Preparation method and application of low-vanadium high-entropy sodium vanadium phosphate sodium positive electrode material

Abstract

The application discloses a low-vanadium high-entropy sodium vanadium phosphate positive electrode material and a preparation method and application thereof, and belongs to the field of energy storage. The application successfully prepares a positive electrode material with low vanadium content, excellent rate performance and long cycle stability through a simple process. Through titanium and multi-element high-entropy element synergistic doping, the content of vanadium element is successfully reduced by 50%, while the cost and environmental toxicity of the material are significantly reduced, the titanium active site compensates for the capacity loss, and the multi-element synergistic effect activates the high-potential V 4+ / V 5+ Oxidation-reduction reaction, enhances structural stability, and gives the material excellent rate performance and long cycle life. The method is simple, efficient and has high yield, and has good large-scale prospect. Compared with the traditional sodium vanadium phosphate material, the material greatly reduces the dependence on the toxic metal vanadium of high valence while maintaining the comprehensive electrochemical performance, and the capacity retention rate at high rate can be relatively improved by 50%.

Description

Technical Field

[0001] This invention relates to a method for preparing and applying a low-vanadium, high-entropy sodium vanadium phosphate cathode material, belonging to the field of energy storage. Background Technology

[0002] The non-renewable nature of traditional fossil fuels and the continuous growth in modern society's energy demand have jointly driven the rapid development of sustainable, low-cost, and highly safe battery energy storage technologies. In recent years, with the widespread adoption of new energy vehicles and large-scale energy storage devices, lithium resource consumption has increased dramatically, leading to rising costs and challenges to supply stability. Therefore, developing new rechargeable battery systems that can replace or supplement lithium-ion batteries is particularly important.

[0003] Sodium-ion batteries, with their advantages of abundant and widely distributed sodium resources and low cost, are considered an important development direction for next-generation energy storage technology. Among the many cathode materials for sodium-ion batteries, sodium vanadium phosphate (Na3V2(PO4)3) with a NASICON-type structure has attracted much attention due to its high operating voltage, stable crystal framework, and good sodium-ion conductivity. However, several key issues still need to be addressed: First, vanadium is expensive and environmentally toxic, and high vanadium content is detrimental to material cost control and green sustainable development; second, the V value in the high-voltage range... 4+ / V 5+ The redox couple is difficult to activate stably, resulting in low actual reversible capacity and poor long-cycle stability. Furthermore, the material's intrinsic electronic conductivity is low, limiting its rate performance. Therefore, developing sodium vanadium phosphate-based cathode materials that combine low vanadium content, high electrochemical activity, and excellent conductivity is of great significance for advancing the practical application of sodium-ion batteries. Summary of the Invention

[0004] Objective: To address the problems of high vanadium content and high toxicity in existing sodium vanadium phosphate cathode materials, this invention provides a method for preparing a low-vanadium, high-entropy sodium vanadium phosphate cathode material for sodium-ion batteries, exhibiting excellent rate performance and superior long-cycle stability, as well as its applications. The preparation method used in this invention is simple, has a high yield, and is suitable for large-scale production. The prepared Na3V1Ti... 0.5 (FeMnMgAlZn) 0.5The (PO4)3@C material has fine and uniform particle composition, which helps to shorten the ion / electron transport path and improve the structural stability of the material. Compared with the prior art, this invention reduces the vanadium content by 50% while maintaining the discharge specific capacity of the prepared material at low rates (e.g., 0.2 C) at more than 90% of that of conventional materials, and the discharge specific capacity under high-rate discharge conditions is relatively improved by 50% compared with conventional materials. This invention significantly reduces dependence on high-valence toxic vanadium while simultaneously improving the overall electrochemical performance, and has good application prospects.

