Composite iron sodium sulfate positive electrode material, its preparation method, positive electrode and sodium ion battery

Abstract

A composite sodium iron sulfate cathode material, its preparation method, cathode, and sodium-ion battery are disclosed. The composite sodium iron sulfate cathode material comprises a sodium iron sulfate substrate, a three-dimensional conductive network embedded within the sodium iron sulfate substrate, and a conductive coating layer covering the sodium iron sulfate substrate. Both the three-dimensional conductive network and the conductive coating layer are formed of PEDOT. The preparation method includes the steps of: mixing PSS, EDOT, sodium sulfate, iron(II) sulfate, and an oxidizing agent as an initiator in an aqueous solution to sufficiently react them to obtain a precursor solution; drying the precursor solution; and heat-treating the composite sodium iron sulfate cathode material. A cathode is prepared using the cathode material. A sodium-ion battery includes the cathode. The cathode material has excellent conductivity, capacity, rate, and interfacial stability.

Description

[Technical Field]

[0001] The present disclosure belongs to the technical field of sodium battery materials, and specifically relates to a composite sodium iron sulfate positive electrode material, a preparation method thereof, a positive electrode and a sodium ion battery.

[0002] (CROSS-REFERENCE TO RELATED APPLICATIONS) This disclosure claims priority to a Chinese application entitled "Composite sodium iron sulfate positive electrode material, preparation method thereof, positive electrode and sodium ion battery," filed with the State Intellectual Property Office of the People's Republic of China on June 25, 2023, bearing application number 202310755581.9, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] Currently, cathode materials for sodium-ion batteries are mainly divided into three types: layered oxides, polyanions, and Prussian white derivative materials. Polyanions are attracting attention because they form a three-dimensional network structure with strong covalent bonds between polyanion polyhedra and transition metal ion polyhedra, resulting in excellent structural stability and long cycle life.

[0004] Iron-based polyanion cathode materials are rapidly developing due to their abundant iron(III) ion content and environmental friendliness. Among them, iron-based pyrophosphate cathode materials have a relatively low operating potential (~3.0 V vs. Na + / Na) and relatively low energy density. Iron sulfate materials have a relatively high operating potential (~3.7V vs. Na + / Na), which has attracted attention due to its higher energy density. Summary of the Invention [Problem to be solved by the invention]

[0005] However, this type of material has a high operating voltage and an upper limit of the charging voltage of 4.2 V vs. Na + / Na, which is likely to lead to oxidative decomposition of the electrolyte at the positive electrode. Furthermore, this type of iron sulfate generally has relatively poor electrical conductivity, resulting in low sodium storage capacity and poor rate performance. Furthermore, when exposed to air, it is prone to water absorption and oxidation, making the material ineffective. A common solution is to improve the electrical conductivity and hydrophobicity of the iron sulfate by compounding it with a carbon-based material.

[0006] However, iron sulfate has a high operating potential, and the upper limit of the charging voltage is generally 4.2 V vs. Na + / Na, and the electrolyte is susceptible to oxidative decomposition on the surface of the iron-based sulfate at this voltage. Simply doping or coating the iron-based sodium sulfate with a carbon-based material does not adequately inhibit the oxidative decomposition of the electrolyte at high voltage. Furthermore, iron-based sulfate decomposes at temperatures above 500°C and cannot be treated with conventional high-temperature carbon coatings. Therefore, it is common to use carbon nanotube-based materials to compound the electrolyte, but this requires a relatively large amount of carbon nanotubes, resulting in relatively high costs.

[0007] Therefore, the development of a material that can simultaneously improve the oxidation stability at high voltage and the electrical conductivity of the material itself is important for sodium iron sulfate materials.

[0008] Conductive polymer materials have relatively good electrical conductivity and, as polymeric materials, relatively good chemical stability. Therefore, they are used as coating materials for battery materials, thereby improving the material's electrical conductivity and interfacial stability. However, when using conductive polymers for coating, the battery material must first be prepared, and then polymerizable monomers must be dissolved in an organic solvent and mixed with the battery material for polymerization. Typically, conductive polymers can only coat the surface of the material; they cannot form a three-dimensional conductive network through cross-linking within the material granules. Furthermore, the synthesis process is complex, requiring the use of organic solvents, which are harmful to the environment and health. Therefore, a suitable method is needed to further improve electrical conductivity while simplifying the process and reducing environmental and health hazards. [Means for solving the problem]

[0009] It is with this in mind that the present disclosure has been devised.

