Preparation method and application of composite sodium ferric phosphate material
By controlling the sodium hole concentration and titanium doping in the composite sodium iron phosphate material, combined with fluorine doping, the problem of low crystal phase purity of NFPP material was solved, and the specific capacity and cycle performance were improved, making it suitable for mass production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUIZHOU DALONG HUICHENG NEW MATERIAL CO LTD
- Filing Date
- 2025-12-22
- Publication Date
- 2026-05-01
AI Technical Summary
Existing NFPP materials have low crystal phase purity and poor electrochemical performance, resulting in low specific capacity and poor cycle performance.
Using Na4-xFe3-yTiy(PO4)2P2O7 material, with a carbon layer coated on the surface and fluorine doped, uniform and efficient doping is achieved by controlling the sodium hole concentration and the titanium-doped iron source, thus suppressing the formation of electrochemically inactive NaFeO4 impurity phase.
It significantly improves the purity of the crystal phase, enhances the specific capacity and cycle performance of the material, and is suitable for mass production and industrialization.
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Figure CN121948404A_ABST
Abstract
Description
A method for preparing and applying a composite sodium iron phosphate material Technical Field
[0001] This invention relates to the field of new energy materials, and in particular to a composite sodium iron phosphate material. Background Technology
[0002] Sodium-ion batteries are abundant, inexpensive, and exhibit excellent low-temperature performance. In the future, sodium-ion batteries will leverage their cost advantage to replace lead-acid batteries in areas such as micro electric vehicles, power tools, energy storage power stations, and start-stop power supplies, effectively complementing lithium-ion batteries and possessing broad application prospects and economic value. Developing novel sodium-ion battery cathode materials is of significant economic and strategic importance for addressing lithium resource shortages and enriching energy storage application scenarios.
[0003] There are three main cathode material routes for sodium-ion batteries: layered oxides, polyanionic cathodes, and Prussian blue analogs. Polyanionic cathode materials for sodium-ion batteries have advantages such as long cycle life, high theoretical capacity, and excellent stability, combining cost and performance advantages, and are currently recognized by the industry as the most promising cathode material for sodium-ion batteries. Iron-based polyanionic cathode materials, such as sodium iron phosphate composites (Na4Fe3(PO4)2P2O7, abbreviated as NFPP), have advantages such as high specific capacity, long cycle life, and environmental friendliness, making them one of the most promising cathode materials for sodium-ion batteries.
[0004] In actual production processes, NFPP materials often exhibit low crystal phase purity, frequently accompanied by the formation of electrochemically inactive NaFeO4 impurities. The presence of these NaFeO4 impurities leads to defects in the electrode materials, such as low specific capacity and poor cycle performance. Furthermore, the inherently poor conductivity of polyanionic materials also limits the further application of NFPP materials. Summary of the Invention
[0005] This invention provides a composite sodium iron phosphate material, its preparation method, and its application, to solve the technical problems mentioned in the background art, such as low crystal phase purity and poor electrochemical performance in the preparation of existing NFPP materials.
[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is: a composite sodium iron phosphate material, wherein the chemical formula of the composite sodium iron phosphate material is Na. 4-x Fe 3-y Ti y (PO4)2P2O7, and the surface of the composite sodium iron phosphate material is coated with a carbon coating layer; wherein, 0 < x ≤ 1, 0.01 ≤ y < 2.
[0007] As a further preferred embodiment of the above technical solution, the composite sodium iron phosphate material is also doped with fluorine, and the chemical formula of the composite sodium iron phosphate material is Na. 4-x Fe3-y Ti y (PO4)2P2O7F z @C; where 0 < x ≤ 1, 0.01 ≤ y < 2, 0 < z ≤ 0.5. Fluorine doping can further improve the specific capacity and cycle life of composite sodium iron phosphate materials.
[0008] As a further preferred embodiment of the above technical solution, the average particle size of the composite sodium iron phosphate material is 800 nm to 20 μm.
