A method for preparing organic carbon source gasification coated sodium ferric sulfate cathode material and its application

Abstract

This invention relates to a method for preparing an organic carbon source-coated sodium ferric sulfate cathode material and its application, belonging to the field of battery materials technology. The method involves placing an organic carbon source on one side of the gas inlet and a mixture of sodium sulfate and ferrous sulfate on one side of the gas outlet of a dual-temperature zone tubular furnace. An asymmetric temperature control method is used to vaporize the organic carbon source and uniformly deposit it on the surface of the sodium ferric sulfate, achieving in-situ carbon coating. This invention employs a one-step sintering method to prepare organic carbon-coated sodium ferric sulfate, simplifying the step-by-step coating process and significantly reducing time and raw material costs. The asymmetric temperature control method for sintering avoids the decomposition of sodium ferric sulfate while effectively solving the problem of incomplete carbonization of the organic carbon source during traditional low-temperature sintering. This achieves in-situ carbon coating of sodium ferric sulfate during sintering, forming a uniform carbon coating layer on the surface of the sodium ferric sulfate, thereby improving the electronic conductivity of the material and giving it better electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology. Specifically, it relates to a method for preparing sodium iron sulfate cathode material coated with gaseous organic carbon source by vaporizing organic carbon source through an asymmetric temperature control method and depositing it on the surface of sodium iron sulfate, and its application in sodium-ion batteries. Background Technology

[0002] In recent years, global environmental pollution and resource shortages have become increasingly serious, making the development of new renewable energy sources an urgent priority. Lithium-ion batteries, due to their high energy density, long lifespan, good stability, and lack of memory effect, have been widely used in various portable mobile devices, electric vehicles, and energy storage. However, due to the limited and uneven distribution of global lithium resources, the production and use costs of lithium batteries are inevitably greatly affected. Sodium-ion batteries are similar to lithium-ion batteries in their working principle and have significant advantages such as abundant sodium salt reserves, low raw material costs, high thermal stability, and a wide operating temperature range. They are considered a powerful complement to lithium-ion batteries, especially with huge application prospects in low-speed electric vehicles and large-scale energy storage. However, the current development of sodium-ion batteries is limited by the cost and electrochemical performance of cathode materials. Therefore, finding low-cost, high-performance cathode materials is key to promoting the development of sodium-ion batteries.

[0003] Currently, cathode materials for sodium-ion batteries are mainly classified into three types: layered oxide, polyanionic, and Prussian blue. Among them, polyanionic cathode materials exhibit significant advantages due to their open framework, stable crystal structure, and low-energy ion migration pathways. Sodium iron sulfate, as a polyanionic material, is considered one of the potential materials for the industrialization of sodium-ion batteries because of its low raw material cost, high operating voltage, and environmentally friendly, pollution-free preparation process. However, sodium iron sulfate has poor conductivity, resulting in low capacity, poor rate performance, and poor cycle stability. In-situ carbon coating using organic carbon sources is a common method to improve the electrochemical performance of low-conductivity cathode materials, but since sodium iron sulfate decomposes above 450℃, the traditional strategy of in-situ carbon coating through high-temperature carbonization is difficult to apply to this material. Existing technologies usually improve conductivity by adding highly conductive inorganic carbon such as carbon nanotubes, graphene, and carbon fibers during solid-phase ball milling. However, the dispersion effect of inorganic carbon is greatly affected by raw materials and experimental conditions, and its high cost also weakens the cost advantage of sodium iron sulfate cathode materials. Therefore, developing a method for in-situ carbon coating of sodium ferric sulfate using an organic carbon source has broad prospects. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of poor electronic conductivity of sodium ferric sulfate, a polyanionic cathode material for sodium-ion batteries, when carbon coating is performed using an organic carbon source. This is due to incomplete carbonization of the organic carbon source during low-temperature sintering. The invention provides a method for preparing sodium ferric sulfate cathode material by vaporization of organic carbon source and its application. This method uses an asymmetric temperature control method. The sintering temperature of the organic carbon source on the gas inlet side of the dual-temperature zone tubular furnace is 600-800℃ to vaporize the organic carbon source, while the sintering temperature of the sodium ferric sulfate on the gas outlet side of the dual-temperature zone is 300-400℃ to prevent decomposition of the sodium ferric sulfate during sintering. After vaporization, the organic carbon source is uniformly deposited on the surface of the sodium ferric sulfate, thereby achieving in-situ carbon coating of sodium ferric sulfate.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing an organic carbon source gasification coated sodium ferric sulfate cathode material, the method comprising: using an asymmetric temperature control method, wherein the organic carbon source is placed in a high-temperature zone, the mixture of sodium sulfate and ferrous sulfate is placed in a low-temperature zone, and a protective gas is introduced for sintering.

