A manganese-rich vacancy sodium manganese vanadium phosphate cathode material, its preparation method and application

Abstract

This invention relates to the field of sodium-ion battery cathode materials, and particularly to a manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, its preparation method, and its application. The manganese-vacancy-rich sodium manganese vanadium phosphate cathode material comprises a cathode material and a carbon coating layer on the surface of the cathode material, wherein the carbon coating layer accounts for 3%-15% of the mass of the manganese-vacancy-rich sodium manganese vanadium phosphate cathode material; the general chemical formula of the cathode material is: Na₄VMn. 1‑x‑y □ x HEA y (PO4)3, 0.1≤x≤0.5, 0<y≤0.3, □ represents manganese vacancies; HEA is a high-entropy alloy, including at least five of Co, Ni, Cu, Zn, Mg, Ca, Al, K, Na, Zr, Ti, Cr, Y, Nb, Mo, Ru, and Cd. This invention, based on the synergistic design of manganese-rich vacancies and high-entropy alloy doping, significantly improves the sodium ion diffusion kinetics, specific capacity, rate performance, and cycle stability of sodium manganese vanadium phosphate cathode material.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials, and in particular to a manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, with their abundant and inexpensive sodium resources, good fast-charging performance, and low-temperature performance, have become an effective complementary technology to lithium-ion batteries in recent years, showing great application potential in low-speed electric vehicles and large-scale energy storage. Currently, there are three main technical routes for sodium-ion battery cathode materials: layered oxides, Prussian blue compounds, and polyanionic compounds. Compared to layered oxides and Prussian blue compounds, polyanionic compounds exhibit higher structural stability, thermal stability, and safety, making them more promising for applications in low-speed electric vehicles and energy storage. Sodium manganese vanadium phosphate (Na4VMn(PO4)3), as one of the representative materials of sodium superionic conductors, possesses a high operating voltage (~3.5V), three-dimensional ion diffusion channels, and excellent structural stability, and is considered one of the most promising cathode materials for the industrial application of sodium-ion batteries. However, this cathode material suffers from low intrinsic electronic conductivity, limited ion diffusion kinetics, and the presence of Mn... 3+ Key issues such as Jahn-Teller distortion lead to problems such as large crystal structure strain (~10%), low specific capacity, poor rate performance and short cycle life.

[0003] To address the above issues, most strategies involve carbon coating and doping to improve electronic conductivity and ion diffusion kinetics. However, these methods do not significantly improve the structural strain of the crystal structure, and the cycle stability is mostly below 1000 cycles, far from meeting the long lifespan requirements of commercial energy storage batteries. Recently, the transition metal vacancy strategy has been proposed to not only broaden sodium ion transport channels and reduce sodium ion diffusion barriers but also effectively suppress structural strain. However, high manganese vacancy content inevitably leads to structural collapse, rapid capacity decay, and short cycle life. Summary of the Invention

[0004] The purpose of this invention is to provide a manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, its preparation method, and its application, effectively solving the defects faced by high-manganese-vacancy-rich sodium manganese vanadium phosphate cathode materials in practical applications, such as structural instability, rapid capacity decay, and poor rate performance.

[0005] To achieve the above objectives, the present invention provides a manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, comprising a cathode material and a carbon coating layer on the surface of the cathode material, wherein the carbon coating layer accounts for 3%-15% of the mass of the manganese-vacancy-rich sodium manganese vanadium phosphate cathode material;

[0006] The general chemical formula of the cathode material is: Na₄VMn1-x-y □ x HEA y (PO4)3, where 0.1≤x≤0.5, 0<y≤0.3, and □ represents manganese vacancies;

[0007] HEA is a high-entropy alloy, which includes at least five of the following: Co, Ni, Cu, Zn, Mg, Ca, Al, K, Na, Zr, Ti, Cr, Y, Nb, Mo, Ru, and Cd.

