Modified sodium ferric sulfate positive electrode material as well as preparation method and application thereof
By synthesizing nano-titanium dioxide particles as a coating layer on the surface of sodium ferric sulfate in situ, the problems of water absorption and conductivity of sodium ferric sulfate cathode material were solved, thus improving its application performance in sodium-ion batteries.
Patent Information
- Application Number
- CN202511647158.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-11
- Publication Date
- 2026-02-13
AI Technical Summary
Sodium iron sulfate cathode material is prone to absorbing water, oxidation, and deactivation in air, and has poor conductivity, which limits its application in sodium-ion batteries, especially due to its low compaction density, which affects battery performance.
In situ synthesis of nano-titanium dioxide particles coated with sodium ferric sulfate precursor was achieved by microwave pyrolysis of titanium oxysulfate in aqueous solution, forming an inert coating layer. Modified sodium ferric sulfate cathode material was obtained by calcination.
It effectively improves the structural stability of the material, reduces water absorption, increases the compaction density to over 2.1 g/cm3, and improves electrochemical performance.
Smart Images
Figure CN121516918A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery materials technology, and relates to a modified sodium iron sulfate cathode material, its preparation method and uses. Background Technology
[0002] Compared to lithium-ion batteries, sodium-ion batteries have gained widespread attention in recent years due to their more abundant resources and lower cost. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, primarily achieving energy storage and release through the insertion and extraction of sodium ions between the positive and negative electrodes. With the increasing demand for high-performance energy storage devices, the development of efficient and stable sodium-ion battery cathode materials has become a research hotspot.
[0003] Among numerous sodium-ion battery cathode materials, the polyanionic material sodium ferric sulfate (Na2Fe(SO4)2, NFS) exhibits a high operating voltage (3.8V), good low-temperature performance, and safety. Furthermore, it is based on iron, making its raw materials widely available, abundant, and inexpensive, suitable for large-scale industrial production. However, despite these advantages, the practical application of sodium ferric sulfate still faces a series of challenges, limiting its commercialization.
[0004] First, sodium ferric sulfate is highly hygroscopic, resulting in poor stability in air. Upon exposure to a humid environment, it rapidly absorbs moisture, causing changes in its crystal structure and even decomposition, severely impacting its electrochemical performance. Furthermore, this material is extremely sensitive to oxygen, easily oxidizing and deteriorating, further reducing its lifespan and cycle stability. These factors contribute to the deactivation of sodium ferric sulfate during storage and use, thus affecting the sodium ion insertion / extraction efficiency. Another significant issue is the low synthesis temperature and poor conductivity of sodium ferric sulfate. To improve its conductivity, conductive agents, such as inorganic carbon materials, are often incorporated, which easily leads to a relatively low compaction density, typically only reaching 1.7 g / cm³. 3 Around this level, it can easily lead to a decrease in battery volume density.
[0005] Although some technologies exist to improve the electronic and ionic conductivity of sodium ferric sulfate, they are still insufficient to address issues such as the material's susceptibility to water absorption, oxidation by oxygen, deterioration, deactivation, and low compaction density. To promote the practical application of sodium ferric sulfate in sodium-ion batteries, it is urgent to develop new technical solutions to overcome existing technological bottlenecks. Summary of the Invention
[0006] In view of the problems existing in the prior art, the purpose of this invention is to provide a modified sodium ferric sulfate cathode material, its preparation method, and its uses. The preparation method involves mixing a sodium ferric sulfate precursor with titanium oxysulfate in water to obtain an aqueous solution. The aqueous solution undergoes an in-situ synthesis reaction under microwave assistance to generate titanium dioxide, which coats the sodium ferric sulfate precursor, yielding an intermediate. The intermediate is then calcined to obtain the modified sodium ferric sulfate cathode material. By utilizing titanium oxysulfate, a specific coating material with reducing properties, nano-titanium dioxide particles are formed in-situ on the surface of the sodium ferric sulfate precursor in an aqueous solution, thereby forming an inert coating layer, improving its structural stability, effectively reducing the water absorption of sodium ferric sulfate, and effectively improving the material's compaction density and electrical properties.
