Preparation method of ferric sodium pyrophosphate positive electrode material with double-layer carbon structure

Abstract

According to the preparation method of the ferric sodium pyrophosphate positive electrode material with the double-layer carbon structure, double-layer carbon layers can be formed through respective coating of different carbon sources, and different carbon layers have different structure types, so that the material has higher phase stability and excellent ionic conductivity, and particularly, through a secondary spraying method, the material can be prepared into the ferric sodium pyrophosphate positive electrode material with the double-layer carbon structure. The high-molecular polymer is coated to form the inner carbon layer during first spraying, the organic matter low molecules are coated to form the outer carbon layer during second spraying, a multi-coating effect is formed, the inner carbon layer is compact and can avoid excessive side reactions between an electrolyte and a positive electrode material, so that the cycle performance is improved, and the outer carbon layer is used for supplementing defects of the inner carbon layer; and meanwhile, as an ion transmission channel between particles, the electrolyte is further prevented from being contacted, so that the conductivity is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion batteries, and in particular relates to a method for preparing a sodium iron phosphate pyrophosphate positive electrode material with a double-layer carbon structure. Background Art

[0002] With the development of lithium-ion batteries, their application areas are constantly expanding. However, as limited lithium resources are consumed in large quantities, there will eventually be a shortage of lithium resources. This has prompted researchers to look for new battery materials. Based on this consideration, sodium-ion batteries came into being.

[0003] Sodium ion positive electrode materials are abundant in resources, low in cost, highly safe and environmentally friendly. After the development in the past two years, sodium ion batteries are currently on the eve of industrial scale and are expected to be widely used in fields such as energy storage and low-speed electric vehicles. Sodium iron phosphate pyrophosphate (NFPP) materials in sodium ion positive electrode materials have the advantages of high cyclic stability, low cost, good safety, and high specific capacity (129mAh / g) and have received widespread attention. However, NFPP materials have the disadvantage of low ionic conductivity, which limits their application in the field of two-wheeled vehicles. Carbon coating is an important method to improve the conductivity of materials. Patent CN117886295A discloses a multi-carbon coating method, and does not emphasize the role of the two types of carbon coating layers in the internal and external composites. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a method for preparing a sodium iron pyrophosphate positive electrode material having a double-layer carbon structure, which is used to overcome the above defects in the prior art.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure comprises the following steps:

[0007] In the first step, sodium source, iron source and phosphorus source are put into a ball mill in a ratio of 4: (2.8-3): 4, and 3-5% of the first carbon source and 0.5-2% of the additives are added into the ball mill.

[0008] Ball milling is performed using methanol or anhydrous ethanol as a medium, the ball milling operation makes the slurry particle size reach 2-4 μm, and the amount of methanol or anhydrous ethanol added is 3-6 kg / L; after spray drying, air flow crushing is sieved through 40-80 meshes to obtain a first spray material;

[0009] The second step is to put the first spray material into a ball mill, add pure water as a solvent at a ratio of 3-5 kg / L, and then add a second carbon source at 2-5% of the weight of the first spray material, and perform low-speed ball milling to make the slurry particle size reach 1.8-3 μm, and then spray dry to obtain a second spray material;

[0010] The third step is to calcine the second spray material in a mixed atmosphere of argon and hydrogen in a ratio of 9:1, quickly heat up to 550-580°C, and keep the temperature for 10 hours to obtain a sodium iron phosphate pyrophosphate positive electrode material with a double-layer carbon structure.

[0011] In one embodiment, the sodium source is one or more of sodium dihydrogen phosphate, sodium carbonate, sodium bicarbonate, sodium acetate, and sodium pyrophosphate;

[0012] The iron source is one or more of ferrous oxalate, ferrous phosphate, ferrous acetate, ferrous sulfate, and ferrous nitrate;

[0013] The phosphorus source is one or more of ammonium phosphate, diammonium phosphate, and ammonium hydrogen phosphate.

