High-conductivity carbon-coated sodium electropolyanion positive electrode material and preparation method thereof

Abstract

The invention relates to the field of sodium-ion batteries, in particular to a high-conductivity carbon-coated sodium-electropolyanion positive electrode material and a preparation method thereof. The nitrogen-containing substance and the high-molecular polymer are compounded, and the high-molecular polymer is an excellent carbon skeleton and a precursor, so that a continuous, compact and uniform carbon coating layer is formed, and a main skeleton of carbon is provided; the rich nitrogen source realizes high-level nitrogen doping, and nitrogen atoms and adjacent carbon atoms form conjugated pi bonds, so that charge transfer and structural stability are facilitated, and the intrinsic conductivity of the carbon layer is remarkably improved; a high-efficiency electronic conductive network can be formed by a strategy of compounding a high-molecular carbon skeleton and a nitrogen-rich molecular dopant, the transmission kinetics of electrons and ions is optimized, high conductivity and good structural characteristics are considered, and the conductivity and stability of the polyanion material are synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more particularly to a carbon-coated sodium electropolymerized anion cathode material with high electrical conductivity and its preparation method. Background Technology

[0002] Iron-based polyanionic materials are more suitable for large-scale energy storage applications due to their advantages such as high structural / thermodynamic stability, abundant raw material resources, and high battery safety. However, polyanionic materials contain PO4 in their structure. 3- SO4 2- P2O7 4- Anionic groups strongly attract and localize the valence electrons of transition metal ions through the "inductive effect," making it difficult for electrons to escape the parent ion and move freely in the crystal lattice, resulting in poor electronic conductivity and slow ion diffusion. However, for polyanionic sodium-ion battery cathode materials, traditional carbon coating processes are often insufficient to provide high electronic conductivity due to the low sintering temperature and inadequate carbonization of the coating layer. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a carbon-coated sodium electropolymerized anion cathode material with high electrical conductivity and its preparation method.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] The first aspect of this invention is to provide a method for preparing a carbon-coated sodium electropolymerized anion cathode material with high electrical conductivity, the steps of which include:

[0006] S1. Weigh out the iron source, sulfur source, sodium source and phosphorus source, mix them and perform the first ball milling treatment to obtain a mixed slurry;

[0007] S2. The mixed slurry is mixed with the polymer and nitrogen-containing substances and then subjected to a second ball milling process, followed by spray drying to obtain precursor powder.

[0008] S3. The precursor powder is carbonized under inert gas protection to obtain the carbon-coated sodium electropolymerized anion cathode material.

[0009] Preferably, in step S1, the iron source includes at least one of ferric phosphate, ferric sulfate, and ferric pyrophosphate; the sulfur source includes at least one of ferric sulfate, sodium sulfate, and sodium ferric sulfate; the sodium source includes at least one of sodium sulfate, sodium ferric sulfate, sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium oxalate, sodium formate, sodium acetate, sodium phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate; and the phosphorus source includes at least one of ferric phosphate, ferric pyrophosphate, sodium pyrophosphate, phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0010] Preferably, the ratio of iron, sulfur, sodium and phosphorus in the mixed slurry is (2.7-3.1):1.7:(2.5-3.0):(0.1-0.5).

[0011] Preferably, in step S2, the polymer comprises at least one of polyvinyl alcohol, carboxymethyl cellulose, and polyethylene glycol; and the nitrogen-containing substance comprises at least one of urea, melamine, and dopamine.

[0012] Preferably, the mass ratio of the nitrogen-containing substance to the polymer is 0.2-0.5; the total amount of the polymer and the nitrogen-containing substance is 5-20% of the iron source.

[0013] Preferably, the time for both the first ball milling treatment and the second ball milling treatment is 3 hours.

[0014] Preferably, in step S2, the inlet air temperature of the spray dryer is 200-350°C and the outlet air temperature is 100-120°C.

[0015] Preferably, in step S3, the inert gas is nitrogen or argon.

[0016] Preferably, in step S3, the carbonization treatment includes: sintering at 300-400℃ for 2-4 hours, followed by sintering at 480-650℃ for 8-15 hours.

[0017] A second aspect of the present invention is to provide a carbon-coated sodium electropolymerized anion cathode material with high electrical conductivity prepared by the above-described preparation method.

[0018] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0019] This invention combines nitrogen-containing substances with polymers. The polymers serve as excellent carbon skeletons and precursors, ensuring the formation of a continuous, dense, and uniform carbon coating layer, providing the main carbon skeleton. Abundant nitrogen sources enable high-level nitrogen doping, with nitrogen atoms forming conjugated π bonds with adjacent carbon atoms, which is beneficial for charge transport and structural stability, significantly improving the intrinsic conductivity of the carbon layer. The strategy of combining the polymer carbon skeleton with nitrogen-rich molecular dopants can form a highly efficient electronic conductivity network, optimizing the transport dynamics of electrons and ions, while simultaneously taking into account high conductivity and good structural characteristics, synergistically improving the conductivity and stability of polyanionic materials. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0022] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0023] Example

[0024] This embodiment provides a method for preparing a carbon-coated sodium electropolymerized anion cathode material with high electrical conductivity, the steps of which include:

[0025] Na3PO4, FeSO47H2O, and Na2SO4 (Na:Fe:S:P = 2.9:1.7:2.7:0.3) were mixed and ball-milled for 3 hours. Then, they were ball-milled with polyvinyl alcohol and melamine (the total amount of polymer and nitrogen-containing substances was 5% of the iron source mass, with a nitrogen-containing substance to polymer mass ratio of 0.4) for 3 hours to obtain a uniform composite slurry. After spray drying, precursor powder was obtained. Finally, the powder was pre-sintered at 350℃ for 3.5 hours under inert gas protection, and then sintered at 650℃ for 6.5 hours to obtain carbon-coated polyanionic material Na... 2.87 Fe 1.7 (SO4) 2.73 (PO4) 0.27 / C.

