Carbon-coated potassium-zirconium co-doped sodium ferric sulfate positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to a carbon-coated potassium-zirconium co-doped sodium ferric sulfate positive electrode material. The positive electrode material comprises a potassium-zirconium co-doped sodium ferric sulfate matrix and a carbon coating layer coating the surface of the matrix, the general formula of the potassium-zirconium co-doped sodium ferric sulfate is NaxKyZrzFem( SO4) n, 2 < = x < = 3, 0 < y < = 0.1, 0 < z < = 0.1, 1.5 < m < = 2, and 2 < = n < = 4; according to the invention, by co-doping the sodium ferric sulfate material with potassium and zirconium and simultaneously carrying out carbon coating, the reaction efficiency and the structural stability of the sodium ferric sulfate material can be effectively improved, so that the rate capability and the cycling stability of the sodium ferric sulfate material are improved, and the sodium ferric sulfate material shows excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode materials, and more specifically, to a carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, with the growing global demand for renewable energy, the development of battery energy storage technology has become one of the keys to achieving efficient energy utilization. Sodium iron sulfate (Na2Fe2(SO4)3), as a sodium-ion battery cathode material with high theoretical energy density, has attracted widespread attention due to its abundant raw material reserves, environmental friendliness, and low price. However, sodium iron sulfate materials face some challenges in practical applications, such as poor conductivity and poor structural stability during the cycle process, which to some extent limits their electrochemical performance. Summary of the invention

[0003] Based on the above technical problems existing in the prior art, the present invention provides a carbon-coated potassium-zirconium co-doped sodium ferric sulfate positive electrode material. By doping potassium-zirconium into sodium ferric sulfate and simultaneously performing carbon coating, the electrochemical performance of the sodium ferric sulfate material can be effectively improved.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows:

[0005] A carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material, comprising a potassium-zirconium co-doped sodium iron sulfate matrix and a carbon coating layer coated on the surface of the matrix; the potassium-zirconium co-doped sodium iron sulfate has a general formula of: Na x K y Zr z Fe m (SO4) n , where 2≤x≤3, 0<y≤0.1, 0<z≤0.1, 1.5<m≤2, 2≤n≤4.

[0006] In some embodiments, 2.5≤x≤3, 0.01≤y≤0.05, and 0.01≤z≤0.05.

[0007] The present invention also provides a method for preparing the above-mentioned carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material, which comprises the following steps:

[0008] S1. Add a sodium source, an iron source, a zirconium source, a potassium source, an antioxidant, and a complexing agent into water according to a stoichiometric ratio and mix them evenly to obtain a mixed solution;

[0009] S2, adding carbon nanotubes to the mixed solution, mixing evenly, and drying to obtain a precursor;

[0010] S3, placing the precursor in a container, first heating it to 150-250° C. for pre-sintering, and then heating it to 300-450° C. for sintering to obtain a carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material.

[0011] In some embodiments, in step S2, the drying method is spray drying, and during the drying process, the inlet air temperature is 180-210°C, and the outlet air temperature is 100-135°C.

[0012] In some embodiments, in step S2, the amount of carbon nanotubes added is 2-8% of the total mass of the solute in the mixed solution.

[0013] In some embodiments, the sodium source is at least one of Na2SO4, CH3COONa, and Na2CO3.

[0014] In some embodiments, the iron source is at least one of FeSO4, FeCl2, Fe(NO3)2, and ferrous glycinate.

[0015] In some embodiments, the potassium source is at least one of K2SO4, K2CO3, CH3COOK, and KNO3.

[0016] In some embodiments, the zirconium source is at least one of ZrO(NO3)2, Zr(NO3)4, and Zr(SO4)2.

[0017] In some embodiments, the chelating agent is at least one of citric acid, disodium edetate, tartaric acid, oxalic acid, gluconic acid, and cysteine.

[0018] In some embodiments, the antioxidant is ascorbic acid.

[0019] In some embodiments, in step S1, the mass fraction of the mixed solution is 30-60%.

[0020] In some embodiments, in step S2, after adding the carbon nanotubes, ultrasonic dispersion is performed for 60-120 minutes.

[0021] The present invention also provides a positive electrode, which includes the positive electrode material mentioned above or the positive electrode material obtained by the preparation method of any one of the above embodiments.

