A sodium-ion battery positive electrode material and a preparation method and application thereof

Abstract

This invention relates to a sodium-ion battery cathode material, its preparation method, and its applications, belonging to the field of secondary battery technology. The core of this cathode material is a two-phase composite of vanadium trioxide and sodium vanadium phosphate-based cathode materials. Vanadium trioxide possesses metal-like properties, and its intrinsic channel structure greatly facilitates ion transport. Therefore, the presence of vanadium trioxide can improve the low intrinsic conductivity of sodium vanadium phosphate-based cathode materials, enhancing their rate performance. Simultaneously, the localized structural distortion and chemical-mechanical coupling at the phase interface of the coexisting two phases accelerate ion and electron diffusion, generating additional electrochemical active sites and mitigating volume expansion, thereby enhancing structural stability. Furthermore, substituting vanadium elements at vanadium sites in the sodium vanadium phosphate-based cathode material with substitution elements mitigates environmental and cost issues caused by the inherent properties of vanadium. Finally, the carbon-based shell enhances the electronic conductivity of the cathode material.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more specifically, to a sodium-ion battery cathode material, its preparation method, and its application. Background Technology

[0002] Currently, commercially available lithium-ion batteries cannot simultaneously meet the requirements of high capacity and high rate capability for power batteries and electronic devices, as well as the low cost and high safety requirements for energy storage, especially in applications such as grid energy storage. Furthermore, the rapid development of the battery market has led to a supply shortage of already scarce lithium resources.

[0003] To address these needs, there is an urgent need to find an energy storage medium that is not limited by resources to meet the requirements of large-scale, low-cost, and high-safety energy storage. In response, China has accelerated the development of new battery technologies, with sodium-ion batteries, which possess low cost, long lifespan, and fast-charging characteristics, receiving extensive research. Among them, polyanion-type sodium-ion batteries have attracted considerable attention due to their high operating voltage, cycle stability, and high safety. A typical NASICON-type structure consists of Na... x M2(XO4)3. Each MO6 octahedron is connected to three tetrahedral XO4 units, forming a lantern-shaped unit, which further constructs a three-dimensional framework with large gaps. Typical structural materials, such as sodium vanadium phosphate, have attracted considerable attention due to their stable 3D crystal structure and high operating potential. However, their large-scale application is limited by many disadvantages, such as low intrinsic capacity, poor rate performance, and the high price and environmental unfriendliness of vanadium. Summary of the Invention

[0004] This application provides a sodium-ion battery cathode material, its preparation method, and its application, enabling sodium vanadium phosphate cathode materials to exhibit good rate performance.

[0005] In a first aspect, this application provides a sodium-ion battery cathode material having a core-shell structure. The core of the cathode material includes a first component and a second component. The first component is vanadium trioxide, and the second component includes sodium vanadium phosphate in which some vanadium sites are replaced by substituted metal elements. The shell of the cathode material includes carbon.

[0006] In the aforementioned implementation process, by making the core of the cathode material a two-phase composite, vanadium trioxide, which possesses metal-like properties, exhibits intrinsic channel structures in its crystals that greatly facilitate ion transport. Therefore, the presence of vanadium trioxide can improve the low intrinsic conductivity of sodium vanadium phosphate-based cathode materials, thereby enhancing their rate performance. Simultaneously, the localized structural distortion and chemical-mechanical coupling at the phase interface of the coexisting two phases accelerate ion and electron diffusion, generating additional electrochemical active sites and mitigating volume expansion, thus enhancing structural stability. Furthermore, by using substituent elements to replace the vanadium at the vanadium sites in sodium vanadium phosphate-based cathode materials, environmental and cost issues caused by the inherent properties of vanadium are mitigated.

[0007] As an optional implementation, the second component includes Na. 3+a M a V 2-a (PO4)3; where 0≤a≤1, and M includes divalent transition metal elements.

[0008] In the above implementation process, a divalent transition metal element is used to replace the vanadium element at the vanadium site in the sodium vanadium phosphate cathode material. Because the unpaired electrons brought by the divalent transition metal element alter the spin polarization characteristics of the original octahedral 3d orbitals of the metal, this not only activates the V... 4+ / V 5+ The redox reaction further improved the discharge capacity and the intrinsic conductivity of the electrode material. At the same time, the iron substitution also changed the migration path of sodium ions and increased their migration rate, thereby improving the rate performance of the battery.

[0009] As an optional implementation, the vanadium trioxide in the cathode material has a mass ratio of 5% to 15%.

[0010] In the above implementation process, by controlling the mass ratio of vanadium trioxide in the cathode material to 5% to 15%, it is beneficial to balance the rate performance and energy density of the cathode material.

[0011] As an optional implementation, the thickness of the shell layer is 5 nm to 10 nm.

[0012] In the above implementation process, by controlling the thickness of the shell to be 5nm to 10nm, it is beneficial to balance the electronic conductivity and energy density of the cathode material.

[0013] Secondly, this application provides a method for preparing a sodium-ion battery cathode material, wherein the cathode material is the cathode material provided in the first aspect; the method includes:

[0014] The substituted metal source, vanadium source and complexing agent are dissolved in a solvent to obtain a coexisting complex;

[0015] The coexisting complex was mixed with a sodium source, then mixed with a phosphorus source, dried and ball-milled to obtain a powder;

[0016] The powder is sintered to obtain a positive electrode material.