[0007] Furthermore, the method specifically includes:

[0008] Step 1: Dry ferrous sulfate heptahydrate and sodium sulfate in a vacuum oven to obtain anhydrous ferrous sulfate and anhydrous sodium sulfate; drying in a vacuum oven is also to prevent the oxidation of ferrous sulfate.

[0009] Step 2: Mix anhydrous sodium sulfate and anhydrous ferrous sulfate evenly to obtain a white mixture;

[0010] Step 3: Place the organic carbon source and the mixture obtained in Step 2 in the middle of the two temperature zones of a dual-temperature zone tube furnace, and sinter them in a flowing protective atmosphere to obtain a black organic carbon-coated sodium ferric sulfate cathode.

[0011] Furthermore, in step one, the drying temperature is 200-300℃ and the time is 10-20h.

[0012] Further, in step two, the uniform mixing involves uniformly mixing the sodium sulfate and ferrous sulfate obtained in step one using high-energy ball milling under a protective gas atmosphere. The ball-to-material ratio is 5-30:1, the rotation speed is 400-800 r / min, and the milling time is 1-24 h. Since ferrous sulfate is easily oxidized, and there is a certain temperature rise during high-energy ball milling, which may accelerate oxidation, this has a significant impact on the final material properties. Therefore, ball milling under an inert gas atmosphere is necessary.

[0013] Furthermore, in step two, the molar ratio of Na to Fe in the white mixture is 1-1.5:1.

[0014] Furthermore, in step three, the organic carbon source is at least one selected from sucrose, ascorbic acid, glucose, citric acid, starch, polyvinylpyrrolidone, succinic acid, and tannic acid.

[0015] Furthermore, in step three, the mass ratio of the organic carbon source to the mixture is 0.01-10:1.

[0016] Furthermore, in step three, the sintering temperature on the organic carbon source side of the dual-temperature zone tube furnace is 600-800℃, which vaporizes the organic carbon source. The sintering temperature on the sodium sulfate and ferrous sulfate mixture side is 300-400℃, where the two react to generate ferrous sulfate, and the organic carbon source is deposited on its surface to achieve uniform carbon coating. The heating rate on both sides is 1-10℃ / min, and the sintering time is 1-30h.

[0017] Furthermore, in step three, the protective atmosphere is at least one of argon, nitrogen, or a hydrogen-argon mixture, and the flow rate of the protective atmosphere is 10-90 mL / min.

[0018] Application of sodium ferric sulfate cathode material prepared by the above preparation method in sodium-ion batteries.

[0019] The technical solution of this invention has the following advantages:

[0020] 1. This invention uses a one-step sintering method to prepare organic carbon-coated sodium ferric sulfate. The low-temperature sintering of sodium ferric sulfate and the organic carbon source coating process are carried out simultaneously in a dual-temperature zone tube furnace, which optimizes the synthesis process, effectively simplifies the complex steps in step-by-step coating and some other synthesis methods, and uses organic carbon source for carbon coating instead of inorganic carbon, which greatly reduces time and raw material costs.

[0021] 2. This invention involves sintering materials in a dual-temperature zone tube furnace, placing the organic carbon source in the high-temperature zone and sodium ferric sulfate in the low-temperature zone. This allows the organic carbon source to vaporize and then uniformly deposit on the surface of sodium ferric sulfate, thus avoiding the decomposition of sodium ferric sulfate and effectively solving the problem of incomplete carbonization of the organic carbon source. This achieves in-situ carbon coating of sodium ferric sulfate during the sintering process and forms a uniform carbon coating layer on the surface of sodium ferric sulfate.

[0022] 3. The cathode material prepared by this invention can be applied to sodium-ion batteries, and the prepared sodium-ion batteries have good electronic conductivity, thereby achieving higher specific capacity. Attached Figure Description

[0023] Figure 1 This is a partial schematic diagram of the sintering process in a dual-temperature zone tubular furnace as described in Embodiment 1 of the present invention.

