Preparation method of phosphorus-based sodium ion battery positive electrode material with excellent electrochemical performance

Abstract

The application discloses a preparation method of a phosphorus-based sodium ion battery positive electrode material with excellent electrochemical performance, and comprises the following steps: 1) dissolving citric acid, sodium fluoride and vanadium chloride in distilled water to obtain a mixed solution A, and dissolving sodium phosphate in distilled water to obtain a phosphate solution; 2) mixing the obtained mixed solution A and the phosphate solution to obtain a mixed solution B; 3) adding a carbon material into the mixed solution B, and adjusting the pH value by using a saturated sodium carbonate solution; 4) when the pH value adjustment in the step 3) is completed, performing a heating reaction to obtain a precipitate; and 5) washing the obtained precipitate, placing the washed precipitate into a tube furnace, and performing high-temperature calcination under a nitrogen environment atmosphere to obtain the phosphorus-based sodium ion battery positive electrode material. The application has the characteristics of simple process operation, easily-obtained raw materials, one-time nano-level product particles and high purity.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material production technology, and in particular to a method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance. Background Technology

[0002] With the increasing global demand for renewable energy, energy storage technology is becoming increasingly important. Lithium-ion batteries dominate the market due to their high energy density and long lifespan. However, lithium resources are relatively scarce and expensive. To reduce costs and promote sustainable development, researchers have begun to explore other ion battery systems, among which sodium-ion batteries have attracted considerable attention.

[0003] As an important energy storage device, improving the performance of batteries is crucial for the development of new energy sources. However, lithium-ion batteries are expensive and have a limited energy density, limiting their application in large-scale energy storage. Currently, commercially available battery cathode materials mainly include lithium cobalt oxide and ternary materials, which are expensive, resource-scarce, and unsuitable for large-scale use.

[0004] Traditional lithium-ion batteries have achieved great success in the field of energy storage, but lithium resources are limited and expensive. Therefore, researchers have begun to focus on alternative energy storage technologies. Sodium-ion batteries have received widespread attention due to the abundance of sodium resources and relatively low cost. The cathode material of sodium-ion batteries is a key component, and its performance and synthesis methods are crucial to the battery's performance.

[0005] Sodium-ion batteries are a more economical alternative to lithium-ion batteries. As a new type of battery, they have become a research hotspot due to their advantages such as high energy density and low cost. Among them, phosphorus-based cathode materials are widely used in sodium-ion batteries due to their good stability and large capacity. However, their application still has some problems, such as the slow diffusion rate of sodium ions in phosphorus-based cathode materials and the rapid capacity decay. At present, the preparation methods of phosphorus-based sodium-ion cathode materials mainly include solid-state method, sol-gel method, and hydrothermal method. These methods have problems such as long preparation cycle, high cost and complex process, which limit the application of phosphorus-based cathode materials. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance. This method solves the problems of poor performance, long preparation cycle, high cost, and complex processes associated with existing phosphorus-based sodium-ion battery cathode materials.

[0007] The solution of the present invention is:

[0008] A method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance includes the following steps:

[0009] 1) Dissolve citric acid, sodium fluoride and vanadium chloride in distilled water to obtain mixed solution A, and dissolve sodium phosphate in distilled water to obtain phosphate solution;

[0010] 2) Mix the obtained mixed solution A with the phosphate solution to obtain mixed solution B;

[0011] 3) After adding carbon material to the mixed solution B, adjust the pH value with saturated sodium carbonate solution;

[0012] 4) After the pH value in step 3) has been adjusted, a heating reaction is carried out to obtain a precipitate;

[0013] 5) The obtained precipitate is washed clean and placed in a tube furnace for high-temperature calcination under a nitrogen atmosphere to obtain a phosphorus-based sodium-ion battery cathode material.

[0014] As a preferred technical solution, in step 1), the molar mass ratio of citric acid, sodium fluoride and vanadium chloride is 0.8-1:2.7-3.3:2-2.2, and the molar mass of sodium phosphate in step 1) is 1.8-2.2.

[0015] As a preferred technical solution, the order of adding citric acid, sodium fluoride and vanadium chloride in step 1) is as follows: first, fully dissolve citric acid in an appropriate amount of water, then add vanadium chloride and stir thoroughly, then add sodium fluoride and stir thoroughly for 30 minutes.

