Chlorine-doped sodium ferric sulfate composite positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a chlorine-doped sodium ferric sulfate composite positive electrode material and a preparation method and application thereof, the chlorine-doped sodium ferric sulfate composite positive electrode material comprises a chlorine-doped sodium ferric sulfate positive electrode material and carbon, and the mass ratio of the chlorine-doped sodium ferric sulfate positive electrode material to the carbon is 1: 0.01-0.1; the chemical formula of the chlorine-doped sodium ferric sulfate positive electrode material is Na < 2.4 > Fe < 1.8 > (SO4) < 3-0.5 > y Cly, wherein y is more than 0 and less than or equal to 0.2. According to the invention, a modification strategy of doping chloride ions with oxygen sites with large ion radius is adopted, a more sufficient migration space is provided for sodium ions by adjusting the local crystal structure of sodium ferric sulfate, enlarging the unit cell volume and the like, and particularly, the migration activity of sodium ions at Na1 / Na2 site is improved, so that the specific capacity and rate capability of sodium ferric sulfate are improved, and the cycle life of sodium ferric sulfate is prolonged.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a chlorine-doped sodium ferric sulfate composite cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, due to their similar charge-discharge mechanism to lithium-ion batteries and the availability and low cost of sodium resources, are considered a promising new electrochemical energy storage technology. Sodium iron sulfate cathode material is favored for its high operating voltage (~3.8V) and high theoretical capacity (120mAh g / g). -1 With its advantages such as low manufacturing cost (annealing temperature ≤400℃) and 100% efficient utilization of raw materials, sodium-ion battery cathode material is considered a highly promising commercial material. However, this material still faces some key technical challenges, such as low electronic conductivity, slow ion diffusion kinetics, poor air stability, low utilization of active materials, low actual capacity, and poor rate performance, which seriously hinder its commercialization process.

[0003] To address the aforementioned issues, related technologies have focused on improving surface electronic conductivity and active material utilization by constructing sodium ferric sulfate / carbon composite materials and suppressing the formation of impurity phases (FeSO4, Fe2O3, etc.) by introducing iron vacancies. However, most of these studies emphasize improving the surface electronic conductivity of the cathode material or suppressing the formation of impurity phases, while research on the regulation of the electrochemical activity of sodium ions at the Na1 / Na2 sites in the intrinsic structure has not yet been conducted. For sodium ferric sulfate cathode materials, during charging, sodium ions typically undergo extraction from the Na3 site and then from the Na1 / Na2 site. Relatively speaking, sodium ions have a higher diffusion barrier at the Na1 / Na2 site. Therefore, lowering the diffusion barrier of sodium ions at the Na1 / Na2 sites can not only promote sodium ion diffusion kinetics but also improve the specific capacity and energy density of the active material.

[0004] Therefore, starting from the intrinsic structural design, improving the electrochemical activity of the Na1 / Na2 sites in sodium ferric sulfate cathode materials and changing the Na-O coordination environment to increase the number of sodium ions extracted and diffusion kinetics, thereby achieving high specific capacity, high rate capability and high energy density, is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a chlorine-doped sodium ferric sulfate composite cathode material, its preparation method, and its application, so as to effectively solve the problems of low sodium ion diffusion quantity and slow diffusion kinetics at the Na1 / Na2 sites in sodium ferric sulfate cathode materials.

[0006] To achieve the above objectives, the present invention provides a chlorine-doped sodium ferric sulfate composite cathode material, comprising chlorine-doped sodium ferric sulfate cathode material and carbon, wherein the mass ratio of the chlorine-doped sodium ferric sulfate cathode material to carbon is 1:0.01-0.1; The chemical formula of the chlorine-doped sodium ferric sulfate cathode material is Na. 2.4 Fe 1.8 (SO4) 3-0.5y Cl y , where 0 < y ≤ 0.2.

[0007] This invention also provides a method for preparing the above-mentioned chlorine-doped sodium ferric sulfate composite cathode material, comprising the following steps: S1. Mix sodium source, iron sulfide compound, chlorine source and carbon source, and ball mill to obtain powder; S2. Under a protective atmosphere, the powder is calcined to obtain the chlorine-doped sodium ferric sulfate composite cathode material.