[0024] Figure 2 This is a schematic diagram of the reaction occurring during the sintering process in an embodiment of the present invention.

[0025] Figure 3 This is the XRD pattern of the sodium ferric sulfate cathode material obtained in Example 1 of this invention.

[0026] Figure 4 These are the 0.1C first charge-discharge curves of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0027] Figure 5 This is a comparison chart of the 1C cycle performance of Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0029] This invention employs a one-step sintering method to prepare organic carbon-coated sodium ferric sulfate, effectively simplifying the complex steps in stepwise coating and other synthesis methods, and significantly reducing time and raw material costs. By using an asymmetric temperature control method for sintering, the decomposition of sodium ferric sulfate is avoided, while effectively solving the problem of incomplete carbonization of the organic carbon source in traditional low-temperature sintering. This achieves in-situ carbon coating of sodium ferric sulfate during sintering, forming a uniform carbon coating layer on the surface of the sodium ferric sulfate, thereby improving the electronic conductivity of the material and giving it better electrochemical performance.

[0030] Example 1

[0031] This embodiment prepares a sodium ferric sulfate cathode material uniformly coated with an organic carbon source. The specific steps include:

[0032] Step 1: Dry ferrous sulfate heptahydrate and sodium sulfate in a vacuum oven at 200°C for 12 hours to obtain anhydrous ferrous sulfate and anhydrous sodium sulfate.

[0033] Step 2: Weigh the Na₂SO₄ and FeSO₄ obtained in Step 1 at a Na to Fe molar ratio of 1.5:1 and premix them by hand. After mixing evenly, use a high-energy ball mill containing zirconia balls to ball mill the mixture 36 times, with each ball milling session lasting 10 minutes and followed by a 5-minute interval, to obtain a highly dispersed powder mixture. The ball milling process is carried out in an argon atmosphere, with a ball-to-material ratio of 20:1, a ball milling speed of 600 r / min, and a total ball milling time of 6 hours.

[0034] Step 3: Transfer the mixture obtained in Step 2 to a ceramic boat and place it in the middle of the heating zone on the side of the gas outlet of the dual-temperature zone tube furnace, which is called the low-temperature zone; add sucrose to another ceramic boat, wherein the mass ratio of sucrose to the total mass of the mixture is 0.5:1, and place it in the middle of the heating zone on the side of the gas inlet of the dual-temperature zone tube furnace, which is called the high-temperature zone.

[0035] Step 4: The sintering temperature in the high-temperature zone is set to 700℃ with a heating rate of 4℃ / min, and the sintering temperature in the low-temperature zone is set to 350℃ with a heating rate of 2℃ / min. Sintering is carried out for 12 hours in an argon atmosphere with an argon flow rate of 40mL / min, finally yielding a black organic carbon-coated sodium iron sulfate cathode.

[0036] Example 2

[0037] This embodiment prepares a sodium ferric sulfate cathode material uniformly coated with an organic carbon source. The specific steps and methods are the same as in Example 1, except that the organic carbon source in step three is glucose.

[0038] Example 3

[0039] This embodiment prepares a sodium ferric sulfate cathode material uniformly coated with an organic carbon source. The specific steps and methods are the same as in Example 1, except that the organic carbon source in step three is tannic acid.

[0040] Example 4

[0041] This embodiment prepares a sodium ferric sulfate cathode material uniformly coated with an organic carbon source. The specific steps and methods are the same as in Example 1, except that in step three, the ratio of sucrose mass to the total mass of the mixture is 5:1.

[0042] Example 5

[0043] This embodiment prepares a sodium ferric sulfate cathode material uniformly coated with an organic carbon source. The specific steps include:

[0044] Step 1: Dry ferrous sulfate heptahydrate and sodium sulfate in a vacuum oven at 250°C for 12 hours to obtain anhydrous ferrous sulfate and anhydrous sodium sulfate.

[0045] Step 2: Weigh the Na₂SO₄ and FeSO₄ obtained in Step 1 at a Na to Fe molar ratio of 1.2:1 and premix them by hand. After uniform mixing, use a high-energy ball mill containing zirconia balls to perform high-energy ball milling 24 times, with each milling cycle lasting 20 minutes and followed by a 5-minute interval, to obtain a highly dispersed powder mixture. The ball milling process is carried out in an argon atmosphere, with a ball-to-material ratio of 15:1, a milling speed of 400 r / min, and a total milling time of 8 hours.

