A niobium-doped sodium fluorophosphate and a preparation method and application thereof

Abstract

The application relates to a ni-doped sodium fluorophosphate and a preparation method and application thereof. According to the atomic molar ratio of each element in a chemical general formula, a sodium source, an iron source, a ni source, a phosphorus source and a fluorine source are weighed to obtain raw materials; the raw materials are ball milled to obtain mixed slurry and dried mixed powder after vacuum drying to remove the ball milling solvent; the dried mixed powder is pressed into a sheet and placed in a crucible, pre-sintering is carried out under inert gas protection, the precursor powder is obtained after being ground after being cooled to room temperature; a carbon source and a ball milling solvent are ball milled with the precursor powder, vacuum drying and tablet pressing are sequentially carried out to obtain a tablet; high-temperature sintering is carried out on the tablet under inert gas protection, the tablet is cooled to room temperature in the furnace after high-temperature sintering, and the ni-doped sodium fluorophosphate is obtained after being ground and crushed. The ni-doped sodium fluorophosphate has good positive electrode material electronic conductivity, high sodium ion diffusion coefficient, good cycle stability and good rate performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials, specifically to a niobium-doped sodium fluorophosphate, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, with their abundant sodium resources, low cost, and high safety, have shown great potential in large-scale energy storage and other fields. The cathode material is a key component determining their core performance. Sodium iron fluorophosphate, as a novel cathode material for sodium-ion batteries, possesses advantages such as high theoretical specific capacity, low cost, and environmental friendliness, and has become one of the research hotspots in this field.

[0003] However, pure-phase sodium iron fluorophosphate has significant drawbacks: firstly, its poor electronic conductivity leads to low charge transport efficiency; secondly, its low sodium ion diffusion coefficient affects the battery's charge and discharge rates. These two major problems directly result in its cycle stability and rate performance failing to meet the requirements of commercial applications, limiting the widespread adoption of sodium iron fluorophosphate as a cathode material in sodium-ion batteries. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a niobium-doped iron fluorophosphate, its preparation method, and its application.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a method for preparing niobium-doped iron fluorophosphate, comprising the following steps: S1, according to the general chemical formula The atomic molar ratio of each element is determined by weighing sodium source, iron source, niobium source, phosphorus source, and fluorine source to obtain raw materials, where 0 < x ≤ 0.1; S2. Mix the raw materials and add ball milling solvent to ball mill to obtain a mixed slurry; S3. The mixed slurry is vacuum dried at 50~80℃ to remove the solvent and obtain a dry mixed powder. S4. After pressing the dry mixed powder into sheets, place them in a crucible and pre-sinter them under inert gas protection. After cooling to room temperature, grind them to obtain precursor powder. S5. Take the carbon source and ball milling solvent and the precursor powder, ball mill and mix them, then vacuum dry and compress them into tablets to obtain tablets. S6. The tablets are sintered at high temperature under inert gas protection. After high-temperature sintering, they are cooled to room temperature in the furnace and then ground to obtain niobium-doped iron fluoride phosphate sodium.

[0006] As a further optimization of the invention of a method for preparing niobium-doped iron fluorophosphate: the chemical formula In the case where 0 < x ≤ 0.1, the atomic molar ratio of the raw materials satisfies Na:(Fe+Nb):P:F = 2:1:1:1.

[0007] As a further optimization of the method for preparing niobium-doped sodium fluoride phosphate, the sodium source is sodium carbonate, the iron source is ferrous oxalate, the niobium source is niobium oxalate, the phosphorus source is ammonium dihydrogen phosphate, the fluorine source is sodium fluoride, and the doping amount of the niobium source is ≤10%.

[0008] As a further optimization of the method for preparing niobium-doped sodium fluorophosphate, the specific method for ball milling to obtain the mixed slurry in steps S2 and S5 includes: In step S2, the raw material is placed in a ball mill jar, and ball milling media and ball milling solvent are added. The mixture is ball milled for 6-10 hours until the particle size is within a certain range. The following process yields a uniform slurry; wherein the milling media are alumina balls, and the ball-to-material ratio is 10-20:1; the milling solvent is acetone, and the amount added is 10-25% of the capacity of the milling jar; in step S5, the precursor powder is mixed with the carbon source and the milling solvent and milled until the particle size is within a certain range. the following.

[0009] As a further optimization of the method for preparing niobium-doped sodium fluorinated phosphate: the inert gas in steps S4 and S6 is argon, and the gas flow rate is 0.1~0.5 L / min, preferably 0.2 L / min.

