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

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a chlorine-doped sodium iron sulfate composite positive electrode material and a preparation method and application thereof, which comprises a chlorine-doped sodium iron sulfate positive electrode material and carbon, and the mass ratio of the chlorine-doped sodium iron sulfate positive electrode material and the carbon is 1:0.01-0.1; the chemical formula of the chlorine-doped sodium iron sulfate positive electrode material is Na 2.4 Fe 1.8 (SO4) 3‑0.5y Cl y , wherein 0 The application adopts a modification strategy of doping oxygen sites with chlorine ions with a large ionic radius, adjusts the local crystal structure of sodium iron sulfate, expands the cell volume, provides more sufficient migration space for sodium ions, especially improves the sodium ion migration activity of the Na1 / Na2 sites, and further improves the specific capacity, rate performance and cycle life of the sodium iron sulfate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a chlorine-doped sodium iron sulfate composite positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Sodium ion batteries are considered to be a new type of electrochemical energy storage technology with great development prospects due to their similar charging and discharging mechanism to lithium ion batteries, more abundant and cheaper sodium resources. Sodium iron sulfate positive electrode material is considered to be a sodium ion battery positive electrode material with great commercial prospects due to its high working voltage (~3.8V), high theoretical capacity (120mAh g -1 ), low manufacturing cost (annealing temperature ≤400℃) and 100% efficient use of raw materials. However, this material still faces some key technical challenges, such as low electronic conductivity, slow ion diffusion kinetics, poor air stability, low active material utilization, low actual capacity and poor rate performance, which seriously hinder its commercialization process.

[0003] To solve the above problems, related technologies construct sodium iron sulfate / carbon composite materials to improve the surface electronic conductivity and active material utilization, and introduce iron vacancies to inhibit the generation of impurity phases (FeSO4, Fe2O3, etc.). However, most of these studies focus on improving the surface electronic conductivity of the positive electrode material or inhibiting the formation of impurity phases, and the regulation of the electrochemical activity of Na1 / Na2 site sodium ions in the intrinsic structure has not been involved. For sodium iron sulfate positive electrode material, during the charging process, sodium ions usually undergo deintercalation from Na3 site, and then from Na1 / Na2 site. Relatively speaking, sodium ions have a higher diffusion energy barrier at Na1 / Na2 site. Therefore, reducing the deintercalation diffusion energy barrier of sodium ions at Na1 / Na2 site not only promotes the sodium ion diffusion kinetics, but also helps to improve the specific capacity and energy density of the active material.

[0004] Therefore, starting from the intrinsic structure design, improving the electrochemical activity of Na1 / Na2 site in sodium iron sulfate positive electrode material and changing the Na-O coordination environment to increase the number of sodium ions and improve the diffusion kinetics of sodium ions, and then realizing high specific capacity, high rate and high energy density are the current problems to be solved. SUMMARY

[0005] The purpose of the present application is to provide a chlorine-doped sodium iron sulfate composite positive electrode material and a preparation method and application thereof, to effectively solve the problems of low sodium ion diffusion number and slow diffusion kinetics of Na1 / Na2 site in sodium iron sulfate positive electrode material.

[0006] To achieve the above object, the application provides a sodium ferric sulfate composite positive electrode material doped with chlorine, which comprises a sodium ferric sulfate positive electrode material doped with chlorine and carbon, and the mass ratio of the sodium ferric sulfate positive electrode material doped with chlorine and the carbon is 1:0.01-0.1.

[0007] The chemical formula of the sodium ferric sulfate positive electrode material doped with chlorine is Na 2.4 Fe 1.8 (SO4) 3-0.5y Cl y , wherein 0

[0008] The application further provides a preparation method of the sodium ferric sulfate composite positive electrode material doped with chlorine, which comprises the following steps:

[0009] S1, mixing a sodium source, a sulfur-iron compound, a chlorine source and a carbon source to obtain a powder by ball milling;

[0010] S2, calcining the powder under a protective atmosphere to obtain the sodium ferric sulfate composite positive electrode material doped with chlorine.

[0011] In the application, the sodium source in S1 comprises one or more of anhydrous sodium sulfate, sodium sulfate decahydrate, sodium carbonate and sodium hydroxide.

[0012] In the application, the sulfur-iron compound in S1 comprises one or more of ammonium ferrous sulfate, anhydrous ferrous sulfate, ferrous sulfate monohydrate and ferrous sulfate heptahydrate.

