Preparation method of ferric sodium pyrophosphate positive electrode material

Abstract

The preparation method comprises the following steps: (1) weighing a sodium source, an iron source, a phosphorus source and a carbon source, quickly and uniformly mixing, and then pre-sintering at low temperature to obtain a precursor; wherein the low-temperature presintering comprises two stages, in the first stage, the temperature is increased to 60-150 DEG C and kept for 1-3 h, and in the second stage, the temperature is increased to 200-350 DEG C and kept for 1-8 h; and (2) adding a carbon source into the precursor to prepare slurry, sanding the slurry, carrying out centrifugal spray drying, and carrying out high-temperature sintering to obtain the ferric sodium pyrophosphate positive electrode material. The precursor of the high-solid-content slurry can be prepared, the problem that the solid content of the slurry is low in the grinding stage of the sodium ferric pyrophosphate positive electrode material prepared by a solid-phase method is effectively solved, the solid content of the slurry is increased, the yield of the precursor is increased, the production cost is reduced, and meanwhile, the product quality is improved. The prepared ferric sodium pyrophosphate positive electrode material has relatively high compaction density, capacity and other performances, and the performance of the product is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of sodium iron pyrophosphate phosphate, and more specifically, to a method for preparing a sodium iron pyrophosphate phosphate cathode material. Background Art

[0002] With the increasing global attention to environmental protection, green travel and low-carbon travel have become the mainstream trends in people's lives. Against this background, the development of electric vehicles has been greatly promoted, and one of the core components of electric vehicles is the battery. Among them, sodium-ion batteries are regarded as one of the most effective electrochemical energy storage systems because of their low cost, high safety, and environmental friendliness. As the cathode material for sodium-ion power batteries, sodium iron pyrophosphate phosphate is widely used in the energy storage field because of its rich raw material sources, low price, environmental friendliness, long life, good safety and thermal stability, etc.

[0003] The solid-phase method is one of the main methods for preparing sodium iron pyrophosphate phosphate. After mixing the raw materials evenly, ball milling, spray drying and high-temperature sintering are carried out to finally obtain the sodium iron pyrophosphate phosphate cathode material; however, due to the nature of the raw materials themselves, the solid content of the slurry in the grinding stage is extremely low, about 20% - 30%, resulting in a low output of the precursor and high energy consumption; at present, there have been studies providing technologies to improve the problem of low solid content of the slurry in the grinding stage of preparing sodium iron pyrophosphate phosphate.

[0004] For example, the invention patent with the publication number of CN118398810A discloses a sodium iron pyrophosphate phosphate cathode material and a preparation method thereof. The sodium iron pyrophosphate phosphate cathode material is prepared from a sodium source, an iron source, a carbon source and a phosphorus source; wherein the sodium source includes sodium polyphosphate, the iron source includes one or more combinations of iron phosphate, ferric oxide, and ferroferric oxide, the carbon source includes one or more combinations of sodium citrate, citric acid, sodium oleate, oleic acid, polyvinylpyrrolidone, polyethylene glycol, glucose, ascorbic acid, sucrose, dopamine hydrochloride, starch, graphene oxide, reduced graphene oxide, carbon nanotubes, Ketjen black, etc., and the phosphorus source includes sodium polyphosphate; this invention solves the problems of low solid content of the raw materials and long grinding time by introducing sodium polyphosphate as a suitable sodium source and phosphorus source. Since sodium polyphosphate has a high chelating effect, it chelates with the iron source to reduce the grinding difficulty and shorten the grinding time. At the same time, when sodium polyphosphate is used as the phosphorus source and sodium source, it also acts as a surfactant, having the effect of locking water, avoiding the agglomeration of particles during grinding, and improving the solid content of the raw materials.

[0005] Although the prior art has adopted dispersant-like substances to improve the viscosity of the slurry, the effect of this method is not significant and it will increase the production cost; moreover, during the subsequent high-temperature sintering process, these substances will decompose, resulting in more impurity phases in the material and affecting the performance of the final product. Therefore, it is necessary to develop a new method to overcome the above problems and make the slurry in the grinding stage have a high solid content when preparing the sodium iron pyrophosphate precursor. Summary of the Invention

[0006] In view of the above, the present invention provides a method for preparing a sodium iron pyrophosphate cathode material, which solves the problem of low solid content of the slurry in the grinding stage of preparing sodium iron pyrophosphate by the solid-phase method.