[0005] To solve the technical problem of this invention, the proposed technical solution is as follows:

[0006] The preparation process includes the following steps: First, sodium dihydrogen phosphate, anhydrous citric acid, and vanadium pentoxide are weighed according to a predetermined molar ratio and placed in a reactor as phosphorus, carbon, and sodium sources, respectively, to form the basic reaction system. Then, a transition metal salt with a predetermined molar ratio and an appropriate amount of solvent are added to the system. The system is continuously stirred at 50–100 °C and 400–800 r / min for 2–4 hours to obtain a homogeneous and stable precursor solution. This solution is then transferred to a forced-air drying oven for drying to obtain a dried precursor. After grinding, the powder is transferred to a tube furnace and calcined at high temperature under an inert atmosphere. After natural cooling to room temperature, a black solid low-vanadium, high-entropy sodium vanadium phosphate target product is obtained, with the general chemical formula Na3V1.5-xTi0.5(FeMnMgAlM)x(PO4)3@C, where M=Zn. 2+ or Ga 3+ , 0≤x≤1.5.

[0007] Preferably, the solvent is at least one of deionized water, methanol, and ethanol.

[0008] Preferably, the metal salt is at least one selected from nitrate, acetate, carbonate, and chloride.

[0009] Preferably, the stirring temperature is 70℃, the stirring speed is 500r / min, and the stirring time is 3 h.

[0010] Preferably, the inert gas is argon.

[0011] To address the technical problem of this invention, another proposed technical solution is: the sodium-ion battery cathode material of low-vanadium, high-entropy sodium vanadium phosphate prepared by any of the methods described herein has the general chemical formula Na3V. 1.5-x Ti 0.5 (FeMnMgAlM) x (PO4)3@C, where M=Zn 2+ or Ga 3+ , 0≤x≤1.5.

[0012] To solve the technical problem of this invention, another technical solution is proposed: the application of the low-vanadium high-entropy sodium vanadium phosphate cathode material, wherein the synthesized low-vanadium high-entropy sodium vanadium phosphate material is used to prepare the cathode of a sodium-ion battery.

[0013] Preferably, the synthesized positive electrode material, Super P, and PVDF are mixed in a mass ratio of 7:2:1, with a total mass of 100 mg. 400 μL of N-methylpyrrolidone is added, and the mixture is stirred at room temperature for 12 h on a stirring table. The stirred material is then coated onto copper foil and dried in a vacuum oven at 60 °C for 8 h. The material is then cut into electrode sheets with a diameter of 14 mm using a cutting machine. Finally, a button cell is assembled using a sodium sheet as the counter electrode, GF / F as the separator, and NaClO4 dissolved in EC:PC = 1:1 + 5% FEC solution as the electrolyte.

[0014] Preferably, the synthesized Na3V1Ti 0.5 (FeMnMgAlZn) 0.5 The (PO4)3@C cathode material can provide 157.2 mAh g⁻¹ at a low rate of 0.2 C. -1 The discharge specific capacity remains at 79.0 mAh g even at a high rate of 30 C. -1 The material exhibits a 50% higher discharge specific capacity compared to traditional sodium vanadium phosphate materials. Furthermore, after 500 cycles at a high rate of 10 C, it retains a capacity of up to 93.2%, demonstrating excellent long-term cycling stability.

[0015] Beneficial effects:

[0016] This invention discloses a method for preparing and applying a low-vanadium, high-entropy sodium vanadium phosphate (Na3V1Ti) sodium-ion battery cathode material, belonging to the field of energy storage. This invention successfully prepares cathode materials (such as Na3V1Ti) with low vanadium content, excellent rate performance, and long cycle stability through a simple and efficient process. 0.5 (FeMnMgAlZn) 0.5 (PO4)3@C). This invention employs synergistic doping of titanium with multiple high-entropy elements to replace part of the vanadium, successfully reducing the vanadium content to 50% of its original level, significantly lowering material costs and reducing the environmental toxicity of vanadium. Simultaneously, the appropriate introduction of active sites in titanium compensates for the capacity loss caused by the reduced vanadium content, and the synergistic effect among the elements effectively activates V at high potentials. 4+ / V 5+The redox reaction enhances the long-cycle stability of the material. The preparation method employed in this invention is simple, efficient, and yields high output, showing promising prospects for large-scale production. Compared with existing technologies, this invention provides a novel method for synthesizing high-performance sodium vanadium phosphate cathode materials, significantly reducing dependence on high-valent toxic metals while maintaining excellent overall electrochemical performance; especially under high-rate charge-discharge conditions, its capacity retention can be improved by 50% compared to traditional sodium vanadium phosphate materials.