[0008] In this invention, the sodium source in S1 includes one or more of anhydrous sodium sulfate, sodium sulfate decahydrate, sodium carbonate, and sodium hydroxide.

[0009] In this invention, the ferrous sulfate compound in S1 includes one or more of ferrous ammonium sulfate, anhydrous ferrous sulfate, ferrous sulfate monohydrate, and ferrous sulfate heptahydrate.

[0010] In this invention, the chlorine source includes one or more of hydroxylamine hydrochloride, sodium chloride, ammonium chloride, sodium chlorate, sodium hypochlorite, ferric chloride, and ferrous chloride.

[0011] In this invention, the carbon source includes one or more of graphite, graphene, carbon nanotubes, and conductive carbon black, and the conductive carbon black is selected from at least one of Super-P and Ketjen black.

[0012] In this invention, the ball milling method in S1 includes solid-phase ball milling or wet ball milling. The dispersant used in wet ball milling includes one or more of ethanol, ethylene glycol, isopropanol, methanol, acetone, and acetonitrile. The amount of dispersant is not limited and any dispersant known to those skilled in the art can be used.

[0013] In this invention, the ball milling rate in S1 is 300-800 rpm, the ball milling time is 4-10 h, and the ball milling atmosphere is air, nitrogen, or argon.

[0014] In this invention, the protective atmosphere in S2 includes one or more of argon, nitrogen, and argon-hydrogen (a mixture of argon and hydrogen), the heating rate of calcination is 2-5℃ / min, the calcination temperature is 350-400℃, and the calcination holding time is 4-12h.

[0015] The present invention also provides the application of the above-mentioned chlorine-doped sodium ferric sulfate composite cathode material in a sodium-ion battery, wherein the sodium-ion battery is a secondary battery.

[0016] The present invention has the following beneficial effects: This invention provides a chlorine-doped sodium ferric sulfate composite cathode material, comprising chlorine-doped sodium ferric sulfate cathode material and carbon, wherein the mass ratio of the chlorine-doped sodium ferric sulfate cathode material to carbon is 1:0.01-0.1; the chemical formula of the chlorine-doped sodium ferric sulfate cathode material is Na. 2.4 Fe 1.8 (SO4) 3-0.5y Cl y , where 0 < y ≤ 0.2.

[0017] This invention replaces some oxygen ions with chloride ions in O 2- A small amount of Cl was introduced at the (1.40 Å) site. - (1.81Å) The ionic radius of chloride ions is larger than that of oxygen ions, which not only changes the Na-O coordination environment and reduces the band gap, but also provides a wider sodium ion diffusion channel, expands the local cell structure and sodium ion migration channel of sodium ferric sulfate, and improves the sodium ion diffusion kinetics, especially the sodium ion diffusion kinetics at the Na1 / Na2 sites. This effectively improves the specific capacity, rate performance and cycle performance of sodium ferric sulfate cathode material, and solves the problem of slow sodium ion insertion / extraction kinetics.

[0018] The initial discharge specific capacity of the chlorine-doped sodium ferric sulfate composite cathode material provided by this invention is significantly improved, and the improvement in capacity mainly comes from the high voltage (4.0-4.5V) region, thereby achieving higher energy density and effectively solving the key problems of low actual capacity and low energy density in sodium ferric sulfate cathodes.

