Metal oxide composite sodium ferric sulfate positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a metal oxide composite sodium ferric sulfate positive electrode material as well as a preparation method and application thereof, and belongs to the technical field of sodium ion battery positive electrode materials. The metal oxide composite sodium ferric sulfate positive electrode material comprises the following raw materials in parts by mass: 1-20 parts of sodium sulfate, 2-40 parts of ferrous sulfate, 0.05-1 part of an antioxidant, 0.05-1 part of a carbon source and 0.01-2 parts of metal oxide, the metal oxide is at least one of ferrous oxide, ferric oxide, ferroferric oxide, manganese oxide, manganese dioxide, cobalt oxide, cobaltosic oxide, cobaltic oxide, vanadium monoxide, vanadium dioxide, vanadium trioxide, vanadium pentoxide, nickel oxide and copper oxide. The invention also discloses a preparation method and application of the metal oxide composite sodium ferric sulfate positive electrode material. The method provided by the invention can solve the problems of low conductivity and specific capacity of the existing sodium ferric sulfate positive electrode material, and has the advantages of low cost, strong process adaptability and wide application prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery cathode materials, specifically relating to a metal oxide composite sodium ferric sulfate cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries (SIBs) play a crucial role in large-scale renewable energy storage systems. Sulfate polyanionic compounds utilize the highly electronegative sulfate ion (SO4) to... 2- It surpasses traditional phosphate and other systems in terms of voltage, a key indicator, while also possessing significant advantages in cost and resource sustainability. This makes it a promising next-generation sodium-ion battery cathode material in the field of large-scale static energy storage, especially in cost-sensitive applications.

[0003] Current research on sulfate-based polyanionic compounds in the sodium-ion battery field mainly focuses on improving their electrochemical performance and solving preparation process challenges. Sodium iron sulfate (SO4) has attracted widespread attention due to its high operating voltage platform (Na2Fe2(SO4)3 reaches 3.8V), minimal structural volume change during charge and discharge, low preparation cost, readily available raw materials, and non-toxic and pollution-free characteristics, and is considered an ideal cathode material suitable for large-scale energy storage. However, these materials have low conductivity, which severely affects the battery's charge and discharge performance at high rates, and they also face a trade-off between voltage and capacity. Although SO4... 2- The functional groups provide a higher operating voltage, but their large molecular weight limits the material's theoretical specific capacity.

[0004] Therefore, improving the electrical conductivity and kinetic properties of sodium ferric sulfate materials has become a key research focus in this field. Summary of the Invention

[0005] The problem this invention aims to solve is to provide a metal oxide composite sodium ferric sulfate cathode material, its preparation method, and its application, in order to address the issues of low conductivity and specific capacity in existing sodium ferric sulfate cathode materials.

[0006] The technical solution adopted to solve its technical problem is to provide a metal oxide composite sodium ferric sulfate cathode material, comprising the following raw materials in parts by weight: 1-20 parts sodium sulfate, 2-40 parts ferrous sulfate, 0.05-1 part antioxidant, 0.05-1 part carbon source and 0.01-2 parts metal oxide; The metal oxide is at least one of ferrous oxide, ferric oxide, iron(II) oxide, manganese oxide, manganese dioxide, cobalt oxide, cobalt(II) oxide, cobalt(III) oxide, vanadium(II) oxide, vanadium(II) oxide, vanadium(II) oxide, nickel(II) oxide, and copper(II) oxide.

