Preparation method and application of iron ion doped sodium vanadium phosphate positive electrode material

Abstract

The invention belongs to the technical field of sodium ion battery positive electrode materials, and discloses a preparation method and application of an iron ion doped sodium vanadium phosphate positive electrode material. Modification is carried out by doping iron ions in vanadium sites and taking citric acid as a carbon source for coating, iron nitrate nonahydrate serves as an iron source to participate in the modification process, meanwhile, citric acid is used for carrying out carbon coating on the material, and the citric acid and the doped iron ions synergistically increase the ionic conductivity, so that the problem that the sodium vanadium phosphate material is poor in conductivity is solved. Besides, in the sintering treatment process, the Na3V1.8 Fe0.2 (PO4) 3 / C positive electrode material obtained by doping 0.2 molar weight of iron ions and coating citric acid is always kept in the atmosphere of argon-hydrogen mixed gas, after circulation at the current density of 0.1 C to 20 C, the capacity recovery rate can reach up to 96.1%, and the capacity can still be kept to be 74.1% of the initial capacity at the high rate of 20 C; after 500 cycles under 1C current density, the capacity retention rate is 89.8%, while the capacity retention rate is only 72% after 500 cycles of pure NVP, the rate capability and cycling stability of the material are both improved, and the electrochemical performance of the material is effectively ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery positive electrode materials, and relates to a preparation method and application of an iron ion-doped sodium vanadium phosphate positive electrode material. Background Art

[0002] At present, lithium-ion batteries are widely studied and applied. They have the advantages of high efficiency, long discharge time, long life, high operating voltage, and wide operating temperature range. However, the content of lithium resources in the earth's crust is relatively small and unevenly distributed around the world, resulting in the high price of lithium resources and limiting the application of lithium-ion batteries in large-scale energy storage. Therefore, we urgently need to develop a new energy storage battery to replace lithium-ion batteries.

[0003] Sodium and lithium are both in Group 1 of the periodic table and share many similar physical and chemical properties. Furthermore, sodium is abundant and inexpensive. Therefore, sodium-ion batteries are considered the best alternative to lithium-ion batteries. Sodium-ion batteries share the same composition as lithium-ion batteries, primarily consisting of a cathode material, a cathode material, a separator, and an electrolyte. The cathode material, which provides sodium ions for energy storage, plays a crucial role in the electrochemical performance of sodium-ion batteries.

[0004] Sodium vanadium phosphate (Na₃V₂(PO₄)₃), or NVP for short, is a typical polyanionic cathode material with a NASICON-type structure. Its framework provides stable sodium ion capacity, and its open three-dimensional channels provide a transfer pathway for sodium ions. With a high theoretical specific capacity of 117 mAh / g, it is a promising cathode material for sodium-ion batteries. However, currently prepared sodium vanadium phosphate cathode materials suffer from poor electronic conductivity, unstable structure, low reversible capacity, and poor cycling and rate performance, making them difficult to meet the development needs of sodium-ion batteries. Therefore, the modification of sodium vanadium phosphate cathode materials has become a research focus. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention addresses the low specific capacity, poor cycle stability, and rate performance of single sodium vanadium phosphate cathode materials. A method for preparing an iron-ion-doped sodium vanadium phosphate cathode material and its application are provided. This preparation method utilizes readily available raw materials and a simple, rapid synthesis process. By modifying the material through doping with iron ions at the vanadium site and coating with citric acid as a carbon source, the material's specific capacity, rate performance, and cycle stability are effectively improved, providing guidance for the development of cathode materials for sodium-ion batteries.

[0006] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0007] A method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material comprises the following steps:

[0008] S1. The raw material sodium source, vanadium source, phosphorus source, iron source, carbon source are dissolved in water and stirred to obtain a mixed solution;

[0009] S2. The mixed solution was heated in an oil bath and stirred continuously until the mixed solution changed from an orange-red suspension to a clear, stable blue gel;

[0010] S3. The blue gel was transferred to a vacuum drying oven for drying to obtain a foamy blue precursor;

[0011] S4. Grind the blue precursor into powder and place it in an ordinary porcelain boat, then calcine it in a tube furnace. After calcination, cool it naturally to room temperature to obtain the target product Na3V 2-x Fe x (PO4)3 positive electrode material; 0.1≤x≤0.4.

[0012] Furthermore, in step S1, the water is deionized water.