[0017] In the above implementation process, by using organic carbon to be blended with other raw materials during the preparation process, in-situ carbon coating is achieved during high-temperature sintering. This not only facilitates electron and ion transport but also restricts the grain growth of the cathode material, thus achieving a balance between kinetics and conductivity.

[0018] As an optional implementation, the substituted metal source includes at least one of ferrous acetylacetone, ferrous acetate, and ferrous oxalate; and / or

[0019] The vanadium source includes at least one of vanadium acetylacetonate and ammonium metavanadate; and / or

[0020] The molar ratio of the substituted metal source and the vanadium source is (0-1):(1-2); and / or

[0021] The complexing agent includes at least one of citric acid, oxalic acid, ethylenediamine, and ethylene glycol; and / or

[0022] The molar ratio of the complexing agent to all metal elements in the cathode material is (1-3):1, based on the amount of substance; and / or

[0023] The dissolution temperature is 80℃~100℃; and / or

[0024] The dissolution process is accompanied by stirring at a rate of 300 r / min to 500 r / min.

[0025] In the above implementation process, by adding an excess of vanadium source, part of it provides vanadium element for sodium vanadium phosphate cathode materials, and the other part is transformed into vanadium trioxide, forming a two-phase structure, which is beneficial to the rate performance of cathode materials.

[0026] As an optional implementation, the sodium source includes at least one of sodium acetate and sodium carbonate; and / or

[0027] The phosphorus source is mixed by dropwise addition, with each dropwise addition not exceeding 0.02 mL; and / or

[0028] The phosphorus source includes at least one of orthophosphoric acid and ammonium dihydrogen phosphate; and / or

[0029] The drying temperature is 80℃~100℃, and the drying time is not less than 10 hours; and / or

[0030] The ball milling speed is 300 r / min to 500 r / min, and the ball milling time is 1 h to 3 h.

[0031] As an optional implementation, the sintering temperature is 650℃~750℃; and / or

[0032] The heating rate of the sintering process is 1℃ / min to 5℃ / min; and / or

[0033] The holding time for the sintering treatment is 5h to 10h; and / or

[0034] The atmosphere for the sintering process includes an inert gas or nitrogen.

[0035] Thirdly, this application provides a positive electrode sheet, which includes the positive electrode material provided in the first aspect.

[0036] Fourthly, this application provides a battery comprising the positive electrode provided in the third aspect. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a SEM image of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0039] Figure 2 This is a low-magnification TEM image of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0040] Figure 3 This is a high-magnification TEM image of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0041] Figure 4 This is a high-magnification TEM image of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0042] Figure 5 This is the Raman diagram of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0043] Figure 6 The image shows the XRD pattern of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application.

[0044] Figure 7 This is the XPS image of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0045] Figure 8 The XPS spectrum of Fe 2p in the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application is shown.

[0046] Figure 9 This is a TGA image of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0047] Figure 10 The XRD pattern of the sodium vanadium phosphate cathode material with a vanadium source reduced by 20% in Comparative Example 1 of this application;

[0048] Figure 11 The XRD pattern of sodium vanadium phosphate cathode material with 20% vanadium source added in Comparative Example 2 of this application;

[0049] Figure 12 The image shows the XRD pattern of the single-phase sodium vanadium phosphate cathode material in Comparative Example 3 of this application;

[0050] Figure 13 XPS plot of the single-phase sodium vanadium phosphate cathode in Comparative Example 1 of this application;

[0051] Figure 14 The image shows the XRD pattern of the three-phase composite sodium vanadium phosphate modified cathode material in Comparative Example 4 of this application.

[0052] Figure 15 This is a diagram showing the first three charge-discharge curves of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0053] Figure 16 The charge-discharge curves of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application at different rates are shown.

[0054] Figure 17 This is a CV cycle curve of the three-phase composite sodium vanadium phosphate modified cathode material in Example 1 of this application;

[0055] Figure 18 The three-phase composite sodium vanadium phosphate modified cathode material obtained in Example 1 of this application was tested at 20 mA g. -1 Cyclic curve at current density;

[0056] Figure 19 The three-phase composite sodium vanadium phosphate modified cathode material obtained in Example 1 of this application was tested at 2A g. -1 Cyclic curve at current density;

[0057] Figure 20The three-phase composite sodium vanadium phosphate modified cathode material obtained in Example 1 of this application was tested at 10 A g. -1 Cyclic curve at current density;

[0058] Figure 21 The graph shows the rate performance test results of the three-phase composite sodium vanadium phosphate modified cathode material obtained in Example 1 of this application under different current densities.

[0059] Figure 22 This is a charge-discharge curve of the sodium vanadium phosphate cathode material with 20% less vanadium source in Comparative Example 1 of this application for the first three cycles;

[0060] Figure 23 The sodium vanadium phosphate cathode material of Comparative Example 1 of this application, which reduces the vanadium source by 20%, is used in a 2A g process. -1 Cyclic curve at current density;

[0061] Figure 24 The first three charge-discharge curves of sodium vanadium phosphate cathode material with 20% vanadium source added in Comparative Example 2 of this application;

[0062] Figure 25 The sodium vanadium phosphate cathode material in Comparative Example 2 of this application, with an increased vanadium source of 20%, was used at 2A g. -1 Cyclic curve at current density;

[0063] Figure 26 This is a diagram showing the first three charge-discharge curves of the single-phase sodium vanadium phosphate cathode material in Comparative Example 3 of this application;

[0064] Figure 27 This is a charge-discharge curve of the single-phase sodium vanadium phosphate cathode material in Comparative Example 3 of this application at different rates;

[0065] Figure 28 This is a CV cycle curve of the single-phase sodium vanadium phosphate cathode material in Comparative Example 3 of this application;

[0066] Figure 29 For the single-phase sodium vanadium phosphate cathode material in Comparative Example 3 of this application, at 20 mA g -1 Cyclic curve at current density;

[0067] Figure 30 For the single-phase sodium vanadium phosphate cathode material in Comparative Example 3 of this application, at 2A g -1 Cyclic curve at current density;

[0068] Figure 31 The graph shows the rate performance test results of the single-phase sodium vanadium phosphate cathode material in Comparative Example 3 of this application at different current densities.