[0007] To achieve this objective, the present invention adopts the following technical solution:
[0008] In a first aspect, the present invention provides a method for preparing a modified sodium ferric sulfate cathode material, the method comprising the following steps:
[0009] Sodium ferric sulfate precursor and titanium oxysulfate are mixed in water to obtain an aqueous solution. The aqueous solution is subjected to an in-situ synthesis reaction under microwave assistance to generate titanium dioxide and coat the sodium ferric sulfate precursor to obtain an intermediate. The intermediate is then calcined to obtain a modified sodium ferric sulfate cathode material.
[0010] The preparation method of this invention utilizes titanium oxysulfate, which has reducing properties, to undergo microwave pyrolysis in an aqueous solution, thereby synthesizing nano-titanium dioxide particles in situ on the surface of sodium ferric sulfate particles. This forms an inert coating layer, which can effectively improve structural stability and reduce the water absorption of the sodium ferric sulfate material. Due to the acidic nature of the sodium ferric sulfate precursor, it can promote the solubility of titanium oxysulfate in water and promote the formation of the coating layer. This preparation method can also effectively improve the compaction density of the obtained modified sodium ferric sulfate cathode material, reaching 2.1 g / cm³. 3 above.
[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.
[0012] As a preferred embodiment of the present invention, the mass of the sodium ferric sulfate precursor accounts for 20% to 50% of the mass of the aqueous solution, for example, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 42%, 45%, 48%, or 50%.
[0013] Preferably, the mass of the titanium oxysulfate accounts for 1% to 5% of the mass of the sodium ferric sulfate precursor, for example, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8% or 5%.
[0014] In this invention, the amount of titanium oxysulfate added affects the coating amount of titanium dioxide synthesized in situ. If the titanium dioxide coating amount is too small, the improvement in compaction density and water absorption is not obvious, while adding too much can easily reduce the electrochemical performance of sodium ferric sulfate material.
[0015] As a preferred technical solution of the present invention, the microwave frequency of the microwave-assisted microwave is 2~3GHz, such as 2GHz, 2.1GHz, 2.2GHz, 2.3GHz, 2.4GHz, 2.5GHz, 2.6GHz, 2.7GHz, 2.8GHz, 2.9GHz or 3GHz, etc., and the microwave temperature is 90~120℃, such as 90℃, 93℃, 95℃, 98℃, 100℃, 103℃, 105℃, 108℃, 110℃, 112℃, 115℃, 118℃ or 120℃, etc.
[0016] In this invention, under certain conditions, microwave frequency and temperature affect the rate of in-situ synthesis of titanium dioxide; the higher the frequency and temperature, the faster the synthesis rate. However, excessively high temperatures can affect the coating amount and uniformity of the in-situ synthesized titanium dioxide.
[0017] Preferably, the in-situ synthesis reaction time is 2 to 8 minutes, such as 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, 5.5 minutes, 6 minutes, 6.5 minutes, 7 minutes, 7.5 minutes, or 8 minutes.
[0018] Preferably, after the in-situ synthesis reaction is completed, solid-liquid separation is performed to obtain the intermediate; the solid-liquid separation method includes centrifugation and / or vacuum filtration.
[0019] Preferably, the calcination is carried out under an inert reducing atmosphere, which includes nitrogen.
[0020] Preferably, the calcination heating rate is 2~5℃ / min, the holding temperature is 350~400℃, such as 350℃, 360℃, 370℃, 380℃, 390℃ or 400℃, and the holding time is 8~10h.
[0021] As a preferred technical solution of the present invention, the method for preparing the sodium ferric sulfate precursor includes: mixing a sodium source, an iron source, a reducing agent and water to obtain a precursor solution, and then drying the precursor solution to obtain the sodium ferric sulfate precursor.
[0022] Preferably, the sodium source includes sodium sulfate.