[0014] In one embodiment, the first carbon source is one or more of polyethylene glycol, polypropylene alcohol, polyaniline, and polyvinyl pyrrolidone;

[0015] The second carbon source is one or more of sucrose, lactose and maltose.

[0016] In one embodiment, the additive is one or more of oleic acid, stearic acid, paraffin, and lauric acid.

[0017] In one embodiment, the spray drying operation in the first step has a spray speed of 10,000 to 12,000 rpm and a temperature of 80 to 90° C.;

[0018] The spraying speed of the spray drying operation in the third step is between 11000 and 12000 rpm, and the temperature is between 110 and 120°C.

[0019] In one embodiment, the rotation speed of the ball milling operation in the first step is between 800-1200 rpm, and the rotation speed of the ball milling operation in the second step is between 600-800 rpm.

[0020] In one embodiment, the heating rate of the rapid heating operation in the third step is 12-15° C. / min.

[0021] In one embodiment, the weight of the second carbon source added in the second step is 5% of the first spray material.

[0022] In one embodiment, the polyethylene glycol is polyethylene glycol 1000.

[0023] Compared with the prior art, the present invention provides a method for preparing a sodium iron phosphate pyrophosphate positive electrode material with a double-layer carbon structure. By coating different carbon sources separately, a double-layer carbon layer can be formed, and different carbon layers have different structural types, which can make the material have higher phase stability and excellent ion conductivity. Specifically, by a secondary spraying method, a high molecular weight polymer is coated in the first spraying to form an inner carbon layer, and an organic low molecular weight is coated in the second spraying to form an outer carbon layer, forming a multiple coating effect. The inner carbon layer is dense and compact, which can avoid excessive side reactions between the electrolyte and the positive electrode material, thereby improving the cycle performance. The outer carbon layer is used to supplement the defects of the inner carbon layer, further prevent the contact of the electrolyte, and at the same time serve as an ion transmission channel between particles to improve the conductivity.

[0024] The present invention provides a method for preparing a sodium iron pyrophosphate positive electrode material with a double-layer carbon structure, which is a convenient and efficient method for improving the ionic conductivity of NFPP. Through the method of carbon coating-solid phase dispersion-secondary carbon coating, two different types of carbon coating layers are formed outside the NFPP material to solve the shortcoming of low ionic conductivity of the NFPP material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a comparison chart of the 0.5C discharge curves of Example 1 and the control group provided by the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments:

[0027] Example 1

[0028] According to the ratio of Na:Fe:P=4:2.9:4, sodium dihydrogen phosphate, ferrous oxalate and sodium dihydrogen carbonate are added into a ball mill, 3% of the material weight of polyethylene glycol 1000 and 1.5% of stearic acid are added into the ball mill, and anhydrous ethanol is used as a medium for ball milling, and the addition amount is 5kg / L. After ball milling, spray drying is performed to obtain a first spray material, the rotation speed of the ball milling operation is between 800-1200rpm, the ball milling operation makes the slurry particle size reach 2-4μm, the spraying rotation speed of the spray drying operation is between 10000 and 12000rpm, and the temperature is between 80 and 90°C;

[0029] Then, the first spray material is put into another ball mill, pure water is added at a ratio of 4 kg / L, sucrose is added at 2% of the mass of the first spray material, and after low-speed ball milling, it is spray-dried again. The speed of the ball milling operation is between 600-800 rpm, and the ball milling operation makes the slurry particle size reach 1.8-3 μm. The spray speed of the spray drying operation is between 11000 and 12000 rpm and the temperature is between 110 and 120° C., so as to obtain a second spray material;

[0030] The second spray material was then calcined in a mixed atmosphere of argon and hydrogen in a ratio of 9:1, and the temperature was rapidly increased to 550°C at a heating rate of 15°C / min and kept at this temperature for 10 hours to obtain a sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure.