[0069] Figure 32 This is a charge-discharge curve of the cathode material obtained in Comparative Example 4 of this application for the first ten cycles;

[0070] Figure 33 The graph shows the rate performance test results of the cathode material obtained in Comparative Example 4 of this application under different current densities. Detailed Implementation

[0071] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0072] Sodium vanadium phosphate has attracted considerable attention due to its stable 3D crystal structure and high operating potential. However, its intrinsic capacity is low, its rate performance is poor, and the vanadium element it contains is expensive and environmentally unfriendly, which limits its large-scale application.

[0073] To address the numerous drawbacks of sodium vanadium phosphate, such as low intrinsic capacity, poor rate performance, high price of vanadium, and environmental unfriendliness, this application aims to provide a three-phase composite sodium vanadium phosphate modified cathode material, which has a two-phase composite core and a carbon shell, and features high capacity, excellent rate performance, and long lifespan.

[0074] This application provides a sodium-ion battery cathode material having a core-shell structure. The core of the cathode material includes a first component and a second component. The first component is vanadium trioxide, and the second component includes sodium vanadium phosphate in which at least some vanadium sites are replaced by substituted metal elements. The shell of the cathode material includes carbon.

[0075] The core of this cathode material is a two-phase composite of vanadium trioxide and sodium vanadium phosphate. Vanadium trioxide possesses metal-like properties, and its intrinsic channel structure greatly facilitates ion transport. Therefore, the presence of vanadium trioxide can improve the low intrinsic conductivity of sodium vanadium phosphate cathode materials, enhancing their rate performance. Simultaneously, the localized structural distortion and chemical-mechanical coupling at the phase interface of the coexisting two phases accelerate ion and electron diffusion, generating additional electrochemical active sites and mitigating volume expansion, thereby enhancing structural stability. Furthermore, substituting vanadium at vanadium sites in sodium vanadium phosphate cathode materials with substitution elements mitigates environmental and cost issues caused by the inherent properties of vanadium. Finally, the carbon shell enhances the electronic conductivity of the cathode material.

[0076] In some embodiments, the substituted metal element may be selected from divalent transition metal elements, such as Fe, Mn, etc.

[0077] In some embodiments, the second component includes: Na 3+a M a V 2-a (PO4)3; where 0 ≤ a ≤ 1, and M includes divalent transition metal elements. Replacing the vanadium element at the vanadium site in sodium vanadium phosphate cathode materials with a divalent transition metal element alters the spin polarization characteristics of the original octahedral 3d orbitals due to the unpaired electrons brought by the divalent transition metal element, thus activating not only V... 4+ / V 5+ The redox reaction further improved the discharge capacity and the intrinsic conductivity of the electrode material. At the same time, the iron substitution also changed the migration path of sodium ions and increased their migration rate, thereby improving the rate performance of the battery.

[0078] It should be noted that the above limitation on 'a' includes the molar content of Na under different charge and discharge states of the battery (typically the battery voltage is between 2-5V).

[0079] Understandably, sodium (Na) is intercalated and deintercalated during the charging and discharging process of a battery. The Na content in the positive electrode varies depending on the state of discharge. The Na content can be measured using molar content, but is not limited to this. Simultaneously, when a positive electrode material is applied to the positive electrode in a battery system, the Na content in the positive electrode material typically changes after charge-discharge cycles. In the examples of positive electrode materials listed in this application, unless otherwise specified, the Na content refers to the initial state of the material. Regarding "Na content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for the positive electrode material; non-limiting examples include coating modification.

[0080] For example, the value of 'a' can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc., or it can be any value in the range of 0 to 1.

[0081] In some embodiments, the vanadium trioxide comprises 5% to 15% of the cathode material by mass. By controlling the vanadium trioxide content in the cathode material to be 5% to 15% by mass, it is beneficial to balance the rate performance and energy density of the cathode material.

[0082] For example, the mass percentage of vanadium trioxide in the cathode material can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, or 15%, etc., or it can be any value within the range of 5% to 15%.

[0083] In some embodiments, the thickness of the shell layer is 5 nm to 10 nm. By controlling the thickness of the shell layer to be 5 nm to 10 nm, it is beneficial to balance the electronic conductivity and energy density of the cathode material.

[0084] For example, the thickness of the shell can be 5nm, 6nm, 7nm, 8nm, 9nm or 10nm, or any value in the range of 5nm to 10nm.

[0085] This application provides a method for preparing a sodium-ion battery cathode material, the method comprising:

[0086] S1. Dissolve the substituted metal source, vanadium source and complexing agent in a solvent to obtain a coexisting complex;

[0087] Specifically, in this embodiment, the complexing agent is mixed in a common solvent at a certain molar ratio and stirred to dissolve it completely. Then, the mixture is heated and stirred on a magnetic stirrer to obtain a clear solution. A certain molar ratio of substituted metal source and vanadium source is added to the obtained clear solution, and the mixture is heated and stirred until the raw materials are completely dissolved to obtain a coexisting complex.