[0007] The beneficial effects of the above-mentioned technical solution in this invention are as follows: Using sodium sulfate and ferrous sulfate as core raw materials, this invention, while ensuring the intrinsic advantage of high working voltage, lays the foundation for low cost and non-toxicity / environmental friendliness; the specially added trace antioxidant can effectively complex ferrous ions and inhibit their oxidation during the preparation process, ensuring that iron is present in the required Fe content during the precursor reaction. 2+ The stable valence state ensures the high electrochemical activity and reversible capacity of the final product. The added carbon source is far more functional than a traditional conductive additive. It can build a highly conductive three-dimensional network between the active material particles, which significantly overcomes the bottleneck of low intrinsic electronic conductivity of sodium iron sulfate and greatly improves the rate performance of the material. The introduction of specific types of metal oxides (such as manganese oxide, vanadium pentoxide, cobalt oxide, etc.) has achieved multiple enhancement effects: (1) These metal ions can be doped into the lattice of sodium iron sulfate, playing a supporting and stabilizing role in the structure and suppressing volume changes during charging and discharging; (2) Metal oxides can provide additional active or inactive electrochemical contributions, and some oxides can even introduce new redox couples, improving the specific capacity of the material while maintaining the high voltage advantage; (3) A large number of defects and dangling bonds will be formed between the metal oxide and sodium iron sulfate phases. The diffusion barrier of ions in these interface regions (or space charge regions) is usually lower than that in the bulk lattice. These interfaces can serve as additional, low-barrier fast transport channels for sodium ions. Sodium ions can preferentially migrate along these interfaces, bypassing the diffusion path with a higher barrier in the bulk sodium iron sulfate phase, thereby improving the overall ionic conductivity.

[0008] Preferably, the metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts antioxidant, 0.05 parts carbon source and 0.05 parts metal oxide.

[0009] More preferably, the metal oxide is ferrous oxide, iron(II) oxide, manganese dioxide, or vanadium(II) oxide.

[0010] More preferably, the antioxidant is ascorbic acid and / or citric acid.

[0011] More preferably, the carbon source is at least one of Ketjen black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, Super P, and conductive graphite.

[0012] This invention also provides a method for preparing the above-mentioned metal oxide composite sodium ferric sulfate cathode material, comprising the following steps: (1) Sodium sulfate, ferrous sulfate, antioxidant and carbon source are dissolved in water under an inert atmosphere to obtain a precursor solution; (2) The precursor solution was heated and stirred under an inert atmosphere, then sonicated and dried to obtain precursor powder. (3) The metal oxide is added to the precursor powder under an inert atmosphere and then wet ball-milled with ethanol, followed by calcination to obtain the product.

[0013] The beneficial effects of the above-mentioned technical solution in this invention are as follows: The preparation method of this invention first controls the solution to a semi-dry state by combining heating, stirring, and ultrasound, effectively promoting the uniform mixing and reaction of the precursor components at the molecular level, laying a solid foundation for the formation of a homogeneous phase; the subsequent drying can gently and thoroughly remove moisture, avoiding damage to the material structure due to stress or excessive water loss during the drying process. Furthermore, by introducing a specific metal oxide and ball milling, not only is a highly uniform composite of the active material and the metal oxide achieved at the nanoscale, but the latter can also act as a lattice dopant or surface modification layer, effectively stabilizing the main structure of the material and broadening the sodium ion migration channels. Finally, a two-stage gradient calcination process can precisely control the crystallization process and grain growth of the material, first initially forming at a lower temperature, and then completing stable crystallization at a moderate temperature, thereby avoiding the loss of sulfur and lattice defects caused by high temperatures while obtaining a final product with high crystallinity and a stable structure. Most importantly, the entire synthesis process is carried out under argon protection, which completely isolates oxygen and moisture, ensuring the presence of ferrous ions (Fe2+) in the system. 2+ The stable valence state of ) prevents it from being oxidized to the electrochemically inert Fe. 3+ This ensures that the material has high and stable first-cycle coulombic efficiency and reversible capacity.

[0014] Preferably, step (2) includes the following steps: under an inert atmosphere, the precursor solution is stirred at a constant temperature of 65~75℃ for 15~25 min, then sonicated for 15~20 min, repeated 2~3 times, and then dried to obtain precursor powder.

[0015] More preferably, step (2) includes the following steps: under an inert atmosphere, the precursor solution is stirred at 70°C for 20 min and then sonicated for 20 min. This process is repeated 3 times and then dried to obtain the precursor powder.

[0016] More preferably, the drying is performed by vacuum drying or evaporation.

[0017] More preferably, the vacuum drying temperature is 120°C.

[0018] Preferably, in step (3), the ethanol wet ball milling speed is 400~500 rpm and the time is 7~9h.

[0019] More preferably, in step (3), the ethanol wet ball milling speed is 500 rpm and the time is 8 h.