[0016] Vanadium chloride dissolves in water and decomposes to form vanadate (V). 5+ The reason for adding vanadium chloride to citric acid, rather than adding citric acid to vanadium chloride, is that citric acid, as a reducing agent, can quickly convert pentavalent vanadium in vanadium chloride to trivalent vanadium if used in large quantities. Moreover, this allows the reaction to be completed quickly and efficiently at room temperature. If citric acid is added to vanadium chloride, the reaction will be slow, and the water in the reaction system will evaporate, affecting the final reactants. The optimal reaction temperature for the complexation of citric acid and vanadium chloride is between 45 and 60 degrees Celsius. Below 45 degrees Celsius, the reaction will be incomplete, while above 60 degrees Celsius, it will promote the transformation of vanadium to other valence states.

[0017] As a preferred technical solution, the amount of carbon material added in step 3) is 0.5% to 2% of the total mass of the mixed solution B.

[0018] As a preferred technical solution, in step 3), after adding carbon material, a dispersant is added, and the pH value is adjusted with a saturated sodium carbonate solution; the dispersant is one or both of sodium dodecyl sulfate K12 or hexadecyltrimethylammonium bromide, and the amount of the dispersant added is 10% to 15% of the mass of the carbon material.

[0019] The carbon material here is extremely difficult to disperse due to the micron to nanometer particle size of both materials, even after stirring. Sodium dodecyl sulfate K12 or hexadecyltrimethylammonium bromide are surface-active materials that have good dispersion performance for both materials. In addition, during the product crystallization process, sodium dodecyl sulfate K12 or hexadecyltrimethylammonium bromide can improve defects in the crystals. Adding a dispersant and then using ultrasound to disperse further improves the dispersion effect.

[0020] As a preferred technical solution, the carbon material includes carbon fiber and conductive carbon black, which are mixed and formulated in a mass ratio of 7:3.

[0021] The carbon material is a mixture of carbon fiber and conductive carbon black in a mass ratio of 7:3. The carbon fiber is in the form of wire, and the conductive carbon black is in the form of granules. The combination of the two makes it easier to insert the carbon material into the product, reducing the energy required to synthesize the product and improving the product's conductivity. However, increasing the proportion of carbon fiber or conductive carbon black will lead to a decrease in the electrical performance of the final product, specifically a decrease in cycle life and rate performance.

[0022] As a preferred technical solution, step 3) involves adjusting the pH value to 9-12 using a saturated sodium carbonate solution.

[0023] As a preferred technical solution, the heating reaction in step 4) to obtain the precipitate is to react at 80-120°C for 30 minutes to obtain the precipitate.

[0024] As a preferred technical solution, the high-temperature calcination temperature in step 5) is 700-1000℃, and the calcination time is 2-8 hours.

[0025] As a preferred technical solution, in step 5), alumina is added to the tube furnace during calcination, and the doping ratio of alumina is controlled at 1‰ to 5‰ of the precipitate mass; at the same time, titanium oxide powder is also added to the tube furnace during calcination, and the amount of titanium oxide powder is 1‰ to 2‰ of the precipitate mass.

[0026] Adding alumina during calcination increases the energy density of the final product by 8%-10% compared to calcination without alumina. The added alumina powder is thoroughly ground and passed through a 350-mesh sieve before being added to the product for calcination. The preferred calcination temperature is 750℃, and the calcination time is 4 hours. Due to the fine particle size, the alumina is evenly distributed throughout the product, compensating for crystal irregularities and improving product stability, thereby enhancing the product's electrochemical performance, including cycle and rate performance. Titanium doping, on the one hand, increases the product's compaction density during calcination, thus increasing energy density; on the other hand, it also compensates for crystal irregularities, improving product stability and thus enhancing the product's electrochemical performance. The addition of titanium oxide complements that of alumina.

[0027] The preparation method of a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance using the above-mentioned technical solution includes the following steps: 1) Dissolving citric acid, sodium fluoride and vanadium chloride in distilled water to obtain mixed solution A, and dissolving sodium phosphate in distilled water to obtain phosphate solution; 2) Mixing the obtained mixed solution A and phosphate solution to obtain mixed solution B; 3) Adding carbon material to the mixed solution B and adjusting the pH value with saturated sodium carbonate solution; 4) After the pH value adjustment in 3) is completed, heating reaction is carried out to obtain precipitation; 5) Washing the obtained precipitate and placing it in a tube furnace for high-temperature calcination in a nitrogen atmosphere to obtain phosphorus-based sodium-ion battery cathode material.