[0088] In some embodiments, the substituted metal source includes at least one of ferrous acetylacetone, ferrous acetate, and ferrous oxalate; the vanadium source includes at least one of vanadium acetylacetone and ammonium metavanadate; the molar ratio of the substituted metal source to the vanadium source is (0-1):(1-2); the complexing agent includes at least one of citric acid, oxalic acid, ethylenediamine, and ethylene glycol; the molar ratio of the complexing agent to all metal elements in the cathode material is (1.5-3):1 by weight; the dissolution temperature is 80°C-100°C; the dissolution process is accompanied by stirring, and the stirring rate is 300 r / min-500 r / min.

[0089] S2. The coexisting complex and sodium source are mixed, then mixed with phosphorus source, dried and ball-milled to obtain powder;

[0090] Specifically, in this embodiment, a certain molar ratio of sodium source is added to the obtained coexisting complex, and the mixture is heated and stirred continuously until the sodium source is completely dissolved, wherein the heating temperature remains constant to obtain a mixed solution. A phosphorus source is slowly added to the obtained mixed solution, and the mixture is heated and stirred continuously while maintaining a constant temperature until the solution is completely evaporated to form a sol. The obtained sol is placed in a vacuum oven and dried thoroughly to remove the residual liquid phase components in the sol to obtain a dry gel. The obtained dry gel is ball-milled in a high-energy ball mill for a certain period of time to obtain a powder.

[0091] In some embodiments, the sodium source includes at least one of sodium acetate and sodium carbonate; the phosphorus source is mixed by dropwise addition, with a single dropwise addition not exceeding 0.02 mL; the phosphorus source includes at least one of orthophosphoric acid and ammonium dihydrogen phosphate; orthophosphoric acid is preferred because it can also adjust the pH of the solution to acidic, promoting the complexation process described above. The drying temperature is 80°C to 100°C, and the drying time is not less than 10 hours; the ball milling speed is 300 r / min to 500 r / min, and the ball milling time is 1 hour to 3 hours.

[0092] S3. The powder is sintered to obtain a positive electrode material.

[0093] Specifically, in this embodiment, the powder is subjected to high-temperature sintering in a tube furnace with an inert gas atmosphere to obtain a three-phase composite sodium vanadium phosphate cathode material.

[0094] In some embodiments, the sintering temperature is 650°C to 750°C; the heating rate of the sintering process is 1°C / min to 5°C / min; the holding time of the sintering process is 5h to 10h; and the atmosphere of the sintering process includes inert gas or nitrogen.

[0095] The cathode material of this application will be further described in detail below with reference to the embodiments.

[0096] Example 1

[0097] This embodiment provides a cathode material, the preparation method of which is as follows:

[0098] First, 3 mmol of citric acid was dissolved in 40 ml of anhydrous ethanol and stirred until fully dissolved. Then, 0.5 mmol of ferrous acetylacetone and 1.5 mmol of vanadium acetylacetone were added, and the mixture was heated and stirred continuously at 80°C until the raw materials were completely dissolved. Next, 3.5 mmol of sodium acetate was added, and the mixture was heated and stirred continuously until the sodium acetate was completely dissolved, while maintaining a constant heating temperature. Then, 0.21 ml of phosphoric acid was added dropwise, and the mixture was heated and stirred continuously while maintaining a constant temperature until the solution was completely evaporated to dryness to form a sol. The resulting sol was placed in a vacuum oven at 100°C and vacuum dried for 12 hours to remove any residual liquid components. The resulting dry gel was ball-milled in a high-energy ball mill for 1 hour. Then, the ball-milled powder was sintered at high temperature in a tube furnace under argon atmosphere at 700°C for 6 hours. Finally, the cathode material was obtained.

[0099] Example 2

[0100] This embodiment provides a cathode material, the preparation method of which is as follows:

[0101] First, 3 mmol of citric acid was dissolved in 40 ml of deionized water and stirred until fully dissolved. Then, 0.5 mmol of ferrous acetylacetone and 1.5 mmol of vanadium acetylacetone were added, and the mixture was heated and stirred continuously at 80°C with a magnetic stirrer until the raw materials were completely dissolved. Next, 3.5 mmol of sodium acetate was added, and the mixture was heated and stirred continuously until the sodium acetate was completely dissolved, while maintaining a constant heating temperature. Then, 0.21 ml of phosphoric acid was added dropwise, and the mixture was heated and stirred continuously while maintaining a constant temperature until the solution was completely evaporated to dryness to form a sol. The resulting sol was placed in a vacuum oven at 100°C and vacuum dried for 12 hours to remove any residual liquid components. The resulting dry gel was ball-milled in a high-energy ball mill for 1 hour. Then, the ball-milled powder was sintered at high temperature in a tube furnace under argon atmosphere at 700°C for 6 hours. Finally, the cathode material was obtained.