[0046] Step 3: Transfer the mixture obtained in Step 2 to a ceramic boat and place it in the middle of the heating zone on the side of the gas outlet of the dual-temperature zone tube furnace, which is called the low-temperature zone; add sucrose to another ceramic boat, wherein the mass ratio of sucrose to the total mass of the mixture is 1:1, and place it in the middle of the heating zone on the side of the gas inlet of the dual-temperature zone tube furnace, which is called the high-temperature zone.

[0047] Step 4: The sintering temperature in the high-temperature zone is set to 800℃ with a heating rate of 4℃ / min, and the sintering temperature in the low-temperature zone is set to 400℃ with a heating rate of 2℃ / min. Sintering is carried out for 12 hours in an argon atmosphere with an argon flow rate of 20mL / min, finally yielding a black organic carbon-coated sodium iron sulfate cathode.

[0048] Example 6

[0049] This embodiment prepares a sodium ferric sulfate cathode material uniformly coated with an organic carbon source. The specific steps include:

[0050] Step 1: Dry ferrous sulfate heptahydrate and sodium sulfate in a vacuum oven at 300°C for 12 hours to obtain anhydrous ferrous sulfate and anhydrous sodium sulfate.

[0051] Step 2: Weigh the Na₂SO₄ and FeSO₄ obtained in Step 1 at a Na to Fe molar ratio of 1.5:1 and premix them by hand milling. After uniform mixing, use a high-energy ball mill containing zirconia balls to perform high-energy ball milling 48 times, with each milling cycle lasting 5 minutes and followed by a 5-minute interval, to obtain a highly dispersed powder mixture. The ball milling process is carried out in an argon atmosphere, with a ball-to-material ratio of 30:1, a milling speed of 800 r / min, and a total milling time of 6 hours.

[0052] Step 3: Transfer the mixture obtained in Step 2 to a ceramic boat and place it in the middle of the heating zone on the side of the gas outlet of the dual-temperature zone tube furnace, which is called the low-temperature zone; add sucrose to another ceramic boat, wherein the mass ratio of sucrose to the total mass of the mixture is 10:1, and place it in the middle of the heating zone on the side of the gas inlet of the dual-temperature zone tube furnace, which is called the high-temperature zone.

[0053] Step 4: The sintering temperature in the high-temperature zone is set to 700℃ with a heating rate of 4℃ / min, and the sintering temperature in the low-temperature zone is set to 350℃ with a heating rate of 2℃ / min. Sintering is carried out for 12 hours in an argon atmosphere with an argon flow rate of 90mL / min. Finally, a black organic carbon-coated sodium iron sulfate cathode is obtained.

[0054] Comparative Example 1:

[0055] This comparative example uses a traditional low-temperature sintering method to prepare an organic carbon source-coated sodium ferric sulfate cathode material. The specific steps include:

[0056] Step 1: Dry ferrous sulfate heptahydrate and sodium sulfate in a vacuum oven at 200°C for 12 hours to obtain anhydrous ferrous sulfate and anhydrous sodium sulfate.

[0057] Step 2: Weigh the Na₂SO₄ and FeSO₄ obtained in Step 1 at a Na to Fe molar ratio of 1.5:1, and add 50% of the total mass of sucrose for hand-milling premixing. After mixing evenly, use a high-energy ball mill containing zirconia balls to ball-mill the mixture 36 times, with each milling cycle lasting 10 minutes and followed by a 5-minute interval, to obtain a highly dispersed powder mixture. The ball milling process is carried out in an argon atmosphere, with a ball-to-material ratio of 20:1, a milling speed of 600 r / min, and a cumulative milling time of 6 hours.

[0058] Step 3: Transfer the mixture obtained in Step 2 to a ceramic boat and sinter it in a tube furnace. Set the sintering temperature to 350℃ and the heating rate to 2℃ / min. Sinter for 12 hours under an argon atmosphere with an argon flow rate of 40mL / min to obtain a black organic carbon-coated sodium ferric sulfate cathode.

[0059] Comparative Example 2:

[0060] This comparative example prepared an organic carbon source-coated sodium iron sulfate cathode material. The specific steps and methods were the same as those in Comparative Example 1. The difference was that in step two, the mass of sucrose was 10% of the total mass of Na2SO4 and FeSO4.