[0007] The present invention provides a method for preparing a sodium iron pyrophosphate cathode material, comprising:

[0008] (1) Weigh sodium source, iron source, phosphorus source and carbon source, mix them evenly quickly, and then carry out low-temperature pre-sintering under a protective gas to obtain a precursor;

[0009] (2) Add the precursor to the carbon source to prepare a slurry, and then carry out sand grinding and centrifugal spray drying on the slurry and then carry out high-temperature sintering to obtain the sodium iron pyrophosphate cathode material.

[0010] The sodium source, iron source and phosphorus source are weighed according to the molar ratio of Na∶Fe∶P of 1∶0.75∶1. The sodium source is one or more of sodium carbonate, trisodium phosphate, sodium pyrophosphate, sodium dihydrogen phosphate, the iron source is one or more of ferrous oxalate, iron phosphate, ferrous sulfate, ferrous nitrate, and the phosphorus source is one or more of ammonium dihydrogen phosphate, phosphoric acid, ammonium phosphate. The carbon sources used in step (1) and step (2) are all one or more of glucose, sucrose, polyethylene glycol and polyvinyl alcohol, and preferably sucrose.

[0011] The carbon content of the precursor is 0.1-0.6 wt%.

[0012] The time for quickly mixing evenly is 5-30 min.

[0013] The low-temperature pre-sintering is gradient heating sintering, including two stages. The first stage is to heat up to 60-150 °C and hold for 1-3 h, and the second stage is to heat up to 200-350 °C and hold for 1-8 h.

[0014] The flow rate of the protective gas in the first stage of the low-temperature pre-sintering is 10-20 L / min, and the flow rate of the protective gas in the second stage is 5-10 L / min. The protective gas is one of nitrogen, argon, and argon-hydrogen mixture.

[0015] In the present invention, through low-temperature pre-sintering, decomposition products such as carbon oxides and hydrogen oxides contained in the raw materials can be decomposed and removed. These decomposition products will affect the viscosity of the subsequent slurry, resulting in a decrease in the solid content of the slurry. Before low-temperature pre-sintering, by rapid mixing, a uniform pre-sintered material can be obtained, which can avoid incomplete decomposition of the decomposition products due to material segregation during the pre-sintering process. Among them, the longer the mixing time, the more uniform the raw material mixing will be. However, considering the later production cost, a good effect can be achieved by mixing for 5 to 30 minutes. At the same time, the decomposition products contained in the raw materials have different types, qualities, and decomposition properties. Therefore, low-temperature pre-sintering adopts gradient heating sintering, using different temperatures and times to decompose different decomposition products, and supplemented with different protective gas flow rates to ensure the reaction quality and product quality of the decomposition process, so that the decomposition products contained in the raw materials can be fully removed without affecting the raw materials themselves, improving the viscosity of the subsequently prepared slurry and increasing the solid content of the slurry.

[0016] In the present invention, adding the carbon source in two times can make the carbon coating more uniform and improve the conductivity of the cathode material.

[0017] Among them, the solid content of the slurry is 40% to 65%.

[0018] Among them, the sanding particle size D50 is 80 to 500 nm.

[0019] Among them, the conditions for high-temperature sintering are to keep the temperature at 400 to 600 °C for 5 to 12 h.

[0020] Among them, the carbon content of the sodium iron pyrophosphate phosphate cathode material is 1 to 2 wt%.

