Composite sodium ferric sulfate positive electrode material and preparation method therefor, positive electrode, and sodium ion battery

Abstract

A composite sodium ferric sulfate positive electrode material and a preparation method therefor, a positive electrode, and a sodium ion battery. The composite sodium ferric sulfate positive electrode material comprises a sodium ferric sulfate matrix, a three-dimensional conductive network embedded in the sodium ferric sulfate matrix, and a conductive cladding layer coated outside the sodium ferric sulfate matrix; and the three-dimensional conductive network and the conductive cladding layer are both formed by PEDOT. The preparation method comprises: mixing PSS, EDOT, sodium sulfate, ferrous sulfate, and an oxidant serving as an initiator in an aqueous solution, and fully reacting to obtain a precursor solution; and drying the precursor solution, and then carrying out heat treatment to obtain the composite sodium ferric sulfate positive electrode material. The positive electrode is prepared from the positive electrode material. The sodium ion battery comprises the positive electrode. The positive electrode material has good conductivity, large capacity, and good rate performance and interface stability.

Description

Composite sodium ferric sulfate positive electrode material and preparation method thereof, positive electrode and sodium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 202310755581.9 filed with the State Intellectual Property Office of China on June 25, 2023, entitled “Composite sodium iron sulfate positive electrode material and preparation method thereof, positive electrode and sodium ion battery,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0003] The present disclosure relates to the technical field of sodium electric materials, and in particular to a composite sodium ferric sulfate positive electrode material and a preparation method thereof, a positive electrode, and a sodium ion battery. Background Art

[0004] Currently, cathode materials for sodium-ion batteries are primarily classified into three categories: layered oxides, polyanions, and Prussian white derivatives. Polyanion materials, in particular, have attracted considerable attention due to their excellent structural stability and long cycling potential, as they form a three-dimensional network structure composed of polyanion polyhedra and transition metal ion polyhedra connected by strong covalent bonds.

[0005] Iron-based polyanion cathode materials have developed rapidly due to their rich iron 3 content and environmental friendliness. Among them, the working potential of iron-based pyrophosphate cathode materials is relatively low (~3.0V vs. Na + / Na), the energy density is low. However, the working potential of iron-based sulfate materials is higher (~3.7V vs.Na + / Na), which can bring higher energy density and therefore attracts attention.

[0006] However, this type of material has a high working voltage and the upper limit of the charging voltage exceeds 4.2V vs.Na + / Na, which can easily cause oxidative decomposition of the electrolyte at the positive electrode. Furthermore, these iron-based sulfates typically have poor conductivity, resulting in low sodium storage capacity and poor rate performance. Furthermore, these materials are prone to water absorption and oxidation when exposed to air, leading to material failure. A common solution is to improve the conductivity and hydrophobicity of iron-based sulfates by combining them with carbon-based materials.

[0007] However, due to the high working potential of iron-based sulfate, the upper limit of the charging voltage is usually higher than 4.2V vs. Na + / Na, the electrolyte is easily oxidized and decomposed on the surface of iron-based sulfate at this voltage. Doping or coating iron-based sodium sulfate with carbon-based materials alone cannot effectively inhibit the oxidative decomposition of the electrolyte at high voltage. In addition, because iron-based sulfate decomposes at temperatures above 500°C, conventional high-temperature carbon coating methods cannot be used. Therefore, carbon nanotubes are usually used for compounding, which requires a large amount of carbon nanotubes and is relatively expensive.

[0008] Therefore, it is of great significance for sodium iron sulfate materials to develop materials that simultaneously improve the oxidation stability under high voltage and the conductivity of the material itself.