[0009] Based on the same technical concept, the present invention also provides a method for preparing the above-mentioned composite sodium iron phosphate material, comprising the following steps: S1, obtaining carbon source, iron source, phosphorus source, titanium source and sodium source according to the stoichiometric ratio of each element in the chemical formula of the composite sodium iron phosphate material, and dispersing them in a solvent to obtain a mixed solution; S2, milling the mixed solution to obtain a primary particle mixed suspension; S3, spray drying the primary particle mixed suspension to obtain an intermediate product, and annealing, cooling and crushing the intermediate product to obtain the composite sodium iron phosphate material.
[0010] This invention precisely controls the concentration of sodium vacancies in the material by adjusting the stoichiometry of sodium, and achieves uniform and efficient titanium doping by using a titanium-doped iron source. Sodium vacancies, as defects in the crystal lattice, provide transport channels for ion diffusion, making it easier for reactants to aggregate in the target proportion, meeting the compositional requirements for crystal phase nucleation. Furthermore, the lattice relaxation brought about by sodium vacancies effectively lowers the activation energy for nucleation of the target crystal phase, making it preferential for nucleation over impurity phases. Titanium doping can replace iron cation sites in the material or occupy lattice interstices, contributing to the formation of a stable solid solution structure. In addition, the introduction of titanium anchors anion clusters, preventing them from detaching from the target crystal lattice to form free phosphide impurity phases, thus lowering the nucleation barrier of the target crystal phase. Essentially, sodium vacancies plus titanium doping enhances the structural advantages of the target crystal phase by improving lattice stability. Furthermore, the synergistic optimization of the reaction kinetics of both enhances the growth competitiveness of the target crystal phase, making it easier for the target crystal phase to nucleate and grow, thereby reducing the impurity phase content. Therefore, the synergistic effect of the two effectively suppressed the formation of electrochemically inactive NaFeO4 impurity phase and significantly improved the crystal phase purity, thereby solving the technical problem that existing preparation methods cannot directly obtain high-purity NFPP materials, and significantly improving the specific capacity and cycle performance of the materials.
[0011] As a further preferred embodiment of the above technical solution, the carbon source includes at least one of citric acid, glucose, sucrose, starch, gelatin, phenolic resin, cellulose, polyvinyl alcohol, and polyvinylpyrrolidone; the iron and titanium sources are titanium-doped iron salts, and the iron salts include at least one of ferric phosphate, ferrous oxalate, ferrous sulfate, ferric nitrate, and ferric acetylacetone; the phosphorus source includes at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, phytic acid, metaphosphoric acid, and hypophosphoric acid; and the sodium source includes at least one of sodium carbonate, sodium dihydrogen phosphate, sodium acetate, and sodium oleate.
[0012] As a further preferred embodiment of the above technical solution, the titanium content in the titanium-doped iron salt is 1000~6000ppm.
[0013] As a further preferred embodiment of the above technical solution, the carbon source accounts for 0.5% to 0.7% of the mass in the mixed solution, more preferably 3%.
[0014] As a further preferred embodiment of the above technical solution, the sand milling time in S2 is 1~10h, more preferably 4~5h, and the average particle size of the material in the primary particle mixing suspension after sand milling is 200~900nm, more preferably 250nm.
[0015] As a further preferred embodiment of the above technical solution, the inlet temperature of the spray dryer in S3 is 100~300℃, more preferably 220℃; the outlet temperature is 60~150℃, more preferably 120℃; and the needle frequency of the spray dryer is 2~20 times / s, more preferably 10 times / second.
[0016] As a further preferred embodiment of the above technical solution, the annealing operation in S3 includes pre-annealing and high-temperature annealing performed sequentially; the temperature of pre-annealing is 150~450℃ and the holding time is 1~15h; the temperature of high-temperature annealing is 500~750℃ and the holding time is 1~20h, and the heating rate of both pre-annealing and high-temperature annealing is 0.5~15℃ / min.
[0017] As a further preferred embodiment of the above technical solution, the pre-annealing is carried out in at least one atmosphere of argon, nitrogen and ammonia, and the high-temperature annealing is carried out in at least one atmosphere of air, argon, nitrogen and ammonia.