[0019] Starting from intrinsic structural design, this invention enhances the electrochemical activity of the Na1 / Na2 sites in sodium ferric sulfate cathode material and alters the Na-O coordination environment to increase the number of sodium ions released and the diffusion kinetics, thereby achieving high specific capacity, high rate capability and high energy density of sodium ferric sulfate cathode material.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 These are the XRD patterns of the chlorine-doped sodium ferric sulfate composite cathode material prepared in Example 2 of this invention and the sodium ferric sulfate composite cathode material prepared in Comparative Example 2. Figure 2 These are SEM images of the chlorine-doped sodium ferric sulfate composite cathode material prepared in Example 2 of this invention and the sodium ferric sulfate composite cathode material prepared in Comparative Example 2. in, Figure 2 In the image, 'a' is a SEM image of the sodium ferric sulfate composite cathode material prepared in Comparative Example 2. Figure 2 b in the image is a SEM image of the chlorine-doped sodium ferric sulfate composite cathode material prepared in Example 2; Figure 3 These are charge-discharge curves of the CR2032 coin cell prepared in Example 2 and the CR2032 coin cell prepared in Comparative Example 2 of the present invention. Figure 4 This is a capacity contribution diagram of the CR2032 coin cell prepared in Example 2 and the CR2032 coin cell prepared in Comparative Example 2 in different voltage ranges. Figure 5 This is a rate performance curve of the CR2032 coin cell prepared in Example 2 of the present invention and the CR2032 coin cell prepared in Comparative Example 2. Figure 6 This is a cycle performance curve of the CR2032 coin cell prepared in Example 2 and the CR2032 coin cell prepared in Comparative Example 2 at 10C. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0023] Example 1 A chlorine-doped sodium ferric sulfate composite cathode material, comprising Na 2.4 Fe 1.8 (SO4) 2.9 Cl 0.2 Cathode material and carbon, Na 2.4 Fe 1.8 (SO4) 2.9 Cl 0.2 The mass ratio of the cathode material to carbon is 1:0.03.

[0024] The preparation method of the above-mentioned chlorine-doped sodium ferric sulfate composite cathode material includes the following steps: S1. Weigh anhydrous sodium sulfate, ferrous sulfate monohydrate, sodium chloride, and Super-P (conductive carbon black) according to the molar ratio and mass ratio of the above chemical formulas, mix them, add them to a ball mill jar, introduce argon gas into the ball mill jar, and then ball mill at a rate of 600 rpm for 4 hours to obtain powder. S2. The powder is transferred to a tube furnace and heated to 380°C at a heating rate of 4°C / min under an argon atmosphere. The temperature is held for 8 hours to complete the calcination and obtain chlorine-doped sodium ferric sulfate composite cathode material.

[0025] Example 2 A chlorine-doped sodium ferric sulfate composite cathode material, comprising Na 2.4 Fe 1.8 (SO4) 2.95 Cl 0.1 Cathode material and carbon, Na 2.4 Fe 1.8 (SO4) 2.95 Cl 0.1 The mass ratio of the cathode material to carbon is 1:0.05.

[0026] The preparation method of the above-mentioned chlorine-doped sodium ferric sulfate composite cathode material includes the following steps: S1. Weigh anhydrous sodium sulfate, anhydrous ferrous sulfate, sodium chloride, and graphite according to the molar ratio and mass ratio of the above chemical formulas, mix them, add them to a ball mill jar, and ball mill them at a rate of 500 rpm for 6 hours under air conditions to obtain powder. S2. The powder is transferred to a tube furnace and heated to 400°C at a heating rate of 3°C / min under an argon atmosphere. The temperature is held for 6 hours to complete the calcination and obtain chlorine-doped sodium ferric sulfate composite cathode material.

[0027] Example 3 A chlorine-doped sodium ferric sulfate composite cathode material, comprising Na 2.4 Fe 1.8 (SO4) 2.95 Cl 0.1 Cathode material and carbon, Na 2.4 Fe 1.8 (SO4) 2.95 Cl 0.1 The mass ratio of the cathode material to carbon is 1:0.06.

[0028] The preparation method of the above-mentioned chlorine-doped sodium ferric sulfate composite cathode material includes the following steps: S1. Weigh anhydrous sodium sulfate, anhydrous ferrous sulfate, ammonium chloride, and Ketjen black (conductive carbon black) according to the molar ratio and mass ratio of the above chemical formulas, mix them, add them to a ball mill jar, then add ethanol to the ball mill jar, and introduce nitrogen gas into the ball mill jar. Then, ball mill at a rate of 400 rpm for 8 hours to obtain powder. S2. The powder is transferred to a tube furnace and heated to 390°C at a heating rate of 5°C / min under an argon-hydrogen atmosphere. The temperature is held for 7 hours to complete the calcination and obtain chlorine-doped sodium ferric sulfate composite cathode material.