[0013] Furthermore, in step S1, the sodium source is one or more of sodium hydroxide, sodium acetate, sodium carbonate or sodium dihydrogen phosphate; the vanadium source is one or more of ammonium metavanadate, vanadium pentoxide or vanadium trioxide; the phosphorus source is one or more of sodium dihydrogen phosphate, sodium pyrophosphate or ammonium dihydrogen phosphate; the iron source is one or more of ferric nitrate nonahydrate, iron powder or ferric oxide; and the carbon source is one or more of glucose monohydrate, sucrose or citric acid.

[0014] The molar ratio of the sodium source, the vanadium source, the phosphorus source, the iron source and the carbon source is 3:2-x:3:3:x:4; wherein 0.1≤x≤0.4.

[0015] Furthermore, in step S1, the raw materials are dissolved in a beaker containing deionized water, and the weight ratio of the raw materials to deionized water is about 1:1.5, and the mixture is stirred evenly with a glass rod.

[0016] Furthermore, in step S2, the oil bath heating reaction conditions are: reaction temperature is 80-100° C., reaction time is 6-8 h, and stirring is always maintained.

[0017] Furthermore, in step S2, the mixed solution is fixed on an iron stand for oil bath heating reaction.

[0018] Furthermore, in step S3, the drying condition is 80-120° C. for 10-12 hours.

[0019] Furthermore, in step S4, the calcination conditions are as follows: annealing at 350-400°C for 3-5h in an Ar-H2 (90:10) mixed gas, heating to 800-850°C at a rate of 5-10°C / min, and calcining at 800-850°C for 6-8h.

[0020] The present invention also claims protection for the use of the iron ion-doped sodium vanadium phosphate positive electrode material prepared by the above-mentioned preparation method in the preparation of a positive electrode for a sodium ion battery. Using N-methylpyrrolidone solution as a solvent, the iron ion-doped sodium vanadium phosphate positive electrode material, polyvinylidene fluoride, and acetylene black are thoroughly mixed and stirred in a ball mill at a mass ratio of 8:1:1 for 12 hours to prepare a positive electrode slurry. The slurry is then evenly coated on aluminum foil using an applicator. After drying in a vacuum drying oven for 12 hours, it is cut into 12mm circular pole pieces to form a positive electrode composite material. The obtained positive electrode composite material is used as a positive electrode in a sodium ion battery, has a higher specific capacity, effectively improves its electrochemical performance, and has excellent rate performance and stable cycle performance.

[0021] The beneficial effects of the present invention compared with the prior art are:

[0022] The present invention addresses the problem of poor conductivity of sodium vanadium phosphate materials by modifying them by doping them with iron ions at the vanadium position and coating them with citric acid as a carbon source. Ferric nitrate nine hydrate is used as an iron source in the modification process. At the same time, citric acid is used to carbon-coat the material, which synergistically increases the ionic conductivity with the doping of iron ions, thereby improving the poor conductivity of sodium vanadium phosphate materials. In addition, during the sintering process, the atmosphere of argon-hydrogen mixed gas is always maintained, and the Na3V3 obtained by doping with 0.2 moles of iron ions and coating with citric acid is heated to 100 ℃. 1.8 Fe 0.2 After cycling at current densities of 0.1C to 20C, the capacity recovery rate of the (PO4)3 / C positive electrode material can reach as high as 96.1%, and the capacity can still be maintained at 74.1% of the initial capacity at a high rate of 20C. After 500 cycles at a current density of 1C, the capacity retention rate is 89.8%, while the capacity retention rate of pure NVP after 500 cycles is only 72%. Both the rate performance and cycle stability have been improved, effectively ensuring its electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 These are the X-ray diffraction patterns of NVFP / C-0.2 prepared in Example 2 of the present invention and NVP prepared in Comparative Example 1.

[0024] Figure 2 This is a scanning electron microscope image of NVFP / C-0.2 prepared in Example 2 of the present invention.

[0025] Figure 3 This is an EDS photograph of NVFP / C-0.2 prepared in Example 2 of the present invention.

[0026] Figure 4The rate performance diagram of NVFP / C-0.1 prepared in Example 1 of the present invention, NVFP / C-0.2 prepared in Example 2, NVFP / C-0.3 prepared in Example 3, NVFP / C-0.4 prepared in Example 4, and NVP prepared in Comparative Example 1.