[0021] The beneficial effects of the present invention are as follows:

[0022] (1) By rapidly mixing the sodium iron pyrophosphate phosphate raw materials and then performing low-temperature pre-sintering, a precursor for preparing a slurry with a high solid content is obtained, effectively solving the problem of low solid content of the slurry in the grinding stage of preparing the sodium iron pyrophosphate phosphate cathode material by the solid-phase method, increasing the solid content of the slurry, thereby increasing the precursor yield and reducing the energy consumption;

[0023] (2) The present invention does not require the use of additional dispersants or auxiliary materials, reducing the production cost and achieving effective cost control;

[0024] (3) At the same time, the sodium iron pyrophosphate phosphate cathode material prepared by the present invention has properties such as a high tap density and capacity, improving the performance of the product;

[0025] (4) The process of the present invention is simple and can improve the production efficiency. Detailed implementation manners

[0026] Embodiments of the present application will be described in more detail below. The present application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to more thoroughly and completely understand the present application. It should be understood that the embodiments of the present application are only for exemplary purposes and are not used to limit the protection scope of the present application.

[0027] Embodiments and comparative examples of the present invention are as follows:

[0028] Example 1:

[0029] (1) Sodium source, iron source, and phosphorus source were weighed according to the molar ratio of Na∶Fe∶P of 1∶0.75∶1, and a carbon source was added. After rapid mixing for 10 min, low-temperature pre-sintering was carried out under nitrogen protection. The conditions for low-temperature pre-sintering were to first heat up to 60°C and hold for 3 h with a gas flow rate of 20 L / min, then heat up to 200°C and hold for 8 h with a gas flow rate of 10 L / min to obtain a precursor; the carbon content of the precursor was 0.4 wt%.

[0030] (2) The precursor was added with a carbon source to prepare a slurry, and then the slurry was subjected to sand grinding and centrifugal spray drying and then high-temperature sintering. The sand grinding particle size was D50 of 200 nm, and the conditions for high-temperature sintering were to keep the temperature at 400°C for 12 h to obtain the sodium iron pyrophosphate phosphate cathode material; the carbon content of the sodium iron pyrophosphate phosphate cathode material was 1.8 wt%.

[0031] Example 2:

[0032] (1) Sodium source, iron source, and phosphorus source were weighed according to the molar ratio of Na∶Fe∶P of 1∶0.75∶1, and a carbon source was added. After rapid mixing for 10 min, low-temperature pre-sintering was carried out under nitrogen protection. The conditions for low-temperature pre-sintering were to first heat up to 100°C and hold for 1.5 h with a gas flow rate of 10 L / min, then heat up to 270°C and hold for 4 h with a gas flow rate of 5 L / min to obtain a precursor; the carbon content of the precursor was 0.4 wt%.

[0033] (2) The precursor was added with a carbon source to prepare a slurry, and then the slurry was subjected to sand grinding and centrifugal spray drying and then high-temperature sintering. The sand grinding particle size was D50 of 300 nm, and the conditions for high-temperature sintering were to keep the temperature at 500°C for 8 h to obtain the sodium iron pyrophosphate phosphate cathode material; the carbon content of the sodium iron pyrophosphate phosphate cathode material was 1.6 wt%.

[0034] Example 3:

[0035] (1) Weigh the sodium source, iron source, and phosphorus source according to the molar ratio of Na∶Fe∶P of 1∶0.75∶1, and add the carbon source. Mix them quickly for 10 min, and then carry out low-temperature pre-sintering under nitrogen protection. The conditions for low-temperature pre-sintering are to first heat up to 150 °C and hold for 1 hour, with a gas flow rate of 10 L / min, then heat up to 350 °C and hold for 1 h, with a gas flow rate of 5 L / min, to obtain the precursor; the carbon content of the precursor is 0.4 wt%.

[0036] (2) Add the carbon source to the precursor again to prepare a slurry, and then carry out sand grinding and centrifugal spray drying on the slurry and then carry out high-temperature sintering. The sand grinding particle size is D50 of 500 nm, and the conditions for high-temperature sintering are to keep the temperature at 600 °C for 5 h to obtain the sodium iron pyrophosphate phosphate cathode material; the carbon content of the sodium iron pyrophosphate phosphate cathode material is 1.6 wt%.

[0037] Example 4:

[0038] (1) Weigh the sodium source, iron source, and phosphorus source according to the molar ratio of Na∶Fe∶P of 1∶0.75∶1, and add the carbon source. Mix them quickly for 10 min, and then carry out low-temperature pre-sintering under nitrogen protection. The conditions for low-temperature pre-sintering are to first heat up to 130 °C and hold for 2 hours, with a gas flow rate of 10 L / min, then heat up to 320 °C and hold for 3 h, with a gas flow rate of 5 L / min, to obtain the precursor; the carbon content of the precursor is 0.4 wt%.

