose crystal structure is an O3-type layered structure, and each metal element is uniformly distributed at the atomic level in the lattice.

[0114] After electrochemical performance testing, the cathode material prepared in this example has a capacity retention rate of up to or exceeding 95.6% after 200 cycles at a 1C rate with a cut-off voltage of 4.3V, and a capacity retention rate of up to or exceeding 81.1% after 1000 cycles at a 5C rate.

[0115] In this example, a cathode material prepared by the sol-gel method commonly used for layered compounds was prepared. Its theoretical chemical formula is Na 0.83 Ni 0.215 Fe 0.215 Mn 0.43 Cu 0.06 Ca 0.03 Sn 0.02 Ti 0.03 O₂ (hereinafter referred to as SG-HEO). In order to verify the stoichiometry, crystal structure, and micro-morphology of the prepared material, the following characterization tests were carried out respectively:

[0116] 1. Stoichiometry analysis

[0117] Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the chemical composition of the sample. The measurement results are shown in Table 1. The atomic ratios of Na, Ni, Fe, Mn, Cu, Ca, Sn, and Ti in the sample are highly consistent with the theoretically set values. This result proves that the prepared SG-HEO material has precise stoichiometric control.

[0118] Table 1. Stoichiometry of the sample determined by ICP-MS

[0119]

[0120] 2. X-ray diffraction (XRD) and Rietveld refinement

[0121] Powder XRD tests were carried out on the original SG-HEO and the reference material NFM respectively.

[0122] Figure 2a This is the XRD schematic diagram of SG-HEO provided in the embodiment of the present invention. As Figure 2a shown, the SG-HEO sample exhibits a pure and highly crystalline O3 phase.

[0123] Figure 2b This is the XRD schematic diagram of the NFM sample provided in the embodiment of the present invention. As Figure 2b shown, it also shows the same O3 phase structure, and both belong to the space group R-3m.

[0124] Based on the obtained XRD data, the crystal structure was further determined using the Rietveld refinement method. The refinement results are shown in Tables 2 and 3.

[0125] Table 2. Crystal structure refinement parameters of SG-HEO

[0126]

[0127] Table 3. Crystal structure refinement parameters of NFM

[0128]

[0129] 3. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM)

[0130] Figure 2c It is a schematic diagram of the transmission electron microscopy image of the SG-HEO cathode material provided by the embodiment of the present invention.

[0131] The SG-HEO powder was observed using TEM, as Figure 2c shown. The sample exhibits a blocky morphology, and the particle size distribution is between 0.5 μm and 1 μm.

[0132] Figure 2d It is a schematic diagram of the high-resolution transmission electron microscopy image of the SG-HEO cathode material provided by the embodiment of the present invention.

[0133] As Figure 2d shown, it clearly reveals a well-defined layered structure inside the material, demonstrating that the material has a layered stacking feature, providing a favorable structural basis for its ion diffusion performance.

[0134] 4. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and selected area electron diffraction (SAED)

[0135]

[001] zone axis observation:

[0136] Figure 2e It is a schematic diagram of the high-angle annular dark-field scanning transmission electron microscopy image of the

[001] zone axis provided by the embodiment of the present invention.

[0137] As Figure 2e shown, the sample was scanned along the

[001] zone axis using HAADF-STEM technology. The image shows that the metal ions are arranged in a hexagonal pattern. The measured interatomic spacing of adjacent transition metal (TM) atoms is about 0.295 nm, which is slightly lower than the 0.298 nm measured in the comparative material NFM, indicating that there is a strong TM-d orbital hybridization effect in SG-HEO, resulting in a slight shortening of the bond length.

[0138] Figure 2f Schematic diagram of the selected area electron diffraction image of the

[001] zone axis provided by the embodiment of the present invention.

[0139] Meanwhile, as Figure 2f shown, regular single-crystal hexagonal diffraction spots are shown, further verifying the layered O3 configuration of the material.

[0140]

[010] zone axis observation:

[0141] Figure 2g Schematic diagram of the high-angle annular dark-field scanning transmission electron microscope image of the

[010] zone axis provided by the embodiment of the present invention.

[0142] As Figure 2g shown, the ABCABC stacking sequence of the oxygen ion framework along the c-axis direction is shown, and the measured spacing between adjacent TM layers is about 0.543 nm. This relatively large layer spacing compared to the NSM material (0.532 nm) is beneficial to the diffusion kinetics of Na + ions, thus possibly improving the electrochemical performance.

[0143] 5. Element distribution and energy spectrum analysis (EDS Mapping)

[0144] Figure 2h Schematic diagram of the transmission electron microscope and the corresponding energy spectrum element mapping of the SG-HEO cathode material provided by the embodiment of the present invention.