[0028] Advantages of this invention:

[0029] The present invention features simple operation, readily available raw materials, and high purity, producing nano-sized particles in a single process. The resulting product is Na3V2(PO4)2F3, which exhibits excellent electrochemical performance, as follows:

[0030] ① High specific capacity: The initial discharge specific capacity is 118 mAh / g at 0.1C rate; ② Good cycle stability: After 200 cycles at 0.5C rate, the discharge capacity is still 114 mAh / g; ③ Excellent rate performance: Cycling tests at different rates show that the material has good rate performance and can maintain a high specific capacity even at high rates.

[0031] Adding carbon materials before adjusting the pH of the solution, along with a dispersant, ensures the homogeneity of the reaction system. This is because the pH is adjusted after adding carbon materials, and the mixture is stirred for 30 minutes, resulting in a more uniform distribution of carbon. Furthermore, adding this portion of carbon materials before pH adjustment helps maintain the stability of the reaction system. Therefore, compared to adding carbon materials after pH adjustment, adding carbon materials before pH adjustment reduces the temperature required for synthesis and improves the crystallinity (purity) and conductivity of the product. Attached Figure Description

[0032] Figure 1 The XRD pattern of Na3V2(PO4)2F3 during detection in Example 1 of this invention;

[0033] Figure 2 This is the SEM electron microscope image of Na3V2(PO4)2F3 detected in Example 1 of the present invention;

[0034] Figure 3 The graph shows the electrochemical cycling performance (200 cycles at 0.5C rate) of Na3V2(PO4)2F3 during testing in Example 1 of this invention.

[0035] Figure 4 This is a graph showing the performance test of Na3V2(PO4)2F3 at high rate during testing in Example 1 of the present invention. Detailed Implementation

[0036] This invention provides a method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance.

[0037] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0038] Example 1:

[0039] Material preparation:

[0040] Citric acid, sodium fluoride, and vanadium chloride were dissolved in distilled water at a molar ratio of 1:3:2 to obtain mixed solution A. Sodium phosphate at a molar mass of 2 was dissolved in distilled water to obtain phosphate solution B. Solutions A and B were mixed together, and carbon material (carbon fiber and conductive carbon black in a 7:3 ratio) was added at a dosage of 1% of the total mass. Then, 10% of the carbon material mass of hexadecyltrimethylammonium bromide was added, and the pH was adjusted to 9 with saturated sodium carbonate solution. The mixture was reacted at 80–120 °C for 30 min to form a precipitate. After the precipitate was washed clean, it was calcined in a tube furnace at 800 °C under a nitrogen atmosphere with 2‰ alumina and 1‰ titanium oxide powder for 4 h to obtain Na3V2(PO4)2F3 powder.

[0041] The obtained material was subjected to electrochemical performance testing.

[0042] Na3V2(PO4)2F3 powder, Super-P carbon black and polyvinyl alcohol (PVA) were mixed evenly in a mass ratio of 8:1:1, coated on aluminum foil, and made into an electrode.

[0043] The Series 4000 high-precision battery testing equipment was used as the testing platform, and pure sodium metal was used as the symmetrical electrode to test the electrochemical performance (cycle and rate performance) of the samples.

[0044] The electrochemical performance test results are as follows:

[0045] The XRD pattern of Na3V2(PO4)2F3 is as follows: Figure 1 As shown, the results are consistent with the standard spectrum, indicating that the obtained product is Na3V2(PO4)2F3 crystal with a crystallinity of 88.1%.

[0046] The SEM image of Na3V2(PO4)2F3 is shown below. Figure 2 As shown, the product has a columnar crystal structure, and the primary particles are all nanoscale.

[0047] After 200 cycles at 0.5C, the discharge capacity remained at 114 mAh / g, exhibiting a capacity retention of 99%, demonstrating excellent cycling performance. Cycling tests at different rates revealed good rate performance, maintaining a high specific capacity even at high rates. Furthermore, at current densities of 0.1C, 0.5C, 5C, and 10C, the initial discharge specific capacities were 118 mAh / g, 115 mAh / g, 100 mAh / g, and 90 mAh / g, respectively. Restoring the current density to 0.1C, the discharge specific capacity recovered to 118 mAh / g, demonstrating excellent electrochemical reversibility. (See details...) Figure 3 and Figure 4 .