[0022] The present invention also provides an electrochemical energy storage device, which includes the above-mentioned positive electrode. Specifically, the electrochemical energy storage device includes a sodium ion battery, a sodium ion capacitor, etc.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention can not only adjust the crystal structure of the material, but also enhance the embedding and de-embedding kinetics of sodium ions by co-doping potassium and zirconium elements into the sodium ferric sulfate material, which is helpful to improve the rate performance and cycle performance of the sodium ferric sulfate material; in addition, a carbon layer is coated on the surface of the potassium-zirconium co-doped sodium ferric sulfate material, which can significantly improve the conductivity of the positive electrode material, and effectively slow down the volume change of the material during the charge and discharge process, improve the structural stability of the positive electrode material, and thus improve the cycle stability of the positive electrode material.

[0025] The present invention optimizes the microstructure and surface characteristics of the positive electrode material through a specific preparation process, thereby significantly improving the electrochemical performance of the positive electrode material, enabling it to perform well in high-rate charge and discharge and long-cycle stability, and has good commercial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a SEM image of the positive electrode material prepared in Example 1;

[0027] Figure 2 This is a SEM image of the positive electrode material prepared in Comparative Example 1;

[0028] Figure 3 XRD diagrams of the positive electrode materials prepared in Example 1 and Comparative Example 1;

[0029] Figure 4 The charge and discharge specific capacity of the positive electrode materials prepared in Example 1 and Comparative Example 1;

[0030] Figure 5 This is a cycle stability diagram of the positive electrode material prepared in Example 1 at a current density of 20C;

[0031] Figure 6 This is a cycle stability diagram of the positive electrode material prepared in Comparative Example 1 at a current density of 20C. DETAILED DESCRIPTION

[0032] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0034] Example 1

[0035] A method for preparing a carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material comprises the following steps:

[0036] S1. Add 13mmol Na2SO4, 0.25mmol K2SO4, 17mmol FeSO4·7H2O, 0.4mmol Zr(SO4)2, 0.25g ascorbic acid and 0.2g citric acid into deionized water, stir magnetically until the raw materials are completely dissolved, and obtain a mixed solution with a mass fraction of 40%;

[0037] S2, adding 0.05 g of carbon nanotubes into water, stirring evenly to obtain a carbon nanotube dispersion; adding the carbon nanotube dispersion into the mixed solution obtained in step S1, stirring and mixing, and ultrasonicating for 90 minutes to obtain a precursor solution;

[0038] S3, spray drying the precursor solution to obtain precursor particles; wherein, during the drying process, the air inlet temperature is controlled to be 200° C., the air outlet temperature is controlled to be 120° C., and the spray feed flow rate is 1000 mL / h;

[0039] S4, sintering the obtained precursor particles in a tube furnace, heating to 200°C at a rate of 5°C / min and keeping the temperature for 4h; then heating to 400°C at a rate of 5°C / min and keeping the temperature for 20h to obtain carbon-coated potassium-zirconium co-doped sodium iron sulfate Na 2.6 K 0.05 Fe 1.7 Zr 0.04 (SO4) 3.105 Positive electrode material.

[0040] Comparative Example 1

[0041] A method for preparing a sodium iron sulfate positive electrode material comprises the following steps:

[0042] S1. Add 13 mmol Na2SO4, 17 mmol FeSO4·7H2O, 0.25 g ascorbic acid and 0.2 g citric acid into deionized water, stir magnetically until the raw materials are completely dissolved, and obtain a mixed solution with a solid content of 40%;

[0043] S2, adding 0.05 g of carbon nanotubes into water, stirring evenly to obtain a carbon nanotube dispersion; adding the carbon nanotube dispersion into the mixed solution obtained in step S1, stirring and mixing, and ultrasonicating for 90 minutes to obtain a precursor solution;

[0044] S3, spray drying the precursor solution to obtain precursor particles; wherein, during the drying process, the air inlet temperature is controlled to be 200° C., the air outlet temperature is controlled to be 120° C., and the spray feed flow rate is 1000 mL / h;

[0045] S4. The obtained precursor particles are placed in a tube furnace for sintering, and the temperature is raised to 200°C at a rate of 5°C / min and kept at this temperature for 4 hours; the temperature is then raised to 400°C at a rate of 5°C / min and kept at this temperature for 20 hours to obtain carbon-coated sodium iron sulfate Na 2.6 Fe 1.7 (SO4)3 positive electrode material.

[0046] The positive electrode materials obtained in Example 1 and Comparative Example 1 were characterized by SEM and XRD. The test results are as follows Figure 1-Figure 3 shown.

[0047] like Figure 1 and Figure 2 As shown, the carbon-coated potassium-zirconium co-doped positive electrode material obtained by the method of the present invention has a more porous structure on the surface and a large specific surface area, which is conducive to contact with the electrolyte and promotes the reaction during the charge and discharge process.

[0048] like Figure 3 As shown, after doping with potassium and zirconium elements, the matrix maintains its phase structure unchanged and does not produce any impurity phase.