[0102] Example 3

[0103] This embodiment provides a cathode material, the preparation method of which is as follows:

[0104] First, 3 mmol of citric acid was placed in a 1:1 mixture of deionized water and anhydrous ethanol in 40 mL of water and stirred until fully dissolved. Then, 0.5 mmol of ferrous acetylacetone and 1.5 mmol of vanadium acetylacetone were added, and the mixture was heated and stirred continuously at 80 °C with a magnetic stirrer until the raw materials were completely dissolved. Next, 3.5 mmol of sodium acetate was added, and the mixture was heated and stirred continuously until the sodium acetate was completely dissolved, while maintaining a constant heating temperature. Then, 0.21 mL of phosphoric acid was added dropwise, and the mixture was heated and stirred continuously while maintaining a constant temperature until the solution was completely evaporated to dryness to form a sol. The resulting sol was placed in a vacuum oven at 100 °C and vacuum dried for 12 hours to remove any residual liquid components. The resulting dry gel was ball-milled in a high-energy ball mill for 1 hour. Then, the ball-milled powder was sintered at high temperature in a tube furnace under argon atmosphere at 700 °C for 6 hours. Finally, the cathode material was obtained.

[0105] The composition of the cathode materials provided in each embodiment was characterized using SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope), Raman spectroscopy, XRD (X-ray Diffraction), XPS (X-ray Photoelectron Spectroscopy), and Thermogravimetric Analyzer (TGA). Since the results are similar, the results of Example 1 are used as an example below. Figures 1 to 9 As shown.

[0106] from Figure 1 SEM and Figure 2 TEM results show that the diameter of the obtained cathode material particles is about 3 μm.

[0107] Figure 3 yes Figure 2 The magnified TEM image shows that the obtained positive electrode material is coated with a carbon layer with a thickness of 2 nm to 5 nm.

[0108] from Figure 4 The TEM images show that there are obvious grain boundaries in the material, indicating that there is a uniformly distributed second phase component.

[0109] from Figure 5 As can be seen, the D peak of carbon (1350 cm⁻¹) is clearly shown in the Raman spectrum. -1 and G peak (1590cm) -1The presence of two characteristic peaks, with an estimated intensity ratio of 1.02 for the D and G peaks, proves that citric acid, as a carbon source, forms a carbon coating layer and partially graphitizes during sintering through in-situ carbonization. Furthermore, at 431 and 993 cm⁻¹... -1 The positions of the two peaks can also correspond to the stretching vibrations of the [PO4] group.

[0110] from Figure 6 It can be seen that the diffraction peaks at 20.1°, 23.7°, and 32.0° are attributed to the (104), (113), and (116) crystal planes of sodium vanadium phosphate, respectively, indicating that iron doping substitution did not affect the original crystal structure of sodium vanadium phosphate. The diffraction peaks at 24.3°, 32.9°, 36.2°, and 53.9° are attributed to the (012), (104), (110), and (116) crystal planes of vanadium trioxide, further demonstrating the presence of the second phase component.

[0111] from Figure 7 The XPS full spectrum shows that the main components of the sample are sodium, iron, vanadium, oxygen, carbon, and phosphorus. Figure 8 The clear Fe 2p XPS spectrum further confirms the successful iron doping and substitution.

[0112] from Figure 9 The TGA curves show that the carbon content of the prepared cathode material is around 6.33%.

[0113] Comparative Example 1

[0114] This comparative example provides a cathode material, the preparation method of which is basically the same as that of Example 1, the only difference being that the vanadium source is reduced by 20% (i.e., the amount used is 1.2 mmol), to obtain the cathode material.

[0115] The cathode material provided in Comparative Example 1 was characterized using XRD (X-ray Diffraction), and the characterization results are as follows: Figure 10 As shown.

[0116] from Figure 10 It can be seen that the diffraction peaks at 20.1°, 23.7° and 32.0° are attributed to the (104), (113) and (116) crystal planes of sodium vanadium phosphate, respectively. The diffraction peaks at 24.3°, 32.9°, 36.2° and 53.9°, which were originally attributed to the (012), (104), (110) and (116) crystal planes of vanadium trioxide, have disappeared. This indicates that reducing the vanadium source will cause vanadium trioxide, as a component of the second phase, to disappear.

[0117] Comparative Example 2

[0118] This comparative example provides a cathode material, the preparation method of which is basically the same as that of Example 1, the only difference being the addition of 20% vanadium source (i.e., the amount used is 1.8 mmol) to obtain the cathode material.

[0119] The sodium vanadium phosphate cathode material without vanadium trioxide in Comparative Example 1 was characterized using XRD (X-ray Diffraction). The characterization results are as follows: Figure 11 As shown.

[0120] from Figure 11 It can be seen that the diffraction peaks at 20.1°, 23.7° and 32.0° are attributed to the (104), (113) and (116) crystal planes of sodium vanadium phosphate, respectively. The diffraction peaks at 24.3°, 32.9°, 36.2° and 53.9°, which were originally attributed to the (012), (104), (110) and (116) crystal planes of vanadium trioxide, are slightly enhanced, indicating that increasing the vanadium source will lead to an increase in vanadium trioxide as a second phase component.

[0121] Comparative Example 3

[0122] This comparative example uses a commercially available sodium vanadium phosphate cathode material (Canrd, MA-EN-CA-0044).

[0123] The composition of the commercial sodium vanadium phosphate cathode material in Comparative Example 3 was characterized using XRD (X-ray Diffraction) and XPS (X-ray Photoelectron Spectroscopy). The characterization results are as follows: Figure 12 and Figure 13 As shown.

[0124] from Figure 12 It can be seen that the diffraction peaks at 20.1°, 23.7° and 32.0° are attributed to the (104), (113) and (116) crystal planes of sodium vanadium phosphate, respectively, and there are no other characteristic peaks, indicating that the commercial cathode material used is pure phase sodium vanadium phosphate without the presence of other phases.