[0029] Example 4 A chlorine-doped sodium ferric sulfate composite cathode material, comprising Na 2.4 Fe 1.8 (SO4) 2.975 Cl 0.05 Cathode material and carbon, Na 2.4 Fe 1.8 (SO4) 2.975 Cl 0.05 The mass ratio of the cathode material to carbon is 1:0.03.

[0030] The preparation method of the above-mentioned chlorine-doped sodium ferric sulfate composite cathode material includes the following steps: S1. Sodium sulfate decahydrate, ferrous sulfate heptahydrate, sodium chloride, and carbon nanotubes were weighed and mixed according to the molar ratio and mass ratio of the above chemical formulas, and then added to a ball mill jar. Ethylene glycol was then added to the ball mill jar, and argon gas was introduced into the ball mill jar. The mixture was then ball milled at a rate of 600 rpm for 5 hours to obtain powder. S2. The powder is transferred to a tube furnace and heated to 390°C at a heating rate of 3°C / min under an argon atmosphere. The temperature is held for 6 hours to complete the calcination and obtain chlorine-doped sodium ferric sulfate composite cathode material.

[0031] Comparative Example 1 A sodium ferric sulfate composite cathode material, comprising Na 2.4 Fe 1.8 (SO4)3 cathode material and carbon, Na 2.4 Fe 1.8 The mass ratio of (SO4)3 cathode material to carbon is 1:0.03.

[0032] The preparation method of the above-mentioned sodium ferric sulfate composite cathode material includes the following steps: S1. Weigh anhydrous sodium sulfate, anhydrous ferrous sulfate, and Super-P (conductive carbon black) according to the molar ratio and mass ratio of the above chemical formulas, mix them, add them to a ball mill jar, add isopropanol to the ball mill jar, then introduce argon gas, and ball mill at a rate of 600 rpm for 4 hours to obtain powder. S2. The powder is transferred to a tube furnace and heated to 380°C at a heating rate of 4°C / min under an argon atmosphere. The temperature is held for 8 hours to complete the calcination and obtain sodium iron sulfate composite cathode material.

[0033] Comparative Example 2 A sodium ferric sulfate composite cathode material, comprising Na 2.4 Fe 1.8 (SO4)3 cathode material and carbon, Na 2.4 Fe 1.8 The mass ratio of (SO4)3 cathode material to carbon is 1:0.05.

[0034] The preparation method of the above-mentioned sodium ferric sulfate composite cathode material includes the following steps: S1. Weigh anhydrous sodium sulfate, anhydrous ferrous sulfate, and graphite according to the molar ratio and mass ratio of the above chemical formulas, mix them, add them to a ball mill jar, and ball mill them at a rate of 500 rpm for 6 hours under air conditions to obtain powder. S2. The powder is transferred to a tube furnace and heated to 400°C at a heating rate of 3°C / min under an argon atmosphere. The temperature is held for 6 hours to complete the calcination and obtain sodium iron sulfate composite cathode material.

[0035] Comparative Example 3 A sodium ferric sulfate composite cathode material, comprising Na 2.4 Fe 1.8 (SO4)3 cathode material and carbon, Na 2.4 Fe 1.8 The mass ratio of (SO4)3 cathode material to carbon is 1:0.03.

[0036] The preparation method of the above-mentioned sodium ferric sulfate composite cathode material includes the following steps: S1. Anhydrous sodium sulfate, ferrous sulfate monohydrate, and graphite are weighed and mixed according to the molar ratio and mass ratio of the above chemical formulas, and then added to a ball mill jar. Acetonitrile is added to the ball mill jar, and then the mixture is ball milled at a rate of 600 rpm for 6 hours under air conditions to obtain powder. S2. The powder is transferred to a tube furnace and heated to 400°C at a heating rate of 3°C / min under an argon atmosphere. The temperature is held for 6 hours to complete the calcination and obtain sodium iron sulfate composite cathode material.

[0037] Comparative Example 4 A sodium ferric sulfate composite cathode material, comprising Na 2.4 Fe 1.8 (SO4)3 cathode material and carbon, Na 2.4 Fe 1.8 The mass ratio of (SO4)3 cathode material to carbon is 1:0.03.

