Carbon-coated ferric sodium pyrophosphate positive electrode material and preparation method thereof

Abstract

The invention discloses a carbon-coated ferric sodium pyrophosphate positive electrode material and a preparation method, the carbon-coated ferric sodium pyrophosphate positive electrode material comprises a Na source, a Fe source, aluminum acetate and a P. The carbon-coated ferric sodium pyrophosphate prepared by the invention is used as the positive electrode material of a sodium ion battery, the electric conductivity of the battery is obviously improved, the discharge capacity is obviously improved, and the service life of the battery is prolonged. The rate capability and the low-temperature performance of the battery are greatly improved, the gel enables the material to form a layer of three-dimensional carbon conductive network during sintering, the layer of three-dimensional carbon conductive network improves the conductivity of the material, the in-situ coated carbon layer well inhibits the growth of primary particles, the transmission distance of sodium ions is reduced, and the performance of the battery is improved. The secondary carbon coating is characterized in that a small amount of uniform fluidized bed vapor deposition (CVD) is carried out on the basis of the primary carbon coating, the surface of the material is coated with a layer of nanoscale conductive carbon film again, relatively good temperature treatment is adopted, and the graphitization degree of the coated carbon layer is high, so that the electronic conductivity of the material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for sodium-ion batteries, and specifically to a carbon-coated sodium iron pyrophosphate cathode material and a preparation method thereof. Background Art

[0002] Sodium-ion batteries are considered to be the most promising alternatives to lithium-ion batteries due to the abundant sodium resources, low cost, and high safety performance. In recent years, great efforts have been made to develop key technologies such as cathode materials, anode materials, and electrolytes for sodium-ion batteries. However, due to inevitable disadvantages such as the relatively large radius of sodium ions and low standard electrochemical potential, the development of cathode materials for sodium-ion batteries is restricted.

[0003] With the development of sodium-ion battery cathode materials, polyanionic sodium-ion battery cathode materials have attracted much attention. Among them, sodium iron pyrophosphate has attracted the attention of major manufacturers due to its low technical barriers and high specific capacity. However, its low conductivity is a major difficulty affecting its industrialization process. Since the sintering temperature is relatively low, the degree of graphitization after carbonization of the organic carbon source is low, and the conductivity is poor, seriously affecting the capacity performance, rate performance, and low-temperature performance of the material. Therefore, we propose a carbon-coated sodium iron pyrophosphate cathode material and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide a carbon-coated sodium iron pyrophosphate cathode material and a preparation method thereof to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A carbon-coated sodium iron pyrophosphate cathode material, comprising a Na source, an Fe source, aluminum acetate, and a P source.

[0006] Preferably, the ratio of the Na source, the Fe source, aluminum acetate, and the P source is Na:Fe:Al:P = 3.90~4.15:2.90~2.98:0.001~0.003:3.90~4.30.

[0007] A preparation method of a carbon-coated sodium iron pyrophosphate cathode material comprises the following steps: Step 1: Mix the Fe source, the C source, aluminum acetate, and pure water, and stir and react at a certain temperature to obtain a reaction solution A; Step 2: Add an appropriate amount of the Na source and the P source to the reaction solution A. After reacting for a period of time, add an appropriate amount of ethylene glycol, raise the temperature, and continue to react for a period of time to obtain a gel B; Step 3: Dry the gel B to remove moisture to obtain a dry gel, then grind the dry gel, and calcine the ground powder in a nitrogen atmosphere to obtain a powder material C; Step 4: Put the powder material C into a fluidized bed for chemical vapor deposition (CVD) to obtain a secondary carbon-coated sodium iron pyrophosphate cathode material.

[0008] Preferably, in the step 1, the Fe source includes one or more of iron oxide, iron phosphate, ferrous oxalate, ferrous sulfate, ferric sulfate, ferric oxalate, metallic iron powder, and ferric nitrate.

[0009] Preferably, in the step 1, the C source includes one or more of glucose, fructose, graphene, graphene oxide, citric acid, sucrose, carbon nanotubes, polyethylene glycol, polyvinyl alcohol, soluble starch, cyclodextrin, carbon black, and acetylene black.

[0010] Preferably, in the step 1, the aluminum acetate used is an aluminum acetate crystal with a purity of more than 98%, a D50 of 50 - 300 nm, a moisture content of less than 3%, and a white color.

[0011] Preferably, in the step 2, the P source includes one or more of phosphoric acid, iron phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0012] Preferably, in the step 2, the Na source includes one or more of sodium carbonate, sodium hydroxide, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium bicarbonate, sodium sulfate, sodium fluoride, sodium citrate, sodium nitrate, and sodium oxalate.

