A high-entropy phosphate sodium-ion battery cathode material, a preparation method and application thereof

Abstract

The application discloses a high-entropy phosphate sodium-ion battery positive electrode material and a preparation method and application thereof, relates to the technical field of battery materials, and has a chemical general formula of Na x (X y1 Q y2 )Mn y3 V y4 Ti y5 (PO4)3. The preparation method comprises the following steps: mixing a sodium source, an X source, a Q source, a manganese source, a vanadium source, a titanium source, a phosphorus source, a chelating agent and a dispersing agent step by step, then heating to evaporate water to obtain a gel, and then drying, grinding and step-by-step calcining under an inert atmosphere to obtain the high-entropy phosphate sodium-ion battery positive electrode material. The high-entropy phosphate sodium-ion battery positive electrode material prepared by the application has good electronic conductivity, strong ion diffusion capacity, high specific capacity and stable structure, can reduce the use of toxic and noble metals, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a high-entropy sodium phosphate battery cathode material, its preparation method, and its application. Background Technology

[0002] Currently, mainstream lithium-ion batteries suffer from problems such as uneven distribution of lithium resources, unstable price fluctuations, and explosion safety hazards. Sodium-ion batteries, as an emerging energy storage technology, are gradually becoming a research and industrialization hotspot due to their unique advantages and broad application prospects. Compared with lithium-ion batteries, sodium-ion batteries have similar working principles, structures, and processes, and also have advantages such as wider raw material distribution, lower cost, less susceptibility to overheating and overcharging, and higher safety performance, making them a potential important supplement to large-scale energy storage and a next-generation energy storage technology. Polyanionic sodium phosphate batteries, as a major popular category, have attracted widespread attention. Their structure consists of [PO4]. 4- Formed by connecting polyhedra with transition metal polyhedra at common vertices, it has a wide three-dimensional open channel, providing a transport path for sodium ions. The strong covalent bond network also ensures its good thermal and mechanical stability.

[0003] However, existing polyanionic sodium phosphate battery cathode materials also suffer from drawbacks such as low intrinsic conductivity, slow ion diffusion rate, and low specific capacity. Furthermore, vanadium-based materials, which have superior performance and are relatively well-developed, still have issues related to the use of large amounts of precious metals and their high toxicity. Summary of the Invention

[0004] The purpose of this invention is to address the problems of low intrinsic conductivity, slow ion diffusion rate, low specific capacity, excessive use of precious metals, and high toxicity in existing polyanionic sodium phosphate battery cathode materials. This invention introduces a high-entropy strategy, providing a new approach and method for solving these problems. The high-entropy phosphate cathode material of this invention uses five or more metal ions to occupy crystal sites to form a solid solution phase. Through the synergistic effect of multiple transition metal elements and the superposition of redox reactions, ion diffusion capability is enhanced, and specific capacity is increased. Simultaneously, by controlling the element ratio, the high-entropy effect and hysteresis effect are utilized to suppress phase transitions, stabilize the structure, and effectively improve the electrochemical performance of the material.

[0005] To achieve the above objectives, this invention provides a high-entropy sodium phosphate battery cathode material, its preparation method, and its application, specifically:

[0006] Firstly, a high-entropy sodium phosphate battery cathode material is provided, with the general chemical formula Na. x (X y1 Q y2 Mn y3 Vy4 Ti y5 (PO4)3, where X and Q are one of Fe, Al, Ni, Co, Cu, Zn, Ca, and Zr, and X and Q are different metallic elements, 1 ≤ x ≤4, y 1. y 2. y 3. y 4. y All 5 values ​​are between 0.1 and 1.