[0020] Preferably, the calcination parameters in step (3) are: first calcining at 150~170℃ for 3~5h, and then calcining at 340~360℃ for 14~16h.

[0021] More preferably, the calcination parameters in step (3) are: first calcination at 160°C for 4 hours, and then calcination at 350°C for 15 hours.

[0022] This invention also provides the application of the above-mentioned metal oxide composite sodium iron sulfate cathode material in the preparation of sodium-ion batteries.

[0023] The present invention has the following beneficial effects: (1) This invention fundamentally solves the core bottleneck of low intrinsic electronic conductivity and slow sodium ion diffusion dynamics by compositing specific metal oxides in sodium ferric sulfate matrix. This is due to the fact that the lattice doping of metal ions effectively stabilizes the material structure and the three-dimensional conductive network constructed in synergy greatly accelerates charge transport.

[0024] (2) The metal oxide composite sodium iron sulfate cathode material of the present invention achieves a breakthrough in performance while also possessing excellent cost control and process adaptability. Compared with the use of expensive carbon nanotubes for full coating or the use of high-cost vanadium-based raw materials, the present invention uses abundant and inexpensive metal oxides as functional additives, which can achieve a qualitative leap in performance with trace amounts, thereby reducing the overall raw material cost. In addition, the process of combining solution mixing and medium-temperature calcination adopted in the present invention effectively avoids the problem of sulfate decomposition caused by high-temperature solid-state methods. The entire process has low equipment requirements and is easy to scale up, providing a highly commercially promising technical path for the large-scale production of high-performance, low-cost sodium-ion battery cathode materials. Attached Figure Description

[0025] Figure 1 The images shown are scanning electron microscope (SEM) images of the metal oxide composite sodium iron sulfate cathode material prepared in Example 6 of this invention; wherein, (a) is a scanning electron microscope image at 5 μm; and (b) is a scanning electron microscope image at 1 μm. Figure 2 The images shown are scanning electron microscope (SEM) images of the metal oxide composite sodium iron sulfate cathode material prepared in Comparative Example 2 of this invention; wherein, (a) is a scanning electron microscope image at 5 μm; and (b) is a scanning electron microscope image at 1 μm. Figure 3 The first cycle constant current charge-discharge comparison diagram of sodium-ion batteries assembled using sodium iron sulfate cathode materials prepared in Example 1 and Comparative Example 1. Figure 4 The image shows a comparison of the first cycle of constant current charge-discharge of sodium-ion batteries assembled using the metal oxide composite sodium iron sulfate cathode materials prepared in Example 6 and Comparative Example 2. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0027] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0028] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0029] Example 1 A metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts ascorbic acid, 0.05 parts Ketjen black, and 0.05 parts vanadium trioxide.

[0030] This embodiment also provides a method for preparing a metal oxide composite sodium ferric sulfate cathode material, including the following steps: (1) Under an inert atmosphere, sodium sulfate, ferrous sulfate, ascorbic acid and Ketjen black are dissolved in water to obtain a precursor solution; (2) Under an inert atmosphere, the precursor solution was stirred at 70°C for 20 min and then sonicated for 20 min. This process was repeated 3 times and then vacuum dried at 120°C to obtain the precursor powder. (3) Vanadium trioxide was added to the precursor powder under an inert atmosphere, and ethanol was added as a grinding aid. The mixture was wet-milled in a ball mill at 500 rpm for 8 hours. Then it was placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain the metal oxide composite sodium iron sulfate cathode material.

[0031] Example 2 A metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts ascorbic acid, 0.05 parts carbon nanotubes, and 0.05 parts vanadium trioxide.

[0032] This embodiment also provides a method for preparing a metal oxide composite sodium ferric sulfate cathode material, including the following steps: (1) Under an inert atmosphere, sodium sulfate, ferrous sulfate, ascorbic acid and carbon nanotubes are dissolved in water to obtain a precursor solution; (2) Under an inert atmosphere, the precursor solution was stirred at 70°C for 20 min and then sonicated for 20 min. This process was repeated 3 times and then vacuum dried at 120°C to obtain the precursor powder. (3) Vanadium trioxide was added to the precursor powder under an inert atmosphere, and ethanol was added as a grinding aid. The mixture was wet-milled in a ball mill at 500 rpm for 8 hours. Then it was placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain the metal oxide composite sodium iron sulfate cathode material.