[0048] Example 2: (Adding carbon material after adjusting the pH of the solution)

[0049] Material preparation:

[0050] Citric acid, sodium fluoride, and vanadium chloride were dissolved in distilled water at a molar ratio of 1:3:2 to obtain mixed solution A. Sodium phosphate at a molar mass of 2 was dissolved in distilled water to obtain phosphate solution B. Solutions A and B were mixed and the pH was adjusted to 9 with saturated sodium carbonate solution. Carbon material (carbon fiber and conductive carbon black at a ratio of 7:3) was added at a dosage of 1% of the total mass. Then, 10% of the carbon material mass of hexadecyltrimethylammonium bromide was added. The mixture was reacted at 80-120℃ for 30 min to form a precipitate. After the precipitate was washed clean, 2‰ alumina and 1‰ titanium oxide powder were added to the tube furnace at a temperature of 800℃ under a nitrogen atmosphere and calcined for 4 h to obtain Na3V2(PO4)2F3 powder.

[0051] The obtained material was tested according to the electrochemical performance testing method in Example 1. The experimental test results are shown in Table 1 below.

[0052] Example 3: (Carbon materials (carbon fiber and conductive carbon black in an 8:2 ratio))

[0053] Material preparation:

[0054] Citric acid, sodium fluoride, and vanadium chloride were dissolved in distilled water at a molar ratio of 1:3:2 to obtain mixed solution A. Sodium phosphate at a molar mass of 2 was dissolved in distilled water to obtain phosphate solution B. Solutions A and B were mixed together, and carbon material (carbon fiber and conductive carbon black at a ratio of 8:2) at a dosage of 1% of the total mass was added. Then, 10% of the carbon material mass of hexadecyltrimethylammonium bromide was added, and the pH was adjusted to 9 with saturated sodium carbonate solution. The mixture was reacted at 80-120℃ for 30 min to form a precipitate. After the precipitate was washed clean, it was calcined in a tube furnace at 800℃ under a nitrogen atmosphere with 2‰ alumina and 1‰ titanium oxide powder for 4 h to obtain Na3V2(PO4)2F3 powder.

[0055] The obtained material was tested according to the electrochemical performance testing method in Example 1. The experimental test results are shown in Table 1 below.

[0056] Example 4: (Dispersant dosage is 5% of carbon material)

[0057] Material preparation:

[0058] Citric acid, sodium fluoride, and vanadium chloride were dissolved in distilled water at a molar ratio of 1:3:2 to obtain mixed solution A. Sodium phosphate at a molar mass of 2 was dissolved in distilled water to obtain phosphate solution B. Solutions A and B were mixed together, and carbon material (carbon fiber and conductive carbon black at a ratio of 8:2) at a dosage of 1% of the total mass was added. Then, 5% of the carbon material mass of hexadecyltrimethylammonium bromide was added, and the pH was adjusted to 9 with saturated sodium carbonate solution. The mixture was reacted at 80-120℃ for 30 min to form a precipitate. After the precipitate was washed clean, it was calcined in a tube furnace at 800℃ under a nitrogen atmosphere with 2‰ alumina and 1‰ titanium oxide powder for 4 h to obtain Na3V2(PO4)2F3 powder.

[0059] The obtained material was tested according to the electrochemical performance testing method in Example 1. The experimental test results are shown in Table 1 below.

[0060] Example 5: (6‰ alumina and 3‰ titanium dioxide powder were added during calcination)

[0061] Material preparation:

[0062] Citric acid, sodium fluoride, and vanadium chloride were dissolved in distilled water at a molar ratio of 1:3:2 to obtain mixed solution A. Sodium phosphate at a molar mass of 2 was dissolved in distilled water to obtain phosphate solution B. Solutions A and B were mixed together, and carbon material (carbon fiber and conductive carbon black in a 7:3 ratio) at a dosage of 1% of the total mass was added. Then, 10% of the carbon material mass of hexadecyltrimethylammonium bromide was added, and the pH was adjusted to 9 with saturated sodium carbonate solution. The mixture was reacted at 80-120℃ for 30 min to form a precipitate. After the precipitate was washed clean, it was calcined in a tube furnace at 800℃ under a nitrogen atmosphere with 6‰ alumina and 3‰ titanium oxide powder for 4 h to obtain Na3V2(PO4)2F3 powder.

[0063] The obtained material was tested according to the electrochemical performance testing method in Example 1. The experimental test results are shown in Table 1 below.