[0010] As a further optimization of the preparation method of niobium-doped sodium fluorophosphate, the carbon source is ascorbic acid, and the amount of carbon source added is 10-40% of the mass of the precursor material.

[0011] As a further optimization of the preparation method of niobium-doped sodium fluorinated phosphate, the pre-sintering heating rate is 2~5 ℃ / min, the reaction temperature is 300~400 ℃, and the holding time is 3~5 h.

[0012] As a further optimization of the method for preparing niobium-doped sodium fluorinated phosphate, the heating rate of the high-temperature sintering is 2~5 ℃ / min, the reaction temperature is 550~650 ℃, and the holding time is 6~12 h.

[0013] The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a niobium-doped iron fluorophosphate sodium, which is prepared by the above method.

[0014] The technical solution adopted by the present invention to solve the above-mentioned technical problems is: the application of the above-mentioned niobium-doped iron fluoride phosphate in the positive electrode material of sodium-ion batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: In the preparation method of the present invention The moderate lattice distortion and strong chemical bonding formed by doping effectively suppress the volume expansion of the material during charging and discharging, improve the stability of the crystal structure, and thus improve the cycle stability of the material. In the preparation method of the present invention The introduction of [a specific substance] optimizes the electronic band structure of the material, and combined with the synergistic effect of carbon coating, significantly improves electronic conductivity; at the same time, lattice defects provide more sodium ion transport channels, improve the sodium ion diffusion coefficient, and improve the rate performance and cycle stability of the material. Attached Figure Description

[0016] Figure 1 This is a flowchart of the preparation method; Figure 2 SEM image of the powder sample from Example 2; Figure 3 The XRD patterns of the powder samples from Examples 1, 2, 3 and Comparative Example 1 are shown below. Figure 4 The graph shows the 1C rate cycling performance of the coin half-cells with positive electrode plates from Examples 1, 2, 3, and Comparative Example 1. Figure 5 The rate performance of the coin half-cells with positive electrode sheets of Examples 1, 2, 3 and Comparative Example 1 at different rates of 0.5C, 1C, 2C, 5C, 10C and 0.5C is shown. Figure 6 The graph shows the long-cycle performance of the coin cell with the positive electrode prepared in Example 2 under 10C cycling. Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Parts not described or disclosed in detail in the following embodiments of the present invention should be understood as prior art known or should be known by those skilled in the art.

[0018] like Figure 1 As shown, a method for preparing niobium-doped iron fluoride phosphate includes steps S1 to S6.

[0019] S1, according to the general chemical formula The atomic molar ratios of each element in the sample are determined by weighing sodium, iron, niobium, phosphorus, and fluorine sources to obtain the raw materials, where 0 < x ≤ 0.1. The atomic molar ratios of the raw materials satisfy Na:(Fe+Nb):P:F = 2:1:1:1. The sodium source is sodium carbonate, the iron source is ferrous oxalate, the niobium source is niobium oxalate, the phosphorus source is ammonium dihydrogen phosphate, and the fluorine source is sodium fluoride.

[0020] S2. The raw materials are ball-milled to obtain a mixed slurry; specifically, the raw materials are placed in a ball milling jar, ball milling media and ball milling solvent are added, and the mixture is ball-milled for 10 h to obtain a uniform mixed slurry; wherein, the ball milling media is alumina balls, and the ball-to-material ratio is 10:1; the ball milling solvent is acetone, and the amount added is 10 mL.

[0021] S3. The mixed slurry is vacuum dried at 70 °C for 10 h to remove the solvent and obtain a dried mixed powder.

[0022] S4. After the dried mixed powder is pressed into tablets by a tablet press mold, it is placed in an alumina crucible and pre-sintered under inert gas protection. After cooling to room temperature, it is ground to obtain precursor powder. The pre-sintering heating rate is 5 ℃ / min, the reaction temperature is 350 ℃, and the holding time is 5h.

[0023] S5. Take the carbon source and ball milling solvent and the precursor powder together and place them in a ball milling jar for ball milling and mixing. Then, vacuum dry and compress them into tablets to obtain tablets. Carbon source and ball milling solvent are added during ball milling and mixing. The ball milling time is 10 h. The vacuum drying conditions in S5 are the same as those in S3.

