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

Abstract

The application discloses a sodium iron sulfate composite positive electrode material and a preparation method and a sodium ion battery thereof. The preparation method of the sodium iron sulfate composite positive electrode material comprises the following steps: ball milling a sodium iron sulfate precursor, a carbon source, a dispersing agent and a metal acetate to obtain a mixture; and sintering the mixture under an inert atmosphere to obtain the sodium iron sulfate composite positive electrode material. The preparation method adopts the carbon source and the metal acetate as a common coating agent, and after sintering under the inert atmosphere, the sintering product of the carbon and the metal acetate is obtained to coat the sodium iron sulfate. The common coating can improve the conductivity of the sodium iron sulfate material, reduce the polarization resistance, reduce the hindrance of the sodium ion in the transmission process, and improve the charging and discharging rate of the battery at a high rate. Meanwhile, the common coating of the sintering product of the carbon and the metal acetate can make the sodium iron sulfate positive electrode material have higher electrochemical activity, can better improve the capacity of the sodium ion battery, and further improve the energy density of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a sodium iron sulfate composite positive electrode material, a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] The sodium iron sulfate has a high working voltage platform, a high theoretical discharge capacity, a small structural volume change in the charging and discharging process, a low preparation cost, easily available raw materials, no toxicity and no pollution, and a three-dimensional ion diffusion channel, and is considered as an ideal positive electrode material suitable for large-scale energy storage of sodium ion batteries. However, as a polyanion material, the sodium iron sulfate has a low electronic conductivity, which seriously affects the charging and discharging performance of the battery at a high rate. Therefore, improving the electronic conductivity and kinetic performance of the sodium iron sulfate material has become a research focus.

[0003] In order to improve the electronic conductivity and kinetic performance of the sodium iron sulfate material and improve the capacity and cycle stability of the battery, the sodium iron sulfate is generally modified by nanocrystallization, doping, carbon coating and the like. Although the above modification can improve the electronic conductivity and kinetic performance, the charging and discharging performance of the sodium ion battery assembled by the sodium iron sulfate at a high rate is improved very limitedly. Therefore, how to further improve the comprehensive performance of the sodium iron sulfate material and improve the charging and discharging performance of the sodium ion battery at a high rate is a problem to be solved. SUMMARY

[0004] The application aims to provide a sodium iron sulfate composite positive electrode material with good electronic conductivity, a preparation method thereof and a sodium ion battery.

[0005] In a first aspect, the application provides a preparation method of a sodium iron sulfate composite positive electrode material, which adopts the following technical scheme:

[0006] The application provides a preparation method of a sodium iron sulfate composite positive electrode material, which includes the following steps:

[0007] The sodium iron sulfate precursor, the carbon source, the dispersant and the metal acetate are ball milled to obtain a mixture; and the mixture is sintered under an inert atmosphere to obtain the sodium iron sulfate composite positive electrode material.

[0008] Preferably, the preparation method of the sodium iron sulfate precursor includes the following steps:

[0009] The sodium sulfate, the ferrous sulfate and / or the ferrous sulfate heptahydrate and the antioxidant are dissolved in water to obtain a slurry; and the slurry is spray dried to obtain the sodium iron sulfate precursor.

[0010] Preferably, the chemical formula of the sodium iron sulfate precursor is Na 2x Fe y (SO4) x+yWherein: 0 < x ≤ 5, 0 < y ≤ 5; the sodium sulfate, ferrous sulfate and / or ferrous sulfate heptahydrate are added according to the stoichiometric ratio in the sodium ferric sulfate precursor chemical formula.

[0011] Preferably, the Fe in the ferrous sulfate and / or ferrous sulfate heptahydrate is 0.5-2.0 wt%. 2+ The molar ratio of the antioxidant is 10: (1-2).

[0012] Preferably, the temperature of the spray drying is 150-200℃.

[0013] Preferably, the carbon source is one or more of acetylene black, Super P, Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive graphite; the mass of the carbon source is 1.0-5.0 wt% of the mass of the sodium ferric sulfate precursor.

[0014] Preferably, the dispersant is one or more of polyethylene glycol-4000 (PEG-4000), polyethylene glycol-6000 (PEG-6000), sodium acrylate (C3H3NaO2), and polyvinylpyrrolidone; the mass of the dispersant is 0.1-1.0 wt% of the mass of the sodium ferric sulfate precursor.