[0031] Example 2

[0032] According to the ratio of Na:Fe:P=4:2.9:4, sodium carbonate, iron phosphate and ammonium phosphate are added into a ball mill, 3% of the material weight of polyethylene glycol 1000 and 1.5% of stearic acid are added into the ball mill, and anhydrous ethanol is used as a medium for ball milling, and the addition amount is 5kg / L. After ball milling, the first spray material is obtained by spray drying, the rotation speed of the ball milling operation is between 800-1200rpm, the ball milling operation makes the slurry particle size reach 2-4μm, the spraying speed of the spray drying operation is between 10000 and 12000rpm, and the temperature is between 80 and 90°C;

[0033] Then, the first spray material is put into another ball mill, pure water is added at a ratio of 4 kg / L, sucrose is added at 2% of the mass of the first spray material, and after low-speed ball milling, it is spray-dried again. The speed of the ball milling operation is between 600-800 rpm, and the ball milling operation makes the slurry particle size reach 1.8-3 μm. The spray speed of the spray drying operation is between 11000 and 12000 rpm and the temperature is between 110 and 120° C., so as to obtain a second spray material;

[0034] The second spray material was then calcined in a mixed atmosphere of argon and hydrogen in a ratio of 9:1, and the temperature was rapidly increased to 550°C at a heating rate of 15°C / min and kept at this temperature for 10 hours to obtain a sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure.

[0035] Example 3

[0036] According to the ratio of Na:Fe:P=4:2.9:4, sodium carbonate, iron phosphate and ammonium phosphate are added into a ball mill, 3% of the material weight of polyethylene glycol 500 and 1.5% of oleic acid are added into the ball mill, and anhydrous ethanol is used as a medium for ball milling, and the addition amount is 5kg / L. After ball milling, the first spray material is obtained by spray drying, the rotation speed of the ball milling operation is between 800-1200rpm, the ball milling operation makes the slurry particle size reach 2-4μm, the spraying rotation speed of the spray drying operation is between 10000 and 12000rpm, and the temperature is between 80 and 90°C;

[0037] Then, the first spray material is put into another ball mill, pure water is added at a ratio of 4 kg / L, sucrose is added at 2% of the mass of the first spray material, and after low-speed ball milling, it is spray-dried again. The speed of the ball milling operation is between 600-800 rpm, and the ball milling operation makes the slurry particle size reach 1.8-3 μm. The spray speed of the spray drying operation is between 11000 and 12000 rpm and the temperature is between 110 and 120° C., so as to obtain a second spray material;

[0038] The second spray material was then calcined in a mixed atmosphere of argon and hydrogen in a ratio of 9:1, and the temperature was rapidly increased to 550°C at a heating rate of 15°C / min and kept at this temperature for 10 hours to obtain a sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure.

[0039] Control group 1

[0040] According to the ratio of Na:Fe:P=4:2.9:4, sodium carbonate, iron phosphate and ammonium phosphate are added to the ball mill, and 3% of the material weight of polyethylene glycol 1000, 2% of sucrose and 1.5% of stearic acid are added into the ball mill, and the ball milling is carried out with anhydrous ethanol as the medium, and the addition amount is 5kg / L. After ball milling, spray drying is performed to obtain the first spray material, and the atomizing disk speed must be greater than 12000prm; then the first spray material is calcined in a mixed atmosphere of argon and hydrogen 9:1, and the heating rate is 15℃ / min to 550℃, and the temperature is kept for 10h to obtain the carbon-coated sodium iron phosphate pyrophosphate positive electrode material.

[0041] Button test: The prepared sodium iron phosphate pyrophosphate and SP, PVDF were mixed and ground evenly in a ratio of 9:0.5:0.5, a certain amount of NMP was added, stirred and slurried, and then coated and dried. GF / D diaphragm and NaPF6 electrolyte were used to prepare 2032 button batteries. The charge and discharge capacity of 0.1-0.2-0.5-1C was tested in the range of 2-4V. The results are shown in the following table.