[0024] S6. The tablets were sintered at high temperature under inert gas protection. After high-temperature sintering, they were cooled to room temperature in the furnace and then ground to obtain niobium-doped iron fluoride phosphate. The carbon source was ascorbic acid. The heating rate of high-temperature sintering was 5 ℃ / min, the reaction temperature was 600 ℃, and the holding time was 8 h.

[0025] The inert gas used in steps S4 and S6 is argon, and the gas flow rate is 0.2 L / min.

[0026] This invention is achieved through Doping modification, combined with the synergistic effect of carbon coating, significantly improves the crystal structure stability, electronic conductivity, and sodium ion diffusion performance of sodium fluorophosphate. Specifically, ionic radius and Reasonable differences exist, and doping can form moderate lattice distortion in the sodium fluorophosphate lattice. The defects formed by the lattice distortion can also provide more transport channels for sodium ions, thereby improving the sodium ion diffusion coefficient. By adding a carbon source during the preparation process, a carbon coating layer is formed, which further improves the electronic conductivity of the material, while inhibiting particle agglomeration and optimizing the microstructure of the material. This method adopts solid-state sintering, and through the process design of two ball millings and two sinterings, it ensures that the raw materials are mixed uniformly and crystallized fully, taking into account both process simplicity and product performance stability.

[0027] Examples and comparative examples are listed below. Example 1

[0028] According to the atomic molar ratio of Na:(Fe+Nb):P:F=2:1 (Fe:Nb=0.97:0.03):1:1, weigh out 0.530 g of sodium carbonate, 1.735 g of ferrous oxalate, 0.1614 g of niobium oxalate, 1.150 g of ammonium dihydrogen phosphate, and 0.42 g of sodium fluoride. Place the above raw materials in an agate ball mill jar, add alumina balls with a ball-to-material ratio of 10:1 and 10 mL of acetone, and ball mill on a planetary ball mill at a speed of 450 r / min for 10 h until the particle size is within the specified range. The following process yielded a homogeneous slurry. The slurry was placed in a vacuum drying oven and dried at 70 °C for 10 h to remove acetone, resulting in a dried mixed powder. The mixed powder was pressed into sheets and placed in a corundum crucible, then placed in a tube furnace. Argon gas was introduced at a flow rate of 0.2 L / min, and the temperature was increased to 350 °C at a heating rate of 5 °C / min, held for 5 h for pre-sintering. The pre-sintered precursor was ground and pulverized, and 0.88 g of ascorbic acid and 10 mL of acetone were added. The mixture was then ball-milled in a planetary ball mill at 450 r / min for 10 h until the particle size was within the specified range. The powder obtained by ball milling was vacuum dried at 70℃ for 10 h and then pressed into sheets. The sheets were placed in a tube furnace and heated to 600℃ at a heating rate of 5℃ / min under an argon atmosphere. The temperature was held for 8 h for high-temperature sintering. After sintering, the product was cooled to room temperature with the furnace. The product was then removed, ground and pulverized to obtain powdered niobium-doped iron fluorophosphate. Example 2

[0029] According to the atomic molar ratio of Na:(Fe+Nb):P:F=2:1 (Fe:Nb=0.95:0.05):1:1, weigh out 0.530 g of sodium carbonate, 1.67 g of ferrous oxalate, 0.269 g of niobium oxalate, 1.150 g of ammonium dihydrogen phosphate, and 0.419 g of sodium fluoride. Place the above raw materials in an agate ball mill jar, add alumina balls with a ball-to-material ratio of 10:1 and 10 mL of acetone, and ball mill on a planetary ball mill at a speed of 450 r / min for 10 h until the particle size is within the specified range. The following process yielded a homogeneous slurry. The slurry was placed in a vacuum drying oven and dried at 70 °C for 10 h to remove acetone, resulting in a dried mixed powder. The mixed powder was pressed into sheets and placed in a corundum crucible, then placed in a tube furnace. Argon gas was introduced at a flow rate of 0.2 L / min, and the temperature was increased to 350 °C at a heating rate of 5 °C / min, held for 5 h for pre-sintering. The pre-sintered precursor was ground and pulverized, and 0.88 g of ascorbic acid (a carbon source) and 10 mL of acetone were added. The mixture was then ball-milled in a planetary ball mill at 450 r / min for 10 h until the particle size was within the specified range. The powder obtained by ball milling was vacuum dried at 70 °C for 10 h and then pressed into sheets. The sheets were placed in a tube furnace and heated to 600 °C at a heating rate of 5 °C / min under an argon atmosphere. The temperature was held for 8 h for high-temperature sintering. After sintering, the sheets were cooled to room temperature with the furnace. The product was then removed, ground, and pulverized to obtain powdered niobium-doped iron fluorophosphate. Example 3

