A potassium carbonate-induced porous carbon skeleton combined with a sodium vanadium phosphate coated with tri-potassium phosphate composite positive electrode material, and a preparation method and application thereof

Abstract

The application belongs to the technical field of sodium ion batteries, and provides a potassium carbonate induced porous carbon skeleton combined with a sodium vanadium phosphate composite positive electrode material coated with potassium phosphate and a preparation method and application thereof to solve the problems of low intrinsic conductivity and poor cycle stability of sodium vanadium phosphate. The composite positive electrode material is a composite material composed of irregular NVP and a porous carbon skeleton, and an amorphous carbon layer and a K3PO4 double conductive layer are coated on the periphery of the NVP sample particles; sodium carbonate, potassium carbonate, ammonium metavanadate and ammonium dihydrogen phosphate are used as raw materials, citric acid is used as a chelating agent, and the composite positive electrode material is obtained by a sol-gel method. The material prepared by the application has excellent cycle stability, and can still remain stable after 14000 times of charging and discharging cycles at a super large rate of 180C. The experimental synthesis process is simple, and there is no complex process and high cost, which has great practical application potential and guiding significance.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery cathode materials, specifically relating to a potassium carbonate-induced porous carbon framework combined with tripotassium phosphate-coated sodium vanadium phosphate composite cathode material, its preparation method, and its application. Background Technology

[0002] In the emerging new energy industry, sodium-ion batteries are considered the most promising energy storage technology to replace lithium-ion batteries due to their low cost and excellent performance. However, the large ionic radius of sodium ions makes them difficult to insert and extract during charging and discharging, resulting in poor kinetic characteristics. Na3V2(PO4)3 (NVP) is an ideal cathode material for sodium-ion batteries, possessing an open and stable three-dimensional NASCION framework and two types of sodium ions that can be inserted and extracted. However, due to the low intrinsic electronic and ionic conductivity of Na3V2(PO4)3, its energy density and discharge specific capacity in practical applications are far lower than theoretical values, which greatly limits its development and commercial application. Therefore, there is an urgent need to develop a novel Na3V2(PO4)3 electrode material with rapid ion-electron migration capabilities.

[0003] In the modification research of Na3V2(PO4)3 materials, simple ionic bulk phase doping and carbon material composite methods are relatively common, but research on morphology control and ionic conductor coating is rarely involved. At the same time, many studies have shown that achieving specific modification effects often requires complex preparation processes and high costs, and few studies have been able to achieve both morphology control and ionic conductor coating through a simple one-step method. Summary of the Invention

[0004] This invention addresses the problems of poor intrinsic conductivity and poor cycle stability inherent in Na3V2(PO4)3 by providing a potassium carbonate-induced porous carbon framework combined with tripotassium phosphate-coated sodium vanadium phosphate composite cathode material, along with its preparation method and applications. The addition of K2CO3 induces the formation of a porous carbon matrix, inhibiting the agglomeration of NVP particles during sintering and allowing NVP to adhere uniformly to the porous carbon matrix. Electrons can then rapidly transport within the interwoven porous carbon network. Furthermore, K2CO3 decomposes during sintering and reacts with other substances to generate K3PO4, forming a bilayer conductive interface with excess amorphous carbon. This further increases conductivity and protects the cathode material from electrolyte corrosion. When loaded into a CR2025 coin cell, the electrode material exhibits excellent cycle stability and high-rate, long-cycle performance, making it a promising cathode material for sodium-ion batteries.

[0005] The present invention is achieved by the following technical solution: a potassium carbonate-induced porous carbon framework combined with tripotassium phosphate-coated sodium vanadium phosphate composite cathode material, the composite cathode material being a composite material composed of irregular Na3V2(PO4)3 and a porous carbon framework, with an amorphous carbon layer and a K3PO4 double conductive layer coated on the periphery of the Na3V2(PO4)3 sample particles. This composite cathode material uses sodium carbonate, potassium carbonate, ammonium metavanadate, and ammonium dihydrogen phosphate as raw materials, citric acid as a chelating agent, and the amount of K2CO3 is determined according to (PO4). 3- The over-design ratio is calculated as (PO4). 3- The excess of (PO4) in the original NVP synthesis formulation. 3- The amount of K2CO3 required is calculated based on the following: the K2CO3-induced porous carbon framework combined with K3PO4-coated sodium vanadium phosphate composite cathode material is prepared by sol-gel method and two-step sintering.