[0007] Secondly, a method for preparing a high-entropy sodium phosphate battery cathode material is provided, including the following steps:

[0008] (1) Weigh out the sodium source, X source, Q source, manganese source, vanadium source, titanium source and phosphorus source respectively according to the predetermined molar ratio in the general chemical formula;

[0009] (2) Mix the vanadium source, chelating agent and water, heat and stir until homogeneous to obtain solution ①;

[0010] (3) Mix the X source, Q source, manganese source and phosphorus source with water at room temperature to obtain solution ②;

[0011] (4) Mix the sodium source with water and stir until homogeneous at room temperature to obtain solution ③;

[0012] (5) Dissolve the titanium source in the dispersant and stir and mix evenly at room temperature to obtain solution ④;

[0013] (6) Under heating and stirring conditions, mix solutions ① and ②, then slowly add solution ③, and finally add solution ④ drop by drop, while keeping the heating and stirring on until the water evaporates to obtain a gel;

[0014] (7) The gel obtained in step (6) is dried and ground to obtain precursor powder;

[0015] (8) The precursor powder obtained in step (7) is placed in a tube furnace and calcined in an inert atmosphere to obtain a high-entropy sodium phosphate battery cathode material.

[0016] Preferably, in step (2), the heating temperature is 60~90℃ and the heating time is 3~10h.

[0017] Preferably, in step (2), the ratio of the number of moles of the added chelating agent to the sum of the number of moles of the X source, Q source, manganese source, vanadium source and titanium source is 2~4:2.

[0018] This invention is based on theoretical design, and the vanadium in the cathode material should be trivalent. Step (2) prioritizes the treatment of vanadium sources containing oxyacid salts. By reducing the high-valence vanadium source with reducing agents such as citric acid or glucose, the material is ensured to match the designed valence state, while avoiding subsequent electron exchange and redox reactions with other low-valence transition metal ions such as manganese and cobalt.

[0019] Preferably, in step (5), the dispersant is one of anhydrous ethanol or 0.1~1 mol / L dilute sulfuric acid.

[0020] Since commonly used metal alkoxide titanium sources are prone to rapid hydrolysis when in direct contact with water, resulting in TiO2 precipitation, the titanium is unevenly distributed or remains attached to the container, causing losses and errors. Step (5) first disperses the titanium source in a dispersant to avoid the above-mentioned losses and errors.

[0021] Preferably, in step (6), the heating temperature is 60~90℃.

[0022] The separate treatment of the sodium source in step (4) and its slow addition in step (6) are to prevent rapid mixing from causing excessively high local pH, which would make iron ions and other substances react rapidly in an alkaline environment to produce precipitation and oxidation. This is especially important when using sodium sources with strong alkalinity, such as sodium carbonate and sodium hydroxide.

[0023] Preferably, in step (7), the drying conditions are: in a vacuum environment, the drying temperature is 80~150℃ and the drying time is 10~24h.

[0024] Preferably, in step (8), calcination is divided into two stages: low-temperature pre-calcination and high-temperature sintering; the temperature of low-temperature pre-calcination is 300~500℃ and the time is 3~5h; the temperature of high-temperature sintering is 600~800℃ and the time is 8~20h; the heating rate is 1~10℃ / min; the inert gas is one of hydrogen-argon mixture, argon, and nitrogen.

[0025] Preferred,

[0026] The vanadium source is one of vanadium sulfate, vanadium acetylacetonate, vanadium oxalate, and ammonium metavanadate.

[0027] The titanium source is one of tetrabutyl titanate, isopropyl titanate, or titanium sulfate;

[0028] The sodium source is one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium acetate, or sodium sulfate.

[0029] The X source, Q source, and manganese source are all one of the following: carbonate, halide, nitrate, acetate, phosphate, sulfate, oxyacid salt, or metal alkoxide of the corresponding metal element.

[0030] The phosphorus source is one of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, or phosphoric acid;

[0031] The chelating agent is one of citric acid, glucose, ascorbic acid, or oxalic acid.

[0032] Thirdly, the present invention applies the above-mentioned high-entropy sodium phosphate battery cathode material to the preparation of sodium-ion batteries.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The V and Mn in the high-entropy sodium phosphate battery cathode material prepared by the present invention can provide multiple redox centers, improve electronic conductivity, and increase material capacity; Ti can improve electronic conductivity and stabilize crystal structure, suppress lattice distortion and capacity decay caused by Jahn-Teller effect of Mn element; On the basis of V, Mn and Ti, the introduction of active variable valence metals such as Fe and Co can further increase redox centers, improve material capacity and rate performance, and the introduction of non-variable valence metals such as Al and Cu is conducive to stabilizing crystal structure, enhancing cycle performance and service life.