[0008] In this invention, Na4VMn 1-x-y □ x HEA y In (PO4)3, y represents the sum of the molar amounts of all elements in the HEA high-entropy alloy.

[0009] In this invention, the elemental composition of the HEA high-entropy alloy is preferably Mg, Ni, Zn, Cu, Ca; Al, K, Mg, Zr, Na; Mg, Ca, Zr, Al, Cu; Mo, Ni, Cu, Ca, Ti.

[0010] In this invention, the valence states of Co, Ni, Cu, Zn, Mg, Ca, Al, K, Na, Zr, Ti, Cr, Y, Nb, Mo, Ru, and Cd in the HEA high-entropy alloy are preferably +2, ...

[0011] This invention also provides a method for preparing the above-mentioned manganese-rich vacancy sodium manganese vanadium phosphate cathode material, comprising the following preparation steps:

[0012] S1. Sodium source, vanadium source, manganese source, HEA source, phosphorus source, carbon source, organic complexing agent and water are mixed and esterified to obtain a sol-gel system. After drying, a carbon-coated precursor is obtained.

[0013] S2. The carbon-coated precursor is ball-milled to obtain carbon-coated precursor powder. Under a protective atmosphere, the carbon-coated precursor powder is calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

[0014] In this invention, the sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, sodium acetate, sodium oxalate, and sodium fluoride.

[0015] The vanadium source includes at least one of vanadium pentoxide, vanadium trioxide, ammonium metavanadate, vanadium oxysulfate, vanadium oxyoxate, and vanadium dioxide.

[0016] In this invention, the manganese source includes at least one of manganese acetate, manganese oxalate, manganese carbonate, manganese dioxide, manganese tetroxide, manganese nitrate, and manganese acetylacetone.

[0017] The phosphorus source includes at least one of the following: ammonium dihydrogen phosphate, phosphoric acid, trisodium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

[0018] In this invention, the carbon source includes one or two of sucrose, citric acid, glucose, starch, polyvinylpyrrolidone, and polyethylene glycol.

[0019] The organic complexing agent includes one or two of ethylenediaminetetraacetic acid, oxalic acid, citric acid, tartaric acid, and aminotriacetic acid. The molar ratio of the organic complexing agent to the total molar ratio of transition metal elements in the cathode material is 0.3-3:1.

[0020] In this invention, the carbon source is a carbon source containing hydroxyl groups, which reacts with an organic complexing agent to form a uniform carbon coating layer.

[0021] In this invention, the HEA source includes compounds corresponding to at least five elements selected from Co, Ni, Cu, Zn, Mg, Ca, Al, K, Na, Zr, Ti, Cr, Y, Nb, Mo, Ru, and Cd;

[0022] The types of compounds include at least one of acetate, nitrate, oxalate, acetylacetone, hydroxide, and oxide.

[0023] In this invention, in the HEA source, the compound of element K is preferably a nitrate, more preferably potassium nitrate; the compound of element Mg is preferably a nitrate, more preferably magnesium nitrate; the compound of element Al is preferably a nitrate, more preferably aluminum nitrate; the compound of element Na is preferably an acetate, more preferably sodium acetate; the compound of element Zr is preferably a nitrate, more preferably zirconium oxynitrate; the compound of element Cu is preferably a nitrate, more preferably copper nitrate; the compound of element Ni is preferably a nitrate, more preferably nickel nitrate; and the compound of element Ca is preferably an acetate, more preferably calcium acetate.

[0024] In this invention, the esterification reaction time in S1 is 0.5-6h, the rotation speed of the esterification reaction is 200-600r / min, and the temperature of the esterification reaction is 60-100℃.

[0025] In this invention, the drying temperature in S1 is 60-120℃, and the drying time is 6-48h.

[0026] In this invention, the ball milling speed in S2 is 150-600 r / min, the ball milling time is 0.5-6 h, and the ball-to-material ratio in the ball milling is 3-20:1.