[0010] The present disclosure aims to provide a composite sodium iron sulfate positive electrode material, a method for preparing the same, a positive electrode, and a sodium-ion battery.

[0011] The present disclosure is realized as follows.

[0012] In a first aspect, the present disclosure provides a composite sodium iron sulfate cathode material, the cathode material comprising granules including a sodium iron sulfate substrate, a three-dimensional conductive network embedded within the sodium iron sulfate substrate, and a conductive coating layer covering the sodium iron sulfate substrate, the three-dimensional conductive network and the conductive coating layer both being formed from PEDOT.

[0013] In an alternative embodiment, the weight ratio of the sodium iron sulfate substrate to PEDOT is 100:1-10.

[0014] In a second aspect, the present disclosure provides a method for preparing a composite sodium iron sulfate cathode material, which includes the steps of: mixing PSS, EDOT, sodium sulfate, iron(II) sulfate, and an oxidizing agent as an initiator in an aqueous solution to sufficiently react them to obtain a precursor solution; drying the precursor solution to obtain a PEDOT-PSS composite sodium iron sulfate precursor; and heat-treating the sodium iron sulfate precursor at 300-450°C for 6-24 hours in an inert gas atmosphere to obtain the composite sodium iron sulfate cathode material.

[0015] In an alternative embodiment, mixing and reacting PSS, EDOT, sodium sulfate, iron (II) sulfate, and an oxidizing agent as an initiator includes first placing PSS, deionized water, and EDOT in a reaction vessel and stirring thoroughly to uniformly disperse them, and then adding sodium sulfate, iron (II) sulfate, and the oxidizing agent to the reaction solution and reacting them with stirring.

[0016] In alternative embodiments, the oxidizing agent comprises at least one of iron (III) sulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, and oxygen gas; preferably, the oxidizing agent is iron (III) sulfate and sodium persulfate.

[0017] In an alternative embodiment, the molar ratio of the added sodium sulfate to iron (II) sulfate is 1:1.5-2.5, and optionally, the mass ratio of the added PSS to EDOT is 10:1-5.

[0018] In an alternative embodiment, the material input amounts, in parts by weight, are 31 to 314 parts total of the PSS and EDOT, 1000 parts of the sodium sulfate, 1605 to 2675 parts of the iron(II) sulfate, optionally 1 to 200 parts of the oxidizing agent, and optionally 2500 to 100,000 parts of the deionized water.

[0019] In an alternative embodiment, the drying method is spray drying.

[0020] In a third aspect, the present disclosure provides a positive electrode, the positive electrode being prepared from a positive electrode material according to the above embodiment or a positive electrode material prepared by a preparation method according to any one of the above embodiments.

[0021] In a fourth aspect, the present disclosure provides a sodium-ion battery, the sodium-ion battery including a positive electrode according to the above embodiment.

[0022] The present disclosure has the following beneficial effects:

[0023] In the composite sodium iron sulfate positive electrode material according to the present disclosure, a conductive network formed by PEDOT is embedded within the sodium iron sulfate substrate and coats the surface of the sodium iron sulfate substrate, thereby improving the conductivity, capacity, and rate of the sodium iron sulfate positive electrode material. PEDOT has relatively good chemical stability and forms a coating layer on the surface of the sodium iron sulfate, thereby improving the interfacial stability of the sodium iron sulfate positive electrode material.

[0024] The preparation method according to the present disclosure utilizes polystyrene sulfonate (PSS) in the preparation process, which forms an ionic bond with PEDOT to increase the solubility of PEDOT in water, thereby forming a more uniformly dispersed aqueous solution of PEDOT, sodium sulfate, and iron(II) sulfate. Thus, the composite sodium iron sulfate cathode material obtained after heat treatment not only has PEDOT coating the surface of the sodium iron sulfate granules, but also forms a PEDOT-based three-dimensional conductive network structure within the granules. Furthermore, during the heat treatment, the sulfonic acid groups of PSS decompose, promoting the loss of the ionic bond between PEDOT and PSS, thereby further improving the conductivity of the polymer. [Brief explanation of the drawings]

[0025] In order to more clearly describe the technical solutions of the embodiments of the present disclosure, the drawings used in the embodiments will be briefly described below. The drawings described are only for illustrating some embodiments of the present disclosure and are not intended to limit the scope. Those skilled in the art can obtain other related drawings based on these drawings without using inventive abilities.