[0013] Preferably, in the step 2, the ethylene glycol used is ethylene glycol with a purity of more than 99.5%.

[0014] Preferably, in the step 3, the protective atmosphere includes one or more of N2, Ar, and CO2 / H2.

[0015] Preferably, in the step 3, the sintering temperature is 400 - 600 °C, and the sintering time is 8 - 16 hours.

[0016] Preferably, in the step 3, the carbon content of the sodium iron pyrophosphate product is 1.5% - 2.5%, and D50 ≤ 4 - 10 μm.

[0017] Preferably, in the step 4, the gas for fluidized bed chemical vapor deposition (CVD) is one of acetylene, methane, ethane, propane, ethylene, and propylene.

[0018] Preferably, in the step 4, the temperature of fluidized bed chemical vapor deposition (CVD) is 500 - 680 °C, and the time is 2 - 6 hours.

[0019] Compared with the prior art, the beneficial effects of the present invention are: The sodium iron pyrophosphate phosphate coated with carbon prepared by the present invention is used as the positive electrode material of a sodium ion battery, which significantly improves the conductivity of the battery, significantly increases the discharge capacity, and greatly enhances the rate performance and low-temperature performance of the battery. Since the gel enables a three-dimensional carbon conductive network to be formed during sintering of the material, this three-dimensional carbon conductive network improves the conductivity of the material, and the in-situ coated carbon layer effectively inhibits the growth of primary particles, reduces the transmission distance of sodium ions. The secondary carbon coating is carried out by a method of a small amount of uniform fluidized bed chemical vapor deposition (CVD) on the basis of the first carbon coating, and a nanoscale conductive carbon film is coated on the surface of the material again. By using a relatively good temperature treatment, the graphitization degree of the coated carbon layer is high, thereby improving the electronic conductivity of the material, forming a relatively good conductive network, and the CVD coating layer is thin and uniform, with a small increase in carbon content, which will not have an obvious impact on the specific surface area of the product, and still can ensure very good processing performance. Description of the Drawings

[0020] Figure 1 It is an X-ray diffraction pattern of a sodium iron pyrophosphate phosphate cathode material coated with carbon; Figure 2 It is a SEM image (50.00kx) of a sodium iron pyrophosphate phosphate cathode material coated with carbon; Figure 3 It is a SEM image (30.00kx) of a sodium iron pyrophosphate phosphate cathode material coated with carbon; Figure 4 It is a SEM image (10.00kx) of a sodium iron pyrophosphate phosphate cathode material coated with carbon. Detailed Embodiments

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0022] Please refer to Figures 1 - 4 , the present invention provides a technical solution: a sodium iron pyrophosphate phosphate cathode material coated with carbon, including a Na source, an Fe source, aluminum acetate, and a P source.

[0023] In the embodiments of the present application, the ratio of the Na source, the Fe source, aluminum acetate, and the P source is Na:Fe:Al:P = 3.90 - 4.15:2.90 - 2.98:0.001 - 0.003:3.90 - 4.30.

[0024] A method for preparing a sodium iron pyrophosphate phosphate cathode material coated with carbon, comprising the following steps: Step 1: Mix the Fe source, C source, aluminum acetate, and pure water, and stir and react at a certain temperature to obtain reaction solution A; Step 2: Add an appropriate amount of Na source and P source to reaction solution A. After reacting for a period of time, add an appropriate amount of ethylene glycol, raise the temperature, and continue to react for a period of time to obtain gel B; Step 3: Dry the gel B to remove moisture to obtain a dry gel, then grind the dry gel, and calcine the ground powder in a nitrogen atmosphere to obtain powder material C; Step 4: Place the powder material C in a fluidized bed for chemical vapor deposition (CVD) to obtain a secondary carbon-coated sodium iron pyrophosphate cathode material.

[0025] In the embodiment of the present application, in Step 1, the Fe source includes one or more of iron oxide, iron phosphate, ferrous oxalate, ferrous sulfate, ferric sulfate, ferric oxalate, metallic iron powder, and ferric nitrate.

[0026] In the embodiment of the present application, in Step 1, the C source includes one or more of glucose, fructose, graphene, graphene oxide, citric acid, sucrose, carbon nanotubes, polyethylene glycol, polyvinyl alcohol, soluble starch, cyclodextrin, carbon black, and acetylene black.

[0027] In the embodiment of the present application, in Step 1, the aluminum acetate used is an aluminum acetate crystal with a purity of more than 98%, a D50 of 50 - 300 nm, a moisture content of less than 3%, and a white color.