[0033] Example 3 A metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts ascorbic acid, 0.05 parts Ketjen black, and 0.05 parts vanadium trioxide.

[0034] This embodiment also provides a method for preparing a metal oxide composite sodium ferric sulfate cathode material, including the following steps: (1) Under an inert atmosphere, sodium sulfate, ferrous sulfate, ascorbic acid and Ketjen black are dissolved in water to obtain a precursor solution; (2) Under an inert atmosphere, the precursor solution was stirred at 70°C for 20 min and then sonicated for 20 min. This process was repeated 3 times and then evaporated for 2 min to obtain the precursor powder. (3) Vanadium trioxide was added to the precursor powder under an inert atmosphere, and ethanol was added as a grinding aid. The mixture was wet-milled in a ball mill at 500 rpm for 8 hours. Then it was placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain the metal oxide composite sodium iron sulfate cathode material.

[0035] Example 4 A metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts ascorbic acid, 0.05 parts Ketjen black, and 0.05 parts manganese dioxide.

[0036] This embodiment also provides a method for preparing a metal oxide composite sodium ferric sulfate cathode material, including the following steps: (1) Under an inert atmosphere, sodium sulfate, ferrous sulfate, ascorbic acid and Ketjen black are dissolved in water to obtain a precursor solution; (2) Under an inert atmosphere, the precursor solution was stirred at 70°C for 20 min and then sonicated for 20 min. This process was repeated 3 times and then vacuum dried at 120°C to obtain the precursor powder. (3) Manganese dioxide was added to the precursor powder under an inert atmosphere, and ethanol was added as a grinding aid. The mixture was wet-milled in a ball mill at 500 rpm for 8 hours. Then it was placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain the metal oxide composite sodium iron sulfate cathode material.

[0037] Example 5 A metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts ascorbic acid, 0.05 parts Ketjen black, and 0.05 parts iron(III) oxide.

[0038] This embodiment also provides a method for preparing a metal oxide composite sodium ferric sulfate cathode material, including the following steps: (1) Under an inert atmosphere, sodium sulfate, ferrous sulfate, ascorbic acid and Ketjen black are dissolved in water to obtain a precursor solution; (2) Under an inert atmosphere, the precursor solution was stirred at 70°C for 20 min and then sonicated for 20 min. This process was repeated 3 times and then vacuum dried at 120°C to obtain the precursor powder. (3) Add iron(III) oxide to the precursor powder under an inert atmosphere, and then add ethanol as a grinding aid. The mixture is wet-milled in a ball mill at 500 rpm for 8 hours. Then it is placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain the metal oxide composite sodium iron sulfate cathode material.

[0039] Example 6 A metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts ascorbic acid, 0.05 parts Ketjen black, and 0.05 parts ferrous oxide.

[0040] This embodiment also provides a method for preparing a metal oxide composite sodium ferric sulfate cathode material, including the following steps: (1) Under an inert atmosphere, sodium sulfate, ferrous sulfate, ascorbic acid and Ketjen black are dissolved in water to obtain a precursor solution; (2) Under an inert atmosphere, the precursor solution was stirred at 70°C for 20 min and then sonicated for 20 min. This process was repeated 3 times and then vacuum dried at 120°C to obtain the precursor powder. (3) Ferrous oxide was added to the precursor powder under an inert atmosphere, and ethanol was added as a grinding aid. The mixture was wet-milled in a ball mill at a speed of 500 rpm for 8 hours. Then it was placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain the metal oxide composite sodium ferric sulfate cathode material.

[0041] Example 7 A metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts citric acid, 0.05 parts Ketjen black, and 0.05 parts ferrous oxide.