[0145] As Figure 2h shown, elements such as Ni, Fe, Mn, Cu, Ca, Sn, and Ti in the sample are analyzed by TEM combined with energy spectrum (EDS). The results show that the elements are evenly distributed in the SG-HEO particles, proving the precise and uniform incorporation of each dopant in the O3-phase stacking structure.

[0146] In this embodiment, the electrochemical performance of the Na 0.83 Ni 0.215 Fe 0.215 Mn 0.43 Cu 0.06 Ca 0.03 Sn 0.02 Ti 0.03 O2 (hereinafter referred to as SG-HEO) cathode material is electrochemically tested and compared with the traditional NFM cathode material.

[0147] 1. Battery assembly and testing method

[0148] In this embodiment, the prepared SG-HEO cathode material is used to assemble a sodium-ion half-cell with Na +Using Li / Na as the counter electrode, 1 M NaClO4 (dissolved in EC:DMC = 1:1 by volume, containing 5% FEC) as the electrolyte, and a glass fiber membrane as the separator. After assembly, galvanostatic charge-discharge tests, electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT) were used to characterize the electrochemical performance and kinetic behavior of the materials.

[0149] 2. Galvanostatic Charge-Discharge Performance Test

[0150] Figure 3a This is a schematic diagram of the galvanostatic charge-discharge curves of the SG-HEO and NFM cathode materials provided in the embodiments of the present invention. As Figure 3a shown, within the voltage range of 2.0 - 4.3 V and under the charge-discharge conditions at a rate of 1C (1C = 120 mA g -1 -1), the charge-discharge curves of the SG-HEO cathode are similar to those of the NFM cathode. However, due to the partial substitution of active metals (Ni, Fe) in the high-entropy structure by other metals, its specific capacity is slightly lower. Nevertheless, compared with NFM, the SG-HEO cathode can still maintain a stable oxygen redox plateau after high-voltage charging, especially showing good reversibility after 20 cycles, while the redox plateau of NFM almost disappears after the first cycle.

[0151] Figure 3b This is a schematic diagram of the differential specific capacity curves of the SG-HEO and NFM cathodes provided in the embodiments of the present invention within three cycles. As Figure 3b shown, the first major redox peak near 3.0 V usually corresponds to the O3-P3 phase transition during the charge-discharge process. The polarization potential difference (ΔE) of SG-HEO is 0.31 V, significantly lower than 0.42 V of NFM, indicating that the high-entropy structure reduces polarization. In addition, the oxygen redox peaks in SG-HEO are around 4.1 V and 3.9 V, and their intensities remain almost unchanged in the first three cycles, further highlighting the high reversibility of the oxygen redox process. In contrast, the oxidation peak of NFM weakens significantly with the increase in the number of cycles, indicating poor reversibility of its oxygen redox reaction.

[0152] 3. Rate Performance Test

[0153] Figure 3c This is a schematic diagram of the specific capacities of the SG-HEO and NFM cathodes provided in the embodiments of the present invention at different rates. As Figure 3c shown, the specific capacities of the SG-HEO cathode are 165.3, 152.7, 135.7, 121.6, 101.5, 90.5, and 72.7 mAh g -1 -1 respectively, and it can still maintain 44% of the initial discharge capacity at 10C, while NFM only maintains 22.2%. When the rate is restored to 0.1C, the specific capacity of SG-HEO can recover to 156.8 mAh g-1 , the capacity retention rate reaches 94.9%, far superior to 77.5% of NFM.

[0154] 4. Long cycle stability

[0155] Figure 3d This is a schematic diagram of the long cycle performance of the SG-HEO and NFM cathodes provided in the embodiments of the present invention at a 1C rate. As Figure 3d shown, after 200 cycles at a 1C rate, the capacity retention rate of the SG-HEO cathode is still as high as 95.6%, significantly superior to 33.4% of NFM.

[0156] Figure 3e This is a schematic diagram of the long cycle performance of the SG-HEO and NFM cathodes provided in the embodiments of the present invention at a 10C rate. As Figure 3e shown, even at a high rate of 10C, the capacity of SG-HEO can still be maintained at 81.1% after 1000 cycles, making it one of the cathode materials with the most excellent cycle stability among the reported O3-type high-entropy layered oxides at present.

[0157] Figure 3f This is a schematic diagram comparing the electrochemical performance of O3-type high-entropy layered oxide cathodes at different upper voltage limits provided in the embodiments of the present invention. As Figure 3f shown, the SG-HEO material of the present invention exhibits more excellent oxygen redox reversibility, lower polarization voltage, higher rate performance, and better cycle stability under high-voltage operation.