[0035] (2) By introducing and controlling the proportion of five different transition metal elements, the present invention realizes a high-entropy strategy, and utilizes the high-entropy thermodynamic effect and kinetic hysteresis effect of high-entropy materials to enhance the stability of the crystal structure and improve the electrochemical performance of the materials.

[0036] (3) By performing stepwise pretreatment on the raw materials, this invention ensures the stability of the valence state of vanadium, avoids the hydrolysis of titanium, ensures the uniformity and stability of the material, allows for flexible composition ratios, reduces the use of toxic precious metals, and obtains a high-entropy sodium phosphate battery cathode material with excellent performance, providing new support for the practical application of sodium ion batteries.

[0037] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0038] Figure 1 The image shows the XRD pattern of the high-entropy sodium phosphate battery cathode material prepared in Example 1.

[0039] Figure 2 This is a SEM image of the high-entropy sodium phosphate battery cathode material prepared in Example 1;

[0040] Figure 3 This is a cycle performance test diagram of the high-entropy sodium phosphate battery cathode material prepared in Example 1;

[0041] Figure 4This is a comparison chart of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Example 1;

[0042] Figure 5 This is a comparison chart of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Example 2;

[0043] Figure 6 This is a comparison chart of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Example 3;

[0044] Figure 7 This is a comparison chart of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Example 4;

[0045] Figure 8 This is a comparison chart of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Example 5;

[0046] Figure 9 This is a comparison chart of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Example 6;

[0047] Figure 10 This is a comparison chart of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Example 7;

[0048] Figure 11 Comparison of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Comparative Example 1;

[0049] Figure 12 Comparison of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Comparative Example 2;

[0050] Figure 13 This is a comparison chart of charge-discharge tests of the high-entropy sodium phosphate battery cathode material prepared in Comparative Example 3. Detailed Implementation

[0051] The present invention will be further described below. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the present invention is not limited to this embodiment.

[0052] Example 1

[0053] This embodiment provides a method for preparing a high-entropy sodium phosphate battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na3Al. 0.3 Ni 0.3 Mn 0.3 V 0.3 Ti 0.8 (PO4)3, the preparation method includes the following steps:

[0054] (1) Weigh sodium acetate, aluminum nitrate, nickel acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid according to the molar ratio of 3:0.3:0.3:0.3:0.3:0.8:3:3; the total molar ratio of the added citric acid to aluminum nitrate, nickel acetate, manganese acetate, ammonium metavanadate, and tetrabutyl titanate is 3:2;

[0055] (2) Pretreatment of ammonium metavanadate: Ammonium metavanadate, citric acid and water are mixed, with a mass ratio of ammonium metavanadate to water of 1:100. The mixture is heated and stirred at 60°C to obtain solution ①.

[0056] (3) Add other metal sources (aluminum nitrate, nickel acetate, manganese acetate) and ammonium dihydrogen phosphate (excluding ammonium metavanadate and tetrabutyl titanate) to water. The mass ratio of the sum of the other metal sources to the mass of water is 1:30. Stir and mix evenly at room temperature to obtain solution ②.

[0057] (4) Mix sodium acetate with water at a mass ratio of 1:30 and stir until homogeneous at room temperature to obtain solution ③;

[0058] (5) Add tetrabutyl titanate to anhydrous ethanol. The volume ratio of tetrabutyl titanate to water is 1:30. Stir and mix evenly at room temperature to obtain a uniformly dispersed solution ④.

[0059] (6) Raise the heating temperature to 80°C, mix solution ① and solution ②, then slowly add solution ③, and finally add solution ④ drop by drop, while keeping the heating and stirring until the water evaporates to obtain a gel;

[0060] (7) The gel obtained in step (6) is placed in a vacuum drying oven and heated to 120°C for drying for 15 hours to remove moisture and volatile substances. After grinding, the precursor powder is obtained.