[0026] Comparative Example 1

[0027] This comparative example provides a method for preparing a cathode material, the steps of which include:

[0028] Na3PO4, FeSO47H2O, and Na2SO4 (Na:Fe:S:P=2.9:1.7:2.7:0.3) were mixed and ball-milled for 3 hours, and then ball-milled with polyvinyl alcohol (the total amount of polymer was 5% of the iron source mass) for 3 hours to obtain a uniform composite slurry. After spray drying, a precursor powder was obtained. Finally, the powder was pre-sintered at 350°C for 3.5 hours under inert gas protection, and then sintered at 650°C for 6.5 hours to obtain a carbon-coated polyanionic material.

[0029] Comparative Example 2

[0030] This comparative example provides another method for preparing a cathode material, the steps of which include:

[0031] Na3PO4, FeSO47H2O, and Na2SO4 (Na:Fe:S:P = 2.9:1.7:2.7:0.3) were mixed and ball-milled for 3 hours, and then ball-milled with melamine (containing 5% of the total nitrogen content of the iron source) for 3 hours to obtain a uniform composite slurry. After spray drying, a precursor powder was obtained. Finally, the powder was pre-sintered at 350°C for 3.5 hours under inert gas protection, and then sintered at 650°C for 6.5 hours to obtain a carbon-coated polyanionic material.

[0032] Detection Examples

[0033] The materials used in Examples 1 and 2 were mixed with a main material, conductive agent Super-P, VGCF, and binder PVDF (mass ratio 8:0.5:0.5:1) to prepare positive electrode sheets, with sodium sheets as the negative electrode, and batteries were assembled. The assembly sequence was: positive electrode shell, positive electrode sheet, electrolyte (3-4 drops), separator, electrolyte (3-4 drops), sodium sheet, gasket, and negative electrode shell, resulting in three types of batteries using Examples 1, 2, and 3 as positive electrode materials. After assembly, the batteries were left to stand at room temperature for 2 hours and then tested. The test results are shown in Table 1.

[0034] Table 1

[0035]

[0036] In summary, this invention combines nitrogen-containing substances with polymers. The polymers serve as excellent carbon skeletons and precursors, ensuring the formation of a continuous, dense, and uniform carbon coating layer, providing the main carbon skeleton. Abundant nitrogen sources enable high-level nitrogen doping, with nitrogen atoms forming conjugated π bonds with adjacent carbon atoms, which is beneficial for charge transport and structural stability, significantly improving the intrinsic conductivity of the carbon layer. The strategy of combining the polymer carbon skeleton with nitrogen-rich molecular dopants can construct a highly efficient electronic conductivity network, optimizing the transport dynamics of electrons and ions, while simultaneously taking into account high conductivity and good structural characteristics, synergistically improving the conductivity and stability of polyanionic materials.

[0037] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-conductivity carbon-coated sodium polymeric anion cathode material, characterized by the steps of The application relates to a high-conductivity carbon-coated sodium electro-polyanion positive electrode material and a preparation method thereof. S1, iron source, sulfur source, sodium source and phosphorus source are weighed, mixed and subjected to first ball milling treatment to obtain mixed slurry; S2, the mixed slurry is mixed with a high-molecular polymer and nitrogen-containing substance, subjected to second ball milling treatment and spray drying to obtain a precursor powder; S3, the precursor powder is subjected to carbonization treatment under the protection of inert gas to obtain the carbon-coated sodium electro-polyanion positive electrode material.

2. The production method according to claim 1, characterized by, In step S1, the iron source includes at least one of iron phosphate, iron sulfate and iron pyrophosphate; the sulfur source includes at least one of iron sulfate, sodium sulfate and sodium iron sulfate; the sodium source includes at least one of sodium sulfate, sodium iron sulfate, sodium pyrophosphate, sodium carbonate, sodium bicarbonate, sodium oxalate, sodium formate, sodium acetate, sodium phosphate, sodium monohydrogen phosphate and sodium dihydrogen phosphate; and the phosphorus source includes at least one of iron phosphate, iron pyrophosphate, sodium pyrophosphate, phosphoric acid, ammonium dihydrogen phosphate and di-ammonium hydrogen phosphate.

3. The production method according to claim 1, characterized by, In the mixed slurry, the ratio of iron, sulfur, sodium and phosphorus is (2.7-3.1):1.7:(2.5-3.0):(0.1-0.5).

4. The method of claim 1, wherein, In step S2, the high-molecular polymer includes at least one of polyvinyl alcohol, carboxymethyl cellulose and polyethylene glycol; and the nitrogen-containing substance includes at least one of urea, melamine and dopamine.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the nitrogen-containing substance to the high-molecular polymer is 0.2-0.5; and the total amount of the high-molecular polymer and the nitrogen-containing substance is 5-20% of the iron source.

6. The method of claim 1, wherein, The time of the first ball milling treatment and the second ball milling treatment is 3h.

7. The preparation method according to claim 1, characterized in that, In step S2, the inlet air temperature of the spray drying is 200-350 DEG C, and the outlet air temperature is 100-120 DEG C.

8. The method of claim 1, wherein, In step S3, the inert gas is nitrogen or argon.

9. The method of claim 1, wherein, In step S3, the carbonization treatment includes sintering at 300-400 DEG C for 2-4h, and then sintering at 480-650 DEG C for 8-15h.

10. A high-conductivity carbon-coated sodium electro-polyanion positive electrode material prepared by the preparation method in any one of claims 1-9.

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