[0017] This invention employs a synergistic doping design of titanium and multiple high-entropy elements in traditional sodium vanadium phosphate materials. This significantly reduces the cost and toxicity of vanadium usage while effectively compensating for capacity loss due to vanadium reduction by rationally introducing titanium active sites. Furthermore, leveraging the entropy stabilization effect and multi-principal element synergy unique to high-entropy systems, the rate performance and cycling stability of the material are further optimized.

[0018] The preparation process employed in this invention is simple and operates under mild conditions, exhibiting good reproducibility and potential for large-scale production. Compared to existing technologies, this method provides a novel approach for preparing high-performance sodium vanadium phosphate cathode materials. Figure 8 As shown, Na3V1Ti synthesized based on this method 0.5 (FeMnMgAlZn) 0.5 (PO4)3@C cathode material (vanadium content 50%) can provide 157.2 mAh g⁻¹ at a low rate of 0.2 C. -1 The discharge specific capacity remains at 79.0 mAh g even at a high rate of 30 C. -1 The material exhibits a 50% higher discharge specific capacity compared to traditional sodium vanadium phosphate materials. A comparison of the performance with different vanadium contents (Examples 2 and 3) shows that when the vanadium content is 25%, the material's discharge specific capacity at a 0.2 C rate is 92.5 mAh·g. -1 Furthermore, at a high discharge rate of 30 C, the capacity almost decays to zero; after being increased to 37.5%, the discharge specific capacity at 0.2 C increases to 120.6 mAh g⁻¹, and it still maintains 50.0 mAh g⁻¹ at 30 C. -1 This trend indicates that capacity performance improves significantly with increasing number of active vanadium sites. Furthermore, after 500 cycles at a high rate of 10 C, the material retains a capacity of 93.2%, demonstrating excellent long-term cycling stability. Therefore, optimizing to a 50% vanadium content achieves the best balance between capacity, rate capability, and cycling stability, resulting in the most outstanding overall electrochemical performance.

[0019] Comparative Example 1 also reduced the vanadium content to 50%, but in its design, titanium was incorporated into the high-entropy composition. Electrochemical testing results showed that the material (HE-NVP@C) exhibited discharge specific capacities of 127.4, 104.1, 93.6, 79.7, 63.7, 55.0, 45.3, and 39.0 mAh g⁻¹ in the rate range of 0.2 C to 30 C. -1 Therefore, with the same vanadium content, insufficient introduction of titanium will not effectively compensate for the capacity loss caused by the reduction of vanadium sites.

[0020] Comparative Example 2 is a conventional NVP@C material without any introduced transition metals. It exhibits only 52.0 mAh g⁻¹ at a high rate of 30 C. -1 The discharge specific capacity is far lower than that of the novel material we synthesized. Comparative Example 3 is a comparative experiment in which Zn in the high-entropy region was replaced with Ga (corresponding chemical formula Na3V1Ti). 0.5 (FeMnMgAlGa) 0.5 (PO4)3@C). When tested at rates of 0.2, 0.5, 1, 2, 5, 10, 20, and 30 C, the discharge specific capacities of this material were 144.0, 133.3, 121.5, 118.4, 108.7, 89.3, 74.0, and 68.0 mAh g, respectively. -1 Although its discharge capacity and capacity retention are slightly lower than those of Example 1 (containing Zn), more importantly, this demonstrates that the high-entropy system has good compatibility with a variety of transition metal elements, providing a basis for further optimization of element combinations.