[0042]

[0043] The above table is a comparison of the discharge data of the example and the control group. It can be seen that the NFPP material prepared by double-layer carbon coating has a higher discharge capacity, and the capacity decreases less with the discharge rate. The comparison between Examples 1 and 2 shows that the selection of sodium / iron / phosphorus sources will have a certain impact on the electrical properties; the comparison between Examples 2 and 3 shows that the type of additive has little effect on the electrical properties, but it should be pointed out that this experimental result is only for reference in the description of the present invention, and the specific implementation plan needs to be adjusted according to the actual situation.

[0044] Referring to the attached figure of the specification: By comparing the 0.5C discharge curves of Example 1 and Control Group 1, it can be seen that the double-layer carbon-coated Example 1 material can have a longer discharge platform, indicating that the electron transmission channel between materials is smoother, thereby indicating that the preparation method of the sodium iron phosphate pyrophosphate positive electrode material with a double-layer carbon structure provided by the present invention has a good effect of improving the electrical properties of the material.

[0045] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0046] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure, characterized in that: The following steps are involved: In the first step, sodium source, iron source and phosphorus source are put into a ball mill in a ratio of 4: (2.8-3): 4, and 3-5% of the first carbon source and 0.5-2% of the additives are added into the ball mill. Ball milling is performed using methanol or anhydrous ethanol as a medium, the ball milling operation makes the slurry particle size reach 2-4 μm, and the amount of methanol or anhydrous ethanol added is 3-6 kg / L; after spray drying, air flow crushing is sieved through 40-80 meshes to obtain a first spray material; The second step is to put the first spray material into a ball mill, add pure water as a solvent at a ratio of 3-5 kg / L, and then add a second carbon source at 2-5% of the weight of the first spray material, and perform low-speed ball milling to make the slurry particle size reach 1.8-3 μm, and then spray dry to obtain a second spray material; The third step is to calcine the second spray material in a mixed atmosphere of argon and hydrogen in a ratio of 9:1, quickly heat up to 550-580°C, and keep the temperature for 10 hours to obtain a sodium iron phosphate pyrophosphate positive electrode material with a double-layer carbon structure.

2. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure according to claim 1, characterized in that: The sodium source is one or more of sodium dihydrogen phosphate, sodium carbonate, sodium bicarbonate, sodium acetate, and sodium pyrophosphate; The iron source is one or more of ferrous oxalate, ferrous phosphate, ferrous acetate, ferrous sulfate, and ferrous nitrate; The phosphorus source is one or more of ammonium phosphate, diammonium phosphate, and ammonium hydrogen phosphate.

3. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure according to claim 1, characterized in that: The first carbon source is one or more of polyethylene glycol, polypropylene alcohol, polyaniline, and polyvinyl pyrrolidone; The second carbon source is one or more of sucrose, lactose and maltose.

4. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure according to claim 1, characterized in that: The additive is one or more of oleic acid, stearic acid, paraffin and lauric acid.

5. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure according to claim 1, characterized in that: The spray drying process in the first step has a spray speed of 10,000 to 12,000 rpm and a temperature of 80 to 90° C. The spraying speed of the spray drying operation in the third step is between 11000 and 12000 rpm, and the temperature is between 110 and 120°C.

6. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure according to claim 1, characterized in that: The rotation speed of the ball milling operation in the first step is between 800-1200 rpm, and the rotation speed of the ball milling operation in the second step is between 600-800 rpm.

7. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure according to claim 1, characterized in that: The heating rate of the rapid heating operation in the third step is 12-15°C / min.

8. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure according to claim 1, characterized in that: The weight of the second carbon source added in the second step is 5% of the first spray material.

9. The method for preparing the sodium iron phosphate pyrophosphate positive electrode material having a double-layer carbon structure according to claim 3, characterized in that: The polyethylene glycol is polyethylene glycol 1000.

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