[0018] Based on the same technical concept, the present invention also provides an application of the above-mentioned composite sodium iron phosphate material, which is used as a positive electrode material in sodium-ion batteries.
[0019] This invention offers the following advantages: It precisely controls the concentration of sodium holes in the material by adjusting the stoichiometry of sodium, and achieves uniform and efficient titanium doping by using a titanium-doped iron source. The synergistic effect of these two methods effectively suppresses the formation of electrochemically inactive NaFeO4 impurity phases, significantly improving crystal phase purity. Furthermore, the addition of fluorine doping further enhances the specific capacity and cycle life of the composite sodium iron phosphate. The sample preparation method of this invention is simple, and the process route is suitable for mass production, making it promising for industrialization. Attached Figure Description
[0020] Figure 1(a) shows the X-ray diffraction patterns of the composite sodium iron phosphate materials of Examples 1 and 2, and Figure 1(b) shows the X-ray diffraction patterns of the composite sodium iron phosphate materials of Comparative Examples 1, 2, 3, and 4.
[0021] Figure 2 is a scanning electron microscope image of the composite sodium iron phosphate material of Example 1.
[0022] Figure 3 shows the charge-discharge curves of the composite sodium iron phosphate materials in Examples 1 and 2. Detailed Implementation
[0023] The present invention will be described in detail below with reference to the accompanying drawings and embodiments, but the present invention can be implemented in many different ways as defined and covered by the claims.
[0024] Example 1: The composite sodium iron phosphate material of this example has the molecular formula Na. 3.85 Fe 2.94 Ti 0.06 (PO4) 1.75 P2O7F 0.25 / C, with an average particle size of 5μm.
[0025] The composite sodium iron phosphate material of this embodiment was prepared by the following method: S1, 300g of titanium-doped iron phosphate (titanium content of 5000ppm), 87g of iron phosphate dihydrate, 152.5g of sodium dihydrogen phosphate, 98g of sodium carbonate, 13.3g of sodium fluoride, and 67g of sucrose were poured into a 2500ml beaker, 2000ml of water was added, and the mixture was stirred for 2h to obtain a uniformly mixed dispersion.
[0026] S2. Add the above dispersion to a nano-sand mill and grind for 3 hours to obtain a mixed solution with an average particle size of 200 nm.
[0027] S3 spray-dries the above solution using a spray dryer with an inlet temperature of 210°C, an outlet temperature of 100°C, and a needle frequency of 10 times / second. The powder sample is collected after spray drying.
[0028] S4. The above powder sample is pre-annealed at a temperature of 290℃, a holding time of 6h, a heating rate of 5℃ / min, and an annealing atmosphere of argon to obtain the pre-annealed sample.
[0029] S5. The pre-annealed sample is annealed at a high temperature of 550°C for 15 hours, with a heating rate of 5°C / min and an annealing atmosphere of argon, to obtain the composite sodium iron phosphate material of this embodiment.
[0030] Example 2: The composite sodium iron phosphate material of this example has the molecular formula Na. 3.85 Fe 2.94 Ti 0.06 (PO4)2P2O7 / C, with an average particle size of 6.5 μm.
[0031] The sodium iron phosphate composite material of this embodiment was prepared by the following method: S1, 300g of titanium-doped iron phosphate (titanium content is 5000ppm), 87g of iron phosphate dihydrate, 152.5g of sodium dihydrogen phosphate, 100.5g of sodium carbonate, and 67g of sucrose were poured into a 2500ml beaker, and 2000ml of water was added and stirred for 2h to obtain a uniformly mixed dispersion.
[0032] S2. Add the above dispersion to a nano-sand mill and grind for 3 hours to obtain a mixed solution with an average particle size of 200 nm.
[0033] S3 spray-dries the above solution using a spray dryer with an inlet temperature of 210°C, an outlet temperature of 100°C, and a needle frequency of 10 times / second. The powder sample is collected after spray drying.
[0034] S4. The above powder sample is pre-annealed at a temperature of 290℃, a holding time of 6h, a heating rate of 5℃ / min, and an annealing atmosphere of argon to obtain the pre-annealed sample.