[0125] from Figure 13 The XPS full spectrum shows that the main components of pure-phase sodium vanadium phosphate are sodium, vanadium, oxygen, carbon, and phosphorus, further indicating that pure-phase sodium phosphate does not contain other impurity elements or a second phase.

[0126] Comparative Example 4

[0127] This comparative example provides a cathode material, which is prepared by simply mixing sodium vanadium phosphate and vanadium trioxide at a mass ratio of 9:1 for a certain period of time to obtain a two-phase mixed cathode material.

[0128] The cathode material provided in Comparative Example 4 was characterized using XRD (X-ray Diffraction), and the characterization results are shown in the figure below.

[0129] from Figure 14 It can be seen that the diffraction peaks at 20.1°, 23.7° and 32.0° are attributed to the (104), (113) and (116) crystal planes of sodium vanadium phosphate, respectively, while the peaks at 24.3°, 32.9°, 36.2° and 53.9° are attributed to the diffraction peaks of the (012), (104), (110) and (116) crystal planes of vanadium trioxide.

[0130] The cathode material provided in Example 1 was assembled into a half-cell, and its performance as a cathode in a sodium-ion battery was tested. The specific process is as follows:

[0131] The positive electrode material from Example 1 was mixed with acetylene black and polyvinylidene fluoride, and then added to N-methylpyrrolidone for magnetic stirring. After 24 hours, it was evenly coated on aluminum foil current collector and then transferred to a vacuum drying oven. It was first dried in an air oven at 70°C for 5 hours to remove most of the solvent, and then dried in a vacuum drying oven at 100°C for 10 hours. After the drying was completed, the electrode was taken out and cut into 12mm diameter round pieces and placed in a glove box. It was then assembled with sodium sheet to form a half cell for testing.

[0132] Electrochemical performance testing of sodium-ion battery cathode: The performance of the sodium-ion battery cathode made using the material obtained in Example 1 was tested using a constant current charge-discharge method. The test results of Example 1 are as follows: Figures 15-21 As shown.

[0133] from Figure 15 The charge-discharge curves show that the reversible discharge capacity of the positive electrode of the battery corresponding to Example 1 after the first three charge-discharge cycles is approximately 127.87 mAh g. -1 The first lap efficiency was 114.93%.

[0134] from Figure 16 The charge-discharge curves at different rates show that the positive electrode of the battery corresponding to Example 1 has a first-cycle charging capacity of 143.5 mAh g at a current of 0.1C. -1 The corresponding discharge capacity is 132.2 mAh g. -1 Furthermore, the charge and discharge curves maintain a consistent shape under different current densities.

[0135] from Figure 17 The cyclic voltammetry curves show that at 0.1, 0.4, 0.8, and 1.6 mV s... -1 At the scan rate, three redox pairs can be clearly seen, corresponding to Fe from low to high. 2+ / Fe 3+ V 3+ / V 4+ and V 4+ / V 5+ Redox reactions.

[0136] from Figure 18 20m Ag -1 As can be seen from the low-current cycling curve, after 100 cycles, the reversible capacity of the positive electrode of the battery in Example 1 reaches as high as 121.29 mAh g. -1 The corresponding capacity retention rate is 94.57%.

[0137] from Figure 19 2Ag -1 The current cycling curves show that after 10,000 cycles, the reversible capacity of the positive electrode of the battery in Example 1 reaches as high as 87.2 mAh g. -1 The corresponding capacity retention rate is 80.0%.

[0138] Depend on Figure 20 10A g -1 The high-current cycling curve shows that after 10 cycles at 0.1 A g -1 After activation with a small current, switch to 10A g -1 The first discharge capacity during high-current cycling is 60.83 mAh g. -1 After approximately 4500 cycles, the capacity reaches a maximum of 82.22 mAh g. -1 After 30,000 cycles, the reversible capacity of the positive electrode of the battery in Example 1 reached 65.83 mAh g. -1 The corresponding capacity retention rate is 107.0%.

[0139] from Figure 21 The rate curves show that the average discharge capacities of the positive electrode of the battery corresponding to Example 1 at current densities of 0.1C, 0.5C, 1C, 2C, 5C, and 10C are 132.2, 126.9, 124.5, 121.1, 115.4, and 109.6 mAh g, respectively. -1 Compared to the capacity obtained at 0.1C, it still retains 82.9% at 10C, and when the current density returns to 0.1C, its reversible capacity is still as high as 128.0 mAh g. -1 .

[0140] The sodium vanadium iron phosphate cathode material obtained by reducing the vanadium source in Comparative Example 1 (which is free of vanadium trioxide) was assembled into a half-cell, and its performance as a cathode in a sodium-ion battery was tested. The specific process is as follows:

[0141] The positive electrode material from Comparative Example 1 was mixed with acetylene black and polyvinylidene fluoride, and then added to N-methylpyrrolidone for magnetic stirring. After 24 hours, it was evenly coated on aluminum foil current collector and then transferred to a vacuum drying oven. It was first dried in an air oven at 70°C for 5 hours to remove most of the solvent, and then dried in a vacuum drying oven at 100°C for 10 hours. After the drying was completed, the electrode was taken out and cut into 12mm diameter round pieces and placed in a glove box. It was then assembled with a sodium sheet to form a half cell for testing.