[0026] [Figure 1] It is a sodium iron sulfate material doped with and coated with a PEDOT-based conductive polymer. [Figure 2] This is a typical sodium iron sulfate material that has not been doped or coated. DETAILED DESCRIPTION OF THE INVENTION

[0027] In order to clarify the objectives, technical solutions, and advantages of the embodiments of the present disclosure, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below. In the embodiments, specific conditions are not specified, but conventional conditions or conditions recommended by the manufacturer can be used. For reagents or equipment whose manufacturers are not specified, conventional products available on the market can be used.

[0028] The composite sodium iron sulfate positive electrode material, its preparation method, positive electrode, and sodium ion battery according to the embodiments of the present disclosure will be specifically described below.

[0029] In the composite sodium iron sulfate cathode material according to the present disclosure, the granules of the cathode material include a sodium iron sulfate substrate, a three-dimensional conductive network embedded in the sodium iron sulfate substrate, and a conductive coating layer covering the sodium iron sulfate substrate, both of which are formed from PEDOT.

[0030] PEDOT is a polymer of EDOT (3,4-ethylenedioxythiophene monomer) with relatively good conductive properties. The conductive network formed by PEDOT is embedded in the sodium iron sulfate substrate and coats the surface of the sodium iron sulfate substrate, thereby improving the conductivity, capacity, and rate of the sodium iron sulfate positive electrode material. PEDOT has relatively good chemical stability and forms a coating layer on the surface of the sodium iron sulfate, thereby improving the interfacial stability of the sodium iron sulfate positive electrode material.

[0031] Preferably, in order to ensure better electrochemical performance of the composite sodium iron sulfate cathode material, the mass ratio of the sodium iron sulfate base material to PEDOT is 100:1-10 (for example, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9 or 100:10), more preferably, for example, 100:1-8. , 100:1-7, 100:1-6, 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.

[0032] A method for preparing a composite sodium iron sulfate cathode material according to an embodiment of the present disclosure includes the steps of: mixing PSS, EDOT, sodium sulfate, iron(II) sulfate, and an oxidant as an initiator in an aqueous solution to allow a sufficient reaction to occur, thereby obtaining a precursor solution; drying the precursor solution to obtain a PEDOT-PSS composite sodium iron sulfate precursor; and heat-treating the sodium iron sulfate precursor at 300-450°C for 6-24 hours under an inert gas atmosphere, thereby obtaining a composite sodium iron sulfate cathode material.

[0033] EDOT, or 3,4-ethylenedioxythiophene monomer, polymerizes to form PEDOT in the presence of an oxidizing agent. Because PEDOT is insoluble in water, directly mixing PEDOT with sodium sulfate or ferrous sulfate fails to achieve uniform dispersion. After heat treatment, PEDOT only coats the surface of the sodium iron sulfate, failing to form a three-dimensional conductive network embedded within the sodium iron sulfate granules. In this study, PSS (polystyrene sulfonic acid) is used to graft PEDOT, making it water-soluble. This allows PEDOT to disperse uniformly with sodium sulfate and ferrous sulfate in aqueous solution. Therefore, the composite sodium iron sulfate cathode material granules obtained after heat treatment not only have a structure in which PEDOT coats the surface of the sodium iron sulfate granules, but also have a three-dimensional conductive network embedded within the sodium iron sulfate granules. During the heat treatment, the ionic bond between PEDOT and PSS is cleaved, and the PSS is partially or completely decomposed, which can further improve the conductivity of the polymer.

[0034] Therefore, the preparation method according to the present disclosure can obtain a composite sodium ferrous sulfate positive electrode material according to the present disclosure, in which a three-dimensional conductive network of PEDOT is embedded inside the granules and the surface is coated with a PEDOT coating layer, and the material has relatively good electrochemical performance.

[0035] The specific preparation method is as follows.

[0036] S1. Mixed reaction First, PSS, deionized water, and EDOT were placed in a reaction vessel and thoroughly stirred to disperse them uniformly.

[0037] Then, sodium sulfate, iron (II) sulfate, and an oxidizing agent are added to the reaction solution, and the reaction is carried out while stirring. When the solution turns dark blue or black, the reaction is complete.

[0038] Optionally, the oxidizing agent comprises at least one of iron (III) sulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, and oxygen gas.

[0039] Preferably, the oxidizing agent is iron(III) sulfate and sodium persulfate. Due to the homogeneity of iron(III) sulfate and sodium persulfate and the iron(II) sulfate in the sodium iron sulfate precursor, the conductive polymer-composite iron sulfate material can be directly synthesized in a one-pot synthesis, eliminating the purification step, significantly reducing the complexity of the synthesis, and improving atom economy and yield. More preferably, iron(III) sulfate is added to the reaction vessel as an aqueous solution to more quickly and uniformly disperse the iron(III) sulfate.