[0023] Preferably, the iron source includes at least one of ferrous sulfate heptahydrate, anhydrous ferrous sulfate, or ferrous sulfate monohydrate.
[0024] Preferably, the total mass of the iron source and the sodium source accounts for 20% to 43% of the precursor solution, for example, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40% or 43%.
[0025] Preferably, the molar ratio of sodium in the sodium source to the molar ratio of iron in the iron source is (1.2~1.6):1, for example, 1.2:1, 1.3:1, 1.4:1, 1.5:1 or 1.6:1, etc.
[0026] Preferably, the reducing agent includes ascorbic acid and / or citric acid.
[0027] Preferably, the reducing agent accounts for 2% to 8% of the mass of the iron source, for example, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.3%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8% or 8%, etc.
[0028] As a preferred technical solution of the present invention, the method for preparing the sodium ferric sulfate precursor further includes: the mixed raw materials also include a conductive agent to obtain the precursor solution.
[0029] Preferably, the conductive agent includes at least one of carbon nanotubes, carbon black, graphene, or aerogel.
[0030] Preferably, the conductive agent accounts for 2% to 5% of the total mass of the sodium source and the iron source, for example, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8% or 5%, etc.
[0031] As a preferred embodiment of the present invention, the method for preparing the sodium ferric sulfate precursor further includes:
[0032] Preferably, the conductive agent and the dispersant are pre-dispersed in water to obtain a conductive agent dispersion; then the conductive agent dispersion is mixed with the sodium source, iron source and reducing agent to obtain the precursor solution.
[0033] Preferably, the dispersant comprises carboxymethyl cellulose and / or polyvinylpyrrolidone (PVP, K30).
[0034] Preferably, the mass of the dispersant accounts for 0.5% to 3% of the mass of the conductive agent dispersion, for example, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8% or 3%.
[0035] Preferably, the dispersion method includes at least one of sand milling dispersion, ultrasonic dispersion, or shear emulsification dispersion.
[0036] As a preferred technical solution of the present invention, the drying method includes at least one of spray drying, coating drying, forced air drying, vacuum drying or high-energy ball milling drying;
[0037] Preferably, the inlet temperature of the spray dryer is 180~250℃, such as 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃ or 250℃, and the outlet temperature is 95~110℃, such as 95℃, 98℃, 100℃, 102℃, 105℃, 108℃ or 110℃.
[0038] Secondly, the present invention provides a modified sodium ferric sulfate cathode material, obtained according to the preparation method described in the first aspect, wherein the chemical formula of sodium ferric sulfate in the modified sodium ferric sulfate cathode material includes Na. x Fe(SO4) y Where 0 < x ≤ 3, for example, x can be 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8 or 3, etc.; y = (2 + x) / 2, for example, y can be 1.05, 1.15, 1.4, 1.5, 1.6, 1.75, 1.9, 2, 2.1, 2.25, 2.4 or 2.5, etc.
[0039] Thirdly, the present invention provides a sodium-ion battery containing the modified sodium ferric sulfate cathode material described in the second aspect.
[0040] It should be noted that, due to space limitations and to avoid redundancy, this invention does not exhaustively list all points within the above numerical range, but it is not limited to the listed values either; other unlisted values within the above numerical range are also applicable.
[0041] Compared with existing technical solutions, the present invention has at least the following beneficial effects:
[0042] The preparation method of this invention utilizes titanium oxysulfate, which has reducing properties, to undergo microwave pyrolysis in an aqueous solution, thereby synthesizing nano-titanium dioxide particles in situ on the surface of sodium ferric sulfate particles. This forms an inert coating layer, which can effectively improve structural stability and reduce the water absorption of the sodium ferric sulfate material. Due to the acidic nature of the sodium ferric sulfate precursor, it can promote the solubility of titanium oxysulfate in water and promote the formation of the coating layer. This preparation method can also effectively improve the compaction density of the obtained modified sodium ferric sulfate cathode material, reaching 2.1 g / cm³. 3 above. Attached Figure Description
[0043] Figure 1 This is a SEM morphology image of the cathode material obtained in Example 1.