[0142] Electrochemical performance testing of the sodium-ion battery cathode: The performance of the sodium-ion battery composed of the cathode material obtained in Comparative Example 1 was tested using a constant current charge-discharge method. The test results are as follows: Figures 22-23 As shown.

[0143] from Figure 22 The charge-discharge curves show that the reversible capacities of the positive electrode of Comparative Example 1 after the first charge-discharge cycle are 108.23 and 109.66 mAh g, respectively. -1 The first-cycle coulombic efficiency was 101.32%. Compared with Example 1, the first-cycle discharge capacity was only 85.7% of that of Example 1, and the first-cycle coulombic efficiency was also reduced by about 13%.

[0144] from Figure 23 The cycling curves show that, for the positive electrode of the battery corresponding to Comparative Example 1, the initial discharge capacity is 91.03 mAh g, and the reversible discharge capacity after 2000 cycles is 86.59 mAh g. -1 The capacity retention rate was 95.11%, and the reversible discharge capacity after 4000 cycles was 75.63 mAh g. -1 The capacity retention rate was 83.09%. Compared with the cycling at the same current in Example 1 (capacity loss per cycle was 0.2%), the capacity loss per cycle in Comparative Example 1 increased to 0.42%, indicating that the cycling stability of the cathode material without vanadium trioxide was not as good as that in Example 1.

[0145] The sodium vanadium phosphate cathode material obtained by adding more vanadium source in Comparative Example 2, with more vanadium trioxide, was assembled into a half-cell, and its performance as a cathode in a sodium-ion battery was tested. The specific process is as follows:

[0146] The positive electrode material from Comparative Example 2 was mixed with acetylene black and polyvinylidene fluoride, and then added to N-methylpyrrolidone for magnetic stirring. After 24 hours, it was evenly coated on aluminum foil current collector and then transferred to a vacuum drying oven. It was first dried in an air oven at 70°C for 5 hours to remove most of the solvent, and then dried in a vacuum drying oven at 100°C for 10 hours. After the drying was completed, the electrode was taken out and cut into 12mm diameter round pieces and placed in a glove box. It was then assembled with a sodium sheet to form a half cell for testing.

[0147] Electrochemical performance testing of the sodium-ion battery cathode: The performance of the sodium-ion battery cathode obtained in Comparative Example 2 was tested using a constant current charge-discharge method. The test results are as follows: Figures 24-25 As shown.

[0148] from Figure 24 The charge-discharge curves show that the reversible capacities of the positive electrode of the battery corresponding to Comparative Example 1 after the first charge-discharge cycle are 92.63 and 96.60 mAh g, respectively. -1 The first-cycle coulombic efficiency was 104.51%. Compared with Example 1, the first-cycle discharge capacity of Comparative Example 2 was only 75.5% of that of Example 1, and the first-cycle coulombic efficiency decreased by about 10%, indicating that excessive unactivated vanadium trioxide could actually affect the capacity.

[0149] from Figure 25 The cycling curves show that, for the positive electrode of the battery corresponding to Comparative Example 1, the initial discharge capacity is 77.84 mAh g, and the reversible discharge capacity after 2000 cycles is 71.40 mAh g. -1 The capacity retention rate was 91.73%. Compared with Example 1 under the same current (capacity loss per cycle was 0.2%), Comparative Example 2 had a capacity loss of approximately 0.41% per cycle, indicating that the cycling stability of the cathode material with excess vanadium trioxide was also inferior to that of Example 1.

[0150] The commercial sodium vanadium phosphate cathode material from Comparative Example 3 was used to assemble a half-cell, and its performance as a cathode in a sodium-ion battery was tested. The specific process is as follows:

[0151] The positive electrode material from Comparative Example 3 was mixed with acetylene black and polyvinylidene fluoride, and then added to N-methylpyrrolidone for magnetic stirring. After 24 hours, it was evenly coated on aluminum foil current collector and then transferred to a vacuum drying oven. It was first dried in an air oven at 70°C for 5 hours to remove most of the solvent, and then dried in a vacuum drying oven at 100°C for 10 hours. After the drying was completed, the electrode was taken out and cut into 12mm diameter round pieces and placed in a glove box. It was then assembled with a sodium sheet to form a half cell for testing.

[0152] Electrochemical performance testing of the sodium-ion battery cathode: The performance of the sodium-ion battery cathode obtained in Comparative Example 3 was tested using a constant current charge-discharge method. The test results are as follows: Figures 26-31 As shown.

[0153] from Figure 26 The charge-discharge curves show that the reversible discharge capacity of the positive electrode of the battery corresponding to Example 1 after the first three charge-discharge cycles is 107 mAh g. -1 The first lap efficiency was 99.07%.

[0154] from Figure 27The charge-discharge curves at different rates show that the positive electrode of the battery corresponding to Example 1 has a first-cycle charging capacity of 108.57 mAh g at a current of 0.1C. -1 The corresponding discharge capacity is 104.92 mAh g. -1 Furthermore, the charge and discharge curves maintain a consistent shape under different current densities.

[0155] from Figure 28 The cyclic voltammetry curves show that at 0.1, 0.4, 0.8, and 1.6 mV s... -1 At the scan rate of [value], one oxidation peak and two reduction peaks can be clearly seen, corresponding to V [value]. 3+ / V 4+ and V 4+ / V 5+ Redox reactions.

[0156] from Figure 29 20m A g -1 The low-current cycling curves show that after 100 cycles, the reversible capacity of the positive electrode of the battery in Example 1 is 94.9 mAh g. -1 The corresponding capacity retention rate is 88.64%.