[0015] Preferably, the metal acetate is one or more of nickel acetate, cobalt acetate, copper acetate, zinc acetate, manganese acetate, aluminum acetate, titanium acetate, magnesium acetate, and calcium acetate; the mass of the metal acetate is 0.5-2.0 wt% of the mass of the sodium ferric sulfate precursor.

[0016] Further preferably, the metal acetate is at least three or more of nickel acetate, cobalt acetate, copper acetate, zinc acetate, manganese acetate, aluminum acetate, titanium acetate, magnesium acetate, and calcium acetate.

[0017] Preferably, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere; the sintering temperature is 350-400℃, and the sintering time is 0.5-1.5 h.

[0018] In a second aspect, the present application provides a sodium ferric sulfate composite positive electrode material prepared by the preparation method described above.

[0019] In a third aspect, the present application provides a sodium ion battery comprising the sodium ferric sulfate composite positive electrode material described above.

[0020] The above one or more technical solutions of the present application can at least achieve one of the following beneficial effects:

[0021] (1) The preparation method of the present invention uses carbon source and metal acetate as co-coating agents. After sintering under an inert atmosphere, sodium iron sulfate co-coated with the sintered product of carbon and metal acetate is obtained. Co-coating can improve the conductivity of sodium iron sulfate material, reduce polarization resistance, reduce the hindrance of sodium ions in the transport process, and improve the charge and discharge rate of the battery at high rates. At the same time, the co-coating of the sintered product of carbon and metal acetate can make the sodium iron sulfate cathode material have higher electrochemical activity, which can better improve the capacity of sodium ion battery, and thus improve the energy density of battery.

[0022] (2) The sodium ferric sulfate precursor prepared by spray drying in this invention has the advantages of narrow particle size distribution and good flowability, which greatly improves the quality and performance of the product. Moreover, it can reduce energy consumption and is environmentally friendly, and has broad application prospects.

[0023] (3) In the ball milling process of the preparation method of the present invention, the addition of solid dispersant can improve the dispersibility of the material and reduce the agglomeration of powder, thereby obtaining a more uniformly mixed material; the dispersant can shorten the ball milling time, improve production efficiency, reduce energy consumption in the ball milling process, thereby reducing production costs. Attached Figure Description

[0024] Figure 1 The image shows a SEM image of the sodium ferric sulfate composite cathode material prepared in Comparative Example 1.

[0025] Figure 2 This is a SEM image of the sodium ferric sulfate composite cathode material prepared in Example 5.

[0026] Figure 3 The graph shows the initial charge-discharge capacity curve of the sodium ferric sulfate composite cathode material prepared in Example 5 at 0.1C.

[0027] Figure 4 The graph shows the cycle performance of the battery assembled with the sodium iron sulfate composite cathode material prepared in Example 5 after 300 charge-discharge cycles at a rate of 10 C. Detailed Implementation

[0028] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention are commercially available or can be prepared by existing methods.

[0029] As mentioned above, a method for preparing a sodium ferric sulfate composite cathode material includes the following steps:

[0030] The sodium ferric sulfate precursor, a carbon source, a dispersant and a metal acetate are ball milled to obtain a mixture; and the mixture is sintered under an inert atmosphere to obtain a sodium ferric sulfate composite positive electrode material.

[0031] The method of the present application can make the carbon source and the metal acetate uniformly distributed on the sodium ferric sulfate precursor by ball milling the sodium ferric sulfate precursor with the carbon source and the metal acetate, and can obtain the sodium ferric sulfate composite positive electrode material coated with the sintering product of the carbon and the metal acetate by sintering. The combination of the two coating agents can improve the conductivity of the material, reduce the polarization resistance, reduce the hindrance of sodium ions in the transmission process, and improve the high-rate charge and discharge rate of the battery. At the same time, the co-coating of the sintering product of the carbon and the metal acetate can make the sodium ferric sulfate positive electrode material have higher electrochemical activity, and can better improve the capacity of the sodium ion battery, thereby improving the energy density of the battery.

[0032] In the preparation method of the present application, the solid dispersant is added for ball milling, which can improve the dispersibility of the material, reduce the powder agglomeration phenomenon, and thus obtain a more uniformly mixed material; the dispersant can shorten the ball milling time, improve the production efficiency, and reduce the energy consumption in the ball milling process, thereby reducing the production cost.

[0033] Preferably, the preparation method of the sodium ferric sulfate precursor comprises the following steps:

[0034] The sodium sulfate, ferrous sulfate and / or ferrous sulfate heptahydrate, and an antioxidant are dissolved in water to obtain a slurry; and the slurry is spray dried to obtain the sodium ferric sulfate precursor.