[0061] (8) The powder material obtained in step (7) is placed in a tube furnace and calcined by introducing a hydrogen-argon mixture (Ar:H2=95:5). The heating rate is 3℃ / min. The temperature is kept at 350℃ for 4h, then raised to 650℃ and kept for 12h to allow the material to react and fuse. Finally, the material is cooled with the furnace to obtain the high-entropy sodium phosphate battery cathode material.

[0062] Example 2

[0063] This embodiment provides a method for preparing a high-entropy sodium phosphate battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na. 3.6 Fe 0.4 Ni 0.4 Mn 0.4 V 0.4 Ti 0.4The preparation method of (PO4)3 differs from that in Example 1 in that:

[0064] Step (1) Weigh sodium acetate, ferric nitrate, nickel acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid according to the molar ratio of 3.6:0.4:0.4:0.4:0.4:0.4:3:3; the total molar ratio of the added citric acid to ferric nitrate, nickel acetate, manganese acetate, ammonium metavanadate, and tetrabutyl titanate is 3:2.

[0065] The other steps are the same as in Example 1.

[0066] Example 3

[0067] This embodiment provides a method for preparing a high-entropy sodium phosphate battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na. 3.4 Ni 0.4 Co 0.4 Mn 0.4 V 0.4 Ti 0.4 The preparation method of (PO4)3 differs from that in Example 1 in that:

[0068] Step (1) Weigh sodium acetate, cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid according to the molar ratio of 3.4:0.4:0.4:0.4:0.4:0.4:3:3; the total molar ratio of the added citric acid to cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, and tetrabutyl titanate is 3:2.

[0069] The other steps are the same as in Example 1.

[0070] Example 4

[0071] This embodiment provides a method for preparing a high-entropy sodium phosphate battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na. 3.4 Ni 0.3 Co 0.3 Mn 0.3 V 0.3 Ti 0.8 The preparation method of (PO4)3 differs from that in Example 1 in that:

[0072] Step (1) Weigh sodium acetate, cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid according to the molar ratio of 3.4:0.3:0.3:0.3:0.3:0.8:3:3; the total molar ratio of the added citric acid to cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, and tetrabutyl titanate is 3:2.

[0073] The other steps are the same as in Example 1.

[0074] Example 5

[0075] This embodiment provides a method for preparing a high-entropy sodium phosphate battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na. 3.4 Ni 0.3 Co 0.3 Mn 0.3 V 0.8 Ti 0.3 The preparation method of (PO4)3 differs from that in Example 1 in that:

[0076] Step (1) Weigh sodium acetate, cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid according to the molar ratio of 3.4:0.3:0.3:0.3:0.8:0.3:3:3; the total molar ratio of the added citric acid to cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, and tetrabutyl titanate is 3:2.

[0077] The other steps are the same as in Example 1.

[0078] Example 6

[0079] This embodiment provides a method for preparing a high-entropy sodium phosphate battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na. 3.8 Ni 0.4 Co 0.4 Mn 0.4 V 0.4 Ti 0.4 The preparation method of (PO4)3 differs from that in Example 1 in that:

[0080] Step (1) Weigh sodium acetate, cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid respectively according to the molar ratio of 3.8:0.4:0.4:0.4:0.4:0.4:3:3; the total molar ratio of the added citric acid to cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, and tetrabutyl titanate is 3:2.

[0081] The other steps are the same as in Example 1.

[0082] Example 7

[0083] This embodiment provides a method for preparing a high-entropy sodium phosphate battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na. 3.4 Al 0.3 Ni 0.3 Mn 0.3 V 0.3 Ti 0.8The preparation method of (PO4)3 differs from that in Example 1 in that:

[0084] Step (1) Weigh sodium acetate, cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid according to the molar ratio of 3.4:0.3:0.3:0.3:0.3:0.8:3:3; the total molar ratio of the added citric acid to cobalt acetate, nickel acetate, manganese acetate, ammonium metavanadate, and tetrabutyl titanate is 3:2.