[0013] In the application, the chlorine source comprises one or more of hydroxylamine hydrochloride, sodium chloride, ammonium chloride, sodium chlorate, sodium hypochlorite, ferric chloride and ferrous chloride.

[0014] In the application, the carbon source comprises 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.

[0015] In the application, the ball milling mode in S1 comprises solid-phase ball milling or wet ball milling, and the dispersant used in the wet ball milling comprises one or more of ethanol, ethylene glycol, isopropyl alcohol, methanol, acetone and acetonitrile, and the amount of the dispersant is not limited and can be determined by those skilled in the art.

[0016] In the application, 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.

[0017] In the application, the protective atmosphere in S2 comprises one or more of argon, nitrogen and argon-hydrogen gas (a mixture of argon and hydrogen), the heating rate of the calcination is 2-5℃ / min, the calcination temperature is 350-400℃, and the holding time of the calcination is 4-12 h.

[0018] The application further provides application of the sodium ferric sulfate composite positive electrode material in a sodium ion battery.

[0019] The application has the following beneficial effects:

[0020] The application provides a sodium ferric sulfate composite positive electrode material, which comprises sodium ferric sulfate doped with chlorine and carbon, and the mass ratio of the sodium ferric sulfate doped with chlorine and the carbon is 1:0.01-0.1; the chemical formula of the sodium ferric sulfate doped with chlorine is Na 2.4 Fe 1.8 (SO4) 3-0.5y Cl y , wherein 0

[0021] The application substitutes part of oxygen ions with chlorine ions to introduce a small amount of Cl 2- (1.40 Å) to Cl - (1.81 Å), the ionic radius of the chlorine ions is larger than that of the 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 of the sodium ferric sulfate and the sodium ion migration channel, improves the sodium ion diffusion kinetics, especially improves the Na1 / Na2 sodium ion diffusion kinetics, effectively improves the specific capacity, rate performance and cycle performance of the sodium ferric sulfate positive electrode material, and solves the problem of slow sodium ion deintercalation kinetics.

[0022] The initial discharge specific capacity of the sodium ferric sulfate composite positive electrode material provided by the application is significantly improved, and the capacity improvement mainly comes from the high-voltage (4.0-4.5 V) region, so that higher energy density is achieved, and the key problems of low actual capacity and low energy density of the sodium ferric sulfate positive electrode are effectively solved.

[0023] The application improves the electrochemical activity of Na1 / Na2 in the sodium ferric sulfate positive electrode material and changes the Na-O coordination environment to improve the number of sodium ions and the diffusion kinetics, so that high specific capacity, high rate and high energy density of the sodium ferric sulfate positive electrode material are achieved.

[0024] The technical solutions of the application are further described in detail below through the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is an XRD graph of the sodium ferric sulfate composite positive electrode material prepared in Example 2 of the application and the sodium ferric sulfate composite positive electrode material prepared in Comparative Example 2;

[0026] Figure 2is the SEM image of the sodium ferric sulfate composite cathode material prepared in Example 2 of the present application and the sodium ferric sulfate composite cathode material prepared in Comparative Example 2;

[0027] wherein, Figure 2 is the SEM image of the sodium ferric sulfate composite cathode material prepared in Comparative Example 2, Figure 2 is the SEM image of the sodium ferric sulfate composite cathode material prepared in Example 2 of the present application;

[0028] Figure 3 is the charge-discharge curve of the CR2032 button cell prepared in Example 2 of the present application and the CR2032 button cell prepared in Comparative Example 2;

[0029] Figure 4 is the capacity contribution graph of the CR2032 button cell prepared in Example 2 of the present application and the CR2032 button cell prepared in Comparative Example 2 in different voltage intervals;

[0030] Figure 5 is the rate performance curve of the CR2032 button cell prepared in Example 2 of the present application and the CR2032 button cell prepared in Comparative Example 2;

[0031] Figure 6 is the cycle performance curve of the CR2032 button cell prepared in Example 2 of the present application and the CR2032 button cell prepared in Comparative Example 2 at 10C. DETAILED DESCRIPTION

[0032] The present application will be further described below in conjunction with the accompanying drawings and examples. Unless otherwise defined, the technical terms or scientific terms used in the present application shall be understood as the usual meanings understood by those skilled in the art to which the present application belongs. The features mentioned above or the features mentioned in the specific examples can be combined arbitrarily, and these specific examples are only used to illustrate the present application and not to limit the scope of the present application.