[0035] The sodium ferric sulfate precursor prepared by the spray drying method in the present application has the advantages of narrow particle size distribution and good flowability, greatly improving the quality and performance of the product, and reducing energy consumption and process environmental protection, and has a wide application prospect.

[0036] Preferably, the chemical formula of the sodium ferric sulfate precursor is Na 2x Fe y (SO4) x+y , wherein: 0 < x ≤ 5, for example, 1, 2, 3, 4, 5, etc.; 0 < y ≤ 5, y can be 1, 2, 3, 4, 5, etc. The sodium sulfate, ferrous sulfate and / or ferrous sulfate heptahydrate are added according to the stoichiometric ratio in the chemical formula of the sodium ferric sulfate precursor.

[0037] Preferably, the molar ratio of Fe 2+ in the ferrous sulfate and / or ferrous sulfate heptahydrate to the antioxidant is 10:(1~2), for example, 10:1, 10:1.3, 10:1.5, 10:1.7, 10:2, etc.

[0038] Preferably, the temperature of the spray drying is 150-200 °C, for example 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, etc.

[0039] Preferably, the carbon source is one or more of acetylene black, Super P, Ketjen black, single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive graphite, and typical but non-limiting combinations include a combination of acetylene black and Super P, a combination of Super P and Ketjen black, a combination of Ketjen black and single-walled carbon nanotubes, a combination of multi-walled carbon nanotubes and conductive graphite, etc.

[0040] Preferably, the mass of the carbon source is 1.0-5.0 wt% of the mass of the sodium ferric sulfate precursor, for example 1.0 wt%, 2.0 wt%, 3.0 wt%, 4.0 wt%, 5.0 wt%, etc.

[0041] Preferably, the dispersant is one or more of polyethylene glycol-4000 (PEG-4000), polyethylene glycol-6000 (PEG-6000), sodium acrylate (C3H3NaO2), polyvinylpyrrolidone, and typical but non-limiting combinations include a combination of polyethylene glycol-4000 and sodium acrylate, a combination of polyethylene glycol-6000 and sodium acrylate, a combination of polyvinylpyrrolidone and sodium acrylate, etc.

[0042] Preferably, the mass of the dispersant is 0.1-1.0 wt% of the mass of the sodium ferric sulfate precursor, for example 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, etc.

[0043] Preferably, the metal acetate is one or more of nickel acetate, cobalt acetate, copper acetate, zinc acetate, manganese acetate, aluminum acetate, titanium acetate, magnesium acetate, calcium acetate, and typical but non-limiting combinations include a combination of nickel acetate and cobalt acetate, a combination of cobalt acetate and copper acetate, a combination of copper acetate and zinc acetate, a combination of zinc acetate and manganese acetate, a combination of magnesium acetate and calcium acetate, etc.

[0044] Preferably, the mass of the metal acetate is 0.5-2.0 wt% of the mass of the sodium ferric sulfate precursor, for example 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, etc.

[0045] Further preferably, the metal acetate is at least three of nickel acetate, cobalt acetate, copper acetate, zinc acetate, manganese acetate, aluminum acetate, titanium acetate, magnesium acetate, calcium acetate, and a typical but non-limiting combination includes: a combination of nickel acetate, cobalt acetate, and copper acetate, a combination of titanium acetate, magnesium acetate, and calcium acetate, a combination of copper acetate, zinc acetate, and manganese acetate, a combination of aluminum acetate, titanium acetate, magnesium acetate, and calcium acetate, a combination of copper acetate, aluminum acetate, titanium acetate, magnesium acetate, and calcium acetate, and the like.

[0046] When multiple metal acetates are used as the coating agent in the present application, the coating layer contains multiple elements, so that the coating layer has a highly disordered high-entropy (HE) surface structure, which can further improve the thermodynamic and electrochemical properties of the material, improve the surface properties of the material, and improve the structural stability thereof.

[0047] Preferably, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0048] Preferably, the sintering temperature is 350-400°C, such as 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, and the like.

[0049] Preferably, the sintering time is 0.5-1.5h, such as 0.5h, 1.0h, 1.5h, and the like.

[0050] In a second aspect, the present application provides a sodium iron sulfate composite positive electrode material prepared by the above preparation method.

[0051] In a third aspect, the present application provides a sodium ion battery comprising the above sodium iron sulfate composite positive electrode material.