[0021] The above comparison shows that the present invention, through the synergistic doping strategy of titanium and multiple high-entropy elements, effectively improves the high-rate capacity and cycle stability of the material while significantly reducing the vanadium content, demonstrating that the material we synthesized has excellent electrochemical performance. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings.

[0023] Figure 1 The image shows the XRD pattern of the V50%-HE-NVTP@C cathode material obtained in Example 1.

[0024] Figure 2 The image shown is a SEM image of the V50%-HE-NVTP@C cathode material obtained in Example 1.

[0025] Figure 3 The image shows the XRD pattern of the V37.5%-HE-NVTP@C cathode material obtained in Example 2.

[0026] Figure 4The image shows the XRD pattern of the V25%-HE-NVTP@C cathode material obtained in Example 3.

[0027] Figure 5 The image shows the XRD pattern of the HE-NVP@C cathode material obtained in Comparative Example 1.

[0028] Figure 6 The image shows the XRD pattern of the NVP@C cathode material obtained in Comparative Example 2.

[0029] Figure 7 Na3V1Ti obtained in Comparative Example 3 0.5 (FeMnMgAlGa) 0.5 XRD image of (PO4)3@C cathode material.

[0030] Figure 8 The graph shows a comparison of the rate performance of the cathode materials prepared in Examples 1-3 and Comparative Examples 1-2.

[0031] Figure 9 The graph shows a comparison of the long-cycle stability of the cathode materials prepared in Examples 1-3 and Comparative Examples 1-2.

[0032] Figure 10 The graph shows the rate performance test results of the cathode material prepared in Comparative Example 3. Detailed Implementation

[0033] Example 1

[0034] 12 mM sodium dihydrogen phosphate, 8 mM anhydrous citric acid, 2 mM vanadium pentoxide, and 0.4 mM each of ferric nitrate, magnesium acetate, manganese acetate, aluminum nitrate, and zinc acetate were weighed and dissolved in 30 mL of deionized water. Separately, 2 mM tetrabutyl titanate was dispersed in an appropriate amount of ethanol and added to the above solution. The mixture was stirred at 70℃ and 500 r / min for 3 hours to form a homogeneous solution. This solution was transferred to a forced-air drying oven and dried at 120℃ for 12 h to obtain the dried precursor. After grinding, the powder was transferred to a tube furnace and calcined at high temperature under an inert atmosphere. After natural cooling to room temperature, a black solid powder, Na3V1Ti, was obtained. 0.5 (FeMnMgAlZn) 0.5 (PO4)3@C, denoted as V50%-HE-NVTP@C.

[0035] Figure 1The XRD pattern of the sample prepared in Example 1 is shown. The results show that the diffraction peaks are in good agreement with the Na3V2(PO4)3 standard card (PDF#97-024-8140), confirming the successful synthesis of V50%-HE-NVTP@C low-vanadium high-entropy sodium vanadium phosphate cathode material with a vanadium molar content of 50% (based on the molar ratio of transition metal elements), and the sample has high purity and good crystallinity. Figure 2 The SEM images show that the material is composed of numerous small and uniform particles, indicating that the introduction of various transition metal elements can effectively control the crystal morphology and size.

[0036] Example 2

[0037] 12 mM sodium dihydrogen phosphate, 8 mM anhydrous citric acid, 1.5 mM vanadium pentoxide, and 0.6 mM each of ferric nitrate, magnesium acetate, manganese acetate, aluminum nitrate, and zinc acetate were weighed and dissolved in 30 mL of deionized water. Separately, 2 mM tetrabutyl titanate was dispersed in an appropriate amount of ethanol and added to the above solution. The mixture was stirred at 70℃ and 500 r / min for 3 hours to form a homogeneous solution. This solution was transferred to a forced-air drying oven and dried at 120℃ for 12 h to obtain the dried precursor. After grinding, the powder was transferred to a tube furnace and calcined at high temperature under an inert atmosphere. After natural cooling to room temperature, a black solid powder, Na3V, was obtained. 0.75 Ti 0.5 (FeMnMgAlZn) 0.75 (PO4)3@C, denoted as V37.5%-HE-NVTP@C.