[0044] Figure 2 This is a SEM image of the cathode material obtained in Comparative Example 1.
[0045] Figure 3 These are XRD structure diagrams of the cathode materials obtained in Example 1 and Comparative Example 1. Detailed Implementation
[0046] The technical solution of the present invention will be further illustrated below through specific embodiments.
[0047] Those skilled in the art will understand that the embodiments described are merely illustrative of the invention and should not be construed as limiting the invention.
[0048] Example 1
[0049] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material, the method comprising the following steps:
[0050] The dispersant carboxymethyl cellulose was dissolved in water by stirring beforehand, and then the conductive agent carbon nanotubes were added and ultrasonically dispersed for 90 minutes to obtain a conductive agent dispersion. The conductive agent dispersion was mixed with a sodium source, an iron source and a reducing agent to obtain the precursor solution. The conductive agent includes at least one of carbon nanotubes, carbon black, graphene or aerogel.
[0051] The conductive agent accounts for 2% of the total mass of the sodium and iron sources; the dispersant accounts for 0.5% of the conductive agent dispersion; the sodium source is anhydrous sodium sulfate, the iron source is ferrous sulfate heptahydrate, the reducing agent is ascorbic acid, and the total mass of the iron and sodium sources accounts for 25% of the precursor solution; the molar ratio of sodium in the sodium source to the molar ratio of iron in the iron source is 1.42:1; the reducing agent accounts for 5% of the mass of the iron source.
[0052] The precursor solution is then spray-dried at an inlet temperature of 200°C and an outlet temperature of 104°C to obtain sodium ferric sulfate precursor.
[0053] A sodium ferric sulfate precursor was stirred in water and then mixed with titanium oxysulfate to obtain an aqueous solution; the mass of the sodium ferric sulfate precursor accounted for 30% of the mass of the aqueous solution; and the mass of the titanium oxysulfate accounted for 1.5% of the mass of the sodium ferric sulfate precursor.
[0054] An aqueous solution was subjected to an in-situ synthesis reaction under microwave assistance for 4 minutes. The microwave frequency of the microwave assistance was 2.5 GHz and the microwave temperature was 95 °C. Titanium dioxide was generated and coated with the sodium ferric sulfate precursor. After the in-situ synthesis reaction was completed, the solution was centrifuged, the supernatant was poured off, and the intermediate was dried by blowing air to obtain a powder sample.
[0055] The intermediate was calcined in an inert reducing atmosphere of nitrogen at a heating rate of 5℃ / min, a holding temperature of 370℃, and a holding time of 10h to obtain the modified sodium iron sulfate cathode material.
[0056] Example 2
[0057] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material. The preparation method adjusts the microwave temperature of the in-situ synthesis reaction of the aqueous solution under microwave assistance from 95°C to 105°C. Except for the above, the other conditions are exactly the same as in Example 1.
[0058] Example 3
[0059] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material. The microwave temperature for the in-situ synthesis reaction of the aqueous solution under microwave assistance is adjusted from 95°C to 110°C, and the time is adjusted from 4 min to 3 min. Except for the above, the other conditions are exactly the same as in Example 1.
[0060] Example 4
[0061] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material. The microwave temperature for the in-situ synthesis reaction of the aqueous solution under microwave assistance is adjusted from 95°C to 120°C, and the time is adjusted from 4 min to 2 min. Except for the above, the other conditions are exactly the same as in Example 1.
[0062] Example 5
[0063] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material. The preparation method adjusts the mass percentage of titanium oxysulfate in the sodium ferric sulfate precursor from 1.5% to 2.5%. Except for the above, the other conditions are exactly the same as in Example 1.
[0064] Example 6
[0065] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material. The preparation method adjusts the mass percentage of titanium oxysulfate in the sodium ferric sulfate precursor from 1.5% to 3.5%. Except for the above, the other conditions are exactly the same as in Example 1.