[0040] Optionally, the molar ratio of the added sodium sulfate to iron (II) sulfate is 1:1.5 to 2.5 (for example, 1:1.5, 1:2, or 1:2.5).

[0041] Optionally, the mass ratio of the added PSS to EDOT is 10:1 to 5 (eg, 10:1, 10:2, or 10:5).

[0042] More specifically, to ensure better performance of the prepared composite sodium iron sulfate cathode material, the material input amounts, in parts by weight, are 31-314 parts of PSS and EDOT in total, 1000 parts of sodium sulfate, and 1605-2675 parts of iron(II) sulfate.

[0043] Optionally, the oxidizing agent is 1 to 200 parts.

[0044] Optionally, the deionized water is 2,500 to 100,000 parts.

[0045] The material input amounts are, for example, 31 parts total of PSS and EDOT, 1000 parts sodium sulfate, 1605 parts iron (II) sulfate, 1 part oxidizer, and 2500 parts deionized water.

[0046] Or, the total amount of PSS and EDOT is 314 parts, sodium sulfate is 1000 parts, iron (II) sulfate is 2675 parts, oxidizer is 314 parts, and deionized water is 100000 parts.

[0047] Alternatively, the total amount of PSS and EDOT is 80 parts, sodium sulfate is 1000 parts, iron (II) sulfate is 1800 parts, oxidizer is 50 parts, and deionized water is 10000 parts.

[0048] Alternatively, the total amount of PSS and EDOT is 150 parts, sodium sulfate is 1000 parts, iron (II) sulfate is 2000 parts, oxidizer is 100 parts, and deionized water is 20000 parts.

[0049] Or, the total amount of PSS and EDOT is 200 parts, sodium sulfate is 1000 parts, iron (II) sulfate is 2200 parts, oxidizer is 200 parts, and deionized water is 40000 parts.

[0050] Or, the total amount of PSS and EDOT is 280 parts, sodium sulfate is 1000 parts, iron (II) sulfate is 2400 parts, oxidizer is 270 parts, and deionized water is 80000 parts.

[0051] S2. Dry the precursor solution. After drying, the sodium iron sulfate precursor of the PEDOT-PSS composite is obtained.

[0052] Preferably, the drying method is spray drying, because the sodium iron sulfate precursor obtained by spray drying has a uniform particle size distribution and good morphology.

[0053] S3.Heat treatment The sodium iron sulfate precursor obtained by spray drying is placed in an inert gas atmosphere and heat-treated at a temperature of 300 to 450°C (e.g., 300°C, 350°C, 400°C, or 450°C) for 6 to 24 hours (e.g., 6 hours, 10 hours, 15 hours, 18 hours, 20 hours, or 24 hours).

[0054] By the heat treatment, the sodium iron sulfate precursor is converted into sodium iron sulfate, the ionic bond between PEDOT and PSS is cleaved, and the PSS is partially or completely decomposed.

[0055] Optionally, the heat treatment is carried out under a nitrogen or argon gas atmosphere.

[0056] A positive electrode according to an embodiment of the present disclosure is prepared using a positive electrode material according to an embodiment of the present disclosure or a positive electrode material prepared by a preparation method according to an embodiment of the present disclosure.

[0057] A sodium-ion battery according to an embodiment of the present disclosure includes a positive electrode according to an embodiment of the present disclosure. [Example]

[0058] The features and performance of the present disclosure will be described in more detail below with reference to examples.

[0059] Examples 1 to 5 The example provides a method for preparing a composite sodium iron sulfate positive electrode material, and the preparation process is as follows:

[0060] PSS, deionized water, and EDOT were placed in a container and dispersed uniformly by stirring.

[0061] An aqueous solution of sodium sulfate, iron (II) sulfate, and a small amount of iron (III) sulfate was placed in a reaction vessel and reacted with stirring until the solution turned dark blue, to obtain a precursor solution.

[0062] The precursor solution was spray-dried to obtain a composite sodium iron sulfate precursor.

[0063] The precursor was heat-treated under a nitrogen gas atmosphere to obtain a PEDOT polymer-based composite sodium iron sulfate cathode material.