[0052] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0053] Example 1

[0054] The preparation method of the sodium iron sulfate composite positive electrode material of the present embodiment is as follows:

[0055] (1) Na2SO4, FeSO4 . 7H2O were dissolved in deionized water according to a molar ratio of Na:Fe of 3:2, followed by the addition of ascorbic acid (the molar amount of ascorbic acid was 10% of the molar amount of FeSO4 . 7H2O), and after being fully dissolved, a mixed slurry was obtained; the mixed slurry was subjected to spray drying at 180°C to obtain a sodium iron sulfate precursor.

[0056] (2) Take the sodium ferric sulfate precursor in a stainless steel ball mill jar, then add the Ketjen black as a conductive coating agent (the amount of addition is 5wt% of the mass of the sodium ferric sulfate precursor), calcium acetate as a metal coating agent (the amount of addition is 1wt% of the mass of the sodium ferric sulfate precursor) and sodium acrylate as a dispersant (the amount of addition is 0.5wt% of the mass of the sodium ferric sulfate precursor), then ball mill for 6h under an argon atmosphere, wherein: the process parameters of the ball milling are: the ball-to-material ratio is 10:1; the ball milling speed is 400rpm; after the ball milling is completed, a mixture is obtained. The mixture is heated to 380℃ at a heating rate of 2℃ / min under an argon atmosphere, and is kept at this temperature for 8h, and after natural cooling, it is crushed and sieved to obtain a sodium ferric sulfate composite positive electrode material.

[0057] Comparative Example 1

[0058] The preparation method of the sodium ferric sulfate positive electrode material in the present comparative example is as follows:

[0059] Na2SO4, FeSO4 . ·7H2O are dissolved in deionized water according to a molar ratio of Na:Fe of 3:2, then ascorbic acid (the molar amount of ascorbic acid is 10% of the molar amount of FeSO4 . ·7H2O) is added, and after being fully dissolved, a mixed slurry is obtained; the mixed slurry is spray dried at 180℃ to obtain a sodium ferric sulfate precursor. The sodium ferric sulfate precursor is heated to 380℃ at a heating rate of 2℃ / min under an argon atmosphere, and is kept at this temperature for 8h, and after natural cooling, it is crushed and sieved to obtain a sodium ferric sulfate positive electrode material.

[0060] The SEM image of the sodium ferric sulfate positive electrode material prepared in the present comparative example is as shown in Figure 1 , which is a spherical structure.

[0061] Comparative Example 2

[0062] It is basically the same as Example 1, except that in step (2), calcium acetate is not added.

[0063] Comparative Example 3

[0064] It is basically the same as Example 1, except that the sodium ferric sulfate composite positive electrode material does not contain carbon; Ketjen black is not added in step (2) of the corresponding preparation method; and the corresponding prepared sodium ferric sulfate composite positive electrode material.

[0065] Example 2

[0066] It is basically the same as Example 1, except that in step (2), calcium acetate and magnesium acetate are used as metal coating agents, and the amount of addition of calcium acetate and magnesium acetate is both 0.5wt% of the sodium ferric sulfate precursor. The corresponding prepared sodium ferric sulfate composite positive electrode material.

[0067] Example 3

[0068] The same as example 1, the difference is that in step (2), calcium acetate, magnesium acetate and aluminum acetate are used as metal coating agent, and the addition amount of calcium acetate, magnesium acetate and aluminum acetate is 0.33wt% of sodium iron sulfate precursor. The structural formula of the corresponding prepared sodium iron sulfate composite positive electrode material is Na3Fe2(SO4) 3.5 @C / M, M is the sintering product of calcium acetate, magnesium acetate, aluminum acetate and zinc acetate.

[0069] Example 4

[0070] The same as example 1, the difference is that in step (2), calcium acetate, magnesium acetate, aluminum acetate and zinc acetate are used as metal coating agent, and the addition amount of calcium acetate, magnesium acetate, aluminum acetate and zinc acetate is 0.25wt% of sodium iron sulfate precursor. The structural formula of the corresponding prepared sodium iron sulfate composite positive electrode material is Na3Fe2(SO4) 3.5 @C / M, M is the sintering product of calcium acetate, magnesium acetate, aluminum acetate and zinc acetate.

[0071] Example 5

[0072] The same as example 1, the difference is that in step (2), calcium acetate, magnesium acetate, aluminum acetate, zinc acetate and titanium acetate are added as metal coating agent; the addition amount of calcium acetate, magnesium acetate, aluminum acetate, zinc acetate and titanium acetate is 0.2wt% of the mass of sodium iron sulfate precursor.