[0066] Example 7
[0067] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material. The mass percentage of titanium oxysulfate in the sodium ferric sulfate precursor is adjusted from 1.5% to 5%, and the in-situ synthesis reaction time under microwave assistance is adjusted from 4 min to 2 min. Except for the above, the other conditions are exactly the same as in Example 1.
[0068] Example 8
[0069] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material. In this method, the mass percentage of titanium oxysulfate in the sodium ferric sulfate precursor is adjusted from 1.5% to 6%. Except for the above, the other conditions are exactly the same as in Example 1.
[0070] Example 9
[0071] This embodiment provides a method for preparing a modified sodium ferric sulfate cathode material. The microwave temperature in the preparation method is adjusted from 95°C to 130°C. Except for the above, the other conditions are exactly the same as in Example 1.
[0072] Comparative Example 1
[0073] This comparative example provides a method for preparing sodium ferric sulfate cathode material. The preparation method does not use titanium oxysulfate, and all other conditions are exactly the same as in Example 1.
[0074] Comparative Example 2
[0075] This comparative example provides a method for preparing sodium ferric sulfate cathode material. The preparation method uses the sodium ferric sulfate precursor obtained in Example 1 and proceeds according to the following steps:
[0076] A sodium ferric sulfate precursor was mixed with an ethylene glycol solution of n-butyl titanate to obtain a mixed solution; the mass of the sodium ferric sulfate precursor accounted for 30% of the mass of the mixed solution; and the mass of the n-butyl titanate accounted for 1.5% of the mass of the sodium ferric sulfate precursor.
[0077] The aqueous solution was reacted under microwave assistance for 4 minutes. The microwave frequency was 2.5 GHz and the microwave temperature was 95 °C. After the reaction was completed, the solution was centrifuged, the supernatant was poured off, and the intermediate was dried by blowing air to obtain a powder sample.
[0078] The intermediate was calcined in an inert reducing atmosphere of nitrogen at a heating rate of 5℃ / min, a holding temperature of 370℃, and a holding time of 10h to obtain the modified sodium iron sulfate cathode material.
[0079] Apart from the above, all other conditions are exactly the same as in Example 1.
[0080] The cathode materials obtained in the examples and comparative examples were characterized and tested:
[0081] 1) Morphological characteristics: Figure 1 This is a SEM image of the cathode material obtained in Example 1. Figure 2 The image shows the SEM test results of the cathode material obtained in Comparative Example 1. The comparison between the two images shows that after modification, the modified sodium ferric sulfate cathode material in Example 1 is coated with nano-sized particles and has a dense structure, while the sodium ferric sulfate particles in Comparative Example 1 are not coated and have a smoother surface.
[0082] 2) Phase characterization: Figure 3 The figures show the XRD patterns of the cathode materials obtained in Example 1 and Comparative Example 1. As can be seen from the figures, there is a clear sodium ferric sulfate phase in both Example 1 and Comparative Example 1, while there are also diffraction peaks of titanium dioxide phase in the diffraction pattern of Example 1, indicating that nano-titanium dioxide was successfully coated in Example 1.
[0083] 3) Moisture content test: The water content was tested using the Karl Fischer method after the storage time was 1h, 2h, 6h, 24h and 48h in a high and low temperature humidity test chamber at 20℃ and 60% humidity to characterize the water absorption. The results are shown in Table 1.
[0084] Table 1
[0085]
[0086] As shown in Table 1, from Examples 1 to 7, the water absorption of sodium ferric sulfate material significantly decreased after being coated with titanium dioxide particles, indicating that the inert titanium dioxide coating layer can indeed alter the structural stability of sodium ferric sulfate material. The titanium dioxide coating obtained from in-situ synthesis of titanate (Comparative Example 2) resulted in less reduction in water absorption, but its waterproofing effect was not as good as that of titanium oxysulfate raw material. The coating layers obtained in Examples 8 and 9 were thicker, further improving the waterproofing effect.