[0006] Furthermore, the amount of K2CO3 used depends on (PO4). 3- The over-design ratio is calculated as (PO4). 3- The excess of (PO4) in the original NVP synthesis formulation. 3- The amount of substance is 1%.

[0007] The specific steps for preparing the K2CO3-induced porous carbon framework combined with K3PO4-coated sodium vanadium phosphate composite cathode material are as follows: (1) Sodium carbonate, ammonium dihydrogen phosphate, and ammonium metavanadate in a molar ratio of 1:2.02:1.33 were mixed and dissolved in deionized water. The mixture was heated to 70°C and stirred continuously until a uniformly mixed yellow transparent solution was formed. The molar ratio of citric acid to ammonium metavanadate was controlled at 1:6. Citric acid was slowly added to the yellow transparent solution until the color finally stabilized at blue. (2) Slowly add potassium carbonate to the blue solution prepared in step (1) until it is completely dissolved, and stir at a constant temperature until the precursor solution is concentrated into a viscous colloid of 20 ml; wherein, the amount of K2CO3 added is (PO4). 3- The excess of (PO4) in the original NVP synthesis formulation. 3- The amount of potassium carbonate in the three samples was calculated to be 0.006823 g, 0.01364 g and 0.06823 g, respectively, based on the percentage of 0.5%, 1% and 5% of the substance. (3) The viscous colloid prepared in step (2) is dried at 80°C for 12 hours to obtain the precursor; the obtained precursor is pre-calcined at 450°C for 4 hours in a nitrogen atmosphere, and then finally calcined at 700°C for 6 hours to obtain the final product.

[0008] Application of the potassium carbonate-induced porous carbon framework combined with tripotassium phosphate-coated sodium vanadium phosphate composite cathode material, or the potassium carbonate-induced porous carbon framework combined with tripotassium phosphate-coated sodium vanadium phosphate composite cathode material prepared by the method, in sodium-ion batteries.

[0009] The specific method is as follows: (1) Preparation of cathode material: The K2CO3-induced porous carbon framework combined with K3PO4-coated sodium vanadium phosphate composite cathode material is used as the active material of cathode material. The total mass of the active material, conductive filler acetylene black and binder polyvinylidene fluoride is controlled to be 0.3g. The active material, conductive filler acetylene black and binder polyvinylidene fluoride are mixed in 1.4 mL of N-methylpyrrolidone NMP solvent at a mass ratio of 7:2:1. The above mixture is placed in a ball mill jar and ball milled unidirectionally for 4h to obtain a slurry, which is then coated on carbon-coated aluminum foil. After drying at 45℃ for 4h, it is vacuum dried at 120℃ for 6h to obtain the cathode material. (2) Battery assembly: The positive electrode material prepared in step (1) is used as the positive electrode, metallic sodium is used as the negative electrode, ceramic Celgard membrane is used as the membrane, and the electrolyte is NaClO4+EC / DEC+5%FEC; wherein, NaClO4, EC, DEC and FEC are sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO4 is dissolved in EC / DEC system with a volume ratio of 1:1, and 5wt% FEC is added to prepare electrolyte, and assembled into CR2025 button battery.

[0010] This invention synthesizes a composite material consisting of K3PO4-coated irregularly shaped Na3V2(PO4)3 and a porous carbon framework through a two-step sintering process using the traditional sol-gel method, significantly improving the material's specific capacity and long-cycle performance. Specifically, the addition of potassium carbonate allows for different decomposition reactions at different temperatures during the two-step sintering process. The resulting gases and potassium compounds can form micropores and expand pore size, thus creating a relatively uniform porous carbon matrix. It is noteworthy that the K3PO4 obtained from the high-temperature decomposition of potassium carbonate... + Able to interact with PO4 3- A novel conductive phase, K3PO4, is formed and coated around the NVP particles. Its excellent conductivity allows it to form a bilayer conductive interface with the amorphous carbon layer, further enhancing conductivity. Furthermore, this bilayer interface can mitigate the capacity decay caused by electrolyte erosion of the Na3V2(PO4)3 cathode material, thereby significantly improving the long-cycle performance of sodium-ion batteries.