[0027] Figure 5 This is a cycle performance diagram of NVFP / C-0.2 prepared in Example 2 of the present invention and NVP prepared in Comparative Example 1. DETAILED DESCRIPTION

[0028] The present invention is described in detail below by specific examples, but the scope of protection of the present invention is not limited. Unless otherwise specified, the experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0029] Example 1

[0030] A method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material comprises the following steps:

[0031] (1) Weigh 0.03 mol of sodium hydroxide, 0.019 mol of ammonium metavanadate, 0.03 mol of ammonium dihydrogen phosphate, 0.04 mol of citric acid, and 0.001 mol of ferric nitrate nonahydrate and dissolve them in a beaker containing 200 mL of deionized water. Stir the mixture with a glass rod to obtain a mixed solution.

[0032] (2) Fixing the mixed solution obtained in step (1) on an iron stand and performing an oil bath heating reaction, setting the reaction temperature to 80-100°C and the reaction time to 8 hours, and always stirring until the mixed solution changes from an orange-red suspension to a clear and stable blue gel;

[0033] (3) The blue gel was transferred to a vacuum drying oven and dried at 120°C for 12 h to obtain a foamy blue precursor;

[0034] (4) The blue precursor was ground into powder and placed in an ordinary porcelain boat, which was then placed in a tube furnace and annealed at 350 °C for 3 h in an Ar-H2 (90:10) mixed gas. The temperature was raised to 800 °C at a rate of 5 °C / min, calcined at 800 °C for 8 h, and naturally cooled to room temperature to obtain the target product Na3V 1.9 Fe 0.1 (PO4)3 / C positive electrode material (NVFP / C-0.1).

[0035] Example 2

[0036] A method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material comprises the following steps:

[0037] (1) Weigh 0.03 mol of sodium hydroxide, 0.018 mol of ammonium metavanadate, 0.03 mol of ammonium dihydrogen phosphate, 0.04 mol of citric acid, and 0.002 mol of ferric nitrate nonahydrate and dissolve them in a beaker containing 200 mL of deionized water. Stir the mixture with a glass rod to obtain a mixed solution.

[0038] (2) Fixing the mixed solution obtained in step (1) on an iron stand and performing an oil bath heating reaction, setting the reaction temperature to 80-100°C and the reaction time to 8 hours, and always stirring until the mixed solution changes from an orange-red suspension to a clear and stable blue gel;

[0039] (3) The blue gel was transferred to a vacuum drying oven and dried at 120°C for 12 h to obtain a foamy blue precursor;

[0040] (4) The blue precursor was ground into powder and placed in an ordinary porcelain boat, which was then placed in a tube furnace and annealed at 350 °C for 3 h in an Ar-H2 (90:10) mixed gas. The temperature was raised to 800 °C at a rate of 5 °C / min, calcined at 800 °C for 8 h, and naturally cooled to room temperature to obtain the target product Na3V 1.8 Fe 0.2 (PO4)3 / C positive electrode material (NVFP / C-0.2).

[0041] Example 3

[0042] A method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material comprises the following steps:

[0043] (1) Weigh 0.03 mol of sodium hydroxide, 0.017 mol of ammonium metavanadate, 0.03 mol of ammonium dihydrogen phosphate, 0.04 mol of citric acid, and 0.003 mol of ferric nitrate nonahydrate and dissolve them in a beaker containing 200 mL of deionized water. Stir the mixture with a glass rod to obtain a mixed solution.

[0044] (2) Fixing the mixed solution obtained in step (1) on an iron stand and performing an oil bath heating reaction, setting the reaction temperature to 80-100°C and the reaction time to 8 hours, and always stirring until the mixed solution changes from an orange-red suspension to a clear and stable blue gel;

[0045] (3) The blue gel was transferred to a vacuum drying oven and dried at 120°C for 12 h to obtain a foamy blue precursor;

[0046] (4) The blue precursor was ground into powder and placed in an ordinary porcelain boat, which was then placed in a tube furnace and annealed at 350 °C for 3 h in an Ar-H2 (90:10) mixed gas. The temperature was raised to 800 °C at a rate of 5 °C / min, calcined at 800 °C for 8 h, and naturally cooled to room temperature to obtain the target product Na3V 1.7 Fe0.3 (PO4)3 / C positive electrode material (NVFP / C-0.3).