[0035] S5. The pre-annealed sample is annealed at a high temperature of 550°C for 15 hours, with a heating rate of 5°C / min and an annealing atmosphere of argon, to obtain the composite sodium iron phosphate material of this embodiment.
[0036] Comparative Example 1 Na was prepared using the following method in this comparative example. 3.85 Fe 2.94 Ti 0.06 (PO4)2P2O7 / C composite material with an average particle size of 4.5μm: S1, 300g ferrous oxalate, 145.5g sodium pyrophosphate, 126.3g ammonium dihydrogen phosphate, 32.55g titanium dioxide and 55g glucose were dispersed in 2000mL of water and stirred for 2h until they were mixed evenly.
[0037] S2. Add the above dispersion to a nano-sand mill and grind for 4 hours to obtain a mixed solution with an average particle size of 230 nm.
[0038] S3. Spray dry the above solution. The inlet temperature of the spray dryer is 200℃, the outlet temperature is 95℃, and the needle frequency is 5 times / second. Collect the powder sample after spray drying.
[0039] S4. The above powder sample is pre-annealed at a temperature of 300℃, a holding time of 5h, a heating rate of 3℃ / min, and an annealing atmosphere of argon to obtain the pre-annealed sample.
[0040] S5. The pre-annealed sample is annealed at a high temperature of 550℃, with a holding time of 12h, a heating rate of 3℃ / min, and an annealing atmosphere of argon to obtain the target sample.
[0041] Comparative Example 2: Na₄Fe was prepared using the following method. 2.94 Ti 0.06 (PO4)2P2O7 / C composite material with an average particle size of 7.0μm: S1, 300g ferrous oxalate, 261.6g sodium dihydrogen phosphate, 126.3g ammonium dihydrogen phosphate, 32.55g titanium dioxide and 60g cellulose are dispersed in 2000mL water and stirred for 2h until uniformly mixed.
[0042] S2. Add the above dispersion to a nano-sand mill and grind for 3.5 hours to obtain a mixed solution with an average particle size of 250 nm.
[0043] S3. Spray dry the above solution. The inlet temperature of the spray dryer is 180℃, the outlet temperature is 90℃, and the needle frequency is 10 times / second. Collect the powder sample after spray drying.
[0044] S4. The above powder sample is pre-annealed at a temperature of 250℃, a holding time of 10h, a heating rate of 3℃ / min, and an annealing atmosphere of argon to obtain the pre-annealed sample.
[0045] S5. The pre-annealed sample is annealed at a high temperature of 500℃, with a holding time of 20h, a heating rate of 3℃ / min, and an annealing atmosphere of argon to obtain the target sample.
[0046] Comparative Example 3: Na₄Fe was prepared using the following method. 2.94 Ti 0.06(PO4)2P2O7 / C composite material with an average particle size of 4.5μm: S1. 350g of titanium-doped iron phosphate (titanium content of 3000ppm), 35g of iron phosphate, 154g of sodium dihydrogen phosphate, 101.9g of sodium carbonate, and 70g of citric acid were poured into a 2500ml beaker, and 2000ml of water was added and stirred for 2h to obtain a uniformly mixed dispersion.
[0047] S2. Add the above dispersion to a nano-sand mill and grind for 4 hours to obtain a mixed solution with an average particle size of 300 nm.
[0048] S3. Spray dry the above solution. The inlet temperature of the spray dryer is 200℃, the outlet temperature is 100℃, and the needle frequency is 5 times / second. Collect the powder sample after spray drying.
[0049] S4. The above powder sample is pre-annealed at a temperature of 200℃, a holding time of 5h, a heating rate of 3℃ / min, and an annealing atmosphere of argon to obtain the pre-annealed sample.
[0050] S5. The pre-annealed sample is annealed at a high temperature of 550℃, with a holding time of 10h, a heating rate of 3℃ / min, and an annealing atmosphere of argon to obtain the target sample.