[0011] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention achieves two beneficial effects by adding potassium carbonate in only one step of the in-situ synthesis stage using the traditional sol-gel method. After two sintering steps, different reactions occur at different stages, demonstrating the process of pore formation, pore enlargement, and ultimately, a stable porous carbon matrix due to the addition of potassium carbonate. The synthesized Na3V2(PO4)3 material also possesses a special K3PO4 coating layer, forming a bilayer conductive and protective interface with the amorphous carbon layer. The material obtained by this invention exhibits extremely excellent cycle stability, remaining stable even after undergoing up to 14,000 charge-discharge cycles at a high rate of 180C. The experimental synthesis process is simple, without complex processes or high costs, and has great potential for practical application and guiding significance. Attached Figure Description

[0012] Figure 1 The image shows the SEM image of the composite cathode material prepared in Example 2, which consists of K3PO4 coated with irregular Na3V2(PO4)3 and a porous carbon framework. The image shows the obvious special morphology of the porous carbon framework, with sodium vanadium phosphate particles attached to the porous structure. Figure 2 The image shows a low-magnification TEM image of the composite cathode material prepared in Example 2, which consists of K3PO4 coated with irregularly shaped Na3V2(PO4)3 and a porous carbon framework. As can be seen from the image, it also has a distinct porous structure. Figure 3 The image shows an HRTEM image of the composite cathode material prepared in Example 2, consisting of K3PO4 coated with irregularly shaped Na3V2(PO4)3 and a porous carbon framework. As can be seen from the image, two lattice stripes that are significantly different from the NVP bulk phase are coated around Na3V2(PO4)3. Measurements show that these stripes correspond to the new conductive phase K3PO4. Figure 4 The XRD spectra of the composite cathode material composed of K3PO4 coated with irregular Na3V2(PO4)3 and porous carbon framework prepared in Examples 2 and 4, and the original Na3V2(PO4)3 cathode material are shown. The XRD spectra show that the two phases of the composite material composed of K3PO4 coated with irregular Na3V2(PO4)3 and porous carbon framework are irregular Na3V2(PO4)3 and K3PO4, respectively. Figure 5 The constant current first-cycle charge-discharge curves were measured when the CR2025 button batteries were assembled in Examples 1, 2, 3, and 4, with a current density of 0.1 C. Figure 6 Comparison curves of rate performance measured at different current densities when the CR2025 button batteries assembled in Examples 1, 2, 3, and 4 are used. Figure 7 Example 2, compared with Example 4, shows the discharge specific capacity after 400 cycles at a current density of 1 C when assembled as a CR2025 button cell. Figure 8 The discharge specific capacity long cycle diagram of the CR2025 button battery assembled in Example 2 at an ultra-high current density of 180 C after 14,000 cycles. Figure 9 The EIS curves of the composite cathode materials prepared in Examples 2 and 4, consisting of K3PO4 coated with irregularly shaped Na3V2(PO4)3 and a porous carbon framework, at 3.7 V when assembled into CR2025 coin cells. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and all materials publicly cited herein and cited by them are incorporated herein by reference.

[0015] Equivalent technologies of the specific embodiments described herein that are readily apparent to those skilled in the art through routine experimentation are included in this application.

[0016] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the instruments and equipment used in the following examples are all standard laboratory instruments and equipment; unless otherwise specified, the experimental materials used in the following examples were all purchased from regular biochemical reagent stores.