[0064] Example 6: (No alumina and titanium dioxide powder were added during calcination)

[0065] Material preparation:

[0066] Citric acid, sodium fluoride, and vanadium chloride were dissolved in distilled water at a molar ratio of 1:3:2 to obtain mixed solution A. Sodium phosphate at a molar mass of 2 was dissolved in distilled water to obtain phosphate solution B. Solutions A and B were mixed together, and carbon material (carbon fiber and conductive carbon black at a ratio of 7:3) at a dosage of 1% of the total mass was added. Then, 10% of the carbon material mass of hexadecyltrimethylammonium bromide was added, and the pH was adjusted to 9 with saturated sodium carbonate solution. The mixture was reacted at 80-120℃ for 30 min to form a precipitate. After the precipitate was washed clean, it was calcined in a tube furnace at 800℃ for 4 h under a nitrogen atmosphere to obtain Na3V2(PO4)2F3 powder.

[0067] The obtained material was tested according to the electrochemical performance testing method in Example 1. The experimental test results are shown in Table 1 below.

[0068] Table 1. Average discharge specific capacity of products obtained from specific examples 1 to 6

[0069]

[0070] By analyzing the electrochemical performance of the products, Example 1 is the best embodiment of this invention. Example 2 involves adding carbon material after adjusting the pH value of the solution. Example 3 involves carbon material (carbon fiber and conductive carbon black in an 8:2 ratio). Example 4 involves a dispersant dosage of 5% of the carbon material. Example 5 involves adding 6‰ alumina and 3‰ titanium oxide powder during calcination. Example 6 involves not adding alumina and titanium oxide powder during calcination. The electrochemical performance of the product in Example 1 is superior to that in Examples 2 to 6.

[0071] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance, characterized in that, Includes the following steps: Step 1) Dissolve citric acid, sodium fluoride and vanadium chloride in distilled water to obtain mixed solution A. At the same time, dissolve sodium phosphate in distilled water to obtain phosphate solution. The order of adding citric acid, sodium fluoride and vanadium chloride is as follows: first, dissolve citric acid in an appropriate amount of water, then add vanadium chloride and stir thoroughly, then add sodium fluoride and stir thoroughly. Step 2) Mix the obtained mixed solution A with the phosphate solution to obtain mixed solution B; Step 3) After adding carbon material to the mixed solution B, adjust the pH value with saturated sodium carbonate solution; Step 4) After the pH value is adjusted in step 3), a heating reaction is carried out to obtain a precipitate; Step 5) The obtained precipitate is washed clean and placed in a tube furnace. It is then calcined at high temperature in a nitrogen atmosphere to obtain a phosphorus-based sodium-ion battery cathode material. During calcination, alumina is added to the tube furnace, and the alumina doping ratio is controlled at 1‰ to 5‰ of the precipitate mass. At the same time, titanium oxide powder is also added to the tube furnace during calcination, and the titanium oxide powder doping amount is 1‰ to 2‰ of the precipitate mass.

2. The method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance as described in claim 1, characterized in that: In step 1), the molar mass ratio of citric acid, sodium fluoride, and vanadium chloride is 0.8–1:2.7–3.3:2–2.2, and the molar mass of sodium phosphate in step 1) is 1.8–2.

2.

3. The method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance as described in claim 1, characterized in that: In step 1), the order of adding citric acid, sodium fluoride and vanadium chloride is as follows: first, dissolve citric acid in an appropriate amount of water, then add vanadium chloride and stir thoroughly, then add sodium fluoride and stir thoroughly for 30 minutes.

4. The method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance as described in claim 1, characterized in that: In step 3), the amount of carbon material added is 0.5% to 2% of the total mass of the mixed solution B.

5. The method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance as described in claim 1, characterized in that: In step 3), after adding the carbon material, a dispersant is added, and the pH value is adjusted with a saturated sodium carbonate solution. The dispersant is one or both of sodium dodecyl sulfate K12 or hexadecyltrimethylammonium bromide, and the amount of the dispersant added is 10% to 15% of the mass of the carbon material.

6. The method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance as described in claim 1, characterized in that: The carbon material includes carbon fiber and conductive carbon black, which are mixed in a mass ratio of 7:

3.

7. The method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance as described in claim 1, characterized in that: Step 3) involves adjusting the pH value to 9-12 using a saturated sodium carbonate solution.

8. The method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance as described in claim 1, characterized in that: The precipitate obtained by heating in step 4) is obtained by reacting at 80-120°C for 30 minutes.

9. The method for preparing a phosphorus-based sodium-ion battery cathode material with excellent electrochemical performance as described in claim 1, characterized in that: In step 5), the high-temperature calcination temperature is 700–1000℃, and the calcination time is 2–8 hours.

Images