[0027] In this invention, the protective atmosphere in S2 includes argon, nitrogen, or an argon-hydrogen mixture. The argon-hydrogen mixture is a mixture of argon and hydrogen.

[0028] In this invention, the heating rate of the calcination treatment in S2 is 2-5℃ / min, the calcination temperature is 650-850℃, and the holding time of the calcination treatment is 4-12h.

[0029] This invention also provides the application of the above-mentioned manganese-vacancy-rich sodium manganese vanadium phosphate cathode material in sodium-ion batteries.

[0030] The present invention has the following beneficial effects:

[0031] This invention provides a manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, comprising a cathode material and a carbon coating layer on the surface of the cathode material, wherein the carbon coating layer accounts for 3%-15% of the mass of the manganese-vacancy-rich sodium manganese vanadium phosphate cathode material; the general chemical formula of the cathode material is: Na₄VMn 1-x-y □ x HEA y (PO4)3, where 0.1≤x≤0.5, 0<y≤0.3, and □ represents manganese vacancies; HEA is a high-entropy alloy, and HEA includes at least five of the following: Co, Ni, Cu, Zn, Mg, Ca, Al, K, Na, Zr, Ti, Cr, Y, Nb, Mo, Ru, and Cd.

[0032] This invention significantly improves the structural stability and cycle life (capacity retention of up to 95.0% after 3500 cycles) of manganese vacancy sodium manganese vanadium phosphate cathode material by constructing manganese vacancies and high-entropy alloys at transition metal sites. Experiments show that the capacity retention of the manganese vacancy sodium manganese vanadium phosphate cathode material provided by this invention is more than 7 times higher than that of ordinary Na4VMn(PO4)3 cathode material. This invention yields a high-stability and high-rate-capacity manganese vacancy sodium manganese vanadium phosphate cathode material, laying a solid theoretical and experimental foundation for its practical application.

[0033] This invention not only solves the problems of low electronic conductivity and slow ion diffusion kinetics in sodium manganese vanadium phosphate (SMP) cathode materials, but also addresses key issues encountered in practical applications of SMP cathode materials with high concentrations of manganese vacancies, such as structural instability, rapid capacity decay, and poor rate performance. By synergistically constructing high-content manganese vacancies and high-entropy alloy doping, highly efficient ion and electron transport in SMP cathode materials is achieved, significantly improving sodium ion diffusion kinetics, specific capacity, and rate performance, providing a new strategy for the development of high-power sodium-ion batteries.

[0034] This invention also provides a method for preparing the above-mentioned manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, comprising the following preparation steps: S1, mixing sodium source, vanadium source, manganese source, HEA source, phosphorus source, carbon source, organic complexing agent, and water, performing an esterification reaction to obtain a sol-gel system, and drying to obtain a carbon-coated precursor; S2, ball milling the carbon-coated precursor to obtain carbon-coated precursor powder, and calcining the carbon-coated precursor powder under a protective atmosphere to obtain the manganese-vacancy-rich sodium manganese vanadium phosphate cathode material.

[0035] This invention introduces an organic complexing agent to perform an atomic-scale chelation reaction of electrochemically active elements vanadium and manganese with elements in the HEA high-entropy alloy. The content of manganese vacancies and the composition of HEA elements are precisely controlled. A carbon source containing hydroxyl groups is selected. The degree of esterification reaction between the organic complexing agent and the carbon source is controlled by adjusting the temperature and time of the esterification reaction. Then, through steps such as ball milling and calcination, a manganese vacancy-rich sodium manganese vanadium phosphate cathode material with uniform carbon coating is prepared.

[0036] 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

[0037] Figure 1 These are the test results of scanning electron microscopy, transmission electron microscopy, and aberration-corrected transmission electron microscopy of the manganese-rich vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 of this invention.