[0017] Example 1: Preparation of sodium vanadium phosphate composite cathode material (NVP / C@0.5%K3PO4) induced by 0.5% K2CO3 porous carbon framework and coated with K3PO4: Dissolve 1.5401 g of ammonium metavanadate and 2.2827 g of ammonium dihydrogen phosphate in 100 mL of deionized water. Heat the solution in a water bath to 70°C and stir continuously until a homogeneous, transparent yellow solution is formed. Slowly add 0.5077 g of citric acid to the clear solution and maintain the temperature at 70°C for 4 hours, stirring until the solution turns deep blue. Slowly add 0.006823 g of potassium carbonate, and finally add 1.0465 g of sodium carbonate. Stir continuously at 70°C until all reactants are completely dissolved. Stir continuously at a constant temperature until the precursor solution becomes a viscous colloid of 20 mL. Dry the colloid in a forced-air oven at 80°C for 12 hours to obtain the precursor. The obtained precursor is pre-calcined at 450°C for 4 hours under a nitrogen atmosphere and then finally calcined at 700°C for 6 hours to obtain the final product.

[0018] Using the positive electrode material prepared in this embodiment as the active material, the active material, conductive filler (acetylene black), and binder (polyvinylidene fluoride) were mixed in 1.4 mL of N-methylpyrrolidone (NMP) solvent at a mass ratio of 7:2:1. The mixture was placed in a ball mill jar and unidirectionally ball-milled for 4 hours to obtain a slurry, which was then coated onto carbon-coated aluminum foil. After drying at 45°C for 4 hours, it was vacuum-dried at 120°C for 6 hours. Using this as the positive electrode, metallic sodium as the negative electrode, and a ceramic Celgard membrane as the separator, the electrolyte consisted of NaClO4 + EC / DEC + 5% FEC; where NaClO4, EC, DEC, and FEC represent sodium perchlorate, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate, respectively; 1 M NaClO4 was dissolved in an EC / DEC system with a volume ratio of 1:1, and 5 wt% FEC was added for preparation. The mixture was assembled into a CR2025 type button cell in a vacuum glove box.

[0019] The assembled coin cells were subjected to constant current charge-discharge tests at room temperature within a voltage range of 2.3-4.1V. Specifically, the initial charge-discharge curves at a current density of 0.1C are shown below. Figure 5 Discharge specific capacity at different rates, such as Figure 6 .

[0020] Testing revealed that this material, when used as the positive electrode material in sodium-ion batteries, exhibits a discharge specific capacity of 98.6 mAh g⁻¹ at 0.1 C, as shown by electrochemical tests. -1 Furthermore, battery cycle rate testing indicates that even at a high rate of 15 C, the material's discharge specific capacity remains at 65.2 mAh g⁻¹. -1 Furthermore, when the discharge rate recovers to 1 C, the material can still quickly recover to 82 mAh g⁻¹. -1 The specific discharge capacity.

[0021] Example 2: Preparation of sodium vanadium phosphate composite cathode material (NVP / C@1%K3PO4) induced by 1% K2CO3 porous carbon framework and coated with K3PO4: The amount of potassium carbonate added was 0.01364 g, and the rest of the method was the same as that described in Example 1.

[0022] To better illustrate its characteristics, the SEM image of the cathode material prepared in this embodiment is shown below. Figure 1 As shown in the image, a relatively uniform porous structure is clearly visible, forming a porous carbon framework. NVP particles adhere to this porous carbon framework, forming a porous carbon conductive network that interconnects the Na3V2(PO4) particles, effectively improving the sample's conductivity. This is even more evident in the TEM image. Figure 2 As shown. The XRD pattern is as follows. Figure 4 As shown, the XRD pattern indicates that the two phases of the K2CO3-induced porous carbon framework and K3PO4-coated sodium vanadium phosphate composite cathode material are random Na3V2(PO4)3 and K3PO4, respectively; this is direct evidence of the synthesis of the new conductive phase.

[0023] The HRTEM image clearly shows the two different phase compositions of the material. Corresponding to the characteristic peaks of the two phases in the XRD spectrum, it can be determined that K3PO4 in the K2CO3-induced porous carbon framework and K3PO4-coated sodium vanadium phosphate composite cathode material acts as a new conductive phase coating layer around the NVP particles, thus forming a double conductive layer with the amorphous carbon layer. This not only improves the conductivity but also protects the cathode material, prevents electrolyte erosion, and promotes the stability of the NVP-modified material.