[0033] Example 1

[0034] A sodium ferric sulfate composite cathode material doped with chlorine, comprising Na 2.4 Fe 1.8 (SO4) 2.9 Cl 0.2 a cathode material and carbon, Na 2.4 Fe 1.8 (SO4) 2.9 Cl 0.2 The mass ratio of the cathode material and carbon is 1:0.03.

[0035] The preparation method of the sodium ferric sulfate composite cathode material doped with chlorine comprises the following steps:

[0036] S1, anhydrous sodium sulfate, ferrous sulfate monohydrate, sodium chloride, Super-P (conductive carbon black) are weighed according to the molar ratio and mass ratio of the above chemical formula, mixed, added to a ball mill tank, argon is introduced into the ball mill tank, then ball milled at a speed of 600 rpm for 4h, to obtain a powder;

[0037] S2, the powder is transferred to a tube furnace, heated to 380℃ at a heating rate of 4℃ / min under an argon atmosphere, and kept for 8h to complete calcination, to obtain a chlorine-doped sodium iron sulfate composite positive electrode material.

[0038] Example 2

[0039] A chlorine-doped sodium iron sulfate composite positive electrode material, comprising Na 2.4 Fe 1.8 (SO4) 2.95 Cl 0.1 positive electrode material and carbon, the mass ratio of Na 2.4 Fe 1.8 (SO4) 2.95 Cl 0.1 positive electrode material and carbon is 1:0.05.

[0040] The preparation method of the above-mentioned chlorine-doped sodium iron sulfate composite positive electrode material, comprising the following steps:

[0041] S1, anhydrous sodium sulfate, ferrous sulfate monohydrate, sodium chloride, graphite are weighed according to the molar ratio and mass ratio of the above chemical formula, mixed, added to a ball mill tank, ball milled at a speed of 500 rpm for 6h under air conditions, to obtain a powder;

[0042] S2, the powder is transferred to a tube furnace, heated to 400℃ at a heating rate of 3℃ / min under an argon atmosphere, and kept for 6h to complete calcination, to obtain a chlorine-doped sodium iron sulfate composite positive electrode material.

[0043] Example 3

[0044] A chlorine-doped sodium iron sulfate composite positive electrode material, comprising Na 2.4 Fe 1.8 (SO4) 2.95 Cl 0.1 positive electrode material and carbon, the mass ratio of Na 2.4 Fe 1.8 (SO4) 2.95 Cl 0.1 positive electrode material and carbon is 1:0.06.

[0045] The preparation method of the above-mentioned chlorine-doped sodium iron sulfate composite positive electrode material, comprising the following steps:

[0046] S1, anhydrous sodium sulfate, anhydrous ferrous sulfate, ammonium chloride, ketjen black (conductive carbon black) are weighed according to the molar ratio and mass ratio of the above chemical formula and mixed, then added to the ball mill tank, then ethanol is added to the ball mill tank, and nitrogen is introduced into the ball mill tank, then ball milling at a speed of 400 rpm for 8h to obtain a powder;

[0047] S2, the powder is transferred to a tube furnace, heated to 390℃ at a heating rate of 5℃ / min under argon-hydrogen atmosphere, and kept for 7h to complete calcination, to obtain a chlorine-doped sodium iron sulfate composite positive electrode material.

[0048] Example 4

[0049] A chlorine-doped sodium iron sulfate composite positive electrode material, comprising Na 2.4 Fe 1.8 (SO4) 2.975 Cl 0.05 positive electrode material and carbon, Na 2.4 Fe 1.8 (SO4) 2.975 Cl 0.05 positive electrode material and carbon, and the mass ratio of the positive electrode material and carbon is 1:0.03.

[0050] The preparation method of the above-mentioned chlorine-doped sodium iron sulfate composite positive electrode material, comprising the following steps:

[0051] S1, sodium sulfate decahydrate, ferrous sulfate heptahydrate, sodium chloride, carbon nanotubes are weighed according to the molar ratio and mass ratio of the above chemical formula and mixed, then added to the ball mill tank, then ethylene glycol is added to the ball mill tank, and argon is introduced into the ball mill tank, then ball milling at a speed of 600 rpm for 5h to obtain a powder;

[0052] S2, the powder is transferred to a tube furnace, heated to 390℃ at a heating rate of 3℃ / min under argon atmosphere, and kept for 6h to complete calcination, to obtain a chlorine-doped sodium iron sulfate composite positive electrode material.