[0085] The second stage of calcination in step (8) is at a temperature of 750°C.

[0086] The other steps are the same as in Example 1.

[0087] Comparative Example

[0088] Comparative Examples 1 and 2 are traditional Na3MnV(PO4)3 and Na, respectively. 3.5 MnV 0.5 Ti 0.5 The preparation of the (PO4)3 sodium-ion battery cathode material, in Comparative Example 3, involved direct mixing without following the predetermined steps; other steps were the same as in Example 1. Details are as follows:

[0089] Comparative Example 1

[0090] This comparative example provides a method for preparing a sodium-ion battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na3MnV(PO4)3, and the preparation steps are as follows:

[0091] (1) Weigh sodium acetate, manganese acetate, ammonium metavanadate, ammonium dihydrogen phosphate and citric acid respectively in a molar ratio of 3:1:1:3:3; the total molar ratio of citric acid to manganese acetate and ammonium metavanadate is 3:2;

[0092] (2) Pretreatment of ammonium metavanadate: Ammonium metavanadate, citric acid and water are mixed, with a mass ratio of ammonium metavanadate to water of 1:100. The mixture is stirred and mixed evenly under heating at 60°C to obtain solution ①.

[0093] (3) Add other metal sources (manganese acetate) and ammonium dihydrogen phosphate, except for ammonium metavanadate and tetrabutyl titanate, to water. The mass ratio of the sum of the other metal sources to the mass of water is 1:30. Stir and mix evenly at room temperature to obtain solution ②.

[0094] (4) Mix sodium acetate with water at a mass ratio of 1:30 and stir until homogeneous at room temperature to obtain solution ③;

[0095] (5) Raise the heating temperature to 80°C, mix solution ① and solution ②, then slowly add solution ③, keep heating and stirring until the water evaporates to obtain a gel;

[0096] (6) The gel obtained in step (5) is placed in a vacuum drying oven and heated to 120°C for drying for 15 hours to remove moisture and volatile substances. After grinding, the precursor powder is obtained.

[0097] (7) The powder material obtained in step (6) is placed in a tube furnace and calcined by introducing a hydrogen-argon mixture (Ar:H2=95:5). The heating rate is 3℃ / min. The temperature is kept at 350℃ for 4h, then raised to 650℃ and kept for 12h to allow the material to react and fuse. Finally, the material is cooled with the furnace to obtain the high-entropy sodium phosphate battery cathode material.

[0098] Comparative Example 2

[0099] This comparative example provides a method for preparing a sodium-ion battery cathode material, the molecular formula of which is Na. 3.5 MnV 0.5 Ti 0.5 The preparation method of (PO4)3 differs from that in Example 1 in that:

[0100] Step (1) Weigh sodium acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid in a molar ratio of 3.5:1:0.5:0.5:3:3; the molar ratio of citric acid to manganese acetate, ammonium metavanadate, and tetrabutyl titanate is 3:2.

[0101] The other steps are the same as in Example 1.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing a high-entropy sodium phosphate battery cathode material. The molecular formula of the high-entropy sodium phosphate battery cathode material is Na3Al. 0.3 Ni 0.3 Mn 0.3 V 0.3 Ti 0.8 (PO4)3, the preparation method includes the following steps:

[0104] (1) Sodium acetate, aluminum nitrate, nickel acetate, manganese acetate, ammonium metavanadate, tetrabutyl titanate, ammonium dihydrogen phosphate, and citric acid were weighed according to the molar ratio of 3:0.3:0.3:0.3:0.3:0.8:3:3 respectively; the total molar ratio of the added citric acid to aluminum nitrate, nickel acetate, manganese acetate, ammonium metavanadate, and tetrabutyl titanate was 3:2;

[0105] (2) Add the raw materials directly to water and mix them. The ratio of the total mass of the raw materials to the mass of the water is 1:200. Heat at 80°C until the water evaporates to obtain a gel.