[0038] Figure 3 The image shows the XRD pattern of the sample prepared in Example 2. The results show that its main diffraction peaks are basically consistent with the standard spectrum of NVP@C, and no impurity phase diffraction peaks were observed. This indicates that we have successfully prepared and synthesized V37.5%-HE-NVTP@C low-vanadium high-entropy sodium vanadium phosphate cathode material with a vanadium content of 37.5%.

[0039] Example 3

[0040] 12 mM sodium dihydrogen phosphate, 8 mM anhydrous citric acid, 1 mM vanadium pentoxide, and 0.8 mM each of ferric nitrate, magnesium acetate, manganese acetate, aluminum nitrate, and zinc acetate were weighed and dissolved in 30 mL of deionized water. Separately, 2 mM tetrabutyl titanate was dispersed in an appropriate amount of ethanol and added to the above solution. The mixture was stirred at 70℃ and 500 r / min for 3 hours to form a homogeneous solution. This solution was transferred to a forced-air drying oven and dried at 120℃ for 12 h to obtain the dried precursor. After grinding, the powder was transferred to a tube furnace and calcined at high temperature under an inert atmosphere. After natural cooling to room temperature, a black solid powder, Na3V, was obtained.0.5 Ti 0.5 (FeMnMgAlZn)1(PO4)3@C, denoted as V25%-HE-NVTP@C.

[0041] Figure 4 The image shows the XRD pattern of the sample prepared in Example 3. The results show that the positions of its main diffraction peaks are basically consistent with the standard spectrum of NVP@C, and no impurity phase diffraction peaks were observed, confirming the successful synthesis of the V25%-HE-NVTP@C low-vanadium high-entropy sodium vanadium phosphate cathode material with a vanadium content of 25% described in Example 3.

[0042] Comparative Example 1

[0043] 12 mM sodium dihydrogen phosphate, 8 mM anhydrous citric acid, 2 mM vanadium pentoxide, and 0.8 mM each of tetrabutyl titanate, ferric nitrate, manganese acetate, aluminum nitrate, and zinc acetate were weighed and dissolved in 30 mL of deionized water. The mixture was stirred at 70 °C and 500 r / min for 3 hours to form a homogeneous solution. The solution was transferred to a forced-air drying oven and dried at 120 °C for 12 h to obtain the dried precursor. After grinding, the powder was transferred to a tube furnace and calcined at high temperature under an inert atmosphere. After natural cooling to room temperature, a black solid powder Na3V1(TiFeMnAlZn)1(PO4)3@C was obtained, denoted as HE-NVP@C.

[0044] Figure 5 The image shows the XRD pattern of the sample prepared in Comparative Example 1. The results show that the positions of the main diffraction peaks in its XRD pattern are basically consistent with the standard pattern of NVP@C, and no impurity phase diffraction peaks were observed, confirming the successful synthesis of the HE-NVP@C cathode material described in Comparative Example 1.

[0045] Comparative Example 2

[0046] 12 mM sodium dihydrogen phosphate, 8 mM anhydrous citric acid, and 4 mM vanadium pentoxide were weighed and dissolved in 30 mL of deionized water. The mixture was stirred at 70 °C and 500 r / min for 3 hours to form a homogeneous solution. The solution was transferred to a forced-air drying oven and dried at 120 °C for 12 h to obtain the dried precursor. After grinding, the powder was transferred to a tube furnace and calcined at high temperature under an inert atmosphere. After natural cooling to room temperature, a black solid powder Na3V2(PO4)3 was obtained, denoted as NVP@C.

[0047] Figure 6The XRD pattern of the sample prepared in Comparative Example 2 is shown in the figure. As shown, each diffraction peak corresponds to the Na3V2(PO4)3 standard card (PDF#97-024-8140), indicating that the comparative sample has high purity, complete crystal structure, and the target product NVP@C was successfully prepared.