[0028] In the embodiment of the present application, in Step 2, the P source includes one or more of phosphoric acid, iron phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0029] In the embodiment of the present application, in Step 2, the Na source includes one or more of sodium carbonate, sodium hydroxide, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium bicarbonate, sodium sulfate, sodium fluoride, sodium citrate, sodium nitrate, and sodium oxalate.

[0030] In the embodiment of the present application, in Step 2, the ethylene glycol used is ethylene glycol with a purity of more than 99.5%.

[0031] In the embodiment of the present application, in Step 3, the protective atmosphere includes one or more of N2, Ar, and CO2 / H2.

[0032] In the embodiment of the present application, in Step 3, the sintering temperature is 400 - 600 °C, and the sintering time is 8 - 16 hours.

[0033] In the embodiment of the present application, in Step 3, the carbon content of the sodium iron pyrophosphate product is 1.5% - 2.5%, and D50 ≤ 4 - 10 μm.

[0034] In the embodiment of the present application, in step 4, the gas for fluidized bed chemical vapor deposition (CVD) is one of acetylene, methane, ethane, propane, ethylene, and propylene.

[0035] In the embodiment of the present application, in step 4, the temperature of the fluidized bed chemical vapor deposition (CVD) is 500 - 680 °C, and the time is 2 - 6 hours.

[0036] Example 1: This example provides a method for preparing a carbon-coated sodium iron pyrophosphate phosphate cathode material, including the following steps: Step 1: Weigh metallic iron powder: citric acid: aluminum acetate = 1:1.8:0.003 in a total of 1000 g according to the stoichiometric ratio, then mix with 2000 g of pure water, keep warm with 85 °C warm water, set the stirring speed at 1500 rpm, and stir and react for 10 h to obtain reaction solution A; Step 2: Weigh sodium bicarbonate: phosphoric acid = 1:1.5 according to the stoichiometric ratio, slowly add it to reaction solution A. After all is added, continue to react for 2 h, then add 300 g of ethylene glycol to the solution and react for 2 h to form gel B; Step 3: Remove the moisture of gel B at 85 °C to obtain a dry gel, then grind the dry gel. The ground powder is calcined in a nitrogen atmosphere, the calcination temperature is 485 °C, the heating rate is 3 °C / min, and the holding time is 12 h.

[0037] Example 2: This example provides a method for preparing a carbon-coated sodium iron pyrophosphate phosphate cathode material, including the following steps: Step 1: Weigh metallic iron powder: citric acid: aluminum acetate = 1:1.8:0.003 in a total of 1000 g according to the stoichiometric ratio, then mix with 2000 g of pure water, keep warm with 85 °C warm water, set the stirring speed at 1500 rpm, and stir and react for 10 h to obtain reaction solution A; Step 2: Weigh sodium bicarbonate: phosphoric acid = 1:1.5 according to the stoichiometric ratio, slowly add it to reaction solution A. After all is added, continue to react for 2 h, then add 300 g of ethylene glycol to the solution and react for 2 h to form gel B; Step 3: Remove the moisture of gel B at 85 °C to obtain a dry gel, then grind the dry gel. The ground powder is calcined in a nitrogen atmosphere, the calcination temperature is 485 °C, the heating rate is 3 °C / min, and the holding time is 12 h.

[0038] Step 4: Put the sintered powder into a fluidized bed, seal and pass nitrogen. After the oxygen content in the fluidized bed reaches the requirement, introduce acetylene gas and heat up to 550 °C. After reacting for 2 hours, cool down and discharge the material.

[0039] Example 3: This example provides a method for preparing a carbon-coated sodium iron pyrophosphate phosphate cathode material, comprising the following steps: Step 1: Weigh metallic iron powder: citric acid: aluminum acetate = 1:1.8:0.003 in a total amount of 1000 g according to the stoichiometric ratio, then mix with 2000 g of pure water, keep warm with 85 °C warm water, set the stirring speed at 1500 rpm, and stir and react for 10 h to obtain reaction solution A; Step 2: Weigh sodium bicarbonate: phosphoric acid = 1:1.3 according to the stoichiometric ratio, slowly add it to reaction solution A. After all is added, continue to react for 2 h, then add 300 g of ethylene glycol to the solution and react for 2 h to form gel B; Step 3: Remove the moisture from gel B at 85 °C to obtain a dry gel, then grind the dry gel. The ground powder is calcined in a nitrogen atmosphere at a calcination temperature of 485 °C, a heating rate of 3 °C / min, and a holding time of 12 h.

[0040] Step 4: Put the sintered powder into a fluidized bed, seal and pass nitrogen. After the oxygen content in the fluidized bed reaches the requirement, pass acetylene gas and heat up to 600 °C. After reacting for 3 hours, cool down and discharge the material.