[0009] Among them, conductive polymer materials have good electrical conductivity in themselves, and as polymer materials, they also have good chemical stability. Therefore, they are often used as coating materials for battery materials to improve the conductivity and interface stability of the materials. However, when using conductive polymers for coating, it is usually necessary to prepare the battery material first, then dissolve the polymer monomer in an organic solvent, mix it with the battery material, and then polymerize it. Conductive polymers can often only be coated on the surface of the material and cannot form a cross-linked three-dimensional conductive network in the bulk phase. In addition, the synthesis steps are complicated and require the use of organic solvents, which are harmful to the environment and health. Therefore, it is necessary to develop a suitable method to further improve the conductivity while simplifying the process steps and reducing environmental and health hazards.

[0010] In view of this, the present disclosure is proposed.

[0011] Summary of the Invention

[0012] The present invention aims to provide a composite sodium ferric sulfate cathode material, a preparation method thereof, a cathode and a sodium ion battery.

[0013] The present disclosure is achieved as follows:

[0014] In a first aspect, the present disclosure provides a composite sodium ferric sulfate positive electrode material, wherein the particles of the positive electrode material include a sodium ferric sulfate matrix, a three-dimensional conductive network embedded in the sodium ferric sulfate matrix, and a conductive coating layer coated outside the sodium ferric sulfate matrix; the three-dimensional conductive network and the conductive coating layer are both formed by PEDOT.

[0015] In an optional embodiment, the mass ratio of the sodium ferric sulfate matrix to the PEDOT is 100:1-10.

[0016] In a second aspect, the present disclosure provides a method for preparing a composite sodium ferric sulfate positive electrode material, comprising:

[0017] PSS, EDOT, sodium sulfate, ferrous sulfate and an oxidant as an initiator are mixed and reacted in an aqueous solution to obtain a precursor solution;

[0018] The precursor solution is dried to obtain a PEDOT-PSS composite sodium iron sulfate precursor;

[0019] The sodium ferric sulfate precursor is heat-treated at 300-450° C. for 6-24 hours under an inert atmosphere to obtain a composite sodium ferric sulfate positive electrode material.

[0020] In an optional embodiment, the method of mixing PSS, EDOT, sodium sulfate, ferrous sulfate and an oxidant as an initiator to react comprises:

[0021] First, add PSS, deionized water and EDOT into the reaction vessel and stir thoroughly to disperse them evenly;

[0022] Then, sodium sulfate, ferrous sulfate and an oxidant are added to the reaction solution, and the reaction is carried out under continuous stirring.

[0023] In an optional embodiment, the oxidant includes at least one of ferric sulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, and oxygen;

[0024] Preferably, the oxidizing agents are ferric sulfate and sodium persulfate.

[0025] In an optional embodiment, the molar ratio of sodium sulfate to ferrous sulfate is 1:1.5 to 2.5;

[0026] Optionally, the mass ratio of PSS to EDOT is 10:1-5.

[0027] In an optional embodiment, the feeding amount is calculated by weight as follows: 31 to 314 parts of the total amount of PSS and EDOT, 1000 parts of sodium sulfate, and 1605 to 2675 parts of ferrous sulfate;

[0028] Optionally, the oxidant is 1 to 200 parts;

[0029] Optionally, the deionized water is 2,500 to 100,000 parts.

[0030] In an alternative embodiment, the drying method is spray drying.

[0031] In a third aspect, the present disclosure provides a positive electrode, which is made using the positive electrode material of the aforementioned embodiment, or the positive electrode material prepared by the preparation method of any one of the aforementioned embodiments.

[0032] In a fourth aspect, the present disclosure provides a sodium ion battery comprising a positive electrode as described in the aforementioned embodiment.

[0033] The present disclosure has the following beneficial effects:

[0034] The composite sodium ferric sulfate positive electrode material provided by the present disclosure has a conductive network formed by PEDOT embedded in the sodium ferric sulfate matrix and coated on the surface of the sodium ferric sulfate matrix, which can improve the conductivity, capacity and rate of the sodium ferric sulfate positive electrode material; and because PEDOT has good chemical stability, it forms a coating layer on the surface of the sodium ferric sulfate, which can improve the interface stability of the sodium ferric sulfate positive electrode material.