[0039] (2) Add the carbon source to the precursor again to prepare a slurry, and then carry out sand grinding and centrifugal spray drying on the slurry and then carry out high-temperature sintering. The sand grinding particle size is D50 of 350 nm, and the conditions for high-temperature sintering are to keep the temperature at 530 °C for 8 h to obtain the sodium iron pyrophosphate phosphate cathode material; the carbon content of the sodium iron pyrophosphate phosphate cathode material is 1.6 wt%.

[0040] Comparative example: Prepared by the conventional solid-phase method:

[0041] (1) Weigh the sodium source, iron source, and phosphorus source according to the molar ratio of Na∶Fe∶P of 1∶0.75∶1, and add the carbon source to obtain the precursor; the carbon content of the precursor is 0.4 wt%.

[0042] (2) Add the carbon source to the precursor again to prepare a slurry, and then carry out sand grinding and centrifugal spray drying on the slurry and then carry out high-temperature sintering. The sand grinding particle size is D50 of 350 nm, and the conditions for high-temperature sintering are to keep the temperature at 530 °C for 8 h to obtain the sodium iron pyrophosphate phosphate cathode material; the carbon content of the sodium iron pyrophosphate phosphate cathode material is 1.6 wt%.

[0043] Table 1 shows the test results of the slurries and the sodium iron pyrophosphate phosphate cathode materials of the examples and comparative examples of the present invention. The solid content of the slurries prepared from the precursors prepared by the method of the present invention is all above 50%, while the solid content of the slurries prepared from the precursors prepared by the conventional solid-phase method in the comparative example is only 26%. This proves that the method of the present invention effectively removes the decomposition products in the raw materials that affect the viscosity of the slurry by means of low-temperature pre-sintering, effectively improves the solid content of the slurry, and effectively solves the problem of low solid content of the slurry in the grinding stage of preparing the sodium iron pyrophosphate phosphate cathode material by the solid-phase method. At the same time, the tap density and capacity of the sodium iron pyrophosphate phosphate cathode material prepared by the method of the present invention are both improved, which proves that the method of the present invention effectively improves the performance of the sodium iron pyrophosphate phosphate cathode material.

[0044] Table 1: Test Results of Slurries and Sodium Iron Pyrophosphate Phosphate Cathode Materials of Examples and Comparative Examples of the Present Invention

[0045]

[0046] As mentioned above, the above are only the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in this application can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. A method for preparing a sodium iron phosphate pyrophosphate positive electrode material, characterized in that: include: (1) weighing a sodium source, an iron source, a phosphorus source, and a carbon source, quickly mixing them uniformly, and then pre-sintering them at a low temperature under a protective gas to obtain a precursor; (2) The precursor is added with a carbon source to prepare a slurry, and the slurry is then sand-milled and centrifugally spray-dried and then sintered at a high temperature to obtain a sodium iron pyrophosphate positive electrode material.

2. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The sodium source, iron source and phosphorus source are weighed according to the molar ratio of Na:Fe:P of 1:0.75:

1.

3. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The carbon content of the precursor is 0.1-0.6wt%.

4. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The time for rapid mixing is 5 to 30 minutes.

5. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The low-temperature pre-sintering is a gradient temperature-raising sintering, which includes two stages. The first stage is to raise the temperature to 60-150° C. and keep it for 1-3 hours, and the second stage is to raise the temperature to 200-350° C. and keep it for 1-8 hours.

6. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The flow rate of the protective gas in the first stage of the low-temperature pre-sintering is 10-20 L / min, and the flow rate of the protective gas in the second stage is 5-10 L / min.

7. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The solid content of the slurry is 40% to 65%.

8. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The sand grinding particle size D50 is 80-500nm.

9. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The high temperature sintering condition is 400-600° C. for 5-12 hours.

10. The method for preparing a sodium iron phosphate pyrophosphate positive electrode material according to claim 1, characterized in that: The carbon content of the sodium iron phosphate pyrophosphate positive electrode material is 1-2wt%.

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