[0061] Application Examples:

[0062] The organic carbon-coated sodium iron sulfate positive electrode material obtained in the above embodiments was mixed with conductive carbon black and binder PVDF (prepared as a 5% mass fraction NMP solution) in a certain amount of NMP at a mass ratio of 8:1:1 to form a positive electrode slurry. This slurry was then uniformly coated onto the surface of aluminum foil, vacuum dried at 120°C for 12 hours in a vacuum oven, and then pressed into shape under 10MPa pressure. The resulting slurry was then punched into 12mm positive electrode discs. A 15.6mm diameter, 0.5mm thick sodium metal disc was used as the negative electrode, and a 16mm diameter GF / D glass fiber disc was used as the separator. A 1mol / L NaClO4 electrolyte was prepared, in which the volume ratio of EC to PC in the solvent was 1:1, and 5% volume fraction FEC was added. A 2025 coin cell sodium-ion battery was assembled in a glove box with a water oxygen content of less than 0.01ppm.

[0063] The assembled sodium-ion battery was charged and discharged using a NEWARE test system at a current density of 10 mA / g, with a cutoff voltage range of 2.0V-4.3V.

[0064] Table 1. Results of the charge-discharge experiment

[0065] Initial charge capacity (mAh / g) Initial discharge capacity (mAh / g) First-time coulomb efficiency (%) Example 1 108.12 95.81 88.61 Example 2 107.42 94.36 87.84 Example 3 106.71 95.04 89.07 Example 4 105.09 90.50 86.12 Example 5 101.83 93.12 91.45 Example 6 112.12 92.22 82.25 Comparative Example 1 104.15 83.60 80.27 Comparative Example 2 94.82 77.36 81.58

Claims

1. A method for preparing an organic carbon source gasification coated sodium ferric sulfate cathode material, characterized in that: The method involves employing an asymmetric temperature control method, placing the organic carbon source in a high-temperature zone and a mixture of sodium sulfate and ferrous sulfate in a low-temperature zone, then introducing a protective gas for sintering; specifically, the method is as follows: Step 1: Dry ferrous sulfate heptahydrate and sodium sulfate to obtain anhydrous ferrous sulfate and anhydrous sodium sulfate; Step 2: Mix anhydrous sodium sulfate and anhydrous ferrous sulfate uniformly to obtain a white mixture; the uniform mixing is to uniformly mix the sodium sulfate and ferrous sulfate obtained in Step 1 using a high-energy ball milling method under a protective gas atmosphere, with a ball-to-material ratio of 5~30:1, a rotation speed of 400~800 r / min, and a ball milling time of 1~24 h; Step 3: Place the organic carbon source and the mixture obtained in Step 2 in the middle of the two temperature zones of a dual-temperature zone tube furnace and sinter them in a flowing protective atmosphere to obtain an organic carbon-coated sodium ferrous sulfate cathode. The sintering temperature on the organic carbon source side of the dual-temperature zone tube furnace is 600~800℃, and the sintering temperature on the sodium sulfate and ferrous sulfate mixture side is 300~400℃. The heating rate on both sides is 1~10℃ / min, and the sintering time is 1~30h.

2. The method for preparing an organic carbon source gasification coated sodium ferric sulfate cathode material according to claim 1, characterized in that: In step one, the drying temperature is 200~300℃ and the time is 10~20h.

3. The method for preparing an organic carbon source gasification coated sodium ferric sulfate cathode material according to claim 1, characterized in that: In step two, the molar ratio of Na to Fe in the white mixture is 1~1.5:

1.

4. The method for preparing an organic carbon source gasification coated sodium ferric sulfate cathode material according to claim 1, characterized in that: In step three, the organic carbon source is at least one of sucrose, ascorbic acid, glucose, citric acid, starch, polyvinylpyrrolidone, succinic acid, and tannic acid.

5. The method for preparing an organic carbon source gasification coated sodium ferric sulfate cathode material according to claim 1, characterized in that: In step three, the mass ratio of the organic carbon source to the mixture is 0.01 to 10:

1.

6. The method for preparing an organic carbon source gasification coated sodium ferric sulfate cathode material according to claim 1, characterized in that: In step three, the protective atmosphere is at least one of argon, nitrogen, or a hydrogen-argon mixture, and the flow rate of the protective atmosphere is 10~90 mL / min.

7. The application of a sodium iron sulfate cathode material prepared by the preparation method according to any one of claims 1 to 6 in a sodium-ion battery.

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