[0035] The preparation method provided in the embodiments of the present disclosure introduces PSS (sodium polystyrene sulfonate) during the preparation process, and through the ionic bond interaction between PEDOT and PEDOT, the solubility of PEDOT in water is improved, so that PEDOT can form a uniformly dispersed aqueous solution with sodium sulfate and ferrous sulfate, thereby forming a PEDOT-based three-dimensional conductive network structure inside the particles of the composite sodium ferric sulfate positive electrode material finally obtained after heat treatment, rather than simply coating PEDOT on the surface of the sodium ferric sulfate particles; and during the heat treatment process, the sulfonic acid groups of PSS will decompose, causing the ionic bonds between PEDOT and PSS to disappear, which will further improve the conductivity of the final polymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0037] FIG1 is a sodium iron sulfate material doped and coated with a PEDOT-based conductive polymer;

[0038] Figure 2 shows ordinary sodium iron sulfate material without doping coating. DETAILED DESCRIPTION

[0039] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0040] The composite sodium ferric sulfate positive electrode material and its preparation method, as well as the positive electrode and sodium ion battery provided in the embodiments of the present disclosure are described in detail below.

[0041] The composite sodium ferric sulfate positive electrode material provided in the embodiment of the present disclosure has particles comprising a sodium ferric sulfate matrix, a three-dimensional conductive network embedded in the sodium ferric sulfate matrix, and a conductive coating layer coated outside the sodium ferric sulfate matrix; the three-dimensional conductive network and the conductive coating layer are both formed of PEDOT.

[0042] PEDOT is a polymer of EDOT (3,4-ethylenedioxythiophene monomer), which has excellent conductive properties. The conductive network formed by PEDOT is embedded in the sodium ferric sulfate matrix and coated on the surface of the sodium ferric sulfate matrix, which can improve the conductivity, capacity and rate of the sodium ferric sulfate positive electrode material; and because PEDOT has excellent chemical stability, it forms a coating layer on the surface of the sodium ferric sulfate, which can improve the interface stability of the sodium ferric sulfate positive electrode material.

[0043] Preferably, in order to ensure that the composite sodium ferric sulfate cathode material has better electrochemical performance, the mass ratio of the sodium ferric sulfate matrix to the PEDOT is 100:1 to 10 (for example, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9 or 100:10); a further preferred range may be, for example, 100:1 to 8, 100:1 to 7, 100:1 to 8. 0:1~6, 100:1~5, 100:1~4, 100:1~3, 100:1~2, 100:2~10, 100:3~10, 100:4~10, 100:5~10, 100:6~10, 100:7~10, 100:8~10, 100:3~7, 100:3~6, 100:3~5, 100:3~4, 100:4~6 or 100:4~5.

[0044] The present disclosure provides a method for preparing a composite sodium ferric sulfate positive electrode material, comprising:

[0045] PSS, EDOT, sodium sulfate, ferrous sulfate and an oxidant as an initiator are mixed and reacted in an aqueous solution to obtain a precursor solution;

[0046] The precursor solution is dried to obtain a PEDOT-PSS composite sodium iron sulfate precursor;

[0047] The sodium ferric sulfate precursor is heat-treated at 300-450° C. for 6-24 hours under an inert atmosphere to obtain a composite sodium ferric sulfate positive electrode material.