[0087] 4) Compacted density test: The compacted density was tested using a compacted density tester at a pressure of 50 MPa for 10 seconds. The results are shown in Table 2.
[0088] Table 2
[0089]
[0090] As shown in Table 2, in Examples 1 to 7, after being coated with titanium dioxide particles, the compacted density of the sodium ferric sulfate material increased from the normal 1.75 g / cm³. 3 Increased to 2.11 g / cm³ 3 This indicates that the inert titanium dioxide coating improves the structural stability of the sodium ferric sulfate material, thereby increasing its compressive strength. After coating with titanium dioxide synthesized in situ from tetrabutyl titanate (Comparative Example 2), the compaction density of the sodium ferric sulfate material increased only slightly (1.75 g / cm³). 3 Increased to 1.91 g / cm³ 3 When the titanium dioxide coating amount exceeds a certain value (Examples 8 and 9), the compaction density of the sodium ferric sulfate material also increases only slightly and no longer.
[0091] 5) Electrical Performance Testing: The obtained positive electrode material was mixed evenly with carbon black and PVDF at a mass ratio of 90:5:5. The mixture was then coated onto aluminum foil using a 100μm four-sided coating tool. The electrode film was pre-dried in an 80℃ forced-air drying oven for 30 minutes, and then transferred to a vacuum drying oven at 110℃ for 10 hours. The electrode film was punched into a 6mm radius disc using a punching machine (compact density testing was performed at this point). Using metallic sodium as the counter electrode and 1mol / L NaClO4 EC+DEC (1:1 vol%)+5% FEC as the electrolyte, and a Whatman-D glass fiber separator, a CR2032 type button cell was assembled in a glove box. The resulting button cell was subjected to constant current charge-discharge testing at a current density of 0.1C (1C=90mAh / g). Rate tests of 0.2C / 0.5C / 1C / 2C / 5C were conducted within a voltage range of 2.5~4.3V. The results are shown in Table 3.
[0092] Table 3
[0093]
[0094] As shown in Table 3, in Examples 1 to 7, the first-efficiency and rate performance of sodium ferric sulfate materials were improved to some extent after being coated with titanium dioxide particles. After coating with titanium dioxide synthesized in situ from tetrabutyl titanate (Comparative Example 2), the first-efficiency of the sodium ferric sulfate material increased from 93.2% to 96.5%, but the rate performance improvement was not significant. When the titanium dioxide coating amount exceeded a certain value (Examples 8 and 9), the electrical properties of the sodium ferric sulfate material decreased because the excessively thick coating layer affected the sodium ion insertion / extraction. Therefore, in order to simultaneously achieve waterproof performance, compaction density, and electrical performance, the coating amount should be reasonably adjusted to the optimal level. For this purpose, the amount of titanium oxysulfate, the synthesis temperature, and the time should be appropriately controlled in the preparation method. Generally, the time should be appropriately reduced when the temperature is higher to facilitate the formation of a uniform coating layer with suitable thickness.
[0095] As can be seen from the above, the preparation method of the present invention utilizes titanium oxysulfate, which has reducing properties, to undergo microwave pyrolysis in an aqueous solution, thereby synthesizing nano-titanium dioxide particles in situ on the surface of sodium ferric sulfate particles. This forms an inert coating layer, which can effectively improve structural stability and reduce the water absorption of sodium ferric sulfate material. Due to the acidic nature of the sodium ferric sulfate precursor, it can promote the solubility of titanium oxysulfate in water and promote the formation of the coating layer. This preparation method can also effectively improve the compaction density of the obtained modified sodium ferric sulfate cathode material, reaching 2.1 g / cm³. 3 above.
[0096] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.
[0097] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.
[0098] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.