[0048] Comparative Example 3

[0049] 12 mM sodium dihydrogen phosphate, 8 mM anhydrous citric acid, 2 mM vanadium pentoxide, and 0.4 mM each of ferric nitrate, magnesium acetate, manganese acetate, aluminum nitrate, and gallium chloride were weighed and dissolved in 30 mL of deionized water. Separately, 2 mM tetrabutyl titanate was dispersed in an appropriate amount of ethanol and added to the above solution. The mixture was stirred at 70℃ and 500 r / min for 3 hours to form a homogeneous solution. This solution was transferred to a forced-air drying oven and dried at 120℃ for 12 h to obtain the dried precursor. After grinding, the powder was transferred to a tube furnace and calcined at high temperature under an inert atmosphere. After natural cooling to room temperature, a black solid powder, Na3V1Ti, was obtained. 0.5 (FeMnMgAlGa) 0.5 (PO4)3@C.

[0050] Figure 7 The XRD pattern of the sample prepared in Comparative Example 3 is shown. The results show that the diffraction peaks are in good agreement with the Na3V2(PO4)3 standard card, confirming that the low-vanadium, high-entropy sodium vanadium phosphate cathode material was successfully prepared, and the sample has high purity and good crystallinity.

[0051] Subsequently, to evaluate the electrochemical performance of each material, the positive electrode materials prepared in each example and comparative example were fabricated into electrode sheets and assembled into button cells for electrochemical testing according to the following steps: The positive electrode material, conductive agent Super-P, and binder PVDF were mixed uniformly at a mass ratio of 7:2:1, with a total mass of 100 mg. 400 μL of N-methylpyrrolidone was added, and the mixture was stirred at room temperature for 12 h. The stirred material was then coated onto copper foil and dried in a vacuum oven at 60 °C for 8 h, and then cut into electrode sheets with a diameter of 14 mm. Finally, button cells were assembled and their electrochemical performance was tested. The synthesized material was used as the positive electrode, a sodium sheet as the counter electrode, glass fiber GF / F as the separator, and NaClO4 dissolved in EC:PC = 1:1 + 5% FEC solution as the electrolyte. The test voltage range was 1.4 V to 4.3 V.

[0052] Figure 8This paper presents a comparison of the specific capacity performance of batteries assembled from the cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 under different discharge rates. The results show that when the test rates are 0.2, 0.5, 1, 2, 5, 10, 20, and 30 C, the discharge specific capacities of V50%-HE-NVTP@C in Example 1 are 157.2, 144.3, 137.6, 132.5, 121.9, 107.7, 86.0, and 79.0 mAh g, respectively. -1 At the same discharge rate, the discharge specific capacities of the ordinary NVP@C material prepared in Comparative Example 2 were 161.9, 149.2, 139.2, 126.8, 105.2, 77.0, 61.4, and 52.0 mAh g⁻¹, respectively. -1 This shows that when the vanadium content in traditional sodium vanadium phosphate materials is reduced to 50%, the initial capacity of the prepared V50%-HE-NVTP@C at low rates (e.g., 0.2 C) is slightly lower than that of the traditional material, but its capacity decay slows down significantly as the rate increases. Especially at high rates of 5 C and above, the discharge capacity of V50%-HE-NVTP@C is significantly higher than that of NVP@C, exhibiting superior rate performance. Furthermore, when the current density increases to 30 C, V50%-HE-NVTP@C still maintains a 50% capacity retention rate, while traditional NVP@C only maintains a 32% capacity retention rate. These results demonstrate that through reasonable titanium doping and high-entropy design, while significantly reducing the vanadium content, it not only activates and stabilizes the high-voltage V... 4+ / V 5+ The redox pair can also utilize the redox active sites of additional titanium elements for capacity compensation. At the same time, the structural stability and ion diffusion kinetics of the material are also enhanced, thus maintaining a high reversible capacity at high rates and achieving an optimized balance between capacity and rate performance.