[0038] The preparation method of the above-mentioned sodium ferric sulfate composite cathode material includes the following steps: S1. Weigh anhydrous sodium sulfate, ferrous sulfate monohydrate, and Ketjen black (conductive carbon black) according to the molar ratio and mass ratio of the above chemical formulas, mix them, add them to a ball mill jar, then add ethanol to the ball mill jar, and introduce nitrogen gas into the ball mill jar. Then, ball mill at a rate of 400 rpm for 8 hours to obtain powder. S2. The powder is transferred to a tube furnace and heated to 350°C at a heating rate of 3°C / min under an argon-hydrogen atmosphere. The temperature is held for 10 hours to complete the calcination and obtain sodium iron sulfate composite cathode material.

[0039] Characterization tests: The chlorine-doped sodium ferric sulfate composite cathode material prepared in Example 2 and the sodium ferric sulfate composite cathode material prepared in Comparative Example 2 were subjected to X-ray diffraction (XRD) tests, and the results are as follows: Figure 1 As shown. From Figure 1 It can be seen that the XRD spectrum of sodium ferric sulfate cathode material after chlorine doping did not produce new impurity peaks. The sharp diffraction peaks indicate that both have good crystallinity, which means that chlorine doping has no significant effect on the crystal structure of sodium ferric sulfate.

[0040] The chlorine-doped sodium ferric sulfate composite cathode material prepared in Example 2 and the sodium ferric sulfate composite cathode material prepared in Comparative Example 2 were observed using scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown. From Figure 2 As can be seen, in the chlorine-doped sodium ferric sulfate composite cathode material prepared in Example 2, the chlorine-doped sodium ferric sulfate cathode material is in the form of nanoparticles, with graphite embedded between the nanoparticles to ensure efficient electron conduction. In the sodium ferric sulfate composite cathode material prepared in Comparative Example 2, Na... 2.4 Fe 1.8 The (SO4)3 cathode material consists of nanoparticles with graphite embedded between them to ensure efficient electron conduction.

[0041] Performance testing: The chlorine-doped sodium ferric sulfate composite cathode material prepared in Example 2 and the sodium ferric sulfate composite cathode material prepared in Comparative Example 2 were used as active materials. They were placed in N-methylpyrrolidone (NMP) solvent with super-P and PVDF (polyvinylidene fluoride) at a mass ratio of 70:20:10, respectively, and ground to obtain cathode slurry. The positive electrode slurry was uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. It was then cut into 12mm diameter discs to serve as the positive electrode of the sodium-ion battery. A metallic sodium sheet was used as the negative electrode, glass fiber was used as the separator, and a 1.0mol / L sodium perchlorate solution (a mixture of sodium perchlorate and 5% propylene carbonate by volume) was used as the electrolyte. The CR2032 coin cell was assembled in a glove box.

[0042] The CR2032 coin cells prepared in Example 2 and Comparative Example 2 were subjected to charge-discharge tests under a voltage range of 2.0-4.5V. The charge-discharge curves of both are shown below. Figure 3 As shown. From Figure 3 As can be seen, the CR2032 coin cell assembled in Example 2, after chloride ion doping, exhibits a higher charge / discharge specific capacity, with a discharge specific capacity of 91.5 mAh g⁻¹ at 0.1C. -1 This is higher than the 81.5 mAh g of Comparative Example 2. -1 .

[0043] Further testing was conducted on the capacity contribution of the CR2032 coin cells prepared in Example 2 and Comparative Example 2 in different voltage ranges, and the results are as follows: Figure 4 As shown. From Figure 4 It can be seen that the CR2032 coin cell assembled in Example 2 has a higher capacity than that of Comparative Example 2 in both the 2.0-4.0V and 4.0-4.5V voltage ranges. Specifically, in the 2.0-4.0V voltage region, Example 2 shows a capacity increase of approximately 5.3 mAh g compared to Comparative Example 2. -1 In the 4.0-4.5V voltage region, it improved by approximately 8.3 mAh g compared to Comparative Example 2. -1 This means that chloride ion doping can encourage more sodium ions to participate in electrochemical reactions.