[0048] EDOT is a 3,4-ethylenedioxythiophene monomer. In the presence of an oxidant, it polymerizes into PEDOT. Since PEDOT is insoluble in water, if PEDOT is directly mixed with sodium sulfate and ferrous sulfate, it cannot be fully dispersed evenly. After the final heat treatment, PEDOT can only be coated on the surface of sodium ferric sulfate, and the three-dimensional conductive network cannot be embedded in the interior of the sodium ferric sulfate particles. In this scheme, PSS (sodium polystyrene sulfonate) is introduced. PSS is grafted onto PEDOT to give it water solubility, so that PEDOT can be fully and evenly dispersed with sodium sulfate and ferrous sulfate in an aqueous solution, so that the particles of the composite sodium ferric sulfate positive electrode material obtained after the final heat treatment have a three-dimensional conductive network structure in which PEDOT is embedded in the interior of the sodium ferric sulfate particles, rather than just coating PEDOT on the surface of the sodium ferric sulfate particles. During the heat treatment process, the ionic bonds between PEDOT and PSS are broken, and the partial or complete decomposition of PSS can further improve the conductivity of the polymer.

[0049] Therefore, the preparation method provided by the present disclosure can produce a composite sodium ferric sulfate positive electrode material provided by the embodiment of the present disclosure, in which the particles have a three-dimensional PEDOT conductive network embedded inside and a PEDOT coating layer coated on the surface. This material has better electrochemical properties.

[0050] The preparation method is specifically as follows:

[0051] S1. Mixed reaction

[0052] First, PSS, deionized water, and EDOT were added to the reaction vessel and stirred thoroughly to disperse them evenly.

[0053] Then, sodium sulfate, ferrous sulfate and an oxidant are added to the reaction solution, and the reaction is carried out under continuous stirring until the solution turns dark blue or black, indicating that the reaction is complete.

[0054] Optionally, the oxidant includes at least one of ferric sulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide and oxygen;

[0055] Preferably, the oxidants are ferric sulfate and sodium persulfate. The homogeneity of ferric sulfate and sodium persulfate with ferrous sulfate, the precursor of sodium ferric sulfate, allows for a one-pot direct synthesis of the conductive polymer-composite sodium ferric sulfate material, eliminating purification steps, significantly reducing synthesis complexity, and improving atom economy and yield. More preferably, to ensure faster and more uniform dispersion of the ferric sulfate, the ferric sulfate is added to the reaction vessel as an aqueous solution.

[0056] Optionally, the molar ratio of sodium sulfate to ferrous sulfate is 1:1.5 to 2.5 (e.g., 1:1.5, 1:2 or 1:2.5);

[0057] Optionally, the mass ratio of PSS to EDOT is 10:1 to 5 (eg, 10:1, 10:2 or 10:5).

[0058] More specifically, to ensure that the prepared sodium ferric sulfate cathode material has better performance, the feed amounts are as follows: 31-314 parts by weight of the total amount of PSS and EDOT, 1000 parts by weight of sodium sulfate, and 1605-2675 parts by weight of ferrous sulfate;

[0059] Optionally, the oxidant is 1 to 200 parts;

[0060] Optionally, the amount of deionized water is 2,500 to 100,000 parts.

[0061] For example, the total amount of PSS and EDOT is 31 parts, sodium sulfate is 1000 parts, ferrous sulfate is 1605 parts, oxidant is 1 part, and deionized water is 2500 parts;

[0062] Alternatively, the total amount of PSS and EDOT is 314 parts, sodium sulfate is 1000 parts, ferrous sulfate is 2675 parts, oxidant is 314 parts, and deionized water is 100,000 parts;

[0063] Alternatively, the total amount of PSS and EDOT is 80 parts, sodium sulfate is 1000 parts, ferrous sulfate is 1800 parts, oxidant is 50 parts, and deionized water is 10000 parts;

[0064] Alternatively, the total amount of PSS and EDOT is 150 parts, sodium sulfate is 1000 parts, ferrous sulfate is 2000 parts, oxidant is 100 parts, and deionized water is 20000 parts;

[0065] Alternatively, the total amount of PSS and EDOT is 200 parts, sodium sulfate is 1000 parts, ferrous sulfate is 2200 parts, oxidant is 200 parts, and deionized water is 40000 parts;

[0066] Alternatively, the total amount of PSS and EDOT is 280 parts, sodium sulfate is 1000 parts, ferrous sulfate is 2400 parts, the oxidant is 270 parts, and deionized water is 80,000 parts.