[0030] According to the atomic molar ratio of Na:(Fe+Nb):P:F=2:1 (Fe:Nb=0.93:0.07):1:1, weigh out 0.530 g of sodium carbonate, 1.6636 g of ferrous oxalate, 0.3766 g of niobium oxalate, 1.150 g of ammonium dihydrogen phosphate, and 0.419 g of sodium fluoride. Place the above raw materials in an agate ball mill jar, add alumina balls with a ball-to-material ratio of 10:1 and 10 mL of acetone, and ball mill in a planetary ball mill at a speed of 450 r / min for 10 h until the particle size is within the specified range. The following process yielded a homogeneous slurry. The slurry was placed in a vacuum drying oven and dried at 70 °C for 10 h to remove acetone, resulting in a dried mixed powder. The mixed powder was pressed into sheets and placed in a corundum crucible, then placed in a tube furnace. Argon gas was introduced at a flow rate of 0.2 L / min, and the temperature was increased to 350 °C at a heating rate of 5 °C / min, held for 5 h for pre-sintering. The pre-sintered precursor was ground and pulverized, and 0.88 g of ascorbic acid (carbon source) and 10 mL of acetone were added. The mixture was then ball-milled in a planetary ball mill at 450 r / min for 10 h until the particle size was within the specified range. The powder obtained by ball milling was vacuum dried at 70℃ for 10 h and then pressed into sheets. The sheets were placed in a tube furnace and heated to 600℃ at a heating rate of 5℃ / min under an argon atmosphere. The temperature was held for 8 h for high-temperature sintering. After sintering, the product was cooled to room temperature with the furnace. The product was then removed, ground and pulverized to obtain powdered niobium-doped iron fluorophosphate.

[0031] Comparative Example 1 According to the atomic molar ratio of Na:Fe:P:F = 2:1:1:1, weigh out 0.530 g of sodium carbonate, 1.789 g of ferrous oxalate, 1.150 g of ammonium dihydrogen phosphate, and 0.42 g of sodium fluoride. Place the above raw materials in an agate ball mill jar, add alumina balls with a ball-to-material ratio of 10:1 and 10 mL of acetone, and ball mill on a planetary ball mill at a speed of 450 r / min for 10 h until the particle size is within the specified range. The following process yielded a homogeneous slurry. The slurry was placed in a vacuum drying oven and dried at 70 °C for 10 h to remove acetone, resulting in a dried mixed powder. The mixed powder was pressed into sheets and placed in a corundum crucible, then placed in a tube furnace. Argon gas was introduced at a flow rate of 0.2 L / min, and the temperature was increased to 350 °C at a heating rate of 5 °C / min, held for 5 h for pre-sintering. The pre-sintered precursor was ground and pulverized, and 0.88 g of ascorbic acid (carbon source) and 10 mL of acetone were added. The mixture was then ball-milled in a planetary ball mill at 450 r / min for 10 h until the particle size was within the specified range. The powder obtained by ball milling was vacuum dried at 70 °C for 10 h and then pressed into sheets. The sheets were placed in a tube furnace and heated to 600 °C at a heating rate of 5 °C / min under an argon atmosphere. The temperature was held for 8 h for high-temperature sintering. After sintering, the sheets were cooled to room temperature with the furnace. The product was then removed, ground, and pulverized to obtain powdered niobium-doped iron fluorophosphate.

[0032] Electrochemical performance tests were conducted on the sodium fluorophosphate cathode materials prepared in the above examples and comparative examples. A mixture of sodium fluorophosphate, Super P, and PVDF at a mass ratio of 7:2:1 was added, along with the organic solvent N-methylpyrrolidone (NMP). After stirring, the mixture was coated onto aluminum foil and dried to form the cathode sheet. A sodium metal sheet was used as the anode. A glass fiber separator was used. 2032 coin cell half-cells were assembled in a glove box. After standing at 25 °C for 6 hours, charge-discharge cycle performance tests were performed. The discharge specific capacity was tested at 0.1 C, 1 C, 2 C, 5 C, and 10 C within a cutoff voltage range of 2–4 V. The electrochemical performance results are as follows: Figure 4 As shown in the figure, the data indicates that the niobium-doped and carbon-coated synergistic modification of sodium fluorophosphate material exhibits high discharge specific capacity and excellent rate performance.