[0051] Comparative Example 4: The Na4Fe3(PO4)2P2O7 / C composite material with an average particle size of 5.0 μm was prepared using the following method: S1. 300 g of ferrous oxalate, 147.3 g of sodium pyrophosphate, 127.8 g of ammonium dihydrogen phosphate, 35 g of glucose, and 15 g of polyethylene glycol were poured into a 2000 ml beaker, and 1500 ml of water was added and stirred for 3 h to obtain a uniformly mixed dispersion.
[0052] S2. Add the above dispersion to a nano-sand mill and grind for 3 hours to obtain a mixed solution with an average particle size of 300 nm.
[0053] S3. Spray dry the above solution. The inlet temperature of the spray dryer is 220℃, the outlet temperature is 100℃, and the needle frequency is 10 times / second. Collect the powder sample after spray drying.
[0054] S4. The above powder sample is pre-annealed at a temperature of 350℃, a holding time of 8h, a heating rate of 3℃ / min, and an annealing atmosphere of argon to obtain the pre-annealed sample.
[0055] S5. The pre-annealed sample is annealed at a high temperature of 500℃, with a holding time of 20h, a heating rate of 3℃ / min, and an annealing atmosphere of argon to obtain the target sample.
[0056] The composite sodium iron phosphate materials of each embodiment and comparative example were tested, and the XRD results are shown in Figure 1. The scanning electron microscope results of Example 1 are shown in Figure 2.
[0057] The electrochemical performance of Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4 was tested using coin-type sodium-ion batteries. The electrode preparation method was as follows: 80 mg of composite sodium iron phosphate material, 15 mg of conductive carbon black, and 5 mg of PVDF were dispersed in 0.8 g of N-methylpyrrolidone solution, stirred for 12 h, and then coated onto aluminum foil. The resulting electrode was vacuum-dried at 110 °C for 12 h to obtain the positive electrode for the sodium-ion battery. The battery test voltage range was 1.7 V–4.0 V. The results are shown in Table 1.
[0058] Table 1: Performance test results of batteries made from composite materials in each embodiment and comparative example
[0059] Analysis of the data in Table 1 shows that: (1) Examples 1 and 2 are designed to contain a certain amount of sodium holes, and in-situ titanium doping is achieved through titanium-doped iron phosphate. Combining the xrd data of the two in Figure 1a, it can be seen that sodium holes and in-situ titanium doping can effectively reduce the formation of sodium iron phosphate impurity phase. In Example 1, fluorine doping further improves the purity of the crystal phase, thus resulting in better specific capacity and cycle stability.
[0060] (2) Through the analysis and comparison of Example 2 and Comparative Example 1, it can be seen that the in-situ titanium-doped sample in Example 2 has advantages in capacity and cycle retention rate under the same doping content. In-situ titanium doping has higher uniformity than non-in-situ doping, and therefore has more advantages in improving crystal phase purity and material cycle stability.
[0061] (3) The analysis results of Comparative Example 1 and Comparative Example 2 show that the sample containing sodium vacancies has a higher specific capacity. This is mainly due to the fact that sodium vacancies can reduce the formation of sodium iron phosphate impurity phase during the preparation process. At the same time, the presence of sodium vacancies can effectively improve the sodium ion migration rate, thus having better rate performance and cycle stability.
[0062] (4) Comparative Examples 2 and 3 show that Comparative Example 2, which has sodium holes, has a higher specific capacity, while Comparative Example 3, which uses in-situ titanium doping, has better cycle stability. This result indicates that sodium holes have a significant effect on improving specific capacity, while in-situ doping has a certain advantage in improving cycle stability.
[0063] (5) Combining the electrochemical data of Comparative Example 4 in Table 1 and the xrd data in Figure 1b, it can be seen that the sample without any optimization measures contains more impurities and has poor electrochemical performance.
[0064] Analysis of the above examples and comparative results shows that controlling the concentration of sodium holes in this invention can effectively reduce the formation of impurity phases and improve the specific capacity and cycling stability of the material. In-situ titanium doping using titanium-doped iron phosphate as a raw material results in better doping uniformity, leading to a more significant improvement in the crystal phase purity and cycling stability of the electrode material at the same doping content. Fluorine doping further enhances the capacity and cycling stability of the material.