[0047] Example 4

[0048] A method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material comprises the following steps:

[0049] (1) Weigh 0.03 mol of sodium hydroxide, 0.016 mol of ammonium metavanadate, 0.03 mol of ammonium dihydrogen phosphate, 0.04 mol of citric acid, and 0.004 mol of ferric nitrate nonahydrate and dissolve them in a beaker containing 200 mL of deionized water. Stir the mixture with a glass rod to obtain a mixed solution.

[0050] (2) Fixing the mixed solution obtained in step (1) on an iron stand and performing an oil bath heating reaction, setting the reaction temperature to 80-100°C and the reaction time to 8 hours, and always stirring until the mixed solution changes from an orange-red suspension to a clear and stable blue gel;

[0051] (3) The blue gel was transferred to a vacuum drying oven and dried at 120°C for 12 h to obtain a blue foam precursor;

[0052] (4) The blue precursor was ground into powder and placed in an ordinary porcelain boat, which was then placed in a tube furnace and annealed at 350 °C for 3 h in an Ar-H2 (90:10) mixed gas. The temperature was raised to 800 °C at a rate of 5 °C / min, calcined at 800 °C for 8 h, and naturally cooled to room temperature to obtain the target product Na3V 1.6 Fe 0.4 (PO4)3 / C positive electrode material (NVFP / C-0.4).

[0053] Comparative Example 1

[0054] A method for preparing a sodium vanadium phosphate positive electrode material comprises the following steps:

[0055] (1) Weigh 0.03 mol of sodium hydroxide, 0.02 mol of ammonium metavanadate, and 0.03 mol of ammonium dihydrogen phosphate and dissolve them in a beaker containing 200 mL of deionized water. Stir the mixture with a glass rod to obtain a mixed solution.

[0056] (2) Fixing the mixed solution obtained in step (1) on an iron stand and performing an oil bath heating reaction, setting the reaction temperature to 80-100°C and the reaction time to 8 hours, and always stirring until the mixed solution changes from an orange-red suspension to a clear and stable blue gel;

[0057] (3) The blue gel was transferred to a vacuum drying oven and dried at 120°C for 12 h to obtain a foamy blue precursor;

[0058] (4) The blue precursor was ground into powder and placed in an ordinary porcelain boat, which was placed in a tube furnace and annealed at 350 °C for 3 h in an Ar-H2 (90:10) mixed gas. The temperature was raised to 800 °C at a rate of 5 °C / min, and calcined at 800 °C for 8 h. The target product, Na3V2(PO4)3 positive electrode material (NVP), was obtained by natural cooling to room temperature.

[0059] Specific application test:

[0060] Applied test materials: NVFP / C-0.1 prepared in Example 1, NVFP / C-0.2 prepared in Example 2, NVFP / C-0.3 prepared in Example 3, NVFP / C-0.4 prepared in Example 4, and NVP positive electrode materials prepared in Comparative Example 1.

[0061] Positive electrode preparation: Using N-methylpyrrolidone solution as solvent, the prepared positive electrode materials (NVFP / C-0.1 prepared in Example 1, NVFP / C-0.2 prepared in Example 2, NVFP / C-0.3 prepared in Example 3, NVFP / C-0.4 prepared in Example 4, NVP prepared in Comparative Example 1), polyvinylidene fluoride and acetylene black were thoroughly mixed and stirred in a ball mill at a mass ratio of 8:1:1 for 12 hours to prepare a positive electrode slurry. The slurry was then evenly coated on aluminum foil using a coater. After drying in a vacuum drying oven for 12 hours, the slurry was cut into 12 mm circular pieces to obtain the positive electrode materials. Five corresponding positive electrode materials were obtained.

[0062] Testing method: 2032 coin cells were assembled in a glove box using the obtained cathode materials as the positive electrode and metallic sodium as the negative electrode. A NaClO₄ + EC:PC = 1:1 + 5% FEC solution was used as the electrolyte, and GF / D glass fiber was used as the separator.

[0063] Battery Performance Testing: After the assembled 2032 button cell batteries were left to rest for 12 hours, the capacity of the battery's positive electrode material was measured. The batteries were then charged and discharged at a current density of 1C, with a voltage setting range of 2.3-4.1V.

[0064] Figure 1 The X-ray diffraction patterns of NVFP / C-0.2 prepared in Example 2 of the present invention and NVP prepared in Comparative Example 1 show that the diffraction peaks are strong and sharp, indicating that Na3V 2-x Fe x The (PO4)3 / C positive electrode material has good crystallinity and no other impurities are present.