[0033] A niobium-doped sodium fluorophosphate cathode material is prepared by the above method. This niobium-doped sodium fluorophosphate cathode material has good electronic conductivity, high sodium ion diffusion coefficient, good cycle stability and rate performance. The moderate lattice distortion and strong chemical bonding formed by doping effectively suppress the volume expansion of the material during charging and discharging, improve the stability of the crystal structure, and thus improve the cycle stability of the material. At the same time, lattice defects provide more sodium ion transport channels, improve the sodium ion diffusion coefficient, and improve both the rate performance and cycle stability of the material.

[0034] A niobium-doped sodium fluoride phosphate can be used as a cathode material in sodium-ion batteries.

[0035] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing niobium-doped iron fluorophosphate, characterized in that, Includes the following steps: S1, according to the general chemical formula The atomic molar ratio of each element is determined by weighing sodium source, iron source, niobium source, phosphorus source, and fluorine source to obtain raw materials, where 0 < x ≤ 0.1; S2. Mix the raw materials and add ball milling solvent to ball mill to obtain a mixed slurry; S3. The mixed slurry is vacuum dried at 50~80℃ to remove the solvent and obtain a dry mixed powder. S4. After pressing the dry mixed powder into sheets, place them in a crucible and pre-sinter them under inert gas protection. After cooling to room temperature, grind them to obtain precursor powder. S5. Take the carbon source and ball milling solvent and the precursor powder, ball mill and mix them, then vacuum dry and compress them into tablets to obtain tablets. S6. The tablets are sintered at high temperature under inert gas protection. After high-temperature sintering, they are cooled to room temperature in the furnace and then ground to obtain niobium-doped iron fluoride phosphate sodium.

2. The method for preparing niobium-doped iron fluorophosphate as described in claim 1, characterized in that, The general chemical formula In the case where 0 < x ≤ 0.1, the atomic molar ratio of the raw materials satisfies Na:(Fe+Nb):P:F = 2:1:1:

1.

3. The method for preparing niobium-doped iron fluorophosphate as described in claim 1, characterized in that, The sodium source is sodium carbonate, the iron source is ferrous oxalate, the niobium source is niobium oxalate, the phosphorus source is ammonium dihydrogen phosphate, and the fluorine source is sodium fluoride. The doping amount of the niobium source is ≤10%.

4. The method for preparing niobium-doped iron fluorophosphate as described in claim 1, characterized in that, In steps S2 and S5, the ball is milled until the particle size is within... The following are specific methods for obtaining a mixed slurry through ball milling: In step S2, the raw material is placed in a ball mill jar, and ball milling media and ball milling solvent are added. The mixture is then ball milled for 6-10 hours until the particle size is within a certain range. The following process yields a uniform slurry; wherein the milling media are alumina balls, and the ball-to-material ratio is 10-20:1; the milling solvent is acetone, and the amount added is 10-25% of the capacity of the milling jar; in step S5, the precursor powder is mixed with the carbon source and the milling solvent and milled until the particle size is within a certain range. the following.

5. The method for preparing niobium-doped iron fluorophosphate as described in claim 1, characterized in that, The inert gas used in steps S4 and S6 is argon, and the gas flow rate is 0.1~0.5 L / min, preferably 0.2 L / min.

6. The method for preparing niobium-doped iron fluorophosphate as described in claim 1, characterized in that, The carbon source is ascorbic acid, and the amount of carbon source added is 10-40% of the mass of the precursor material.

7. The method for preparing niobium-doped iron fluorophosphate as described in claim 1, characterized in that, The pre-sintering heating rate is 2~5 ℃ / min, the reaction temperature is 300~400 ℃, and the holding time is 3~5 h.

8. The method for preparing niobium-doped iron fluorophosphate as described in claim 1, characterized in that, The heating rate of the high-temperature sintering is 2~5 ℃ / min, the reaction temperature is 550~650 ℃, and the holding time is 6~12 h.

9. A niobium-doped sodium fluorophosphate, characterized in that, The general chemical formula of the niobium-doped iron fluorophosphate is: Where 0 < x ≤ 0.1, Nb element is doped at Fe lattice sites; the particle size of the powder is less than It is prepared by the method described in any one of claims 1 to 8.

10. The application of niobium-doped sodium fluoride phosphate as described in claim 9 in the cathode material of sodium-ion batteries.

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