[0044] Further testing of the rate performance of the CR2032 coin cells prepared in Example 2 and Comparative Example 2 yielded the following results: Figure 5 As shown. From Figure 5 It can be seen that the coin cell assembled in Example 2 has a higher discharge specific capacity at all rates than that of Comparative Example 2, with discharge specific capacities of 91.3 mAh g at 0.2C, 0.5C, 1C, 2C, 5C, 10C, and 15C, respectively. -1 89.1mAh g -1 86.7mAh g -1 84.2mAh g -1 79.7mAh g -1 74.4mAh g -1 and 70.0mAh g -1 This demonstrates superior rate capability.

[0045] The cycle performance of the CR2032 coin cells prepared in Example 2 and Comparative Example 2 at 10C was tested, and the results are as follows: Figure 6 As shown. From Figure 6 It can be seen that the CR2032 coin cell assembled in Example 2 still has a specific capacity of 59.7 mAh g after 3000 discharge cycles at 10C. -1 The capacity of Comparison Example 2 (48.8 mAh g) -1 ) high 10.9mAh g -1 Its capacity retention rate was 79.2%, demonstrating good cycle life.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A chlorine-doped sodium ferric sulfate composite cathode material, characterized in that, It includes chlorine-doped sodium ferric sulfate cathode material and carbon, wherein the mass ratio of the chlorine-doped sodium ferric sulfate cathode material to carbon is 1:0.01-0.1; The chemical formula of the chlorine-doped sodium ferric sulfate cathode material is Na. 2.4 Fe 1.8 (SO4) 3-0.5y Cl y , where 0 < y ≤ 0.

2.

2. A method for preparing the chlorine-doped sodium ferric sulfate composite cathode material as described in claim 1, characterized in that, Includes the following steps: S1. Mix sodium source, iron sulfide compound, chlorine source and carbon source, and ball mill to obtain powder; S2. Under a protective atmosphere, the powder is calcined to obtain the chlorine-doped sodium ferric sulfate composite cathode material.

3. The method for preparing chlorine-doped sodium ferric sulfate composite cathode material according to claim 2, characterized in that, The sodium source in S1 includes one or more of anhydrous sodium sulfate, sodium sulfate decahydrate, sodium carbonate, and sodium hydroxide.

4. The method for preparing chlorine-doped sodium ferric sulfate composite cathode material according to claim 2, characterized in that, The ferrous sulfate compounds in S1 include one or more of ferrous ammonium sulfate, anhydrous ferrous sulfate, ferrous sulfate monohydrate, and ferrous sulfate heptahydrate.

5. The method for preparing chlorine-doped sodium ferric sulfate composite cathode material according to claim 2, characterized in that, The chlorine source includes one or more of hydroxylamine hydrochloride, sodium chloride, ammonium chloride, sodium chlorate, sodium hypochlorite, ferric chloride, and ferrous chloride.

6. The method for preparing chlorine-doped sodium ferric sulfate composite cathode material according to claim 2, characterized in that, Carbon sources include one or more of graphite, graphene, carbon nanotubes, and conductive carbon black.

7. The method for preparing chlorine-doped sodium ferric sulfate composite cathode material according to claim 2, characterized in that, The ball milling method in S1 includes solid-phase ball milling or wet ball milling. The dispersant used in wet ball milling includes one or more of ethanol, ethylene glycol, isopropanol, methanol, acetone, and acetonitrile.

8. The method for preparing chlorine-doped sodium ferric sulfate composite cathode material according to claim 2, characterized in that, In S1, the ball milling rate is 300-800 rpm, the ball milling time is 4-10 h, and the ball milling atmosphere is air, nitrogen, or argon.

9. The method for preparing chlorine-doped sodium ferric sulfate composite cathode material according to claim 2, characterized in that, The heating rate for calcination in S2 is 2-5℃ / min, the calcination temperature is 350-400℃, and the holding time for calcination is 4-12h.

10. The application of the chlorine-doped sodium ferric sulfate composite cathode material according to claim 1 in a sodium-ion battery.

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