[0053] Further testing showed that the rate performance of the material exhibited a regular change as the vanadium content continued to decrease. In Example 2, the discharge specific capacities of V37.5%-HE-NVTP@C at rates from 0.2 C to 30 C were 120.6, 108.3, 100.3, 94.7, 80.6, 65.0, 55.3, and 50.0 mAh·g, respectively. -1 In Example 3, the corresponding capacities of V25%-HE-NVTP@C further decreased to 92.5, 75.0, 64.6, 54.4, 39.5, 27.0, 14.7, and 9.0 mAh·g. -1In summary, the above results indicate that the reversible capacity and rate performance of the material systematically decrease with decreasing vanadium content. This is mainly due to the reduction in active vanadium sites, leading to a decrease in the number of active centers available for redox reactions. Therefore, when optimized to a vanadium content of 50%, the material in Example 1 achieves the best balance between capacity, rate performance, and cycle stability, exhibiting the most outstanding overall electrochemical performance.

[0054] Comparative Example 1 also reduced the vanadium content to 50%, employing only a high-entropy element doping strategy. Electrochemical tests showed that, within the rate range of 0.2 C to 30 C, the discharge specific capacities of HE-NVP@C were 127.4, 104.1, 93.6, 79.7, 63.7, 55.0, 45.3, and 39.0 mAh·g⁻¹, respectively. -1 This demonstrates that, with the same vanadium content, insufficient titanium introduction cannot effectively compensate for the capacity loss caused by the reduction in vanadium sites. This result further illustrates that titanium, as one of the key redox active sites, plays an irreplaceable role in maintaining the reversible capacity of materials at high rates.

[0055] Figure 9 The graph shows a comparison of the long-term cycle stability of batteries assembled from the cathode materials prepared in Examples 1-3 and Comparative Examples 1-2 at a discharge rate of 10 C. The results show that after 500 cycles at 10 C, the V50%-HE-NVTP@C electrode in Example 1 still maintains the highest specific capacity, with a capacity retention rate as high as 93.2%, significantly better than the 57.7% capacity retention rate of the NVP@C electrode in Comparative Example 2. Although the specific capacities of V25%-HE-NVTP@C, V37.5%-HE-NVTP@C, and HE-NVP@C are lower than those of ordinary NVP@C, they exhibit excellent cycle stability, indicating that the high-entropy strategy has a significant advantage in improving the cycle stability of materials.

[0056] To further verify the tunability of this material system for elements in the high-entropy region, a comparative experiment was conducted under the same preparation conditions, replacing Zn in the high-entropy region with Ga (corresponding chemical formula Na3V1Ti). 0.5 (FeMnMgAlGa) 0.5 (PO4)3@C). Test results show that this comparative sample also has a stable crystal structure. When the test rates are 0.2, 0.5, 1, 2, 5, 10, 20, and 30 C, the discharge specific capacities of this material are 144.0, 133.3, 121.5, 118.4, 108.7, 89.3, 74.0, and 68.0 mAh g, respectively. -1Although its discharge capacity and capacity retention are slightly lower than those of Example 1 (containing Zn), more importantly, this demonstrates that the high-entropy system has good compatibility with a variety of transition metal elements, providing a basis for further optimization of element combinations.

[0057] The present invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a low-vanadium, high-entropy sodium vanadium phosphate cathode material, characterized in that, The preparation steps include the following: First, sodium dihydrogen phosphate, anhydrous citric acid and vanadium pentoxide are weighed according to the set molar ratio and placed in a reactor as phosphorus source, carbon source and sodium source to form a basic reaction system. Then, a transition metal salt with a set molar ratio is added to the system and an appropriate amount of solvent is added. The system is stirred continuously at 50~100℃ and 400~800 r / min for 2~4 hours to finally obtain a homogeneous and stable precursor solution. The solution was transferred to a forced-air drying oven for drying to obtain the dried precursor. After grinding, the powder was transferred to a tube furnace and calcined at high temperature under an inert atmosphere. After natural cooling to room temperature, the target product, sodium vanadium phosphate with low vanadium and high entropy, was obtained as a black solid with the chemical formula Na3V. 1.5-x Ti 0.5 (FeMnMgAlM) x (PO4)3@C, where M=Zn 2+ or Ga 3+ , 0≤x≤1.