[0106] (3) The gel obtained in step (2) is placed in a vacuum drying oven and heated to 120°C for drying for 15 hours to remove moisture and volatile substances. After grinding, the precursor powder is obtained.

[0107] (4) The powder material obtained in step (3) is placed in a tube furnace and calcined by introducing a hydrogen-argon mixture (Ar:H2=95:5). The heating rate is 3℃ / min. The temperature is kept at 350℃ for 4h, then raised to 650℃ and kept for 12h to allow the material to react and fuse. Finally, the material is cooled with the furnace to obtain the high-entropy sodium phosphate battery cathode material.

[0108] Characterization results

[0109] The sodium-ion battery cathode materials of the examples and comparative examples were characterized, and the characterization results are as follows:

[0110] from Figure 1 It can be seen that the high-entropy sodium phosphate battery cathode material prepared in Example 1 has a typical sodium superionic conductor structure.

[0111] from Figure 2 It can be seen that the high-entropy sodium phosphate battery cathode material prepared in Example 1 exhibits sheet-like particles.

[0112] from Figure 3 It can be seen that the high-entropy sodium phosphate battery cathode material prepared in Example 1 maintained 90% of its specific capacity after 200 cycles.

[0113] Preparation method of positive electrode sheet: Active material, conductive super carbon powder, and binder polyvinylidene fluoride (PVDF) are weighed sequentially in a mass ratio of 8:1:1. The active material and super carbon powder are first ground in a mortar and ground until uniformly mixed. Then, the mixture is added to a stirring flask along with the binder (PVDF) and N-methylpyrrolidone (N-methylpyrrolidone), and stirred for 50 minutes in a planetary stirrer to achieve a solid content of approximately 60%. The slurry is then coated onto aluminum foil using a coating machine and dried in a vacuum drying oven at 120°C for 12 hours. After natural cooling, it is removed to obtain the current collector. The current collector is then rolled several times using a roller press, and finally cut into circular positive electrode sheets matching the inner diameter of the battery casing using a stamping machine.

[0114] Battery assembly method: In an argon-filled glove box, assemble a CR2032 coin cell in the following order: negative electrode shell, electrolyte, positive electrode plate, separator, counter electrode, gasket, spring, and positive electrode shell. Use a sodium metal plate as the counter electrode and a 1M NaClO4 / EC:DMC (V / V=1:1) solution as the electrolyte. Then place the battery in a 30℃ constant temperature test chamber and let it stand for 24 hours before testing.

[0115] Electrochemical performance testing method: The assembled CR2032 button cell was placed in the CT2001A Wuhan Landian Battery Testing System for testing. The charge and discharge cutoff voltage was 1.5~4.5V (vs. Na+ / Na).

[0116] from Figures 4-13 As can be seen, the design of different element types and proportions has different effects on the specific capacity of the charge-discharge platform and the cathode material. The specific capacity of the comparative and embodiment examples is shown in Table 1.

[0117] Table 1. Electrochemical performance test results of the examples and comparative examples.

[0118]

[0119] Examples 1 and 7 introduced Al and Ni. Compared with Comparative Examples 1 and 2, the plateau was more obvious and gentler. With the reduction of the use of V and Mn, two metals with variable valence, the crystal structure and valence distribution were optimized by relying on the high entropy effect, which improved the specific capacity of the material. The calcination temperatures of Examples 1 and 7 were 650℃ and 750℃, respectively. The plateaus of the two were similar, with the capacity being slightly higher at 750℃.

[0120] Compared with Comparative Example 3, the sodium-ion battery cathode material prepared by mixing according to the steps described in this invention in Example 1 has a higher specific capacity and is more in line with the theoretical design than that prepared by directly mixing in Comparative Example 3.