[0073] The SEM image of the sodium iron sulfate composite positive electrode material prepared in this example is shown in Figure 2 , and the micro surface layer is a highly disordered coating layer.

[0074] Example 6

[0075] The preparation method of the sodium iron sulfate composite positive electrode material in this example is as follows:

[0076] (1) Na2SO4, FeSO4 . 7H2O are dissolved in deionized water according to the molar ratio of Na:Fe is 6:5, then citric acid (the molar amount of citric acid is 15% of the molar amount of FeSO4 . 7H2O) is added, and after fully dissolving, a mixed slurry is obtained; the mixed slurry is spray dried at 200℃ to obtain sodium iron sulfate precursor.

[0077] (2) Take the sodium iron sulfate precursor in a stainless steel ball mill jar, then add carbon nanotubes (CTS600) as a conductive coating agent (the addition amount is 3wt% of the mass of the sodium iron sulfate precursor), nickel acetate, cobalt acetate, zinc acetate, manganese acetate and magnesium acetate as metal coating agents (the addition amount of nickel acetate, cobalt acetate, zinc acetate, manganese acetate and magnesium acetate is 0.4wt% of the mass of the sodium iron sulfate precursor) and polyethylene glycol-4000 as a dispersing agent (the addition amount is 1.0wt% of the mass of the sodium iron sulfate precursor), then ball mill for 5h under an argon atmosphere, wherein: the process parameters of ball milling are: the ball-to-material ratio is 15:1; the ball milling speed is 500rpm; after ball milling, a mixture is obtained. The mixture is heated to 400℃ at a heating rate of 4℃ / min under an argon atmosphere, and is kept at this temperature for 4h, and after natural cooling, it is crushed and sieved to obtain a sodium iron sulfate composite positive electrode material.

[0078] Example 7

[0079] The preparation method of the sodium iron sulfate composite positive electrode material in this example is as follows:

[0080] (1) Dissolve Na2SO4, FeSO4 . · 7H2O in deionized water according to a molar ratio of Na:Fe of 8:5, then add oxalic acid (the molar amount of oxalic acid is 20% of the molar amount of FeSO4 . · 7H2O), and after fully dissolving, a mixed slurry is obtained; the mixed slurry is spray dried at 150℃ to obtain a sodium iron sulfate precursor.

[0081] (2) Take the sodium iron sulfate precursor in a stainless steel ball mill jar, then add carbon nanotubes (CTS720) as a conductive coating agent (the addition amount is 8wt% of the mass of the sodium iron sulfate precursor), nickel acetate, cobalt acetate and zinc acetate as metal coating agents (the addition amount of nickel acetate, cobalt acetate and zinc acetate is 0.2wt% of the mass of the sodium iron sulfate precursor) and polyvinylpyrrolidone as a dispersing agent (the addition amount is 0.2wt% of the mass of the sodium iron sulfate precursor), then ball mill for 6h under an argon atmosphere, wherein: the process parameters of ball milling are: the ball-to-material ratio is 20:1; the ball milling speed is 300rpm; after ball milling, a mixture is obtained. The mixture is heated to 350℃ at a heating rate of 3℃ / min under an argon atmosphere, and is kept at this temperature for 12h, and after natural cooling, it is crushed and sieved to obtain a sodium iron sulfate composite positive electrode material.

[0082] The positive electrode materials prepared in Examples 1-7 and Comparative Examples 1-2 were assembled into button cells in the following manner: the positive electrode material, acetylene black, and PVDF were weighed and mixed in a mass ratio of 8:1:1, and N-methyl pyrrolidone solution (NMP) was added for homogenization. The slurry was then uniformly coated on an aluminum foil, which was dried in a vacuum drying oven at 80°C for 6 hours. After rolling and cutting (diameter of 14 mm), the positive electrode sheet was obtained. Sodium metal was used as the counter electrode, 1 mol / L NaClO4 was used as the electrolyte, and the solvent of the electrolyte was a combination of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (volume ratio of ethylene carbonate to propylene carbonate was 1:1; fluoroethylene carbonate accounted for 5% of the total volume of the solvent). Glass fiber was used as the separator, and the button cell was assembled in an argon-filled glove box to obtain a sodium-ion battery.