[0067] S2. Drying the precursor solution

[0068] After drying, a PEDOT-PSS composite sodium iron sulfate precursor is obtained.

[0069] Preferably, the drying method is spray drying. The reason for choosing spray drying is to obtain a sodium iron sulfate precursor with uniform particle size distribution and good morphology after spray drying.

[0070] S3. Heat treatment

[0071] The spray-dried sodium iron sulfate precursor is placed in an inert gas atmosphere and heat treated at a temperature of 300-450° C. (e.g., 300° C., 350° C., 400° C., or 450° C.) for 6-24 h (e.g., 6 h, 10 h, 15 h, 18 h, 20 h, or 24 h).

[0072] The heat treatment converts the sodium ferric sulfate precursor into sodium ferric sulfate, breaks the ionic bond between PEDOT-PSS, and partially or completely decomposes PSS.

[0073] Optionally, the heat treatment process is performed under a nitrogen or argon atmosphere.

[0074] The positive electrode provided in the embodiments of the present disclosure is made using the positive electrode material provided in the embodiments of the present disclosure, or the positive electrode material prepared by the preparation method provided in the embodiments of the present disclosure.

[0075] The sodium ion battery provided by the embodiment of the present disclosure includes the positive electrode provided by the embodiment of the present disclosure.

[0076] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0077] Examples 1-5

[0078] The embodiment provides a method for preparing a composite sodium iron sulfate positive electrode material, and the preparation process is as follows:

[0079] Add PSS, deionized water, and EDOT into the container and stir to disperse evenly;

[0080] Add an aqueous solution of sodium sulfate, ferrous sulfate, and a small amount of ferric sulfate into a reaction vessel, and stir the mixture until the solution turns dark blue to obtain a precursor solution;

[0081] The precursor solution is spray-dried to obtain a composite sodium iron sulfate precursor;

[0082] The precursor is heat-treated in a nitrogen atmosphere to prepare a PEDOT polymer-based composite sodium iron sulfate positive electrode material.

[0083] The specific parameter settings are shown in Table 1 below:

[0084] Table 1 Specific parameter settings of each embodiment

[0085] Comparative Example 1

[0086] In this comparative example, compared with Example 1, PSS was not added. After EDOT, sodium persulfate and ferric sulfate were added, the solution reacted rapidly and produced a large amount of precipitation, and a uniformly dispersed solution could not be formed for the next spray granulation experiment.

[0087] Comparative Example 2

[0088] In this comparative example, compared with Example 1, no PSS, EDOT and oxidant were added.

[0089] Experimental Example 1

[0090] SEM images of the composite sodium ferric sulfate cathode material particles prepared in Example 1 and Comparative Example 2 are shown in Figures 1 and 2, respectively. As can be seen from Figures 1 and 2, the composite sodium ferric sulfate cathode material particles in Example 1 all have a structure with a three-dimensional conductive network embedded in the sodium ferric sulfate matrix and a coating layer on the surface; whereas the composite sodium ferric sulfate cathode material particles in Comparative Example 2 have neither a surface coating nor an embedded conductive network structure, and are therefore ordinary sodium ferric sulfate cathode materials.

[0091] Experimental Example 2

[0092] Conductivity test: Weigh 3g of compacted powder and place it into the mold cavity. Vibrate the mold to make the sample flat and uniform. Pressurize the mold to 30 MPa and use a four-probe method to test the conductivity of the pressurized powder.