[0064] The specific parameter settings are shown in Table 1 below. [Table 1]

[0065] Comparative Example 1 This comparative example differs from Example 1 in that no PSS was added. After EDOT, sodium persulfate, and iron (III) sulfate were added, the solution reacted rapidly to produce a large amount of precipitate, and a uniformly dispersed solution could not be formed, making it impossible to carry out the subsequent spray granulation experiment.

[0066] Comparative Example 2 This comparative example differs from Example 1 in that PSS, EDOT, and an oxidizing agent were not added.

[0067] Experimental Example 1 SEM photographs of the composite sodium iron sulfate positive electrode material granules prepared in Example 1 and Comparative Example 2 were taken, and the SEM photographs are shown in Figures 1 and 2, respectively. As shown in Figures 1 and 2, the composite sodium iron sulfate positive electrode material granules prepared in Example 1 had a structure in which a three-dimensional conductive network was embedded in a sodium iron sulfate base material and a coating layer was formed on the surface, while those prepared in Comparative Example 2 had neither a surface coating layer structure nor an embedded conductive network structure, and were a typical sodium iron sulfate positive electrode material.

[0068] Experimental Example 2 Conductivity measurement: 3 g of the tapped powder was weighed, placed in a mold cavity and vibrated to make the sample flat and uniform, and then pressurized to 30 MPa. The powder conductivity after pressing was measured using a four-point probe.

[0069] Performance evaluation of sodium ion full cell The AZO-doped sodium iron sulfate prepared in the above example was used as the cathode material for a sodium-ion battery. A CR2032 coin-type battery was assembled using a metallic sodium sheet. A uniform slurry of sodium iron sulfate, SP, and PVDF in a mass ratio of 9:0.5:0.5 was prepared in an NMP solution. This slurry was then applied to aluminum foil and dried to form the cathode plate. The metallic sodium sheet was used as the battery anode. The electrolyte was prepared by dissolving 1.0 mol / L NaPF6 in a PC:EMC:FEC solution in a 4:6:0.5 ratio. The coin-type battery was assembled in an argon-filled glove box, and the capacity, rate performance, and cycle performance were measured.

[0070] Battery capacity measurement: The assembled battery was charged at 0.1C to 4.3V and discharged at 0.1C to 2.0V.

[0071] Battery rate performance measurement: The assembled battery was charged at 0.1C to 4.3V and discharged at 2C to 2.0V.

[0072] Cycle life measurement: The assembled battery was charged to 4.3 V at 1 C and discharged to 2.0 V at 1 C for 100 cycles, and the capacity retention rate was recorded.

[0073] [Table 2]

[0074] As can be seen from Table 2, all batteries fabricated using the cathode materials prepared according to the examples of the present disclosure exhibited relatively good electrochemical performance. Examples 1 to 3 exhibited relatively good performance because the materials were within the preferred ranges of the present disclosure. In Example 4, the amounts of PSS and EDOT added were relatively small, and the resulting cathode material was inferior in performance, such as conductivity and capacity, to Examples 1 to 3. However, the performance was significantly better than that of the comparative cathode material in which no PSS or EDOT was added. In Example 5, the amounts of PSS and EDOT added were relatively large, and the resulting cathode material was inferior in performance, such as conductivity and capacity, to Examples 1 to 3. However, the performance was significantly better than that of the comparative cathode material in which no PSS or EDOT was added.

[0075] Comparing Comparative Example 1 with Example 1, because no PSS was added during the preparation process in Comparative Example 1, the polymer formed during the oxidative polymerization of EDOT precipitated directly and could not be dissolved in the aqueous solution of iron (II) sulfate and sodium sulfate. Therefore, a uniformly dispersed solution could not be prepared. Therefore, a uniform mixture of sodium iron sulfate precursor and PEDOT could not be formed by spray granulation. Comparing Comparative Example 2 with Example 1, because no conductive polymer was added in Comparative Example 2, the conductivity of the material and the battery performance were poor.

[0076] As described above, in the composite sodium iron sulfate positive electrode material according to the embodiment of the present disclosure, the conductive network formed by PEDOT is embedded in the sodium iron sulfate substrate and coats the surface of the sodium iron sulfate substrate, thereby improving the conductivity, capacity, and rate of the sodium iron sulfate positive electrode material. Furthermore, PEDOT has relatively good chemical stability and forms a coating layer on the surface of the sodium iron sulfate, thereby improving the interfacial stability of the sodium iron sulfate positive electrode material.