[0041] Example 4: This example provides a method for preparing a carbon-coated sodium iron pyrophosphate phosphate cathode material, comprising the following steps: Step 1: Weigh metallic iron powder: citric acid: aluminum acetate = 1:1.8:0.003 in a total amount of 1000 g according to the stoichiometric ratio, then mix with 2000 g of pure water, keep warm with 85 °C warm water, set the stirring speed at 1500 rpm, and stir and react for 10 h to obtain reaction solution A; Step 2: Weigh sodium bicarbonate: phosphoric acid = 1:1.2 according to the stoichiometric ratio, slowly add it to reaction solution A. After all is added, continue to react for 2 h, then add 300 g of ethylene glycol to the solution and react for 2 h to form gel B; Step 3: Remove the moisture from gel B at 85 °C to obtain a dry gel, then grind the dry gel. The ground powder is calcined in a nitrogen atmosphere at a calcination temperature of 485 °C, a heating rate of 3 °C / min, and a holding time of 12 h.

[0042] Step 4: Put the sintered powder into a fluidized bed, seal and pass nitrogen. After the oxygen content in the fluidized bed reaches the requirement, pass acetylene gas and heat up to 650 °C. After reacting for 3 hours, cool down and discharge the material.

[0043] Example 5: This example provides a method for preparing a carbon-coated sodium iron pyrophosphate phosphate cathode material, comprising the following steps: Step 1: Weigh metallic iron powder: citric acid: aluminum acetate at a stoichiometric ratio of 1:1.8:0.003, a total of 1000 g. Then mix it with 2000 g of pure water, keep it warm with water at 85°C, set the stirring speed at 1500 rpm, and stir and react for 10 h to obtain reaction solution A; Step 2: Weigh sodium bicarbonate: phosphoric acid at a stoichiometric ratio of 1:1.2, and slowly add it to reaction solution A. After adding it all, continue to react for 2 h. Then add 300 g of ethylene glycol to the solution and react for 2 h to form gel B; Step 3: Remove the moisture from gel B at 85°C to obtain a dry gel. Then grind the dry gel, and calcine the ground powder in a nitrogen atmosphere. The calcination temperature is 485°C, the heating rate is 3°C / min, and the holding time is 12 h.

[0044] Step 4: Put the sintered powder into a fluidized bed, seal it and pass nitrogen. After the oxygen content in the fluidized bed reaches the requirement, introduce acetylene gas and heat up to 650°C. After reacting for 4 hours, cool down and discharge the material.

[0045] Example 6: This example provides a preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material, including the following steps: Step 1: Weigh metallic iron powder: citric acid: aluminum acetate at a stoichiometric ratio of 1:1.8:0.003, a total of 1000 g. Then mix it with 2000 g of pure water, keep it warm with water at 85°C, set the stirring speed at 1500 rpm, and stir and react for 10 h to obtain reaction solution A; Step 2: Weigh sodium bicarbonate: phosphoric acid at a stoichiometric ratio of 1:1.2, and slowly add it to reaction solution A. After adding it all, continue to react for 2 h. Then add 300 g of ethylene glycol to the solution and react for 2 h to form gel B; Step 3: Remove the moisture from gel B at 85°C to obtain a dry gel. Then grind the dry gel, and calcine the ground powder in a nitrogen atmosphere. The calcination temperature is 485°C, the heating rate is 3°C / min, and the holding time is 12 h.

[0046] Step 4: Put the sintered powder into a fluidized bed, seal it and pass nitrogen. After the oxygen content in the fluidized bed reaches the requirement, introduce acetylene gas and heat up to 680°C. After reacting for 3 hours, cool down and discharge the material.

[0047] Example 7: This example provides a preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material, including the following steps: Step 1: Weigh metallic iron powder: citric acid: aluminum acetate = 1:1.8:0.003 in a stoichiometric ratio, totaling 1000 g. Then mix it with 2000 g of pure water, keep it warm with water at 85 °C, set the stirring speed at 1500 rpm, and stir and react for 10 h to obtain reaction solution A; Step 2: Weigh sodium bicarbonate: phosphoric acid = 1:1.2 in a stoichiometric ratio, slowly add it to reaction solution A. After adding it all, continue to react for 2 h, and then add 300 g of ethylene glycol to the solution and react for 2 h to form gel B; Step 3: Remove moisture from gel B at 85 °C to obtain a dry gel. Then grind the dry gel, and calcine the ground powder in a nitrogen atmosphere. The calcination temperature is 485 °C, the heating rate is 3 °C / min, and the holding time is 12 h.