5.

2. The method for preparing sodium vanadium phosphate cathode material with low vanadium and high entropy according to claim 1, characterized in that: The solvent is at least one of deionized water, methanol, and ethanol, and the metal salt is at least one of nitrate, acetate, carbonate, and chloride.

3. The method for preparing sodium vanadium phosphate cathode material with low vanadium and high entropy according to claim 1, characterized in that: The stirring temperature was 70℃, the stirring speed was 500 r / min, and the stirring time was 3 h.

4. The method for preparing sodium vanadium phosphate cathode material with low vanadium and high entropy according to claim 1, characterized in that: The inert gas is argon.

5. The method for preparing sodium vanadium phosphate cathode material with low vanadium and high entropy according to claim 1, characterized in that: Weigh out 12 mM sodium dihydrogen phosphate, 8 mM anhydrous citric acid, 2 mM vanadium pentoxide, and 0.4 mM each of ferric nitrate, magnesium acetate, manganese acetate, aluminum nitrate, and zinc acetate, and dissolve them together in 30 mL of deionized water; separately, dissolve 2 mM tetrabutyl titanate in an appropriate amount of ethanol and then add it to the above solution. The mixture was stirred at 70℃ and 500 r / min for 3 hours to form a homogeneous solution. The solution was transferred to a forced-air drying oven and dried at 120°C for 12 h to obtain the dried precursor. After grinding, the powder was transferred to a tube furnace and calcined at high temperature under an inert atmosphere; after natural cooling to room temperature, a black solid powder Na3V1Ti was obtained. 0.5 (FeMnMgAlZn) 0.5 (PO4)3@C.

6. The low-vanadium, high-entropy sodium vanadium phosphate cathode material prepared by the method according to any one of claims 1-5 has the general chemical formula Na3V. 1.5-x Ti 0.5 (FeMnMgAlM) x (PO4)3@C, where M=Zn 2+ or Ga 3+ , 0≤x≤1.

5.

7. The application of the sodium vanadium phosphate cathode material according to claim 6, characterized in that: The synthesized low-vanadium, high-entropy sodium vanadium phosphate cathode material was used to prepare the cathode for sodium-ion batteries.

8. The application of the sodium vanadium phosphate cathode material with low vanadium and high entropy according to claim 7, characterized in that: The synthesized low-vanadium, high-entropy sodium vanadium phosphate cathode material, conductive agent Super P, and binder PVDF were mixed and ground evenly in a mass ratio of 7:2:1, with a total mass of 100 mg. 400 μL of N-methylpyrrolidone was added, and the mixture was stirred at room temperature for 12 h on a stirring table. The stirred material was then coated onto copper foil and dried in a vacuum oven at 60 °C for 8 h. The material was then cut into electrode sheets with a diameter of 14 mm using a cutting machine. Finally, a button cell was assembled using a sodium sheet as the counter electrode, GF / F as the separator, and NaClO4 dissolved in EC:PC = 1:1 + 5% FEC solution as the electrolyte.

9. The application of the sodium vanadium phosphate cathode material with low vanadium and high entropy according to claim 7, characterized in that: Synthesized Na3V1Ti 0.5 (FeMnMgAlZn) 0.5 The (PO4)3@C cathode material can provide 157.2 mAh g⁻¹ at a low rate of 0.2 C. -1 The discharge specific capacity remains at 79.0 mAh g even at a high rate of 30 C. -1 The material exhibits a high discharge specific capacity, which is 50% higher than that of traditional sodium vanadium phosphate materials. In addition, after 500 cycles at a high rate of 10 C, the capacity retention rate is as high as 93.2%, demonstrating excellent long-term cycling stability.

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