Claims
1. A method for preparing a modified sodium ferric sulfate cathode material, characterized in that, The preparation method includes the following steps: Sodium ferric sulfate precursor and titanium oxysulfate are mixed in water to obtain an aqueous solution. The aqueous solution is subjected to an in-situ synthesis reaction under microwave assistance to generate titanium dioxide and coat the sodium ferric sulfate precursor to obtain an intermediate. The intermediate is then calcined to obtain a modified sodium ferric sulfate cathode material.
2. The method for preparing the modified sodium ferric sulfate cathode material according to claim 1, characterized in that, The sodium ferric sulfate precursor accounts for 20% to 50% of the mass of the aqueous solution; The mass of the titanium oxysulfate accounts for 1% to 5% of the mass of the sodium ferric sulfate precursor.
3. The method for preparing the modified sodium ferric sulfate cathode material according to claim 1 or 2, characterized in that, The microwave-assisted process uses a microwave frequency of 2-3 GHz and a microwave temperature of 90-120°C; the in-situ synthesis reaction takes 2-8 minutes. After the in-situ synthesis reaction is completed, solid-liquid separation is performed to obtain the intermediate; the solid-liquid separation method includes centrifugation and / or vacuum filtration.
4. The method for preparing the modified sodium ferric sulfate cathode material according to any one of claims 1-3, characterized in that, The calcination is carried out under an inert reducing atmosphere, which includes nitrogen; the heating rate of the calcination is 2~5℃ / min, the holding temperature is 350~400℃, and the holding time is 8~10h.
5. The method for preparing the modified sodium ferric sulfate cathode material according to any one of claims 1-4, characterized in that, The method for preparing the sodium ferric sulfate precursor includes: mixing a sodium source, an iron source, a reducing agent and water to obtain a precursor solution, and then drying the precursor solution to obtain the sodium ferric sulfate precursor; The sodium source includes sodium sulfate; the iron source includes at least one of ferrous sulfate heptahydrate, anhydrous ferrous sulfate, or ferrous sulfate monohydrate; the total mass of the iron source and the sodium source accounts for 20% to 43% of the mass of the precursor solution; the molar ratio of sodium in the sodium source to the molar ratio of iron in the iron source is (1.2 to 1.6):
1. The reducing agent includes ascorbic acid and / or citric acid; the mass of the reducing agent accounts for 2% to 8% of the mass of the iron source.
6. The method for preparing the modified sodium ferric sulfate cathode material according to claim 5, characterized in that, The method for preparing the sodium ferric sulfate precursor further includes: mixing raw materials that also include a conductive agent to obtain the precursor solution; The conductive agent includes at least one of carbon nanotubes, carbon black, graphene, or aerogel; the mass of the conductive agent accounts for 2% to 5% of the total mass of the sodium source and the iron source.
7. The method for preparing the modified sodium ferric sulfate cathode material according to claim 6, characterized in that, The method for preparing the sodium ferric sulfate precursor further includes: pre-dispersing a conductive agent and a dispersant in water to obtain a conductive agent dispersion; then mixing the conductive agent dispersion with the sodium source, iron source and reducing agent to obtain the precursor solution; The dispersant comprises carboxymethyl cellulose and / or polyvinylpyrrolidone; the mass of the dispersant accounts for 0.5% to 3% of the mass of the conductive agent dispersion; The dispersion method includes at least one of sand milling dispersion, ultrasonic dispersion, or shear emulsification dispersion.
8. The method for preparing the modified sodium ferric sulfate cathode material according to any one of claims 5-7, characterized in that, The drying method includes at least one of spray drying, coating drying, forced air drying, vacuum drying, or high-energy ball milling drying; the inlet temperature of the spray dryer is 180~250℃, and the outlet temperature is 95~110℃.
9. A modified sodium ferric sulfate cathode material, characterized in that, The modified sodium ferric sulfate cathode material obtained according to any one of claims 1-8 has the chemical formula of sodium ferric sulfate including Na. x Fe(SO4) y , where 0 < x ≤ 3, y = (2 + x) / 2.
10. A sodium-ion battery, characterized in that, It contains the modified sodium ferric sulfate cathode material as described in claim 9.