[0077] The preparation method according to the present disclosure uses polystyrene sulfonate (PSS) during the preparation process, which forms an ionic bond between PSS and PEDOT molecules, improving the solubility of PEDOT in aqueous solution and allowing PEDOT to be uniformly dispersed with sodium sulfate and iron(II) sulfate in aqueous solution. Therefore, the granules of the composite sodium iron sulfate positive electrode material obtained after heat treatment have a three-dimensional conductive network structure in which PEDOT is embedded within the sodium iron sulfate granules. The heat treatment process completely decomposes the sulfonic acid groups in PSS, eliminating the ionic bond between PEDOT and PSS, further improving the conductivity of the polymer.

[0078] The above is only a preferred embodiment of the present disclosure and does not limit the present disclosure. Those skilled in the art may have various modifications and changes to the present disclosure. As long as they do not deviate from the spirit and principle of the present disclosure, any modifications, equivalent replacements, improvements, etc., fall within the scope of protection of the present disclosure. [Industrial Applicability]

[0079] The present disclosure provides a composite sodium iron sulfate positive electrode material, a method for preparing the same, a positive electrode, and a sodium-ion battery. The granules of the composite sodium iron sulfate positive electrode material include a sodium iron sulfate substrate, a three-dimensional conductive network embedded within the sodium iron sulfate substrate, and a conductive coating layer covering the sodium iron sulfate substrate. Both the three-dimensional conductive network and the conductive coating layer are formed by PEDOT. The preparation method for the composite sodium iron sulfate positive electrode material includes the steps of: mixing PSS, EDOT, sodium sulfate, iron(II) sulfate, and an oxidizing agent as an initiator in an aqueous solution and allowing them to react sufficiently to obtain a precursor solution; drying the precursor solution; and heat-treating the composite sodium iron sulfate positive electrode material. A positive electrode is prepared using the above positive electrode material. A sodium-ion battery includes the above positive electrode. The positive electrode material has excellent conductivity, capacity, rate, and interfacial stability.

[0080] The composite iron sodium sulfate positive electrode material, its preparation method, positive electrode, and sodium ion battery according to the present disclosure are operable and can be used in various industrial applications, such as in the technical field of sodium battery materials.

Claims

1. 1. A composite sodium iron sulfate cathode material comprising: The granules of the composite sodium iron sulfate positive electrode material comprise a sodium iron sulfate base material, a three-dimensional conductive network embedded in the sodium iron sulfate base material, and a conductive coating layer coating the sodium iron sulfate base material, and the three-dimensional conductive network and the conductive coating layer are both formed from PEDOT.

2. 2. The composite sodium iron sulfate positive electrode material according to claim 1, wherein the mass ratio of the sodium iron sulfate base material to PEDOT is 100:1-10.

3. Mixing PSS, EDOT, sodium sulfate, iron (II) sulfate, and an oxidizing agent as an initiator in an aqueous solution to sufficiently react with each other to obtain a precursor solution; drying the precursor solution to obtain a PEDOT-PSS composite iron sodium sulfate precursor; and heat-treating the sodium iron sulfate precursor at 300 to 450°C for 6 to 24 hours in an inert gas atmosphere to obtain the composite sodium iron sulfate positive electrode material.

4. Mixing and reacting PSS, EDOT, sodium sulfate, iron (II) sulfate, and an oxidizing agent as an initiator results in the following reaction: First, PSS, deionized water, and EDOT are placed in a reaction vessel and thoroughly stirred to disperse uniformly. The method according to claim 3, further comprising adding the sodium sulfate, the iron (II) sulfate, and the oxidizing agent to the reaction solution and reacting them with stirring.

5. the oxidizing agent includes at least one of iron (III) sulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, and oxygen gas; 4. The method according to claim 3, characterized in that the oxidizing agents are preferably sodium persulfate and iron(III) sulfate.

6. The molar ratio of the sodium sulfate to the iron (II) sulfate to be added is 1:1.5 to 2.5, 4. The method according to claim 3, wherein the mass ratio of the PSS and the EDOT added is 10:1-5.

7. In parts by weight, the material input amounts are 31 to 314 parts of the total amount of the PSS and EDOT, 1000 parts of the sodium sulfate, and 1605 to 2675 parts of the iron (II) sulfate; Optionally, the oxidizing agent is 1 to 200 parts; 7. The method of claim 6, wherein the deionized water is 2,500 to 100,000 parts.

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

9. A positive electrode prepared from the positive electrode material according to claim 1 or 2, or the positive electrode material prepared by the method according to any one of claims 3 to 8.

10. A sodium ion battery comprising the positive electrode according to claim 9.

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