[0024] Using the positive electrode material prepared in this embodiment as the active material, a CR2025 type button cell was assembled in a vacuum glove box. The remaining preparation methods are the same as those described in Example 1.

[0025] The assembled coin cells were subjected to constant current charge-discharge tests at room temperature within a voltage range of 2.3-4.1V and within 0.1-5 mV s. -1 Cyclic voltammetry measurements were performed within the scan rate range at a current density of 0.1 C. Specifically, the initial charge-discharge curve at 0.1 C is shown below. Figure 5 As shown, the rate performance at different magnifications is as follows: Figure 6 As shown; the specific capacity of 400-cycle discharge at a current density of 1 C is as follows: Figure 7 As shown, the discharge specific capacity after 14,000 long cycles at an ultra-high current density of 180 C is as follows: Figure 8 As shown. The EIS test curve at 3.7 V is shown below. Figure 9 As shown.

[0026] Testing revealed that this material, when used as the positive electrode material in sodium-ion batteries, exhibits a discharge specific capacity of 122.3 mAh g⁻¹ at 0.1 C, as shown by electrochemical tests. -1 The battery cycle rate indicates that, even at a high rate of 15 C, the material's discharge specific capacity can still be maintained at 105.1 mAh g⁻¹. -1 Furthermore, when the discharge rate recovers to 1 C, the material can still rapidly recover to 115.9 mAh g⁻¹. -1 The discharge specific capacity indicates that this material exhibits excellent rate performance when incorporated into the CR2025 coin cell. Furthermore, after 400 cycles at a 1C current density, the material still maintains a discharge specific capacity of 102.3 mAh g⁻¹. -1 This indicates that the material possesses excellent cycle stability, which is... Figure 8 This is even more evident in the medium, where the material still achieves 79.97 mAh g⁻¹ at an ultra-high rate of 180 C. -1 It has a high specific capacity and can maintain 49.8 mAh g after undergoing up to 14,000 cycles. -1 The average capacity decay rate per cycle is as low as 0.00269%, which is extremely rare in many studies.

[0027] Furthermore, the electrochemical impedance spectroscopy (EIS) performance of NVP / C@1%K3PO4 was characterized by curves at 3.7 V. The high-frequency region is a semi-circle, while the low-frequency region is a straight line, corresponding to the charge transfer resistance and Warburg impedance of the material, respectively. The charge transfer resistance of this material is only 67.2 Ω, demonstrating its excellent electronic conductivity. This can be attributed to the uniform porous carbon matrix formed by the potassium carbonate activation of the carbon material. Such a porous carbon conductive network greatly promotes electron transport, reduces resistance, and increases conductivity. In addition, the sodium ion diffusion coefficient is negatively correlated with the slope of the Warburg impedance section. According to calculations, its sodium ion diffusion coefficient is as high as 2.16 × 10⁻⁶. -14 cm 2 s -1 This is due to the synergistic effect of the new conductive phase K3PO4 coated on the surface of NVP particles and the porous carbon network. The porous structure results in a large specific surface area and pore size, allowing the electrolyte to fully contact the cathode material. + The transport path is shortened, effectively improving ion transport capability. Furthermore, the interface modulation of K3PO4 can both increase conductivity and protect NVP materials from corrosion, thus enabling Na… +The ability to stably transport ions between channels further enhances ionic conductivity. Compared to conventional Na3V2(PO4)3, the prepared K2CO3-induced porous carbon framework and K3PO4-coated sodium vanadium phosphate composite cathode material exhibits superior electronic and ionic conductivity.

[0028] Example 3: Preparation of sodium vanadium phosphate composite cathode material (NVP / C@5%K3PO4) induced by 5% K2CO3 porous carbon framework and coated with K3PO4: The amount of potassium carbonate added was 0.06823 g, and the rest of the method was the same as that described in Example 1. Using the positive electrode material prepared in this embodiment as the active material, a CR2025 type button cell was assembled in a vacuum glove box. The remaining methods are the same as those described in Example 1.