[0121] Examples 2, 3, 4, 5, and 6 introduce Fe, Ni, and Co, and adjust different sodium ion ratios to maintain valence equilibrium. The introduction of these high-valence variable metals enhances the electronic conductivity of the sodium-ion battery cathode material, which is based on the different redox pairs of Fe, Ni, and Co at different voltages. This gives the sodium-ion battery cathode material more or a wider platform, further improving the specific capacity of the sodium-ion battery cathode material.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high-entropy sodium phosphate battery cathode material, characterized in that: The cathode material of the high-entropy sodium phosphate battery is Na. 3.4 Ni 0.3 Co 0.3 Mn 0.3 V 0.3 Ti 0.8 (PO4)3 or Na 3.4 Al 0.3 Ni 0.3 Mn 0.3 V 0.3 Ti 0.8 (PO4)3; The preparation method of the high-entropy sodium phosphate battery cathode material includes the following steps: (1) Weigh out the sodium source, cobalt source, aluminum source, nickel source, manganese source, vanadium source, titanium source and phosphorus source respectively according to the predetermined molar ratio in the general chemical formula; The vanadium source is one of vanadium oxysulfate, vanadium acetylacetonate, vanadium oxalate, and ammonium metavanadate; the titanium source is one of tetrabutyl titanate, isopropyl titanate, and titanium sulfate; the sodium source is one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium acetate, and sodium sulfate; the cobalt, aluminum, nickel, and manganese sources are all one of the carbonates, halides, nitrates, acetates, phosphates, sulfates, and metal alkoxides of the corresponding metal elements; the phosphorus source is one of sodium dihydrogen phosphate, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, and phosphoric acid; and the chelating agent is one of citric acid, glucose, ascorbic acid, and oxalic acid. (2) Mix the vanadium source, chelating agent and water, heat and stir until homogeneous to obtain solution ①; the heating temperature is 60~90℃ and the heating time is 3~10h; (3) Mix cobalt or aluminum, nickel, manganese and phosphorus sources with water at room temperature to obtain solution ②; the ratio of the number of moles of the added chelating agent to the sum of the number of moles of cobalt or aluminum, nickel, manganese, vanadium and titanium sources is 2~4:2; (4) Mix the sodium source with water and stir until homogeneous at room temperature to obtain solution ③; (5) Dissolve the titanium source in the dispersant and stir and mix evenly at room temperature to obtain solution ④; (6) Under heating and stirring conditions, mix solutions ① and ②, then slowly add solution ③, and finally add solution ④ drop by drop, while keeping the heating and stirring on until the water evaporates to obtain a gel; (7) The gel obtained in step (6) is dried and ground to obtain precursor powder; (8) The precursor powder obtained in step (7) is placed in a tube furnace and calcined in an inert atmosphere to obtain a high-entropy sodium phosphate battery cathode material.

2. The method for preparing the high-entropy sodium phosphate battery cathode material according to claim 1, characterized in that: In step (5), the dispersant is one of anhydrous ethanol or 0.1~1 mol / L dilute sulfuric acid.

3. The method for preparing the high-entropy sodium phosphate battery cathode material according to claim 1, characterized in that: In step (6), the heating temperature is 60~90℃.

4. The method for preparing the high-entropy sodium phosphate battery cathode material according to claim 1, characterized in that: In step (7), the drying conditions are: in a vacuum environment, the drying temperature is 80~150℃ and the drying time is 10~24h.

5. The method for preparing the high-entropy sodium phosphate battery cathode material according to claim 1, characterized in that: In step (8), calcination is divided into two stages: low-temperature pre-calcination and high-temperature sintering. The temperature of low-temperature pre-calcination is 300~500℃ and the time is 3~5h. The temperature of high-temperature sintering is 600~800℃ and the time is 8~20h. The heating rate of the calcination process is 1~10℃ / min. The inert gas is one of hydrogen-argon mixture, argon, and nitrogen.

6. A high-entropy sodium phosphate ion battery cathode material, characterized in that, It was prepared using the method for preparing high-entropy sodium phosphate battery cathode material as described in any one of claims 1 to 5.

7. The application of the high-entropy sodium phosphate battery cathode material according to claim 6, characterized in that: High-entropy sodium phosphate battery cathode material is applied in the preparation of sodium-ion batteries.

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