[0093] Sodium ion full battery performance test:

[0094] The AZO-doped sodium ferric sulfate prepared in the above example was used as the positive electrode material for a sodium-ion battery and assembled into a CR2032 button cell with a sodium metal sheet. The sodium ferric sulfate, SP, and PVDF were homogenized in an NMP solution at a mass ratio of 9:0.5:0.5, coated onto aluminum foil, and dried to form the positive electrode sheet. A fresh sodium metal sheet served as the negative electrode, and the electrolyte, 1.0 mol / L NaPF6 dissolved in a PC:EMC:FEC ratio of 4:6:0.5, was used. The button cells were assembled in an argon-filled glove box and tested for capacity, rate capability, and cycling performance.

[0095] Battery capacity test: Charge the installed battery at 0.1C to 4.3V, then discharge it at 0.1C to 2.0V.

[0096] Battery rate performance test: Charge the assembled battery at 0.1C to 4.3V, and then discharge it at 2C to 2.0V.

[0097] Cycle life test: Charge the assembled battery to 4.3V at 1C, then discharge it to 2.0V at 1C for 100 cycles, and record the capacity retention rate.

[0098] Table 2 Test results of various embodiments and comparative examples

[0099] As can be seen from Table 2, the cathode materials prepared in each embodiment of the present disclosure have good electrochemical properties after being made into batteries, among which Examples 1-3 have better performance because the feeding range is within the preferred scheme of the present disclosure. The PSS and EDOT feeding amounts of Example 4 are relatively small, and the conductivity, capacity and other properties of the cathode material prepared are worse than those of Examples 1-3, but the performance of the cathode material prepared without adding PSS and EDOT is still significantly better than that of the comparative example; the PSS and EDOT feeding amounts of Example 5 are relatively large, and the conductivity, capacity and other properties of the cathode material prepared are worse than those of Examples 1-3, but the performance of the cathode material prepared without adding PSS and EDOT is still significantly better than that of the comparative example.

[0100] Comparing Comparative Example 1 with Example 1, since PSS was not added during the preparation process, the polymer formed during the oxidative polymerization of EDOT precipitated directly and could not be dissolved in the aqueous solution of ferrous sulfate and sodium sulfate, preventing the formation of a uniformly dispersed solution. Consequently, a uniformly mixed mixture of the sodium ferrous sulfate precursor and PEDOT could not be formed through spray granulation. Comparing Comparative Example 2 with Example 1, which did not add any conductive polymer, resulted in a material with poor conductivity and battery performance.

[0101] In summary, in the composite sodium ferric sulfate positive electrode material provided by the embodiments of the present disclosure, the conductive network formed by PEDOT is embedded in the sodium ferric sulfate matrix and coated on the surface of the sodium ferric sulfate matrix, which can improve the conductivity, capacity and rate of the sodium ferric sulfate positive electrode material; and because PEDOT has good chemical stability, a coating layer is formed on the surface of the sodium ferric sulfate, which can improve the interface stability of the sodium ferric sulfate positive electrode material.

[0102] In the preparation method provided in the embodiments of the present disclosure, PSS (sodium polystyrene sulfonate) is introduced during the preparation process, and ionic bonds are formed between PSS and PEDOT molecules, thereby improving the solubility of PEDOT in aqueous solution, so that PEDOT can be fully and evenly dispersed with sodium sulfate and ferrous sulfate in the aqueous solution, thereby achieving a three-dimensional conductive network structure in which PEDOT is embedded in the sodium ferric sulfate particles in the particles of the composite sodium ferric sulfate positive electrode material obtained after the final heat treatment; and the sulfonate groups in the PSS are completely decomposed during the heat treatment process, resulting in the disappearance of the ionic bonds between PEDOT and PSS, which can also further improve the conductivity of the polymer.