[0029] The assembled coin cells were subjected to constant current charge-discharge tests at room temperature within a voltage range of 2.3–4.1 V. Specifically, the first charge-discharge curves at a current density of 0.1 C are shown below. Figure 5 Discharge specific capacity at different rates, such as Figure 6 As shown.

[0030] Testing revealed that this material, when used as the positive electrode material in sodium-ion batteries, exhibits a discharge specific capacity of 92.7 mAh g⁻¹ at 0.1 C, as shown by electrochemical tests. -1 Furthermore, battery cycle rate testing indicates that even at a high rate of 15 C, the material's discharge specific capacity remains at 77 mAh g⁻¹. -1 Furthermore, when the discharge rate recovers to 1 C, the material can still quickly recover to 84 mAh g. -1 The specific discharge capacity.

[0031] Example 4: Unmodified Na3V2(PO4)3 prepared according to the method described in this invention: Dissolve 1.5401 g of ammonium metavanadate and 2.2827 g of ammonium dihydrogen phosphate in 100 mL of deionized water. Heat the solution in a water bath to 70 °C and stir continuously to form a clear yellow solution. Slowly add 0.5077 g of citric acid to the clear solution and maintain the temperature at 70 °C for 4 hours, stirring until the solution turns dark blue. Continue stirring at a constant temperature until the precursor solution becomes a 20 mL viscous colloid. Dry the colloid in a forced-air oven at 80 °C for 12 hours. The obtained precursor is then pre-calcined at 450 °C for 4 hours under a nitrogen atmosphere, followed by a final calcination at 700 °C for 6 hours to obtain the final product.

[0032] Using the positive electrode material prepared in this embodiment as the active material, a CR2025 type button cell was assembled in a vacuum glove box. The remaining methods are the same as those described in Example 1.

[0033] The assembled coin cells were subjected to constant current charge-discharge tests at room temperature within a voltage range of 2.3–4.1 V. Specifically, the initial charge-discharge curves at 0.1 C are shown below. Figure 5 Discharge specific capacity at different rates, such as Figure 6 The EIS test curve at 3.7 V is shown below. Figure 9 As shown.

[0034] Testing revealed that this material, when used as the positive electrode material in sodium-ion batteries, exhibits a discharge specific capacity of 63.7 mAh g⁻¹ at 0.1 C, as shown by electrochemical tests. -1 Battery cycle rate data shows that even at a high rate of 15 C, the material's discharge specific capacity can still be maintained at 49 mAh g⁻¹. -1 Furthermore, when the discharge rate increases to 1 C, the material can achieve a discharge capacity of 65.8 mAh g⁻¹. -1 The discharge specific capacity is [not specified]. At 3.7 V, its EIS curve shows a semi-circular high-frequency region and a straight line in the low-frequency region, corresponding to the material's transfer resistance and Warburg impedance, respectively. The material exhibits a high transfer resistance of 329 Ω and a relatively high slope in the Warburg impedance portion, while its sodium ion diffusion coefficient is only 2.37 × 10⁻⁶. -16 cm 2 s -1 This demonstrates that the material has relatively low electronic and ionic conductivity.