[0065] Figure 2 Shown in FIG is a scanning electron microscope image of NVFP / C-0.2 prepared in Example 2 of the present invention. Figure 3The EDS photograph of NVFP / C-0.2 prepared in Example 2 of the present invention shows that the particles obtained when the molar amount of doped iron is 0.2 are more dispersed and the particle size is more uniform, that is, appropriate iron ion doping can inhibit the agglomeration of particles and each element is evenly distributed in the material.

[0066] Figure 4 It can be seen that among the materials obtained by comparing different molar doping amounts of iron ions, the Na3V 1.8 Fe 0.2 The (PO4)3 / C material has excellent rate performance. After cycling at current densities from 0.1C to 20C, the capacity recovery rate can be as high as 96.1%, and at a high rate of 20C, the capacity can still be maintained at 74.1% of the initial capacity.

[0067] Figure 5 The cycling performance of NVFP / C-0.2 prepared in Example 2 of the present invention and NVP prepared in Comparative Example 1 at a current density of 1C. 1.8 Fe 0.2 After 500 cycles at a current density of 1C, the capacity retention rate of (PO4)3 / C is 89.8%, while the capacity retention rate of pure NVP after 500 cycles is 72%. This shows that the modified material has better cycle stability.

[0068] The positive electrode material prepared in Example 2 of the present invention is specifically applied to the obtained battery, which has high battery capacity, better cycle stability and rate performance. On the basis of the original sodium vanadium phosphate material, iron element is doped and citric acid is used as a carbon source for coating. The synergistic effect between the two reduces the particle size of the material, increases the electronic conductivity of the material, shortens the sodium ion transfer path, and thus improves the overall electrochemical performance of the positive electrode material.

[0069] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material, characterized in that: The following steps are involved: S1. The raw material sodium source, vanadium source, phosphorus source, iron source, carbon source are dissolved in water and stirred to obtain a mixed solution; S2. The mixed solution was heated in an oil bath and stirred continuously until the mixed solution changed from an orange-red suspension to a clear, stable blue gel; S3. The blue gel was transferred to a vacuum drying oven for drying to obtain a foamy blue precursor; S4. Grind the blue precursor into powder and place it in an ordinary porcelain boat, which is then placed in a tube furnace for calcination. After calcination, naturally cool it to room temperature to obtain the target product, Na3V2-xFex(PO4)3, a positive electrode material; 0.1≤x≤0.

4.

2. The method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material according to claim 1, wherein: In step S1, the sodium source is one or more of sodium hydroxide, sodium acetate, sodium carbonate or sodium dihydrogen phosphate; the vanadium source is one or more of ammonium metavanadate, vanadium pentoxide or vanadium trioxide; the phosphorus source is one or more of sodium dihydrogen phosphate, sodium pyrophosphate or ammonium dihydrogen phosphate; the iron source is one or more of ferric nitrate nonahydrate, iron powder or ferric oxide; and the carbon source is one or more of glucose monohydrate, sucrose or citric acid.

3. The method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material according to claim 1, wherein: In step S1, the water is deionized water.

4. The method for preparing an iron ion-doped sodium vanadium phosphate cathode material according to claim 1, wherein the steps In S1, the molar ratio of the sodium source, vanadium source, phosphorus source, iron source, and carbon source is 3:2-x:3:3:x:4; wherein 0.1≤x≤0.

4.

5. The method for preparing an iron ion-doped sodium vanadium phosphate positive electrode material according to claim 1, wherein: In step S2, the oil bath heating reaction conditions are: reaction temperature is 80-100° C., reaction time is 6-8 h, and stirring is always maintained.

6. The method for preparing an iron ion-doped sodium vanadium phosphate cathode material according to claim 1, wherein: In step S3, the drying condition is 80-120° C. for 10-12 hours.

7. The method for preparing an iron ion-doped sodium vanadium phosphate cathode material according to claim 1, wherein: In step S4, the calcination conditions are as follows: annealing at 350-400° C. for 3-5 h in an Ar-H 2 (90:10) mixed gas, heating to 800-850° C. at a rate of 5-10° C. / min, and calcining at 800-850° C. for 6-8 h.

8. Use of the iron ion-doped sodium vanadium phosphate positive electrode material prepared by the preparation method according to any one of claims 1 to 6 in preparing a positive electrode for a sodium ion battery.

9. The use of the positive electrode material according to claim 8, characterized in that: The mass ratio of positive electrode material: polyvinylidene fluoride: acetylene black is 8:1:1.

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