[0103] The above are merely preferred embodiments of the present disclosure and are not intended to limit the present disclosure. Those skilled in the art will readily appreciate that various modifications and variations of the present disclosure are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present disclosure shall be included within the scope of protection of the present disclosure. Industrial Applicability

[0104] The present disclosure provides a composite sodium ferric sulfate positive electrode material, a preparation method thereof, a positive electrode, and a sodium ion battery. For the composite sodium ferric sulfate positive electrode material, the particles of the positive electrode material include a sodium ferric sulfate matrix, a three-dimensional conductive network embedded in the sodium ferric sulfate matrix, and a conductive coating layer coated outside the sodium ferric sulfate matrix; the three-dimensional conductive network and the conductive coating layer are both formed by PEDOT. For the preparation method of the composite sodium ferric sulfate positive electrode material, the steps include mixing PSS, EDOT, sodium sulfate, ferrous sulfate, and an oxidant as an initiator in an aqueous solution to fully react to obtain a precursor solution; drying the precursor solution, and then heat-treating to obtain the composite sodium ferric sulfate positive electrode material. For the positive electrode, the above-mentioned positive electrode material is used to prepare it. For the sodium ion battery, the above-mentioned positive electrode is included. The positive electrode material has good conductivity, capacity, rate and interface stability.

[0105] Furthermore, it is understood that the composite sodium ferric sulfate cathode material, preparation method thereof, cathode, and sodium ion battery disclosed herein are reproducible and can be used in a variety of industrial applications. For example, the composite sodium ferric sulfate cathode material, preparation method thereof, cathode, and sodium ion battery disclosed herein can be used in the field of sodium electric material technology.

Claims

1. A composite sodium iron sulfate positive electrode material, characterized in that: The particles of the positive electrode material include a sodium ferric sulfate matrix, a three-dimensional conductive network embedded in the sodium ferric sulfate matrix, and a conductive coating layer coated outside the sodium ferric sulfate matrix; the three-dimensional conductive network and the conductive coating layer are both formed of PEDOT.

2. The positive electrode material according to claim 1, characterized in that The mass ratio of the sodium ferric sulfate matrix to PEDOT is 100:1-10.

3. A method for preparing a composite sodium iron sulfate positive electrode material, characterized in that: include: PSS, EDOT, sodium sulfate, ferrous sulfate and an oxidant as an initiator are mixed and reacted in an aqueous solution to obtain a precursor solution; Drying the precursor solution to obtain a PEDOT-PSS composite sodium iron sulfate precursor; The sodium iron sulfate precursor is heat-treated at 300-450° C. for 6-24 hours under an inert atmosphere to obtain the composite sodium iron sulfate positive electrode material.

4. The preparation method according to claim 3, characterized in that: The method of mixing PSS, EDOT, sodium sulfate, ferrous sulfate and an oxidant as an initiator to react includes: First, add PSS, deionized water and EDOT into the reaction container and stir thoroughly to disperse them evenly; Then, the sodium sulfate, the ferrous sulfate and the oxidant are added to the reaction solution, and the reaction is carried out under continuous stirring.

5. The preparation method according to claim 3, characterized in that: The oxidant comprises at least one of ferric sulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide and oxygen; Preferably, the oxidizing agent is sodium persulfate and ferric sulfate.

6. The preparation method according to claim 3, characterized in that: The molar ratio of the sodium sulfate to the ferrous sulfate is 1:1.5-2.5; Optionally, the feed mass ratio of the PSS to the EDOT is 10:1-5.

7. The preparation method according to claim 6, characterized in that: In terms of weight, the feeding amounts are: 31-314 parts of the total amount of PSS and EDOT, 1000 parts of sodium sulfate, and 1605-2675 parts of ferrous sulfate; Optionally, the oxidant is 1 to 200 parts; Optionally, the deionized water is 2500 to 100000 parts.

8. The preparation method according to claim 3, characterized in that: The drying method is spray drying.

9. A positive electrode, characterized in that: The positive electrode material is prepared by the positive electrode material as claimed in claim 1 or 2, or the positive electrode material prepared by the preparation method as claimed in any one of claims 3 to 8.

10. A sodium ion battery, characterized in that: Comprising the positive electrode as claimed in claim 9.

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