[0053] Comparative Example 1

[0054] A sodium iron sulfate composite positive electrode material, comprising Na 2.4 Fe 1.8 (SO4)3positive electrode material and carbon, Na 2.4 Fe 1.8 (SO4)3positive electrode material and carbon, and the mass ratio of the positive electrode material and carbon is 1:0.03.

[0055] The preparation method of the above-mentioned sodium iron sulfate composite positive electrode material, comprising the following steps:

[0056] S1, anhydrous sodium sulfate, anhydrous ferrous sulfate, Super-P (conductive carbon black) are weighed according to the molar ratio and mass ratio of the above chemical formula, mixed and added to the ball mill jar, isopropanol is added to the ball mill jar, then argon is introduced, and ball milling is carried out at a speed of 600 rpm for 4 h to obtain a powder;

[0057] S2, the powder is transferred to a tube furnace, heated to 380℃ at a heating rate of 4℃ / min under argon atmosphere, and kept for 8h to complete calcination, to obtain a sodium iron sulfate composite positive electrode material.

[0058] Comparative Example 2

[0059] A sodium iron sulfate composite positive electrode material, comprising Na 2.4 Fe 1.8 (SO4)3positive electrode material and carbon, Na 2.4 Fe 1.8 The mass ratio of the (SO4)3positive electrode material and carbon is 1:0.05.

[0060] The preparation method of the above-mentioned sodium iron sulfate composite positive electrode material comprises the following steps:

[0061] S1, anhydrous sodium sulfate, anhydrous ferrous sulfate, graphite are weighed according to the molar ratio and mass ratio of the above chemical formula, mixed and added to the ball mill jar, ball milling is carried out at a speed of 500 rpm for 6h under air condition to obtain a powder;

[0062] S2, the powder is transferred to a tube furnace, heated to 400℃ at a heating rate of 3℃ / min under argon atmosphere, and kept for 6h to complete calcination, to obtain a sodium iron sulfate composite positive electrode material.

[0063] Comparative Example 3

[0064] A sodium iron sulfate composite positive electrode material, comprising Na 2.4 Fe 1.8 (SO4)3positive electrode material and carbon, Na 2.4 Fe 1.8 The mass ratio of the (SO4)3positive electrode material and carbon is 1:0.03.

[0065] The preparation method of the above-mentioned sodium iron sulfate composite positive electrode material comprises the following steps:

[0066] S1, anhydrous sodium sulfate, anhydrous ferrous sulfate, graphite are weighed according to the molar ratio and mass ratio of the above chemical formula, mixed and added to the ball mill jar, ball milling is carried out at a speed of 500 rpm for 6h under air condition to obtain a powder;

[0067] S2, transfer the powder into a tube furnace, heat to 400℃ at a heating rate of 3℃ / min under argon atmosphere, keep for 6h, complete calcination, and obtain the sodium ferric sulfate composite positive electrode material.

[0068] Comparative Example 4

[0069] A sodium ferric sulfate composite positive electrode material, comprising Na 2.4 Fe 1.8 (SO4)3positive electrode material and carbon, Na 2.4 Fe 1.8 (SO4)3positive electrode material and carbon, and the mass ratio of the sodium ferric sulfate composite positive electrode material to the carbon is 1:0.03.

[0070] A preparation method of the sodium ferric sulfate composite positive electrode material, comprising the following steps:

[0071] S1, weigh the anhydrous sodium sulfate, ferrous sulfate monohydrate, and Ketjen black (conductive carbon black) according to the molar ratio and mass ratio of the above chemical formula, mix them, add them into a ball mill jar, then add ethanol into the ball mill jar, and introduce nitrogen into the ball mill jar, then ball mill at a speed of 400 rpm for 8h to obtain a powder;

[0072] S2, transfer the powder into a tube furnace, heat to 350℃ at a heating rate of 3℃ / min under argon-hydrogen atmosphere, keep for 10h, complete calcination, and obtain the sodium ferric sulfate composite positive electrode material.