[0035] The above embodiments illustrate that this invention uses a traditional and simple solution-gel method to synthesize sodium vanadium phosphate composite cathode materials with potassium carbonate as an additional activator and source material. The product comprises a porous carbon matrix and two-phase materials of K3PO4 and amorphous carbon-coated Na3V2(PO4)3. Through activation by K2CO3 and other reactions during the two-step sintering process, a rich and stable porous carbon network is formed in the synthesized material. This synergistic effect of special morphology and interface regulation enables the composite cathode material to effectively improve ionic and electronic conductivity, addressing the inherent problems of Na3V2(PO4)3 materials. Electrochemical and kinetic performance tests have also demonstrated that the product exhibits outstanding high discharge specific capacity and ultra-long stable cycling performance. Furthermore, the synthesis method and raw materials used in the product synthesis stage do not involve complex operations or high-cost consumption; a single operation achieves multiple excellent performance improvements, which is expected to be promoted and practiced in subsequent industrial production.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. 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 be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A potassium carbonate-induced porous carbon framework combined with tripotassium phosphate-coated sodium vanadium phosphate composite cathode material, characterized in that: The composite cathode material is a composite material in which irregularly shaped Na3V2(PO4)3 particles are uniformly attached to a porous carbon framework. An amorphous carbon layer and a K3PO4 double conductive layer are coated around the Na3V2(PO4)3 sample particles; the K3PO4 is obtained from the high-temperature decomposition of potassium carbonate. + With PO4 3- The reaction produces; This composite cathode material uses sodium carbonate, potassium carbonate, ammonium metavanadate, and ammonium dihydrogen phosphate as raw materials, citric acid as a chelating agent, and the amount of K2CO3 is determined according to (PO4). 3- The over-design ratio is calculated as (PO4). 3- The excess of (PO4) in the original NVP synthesis formulation. 3- The amount of K2CO3 required is calculated based on the following: the K2CO3-induced porous carbon framework combined with K3PO4-coated sodium vanadium phosphate composite cathode material is prepared by sol-gel method and two-step sintering. The specific steps for preparing the K2CO3-induced porous carbon framework combined with K3PO4-coated sodium vanadium phosphate composite cathode material are as follows: (1) Sodium carbonate, ammonium dihydrogen phosphate, and ammonium metavanadate in a molar ratio of 1:2.02:1.33 were mixed and dissolved in deionized water. The mixture was heated to 70°C and stirred continuously until a uniformly mixed yellow transparent solution was formed. The molar ratio of citric acid to ammonium metavanadate was controlled at 1:

6. Citric acid was slowly added to the yellow transparent solution until the color finally stabilized at blue. (2) Slowly add potassium carbonate to the blue solution prepared in step (1) until it is completely dissolved, and stir at a constant temperature until the precursor solution is concentrated into a viscous colloid of 20 ml; wherein, the amount of K2CO3 added is (PO4). 3- The excess of (PO4) in the original NVP synthesis formulation. 3- The molar percentages of the substances were 0.5%, 1%, or 5%, and the amounts of potassium carbonate in the three samples were calculated to be 0.006823 g, 0.01364 g, and 0.06823 g, respectively. (3) The viscous colloid prepared in step (2) is dried at 80°C for 12 hours to obtain the precursor; the obtained precursor is pre-calcined at 450°C for 4 hours in a nitrogen atmosphere, and then finally calcined at 700°C for 6 hours to obtain the final product.

2. The application of the potassium carbonate-induced porous carbon framework combined with tripotassium phosphate-coated sodium vanadium phosphate composite cathode material as described in claim 1 in sodium-ion batteries.

3. The application according to claim 2, characterized in that: The specific method is as follows: (1) Preparation of cathode material: The K2CO3-induced porous carbon framework combined with K3PO4-coated sodium vanadium phosphate composite cathode material is used as the active material of cathode material. The total mass of the active material, conductive filler acetylene black and binder polyvinylidene fluoride is controlled to be 0.3g. The active material, conductive filler acetylene black and binder polyvinylidene fluoride are mixed in 1.4 mL of N-methylpyrrolidone NMP solvent at a mass ratio of 7:2:

1. The above mixture is placed in a ball mill jar and ball milled unidirectionally for 4h to obtain a slurry, which is then coated on carbon-coated aluminum foil. After drying at 45℃ for 4h, it is vacuum dried at 120℃ for 6h to obtain the cathode material. (2) Battery assembly: The positive electrode material prepared in step (1) is used as the positive electrode, metallic sodium is used as the negative electrode, ceramic Celgard membrane is used as the membrane, and the electrolyte is NaClO4+EC / DEC+5%FEC; wherein, NaClO4, EC, DEC and FEC are sodium perchlorate, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, respectively; 1M NaClO4 is dissolved in EC / DEC system with a volume ratio of 1:1, and 5wt% FEC is added to prepare electrolyte, and assembled into CR2025 button battery.

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