[0038] in, Figure 1 In the image, 'a' represents a scanning electron microscope (SEM) image. Figure 1 In the image, b is a transmission electron microscope (TEM) image. Figure 1 In the image, c represents an aberration-corrected transmission electron microscope (AC-TEM) image.

[0039] Figure 2 These are the X-ray diffraction (XRD) patterns of the manganese-rich vacancy sodium manganese vanadium phosphate cathode materials prepared in Examples 1-4 of this invention and the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1.

[0040] Figure 3These are paramagnetic resonance (EPR) spectra of the manganese-rich vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 and the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1.

[0041] Figure 4 These are extended X-ray absorption fine structure (EXAFS) images of the manganese-rich vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 and the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1.

[0042] Figure 5 This is a charge-discharge curve of a battery assembled from the manganese-rich vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 at 0.1C.

[0043] Figure 6 This is a comparison chart of the rate performance of the batteries assembled in Example 1, Example 2, Example 4, and Comparative Example 1;

[0044] Figure 7 This is a comparison chart of the cycle performance of batteries assembled in Example 1, Example 2, Example 3, Example 4, and Comparative Example 1 at a 5C rate. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0046] Example 1

[0047] A manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, with the chemical formula: Na₄VMn 0.45 □ 0.45 Zr 0.0133 Na 0.0267 K 0.0 2Mg 0.02 Al 0.02 (PO4)3.

[0048] The preparation method of the above-mentioned manganese-rich vacancy sodium manganese vanadium phosphate cathode material includes the following preparation steps:

[0049] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 0.2 mmol potassium nitrate, 0.2 mmol magnesium nitrate, 0.2 mmol aluminum nitrate, 10.267 mmol sodium acetate, 4.5 mmol manganese acetate, 0.133 mmol zirconium oxynitrate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0050] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was held for 8 h and then calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

[0051] Example 2

[0052] A manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, with the chemical formula: Na₄VMn 0.6 □ 0.3 Zr 0.0133 Na 0.0267 K 0.02 Mg 0.02 Al 0.02 (PO4)3.

[0053] The preparation method of the above-mentioned manganese-rich vacancy sodium manganese vanadium phosphate cathode material includes the following preparation steps:

[0054] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 0.2 mmol potassium nitrate, 0.2 mmol magnesium nitrate, 0.2 mmol aluminum nitrate, 10.267 mmol sodium acetate, 6 mmol manganese acetate, 0.133 mmol zirconium oxynitrate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0055] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was held for 8 h and then calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

[0056] Example 3

[0057] A manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, with the chemical formula: Na₄VMn 0.7 □ 0.2 Zr 0.0133 Na 0.0267 K 0.02 Mg 0.02 Al 0.02 (PO4)3.

[0058] The preparation method of the above-mentioned manganese-rich vacancy sodium manganese vanadium phosphate cathode material includes the following preparation steps:

[0059] S1. 30 mmol citric acid, 2 mmol sucrose, 10 mmol ammonium metavanadate, 0.2 mmol potassium nitrate, 0.2 mmol magnesium nitrate, 0.2 mmol aluminum nitrate, 10.267 mmol sodium acetate, 7 mmol manganese acetate, 0.133 mmol zirconium oxynitrate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0060] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was held for 8 h and then calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

[0061] Example 4

[0062] A manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, with the chemical formula: Na₄VMn 0.8 □ 0.1 Zr 0.0133 Na 0.0267 K 0.02 Mg 0.02 Al 0.02 (PO4)3.

[0063] The preparation method of the above-mentioned manganese-rich vacancy sodium manganese vanadium phosphate cathode material includes the following preparation steps:

[0064] S1. 30 mmol citric acid, 0.1 g polyethylene glycol, 10 mmol ammonium metavanadate, 0.2 mmol potassium nitrate, 0.2 mmol magnesium nitrate, 0.2 mmol aluminum nitrate, 10.267 mmol sodium acetate, 8 mmol manganese acetate, 0.133 mmol zirconium oxynitrate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0065] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was held for 8 h and then calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

[0066] Example 5

[0067] A manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, with the chemical formula: Na₄VMn 0.7 □ 0.2 Mg 0.02 Zn 0.02 Cu 0.02 Ni 0.02 Ca 0.02 (PO4)3.