[0073] Characterization test:

[0074] The sodium ferric sulfate composite positive electrode material prepared in Example 2 and the sodium ferric sulfate composite positive electrode material prepared in Comparative Example 2 are subjected to X-ray diffraction (XRD) test, and the results are shown in Figure 1 From Figure 1 it can be seen that the XRD spectrum of the sodium ferric sulfate composite positive electrode material after chlorine doping does not produce new impurity peaks, and the sharp diffraction peaks show that both of them have good crystallinity, indicating that chlorine doping has no obvious effect on the crystal structure of sodium ferric sulfate.

[0075] The sodium ferric sulfate composite positive electrode material prepared in Example 2 and the sodium ferric sulfate composite positive electrode material prepared in Comparative Example 2 are observed by scanning electron microscope (SEM), and the results are shown in Figure 2 From Figure 2 it can be seen that in the sodium ferric sulfate composite positive electrode material prepared in Example 2, the sodium ferric sulfate composite positive electrode material is a nanoparticle, and the graphite is embedded between the nanoparticles to ensure efficient electron conduction. In the sodium ferric sulfate composite positive electrode material prepared in Comparative Example 2, the Na 2.4 Fe 1.8 (SO4)3positive electrode material is a nanoparticle, and the graphite is embedded between the nanoparticles to ensure efficient electron conduction.

[0076] Performance test:

[0077] The sodium ferric sulfate composite positive electrode material prepared in Example 2 and the sodium ferric sulfate composite positive electrode material prepared in Comparative Example 2 were taken as active substances, and were mixed with super-P and PVDF (polyvinylidene fluoride) in a mass ratio of 70:20:10 in an N-methyl pyrrolidone (NMP) solvent, and were ground to obtain positive electrode slurries;

[0078] The positive electrode slurries were uniformly coated on aluminum foils, which were vacuum dried at 80°C for 12h, and were cut into circular pieces with a diameter of 12mm as sodium ion battery positive electrodes, with a metal sodium sheet as a negative electrode, glass fiber as a separator, and a 1.0mol / L sodium perchlorate solution (sodium perchlorate mixed with propylene carbonate with a volume concentration of 5%) as an electrolyte, to assemble CR2032 button cells in a glove box.

[0079] The CR2032 button cells prepared in Example 2 and Comparative Example 2 were subjected to charge-discharge tests under the condition of a voltage interval of 2.0-4.5V, and the charge-discharge curves of the two were as shown in Figure 3 From Figure 3 it can be seen that, after doping with chloride ions, the CR2032 button cell assembled in Example 2 exhibited higher charge-discharge specific capacity, and the discharge specific capacity at 0.1C could reach 91.5mAh g -1 , higher than 81.5mAh g -1 of Comparative Example 2.

[0080] The capacity contribution of the CR2032 button cells prepared in Example 2 and Comparative Example 2 at different voltage intervals was further detected, and the results were as shown in Figure 4 From Figure 4 it can be seen that the capacity of the CR2032 button cell assembled in Example 2 was higher than that of Comparative Example 2 in the voltage intervals of 2.0-4.0V and 4.0-4.5V. Obviously, the capacity of Example 2 was increased by about 5.3mAh g -1 compared with Comparative Example 2 in the voltage region of 2.0-4.0V, and was increased by about 8.3mAh g -1 compared with Comparative Example 2 in the voltage region of 4.0-4.5V, which meant that doping with chloride ions could promote more sodium ions to participate in electrochemical reactions.

[0081] The rate performance of the CR2032 button cells prepared in Example 2 and Comparative Example 2 was further detected, and the results were as shown in Figure 5 From Figure 5It can be seen that the discharge specific capacity of the button cell assembled in Example 2 is higher than that of Comparative Example 2 at each rate, and the discharge specific capacity thereof at 0.2C, 0.5C, 1C, 2C, 5C, 10C and 15C is 91.3mAh g -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 , respectively, showing more excellent rate capacity.

[0082] The cycle performance at 10C of the CR2032 button cell prepared from Example 2 and Comparative Example 2 was detected, and the results are shown in Figure 6 It can be seen from Figure 6 that the discharge specific capacity of the CR2032 button cell assembled in Example 2 is still 59.7mAh g -1 at 10C after 3000 cycles, which is 10.9mAh g -1 higher than that of Comparative Example 2 (48.8 mAh g -1 ), and the capacity retention rate thereof is 79.2%, showing good cycle life.

[0083] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: it can still modify or equivalently replace the technical solutions of the present application, and these modifications or equivalent replacements also cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

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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