[0157] from Figure 30 2A g -1 The current cycling curves show that after 10,000 cycles, the reversible capacity of the positive electrode of the battery in Example 1 is 66.29 mAh g. -1 The corresponding capacity retention rate was 69.92%.

[0158] from Figure 31 The rate curves show that the average discharge capacities of the positive electrode of the battery in Example 1 at current densities of 0.1C, 0.5C, 1C, 2C, 5C, and 10C are 104.68, 99.62, 97.13, 94.63, 91.2, and 88.27 mAh g, respectively. -1 Compared to the capacity obtained at 0.1C, it retains 84.32% at 10C, and when the current density returns to 0.1C, its reversible capacity is 99.97 mAh g. -1 .

[0159] The following section uses the biphase hybrid cathode material obtained by simply mixing sodium vanadium phosphate and vanadium trioxide at a mass ratio of 9:1 in Comparative Example 4 for a certain period of time. This material was assembled into a half-cell, and its performance as a cathode in a sodium-ion battery was tested. The specific process is as follows:

[0160] The positive electrode material from Comparative Example 4 was mixed with acetylene black and polyvinylidene fluoride, and then added to N-methylpyrrolidone for magnetic stirring. After 24 hours, it was evenly coated on aluminum foil current collector and then transferred to a vacuum drying oven. It was first dried in an air oven at 70°C for 5 hours to remove most of the solvent, and then dried in a vacuum drying oven at 100°C for 10 hours. After the drying was completed, the electrode was taken out and cut into 12mm diameter round pieces and placed in a glove box. It was then assembled with a sodium sheet to form a half cell for testing.

[0161] Electrochemical performance testing of the sodium-ion battery cathode: The performance of the sodium-ion battery cathode obtained in Comparative Example 4 was tested using a constant current charge-discharge method. The test results are as follows: Figures 32-33 As shown.

[0162] from Figure 32 The charge-discharge curves show that the battery corresponding to Comparative Example 4 exhibits a significant capacity activation process after five charge-discharge cycles. The charge-discharge curves after activation are significantly different, which may be related to the activation of the sodium storage process by vanadium trioxide.

[0163] from Figure 33 The charge-discharge cycles show that the battery corresponding to Comparative Example 4 exhibits a significant capacity activation process after five charge-discharge cycles, with the highest activated charging capacity reaching 127.5 mAh g. -1 Its subsequent reversible discharge capacity is approximately 100 mAhg. -1 The average coulomb efficiency is approximately 93%.

[0164] The above description is merely a specific embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A sodium-ion battery cathode material, characterized in that, The cathode material has a core-shell structure. The core of the cathode material includes a first component and a second component. The first component is vanadium trioxide, and the second component includes sodium vanadium phosphate in which at least some vanadium sites are replaced by substituted metal elements. The shell of the cathode material includes carbon.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The second component includes: Na 3+ a M a V 2-a (PO4)3; where 0≤a≤1, and M includes divalent transition metal elements.

3. The sodium-ion battery cathode material according to claim 1, characterized in that, The vanadium trioxide comprises 5% to 15% of the mass of the cathode material.

4. The sodium-ion battery cathode material according to claim 1, characterized in that, The thickness of the shell is 5nm to 10nm.

5. A method for preparing a sodium-ion battery cathode material, characterized in that, The cathode material is the cathode material according to any one of claims 1 to 4; the method includes: A coexisting complex was obtained by dissolving a substituted metal source, a vanadium source, and a complexing agent in a solvent. The coexisting complex was mixed with a sodium source, then mixed with a phosphorus source, dried and ball-milled to obtain a powder; The powder is sintered to obtain a positive electrode material.

6. The method for preparing the sodium-ion battery cathode material according to claim 5, characterized in that, The substituted metal source includes at least one of ferrous acetylacetonate, ferrous acetate, and ferrous oxalate; and / or The vanadium source includes at least one of vanadium acetylacetonate and ammonium metavanadate; and / or The molar ratio of the substituted metal source and the vanadium source is (0-1):(1-2); and / or The complexing agent includes at least one of citric acid, oxalic acid, ethylenediamine, and ethylene glycol; and / or The molar ratio of the complexing agent to all metal elements in the cathode material is (1-3):1, based on the amount of substance; and / or The dissolution temperature is 80℃~100℃; and / or The dissolution process is accompanied by stirring, and the stirring rate is 300 r / min to 500 r / min.

7. The method for preparing the sodium-ion battery cathode material according to claim 5, characterized in that, The sodium source includes at least one of sodium acetate and sodium carbonate; and / or The phosphorus source is mixed by dropwise addition, with each dropwise addition not exceeding 0.02 mL; and / or The phosphorus source includes at least one of orthophosphoric acid and ammonium dihydrogen phosphate; and / or The drying temperature is 80℃~100℃, and the drying time is not less than 10 hours; and / or The ball milling speed is 300 r / min to 500 r / min, and the ball milling time is 1 h to 3 h.

8. The method for preparing the sodium-ion battery cathode material according to claim 5, characterized in that, The sintering temperature is 650℃~750℃; and / or The heating rate of the sintering process is 1℃ / min to 5℃ / min; and / or The holding time for the sintering treatment is 5h to 10h; and / or The atmosphere for the sintering process includes inert gas or nitrogen.

9. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 4.

10. A battery, characterized in that, The battery includes the positive electrode as described in claim 9.

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