[0042] This embodiment also provides a method for preparing a metal oxide composite sodium ferric sulfate cathode material, including the following steps: (1) Under an inert atmosphere, sodium sulfate, ferrous sulfate, citric acid and Ketjen black are dissolved in water to obtain a precursor solution; (2) Under an inert atmosphere, the precursor solution was stirred at 70°C for 20 min and then sonicated for 20 min. This process was repeated 3 times and then vacuum dried at 120°C to obtain the precursor powder. (3) Ferrous oxide was added to the precursor powder under an inert atmosphere, and ethanol was added as a grinding aid. The mixture was wet-milled in a ball mill at a speed of 500 rpm for 8 hours. Then it was placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain the metal oxide composite sodium ferric sulfate cathode material.

[0043] Comparative Example 1 A sodium ferric sulfate cathode material, compared with the raw material of Example 1, without the addition of 0.05 parts by weight of vanadium trioxide.

[0044] The preparation method of the sodium ferric sulfate cathode material in this comparative example includes the following steps: (1) Under an inert atmosphere, sodium sulfate, ferrous sulfate, ascorbic acid and Ketjen black are dissolved in water to obtain a precursor solution; (2) Under an inert atmosphere, the precursor solution was stirred at 70°C for 20 min and then sonicated for 20 min. This process was repeated 3 times and then vacuum dried at 120°C to obtain the precursor powder. (3) Ethanol was added to the precursor powder under an inert atmosphere as a grinding aid and wet ball milled in a ball mill at a speed of 500 rpm for 8 hours. Then it was placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain sodium iron sulfate cathode material.

[0045] Comparative Example 2 A metal oxide composite sodium ferric sulfate cathode material comprises the following raw materials in parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts ascorbic acid, 0.05 parts Ketjen black, and 0.05 parts ferrous oxide.

[0046] This comparative example also provides a method for preparing a metal oxide composite sodium ferric sulfate cathode material, including the following steps: Under an inert atmosphere, sodium sulfate, ferrous sulfate, ascorbic acid, Ketjen black and ferrous oxide are mixed, and ethanol is added as a grinding aid. The mixture is then wet-milled in a ball mill at 500 rpm for 8 hours. The mixture is then placed in a tube furnace and calcined at 160°C for 4 hours, and then calcined at 350°C for 15 hours to obtain the metal oxide composite sodium ferric sulfate cathode material.

[0047] Experimental Example 1. Morphological characteristics Scanning electron microscopy (SEM) observations of the metal oxide composite sodium ferric sulfate cathode materials prepared in Example 6 and Comparative Example 2 yielded the following results: Figures 1-2 As shown.

[0048] from Figures 1-2 As can be seen from the above, the metal oxide composite sodium ferric sulfate cathode material prepared in Example 6 is aggregated together and has certain gaps; while the metal oxide composite sodium ferric sulfate cathode material prepared in Comparative Example 2 has a large number of coral-like shapes on its surface, and the particle size of this material is uneven, with the overall particle size being relatively large.

[0049] 2. Electrochemical performance analysis Sodium-ion batteries were assembled using the cathode materials prepared in Examples 1 and 6, and Comparative Examples 1 and 2, and their first-cycle constant current charge-discharge performance was tested. Specifically, the cathode material, conductive agent acetylene black, and polyvinylidene fluoride (PVDF) were thoroughly ground in a slurry at a weight ratio of 8:1:1, and then dispersed in N-methylpyrrolidone (NMP) solvent for electrochemical measurements. The resulting material was uniformly cast onto aluminum foil and dried in a vacuum furnace at 80°C for 12 hours. The electrode was then sliced ​​into circular pieces, each with a diameter of 14 mm. The separator was made of glass fiber (GF / D grade). The electrolyte consisted of 1 M NaClO4 dissolved in a solvent composed of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) at a volume ratio of 1:1:1, with the addition of 5.0% vinyl fluorocarbonate (FEC). CR2032 coin-shaped half-cells were assembled in an argon-filled glove box, following the sequence of negative electrode shell, spring, gasket, sodium plate, electrolyte, separator, electrolyte, positive electrode material, and positive electrode shell. The first cycle of constant current charge-discharge testing was conducted on a NEWARE battery testing system (CT4008). Results are as follows: Figures 3-4 As shown.