[0083] The sodium-ion battery was aged for 12 hours, then activated at a rate of 0.1C for 3 cycles at 25°C and a charge-discharge voltage of 2.0-4.3V, and then cycled at a rate of 10C for 300 cycles. The test data is shown in Table 1, and the test performance graph in Example 5 is shown in Figure 3 and Figure 4 .

[0084] Table 1

[0085]

[0086] From the data in Table 1 and Figures 3-4 , it can be seen that the sodium-ion battery assembled with the uncoated sodium iron sulfate positive electrode material in Comparative Example 1 has essentially no cycle performance at a rate of 10C; the sodium-ion battery assembled with the sodium iron sulfate composite positive electrode material in Comparative Example 3 has essentially no cycle performance at a rate of 10C, indicating that the sintered product of calcium acetate alone under an inert atmosphere has little effect on the performance of the sodium iron sulfate coated positive electrode material. The cycle performance of the sodium battery assembled with the sodium iron sulfate composite positive electrode material in Comparative Example 2 at a rate of 10C is significantly improved compared to Comparative Example 1, indicating that carbon coating can significantly improve the electrochemical performance of sodium iron sulfate. The battery assembled with the sodium iron sulfate composite positive electrode material in Example 1 has further improved specific capacity and cycle performance compared to Comparative Example 2. In Examples 2-5, the types of acetate salts are successively increased, and the specific capacity and cycle performance of the sodium-ion battery assembled with the sodium iron sulfate composite positive electrode material will increase slightly with the increase in the number of types. In Examples 6 and 7, the process parameters are different, and the performance of the sodium-ion battery assembled with the sodium iron sulfate composite positive electrode material prepared in Examples 6 and 7 will have a small range of fluctuations.

[0087] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or mixtures made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for preparing a sodium ferric sulfate composite cathode material, characterized in that, The method comprises the following steps: ball-milling the sodium ferric sulfate precursor, a carbon source, a dispersing agent and a metal acetate to obtain a mixture; and sintering the mixture in an inert atmosphere to obtain the sodium ferric sulfate composite positive electrode material; The mass of the metal acetate is 0.5-2.0 wt% of the mass of the sodium ferric sulfate precursor. The metal acetate is three or more than three of nickel acetate, cobalt acetate, copper acetate, zinc acetate, manganese acetate, aluminum acetate, titanium acetate, magnesium acetate and calcium acetate. The carbon source is one or more than one of acetylene black, Super P, Ketjen black, single-walled carbon nanotube, multi-walled carbon nanotube and conductive graphite. The sintering temperature is 350-400℃.

2. The method according to claim 1, wherein the sodium ferric sulfate precursor is prepared by the following steps: dissolving sodium sulfate, ferrous sulfate and / or ferrous sulfate heptahydrate and an antioxidant in water to obtain a slurry; and spray-drying the slurry to obtain the sodium ferric sulfate precursor.

3. The method according to claim 2, wherein the spray-drying temperature is 150-200℃.

5. The method according to claim 1, wherein the mass of the carbon source is 1.0-5.0 wt% of the mass of the sodium ferric sulfate precursor; and the dispersing agent is one or more than one of polyethylene glycol-4000, polyethylene glycol-6000, sodium acrylate and polyvinylpyrrolidone, and the mass of the dispersing agent is 0.1-1.0 wt% of the mass of the sodium ferric sulfate precursor. The chemical formula of the sodium ferric sulfate precursor is Na 2x Fe y (SO4) x+y wherein: 0 < x < 5, 0 < y < 5; sodium sulfate, ferrous sulfate and / or ferrous sulfate heptahydrate are added in stoichiometric ratios in the chemical formula of the sodium ferric sulfate precursor; Fe in the ferrous sulfate and / or ferrous sulfate heptahydrate 2+ molar ratio with the antioxidant is 10:(1-2).

4. The method of claim 2 or 3, wherein the method is characterized by, The inert atmosphere is a nitrogen atmosphere or an argon atmosphere; and the sintering time is 0.5-1.5 h. The sodium ferric sulfate composite positive electrode material is prepared by the method according to any one of claims 1-6. The sodium ferric sulfate composite positive electrode material according to claim 7. ​ 6. The method of claim 1, wherein the sodium ferric sulfate composite cathode material is prepared by the steps of: mixing a sodium sulfate solution with a ferric sulfate solution; and precipitating the sodium ferric sulfate composite cathode material. ​ 7. A sodium ferric sulfate composite cathode material, characterized in that, ​ 8. A sodium-ion battery, characterized in that, ​

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