[0158] 5. Charge transfer and Na + Diffusion kinetics analysis

[0159] (1) Electrochemical impedance spectroscopy (EIS) analysis

[0160] Figure 3g This is a schematic diagram of the electrochemical impedance spectroscopy (EIS) of the SG-HEO and NFM cathodes before and after cycling provided in the embodiments of the present invention. As Figure 3g shown, both the charge transfer resistance (Rct) and the solid electrolyte interface resistance (Rst) of SG-HEO in the initial state are lower than those of NFM. In addition, with the increase in the number of cycles, the impedance increase rate of SG-HEO is much lower than that of NFM, indicating that SG-HEO has more excellent charge transport ability, thus effectively slowing down the structural degradation and improving the long-term cycle stability.

[0161] (2) Na + Diffusion coefficient (DNa + ) analysis

[0162] Figure 3hCalculated logDNa of SG-HEO and NFM cathodes provided in the embodiments of the present invention during initial and secondary charge and discharge processes + Schematic diagram. As Figure 3h shown, during the charging process, due to the O3-P3 phase transition, the diffusion coefficient (DNa + ) of Na + shows a trend of first decreasing and then increasing. At the end of charging, due to the weakening of the electrostatic repulsion caused by the decrease in the Na + concentration, DNa + significantly decreases. However, compared with NFM, DNa of SG-HEO + always remains at a high level and can still maintain a fast Na + diffusion rate during the second cycle, further confirming the excellent ion transport ability of SG-HEO under high voltage and long-term cycling.

[0163] In summary, due to its unique high-entropy structure, the SG-HEO cathode material exhibits more excellent oxygen redox reversibility, lower polarization voltage, higher rate performance, better cycle stability, and faster Na + diffusion ability under high-voltage operation. Compared with the traditional NFM cathode material, it shows more excellent electrochemical performance under long-term cycling and high-rate charge and discharge conditions.

[0164] In this embodiment, in order to reflect the structural evolution behavior of the prepared Na 0.83 Ni 0.215 Fe 0.215 Mn 0.43 Cu 0.06 Ca 0.03 Sn 0.02 Ti 0.03 O2 (hereinafter referred to as SG-HEO) during the charge and discharge process, the in-situ X-ray diffraction (XRD) test technology was used to characterize the phase transition process in the voltage range of 2.0 - 4.3V, and a comparative analysis was carried out with the traditional Ni-Fe-Mn (NFM) cathode material.

[0165] 1. In-situ XRD study on the structural evolution process

[0166] Figure 4a Schematic diagram of the in-situ XRD pattern and the a-axis and c-axis parameters of the dominant phase during the first charge and discharge process of the SG-HEO cathode material provided in the embodiments of the present invention.

[0167] As Figure 4aAs shown, the test results indicate that both the initial SG-HEO and NFM cathode materials exhibit an O3-type layered structure, and their diffraction peaks correspond to the R3m space group. During the charging process, the characteristic diffraction peaks of the O3 phase of SG-HEO rapidly decay, and at the same time, diffraction peaks of the P3 phase appear, indicating that the material undergoes an O3→P3 phase transition during the sodiation process. Before the P3 phase completely dominates, a short coexistence of the O3 and P3 phases can be observed, indicating that the formation process of the P3 phase is relatively mild and has strong diffraction reflection characteristics.

[0168] Figure 4b This is a schematic diagram of the coexisting phases and the two-phase coexistence path during the P3→OP2 phase transition under high sodiation conditions provided by the embodiments of the present invention.

[0169] With the further removal of Na + , the interlayer repulsive force increases, resulting in the gradual shift of the (003) diffraction peak of the P3 phase towards a lower angle. It is worth noting that, as Figure 4b shown, when the voltage reaches 4.15 V, the (003) peak of the P3 phase disappears in the low-angle region, and at the same time, a broader and weaker Bragg diffraction peak appears, indicating that the material further undergoes a P3→OP2 phase transition.

[0170] At a lower Na + concentration, the diffraction peak of the OP2 phase moves towards a higher angle, forming a continuous peak evolution trajectory similar to a triangular trajectory, which corresponds to the oxygen redox process observed in the electrochemical dQ / dV curve. Subsequently, during the discharging process, the crystal structure undergoes an opposite evolution path and finally returns to the O3 phase, that is, the SG-HEO undergoes a reversible O3→O3+P3→P3→OP2→P3→O3+P3→O3 structural transformation during the charge-discharge process.