[0065] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.
[0066] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. A composite sodium iron phosphate material, characterized in that, The chemical formula of the composite sodium iron phosphate material is Na. 4-x Fe 3- y Ti y (PO4)2P2O7, and the surface of the composite sodium iron phosphate material is coated with a carbon coating layer; wherein, 0 < x ≤ 1, 0.01 ≤ y < 2.
2. The composite sodium iron phosphate material according to claim 1, characterized in that, The composite sodium iron phosphate material is also doped with fluorine. The chemical formula of the composite sodium iron phosphate material is Na. 4-x Fe 3-y Ti y (PO4)2P2O7F z @C; where 0 < x ≤ 1, 0.01 ≤ y < 2, 0 < z ≤ 0.
5.
3. The composite sodium iron phosphate material according to claim 1 or 2, characterized in that, The average particle size of the composite sodium iron phosphate material is 800 nm to 20 μm.
4. A method for preparing the composite sodium iron phosphate material according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Obtain carbon source, iron source, phosphorus source, titanium source and sodium source according to the stoichiometric ratio of each element in the chemical formula of the composite sodium iron phosphate material, and disperse them in a solvent to obtain a mixed solution; S2. Sand mill the mixed solution to obtain a primary particle mixed suspension; S3. Spray dry the primary particle mixed suspension to obtain an intermediate product, and anneal, cool and crush the intermediate product to obtain the composite sodium iron phosphate material.
5. The method for preparing the composite sodium iron phosphate material according to claim 4, characterized in that, The carbon source includes at least one of citric acid, glucose, sucrose, starch, gelatin, phenolic resin, cellulose, polyvinyl alcohol, and polyvinylpyrrolidone; the iron and titanium sources are titanium-doped iron salts, and the iron salts include at least one of ferric phosphate, ferrous oxalate, ferrous sulfate, ferric nitrate, and ferric acetylacetone; the phosphorus source includes at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, phytic acid, metaphosphoric acid, and hypophosphoric acid; the sodium source includes at least one of sodium carbonate, sodium dihydrogen phosphate, sodium acetate, and sodium oleate.
6. The method for preparing the composite sodium iron phosphate material according to claim 4, characterized in that, The titanium-doped iron salt contains 1000~6000ppm of titanium.
7. The method for preparing the composite sodium iron phosphate material according to claim 4, characterized in that, The carbon source accounts for 0.5% to 0.7% of the mass of the mixed solution.
8. The method for preparing the composite sodium iron phosphate material according to claim 4, characterized in that, The sand milling time described in S2 is 1~10h, and the average particle size of the material in the first particle mixed suspension after sand milling is 200~900nm.
9. The method for preparing the composite sodium iron phosphate material according to claim 4, characterized in that, The inlet temperature of the spray dryer described in S3 is 100~300℃, the outlet temperature is 60~150℃, and the needle frequency of the spray dryer is 2~20 times / s.
10. The method for preparing the composite sodium iron phosphate material according to any one of claims 4-9, characterized in that, The annealing operation described in S3 includes pre-annealing and high-temperature annealing performed sequentially; the temperature of pre-annealing is 150~450℃ and the holding time is 1~15h; the temperature of high-temperature annealing is 500~750℃ and the holding time is 1~20h, and the heating rate of both pre-annealing and high-temperature annealing is 0.5~15℃ / min.
11. The method for preparing the composite sodium iron phosphate material according to claim 10, characterized in that, The pre-annealing is carried out in at least one atmosphere of argon, nitrogen and ammonia, and the high-temperature annealing is carried out in at least one atmosphere of air, argon, nitrogen and ammonia.
12. The application of a composite sodium iron phosphate material according to any one of claims 1-3 or a composite sodium iron phosphate material prepared by the preparation method according to any one of claims 4-11, characterized in that, The composite sodium iron phosphate material is used as a positive electrode material in sodium-ion batteries.