[0068] The preparation method of the above-mentioned manganese-rich vacancy sodium manganese vanadium phosphate cathode material includes the following preparation steps:

[0069] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 0.2 mmol magnesium nitrate, 0.2 mmol zinc nitrate, 0.2 mmol copper nitrate, 0.2 mmol nickel nitrate, 0.2 mmol calcium acetate, 10 mmol sodium acetate, 7 mmol manganese acetate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0070] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was held for 8 h and then calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

[0071] Example 6

[0072] A manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, with the chemical formula: Na₄VMn 0.6 □ 0.3 Mg 0.02 Zn 0.02 Cu 0.02 Ni 0.02 Ca 0.02 (PO4)3.

[0073] The preparation method of the above-mentioned manganese-rich vacancy sodium manganese vanadium phosphate cathode material includes the following preparation steps:

[0074] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 0.2 mmol magnesium nitrate, 0.2 mmol zinc nitrate, 0.2 mmol copper nitrate, 0.2 mmol nickel nitrate, 0.2 mmol calcium acetate, 10 mmol sodium acetate, 6 mmol manganese acetate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0075] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was held for 8 h and then calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

[0076] Example 7

[0077] A manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, with the chemical formula: Na₄VMn 0.6 □ 0.3 Mg 0.02 Zn 0.02 Cu 0.02 Ni 0.02 Ca 0.02 (PO4)3.

[0078] The preparation method of the above-mentioned manganese-rich vacancy sodium manganese vanadium phosphate cathode material includes the following preparation steps:

[0079] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 0.2 mmol magnesium nitrate, 0.2 mmol zinc nitrate, 0.2 mmol copper nitrate, 0.2 mmol nickel nitrate, 0.2 mmol calcium acetate, 10 mmol sodium acetate, 6 mmol manganese acetate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0080] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 700 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was held for 8 h and then calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

[0081] Comparative Example 1

[0082] The preparation of Na4VMn(PO4)3 cathode material includes the following steps:

[0083] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 10 mmol sodium acetate, 10 mmol manganese acetate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80℃ and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100℃ for 12 h to obtain a carbon-coated precursor.

[0084] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere. The temperature was held for 8 h and then calcined to obtain Na4VMn(PO4)3 cathode material.

[0085] Comparative Example 2

[0086] Preparation of Na4VMn 0.7 □ 0.3 (PO4)3 cathode material, comprising the following preparation steps:

[0087] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 10 mmol sodium acetate, 7 mmol manganese acetate, and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80℃ and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100℃ for 12 h to obtain a carbon-coated precursor.

[0088] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere, held at that temperature for 8 h, and then calcined to obtain Na4VMn. 0.7 □ 0.3 (PO4)3 cathode material.

[0089] Comparative Example 3

[0090] Preparation of Na4VMn 0.9 Zr 0.0133 Na 0.0267 K 0.02 Mg 0.02 Al 0.02 (PO4)3 cathode material, comprising the following preparation steps:

[0091] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 0.2 mmol potassium nitrate, 0.2 mmol magnesium nitrate, 0.2 mmol aluminum nitrate, 10.267 mmol sodium acetate, 9 mmol manganese acetate, 0.133 mmol zirconium oxynitrate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0092] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere, held at that temperature for 8 h, and then calcined to obtain Na4VMn. 0.9 Zr 0.0133 Na 0.0267 K 0.02 Mg 0.02 Al 0.02 (PO4)3 cathode material.