[0050] from Figure 3 As can be seen from the data, the specific capacity of the sodium-ion battery assembled in Example 1 during the first charge cycle is 91.12 mAh g. -1The specific capacity of the sodium-ion battery assembled in Comparative Example 1 was higher than that of Comparative Example 1, and a small plateau appeared near the 3.2V voltage. This was mainly due to the incorporation of V2O3. Doping with V2O3 can introduce multivalent vanadium ions to construct an electronic conductive network and act as a robust structural pillar to synergistically improve the specific capacity of the material. Comparative Example 1's assembled sodium-ion battery only showed 76.23 mAh g⁻¹. -1 The first charge capacity; and from Figure 4 As can be seen from the data, the specific capacity of the sodium-ion battery assembled in Example 6 during the first charge cycle is 95.84 mAh g. -1 This is higher than that of Comparative Example 2, where the sodium-ion battery assembled in Comparative Example 2 exhibited 81.83 mAh g⁻¹. -1 The initial charge capacity. Combined with... Figure 1 and Figure 2 A comparison of the morphologies of the two materials shows that the pores created by the material prepared in Example 6 can adsorb Na. + This provides additional capacity, thereby increasing the overall energy density of the material.

[0051] The present invention has been described according to the above embodiments. It should be understood that the above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the scope of the present invention.

Claims

1. A metal oxide composite sodium ferric sulfate cathode material, characterized in that, The raw materials include the following parts by weight: 1-20 parts sodium sulfate, 2-40 parts ferrous sulfate, 0.05-1 part antioxidant, 0.05-1 part carbon source and 0.01-2 parts metal oxide; The metal oxide is at least one of ferrous oxide, ferric oxide, iron oxide, manganese oxide, manganese dioxide, cobalt oxide, cobalt tetroxide, cobalt trioxide, vanadium monoxide, vanadium dioxide, vanadium trioxide, vanadium pentoxide, nickel oxide, and copper oxide.

2. The metal oxide composite sodium ferric sulfate cathode material as described in claim 1, characterized in that, The raw materials include the following parts by weight: 1 part sodium sulfate, 2 parts ferrous sulfate, 0.05 parts antioxidant, 0.05 parts carbon source and 0.05 parts metal oxide.

3. The metal oxide composite sodium ferric sulfate cathode material as described in claim 1 or 2, characterized in that, The metal oxide is ferrous oxide, iron(II) oxide, manganese dioxide, or vanadium(II) oxide.

4. The metal oxide composite sodium ferric sulfate cathode material as described in claim 1 or 2, characterized in that, The antioxidant is ascorbic acid and / or citric acid.

5. The metal oxide composite sodium ferric sulfate cathode material as described in claim 1 or 2, characterized in that, The carbon source is at least one of Ketjen black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, Super P, and conductive graphite.

6. The method for preparing the metal oxide composite sodium ferric sulfate cathode material according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Sodium sulfate, ferrous sulfate, antioxidant and carbon source are dissolved in water under an inert atmosphere to obtain a precursor solution; (2) The precursor solution was heated and stirred under an inert atmosphere, then sonicated and dried to obtain precursor powder. (3) The metal oxide is added to the precursor powder under an inert atmosphere and then wet ball-milled with ethanol, followed by calcination to obtain the product.

7. The preparation method of the metal oxide composite sodium ferric sulfate cathode material as described in claim 6, characterized in that, Step (2) includes the following steps: under an inert atmosphere, the precursor solution is stirred at a constant temperature of 65~75℃ for 15~25 min, then sonicated for 15~20 min, repeated 2~3 times, and then dried to obtain precursor powder.

8. The preparation method of the metal oxide composite sodium ferric sulfate cathode material as described in claim 6, characterized in that, In step (3), the ethanol wet ball milling speed is 400~500 rpm and the time is 7~9h.

9. The preparation method of the metal oxide composite sodium ferric sulfate cathode material as described in claim 6, characterized in that, The calcination parameters in step (3) are: first calcination at 150~170℃ for 3~5h, then calcination at 340~360℃ for 14~16h.

10. The application of the metal oxide composite sodium iron sulfate cathode material according to any one of claims 1 to 5 in the preparation of sodium-ion batteries.

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