[0049] The electrochemical performance of the positive electrode materials prepared in Example 1 and Comparative Example 1 was tested as follows:

[0050] The positive electrode material, conductive agent carbon black: binder PVDF were mixed in a mass ratio of 8:1:1, and after sufficient grinding, an appropriate amount of NMP was added to obtain a uniform slurry. The slurry was coated on an aluminum foil current collector, placed in a vacuum drying oven, dried at 120°C, then taken out and cut into discs; a metallic sodium sheet was used as a counter electrode; 1M NaClO4 / EC:DMC:EMC (1:1:1) was used as an electrolyte, and the electrochemical performance of the button battery was tested after assembly.

[0051] Test results such as Figure 4-Figure 6 shown.

[0052] like Figure 4 The positive electrode material prepared in this embodiment has a discharge specific capacity of 93.28 mAh / g and a coulombic efficiency of 94.56% at a voltage of 2.0-4.5 V and a current density of 0.1 C; while the discharge specific capacity of comparative document 1 at a voltage of 2.0-4.5 V and a current density of 0.1 C is 75.50 mAh / g, and the coulombic efficiency is 85.54%.

[0053] like Figure 5 and Figure 6The positive electrode material prepared in Example 1 has a capacity retention rate of more than 60% after 1000 cycles at a voltage of 2.0-4.5V and a current density of 20C; while the positive electrode material obtained in Comparative Example 1 has a capacity retention rate of only about 13.9% after 1000 cycles at a voltage of 2.0-4.5V and a current density of 20C, and the capacity decay is serious.

[0054] In summary, by co-doping sodium iron sulfate material with potassium and zirconium and simultaneously carbon-coating it, the reaction efficiency and structural stability of the sodium iron sulfate material can be effectively improved, thereby improving its rate performance and cycle stability at high current density, making it exhibit excellent electrochemical properties.

[0055] 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.

[0056] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. 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, and these 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 carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material, characterized in that: It comprises a potassium-zirconium co-doped sodium iron sulfate matrix and a carbon coating layer coated on the surface of the matrix; the potassium-zirconium co-doped sodium iron sulfate has a general formula of: Na x K y Zr z Fe m (SO4) n , Among them, 2≤x≤3, 0<y≤0.1, 0<z≤0.1, 1.5<m≤2, 2≤n≤4.

2. The carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material according to claim 1, characterized in that: 2.5≤x≤3, 0.01≤y≤0.05, 0.01≤z≤0.

05.

3. The method for preparing the carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material according to claim 1 or 2, characterized in that: The following steps are involved: S1. Add a sodium source, an iron source, a zirconium source, a potassium source, an antioxidant, and a complexing agent into water according to a stoichiometric ratio and mix them evenly to obtain a mixed solution; S2, adding carbon nanotubes to the mixed solution, mixing evenly, and drying to obtain a precursor; S3, placing the precursor in a container, first heating it to 150-250° C. for pre-sintering, and then heating it to 300-450° C. for sintering to obtain a carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material.

4. The method for preparing the carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material according to claim 3, characterized in that: In step S2, the drying method is spray drying. During the drying process, the inlet air temperature is 180-210°C and the outlet air temperature is 100-135°C.

5. The method for preparing the carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material according to claim 3, characterized in that: In step S2, the amount of carbon nanotubes added is 2-8% of the total mass of the solute in the mixed solution.

6. The method for preparing the carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material according to claim 3, characterized in that: The sodium source is at least one of Na2SO4, CH3COONa, and Na2CO3; and / or the iron source is at least one of FeSO4, FeCl2, Fe(NO3)2, and ferrous glycinate; and / or the potassium source is at least one of K2SO4, K2CO3, CH3COOK, and KNO3; and / or the zirconium source is at least one of ZrO(NO3)2, Zr(NO3)4, and Zr(SO4)2; and / or the chelating agent is at least one of citric acid, disodium ethylenediaminetetraacetic acid, tartaric acid, oxalic acid, gluconic acid, and cysteine; and / or the antioxidant is ascorbic acid.

7. The method for preparing the carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material according to claim 3, characterized in that: In step S1, the mass fraction of the mixed solution is 30-60%.

8. The method for preparing the carbon-coated potassium-zirconium co-doped sodium iron sulfate positive electrode material according to claim 3, characterized in that: In step S2, after adding carbon nanotubes, ultrasonic dispersion is performed for 60-120 minutes.

9. A positive electrode, characterized in that: The invention comprises the positive electrode material according to claim 1 or 2 or the positive electrode material obtained by the preparation method according to any one of claims 3 to 8.

10. An electrochemical energy storage device, characterized in that: Comprising the positive electrode as claimed in claim 9.

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