[0048] Step 4: Put the sintered powder into a fluidized bed, seal it and pass nitrogen. After the oxygen content in the fluidized bed reaches the requirement, pass acetylene gas and heat up to 680 °C. After reacting for 4 h, cool it down and discharge the material.

[0049] Test example: Rate performance test: Using the above-mentioned examples and comparative examples as the positive electrode materials, assemble coin cells, charge and discharge at a current rate of 0.1 C, evaluate the rate performance of the materials, and the test results are shown in Table 1. Serial number Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Discharge specific capacity (mAh / g) 95.4 100.4 102.2 105.3 108.2 112.5 115.8 Carbon content 1.80 1.85 1.90 1.93 1.95 2.02 2.18 Specific surface area 10.0 10.2 10.5 10.8 11.2 11.5 11.8 Capacity retention rate at -20°C 80% 85% 87% 88% 90% 91% 92% Capacity retention rate of coin cell at 1C / 0.1C 88% 92% 93% 95% 96% 97.5% 98.0% Table 1 According to the above test results of the examples, it can be seen that for the sodium iron pyrophosphate phosphate cathode material coated with carbon prepared by the method of the present invention, the conductivity of the battery is significantly improved, the discharge capacity is significantly increased, and the rate performance and low-temperature performance of the battery are greatly improved.

[0050] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0051] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A carbon-coated sodium iron pyrophosphate phosphate cathode material, characterized in that, The invention comprises a Na source, an Fe source, aluminum acetate and a P source, wherein the ratio of the Na source, the Fe source, the aluminum acetate and the P source is Na:Fe:Al:P=3.90-4.15:2.90-2.98:0.001-0.003:3.90-4.

30.

2. A preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material, applicable to the carbon-coated sodium iron pyrophosphate phosphate cathode material described in claim 1, characterized in that, The following steps are involved: Step 1: Mix the Fe source, C source, aluminum acetate and pure water, and stir to react at a certain temperature to obtain reaction solution A; Step 2: Add appropriate amounts of Na source and P source to reaction solution A. After a period of reaction, add appropriate amount of ethylene glycol, raise the temperature, and continue the reaction for a period of time to obtain gel B. Step 3: Gel B is dried to remove moisture to obtain a dry gel, and the dry gel is then ground. The ground powder is calcined under a nitrogen atmosphere to obtain powder material C; Step 4: Place the powder material C into a fluidized bed for vapor deposition (CVD) to obtain a secondary carbon-coated sodium iron pyrophosphate positive electrode material.

3. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, characterized in that: In step 1, the Fe source includes one or more of iron oxide, iron phosphate, ferrous oxalate, ferrous sulfate, ferric sulfate, ferric oxalate, metallic iron powder, and ferric nitrate.

4. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, characterized in that: In step 1, the C source includes one or more of glucose, fructose, graphene, graphene oxide, citric acid, sucrose, carbon nanotubes, polyethylene glycol, polyvinyl alcohol, soluble starch, cyclodextrin, carbon black, and acetylene black.

5. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, characterized in that: In the step 1, the aluminum acetate used is white aluminum acetate crystals with a purity of more than 98%, a D50 of 50-300 nm, a moisture content of less than 3%, and a color.

6. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, wherein: In step 2, the P source includes one or more of phosphoric acid, ferric phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

7. The method for preparing a carbon-coated sodium iron pyrophosphate positive electrode material according to claim 2, characterized in that: In step 2, the Na source includes one or more of sodium carbonate, sodium hydroxide, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium bicarbonate, sodium sulfate, sodium fluoride, sodium citrate, sodium nitrate, and sodium oxalate.

8. A carbon-coated sodium iron pyrophosphate phosphate cathode material and a preparation method according to claim 2, characterized in that: In step 2, the ethylene glycol used is ethylene glycol with a purity of 99.5% or more.

9. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, characterized in that: In step 3, the protective atmosphere includes one or more of N2, Ar, CO2 / H2.

10. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, characterized in that: In step 3, the sintering temperature is 400-600° C., and the sintering time is 8-16 hours.

11. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, characterized in that: In step 3, the carbon content of the sodium ferric pyrophosphate product is 1.5% to 2.5%, and D50 is ≤ 4-10 um.

12. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, characterized in that: In step 4, the gas used in fluidized bed vapor deposition (CVD) is one of acetylene, methane, ethane, propane, ethylene, and propylene.

13. The preparation method of a carbon-coated sodium iron pyrophosphate phosphate cathode material according to claim 2, characterized in that: In step 4, the temperature of fluidized bed vapor deposition (CVD) is 500-680° C., and the time is 2-6 hours.

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