[0093] Comparative Example 4

[0094] Preparation of Na4VMn 0.8 □ 0.1 Mg 0.1 (PO4)3 cathode material, comprising the following preparation steps:

[0095] S1. 30 mmol citric acid, 2 mmol glucose, 10 mmol ammonium metavanadate, 1 mmol magnesium nitrate, 10 mmol sodium acetate, 8 mmol manganese acetate and 30 mmol sodium dihydrogen phosphate were added sequentially to deionized water and mixed. Then, the mixture was subjected to esterification reaction at 80 °C and 500 r / min for 3 h to obtain a sol-gel system. The sol-gel system was placed in a forced-air drying oven and dried at 100 °C for 12 h to obtain a carbon-coated precursor.

[0096] S2. The carbon-coated precursor was ball-milled at 500 r / min for 1 h (ball-to-material ratio of 10:1) to obtain carbon-coated precursor powder. The carbon-coated precursor powder was placed in a tube furnace and heated to 750 °C at a heating rate of 3 °C / min under an argon atmosphere, held at that temperature for 8 h, and then calcined to obtain Na4VMn. 0.8 □ 0.1 Mg 0.1 (PO4)3 cathode material.

[0097] Performance testing:

[0098] The manganese-rich vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 was tested by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and aberration-corrected transmission electron microscopy (AC-TEM). The results are as follows: Figure 1 As shown. From Figure 1 As can be seen from 'a' and 'b' in Example 2, the manganese-rich vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 consists of particles with a size of 500-600 nanometers. From... Figure 1 As can be seen from 'c' in Example 2, the bright spots of atoms in the lattice fringes of the manganese-vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 appear as dark areas. Combined with the signal intensity curve below, a significantly weakened peak intensity is found, proving the existence of vacancies.

[0099] The manganese-rich vacancy sodium manganese vanadium phosphate cathode materials prepared in Examples 1-4, and the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1, were subjected to X-ray diffraction (XRD) tests. The results are as follows: Figure 2 As shown. From Figure 2It can be seen that the main XRD diffraction peaks of the manganese-vacancy sodium manganese vanadium phosphate cathode materials prepared in Examples 1-4 and the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1 all correspond to the standard diffraction peaks of sodium manganese vanadium phosphate. However, a small number of impurity peaks were observed in the manganese-vacancy sodium manganese vanadium phosphate cathode materials prepared in Examples 1, 2, 3 and 4 at 26.4-33.2°. This may be due to the large number of manganese vacancies leading to a small amount of Na4P2O7 impurity phase.

[0100] The manganese-rich vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 and the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1 were tested by paramagnetic resonance spectroscopy (EPR). The results are as follows: Figure 3 As shown. From Figure 3 It can be seen that no obvious EPR signal peak was detected in the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1, while obvious EPR signal peaks were observed in the manganese-vacancy-rich sodium manganese vanadium phosphate cathode material prepared in Example 2, indicating that a large number of manganese vacancies exist in the manganese-vacancy-rich sodium manganese vanadium phosphate cathode material prepared in Example 2.

[0101] The manganese-rich vacancy sodium manganese vanadium phosphate cathode material prepared in Example 2 and the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1 were subjected to extended X-ray absorption fine structure (EXAFS) testing. The results are as follows: Figure 4 As shown. From Figure 4 It can be seen that, compared with the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1, the Fourier transform amplitude of the Mn-Mn bond in the manganese-vacant sodium manganese vanadium phosphate cathode material prepared in Example 2 is significantly reduced, further proving the presence of manganese vacancies in the manganese-vacant sodium manganese vanadium phosphate cathode material prepared in Example 2. Meanwhile, the Mn-Mn bond length in the manganese-vacant sodium manganese vanadium phosphate cathode material prepared in Example 2 is similar to the Mn-Mn bond length in the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1, while the Mn-O and Mn-Na / P bond lengths are significantly shortened, indicating that manganese vacancies reduce the lattice spacing and strengthen the interaction between Mn-O and Mn-Na / P bonds.