[0171] In contrast, the NFM material mainly exhibits a two-phase coexistence characteristic during the electrochemical process, that is, the double-peak evolution of the O3 and P3 phases. Above 4.15 V, the diffraction peak of the OP2 phase of the NFM material directly appears at 17.2° without a gradual displacement, indicating that it has strong interdomain anisotropy and large structural stress, making the phase boundary easier to form and hindering the reversible structural transformation.

[0172] 2. Comparative analysis of crystal structure stability

[0173] As Figure 4b shown, under high sodiation conditions, before and after the P3→OP2 phase transition, the displacement of the (003) diffraction peak of the SG-HEO material is only 0.79°, much lower than 2.0° of the NFM material. In addition, as Figure 4aAs shown, by calculating the lattice shrinkage rates of the a-axis and c-axis, it can be obtained that the maximum shrinkage rates of the a-axis and c-axis of the SG-HEO material are 3.84% and 5.97% respectively, while the corresponding shrinkage rates of the NFM material are 6.37% and 6.42% respectively. This indicates that the crystal structure of SG-HEO has better stability during charge and discharge processes.

[0174] Figure 4c This is a schematic HAADF-STEM diagram of the SG-HEO cathode material provided in the embodiment of the present invention after 100 cycles. Figure 4d This is a schematic HAADF-STEM diagram of the NFM cathode material after 100 cycles.

[0175] As Figure 4c and Figure 4d shown, the microstructure of the cathode material after 100 cycles was observed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The test results show that the layered structure of the NFM cathode material collapsed significantly after cycling, while SG-HEO still maintained a complete regular layered structure. This indicates that during long-term cycling, the structural stress-strain evolution of SG-HEO is effectively alleviated.

[0176] The above results indicate that the high-entropy effect can promote the co-existing structure evolution of the SG-HEO material during charge and discharge processes, rather than a simple two-phase coexistence mode. This co-existing phase evolution mechanism effectively reduces the structural stress at the phase interface and reduces the irreversible damage caused by lattice distortion, thereby significantly improving the structural reversibility and cycle stability of the SG-HEO material under high-voltage conditions. Therefore, SG-HEO exhibits excellent application potential in terms of high rate and long cycle life.

[0177] In this embodiment, to further illustrate the electrochemical performance of the SG-HEO cathode material in practical applications, in this embodiment, SG-HEO was used as the cathode and hard carbon (HC) as the anode to assemble a pouch full cell, and its performance under different rates and cycling conditions was tested. The specific content is as follows:

[0178] Figure 5a This is a schematic diagram of a SG-HEO / / HC battery provided in the embodiment of the present invention.

[0179] As Figure 5a shown, the pouch full cell assembled in this embodiment uses SG-HEO as the cathode and hard carbon (HC) as the anode, and the two are connected by an electrolyte. During the assembly process, the capacity ratio of the negative electrode to the positive electrode was optimized and adjusted to about 1.2 to ensure balanced reactions at both electrodes during charge and discharge and improve the overall performance stability.

[0180] Figure 5b Schematic diagram of the capacity comparison between the SG-HEO cathode and the hard carbon anode of the SG-HEO / / HC battery provided by the embodiment of the present invention under 0.1C condition.

[0181] As Figure 5b shown, the initial capacity comparison results between the SG-HEO cathode and the hard carbon anode at 0.1C rate. The initial charge-discharge characteristics exhibited by the SG-HEO cathode are highly consistent with those observed in the half-cell structure previously, indicating that the material still maintains excellent electrochemical activity in the actual full-cell structure.

[0182] Figure 5c Schematic diagram of the constant current charge-discharge curve of the SG-HEO / / HC battery system provided by the embodiment of the present invention under 0.1C condition.

[0183] As Figure 5c shown, the charge-discharge plateau is clear and the slope is gentle, indicating that the battery has low polarization and stable reaction kinetics at low rates, thus verifying the good charge-discharge performance of the SG-HEO cathode material.

[0184] Figure 5d Schematic diagram of the rate performance test curve of the SG-HEO / / HC battery provided by the embodiment of the present invention.

[0185] As Figure 5d shown, even when the rate is increased to 5C, the battery can still maintain a high specific capacity, fully demonstrating the excellent kinetic response ability of the positive electrode material of the present invention under high-rate discharge conditions. In addition, the long-term cycle test results show that after 100 cycles at 1C rate, the battery still has a satisfactory capacity retention rate (74.5%), further verifying its long-term cycle stability.