[0102] The manganese-rich vacancy sodium manganese vanadium phosphate cathode materials prepared in Examples 1, 2, 3, and 4, and the Na4VMn(PO4)3 cathode material prepared in Comparative Example 1, were used as active materials and assembled into coin cells for electrochemical performance testing. The specific process included:

[0103] The active material, conductive agent (Super P), and binder (polyvinylidene fluoride, PVDF) were mixed uniformly at a mass ratio of 7:2:1. N-methylpyrrolidone (NMP) was added dropwise as a dispersant, and the mixture was ground to form a fluid slurry. This slurry was coated onto aluminum foil and dried in a vacuum oven at 80°C. After drying, the slurry was removed and cut into 12mm diameter electrode sheets. Battery assembly was performed in a glove box under a high-purity argon atmosphere (H₂O < 0.1 ppm, O₂ < 0.1 ppm). A sodium metal sheet was used as the negative electrode, glass fiber as the separator, and a mixed solution of 1.0 mol / L sodium perchlorate (NaClO₄) and 5% polycarbonate (PC) as the electrolyte. The assembled batteries were placed in a 25°C constant-temperature battery test chamber for 12 hours, and then electrochemical performance tests were conducted within a voltage range of 2.3–3.9 V.

[0104] The battery prepared in Example 2 was subjected to constant current charge-discharge testing at 0.1C, and its first charge-discharge curve is shown below. Figure 5 As shown. From Figure 5 It can be seen that the first discharge capacity of the battery prepared in Example 2 with the manganese-rich vacancy sodium manganese vanadium phosphate cathode material is 90 mAh / g.

[0105] The batteries prepared in Examples 1, 2, and 4, and the battery prepared in Comparative Example 1, were subjected to rate performance tests, and the results are as follows: Figure 6 As shown. From Figure 6 It can be seen that at a rate of 0.5C, the manganese-vacancy-rich sodium manganese vanadium phosphate cathode material in Example 4 and the Na4VMn(PO4)3 cathode material in Comparative Example 1 exhibited higher capacity. With increasing rate, the capacity of the Na4VMn(PO4)3 cathode material in Comparative Example 1 decreased significantly, while the capacity decrease of the manganese-vacancy-rich sodium manganese vanadium phosphate cathode materials in Examples 1, 2, and 4 was more gradual. At 50C, the manganese-vacancy-rich sodium manganese vanadium phosphate cathode materials in Examples 1, 2, and 4, and the Na4VMn(PO4)3 cathode material in Comparative Example 1, exhibited discharge capacities of 59.0 mAh / g, 64.9 mAh / g, 52.6 mAh / g, and 4.6 mAh / g, respectively. The results indicate that the synergistic effect of high-concentration manganese vacancies and high-entropy alloys effectively broadens the sodium ion transport channels and reduces the sodium ion diffusion barrier, thereby improving its rate performance. However, excessively high manganese vacancy content is detrimental to sodium ion storage.

[0106] The batteries assembled from Examples 1, 2, 3, 4, and Comparative Example 1 were subjected to cycle performance testing at a 5C rate. The results are as follows: Figure 7 As shown. From Figure 7It can be seen that after 3500 cycles, the capacity retention rates of the manganese-vacancy-rich sodium manganese vanadium phosphate cathode materials in Examples 1, 2, 3, and 4 were 88.9%, 95.0%, 48.6%, and 34.3%, respectively, which are significantly better than those of Comparative Example 1, which has no vacancies or high-entropy alloy doping. The results show that the synergistic regulation of high-concentration manganese vacancies and high-entropy alloys can significantly improve the cycling stability of sodium manganese vanadium phosphate.

[0107] 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 manganese-vacancy-rich sodium manganese vanadium phosphate cathode material, characterized in that, It includes the cathode material and a carbon coating layer on the surface of the cathode material, with the carbon coating layer accounting for 3%-15% of the mass of the manganese-vacancy sodium manganese vanadium phosphate cathode material; The general chemical formula of the cathode material is: Na₄VMn 1-x-y □ x HEA y (PO4)3, where 0.1≤x≤0.5, 0<y≤0.3, and □ represents manganese vacancies; HEA is a high-entropy alloy, which includes at least five of the following: Co, Ni, Cu, Zn, Mg, Ca, Al, K, Na, Zr, Ti, Cr, Y, Nb, Mo, Ru, and Cd.

2. A method for preparing the manganese-rich vacancy sodium manganese vanadium phosphate cathode material according to claim 1, characterized in that, The preparation steps include the following: S1. Sodium source, vanadium source, manganese source, HEA source, phosphorus source, carbon source, organic complexing agent and water are mixed and esterified to obtain a sol-gel system. After drying, a carbon-coated precursor is obtained. S2. The carbon-coated precursor is ball-milled to obtain carbon-coated precursor powder. Under a protective atmosphere, the carbon-coated precursor powder is calcined to obtain manganese-vacancy sodium manganese vanadium phosphate cathode material.

3. The method for preparing the manganese-rich vacancy sodium manganese vanadium phosphate cathode material according to claim 2, characterized in that, Sodium sources include at least one of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, sodium acetate, sodium oxalate, and sodium fluoride; The vanadium source includes at least one of vanadium pentoxide, vanadium trioxide, ammonium metavanadate, vanadium oxysulfate, vanadium oxyoxate, and vanadium dioxide.

4. The method for preparing the manganese-rich vacancy sodium manganese vanadium phosphate cathode material according to claim 2, characterized in that, The manganese source includes at least one of manganese acetate, manganese oxalate, manganese carbonate, manganese dioxide, manganese tetroxide, manganese nitrate, and manganese acetylacetone. The phosphorus source includes at least one of the following: ammonium dihydrogen phosphate, phosphoric acid, trisodium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

5. The method for preparing the manganese-rich vacancy sodium manganese vanadium phosphate cathode material according to claim 2, characterized in that, Carbon sources include one or two of sucrose, citric acid, glucose, starch, polyvinylpyrrolidone, and polyethylene glycol; The organic complexing agent includes one or two of ethylenediaminetetraacetic acid, oxalic acid, citric acid, tartaric acid, and aminotriacetic acid. The molar ratio of the organic complexing agent to the total molar ratio of transition metal elements in the cathode material is 0.3-3:

1.

6. The method for preparing the manganese-rich vacancy sodium manganese vanadium phosphate cathode material according to claim 2, characterized in that, HEA sources include compounds corresponding to at least five of the elements selected from Co, Ni, Cu, Zn, Mg, Ca, Al, K, Na, Zr, Ti, Cr, Y, Nb, Mo, Ru, and Cd; The types of compounds include at least one of acetate, nitrate, oxalate, acetylacetone, hydroxide, and oxide.

7. The method for preparing the manganese-rich vacancy sodium manganese vanadium phosphate cathode material according to claim 2, characterized in that, The esterification reaction time in S1 is 0.5-6 hours, the rotation speed is 200-600 r / min, and the temperature is 60-100℃.

8. The method for preparing the manganese-rich vacancy sodium manganese vanadium phosphate cathode material according to claim 2, characterized in that, In S2, the ball mill speed is 150-600 r / min, the ball milling time is 0.5-6 h, and the ball-to-material ratio is 3-20:

1.

9. The method for preparing the manganese-rich vacancy sodium manganese vanadium phosphate cathode material according to claim 2, characterized in that, The heating rate of the calcination treatment in S2 is 2-5℃ / min, the calcination temperature is 650-850℃, and the holding time of the calcination treatment is 4-12h.

10. The application of the manganese-vacancy-rich sodium manganese vanadium phosphate cathode material as described in claim 1 in sodium-ion batteries.

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