[0186] In addition, after testing, the SG-HEO / / HC battery assembled in this embodiment has a maximum energy density of up to 370.7 Wh / kg and an average working voltage of about 3.15V. These comprehensive data reflect the excellent performance of this battery system in high energy density and long-life applications, fully demonstrating the application prospect of the SG-HEO cathode as a candidate material for high energy density and long-term recyclability in advanced battery systems.

[0187] In the method embodiments provided by the embodiments of the present invention, the various steps recorded can be executed in different orders and / or 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.

[0188] The term "embodiment" in this specification means that the specific features, structures or characteristics described in connection with the embodiments 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 being independent or alternative to other embodiments and mutually exclusive. The embodiments in this specification are described in a related manner, and the same or similar parts among the embodiments are cross-referred to each other. In particular, for the embodiments of devices, equipment, and systems, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts refer to the partial description of the method embodiments.

[0189] 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 fall within 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 seven-element high entropy layered metal oxide sodium ion battery positive electrode material, characterized in that: The method comprises: dissolving titanium acetylacetonate in an organic solvent, ultrasonically treating and stirring to obtain a titanium precursor organic solution; Dissolve citric acid in water and stir to form a chelating agent aqueous solution; Dissolving a sodium source, a nickel source, a manganese source, a copper source, a calcium source, a tin source and an iron source in water, and stirring to form a mixed metal salt precursor aqueous solution; adding the chelating agent aqueous solution into the titanium precursor organic solution and stirring, so that the titanium acetylacetonate is chelated with the citric acid to obtain a mixed solution; Adding the mixed solution into the mixed metal salt precursor aqueous solution, and heating under preset heating conditions to form a sol; The sol is evaporated to dryness to form a gel, and then vacuum dried and low-temperature carbonized to generate a carbonized precursor; The carbonized precursor is pressed into a sheet, calcined at a high temperature in an oxygen atmosphere and ground to obtain a positive electrode material for a battery.

2. The preparation method according to claim 1, characterized in that: The organic solvent is isopropanol, and the concentration of titanium acetylacetonate is 0.35mmol / 20ml; When dissolving titanyl acetylacetonate in an organic solvent, ultrasonically treating and stirring, the ultrasonic treatment time is 30 minutes, and the stirring time is 20 minutes.

3. The preparation method according to claim 1, characterized in that: The amount of citric acid is 5.1683 g / 30 ml water; When the citric acid is dissolved in water and stirred to form the chelating agent aqueous solution, the stirring speed is 300 rpm and the stirring time is 15 minutes.

4. The preparation method according to claim 1, characterized in that: The sodium source is sodium acetate trihydrate, the nickel source is nickel acetate tetrahydrate, the manganese source is manganese acetate tetrahydrate, the copper source is copper acetate monohydrate, the calcium source is calcium acetate monohydrate, the tin source is divalent tin acetate, and the iron source is ferric acetate; The molar ratios of the sodium source, the nickel source, the manganese source, the copper source, the calcium source, the tin source and the iron source are 9.3:2.5:5:0.7:0.35:0.23:2.5 respectively.

5. The preparation method according to claim 1, characterized in that: The preset heating condition is oil bath at 70° C., keeping warm for 12 hours.

6. The preparation method according to claim 1, characterized in that: The treatment conditions of the low temperature carbonization treatment are calcination at 450°C for 6 hours and a heating rate of 5°C / min; The treatment conditions of the high temperature calcination are 900° C., oxygen flow rate 20 mL / min, heat preservation for 15 hours, and heating rate 5° C. / min.

7. A seven-element high entropy layered metal oxide sodium ion battery positive electrode material, characterized in that: The chemical formula of the battery positive electrode material is: Na 0.83 Ni 0.215 Fe 0.215 Mn 0.43 Cu 0.06 Ca 0.03 Sn 0.02 Ti 0.03 O2; wherein the battery positive electrode material has a layered crystal structure, and the nickel element, iron element, manganese element, copper element, calcium element, tin element and titanium element in the layered crystal structure are evenly distributed at the atomic level in the lattice.

8. The battery positive electrode material according to claim 7, characterized in that: The battery positive electrode material has a capacity retention rate of ≥95.6% after 200 cycles at 1C rate and a capacity retention rate of ≥95.6% after 1000 cycles at 5C rate. ≥81.1％。 9. The battery positive electrode material according to claim 7, characterized in that: The crystal structure of the battery positive electrode material is an O3-type layered structure, the space group is R-3m, and the unit cell parameters satisfy:

10. The battery positive electrode material according to claim 7, characterized in that: The particle size distribution of the battery positive electrode material is 0.5 μm to 5 μm, and the specific surface area is 2 m 2 / g~5m 2 / g.

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